ELEMENTS * / — OF CHEMISTRY: far the In of Colleges, Jtnhenues, suh 3G]00b. BY M. Y. REGYAULT. ILLUSTRATED BY NEARLY 700 WOOD-CUTS. TRANSLATED FROM THE FRENCH By THOMAS R. BETTON, M.D. AND EDITED WITH NOTES, By JAMES C. BOOTH, AND WILLIAM L. FABEB, METALLUBGIST AND MINING ENGINEER IN TWO VOLUMES—VOL. II. PHILADELPHIA: PARRISH, DUNNING, AND HEARS. 1852. Entered according to Act of Congress, in the year 1852, by AMBROSE W. THOMPSON, in the Clerk’s Office of the District Court for the Eastern District of Pennsylvania. STEREOTYPED BY L. JOHNSON & CO. PHILADELPHIA. TABLE OF CONTENTS OF VOL. II. PAGE Preparation of Ores 9 Washing 10 Crushing by cylinders 11 Swing-sieve 15 Jigging-machine 16 Stamping ore 17 Deposite-trough 18 Sleeping-table, or nicking-buddle 19 Percussion-table, or brake-table 20 Manganese 23 “ oxides of. 23 “ acids of 25 “ salts of 28 . “ sulphide and chloride of..... 29 “ analytic determination of.... 31 Iron, metallic 36 “ oxides of 40 “ salts of. 44 “ sulphide of. 47 “ chloride of 49 “ cyanides of .' 50 “ carburet of, cast-iron 53 “ analytic determination of 54 “ ores of 59 “ reduction of its ores, by the Cata- lonian forge 61 Reduction in the blast-furnace 66 “ the blast 67 “ mixing ores 70 “ blowing the furnace 71 “ hot-blast 77 “ waste-heat of blast-furnace 78 “ remelting pig-metal 80 “ conversion of cast into bar-iron.... 82 “ refining on the forge-hearth 83 “ “ by puddling 87 “ blooming and rolling 92 “ Making sheet and tin plate 99 “ wire-drawing 101 “ making steel 102 “ forge steel 103 “ “ blistered and cast-steel... 104 “ tempering steel 107 “ dry assay of iron-ores 108 “ analysis of cast, and steel Ill PAGE Iron, composition of bar and cast-iron, and steel 116 Chromium, oxides of 118 “ chromic acid 122 “ salts of 123 “ chromates 125 “ analytic determination of... 128 Cobalt, metal and oxides 130 “ salts of 131 “ arsenical ores 132 “ analytic determination of 133 “ smalt and zaffre 134 “ Thenard’s blue 135 Nickel, metal and oxides of 136 “ salts of. 137 “ German silver 138 “ analytic determination of 139 Zinc, distillation of. 141 “ oxide of 142 “ salts of 143 “ sulphide and chloride of 144 “ analytic determination of. 144 “ metallurgy of. 146 “ “ in Belgium 147 “ “ in Silesia 150 “ “ in England 151 Cadmium, compounds of 153 “ analytic determination of..... 154 Tin 156 “ oxides of. 158 “ salts of 160 “ sulphides of 161 “ chlorides of 162 “ behaviour of salts of 164 “ metallurgy of. 166 Titanium 169 “ oxides of 170 “ chlorides of 171 Columbium, Niobium, Pelopium, II- MENIUM 174 Lead 174 “ oxides of, litharge 175 “ red, or minium 178 “ salts of 179 “ acetates of, sugar of lead 183 4 TABLE OF CONTENTS, PAGE Lead, carbonate of, white-lead 184 “ behaviour of salts of 186 “ sulphide of. 186 “ chloride of 188 “ analytic determination of 188 “ alloys, type-metal, and soft solder 189 “ metallurgy of. 190 “ “ reduction by iron.... 192 u “ reverberatory pro- cess 196 “ “ Scotch hearth 198 “ “ cupellation 198 “ “ Pattinson’s process.. 202 “ making sheet, and pipe 202 “ casting shot 203 Bismuth 204 “ oxides of 205 “ salts of, pearl-white 206 “ alloys of, fusible metal 208 “ analytic determination of 208 “ • metallurgy of 209 Antimony 211 “ oxides and acids of 212 “ salts of 214 “ sulphides of, Kermes mineral 215 “ chlorides of 217 “ behaviour of salts of 218 “ analytic determination of..... 219 “ detection of, in poisoning 221 “ alloys of 221 “ metallurgy of. 222 Uranium, and its oxides 224 “ salts of. 225 “ analytic determination of 228 Tungsten, and its oxides 230 “ analytic determination of.... 232 Molybdenum, its oxides and salts 233 Vanadium 235 Copper 236 “ oxides of 237 “ salts of 239 “ “ blue vitriol 240 “ “ mineral and Scheele’s green 242 “ “ verdigris 243 “ sulphides of 243 “ chlorides of 244 “ analytic determination of 245 “ metallurgy of. 247 “ “ Mansfeld process.. 249 “ “ eliquation of silver 251 “ “ English process.... 256 “ alloys of, and zinc 263 “ “ “ brass 264 “ “ tin, bronze 265 “ “ “ cannon-casting 266 “ “ tinning copper and brass 269 “ analysis of brass and bronze 270 Mercury 271 “ purification of 272 “ oxides of 273 “ salts of 275 “ fulminating 279 “ amide-base of 279 “ sulphides of, cinnabar 281 PAGE Mercury, chlorides of, calomel 282 “ “ corrosive subli- mate 284 “ “ white precipitate 285 “ iodides of. 286 “ cyanide of. 287 “ analytic determination of 288 “ amalgams of, mirrors 289 “ metallurgy of, in Idria 290 " “ at Almaden... 291 Silver 293 “ oxides of 294 “ fulminating 295 “ salts of 296 “ “ lunar caustic 297 “ sulphides of 300 “ chlorides of 301 “ analytic determination of 303 “ metallurgy of. 304 “ “ Freiberg process... 305 " “ Mansfeld “ 309 “ “ American “ 310 “ alloys of. 311 “ “ coin and plate 312 “ assay of alloys of, by cupella- tion 313 “ assay of alloys of, in the wet way 316 “ assay of ores of 321 Gold and its compounds 322 “ purple of Cassius 325 “ analytic determination of 326 “ metallurgy of. 326 “ “ Tyrolese bowls 328 “ alloys of 329 “ separation of, and silver, by sul- phuric acid 329 “ separation of, and silver, by ni- tric acid 331 “ gilding and silvering 331 “ “ “ by immer- sion 332 “ galvanic gilding 333 “ “ silvering 334 “ galvanoplastics 335 “ assay of alloys of, by quartation. 336 “ “ by the touch- needle 338 Platinum 339 “ black 340 “ flameless lamp 341 “ oxides of 342 “ salts of 343 “ chlorides of 345 “ ammonia-bases of 346 “ analytic determination of 347 “ extraction of 349 Osmium 350 “ compounds of 351 “ extraction of. 352 Iridium 353 “ compounds of. 354 Palladium, and its compounds 356 Rhodium, and its compounds 358 Ruthenium 360 TABLE OF CONTENTS. 5 FOURTH PART. ORGANIC CHEMISTRY, PAGE Introduction 361-445 Organized and organic bodies 362 Proximate analysis of organic sub- stances 363 Ultimate analysis of organic sub- stances 366 Ultimate analysis, determination of carbon and hydrogen 367 Ultimate analysis, desiccation 369 “ “ combustion 371 “ “ of non-volatile li- quids 374 “ “ of volatile sub- stances 375 “ “ of gaseous organic bodies 375 “ “ determination of carbonic acid by volume 377 “ “ determination of nitrogen by vo- lume 380 Ultimate analysis, determination of nitrogen as ammonia 382 Ultimate analysis, determination of sulphur 385 Ultimate analysis, determination of phosphorus 385 Ultimate analysis, determination of chlorine, bromine, iodine, and oxy- gen 386 Construction of a formula for an organic substance 387 “ “ when it is acid 387 “ “ from its mine- ral base 393 “ xt when it is basic 397 “ u when neither acid nor basic 399 Determination of density of vapours 406 Simultaneous temperatures in thermo- meters differently constructed 413 Air-thermometer (note) 414 Analysis of gases, apparatus for 422 “ absorbing reagents... 430 “ “ examples of 433 “ “ oxygen and nitrogen 433 Analysis of gases, oxygen, nitrogen, and hydrogen 435 Analysis of gases, oxygen, nitrogen, and carbonic oxide 436 Analysis of gases, oxygen, carburetted hydrogen, etc 437 Analysis of gases, complex mixtures.... 443 PAGE Essential Proximate Principles op Plants 446 Cellulose 446 Lignin 449 Albuminous Vegetable Substances 451 Albumen 453 Circular polarization (note) 454 Gluten, vegetable fibrin, and casein... 460 Amylaceous Substances 461 Inulin and lichenin 467 Gums, arabin, cerasin, bassorin 468 Sugar 469 Cane-sugar 470 Caramel, saccharic acid 471 Eruit-sugar 474 Grape-sugar 475 Glucic acid 476 Determination of sugar by oxide of cop- per 477 Determination of sugar by polarization 478 Gelatinous Principles, pectose 478 Pectin and pectic acid 479 Table of pectic acids 483 Mannite 484 Action of Acids on Lignin, Starch, and Sugar 485 Dextrin 485 British gum 486 Diastase < 487 Glucose, manufacture of 487 Ulmin and humin 489 Action of nitric acid, oxysaccharic acid 491 Gun-cotton 491 Collodion 492 Mucic acid 493 Spontaneous Decomposition of Plants... 494 Mineral fuel 494 Varieties of coal 496 Analysis “ 497 Tables of composition of coal.... 500, 503 Alcoholic Fermentation 505 Yeast or ferment 507 Alcohol 511 Alcoholometry 513 Sulphovinic acid 515 Ether 516 Olefiant gas . 520 Ethionic acid 522 Dutch liquid 523 Chlorinated olefiant gas 524 Oil of wine 528 Ethers and vinic acids 529 Phosphovinic acid 530 6 PAGE Nitric ether 530 Nitrous and sulphurous ethers 531 Boracic and silicic ethers 532 Carbonic ethers, urethan 533 Oxalic ethers, oxamic ether 534 Mucic ether 535 Sulphocarbovinic or xanthic acid 536 Chlorohydric ether 536 Bromo, iodo, and cyanohydric ethers 537 Sulfhydric ethers 538 Mercaptan 539 Oxidation of alcohol and ether 541 Aldehyde 541 Acetic acid 542 Manufacture of vinegar 543 Pyroligneous acid 545 Acetates 546 Acetic ether 548 Acetone 549 Mesitylen 550 Cacodyl, alcarsin 551 Chlorinated chlorohydric ether 554 Chlorinated ether 558 Chloral 561 Chloracetic acid 563 Chlorinated compound ethers 564 Table of alcoholic compounds by sub- stitution 566 Ethyl theory (note) 568 Lactic and butyric fermentations 569 Lactic acid 573 Butyric acid, butyramide 574 Methylic alcohol, wood-spirit 575 Methylic ether 576 Methylsulphuric ether 577 Compound methylic ethers 578 Marsh-gas 582 Formic acid 583 Methylal 585 Chlorinated methylchlorohydric ether 585 Chloroform 586 Bromo, iodo, sulphoform 588 Chlorinated methylic ether 588 Table of methylic compounds by sub- stitution 591 Methyl 593 Acids Existing in Plants 594 Oxalic acid 594 Malic acid 595 Equisetic and fumaric acids 596 Citric acid 596 Aconitie acid 597 Tartaric acid 598 Tartar emetic 600 Action of heat on tartaric acid 601 Racemic acid 603 Tannic acid 605 Gallic acid 607 Ellagic or bezoaric acid 609 Meconic acid 609 Chelidonic acid 611 Quinic acid, quinone 611 Organic Alkaloids 612 Quinin 613 Cinchonin 614 Morphin 615 Narcotin 616 TABLE OF CONTENTS. PAGE Codein 617 Strychnin and brucin 617 Caffein or them 618 Nicotin 618 Conicin 620 Quinole’in or leucole 620 Anilin or kyanole 621 Ethylammonia 622 Methylammonia 623 Amylammonia 624 Neutral Substances in Plants 625 Piperin, picrotoxin, cantharidin 626 Asparagin, aspartic acid 627 Phloridzin, glycyrrhizin 628 Nitrils 629 Cyanogen, products of 630 “ oxacids of 631 “ fulminic acid 632 “ sulphocyanides 633 Essential Oils 634 Oil of terpentine or terebenthen 635 Camphilen, terebilen, tereben 637 Oils of lemon, orange, etc 638 Camphor, Japan 639 “ Borneo 640 Menthen, eedren, etc 641 Benzoic Series 641 Oil of bitter almonds 642 Benzamide 643 Benzoic acid 644 “ ethers 645 Sulpho-nitrobenzoic acids 646 Benzoin, benzil, benzin 648 Benzone, amygdalin 650 Emulsin, synaptase 651 Salicin 652 Saligenin 653 Salicylous acid, oil of spiraea..- 654 Salicylic acid and ether 656 Oil of wintergreen 656 Oil of Cinnamon 658 Cinnamic acid, cinnamen 659 Balsams of Peru and Tolu 660 Coumarin 661 Oil of Aniseed, anisic acid 662 Anisen, toluidin 663 Oil of Cumin, cuminic acid, cymen 664 Oil of Cloves, eugenic acid 665 Amylic Alcohol 665 Amylin 666 Amylic ethers 667 Valerianic acid . 669 Enanthic Acid 670 Caoutchouc 671 Gutta-percha 673 Resins 673 Pimaric acid 674 Oil of Garlic, allyl 675 Oil of mustard 676 Thiosinnamin 676 Myronic acid 677 Products of Dry Distillation 678 Naphthalin 678 Paraffin 681 Phenic or carbolic acid 682 Creasote 683 Naphtha 683 TABLE OF CONTENTS. 7 PAGE Fats 684 Glycerin 689 Stearic acid, stearic candles 690 Margaric acid 692 Oleic acid.. 693 Action of sulphuric on the fat acids.. 694 “ nitric “ “ .. 695 Succinic and adipic acids 697 Suberic and sebacic acids 698 Caproic, caprylic, and capric acids ... 699 Palm-oil, castor-oil 700 Spermaceti, ethal 701 Wax, cerin, myricin 703 Organic Colouring Matters 704 Madder 705 Logwood 706 Saffron, Quercitron, etc 707 Euxanthic acid 708 Carotin 709 Chlorophyll 709 Cochineal k 710 Lichens 710 Indigo 712 White indigo 714 Isatin 715 Action of Plants on the Atmosphere 716 Animal Chemistry 719 Bone 721 Teeth, cartilage, horn 722 Hair, skin, muscular tissue 723 Fibrin, creatin * 724 Inosic acid 725 Gelatin, glue 726 Ichthyocolla, glycocoll 727 Cerebral substance 728 Nutrition , 729 Digestion 730 Blood, circulation of the 732 Bespiration and animal heat 734 Secretions 738 Blood 738 “ globules 739 PAGE Blood hematosin 740 “ coagulum 741 “ analysis of 742 Lymph 743 Saliva, gastric juice 744 Bile 745 “ cholic acid 746 Biliary calculi and cholesterin 747 Pancreatic and intestinal juice 747 Chyle and milk 748 Lactometry 750 Sugar of milk 751 Casein 752 Making butter 752 Making cheese 753 Excretions 754 Urine 754 Urea 755 Urie acid and derivatives 757 Hippuric acid 760 Urine, analysis of 761 Urinary calculi 762 Sweat 763 Excrements 763 Intestinal gases 763 Technical Organic Chemistry 763 Manufacture of bread 764 Brewing 766 Cider and perry 768 Wine-making 769 Manufacture of beet-sugar 771 “ cane-sugar 773 Sugar-refining 775 Manufacture of bone-black 777 Soap-boiling 778 Principles of dyeing 781 Mordants 785 Calico printing 787 Tanning 788 Charring wood and coal 790 Manufacture of illuminating gas 792 into the deposite reservoirs. m.. m . g. (/Trough for conveying -water through the. whole establishment, • distributing it through the spouts, h.h . The renewing basins, m,.m.m . into which the- muddy waters | flow constitute a kind of labyrinth of great extentbut, the muddy waters from different parts of the estah - Ushment entering the basins at different points .the same part of the basins contains the same-kind of deposits,. The waters m passing from die labyrinth enter large re- servoirs outside of the works.where they gradually deposits, ■ all the matters they hold in suspension . GENERAL VIEW OF STAMPING Sc WASHING ORES B Jigging machine, moved, by hand, but in more modern, establishments, by machinery. E.E.E. Deposits /roughs, for -washing coarse shltehs. which empty their muddy waters through the. troughs o. o into the basins m m, F Shaking table, .moved by the. small camwheel r. on the, mam shaft, of the water-wheel. The waters from it pass through the, troughs. u„ it. into the, deposits basins, m m,. G,G Sleeping tables. The sludge is stirred up in the water by thr' small dash wheel i. moved, by the small wheel S -. & the, muddy waters pass through, the trough, u . R, Water-wheel, owing movement to the, -whole machinery, Sc. receiving water from the trouah, C e d,. Shaft, of the, water wheel, provided with, cams for raising the stamps D D. Two sets of stamps, one fen- course, the other forfine sludge The water from the stamps containing fine matter ui. suspension , deposites the sand in thereservoirs.k.k. from which it,passes through, a, series of canals & basins. It p.n, where, it, successiyely deposites the. finer matter suspended, in. it. A . Shaking sieve,, for assorting the, sixes of ore, moved, by the, arms, a, h b o. ELEMENTS OF CHEMISTRY THIRD PART. §732. Although the metals described in the second part of this work are never technically employed in the metallic state, they still find very extensive application in the state of various compounds, all of which are manufactured in chemical works by processes similar to those employed for obtaining them in the laboratory on a smaller scale. Among the metals yet remaining for our examination, however, a considerable number are employed in the metallic state, and are extracted from their ores by processes of a particular kind, called metallurgical processes. In every case when they are to be used in the metallic state they must fulfil all the conditions enumerated (§276); which, however, many do not, as some are of rare occur- rence, while the extracting of others presents too great practical difficulties, and still others have as yet found no technical applica- tion, being, therefore, of purely scientific interest. Nevertheless, on account of the great analogy existing between them in a chemi- cal point of view, the study of those which find a technical appli- cation cannot be separated from that of those which are not so applied. The latter will, therefore, occupy our attention as well as the former, but to a much more limited extent. MECHANICAL PREPARATION OF ORES. § 733. Under the general name of ores are comprised such com- binations of metals, occurring in nature, as contain a sufficient proportion of metal to be worked with profit. The proportion varies with the marketable value of the metal, and according to the greater or less facility with which it can be obtained from its combination in the ore: iron ores, for instance, the commercial price of which metal is very low, must therefore be very rich if they are to be profitably worked. The poorest minerals from which iron 10 PREPARATION OF ORES. could be extracted must contain at least 25 per cent, of iron; and the metal must moreover exist in them in a state from which it can be easily reduced, in order to be iron ores. A mineral of frequent occurrence is iron pyrites, a combination of iron with sulphur, which contains about 47 per cent, of the former, but still cannot be considered as an ore, as the treatment to which it must be subjected in order to obtain a good quality of iron would be far too costly. Copper, on the contrary, the commercial value of which is much higher than that of iron, can be extracted with ad- vantage from ores containing only a few per cent, of the metal, even if these be in combination with sulphur; and ores which con- tain only some thousandths of silver or of gold can be worked to advantage. § 734. An ore, of whatever kind it may be, is seldom sufficiently rich to be at once subjected to metallurgical processes, but is, in general, worked with greater advantage after having been sorted, and prepared by various mechanical operations, which tend to separate from them the greater part of the earthy substances, technically termed gangue, with which they were mixed. The larger pieces of the gangue are usually separated from the ore in the mine itself, and used to fill up the excavations already made in the rock; so that only such fragments are taken out of the mine as can be advantageously prepared for smelting by mechanical operations. § 735. The ores of iron employed are always very rich, as those which are not so have not sufficient value to be made richer by costly mechanical processes; in general, therefore, the argillaceous parts are merely separated by washing (debourbage).* Sometimes the ore is left exposed to the atmosphere for several months, as the clay is thus rendered more friable and more easily detached. The washing of iron ores is performed (in France) in the middle of a stream of water, in a series of apparatus called patouillets. It is sometimes considered sufficient to turn and stir the ore in the stream with a spade, by which the argillaceous parts are detached and carried'away; but the shaking up of the ore is more frequently effected by means of a small water-wheel R (fig. 461), set in motion by the stream. The ore, thrown with a spade into the long trough A, where the water running over it frees it from a part of its clay, is thence transferred to the semi-cylindrical box B, which is filled with water, where it is stirred by iron arms attached to the axle of the water-wheel. The muddy water runs off by an outlet at the top of the box, and the washed ore, which is taken out through the orifice o in the lower part of the box, falls into the trough I), * Since hard ores are more abundant than soft in the United States, the poorer clayey ores, instead of being enriched by anj'- mechanical process, are usually sought after to mix with the harder ores and render them more easy of fluxion in the furnace.—J. C. B. 11 whence the workman removes it when he finds it to be sufficiently washed. PREPARATION OF ORES. Fig. 461. § 736. The ores of other metals, when taken from the mine, are generally sorted by the hands of females and children, who separate them into—1st, pieces rich enough to be immediately sent to the smelting-works; 2dly, fragments composed of ore and gangue, which must be subjected to mechanical preparations; and 3dly, pieces of gangue, which are thrown aside as useless. Let us now examine the mechanical operations to which the second class is subjected. When the metalliferous mineral is so intimately mixed with the gangue that it cannot be separated by the hammer, the pieces are reduced to a small size between cast-iron cylinders or under stampers. Fig. 462 represents an apparatus of crushing- cylinders, and figs. 463 and 464 show the arrangement of the cylinders. Two kinds of hard cast-iron cylinders are employed; fluted (fig. 464), and smooth ones (fig. 463); in the former of which the large fragments are broken, while the smooth cylinders reduce the pieces furnished by them to a still smaller size. Only one of these cylinders, A, receives motion from the water- wheel, the desired velocity being given to it by a system of cogs, while the second cylinder B is moved by the former. The cylin- der A is borne by two fixed uprights K, while the supports L of B are movable on the sliding-boards ab, cd. The cylinder B there- fore moves away from A whenever a piece presents itself which would oppose too much resistance to crushing; but at other times, it is kept pressed against A by the weight P, suspended to the ex- tremity of a long lever ST. The ore is brought to the crushing machine by cars, moving on a railroad FF'. The workman throws it with a spade into a wooden hopper U placed above the cylinders; and when it is reduced in size by passing between them, it falls on an inclined jolting-box M, the bottom of which consists of a wire sieve, with very small open- ings at the top, and larger ones at the lower part. The finest 12 PREPARATION OF ORES. Fig. 462. grains pass through the upper sieves; while those fragments which have passed the under ones roll to the bottom of the box M, and fall into a wheel RR'R", provided with boxes; which, by a slow rotary movement, brings the pieces of ore up again into the box U, Fig. 463. Fig. 464. PREPARATION OF ORES. 13 whence they again pass between the cylinders with the ore recently supplied from the mine. The ore, when broken by the fluted cylinders, is thus sorted by the sieves in the box M into different sized grains, from the heaps of which the largest pieces are often removed by hand; then such portions are separated as are fit for immediate smelting, the pieces of gangue are thrown aside, and the mixture of ore and gangue which requires again to be reduced in size is passed through the system of smooth cylinders. In this case the ore is not thrown directly into the box U, but into a box V divided into different parts (fig. 462), the bottom of which consists of a sieve, which, keeping back the too large fragments, allows only those of the proper dimensions to fall on the cylinders. The crushed ore is again received in a box M, the sieves of which are much finer than those which receive the pieces falling from the fluted cylinders. By this operation pieces of 4 or 5 millimetres (about inch) are obtained, which is a convenient size for the subsequent operations. The forming of smaller pieces and of dust cannot entirely be avoided, although it is sought to diminish their quantity as much as possible. § 737. The ore, reduced to more or less fine grains, is submitted to further operations in the jigging machine, (crible a depot,) the theoretical principles of which are the following : If bodies differing in shape, size, and specific gravity be let fall into a liquid which is quiet at the time, these bodies will experi- ence different resistances in their fall, and arrive at different times at the bottom of the liquid ; so that a kind of separation is effected, during their fall, by the position the pieces occupy in the deposite formed at the bottom of the vessel. If we suppose these bodies to be similar as to shape and size, but differing in their specific gravity, then they will all experience equal loss in the totality of their movement in the liquid, because the resistance a body meets with in passing through a liquid, de- pends entirely on its forili and extent of surface, but not on its density. But the loss will be more sensible as the momentum of the bodies is greater, that is, as their specific gravity is higher; so that the least dense particles, traversing the central strata of the liquid more slowly than the others, will arrive last at the lower part of the vessel; and the deposite formed will thus consist of different layers, in which the particles will have arranged themselves ac- cording to their specific gravities, the most dense occupying the lowest place and the lightest ones the top. Supposing, on the other hand, the bodies falling into the liquid to be all of equal density, and, moreover, all to have the same form,— for example, to be all cubes or spheres,—but differing in size, then will their momentum during their fall be in proportion to their volume. The resistance opposed to the particles by the liquid will 14 PREPARATION OF ORES. be proportioned to their surfaces, as we have supposed both their form and relative position while passing through the liquid to be the same. Therefore, since volumes vary as the cubes of homolo- gous dimensions, while surfaces only vary as the squares of such dimensions, the momenta of the bodies will stand in proportion to the cubes d3 of one of their dimensions, while the resistance offered to them by the liquid will be proportional only to the squares d2 of the same dimension. If M and m represent the volumes of two bodies of the same density, and D and d their homologous dimen- sions, then will their momenta be proportional to and mg, or to D3sy and d38g ; 8 representing the specific gravities of the bodies, and g their absolute weight. The loss of momentum they experi- ence by the resistance of the liquid will be proportional to D2 and cP; and is a fractional part of the whole momentum, larger for the smaller bodies than for those of a larger size, this fraction being or j^7/ for the largest, and ~ or for the smallest, where a represents the coefficient of resistance, which is constant in both cases. The largest particle will therefore arrive first at the bottom of the liquid, and the deposite will consist of strata arranged accord- ing to the size of the pieces constituting them, the largest occupy- ing the lowest situation. Lastly, we will suppose the bodies to be equal as regards density and volume, but differing in form,—some for instance, being cubes, and others laminated rectangles; then will the latter, having a greater extent of surface than the cubes, meet with a greater re- sistance while traversing the liquid; and the cubes, arriving first at the bottom of the vessel, will leave the flattened particles in a layer on the upper surface of the deposite formed. Let us now examine how these principles may be applied to the preparation of ores. We have seen that the sieves placed under the crushing-cylinders divide the material into equal classes, each of which is composed of pieces of a nearly uniform size; but we will now, to make the reasoning more simple, suppose these frag- ments, consisting of pure ore, or pure gangue, or a mixture of the two, to be exactly equal as to form and volume. Metalliferous ores being in general much heavier than the gangue by which they are accompanied, the fragments of the former will evidently first arrive at the bottom of the vessel, and on them the pieces composed of ore and gangue will deposit, while the fragments of pure gangue will constitute the uppermost layer. The deposite can then be divided into three parts: pure gangue, which lies uppermost, and is rejected; pure ore, forming the lowest stratum, which is sent to the smelting-works; and lastly, an intermediate layer, consisting of ore and gangue not sufficiently rich for immediate smelting, which must again be crushed, and undergo the process of washing over again. It is evidently essential for the process of separation to obtain PREPARATION OF ORES. 15 the fragments ns equal as possible, regarding both form and size ; but this condition cannot be fulfilled at will. By means of sieves of different fineness equality of size can be attained with more or less accuracy; but by no known process can the pieces be obtained of a similar form, because this latter character depends on the molecular constitution of the minerals to be separated, on their cleavage, etc. It may therefore very well occur that a species of crushed ore may contain lamillar fragments of pure metalliferous ore, and cubic or spherical pieces of gangue, which nevertheless passed through the same sieve; and that therefore the ore, which by virtue of its greater specific gravity tends to fall faster through the water than the gangue, will still form the upper layer of the deposite, on account of the greater resistance the liquid offers its lamillar fragments compared with that opposed to the cubic pieces of gangue. As all these circumstances present themselves simul- taneously in practice, the separation of ores from their gangue is prevented from being as perfect as it would be if the simple cases just now supposed could be realized. § 738. The separation of ores into pieces of an equal size is of such importance, that it is frequently done with the pieces which have already been sorted by hand, or with the larger pieces from the crushing cylinders. Fig. 465 represents the swing-sieve (crible a secousses) employed for this purpose, which consists of two boxes Fig. 465. ABCD, ef, placed one above the other, both of which are kept in motion by the rods tr and uv, connected with a water-wheel. Part of the water led into the first box by means of the canal os passes, 16 PREPARATION OF ORES. by the canal g, into the box underneath ; and the bottom of both boxes consists of a sieve, the meshes of which are larger in the box ABCD than in the other. A part of the ore which is placed in the upper sieve falls through into the sieve ef, where it is again sifted ; and the ore is thus divided into grains of three different sizes. That which is too coarse to pass through the meshes of the sieve in ABCD falls on the platform mn, while the grains which remained on the sieve in ef are collected in the box 6R, and lastly, the finest quality, which has escaped through the under- most sieve, is received by a box placed directly underneath the latter. § 739. A jigging machine (fig. 466) consists of a cylindrical box C, the bottom of which is a piece of wire-gauze or netting, with meshes of sufficient fineness to retain the fragments of ore. The sieve is suspended by an iron bar A, attached to a horizontal bar qh, and counterbalanced by the weight P; and is kept in a tub B, which is filled with water. The work- man sets the machine in motion by means of a ver- tical wooden pole E, which is guided by moving in the slider D. Taking the ore to be washed from the table A, he half-fills the sieve C, and then keeps the latter in a lively jolt- ing motion in the water. The sieve receives during its descent a violent con- cussion against of the tub, when the water, penetrating through the sieve, holds in suspension the ore, which by the shock is for a mo- ment not influenced by its own weight; and the different pieces which fall back from the centre of the liquid have a tendency to separate, according to the laws developed above. When the height of the fall is small, a numerous repetition of shocks has the same effect in separating the pieces as when they fall from a greater height. The workman then, after some time, finds—1st, at the upper surface of his sieve, a layer of pure gangue, which can be thrown aside, or, at least, very poor ore, which must be stamped to powder in order to separate any parts that might be worth smelting ; 2dly, a central stratum, consisting of fragments of ore and gangue com- Fig. 466. PREPARATION OF ORES. 17 bined, which ought to be reduced in size before being again jigged; and 3dly, at the bottom of his sieve, a layer of ore of sufficient purity to be smelted. The central layer is generally set aside, and, when a sufficient quantity has been collected, is subjected to another jigging without being first reduced in size, by which he obtains again a quantity of ore fit for smelting. In well-arranged works the jigging-machines are set in motion by water-power, in which case apparatus of a much larger size may be used, and may, moreover, be superintended by children. By this process very small fragments of ore, of the diameter of 1 millimetre, may be purified ; but the meshes of the wire-gauze in the jigging-machine must then be much finer than those employed for washing larger fragments. § 740. Such ores as cannot be sufficiently enriched by the use of sieves are sent to the stamping-mill (fig. 467), wdiich is com- posed of a sys- tem of stampers PP', consisting of pieces of tim- berP',shodat the lower end by cast- iron pieces P. All the stampers fall into a single trough u, the bot- tom of which con- sists of a strong sheet-iron plate, sustained by a solid foundation of masonry,while its sides are made of iron sieves, or plates of sheet- iron pierced with holes. A water- wheel moves the axle xy, on the surface of which cams are fixed, which, by lifting the catches m, set the stampers in motion. (In the cut, the lateral walls of the trough are supposed to have been removed from before three of the stampers, in order to show the iron ends P of the lat- ter.) The cams are so arranged on the axle xy, that by always lifting but one of the stampers at a time, the strain on the ma- chinery is kept as constant as possible. A current of water constantly flowing through the trough of the stamping-mill, into which ore is thrown with a spade, the parts which are already reduced to a sufficient fineness flow off through Fig. 467. 18 PREPARATION OF ORES. the lateral sieves, being held in suspension by the water, from which they tend to deposit in the canals CD, E extending along the whole length of the battery of stampers. They are thence led in circuitous windings, called a labyrinth, over the floor of the building. The coarser particles are deposited at the heads of the various canals, while the fine grains are carried farther away ; and as the waters, which traverse the channels at a very slow rate, are often still muddy after having passed through the wThole sys- tem, they are conducted into large reservoirs, where they deposit even the finest particles they held in suspension. The deposite in the channels is called sludge, (schlich;) while that in the reservoirs, which resembles a thin mud, is termed mud or fine sludge, (schlamm:) the former differs in size of grain as well as in metallic richness, according to the different parts of the canals from which it is taken, and is thus divided into several classes, each of which is separately subjected to further operations. The sludge is washed in three different kinds of apparatus : the deposit-trough, (caisse a tombeau,) the sleeping-table or nicking- buddle, (table dormante,) and the percussion-table or brake-table, (table a secousse.) §741. The physical principles on which the washing of sludge is founded are rather different from those of the washing in sieves, as the latter is applicable only to fragments of a certain size. The ore no longer acts by its weight in a quiet liquid, but is in this case submitted to the action of running water on an inclined plane. The impulse imparted to the different pieces by the water being now proportional to their surfaces, but independent of their volumes and densities, they would, were their surfaces equal, be carried more or less far by the impulse of the liquid, according to their weight; and, if their form were similar at the same time, those of the least specific gravity would be carried farthest. But if their densities and volumes were equal, those presenting the greatest extent of surface would be deposited farthest off; and lastly, with equal densities and forms, the smaller particles would go farther than the larger ones, beoause they present the greater relative extent of surface. We see, therefore, that in these new opera- tions, as well as in washing with sieves, the separation of the ore depends not only on the specific gravities, but also on the volumes and forms of the small pieces ; for which reason, the ore to be washed must be of as equal a grain as possible. § 742. The deposit-trough consists of long wooden troughs BC (fig. 468), the bottoms of which are slightly inclined, and closed at their extremity C by a board pierced with several holes at different heights, which are closed with stoppers during the operation. The sludge to be washed is placed on the benches A at the head of the machine, where it is met by a current of water, which, taking the ore into suspension, falls into the boxes BC, and there deposits it PREPARATION OF ORES. 19 Fig. 468. again at different distances from the bench A, while the finest par- ticles still remain in the water and render it muddy. As soon as the boxes are filled with water, the supplying stream is turned off, and the openings at the extremity C are uncorked; the muddy water, then running through the canal ITU' and a system of troughs into reservoirs, there deposits the particles it carried away. The washing of a fresh quantity of ore is then begun immediately, the sludge and mud of which is again borne by the water to the reser- voirs and there deposited; and so on until the deposit has attained the thickness of a foot or two; each operation differing from the former only in the manner in which the water is let off through C, as each time a higher opening is unplugged. The deposite of ore in the bottom of the box AB is divided into three parts, which are treated separately in the subsequent opera- tions. The sludge on the highest part of the inclined is often rich enough to be sent to the furnaces at once; while the deposite on the centre and lowest part, the latter of which is the poorest, are subjected to new washings, either in the machine just described or on the percussion or the sleeping-tables. § 743. The sleeping-tables (sometimes, called in the French, tables jumelles, from their being generally arranged in pairs) consist of inclined tables AB (fig. 469), from 20 to 24 feet long, furnished with borders of wood, serving to keep the water running over them in Fig. 469. 20 its place. At the head A of the table, two laths are set at the angle BAC (fig. 470), on a plane which is more inclined than the long plane ; and between which only a small aperture A is left, through which the water with suspended sludge is introduced. Small trian- gular prisms of wood, set up on this inclined plane, equally divide the arriving stream, and cause the water to flow in a uniform layer over the whole surface of the plane. The ore to be washed is thrown into a trough M (fig. 469), into which a thin stream of water is constantly falling, and where it is constantly kept in motion by a small bucket- wheel, which again is moved by an overshot water-wheel, fed by the canal oo'. The ore is thus put in suspension in the water, which, continually flowing into a canal placed lengthwise at the head of the tables, finds its way on to the sleeping-tables through the openings A (fig. 470); and the plane A (fig. 469), on which it first arrives, being too much inclined to allow any ore to deposit, the forming of a deposite first commences on the tables intended for the purpose. Here the richest parts will form the sediment at the higher end of the table, while the poorest grains will only be de- posited at the bottom of the inclined plane, or even carried away into the canal CC', which leads them into other canals and depo- siting reservoirs. As soon as the table is covered with a sufficient quantity of ore, the workman cuts off the further supply of sludge, and, after having swept all the ore lying between A and uv towards A with a broom, allows a current of clear water to flow over the tables, by which the ore is again spread over the latter; and while the poorer parts collect towards the bottom of the inclined plane, that lying on the higher parts can in general be at once sent to the smelting-works. The table has at uv a transverse opening, which remains closed during the washing by a valve, which should not project above the table; but at the close of the operation, the valve being opened, the workman sweeps the sludge through the opening uv into boxes placed beneath. The sleeping-tables are more or less inclined, according to the nature of the ore to be washed; the finest ores requiring the greatest inclination. § 744. The percussion-table serves for washing the same kinds of ore as the sleeping-table, the one or the other being preferred according to the nature of the ore and gangue in each special case. The percussion-table consists of an inclined board BC (fig. 471), resting on beams of wood to give it greater weight and solidity. PREPARATION OF ORES. Fig. 470. PREPARATION OF ORES. 21 The whole is suspended in the air by four chains or bars of iron ah, a'h', tt', tt', of which the former two are attached to fixed sup- ports, while the chains tt', tt' are fixed to a long movable lever LL', which turns by the axis OO', and serves to vary the degree of in- clination of the plank BC, being held in the height desired by means of iron pins entering the horizontal beam xy. Fig. 471. The cams cc on the axle XX', which is turned by a water-wheel, act on a curved wooden lever K, which pushes forward the sus- pended plank BC, and immediately abandons it again, so that the latter, falling forcibly back against the wooden supporting beams, receives a violent shock throughout its whole mass. Above the head B of the suspended plank is a triangular inclined plane A, fortified with small prisms, and similar to that in fig. 470. The ore to be washed is heaped in the box Y, which receives a continual stream of water; from there it spreads over the slope A and the suspended plank BC, where it has a tendency to deposit. But the violent shocks the plank is constantly receiving, causes the particles to be continually detached and taken into suspension by the water; so that they are then under the most favourable cir- cumstances to be carried off precisely according to the order of their density and size. The inclination of the plank, the violence and frequency of the shocks, and the quantity of water holding the sludge in suspension, are varied according to the nature of the ore to be washed. § 745. By these different methods of washing, sludges of greater or less fineness of grain and richness in metal are obtained, and are sorted accordingly. Each of these kinds of sludge is generally subjected to a chemical test, to ascertain their nature and richness in metal. They are then mixed, according to certain proportions which practice has shown to be the most convenient, foreign sub- stances being added if necessary. These mixtures, called charges, are then ready for fusion in the furnaces. 22 PREPARATION OF ORES. The mechanical preparation of ores is one of the most important operations in the extraction of certain metals. Great intelligence is required in the arrangement of such works, as the processes which perfectly succeed in one locality may be quite inefficient in another, where the ore occurs in a different gangue or presents a different state of aggregation. The adjoined plate gives a connected view of the different appa- ratus for mechanical preparation and washing just described, as well as the succession of canals and arrangement of the depositing reservoirs, which are generally placed under the flooring of the building. The canals and basins form a large labyrinth, the cor- responding parts of which, coming from different washing-machines, unite at points where the muddy water contains similar substances in suspension. The whole apparatus is moved by the same water- wheel RE/. 23 MANGANESE. Equivalent = 28 (350; 0 = 100.) § 746. Manganese* is obtained by reducing one of its oxides by charcoal at a high temperature. A pure and very dense protoxide, obtained by subjecting carbonate of manganese to strong calcina- tion in a closed crucible, is mixed with TJg its weight of charcoal and Jg of fused borax, and heated to the highest possible tempera- ture in a forge-fire, in a “brasqued” or charcoal crucible. The borax added facilitates the union of the metallic globules into a button. The carburetted metal thus obtained is to the pure metal as cast- iron is to malleable iron, and may be purified by a second fusion with a small quantity of carbonate of manganese, in a small, well-closed porcelain crucible, luted into an earthen crucible, as shown in fig. 472. The manganese thus obtained possesses a certain degree of ductility; and, although it may be filed, breaks under the blow of a hammer, showing a gray fracture much resembling that of certain kinds of cast-iron. Its specific gravity is about 8.0; and it is as difficult of fusion as iron. Manganese has a great affinity for oxygen, as its surface becomes tarnished by exposure to a moist atmosphere, and covered with dark-brown rust. It decomposes water slowly at ordinary temper- atures with the evolution of hydrogen, but effects rapid decom- position at 212°. By blowing on a piece of manganese, the same disagreeable odour is perceived which is given off by a carburetted metal dissolving in a weak acid. To preserve the metal, it must be kept from contact with the air, and is therefore generally kept in naptha, like potassium; but it is better to put the button in a hermetically sealed glass tube. Fig. 472. § 747. Five compounds of manganese with oxygen are known; the first of which MnO is a strong base; the second, Mn303, plays the part of a very weak base ; the third, Mn03, is neither base nor acid; while the two last, Mn03 and Mna07, are well characterized acids. COMBINATIONS OF MANGANESE WITH OXYGEN. * Peroxide of manganese lias been known for a long time, but it was not until 1774 that Seheele proved it to be a peculiar oxide, from which Gahn obtained the metal several years after. 24 MANGANESE. Protoxide of Manganese MnO. § 748. Protoxide of manganese is obtained by reducing one of the higher oxides of the metal with hydrogen, or by calcining the carbonate without the contact of air; which is effected by placing the carbonate in a glass bulb A (fig. 473), blown on a tube ab, and com- municating with an ap- paratus disengaging dry hydrogen gas. As soon as the air is completely driven out of the appa- ratus by the hydrogen, the bulb A is heated with an alcohol-lamp; when the carbonate, disengaging its carbonic acid, leaves the prot- oxide, the hydrogen preventing the latter from being surrounded by air. The parts b and c of the tube (fig. 474) are then drawn out and closed by means of a lamp. The protoxide of manganese thus prepared, is a clear, delicate green powder, which oxidizes rapidly in the air, unless it has been subjected to a slightly elevated temperature. The protoxide is better aggregated and less change- able when the decomposition of the carbonate has been effected in a porcelain tube strongly heated in a reverberatory furnace. By heating native peroxide of manganese, or a large mass of carbonate, in a “brasqued” crucible in a forge-fire, a well-aggre- gated, fine green mass is obtained, which the air does not affect at ordinary temperatures. The surface of the mass often consists of a thin pellicle of reduced metal; but a complete reduction is not propagated by cementation, the immediate contact of charcoal being essential. Protoxide of manganese is a powerful base. Caustic potassa precipitates it from its solutions as white hydrated protoxide, which rapidly changes into brown sesquioxide by absorbing oxygen from the atmosphere. Fig. 473. Fig. 474. Sesquioxide of Manganese Mn203. § 749. Sesquioxide of manganese Mn303 occurs crystallized in nature, both in the anhydrous and hydrated state; the latter much resembling in its external appearance the peroxide, with which it is often associated. But the two oxides are easily distinguished by the colour of their streak or powder, that of the peroxide being dark gray, while that of the sesquioxide is brown. OXIDES OF MANGANESE. 25 § 750. This oxide, the most abundant of all the oxides of man- ganese, is also the most valuable, from its property of giving with chlorohydric acid the greatest quantity of chlorine. It occurs crys- tallized in elongated prisms of a gray colour and metallic lustre. Hydrated peroxide of manganese is obtained as a dark-brown powder by decomposing manganate of potassa with hot water, or by passing chlorine through water containing carbonate of manga- nese in suspension. By calcining peroxide of manganese in an earthenware retort until the evolution of oxygen ceases, a brown powder containing 27.6 per cent, of oxygen is obtained, with the formula Mn304. It is generally called red oxide of manganese, and, as it behaves as a combination of protoxide with sesquioxide, is often written MnO, Mna03; for when it is treated with an acid, protoxide is dissolved and sesquioxide remains. Peroxide of Manganese MnOa. Manganic and Permanganic acids Mn03 and Mna07. § 751. The two acid combinations of manganese with oxygen are obtained by treating caustic potassa with peroxide of manga- nese, either with access of air, or with substances possessing high oxidizing properties. By heating equal proportions of finely pow'- dered peroxide and caustic potassa without access of air, and dis- solving the substance obtained in cold water, a green solution is formed, and a mixture of hydrated sesquioxide and binoxide re- mains as a reddish-brown powder. The green liquid contains, besides some potassa in excess, manganate of potassa KO,MnOs, a portion of the binoxide MnOa having been reduced to sesquioxide Mn203, by giving off oxygen to another portion of the binoxide, which was thus oxidized to manganic acid Mn03. A greater pro- portion of manganate of potassa is obtained by making the calcina- tion in the air; or still better, in an atmosphere of oxygen. Some peroxide of manganese, reduced to an impalpable powder, is well mixed with some caustic potassa dissolved in as little water as pos- sible ; the paste is dried in a porcelain capsule, and introduced in fragments into a glass tube difficult of fusion, communicating with a retort filled with chlorate of potassa. The tube is heated to a dull-red, and at the same time oxygen is disengaged by heat- ing the chlorate; but, in order to obtain a considerable quantity of manganate, the operation should be continued for some time. The substance gives with cold water an intense emerald-green solution, which, after being filtered through a small plug of asbes- tus placed in the bottom of a glass funnel, is evaporated under the receiver of an air-pump, over a capsule filled with concentrated sulphuric acid, when beautiful green crystals of manganate of Vol. II.—C 26 potassa are obtained, generally mixed with white crystals of hy- drated potassa, which may be easily separated by hand. The green crystals are forced from the mother liquid still moistening them, by placing them for a time on a piece of unburned porous clay. The green crystals of manganate of potassa K0,Mn03 dissolve without change in a solution of caustic potassa, and are again de- posited on evaporating the liquid; but on dissolving them in pure water immediate decomposition takes place, the colour of the solu- tion changing to a beautiful red, and a brown precipitate of brown hydrated peroxide being formed. The red solution then contains permanganate of potassa K0,Mns07. The easy decomposition of manganic acid, even when in combination with as strong a base as potassa, renders it impossible to obtain the acid isolated. By heating peroxide of manganese with soda or baryta in con- tact with oxygen, the manganates of soda and baryta are obtained, the latter of which is a green powder, nearly insoluble in water. When the green mass containing the mixture of manganate of potassa, caustic potassa, and oxide of manganese is dissolved in boiling water, and boiled for several minutes longer, an intense red solution is obtained, which, after being filtered through asbestus and evaporated under the receiver of an air-pump, gives prismatic dark-red crystals of permanganate of potassa. But the most simple process for obtaining this substance in any quantity is the following :—One part of peroxide of manganese, reduced to impal- pable powder, is mixed with one part of chlorate of potassa, and one and a quarter parts of caustic potassa, dissolved in the least possible quantity of water, are added : the paste thus formed is dried in a porcelain crucible, during which process a considerable quantity of manganate of potassa already forms. The whole is af- terwards heated slowly to a dull-red in an earthen crucible, then boiled with water in a glass flask, filtered through asbestus, and the liquid concentrated in a porcelain capsule over an alcohol- lamp, when, on cooling, crystals of permanganate of potassa are deposited, which may be purified by recrystallization. Perman- ganate of potassa is not very soluble, as it requires 16 parts of water to dissolve 1 of the salt at 59°, while warm water will dis- solve much more. On adding nitrate of silver to a hot solution of permanganate of potassa, fine crystals of permanganate of silver are deposited on cooling, from which other permanganates may be prepared by adding to it an equivalent quantity of a metallic chloride, for the silver combining with the chlorine leaves its permanganic acid to combine with the metal which existed as chloride. After rubbing the two substances with water, the chloride of silver may be sepa- rated by decantation or by filtration through asbestus. Free permanganic acid can be obtained in aqueous solution by decomposing permanganate of baryta with sulphuric acid, added MANGANESE. 27 by drops; when insoluble sulphate of baryta is formed, and the decanted liquid contains permanganic acid. The solution is of a fine red colour, but the acid decomposes easily even in the cold. Organic substances rapidly decompose the salts of both manganic and permanganic acid by taking up a part of their oxygen, for which reason their solutions must not be filtered through paper. If a red solution of permanganate of potassa, containing caustic potassa, is filtered through paper, the filtrate is generally green from containing manganate; but if the solution is very dilute, or the filtration slow, the liquid completely loses its colour, while the paper takes a deep-brown tinge from the hydrated peroxide which fills its pores. Caustic potassa, added to a dilute solution of permanganate of potassa, immediately changes the colour of the solution, first to violet and then to a fine emerald-green, the permangate being reduced to manganate, while another quantity of potassa has en- tered into combination: MANGANATES AND PERMANGANATES. K0,Mn20?+K0=2(K0,Mn03)+0. The oxygen remains in solution in the water, since only a small quantity was disengaged, and the permanganic solution is very dilute. The decomposition is owing to the strong basic properties of the potassa, which tends to saturate as much acid as possible. The changing from red to green does not take place instantane- ously, and, by adding the potassa in small quantities at a time, the liquid passes through all the intermediate shades between red and green, that is, through all the shades of violet. It was stated that the colour of a green solution of manganate of potassa changes to red by boiling, hydrated peroxide of manga- nese being precipitated; but this takes place only when the solu- tion is not too concentrated. Green manganate is also changed to red permanganate in the cold, without any visible precipitation of peroxide, by adding more and more cold water, the oxygen dis- solved in which effects the oxidation; the liquid again passing through all the shades produced by a combination of green and red. If it is desirable that the solution should not be very dilute, it is sufficient to leave it in contact with the air, or to pass a current of oxygen through it. The name of chameleon mineral has been given to this substance, on account of the phenomena of changing colour. Manganate of potassa is most rapidly converted into permanga- nate by the addition of any acid, even of carbonic; but an excess of acid completely discolours the liquid, by forming a salt with the reduced protoxide of manganese, while oxygen is given off. Of the oxides of manganese, only the protoxide and sesquioxide are bases. 28 MANGANESE. PROTOSALTS OF MANGANESE. § 752. The protosalts of manganese are of an amethyst, or light rose colour, which, however, very soon changes by agitating the liquid in contact with the air, or even by pouring it from one ves- sel into another.* Caustic potassa or soda precipitates white hy- drated protoxide, which soon changes to brown in the air; while ammonia has the same effect in a smaller degree, a similar phe- nomena taking place to that mentioned in § 589 for the salts of magnesia, viz. that the ammoniacal salt formed combines with the salt of manganese, and gives a double salt which an excess of am- monia will not decompose. A perfect precipitation cannot there- fore be effected, whatever may be the quantity of ammonia added; for, if the salt of manganese is neutral, the first drops of ammonia precipitate some protoxide, but at the same time a corresponding quantity of ammoniacal salt is formed, which is soon present in suf- ficient quantity to form with the salt of manganese yet in solution a soluble double salt which is not decomposed by ammonia. An excess of ammonia redissolves the hydrated protoxide already precipitated, by entering into combination with it, unless the precipitate has not already changed to brown sesquioxide, which is insoluble in am- monia. By exposing the ammoniacal solution of protoxide to the air, oxygen is absorbed, and the manganese is at last completely precipitated as hydrated sesquioxide. The alkaline carbonates give a dirty white, and ferrocyanide of potassium a rose-coloured precipitate. The alkaline sulfhydrates precipitate the protosalts of manganese with an orange colour, and sulf hydric acid will not throw them down in the presence of a slight excess of acid, sulphide of manganese being easily decomposed by weak acids. Sulphate of Manganese. § 753. Sulphate of manganese is obtained by heating native peroxide with concentrated sulphuric acid, while oxygen is given off; but the residues of red oxide, which remain after the calcina- tion of peroxide for obtaining oxygen gas, are also profitably em- ployed for this purpose. The sulphate is also sometimes prepared by heating the protochloride of manganese obtained by the prepa- ration of chlorine with sulphuric acid. The sulphate crystallizes with different quantities of water, and in different forms, according to the temperature at which the crystallization takes place : thus, when the temperature is below 43°, the crystals contain 7 equiva- * The pink colour of protosalts of manganese I have found to be mostly, if not always, due to the presence of a minute percentage of cobalt, which is rarely absent from the ores of manganese. I have these ores containing from 0.01 up to 7.0 per cent, of oxide of cobalt.—J. C. B. 29 lents of water, and are isomorphous with sulphate of iron, FeO, S03+7H0 ; while the crystals formed at a temperature between 43° and 68° present the form of sulphate of copper Cu0,S03 + 5IIO, the sulphate of manganese also containing 5 equivalents of water: lastly, between 68° and 86° the salt crystallizes with 4 equivalents of water, and is isomorphous with the sulphate of iron FeO,S03+4H0, which has also been obtained crystallized. These are important facts for the theory of isomorphism. SESQUISALTS OF MANGANESE. Carbonate of Manganese. § 754. Carbonate of manganese occurs in nature in rhombohe- drons, which present the same form as those of carbonate of lime, and are generally of a rose or violet colour. Carbonate of iron and carbonate of lime frequently replace part of the carbonate of man- ganese in the same crystal, thus offering a new proof of the isomor- phism of the protoxides of iron and manganese. Carbonate of manganese may be obtained as a dirty white powder by adding carbonate of soda to a solution of sulphate or chloride of manga- nese. It is soluble in water containing carbonic acid. Other salts of manganese are easily obtained by dissolving the carbonate in the corresponding acids. SESQUISALTS OF MANGANESE. § 755. Although sesquioxide of manganese combines with acids, the salts it forms are not durable. By slightly heating hydrated peroxide of manganese with sulphuric acid, the former dissolves with a beautiful red colour, which solution, mixed with sulphate of potassa or ammonia, yields by evaporation octohedral crystals of a true manganic alum K0,S03+Mn303,3S03+24H0, the exist- ence of which proves sesquioxide of manganese to be a particular oxide, and not a combination of protoxide with peroxide. Oxidizable substances instantly change sesquisulphate of manganese to proto- sulphate, the liquid losing its colour; a property of the sesquisul- phate which is often made use of in the laboratory to ascertain whether an oxide is present in its highest stage of oxidation,—for example, to ascertain whether sulphuric acid contains any sulphu- rous acid, or whether nitric be free from nitrous acid. COMBINATION OF MANGANESE WITH SULPHUR. § 756. A hydrated protosulphide of manganese is obtained by adding a solution of an alkaline monosulphide to that of a proto- salt of manganese, when a light-red precipitate is formed, which disengages sulfhydric acid on being dissolved in acids. Anhydrous 30 monosulphide is obtained by heating peroxide of manganese with sulphur, when sulphurous acid is set free : MANGANESE. MnOa+2S=MnS+SOa. The excess of sulphur is driven off by heating to redness, but the monosulphide thus prepared is almost always mixed with pro- toxide, and may be obtained in a state of greater purity by decom- posing oxide of manganese with sulphide of carbon at a red-heat. COMBINATIONS OF MANGANESE WITH CHLORINE. § 757. Protochloride of manganese is prepared by heating native peroxide with chlorohydric acid, while chlorine is disengaged; but as the native peroxide always contains a certain quantity of iron, the solution usually contains some perchloride of iron, to separate which the solution must be completely evaporated to dryness, by which the excess of chlorohydric acid is also driven off. The residue is dissolved in water, and the liquid boiled for some time ■with a little carbonate of manganese, which effects the precipita- tion of the peroxide of iron, while carbonic acid is disengaged, as protoxide of manganese is a much stronger base than peroxide of iron.* Protochloride of manganese crystallizes with 4 equivalents of water, one-half of which it gives off at 212° ; but when heated still higher, it becomes completely anhydrous and at last fuses. When fused in contact with the air, the oxygen of the latter expels the chlorine, and the protochloride is converted into protoxide. Ex- periments have been made to turn this property to technical use, by regaining part of the chlorine contained in the protochloride of manganese, which is a residue in the manufacture of bleaching- powder; and it was effected by roasting the protochloride in rever- beratories, and leading the gases, which were highly charged with chlorine, into the chambers where chloride of lime is prepared. The roasting, which was done at as low a temperature as possible, converted the protochloride into sesquioxide, which was treated with chlorohydric acid to obtain a new quantity of chlorine. But, as the oxide thus obtained only gives one-lialf the quantity of chlorine that an equal weight of peroxide would, and as the opera- tions are too costly, they are no longer continued. § 758. Sesquichloride of manganese Mn3Cl3, is obtained by treat- ing hydrated sesquioxide with chlorohydric acid, without applica- tion of heat. The red solution obtained develops chlorine by heating, and changes into protochloride. * The same insolubility of the percliloride of iron is effected by heating the mixture, when dry, to full redness.—J. C. B. TESTING THE OXIDES OF MANGANESE. 31 DETERMINATION OF MANGANESE, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. §759. The manganese existing in a solution is usually deter- mined by adding carbonate of soda to the boiling liquid, washing the precipitated carbonate of manganese wTell with boiling water, and calcining it to a high red-heat, by which it is converted into red oxide Mn304 containing 72.11 per cent, of manganese. The carbonate is dried and calcined with its filter in a platinum crucible, which, being covered with its lid, is placed in an earthen crucible and heated to a strong red-heat. When the liquid from which the oxide of manganese is to be precipitated contains any quantity of ammoniacal salt, it must be evaporated with an excess of carbonate of soda and the residue redissolved in water. § 760. Manganese is separated from the alkaline metals by means of carbonate of soda, or by sulfhydrate of ammonia, which pre- cipitates it as sulphide, which, after being washed with water con- taining some sulfhydrate, is dissolved in an acid, and reprecipitated by carbonate of soda. It is easily separated from baryta and strontia by adding sul- phate of soda to the liquid, which precipitates the. baryta and strontia as sulphates. It is separated from lime and magnesia by sulfhydrate of ammonia, which precipitates only the manganese as sulphide, if the solution is sufficiently dilute. Its separation from alumina and glucina is easily effected by boiling the liquid for some time with an excess of caustic potassa in contact with the air, when the manganese is precipitated as hydrated sesquioxide, while the two earths dissolve in the excess of alkali. TESTING THE OXIDES OF MANGANESE. §761. In works where bleaching-powder is made, considerable quantities of peroxide of manganese are used, the commercial value of which depends on the quantity of chlorine it will develop when treated with chlorohydric acid; but, as the native peroxide is always mixed with more or less gangue and sesquioxide of man- ganese, it is important that the purchaser should be able to deter- mine the quantity of chlorine which a given weight of oxide will develop by a simple process. One litre of dry chlorine is disengaged by 3.98 gm. of perfectly pure binoxide of manganese at 32° and under the pressure of 760 mm.; and if it be absorbed by a dilute solution of caustic potassa, and water added until the volume of the liquid is 1 litre, a solution is obtained containing precisely its volume of chlorine, and therefore marking 100 chlorometric degrees. But 3.98 gm. of a peroxide of commerce will, when treated in the same manner, give 32 MANGANESE. a solution containing a less volume of chlorine, the quantity of which, when determined by the common chlorometric processes (§ 572), expresses the value of the peroxide employed. Supposing the quantity of chlorine found to be 60, the conclusion follows that the oxide in question only gives a quantity of chlorine represented by 60, while the same weight of pure binoxide yields a quantity represented by 100; and, to obtain the same quantity of chlorine as one kilog. of pure binoxide would give, = 1.67 kilog. of the other oxide must be employed. § 762. An average sample of the peroxide to be examined being first made by picking small quantities from all parts of the mass, it is reduced to a fine powder, of which exactly 3.98 gm. are intro- duced into a small flask A (fig. 475), about 5 centimetres in dia- meter. By means of a well-fitting cork the flask is furnished with a tube, bent as in the figure, to convey the gas into a long-necked flask B, hold- ing about | litre. The latter is placed in an in- clined position, and filled up to the neck with a weak solution of caustic potassa. The peroxide is introduced into the flask A with a suitable quantity of chlorohydric acid, which is measured in a tube graduated to 25 cubic centimetres; and after adjusting the cork, the temperature is gradually raised. The chlorine first expels the air from the flask A, and causes it to fill the upper part of the bulb B, while the water it displaces rises in the neck. Toward the end of the operation, the liquid in A is heated to the boiling point, so that the steam generated drives all the chlorine into the alkaline liquid. The flask B is then taken away, while the boiling is continued in A to prevent any absorp- tion, and the chlorine is determined in the alkaline liquid by one of the chlorometric methods. § 763. A solution of sulphurous acid, perfectly free from sul- phuric, may be substituted for the alkaline liquid in the flask B, as the chlorine, when led into the former, converts a corresponding quantity of sulphurous acid into sulphuric, the quantity of which is determined by adding chloride of barium, boiling to expel the excess of sulphurous acid, collecting the precipitate on a filter, and weighing it after calcination. The quality of the peroxide is then proportional to the weight of the sulphate of baryta obtained, 3.98 gm. of pure peroxide giving 10.65 gm. of sulphate of baryta. As the sulphurous acid used must be perfectly free from sul- phuric, it is important to test it to this effect before each determi- nation, which is done by adding a few drops of chloride of barium, Fig. 475. TESTING THE OXIDES OF MANGANESE. 33 which should give no precipitate. A certain quantity of chloride of barium may at once be added to the liquid, so that sulphate of baryta forms as the sulphurous acid oxidizes by the oxygen of the air; and when the solution is to be used, the clear liquid, which of course is free from sulphuric acid, can be decanted off from the precipitate. The best method of conducting the experiment is that repre- sented in fig. 476. Water, freed from air by boiling, and some Fig. 476. chloride of barium, are introduced into the flask A, into which, as soon as the water has cooled, a current of hydrogen is led, supplied hy the generator B. As soon as the air is expelled from A by the hydrogen, a current of sulphurous acid gas is introduced, obtained by heating concentrated sulphuric acid with copper or mercury in the flask C, and purifying it by washing with water in the small flask D. Lastly, the 3.98 gm. of peroxide are heated in the flask E with chlorohydric acid, and the chlorine disengaged is led into the flask A, where it oxidizes a corresponding quantity of sulphur- ous acid to sulphuric, which precipitates as sulphate of baryta, while there is no fear that sulphuric acid might form by the contact of sulphurous with the air. Toward the end of the operation the liquid in A is boiled to expel the excess of sulphurous acid, the oxidation of which is still prevented by continuing the stream of hydrogen; and finally the sulphate of baryta formed is collected on a filter. § 764. The finely powdered oxide of manganese may also be heated with a concentrated solution of oxalic acid, which forms protoxalate of manganese, while the oxygen given off by the re- duction of the higher oxides to protoxide converts a corresponding quantity of oxalic -into carbonic acid, which may be precipitated as carbonate of baryta by being led into a solution of baryta, or better still, may be conducted into a weighed bulb-apparatus containing a concentrated solution of caustic potassa, the increase of weight of which after the operation corresponds exactly to the carbonic 34 MANGANESE. acid. In either case the gas must be dried by being passed through a tube containing concentrated sulphuric acid. § 765. For an accurate estimation of the value of an oxide of manganese it is not sufficient merely to determine the quantity of chlorine it will develop, hut the quantity of chlorohydric acid required to disengage the chlorine must also be found. If the oxide is pure binoxide, the chlorine of one-half of the acid is neces- sarily disengaged, while pure sesquioxide will only give one-third of the chlorine; for which reason, in the latter case, one and a half times the quantity of acid is required to give the same quantity of chlorine as when pure binoxide is used; and lastly, if the oxide is mixed with a gangue of lime, baryta, or oxide of iron, these bases will neutralize a part of the acid without disengaging chlorine. To find the quantity of chlorine required, the acidimetric percentage of 25 cubic centimetres of the acid employed is first determined, and 3.98 gm. of the oxide of manganese are treated with other 25 cubic centimetres of the same acid, the flask containing the mixture being kept heated. The chlorine is lost, but the small quantity of chlorohydric acid which might distil over is condensed in a moist flask through which the gas is led. When all the chlorine is dis- engaged, the small quantity of liquid in the moist flask is added to the residue in the flask in which the gas was developed, the liquid is diluted to the volume of half a litre, and the remaining acid is determined by adding a standard alkaline solution until the pre- cipitate of hydrated oxides, which forms on the addition of every drop, is no longer redissolved by shaking the liquid. This experi- ment gives the quantity of acid which has remained free, and show's, when compared with the former experiment, the quantity of acid required by the oxide of manganese.* * The following is a shorter method of testing peroxides of manganese. The chlorine disengaged from a weighed quantity of the oxide is conducted into the solution of a given quantity of a protosalt of iron, an equivalent quantity of which it oxidizes to peroxide; so that, if the remaining quantity of protoxide of iron which is determined with permanganate of potassa (as will he described in § 804) be subtracted from the quantity contained in the protosalt employed, the differ- ence will be in proportion to the chlorine disengaged. The protosalt of iron best adapted to the purpose is the protosulphate of iron and ammonia, which is easily obtained by mixing equal volumes of saturated solu- tions of sulphate of iron and sulphate of ammonia, when the liquid on evaporating yields prismatic crystals of the salt, the formula of which is Fe0,S03-(-NH40, SO3+6HO. One hundred grammes of the salt are dissolved in 1837 cubic centi- metres of water, so that the solution contains 5.44 per cent, of the salt; or, 544 parts of the salt corresponding to 184 parts of pure protoxide, exactly one per cent, of protoxide of iron: and the standard solution thus obtained, which is best prepared in larger quantities at a time, is used for all chlorometric determina- tionSj as well as for that of chrome. Supposing the quantity of oxide subjected to the test to be exactly one gramme, and the substance to be pure peroxide, which gives one equivalent of chlorine; then will the quantity of chlorine developed be 0.807 gm.; and supposing the quantity of the standard solution of iron employed to be 200 cubic centimetres, ■which contain 2 gm. of protoxide, only 1.63 of which are oxidized by the chlorine; 35 then will the 0.37 gm. of protoxide, determined directly by permanganate of po- tassa, and subtracted from the 2 gm. employed, give the quantity of protoxide which was oxidized, viz. 1.63 gm., which correspond to 0.807 gm. of chlorine, as one equivalent of chlorine oxidizes two equivalents of protoxide of iron.— W. L. F. Another method of determining the commercial value of peroxide of manganese, better than that described in the text, is to employ dry oxalate of soda, which is easily prepared and preserved, and of which 152J grains are just sufficient for 100 grs. of pure binoxide, in order that its oxalic acid may be wholly converted into 100 grs. of carbonic acid. 76 grs. of the dry oxalate and 50 grs. of the per- oxide are introduced with about J oz. of water into a small flask containing two tubulures, through one of which an S-tube passes, and through the other a small tube connected with a tube of sulphuric-pumice or chloride of calcium. The whole apparatus being weighed at once, together with about 200 grs. of oil of vitriol, the latter is gradually poured through the S-tube into the little flask. The oil of vitriol disengages the oxalic acid, which is oxidized into carbonic acid by the excess of oxygen over that in the protoxide, and since it cannot pass through either escape-tubes without being dried, the loss of weight of the whole apparatus indicates the loss of carbonic acid alone. The number of grains of loss being doubled, gives the percentage of peroxide equivalent to pure binoxide. The dif- ferent methods of arranging the apparatus will be found in the analytical chemis- tries of Rose and Fresenius, and others, and in the Encyclop. of Chem. The best commercial varieties contain from 80 to 98 per cent, of binoxide.—J. C. B. TESTING THE OXIDES OF MANGANESE. 36 IRON. Equivalent = 28.0 (0=100; 350.0). §766. On account of its numerous technical applications, iron is the most important of all the metals. It is used in three states: 1. Bar or malleable iron. 2. Steel. 3. Crude or cast-iron. Steel and cast-iron are combinations of iron with small hut vari- able quantities of carbon and silicium. The bar-iron of commerce is not chemically pure, as it contains a small quantity of carbon, and often traces of silicium, sulphur, or phosphorus, which latter remarkably affects its quality. The iron used in fine locksmith’s work approaches a state of purity ; but the purest iron is found in piano-forte wires, or ordinary wire, because only iron of great purity can be drawn out into very fine threads. In order to obtain iron chemically pure, some wire is cut into pieces of the same length, and tied in bundles ; when their surface is oxidized, by heating them for a few moments exposed to the air, or better still, in a porcelain tube through which steam is passed. The bundles of oxidized iron are then placed in a small porcelain crucible with a small quantity of powdered glass ; and the crucible being set in a second earthen crucible, luted externally with clay, is heated in a blast-furnace at the highest temperature that can be produced. The small quantities of foreign matter contained in the iron, are burned by the oxygen of the oxide, while the excess of oxide of iron, combining with the glass, forms a slag. If the temperature be sufficiently elevated the purified iron fuses to a single lump. Pure iron is whiter and more malleable than the iron of commerce, but less tenacious. Pure iron may likewise be obtained by the reduction of one of its oxides by hydrogen, which takes place at a dull red-heat, and may be effected in the small apparatus described (fig. 473) for the preparation of the protoxide of manganese. The metallic iron remains in the tube, in the form of a grayish-black powder, which may be preserved by closing hermetically both ends of the tube while it is filled with hydrogen gas ; for very finely divided iron has so great an affinity to oxygen that it is inflamed by contact with the air; a property which has given to it the name of pyro- phoric iron. If the reduction be made in a porcelain tube at a high temperature, the metal becomes solid, assuming a metallic lustre, and no longer oxidizing in dry air. < 37 Perfectly pure iron may also be procured, by heating protochlo- ride of iron in a glass tube, through which a current of hydrogen gas is passed; when the iron forms on the sides of the glass a glit- tering, brilliant coating, in which small cubic crystals may often be seen. § 767. The texture of commercial iron varies greatly, according to its mode of manufacture. Pure iron which has been forged and rolled equally in all directions, exhibits a texture of very small, brilliant grains; but, when drawn out into bars, its texture is often decidedly fibrous, the fibres always running in the direction of the bar, which may be readily proved by breaking the latter. The fibrous texture is highly esteemed, because the iron possessing it is much more tenacious than granular iron, and bears a greater weight without breaking. The fibrous texture of iron is generally regarded as an index of its good quality; however, skilful work- men can impart this quality also to bars of an inferior sort. Iron of fibrous texture does not always remain in that state, but after some time changes into the granular, or even the laminated tex- ture ; which change ensues most rapidly when the bars are sub- jected to vibration, as, for instance, when they support the floor of a suspension-bridge. The tenacity of the metal diminishes at the same time in a remarkable manner, and it frequently breaks with a load which the bar would easily have borne when its tex- ture was fibrous. A change of this kind is frequently observed in the axles of locomotives and railway-cars.* The specific gravity of wrought-iron varies from 7.7 to 7.9. Iron is the most tenacious of all the metals, a cylindrical iron-wire of 2 millimetres in diameter being able to sustain a load of 250 kilogs. § 768. The highest temperature that can be produced in a blast- furnace is required for the fusion of iron, which, however, is more easy when it can be combined with carbon. Iron passes from the fluid to the solid, through the doughy state, and therefore belongs to that class of substances which crystallize with difficulty by fusion. However, if large masses of iron, heated to a very high temperature, be allowed to cool very slowly, indications of crystallization of the cubic form are found in the interior of these masses.f Heated to a white-heat, iron becomes sufficiently soft to assume any form under the hammer; and two bars, when heated to redness, can be readily soldered to each other without the interposition of another metal, when the surfaces to be joined are completely free from oxide. IRON, * The fibrous texture of iron is also changed to the granular by heating the metal to redness, and immersing it while hot into cold water.— W. L. F. f Some species of cast-iron, as, for example, that made from the manganiferous sparry iron-ore of Muesen in Westphalia, and that made at Easton, in Pennsyl- vania, the latter of which is remarkable for its extreme ductility when converted into bar-iron, show a laminated texture, which is owing to its being an aggregated mass of laminated prismatic crystals, the angles of which are about 112°.— W. L. F. 38 IRON, Now, as it is known that iron heated in the air soon oxidizes, the blacksmith generally throws a small quantity of sand upon the bars he wishes to solder, which, by combining with the oxide of iron, produces a very fusible silicate, which, forming a kind of varnish on the surface of the metal and preventing its further oxi- dization, is afterward, from its extreme fluidity, entirely driven off by the blows of the hammer. § 769. Iron, cobalt, and nickel are the only metals which are remarkably magnetic at the ordinary temperature. A piece of pure iron immediately becomes a magnet, either by contact with or at a short distance from a native magnet, its magnetic properties dis- appearing again as soon as the magnet is removed; but if the iron is combined with a small quantity of carbon, if it is steely, the magnetism is slower of development, but continues longer after the removal of the magnet. A bar of steel, rubbed against a magnet, acquires permanent magnetic properties, and becomes a true mag- net. The magnetic properties of iron diminish rapidly with the temperature, an iron ball heated to a whitish red-heat no longer exerting any influence over the needle, but recovering its magnetic virtue on cooling. § 770. Iron remains unchanged for an indefinite time in dry air, and even in dry oxygen, at the ordinary temperature; but soon alters in moist air, by becoming covered with rust. The rust of iron, which consists of an oxidation of its surface, is most readily formed in the presence of carbonic acid, of which the air always contains a small quantity. Under the influence of the carbonic acid and the oxygen, the surface of the iron is converted into proto- carbonate, which, on absorbing a new portion of oxygen, is trans- formed into hydrated peroxide of iron, while the carbonic acid disengaged favours the oxidation of an additional quantity of metal- lic iron. It has been observed, that when iron has begun to rust at any particular point, it changes very rapidly around this point, which is produced by a galvanic phenomenon accelerating the oxi- dation. The iron and thin layer of oxide which forms on its surface constitute the two elements of a pile in which the iron becomes posi- tive, and thus acquires an affinity for oxygen sufficiently great to decompose water at the ordinary temperature, with the evolution of hydrogen gas. This phenomenon is rendered very evident by allow- ing moist iron-filings to rust in the air, when, after some time, the odour exhaled by hydrogen gas* made from the carburetted metals is easily recognised. Rust almost always contains a small quantity of ammonia, the presence of which may be recognised by heating it with potassa, and is explained as follows :—It has been shown (§122) * This peculiar odour is not exhaled by hydrogen gas, but is that of a certain substance called ozone, and shown by Bunsen to be a combination of one atom of hydrogen with three of oxygen, which forms under almost all circumstances where a galvanic current is active.— W. L. F. IRON 39 that when hydrogen and nitrogen meet in the nascent state in a liquid, they combine and form ammonia: now, the water which moistens the rust, being in contact with the air, contains nitrogen in solution, and on the other hand, hydrogen is disengaged by the decomposition of the water. The circumstances under which am- monia can form by the direct combination of hydrogen and nitro- gen are therefore realized. The peroxide of iron, which acts wTith very powerful bases the part of a feeble'acid, retains the ammonia and prevents it from being disengaged. It is important to he aware of the presence of ammonia in rust, as it has been long since admitted, that when spots of rust which were found on sidearms or steel weapons, suspected to have been used in the commission of a crime, evolved ammonia by contact with potassa, it was a proof that the rust was formed by contact with animal matter, and these spots of blood were the cause of its pre- sence. This presumption was erroneous ; for as we have just seen, steel-rust formed by the contact of air alone may contain an appre- ciable quantity of ammonia. Rust soon changes in fresh water, hut very slightly in water containing a few thousandths of carbonate of soda or potassa. During the last few years, iron has been preserved from rust by covering its surface with a very thin layer of metallic zinc,* and iron thus coated is called galvanized iron. This phenomenon Avas explained in § 305. Iron soon oxidizes by contact with the air when heated to red- ness, becoming covered with a black pellicle of oxide, which falls off under the hammer. To this easy combustion of iron in the air may be attributed the property which it possesses of giving out sparks when struck by a flint, in which case small particles are detached, which, being strongly heated by friction against the flint, become incandescent by combining with the oxygen of the air, and may easily inflame combustible substances, such as tinder. If the steel be struck for some time over a sheet of white paper, the latter will be covered with small black particles, which are attracted by the magnet, and are, in fact, small spherical globules of mag- netic iron. § 771. Iron is readily acted on by chlorohydric acid, protochlo- ride of iron being formed, and hydrogen disengaged. Dilute cold sulphuric acid dissolves it with the evolution of hydrogen, wdiile the concentrated acid also attacks it, but disengages sulphurous acid. Concentrated nitric acid attacks it sharply with a copious * A patent has lately been taken out in Europe (Vienna ?) for preserving iron from rust by a coating of metallic cadmium, which at the same time imparts a silvery lustre to the surface. Silicate of potassa, the German wasserglas, has also been employed.— W. L. F. 40 IRON, disengagement with nitrous fumes,* while the dilute acid dissolves it without any apparent evolution of gas, forming at the same time protonitrate of iron and nitrate of ammonia (122). COMPOUNDS OF IRON WITH OXYGEN. § 772. Three compounds of iron with oxygen are known : 1. A protoxide FeO, which is a powerful base, isomorphous with the bases of which the formula is RO. 2. A sesquioxide Fe203, being a very feeble base, analogous to alumina, and isomorphous with the oxides of which the formula is 3. Lastly, an acid Fe03, analogous to manganic acid. A fourth compound of iron with oxygen, of the formula Fe304, is also known, and is called magnetic oxide; but as it behaves like a compound of protoxide and sesquioxide FeO,FeaOa, it is regarded as such. Protoxide of Iron FeO. § 773. Protoxide of iron has hitherto not been obtained in a state of purity. When a large bar of iron heated to redness is allowed to cool slowly in the air, its surface oxidizes, and a black pellicle of a metallic lustre is formed, which falls off under the hammer, and is called finery cinder. If a thin piece of cinder be examined with a lens, it is seen to be composed of several layers; the outer stratum showing nearly the composition of magnetic oxide Fe304, while the inside layer, or that immediately in contact with the metal, resembles the protoxide very closely. If a solution of caustic potassa be added to a protosalt of iron, a white precipitate of hydrated protoxide is obtained, which soon turns green on exposure to the air, by forming hydrated sesqui- oxide by absorption of oxygen. If boiling solutions be used, and the ebullition prolonged for some time, the white precipitate loses its water of hydration and becomes black; but the oxide has such an affinity for oxygen that it is impossible to collect it unchanged. It even decomposes water at the boiling point, and is ultimately converted into magnetic oxide. French bottle-glass owes its hue to the presence of this oxide (§ 684), which imparts a deep green colour to fluxes. * Very concentrated nitric acid will not dissolve pure iron at all, owing to an electrical phenomenon by which the iron is brought to the passive state, and changes its electropositive power. The iron will continue in this state, and not be attacked by the acid, even on diluting the latter to almost any degree; but on touching the piece of passive iron, lying in the diluted acid, with a piece of common.iron, such as a key, the galvanic current produced by the contact of the two pieces, whose electromotive power is yet different, instantly changes the passive iron back to its natural state, and renders it soluble.— W. L. F. OXIDES OF IRON. 41 Sesquioxide of Iron Fe303. § 774. The sesquioxide Fe303, or peroxide, is a substance abun- dantly met with in nature, occurring either in the anhydrous or the hydrated state. The anhydrous peroxide forms flattened rhombo- hedral crystals, very brilliant and nearly black, while their powder is of a deep red colour. Mineralogists call it specular iron: it is found in veins in the old rocks. In the fissures of volcanic lavas, thin and brilliant laminae of peroxide of iron are often found, having the form of regular hexagons, and also belonging to the class of specular iron. Anhydrous peroxide of iron, which is also found in compact masses, of an intense red colour, is called by mine- ralogists red hematite, and is known in the arts by the name of bloodstone, a substance extensively employed for polishing metals. Peroxide of iron is prepared artificially by calcining protosul- phate of iron, when sulphurous and sulphuric acids are disengaged, and the peroxide remains in the form of a red powder : 2(S03,Fe0)=Fe303+S03+S03. Peroxide of iron thus prepared is known by the name of colco- thar, and used for painting, for polishing silver, and for giving the last polish to mirrors. The intensity of colour of peroxide of iron is in proportion to its compactness. Peroxide of iron may be obtained in the form of small crystal- line lamellae, of great lustre and nearly black, by calcining in a crucible 1 part of sulphate of iron with 3 parts of sea-salt. The calcined matter is treated with boiling water, which leaves the per- oxide. § 775. Hydrated peroxide of iron is prepared by adding potassa or ammonia to the solution of a sesquisalt of iron, when a copious brown precipitate is formed. When the reaction has been effected by caustic potassa, the precipitate always retains a small quantity of alkali, which is removed with difficulty only by prolonged boil- ing with pure water. The precipitation may be made by a solution of carbonate of potassa or soda, in which case the precipitate is also hydrated peroxide of iron, the carbonic acid being disen- gaged, or combining with the excess of neutral carbonate, which it transforms into bicarbonate. Hydrated peroxide of iron parts readily with its water by the application of heat, but when heated still further, a temperature is soon attained at which the oxide suddenly becomes incandescent from a spontaneous evolution of heat. This incandescence is only momentary, and the temperature of the oxide again falls to that of the vessel in which it is heated; but its physical and chemical properties have been remarkably modified, as it has become more compact, and dissolves with great difficulty even in highly concen- 42 IRON trated acids. Sesquioxide of iron, heated to a high white-heat, loses a portion of its oxygen, and is converted into magnetic oxide Fe304. Peroxide of iron colours fluxes of a reddish yellow, but a consi- derable quantity is necessary to produce this effect in glass. The small quantity of protoxide which imparts a deep green hue to a vitreous flux, does not colour it appreciably when converted into peroxide (§ 674). Magnetic oxide of iron Fe304. § 776. A native oxide of iron, intermediate between the prot- oxide and peroxide, is often found in very regular, brilliant octa- hedrons, of a fine metallic lustre. At other times it is found in the old rocks in compact masses, often very large, and is worked as an iron ore. Large quantities of it are found at Dannemora, in Sweden, and from this ore the best quality of iron is obtained. This compound has been called magnetic oxide, from its possessing very highly developed magnetic properties. Native loadstone is formed of this oxide of iron. Magnetic oxide of iron is only produced when iron burns at a high temperature in the air, or in oxygen; for example, by the rapid combustion of iron-wire in pure oxygen (§ 64). But the,most certain method of obtaining it in the laboratory consists in heating iron-wire in a porcelain tube, in a current of steam, as in the ex- periment described in § 68, Avhen the surface of the wire becomes covered with an infinite number of small, very brilliant crystals, which by the aid of a lens are seen to be regular octahedrons, resem- bling those of the native magnetic oxide. This oxide may also be obtained in the hydrated state, by dis- solving the magnetic oxide in chlorohydric acid, and adding a large excess of ammonia, when a deep green precipitate, becoming black by desiccation, is formed. This hydrate is magnetic, like the anhydrous oxide. Hydrated magnetic oxide may likewise be pre- pared by pouring into ammonia a mixture of equal equivalents of persulphate and protosulphate of iron. In order to make this mixture, two equal volumes of the same solution of protosulphate of iron are used, one of which is transformed into persulphate by evaporating it to dryness with nitric and sulphuric acids, and then redissolved in the other volume of protosulphate. The magnetic oxide does not behave like an oxide per se, but rather like a compound of protoxide and peroxide. Its formula is properly Fe0,Fe303, analogous to that of red oxide of manganese Mn0,Mn203. The solution of magnetic oxide in an acid possesses the properties of a mixture of a protosalt with a sesquisalt; and if an alkali is dropped into the liquid, the peroxide is precipitated before the protoxide. In order to precipitate the two oxides in OXIDES OF IRON. 43 combination the proceeding must be inverted, and the solution of the salt of iron be poured into the alkaline liquid. We shall, more- over, soon see several compounds presenting a similar chemical formula, and affecting identical crystalline forms, but in which the peroxide of iron is often replaced by alumina or by oxide of chrome, while magnesia, protoxide of manganese, or oxide of zinc often take the place of the protoxide. Ferric acid FeOa. § 777. The third compound of iron with oxygen possesses the properties of an acid corresponding with manganic acid, and is formed under the same circumstances. A mixture of iron filings and nitrate of potassa is heated to redness in an iron crucible, when a beautiful red solution of ferrate of potassa is obtained by treating the mass with water, resembling permanganate of potassa in colour. It is also procured by passing chlorine through a concentrated solution of caustic potassa, containing hydrated peroxide of iron in suspension. Pieces of caustic potassa are added from time to time, in order constantly to maintain a large excess of alkali in the liquid. Ferrate of potassa, being nearly insoluble in a concentrated solu- tion of potassa, is deposited in the form of a black powder, which may be almost entirely separated from the mother liquid by drying it on unglazed porcelain. Ferrate of potassa is still less fixed than the manganate, and has not yet been obtained in a crystalline form. Its solution cannot be filtered through paper, as it immediately decomposes when in contact with organic matter, forming hydra- ted sesquioxide of iron. § 778. The following is the composition of the four oxides of iron: Protoxide FeO Iron 77.78 28 Oxygen 22.22 8 100.00 ~36 Sesquioxide FeaOa Iron 70.00 56 Oxygen 80.00 24 100.00 ~80 Magnetic oxide FeO,Fe203 Iron 72.42 84 Oxygen 27.58 32 100.00 Il6 Ferric acid Fe03 Iron 53.84 28 Oxygen 46.16 24 100.00 ~~52 The equivalent of iron is 28, or 350 when that of oxygen is as- sumed as 100. 44 IRON, SALTS OF PROTOXIDE OF IRON. § 779. The hydrated protosalts of iron are of a bright green colour, which they nearly lose by parting with their water; and their solutions are also of a bright green. Their taste is astringent and metallic. Potassa and soda, poured into the solution of a protosalt of iron, yield a white precipitate, which immediately turns green by contact with the air, and, when left exposed to the atmosphere for an in- definite time, becomes ochrous, and is converted into hydrated ses- quioxide. This property distinguishes the protosalts of iron from those of manganese, the latter yielding with the alkalies a white precipitate, which turns brown in the air, without passing through the intermediate green. Ammonia produces with the protosalts of iron a reaction re- sembling that with the salts of manganese (§ 752). An excess of ammonia redissolves the protoxide; but by absorbing the oxygen of the air, the liquid soon becomes clouded, and hydrated sesqui- oxide is precipitated. The alkaline carbonates, poured into a very cold solution of a protosalt of iron, throw down a white precipitate of protocar- bonate, which, not being very fixed, soon parts with its carbonic acid. Sulfhydric acid does not precipitate the protosalts of iron, how- ever slightly acid they may be, while the sulfhydrates give black precipitates. Yellow ferro-cyanide of potassium yields a white precipitate, which soon turns blue by absorbing the oxygen of the air. The red ferro-cyanide gives a beautiful deep-blue precipitate. Succinate and benzoate of ammonia do not precipitate the proto- salts of iron. Phosphate of potassa gives a white precipitate, which turns blue by exposure to the atmosphere. Arseniate of potassa yields a white precipitate, which turns green in the air. Tannin forms no precipitate with the protosalts of iron, but the liquid soon blackens in the air. Protosulphate of Iron. § 780. The sulphate is the most important of the protosalts of iron, being used in dyeing, under the name of green vitriol, or cop- peras. It is prepared in the laboratory by dissolving metal- lic iron in dilute sulphuric acid, when hydrogen is disengaged. This process is sometimes adopted in the arts; but copperas is generally obtained from the native sulphides of iron or pyrites, which are abundantly found in nature, but cannot be used as iron SALTS OF IRON. 45 ores, because the reduction of the metal would be too expensive, and iron of an inferior quality would be obtained; but as the py- rites frequently contain some hundredths of sulphide of copper, this metal is extracted from them. For this purpose they are roasted, by a process hereafter to be described, when the metals are oxidized, and a great portion of the sulphur is disengaged in the state of sulphurous acid, while another portion is oxidized still higher, and, by combining with the metallic oxides as sulphuric acid, yields sulphates which are removed by washing. In some localities sulphur is obtained from pyrites by calcining them in retorts, when a portion of the sulphur is disengaged, and a disaggregated magnetic sulphide of iron remains in the retort, absorbing rapidly the oxygen of the moist air, and changing into a sulphate. In other localities, schistous rocks filled with small crystals of pyrites are found, which sometimes change rapidly in the air and fall; that is to say, soon become reduced to powder. The sul- phide of iron is then changed into a sulphate, while the schist itself is more or less decomposed, and yields sulphate of alumina, when the two sulphates are dissolved in water. The vitriolic liquids are evaporated in leaden boilers, and con- ducted, when suitably concentrated, into a large vat, where they are allowed to settle for some time, and then are run off into large crystallizing-vats. Strings, on which the crystals of sul- phate of iron form, are suspended in the liquid. When the mother liquid yields no more crystals of the sulphate, even after additional concentration, it is used for the preparation of alum. The water contains sulphate of alumina, which crystallizes with difficulty; but an addition of sulphate of potassa soon effects the deposition of crystals of alum, which are purified by recrystallization. The sulphate of iron of commerce is often covered with a basic persulphate, rendering its surface ochreous, which is removed by dissolving it in water and boiling the solution with iron filings, which reduce the sesquisulphate of iron to protosulphate. Sul- phate of iron crystallizes at the ordinary temperature with 7 equi- valents of water, while the crystals deposited at 176° contain only 4 equivalents. The same salt readily parts with a portion of its water when heated, but a temperature of nearly 572° is requisite to drive off the last particles of it. Dishydrated sulphate of iron forms a white powder, which, if heated still further, is decomposed by disengaging sulphurous and sulphuric acids, while peroxide of iron remains (§ 138). 100 parts of water at 59° dissolve 73 of crystallized sulphate, and at 212° more than 300 parts. Protonitrate of Iron. § 781. This salt is obtained by dissolving metallic iron in cold dilute nitric acid, when a certain quantity of nitrate of ammonia 46 IRON, is also formed, which combining with the nitrate of iron, produces a double salt, which is deposited in crystals. The formation of nitrate of ammonia is owing to the fact, that while the iron is being oxidized at the same time at the expense of the oxygen of the water and of that of the nitric acid, hydrogen and nitrogen gas are simultaneously disengaged, and combine in the nascent state to form ammonia. The best method of obtaining protoni- trate of iron consists in decomposing a solution of protosulphate of iron by nitrate of baryta. Carbonate of Iron. § 782. Carbonate of iron is found in nature as sparry iron, crystallized in rhombohedrons, resembling those of carbonate of lime, and is highly esteemed as an ore. It is found in veins in the old rocks. Carbonate of iron, heated in an earthen retort, yields magnetic oxide of iron as a residue, and disengages a mix- ture of carbonic oxide and acid. Carbonate of iron has not yet been artificially prepared. Sesquisalts of Iron. § 788. These salts are prepared by dissolving the hydrated peroxide in acids, or by subjecting the protosalts to an oxidizing agency in the presence of an excess of acid. Thus, protosulphate of iron is converted into a persulphate by heating it with nitric acid, while reddish vapours are given off, and the substance be- comes brown. This colour is owing to the fact that the deutoxide of nitrogen which is formed dissolves in the undecomposed proto- sulphate, and produces a highly coloured liquid (§ 114). But protosulphate of iron Fe0,S03 can only be converted into neutral persulphate Fea03,3S03 by adding a certain quantity of sulphuric acid. The salts of protoxide of iron are likewise changed into salts of peroxide by treating their solution with chlorine, in the presence of an excess of acid. Reciprocally, it is easy to transform a sesquisalt of iron into a protosalt, by subjecting it to a deoxidizing action: for example, by boiling its solution with iron filings, or treating it with sulf- hydric acid, in which latter case sulphur is deposited, rendering the liquid milky: Fe303,3S03+HS=2(Fe0,S08)+S03,H0+S. § 784. The salts of peroxide of iron afford yellow precipitates, the colour of which is deeper in proportion as they approach neu- trality. The fixed alkalis and ammonia yield a brown precipitate of hydrated peroxide, insoluble in an excess of ammonia. The alkaline carbonates give the same brown precipitate of hy- drated peroxide. SALTS OF IRON. 47 Sulfhydric acid produces a white precipitate of very finely divided sulphur (§ 783), while the sulfhydrates give brown preci- pitates. Yellow prussiate of potash gives a beautiful blue precipitate. lied prussiate does not precipitate the sesquisalts of iron. These two characters signally distinguish the salts of peroxide of iron from those of protoxide. Benzoate and succinate of ammonia give brown precipitates. The sesquisalts of iron rarely exist in the neutral state, as their solutions always contain an excess of acid. A neutral salt is de- composed by treatment with water into a very basic salt which is precipitated, and an acid salt which remains in solution. Persulphate of iron forms alum with the sulphates of potassa and ammonia, the formulae of which correspond to those of ordinary alum, namely, Fe303,3S03+K0,S03-fi24H0 and Fe303,S03-t- NH40,S03-f 24HO. They crystallize in regular octahedrons of a violet hue, and are obtained by adding sulphate of potassa or of ammonia to a solution of persulphate of iron, prepared by the process indicated (§ 776,) and evaporating the liquid at a low temperature. These alums are easily destroyed by heat. COMPOUNDS OF IRON WITH SULPHUR. § 785. Several compounds of iron with sulphate are known. Proto sulphide of Iron FeS. § 786. Protosulphide of iron is obtained by direct combination of iron with sulphur. When an iron bar, heated to whiteness, is plunged into fused sulphur, the combination takes place with great evolution of heat, the bar becomes corroded, and the fused sulphide of iron falls to the bottom of the crucible. A more convenient method of preparing it consists simply in heating a mixture of iron filings and sulphur in a crucible. Protosulphide of iron combines readily with an excess of iron, producing sub-sulphides, which are met with in several metallurgic processes; and it also combines very easily with a greater proportion of sulphur. In order to obtain pure protosulphide of iron, the product formed in the pre- sence of an excess of sulphur must be fused in a crucible covered with damp charcoal, in a forge-fire; when the excess of sulphur is disengaged in the state of sulphide of carbon, and protosulphide remains in the form of a lump possessing a metallic lustre. This sulphide is obtained hydrated in the form of a black powder, when a protosalt of iron is precipitated by a solution of an alkaline sulfhydrate. Sulphur and iron combine together in the presence of water, even at the ordinary temporature. If iron filings and flowers of sulphur are intimate mixed in an earthen vessel and moistened with water, the temperature soon rises, while the colour of the 48 IRON. paste becomes deeper, and, in a few hours, the twro substances have combined together. This preparation is sometimes made in the laboratory, as the product finds extensive use in the prepara- tion of sulfhydric acid. When the quantity of material acted on is at all considerable, the reaction is sometimes very powerful and the mixture is thrown from the vessel: great care is therefore re- quisite. Formerly chemists supposed even volcanos to be produced by similar reactions, for which reason the name of L6mery's volcano was given to this preparation. Sesquisulphide of Iron Fe3S3. § 787. Sesquisulphide of iron, corresponding to the sesquioxide, is obtained by decomposing hydrated peroxide of iron by sulfhy- dric acid, at a temperature of 212°. This compound easily de- composes. Bisulphide of Iron FeS3. § 788. Bisulphide of iron FeS3, which corresponds to no known oxide of iron, is abundantly found in nature, occurring in the form of brilliant cubic crystals, of a brass-yellow colour, and called by mineralogists iron pyrites, or simply pyrites. Pyrites are often sufficiently hard to strike fire with steel. The same product may be obtained in the laboratory, in the form of a yellow powder, by heating very finely dissolved protosulphide of iron with half its weight of sulphur, until the excess of the latter is volatilized. Its density is 4.98. Bisulphide of iron is not attacked by dilute acids, while the protosulphide, under the same circumstances, gives off sulf- hydric acid in abundance. Iron pyrites, subjected to the action of heat, parts with a portion of its sulphur, which distils over, while a sulphide composed of 100 parts of iron and 68 of sulphur remains, which may be considered as a special sulphide. Magnetic Pyrites. § 789. Native sulphides of iron, of a bronze colour, are found in crystalline masses, the form of which is a regular hexahedral prism: they contain less sulphur than the bisulphide, or ordinary pyrites, and are called magnetic pyrites, because they affect the needle. Their composition corresponds in general to the formula Fe7S8= 5FeS+Fe3S3. COMPOUND OF IRON WITH NITROGEN. § 790. When dry ammoniacal gas is passed over fine iron-wire, heated to a dull red-heat in a porcelain tube, the metal becomes very brittle, and increases remarkably in weight, while a nitruret of iron is formed, containing 12 or 13 per cent, of nitrogen. This product is more readily obtained by heating anhydrous protochlo- ride of iron in a glass tube, in a current of dry ammoniacal gas, COMPOUNDS OF IRON. 49 when nitruret of iron remains in the form of a metallic sponge, of a silvery whiteness. COMPOUND OF IRON WITH PHOPHORUS. § 791. A combination of iron and phosphorus is obtained by heating a mixture of phosphate of lk»e and charcoal in a forge- fire, in a crucible covered with charcoal, when a very hard and brittle gray metallic lump remains, capable of a fine polish. The composition of this substance corresponds to the formula Fe4P. A very small quantity of phosphorous changes the qualities of iron in a remarkable manner, and renders it brittle when cold. Phosphuretted ores may do for cast-iron, but never are fit to be rolled into good bar-iron. COMPOUNDS OF IRON WITH ARSENIC. § 792. Arsenic readily combines with iron in a great number of proportions, forming in all cases very brittle compounds, several of which are found crystallized in nature. The mineral called mispickel is a compound of iron with arsenic and sulphur, of the formula FeSa-fFeAsa, while its crystalline form is that of a right prism with a rhombic base. § 793. Two combinations of iron with chlorine, corresponding to the protoxide and sesquioxide, arq known. COMPOUNDS OF IRON WITH CHLORINE. Protochloride of Iron FeCl. § 794. This compound is obtained when iron filings are heated with chlorine, care being taken that the latter is not in excess, as otherwise sesquichloride would be formed. It is obtained with greater certainty in a state of purity by heating iron in a current of chlorohydric acid gas. Protochloride of iron forms a brown fluid mass, which crystal- lizes on cooling: it is prepared in solution in water, by heating iron filings with chlorohydric acid and evaporating the liquid, when green crystals of the formula FeCl-f 6HO are obtained. § 795. Sesquichloride or chloride of iron is prepared by heating iron in a current of chlorine, and volatilizing the product in this gas, when beautiful rainbow-like spangles of a brown or deep green colour are obtained. The chloride dissolves in water, yielding a yellow solution, which can be immediately obtained by treating iron with aqua regia. The solutions of sesquichloride of iron in alcohol and in ether lose their colour and precipitate protochloride of iron when exposed to the solar light. Sesquichloride of iron is decomposed by steam at a red-heat, Sesquichloride of Iron FeaCl3. 50 IRON, when chlorohydric acid is disengaged, and on the sides of the tube in which the experiment is made small glittering spangles of ses- quioxide of iron are deposited, resembling the specular oxide found in the fissures of volcanic lavas. This mineral has been supposed to have been formed in a similar manner. § 796. Iron forms several compounds with cyanogen, particu- larly remarkable for their multiple combinations. If cyanide of potassium be added to a solution of a protosalt of iron, protocyanide of iron is obtained as a white precipitate, which retains with great energy a portion of the reagent which served to produce it. It is obtained in greater purity by treating Prussian blue with sulfhydric acid, when a Avhite precipitate, Avhich soon changes to blue in the air, is formed. Cyanide of iron combines Avith a great number of other metallic cyanides, producing double cyanides, Avhich, besides being of great technical importance, are much used in the laboratory as reagents. In these compounds the iron has lost its habitual characteristic properties, being no longer precipitated by the reagents Avhich usually throAV it doAvn from its saline solutions or from the chlo- rides. The characteristic properties of the simple cyanides are also modified in such double salts, for which reason these com- pounds have been considered, not as real double cyanides, but as combinations of the metal Avith h compound electro-negative body, called ferro-cyanogen. Double Cyanide of Iron and Potassium, or Fcrrocyanide of Potas- ' sium FeCy+2KCy. § 797. This double cyanide, which is also called prussiate of pot- ash, is the most important of these compounds, and is brought into commerce in the form of beautiful yelloAv crystals, of the formula COMPOUNDS OF IRON AVITH CYANOGEN. FeCy+2KCy+3HO. It contains 12.8 per cent, of water, which it readily loses on a slight elevation of temperature: 100 parts of vTater dissolve 25 parts of the salt at ordinary temperature, and 50 parts at the boiling point. This double cyanide is very fixed, being neither decomposable by the alkalis nor even the alkaline sulfhydrates ; while the action of heat destroys the salt and evolves nitrogen, when the residue, treated with water, yields a solution of cyanide of potassium and an insoluble black substance, which is a true car- buret of iron, of the formula FeC3. This salt is prepared on a large scale by fusing carbonate of potassa with animal charcoal, which must be prepared expressly from animal matter containing but few phosphates. Calcined bone, dried flesh, skins, and principally old shoes are used for its PRUSSIATE OF POTASH. 51 preparation: these substances leave a carbonaceous residue, highly charged with nitrogen, which is afterward heated with about its own weight of carbonate of potassa, in large cast-iron kettles into which the smoky flame of a reverberatory furnace enters. The carbonate of potassa is first fused alone, and then the animal charcoal is added, when a reaction takes place accompanied with effervescence, and the mass is continually stirred with iron rods. Cyanide of potassium and cyanide of iron are formed, the iron being furnished by the sides of the kettle and the rods; and when the reaction is ended, the matter is removed and treated with boiling water. The hot solution is filtered, and evaporated to crystallization ; while the mother liquid, on being again concen- trated, still yields crystals, which, with the former ones, are puri- fied by dissolving them in boiling water and allowing the liquid to cool slowly. Within a few years, cyanide of potassium has been prepared by the direct combination of carbon with nitrogen, in the presence of carbonate of potassa; and this process is now applied to the manufacture of prussiate of potash on a large scale. Wood char- coal, impregnated with a concentrated solution of carbonate of potassa, is heated to a high temperature in brick vent-holes, in a current of hot air which has been deprived of its oxygen by pass- ing over a long column of burning coke. From time to time the portion of potashed charcoal at the lower part of the holes is with- drawn, and additional charcoal is introduced through the upper opening to keep the supply constant. The alkaline charcoal, in this operation, is exposed for 10 hours to the action of nitrogen, and then is heated in an iron boiler, with water and finely pow- dered sparry iron. The liquid yields when evaporated beautiful crystals of very pure prussiate of potash, while the residue of the charcoal is again soaked in a concentrated solution of carbonate of potassa and the operation recommenced. The solution of prussiate of potash, added to the solutions of a great number of metallic salts, affords precipitates which are often remarkable for their brilliant colours, and serve as distinguish- ing characters of the metals. In these double decompositions, the cyanide of potassium alone is decomposed, by being changed into a cyanide of the metal which exists in the reacting solution, while this new cyanide combines with the cyanide of iron. If prussiate of potash FeCy + 2KCy be added to a solution of sulphate of copper Cu0,S03, a characteristic reddish-brown precipitate, of the for- mula FeCy + 2CuCy, is obtained. The prussiate, poured into a solution of sulphate of zinc Zn0,S03, gives a white precipitate FeCy-f 2ZnCy. A series of compounds of similar formulae, all of which contain protocyanide of iron, is thus obtained. The formula of the precipitate obtained with a salt of lead is FeCy-t-2PbCy, which, by treatment with sulfhydric acid, forms an 52 IRON, insoluble sulphide, and an acid liquid which yields white crystals when evaporated under cover near a saucer filled with concentrated sulphuric acid. These crystals are formed by a real hydracid FeCy-f 2HCy, called ferro-liydrocyanic acid, or hydrocyano-ferric acid, or ferro-cyanhydric acid, the solution of which is inodorous and posseses none of the properties of hydrocyanic acid. The double cyanides may therefore be regarded as ferrocyanides. Prussiate of potash yields a white precipitate with protosalts of iron, composed for the greater part of protocyanide of iron, but always retaining a certain quantity of alkaline cyanide. This pre- cipitate soon changes in the air. With the salts of peroxide of iron, prussiate of potash gives a beautiful blue precipitate, called Prussian blue, which is used in dyeing and in oil-painting. The following reaction ensues between perchloride of iron and prussiate of potash: 2FeaCl3+3(FeCy+2KCy)==6KCl+(3FeCy+2FeaCy8). The formula of Prussian blue is 3FeCy+2FeaCy3. § 798. If a current of chlorine be passed through a solution of prussiate of potash and the liquid boiled, a green precipitate is formed, which, when heated with chlorohydric acid, gives off a cer- tain quantity of mixed oxides of iron, and leaves a green residue, of the formula FeCy+FeaCy3+4HO. It is a compound resembling magnetic oxide, if the water of combination be overlooked. § 799. If the current of chlorine be stopped at the moment wdien the solution no longer throws down a blue precipitate of sesquisalts of iron, a liquid, yielding beautiful red crystals on evaporation, is obtained. It is important not to prolong the action of the chlorine too much, and to keep the liquid constantly agitated. The solu- tion is frequently tested with a sesquisalt of iron, and the current of chlorine is arrested as soon as a precipitate is no longer formed. It is also wrell to neutralize the liquid gradually with a little potassa. The red salt, which has been called cyanoferride or ferricyanide of potassium, has the formula 3KCy+FeaCy3; and contains no water of crystallization. The reaction from which it originates is the following: 2(FeCy+2KCy) + Cl=(3KCy+FeaCy3)+KCl. The red prussiate is much less soluble than the yellow7, 38 parts of cold water being required to dissolve 1 part of it. Protosalts of iron yield wfith red prussiate of potash a beautiful blue precipi- tate of the formula 3FeCy+Fe2Cy3, the reaction being as follows: (3KCy+Fe3Cy3)+3(F eO, SO.)=3(K0,S03) 4- (3FeCy+FeaC j3). Red prussiate of potash yields with salts of lead a precipitate 3PbCy-j-FeaCy3, which gives, when treated with sulphuric acid, a precipitate of sulphate of lead and a compound 3HCy+FeaCy3, CAST-IRON. 53 called hydro-ferricyanic acid, which dissolves with a red colour. The solution, when evaporated, deposits the salt in yellowish- brown crystals. § 800. Iron combines with carbon when in presence of this sub- stance, at a very high temperature. It has been shown (§ 795) that a carburet of iron FeC3 is obtained by decomposing prussiate of potash by heat: by the direct combination of iron with carbon, compounds so rich in carbon are never obtained, as the most car- buretted products only contain about 5 per cent, of carbon, their composition resembling the formula Fe4C. These carburetted irons are called cast-iron, which is again divided into white cast- iron and gray cast-iron. Iron, heated in blast-furnaces at a very high temperature in contact with charcoal, passes into the state of cast-iron, which, by cooling suddenly on leaving the furnace, forms hard and brittle metallic masses, whiter than the soft iron, and consisting of white cast-iron. If, on the contrary, the iron be cooled slowly, the carbon which was in combination with the iron separates by crys- tallization, forming an infinite number of small black graphitose spangles, which impart a deep gray colour to the mass. The small spangles of carbon are scattered through the iron, the greater part of which is decarburetted, and such iron, which is called gray or soft cast-iron, is much more malleable than the white sort, and can be cut with a file. All kinds of cast-iron do not lose their combined carbon with equal readiness; when the iron-ore contained phosphorus or sulphur, the metal retains the character of white cast-iron, even after a very slow cooling. Certain kinds of cast-iron, which contain manganese in combination, possess also the property of retaining their com- bined carbon, and present, after cooling, a crystalline fracture, with very large brilliant laminse, which intersect each other at angles of 120°; hence the crystalline form is inferred to be a regular hexahedral prism. This iron is called lamellar cast-iron, and is obtained from the manganiferous sparry ores (§ 782). When white cast-iron is treated wfith chlorohydric acid or dilute sulphuric acid, the metal dissolves with evolution of hydrogen gas, but at the same time a volatile oil of a nauseous smell is generated, resulting from the combination of the hydrogen with carbon in the nascent state. If, on the contrary, gray cast-iron is dissolved, a certain quantity of this oil is produced, by the combination of hy- drogen with the portion of carbon which was in combination with the iron, while the free carbon remains in the form of small crys- talline spangles. Cast-iron, under certain circumstances, assumes an intermediate COMPOUNDS OF IRON WITH CARBON. 54 IRON, state between the gray and white, when, the separation of graphite not taking place throughout the whole mass, but only in some por- tions, the substance presents the appearance of white cast-iron, more or less spotted with gray. This kind is called spotted or mottled cast-iron, (fonte truitee.) COMPOUND OF IRON WITH SILICIUM. § 801. A compound of iron with silicium is obtained by heating in a crucible covered with damp charcoal a mixture of iron filings, silicic acid, and charcoal, in a forge-fire, when a fused metallic lump, possessing a certain degree of malleability, is formed. Iron can combine, in this case, with 9 or 10 per cent, of silicium. Cast-iron, particularly that made in blast-furnaces at very high temperatures with coke, generally contains 1 or 2 hundredths of silicium. DETERMINATION OF IRON, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. § 802. In chemical analyses iron is nearly always determined in the state of sesquioxide, and when it exists as such in its solutions is precipitated by ammonia or carbonate of ammonia. It is best to make the precipitation in a hot liquid, as the hydrated sesquioxide is then less gelatinous and more easily washed on the filter. When the iron exists in the state of protoxide, it must be converted into sesquioxide by evaporating the liquid with nitric acid, or bypassing a current of chlorine through it; in which latter case the excess of chlorine must be driven off by boiling. Sesquioxide of iron is then precipitated by ammonia. The superoxidation of the iron may also be affected by adding chlorohydric acid, and then a small quantity of chlorate of potassa, to the liquid, when, by boiling, the chlorohydric acid and chlorate of potassa mutually decompose each other, while chlorine is set free, which produces the superoxida- tion of the iron. Frequently it is preferable to precipitate sesqui- oxide of iron by succinate of ammonia, which throws it down more completely than ammonia, as an excess of this last reagent may redissolve a small quantity. The precipitate of sesquisuccinate of iron is decomposed by heat, leaving pure peroxide of iron. In some cases, sesquioxide of iron must be precipitated with caustic potassa in excess; but the precipitate then retains a small quantity of potassa with great obstinacy, and is freed from it only by boiling several times with distilled water. When the precipi- tate is copious, it is better, after having collected it on the filter and washed it with a small quantity of hot water, to redissolve it in weak chlorohydric acid, saturate the liquid by ammonia, and precipitate again with succinate of ammonia. When the solution contains organic substances, such as sugar, tartaric acid, etc., ammonia no longer precipitates sesquioxide of iron, nor does even carbonate of ammonia; and the iron must then 55 be precipitated as sulphide by sulfhydrate of ammonia. The pre- cipitate is collected on a filter, and washed with water, to which a small quantity of sulfhydrate of ammonia is added, in order to prevent the sulphide of iron from being converted into sulphate by contact with the air; after which the precipitate is redissolved in chlorohydric acid, the iron brought to the state of peroxide, either by means of chlorine or by evaporating the solution with a small quantity of nitric acid, and the sesquioxide formed is then precipi- tated by succinate of ammonia. § 803. In order to separate the alkaline metals, ammonia or succinate of ammonia is used after the iron has been brought to the state of sesquioxide. It is separated from the alkalino-earthy metals by the same reagents, care being taken at the same time that the ammonia contains no carbonate, or cannot absorb carbonic acid from the air, as the carbonate of ammonia formed would cause the precipitation of the earths. When iron is to be separated from magnesia, a quantity of sal ammoniac sufficient- to prevent the magnesia from being precipitated by an excess of ammonia must be added to the liquid ; but the latter, most frequently, already contains free acid enough to produce the quantity of ammoniacal salt necessary during its saturation by ammonia. In order to separate iron from alumina, the iron is first brought to the state of sesquioxide, if it does not already exist in that state, and then an excess of caustic potassa is added; when, by boiling the liquid for some time, all the alumina dissolves in the potash, leaving only the sesquioxide of iron as a precipitate. The filtered alkaline liquid is then supersaturated with chlorohydric acid, and the alumina precipitated by an excess of carbonate of ammonia. The separation of iron and manganese is easily effected when the iron exists as sesquioxide, and we have seen that it can always be readily brought to that state. The manganese, moreover, is always present as a protosalt; for the other salts of manganese, not being very fixed, are soon converted by ebullition into proto- salts. The same process as described for the separation of sesqui- oxide of iron from, magnesia is adopted; that is, a quantity of ammoniacal salt sufficient to prevent the precipitation of the oxide of manganese is added to the liquid: generally, however, the am- monia necessary to saturate the acid liquid is sufficient to produce the ammoniacal salt required. The sesquioxide of iron is then precipitated by ammonia or succinate of ammonia, and the man- ganese is obtained from the filtered liquid by sulfhydrate of am- monia as sulphide. When a solution of a sesquisalt of iron is precipitated by ammo- nia or carbonate of soda, changes of colour are observed, which may guide the operator in the separation of the iron, and allow the iron and other metals which exist in the liquid to be successively pre- cipitated. The sesquisalts of iron, dissolved in an acid liquid, are DETERMINATION OF IRON. 56 IRON, of a very pale yellow colour, and when ammonia or carbonate of soda are added by small quantities at a time, the liquid becomes more and more deeply coloured as it approaches saturation, and at last assumes a deep brown colour before any deposit is formed. If it is then subjected to ebullition, the peroxide of iron is com- pletely precipitated: the liquid is bleached, retaining still all the oxides of the formula RO in solution, which are much more power- ful bases than sesquioxide of iron, and, in general, than the oxides of the formula R303. In order to make the separation properly, the liquid is first heated to boiling, and the ammonia or carbonate of soda then added, stirring it continually, and discontinuing when the liquid has turned brown. It is then boiled for some time, when a brown precipitate of hydrated sesquioxide of iron is generally formed. If the liquid is not discoloured, a few drops of the reagent are added, it is again boiled, and this is continued until discolora- tion takes place. It is then filtered while boiling, and a consider- able quantity of carbonate of soda is added to effect the precipita- tion of the other metallic oxides which exist in the solution. There is, therefore, a considerable interval between the moment of the complete precipitation of the oxides of the formula RsOs and that of the commencement of the precipitation of the oxides RO. In this way, sesquioxide of iron may be separated with a con- siderable degree of accuracy from all protoxide with which it is mixed in the liquid; but the admission of air must be avoided as much as possible, as its oxygen would convert a portion of the protoxide into sesquioxide. It is often necessary, in the analysis of mineral substances, to determine the relative proportions of the sesquioxide and protoxide of iron they contain, which can be done exactly when the mineral dissolves readily in non-oxidizing acids, such as chlorohydric. The material is finely powdered, and treated in a small flask with hot concentrated chlorohydric acid, the liquid being continually boiled, in order that the steam disengaged may prevent the admission of air into the flask; and the boiling is con- tinued until the greater part of the acid in excess is evaporated. It is then treated with boiling water, and the sesquioxide preci- pitated by carbonate of soda, added by drops, avoiding as much as possible the contact of the air. When the liquid is deprived of colour, it is allowed to rest for some time in the flask, which is corked: the clear liquid is decanted, collected rapidly on a filter, and washed with boiling water. The filtrate contains the prot- oxide of iron, which is brought to the state of sesquioxide by means of chlorine, and precipitated by an excess of carbonate of soda. '> § 804. It is, however, difficult to prevent a portion of the prot- oxide of iron from changing into sesquioxide by absorption of the oxygen of the air. Greater exactness is obtained by another process, which may be applied to various other cases. If a solu- DETERMINATION OF IRON. 57 tion of permanganate of potassa be added to a solution of a proto- salt of iron, the permanganate immediately loses its colour, by being decomposed into protoxide of manganese and potassa, which base combines with the acid, and into oxygen, which converts the protoxide of iron into sesquioxide.* The discolouration of the permanganate of potassa takes place as long as any protoxide of iron remains in the liquid; but as soon as all the protoxide is changed into sesquioxide, the smallest drop of the solution of permanganate of potassa gives the liquid a very decided red tinge. If the solu- tion of permanganate of potassa is of standard quality, it suffices to measure exactly the quantity necessary to produce a permanent red colour, and the quantity of iron which existed in the state of protoxide can thence be directly inferred. The permanganate of potassa used to make the standard solu- tion is prepared by heating, for two hours, in an earthen crucible, a mixture of 2 parts of binoxide of manganese, 3 parts of caustic potassa, and 1 part of chlorate of potassa.f The mass is broken to pieces after cooling, treated with 3 or 4 times its weight of water, and the liquid filtered through asbestus or powdered glass, to sepa- rate the sesquioxide of manganese. Weak nitric acid is then added until the liquid assumes a beautiful violet-red colour. The solution is preserved in a well-corked bottle, as it would be soon changed by the particles of organic dust floating in the air.| In order to determine the standard of the solution, 1 gramme of highly-polished piano-forte wire, exactly weighed, is dissolved in 25 cubic centimetres of chlorohydric acid, and the liquid diluted with water recently boiled, so as to increase its volume to about 1 litre.§ Again, 100 divisions of the solution of permanganate of * The solution must necessarily contain free acid enough to dissolve the oxide of manganese formed.— W. L. F. -j- Another proportion, given by Gregory, is as follows:—8 parts of peroxide of manganese, 10 parts of caustic potassa, and 3 parts of chlorate of potash. But the best method, as the only one by which permanganate of potassa can be ob- tained in crystals and free from chloric acid, according to Liebig, is by igniting pure peroxide of manganese with a fixed alkali, with access of air.— W. L. F. J The use of permanganate of potassa as a means of determining iron in any case has been objected to by many chemists, on the ground that a standard solu- tion would not keep uniform for any length of time. This objection is unfounded; for a solution made by dissolving crystals of the salt remained perfectly Unaltered for a period of six months, during which time it was often tested. The solution must, however, be kept in a bottle with a tight-fitting ground-glass stopper, and the bottle ought always to be kept as full as possible. The manganate should be converted into permanganate, rather by adding a quantity of boiling water to its concentrated solution than by introducing nitric acid.— W. L. F. $ As not even piano-forte wires consist of pure iron, it is better to employ a protosalt at once : of these the protosulphate of iron and ammonia is most com- mendable, as being least of all subject to decomposition, and easy to prepare. Of this salt, 6.429 gm., which correspond exactly to 1 gm. of metallic iron, are dis- solved, and the solution having been made acid, the permanganate may be imme- diately added.— W. L. F. 58 IRON, potassa are introduced into a graduated alkalimeter (fig. 477), and poured from it into the vessel B (fig. 478), which contains the protochloride of iron, stirring constantly to facilitate the mixture. The solution of the permanganate is added, by small quantities at a time, until the liquid as- sumes a permanent roseate tinge. The number of divi- sions and fractions of a division necessary to produce this result are noted down: supposing this number to be 75.5 div., the conclusion will follow that 75.5 div. of the solution of permanganate correspond to 1 gramme of protoxide of iron, and consequently that 1 div. of permanganate corresponds to 0.01325 gr. of metallic iron.* This being done, in order to analyze a substance containing protoxide and sesquioxide of iron at the same time, 1 gramme of it is dissolved in chlorohydric acid, the liquid is diluted with boiled water until it oc- cupies the volume of about 1 litre, and then the standard solution of permanganate of potassa is carefully added until the liquid assum’es a roseate tinge. Let us suppose that to produce this effect, 22.0 div. of the solution of the permanganate were required ; the gramme of the substance subjected to analysis will then con- tain 22.0x0.01324 gr., or 0.291 gr. of iron, existing in the state of protoxide, or, lastly, 0.374 gr. of protoxide of iron. The quantity of sesquioxide can readily be determined by the same process :—1 gramme of the substance is again dissolved in concentrated chlorohydric acid, and then 4 grammes of sulphite of soda, dissolved in a small quantity of water, are poured into the solution gradually and by small quantities. The sulphurous acid which is set free by the reaction of the chlorohydric acid on the alkaline sulphite converts the perchloride of iron into protochlo- ride, so that all the iron in the substance then exists in the solu- tion as protochloride. The liquid is boiled to drive off the excess of sulphurous acid, diluted with water to about the volume of 1 litre, and the standard solution of permanganate is added. Sup- posing that it was necessary to add 36.0 div. of the alkalimeter, in order to obtain a permanent rose-colour, the conclusion follows that the substance contains 36.0x0.01324 gr., or 0.477 of metallic iron. Now, as it has been already found to contain 0.291 of iron in the state of protoxide, there are 0.186 gr. present in a more highly oxidized state, corresponding to 0.266 gr. of sesquioxide. Fig. 477. Fig. 478. * The result will be the more exact the more dilute a solution of permanga- nate of potassa is employed, and the accuracy of the determination may, in fact, be carried to almost any degree.— W. L. F. METALLURGY OF IRON. 59 METALLURGY OF IRON. § 805. The only ores of iron employed are the oxides and the carbonate; while the sulphides, although very abundant in nature, are not used for the extraction of iron, as the process would be too expensive, and, besides, a metal of inferior quality would be ob- tained. The principal ores which are worked are— 1. The magnetic oxide, found in considerable masses in the old rocks, principally in the micaceous schists,* in which w’ell-defined octahedral crystals are often found scattered, is generally a very rich ore, affording iron of excellent quality: the greater portion of Swedish iron is procured from it. 2. The anhydrous peroxide of iron, which is found in some transition rocks, and in the secondary rocks, in large masses, re- sembling sometimes real strata. The oxide, in this case, is amor- phous, and is called red hematite. It also constitutes veins in the old rocks, as at Framont, in the Yosges. This ore is used in many of the foundries in the north of Germany. Specular iron is generally found in veins, but rarely in suffi- cient quantity for foundry use. It also forms considerable masses in the old rocks, a most remarkable example of which is the de- posit in the island of Elba.f 8. Hydrated peroxide of iron, which is found in the transition rocks, or at the junction of the transition and secondary rocks, in the form of concrete brown masses, when it is called brown hema- tite. In France, the foundries in the Pyrenees use this ore. 4. Hydrated peroxide of iron, which is also found in small con- crete grains, and is called granular iron ore. It forms deposits A (fig. 479) at the time of separa- tion of certain strata of the jurassic rocks, but more fre- quently in the middle tertiary rocks, covering the layers of jurassic limestone and chalk. The size of the grains varies from that of a pea to that of a millet- seed. The majority of the foundries in the middle of France, and in Champagne and Berry, smelt this ore. An ore is also found in certain stages of the jurassic rocks, con- sisting of small grains of hydrated peroxide of iron, adhering Fig. 479. * A mistake has here crept into the text; magnetic oxide being seldom or never found in micaceous schists, but occurring in abundance in talcose and chloritic schists, and in serpentine; while the largest masses of it are found in various igneous rocks of a more recent origin, especially in basalt and dolerite. — W. L. F. •j- At the Serra da Piedade and the Pico da Itabira, both in Brazil, specular iron occurs in such quantity as to form a peculiar species of rock, called itabirite, of a dense and slaty character.— W. L. F. 60 firmly to each other, and forming real strata; and this ore, from its resemblance to the eggs of fish, is called oolithic ore. 5. Sparry iron, or crystallized protocarbonate, sometimes mixed with considerable proportions of carbonate of manganese, which is found in veins in the old and transition rocks. It sometimes also accompanies the brown hematites which are met with at the line of separation of the old and transition rocks. This ore, smelted with charcoal, yields laminated cast-iron, which is used for manufacturing steel. 6. In the argillaceous strata of the coal-fields, flattened nodules of carbonate of iron, mixed with clay, are frequently found, and are sometimes very rich in iron, constituting an ore the more valuable because it is found in the midst of fuel, and is easily ex- tracted. This ore is very abundant in England. 7. Lastly, an iron-ore is found in some low places, immediately beneath the soil, consisting of hydrated peroxide, mixed with phosphate. This ore yields phosphorous cast-iron, the use of which is limited. It is called bog ore. Iron* is sometimes found in the native state, forming often very large compact masses, which are never in place, but have fallen from space as aerolites. This iron, which is never pure, being always more or less mixed with nickel, is often scattered through a grayish stone, the surface of which appears to have undergone an incipient fusion. These masses are called meteoric stones, aerolites, or meteorolites. Probably, a great number of such meteors circulate in space, influenced by the same forces which maintain the planets in their orbit, and fall to the surface of the earth when, by virtue of their motion, they approach near enough to this planet to be acted on by the attraction of the lat- ter. Sometimes meteoric iron possesses all the qualities of mal- leable iron, and cutting-instruments even have, for sake of curiosity, been made of it. § 806. Iron ores are never subjected to any complicated prelimi- nary operations. The granular ores are generally held together by a clay, very poor in oxide of iron, and easily removed by wash- ing (§ 785). Other ores often require a preliminary roasting, which renders their smelting more easy, by driving off the water, and carbonic acid, if the ore is carbonated, and acting especially by disagregat- ing the ore, and rendering it porous and more friable. § 807. We have seen (§ 766) that the oxides of iron are very easily reduced when heated in a current of hydrogen : their reduc- tion is also effected under the same circumstances by carbonic oxide gas. It may hence be supposed that the reduction of oxide of iron in ores is not very difficult; but then the metallic iron formed is still intimately mixed with the gangue, which prevents its particles from uniting together. If the gangue were very IRON, METALLURGY OF IRON. 61 fusible, it would be sufficient to heat the ore to a degree sufficient to fuse the former, and by then hammering this metallic sponge, the particles of iron would unite together, while the gangue would be pressed out in the form of scoriae. But, if the gangue fuses with difficulty, it would melt only at the temperature at which the iron, in contact with charcoal, is converted into cast-iron, and we should no longer obtain malleable, but cast-iron. Now, the ordi- nary gangue of iron-ore being quartz or clay, which are two nearly infusible substances, two processes are adopted to fuse them. If soft iron is to be obtained immediately from very rich ores, the latter are heated with charcoal, when the gangue, combining with a portion of the unreduced oxide of iron, forms a very fusible double silicate of alumina and protoxide of iron. A very high temperature, therefore, is not required; the iron does not pass into the state of cast-iron, and it suffices to hammer the spongy metal to unite it together and press out the scoriae. But a quantity of oxide of iron, proportioned to the quantity of gangue in the ore, is necessarily lost, for which reason this process can only be adopted in the case of very rich ores. If, on the contrary, the iron is to be extracted completely from the ore, the silicate of alumina must be made fusible by giving it another base than oxide of iron. The only base which can be economically substituted is lime ; but as the double silicate of alu- mina and lime is much less fusible than that of alumina and iron, a high temperature is required, and the iron passes into the state of cast-iron, which liquifies at the same time with a double silicate, or slag. As may be seen, the results of these two methods are very dif- ferent. The first is used only in a few places, as it requires rich and very pure ores, and consumes an immense quantity of fuel. It is adopted in the Pyrenees, and known as the Catalan method. TREATMENT OF IRON-ORE BY THE CATALAN METHOD. ♦ § 808. The Catalan forge consists of a crucible, or hearth, made by a quadrangular cavity U (figs. 480 and 481), of about 0.7 m. in depth, and supported by one of the walls of the forge. The crucible is built in solid mason-work of dry stones, fastened together with clay. The part of the mason-work occupied by the crucible does not rest immediately on the ground, but on several small arches, which prevent the dampness from penetrating the crucible and deranging the hearth. Above the arches is a layer of scoriae and clay, covered by a granite slab, which forms the bottom, or the Jloor of the hearth. The four lateral faces of the crucible rise above the bottom stone. 62 IRON The front face li is called the chio, or floss- hole. The opposite face i is called the cave. The left one R is called the porges. Lastly, the right face l is called the ore or contrevent. The face of the chio, which presents a ver- tical surface of about 0.65 m., is formed by three pieces of iron placed end to end, the two extreme ones of which are called latai- roles; that in the middle, the restanque, serves as a point d’appui for the levers, or fire-irons, with which the workmen raise the mass of iron formed during the process. The left face, the porges, is vertical, and composed of pieces of iron t, t, t (fig. 483) laid endwise upon each other. The right face, the ore or contrevent, is composed of pieces of iron s, s, s (fig. 483),which are wedge-shaped, and slightly in- clined, being so arranged that their sur- face forms a curve. The cave i, which consists wholly of ma- son-work, fast- ened with clay, is slightly in- clined outward to 5° or 8°. The twyerh, which conveys the blast into ...... . 4. ■sasJthe furnace, rests on the upper piece of the porges, and is made of a conical piece of copper, the edges of which are merely brought together without soldering. The position of the twyer exerts great influence over the operation: its inclination varies from 35° to 40°. The wind is conveyed from the bellows into the twyer through a copper nozzle T, fastened to the wind-trunk G of the bellows by a leather tube. Fig. 480. Fig. 481. METALLURGY OF IRON. 63 The depth of the Catalan furnace is about 0.7m. Its average width, from the chio to the cave 0.6 Its average width, from the porges to the lower part of the contrevent 0.7 Its average width, from the porges to the upper part of the contrevent 1.0 The bellows of the Catalan forges of Aridge is called a trumpet, (trompe,) and is composed of— 1st. An upper basin A (fig. 481), fed by spring-water. 2d. Two pipes B, of about 6 metres in height, formed by trees hollowed out, and crossing the bottom of the basin A. 3d. A lower box C, having two openings, one at D below, the other above at E, to which is fitted a tube EF, terminated by the wind-trunk G. The upper opening of the tubes B is contracted by the boards a a which are supported by bars. The aperture formed by the lower part of the boards is called the etranguillon, on a level with which the sides of the tubes are pierced with inclined holes c c, called breathing-holes, (aspirateurs.) Lastly, the tubes enter the upper wall of the box C, and open at a small distance above a bench d. The water of the upper basin A, passing through the etranguil- lon into the vertical pipes B, carries with it the external air, which in this way passes through the openings c c. The water breaking over the bench escapes through the lower orifice D, while the air passes out by the nozzle G. The position of the boards forming the etranguillon is regulated by wooden wedges g, which, being fixed to the end of a jointed lever, which a man works by a chain at the bottom of the forge, is elevated or depressed in order to obtain the quantity of air necessary for the various stages of the operation. The beetle, or tilt-hammer, used in forging iron, represented in fig. 482, consists of a cast-iron face P, weighing about 600 kilogs., mounted on a helve of beech-wood, and secured by iron bands, while the gudgeons on which the hammer turns are fastened to a cast-iron piece H fixed to the helve. Fig. 482. 64 IRON, The hammer is raised by means of iron cams b, b, b on the water- wheel A. The iron anvil S is fastened by a tenon c to a piece of cast-iron r, which is itself solidly set by means of wooden wedges into a large block of wood, or a piece of granite, B. In order to accelerate the fall of the hammer, which should strike from 100 to 125 blows per minute, a stone on which the heel strikes is placed under the latter. § 809. These general arrangements of the forge being understood, let us now examine it in operation. We shall suppose that the mass or stack of the preceding opera- tion has been removed from the furnace to be forged under the hammer; and that the workmen are therefore occupied in getting up the fire for another smelting. For this purpose they withdraw from the hearth the hot coals which are still there, detach from the bottom and sides the adhering slag, and return the hot coals to the hearth, which is thus filled as high as the twyer. A work- man divides the hearth into two parts, by a shovel which he places vertically and parallel to the porges, so that the division between the shovel and the porges shall be double of that between the former and the contrevent. Other workmen heap charcoal in the division between the shovel and the porges, and ore, broken to the size of a walnut, between the shovel and the contrevent. The shovel is gradually raised, as the space below is filled, and a wall of ore is thus formed rising to about 0.2 m. above the contrevent. The ore is spread so as to form a saddle- back dfg (fig. 483), of wThich the edge f rests on the one side against the cave, and on the other on the bench of the chio. The surface fg is covered by a layer of brasquef (damp char- coal,) well heaped up, while the space M, comprised between the of ore and the furnace, is filled with charcoal. The furnace being thus charged, the blast is admitted, at first slowly, and then its force is in- creased. The ore is thus gradu- ally reduced; while the workmen take advantage of this period to forge into bars the stack of the preceding operation, Avhich they have divided into four parts, as we shall presently see. To do this, they heat these masses of iron in the furnace, by placing them in the middle of the burning char- Fig. 482. METALLURGY OF IRON. 65 coal in the space M above the twyer. When they are sufficiently heated, they are removed and forged. As the charcoal diminishes, fresh fuel is added, and small ore, called greillade, which is made by the breaking of the ore as it comes from the mine, is thrown in, being slightly moistened with water, to prevent it from falling too easily between the interstices of the charcoal. Influenced by the wind projected through the twyer, the char- coal burns to carbonic acid in the space near the twyer, while farther off the carbonic acid is reduced, by the charcoal in excess, into carbonic oxide gas, the greater part of which, being obliged to pass through the highly heated ore, reduces the oxide of iron to the state of metallic iron. But the whole of the oxide is not re- duced, as a portion, remaining in the state of protoxide, combines with the gangue of the ore, forming a very fusible compound sili- cate, a large portion of which runs off and collects in the bottom of the hearth, whence it is removed by a small opening in the chio. In two hours, the greillade which falls with the fuel has depo- sited a certain quantity of iron at the bottom of the hearth, and the workman then commences the formation of the mass. He increases the draught of air, and, by carefully introducing a bar between the ore and the contrevent, draws that ore which seems more advanced near to the twyer, and adds at the same time an- other charge of charcoal and greillade. Five hours after the commencement of the operation the ore has entirely fallen into the hearth, and the workman endeavours to unite the various fragments of spongy iron. During the last hour of the process, the workmen break the ore under the forge-hammer, and then sift it, in order to separate the pulverulent material constituting the greillade, of which we have spoken. They then remove the mass from the furnace and carry it to the hammer, where the liquid scoriae are pressed out, and the spongy iron is rendered more compact. The mass is then, by means of a long iron wedge, divided into two equal parts, called massoques, which are hammered into long parallelopipedons, and again cut into two equal parts. Four pieces of iron, called massoquettes are thus obtained, which are rolled into bars in the first stage of the suc- ceeding operation. A smelting by the Catalan method generally lasts 6 hours, pro- ducing 140 to 150 kilogs. of merchantable iron, from 470 kilogs. of ore and about 500 kilogs. of charcoal. The direct extraction of iron in the state of ductile metal is now performed only in the Pyrenees, Corsica, and a few provinces of Spain, the greater portion of iron being obtained by means of blast- furnaces, in which the metal is separated from its ores, as perfectly as possible, by using a very high temperature, at which the iron 66 IRON, combines with a certain quantity of carbon, forming a much more fusible compound than ductile iron. TREATMENT OF IRON-ORES IN THE BLAST-FURNACE. § 810. The blast-furnace (fig. 484) is composed of two truncated cones C, B, united at their bases. The upper cone C, called the belly, (cuve,) is made of an inner lining ii' of refractory bricks, sur- rounded by a stratum of scorise, or broken slag, which separates it from a second brick lining IV, built against an outer wall pp', qq' of cut stone or common brick, constituting the main part of the blast-furnace. The upper opening G of the belly is called the Fig. 484. tunnel-head, (gueulard,) and is surmounted by a chimney F, having one or several doors, through which the charges are introduced. The lower cone B, called the boshes, (etalages,) is generally made of quartzose stones difficult of fusion, and which must be very METALLURGY OF IRON. 67 carefully selected, as on them the duration of the furnace greatly depends. In some furnaces the boshes are made of refractory bricks. They are sometimes joined to the belly by a cylindrical union or curve A, in order to avoid a re-entering angle. Below the boshes is a prismatic space E, called the top of the hearth, made of refractory stones, (firestone.) Three of its sides descend to the bottom of the furnace, or the crucible D, while the fourth t stops at a few decimetres above the bottom: this side, which is called the tymp-plate, is supported by strong pieces of iron let into the side-walls of the hearth. The bottom of the hearth is formed of a quartzose stone, beneath which are openings to allow the air to circulate freely below the furnace ; and, in order to prevent the accumulation of water, which would cool the hearth, and even give rise to serious accidents, the main body of the blast-furnace is built on arched galleries 11. Three of the walls of the crucible are merely prolongations of its sides, while the fourth is formed by a prismatic stone d, called dam-stone, and which is slightly in front of the tymp-plate; so that the anterior part of the hearth has an opening between the dam-stone and the tymp-plate. We shall call that part of the fur- nace on which the dam-stone and tymp-plate rest the anterior part; the opposite will therefore be the posterior part, and the other two the sides. The posterior part and two sides have lateral openings o, called the tuyeres, or twyers, through which the pipes which convey air enter the furnace: these openings are on the same horizontal plane, a little above the lower edge of the tymp-plate. To assist the workmen, four niches, allowing them to approach the twyers and hearth, are made in the main body of the furnace, while lateral galleries R permit them to walk more freely around the furnace and to examine the twyers. The arrangement of the twyers and the pipes which con- vey the air from the blast-machine is seen in fig. 485, which repre- sents a horizontal section of the furnace at the height of the twyers. Each wind-trunk has a register or valve, to regulate the quantity of air admitted. The blast-furnace is generally built, when practicable, against a hill (fig. 484), and strengthened by mason-work. A terrace is made, at the height of the mouth, Fig. 485. 68 IRON. on the sides or top of the hill, a bridge aa! communicating between this terrace and the platform pp' of the mouth. The terrace is reached by an inclined plane, to which the ore and fuel are con- veyed by machinery. The material is then transported in wagons on a railway to the platform pp'. The twyers of blast-furnaces are double conical tubes abed of cast-iron, or copper (fig. 486), and as their ends might melt, in con- sequence of the high temperature to which they are exposed, a current of cold water is continually circulated through them, which, being introduced through the small tube t, runs off through the tube t'. The openings of the twy- ers advance as far as the inner wall of the hearth. The nozzle of the wind-tube B is disposed in the twyer, and communicates with the cast-iron tubes of the blowing-machine by a flexible leather tube A. The three twyers are on the same horizontal plane, but the axes of the two twyers on the sides of the hearth are not prolongations of each other, being separated by some centimetres, so that the two currents of air may not interfere with each other. § 811. The blowing-machine of a blast-furnace consists of a large cast-iron cylinder A (fig. 487), in which works a cast-iron piston P, packed with tow or leather to render it air-tight. The cylinder is closed above and below, and on the upper lid is a stuffing-box m, through which the piston passes. The lid has also two side-openings c, c', one of which c communicates with the external air and is fur- nished with a valve which opens from without inward, while the other c' communicates with a late- ral cast-iron cylinder B and has a valve opening from within out- ward. The bottom of the cylinder has also two openings; one at e, having a valve which opens from without inward, establishing a communication between the lower part of the cylinder and the external air; and one at e', which communicates with the lateral cylinder B, opening from within outward. Let us suppose that the piston has reached its maximum ascent, and begins to descend. If the valves c, c' are closed, the air will be expanded in the upper part of the pump, and its elastic force will Fig. 486. Fig. 487. METALLURGY OF IRON. 69 be more and more feeble; when, the external exceeding the inter- nal pressure, the valve c' will be forcibly applied against the open- ing c' and intercept the communication between the upper part of the pump and the lateral cylinder B. The valve veak nitric acid, which dissolves only the carbonates of lime and magnesia which may be in the gangue. (If none existed, there would be no effervescence, and the use of the weak nitric acid would be superfluous.) When the effervescence has ceased, even after the addition of a fresh quantity of acid, the residue is col- lected on a small filter, washed with a little water, and calcined in a platinum crucible. If p' be the weight of this residue, (10—p') will represent the weight of the water, carbonic acid, and lime contained in the ore; and consequently, (p—p') will be the weight of the lime. Lastly, 10 gm. of powdered ore are attacked with concentrated chlorohydric acid, and the solution boiled until the residue has en- tirely lost its colour. The quartz and clay, Avhich alone remain as a residue, are collected on a filter and weighed after calcination. Their weight being represented by p", we shall have for the compo- sition of the ore, by collecting the results of all these operations : Water and carbonic acid (10—p) Lime ip~p') Quartz and clay p" Oxides of iron and manga- nese, (differentially) 10—(10 —p)—{p—p') —p"=(pf —p")- If the ore contains only a small quantity of manganese, which is TESTING OF IRON-ORES. 109 easily recognised by the ochreous colour of its powder, the weight (p'—p") will represent pretty exactly the weight of the anhydrous sesquioxide of iron in the ore, and, consequently, £ {p'~p") will be the weight of the metallic iron. It is more easy to make the assay by the dry way, under the most favourable conditions. Experiment has shown that the cast-iron most readily separates, and a well-fused slag, nearly entirely freo from oxide of iron, is obtained when the gangue is composed of clay and carbonate of lime, in such proportions that the latter should be two-thirds of the clay. An addition of chalk or kaolin to 10 gm. of powdered ore is then made, until the mixture resembles the composition just indicated ; which, after being well ground in an agate mortar, is introduced into the cavity abc of a crucible covered with damp char- coal* (fig. 516). The ore is inserted in a heap m into the cavity made with a glass rod, and the crucible is filled with damp charcoal. The lid is luted with clay, and the crucible itself, being set on fire-bricks, or pieces of burnt earth, and secured with clay, is heated in an air-furnace, or in a forge. Fi- gure 517 represents the construction of an air-furnace very suitable for test- ing iron-ores ; it resembles the furnace for melting steel (§ 856), but is smaller. Four crucibles may be arranged in this furnace, and 4 tests made at once. The fuel used is a mixture of equal parts of charcoal and coke, taking care to raise the temperature gradually, so that the crucibles may dry slowly, while the register r regulates the draught. Dur- ing the last quarter of an hour the temperature is raised as high as pos- sible. The operation lasts in all an hour and a quarter, after which the crucibles are removed and allowed to Fig. 516. Fig. 517. * The preparation of a “brasqued” crucible requires some precautions, which it may be worth while to indicate. “ Brasque” is composed of charcoal, powdered and sifted, moistened with water so as to give it a certain degree of consistency, and introduced into a crucible of refractory clay, into which it is rammed with a wooden stamper. This requires several additions of the material, as it becomes compressed by pounding. Before adding a new layer, the surface of the preceding must be made rough, as otherwise it would not incorporate itself with the succeed- ing stratum, and the two layers might separate during the heating, causing cracks to form, through which the liquid substances might escape. When the crucible is filled and the charcoal well-heaped in, a part of the “brasque” is removed with a knife, so as to form a rounded cavity abc (fig. 516), the material taken from which is heaped along the sides of the crucible; and the surfaces are then rubbed smooth with a strong glass rod. 110 IRON cool. The fused lump taken from the bottom of the crucible is composed of a button of cast-iron, surmounted by slag, both of which are weighed together. The slag is then broken off and pounded to pieces, to ascertain that it contains no metallic globules, and the button and globules are weighed. It is proper to remark that as the metal weighed is in the state of cast-iron, that is, combined with a certain quantity of carbon, its weight is consequently rather too great; but at the same time this excess of weight nearly compensates for the small quantity of iron which always remains in the state of oxide in the slag. Instead of the air-furnace of fig. 517, which is found only in laboratories where such tests are made in quantity, an ordinary blacksmith’s forge may be used, when a sort of hearth can con- veniently be made with refractory bricks, in the midst of which the crucible is to be placed. Fig. 518 represents a small portable furnace, which may be con- structed without much expense, and is well adapted for testing iron-ores. It is made of two large refractory crucibles ABcd, ABEF, the upper one of which, forming the lid, has a large opening 0, through which the fuel is charged and the air escapes, while the lower crucible has three holes o, o', o", and its bottom rests on a cup U of baked clay, into which the nozzle a of a bellows enters. The small “brasqued” cru- cible is, in order to place it in the middle of the furnace, set on several pieces of brick placed on each other, to the upper one of which it is luted with clay. The fuel used is charcoal or a mixture of charcoal and coke. 2. When the ore consists of anhydrous peroxide of iron, the proportion of siliceous gangue can no longer be determined by acting on it with chlorohydric acid, because the native peroxide is unaffected by this acid, and the latter therefore dissolves only the carbonate of lime, which may be thus determined:—In order to make the assay in the furnace, of its weight of a fusible silicate, white glass, for example, is mixed with the ore, in order to prevent the too siliceous scoriae from retaining oxide of iron. If this should nevertheless take place, which would be known by the deep green colour of the slag, the test must be repeated, but with an increased proportion of carbonate of lime, or with less glass than before. 3. As even the most concentrated acids act with difficulty on native magnetic iron, the proportion of quartzose gangue by which such ores are accompanied cannot be determined by chlorohydric Fig. 518. TESTING OF IRON-ORES. 111 acid, and the assay must be made as in the preceding case, that is, the ore must be immediately fused in a forge-fire with an ad- mixture of white glass and carbonate of lime. 4. Although the native protocarbonate of iron is converted by calcination into magnetic oxide, the loss of weight which sparry ores suffer by heat does not exactly represent the weight of the disengaged water and carbonic acid, because the protoxide of iron absorbs a portion of the oxygen of the carbonic acid which it decomposes. By treating the ore with weak nitric acid, the car- bonate of lime is dissolved; but a certain quantity of iron being dissolved at the same time, the lime cannot be determined as in the first case, and it becomes necessary to act on the ore with con- centrated boiling chlorohydric acid, in order to convert the iron into sesquioxide. The solution is evaporated to dryness at a gentle heat to drive off the excess of acid, and treated with water, which leaves the quartzose and argillaceous gangue undissolved; after which the sesquioxide of iron, the protoxide of manganese, and the lime are then successively separated in the liquid by the processes described § 803. § 859. When the oxide of iron readily dissolves in acids, the quantity of iron existing in an ore can be exactly and rapidly determined by boiling 3 grammes of the finely powdered ore with chlorohydric acid, until the solution loses its colour, evaporating to drive off the excess of acid, and treating the residue with water. The latter, which consists of the quartzose and argillaceous gangue, is collected on a filter and weighed. A standard solution of permanganate of potassa is then poured into the liquid, using the precautions indicated (§ 804), until the liquid assumes a perma- nent rose-colour, and the quantity of metallic iron existing in the 3 grammes of ore is determined from the quantity of permanganate of potassa used. If the ore be specular iron, or magnetic oxide, it can only be acted on by chlorohydric acid, after being heated to a high red- heat in a platinum crucible, with 3 or 4 times its weight of car- bonate of soda, or bisulphate of potassa. The peroxide of iron, in this way, becomes disaggregated and easier soluble in chlorohydric acid. ANALYSIS OF CAST-IRON AND STEEL. § 860. Cast-iron is a compound of carbon with iron, frequently containing, in addition, a certain quantity of silicium, sulphur, phosphorus, and manganese. We shall proceed to describe the mode of successively determining these several elements. 112 IRON, Determination of Carbon. § 861. Gray cast-iron can be easily filed, while white cast-iron and fine metal are, on the contrary, very hard, but when the file will not cut them, they can be pounded in a mortar. Fig. 519 represents a small apparatus of cast-steel, in which the pulverization can be easily effected. It is com- posed of a steel receiver abed, to which is fitted a cylinder efgh, exactly filled by a steel piston P. Some pieces of white cast-iron are placed in the cylinder, the piston P is introduced, and resting the base be on an anvil, the head of the piston is struck with a hammer. After a certain number of blows, the powdered substance is removed, and passed through a silk sieve; the fragments then remaining on the sieve being again broken up in the apparatus, and this process repeated until the whole quantity is reduced to fine powder. Five grammes of powdered cast-iron are then mixed with 100 or 120 gm. of chromate of lead, £ of the mixture is set aside, and with the remaining f-, 5 gm. of chlorate of potassa are inti- mately mixed, when the whole is introduced into a tube closed at one end, resembling those used for the combustion of organic sub- stances with oxide of copper; and on it the mixture containing no chlorate of potassa is placed. The tube is rested on a sheet- iron grate, while a tube containing chloride of calcium, or pumice- stone soaked in concentrated sulphuric acid, to absorb the moisture given off by the materials, is fitted to its extremity, and the whole apparatus is then arranged as represented in fig. 279. The anterior part of the combustion-tube, which does not con- tain chlorate of potassa, is first heated, and the coals are then slowly approached to that part containing the chlorate. The cast- iron burns, partly at the expense of the oxygen of the chromate of lead, and partly by that disengaged by the chlorate, and car- bonic acid is formed and collected in the globe apparatus. Fresh coals are added, until the end of the tube is reached. The excess of oxygen gas arising from the decomposition of the chlorate is at the same time disengaged and driven through the apparatus; but a little experience soon teaches how to avoid any danger of an explosion. It is well to place a small quantity of a mixture of chromate of lead and chlorate of potassa at the end of the com- bustion-tube, as the oxygen disengaged from this drives the last traces of carbonic acid through the globe apparatus. The increase of weight of the latter gives very exactly the carbonic acid arising from the carbon of the cast-iron, while the sulphur it may contain Fig. 519. ANALYSIS 01' CAST-IRON. 113 remains in the combustion-tube in the state of sulphate of lead, and does not affect the result of the experiment. It is important to keep the mixture in the combustion-tube so that a free space may remain in the upper part of the tube, as otherwise the chromate of lead, on becoming doughy and expanded, might obstruct the tube and cause an explosion. The same process necessarily applies to the determination of the carbon which exists in steel and in soft iron. The carbon contained in cast-iron and steel may also be exactly determined by causing these substances to react slowly on chloride of silver. To do this, 30 or 40 grammes of chloride of silver are fused in a porcelain capsule, a piece of iron or steel weighing about 5 gm. and exactly weighed is placed on it, and then water containing a few drops of chlorohydric acid is added. The chlo- ride of silver is gradually decomposed, while protochloride of iron is formed and the carbon set free; but the reaction is very slow, and often requires several wTeeks for its completion. There re- mains, at last, a spongy mass of carbon and silicic acid, from which the last traces of iron are extracted by boiling with dilute chlorohydric acid. The precipitate is collected on a filter and weighed after being well dried, or better still, after a calcination in a current of hydrogen gas. Its weight is that of the carbon and silicic acid united; and it is then calcined in a platinum capsule, by which the carbon burns off, when the weight of the silicic acid remaining can be directly determined, and that of the carbon cal- culated by the difference. As a substitute for chloride of silver, chloride of copper may be employed, which acts more rapidly on the cast-iron, but always disengages a small quantity of carburetted gas, so that the weight of the carbon found is rather too small. § 862. We have seen that carbon could exist in cast-iron in two states: 1st, in that of combined carbon, as in white cast-iron and steel; 2dly, in the state of small isolated laminae, as in gray cast- iron. It is of the highest importance to distinguish these two states of carbon, as they exert a remarkable influence over the nature of the cast-iron, and moreover are easily determined by analysis. In fact, when chlorohydric acid is allowed to act on a white cast-iron or steel, the metal dissolves and evolves a very fetid hydrogen gas, containing a considerable quantity of gaseous carburetted hydrogen, and vapours of certain liquid carburetted hydrogens which have been not yet studied. All the carbon of the cast-iron disappears in these hydrogenated products, and the residue is composed only of the silicic acid produced by the silicium of the cast-iron. If, on the contrary, a gray cast-iron be treated with chlorohydric acid, the gas evolved is still fetid, as the carbon which was in intimate combination with the iron is converted into 114 IRON, gaseous or liquid carburets of hydrogen, but the isolated carbon which existed in it in the state of graphite remains intact with the silicic acid. The residue is collected on a small filter, and, after being well washed, is dried. Some ether is then poured over the filter, to dissolve any oil which may remain, after which it is again dried at a temperature above 212°, and the residue weighed: the weight of the graphite and silicic acid united is thus obtained. The substance is heated in a platinum capsule in the open air, or better still, in a current of oxygen, by which the graphite burns, and leaves as a residue only silicic acid, which can be determined by weight. By subtracting from the whole weight of the carbon obtained by the combustion of the cast-iron the weight of graphite first obtained, the weight of the combined carbon is ascertained. Determination of Silicium. § 863. The silicium of cast-iron is determined by dissolving the latter in chlorohydric acid, which converts the silicium into gelati- nous silicic acid. The liquid is evaporated to dryness to render the silex insoluble, then treated with water, and the residue collected on a filter. The silex is weighed, after having been cal- cined at a dull red-heat, and the weight of the silicium is deduced from it. Cast-iron frequently contains particles of slag, so that the residue is composed not only of the silicic acid furnished by the silicium of the cast-iron, hut also that of the slag, which may have been more or less altered by the chlorohydric acid. The slag of char- coal furnaces generally resists this acid, while that of coke furnaces is more or less completely acted on by it. By treating powdered cast-iron with weak chlorohydric acid, the iron may be entirely dissolved, without sensibly affecting the slag, while the residue consists of gelatinous silex and slag, and is treated by a solution of caustic potassa, which dissolves the silex and leaves the slag. The silicic acid which has been furnished by the silicium of the cast-iron can thus be exactly ascertained. § 864. The cast-iron is acted on by aqua regia, which dissolves the iron as perchloride, and converts the sulphur into sulphuric acid. The liquid is diluted with water, and the sulphuric acid pre- cipitated by chloride of barium as sulphate of baryta, from which the weight of the sulphur in the cast-iron may be deduced. Determination of Sulphur. § 865. The cast-iron is acted on by aqua regia, evaporated to dry- ness to drive off the excess of acid, and then treated with water. The liquid, containing phosphorus in the state of phosphoric acid, is Determination of Phosphorus. ANALYSIS OF SLAGS. 115 then allowed to digest at a temperature of about 212°, for several hours, with an excess of sulfhydrate of potassium, which precipitates iron and manganese in the state of sulphides. After separating these by filtration, the liquid contains phosphoric acid and alkaline sulphides, which are decomposed by a slight excess of chlorohy- dric acid, after which the liquid is boiled to drive off the sulf hydric acid. One decigramme of piano-forte wire is then weighed very exactly, dissolved in aqua regia, and added to the solution of per- chloride of iron obtained. An excess of ammonia poured into the liquid then completely precipitates the iron added in the state of hydrated sesquioxide, and carries with it all the phosphoric acid which existed in the liquid, precipitated as a basic perphosphate of iron. This precipitate is weighed after calcination in the air; and if from it 0.143 gm., the weight of the sesquioxide of iron yielded by 0.100 gm. of metallic iron, are subtracted, the weight of the phosphoric acid, whence that of the phosphorous in the cast- iron may be deduced, is obtained. The same determination may be made in the following manner:— After having dissolved the cast-iron in chlorohydric acid, the liquid is filtered and an excess of acetate of soda added, the acetic acid of which is set free and chloride of sodium is formed. Now, as sesquioxide of iron forms with phosphoric acid a phosphate Fe303 PhOs insoluble in acetic acid, the phosphoric acid combines with the proper quantity of sesquioxide of iron to form this phosphate, which is precipitated, collected on a filter, washed with boiling water, and weighed after calcination. The precipitate may also be redissolved in chlorohydric acid, the liquid boiled with sulphite of soda to bring the perchloride of iron to the state of protochlo- ride, and the standard solution of permanganate of potassa poured in to determine the quantity of iron it contains. The weight of phosphoric acid is thence easily deduced, and, consequently, that of the phosphorus contained in the cast-iron. Determination of Manganese. § 866. The manganese contained in cast-iron is easily ascertained by the processes described § 803. ANALYSIS OF SLAGS AND FURNACE SCORL33. § 867. Slag is composed chiefly of silicates of alumina and lime, but often contains, in addition, small quantities of the silicates of iron and manganese. The various scoriae arising from the refining of cast-iron are composed of silicates of iron and manganese, but may also contain small quantities of silicates of alumina, lime, and potassa, arising from the ashes of the fuel used. Forge scoriae are readily acted on by concentrated chlorohydric acid, by which the ma- 116 IRON, jority of slags is, however, not attacked. These products are ana- lyzed by the processes described in the analysis of glass (§ 704), except that, in the case of forge scoriae, it is useless to employ car- bonate of soda and fluohydric acid, as the substance is acted on immediately by chlorohydric acid. REMARKS ON THE COMPOSITION OF IRON, STEEL, AND CAST-IRON. § 868. By the hardness of wrought-iron is understood the resist- ance it presents when filed, cut, bored, or struck with a hammer while it is cold, which properties vary greatly in the different kinds of iron manufactured in different furnaces. Iron which when cold readily takes the impression of the hammer, is commonly flexible and tough, but, although of an excellent quality, cannot be univer- sally applied,—that which is, at the same time, hard and tough being preferred. The best iron is that which is very hard, without being brittle, that is, without breaking easily under the hammer. Iron which breaks or splits easily w'hen heated is said to be short; a defect which is produced by a small quantity of sulphur: part of sulphur will make iron slightly short. When iron contains 0.5 per cent, of phosphorus, it is brittle when cold, while a smaller quantity only renders the metal harder, still giving iron of good quality. Wrought-iron may contain 0.25 per cent, of carbon, without pos- sessing the property of remarkably hardening by tempering, which is regarded as characteristic of steel (§ 857). When the carbon rises to 0.60 per cent, the metal becomes too steely, and strikes fire with a flint after tempering. The quantity of carbon which renders iron steely, varies with the purity of the metal; for very pure iron, for example, a larger proportion than for that containing smaller quan- tities of sulphur and phosphorus is required. Steel, refined by fagoting, and which is, at the same time, suffi- ciently hard and tough for cutting instruments, contains from 1.0 to 1.5 per cent, of carbon. When the proportion of the latter is greater, the steel becomes harder, but loses in toughness and par- ticularly in the property of being welded. Steel containing 1.75 per cent, of carbon cannot be welded at any temperature. When iron is combined with 2 per cent, of carbon, it cannot be forged under the hammer. This property may be regarded as dis- tinguishing steel from cast-iron, the compounds of iron with a greater proportion of carbon than 1.9, consequently, being no longer steel, but cast-iron. Cast-steel which contains from 1.9 to 2 per cent, of carbon, cannot be forged, but it never parts with its graphite, even by very slow cooling. Graphite separates by slow cooling, only when the iron is combined with at least 2.5 per cent, of carbon. PROPERTIES OF CAST-IRON. 117 The properties of cast-iron do not depend so much on the whole quantity of carbon contained, as on that with which it is intimately combined. Gray cast-iron most frequently contains only 2 or 2.5 per cent, of combined carbon, the rest of this substance being scat- tered through it in the form of graphitous spangles. Gray cast- iron requires a higher temperature for fusion than white cast-iron, and passes almost suddenly from the liquid to the solid state, while white iron passes through an intermediate doughy state; on which account, probably, white cast-iron is more easily refined than gray iron containing the same quantity of carbon. Therefore, it is always endeavoured to obtain wThite cast-iron for refining, when the purity of the ore and the fuel will allow it; for we have already said (§ 826) that wfith impure ores and fuels, the temperature of a blast furnace producing gray cast-iron must be greatly elevated, unless the gray iron be suddenly cooled on leaving the furnace. Gray cast-iron is converted into white cast iron by sudden cool- ing, while the white passes into the gray state at a higher tem- perature, and by slow cooling. 118 CHROMIUM. Equivalent = 26.7; (333.75,0 = 100.) § 869. Chromium* is obtained combined with a certain quantity of carbon, by heating, in a “brasqued” crucible, an intimate mix- ture of sesquioxide of chromium and 15 or 20 per cent, of carbon in a forge-fire, when the carburetted metal remains in the form of a porous lump, as the heat was not sufficient to fuse it. This metallic mass is finely powdered in a steel mortar, intimately mixed with a few hundredths of the green oxide of chromium, and the mixture heaped in a porcelain crucible accurately covered by its lid, which is then placed in a second earthen crucible, likewise “ brasqued,” and heated to the highest temperature of a forge-fire. The carbon of the carburetted chromium is burned by the oxygen of the oxide, and a purer metal is obtained, in the form of a gray agglutinated mass. This metal is brittle, but may be polished, and then displays a brilliant metallic lustre. It is very hard and scratches glass readily, and its specific gravity is about 6.0. It does not oxidize in dry air at the ordinary temperature, but com- bines rapidly with oxygen when heated to a dull red-heat. It dissolves in chlorohydric and dilute sulphuric acid with evolution of hydrogen gas. Pure metallic chromium is obtained, in the form of a dark-gray powder, by decomposing the violet sesquichloride of chromium by potassium. The pulverulent metal has so powerful an affinity for oxygen, that it ignites before it reaches a dull red-heat, and is converted into green oxide of chromium when heated in contact with the air. COMPOUNDS OF CHROMIUM WITH OXYGEN. § 870. Chromium forms many compounds with oxygen : 1. The protoxide CrO, isomorphous with protoxide of iron FeO. 2. The sesquioxide Cr303, isomorphous with alumina and ses- quioxide of iron Fe303. 3. An oxide Cr304, intermediate between the first two, and cor- responding to magnetic oxide of iron Fe0,Fe303; so that its formula should be written Cr0,Cr303. 4. Chromic acid Cr03, corresponding to ferric acid Fe03, and manganic acid Mn03. 5. An intermediate oxide Cr03, which should, however, rather * Discovered in 1797 by Vauquelin. OXIDES OF CHROME. 119 be considered as a combination of chromic acid with protoxide of chromium: Cr0,Cr08. 6. Lastly, a perchromic acid Cr307, corresponding to permanganic acid Mn307. Protoxide of Chromium, CrO. § 871. Protoxide of chrome is obtained by adding caustic potassa to a solution of protochloride of chromium, when a deep brown precipitate of hydrated protoxide is formed. But this substance has so great an affinity for oxygen that it decomposes water as soon as it is set free, disengaging hydrogen, and being converted into a tobacco-coloured powder, which is the hydrate of a definite oxide Cr304, corresponding to magnetic oxide of iron, and which should consequently assume the formula Cr0,Cr303. The trans- formation takes place very rapidly, at the temperature of boiling water. The hydrate of the oxide of chrome Cr0,Cr303, heated in a closed tube, is converted into the green oxide Cr303, with the evolution of hydrogen gas. The composition of protoxide of chrome has never been directly ascertained, but has been inferred from the analysis of protochlo- ride of chrome. This oxide contains 1 eq. chromium 26.7 or 333.7 78.53 1 “ oxygen 8.0 100.0 21.47 1 “ protoxide 34.0 433.7 100.00 Sesquioxide of Chromium Cr303. § 8T2. Sesquioxide of chromium is prepared in several ways : 1. By heating protochromate of mercury Hg30,Cr03; when oxygen is disengaged, the mercury distils, and sesquioxide of chrome remains in the form of a deep-green powder: 2(Hg30,Cr03)=Cra03+4Hg+50. 2. By heating in a crucible a mixture of 1 part of bichromate of potassa, 1J “ sal ammoniac, 1 “ carbonate of potassa, when chloride of potassium and oxide of chrome are formed, while the oxygen given off by the chromic acid combines with the hy- drogen of the ammonia: K0,2Cr03+K0,C03+2(NH3,HCl) = 2KC1 + Cr303+5HO+N+ NH3,C03. By treating the substance with water, the chloride of potassium is dissolved, leaving the sesquioxide of chrome in a state of purity. 3. By heating at a suitable temperature, in an earthen crucible 120 CHROMIUM. or in a retort, 2 parts of bichromate of potassa, and 1 part of sulphur; when the sulphur forms, with the oxygen given off by the chromic acid, sulphuric acid, which combines with the potassa: K0,2Cr03+S=Cr303+K0,S03. But an excess of sulphur is necessary, as a portion of this sub- stance is volatilized without reacting on the chromate. By treat- ing it wfith water, the oxide of chrome often remains mixed with a small quantity of sulphur, which may be expelled as sulphurous acid by heating it in contact with the air. 4. By calcining bichromate of potassa in a “brasqued” crucible, when carbonate of potassa, which is removed by water, and sesqui- oxide of chrome are formed: 2(K0,2Cr08)+3C=2(K0,C03)+C03+2Cr303. 5. By heating bichromate of potassa to a high white-heat, when half of the chromic acid is decomposed into sesquioxide of chrome and oxygen, and a neutral chromate of potassa is formed, which is removed by water : 2(K0,2Cr03)=Cr203+30+2(K0,Cr03). In this case the sesquioxide of chrome assumes the form of crys- talline lamellae. 6. By heating chromate of potassa to a red-heat, in a current of chlorine, when chloride of potassium is formed, and the chromic acid is decomposed into sesquioxide of chrome and oxygen: 2(K0,Cr03)+2Cl=2KCl+Cr203+30. Sesquioxide of chrome, thus prepared, appears in the form of green crystalline lamellae. 7. Lastly, sesquioxide of chrome is obtained, in the form of small rhombohedral crystals, isomorphous with native crystallized alumina or corundum, by passing through a heated tube a red volatile liquid of the formula Cr03Cl, which we shall describe under the name of chlorochromic acid. 2Cr03Cl=Cr203+2Cl+0. The crystals which are deposited on the sides of the tube are often 1 or 2 millimetres in size, very brilliant, and of so deep a green colour as to appear black. They are as hard as corundum and readily scratch glass. Their specific gravity is 5.21. Sesquioxide of chrome cannot be decomposed by heat. Hydrogen even does not reduce it at the highest temperature of our labora- tory furnaces; but charcoal decomposes it in a forge-fire, when it is intimately mixed with the oxide. Vapour of sulphur does not act on it at a white-heat, while sulphide of carbon decomposes it at this temperature, and converts it into sulphide of chromium. Sesquioxide of chrome imparts a green colour to fluxes, and we have already seen that this oxide is used for painting on glass and SESQUIOXIDE OF CHROME. 121 porcelain. A red colour, called pink-colour, is also prepared with chrome, and was first used on porcelain by the English. It is obtained by heating to redness an intimate mixture of 100 parts of stannic acid, 34 of chalk, and 3 or 4 of chromate of potassa, and then treating the powdered material with chlorohydric acid until it has acquired a beautiful rosy tinge. The colouring prin- ciple of this substance is probably an oxide of chrome superior to the sesquioxide. Strongly calcined, it combines with the acids, even when they are concentrated, only with great difficulty; the hydrate must therefore be dissolved when salts of the oxide are to be prepared. In order to prepare the hydrated sesquioxide of chrome, a solu- tion of the sesquichloride is precipitated by ammonia, when a gelatinous bluish-gray precipitate is formed, which must be washed with boiling water. The sesquichloride of chrome used in this preparation is obtained by decomposing bichromate of potassa by sulphurous acid, in the presence of an excess of chlorohydric acid. To effect this a current of sulphurous acid gas is passed through a concentrated hot solution of bichromate of potassa, mixed with chlorohydric acid, when the liquid soon changes in colour, be- coming first brown, and subsequently assuming a beautiful emerald green hue. The reaction is terminated when the liquid still exhales a strong smell of sulphurous acid, after having been left to itself for several hours in a well-corked bottle. Hydrated sesquioxide of chrome dissolves readily in acids. Moderately heated, it loses its water, still preserving the property of easily combining with acids; but if the temperature be further elevated, the substance suddenly becomes incandescent before reaching a red-heat, and, after incandescence, the oxide is nearly insoluble in acids. § 873. Sesquioxide of chrome can combine with powerful bases, and one of these compounds, found in nature, acquires great im- portance from being the ordinary chrome ore. It consists of ses- quioxide of chrome and protoxide of iron, combined according to the formula Fe0,Cr303: in mineralogy, it is called chromate of iron, or chromic iron. Chromic iron has sometimes been found crystallized in regular octahedrons, presenting, therefore, the same form as magnetic oxide of iron FeO,Fea03, and spinell MgO,Ala03, which have similar formulae. Most frequently, chromic iron forms considerable masses, of a deep gray colour and a greasy lustre; and its bearings resemble those of magnetic oxide of iron. The principal mines of chromic iron are in Sweden, the Ural, and near Baltimore in the United States.* It has been found in * The most extensive and important locality by far, is that of Lancaster and Chester counties, Pennsylvania, which now supplies both the United States and Europe. A considerable part of the ore is now obtained by simply washing the sands of brooks.— W. L. F. 122 CHROMIUM. France, in the department of Var, but the mine appears nearly exhausted. Chromic Acid CrO„. § 874. In order to prepare chromic acid, one and a half times its volume of sulphuric acid is added gradually and in small quan- tities to a solution of bichromate of potassa, saturated at a tem- perature of from 130° to 140°, when bisulphate of potassa is formed, which remains in solution, and the liquid deposits on cool- ing long red needles of chromic acid. When the solution is cooled and the acid liquid decanted off, the crystals are allowed to drain in a funnel stopped with asbestus, and are then spread upon un- burnt porcelain, which absorbs the remaining water. In order to purify them, their aqueous solution is treated with a small quantity of chromate of baryta, which combines wfith the sulphuric acid, and the filtered liquid is evaporated in vacuo. Chromic acid is of a beautiful red colour at the ordinary tem- perature, but becomes almost black when heated. It decomposes before attaining a red-heat into sesquioxide of chrome and oxygen, and is deliquescent and very soluble, with an orange-yellow colour. Chromic acid is a very powerful oxidizing agent: a few drops of absolute alcohol thrown on it, instantly convert it into sesqui- oxide, with so great an evolution of heat that the alcohol some- times ignites. Hot concentrated sulphuric acid decomposes chromic acid, disengaging oxygen and forming sesquisulphate of chrome. Oxygen is sometimes prepared in the laboratory by heating together equal weights of bichromate of potassa and con- centrated sulphuric acid. Chlorohydric acid converts chromic acid into sesquichloride of chrome, with disengagement of chlo- rine : 2Cr03+6HCl=Cr8Cl,+6H0+3Cl. § 875. Chromic acid appears to be able to combine in several proportions with sesquioxide of chromium. If a solution of bichro- mate of potassa be treated with sulphurous acid until it assumes a brown colour, and at that moment ammonia be added to the liquid, an ochreous precipitate is obtained, which hot water, after some time, decomposes into chromic acid which dissolves, and hydrated sesquioxide of chrome which remains. A similar compound is obtained by decomposing nitrate of chrome by a suitable degree of heat, when a brown spongy mass remains, of which the compo- sition is represented by Cr02, but to which the formula Crs03, CrOs has been assigned. Per chromic Acid. § 876. By treating chromic acid with oxygenated water, a beautiful blue solution is obtained, which, when shaken with ether, loses its colour, and imparts the blue compound to the ether. PROTOSALTS OF CHROME. 123 This compound, which is not very stable, has not yet been ob- tained in an isolated state, nor has it been combined with the mineral bases. Its formula is supposed to be Cr2Or § 877. Protoxide of chrome CrO is a powerful base, but never- theless has been combined with only a small number of acids, on account of the difficulty of obtaining it pure, and the ready sus- ceptibility of change of the salts themselves, which rapidly absorb- ing the oxygen of the air, are converted into sesquisalts. The acetate and the double sulphate of protoxide of chrome and potassa only are known; but in order to ascertain the distinctive charac- ters of the protosalts of chrome, the protochloride must be resort- ed to. These compounds are known by the following reactions :— Caustic potassa at first affords a deep brown precipitate of hy- drated protoxide, but which is immediately changed into a clear brown hydrated magnetic oxide, with the evolution of hydrogen gas. Sulfhydric acid does not precipitate them, while sulfhydrates yield a black precipitate. Bichloride of mercury gives a white precipitate of protochloride of mercury. Lastly, oxidizing reagents, such as chlorine, nitric acid, etc., immediately convert the proto- salts of chromium into sesquisalts. SALTS FORMED BY PROTOXIDE OF CHROME. SALTS FORMED BY SESQUIOXIDE OF CHROME. § 878. Sesquioxide of chrome is a feeble base, analogous to ses- quioxide of iron. The salts formed by this oxide may exist under two different modifications, which are distinguished by their co- lours, the first being violet, while the second is green. Several acids produce both modifications; but with others only one of the colours has hitherto been obtained. A green and a violet sulphate are known. Ammonia forms in the solutions of these two salts precipitates which are distinguished by their shades of colour; the precipitate of the green sulphate being bluish gray, and producing a green solution with sulphuric acid, while that furnished by the violet modification is of a greenish gray, but also produces a green solution when treated with sul- phuric acid. Potassa and soda yield bluish-gray or greenish-gray precipi- tates, which dissolve in an excess of alkali, forming a green liquid, which loses its colour by boiling, as the hydrated oxide is again precipitated. The alkaline carbonates give a greenish precipitate, perceptibly soluble in an excess of the reagent. Sulfhydric acid does not precipitate the sesquisalts of chrome, but the sulfhydrates precipitate those of the hydrated sesquioxide. The sesquisalts of chrome produce, like the protosalts, a glass 124 CHROMIUM. of a characteristic green colour when fused with borax. Fused with the alkaline carbonates, or better still, with the nitrates, they form alkaline chromates, which are recognised by the yellow solu- tions they produce, and by their great colouring power. Sesquinitrate of Chrome. § 879. Hydrated sesquioxide of chrome dissolves immediately in nitric acid, furnishing a green solution wdiich leaves, after eva- poration, a very soluble green salt, readily decomposable by heat. At a moderate temperature, it yields a brown substance, which is regarded as a sesquichromate of chrome Cra03,Cr03. Sesquisulphates of Chrome. § 880. The neutral sesquisulphate of chrome Cr203,3S03 has been obtained with three different colours, violet, green, and red, which appear to correspond to three modifications of the salt. The violet sulphate is obtained, by leaving for several weeks, in a badly-corked bottle, 8 parts of hydrated sesquioxide of chrome, dried at 212°, and 8 or 10 parts of concentrated sulphuric acid. The solution, which is at first green, gradually becomes blue, and, after some time, a greenish-blue crystalline mass is deposited. With an aqueous solution of this substance, alcohol gives a violet- blue crystalline precipitate, which, after having been dissolved in very weak alcohol, is left to itself. After some time, the liquid deposits small regular octohedrons of the formula Cra03,3S03+ 15HO. The green sulphate is prepared by dissolving sesquioxide of chrome, at a temperature of 120° to 140°, in concentrated sul- phuric acid, or by boiling the solution of the violet sulphate. The liquid, when rapidly evaporated, yields a green crystalline salt, having the same composition as the violet sulphate. The green sulphate readily dissolves in alcohol with a blue colour, while the violet sulphate is insoluble in it. The violet and green sul- phates are also distinguished by several chemical reactions; thus, the cold solution of the green sulphate is not completely decom- posed by the soluble salts of baryta, and the decomposition is complete only when the liquid is boiled, while all the sulphuric acid of the violet solution may, on the contrary, be precipitated when cold by salts of baryta. If the violet or green sulphate be heated to a temperature of 392°, with an excess of sulphuric acid, a cljear yellow mass is obtained, which leaves as a residue the red neutral sulphate of chrome, after the evaporation of the excess of acid. This anhy- drous sulphate is insoluble in water, and dissolves with difficulty even in acid liquids. CHROMIC ALUMS. 125 Chromic Alums. § 881. Sesquisulphate of chrome is isomorphous with, sulphate of alumina, and may take the place of the latter in the alums. The crystallizable chromic alums contain the violet modification of sulphate of chrome. Three of these alums are known, affording beautiful crystals : Potassic alum Cr3033S03+K0,S03+24H0. Sodic alum Cra03,3S03-j-Na0,S03-f-24H0. Ammoniacal alum Cra03,3S03+(NH3,H0)S03+24H0. Potasso-chromic alum is prepared by heating slightly a mixture of bichromate of potassa and sulphuric acid dissolved in water, with a reducing substance, such as sugar, alcohol, etc.; or by passing a current of sulphurous acid through the liquid. The solution depo- sits by spontaneous evaporation, or even on cooling, if it be suffi- ciently concentrated, large regular octahedrons, like those of ordi- nary alum, of a deep violet red. They dissolve readily in water, with a dirty violet colour, but are insoluble in alcohol. Heated to 176°, the solution becomes green, and deposits by evaporation red crystals of alum, but leaves as a residue an uncrystallized mass, which is still a double sulphate of potassa and chrome, but which no longer presents any of the characters of potassa-chromic alum. The solutions of the green sulphates of chromium give the same green product when they are evaporated with sulphate of potassa. CHROMATES. § 882. Chromic acid combines with nearly all the bases, forming with the alkalies salts which crystallize perfectly, and are isomor- phous with the corresponding sulphates. The chromates of stron- tian, lime, and magnesia are soluble, while the other metallic chro- mates are insoluble, or nearly so. Chromic acid forms with the alkalies two series of salts: neutral chromates and bichromates, the former of which are of a bright yellow colour, while the bichromates are orange-red. The soluble chromates are easily distinguished: first, by their colour, which is very decided, even in very dilute solutions; and also, by the cha- racteristic colours of the precipitate they yield with various metallic salts. They form a yellow precipitate with the salts of lead and bismuth, a bright red one with those of mercury, and a deep red one with those of silver. The chromates, heated with concen- trated chlorohydric acid, give a green solution of sesquichloride of chrome. Chromates of Potassa. § 883. The compounds of chromic acid with potassa are the most important products of chrome, as large quantities of them are used in dyeing and calico-printing. They are obtained directly from 126 CHROMIUM. chrome-ore, that is, from chromic iron. The chrome-ore, which even when purified by washing always contains a certain quantity of quartzose and aluminous minerals, is heated, finely powdered, in a reverberatory furnace, with carbonate of potassa, to which some nitrate of potassa is frequently added, and the material is constantly stirred to facilitate its oxidation. Chromate of potassa, but at the same time, a certain quantity of silicate and aluminate of potassa, are formed, to separate which the roasted substance is treated with water, which dissolves the soluble alkaline salts, after which acetic acid is added to the liquid until it assumes an acid reaction, which is a sign that the neutral chromate of potassa is converted into a bichromate and that the silicic acid is deposited. The bichromate, being much less soluble than the neutral salt, is easily separated by crystallization, and purified by recrystallization. Bichromate of potassa forms beautiful red crystals, which fuse without change before attaining a red-heat, but decompose at a higher temperature into neutral chromate, sesquioxide of chrome, and oxygen which is given off. This salt contains no water of crystallization, and is soluble in 10 parts of cold and in a much less quantity of boiling water. Neutral chromate of potassa is obtained by adding chromate of potassa to a solution of the bichromate until the latter assumes a clear yellow colour, and evaporating the liquid, when yellow anhy- drous crystals are obtained, presenting exactly the same form as sulphate of potassa. The neutral chromate is very soluble, as cold water dissolves more than double its weight of it, and hot water still more. The solution of the neutral chromate of potassa turns the red tincture of litmus blue. The neutral chromate of soda is very soluble in water, and, during cooling from a hot saturated solution, forms crystals corresponding to the formula NaO,CrO3-|-10IIO, and is isomorphous with sul- phate of soda NaO,SOg-f lOIIO. Bichromate of Chloride of Potassium, or Clilorochromate of Potassa. § 884. If a solution of bichromate of potassa be boiled with chlo- rohydric acid until chlorine begins to be evolved, a brown liquid is obtained, which on cooling deposits beautiful orange-coloured crystals of a salt which may be regarded as a bichromate of chlo- ride of potassium KCl,2CrOs. This substance may also be con- sidered as a bichromate of potassa, in which one of the equivalents of chromic acid is replaced by 1 equiv. of chlorochromic acid, Cr03Cl; but then its formula should be written, Iv0(Cr03+Cr02Cl.) Chlorochromic Acid. § 885. A chlorochromic acid CrOaCl may be obtained isolated, by fusing in an earthen crucible 10 parts of sea-salt and 17 parts of bichromate of potassa. The liquid matter is run on a sheet-iron COMPOUNDS OF CHROMIUM. 127 plate, and, when cool, broken into fragments, which are introduced into a glass retort with 30 parts of concentrated sulphuric acid. Reaction commences immediately, a gentle heat is subsequently applied, and a blood-red liquid condenses in the receiver, which should be cooled with ice. The density of this liquid is 1.71; it boils at 248°. By contact with water it is decomposed into chromic and chlorohydric acids: Cr03Cl+H0=Cr03+HCl. It should be kept in glass tubes hermetically sealed. COMPOUND OF CHROMIUM WITH SULPHUR. § 886. If sulphide of carbon in vapour be passed through a heated porcelain tube containing sesquioxide of chrome, the latter is con- verted into crystalline spangles of sulphide of chromium CraS3, re- sembling native graphite. COMPOUND OF CHROMIUM WITH NITROGEN. § 887. A compound of chromium with nitrogen is obtained by heating sesquichloride of chrome in a current of dry ammoniacal gas. This substance then presents the form of a brown powder, which is unchangeable in the atmosphere at the ordinary tempera- ture, but readily ignites and is converted into sesquioxide when heated in the air. § 888. Chromium forms two compounds with chlorine: a proto- chloride CrCl, corresponding to the protoxide CrO; and a sesqui- chloride Cr3Cl3, corresponding to the sesquioxide Cr303, and capable of existing under two different modifications. jProtochloride of chrome CrCl is obtained by passing hydrogen gas over anhydrous sesquichloride heated to redness in a porcelain tube. Protochloride of chrome is white, dissolves in water, yield- ing a blue solution, which absorbs rapidly the oxygen of the air, thus converting the protochloride into an oxychloride Cr3Cl30. The solution of protochloride of chrome readily absorbs deutoxide of nitrogen, like the protochloride and protosulphate of iron. § 889. Anhydrous sesquichloride of chrome is prepared by heat- ing an intimate mixture of sesquioxide of chrome and charcoal in a current of dry chlorine, the process otherwise exactly resembling that for the preparation of chloride of aluminum (§ 604). The sesquichloride is deposited in the anterior part of the tube, in the form of small spangles of a peach-blossom colour. Anhydrous sesquichloride of chrome may be brought in contact with water without being dissolved by it in the slightest degree, but boiling water dissolves it after some time, giving a green solution. If a very small quantity of protochloride of chrome CrCl be added to cold water, sesquichloride immediately dissolves with evolution of heat, and yields a green solution identical with that obtained by COMPOUNDS OF CHROMIUM WITH CHLORINE. 128 CHROMIUM. dissolving hydrated sesquioxide of chrome in chlorohydric acid. The smallest quantity of protochloride of chrome, is sufficient to produce this remarkable effect. By dissolving hydrated sesquioxide of chrome in chlorohydric acid, a green solution is obtained, which yields, on evaporation, a deliquescent green mass, the formula of which, when evaporated in dry air, is CrCl3d-9HO. Heated, it evolves water and chloro- hydric acid, while oxychlorides remain. Some chemists regard this body as resulting from the direct combination of chlorohydric acid with sesquioxide of chromium, as a chlorohydrate of sesqui- oxide of chrome, and give it the formula Cr303,3HCl-f 6IIO. If the hydrated sesquichloride be heated in a current of chlorohydric acid gas, it only loses its water, and is converted into a violet anhy- drous sesquichloride. By pouring chloride of barium into a solution of violet sulphate of chrome, sulphate of baryta is precipitated, and there remains in the liquid a violet sesquichloride of chrome, presenting the same composition as the green sesquichloride. These two modifications are observed in several chemical reactions; thus nitrate of silver only precipitates when cold § of the chlorine of the green chloride, while the violet sesquichloride immediately parts with the whole of it at the boiling point. The violet chloride is rapidly trans- formed into the green chloride. DETERMINATION OF CHROME; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 890. Chrome is always determined in the state of green oxide. To do this, the chrome is converted into chloride or sulphate of sesquioxide, and the boiling solution is precipitated by ammonia. The gelatinous precipitate of the hydrate is collected on a filter, and, after being well washed, is calcined in a closed platinum crucible.* * A much more exact method is the alkalimetrical determination of chrome, which depends on the same principle as that of peroxide of manganese, described in the note to § 765. The chrome must first be converted into chromic acid, unless it be already in that state, by a fusion with caustic potassa and chlorate of potassa. Chlorohydric acid being added to the solution of the chlorate formed, the latter is then reduced by a protosalt of iron according to the formula, 6Fe0-f2CrO3=3Fe1O3+CraO3. Now, if a certain quantity of a protosalt of iron has been added, and the surplus of this be determined by permanganate of potassa, according to $ 804, the quantity of chromic acid or oxide may be found by the above formula; as six equivalents of the protoxide of iron found by subtracting the quantity determined from the whole quantity added, correspond exactly to two equivalents of chromic acid, or to one of sesquioxide of chrome. The protosalt of iron employed is the protosulphate of iron and ammonia, of which a standard solution is kept for the determination of peroxide of manganese. The methods of determining chrome by weight are inexact; as sesquioxide of chrome cannot entirely be freed from a part of the fixed alkali used for its pre- CHROME. 129 When chrome exists in solution as chromic acid, nitrate of mer- cury is added, and the precipitate of chromate of mercury formed is calcined in a platinum crucible, leaving sesquioxide of chrome, which is weighed. Chromic acid may, also, he converted into ses- quichloride of chrome, by heating the liquid with chlorohydric acid, and passing a current of sulphurous acid gas through it, when oxide of chrome may be precipitated by ammonia. When the oxide of chrome exists in the state of a salt mixed with alkaline or alkalino-earthy salts, it is precipitated when hot by caustic ammonia, which only precipitates the oxide of chrome, and is filtered rapidly, so as to avoid, as much as possible, the con- tact of the air, in order that the carbonic acid of the air may not precipitate the alkaline earths. If the liquid contains manganese, an ammoniacal salt must first be added in sufficient quantity to prevent the magnesia from being precipitated by the ammonia. The oxides of chrome and the alkaline earths may also be precipi- tated by an alkaline carbonate, but the mixture must then be fused in a platinum crucible with carbonate of soda, when chromate of soda is formed which is dissolved in water. The chrome is then precipitated by the processes described. Oxide of chrome is separated from alumina by boiling the hy- drated oxides with caustic potassa, which dissolves only the alumina. Oxide of chrome is separated from oxide of manganese by adding to the liquid containing the two oxides a quantity of ammoniacal salt sufficient to prevent the oxide of manganese from being pre- cipitated by the ammonia. The liquid is then boiled, and an ex- cess of ammonia added, which completely precipitates the oxide of chrome.* In order to separate oxide of chrome from the oxides of iron, the substance must be heated with caustic potassa in a silver crucible, when chromate of potassa is formed, which is dissolved in water, leaving the peroxide of iron isolated. cipitation, and ammonia does not precipitate it perfectly; and the other method, not mentioned in the text, of precipitating chromic acid by acetate of lead, and weighing the chromate of lead formed, has the disadvantage that chromate of lead is not absolutely insoluble in water.—W. L. F. * By far the best method of separating chrome from manganese is to precipi- tate the former as sesquioxide by carbonate of baryta, which leaves the manga- nese in solution.— W. L. F. 130 COBALT. Equivalent = 29.5 (369.0; 0=100). § 891. Pure metallic cobalt* is obtained by reducing its oxides in a current of hydrogen gas; but the metal is then in the form of a black powder w'hich is pyrophoric, like oxide of iron under the same circumstances: it becomes incandescent when projected in contact with the air. The metal is obtained in a more aggre- gated and less oxidizable form, by making the reduction by hydro- gen at a higher temperature, in a porcelain tube heated in a rever- beratory furnace. The oxides of cobalt, like those of iron, are easily reduced by cementation in contact with charcoal. If oxide of cobalt be heaped in a “brasqued” crucible, and heated in a forge-fire, precisely as in the assay of iron, a fused metallic lump of carburetted cobalt is obtained, which is gray, possessing a lustre resembling that of cast-iron; but it has but little malleability, and breaks under the hammer. Pure fused metallic cobalt may be obtained by adopting a process which does not succeed for iron. Oxalate of cobalt is heaped in a porcelain tube closed at one end, so as to introduce as great a quantity as possible; and this tube, closed with a lid, is placed in an earthen crucible, and the whole is then heated in a strong forge-fire, after the interstices have been filled with clay. The oxalate of cobalt is decomposed with evolu- tion of carbonic acid, according to the reaction, CoO,C303=Co+2C03, when the metallic cobalt alone remains, and, if the temperature be sufficiently high, fuses into a button. The cobalt thus obtained is of a steel-gray colour, susceptible of a fine polish, and of the spe- cific gravity 8.5. Cobalt is nearly as magnetic as iron. Cobalt is less affected by damp air than iron, but after some time becomes covered with a brownish-black rust. Heated in the air, it is converted into an oxide. Cobalt dissolves in chlorohydric and dilute sulphuric acids, with disengagement of hydrogen gas; but the solution is effected more slowly than that of iron or zinc. COMPOUNDS OF COBALT WITH OXYGEN. § 892. Cobalt forms two well defined oxides: a protoxide con- taining 21.32 per cent, of oxygen, and a sesquioxide containing for the same quantity of metal one and a-half times more oxygen. * Cobalt was first obtained in the metallic state by Brandt, in 1733. SALTS OF COBALT. 131 The equivalent of cobalt, deduced from the composition of these oxides by giving to the protoxide the formula CoO, is 29.5. Hydrated protoxide of cobalt is obtained by adding caustic po- tassa to the solution of a salt of cobalt, a sulphate or a nitrate for example. The gelatinous precipitate, of a lavender-blue colour, should be well washed with boiling water to remove the last traces of potassa, and calcined protected from the air. The protoxide is also prepared by calcining carbonate of cobalt in a close crucible. Protoxide of cobalt is a powder of a deep ash-gray colour, which, when heated in the air, absorbs oxygen, and appears to be con- verted into an oxide CoO-f Coa03, corresponding to magnetic oxide of iron. It is a powerful base, which forms red salts, isomorphous with those yielded by the other metallic oxides of the same formula. Sesquioxide of cobalt is obtained by passing a current of chlorine through water containing hydrated protoxide in suspension ; when the liquid becomes rose-coloured and a black precipitate is formed. Under these circumstances, a portion of the protoxide is changed into a chloride, which dissolves, and parts with its oxygen to an- other portion of the protoxide, which is changed into sesquioxide: 3CoO + Cl=CoaO,+CoCl. The whole of the protoxide may be converted into sesquioxide by precipitating the dissolved protochloride by potassa, and again passing chlorine through the liquid; which is the same as imme- diately treating the hydrated protoxide by a solution of an alkaline hypochlorite. SALTS FORMED BY PROTOXIDE OF COBALT. § 893. The protosalts of cobalt are generally of a currant-red or peach-blossom colour. Their solutions are of a currant-red; but some of them, principally that of the protochloride, are red only when diluted, and change to a bright blue when concen- trated, owing to a dehydration of the salt, or to an isomeric modi- fication. It also occurs when the temperature is elevated. Crys- tals of chloride of cobalt, when cold, are rose-coloured, but when slightly heated, assume a beautiful blue, without perceptibly losing any water; for they return to the rose colour on cooling. Charac- ters written upon paper with a dilute solution of chloride of cobalt, disappear after the evaporation of the water, because the chloride of cobalt is then in its rose-coloured modification; but if the paper be brought near to the fire, the chloride is transformed by the ele- vation of temperature into its blue modification, by which the characters become apparent, as the polour of this modification is deeper. As the paper cools, the characters disappear again en- tirely, unless the paper has been too highly heated. This property of chloride of cobalt has given it some celebrity as a sympathetic ink. 132 COBALT. The characters only become blue if the chloride of cobalt used is very pure; but when it contains a small quantity of nickel they turn green : the purity of the liquid may thus be ascertained. Salts of cobalt yield, with potassa and soda, lavender-blue pre- cipitates. Ammonia does not precipitate the solutions containing an excess of acid, as a double ammoniacal salt, not decomposable by an excess of ammonia, is then formed. The alkaline carbonates produce a rose-coloured precipitate of carbonate of cobalt, while the alkaline phosphates and arseniates throw down peach-blossom coloured precipitates readily soluble in an excess of acid. Yellow prussiate of potash gives a dirty-green precipitate. When the salts of cobalt contain an excess of acid they are not precipitated by sulphuric acid. The alkaline sulf- liydrates afford a black hydrated sulphide. Sulphate of cohalt is obtained by dissolving the oxide in sulphu- ric acid, and crystallizes, at the ordinary temperature, with 7 equivs. of water CoO,S03+7IIO, in the same form as sulphate of iron. The formula of the crystals formed between 68° and 86° is CoO,S03-|-6HO, and they are isomorphous with sulphate of magnesia. Nitrate of cohalt is obtained by dissolving the metal, or the oxide, in nitric acid. The nitrate is easily decomposed by heat, and leaves, when subjected to a moderate temperature, the oxide CoO,Co303 as a residue. Oxalate of cohalt is deposited in small rose-coloured crystals, when oxalic acid is added to a solution of sulphate of cobalt. The salt is but slightly soluble in water, The alkaline carbonates produce in solutions of the salts of cobalt a pale rose-coloured precipitate of the hydrocarbonate 2(CoO,COa)+3(CoO,HO.) COMPOUND OF COBALT WITH SULPHUR. § 894. Sulphide of cohalt is prepared by heating the oxide with an alkaline polysulphide ; if the calcination be carried to a white- heat, a bronze-coloured metallic button is obtained. COMPOUND OF COBALT WITH CHLORINE. § 895. Chloride of cobalt is prepared by dissolving the oxide in chlorohydric acid. We have already said that this chloride exists under two modifications, as a rose-coloured, and as a blue com- pound. § 896. Two crystallized arseniurets of cobalt are found in nature; but these minerals generally contain at the same time arseniurets of nickel and iron. Cobalt is also found in combination, at the COMPOUNDS OF COBALT WITH ARSENIC. ANALYTIC DETERMINATION. 133 same time, with arsenic and sulphur, in the state of a sulfarseniuret CoAsa+CoS3: mineralogists call it gray cobalt. Its most ordinary crystalline form is the cubo-octahedral. The gray cobalt worked at Tunaberg, in Sweden, which is very pure, is mostly used in labo- ratories to obtain the products of cobalt. To effect this, the pow- dered ore is first roasted in the muffle of a cupelling-furnace, with a gentle heat at the commencement, in order to avoid the fusion of the material, when the sulphur burns to sulphurous acid, a large portion of the arsenic is changed into arsenous acid which is disengaged in white fumes, and another portion of the arsenic is transformed into arsenic acid which remains in combination with the oxidized cobalt, forming arseniate of cobalt. When white fumes are no longer disengaged, a small quantity of powdered charcoal is thrown on the material, and the whole is mixed; after which the door of the muffle is closed, when the charcoal reduces the arseniate to the state of an arseniuret; and, if air be admitted, the roasting recommences and removes an additional quantity of arsenic. As this substance, however, cannot be entirely separated in this way, the whole must be roasted with carbonate of soda and a small quantity of nitre, and then heated in a crucible, when the last portions of arsenic combine with the soda, forming arseniate of soda, which is removed by treating the material with boiling water. The cobalt remains in the state of an oxide, generally con- taining a small quantity of peroxide of iron, which is separated by dissolving in nitric acid, evaporating to drive off the excess of acid, and then treating with water. A few drops of carbonate of soda added to the liquid precipitate hydrated peroxide of iron. Lastly, the oxide of cobalt is obtained by adding caustic potassa; or, when metallic cobalt is to be prepared, the oxalate intended for this pur- pose is obtained by an addition of oxalic acid. The powdered ore may also be immediately fused with a mixture of carbonate of soda and sulphur, when a sulfarseniate of sodium and sulphide of cobalt are formed, which collect at the bottom of the crucible in the form of a ball. This sulphide, heated with dilute sulphuric acid, dissolves by disengaging sulfhydric acid, yielding a solution of sulphate of cobalt. DETERMINATION OF COBALT ; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 897. Cobalt is determined either as protoxide or in the me- tallic state. It is generally precipitated from its solutions by caustic potassa, when the precipitate, being washed with boiling water and calcined at a strong red-heat in a close platinum crucible, leaves protoxide of cobalt; but it is always to be feared that a por- tion of the cobalt may remain in the state of sesquioxide. It is, therefore, best to place the oxide in a glass bulb A (fig. 520), and heat it in a current of hydrogen gas, thus restoring the oxide to 134 COBALT. the state of metallic cobalt, which is weighed as such. When the liquid contains ammonia- cal salts, it must be eva- porated to dryness with excess of potassa to drive off the ammonia, and then treated with water. Co- balt may also be precipi- tated as sulphide by sulf- hydrate of ammonia; but the sulphide must then be redissolved in nitric acid, and the oxide precipitated by potassa. § 898. Cobalt is separated from the alkaline and alkalino-earthy metals by sulf hydrate of ammonia, which precipitates the cobalt alone as sulphide. If the solution contains magnesia, care must be taken to add an ammoniacal salt, to prevent the precipitation of this substance. The separation of the oxides of cobalt and alumina is easily ef- fected by caustic potassa in excess, which dissolves the alumina and precipitates the oxide of cobalt. It is very difficult satisfactorily to separate cobalt from manga- nese. The best method is to heat the two oxides, first in a current of chlorohydric acid gas, which transforms them into chlorides, and then in a current of hydrogen, which restores the chloride of cobalt to the metallic state, but does not decompose the chloride of man- ganese ; when, by treatment with water, the latter chloride only is dissolved. In order to separate cobalt from iron, the iron is brought to the state of peroxide, and enough sal-ammoniac added to prevent the precipitation of the cobalt by an excess of ammonia, which throws down only the sesquioxide of iron: the cobalt is then precipitated in the filtered liquid by sulf hydrate of ammonia. Fig. 520. SMALT, AZURE, OR ZAFFRE. § 899. Oxide of cobalt readily combines with fusible silicates, producing beautiful blue glasses, which find an extensive use in por- celain-painting, and are highly valued for their property of resist- ing the highest temperatures, provided no deoxidizing substances be present. A blue glass containing oxide of cobalt is technically prepared, which, when finely powdered, is used for colouring wall and writing paper, and for bluing linen. This glass, called smalt, or azure, is manufactured in large quantities, from the native sulfarseniuret of cobalt, in Saxony and other parts of Germany. The ore is roasted in a reverberatory furnace, in which the vapours of arsenious acid condense in the pipes just below the return-chimney. The ore, properly roasted, is mixed with white sand and very pure carbonate SMALT, 135 of potassa, in determinate proportions, and fused in glass-house pots. A metallic button, which is called speiss, composed chiefly of arseniurets of nickel and iron, is often deposited at the bottom of the pot. The vitreous substance, which has an intense blue colour, is pounded after cooling, and then ground to a fine powder, which is then suspended in water, when the grosser particles are first deposited, and must again be ground. The supernatant muddy waters are decanted after some time, and poured into buckets, where they gradually deposit finer and finer powder. The clearness of the blue colour depends on the fineness of the particles. § 900. Oxide of cobalt also enters as a colouring principle into another colour used in painting, and called cobalt-blue, or Thenard’s blue. This colouring matter is prepared as follows :—A solution of sulphate or nitrate of cobalt is precipitated by phosphate of potassa; and, on the other hand, a solution of alum is treated with carbonate of soda. The two gelatinous precipitates of alumina and phosphate of cobalt are intimately mixed, in the proportion of 3 volumes of phosphate, and from 12 to 15 parts of alumina; when the mixture, dried and calcined in a crucible, changes into a beautiful blue powder. It is important to prevent the combustible vapours of the furnace from entering the crucible, as they would seriously injure the shade. This inconvenience is avoided with certainty by placing at the bottom of the crucible a small quantity of oxide of mercury, which produces an atmosphere of oxygen gas, and preserves the oxide of cobalt from reduction. COBALT-BLUE, OR THENARD’S BLUE. 136 NICKEL. Equivalent = 29.6 (370.0; O = 100.) § 901. Metallic nickel* is obtained in precisely the same manner as cobalt. Oxide of nickel, reduced by oxygen at a low tempera- ture, yields a pulverulent metal, which becomes incandescent in the air, and, when reduced in a “brasqued” crucible in a forge-fire, produces a well-fused carburetted metal. Pure melted metallic nickel is obtained by heating oxalate of nickel in a closed vessel in a strong forge-fire. Nickel is a slightly-grayish white metal, which is so much more malleable than cobalt, that it can be hammered and drawn out into fine wire. Its density is about 8.8. It is nearly as magnetic as iron, but loses this property when heated to about 400°. Nickel bears pretty well the contact of a damp atmosphere, but by heating in the air is converted into an oxide. It dissolves in chlorohydric and dilute sulphuric acids, with disengagement of hydrogen gas. COMPOUNDS OF NICKEL WITH OXYGEN. § 902. Nickel forms two oxides: A protoxide composed of..... Nickel 78.72 Oxygen 21.28 100.00 and a sesquioxide composed of..... Nickel 71.13 Oxygen 28.87 100.00 From this the equivalent of nickel is 29.6, differing by only one decimal from that of cobalt. Protoxide of nickel is obtained in the hydrated state by treating a solution of sulphate of nickel with caustic potassa, when an apple- green precipitate forms, which, when well-washed in boiling water, and then calcined and protected from the air, yields anhydrous oxide as an ash-gray powder. It is also obtained by the calcina- tion of the hydrocarbonate. Although calcined nitrate of nickel leaves some oxide, the temperature must be very high to convert it entirely into protoxide. Sesquioxide of nickel is prepared by subjecting hydrated prot- oxide suspended in water to the action of chlorine, or treating it * Recognised as a peculiar metal, in 1751, by Cronstedt and Bergmann. SALTS OF NICKEL. 137 by an alkaline chlorite. This oxide forms a black powder, which dissolves in hydrochloric acid with disengagement of chlorine. § 903. The hydrated salts of nickel are of a beautiful green colour, the majority of them becoming yellow by losing their water of crystallization, while their solutions are of a beautiful emerald green. From the salts of nickel the fixed alkalies throw down an apple-green gelatinous precipitate, while ammonia does not preci- pitate highly acid solutions, and gives only a partial precipitation with neutral solutions, as an excess of the reagent redissolves the precipitate, and the liquid turns blue. The carbonates of soda and potassa produce bright-green precipitates of the hydrocarbonate NiO,COa+NiO,IIO, while the alkaline phosphates and arseniates throw down pale-green precipitates. Prussiate of potash gives a greenish-white precipitate. The acid solutions of salts of nickel are not affected by sulfhydric acid, but are partially precipitated when neutral, especially if the acid of the salt is feeble ; while the alkaline sulfhydrates give a black precipitate of hydrated sulphide soluble in an excess of the precipitant. § 904. Sulphate of nickel is generally obtained from the nickel-ore, which is the metallic speiss deposited in the bottom of the crucible in the manufacture of smalt. It is principally composed of arseni- urets of nickel and iron, but frequently contains some traces of cobalt; in which case, the powdered speiss is fused with a small quantity of alkaline glass, to which a little nitre is added, when the oxide of cobalt passes into the vitreous scoriae, and the purified nickel is concentrated in the lump of arseniuret, because cobalt is more oxidizable than nickel, which has, on the contrary, a greater affinity for arsenic. The arseniuret of nickel is then roasted to drive off the arsenic as completely as possible, and the residue of basic arseniate, after being heated in a crucible with a mixture of carbonate of soda and a small quantity of nitre, is treated with hot water, which dissolves the alkaline salts containing all the arsenic acid in the state of arseniate of soda. The oxide of nickel remain- ing is dissolved in sulphuric acid, the small quantity of persulphate of iron Avhich the sulphate thus formed always contains being easily removed by boiling the liquid with carbonate of lime, which preci- pitates only the peroxide of iron, and introduces no foreign salts into the liquid, as sulphate of lime is very slightly soluble. Sulphate of nickel crystallizes at the ordinary temperature with 7 equiv. of water, but may be obtained combined with 6 equiv. by crystallization from a hot solution. Crystals of sulphate of nickel with 7 equiv. of water often attain a very large size, and exhibit a remarkable phenomenon of molecu- lar movement: on leaving a large crystal to itself for some days, especially if exposed to solar light, it preserves its outward form, SALTS FORMED BY PROTOXIDE OF NICKEL. 138 NICKEL.' but loses its transparency; and, if it be then broken, will be found filled with cavities, the walls of which are lined with brilliant crys- tals of quite another form, and in which the molecules are grouped in a completely different manner, 'while the substance has not be- come liquid. By adding oxalic acid to a solution of sulphate of nickel, no precipitate is immediately formed, while, after some time, a crys- talline powder of oxalate of nickel is deposited, and only a very small quantity of the metal remains in solution. COMPOUND OF NICKEL WITH SULPHUR. § 905. Sulphide of nickel is prepared by heating a mixture of oxide of nickel, carbonate of soda, and sulphur, when the sulphide fuses into a bronze-yellow button, if the temperature is sufficiently elevated. COMPOUND OF NICKEL WITH CHLORINE. § 906. Chloride of nickel is obtained by dissolving the oxide, or metallic nickel, in concentrated chloroliydric acid, when the solu- tion deposits green crystals, which, when heated in a tube pro- tected from the air, part with their water, and yield a volatile anhydrous chloride, which sublimes on the sides of the tube in the form of gold-coloured spangles. COMPOUNDS OF NICKEL WITH ARSENIC. § 907. Nickel is found in nature combined with arsenic, in the state of arseniurets, NiAs and NiAsa and also occurs as a sulf- arseniuret NiS3-f-NiAs3. The native arseniurets are sometimes used for the extraction of nickel, but generally the speiss arising from the manufacture of smalt is preferred for that purpose. GERMAN SILVER, ARGENTAN, OR MAILLECHORT. § 908. Nickel is technically used for making an alloy capable of a high polish and the lustre of silver. This alloy, which is com- posed of 100 parts of copper, 60 of zinc, and 10 of nickel, is known in commerce by the various names of Cerman silver, maillechort, packfong, argentan. Various ornamental objects are made of it, but it is chiefly used for spurs, for carriage and harness mount- ings, etc.* It has been proposed for kitchen utensils, but this use would be dangerous, as the alloy readily oxidizes, particularly wdien in contact with acid liquids, and produces very poisonous salts, j* * In England. f German silver finds mucli more extensive use in Great Britain and the United States, being now a substance almost universally employed for the manufacture of all articles for useful and ornamental purposes which are to be electro-plated. At Birmingham alone, hundreds of tons are annually fashioned into plate of every description, and subsequently coated with silver or gold by the galvanic process.— W. L. F. ANALYSIS. 139 DETERMINATION OF NICKEL, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 909. Nickel is precipitated from its solutions by caustic po- tassa, or by sulf hydrate of ammonia, and is determined in the state of protoxide, like cobalt, after having been highly calcined ; but, as is the case with cobalt, the degree of oxidation of the oxide which remains is uncertain. In exact analyses, it is preferable to reduce the oxide by hydrogen and weigh the nickel in the metallic state. § 910. As nickel is separated from the metals previously studied, by the same processes as those described for cobalt, we shall refer the reader to them (898), and proceed to examine only the separa- tion of cobalt and nickel. Nickel and cobalt are frequently found associated, and their separation, wdiich presents some difficulties, becomes necessary. One of the most simple processes consists in pouring oxalic acid into the solution which contains the two oxides, after which the two oxalates, which precipitated together, are redissolved in ammonia, and the ammoniacal liquid is left in an uncorked bottle, when the ammonia is slowdy disengaged, and, as its quantity diminishes, the liquid loses more and more its power of dissolving the oxalates. Now, the two salts not being equally soluble in the ammoniacal liquid, a moment arrives at which the latter does not contain enough ammonia to hold the oxalate of nickel in solution, which is the less easily soluble salt, but at which it can still dissolve the oxalate of cobalt: the oxalate of nickel is then deposited, and the liquid as- sumes a deeper red tinge. When a bright currant-colour is attained, the liquid is decanted, and then contains only cobalt. The small quantity of cobalt which the precipitate of oxalate of nickel always contains, is separated by again dissolving the oxalate of ammonia, and allowing the liquid to evaporate. Another process consists in pouring alternately chlorohydric acid and ammonia into the solution which contains the two oxides, until the liquid yields no precipitate with an excess of ammonia, when a sufficient quantity of ammoniacal salt has formed to constitute, with the metallic salts, double salts which are indecomposable by ammo- nia. The liquid is bottled, and caustic potassa added to it, which does not decompose the double ammoniacal salt of cobalt, while that of nickel parts with the oxide of nickel, which is precipitated. The contact of the air must be avoided during this experiment, as otherwise the cobalt would absorb oxygen and be precipitated in the state of hydrated sesquioxide. The cobalt which remains in the liquid is then precipitated by an alkaline sulphide. These metals may also be separated very accurately by dissolv- ing them in an excess of chlorohydric acid, and diluting with a large quantity of water, after which the liquid is saturated with chlorine gas, and carbonate of baryta in excess added. The liquid 140 NICKEL. is then allowed to rest for 18 hours without being heated, when the whole of the cobalt is precipitated as sesquioxide, while the nickel remains in solution. The precipitate, which consists of sesquioxide of cobalt and the excess of carbonate of baryta, is col- lected on a filter, and, after being well washed with cold water, is dissolved in concentrated chlorohydric acid, after which the baryta is precipitated by sulphuric acid, and then the oxide of cobalt by potassa.* * Since the author has published the above methods, a still better one has become known, which is the discovery of Liebig and Wohler, and consists in the following operations:—The two oxides intended to be separated are dissolved in pure cyanide of potassium, and the red solution obtained is boiled to expel the excess of prussic acid; when hydrogen is at the same time evolved, and the cyanide of cobalt changes to cobaltidcyanide of potassium Co2Cy3,3KCy, while the nickel remains as potasso-cyanide nickel NiCy,2KCy. An addition of pure oxide of mercury, suspended in water, then precipitates all the nickel as a mixture of oxide and cyanide, while the mercury replaces the nickel in the double cyanide; after which the precipitate, consisting of oxide and cyanide of nickel, and the ex- cess of oxide of mercury added, is washed and calcined, when pure oxide of nickel remains, and is weighed. The cobalt, which still exists in the solution as cobaltid- cyanide of potassium, is then precipitated by protonitrate of mercury, after having neutralized the liquid with nitric acid; when a heavy white precipitate is formed, containing all the cobalt as cobaltidcyanide of mercury, which, by calcina- tion in the air, is converted into pure oxide of cobalt, which is weighed.— W. L. F. 141 ZINC. Equivalent — 32.6 (407.5; 0 = 100). § 911. Zinc is now technically employed in a great number of different ways. That found in commerce is not perfectly pure, while the sheet-zinc more nearly approaches perfect purity, be- cause the presence of the smallest quantity of foreign matter con- siderably diminishes the malleability of the metal and renders it unfit for rolling. Zinc fuses at a temperature of about 930°, and boils at a white-heat, when it may he purified by distillation; to effect which, commercial zinc is placed in an earthen retort, which is arranged in a reverberatory furnace, while below the open neck of the retort a vessel containing water is placed to receive the zinc. Another and more suitable apparatus for this distillation consists of a clay crucible A (fig. 521), the bottom of which is perforated, and rests on a clay disk, or cheese (fromage) B, pierced likewise with a hole. A clay pipe ah, the upper end of which reaches the top of the crucible, being hermetically fastened in both apertures, the zinc to be distilled is placed in the crucible, which, after the lid is luted on, is arranged in a furnace so that the pipe may pass through the grate, beneath which is placed a pan C filled with water. When the temperature rises in the furnace, the zinc first fuses, and then boils, when its vapour, descending through the pipe and there condensing, allows the liquid metal to run into the pan. This process is called distillatio per descensum. The distillation of zinc does not free it entirely from the metals with which it is combined, since the very high temperature at which the distillation takes place, causes a small portion of the other me- tals to he carried over with the vapours of the zinc. Zinc is of a bluish-white colour, and its fresh fracture exhibits large and very brilliant crystalline laminae. While it is brittle at the ordinary temperature, it becomes malleable at a few degrees above 212°, and, when heated to 392°, again becomes so brittle that it may be pounded in a mortar. Ignorance of these remarkable pro- perties of zinc for a long time prevented its extensive technical use, and formerly it was only employed for making alloys. It is now rolled into thin sheets for roofing houses, and making bathing-tubs and other vessels of great capacity. Zinc vessels must not be used Fig. 521. 142 ZINC for the preparation of food, because the metal readily oxidizes in contact with the air, when in presence of even the weakest acids, and produces poisonous salts. The density of zinc varies from 6.86 to 7.20, according as the metal has been cast, or rolled. § 912. Zinc is a very oxidizable metal, as its surface soon tar- nishes by superficial oxidization in a damp atmosphere, while, when heated in contact with the air at a temperature above its melting point, it becomes incandescent and burns with a dazzling white flame, the brilliancy of which is owing to the vapour of zinc, which, by burning in the air, forms oxide of zinc, a perfectly fixed com- pound, of which the particles, heated to whiteness, communicate a bright lustre to the flame. Zinc dissolves readily in chlorohydric and dilute sulphuric acid, and disengages hydrogen; and the metal, when impure, dissolves more rapidly than perfectly pure zinc. It decomposes aqueous vapour with disengagement of hydrogen, and is converted into an oxide, the reaction commencing at a tempera- ture a little above 212°, when the metal exists in a very finely divided state. Zinc also dissolves with disengagement of hydrogen in a boiling so- lution of potassa and soda, and forms soluble alkaline zincates. When an iron blade is at the same time dipped into the alkaline solution, the water is decomposed even when cold, while the zinc alone dis- solves, the iron acting only by producing with the zinc a voltaic current, in which the latter metal becomes the positive element, and thus acquires an affinity for oxygen sufficiently great to de- compose water at the ordinary temperature in the presence of potassa. The decomposition of water in the presence of potassa, is effected very remarkably by plates of galvanized iron, when very brilliant small crystals, consisting of a hydrated ozide of zinc ZnO+IIO are deposited on the sides of the vessel. § 913. Only one oxide of zinc, a very powerful base, is known, the salts of which are isomorphous with those of magnesia and with the protosalts of iron, cobalt, and nickel. The oxide is obtained by heating the metal in contact with the air until it ignites, when a white flocculent substance, of which a portion is carried off by the current of air, is deposited on the edges of the crucible. The old chemists called it lana philosophica, or pompholix.* The oxide thus obtained always contains particles of the metal, which it may be freed from by levigation. When pure oxide of zinc is to be prepared, it is better to decompose by heat either nitrate of zinc or the hy- drocarbonate which is obtained by adding an alkaline carbonate to the solution of a salt of zinc. When caustic potassa is poured into COMPOUND OF ZINC WITH OXYGEN. * It also bore the curious name of nihil album, “white nothing.” SALTS OF ZINC. 143 a salt of zinc, a white precipitate of hydrated oxide of zinc is obtained, which retains a certain quantity of alkali with great obstinacy. Anhydrous oxide of zinc is white, and assumes a yellow shade on the application of heat, which disappears on cooling. Oxide of zinc is formed of Zinc 81.5 Oxygen 18.5 100.0 whence the equivalent of zinc is 32.6. Oxide of zinc, when mixed with drying oils, produces a white paint, which may be substituted for white-lead, or ceruse, and has been recently manufactured on a large scale.* It has the advan- tage of not being blackened by sulphurous gases, and not exposing the workmen to the same dangerous affections. SALTS FORMED BY OXIDE OF ZINC. § 914. The salts of zinc are colourless when the acid is not coloured. Their solutions yield, with potassa, soda, and ammonia, white precipitates which dissolve in an excess of the reagent; and the alkaline carbonates throw down a white precipitate, which also takes place wTith prussiate of potash and the alkaline phosphates and arseniates. Sulfhydric acid does not precipitate the salts of zinc when they contain an excess of acid, but the sulf hydrates give white precipitates. Sulphate of Zinc. § 915. The sulphate, which is the most important of the salts of zinc, is readily prepared in the laboratory by dissolving metallic zinc in dilute sulphuric acid. It crystallizes at the ordinary tem- perature with 7 equiv. of water, of which 6 are easily driven off by subjecting the salt to a temperature above 212°. Crystallized sulphate of zinc dissolves in tw’o or three times its weight of water, at the ordinary temperature, while at 212° its solubility may be said to be infinite, as it melts in its water of crystallization. Sulphate of zinc is prepared on a large scale by roasting blende in heaps, when a portion of the sulphur is disengaged in the state of sulphurous acid, while the greater part of the blende is con- verted into sulphate of zinc, provided the temperature does not rise above a certain point. The roasted matter is treated with water, and the solution evaporated to crystallization; and in order to render the salt easily transportable, it is generally melted in its water of crystallization, and poured into square moulds of the size * It is extensively manufactured at Vieille Montagne, and also in New Jersey, from the red oxide occurring near Franklin. 144 ZINC. of a common brick. The salt is called in commerce white vitriol, and is used in the manufacture of calico. ■ Carbonate and Hydrocarbonate of Zinc. § 916. When an alkaline carbonate is poured into a solution of sulphate of zinc, a precipitate is obtained, which is not a carbonate, but a hydrocarbonate of zinc (2ZnO,COa+3ZnO,IIO). Anhydrous carbonate of zinc is found in nature, constituting a mineral called calamine, which acquires great importance from being the ordinary ore of zinc. Most frequently, calamine exists in compact masses, and more rarely exhibits distinct crystals belonging, like carbonate of lime, to the rhombohedric system. § 917. Zinc in the state of filings is, when heated with flowers of sulphur, converted into a sulphide; but it is difficult thus to ob- tain a perfect sulphuration. It is better to heat a very intimate mix- ture of oxide of zinc and flowers of sulphur, when sulphurous acid is disengaged, and sulphide of zinc ZnS, in the form of a yellowish- white powder, remains. Sulphide of zinc is found abundantly in nature, forming a brownish-yellow translucid mineral, crystallized in regular octahedrons, or cubo-octahedrons, and called blende. COMPOUND OF ZINC WITH SULPHUR, § 918. Zinc is easily acted on by gaseous chlorine, and converted into a white, butyrous, very fusible substance, which distils only at a red-heat. This chloride is obtained in solution in water, by treating zinc with chlorohydric acid, when the solution, on being evaporated and cooled, becomes crystalline. Chloride of zinc is soluble in water and in alcohol to such .an extent, that when an aqueous solution of the salt is concentrated by ebullition, the tem- perature rises continually to 482°, at which point the chloride becomes anhydrous, but still preserves its liquid state. This pro- perty suggests the use of a solution of chloride of zinc instead of oil, for baths in which substances are to be heated to a high but certain temperature. COMPOUND OF ZINC WITH CHLORINE. DETERMINATION OF ZINC, AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 919. Zinc is generally precipitated from its solutions by car- bonate of soda, after which the liquid is boiled, and the gelatinous precipitate of hydrocarbonate of zinc washed with boiling water, when it is determined in the state of oxide after calcination. If the liquid contains much ammoniacal salt, it must be evaporated to dryness with an excess of carbonate of soda, and then treated with water. DETERMINATION OF ZINC. 145 Zinc is frequently precipitated as sulphide by sulfhydrate of ammonia; when the precipitate is washed with water containing a small quantity of the sulfhydrate, in order to prevent the forma- tion of sulphate of zinc by contact with the air. The hydrated sulphide is redissolved in chlorohydric acid, and the zinc precipi- tated by carbonate of soda as carbonate. § 920. In general, zinc is separated from the alkalies and alka- line earths by means of sulfhydrate of ammonia, which precipitates the zinc only as sulphide; but it is more readily separated from baryta by means of sulphuric acid. Lime may also be separated from oxide of zinc by adding to the liquid containing the two bases an excess of ammonia, and some oxalate of ammonia, which precipitates only the lime in the state of oxalate of lime, while the oxide of zinc remains in solution in the excess of ammonia. The separation of oxide of zinc from magnesia is effected by means of sulfhydrate of ammonia, the precaution being used first to add an ammoniacal salt in sufficient quantity to the liquid to prevent the precipitation of the magnesia by ammonia. Oxide of zinc is separated from alumina by ammonia in excess, which dissolves the former and precipitates the alumina, while a perfect separation is, however, difficult, as alumina is slightly so- luble in ammonia. Oxide of zinc is separated from oxide of manganese by caustic potassa, which redissolves the former and leaves the oxide of man- ganese, especially if the liquid is left exposed to the air for some time, so that the protoxide of manganese may be changed into ses- quioxide. The separation is, however, rarely effected perfectly, the oxide of manganese always retaining some oxide of zinc ; and the precipitate must be redissolved in chlorohydric acid and precipi- tated anew by an excess of potassa. In order to separate zinc from iron, the latter metal is first brought to the state of a sesquisalt by means of nitric acid or chlorine, and then ammonia in excess is added, which redissolves the oxide of zinc and precipitates only the hydrated sesquioxide of iron. It is well to redissolve the oxide of iron in an acid and precipitate it a second time by ammonia in excess, as the small quantities of oxide of zinc, which in the first precipitation had been carried down with the sesquioxide of iron, are thus separated. The separation of zinc from cobalt and nickel is more difficult. The best plan consists in precipitating the metals together by car- bonate of soda, and weighing them in the state of oxides after cal- cination. The mixture of oxides is then placed in a glass globe D (fig. 522), terminating in a curved end bed, which descends to the level of a small quantity of water in the bottle E, and a current of dried chlorohydric acid gas is passed through the tube ab, while the globe D is heated by an alcohol-lamp. The oxides are thus changed into chlorides, when the chloride of zinc, being very volatile, distils 146 ZINC, Fig. 522. over, and condenses in the tube bed and in the water in the bottle. The chlorides of cobalt, or nickel, on the contrary, remain in the globe D. At the close of the operation, the tube bed is detached and thrown into the bottle E, when all the chloride of zinc is dis- solved ; while, on the other hand, the globe D is heated with acidu- lated water. The metals, being thus separately dissolved, are pre- cipitated in the ordinary manner. METALLURGY OF ZINC. § 921. Calamine is the principal ore of zinc. Silicate of zinc is frequently mixed with calamine, but, as it yields very little metal- lic zinc, should not be regarded as a true ore. A certain quantity of zinc is extracted from blende. The principal mines of zinc are those of Tarnowitz, in Silesia, Vieille Montagne, near Liege, and several counties in England. The theory of the metallurgic treatment of calamine is very simple :—The ore is calcined, by which process its carbonic acid is driven off and it is rendered friable, after which it is powdered in mills with edge-stones, and the powder, mixed with charcoal, is heated in earthen retorts in a furnace to a strong white-heat. The oxide of zinc is reduced by the charcoal, while carbonic oxide gas is disengaged, and the metallic zinc condenses in allonges fitted to the retorts. § 922. The ore of Vieille Montagne is a mixture of silicate and carbonate of zinc, being sometimes compact and sometimes crys- tallized. The gangue consists exclusively of clay, in amorphous masses, scattered through the fragments of calamine. The ore is exposed to the air for several months, to allow the clay to rot, after which it is easily separated; while sometimes it is washed, and the clay in this manner almost entirely removed. Two classes of ore are distinguished, according to their aspect and chemical composition, the white ore and red ore, the latter of which con- tains more iron than the first, and is less rich in zinc, but more METALLURGY OF ZINC. 147 easily worked. The following is the average composition of these two kinds of ore : White ore. Red ore. Oxide of zinc / n l Oxygen 46.6 ... 11.7 ... ... 33.6 ... 8.4 Silex and clay 14.0 ... ... 20.0 Water and carbonic acid 22.7 ... ... 20.0 Sesquioxide of iron 5.0 ... ... 18.0 100.0 100.0 The washed ore is calcined in conical kilns (fig. 523), resembling limekilns, and heated by two lateral fur- naces, covered by an arch, and terminating in a canal which opens into the kiln by 20 working-holes 0,0,0, arranged in 4 or 5 rows, each opening being four inches square. At the lower part of the furnace are two rec- tangular openings A, intended for the re- moval of the roasted ore, while two cast-iron plates f, f, having an inclination of 45°, divide the descending column of ore, and facilitate its escape from the kiln. The Fig. 523. Fig. 524. Fig. 525. 148 ZINC calcination is continuous, and the ore is charged from above, the large and small pieces being so mixed as to allow an easy passage for the flame. The ore loses during the calcination its water and carbonic acid; the loss being about 25 per cent. The kilns are heated with pit-coal. The calcined ore is finely powdered in edge-stone mills, sifted, and then sent to the reducing furnace. The furnace is composed of four kilns joined together, the shape of each being that of a cylindrical cradle A (figs. 524 and 525), the upper edge of which is about 8.5 feet above the floor. The posterior part of the furnace is made by a wall bd, inclined back- ward, while the anterior part ac is, on the contrary, entirely open. The hearth F is below the floor of the furnace, into which the flame enters by 4 holes o, o, and at the top of the wall are two flues U, U, which open into a chimney in the centre of the building. The chimney, which serves for the 4 kilns, is divided into 4 compart- ments, each having its own register T. In each furnace 42 retorts of refractory clay are arranged, consisting of long earthen pipes bd (fig. 526), closed at one end d, 3.4 feet long, with an internal dia- meter of 5.9 inches. Into each tube a conical cast-iron pipe cd (fig. 527) is inserted, which acts as a condenser, and to which is Fig. 526. Fig. 527. Fig. 528. fitted a second conical sheet-iron pipe ef {fig. 528), having at/an opening of only 0.8 inch. The earthen pipes are arranged in the kiln in 8 rows above each other, their closed ends resting on 8 projecting edges built in the back wall bd of the oven (fig. 524). On the front wall ac, which is open, are arranged 8 cast-iron plates, supported by bricks, and intended for the reception of the anterior part of the tubes, which are slightly inclined forward. The kilns are kept burning for 2 months, after which they generally need repairing. In order to start a new furnace, the open face of the kiln is first closed with brickbats and broken tubes, and cemented with mortar, after which it is heated for several days, at first gradually, and then to a white-heat. After 4 days of preliminary heating, the tubes are introduced by removing the anterior part of the furnace and ar- ranging them after they have been previously heated; the inter- stices between the tubes and the anterior compartment through which they pass being luted with mortar; and lastly, the conical allonge being adapted to each tube. When the crucibles are arranged in the furnace, a small quantity of ore and charcoal is first introduced, these charges being succes- sively increased until, after several days, the regular work of the METALLURGY OF ZINC. 149 furnace begins. This period of the operation is that which will alone occupy our attention. The ore is brought in a wooden box, where it is mixed with char- coal, and a little water added. The charge of a furnace consists of 10 cwt. of calcined calamine, and 5 cwt. of dried pulverized pit- coal, which substances are intimately mixed with an iron shovel. The residue of the preceding distillation is removed from each tube, which then, with its cast-iron receiver, is cleaned by means of an iron rpd. The lower tubes are first charged. The mixture is introduced by means of semi-cylindrical sheet-iron shovels (fig. 529), fastened to an iron handle; and when the charging is corn- Fig. 529. pletecl the fire is blown up. A large quantity of carbonic oxide is soon disengaged, and burns with a blue flame at the openings of the cast-iron receivers, while in a short time this flame becomes more brilliant, of a greenish-wrhite colour, and evolves white fumes, which is a sign that the distillation of the zinc has commenced, and that it is time to fit the sheet-iron allonges to the tubes. Whatever care may be taken to obtain a uniform temperature, the heat is always greater in some parts of the kiln than in others; for which reason the upper tubes are charged only with the red ore, as being the most easily reduced, while the white is introduced into the lower ones. After 2 hours’ firing, the workman detaches the sheet-iron allonges, and shakes them over a sheet-iron receiver, when a dust of zinc and oxide of zinc, called cadmie, falls down, which is added to the ore in the succeeding operations. An assistant then holds a large sheet-iron spoon (fig. 530), called a poelon, near the opening of each cast-iron receiver, while the master workman introduces an iron rake, with which he draws out the distilled zinc, which has ac- cumulated in a liquid state at the bottom of the allonge, and in the same way detaches the drops adhering to its sides. The liquid zinc collected in the poelons is covered with metallic scum, con- sisting chiefly of oxide of zinc, which is carefully removed, and the zinc run into rectangular moulds, in pieces weighing from 60 to 70 lbs. The sheet-iron allonges are immediately replaced and the fire continued. In 2 hours a second drawing is made, and so on until 5 o’clock P. M., when the operation is generally terminated. The tubes are then cleaned, and new ones substituted for those destroyed in the preceding operation. Two operations are thus made in 24 hours, producing together about 6 cwt. of zinc and 30 to 50 lbs. of metallic dust; so that by this treatment, calamine yields about 31 per cent, of zinc, about 10 per cent, remaining in the residue. The metal contained in the residue existed in the state of silicate of zinc, which is not reduced by the charcoal. Fig. 530. 150 ZINC. The greater part of manufactured zinc being used in the shape of rolled zinc, it is necessary again to melt the ingots, which is done in a reverberatory furnace with an elliptical floor of refrac- tory clay and slightly inclined backward. At the lowest part of the floor is a hemispherical crucible in which the melted zinc col- lects, and from which it is dipped out and run into moulds of a suitable form for rolling. The plates are being reheated in a second furnace adjoining the first, by means of the hot gases of the former, and, when they have reached a temperature not exceeding 212°, are passed between cast-iron rollers. When they are of suitable size, they are cut into rectangular sheets of the dimen- sions required, the clippings being again fused. Formerly, zinc was fused in large cast-iron pots, which, however, soon became perforated, while the zinc lost many of its qualities by being com- bined with a small quantity of iron. § 923. The furnaces and distilling apparatus used in Silesia dif- fer essentially from those in Belgium. Fig. 531 gives a view of a Fig. 531. Silesian furnace, of which fig. 532 is a vertical section. The distilla- tion is effected in muffles of baked clay M (figs. 533 and 534), about 3 feet in length and 1.5 feet in height, the anterior part of which has 2 openings: the lower opening a, through which the residue of distillation is withdrawn, is closed during the operation by a clay Fig. 532. METALLURGY OF ZINC. 151 door, tightly luted, while into the upper opening a right angled clay tube bed, closed at d, is introduced. The ore is charged with a shovel through a hole c, which is closed during the distillation Fig. 533. Fig. 534. with a baked-clay stopper. Six or ten muffles are arranged in two rows in a kiln, the side Avails of which have apertures for their pas- sage, which are closed by sheet-iron doors, preventing too sudden a cooling of the allonges bed. The kiln is heated with pit-coal burned on the grate G, and they are charged with a mixture of equal parts of calcined calamine and charcoal cinders, which, having fallen through the grate, are immediately extinguished in water placed beneath. No pulverized pit-coal is used, lest any coal-dust, carried by the current of gas, should obstruct the allonges; and the calamine itself is reduced to the size of a pea. The zinc runs through the opening d of the allonge, and is collected in the spaces t of the furnace. Although the operation lasts only 24 hours, the muffles are not emptied until after three operations, when a half- fused greenish mass is extracted as a residue. The calamine is roasted in reverberatory furnaces heated by the waste flame of the reducing furnace. Silesia furnishes the greater portion of the zinc which is brought into commerce. § 924. In the Belgian and Silesian processes, the distillation of the zinc is effected per ascensum, while the process employed in England furnishes an example of distilla- tion per descensum. The reducing fur- naces, resembling very much the ordi- nary glass-furnace, being circular (fig. 535), and having the hearth F in the middle, at a certain distance below the floor of the furnace. The ore, mixed with charcoal, is charged in the crucibles place, and the lead is separated. § 984. The reduction of galena by iron is used especially in the case of ores which are accompanied by a very siliceous gangue, and which are not very amenable to the process by reaction, because a great part of the oxide of lead combines with the silex and no longer reacts on the sulphide. The process by iron is employed to a great extent on the Hartz Mountains; and the following is the plan adopted in the smelting works of Clausthal: A melting-bed is made of sorted ores and sludges, which are mixed with granular cast-iron, and with various secondary products of the further treatment of the ores, the origin of which we shall successively explain. The charge is generally composed of 34 cwt. of sorted ore and sludge, containing 24 cwt. of pure galena. 4 to 5 “ of the debris of the cupelling furnaces, which is strongly impregnated with litharge. 1 “ of scrapings (abstrich) of cupellation. 39 “ of slag arising from a first fusion of the ore, or yielded by the fusion of the leaden stones, or matts, the ob- ject of which addition is to assist the fusion of the gangues. li “ °f granular cast-iron. The fusion is effected in a blast-furnace (figs. 540, 541, 542, and 543), about 18 or 20 feet high, and measuring 3 feet at its greatest width. At the bottom of the hearth is a crucible which partly pro- jects from the furnace, the base of which is formed of two blocks of sandstone, making a gutter, on which a mixture of clay and char- coal* is heaped, so as to form a cavity which extends beyond the * Two different mixtures of clay and cliarcoal are employed in various opera- tions occurring in the German methods of smelting: one consisting of 2 parts of METALLURGY OF LEAD. 193 furnace. A tap-hole opening at the lower part of the crucible per- mits the escape of the liquid products which have there accumulated; and they are led into a second crucible E, which is wholly external. The furnace receives the blast of two tuyers arranged on the oppo- site side of the tymp. Fig. 540. Fie. 541. Fig. 542. The ore is charged on the side of the tuyers, and the fuel on that of the centre-vent. As slag suddenly cooled by the cold air always adheres around the tuyers, the workman arranges them so as to form a canal which projects for about 6 inches into the furnace, and thus makes a prolongation of the tuyer, which he calls the nose clay and 1 of charcoal, called schweres gestuebbe; and one containing 1 of clay and 2 of charcoal, called leichtes gestuebbe. The first I shall, in the following, translate by heavy brusque, and the second by light brasque. To the “ leaden stones” (bleistein) I shall give the French name of matt.— W. L. F. 194 LEAD. of the tuyer. The object of the nose is to convey the air imme- diately upon the fuel, and prevent it from first passing through the ore, which would be thus exposed to an oxidizing action, and part with a great deal of oxide of lead to the scorise. The smelter must also be careful to give a proper shape to the nose of the tuyer, and to modify it according to the blast of the furnace. The temperature must not be very high in the upper part of the furnace, as otherwise a large proportion of galena would be vola- tilized. In all cases, the gases pass, on leaving the throat G, and before reaching the chimney T, several condensing-chambers ar- ranged above the smelting-furnace; where a plumbiferous dust is copiously deposited, which is carefully collected and thrown into the melting-beds. During the smelting, the scoriae flow off continually, an assistant detaching those which have become solid, and drawing them out with a hook. When the inner basin is full of metallic products, the canal communicating with the basins D and E is opened; when the substance flows into the external crucible E, and there divides into two layers; the infe- rior layer being metallic lead, and the upper stratum consisting of subsulphide of lead Pb3S, mixed with other metallic sulphides which existed in the ore, and with that of iron arising from the reaction of the metallic iron on the galena. This substance, which is called the first leaden matt, soon solidifies, and is then withdrawn with a hook and set aside. The workman then removes the lead with a ladle, and runs it into moulds which give it the shape of lenticular disks. The poorest scoriae, that is, those least rich in lead, are rejected, while those which float on the matt in the pot, and which always contain some grains of lead, are set aside to be added to a subsequent charge; though poor scoriae are sometimes used for this purpose when rich scoriae are wanting. The charges, or smelting-beds, the composi- tion of which we have just indicated, yield 19 cwt. of lead, and 7 or 8 cwt. of the first leaden matt, containing from 2 to 2J cwt. of lead. § 985. The first matts are collected in the foundry, and when there is sufficient quantity of them to be worked up, they are roasted in heaps on a layer of fuel; when a large portion of the sulphur is disengaged in the state of sulphurous acid. The roasting lasts for 3 or 4 weeks ; after which the material is sorted, and, while the pieces sufficiently roasted are considered as ready for smelting, the others are again roasted. Four successive roastings are necessary for the proper preparation of the material. Fig. 543. METALLURGY OF LEAD. 195 A charge of matt is composed of 32 cwt. of roasted matt. 32 “ of rich scoriae, arising from the smelting of the ores. 4 or 5 “ of debris of cupellation. 2 “ of scrapings, (abstrich.) 2 “ of scoriae arising from the reduction of litharge. 1 “ of granular cast-iron. The roasted matts are smelted in an elbow-furnace, which is a small blast-furnace (figs. 544, 545, and 546), about 4.5 feet in height, widened at its upper part C. Fig. 546 represents a horizontal sec- tion of it made at the height of the tuyer, while fig. 545 shows a vertical section through the line XY of the plane (fig. 546); and lastly, fig. 544 gives an anterior view. The furnace is fed by a Fig. 544. Fig. 545. Fig. 546. single tuyer T, at the extremity of which a nose of 4 inches in length is allowed to form. At the bottom of the furnace is a brasqued crucible E, projecting partly from the furnace, and com- municating, by means of a canal, with an external crucible F, placed on a lower level.—Coke is the fuel used. 196 LEAD By the roasting of the matt, a large portion of the sulphide of iron has passed into the state of oxide, which, during the fusion in the elbow-furnace, combines with the silicates of the scoriae and with the ashes of the fuel, forming very fusible scoriae, which flow constantly from the furnace. The sulphide of lead is reduced by the metallic iron, and a fresh quantity of lead and a second matt analogous to the first are formed. When the matt is solidified it is removed and set aside to be again worked, while the metallic lead is run into disks. A smelting-bed of first matt, composed as we have indicated, yields 12 cwt. of lead and 8 cwt. of second matt. The second matts are subjected to a similar treatment, being sub- jected to 3 or 4 successive roastings, and then passed through the elbow-furnace, with additions similar to those of the first. A cer- tain quantity of metallic lead is thus obtained, and a third matt, which is roasted in its turn and melted in the elbow-furnace, yield- ing an additional quantity of lead and a fourth matt. The affinity of the copper existing in the original ore for sul- phur being greater than that of the lead, the former passes indefi- nitely into the matts; so that the metal, which is found in a very small quantity in the original ore, is concentrated in the fourth matt in sufficient quantity to make it a very rich ore of copper, and capable of being advantageously worked. It is called the copper matt. § 986. When the gangue of the galena is hut slightly siliceous, the process by reaction is preferred. It is adopted in England, in Carinthia, and the majority of the lead-foundries in France, par- ticularly at Poullauen in Brittany, and Pont-Gibaud in Auvergne. The ore is deposited in the state of sludge on the floor of a rever- beratory furnace (figs. 547 and 548) of about 9 or 12 feet in length, and nearly tlie same width, formed either of pulverized scoriae or of a slightly siliceous clay. In the centre there is an excavation B, Fig. 547. METALLURGY OF LEAD. 197 in which the fused lead collects, and whence it flows through a small canal into cast-iron pots Gr. The charge is inserted through an Fig. 548. upper aperture T, furnished with a hopper. Three lateral open- ings o, o, o are made in both of the opposite faces of the furnace, and serve as working-holes. Pit-coal is burned on the grate F; and the flame and current of hot air, after having passed through the furnace, traverse long condensing chambers, in which they deposit the substances carried over mechanically or by volati- lization. The quantity of ore treated in the furnace at a time varies in different foundries : 20 or 25 cwt. are used in England. The ore is spread evenly over the floor, and roasted from 2 to 4 hours at a dull red-heat; when sulphurous acid is disengaged, while a large quan- tity of oxide and sulphate of lead is formed. The workman stirs it frequently, in order to hasten the roasting, at the end of which operation the working-doors are closed and a blast of air is ad- mitted. The unaltered sulphide of lead then reacts on the oxide and on the sulphate; metallic lead and also the subsulphide Pb3S, which forms a very fusible plumbeous matt, are separated. The fused substances collecting in the inner excavation are allowed to run out after some time, after which the material remaining on the floor is again roasted by opening the working-doors, and stirring the mass with iron rods, while the temperature of the furnace is at the same time allowed to fall. The doors are then again closed, and, another blast of air being admitted, an additional quantity of metallic lead is reduced. These alternate operations are several times repeated. In some works small quantities of lime are from time to time thrown on the floor, in order to lessen the fusibility of the slag; while in others powdered charcoal is added at a certain period, in order to decompose the oxysulphides of lead which form, and retard the roasting when it progresses too rapidly. Toward the close of the operation, when the greater part of the lead has run off, there remains on the hearth a scorified slag, impregnated with metallic 198 LEAD, lead; a large portion of which is separated by admitting a blast, and allowing the furnace to cool slowly. This last stage of the ope- ration is called the sweating. The whole operation requires 7 or 8 hours in England, and 12 or 16 in France. The matts arising from the reverberatory furnace are added, in the English works, to the roasting of a fresh quantity of ore; while in most of the continental works they are passed through an elbow- furnace. The matts are frequently roasted in a heap, and then smelted, after a pro- per addition of scoriae, in a very low i> elbow-furnace, called a Scotch, hearth, in which a reaction takes place between the sulphate, the oxide, and sulphide of lead, while metallic lead, a matt, and scoriae are obtained. Fig. 550 repre- sents a horizontal section of a Scotch furnace; and fig. 549 shows a vertical cut through the line AB in' fig. 550. The furnace is only 3 feet in height; and the blast is furnished by a single tuyer T. The metallic lead and matt are collected in a cast- iron pot M. The workman removes, from time to time, the slag which accumulates at the bottom of the fur- nace, and as it contains a considerable quantity of lead, he throws it back into the furnace. § 987. The lead arising from these different processes often con- tains enough silver to allow the extraction of the latter to be made to advantage, and is then called pig-lead, (werkblei.) The silver is separated by the process of cupellation, which is founded on the property of lead to oxidize when heated in contact with the air, while the silver, which remains unaltered, concentrates indefinitely in the lead which remains in the metallic state, and is left isolated at the end of the operation, when all the lead is oxidized. In order to accelerate the oxidation of the lead, the litharge formed must be removed as fast as it is produced, for which purpose the tempera- ture is kept sufficiently elevated to fuse the oxide of lead. As the melted metal forms a convex surface, the litharge flows constantly into the space between the metal and the side of the vessel, and the litharge runs off as it is formed, without the loss of any metal- lic lead, through little gutters cut into the side of the vessel, which are made deeper as the level of the metal sinks. Fig. 549. Fig. 550. METALLURGY OF LEAD. 199 Figs. 551, 552, and 553 represent a cu- pelling-furnace, used at Clausthal in the Hartz. Fig. 552 gives a horizontal section, made at the height of the line X Yof fig. 551; and fig. 551 represents a vertical section made through the plane pass- ing through the line ED of fig. 552. Lastly, fig. 553 furnishes an interior view of the furnace. The cupelling- furnace is a kind of reverberatory, consisting of a lateral hearth F, and a circular one A, the floor of which, having the shape of a spherical cap, is composed of bricks ii, placed edgewise on a base uu of scoriae. It is lined internally with a layer of marl »im, which is carefully heaped, and renewed at each operation, and which constitutes the cupel properly so called. The arch of the oven is formed of a riveted sheet-iron cover C, lined with clay, and suspended, by means of chains, to a crane GG'G", by which it can he easily raised and replaced. The furnace has four openings: that by which the flame from the hearth is introduced; two openings a, a, which receive the nozzles of two bellows which constantly drive air over the surface of the bath, and assist the oxidation, while, at the same time, they remove the litharge from the surface; the aperture P, serving for the in- troduction of the disks of lead; and lastly, the opening o, which is the tap-hole for the litharge. At the commencement of the operation, this last open- ing is closed by the cupel, but the latter is gradually notched, so as to keep the spout on a level with the bath of metal. The litharge flowing from the hole o accumulates at L on the floor of the foun- dry, where it solidifies. The cupel must be arranged before commencing the process, for which purpose the cover is removed, and the old cupel, being strongly impregnated with litharge, broken into pieces, which are added to the charges of the ores and matts, as stated in §§ 984 Fig. 551. Fig. 552. 200 LEAD and 985. The brick floor ii is moistened with water, and succes- sive layers of marl are beaten down upon it with a stamper.* The cover then being replaced, all the joints are accurately luted with clay. Fig. 553. One hundred and sixty cwt. of lead being introduced into the furnace, and heat applied, the metal soon comes into fusion; and the bellows then being gently worked, the oxidation commences, and the surface of the bath becomes covered with a black dust of oxide of lead, mixed with foreign substances. The dust, which is infu- sible at the temperature applied, constitutes the scrapings, (ab- strichs.) The workman throws from time to time a small quantity of powdered charcoal on the bath, and, by means of a billet of wood placed crosswise at the end of an iron rod, removes the abstrichs from the furnace. After some time, the fused litharge begins to appear; and after the first portions, which, being impure, are allowed to flow off, and are set aside, comes the pure litharge, called merchantable litharge, which can be sold in this state, when it is not mixed with the former. The cupellation is continued, the blast being gradually increased to accelerate the oxidation, until all the lead is converted into litharge, and the silver remains isolated in the shape of a disk. At the moment when the oxidation is arrested, and consequently when the cupellation is finished, a peculiar phenomenon is mani- * A layer of marl about an inch in thickness being stamped down, its surface is again loosened by means of an iron rake, to the depth of about half an inch, before the next layer is heaped on; as without this precaution the layers would form successive strata by the heat of the furnace, and not a consolidated mass.— W. L. F. METALLURGY OF LEAD. 201 fested, called the brightning. During the whole period of oxida- tion, the metallic bath appears to be more brilliant than the sides of the furnace; and its temperature is in fact higher, since it shares not only that of the surrounding space, but also takes ad- vantage of all the heat developed by the chemical combination of the lead with oxygen. But when the lead is completely oxidized, the second source of heat disappears, the small disk of metallic sil- ver falls rapidly to the temperature of the oven, and its original brilliancy is replaced by a dull colour. On the other hand, at the moment when the last traces of lead are oxidized, there exists only on the brilliant surface of the metallic bath a pellicle of melted litharge, which rapidly grows thinner, presenting the rapid succes- sion of colours of a soap-bubble, and at last tears like a veil, dis- playing the surface of the metal. The name of brightning, or figu- ration, is given to this rapid succession of optical phenomena. As soon as the brightning appears, the workman pours first hot and then cold water on the hearth, and then removes the cake of solid silver. The silver, called cupel silver, which is not pure, but contains about T of lead, is afterwards refined, as will be de- scribed when treating of silver. A cupellation generally lasts 30 hours, including the time neces- sary for the arrangement of the cupel. The cupellation of 160 cwt. of pig-lead, arising from the smelting of the schlichs, yields at Clausthal, 56 marcs of silver, (a marc = J pound.) 118 cwt. of litharge. 21 “ of debris of cupellation, (German, heerd.) 15 “ of scrapings. 6 “ of rich litharge. The rich litharge, which is that obtained during the last stage of cupellation, is not mixed with the rest because it contains a consi- derable quantity of silver. 160 cwt. of pig-lead, arising from the smelting of the matts, yield 62 marcs of silver. 112 cwt. of litharge. 21 “ of debris of cupellation. 18 “ of abstrich. 9 “ of rich litharge. Wood is the fuel used in cupellation. The litharge arising from cupellation is reduced to metallic lead, a small quantity only being sold as litharge. The conversion of litharge into metallic lead, which is called the revival of the litharge, is effected by smelting the litharge in contact with charcoal in an elbow-furnace, furnished with an outer crucible. The scoriae arising from this fusion are added to the charges of ore, and the lead, after being run into bars, is sent to market. 202 LEAD, § 988. Silver can be advantageously extracted from pig-lead by direct cupellation, only when it contains at least part of silver; but latterly, much poorer lead has been profitably worked, by first subjecting it to a process called refining by crystallizaton.* This operation, which separates the lead into very poor lead and into such sufficiently rich for cupellation, is based on the following prin- ciple :—By allowing a large quantity of melted argentiferous lead to cool slowly, and frequently stirring the liquid mass with an iron spatula, a crystalline powder of a poor lead is soon formed, which may be skimmed off as fast as it is produced; and by thus succes- sively separating a portion of the lead in the state of imperfect crys- tals, the greater part of the silver is left in the metal remaining fluid, which thus becomes much richer. By properly repeating these operations, either on the mass which has been removed in the solid state, or on the portion poured off in the liquid state, on the one hand a poorer and poorer lead is obtained, and on the other, lead which is more and more rich in silver. Only that lead which con- tains a proper quantity of silver is subjected to cupellation, the re- mainder being sold. § 989. Metallic lead is technically used in the shape of sheet-lead, for roofing houses, lining bathing-tubs, making gutters and spouts for conveying wTater, etc. etc. In the manufacture of sheet-lead, the melted metal is allowed to run over a marble table into plates, the size of which is regulated by wTooden rulers, and which are then passed through rollers. The rolling-machine is composed of two cast-iron cylinders, the lower one of which alone is turned by machinery, wdiile the upper one is carried round simply by adhesion, the pressure it exerts on the sheet of lead being regulated by a counter weight. Return screws, which fasten the upper boxes of the two gudgeons, limit the elevations of the cylinder, and regulate the thickness of the sheet; and, as the screws work independently of each other, the side on which the plate is least rolled may be tightened, so as to obtain a uniform thickness. On each side of the cylinders are tables furnished with iron rails, which receive and guide the sheets. Five or six sheets are rolled, and then passed in an opposite direction between the cylinders, their mo- tion being reversed; which is repeated until the sheets have acquired the requisite thickness. Leaden pipe is made on a iron mandrel between grooved cylinders, after having been run into a cast-iron mould, abed (fig. 554), in the axis of which is an iron mandrel ef, of the proposed diameter of the leaden pipe. A thick leaden-tube, of from 2.0 to 2.3 feet in length, is thus obtained, and is then fastened on an iron mandrel of Fig. 554. * Commonly known as Pattinson's process.— W. L. F. LEAD. 203 the same diameter as that ef of the mould, after which the whole is drawn out between cylinders resembling those used for the drawing of iron-wire. The sides of the pipe are thus reduced in thickness until it attains the length required.* MANUFACTURE OF LEAD-SHOT. § 990. Lead alloyed with 0.3 to 0.8 per cent, of arsenic is gene- rally used in the manufacture of lead-shot; the addition of this small quantity of arsenic giving the lead the property of forming perfectly spherical globules. A sheet-iron sieve is used, shaped like a spherical cap, and pierced with holes of the size of the shot to be made. The dross which forms on the fused lead is first pressed into the sieve, so as to completely line its sides, and the melted metal, being then poured in by small quantities with a spoon, filters through the dross and drops from the perforations. The drops, which should be made to fall from a great height, in order to become solid during their descent, are collected in a reservoir of water; a greater eleva- tion being required according to the size of the shot. The shot, being sorted into sizes by means of sieves, is polished by causing it to revolve in wooden barrels with a small quantity of plumbago. * The new method of making lead-pipe consists of a powerful press, which forces the lead in a heated and soft state out of an opening in an iron reservoir, having a solid and short mandrel of iron in the centre of the opening, of the same diameter as the interior of the tube to be made. The lead is perfectly hard when issuing from the opening, and presents a tubing of a fine glaze interiorly and exteriorly. By this machine also tubes of any length may be manufactured.— J. C. B. 204 BISMUTH. Equivalent = 213 (2662.5; 0 = 100). § 991. The bismuth* of commerce is never absolutely pure; but, as the foreign metals with which it is alloyed are generally more oxidizable than itself, it may be purified by heating the pulverized metal with of its weight of nitre in an earthen crucible. The temperature should be gradually raised until the nitrate is decom- posed ; when the foreign metals oxidize and combine with the po- tassa as well as a portion of the bismuth, the remainder of the latter being left as a button at the bottom of the crucible. In order to obtain bismuth chemically pure, a mixture of sub- nitrate of bismuth and black flux must be fused in a crucible. Bismuth is a grayish-white metal, having at the same time a very decided reddish shade, which is easily seen by placing a piece of bismuth alongside of a specimen of a white metal, such as zinc, an- timony, etc. Its density is 9.9. It presents a crystalline fracture with large glittering lamellae, has but slight malleability, and crys- tallizes readily by fusion. Beautiful crystals may be obtained by fusing in an earthen capsule some kilogrammes of bismuth of com- merce, purified by fusion with nitre, and allowing to cool very slowly. To effect this, the capsule is placed on a bath of heated sand, and covered with a sheet-iron plate, on which burning charcoal is placed. In a short time a hole is made in the solid crust which forms on the surface, and the liquid metal is allowed to run off. The crust being carefully removed, a geode of very beautiful crystals, frequently of several centimetres in diameter, is displayed. These crystals, which are cubes, or rather pyramidal figures resembling those of sea-salt (493), exhibit very elegant iridescent colours, produced by the very thin pellicles of oxide which form on the surface of the metal as it is brought, while hot, in contact with the air. The pellicles present the play of thin scales or soap-bubbles. Bismuth fuses at 507.2°; and a thermometer plunged into melted bismuth marks this temperature during the whole period of its solidification. Like water, bismuth expands at the moment of solidifying, and is therefore lighter when solid than when liquid. It is volatile at a very high temperature, but nevertheless difficult to distil. Bismuth remains unchanged in a dry atmosphere, but when ex- posed to damp air, becomes covered with a very thin pellicle of * Bismuth was known to the ancients, who often confounded it with lead and tin. Stahl and Dufay first proved it to he a peculiar metal. OXIDES. 205 oxide after some time. Heated in the air, it burns with a small bluish flame, giving off yellow fumes. Bismuth decomposes water only at a very high temperature, and effects no decomposition of cold water in the presence of powerful acids. Concentrated chloro- hydric acid acts on it with difficulty, while sulphuric acid attacks it only when concentrated and hot, with disengagement of sulphurous acid. Nitric acid attacks it very energetically, and dissolves it completely. COMPOUNDS OF BISMUTH WITH OXYGEN § 992. Bismuth forms two compounds with oxygen: 1. An oxide Bi03; 2. An oxide BiOs, or bismuthic acid. An intermediate oxide Bi04 is known, but should be regarded as a compound of the two preceding, and its formula should be writ- ten Bi03,Bi05. Oxide of Bismuth Bi03. § 993. The oxide of bismuth BiOa, which is obtained by roasting the metal in the air, or better still, by decomposing the basic nitrate of bismuth by heat, presents the appearance of a bright-yellow pow- der, fusible at a red-heat, and producing on solidification a deeper yellow glass, which readily perforates earthen crucibles. The oxide of bismuth is fixed, and its density is 8.45. The oxide can be obtained hydrated in the form of a white pow- der, by decomposing the basic nitrate by an alkali, or by ammonia. On boiling the hydrate in a solution of potassa, it parts with its water, and is converted into a yellow crystalline powder, which is the anhydrous oxide. The chemical composition of the oxide is, Bismuth 89.87 Oxygen 10.13 100.00 Some chemists, regarding this oxide as formed of 1 equiv. of the metal and 1 of oxygen, write its formula BiO, and adopt for the equivalent of the metal the number 71, which is given by the proportion: 10.13 : 89.87 :: 8 : x, whence £=71. But as this hypothesis is contrary to all analogy, and is sustained by no example of isomorphism, we shall assign to oxide of bismuth the formula Bi03, and the equivalent of the metal will be deduced from the proportion: 10.13 : 89.87 :: 24 : z, whence £=213. 206 BISMUTH. Bismuthic Acid BiOs. § 994. Bismuthic acid Bi05 is prepared by passing a current of chlorine through a concentrated solution of potassa in which very finely divided oxide of bismuth is suspended; or by heating for a long time in the air a mixture of potassa and oxide of bismuth; or better still, by calcining a mixture of oxide of bismuth, caustic po- tassa, and chlorate of potassa. Bismuthic acid prepared by either of these processes is always mixed with a certain quantity of oxide of bismuth, which may be separated by treating the substance with weak nitric acid, which dissolves the oxide of bismuth, and, when cold, does not affect the bismuthic acid. Bismuthic acid is a bright- red powder, which readily parts with a portion of its oxygen at a temperature slightly above 212°, and is then converted into an inter- mediate oxide Bi04. Concentrated acids also decompose it, reducing it to the state of oxide Bi03, which combines with the acid. Bismuthic acid can combine with oxide of bismuth, and thus pro- duce saline oxides; but these compounds have not yet been much studied. They are obtained by heating in the air a mixture of oxide of bismuth Bi03 and caustic potassa, or by passing a current of chlorine through a solution of potassa which contains oxide of bismuth in suspension. When these reactions are terminated, bis- muthic acid is obtained, while, if they are prematurely arrested, brown compounds of variable proportions result, which are combi- nations of bismuthic acid BiOs with oxide of bismuth Bi03. SALTS FORMED BY OXIDE OF BISMUTH. § 995. Oxide of bismuth is a feeble base, forming with acids seve- ral crystallizable salts, which water decomposes into basic salts which are precipitated, and into very acid salts which remain in the solu- tion. § 996. The nitrate, which is the most important of the salts of bismuth, is obtained by dissolving bismuth in nitric acid. The liquid, when evaporated, yields large, colourless, and deliquescent crystals, of the formula Bi03,3N0s+3II0. It dissolves without decomposition in a small quantity of water, particularly when acidu- lated with a few drops of nitric acid, but is decomposed if the quan- tity of water is greater, a white precipitate of a basic nitrate being formed, which is known by the name of pearl powder. This sub- stance is used for whitening the skin, but is liable to the objection of being blackened by sulfhydric acid. Its composition varies ac- cording to the quantity of water used in the precipitation, the tem- perature, and duration of contact of the basic salt with the water. Boiling water ultimately removes all its acid, and leaves only hydrated oxide. Nitrate of Bismuth. BINARY COMPOUNDS. 207 Sulphate of Bismuth. § 997. By heating powdered bismuth with concentrated sulphuric acid, sulphurous acid is disengaged, and the metal is converted into a white, insoluble powder of sulphate of bismuth Bi63,3S03. This salt is decomposed by treatment with water into a very acid salt which remains in solution, and an insoluble bi-basic sulphate BiO„ so3+ho. § 998. By adding carbonate of soda to an acid solution of nitrate of bismuth, a white precipitate of a basic carbonate Bi03,C0a is obtained, which is easily destroyed by heat, leaving a residue of oxide. Carbonate of Bismuth. COMPOUND OF BISMUTH WITH SULPHUR. § 999. Bismuth combines directly with sulphur when assisted by heat. To effect the combination, it is sufficient to heat together the two substances in the state of fine powder, a certain quantity of metallic bismuth always remaining mixed or dissolved in the sulphide. In order to obtain the latter pure, the product of the first fusion must be reduced to a fine powder, and again fused in a crucible with an additional quantity of sulphur. The sulphide then appears under the form of a gray ball, possessing a metallic lustre, and evincing in its fracture a fibrous texture. The formula of the sulphide is BiS„. It has been found crystallized in nature, and appears to be isomorphous with the sulphide of antimony to which the same formula is assigned. Sulphide of bismuth may be obtained by the humid way in the form of a black powder, by passing a current of sulfhydric acid through a solution of a salt of bismuth. COMPOUNDS OF BISMUTH WITH CHLORINE. § 1000. Bismuth combines directly with chlorine with disengage- ment of heat, and even of light, when the metal is very finely divided. If a current of chlorine be led over bismuth heated in a tubulated retort, the chloride distils over and condenses in the form of a readily fusible white substance. The same substance is ob- tained by distilling in a small retort a mixture of 1 part of metallic bismuth and 2 parts of bichloride of mercury. Chloride of bismuth rapidly attracts the moisture of the air, and is converted into a crystallizable hydrated chloride; which may also be obtained by dissolving metallic bismuth in aqua regia, and evaporating the liquid. Chloride of bismuth BiCl3 dissolves without change in water acidulated with chlorohydric acid, but is decomposed by fresh water; when a portion of the chloride dissolves by means of the chlorohydric acid which is set free, while a white precipitate of oxychloride of bismuth BiCl3+2(Bi03-|-3H0) remains. 208 BISMUTH. On pouring an acid solution of nitrate of bismuth into a solution of sea-salt, a white precipitate of very fine crystalline spangles is formed, which is an oxychloride of bismuth of the formula BiCl3-f- 2(Bi03-(-3H0). This substance is used for whitening the skin, and is called pearl-white. § 1000 bis. By alloying bismuth with lead and tin, very fusible alloys are obtained, which are used for taking impressions, making stereotype-plates, etc. The alloy composed of 1 part of lead, 1 part of tin, and 2 of bismuth fuses at 200°, while that containing 5 of lead, 3 of tin, and 8 of bismuth fuses at about 208.4°. By diminishing the proportion of bismuth, the fusing point of the alloys obtained varies between 212° and 392°, and these substances have been used as washers for the safety-valves of the boilers of high- pressure steam-engines. Their composition was such as to fuse at a point slightly above the temperature corresponding to the maxi- mum of tension which the steam should not exceed. When the safety-valves were out of order or overloaded, and the elastic force of the steam surpassed the maximum, the washers, by beginning to fuse, allowed the steam to escape. This means of safety wTas soon found to be useless, as the alloy, being kept for a long time at a temperature approaching its melting point, underwent a kind of eliquation—a more fusible alloy separated from it, and that which remained was much less fusible than the original alloy. For this reason the use of fusible washers has been abandoned. ALLOYS OF BISMUTH. DISTINCTIVE CHARACTERS OF THE SOLUBLE COMPOUNDS OF BISMUTH. § 1001. We have seen that all the compounds of bismuth, being soluble in a very small quantity of water, are decomposed when treated with a larger quantity, and yield white precipitates of basic salts: therefore, one of the distinctive characters of solutions of bismuth is to become cloudy when diluted with a large quantity of water. The caustic alkalies and alkaline carbonates throw dowm white precipitates, insoluble in an excess of the reagent. Sulf hydric acid and the sulfhydrates afford black precipitates, which do not redissolve in an excess of sulfhydrate. Iron, zinc, and copper precipitate bismuth in the form of a black powder, which fuses readily on charcoal in the reducing flame of the blowpipe into a metallic globule, which becomes very brittle after cooling, and yields a powder of a characteristic rose-colour. DETERMINATION OF BISMUTH; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 1002. Substances containing bismuth which are to be subjected to chemical analysis are always dissolved in nitric acid, and the METALLURGY OF BISMUTH. 209 boiling liquid is precipitated by an excess of carbonate of ammonia. The precipitate is washed on the filter, and then calcined in a small porcelain capsule, in which it remains in the state of the oxide Bi03. The calcination should not be made in a platinum crucible, because this metal is easily attacked by oxide of bismuth, especially when a small quantity of metallic bismuth can be produced by a reducing action. The filter should be calcined separately, its ashes sprinkled Avith a few drops of nitric acid, and then recalcined to decompose the nitrate of bismuth which is formed. It is often necessary to precipitate bismuth in the state of sul- phide by means of sulfhydric acid, as, for example, when the metal exists in a liquid with other metals which are precipitated by the alkalies or alkaline carbonates, but not by sulfhydric acid. It is also precipitated as sulphide when the liquid contains chlorohydric acid, because the precipitate formed by the alkaline carbonates would in this case contain chloride of bismuth, which is difficult to decompose by an excess of alkaline carbonate. The bismuth being in the state of sulphide is collected on a filter, dissolved in nitric acid, and then reprecipitated by an excess of carbonate of ammonia. Lastly, bismuth is sometimes precipitated in the metallic state by a blade of iron or zinc, and the metallic powder, being collected on a filter, is calcined in a porcelain capsule; after which a few drops of nitric acid are added, it is recalcined, and the bismuth deter- mined in the state of oxide. Bismuth is easily separated by sulfhydric acid passed through an acid liquid, from all the metals we have hitherto studied, with the exception of cadmium, tin, and lead. It is separated from tin by treating the sulphides, immediately after their being precipitated, with a solution of sulfhydrate of ammonia, which dissolves only the sulphide of tin. In order to separate bismuth from lead, both metals are dissolved in nitric acid, and evaporated with an excess of sulphuric acid until the vapours of the acid begin to pass over, after which they are treated with water, which dissolves only the sulphate of bismuth by means of the excess of acid. This process does not effect a very accurate separation. No method of sepa- rating bismuth from cadmium is yet known.* § 1003. Bismuth has hitherto been found only in a small number of minerals, the only one of which sufficiently abundant and rich to he used as an ore is native bismuth, which constitutes metallic veins METALLURGY OF BISMUTH. * A perfect separation of bismuth from cadmium is effected by adding a solu- tion of cyanide of potassium to the solution of the two oxides, by which the bis- muth is precipitated, while the cadmium remains in solution as a double cyanide of cadmium and potassium. Another method might be based on the solubility of oxide of cadmium in am- monia, in which oxide of bismuth is insoluble.— W. L. F. 210 BISMUTH. in the quartzose rocks of the old formations. All the bismuth used in the arts comes from Saxony, and is extracted by a very simple process: the ore being heated in close vessels, the bismuth fuses, separates from the gangue, and falls to the bottom of the vessel. The fusion is effected in sheet-iron or cast-iron tubes bd (fig. 555), arranged in a furnace, and inclining down- ward. The ore being intro- duced through the opening d, the latter is closed, while the other end b is closed by a plate having a hole o, through which the metal escapes. It is received in earthen cups a, a, heated by charcoal placed in the space K beneath, in order to keep the metal fluid. It is then scooped out and run into moulds. The metal thus obtained, wrhich always contains, besides metallic sulphides and arseniurets, some foreign metals, is purified by fusion with T\j of its weight of saltpetre. Fig. 555. 211 ANTIMONY. Equivalent = 129 (1612.5; 0 = 100). § 1004. The antimony* of commerce, which is rarely pure, con- taining most frequently a small admixture of iron, lead, arsenic, and sulphur, is purified in the laboratory by mixing it intimately with y of its weight of nitre, and fusing the mixture in an earthen cru- cible ; when the antimony appears in the form of a metallic button, composed of very small crystalline lamellae. The fineness of the grain of antimony is an index of its purity. Antimony is a metal of a slightly bluish, very brilliant, silvery white colour. It fuses at 842°, and at a white-heat gives off appre- ciable vapours, at which temperature it may be distilled in a current of hydrogen gas ; but the tension of its vapour being still very feeble, the distillation is slow. Antimony crystallizes readily from fusion, and its fracture presents very brilliant surfaces of cleavage, the disposition of which leads to the rhombohedron, and which are fre- quently of great extent. The tendency of the metal to crystallize may be well seen in the cakes of commercial antimony, their upper surfaces often exhibiting a beautiful star, the rays of which resemble the fern-leaf. It is a very brittle metal and easily reduced to pow- der in a mortar. Antimony does not sensibly alter in the air at the ordinary tem- perature, while it readily oxidizes when kept in a fused state in contact with the air. Heated to a high temperature, it burns with a white flame and' gives off copious fumes. If the fused metal, heated to redness, be thrown from a certain height on the floor, a very brilliant phenomenon of combustion is observed, accompanied by thick white fumes. Finely powdered antimony dissolves in boiling concentrated chlo- rohydric acid, with disengagement of hydrogen gas, but does not decompose water in the presence of sulphuric acid, which will not oxidize it except when concentrated and hot, when sulphurous acid is disengaged. Nitric acid, even when dilute, readily attacks it, converting the metal into an insoluble white precipitate. Aqua regia transforms antimony into a chloride which dissolves without change in an excess of chlorohydric acid. COMPOUNDS OF ANTIMONY WITH OXYGEN. § 1005. Two well-defined compounds of antimony with oxygen are known, the quantities of oxygen contained in which are as 3 to 5. * Although the ores of antimony were known to the ancients, Basil Valentine was the first who made mention of metallic antimony. 212 ANTIMONY. The most oxygenated compound, of which the formula is Sb05, and which plays the part of an acid, is antimonic acid; while that con- taining the least amount of oxygen, and is expressed by the formula Sb03, acts as a feeble base. We shall call it sesquioxide of anti- mony, or simply oxide of antimony. A third oxide Sb04, which by some chemists is regarded as an oxide per se, and called antimonious acid, should rather be consi- dered as an antimoniate of oxide of antimony, Sb03.Sb05. Oxide of Antimony Sb03. § 1006. Oxide of antimony is formed when antimony is heated in an imperfectly closed crucible, Avhen small elongated and very bril- liant prismatic crystals, which have been called argentine flowers of antimony, are deposited on the sides of the crucible at a little distance above the fused metal. But as it is difficult to prevent the oxide prepared in this way from containing some antimoniate of oxide of antimony, a better method of obtaining the oxide in a state of purity consists in pouring, by small quantities at a time, a solu- tion of chloride of antimony SbCl3 into a boiling solution of carbo- nate of soda ; when the oxide of antimony separates in the form of small crystals. Oxide of antimony, the colour of which is a grayish white, fuses at a red-heat, and sublimes at a higher temperature. It readily absorbs oxygen when heated in the air, and is converted into anti- moniate of oxide of antimony, while it is indecomposable by heat alone, but is easily reduced by hydrogen or by charcoal. The oxide of antimony, precipitated when cold from the solution of the chloride by carbonate of soda, which is hydrated, and has the formula Sb03-fII0, dissolves readily in alkaline liquids, form- ing true salts in which it acts the part of an acid. Oxide of antimony contains : Antimony • 84.31 Oxygen 15.69 100.00 Its formula is written Sb03; and consequently the equivalent of antimony is obtained from the proportion: 15.68 : 84.32 : : 24 : a;, whence z=129. Antimonic Acid Sb05. § 1007. Antimonic acid is obtained by attacking antimony by nitric acid, or better still, by aqua regia containing an excess of nitric acid, when an insoluble white powder of hydrated antimonic acid is formed, which loses its water at a slightly elevated tem- perature, and is converted into anhydrous antimonic acid. The hydrated acid is also obtained by decomposing the percliloride of ANTIMONIC ACID. 213 antimony SbCls by water; but the hydrates obtained by these two processes are far from being identical. Their capabilities of satu- ration with bases being different, they in this respect exhibit a phe- nomenon analogous to that observed in stannic acid, and which was treated of (§479 et seq.) when speaking of phosphoric acid, which presents the same feature. The product obtained by attacking an- timony by nitric acid, and to which the name of antimonic acid has been preserved, only saturates 1 equivalent of a base, producing neutral salts of the general formula RO,SbOs; while the precipi- tate obtained by decomposing perchloride of antimony by water saturates 2 equiv. of a base, and forms neutral salts of the formula 2 RO,SbOs. It has been called metantimonic acid. Anhydrous antimonic acid is a powder of a yellowish-white co- lour, which is decomposed by a red-heat, producing antimoniate of oxide of antimony Sb03,Sb05. The neutral antimoniate of potassa is prepared by heating in an earthen crucible 1 part of metallic antimony and 4 parts of nitrate of potassa, and treating the powdered mass with a small quantity of tepid water, which dissolves the potassa in excess and the unde- composed nitrite of potassa. The residue is then boiled with water for several hours, by which the anhydrous antimoniate of potassa, which is insoluble, is converted into a soluble hydrated antimoniate. An insoluble residue remains, which is the bi- antimoniate of potassa KO,2SbOs; and the liquid leaves after evaporation a gummy mass which presents no appearance of crystallization, and the formula of which, when desiccated in dry air, is KO,SbOs+5IIO. This neu- tral antimoniate KO,SbOs+5HO is converted into a crystalline powder of bi-antimoniate K0,2Sb05 by passing a current of car- bonic acid through its solution. By heating in a silver crucible antimonic acid or neutral antimo- niate of potassa with a large excess of potassa, a fused mass which completely dissolves in a small quantity of cold water is obtained; and the solution, when evaporated in vacuo, deposits small crystals of metantimoniate of potassa 2KO,SbOs. This salt dissolves, without apparent decomposition, in a small quantity of cold water to which a certain quantity of caustic potassa has been added, while it is decomposed by pure water into potassa and acid metaantimo- niate of potassa K0,Sb05-f-7H0, which is but slightly soluble in cold water. Water dissolves it more freely at a temperature of 105° or 120°, while a prolonged contact with cold water transforms it into neutral antimoniate of potassa; which transformation is rapidly effected by boiling the liquid. The solution of the acid metantimoniate of potassa possesses the property of precipitating the salts of soda, and yielding an acid metantimoniate of soda, which is almost insoluble in water. It is the only reagent as yet known which precipitates soda from its solutions; but it is necessary to use freshly prepared acid metantimoniate of potassa, as the salt 214 ANTIMONY. is after some time converted into the common antimoniate, which does not precipitate the salts of soda. Antimoniate of Oxide of Antimony Sb03,Sb05. § 1008. By heating antimonic acid until oxygen is no longer given off, a white powder, of which the composition is Sb04, but which should be written Sb04,Sb05, remains. This product, which is sometimes called antimonious acid, is also formed when antimony is roasted in the open air. A solution of tartaric acid or bi-tartrate of potassa abstracts its oxide of antimony, leaving the antimonic acid, while a solution of caustic potassa dissolves, on the contrary, the antimonic acid, and leaves the oxide of antimony; which reac- tions render the existence of both oxide of antimony and antimonic acid in this body very probable. Antimoniate of oxide of antimony is infusible. SALTS FORMED BY OXIDE OF ANTIMONY. § 1009. Oxide of antimony SbOs is a feeble base, which neverthe- less forms several salts with acids. A nitrate of antimony is obtained by treating cold antimony with fuming nitric acid, in the shape of crystalline spangles of the for- mula 2Sb03,N0s. The salt is decomposed by water, and trans- formed into hydrated oxide of antimony. Several compounds of oxide of antimony with sulphuric acid are known, and present the following composition: Sb03,4S03+H0 ? A - Sb03,2S03 Sb03, S03 2Sb03, SOs. We do not find among these salts the compound Sb03,3S03, which should be regarded as the neutral sulphate of antimony, from the formula Sb03 which we have adopted to represent oxide of antimony. The oxychloride of antimony SbCl3,2Sb03+II0, the prepara- tion of which will be explained hereafter, is converted into the sulphate Sb03,4S03+H0 when it is treated with concentrated sulphuric acid, while the sulphate Sb03,2S03 is obtained by treat- ing oxide of antimony with fuming oil of vitriol, (Nordhausen sul- phuric acid.) Lastly, the sulphate Sb03,4S03-f HO is decomposed by treatment with hot water, leaving a residue of the formula 2Sb03,S03. COMPOUND OF ANTIMONY WITH HYDROGEN. § 1010. Antimony forms a gaseous compound with hydrogen, which resembles in its composition that of arseniuretted hydrogen and phosphuretted hydrogen gas, but which hitherto has not been SULPHIDES. 215 obtained in a state of purity. By introducing a solution of proto- chloride of antimony into a bottle in which hydrogen is being dis- engaged by the reaction of dilute sulphuric acid on zinc, the hydro- gen always contains a certain quantity of antimoniuretted hydrogen gas, which is easily recognised on igniting the gas, when it burns with a yellowish flame which evolves white fumes, and which, on being allowed to play on a cold porcelain capsule, yields glittering spots of metallic antimony. If the gas be passed through a heated tube, a brilliant ring of metallic antimony forms on the sides of the tube, in front of the heated portion. § 1011. Two combinations of antimony with sulphur are known; and while the formula of the first, which we shall call sulphide of an- timony, is SbS3 corresponding to the oxide Sb03, the second cor- responds to antimonic acid, and its formula being SbSs, we shall call it sulfantimonic acid. Sulphide of antimony is found in nature, and is the only ore of antimony. It always occurs crystallized, but the prismatic crys- tals are so dovetailed into each other, that it is often difficult to ascertain their form. It is sometimes found in isolated crystals, which are prisms belonging to the fourth system. Sulphide of anti- mony, which is of a deep gray colour, and a very decided metallic lustre, fuses below a red-heat, and readily crystallizes on cooling from a white-heat. It exhales copious fumes, and may be distilled in a current of nitrogen gas. Its density is 4.62. The sulphide is formed by the direct combination of antimony with sulphur, by several successive fusions, when a purer sulphide than that occur- ring in nature is obtained, which always contains a small quantity of other metallic sulphides. Sulphide of antimony is easily roasted in the air, during which operation no sulphate is formed, but only oxide of antimony, which combines with the undecomposed sulphide, especially under the in- fluence of an elevated temperature. Fusible oxysulphides are thus formed, which, after cooling, yield brown vitreous substances, called in commerce glass of antimony, liver of antimony, or crocus, accord- ing to the proportions of the substances entering into their compo- sition. Glass of antimony, which contains about 8 parts of oxide and 1 of sulphide, is transparent and of a reddish-yellow colour, while crocus, which contains 8 parts of oxide and 2 of sulphide, is opake and reddish yellow. Liver of antimony is opake and of a deep brown colour, and contains nearly 4 parts of sulphide for 8 of oxide. Hydrogen decomposes sulphide of antimony at a red-heat with disengagement of sulfhydric acid, while the antimony remains in the metallic state; but it is difficult to prevent a small quantity of antimony from being disengaged in the state of antimoniuretted COMPOUNDS OF ANTIMONY WITH SULPHUR. 216 ANTIMONY. hydrogen gas. Charcoal also decomposes sulphide of antimony at a high temperature, while sulphide of carbon is disengaged, and the antimony remains in the metallic state. It is, however, difficult by these methods to obtain antimony entirely free from sulphur. Iron, zinc, and copper decompose sulphide of antimony at a red- heat ; but the metallic antimony thus obtained always contains a certain quantity of these metals. Concentrated chlorohydric acid readily dissolves sulphide of antimony with disengagement of sulf- hydric acid, which reaction is sometimes applied in the laboratory to the preparation of sulfhydric acid (§ 149). Boiling concentrated sulphuric acid attacks sulphide of antimony and evolves sulphurous acid. Nitric acid converts it into an insoluble oxide of antimony and sulphuric acid. The alkalies and alkaline carbonates decompose sulphide of anti- mony both in the dry and humid way, sulphide of antimony and a compound of oxide of antimony with potassa being formed. When the sulphide of antimony is in excess, there is formed in addition a compound of sulphide of antimony with monosulphide of potassium, in which combination the sulphide of antimony acts the part of an acid. If the decomposition be effected in a brasqued crucible, a portion of the antimony separates in the metallic state. The sulphide of antimony SbS3 may be prepared in the humid way, by passing a current of sulfhydric acid gas through a solution of chloride of antimony SbCl3 in water charged with chlorohydric acid, when an orange-coloured precipitate of hydrated sulphide is formed, which dissolves readily in the alkaline sulphurets, wffien it plays the part of an acid. Acids precipitate anew the hydrated sulphide from solutions of the sulphosalts. Heat easily drives off the water from the hydrated sulphide, which then is converted into a gray anhydrous sulphide.' In medicine the hydrated sulphide is used either mixed or com- bined with oxide of antimony, and often with sulfantimonic acid SbS5, and is known by the name of kermes mineral, golden sul- phide of antimony, etc. Kermes is prepared either in the dry or humid wray. In the former case, a mixture of 5 parts of native sulphide of an- timony and 3 parts of dried carbonate of soda is fused in an earthen crucible, and the fused substance, after being reduced to powder, is boiled with a large quantity of water. The hot liquid is rapidly filtered, taking care that it does not cool in the filter; when the liquid, which is nearly colourless, or but slightly yellow, deposits on cooling a copious brown flaky precipitate, which is the kermes. It should be quickly washed, dried at a low temperature, and kept in well-stoppered bottles. It is obtained in the humid way by boiling 1 part of native sul- phide of antimony, finely powdered, with 20 or 25 parts of dried CHLORIDES. 217 carbonate of soda, and 250 parts of water; the liquid, which is almost colourless, depositing the kermes on cooling. By pouring chlorohydric acid into the mother liquid from which the kermes has been deposited, a precipitate of a deeper red colour than the precipitate is obtained, which has been called the golden sulphide. It is a mixture of sulphide of antimony SbS3, sulfanti- monic acid SbS5, and oxide of antimony Sb03. It is easy to ascertain that the oxide of antimony exists only as an admixture in kermes mineral and in the golden sulphide; an examination with the microscope shows the oxide of antimony in the form of white points scattered through the mass. Kermes contains, also, a small quantity of sulphide of potassium combined with the oxide, or with a portion of the sulphide of an- timony. Sulfantimonic acid SbS5 is obtained by passing a current of sulfhydric acid through a solution of perchloride of antimony SbCl5 in dilute chlorohydric acid, when a yellow precipitate is formed, readily dissolving in the alkaline sulphides, and forming sulphosalts which frequently crystallize with great facility. For medicinal purposes, a sulfantimoniate of sodium is often prepared by mix- ing intimately 18 parts of very finely powdered sulphide of anti- mony, 12 parts of dried carbonate of soda, 13. of lime and of sulphur, and allowing the mixture, after it has been triturated for a long time, to digest for several days in a flask filled with water, the vessel being frequently shaken. The liquid, when evaporated, first by heat, and then under the receiver of an air-pump, yields large crystals of a pale yellow colour, and of which the formula is 3NaS,SbSs+18HO. COMPOUNDS OF ANTIMONY WITH CHLORINE. § 1012. Antimony forms two compounds with chlorine, SbCl3 and SbCls, corresponding to the oxide of antimony Sb03 and antimonic acid Sb05. The chloride of antimony SbCl3 is obtained by passing chlorine slowly through a tube containing antimony in excess, while the per- chloride SbCl5 would be formed if the chlorine be in too great quantity. The chloride is also obtained by distilling in a glass retort an intimate mixture of 1 part of antimony and 2 parts of bi- chloride of mercury ; but the most economical method of preparing it consists in dissolving native sulphide of antimony in chlorohydric acid, and evaporating the liquid with an excess of acid. In the laboratory the residue of the preparation of sulfhydric acid is used for this purpose. Chloride of antimony SbCl3 is a white, readily fusible substance, which, from its consistence at the ordinary temperature, was for- merly called butter of antimony. It volatilizes at a temperature below a red-heat. 218 ANTIMONY. The protochloride of antimony is deliquescent m a moist atmo- sphere, and dissolves without change in a small quantity of water, while the addition of chlorohydric acid is necessary for its solution in larger quantities of the same liquid ; as with much pure water de- composition would ensue, a white soluble powder of an oxychloride of antimony SbCl3,2Sb03-f HO, called by the old chemists powder of Algarotli, being formed. By treating a chlorohydric solution of chlo- ride of antimony with hot water, the clear liquid deposits, on cool- ing, crystals of another oxychloride of the formula SbCl3,5Sb03. Repeated washings decompose the oxychlorides of antimony and leave pure oxide. The best method of preventing solutions of chlo- ride of antimony from being clouded by water consists in the addi- tion of a certain quantity of tartaric acid. Anhydrous chloride of antimony combines with dry ammoniacal gas, yielding a compound of which the formula is NIl3,SbCl3. With the alkaline chlorides and chlorohydrate of ammonia it forms dou- ble crystallizable chlorides. In surgery, chloride of antimony is used to cauterize wounds. Gunsmiths employ it for bronzing gun-barrels, the iron of which, being thus covered with a very thin pellicle of metallic antimony, is preserved from rust. Perchloride of antimony SbCl5 is prepared by heating antimony in a current of dry chlorine, the same apparatus being used as that employed for the preparation of the perchloride of tin. The liquid collected in the receiver, which always contains some protochloride SbCl3 in solution, must be completely saturated with chlorine, and then distilled in a small retort. The first portions which pass over contain a considerable quantity of dissolved chlorine, and are co- loured deeply yellow, while the subsequent liquid, being nearly colourless, is collected by itself. Perchloride of antimony never- theless appears to decompose at the temperature of its ebullition under the ordinary pressure of the atmosphere, as it always disen- gages chlorine when subjected to distillation. DISTINCTIVE CHARACTERS OF THE SOLUBLE COMPOUNDS OF ANTIMONY. § 1013. The characteristic reactions of solutions of antimony which we are about to indicate refer to the protochloride of anti- mony and to emetic tartar, which is a double tartrate of antimony and potassa. They will serve to distinguish antimony in all cases, because it is always easy to convert its other compounds into these two products. Solutions of antimony produce with potassa and soda white pre- cipitates, which are easily redissolved in an excess of alkali. Ammonia throws down a white precipitate insoluble in an excess of the reagent. The alkaline carbonates yield, carbonic acid being at the same ANALYTIC DETERMINATIONS. 219 time evolved, a white precipitate of the hydrated oxide, which does not dissolve in an excess of carbonate. Sulfhydric acid and sulf hydrate of ammonia yield a characteris- tic orange-coloured precipitate, which dissolves in an excess of sulf- hydrate. A blade of iron or zinc precipitates antimony in the form of a black powder, from which, by fusion on charcoal before the blow- pipe, metallic antimony is obtained, possessing the characteristic physical properties which distinguish it from tin, this metal being analogous to it in its chemical reactions. DETERMINATION OF ANTIMONY; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 1014. Antimony can neither be determined as the oxide Sb03 nor as antimonic acid Sb05, as the purity of these substances would always be questionable. It is precipitated from its solution by sulf- hydric acid, a sufficient quantity of chlorohydric acid being added to prevent the liquid from being clouded by water, or still better, tartaric acid, when the addition of this substance does not interfere with the determination of the remaining substances. The liquid, after being saturated with sulfhydric acid gas, is exposed to a gentle heat for several hours in an imperfectly closed bottle, in order to allow the greater portion of the sulfhydric acid to be dis- engaged ; when the precipitate of sulphide of antimony is collected on a filter, and, after being well washed, is dried on the filter at a temperature of 212°. The filter, with the substance it contains, being weighed, the latter is separated as completely as possible, and dropped into a small flask; when the weight of the filter, sub- tracted from that of the filter and substance together, gives the weight of the sulphide. The small quantity which always remains in the pores of the filter can be taken into account by incinerating the paper and considering the residue as antimoniate of antimony Sb03,Sb0s. The sulphide of antimony being now treated with hot aqua regia, the antimony dissolves as perchloride, and the sul- phur in the state of sulphuric acid, the oxidation of the sulphur being accelerated by an addition of a small quantity of chlorate of potassa. Chloride of barium is then poured into the liquid pro- perly diluted with water, while a small quantity of tartaric acid is added to prevent the precipitation of oxychloride of antimony; when sulphate of baryta is precipitated and weighed after calcina- tion. By subtracting from the weight of the sulphide of antimony the weight of sulphur corresponding to the sulphate of baryta, the weight of the metallic antimony is obtained.* * The method given in the text may be considerably shortened, by collecting the sulphide of antimony on a weighed filter, which has been previously dried at 212°, (a balanced filter;) when the weight of the filter with the precipitate, after being dried at the same temperature, minus the weight of the filter, gives imme- 220 ANTIMONY. The sulphide of antimony may also be heated in a current of hydrogen gas, when metallic antimony remains, sulfhydric acid and vapour of sulphur being disengaged. For this purpose, the sulphide of antimony is placed in a small porcelain crucible, through the lid of which a tube passes conveying dry -hydrogen to the bot- tom of the crucible, and, the temperature being gradually raised, the reaction is maintained until the crucible no longer alters in weight. In no case can antimony be weighed in the state of sulphide, its composition always being a matter of uncertainty. § 1015. In order to separate antimony from the metals we have previously studied, the insolubility of antimonic acid in nitric acid is sometimes relied on, and sometimes its precipitation by sulfhy- dric acid, and the solubility of sulphide of antimony in alkaline sulfhydrates. Antimonic acid not being absolutely insoluble in nitric acid, it is always necessary to test for antimony in the liquid by means of sulfhydric acid. In order to separate antimony from the alkaline, alkalino-earthy, and earthy metals, chlorohydric acid is added to the liquid to pre- vent the deposit of oxychloride of antimony, and sulfhydric acid gas is passed through it. When the antimony is nearly wholly pre- cipitated, the liquid is diluted with water, because sulphide of anti- mony is slightly soluble in chlorohydric acid, unless the latter is very dilute; and sulfhydric acid is again passed through it. The precipitate of sulphide of antimony having been separated on a fil- ter, the substances remaining in solution may be determined by the ordinary processes. Antimony is separated from manganese, iron, chrome, cobalt, nickel, and zinc by passing sulfhydric acid through the liquid acidu- lated with chlorohydric acid. The precipitation of oxychloride of antimony is frequently prevented by the addition of tartaric acid, in which case, however, the other metals can no longer be com- pletely separated from their solutions either by ammonia or the alkaline carbonates, because tartaric acid prevents their precipita- tion. The liquid then being saturated with ammonia, the metals are precipitated by sulf hydrate of ammonia. Antimony is separated from cadmium, lead, and bismuth by saturating the chlorohydric solution with ammonia, and adding a large excess of sulf hydrate of ammonia in which a certain quantity of sulphur has been dissolved. The bottle, imperfectly closed, is exposed for several hours to a temperature of from 120° to 140° ; when the antimony dissolves in the state of sulphide, while the sul- phides of the other metals are precipitated. By decomposing the diately the weight of all the antimony as sulphide SbS„ whence that of the me- tallic antimony may he deduced. The antimony having been in the state of proto- chloride SbCl3, is precipitated entirely as protosulphide SbSs, in all cases when the antimonial compound has not been dissolved in nitromuriatic acid.— W. L. F. ANALYTIC DETERMINATION. 221 filtered liquid by dilute chlorohydric acid, the sulphide of antimony separates, mixed with a large quantity of free sulphur. Antimony cannot be separated from tin by any of the processes just described. The reactions of these metals being very similar, their separation is consequently a matter of some difficulty. Both metals being dissolved in aqua regia, are precipitated together by a blade of zinc, and the metallic precipitate is weighed. It is then dissolved in aqua regia with an excess of chlorohydric acid, and a blade of tin dipped into the liquid when properly diluted, by which the antimony alone is precipitated, and perfectly, if care be taken to keep the liquid gently heated, with a slight excess of chlorohydric acid. § 1016. As compounds of antimony act as poisons on the animal economy, it occasionally falls to the lot of the medical man to in- vestigate their toxicological effects, the subject of investigation being sometimes food and sometimes portions of the human body. For this purpose, the suspected matter being diluted with water, a certain quantity of pure chlorohydric acid added, and the liquid boiled, 20 gm. of chlorate of potassa for every 100 parts of mat- ter are thrown into it by small quantities at a time, the liquid is filtered while boiling, and concentrated by evaporation. It is then introduced into a Marsh’s apparatus, as represented in fig. 260; when a glittering ring of metallic antimony forms in the tube fg, in which all the characteristic reactions of antimony may be observed. A blade of tin may also be plunged into the filtered liquid after it has been properly concentrated, when the antimony is deposited on the tin. The tin is dissolved in aqua regia, with the black precipi- tate which may have separated from it, after which it is evaporated with an excess of chlorohydric acid, redissolved with the same acid in a very dilute state, and the solution treated, as before, in Marsh’s apparatus. DETECTION OF ANTIMONY IN CASES OF POISONING. § 1017. Although antimony combines with a great number of metals, the only alloys used in the arts are those of antimony and lead for printers’ types, and those of antimony and tin for various purposes. Antimony combines readily with potassium and sodium, produc- ing alloys which decompose water at the ordinary temperature Avith disengagement of hydrogen gas, and which frequently detonate sud- denly when moistened with a small quantity of water or exposed to a damp atmosphere. An alloy of antimony and fused potassium is prepared by heating for several hours, in an earthen crucible, a mixture of 6 parts of tartar emetic and 1 of nitre, or equal parts of metallic antimony and black flux; when the metallic button ALLOYS OF ANTIMONY. 222 ANTIMONY. found at the bottom of the crucible will decompose water at the ordinary temperature, with disengagement of hydrogen. A finely divided alloy, which explodes when moistened with a drop of water, is obtained by heating for several hours in an earthen crucible, at a high temperature, 100 parts of tartar emetic and 3 parts of lamp- black. The crucible should be placed, after the calcination, under a well-dried bell-glass, which should be removed only when it is perfectly cool. This substance requires the most careful handling, as it frequently gives rise to fearful accidents by detonating spon- taneously. By fusing in an earthen crucible, at a strong white-heat, a mix- ture of 70 parts of metallic antimony and 30 of iron-filings, a very hard metallic globule is obtained, which on being filed emits sparks of fire. This substance is known, in the laboratory, under the name of Reaumur's alloy. METALLURGY OF ANTIMONY. § 1018. Wc have said that the sulphide is the only ore of anti- mony. It is first separated from its gangue by simple fusion, for which purpose the ore is placed in large crucibles P (fig. 556), ar- ranged in two rows in a furnace. Each crucible has, at its lower part, an aperture corresponding to an opening made in the benches on which it rests. Under the crucibles, and in the compart- ments D of the furnace, are earthen pots <5, in which the fused antimony is collected, while pine wood is burned on the grates Gr. Sometimes the ore is heated in a reverberatory fur- nace, when the fused sulphide runs into a cavity in the hearth, and flows outwardly into iron pots. The sulphide of antimony is then roasted in a reverberatory furnace, where it is converted into oxysulphide or glass of an- timony ; after which the roasted substance is pulverized, and then mixed with 20 per cent, of charcoal soaked in a strong solution of carbonate of soda. This mixture being calcined in crucibles, the oxide of antimony is reduced to the metallic state, while a portion of the sulphide is decomposed by the carbonate of soda and yields an additional quantity of metal. A globule of antimony, called Fig. 556. ANTIMONY. 223 r eg ulus of antimony, is found at the bottom of the crucibles, sur- mounted by an alkaline dross containing sulphide and oxide of anti- mony, and which may be used for the preparation of kermes mineral. Metallic antimony may also be obtained by decomposing sulphide of antimony by iron; but its quality is then inferior, as it contains a large proportion of iron; and although the latter may be sepa- rated by subjecting the substance to a partial roasting, a consider- able quantity of antimony must be oxidized in order to effect a complete separation of the iron. 224 URANIUM. Equivalent = 60 (750.0; O = 100). § 1019. Uranium* is prepared in the same way as magnesium ; that is, by decomposing its chloride by means of potassium, for which purpose a mixture of about 2 parts of protochloride of ura- nium and 1 of potassium is gently heated in a platinum crucible, the lid of which is fastened down by iron Avire. When the reaction, which ensues with lively incandescence, is terminated, the crucible is again heated in order to volatilize the greater portion of the potassium in excess, after which the crucible is allowed to cool, and the substance treated Avith Avater, Avhich, dissolving the chloride of potassium, leaves the uranium in the form of a black powder. Small plates of ura- nium are often found on the sides of the crucible, in Avhich case the metal possesses a lustre resembling that of silver, and a certain degree of malleability. Uranium is very combustible: it ignites in the air when heated above 392°, burning with great brilliancy, and being transformed into a deep-green oxide. It remains unchanged in the air at the ordinary temperature, and does not decompose cold water. It dis- solves Avith disengagement of hydrogen in the dilute acids, and pro- duces green solutions. It unites Avith chlorine with great disen- gagement of heat and light, forming a green volatile chloride. With sulphur it combines directly, and at a low temperature. « COMPOUNDS OF URANIUM WITH OXYGEN. § 1020. Two compounds of uranium with oxygen are known: A protoxide UO; A sesquioxide U303. Several intermediate oxides, which are regarded as compounds of the first two, are also known. Protoxide of uranium UO is prepared by decomposing the ses- quioxalate of uranium U303,C303 by hydrogen at a red-heat, when a brown powder remains, which must be preserved in an atmosphere of hydrogen, by hermetically sealing the ends of the tube in which the decomposition has been effected. The oxide is very pyrophoric, becoming feebly incandescent in the air, and being converted into a black powder, which is an intermediate oxide U40s, and the for- mula of which should probably be written 2U0,II303. The pro- toxide is obtained in a more aggregated form by decomposing the * Oxide of uranium was discovered in 1789, by Klaproth; while metallic ura- nium was isolated by M. Pdligot only as late as 1842. SALTS 225 double chloride of uranium and potassium by hydrogen, when the protoxide of uranium remains, after treatment with water, in the form of crystalline spangles which do not change in the air at the ordinary temperature.' Protoxide of uranium may also be obtained in the hydrated state by decomposing by ammonia the green solution of protochloride of uranium UC1; a flaky, reddish-brown precipitate being formed, which readily dissolves in acids. By heating protoxide of uranium in the air to a dull red-heat, it is converted into an oxide of a deep olive colour and a velvety ap- pearance, the composition of which is U304, or more probably, U0,U303, as by solution in acids a protosalt and a sesquisalt are formed. At a higher temperature this oxide is decomposed and changed into a black oxide 2U0,U303. The oxide of uranium has been long regarded as a metal, and called uranium. Sesquioxide of uranium U203, which is the base of the yellow salts of uranium, has not yet been isolated. When the sesqui- nitrate is decomposed by a properly regulated heat, an orange- coloured basic salt is first obtained, while on still increasing the temperature it loses a portion of its oxygen, while it at the same time parts with the last traces of its acid. By precipitating a solu- tion of a yellow salt of uranium by potassa or ammonia, a yellow precipitate is formed, which is a true uranate of the base which effected the precipitation. Hydrated sesquioxide of uranium is prepared as follows :—A solution of the yellow oxalate of uranium is exposed to the action of solar heat, which effects the disengage- ment of a mixture of carbonic acid and oxide, while a flaky preci- pitate of a violet-brown colour is formed. The precipitate rapidly absorbs the oxygen of the air while it is being collected on a filter, and is converted into a yellow substance, which is the hydrated sesquioxide U303+2H0. § 1021. Only a small number of protosalts of uranium are known, from the solutions of which ammonia and the alkalies throw down brownish black precipitates, which turn yellow by exposure to the air, being then converted into sesquioxide, which remains in com- bination with the alkali. Sulfhydric acid exerts no action on these salts, while the sulfhydrates yield black precipitates. The green salts of the protoxide of uranium are readily converted into yellow salts of the sesquioxide by oxidizing reagents; and nitric acid or chlorine effect the same change, even Avhen cold. Protosulphate of uranium is prepared by pouring sulphuric acid into a concentrated solution of green protochloride, heat being ap- plied to drive off the ehloroliydric acid. By treatment with water a liquid is obtained which deposits green crystals of the protosul- phate, of which the formula is U0,S03-f 4HO. PROTOSALTS OP URANIUM. 226 URANIUM. By adding oxalic acid to a solution of the green protochloridc, a greenish-white precipitate is obtained, which may be washed in in boiling water without dissolving, and consists of protoxalate of uranium, with the formula U0,Ca03+3II0. SESQUISALTS OF URANIUM. § 1022. The sesquioxide of uranium Us03 forms a great number of crystallizable salts, the peculiarity of whose composition distin- guishes them from salts formed by the other metallic sesquioxides. We have seen that, in all the neutral salts formed by a same acid, the ratio between the oxygen of the base and that of the acid is constant; being as 3:1 for the sulphates: the formula of the neutral sulphates are therefore RO,SOs for the protoxides, and R303,3S03 for the sesquioxides. The ratio being as 5 : 1 for the nitrates, RO,NOs is the formula of the protonitrates, and Ra03,3N05 that of the sesquinitrates. But, when the sulphate, or nitrate, of the sesquioxide of uranium is crystallized in any excess whatever of its respective acid, the crystallized salts always present the for- mula U203,S03 and U„03,N05. If, therefore, we admitted the general application of the law of composition of salts first laid down, these salts would be tri-basic salts, which would be very remarkable, inasmuch as they have crystallized in presence of a great excess of acid. In order to remove this anomaly, several chemists have sup- posed the sesquioxide of uranium to he a true protoxide, formed by the combination of one equivalent of oxygen with an already oxidized radical, which would present the composition of protoxide of ura- nium, and which they call uranyle. Sesquioxide of uranium being therefore, in their opinion, a protoxide of uranyle, they write its formula (2U0)0, and the salts of the sesquioxide of uranium are neutral salts of protoxide of uranyle (2U0)0,S03,(2U0)0,N()s, etc. etc. We shall have occasion to meet with several other com- pounds of uranium which may be cited in favour of this opinion. Solutions of the sesquisalts of uranium, or protosalts of uranyle, are of a beautiful yellow colour, and throw down with the alkalies yellow precipitates of uranates, in which the sesquioxide of uranium acts the part of a weak acid with powerful bases. The alkaline carbonates and carbonate of ammonia throw down granular yellow precipitates, which are double carbonates and dissolve in an excess of the reagent. Sulfhydric acid exerts no action on solutions of sesquisalts of uranium, while the sulfhydrates yield a brownish- yellow precipitate. Prussiate of potash gives a brownish-red pre- cipitate. Sesquinitratc of uranium, which is the most important of all the salts of this metal, is obtained directly from the ore of uranium. The principal minerals containing uranium are 'pitchblende and uranite. Pitchblende, which chiefly consists of oxide of uranium U0,U20u, and forms compact black masses, with a brilliant frac- SALTS, 227 ture, resembling pitch, occurs principally in Bohemia; while uranite, which is a double phosphate of the sesquioxide of uranium and lime (Ca0,2U303)Ph05+8H0, and forms yellow crystalline lamellae, with greenish reflections, is found in most abundance in the envi- rons of Autun. Bohemian pitchblende is the material which is always used for the preparation of the compounds of uranium. The mineral, being reduced to a fine powder, is levigated to separate the lighter earthy matter, and then treated with nitric acid, which readily attacks it; after which the solution is evaporated to dryness and treated with water, which leaves undissolved a brick-red residue, consisting of sulphate of lead and sesquioxide of iron combined with a certain quantity of arsenious acid; while the liquid, which is of a greenish- yellow colour, aft’ords after suitable evaporation a copious and con- fused crystallization of sesquinitrate of uranium. The sirupy mother liquid is decanted, and the crystals, after having been allowed to drain, are redissolved in water for the purpose of recrystallization. As the mother liquid still contains a considerable quantity of ses- quinitrate of uranium which cannot crystallize on account of the presence of foreign salts, it is diluted with water, and treated with a current of sulfhydric acid gas to precipitate the sulphides of cop- per, lead, and arsenic, after which the filtered liquid is again evapo- rated to dryness and treated with cold water, when a ferruginous deposit remains. The liquid then yields on evaporation an addi- tional quantity of crystallized sesquinitrate of uranium. The nitrate of uranium thus prepared undergoes a last purifica- tion by being placed in a flask with ether, in which it is consider- ably soluble, and from which, by evaporation of the ether, pure nitrate of uranium is deposited, which, after being redissolved in water, is again crystallized. Sesquinitrate of uranium forms beautiful, often very large, yellow crystals, which exhibit green reflections, like nearly all the sesqui- salts of uranium. Its formula is U303,N05+6H0, or (2U0)0, NOs + 6HO. It melts in its water of crystallization, with which it parts nearly wholly, yielding a crystalline mass after cooling. This salt is used for the preparation of all the other compounds of ura- nium : calcination converts it into oxide. Sesquisulphate of uranium, which is prepared by decomposing the nitrate by sulphuric acid, forms several crystallizable double sulphates. The formula of the double sulphate of uranium and po- tassa is U303,S03-f K0,S03-f 2IIO, and will be seen to possess no analogy with the alums. Sesquioxalate of uranium, being but slightly soluble in water, is precipitated when oxalic acid is poured into a solution of the sesqui- nitrate. The formula of the salt is U203,C203+8110, which should be written (2U0)0,Ca03-fi3II0, if the hypothesis of uranyle be admitted. 228 Sesquioxide of uranium communicates a clear yellow colour with beautiful green reflections to vitreous fluxes, and has been used for several years for colouring glass. URANIUM. § 1023. Two compounds of uranium with chlorine are known: The protochloride UC1 is obtained by subjecting a mixture of oxide of uranium and charcoal to the action of chlorine. The mix- being introduced into a tube of hard glass, so as to half fill it, and dry chlorine passed through the end containing the mixture, the latter is heated to redness, when the protochloride of uranium ap- pears in the form of red vapours, which condense in the cold part of the tube in very brilliant and nearly black octahedric crystals. The chloride, which is very susceptible of moisture, dissolves readily in water, and produces a deep-green solution. If the protochloride be heated in a glass tube in a current of hy- drogen gas, it loses a portion of its chlorine, and is converted into a slightly volatile, deep brown product, of which the formula is U4C13. This chloride dissolves readily in water, and yields a purple solution, which soon turns green by disengaging hydrogen gas. COMPOUNDS OF URANIUM WITH CHLORINE. Oxychloride of Uranium, or Chloride of Uranyle. § 1024. By heating protoxide of uranium in a current of chlorine, a yellow, very fusible, and but slightly volatile crystalline compound is formed, which shows the formula U302C1, or (2UO)Cl, if it be regarded as protochloride of uranyle. When heated with potassium it loses only its chlorine, and the residue consists of the protoxide (2UO), or uranyle. This compound is soluble in water, with a yel- low colour, and forms crystallizable compounds with chloride of potassium and chlorohydrate of ammonia. The formulae of these double chlorides are (2U0)C1+KC1+2H0 and (2U0)C1+NII3, HC1+2HO. DETERMINATION OF URANIUM; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 1025. Uranium is determined as protoxide, for which purpose the superior oxides are reduced by hydrogen at a red-heat. It is sometimes weighed in the state of the black oxide 2UO,UaOs, in which case it is sufficient to roast the oxides in the air and calcine at a strong red-heat. Sesquioxide of uranium is generally precipi- tated by ammonia, which yields a yellow precipitate of uranate of ammonia; and as the precipitate is apt to pass through a filter, this inconvenience is remedied by adding a certain quantity of sal-am- moniac to the liquid. Sesquioxide of uranium is separated from the alkalies by am- monia, and from baryta by sulphuric acid, which precipitates the latter base; while it is separated from lime and strontian by evapo- ANALYTIC DETERMINATION. 229 rating the liquid with sulphuric acid, and treating it with alcohol, which dissolves only the sesquisulphate of uranium. In order to separate iron from uranium, the former is brought to the state of sesquisalt, and a large excess of carbonate of ammonia is added, which, precipitating the sesquioxide of iron, maintains the uranium in solution. The sesquioxide of uranium may be separated from alumina, and the oxide of chrome by the same process. The separation of uranium from magnesia and the oxides of manganese, zinc, cobalt, and nickel is founded on the solubility of sesquioxide of uranium in bicarbonate of potassa : an excess of bi- carbonate of potassa is poured into the acid liquid, when a soluble double carbonate of sesquioxide of uranium and potassa is formed, while the carbonates of the other metals are precipitated. In order to separate uranium from cadmium, tin, lead, bismuth, and antimony, it suffices to pass a current of sulfhydric acid gas through the acid solution, by which means all these metals are pre- cipitated, while the uranium alone remains in the liquid. 230 TUNGSTEN. Equivalent = 95 (1187.5; 0 = 100). § 1026. Tungsten* is obtained by heating at a strong red-heat tungstic acid in a current of hydrogen gas in a porcelain tube, when the metal remains in the form of a deep gray powder. It is obtained in a more aggregated form by heating tungstic acid in a “brasqued” crucible in a forge-fire, in which case the metal is in a consistent, but not fused mass, which, when filed, assumes a metallic lustre. Its density is considerable, being about 17.5. It does not oxidize in the air at the ordinary temperature, but at a red-heat is converted into tungstic acid, into which it is also converted when brought at a red-lieat into contact with water, which it decomposes. Chlorohydric acid does not act sensibly on metallic tungsten, while nitric acid attacks it actively, and transforms it into tungstic acid, which effect is also produced by sulphuric acid, when concentrated and hot. COMPOUNDS OF TUNGSTEN WITH OXYGEN. § 1027. Tungsten forms two well-defined compounds with oxy- gen : a binoxide WOa and tungstic acid W03. Tungstic acid, which is the most important of these compounds, is used in the preparation of the other compounds of tungsten. Tungsten occurs in nature as tungstic iron, or wolfravi,f which is a double tungstate of iron and manganese, of the general formula (Fe0,Mn0)W03; the formulae of the minerals from the various localities which have hitherto been analyzed being 2(Fe0,W03)-f 3(Mn0,W03), or 4(Fe0,W03)+Mn0,W03. Wolfram, which is found in large blackisli-brown crystals in the primitive rocks, in which it frequently accompanies oxide of tin, is found in many places, particularly in the environs of Limoges. In order to obtain tungstic acid from wolfram, the mineral is treated with aqua regia, which dissolves the iron and manganese as chlorides, while the tungsten remains in the state of insoluble tungstic acid. It is col- lected on a filter, and, after being well-washed, is treated by a solu- tion of ammonia; when tungstate of ammonia is formed, which dis- solves and separates from the quartzose gangue and the untouched ore. The solution yields small prismatic crystals of tungstate of * Scheele discovered tungstic acid, while the brothers Elhujart first separated the metal from it. -j- In German, the metal is called wolfram, after the mineral; or scheel, after its discoverer; and from the name of wolfram, the symbol of tungsten, W, is derived. — IK. L. F. OXIDES AND SALTS. 231 ammonia, which, when heated in the air, is converted into tungstic acid. Tungstic acid is a bright-yellow powder, insoluble in water and the acids, but readily soluble in alkaline liquids and ammonia when it lias not been calcined. By heating tungstic acid at a moderate temperature in a cur- rent of hydrogen gas, a brown powder of the binoxide WOs re- mains, the best method of preparing which consists in fusing 1 part of wolfram and 2 of carbonate of potassa in a platinum crucible, and treating the mass with water; after which the filtered liquid containing tungstate of potassa in solution is evaporated to dryness with a J part of sal-ammoniac. The calcined matter being treated with water, the oxide of tungsten WOa remains in the form of a black powder, which changes readily into tungstic acid by heating it in the air. When heated with a concentrated solution of caustic potassa, it decomposes water and is converted into tungstic acid. Binoxide of tungsten forms with soda a compound of the formula NaO,2WOa, which is obtained by heating bi-tungstate of soda in a current of hydrogen gas, and purified by treatment, first with clilo- rohydric acid, and then with a solution of potassa, which removes the tungstic acid in excess. The substance forms small cubic crys- tals of a beautiful golden yellow colour. When tungstic acid is subjected to a partial reduction, a blue oxide is obtained, which is regarded as a compound of the two pre- ceding oxides, having the formula W02,W03. For this purpose, tungstate of ammonia is decomposed in a close tube, or a blade of zinc is plunged into a liquor containing both tungstic and cliloro- hydric acids. TUNGSTATES. § 1028. No salts formed by a combination of the oxides of tung- sten with acids are known, while tungstic acid has been obtained combined with powerful bases. The tungstates of potassa, soda, and ammonia are soluble, while those of the other bases are inso- luble. These salts are easily recognised by the residue of tungstic acid which they leave on being decomposed by acids; but in order to obtain a perfect decomposition it is often necessary to boil the tungstate with concentrated acid. Sulphurous acid does not de- compose the salts of tungsten, and they are not precipitated by sulfhydric acid and the alkaline sulfhydrates. The formulae of the tungstates of potassa, soda, and ammonia, obtained by dissolving tungstic acid, prepared in the humid way, in alkaline solutions, are K0,W03+5H0, Na0,W03+2H0, (NH3H0),W08. Tungstic acid appears to be able to exist under several modifica- tions, corresponding to different degrees of saturation. 232 TUNGSTEN. § 1029. Non-calcined tungstic acid dissolves readily in the sulf- hydrates of the alkaline sulphides, forming sulphotungstates of an alkaline sulphide. By adding an acid to these solutions, sulpho- tungstic acid WS3 is thrown down in a brown precipitate. Sulphotungstic acid is decomposed by heat, leaving as a residue bisulphide of tungsten WS3, in the form of a black powder, which may also be obtained by distilling 1 part of tungstic acid with 5 or 6 times its weight of sulphide of mercury. COMPOUNDS OF TUNGSTEN WITH SULPHUR. § 1030. Metallic tungsten unites directly with chlorine, with dis- engagement of light; and if the experiment be made in a heated glass tube, .traversed by a current of chlorine, the cold portions of the tube become covered with small deep-red needles of bichloride of tungsten WC12, which is very fusible and volatile. Water de- composes it into binoxide of tungsten which is precipitated, and chlorohydric acid. By heating sulphotungstic acid in a current of chlorine, a tri- chloride of tungsten WCL is obtained, which sublimes in the form of small red crystals. This chloride is decomposed by water into tungstic and chlorohydric acids. If gaseous chlorine be passed over tungstic acid, small yellow needles, of the formula W02C12, corresponding in composition to chlorochromic acid (§ 884), sublime in the cooler parts of the tube. COMPOUNDS OF TUNGSTEN WITH CHLORINE. DETERMINATION OF TUNGSTEN; AND ITS SEPARATION FROM THE METALS PREVIOUSLY STUDIED. § 1031. Tungsten is always determined in the state of tungstic acid. In order to separate it from other metals, either the insolubility of tungstic acid in water and the acids, or its solubility in the alka- line sulfhydrates, is relied on. The insolubility of tungstic acid in dilute acids insures its sepa- ration from the alkaline, alkalino-earthy, and earthy metals, from manganese, iron, chrome, cobalt, nickel, zinc, cadmium, lead, cop- per, mercury, and silver; while its solubility in ammonia allows its separation from iron, chrome, tin, bismuth, etc. Lastly, its sepa- ration from the metals the sulphides of which are not soluble in the sulfhydrates; that is, from iron, zinc, manganese, copper, lead, silver, etc. etc., is effected by its solubility in the alkaline sulf- hydrates. 233 MOLYBDENUM. Equivalent = 46 (575.0; 0 = 100). § 1032. Molybdenum* is obtained by heating in a porcelain tube any oxide of the metal in a current of hydrogen gas; when the molybdenum remains in the form of a gray powder, which, when burnished, assumes a metallic lustre. Molybdenum is obtained in a more aggregated form, by reducing the oxide in a “brasqued” crucible in a forge-fire; and if the temperature be raised as high as possible, small fused masses, having a dead silvery hue, and the density of which is then 8.62, are sometimes obtained. Molybde- num is so easily oxidizable, that that obtained by reduction by hy- drogen is entirely converted, when exposed to the air for some time, into a brown powder of the oxide; and by heating the metal in the air it becomes incandescent, and is transformed into molyb- dic acid. Chlorohydric and dilute sulphuric acid do not attack molybdenum, while nitric acid, on the contrary, acts very power- fully upon it, converting it into molybdic acid. COMPOUNDS OF MOLYBDENUM WITH OXYGEN. § 1033. Molybdenum forms three compounds with oxygen the protoxide MoO and the hinoxide MoOa, which are both bases form- ing salts; and a third oxide MoOs, which is an acid. Molybdic acid Mo03, which is the most important compound of molybdenum, serves for the preparation of the other combinations of this metal. Molybdenum is chiefly found in nature in the state of sulphide MoSa, forming gray spangles of a metallic lustre, and resembling native graphite, like which substance it leaves gray marks on paper. It occurs in the granitic rocks, frequently ac- companying ores of tin, and is principally found in Bohemia and Sweden. After treating the sulphide of molybdenum with aqua regia, which converts the sulphur into sulphuric acid, and the mo- lybdenum into molybdic acid, the liquid is evaporated to dryness and the residue treated with ammonia, which dissolves the molybdic acid during the evaporation of the liquid. The molybdate of am- monia, which separates in crystals, is converted into molybdic acid when heated in the air. Molybdic acid may also be separated by pouring chlorohydric acid into a solution of a molybdate. Molybdic acid is a white powder, which sublimes at a strong red- heat in white crystalline spangles; which operation can be well * Discovered by Scheele, in 1778. 234 MOLYBDENUM. performed only in a current of gas. Although molybdic acid is very feebly soluble in water when freshly precipitated by an acid, it readily dissolves after calcination. It is easily soluble in the acids. Protoxide of molybdenum MoO is obtained by pouring chloro- liydric acid into the solution of an alkaline molybdate, until the molybdic acid, which is at first precipitated, is redissolved, when a blade of zinc is plunged into the liquid, which is turned black, after passing through the shades of blue and brownish-red successively. Ammonia is then carefully added to the liquid containing proto- chloride of molybdenum and chloride of zinc ; and, as the protoxide of molybdenum is precipitated first, the addition of ammonia is ar- rested as soon as the liquid becomes clouded. The precipitate should be washed rapidly, and protected as much as possible from the air, because it is a great absorbent of oxygen. Binoxide of molybdenum Mo03is prepared by decomposing molyb- date of ammonia by heat, protected from the air, or by calcining a mixture of molybdate of soda and sal-ammoniac. This oxide, a red- dish-brown crystalline powder, forms a reddish-brown hydrate, which resembles the hydrate of sesquioxide of iron. By adding ammonia to the blue liquid obtained by partially re- ducing by zinc a chlorohydric solution of molybdic acid, a blue pre- cipitate is formed, which is a saline oxide resulting from the com- bination of molybdic acid with binoxide of molybdenum. SALTS FORMED BY THE OXIDES OF MOLYBDENUM. § 1034. Both the protoxide and binoxide of molybdenum form salts by combining with acids. These two classes of salts present the following reactions:—The alkalies and ammonia yield brown precipitates, while the alkaline carbonates afford the same coloured precipitate, which dissolves in a large excess of the carbonate of ammonia. Sulf hydric acid precipitates them completely after some time as a black deposit, the same precipitate being formed with the alkaline sulf hydrates; in an excess of which it is soluble. The salts of the protoxide im- part to their solutions a brown colour approaching a black, while those of the sesquioxide produce a deep red colour. Molybdates. § 1035. Molybdic acid forms two series of salts : neutral molyb- dates RO,Mo03 and bimolybdates RO,2Mo03; the former of which are obtained by dissolving molybdic acid in an excess of alkali, and the latter by boiling a solution of an alkali or an alkaline carbonate with an excess of molybdic acid. The bimolybdates generally crys- tallize during the cooling of the liquid. VANADIUM. 235 COMPOUNDS OF MOLYBDENUM WITH CHLORINE. § 1036. Metallic molybdenum combines directly with chlorine, yielding at a high temperature a red vapour, which condenses in the form of crystals closely resembling those of iodine. The for- mula of the chloride, which dissolves freely in water, is MoCla. A protochloride of molybdenum is obtained by dissolving the hy- drated protoxide in chlorohydric acid. By passing chlorine over heated binoxide of molybdenum, small and very soluble spangles are sublimed, the formula of which is MoOaCl, corresponding to chlorochromic and chlorotungstic acids. VANADIUM. Equivalent = 68.6 (857.5; 0 = 100). § 103T. Vanadium* is an exceedingly rare metal, found in very small quantities in certain Swedish iron-ores, and also occur- ring in the state of vanadate of lead. Vanadium is obtained by heating vanadic acid with potassium in a platinum crucible ; when active reaction takes place, after which the substance is treated with water to dissolve the potassa, and the metal remains in the form of a black powder. It may also be prepared by decomposing chloride of vanadium by ammoniacal gas at a red-heat, in which case it presents the appearance of a flaky, silvery-white mass. § 1038. Vanadium forms three compounds with oxygen: the protoxide VO, the binoxide V03, and vanadic acid V03. Vanadic acid is readily obtained from the native vanadate of lead, by heating the mineral with nitric acid, when vanadic acid is set free, while nitrate of lead is formed. It is treated with water, which leaves the vanadic acid. The acid is dissolved in ammonia, and the vanadate of ammonia crystallized by the evaporation of the liquid, after which it is converted into vanadic acid by calcina- tion in the air. Vanadic acid is an orange-coloured or broAvn powder, nearly insoluble in water. It is reduced to a lower degree of oxidation by many reducing substances, such as alcohol, sugar, oxalic and sulphurous acids. It dissolves in cold chlorohydric acid, while, if heat be applied, chlorine is disengaged, and the solution contains chloride of vanadium VCl3. By pouring carbonate of po- tassa into this solution, hydrated binoxide of vanadium is precipi- tated as a gray flaky substance, which dissolves readily in acids, and produces crystallizable salts, of which the solutions are blue. * Vanadium was discovered in 1830, by M. Sefstrom, a Swedish chemist. 236 COPPER. By heating vanadic acid in a current of hydrogen gas, a black powder of protoxide of vanadium YO is obtained, no saline com- pounds of which are known. If a mixture of vanadic acid and charcoal be heated in a current of chlorine, a volatile chloride VC13 is formed, which condenses as a yellow liquid. It boils at a few degrees above 212°, and exhales copious fumes in the air. COPPER. Equivalent == 31.7 (396.25; 0 = 100). § 1039. Copper has been known from the earliest times. Although it sometimes occurs in the native state, it exists more frequently in combination with oxygen, sulphur, or arsenic. Some salts of the oxide of copper, chiefly carbonates, are also found. Some kinds of commercial copper are nearly pure; the Russian containing only a trace of iron. Native copper is often crystal- lized in the form of small, regular octahedrons, which form it also assumes when precipitated slowly from its solutions by galvanic processes, or on being allowed to cool slowly after fusion in a small quantity in a crucible, the liquid portion having been poured off. Chemically pure copper is obtained by reducing pure oxide of cop- per heated in a tube by means of hydrogen, the reduction taking place at a temperature below a red-heat, and leaving the metal in the form of a red powder, which assumes a brilliant metallic lustre under the burnisher. Copper has a characteristic red colour, and becomes transparent when reduced to a very thin pellicle; in which case it displays, by transmitted light, a beautiful green colour. Coppery pellicles suit- able for the experiment are obtained by reducing by hydrogen, in a heated glass tube, a small quantity of oxide or chloride of copper ; when a very thin layer of metallic copper, which displays a red colour by reflected, and a beautiful green by transmitted light, is deposited in certain parts of the tube. Copper possesses a sufficient degree of malleability to allow its being hammered into thin sheets or drawn out into very fine wire; and at the same time is considerably tenacious, as it requires a weight of 140 kilog. to break a wire of 2 mm. in diameter. The density of copper varies from 8.78 to 8.96, according to the greater or less degree of aggregation it has received during its manufacture. By rubbing, copper acquires a disagreeable smell and a peculiar taste. It fuses at a strong red-heat, and at a white-heat gives off vapours which burn with a green flame in the air. COMPOUNDS OF COPPER AVITII OXYGEN. 237 At the ordinary temperature copper does not oxidize in dry air, but soon changes in a moist atmosphere, especially if acid vapours be present, becoming covered with a green substance commonly called verdigris. A blade of copper, moistened by an acid, and exposed to the air, combines with the oxygen of the air, and first produces a neutral salt, which after some time is converted into a basic salt. A blade of copper also oxidizes in the air when moist- ened with an ammoniacal solution; and dilute solutions of sea-salt attack copper very powerfully, while concentrated solutions exert less influence on it. Copper decomposes aqueous vapour at a strong white-heat, while hydrogen gas is disengaged. A concentrated solu- tion of chlorohydric acid attacks finely divided copper with disen- gagement of hydrogen, while it scarcely affects the metal in a solid form. Copper does not decompose water in the presence of pow- erful acids : concentrated sulphuric acid dissolves it with disengage- ment of sulphurous acid; and it dissolves readily in cold nitric acid of any degree of concentration, with disengagement of deutoxide of nitrogen. COMPOUNDS OF COPPER WITH OXYGEN. § 1040. Copper forms four compounds with oxygen: 1. The suboxide Cu30,* or red oxide. 2. The protoxide CuO, or black oxide. 3. The binoxide Cu02. 4. Cupric acid, the composition of which is not yet known. The first two compounds are basic, and form well-defined and crystallizable salts, while the third is an indifferent oxide; and lastly, the fourth is an acid. Suboxide of Copper CuaO. § 1041. Suboxide of copper is found in nature in masses of a beautiful red colour, possessing occasionally a vitreous lustre, and sometimes consisting of beautiful red crystals. It may be obtained artificially by several processes :—1st, by heating in an earthen crucible equivalent parts of black oxide of copper CuO and finely powdered metallic copper; which mixture aggregates when fused at a high temperature; 2d, by heating in a crucible a mixture of chlo- ride of copper Cu2Cl with carbonate of soda, and then treating the substance with water, which dissolves the chloride of sodium and ex- cess of carbonate of soda, leaving the suboxide of copper in the form of a deep red crystalline powder; 3d, by adding to a solution of a salt of copper, for example, the sulphate CuO,S03, sugar and potassa, until the oxide of copper, which is at first precipitated, is * The name of protoxide of copper is often given to the suboxide Cu20, and that of binoxide of copper to the oxide CuO. We shall not adopt this nomenclature because it does not agree with that which we have thus far adopted. 238 COPPER. redissolved, and by then boiling the liquid; when suboxide of copper is deposited in the form of small bright-red crystals. Hydrated suboxide of copper is obtained by adding potassa to a solution of protochloride of copper, in the form of a yellow powder, which soon absorbs oxygen from the air, and which, when dried in vacuo, presents the formula 4CuaO-fHO. Hydrated suboxide of copper dissolves in ammonia without colouring the liquid, but by its rapid absorption of oxygen from the air soon changes the colour of the solution to a beautiful blue. Suboxide of copper imparts a beautiful red colour to fluxes (§ 702). When heated with concentrated acids it is generally decomposed into protoxide of copper CuO which dissolves, and metallic copper which is separated. Protoxide of Copper CuO. § 1042. On heating metallic copper in the air, its surface first becomes covered with suboxide CuaO, wdiich subsequently changes into the black oxide CuO. Although protoxide of copper is often prepared by roasting copper turnings, or better still, the very finely divided copper which remains after the calcination of the acetate with access of air, it is obtained more readily by decomposing the nitrate by heat, w'hen the oxide remains in the form of a black powT- der, which rapidly condenses the moisture of the atmosphere. When caustic potassa is poured into the solution of a protosalt of copper, a grayish-blue precipitate of hydrated protoxide is formed, the water of which is readily driven off by heat: it suffices to boil the solution in which it has been precipitated to convert it into a black powder of anhydrous oxide. Hydrated protoxide of copper dissolves in ammonia, producing a solution of a slightly purple-biue colour, called celestial water. Deutoxide of Copper. § 1043. This oxide is prepared by treating the hydrated prot- oxide of copper with oxygenated water, when the blue matter is changed into a brownish-yellow substance, from which a slight ele- vation of temperature easily abstracts one-half of its oxygen. Cupric Acid. § 1044. An intimate mixture of very finely divided copper, po- tassa, and nitre, heated to redness and then treated with water, yields a blue solution which appears to contain a combination of an oxide of copper containing more oxygen than the preceding with potassa. This compound, however, is so evanescent that, if the liquid be heated, oxygen is disengaged, and the copper is precipi- tated in the state of black oxide CuO. SALTS 239 § 1045. The salts of the suhoxide of copper are obtained by dis- solving hydrated suboxide in dilute acids, which, when they are con- centrated, decompose the suboxide into metallic copper which sepa- rates, and protoxide which combines with the acids. A subsulphite of copper Cu30,S0a, is prepared by decomposing a solution of protosulphate of copper CuO,S03 by a solution of sul- phite of soda, when an orange precipitate is formed which is con- verted, by boiling, into a red crystalline powder. When acetate of copper is distilled, a small quantity of a white sublimate, consisting of sub-acetate of copper, is found in the upper part of the retort. The soluble subsalts of copper produce colourless solutions, from which alkalies throw down an orange-yellow precipitate. Ammo- nia gives the same reaction, but an excess of the reagent redissolves the precipitate, producing a colourless liquid which soon turns blue in the air. Sulfhydric acid throws down a black precipitate of these salts, for the study of whose reactions the subchloride CuCl is ex- actly suitable. SALTS FORMED BY THE SUBOXIDE OF COPFER CuaO. SALTS FORMED BY THE PROTOXIDE OF COPPER CuO. § 1046. These salts, which are obtained by dissolving protoxide of copper, or better still, its hydrate or its carbonate, in acids, are blue or green, when they contain water of crystallization, while in the anhydrous state they are of a dirty white, when the acid is colourless, and their solutions are blue or green. They exhibit the following characteristic reactions: Caustic potassa and soda yield a grayish-blue precipitate of hy- drated protoxide, which is converted into a brown precipitate by boiling. The blue precipitate, which is insoluble in. weak alkaline liquids, dissolves with a blue colour in the latter when they are con- centrated. Ammonia throws down the same precipitate, while an excess of the reagent dissolves the precipitate and produces a beautiful blue solution, which then contains a double salt of copper and ammonia, from which caustic potassa precipitates oxide of copper. Sulfhydric acid and the sulfhydrates throw down black precipi- tates, which are insoluble in an excess of sulf hydrate. Prussiate of potash forms, with protosalts of copper, a chestnut- brown precipitate, which assumes a purplish shade when the precipi- tate is very weak. The test is a very delicate one, and will detect the presence of the smallest quantities of copper in a solution. Iron and zinc precipitate metallic copper in the form of a brown powder, which, when burnished, assumes the metallic lustre and ordinary appearance of copper. Protoxide of copper turns borax, and in general all vitreous 240 COPPER. fluxes, green. If the glass be heated in the reducing portion of the flame, it acquires a beautiful red colour, produced by the reduc- tion of the protoxide of copper CuO into the suboxide Cu30. Sulphate of Copper. § 1047. Sulphate of copper is found in commerce, where it is known by the name of blue vitriol, in which state it generally con- tains variable quantities of sulphate of iron. It may be obtained in a state of purity by treating copper of the first quality Avith sul- phuric acid diluted Avith one-half its Aveight of Avater; Avhen sulphur- ous acid is disengaged, and sulphate of copper is formed which contains only a trace of sulphate of iron. It is evaporated to dry- ness, and, toward the close of the evaporation, a feAV drops of nitric acid are added, which convert the iron into sesquioxide. By dis- solving it in water the greater portion of the iron remains' in the state of an anhydrous basic sesquisulphate; when, after boiling the liquid Avith a small quantity of the hydrate or carbonate of the protoxide of copper, Avhich precipitates the least traces of iron, the liquor is crystallized. Sulphate of copper is soluble in 4 parts of cold and 2 parts of boil- ing Avater, and crystallizes at the ordinary temperature in beautiful blue crystals, which belong to the sixth system, and of Avhicli the formula is CuO,SOs+5HO. They are isomorphous with those pro- duced by protosulphate of iron Avhen crystallized at a temperature of about 40°, and which likeAvise contain 5 equiv. of water. When these tAvo sulphates are mixed together, and the compound solution is crystallized, crystals are deposited containing the tAvo sulphates in different proportions, according to the respective quantities of the salts in the solution. A crystal of sulphate of copper may even be made to groAV at pleasure, in a solution of sulphate of iron. The crystal then increases by the superaddition of layers of sulphate of iron, which are easily distinguished by their colour. The same crystal, suspended in a solution of sulphate of copper, becomes covered with layers of this latter sulphate, without any remarkable change in its external appearance. Sulphate of copper readily parts by heat with 4 equiv. of Avater, but retains the fifth Avith more tenacity. It is entirely decomposed at a high temperature, into oxide of copper Avhich remains, and a mixture of sulphurous acid and oxygen which is disengaged. Sulphate of copper is manufactured in various Avays; and a cer- tain quantity of this salt is obtained in copper furnaces. When sulphuretted copper ores or cupreous matts, are roasted, and the roasted matter is sprinkled with Avater, a certain quantity of the sulphates of iron and copper is dissolved, and separates by crystal- lization. The sulphate of copper thus obtained, ahvays contains a large proportion of sulphate of iron. Large quantities of sulphate of copper are manufactured from the SALTS. 241 copper sheathing of ships which has been rendered useless by the corrosive action of salt water. The copper is heated to a dull red- heat in a reverberatory furnace, and sulphur thrown in, the doors of the furnace being previously closed, when the sulphur attacks the surface of the copper, covering it with sulphide of copper Cu2S, after which it is roasted, and air allowed to enter the furnace freely. A portion of the sulphur is then disengaged in the state of sulphur- ous acid, while another portion changes into sulphuric acid, and forms a basic protosulphate of copper. The sulphatized sheets are then placed in large boilers filled with water, to Avhich a certain quantity of sulphuric acid has been added, when neutral protosul- phate of copper dissolves, and is crystallized by evaporation as soon as the liquid contains a sufficient quantity of it. This process is repeated until the sheets of copper have disappeared. Large quantities of sulphate of copper have been obtained in the refining of old silver coin, as we shall mention hereafter. If sulphate of copper be dissolved in a hot solution of ammonia, a beautiful blue solution is obtained, which deposits on cooling deep blue crystals, the composition of which is represented by the formula CuO,Sbs+2NHs+HO. By digesting hydrated oxide of copper with a solution of proto- sulphate of copper, a green powder, consisting of a hydrated basic sulphate of copper Cu0,S03+2Cu0 + 3H0 is obtained. Analo- gous basic sulphates are precipitated when solutions of sulphate of copper are incompletely precipitated by the alkalies. Sulphate of copper forms with the alkaline sulphates double salts which are readily crystallizable, and also produces double sulphates, of various proportions, with the sulphate of magnesia, and with those of the protoxides of iron, zinc, nickel, etc., which are all iso- morphous. These double sulphates, crystallized at the ordinary temperature, contain 5 equiv. of water when the sulphate of copper predominates, and 7 equiv. of water, on the contrary, when the other metallic sulphate is prevailing. In both cases, the sulphates are isomorphous whenever they contain the same quantity of water. Nitrate of Copper. § 1048. This salt is prepared by dissolving copper in dilute nitric acid, when the liquid yields on evaporation beautiful blue crystals, which contain 8 or 6 equiv. of water, according to the temperature at which the crystallization has been effected. It is used in dyeing. The influence of heat changes nitrate of copper into the green basic nitrate 4CuO,NOs, and subsequently decomposes it at a more elevated temperature, leaving protoxide of copper. The same basic nitrate is obtained by precipitating the neutral nitrate of ammonia. Carbonates of Copper. § 1049. By adding a solution of an alkaline carbonate to a solu- 242 COPPER. tion of sulphate of copper, a bright blue gelatinous precipitate is obtained, which, after some time, changes into a green powder, the composition of which is represented by the formula 2CuO,COa-f-HO; the blue gelatinous precipitate appearing to differ from it only in containing more water. By boiling the liquid with the precipitate, the latter is converted into a brown powder of anhydrous protoxide of copper. The green carbonate of copper is used in oil-painting, under the name of mineral green. A liydrocarbonate of copper, of the formula Cu0,C03-)-Cu0,II0, called malachite, is found in nature in the form of green concrete masses, which are often very compact and of considerable size, and are fashioned into ornamental objects, such as vases, shafts of columns, and table and chimney tops, which are of great value. When polished they display veins of different shades of colours, which are produced by the mammillary structure of the material, and impart a very beautiful appearance to the polished surfaces. Malachite is sufficiently abundant in Siberia to be worked as an ore of copper. Another liydrocarbonate of copper, of which the formula is 2CuO,COa-f CuO,lIO, and which yields fine blue crystals, also occurs in nature, which substance existed in great abundance in the mines of Chessy, near Lyons, where it was long smelted as an ore of copper. When finely powdered it is of a beautiful blue colour, in which state it is used in the manufacture of coloured wall-paper, and is called mountain blue, or native blue ashes, (bleu de montagne, or ccndrcs bleues naturelles.) Artificial blue ashes, of a more brilliant shade than the native product, are made in En- gland, by a process which is kept secret. Arsenite of Copper. § 1050. Arsenite of copper, which is used in oil-painting, under the name of Scheele's green, is prepared by dissolving 3 kilog. of carbonate of potassa, and 1 kilog. of arsenious acid in 14 litres of water, and pouring the solution, by small quantities at a time, into a boiling solution of 3 kilog. of sulphate of copper in 40 litres of water, the solutions being stirred constantly during the precipita- tion. The shade of colour is modified by varying the proportions of arsenious acid. Silicates of Copper. § 1051. By means of fusion the oxide of copper combines in all proportions with silicic acid, forming green vitreous substances. A crystallized silicate of copper, called dioptase by mineralogists, is found in nature, and presents the formula 3Cu0,2Si03+31I0. Acetates of Copper. § 1052. By dissolving protoxide of copper in acetic acid, a green liquid is obtained, which, when evaporated at a proper temperature, SULPHIDE. 243 deposits beautiful green crystals of the formula Cu0,C4II30s+H0, and which are soluble in 5 parts of boiling water. It is known in commerce by the name of verdigris, and is manufactured by dis- solving the basic acetate of copper in vinegar. When the salt crystallizes at a low temperature, the crystals are blue, and present the formula CuO,C4H3Os+5HO. A basic acetate of copper is prepared in the South of France by allowing sheets of copper, moistened with vinegar or brought into contact with the grape mash which is undergoing the acid fermenta- tion, to oxidize in the air. The copper sheets become covered with a greenish-blue coat, which is scraped off from time to time, and of which the formula is Cu0,C4tI303-f CuO,IlO-f 5IIO. If it be treated with water, insoluble crystalline spangles of the formula 3Cu0,C4Hs03 separate, while a mixture of neutral acetate CuO, C4H303 and basic acetate 3Cu0,2C4II303 dissolves. A basic acetate of copper is made at Grenoble, by exposing sheets of copper moistened with vinegar in hot stoves. This sub- stance appears to be a mixture of the two sub-acetates 3Cu0,2C4II303 and 3Cu0,C4II303. A colour which is a compound of acetate and arsenite of copper Cu0,C4II303+3(2Cu0,As03) is likewise used in oil-painting, under the name of Schweinfurt green, and is prepared by mixing boiling solutions of equal parts of arsenious acid and acetate of copper, and boiling the mixture for some time. COMPOUNDS OF COPPER WITH SULPHUR. § 1053. Copper burns actively in the vapour of sulphur (§ 306), while a sulphide of copper Cu2S corresponding to the suboxide Cu30 is formed. This sulphide fuses more easily than metallic copper, and becomes crystalline on cooling: it is sometimes found in copper furnaces, crystallized in regular octahedrons. It is prepared in the laboratory by heating a mixture of 3 parts of sulphur and 8 of cop- per turnings, grinding the substance obtained again to powder, and reheating with sulphur. This sulphide of copper exists in nature, and sometimes forms beautiful crystals, which are sufficiently soft to be cut with a knife. The sulphide of copper CuS corresponding to the protoxide CuO cannot be prepared by the humid way, by decomposing the solution of a protosalt of copper by sulfhydric acid or a sulf hydrate, as the black powder thus obtained soon changes in the air. In analyses, it is necessary to wash it with water containing a small quantity of sulfhydric acid. The sulphide of copper CuS, when heated, parts readily with one-half of its sulphur, and is converted into the sulphide CuaS. Compounds of sulphide of copper CuaS and sulphide of iron FeaSa in very various proportions are found in nature, constituting mine- rals which are called copper pyrites, pyritous copper, and variegated 244 COPPER. copper, according to their external mineralogical characters, which frequently agree with their chemical composition. These minerals are very important, as they are the most common ores of copper, and furnish the largest proportion of this metal. COMPOUND OF COPPER WITH ARSENIC. § 1054. Copper, heated in a vapour of arsenic, combines readily with a small quantity of this substance, becoming white and very brittle; but hitherto no definite compound of these substances has been obtained. COMPOUND OF COPPER WITH PHOSPHORUS. § 1055. A gray and very brittle phosphuret of copper, contain- ing about 20 per cent, of phosphorus, is formed when very finely divided copper is heated in the vapour of phosphorus. A definite compound of copper and phosphorus Cu2Ph is obtained by decom- posing neutral phosphate of copper by hydrogen at a low tempera- ture. Phosphurets of copper are also obtained by the humid way, by passing a current of phosphuretted hydrogen gas through a solu- tion of sulphate of copper. COMPOUND OF COPPER WITH NITROGEN. § 1056. A nitride of copper of the formula Cu6N is obtained by heating, at a temperature of 509°, oxide of copper CuO in a cur- rent of dry ammoniacal gas, when the substance is treated with a solution of ammonia, which dissolves the oxide of copper in excess. Nitride of copper is a deep green powder, which is easily decom- posed by heat, with a slight explosion. COMPOUND OF COPPER WITH HYDROGEN. § 1057. A compound of copper with hydrogen is obtained by heating, at a temperature of 158°, a solution of sulphate of copper with hypophosphorous acid. The hydride of copper thus prepared is hydrated, and forms a bright brown powder, which suddenly de- composes at about 140° into metallic copper and hydrogen gas, which is disengaged. Chlorohydric acid decomposes it, forming protochloride of copper, while the hydrogen is set free. COMPOUNDS OF COPPER WITH CHLORINE. § 1058. Two compounds of copper with chlorine are known : the first Cu3Cl corresponds to the suboxide, while the second CuCl cor- responds to the protoxide. Subohloride of copper CuaCl is obtained by boiling a solution of protochloride of copper CuCl with very finely divided metallic cop- per, when the colour of the liquid changes from green to brown, while white crystalline chloride of copper CusCl is soon deposited. ANALYTIC DETERMINATION. 245 The chloride is also obtained by decomposing the protochloride CuCl by heat, the latter parting with one-half of its chlorine. The protochloride CuCl may be reduced to the state of subchloride CuaCl by pouring protochloride of tin into a solution of protochlo- ride of copper, the decomposition taking place in the cold, while chlorohydric acid, which prevents the precipitation of the oxide of tin, is added to the liquid. The chloride CuaCl may be obtained crystallized in small tetrahedrons by dissolving it, assisted by heat, in chlorohydric acid, when the chloride is deposited during the cool- ing of the liquid. Chloride of copper Cu3Cl fuses at a temperature of about 752°, and volatilizes at a red-heat. It is very slightly soluble in water, but dissolves more freely in chlorohydric acid, and particularly in ammonia. It soon alters in the air, and is converted into a green powder consisting of a compound of hydrated oxide of copper CuO and protochloride CuCl. In consequence of the affinity of this sub- stance for oxygen, it is frequently used in eudiometric analyses, and generally in the form of solution in ammonia. Subchloride of copper CuCl is obtained by dissolving the prot- oxide CuO in chlorohydric acid, or by dissolving metallic copper in aqua regia. The chloride is very soluble in "water, and crystallizes on cooling from a concentrated solution in the form of long bluish- green needles, of which the formula is CuCl+2HO. This chloride is prepared in the anhydrous state by slightly heat- ing copper in an excess of chlorine, when a yellowish-brown com- pound is obtained, which evolves chlorine when heated to a dark red-heat, and is converted into the chloride Cu2Cl. The chloride dissolves readily in alcohol, and imparts to it the quality of burning with a beautiful green flame. DETERMINATION OF COPPER, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. § 1059. Copper is determined either as anhydrous protoxide CuO or in the metallic state. When copper exists alone in a liquid, it is precipitated by caustic potassa, after which the liquid should be boiled, because the hydrated protoxide is then changed into an an- hydrous oxide, which is more easily washed: the oxide is weighed after being calcined in the air. Copper is frequently precipitated by a blade of iron or zinc, and, if it is to he weighed in this state, must be rapidly washed with boiling water and dried excluded from the air, from which it promptly absorbs oxygen. When copper is precipi- tated from its solutions by sulf hydric acid gas, the precipitate must he washed with water charged with sulfhydric acid, while the filter on which the substance has been collected must he calcined, and the whole dissolved in aqua regia, from which solution the copper is then precipitated by caustic potassa. 246 COPPER. Copper is very accurately determined by the following process, used in the analysis of many cupreous substances: The substance being dissolved in an acid, an excess of ammonia is added to it, which redissolves the oxide of copper, forming a blue solution, remarkable for its great colouring powTer. A standard so- lution of sulphide of sodium is poured into the liquid from an alkali- meter ; when the copper is precipitated in the state of an oxysul- pliide of the formula CuO,5CuS. By careful manipulation, the moment at which the copper is entirely precipitated may be exactly ascertained, as the reaction is finislmd when the liquid has lost its colour. It is then easy to calculate the quantity of copper precipi- tated, from the volume of the standard solution of sulphide of sodium, supposing always that no other substances which are pre- cipitable by the alkaline sulphide exist in the liquid. In order to prepare the standard solution of sulphide of sodium, 1 gm. of pure copper is dissolved in 5 or 6 gm. of nitric acid; and about 50 gm. of a concentrated solution of ammonia being added, gentle heat is applied to dissolve completely the precipitate. The solution of sulphide of sodium, the initial volume of which has been measured on the division of the alkalimeter containing it, is then poured into the deep-blue liquid; and when the latter is only of a light blue, the flask is shaken several times, and then allowed to rest for a few moments. The sulphide of sodium is then added, drop by drop, in order to observe exactly the moment at which the liquid loses its colour, at which point the volume of solution added is marked on the division of the alkalimeter. Supposing this vo- lume to be represented by 137.5 div., it will be thence inferred that 137.5 div. of the solution of sulphide of sodium correspond to 1.000 gm. of metallic copper; and consequently, if, in order to remove the colour of an ammoniacal cupreous liquid, 97.5 div. of the solution of sulphide of sodium are required, the conclusion fol- lows that the tested solution contained ~ . 1.000 gm., or 0.709 gm. of metallic copper. The described process may be applied to solutions containing other metals than copper, as experiment has shown that it gave exact results even when the liquid contained iron, zinc, cadmium, tin, and lead or antimony, because the alkaline sulphide only com- mences to act on the metals named after the copper has been com- pletely precipitated in the state of oxysulphide. It is nevertheless indispensable that the iron should be in the state of sesquioxide, since the presence of protoxide would derange the result. It is not necessary to separate by filtering the deposit thrown down by seve- ral of these metals at the moment of adding the excess of ammonia; although it may be of advantage when the deposit is very copious, because the latter would prevent the colour of the liquid from being distinguished. The process of determination just described becomes inaccurate METALLURGY OF COPTER. 247 when the liquor contains cobalt, nickel, mercury, or silver. The presence of silver may be easily avoided, as it is suflicient to add a few drops of sulfhydric acid to the nitric solution, when the silver is entirely precipitated as insoluble chloride. § 1060. Copper is easily separated from the alkaline, alkalino- earthy, and earthy metals, from manganese, iron, chrome, cobalt, nickel, zinc, titanium, and uranium, by means of sulfhydric acid, passed through the liquid acidulated by chlorohydric acid, when the copper alone is precipitated in the state of sulphide. It is separated from cadmium, bismuth, and lead, when these metals are dissolved in nitric acid, by means of an excess of carbo- nate of ammonia, which does not dissolve the copper; which same process may be employed to separate copper from alumina and the sesquioxides of iron and chrome; hut the results are less exact than those of precipitation by sulfhydric acid. The best method of se- parating copper from lead is to add sulphuric acid to the nitric solution of the two metals, and evaporate to dryness to drive off the excess of acid, when the residue, after being moistened with a small quantity of nitric acid and treated with water, consists only of sul- phide of lead. Copper is separated from tin by treating the two metals with nitric acid, evaporating to dryness, moistening the residue with a small quantity of nitric acid, and dissolving it in water, when the tin remains in the state of stannic acid. By the same process, copper may he separated from antimony; but the results are less exact, because a small proportion of antimony is always dissolved. It is therefore better, after having dissolved the metals in aqua regia, to saturate the solution by ammonia, and add an excess of sulfhydrate of ammonia, in which sulphide of antimony is soluble. The same process will serve to separate copper from tin and arsenic. METALLURGY OF COPPER. § 1061. Copper is found in nature chiefly in the state of sulphide, which is rarely isolated, being generally combined with sulphide of iron, constituting copper pyrites Cu3S+Fe2Sa, and frequently mixed, in greater or less proportions, with iron pyrites FeSa. The most common ores of copper are therefore mixtures of sulphide of iron and copper. Besides copper pyrites, the following ores occur: variegated copper 2CusS+FeS ; fahlerz, or gray copper, which is a double sulphide of antimony and copper; and bournonite, which is a multiple sulphide of antimony, copper, and lead; all of which are very important minerals, being generally very rich in silver. All the ores just named are found in veins traversing the old rocks; while near these primitive veins deposits of copper ores are often seen, evi- dently arising from the alteration of the ore by the action of water. When slow streams of water, which, in their course, pass over beds of copper ore, and thus generally contain sulphate of copper, drop 248 COPPER. into calcareous earths, or remain in the cavities of calcareous rocks, sulphate of lime is formed and carried off bj the water, while car- bonate of copper is deposited ; and if the reaction takes place at a high temperature, oxide of copper is deposited instead of the car- bonate. Lastly, if organic substances be present, the sulphate of copper may be reduced either to the metallic state or to that of sulphide of copper. The occurrence of masses of carbonate and oxide of copper, which are frequently found near veins of copper pyrites, is thus explained, as is also the origin of small crystals of sulphide of copper scattered through certain schistose rocks which are impregnated with bitumen and contain many organic remains. In this way, geologists explain the formation of the cupreous pyrites found scattered in small crystals through bituminous schist, and exhibiting impressions of fishes, which form the bottom of a very extensive basin of secondary rocks in Mansfeld, in the north of Germany. More or less considerable masses of suboxide of copper CuaO are sometimes found, which yield a very rich copper ore, very valuable mines of which are in Peru and Chili. The principal localities of copper ore in Europe are in the county of Cornwall in England, Mansfeld and Rammelsberg in the north of Germany, in Sweden, Norway, and the Ural and Altai mountains in Russia. There for- merly existed at Chessy and Saint-Bel, near Lyons, a very pro- ductive mine of oxide and carbonate of copper, which is now exhausted.* § 1062. The ores of the oxide and carbonate of copper are very easily worked. It is sufficient to smelt them in contact with char- coal, in cupola furnaces, with scoriae more or less silicious, when an impure copper, called black copper, is obtained, which, after refining, yields marketable copper. § 1063. The treatment of the sulphuretted ores is much more complicated. They are first subjected to several preliminary roast- ings, in order to convert a certain portion of the sulphides into ox- ides, after which the roasted ores are smelted in blast or in rever- beratory furnaces, with the addition of scoriae or other fluxes, if the ore does not itself contain a sufficient proportion of silicates. Cop- per has a greater affinity for sulphur than iron, while the latter metal, on the contrary, has a greater affinity for oxygen, especially in the presence of silicic acid; the oxide of copper, which forms during the roasting, therefore passes entirely into the state of sul- phide, by abstracting the sulphur from the sulphide of iron which remained in the roasted material, the products of the operation being a slag, which contains the greater part of the iron of the * The principal locality of copper ores in the United States is that at Kewenaw Point, Lake Superior, where large masses of native copper are found. Other great localities, omitted in the text, are those in Cuba, Siberia, and Burra Burra in Australia, all of which yield principally oxidized ores.— W. L. F. METALLURGY OF COPPER. 249 copper pyrites, and a sulphide of iron and copper, and the cupreous matt, containing nearly all the sulphide of copper of the pyrites, and a much smaller proportion of sulphide of iron. The matt is, consequently, a sulphuretted ore of copper, much richer in copper than the original pyrites. It is again roasted, and melted with silicious scoriae, and frequently with ores of oxide of copper, when they are at hand, which process produces a new slag, containing a great portion of the iron of the first matt, and a second cupreous matt, still richer in copper than the first. These successive opera- tions are repeated until an impure copper, black copper, a last cupreous matt, and scoriae, are obtained, the matt being then sub- jected to similar processes, or added to the preceding matt, so that the ultimate product is black copper, which is refined. We shall give examples of this metallurgic process as adopted in some of the most important European works. § 1064. At Fahlun, in Sweden, the principal ore is copper pyrites, mixed intimately with iron pyrites and accompanied by a quartzose gangue. The pyritous ores are roasted, mixed with silicious ores, in the proportion of 2 parts of pyritous and 1 of silicious ore, and 10 to 30 per cent, of scoriae, arising from a previous smelting, added. This mixture is smelted in a blast-furnace of about 3 metres in height, and a matt composed of sulphide of iron Fe3S and sul- phide of copper CuaS, with a slag which should present nearly the composition of bisilicate of iron Fe0,2Si03, are removed from it. The matt, which contains 8 to 10 per cent, of copper, is subjected to four successive roastings, wdiich remove nearly all the sulphur and leave the metals in the state of oxide. The roasted matts are smelted in blast-furnaces, resembling those used for the smelting of the roasted ores, quartz and oxidized or sulphuretted silicious ores wdiich have been previously roasted being added. This smelting yields black copper, a small quantity of cupreous matt, and scoriae, which are chiefly simple silicates of iron Fe0,Si03. The cupreous matt is then treated like the first matt arising from the smelting of the ores, while the black copper is refined by a process soon to be described. § 1065. The copper ores of Mansfeld are argillaceous schists, containing pyrites scattered through in small crystals, their rich- ness in copper being very variable, while they are strongly impreg- nated with bitumen. They are roasted by being heaped on a pile of w'ood, which is easily done, the consumption of fuel being small, as the fire is kept up by the bitumen. Five to eight per cent, of fluor-spar, scoriae poor in copper, arising from subsequent opera- tions, and frequently small quantities of cupreous schists containing carbonate of lime, are added, and the mixture is smelted in blast- furnaces 5 or 6 metres high, heated by coke. Fig. 558 represents a vertical section of the furnace passing through one of the twyers, while fig. 557 represents a front view. (The breast of the furnace has 250 COPPER. been removed to show the interior.) The lower part of the furnace is built of quartzose sandstone, and the upper part of bricks. The Fig. 557. Fig. 558. furnace has two twyers, either on the same side, as in fig. 559, or on opposite sides. At the base of the breast of the furnace are two openings o, o', which are opened alternately for the escape of the liquid products, and which communicate by means of canals with two large crucibles C, C' outside. The smelter allows a nose of 0.2 m. in length to form in front of the twyers, and the fuel and ore are charged alternately in layers. The furnaces are surmounted by chimneys of 12 or 15 metres in height, to carry off the products of combustion. The matts and scoriae escape constantly from the furnace, and flow into One of the receiving basins C, the opening o' corre- sponding to the basin C' being closed. When the crucible C is filled, the hole o' is opened and the material allowed to run into C', after which the products in the basin C are immediately removed. The slags are generally moulded into large bricks, which are ’Jised in building; while the matts, in the shape of disks, are removed as fast as their surface solidifies. The crucible C being emptied, when C' is filled, the substances flowing from the furnace are again col- lected. The matt, which forms only about A of the weight of the melted ores, is composed of sulphide of iron FeS and sulphide of copper Cu3S; its proportion of copper varying from 20 to 60 per cent., according to the nature of the ore. When the matt contains only 20 or 30 per cent, of copper, it is subjected to three successive Fig. 559. METALLURGY OF COPPER. 251 roastings on heaps of wood, and is again passed through the fur- nace, with the addition of a certain quantity of slag arising from the first smelting of the ores; for which purpose the slag which immediately covered the matt in the receiving basins, and which is richer than the superficial scoriae, is selected. A new matt is thus obtained, presenting the same percentage of copper as that arising from the smelting of rich ores. § 1066. The rich matts are subjected to six successive roastings on heaps of wood, the operation being performed in small stalls (fig. 560), formed by three stone walls, and having openings at o, to facilitate the draught. The matt which has been roasted in the first stall is passed to that of No. 2, and so on until it ! reaches No. 6. A considerable quantity of sulphate of copper, which is formed during the roasting, is subsequently removed by washing, as it can be sold to a good profit. Beginning with the third roasting, the matts are lixiviated, after each roasting, in large wooden boxes, superimposed upon each other, a methodical process of washing (§ 447) being adopted, so that the water which flows from the last box is nearly saturated, and soon deposit crystals when evaporated by heat in leaden boilers. The roasted matt is smelted in a blast-furnace resembling that in which the ores are smelted, but smaller; the scoriae intended to combine with the oxide of iron of the matt being added. This smelting yields black copper, scoriae, and a matt which, being very rich in copper, is added to the second matts resulting from the preceding operation. The black copper is removed in disks, for which purpose a small quantity of water is poured on the melted mass, to render the superficial stratum solid. Black copper con- tains about 95 per cent, of copper, 3 or 4 of iron, and small quanti- ties of silver and antimony. § 1067. Cupreous ores often contain enough silver to render the extraction of this metal advantageous; which operation is effected either on the black copper or on the last roasted matts. The black copper is worked by eliquation, and the matts by amalgamation. The following is the principle of eliquation :—By fusing copper and lead in an elbow-furnace, the two metals are alloyed; and if the fused alloy be suddenly cooled at the moment of its escape from the furnace, the metals remain intimately mixed. But, if the solid alloy be gradually reheated, or if the melted alloy be slowly cooled, the metals separate, and the lead retains all the silver which origin- ally existed in the copper, while the latter metal is merely com- .Fig. 500. 252 COPPER. bined with a certain quantity of lead. By cupellation the lead gives up its silver, and the impure copper is refined. Three parts of black copper, and 10 or 12 parts of lead, as argentiferous as possible, are fused in a small elbow-furnace, litharge rich in silver being often substituted for the lead. The fused alloy is run into cast-iron moulds, where it suddenly cools, and takes the shape of disks, which are heated on the eliquat- ing furnace. This apparatus consists of two cast-iron plates (figs. 561 and 562), slightly inclined to- ward each other, and leaving a small space above an empty space M in the ma- son-work which supports the plates. The disks D are placed perpendicularly on the plates, and kept separate by wooden wedges, the open part of the floor being closed by sheet-iron plates F, F. Char- coal is heaped between the disks, and the wedges are removed, after which wood is placed in the space M and kindled, the draught being increased by small chimneys o made in the mason- work. As the temperature rises, the lead fuses and runs through a canal a in the floor of the space M, into a crucible c, whence it is run into moulds of a lenticular shape. The copper, still alloyed with a certain quantity of lead, remains on the floor in the form of a half-melted, spongy mass, while the lead which separates by eliquation contains nearly all the silver, which is afterward sepa- rated by cupellation. As the cupreous masses may still yield a certain quantity of argentiferous lead, if the temperature be raised, they are heated in a peculiar furnace, called a sweating-furnace, of which fig. 564 represents a vertical section through the line CD of the plane (fig. 565), while fig. 565 shows a horizontal section at the height of the line AB (fig. 564); and lastly, fig. 563 exhibits a front view of the same. The cupreous masses are placed on the floor of the furnace above the strainers F, F, which are filled with wood ; when the door of the furnace is closed and the fuel kindled, the draught being assisted by small holes o, o, which open into a chimney II. An additional quantity of lead separates by eli- quation ; but as the air in the furnace is very oxidizing, the greater portion of this lead is converted into litharge, which falls Fig. 561. Fig. 562. METALLURGY OF COPPER 253 to the bot- tom of the strainers F. A small quantity of oxide of copper also oxid- izes, but remains dissolved in the 1 i tharge. There will be, therefore, on the floor, black copper which has lost the greater proportion of the lead and silver it retained, and argen- tiferous litharge rich in copper, which are thrown as plumbeous material into the elbow-furnace in which the black copper is smelted with lead, for the preparation of disks for eliquation. § 1068. The black cop- per produced by eliquation is refined in a reverberatory resembling a cupelling fur- nace, of which fig. 566 re- presents a vertical section through the line YX of the plane (fig. 567), while fig. 567 gives a horizontal sec- tion through the line YU of fig. 566. Wood is burned on the grate F, and the flame passes through the furnace A into the chim- ney C. The copper to be refined is placed on the hearth-sole of the furnace, made of moistened charcoal solidly pounded; the charging be- ing done through an open- ing D, which is afterward closed by a door. When the metal is fused, the wind of Fig. 563. Fig. 564. Fig. 565. Fig. 566. Fig. 567. 254 COPPER. two twyers t is allowed to blow over the surface of the bath, by the oxidizing action of which the sulphur, lead, and iron first oxidize, while scoriae and skimmings are formed, which are removed through the door A. After a certain time, the copper has lost its foreign metals, and red scoriae, very rich in suboxide of copper Cu30, are formed. The workman judges of the progress of the operation by plunging an iron rod from time to time into the bath of metal, thus taking out a thimble of copper, which he hammers to ascertain its physical qualities. When the refining is finished, he runs the metal into the basins B, B', pours into them a small quantity of water to solidify the superficial stratum, which he immediately re- moves, and so on, until he has removed all the copper. The me- tallic disks are called rosettes. In this state the copper is not malleable, as a small quantity of suboxide of copper Cu30, which it always contains, destroys this property. Black copper is frequently refined, in this way, before being subjected to eliquation; but it is not carried so far, and the par- tially refined black copper is run into cold water, which reduces it to the state of grains, or drops. The granulated metal is then fused with the plumbeous material in the elbow-furnace, by which more homogeneous alloys of copper and lead are obtained, than, when disks of black copper are fused with lead. After eliquation and sweating, the cupreous material is refined by a process pre- sently to be described. The process by amalgamation will be described in treating of the metallurgy of silver.* § 1069. When black copper contains no silver, it is not subjected to eliquation, but is generally refined in a refining-furnace, a verti- cal section of which is seen in fig. 568, and a perspective view in fig. 569. It is composed of a hemispherical crucible C, of a radius * A recently introduced process of extracting the silver from cupreous matts is now employed to great advantage in Swansea, South Wales, and at several places in Germany. The manipulations are as yet kept secret, while the succes- sive operations are as follows:—The second or third cupreous matt, after having been granulated, or stamped, and reduced to an impalpable powder, is roasted in a reverberatory until all the sulphate of copper formed is decomposed, and the sulphuric acid is completely expelled. The roasted substance is again powdered, and roasted with a certain quantity of common salt, the chlorine of which com- bines with the silver to form chloride of silver. The product resulting from this operation is sieved; and while the coarser particles, which consist of imperfectly roasted matt which has sintered together, are again roasted with common salt, the powder which has passed through the sieve is treated with a boiling saturated solution of common salt, which dissolves the chloride of silver. The silver is precipitated from its solution in the metallic state by pieces of metallic copper, tvhile the copper in solution is in its turn precipitated by iron. The more per- fectly the first roasting was effected, i. e. the less sulphuric acid was allowed to remain, the less chloride of copper will form by the subsequent roasting with common salt; and the less copper the solution of silver contains, the more per- fectly will the silver be precipitated, and consequently, the more economical will the operation be. The whole process requires great care.— W. L. F. METALLURGY OF COPPER. 255 of about 0.2 m. lined with brasque made of 2 parts of charcoal and 1 of clay. It is surrounded by an edge having an opening A, closed by a door, the object of which is to more readily support the charcoal. When first made, or repaired, it is dried for several hours, by filling it with burning charcoal; and, fresh charcoal being added, the pieces of black copper are placed on the side opposite to the twyer T, and the blast is admitted. When the charge of black copper is melted, fresh is added, taking care to always keep the furnace filled with charcoal. A tap-hole it', allows the escape of the scoriae which form during the refining. Sulphurous acid, and white vapours of oxide of antimony, when this metal exists in the black copper, are disengaged, while the first scoriae contain a Fig. 568. Fig. 569. considerable amount of oxide of iron, which gives them a greenish hue, while the succeeding slag is of a deep red colour, and very rich in oxide of copper. When the workman has melted the quantity of black copper intended for a single operation, he takes, from time to time, a thimble of copper on the end of an iron rod, and judges, by the appearance of the metal, of the progress of the operation. When he thinks the refining is terminated, he stops the blast, throws a bucket-full of water on the hearth, removes the charcoal, uncovers the surface of the metallic bath, and skims off the supernatant scoriae; and when its surface is clean, throws on it a small quantity of water to consolidate its superficial stratum, and immediately removes it in the form of a rosette. Water is again poured on, a second rosette removed, and so on, until the operation is terminated. The process generally lasts two hours, and produces a loss of about 25 per cent, on black copper, furnishing 75 per cent, of rosette copper. § 1070. Rosette copper does not possess the malleability of the copper of commerce, and, in order to give it the desired properties, must be subjected to a very delicate operation, requiring a skilful workman. The rosettes are remelted in a small furnace, resem- bling that of figs. 568 and 569, for refining black copper, and, when the fused metal has run into the crucible, it is covered with fine charcoal, when, after some time, all the suboxide of copper is reduced, and the metal has attained its greatest degree of mallea- 256 COPPER. bility. But if the workman does not seize exactly the proper moment, the metal again loses its malleability by combining with a small quantity of carbon. When this happens, (which the refiner soon discovers by occasional experiment,) he uncovers the metal, and allows the air of the twyer to play for a few moments over the surface of the bath, which operation he repeats until he attains the favourable period. The purified metal is then run into moulds of various shapes and sizes. § 1071. England alone manufactures more than half of the copper used in the world. The most important copper-mines are in Devonshire and Cornwall, while the principal smelting-works are in Wales, and smelt, besides the British ores, many foreign ores coming from Chili, Peru, Cuba, New Zealand, Algiers, Nor- way, &c. The ores smelted in the Welsh copper-works may be divided into several classes, according to their richness in copper and their chemical composition: 1. Copper pyrites, mixed with a large proportion of iron pyrites, and containing but a small quantity of oxidized cupreous sub- stances, and accompanied by a quartzose and earthy gangue of little value. They contain from 3 to 15 per cent, of copper. 2. Copper pyrites, presenting the same composition as the fore- going, but containing from 15 to 25 per cent, of copper. 3. Copper pyrites, containing very little iron pyrites and matter injurious to the quality of the copper, but in larger pro- portion of oxidized cupreous substances, and the gangue of which is essentially quartzose, while they yield from 12 to 20 per cent, of copper. 4. Ores composed principally of oxidized copper-ores, mixed with pyritous and variegated copper. Their gangue is quartzose, and they contain from 25 to 45 per cent, of copper. 5. Very rich oxidized ores, free from sulphides and injurious substances, accompanied by a quartzose gangue, and containing from 60 to 80 per cent, of copper, in fhe metallic state, and in that of suboxide or carbonate. This valuable ore is imported chiefly from Chili. § 1072. The metallurgic treatment begins with ores of the first class, which are roasted in large reverberatory furnaces, a hori- zontal section of one of which is represented in fig. 571, while fig. 570 shows a vertical section through the line XY in fig. 571. The hearth-sole of this furnace is 21 feet in length by 21 in width, and made of refractory bricks. The vaulted roof descends rapidly from the grate F to the flue B, which conveys the gases into a tall chimney. Four doors p on the sides of the furnace serve as working-holes, while an opening o near the fire-bridge or altar, serves for the introduction of a certain quantity of fresh air, which can be regulated by a register. The liearth-sole has four METALLURGY OF COPPER. 257 Fig. 570. Fig. 571. rectangular apertures r immediately against the working-doors, serving for the extraction of the roasted material, and which are kept closed during the roasting, by cast-iron plates. In the vaulted roof are two large sheet-iron hoppers, through which the ore to be roasted is introduced, and which are provided with re- gisters which on being opened allow the material to fall on the hearth-sole. The combustible employed for the roasting and smelting is the Welsh anthracite, which, as it burns with difficulty, and is reduced to dust by the influence of heat, cannot furnish, under ordinary circumstances, the necessary flame to heat a reverberatory of 21 feet-in length throughout the whole of its extent; and which, moreover, cannot be burned on a common grate, as it would either fall through between the bars, or completely fill up the interstices. These inconveniences have been remedied in a very ingenious way, by which the manner of combustion is rendered different from that generally taking place in reverberatories. The anthra- cite leaves, on being burned at a high temperature, an ash which by 258 COPPER. fusion is rendered pasty, and constitutes a vitreous slag, a pro- perty which the workmen make use of to obtain a kind of earthy grate, which is supported only by a few bars of iron, placed wide apart. Different-sized fragments of this slag are heaped on the bars, until the layer has attained the thickness of about 1 or 1J feet, after which the ash of the fuel burned on this support forms a kind of slag, which encloses numerous pieces of coal; and when the slag, owing to the accumulation of a fresh quantity above, becomes further removed from the source of heat, it cools, and thus forms new interstices, large enough to allow the current of air necessary for the combustion to pass, but too narrow to permit the escape of powdered fuel. The workman contrives to keep the thickness of the layer of slag uniform, by breaking away pieces from below from time to time, and allowing them to fall into the ash-pit. About \ of its weight of bituminous coal, in small pieces, is added to the anthracite, in order that the former, by adhering to the anthracite, and swelling by the heat, may maintain the desired porosity throughout the mass. The thickness of the layer of anthracite is about 1 foot above the support of slags. The air traverses the layer at innumerable points, and its oxygen is en- tirely converted into carbonic oxide, which, with the nitrogen, enters the furnace, where it is consumed at the expense of the cold air introduced through the aperture o and through the small holes in the working-doors. The whole of the inside of the furnace is thus filled with a long flame of carbonic oxide, which burns by contact with jets of air containing an excess of oxygen, and which spread out like a sheet on the floor of the furnace, because they enter through holes pierced as low as possible. The ore spread out on the floor of the furnace is thus constantly exposed to a layer of oxidizing air, near a mass of combustible gas which is consumed slowly on its under surface, thus furnishing the heat necessary to the roasting. The roasting of a charge of ore is commenced immediately after the former charge has been ex- tracted, without allowing the furnace to rest. Each charge consists of 3|- tons, which are introduced by opening the valves of the hoppers in which the ore has been previously heaped; and the workmen immediately spread the whole charge uniformly over the floor, by means of iron rakes, introduced through the four working- holes, which are afterward closed. Every 2 hours a fresh surface is exposed by stirring with long iron poles ; and the whole roasting lasts 12 hours. In order to extract the roasted ore, the workmen open the working-doors, and lift up the cast-iron plates which cover the openings r, into which they rake the ore, thus causing it to pass into a reservoir U under the furnace, whence other work- men take it, after it has cooled, to the smelting-furnace. § 1073. The smelting-furnace is a reverberatory, fed by a METALLURGY OF COPPER. 259 mixture of § of anthracite and of fine pit-coal, which are burned on a bed of scoriae, the flame being produced by the combustion of the carbonic oxide gas which forms in the stratum of fuel. By forcing the draught a higher temperature can be attained than in the roasting-furnace. Fig. 573 represents a horizontal, and fig. 572 a vertical section of the furnace. The hearth-sole is made of scoriae, having a depression at B, constituting a kind of inner basin. The roasted ores are smelted by adding to them the rich Fig. 572. Fig. 573. scoriae arising from the preceding operations and unroasted crude ores belonging to the third class; a certain quantity of fluor-spar being added, to give fluidity to the scoriae. Influenced by the high temperature, the oxides and sulphides react upon each other, 260 COPPER. and while the copper combines chiefly with the sulphur, the iron selects the oxygen and passes into the scoriae. There is, more- over, a reaction between the oxygen of the oxides and the sulphur of the sulphides, and, consequently, disengagement of sulphurous acid. The operation is terminated in 4 hours, and the products of smelting are—a matt which contains the greater portion of the copper combined with the sulphur and a certain quantity of sulphide of iron ; and a slag highly charged with oxide of iron, and containing many fragments of quartz, giving it a muddy con- sistence. The workman draws out the slag, by means of his rake, which he introduces through the working-hole p near the flue, and causes the slag to fall into rectangular cavities U, made in the same, the shape of which it assumes. At the same time, the smelter opens a tap-hole which penetrates to the bottom of the inner reservoir B, when the matt flows in a small stream, and is conducted by a canal ab into a reservoir 11 filled with water, when it is divided into very small grains. The matt arising from this smelting is called coarse metal, and contains about 33 per cent, of copper. The scoriae are broken up, and the pieces sorted; the richest being kept to be added to an- other smelting of roasted ore, while the remainder is rejected.* § 1074. The coarse metal is then roasted, and again smelted. As the substance has lost the greater part of its sulphur during the roasting, it is not to be prevented that a certain portion of copper should pass into the slag, in the state of oxide, which is, however, of no importance, as the scoriae must pass through other operations. The furnaces for roasting the coarse metal resemble those for roasting the ore, and the process is similarly conducted, with the exception that toward the close of the operation the tem- perature is raised higher. The charge is 4J tons, and the roasting lasts 36 hours, during which time the material must be frequently turned with a rake. The roasted substance falls through the working-holes r. The roasted coarse metal is smelted with the copper ore of the fourth class, scorise very rich in copper arising from the refining of the crude copper, as will be hereafter described, and the scales from the rollers being added. The smelting-furnace resembles that for smelting roasted ores, but the hearth has no inner reser- * The rich slag is separated from the poorer portions in an ingenious manner: —The slag being run out from the furnace into rectangular cavities, and thus obtained in blocks of about feet by 1J, by 1 in depth, is removed before it has solidified, but not before an outer crust of a certain thickness has formed, and set up in a slanting position, the side -which lay undermost in the pit, and which consequently contains all the grains of matt, which, by their greater specific gravity, occupy the lowest position, now forming the upper surface. The cake is then tapped at both ends, when the liquid interior, which is poor in copper, flowing out, leaves a hollow box of slag, the upper side of which is broken out and used, while the other parts are rejected.— W. L. F. METALLURGY OF COPPER. 261 voir. The fire is managed in the same way, but a higher tempe- rature is produced, and the operation lasts 2 hours longer. It is endeavoured to mix the materials in such proportions that the sulphide of iron in the smelting-bed may be oxidized by the oxygen of the metallic oxides, and pass nearly wholly into the slag, while the copper combines with the superfluous sulphur to form the matt. The materials react upon each other principally after fusion, the reaction being almost entirely limited to a double decomposition between the sulphide of iron and the oxide of copper, while very little sulphurous acid is disengaged. Toward the close of the operation, the workman stirs the mass with his rod, and then blows up the fire in order to properly separate them; after which he opens the tap-hole, when the matt runs out first, and is received in small canals, while it is followed by the fluid slag. The latter is separated into 2 parts, and while the richest are reserved for special treatment, which yields copper of the first quality, the poorest are added to a new smelting of roasted coarse metal. The matt is of a grayish-white colour, sometimes slightly bluish, and is called fine metal. It contains about 73 per cent, of copper, and resembles in composition the sulphide of copper Cu2S, although it is rarely entirely free from sulphide of iron. The rich scoriae arising from this smelting are subjected, as we have before said, to a special treatment, being smelted in a rever- beratory furnace with a certain quantity of crude ores of class No. 3, which contain but few injurious substances, and sulphur sufficient to transform the copper of the smelting-bed into sulphide, which passes into a matt, which is then treated like the ordinary matts. § 1075. The fine metal is subjected to an operation of which the object is to ultimately expel, in the form of sulphurous acid, the sulphur which, until then, had been preserved as an agent of concentration for the copper, and to drive off, at the same time, either by gasification by the assistance of oxygen alone, or by scorification by the united aid of oxygen and silex, the foreign matters, such as arsenic, iron, nickel, cobalt, tin, &c. This is effected by means of two successive reactions which take place in the same furnace : first, by the direct action of the air on the mate- rial kept at a temperature near its fusing point, and liquefying drop by drop, which operation is the roasting of the matt; and secondly, by the reaction of the oxide of copper, which is formed in great excess, on the sulphides which are not decomposed by roasting. The two products of the operation are coarse or blistered copper, which is purer than the black copper of the continental manufac- tories, and a very rich scoriae, which is passed through the smelting of the roasted coarse metal. This process is carried on in a reverberatory furnace resembling other smelting-furnaces, but having a side-door through which the 262 COPPER. matt is charged. The matt is in pretty large cakes, which are heaped upon the hearth-sole, while the rich oxidized ores of the fifth class are added; the charge being about 3 tons. In half an hour the matt begins to fuse, and the first liquid drops fall upon the sole, which process lasts about 4 hours; after which all the materials are collected on the sole in a semi-doughy state, when a strong bubbling is observed, owing to the disengagement of sul- phurous acid produced by the reaction of the oxides on the sulphides. The temperature is allowed to fall, so as to prolong this reaction until the twelfth hour, at which period the disengage- ment of sulphurous acid ceases, because the temperature has greatly fallen. The fire is then blown up, the materials become more fluid, and the reaction is completed. In 18 hours, reckon- ing from the commencement of the operation, the material contains but little sulphur, and the smelter then raises the temperature as high as possible, in order to assist the separation of the substances. In 24 hours he skims the bath with his rake, and runs off the coarse copper into thin cakes, the surface of which is covered with blisters. The scoriae contain about 20 per cent, of copper.* § 1076. Blistered copper is refined without the admixture of any other substance, the reagents being atmospheric oxygen, the siliceous material of the sole and sides of the furnace, and that furnished by the sand, adhering to the cakes of copper. The refining-furnace differs but slightly from other smelting-furnaces, the grate being merely deeper, in order to accommodate more fuel, and its capacity being more ample. As much as 10 tons of blistered copper are charged on the sole, arranged in a heap rising as high as the vault of the furnace. The process lasts 24 hours, comprising the time necessary for charging; but, during the first 18 hours, the workman attends only to the fire. The copper melts gradually under the oxidizing influence of the air, and the oxide of copper thus formed reacts, either immediately, or by combination with the silex, on substances more oxidizable than copper, while a slag is formed, into which, in addition to suboxide of copper CuaO in great excess, the oxides of all the other foreign metals enter. In 22 hours, the copper is completely freed from the sulphur and foreign metals, and the workman then skims the bath and removes all the scoriae from its surface. The copper is then in the same state as the rosette copper of the continental foundries, and contains a certain quantity of oxide of copper, which destroys its malleability; but it is obtained * In most of the Welsh copper-works the fine metal is subjected to a third successive roasting and smelting, from which there results a matt which in this case is called coarse copper, while the product arising from the operations described in this section is called blistered copper. ALLOYS 263 directly in a malleable state in the English works by the following process:—Four or five shovelfuls of charcoal are thrown on the bath, which spread immediately over its whole surface, and then a long stick of green wood is plunged into the bath. In consequence of the elevated temperature to which it is suddenly subjected, the wood disengages reducing gases, which cause the metallic bath to bubble strongly, and considerably hasten the effect which would be ulti- mately produced by the charcoal on the surface. After twenty minutes of this bubbling, the refiner tests the copper by means of a small mould fastened to an iron rod: he dips out a small sample of copper, places it on an anvil, and tests its malleability by striking it with a hammer. When he is satisfied with its quality, he makes a last skimming and removes the balance of the charcoal and the small quantity of scoriae which has formed, and then runs the cop- per into moulds. COPPER OF CEMENTATION. § 1077. The water of copper-mines, or that flowing from the washing of roasted copper-ores, often contains a large quantity of sulphate of copper, which is separated by precipitating it by metallic iron. The water is conveyed into large basins, in which iron bars, plates of sheet-iron, or scrap-iron, are placed, on which the copper precipitates in the form of a crystalline powder, while an equiva- lent quantity of iron dissolves. The copper thus obtained is called copper of cementation, (cuivre de cement,) and is refined as above described.* ALLOYS. Alloys of Copper and Zinc. § 1078. Pure copper is moulded with difficulty, because it is often filled with flaws and air-bubbles, which spoil the casting; hut by al- loying it with a certain quantity of zinc, a metal is obtained free from this objection, harder, and more easily worked in the lathe. Zinc renders the colour of copper more pale; and when it exists in certain proportions in the alloy, it communicates to it a yellow hue, resembling that of gold ; but when present in larger quantity, the colour is a bright yellow ; and lastly, when the zinc predominates, the alloy becomes of a grayish white. Various names are given to these different alloys. The one most used in the arts is brass, or * A similar method is employed at Stadtberg, in Westphalia, and on Anglesea, England, to extract copper from carbonated ores ; the latter being heaped in large pits, and covered with water, while sulphuric acid, generated on the spot by burn- ing sulphur and a small quantity of nitre in a small furnace with a closed top, is led into the pits, and gradually converts the copper entirely into sulphate. When the mother liquid has become neutral, it is pumped off, and the copper is precipi- tated from it by scraps of iron. The same method would probably apply to the working of the large blocks of copper found at Lake Superior.— W. L. F. 264 COPPER. yellow copper, composed of about § of copper and £ of zinc. Other alloys are also known in commerce, by the names of tombac, similor or Mannheim gold, pinchbeck or prince's metal, (chrysocale,) etc.: they contain in addition greater or less quantities of tin. Tombac, used for ornamental objects which are intended to be gilded, contains 10 to 14 per cent, of zinc ; the composition of Dutch gold, which can be hammered into very thin sheets, being nearly the same. Similor, or Mannheim gold, contains 10 to 12 per cent, of zinc, and 6 to 8 of tin; and pinchbeck contains 6 to 8 per cent, of zinc, and 6 of tin. The statues in the park of Versailles are made of the following alloy: Copper 91 Zinc 6 Tin 2 Lead 1 The alloys of copper and zinc are altered by a high temperature and a portion of the zinc is volatilized. If brass be heated in a brasqued crucible in a forge-fire, the zinc is nearly wholly driven off". Brass is made by melting directly copper and zinc; rosette cop- per being used, fused in a crucible, and run into water to granulate it. The zinc is broken into small pieces. The fusion is effected in earthen crucibles which can contain from 80 to 40 pounds of alloy, the metals being introduced in the proportion of § of cop- per and J of zinc, to which scraps of brass are added. A certain number of crucibles are placed in an egg-shaped furnace A, (fig. 574,) lined with refractory bricks, and supported by a brick dome, having apertures through which the flame of the fuel passes, the grate F being immediately beneath the dome. The crucibles are in- troduced through the upper opening of the furnace, which is covered, during the smelting, by a lid having a hole 0 for the escape of the gases. A register beneath the grate regulates the draught, and serves for the extraction of the crucibles. When the alloy is fused, the crucibles are removed with tongs, and the brass run into clay moulds; and, sometimes it is run between two very smooth slabs of granite, kept at a proper distance from each other by iron rods. Small quantities of lead and tin are frequently added to brass to make the alloy harder and more easily worked: brass which con- tains no lead soon chokes a file, which defect is remedied by the addition of 1 or 2 hundredths of lead. Fig. 574. ALLOYS. 265 ALLOYS OF COPPER AND TIN. § 1079. Copper and tin mix in various proportions, and form alloys which differ vastly in appearance and physical properties, as tin imparts a great degree of hardness to copper. Before the an- cients became acquainted with iron and steel, they made their arms and cutting instruments of bronze, composed of copper and tin. Copper and tin, however, combine with difficulty, and their union is never very perfect. By heating their alloys gradually and slowly to the fusing point, a large portion of the tin will separate by eli- quation, which effect also occurs when the melted alloys solidify slowly, causing circumstances of serious embarrassment in casting large pieces. Different names are given to the alloys of copper and tin, accord- ing to their composition and uses: they are called bronze or brass, cannon metal, bell metal, telescope-speculum metal, etc. All these alloys have one remarkable property: they become hard and, fre- quently, brittle, when slowly cooled; while they are, on the contrary, malleable, when they are plunged into cold water, after having been heated to redness. Tempering produces, therefore, in these alloys an effect precisely opposite to that produced on steel. When alloys of copper and tin are melted in the air, the tin ox- idizes more rapidly than the copper, and pure copper may be sepa- rated by continuing the roasting for a sufficient length of time. The following are the principal alloys of copper and tin: Cannon metal, which in France is thus composed: Copper 100 90.09 Tin 11 0.91 111 100.00 Bell metal, which contains Copper 78 Tin _22 100 Cymbal and tam-tam metal, composed of Copper 80 Tin 20 100 Telescope-speculum metal, made of Copper 67 Tin _83 100 Bronze for medals varies slightly in its composition, and generally consists of Copper 95 Tin 5 Zinc some thousandths. Voi. II.—X 266 COPPER. Bronze used for the manufacture of ornamental objects generally contains larger quantities of zinc. A portion of the small French coin is made of alloys of copper and tin; and although the red “sous” consist of nearly pure copper, the yellow “sous,” coined under the Republic, from a metal obtained by melting the bells, contain on an average 86 of copper and 14 of tin. Other “sous” made during the Republic, with refined bell-metal, are composed of 96 of copper and 4 of tin. Cannon-casting. § 1080. Gun-metal must fulfil several important conditions. It should be very tenacious, that the pieces may not burst under the enormous pressure caused by the explosion of the powder, while it should he sufficiently hard not to he injured by the ball, which strikes the sides several times before leaving the muzzle; and, lastly, it should he fusible, because large guns can only be made by casting. Copper and iron are the only metals which possess sufficient tenacity; hut as pure iron will not fuse very readily, it is necessary to substitute for it cast-iron, the tenacity of which is much inferior. Copper possesses great tenacity, but is too soft; and, in rapid ser- vice, would soon be so battered as to be useless. Recourse must then be had to alloys of copper with other metals; and long experience has shown that alloys of copper and tin are the most suitable; but as, wThile tin greatly increases the hardness of copper, it diminishes its tenacity, it becomes necessary to stop at certain proportions of the two metals, at which the alloy possesses both the requisite de- gree of hardness and tenacity. These proportions, which have been determined by numerous experiments, made at various times and in different countries, have been fixed at 11 of tin for 100 of copper. It has, however, been ascertained, that for pieces of a calibre below 8, an alloy of 8 or 9 per cent, of tin is preferable. Many experi- ments have also been made to ascertain if the alloy could not be improved by the addition of other metals, as zinc, iron, or lead; but these complicated alloys have all been rejected, on account of the great variation of their results; and pieces were frequently ren- dered useless in consequence of the difficulty of obtaining such alloys homogeneous and of uniform composition. The use of cast-iron for the manufacture of cannon is long subse- quent to that of brass. As it is cheaper, it might be very advan- tageously substituted for bronze, but it is very brittle, and pieces of the same calibre must be much thicker than of the latter metal, thus becoming too ponderous for field-service. They are wrell adapted to stationary batteries, fortifications, coast defence, and ships of war. Cast-iron guns ring much less than those of bronze, and, for this reason, are preferable on board of ships, where brass pieces, on the lower-deck batteries, would make a noise insupportable by the gun- ALLOYS OF COPPER. 267 ners. Yery soft cast-iron, made with charcoal, should alone he used for artillery; and some of the Swedish iron is highly valued for this purpose. The furnaces in which bronze is melted should contain no oxidiz- ing gases, and the atmospheric air traversing them should be de- prived by combustion, as far as possible, of its oxygen, because the tin, which is more oxidizable than copper, would constantly separate from the alloy in the form of oxide, and the composition of the bronze, at the time of casting, would not be known with certainty. Figs. 575 and 576 represent a melting-furnace, used in the cannon-foundry at Toulouse. It is a circular reverberatory furnace A, with a surbased dome, heated by the grate F, on which small billets of wood are burned. The wood being charged through the Fig. 575. Fig. 576. opening o, a thick layer of fuel is heaped on the grate, in order that the atmospheric air, which does not enter the furnace until it has passed through the fuel, shall be completely deprived of its oxygen. The draught is regulated by 4 elongated working-holes A, A, arising 268 COPPER. from the hearth-sole and terminating at the vent-holes eg, eg, which open into the chimney C, by means of which arrangement the flame is obliged to spread over the metallic bath which covers the hearth- sole. Near the furnace are cavities M, M', lined with cement to preserve them from dampness, and in which the moulds are placed, and kept firm by heaping earth around them. The moulds, which are made of clay, cow’s-hair, and horse-dung, intimately mixed, are fashioned on a model in relief, partly of earth and partly of plaster, which is destroyed when the mould is finished, and strengthened by iron bands or loops. Above the mouth of the gun is a prolongation, called the masselotte, or lump, the use of which will soon be ex- plained. The moulds, after being baked at a high temperature, so as to dry them as much as possible, are fixed in their places, the breech being downward. Between the tap-hole i and the moulds, canals are made which convey the liquid bronze into each mould; and above is a railway ah, with a car R, containing a capstan, by means of which the moulds, when filled, can be lifted out and carried away. Moulding-sand, so well adapted to the moulding of cast-iron and other metals, has been substituted for the earth with which the moulds are made, but never with success, as the walls of the sand- mould are too compact and too impervious to gases. Now, imme- diately after the casting of bronze, the metal disengages numerous gaseous bubbles, which pass through the porous walls of the mould, and present less resistance than the high column of melted metal; while in the sand-moulds, the gases not being able to escape through the sides, produce a constant bubbling in the mass, giving rise to numerous flaws, and assisting the separation, by eliquation, of the tin, or alloys rich in tin. The charge of a furnace is composed of old brass, chiefly con- demned cannons, and masselottes taken from pieces previously cast, with brass turnings taken from the lathe or the boring-machine, and a certain quantity of new metals, copper and tin, besides white metals, or alloys very rich in tin, which separate by eliquation in the moulds. The proportions of copper and tin in the several com- ponents being determined by analysis, they are mixed in the pro- portion of 100 copper to 13 or 14 tin, which is reduced by oxidation of tin in the furnace to the normal proportion of 100 : 11. The condemned cannons and masselottes are laid on the hearth- sole, near the bridge, where the temperature is highest; while the copper, which should be very pure, in bars, and the turnings, are placed thereon, the white metals and tin being added at a later period. In 6 or 7 hours the mass is almost entirely fused, and the flame escapes by every avenue. The smelter first stirs the material with sticks of very dry wood, and draws the portions which are not melted toward the bridge; after which he completes the charge by adding the white metals and tin, which he runs in the form of pigs TINNING OF COPPER AND BRASS. 269 into different parts of the bath. He stirs it a second time, in order to render it homogeneous, and, after skimming off the superabun- dant scoriae, closes the doors of the furnace and blows up the fire, to bring the alloy to a proper state of liquidity; stirs and skims it a third time, and then opens the tap-hole. Other workmen direct the melted metal into each mould. A remarkable phenomenon ensues in a few moments after the casting. A bubbling takes place in the upper part of the mould, proportioned to the size of the piece and the elevation of tem- perature, and a portion of the bronze rises in the form of a mush- room, being an alloy much richer in tin than the cast metal. A partial eliquation therefore takes place during the cooling, which causes the separation of an alloy more fusible and containing more tin. The composition of the piece itself is not uniform, as the pro- portion of tin diminishes from the breech to the upper part of the masselotte. The intention of the masselottes is, not only to exert considerable hydrostatic pressure on the lower strata of the piece, but also to furnish metal necessary to compensate for the contrac- tion of the metal by cooling and its loss of substance by eliquation. Twelve hours after the casting, the earth is cleared away in order to hasten the cooling of the moulds ; and the latter are removed after 48 hours, broken, and the cast guns carried to the boring and turn- ing shops. When the surface of the piece is turned, and it has been bored to a certain point, it is examined to ascertain if it be free from such defects as would render it unserviceable. Such defects are various, and called by different names; but they are nearly all produced by eliquation of the tin or very fusible alloys. Flaws, or bubbles, are cavities with smooth surfaces, produced by bubbles of gas which have been unable to escape; while honeycombs are cavities with rough surfaces, arising from irregular distribution of the materials or badly proportioned alloy; and worm-holes are similar but smaller cavities. Cendrures are owing to impurities in the alloy, remaining in the metal, or detached from the sides of the mould; and tin-spots are produced by small, very hard masses of an alloy containing 20 or 25 per cent, of tin, which became separated by eliquation, and were unable to ascend as far as the masselotte. Blasts, or cracks, (sifilets,) which are longitudinal or traverse grooves, sometimes extending through the whole thickness of the piece, are likewise owing to a separation of the tin. If the piece is found to be perfect, the boring and turning are completed, and it is subsequently examined and proved according to the regulations of the service. § 1081. The use of copper and brass for culinary purposes is dangerous, on account of the ease with which copper, on oxidizing TINNING OF COPPER AND BRASS. 270 by contact with the air and acid substances, forms very poisonous salts, unless the vessels are lined with a coat of tin, which prevents the liquids from coming in contact with the copper. The tinning of copper is effected by cleansing the pieces with chlorohydrate of ammonia, and spreading, with a piece of cloth or tow, melted tin over their surface when properly heated. The tin thus adheres to the copper and covers it completely. Pins are made of brass wire, and whitened by being covered with a thin coat of tin by the humid way. The pins are first cleansed by heating them in a solution of cream of tartar, and then placed in a copper basin with a solution of cream of tartar and tin. The liquid is boiled for about one hour, when the tin dissolves in the cream of tartar with disengagement of hydrogen gas, and is pre- cipitated on the brass of the pins, covering them with a very thin pellicle of metal. COPPER. § 1082. We have said (§ 1078) that brass is composed of copper and zinc, but that a small quantity of lead and tin is usually added, to make the alloy more easy to work. Cannon-metal is composed of copper and tin alone, but the metal used for ornamental objects and medals contains in addition zinc and frequently lead. We shall therefore consider the more general case, and suppose that the alloy to be analyzed contains copper, zinc, tin, and lead. The alloy is dissolved in pure nitric acid, which converts the tin into insoluble metastannic acid ; while the copper, zinc, and lead are transformed into soluble nitrates. After treatment with water, the metastannic acid is collected on a filter; and the weight of tin in the alloy is inferred from that of the metastannic acid. The filtered liquid is evaporated to dryness, and sulphuric acid added, which converts the nitrates into sulphates; and then, after having driven olf the nitric acid by heat, the residue is dissolved in water, when the sulphate of lead, being insoluble, is separated on a filter and weighed after calcination, the quantity of lead in the alloy being deduced from its weight. The liquor is then supersaturated with sulf hydric acid gas, which precipitates the copper entirely in the state of sulphide, while the zinc remains in solution, because it is not precipitated by sulf hydric acid in a liquid containing an excess of acid. The sulphide of cop- per is treated as described, (§ 1059,) and the copper is determined in the state of oxide, by means of the standard solution of sulphide of sodium. The liquid is boiled in order to drive olf the sulfhydric acid, and carbonate of soda is added, which precipitates the zinc in the state of hydrocarbonate, which is collected on a filter and weighed after calcination, the zinc being thus determined in the state of oxide. In very accurate analyses, it is proper to ascertain if the filtered ANALYSIS OF BRASS AND BRONZE. MERCURY. 271 liquid does not still contain a small quantity of zinc, which often happens, because, when acting on the alloy by nitric acid, ammo- niacal salts are frequently formed, which prevent the complete pre- cipitation of the zinc by the alkaline carbonates. In order to be sure of this, the liquid is evaporated to dryness and the residue cal- cined to drive off the ammonia, when, by treatment with water, the zinc remains in the state of carbonate. It frequently happens that brass or bronze contains a small quanty of iron, introduced by the fact of impure metals being used in making the alloy. In this case, after having boiled the liquid, the copper of which is precipitated by sulfhydric acid, a few pinches of chlorate of potassa must be thrown into the boiling liquid, or a current of chlorine passed through the solution, in order to convert the iron into the sesquioxide. The liquid is saturated by ammonia, and the succinate of ammonia, which precipitates the iron from it, is added. The filtered liquid which contains the zinc, contains too large a proportion of ammoniacal salts to allow this metal to be imme- diately precipitated by carbonate of soda, for which reason the liquid must be evaporated, the carbonate of soda added, and the substance be perfectly dried. By treating it with water the hydrocarbonate is wholly precipitated. MERCURY. Equivalent = 109 (1250.0; O = 100). § 1083. Mercury is the only metal which is liquid at the ordinary temperature. It congeals at temperatures below 40°; and then forms a white, very brilliant metal, resembling silver. Solid mer- cury is malleable, and flattens under the hammer, so that medals may be struck of it. In the polar regions, mercury frequently con- geals from the intense degree of cold ; and it may be solidified in a refrigerating mixture of solid carbonic acid and ether, (§ 254,) or in a mixture of ice and chloride of calcium, (§ 374). It is sufficient to use finely pounded ice, cooled below 32°, and small crystalline grains of chloride of calcium, such as are obtained by crystallizing a concentrated hot solution, and disturbing the crystallization. By operating on a moderate quantity of mercury, placed in a large crucible, which is gradually cooled in the refrigerating mixture, the metal may be obtained crystallized, if, as soon as a thin crust of solid mercury forms on the sides of the crucible, the liquid portion is poured off; when brilliant regular octohedrons, often clearly ter- minated, are found on the inside. The density of solid mercury has been found to be 14.4, at a tem- perature a little below that of its congelation; while the specific 272 MERCURY. gravity of the metal in the liquid state is 13.596, at a temperature of 32°. Mercury expands, while passing from 32° to 212°, by a fraction 0.018153 of its volume at 32°, or by Ag for every degree, which is equal to gA for each centigrade degree. It boils at 662° of the air thermometer, and the density of its vapour is 6976. The tension of the vapour of mercury is appreciable at the ordinary tem- perature, although it is too feeble to be accurately measured; but the volatility of mercury is placed beyond doubt by the action which the metal exerts, at the ordinary temperature and distance, on da- guerreotype plates which have been exposed to iodine and affected by light. The globules of mercury which condense in the upper part of the vacuum of barometers, also attest its volatility. At the temperature of 212° the tension of mercurial vapour is about \ millimetre. By boiling the metal with water, in a glass retort, a considerable quantity of mercury is distilled. Below 32° the vola- tilization of mercury is nearly inappreciable, and its vapour appears to no longer possess the expansive force characterizing elastic fluids. In fact, on suspending a leaf of gold in a bottle containing a small quantity of mercury, and allowing the bottle to rest for several clays in a low temperature, the leaf is whitened by the mercurial vapour only to the height of a few centimetres above the surface of the bath, the upper portion always retaining its characteristic yel- low colour. § 1084. The mercury of commerce is nearly pure when it comes directly from the furnace, Avhile that used in the laboratory almost always contains small quantities of foreign metals and oxide of mer- cury in solution. After some time, especially in summer, mercury absorbs oxygen from the air; and when the metal is agitated, the oxide is scattered through the whole mass, but, wrhen at rest, rises to the surface and forms a gray pellicle. When mercury is pure, it adheres neither to glass nor to porcelain, but flows freely over its surface; but when it contains foreign matters, or even oxide of mercury, it adheres remarkably, and on rolling it slowly over a glass plate, does not form spherical globules, but drops elongated in the shape of tears, which are wrinkled on their surface, and leave a gray pellicle adhering to the glass: the mercury is then said to leave a tail, (faire une queue.) The mercury of the laboratory cistern may be greatly purified by passing over the surface of the bath, a very dry, large glass tube, to which the superficial pellicle of gray oxide adheres, and may thus be removed. Mercury is purified, in the first place, by distillation, which opera- tion is easily effected in the cast-iron bottles in which it is usually transported. One of these bottles being half-filled with mercury, and a curved gun-barrel abc introduced into its mouth, the bottle is arranged in a furnace, as represented in fig. 577, and a tube cd, formed of several layers of linen and dipping into a pan of water, is attached to the gun-barrel. The end of the latter and the linen MERCURY. 273 are kept wet by a stream of water flowing constantly; and, lastly, the bottle is heated to the boiling point of mercury, when ebullition takes place with violent bubbling, and the mercury distils over, leaving the greater pro- portion of the foreign metals in the bottle. A considerable quantity, however, is carried over by distillation, and it cannot be expected to obtain pure mercury from a single operation. The distilled mercury is placed in a cast-iron re- ceiver, ordinary nitric acid diluted with twice its weight of water is poured upon it, and it is heated to 50° or 60°; when protonitrate of mercury is formed, which, together with the free acid, react on the foreign metals, while the latter dissolve in the acid liquid, the oxide of mercury which may have formed by contact with the air, during distillation, also entering into solution. The acid is allowed to act for at least 24 hours, stirring the mass from time to time; and lastly, it is gently heated to drive off the water, when the nitrate of mercury remains in the form of a crystalline crust, which is re- moved, and from which the metallic mercury can be extracted. The mercury is washed rapidly in water, and dried, first with tissue paper, and then under a bell-glass with quicklime. The distillation of mercury frees it so imperfectly from foreign substances that it is rarely useful, and it is in all cases preferable to treat the impure mercury directly with nitric acid and repeat the operation as often as may be necessary. When mercury merely contains oxide, it is sufficient to place it in a bottle with a small quantity of concentrated sulphuric acid, and to shake it from time to time, in order to bring all its parts into con- tact with the acid. In 2 or 3 days the acid is poured off and the mercury washed. After a time, mercury exerts a deleterious action on the animal economy. Workmen in this metal, or those who are frequently exposed to its vapours, are liable to paralysis and copious salivation. We have mentioned that mercury absorbs, after some time, a small quantity of oxygen from the air, even at the ordinary tem- perature ; but the oxide, mixed with or dissolved in a large quantity of free metal, forms a gray pellicle, which adheres to glass, or the surface of the bath. In order to ascertain that the pellicle contains oxide of mercury, it suffices to distil a certain quantity of it in a current of nitrogen gas, when it deposits a small crystalline residue Fig. 577. 274 MERCURY. of red oxide of mercury. Oxidation advances more rapidly at the boiling point of mercury; and by boiling the metal slowly in a long- necked balloon, into which the air enters freely, a considerable quantity of oxide of mercury can be produced in the form of small, red prismatic crystals. This oxide was originally prepared in this way, and called by the old chemists precipitate per se ; and it has already been shown (note to § 95, vol. i.) that by keeping mercury for a very long time at a temperature approaching its boiling point, it is possible to determine by approximation the composition of at- mospheric air. Concentrated chlorohydric acid does not sensibly act on mercury even when hot, and dilute sulphuric acid does not attack it; while concentrated hot sulphuric acid soon transforms it into sulphate of mercury, with disengagement of sulphurous acid. Nitric acid, even when cold, attacks mercury when the acid is dilute, while deutoxide of nitrogen is disengaged. COMPOUNDS OF MERCURY WITH OXYGEN. § 1085. Two compounds of mercury with oxygen are known : the less oxygenated, to which we shall give the name of black-oxide, or suboxide of mercury,* corresponding to the formula HgaO ; while the formula of the more oxygenated, which we shall call red, or protoxide of mercury, is HgO. Suboxide of mercury Hg20 is not a very fixed compound, but forms with the acids well-defined salts, which crystallize readily. It is obtained by precipitating one of its salts, the nitrate, for example, by caustic potassa, when a black precipitate is formed, which de- composes spontaneously into the red oxide and metallic mercury. By grinding the powder in a mortar for some time, small globules of metallic mercury will be found, which decomposition takes place much more rapidly at the temperature of 212°, or even at the or- dinary temperature, when assisted by solar light. The protoxide or red oxide of mercury HgO is formed when mer- cury is exposed to the air at a high temperature, which process, however, yields only a small quantity; and it is more easily ob- tained by decomposing nitrate of mercury by moderate heat. The same oxide is obtained by calcining the subnitrate Hg20,N05 or the protonitrate HgO,NOs; but the product differs slightly in ap- pearance, according to the nature of the nitrate from which it was formed. Thus, the nitrate IIgO,NOs in small crystals, produces crystalline oxide of mercury of a brickdust colour, while the nitrate Hg30,N05 yields an orange-yellow oxide. By adding potassa to a solution of protonitrate of mercury * The name of protoxide is sometimes given to the suboxide of mercury and that of binoxide to the protoxide HgO : we shall not adopt this nomenclature, for the reasons given, (§ 1040,) because it does not agree with our chemical formulae. SALTS OF BLACK OXIDE. 275 HgO,NOs, a yellow precipitate of anhydrous oxide of mercury is obtained. The red and the yellow oxide of mercury constitute two isomeric states, which are evinced in some chemical reactions. The non- calcined yellow oxide, that is, the oxide obtained by the humid way, is more easily attacked by chlorine than the red oxide, and, when cold, combines with oxalic acid, which under the same circumstances exerts no action on the red oxide. SALTS FORMED BY THE SUBOXIDE OF MERCURY, HgaO. § 1086. The suboxide of mercury Ilg30 forms with the majority of the acids well-defined salts, which are often called salts of mer- cury at the minimum. The subnitrate is obtained by dissolving cold mercury in dilute nitric acid, taking care to keep the mercury in excess; And the subsulphate is prepared by heating mercury in excess with concentrated sulphuric acid. Many salts of mercury at the minimum are prepared by double decomposition. Suboxide of mercury forms several salts with the same acid; and the neutral salts are colourless when the acid is free from colour, while the basic salts are yellow. The latter are insoluble in water, while the majority of the neutral salts produce colourless solutions. Some neutral salts of the suboxide are decomposed by water into basic salts which are precipitated, and salts with excess of acid which dissolve. These salts are known by the following characters: The caustic alkalies and ammonia throw down a black precipitate, insoluble in an excess of reagent, and which, when slightly heated, yields globules of metallic mercury. If it be rubbed with a blade of very bright copper, the latter becomes white by being alloyed with the mercury. The alkaline carbonates yield dirty-yellow pre- cipitates which soon turn black. Prussiate of potash throws down a white precipitate. Sulf hydric acid gives a black precipitate, and the alkaline sulf- hydrates yield the same precipitate, which does not dissolve in an excess of the reagent. Chlorohydric acid and the chlorides throw down a white precipi- tate of chloride of mercury Hg3Cl, perfectly insoluble in water and dilute acids. Iodide of potassium gives a greenish-yellow precipitate, which dis- solves in an excess of reagent. Iron, zinc, and copper precipitate mercury from its solutions, in the state of an amalgam. Subnitrates of Mercury. § 1087. Suboxide of mercury forms several compounds with nitric acid. The neutral nitrate is obtained by pouring an excess of dilute nitric acid on metallic mercury, and allowing the action to ensue in the cold; when the mercury oxidizes at the expense of the oxygen 276 MERCURY. of a portion of the nitric acid, and, after some time, large, colour- less crystals of subnitrate separate, the formula of which is Hg30,N0s + 2IIO, and which dissolve in a small quantity of cold water, but are decomposed by a large quantity of this fluid, a basic nitrate being precipitated, which may be redissolved by the addition of nitric acid. If, on the contrary, dilute nitric acid be added to a large excess of metallic mercury, and allowed to react, when cold, for a sufficient length of time, the metal becomes covered with large, colourless crys- tals, generally well defined, belonging to a basic nitrate, of which the formula is 3HgaO,2NOs+3IIO. If this salt or the neutral ni- trate be treated with tepid water, a bibasic nitrate of the formula 2IIgaO,NOs is obtained. By boiling the latter compound with water, it is converted into a green powder, which appears to be a still more basic nitrate. The neutral nitrate is easily distinguished from the basic nitrates by rubbing them up with a concentrated solution of sea-salt, in which case the neutral nitrate remains colourless, because the mer- cury passes entirely into the state of chloride HgaCl, while the basic nitrates turn blackish gray, because suboxide of mercury IIg30 is separated simultaneously with the chloride HgaCl. When a dilute solution of ammonia is added to an equally dilute solution of subnitrate of mercury, a gray precipitate of the formula (NH3+3Hga0)N05 is obtained, and which is used in pharmacy under the name of soluble mercury of Hahnemann. The composi- tion of this precipitate varies according to the concentration and temperature of the solutions. Subsulphate of Mercury. § 1088. By adding sulphuric acid to a solution of subnitrate of mercury, the subsulphate is precipitated as a white crystalline pow- der, which is very slightly soluble in water, one part of the salt requiring 500 parts of cold and 300 of boiling water. It is also obtained by heating concentrated sulphuric acid with a large excess of mercury, but it is difficult to prevent the formation of the proto- sulphate Hg0,S03. § 1089. By pouring a solution of carbonate of soda into a solu- tion of subnitrate of mercury, a white granular precipitate of the formula HgaO,COa is obtained. Subcarbonate of Mercury. § 1090. The neutral salts of the protoxide of mercury HgO are colourless, while the basic salts are yellow; and their solutions ex- hibit the following reactions: Caustic potassa and soda, in excess, yield a yellow precipitate of SALTS OF THE PROTOXIDE OF MERCURY, HgO. SALTS OF RED OXIDE. 277 the protoxide, while ammonia in general produces white precipitates, containing ammonia or its elements. Carbonate of potassa throws down a red precipitate, which does not dissolve in an excess of reagent, and carbonate of ammonia gives a white precipitate. The alkaline phosphates and arseniates form white precipitates, easily soluble in an excess of acid. Sulfhydric acid, in small quantity, throws down a white precipi- tate, which contains, at the same time, sulfhydric acid and the elements of the mercurial salt; while the same acid, in larger quantity, produces an orange precipitate. But if the solution of the mercurial salt be digested with an excess of sulfhydric acid, the precipitate turns black, owing to the forming of sulphide of mer- cury HgS. The alkaline sulfhydrates also yield white or orange precipitates when used in small quantity, and in excess they turn the precipitate black. Ferrocyanide of potassium throws down with protosalts of mer- cury in solution a white precipitate, which turns blue after long ex- posure to the air, the ferrocyanide of mercury being then decom- posed ; and while soluble simple cyanide of mercury is formed, prus- sian-blue is separated. Iodide of potassium gives a beautiful red precipitate, which may dissolve both in an excess of alkaline iodide and in an excess of the mercurial salt, soluble double iodides being formed in both cases. Chlorohydric acid and the solutions of the soluble chlorides do not precipitate protosalts of mercury, unless their solution be very con- centrated ; which characteristic distinguishes them from the subsalts of mercury, which yield, in this case, a white precipitate HgaCl, whatever may be the degree of their dilution. In order to ascer- tain if a mercurial solution contains, at the same time, subsalts and protosalts of mercury, chlorohydric acid is poured into it, when all the mercury which existed in the state of suboxide is precipitated in the form of chloride HgaCl, while that which was in the state of protoxide is dissolved. It is, therefore, sufficient to ascertain if the filtered solution produces a yellow precipitate of protoxide of mer- cury with potassa, or a red precipitate with iodide of potassium. § 1091. Protonitrate of mercury is obtained by dissolving mer- cury, when hot, in an excess of nitric acid, and boiling the salt with nitric acid until no more reddish vapours are disengaged. It may be admitted that the neutral salt exists in the acid solution, but, if the latter be evaporated, it deposits, on cooling, crystals of the basic nitrate 2Hg0,N05+2H0. The neutral nitrate cannot be separated by pouring alcohol into the solution, as the bibasic nitrate is again precipitated. Nevertheless, the solution with an excess of acid, evaporated to the consistence of syrup, deposits crystals of Protonitrate of Mercury. 278 MERCURY. neutral nitrate, when kept for some time in a refrigerating mixture. If the preceding nitrates be dissolved in a large quantity of water, they are decomposed, and throw down a wdiite precipitate, of which the formula is 3HgO,NOs-f HO, and which is remarkable for its great fixedness, for it dissolves with difficulty in nitric and sulphuric acid. Boiled with water, it again gives off acid, and, if the ebulli- tion were sufficiently prolonged, it wTould probably be converted into an oxide. If a solution of protonitrate of mercury be boiled with metallic mercury, the subnitrate IIg20,N05 is obtained. Protosulphate of Mercury. § 1092. Protosulphate of mercury is obtained by heating metallic mercury with concentrated sulphuric acid in excess, a white crys- talline powder being formed. But the evaporation with sulphuric acid must be prolonged until copious vapours of the acid are given off, as, otherwise, the protosulphate of mercury would be mixed with subsulphate. This compound is often prepared in manufactories of chemicals, because it is used in the manufacture of the chloride of mercury HgCl, or corrosive sublimate. One part of mercury and slightly more than 1 part of concentrated sulphuric acid are then heated in a glass retort, and when the metallic mercury has disappeared, the heat is still continued in a sand-bath until the pro- duct is perfectly dried, when anhydrous sulphate is obtained. It is decomposed, when treated by a large quantity of water, into a yel- low basic salt 3IIgO,SOa, used in medicine under the name of turpeth mineral, and into a salt with a great excess of acid, which crystallizes on the evaporation of the liquid. Turpeth mineral is itself decomposed by being boiled with water, and oxide of mercury is left only at last. Protochromates of Mercury. § 1093. Two protochromates of mercury are known, the formulae of which are 3Hg0,Cr03 and 4Hg0,Cr03. The first is obtained by pouring protonitrate of mercury into a solution of bichromate of potassa, or by boiling the yellow oxide of mercury with the bi- chromate ; it is a brick-red precipitate. The chromate 4Hg0,Cr03 is obtained by boiling for a long time the red protoxide of mercury with a solution of bichromate of potassa. Protocarbonates of Mercury. § 1094. By adding a solution of protonitrate of mercury to a solution of neutral carbonate of potassa in great excess, an ochrous brown precipitate of carbonate of protoxide of mercury is formed, having the formula 4Hg0,C02; and if the same experiment be made by substituting the bicarbonate for the neutral alkaline car- bonate, a brown precipitate of the formula 3IIg0,C02 is obtained. The precipitates which are formed when alkaline carbonates are SALTS OF RED OXIDE. 279 poured into a solution of nitrate of mercury are very complicated, because subnitrates of mercury are first deposited. Fulminate of Mercury. § 1095. This is a highly explosive compound, consisting of prot- oxide of mercury united with an acid, fulminic acid, formed of cyanogen and oxygen, and of which the formula is CyO or CaNO, and used for the manufacture of percussion caps. Fulminate of mercury is prepared by causing alcohol to react on the acid proto- nitrate. A quantity of mercury is dissolved in 12 parts of nitric acid of 35° or 40° of Baumd, and 11 parts of alcohol at .86 are gradually added to the solution; and, while the temperature is slowly elevated, a lively reaction accompanied by a copious evolu- tion of reddish vapours soon ensues, when the liquid, on cooling, deposits small crystals of a yellowish-white colour. Fulminate of mercury is one of the most explosive compounds known, and should be handled with great care, especially when it is dry, as it detonates w’hen rubbed against a hard body. It dissolves readily in boiling water, but the greater portion of it is again de- posited in crystals during cooling. The fulminating material of percussion caps is made of fulminate of mercury, prepared as just stated, after having been washed in cold water. The substance is allowed to drain until it contains only about 20 per cent, of water, and is then mixed with § of its weight of nitre, which mixture is ground on a marble table with a muller of guaiacum-wood. A small quantity of the paste is then placed in each copper cap and allowed to dry, the fulminating pow- der in the cap being often covered with a thin coat of varnish to preserve it from moisture. OXIDE OF MERCURY AND AMMONIA. § 1096. By treating protoxide of mercury HgO with a large ex- cess of perfectly caustic liquid ammonia, a yellow powder is ob- tained, which must be rapidly washed and dried under a bell-glass with quicklime, and the composition of which is expressed by 4HgO,NH3-f 2HO, although a more rational formula would be 3HgO,HgNHa-|-3HO. It is called oxide of mercury and ammonia. The preparation of this substance must he effected without access of air, as, otherwise, the compound would soon absorb carbonic acid, and a mixture of oxide of mercury and ammonia with carbonate of the same compound oxide would be obtained; for which purpose, the oxide of mercury is placed in a bottle completely filled with a concentrated solution of perfectly caustic ammonia, and then corked. Either the red or yellow variety of protoxide of mercury may be used, but the red oxide requires a greater length of time. The hydrated oxide of mercury and ammonia, when left for a long time 280 MERCURY. in a dry vacuum, loses its water; and if it be left until it no longer loses in weight, a brown powder remains, which consists of anhy- drous oxide of mercury and ammonia 3IIgO,HgNH3. The dishy- dration takes place very rapidly at a temperature of 266°, without any decomposition of the substance. The hydrated oxide of mercury and ammonia is insoluble in water and in alcohol. A cold solution of caustic potassa exerts scarcely any action on it; while at the boiling point ammonia is disengaged, but the ebullition must be long continued to effect complete decom- position. Anhydrous oxide of mercury and ammonia is much more fixed, as potassa decomposes it only when heated to the fusing point of the alkali. The combination exhibits all the characters of a power- ful base: it combines with the acids and forms well-defined salts. It absorbs carbonic acid nearly as readily as lime and baryta, and its carbonate does not decompose at 212° ; it also expels ammonia from its salts as rapidly as lime and baryta. The proportion of oxide of mercury and ammonia represented by the formula 3HgO,HgNH2, corresponds to 1 equivalent of a base RO, and saturates 1 equiva- lent of acid. The following compounds have, thus far, been obtained: Hydrated base 3HgO,HgNHa+3HO. Intermediate hydrate 3HgO,HgNH2+HO. Anhydrous base 3IIgO,HgNH3. Sulphate (3Hg0,HgNH2),S03. Hydrated carbonate (3HgO,IIgNH2),COa+HO. Carbonate dried at 275° (3Hg0,HgNH2),C03. Oxalate (3Hg0,IIgNH3),C303. Nitrate (3HgO,HgNHfl),NOs+HO. Bromate (3Hg0,HgNHa),Br05. Several chlorides and iodides are also known which are derived from the oxide of mercury and ammonia by reactions resembling those by which the ordinary metallic oxides are converted into chlorides and iodides. The formulae of these compounds are: Chloride (2HgO,HgCl),HgNHa. Another chloride 3HgCl,HgNHa. Iodide (2HgO,IIgIo),HgNHa. Sulphate of Mercury and Ammonia. § 1097. If protosulphate of mercury HgO,S03 be added, by small quantities at a time, to caustic ammonia, the salt is dissolved in very large quantity; but if the liquid be diluted with a great deal of water, a copious white precipitate forms, which was long known as ammoniacal turpeth, and which may be regarded as the sulphate of CINNABAR. 281 mercury and ammonia (3Hg0,HgNII3)S03. The composition of this product does not, however, appear to be constant. Carbonate of Mercury and Ammonia. § 1098. This salt is readily prepared by the direct combination of carbonic acid with oxide of mercury and ammonia suspended in water; when an insoluble yellow compound, consisting of the hy- drated carbonate, is obtained. It parts with its water at about 284° and passes into the state of anhydrous carbonate. Oxalate of Mercury and Ammonia. § 1099. The oxalate of mercury and ammonia is obtained by digesting the protoxalate of mercury, made by double decomposi- tion, with caustic ammonia in excess, when a white granular pow- der is obtained, which explodes when heated. § 1100. If a current of sulfhydric acid be passed through a solu- tion of a subsalt of mercury a black precipitate is obtained, which is the sulphide of mercury Hg2S, corresponding to the suboxide Hg20; but if the temperature be raised the precipitate is rapidly converted, even in the water, into the protosulphide HgS, and into metallic mercury. If a current of sulfhydric acid be passed through a solution of a protosalt of mercury, there results first a white precipitate, which is a compound of protosulphide of mercury with the mercurial salt subjected to the reaction. Thus, the protosulphate IIgO,S03 is con- verted into a compound of which the formula is Hg0,S03-f2HgS, while the protonitrate Hg0,N05 gives the compound HgO,NOs+ 2HgS, and the protochloride HgCl yields the product HgCl+2HgS. But if the liquid be completely saturated by the gas, the precipitate turns black, and consists entirely of sulphide of mercury HgS, which, when heated in a retort, sublimes completely without change, and yields a red product of a crystalline fibrous texture, having the same composition as the black precipitate, and known by the name of cinnabar. The same compound is obtained by a continued trituration of mercury with sulphur, when a black substance is formed, which is sometimes used in medicine under the name of sethiops mineral. In order to obtain the sulphide of mercury HgS, it is better to rub together 6 parts of mercury and 1 of sulphur, the black substance which results yielding cinnabar by sublimation. Sulphide of mercury HgS is found in nature, most frequently in deep red, compact masses, but also forming, sometimes, beautiful red transparent crystals derived from the rhombohedron of 71°. It is the principal ore of mercury. Under the ordinary pressure of the atmosphere, cinnabar vola- tilizes before fusing, and produces a brownish-yellow vapour, the COMPOUNDS OF MERCURY WITH SULPHUR. 282 MERCURY. density of which is 5.4, while the specific gravity of solid cinnabar is 8.1. The sulphide of mercury HgS sometimes exhibits a red colour more beautiful than that of sublimed cinnabar, and is used in oil and aquarelle painting under the name of vermilion. The most beautiful vermilion is prepared by the reaction, assisted by water, of the alkaline polysulphides on sulphide of mercury: 300 parts of mercury and 114 of sulphur being triturated for 2 or 3 hours in a mortar, and 75 parts of potassa and 400 of water added, the whole is maintained at a temperature of about 113°, and shaken from time to time, Avhen the black precipitate soon turns red ; and when it has attained the proper shade, it is rapidly washed with hot water. If the action of the alkaline sulphide were prolonged too much, the substance would again become brown. Very fine vermilion is also obtained by heating, for a considerable length of time, at an average temperature of 122°, ordinary cinnabar, reduced to an impalpable powder, with a solution of alkaline sulphide. The phenomenon of the change of colour of the sulphide of mercury, by contact with the alkaline sulphides, has not yet been properly explained. Cinnabar is manufactured on a large scale in the furnaces for working ores of mercury. At Idria, in Carinthia, 100 parts of mer- cury and 18 parts of powdered sulphur are placed in small wooden tubs, which are turned for 3 or 4 hours around their horizontal axis, when a black sulphide of mercury is formed, which is then sublimed in cast-iron vessels, covered with capitals of baked clay, on which the cinnabar condenses. Cinnabar is readily roasted in the air, sulphurous acid being dis- engaged, while metallic mercury distils over. It is easily decom- posed by hydrogen, carbon, and many of the metals. The non- oxidizing acids act on it with difficulty, Avhile it is readily attacked by concentrated nitric acid, and especially by aqua regia. § 1101. Two compounds of mercury with chlorine are known: The subchloride HgaCl, called calomel; and The protochloride HgCl, commonly called corrosive sublimate. The majority of chemists, even at this day, give the name of pro- tochloride of mercury to calomel HgaCl, and that of bicldoride to corrosive sublimate HgCl; but we have not retained these names, because they clash with the rules of nomenclature and chemical formulse which it has been agreed to assign to these substances. We deem it necessary to insist particularly on this point, in order to avoid mistakes, which might prove very serious, because these substances are used in medicine. The subchloride HgaCl may be prepared by pouring a solution of subnitrate of mercury into a dilute solution of sea salt, the sub- chloride of mercury HgaCl being precipitated in the form of a white COMPOUNDS OF MERCURY WITH CHLORINE. CALOMEL. 283 powder. It may he also obtained by the reaction of metallic mer- cury on protochloride of mercury HgCl, or corrosive sublimate, for which purpose 4 parts of corrosive sublimate and 3 parts of mercury are mixed and rubbed together for some time, moistening the whole with a small cpiantity of alcohol, to prevent injury from the poisonous dust of the sublimate. It is then heated in a large phial, in a sand- bath, when the calomel sublimes and condenses in the upper part of the phial. As this product may be mixed with corrosive sub- limate, it is necessary to reduce it to a fine powder, and wash it with boiling water until the water affords no precipitate with po- tassa or sulfhydric acid. Calomel is prepared in manufactories of chemical products by heating a mixture of subsulphate of mercury Hg30,S03 and sea salt; but as the preparation of the subsulphate is somewhat difficult, a mixture of protosulphate of mercury IIgO,S03 and metallic mercury is substituted. Sixteen parts of mercury being divided into two equal portions, the first is converted into protosulphate (§ 1092) and mixed intimately with the second por- tion, after which the mixture is rubbed up with 3 parts of sea salt and the whole distilled. Calomel used in pharmacy should be very finely powdered, be- cause it is then more easily separated from the corrosive sublimate, which acts as a poison on the animal economy. It is obtained im- mediately in an impalpable powder by effecting the distillation in a vessel, the wide and short neck of which enters a large receiver, where the calomel vapour condenses before touching its sides. The calomel thus obtained should be washed with boiling water until no precipitate is formed by potassa or sulfhydric acid. By subliming large quantities of calomel, beautiful transparent crystals are frequently obtained, which are square prisms, having an octohedral termination. They are remarkable for their great refracting and dispersive power, and belong to the second system of crystallization. Light slowly decomposes subchloride of mercury, and causes it to assume a grayish hue, owing to the disengagemertt of chlorine, while a portion of the mercury is set free. The density of this substance is 6.5; and it fuses and volatilizes at nearly the same temperature under the ordinary pressure of the atmosphere. The density of its vapour is 8.2, the gaseous chloride being there- fore composed of 1 vol. vapour of mercury 6.9T6 J “ chlorine 1.220 1 vol. gaseous suhchloride HgaCl 8.196 Calomel is very slightly soluble in water, and a solution of 1 part of chlorohydric acid in 250,000 parts of water is very sensibly alfeeted by subnitrate of mercury. In time, chlorohydric acid acts on it at the boiling point, when metallic mercury separates, while the protochloride HgCl is dissolved. Concentrated nitric acid soon 284 MERCURY. converts it into corrosive sublimate and protonitrate of mercury. Aqua regia and a solution of chlorine dissolve it in the state of protochloride IlgCl. Calomel combines readily with dry ammo- niacal gas, producing a black compound, of which the formula is HgaCl+NHa, and which, when treated with liquid ammonia, yields a gray powder of the formula IIg3Cl,IIgNII3. Calomel is used in medicine as a vermifuge and purgative, and is also applied to the treatment of venereal diseases. Protochloride of Mercury IlgCl, or Corrosive Sublimate. § 1102. Corrosive sublimate can be prepared by dissolving mer- cury in aqua regia containing an excess of chlorohydric acid, when, by treatment with boiling water, the greater part of the proto- chloride is deposited in acicular crystals during the cooling of the liquid. This compound is generally prepared on a large scale, by heating on a sand-bath a mixture of protosulphate of mercury HgO,S03 and sea salt, when the protochloride sublimes on the upper parts of the distilling apparatus. The protosulphate of mer- cury often contains a small quantity of subsulphate, which yields calomel by its reaction on sea salt; to avoid which, a small quantity of peroxide of manganese is generally added to the mixture. As corrosive sublimate fuses at a pressure much below that at which it distils at the ordinary pressure of the atmosphere, advantage is taken of this property to give more consistency to the sublimed pro- duct ; to effect which, the fire is increased toward the close of the operation, when the sublimate, by beginning to fuse, is more com- pactly aggregated. When the distilling vessels are cool they are broken, and the cakes of corrosive sublimate removed. Protochloride of mercury is colourless, and its density is 6.5. It fuses at about 509°, and boils at about 563° under the ordinary pressure of the atmosphere, yielding a colourless vapour, the density of which is 9.42. Gaseous protocliloride therefore contains 1 vol. vapour of mercury 6.976 1 “ chlorine 2.440 1 vol. gaseous chloride HgCl 9.416 Corrosive sublimate dissolves in 16 parts of cold and 3 parts of boiling water, and its curve of solubility is represented on the plate at page 407, vol. i. It is more easily soluble in alcohol than in water, as 2J of absolute and 1J of boiling alcohol dissolve 1 part of the binary compound. It is also soluble in 3 parts of cold ether. It dissolves readily in a solution of chlorohydric acid, especially when the latter is hot, and the liquid sets in a crystalline mass on cooling. Corrosive sublimate is often used in the laboratory as an agent of chlorination; and it has already been shown (§ 943) that bi- chloride of tin is obtained by distilling a mixture of 1 part of tin CORROSIVE SUBLIMATE. 285 filings and 5 parts of sublimate. Many substances also abstract from it, by the humid way, a portion of its chlorine, and cause it to pass into the state of subchloride, which decompositions are more easily effected when assisted by solar light. Corrosive sublimate is sometimes employed in medicine, chiefly in the treatment of venereal diseases; but, being a dangerous medi- cine, it should only be administered with the greatest care. It is used advantageously to protect wood from insects, and wooden bed- steads may be kept free from vermin by impregnating the wood with a weak solution of sublimate. Zoological specimens and anatomical preparations are frequently preserved by being soaked in a dilute solution of it.* Protochloride of mercury forms, with the metallic chlorides, a great number of crystallizable double chlorides. Three of these compounds with chloride of potassium have been obtained, the formulae of which are KCl+HgCl+HO,KCl+2HgCl-f-2HO and KCl-f 4IIgCl+4HO. But one compound has been obtained with chlorohydrate of ammonia, with the formula NH3,HCl-fHgCl + HO, and isomorphous with the corresponding compound with chloride of potassium. When caustic alkalies or alkaline carbonates are poured into a solution of corrosive sublimate, very variable compounds are ob- tained, according to the proportions of the reacting substances and the temperature and degree of concentration of the liquids. When the alkali is in excess the yellow or red oxide is produced; but by using the reagent in weaker and more varying proportions, gray, red, or violaceous precipitates are obtained, which are oxychlorides; the formulm are 2HgO,HgCl, 3HgO,HgCl, 4HgO,HgCl. Analo- gous oxychlorides are obtained by boiling oxide of mercury with a solution of corrosive sublimate. Ammonia, poured into a solution of corrosive sublimate, throws down white precipitates, making the liquid emulsive and varying in composition. They have all, for a long time, been indiscriminately called white precipitate, but are now divided into several well- defined compounds. If a solution of corrosive sublimate be poured into a solution of caustic ammonia, and the precipitate be washed with cold water, a wdiite substance is obtained, of which the formula is Hg3ClNH3, and which is called chloramide of mercury, because it is admitted to contain the compound NH3, which is called amide, (§ 514.) The reaction from which this product arises is represented by the following equation: 2HgCl+2NH3 = NH3,HCl+Hg3ClNH3. * Meat may be kept fresh for a great length of time, by being allowed to re- main for several hours in a bucket filled with water into which the merest trace of corrosive sublimate has been thrown; and several other metallic salts, espe- cially nitrate of silver, have the same property. This method of preserving meat would, however, be too dangerous for family use.—W. L. F. 286 MERCURY. The formula HgCl,HgNH3 is sometimes assigned to this sub- stance. It is decomposed by boiling water, and, when heated, gives off ammonia, ammoniacal chloride of mercury 2IIg2Cl,NH3, and leaves in the retort a red compound, which is destroyed only at a temperature of 662°, and of which the composition is represented by the formula 2HgCl+NHg8. By boiling chloramide of mercury with water until the sub- stance no longer undergoes any change, a white compound of which the formula is (2HgO,HCl)IIgNH3 is obtained, which may be re- garded as the chloride of the compound oxide of mercury and am- monia 3HgO,IIgNII3; and, in fact, when treated with potassa, it is converted into oxide of mercury and ammonia. If caustic ammonia be dropped into a solution of corrosive subli- mate, taking care to keep the latter substance always in excess, a white precipitate is obtained, of which the formula may be written 3HgCl,HgNH2, and which is then regarded as oxide of mercury and ammonia, in which all the oxygen is replaced by an equivalent quantity of chlorine. This compound is soon changed even by wash- ing in cold water. COMPOUNDS OF MERCURY WITH BROMINE. § 1103. Mercury forms with bromine two compounds which cor- respond to the two chlorides. The bromide Hg3Br is obtained by pouring a solution of bromide of potassium into that of subnitrate of mercury, when the precipitate which forms is nearly insoluble in wrater, and volatilizes without change. The bromide of mercury HgBr is obtained by pouring bromine in excess on mercury covered by a stratum of water, when the mercury soon dissolves in the state of protobromide, which may be crystallized by evaporation. The protobromide may then be sublimed without alteration, and it forms crystallizable compounds with the alkaline bromides. COMPOUNDS OF MERCURY WITH IODINE. § 1104. By adding iodide of potassium to a solution of corrosive sublimate, a red precipitate of protiodide of mercury Ilgl is ob- tained, which may also be prepared by triturating together equal quantities of mercury and iodine, with a small quantity of alcohol to assist their reaction. The protiodide of mercury dissolves largely in a hot solution of iodide of potassium, and the liquid, on cooling, deposits a portion of the protiodide in the form of beautiful red crystals. If the red iodide of mercury be heated, it suddenly changes colour and becomes of a clear yellow, while, if the tem- perature be raised still higher, it fuses into a yellow liquid, and sub- limes in the form of yellow crystals. The fused yellow iodide and the large yellow crystals frequently retain their colour, even after cooling; but the substance, on being broken, turns red, first at the CYANIDE. 287 point of the rupture, and then gradually through the whole mass, which change of colour is very rapid when the substance is pow- dered. The protiodide of mercury presents, therefore, two modifi- cations, distinguishable by their colour, and which also affect two different crystalline forms, the primitive form of the red crystals being an octahedron with a square base belonging to the second system, while the yellow crystals belong to the fourth. Protiodide of mercury volatilizes without change, and the density of its vapour has been found to be 15.68, being the greatest of all gaseous bodies. It is very slightly soluble in water, only in the proportion of 1 to 150. An iodide of mercury Hg3I is obtained by pouring iodide of po- tassium into a solution of subnitrate of mercury, as a dirty-green precipitate, which volatilizes unchanged when rapidly heated, and which, on the contrary, is decomposed into protiodide of mercury Hgl and metallic mercury when heated slowly. § 1105. Only one compound of mercury with cyanogen is known, corresponding to the protoxide HgO. The combination is made by dissolving protoxide of mercury in cyanohydric acid, for which pur- pose the dilute cyanohydric acid obtained by the solution of the ferrocyanide of potassium in dilute sulphuric acid is used. Cyanide of mercury is generally prepared in the laboratory by boiling to- gether 8 parts of Prussian blue, 1 of protoxide of mercury, and 8 of water, when the boiling solution, after being filtered, deposits on cooling white prismatic crystals of anhydrous cyanide of mercury IlgCy or HgC2N. When, as often happens, the liquid contains a small quantity of iron in solution, it is boiled with protoxide of mer- cury, which precipitates the oxide of iron. Cyanide of mercury may also be prepared by boiling 2 parts of ferrocyanide of potassium with 3 of protosulphate of mercury dissolved in 15 or 20 parts of water; when the liquid deposits, on cooling, crystals of cyanide of mercury. The affinity of mercury for cyanogen is considerable, as oxide of mercury decomposes cyanide of potassium, potassa and cyanide of mercury being formed. When boiled for a long time the prot- oxide of mercury dissolves in the cyanide of mercury, and the liquid deposits crystals of oxycyanide of mercury. Cyanide of mercury combines with a great number of metallic cyanides, and yields crystallizable double cyanides. The double cyanide of mercury and potassium crystallizes in regular octahedrons of the formula KCy+HgCy. Cyanide of mercury also combines with the chlo- rides, alkaline bromides, and iodides, forming several crystallizable compounds. COMPOUND OF MERCURY WITH CYANOGEN. 288 MERCURY. § 1106. If dry ammoniacal gas be passed over protoxide of mer- cury, prepared by the humid way, until the latter can absorb no more, and the product be then slowly heated in an oil-bath to 302°, still maintaining the current of ammonia, a brown powder is ob- tained, which is a compound of mercury with nitrogen, having the formula HguN. The substance is generally mixed with a small quantity of suboxide of mercury, which can be removed by weak nitric acid. Nitride of mercury detonates by heat, and by percus- sion, or by contact with concentrated sulphuric acid properly pre- pared. Acids dissolve it, producing fixtures of mercurial and am- moniacal salts. COMPOUND OF MERCURY WITH NITROGEN. DETERMINATION OF MERCURY, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. § 1107. Mercury is generally determined in the metallic state, and sometimes also in the state of subchloride IIgsCl. In order to separate mercury from its compounds, under conditions in which the metal can be very exactly weighed, a tube ah of hard glass is employed, resembling those used in the analysis of organic sub- stances, and drawn out in one of its ends, as represented in fig. 578, having a globe A at the narrow portion, in which the mercury condenses. A small quantity of as- bestus being placed at a in the tube, upon it is poured a volume of quicklime, and the mercurial substance, exactly weighed, is intro- duced at c, and lastly, the tube is filled with lime. This being done, the tube is arranged over a sheet-iron furnace, and a current of dry hydrogen gas passed through the extremity b ; the anterior portion ca of the tube containing the lime being first heated, while the coals are gradually carried toward the end b. The mercurial product is decomposed, the mercury is carried over in the state of vapour by the hydrogen gas and condenses in the globe A, wdiile the small quan- tity of water which sometimes also collects there is soon carried off by the dry hydrogen. At the close of the operation, the globe A is detached and weighed with the mercury it contains ; after which the metal is poured out, and, for greater exactness, the interior of the globe is washed with nitric acid and then with distilled water. The globe, being empty and perfectly dry, is wmighed, and the weight of the condensed mercury thus ascertained. In order to obtain exact results, care must be had that the temperature of the globe does not rise, in consequence of the condensation of a large quantity of water, as in that case a small quantity of vapour of mercury would be lost. When the mercurial product contains nitric acid metallic copper must be substituted for the lime, in order to decompose the nitrous vapours, which would attack the mercury in the globe A. Fig. 578. AMALGAMS. 289 § 1108. Advantage is generally taken of the volatility of mer- cury to separate it from the other metals with which it is mixed. When it is dissolved in acids it is always precipitated by sulfhydric acid, and the precipitate is then restored to the metallic state by heating the product, mixed with a small quantity of quicklime, in a current of hydrogen gas. When the sulphide of mercury is mixed with other metallic sulphides the latter are separated, as the mer- cury alone distils over. When the mercury is precipitated from its solutions in the me- tallic state by a blade of iron, or by protochloride of tin, it is still necessary, in order to obtain it perfectly pure, to distil it in the apparatus first described. ALLOYS OF MERCURY, OR AMALGAMS. § 1109. Mercury combines with a large number of metals, form- ing alloys, called amalgams, which are fluid when the mercury largely predominates, and solid in the contrary case. The presence of a very small quantity of foreign metal suffices to destroy the fluidity of mercury and its other physical characters. Mercury combines with potassium and sodium and evolves heat, while doughy amalgams are formed which decompose water. With lead and tin it forms amalgams the consistency of which varies with the proportion of metal combined. If these amalgams be heated so as to make them perfectly liquid, and then allowed to cool slowly, crystals of solid amalgam separate, exhibiting compounds of definite proportions. An amalgam of silver, crystallized in regular dode- cahedrons, and the usual composition of which is expressed by the formula HgaAg, is found in nature. Amalgams are readily decom- posed by heat, and give off the whole of their mercury, which distils over. PLATING OF MIRRORS. § 1110. Mirrors are made by covering one side of the glass with an amalgam of mercury and tin in the following manner:—A sheet of tin-foil, of the same size as the glass, is laid upon a very smooth marble table, set in a wooden frame and surrounded by little canals. The table, which is movable and may be inclined in various ways, is first made perfectly horizontal, and the sheet of tin, being smoothed with a hare’s foot, is then completely saturated with mercury ap- plied by the same instrument. It is then covered with a coat of mercury 4 or 5 millimetres in thickness, after which the glass plate is brought to the end of the table, and pushed over the sheet of tin, so as to drive before it the mercury in excess, which runs into the canal around the table. The glass is then loaded with lumps of plaster, distributed uniformly over its surface, and the table is in- clined to facilitate the escape of the mercury expelled by pressure. It is then left in this position for 15 or 20 days, after which the 290 MERCURY. coating adhering to the glass is composed of about 4 parts of tin and 1 of mercury. METALLURGY OF MERCURY. § 1111. The principal ore of mercury is the sulphide or cinnabar, which mineral is found in two different geological positions. It sometimes forms veins in the oldest transition rocks, and sometimes is scattered through the strata of sandstone, schist, or compact lime- stone, which appear to belong to the Jurassic epoch. The famous mines of Almaden, in the province of La Mancha in Spain, consist of veins traversing micaceous transition schists, while the mines of Idria, in Illyria, are an example of the second formation. Mercury is also found in the native state, in small globules scattered through bituminous strata, but always in the vicinity of bearings of cinnabar, and probably arising from certain chemical reactions which have taken place in the bosom of the earth. Mercury is procured from cinnabar, at Idria and Almaden, by roasting the ore in a distilling apparatus, when the sulphur burns in the state of sulphurous gas, while the mercury, being set free, distils over and condenses in the chambers. § 1112. Figures 579, 580, and 581 represent the apparatus used at Idria. A is a large roasting furnace (figs. 579 and 581) furnished on each side with a series of condensing chambers C, C,...D. The ore in large pieces is heated on an arch nn' having a great num- Fig. 579. Fig. 580. ber of holes, until the space Y is entirely filled with it, while on the second arch pp' smaller pieces of Ore are placed; and lastly, on a third rr', the dust and mercurial residues of preceeding operations are changed. The pulverulent ore is placed in earthen vessels with METALLURGY OF MERCURY. 291 which the space U is entirely filled; and when the furnace is charged, fire is kindled on the grate F, and the temperature is gradually raised. The sulphide of mercury roasts in a very oxidiz- ing current of air, which enters the furnace by small canals opening into the spaces G, H, and the mercurial va- pours are carried into the condensing cham- bers C, C, C, C, in the first three of which the greater portion of the metal condenses, whence it flows into the conduits abed, a'b'c'd', which con- convey it into a reser- voir. A great deal of water and but little mer- cury condenses in the last chamber; and as the latter is mixed with dust, it is collected in separate conduits, and then purified by filter- ing, while the residue is again introduced into the furnace. In order to condense the last mercurial vapours in the last chambers E, D, water is poured over the inclined planes which extend from one side to the other, and between which the gas and vapours are obliged to circulate before passing out into the atmosphere. The mercury is filtered through ticking-cloth, and then placed in cast-iron bottles, each containing about 60 pounds. The ore at Idria consists of several kinds, according to the nature of the substances with which the cinnabar is intimately mixed. The richest ores, which are found in limestone, and yield 50 to 60 per cent, of mercury, are called stalilerz ; and the lebererz, or cinnabar scattered through very bituminous schist yields 40 to 50 per cent, of mercury. The ziegelerz only contain from 10 to 20 per cent., as in them the sulphide is disseminated in schists and quartzose sandstone. § 1113. Certain parts of the veins at Almaden contain pure cin- nabar, while the greater portion is composed of cinnabar scattered through quartzose and argillaceous gangues, yielding only about 10 per cent, of mercury. The Spanish mines furnish annually more than 2000 tons of mercury. At Almaden, as at Idria, the treatment consists in roasting the ore in furnaces, one of which is represented in figs. 582 and 583, and which, in Spain, are called buytrones. The furnace consists of a prismatic space AB, separated into two compartments by a brick arch pierced with holes. The ore is heaped in the space B above the arch, the larger pieces being at the bottom, and the whole is covered with bricks made of a mixture of clay, powdered ore, and mercurial dust arising from the operation. At the upper part of Eig. 581. 292 MERCURY. Fig 582. Fig. 583. the furnace B, apertures p communicate with earthen receivers, arranged on each other in rows. Fig. 584 represents some of these receivers or aludells. The condensed mercury oozes through the joints of the aludells on the lower row, and flows into a canal bb, which conveys it into a receiving basin m, n, n, while the gases, mixed with the mercurial vapours which have not been condensed, are conveyed into a chamber E, where mercurial dust, which is to be removed from time to time, is deposited. The dust yields, by filtering, a certain quantity of fluid mercury, and the residue is mixed with clay of which clay bricks are made, to be again heated in the furnace as above stated. The firing lasts for 12 or 13 hours, after which the furnace is allowed to cool for 3 or 4 days, when the materials are withdrawn and a second operation commenced. § 1114. Mercurial ores, consisting of mixtures of cinnabar and lime- stone, are also found in the duchy of Deux-Ponts, (France,) and are worked by being heated in earthen retorts A (fig. 585) furnished with Fig. 584. Fig. 685. SILVER. 293 earthen receivers B, and disposed in a galley-furnace M. A cer- tain quantity of water is placed in the receivers, where the sulphide of mercury in this case is decomposed by the lime, while sulphide of calcium and sulphate of lime are found. The mercury set free condenses in the receivers. SILVER. Equivalent = 108 (1350.0) O = 100). § 1115. The silver used for coin and plate is never pure, but contains a certain proportion of copper. In order to obtain pure silver the alloyed metal is dissolved in nitric acid and sea-salt added to the solution, when the silver is precipitated in the state of insoluble chloride, while the other metals remain in solution. 100 parts of the dried chloride of silver being mixed up with TO of chalk and 4 or 5 of charcoal, are introduced into a clay crucible and heated to a strong, white-heat, when carbonic oxide is disengaged, while chloride of calcium and metallic silver are formed. After cooling, the silver is found in a button, at the bottom of the crucible, covered by a slag of chloride of calcium. Silver is distinguished from all other metals by its brilliant white colour, and a lustre which does not tarnish in the air, unless the latter contain sulphuretted vapours. When highly polished, silver reflects light and heat better than any other metal, and its radiating power is, consequently, very feeble, for which reason a close silver vessel will retain the heat of a liquid which it may contain longer than a vessel of any other metal. Silver, the density of which of 10.5, is harder than gold, but softer than copper, while the addition of a small quantity of copper increases its hardness. It is the most malleable of the metals, after gold, and can be beaten into very thin leaves, and drawn out into extremely fine wire. It possesses also great tenacity, for a wire of 2 millimetres in diameter breaks only under a weight of 85 kilogrammes. The fusing point of silver, which is at a white-heat, is supposed to be about 1000° of the air thermometer. It gives off very appre- ciable vapours at the temperature of a forge-fire, and soon vola- tilizes when exposed to the elevated temperature obtained between two coals terminating the conductors of a powerful battery. Silver may be crystallized in cubes by fusion by the method stated, (§ 991), and native silver, which is often found in beautiful crystals, also affects the cubic form, modified by the faces of the octahedron or other simple forms of the regular system. The small 294 SILVER. crystals obtained by precipitating silver by means of feeble galvanic action are likewise cubes. Although silver neither absorbs oxygen at the ordinary tempera- ture, nor combines permanently with that substance at a high tem- perature, it will, when kept in a very pure state for a long time fused in the air, absorb a considerable proportion of oxygen, with which it parts, on cooling, before solidifying. A portion of the metal is frequently thrown out of the crucible by the evolution of the gas. The absorbing power of silver is shown by the following experiment:—3 or 4 kilogrammes of very pure silver are fused in an earthen crucible, and when the metal has attained a very high temperature the crucible is uncovered, and a small quantity of salt- petre is added, which, by decomposing, maintains an atmosphere of oxygen in the crucible. After the addition of the last portion of the saltpetre the crucible is kept covered for half an hour, the high temperature still being maintained, and is then plunged into a water-cistern, beneath a bell-glass filled with water, when the oxy- gen absorbed is immediately disengaged, and collected in the glass. It has been ascertained that silver can absorb 22 times its volume of oxygen, which property is destroyed by the presence of a very small quantity of foreign metals. Silver is not oxidized, at a red-heat, by contact with the caustic alkalies and alkaline nitrates, for which reason silver crucibles are used when, in chemical analysis, substances are to be treated with caustic potassa or saltpetre, which would attack platinum crucibles. But silver is affected by fused alkaline silicates, oxide of silver, which dissolves in the silicate and colours it yellow, being formed. Silver decomposes, only in a very feeble manner, chlorohydric acid in solution, and reaction takes place only when the metal is very finely divided and the acid is kept at the boiling point. Dilute sulphuric acid does not attack silver, while the acid when hot and concentrated soon decomposes it, sulphurous acid being disengaged while sulphate of silver is formed. Nitric acid acts on silver, even at the ordinary temperature, disengaging deutoxide of nitrogen and converting the silver into a nitrate. Sulfhydric acid is decomposed by silver at the ordinary temperature; and a polished blade of silver soon blackens in a solution of a sulfhydric acid, and becomes covered with a black pellicle of sulphide of silver. Chlorine, bromine, and iodine act on silver even when cold. COMPOUNDS OF SILVER WITH OXYGEN. § 1116. Three compounds of silver with oxygen are known : The suboxide, AgaO. The protoxide, AgO. The binoxide, AgOa. The protoxide is the only oxide of silver possessing any interest. FULMINATING SILVER. 295 By heating to 212° in a current of hydrogen gas, certain salts formed by the protoxide of silver with organic acids, for example the nitrate, the protoxide loses one-half of its oxygen, and a subsalt of silver is formed, which dissolves in water and produces a brown solution, from which caustic potassa precipitates the suboxide Ag30 as a black powder. The subsalts of silver appear to be formed under several other circumstances, when protosalts of the metal are sub- jected to deoxidizing agencies. Protoxide of silver AgO is obtained by pouring potassa in excess into a solution of nitrate of silver, when a brown precipitate of hydrated protoxide is formed, which readily parts with its water in a dry vacuum or at a moderate heat, becoming converted into an olive-coloured powder of anhydrous protoxide. Heat soon drives off the oxygen from the protoxide of silver, and it is also decomposed by the solar rays. The hydrated protoxide dissolves slightly in water and causes the latter subsequently to exert an alkaline reaction on coloured tinctures; but it does not combine with the caustic alkalies. Prot- oxide of silver is a powerful base which combines with even the most feeble, and completely neutralizes the most powerful acids; thus ni- trate of silver behaves perfectly neutral with coloured litmus paper. When the two platinum conductors of a battery are dipped into a dilute solution of nitrate of silver, contained in a W shaped tube, the positive conductor becomes coated with brilliant, black prismatic crystals of binoxide of silver AgG3, which is more fixed than the protoxide, as it resists a temperature of 212° and is decomposed only at about 302°, when it is converted immediately into metallic silver. It disengages oxygen when in contact with acids, yielding protosalts of silver. With chlorohydric acid it evolves chlorine. It decomposes ammonia with effervesence, the oxygen given off by the binoxide while the latter is reduced to protoxide, uniting to form water with the hydrogen of the ammonia, while nitrogen is disengaged. Ammoniuret of Oxide of Silver. § 1117. By digesting oxide of silver with a concentrated solution of caustic ammonia, a black, highly explosive powder is formed, which is also obtained by pouring caustic potassa into the solution of a salt of silver in an excess of caustic ammonia. This compound, called fulminating silver, detonates very easily, and should be handled with the greatest care, as it even explodes under water when the latter is heated to 212°. Chemists are not agreed as to the composition of fulminating silver; while some regard it as formed by the direct combination of ammonia with oxide of silver, and assign it the formula AgO,NH3, others consider it as an amidide of silver AgNH2 produced by the reaction AgO-fNH3 = AgNH3-f HO ; and lastly, a large number suppose it to be a simple nitrate of silver arising from the reaction expressed by the equation 3AgO-f NH3 = Ag3N-f3HO. 296 SILVER. SALTS FORMED BY PROTOXIDE OF SILVER. § 1118. As has already been said, (§ 1116,) protoxide of silver is a powerful base, which combines with even the weakest acids, and perfectly neutralizes powerful acids as regards their action on coloured reagents. Under some circumstances potoxide of silver even behaves like a base stronger than the alkalies, for it decom- poses some alkaline salts by abstracting a portion of their acid; which reaction, however, only takes place when a double salt can be formed. The salts of silver are colourless when the acid itself is colourless. The soluble salts of silver are obtained by dissolving the carbonate of silver in acids, wdiile those that are insoluble are prepared by double decomposition by means of the nitrate of silver obtained by dissolving the metal in nitric acid. The soluble salts of silver have a disagreeable metallic taste, and are very poisonous. All the salts of silver are blackened by solar light: they are decom- posed, and metallic silver separates. The soluble salts present the following characteristic reactions: Potassa and soda throw down a brown precipitate of hydrated protoxide, wrhich does not dissolve in an excess of reagent, while ammonia produces the same precipitate in neutral solutions, but re- dissolves it entirely when present in excess; and if the solution contains a great excess of acid, it is not clouded by ammonia, be- cause a double salt of silver and ammonia, indecomposable by an excess of ammonia is formed. Carbonates of potassa and soda yield a dirty-white precipitate of carbonate of silver, which does not dis- solve in an excess of reagent, and carbonate of ammonia produces the same precipitate, which dissolves in an excess of carbonate of ammonia and in caustic ammonia. The precipitated oxide and car- bonate of silver are easily decomposed by heat, and yield a spongy mass of metallic silver, which becomes compact by percussion and presents all the physical characters of malleable silver. Sulf hydric acid produces a black precipitate of sulphide of silver, and the alkaline sulf hydrates yield the same black precipitate, which does not dissolve in an excess of sulf hydrate. Ferrocyanide of potassium yields a white, and the cyanoferride or red prussiate, a brownish-red precipitate. Chlorohydric acid and the soluble chlorides form in solutions of silver a white precipitate, which readily collects, on shaking, into a consolidated mass if the liquid contains an excess of nitric acid. This precipitate is insoluble in an excess of nitric acid, but dissolves readily in ammonia; and if the latter be saturated by an acid the chloride of silver is again precipitated. The precipitate soon turns black in the light, first assuming a violaceous hue, which distinguishes it from freshly precipitated subcliloride of mercury Hg3Cl, which is formed when a soluble chloride is poured into a solution of a subsalt of mercury, and which remains white for a long time. A blade of NITRATE OF SILVER. 297 zinc or iron brought into contact with the moist chloride decom- poses it and separates the metallic silver. The soluble iodides form, in solutions of silver, a yellowish-white precipitate of iodide of silver, which dissolves with difficulty in a great excess of acid or ammonia. Silver is precipitated from its solutions in the metallic state by a great number of metals, particularly by iron, zinc, and copper. Mercury effects the same decomposition, but the silver precipitated combines gradually with the mercury until a solid amalgam is formed, the silver subsequently deposited forming long brilliant needles of an amalgam of silver, filling sometimes the whole solu- tion. This crystallization is called the arbor Dianae. Nitrate of Silver. § 1119. Silver dissolves readily in nitric acid, and on evaporating the liquid the nitrate of silver formed crystallizes, in the anhydrous state, in the form of large colourless plates. Nitrate of silver is generally made, in the laboratory, from coin which contains of its weight of copper, by dissolving it in nitric acid, and evaporating to dryness the blue solution obtained, which contains both nitrate of silver and nitrate of copper. The residue is fused in a porcelain capsule, at a temperature below a dull-red heat, when the nitrate of copper is converted into protoxide of copper CuO, which colours the fused nitrate of silver black. The temperature is maintained until the nitrate of copper is entirely decomposed, which is ascer- tained by extracting a certain portion by means of a glass rod, dis- solving it in a small quantity of water, and pouring an excess of ammonia into the filtered solution ; if the liquid does not turn blue the nitrate of copper is entirely decomposed. The substance is then dissolved in water, and the oxide of copper separated by fil- tration. The oxide of copper remaining in the liquid may also he precipi- tated by oxide of silver. After having evaporated to dryness the solution of the nitrates to drive off the excess of acid, and dissolved the residue in water, about | of the liquid is separated, and is com- pletely precipitated by caustic potassa in excess, when the oxides of silver and copper are deposited. They are washed with cold water and then boiled with the remaining £ of the liquid, when the oxide of silver completely precipitates the oxide of copper, while nitrate of silver alone remains in solution, the deposit consisting of a large quantity of oxide of copper and very little oxide of silver. Nitrate of silver is also frequently prepared from the chloride, which is always obtained in large quantities in laboratories where minerals are analyzed. The chloride of silver may be decomposed by lime, in a crucible heated to a white-heat, as stated, (§ 1115), and pure metallic silver may be thus obtained and afterwards dis- solved in nitric acid; but generally, an iron rod, previously moist- 298 SILVER. ened with water acidulated by chlorohydric acid, is dipped into the chloride of silver, which is thus gradually decomposed and, after some time, leaves only metallic silver, which is washed with acidu- lated water and dissolved in nitric acid. Nitrate of silver is soluble in its wreight of cold, and one-half of its weight of boiling water, and also dissolves in 4 parts of boiling alcohol. It has been mentioned that nitrate of silver fuses without change at a temperature below a dull-red: it solidifies on cooling into a crystalline mass, and, if further heated, it decomposes. At the commencement of the decomposition oxygen alone is disen- gaged, and the salt is transformed in the nitrite AgO,N03, while subsequently, both oxygen and nitrogen are disengaged, and finally metallic silver alone remains. Fused nitrate of silver is used in surgery as a cautery, under the name of lapis infernalis, which is usually employed in the shape of small sticks fixed in the end of a pencil-holder. The sticks are made by pouring fused nitrate of silver into an iron mould similar to that represented in fig. 323, (page 445, vol. i.;) and because the sides of the mould decompose a small quantity of the nitrate, the sticks generally appear black at the surfaces. Nitrate of silver is also used internally in certain forms of epi- lepsy, but it is a dangerous remedy and should be administered with great prudence. Persons who have taken this medicine should avoid exposure to the light of day until the salt of silver, which is distributed throughout the whole organism, has been carried off, without which precaution all the parts of the body exposed to light turn blue, in consequence of the decomposition of the salt of silver in the subcutaneous tissue. Nitrate of silver is decomposed feebly by solar light, and more rapidly in the presence of organic substances. A drop of a solution of nitrate produces a brownish-black mark on the skin, which can be removed only by a solution of cyanide of potassium. When a piece of linen soaked in nitrate of silver is exposed to a current of hy- drogen gas, it remains covered with metallic silver presenting a certain degree of lustre; which property has been applied to the silvering of designs on muslins, but without much success. Nitrate of silver absorbs dry ammoniacal gas, and forms a com- pound of the formula AgO,NOs-f 3NII3, from which heat com- pletely expels the ammonia. If nitrate of silver be poured into an excess of ammonia and the liquid be evaporated, it deposits crystals of which the formula is AgO,NOs+2NA3. When a solution of nitrate of silver is boiled writh very finely divided metallic sliver, obtained by chemical preparation, a consi- derable quantity of silver will be found to dissolve; and compounds, analogous to those formed when a solution of nitrate of lead is boiled with metallic lead, (§ 967,) are probably produced. ACETATE OF SILVER. 299 Sulphate of Silver, § 1120. Sulphate of silver is obtained by heating metallic silver with concentrated sulphuric acid, when sulphurous acid is disen- gaged while a white crystalline powder of sulphate of silver is formed. It is also obtained by pouring sulphuric acid or sulphate of soda into a boiling solution of nitrate of silver, in which case the sulphate of silver is precipitated in the form of small prismatic crys- tals. During the cooling of the liquid, new crystals are deposited which are sufficiently developed to allow their shape, which is the same as that of anhydrous sulphate of soda, to be distinguished. Sulphate of silver is very slightly soluble in water, as hot water scarcely dissolves A part of it; but it readily dissolves in ammonia, and the liquid, when evaporated, yields crystals of a compound sulphate of silver and ammonia of the formula Ag0,S03+2NII3. Hyposulphite of Silver. § 1121. Protoxide of silver has so great an affinity for hyposul- phurous acid that it abstracts it from potassa and soda. If oxide of silver be digested with a solution of hyposulphite of soda, a con- siderable proportion of oxide of silver dissolves, and the liquid, when evaporated, yields crystals of the double hyposulphite of soda and silver. The chloride, bromide, and iodide of silver also dissolve readily in a solution of hyposulphite of soda, and after evaporation the liquid affords the same crystals of double hyposulphite. The solubility of the chloride, bromide, and iodide of silver is applied in photography, to the fixing of the image: that is, to the removal of the compounds of silver from the parts which have not been acted on by light. Solutions of the double hyposulphites when boiled give off sulphide of silver, and sulphate of soda is formed. The hy- posulphite of silver can be obtained isolated, in the form of a white powder, by pouring a solution of hyposulphite of soda into a solu- tion of nitrate of silver; but the precipitate soon blackens in the light, sulphide of silver being formed. Carbonate of Silver. § 1122. Carbonate of silver, which is obtained in the form of a white precipitate, by pouring carbonate of soda into a solution of nitrate of silver, soon turns brown when exposed to solar light, and is readily decomposed by heat. Acetate of Silver. § 1123. Acetate of silver is prepared by dissolving the carbonate in acetic acid, or by pouring acetate of soda into a concentrated hot solution of nitrate of silver; in which case the acetate of silver crystallizes in small prisms during the cooling of the liquid. 300 SILVER. § 1124. Silver and sulphur combine directly when a mixture of the two substances is heated. The excess of sulphur distils over, and if it be heated to redness, the sulphide of silver fuses and so- lidifies into a crystalline mass on cooling. Sulphide of silver cor- responds to the protoxide: its formula is, consequently, AgS. It is found crystallized in nature in regular octohedrons, commonly modified by secondary facets, forming a blackish-gray mineral of a metalloid lustre, the density of which is 7.2. Sulphide of silver possesses a certain degree of malleability, and will receive impres- sions under the coining-press; but it is so soft that it can be scratched with the nail. Sulphide of silver is converted by roast- ing into sulphurous acid and metallic silver. Concentrated boiling chlorohydric acid decomposes it by disengaging sulf hydric acid and forming the chloride. Concentrated hot sulphuric acid also acts on it and converts it into a sulphate, the action of nitric acid yielding the same product. Sea-salt, protochloride of copper, and some other metallic chlorides convert the sulphide of silver into a chlo- ride when assisted by heat. The same sulphide of silver is produced, by the humid way, when a salt of silver is precipitated by sulf hydric acid, or by an alkaline sulf hydrate. Silver decomposes sulf hydric acid even when cold, especially in the presence of water, and its surface becomes covered with a black pellicle of sulphide. On account of which property, silver soon blackens in the vicinity of sulphuretted emanations; as for example, silver plate soon becomes tarnished when eggs or fish, or any kind of food which can evolve sulf hydric acid, is heated in it; especially when the articles are not very fresh. Sulphide of silver combines with a great number of metallic sul- phides, and principally with the electro negative sulphides, such as those of arsenic and antimony, forming double sulphides, many of which occur crystallized in nature. Native sulphide of silver is isomorphous with native subsulphide of copper Cu3S, and the two sulphides appear to possess the pro- perty of replacing each other in every proportion, as occurs for ex- ample, in the gray copper-ore or fahlerz. We have said that such isomorphism exists only between substances presenting the same chemical formulae, and have frequently insisted on this law to esta- blish the equivalents of simple bodies. But sulphide of silver would present an exception to the law if its formula was written HgS, that is, if the number 108 were adopted for the equivalent of the metal; which consideration has induced several chemists to assign to sul- phide of silver the formula AgaS, that of AgaO to our protoxide of silver, and to take the number 54 for the equivalent of silver. This opinion is also confirmed by several other circumstances, on which we shall briefly dwell. It has been demonstrated by a great number COMPOUNDS OF SILVER WITH SULPHUR. COMPOUND OF SILVER AVITII CHLORINE. 301 of experiments, that a very simple ratio exists between the specific heats of simple bodies and their chemical equivalents, and a law has been observed according to which the specific heats of simple bodies are to each other nearly in the. inverse ratio of their equivalents. Now, silver only satisfies this law by admitting the number 54 for its equivalent. Moreover, an analogous law has been found for compound bodies, by which the specific heats of compound bodies, of the same formula, are to each other very nearly in the inverse ratio of the numbers which represent their chemical equivalents. Now, the sulphides of silver and copper Cu3S satisfy this law, if the formula Ag3S be admitted for the sulphide of silver. But, if the formula of sulphide of silver be written Ag3S, and, consequently, that of our protoxide of silver Ag30, the formula of soda should be written Na30 and not NaO, as we have hitherto done; for we have seen (§ 1120) that sulphate of silver is isomor- phous with anhydrous sulphate of soda. The salts of potassa and lithia being isomorphous with the corresponding salts of soda, when they contain the same quantity of water of crystallization, the formula of potassa should be written K30 and that of lithia Li30; which new formulae are justified by the laws of specific heat, and by several important considerations. In fact, it has been found that the spe- cific heats of the chlorides of potassium, sodium, silver, and the sub- chlorides of mercury IIg3Cl and copper Cu3Cl, are to each other in the inverse ratio of the equivalents of these substances. Now, there is no doubt that Cu3Cl is the formula of subchloride of copper, on account of the indisputable isomorphism of the salts of the protoxide of copper CuO with the corresponding salts of the protoxide of iron, manganese, zinc, and nickel. The chlorides of potassium, sodium, and silver should, therefore, have formulae similar to that of sub- chloride of copper Cu3Cl, and these should be written KaCl, Na3Cl, AgjjCl. On the other hand, potassa, soda, and lithia have hitherto presented no case of isomorphism with the oxides, the formulae of which are written RO ; they never replace baryta, lime, magnesia, the protoxides of iron, manganese, zinc, etc., which circumstance becomes very natural if the formula R30 is assigned to the alkaline oxides, but is not explained if the formula RO be retained. Considering these circumstances, it appears that the equivalents of the alkaline metals ought to be reduced to their half: we have, however, been unwilling to make this change in the present work before it has been adopted by a majority of chemists. COMPOUND OF SILVER WITH CHLORINE. § 1125. Only one combination of silver with chlorine is known, corresponding to the protoxide. Chloride of silver AgCl is ob- tained by adding chlorohydric acid or a solution of sea-salt to the solution of any soluble salt of silver, when a white precipitate is foi’med, which soon collects, by shaking, in cheesy lumps, especially 302 SILVER. if the liquid contains an excess of nitric acid. Chloride of silver is nearly insoluble in water and in weak solutions of nitric acid, but dissolves sensibly in solutions of chlorohydric acid or the alkaline chlorides. Concentrated boiling chlorohydric acid dissolves a con- siderable quantity of chloride of silver, and the saturated solution deposits, on cooling, small octohedral crystals of the chloride. Am- monia is a very powerful solvent of chloride of silver, and the liquid, on being exposed to the air, gradually loses its ammonia and de- posits octohedral crystals of chloride of silver, which frequently attain quite a considerable size. By saturating the ammoniacal liquid with nitric acid, the chloride of silver is again deposited. Solutions of the alkaline hyposulphites dissolve a large quantity of the chloride, (§ 1121.) Chloride of silver fuses at about 500°, forming a yellow liquid, which, on solidifying, yields a translucent substance resembling horn, easily cut with a knife. At a red-heat, chloride of silver gives off appreciable vapours, although it is not sufficiently volatile to allow of distillation. It soon blackens in solar light. If the chloride be suspended in water, oxygen is given off, and, after some time, the liquid contains chlorohydric acid, while, if the chloride be dry, chlorine is disengaged: in both cases, by treating the altered substance with ammonia, chloride of silver is dissolved without colour, while metallic silver remains in the form of a black powder. Chloride of silver absorbs, when cold, a large quantity of dry ammoniacal gas, giving rise to a compound, the composition of which is expressed by the formula AgCl-f3NH3, and which readily parts with its ammonia by the application of heat. It has been shown (§ 123) that liquid ammonia can be obtained from this sub- stance. Chloride of silver is sometimes found crystallized in nature, form- ing cubic or octohedral crystals, of a pearl-gray colour when found in the interior of the rock, and of a more or less violaceous hue when occurring very near to or off the surface. § 1126. A bromide of silver AgBr, resembling the chloride, is obtained by pouring an alkaline bromide into a solution of nitrate of silver, in the shape of a white, slightly yellowish precipitate, which is insoluble in water and nitric acid, but readily dissolves in ammonia and the alkaline hyposulphites. Chlorine easily decom- poses bromide of silver, and transforms it into chloride. Bromide of silver has been found native in certain silver-ores from Mexico. COMPOUND OF SILVER WITH BROMINE. COMrOUND OF SILVER WITH IODINE. § 1127. By adding iodide of potassium to a solution of nitrate of silver, a yellowish-white precipitate of iodide of silver Agl is ob- tained, which is insoluble in water, slightly soluble in nitric acid, DETERMINATOIN OF SILVER. 303 and soluble but to a small degree in ammonia, which properties serve easily to distinguish it from the chloride and bromide of silver. Chlorine decomposes it and sets the iodine free, and chlorohydric acid converts it into a chloride. It fuses below a red-heat. Al- though the effect of light on the iodide is less rapid than on the chloride, the former soon turns black, first assuming a brown tinge. Iodide of silver dissolves easily in a solution of iodide of potassium, and the liquid deposits, on evaporation, crystals of a double iodide Agl+KI. Native iodide of silver has been found in several silver- ores, in crystals belonging to the regular system. COMPOUND OF SILVER WITH FLUORINE. § 1128. Fluoride of silver is obtained by dissolving the oxide or carbonate in fluohydric acid, forming a compound which is very soluble in water and partly decomposes by evaporation. COMPOUND OF SILVER WITH CYANOGEN. § 1129. By adding a solution of cyanohydric acid to a solution of nitrate of silver, a white precipitate of cyanide of silver AgCy or AgC3N is obtained, which is insoluble in water and dilute nitric acid, while chlorohydric acid decomposes it and converts it into a chloride. Ammonia dissolves it readily, and it is also easily soluble in the alkaline cyanides, with which it forms crystallizable double cyanides. COMPOUNDS OF SILVER WITH CARBON. § 1130. Definite compounds of silver with carbon are obtained by decomposing by heat certain salts formed by the oxide of silver with organic acids. Two definite carburets have hitherto been ob- served, corresponding to the formulae AgC and AgCa. When heated in the air they become incandescent, and, after burning like tinder, leave metallic silver. DETERMINATION OF SILVER, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. § 1131. Silver is determined either in the metallic state, or in that of the chloride, the first-named method being employed in the case of cupellation, a process presently to be described. When silver is in solution, it is generally precipitated by a slight excess of chlo- rohydric acid; and, in order to collect the precipitate more easily, it is better to employ a boiling solution to which an excess of nitric acid has been added. The clear supernatant liquid may be de- canted off, and, if proper care be taken, none of the precipitate need be lost. In order to wash chloride of silver, it is poured into a thin porcelain capsule, filled with water slightly acidulated with nitric acid, and the liquid is heated to ebullition by means of an alco- hol-lamp, the precipitate being kept suspended in the liquid by 304 SILVER. stirring with a glass rod. After it has been allowed to rest, and the chloride has settled at the bottom of the capsule, the clear liquid is removed with a pipette and introduced into a cylinder, which process is repeated until the washing is completed. Lastly, any particles of chloride that may have found their way into the cylinder, are removed thence and added to that in the capsule, where the whole is dried; for which purpose, the capsule is placed upon another capsule heated by an alcohol-lamp, by which means a hot-air hath is obtained which completely dries the chloride. Finally, the capsule is weighed when cooled, and, the chloride being removed, the equilibrium is restored by weights. The dried chloride is sometimes fused in the capsule, in which case the separation, which is attended with some difficulty, is effected by boiling a small quantity of concentrated chlorohydric acid in the capsule contain- ing the chloride, when the latter generally separates in a single mass. If it still adheres, water must be added, and a piece of zinc must be placed on the chloride, which, by being restored to the metallic state by the zinc, immediately separates. The chloride of silver may also be collected in a very finely pointed glass tube, the aperture of which soon becomes closed, by small lumps of chloride, sufficiently to prevent the escape of any of the precipitate, without interfering with the filtration of the clear liquid. The chloride is washed in the tube, which is then dried in a stove. In all cases, chloride of silver should be washed in a room lighted by a lamp, so that it may not be affected by solar light. § 1132. The solubility of silver in nitric acid, and the complete insolubility of chloride of silver, renders the separation of this metal from all the metals previously described an easy matter. Silver cannot be immediately precipitated by chlorohydric acid, only in the case when it exists in solution with a subsalt of mercury, because a mixture of chloride of silver and chloride of mercury HgaCl is de- posited. But it is sufficient to treat the precipitate with boiling nitric acid, to which a few drops of chlorohydric acid have been added, to dissolve the mercury in the state of protochloride HgCl. The two metals may also be precipitated by sulfhydric acid, and the mixture of the sulphides roasted in the air, when the mercury volatilizes, while the silver remains entirely in the metallic state. METALLURGY OF SILVER. § 1133. The most common ores of silver are:— 1. Sulphide of silver, either pure, or mixed with greater or less quantities of sulphide of copper CuaS, which do not change its crys- talline form. 2. Sulphide of silver, combined with the sulphide of arsenic and antimony, forming a great number of minerals, to which mineralogists give different names; e.g., sulfantimoniate of silver, of which the formula is and sulfarseniate of silver 3AgS+As3Ss. METALLURGY OF SILVER. 305 These two minerals affect the same form of crystallization, clearly proving the isomorphism of the sulphides of arsenic AsaS3 and of antimony Sb3S3, which, however, is still better established in certain minerals containing at the same time sulphide of arsenic and sul- phide of antimony in varying proportions 6AgS + (Sb3,AS3)S3. Sulf- arseniates and sulfantimoniates of silver are also found in which a portion of the silver is replaced by copper 9(Cua,Ag)S-f (Sb3,As3)Sa. 3. The arseniuret of silver AgaAs, and the antimoniuret AgaSb. 4. The chloride, bromide, and iodide of silver, which are some- times found in sufficient quantity to be worked as ores of silver. 5. Many galenas, and cupreous ores containing silver, are the most common ores of silver on the European continent. 6. Native silver, frequently scattered through the levellings of lead and argentiferous copper veins, and probably owing its pre- sence to chemical reactions to which the ore has been subjected in the bosom of the earth, and which have removed the other metals in the state of soluble compounds, and left the metallic silver. Large masses of native silver are sometimes found, and at Konigs- berg, in Norway, have been seen to weigh 280 kilogs. § 1134. Argentiferous lead-ores are first worked for their lead, from which, as it retains all the silver, the latter is separated by cupellation, (§ 987.) Argentiferous copper-ores are also worked for their copper, and the black copper resulting, is passed through a furnace with lead, furnishing an alloy, from which the argentiferous lead is separated by eliquation, (§ 1067,) and is subsequently sub- jected to cupellation. Again, the last coppery matts are subjected to an amalgamation, which shall soon be described. Ores of silver which are too poor in lead or copper to be worked for the advantageous extraction of these metals, are immediately subjected to amalgamation, after having undergone a preliminary preparation. Two different methods of amalgamation are used—• that of Freiberg, in Saxony, generally adopted in Europe, and the American method, which differs essentially from the European plan in requiring no fuel, and in being the only applicable method where fuel is scarce, as it is in Mexico and South America. Freiberg Process. § 1135. The argentiferous ores of Saxony are composed of sul- phide of silver combined or mixed with sulphides of arsenic, anti- mony, iron, zinc, etc. It is important that they should not contain more than 5 per cent, of lead, and, at most, 1 per cent, of copper, as these metals greatly interfere with the amalgamation: they amal- gamate with mercury as readily as silver, and render the amalgam very tough. The various ores are sorted so that the charge shall contain 2 or 8 thousandths of silver and a proper quantity of py- rites, which latter are necessary, because, during the preliminary roasting, they furnish a certain proportion of oxide and sulphate of 306 SILVER. iron, indispensable in the chemical reactions of amalgamation. They are to be added, if they do not exist in sufficient proportion; and sometimes a certain quantity of sulphate of iron is also added. Lastly, 10 or 12 parts of sea-salt are added to 100 parts of ore. The mixture is roasted in a reverberatory furnace, heated at first very gently, in order to dry the material, which is then spread over the sole of the furnace, and the temperature being gradually raised, a red-heat is maintained for about 4 hours, when a large quantity of sulphurous acid is disengaged while the metals oxidize. The temperature being now raised still higher, sulphurous acid is dis- engaged anew, accompanied by vapours of sesquichloride of iron and chlorohydric acid, arising from the action of the steam and oxygen on the chloride of iron. After roasting for £ of an hour, the roasted ore is withdrawn and thrown on a screen, where the consolidated fragments are retained, which are again ground, mixed with 2 per cent, of sea-salt, and subjected to a new roasting. The ore wffiich has passed through the screen is again sifted, ground to an impalpable powder, bolted, and then sent to the amalgamating barrels. During the roasting, the sulphides of iron and copper disengage sulphurous acid, oxides and sulphates being formed, while the sulphide of silver, being heated with the sulphates of iron or copper, is entirely converted into sulphate at the expense of the sulphates of iron and copper, which, while being transformed into oxides, cause the dis- engagement of sulphurous acid. The sulphates of iron and copper fuse together with the sea-salt before attaining a red-heat; and if the mixture contain sulphide of silver, sulphurous acid is disengaged by the reaction of the sulphur of the sulphides on the sulphuric acid of the sulphates, and the final products resulting from the roasting are thus, sulphate of soda, chloride of silver, and the chlorides of copper and iron. If the reaction takes place in the air, the iron passes partly into the state of sesquichloride and partly into that of sesquioxide; and the sulphides of arsenic and antimony are also oxidized. As all these reactions take place during the roasting in the reverberatory fur- nace, the roasted ore may be admitted to consist, in addition to the quartzose gangues, of sulphate of soda, chloride of sodium, chlorides of manganese and lead, sesqui- chloride of iron FeaCl, subchloride of copper Cu3Cl, chloride of silver, and several me- tallic oxides. The amalgamating barrels are made of wood, (fig. 586,) strengthened by iron hoops and bars, and the ends have iron plates, furnished with gudgeons exactly in the axis of the barrel. A cog-wheel rr" is attached to one end, working in Fig. 586. METALLURGY OF SILVER. 307 another cog-wheel rr' (figs. 587 and 588) on a shaft AB turned by a water-wheel. Each barrel has a hole a closed by a hung kept in place by an iron stirrup. One of the pedestals on which the gud- geons revolve is fixed, while the other is rendered mov- able by the screw v, so that the wheel rr" may be thrown into or out of gear without attesting the other barrels C, C placed near the hori- zontal staff A B, and work- ing in the same cog-wheel rr'. Above each barrel is a box E containing the bolted ore, which is introduced into the former by means of a leather hose /, entering the opening a, while reservoirs D placed above each barrel contain the quantity of water necessary for a charge. Be- neath ' the barrels are re- ceivers mnm', intended to hold the material after the opera- tion. After 150 litres of water have been introduced into each barrel, the charge of ore, amounting to 500 kilogs., is inserted, being taken from the box E, while 50 kilogs. of scrap sheet-iron are added. The opening in the barrel is then closed with the bung, and when all the barrels are charged in the same manner, they are made to revolve gently for 2 hours, after which each barrel is successively thrown out of gear, in order to allow of an examination of the consistence of the muddy substance it con- tains. If it is too tough, water is added; and if too liquid, more roasted ore is thrown in; and when the proper consistency is at- tained, 250 kilogs. of mercury are thrown into each barrel, and the whole is again set in motion, the temperature in the barrels rising considerably after some time, in consequence of the chemical re- actions which take place in the mixture. After the barrels have revolved for 20 hours, at the rate of 20 revolutions a minute, they are stopped, completely filled with water, and made to revolve for 2 hours more, making 8 revolutions per minute, when the amalgam separates from the muddy substances, which have now become very Fig. 587. Fig. 588. 308 SILVER. fluid. Each barrel being then successively thrown out of gear, and the bung turned downward, the small cork of the bung is removed, and as soon as all the amalgamated mercury has escaped and fallen into the receiver mnm', which is the case as soon as the mud ap- pears, the workman replaces the cork. The mercury runs through the tube ii' into a canal A, which leads it into a particular reservoir. When all the mercury has escaped, the bung of the barrel is re- moved, the opening a turned downward, and the mud allowed to run into the box mnm'*whence it flows into large reservoirs be- neath, the scrap-iron being retained by a grate. We have said that, before adding the mercury, the loaded barrels are turned for 2 hours: the intention of this is to decompose, during this period of the process, the sesquichloride of iron by the metallic iron, and restore it to the state of protochloride, because, if the mercury were introduced immediately, it would act on the sesqui- chloride of iron which it would reduce to protochloride, while a certain quantity of subchloride of mercury IIg2Cl would be formed, which would decompose no longer, and occasion a considerable waste of mercury; all of which is avoided by first bringing the ses- quichloride of iron to the state of protochloride. The chloride of silver, which dissolves in the solution of sea-salt, is decomposed by metallic iron, while the silver set free combines with the mercury; and the chlorides of copper and lead being decomposed in the same way by contact with the iron, these metals also amalgamate with the mercury. About 1 kilog. of iron is dissolved in each operation. The mud escaping from the barrels is placed in tubs, where it is stirred by paddles attached to a vertical axis, after being diluted with a large quantity of water, the tubs being provided with open- ings at different levels, through which the muddy water escapes. A certain quantity of amalgam, which separates and falls to the bottom of the tubs, is then removed and added to that taken from the amalgamating barrels. The mercury is filtered, with the assistance of slight pressure, through leather bags, through the pores of which, a small portion of liquid mercury, containing only a slight admixture of foreign metals, escapes; while a doughy amalgam, con- taining nearly 5 parts of mercury and 1 part of silver, mixed with foreign metals, remains in the bags. The mercury is separated from the amal- gam by distillation, which is effected by various kinds of apparatus, of which it will suffice to describe the most simple one. To the opening of the cast-iron tube ab, (fig. 589,) which is closed at one end a, and has been charged with Fig. 589. METALLURGY OF SILVER. 309 about 150 kilogs. of amalgam, is fitted a bent tubing cde, the tubu- lure e of which enters a sheet-iron tube fg, which dips slightly into the water contained in the receiver Y. The tube ab being gradually heated to redness, the mercury distils and condenses in the receiver Y, while the silver, mixed with a greater or less quantity of copper and lead, remains in the tube ab. Amalgamation of the Cupreous Matts by the Mansfeld Process. § 1136. Amalgamation is applied to the last cupreous matts arising from the process described, (§ 1066). The matt is stamped and sifted, and then ground to an impalpable powder, which is moistened with a small quantity of water and roasted in a reverbe- ratory furnace. The furnace, a vertical section of which is seen in fig. 590, has generally 2 stories, surmounted by condensing chambers where the vapours and dust carried over are retained. The matt is first roasted in the upper space B, while in the lower space A a charge is being roasted, consisting of about 200 kilogs. of matt, spread in a thin layer over the sole. A very high temperature is not applied, because it is indispensable to prevent the softening of the substance, which would interfere with the roast- ing. The workman stirs the material with an iron rake, in order to renew the surfaces exposed to the oxidizing action of the air, and the roasting lasts about 3 hours, after which the mate- rial is removed with an iron scoop and dropped into a box. After the first roasting, the material is mixed with 9 or 10 per cent, of sea-salt and 10 per cent, of very finely powdered limestone; water is added, and the whole is worked into a homogeneous paste, which is dried in stoves. The mass is again ground to powder and roasted in a lower furnace A, where a higher temperature prevails. The limestone is added to decompose a portion of the sulphates of iron and copper; which, if present in too great quantity for amal- gamation, would occasion a waste of mercury. When the workman supposes that the material is sufficiently prepared, he proceeds to test it by mixing a small quantity of the roasted powder with water and mercury, and, after diluting it with a larger quantity of water, separating a mercurial amalgam, the nature of which he estimates by its physical properties. According to the appearance of the amalgam, he adds a small quantity of salt, lime, or even of roasted matt. The second roasting lasts only about 1J or 2 hours. Fig. 590. 310 The material thus prepared is poured into the amalgamating barrels, which resemble those of Freiberg, 500 kilogs. of roasted ma- terial, 150 litres of hot water, and 40 kilogs. of scrap-iron being introduced into each barrel. After having caused the barrels to revolve for some time, 150 kilogs. of mercury are added, and then the barrels are made to turn at the rate of 15 revolutions per minute for 14 hours. 100 litres of vrater are then added to each barrel, which is turned gently for some time to facilitate the sepa- ration of the amalgam. The deposit of cupreous matt which remains after the complete separation of the amalgam, after being mixed and pounded with 15 per cent, of clay, is made into lenticular cakes, which are smelted, after drying, in a furnace, w7ith the addition of quartz, furnishing black copper, which is subsequently refined, (§ 1068.) The amalgam of silver is treated in the same way as at Freiberg. SILVER. § 1137. The principal mines in America are those in Mexico and Chili, which furnish ores consisting of metallic silver, sulphide of silver isolated or combined with sulphides of arsenic and antimony, chloride of silver, etc., these minerals being generally disseminated in such fine particles as not to be perceived in the gangue. The ores are first stamped, then ground to a fine powder, and made into heaps, called tarts, (tourtes,) containing 500 to 600 quin- tals, on platforms built of stone. The material, after being moist- ened with water, to which 2 to 5 per cent, of sea-salt are added, is rendered homogeneous by being stamped by horses or mules. In a few days, about J or 1 per cent, of magistral is added to it, con- sisting of a roasted copper pyrite, containing 8 to 10 per cent, of sulphate of copper. It is again stamped, and the first portion of mercury added; and when this has been well disseminated through the mass, a small portion of the material is washed in a wooden bowl to separate the amalgamated mercury. By its appearance the workman judges if it be necessary to add lime or magistral. If the surface of the amalgam is grayish and the metal agglomerates easily, the amalgamation is going on correctly; but if the mercury is much divided, and its surface exhibits a dark colour with brown spots, the magistral is in excess, and the tart is then said to be too hot. As a continuation of the process under these conditions would occasion a great loss of mercury, lime is added, which decomposes a portion of the sulphate and chloride of copper produced by the re- action. If, on the contrary, the mercury retains its fluidity, the chemical reactions do not advance, and the tart, being too cold, must be heated by the addition of magistral. After about 15 days, when the first portion of mercury has com- bined with a sufficient quantity of silver to be converted into a doughy amalgam, a second portion of mercury is added; and when American Process. REFINING OF SILVER. 311 this is well incorporated with the mass, a third and last addition is made; the test just described being frequently repeated, in order to judge of the progress of the operation. The whole process lasts 2 or 3 months, according to the nature of the ore and the tempera- ture. When it is finished, the material is washed in water to sepa- rate the amalgam from it, which is filtered through cloth, and the solid part which remains is distilled. By the American process, 1 to 3 parts of mercury are lost for 1 part of silver obtained. The following is the theory of the operation:—The sea-salt and sulphate of copper of the magistral usually decompose each other, protochloride of copper CuCl and sulphate of soda being formed, while the metallic silver decomposes the protochloride of copper, and, by restoring it to the state of subchloride Cu2Cl, is itself con- verted into chloride of silver. The subchloride of copper dissolves in the solution of sea-salt, and reacts on the sulphide of silver, form- ing sulphide of copper and chloride of silver. The mercury, in its turn, acts on the chloride of silver, which dissolves in a solution of sea-salt, forming subchloride of mercury HgaCl, while the metallic silver combines with the rest of the mercury. It is necessary, in this operation, as in the Freiberg process, that no free protochloride of copper should remain, because this would increase the waste of mercury, by parting with one-half of its chlorine to the latter metal in order to transform it into subchloride HgaCl. The intention of the addition of lime is to decompose the chloride of copper in excess, and destroy the bad effects of an excess of magistral. The subchloride of copper Cu3Cl exerts no injurious influence. REFINING OF SILVER ARISING FROM CUPELLATION OR AMALGAMATION. § 1138. The impure silver is melted, exposed to a current of air which oxidizes the foreign metals, in a furnace consisting of a hemi- spherical cast-iron cavity, lined with a thick coat of marl or wood- ashes, which forms a sort of porous cupel, serving to absorb the liquid oxides produced by the oxidation of the foreign metals. The cavity is filled with charcoal, on which the silver to be refined is placed, and the combustion is assisted by a bellows, which, at the same time, furnishes the air necessary for oxidation. When the silver has become liquid in the cupel, the air is projected over the surface of the bath until no spots form on its surface, and the metal, being then refined, contains at most 1 per cent, of foreign matter. § 1139. Silver is rarely used in a state of purity, as it is too soft, and articles made of it would soon be worn and lose the sharpness of their edges and angles. It is generally alloyed with a certain quantity of copper, which increases its hardness; and the alloy does not assume a decided yellow tinge unless a considerable quantity Alloys of Silver. 312 SILVER. of copper is present, more than | being necessary to destroy the white colour, to Avhich, as it is less fresh than that of pure silver, the brilliancy of the latter is artificially given, by a process called washing. The intention of this operation is to remove the copper which is immediately on the surface of the alloy; for which purpose the article is heated to a dull red-heat, when the superficial layer of copper oxidizes, and by plunging it immediately into water, acidu- lated by nitric or sulphuric acid, the oxide of copper dissolves. After the washing, the surface of the article is necessarily dead, because the particles of silver are, as it were, separated from each other ; but it is readily polished by burnishing. Alloys of silver for coin, jewelry, and plate are subjected to a legal standard, regulated by law, and secured by a stamp for jewelry and plate. The standard of French coin is that is, it must contain 900 of silver and 100 of copper; but as the exact proportions cannot always be obtained, a variation of is allowed. Thus an alloy of 897 of silver and 103 of copper is received, while an alloy of 896 of silver and 104 of copper is illegal. Alloys containing more than 903 of silver are not admitted, as it is more advantageous to melt them again with a small quantity of copper, to reduce them to the legal standard. The standard of silver medals is with a variation of as for coin. The ordinary standard of jewelry and plate is -5°, but the varia- tion is greater than in coin, being allowed to reach below. No superior limit is fixed, because it is not the interest of the silver- smith to exceed the legal standard. The solder used for silver plate consists of 667 parts of silver, 233 of copper, and 100 of zinc. § 1140. Many articles are made of sheet-copper covered with a lamina of silver, and are then called plated-ware, the ordinary standard of which is that is, the sheet should be composed of of copper and T 0f silver; while sometimes, however, an inferior standard is adopted. Plated-Avare is made in the following manner:— A plate of copper, and one of silver having the same surface and weighing ~ of the copper, being selected, the surface of the copper is carefully scraped, and it is then dipped into a strong solution of nitrate of silver, Avhere it is covered with a Ihin coat of metallic silver. This being done, the silver plate is applied to the copper, and, the whole being heated to a brownish-red colour in an oven, is then passed through a roller until the sheet has attained the re- quired thickness. The two metals adhere so strongly as to defy mechanical separation. ASSAY OF ALLOYS OF SILVER. 313 ASSAY OF ALLOYS OF SILVER. § 1141. It is important to be able to ascertain quickly and ex- actly the standard of alloys of silver, in order that the manufacture of coin and silver plate shall remain under protection of the govern- ment. The assay is made in two ways: the first, and older, by cu- pellation ; and the second, by analysis by the humid way, which latter process, being much more exact, has taken the place of cupel- lation in the government assay-office. § 1142. The analysis of alloys of silver and copper by cupellation is founded on the property of silver not to oxidize when kept in a fused state in the air, and to yield nearly insensible vapours; while copper, on the contrary, oxidizes under these circumstances, and is converted into the suboxide Cu30; but, in order to separate this substance from the alloy, it has been found necessary to introduce into the latter a certain quantity of lead, which, by oxidizing, pro- duces liquid litharge in which the suboxide of copper dissolves. The roasting is effected in a cupel, (fig. 591,) that is, in a thick porous capsule made by compressing bone- ashes, slightly moistened with water, in moulds, where it takes the shape of which a vertical sec- tion is seen in fig. 592. The fused oxide of lead, which holds the other oxides in solution, soaks into the cupel, and nothing remains at last in the latter but the globule of refined silver. A cupel of bone-ash can absorb about its own weight of litharge. The quantity of lead necessary to add to an alloy of silver and copper, to effect its easy cupellation, should be in proportion to the quantity of copper contained; because the litharge, after having dissolved the suboxide of copper, which is simultaneously formed, must preserve sufficient fluidity to soak readily into the cupel. If the infiltration does not ensue, the metal becomes covered with litharge and oxidation ceases, in which case the assay is said to be drowned, (noyA) Assay by cupellation is generally performed upon 1 gramme of alloy ; and experience has shown that the following quantity of lead must be added according to the standard of the alloy. Assay by Cupellation. Fig. 591. Fig. 592. Standard of the Alloy. Lead necessary for refining 1 gramme of silver. Silver at 1000 u 950 3 u 900 7 a 800 10 u 700 12 u 600 14 314 SILVEK. Lead necessary for refining standard of the Alloy. 1 gramme of silver. Silver at 500 u 400 a 300 a 200 > 16 to 17 gm. a 100 Pure copper. J The standard of the alloy, of which the exact composition is to he ascertained, being in general approximately known, an inspection of the table, therefore, gives immediately the quantity of lead to be added. Supposing, for example, that the standard of a piece of coin is to be exactly determined; knowing that its standard must be nearly an addition of about 7 gm. of lead must be made to 1 gm. of alloy very exactly weighed. Fig. 593 repre- sents a cupelling- furnace, of which a vertical section is seen in fig. 594. The muffle A, which is the most important part of the furnace, is a semi-cylindri- cal earthen cradle (fig. 595) closed at one end, and arranged in the furnace so that it can be entirely surrounded with fuel, and its open- ing corresponds exactly to the aperture D of the furnace. The sides of the muffle are furnished with longitudi- nal slits, through which the external air which enters at the mouth of the muffle escapes into the current of air in the furnace; by which arrangement the muffle is constantly traversed by a very oxidizing current of air. The reverberatory furnace has generally a sheet-iron pipe M to increase its draught. The furnace being filled with charcoal through the hole F, the cupels are introduced into the muffle, after having been previously dried on the platform N, if newly made. When the cupels are in the muffle, the open- ing D is closed with the door E, in order to raise the Fig. 593. Fig. 694. Fig. 595. ASSAYING OF SILVER. 315 temperature in the muffle, and when this is done the aperture D is opened, through which the portion of lead to be added to each assay is dropped into each cupel. As soon as the lead is in fusion, the assay (prise d’essai) is introduced, when the metals soon melt, while the alloy of silver dissolves entirely in the lead; and in a few mo- ments the alloy forms in each cupel a round liquid globule. White vapours, arising from the oxidation of the metallic lead in the air, are soon disengaged, and the surface. of the metallic globule is covered with a pellicle and fine drops of fused oxide, which move rapidly over its surface. The oxides gradually soak into the cu- pel, and when the lead and copper are completely converted into oxides and absorbed by the bone-ash, the silver is refined, and the motion on its surface ceases; the phenomenon of lightning, as de- scribed § 997, being produced on a small scale. The cupel must then be brought slowly to the opening of the muffle, in order that the globule of silver may not be too rapidly cooled. It has been mentioned (§ 1115) that pure silver absorbs a certain quantity of oxygen from the air, and that the absorbed gas is suddenly disen- gaged at the moment of solidification, while the metal is cooling rapidly, causing a sudden evolution of gas by which a small quantity of the metal is generally projected from the vessel, in which case the silver is said to sputter, (roche.) It is easy to tell by the appearance of the button, when cooled, whether a sputtering has taken place, as in that case a kind of vegetation, like a little mush- room, may always be seen at the places where the gas has escaped; and all assays presenting this character should be rejected, as they necessarily imply too small a quantity of silver. In order that the assay may be admitted, the globule should be slightly adherent to the cupel, its lower surface should appear very smooth and of a dead colour, and the upper surface polished and free from roughness. When the upper surface is dull and furrowed, it proves either that the silver has sputtered, that the refining has been imperfect because the temperature has been too great, or that there was too little lead. § 1143. As the temperature of the furnace exerts great influence over the cupellation, the assay always presents some degree of un- certainty, and the assayer is, in fact, between two difficulties : if the temperature rises too high, the silver is perfectly refined, but there is considerable loss from volatilizing, and a small quantity of silver is carried into the cupel by the litharge, which, in that case, is very fluid; while, if not heated sufficiently high, the loss of silver is less, but the refining is imperfect, and the globule retains a small quantity of lead. These two causes of error exist simulta- neously in all assays, and neutralize each other more or less com- pletely ; and, accordingly, as one or the other predominates, the standard will be found too low or too high. The assayer should always endeavour to heat his furnace in the 316 SILVER, same manner, and he can then construct a table by which he knows, for each alloy, the correction which should be made in each assay in order to obtain the exact standard. A table of this kind, which is made by cupelling alloys of knoAvn proportions, obtained by melt- ing, with a proper quantity of lead, determinate proportions of silver and copper, can be of use only to the assayer who has made it, and who always operates with the same furnace. As a measure of greater certainty, the assayer, from time to time, performs a cupel- lation on a trial-piece, (t£moin,) that is, on an alloy the composition of which he knows a priori, in order to ascertain whether the assay yields a loss equal to that indicated by his table. If otherwise, he modifies the results of all the assays simultaneously made, in the manner suggested by the assay of the trial-piece. We subjoin the table adopted in the Mint at Paris, according to the standard of the alloys: Real Standards. Waste, or quantities necessary to add by cupellation. to the standard obtained, in order to produce the real standard. 1000 998.97 1.03 950 947.50 2.50 900 896.00 4.00 850 845.85 4.15 800 795.70 4.30 750 745.48 4.52 700 695.25 4.75 650 645.29 4.71 600 595.32 4.68 550 545.32 4.68 500 495.32 4.68 400 396.05 3.95 300 297.40 2.60 200 197.47 2.53 100 99.12 0.88 When the cupellation has been carefully performed, the true com- position may be ascertained within 2 or 3 thousandths. The lead used in cupellation, which should be as free as possible from silver, is called in commerce assay-lead. In all cases, the assayer should ascertain previously the purity of his lead by a pre- liminary assay. Assays by the Humid Way. § 1144. Assays by the humid way are made by precipitating sil- ver in the state of insoluble chloride by a standard solution of com- mon salt. As chloride of silver readily aggregates by agitation, in a liquid acidulated with nitric acid, the exact moment when precipi- tation of silver no longer takes place may be easily ascertained. The solution of salt used being such that 1 cubic diameter of the HUMID AySAY OF SILVER. 317 liquid exactly precipitates 1 gm. of pure silver, the standard of an alloy is determined by dissolving 1 gm. of it in 5 or 6 gm. of nitric acid, and carefully pouring the solution of salt into the liquid until precipitation ceases after the addition of one drop. After each addition of the saline solution, when the moment of complete pre- cipitation approaches, the bottle containing the solution of silver must be shaken in order to aggregate the precipitate and clear the liquid. The number of cubic centimetres necessary to completely precipitate the silver gives the standard of the alloy. The process may be simplified and brought to great exactness when it is applied to the exact determination of the standard of an alloy of which the approximate value is known; for example, of a piece of silver coin or plate. Two solutions of sea-salt are then used: one, which is called the normal solution, and which is such that 1 decilitre precipitates exactly 1 gm. of pure silver; and another, called the decimal liquid, which is 10 times more dilute, and of which 1 litre is required to precipitate 1 gm. of silver. Lastly, a third standard solution is sometimes used, called the deci- mal solution of silver, which contains 1 gm. of silver in 1 litre. Supposing that the standard of a piece of coin is to be ascer- tained, consisting of an alloy which must contain, at least, ~ of silver, but which we will assume tp contain only ; then, accord- ing to the latter composition, 1.116 gm. of alloy contains 1 gm. of silver. After having dissolved 1.116 gm. of alloy, very exactly weighed, in a ground-stoppered bottle, by means of 5 or 6 gm. of pure nitric acid, 1 decilitre of the normal solution of sea-salt is poured into the bottle. It is evident that, if the standard of the alloy be really the silver will be completely precipitated, and the liquid will not contain an excess of salt, wdiile, if the standard be higher, silver still remains in solution, and if lower, the silver has been completely precipitated, but there is an excess of salt in the liquid. In order to ascertain this, the bottle is corked and shaken quickly, in order to clear the liquid, after which one cubic centimetre of decimal saline solution is added, which can precipitate 1 thousandth of silver. If silver is still contained in the liquid, a very perceptible white cloud is formed, and the bottle being then again shaken, a second cubic centimetre of decimal solution is added. If a precipitate be produced, the same process is repeated until the liquid remains clear. Supposing that 5 cubic centimetres of the decimal solution, gradually added, .have produced precipitates, but that the 6th cubic centimetre has not affected the transparency of the liquid, it will be hence inferred, that after the precipitation of 1 gm. of pure silver by the cubic decimetre of the normal solution of salt, the liquid contained, at least, 4 thousandths of silver. The fifth cubic centimetre of decimal solution having produced cloudi- ness, while the 6th did not, it is evident that the liquid did not 318 SILVER. contain more than 5 thousandths of silver, and, by assuming 4J thousandths, we are sure of having found the amount of silver con- tained in the alloy within nearly J thousandth. The real standard of the alloy is, therefore, 896 -f 4J, or 900J thousandths. If the first cubic centimetre of a decimal saline solution does not yield a fresh precipitate in the solution of silver which has already received the cubic decimetre of normal saline solution, it is evident that the standard of the alloy is not above and that, consequently, it should be rejected. The exact composition of the alloy may be determined by means of the decimal solution of silver, always beginning by adding one cubic centimetre of the latter, which precipitates the cubic centimetre of decimal saline solution which had been added, and which must be neutralized. The liquid being cleared by agitation, one more cubic centimetre of decimal solution of silver is added, and if cloudi- ness be produced, the bottle is again shaken before a second cubic centimetre of the same liquid is added, which process is continued until the addition of another cubic centimetre of the decimal solu- tion of silver no longer clouds the liquid. Supposing that the first three cubic centimetres have yielded precipitates, but that the liquid remains clear on the addition of the fourth, it is very probable that the third cubic centimetre has .not been entirely decomposed, and it may be admitted that one-half of it has been useless, and that 2 J cubic centimetres of the decimal solutionof silver have sufficed to decompose the salt which remained free after the addition of the cubic decimetre of the normal saline solution; for which reason thousandths must be subtracted from the standard thus leaving for the exact standard of the coin exa- mined —A low We shall now briefly describe the assay- ing apparatus used in the Mint at Paris, where these assays are daily made. The normal solution of salt is contained in a copper vessel V, (fig. 596,) tinned on the inside, and completely closed to pre- vent evaporation, which would alter the standard of the liquid, only a Mariotte’s tube uv allowing the extrance of air. The vessel, which is fixed in the upper part of the laboratory, has a curved tube cde, with a stopcock r, and to the lower part of which the pipette A, which measures exactly 1 decilitre of normal solution, is Fig. 596. HUMID ASSAY OF SILVER. 319 connected by means of a tube be which contains a thermometer. The metallic piece which connects the glass tube be with the pipette (fig. 597) has two stopcocks r', r", the one of which shall presently be explained. The assayer having closed the end a of the pipette with his finger, opens the stopcocks r', r", thus allowing the saline solution to flow in a thin stream into the pipette, without stopping the upper tube of the latter, so that the air contained in the pipette can escape freely through the stopcock r' and the small tubulure which terminates it. When the pipette is filled a little above the mark a, the assayer closes the stopcocks r' and r". The bottle which contains the alloy dissolved in nitric acid is placed in the compartment C of a support I, (fig. 596,) which slides between the grooves MN, M'N', and which is provided with an appendix D, furnished at its upper part with a small sponge k, placed at the height of the lower orifice a of the pipette. The assayer having so placed the support as to bring the sponge in contact with the pi- pette, opens the stopcock r', and allows the liquid to descend slowly to the level a, where the sponge absorbs the last drop of liquid, which would adhere to the end of the pipette. The assayer then brings the opening of the bottle under the pipette, and empties it entirely by opening the stopcock r'. As a large number of assays is gene- rally made at once, there are a series of bottles numbered, in each of which are dis- solved 1.116 gm. of alloy of coin. In order to hasten the solution, all the bottles are placed on a stand, (fig. 598,) and after hav- ing introduced into each the alloy and the nitric acid which is to dissolve it, the stand is plunged into hot water. When the metals are dissolved the nitrous vapours are driven off by blowing into the bottles, and the decilitre of normal solution is introduced, after which they are placed on a second stand, (fig. 599,) suspended on a steel spring, and held below by a spiral spring ab. The bottles having been closed by their ground stoppers, the assayer grasps the handle ef of the stand and shakes it for a few moments, in order to collect the precipitate and render the liquids Fig. 597. Fig. 598. Fig. 599. 320 SILVER, clear. He then carries the bottles to a black table having numbered compartments, each one being placed in the compartment corre- sponding to its number. The decimal solution is contained in a bottle (fig. 600) provided with a tube, drawn out at its lower extremity and having a mark corresponding to a capacity of 1 cubic centimetre, which dips into the liquid. The as- sayer, applying his finger to the upper aperture of the tube, withdraws the latter, and allows the liquid to flow slowly until it reaches the level of the mark, and then carries the cubic centimetre thus measured off into the first bottle, re- peating the process with the other bottles. He then examines the bottles successively, and makes with chalk a mark on the black table near each bottle in which a precipitate is formed, and then replaces the bottles on the stand of fig. 599, clears the liquids by agitation, deposits the bottles on the table, and adds another cubic centimetre of the decimal solution to all the bottles in which there was pre- viously a precipitate formed, gradually excluding the bottles in which the liquid was not clouded. By counting the number of chalk-marks near each bottle, a number which represents that of the cubic centi- metres of decimal solution which have been efficient, and deducting J for the last cubic centimetre, which, probably, has not been wholly used, the assayer finds the number of thousandths which must be added for each alloy to the supposed standard of -^j|. As the standard solution of sea-salt has been prepared for the temperature of 59° degrees, and as it expands by heat, it is evident that its standard must be altered in volume by the changes of tem- perature. It is therefore indispensable, when the temperature of the solution is not 59°, to correct all the results by means of tables made for the purpose, the temperature of the saline solution being read off on the thermometer contained in the tube cb, (fig. 596.) But the corrections are always uncertain, and may be avoided by the following device, by means of which, at the same time, any wrong preparation of the normal solution is ascertained. An assay upon 1 gm. of pure silver, made daily, simultaneously with the tests on the coin, gives for each day the exact value of the standard of the normal saline solution, and all assays made simultaneously may be corrected by the difference of the standard thus found with the normal standard. A large quantity of normal solution of salt is generally made at once, by dissolving 500 gm. of common impure salt of commerce in 4 litres of water, filtering the liquid, and adding the quantity of water necessary to obtain the necessary degree of dilution of the normal solution, supposing the salt to be pure; by Avhich means a solution is obtained of a degree of concentration only approximative to that desired. In order to ascertain its exact concentration, 1 cubic decimetre of the liquid is poured into a solution of 1 gm. of pure silver in nitric acid. The liquid being cleared by agitation, it Fig. 600. ASSAYING OF SILVER ORES. 321 is easy, by means of a decimal saline solution or a decimal solution of silver, to determine exactly the number of thousandths of silver, or of salt, Avhich remain free. The additional quantity of water or salt necessary to obtain the proper dilution of the saline solution is thus found, and, after it has been added, a neAv test is made, and so on, until the normal degree of concentration is attained. In order to prepare the decimal solution, a decilitre of the normal solution is introduced into a bottle which measures 1 litre to a mark traced on its neck, up to which the bottle is then filled with distilled Avater. The decimal solution of silver is prepared by dissolving 1 gm. of pure silver in 5 or 6 gm. of nitric acid, and diluting Avith water until the liquid exactly assumes the volume of 1 litre. When silver contains mercury, the results of the assay by the humid Avay are inaccurate, because the mercury, being precipitated in the state of chloride, decomposes a portion of the chloride of sodium. The presence of any considerable quantity of mercury in an alloy is easily perceived, because the liquid, in that case, is not cleared by shaking, and the first deposite of chloride of silver does not blacken in the light. The exact standard of the alloy may, hoAvever, be obtained by the humid Avay, by recommencing the test on another portion of the substance after having added a certain quantity of acetate of soda to the nitric solution, by which means the precipitation of the mercury is prevented. § 1145. The argentiferous galenas are assayed by cupelling the lead, after having isolated it by the process described § 980. The galena is sometimes also fused with 3 or 4 tenths of its weight of nitre, when the sulphur of the galena is converted into sulphuric acid which combines Avith the potassa, Avhile the greater portion of the lead separates in the metallic state, retaining the A\Thole of the silver. The argentiferous copper-ores are first assayed for their copper, after which the lump of copper is introduced into the cupel, with the addition of 16 times its weight of lead. The assay for copper is made as follows:—If the ore he sulphu- retted, it is first roasted in a small earthen capsule, (called tile in England,) the heat being properly regulated in order to prevent the substance from running together, and the temperature being kept elevated until sulphurous acid is no longer disengaged. The tile being then covered with its lid, the temperature is raised to a white-heat, in order to decompose the sulphates; after which the roasted material is fused in an earthen crucible with 3 or 4 times its weight of black flux, the fusion being effected in a forge-fire or an ordinary calcining furnace, having a strong draught. After cool- ing, the crucible is broken, and a lump of malleable copper and an ASSAYING OF SILVER ORES. 322 GOLD, alkaline slag containing merely a trace of copper are found. Oxi- dized copper-ores need not be previously roasted, but can be imme- diately subjected to the fusion with black flux. Oxidized silver-ores are mixed with 8 or 10 times their weight of litharge and double their weight of black flux, and the mixture is fused in an earthen crucible, when a portion of the litharge is con- verted, by the carbon of the black flux, into metallic lead, which carries with it all the silver; the quartzose and earthy gangues being transformed into slag with the litharge and potassa of the black flux. Ores of silver which contain sulphides and arseniurets are also fused with litharge, but it is in this case frequently unne- cessary to add black flux, because the reaction of the sulphides and arseniurets on the litharge furnishes a sufficient quantity of metallic lead to entirely remove the silver. GOLD. Equivalent = 98.5 (1231.25; 0 = 100). § 1146. The gold in gold coin and jewelry is never pure, being alloyed with a certain quantity of copper and frequently of silver, to give it a greater degree of hardness. In order to obtain pure gold, gold coin is dissolved in aqua regia, and the solution being evapo- rated to dryness, by gentle heat, to drive off the excess of acid, the residue is treated with water, by which means the silver is separated as insoluble chloride. An excess of protosulphate of iron, which pre- cipitates the gold in the metallic state, in the form of brown powder, is then poured into the liquid, the reaction ensuing according to the following equation: Au2Cl3+6(Fe0,S03) = 2Au+2(Fea03,3S03)+Fe2Cl3. The precipitate is digested with weak chlorohydric acid, and, after being well washed, is fused in an earthen crucible with a small quantity of borax and saltpetre. The protosulphate of iron may be replaced by sesquichloride of antimony Sb3Cl3 dissolved in an excess of chlorohydric acid; the sesquichloride of antimony being con- verted into the perchloride SbaCl5, while the gold is precipitated in the metallic state. Gold has a characteristic yellow colour, and its density is 19.5. It fuses at a strong white-heat, or at about 2200° of the air ther- mometer, giving off sensible vapours at a very high temperature. A gold wire is converted into vapour when traversed by the current of a powerful electric battery; and if this take place over a sheet PROPERTIES OP GOLD. 323 of paper placed at a small distance, the paper becomes coloured of a purplish brown, by the very finely divided gold which is precipi- tated on it. A blade of silver substituted for the paper soon becomes gilded. A globule of gold gives off vapour very copiously when held betAveen two pieces of charcoal terminating the conductors of a pow- erful galvanic battery. Gold is the most malleable of all the metals, (§ 295,) and when beaten into very thin leaves is transparent, the transmitted light appearing of a beautiful green colour. Gold may be crystallized by fusion, when it assumes the shape of cubes modified by other facets of the regular system. Native gold is sometimes found in well- defined crystals presenting the same form. When precipitated in a metallic state from its solutions, gold forms a brown powder, which by burnishing soon recovers the me- tallic lustre and characteristic colour of malleable gold, and which aggregates by percussion. If the mass be heated to redness before being hammered, a perfectly aggregated metal can be obtained without having heated it to fusion. Gold does not combine directly with oxygen at any temperature. Chlorohydric, nitric, and sulphuric acids do not affect it, while aqua regia, on the contrary, readily dissolves it in the state of sesqui- chloride, Au3C13. Gold is also dissolved by chlorohydric acid when a substance capable of disengaging chlorine is added, such as per- oxide of manganese, chromic acid, etc. Chlorine and bromine also attack gold, even when cold, while iodine acts on it but feebly. Sulphur does not attack gold at any temperature, nor does the metal decompose sulf hydric acid; but by fusing it with the alkaline polysulphides it is powerfully acted on, a double sulphide being formed, in which the sulphide of gold Au3S3 acts the part of a sulph- acid. Arsenic when assisted by heat combines with gold, and forms a very brittle alloy. Gold is attacked neither by the alkalies nor the alkaline carbo- nates or nitrates. § 1147. Two combinations of gold with oxygen are known: 1. A suboxide AuaO, 2. A sesquioxide Au303, neither of which forms salts with the oxides. The suboxide Au20 is obtained by decomposing the chloride AuaCl by a dilute solution of potassa, in the shape of a deep violet- coloured powder, which decomposes at about 77°, disengaging oxy- gen. The oxacids exert no action on this substance, while chloro- hydric acid decomposes it, forming sesquichloride of gold Au2C13, while metallic gold is separated. Sesquioxide of gold (often called auric acid on account of its property of combining with bases) is prepared by digesting a hot COMPOUNDS OF GOLD WITH OXYGEN. 324 GOLD solution of sesquichloride of gold with magnesia, when aurate of magnesia is formed, which remains mixed with the free magnesia. The deposit is boiled with nitric acid, which dissolves the magnesia and leaves hydrated sesquioxide of gold. Auric acid may also be obtained by exactly saturating a solution of sesquichloride of gold by carbonate of soda, and then boiling the liquid, when a large proportion of the gold is precipitated in the state of sesquioxide, while the other portion remains in solution, but may be precipitated by successively adding to the liquid an excess of caustic potassa and acetic acid. Hydrated auric acid is a yellow or brown powder, which loses its water at a low temperature and becomes anhydrous, while at about 482° it decomposes into gold and oxygen, which reaction is also effected by the solar light. Deoxidizing substances, such as the organic acids, or boiling alcohol, reduce it to the metallic state; while chlorohydric acid dissolves it and produces the sesquichloride Au2C13. The most energetic oxacids do not form definite com- pounds with sesquioxide of gold, while the latter dissolves, on the contrary, readily in cold alkaline solutions, producing alkaline aurates which crystallize by evaporation. By adding a small quantity of ammonia to a solution of sesqui- chloride of gold, a fulminating substance is produced, which con- tains, at the same time, oxide of gold, ammonia, and chloride, and which, by digesting with an excess of ammonia, furnishes a bright brown powder of still higher detonating properties than the first, and which is a simple combination of sesquioxide of gold with am- monia Au303+2NH3+H0. § 1148. Although sulphur does not combine directly with gold, two sulphides corresponding to the two oxides are obtained by de- composing the sesquioxide of gold by sulfhydric acid, which, on being passed through a cold solution of sesquichloride of gold, yields a brownish-yellow precipitate, which is the sulphide Au2S3, readily soluble in the alkaline sulphides. If the solution of the chloride is boiling, a sulphide Au2S, of a deep brown colour, is precipitated, while sulphuric and chlorohydric acids are formed: COMPOUNDS OF GOLD WITH SULPHUR. 2 Au3C13+3HS+3H0 = 2AusS+6HCl+SOa. COMPOUNDS OF GOLD WITH CHLORINE. § 1149. By dissolving gold in aqua regia a yellow solution of sesquichloride of gold Au2C13 is obtained, which, when allowed to evaporate slowly in dry air, deposits yellow crystals of a compound of sesquichloride of gold and chlorohydric acid. If the solution be evaporated to drive off the excess of acid, the substance assumes a brown colour, and a deliquescent crystalline mass remains, which HALOID COMPOUNDS OF GOLD. 325 dissolves readily in alcohol and in ether. Sesquichloride of gold dissolves even more rapidly in ether than in water; for, if an aque- ous solution of the chloride be shaken with ether and water, the supernatant ether contains nearly all the chloride of gold in solu- tion. The solution of sesquichloride of gold in ether was formerly used in medicine under the name of aurum potabile. Sesquichloride of gold forms with several other metallic chlorides double crystallizable chlorides, in order to obtain which it is suffi- cient to mix and evaporate the solutions of the two chlorides. The formula of the double chloride of gold and potassium, which is deli- quescent, is KCl-f Au3C13+5HO, while the formula of that of gold and sodium is NaCl+Au3Cl3+4HO, and that of the double chloride of gold and ammonia is NH3HC1+Au3C13+2HO. Compounds of chloride of gold with the chlorides of barium, calcium, manganese, iron, zinc, etc., are also known. Subchloride of gold Au3C1 is prepared by heating the sesquichlo- ride of gold Au3C13 to a temperature of about 400°, when chlorine is disengaged, while a greenish insoluble powTder remains. COMPOUND OF GOLD WITH CYANOGEN. § 1150. By adding a solution of cyanide of potassium to a con- centrated hot solution of perchloride of gold, until the liquid loses its colour, a solution is obtained, wdiich, on cooling, deposits pris- matic crystals of a double cyanide of gold and potassium of the formula KCy+Au2Cy3. The crystals, which are efflorescent and very soluble, disengage cyanogen when subjected to moderate heat; and, when treated with water, a solution is obtained, which, on cool- ing, deposits a double cyanide of the formula KCy+AuaCy. PURPLE OF CASSIUS. § 1151. The name of purple of Cassius is given to a precipitate containing gold, tin, and oxygen, which is used by painters on por- celain and glass, (§ 730,) and which is prepared in various ways. Its composition not being always uniform, chemists are not yet agreed upon its nature. It is generally obtained by pouring into a sufficiently dilute solution of sesquichloride of gold, a mixture of protocliloride and bichloride of tin, the precipitate showing a beau- tiful purple hue when it is of small bulk, wffiile it assumes a brown colour when more copious. A purple of Cassius of uniform composition is prepared by dis- solving 20 gm. of gold in 100 gm. of aqua regia made of 20 parts of nitric and 80 of chlorohydric acid ; driving off the excess of acid by evaporation in a water-bath and dissolving the residue in 7 or 8 decilitres of water. Some pieces of tin being then placed in the liquid, a purple precipitate of the formula Au30,Sn03+Sn0,Sn03-f 4HO is formed, but which may also be considered as 2Au+3SnOa+4IIO. The substance, on being subjected to heat, evolves water alone and 326 GOLD, no oxygen, while the calcined residue presents all the characters of a mixture of metallic gold and stannic acid. But as before calcina- tion the substance will not give off gold to mercury, it is evident that the gold did not exist in it in the metallic state. A beautiful purple of Cassius is obtained by heating suboxide of gold Au20 with a solution of stannate of potassa. Lastly, purple of Cassius is obtained by fusing together in a cru- cible 1 part of gold, J part of tin, and 4 or 5 of silver, forming a ternary alloy, from which nitric acid extracts the silver, while the gold and tin are precipitated in combination with oxygen, and a brilliant purple is formed, the shades of which can be changed by altering the relative proportions of gold and tin. A solution of sesquichloride of gold stains linen of a purple colour, as it also does the skin and the organic tissues generally ; which colouring is probably owing to suboxide of gold, as friction does not restore a metallic lustre to the spots, although they acquire it in a short time when exposed to solar light in a bottle filled with hydrogen gas. DETERMINATION OF GOLD, AND ITS SEPARATION FROM TIIE METALS PREVIOUSLY DESCRIBED. § 1152. Gold is always determined in the metallic state, and is precipitated from its solutions by means of protosulphate of iron, after having added chlorohydric acid to the liquid in order to main- tain the sesquioxide of iron which forms during the reaction in so- lution. But it is important, in order to completely precipitate the gold, that the liquid should contain no nitric acid; in which case it must be previously evaporated with chlorohydric acid. The gold, when collected on a filter, is calcined to redness before being weighed. § 1153. In order to separate gold from the metals previously de- scribed, the insolubility of the metal in nitric acid is sometimes relied on, while at other times all the metals are dissolved in aqua regia, and the gold is precipitated by protosulphate of iron, or, better still, by heating the solution with a certain quantity of oxalic acid; which latter method has the advantage of not introducing a new metal into the liquid. Gold is sometimes also separated by precipi- tating it in the state of sulphide, by sulfliydric acid gas, the sul- phide leaving metallic gold after calcination. METALLURGY OF GOLD. § 1154. Gold is almost always found in the native state, being sometimes pure, but more generally alloyed with certain quantities of silver. It occurs in three kinds of bearings: 1. In veins, generally quartziferous, which contain other metallic minerals, as ores of copper, lead, silver, and pyrites; the veins usually traversing the primitive rocks. METALLURGY OF GOLD. 327 2. In small veins scattered through rocks situated at the separa- tion of the crystalline and stratified rocks. 3. In disaggregated quartzose sands, often extensively seen in alluvial formations, and owing their presence to the disintegration of auriferous crystalline rocks which exist in the vicinity. The greater specific gravity of the gold prevents its particles from being carried as far as those of the other minerals with which it was mixed, and its resistance to the action of the greater part of chemi- cal agents preserves it in the state of spangles. Alluvious soils containing gold chiefly occur in open valleys between primitive mountains, where gold is frequently found in place. The principal localities of auriferous sands are in California, Australia, Brazil, Mexico, Chili, Africa, the Ural and Altai Mountains in Siberia—the quantity of gold annually extracted from all of which Amounted, in 1851, to 178 tons, of which California alone produced 110. Gold is generally found in the sands in the form of spangles, or shapeless and rounded grains, which, when they are of any considerable size, are called river or wash gold, (pdpites.) Grains are sometimes found of the size of a hazel-nut, and pieces weighing several kilogs. have been met with: one lump weighing 36 kilogs. was found in the Ural. Gold- exists in the drift-sand of all rivers which arise from, or flow over a large extent of, primitive rocks; and several auriferous alluvim are known in France, such as those of the Ariege in the Pyrenees, of the Gardon in Cevennes, the Garonne, and the Rhine near Strasburg. It is found in too small quantity to be worked to advantage; but the inhabitants look for it when they would other- wise be idle, and are then called gold-finders. The spangles of gold scattered through the river-sand are generally so excessively small that more than 20 are often required to make a milligramme. In Siberia, sands containing only 0.000001 of gold are not con- sidered worthy of being worked; and the Rhenish sands contain, on an average, about of this quantity. Gold exists also, combined with tellurium, in certain mines of Transylvania. An alloy of gold with silver and palladium, in the form of small crystalline grains, occurs in Brazil, and is called auro- powder or auro-dust. Lastly, all pyrites in primitive rocks contain a small quantity of gold, and are often rich enough to be worked to advantage. § 1155. When gold exists in veins which contain other metals, as lead, copper, or silver, those metals in which the gold is concen- trated are first extracted from the ores, and the gold is then sepa- rated by refining, a process presently to be described. The ore is frequently first subjected to amalgamation, as in the case of silver ores, Avhen the gold dissolves in the mercury, and, after the liquid amalgam has been filtered, a more solid amalgam is obtained, from which the gold is separated by distillation. The ore 328 GOLD, is then smelted, so as to obtain a matt from which a certain quantity of gold can still be extracted. § 1156. Auriferous sands are washed in the most simple manner, either in wooden tubs, or on inclined planes over which a current of water flows, and they are then treated by amalgamation. In the Ural, the auriferous sand is poured into boxes, the sheet- iron bottom of which is provided with openings of 2 centimetres in diameter, and, while a stream of water flows through the boxes, the workman stirs the sand constantly with a shovel, when the finer portions fall through the holes and are collected on large sleeping tables covered with muslin. The sand is frequently swept toward the head of the table, where the gold remains with the heavier mine- rals ; and the sand, being enriched by this washing, is again more carefully washed on smaller tables. The titanic iron and magnetic oxide of iron being separated by a magnet, the material is fused in large graphite crucibles, at the bottom of which the gold collects, while the upper part is filled by a slag containing a quantity of un- melted grains of gold. The slag being stamped and washed, the rich schlich thus obtained is smelted, yielding an auriferous lead, from which the gold is separated by cupellation. § 1157. In Tyrol a certain quantity of gold is extracted from pyrites by amalgamating them in mills resembling that represented in fig. 601, several mills being generally placed above each other. (The figure gives an external view of the upper mill and a section of the lower one.) The pyrites, in the state of an impal- pable powder, is suspended in water, and conveyed into the upper mill by the conduit G, whence it flows into the second mill by the sluice G'. The bed of each mill is made of a cast-iron vessel cdef., securely fastened on a strong wooden table; and in the centre of the vessel is a tubulure traversed by an axis of rotation ab, set in motion by the cog-wheel rr'. The runner-stone mm' of each mill is of wood, and resembling the shape of the bed; but, being about 2 centimetres smaller, is furnished with several sheet-iron teeth projecting about 1 centimetre. The upper surface of the runner-stone is shaped like a funnel, into which is poured the liquid mud, which passes between the stones and flows out by the conduit G'. The stones make about 15 or 20 revolutions per minute; and 25 Fig. 001. SEPARATION OF GOLD AND SILVER. 329 kilogs. of mercury are placed at the bottom of each, making a layer of about 1 centimetre in thickness, against which the teeth of the wheel constantly strike, while at the same time they stir up the ore. The gold is dissolved by the mercury, and, after continuing this process for 4 weeks, it is withdrawn and filtered through a chamois- skin, which retains a solid amalgam containing nearly one-third of its weight of gold, which is then separated from the other metals by cupellation. ALLOYS OF GOLD. § 1158. Gold is rarely used in a state of purity, as it is too soft, and its hardness must be increased by the addition of a small quan- tity of silver or copper, forming more fusible alloys than pure gold. The standard of French gold coin is T9^°5, the law allowing a va- riation of To2m above and below; while medals contain 0.916 per cent, of gold, with the same variation. There are three legal standards for jewelry, the most common of which is T7055°0, while those of t83$j and T9020°0 are rarely used; and the legal variation is jfaf below the standard, no superior limit being fixed. Gold is soldered with an alloy called red gold, of 5 parts of gold, and 1 of copper; an alloy made of 4 parts of gold, 1 of copper, and 1 of silver also being used. The clear colour of gold is given to jewelry by dissolving the cop- per which exists in the superficial layer ; to effect which the articles are heated to a dull red-heat, and dipped, after cooling, into a weak solution of nitric acid, which dissolves the copper. A thicker coat- ing of pure gold is obtained by allowing them to remain for 15 minutes in a paste formed of saltpetre, common salt, alum, and water; the chlorine set free by the action of the sulphuric acid on the salt and saltpetre dissolving the copper, silver, and gold, while the latter metal is again deposited on the article. The sur- faces are then burnished. SEPARATION OF GOLD AND SILVER. § 1159. The separation of gold and silver, more generally called the refining of the precious metals, is now done by treating the alloy by concentrated hot sulphuric acid, which dissolves the silver only. But, in order that the alloy may be completely acted on, it should neither contain more than 20 per cent, of gold, nor than 10 per cent, of copper, because sulphate of copper is but slightly soluble in concentrated sulphuric acid. The alloys are fused in crucibles, and when they are too rich in gold, a certain quantity of silver is added—silver containing a small quantity of gold being preferred. The fused alloy is granulated by being poured into water, and then placed in a large kettle with 2 J times its weight of concentrated sulphuric acid marking 66° on the areometer, the kettle being co- vered with a lid furnished with a disengaging tube. The acid, being 330 GOLD, heated to boiling, is partly decomposed, and sulphates of silver and copper are formed, while sulphurous acid is disengaged, which is sometimes passed into the leaden chambers where sulphuric acid is manufactured, (§ 139.) When gold coin is to be refined, it is merely roasted. After 4 hours, when the alloy is completely destroyed, there is introduced into the kettle a certain quantity of sulphuric acid marking 58°, and obtained by the concentration of the acid mother liquid of the sulphate of copper obtained in refining, as will pre- sently be explained. After having boiled the liquid for fifteen minutes, the kettle is taken from the fire and allowed to rest, when the greater part of the gold collects at the bottom of the vessel, from which the nearly boiling liquid is decanted off into leaden boilers containing the mother liquid arising from the purification of the sulphate of copper by crystallization. The boilers are heated by steam; and after the sulphate of copper at first deposited is re- dissolved, the liquid is allowed to rest for some time, when the whole of the gold is deposited. The clear liquid is then drawn off by a siphon, and passed into other boilers heated by steam, and contain- ing blades of copper, which precipitate the silver in the form of small crystalline grains; the metal being in a short time so per- fectly precipitated that the liquid is not clouded by common salt. The precipitated silver is carefully washed, and then compressed by an hydraulic press into compact prisms, which, after being dried, are melted in earthen crucibles, furnishing a metal which contains only a few thousandths of copper. As the gold arising from the first action of the sulphuric acid still contains a certain quantity of silver, it is heated anew, in a platinum crucible, with concentrated sulphuric acid, which abstracts the balance of the silver; a third treatment with sulphuric acid being often required. The gold dust, after being well washed and fused, contains 995 thousandths of pure gold. The acid solution of sulphate of copper which arises from the precipitation of the silver by copper is evaporated in leaden kettles until it marks 40° on the areometer; a large proportion of the sul- phate of copper being deposited in small crystals during the cool- ing. After another evaporation, the mother liquid yields an addi- tional quantity of crystals; and the last liquid, which refuses to crystallize, is used as a solution of sulphuric acid, and poured into the cast-iron boiler, after this action on the alloy. The sulphate of copper is purified by recrystallization. When the quantity of gold and silver contained in an alloy does not exceed 0.200 or 0.300, the granular material is first heated in a reverberatory furnace, when a portion of the copper is converted into oxide, which is dissolved by treating the roasted substance with weak sulphuric acid; and the alloy, being thus brought to the me- GILDING AND SILVERING. 331 dium standard of 0.500 or 0.600, may be refined by the ordinary process.* § 1160. Ornamental objects of copper or bronze were formerly- gilded by means of an amalgam of gold, which method has now been superseded by galvanic processes. The amalgam used in mercurial gilding is prepared in the following manner :—Gold-leaf is heated to a dull red-heat in a crucible, and triturated with eight times its weight of mercury, and, when the gold is dissolved, it is GILDING AND SILVERING. * The process of refining gold pursued at the United States Mint, in Philadel- phia, is similar to the method formerly called, quartation, and consists in melting gold with silver, and then extracting the silver with pure nitric acid. The depo- site of grains of native gold is first melted with borax and saltpetre, occasionally with soda to remove quartz, and being cast into a bar, is carefully weighed, accu- rately assayed to for gold, and from the assay and weight the value of the deposite calculated. Although a million of dollars may be deposited in a day, upon an arrival from California, yet such is the expedition of the assay-depart- ment, that in a few days the deposites are all paid off. As soon as the gold is as- sayed, each pound of it is melted with 2 pounds of pure silver, and the mixture, after stirring, poured into cold water, by which it is granulated, divided into small irregular fragments, presenting a large surface to the subsequent action of the acid. The granulations are then put into large porcelain jars of 50 gallons each, of which there are about 70 in use, and nitric acid poured in them. The jars being placed in leaden-lined wooden troughs, containing water, are heated by a steam coil in the water, causing the nitric acid to dissolve out the larger propor- tion of silver. A steam-heat is given during several hours, and the liquid allowed to repose until the following morning, when the solution of nitrate of silver is drawn off by a gold siphon, and transferred to a large vat of 1200 gallons, con- taining a saturated solution of common salt; Fresh acid is then added to the gold in the pots, already nearly parted, steam-heat applied again for several hours, and the whole left again to repose. On the following morning the acid liquid of one of the pots being drawn off and the fine gold removed to its filter, fresh granu- lations of gold and silver are introduced, and the acid liquid of the adjoining pot, containing only a small quantity of nitrate of silver poured over it. A fresh charge of granulated metal is thus first worked by the yet strong acid, which acted on the nearly fine gold of the previous charge. A charge of $800,000 or more is easily worked off, refined, in two days, by 4| pounds of parting acid to every pound of gold. The gold is washed thoroughly on a filter by hot water, pressed in a hydraulic press, further dried, melted with copper, and cast into bars, about 2400 ounces Troy constituting a melt. After being assayed, they are then remelted with the calculated quantities of copper or fine gold requisite to bring them to our standard of 900 thousandths fine, and cast into ingots. Upon their proving correct in the assay, usually to within of the standard, they are delivered to be coined. The chloride of silver, accurately precipitated with a slight excess of salt, is filtered and washed thoroughly on large filters, of 3 by 5 feet and 14 inches deep. It is then transferred to lead-lined wooden vats, reduced to metallic silver by granulated zinc, and, the excess of zinc being removed by sulphuric acid, washed, pressed in the hydraulic press, dried by heat, and remelted with a new portion of gold. This method of parting formerly required 3 parts of silver to 1 part of gold, and the latter constituting a fourth part of the alloy, the process was termed quartation. We have, however, found that 2 parts silver to 1 part gold are quite sufficient; and if the metal be well granulated, the acid will not leave 10 thou- sandths of silver in the gold, which is sufficient to prevent the too darkening effect of copper in the coin.—J. C. B. 332 GOLD thrown into cold water, in order to prevent the formation of crystals by slow cooling. The excess of mercury being removed by pres- sure, a doughy amalgam remains, consisting of 2 parts of gold and 1 of mercury. Bronze objects require several preliminary preparations. They are heated to redness and then dipped into dilute sulphuric acid to dissolve the oxide which forms on the surface, which operation is called the cleaning, (ddrochage,) and they are sometimes dipped for a moment into concentrated nitric acid, in order to obtain a more perfect cleansing, called ravivage. The surface is then amalgamated by means of the scratch-brush, made of fine brass wire, which is first dipped into a solution of nitrate of mercury, and then pressed on the amalgam of gold, part of which adheres. The article, being rubbed with the brush, is placed on an iron grate over coals, in a chimney which must draw well, in order to carry off' the mercurial vapours, which would injure the health of the workmen. The arti- cle is then cleaned with a brush dipped in vinegar, and the parts which are to be bright are polished with blood-stone. By substituting an amalgam of silver for one of gold, and ope- rating in the same manner, copper, bronze, and brass can be covered with a coating of silver. The brass scales of barometers and other instruments are silvered by being rubbed with a cork moistened with mixture of 1 part of chloride of silver, 2 of carbonate of potassa, 1 of common salt, and § of a part of chalk. Crilding by Immersion. § 1161. This process, which is chiefly used for gilding copper jewelry, consists in plunging the articles, after being cleanly scraped, into a boiling solution of chloride of gold in an alkaline carbonate, which is prepared by dissolving, on the one hand, 100 grammes of gold-leaf in 250 grammes of nitric acid at 97°, 250 gm. of concentrated chlorohydric acid, and 250 of water, and on the other hand, 3 kilogs. of carbonate of potassa in 20 litres of water, heated in a cast-iron kettle. When the gold is entirely dissolved in the aqua regia, the liquid is poured into a porcelain capsule, and 3 kilogs. of bicarbonate of potassa are gradually added, when a lively effervescence ensues, after the termination of which the contents of the capsule are thrown into the kettle. The liquid is boiled for 2 hours, replacing by hot water that which evaporates; after which the gold-bath is ready for gilding. When the copper articles are prepared for gilding, they are bound together with a brass wire and suspended to a glass hook. At the right of the bath are placed, 1st. A vessel containing a mixture of nitric, sulphuric, and chlorohydric acids; 2d. Two ves- sels filled with water ; 3d. A vessel containing a solution of nitrate of mercury; 4th. A vessel containing water; while at the left of the bath are 2 or 3 pots holding water. The workman first dips GALVANIC GILDING. 333 the articles into the acid liquid, and then, successively, into the two vessels holding water, into that of nitrate of mercury, into the suc- ceeding one of water, and lastly, into the gold-bath. When they have remained in the bath for about 30 seconds they have taken all the gold they can receive, and are then removed, washed in the pots on the left, and dried in heated sawdust. Their colour is then given by means of a mixture of 6 parts of nitre, 2 of sulphate of iron, and 1 of sulphate of zinc, dissolved in a small quantity of boiling water, into which the gilded articles are dipped; after which they are dried before a bright fire until the saline coating turns brown. They are then washed with water. Galvanic Gilding. § 1162. By means of galvanism a perfectly adherent coating of gold, of any desired thickness, may be applied to copper, brass, bronze, silver, platinum, iron, steel, etc.; and by using corre- sponding solutions, silver, platinum, cobalt, zinc, etc., can also be deposited on copper and its alloys. The solutions used for galvanic processes are those of cyanide of potassium in which a cyanide of the metal to be deposited has been dissolved; and the same liquid may be used ad infinitum if a clean blade of the metal to be precipitated be kept in the solution and placed in communication with the positive pole of the battery. As the metal in solution is deposited on the articles which communicate with the negative pole, an equivalent quantity of the metal fixed to the positive pole dissolves, while the composition of the liquid remains uniform, if the surface of the metallic blade is nearly equal to that of the ob- jects to be covered. The best solution for gilding is made of 100 parts of distilled water, 10 parts of cyanide of potassium, and 1 part of cyanide of gold. The liquid is placed in a large wooden vat CC' (fig. 602) lined with mastic, and tra- versed by twro gilded metallic rods tt', vv', which dip into the liquid, the rod tt' communicating with the negative pole, and the rod vv' with the positive pole of the battery, while two large sheets of gold or heavily gilded copper oo' dip into the bath and communicate with the rod vv'. Besting on the rods tt' and vv' are movable rods ab, of gilded brass, to which the objects to be gilded are suspended. The battery is formed of plates of zinc and copper, dipping into a weak solution of sulphuric acid; each element being commonly Fig. 602. 334 GOLD composed of a wooden vessel, lined with mastic, in which two con- centric cylinders of copper and zinc, kept apart by wooden pegs, are arranged. The zinc cylinder has been first amalgamated with mercury, in order to protect it from too rapid solution. Water acidulated with sulphuric acid, marking 5° degrees on Baumd’s areometer, being placed in the vessels, the zinc of each element is made to communicate with the copper of the succeeding one by means of a strong wire attached to the upper part of the cylinders, while the free zinc cylinder of one of the two extreme elements is placed in communication with the rod vv' which forms the positive pole, and the copper cylinder of the other extreme ele- ment communicates with the rod tt' which constitutes the negative pole of the battery. The objects to be gilded should be prepared as for gilding by immersion, but the ravivage is unnecessary. The time of immer- sion varies with the thickness of the coat required; and the tem- perature of the bath should be between 59° and 68°. In order to ascertain the quantity of gold deposited, it is sufficient to weigh the object before and after immersion. Although the solution, the composition of which was just ex- plained, is ordinarily used, the same effect can be obtained with different materials; and either the cyanide of potassium may be replaced by the double cyanide of iron and potassium, or the cyanide of gold by its sesquioxide, or by the double chloride of gold and po- tassium, or, lastly, by sulphide of gold. The same process is adopted for the gilding of iron, steel, or tin ; but a small quantity of copper must previously be deposited on the object by dipping it, for a few moments, in a bath composed of 1 part of cyanide of copper and 10 parts of cyanide of potassium dissolved in 100 parts of water. G-alvanic Silvering. § 1163. Galvanic silvering is applied chiefly to objects made of German silver, or other compositions which closely resemble silver- plate. The thickness of the coating of silver may be increased at pleasure. The solution used for silvering is made of 100 parts of distilled water, 10 of cyanide of potassium, and 1 of cyanide of silver; the process being the same as that for gilding, with the exception that the sheets of gold in the bath (fig. 602) are necessarily replaced by sheets of silver. The silvered pieces, which, on leaving the bath are of a dead-white colour, are polished by the burnisher, and then heated to a dull red-heat in a muffle, after being dipped into a solu- tion of borax. When cooled, they are plunged into a weak solution of sulphuric acid, and then dried. By an analogous process, platinum may be deposited on copper or silver; but it adheres with difficulty, and, as yet, it has been found impossible to protect articles covered with platinum from the action GALVANOPLASTICS. 335 of nitric acid. Solutions for the deposition of zinc and lead are prepared by dissolving oxide of zinc or oxide of lead in a solution of cyanide of potassium. GALVANOPLASTICS. % § 1164. By means of a feeble electrical current a uniform and firm coat of copper can be deposited on any given object, and a raised surface thus be reproduced in relief with extreme exactness. The copper plate thus produced can be used as a mould to form, by means of a galvanic current, a second deposit of metallic copper, reproducing faithfujly the original object. These processes are applied to the reproduction of medals and copper plates, the battery used being the same as that employed for gilding, while the liquid for coppering consists of a slightly acidulated saturated solution of sulphate of copper, into which the object on which the metallic copper is to be precipitated is dipped, after being brought into com- munication with the negative pole. The positive pole terminates in a plate of copper of about the same size as the object to be cop- pered, and parallel to it at a short distance. In order to reproduce a medal, the first step is to make its mould in relief, either with plaster, (§ 560,) or with fusible alloy, (§ 316,) or with stearic acid, and afterwrard render it impervious, by immersing it, for a few mo- ments, in a melted mixture of stearic acid and white wax, after which it is lined with plumbago, uniformly spread over it with a brush. The object of this coating is to render the surface of the mould a conductor of electricity; which being done, the mould is dipped into the solution of sulphate of copper, after having secured it by a small copper band around its circumference and fastened it to the negative wire of the battery. The copper which is deposited on the mould can be made of any thickness by keeping it for a sufficient length of time in the bath, and it separates very readily from the mould, which can be used for any number of times. The copper thus precipitated by the galvanic current is in crystalline grains, which are the smaller the more feeble the current is. In order to reproduce the medal, it is not necessary to use a separate battery, as the experiment may be so arranged as to produce the galvanic current in the bath itself. Fig. 603 represents a small apparatus generally used for this purpose. A is a glass vessel, filled with a saturated solution of sulphate of copper, to maintain the saturation of which crystals of sulphate of copper are placed on the stand m. A glass cylinder B, open at both ends, is held up by the support 7, 7', l" in the vessel A; the bottom of the cylinder being made of Fig. 603. 336 GOLD, some porous membranes—a bladder, for instance. A weak solution of sulphuric acid is poured into the vessel B; and two metallic rings a, b, terminating in metallic rods united at their upper part, are dipped, the one b into the solution of sulphate of copper, the other a into a solution of sulphuric acid, and are ,kept separated by the membrane. A plate of amalgamated zinc is placed on the ring a, while the mould, on which the copper is to be precipitated is set on the ring b; and the intensity of the electrical current is gauged by passing the upper leg, ii', of the metallic rods which sup- port the rings a and b, below a movable magnetic ring, the devia- tions of which are in proportion to the activity of the current. ANALYSIS AND ASSAYING OF ALLOYS OF GOLD. § 1165. Alloys of gold and copper may be analyzed by cupelling them with lead, and following exactly the same process as described for the cupellation of alloys of silver and copper. If the alloy con- tains no silver, the weight of the lump obtained represents pretty exactly the quantity of pure gold which existed in the alloy; but if, as more frequently happens, the alloy contains a certain propor- tion of silver, this latter metal remains alloyed with the gold after the cupellation. However, the process of direct cupellation is at- tended with surplusses and losses which sometimes reach 3 thou- sandths: when the temperature of the muffle is very great, there is a small loss arising from the absorption of a small quantity of gold by the cupel; and when the heat is too low, the gold retains a small quantity of copper and lead; although gold loses less by volatilizing than silver. In order to determine exactly the quantity of gold existing in a ternary alloy of gold, silver, and copper, it is cupelled at a mode- rate heat with a certain quantity of silver and lead, in order to obtain an alloy of silver and gold, from which the latter can be perfectly separated by means of an excess of nitric acid, which dissolves the silver and leaves the gold pure. In order, however, to insure exact results, there must be a certain ratio between the quantities of gold and silver; because, if the proportion of silver be too small, the nitric acid does not dissolve it entirely; and if, on the contrary, the quantity of silver be too great, the silver and copper are com- pletely dissolved, while the gold separates in the form of powder, which it is difficult to collect without loss. Experience has shown that the most favourable conditions for the assay, commonly called the parting, (depart,) consist in reducing the alloy to of gold and | of silver, in which case it is completely acted on, while the sepa- rated gold preserves the form of the oi’iginal alloy, and does not become divided, if the operation be carefully conducted. This operation has received the name of quartation. The proportion of lead to be added, which varies with the standard of the alloy, is indicated in the following table:— ASSAYING OF ALLOYS OF GOLD. 337 Standard of gold alloyed Quantity of lead necessary to be added to entirely with copper. remove the copper by cupellation. 1000 thousandths .... 900 u 10 a 800 « 16 a 700 a .... 22 u 600 u 24 u 500 u 26 a 400 1 300 I 200 | [ “ •••• 34 a 100 J . Let us suppose that the standard of a piece of coin is to he determin- ed, the legal standard of which which may be regarded as its approxi- mate standard, is T9o°g05. The quantity of alloy usually operated on being 0.500 gm., containing, according to the legal standard, 0.450 gm. of gold, therefore 1.350 gm. of silver and 5 gm. of lead must be added. But if an alloy is to be assayed the legal standard of which is entirely uuknown, the first step is to ascertain the latter by ap- proximation, by means of the assay by the touch-needle, about to be described, after which the process is continued as usual. The lead is first placed in the heated cupel, and when it is in fusion, the mixture of gold and silver is introduced, having been previously weighed and wrapped in a piece of paper. The cupel- lation is allowed to go on as usual, and requires less care than the cupellation of silver, because silver alloyed with gold is not liable to blister; but the cupel should be removed immediately after the lightning to avoid loss by volatilization. The lump is removed after cooling, flattened under a hammer, annealed for a few moments, and then rolled between cylinders; after which the sheet thus obtained is rolled into a spiral form, and subjected to the action of nitric acid in a small assayer’s flask, (fig. 604,) into which 30 grammes of nitric acid of 22° Baum(3 are poured, and boiled for 20 minutes. The acid is then decanted and replaced by 30 gm. of pure concentrated nitric acid marking 32°, which is boiled for 10 minutes; when the acid is decanted, and the gold, which has preserved the shape of the alloy, washed several times. The flask being afterward completely filled with water, its mouth is closed with the thumb, and it is inverted, when the spiral sheet of gold falls slowly through the liquid column, and is received in a small earthen crucible, after which the water is poured off, and the crucible heated to redness in the muffle. The acid should not be too concentrated, because the gold might be divided. When the assay has been made with the precautions indicated, the gold remains in the form of a spongy, brown, and very friable mass, of nearly the same volume as the original alloy; Fig. 604. 338 GOLD but it contracts considerably when heated in the small crucible, becoming harder and assuming the lustre and colour of malleable gold. The calcined gold being exactly weighed, the standard of the alloy is thus obtained within nearly 1 thousandth. Direct assays made on knowm alloys of gold and silver have shown that the operation, when carefully performed as just de- scribed, can give rise only to the following errors:— True standards of the alloy. Standards found. Differences. 900 900.25 .... +0.25 800 800.50 +0.50 700 700.00 .... 0.00 600 600.00 .... 0.00 500 499.50 -0.50 400 399.50 -0.50 300 299.50 -0.50 200 199.50 -0.50 100 99.50 -0.50 Assaying by the touch-needle. § 1166. The assay just described cannot be applied to fine jewelry, because the article would be destroyed by the process, and gold jewTelry is therefore subjected to a test called the assay by the touch-needle, which does not injure it, and yet enables a skilful assayer to determine its standard within nearly 1 thousandth. The method consists in rubbing the object against a very hard black- stone, on which it leaves marks, from the colour of which, and their behaviour when moistened with a mixture of nitric acid of a density of 1.34 with 2 per cent, of chlorohydric acid, the assayer forms an approximate opinion of the standard of the alloy. The black-stone used, called touch-stone, is a kind of quartz, coloured with bitumen, which formerly was imported from Lydia, but has likewise been found in Bohemia, Saxony, and Silesia. The conditions essential to a good touch-stone are: an intense black colour, incapability of being acted on by acids, hardness, and a sufficient degree of rough- ness to retain some of the gold. The assayer is provided with a series of small blades, called touch- needles, consisting of alloys of copper and gold, the standard of each of which is exactly known, wdiich enable him to compare the marks they leave on the touch-stone, before and after the action of the acid, with that of the alloys to be assayed. No regard should be paid to the first marks left by the articles on the touch-stone, as they are made by the superficial layer, and always show a higher standard, because the surface consists of pure gold; and several marks should therefore be made, the last of which only is examined. Alongside of these marks others are made with that touch-needle the composition of which approaches nearest to PROPERTIES OF PLATINUM. 339 that of the article; when a glass rod, dipped in the acid, is drawn over both, after which the colour of each mark and the manner of action of the acid are examined. PLATINUM. Equivalent = 98.7 (1233.7; 0 = 100). § 1167. Platinum, which was imported into Europe only about the middle of the last century, but was long known in America by the Spanish name of platina, a diminutive name for silver, was for a long time quite useless, because no one could work it. The pla- tinum of commerce is nearly pure, as it commonly contains only a small quantity of iridium, which increases its hardness, but dimi- nishes its malleability. In order to obtain perfectly pure platinum, the metal of commerce is dissolved in aqua regia, the solution fil- tered, and chloride of potassium is added, which yields a copious yellow precipitate of a double chloride of platinum and potassium, very slightly soluble in water, but generally mixed with a small quantity of the corresponding double chloride of iridium and potas- sium. The precipitate is mixed with carbonate of potassa and heated to redness in an earthen crucible, when the chloride of platinum gives off its chlorine to the potassium of the carbonate of potassa, leaving the platinum isolated, while oxygen and carbonic acid are disengaged. The double chloride of iridium is also decomposed, but the iridium remains in the state of oxide. The calcined mass is treated with hot water, which dissolves the alkaline salts, and the residue is acted on by weak aqua regia, which dis- solves the platinum alone and leaves the oxide of iridium. Sal ammoniac is added to the solution of chloride of pla- tinum, when a yellow crystalline precipitate of double chloride of platinum and ammonia PtCla+NH3,IICl is formed, which, on being calcined to redness after wash- ing, leaves a spongy mass of platinum, called platinum sponge. In order to reduce platinum-sponge to the state of mal- leable platinum, it is introduced into a brass cylinder efgh, (fig. 605,) the bottom of which fits into a steel cup abed, while a steel piston ik moves in the cylinder. When the cylinder is half-filled with platinum-sponge, the piston is introduced and struck with a hammer, at first gently, afterward more powerful; by which means a solid disk of platinum, is obtained in a short time, which is heated Fig. 605. 340 PLATINUM. to a white-heat in a muffle, and again hammered on a steel anvil. By repeating these operations, a perfectly malleable plate of plati- num is obtained, which can be rolled into sheets in a small rolling- machine. §1168. Platinum resists the highest temperature of a forge-fire without fusing, but it melts before the oxyliydrogen blowpipe, or between the pieces of charcoal terminating the conductors of a pow- erful battery. Platinum possesses the property of being welded and soldered on itself at a white-heat, the application of which property has just been mentioned in the transformation of sponge platinum into the malleable metal. Platinum is of a grayish-white colour, susceptible of a high polish, and possessing great malleability when pure, while the presence of a very small quantity of foreign matter will profoundly affect this quality. Although the tenacity of pure platinum is hardly inferior to that of iron, the platinum of commerce, which always contains small quantities of iridium, is much less tenacious, for a wire of 2 millimetres in diameter frequently breaks under a weight of 125 kilogs. The density of hammered or rolled platinum is 21.5. Platinum does not oxidize in the air at any temperature, and is acted on by only a limited number of acids. Chlorohydric and concentrated sulphuric acid do not affect it, neither does nitric acid attack it, although it is soluble in this acid when alloyed with a sufficient quantity of silver. Aqua regia is the true solvent of platinum. Platinum is acted on at a red-heat by potassa, soda, and particu- larly by litliia, hut remains unchanged when exposed to the action of the alkaline carbonates. A mixture of nitrate of potassa and potassa acts on it much more readily than pure potassa. Sheet- platinum is acted on, only after a long time, by sulphur, phosphorus, and arsenic, while platinum-sponge combines readily with these substances, producing fusible and very brittle compounds. A mix- ture of silex and carbon attacks platinum; in which manner plati- num crucibles are frequently rendered useless. As the surface of a platinum crucible becomes rough from repeated heating, and the metal very brittle, it should never be heated in contact with char- coal, but rather be placed in earthen crucibles, at the bottom of which a small quantity of quicklime or magnesia is deposited. § 1169. Metallic platinum may also be obtained in the form of a very finely divided precipitate, called platinum-black, and then pos- sesses remarkable properties, on which we shall dwell for a short time. Platinum-black is obtained by reducing platinum in solution by an easily combustible organic substance; to which effect a solu- tion of chloride of platinum PtCla is generally boiled with carbonate of soda and sugar, when chloride of sodium is formed, while the plati- num is precipitated in the metallic state and the oxygen given off by the soda decomposes a portion of the sugar into water and carbonic PLATINUM-BLACK. 341 acid. The flask in which the operation is performed must he fre- quently shaken to prevent the precipitated platinum from adhering to its sides. The precipitate is collected on a filter and dried be- tween tissue-paper. Platinum-black ‘is also prepared by dissolving protochloride of platinum PtCl in a concentrated solution of potassa, boiling the liquid, and then adding a small quantity of alcohol; when a very lively effervescence of carbonic acid ensues, while the platinum is precipitated. Lastly, it is sometimes obtained by decomposing sulphate of platinum by alcohol with the assistance of heat. Finely divided metallic platinum possesses the property of con- densing gases in very large quantities. Thus, platinum-black which is allowed to remain in an atmosphere of oxygen gas will condense several hundred times its volume of the gas and afterward exhibits very intense phenomena of combustion. If, for example, a drop of absolute alcohol be thrown on platinum-black thus charged with oxygen, the whole substance becomes incandescent; and if a cap- sule containing platinum-black be placed under a bell-glass filled with air, the sides of which are moistened with alcohol, the vapours of the alcohol undergo a slow oxidation, which converts them into acetic acid. This property of platinum-black depends, in a great measure, on the method employed in its preparation; as for ex- ample, that obtained by decomposing sulphate of platinum by alco- hol is the most active. The action may be measured in the following manner:—Having passed to the top of a graduated bell-glass filled with mercury, a small quantity of a solution of formic acid, (an organic acid which is readily converted in water and carbonic acid by oxidizing agencies,) a known weight of platinum-black wrapped in tissue-paper is introduced into the bell-glass; when the evolution of carbonic acid immediately begins, but ceases again in a few mo- ments. By ascertaining the volume of gas disengaged, the quantity of oxygen condensed by the platinum-black can be measured. The absorbing property of platinum black is also perceptible, though in a less degree, in platinum sponge, and even in sheet pla- tinum. Thus, it has been shown (§ 74), that on throwing a piece of platinum-sponge into a bell-glass containing a detonating mix- ture of oxygen and hydrogen, an explosion immediately ensues: so again, if a current of hydrogen gas be projected on platinum- sponge exposed to the air, the jet of hydrogen ignites. Sheet-platinum does not present these properties at the ordinary temperature, but exhibits them when heated to about 390°. If a coil of platinum wire (fig. 606) be placed over the wick of an alcohol-lamp, and the lamp lighted so as to heat the wire to redness, the wire remains incan- descent for an indefinite length of time after the flame be- neath has been extinguished, because the vapour of alco- hol, disengaged from the wick, burning when it comes into contact Fig. 606. 342 PLATINUM. with the wire, develops heat enough to keep it incandescent. The experiment proceeds better by adding a small quantity of ether to the alcohol; and the little apparatus is known by the name of Davy's jlameless lamp. In the same way, if a small quantity of ether he placed at the bottom of a wineglass, (fig. 607,) and a coil of platinum wire, which has been previously heated to redness, be fastened to a pasteboard lid which closes partly the mouth of the glass, the wire remains incan- descent for a long time. In these experiments, the vapours of alcohol and ether are only imperfectly burned, yielding, as products of combustion, volatile substances of highly suffocating properties and con- taining an organic acid; all of which shall hereafter be described. Deutoxide of nitrogen, and ammonia, mixed with oxygen gas, are converted, by contact with platinum-sponge, into nitric acid, while the compounds of nitrogen and oxygen, on the contrary, are changed into ammonia, by contact with the sponge in an atmosphere of hy- drogen. In order to succeed in the experiment, it is better to heat the platinum-sponge to a temperature of 300° or 400°, in a glass tube traversed by the gaseous mixture. Platinum-sponge loses its absorbing property after some time, but regains it by being heated for a few moments in nitric acid, and then calcined at a dull red-heat. Platinum-black, which also loses its activity after some time, is restored to its former state by heat- ing it with nitric acid, washing it with water, and drying it by a gentle heat. Fig. 607. § 1170. Platinum does not combine directly with oxygen, except at a red-heat, or when assisted by the caustic alkalies. Two oxides of platinum are known— The protoxide PtO, The binoxide PtO,2 each of which is a feeble base, forming with powerful acids a series of salts which are easily decomposed by heat and leave metallic platinum. Protoxide of platinum PtO is prepared by decomposing the protochloride PtCl by a solution of caustic potassa, when hydrated protoxide remains in the form of a black powder, which dissolves with a brown colour, in a concentrated solution of potassa. When heated, it first gives off' its water, and then oxygen. Hydrated protoxide of platinum dissolves in acids and yields solutions of a deep brown colour, which are not precipitated by sal-ammoniac. Binoxide of platinum Pt03 is obtained by adding to nitrate of platinum one-half of the potassa which would be necessary to COMPOUNDS OF PLATINUM WITH OXYGEN. OXIDES OF PLATINUM. 343 completely decompose the salt, when a voluminous brown precipi- tate is formed, consisting of hydrated binoxide of platinum Pt03 + 2HO. If a larger quantity of alkali were added, the precipitate would contain potassa in combination. But this oxide is more easily prepared by adding to a solution of perchloride P1C13 a large excess of caustic potassa, when at first a yellow precipitate of double chloride of platinum and potassium is formed, but again dissolves if the liquid be heated. The platinum then exists in the solution in the state of platinate of potassa; and the liquid being supersatu- rated by acetic acid, hydrated oxide of platinum is precipitated. The hydrate parts with its water at a moderate heat and turns black, while it loses its oxygen when exposed to higher a temperature. It dissolves in the acids, and yields orange-yellow solutions, while after calcination it is insoluble. The hydrate also dissolves very readily in a concentrated solution of caustic potassa, and the liquid by evapo- ration deposits crystals of platinate of potassa. Insoluble platinate of potassa is also obtained by mixing the double chloride of plati- num and potassium with a concentrated solution of potassa, drying the substance and heating it until the alkali is fused. By treating it with water the alkaline salts are dissolved, and a brown mass of platinate of potassa remains, which, when treated with acetic acid, leaves hydrated binoxide of platinum. By adding ammonia to a solution of sulphate of platinum, a brown precipitate is obtained, which is a double basic salt, and which, on being diluted for some time with a weak solution of caustic soda, yields a substance of detonating properties when heated to about 410°. This fulminating compound, which, however, does not de- tonate by percussion, is regarded as a compound of platinum and ammonia. SALTS FORMED BY THE PROTOXIDE OF PLATINUM. § 1171. These salts present but little interest, and have hitherto been but little studied. They form brown solutions which do not crystallize, and from which potassa does not precipitate them when sufficiently diluted, while the alkaline carbonates yield a brown pre- cipitate, which remains suspended in the liquid. Sulfhydric acid and the sulf hydrates throw down a black precipitate. The protoxalate, which is the only protosalt of platinum which has hitherto been obtained in a crystalline form, is prepared by heating the hydrated binoxide of platinum with a solution of oxalic acid, when the former is reduced to the state of protoxide, which dissolves in the excess of oxalic acid, while carbonic acid is disen- gaged. The liquid, when evaporated, deposits the protoxalate of platinum in small coppery-red needles. SALTS FORMED OF THE BINOXIDE OF PLATINUM. § 1172. The salts of the binoxide of platinum are of an orange- 344 PLATINUM. yellow colour, and caustic potassa throws down from their solutions a brown precipitate of the platinate of potassa, which dissolves in an excess of caustic potassa. Sulfhydric acid and the alkaline sulf- hydrates yield black precipitates which dissolve in a large excess of sulfhydrate. All the salts are decomposed by heat and leave me- tallic platinum; and iron as well as zinc decomposes their solutions by precipitating metallic platinum in the form of a black powder. Chloride of potassium and chlorohydrate of ammonia throw down, from solutions of salts of the binoxide of platinum double chlorides, PtCl2+KCl, PtCl3+NH3HCl, as yellow crystalline precipitates, which are very slightly soluble in water, and nearly insoluble in a mixture of alcohol and water. The double ammoniacal chloride yields, by calcination, platinum-sponge; while the double chloride of platinum and potassium is decomposed by heat into metallic pla- tinum and chloride of potassium; after which the substance, by treatment with water, yields pure platinum. Bichloride of platinum is the solution extensively used in the laboratory, and presents some peculiar reactions which should be here noted. Potassa and ammonia, their carbonates, and, in gene- ral, all the salts of potassa and ammonia, precipitate platinum in the state of double chlorides, while soda and the salts of soda yield no precipitates. Sulphate of Binoxide of Platinum. § 1173. The sulphate of binoxide of platinum is most easily pre- pared by treating the sulphide of platinum obtained by precipitating the chloride with sulfhydrate of ammonia, with fuming nitric acid, and evaporating the solution with a few drops of sulphuric acid to drive off the last particles of nitric acid; when a deep-brown mass remains which dissolves in water with a brown colour. Nitrate of Binoxide of Platinum. § 1174. The nitrate of binoxide of platinum is prepared by care- fully pouring nitrate of silver into a solution of bichloride of pla- tinum until a precipitate no longer forms; when the chlorine is precipitated in the state of chloride of silver, while the solution contains nitrate of platinum, which crystallizes with difficulty. The salt may also be obtained by dissolving the hydrated binoxide in nitric acid. § 1175. Platinum combines directly with sulphur, when the metal in a very finely divided state is heated to redness in vapour of sulphur; but a purer product is obtained by heating in a crucible equal parts of ammoniacal chloride of platinum and sulphur until the chlorohy- drate of ammonia and the sulphur in excess are reduced to vapour. COMPOUND OF PLATINUM WITH SULPHUR. COMPOUNDS OF PLATINUM WITH CHLORINE. 345 The sulphide thus obtained corresponds to the protoxide, and ap- pears as a gray and very brittle mass. The sulphide of platinum corresponding to the binoxide can only be prepared by the humid way, and is obtained by passing a current of sulfhydric acid gas through a solution of the double chloride of platinum and sodium. The bisulphide is a sulphacid which enters into combination with the alkaline sulphides. COMPOUNDS OF PLATINUM WITH CHLORINE. §1176. Two compounds of platinum with chlorine are known, corresponding to the two oxides. The protochloride PtCl is ob- tained by heating dried bichloride of platinum PtCl3 in an oil-bath, gradually raised to 392°, and maintained at this temperature as long as any chlorine is disengaged. The bichloride thus parts with half its chlorine and is converted into a deep-green powder, which is the protochloride of platinum. The protochioride can also be obtained in the form of a greenish-gray precipitate, by passing a current of sulphurous acid gas through a solution of bichloride of platinum which does not contain an excess of acid: sulphuric and chlorohydric acids are formed at the same time. The protochioride is insoluble in water, but dissolves in chlorohydric acid ; and if sal- ammoniac or chloride of potassium be added to this solution, no precipitate is formed, while, by evaporating the liquid, beautiful crystals of double chlorides, of which the formulae are PtCl+KCl and PtCl-(-NH3,HCl, are obtained. The bichlor ide of platinum is prepared by dissolving platinum in aqua regia, evaporating the liquid at a moderate heat to drive off the excess of acid, and then treating with water. The solution of the bichloride, wdiich is of a slightly-brownish yellow colour, be- comes deeper when it contains a small quantity of protochioride of platinum. Bichloride of platinum does hot crystallize, but remains after evaporation in the form of a deliquescent brown mass, readily soluble in alcohol. It combines with a great number of metallic chlorides ; and the double chlorides of platinum with potassium and with ammonia present peculiar interest in chemical analysis, because they are very slightly soluble in water and insoluble in alcohol. These compounds have already been mentioned when speaking of the determination of potassium, (§ 527.) If the double chlorides be dissolved in a large quantity of hot water, and the liquid allowed to evaporate spontaneously, they crystallize in well-defined, regular octahedrons of an orange-yellow colour. It has already been men- tioned that their formulae are PtCl2+KC1 and PtCla-f NH3,HC1. Chloride of sodium forms an analogous double chloride with chloride of platinum, which is, contrary to the corresponding compounds of potassa and ammonia, very soluble in water, and even in alcohol; and the solution of which yields, by evaporation, beautiful yellow crystals of the formula PtCl3-f NaCl + 6IIO. 346 PLATINUM. If one of these double alkaline chlorides is intimately mixed with 2 or 3 times its weight of alkaline chloride, and heated slowly in a crucible, metallic platinum is separated in the shape of brilliant crystalline lamellae, which are easily isolated by dissolving the alka- line chloride in water. § 1177. If a solution of protochloride of platinum, dissolved in an excess of chlorohydric acid, be gradually poured into caustic am- monia, small green needles of the formula PtCl,NH3 are deposited, forming a substance called ammoniacal protochloride of platinum ; the simplest way of preparing which consists in passing a current of sulphurous acid gas through a boiling solution of bichloride of platinum containing an excess of chlorohydric acid, until the liquid no longer gives a precipitate with sal-ammoniac; by which means the bichloride of platinum is reduced into protochloride. Ammonia is then added, and the solution, on cooling, deposits am- moniacal protochloride of platinum, which is remarkable for its great stability; as it is scarcely acted on by the most powerful acids, and its ammonia can be driven off only by heating it for a long time with these acids. Ammoniacal protochloride of platinum is soluble in a hot solu- tion of sulphate or nitrate of ammonia, and deposits small yellow crystals on cooling, which appear to be an isomeric modification of the original product. The combination is decomposed at a tempera- ture of 570°, leaving metallic platinum. § 1178. By digesting ammoniacal protochloride of platinum for some time in a concentrated solution of ammonia, there results a yellowish-white compound, which dissolves in the hot liquid, and is subsequently deposited, on cooling, in large prismatic crystals of the formula PtCl,N2Ha+HQ. By pouring nitrate of silver into a hot solution of this substance, the liquid after evaporation yields a white crystallized salt, of whieh the formula is (Pt0,N2He),N0s; and if sulphate of silver be substituted for the nitrate, the chlorine is still precipitated in the state of chloride of silver, and the evaporated liquid deposits a second crystallized salt, of which the formula is (PtO,N8H8),S03. The compound (PtO,N2H6) is, therefore, a true base, which forms crystallizable salts with the acids, and which may also be obtained in an isolated state by adding a solution of hydrate of baryta to the solution of the sulphate (Pt0,N2H6),S03 until a precipitate no longer forms; when the sulphuric acid is precipitated in the state of sulphate of baryta, while the liquid remaining exerts a powerful alkaline reaction on coloured tests, and when evaporated under the receiver of an air-pump, deposits white crystalline needles of the formula (PtO,N8H6),HO. This base, which we shall call binammonia-oxide of platinum, combines directly with acids, even with carbonic, and is powerful enough to expel ammonia from its saline compounds. SALTS OF PLATINUM. 347 The following compounds have been obtained in a crystallized form: Hydrated base (PtO,NaH6),HG. Sulphate (PtO,NaII8),S03. ■ • Nitrate (Pt0,NaH8),N05. Neutral carbonate (PtO,NaH8),COa+HO. Sesquicarbonate 2(PtG,NaH8),3COa-fHG. Bicarbonate (PtG,NaH8),2CGa+HG. Chloride (PtCl,NaH8). Bromide (PtBr,NaII8). Iodide (PtI,NaHe). § 1179. The base (PtO,NaH6) at 110° loses by heat one equiva- lent of water and one of ammonia, being converted into a new com- pound, insoluble in water, of which the formula is (PtO,NH„). This substance, which we shall call protammonia-oxide of platinum, possesses basic properties in a high degree, as it combines directly with the acids, and yields the following series of products: Anhydrous base (PtO,NH3). Nitrate (PtO,NH3),NG5. Sulphate (Pt0,NH3),S03+H0. Chloride (isomeric with ammonia- cal protochloride of platinum)... (PtCl,NH3). Iodide (PtI,NH3). Cyanide (PtCy,NH3). Salts of the protammonia-oxide of platinum are readily con- verted into those of the binammonia-oxide of platinum, by dis- solving them in an excess of caustic ammonia, when they take up 1 equiv. of ammonia and reproduce the salts of the binammonia- oxide of platinum. Reciprocally, salts of the binammonia-oxide of platinum are easily converted by heat in those of the protammo- nia-oxide of platinum by losing 1 equiv. of ammonia. § 1180. The two series of salts just described are not the only ones which have been obtained by means of the ammoniacal proto- chloride of platinum. If the chloride (PtCl,NaH6) of the binammo- nia platinic series be boiled with weak nitric acid, reddish vapours are disengaged, and, on cooling, a substance is deposited of the formula (PtCl,NaH8)0,N05, which may be regarded as the nitrate of a third base represented by the formula (PtCl,NaH8)0. If ammoniacal protochloride of platinum be boiled with a large excess of nitric acid a liquid is obtained which deposits successively, by evaporation, two crystallizable compounds, the formula of the first of which is (PtClG5,N4Hla),2N05, which forms small brilliant needles, very slightly soluble in water, and deflagrating when 348 PLATINUM. heated. This compound contains a fourth base, of which the very complex formula is (PtC10s,N4H13). This base has been obtained in combination with carbonic, oxalic, phosphoric, and chromic acids, forming salts which crystallize readily, because they are very slightly soluble in water. The formula of the second compound, which remains in the mother liquid, is (PtCl304,N4H13),2N05, and it may be considered as the ni- trate of fifth base (PtCl304,N4lI13). COMPOUND OF PLATINUM WITH CYANOGEN. § 1181. By heating an intimate mixture of finely divided platinum and ferrocyanide of potassium to a dull red-heat in an earthen cru- cible, and then treating the mass, when cooled, with water, a solution is obtained, which first deposits crystals of undecomposed ferrocy- anide of potassium, but which yields, after additional evaporation, a double cyanide of platinum and potassium. This substance, after being purified by a second crystallization, appears in the form of beautiful crystals of the formula KCy+PtCy-f 3110. Its solutions precipitate a great number of metallic salts, in which precipitates the potassium of the preceding compound is replaced by 1 equiv. of the metal, of which the salt effects the precipitation. DETERMINATION OF PLATINUM, AND ITS SEPARATION FROM THE METALS PREVIOUSLY DESCRIBED. § 1182. Platinum is determined in the metallic state, or in that of dried double ammoniacal chloride. When platinum exists in a liquid in the state of bichloride, the liquid is concentrated by eva- poration, and twice its volume of alcohol is added, after which chlo- rohydrate of ammonia is poured into the solution, to completely precipitate the platinum in the state of double chloride of platinum and ammonia. The precipitate is washed Avith alcohol, and dried under the receiver of an air-pump; and the weight of the platinum is subtracted from that of the double chloride, which contains 44.23 per cent, of metallic platinum. The double ammoniacal chloride may also be calcined in a covered crucible, when sal-ammoniac is disengaged, while metallic platinum remains, which is weighed. But the decomposition by heat requires great care, because it is difficult from preventing some particles of platinum from being carried off by the vapours which are disengaged. Platinum may also be precipitated in the state of double chloride of platinum and potassium, by using the same precautions as in the precipitation by sal-ammoniac; and by decomposing the double potassic chloride by heat, there is less fear of the platinum being carried oft' by the gases; but as the platinum remains mixed with chloride of potas- sium, the residue must be washed several times to dissolve the alka- line chloride. § 1183. In order to separate platinum from the metals previously EXTRACTION OF PLATINUM. 349 described, either the insolubility of metallic platinum in all acids except aqua regia and acid mixtures which can evolve chlorine, or the precipitation of platinum by sulfhydric acid, even in acid liquids, or, lastly, its complete precipitation by chloride of potassium or chlo- rohydrate of ammonia, is relied on. It is, however, important to observe that platinum, when alloyed with a considerable quantity of metal soluble in nitric acid, is itself dissolved in the acid; so that only isolated platinum can be considered as insoluble in nitric acid. EXTRACTION OF PLATINUM. § 1184. Platinum occurs in the native state in alluvial sands, re- sembling those in which gold is found, generally in open valleys or amid serpentine rocks. The principal localities of platinum are in Colombia, Brazil, and the Ural Mountains in Siberia. It generally occurs in small grains, although pieces weighing 10 kilogs. have been met with. The platiniferous sands, by washing, ultimately yield a sand rich in platinum, but of a very complicated composi- tion ; as it contains, in addition to the platinum, the metals which constantly accompany it, namely, osmium, iridium, palladium, rho- dium, and ruthenium ; and, moreover, gold, silver, iron, and copper; and lastly, many heavy minerals, such as magnetic oxide of iron, titanic iron, chromate of iron, pyrites, etc. When the platiniferous sand contains any considerable quantity of gold, this metal is first extracted by amalgamation ; when the ore, after being purified as much as possible by mechanical means, is acted on, in glass balloons heated in a sand-bath, by aqua regia con- taining an excess of chlorohydric acid, a small quantity of water being added, so that as little iridium as possible, which would render the platinum brittle, may be dissolved. The aqua regia is renewed several times until the platinum is completely dissolved; and the operation must be effected in a chimney which draws well, in order to carry off the vapours which are disengaged, and which are ren- dered injurious by the presence of osmic acid. The solution of pla- tinum is decanted, after having been allowed to become clear by rest, and a concentrated solution of sal-ammoniac is added, which precipitates the platinum almost entirely in the state of double chlo- ride of platinum and ammonia. As the mother liquid still contains some platinum and some quantity of foreign metals, the latter are precipitated by blades of iron and zinc, while a black deposit is ob- tained, from which a certain quantity of platinum may be extracted. For this purpose, the deposit is first treated with chlorohydric acid, which dissolves the foreign metals, and the residue is then acted on by very weak aqua regia, which readily dissolves the divided plati- num, without sensibly affecting the iridium; when sal-ammoniac is added, which precipitates the double chloride of platinum and am- monia. 350 The double chloride of platinum and ammonia is calcined at a dull red-heat, and the platinum-sponge which is thus obtained is pulverized by hand, and then diluted with wrater so as to form a homogeneous mud, which is passed over a sieve, the grosser particles remaining on, which are again pulverized. The workman must ob- serve the greatest cleanliness in the various operations, as the pre- sence of dust, or even a single hair in the mud, will give rise to serious defects in the forged platinum. The powdered platinum is, therefore, generally washed several times, in order to remove all the dust. The platinum paste is introduced into an apparatus resembling that of fig. 605, only larger, care being taken that no bubbles of air are inclosed. The substance is first compressed with a wooden pestle, then with a metallic piston; when the water separates from the platinum, while the latter becomes more solid; and the process is terminated by compressing it with great force. The platinum disc is then heated to whiteness in an earthen crucible, placed on an anvil and struck with a heavy hammer, after which it is again heated to whiteness before being forged. OSMIUM. OSMIUM. Equivalent = 99.6 (1245.9; 0=100) § 1185. Osmium, prepared by calcining the double chloride of osmium and ammonia, is of a metallic-gray colour, resembling pla- tinum, while, when it has been reduced by the humid way, it often shows a bluish fringe. The metal is sufficiently malleable to allow of its being rolled into plates or sheets, although it is reduced to powder by percussion. Osmium neither fuses nor volatilizes in a forge-fire, and its density is about 10. The metal combines readily with oxygen; and when it has been reduced by the humid way, it rapidly absorbs the oxygen of the air, especially when assisted by water, and is converted into osmic acid; and when heated in oxygen at a low temperature, it ignites and is converted into osmic acid, which sublimes. Concentrated nitric acid acts readily on it and disengages copious reddish vapours, producing soluble osmic acid, which product is also obtained by the action of aqua regia on the metal. The caustic alkalies and alkaline nitrates attack it at a red- heat, the osmic acid combining with the alkalies. Powdered osmium, heated on a blade of platinum, in the flame of an alcohol-lamp, dis- engages vapours of osmic acid, the characteristic penetrating odour of which evinces the presence of very small quantities of osmium. COMPOUNDS OF OSMIUM. 351 § 1186. Osmium forms a large number of compounds with oxygen, five of which are known, and are The protoxide OsO. “ sesquioxide 0s203. “ binoxide 0s02. “ osmious acid 0s03. “ osmic acid 0s04. The two acid compounds are the most important, and the best un- derstood. Protoxide of osmium OsO is prepared by pouring potassa into a solution of the double protochloride of osmium and potassium, when a deep-green precipitate is formed, lvhich dissolves with a green colour in acids, and which is easily reduced to the metallic state by deoxidizing agencies. Sesquioxide of osmium 0s203 is obtained by maintaining, for some time, at a temperature of 122°, a mixture of osmic acid and ammonia, when a precipitate is formed which is a compound of the sesquioxide of osmium $,nd ammonia, and which dissolves in acids, producing yellow solutions which do not crystallize. If chlorine be passed over a mixture of divided osmium and chloride of potassium, gently heated in a glass tube, a double chlo- ride is obtained, of which the formula is OsCl +KC1, and which when treated while hot by a solution of carbonate of potassa, yields a black precipitate of binoxide of osmium 0s02. Osmic acid 0s04 is formed in many ways :—1. By the roasting of osmium in the air, or better still, in an atmosphere of oxygen ; 2. By acting on osmium by nitric acid; 3. By heating to redness metallic osmium with nitrate of potassa, and decomposing the os- miate of potassa by an acid. Osmic acid is a white substance, which crystallizes in brilliant prisms, and exhales a very penetrating odour resembling that of chloride of sulphur; and as its vapour excites coughing and irri- tates the eyes and skin, the substance should be avoided with great care. Osmic acid liquifies at a temperature below 212°, and boils below a red-heat. It is very soluble in water, although the sub- limed acid requires a long time for solution; and it also dissolves largely in alcohol and in ether, but after some time is reduced by these liquids, especially under the influence of polar light. It is readily decomposed by deoxidizing agencies, and by the majority of organic substances: it stains the skin and linen black. Iron, zinc, tin, copper, &c. precipitate metallic osmium from its solutions. Osmic acid is a weak acid, which does not directly redden the tincture of litmus, and does not decompose the carbonates, but which combines with the alkalies, although the resulting compounds COMPOUNDS OF OSMIUM AVITH OXYGEN. 352 OSMIUM. are not very fixed, as solutions of the alkaline osmiates disengage, when boiled, vapours of osmic acid. Osmious acid 0s03 only exists in combination with alkaline bases, and by endeavouring to isolate it, it is decomposed into osmic acid and binoxide of osmium. Osmite of potassa is obtained by pouring a few drops of alcohol into a solution of osmiate of potassa, when the salt is deposited as a rose-coloured crystalline powder, in which case the osmic acid im- parts a portion of its oxygen to the alcohol. Large crystals of os- mite of potassa are obtained by allowing a solution which contains, at the same time, osmiate and nitrite of potassa to rest; when the osmic is slowly decomposed by the nitrous acid, causing beautiful crystals of osmite of potassa to be deposited. Osmite of soda, which is prepared in the same way, and yields rose-coloured solutions, crystallizes with much difliculty, because it is more soluble. No osmite of ammonia is known, and ammonia immediately re- duces the solutions of osmite of potassa and osmite of soda. We shall not treat of the salts formed by the oxides of osmium with acids, as they are, as yet, but little understood. COMPOUNDS OF OSMIUM WITH CHLORINE. § 1187. If osmium be heated in a current of chlorine, two chlo- rides are produced: a bichloride 0sCl2 and a protochloride OsCl, the latter, which is the more volatile, condensing in the most re- mote portions of the tube. It is an orange-coloured, very fusible and deliquescent substance, while the protochloride is of a beautiful green, and its solution in water soon decomposes, chlorohydric and osmic acids being formed, while metallic osmium is precipitated. § 1188. Osmium always accompanies platinum-ore, but exists in it chiefly in combination with iridium, forming compounds of very variable proportions, called iridosmiums. Iridosmium is found in small, gray, very dense spangles, sometimes presenting the form of lamellae with six facets of the rhomboliedric system. Being acted on with difficulty by aqua regia, it remains in the residue after the treatment of platinum-ores. Osmium and iridium are prepared by heating in an earthen crucible, for an hour, at a strong red-heat, 100 parts of pulverized iridosmium and 300 parts of nitre, when osmiate and iridiate of potassa are formed. The fused material being run on a cold metallic plate, is then broken to pieces, and intro- duced into a tubulated retort, with a large excess of nitric acid, a well-cooled receiver being fitted to the retort as soon as heat is ap- plied. A great proportion of the osmic acid volatilizes, and con- denses on the sides of the receiver, in the form of beautiful white crystals, which are subsequently dissolved in a concentrated solu- EXTRACTION OF OSMIUM. IRIDIUM. 353 tion of potassa, from which all the osmium is afterward precipitated by alcohol, in the state of osmite of potassa, which salt is used in preparing metallic osmium and all its products. When the substances heated in the retort no longer disengage osmic acid, water is added, and the insoluble residue being collected on a filter, then contains a certain quantity of oxide of osmium and a large quantity of oxide of iridium. It is boiled with aqua regia, which dissolves the osmium and iridium in the state of chlorides, after which sal-ammoniac is poured into the solution, when the double chloride of osmium and ammonia is precipitated, together with the corresponding compound of iridium and ammonia IrCl2+NH3HC1. The double chlorides are suspended in water and subjected to the action of a current of sulphurous acid, when the double chloride of iridium IrCl3+NH8HCl is transformed into the double chloride IrCl-f NHSHC1 which dissolves, while the double chloride of osmiitm remains unchanged and is precipitated. The latter yields metallic osmium by calcination, while the solution which contains the double chloride of iridium and ammonia deposits, by evaporation, beautiful brown crystals, which yield iridium when calcined. IRIDIUM. Equivalent == 99.0 (1287.5; 0 = 100). § 1189. Iridium prepared by the calcination of the double ammo- niacal chloride (§ 1188) presents the appearance of a gray spongy mass, resembling platinum. Iridium is difficult to solder, and hitherto has not been obtained in a malleable state; while it is still more difficult of fusion than platinum. The metal is obtained in a compact mass, very hard, and capable of a fine polish by mois- tening powdered iridium with water, compressing it, at first slightly between tissue-paper, and then powerfully by means of a press, and calcining it at a strong white-heat in a forge-fire. The metal thus obtained is very porous, and its specific gravity does not exceed 16.0, while the density of compact iridium is probably equal to that of platinum; as a native alloy of iridium and platinum is found, con- taining 20 per cent, of platinum, and crystallized in regular octohe- drons, the density of which is 22.3. Nitric acid and even aqua regia do not attack iridium when isolated, although aqua regia dis- solves it when alloyed with platinum or other metals. Heated to redness with potassa or nitre, iridium oxidizes, and iridiate of potassa is formed. It is attacked by chlorine at a red-heat and in the presence of chloride of potassium, a double chloride of iridium and potassium being formed. 354 IRIDIUM. COMPOUNDS OF IRIDIUM WITH OXYGEN. § 1190. Four compounds of iridium with oxygen are known : The protoxide Ir20. “ sesquioxide Ir203. u binoxide Ir02. “ trinoxide ; Ir03. The protoxide of iridium is obtained by precipitating by an alka- line carbonate the double protochloride of iridium and potassium, when a greenish-gray precipitate is formed which dissolves in acids, yielding green solutions. The oxide is undecomposable by heat, but is easily reduced by hydrogen at a red-heat. Sesquioxide of iridium is formed when iridium is attacked by the alkalies or alkaline metals, and appears as a black powder, inso- luble in acids, but combining with the alkalies, producing brown solutions. Heat restores this oxide to the state of protoxide. If the sesquioxide be dissolved in a solution of potassa, and the liquid be afterward saturated by an acid, a precipitate is thrown down, which turns blue by absorbing the oxygen of the air, and at last assumes an indigo colour, when it has passed into the state of hydrated binoxide of iridium IrOa+2HO. The binoxide may also be obtained by pouring potassa into a solution of sesquichloride of iridium, when no precipitate is formed at first, while the liquid, on being exposed to the air, deposits ultimately a deep-blue precipitate. Lastly, when the trichloride of iridium IrCl3 is precipitated by an alkali, there results a greenish-yellow precipitate of trinoxide of iridium Ir03, which, however, is always combined with a certain quantity of alkali. If an oxide of iridium be digested with a solution of formic acid until carbonic acid is no longer disengaged, a very finely divided black powder of iridium is obtained, which exerts a powerful absorb- ent action on gases, and causes the ignition of an explosive mixture of hydrogen and oxygen. COMPOUNDS OF IRIDIUM WITH CHLORINE. § 1191. Four chlorides of iridium, corresponding to the four oxides, are known. Protochloride of iridium, which is obtained by heating to a dull- red very finely divided iridium in a current of chlorine, combines with the alkaline chlorides and with chlorohydrate of ammonia, yielding products which readily crystallize. Iridium is acted on more powerfully by chlorine when previously mixed with chloride of potassium. Sesquichloride of iridium Ir2Cl3 is prepared by dissolving the sesquioxide in chlorohydric acid, and appears as a hard, uncry stal- lizable, and deliquescent substance, which forms soluble double COMPOUNDS OF IRIDIUM. 355 chlorides with the alkaline chlorides and with chlorohydrate of ammonia. When solutions of these double chlorides are boiled, they deposit very slightly soluble double chlorides, which contain bichloride of iridium IrCl2, while corresponding double compounds, containing protochloride of iridium IrCl, remain in the liquid. Sul- phurous acid converts them into double chlorides containing the protochloride. Bichloride of iridium is formed when finely divided iridium or its oxides are dissolved in aqua regia and heated to the boiling point, when solutions of a reddish-yellow colour are obtained. If chloride of potassium be poured into the liquid, a double chloride is obtained, the solution of which is red and deposits octohedric crys- tals, which are of such an intense red colour as to he nearly black, and the formula of which is IrCl2+KCl + H0. The ammoniacal bichloride of iridium is very slightly soluble in cold water, but forms with boiling water a solution which on cooling deposits octo- hedral crystals of a deep-red colour. The colouring power of this compound is very great, as 1 part will sensibly colour 40,000 parts of water; and it is a small quantity of this double chloride which often gives a red hue to the double chloride of platinum and am- monia. Sulphurous acid converts these double compounds into soluble double chlorides, containing protochloride of iridium IrCl, and which are much more soluble, (§ 1188.) Lastly, if an oxide or chloride of iridium be treated with concen- trated aqua regia not exceeding the temperature of 110° or 120°, a deep-brown solution is obtained, which contains trichloride of iri- dium IrCl3. This chloride does not crystallize, but also forms double chlorides with the alkaline chlorides. The solutions of iridium and its different oxides are variously co- loured, from which property the name of iridium has been derived. § 1192. Iridium combines directly with sulphur when the finely divided metal is heated in a current of vapour of sulphur, but it is difficult to thus obtain a perfect sulphuration of the metal. If sulf- hydric acid gas be passed through solutions of the various chlorides of iridium, brown precipitates are obtained which are sulphides cor- responding to the chlorides. The most sulphuretted compounds act the part of sulphacids with regard to the alkaline sulphides. The affinity of iridium for sulphur is sometimes applied to the prepara- tion of the metal, iridosmium being fused with a mixture of carbon- ate of soda and sulphur, when the material is acted on, and sulph- ides of iridium and osmium are formed, which are separated by means of water. The sulphides are easily attacked by chlorine, and yield chlorides which are isolated by the processes detailed in § 1188. COMPOUNDS OF IRIDIUM WITH SULPHUR. 356 PALLADIUM. PALLADIUM. Equivalent = 53.3 (665.2; 0 = 100). § 1198. Palladium is a brilliant metal, of the specific gravity 11.8, and of a white colour intermediate between silver and plati- num, and which begins to fuse at the highest temperature of a forge-fire, and melts readily before the fftwne of the oxyhydrogen blowpipe. It can be soldered and forged at a white-heat, and it is malleable and readily worked into thin sheets and wire. Palladium does not combine directly with oxygen, but it oxidizes when fused with potassa, or better still, with nitrate of potassa. Sulphuric acid does not act upon it, while nitric acid easily dis- solves it when assisted by heat, and aqua regia dissolves it rapidly. It combines directly with chlorine, sulphur, and silver. Palladium has within the last few years been brought into com- merce, being obtained as an accessory product in the treatment of certain gold-ores and the gold-dust of Brazil, (§ 1154,) which con- sist chiefly of an alloy of gold and palladium. Palladium alloyed with A of silver is used by dentists, and it has been proposed to use it for the construction of the graduated scales of astronomical instru- ments, because, while it is nearly as white as silver, it is not black- ened by sulf hydric acid; and the divisions on one of the largest instruments in the Paris observatory are drawn on palladium. COMPOUNDS OF PALLADIUM WITH OXYGEN. § 1194. Two combinations of palladium with oxygen are known : a protoxide PdO, and a binoxide Pd02. Anhydrous protoxide of palladium is obtained by decomposing nitrate of palladium by gentle heat, when a deep-gray, metallic powder remains, which loses all its oxygen at a higher temperature. By pouring an alkaline carbonate into a solution of protonitrate of palladium, a deep-brown precipitate of hydrated protoxide results, which readily dissolves in dilute acids. Binoxide of palladium has not yet been obtained in an isolated form, and when caustic potassa or carbonate of potassa is added to a solution of bichloride of palladium, the brown precipitate which forms always contains alkali. Binoxide of palladium readily parts with half its oxygen at a slightly elevated temperature, and is com- pletely reduced at a higher degree of heat. SALTS FORMED BY THE PROTOXIDE OF PALLADIUM. § 1195. The protosalts of palladium yield solutions of a reddish- brown colour, from which potassa throws down a brown precipitate HALOID COMPOUNDS OF PALLADIUM. 357 which, dissolves in an excess of alkali, while sulf hydric acid and the alkaline sulphides give black precipitates which do not dissolve in an excess of sulf hydrate. Cyanide of mercury yields a white, slightly grayish precipitate of cyanide of palladium; and iron or zinc precipitate palladium in the form of a black powder, which assumes a metallic lustre when burnished. Nitrate of palladium is obtained by dissolving palladium in nitric acid, but the evaporated liquid does not deposit crystals, although, if ammonia be added, a crystallizable double nitrate is formed. COMPOUNDS OF PALLADIUM WITH CHLORINE. § 1196. Two chlorides of palladium, corresponding to the two oxides, are known. Protochloride of palladium PdCl is obtained by dissolving palladium in aqua regia, when a red solution is formed, yielding on evaporation deep-red crystals, which by the action of heat are decomposed and converted into metal. Proto- chloride of palladium forms double chlorides with the alkaline chlo- rides and chlorohydrate of ammonia. The double chlorides of potassium and ammonia are very slightly soluble in water and inso- luble in alcohol; their formulae are PdCl+KCl, PdCl-fNH?,HCl, and they form beautiful crystals; while the double chloride of sodium, on the contrary, is deliquescent and very soluble in water. The colour of these double chlorides in small crystals is of a slightly reddish-yellow. Protochloride of palladium is converted by the action of aqua regia and moderate heat into the bichloride PdCl3, which after eva- poration under an air-pump assumes the form of a brown crystal- line mass. Bichloride of palladium, which is not very fixed, and the solutions of which are readily decomposed by heat, forms with chloride of potassium a double chloride of the formula PdCl2+KCl, which, being very slightly soluble, is precipitated in red crystalline powder, consisting of small regular octohedrons.* COMPOUND OF PALLADIUM WITH CYANOGEN. § 1197. Palladium has a great affinity for cyanogen, and a cyanide of palladium is obtained in the form of a slightly-grayish white precipitate, by adding a soluble cyanide to the solution of a protosalt or of protochloride of palladium, the precipitation, how- * The combination of palladium with iodine deserves some notice, as it is of importance in analytical chemistry, being obtained in the determination of iodine. The iodine contained in any soluble iodide may be very exactly determined by precipitating it by means of nitrate or chloride of palladium, when a black fleecy deposit of iodide of palladium is formed, which does not completely settle down until after 24 hours, and which is insoluble in water, alcohol, and ether. It begins to lose its iodine at a temperature of 212°, and is entirely freed from it when heated to about 580°, when pure palladium remains, from the weight of which the weight of the iodine with which it was combined may be deduced.— W. L. F. 358 RHODIUM ever, being complete only when the liquid does not contain an excess of acid. Cyanide of palladium combines with the alkaline cyanides and with cyanohydrate of ammonia. A hot and saturated solution of the double cyanide of palladium and potassium deposits, on cooling, small crystalline spangles of the formula PdCy + KCy + HO; while the same solution by sIoav eva- poration at the ordinary temperature yields larger crystals of the formula PdCy+KCy + 3IIO. EXTRACTION OF PALLADIUM. § 1198. Palladium exists in small quantities in platinum-ore, and remains in the mother liquid which is obtained when a solution of platinum-ore in aqua regia is precipitated. It has already been mentioned (§ 1184) that the metals which remain in this mother liquid are generally precipitated by a blade of iron; they are then redissolved in aqua regia, and the excess of acid being driven olf by evaporation, the residue is treated with water and poured into a solution of cyanide of mercury, which produces a solution of cyanide of palladium, which by the application of heat leaves metallic palla- dium. The greater proportion of palladium is obtained from the Brazil gold-dust, which is dissolved in aqua regia saturated with potassa, and then treated with a solution of cyanide of mercury, which precipitates the palladium alone. Palladium-sponge is con- verted into malleable metal by the same process as that described for platinum. RHODIUM. Equivalent = 52.2 (652.5; 0 = 100). § 1199. Rhodium exists in small quantities in the majority of platinum-ores, and has also been found in America combined with gold. It is extracted from the metallic precipitate which is obtained by decomposing by a blade of iron the mother liquid which remains after the precipitation of the solutions of platinum-ore in aqua regia by sal-ammoniac. These metals being dissolved in aqua regia, the palladium is precipitated by cyanide of mercury, and the liquid is evaporated to dryness, after having added common salt and an excess of clilorohydric acid ; when the excess of cyanide of mercury is converted into chloride of mercury, while double chlorides are formed with the chloride of sodium. The substance, when dried, is treated with alcohol, which dissolves the double chloride of platinum and sodium as well as that of iridium and sodium; the double chlo- ride of rhodium and sodium, which is insoluble in alcohol, alone COMPOUNDS OF RHODIUM. 359 remaining. This compound, after being purified by crystallization, is heated in a glass tube in a current of hydrogen, when metallic rhodium remains on dissolving the substance in water. Rhodium has been thus called on account of the rose colour of its solutions. It is a gray metal of the specific gravity 10.6, resembling platinum, but more difficult to solder and fuse than this latter metal. Rhodium does not oxidize in the air at the ordinary temperature, hut when very finely divided readily combines with oxygen at a red-heat. The most powerful oxidizing acids, even aqua regia, do not act on the metal when pure, but it readily dissolves in aqua regia when alloyed with platinum or other metals. Potassa and nitre act on it at a red-heat, and convert it into the sesquioxide; and bisulphate of potassa also attacks it at a red-heat, forming a double sulphate of potassa and sesquioxide of rhodium. § 1200. The existence of two oxides of rhodium, the protoxide RhO and the sesquioxide Rh203, is admitted. The protoxide RhO is formed when very finely divided rhodium is roasted in the air at a high temperature; while if the temperature he lower, oxides intermediate between the protoxide and sesquioxide are obtained. The sesquioxide Rh303 is produced when powdered rhodium is attacked by a mixture of nitre and potassa, when, after treating the substance with water and washing the residue with a weak acid, the sesquioxide remains in the form of a black powder. This is the most important oxide of rhodium, as it combines with the acids and forms salts of which the solutions are red when concentrated, and rose-coloured when more diluted. Potassa precipitates the hydrated sesquioxide from its solutions on boiling the liquid, while ammonia throws down, when cold, a yellow precipitate, which is not deposited for some time, and which is a compound of the sesquioxide with am- monia. Sulfhydric acid and sulf hydrate of ammonia give brown precipitates. Hydrogen reduces solutions of rhodium when aided by solar light, and precipitates from them metallic rhodium; and iron, zinc, and copper precipitate the metal in the form of a black powder. COMPOUNDS OF RHODIUM WITH OXYGEN. COMPOUNDS OF RHODIUM WITH CHLORINE. § 1201. Two chlorides of rhodium corresponding to the two oxides are known, and are prepared by treating the mixture of oxides obtained by roasting rhodium in the air with chlorohydric acid, when two chlorides are formed: the protochloride RhCl, which remains in the form of an insoluble reddish powder, and the sesquichloride RhsCla, which dissolves. The sesquichloride pro- duces brown solutions, and does not crystallize, but forms with 360 RUTHENIUM. the alkaline chlorides crystallizable double chlorides, of a beautiful red colour, the best method of preparing which consists in heating, in a current of chlorine, a mixture of finely divided rhodium and alkaline chloride. The double chloride of rhodium and sodium crystallizes in beau- tiful red crystals, of which the formula is Rh3Cl3 + 3NaCl +18110. COMPOUND OF RHODIUM WITH SULPHUR. § 1202. Rhodium combines directly with sulphur at a red-heat, forming a sulphide which is fusible in a forge-fire. When sulf- hydrate of ammonia is poured into a solution of the double chloride of rhodium and sodium, a brown precipitate of the sulphide Iih3S3 is obtained. RUTHENIUM. Equivalent = 52.2(652.5; 0 = 100). § 1203. A new metal, to which the name of ruthenium has been given, has been recently found in the platiniferous sands, occurring principally in iridosmium, which sometimes contains 5 or 6 per cent, of it. In its chemical properties, ruthenium closely resembles iridium, with which it was for a long time confounded. Ruthenium is extracted from iridosmium by heating to redness in a porcelain tube, traversed by a current of moist chlorine, a mixture of finely powdered iridosmium with one-half its weight of common salt. The mass, when cooled, is dissolved in water, producing a brownish-red solution, into which a few drops of ammonia are poured after hav- ing heated it to about 120°, when a brownish-red precipitate of sesquioxide of ruthenium, mixed with oxide of osmium, is formed. The precipitate is heated in a retort with nitric acid, to convert the oxide of osmium into osmic acid, which is driven off by boiling for a short time. The residue is calcined for one hour in a silver crucible, with a mixture of potassa and nitre, when the material is treated with water deprived of air by boiling, and allowed to rest for 12 hours in a bottle closely corked and wholly filled. The liquid, which is of an orange-yellow colour, is then decanted and saturated with nitric acid, when the sesquioxide of ruthenium is precipitated in a black velvetlike powder, which, by calcination in a current of hydrogen gas, yields metallic ruthenium. Ruthenium is a gray metal, of the specific gravity of 8.6, resem- bling iridium ; and it is infusible, does not consolidate at a red-heat, and is acted on with great difficulty by aqua regia. Several oxides and corresponding chlorides of ruthenium have been obtained. FOURTH PART. ORGANIC CHEMISTRY. INTRODUCTION. § 1204. In this fourth part it is intended to give a description of the substances found in organized beings, as well as the combina- tions derived from them by various chemical processes performed in the laboratory. The majority of organic compounds may be com- pared with those comprised under the head of inorganic chemistry, and, like the latter, may be crystallized by fusion, sublimation, or solution; and can combine either with acids, or with bases, or may he decomposed into acid and into basic elements, their compounds being subject to the laws of definite proportions in the same man- ner as substances belonging to mineral chemistry. In a word, they possess no peculiar character which authorizes, in a methodic classi- fication, their separation from compounds of mineral chemistry, from which they are distinguished by their origin alone; the sepa- ration being only admitted because it facilitates the study of organic compounds, which are generally of a complex character, and the properties of which are more readily understood after the student has become familiarized with the most frequent and simple reac- tions of mineral chemistry. There exists, however, in organized beings, a certain number of substances, the essential physical properties of which differ greatly from those just mentioned, and which constitute the organs of vege- tables and animals. They are distinguished by their insolubility in solvents, and by the peculiar forms they assume under the influence of vitality. They undergo, in organized beings, a host of trans- formations, frequently without experiencing any remarkable change in their elementary composition, and thus become fitted for the va- rious parts which they are destined to constitute in organic life. They can in no manner be made to assume a crystalline form; and whenever they are crystallized or included in compounds subjected to the ordinary laws of definite proportions and capable of crystal- lization, it will be found that they have been completely changed, and that the new differ very materially from the original substances, although their elementary composition is frequently identical. 361 362 ORGANIC CHEMISTRY. We shall call these compounds organized substances, or organized matter, to distinguish them from other substances found in living beings, and often confounded with them under the general name of organic substances or matter, which should only be considered as indicating their common origin. The latter name, however, should he applied only to substances of the organic kingdom which are not also found in the mineral kingdom. § 1205. Some organic substances contain only carbon and hy- drogen ; and, while the majority of substances found in vegetables contain carbon, hydrogen, and oxygen, those forming the organs of animals consist of carbon, hydrogen, oxygen, and nitrogen. Similar quaternary compounds are found in almost all parts of vegetables, principally in the cereals, which, thence derive their property of nourishing animal life. Some organized beings also contain a greater number of simple bodies: thus, some contain sulphur, others phosphorus. Animals provided with a stony case, or shells, contain a large proportion of carbonate of lime, forming nearly the whole of their external envelop; while the bones of vertebrated animals contain a large quantity of phosphate and a small proportion of carbonate of lime. Lastly, in all animals and vegetables, salts are found, formed by the mineral bases, combined either with mineral or organic acids, and which, in many cases, ap- pear essential to the existence and development of the organized being. The principal mineral bases found in organized beings are potassa, soda, lime, magnesia, alumina, oxides of iron and manga- nese ; while the mineral acids are carbonic, phosphoric, sulphuric, nitric, and silicic acid. In addition to the salts formed by these substances, the chlorides of potassium, sodium, calcium, and magne- sium, and more rarely their bromides and iodides, also occur. These mineral substances, with the exception of nitric acid, are found in the ashes of organized beings after their combustion. Carbon and its compounds with, oxygen may be ranked among organic substances, as they are, in most cases, extracted from them; and with still greater reason may ammonia be included among them, as it is always prepared from organic matter. We shall not, howT- ever, recur to those substances which have been considered in the preceding parts of this work. § 1206. The various organic compounds may be divided into— 1. Compounds which cannot be separated into several kinds of substances without evidently changing their constitution and nature, which we shall call simple proximate principles ; 2. Compounds formed of one or two proximate principles, united in definite proportions ; 3. Compounds formed by the union, in indefinite proportions, either of proximate principles, or definite compounds of these same principles. We shall give the name of species to compounds of the first two INTRODUCTION. 363 classes, while substances of the third class will be considered as mixtures of several species, which latter it is always possible to separate, either by mechanical means or chemical processes, with- out altering their nature. The name of proximate analysis is given to the mechanical or chemical operations, the objects of which are to separate the species which immediately constitute organized beings; and elementary analysis is the operation by which the nature and proportions of the simple bodies composing these beings is determined. Element- ary analysis is generally applied to species, because the knowledge of their composition furnishes one of their most distinctive charac- teristics. § 1207. The proximate analysis of organic substances is one of the most difficult problems of this branch of chemistry, because the great instability of organic matter, the facility with which it is al- tered by chemical agents, and the great diversity of its nature, do not permit the establishing of well-defined rules, such as those applied to the analysis of mineral substances. Mechanical separation by the lens and microscope affords a means of separation which sometimes succeeds ; and in some cases leviga- tion may he used, by suspending the mixture in water, when the various insoluble species composing it are deposited, more or less rapidly, according to their varieties of density and shape. Neutral solvents, that is, those which exert no chemical action on the organic species to be separated, afford the most ordinary means for the isolation of the latter ; and the substances most frequently employed for the purpose are water, alcohol in various degrees of concentration, ether, and wood-spirit. As they are used sometimes cold and sometimes hot, it is important in the latter case to ascer- tain whether some of the organic species are not modified by the temperature at which the operation is being carried on. Soluble and insoluble organic substances constituting a mixture may be separated by means of neutral solvents, and the solutions, when slowly evaporated at a proper temperature, frequently deposit the species successively in the form of crystals, which can thus he iso- lated ; and, although the separation is generally incompletely effected by the first crystallization, by redissolving the crystalline deposits which have successively formed in the same solvent, as before, and recrystallizing them, the species may he separated in a state of purity. By subjecting a mixture of organic species to the successive action of various solvents, they can generally be separated into several parts, each of which is formed of a more simple mixture than the original mixture. By skilfully applying the action of neutral solv- ents, substances which do not even present great differences of solu- PROXIMATE ANALYSIS OF ORGANIC SUBSTANCES. 364 ORGANIC CHEMISTRY. bility in the same solvent can be separated, remarkable instances of which will be mentioned when treating of the analysis of fat sub- stances. Solvents which exert a chemical action on the organic species composing the mixture, but without modifying the species so that it cannot be restored to its original state, are frequently used with success; but their action must be limited, either to the decomposi- tion of a compound species into simple species, or to simple combi- nations of the species with the substance of the solvent; in which case one or several of the species combine with the substance of the solvent, and form soluble compounds, the simple species of which may be separated without change. Thus, an insoluble salt, formed by an organic acid with a mineral or an organic base, may be de- composed by a solution of potassa or carbonate of potassa, so that the organic acid shall form a soluble compound with the alkalies, from which it may then be separated without change. Acid solvents are also sometimes employed, as, for example, when an insoluble organic base is combined with an organic or mineral acid, forming an insoluble salt: by treating the substance with a weak solution of chlorohydric or sulphuric acid, the base is dissolved, and may be precipitated by supersaturating the liquid by potassa or ammonia. The metallic salts are sometimes employed to effect double de- composition, in solutions obtained by treating organic mixtures by neutral or alkaline solvents. Thus, a great number of organic acids form insoluble salts with protoxide of lead; and by adding acetate of lead to their solutions, previously neutralized by potassa or ammonia, an insoluble salt, formed by the oxide of lead Avith the organic acid, is precipitated; and the precipitate, after being well washed, is suspended in water, through which a current of sulfhy- dric acid gas is passed, when the lead is converted into insoluble sulphide, while the organic acid separates and generally dissolves in the liquid. Many organic substances, which do not change in the air in the presence of neutral solvents at the ordinary temperature, possess the property of absorbing oxygen rapidly Avlien in contact Avith an alkaline liquid, in which case they are converted into acids which combine Avith the alkali; and it is therefore important, when alkaline solvents are used, to determine by a preliminary experiment Avhether the phenomenon just mentioned will take place; which is done by introducing a small quantity of the organic substance and the alka- line solvent into a graduated bell-glass-, filled with air over mer- cury, and to observe Avhether the volume of air is lessened. § 1208. Certain organic species are isolated by distillation, which process requires great caution; and it is necessary to ascertain whether the product of distillation really pre-existed in the mixture, or Avhether it has resulted from changes effected by heat in the INTRODUCTION. 365 original substances. Distillation or sublimation must, in many cases, be effected at a temperature below that of the boiling point of substances which volatilize under the ordinary pressure of the atmosphere, because the temperature of ebullition is often sufficiently elevated to change the other organic species which exist in the mix- ture. The substances are then heated in a current of steam, when the vapours of the organic volatile species, having considerable ten- sion at the temperature of 212°, are continually carried over by the aqueous vapour, and condensed with it. By this process many of the odoriferous essential oils contained in plants are separated. By applying distillation to organic substances, a mixture of seve- ral volatile species is frequently obtained, which are soluble in each other, and cannot be separated by the means of chemical combina- tion. When such species are unequally volatile, a separation may be effected by subjecting them to successive distillations and dividing the products into fractions, if not absolute, at least sufficient for the study of the properties of the species. The difficulties of such a separation increase as the difference between the boiling points is smaller; and it is often more advantageous, instead of distilling the mixture under the ordinary pressure of the atmosphere, to boil it under a much weaker pressure, because, in that case, the ratio between their elastic forces becomes much less. We will endeavour to explain this by an example. Let us suppose a mixture of alcohol and ether, in nearly equal proportions. Alcohol alone boils at 173.3°, and ether isolated at 94.5°, under the pressure of 29.922 inches; and we will admit, although the supposition is not entirely exact, that the mixture of alcohol and ether boils at 94.5°. The normal tension of the va- pour of ether at this temperature is 29.922 inches, while that of alcohol is 4.055 inches, and the ratio of the two tensions is there- fore 0.136. It is evident that the first portions which pass over in distillation will contain much more ether than alcohol, but that this will contain, nevertheless, a considerable proportion of the latter substance, since the ratio of the two tensions is represented by 0.136. If, on the contrary, the mixture be boiled under a pressure suffi- ciently feeble for the boiling point to sink down to 32°, the normal tension of alcohol at this temperature being 0.492 inches, while that of ether is 7.165 inches, the ratio between the two elastic forces is only 0.068, and consequently much more feeble than at the tempe- rature of 94.5°. If, therefore, the retort containing the mixture be surrounded with ice, and the distillation effected by rarefying the air by means of an air-pump', the proportion of alcohol which will pass over in distillation at the same time with the ether will scarcely be one-half of that which distilled at the temperature of 94.5° ; and the proportion will be still less if the retort be surrounded by a refrigerating mixture of ice and common salt at 14°. In fact, at this temperature, the tension of the vapour of alcohol is 0.251 366 ORGANIC CHEMISTRY. inches, while that of the vapour of ether is 4.468 inches; and the ratio of the two elastic forces is only 0.056.* We will not devote too much time to a general indication of the principal processes employed for the analysis of organic mixtures, as in the following a large number of examples will be given, which are better adapted to illustrate the methods. ELEMENTARY ANALYSIS OF ORGANIC SUBSTANCES. § 1209. Although, in the preceding parts of this work, the greater part of the processes employed in chemistry, to determine the ele- mentary composition of organic substances, have been already ex- plained, we still think it necessary to add some new details, and indicate the various precautions to he observed, according to the nature and physical properties of the organic substances to be analyzed. It has been mentioned (§ 1205) that the majority of substances extracted from the vegetable kingdom were composed only of carbon, hydrogen, and oxygen, while a certain number of vegetable species and the majority of animal substances contain nitrogen in addition ; and lastly, that some organic substances contain sulphur and phos- phorus. But, by subjecting organic substances to the various reac- tions capable of being performed in the laboratory, other substances are obtained, which are not organic substances, properly so called, because they have not been directly extracted from the organic kingdom, but the study of which presents great interest. Such sub- stance, produced by chemical reactions, often contain elements which have not been met with in organic substances, properly so called, as, for example, chlorine, bromine, iodine, arsenic. Again, organic species which act the part of acids may form salts with mineral bases, while basic organic species form salts with the mineral acids. * The apparatus used for distillation under reduced pressure consists in a re- tort A (fig. 608) arranged in a small kettle containing ice or the refrigerating mix- ture. The retort is fitted to an or- dinary tubulated receiver 13, the corks of which are covered with sealing-wax, and which is arranged in a vessel, so that it may be en- tirely covered by a refrigerating mixture of crystallized chloride of calcium and ice; the temperature of which mixture must necessarily be much lower than that surround- ing the retort. To the second tu- bulure of the receiver a leaden- pipe, having a stopcock r and communicating with an air-pump, is fitted. A vacuum is made until the liquid in the retort boils, when the stopcock r is closed, and the distillation is effected by means of the difference of temperature in the retort and the receiver. The distillation can be arrested at will, by allowing air to enter the apparatus through the stopcock r. Fig. 608. INTRODUCTION. 367 Now, the study of these salts possesses great interest, because they are more easily obtained in a state of purity than the isolated or- ganic species, and their analysis furnishes very valuable elements for the determination of the composition and constitution of the species. From all this it will be seen that the chemist who devotes himself to the investigation of organic substances must frequently examine elements quite different from those which exist naturally in the substances subjected to analysis, and that the presence of such new elements sometimes obliges him to modify his ordinary pro- cesses. DETERMINATION OF CARBON AND HYDROGEN. § 1210. The carbon and hydrogen of an organic compound are always determined by completely burning the substance, either in free oxygen, or by means of the oxygen contained in an easily re- ducible metallic oxide; when the hydrogen is converted into water, which is absorbed by some highly hygroscopic substance, such as chloride of calcium or concentrated sulphuric acid, while the carbon passes into the state of carbonic acid, which combines with a known quantity of caustic potassa; the increase of weight of the potassa representing the weight of carbonic acid formed. Oxide of copper CuO, which is generally used to effect the com- bustion, may be prepared in several ways, and in each case presents some special properties on which it is proper to dwell. One of the most simple processes consists in roasting copper turnings at a red-heat in the muffle of a cupelling furnace, (fig. 594,) when, the surface of the copper becoming oxidized, the whole is re- moved after a few hours’ roasting, and rubbed in a mortar to detach the oxide, or to pulverize those sheets of copper which are entirely converted into oxide. The substance is passed over a coarse sieve to separate the sheets of metal, which are again roasted. A very coarse-grained oxide is thus obtained, which attracts but slightly the moisture of the air. A finer oxide, the hygrometric power of which is equally feeble, is prepared by substituting for the copper turn- ings, copper precipitated chemically, or produced by decomposing acetate of copper by heat. An oxide of copper in fine powder, and more easily reducible than that prepared by roasting, may be obtained by dissolving the metal in nitric acid, evaporating the solution to dryness, and cal- cining for an hour, at a dull red-heat, the subnitrate of copper which remains after evaporation. The oxide, which, when ground, pre- sents the appearance of a fine, velvet-black powder, is well adapted to the combustion of organic substances, but rapidly attracts the moisture of the air, and, on this account, requires great caution in analysis, if the amount of hydrogen is to be accurately determined. The oxide of copper produced by the decomposition of the car- bonate by heat is also well adapted to the combustion of organic 368 ORGANIC CHEMISTRY. substances, but is at least as hygrometric as that prepared by calcining the nitrate ; which property, however, may be lessened by heating it longer and at a higher temperature, when it again becomes more compact, and is reduced with greater difficulty by combustible substances. Chromate of lead PbO,Cr03 is sometimes substituted for oxide of copper, because organic substances burn readily in contact with the salt; and, as the chromate fuses at quite a low temperature, the heat is raised toward the close of the combustion, so as to cause its fusion ; by which means the last particles of carbon which may remain after the decomposition of the organic matter are forced into contact with the burning substance, and their combustion is necessarily complete. Chromate of lead possesses another advan- tage in being less hygrometric than oxide of copper, so that the determination of hydrogen may be made more accurately. The chromate of lead should be previously fused in an earthen crucible, rolled into a plate on a sheet of copper, reduced to powder, and im- mediately preserved in a well-stoppered bottle. Before using oxide of copper for combustion, it is always heated to redness in an earthen crucible, in order to destroy the organic dust with which it may be mixed and drive off its moisture; and the crucible, when removed from the fire, is placed under a bell- glass containing some pieces of quicklime, and allowed to cool. It is frequently used before it is entirely cooled, as there is then less fear of its attracting moisture. § 1211. As organic matter burns under conditions differing slightly according to the nature of the substance, we shall pay at- tention to several cases. We will suppose, in the first place, that the organic substance contains only carbon, hydrogen, and oxygen, and will also examine several points, according to the state of the substance and its greater or less volatility, assuming the substance to be solid, non-volatile, and not decomposable below 212°. The combustion is effected in a glass tube ab, (fig. 609,) made as strong as possible, and of an internal diameter of about 15 millimetres, being J metre in length, while one of its ends is drawn out to a point c and turned upward. The other end a, which remains open, has its edges slightly roufided, so as not to injure the cork fitted into it; which latter should be previously dried in a stove at the temperature of 212°, to prevent it from giving off moisture. The glass tube intended for analysis, and which we shall call the combustion-tube, should be thoroughly cleaned by wiping it out with tissue-paper, and then heated throughout its whole length, while a tube open at both ends, and fitted to the nozzle of a bellows, is in- troduced into it, when the current of air thus established removes Fig. 609. INTliODUCTION. 369 all moisture ; after which the tube must he closed with a cork. As the combustion-tube may still contain some organic dust, a small quantity of hot oxide of copper, recently calcined, is introduced into it, and, after having shaken the tube, the oxide is set aside. The organic matter intended for analysis having been previously finely powdered, the portion to be subjected to combustion, which varies in weight from 8.300 gm. to 0.500 gm., is very accurately weighed. Larger quantities are sometimes taken when the substance contains but little carbon or hydrogen and great exactness is re- quired in the analysis. It is to be weighed in a small glass tube closed at one end; and if the matter is hygroscopic, the open end of the tube should be closed with a ground-glass stopper. The mixture of the organic matter with oxide of copper is made in a mortar of glazed porcelain or glass, which has previously been perfectly dried by being heated in a stove; but it is better to use a metallic mortar, (fig. 610,) not very deep, and highly polished on the inside, because it is more easily heated, and be- cause metal does not attract moisture like glass. The inside of the mortar should be cleaned, before using it, with a small quantity of oxide of copper, which is afterward rejected. The quantity of oxide of copper to be mixed with the organic matter, and which should be such as to occupy a length of 1 or 2 decimetres in the combus- tion-tube, being first placed in the mortar, the organic matter con- tained in the small tube in which it has been weighed is added; while, in order that none may adhere to its sides, a small quantity of oxide of copper is passed through the small tube several times and then poured into the mortar. The substance is ground rapidly with the pestle, in order to make a uniform mixture, which is immediately introduced into the combustion-tube, at the bottom of which a small column of pure oxide, of 3 or 4 centimetres in length, has been pre- viously deposited; for which purpose the substance in the mortar is dipped up with the tube, or first poured on a copper spoon C, (fig. 611,) and thence, by a copper funnel, into the combustion-tube. A small quantity of oxide of cop- per being rubbed in the mortar to remove any par- ticles of the mixture which may adhere, and then dropped into the tube, the latter is then filled with pure oxide of copper.* Fig. 610. Fig. 611. * As Mitcherlich’s old method of filling combustion-tubes, which for a long time was rejected by the majority of chemists, seems now again to be brought into use, it will be well to mention it. The organic substance is contained in a long tube, the external diameter of which is sufficiently small as to allow of its being inserted into the combustion-tube; and the oxide of copper is used, after being heated to a dull-red, while it is still of a temperature of about 212°, at which degree of heat the organic substance is supposed not to decompose. The absorption of moisture by the oxide of copper is thus prevented during the filling, which is done as fol- lows :—Supposing the combustion-tube to be 16 inches long, the lower 2 inches would be filled with coarse oxide, and then a column of fine oxide would be in- 370 ORGANIC CHEMISTRY. If the oxide of copper employed is very finely powdered, there is danger that the column will not be sufficiently porous to allow an easy disengagement of gas; and a small canal must therefore be made in the upper part of the tube throughout its whole length, which is easily effected by carefully dropping the tube lengthwise on a smooth table, and perhaps applying a few slight shocks at the ends. As the oxide of copper during this manipulation has almost always attracted an appreciable quantity of moisture, this must be removed if the exact amount of hydrogen in the substance is to be determined; which is effected by placing the combustion-tube in a tin vessel V (fig. 612) filled with hot water, and made to communicate with a small air-pump P, to the second tubulure of which is fit- ted a tube T, filled with pumice-stone soaked in sul- phuric acid. By working the pump se- veral times, and each time allowing the air to enter which was dried by passing through the tube T, the hygroscopic moisture is completely removed; but the process can only be employed wdien the organic substance does not give off sensibly any vapour, in vacuo, at a temperature of 212°, and when it cannot, under these circumstances, either give off water •or decompose. In any other case the process of desiccation just mentioned could not be employed, and recourse must be taken to the use of coarser and more highly calcined oxide of copper, while Fig. 612. serted, occupying about 6 inches; after which the organic substance is introduced, by inserting the tube containing it in the combustion-tube, and allowing the desired quantity to fall out; after which the small tube is corked, and subsequently weighed to ascertain the amount of substance extracted. The combustion-tube is then filled with another column of 6 inches of fine oxide of copper, and the or- ganic substance is mixed up thoroughly, by means of the spirally-twisted end of a long and clean copper wire, with the columns of oxide below and beneath it; which is easily done by successively screwing the wire down to the layer of coarse oxide, and working it backward and forward for about 5 minutes; the tube being held with a cloth, because the oxide has the temperature of boiling water. Another inch of pure fine oxide is then added, and the tube is corked. There will then be contained in the tube, 1st, two inches of coarse oxide; 2dly, twelve inches of an intimate mixture of fine oxide and the organic substance; 3dly, one inch of fine oxide; and, lastly, a free space of one inch, to allow of rendering the whole co- lumn porous by shaking.— W. L. F. INTRODUCTION. 371 the mixture must be made in the mortar as rapidly as possible, taking care to hold the breath. The combustion-tube, after being charged, is enveloped with a thin ribbon of brass, previously annealed, and fastened with copper-wire, as represented in fig. 613, after which the tube, thus protected, may be heated to a very high temperature without danger. The combustion-tube being placed on a long sheet-iron furnace, (fig. 614,) the appa- ratus in- tended to absorb wa- ter is fitted to it by means of a very well dried cork. The apparatus con- sists of a tube filled with pieces of chloride of calcium, arranged as in fig. 615, while plugs of cotton, placed at a and b, pre- vent the small particles of chlo- ride from escaping from the tube. The cork a is covered with sealing-wax, in order that its weight may not change by absorbing or exhaling moisture, if any existed in the air. A U-tube, filled with pumice-stone soaked in concentrated sulphuric acid, is some- times substituted for the tube containing chloride of calcium. The carbonic acid formed by combustion condenses in a concen- trated solution of caustic potassa, marking about 45° Baume, and placed in the apparatus B (fig. 614) described on page 324, vol. i., which is fitted, by means of a caoutchouc connecter, to a tube in- tended to condense the water. As it might be feared that the solution of potassa, notwithstanding its concentration, might part with a small quantity of water to the very dry gases which traverse it, a small U-shaped tube C, containing pieces of caustic potassa, which absorb at the same time the vapour of water and the small quantity of carbonic acid which escapes absorption in the apparatus B, is affixed to the latter. Lastly, a hottle V, the cork of which has a stopcock r, is fitted to this apparatus, thus establishing or interrupting at will commu- nication with the outer air. To the bottle is permanently fitted a U-tube filled with sulphuric pumice-stone, intended to prevent the vapour of water from passing from the bottle V into the tube C. (The U-tube is not represented in the figure.) Fig. 613. Fig. 614. Fig. 615. 372 ORGANIC CHEMISTRY. The drying-tube A and the whole of the apparatus B and C hay- ing been previously exactly weighed, their increase of weight during the experiment gives respectively the quantity of Avater and of car- bonic acid formed by combustion. When the apparatus is arranged, the anterior portion a F of the combustion-tube, which contains only pure oxide of copper, is sur- rounded by burning coals; and in order that the heat may not communicate by radiation to the parts of the tube containing the mixture of oxide and organic matter, a double screen F, made of sheet-iron, and represented in fig. 616, is interposed. When the anterior portion of the tube is heated to redness, the coals are gradually moved toward the part containing the mixture of oxide and organic matter, the rapidity of moving the coals being guided by the evolution of gas which is ob- served rising in bubbles through the potash apparatus, and Avhich should never folloAv so rapidly as not to alloAv the counting the bubbles which traverse the apparatus B. This is continued until the tube is completely surrounded with coals, Avhen the combustion is terminated, and the evolution of the gases ceases, and very soon the potassa ascends into the globe which communicates with the drying-tube, in consequence of the absorption of the carbonic acid contained in this globe. The globe apparatus is then moved from the position of fig. 617 to that of fig. 618, and if the globes are of suitable dimensions, the solution of potassa will certainly ascend to the drying-tube, (§ 260,) and very soon, the absorption of carbonic acid continuing, bubbles of air re-enter the apparatus, passing through the solution of potassa. The coals surrounding the end c of the combustion-tube are then re- moved, and, Avhen the latter is sufficiently cooled, its point is broken with a pincers, (fig. 619;) Avlien the gas in the apparatus being rarefied, the outer air enters through the broken point and establishes the equilibrium. A tube S, (fig. 620,) containing pieces of caustic potassa, and furnished Avith a caoutchouc tube, which it is sufficient to press against the combustion-tube to render the opening tight, is then adapted to the point; after which the stopcock r of the bottle V is closed, and by opening the stopcock r' the water in this bottle is allowed slowly to escape. The atmo- spheric air, freed from moisture and carbonic acid by its passage through the tube S, removes the small quan- tities of vapour of water and carbonic acid which still remained, and con- veys them into the apparatus A, B, C, Avliere they are condensed. Fig. 616. Fig. 617. Fig. 618. Fig. 619. Fig. 620. INTRODUCTION. 373 When about 1 litre of water has escaped, the apparatus is taken apart, weighed, and the carbonic acid and water formed during com- bustion exactly ascertained, whence the quantity of carbon and hy- drogen contained in the organic matter can be calculated. As we have supposed the substance subjected to analysis to contain only carbon, hydrogen, and oxygen, the oxygen may be obtained differ- entially, that is, by subtracting the weight of hydrogen and carbon united, from that of the substance subjected to analysis. It frequently happens that it is difficult to completely burn or- ganic substances, either because they cannot be intimately mixed with the oxide of copper, or because, by being decomposed by heat, they leave a charcoal of difficult combustion, which is sometimes de- posited in the upper portions of the combustion-tube, out of contact of the oxide of copper. In this case, it becomes necessary to termi- nate the combustion in a current of oxygen; for which purpose a mixture of 2 or 3 gm. of chlorate of potassa, coarsely powdered, and 15 or 20 gm. of oxide of copper, is introduced into the bottom of the combustion-tube, while upon this is placed a column of 3 or 4 centimetres of pure oxide, then the mixture of oxide of copper and the organic substance, and lastly the tube, is filled with pure oxide. The apparatus is arranged as has been described. When the organic matter has been completely burned, and the hot coals surround the tube, even as far as the extreme portion which contains the chlorate of potassa, some coals are carefully moved toward this end, in order to disengage oxygen. The first portions of the gas are absorbed by the copper reduced by combustion, and it is only after the entire oxi- dation of this metal that free oxygen begins to pass through the tube, and care must be taken that its evolution be not too rapid. The organic matter is necessarily entirely burned in the atmosphere of oxygen, and the carbonic acid produced is carried by the current of oxygen into the absorbing apparatus, which renders the aspirator useless. The chlorate of potassa should have been previously fused, in order to free it from organic substances and moisture. In this method of operating, it may be feared that the chlorate, by contact with the oxide of copper, may give off a small quantity of chlorine which is not completely retained in the combustion-tube; which difficulty, however, is remedied by using a longer combustion-tube, and placing, in front of the oxide of copper, a length of 8 or 10 centimetres of litharge, which, at a red-heat, retains the whole of the chlorine. Sometimes the oxygen is prepared in a small separate retort, which is made to connect with the small end of the tube, instead of evolving oxygen by means of the chlorate of potassa placed in the combustion-tube itself. Although the majority of organic substances will burn completely by contact with oxide of copper alone, it is always prudent to per- form one, at least, of the combustions with the addition of chlorate 374 ORGANIC CHEMISTRY. of potassa, in order to ascertain whether the amount of carbon found has not been too small in the preceding analyses. § 1212. If the substance to be analyzed is liquid and non-volatile, as, for example, a fixed oil, it is weighed in a small tube, closed at one end, and introduced into the combustion-tube, after having poured into the latter a column of oxide of copper of 4 or 5 centi- metres in height; after which the tube is inclined so as to spread the oil over a certain extent of its sides, and then entirely filled with oxide of copper. It frequently happens that complete combus- tion is not effected by the oxide of copper alone, and must be ter- minated in a current of oxygen. Greasy and easily fusible substances should not be triturated with the oxide of copper, because some particles might adhere to the mor- tar and pestle; but a suitable quantity of the material should, in this case, rather be melted in a small glass boat, made of a piece of tube divided longitudinally, and introduced, after being weighed, into the tube, at the bottom of which the oxide of copper is placed. By heating that portion of the tube which contains the boat, the grease melts, and flows over a certain extent of the tube, which is then to be filled with oxide of copper. It is, in this case, equally prudent to terminate the combustion in a current of oxygen. § 1213. Volatile liquid substances are weighed in glass bulbs (fie:. 6211 hermeticallv sealed, the manner of making which has been described, (§ 699,) and the manner of filling them in § 269. It is essential not to bring the bubbles in contact with the hot oxide of copper after they have been opened, as vapours affecting the accuracy of the analysis would infallibly be produced. Two tubes of nearly the same capacity are used, and one of them being filled with recently calcined and still hot oxide of copper, is closed, and allowed to cool completely; while into the second tube, which is to serve as a combustion-tube, a column of 4 or 5 centimetres of oxide of copper is introduced, and afterward the bubbles are inserted, of which one of the points is broken; and, lastly, the second tube is filled with the oxide of copper which has been allowed to cool in the first, and is, consequently, free from moisture. It is better, in such analyses, to use coarse oxide of copper, mixed with roasted turnings, because this oxide, even when it completely fills the sec- tion of the tube, is sufficiently porous to afford an easy passage for gases and vapours. The absorbing apparatus is arranged as usual, but the operation is conducted as rapidly as possible, in order that the vapours of the volatile substance may only have time to reach the anterior part of the combustion-tube, which is heated to redness, while the part containing the bubbles is protected by several screens. When the oxide of copper is red for a length of several decimetres, some coals are carefully moved toward the part containing the bubbles, while the distillation of the substance is Fig. 621. INTRODUCTION. 375 regulated by the position of the coals. The vapours burn while traversing the oxide of copper; and when combustion ceases, the tube is surrounded with burning coals, and heated throughout its whole length, after which the experiment is terminated as usual. If the substance to be analyzed is very volatile—if it boils, for example, at a temperature below 122° under the ordinary pressure of the atmosphere—it is difficult to obtain an exact analysis by the process just stated. The vapours of the substance cannot be pre- vented from penetrating the anterior part of the combustion-tube, before this part is heated to redness, and they thus escape combus- tion and render the analysis inaccurate. The experiment is then arranged in the following manner:—The combustion-tube is drawn out at its posterior portion, so as to form a tubulure c, while the liquid to be analyzed is contained in a globe U bent into the form of a retort (fig. 622) and terminating in two closed points, one of which enters the tubulure of a combustion-tube previously filled with oxide of copper and arranged on its sheet-iron furnace. The globe is hermetically fastened by caoutchouc, while the ordinary condensers are fitted to the combustion-tube, which is surrounded by burning coals. When the whole length of the tube is red, the anterior point of the globe is broken, by pressing it against the sides of the tubu- lure ; and if the liquid is very volatile, it sometimes boils immediately, and the analysis may fail in consequence of a too sudden evolution of gas. If such an accident is to be feared, the globe should be surrounded by a refrigerating mixture before breaking the point; udien the ebullition is easily regulated, either by heating the globe with the hand, or by hot coals. When the whole of the liquid is distilled, and the absorption of carbonic acid causes the potassa to ascend into the globe apparatus, the second point b of the bubble is burst, when the external air, entering the combustion-tube, carries into it the last portions of vapour which remained in the bubble. The latter is then detached, replaced by the tube S filled with pieces of potassa, (fig. 620,) and lastly, water is allowed to escape from the aspirator-bottle to terminate the analysis in the ordinary way. § 1214. We will suppose, lastly, that the organic substance to be analyzed is gaseous, and that it cannot be condensed in a refrige- rating mixture at —20°, in which case it could still be analyzed by the processes described for very volatile liquids; and the proceeding of the analysis is then as follows: When the gas contains only carbon and hydrogen, its analysis can be very readily made. The apparatus is arranged as for the analysis of very volatile liquids, and, when the combustion-tube is heated to redness throughout its Avliole length, the disengaging-tube of the apparatus which produces the gas to be analyzed is fitted to its tu- bulure by means of caoutchouc. The gas burns when in contact Fig. 622. 376 ORGANIC CHEMISTRY. with the incandescent oxide of copper, while the vapour of water and carbonic acid are arrested in the ordinary condensers; and, when a sufficient quantity of gas is supposed to be burned, the dis- engagement-tube which conveys the gas is detached, and water al- lowed to escape from the aspirator-bottle, in order to burn the last portions of gas which remain in the combustion-tube, and drive their products into the condensers. This experiment gives the weight of carbon and hydrogen contained in the gas burned; but as the weight of this gas is not known, it is evident that only the ratio between the weight of the hydrogen and carbon can be inferred from it, which, however, will give a sufficient clue as to the composition of the gas. It is better to operate so as to ascertain the volume of the gas subjected to experiment, and, consequently, also its weight, if its density has been de- termined by previous experiment, in which case the process can also be applied to gases containing oxygen and nitrogen. For this purpose the apparatus represented in fig. 623 is used. The pipette ab, containing 400 or 500 cubic centimetres, terminates at its upper part, in a straght tube cr, to which is luted a steel tubulure, having a stop- cock r, while the lower tube af of the pipette is luted to one of the tubulures of a cast- iron piece having a stopcock R, furnished with a second tubulure g. A tube gh, open at both ends, is luted to the tubulure g, and the whole apparatus is fastened to an up- right board. The stopcock R has three apertures, as figures 624, 625, and 626 show which represent transverse sections ?of the stopcock, in the three principal po- sitions which may be given to it. In fig. 624, the branches bf and gh communi- cate, and in fig. 625 the branches bf, gh communicate with each other, and with the external air by the tubulure t, while mercury escapes; and lastly, in fig. 626 the branches do not communicate Fig. 623. with each other, but the branch bf communicates with the external Fig. 624. Fig. 625. Fig. 626. INTRODUCTION. 377 air by the tubulure t, while the mercury contained in this branch alone escapes. The stopcock R being in the position of fig. 624, and the cock r being open, the apparatus is filled with mercury through the tube gh ; and when it begins to escape through the tubulure r, the cock R is brought to the position of fig. 626, and the mercury wdiich escapes is collected in a bottle. The level of the mercury is allowed to fall until it exactly reaches the mark a on the tube fa ; and the capacity of the pipette is then inferred from the weight of the mer- cury. The apparatus is then again filled with mercury, and the tubulure r made to communicate with the apparatus which disengages the gas to be analyzed. As the gas is produced, mercury is allowed to escape, so as to fill the pipette with gas to just below the mark a; after which the stopcock r is closed, the chemical apparatus which evolves the gas removed, and, bringing the cock R to the position of fig. 624, mercury is carefully poured into the branch gh, so as to bring the level exactly to a. By adding the difference of height h, between the levels of mercury in the two branches bf gh, which is then measured, to the height H of the mercury in the barometer, the pressure (H-f h) to which the gas is subjected is obtained, while the thermometer T (fig. 623) shows its temperature. If, therefore, the density of the gas be known, its weight can be easily calculated. In order to burn the gas, it suffices to cause the tubulure r to communicate with the pointed tubulure c of the combustion-tube heated to redness (fig. 614) and furnished with its ordinary con- densing apparatus. The stopcock r being carefully opened, mer- cury is poured into the branch gh by means of a funnel which only allows the proper quantity of mercury to escape; and as soon as the pipette is entirely filled with mercury, so that the latter reaches the stopcock r, this cock is closed, the apparatus of fig. 623 re- moved, and the operation terminated as usual. § 1215. In the processes just described, the weight of the carbon is inferred from that of the carbonic acid absorbed by the potassa: it may also be determined by measuring the volume of gas, by which method the first exact analyses of organic substances were made. The hydrogen and carbon are then determined separately, the determination of the former being made in the ordinary manner, by burning the organic matter with oxide of copper, and collecting the water produced in a tube filled with pieces of chloride of calcium, and fitted to the combustion-tube by means of a cock. The determi- nation of carbon is performed in an apparatus represented in fig. 627. The tube ab contains the mixture of the organic substance with oxide of copper, and at its anterior portion contains pure oxide of cop- per ; while a bent tube cdef the two vertical legs of which, de, ef descend to the bottom of the test-glass AB filled with mercury, is fitted by means of a cock, to the combustion-tube, which therefore communicates with the external air by the tube cdef. A bell-glass 0, 378 ORGANIC CHEMISTRY. divided into cubic centimetres, and of which the sides, after being wiped with tissue-paper, retain sufficient water to saturate the air re- maining in the bell-glass with moisture, is passed over the leg ef. Before fitting the branch c to the combustion-tube, the bell-glass C is made to descend, until a very .small volume of air (50 c. c. for example) alone remains, the mercury being on a level in the bell-glass and the cir- cular space comprised between the bell-glass and the test-glass. The cock c is then fitted, and the apparatus allowed to attain the tempera- ture of the surround- ing medium. The temperature t and the height of the barometer H0 being noted down, we will designate by v the volume of air in the combustion-tube and in the tube cdef; by/the elastic force of the vapour of water at the temperatue t, when the volume of air in the apparatus, supposing it to be dry, reduced to 32°, and under the pressure of 0.760 m., 29.922 inches, will be (”+50) The organic matter is then subjected to combustion ; and as car- bonic acid is disengaged, the bell-glass C is raised, in order to keep the surface of the mercury in the bell-glass nearly level ivith that in the test-glass. When the combustion is terminated, the coals are removed, and the apparatus allowed to fall to the sur- rounding temperature t'; after which the mercury inside is brought exactly to the level of that outside, by raising or depressing the bell-glass, or by pouring mercury into the test-glass. Lastly, the volume Y occupied by the gas in the bell-glass is marked, as Avell as the height H'0 of the barometer. The volume of gas in the ap- paratus, reduced to dryness, at the temperature of 32°, and under a pressure of 0.760 m., will be— V"' ’/ 1+0.00367. f 760 i and the volume of carbonic acid formed by combustion, AA’hen dry and under normal conditions of pressure and temperature, is therefore (y-+Yl - YW_ (WSOt l H°~f \ 1 ) 1+0.00367 • t' 760 Vw“tJV/ 1+0.00367 .t • 760 ’ Fig. 627. INTRODUCTION. 379 In order to obtain the weight of carbonic acid furnished by the or- ganic matter, it is sufficient to multiply this volume, in cubic centi- metres, by the weight 0.0019774 m. of 1 cubic centimetre of car- bonic acid. The determination of carbonic acid by volume is much more deli- cate than that by weight. It is essential that the shape of the combustion-tube should not be altered during the combustion, as this would change the volume v ; and the volume of gas at the close of the experiment must not be measured until the combustion-tube at- tains the surrounding temperature, which often requires a long time. Lastly, it is necessary to use very coarse oxide of copper, for finely divided and feebly calcined oxide absorbs carbonic acid, in the pre- sence of moisture, when it falls to the ordinary temperature. All these difficulties have caused this method of analysis to be neglected, although its results are accurate in the hands of a skilful mani- pulator. § 1216. When the organic substanee contains, at the same time, carbon, hydrogen, oxygen, and nitrogen, the determination of carbon and hydrogen requires peculiar care. A portion of the nitrogen which is set free during the combustion of the substance by the oxide of copper, does not affect the results of the analysis, while another portion is converted into deutoxide, which, being changed into nitrous gas by contact with the oxygen of the air, condenses partly in the tube which absorbs the water, and partly in the potassa, rendering the analysis inaccurate. This is avoided by placing near the orifice of the combustion-tube a column of metallic copper of about 2 de- cimetres in length; when the gases which arise from combustion traversing the incandescent copper, before reaching the absorbing tubes, the oxides of nitrogen are decomposed by giving off free ni- trogen, while the carbonic acid and water undergo no change. The metallic copper used to decompose the oxide of nitrogen is prepared by roasting copper turnings in the air, so as to oxidize its surface, and then reducing the surface to the metallic state, by heating the roasted turnings in a glass tube in a current of hydrogen, by which means the surface of the metal becomes very porous, and exerts a much more powerful reducing action than if it were smooth and polished. If the organic substance contains sulphur, the process of ordi- nary combustion must again be slightly modified, because the sulphur, by burning in contact with the oxide of copper, is largely converted into sulphurous acid, which condenses the apparatus con- taining potassa, thus rendering the determination of the carbonic acid inaccurate. But the sulphurous acid is entirely retained in the combustion-tube, by placing in the anterior part of the tube a length of 0.2 m. of litharge, which, at a red-heat, absorbs sulphur- ous acid wholly, provided the current of gas be not too rapid. It is also necessary to place a column of litharge in the tube, in 380 ORGANIC CHEMISTRY. front of the oxide of copper, when the organic substance contains chlorine, bromine, or iodine, because, in that case, a chloride, bro- mide, or iodide of copper is formed, which is sufficiently volatile to permit its vapours to reach the tube containing the chloride of cal- cium, and falsify the determination of water. Litharge decomposes and perfectly retains these vapours at a red-heat. The analysis of salts formed by organic acids with mineral bases the carbonates of which are indecomposable, or decompose with diffi- culty by heat, also requires peculiar precautions. Such bases are the alkalies and alkaline earths, which remain partly in the combus- tion-tube in the state of carbonates, while it cannot be admitted that they do so entirely, because the carbonates are partially de- composed by the oxide of copper, the sides of the tube, and, par- ticularly, by the mineral acids, chlorine, and other elements which may exist in combination with the oxide of copper or with the reduced copper. The carbonic acid may be completely disengaged by substituting chromate of lead for the oxide of copper, especially if a small quantity of bichromate of potassa be added to the chromate. Otherwise, the combustion is conducted in the same manner as for the oxide of copper. § 1217. The nitrogen contained in organic substances is deter- mined by the process described for the analysis of the nitrates, (§ 108.) A combustion-tube fa, (fig. 628,) closed at one end, and about 0.8 m. in length, is used, at the bottom of which about 20 gm. of bicarbonate of soda ab are placed, and above it a column be of pure oxide of copper, of five or six cen- timetres in length, after- ward the mixture cd of the organic substance with oxide of copper, and lastly a length de of 0.2 m. of pure oxide of copper. Over the whole is superimposed a column ef of 0.2 m. of metallic copper, prepared from copper turnings previously roasted in the air to oxidize their surface, and then reduced in a current of hydrogen. The tube being arranged on a long sheet-iron furnace, (fig. 629,) a glass tube, which is made to communicate with the tubulure of a small air-pump P, is fitted to its orifice by means of a cork, while to the second tubulure d of the pump a glass tube def is fastened, of which the vertical leg ef is about 0.8 m. in length, and the curved extremity of which dips into the small mercurial bottle B. In the first place, the air must be completely removed from the apparatus, for which purpose as perfect a vacuum as possible is made with the pump, and the stopcock s is closed, leaving open those at r, r'. After a few moments it is ascertained whether the DETERMINATION OF NITROGEN. Fig. 628. INTRODUCTION. 381 apparatus remains empty, in which case the column of mercury in the tube ef should remain absolutely stationary. Some coals are Fig. 629. brought near the end of the tube containing the bicarbonate of soda, when the carbonic acid disengaged drives the air from the tube ; and as soon as the gas begins to be evolved under the mer- cury, the anterior part of the tube, which contains the metallic mercury and a length of some centimetres of pure oxide of copper, is surrounded with hot coals, and it is then ascertained whether the gas which is evolved be pure carbonic acid. For this purpose it is sufficient to collect the gas in a small bell-glass filled with mercury, at the top of which a solution of potassa has been placed; and if the gas formed is pure carbonic acid, its bubbles will be im- mediately dissolved. When this result is obtained, the coals which effected the decomposition of the bicarbonate of soda are removed, and above the orifice of the disengaging-tube def a large bell-glass C is placed, filled with mercury, and to the top of which fifty or sixty cubic centimetres of a concentrated solution of potassa have been passed. The coals are gradually moved toward the part con- taining the organic matter, conducting the operation as in the de- termination of carbon and hydrogen. Carbonic acid, vapour of water, nitrogen and its oxides, are formed; but the oxides of nitrogen are restored to the state of free nitrogen while passing 382 ORGANIC CHEMISTRY. through the portion of the tube which contains metallic copper, so that only a mixture of carbonic acid and nitrogen reaches the bell- glass, in which the carbonic acid is dissolved by the potassa, while the nitrogen remains free. When the combustion is terminated, the column of pure oxide of copper which separates the carbonate of soda from the original mixture of oxide and organic matter is surrounded with coals; and lastly, by again heating the carbonate, a new evolution of carbonic acid is produced, which completely drives the gaseous products of combustion into the bell-glass C. It now only remains to measure exactly the nitrogen gas col- lected, for which purpose the bell-glass is carried over a large vessel filled with water, when, by opening the orifice of the former, the mercury contained in it falls to the bottom of the vessel, and is replaced by water. The gas is poured into a smaller bell-glass, divided into cubic centimetres, and held in a vertical direction by means of a stand, while the water on the inside and outside of the bell-glass is brought to the same level. When the gas has attained an equilibrium of temperature, its volume Y, the temperature t, and the height H0 of the barometer are marked, and the weight of nitrogen gas attained is therefore 0.0012562 gm. Y 1 JW. ° 1+ 0.00367. t 760 It is important to ascertain whether the gas contains no deutoxide of nitrogen; to which effect a few bubbles of air are introduced into the bell-glass, when the gas instantly turns red if it contains any appreciable quantity of deutoxide. We shall subsequently point out the means of measuring nitrogen more exactly, and of accurately ascertaining its purity. When the nitrous substance is volatile, the length of the column of pure oxide of copper between the mixture of the oxide with the organic matter, and the bicarbonate of soda, must be increased; and before commencing the combustion, both the anterior part of the tube and the column of pure oxide must be heated to redness. Instead of placing at the bottom of the tube the bicarbonate of soda, intended to disengage carbonic acid, this end of the tube may be terminated by a fine tubulure, which is made to communi- cate, by means of caoutchouc, with an apparatus for disengaging carbonic acid, in which case the exhaustion by the air-pump may be omitted, because the evolution of carbonic acid is prolonged until all the air is driven out. When the combustion is terminated, the cur- rent of carbonic acid is re-established, in order to drive all the nitrogen into the bell-glass. § 1218. Nitrogen is also dosed by another process, not of so general application as the one just described, because it is not adapted to the nitrates, but which yields, in the majority of cases, exact results. This process is founded on the fact that nitrous substances, with the exception of those containing nitre or nitrous INTRODUCTION. 383 acid, when heated in contact with hydrated alkalies, give off their nitrogen in the state of ammonia, which can be collected in an acid, and determined in the state of double chloride of platinum and ammonium. In order to effect the decomposition of the nitrous substance, a mixture of lime and hydrated caustic soda is used, which is prepared by slaking quicklime in a solution of caustic soda containing a quantity of soda equal to nearly half of that of the lime employed, after which the substance is successively ground, dried, calcined in an earthen crucible, again pulverized, and then preserved in a close bottle. We shall call it, for the sake of short- ness, soda-lime. An accurately weighed quantity of the organic matter is mixed with a certain quantity of soda lime, and placed at the bottom of a glass tube abc. (fig. 630) resembling the tubes used for the com- bustion of organic substan- ces by the oxide of copper, and tube is then filled with pure soda lime, while the bulb apparatus A, contain- ing concentrated chlorohy- dric acid, is fitted to the orifice of the tube. The tube is gradually surrounded by hot coals, as in the ordinary combustions of organic substances, the ammonia produced being dissolved in the cliloro- hydric acid. When the decomposition is effected, the point of the combustion-tube is broken, and, by blowing through the tube e of the bulb apparatus, the ammonia still remaining in the tube is driven into the chlorohydric acid. The apparatus A is then re- moved, the acid it contains poured into a porcelain capsule, and the apparatus washed several times with a mixture of two parts of alcohol and one of ether, which is then added to the capsule, into which an excess of bichloride of platinum is then introduced, to precipitate the ammonia as double chloride of platinum and am- monium. The precipitate is collected on a small filter, washed with a mixture of alcohol and ether, and weighed after drying: one gramme of double chloride of platinum and ammonium contains 0.06349 gm. of nitrogen. This process of decomposition may be modified so as to obtain a more rapid, and yet very exact analysis, by placing in the bulb apparatus ten cubic centimetres of a standard solution of sulphuric acid, obtained by mixing 61.250 gm. of monohydrated sulphuric acid with one litre of water; so that 100 cubic centimetres of the liquid will saturate 2.12 gm. of ammonia, corresponding to 1.75 gm. of nitrogen. The decomposition of the nitrous substance is effected in the usual w'ay, and the ammonia dissolves in the sulphuric acid and weakens its standard. If, therefore, the new strength of the liquid be ascertained after the operation, and the strength of the original acid subtracted from it, a difference corresponding to the quantity Fig. 630. 384 ORGANIC CHEMISTRY. of ammonia absorbed, and from which the latter may be deduced by a very simple calculation, is obtained. The standard of the acid liquid is determined by means of a solution of saccharate of lime, that is, a solution of caustic lime in sugar and water, which dissolves a much larger proportion of lime than pure water; and the solution may be kept unchanged in well- stoppered bottles. The first step is to ascertain the number of cubic centimetres of the alkaline solution necessary to exactly saturate 10 cubic centimetres of the normal acid solution; for which pur- pose the 10 cubic centimetres of normal acid solution are poured into a beaker containing a small quantity of tincture of litmus; and then the solution of saccharate of lime is added by means of an alkalimeter, until the liquid turns blue, marking the number N of divisions added. In order to be very accurate, the solution of lime must be sufficiently diluted for the saturation to require about 100 divisions of the liquid. The 10 cubic centimetres of the acid solu- tion, which have absorbed the ammonia disengaged by the decom- position of the nitrous substance, are acted on exactly in the same manner. Let us suppose that n represents the number of divisions of saccharate of lime which have effected the saturation ;; then will 0.212 gm. represent the quantity of ammonia absorbed, and l 0.175 gm. the corresponding quantity of nitrogen.* * Bunsen has recently introduced a new method for determining nitrogen, which, on account of its extreme exactness, especially when the substance is very nitrogenous, deserves to be described. About 5 centigrammes of the substance, without being exactly weighed, are inti- mately mixed with about 5 grammes of fine oxide of copper, and a small quantity of reduced copper filings, and introduced into a very strong glass tube, difficult of fusion, of about 5 inches in length and f inches internal diameter, one end of which, having previously been drawn out, is now connected with an air-pump, after the other end has been sealed, and the air is totally exhausted from the tube; after which the other end is also hermetically sealed, and both points are strengthened in the flame by thickening the glass. The tube thus prepared is packed with plaster in a strong iron box, or coffin, the lid of which is well se- cured, and the whole is then exposed to a strong white-heat for several hours; when the organic substance in the tube is entirely converted into carbonic acid, water, and free nitrogen. After cooling, the tube is taken out of the iron box and brought under a graduated cylinder filled with mercury, in a mercury- trough, where one end of the tube is broken off, and the gases, consisting only of carbonic acid and nitrogen, are allowed to pass up into the cylinder. The exact volume of the two gases being now ascertained, and reduced to the cor- rected volume at 32° and 30 inches pressure, the carbonic acid is removed by absorbing it with a bullet of caustic potassa, fixed to the end of a platinum wire, and thus introduced into the gases through the column of mecury. After all the carbonic acid is absorbed, which is the case when a diminution of volume no longer ensues, the exact volume is again ascertained and reduced to 32° and 30 inches, when the difference will give the carbonic acid, while the gas remaining in the cylinder, and measured, is pure nitrogen. The ratio of the nitrogen to the carbonic acid, and consequently to the carbon in the organic substance, being thus obtained, and the carbon being previously determined in the usual manner by combustion, the percentage of nitrogen may easily be calculated.— W. L. F. INTRODUCTION. 385 DETERMINATION OF SULPHUR. § 1219. The determination of the sulphur contained in organic substances is frequently a matter of great difficulty. Some of these substances are destroyed by contact with concentrated and boiling nitric acid, while the sulphur is converted into sulphuric acid, which is precipitated by the chloride of barium ; but as many organic sub- stances resist the action of nitric acid, the sulphur cannot always in this manner be converted into sulphuric acid. When the organic matter is not volatile, it is mixed with 20 or 25 times its wffight of a mixture of nitre and carbonate of soda, and the mixture is thrown, by small quantities at a time, into a platinum crucible heated to redness by an alcohol-lamp. The alkaline sub- stance is then dissolved in water, supersaturated by chlorohydric acid, and the sulphuric acid precipitated by chloride of barium. If the organic substance is volatile these processes are inapplicable, and the operation is then conducted as follows, by a method which suits all cases:—The organic matter is subjected to combustion with oxide of copper, as in the determination of carbon and hydro- gen, with the exception that the combustion-tube is provided only with the bulb apparatus (fig. 631) containing a solution of caustic potassa. The greater part of the sulphur is converted into sulphuric and sulphurous acid, which dissolve in the potassa, while a portion of the sulphur, nevertheless, remains in the combus- tion-tube in the state of sulphide and sulphate of copper. The tube, after being allowed to cool, is broken, and the pieces of glass and the oxide are throwm into a flask, where they are boiled with a wTeak solution of caustic potassa, which completely removes the sulphur and sulphuric acid. The liquid is filtered, and the potassa in the bulb apparatus is added to the filtrate, which is then boiled, and treated with a current of chlorine, which transforms all the sulphur into sulphuric acid. The solution is supersaturated by chlorohydric acid, and the sulphuric acid precipitated by chloride Fig. 631. DETERMINATION OF PHOSPHORUS. § 1220. When the phosphuretted organic matter is not volatile, it is mixed with 20 or 25 times its weight of a mixture of carbonate of soda and nitre, and the mixture is thrown, by small portions, into a heated platinum crucible, where the phosphorus passes into the phosphate of soda. The alkaline substance is dissolved in water, saturated with chlorohydric acid, and then 1 gramme of pure iron dissolved in aqua regia is added to the solution. Lastly, the ses- quioxide of iron combined with phosphoric acid is precipitated by an excess of ammonia; and by subtracting from the weight of this precipitate the weight of the sesquioxide of iron produced by 1 gm. IT XT n TT r 386 ORGANIC CHEMISTRY. of pure iron, the weight of the phosphoric acid is obtained, whence that of the phosphorus may be deduced. If the substance is volatile, it is first decomposed by carbonate of soda in a combustion-tube, and then dissolved in water, the analysis being completed as in the preceding case. DETERMINATION OF CHLORINE, BROMINE, AND IODINE. § 1221. No organic substances have as yet been found in nature containing chlorine, bromine, or iodine, but a great number of them have been artificially produced in the laboratory. The determina- tion of these elements is very easily made by heating the organic matter in a combustion-tube, in contact with quicklime, obtained by slaking ordinary quicklime, washing it with water to remove chlorides arising from the ashes of the combustible with which the limestone was originally burned, and then heating it to redness in order to expel the water from the hydrated lime. The lime thus prepared is preserved in a ground-stoppered bottle. If the organic substance is solid and not volatile, it is mixed with a certain quantity of quicklime, and the mixture is introduced into the combustion-tube which is to be filled with pure lime; but if the substance is liquid and volatile, it is weighed in the glass bubbles before mentioned, which are dropped, after breaking their point, to the bottom of the tube, which is afterward filled with lime. The decomposition of the substance by heat should be effected with the same precautions as combustion by the oxide of copper. The chlorine, bromine, or iodine remain in the tube in the state of chlo- ride, bromide, or iodide of calcium. At the close of the operation, the lime, together with the fragments of the tube, is dropped into a flask, where it is treated with weak nitric acid until the lime is en- tirely dissolved. The liquid is then filtered, and precipitated by nitrate of silver; the process indicated in § 1131 being followed in order to collect and wash the chloride of silver. The determination of iodine is, however, rather more difficult, as a portion of this substance often passes into the state of iodic acid, which, however, is destroyed by passing a current of sulphurous acid through the liquid at a moderate temperature, after having added nitrate of silver to it. DETERMINATION OF OXYGEN. § 1222. The oxygen contained in organic substances is always determined differentially, as, hitherto, a suitable process of direct determination has not been discovered. It will hence be seen how important it is to ascertain, with the greatest care, the nature of the elements composing the organic substance; for if a single element escapes the experimenter, the analysis is inaccurate, not only on account of the omission of the element which was overlooked, but INTRODUCTION. 387 also because the weight of the elementary substance neglected is computed as oxygen. ESTABLISHMENT OF THE CHEMICAL FORMULA OF AN ORGANIC SUBSTANCE. § 1223. The elementary analysis of an organic substance is not alone sufficient to establish its chemical formula, because it indicates only the ratios which exist between the weight of the elements which compose it; and as an infinite number of formulae, the multiples of each other, will all satisfy the ratios given by analysis, the question is, which of these formulae to choose. By studying the various com- binations which the organic Substance can form with mineral sub- stances, and the new organic compounds to which they give rise when subjected to the various processes of the laboratory, the chemist can generally collect facts from which a formula may be deduced; and it is only when the substance has been studied under all its aspects, and in the case that it forms a great number of com- pounds, that its formula, and, consequently, its chemical equivalent, presents any degree of certainty. The numerous changes which, in latter years, the formulae of organic compounds have undergone will therefore not appear surprising, being occasioned by the dis- covery of new compounds, or new chemical reactions, which deprive the formulae adopted of the character of probability they had ac- quired from the facts previously known. As it is impossible to advance any general rules for the establish- ment of the formula of an organic compound, we shall only cite a few examples, to show the spirit which governs such researches. We shall distinguish three cases : 1st, that in which the organic substance is acid; 2dly, that in which it possesses basic properties; and 3dly, that in which the organic substance is neutral. CASE IN WHICH THE ORGANIC SUBSTANCE IS ACID. § 1224. As the first example, we shall take acetic acid, which contains only carbon, hydrogen, and oxygen. At its maximum point of concentration, acetic acid is a colourless and volatile liquid, which, by combustion with oxide of copper, yields the following composition :* Hydrogen 6.67 Carbon 40.00 Oxygen 53.33 100.00 Dividing the weight of each of these elements by its equivalent, the quotients will necessarily be to each other as the equivalent * In order to render our arguments more simple, we shall always suppose that the results of the direct analyses are scrupulously exact. 388 ORGANIC CHEMISTRY. numbers of the simple elements which enter into the compound, and we thus obtain: For hydrogen = 6.67 “ carbon = 6.67 “ oxygen = 6.67 These quotients being equal, we shall conclude that concen- trated acetic acid contains equal numbers of each of the three elements which compose it, and the most simple formula which can represent the acid is therefore CHO ; while it is evident that the formulae C2II30a, C3H303, C4II404, CsII5Os represent equally the re- sults of the analysis. On the other hand, we have seen that the greater part of the mineral acids, when brought to their maximum of concentration without any essential change in their chemical pro- perties, are compounds of the anhydrous acid with one or several equivalents of water, which can be replaced by a corresponding num- ber of equivalents of a base, and it must therefore be ascertained Avhether this is the case also with acetic acid. Moreover, we have seen, in the case of the mineral acids, that the knowledge of the composition of a salt formed by the acid and a mineral base of which the chemical equivalent had been previously ascertained, fre- quently gives the equivalent of the acid itself, and is sufficient to establish its formula. However, the example of phosphoric acid has shown that the same base frequently forms several salts with the same acid, and that it is not sufficient, to establish the formula of the acid, to determine the composition of one of these salts, be- cause the formula would vary with the salt selected. It therefore becomes necessary to determine the composition of all the salts, either in the crystallized state, or after having dried them as much as possible, always avoiding such a change in their chemical consti- tution that the dried salt, when redissolved in water, will not pro- duce the original salt by crystallization. The study of these va- rious compounds furnishes a clue as to whether the salt should be regarded as monobasic, bibasic, tribasic, &c., and thus give the ele- ments necessary to establish its formula. The same method must be observed in establishing the formulae of organic acids; and we thereupon proceed to apply it to acetic acid. Protoxide of silver is distinguished among mineral bases by the property of forming immediately anhydrous salts, which are in most cases easily obtained in a state of purity, being generally inso- luble, or nearly so ; for which reasons salts of silver are very valu- able in ascertaining the composition of organic acids, and the more so as their analysis can be made with great accuracy. We shall therefore analyze the acetate of silver, for which purpose an accu- rately weighed quantity of the salt is roasted in a platinum cruci- ble, when, the organic matter being destroyed, metallic silver re- INTRODUCTION. 389 mains, which is weighed. The proportion of protoxide of silver to which it corresponds is then calculated, and the result will be that acetate of silver is composed of Oxide of silver 69.45 Acetic acid 30.55 100.00 Admitting that acetic acid is monobasic, that acetate of silver is anhydrous and formed of 1 equivalent of oxide of silver (116.0) and 1 equivalent of acetic acid, the equivalent of acetic acid will be de- duced from the proportion: 69.45: 30.55 : : 116.0 : x whence x = 51.0. Now, there is only one way of forming the number 51.0 with whole numbers of equivalents of hydrogen, carbon, and oxygen, and that is by giving to anhydrous acetic acid the formula C4II303, and consequently, to concentrated acetic acid, the formula C411303 -f IIO, which satisfies the analysis we have given of this acid. We have, in fact, 3 eq. of hydrogen 3.0 4 “ carbon 24.0 3 “ oxygen . 24.0 5L0 It is, moreover, easy to ascertain that such is, in reality, the com- position of the acetic acid contained in the acetate of silver. By burning this salt with oxide of copper, it will be found to contain Oxide of silver 69.45 Hydrogen 1.80 Carbon 14.37 Oxygen 14.38 100.00 Now, the formula AgO,C4II303 gives 1 eq. of oxide of silver 116.0 69.45 3 “ hydrogen 3.0 1.80 4 “ carbon 24.0 14.37 3 “ oxygen 24.0 14.38 167.0 100.00 But acetic acid might possibly be bibasic, and the salt of silver contain 2 equivalents of oxide of silver ; in which case the formula of the salt would be 2Ag0,C8HG06, that of the concentrated acetic acid C8H606+2II0, and the equivalent of anhydrous acetic acid would be 102.0. The acetic acid might be tribasic, and the formula of acetate of silver 3Ag0,C12H909, that of the concentrated acetic 390 ORGANIC CHEMISTRY. acid C12H9Ofl+3HO, and the equivalent of the anhydrous acetic acid might be 153.0. Now, when an acid is bibasic, it forms two series of salts with bases: salts which contain 2 equivalents of base 2RO, and salts containing 1 equivalent of base RO, and 1 equivalent of basic water. If, therefore, acetic acid were bibasic, two series of acetates would be obtained: 1st series 2RO,C8II8O0, 2d series (R0+H0),C8II609; and the salts of the second series could not lose their equivalent of basic water, without a great change in their properties. If the acetic acid were tribasic, it should form three series of salts:— 1st series 3R0,C12II909, 2d “ (2RO -F HO), C12II909, 3d “ (R0+2H0),C13H906; and the salts of the two last series again could not part with their water without an important modification of their properties. In order to decide the question, it is therefore necessary to pre- pare a great number of acetates, dry them as much as possible, without affecting their chemical constitution, that is, in such a man- ner that the dried acetate, redissolved in water, shall reproduce the original salt hy crystallization; and lastly, subject these acetates to analysis. It will thus be found that several of these crystallized acetates contain water ; but this should be considered as their water of crystallization, as it may be driven off by heat, and the dried salt, dissolved in water, reproduces, by crystallization, the original salt. The dried salts will present the composition given by the formulae RO,C4II303, 2RO,C8H0O6, 3R0,C12H909, &c.; and there being consequently no reason for regarding acetic acid as polybasic, it is considered as a monobasic acid, and the formula C4II303 has been adopted as that of the anhydrous acid. § 1225. For the second example in establishing the formula of an organic acid, we shall choose malic acid, which, when crystallized, is composed as follows: Hydrogen 4.48 Carbon 35.82 Oxygen 59.70 100.00 Dividing the preceding numbers by their respective equivalents, there results: INTRODUCTION. 391 For hydrogen hi8 = 4.48 “ carbon = 5.97 “ oxygen ®g“ = 7.46 The quotients follow the ratios of the numbers 3:4: 5; and the most simple formula adapted to crystallized malic acid is therefore C4H305, Avhile the true formula may be one of the multiples Ci3H9015, CjgHjgOgjj, etc., etc. The analysis of malate of silver shows that this salt contains : Oxide of silver 66.67 Malic acid 33.33 100.00 This salt does not give off water before decomposing, which leads to the supposition that it is anhydrous; and if it be regarded as formed of 1 equivalent of oxide of silver and 1 equivalent of malic acid, the equivalent of malic acid will therefore be deduced from the proportion: 66.67 : 33.33 : : 116.0 : x, whence x=58 The combustion of the silver salt with oxide of copper gives for its composition: Hydrogen 1.15 Carbon 13.79 Oxygen 18.39 Oxide of silver . 66.67 100.00 which exactly corresponds to that given by the formula Ag0,C4H304, as may be readily seen : 2 eq. of hydrogen 2.01 1.15 4 “ carbon 24.0 V 58.0 13.79 4 “ oxygen 32.0 J 18.39 1 “ oxide of silver... 116.0 66.67 174.0 100.00 The formula of crystallized malic acid will therefore be C4H304 -f HO; but it remains to be seen whether the acid is monobasic, in which case the formula of the crystallized acid would be C4H304+ HO, and that of malate of silver Ag0,C4H304; Or, whether it is bibasic, which would give to malate of silver the formula 2Ag0,C8H408, and to the crystallized acid the formula C8H408+2H0; Or lastly, whether it is tribasic, in which case the formula of malate of silver would be 3Ag0,C13H6012, and that of the crystal- lized acid C13Ha013-f 3HO. 392 ORGANIC CHEMISTRY. In order to decide the question, other salts formed by malic acid must be analyzed. Now, two malates of lime are known: The formula of the first in the crystallized state is “ second “ “ Ca0,C4H204. The first salt loses 6IIO by the action of heat, without change; for, when dissolved in water, it reproduces the original salt by crys- tallization; and the formula of the dried salt is therefore CaO,C8 IIs09, which may be written Ca0,2(C4lI204)-f HO, in which case it is considered as a bimalate of lime containing 1 eq. of water of crystallization. But as this water cannot be driven off without injury to the salt, it must be regarded as basic water, and the formula of the malates of lime must be written, 1st malate 2Ca0,CgII408. 2d malate (Ca0 + II0),C8H408. In this case, malic acid is considered as a bibasic acid. An examination of the other malates leads to the same conclusion. Thus, oxide of zinc forms two malates, the composition of which, in the crystallized state, is represented by the following formulae : 1st malate Zn0,C4II,07, 2d malate Zn0,C8II8012, which, when subjected to the action of heat, lose a portion of their water without change, and become, The 1st Zn0,C4H204. The 2d Zn0,C8II509. If they be further heated, they again lose water, but are altered. The formulae of dried malates of zinc become very simple, and similar to those of malates of lime, if the malic acid be regarded as bibasic, in which case they are, 2Zn0,C8H408. (Zn0+II0),C8H408. Again, a malate of ammonia is known which crystallizes readily in beautiful crystals, and shows the formula (NH3,H0),C8II408+H0. But as this salt does not lose water by heat before attaining a temperature at which it is completely altered, the water it contains is therefore basic, and its formula should be written (NH3HO+HO) C.H40.. . . . All these considerations must lead us to regard malic acid as a bibasic acid, forming two series of salts, of which the formulae are 2R0,C8H408 and (R0 + H0),C8H408. §1226. An argument of the same nature, founded on the composition of the various scries of salts which the organic acid can form with the INTRODUCTION. 393 same base, after the salts have been dried as far as their chemical constitution will permit, will decide if it be proper to regard this acid as a tribasic acid, in which case three series of salts will in general be obtained, which may be represented by the following formulae, the symbol A designating the equivalent of the tribasic acid: 3RO,A, (2RO+HO),A, (RO-f2HO),A. The crystallized salts may contain, in addition, water of crystal- lization, which will be recognised by the fact that in most cases it can be driven off by heat, without altering the constitution of the salt. DETERMINATION OF THE PROPORTION OF BASE WHICH EXISTS IN COMBINATION WITH AN ORGANIC ACID. § 1227. In order to establish with any degree of certainty the equivalent of an organic acid, it is necessary, as has been shown, to analyze a great number, of the salts which it forms with mineral bases; and it is consequently useful to dwell for a short time on the processes employed by chemists for this purpose. The proportion of base which exists in a salt formed by an organic acid is almost always determined by calcining the salt in the air, when the mineral base remains, either in the metallic state after the decomposition by heat, or in a state of superior oxidation, when it absorbs oxygen from the air; or lastly, in the state of carbonate, when the salt is not decomposed by the degree of heat at which the incineration took place. If the organic acid contains sulphur or phos- phorus, the base may remain partly in the state of sulphate or phosphate ; and if it contains chlorine, bromine, or iodine, a portion or the whole of the base may be converted into chloride, bromide, or iodide. The salts formed by the organic acids with the alkalies, leave after calcination an alkaline carbonate; but the base is never determined in this state, because alkaline carbonates attract too readily the moisture of the air. They are converted into sulphates by pouring into the crucible in which the incineration has been effected a weak solution of sulphuric acid, taking care that the effervescence produced does not project any of the substance out of the crucible. It is evaporated to dryness; and lastly, the crucible is heated to a strong red-heat, in order to decompose the bisulphate which has formed, when the weight of the base is deduced from that of the sulphate. When the organic salt contains baryta or strontia, the base remains in the state of carbonate, and may be weighed as such; and if it contains lime, the base still remains in the state of carbon- ate, if the incineration has been effected at a low temperature ; but if the calcination has required a red-heat, the greater portion of the base passes into the state of quicklime. The base may still in this 394 ORGANIC CHEMISTRY. case be determined as carbonate, if the precaution is taken to moisten the matter, after roasting, with a solution of carbonate of ammonia, which is then evaporated at a gentle heat. It is better to weigh the lime in the state of sulphate, to which effect the residue is moistened after incineration with sulphuric acid, and, after having driven off the excess of acid by heat, the crucible is heated to red- ness. The determination of magnesia in the state of sulphate should be performed in the same manner. If the base combined with the organic acid be protoxide or ses- quioxide of iron, the salt is roasted in the air; and in order to be sure that the residue is composed only of sesquioxide of iron, it is moistened with nitric acid, and again calcined; a similar process being applicable to salts of copper, in which case protoxide of cop- per CuO remains. Zinc, combined with an organic acid, is also determined in the state of oxide ZnO; but the roasting must be commenced at the lowest temperature possible, in order not to pro- duce metallic zinc, a portion of which might be lost in the state of vapour; and the roasted matter is moistened with a small quantity of nitric acid, and calcined to redness. The determination of manganese combined with an organic acid presents some difficulties, because the composition of the oxide which remains after the calcination is never exactly known. The salt being first calcined in a small platinum boat, in order to destroy the organic matter, the boat is introduced into a porcelain tube heated to redness, and traversed by a current of hydrogen gas, which is maintained until the tube is completely cooled; when the boat, which then contains non-pyrophoric protoxide of manganese, is removed. As the compounds of the organic acids with cobalt and nickel leave oxides after incineration, the composition of which is always uncertain, it is best to roast the salt in a platinum boat, and then heat it in a porcelain tube in a current of hydrogen, when the pla- tinum contains the reduced metal, which is not pyrophoric if the calcination has been effected at a sufficiently high temperature. The incineration of salts formed by the organic acids with oxides of chrome leaves pure sesquioxide of chrome, which can be imme- diately weighed. "By incinerating the salts formed by protoxide of lead with organic acids, the metal frequently remains in the state of protoxide, although a portion of the oxide of lead is also frequently reduced to the metallic state, so that it is better never to make these incine- rations in platinum vessels, because they might be greatly injured. They are performed in porcelain capsules heated by an alcohol- lamp, so as not to attain the point of fusion of oxide of lead, which in the fused state would attack the glazing of the porcelain. After incineration, concentrated nitric acid is poured into the saucer, which disengages reddish vapours if the substance contains metallic INTRODUCTION. 395 lead. The acid is gently evaporated, and the residue, which is composed of pure protoxide of lead, is calcined at a dull red- heat. The capsule may also he weighed after incineration, and acetic acid afterward poured into it, which dissolves the oxide of lead, and separates the metallic lead which remains in the form of small globules. The globules are washed several times, by decant- ation, in the capsule, which is then dried at a gentle heat; the latter is then weighed a second time, when the difference gives the weight of oxide of lead formed in the roasted matter. By weigh- ing the capsule a third time, and subtracting this weight from that, obtained by the second weighing, the quantity of lead reduced is found, which is to be converted into oxide, by calculation. Lastly, the oxide of lead may be determined in the state of sulphate, in which case, the incinerated matter is moistened Avith nitric acid, which is evaporated, and then with sulphuric acid, which transforms the nitrate into a sulphate. The excess of sulphuric acid being evaporated, the sulphate is calcined to redness. Oxide of bismuth is determined in the state of oxide BiOs, and protoxide of tin in the state of stannic acid Sn03, the operation being conducted as in the case of oxide of lead; that is, the sub- stance is incinerated in a porcelain capsule, and the residue, after being moistened with nitric acid, is calcined after the evaporation of the acid. The exact determination of oxide of antimony is very difficult. The best method consists in roasting the salt in a porcelain crucible, and, when the organic matter is burned, to cover the crucible with a lid having a hole in the centre, through which is passed the end of a disengaging-tube which conveys dry hydrogen into the crucible; when by heating the latter to redness, the oxide of antimony is re- duced to the metallic state. The current of hydrogen is maintained until the crucible is completely cooled, after which the metallic an- timony is weighed. The salts formed by the protoxide and sesquioxide of uranium leave, after roasting, an oxide of uranium, the composition of which is uncertain; but if the residue be calcined, at a strong red-heat, by placing the platinum crucible which contains it in an earthen crucible heated in a charcoal fire, the oxide 2U0,U203 (§ 1025) remains, although it is better to restore, by means of hydrogen, the oxide of uranium to the state of protoxide, by operating as was stated for manganese. The quantity of oxide of silver found in combination with an organic acid may be very accurately ascertained by simple incine- ration, which leaves the silver in the metallic state. If the salt of silver is soluble, it may be dissolved in water and the silver precipi- tated in the state of chloride, in which case a standard solution of common salt may also be used, and the process explained in § 1144 adopted. 396 ORGANIC CHEMISTRY. Incineration also gives-exactly the platinum contained in the salts formed by organic acids, when metallic platinum remains, from which the quantity of oxide may be deduced by calculation. Salts formed by the organic acids with oxides of mercury are analyzed by the general process described § 1107. The ammonia combined with an organic acid is generally inferred from the quantity of nitrogen yielded by the ammoniacal salt in its combustion with oxide of copper, (§§ 1217 and 1218,) although this base may be directly determined in the state of double chloride of pla- tinum and ammonia, as in the case of ammoniacal salts formed by the mineral acids; for which purpose the ammoniacal salt is dissolved in a small quantity of water, and a slight excess of bichloride of platinum is added, when, after evaporating to dryness at a gentle temperature, and washing the residue with a mixture of alcohol and ether, the double chloride of platinum and ammonia is obtained isolated. Lastly, the ammoniacal salt may be destroyed by sodic lime at a red-heat, the ammonia collected in an acid solution, and the base determined by one of the two methods described in §§ 1217 and 1218. § 1228. The processes just described are applicable with absolute exactness only when the organic acid contains carbon, hydrogen, oxygen, and nitrogen alone, and their results would be frequently inaccurate if the acid contained, in addition, sulphur, phosphorus, or chlorine. If the acid contains sulphur, the processes described may be em- ployed whenever the sulphate of the metallic oxide is easily decom- posed by heat, and the metallic sulphide is quickly changed into oxide by roasting; but in every other case some of the processes spoken of would give inexact results. When the base of the salt is an alkaline or alkalino-earthy oxide, or oxide of lead, it is sufficient to heat the incinerated substance with sulphuric acid, when the base remains in the state of sulphate, which is weighed. If the oxide forms a sulphate readily decomposable at a red-heat, the residue after roasting is calcined at this temperature, after having been treated with a small quantity of nitric acid, to prevent the presence of a metallic sulphide, which might injure the platinum crucible. In all cases it is prudent to moisten the substance, after calcina- tion, with a small quantity of carbonate of ammonia, evaporate and recalcine it, by which means the last traces of sulphuric acid are more easily driven off. If the organic acid contains phosphorus, all the processes de- scribed are faulty, and, in order to determine the oxide, the processes by the humid way, described under the head of each metal, must be adopted. Lastly, if the organic acid contains chlorine, bromine, or iodine, it is often necessary to modify the ordinary processes. When the base combined with the organic acid is an alkaline or alkalino-earthy INTRODUCTION. 397 oxide, the residue after incineration is moistened with sulphuric acid, which drives off the chlorine, bromine, or iodine, after which the excess of acid is evaporated and the substance calcined, when the base remains in the state of sulphate. This process does not always succeed easily if the base he oxide of lead, in which case it must be several times evaporated with sulphuric acid, or better still, with a small quantity of a concentrated solution cff sulphate of ammonia. The majority of the metallic chlorides, bromides, and iodides are so volatile at a red-heat that the calcination, in the air, of the or- ganic salt containing the chlorine should be avoided; and, in order to determine the oxide, recourse must then he had to the process of determining by the humid way, described under each metal. The presence of the organic acid sometimes, however, prevents the reactions which the metallic oxide presents when combined with mineral acids, in which case the organic acid must be destroyed, either by concentrated nitric acid, when this is possible, or by mix- ing it with 15 or 20 times its weight of a mixture of carbonate of soda and nitre, thrown, by small quantities at a time, into a silver crucible, heated over an alcohol-lamp ; when the metallic oxide is found in the alkaline residue. CASE IN WHICH THE ORGANIC SUBSTANCE POSSESSES BASIC PROPERTIES. § 1229. All the basic organic substances, at present known, con- tain nitrogen. In order to ascertain their equivalent, not only the isolated bases, hut also a certain number of salts which these bases form with mineral acids, must therefore be analyzed, preferring those which are most readily obtained in the crystallized form, and which can be most accurately analyzed. We shall take strychnine as an example. The elementary analysis of strychnine yields the following results: Hydrogen 6.58 Carbon 75.45 Nitrogen 8.38 Oxygen 9.59 100.00 Dividing the preceding numbers by the corresponding equivalent of each simple substance, there results : For hydrogen = 6.58 “ carbon = 12.57 “ nitrogen = 0.60 “ oxygen = 1.20 The most simple ratios which exist between these quotients are as the numbers 11 : 21: 1: 2. The most simple formula of strych- 398 ORGANIC CHEMISTRY. nine is, therefore, C21IInN02; but as the multiple of the formulae C42H22N204, C63H33N306, etc. etc. satisfy equally the results of the analysis, the salts of strychnine must also be analyzed. The organic alkalies combine either with hydracids, without de- composing them, or with oxacids; in which latter case they always acquire the elements of 1 equiv. of water, which cannot be driven oft’ without injury to the salt; and, in this respect, the organic bases behave like ammonia, in their compounds with hydracids and oxacids. We shall first analyze the chlorohvdrate of strychnine, after hav- ing dried it at 212°, in a current of dry air, because the crystallized salt contains water of crystallization. The elementary analysis will yield for its composition : Hydrogen 6.21 Carbon 68.02 Nitrogen 7.56 Oxygen 8.64 Chlorine 9.57 100.00 The determination, for itself, of the chlorine is sufficient to esta- blish the equivalent of strychnine, admitting that the salt is consti- tuted like the clilorohydrate of ammonia; that is, that its formula is + + Sty,HCl, the symbol Sty representing the equivalent of strychnine. In fact, 9.57 of chlorine correspond to 9.841 of chlorohydric acid, and, consequently, 100 of chlorohydrate of strychnine contain 9.841 of chlorohydric acid, and 90.159 of strychnine ; whence the equiva- lent of strychnine will he obtained by the proportion, 9.841 : 90.159 : : 36.5 : x, whence 2=334. Now this equivalent corresponds to the formula C4aH2aN304, which gives 22 eq. of hydrogen 22.0 42 “ carbon 252.0 2 nitrogen 28.0 4 “ oxygen 32.0 334.0 The formula of free strychnine is therefore C42II22N204, and that of the dried chlorohydrate C42H22N204,IIC1. The crystallized base is anhydrous. It is easy to ascertain, by calculating the composi- tion of the chlorohydrate of strychnine in hundredths, from the formula just given, that there result, for each element, numbers identical with those above transcribed, and which we have supposed to be obtained by direct analysis. The formula of strychnine may be verified by the analysis of INTRODUCTION. 399 other salts of the base, as, for example, that of the sulphate. The formula of crystallized sulphate of strychnine, dried at 266°, is thus found to be (C42H22N204,H0),S03. § 1230. The quantity of mineral acid which exists in combina- tion with an organic alkali is determined by the same means as those used to determine the acid in a mineral salt; but the analysis demands the greatest care, because the smallest error may seriously affect the generally very complicated formula of the organic alkali. In -order to determine the quantity of chlorohydric acid which exists in chlorohydrate of strychnine, the chlorohydric acid is first deter- mined by precipitating it’in the state of chloride of silver, in the manner stated in § 1131. The weight obtained is generally too small. Admitting, for the moment, the weight obtained to be exact, from this weight may be calculated the quantity of pure silver which would exactly precipitate the chlorohydric acid con- tained in 5 grammes of chlorohydrate of strychnine. The silver is dissolved in nitric acid, and the liquid poured into a solution of 5 grammes of chlorohydrate of strychnine; after which the solu- tion, when clear, is filtered, and, by the assistance of a decimal solution of silver, the quantity of chlorohydric acid which still remains in the liquid is determined, (§ 1144.) Salts formed by the other mineral acids can be analyzed by analogous processes. The compounds which the chlorohydrates of organic bases form with bichloride of platinum are frequently subjected to analysis, by being precipitated in the form of small yellow granular crystals. The composition of the double chloride of platinum and strychnine is analogous to that of the double chloride of platinum and am- monia, and its formula is (C42H33N204)HCl-|-PtCl3. By roast- ing this and similar compounds in the air, the organic matter is destroyed and the chlorine disengaged, while the platinum remains ; which process is well adapted to the determination of the equiva- lent of the organic base, and is capable of great exactness, on account of the great weight of the equivalent of platinum. CASE IN WHICH THE ORGANIC SUBSTANCE IS NEITHER ACID NOR BASIC. § 1231. When the simple organic substance possesses neither acid nor basic properties, there is no general rule for establishing its equivalent and its formula; and chemists are then guided by the composition of the products of combination, or decomposition, to which the substance gives rise under the influence of various che- mical agents. They choose, among all the equivalent formulae, that which expresses most simply the whole of the reactions, fre- quently giving preference to the formula which establishes an analogy of constitution with other substances presenting similar reactions. We shall be satisfied with two examples, which we shall select from the most simple. 400 ORGANIC CHEMISTRY. The method of preparing bicarburetted hydrogen or olefiant gas has already been shown, (§ 266.) The most simple formula which satisfies the direct analysis of this gas is CH, and we will proceed to show why the formula C4II4 has been assigned to it. By mixing in a large bell-glass equal volumes of olefiant gas and chlorine, a liquid substance condenses, of which the most sim- ple formula is C2H2C1, and which, by treatment with an alcoholic solution of caustic potassa, loses one-half of its chlorine, and one- fourth of its hydrogen, in the state of chlorohydric acid, which combines with the potassa (KO + IIC]=KCl + lIO); while at the same time a very volatile substance is formed, of which the most simple formula is C4H3C1. It is but natural to regard the chlorine and hydrogen, which were separated in the state of chlorohydric acid, as united in the compound C2H2C1, differently from the other portions of chlorine and hydrogen which remain, and which enter into the constitution of the compound C4tI3Cl; but chemists have gone still further in admitting that the chlorine and hydrogen removed by the action of the potassa existed really in the state of chlorohydric acid in the substance C2II2C1; and, in order to avoid fractional numbers of equivalents, they replace the formula C2II2C1 by the multiple formula C4II4C13, which they write C4H3C1,HC1. If the formula C4H4 is assigned to olefiant gas, the reaction of chlorine on this substance is expressed in the most simple manner possible, by the following equation: C4H4+2Cl=C4HaCl,HCl. 9 Now, if chlorine is made to act on the substance C4H3C1, or on the compound C4II3C1,HC1, a new substance is formed, of which the most simple formula is C4H3C13, which, Avhen treated by an alcoholic solution of potassa, gives off 1 equiv. of hydrogen and 1 equiv. of chlorine. We shall regard these equivalents as existing in the state of chlorohydric acid in the substance C4H3C13, as we have done for the substance C4II4C12, and shall write the formula of the new compound C4H2C13,HC1. The reactions by which it is derived either from the substance C4II3C1, or from the compound C4H3C1,HC1, or lastly, from the olefiant gas C4II4, are of the most simple cha- racter. C4H,C1 +2C1=C4H9C19,HC1. C4H3C1,HC1+2C1=C4H3C12,HC1+HC1. C4II4 +4C1=C4H9C19,HC1+HC1. In the last two cases, 1 equiv. of chlorohydric acid is set free. The product C4II3C12, or the compound C4II3CL,HC1, being sub- mitted, in their turn, to the action of chlorine, yields a new pro- duct, of which the most simple formula is C3IIC12. If we write this formula C4II2C14, and if we give it the form C4HC13,HC1, the reactions which produce it by the action of chlorine on the various INTRODUCTION. 401 substances C4H3Cla, C4H3Cla,HCl, C4H3C1, C4H3C1,HC1, and C4II4, are the following: C4HaCl3 +2C1=C4HC18,HC1. C4H3C13,IIC1+2C1=C4HC13,HC1+ HC1. C4H3C1 +4C1=C4HC13,HC1+ HC1. C4HsC1, HC1+4C1=C4HC13,HC1+2HC1. C4H4 +6C1=C4HC13,HC1+2HC1. The compound C4HCla,HCl is also decomposed by contact with the alcoholic solution of potassa, but the substance C4HC13 has not yet been obtained in a state of purity, and seems to be altered itself by the alcoholic solution of potassa. It cannot the less be admitted that this substance pre-exists in the compound C4H3C13, for the very reason that this establishes perfect uniformity in all the derived compounds—a uniformity which, moreover, has hither- to been destroyed by no other reaction. Lastly, the substance C4HC13HC1, when subjected to the action of chlorine, assisted by solar light, parts with the whole of its hydrogen, which is disengaged in the state of chlorohydric acid, while a crystalline compound, which is a simple chloride of carbon, the most simple formula of which is C3C13, is formed. Various chemical reactions show that one of the equivalents of chlorine is not as deeply interested in the compound as the other two. Removing, for example, this equivalent by an alcoholic solu- tion of monosulpliide of potassium, a new chloride of carbon, of which the most simple formula is CC1, will separate, to which, for the moment, we will give the formula C3C13, in which case the first could be written C3C13,C1. But it would be more pro- per to write their formulae C4C14 and C4C14,C13, because, with these last formulae, the reactions which give rise to the chloride of carbon C4C14,C13, by the action of chlorine on all the successive compounds of which we have previously established the formulae, are of the most simple kind : C4H3C13,HC1 + 401=C4C14C13,+2 H Cl. C4H3C13 + 601=C4C14C13,+2HC1. C4H3C13,HC1 + 6 Cl=C4C14C13, -f 3 H Cl. C4H3C1 + 8C1=C4C14C13,+3HC1. C4H3C1,HC1 + 8Cl=C4Cl4Cl3,-f4HCl. C4H4 -f 10Cl=C4Cl4Cl3,-f 4HC1. We will remark, in addition, that olefiant gas C4H4, and all the chlorinated products C4H3C1, C4H3C13, C4HC13, C4C13 derived from it, present this remarkable property, that they may be regarded as one and a single molecular grouping C4H4, modified only by the successive substitution of an equal number of equivalents of chlo- rine for its equivalents of hydrogen. This fact is again corrobo- 402 rated by the following: If the substances are operated on at a tem- perature sufficiently high to allow all of them to exist in the gaseous state, the formulae C4H4, C4H3C1, C4Id2Cl2, C4HC13, C4C13 would re- present the same volume of these various gases ; each of these for- mulae corresponding, in fact, to 4 volumes of the vapour of the body to which it relates. The comparisons and similarity of composition just pointed out among all these substances would disappear, if for each of them equivalent formulae more simple than those we have admitted were adopted, although they would still exist if equivalent formulae were admitted, multiples of those just established; but there is no reason whatever for thus complicating the formulae. § 1232. For the second example we shall choose alcohol, which liquid is composed as follows: Hydrogen 13.05 Carbon 52.17 Oxygen „ 34.78 100.00 Dividing each of these numbers by the equivalent of the sub- stance to which it belongs, the folio-wing quotients result: For hydrogen = 13.05 “ carbon .. = 8.69 “ oxygen wr = 4.35 The ratio of these quotients to each other being that of the num- bers 3 : 2:1, the most simple formula which can be given to alcohol is C2II30, while all its multiple formulae represent equally well the results of the analysis. Alcohol is a substance possessing neither acid nor basic proper- ties ; and as its equivalent and chemical formula cannot therefore be established by the methods described for the acids and bases, resort must be had to the chemical reactions which ensue when al- cohol is subjected to the various agents in the laboratory, and from these the formula which explains them all in the simplest manner must be deduced. By mixing together equal parts of alcohol and sulphuric acid, and exposing the mixture for several hours to a temperature of 120° or 140°, a compound acid is obtained containing sulphuric acid and some of the elements of alcohol. This acid, called sulphovinic, forms readily crystallizable salts with bases, and, as it is an acid, its equivalents and consequently its formula, can be determined by the methods explained, (§1224.) The result is then found that the formula of anhydrous sulphovinic acid, that is, of the acid as it exists in salts which contain no water of crystallization, is C4H,0, 2SOs; and if the formula CsH30 is assigned to alcohol, the reaction ORGANIC CHEMISTRY. INTRODUCTION. 403 which produces sulphovinic acid is not explained in a simple man- ner, as it is then supposed that the reaction takes place between 2 equivalents of sulphuric acid, and 2 equivalents of alcohol C„1I30, one of which does not behave in the same manner as the other. If, on the contrary, the equivalent formula C4HB02 be adopted for al- cohol, the reaction is of the most simple kind: 1 equivalent of al- cohol gives off 1 equivalent of hydrogen and 1 equivalent of oxygen in the state of water, while the product C4II50, remaining after this separation, combines with 2 equivalents of sulphuric acid to form sulphovinic acid C4Hs0,2S03, which retains in combination the equivalent of water separated, to form hydrated sulphovinic acid C4H50,2S0s+H0. By distilling the mixture of alcohol and sulphuric acid in a retort, a very volatile liquid, called ether, passes over, the most simple for- mula of which is C4II50. Now, it will be seen that if the formula C4H602 for alcohol be adopted, ether is derived from it simply by the abstraction of 1 equivalent of water; and the facility with which alcohol loses 1 equivalent of hydrogen and 1 of oxygen, which separate in the state of water, has led many chemists to ad- mit the existence in this body of 1 equivalent of water ready formed, and to, consequently, regard alcohol as a combination of 1 equivalent of ether and 1 of water, and to write its formula C4H50,H0.* But is it more suitable to adopt for ether its most simple formula C4HsO or an equivalent multiple formula ? This question must be answered by the chemical reactions of the sub- stance. Now, ether combines with the mineral acids, and the re- sulting compounds, called compound ethers, should not be considered as salts, because they have none of their characteristic properties, but rather as definite compounds, of which the composition should be simply expressed by the assistance of the formula adopted for ether. Now, there is known A nitric ether C4H.O,NOs, A carbonic C4H50,C0a, An oxalic “ C4H50,C203, An acetic “ C4H50,C4II303 : the formula C4H50 adopted for ether, gives to all these compounds the most simple formulae possible. Ether, subjected to an oxidizing agency, gives off its water and is converted into a new substance, called aldehyde, of which the most simple formula is C2H20, but which is written C4H402, be- * Since the original was written, Mr. Frankland has succeeded in isolating, by decomposing iodic ether, or iodide of ethyl, C4H5I, with zinc, the until then hypo- thetic substance ethyl, which thus must be considered as a compound organic radical, corresponding to a metal in mineral chemistry, and of which ether is the oxide, while alcohol then necessarily must be regarded as its hydrate.— W. L. F. 404 ORGANIC CHEMISTRY. cause the reaction which produces it is then expressed in the most simple manner by the equation C4Hs0+20=C4II402+H 0 : the molecular constitution of aldehyde is therefore the same as that of ether, there being simply a substitution of 1 equivalent of oxygen for 1 equivalent of hydrogen. The oxidizing agency being still continued, aldehyde is converted into acetic acid, the formula of which, from its acid properties, may be determined according to § 1224. It has been shown that an- hydrous acetic acid, as it exists in salts, is C4II303. Now, the new reaction is again expressed in the most simple manner, by admitting the formula C4H50 for ether, and the formula C4H402 for aldehyde ; and acetic acid is in fact derived from aldehyde by a reaction simi- lar to that which transforms ether into aldehyde: C4H402+20=C4H303-f HO; the equivalent of water formed remaining combined with the acetic acid, and giving to the latter its maximum of concentration. In acetic acid, as in aldehyde, the molecular constitution of ether is preserved, a new equivalent of hydrogen being merely replaced by 1 equivalent of oxygen. Alcohol, subjected to oxidizing agencies, furnishes the same pro- ducts as ether; that is, aldehyde at first, and subsequently acetic acid, which is one of the reasons which have confirmed chemists in regarding alcohol as a hydrate of ether. Lastly, ether, when subjected to the action of dry chlorine, and exposed to solar light, yields a series of products, of which the most simple formulae are C4II4C10, C4H3ClaO, C4CLO, which sub- stances are derived from ether C4II50, by reactions resembling those which take place in the action of oxygen, and which are ex- pressed by the equations: C4IIS 0+2C1=C4H4C10+HC1. C4Hs0+4C1=C4H3C120+2HC1. C4H{0+10C1=C4C140+5HC1. The new substances C4H4C10, C4H3C120, C4C150 present the same molecular constitution as ether C4ILO; 1, 2, or 5 equivalents of hydrogen of the original ether being replaced by 1, 2, or 5 of chlorine. Numerous additional examples of products derived from ether under the influence of various chemical agents might be given, and in all cases it would be found that the reactions explain them- selves in the most simple and natural manner, by adopting the formula C4Hs0 for ether, and, as none of the explanations would become more simple if an equivalent multiple formula were substi- INTRODUCTION. 405 tuted for the one adopted, the formula C4II50 for ether must he considered as established, and consequently the formula C4II802 or C.H.O,HO for alcohol. These formulse being once admitted, those of all the products of ether and alcohol, which have just been men- tioned, are equally established. § 1233. In the preceding remarks, the results of the chemical analyses have been supposed to he absolutely accurate, which, how- ever, is rarely the case, as the most carefully conducted analysis is liable to trifling errors, which frequently leave the chemist uncertain as to the formula he should adopt for the substance analyzed, when the latter contains a great number of equivalents of its elementary principles, and whep, consequently, its equivalent is very high. This uncertainty can he removed only by a new analysis, more carefully conducted, operating on larger quantities of matter, and directing the operations chiefly with the intention of ascertaining exactly the element of which the number of equivalents is most uncertain. It is also frequently sought to determine with most exactness the atomic weight of the compound, by using the method of successive approximation, of which an example has been given (§ 1230) in the determination of the chlorine contained in the clilo- rohydrate of strychnine. The chemist is also guided by the probable analogies of constitu- tion which should exist between the substances of which he seeks the formula, and other substances presenting notorious resemblances in their chemical properties with the first, and the formulae of which are already established. We shall observe, subsequently, that all organic compounds, of which the composition and formula are known with some degree of certainty (and the number of them is quite large) contain, in their equivalent, an even number of equivalents of carbon. This fact is certainly not accidental, and renders it very probable that for the equivalent of carbon, a number double of that which has been hitherto admitted must be adopted. The number 6.0 has been adopted as the equivalent of carbon, on account of the compounds which this substance forms with oxygen, as these compounds are thus represented: Oxide of carbon by the formula CO. Carbonic acid “ C03. Oxalic acid u C303. Oxalic acid alone, of these compounds, contains an even number of equivalents of carbon, and consequently belongs to the category of other organic substances. No means is known of fixing directly the value of the equivalent of oxide of carbon, because this substance is neutral and forms no well-marked compound; and the formula C303 might therefore, without any inconvenience, be adopted for 406 ORGANIC CHEMISTRY. oxide of carbon. The equivalent of carbonic acid is deduced from the analysis of the carbonates. Now, twm series of carbonates are known, which, with the equivalent of carbon now adopted, are written R0,C02, I10,2C02. But it has not yet been decided with certainty which of this series should be considered as containing the neutral carbonates. If, contrary to what the majority of chemists have admitted, we were to regard the second series as that of the neutral carbonates, we must write the formula of the two series 2R0,C304, R0,C304; and carbonic acid would then contain also an even number of equivalents of carbon. Be this as it may, the chemist will necessarily regard the general observation we have just made, and g,void adopting a formula which contains an uneven number of equivalents of carbon. DETERMINATION OF THE DENSITY OF THE VAPOURS OF VOLATILE SUBSTANCES. § 1234. It has already been shown, in the preceding parts of this work, that in the combinations of elementary gases there always exists a very sensible ratio between the volumes of these gases; and that when the resulting compound itself is gaseous, a very simple ratio between its volume and the sum of the volumes of the component gases is observed. This law applies not only to substances which are gaseous at the ordinary temperature, but probably to all vola- tile substances, if they are observed at a temperature sufficiently high for them to exist in the state of vapour, and if this temperature is sufficiently above the point of liquefaction to enable the vapour to follow, at least by approximation, the laws of expansion and elasticity admitted for the permanent gases. It has been shown, moreover, that in the compound gases to which similar chemical formulae are assigned, the equivalents are represented same number of volumes of vapour. Thus chlorohydric, bromohydric, and iodohydric gas, resulting from the combination of 2 volumes of hydrogen with 2 volumes of gaseous chlorine, bromine, and iodine, have, as their equivalents in volume, 4 volumes of gas. The equi- valents which we shall be led to adopt for the numerous carburetted hydrogens, if wTe are guided by considerations analogous to those advanced in § 1231 for olefiant gas, are all represented by 4 volumes of vapour. The equivalent of gaseous alcohol is represented by 4 volumes, if we adopt for its formula C4II602. The chemical reactions of several organic substances are perfectly analogous to those of alcohol; and the formulae which we are led to adopt for them, from considerations analogous to those indicated, (§ 1232,) fix their gaseous equivalents at 4 volumes. Ether, to which we assign the formula C4Hs0, is represented by 2 volumes of vapour, and consequently the organic substances, the chemical reactions of which are analogous to ether, are also repre- sented by two volumes of vapour. INTRODUCTION. 407 It will from this be understood that the density of the vapours of volatile compounds furnishes, in a great number of cases, data valuable in guiding the choice of their chemical formulae, especially when such compounds have been hut little studied, and hut a small number of their chemical reactions (and these not very well marked) are known. Some volatile substances yield vapours which obey the laws of permanent gases, starting at temperatures raised only 70° or 100° above their boiling point; while other vapours, on the contrary, only obey these laws approximately, when they are heated 360° or 450° above this point. Now, as the laws which govern the com- binations of gaseous bodies exist rigorously, only under circum- stances in which the gases follow the law of Mariotte in their elas- ticities, and present equal coefficients of expansion, it will be necessary, in determining the density of a vapour, compared with that of atmospheric air under the same circumstances of temperature and pressure, to ascertain if the density found at one temperature remains the same at temperatures which differ less than 90° or 108°; and it is only when this condition is satisfied that the vapour can be admitted to belong to the permanent gases, and that the formula of the substance may be established on the density of its vapour. We will adduce a few examples in support of the truth of what has just been said. Monohydrated acetic acid C4H303+H0 boils at 240° under the ordinary pressure of the atmosphere ; and the density of its vapour, compared with atmospheric air under the same circumstances of pressure and temperature, have been found at 257° 3.180 266 3.105 284 2.907 302 2.727 320 2.604 338 2.480 356 2.438 374 2.378 392° 2.248 428 2.132 464 2.090 518 2.088 590 2.085 608 2.083 637 2.083 It will be seen that the density of this vapour diminishes con- tinually to the temperature of 464°, which is 216° above the boiling point of the substance. But it will also be seen that from 464° to 637° the density does not sensibly vary : this constant value of the density must therefore be adopted when the vapour of acetic acid is compared with the permanent gases. In a great number of other volatile substances, the density of the vapour attains its constant value at a few degrees above its boiling point: thus for alcohol, which boils at 173.3°, the following densi- ties of vapour have been found : 408 ORGANIC CHEMISTRY. 190.4° 1.725 208.4 1.649 230 1.610 257 1.603 302° 1.604 347 1.607 392 1.602 From 230°, which is only about 56° above the boiling point, the vapour of alcohol preserves an almost constant density. § 1235. The density of a vapour is the ratio between the weight of a certain volume of this vapour and that of the same volume of atmospheric air, under the same circumstances of temperature and pressure. The weight of a given volume Y of atmospheric air, at a known temperature and under a known pressure, is easily deter- mined. If the temperature is expressed by T, and the pressure by H0, the weight P of the volume Y of air will be, supposing Y to represent the volume expressed in cubic centimetres, P = 0.0012932 gm. V. . fe. The elastic force H0 is supposed to be represented by the height of the column of mercury at 32°, which will balance it, expressed in millimetres, while T represents the centigrade temperature of an air thermometer. To obtain the density of a vapour, it is, therefore, sufficient to determine the weight P' of a known volume Y of this vapour, at a temperature T and under a pressure H0. Two different methods are used for this purpose: in the first, the volume occupied by a known weight P' of the volatile substance, at the temperature T and under the pressure II0, is measured: while in the second method, on the contrary, the substance is vaporized in a flask, of which the volume is known a priori, and the weight of the vapour which fills it is determined by experiment. In order to ascertain the density of a vapour by the first method, a large bell-glass C,(fig. 632,) accurately divided into cubic centimetres, and previously dried with the greatest care, is filled ■with very dry mercury, and then inverted over a mercurial bath, also very dry, contained in a cast- iron pot Y; while, on the other hand, a small globe (fig. 633) is filled with the volatile liquid, the specific gravity of which is to be ascer- tained ; and having hermetically sealed its points, the weight of the liquid contained in it is exactly determined. The small globe being introduced into the bell-glass C, the latter is then surrounded by a glass cylinder maintained in a vertical position, and is filled with water, if the temperature Fig. 632. Fig. 633. INTRODUCTION. 409 is not to exceed 212°, while a thermometer t is so kept in the water that the mercurial column is always under the level of the liquid. The diameter of the cylinder should be 5 or 6 centimetres less than that of the pot, so that the atmospheric pressure may be directly exerted on a circular surface of mercury, comprised be- tween the outside of the cylinder and the inside of the pot, and of which the level may be accurately ascertained by a double-pointed screw r, the lower point of which is in exact contact with the sur- face in the mercury. The kettle being placed on the furnace, the temperature is gradu- ally raised, when the expansion of the liquid soon breaks the glass globe; and, when the temperature is sufficiently elevated, the liquid is converted into vapour, which depresses the mercury in the bell-glass. The heat is continued until the water in the cylinder boils, after which the volume occupied by the vapour and the pressure to which it is subjected are accurately noted down. In order to obtain the latter datum, the lower point of the screw is brought to the exact level of the surface of the mercury between the cylinder and the kettle, and, by means of a cathetometer, the difference of level between the surface of the mercury in the bell-glass and the upper point of the screw is determined, to which length must be added that of the screw already known a priori, in order to obtain the height h of mercury which, in addition to the elastic vapour, balances the external barometric pressure. The column h of mer- cury, reduced by calculation to 32°, being subtracted from the height of the barometer, also reduced to 32°, will give the elastic force H'0, of the vapour. The fact that the cylinder surrounding the bell-glass is rarely perfectly cylindrical, gives rise to deviations in the luminous rays, which may affect the determination of the height A, by means of the cathetometer, while the cylinder is filled with water. To be sure of this, the micrometric wire of the telescope of the cathetometer is directed over the division of the bell-glass nearest to the level of the mercury inside, and the water is then removed from the cylin- der by means of a siphon; when it is easy to ascertain whether the wire of the micrometer remains over the division, in which case the interposition of the liquid filling the cylinder has certainly pro- duced no abnormal deviation of the ray. If there has been any dis- placement, the micrometer is again brought over the same division, and the distance travelled by the vernier of the instrument then gives the correction to be made in the height h observed in the first case. When no cathometer is at hand, the simplest way of determining the height h consists in carefully marking the position of the inner level of the mercury on the divisions of the bell-glass, and levelling exactly the external circular surface of the bath with the lower point of the screw r. The water is then entirely removed from the cylin- 410 OKGANIC CHEMISTKY. der, the last drops being soaked up by tissue-paper, and then mercury is poured into the kettle, so as again to bring the external surface of the mercury on a level with the point. As the mercurial bath is on the same level, both on the inside and outside of the cylinder, it suffices to mark on the bell-glass the division to which the level reaches. The height h is then equal to the distance between this division and that at which the level of the mercury on the inside of the bell-glass stops at the moment of measuring the volume of a vapour. If the substance boils at a very low temperature, the density of its vapour is sometimes determined at a temperature below 212° ; and it is then sought to render stationary the temperature of the water in the cylinder at the exact temperature at which the volume of vapour is to be observed. By properly regulating the fire under the kettle, a moment arrives at which the apparatus receives from the furnace a quantity of heat equal to that which it loses from its whole surface by contact with the surrounding air, and by the va- porization of the water in the cylinder; which period, frequently lasting 8 or 10 minutes, is chosen for the observation. The water must be constantly stirred with the agitator pmn, in order to obtain a uniform temperature throughout. If it is required to observe the volume of a vapour at a tempera- ture above 212°, the water in the cylinder is replaced by a fixed oil, which should be as colourless and transparent as possible; but the experiment is then more difficult and the results less exact. The oil, of which the capacity for heat is much less than that of water, cools rapidly in the air, and, in order to obtain a high sta- tionary temperature in the oil-bath, the mercury in the kettle must be heated to a greater degree, and, therefore, evolves copious va- pours, Avliich must be avoided. It is also a matter of uncertainty whether the temperature of the column of mercury, which is raised in the bell-glass, and stands in immediate contact with the vapour the volume of which is to be found, is not higher than that of the surrounding oil; and, lastly, if the tension of the mercurial vapour can be neglected, without any appreciable error, for temperatures below 212°, (for at this temperature it only reaches a J millimetre,) this is not the case when high temperatures are necessary; and the tension of the mercury must then also be taken into account, by being added to the elastic force of the vapour. For these various reasons, the process just described is not so well adapted to tem- peratures above 300° or 350°. § 1236. The second method is applicable, on the contrary, to any temperature whatever; and the only difficulty it presents is that of procuring vessels to hold the vapour, which are not mis- shapen, or liable to injury when exposed to a very high tem- perature. INTRODUCTION. 411 A glass balloon A, (fig. 634,) containing 400 or 500 cubic centi- metres, and drawn out into an open and curved point, as represented in the figure, is used, and, in the first place, dried per- fectly by means of an air-pump; after which it is placed on the disk of a scale, near a thermometer arranged in the cage. In 15 minutes, in which time it may be supposed that the balloon has attained the surrounding temperature, its exact weight P is ascertained, while at the same time, the temperature t of the thermometer and the height II of the barometer are marked; the weight found by direct weighing being that of the balloon itself, in addition to the weight p of air it contains. Let Y be the capacity of the balloon expressed in cubic centimetres, then will the weight p of the air which it contains be Fig. 634. *,=0.0012932. and the weight of the balloon alone is therefore (P—p). About 10 grammes of the liquid, the density of whose vapour is to be determined, being introduced into the balloon, the latter is fast- ened on a copper support, with its tubidure upward, to facilitate the escape of the air which is expelled by the vapour developed during the experiment. This support may be variously shaped: in fig. 634 it is composed of two metallic rings, the lower one of which ab is supported by three small feet which keep it at a distance of 3 cen- timetres from the floor, while it is provided with two grooved up- rights ae, bf, fastened together by a crosspiece ef. The upper ring ed has two ears, which slide in the grooves of the uprights ae, bf; and the balloon A is fitted between the two rings, and held firmly by two corks h, h’, which are pressed by two screws g, g'. A verti- cal piece has a movable crosspiece mn, serving to support two ther- mometers T, T, of which the bulbs should be at the height of the centre of the balloon. As the crosspiece mn is movable, various positions in the bath can be given to the thermometers, in order to ascertain whether the temperature of the latter be the same throughout. The liquid bath in which the balloon is heated is contained in a cast-iron kettle placed over a furnace. When the temperature is not to exceed 212°, the kettle is filled with water, while, if it is comprised between 212° and 257°, it should contain a solution of chloride of calcium. When a temperature of from 257° to 302° is required, a fixed oil is used, giving the preference to animal oils, such as neatsfoot oil, as they yield less vapour at the same temper- ature, and their vapours are less acid than those of vegetable oils. 412 ORGANIC CHEMISTRY. Lastly, if the operation demands a still higher temperature, metallic baths, formed of alloys of lead, bismuth, and tin, are em- ployed. Fig. 635 represents a more simple apparatus than that of fig. 634, and which possesses some advantages over the latter. It is com- posed of an iron rod tp, fastened by means of a thumbscrew to one of the ears s of the kettle V. Along the rod tp slides a piece of bent iron cd terminating below by a ring gh, on which the balloon A rests; while a second ring ef, fastened to an iron rod, slides along the rod cd, and may be fastened to it at any height by a thumbscrew i, serving to hold the balloon in a fixed position. It is suffi- cient to slide the movable part cd of the support along the upright tp to cause the balloon to dip into the kettle V, where it is then secured by the thumbscrew r. When the metallic bath is used, it should be brought to the liquid state before dipping the balloon into it. A second iron rod t'p', fastened to the ear s', holds the air thermometer B, resembling that which will be described in a note at page 414. The bath is gradually heated, taking care that the temperature shall constantly rise; and wThen the liquid contained in the bal- loon has boiled, it begins to distil, and its vapour drives off the air contained in the vessel, which partly escapes by the point a. If the substance be valuable, the greater portion of that which is evolved can be collected, by introducing the point a into a small tube closed at one end. The temperature is then raised until the point at which the examination is to be made is approached, when all the doors of the furnace are closed, and, stirring the bath con- stantly, the moment is awaited when the temperature becomes sta- tionary. The temperature being marked, the flame of an alcohol lamp is passed under that part of the stem of the balloon which projects from the fluid, in order that no condensed drops shall remain; after which the point a is quickly closed, and the height T' of the barometer noted down. The balloon is then removed from the bath, and detached when it is cooled. The temperature T of the mercurial thermometer requires a cor- rection, which becomes of great importance in high temperatures, and which is owing to the circumstance that a considerable portion of the mercurial column, not being plunged into the bath, remains at a very low temperature. Let t be the temperature indicated by a small thermometer, the bulb of which is kept in contact with the tube of the principal thermometer, at the height of about one-half of the mercurial column which rises above the level of the bath; Fig. 685. INTRODUCTION. 413 and 9 the division of the principal thermometer, at about 2 or 3 centimetres above the level of the hath: it may then be admitted that (T—e) represents the portion of the mercurial column at the average temperature t. Now, this portion would dilate by (T—e). if it were heated from t to T; for which reason the true temperature T' of the bath is obtained by adding to the tem- perature observed T the number of degrees represented by the expression (T-fl). —■ But as the temperature T' is that of the mercurial thermometer, it is necessary to find the temperature T" which corresponds to it on the air thermometer. Mercurial thermometers agree necessarily from 32° to 212°, which are the fixed points by which their scales are governed; while they differ at a temperature above 212°, because the various kinds of glass of which the bulbs of thermome- ters are made do not obey the same law of expansion. The fol- lowing table shows the simultaneous temperatures indicated, 1st, by a mercurial thermometer, of which the bulb is made of the ordi- nary glass used in Paris for making chemical tubes; 2dly, by a mer- curial thermometer, of which the bulb is of crystal from Choisy-le- Roi; and 3dly, by an air thermometer, of which the volume of air is constant and the pressure variable.* Simultaneous Temperatures Of a mercurial thermo- Of a mercurial thermo- meter of ordinary glass. meter of crystal. Of an air- thermometer. 100° centigrade 100° 100° 109.98 .... 110.05 110 119.95 .... 120.12 120 129.91 .... 130.20 130 139.85 .... 140.29 140 149.80 .... 150.40 150 159.74 ... 160.52 160 169.68 ... 170.65 170 179.63 .... 180.80 180 189.65 ... 191.01 190 199.70 .... 201.25 200 209.75 ... 211.53 210 219.80 ... 221.82 220 229.85 .... 232.16 230 239.90 ... 242.55 240 250.05 .... 253.00 250 260.20 .... 263.44 260 270.38 .... 273.90 270 280.52 .... 284.48 280 290.80 .... 295.10 290 * This being a merely comparative table, the centigrade divisions have not been corrected to the corresponding temperatures of the Fahrenheit scale.— W. L. F. 414 ORGANIC CHEMISTRY. Of a mercurial thermo- Of a mercurial thermo- Of an air meter of ordinary glass. meter of crystal. thermometer. 301.08° 305.72 300 311.45 316.45 310 321.80 327.25 320 332.40 338.22 330 343.00 349.30 340 354.00 360.50 350 When the operation is performed at higher temperatures, above 570° (Fahrenheit) for example, and great exactness is required, it is better to substitute an air for a mercurial thermometer ; which is absolutely necessary when 660° is exceeded, since at this temper- ature mercury boils under the ordinary pressure of the atmosphere; and the boiling manifests itself even at somewhat lower tempera- tures in thermometers perfectly freed from air, unless the calibre of the tube he so small as to present great resistance to the ascent of the metal. In a note,* at the bottom of this page, we shall explain * The air thermometer used in these experiments consists of a simple cylin- drical glass reservoir, of about 2 centimetres in diameter and 12 or 15 centimetres in length, and terminating by a capillary tube, of -which the calibre is 1 or 2 milli- metres, and which is bent to a right angle, and drawn out at its end. The reservoir ab is kept in the bath, alongside of the balloon in which the vapour is to be generated. The first step is to perfectly dry the reservoir ab, by creating a vacuum in it several times, and allowing air to enter which has been dried, by passing through a tube filled with pumice-stone soaked in concentrated sulphuric acid; after which the bath is heated, and, when the temperature becomes station- ary at the point at which the experiment is to be terminated, the point of the bal- loon and that of the air thermometer are closed simultaneously, by means of a lamp. The air reservoir is then placed on the metallic support represented in fig. 636, the stem passing through a cork which closes a tubulure made in the centre of the disk gh, while the curved point cd enters a small mercurial bath. The extremity of the point being broken with a pincers, the mercury rises in the tube and partly fills the reservoir ab, which is surrounded with pounded ice, in order to reduce the temperature of the air it contains to 32°, when the open point is closed with a ball of soft wax. In order to perform this operation easily, without changing the level of the mercury in the vessel A, a small iron spoon u is used, soldered to an iron rod uv, which slides along a hori- zontal bar vs, itself movable along the ver- tical foot st; the movable rod vs being fixed at such a height that the bowl of the spoon, filled with soft wax, is exactly at the height and in the direction of the point cd. It is therefore suffi- cient, in order to close the point, to slide the end uv along the horizontal rod vs. The mercury in the vessel A is then exactly levelled to the point t of a double-pointed screw ki; the ice which sur- rounded the reservoir ab is removed, and, when the mercurial column attains the temperature of the surrounding air, the difference of height be- tween the mercury in the reservoir ab and the upper point k is exactly measured, by means of Fig. 636. INTRODUCTION. 415 the manner of arranging an air thermometer, and deducing the temperature from it. The balloon A having been well wiped and washed with alcohol, a cathetometer; and by adding to this difference the length of the screw ki, the height h of the column of mercury elevated in the air thermometer is obtained. Let h0 be this height at 32°, H0 the height of the barometer also at 32°, when the point d is closed with wax; then will (H0 — h0) represent the elastic force of the air in the reservoir ab at the temperature of 32°. The support is then inverted, the air thermometer removed, after having detached the spoon u, and it is weighed with the mercury contained: let its weight be represented by Q. The thermome- ter is theii filled with mercury, which is boiled to drive off the last bubbles of air ; the point cd being kept, during this time, in a small capsule filled with mercury. When the apparatus is cooled, it is surrounded with melting ice, and completely filled with mercury at 32°; when it is again weighed, giving now the weight QL The weight q of the envelope of glass alone being ascertained, after having emptied it of mercury, (Q — q) is therefore the weight of the mercury at 32°, and (Q — q) is the weight of the mercury in the thermometer when it was on the support. (Q'— Q) therefore represents the weight of the mercury at 32°, which occupies the same volume as the air remaining in the thermometer when it is at 32°, and under the pressure (H0 — h0.) If we designate by S the density of the mercury at 32°, Q—0. . , Q—Q —g— represents the capacity in cubic centimetres of the thermometer, and —^— the volume which the air occupies in this apparatus at the moment of closing the point c with wax. Now, the capacity of the thermometer, at the temperature T, being (1—J—7cT), the volume of air Q at 32° and under the pressure (H0 — ho), there- fore occupies, when it is raised to the temperature T, and under the pressure H6, a volume (1+&T). The volume assumed by a volume of air at 32° and under the pressure (H0—h0), when raised to the temperature T and under the pressure H'0, may be calculated, by the known laws of the expansion of air, under changes of temperature and pressure; and is thus found to be, 0.00367, which leads to the equation, o=^p^(l—kT), whence 1 + fcT Q'—Q Ho — h0 1 + 0.00367.T Q' — q ' H'o T may be deduced from this equation, but there is no necessity of knowing its value in order to calculate the density of the vapour, which, in fact, is represented by the expression P' — p + p 0.0012932 . V. 1+fcT - . 1 + 0.00367.T 760 Substituting for J + the value first found, there results for the expres- 1 “j- 0.0036/ .T sion of the density of the vapour, P'-P+P 0.0012932. V. Q,~Q . Q' — q 760 416 ORGANIC CHEMISTRY. if necessary, its weight P' is accurately ascertained, taking care to operate as much as possible under the same circumstances of tem- perature and pressure as were observed in weighing the empty bal- The process described (§ 1236) is applicable to the determination of the densities of the vapour of all volatile organic substances, and that of volatile mineral sub- stances, when the temperature need not be raised above 930° ; but it is of difficult application to higher temperatures, because the glass softens, and the balloon becomes misshapen from the pressure of the metallic bath in which it is heated. By conducting the experiment in the method about to be described, exact results may be obtained even at the temperature of 1100° or 1200°. Two tubes ab, a'b', (fig. 637,) of the same length and diameter, made of as hard glass as possible, are used, one of which serves as an air thermometer, while the second is intended to contain the vapour of the volatile substance. The latter is composed of a reservoir a'b', a capillary portion b'c', and a larger portion c'd!, in which a portion of the volatilized substance which escapes from the reservoir a'b' is condensed; and the air thermometer terminates in a capillary tube be, to the end of which is luted a small steel stopcock r. The two tubes are arranged alongside of each other, on a small support made of three parallel disks of sheet-iron, held together by iron rods. The air thermometer has previ- ously been filled with dry air, and a certain quantity of the substance, the den- sity of the vapour of which is to be determined, has been introduced into the tube a'b'c'. They are heated simultaneously in air ap- paratus (fig- 638), made of two or three concentric sheet-iron tubes, closed at one end, and distant from each other about one centi- metre, the pipes being intro- duced into a cast-iron tube ABCD, placed on a semi- cylindrical grate, so that it may be surrounded by char- coal. The apparatus being ar- ranged, the grate is filled with burning coals, and the temperature rapidly raised, avoiding all cause of sudden cooling. When the volatile substance is distilled, and the excess has condensed in the cold portion of the tube c’d', the temperature is again raised, (if the glass does not become misshapen,) this time as slowly as possible. The stopcock r of the air thermometer is then closed, while at the same time the capillary tube b'c' which terminates the vapour reservoir a'b' is sealed by means of the flame of a lamp. The height H' of the barometer being now noted down, the support, with the two tubes, which are allowed to cool completely, is removed. In order to determine the temperature T to which the air thermometer has been raised, the latter is placed in communication with the manometric apparatus, (fig. 639,) which is composed of two tubes fg, hi, luted into a piece having a stop- cock R, resembling that of the figure, the upper end of the tube hi being open, while the tube./# is terminated by a bent capillary tube, to which a steel tubulure s has been luted. Fig. 640 represents a section of the stopcock tubulure r, mounted on the air thermometer, and a section of the tubulure s of the manome- ter. It will be seen that the first tubulure is terminated by a plain surface ab and a projecting cone o, while the second has also a plain surface a'b' and a hollow cone o', which exactly fits the plain surface and projecting cone of the other. In order to close them hermetically, it is sufficient to press the two parts against each other, by means of the pincers, (fig. 641,) which is tightened with screws, after having poured in a small quantity of melted caoutchouc. Fig. 637. Fig. 638. INTRODUCTION. 417 loon ; and in case the new circumstances should differ greatly from the former ones, a correction will be necessary, which, however, we shall not mention, as in general it may be neglected. The mano- meter has been filled with mer- cury before adapting the thermometer to it; and the lat- ter is then completely sur- rounded by melting ice, when the mer- cury of the ma- nometer is al- lowed to escape through the stopcock R so as to produce a great differ- ence between the level in the columns fg, hi. The stopcock r is then opened, and a portion of the reservoir ab allowed to enter the tube gh, after which mercury is carefully poured into the tube fi, so as to bring its level accurately to a mark a at the top of the tube gh. The next step is to mea- sure, by the cathetometer, the difference h of the height of the mercurial columns, and to mark the temperature 0 of the small thermometer at the side of the manome- ter, as well as the height H" of the barometer. The volume of air is then composed of the volume V', equal to the capacity of the air thermometer abc, kept at 32°, and of the volume v which the air occupies in the manometer at the tempera- ture 9. The weight of this air is 0.0012932 gm. i+o.oo367. 0] 760 Now the same quantity of air occupied, at the unknown temperature T, at the mo- ment of closing the stopcocks, a volume V' (l-f-&T), and its weight was expressed by T TT' 0.0012932 gm. . r,i+o.oo367. t • 760» so that 0.0012932 [v'-ffl xq-00367. f)] 760 “ 0.0012932 •V'-1_|_0 00367> T, • 7^5» whence 1+/.-T _ r » 1 “I Ho—h0 1+0.00367. T' L1-! V''1+0.00367.0J H' The second member of the equation contains only known quantities, except, indeed, the ratio , which is determined in the following manner:—The tube abc being detached from the manometer, the tube gh is completely filled with mercury; and then, bringing the stopcock R into the position of fig. 639, the mercury in the leg gh is allowed to escape until its level reaches the mark a., while the mercury Fig. 639. Fig. 641. 418 ORGANIC CHEMISTRY. P'— (P—p) therefore represents the weight of the volatile sub- stance which remains in the balloon, the point of which being broken under the mercury, the atmospheric pressure causes the which escapes is collected in a small bottle and weighed. Its weight may be con- sidered as representing the volume v. The mercury is allowed to escape from the leg ffh, it until its level reaches another mark /g, on the tube gh, when the quantity thus obtained, being weighed, compounds to a volume v’ which should be a notable fraction of the capacity of the thermometer-tube. This being done, and the level of the mercury reaching the mark a of the manometer, under the pressure of the atmosphere, the air thermometer is fitted to the manometer, the reservoir ab being kept at the temperature of the surrounding medium. As the two columns of mercury are on a level in the manometer, there is a volume of air (V'-J-d) under the exter- nal pressure H. The mercury is allowed to flow from the two legs of the mano- meter, by bringing the stopcock R into the position in the figure, and the level of the mercury is brought to the mark fib; when the two columns are now no longer on a level, and their difference of height h can be measured. There is, therefore, a volume of air under the pressure (H—li); and agreeably to the law of Mariotte, V'+® H—h ~ ~H_’ whence the volume V'may be deduced. It now only remains to ascertain the weight of the vapour which filled the re- servoir a'b' at the moment of closing it, and the capacity of the reservoir. It may be admitted that the reservoir a'b' does not contain any air, because there was originally introduced into it a quantity of volatile matter sufficient to expel all the air. The closed end of the tube is, therefore, broken, and the latter weighed filled with air and the substance it contains ; after which its weight is again ascer- tained when the substance has been removed, the difference of weight jr represent- ing the weight of the substanee. In order to obtain the volume V of the reservoir, the quantity of water which will fill it is weighed; and now all the elements are known which are necessary to calculate the density of the vapour, by means of the formula 7T 0 0012Q32-' V — H'° v. 1+000367 T- 7eo, the value ascertained by the air thermometer being substituted for t~ It frequently happens that the substance, the density of whose vapour is to he determined, is changed by absorbing oxygen from the air at the high tem- perature at which it volatilizes; in which case it becomes necessary to fill the tube a'b' with nitrogen gas, and further, in order to prevent the air from entering freely, to fit a pointed tube by means of a cork to the tube c'd'. By means of the process just described, the density of any vapour might be de- termined at very high temperatures, if it were possible to procure glass tubes of sufficient hardness; but, unfortunately, the strongest glass softens at a red-heat, and, therefore, cannot be used for higher temperatures. Porcelain tubes, how- ever, made of the same shape as the glass tubes, by the process described in § 715, might answer the purpose. It is, moreover, unnecessary to hermetically seal the fine point c'd', when the substance boils at a very high temperature, because there is then no fear, at the moment of withdrawing the tubes from the cylinders, that a portion of the vapours which escape from the reservoir might re-enter the latter. But there are volatile substances, the density of the vapour of which it would be very interesting to know, and which, at a high temperature, attack the alka- line silicates; in which case tubes of glass or porcelain can no longer be used, and resort must be then had to metallic tubes, previously filled with nitrogen gas. The portion of the volatile substance which remains in the reservoir intended to contain the vapour is then determined by chemical processes. INTKODUCTION. 419 liquid to ascend, and completely fill the balloon, if the air lias been entirely driven out by the vapour, as we shall suppose to be the case. The balloon is then inverted, when the volatile substance, if it is liquid, ascends in the neck, and may be removed with a pipette. The balloon is filled with mercury, which is afterward measured by being poured into a large bell-glass divided into cubic centimetres; by which means the capacity Y of the balloon, at the ordinary tem- perature t, is exactly found. If k represents the coefficient of the average expansion of glass, between the temperature t and T, the capacity of the balloon will be Y (1 + &T) at the temperature T. The volume Y (1-f 7cT) of vapour of the volatile substance, at the temperature T and under the pressure H'0, therefore weighs (P'— P-fp), while the weight of an equal volume of atmospheric air, under the same circumstances of temperature and pressure, is 0.0012982 gm.V(l-f^T)lT^.g. Thus the density of the vapour of the substance is represented by P'—P+p 0.0012982. VO+iTJ.rf^.jg, We have supposed that the vapour had entirely expelled the air from the balloon, and consequently that the latter was entirely filled with mercury; which, however, is rarely the case, as most fre- quently a bubble of air remains, and sometimes the remaining vo- lume of air amounts to even more than that, when the vapour is very dense, and a large quantity of material has not been origin- ally introduced into the balloon. The experiment does not fail on this account, for it is sufficient to collect this volume v of air in a small graduated bell-glass, and to measure it exactly. This volume v weighs 0.0012932 gm. v 1+0,^36^. §£=/, t" and H"0 representing the surrounding temperature and pressure of the air at the moment of measuring the volume v. The weight of vapour in the balloon, at the moment of closing it, is therefore (P'—P+p—pr). The volume v of air occupies in the balloon, at the moment of closing it, at the temperature T, and supposed to be reduced to the pressure Hr0, a volume ,, 1+0-00367.T H"o J 1+0.00367. t" ■ H'o • The volume occupied by the vapour in the balloon, at the tempera- ture T and under the pressure IP0, is therefore only [Y (1 + &T)—t/]; and as an equal volume of air, under the same circumstances of tem- perature and pressure, weighs 0.001293 gm. [V (1+4T) - „'] 420 ORGANIC CHEMISTRY. the density of the vapour is therefore p/—P -\-p—p' 0.0012932 [V(l+iT)-i/]Tf^ss3^'. In accurate experiments, care must be taken to leave but a very small quantity of air in the balloon, in order as much as possible to avoid corrections, which always possess some degree of uncertainty. The average coefficient lc of the expansion of glass, between the temperatures 0 and T, varies with the different kinds of glass; and varies, moreover, in the same glass, with the temperature T. We subjoin its value, at different intervals of temperature, for the ordi- nary glass of which the balloons used in Parisian laboratories are made: Between 0° and 100° £=0.0000276 “ 150 0.0000284 “ 200 0.0000291 “ 250 0.0000298 “ 300 0.0000306 “ 350 0.0000313 Organic substances Avhich boil at high temperatures are fre- quently easily altered by the air, at the temperature to which their vapours must be heated in order to obtain constant densities; in which case, care must be taken to fill the balloon with carbonic acid gas, when it is placed in the kettle, before heating the latter. For this purpose, the point of the balloon is made to communicate with a small air-pump, to the second tubulure of which an apparatus disengaging carbonic acid gas is adapted; and a vacuum being made several times, and carbonic acid gas allowed to enter each time, the rest of the experiment is then conducted as usual. In many cases it may be of advantage to determine the density of a vapour under a pressure below that of the atmosphere, because then the substance boils at a louver temperature, and in general it is not necessary to raise the temperature so high in order to obtain constant densities. This result is particularly advantageous when substances easily altered by heat are operated on, and the boiling point of which is high. In this case, a capillary tube ab, terminat- ing in a larger one cd, is soldered to the balloon, (fig. 642;) and the latter being placed in the bath, the tube cd is made to communicate with a large bottle placed in a wTater-bath kept at a constant temperature, approach- ing that of the surrounding temperature; while the second tubulure of the bottle is made to communicate with a mercurial manometer which indicates the inter- nal pressure at every moment, and with an air-pump, by means of which the air in the bottle and balloon is reduced to the desired Fig. 642. INTRODUCTION. 421 degree of elasticity. The experiment is then conducted in the same manner as when the operation is performed under the pressure of the atmosphere; it being sufficient to substitute in the formula the elastic force of the air observed on the manometer, for the baro- metric pressure H'0. The second method, which has just been described, to determine the densities of vapours of volatile substances, may furnish very in- accurate results when it is applied to very impure substances, for example, to those containing a small quantity of less volatile .mat- ter, the density of whose vapour is very different from that of the substance being examined. The error increases with the quantity of the substance introduced into the balloon, because the less vola- tile matter is necessarily concentrated in it, and the vapour finally filling the balloon contains a much larger proportion of the foreign matter than the substance which was introduced into it. It is necessary, whenever any doubt may be entertained as to the purity of the substance, the density of whose vapour is to be determined by this method, to carefully collect the portion of matter which remains in the balloon, and subject it to analysis, in order to ascer- tain if its composition differs appreciably from that of the original substance. § 1237. It still remains to explain the method of comparing the density of vapour afforded by experiment with the theoretical den- sity calculated from the formula, when the latter is determined. We will take alcohol as an example. The experiments detailed (§ 1234) assign 1.602 for the density of the vapour of alcohol, within the limits of temperature in which this vapour obeys the laws of permanent gases. The formula which we have adopted for the equivalent of alcohol is C41I602. Now, as the density of hydrogen is known to be 0.0692, and 2 volumes have been adopted as its gaseous equivalent, the 6 equivs. of hydrogen are therefore represented by 12 volumes of this gas, which weigh 12+0.0692=0.8304. The hypothetic density of the vapour of carbon being 0.8290, (§ 203,) and its gaseous equivalent being represented by 1 vol., the 4 equivs. of carbon are therefore represented by 4 vols. of vapour of carbon, which weigh 4x0.8290 = 3.3160. The density of oxygen gas is 1.1056, and its equivalent is repre- sented by 1 vol.; and 2 equivs. of oxygen are therefore represented by 2x1.1056 = 2.2112. The formula C4H603 therefore gives 4 eq. of carbon 3.3160 6 “ hydrogen 0.8304 2 “ oxygen 2.2112 6.3576 Now, since pp = 1.5894 differs but little from the number 1.602, 422 ORGANIC CHEMISTRY. which has been found by direct experiment, the conclusion may be drawn that the equivalent C4II80a of alcohol is represented by 4 volumes of vapour. The difference between the theoretical number 1.5894 and the number 1.602 found by experiment, may be partly attributed to slight errors which always occur in determinations of this kind; and similar, and even greater differences are observed, when the experiments are conducted with the greatest exactness.' This is owing to the fact that the laws of elasticity of gases, and their expan- sion by heat, which we have admitted as being strictly the same for all the gases above taken into account, are not really so under the cir- cumstances accessible to our means of observation. The gases which have not yet been liquefied differ from it themselves very widely, at the ordinary temperature; and it is, therefore, very probable that the differences are greater for the majority of vapours, even under the most favourable circumstances of temperature and pressure. OF THE ANALYSIS OF GASES. § 1238. We have frequently had occasion to refer to the analysis of gaseous substances in the first part of this work, either for the sake of determining the composition of definite gases, or the pro- portions in which such gases existed in mixtures. We have described the most simple processes used by chemists, but as the processes do not afford the degree of precision demanded by the subject, we shall now describe other processes by which a precision can be attained, in the analysis of gases, which is not exceeded by any of the most exact manipulations of chemical analysis. We shall, in the first place, suppose that it is required to analyze a mixture of atmo- spheric air and carbonic acid; and, while applying the processes already described, we shall discuss the causes of error to which they are subject. It will be recollected that a certain volume of this mixture is measured over mercury in a'graduated cylinder, and that in order to be more certain of the degree of moisture of the gas, the latter was saturated with moisture by leaving the sides of the cylinder slightly damp. The first difficulty which presents itself is, What is the tempera- ture of the gas, and what its elastic force ? The temperature of the gas is generally assumed as that indicated by a thermometer placed in the vicinity of the cylinder; but is it always certain that the two temperatures are identical? As to the pressure, it is generally reduced to an equality with that of the atmosphere, by properly sinking the cylinder into the mercury-bath; a process which pos- sesses but little accuracy; or, indeed, when the operation is effected more exactly, a certain column of mercury is left upraised, and measured by a graduated scale, or better still, by the process de- scribed in the note to page 414. INTRODUCTION. 423 In order to absorb the carbonic acid, a small quantity of a con- centrated solution of caustic potassa is introduced into the bell-glass, and the latter is shaken; after which the proportion of carbonic acid is determined by again measuring the gaseous volume. But the second measuring is still more uncertain than the first, for, to the difficulties already pointed out, is added that of ascertaining the degree of moisture of the gas in the presence of the solution of potassa ; in addition to which, the form of the meniscus of the liquid is now changed from convex to concave; and the sides of the bell-glass are moistened with a viscous liquid, which diminishes ap- preciably its diameter. These difficulties are overcome by replacing the solution of potassa by a small ball of potassa affixed to a platinum wire, by which it is introduced into the bell-glass through the mercury; but in this case the carbonic acid is very slowly absorbed, which renders it neces- sary to wait, not only until the absorption of carbonic acid is complete, but also until the potassa has ab- sorbed all the vapour of water which existed in the gas or on the sides of the bell-glass; be- cause it would otherwise be im- possible to as- certain its state of saturation. In order to be sure that this condition is ful- filled, the gas | must be exactly measured after having with- drawn the ball of potassa, and the latter must be again introduced and allowed to remain for at least 12 hours; when the result of a second measurement of the gas should be identical with the first. The proportion of oxygen in the remaining gas is determined, either from the gaseous volume which disappears when this gas is burned with an excess of hydrogen, or by the diminution of a volume of the gas when left for a sufficient length of time in con- Fig. 643. Fig. 644. 424 ORGANIC CHEMISTRY. tact with a substance which combines with oxygen. The manner of effecting this absorption by phosphorus has already been ex- plained, (§ 946;) and in § 83 the eudiometer in which the analysis is made by combustion was described; but the process is always liable, without regard to the method adopted, to some of the causes of error pointed out above. § 1239. With the eudiometric apparatus about to be described these analyses can, on the other hand, be performed very rapidly, and without any danger of the uncer- tainties just mentioned. Fig. 643 represents the geometrical projection of the anterior surface, and fig. 644 gives a vertical section made through a plane perpendicular to this face; while lastly, fig. 645 showrs a perspec- tive view of the whole. The apparatus is com- posed of two parts, which may be separated and united at pleasure; and, while the first, or the measurer, serves to mea- sure the gas under given conditions of temperature and moisture, in the se- cond the gas is subjected to various absorbent re- agents, on which account we shall call it the absorption-tube. The measurer is composed of a tube ab of 15 to 20 millimetres diameter internally, divided into millimetres, and terminating above by a curved capillary tube ber', while the lower end is luted into a cast-iron piece p'q', having two tubulures a, i, and a stopcock R. To the second tubulure i is luted a straight tube ih, open at both ends, of the same diameter as the tube ab, and also divided into millimetres. The stopcock R has three openings, and resembles precisely that of which sections are seen in figs. 624, 625, and 626, in the three principal positions in which the key may be turned. A communication can therefore be established at will between the tubes ab, ih, or one or other of these tubes only may be opened to the external air. The two vertical tubes and the cast-iron piece form a manometric Fig. 645. INTRODUCTION. 425 apparatus contained in a glass cylinder pqp'q' filled with water, which is maintained at a constant temperature, marked by the thermometer T, during the whole time of the analysis. The mano- metric apparatus is fixed on a cast-iron stand ZZ' furnished with adjusting screws. The absorption-tube is composed of a bell-glass gf’ open at the bottom, and terminated above by a curved capillary tube fer. The bell-glass dips into a small mercurial bath U, of cast-iron, exactly represented in figs. 646 and 647 ; while the basin U is fixed on a plate which can be raised at will along the vertical J support ZZ', by means of the toothed rack vw, which works with the toothed pinion o set in motion by the crank B. The ratchet r arrests the toothed- racks and consequently keeps the basin U in any given position. A counterpoise affixed to the ratchet facili- tates its working, and, as it is turned to one side or the other, the ratchet is thrown in or out of gear with the pinion. The ends of the capillary tubes which terminate the absorption-tube and measurer are luted to two small steel stopcocks r, r', the ends of which exactly fit each other, and which have the same shape as those represented in fig. 639, sections of which are seen in figs. 640 and 641. The absorption-tube is maintained in a vertical position by means of pincers u lined with cork, which are easily opened or closed wdien the tube is to be removed or replaced. The measurer ab is traversed at b by two platinum wires opposite to each other, the ends of which approach to the distance of a few millimetres from the inside of the bell-glass, and of which the other ends are fast- ened with wax to the lower edge of the large cylinder. The elec- tric spark is passed into the bell-glass by means of these wires ; and the water in the cylinder is no obstacle if the spark be furnished by a Leyden jar. § 1240. Let us suppose that in this apparatus a mixture of atmo- spheric air and carbonic acid is to be analyzed. Through the tube ih the measure ab is filled with mercury, until the latter escapes through the stopcock r, which is then closed; and at the same time the absorption-tube gf is filled with mercury; to effect which the tube gf is detached from the pincers u, and plunged into the bath U, the stopcock r being open; and the operator sucks with a glass tube furnished with a caoutchouc tubulure, the edge of which is applied to the plane part of the tubulure r. When the mercury begins to escape, the stopcock r is closed. The gas to be analyzed, which has been collected under a small bell-glass, is then introduced into the absorption-tube, and the extra- vasation is easily performed in the bath U, on account of the shape Fig. 646. Fig. 647. 426 ORGANIC CHEMISTRY. given to the latter. The ahsorption-tube being then replaced by the pincers u, the two tubulures r, r' are fitted to each other : then, elevating one end of the hath U, and allowing the mercury of the measurer to flow from the other through the cock 11, and lastly, opening the stopcocks r, r', the gas is caused to pass from the absorption-tube into the measurer. When the mercury begins to rise in the capillary tube fe, its escape through the stopcock R is slackened, so as to cause the mercury to rise very gently in the tubefer, and the cock r is closed when the mercurial column reaches a mark a, on the horizontal leg er, at a small distance from the tuhulure r. The level of the mercury is then brought to a given division m of the tube ab, and the difference in height of the two columns can immediately be read on the scale of the tube ih. The water in the cylinder has been several times agitated, throughout, by blowing air into it by means of a tube which descends to the bottom. Let t he the temperature of the water, which is to be stationary during the analysis, f the elastic force of the aqueous vapour satu- rated at this temperature, Y the volume of the gas, H the height of the barometer, and lastly, h the height of the mercury elevated : then will H+A—/ be the elastic force of the gas when supposed dry. The temperature of the water in the cylinder should be nearly that of the surrounding air, which does not vary sensibly during the short duration of the experiment; and it is therefore unnecessary to reduce to 32°, by calculation, the height of the barometer, and that of the mercury elevated in the manometric apparatus abih. The gas collected in the measurer is moreover always saturated with moisture, because the sides of the tube ab are moistened with a small quantity of water; and this is constantly the same, since it is that which the mercury does not remove when the tube is filled with it. When this is done, the mercury is again allowed to flow through the stopcock R, and the cock r is opened in order to allow all the gas as well as a column of mercury to pass into the tube rcb, after which the stopcock r' is closed. The absorption-tube is then detached; and a drop of a concentrated solution of potassa is passed up by means of a curved pipette; when the absorption-tube is again fitted to the measurer, and the bath U allowed to fall to its full extent; and then, after having poured a large quantity of mercury into the tube hi, the stopcocks r, r' are successively opened. The gas thus passes from the measurer into the absorption-tube, and the small quantity of solution of potassa completely moistens the sides of the bell-glass. The cock r is closed when the mercury begins to fall in from the measurer into the vertical leg ef of the absorption- tube ; and after waiting for a few moments, in order to give time for the absorbing action of the potassa, the gas is passed from the absorption-tube back into the measurer, by causing the bath U to ascend, and the mercury to flow through the cock R. As soon as INTRODUCTION. 427 the alkaline solution begins to rise in the tube/e, an inverse move- ment is caused by closing the stopcock r; that is, the gas is again passed from the measurer into the absorption-tube, by lowering the bath U, and again pouring mercury into the tube ill. The inten- tion of this operation is to again moisten the sides of the bell-glass fg with the solution of potassa, and subject the gas to the absorbing action of the new layer of potassa. If it be deemed necessary, these operations may be repeated several times; although, after the second, the whole of the carbonic acid is generally absorbed. The gas is then passed for the last time from the absorption-tube into the measurer, and the cock r is closed when the top of the alkaline column reaches the mark a. The level of the mercury in the tube ab being brought to m, the difference of height h' of the mercury in the two legs ab and ih is measured, and the height H7 of the barometer is noted down. We shall suppose that the temperature of the water in the cylinder has not changed: if otherwise, it must be restored t’o the temperature t, by the addi- tion- of hot or cold water. The elastic force of the gas, dry and deprived of carbonic acid, is therefore (H'-T h'—f); and consequently (H+h—f)—(H'-f-h'—f) =H—H'-\-li—h' is the diminution of elastic force caused by the absorption of the carbonic acid; and represents the pro- portion of carbonic acid in the gas when supposed dry. § 1241. The proportion of oxygen which exists in the gas remaining must now be determined; for which purpose the absorp- tion-tube is detached and washed several times with water. It is dried, first with tissue-paper, and then by bringing it into combina- tion with an air-pump; and lastly, after having filled it with mercury, it is fitted to the measurer. The bath U being raised as high as possible, the mercury is allowed to run through the stopcock R: then, opening carefully the cocks r and r', the mercury of the absorption-tube is passed into the tube ar' of the measurer, taking care to close the cock r' when the extremity of the mercurial column reaches a second mark 6 on the vertical leg bo. The mer- cury in the measurer is again brought to the level m, and the difference of level h" and the height II" of the barometer is ascer- tained. IT" 4-h"—f is therefore the elastic force of the dry gas, the quantity of which is somewhat smaller than in the measure made immediately after the absorption of the carbonic acid, because a small quantity (about has been lost by detaching the absorption- tube from the measurer. This small loss does not affect the result of the analysis, because the gas is again measured. The absorption-tube being once more detached from the measurer, the hydrogen gas intended to burn the oxygen is now introduced into the latter by arresting the ascending mercury at-the mark 6. The mercury is again levelled to m, the difference of height h'" of 428 ORGANIC CHEMISTRY. the two columns of mercury measured, and the height II'" of the barometer observed. II'"-f h'"—f is therefore the elastic force of the mixture of hydrogen and oxygen to be analyzed. As some time is required for the perfect admixture of the gases, combustion by the electric spark cannot he immediately effected. The gas must again be passed from the measurer into the absorption-tube, and a small quantity of mercury, which produces an agitation in the gas, allowed to flow through the tube cdef; and lastly, the mixture is passed back into the measurer, this time allowing the mercury to entirely fill the tube r'cb, in order that the whole volume of gas may be subjected to combustion. The electric spark is then applied, and after having established an excess of pressure in the measurer ah, the stopcocks r, r' are carefully opened, in order to allow the mercurial column to retro- grade into the tube her'; and it is stopped when it reaches the mark z=n, whence a._2m—n _ 3 It is necessary to add a considerable volume of oxygen, in order that there shall remain, after explosion, enough gas to allow it to be accurately measured. If the original mixture contained very little hydrogen, it would be prudent, after combustion, to introduce gas from the battery, and effect a new explosion, in order to be sure of completely burning the oxide of carbon. Mixture of Nitrogen, Oxygen, and Oxide of Carbon. \ 1253. If this mixture contains a large amount of nitrogen, a small quantity of oxide of carbon, and oxygen more than sufficient to convert the oxide of carbon into carbonic acid, gas from the battery is added to the mixture, and an explosion effected. Let m be the absorption produced by the combustion : the volume n of cai’bonic acid formed is then determined. Let V be the volume of the original mixture, y the volume of oxygen, z that of oxide of carbon, and lastly u that of the nitrogen; there will then result, in the first place, the two equations: z=n, |=?w, whence n=2m, which should give the same value for z; proving that it was in fact oxide of car- bon which existed in the mixture. An excess of hydrogen is then added, and a certain quantity of gas from the bat- tery if it is probable that but very little oxygen remains in the mixture: let m' be the new absorption effected by the combustion, and there results, n . to' u—Y—y—2=V — y' If the oxide of carbon predominates over the oxygen, an excess of oxygen a must be immediately added, and then the equations are as follows: z=n, z=2m, n . m' 3 ; u=Y—y—z=Y—2>m—~ -fa. If the nitrogen existed in small quantity, it would be necessary to add for the first combustion a large quantity of oxygen in case the oxide of carbon should predominate, and, for the second combustion, a large excess of hydrogen, in order to have, after each of these combustions, a gaseous residue sufficient to enable its accurate measurement in the apparatus. If one or the other of these combustions INTRODUCTION. 437 appear feeble, gas from the battery must be introduced before passing the spark, and it must be ascertained if the volume is altered by this new explosion. Mixture of Nitrogen, Oxygen, Hydrogen, and Oxide of Carbon. \ 1254. Several cases of this mixture may occur, according as one or the other gas predominates. We shall, in the first place, suppose that the oxygen exists in greater quantity than that necessary to completely burn the hydrogen and oxide of carbon: combustion is immediately etfected by the spark, if the combustible mixture forms a considerable proportion of the inert gas; but if otherwise, the spark is passed only after having added the gas from the battery. Let m be the volume which disappears by the combustion, x the volume of hydrogen; then, re- taining for the other gases the same characters as above, we shall have 3 . l 2x+2Z=m- The carbonic acid is absorbed by potassa, causing a diminution of volume n, which gives: z=n. An excess of hydrogen being then introduced and the explosion effected, a new absorption m' is observed, whence Hr4+r lastly, u=V—x—y—z: whence follows 2m—n, x= ; 3 v m + m' + w, J 3 z=n, M_y 3TO+m'+3w. The quantity u can be verified by exploding the last gaseous residue, consisting only of nitrogen and oxygen, with an excess of hydrogen. If oxygen exists in the mixture in a quantity insufficient to completely burn the hydrogen and oxide of carbon, a certain quantity a of it is added, and for the moment this new mixture is regarded as that to be analyzed: the equations of the preceding case are consequently applicable, and it is sufficient, at the end of the analysis, to diminish the oxygen y by the quantity a which had been added. Lastly, if the nitrogen be present in very small quantity, the same method could be employed; and it would suffice to add, before each combustion, a suffi- ciently large excess of the gas which is to effect it, in order that the gaseous re- sidue may be exactly and easily measured in the apparatus. A cortain quantity of atmospheric air may also, in this case, be added to the original mixture, which is to be brought into the final calculation. Mixture of Oxygen and Protocarburetted Hydrogen. g 1255. If the oxygen does not exist in a quantity more than sufficient to com- pletely burn the protocarburetted hydrogen, a quantity a of oxygen must be added, which rs to be afterward remembered in the calculation. Let m be the diminution of volume produced by the explosion, and n that effected by the absorption by potassa. As 1 volume of protocarburetted hydrogen consumes 2 vols. of oxygen and yields 1 vol. of carbonic acid, we shall have, designating by v the volume of protocar- buretted hydrogen, 2 v=m, v=n, whence 2n=m; which two relations should give the same value for v, if the gas is protocarbu- retted hydrogen. 438 ORGANIC CHEMISTRY. Mixture of Hydrogen and Protocarburetted Hydrogen. § 1256. To this mixture a large excess of oxygen is added, in order that, after the combustion and absorption of the carbonic acid, there shall remain a volume which can be exactly measured in the apparatus. After passing the electric spark, and observing the absorption m, the carbonic acid is absorbed by potassa. Let us always designate the hydrogen by x, the protocarburetted hydrogen by v, and by n the carbonic acid formed ; we shall have, Zx-\-2v=m, v=n, , 2m,—in whence x=—, and V=z+r; which result may also be verified by determining the quantity a of oxygen con- sumed in the combustion, giving *-\-2v=a. Hence is deduced the equation : • V+a=m+ra, which moreover exists for carburetted hydrogens, their mixtures with hydrogen, the mixtures of hydrogen with oxide of carbon, and, consequently, for all the mix- tures of these various gases. Mixture of Oxide of Carbon and Protocarburetted Hydrogen. % 1257. This mixture is exploded with a large excess of oxygen, in order to be able to measure exactly the last gaseous residue; there is again observed a de- crease of volume m, and, by means of potassa, it is ascertained that a quantity n of carbonic acid has formed. If z and v still represent the proportions of oxide of carbon and hydrogen, we shall have J + 2 v=m, z-\-v=n, whence in — 2 to 2m — re. 2— 3 > v 3 » or, to verify it, V=z-f- v. By ascertaining the quantity of oxygen which has disappeared, there results | + 2 «>=«; whence is again deduced V+a=m+n. A certain quantity k of atmospheric air, and then an excess of oxygen, may also be added to the gas, taking care to avoid the condition in which nitrous products may be formed; but the first plan is preferable. Mixture of Nitrogen, Oxygen, and Protocarburetted Hydrogen. $ 1258. A quantity b of oxygen being added to the mixture in order that this gas may be in excess, the explosion is effected and the decrease of volume m marked; after which the volume n of carbonic acid, produced by absorption by potassa, is ascertained. Then is 2 v=m, vz=n, V=y + »+«. The next step is to determine, by means of combustion with an excess of hydro- gen, the quantity y' of oxygen which remains in the residue. If m' represents the decrease of volume effected by this combustion, we have . m' y=T- INTRODUCTION. 439 We have, moreover, for the quantity of a of oxygen consumed in the first com- bustion, 2 v=a, consequently, y=a + y' — b=.a-\- b, whence may be deduced n y=a+Y— •wj I 1 m' w=V-f-o— a — -g- — n. Mixture of Nitrogen, Oxygen, Hydrogen, and Protocarburetted Hydrogen. % 1259. This mixture frequently exists in air which has passed through the lungs; in which case the nitrogen predominates, and oxygen is present in much larger quantity than would be necessary to completely burn the combustible gases ; but the mixture cannot be exploded. After adding gas from the battery, and ob- serving the decrease of volume m which results, the quantity n of carbonic acid formed is ascertained, and these operations furnish 3x i o 2—f-2 v=m, vz=n; whence 2m— 4 n X 3 The quantity y' of oxygen consumed by this combustion is , x ■ r, m + in y’=-+2v=-—. After these operations there remains a mixture of y" of oxygen and u of nitro- gen, referred to the original volume, which is analyzed by the process explained in § 1246. The whole quantity y of oxygen contained in the mixture is y=y'-\-y"- As a measure of greater certainty, it is well to determine directly, by absorp- tion, in another portion of the original gas, the whole quantity y of oxygen con- tained in the gaseous mixture, which thus affords a verification, proving the combustible mixture to be formed of hydrogen and protocarburetted hydrogen. If the oxygen contained in the mixture were not sufficient to completely burn the hydrogen and protocarburetted hydrogen, a certain quantity a of oxygen, to be taken into account at the close of the experiment, would be added, and to this new mixture the process just described would be applied. Mixture of Nitrogen, Oxygen, Oxide of Carbon, Hydrogen, and Protocarburetted Hydrogen. § 1260. We shall again suppose that the oxygen is present in sufficient quantity to completely burn all the combustible gases; for, if it were otherwise, a sufficient quantity of oxygen must be added, and the new mixture then be considered as the original gas. The mixture is exploded in the eudiometer, either alone or after the addition of the gas from the battery ; and the absorption m being marked, and the quantity n of carbonic acid produced determined, there results, I- |+y + 2 v=m, ■ II. z-\-v=.n, III. y'=J+f + 2* The gas which remains after these operations is composed only of nitrogen and oxygen, of which the quantities u and y", which may from this time be considered as fixed, are next ascertained. 440 ORGANIC CHEMISTRY. Lastly, in a fresh quantity of the original gaseous mixture, the whole quantity y of oxygen which exists in it is determined by absorption, which gives IV. y'=y — y". The equations I. II. III., which are then sufficient for the calculation of the three unknown quantities z, y, and v, give , , mA-n m+4 n , x=m — y, v=y' z= — y . Mixture of Oxygen and Bicarburettcd Hydrogen. \ 1261. If this mixture does not contain a sufficient quantity of oxygen, it is to be added in such a proportion, that after the explosion and absorption of the car- bonic acid by potassa, there shall remain a residue of oxygen which can be exactly measured. It is, moreover, necessary that there should exist in the mixture a considerable proportion of inert gas, as, otherwise, the eudioinetric tube might be broken by the violence of the explosion. If the proportion of bicarburetted hy- drogen is very great, it is preferable to first measure in the apparatus a certain quantity of atmospheric air, and then introduce the gas to be analyzed, and, if it be necessary, a certain quantity of oxygen, but not enough to completely burn the combustible gas. After having effected the explosion, which is much less vivid than if the combustion were complete, an excess of oxygen is introduced and ex- actly measured, after which the mixture is again exploded in order to perfect the combustion ; and, if the latter be feeble, it w'ould be prudent again to pass the electric spark, after having added gas from the battery. Let m be the volume which has disappeared in the successive combustions, and n the volume of carbonic acid absorbed by the potassa; then, as 1 volume of bicarburetted hydrogen con- sumes 3 vols. .of oxygen and produces 2 vols. of carbonic acid, we have, desig- nating by w the volume of bicarburetted hydrogen, 2 w=m, 2w=n, whence m=n. In the last mode of operating there is less danger of bursting the eudiometer, and the formation of nitrous products is also avoided; for it would only take place in the second combustion, which generally disengages but little heat. Mixture of Hydrogen and Bicarburetted Hydrogen. § 1262. In order to analyze this mixture, when the bicarburetted hydrogen is in small quantity, it is sufficient to mix it with a large excess of oxygen, explode it, and ascertain the volume of gas -which has disappeared, and that of the carbonic acid absorbed by the potassa. The only precaution necessary is to. add enough oxygen to enable the last gaseous residue to be measured. There then results — 4-2 w—m, whence w=z — 2 1 2 ’ 2 2w=n, x=s (m — w). If the bicai’buretted hydrogen exist in large quantities, it is better to effect the combustion at two periods, and in atmospheric air. In this case, a certain quan- tity of atmospheric air is first measured, to which the gas to be analyzed, the volume of which is exactly determined, and then a quantity of oxygen, is added, so that, with the oxygen contained in the air, there shall not be enough of that gas to effect complete combustion. The electric spark being passed, an excess of oxygen is added, with a small quantity of gas from the battery, if this be deemed useful, and the mixture is exploded a second time. The analysis may be verified by determining the quantity of oxygen which remains in the eudiometer after the combustion; after which the whole quantity y of oxygen consumed is known, furnishing the equation : y=r2 + 3 w. A verification is always useful, and becomes indispensable when it is not certain that the gaseous mixture is composed only of hydrogen and bicarburetted hydrogen. INTRODUCTION. 441 Mixture of Oxide of Carbon and Carburetted Hydrogen. ? 1263.. This analysis is made like the preceding, and with similar precautions. The relations giving the proportion of the two gases are Z 2 + 2tt>=w, whence x=2(n—m), z4- 2w=n, w=m — -• 2 If a represent the volume of oxygen consumed, the following relations again exist: z-\-w=V, |-(-3w=a, whence \a=m-\-n. Mixture of Protocarburetted and Bicarburetted Hydrogen. 1 1264. The analysis will be conducted as in the preceding cases; and the fol- lowing equations will be found: 2vf-2 w=m, whence v=2 (re — m), v-\-2w=.n in—2to n ; 2 ’ to which the other relations must be added, from which are deduced the verifica- tions, t>-f- w=V, 2v-\-Zw—a, which again give V-|- a=m -f- n. Mixture of Hydrogen, Protocarburetted and Bicarburetted Hydrogen. § 1265. The analysis is conducted as in the preceding case; but it now becomes necessary to determine the volume a of oxygen consumed in the combustion, which furnishes 2v-\- 2w=m, whence x-2(m-\-2n — 2a), v-\-2 w=n, v=Q a — In — 2m, -f- 2v -|— 3w=a, w=m-\-4n — 3a. There remains only one verification given by the relation Y=x-\- v-\-w, but which is reduced to the equation V-|- a=m-\- n. Mixture of Oxygen, Protocarburetted and Bicarburetted Hydrogen. § 1266. The analysis is conducted as in the preceding cases; and the following equations result: 2v-\-2w=m, whence v=m — n, v -\-2w=n, y_|_„_l_M,=y) t/=V—~ A verification is obtained by determining the quantity a of oxygen added, which has been used in combustion; which will give the relation 2v -1- 3 w=a -4- y . leading to the equation V-}- a=m-\-n. Mixture of Nitrogen, Protocarburetted and Bicarburetted Hydrogen. 1 1267. The analysis will be conducted as in the preceding cases; and we shall have the relations 442 2v-\-2w=m, whence v=m — n, v+2w=n, v>= u-\-v-\-w—V, w=V—*^> with a verification given by the relation 2v-\- 3w=a; which is again reduced to V-f- a=m-f- n. Mixture of Nitrogen, Oxygen, Protocarburetted and Bicarburetted Hydrogen. \ 1268. The analysis is made in the same way, taking care to determine, at the close of the experiment, the portion a of oxygen added, which has disappeared in combustions; and- the relations are as follows: 2v -\-2w=m) whence r=m— n, v 2w=-n, w= 2”~m, 2v-\-‘d w y=a, y — a, yu-\rVw=Y, u = V-|- a — m — n. Eudiometric analysis furnishes no verification; but the quantity y may be directly determined by absorption. Mixture of Oxygen, Hydrogen, Protocarburetted and Bicarburetted Hydrogen. \ 1269. The analysis is again conducted as in the preceding cases, and the rela- tions are the following: I. 2v-±- 2w=m, II. v-j- 2 w=n, III. —j— 2w —J— 3 w — y—a, IV. z-\- y -f- v -f- w—Y. These four equations are not sufficient to determine the four unknown quanti- ties ; and in fact it is easily seen* that one of them is a consequence of the other three, on account of a peculiar relation introduced by the data of the problem. By adding together III. and IV. there results w=V+ a, which becomes, on account of II., 2v -f 2w=V+ a — n \ giving rise, in consequence of the chemical composition of the mixed gases, to the equation: ,r . ,r . . 1 V-f- a — n=m, or, V-f- a=m-f- n, which includes the equation I. in the other three. In order to solve the question, the quantity y of oxygen must be determined directly by absorption, after which we have for the determination of the three other unknown quantities, ~-|- 2o-f- 2tc=m, whence z=2(m-f- 2n — 2a — 2y), v-\-2 w=zn, r=6 a-|-6y— In — 2m, ~-\-2v-\- 3w=a-f- y, w>=m-f-4n— 3a — 3y. Mixture of Oxygen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. % 1270. The analysis is conducted as in the preceding cases, and from it are deduced the relations, ORGANIC CHEMISTRY. INTRODUCTION. 443 2v-\-2w=m, z-\- v-\- 2w=n, |-j_ 2v-f 3w — y=a, z-\-y + v + w=Y; which four equations are not sufficient to determine the unknown quantities, because they are connected together by the condition V -J- a=.m-\- n. The quantity y of oxygen must be determined directly by absorption, which furnishes the equations w=a-\-y — m, z= | (2« -\- m — 2a — 2y), v= i (4m—n — 2a — 2y). Mixture of Oxygen, Nitrogen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. \ 1271. The analytic operations having been conducted as in the preceding cases, and the oxygen y=b having been determined by absorption, and lastly, the whole quantity a' of oxygen consumed in combustion having been equally ascer- tained, the following relations are established: |-f-2r-f-2 w=m, whence y=b, z-\-v-\-2w-=n, — 2a'), £ 1 %-\-2v-\-3 w=a', v=-(4 m — n — 2a'), w=a'— m, z~i-y-\-u-\-v-\-w=Y, w=(V—b) -f- a'—(m-\-n). Eudiometric analysis furnishes no verification. Mixture of Oxygen, Hydrogen, Oxide of Carbon, Protocarburetted and Bicarburetted Hydrogen. | 1272. The analysis having been made as in the preceding cases, the oxygen y=b having been determined by absorbent reagents, and lastly the whole quan- tity a' of oxygen consumed having been equally determined, we have the relations Y +1 -f 2w=m, z-\-v-\- 2w=n, f + |4-2i> + 3 »*=«', x-\- z-\- v -f- w=V — b ; which four equations are not sufficient to determine the four unknown quanti- ties x, z, v, and w, because the constant quantities are connected together by the relation m-J- ra=(V—b) -f- a', which reduces the four equations to the four really distinct ones. A new relation between the unknown quantities m ist therefore be sought experimentally ; and one can be obtained by determining exactly the specific gravity D of the mixture. By designating by dx. dy dz, dv, dw, the respective densities of hydrogen, oxygen, oxide of carbon, protocarburetted and bicarburetted hydrogen, there results the relation B=xdx-\- ydy-\- zdz-f vdv -f wdw; 444 ORGANIC CHEMISTRY. which new equation, added to the first four, renders the problem algebraically determinate. A given quantity of the gaseous mixture may also be burned with oxide of copper, and the water formed weighed by using the apparatus described in $ 1214. If p be the weight of the water obtained, W the volume of gas formed by the oxide of copper, t and H its temperature and pressure at the moment of being weighed; then will the weight of the gas burned be W.0.M129S.D.£aiB-,.£> and the ratio of the weight of water formed to the weight of gas burned will be P W . 0.001293 . D . iq. 0.00367 .£ " 760 On the other hand, let U be the constant volume to which the gas has been re- duced by eudiometric analysis, 6 the equally constant temperature of the water in the cylinder, the elastic force of the original gas being V, we have, for the weight of the gas, U. 0.001293 . D. iq.0.00367.0 ' 760‘ If 7r designate the weight of water yielded by the gas when completely burned, we should have, for the ratio between this weight and that of the gas, 7C U. 0.001293 . D . iq.0.00367.0 ’ 760 whence the equation, p 7T y W . 0.001293 . D • 1 q-0.00367.t' 760 • 0.001293 . D • iq-0.00367.0 ' 760 or simply, p 7T , W 1 H U l -. V 1 + 0.00367. t 1 + 0.00367.0 whence T U 1 + 0.00367. t V T P' W' 1 + 0.00367.0' H* Now the weight of the water is equally expressed by 3z i , 1 -O-+0+W U. 0.001293.0.622 • 1q.0 00367 e 706 -» giving rise to 3» , , it.760(1 + 0,00367.0). 2 ■* V + W U.0.001293.0.622 ’ which new relation may be introduced into the calculation. Mixture of Oxygen, Nitrogen, Hydrogen, Oxide of Carbon, Proto and Bicarburetted Hydrogen. | 1273. This is the most complex mixture which will fall under our notice. Its eudiometric analysis will be conducted as in the preceding cases : after having determined directly the quantity y—b of oxygen by absorption, and burned a certain quantity of gas by oxide of copper to ascertain its weight of water formed, the carbonic acid formed during this combustion may also be collected and determined, which furnishes no new relation, but only a verification of the INTRODUCTION. 445 quantity of carbonic acid n found in the eudiometric analysis. The relations are the following; !f=b, 'If 2v -(- 2w—m, Z_J_ 2w=n, | +|+ + 3 w=.a\ xz-\-uvw=Y — b, 3x i , 7T.760(1+ 0.00367.0) A 2~ ' U. 0.001293.0.622 ’ to which may be added, if the density D of the gasqpus mixture has been deter- mined, the relation xdx -j- ydv -{- zdz -f- udu vdv wdw= D. The problem is thus algebraically determined. If each of the numerical deter- minations were made with mathematical precision, the values of the unknown quan- tities, reduced by calculation, would be strictly correct. But, however carefully the operation may be conducted, each of these determinations is liable to slight error. Now, it is easy to be certain that by varying, by a very small quantity, each of the experimental data, b, m, n, a', V, A, and D, the value of the unknown quantities vary often by much larger quantities; and, by marking certain hypo- theses, properly selected, on the composition of the gaseous mixture, it will be seen that by applying to the formulse numerical data which differ very slightly, the calculated composition of the gaseous mixture ranges often between very extended limits. This observation is particularly applicable to the relation afforded by the density of the gaseous mixture, because the latter is composed of gases of which the individual densities, in general, differ but slightly. This relation must therefore be used with great caution. We have supposed, in the preceding observations, that the nature of the ele- mentary gases composing the mixture was known; but the question becomes much more difficult when this is not the case, and can, most frequently, only be answered by analysis, which must be most carefully conducted, and repeated several times ; and the operator must satisfy himself that the relations which fre- quently exist between the experimental data, and which we have given in each case, are fulfilled. If the experimental data were mathematically exact, the formulae suitable to the most complicated mixture might be applied to them at once, and the calculation would give no values for the gases which do not exist in the mixture. But, as these data are liable to trifling errors, small values for the gases which do not exist will generally be found, which values the operator must then examine with great care, and particularly the equations which often exist between the numerical data, in order to ascertain if these equations would not be rigorously fulfilled by the experimental data, by altering the latter by quan- tities equal to the extent of error to which each one is liable. None of the me- thods of analysis by absorption indicated (§ 1244) should be neglected while examining the errors which each may have produced on the gaseous residue, by the solvent action which the reagents exert on the gas composing this residue. Lastly, if the analyst is provided with large quantities of gas, he may, by sub- jecting them to suitably selected chemical reactions, obtain some light on the nature of the component gases.* * The method for analyzing complicated gaseous mixtures is due to Bunsen, who first employed them in his masterly investigation of the gases issuing from blast furnaces.— W. L. F. 446 PROXIMATE PRINCIPLES OF PLANTS. ESSENTIAL IMMEDIATE PRINCIPLES OF PLANTS. § 1274. A microscopic examination of the various component parts of plants shows them all to be constituted of cellular tissue, varying in form according to the part of the vegetable subjected to inspection. The cavities of the tissue are filled with very diversified matter ; sometimes, as in the case of wood, the parietes of the cells are covered by a hard and brittle substance, called lignine, or woody fibre, which frequently almost completely fills their interstices; while at other times, as in the grains of the cerealia, potatoes, and other tubers, the cells contain a quantity of small ovoidal globules, varying in size, constituting fecula, or starch ; and lastly, in the case of the young organs of plants, the cells contain only a more or less viscous fluid, holding in solution mineral salts and various organic substances, the principal of which are gums, gelatinous sub- stances, and certain nitrogenous combinations, designated by the general name of albuminous substances. Oils or fat substances are frequently found in the cells, as in the oleaginous grains, some- times in large quantities. We shall begin by the study of these various substances, which are found in all members of the vegetable world, and which are essential to the existence of plants. CELLULAR TISSUE, OR CELLULOSE, C12II10010 § 1275. The cellular tissue is particularly evident in the young organs of vegetables. The cell is formed in the liquids which cir- culate through the plant, and grows by successive agglutina- tion with the cells previously formed, which occasions a modi- fication in the original forms of the cells. Sometimes they are rounded, and show a cer- tain regularity, as in the pith of the elder, (fig. 649,) and in the potato, in which case they con- stitute the cellular tissue pro- perly so called. At other times the cells form elongated tubuli, communicating by their con- tracted extremities, as seen in fig. 650, which repi'esents the longitudinal section of a stalk of asparagus, of which a transverse section is seen in fig. 651; and in figs. 652 and 653, which exhibit Fig. 049. CELLULOSE. 447 (fig. 653) a fibre of flax or hemp, and (fig. 652) a fibre of cot- ton : the tissue is then called a vascular tissue. As the vegetable portions grow old on the living plant, the vascular vessels are filled with woody fibre, which increases gradually in thickness, and leaves only very narrow canals for the cir- culation of the sap. The whole of this mechanism consti- tutes wood. Among all the substances entering; into the composi- tion of plants, the cellular tissue is dis- tinguished by its great resistance to chemical agents—a resistance which allows its separation in a state of purity sufficiently perfect to permit the study of its chemical proper- ties, and to ascertain its ele- mentary composition. It has thus been found to be identi- cal, in this respect, not only in all parts of the same plant, but also in all different vege- tables. Chemists have given the name of cellulose to that constant substance which they regard as forming the cellular tissue of all plants. Cellulose is nearly pure in cotton, in which case it consists of the down of the cotton- seed ; and in hemp and flax, that is in the textile fibres extracted from the plants of these names. Cellulose is also nearly pure in paper and old linen, which are made of the substances just men- tioned, and which, during their prepartion and use, have been sub- jected to various chemical reactions, which have gradually effected the entire destruction of the more changeable foreign substances, mixed with the cellular tissue properly so called. Cellulose is extracted from various parts of plants by subjecting them to successive chemical reactions which destroy the more altera- ble woody fibre, the preparation being longer and more difficult in proportion to the quantity of woody fibre. The substance, when obtained in as disaggregated a form as possible, is digested with hot solutions of caustic potassa or soda, and, after washing the residue, is treated with weak chlorohydric acid, and washed with Fig. 650. Fig. 651. Fig. 652. Fig. 653. 448 PROXIMATE PRINCIPLES OF PLANTS. water. By a repetition of this process for a certain number of times, the woody fibre may be completely removed; although the same result may be obtained more quickly by subjecting the sub- stance to more powerful oxidizing reagents, such as a weak solution of chlorine or hypochlorite of lime, and following each of these treatments with an alkaline solution and dilute chlorohydric acid. Although these various reagents attack the cellular tissue itself, the action on it is much less active than on the substances surround- ing it; so that if the operation be carefully conducted, and reagents diluted with water be alone used, the greater portion of the cellu- lose escapes destruction. It is washed successively with alcohol and ether to dissolve the fatty matter. Pure cellulose, which is white and transparent, is insoluble in water, alcohol, ether, and the fixed or volatile oils. Dilute acid solutions have but little effect upon it, even at the boiling point, which is also true of sufficiently diluted alkaline solutions. The resistance which cellulose presents to these reagents varies with its cohesion; recently formed cellulose being much more easily changed than that of older date. Concentrated sulphuric and phosphoric acid attack cellulose, and cause it to undergo a remarkable metamorphosis: after converting it into a soluble substance, called dextrine, they change it to a sugary substance, or glucose. Fuming nitric acid combines, when cold, with cellulose, and converts it into an insoluble sub- stance, eminently combustible and explosive, and which will be de- scribed hereafter. At the boiling point, nitric acid dissolves it, and oxalic acid is formed. Acetic acid, even in a concentrated state, has no action on cellulose. Cellulose, as it exists in the untouched cellular tissue of plants, is not coloured by an aqueous solution of iodine; but when it has commenced to be disaggregated by sulphuric acid, it assumes a beau- tiful blue colour; which reaction is frequently used in the study of vegetables under the microscope, because it distinguishes the cellu- lar tissue from certain nitrogenous membranes, which do not possess this property. After some time, a solution of chlorine, or a hypochlorite, com- pletely burns cellulose, forming water and carbonic acid; which combustion is rapid in a concentrated and hot solution of hypochlorite. The elemetary composition of cellulose is, Carbon 44.44 Hydrogen 6.18 Oxygen 49.38 100.00 The formula C12H10O10 is generally assigned to it; but as there are no means of determining its chemical equivalent, the formula representing its molecular composition may be a multiple of the LIGNIN. 449 above. It will be remarked that hydrogen and oxygen exist in it in the proportions constituting water. LIGNIN. § 1276. It has been mentioned that the sides of the cells become generally incrusted with a substance formed at the expense of the organic substances dissolved in the sap; which constitution of ligneous matter is very well exhibited in fig. 654, representing a transverse section of a piece of oak-wood, as seen through the microscope. The black spaces are the canals which still re- main in the cells; some of which former, as a, are larger, and appear to be principally used for the circula- tion of the sap. As the wood grows by annual concentric layers, easily counted in old trees, the centre layers are older than the external ones, and their cells are also much more incrust- ed with ligneous matter than the latter. The central layers of the trunk of a tree, constituting the heart, are there- fore firmer and harder than the outer layers, forming the sap-wood; and they are also less subject to change, because they contain less sap and albuminous matter, which are the principal causes of the changes and rotting of wood. Although pure ligneous matter is sometimes deposited in the cells, resinous substances, which colour the wood and increase its combus- tibility, are generally precipitated at the same time; while pellicles of nitrogenous matter are also formed. No way of isolating the ligneous matter in a state of purity being known, it has hitherto remained undecided whether the chemical composition of this substance is always identical; but sensible dif- ferences, which are observable in chemical reactions on the ligneous matter of various parts of vegetables, may possibly be produced by greater or less aggregation of the substance. Sawdust, successively subjected to the action of water, alcohol, and ether, presents a mix- ture of cellulose, lignine, a small quantity of nitrogenous matter, and several insoluble mineral salts; and by analysis it is found to contain more carbon and hydrogen than pure cellulose: thus, lig- nine contains more carbon than cellulose, and hydrogen exists in it in a proportion larger than that which wTould form water with oxygen. The following tables exhibit the elementary composition of several kinds of wood, previously dried in vacuo at a temperature of 212°: Fig. 654. 450 PROXIMATE PRINCIPLES OF PLANTS. Wood from the Trunk of the Tree. Beech. Oak. Birch. Aspen. Willow. Carbon .. 49.46.... ... 49.58... ... 50.29... ... 49.26... ... 49.93 Hydrogen.. .. 5.96.... ... 5.78... ... 6.23... ... 6.18... ... 6.07 Oxygen .. 42.36... ... 41.38... ... 41.02... ... 41.74... ... 39.38 Nitrogen.... .. 1.22..., ... 1.23... ... 1.43... ... 0.96... ... 0.95 Ashes .. 1.00... .. 2.03... ... 1.03... ... 1.86... ... 3.67 100.00.... ...100.00... ...100.00... ...100.00... ...100.00 Wood from the Branches. Beech. Oak. Birch. Aspen. Willow. Carbon .. 50.37.., .... 50.08... ... 51.29... ... 49.59... ... 51.39 Hydrogen.. .. 6.21.. .... 6.14... ... 6.17... ... 6.20... ... 6.18 Oxygen .. 41.14.. .... 41.38... ... 40.41... ... 40.23... ... 36.45 Nitrogen.... .. 0.78.. .... 0.95... ... 0.87... ... 1.00... ... 1.41 Aslies .. 1.50.. .... 1.45... ... 1.26... ... 2.98... ... 4.57 100.00.. ....100.00... ...100.00... ...100.00... ...100.00 § 1277. Wood is decomposed after some time, when subjected to the simultaneous influence of air and moisture, by the influence of a species of fermentation owing to the presence of nitrogenous albu- minous substances, and carbonic acid is disengaged, while the wood is converted into a brown or black substance, called humus, or moydd; an alteration which is the more rapid when the wood is of recent formation, because its canals, being less incrusted with woody fibre, contain more sap, and, consequently, more albuminous nitrous mat- ter, which is the principal cause of the change. This substance, by its alteration, gives rise to true ferments, and serves as food for various insects which lodge in the wood and ultimately destroy it. If this be the cause of the rotting of wood, it might readily be pre- vented, if, by certain chemical agents, the alteration of the nitro- genous matter could be prevented, thus rendering it unfit for the food of animals. All poisonous substances which prevent the putre- faction of animal matter produce this effect; but the difficulty con- sists in making it penetrate all the vessels and cells of the wood. This question has attracted a good deal of attention in latter years, and several processes have been invented for its economical deter- mination on a large scale. The liquid containing the antiseptic substance has been made to penetrate the smallest vessels of the wood, by immersing one end of the trunk of a tree, of 2 to 4 metres in length, in a tub contain- ing the solution, while to the other end is fitted a cast-iron vessel, in which a vacuum is produced by the combustion of tow soaked in alcohol. By repeating this operation 2 or 3 times, the liquid is forced by the pressure of the atmosphere to traverse the whole length of the trunk. ALBUMINOID SUBSTANCES. 451 Advantage may also be taken of the vital circulation to cause the antiseptic fluid to penetrate trees when standing or when re- cently felled. When the tree is standing, it is sufficient to make at its foot two incisions, separated by an interval of a few centime- tres, and wrap around it a bandage of water-tight stuff, which re- ceives from a tub the liquid to be imbibed by the tree. The sap- wood, of which the canals are very open, is soon injected with the liquid, winch, however, penetrates with more difficulty into the heart and the parts thickly incrusted with lignine. When the liquid is coloured, this irregular impregnation is manifested by the differences of shade and by veins, which often gives to the boards an appearance rendered very beautiful by polishing. Lastly, a process called displacement is sometimes used success- fully, which consists in placing the recently felled tree in a hori- zontal position and surrounding the trunk near its butt with a water- tight bag, held in place by a band over a pad of clay, and pouring into the bag the antiseptic liquid by means of a tube entering a tub placed somewhere near. The liquid displaces the sap and takes its place. In this way, the delicate woods, such as the pines and firs, may be rapidly and uniformly injected, but it is not so in the case of hard woods; as, although the sap-wood is soon injected, the liquid penetrates with difficulty and irregularity into the heart of the tree. This process has been greatly improved, for railroad sleepers, in the following manner:—A piece of wood, of twice the length of the sleeper, being sawed in the middle to within 8 or 4 centimetres of the opposite side, and the crack opened writh a wedge, between the vertical sides of the crack a tarred rope is in- terposed, which, being strongly compressed when the wedge is re- moved, closes the sides hermetically and forms a small narrow re- servoir in the middle of the piece of wood. The antiseptic liquid, being then poured into this reservoir, ultimately penetrates the whole piece of wood. Of the many chemical substances which may be used for this purpose, the pyrolignite of iron or impure acetate of the protoxide of iron is generally preferred, on account of its efficiency and low price. This substance, which is obtained by means of the acid liquid produced by the distillation of wood in close vessels, contains, in addition to the acetate of iron, creasote and tar, which assist in the preservation of the wood. Wood is frequently covered with tar and a substance called ma- rine glue, made by melting together 1 part of gum shellac and 2 parts of essence of coal-tar. NITROGENOUS OR ALBUMINOUS VEGETABLE SUBSTANCES. §1278. The nitrogenous matter of plants, designated under the general name of albuminoid substances, play an important part in vegetable physiology; but as they have hitherto been but imper- 452 PROXIMATE PRINCIPLES OF PLANTS. fectly studied, we shall only state what is with certainty known con- cerning them. All these substances are solid; some being soluble in water, as albumen, vegetable casein, and legumin ; while others are insoluble, as gluten. They are decomposed by heat, and exhale an odour similar to that peculiar to burnt feathers, giving rise to empyreu- matic gases and products, and leaving as an ultimate residue a black and brilliant spongy coal, the separation of which has been preceded by the fusion and swelling of the original matter. These substances may be indefinitely preserved after being perfectly dried; and in the moist state they can be preserved for a long time, if pro- tected from the air; while, when placed under the simultaneous in- fluence of air and water, they soon decompose, rot, and call into existence a host of microscopic animalcule. All albuminous substances dissolve in caustic potassa and soda, and, on adding an acid to the solution, a nitrogenous substance sepa- rates, in the form of grayish flakes, which contract, on drying, into a hard and brittle mass, while at the same time a decided smell of sulfhydric acid is disengaged, and the liquid contains a certain quantity of phosphoric acid. The name of protein has been given to this nitrogenous substance, which appears to form the essential principle of all albuminous matter. It is not yet known with cer- tainty in what state the sulphur and phosphorus exist in these sub- stances ; but some chemists suppose albuminous substances to be compounds of protein with different proportions of sulphimide NH2S, and phosphimide NH2Ph. These sulphuretted and phos- phuretted substances are moreover found in very minute quantities in them. In order to separate protein from the alkaline liquid, acetic acid must be used, because the majority of the mineral acids combine with that substance. Protein is tasteless and inodorous; soluble in water, alcohol, ether, and the essential oils; soluble with alteration after some time in boiling water; and its composition is represented by the formula C36H25N4O10. Protein combines with acids, forming compounds soluble in water, but which are precipitated by the addition of a great excess of acid, and which are decomposed by the alkalies with the precipita- tion of the protein, which is again dissolved if an excess of alkali be added. Chlorohydric acid yields with protein, and, in general, with all albuminous substances, a blue liquid. Weak sulphuric acid destroys protein at the temperature of 212°, forming several new products, among which is distinguished a white crystallizable sub- stance, called leucin. Nitric acid acts powerfully on protein, forming a yellow acid, called xanthoproteic, which combines, at the moment of its forma- tion, with a portion of the nitric acid; but the compound is destroyed by boiling water and the xanthoproteic acid is precipitated. The ALBUMEN. 453 acid, which, when pure, is of an orange-yellow colour, pulverulent, and tasteless, combines with mineral bases and acids, yielding com- pounds of a more or less deep yellow colour. The xanthoproteates of potassa, soda, and ammonia are soluble; and the other salts, which are all insoluble, are easily obtained by double decomposition. This reaction of nitric acid on protein is frequently applied in the study of vegetable anatomy to detect albuminous substances, since they are the only ones which turn yellow by contact with nitric acid. There is a still more delicate test in the reddish colour as- sumed by albuminous solutions when in contact with a mixture of nitrate and nitrite of mercury, which is easily obtained by dissolv- ing mercury in an equal weight of nitric acid containing 4|- equi- valents of water, and then diluting the liquid with twice its volume of water. This liquid reacts, when cold, on albuminoid substances, and the discoloration is more rapid when it is heated to 212°. Chlorine attacks protein suspended in water, and converts it into a white flaky substance, regarded as a chlorite of protein, because its composition is represented by the formula C3SH2JN4010C103. This substance, treated with an alkaline solution, loses its chlorine, disengages ammonia, and is converted into a soluble substance, called tritoxide of protein, because its composition corresponds to the formula C3BHS5N4012H0. Chlorine produces a similar reaction on all albuminous matter; and the same substance is also formed when water containing albumen in suspension is boiled for several days. Protein also combines with the alkaline earths, forming a pitchy substance, which becomes very hard by drying; which property is applied to the manufacture of a luting made of white of egg and slaked lime, (§ 661.) Albumen. § 1279. Albumen is a principle widely disseminated throughout plants, and existing in them either coagulated in their tissues or dissolved in the liquids which circulate through their vessels. It is also largely found in the animal economy: the serum of the blood and the white of the egg are essentially composed of a solution of albumen in water. Animal albumen appears to be identical in com- position and chemical qualities with vegetable albumen, and many physiologists admit that this substance is furnished immediately to animals by the plants on which they feed. Albumen assumes two very distinct forms: soluble albumen, and coagulated or insoluble albumen ; and in both states, its chemical composition is the same. They will be easily understood by com- paring the albumen of a raw egg to that of one when cooked. The albumen of an egg begins to coagulate at about 140°, while that of human serum remains unchanged until about 158°; and as a gene- ral rule, albumen coagulates with greater difficulty in proportion to 454 PROXIMATE PRINCIPLES OF PLANTS. the quantity of water in which it is dissolved. Coagulated albumen no longer dissolves in water, but merely swells in it; while the sub- stance obtained by evaporation, at a low temperature, from an al- buminous fluid, dissolves, on the contrary, in cold water, yielding a stringy liquid. Liquid albumen generally presents an alkaline reac- tion, and turns the plane of polarization of luminous rays toward the left; serum of the blood and all albuminous liquids exhibiting the same property.* * A large number of substances in the organic kingdom exhibit a physical pecu- liarity belonging to their molecular constitution, which appears to be a special effect of organization, as it has hitherto not been observed in any inorganic sub- stance. It consists in the property possessed by their molecules of impressing modifications on polarized light, which are analogous, in many respects, to those it experiences when passing through non-symmetrical crystallized bodies, which faculty has been called the rotatory power, from the character of the effects which it produces. In this note we shall endeavour to explain its mode of manifesta- tion and the method of measuring its principal peculiarities; and the idea we shall give it will suffice to attach it, from this time, as a specific character, to substances which possess it, as they will be described. We shall subsequently explain one of its practical applications in detail, and show how it may be applied to the exact determination, in a solution, of the proportion of matter in it which exerts the rotatory power. But, in order that these phenomena may be under- stood by persons who have not made a special study of optics, it is necessary to recapitulate a few of the chief laws of this science, on which the theory of these phenomena is based. When a simple ray of light, emanating directly from a luminous source, falls, at an angle i, on the surface of a transparent medium, a greater or less portion of the ray is reflected; and, if the medium is perfectly transparent and its sur- face polished, the portion of light not reflected traverses the medium. The plane containing the incident ray is called the plane of incidence, and the reflecting sur- face at the point of incidence is called the normal. The reflected ray remains in the plane of incidence, and its direction makes an angle i with the normal, equal to that which the incident ray makes with the same normal. The laws which the transmitted ray obeys, when the medium traversed is homogeneous in all direc- tions, are the following:—If the transmitted ray is simple, it remains in the plane of incidence, and makes, with the normal, an angle r, so that there always exists between the angle of incidence i and that of refraction r the relation s?” %=.m, ° sin r 1 m being a constant quantity for the same medium, and called the index of refraction of the medium. The same laws apply to the case in which the ray of light, instead of falling from empty space on the medium, reaches it after having traversed a first medium equally homogeneous ; and the constant quantity m is then the relative index of re- fraction of the two media, and equal to the ratio of the indices of refraction of these media with regard to the space. The light of the sun is composed of an infinity of variously coloured rays, each of which has its own index of refraction; and if therefore a mass of solar light be passed through a transparent prism, the rays separate and yield a coloured image, the solar spectrum, elongated in the direction of the refraction; the rays which have the greatest index of refraction being the farthest removed from the direction of the incident ray. The light of burning bodies affords a similar spectrum, which differs from the solar spectrum in the ratio of intensity of the various coloured parts. The portion of light reflected at the surface of separation of two media varies with the angle of incidence, and is smallest when this angle is 0, that is, when the incident ray is normal to the surface; while it increases with the value of this angle, and is equal to the incident light, when the angle of incidence is equal to 90°, in which case the light is wholly reflected. However, when the ray passes ALBUMEN. 455 Many chemical reagents coagulate albumen when cold. Alcohol reduces it immediately to the insoluble state; and ether produces the same effect, though more slowly. from a first medium into a second, of which the index of refraction is more feeble, in which case the value of m is smaller than 1, the total reflection of the incident ray commences before the rasant ray; which occurs at all the incidences for which the relation gives values for the sin r greater than 1. Thus, the total reflection begins at the angle I, for which we have sin I=m; that is, the angle of total reflection. By being reflected at the surface of separation of two media, the nature of light is remarkably modified; which is readily demonstrated by the apparatus, (tig. 655,) ab and cd are two polished transparent mirrors which revolve around horizontal axes o, o', perpendicular to the plane of the figure. The axes are supported by frames om, o'm', mounted on drums ef, e’f> which turn around the hollow cylinder gh, to which any inclination around the horizontal axis/; can be given. A narrow bundle of rays is received on the first mirror ab, at an incidence i, and the whole instrument is arranged so that the reflected ray shall follow the direction of the axis of the cylinder gh. This reflected ray is received on the second mirror cd at the same angle of incidence i; and by turning the drum ef around the cylinder gh, all possible angles can be made on the second plane of reflection with the plane of reflection on the first mirror, without changing the angle of incidence i. Now, if the light reflected by the first mirror were still na- tural light, it would be always reflected in the same proportion on the second, whatever might be the azimuth of the plane of the second reflection compared with that of the first. But this is not the case, and the intensity of the light re- flected by the second mirror diminishes in proportion as the azimuth of the second plane of reflection increases, and is a minimum when the azimuth is 90°; its variations being moreover symmetrical around the azimuths 0 and 90°. By vary- ing the common angle of incidence i, it can be ascertained that the variations of intensity of the light reflected on the second mirror in the various azimuths in- crease as we approach nearer the value of i given by the formula tang i=m, m being the index of refraction of the glass. Light which possesses this property is said to be polarized, and the angle at which it must be reflected from a transparent medium to acquire it is called the angle of polarization: it will be seen that this angle depends on the index of refrac- tion of the substance composing the mirror. Polarized light differs therefore from natural light in this, that while the latter is always reflected in the same proportion from a mirror inclined at the angle i with the incident ray, for all azi- muths of the plane of reflection, polarized light is reflected in proportions varying with the azimuth of the plane of polarization; and, if the angle i satisfies the rela- tion tang i=m, there is a position of the plane of reflection in which the reflected ray is null. The plane perpendicular to this particular direction of the plane of reflection is called the plane of polarization. When a ray of light falls on a mirror at the angle of polarization, the portion reflected is polarized in the plane of incidence; and if the properties of the re- fracted ray be examined by means of a second mirror which receives it at the Fig. 655. 456 Albumen is extracted from flour by rubbing it with ten times its weight of cold water, allowing it to digest for several hours, de- canting off the water, and digesting with an additional quantity of PROXIMATE PRINCIPLES OF PLANTS. angle of polarization, it is ascertained that the transmitted ray presents the pro- perties of a ray partially polarized, or of a mixture of natural and polarized light; but the plane of polarization of the polarized portion is perpendicular to the plane of polarization of the reflected portion. It may therefore be admitted that when a ray of natural light falls on a mirror at the angle of polarization, a portion of the light traverses the mirror without modification, but that the other portion is divided into two bundles polarized in planes perpendicular to each other; and while the first bundle, which is polarized in the direction of the plane of incidence, is reflected, the second, polarized perpendicularly to this plane, is refracted. We recognise, moreover, that these two rectangularly polarized bundles are equal to each other, and that their union produces natural light; which may therefore be regarded as formed by the union of two equal bundles, polarized at right angles. When the bundle of light which has traversed a first mirror at the angle of polarization traverses a second at the same angle, a portion of the natural light is divided into two bundles rectangularly polarized; and the bundle polarized in the direction of the plane of reflection is reflected, -while the bundle polarized perpendicularly to this plane is refracted and joins the portion polarized by the first refraction. After its passage through the second mirror, the bundle con- tains a portion of polarized light much greater than when it left the first. Trans- mission through a third mirror again increases the polarized portion; so that after passing through a sufficient number of mirrors, at the angle of polarization, the bundle of natural light is entirely separated into light polarized in the direc- tion of the plane of incidence which is reflected, and into light polarized perpen- dicularly to the plane of incidence which traverses the mirrors. Crystallized media which do not belong to the regular system, effect imme- diately the separation of natural light into its two rectangularly polarized bundles. A bundle of natural light which falls on a rhomboid of Iceland spar, is divided in the crystal into two bundles, of equal intensity, polarized rectangularly, and which separate because they obey different laws of refraction. One of these bundles is polarized in the direction of the plane of the principal section of the rhombohe- dron; while the plane of polarization of the second is perpendicular to the plane of the principal section. The first obeys the ordinary laws of the refraction of light inhomogeneous media, and remains in the plane of incidence, the law being satisfied for all incidences; for which reason it is called the ordinary ray. The second ray obeys very different laws : it remains in the plane of incidence only when this plane coincides or is perpendicular to the plane of the principal section, and it is only in this case that it satisfies a law S?n *=.?»' similar to that J sm r which the ordinary ray obeys. In all other directions of the incident ray the law of the second refracted ray is more complex; on which account this ray has been called the extraordinary ray. These two rays do not separate sufficiently to form two isolated images, except when the rhomb of spar is very thick; but a great separation may be produced by replacing the rhomb of spar by a prism cut out of this mineral; so that the edges of the prism shall be perpendicular to the principal section of the rhombo- liedron. When the refracting angle of the prism is only 5° or 10°, the two bundles separate sufficiently, but the images are coloured if the incident ray is not simple. This discoloration is avoided by gluing to the prism of spar a glass prism of a proper angle, the refraction of which, acting in a direction contrary to that of the prism of spar, almost entirely destroys the dispersion of colours. This apparatus, which is frequently used in the study of polarized light, is called an achromatic bircfracting prism,; and it enables us to examine, with ease, the pro- perties of light polarized by reflection from a mirror: when used for this purpose, it is often called an analyzing prism. If the light is completely polarized in the direction of the plane of reflection, it is evident that when the plane of the prin- cipal section of the birefracting prism coincides with the plane of reflection, all 457 flour. After having repeated this operation three or four times, a liquid is obtained containing a certain quantity of albumen, which can be separated by evaporation at a low temperature. ALBUMEN. the light will traverse the prism in the state of an ordinary ray, and the extra- ordinary ray will be extinguished. When, on the contrary, the plane of the principal section is perpendicular to the plane of polarization of the ray, the light will pass wholly in the extraordinary ray, and the ordinary ray will be null. In all the intermediate azimuths of the principal section of the birefracting prism, there will be an ordinary and an extraordinary image; and their relative intensities will vary according to the position of the principal section. The law of these varia- tions is very simple : let C be the angle which the plane of the principal section of the birefracting prism makes with the plane of original polarization; and I the intensity of the polarized ray which falls on this prism: the intensity of the ordi- nary ray is I cos X, and that of the extraordinary ray I sin X: in all cases the rays are complements of each other, for we always have I cos af-|-Isin *f=l. The birefracting prism is very convenient for determining the direction of the plane of polarization of a polarized ray; as it is sufficient to find the direction to be given to the plane of the principal section of the prism, in order that the extra- ordinary fasciculus furnished by the normal incident ray may become null. In order to understand the modifications experienced by polarized light when it traverses various media, the apparatus represented in fig. 656 is frequently used; in which ab represents a polished mirror, receiving the luminous rays at the angle of polarization, and reflecting them in the line cd, while at n is an achromatic bi- Fig. 656. refracting prism, mounted on the centre of a movable index mn, which moves on a graduated circle pq perpendicular to the line cd. The plane of polarization of the ray reflected by the mirror being vertical, the extraordinary image afforded by the birefracting prism will vanish when its principal section is in the vertical plane, and the alidade will then correspond to 0 of the division. AB is a support on which various transparent media, which will be traversed by the polarized ray, as, for example, fluids contained in tubes, can be placed. Fig. 657 represents the longitudinal section of one of these tubes; which is composed of a tube of thick glass, generally enclosed in a metallic tube to which are fitted the two ferrules m, n, which support the glass plates closing the ends of the tubes. If AB, one of those tubes, filled with water, alcohol, or ether, be placed on the support, so that the ray of polarized light may be obliged to tra- Fig. 657. 458 In order to extract albumen from potatoes, they are cut into thin slices, which are digested in water containing two per cent, of sul- phuric acid. The water is decanted after twenty-four hours, and PROXIMATE PRINCIPLES OF PLANTS. verse the liquid before reaching the birefracting prism, it will be seen that the ray has suffered no essential change in its properties by its passage through the fluid; it is still completely polarized, and its plane of polarization remains ver- tical. But, on substituting for pure water several other liquids, as, for example, a solution of cane-sugar, the properties of the polarized light are completely modified. Thus, before the interposition of the tube containing the solution of sugar, the extraordinary image of the birefracting prism is null when the index marks 0°; and the image reappears if the tube be interposed. Nevertheless, the light has not been depolarized by its passage through the solution of sugar, and remains completely polarized ; but its plane of polarization is no longer vertical, and it has been deviated by a certain angle toward the right of the observer who looks through the birefracting prism; and, in fact, if the index be turned to the right by a certain angle ct, the extraordinary image disappears entirely. The solution of sugar has, therefore, turned toward the right, by an angle n, the plane of polarization of the light. If tubes of different lengths be filled with the same solution of sugar, it will be found that the angles of deviation are in pro- portion to the lengths of the tubes. On filling a tube of uniform length, successively, with solutions more and more rich in sugar, it is found that the angles of deviation ■t are in proportion to the quantities of sugar contained in the same volume of liquid. It may, therefore, be said in general terms that the deviations, or rotations, of the plane of polarization are in proportion to the number of molecules of sugar which the luminous ray meets in its passage. Let u be the deviation impressed by a homogeneous liquid on the plane of polarization of the simple ray, acting on it under the same cir- cumstances, through units of space and with an imaginary density equal to unity. The density becoming/, without any change in the energy of the molecular action, the deviation, through the unity of thickness, will be [a] 3: then, the length becoming l for the same density, the total deviation will be [a] 13. If, therefore, a. represent the deviation observed experimentally, we shall have [a]W=a, whence [«] = The quantity [a] is characteristic of the active substance; and is the same, at equal temperatures, for all the values of l and S, and may be considered as the molecular or specific rotatory power of the homogeneous liquid observed. We have supposed that the polarized ray was simple light; which condition, though strictly fulfilled with difficulty, can nevertheless be sufficiently satisfied by placing between the birefracting prism and the eye a glass coloured red by sub- oxide of copper, which allows the red rays only to pass, and extinguishes all the others. When the polarized ray is composed of white light, and traverses a medium endowed with a moderately powerful rotatory power, the extraordinay ray is not extinguished in any position of the birefracting prism; and the two bundles dis- play very beautiful colours, which are always complementary in the two images: that is to say, which are such that they reproduce white light when superimposed on each other. It is easy to calculate these discolorations & priori, when the de- viations a3 are known which the medium exerts on the plane of polarization of each simple ray, and the intensities i„ 4, 4 of these rays in white light. Let us suppose, in fact, that the plane of the principal section makes an angle e with the vertical plane of the primitive polarization of all the rays. This plane will make an angle at,—i with the plane of polarization deviated from the first ray, and, if the medium possessing the rotatory power is colourless, that is, if it al- lows the simple rays to pass precisely in the proportion in which these rays exist in white light, the intensity of the first ray in the ordinary image will be f.cos *(*— *), and the intensity of the same ray in the extraordinary image will be t,sin —i); so again the second ray will give in the ordinary image 4cosa(«a— ), and in the extraordinary image 4sin'1(a2—e); while the third ray will give in the ALBUMINOUS SUBSTANCES. 459 allowed to rest for the same space of time on fresh slices of pota- toes ; when, after several similar operations, a yellowish liquid is ob- tained, which must then be saturated with a small quantity of po- tassa, taking care to preserve a slight acid reaction. The liquids, evaporated at a low temperature, yield soluble albumen, mixed with salts, and probably with dextrin; but if the liquid be boiled, the ordinary image ?3cosa(a3—«), and in the extraordinary image t3sina(a3—t), and so on. The ordinary image will therefore be formed by the superposition of a portion t1cos,(st1—i) of the colour of the first ray, a portion «acos*(«,—s) of the colour of the second ray, a portion t3cosa(a3—s) of the colour of the third ray, and so on. The colour resulting from the ordinary image, and its intensity, may be calculated, by means of these elements, by a peculiar law established by Newton. The colour and intensity of the extraordinary image will be calculated in the same way, by means of the constituent parts qsina(a,— t), i3sina(si2 — s), qsin' (st3—i) of each of the simple rays which compose it. Now, it has been observed, that for all media endowed with rotatory power, with the exception of tartaric acid, the relative deviations of the simple rays which constitute white light obey very nearly the same law: in other words, the deviations of the planes of polarization of the various simple rays are always proportional to each other. So that, instead of measuring the deviations produced by media endowed with rotatory power upon one simple ray, the red ray, for example, the deviations may be measured for which the ordinary and extraordinary image pre- sent identical hues. But all these hues cannot be measured with equal precision, because they are not all subject to variations equally sensible to the eye, for they have very small variations of the azimuth t of the principal section of the analy- zing prism. The variations of tint are most sensible in a certain violaceous hue of the extraordinary image ; because, however slightly the index may be turned to the right or left, the image passes suddenly from blue to red and from red to blue. This particular tint has been adopted by all experimenters, and is generally called the tint of passage, or sensible tint. The white light of the sun, and particularly that transmitted through whitish clouds, can therefore be used; and in the comparison of the molecular rotatory powers of various active media, the formula M=5 can be applied, in which * is the deviation of the index, in which the tint of pas- sage has been observed. It is important, however, to remark that these measures will be exact only if the white light used in the observation is always composed of exactly the same materials, and this proposition is not rigorously accurate, at all times, as regards the light transmitted by the vault of heaven, in which blue light more or less predominates. It would be still more inaccurate to substitute for this the light of a lamp, the composition of which differs greatly from that of solar light. The result might also be very erroneous if the media were coloured; for, in that case, they would not allow the simple rays to pass in the proportions in which they exist in white light, and it then becomes necessary to make the observation with homogeneous light. It is always useful, when the molecular rotatory powers of substances are to be measured by observing the tint of passage, to operate with tubes of suitable length, or with solutions so diluted that the angular deviations corresponding to the tint of passage shall differ but slightly; because the composition of the sensible tint differs remarkably in very diverse absolute deviations. We have endeavoured, in the preceding note, to give a general idea of the special action which certain organic substances exert on polarized light. The reader who may desire to study this subject more deeply should consult the memoirs of M. Biot, to whom the discovery of these interesting phenomena, and their application to the study of a vast number of chemical phenomena, is due. (See Annales de Chimie et de Physique, Be serie, tomes x. et xi.) 460 ESSENTIAL PRINCIPLES OF VEGETABLES. albumen is precipitated, on the contrary, in flakes, and is then pure, but has become insoluble in water. It is more easy to prepare albumen from animal liquids—for ex- ample, from serum of the blood or white of egg—as it is then suffi- cient to evaporate these liquids at a temperature below 122° to obtain it in the form of a transparent layer resembling paste. This substance, finely powdered, should be treated with ether, and then with alcohol, which dissolves the fatty substances, after which the residue is composed of soluble albumen mixed with salts. A purer albumen is obtained by pouring into the white of egg, or the serum, chlorohydric acid, which precipitates the albumen, by forming with it a scarcely soluble compound. The precipitate being separated and treated with a large quantity of water, which redissolves it, carbonate of ammonia, which precipitates the coagulated albumen in the form of white flakes, is poured into the liquid, and the preci- pitate, after being washed in water, dried, and then treated suc- cessively with water and alcohol, furnishes pure, but insoluble al- bumen. The action of acids and alkalies on albumen is inferred from what has been said touching the action of the same substances on protein. We shall merely mention the difference of action exhibited by phos- phoric acid in different degrees of hydration. Monohydric phos- phoric acid P05,II0 coagulates albumen immediately, while the triliydric acid PO„3HO not only does not coagulate it, but will even dissolve the substance precipitated by the monohydric acid. Albumen forms insoluble compounds with several metallic salts, particularly with corrosive sublimate, for which reason the white of eggs is used as an antidote in cases of poisoning by this medicine. On account of this property, also, corrosive sublimate is used in the pre- servation of anatomical specimens, as, by combining with the albumen, it prevents it from putrefying, and keeps worms from attacking them. § 1280. Gluten is most easily extracted from the cerealia, and principally from wheat, by making a thick paste with wheat flour, and kneading it under a stream of water until the water is no longer milky; when the water carries off the fecula and soluble matter, while a glutinous and elastic substance remains, which, when dried, is converted into a yellowish, translucid, and bi’ittle mass, consisting chiefly of gluten, but containing likewise cellulose, some grains of fecula which have not been removed by the water, and fatty sub- stances which can be dissolved in ether after the dried matter has been finely powdered. There are, in addition, substances which can be removed by treating them, when hot, first with concentrated, and subsequently with Aveak alcohol. The alcoholic liquors deposit, on cooling, a substance which resembles, in its composition and che- mical properties, the casein of cheese, for which reason it has re- Grluten, Vegetable Fibrine, Crlutin, Vegetable Casein. AMYLACEOUS MATTER. 461 ceived the name of vegetable casein. The alcoholic liquors, on cooling, deposit after evaporation a substance called glutin, having the same composition as albumen, and scarcely differing from it in its chemical properties. To the substance left by gluten after these various processes, the name of vegetable fibrin has been given, which substance, in fact, pre- sents the same composition as animal fibrin, which it closely resembles in its chemical properties. Vegetable fibrin combines with sul- phuric acid, producing a compound soluble in pure water, and which dissolves in a weak solution of caustic potassa, furnishing a liquor resembling in its properties that produced by animal fibrin under the same circumstances. Legumin. § 1281. Legumin is extracted from peas, beans, and lentils, which contain about 18 per cent, of it. They are chopped, and digested for two or three hours with tepid water, when the greater part of the legumin dissolves. In order to extract that which remains in the pulp, the latter is washed and again macerated with hot water, and the substance being expressed in a cloth and the liquid filtered, the legumin is precipitated from it by the addition of acetic acid. Some of the fatty substances are removed by treating the dried matter with ether and alcohol. The substance thus obtained resembles starch, when it has been precipitated by acetic acid; and when dried, it forms a brilliant and transparent mass. Its aqueous solution is precipitated by alcohol and the acids ; and it dissolves in the caustic alkalies, which appear to have no effect upon it. Its composition corresponds to the for- mula but the substance to which the name of legumin has been given is probably a mixture of several substances, which have not yet been separated. AMYLACEOUS MATTER CiaH10Olo. § 1282. The name of amylaceous matter is given to a substance which forms rounded grains, varying in appearance, with which the cells of certain parts of plants are filled. That extracted from potatoes is commonly called fecula, and that obtained from the grains of the cerealia is known by the name of starch. When the fecula of the potato is examined by the micro- scope, it will be found to consist of ovoidal granules, the surface of each of which exhibits a particular point Fig. 658. 462 ESSENTIAL PRINCIPLES OF VEGETABLES. a, the hilum, around which the substance is arranged in concen- tric layers. On the surface of each granule curves can be perceived, which sur- round the hilum concentrically, and with apparent regularity. If Fig. 659. Fig. 660. one of these grains be strongly compressed between two plates of glass, it breaks into several pieces, (fig. 659,) and all the planes of rupture generally pass through the hilum, as if the substance were less resistant at this point. Each grain is formed by the superpo- sition of a great number of very thin pellicles, which sometimes ap- pear immediately in the broken granules. They can always be shown by heating the fecula to 392°, a temperature which effects its disaggregation, and then moistening them with water,when the granules swell considerably, and the pellicles which compose them separate. Fig. 660 repre- sents a grain of potato fecula Avhich has begun to exfoliate. The pellicles may be rendered still more visible under the mi- croscope, by moistening them with an aqueous solution of io- dine, which turns them intensely blue. Two grains are frequent- ly united together, and new pel- licles of amylaceous matter are deposited on the united grains, thus forming a single irregular grain, having two hila. By triturating a small quantity of fecula, for a long time, in a rough mortar, the greater part of the granules are burst, and if the broken grains be examined by the microscope,no appearance of liquid can be recognised, and Fig. 661. Fig. G62. FECULA AND STARCH. 463 no portion of the substance can be dissolved in cold water. The entire grain is, therefore, formed of solid matter, and contains no gummy fluid, as was long supposed. The liilum is not always as apparent in the amylaceous gra- nules of other vegetables as in those of the potato, and can fre- quently only be shown by desiccation, which produces, at this point of the granules, a greater contraction than at the other points, and a depression which can be immediately recognised. The sym- metrical arrangement of the amylaceous molecules around the hilum is particularly evident on examining by the microscope potato fecula illuminated by polarized light, (fig. 661,) and interposing a rhomb of Iceland spar between the object and the eye, when a black cross, of which the centre is lost in the hilum, is observed, analogous to that produced under the same circumstances by thin plates of crystal of the same axis, cut perpendicularly to this axis. Fig. 661 repre- sents the same grains of fecula as fig. 658, but seen with polarized light. The amylaceous grains of se- veral vegetables exhibit a pecu- liar appearance which enables an experienced eye to recognise immediately the vegetable to which they belong. This fact is easily proved by figs. 658, 662, 663, and 664, which represent amylaceous grains of various kinds, seen by the microscope and illuminated by natural light. In fig. 658 there are grains of po- tato fecula; in fig. 662, grains of wheat starch; in fig. 663 are seen the amylaceous grains of peas, (the grains a belonging to dried peas, and the grains b to green peas ;) and lastly, fig. 664 repre- sents the starch from Indian corn. Potato fecula is still more easily distinguished from other fecula when seen by polarized light, as it is the only one which exhibits in this case a well- marked black cross, (fig. 661.) By this character it is possible to discover by the microscope if wheat flour has been adulterated with potato starch. The absolute size of amyla- Fig. 663. Fig. 664. 464 ESSENTIAL PRINCIPLES OF VEGETABLES. ceous grains varies greatly in different vegetables ; and the follow- ing table gives the extreme length of the granules extracted from some of them: Granules of potato 0.185 mm. “ beans 0.075 “ sago 0.050 “ wheat ! 0.045 u sweet-potato 0.040 “ Indian corn 0.025 “ millet 0.010 “ parsnip 0.007 “ mangel-wurzel 0.004 The grains of potato starch are collected in particular cells, nearly as is seen in fig. 665, which represents some full cells. § 1283. The amylaceous matter extracted from various vegeta- bles presents exactly the same chemical composition, which is iden- tical with cellulose, when the two substances have been dried under the same circumstances. Amylaceous matter, dried in vacuo at 284°, contains Carbon 44.44 Hydrogen 6.18 Oxygen 49.38 moo which composition corresponds to the formula C12HloO10; although it is generally admitted that 1 equivalent of oxygen and 1 equivalent of hydro- gen exist in it in the state of water, notwithstanding that this water cannot be driven off without injuring the amylaceous matter. Chemists have therefore as- signed to the substance sup- posed to be anhydrous the formula C12II909, and the formula C12H10O10 to those dried in vacuo at 284°. Amylaceous matter may exist in different states of hydration; and fecula, with only 1 equivalent of water, forms a very light powder, rapidly attracting the moisture of the air; but when ex- posed for some time to air which is far from its state of saturation, it increases 11 per cent., by absorbing 2 equivalents of water. The same state of hydration is obtained by drying the most hydrated fecula in vacuo, at the ordinary temperature. In moister air, it ab- Fig. 665. FECULA AND STARCH. 465 sorbs still 2 equivalents of water, and then contains 18 per cent, of it; and lastly, in air saturated with moisture it may still absorb 6 equivalents, so that it will contain in all 6 equivalents or 35 per cent, of water. In this state of hydration the grains adhere remarkably to each other, and the substance is easily compressed into balls. Moist fecula, recently extracted from the tubers, and merely sepa- rated from its water of combination by the absorbent action of plaster, retains 45 per cent, of water, and is called, in commerce, green fecula. Fecula perfectly dried in vacuo, and then exposed to a tempera- ture of 536°, assumes an amber colour without losing any of its weight; but not without being greatly modified, and transformed into a substance of the same chemical composition, but very soluble in water, and known by the name of dextrin. When the fecula has not been previously dried, this transformation is effected at a lower temperature, and it is still more rapid when heated in a tube hermetically sealed, preventing the evaporation of the water. If water containing 1 or 2 hundredths of fecula be boiled, the latter swells and separates so as to appear to dissolve in the water; but if the liquid be then exposed to a temperature below 32°, it freezes, and the amylaceous matter becomes to a certain degree ag- gregated, and separates from the liquid in the form of small pelli- cles. When fecula is diluted with 12 or 15 times its weight of water, the temperature of which is slowly raised, all the grains ex- foliate on approaching the boiling point, and swell to such a degree as to occupy nearly the whole volume of the liquid, thus converting the latter into a gelatinous paste, which is used for pasting paper. The fecula swells also, even in cold water, if 1 or 2 hundredths of caustic potassa or soda be added to it. Sulphuric, chlorohydric, phosphoric, and nitric acid also produce, when cold, the swelling and disaggregation of the amylaceous gra- nules ; the disaggregation being very rapid if the acid liquid con- tains at least 0.2 of real acid, while it follows in time, even when the quantity of acid is very small. When dilute acids are made to act on starch, at the temperature of 212°, the amylaceous matter is soon disaggregated, being converted first into dextrin, and then into a sugar-like substance, glucose, which both exert rotation to- ward the right. We shall again recur to this remarkable action. When an aqueous solution of iodine is poured upon fecula, the latter turns of a beautiful blue colour ; and the same discoloration is produced on starch in the state of paste, and even in the water in which it has been boiled. The colour changes with the more or less advanced stage of disaggregation of the fecula, and becomes insensible when the fecula has assumed the condition of dextrin soluble in water, even when cold. When water is heated contain- ing fecula coloured by iodine, the blue colour disappears com- pletely as soon as the temperature reaches 150.8°, and does not 466 ESSENTIAL PRINCIPLES OF VEGETABLES. reappear at a higher temperature; hut on allowing it to cool, the colour reappears. These effects may be reproduced several times ; hut the intensity of colour lessens each time, because a portion of the iodine is vaporized. Iodinated starch, suspended in water, is bleached by the action of solar light, the iodine being then converted into iodic and hy- driodic acid. A few drops of chlorine will cause the colour to re- appear, because they decompose the hydriodic acid, and set at liberty the iodine, which again seeks the starch. Alkaline solutions all bleach iodinated starch, by attacking the iodine, and the addition of an acid restores the colour. Neither acetic acid nor ammonia act on fecula; while fuming nitric acid combines with amylaceous matter, and forms a compound insoluble in water, called xyloidin, which is regarded as a combi- nation of 1 equivalent of amylaceous matter and 1 equivalent of nitric acid. If the nitric acid he hot, oxalic acid is immediately obtained. When fecula is ground with a concentrated solution of caustic potassa, it is converted into a substance which dissolves in cold water; and when a soluble salt of baryta or lime is poured into the solution, precipitates are obtained, which are compounds of the amylaceous matter with baryta or lime. By treating the precipi- tates with an acid, the amylaceous matter is again isolated, and the latter, in however separated a form it may exist, is again coloured blue by iodine. Chlorine, in the presence of water, acts powerfully on fecula, and ultimately transforms it into carbonic acid and water. Concen- trated solutions of the hypochlorites produce the same effect at a temperature of 212°. Cellulose, the chemical composition of which is the same as that of amylaceous matter, is not coloured blue by a solution of iodine; which reaction easily distinguishes the two substances in the micro- scopic study of the organs of vegetables. But when cellulose has been brought into contact for a few moments with sulphuric acid, it has acquired the property of turning blue by iodine; a fact which seems to prove that, by the influence of sulphuric acid, cellulose passes into a state in which it exhibits the properties of amylaceous matter. § 1284. In order to extract fecula from potatoes, the tubers are first reduced to a pulp, by means of a grater, which destroys their cells, and the pulp is then exposed to a current of water, which removes the fecula and conveys it into a proper receiver. The fecula is mixed with a small quantity of cellular tissue, which is easily removed by fresh levigation; for the grains of fecula, on account of their rounded form, fall to the bottom of the water, while the pellicles of cellulose, remaining longer in suspension, form the su- perficial layer of the deposit. INULIN AND LICHENIN. 467 Wheat starch is made in the same manner, by working a paste of flour under a stream of water, as in the method of separating the gluten, (§ 1280;) when the Avater, after being alloAved to rest, de- posits the starch it held in suspension. If flour moistened with Avater be exposed to the air, it soon putrefies, but the nitrogenous matter alone is decomposed and changed into soluble products; so that, if the deposit be A\Tashed after some time, the starch, mixed with a small quantity of cellular tissue, only remains. The putre- faction of the gluten is hastened by pouring on the flour the water arising from a previous operation, Avhich is called the mother liquid by manufacturers of starch. Inulin C12H10O10. § 1285. Certain roots contain a peculiar substance, inulin, having the same composition as amylaceous matter, and appearing to play the same part, while its rotatory power is toAvard the left, contrary to that of amylaceous matter. Inulin is generally extracted from the root of the elecampane, (inula helenium;) for which purpose the bruised roots are digested with boiling water, and the solution clarified with Avhite of egg ; when the liquid deposits inulin on cool- ing, in the shape of a white powder. This substance, which is almost insoluble in cold, dissolves freely in boiling Avater; and if the water be boiled for a long time, the inulin is changed into a sugar-like substance. Inulin dissolves readily in acids, but, at the boiling point, it is more rapidly converted into sugar, Avithout any change in the direction of the rotatory power. Boiling nitric acid converts it into oxalic acid, which transformation is probably ef- fected only after intermediate stages of condition which have not yet been observed. Lichenin C12H10O10. § 1286. Several species of moss and lichen contain a substance, called lichenin, of the same composition as amylaceous matter, but differing from it in several points. It is generally obtained from Iceland moss, by digesting the chopped moss for 24 hours with 20 times its Aveight of cold Avater, to which a small quantity of car- bonate of soda has been added, and repeating the Avashing until the Avater is altogether free from bitterness. The moss is then boiled Avith ten times its weight of water, and the boiling liquid expressed in a cloth ; Avhen, on cooling, it becomes a transparent jelly, Avhich, after being dried, is a transparent, hard, and brittle mass, soluble in boiling AArater, from Avhich alcohol precipitates it. If a solution of lichenin be boiled for a long time, it is no longer precipitated by cooling, and is converted into a gummy substance. Lichenin dis- solves readily in acids, which convert it into sugar at the boiling point; and Avhen heated Avith dilute nitric acid, it yields oxalic acid. Gelatinous lichenin is coloured blue by iodine. 468 ESSENTIAL PRINCIPLES OF VEGETABLES. Gums C12H10O10. § 1287. Certain substances, as jet imperfectly understood, which issue from trees, are called gums. Their elementary composition is the same as that of amylaceous matter, but they differ from it in several of their chemical properties : thus amylaceous matter forms oxalic with nitric acid, while, under the same circumstances, gums produce both oxalic and a peculiar acid called mucic acid. Gums may be divided in three species: 1. Gum arabic, or arabin. 2. The gum of our indigenous fruit-trees, or cerasin. 3. Gum tragacanth, of which the essential principle has received the name of bassorin. Gum arabic issues, in the form of a viscous solution, from certain species of acacia, and after some time the substance coagulates and dries on the tree. Large quantities of this gum are imported from Senegal. Gum arabic is found in small round masses, having a conchoidal and vitreous fracture; and its taste is sweetish and nearly insipid. It dissolves, in indefinite proportions, in water, imparting to it a peculiar consistence, called gummy. It dissolves slowly in cold, and rapidly in boiling water; and the liquid, when evaporated, be- comes more and more thick, and finally solidifies into a transparent mass, which presents no traces of crystallization. The purest gum arabic of commerce has always a slightly yellow- ish tinge; but it may be made perfectly colourless by passing chlorine through a boiling solution of gum and di’ying the substance. Gum arabic, being insoluble in alcohol and ether, is precipitated from its aqueous solutions when alcohol is added; which method is sometimes adopted in proximate analysis to separate gum from sugars, which dissolve, on the contrary, very readily in dilute alco- hol. The aqueous solution of gum arabic exerts a rotatory power toward the left. Gum arabic, dried in vacuo at 266°, exhibits the same elementary composition as amylaceous matter dried under the same circum- stances, and its formula is therefore Cia H10 010, or a multiple of it. Caustic potassa coagulates a concentrated solution of gum arabic; but if the solution is diluted, no precipitate is formed, although, by afterward adding alcohol, a compound of gum with potassa is formed. Subacetate of lead, poured into a solution of gum arabic, yields a white precipitate, of which the formula is PbO,C12H10O10. Under these circumstances, therefore, gum arabic behaves like an acid. Cold sulphuric acid, introduced into an aqueous solution of gum arabic, slowly inverts its primitive rotatory power, and changes it from the left to the right; the inversion ensuing more rapidly when assisted by heat; and if the liquor be boiled, the gum thus modified SUGARS. 469 is finally converted into a fermentable sugar, which also exerts a rotatory power in the latter direction. The transformation is effected by passing through a series of intermediate states, which may be observed, by saturating the acid with chalk, and precipitat- ing by alcohol the already partially modified substance. Cherry-trees, plum-trees, and various other fruit-trees exude a viscous matter, which solidifies in the air, and produces a gum called cerasin, probably a mixture of several substances. It swells in cold water, and dissolves with difficulty; but when boiled for a long time, a considerable portion of it dissolves, and the dissolved portion closely resembles arabin. Gum tragacanth flows from certain vegetables of the genus astra- galus, which are cultivated chiefly in the East: it exudes in the shape of a very thick gummy juice, which, on solidifying, forms small contorted strips. This gum is also probably a mixture of several substances; and the name of bassorin has been given to that which predominates and is regarded as its essential principle. Bassorin does not dissolve in water, even at the boiling point; but it swells and is converted into a gelatinous substance. It dissolves rapidly in the alkalies; while dilute sulphuric acid, at the boiling point, converts it into glucose. Cerasin and bassorin, when treated with nitric acid, yield a mix- ture of oxalic and mucic acid; the formation of which latter, which is easily proved, because the acid is insoluble in cold water, is a very well-marked characteristic, by which gums may be distinguished from amylaceous matter. Iodine does not colour gums when they are pure ; and when gum tragacanth assumes a blue tinge, it is easily seen that this arises from the presence of a small quantity of fecula. Vegetable Mucilage. § 1288. Many grains, such as flaxseed, and many leaves, stems, and roots of vegetables, as the mallow, marsh-mallow, borage, etc. etc., when macerated in cold, or better still, in boiling water, yield gummy and stringy liquids, in which alcohol produces a gelatinous precipitate, the nature of which has not been well ascertained. The general name of vegetable mucilage has been given to these sub- stances. The mucilage of flaxseed presents, when dried, the same elementary composition as amylaceous matter and gums. SUGARS. § 1289. Sugars are substances soluble in water, having a sweet taste, and possessing the property of being converted into alcohol and carbonic acid, when left in contact with certain nitrogenous organic substances, called yeasts, or leaven. Sugars are widely diffused through the vegetable kingdom; and three principal spe- cies have been distinguished by chemists. 470 1. Cane-sugar. 2. Grape-sugar. 3. The uncrystallizable sugar of fruits. The first species is perfectly well known, while the others are less so; and when their properties are more accurately ascertained, they will probably be subdivided. A crystallizable substance, sugar of milk, is also found in the milk of animals, and should be classed among the sugars, from the definition we have just given of these substances ; but we shall reserve its examination until the study of the fluids of the animal economy shall occupy our atten- tion. In their composition, sugars present this remarkable fact, already remarked in other substances, that their hydrogen and oxygen exist in exactly the proportions which form wTater. ESSENTIAL PRINCIPLES OF VEGETABLES. Cane-sugar C^H^O^. § 1290. Cane sugar exists in solution in the juice of a large num- ber of vegetables; and may be said to be found in all vegetables the juice of which is not acid, as acids react powerfully on cane- sugar, and convert it into fruit-sugar. Cane-sugar is also abun- dantly found in the sugar-cane, the sugar-beet, melons, turnips, carrots, the stalk of Indian corn, the ascending sap of the maple, the descending sap of the birch, and in a great number of tropical fruits, as the cocoa-nut, pineapple, etc. etc. It is principally derived from the sugar-cane and sugar-beet; and large quantities are also extracted from the sugar-maple. Very pure cane-sugar is found in commerce, either in the form of large colourless and transparent crystals, constituting sugar- candy, or in that of small crystals adhering to each other, as in our common loaves of sugar. Cane-sugar is inodorous, possesses a very sweet taste, and its density is about 1.60. It dissolves in J of its weight of cold and in a still smaller quantity of boiling water; and the solution, when concentrated, produces, by evaporation at a low temperature, beautiful crystals. It dissolves in 80 times its weight of boiling absolute alcohol, hut the greater portion of it is deposited during cooling; and it may be said to be nearly insoluble in cold alcohol. Sugar dissolves much more easily in slightly diluted alco- hol, for 4 parts of alcohol at 181.5° will dissolve 1 of sugar. Cane- sugar melted or dissolved in water turns the plane of polarization of polarized light toward the right. Cane-sugar fuses when heated above 820°, forming a viscous mass, flowing with difficulty, which solidifies into a transparent mass having a vitreous fracture. This mass, rolled out on marble tables, is sold under the name of barley-sugar; in making which article, confectioners are in the habit of adding a small quantity of vine- gar before melting the sugar. In this state, the sugar is vitreous and transparent, but in a short time, especially if the air have ac- cess to it, the outer layers become opake and fall in consequence CANE-SUGAR. 471 of the crystallization which takes place. Melted sugar, kept for some time at the temperature of 356°, loses the property of crys- tallizing when redissolved in water; and its constitution is, in that case, deeply altered. The composition of crystallized cane-sugar and that of barley- sugar corresponds to the formula C12Hn0n. If cane-sugar be heated to 410° or 428°, it loses 2 equiv. of water, and is converted into a black substance called caramel, of which the formula is consequently C12Hg09. This substance is deli- quescent, no longer tastes of sugar, is very soluble in water, which it turns of a deep brown colour, and acts the part of a weak acid, dissolving in the alkalies, and forming black precipitates with baryta and oxide of lead. On continuing to heat caramel, it parts with more water, and is converted into a black insoluble product; and, lastly, if the tem- perature be still raised, acid products and inflammable gases are disengaged, while a puffy black coal remains. All these products are obtained mixed when sugar is suddenly heated. When pounded or rubbed in the dark, sugar becomes phospho- rescent ; and when grated it has a slight taste of burnt sugar, owing to the production of a small quantity of caramel by the elevation of the local temperature. When a solution of cane-sugar is boiled for a long time, the sugar undergoes alteration, which may be readily observed by examining the successive effects of the liquid on polarized light. It first loses the property of crystallizing, and closely resembles sugar which has been heated for some time to 356° ; which alteration is effectually prevented by the presence of a small quantity of alkali. The mineral acids, even Avhen very dilute, and the greater part of the organic acids, alter cane-sugar and transform it into a sugar which no longer crystallizes as formerly by evaporation, and which turns the plane of polarization of polarized rays toward the left. This new sugar may be called sugar inverted by acids, and in its chemical properties it closely resembles fruit-sugar. Acids which produce the same transformation undergo no change themselves, and are found intact in the liquor; and the transformation takes place with the mineral acids even when cold, and much more rapidly if the temperature be raised. § 1291. Cane-sugar combines with bases, and forms, in certain cases, crystallizable compounds, called saccharates. If concentrated water of baryta be poured into a concentrated boiling solution of sugar, a crystalline mass of saccharate of baryta is deposited on cooling, having for its formula BaO + C12Hn0n. This salt hears a temperature of 392° without decomposing or 472 losing its water; but carbonic acid readily decomposes it, the sugar being redissolved and carbonate of baryta precipitated. Two compounds of cane-sugar with lime may be obtained, the first of which is produced by pouring a solution of sugar upon an excess of slaked lime, when a compound, very soluble when cold, is formed, and can be separated by filtering. If the liquid be heated to boiling, the greater part of this compound is precipitated, since it presents the remarkable property of being much less soluble in hot than in cold water; so much so, that it may even be washed in hot and then redissolved in cold water. The formula of this sac- charate, when dried at 212°, is SUGARS. 3CaO,2(C12HuOu). If, on the contrary, hydrate of lime be added, by small quan- tities at a time, to a concentrated solution of cane-sugar, until no more will dissolve, and then alcohol be poured into the liquor at 185°, a saccharate of lime is precipitated, of which the formula is Solutions of saccharate of lime have a strong alkaline reaction; and they rapidly attract the carbonic acid of the air, causing the formation of small transparent crystals of carbonate of lime, resem- bling those of the native crystals of the substance, which are depo- sited on the sides of the vessel containing them. If finely divided protoxide of lead be digested with a concen- trated solution of sugar in excess, an insoluble saccharate of lead is formed; and the liquid contains a small quantity of oxide of lead in solution. The same insoluble compound is obtained by pouring into a solution of sugar acetate of lead, which forms no precipitate, and then ammonia, which precipitates the saccharate of lead; when, by allowing the liquid and the precipitate to rest for some time in a hot place, they assume a crystalline appearance. The composition of saccharate of lead dried in vacuo corresponds to the formula Ca0,C12Hn0u. 2PbO,C12H10O10. By being heated to 320°, it loses 1 equiv. of water, and its for- mula becomes 2Pb0,C12H909; and in both states of desiccation it yields, when decomposed by sulf hydric acid, a sugary liquor, which by evaporation produces sugar. The sugary substance has there- fore undergone no permanent alteration by losing 2 equiv. of water, and it is reasonable to suppose then the formula of anhydrous cane- sugar to be C12Hg09, which would give for that of crystallized sugar C12H9,09,2II0; CANE SUGAR. 473 and the formulae of the saccharates are C12H909, BaO+2HO, Cr,H909, CaO+2HO, 2(C13H909),3Ca0+4H0. By evaporating a concentrated solution of 1 part of sea-salt and 4 parts of cane-sugar, crystals of sugar-candy are first formed, but the mother liquid subsequently deposits crystals having at the same time a sweet and a saline taste, of a deliquescent combination, of which the formula is NaCl,2(CuHuOu). Chloride of potassium and chlorohydrate of ammonia form simi- lar compounds, which often cause the loss of a large quantity of sugar, in the manufacture of beet-sugar, when the roots contain much sea-salt, as is the case when they have grown near the sea. As these compounds are deliquescent, they remain in the mother liquid or in the molasses. The presence of sugar prevents the precipitation of several me- tallic oxides by alkalies, which is especially evident in the ses- quisalts of iron and those of oxide of copper CuO, and which is readily explained, as the hydrates of the sesquioxide of iron and oxide of copper dissolve in a solution of sugar to which a certain quantity of potassa has been added. Concentrated sulphuric acid blackens cane-sugar, and yields complicated products; its action when very dilute has already been described, (§ 1290.) Monohydrated nitric acid produces with sugar an insoluble, very combustible substance, analogous to that yielded by starch. The ordinary nitric acid of commerce attacks sugar when hot, and transforms it into a very soluble and deliquescent acid, to which the names of oxalhydric and oxysaccliaric acid have been given. If the action of the nitric acid be much prolonged, a great deal of oxalic acid, which is finally converted into carbonic acid, is formed in the liquor. At the boiling point sugar reduces several metallic salts; it pre- cipitates suboxide of copper Cu20 from the acetate of copper, and metallic copper from the sulphate and nitrate of this metal; and it precipitates metallic silver from the solution of nitrate of silver, at the same time disengaging products of the oxidation of sugar, such as formic, carbonic acid, etc. etc. By distilling a mixture of 1 part of cane-sugar and 8 parts of quicklime, in a glass retort scarcely filled to one-half at a certain temperature, the mixture swells, gases are disengaged, and an oily liquid can be collected in a receiver properly cooled. The liquid, shaken with water, parts to it with a product C3H30 which is copi- ously obtained in the distillation of the acetates, and is known by the name of acetone. The liquid, exhausted by water, decomposes 474 SUGARS. nearly wholly, into an oily liquid C8II50, boiling at 183.2°, and called metacetone. Sugar of Acid Fruits C12H12012. § 1292. The second kind of sugar found in vegetables, and which is often called uncrystallizable or fruit-sugar, possesses the property of turning the plane of polarization to the left; and exists exclu- sively in the sour juices of vegetables, principally in fruits, as grapes, currants, cherries, plums, etc. etc. In order to extract it, the juice must be expressed, the acids saturated with chalk, the juice boiled with white of egg, which, by coagulating, removes the mucilaginous substances, and lastly, the liquid evaporated at a gentle heat. The substance thus obtained presents, when dried, the appearance of gum, being very deliquescent, dissolving largely in water, and even in alcohol at 91.40°, while it is insoluble in abso- lute alcohol. In contact with yeast it ferments immediately, and produces alcohol and carbonic acid. It is found already formed in the ascending sap of the birch and in the descending sap of the maple. Cane-sugar is readily converted into this second species of sugar by boiling its solutions with dilute acids, which transformation also takes place, in the presence of these acids, when cold, as well as in that of organic acids, such as tartaric, citric, malic, and oxalic, hut it requires a much longer time. Cane-sugar always undergoes this first transformation, under the influence of yeast, before that of fer- mentation properly so called, that is to say, before being converted into alcohol and carbonic acid. It is generally admitted that the uncrystallizable sugar of all fruits is identical, although this is by no means clearly proved, and several varieties will probably be found hereafter. The chemical composition of sugar fuming to the left, dried in a wTater hath, corresponds to the formula C12II12Oia. When a syrupy solution of this sugar is allowed to rest for some time, it deposits small crystalline grains of a sugary substance, which has been called, improperly, grape-sugar, being very different from the sugar which produced it, as its composition differs in contain- ing, in addition, the elements of 2 equiv. of water, thus making its formula C12H14014. By dissolving it in water a liquor is obtained which is also very different from that afforded by the non-crystalline sugar which produced it: thus, while a solution of the latter turned the plane of polarization toward the left, a solution of the crystalline sugar turns it toward the right, like cane-sugar. This granular sugar differs, moreover, from cane-sugar, not only in its crystalline appearance, but also in the manner in which it behaves with various chemical agents, and by the intensity of its rotatory power. One of the most striking differences, and one of the most easy to prove, is, that cane-sugar, boiled with dilute acids, is converted into sugar GRAPE SUGAR. 475 turning the plane of polarization toward the left; while under the same conditions, grape-sugar undergoes no change, and continues to turn toward the right. Grape-sugar C12II140S4. § 1293. We have just seen that the syrupy solution of sugar, turning to the right, yielded hy sour fruits, as well as the liquor obtained by boiling cane-sugar with dilute acids, deposit, after a time, a sugary substance in crystalline grains, to which the name of grape-sugar has been given. It is the same substance which forms the white powder on dry grapes, or raisins, and which con- stitutes the grains of sugar found in the inside. If the pulp of these fruits, freed as much as possible from their crystalline granules, be treated with water, a solution is obtained which still contains a large quantity of sugar turning to the left. The urine of patients labouring under a peculiar disease, called diabetes mellitus, or saccharine diabetes, contains sometimes 10 per cent, of a sugar, the chemical properties of which appear to be iden- tical with those of grape-sugar. A precisely similar sugar is ob- tained when starch is boiled with a weak solution of sulphuric acid, and the solution is evaporated after having been saturated with chalk; which species is generally called glucose. The granular sugar found in honey appears to be identical with grape-sugar ; and lastly, the same sugar is frequently separated from preserves made of acid fruits, in the form of crystalline crusts; in which case it has been produced by the alteration of the cane-sugar used in their manufacture, which, by virtue of the acids of the fruit, is con- verted into uncrystallizable sugar turning to the left, the latter product itself, in time, changing into grape-sugar. Grape-sugar crystallizes with much more difficulty than cane- sugar, always producing a compound crystallization; and it is less soluble in water than cane-sugar, for it requires 1J parts of cold water to dissolve 1 of grape-sugar. Its taste is also less sweet. Grape-sugar, on the contrary, dissolves somewhat more freely in alcohol than cane-sugar; as 1 part of it dissolves in 60 parts of boil- ing absolute alcohol, and in 5 or 6 parts of alcohol at 181.40. Solutions of grape-sugar turn the plane of polarization to the right. The composition of crystallized grape-sugar corresponds to the formula C12H140,4. This sugar softens at about 140°, and is completely liquefied at 212°, at which temperature it loses 2 equiv. of water, and is con- verted into a new sugar of which the formula is Cialll2012, and which then presents the composition of the fruit-sugar just described, although it continues to turn polarized light to the right. This latter sugar leaves, after evaporation, a pitch-like mass; but if this be allowed to rest for some time in contact with water, crystals of 476 SUGARS. grape-sugar are formed. If grape-sugar be further heated, it becomes brown and converted into caramel. § 1294. Grape-sugar combines less readily with bases than cane- sugar ; and, when boiled with alkaline solutions, the liquor turns brown and exhales a smell of burnt sugar, acid products being formed which combine with the alkali. If slaked lime be poured into a solution of grape-sugar, a large quantity of the lime is dissolved, and the liquor first exerts an alkaline reaction, but at a later period becomes neutral, and carbonic acid no longer forms a precipitate. The sugar is then converted into a powerful acid called glucic, of which the formula is C8II505, and which forms soluble salts with nearly all the bases; the formula of glucate of lime being Ca0,2C8IIs054-H0. The acid may be isolated by pour- ing oxalic acid into glucate of lime until no precipitate is thrown down; when, by evaporating the solution, a white acid is obtained, of a gummy appearance, very soluble in water and deliquescent. The acid forms with oxide of lead an insoluble salt of the formula 2Pb0,C8H505, which is prepared by pouring subacetate of lead into a solution of glucate of lime. The glucate of lead, suspended in Avater, is readily decomposed by sulfhydric acid, and yields free glucic acid. Glucic acid is also formed when a solution of cane or grape-sugar is boiled for a long time with sulphuric or hydrochloric acid. When a solution of glucic acid is boiled in the air, the liquid turns brown, and a new acid, called apoglucic, is formed; and by saturating the liquor with chalk, after some time, acid glucates and apoglucates of lime are formed; after which the liquid is reduced to the consistence of syrup and treated with alcohol, which dissolves the acid glucate and leaves the apoglucate of lime. The latter salt, being redissolved in water, is treated with acetate of lead, which yields a precipitate of apoglucate of lead, which, while suspended in water, is decomposed by sulfhydric acid, and yields free apo- glucic acid. Apoglucic acid is a brown, non-deliquescent substance, which readily dissolves in water, but very feebly in alcohol; and its formula, when dried at 248°, is while that of apoglucate of lead is PbO,C18H908. The same acid is formed when solutions of the alkaline glucates are boiled in the air. By pouring 1J part of concentrated sulphuric acid gradually, and by small quantities at a time, upon 1 part of grape-sugar melted at 212°, treating it with water, and lastly saturating the liquor with carbonate of baryta, a large proportion of the baryta remains in the state of insoluble sulphate of baryta, while the liquid contains a soluble salt of baryta, the sulphosaccharate. If subacetate of ba- ryta be poured into this liquid, a precipitate of sulphosaccharate of lead is formed, of which the formula, when it has been dried at 338°, is The sulphosaccharic acid is easily separated by decomposing the sulphosaccharate of lead, suspended GRAPE-SUGAR. 477 in water, by sulf hydric acid; but it is not very fixed, and is easily decomposed by a slight elevation of temperature. Grape-sugar forms a crystallizable compound with sea-salt, ob- tained by dissolving in water 6 parts of sugar and 1 of salt, and allowing the liquid to evaporate spontaneously, when beautiful well terminated crystals are deposited, of which the formula is NaCl,2(C12H12013)-f 2HO. In a dry vacuum, or under the influ- ence of heat, these crystals part with 2 equivalents of water and fall to dust. § 1295. A boiling solution of grape-sugar reduces immediately the blue liquor obtained by pouring potassa and tartrate of potassa into salts of the oxide of copper CuO, and precipitates from it the red suboxide of copper Cu30 ; which reaction is extremely sensible, because these cupreous compounds possess considerable colouring power; and it enables the chemist to detect the presence of very small quantities of sugar in a liquor, besides affording an easy means of distinguishing grape-sugar from cane-sugar, which produces no similar effect. It has been proposed to apply this reaction to the purpose of ascertaining the quantity of grape-sugar existing in a fluid. The cupreous liquor is prepared by dissolving together sulphate of cop- per, tartrate of potassa, and caustic potassa, which produce an in- tensely blue liquor ; after which the solution is reduced to a certain standard, such, for example, that 100 cubic centimetres of it shall be exactly discoloured when boiled with 1 gm. of grape-sugar.* In order to use the standard solution, 100 cubic centimetres of it are boiled in a porcelain capsule, and the liquor to be tested is gradually added to it by means of an alkalimeter. The volume of liquor which produces the exact effect contains precisely 1 gm. of sugar. This process will also serve to determine the quantity of cane- sugar contained in a liquid, as it suffices to convert the sugar, by boiling it with an acid, into sugar turning to the left, which pro- duces the same effect on the cupreous liquid, and then to operate with this liquid as has been stated, after having saturated the excess of acid. Lastly, the process may also be applied to the determination of the proportions of cane-sugar and grape-sugar which may be mixed, by first ascertaining the discolouring power of a simple solution of * The solution which has been found moat efficient is prepared by first dis- solving 20 gm. sulphate of copper in 80 cubic centimetres of water; and then adding 343.8 gm. of a solution of caustic potassa, of the specific gravity 1.12, to a solution of 80 gm. neutral tartrate of potassa in 80 cubic centimetres of water. Mix the two solutions by pouring the cupreous solution into the alkaline liquid, by small quantities at a time, and dilute the whole to the volume of 1 litre. When thus prepared the solution will keep unchanged for years.— W. L. F. 478 SUGARS. the mixture, and then that of an equal quantity of the mixture after the cane-sugar has been changed by boiling with an acid.* GELATINOUS PRINCIPLES OF FRUITS. § 1296. The juices of all ripe fleshy fruits yield, by continued boiling under certain conditions, gelatinous substances, which are derived from an immediate principle, insoluble in water, which ex- ists in greater or less proportion in all vegetables, and to which the name of pectose has been given. Pectose, which is chiefly found in the pulp of unripe fruits and certain roots, such as carrots and turnips, is intimately mixed with the cellulose which composes the cells. As it is entirely insoluble in water and all other solvents, and moreover very easily changeable, it has hitherto not been isolated, and its chemical composition has not been ascertained; but we are led to admit its existence from the peculiar products which it affords under the influence of various * By measuring the deviations produced on the plane of polarization, the quan- tity of cane-sugar contained in solutions can be ascertained with great exactness, when the liquid to be tested contains no other principles which cause the plane of polarization to deviate. For this purpose a preparatory experiment is made, on a known weight, for example, 20 gm. of very pure cane-sugar, by dissolving them in a quantity of water such that the solution shall occupy a given volume, which we will call V, and using of this solution as much as is necessary to fill a tube the constant length of which shall be, for example, 0.3 m.: let N be the deviation observed through the tube, under these circumstances. On now making, with other weights of the same sugar, solutions of equal volume V, and filling the same proof-tube with them, they will produce deviations n, n', n", and the weight of sugar con- tained in the volume Y of these solutions will be respectively 20 gm. gm. 20 gm. etc. From this, if the sugar thus tested be impure, but only mixed with substances deprived of the rotatory power, the same products 20 gm. etc., will express the absolute wreight of pure sugar contained in the gross weight used to form V. Tubes of different lengths may also be used, and the deviations observed re- duced by calculation to that which they would have been if they had been mea- sured in the same tube. As the sugar of acid fruits turns the plane of polarization to the left, the quan- tity of this sugar formed, either in its artificial solutions or in the juices of fruits which do not contain other substances acting on the plane of polarization, may be ascertained by analogous processes; the molecular rotatory power of the fruit- sugar, or the deviation produced in the tube of 0.3 m. by the solution containing 20 gm. of the sugar in a volume of 100 cub. cent., having been equally determined <1 priori. It is necessary to operate always at the same temperature, for the molecular rotatory power of this kind of sugar varies considerably with the tem- perature. The crystalline sugar of grapes and glucose turn the plane of polarization toward the right; and the preceding methods are therefore applicable to the determina- tion of those sugars which exist in solutions containing no other active ingre- dients. When cane-sugar is mixed with the sugar of acid fruits it is evident that the deviation n observed is only the difference between the deviation n' to the right of cane-sugar, and the deviation n" to the left of the sugar of acid fruits ; but even in this case the quantities of the two species of sugar which exist in the solution can PECTIN. 479 chemical agents. The characteristic property of pectose is that of being transformed, under the simultaneous influence of acids and heat, into a substance soluble in water, and called pectin, which distinguishes pectose from cellulose, as the latter yields no similar product. Pectin, which is found ready formed in ripe fruits, is developed in green fruits by the action of heat, their pectose being converted into pectin by the vegetable acids which they contain. Pectin is also obtained by boiling carrots and turnips with feebly acidulated water; but the most simple process consists in extracting it from ripe fruits. By expressing, for example, the pulp of ripe pears, and, after having filtered the juice, adding carefully oxalic acid, which precipitates the lime, and then a concentrated solution of tannin, which precipitates the albuminous matter, and, lastly, by pouring in alcohol, the pectin is precipitated in the form of long gelatinous filaments. This, being washed with alcohol and redis- be determined. After having measured the deviation n produced by the mixed solution, exactly of its volume of chloroliydric acid is added, and the liquid, having been well mixed, is maintained for 10 minutes at a temperature of 140° or 150°, by which means the cane-sugar is entirely changed into sugar turning to the left. After having reduced the temperature to exactly 59°, the deviation n of the new solution is again observed; and it now consists of the deviation n' of the original sugar of the acid fruits, and the deviation n" of the inverted sugar pro- duced by the cane-sugar. But the state of saturation of the liquor has been changed by the addition of the chlorohydric acid, and in order to take it into account, the deviation observed n' must be replaced by the deviation -L°m, which would have been observed had it not been necessary to add the acid in order to produce the inversion. We have evidently, by admitting that a quantity of cane- sugar producing a deviation n' to the right yields a quantity of fruit-sugar devi- ating by Km' to the left, n = n' — n" Jg°Mj == n"-f Kra'; which two equations will serve to determine the unknown deviations n' and n", from which may be calculated the proportions of the two kinds of sugar. The proportional coefficient K is determined, once for all, by a first experiment, made with very pure crystallized cane-sugar, at the temperature at which the test is to be made. If the cane-sugar were mixed with grape-sugar or glucose, the solution of the solution n would still be observed, and would be the sum of the separate rota- tions n' and n" of the cane-sugar and glucose. By then heating the liquor with of its weight of chlorohydric acid, the cane-sugar alone would be changed into sugar turning to the left, while the glucose would remain unchanged. Supposing n' to be the rotation of the new liquor in a tube of the same length, there would exist for the determination of the unknown n', n" the two equations n = n'~n" Jg° n, = n" — Km'. If the glucose were mixed with fruit-sugar the problem would be undeter- mined, because neither of these substances could be inverted in its action on the plane of polarization. These methods may be successfully used to determine in solutions several other substances which turn the plane of polarization, and to study in these sub- stances chemical phenomena which are with difficulty explained by ordinary chemical experiments. 480 GELATINOUS PRINCIPLES OE FRUITS. solved in water, is again precipitated by alcohol and dissolved in water, which processes are repeated until reagents no longer indicate the presence of sugar or any organic acid. Pectin thus obtained is an uncrystallizable wThite substance, though soluble in water, from which alcohol precipitates it in a jelly; or, when this solution is somewhat concentrated, in the shape of long filaments. Pectin behaves like a neutral substance to coloured re- agents, and is not precipitated by the neutral acetate of lead, while the subacetate, on the contrary, throws it down from its solutions in combination with the oxide of lead. It exerts no action on polarized light; and its composition corresponds to the formula C64II48064. An aqueous solution of pectin is converted, by boiling for several hours, into a new white substance, called parapectin, presenting the same chemical composition as pectin, and, being neutral with colour- ed reagents, very soluble in water, uncrystallizable, and insoluble in alcohol, which precipitates it in a transparent jelly. It therefore closely resembles pectin, but is distinguished from it by being pre- cipitated by neutral acetate of lead. The composition of parapectin, dried at 212°, is the same as that of pectin ; but it affords two com- pounds with oxide of lead, which are obtained by precipitating its solutions by the neutral acetate and subacetate. The formulae of these compounds are PbO,C04H48O64,HO, 2Pb0,C64H48063. Parapectin, when heated to ebullition with very dilute acids, is converted into a new isomeric modification, called metapectin ; which is distinguished from pectin and parapectin by sensibly reddening the tincture of litmus, and, being precipitated by chloride of barium ; properties possessed neither by pectin nor parapectin. Metapectin is soluble in water and uncrystallizable. It is precipitated by al- cohol, and combines with acids, forming compounds soluble in water, but precipitable by alcohol. Pectin, parapectin, and metapectin are converted into an insoluble acid, called pectic acid, by contact with the alkalies and alkaline earths. . § 1297. The vegetable parts which contain pectose, contain also a peculiar substance called pectase, which exerts quite a special in- fluence on pectin and its isomerics, analogous to that of beer-yeast on sugars. This substance may be separated by precipitating the juice of fresh carrots by alcohol; and after the precipitation the pectase has become insoluble in water, without losing its power of action on pectin. Pectase possesses the remarkable property of transforming, in a short time, pectin into a gelatinous substance, insoluble in cold water, without any apparent chemical intervention of its elements in the transformation. This phenomena, which is called pectic fermenta- PECTIC ACID. 481 tion, resembles other phenomena of fermentation, which shall soon be described in detail. The reaction may be effected when protected from the air, is accompanied by no evolution of gas, and is particu- larly easily performed at the temperature of 86°. Pectase is uncrystallizable, and, when left in water for 2 or 3 days, decomposes rapidly, becoming covered with mould, and no longer acting as pectin leaven. Its action on pectin is also de- stroyed by heating it for some time in boiling water. Pectase exists in vegetables, sometimes in its soluble and sometimes in its insolu- ble modification; while acid fruits, on the contrary, contain it only in its insoluble modification. § 1298. By introducing pectase into a solution of pectin, the latter is converted into an acid called pectosic acid, very slightly soluble in cold water, and which is precipitated in the gelatinous state. The acid is also obtained by causing cold and very dilute solutions of potassa, soda, ammonia, or the alkaline carbonates, to act on pectin; when pectosates are formed, from which the pectosic acid may be precipitated by an acid. It is essential that the alkaline liquids should not be concentrated, nor act for too long a time, for the pectosic acid would be transformed into a new acid, called pectic. Pectosic acid is gelatinous, almost insoluble in cold, but soluble in boiling water; and the solution made when hot becomes gelatinous on cooling. Pectosates are gelatinous and uncrystallizable; and the formula of the lead-salt is 2Pb0,C32H31029. § 1299. If the action of pectase on pectin be continued for a suf- ficient length of time, the latter is converted first into pectosic and then into pectic acid; which latter transformation pectin also undergoes when it is treated with dilute solutions of the alkalies or alkaline carbonates, or with lime and baryta. By treating the pectates with chlorohydric acid, the pectic acid is precipitated. Pectic acid is generally obtained from carrots or turnips, by washing the pulp of the roots until the water is colourless and taste- less ; after which it is heated for 15 minutes with a weak solution of carbonate of soda, which converts the pectin into pectic acid, forming a soluble pectate of soda. The liquor is separated, and chlorohydric acid added, which precipitates the impure pectic acid in the state of jelly. It is washed as completely as possible, and redissolved in ammonia; and, after boiling the liquid, a few drops of subacetate of lead are poured in, which precipitate a small quantity of pectic acid, with some albuminous matter which perti- naceously follows the pectic acid; after which the pectic acid re- maining in the solution is precipitated by chlorohydric acid. Pectic acid is quite insoluble in cold, and nearly so in boiling water, which distinguishes it from pectosic acid, which dissolves, on the contrary, largely in hot water. Pectic acid dissolves readily in alkaline solutions, even Avhen very dilute. The pectates of the alkalies and that of ammonia alone are soluble, while all other pec- 482 GELATINOUS PRINCIPLES OF FRUITS. tates are insoluble, and precipitate in very voluminous gelatinous masses. No soluble pectate crystallizes, but remains, after evapora- tion, in the form of a gummy mass. It is very difficult to ol)tain well-defined salts, as the composition of those procured by double decomposition varies greatly with that of the soluble pectate and the circumstances under which the precipitation takes place. The formula of pectic acid has been deduced from the analysis of the pectate of baryta obtained by treating, when cold and protected from the air, a solution of pectin with a large excess of water of baryta, when at first a precipitate of pectosate of baryta forms, which, under the influence of the excess of base, is converted into pectate of baryta. The salt, first dried in vacuo, then in an air- bath at 248°, presents the composition 2BaO,CS2H20O28. When pectic acid is boiled for a long time in water it dissolves in it completely; but is then converted into a new soluble acid, called parapectic. Pectates kept for a long time at a temperature of 302° are also changed into parapectates; the same transforma- tion taking place as when their solutions are boiled for a long time. Parapectic acid, which is very soluble in water and uncrystalliz- able, exerts an acid reaction on coloured tinctures, and forms soluble salts with potassa, soda, and ammonia; while its other salts are in- soluble, and prepared by double decomposition. The formula of the parapectate of lead, dried at 302°, is 2Pb0,C34H15031. § 1300. A solution of pectin left to itself for several days becomes strongly acid, and loses the property of being precipitated by alco- hol; after which it contains a new acid, called metapectic; the transformation taking place much more rapidly in the presence of pectose, or the pulp of green fruits. Pectin undergoes the same changes in a very short time, when boiled with dilute acids, or with slightly concentrated alkaline solutions; and lastly, pectic and para- pectic acids are converted into metapectic acid when they are boiled with dilute acids, and even undergo this change, after a length of time, in cold water. Metapectic acid, which is very soluble in cold water, is uncrys- tallizable, and forms soluble salts, which do not crystallize, with a great number of bases. Its solutions are not precipitated by waters of lime and baryta, but they afford precipitates with the subacetate of lead. Two metapectates of lead are known, of which the formulae are 2Pb0,C8H507 and 8Pb0,C8H507. Metapectic acid is as powerful an acid as the majority of acids found in fruits. PECTIN. 483 At the boiling point, parapectic and metapectic acids decompose the double tartrate of potassa and copper, and precipitate from it red suboxide of copper; in which respect they behave like grape- sugar, and sugar turning to the left; while these acids, like all the products derived from pectin, are distinguished from sugars by ex- erting no action on polarized light. § 1301. The following table shows the composition of the various substances derived from pectose, and exhibits the relations between their formulae : Formula of the free substance. Formula of the compound with oxide of lead. Pectose unknown, unknown. Pectin - C64H40O58,8HO, unknown. Parapectin - C64H40O56,8HO, PbO,C64H40O58,7HO. Metapectin ... C64H40056,8IIO, 2PbO,C84H40Os6,6HO. Pectosic acid C^O^SHO, 2PbO,C33H20038,HO. Pectic acid ... CaHa)Ott,2HO, 2PbO,C33H20028. Parapectic acid - C24H1503l,2H0, 2Pb0,C24H15011. Metapectic acid .. C8H507,2H0. 2PbO,CsHsOr From this manner of writing the formulae, it will be seen that they are all multiples of the most simple formula, CsIIs07, if cer- tain quantities of hydrogen and oxygen be neglected, which we have separated from the formulae, as if they existed in the state of water. If these relations are correct, it may be said that all the substances are derived from the first, pectin, by simple molecular partitions, and by separations or absorptions of water. Pectin is a neutral substance, and in its modifications acquires more and more decided acid properties, the last transformation being an acid as powerful as the majority of those of the vegetable kingdom. But it is important to remark that the determination of the formulae of uncrystallizable substances as unstable as those first described, and of which the acid properties are so slightly marked, presents great difficulties, and too much importance must not be attached to them. § 1302. The successive transformations of pectin under the influ- ence of pectase and the acids explain readily the modifications of this substance during the ripening of fruits, and during the process of cooking which yields jellies. Vegetable jellies are produced by the transformation of pectose or pectic acid under the influence of pectase, which transformation most frequently stops at pectosic acid; for jellies generally disap- pear when they are heated to 212°, because the pectosic acid is then dissolved; while the syrupy juice again sets into a jelly on cooling, on account of the separation of gelatinous pectosic acid. It must be admitted that, under the influence of heat and the vege- 484 table acids which exist in the pulp, pectose is first converted into pectin, and that the latter, under the influence of pectase, is con- verted into pectosic acid; and that it may even be changed into pectic acid if the action of the pectase be sufficiently prolonged. It is important to raise the temperature slowly, because, if the fruit were suddenly exposed to a temperature of 212°, the action of the pectase would be paralyzed, and the pectic fermentation would no longer be produced ; which happens in preserving fruits : they are dipped only for a few moments in boiling water, and the pectase is thus rendered inactive. MANNITE. § 1303. Mannite, which is a substance widely scattered through the vegetable organization, exists in the proportion of 60 per cent, in manna, the dried juice Avhich flows spontaneously from certain species of ash-trees in the south of Europe, and from which man- nite is easily extracted by boiling it with concentrated alcohol, which dissolves the mannite and again deposits it on cooling. Mannite also exists in the juice of onions, asparagus, celery, and mushrooms, together with sugar and other soluble vegetable substances, and is obtained from them by first destroying the sugar by fermentation, which does not alter the mannite, and then evaporating the liquor to dryness and treating it with boiling alcohol, which dissolves the mannite. The juice of sugar-beets, which after fermentation con- tains a large quantity of mannite, is evaporated to the consistence of syrup, and treate.d with alcohol to dissolve the mannite. Mannite, crystallized in alcohol, presents the appearance of long acicular crystals : it dissolves in 5 parts of cold, and in a smaller quantity of boiling water; and its aqueous solution, slowdy evapo- rated, yields larger and better-defined prismatic crystals. Heated slightly above 212°, it melts into a colourless liquid which, on cool- ing, assumes a crystalline texture; but if heated still further, it is decomposed and yields products analogous to those of the sugars. Mannite is distinguished from the sugars by exerting no rota- tory power on polarized light, by yielding no sugar turning to the left when treated with acids, and by not fermenting by contact with the leaven of sugar-like substances. Fuming nitric acid transforms it into an explosive substance, resembling that produced under the same circumstances by lignin, starch, and sugar; wdiile the nitric acid of commerce yields, when hot, oxysaccharic and oxalic acids. The formula admitted for mannite is C6H706, but it should be pro- bably doubled or trebled. Mannite combines with oxide of lead, when a very concentrated aqueous solution of it is poured into a hot solution of ammoniacal acetate of lead; when the compound separates, on cooling, into small crystalline lamellae of the formula 2Pb0,CflH304. The com- Mannite CaII706. DEXTRIN. 485 position of this product indicates that the formula of mannite should be written C8IL04,2II0. PRODUCTS OF THE ACTION OF ACIDS ON LIGNIN, CELLULOSE, AMYLACEOUS MATTER, AND TIIE SUGARS. ACTION OF DILUTE ACIDS ON STARCH. Dextrin C12H10010. § 1304. It has been mentioned (§ 1283) that fecula, when boiled for some time with water containing some hundredths of sulphuric acid, is soon completely dissolved, being first converted into a sub- stance closely resembling gum arabic, and then, if the ebullition be continued, changing into a sugar turning the plane of polarization of polarized light to the right. The first product of transformation of the amylaceous matter has received the name of dextrin, be- cause it possesses the property of deviating polarized light more powerfully to the right than any other known substance. As the elementary composition of dextrin is the same as that of amyla- ceous matter, this transformation can only be owing to disaggrega- tion ; the sulphuric acid by which it has been effected being found unchanged in the liquid. Dextrin is very soluble in water, and dissolves also in dilute alcohol, but is insoluble in absolute alcohol. As it dissolves but sparingly in concentrated alcohol, which dissolves a much larger proportion of sugar turning to the left and grape-sugar, this solv- ent is frequently employed to separate dextrin from those sugars with which it is ordinarily mixed when prepared by the process just indicated. Dextrin separated from its solutions by evaporation assumes the form of a colourless, transparent substance, without any appearance of crystallization, closely resembling gum arabic, but possessing an opposite rotatory power. Heated with the nitric acid of commerce, it yields oxalic acid, but not mucic acid, thus distin- guishing it chemically from the gums. Iodine does not colour so- lutions of dextrin, which affords an easy method for ascertaining when the transformation of the amylaceous matter is completed, and which exhibits the action of sulphuric acid in the preparation just indi- cated. By pouring into a small quantity of the hot liquor, previous to boiling, a few drops of an aqueous solution of iodine, the beau- tiful indigo-blue colour peculiar to the pure amylaceous matter is produced; while, if the same experiment be repeated some time after, the iodine produces a violet tinge, and, at a still later period, a purplish or reddish hue: lastly, no change of colour is effected; the yellowish tinge being merely due to the aqueous solution of iodine. But at this period a portion of the dextrin formed has generally undergone a more advanced transformation, and is changed 486 ACTION OF ACIDS ON STARCH. into sugar turning to the right, but of which the rotatory power is less than its own. Solutions of dextrin possess some properties of solutions of gum, and may be substituted for them occasionally in the arts. One method of preparing dextrin consists in heating fecula to a temperature of about 410°, when it becomes disaggregated and converted into dextrin; the dried fecula being spread in layers of 3 or 4 centimetres in thickness, on sheet-iron tables in a furnace heated by a regular circulation of hot air, the temperature of which must not exceed 410°. The product thus obtained is called torrefied starch, or leiocomme, and exhibits the pulverulent appearance of fecula, while its colour is slightly yellowish, owing to a more advanced decomposition. Another process consists in moistening 1000 kilogs. of fecula with 300 of water, containing 2 kilogs. of nitric acid, and, after allowing the substance to dry spontaneously, heating it for 1 or 2 hours in a stove at 212° or 230° ; when the transformation is perfected and the acid is evaporated. § 1305. Diastase.—A peculiar nitrogenous substance, called dias- tase, which possesses the property of converting a large proportion of fecula into dextrin, and even into sugar when its action is suf- ficiently prolonged, exists in the germ of the cerealia and tubercular vegetables. It appears to be formed at the moment of germination, probably at the expense of the albuminous matter contained in the grain, as it resides in the very origin of the germ, and in the eye of the tuber; and its use in the vegetable economy appears to be that of disaggregating the amylaceous matter and transforming it into an isomeric soluble substance, which the vital forces then change into other isomeric, but insoluble substances, such as cellulose, which is to form the frame-work of the growing plant. Diastase is generally extracted from barley which has sprouted, by digesting the powdered grain in water at 77° or 86°, and, after several hours, compressing the paste in a cloth and filtering; when the liquid contains diastase in solution, and may be used immediately to effect the solution of starch. If the active principle is to be sepa- rated from it, it must be heated to 167°, a temperature which does not alter the diastase, but at which an albuminoid substance mixed with it coagulates. Anhydrous alcohol is then poured into the liquor as long as any precipitate is formed, when the diastase is precipitated in flakes, which are rcdissolved in water and again precipitated by alcohol. The substance, dried in vacuo, is white, amorphous, soluble in water and weak alcohol, but insoluble in con- centrated alcohol. The aqueous solution is neutral and tasteless, and is not precipitated by acetate of lead. Diastase may be pre- served for a long time in dry air, but soon putrefies in dampness; and a temperature of 212° deprives it entirely of its action on starch, which is very powerful, for 1 part of diastase is sufficient to trans- GLUCOSE. 487 form into dextrin, and subsequently into sugar, 2000 parts of fecula; to produce which effect by the action of acid, it would require 30 times the weight of sulphuric acid. It cannot be supposed, on ac- count of the small proportion of diastase, that any ordinary chemical reaction takes place; and the phenomenon must rather be com- pared to those mysterious actions, called actions by contact, of which several examples have been pointed out in mineral chemistry; and it may also be assimilated to other phenomena, also imperfectly ex- plained, known by the name of fermentation, of which we have seen the first instance in the action of pectase on pectin. Diastase appears to be most active between the temperatures of 149° and 167°, the action ceasing at a higher degree. At 32° it still converts starch into dextrin and sugar, but at 10.4° dextrin only is formed. Diastase exerts no action on cellulose, lignin, nor even on cane-sugar, which is so easily changed by dilute acids. The action of diastase is likewise applied in the arts to the purpose of obtaining dextrin with more or less sugar, the transformation being effected in a double boiler, between the sides of which steam is made to circulate. The ground barley, called malt, being sus- pended in water heated to 167°, the fecula is added to it by small quantities as it dissolves. The operation is watched, and the liquor tested from time to time with the aqueous solution of iodine, and, when a vinous colour is produced, the action of the diastase must be quickly paralyzed, as, otherwise, >a large quantity of sugar would be formed; and it is done by rapidly heating the liquor to 212°, by passing steam through it. It is then decanted and evaporated to the consistence of syrup. The dextrin thus prepared is used in the baking of pastry, or in the manufacture of beer, cider, alcohol, and various other alcoholic liquors; while that arising from the torrefied fecula, or the action of acids, is used in the finishing of muslins, the thickening of mor- dants in dyeing and calico printing and wall-paper printing, etc. etc. Of later years it has been used in surgery, in what is called the immovable treatment of fractures:—Muslin bandages, soaked in a mucilaginous preparation, obtained by dissolving 100 gm. of dex- trin in 50 of camphorated brandy, and adding, soon after, 40 gm. of water, are rolled around the limb, and the apparatus becomes immovable when the dextrin is dry. They are easily removed, when necessary, by softening the dextrin with warm water. Glucose C13H14014. § 1306. If the action of diastase, or that of the acids on starch, be prolonged, the dextrin which is first formed is converted into sugar; and the solution, when evaporated, sets into a crystalline mass re- sembling that formed by grape-sugar. This sugar is called glucose, and its identity with grape-sugar is generally admitted. In the transformation the amylaceous matter CiaII10Olo absorbs 4 equiv. 488 ACTION OF ACIDS ON STARCH. of water to constitute glucose C12H14014; and it is important to remark that cane-sugar C12IIn0n is intermediate between these two substances, while it has hitherto been impossible to arrest the absorption of water at 1 equiv.; for it would he of immense com- mercial value if the intermediate product were cane-sugar, which is much more valuable than glucose. Glucose is found in commerce under three different forms: syrup of fecula, glucose in mass, and granulated glucose. The saccharification is generally effected by sulphuric acid, di- luted with 33 times its weight of water, and heated to a tempera- ture slightly above 212°, the operation being performed in large wooden tubs, at the bottom of which a leaden tube, having a great number of holes, is placed. The tube may be made to communicate with a high pressure steam-generator, which drives steam imme- diately into the water in the tub, which, being -f filled with acidu- lated water, is thus rapidly heated to 212°. The fecula previously diluted with water is gradually added, and in 30 or 40 minutes after the last addition of fecula the conversion into sugar is com- pleted. In order to ascertain this, a few drops of the liquid are allowed to cool on a plate, and then treated with a small quantity of a solution of iodine, which should produce no change of colour. When this result is obtained, the flow of steam is arrested, and the acid is saturated with powdered chalk, which should be gradually added, lest the effervescence produced should cause the liquid to overflow ; and the moment of saturation is ascertained by means of the tincture of litmus. The liquor is allowed to rest for 12 hours, after which it is decanted and bleached by filtration through animal black, and it is then evaporated in order to reduce it to the degree of concentration required. If solid glucose is to be obtained, the syrup is concentrated until it marks 40° or 42° of Baumd, and then, when sufficiently cool, it is run into barrels, in which it soli- difies. In order to granulate it, it is evaporated to only 32° B., and then allowed to remain for 24 hours in reservoirs, in which it cools as rapidly as possible, while the calcareous salts are deposited ; after which the syrup is brought into vats, the bottoms of which are pierced with small holes closed with pins ; fermentation being pre- vented by pouring into each vat 2 decilitres of an aqueous solution of sulphurous acid. Crystallization does not commence for 8 days : when § of the mass are solidified the pins are removed and the liquid flows out. The crystals are then dried on cakes of plaster, in a drying machine, of which the temperature should not exceed 77°, in order to prevent the fusion of the grains. Glucose in grains is rarely made, except for the purpose of adul- terating brown sugar. Glucose, in syrup or in bulk, is used in the manufacture of beer and alcohol, and for the improvement of common wines. ULMIN. 489 ACTION OF ACIDS ON SUGxiRS. § 1307. It has been mentioned that cane-sugar, by being boiled with acids, is readily converted in sugar turning to the left, which itself, after some time, undergoes a change, and separates from its solutions in the form of grape-sugar or glucose. If the action of the acids be continued, and especially if they be highly concen- trated, the reactions produced are much more complicated. Fruit- sugar and glucose should, moreover, evidently yield the same products. On dissolving 100 parts of cane-sugar in 300 parts of water, to which 30 parts of sulphuric acid are added, and heating the liquor, it will soon be seen to turn brown. The new products formed vary with the temperature of the liquor; and if the experiment be made in a retort communicating with a receiver in which a vacuum has been effected, the liquor boils at a low temperature; while if the operation be arrested after the distillation of a portion of the water, the residue is found to contain glucic acid, in larger quantity according to the prolongation of the action; besides a small quan- tity of apoglucic acid. If, on the contrary, the liquor be boiled, under the pressure of the atmosphere, after having previously filled the apparatus with carbonic acid or hydrogen gas, in order to pre- vent the oxygen of the air from affecting the reaction, it turns brown, and soon deposits black flakes, formed by the admixture of two new substances, ulmin and ulmic acid. These substances are separated by means of potassa, which forms a soluble salt with ulmic acid, while the ulmin is isolated. The formula of ulmin, dried at 284°, is C40Hl6Ol4; and the solution of ulmate of potassa, which is of a deep red colour, deposits, when saturated with an acid, ulmic acid in the form of a gelatinous black precipitate. The acid is slightly soluble in fresh water, but does not dissolve in water containing acids or salts. The composition of ulmic acid, dried at 284°, is the same as that of ulmin, but at 383° it loses 2 equivalents of water without further change, and takes the formula C40H14013. The acid dried at 284° is therefore a hydrate By dissolving ulmic acid in ammonia, a soluble salt is obtained, of the formula (NII3,H0),C40H14012; and by pouring soluble metallic salts into a solution of ulmate of ammonia, double ammoniacal ulmates are precipitated. Thus, the formula of the precipitate yielded by nitrate of silver is (NH3H0),C40H14013+Ag0JC40H1401, The water which distilled over during the ebullition of the sugar with sulphuric acid contains a certain quantity of formic acid C2H03,H0 ; the production of which, being rich in oxygen, explains how sugar, in which oxygen and hydrogen exist in quantities form- ing water, yields, in this new reaction, substances in which hydro- gen predominates. If the contact of air is not avoided in this ex- 490 ACTION OF ACIDS ON CELLULOSE. periment, or better still, if the boiling be effected in glass vessels, the ulmin and ulmic acid undergo new transformations, which, to be perfect, require a prolonged action of the sulphuric acid, which is still further concentrated by evaporation: two black substances, humin, and humic acid, are formed, and are separated by potassa, which dissolves the latter. The formula of humin is and that of humic acid ; and these substances are therefore derived from ulmin and ulmic acid by simple oxidation. The for- mula of hydrated humic acid is C40II15O15, showing it to be isomeric with humin; but as it loses 3 equivalents of water by heat, its for- mula should be written 3HO. In fact, the formula of the humate of silver, dried at 212°, is AgO,C40H12013. When the action of acids is continued for a long time, and espe- cially when the humin and humic acid are boiled with concentrated chlorohydric acid, formic acid is again disengaged, and a black substance is obtained, the composition of which, dried at 293°, corresponds to C34H130g. The same substance is formed when humin and humic acid are boiled with a concentrated solution of caustic potassa, and the residue of evaporation is heated to 572°. When the action of the caustic potassa is continued, raising the temperature more and more, there are successively formed two new substances, insoluble in potassa, the formula of the first of which is C34II10O8, and that of the second C34H703. By comparing the formula of these compounds, it will be observed that the potassa immediately effects the separation of new quantities of water. ACTION OF SULPHURIC ACID ON CELLULOSE. § 1308. Cellulose dissolves readily in cold concentrated sulphuric acid, being first converted into dextrin, and then into glucose. The experiment is made by wetting 2 parts of old linen, or paper, with 3 parts of concentrated sulphuric acid, digesting the mixture for several hours, and treating the gummy matter, which remains per- fectly colourless, with water. The sulphuric acid is then saturated with carbonate of baryta, and filtered, when the liquor contains dextrin, and a very small quantity of a soluble salt of baryta, formed by a peculiar acid containing sulphuric acid. If, on the contrary, the mixture be boiled for several hours with water, the dextrin is completely converted into glucose, and a weight of this sugar may be obtained greater than that of the linen used in the experiment; which result is explained by the formulae of the two substances; that of cellulose being C13H10O10, while that of glucose is C12H14014; showing that the cellulose combines with water to form glucose. Starch, inulin, and the gums likewise dissolve in cold concen- trated sulphuric acid, and are converted into products analogous to those yielded by cellulose. OXYSACCHARIC ACID. 491 ACTION OF NITRIC ACID ON CELLULOSE, AMYLACEOUS MATTER, DEXTRIN, AND SUGARS. § 1309. The concentrated nitric acid of commerce acts energe- tically, when hot, on all these substances, first dissolving them, and then giving off nitrous vapours while, if the operation he sufficiently prolonged, the liquid is found to contain only oxalic mixed with an excess of nitric acid. It has been mentioned (§ 259) that this is one way of preparing oxalic acid. But by using more dilute nitric acid, and heating it in a water-bath, a new acid, which has been called oxysaccharic, and sometimes oxalhydric acid, is first formed ; the best method of obtaining which consists in heating in a water- bath 1 part of cane-sugar dissolved in a large quantity of water, with 2 parts of nitric acid. When the evolution of nitrous vapours ceases, the liquor is saturated with chalk, and then filtered to sepa- rate the oxalate of lime and chalk in excess; after which acetate of lead is added, which throws down a white precipitate of oxysac- charate of lead. The precipitate is suspended in water, and decom- posed by a current of sulfhydric acid gas, wrhich precipitates sulphide of lead, while the oxysaccharic acid remains isolated in the liquor. This is divided into 2 equal parts, one of which being exactly saturated by carbonate of potassa, the other half is added to it; by which means a binoxysaccharate of potassa is produced, a salt which crystallizes readily, and may be purified by successive crystallizations. It is easy to prepare oxysaccharic acid by means of this salt, by again precipitating it by acetate of lead, and decom- posing the salt of lead by sulfhydric acid. Oxysaccharic acid is very soluble in water, and has never been obtained in a crystalline form. The binoxysaccharate of potassa, which dissolves in 4 parts of boiling water, but is very slightly soluble in cold water, has the formula (K0-f-H0),C12H807. The formula of oxysaccharate of zinc is 2Zn0,C13H807, showing the acid, therefore, to be bibasic, (§ 1225.) Nitric acid readily converts oxysaccharic into oxalic and carbonic acids. § 1310. Monohydrated nitric acid, when cold, exerts on starch, cellulose, and sugar—an action very different from that of the same acid when hot and more dilute ; forming highly explosive, insoluble substances, which are suddenly converted into a gaseous volume 600 or 800 times larger than themselves. During the last few years, these substances have attracted considerable attention, as it was supposed that they could be substituted for gunpowder. When cotton is dipped, for 12 or 15 minutes, into monohydrated nitric acid, it does not change its appearance, although it absorbs a certain quantity of the acid; but if it be washed and carefully dried, a substance retaining the appearance of cotton, but which suddenly deflagrates when touched with a burning coal, is obtained. 492 ACTION OF NITRIC ACID ON STARCH, &C. This substance has been called gun-cotton, nitric cotton, andpyroxyl. Its composition, from the most correct analysis, corresponds to the formula C34H17017,5N0S; according to which, 2 equivalents of cellulose CiaH10O10 have lost 3 equivalents of water and gained 5 of nitric acid. Pyroxil is insoluble in water, alcohol, and acetic acid, but dis- solves sparingly in pure ether, while a much larger proportion dissolves in ether to which a few hundredths of alcohol have been added; and it also dissolves slightly in acetic ether. When pro- perly prepared, pyroxil explodes at a temperature of about 338°, and yields a mixture of oxide of carbon, carbonic acid, nitrogen, and vapour of water. Hemp, flax, linen, paper, and, in short, all substances consisting of cellulose, yield analogous products, the inflammability and pro- jectile force of which are, however, not the same, owing undoubt- edly to the difference of cohesion of the cellulose in the original substance. Starch yields a similar product, called nitric starch, or pyroxam, the chemical composition of which appears to be the same as that of pyroxyl. But pyroxam is soon spoiled spontane- ously, especially in a moist atmosphere. It has been ascertained that a mixture of equal equivalents of monohydrated nitric acid and concentrated sulphuric acid can be advantageously substituted for pure monohydrated nitric acid. The cotton is dipped into it, withdrawn in 15 or 20 minutes, and com- pressed with a glass spatula so as to dry it as much as possible; after which it is washed several times, and carefully dried at a tem- perature not exceeding 212°. Gun-cotton, when used in firearms, communicates to the ball the same initial force as four times the same weight of powder, and possesses in addition the advantage of not fouling the piece nearly so much. It is also more easily transported, and is not injured by moisture; but all these good qualities are more than counter- balanced by great disadvantages, which have led to its rejection, after numerous experiments in various countries. Its chief objec- tion is its liability to burst the gun, and in all cases to strain it more than common powder. Its price is also six times greater than that of powder; and several serious accidents have occurred in its manufacture, which, however, might possibly be avoided by greater care. Comparative experiments made in mining with gun-cotton and blasting-powder have proved the great superiority of the former ; the explosive force of gun-cotton having been found to be 4 times that of blasting-powder; and still greater effect, with more economy, has been produced by adding A of its weight of nitrate of potassa to the pyroxyl. § 1311. A solution of gun-cotton in ether yields by evaporation a transparent substance insoluble in water, and adhering power- MUCIC ACID. 493 fully to any bodies to which the etherial solution is applied. This substance, called collodion, is now extensively used in surgery; and in its preparation the process just described for the manufac- ture of pyroxyl is slightly modified; the cotton being allowed to remain for 1 or 2 hours in a mixture of 3 parts of concentrated sulphuric acid and 2 parts of nitrate of potassa, and then washed and dried as usual; after which the product is treated with ether containing 6 or 8 hundredths of alcohol, which dissolves a portion of it. The syrupy solution, spread over the skin, leaves, after the evaporation of the ether, an impervious pellicle insoluble in water, and sufficiently adhesive to be advantageously substituted for the ordinary adhesive plaster sometimes called court-plaster. ACTION OF NITRIC ACID ON GUMS. Mucic Acid CBH407,H0. § 1312. Gums treated with hot nitric acid of commerce (§ 1287) yield, in addition to oxalic and carbonic acids, another, the mucic, which is very slightly soluble in cold water; and we have said before that the production of this acid established a ready distinc- tion between gums, amylaceous matter, dextrin, and the mucilagi- nous and gelatinous principles of vegetables. A peculiar kind of sugar, called sugar of milk, is found in the milk of mammiferous animals, differing essentially from the various kinds of sugar hitherto described, and also yielding mucic acid with nitric acid. It is gene- rally employed in the preparation of the acid, by boiling 1 part of powdered sugar of milk with 6 parts of ordinary nitric acid, and allowing the liquid to cool as soon as the nitrous vapours cease passing over, when the mucic acid is deposited in the form of small granular crystals. It is washed in cold and then dissolved in boil- ing water, from which the liquor deposits pure mucic acid on cool- ing. Mucic acid dissolves in 66 parts of boiling water, is almost insoluble in cold water, and reddens tincture of litmus. If a solu- tion of it be rapidly evaporated, the substance undergoes an iso- meric modification and becomes soluble in alcohol, which does not dissolve ordinary mucic acid; and the alcoholic solution deposits, by evaporation, flattened crystals which dissolve in 17 parts of boiling water. But this modification of mucic acid is not very fixed, being rapidly converted into ordinary mucic acid when its solutions are allowed to cool. The two modifications of mucic acid yield dif- ferent salts; and those of the second modification, which are the more soluble, are converted, when cold, into salts of the first modi- fication. The alkaline mucates are but slightly soluble in cold water, and the other salts are insoluble. The formula of mucate of silver is 494 DECAY OF VEGETABLE MATTER. AgO,C6H407; and the formula of crystallized mucicacid is C0H.O8, which should perhaps rather be written C8II407,II0. Mucic acid, heated in a glass retort furnished with a receiver, is decomposed and yields, together with very complicated empyreu- matic products and a residue of carbon, a new acid, called pyro- mucic, which is partly deposited in the form of crystals in the neck of the retort. By dissolving these crystals in the liquor collected in the receiver, evaporating it to dryness, and subjecting the resi- due to resublimation, purer pyromucic acid is obtained ; and lastly, the acid is redissolved in water and purified by crystallization. Pyromucic acid, which is colourless, melts at about 266°, volatiliz- ing at a higher degree, and dissolves in 26 parts of cold and 4 of boiling water. The alkaline pyromucates are very soluble in water, while those of the alkaline earths are very slightly so. The formula of pyromucate of silver is AgO,C10II3O5, and that of sublimed pyromucic acid is C10H3O5+HO. PRODUCTS OF THE SPONTANEOUS DECOMPOSITION OF CELLULOSE AND OF THE OTHER ESSENTIAL PRINCIPLES OF VEGETABLES. § 1313. Vegetables decompose spontaneously when exposed to moisture and the oxygen of the atmospheric air, being converted into a brown substance called humus, or mould, the nature of which is very imperfectly known. Peat in an advanced stage of decom- position, as well as the decomposed ligneous substances found in the cavities of certain trees, contain the same substances. Four prin- cipal substances have been procured from it, which appear to be identical with those obtained by causing acids to act on sugar at the temperature of ebullition, and which we have designated by the names of humin, humic acid, ulmin, and ulmic acid; although they sometimes, indeed, present states of hydration differing from those of the analogous products prepared with sugar. The formula of an ulmic acid obtained from a peat from Frise wTas C40Hl8014+2HO, that is, it contained 2 equivs. of water more than the ulmic acid of sugar ; and the composition of its ammonia- cal salt was (NH3,HO),C40H18O14. A black peat from Harlem (Holland) yielded a humate of ammo- nia (NH3,IIO),C40H14012+3HO; which retained its water at the temperature of 284°, which is not the case in the analogous salt prepared with the humic acid resulting from the decomposition of sugar. § 1314. Enormous quantities of combustible substances, of im- mense importance in metallurgy and the various arts, are found in MINERAL FUEL. COAL FORMATIONS. 495 the bosom of the earth. They are evidently produced by the de- composition of vegetables which grew in the vicinity, or the debris of vegetables carried down by rivers. Peat mosses exhibit, though on a smaller scale, an example of this formation; as they consist of innumerable herbaceous vegetables, spontaneously decomposed by the action of water and atmospheric air; and their various stages of alteration may be followed, from the perfectly herbaceous turf to the earthy turf presenting but few or no recognisable remains. The vegetable structure is frequently perfectly preserved in the mineral combustibles of the tertiary formation, where pieces of wood, called lignite, are found still retaining their original form, but having become friable, and yielding a brown powTder by pul- verization. In the mineral fuel of older formations, the vegetable structure has generally disappeared, and it forms black, brilliant, compact masses, of a schistose texture, yielding a black or more or less brown powder; it is called pit-coal, or sea-coal, and is rare in the secondary, but very abundant in the transition formation; in the upper stratum of which they are so frequent as to characterize them by the name of coal formation. In the upper strata of the transition rocks the mineral fuel, which is sometimes called anthracite, is generally very compact, rich in carbon, difficult to ignite, and yielding but little volatile mat- ter by calcination. Anthracite is sometimes, though rarely, found in the superior strata, and even in the secondary rocks. Pit-coal of the coal formation yields on calcination a great quan- tity of volatile substances and inflammable gases, and experiences, prior to decomposition, an incipient fusion, while the coal remaining, or the coke, presents the appearance of a swollen or bloated mass. Al- though the structure of plants can no longer be recognised in certain combustible minerals, their vegetable origin is undoubted, for in the layers of schist or sandstone which bound the layers of coal, impres- sions of plants are frequently found, which are so distinct and clear as to enable the botanists to detect the family to which they belong, and thus, partly, to restore the flora of antediluvial epochs. In the tertiary rocks a mineral fuel is also found, which is soft, or easily fusible, forming irregular masses, or a kind of strata, and pre- senting a bearing analogous to that of the lignites, while at other times they permeate layers of schist or sandstone belonging to va- rious geological formations, and then seem to arise from the decom- position, by heat, of other combustible minerals contained in the earth. Some of these substances, which are called bitumen, con- tain a large amount of nitrogen, and are fetid, yielding, on distilla- tion, considerable quantities of carbonate of ammonia. They appear to have been generated by the putrefaction of animal matter, chiefly by that of fishes, the impressions of which are frequently found in the neighbouring rocks. 496 DECAY OF VEGETABLE MATTER. § 1315. Coals may be divided into five classes: 1. The anthracites. 2. Fat and strong, or hard pit-coal. 3. Fat blacksmith’s or bituminous coal. 4. Fat coal burning with a long flame. 5. Dry coal burning with a long flame. 1. Calcination scarcely changes the appearance of anthracites, as their fragments still retain their sharp edges, and do not adhere to each other. They have a vitreous lustre, and their surface is some- times iridescent, while their powder is black or grayish-black. They burn with difficulty, but generate a large amount of heat when their combustion is properly effected. In blast-furnaces anthracites re- quire a great blast, and those only can be used which do not soon fall to powder, as otherwise the furnace would be speedily choked. We have seen (§ 1072) that anthracite is used in Wales for heating re- verberatory furnaces; and it is now proper to remark, that the flame produced by the combustible under these circumstances is not owing to the combustion of the volatile substances given off by the anthra- cite, but rather to the combustion of the carbonic oxide formed by the passage of air through a thick layer of fuel. 2. Fat and strong, or hard pit-coals, yields a coke with metallic lustre, but less bloated and more dense than that of blacksmiths’ coals. They are more esteemed in metallurgic operations requiring a lively and steady fire, and yield the best coke for blast-furnaces. Their powder is brownish-black. 3. Fat bituminous, or blacksmith’s coals, yield a very bloated or swollen coke, with metallic lustre, and are more highly valued for forging purposes, because they produce a very strong heat, and allow the formation of small cavities, in which the pieces to be forged can be heated. Blacksmith’s coal is of a beautiful black colour, and exhibits a characteristic fatty lustre: its powder is brown. It is generally brittle, and breaks into cubical fragments, which adhere to each other in the fire. 4. Fat coals burning with a long flame generally yield a swollen, metalloid coke, less bloated, however, than that of blacksmith’s coal. These coals are much esteemed in a reverberatory furnace, particularly when a sudden blast is required, as in puddling, and are also well adapted to domestic purposes, and are preferred for the manufacture of illuminating gas. They yield a good coke, but in small quantity, and their powder is brown. 5. Dry pit-coal burning with a long flame yields a solid, me- talloidal coke, the various fragments of which scarcely adhere to each other by carbonization. This coal is also applicable to steam-boilers, and burns with a long flame, which, however, soon fails, and does not produce the same amount of heat as the coals of the preceding class. ANALYSIS OF MINERAL FUEL. 497 § 1316. The elementary analysis of combustible minerals, which easily explains their various properties, and indicates the uses to which each is most applicable, is effected like that of organic sub- stances, (§1210 et seq.;) but as coal is generally difficult to burn, it is necessary, at the close of the experiment by which the quantity of water and carbonic acid it contains is determined, to pass a cur- rent of oxygen gas through the tube, (§ 1211,) which burns the last particles of carbon. The organic analysis of coal yields the hydro- gen, carbon, and nitrogen which they contain; but it is also neces- sary to determine the proportion of earthy matter which exists in very various degrees in them, and which remains in the ashes after combustion. For this purpose two grammes of the coal are ignited in a thin platinum capsule, heated by an alcoholic-lamp, and the ashes re- maining are weighed. This method of incineration is difficult, and requires considerable time, only in those anthracites which do not burn readily, and it is then more easily effected if the coarsely pow- dered anthracite be placed in a small platinum vessel, heated in a current of oxygen in a porcelain tube. It is essential carefully to examine the nature of the ashes. Sea-coal of the coal formation frequently leaves argillaceous ashes, in which case there is a trifling error in the supposed composition of the fuel, because the small quantity of water always contained in clay, and which it loses at a red-heat, is regarded as existing in the state of hydrogen; and this error, which is of no importance if the quantity of ashes is small, may be considerable in the opposite case. The ashes often contain, likewise, peroxide of iron, wdiich metal ge- nerally exists in coal in the state of pyrites, and the analysis is thus inaccurate for two reasons: the proportion of ashes is valued at too low a rate, because, instead of the iron pyrites, sesquioxide of iron is weighed, the weight of which, for the same quantity of iron, is less; and again, in combustion by oxide of copper, the substance may yield sulphurous acid, which interferes with the deter- mination of hydrogen and carbon. The latter cause of error is avoided by placing in the combustion-tube, in front of the oxide of copper, a column of one or two decimetres of oxide of lead, which completely retains the sulphurous acid, (§ 1216.) The quantity of pyrites in the coal may be ascertained by determining, on the one hand, the quantity of sesquioxide of iron which exists in the ashes, and, on the other, the quantity of sulphuric acid yielded by a known weight of coal, powdered very finely, and acted on by fuming nitric acid, or ordinary nitric acid, to which small quantities of chlorate of potassa are gradually added. It is evident that these determina- tions are necessary only when the combustible produces a large quan- tity of ashes, and when the latter are very ochrous. Coal belonging to the secondary and tertiary formations often 498 DECAY OF VEGETABLE MATTER. yields calcareous ashes, in which case it becomes necessary, before weighing them, to sprinkle them with a solution of carbonate of am- monia, which is subsequently evaporated at a gentle temperature. But the determination of the carbon is generally inaccurate, because the carbonate of lime of the ashes gives off, by contact with the ox- ide of copper in the combustion-tube, a portion of its carbonic acid ; and the oxide of copper must then be replaced by chromate of lead, intimately and largely mixed, with the coal reduced to impalpable powder, (§ 1216,) after which the carbonic acid produced by the car- bonates of the ashes, which has been determined by direct weighing of these carbonates, is subtracted from the carbonic acid formed by combustion. Coal also retains one or two per cent, of hygrometric water, which must be previously driven off by drying it in a stove at 270° or 280°. § 1317. It is necessary, in order to form a correct judgment of the nature of a combustible, to determine the weight of coke it yields by burning ; and it is indispensable that this operation should always be conducted under the same circumstances, as the quantity and nature of the coke depend on the manner of calcination. The best method consists in placing 3 gm. of the coal in a thin pla- tinum crucible, accurately covered by its lid, and rapidly heating it to a red-heat. The crucible is kept at a red-heat for eight minutes, and after cooling without being uncovered, the coke is weighed, and carefully examined.* § 1318. The calorific power of fuel is calculated from its chemi- cal composition; admitting that this power is equal to the sum of that of the carbon it contains, and that of the hydrogen obtained by subtracting from the total quantity of hydrogen that which would form water with the oxygen contained in the fuel. This hy- pothesis is not strictly true, but it may be admitted when the quan- tities of heat afforded by various kinds of fuel are only to be com- pared by approximation.f This comparison is generally made in another way, based on the supposition that the calorific powers of combustibles are in propor- tion to their reducing powers; that is, to the weight of the same oxide which they can reduce to the metallic state. An intimate mixture of 1 gramme of finely powdered combustible and 40 gm. of litharge being introduced into an earthen crucible, 20 gm. of litharge are added, and the crucible is covered with its lid and rapidly heated to a red-heat. It is allowed to cool, and, after being broken, the lump of lead is weighed, which rapidly separates from the scoria of the litharge; and it is assumed that the calorific powers of combus- * Rapid coking is very wasteful of coke, and yields a larger amount of tar and gaseous products.—J. C. B. t M. BuR’s experiments on fuel, the best ever made, have shown the fallacy of the assumption named in the text.—J. C. B. MINERAL FUEL. 499 tibles are in proportion to the weight of lead yielded by this experi- ment. This supposition is not absolutely exact, because combusti- bles yield, before attaining the temperature at which they act on the litharge, a small quantity of volatile substances possessing a re- ducing power—which substances are more abundant in combustibles of recent formation than in those containing a larger proportion of oxygen. § 1319. The following table exhibits the composition of a large number of kinds of mineral fuel, taken from various geological for- mations, and from the kinds best marked and most extensively ap- plied in the arts. The fragments containing least ashes have also been chosen, in order to cast no uncertainty on the composition of the combustible itself. The table contains, 1st, the actual composition of the coal, as afforded by direct analysis; and, 2dly, the composition calculated by abstracting the ashes contained:— 500 MINERAL FUEL. Species of Combustible. Locality. Nature of the Coke, and other remarks. f Pennsylvania. ' Is found in an argillaceous transition schist; fracture vitreous; coke r I. Anthracites.. Wales Mayenne ] In the lower portion of the coal for- mation ; fracture vitreous and con- choidal; coke pulverulent In argillaceous transition schist ; fracture conchoidal and vitreous; Roldue 1 Lower part of the coal formation ; fracture vitreous, hut texture lami- nated; coke slightly adherent II. Fat and hard pit-coal." - Alais (Roche- Belle) Rive-de-Gier. (P. Henri).. 1 1 'Coal sandstone; fracture unequal; coke metalloid; slightly swollen or bloated Coal sandstone ; fracture schistose ; coke metalloid and swollen m M o o III. Fat black- smith’s coal." Rive-de-Gier. 1. Rive-de-Gier. 2. Newcastle 1 Coal formation; of a beautifully black, greasy lustre; very swollen metalloid coke ' Coal formation; of a beautiful black ; fracture more schistose; coke rather less swollen ’ Coal formation ; of a beautiful black; fracture schistose and prismatic; coke swollen P5 o M Flenu of Mons 1. Coal formation; rhomboidal frag- ments; coke swollen Coal formation; less marked rhom- M CO Jz; <1 P$ H IV. Fat pit- coal burning Rive-de-Gier. (cemetery) 1. Idem 2 Rive-de-Gier. Couzon 1.... J boidal cleavage; coke swollen Coal formation ; lustre feeble, texture schistose; coke swollen, but less brilliant The same as No. 1 ' Coal formation ; lustre more marked, texture very schistose ; coke swol- len, but less brilliant Coal formation; lustre very feeble; fracture unequal, and not schistose; coke less swollen ’ Coal formation ; lustre brilliant; frac- ture conchoidal; coke swollen and . light Coal formation; English cannel-coal; without lustre; fracture conchoidal; coke fritted and brilliant Coal formation ; lustre brilliant, tex- ture schistose; adherent metalloid coke, but slightly swollen Coal formation; resembling cannel- coal; fracture conchoidal; metal- loid fritted coke with a long' flame. Lavaysse Lancashire.... Epinac Commentry... V. Dry pit-coal' burning with a long flame. Blanzy 1 Coal formation; fracture laminated; lustre brilliant; coke slightly ad- herent, but not swollen MINERAL FUEL. 501 Density. Coke yielded by calci- nation. ELEMENTARY COMPOSITION. COMPOSITION, THE ASHES BEING REMOVED. Carbon. Hydrogen. Oxygen and Nitrogen. Ashes. Carbon. Hydrogen. Oxygen and Nitrogen. 1.462 89.5 89.21 2.43 3.69 4.67 93.59 2.55 3.86 1.348 91.3 91.29 3.33 4.80 1.58 92.76 3.38 3.86 1.367 90.9 90.72 3.92 4.42 0.94 91.58 3.96 4.46 1.343 89.1 90.20 4.18 3.37 2.25 92.28 4.28 3.44 1.322 77.7 88.05 4.85 5.69 1.41 89.31 4.92 5.77 1.315 76.3 86.65 4.99 5.49 2.96 89.29 5.05 5.66 1.298 68.5 86.25 5.14 6.83 1.78 87.82 5.23 6.95 1.302 69.8 86.59 4.86 7.11 1.44 87.85 4.93 7.22 1.280 U 86.75 5.24 6.61 1.40 87.97 5.31 6.72 1.276 69.8 83.51 5.29 9.10 2.10 85.30 5.40 9.30 1.292 (< 82.72 5.42 8.18 3.68 85.88 5.63 8.49 1.288 70.9 80.92 5.27 10.24 3.57 83.91 5.46 10.63 1.294 69.1 83.67 5.61 7.73 2.99 86.25 5.77 7.98 1.298 64.6 81.45 5.59 10.24 2.72 83.73 5.75 10.52 1.311 65.6 80.59 4.99 9.10 5.32 85.12 5.27 9.61 1.284 57.9 81.00 5.27 8.60 5.13 85.38 5.56 9.06 1.317 57.9 82.60 5.66 9.19 2.55 84.63 5.85 9.52 1.353 62.5 80.01 5.10 12.36 2.53 82.08 5.23 12.69 1.319 63.4 81.59 5.29 12.88 0.24 81.79 5.30 12.91 1.362 57.0 75.43 5.23 17.06 2.28 77.19 5.35 17.46 502 MINERAL FUEL. Species of Combustible. Locality. Nature of the Coke, and other remarks. r r Anthracites Lamure ( Jurassic formation; grayish-black; -j lustre vitreous; fracture conchoi- a g a ( Jurassic formation; grayish-black ; m W a o Ph Ph t <1 Q eg #o *c «2 P Pit-coal wf Obernkirchen Ceral { lustre vitreous ; coke pulverulent.. J Jurassic formation; aspect of fat ( coals; coke metalloid and swollen, f Marls of the lower oolite ; aspect of ■< coals burning with a long flame; • it Noroy f Variegated marls; of a dull black; -< fracture unequal; coke not adhe- o w m *-< • Z' .2 2 *■« p 1 Saint-Girons.. f Green sandstone; very brilliant; p “ Belestat The same as that from Saint Girons. f Of a beautiful black; fracture un- t equal; free from ligneous texture; r I. Perfect lig- nites 1 Bouches-du- Rhone f Schistose; pure and brilliant black ; < free from ligneous texture; coke Mt. Meissner. f Brilliant; fracture conchoidal; coke - Lower Alps... j Black; lustre greasy; coke slightly CQ M o o . pH N p3 i O M II. Imperfect lignites 1 Greece Cologne f Laminated ; of a dull black; indices t of vegetable organization; coke not ( adherent C Umber-coloured; friable; streak red- < dish-brown; texture ligneous; coke ( not adherent ( Fossil wood; woody texture; very pq H III. Lignites passing into ■ bitumen Ellebogen Cuba f Compact, homogeneous; fracture con- { choidal; very light metalloid coke | Velvet-black colour; lustre greasy; { coke swollen and very light IV. Asphaltum.. f Black; very brilliant; strong smell; ( ingly swollen •P 65 1 c S Turfs or Peats ■ Yulcaire f In a very advanced stage of altera- ■< tion, though still exhibiting some ( remains of vegetables a * P J Champ-du- f In a less advanced stage of altera- < tion, though still containing some ( vegetables Wood MINERAL FUEL. 503 Density. Coke yielded by calci- nation. ELEMENTARY COMPOSITION. COMPOSITION, THE ASHES BEING REMOVED. Carbon. Hydrogen. Oxygen and Nitrogen. Ashes. Carbon. Hydrogen. Oxygen and Nitrogen. 1.362 89.5 88.54 1.67 5.22 4.57 92.78 1.75 5.47 1.919 88.9 70.51 0.92 2.10 26.47 95.90 1.25 2.85 1.279 77.8 88.27 4.83 5.90 1.00 89.16 4.88 5.96 1.294 53.3 74.35 4.74 10.05 11.86 83.40 5.32 11.28 1.410 51.2 62.41 4.35 14.04 19.20 77.25 5.38 17.57 1.316 42.5 71.94 5.45 18.53 4.08 75.02 5.69 19.29 1.305 42.0 74.38 5.79 18.94 0.89 75.06 5.84 19.10 1.272 49.1 69.52 5.59 19.90 4.99 73.18 5.88 21.14 1.254 41.1 63.01 4.58 18.98 13.43 72.78 5.29 21.93 1.351 48.5 70.73 4.85 22.65 1.77 72.00 4.93 23.07 1.276 49.5 69.05 5.20 22.74 3.01 71.20 5.36 23.44 1.185 38.9 60.36 5.00 25.62 9.02 66.36 5.49 28.15 1.100 36.1 63.42 4.98 27.11 5.49 66.04 5.27 28.69 1.167 “ 55.27 5.70 36.84 2.19 56.50 5.83 37.67 1.157 27.4 72.78 7.46 14.80 4.96 76.58 7.85 15.57 1.197 39.0 74.82 7.25 13.99 3.94 77.88 7.55 14.57 1.063 9.0 78.10 9.30 9.80 2.80 80.34 9.57 10.09 U « 56.25 5.63 32.54 5.58 59.67 5.96 34.47 u (< 57.29 5.93 32.17 4.61 60.06 6.21 33.73 t( U 57.00 6.11 31.56 5.33 60.21 6.45 33.34 (t u 49.60 5.80 42.56 2.04 50.62 5.94 43.44 504 DECAY OF VEGETABLE MATTER. § 1320. In order to see how the composition of mineral com- bustibles varies with their qualities in the arts and geological age, the numbers contained in the last three columns of the table must be compared; that is, those which exhibit the composition of these combustibles after the ashes are removed. On assuming as a standard of comparison the coals of the third class, and ascending from this to those of the second, it will be found that the quantity of hydrogen is nearly the same, but that the oxygen has remarkably decreased and been replaced by carbon. On passing from the second class to the first, it will be observed that both the hydrogen and oxygen decrease, while the carbon increases in the same ratio. Starting always from the blacksmith's coal, we descend toward the fourth class, and remark that, generally, the hydrogen exists in greater quantity; and that the carbon decreases remarkably and is replaced by oxygen. Lastly, in the fifth class, the oxygen has still increased, and taken the place of a corresponding quantity of carbon. Fat pit-coal may become dry in two ways: either by passing into anthracite, the hydrogen and oxygen both decreasing, and the carbon increasing in the same ratio, or by approaching the more modern combustibles, the lignites, the carbon decreasing and being replaced by oxygen; in which latter case the ratio between the oxygen and hydrogen increases. By now comparing the combustibles of the secondary with those of the coal formation, it will be seen that, in the inferior stratum of the latter formation, the same variety can be distinguished. Thus, the anthracites of Lamure and Macot, which are found in the lower part of the jurassic rocks, present the same composition as' those in the transition rocks; while the coal from Obernkirchen, which also exists in the jurassic formation, has the same properties and composition as those of the carboniferous formation. Lastly, the coal from Ceral, which also occurs in the jurassic formation, belongs, on account of its composition and applications in the arts, to the class of fat coal burning with a long flame. The coal found in the upper stratum of secondary rocks re- sembles, on the contrary, the combustibles of the tertiary rocks or the lignites, which differ from the coal of the older rocks by con- taining less carbon and more oxygen ; and, as their formation approaches a modern period, their composition resembles more closely that of wood. The charcoal they yield by calcination be- comes more and more dry : thus, the jet of chalk still yields a fritted metalloid coke, while the lignites of the tertiary rocks produce a non-metalloid charcoal, the fragments of which do not adhere to each other, and resemble in appearance wood charcoal. The bitumens, which are evidently products of distillation of older combustibles, or produced by the spontaneous decomposition ALCOHOLIC FERMENTATION. 505 of animal substances, differ essentially from coal properly so called, by containing much larger quantities of hydrogen. § 1321. The majority of vegetables containing amylaceous matter contain, at the same time, substances which can, under favourable circumstances, convert this matter into sugar. These substances are sometimes developed only at certain stages of vegetation; as, e. g. the grains of the cerelia contain at the moment of germination a peculiar substance, diastase, (§ 1305,) which chiefly resides at the point of insertion of the germ in the grain, and which, under fa- vourable conditions, rapidly converts starch into a soluble sub- stance, dextrin, and then into sugar, if its action be continued for a sufficient length of time. In these successive transformations the chemical composition of the amylaceous matter is unchanged, while it has become soluble, and may be carried into the circulation of the sap, where it aids in the development of the vegetable, by forming the cellulose which is to constitute the skeleton of the new plant. Ripe* fruits which contain a large quantity of sugar, like- wise contain a peculiar substance, called ferment, which, under certain circumstances, possesses the property of decomposing the sugary matter into alcohol and carbonic acid ; a certain tempera- ture and the contact of oxygen or atmospheric air being required for the exercise of the action. If ripe grapes be expressed under mercury, and the juice collected in a bell-glass completely filled with mercury, it will remain unchanged for several days; but if a few bubbles of oxygen or atmospheric air be introduced into the bell-glass, a considerable volume of gas is disengaged, the evolution of which ceases generally in 2 or 3 days. If the juice be then ex- amined, a volatile liquid, called alcohol, will be found to have taken the place of all the sugar; but if the sugary substance of the fruit is not decomposed in the uninjured fruit, it is because the active principle, or ferment, or the substances which produce it, did not come in contact with oxygen, a condition indispensable for the pro- duction of fermentation. Ferment is also produced when animal or vegetable matter is allowed to decompose spontaneously, as in the manufacture of beer, when it is called yeast of beer, or simply yeast, which substance soon effects the fermentation of the aqueous solution of the sugars and their complete conversion into alcohol and carbonic acid. Muscular flesh, urine, gelatin, white of eggs, cheese, gluten, legumin, extracts of meat and blood, left to themselves for some time, exposed to air and moisture, and thus undergoing the process known as putrefac- tion, cause sugars to ferment, and convert them into alcohol and carbonic acid. All the sugars above described undergo this decomposition under the influence of ferment, and it is a distinctive character of this ALCOHOLIC FERMENTATION. 506 ACTION OF FERMENTS. class of organic products, although they do not all experience it in the same space of time; the sugar of acid fruits turning to the left, the solid sugar of dry fruits and glucose being very rapidly de- stroyed by fermentation, while cane-sugar requires a longer time. It is even easy to perceive, by the inversion of the rotatory powers, that cane-sugar undergoes fermentation only after being converted into fruit-sugar. Fresh ferment always contains a considerable quantity of acid, which first changes the cane-sugar into fruit sugar; but as vegetable acids require considerable time to effect this transformation, its fermentation is very slow. Yeast, freed from these acids by washing, for a long time exerts no action on cane-sugar, and fermentation commences only when fresh quantities of acid are formed by the spontaneous change in the yeast from ex- posure to air and water. If, on the contrary, the acid liquid arising from washing the yeast be added to the solution of sugar, the cane- sugar is gradually transformed into fruit-sugar, which immediately ferments when brought into contact with the washed yeast. One hundred parts of fruit-sugar yield by fermentation 48.88 of carbonic acid and 51.12 of alcohol; so that the chemical elements of the yeast appear to have no agency in the reaction, which is expressed by the following equation: C13H120ia=4C02+2C4.H60a. Sugar. Alcohol. § 1822. That the decomposition of sugar by fermentation is effected only by tho immediate contact of yeast, is easily showm by the follow- ing experiment:—Having adapted, by means of a cork, to the mouth of a bottle A, (fig. 666,) containing a solution of sugar, a large tube ab open at both ends, the lower one of which is covered by a sheet of bibulous paper, a small quantity of yeast of beer slightly diluted with water is introduced into the tube. As the solution of sugar penetrates the tube ab through the paper, fermentation ensues very actively, and carbonic acid is copiously disengaged, while no similar reaction takes place in the liquor in the bottle, which remains unchanged for any length of time. During the decomposition of sugar by fermentation, the ferment itself is destroyed, so that a small quantity of the active principle cannot decompose an indefinite quantity of sugar; and if the pro- portion of yeast be too small, its decomposition is effected before that of the sugar, a portion of which then remains unchanged in the liquor. If, on the contrary, the yeast predominates, the de- composition of the sugar is effected before that of the yeast, and the latter continues to change spontaneously; and if an additional quantity of the solution of sugar be introduced, it produces fermenta- tion until it is entirely destroyed. The best proportions to induce Fig. 666. ALCOHOLIC FERMENTATION. 507 rapid fermentation are 1 part of cane-sugar, 3 or 4 of water, and \ of fresh yeast; and if the proportion of sugar be increased, the fermentation becomes less active, and ceases entirely if a saturated solution of sugar be used. In all cases sugar does not destroy more than 2 per cent, of its weight of ferment. The wrnak acids, in small quantities, increase fermentation, while alkalies, on the contrary, arrest or completely modify the process. § 1323. Ferment is a species of microscopic vegetable, which is spontaneously developed in the organs of plants, and in a large number of nitrogenous substances wiien left to putrefy; and which is also formed by exposing to the ordinary temperature a solution of sugar mixed with albuminous substances of vegetable or animal origin. After some time the liquor becomes cloudy, and small ovoidal bodies are deposited, gradually increasing in size until they attain a diameter of the of a millimetre. Two species of fer- ments, differing in their manner of development and mode of action on solutions of sugar, may be observed. The first, called upper yeast, is developed in a mixture of sugar and water and albuminous substances, when the temperature is comprised between 64.5° and 77° ; while the second, or lower yeast, is only found at temperatures between 32° and 46.4°. In order to study the shape and develop- ment of the globules under the microscope, a very small quantity of yeast is diluted in an infusion of grain, sprouted barley for example, and a drop of the liquid is placed between two pieces of thin glass, the edges of which are luted to prevent the evaporation of the water. These plates are placed under the microscope, taking care to bring an isolated globule of yeast under the centre cross- threads of the micrometer, in order to study its development. Figs. 667 to 674 represent the arrangement of the new globules of fer- ment which form successively around an original globule 1, the temperature being about 66.2°. During the first two hours the globule 1 (fig. 667) exhibits nothing peculiar ; while, after this period, there forms at a point of its surface a rupture which gradu- ally increases for six hours, until it has attained the dimensions of the original globule, (fig. 668.) The second globule soon generates a third, which arises on the sides of the second (figs. 669 and 670) in the same way as this grew on the first, and so on. In an ex- periment lasting three days, 30 globules (fig. 674) had formed around the original globule 1; and on the fourth day another formed, which was the last, the albuminous matter necessary for their formation having probably been exhausted. Six successive generations, which were thus observed, are indicated in the figures by ciphers, according to the order of their origin. The various globules adhered to each other, but there appeared to be no inter- communication. It will hence be perceived that, on adding an albuminous sub- stance to a mixture of sugar and ferment, the sugar is not alone 508 ACTION OF FERMENTS. affected by the ferment, as the albuminous matter itself undergoes several metamorphoses and is converted into yeast; which fact ex- plains the reason why, in breweries, at the close of the operation, Fig. 667 Fig. 668. Fig. 669. Fig. 670. Fig. 671. Fig. 672 Fig. 673. Fig. 674. a quantity of yeast is withdrawn seven or eight times greater than that which had been originally used. The yeast is carefully col- lected, and subsequently used to effect other fermentations, par- ticularly in the making of bread. It is easy to observe that each globule is composed of a solid envelope containing a liquid; and it therefore forms a sort of cell, which is lined with a layer of mucilaginous substance. On ob- serving for several days the systems of globules which have acquired their perfect development, it will be seen that smaller granules, whose rapid motion proves that they float in a liquid, are formed in each globule ; and after a sufficient length of time the whole of the contained liquid is converted into granules. The globules the development of which we have followed belong ALCOHOLIC FERMENTATION. 509 to the upper yeast; and it is easy to see that they are formed by shoots upon each other. The lower yeast is always composed of isolated globules scattered through the liquid; their formation obeying the same laws as those of the upper yeast, while the tem- perature must not exceed 44.6° or 46.4°. Each globule appears at first like an isolated point in the liquid, and gradually increases until it attains a diameter of about of a millimetre. Some ob- servers think that the old globules of lower yeast burst and suspend in the liquor the granules they contain, each of which would then be transformed into a globule; in which case the mode of genera- tion of the lower would differ totally from that of the upper yeast. If the temperature be raised to 68° or 77°, the isolated globules of lower yeast are immediately developed by shoots, and then pro- duce upper yeast. § 1324. The action of the two kinds of yeast on solutions of sugar is also very different; upper yeast producing a much more active fermentation, with a copious evolution of carbonic acid, while the yeast is violently agitated in the liquid, and ascends to its surface; while, on the other hand, lower yeast acts much more slowly, and frequently requires two or three months to effect the complete transformation of sugar into alcohol and carbonic acid, the ferment being disturbed by no rapid movement, but on the contrary gently deposited at the bottom of the liquid. Lower yeast is used in the manufacture of certain kinds of beer, particularly that called Bavarian. It has been impossible to follow with the microscope the trans- formations of yeast during the fermentation of sugar, on account of the disengagement of carbonic acid ; and it has been merely as- certained that the yeast increases by about \ of its weight. Its chemical composition is also changed; and while fresh yeast has been found to contain Carbon 47.0 Hydrogen 6.6 Nitrogen 10!0 Oxygen, about 35.0 and, in addition, small quantities of sulphur, phosphorus, and some mineral bases, such as potassa and lime ; the same yeast, after fer- mentation was composed of Carbon 47.6 Hydrogen 7.2 Nitrogen 5.0 Thus, the carbon remained nearly the same, while the hydrogen sensibly increased, and the nitrogen decreased by one-half. On bringing an aqueous solution of iodine into contact with globules of ferment, the outer envelope is not coloured, while the o ~ 510 liquid inside becomes of a brown colour, which may be proved by crushing the globules between plates of glass, when the envelopes exhibit the characters of cellulose. When a certain quantity of yeast is allowed to decompose completely, in contact with a solu- tion of sugar, and the residue is bruised in a mortar, and perfectly exhausted by water, alcohol, and ether, a white substance remains, which yields glucose with sulphuric acid, and does not dissolve in alkaline liquids, which, on the contrary, immediately dissolve the albuminous substances in yeast.* § 1325. Ferment, dried in vacuo or at a low temperature, yields a hard, corneous, semi-transparent, and reddish-gray mass ; the pro- perty of which, of causing the fermentation of saccharine liquors, is only suspended, and is again called forth by digesting the substance for some time in water. If it be boiled for a few moments, it loses this property; but may recover it by contact with the air, when it has not been exposed for too long a period to a temperature of 212°. Alcohol, sea-salt, and a great excess of sugar, oxide of mercury, corrosive sublimate, pyroligneous acid, sulphurous acid, nitrate of silver, the essential oils, etc. etc. destroy the fermenting power of yeast; while certain substances, which are very violent poisons to animals, such as arsenious acid and tartar emetic, do not produce this effect; and neither do these substances prevent the fermentation of certain microscopic plants, for solutions of tartar emetic, if exposed to the air, become covered with confervae. The action by which ferment converts sugar into alcohol and carbonic acid is yet unexplained. Some chemists insist that vital force causes the development and successive metamorphoses of the globules of ferment; while others think that ferment only acts by its presence, and that its action should be compared to that by which certain mineral substances effect the decomposition of feeble compounds without any change in their elementary composition. Thus, binoxide of manganese will decompose binoxide of hydrogen into oxygen and water, without being itself in the least changed; and so again, chlorate of potassa, which is decomposed only at a temperature of 930° or 1020° when heated alone, experiences this de- composition at a much lower temperature when it is intimately mixed with oxide of copper or binoxide of manganese, oxides which remain unchanged in the residue. Lastly, according to some authors, the movements of the particles of ferment during their successive meta- morphoses are the principal cause of the decomposition of sugar; as these movements, by being communicated to the saccharine par- ACTION OF FERMENTS. * In an investigation of the products of the spontaneous decomposition, or fer- mentation, of yeast of beer alone, I found the liquid contained in the small cells to be completely decomposed into butyric acid with traces of valerianic, and into a substance the behaviour of which corresponded in all respects to leucin, but the analysis of which was unfortunately prevented by accident.— W. L. F. ALCOHOL. 511 tides, destroy their inertia, and cause the elementary molecules to be grouped so as to form more fixed compounds. We shall be satisfied with stating what is known concerning alcoholic fermenta- tion, and shall venture no explanation of this mysterious phenomenon, which is as yet too imperfectly understood to allow the establish- ment of any theory upon certain data. Alcohol C4II603. § 1326. It has been mentioned that a solution of sugar, when left for some time in contact with yeast of beer, soon ferments, and is converted into alcohol and carbonic acid; but the same decompo- sition takes place spontaneously in the saccharine juice of many fruits, such as grapes, cherries, currants, apples, pears, etc.; and also ensues, when assisted by yeast, in the saccharine liquors pro- duced by amylaceous substances in the presence of diastase. The alcohol remains in the liquor, and may be separated from it by distillation, because it is more volatile than water. In fact, on dis- tilling in an alembic, wine, beer, cider, or other alcoholic liquors, the first portions of liquid which pass over are much richer in alco- hol than the residue; and if the distillation be arrested at the proper moment, the residue contains scarcely any alcohol. For this purpose, alcoholic liquors are used, the production of which exceeds their consumption, or the inferior quality of which renders them unfit for market. If the distilled portions be redistilled, the first liquors are still richer in alcohol, and thus alcoholic liquors are obtained bearing different names, according to their strength; and while liquors containing 50 to 55 per cent, of alcohol are called brandies, those containing more are called spirits. By a proper process of distilla- tion, liquors containing from 85 to 90 per cent, of alcohol may be obtained, which then nearly consist of 1 eq. of alcohol C4H603 46 83.T 1 eq. of water 9 16.3 55 100.0 The last portions of water cannot be removed bj distillation, but they are separated by combining them with substances which have a great affinity for water, and which do not unite permanently with alcohol. The best method of obtaining anhydrous alcohol consists in pour- ing alcohol of 85 or 90 per cent, into a large bottle containing quick- lime prepared by the process mentioned § 555, shaking the bottle several times, and allowing it to rest for 24 hours ; after which the liquid is distilled in a water-bath, arranged as in fig. 149, until no more liquid passes over. The alcohol thus obtained being not entirely freed from water, the operation must be renewed; but this process will often not yield completely anhydrous alcohol; and 512 FERMENTATION. the highly concentrated alcohol must be dissolved in a certain quan- tity of melted caustic potassa, and distilled over a fire, or in a bath of chloride of calcium, until f of the liquor have passed over. The distilled liquid, which is then anhydrous or absolute alcohol, has a peculiar odour, owing probably to the presence of a small quantity of volatile oil, formed by the reaction of the oxygen of the air on the alcohol in the presence of alkaline substances. The alcoholic liquor which remains in the distilling apparatus is coloured brown by a small quantity of resinous matter, also produced by the reaction. § 1327. Absolute alcohol is a colourless liquid, more fluid than water, of a burning taste and agreeable odour. It does not solidify, even at the lowest temperature which can be produced ; and it boils at the temperature of 173.1° under a pressure of 760 millimetres, or 29.92 inches. The density of its vapour, compared with air, is 1.5890; and its specific gravity in the fluid state is, At 32° 0.8151 41 0.8108 50 0.8065 At 59° 0.8021 68 0.7978 77 0.7933 Alcohol is composed of 4 eq. of carbon 24 52.65 6 eq. of hydrogen 6 12.90 2 eq. of oxygen 16 34.45 46 100.00 1 volume of vapour of alcohol contains 1 vol. of vapour of carbon 0.8290 1 “ “ hydrogen 0.2074 \ “ oxygen 7 0.5526 1.5890 Its equivalent C4II6Os is therefore represented by 4 volumes of vapour, (§ 1237.) A weak solution of alcohol, left in a bladder exposed to the air, allows more water than alcohol to pass, and in time becomes stronger. Absolute alcohol attracts the moisture of the air. The temper- ature rises and contraction ensues when it is mixed with water; the maximum of contraction being produced by mixing 53.7 volumes of alcohol, 49.8 “ water, 103.5 which are reduced to 100 volumes; which proportions correspond to 1 equivalent of alcohol and 6 equivalents of water. Very cold absolute alcohol, mixed with snow, lowers the temperature to 34.6°; all which facts show a powerful affinity between alcohol and water: ALCOIIOLOMETRY. 513 the two liquids, however, dissolve each other, in all proportions. Alcohol burns in the air with a feebly brilliant flame, and in the open air its combustion is perfect. Alcohol is frequently used, either absolute, or mixed with greater or less proportions of water, in the laboratory as a solvent. Generally speaking, it dissolves gases more largely than water; and a great number of very soluble and deliquescent compounds dissolve in even absolute alcohol, as, for example, caustic potassa and soda, the chlorides of calcium, strontium, nitrates of lime, magnesia, etc. etc.; and it frequently dissolves certain compounds which are not very soluble in water more freely than the latter liquid, as, for example, corrosive sublimate, and the corresponding bromide and iodide of mercury. Lastly, it dissolves a large number of organic substances insoluble in water. Alcohol is frequently used in che- mical analyses, in order to separate substances soluble in water but very unequally soluble in alcohol; the differences of solubility being sometimes increased by adding ether to the alcohol. Alcohol also combines with several salts, which are soluble in it, playing a part analogous to that of water of crystallization, and forming compounds, called alcoates. When dry chloride of calcium is brought into contact with alcohol, the temperature rises consider- ably, in consequence of the formation of an alcoate. When substances are dissolved in alcohol, their reactions are frequently very different from those of their solutions in water. It has been mentioned (§378) that acetic acid will readily expel carbonic acid from carbonate of potassa dissolved in water; but, on the other hand, carbonic acid will displace the acetic acid of acetate of potassa dissolved in alcohol; the insolubility of carbonate of potassa in alcohol thus becoming a new condition, which changes the order of affinities. § 1328. By adding larger and larger proportions of water to alcohol, its specific gravity increases progressively; and processes for determining the richness in alcohol of these mixtures have been based on the variation of density. An areometer was formerly used, called Cartier s hydrometer for spirits, which marked 0° in pure water and 44° in absolute alcohol, the space between these points being divided into 44 equal parts; but this instrument has been superseded by Cray Lussac s alcoholometer, of which the gra- duation marks the richness immediately in hundredths. The zero of the instrument corresponds to pure water, while absolute alcohol marks 100; and several intermediate points have been fixed by plunging it into liquors the composition of which was known. The centesimal alcoholometer only gives the exact quantity of alcohol when the liquid is at a temperature of 59°, at which the graduation was made ; and as alcohol expands considerably by heat, corrections must be made for all other temperatures; which have been carefully 514 FERMENTATION. calculated and set down in tables for a certain extent of the ther- mometric scale. The alcoholometer can show the richness in alcohol only of those liquids which contain merely water and alcohol; for if they con- tained sugar or saline substances, the result Avould be inaccurate, because these substances would increase the density of the liquor. This process, therefore, cannot indicate immediately the richness of alcoholic drinks, which always contain sugar and saline substances; and for this purpose the following method is used:—After intro- ducing 300 cub. cent, of the liquor to be tested into a small alembic of tinned copper, it is distilled by means of an alcohol-lamp, and the liquid which condenses in the worm is collected in a test-tube, graduated to cubic centimetres. The distillation is arrested as soon as 100 cub. cent, have collected, when the liquor is reduced to the temperature of 59°, and the quantity of alcohol it contains deter- mined by the alcoholometer; after wThich J of the quantity found represents the richness in alcohol of the liquor subjected to the test. If the liquor were very poor in alcohol, only 50 cub. cent, would be distilled, in order to obtain a distilled liquor somewhat rich in alco- hol, for the test then affords a greater degree of accuracy, and the percentage of alcohol in the liquor tested is, in this case, £ of that obtained on the product distilled. If, on the contrary, the liquor were very rich in alcohol, it would be proper to distil only or § of it, and take the J or § of the standard found. The richness of an alcoholic liquor may also be determined by as- certaining the temperature marked by a thermometer, the bulb of which is dipped into the liquor at the moment it boils. A table, which shows the temperature of ebullition corresponding to the various mixtures of alcohol and water, must then be made, and de- duced from direct experiments made in the same apparatus and on known mixtures of alcohol and water. This process shows the richness of alcoholic liquors used as beverages pretty exactly, be- cause the quantities of sugar and salt they contain affect their temperature of ebullition but slightly. Lastly, the calculation may be based on the great differences of expansibility between alcohol and water, by using a kind of ther- mometer having the form of a pipette, the lower tube terminating the bulb of which is very short, and its orifice may be closed by a stopper fitting exactly by means of a spring. The liquor to be tested is brought exactly to the temperature of 77°, and the ther- mometric apparatus, having the lower orifice open, is plunged into it. The fluid is made to rise by means of sucking above the zero in the upper graduated stem; and it is then allowed to recede slowly until it exactly reaches the division 0. The stopper being then fitted, and the apparatus immediately introduced into a vessel containing water at 122°, the division at which the level of the liquid remains stationary indicates the richness in alcohol, because the instrument SULPHOVINIC ACID. 515 has been graduated by direct experiments made on mixtures of al- cohol and water, the composition of which was exactly known. This process is applicable to alcoholic liquors containing sugar or salts, because they influence but slightly the expansibility of the liquid. Concentrated alcohol acts as a poison on the animal economy, and will produce death when taken in large quantities; but when more dilute, its effects are merely intoxication. Injected into the veins, it produces almost sudden death, by coagulating the albumen of the blood. PRODUCTS OF THE ACTION OF SULPHURIC ACID ON ALCOHOL. § 1329. When brought into contact with sulphuric acid in various proportions and at different temperatures, alcohol yields several very important products, which are now to be described. SULPHOVINIC ACID CJIs0,2S03+H0. § 1330. By pouring concentrated sulphuric acid into absolute alcohol, the two liquids dissolve with an elevation of temperature, while a peculiar acid, called sulphovinic, is formed, the best pro- portion for producing which is 1 part of alcohol to 2 parts of sul- phuric acid. A considerable quantity of sulphovinic acid is also formed when alcohol of 85 per cent, is substituted for absolute al- cohol ; but if the alcohol is more dilute, the proportion of sulpho- vinic acid is very small: the temperature must be prevented, during the reaction, from rising above 158°, for which reason the alcohol should be added very gradually. The liquid is then diluted with water and saturated with carbonate of baryta, with which the excess of sulphuric acid forms the insoluble sulphate, while the sulphovinic acid yields a soluble salt. The liquid being evaporated at a gentle heat, or still better, in vacuo, a salt crystallized in beautiful colour- less laminae is obtained. The formula of crystallized sulphovinate of baryta is Ba0,(C4H50,2S03)+2H0; but it readily parts with these two equivalents of water, in a dry va- cuum, at a temperature between 104° and 122°. The sulphovinic acid may be easily extracted from sulphovinate of baryta, by pouring sulphuric acid, drop by drop, into a solution of the salt, until a precipitate is no longer formed; when an acid liquid is obtained, which, being evaporated in a cool place, under the receiver of an air-pump, finally leaves sulphovinic acid in its highest state of concentration, as a syrupy liquid of the formula H0,(C4H50,2S03). It decomposes very easily, even at the ordi- nary temperature, the decomposition becoming very rapid if it is heated, when free sulphuric acid is found in the liquid. Two equivalents of anhydrous sulphuric acid combine in this re- 516 TRANSFORMATIONS OF ALCOHOL. action with 1 equivalent of alcohol C4II6Oa and form sulphovinic acid C4II60a,2S03; but the formula of the acid must be written I10,(C4II50,2S03), as the equivalent of water may be replaced by 1 equivalent of base. Anhydrous sulphovinates may be regarded as double sulphates of the base and the substance C4IIs0, or ether, which shall soon be treated of, or an isomeric of this body. All the sulphovinates being soluble, they are easily made, by double decomposition, by pouring into a solution of sulphovinate of baryta a soluble sulphate of the base, until a precipitate ceases to form. Generally speaking, they crystallize readily. Crystallized sulphovinates of potassa and ammonia are anhydrous, and their formulae are that of crystallized sulphovinate of lime is Ca0,(C4II50,2S03) -j-IIO; and it loses its water in vacuo. Crystallized sulphovinate of copper is represented by Cu0,(C4II50,2S03)-|-4H0, and that of silver by Ag0,(C4II50,2S03)-t-2II0. Solutions of the sulphovinates are easily decomposed by boiling; and the dry salts of the acid yields, when heated, an oleaginous product, which will subsequently be met with under the name of heavy oil of wine. K0,(C4H50,2S0,), (NH3H0),(C4Hs0,2S03) ; ETHER C4II50. § 1331. By heating to 185° a mixture of 2 parts of alcohol and 3 parts of concentrated sulphuric acid, a very volatile liquid, called ether, of which the formula is C4ILO, is formed. The formula of alcohol being C4H80fl, we are naturally led to admit that the alco- hol parts with 1 equivalent of water to the sulphuric acid, and is converted into ether C4I150 ; but on examining the reaction more closely, it will not be found quite so simple. In fact, the ether does not pass over alone in distillation, as water distils at the same time, and in such quantity that it would exactly reproduce alcohol with ether formed; for which reason it cannot be admitted that al- cohol is transformed into ether by the affinity of sulphuric acid for water. In order to analyze all the circumstances of the production of ether, the operation must be arranged as follows :—Place in a flask A (fig. 675) 100 parts of concentrated sulphuric acid, containing consequently 18.5 of water, and add 20 parts of water and 50 of absolute alcohol; then close the mouth of the flask with a cork pierced with three holes, through one of which passes a thermome- ter t, the bulb of which enters the fluid mixture, while the second is traversed by a tube ab descending to the bottom of the flask and terminating in a funnel a; and lastly, through the third hole passes a curved tube cde, the end c of which is drawn out so that the liquid drops which condense in it may fall more easily into the balloon. ETHER 517 The tube ede is fitted to an ordinary cooling apparatus BC, resem- bling that used in distilling, the end fg of the cooled tube being bent in order that it may descend to the bottom of the bottle D. Fig. 675. The flask is heated with an alcohol-lamp until the thermometer marks 284°, while a small circular piece of paper pasted on the balloon indicates the original level of the liquid. After carefully opening the stopcock r, in order to allow the flow of a continuous current of absolute alcohol contained in the bottle E, the current is so regulated that the thermometer t shall always mark 284° ; and if the temperature should rise above this point, more alcohol is poured in; while if, on the contrary, the temperature falls, the stream of alcohol is diminished. A mixture of ether and water which collects in the bottle D then distils constantly, and care must be taken to keep very cold water in the refrigerator BC. For greater certainty, the tube fg is slightly dipped into the bottle D, when a stratum of liquid has col- lected there; and as the level of the latter rises, the bottle is gra- dually lowered. By operating in this manner, ether may be formed, with the same quantity of sulphuric acid, from an almost indefinite quantity of alcohol. The bottle D receives a mixture of water and ether, the weight of which is exactly equal to that of the alcohol used, if the flask has been carefully maintained at the temperature of 284°, and the ether and water exist in this mixture precisely in the proportions constituting alcohol. The sulphuric acid, under the circumstances in which the opera- 518 TRANSFORMATIONS OF ALCOHOL. tion has been performed, has merely effected the separation of the alcohol into ether and water, without attacking either of these pro- ducts ; and the affinity of sulphuric acid for water did not therefore • cause the reaction. Alcohol may moreover he distilled with a large excess of caustic potassa, or its vapours be passed over potassa heated to any temperature, -without ether being formed, and yet potassa has a greater affinity for water than sulphuric acid. As by the direct mixture of alcohol with sulphuric acid sulpho- vinic acid is formed, it might be supposed that this acid plays a part in the phenomenon: it might, for example, be assumed that when the alcohol comes into contact with the sulphuric acid, the temperature is depressed by the arrival of cold alcohol sufficiently to allow sulphovinic acid to form, and that this acid, expanding afterward in the heated mixture, is decomposed into ether and sul- phuric acid. But it must he remembered that, by placing in the flask A (fig. 675) sulphuric acid diluted with water sufficient to make it boil naturally at 293° under the ordinary pressure of the atmo- sphere, and by passing into the acid vapours of alcohol heated to 212° or over, there distils constantly a mixture of ether and water, with a small quantity of alcohol; which arises from the circumstance that a portion of the alcoholic vapours escape the action of the sul- phuric acid. It is difficult to admit that sulphovinic acid is formed in this case, for it would be necessary to grant that the acid was formed and decomposed under the same circumstances. The transformation of alcohol into ether by sulphuric acid is therefore as yet an unexplained phenomenon, unless we admit that sulphuric acid here exerts an action of presence, or catalytic ac- tion ; which is putting a word in the place of a fact. A highly concentrated solution of phosphoric acid also converts alcohol when hot into ether and water, but the water is retained by the phosphoric acid; and when it is sufficiently hydrated, it no longer acts on the alcohol. Several chlorides and fluorides, for ex- ample the chloride of boron, effect the same transformation, as well as several metallic chlorides. The anhydrous chloride of zinc dis- solves largely in alcohol; and if the liquor be distilled, alcohol first passes over; but the temperature now rising above 392°, a large quantity of ether, which distils over with the alcohol, is formed ; and if the heat be continued, two carburetted hydrogens pass over with the ether ; the formula of one, which boils below 212°, being C8II9, and the density of its vapour 3.96, while the formula of the second, which boils at about 572°, and is of a syrupy consistence, is C8II7. It should be remarked that C8H9+C8H7=4C4II603—8IIO ; thus, 4 equiv. of alcohol would yield 1 equiv. of each of these substances, by losing 8 equiv. of water. Ether is manufactured on a large scale by a continuous process analogous to that just described; the distillation being arrested when the sulphuric acid has transformed into ether a weight of ETHER. 519 alcohol 30 or 40 times greater than its own; for if it were con- tinued for a longer time, the ether would be impure and contain a considerable quantity of oil of wine. The ether collected in the receiver is shaken with a small quantity of water, which dissolves the greater portion of the alcohol it contains, after wdiich it is mixed with milk of lime, and distilled after some time in a water- bath. The lime retains the acid products which the ether may contain, while the ether distilled still retains water and alcohol; to free it entirely from which it must be digested with a large quan- tity of powdered chloride of calcium and distilled by means of a water-bath. When the alcohol which is to be converted into ether contains a large proportion of water, or when the sulphuric acid is very aque- ous, ether is not generated, but water and alcohol pass over. If the alcohol is in excess, it passes over isolated until the residue contains alcohol and sulphuric acid in the proportions which form ether, and then the ordinary transformation into ether and water commences. By rectifying considerable quantities of crude ether over lime, a yellow oleaginous liquid remains in the distilling vessel, wdiich, being distilled several times over lime and then over potassium, becomes fluid and completely colourless. Its density is 0.897, and it boils at 545°. This carburetted hydrogen is probably furnished by the impure alcohol used in the preparation of ether. § 1332. Ether is a colourless, very fluid liquid, of an agreeable and pungent odour, and an acid and burning taste. Its density at 32° is 0.736, and it boils at 95.9° under the pressure of 29.92 inches, the density of its vapour being 2.586. Its composition is expressed by 4 eq. of carbon 24 65.31 5 “ hydrogen 5 13.33 1 “ oxygen 8 21.36 37 100.00 One vol. of vapour of ether contains 2 vol. of vapour of carbon 1.6876 5 “ hydrogen 0.3465 J “ oxygen 0.5528 2.5869 and its equivalent C4H50 is therefore represented by 2 volumes of vapour. Ether is very inflammable, and burns with a flame possessing a certain degree of brilliancy, and depositing lamp-black on cold substances introduced into it. Being extremely volatile, it evapo- rates rapidly in the air, producing detonating mixtures which have occasioned serious accidents. 520 TRANSFORMATIONS OF ALCOHOL. Ether is soon changed by the oxygen of the air, which converts it into acetic acid; and in order to preserve it in a state of purity, it should be kept in Avell-stoppered bottles, completely filled, or better still, in tubes hermetically closed. The alteration is more rapid under the influence of alkaline bases. Ether dissolves in 9 parts of water; and if a larger quantity of ether be added, the por- tion which does not dissolve floats on the water. Ether also dis- solves a small quantity of water, while alcohol and ether dissolve each other in all proportions. Ether dissolves about of sulphur and of phosphorus, which substances separate in the form of crystals after evaporation. Chlo- rine and bromine act powerfully on ether, and yield peculiar pro- ducts, which shall soon be described; while iodine at first simply dissolves in it, but is changed in a short time. Ether exerts an energetic action on the animal economy: its vapour being rapidly absorbed by the respiratory organs, soon causes a kind of intoxication, accompanied by insensibility, which curious effect has been latterly applied as an anaesthetic agent in surgical operations. BICARBURETTED HYDROGEN, OR OLEFIANT GAS, C4H4. § 1333. When an excess of concentrated sulphuric acid acts upon alcohol at a temperature of 320° or over, only a small quantity of ether results, while a gaseous carburetted hydrogen of the formula C4H4 is formed. On comparing the formula of this body with that of alcohol, it would he natural to explain the decomposition by as- suming that sulphuric acid determines the formation of 2 equiv. of water, which combine with it, and that it sets free bicarburetted hydrogen C4II4. C4H608=C4H4+2H0. But the following experiment seems to contradict this explanation, Having placed in the flask A (fig. 676) concentrated sulphuric acid, to which a quantity of water has been added, such that the mixture shall boil at about 320°, (for which purpose 100 p a r ts of m o n o h y- drated sul- phuric acid Fig. 67G. OLEFIANT GAS. 521 and 30 of water must be used,) the acid is heated to boiling. The flask B contains absolute alcohol, which is heated to ebullition, and the vapours of alcohol traverse the flask A, the temperature of which is kept constantly at about 329°, by allowing more or less alcohol to enter, and by increasing or diminishing the flame of the lamp which heats the flask. Olefiant gas is disengaged in the form of small bubbles from the acid mixture, and carries over vapours of water and alcohol, which condense in the bottle C, while thg gas may be collected in a gasometer, or in bottle D over a pneumatic trough. The alcohol carried over is that which has escaped the action of the sulphuric acid, and the water which distils is exactly equal to that which would form alcohol with the bicarburetted hy- drogen ; while the acid liquor in the flask A retains the same com- position, and can convert an almost indefinite quantity of alcohol into bicarburetted hydrogen and water; very little ether being formed. The experiment shows that the decomposition of alcohol into bicarburetted hydrogen and water, by contact with sulphuric acid, is not owing to the affinity of the acid for water, since water and olefiant gas are both disengaged at the same time. Bicarburetted hydrogen is generally prepared in the laboratory by heating a mixture of 1 part of alcohol at 0.85 and 6 parts of concentrated sulphuric acid in a retort, (fig. 285,) which should be only be J filled; the gas evolved being made to pass first through a bottle containing concentrated sulphuric acid, which retains the vapours of alcohol and ether, and then through a second bottle con- taining a solution of caustic potassa, to absorb the sulphurous acid and carbonic acid which are copiously evolved toward the close of the operation; the cause of which evolution is the reaction which ensues between the concentrated sulphuric acid and the carbona- ceous substances remaining in the retort. The disengagement of gas, which is pretty regular at the commencement of the operation, soon becomes tumultuous and violent, when the acid mixture turns black, becomes viscous, and swells to such a degree that if the re- tort be not very large it will fill the neck. At the end of the ex- periment there remains in the retort a solid black substance, which gives off to water sulphuric acid, and sulphovinic acid, or an iso- meric of it; while the composition of the black insoluble residue is very complex, and corresponds to the formula C80HS4O20S3. § 1334. Bicarburetted hydrogen is a colourless gas which does not liquefy at the lowest temperatures: its density is 0.978, and it burns with a very brilliant flame, which deposits a large quantity of lamp- black on cold substances immersed in it. When passed through a procelain tube heated to redness, charcoal is deposited on the sides of the tube, and it is transformed into protocarburetted hydrogen; but if the temperature is more elevated, all the carbon is deposited, and hydrogen only disengaged. The formula of bicarburetted hy- 522 TRANSFORMATIONS OF ALCOHOL. drogen is C4II4, (266,) and its equivalent is represented by 4 vo- lumes of gas. § 1335. Bicarburetted hydrogen combines with anhydrous sul- phuric acid, forming a white compound, fusible at about 176°, and of the formula C4II4,4S03, which has been improperly called sul- phate of carbyle. In order to prepare it, olefiant gas, totally free from ether, and vapours of anhydrous sulphuric acid, are passed simultaneously into a U-tube, when the combination takes place with great elevation of temperature, while the substance, which is at first liquid, solidifies into a radiated crystalline mass on the sides of the tube. In order to purify it, it is left for several days in vacuo, over a cup containing caustic potassa, which absorbs the vapours of the anhydrous sulphuric acid. The same product is formed by placing an open tube containing absolute alcohol in a bottle containing anhydrous sulphuric acid, and allowing the bottle, after being well corked, to rest for several days. The vapours of alcohol and sulphuric acid combine and sul- phate of carbyle is formed, but the latter is injured by hydrated sulphuric acid, from which it is freed with difficulty. The reaction in this case is expressed by the following equation: « C4H603+6S03=C4H4,4S08+2(S08,H0). Sulphate of carbyle absorbs moisture from the air; and if the absorption take place slowly, and without any elevation of tempera- ture, a peculiar acid, called ethionic, is obtained, of which the for- mula is C4H50,4S0s. This acid forms, with baryta, a salt soluble in water but insoluble in alcohol; and it yields crystallizable salts with the majority of bases. By boiling the solution of ethionic acid for a few moments, or by dissolving the sulphate of carbyle in hot water, a new acid, called isethionic, is obtained, presenting the same composition C4IIs0,2S03 as sulphovinic acid, while the liquid contains free sulphuric acid. Is- ethionic acid differs from sulphovinic acid by being much more fixed, as its solution may be boiled indefinitely without undergoing any change. Isethionates are also much more stable than sulphovinates,- for they bear without decomposition temperatures of 400° or 550°. Action of Chlorine, Bromine, and Iodine on Bicarburetted Hydrogen. § 1336. By causing chlorine in greater or less quantity to act upon bicarburetted hydrogen, and under the influence of a more or less intense degree of light, various products result, which shall be mentioned: if both gases, moist, and in nearly equal volumes, be introduced into a large flask exposed to the diffuse light of day, they combine with evolution of heat, and an oleaginous liquid trickles down the sides of the flask. If the gases were dry, reaction would ensue under the influence of direct solar light. DUTCH LIQUID. 523 When any considerable quantity of this product is to be prepared, the apparatus must be arranged as represented in fig. 677. A is a large retort, in which is prepared the olefiant gas which traverses the washing bottle B containing concentrated sulphuric acid, which retains the vapours of alcohol and ether, and then the bottle C con- Fig. 677. taining a solution of potassa to absorb the sulphurous carbonic acids; whence it passes into a flask D having 3 tubulures, which also receives the chlorine disengaged from the flask G, having been made to traverse the water in the bottle F. The ends of the tubes which convey the two gases into the flask D are placed op- posite to each other, so that the gases may mix immediately; while the liquid formed falls through the lower part of the flask into a well-cooled bottle E; the excess of gas escaping by the same tubulure. The liquid obtained is shaken several times with water, and then distilled again and again, alternately wTith sulphuric acid and potassa, which destroy a small quantity of the foreign sub- stances produced by the reaction of chlorine on the vapour of ether which accompanies olefiant gas when the evolution of the gas is too rapid. If the operation be continued for a long time, by exhausting the action of the sulphuric acid on the alcohol, it frequently hap- pens toward the close that the potassa of the bottle C passes into the state of bisulphite of potassa, and the sulphurous acid is no longer absorbed; in which case a certain quantity of chlorosul- phuric acid (§ 132) is obtained intimately mixed with the principal product. The liquid condensed in the bottle E, which then pos- sesses a sulphurous, acid, and extremely penetrating odour, becomes heated when it is shaken with water, and yields a large quantity of sul- phuric and chlorohydric acids, arising from the decomposition of the chlorosulphuric acid. It is important to remark that chlorine and sulphurous acid, alone, do not combine in the presence of the most intense solar rays, while in the presence of bicarburetted hydrogen 524 TRANSFORMATIONS OF ALCOHOL. the combination takes place in diffuse light. The chlorine and bicarburetted hydrogen, which, when dry, exert no action on each other in diffuse light, combine, on the contrary, very readily, when sulphurous acid exists in the mixture; the latter then forming chlorosulphuric acid with a portion of the chlorine. The formation of one of these compounds assists, therefore, the production of the other. The product resulting from the combination of 1 vol. of chlorine with 1 vol. of olefiant gas, Avhich has long been known under the name of Dutch liquid, because it was discovered by an association of chemists in Holland, is a colourless liquid, of an agreeable odour. Its density is 1.280 at 32°, and it boils at 184.1°. The density of its vapour being 3.45, its composition is represented by the for- mula C4H4C13, which corresponds to four volumes of vapour, but it is generally written C4II3C1,HC1, from the manner in which the substance behaves with an alcoholic solution of potassa. § 133T. Dutch liquid is not decomposed by an aqueous solution of potassa, and may be distilled with it without any apparent change; while if it be dissolved in an alcoholic solution of potassa, it is immediately decomposed, and a large quantity of chloride of potassium is deposited, while the alcohol contains in solution a new and very volatile substance. In order to separate it, the liquid must be distilled in a wTater-bath slightly heated, and the gas disengaged must be passed first through an apparatus containing concentrated sulphuric acid, which retains the vapours of the alcohol, and then into a receiver reduced to a low temperature by a mixture of ice and chloride of calcium. A very volatile liquid condenses in the re- ceiver, boiling below 32°, having a sharp and slightly alliaceous smell, and of which the composition corresponds to the formula C4H3C1, represented by 4 vol. of vapour. The composition of this substance is exactly the same as that of bicarburetted hydrogen, ex- cept that 1 equiv. of hydrogen is replaced by 1 equiv. of chlorine. Dutch liquid may itself be considered as a combination of the substance C4II3C1 and chlorohydric acid. When the chlorine reacts on the bicar- buretted hydrogen, 1 equivalent of chlorine abstracts 1 equivalent of hydrogen to form 1 equivalent of chlorohydric acid, while the place thus made empty in the molecule of olefiant gas is immediately filled by 1 equivalent of chlorine, forming 1 equivalent of monocldori- nated bicarburetted hydrogen, which remains in combination with the equivalent of chlorohydric acid formed. § 1338. The action of chlorine on bicarburetted hydrogen is not confined to the abstraction of but one equivalent of hydrogen and its replacement by 1 equiv. of chlorine ; and the other three equiva- lents of hydrogen may successively be replaced by a corresponding number of equivalents of chlorine, thus furnishing the series of pro- ducts : DUTCH LIQUID. 525 C4H4 and their compounds with chlorohydric acid. C4H3C1 “ “ C4II3C1,IIC1. C4H3Cla “ “ C4H3Cla,HCl. C4HC13 “ “ C4HC13,HC1. C4C14 “ “ C4C14,HC1. On passing dry chlorine through Dutch liquid, the latter will be found to dissolve it largely, and if the bottle be then placed in the sun, a powerful reaction ensues, a large quantity of chlorohydric acid being disengaged, while the liquid is completely discoloured; and by repeatedly saturating it with chlorine, and exposing it to the rays of the sun, at properly regulated intervals, Dutch liquid may be con- verted into a less volatile product, which boils at 239°, and of which the density in the liquid state is 1.422, while that of its vapour is 4.60. The formula of this substance being C4H3C13, it will be re- cognised as Dutch liquid, in which 1 equiv. of hydrogen is replaced by 1 equiv. of chlorine. The same product is formed when chlorine is caused carefully to act upon monochlorinated bicarburetted hydro- gen C4H3C1, but it is more easily obtained by passing the latter substance in the state of gas through the percliloride of antimony Sb205, which dissolves it freely. When the perchloride of antimony is saturated, it is distilled, and a colourless liquid, consisting of C4II3C13, or monochloruretted Dutch liquid, is collected. The for- mula of this substance may be written C4H2Cla,HCl for the same reasons which have been stated for Dutch liquid. In fact, on dis- solving monochlorinated Dutch liquid in an alcoholic solution of potassa, a precipitate of chloride of potassium is formed, and a liquid of which the formula is C4H2Cla separates by distillation. The density of this liquid, which may be considered as bichlorinated bi- carburetted hydrogen, is 1.250, and it boils between 95° and 104°. The density of its vapour 3.35, and the equivalent C4H2Cla there- fore correspond to 4 vol. of vapour like that of olefiant gas. By operating on monochlorinated Dutch liquid C4H2C12,HC1, in the same manner as has been explained for the original liquid C4H3C1,HC1, the chlorine again abstracts hydrogen in the state of chlorohydric acid, while a substance results which may be con- sidered as bichlorinated Dutch liquid, and of which the formula is C4H2C14. The density of this substance is 1.576: it boils at 275°, the density of its vapour being 5.79, so that the equivalent C4H2C14 is again represented by 4 vol. of vapour. We shall write the formula of this product CHC13,HC1, because, in contact with an alcoholic solution of potassa, it is decomposed into chlorohydric acid, which combines with the potassa, and into a new substance C4HC13, which is trichlorinated bicarburetted hy- drogen. Bichlorinated Dutch liquid, subjected again to the action of chlorine in the manner above indicated, is converted into trichlorinated Dutch 526 TRANSFORMATIONS OF ALCOHOL. liquid C4IIC15, which boils at 307°, and the density of which at 32° is 1.663, Avhile that of its vapour is 7.08, and the equivalent CjHClj is therefore still represented by 4 vol. of vapour. The for- mula C4HC1s may be written C4C14,IIC1, because this substance, in contact with an alcoholic solution of potassa, is decomposed and yields the product C4C14, which should be considered as quadrichlo- rinated or per chlorinated bicarhuretted hydrogen, all the hydrogen of the olefiant gas being here replaced by an equivalent quantity of chlorine, while the new substance is a simple chloride of carbon, but its composition is still the same as that of bicarhuretted hydro- gen, since its formula corresponds to 4 vol. of vapour. The density of chloride of carbon C4C14 is 1.61: it boils at 251.6°. Finally, by treating trichlorinated Dutch liquid C4HC15 with an excess of chlorine, in the sun, it loses the last equivalent of hy- drogen, which is replaced by 1 equiv. of chlorine, when a chloride of carbon C4C18, which may be considered as quadrichlorinated or perchlorinated Dutch liquid, is formed. This chloride of carbon, sometimes called sesquichloride of carbon on account of its compo- sition, is solid and crystalline, having a peculiar aromatic smell, and is readily purified by dissolving it in boiling alcohol, when the liquid deposits the chloride of carbon, on cooling, in the form of small white crystals, which melt at 320°, while the substance boils at 356°. The density of its vapour being 8.16, the equivalent C4Cle is there- fore represented by 4 vol. of vapour. The chloride of carbon C4C14, of the series of bicarhuretted hy- drogen, combines readily with chlorine, and is converted into solid chloride of carbon C4C16, of the series of Dutch liquid; while, reci- procally, the chloride of carbon C4C1B is readily transformed into chloride of carbon C4C14. By passing the vapour of the chloride of carbon C4C18 through a tube heated to redness, it is converted into chloride of carbon C4C14 and chlorine; but it is difficult by this me- thod to obtain the chloride C4C14 pure, on account of the facility with which it combines with chlorine when it passes with the latter gas into the receiver in which it is condensed. This transforma- tion is more readily effected by dissolving the chloride of carbon in an alcoholic solution of sulfhydrat.e of sulphide of potassium, when a very energetic reaction ensues if it be slightly heated, while a large quantity of sulf hydric acid is disengaged. The chloride of carbon should be added by small quantities at a time, and too great an excess of sulf hydrate of sulphide of potassium must be avoided. When the solution of gas ceases, the alcoholic liquor collected in the receiver is distilled and diluted with water, when the chloride of carbon 04C14 is deposited in the form of a colourless liquid. § 1339. There exist, therefore, two series of products derived from two original substances, bicarburetted hydrogen C4II4 and Dutch liquid C4H4C1S, by the successive substitution of equivalent quantities of chlorine for hydrogen, while Dutch liquid itself may be considered DUTCH LIQUID. 527 as being derived, by the same mode of generation, from a carbu- retted hydrogen C4II0 as yet unknown. In proportion as the chlorine thus replaces the hydrogen, the density of the substance increases, and its boiling point rises; which relations are easily seen in the following tables: Series of Bicarburetted Hydrogen. Bicarburetted hydrogen C4II4, gas does not liquefy at any tem- perature. Monochlorinated bicar- buretted hydrogen... C4H3C1, boils at about 14°. Bichlorinated bicarbu- retted hydrogen C4II3C13, boils at 95°, density 1.250. Trichlorinated bicarbu- retted hydrogen C4IIC13, “ “ “ u Quadrichlorinated bi- carburetted hydrogen C4C14, “ 251.6°, “ 1.619. Series of Dutch Liquid. Carburetted hydrogen (unknown) C4H6. Dutch liquid C4lI4Cla boils at 180.5°, density 1.256. Monochlorinated Dutch liquid C4II3C13 “ 239°, “ 1.422. Bichlorinated Dutch liquid C4II3C14 “ 275°, “ 1.576. Trichlorinated Dutch liquid C4I1C15 “ 307.4°, “ 1.619. Quadrichlorinated Dutch liquid C4C16 a 356°. In all these products, the equivalent is represented by 4 volumes of vapour, and it may be admitted that the substances of the same series present the same molecular grouping, and only differ from each other in the chemical nature of one of their elements, hydrogen, which is more or less completely replaced by equivalent quantities of chlorine. § 1340. Bromine also combines with bicarburetted hydrogen, and yields a substance C4II4Br3 which corresponds exactly to Dutch liquid. It is prepared by dropping bromine into a current of bicar- buretted hydrogen; when the bromine is almost instantaneously discoloured and converted into an etherial liquid, the odour of which resembles that of Dutch liquid. In order to purify it, it is washed with a small quantity of water, and then distilled several times, alternately, over concentrated sulphuric acid and baryta. The density of the liquid is 2.16 at 69.8° ; it boils at 271.4°, and so- lidifies at 55.4° into a white crystalline mass resembling camphor. Its equivalent is represented by 4 volumes. The product C4II4Br3 undergoes, by distillation with an alcoholic 528 TRANSFORMATIONS OF ALCOHOL. solution of potassa, a decomposition analogous to that experienced by Dutch liquid; bromide of potassium and a gas C4H3Br, which condenses readily in a mixture of ice and sea-salt, being formed. It is monohrominated bicarburetted hydrogen, and its density is about 1.52, while the density of its vapour is 3.64, and its equivalent is represented by 4 volumes of vapour. Bromine attacks monobrominated bicarburetted hydrogen, and converts it into a liquid C4H3Br3 which corresponds to monochlo- rinated Dutch liquid. The action of bromine does not appear to extend any further, even by long exposure to the rays of the sun. § 1341. If bicarburetted hydrogen be passed to the bottom of a matrass containing iodine and heated to 120° or 140°, the iodine soon fuses, and yellowish needles, which become completely white by the prolonged action of the olefiant gas, condense in the neck of the matrass; by treating which with alkaline or ammoniacal water, a crystalline substance C4II4I2 is obtained corresponding to Dutch liquid. This substance becomes slightly yellow by dry- ing, but recovers its whiteness when exposed to a current of bicar- buretted hydrogen. It has an ether-like, sharp, and penetrating odour, causing a flow of tears; and light decomposes it spontane- ously. It melts at 167°, but is destroyed at a temperature slightly above that point. Potassa dissolved in alcohol decomposes it, and produces moniodinated bicarburetted hydrogen C4H3I, which is a volatile liquid; while the greater part of the product is still further decomposed and yields a gaseous carburetted hydrogen. By decomposing Dutch liquid by alcoholic solutions of mono- sulphide of potassium, solid products result, in which the sulphur replaces the chlorine of the original substances ; but these products have been but little studied, and as yet only the compound C4H4S2, which corresponds to Dutch liquid, is known with certainty. Oil of Wine. § 1342. During the preparation of ether or bicarburetted hydro- gen by the reaction of concentrated sulphuric acid on alcohol, a certain quantity of a very heavy oily substance, called heavy oil of wine, which dissolves in ether, but separates from it when it is diluted with a sufficient quantity of water, is constantly formed. The best method of preparing it consists in heating 1 part of abso- lute alcohol and 2J parts of concentrated sulphuric acid, and first collecting the products in a bottle kept at the temperature of 95° or 104°, in which very little ether, but the greater portion of the heavy oil of wine condenses; and then in a second cold receiver, if the ether is to be preserved. The same substance is obtained by decomposing by heat well-dried sulphovinates. It is washed several times with cold water, in order to remove the alcohol, ether, the sulphurous and sulphuric acids which impurify it, and then exposed for several days in vacuo over concentrated sulphuric acid, in order ETHERS. 529 to absorb the water. It is, however, difficult to obtain a uniform composition of the substance, and chemists are not agreed as to its nature. From analyses most worthy of confidence, its formula would be C8IIg0,2S03, although it may possibly be true sulphuric ether C4II50,S03, belonging to the series of compound ethers of which we are about to treat, and mixed with a small quantity of foreign substances, principally carburetted hydrogen, which may, in fact, be separated from it. It is sufficient to digest heavy oil of wine for some time with hot water, or better still, with an alkaline liquid, in order to decompose it into sulphovinic acid and a light oil having the same elementary composition as bicarburetted hydrogen, but the boiling point of which is as high as 536°. It is not yet decided whether this latter substance is a product of the decompo- sition of heavy oil of wine, or if it be merely mixed with it. This oily carburetted hydrogen, allowed to rest for some time, deposits crystals which are purified by pressing them between tissue-paper, and the composition of which is the same as that of liquid carbu- retted hydrogen: they melt at 230°, and distil at 320°. COMPOUND ETHERS AND VINIC ACIDS. § 1343. The action of acids on alcohol calls into existence nume- rous compounds, formed by the combination of 1 equiv. of ether C4II50 with 1 or 2 equiv. of acid. Compounds containing 2 equiv. of acid are powerful acids, which accurately saturate the bases, and form a great number of crystallizable salts, and they are commonly called vinic acids; sulphovinic acid, the preparation and properties of which we have described, (§ 1330,) belonging to this class. The compounds containing only 1 equiv. of acid are neutral with re- agents, and are called compound ethers. Certain acids, such as oxalic and carbonic, form both compounds, while others, as phosphoric, form only the acid compound, vinic acid; and, lastly, others, as nitric and acetic, yield the neutral compound alone. The majority of compound ethers may be distilled without alteration, but are decomposed by being boiled with an alkaline so- lution ; the acid of the compound ether generally combining with the alkali, while the ether C4Hs0 set free combines with 1 equiv. of water to form alcohol. Nearly all the known acids are capable of forming with alcohol compound ethers or vinic acids; a/rhl we shall now de- scribe such of these compounds as are formed by mineral acids and some organic acids already described, and shall refer the study of the others to those chapters in which the properties of the acid en- tering into their composition is to be described. We shall not again touch on sulphovinic acid, which has been sufficiently described, (§ 1330;) and the neutral compound, sul- phuric ether C4H.0,S03, has hitherto not been obtained.* * It was recently formed by Dr. C. Wetherill.—J. O. B. 530 TRANSFORMATIONS OF ALCOHOL. jPhosphovinic Acid (C4H50 + 2H0),P05. § 1344. Phosphovinic acid is obtained by heating for some time, at a temperature of 176°, equal parts of absolute alcohol and a syrupy solution of phosphoric acid; after which the liquid is allowed to rest until the following day, when it is diluted with water and saturated with carbonate of baryta, when the free phosphoric acid forms an insoluble phosphate with baryta, while -the phosphovinate produced with this base is soluble. The solution, when evaporated, deposits, on cooling, crystals of phosphovinate of baryta, which is much less soluble than the sulphovinate : at 104°, its greatest point of solubility, 100 parts of water dissolve only 9.3. It is also much more fixed than the sulphovinate, for it may be heated up to 570° without change. By dropping sulphuric acid into a solution of phos- phovinate of baryta, the baryta is precipitated and a solution of phosphovinic acid obtained, which may be boiled without alteration, and which, when evaporated to the consistence of syrup in the vacuum of an air-pump, deposits crystals, if the temperature be low. The majority of the phosphovinates being soluble in water, are easily prepared by double decomposition, by pouring the sulphate of the base into a solution of phosphovinate of baryta. Crystallized phosphovinate of baryta contains 12 equiv. of water of crystallization, which may be driven off by heat without altera- tion. The formula of the dried salt is (2Ba0 + C4H50),P0s; and it presents, therefore, the composition of the tribasic phosphates, by admitting that ether C4IIsO replaces 1 equiv. of base. The compo- sitions of the other phosphovinates are analogous. No neutral compound of ether with phosphoric acid is known. § 1345. Nitric acid forms with ether only a neutral compound, nitric ether ; no vinic acid having hitherto been discovered. On mixing alcohol with nitric acid and heating it gently, a violent reaction ensues, and a large quantity of nitrous gas is disengaged, while, together with other products, there results an ether which is not nitric ether OfTf-O,N05, but nitrous ether C4II50,N03. Nitric ether may, however, be produced by the direct action of nitric acid on alcohol, if the forming of nitrous acid be avoided, because this acid, on account of its more powerful oxidizing agency, yields very complicated products. It is effected by gently heating in a retort 150 gm. of a mixture of equal parts of alcohol at 0.85° and very pure concentrated nitric acid, of the density of 1.4, to which is added 1 gm. of urea, an organic substance which shall be described among the products of the animal economy. The first product of distillation is composed chiefly of alcohol diluted with water, but the nitric ether itself very soon distils over, and, toward the close of the operation, this liquor forms a denser layer at the bottom of the Nitric Ether C4II50,N0s. ETHERS. 531 receiver. The operation is arrested when about | of the liquid still remains in the retort; and in order to separate that which is dis- solved in the supernatant alcoholic liquor, water is added to it and it is shaken; after which the ether is decanted, washed with an alkaline solution, then with water, and, lastly, it is distilled over chloride of calcium. The object of the small quantity of urea added to the mixture is to prevent the formation of nitrous acid, or rather to effect the destruction of this acid as fast as it is formed. The urea combines with the nitric acid and constitutes nitrate of urea, which compound is readily destroyed by contact with nitrous acid, the two substances being converted into nitrogen, water, and carbonic acid. Nitric ether has a pleasant and sweet smell, and a saccharine taste : its density is 1.112, and it boils at 185°, decomposing at a tempera- ture slightly above its boiling point, and forming explosive vapour when heated above 212°. An aqueous solution of potassa does not decompose nitric ether, but an alcoholic solution of potassa de- stroys it, even wThen cold, alcohol and nitrate of potassa being formed. § 1346. It has just been said that nitrous ether is one of the products of the action of ordinary nitric acid on alcohol, but the reaction is extremely tumultuous, and if large quantities of the mixture are ope- rated on, especially when in a small-necked retort, an explosion may ensue. The best method of preparing it consists in pouring carefully into a bottle, by means of a funnel terminating in a narrow tube descending to the bottom of the bottle, first, one part in volume of alcohol of 0.85, then one part of nitric acid with 4 equiv. of water. The bottle, loosely corked in order to allow the gases to escape, is left for 2 or 3 days in as cold a place as possible, when the upper layer, which contains a large quantity of nitrous ether, is decanted, and then agitated with a weak solution of caustic potassa, and digested with chloride of calcium. Pure nitrous ether is colourless, and its odour resembles that of pippin apples, while its density is 0.886, and it boils at about 69.8°. Nitrous Ether C4IT50,N03. Sulphurous Ether C4Hs0,S03. § 1347. This compound ether is not formed by the direct action of sulphurous acid on alcohol, or on a mixture of alcohol and sul- phuric acid, hut is obtained by pouring alcohol on protochloride of sulphur, when the mixture becomes heated, while chlorohydric acid is disengaged and sulphur deposited. By distillation, alcohol first passes over, and then, when the temperature approaches 338° a colourless liquid, having the smell of mint, and the density 1.085. and which is sulphurous ether C4H50,S02. It decomposes slowhv in a moist atmosphere. 532 TRANSFORMATIONS OF ALCOHOL. § 1348. On mixing equal weights of fused and finely powdered boracic acid, and absolute alcohol, a considerable quantity of heat is evolved; and if the mixture be distilled in a retort furnished with a thermometer, alcohol first passes over, while the tempera- ture gradually rises and soon exceeds 212°. The distillation is arrested when the temperature reaches 230° ; and the mass, when cooled, is dissolved in ether, the etherial solution is evaporated, and the viscous residue heated to 392° in an oil-bath; when the substance remaining is boracic ether. It is a transparent glass, somewhat soft at the ordinary temperature, and which, at the tem- perature of 104° or 120°, maybe drawn out into thread. It smells feebly of ether, and at 392° it yields white vapours, while a tem- perature of 570° decomposes it, disengaging very pure bicarburetted hydrogen. Tepid water also decomposes it, forming alcohol and boracic acid. Alcohol and ether dissolve boracic ether and form solutions which set into gelatinous masses on the addition of water. When an alcoholic solution of boracic ether is distilled, a consider- able quantity of it is carried over by the alcoholic vapours, which then burn with a beautiful green flame, owing to the presence of boracic acid. Boracic Ether C4TI50,2B03. Silicic Ethers 3C4II50,Si03 and 3C4II50,2Si03. § 1349. When absolute alcohol is carefully poured into chloride of silicium, a very energetic reaction ensues, and a large quantity of chlorohydric acid gas is generated. Alcohol is gradually added until a new addition produces no evolution of gas; and on then distilling the mixture, chlorohydric ether is first disengaged, and the temperature in the retort soon rises to 320°, while the greater portion of the substance distils between 320° and 338°, which is separately collected. When the temperature exceeds 338° the receiver is changed, and distillation is carried to dryness. The product distilled between between 320° and 338° is again rectified, and then is almost entirely composed of a liquid boiling between 323.5° and 325.5, and of which the formula is 3C4II50,Si03. It is a silicic ether, differing in composition from the compound ethers hitherto described, in containing 3 equiv. of ether C4II50 for 1 equiv. of silicic acid. Silicic ether is a colourless liquid, of an ether-like and penetrating smell, of a taste like pepper, and of the density 0.942. Water does not dissolve it, but decomposes it after a time, and silicic acid is separated. When silicic ether is left for a very long time in a badly-stoppered bottle, decomposition is gra- dually effected at the expense of atmospheric moisture, the silicic ether becoming more and more viscous, while it still preserves its transparency, while there remains at last a perfectly transparent, vitreous mass, of great hardness, consisting of hydrated silicic acid. ETHERS. 533 By again rectifying the products of the action of alcohol on chloride of silicium which have distilled above 392°, and collecting separately the product which distilled above 572°, a new ether of the formula 3C4II50,2Si03 is obtained. The formula of the two silicic ethers differ greatly from those of other compound ethers. It has been seen (§ 244) that chemists are not agreed upon the equivalent of silicium and the formula of silicic acid, and that some think that the formula should be written SiO; in which case the two silicic ethers would assume the formula C4II50,Si0 and C4II50,2Si0, the former being analogous to that of ordinary com- pound ethers, and the latter to that of vinic acids. Carbonic Ether C4tI50,C0a and Carbovinic Acid C4H50,2C0a. § 1350. Carbonic ether is not obtained by the direct action of carbonic acid on alcohol, but has been produced by distilling oxalic ether with potassium. The oxalic ether is introduced into a tubu- lated retort and heated, potassium or sodium being gradually added until gas, consisting of carbonic oxide, is no longer evolved. The colour of the substance remaining in the retort is of a deep red; and when it is again distilled with a quantity of water, the carbonic ether forms the upper layer of the distilled liquid, which is decanted and redistilled over chloride of calcium. Carbonic ether is a colourless, very fluid liquid, of an aromatic smell and acrid taste, and its density is 0.975, while it boils at 258.8°, yielding a vapour of the density 4.1; and its equivalent C4H50,C0a is represented by 2 volumes of vapour. Potassa dis- solved in alcohol changes it but slightly when cold; while, when hot, carbonate of potassa is formed, and alcohol is separated. Carbonic ether is decomposed by a solution of ammonia, and yields alcohol, and a white crystalline substance soluble in water and alcohol, to which the name of urethan has been given. The formula of urethan is C4II50,(Ca03,NHa); and it may be regarded as a compound ether, formed by a peculiar acid Ca03,NIIa, which has been called carbamic acid ; in which case urethan would be car- bamic ether. We have, in fact, 2(C4H50,C03)+NH,=C4H50,(NH33C303)+C4H603. If a concentrated solution of caustic potassa in anhydrous alcohol he saturated with carbonic acid gas, the liquor at last sets into a mass, in consequence of a copious deposit of carbonate, bicarbonate, and carbovinate of potassa. Ether, which completes the precipita- tion of the carbovinate of potassa, is poured into the flask, and after having decanted the liquor, the deposit is shaken with absolute alcohol, which dissolves only the carbovinate. The alcoholic solu- tion is filtered and dropped into very anhydrous ether, which again precipitates the carbovinate of potassa. The formula of the salt, dried in vacuo, is K0,(C4H50,2C0a); and it forms white, pearly 534 TRANSFORMATIONS OF ALCOHOL. spangles, greasy to the touch. Water decomposes it instantly into alcohol and bicarbonate of potassa. § 1351. On pouring absolute alcohol into a matrass filled Avith chlo- rocarbonic gas, COC1 (§258,) the temperature rises, and the liquid separates into two layers, the loAver of Avhich is formed of oxychlo- rocarbonic ether. It is purified by digesting it over litharge or chloride of calcium, and then distilling it. This ether is liquid, colourless, having a penetrating odour, Avhich excites to tears; and its density is 1.133, Avhile it boils at 201.2°, and burns with a green flame. Boiling Avater decomposes it; and it may be considered as a compound of carbonic ether C4H50,Ct)3 and chlorocarbonic gas COC1. Ammonia decomposes it, chlorohydrate and carbonate of ammonia, and carbonic ether, being formed. Oxychlorocarbonic Ether C4II50C303C1. Oxalic Ether C4II50,C303, and Oxalovinic Acid C4II50,2C303. § 1852. The best method of preparing oxalic ether consists in mixing in a tubulated retort 1 part of oxalic acid dried at 212°, the formula of which is then C303,II0, with 6 parts of absolute alcohol. A thermometer, the bulb of which reaches nearly to the bottom of the retort, is fitted to its tubulure, and the distillation is continued until the thermometer marks 284°, when distilled alcohol is intro- duced and the distillation repeated, ceasing only when the thermo- meter marks 320°. The liquid remaining in the retort is then poured into Avater, when oxalic ether separates as a heavy liquid, Ayliich, after being Avashed several times with Avater, is again distilled over litharge, which seizes upon the free oxalic acid. The product, after being left for some time in contact with fused chloride of cal- cium, is pure oxalic ether. It is colourless, and of an aromatic odour; and its density is 1.093, while it is very slightly soluble in Avater, but perfectly so in alcohol. The density of its vapour is 5.078: it boils at 363.2°, and its equivalent .C4H50,Ca03 corre- sponds to 2 volumes of vapour. Oxalic ether is decomposed by contact with a solution of potassa, into alcohol and oxalic acid, Avhich decomposition is also effected, after a long time, by pure water ; and Avhen left in a badly-stoppered bottle, in contact Avitli moist air, it deposits crystals of hydrated oxalic acid. Ammonia exerts a remarkable action upon it, forming tAvo neAV products, oxamul and oxamic ether. On dropping oxalic ether into a solution of ammoniacal gas in absolute alcohol, a peculiar substance, first called oxamethan, is formed, Avhich is iioav regarded as a compound ether, formed by a peculiar acid, called oxamic, C303NH3,C30g. On evaporating the liquid, the substance separates in the form of lamellated crystals, of a greasy aspect, melting at about 212°, and distilling Avithout change .at 248°. It dissolves readily in A\rater and in alcohol, its ETHERS. 535 aqueous solution being decomposed, by boiling, into binoxalate of ammonia and alcohol. The formula of oxamic ether is C4H50, (Ca03NH3,C203); and the reaction from which it arises is expressed by the following equation : 2(C4H50, Cfl08)+NH3=C4H50,(C303NH3, Ca03)+C4H803. It has already been shown that the oxamid CaOaNHa is formed during the distillation of oxalate of ammonia. This substance is more easily prepared by decomposing oxalic ether by an aqueous solution of ammonia. Oxamid is a white crystalline substance, having no action on coloured tests; and cold water does not sensi- bly dissolve it, while hot water dissolves a small quantity of it, which is again deposited on the cooling of the liquid. Dilute acids and alkalies, when cold, do not affect oxamid; but at the boiling point, oxamid again takes up two equivalents of water, and yields ammonia NH3,H0 and oxalic acid C303. On adding to oxalic ether dissolved in absolute alcohol a quan- tity of potassa also dissolved in anhydrous alcohol, in such quantity that it shall saturate one-half of the oxalic acid existing in the ether, a salt almost insoluble in absolute alcohol is precipitated in the form of small crystalline lamellae, consisting of oxalovinate of potassa, which dissolves without alteration in water, but subse- quently crystallizes with difficulty. If too great a quantity of potassa be added, oxalate of potassa and alcohol only are obtained. The formula of the salt is K0,(C4H50,2C203); and when it is pre-. cipitated mixed with a certain quantity of oxalate of potassa, it may be separated from it by treating the precipitate with slightly diluted alcohol, which dissolves only the oxalovinate of potassa. By adding sulphuric acid to this solution, the potassa is precipitated in the state of sulphate, and, if the liquid be then saturated with caustic baryta, a solution of oxalovinate of baryta is obtained. The aqueous solution of oxalovinic acid is readily decomposed by evaporation, and crystals of hydrated oxalic acid are obtained. Mucic Ether C4H50,C6H807. § 1353. Mucic acid does not form a compound ether by its direct action on alcohol, hut a mucic ether is obtained by dissolving, with the aid of heat, 1 part of mucic acid in 4 of sulphuric, and then adding to the liquid, when cooled, 4 parts of alcohol. After some time a copious deposit of acicular crystals is formed, which are purified by solution in boiling alcohol, from which they again sepa- rate on cooling. The crystals are mucic ether C4H50,CeH807, which melts at about 284°, and is decomposed at 338° without dis- tilling. It dissolves in boiling water, from which it again separates almost entirely on cooling; and boiling alcohol also dissolves it, while after cooling it retains but very feeble traces of it. 536 TRANSFORMATIONS OF ALCOHOL. Compounds of Ether C4I150 with the Metallic Chlorides. § 1354. Simple ether forms crystallizable compounds with several metallic chlorides, particularly with the bichlorides of tin and titanium. By introducing into a very dry bottle, containing bichloride of tin or titanium, an open tube containing ether, and allowing the bottle to rest, crystals remarkable for their sharpness, and of which the formula is 2C4ILO,SnCl3, 2C4II50,TiCl3, are formed on its sides. The crystals dissolve without change in ether and absolute alcohol, but are decomposed by contact with water, the ether being set free. Compound of Ether with Sulphide of Carbon, Sulphocarbovinic Acid or Xanthic Acid C4Hs0,2CS2. § 1355. These compounds are obtained by dropping into a solu- tion of potassa in absolute alcohol sulphide of carbon until the liquid has lost its alkaline reaction, when a peculiar salt of potassa is formed, the greater portion of which separates in the form of orange- coloured crystals. The composition of the salt corresponds to the formula KO,(C4HsO,2CS3), and it may therefore be regarded as a vinic acid in which the ether C4H50 is combined with sulphocar- bonic acid CS3: it is also called xanthic acid. The acid is separated by pouring sulphuric or chlorohydric acid into a solution of xanthate of potassa, when the liquid becomes milky, while a colourless oil separates from it, which is several times washed with water. This is xanthic acid, which is not very fixed when isolated. The alkaline xanthates are soluble in water, while the other metallic xanthates are insoluble and are precipitated in the form of yellow powders. Xanthates yield, by distillation, several new products, which, however, have not been hitherto suffi- ciently investigated. SIMPLE ETHERS. § 1356. The equivalent of oxygen in ether C4H50 may be re- placed by respectively 1 equivalent of chlorine, bromine, iodine, sulphur, selenium, tellurium, and cyanogen ; and volatile substances may be thus obtained, some of which can form compound ethers and vinic acids. We shall call this class of ethers simple ethers; and ordinary ether C4II.O necessarily belongs to it. Chlorohydric Ether C4H5C1. § 1357. This substance is directly formed by the reaction of chlorohydric acid on alcohol. Absolute alcohol, made very cold by being surrounded with ice, is completely saturated with chlorohydric acid gas, and the liquid is then distilled, the gas evolved being con- veyed through a washing-bottle containing water and kept at a tem- perature of 77° or 86°, and thence into a receiver cooled by a re- ETHEKS. 537 frigerating mixture. Chlorohydric ether being gaseous at a tem- perature above 55.4°, traverses the water in the washing-bottle, Avhich retains the excess of chlorohydric acid or alcohol; and con- denses in the receiver. In order to remove all traces of alcohol and water, the chlorohydric ether is distilled with concentrated sul- phuric acid. The reaction from which it arises is expressed by the following equation: Chlorohydric ether may also be prepared by heating in a flask a mixture of alcohol at 0.85 and concentrated chlorohydric acid of commerce ; the gas being first passed through a washing-bottle containing water, and then through a second containing concentrated sulphuric acid; both bottles being kept at a temperature of 68° or 77°. It may also be procured by introducing into the flask 12 parts of sea-salt, and then adding a mixture of 1 part of sulphuric acid and 5 parts of alcohol. If the temperature of the laboratory exceed 59°, the ether may be collected in the gaseous state in bell- glasses over mercury. Chlorohydric ether, at a low temperature, is a colourless liquid, of a sharp, slightly alliaceous smell; and its density at 82° is 0.291, while it boils at 54.5° under the ordinary pressure of the atmosphere. It should be preserved in a vessel the neck of which is hermetically sealed. It dissolves in 50 parts of water at 32°, and mixes with alcohol in every proportion. The density of its vapour is 2.235, and its equivalent C4H5C1 corresponds to 4 volumes of vapour. Aqueous alkaline solutions decompose it slowly into alcohol and chlorohydric acid, the decomposition being immediate if the alkali is dissolved in alcohol. Chlorohydric ether combines with several metallic chlorides, and its compounds may be regarded as compound ethers of the simple ether. It is largely soluble in perchloride of tin, and a definite compound in the form of acicular crystals separates from it. Per- chloride of antimony also forms a crystalline compound, but very soon reaction ensues with the formation of protochloride of anti- mony. Chlorohydric ether also combines with sesquichloride of iron; but all these compounds are destroyed by water, and the chlorohydric ether again becomes free. Chlorohydric ether is freely absorbed by anhydrous sulphuric acid; a liquid, fuming in the air, and readily decomposed by heat, being formed. C4H80s+HC1=C4H5C1+2H0. Bromohydric Ether C4II5Br. § 1358. This ether is prepared by placing in a tubulated retort, furnished with its receiver, 1 part of phosphorus and 40 parts of alcohol at 0.85, and then adding, drop by drop, through the tubu- lure, 7 or 8 parts of bromine. By the reaction of the bromine on 538 TRANSFORMATIONS OF ALCOHOL. the phosphorus, in presence of the water contained in the alcohol, phosphorus and bromoliydric acid are formed, which latter converts the alcohol into bromoliydric ether C4II602+IIBr==C4ILBr-l-2H0. When the reaction is terminated the retort is heated, still keeping the receiver very cold; and the bromoliydric ether is washed with a very weak solution of potassa, andithen distilled over chloride of calcium, when it appears as a colourless liquid, having a density of 1.473, at 32°, and boiling at 105.8°. lodohydric Ether C4II5I. § 1359. It is prepared by heating in a retort 5 parts of iodide of phosphorus with 2 parts of alcohol at 0.85, shaking with alkaline water the liquid collected in the receiver, and then distilling over chloride of calcium, lodohydric ether is a colourless liquid, having a density of 1.97 at 32°, and boiling at 158°. Light soon turns it brown, announcing the commencement of decomposition. Its for- mula C4HsI corresponds to 4 volumes of vapour. Cyanohydric Ether C4II5Cy. § 1360. This ether is obtained by distilling a concentrated solu- tion of sulphovinate of baryta with cyanide of potassium, washing the distilled product with water slightly alkaline, and distilling over chloride of calcium. Cyanohydric ether is a colourless liquid having a strongly alliaceous smell, and highly poisonous: its density is 0.787, and it boils at 179.6°. Alkalies dissolved in water decom- pose it slowly, while oxide of mercury effects a much more rapid decomposition, resulting in cyanide of mercury, cyanohydric acid, and alcohol. Sulf hydric Ether C4II5S and its Compound Ethers. § 1361. Sulf hydric ether is prepared by passing chlorohydric ether through an alcoholic solution of monosulphide of potassium, after which the liquid is allowed to rest, for 24 hours, in a well- corked bottle, and then distilled; when alcohol, sulf hydric ether, and chlorohydric ether condense in the receiver. This mixture is shaken several times with water, which dissolves the alcohol and chlorohydric ether, and the supernatant fluid, being then separated by means of a pipette, is distilled over chloride of calcium. The first portions which pass over in distillation should be rejected, be- cause they may contain chlorohydric ether. Sulf hydric ether is a colourless, very volatile liquid, of a pene- trating alliaceous smell, to which it is dangerous to be long ex- posed ; and its density is 0.825, while it boils at 163.4°. It is slightly soluble in water, hut in all proportions in alcohol. The density of its vapour is 3.138 ; and the equivalent C4II5S therefore corresponds to 2 vols. of vapour like ordinary ether C41I50. § 1362. If chlorohydric ether he passed through an alcoholic ETHERS. 539 solution of sulfhydrate of sulphide of potassium KS,HS, and be distilled, a much more volatile liquid is obtained, the composition of which is represented by C4H6Sa; and which is therefore alcohol c4h603 with 2 equiv. of sulphur substituted for 2 equiv. of oxygen. It may be called sulfhydric alcohol, and its formula may also be written C4H5S,HS, regarding it as a compound ether of sulfhydric ether C4II5S. It has been called mercaptan, on account of its pro- perty of combining with oxide of mercury, (mercurium captans.) This compound is also obtained by distilling in a water-bath a mixture of a solution of sulfhydrate of sulphide of potassium and a concentrated solution of sulphovinate of lime. The receiver should, in all cases, be cooled, because the product is very volatile: KS,HS+Ca0,(C4H#0,2S0,)=C4H5S,HS+K0,S08+Ca0,S08. The substance is freed from a small quantity of sulfhydric acid by distilling it over red oxide of mercury. Sulfhydric alcohol is a colourless liquid, of very disagreeable and penetrating alliaceous smell: its density is 0.84 ; it solidifies at about —7.6°, and boils at +96.8° ; the density of its vapour being 2.14, so that its equivalent C4HsS,HS is represented by 4 volumes, like that of alcohol. Sulfhydric alcohol forms, with the metallic oxides, compounds in which the hydrogen of the sulfhydric acid is replaced by 1 equiv. of metal, and these compounds have been called mercaptides. The most interesting, on account of the facility with which it is pro- duced, is the mercaptide of mercury, which may be called sulpho- mercuric alcohol. In order to prepare it, an alcoholic solution of sulfhydric alcohol is gradually poured upon red oxide of mercury, when they combine with elevation of temperature, while a white substance is formed. It is dissolved in boiling alcohol, and, on cooling, separates into white, pearl-like spangles, of which the for- mula is C4H5S,HgS. This substance melts at about 185°, and de- composes above 248°. Treated with sulfhydric acid it yields sul- phide of mercury and sulfhydric alcohol. If sulfhydric alcohol be poured into an alcoholic solution of acetate of lead, a yellow crystalline precipitate of sulphoplumbic alcohol C4H5S,PbS is formed. When sulfhydric alcohol is heated with potassium, hydrogen is disengaged, and a sulphopotassic alcohol C4H5S,KS is formed: c4h5s,hs+k=c4h5s,ks+h. A solution of the product in alcohol yields, on evaporation, a white granular substance; and the salt, when treated with acids, yields a salt of potassa and sulfhydric alcohol. When mixed with an alcoholic solution of chloride of mercury, sulphomercuric alcohol is formed.* By distilling a concentrated solution of 2 parts of pentasul- * These bodies maybe viewed as sulfhydrates conjugate with 2CaH2.—J. G. B. 540 TRANSFORMATIONS OF ALCOHOL. phide of potassium KSs with 3 parts of sulphovinate of lime, water and a peculiar etherial liquid pass over, by washing which with water, and distilling it over chloride of calcium, a liquid results of a very disagreeable alliaceous odour, boiling at 303.8°, and of which the formula is C4II5S3. On heating an excess of sulfhydric alcohol with dilute nitric acid the liquor becomes red, from the production of a certain quantity of deutoxide of nitrogen which dissolves in it, but it loses its colour when heated, and after some time an oleaginous liquid separates from it. Nitric acid is gradually added, until the sulf- hydric alcohol is entirely decomposed; after which the liquid is diluted with water, and, after having washed the oleaginous sub- stance several times, it is distilled. This new substance is without colour, of an extremely disagreeable odour, of the density 1.24; and it boils at about 266°, but not without alteration. Its com- position is represented by the formula C4H5S,SOa; and it would therefore be a compound ether, formed by the combination of sulf- hydric ether with sulphurous acid. When the action of dilute nitric acid on sulfhydric alcohol is prolonged until the oxidizing action ceases, an acid compound is obtained, which forms crystallizable salts with bases; and from the analyses which have been made, the formula of the salt of baryta would be Ba0,(C4IIsS304)+HO. § 1363. If chlorohydric ether be passed through an alcoholic solution of sulphocarbonate of sulphide of potassium KS,CSa, a sulphocarbonic ether C4II5S,CS3 which corresponds to carbonic ether C4H50,C03 is formed. After having allowed the substances to act for some time, the liquor is heated to drive off the excess of chlorohydric ether, and it is treated with water; when a liquid of an alliaceous smell, heavier than water, separates from it, which new substance is sulphocarbonic ether C4H5S,CS3. A sulphocyanohydric ether C4HsS,C3NS is obtained by distil- ling a mixture of equal parts of sulphovinate of lime and sulpho- cyanide of potassium, both in concentrated solution. The product, purified by washing, and then by distillation, is a colourless, very limpid liquid, of the density 1.020, boiling at 294.8°. Its equiva- lent is represented by 4 volumes of vapour. Sclenohydric Ether C4H5Se. § 1364. It is obtained by distilling selenide of potassium with sulphovinate of potassa; but its properties are little known. Tellurohydric Ether C4H5Te. § 1365. By projecting telluride of potassium into a hot solution of sulphovinate of baryta, and then distilling, a liquid is obtained ol a reddish-yellow colour, heavier than water, very poisonous, and ALDEHYDE. 541 which boils above 212°. It is tellurohydric ether; and oxidizes slowly in the air, depositing tellurous acid. PRODUCTS OF THE OXIDATION OF ALCOHOL AND ETHER. § 1366. When alcohol and ether are subjected to a very powerful oxidizing action, they are completely consumed, and converted into water and carbonic acid; while, when the oxidizing action is less powerful, they are converted into acetic acid C5H303,H0, in which case they lose 2 equiv. of hydrogen, which form water with 2 equiv. of oxygen given off by the oxidizing substance, while the 2 equiv. of hydrogen are replaced by 2 equiv. of oxygen, also given oft' by the oxidizing reagent. We thus have C4H50 -f 40=C4H303, HO+HO, C4Hs0,H0+40=C4H303,H0+2H0. or When the oxidizing action is still more feeble, it is limited to the abstraction of a single equiv. of hydrogen, and to its replacement by 1 equiv. of oxygen, which furnishes aldehyde C4H40a, according to the formulae C4H50-f20=C4H402-fH0, C4Hs0,H0+20=C4H403+2H0. and Aldehyde C4H40a. § 1367. Aldehyde is formed under a number of circumstances, in which alcohol, ether, and the compound ethers are subjected to oxidizing agencies; while the best method of preparing it consists in distilling in a retort, at a gentle heat, a mixture of 6 parts of con- centrated sulphuric acid, 4 parts of water, 4 parts of alcohol at 0.80, and 6 parts of finely powdered peroxide of manganese. The retort should only be one-third filled, because the mixture swells considerably during the operation; and a cooling apparatus, through which very cold water passes, and a receiver surrounded by a re- frigerating mixture are fitted to the retort. When the reaction appears to he terminated in the retort, the liquid which condensed in the receiver is withdrawn and distilled at two different times over an equal weight of chloride of calcium. The liquid obtained is composed of aldehyde, a small quantity of alcohol and water, and acetic and formic ether. In order to obtain the aldehyde, it is poured into ether saturated with ammoniacal gas; when white crystals, consisting of a combination of aldehyde and ammonia NII3,C4H402 are separated. The crystals are dissolved in their own weight of water, and the solution is introduced into a retort furnished with a receiver cooled by a refrigerating mixture, while sulphuric acid diluted with its volume of water is poured through the tubulure. On distilling it over a water-bath, a liquid is ob- tained which, when distilled over melted chloride of calcium, yields pure aldehyde. 542 TRANSFORMATIONS OF ALCOHOL. Aldehyde is a colourless, very limpid liquid, of a suffocating odour, and its density is 0.790 at 64.4°, while it boils at 71.3°, the density of its vapour being 1.479, and its equivalent C4II402 there- fore corresponding to 2 vol. of vapour. It dissolves, in all propor- tions, in water, alcohol, and ether, burns with a white flame, and exerts no action on vegetable colours. Aldehyde readily absorbs oxygen from the air, particularly in the presence of water, and is converted into acetic acid, which transformation is effected by all oxidizing agents: thus oxide of silver is reduced by a solution of aldehyde, the metallic silver adhering to the sides of the vessel and covering them with a glittering coating; and nitrate of silver pro- duces the same effect if a small quantity of ammonia be added. Alkalies decompose aldehyde, forming, together with other products, a brown resinous matter, which reaction is often indicated as being characteristic of aldehyde. Pure and anhydrous aldehyde, preserved for some time in a tube hermetically closed, undergoes isomeric modifications, differing ac- cording to the temperature. At 32° it is converted into a crystal- line, colourless, and transparent substance, which melts at 35.6°, and boils at 201.2°. The density of its vapour being three times greater than that of aldehyde, its formula may be assumed to be C12H1306. It has been called elaldelvyde. If, on the contrary, the external temperature range from 59° to 68°, elongated prismatic crystals, which finally fill the tube, are developed in the aldehyde, and which volatilize at 248° without melting. This second isome- ric modification of aldehyde has been called metaldehyde, and the density of its vapour is unknown. Aldehyde is also formed whenever alcohol is burned imperfectly in contact with the air; for example, when that liquid is dropped upon metallic plates heated to 482°, or when a wick soaked in alcohol is lighted, and extinguished as soon as the greater portion of the alcohol has evaporated; when the wick is carbonized, and the small quantity of vapour of alcohol which comes in contact with the ignited portions is imperfectly burned, and yields aldehyde, which is known by its suffocating smell. A large quantity of aldehyde is also produced in the experiment of Davy’s flameless lamp, (§ 1169.) When chlorine is passed through diluted and cold alcohol, chloro- liydric acid and aldehyde only are formed, the chlorine then exert- ing an oxidizing agency on the alcohol, by decomposing the water and combining with its "hydrogen : C.II50,il0+2Cl+II0=2HCl + C4H40a. Acetic Acid C4H303,H0. § 1368. Alcohol, when pure, or merely diluted with water, does not combine with the oxygen of the air, while the combination is readily effected in the presence of certain substances the chemical elements of which do not interfere, as, for example, very finely di- ACETIC ACID. 543 vided platinum, which metal may cause the oxidation of a large quantity of alcohol at the expense of the oxygen of the air. In order to perform the experiment, a capsule a (fig. 678) containing platinum-black is placed on a plate, and the capsule is covered with a large bell-glass hav- ing an opening o at the top, and which rests on three small wooden w’edges, to allow the air to enter from beneath; and finally, a funnel b having a long and delicate neck c is introduced into the opening. By pouring alcohol into the funnel, the liquid drops on the platinum con- tained in the capsule, and while a slight eleva- tion of temperature ensues, vapours which con- dense and trickle down the sides of the glass are developed therein. The liquid thus formed on the bottom of the plate is nearly pure acetic acid ; but there is produced at the same time, 1st, a certain quantity of aldehyde, easily recognised by its smell; 2dly, a peculiar substance called acetal; and 3dly, a small quantity of acetic ether, arising from the reaction of the acetic acid on the undecomposed alcohol. If the acid liquor be saturated with chalk and distilled, there is obtained in the receiver, water holding in solution aldehyde, acetic ether, and acetal. If this new liquid be digested with its own weight of chloride of calcium, the latter combines with the water and acetic acid, and etherial liquid separates, which is again distilled, the first portions which pass over being rejected, because they contain a large amount of aldehyde, while the last portions are pure acetal. Acetal is a colourless liquid, boiling at 167°, of a density of 0.844, and so- luble in water and alcohol. Its composition corresponds to the for- mula C14II404, and it may be regarded as being formed by the union in a single group of three molecules of ether, one of them having been modified, under the oxidizing influence, by the substitution of 1 equiv. of oxygen in the place of 1 equiv. of hydrogen, 3C4II50 + 20 = C12H1404+HO. § 1369. The oxidation of alcohol at the expense of the oxygen of the air is also effected by organic ferments, and in general by all albuminous substances, upon which mysterious action is based the conversion of spirituous liquors into vinegar, that is to say, into acetic acid. Wines of certain vintages, rich in albuminous matter, soon turn sour in the air, and become vinegar; which change new wines undergo much more rapidly than the old, because the latter are freed from albuminous substances, which coagulate and fall to the bottom of the barrel; and therefore, in order to make them fer- ment, they must be diluted with a small quantity of water and be exposed to the air. What has just been said of wines is equalty ap- plicable to other alcoholic liquors, and even to solutions of sugar mixed with yeast and exposed to the air. During the acid ferment- Fig. 678. 544 ation of alcoholic liquors, a mucilaginous substance, which greatly assists this fermentation, is separated, and which, consisting chiefly of albuminous matter, is called the mother of vinegar. In order that acetification may progress rapidly, the alcoholic liquor must be sufficiently diluted with wTater, and present a large surface to the oxidizing action of the air. These conditions are ful- filled on a large scale by using an alcoholic liquor containing 1 part of alcohol to 8 or 9 parts of water, and adding about of ferment- able liquor, such as beet-juice, potato-juice, or small beer, wdien the liquor thus prepared is dropped into barrels (fig. 679) filled with beech shavings. The lower part of the barrel is pierced with seve- ral holes a, and the upper part with other holes b, b, while a false bottom cde forms a vat, into which the alcoholic liquor is poured. The false bottom has a great number of holes, through wdiicli pass pieces of twine, having a knob on the end to prevent them from slipping through. The alcoholic liquor flow's along the twrine, and dropping on the shavings, spreads into a thin layer, and pre- sents a large surface to the oxidiz- ing action of the air, oxidation being effected by means of the ferment con- tained in the liquor and the albumi- nous substances in the wrood, wdiile the temperature rises and produces a current of air which enters at the lowrer holes a and escapes through the upper ones b. Oxidation is so rapid that when the liquid reaches the bottom of the barrel, it frequently no longer contains any alcohol, but if, after one pas- sage, the alcohol is not completely converted into acetic acid, it is passed through a second time. The presence of acetic acid itself assists the acetic fermentation, for which reason the fresh shavings to be used are previously left for some time in concentrated vine- gar. The temperature of the barrel also exerts great influence, and, if it be too cool, heated alcoholic liquor must be added to bring the temperature to between 86° and 97°. The acid liquors thus obtained, wrhich constitute common table- vinegar, are dilute solutions of acetic acid, containing in addition the non-fermentable principles which exist in alcoholic liquors. Pure acetic acid is obtained from this liquid by distillation, a very weak acid first passing over, while the following portions contain more acid, and the latter are richer, but are generally deteriorated by the products of the decomposition of foreign substances. The richer liquors are saturated with carbonate of soda, and crystallized acetate of soda is separated by evaporation, and then decomposed TRANSFORMATIONS OF ALCOHOL. Fig. 679. ACETIC ACID. 545 by sulphuric acid, more or less dilute, according to the desired strength of the acetic acid. § 1370. Acetic acid is now largely obtained from the acid liquors obtained by the distillation of wood, which yields very complicated products: carbonic acid gas, oxide of carbon, protocarburetted hy- drogen, water containing acetic acid in solution, a volatile liquid called spirit of wood, some other soluble substances, and, lastly, a black, pitchy portion. The solution of impure acetic acid is called in the arts pyroligneous acid; and in order to separate acetic acid from it, it is first saturated with chalk, which furnishes a solution of acetate of lime decomposable by sulphate of soda, acetate of soda and sulphate of lime being formed, which latter, being but slightly soluble, is nearly wholly deposited. The solution is eva- porated to dryness, and the residue heated to 400 or 480°, a temperature which does not affect the acetate, but decomposes the empyreumatic substances Avith which it is mixed. Three parts of roasted acetate of soda being then treated in a distilling vessel with 9.7 of sulphuric acid, the first third of the liquid Avhich distils over, consisting of a weaker acetic acid, is set aside, Avhile the other tAvo- thirds, Avhicli are composed of very concentrated acid, always con- tain a small quantity of sulphuric acid, in order to free' the product from which it is distilled over anhydrous acetate of soda. The acetic acid thus obtained, having not yet reached its greatest degree of concentration, is exposed to a Ioav temperature by surrounding with ice, or better still by a refrigerating mixture, the vessels contain- ing it; when the acid, at its maximum of concentration C4H303,H0, sets in a crystalline mass, and the more Avatery acid is decanted. The crystallized acid is remelted and again cooled, when only one- half of the product is congealed, and the liquid portion being de- canted off, the solid acid may be considered as haAring attained its maximum of concentration. § 1371. Acetic acid, monohydrated, or at its maximum of concen- tration C4H303,H0, is solid at low temperatures, but melts at 60.8°. The acid liquid may be cooled often to 32° and beloAV, Avithout crys- tallizing, and the bottle may even be shaken Avithout causing crys- tallization ; but if a small glass point be introduced, a crystal is immediately formed at the end of the point, and the whole mass gradually crystallizes; the temperature rapidly rising to 60.8°, and remaining stationary until the solidification is complete. The density of monohydrated liquid acetic acid is 1.063 at 64.4°, and its smell is sharp and penetrating, while its taste is highly acid; but in this state of concentration it exerts a vesicating action and raises blisters on the skin. It boils at 248°, the density of its vapour being 2.09; but it is necessary to measure the density at a very high temperature, because the vapour of acetic acid differs considerably from the laws of permanent gases at temperatures which exceed but slightly its boiling point, (1234.) The equivalent 546 TRANSFORMATIONS OF ALCOHOL. c4h3o3,iio is represented by 4 volumes of vapour, like that of alcohol. Acetic acid mixes with water in all proportions; and for the first quantities of water added, the acid liquor acquires a density greater than that of the monohydrated acid; the maximum of density which corresponds to the acid C4H303 + 3H0 being 1.079. By adding larger quantities of water the density diminishes, and the hydrometer can, therefore, not be used to ascertain the strength of acetic liquids. Chlorine acts powerfully on acetic acid, forming, when the latter is in the monohydrated state C4H303,H0 a new acid C4C1303,H0, called chloracetic acid, in which the hydrogen of the anhydrous acid is replaced by an equivalent quantity of chlorine; while, if the acid is further diluted with water, the chlorine exerts an oxidizing action by decomposing the water, and the acetic acid is converted into oxalic and then into carbonic acid. Ordinary nitric acid acts but feebly on acetic acid, even when assisted by heat. § 1372. Acetic acid forms, with bases, a numerous series of salts, several of which are applied in the arts. They are generally solu- ble in water, and some dissolve in alcohol; and the acid forms fre- quently seve'ral salts with the same base. All the acetates are decomposed by heat, but the decomposition takes place at very different temperatures, and its products vary according to the nature of the base. The acetates formed by the easily reducible metallic oxides, such as the oxides of silver and mercury, leave a metallic residue, and evolve a portion of their acetic acid unchanged, while another portion of the acid is com- pletely consumed by the oxygen given off by the metallic oxide, and yields water and carbonic acid. The acetates formed by the more powerful bases, as the alkaline acetates, leave as a residue an alka- line carbonate, the acetic acid being converted into a neutral vola- tile liquid C3H30, called acetone, or pyroacetic spirit; which reaction is expressed by the following equation: NaO, CJI3O3=NaO, C 02+C8H30. Acetates formed by bases of medium strength, as oxide of lead, undergo a complicated decomposition: unchanged acetic acid and acetone are both disengaged at once, while the carbonic acid arising from the portion of decomposed acetic acid is disengaged or remains combined with the base, according to the temperature. Lastly, wrhen the metallic oxide of moderate strength is easily reduced, as oxide of copper, a portion of the acetic acid is consumed by the oxygen of the oxide, and yields carbonic acid, while the residue of the distillation is composed of metal, or suboxide. Acetic acid forms two cry stall izable salts with potassa: the neutral acetate K0,C4II303 and the binacetate K0,C4II303 + II0,C4H303; the former of which is obtained by saturating acetic acid by car- ACETIC ACID. 547 bonate of potassa and evaporating the liquor. The salt crystallizes with difficulty and is soluble in water and alcohol; and, if it be dis- solved in an excess of acetic acid and evaporated, crystals of the binacetate are obtained, which is deliquescent, melts at 298.4°, and at 392° yields monohydrated acetic acid, furnishing the means of preparing very pure acid. Acetate of soda Na0,C4II303-f 6IIO. It has been seen that this salt is prepared on a large scale in the manufacture of wood-vinegar. It crystallizes in large colourless and transparent prisms, which are often remarkable for the great sharpness of their faces. It has a cool and saltish taste, and dissolves in 3 parts of cold water and 5 of alcohol. When heated, it first dissolves in its water of crystalliza- tion, but soon parts with it; while, if further heated, it undergoes igneous fusion without decomposition, which begins to ensue only at a degree of heat approaching a dull red. Acetate of ammonia (NH3,II0),C4II303, which is obtained by the direct combination of ammonia with acetic acid, is very soluble in water and alcohol, and is used in medicine. When boiled, it loses a portion of its ammonia and is converted into binacetate. Acetate of baryta Ba0,C4H303 + 3H0 forms brilliantly white prismatic crystals, which readily part with 2 equiv. of water at a slightly elevated temperature. Acetate of lime produces only confused crystallizations, resem- bling cauliflowers. Acetate of alumina is prepared by pouring a solution of sulphate of alumina into a solution of acetate of baryta or lead, until no precipitate is thrown down; and the solution, which then contains acetate of alumina, is used in dyeing. In order to separate the salt from it, the liquor must be evaporated in vacuo, because, when heated, acetic acid is disengaged; when the acetate of alumina re- mains in the form of a gummy mass, without any appearance of crystallization. The properties of the acetates of lead and copper, which are of important application in the arts, have already been sufficiently de- tailed when treating of those metals. When concentrated acetic acid is poured into a boiling solution of subnitrate of mercury IIg20,N05, anhydrous white crystalline lamellae of subacetate of mercury Hga0,C4H303 are deposited on cooling. Red oxide of mercury dissolves readily in acetic acid, and the liquid yields by slow evaporation beautiful colourless crystals of protoacetate of mercury Hg0,C4H303, which dissolves without change in cold water, but on boiling deposits perfectly pure red oxide of mercury. Acetate of silver Ag0,C4H303 is obtained by dissolving carbonate of silver in acetic acid; and as it is but little soluble in cold water, it may also be prepared by double decomposition, by pouring nitrate 548 TRANSFORMATIONS OF ALCOHOL. of silver into a solution of acetate of soda. If the liquors are con- centrated, the acetate of silver is deposited on cooling. Acetic Ether, C4II50,C4II303. § 1373. Acetic ether is formed by the direct reaction of acetic acid on alcohol, but the combination is effected rvith difficulty, because it is necessary to use anhydrous alcohol and acetic acid at its maximum of concentration, and pour back again into the retort the liquor which has passed over in distillation; and the formation of acetic ether is much more rapid if 10 or 15 per cent, of sulphuric acid be added. The best method of preparing this ether consists in pouring a mixture of 7 parts of concentrated sulphuric acid with 8 of ab- solute alcohol, or 10 parts of anhydrous acetate of soda, or 20 parts of acetate of lead, into a retort, and distilling as long as any etherial liquor passes over, the product being collected in a well-cooled re- ceiver. The liquor is poured upon dried pulverized carbonate of soda, which abstracts the greater portion of water from the acetic ether, and combines with the free acetic acid which passes over in distillation. The supernatant liquid stratum is decanted, and dis- tilled over chloride of calcium, which takes up the alcohol; but the complete purification of acetic ether is very difficult, because it com- bines with chloride of calcium, and forms a crystalline compound, which is destroyed only by the addition of water. Acetic ether is a colourless, very mobile liquid, of an agreeable ether-like smell, and of the density 0.907 at 32°. It boils at 165.2°, and the density of its vapour is 2.920, its equivalent C4II50,C4II303 being therefore represented by 4 volumes of vapour. It mixes in all proportions with alcohol and ether, and dissolves in 7 parts of water. It is used in medicine. Sulpliacetic Acid C4H404,2S03. §1374. By bringing into contact anhydrous sulphuric acid and monoliydrated acetic acid C4H30,H03, the two acids combine and form a compound acid. The liquid is diluted with water and satu- rated with carbonate of baryta, when the free sulphuric acid forms insoluble sulphate of baryta, while the sulphacetic acid yields a soluble sulphacetate of baryta. The liquor, when evaporated, affords crystals of the formula 2Ba0,(C4H404,2S03)-|-II0, and which part with their water without decomposition. If the baryta be pre- cipitated from sulphacetate of baryta, by sulphuric acid poured in by drops, or if a solution of sulphacetate of lead be decomposed by sulfhydric acid, an acid liquid results, which on evaporation yields deliquescent crystals, melting at 143.6°, and solidifying in a crys- talline mass on cooling. At a more elevated temperature the sulphacetic acid is decomposed. Crystallized sulphacetic acid, placed, in vacuo, over anhydrous phosphoric acid, gives off one equivalent of water, and then assumes ACETONE. 549 the formula C4II404,2S03-f 2IIO; the 2 equivalents of water which it retains being basic. Acetone C3II30 §1375. It has been said (§1372) that the alkaline acetates yield acetone when they are decomposed by heat; but the best method of preparing it consists in heating a mixture of 2 kilog. of acetate of lead Avith 1 kilog. of finely powdered quicklime, in an earthen retort, or in the iron bottles used for the transportation of mercury; the temperature being gradually raised to a dull red- heat. The liquor condensed in the receiver is rectified over chloride of calcium, and then allowed to rest for several days on melted chloride of calcium; after which it is distilled, the first f only of the product being collected, while the other fourth contains, besides a still large quantity of acetone, a considerable quantity of a peculiar substance, boiling at 248°, and which has been called dumasin. Acetone is a very mobile, colourless liquid, of a peculiar odour; and its density is 0.792, while it boils at 132.1°, the density of its vapour being 2.022; so that its equivalent C3H30 is represented by 2 volumes of vapour. The formula of acetone may be written C6II602 or C6H50,H0, in which case its equivalent is represented by 4 volumes of vapour like that of alcohol. It burns with a bril- liant flame; and is soluble in all proportions in water, alcohol, and ether, while chloride of calcium and caustic potassa readily abstract its water. § 1376. On mixing acetone with twice its weight of concentrated sulphuric acid, heat is evolved, and the mixture turns brown, while the smell of sulphurous acid is perceived at the same time; and if the liquor be then diluted with water and saturated with carbonate of baryta, insoluble sulphate of baryta is separated, and a soluble salt of baryta, which crystallizes in pearly lamellae, is obtained. The formula of the salt is 2Ba0,(C6H.0,2S03)+H0; its equivalent of water being removed by drying. If the acid liquor be saturated with carbonate of lime, a salt of lime is obtained: 2Ca0,(C6H50,2S03)+H0. If a smaller quantity of sulphuric acid be used, for example, by treating two volumes of acetone with 1 volume of sulphuric acid, a soluble salt of baryta is still obtained by saturating with carbonate of baryta, but which contains only one-half of the sulphuric acid of the preceding acid, and only 1 equivalent of base. The formula of this salt is Ba0(C6Il50,S03') + H0. § 1377. By distilling 2 volumes of acetone and 1 volume of sul- 550 TRANSFORMATIONS OF ALCOHOL. phuric acid, two new products result, mesitylen C6H4 and mesitic ether C6II50. The mesitylen floats on the surface of the distilled liquid, from which it is separated with a pipette, and shaken several times with pure water, and then distilled over chloride of calcium. Mesitylen is an oleaginous, colourless liquid, of an alliaceous odour, lighter than water, and boiling at 276.8°. § 1378. Impure mesitic ether is obtained by treating acetone with sulphuric acid; while it is obtained in a very pure state by decom- posing the chlorohydric ether C0II5C1 of acetone by an alcoholic solution of potassa. To effect this, the ether is dissolved in alcohol, and, after having heated it, an alcoholic solution of potassa is added until an alkaline reaction is produced; when, on diluting the liquor with water, an etherized liquid separates, forming the upper stratum, which is drawn off by a pipette, Avashed several times with water, and distilled over chloride of calcium. It is a colourless liquid, boiling at 248°, insoluble in water, but soluble in alcohol, and its formula is C6IIsO. §1379. On passing chlorohydric acid gas through acetone, it dissolves largely in it, and a brown oleaginous liquid results, which is to be digested for some time over litharge to remove the free chlorohydric acid ; after which it is washed several times with water, and dried by means of chloride of calcium. This liquid is the chlorohydric ether of acetone C6II5C1, but it is difficult to obtain it pure by this method, and it is more easily effected by pouring into 1 part of acetone, cooled by ice, 2 parts of perchloride of phosphorus PC15, added by small quantities at a time. It is then treated with water, which causes the separation of the chlorohydric ether in the form of a yellow oleaginous liquid. It cannot be distilled, because it is destroyed by heat; and the alkaline liquids decompose it, even water effecting decomposition after some time. Concentrated nitric acid acts powerfully on acetone, forming several products, the nature of which is, however, not yet sufficiently understood. § 1380. From the nature of its compounds, acetone will be seen to resemble alcohol, if its formula be written C6II602. But the acid C(.IL0,2S03, which may be assimilated with sulphovinic acid, differs from it by saturating 2 equivalents of base, while sulphovinic acid saturates only one. Sulphovinic acid, chlorohydric ether, and the compound ethers of alcohol reproduce alcohol when boiled with alkaline liquids; while the corresponding products of acetone do not yield acetone under the same circumstances. When the vapour of alcohol is passed over hydrated potassa heated to about 500°, acetate of potassa is obtained; but under the same circumstances acetone does not yield an acid corresponding to acetic acid. Lastly, no compound ether has hitherto been obtained with acetone. CACODYL. 551 § 1381. By distilling, in a retort furnished with a receiver, a mixture of equal parts of anhydrous acetate of potassa and arsenious acid, a liquid product is obtained, called at first Cadet's liquid, then alearsin, and lastly oxide of cacodyl; and which ignites when exposed to the air, and possesses many other remarkable properties. The composition of this substance, supposed to be pure, corresponds to the formula C4II6AsO. It behaves in its chemical reactions like the oxide of a radical C4II6As, playing a part analogous to that of cyanogen, and has been called cacodyl. This radical enters into a great number of other compounds, as shall presently be described.* In consequence of the facility with which this substance changes when exposed to the air, and its poisonous action on the animal economy, great caution must be used in preparing it; and the retort should be hermetically fitted to the receiver, which must he furnished with a tube to conduct the vapours out of the laboratory. At the close of the operation the receiver contains 3 strata of liquid; the middle one, which is brown and of an oleaginous consistence, consists of impure oxide of cacodyl, and is decanted by means of a siphon filled with water, and conveyed to the bottom of a bottle filled with boiled water. It is shaken several times with the water, which is then poured otf and replaced by alcohol, which dissolves the oxide of cacodyl. By pouring the alcoholic solution into boiled water, the oxide of cacodyl is again precipitated in the form of a liquid layer at the bottom of the bottle; and the supernatant water being rapidly removed, the access of air is prevented by a rapid current of hydrogen which is passed into the bottle. The latter is then closed, after having introduced into it chloride of calcium in- tended to absorb the water and alcohol; and the liquid is first decanted in a tubulated retort traversed by a current of hydrogen, and to which a receiver is fitted; and is then distilled, still keeping up the current of hydrogen, wrhen pure oxide of cacodyl is obtained as a colourless, very fluid liquid. It has a strong and very disa- greeable smell, is very poisonous, and its density is 1.46. It soli- difies at —9.4°, and boils at about 302°, the density of its vapour being 7.8, and 1 volume of the gaseous substance therefore consist- ing of 2 vol. of vapour of carbon 0.552 6 “ hydrogen 0.662 J “ vapour of arsenic 5.185 \ •“ oxygen 1.688 7.977 and its equivalent C4H6AsO is represented by 2 volumes of vapour. Cacodyl Series. * The discovery of cacodyl, and the masterly investigation of all the compounds of this radical, is wholly due to Robert Bunsen.— W. L. F. 552 TRANSFORMATIONS OF ALCOHOL. The chemical reaction which produces it is represented by the folloAving equation: 2(K0,C4H308)+As03=2(K0,C03)+2C03+C4H6As0. Oxide of cacodyl is insoluble in water, but it dissolves largely in alcohol and ether. It dissolves phosphorus and sulphur without any change, while chlorine, bromine, and iodine decompose it rapidly. It combines with anhydrous sulphuric acid and forms a crystalline, deliquescent compound, which dissolves in water, yield- ing an acid liquid. By pouring a dilute solution of corrosive sublimate into an alco- holic solution of oxide of cacodyl a white precipitate is formed, which is a simple combination of oxide of cacodyl with chloride of mercury, according to the formula C4II6AsO,2IIgCl, and which dissolves in boiling water, and again separates from it in crystals on cooling. Bromide of mercury forms an analogous compound. Oxide of cacodyl dissolves in several acids, with which it appears to play the part of a weak base. By adding nitrate of silver to a solution of oxide of cacodyl in nitric acid a white crystalline precipi- tate is formed, of which the formula is 3C4II8AsO,(AgO,NOs). § 1382. Exposed to the air, oxide of cacodyl becomes heated and incandescent, its combustion being complete, while thick vapours of arsenious acid are formed. But if cacodyl covered with a stratum of water be exposed to the air, the oxygen is slowly absorbed, and arsenious acid, a peculiar etherial substance, and a more oxy- genated product of cacodyl, cacodylic acid, are formed. By adding a sufficient quantity of water the cacodylic acid is dissolved; and by evaporating the solution and treating with boiling alcohol, the alcoholic liquor deposits, on cooling, cacodylic acid in colourless cystals. This substance, which is inodorous and nearly tasteless, does not change in the air, and is poisonous, but less so than arse- nious acid. It is decomposed at 446° Avithout distilling ; its formula is C4II6As04-f-II0; and it combines with bases without yielding crystallizable salts. Protocliloride of tin and phosphorous acid abstract its oxygen and restore it to the state of oxide of cacodyl. § 1383. By distilling Avith highly concentrated chlorohydric acid the compound of oxide of cacodyl with chloride of mercury, a chlo- ride of cacodyl C4H8AsC1 is obtained, which should be brought into contact with chloride of calcium and quicklime, and then redistilled. Chloride of cacodyl is a colourless liquid, heavier than Avater, of a sharp smell, and insoluble in Avater and ether, but soluble in all pro- portions in alcohol. It resists a temperature of —49° AATithout be- coming solid, and boils at a little above 212°, its vapour becoming incandescent in contact with the air. Nitrate of sihrer wholly abstracts its chlorine and reproduces oxide of cacodyl. When oxide of cacodyl is treated with gaseous chlorohydric acid, chloride of cacodyl is also formed, but a portion is precipitated in combina- CACODYL. 553 tlon with the water formed. The density of the vapour of chloride of cacodyl is 4.86 ; and its equivalent corresponds, therefore, to 4 volumes of vapour. A bromide and iodide of cacodyl may be obtained by similar processes. Chloride of cacodyl is partially decomposed by contact with water, a combination of 3 equiv, of oxide of cacodyl with 3 equiv. of chloride of cacodyl being formed, which is volatile, and boils at 228.2°, the density of its vapour being 5.35, so that it is formed of 3 vol. of vapour of chloride of cacodyl and 1 vol. of oxide of cacodyl without condensation. The bromide and iodide of cacodyl yield similar compounds. By adding perchloride of platinum to an alcoholic solution of chloride of cacodyl, a brick-red precipitate is obtained, which is, probably, a simple combination of the two substances ; while, if the liquid be boiled, the precipitate is redissolved, and yields a liquor from which neither the platinum nor the chloride of cacodyl can be precipitated by reagents which commonly produce that effect. This new compound is a true base which forms crystallizable compounds with several acids. § 1384. A sulphide of cacodyl C4HfiAsS is obtained by distilling chloride of cacodyl with sulfhydrate of sulphide of barium, when sulfhydric acid is disengaged, while water and the sulphide of cacodyl pass over in distillation, the latter of which is purified by digesting it over chloride of calcium and carbonate of lead, and then distilling it in a current of hydrogen. Sulphide of cacodyl is a colourless liquid, which does not fume in the air, is insoluble in water, but readily soluble in alcohol and ether. It combines di- rectly with sulphur and forms a more sulphuretted compound, which may be obtained crystallized by dissolving it in ether. It rapidly absorbs the oxygen of the air, and then forms several com- pounds, among which cacodylic acid is observed. Chlorohydric acid decomposes sulphide of cacodyl, disengaging sulfhydric acid, while chloride of cacodyl is formed; sulphuric and phosphoric acids also decompose it, a sulphate and phosphate of oxide of cacodyl being formed. The density of the vapour of sulphide of cacodyl is 8.39, and its formula therefore corresponds to 2 of vapour. § 1385. Cyanide of cacodyl is obtained by distilling oxide of cacodyl with cyanide of mercury, when oxide of mercury remains in the retort, while the cyanide of cacodyl distils over and forms, at the bottom of the water in the receiver, an oily stratum, which, on cooling, assumes a crystalline appearance. The crystals are pressed between several folds of tissue-paper, and distilled over baryta. Cyanide of cacodyl melts at 90.5°, boils at 284°, and is but slightly soluble in water, but largely so in alcohol and ether. It is an excessively poisonous substance, the vapour of which it 554 TRANSFORMATIONS OF ALCOHOL. is very dangerous to inhale, and it oxidizes rapidly in the air. The density of its vapour is 4.55, and its equivalent is represented by 4 volumes of vapour. § 1386. By heating, protected from the air, cleanly scraped zinc with chloride of cacodyl, the metal is attacked without any evolu- tion of hydrogen, and a white crystalline mass is obtained, on treating which with water to dissolve the chloride of zinc, an olea- ginous liquid, heavier than water, separates, which is digested for some time with highly polished zinc, and then distilled after having been allowed to remain for some time over chloride of calcium and quicklime. This substance, which is cacodyl, the radical of all the compounds just described, consists of a colourless, highly refracting liquid, still more inflammable than the oxide of cacodyl, which it closely resembles: it solidifies at 212°, and boils at about 338°. Exposed to a feeble current of air, it forms a thick cloud, and is first converted into oxide of cacodyl, and then into cacodylic acid. Sulphur, chlorine, and bromine combine directly with it, and form sulphide, chloride, and bromide of cacodyl. The density of its vapour is 7.28, and its equivalent C4II6As cor- responds to 2 volumes of vapour. The products of cacodyl present a double interest, first as organic substances of which arsenic is the chief constituent, and secondly, because they belong to the small number of organic substances in which the existence of a compound radical has been proved, which, when isolated, reproduces, by direct combination, all the substances of the series. PRODUCTS OF THE ACTION OF CHLORINE ON SUBSTANCES OF THE ALCOHOLIC SERIES. Action of Chlorine on Chlorohydric Ether. § 1387. In a badly lighted situation, chlorine exerts no action on chlorohydric ether; while in a bright light, or still better, in the direct rays of the sun, reaction ensues with development of heat, chlorohydric acid being disengaged, while an etherial liquid con- denses. When any considerable quantity of this liquid is to be prepared, the apparatus is arranged as represented in fig. 680. Into the flask A is introduced, alcohol saturated with chlorohydric acid gas, or merely a mixture of equal volumes of alcohol and highly fuming chlorohydric acid of commerce. The gas is passed through a first washing-bottle B containing water, then through a second bottle C with concentrated sulphuric acid, and lastly through a third bottle D again containing water. Into another flask 1 is in- troduced peroxide of manganese and chlorohydric acid to generate the chlorine, which is waslicd in the water in the bottle II. The two gases are conveyed, by two tubes, the orifices of which are op- posite to each other, into the llask E, having three tubulures, the ACTION OF CHLORINE ON ETHERS. 555 lower of which passes into the bottle F intended to collect the least volatile portion of the product, while the most volatile portion col- lects in the bottle G, which should be well cooled. The flask E in Fig. 680. which the two gases unite should be exposed to the sun, at least in the commencement of the operation; for when the reaction is once established, it continues in the shade, and does not cease with the setting of the sun. Care must be taken to keep the chlorohydric ether in excess as regards the chlorine, as otherwise the latter Avould exert a subsequent action on the first product and produce a second one more chlorinated. It is moreover difficult to avoid, in an ope- ration which lasts for a long time, the formation of a small quantity of this product, unless the operation be continued in the shade; but, as it is less volatile, nearly the whole of it remains in the first receiving-bottle. The liquid is washed several times with water, and then distilled in a water-bath, over quicklime, in order to en- tirely deprive it of water and chlorohydric acid. The first drops which pass over in distillation should be rejected, because they often contain a small quantity of unaltered chlorohydric ether, which re- mains in solution; and the last fourth is also set aside because it may contain a small proportion of more highly chlorinated pro- ducts. The formula of the liquid thus obtained is C4H4C12; and it is monochlorinated chlorohydric ether, presenting the same composition as Dutch liquid, the taste and smell of which it exactly resembles. The density of its vapour is also exactly the same, 3.42 ; while its boiling point is very different, for monochlorinated chlorohydric ether boils at 147.2°, while Dutch liquid boils at 180.5°. These two substances also differ entirely in their chemical reactions: thus, an alcoholic solution of potassa immediately decomposes Dutch liquid when cold, chloride of potassium being formed and monochlo- rinated bicarburetted hydrogen C4II3C1 disengaged. Nothing simi- 556 TRANSFORMATIONS OF ALCOHOL. lar occurs in monochlorinated chlorohydric ether; and if this sub- stance be distilled with an alcoholic solution of potassa, a very small fraction only of it is changed, without producing monochlori- nated bicarburetted hydrogen. Dutch liquid is acted on immedi- ately, when cold, by potassium, hydrogen being disengaged, while chloride of potassium and monochlorinated bicarburetted hydrogen are formed; but in monochlorinated chlorohydric ether, on the con- trary, the potassium preserves its metallic brilliancy. Dutch liquid differs therefore from its isomeric, monochlorinated chlorohydric ether, in the fact that 1 equivalent of hydrogen and 1 equivalent of chlorine exist in the compound in quite different conditions. In the reactions just described, these two elements behave as if they existed, in Dutch liquid, in the state of chlorohydric acid; for which reason some chemists have assigned to Dutch liquid the for- mula C4H3C1,IIC1, and to monochlorinated chlorohydric ether the formula C4II4C13, which perfectly represents the difference of the chemical reactions. § 1888. By causing chlorine to act gradually and with the assistance of solar light on monochlorinated chlorohydric ether, with the precautions described in the preparation of the various degrees of chlorination of Dutch liquid, the following products are obtained: Bichlorinated chlorohydric ether C4H3C13, isomeric with monochlorinated Dutch liquid; Terchlorinated chlorohydric ether..., C4II3C14, isomeric with bichlorinated Dutch liquid; Quadriclilorinated chlorohydric ether,.,..,,.. C4IIC1S, isomeric with terchlorinated Dutch liquid; Perchlorinated chlorohydric ether C4C10, identical with perchlorinated Dutch liquid, or sesquichloride of carbon. The final product of the action of chlorine on chlorohydric ether is therefore the same as that afforded by Dutch liquid: it is crys- tallyzed sesquichloride of carbon, the properties of which have been described, (§ 1838.) The three products C4H3C13, C4H3C14 and C4IIC15 derived from chlorohydric ether, differ entirely in their phy- sical properties from the isomeric products obtained from Dutch liquid ; and, in fact, Bichlorinated chlorohydric ether,.... C4IISC1S boils at.,. 167.0° Monochlorinated Dutch liquid “ “ 239.0° Terchlorinated chlorohydric ether... C4II3C14 “ 215.6° Bichlorinated Dutch liquid “ <( 275.0° Quadrichlorinated chlorohydric ether C4IIC15 “ 294.8° Terchlorinated Dutch liquid.,... “ “ 307.4° The last product, the sesquichloride of carbon, which is common to both series, boils at 356°, ACTION OF CHLORINE ON ETHERS. 557 The difference between the boiling points of isomeric chlorinated products of chlorohydric ether and Dutch liquid becomes smaller and smaller, as the quantity of chlorine substituted for the hydro- gen increases; and lastly, it is reduced to nothing in the perclilo- rinated products, which are identical: thus The difference of ebullition between monochlorinated chloro- hydric ether and Dutch liquid is 71.0° Between bichlorinated chlorohydric ether, and monochlori- nated Dutch liquid, it is 72.0° Between terchlorinated chlorohydric ether and bichlorided Dutch liquid, it is 59.4° Between quadrichlorinated chlorohydric ether and terchlori- nated Dutch liquid, it is 12.6° Lastly, between identical perchlorinated products, it is ne- cessarily 0.0° § 1389. Bichlorinated and terchlorinated chlorohydric ethers differ very distinctly in their chemical reactions from their isomerics, monochlorinated and bichlorinated Dutch liquid. In fact, the pro- ducts derived from Dutch liquid yield, with an alcholic solution of potassa, the former, bichlorinated bicarburetted hydrogen C4II2C12, the latter, terchlorinated bicarburetted hydrogen C4IIC13; while the isomeric products derived from chlorohydric ether afford no similar results: they resist the action of potassa, and, after a long time, sub- stitutions of oxygen for chlorine alone are formed. The differences exhibited in this chemical reaction by the two isomeric series is therefore perfectly explained by writing the products derived from Dutch liquid C4H2C12,HC1 and C4HC13,HC1. Quadrichlorinated chlorohydric ether and its isomeric terchlori- nated Dutch liquid exhibit also remarkable differences in their chemical reactions; the latter substance being readily acted on by the alcoholic solution of potassa, and yielding perchlorinated bicar- buretted hydrogen C4C14 or chloride of carbon; while quadrichlori- nated chlorohydric ether is much more easily acted on by the alcoholic solution of potassa than the products which preceded it, but the reaction is far from being as simple as that exerted on its isomeric. § 1390. Chlorohydric ether may be regarded as being derived from a carburetted hydrogen C4H6, which has hitherto not been obtained, and which, in its constitution, would differ from carburet- ted hydrogen, which we assumed (§1339) as the starting point of the series of Dutch liquid, and we should then have the following series: Carburetted hydrogen unknown C4H6, density “ boils at “ Chlorohydric ether C4II5C1 “ 0.840 “ 54.5° Monochlorinated chlorohydric ether. C4H4C12 “ 1.174 “ 147.2° Bichlorinated “ “ C4IIC13 “ 1.372 “ 167.0° 558 TRANSFORMATIONS OF ALCOHOL. Terchlorinated chlorohydric ether C4H2C14 density 1.530 boils at 215.6° Quadrichlorinated chlo. ether.. C4IIC15 “ 1.644 “ 294.8° Perchlorinated “ u C4C16 “ “ “ 356.0° Products of the Action of Chlorine on Ether C4II50. § 1391. Ether is very violently acted on by chlorine, the temper- ature rising considerably, while the substance turns black and ignites, if the chlorine be in too great quantity, and if the apparatus is exposed to the sun. By operating in a darkened room, and ex- hausting the action of the chlorine by elevating even slightly the temperature toward the close of the operation, a product is obtained which may be regarded as bichlorinated ether, for its formula is C4II3C120. It is a colourless, oleaginous liquid, of a smell resem- bling fennel; and its density is 2.5, while it decomposes at about 284° without boiling. Heated with an alcoholic solution of potassa, chloride of potassium and acetate of potassa are formed, from the following equation: C4II30 Cl2+3K 0=2K Cl+K 0, C4H303, the 2 equiv. of chlorine are therefore replaced by 2 equiv. of oxygen. By heating bichlorinated ether in a current of sulf liydric acid gas, chlorohydric acid is disengaged, and, if it be sufficiently heated, an oleaginous liquid, the greater portion of which solidifies on cool- ing, passes over in distillation. This substance is removed, pressed between several folds of tissue-paper, and dissolved in boiling alco- hol. On cooling, crystals of the two substances are separated, which are again crystallized, until only the prismatic forms of a single species are obtained. The composition of the substance then cor- responds to the formula C4H3S20, and is derived from the primitive substance C4II3C120, bichlorinated ether, by 2 equiv. of sulphur being substituted for 2 equiv. of chlorine; and it is therefore ether C41I50 of which 2 equiv. of hydrogen have been replaced by 2 equiv. of sulphur, or bisulphuretted ether. It is insoluble in water, and decomposed at about 248°, without distilling. An alcoholic solution of potassa decomposes it, forming sulphide of potassium and acetate of potassa: C4H3S20+3K0=2KS+K0,C4H303. Alcoholic liquors which have been used in the purification of bisulphuretted ether deposit, after evaporation, yellow acicuhu of the formula C4II3C1S0, which consist of bichlorinated ether, in which a single equivalent of chlorine has been replaced by 1 equiv. of sulphur. § 1392. By arresting the action of chlorine on ether at a suitable moment, the liquid contains a large quantity of monochlorinated ether C4II4C10, which is particularly formed when chlorine and ACTION OF CHLORINE ON ETIIER. 559 vapour of ether in excess are introduced into a flask exposed to dif- fused light, and the liquid obtained is distilled, dividing the pro- ducts into fractions, when the first portions which pass over in dis- tillation contain a large amount of ether and chlorohydric ether, while the monochlorinated ether C4H4C10 does not distil before about 356°. This product is often formed in large quantities in the preparation of Dutch liquid when the bicarburetted hydrogen be- comes loaded with vapours of ether. The preparation of pure chlorinated ethers is often very difficult, and would be almost impossible if carried on in the sun. A large quantity of chlorohydric ether is necessarily formed in this prepara- tion, from the reaction which the chlorohydric acid, arising from the combination of the chlorine with the hydrogen abstracted from the ether, exerts on the unaltered ether C4H50; and if the operation be carried on in a darkened place, the chlorohydric ether is disengaged almost entirely, without being ultimately attacked by the chlorine; which would not be the case in the light of the sun, because the chlorohydric ether would then be attacked by the chlorine, and yield chlorinated chlorohydric ethers, much less volatile, and which would remain dissolved in the chlorinated ethers. § 1393. The action of chlorine on ether does not stop at bichlori- nated ether C4H3C120, but continues, if the experiment be made in the sun, furnishing liquids richer and richer in chlorine, and corre- spondingly poor in hydrogen. By exhausting the action of the chlorine, by pouring the highly chlorinated liquid into large bottles filled with dry chlorine, and exposed to intense solar light, there are found white crystals, remarkable for their beautiful forms and their size, consisting of perchlorinated ether C4C150, in which all the hydrogen of ether C4I150 has been replaced by chlorine. Perchlo- rinated ether melts at 156.2°, and, when heated to 572°, it does not boil, but is decomposed into sesquichloride of carbon C4C16, and a liquid product of the formula C4C1402, consisting of chlorinated aldehyd. The decomposition is represented by the following equation: 2C4C150=C4C16+C4C1402. When perchlorinated ether is heated with an alcoholic solution of monosulphide of potassium, chloride of potassium and a new com- pound of the formula C4C130 are found, which substance evidently belongs to the series of bicarburetted hydrogen C4H4; 3 equiv. of chlorine having replaced 3 of hydrogen, and 1 equiv. of oxygen oc- cupying the place of the last equiv. of hydrogen. Treated with chlorine, in the sun, the substance C4C130 reproduces perchlorinated ether C4C150. The two substances C4C150 and C4C130 present, therefore, relations precisely similar to those existing between the two chlorides of carbon C4C16 and C4C14, the first of which belongs to the series of chlorohydric ether, and the second to that of bicar- buretted hydrogen. 560 TRANSFORMATIONS OF ALCOHOL. It is essential, in order to obtain pure perchlorinated ether, to expose to the action of chlorine in excess, influenced by the solar rays, only ether already completely chlorinated in the shade and freed from ether and chlorohydric ether; as otherwise large quan- tities of chloride of carbon C4C16, which would remain mixed with the chlorided ether, would be inevitably formed. It is equally necessary to operate upon anhydrous ether, and with perfectly dried chlorine, for, if water be present, it is entirely de- composed by the chlorine, and its nascent oxygen exerts an oxidizing action on the ether, (§1366,) forming aldehyd C4II402, and conse- quently causing the products of the action of chlorine on aldehyd to be mixed with those of the action of chlorine on ether C4II50. Action of Chlorine on Sulfhydric Ether, C4H5S. § 1394. Sulfhydric ether is powerfully acted on by chlorine, with disengagement of clilorohydric acid, and it even ignites when pro- jected into a bottle filled with gaseous chlorine. After attacking the sulfhydric ether by chlorine, in a darkened place, and intro- ducing the chlorine slowly, in order to avoid too great an elevation of temperature, the apparatus is exposed to the sun as soon as the action ceases, and chlorine passed through until chlorohydric acid is no longer disengaged. The liquid is exposed in vacuo near a cup filled with a concentrated solution of caustic potassa, which absorbs the chlorine and chlorohydric acid it contains; and there remains a yellow liquid, of an extremely disagreeable and persistent smell, of the density 1.673, and which decomposes at about 320°. Its for- mula is C4HC1 S, and it constitutes quadrichlorinated sulfhydric ether: intermediate products probably exist, but they have not yet been discovered. Action of Chlorine on Alcohol C4II602. § 1395. Chlorine acts very powerfully on alcohol, and yields very various products, according to the strength of the alcohol. We shall suppose the most simple case, that in which the alcohol is anhydrous, and admit that the chlorine is perfectly dry. Alcohol absorbs a large quantity of chlorine, without any disengagement of clilorohydric acid, if its temperature he kept sufficiently low; and if, after a certain length of time, water be poured on the product, an oleaginous liquid is separated from it, which falls to the bottom of the vessel, and is a mixture of several chlorinated substances: this substance is called chloralcoholic oil, but the substances com- posing it are unknown. If the action of chlorine on alcohol be indefinitely continued, an oily liquid soon separates, which gradually increases, and finally constitutes the whole mass. This liquid, which is also very complex, is gently heated, in order to disengage the very volatile products, such as clilorohydric ether and its highly chlorinated products, which, if they remained in the mixture, would OHLORAL. 561 be subsequently transformed into chloride of carbon C4C10. The action of the chlorine is continued, the temperature elevated, and it is terminated by the assistance of the solar rays. The liquid obtained should be mixed with 3 or 4 times its volume of sulphuric acid, and the bottle is shaken several times, after which its contents are distilled over sulphuric acid. The product of this distillation is again distilled in a tubulated retort furnished with a thermo- meter, and the first products, containing a large amount of chlo- rohydric acid, are rejected, the product distilling at 201.2° being separately collected, which forms a colourless liquid, of a suffocat- ing odour, and exciting to tears. Its density is 1.502, and its com- position corresponds to the formula C4IIC1302: it is called chloral, but is only terchlorinated aldehyd. Its equivalent corresponds to 4 volumes of vapour. The formation of chloral by the action of chlorine on alcohol, is explained in the following manner:—The formula of anhydrous alcohol is C4II802, while, in the majority of its reactions, it behaves like a compound of ether C4II50 and water IIO \ and the action of chlorine on alcohol yields the same products as if it acted on a mixture of 1 equivalent of ether and 1 equivalent of water: it first exerts an oxidizing action, by decomposing the equivalent of water, and the product of this action is aldehyd C4H403, which is in fact obtained in large quantity during the first periods of the action of chlorine on alcohol, and may be separated by distillation. But if the action of the chlorine continues, as there is no more water, the previous oxidizing action is replaced by a chlorinating action, by which the substance loses hydrogen and gains equivalent quantities of chlorine; the reaction ceasing, even in the most intense solar heat of our climate, at the moment when the substance still retains 1 equivalent of hydrogen, and is converted into chloral C4IIC1303. The reaction is expressed by the following equation: C4Hs0,H0+8C1=C4HC1303+5HC1. Chloral should therefore he considered as terchlorinated aldehyd. It has hitherto been in vain attempted to remove directly by chlorine the equivalent of hydrogen which remains in terchlorinated aldehyd, so as to produce quadrichlorinated or perchlorinated aldehyd C4C1402, although this substance has been indirectly obtained, it being one of the products of the decomposition of perchlorinated ether C4C150, by heat, (§ 1393.) Chloral dissolves largely in water without decomposing, and if the solution be evaporated in vacuo over concentrated sulphuric acid, crystals are formed consisting of a combination of chloral with water, hydrated chloral C4HC1302,H0, which exhibits the molecular grouping of alcohol C4H50,II0. Chloral has so great an affinity for water that it attracts the moisture of the air, and is con- verted into crystals' of hydrated chloral. The crystals may be 562 TRANSFORMATIONS OF ALCOHOL. sublimed without decomposing, while they give off their water when they are distilled with concentrated sulphuric acid, and allow anhy- drous chloral to pass over in distillation. Chloral is decomposed by an aqueous solution of potassa, two pro- ducts belonging to the series of protocarburetted hydrogen C2II4 being formed, namely, formic acid C3H303 and chloroform C2IIC13; and the reaction is expressed by the following equation: C4HCl302,II0+K0==K0yC2II03+C2HCl3. The molecular grouping of alcohol is therefore doubled in this case, and produces two groups, exhibiting the grouping of protocarburet- ted hydrogen. When anhydrous chloral is left for some time in a tube hermeti- cally closed it becomes cloudy, and a white substance, which in- creases until it has taken the place of the whole of the liquid, is de- posited on the sides of the tube. This is an isomeric modification of chloral, which no longer presents any of the characteristic proper- ties of the latter substance: thus it is inodorous, resembles porcelain in appearance, and no longer dissolves in water, whence it has been called insoluble chloral. It reproduces, when heated, ordinary chloral, which distils over. If the tube in which the chloral is contained be shaped as represented in fig. 681, the part a, in which the chloral is solidified, may be heated, and the liquid chloral obtained in the part b; and since the liquid chloral soon solidifies again, the experiment may be indefinitely repeated in the same tube. It is important to remark that liquid chloral C4HC1302 does not correspond exactly to aldehyd, for its equivalent is represented by 4 volumes of vapour, while that of aldehyd C4II402 is represented by 2 volumes. It must therefore be admitted that in the conversion of aldehyd into terchlorinated aldehyd or chloral, each molecule of aldehyd has afforded 2 molecules of chloral, or rather that the mole- cules, by being charged with chlorine, have separated so as to fill a double space. If the first hypothesis is correct, insoluble chloral may possibly present the molecular grouping of aldehyd ; while insoluble chloral may possibly also correspond to one of the isomeric modifications of aldehyd described § 1367—to elaldehyd or metal- dehyd. If the alcohol contained water, or if the chlorine were not per- fectly dry, the reaction might be still more complicated. Supposing the alcohol to contain an equivalent of water, the first stage of oxidation due to the decomposition of the water would not stop at the formation of aldehyd C4II40a, but would convert this substance into acetic aid C.HaO,. 4 a 4 Fig. 681. C4H50,H0+H0+2Cl=C4H303-f2HCl; and at a later period during the stage of chlorination, products of the action of chlorine on acetic acid would be formed. CHLORACETIC ACID. 563 But again, acetic acid, by dissolving in unaltered alcohol, might produce, particularly under the influence of the chlorohydric acid, which is copiously formed, acetic ether, which at a later period would form, by the action of chlorine, chlorinated acetic ether. It will hence be seen how complicated these products may become, and it would be often impossible to disentangle the reactions, unless guided by theory. Lastly, if the alcohol were very hydrated, the oxidizing stage would continue until the alcohol was wholly converted into water and carbonic acid. §1396. From what has been just said concerning the action of chlorine on alcohol, there remains but little to add touching the action of chlorine on aldehyde. By causing chlorine to act on alde- hyde C4II403, a large quantity of chloral C4IIC1303 is obtained, which is mixed with other less volatile products, which have not yet been examined. They are probably the chlorinated aldehydes C4H3C103 and C4II3C1203, which a more prolonged action of the chlorine would have converted into chloral. Products of the Action of Chlorine on Aldehyde C4H403. Products of the Action of Chlorine on Acetic Acid, C4H303,H0. § 1397. Chlorine acts powerfully on monohydrated acetic acid, and at last, when assisted by the rays of the sun, deprives it wholly of its oxygen, which is replaced by an equivalent quantity of chlo- rine ; a crystallized product C4C1303,H0, or cJiloracetic acid, which is powerfully acid, and possesses the same capacity of saturation as acetic acid, being formed. Intermediate chlorinated compounds probably exist, but they have not yet been examined. In order to prepare chloracetic acid, ground-stoppered bottles, holding 5 or 6 litres, are filled with very dry chlorine, and into each is poured 4 or 5 grammes of monohydrated acetic acid, after which the bottles are exposed to the sun; when their sides soon become covered with crystals, which consist of a mixture of oxalic and chloracetic acid, while the gas in the bottle is formed of chlorohydric acid and chlorocarbonic gas, resulting from a more advanced decomposition, which takes place, perhaps, in consequence of the small quantity of water from which it is difficult to free the chlorine and the sides of the flask. The crystals being dissolved in water, and the solution evaporated in vacuo over concentrated sulphuric acid, the oxalic acid crystallizes first, when the mother liquid is decanted, completely evaporated, and the residue distilled with anhydrous phosphoric acid. The oxalic acid which might remain is decomposed into oxide of carbon and carbonic acid, and the chloracetic acid distils over, but the first product should not be collected, because it may contain a small proportion of acetic acid. 564 TRANSFORMATIONS OF ALCOHOL. Chloracetic acid crystallizes in rhombohedral lamellae or in colourless aciculae, deliquescent in the air; and it melts at 113° and boils at about 392°. It combines with bases and forms a large number of soluble and crystallizable salts. The formula of chloracetate of potassa is K0,C4Cl303-f 2IIO. “ of chloracetate of ammonia, (NII3,H0),C4Cl303-»-4II0. “ of chloracetate of silver, Ag0,C4Cl303. The chloracetatcs heated with an excess of potassa yield chloro- form and an alkaline carbonate ; and if the action be prolonged, the chloroform is itself converted into formic acid. We have, in fact, K0,C4C1303+K0,H0=C2HC13+2(K0,C02,) K 0, C4C1303+5K0=K0, C2H03+2(K0, C0S)+3KC1. When chloracetic acid is treated with an amalgam formed of 1 part of potassium and 150 parts of mercury, it is converted into ordinary acetic acid, and hydrogen is substituted for the chlorine: C4C1303,II0 -f 7K+2H0=KO, C4H3034-3KC1+3KO. § 1398. Chloracetic acid forms a compound ether, chloracetic ether C4IL0,C4C1303, and a perchlorinated chloracetic ether C4C1S0, C4C1303. Chloracetic ether is prepared by distilling chloracetic acid, or a chloracetate, with a mixture of alcohol and sulphuric acid, and diluting the distilled product with water, when the ether sepa- rates in the form of oil. By exposing it to the sun in bottles filled with dry chlorine, it is converted into an oleaginous product, per- chlorinated chloracetic ether, which boils at 473°. Action of Chlorine on Compound Ethers. § 1399. Chlorine acts on the compound ethers and removes their hydrogen; the hydrogen removed being, in all cases, replaced by an equivalent quantity of chlorine. The first action of chlorine on acetic ether C4II50,C4II303 consists in removing 2 equiv. of hydrogen from simple ether C4II50, and replacing them by 2 equiv. of chlorine; which furnishes a hichlori- nated acetic ether of the formula C4II3C1„0,C4II303. It is decom- posed by an alcoholic solution of potassa, and yields of acetate of potassa and chloride of potassium C4II3C130, C4H303+4KO=2(KO, C4II303)+2KC1. If, on the contrary, the action of the chlorine be exhausted by intense solar radiation, perchlorinated chloracetic ether results, C4C150,C4C1303. By passing chlorine, under the influence of the solar rays, into oxalic ether C4II50,C303 until chlorohydric acid is no longer disen- gaged, the ether is converted into a crystalline mass, which may be purified by pressing it between tissue-paper. This is perchlorinated oxalic ether C4C150,C303, which melts at 291.2°, and is decomposed at a higher temperature. SUBSTITUTION. 565 Carbonic ether C4II50,C03 subjected to the action of chlorine in diffused light yields chlorinated ether C4II3Cla0,C03; and if the action of the chlorine be continued under the influence of the direct rays of the sun, perchlorinated carbonic either C4Cl50,COa is ob- tained. § 1400. By comparing together the numerous compounds derived from alcohol, it will be observed that the greater part of them are formed by means of the molecule of ether C4Hs0, or that of alcohol C4IIsO,HO, in which the hydrogen or oxygen is replaced by equi- valent quantities of other elements: oxygen, sulphur, chlorine, etc. When the hydrogen is replaced by equivalent quantities of chlorine, the equivalent of the derived substance is, in general, represented by the same number of volumes of vapour as the substance from which it is derived, as in the chlorinated products derived from chlorohydric ether. The same is true when oxygen is replaced by sulphur, as in ether C4H.O and sulfhydric ether C4HsS. In these different cases the gaseous volume of the element substituted is the same as that of which it takes the place. But when oxygen, the equivalent of which is 1 vol., is replaced by chlorine, of which the equivalent is 2 vol., the equivalent in volume of the substance de- rived is often different from that of the original substance: thus, the equivalent of ether C4II50 is 2 vol., while that of chlorohydric ether is 4 vol. Many exceptions to these rules nevertheless occur: thus, aldehyde is derived from ether by the replacement of 1 equiv. of hydrogen (2 vol.) by 1 equiv. of oxygen, (1 vol.,) and yet aldehyde C4H403 is represented by 2 vol. of vapour, like ether C4H50; while by replacing 3 equiv. of hydrogen (6 vol.) by 3 equiv. of chlorine (6 vol.) in the molecule of aldehyde, chloral or terchlorinated alde- hyde is obtained, of which the equivalent C4HC1303 is represented by 4 vol., while that of aldehyde is represented by 2 vol. When chlorine is substituted for hydrogen, the chemical proper- ties of the compound, as regards its acid, basic, or neutral reactions, do not, in general, appear to be changed; the most striking example of which is given by chloracetic acid, which is an acid as powerful as acetic, and possesses exactly the same capacity of saturation. The compound chlorinated ethers present additional examples, and others shall subsequently be described which are not less remarkable. But when hydrogen is replaced by oxygen, the basic, acid, or neu- tral properties of the substances change wonderfully. Thus ether c4h5o, which has a manifest affinity for acids, loses this property when it is converted into aldehyde C4H402, and becomes a powerful acid when changed into acetic acid C4H303. In order to appreciate more readily the relations of composition of the substances belonging to the alcoholic or vinic series, we have collected them in the following table: 566 TRANSFORMATIONS OF ALCOHOL. TABLE OF THE COMPOUNDS DERIVED FROM ETHER, C4II60, OR FROM ALCOHOL, C4II60,II0, BY MEANS OF SUBSTITUTION. Carburetted hydrogen unknown C4H6, which may be regarded as the starting point of the whole series. Ether C4H80 2 vol. of vapour. Sulfhydric ether C4H8S 2 “ “ Hydroselenic “ C4H8Se “ “ “ Hydrotelluric “ C4H5Te “ “ “ Chlorohydric “ C4H8C1 4 “ “ Bromohydric “ C4II6Br 4 “ Iodohydric “ C4H6I 4 “ “ Cyanohydric “ C4IIsCy 4 “ “ Sulphocyanhydric ether C4IIsSCy 4 “ “ SIMPLE ETHERS. Alcohols. Ordinary alcohol C4Hs0,II0 4 vol. of vapour. Sulfhydric “ C4HsS,HS 4 “ “ Sulphopotassic alcohol C4I1sS,KS Sulphoplumbic “ C4H6S,PbS Sulphomercuric “ C4HsS,HgaS. Compound Ethers properly so called. General formula (A representing the acid) C4H60,A 2 or 4 vol. Boracic ether C4HS0,2B03 1st Silicic ether 3C4Ht0,Si03 2d Silicic ether 3C4IIs0,2Si08. Vinic acids. General formula of vinic acids formed by the monobasic acids A (C4HsO-f- II0),2A Formula of vinic acids produced by the tribasic acids, such as PO„3HO (C4IIs0-j-2H0),P06. COMPOUND ETHERS. PRODUCTS SUCCESSIVELY DERIVED FROM ETHER C4H,0. lsi. By oxidation. Ether C4Hs0 2 vol. Acetal (2C4H50,C4H40a) Aldehyde C4H40a 2 “ Anhydrous acetic acid...- C4H303 unknown, remains in combination with the water formed, and yields Hydrated acetic acid C4H30„H0 4 vol. but corresponding to alcohol C4Ht0,H0. ‘Idly. By the action of Chlorine. Ether C4H6 0 Monochlorinated ether C4H4C1 0 Biclilorinated ether C4H3ClaO Perchlorinated ether C4C1S 0. TRANSFORMATIONS OF ALCOHOL. 567 3dly. By the successive action of Chlorine and Sulphur. Monochlorinated and monosulphuretted ether C4H3C1S0 Bisulphuretted ether C4II3SaO. PRODUCTS DERIVED FROM SULFHYDRIC ETHER C4HsS. By the action of Chlorine. Sulfhydric ether C4IIsS Quadrichlorinated sulfhydric ether C4HC14S. PRODUCTS DERIVED FROM CIILOROHYDRIC ETHER, C4H,C1. By the action of Chlorine. Chlorohydric ether C4HSC1 4 vol. Monochlorinated chlorohydric ether . C4H4Cla 4 “ Bichlorinated “ “ C4H3C13 4 “ Terchlorinated “ “ C4IIaCl4 4 “ Quadrichlorinated “ “ C4H Clt 4 “ Perchlorinated “ “ C4 Cl6 4 “ PRODUCTS DERIVED FROM ALDEHYDE C4H40a. ls£. By the action of Oxygen. Aldehyde C4II3Oa Acetic acid C4H303 which remains in combination with the water formed. ‘Idly. By the action of Chlorine. Aldehyde C4Ha0a 2 vol. Terchlorinated aldehyde or chloral C„HC1300 4 “ Perchlorinadte aldehyde C4Cl40a. PRODUCTS DERIVED FROM ALCOHOL C4H40,H0. Is/!. By the action of Oxygen. Alcohol C4Hs0,H0 4 vol. Aldehyde C4H40a 2 “ parts with its equivalent of water, and belongs to the series of ether. ‘Idly. By the action of Chlorine. Alcohol C4Hs0,H0 4 vol. Aldehyde (1st stage of oxidation) C4H40a 2 “ Chloral (2d stage of chlorination) C4HCl3Oa 2 “ Aqueous ether C4Hs0-{-H0 yields the same products. PRODUCTS DERIVED FROM AQUEOUS ALCOHOL, C4HsO,HO+HO. By the action of Chlorine. By an oxidizing action, acetic acid C4H303,H0. Aqueous ether C4H50-f-2H0 yields the same product. PRODUCTS DERIVED FROM ACETIC ACID C4H303,H0. By the action of Chlorine. Acetic acid C4H303,II0 4 vol. Chloracetic acid C4C1303,II0 4 “ 568 TRANSFORMATIONS OF ALCOHOL. PRODUCTS DERIVED FROM COMPOUND ETHERS On Carbonic ether C4HsO,COa Bichlorinated carbonic ether C4H3Cl.,0,COa Perclilorinated carbonic ether C4Cl40,COa On Oxalic ether C4II50,Ca03 Perchlorinated oxalic ether C4Cls0,Ca03 On Acetic ether C4H(0,C4IIs03 Bichlorinated acetic ether C4H3Cla0,C4H303 Chloracetic ether C4TIj0,C4C1303 Perchlorinated chloracetic ether C4Clj0,C4Cl303. the action of Chlorine. § 1401. Some chemists regard ether as a hydrate of bicarburetted hydrogen, and give it the formula C4II4,II0 ; in which case alcohol becomes a bihydrate of bicarburetted hydrogen, and all the products of the vinic series are considered as derived from the same radical, bicarburetted hydrogen C4II4. In this point of view, chlorohydric ether is a chlorohydrate of bicarburetted hydrogen C4H4,HC1, and should be the first of the series of Dutch liquid C4II3C1,IIC1 (§ 1338); and the action of chlorine upon chlorohydric ether should therefore yield products identical with those composing this series. Now we have seen that the products derived from chlorohydric ether exhibit, in fact, the same composition as those derived from Dutch liquid, but that they differ essentially in their properties; and it is there- fore evident that ether cannot be regarded as a hydrate of olefiant gas. Other chemists consider ether C4II50 as an oxide of carburettcd hydrogen C4II5, to which they have given the name of ethyl, and have supposed it to be the radical of the ethers. All attempts to obtain this hypothetical root in an isolated form, have hitherto failed; and its supposition being entirely gratuitous, does not assist the explanation of chemical reactions.* * The theory adopted by the author, in which the unknown carburetted hydro- gen C4HS is assumed as the starting point of the ether or alcohol series, is entirely French, and is in other countries regarded in a similar manner as the author regards the 'theory which assumes the hydrocarbon ethyl, C„HS, as the radical of which ether is the oxide; but since the masterly investigations of Prof. Frankland, who actually succeeded in isolating ethyl, probability inclines very much to the side of the ethyl theory, which requires description in a work like the present. Before treating particularly of ethyl one general feature of the theory, which equally applies to a number of other substances, must be described: the theory of the pairing or conjugation of organic compounds. An organic body is said to be paired with another when the latter, termed the pairling or conjugate, enters into combination with the former without the former losing its essential pro- perties ; examples of which also occur in inorganic chemistry, when e. g. oxide of platinum combines with ammonia to form a new oxide, the compound oxide of platinum and ammonia, described (§1178,) the salts of which present the same general character with those of oxide of platinum. The formula of the compound oxide is PtO,NaH6, or PtO,2NHg, and it may be regarded as the oxide of a new base, consisting of PtNJT6 or Pt,2NIIa, 1 cquiv. of platinum being paired with LACTIC AND BUTYRIC FERMENTATION. 569 § 1402. Under certain conditions, and when assisted by ferments, sugars and their congeners experience decompositions very different from those which take place in alcoholic fermentation; and they then give rise to peculiar acids, called lactic and butyric, and to other substances, the nature of which is but little known. The concomitant circumstances, or those which produce lactic and butyric fermentations, are still less known than those of the alcoholic fermentation. The various kinds of sugar, dextrin, sugar of milk, yield a large LACTIC AND BUTYRIC FERMENTATION. 2 equiv. of ammonia; in which case the formula of the oxide in order to express the phenomenon of pairing, would be written Pt(NaHe)0 or Pt(2NHs)0. In organic chemistry the pairing of combinations is of frequent occurrence; and one of the most beautiful instances of it is the pairing of hydrogen with one or more equivalents of bicarburetted hydrogen or olefiant gas. Hydrogen may, for the moment, be regarded as a radical, or a metal, of which water is the oxide, sulfhydric acid the sulphide, chlorohydric acid the chloride, etc.; and now, by pairing it with 1 equiv. of olefiant gas, (assumed to be C2H2) there results the com- pound H(C2Ha) or CaHs; which, if the theory be correct, ought to form compounds with oxygen, sulphur, chlorine, etc. corresponding to the compounds of those ele- ments with hydrogen. This is actually found to be the case, as will be seen in the description of the substance CaHa, or methyl, the radical of its oxide mether, of which methylic alcohol, or ivood-spirit, is the hydrate, ($ 1406.) Hydrogen paired with 2 equivalents of olefiant gas, forms the compound H(C4H4), or C4H5, which is the formula of ethyl, and forms an oxide H(C4H4)0, or ether, corresponding to water, of which alcohol is the hydrate. Ethyl, C4HS, is an or- ganic radical, corresponding to a metal in inorganic chemistry, because it has its oxide C4H50, its chloride C4HSC1, its sulphide C4H5S, and similar compounds with other metalloids, and because its oxide, ether, forms salts with acids corre- sponding to those of a metallic base RO. Chloride of ethyl, which the author calls chlorohydric ether, undergoes mutual decomposition with hydrate of po- tassa, forming chloride of potassium and hydrated oxide of ethyl, or alcohol; which behaviour is peculiar to the metals. If the radical be really hydrogen paired with 2 equivalents of olefiant gas, then will the behaviour of ethyl be in all respects analogous to that of hydrogen; and its chloride, sulphide, etc., will have the properties of acids corresponding to chlorohydric, sulfhydric, etc.; which is, in fact, the case, as chloride of ethyl forms double chlorides with many matallic chlorides, the formulae of which may be written RC1,H(C4H4)C1; and the mercap- tids, the general formula of which is RS,H(C4H4)S, are instances of double sul- phides. Nor does the analogy of hydrogen with its paired compounds stop here; for as hydrogen forms compounds with arsenic, antimony, and phosphorus, so it is probable that methyl H(CaH2) and ethyl H(C4H4) will form similar substances; and Frankland has actually succeeded in forming several of them. Cacodyl, which has been described (§ 1881) is arseniuretted methyl, corresponding to arse- niuretted hydrogen, and even possessing its properties; a phosphuretted methyl has been obtained, similar to phosphuretted hydrogen; and combinations of both ethyl and methyl with zinc, according to the formulas H(C4H4)Zn and H(C2H3)Zn, are already discovered; the corresponding compound of hydrogen, however, being yet unknown, which would take the formula HZn. If hydrogen be paired with more than 2 equivalents of olefiant gas, other ra- dicals are formed, which shall be duly mentioned in their proper places; they are butyryl, valyl, amyl, and several others, corresponding to the formula H(C„H6), H(C„H8), Ii(CI0H,0), etc. Hydrogen, and all radicals formed by its pairing with olefiant gas, will again form a paired compound with oxalic acid CsOa, constituting a series of acids, 570 LACTIC AND BUTYRIC FERMENTATION. amount of lactic acid when they are mixed with a solution of di- astase, which has been exposed to the air for some time. Sprouted barley, -which has been well soaked in water, is left in the air for two or three days, and then bruised, and, after having diluted it with water it is subjected for several days to a temperature of 77° which will he described in the text. It will suffice at present to give a tabular view of the series, since only one of these acids, the acetic, has been already de- scribed in the present work. Hydrogen.. II paired with Ca03 forms formic acid... CaII03 or H (Ca03) Methyl CJI3 “ “ C203 “ acetic acid. C4II303 or CaII3(Ca08) Ethyl C4II5 “ “ C203 “ me/acelonic acid CeHsO3 or C4IIs(Ca08) Butyryl.... C8II, “ “ CaO? " butyric acid.... C8H,03 or C8II,(Ca03) Yalyl C8II9 “ “ Ca08 “ valeric acid.... C10HsO3 or C8lI9(Ca03) Amyl CjoHj, “ “ Ca03 “ caproic acid... or CjoH^CaO,) l l ll l l ll l l ll I l ll Margaryl.. C3JI33 “ M Ca03 “ margaric acid C31H3303 or C3aH33(Ca03) The series is nearly complete, and it is probable that the connecting links, up to margaryl, will be discovered ere long. In the foregoing I have endeavoured to present a general view of the theory adopted in Germany and England, in relation to organic radicals, and paired compounds, without entering into details; and it now remains only to describe the substances which have been discovered since the original was written, and which will be noticed under the chapters where the new compound ought to find its place. Ethyl C4H8, This, for a long time hypothetic radical, is obtained isolated by decomposing iodohydric ether, C4H5I, more properly called iodide of ethyl, by means of me- tallic zinc, in an hermetically sealed tube which has been freed from oxygen by exhaustion with an air-pump. The tube contains, after being heated to above 300°, ethyl C4H6, olefiant gas CaHa, and methyl CaH3 formed by the decomposition of a certain quantity of ethyl, besides iodide of zinc, which with the methyl forms methylide of zinc CaH3Zn. The gaseous ethyl, and the olefiant gas are brought into a glass-tube over mercury, and after absorbing the carburetted hydrogen by fuming sulphuric acid, the tube contains pure ethyl, as a colourless and inodorous gas, burning with a brilliant white flame, and condensing at 9.4° to a very mobile fluid. The density of the gas being 2.000, its formula C4H6 corresponds to 2 volumes. Stibethyl SbC,aII,5. By moistening with iodohydric ether, in a small flask, a mixture of antimoni- uret of potassium with quartzose sand, and distilling as soon as iodoh}rdric ether no longer evaporates, the receiver is found to contain stibethyl, a compound of an- timony with 3 equivalents of ethyl, corresponding to antimoniuretted hydrogen SbHs, and the formula of which is SbC,aH,s or rather Sb,3H(C4H4). Stibethyl, is a very mobile and highly refracting fluid of a disagreeable alliaceous odour, of the density 1.324, boiling at 317.3°, and yielding a vapour of the density of 7.440, so that its equivalent corresponds to 4 volumes. It is soluble in alcohol and ether, and a drop of the solution ignites in the air. A compound Sb,H(C4H4) has also been obtained. Bismethyl BiC,aII15. It is obtained with bismuth-potassium similarly as stibethyl is formed with an- LACTIC AND BUTYRIC FERMENTATION. 571 or 86°. The starch of the barley is first converted into glucose by the diastase, after which lactic fermentation is developed by the influence of the air, and the liquid becomes very acid by the quan- tity of lactic acid formed, which is then saturated with lime, evapo- rated to the consistence of syrup, and treated with boiling alcohol, which dissolves the lactate of lime. Lactic acid is still more easily obtained by means of milk, which contains at the same time, the fermenting substance, sugar of rnilk, and an albuminoid matter, casein, which acts as a ferment, or gene- rates it. When it is allowed to sour in the air, or to turn, a coag- ulum, which is a combination of lactic acid with casein, is formed; and if bicarbonate of soda be added to neutralize the acid, lactate of soda is formed, while the casein, thus set free, again acts as a fer- ment on the sugar of milk, and converts an additional quantity of it into lactic acid. A new coagulum of lactate of casein is thus formed, which is also decomposed by bicarbonate of soda; and the process is continued until no caseous precipitate of lactate of casein is formed, that is, until the sugar of milk is wholly decomposed. At the close of the operation, acetic acid is poured into the liquor, which is then boiled, when the casein is wholly precipitated in the form of acetate of casein. The filtered liquor is evaporated to dry- ness and the residue treated with boiling alcohol, which dissolves the lactate of soda. Instead of the sugar of milk, glucose or even cane-sugar may be added, hut the lactic fermentation of the latter kind of sugar is very slow, and in order that it may take place, the cane-sugar must, probably, be previously converted into fruit-sugar, which transformation is very slow, because it is essential to lactic fermentation that the liquid should not contain much acid. Other albuminoid substances may be substituted for casein: the presence of fatty substances apppears to assist the formation of lactic acid, and some chemists even suppose it to be essential. The formula of lactic acid being C6H505-f HO, 2 equivalents of the acid, therefore contain all the elements of an equivalent of fruit-sugar C12H12012; whence it may be admitted that, in lactic fermentation, the molecules of sugar merely change their grouping, without the intervention of any new elements in the reaction. § 1403. When liquors which have undergone lactic fermentation, timoniuret of potassium, and behaves analogous to stibethyl, from which it differs essentially by decomposing at a certain temperature with a powerful explosion. It is a mobile fluid of the density 1.82, and a highly disagreeable odour; in the air it throws out thick fumes, inflames with a slight explosion and diffuses a deep- yellow smoke of oxyd of bismuth. Composition, Bi,3H(C„H4). Zinckethyl ZnC4H5. It is formed in the decomposition of iodohydric ether, or iodide of ethyl by zinc, and its formula is Zn,H(C4H4). In contact with the air it burns with a bril- liant flame, giving off dense fumes of oxide of zinc.— W. L. F. 572 LACTIC AND BUTYRIC FERMENTATION. are left to themselves for a longer time, another fermentation is de- veloped, and a new acid, called butyric is formed. Introduce into a large bottle 1. A solution of glucose, marking 8 or 10° of Baume. 2. A quantity of chalk equal to one-half of the sugar used. 3. A quantity of casein representing, in the dry state, 8 or 10 per cent, of the weight of sugar contained in the solution, for which purpose either cream-cheese, or Brie-cheese is used; freshly pre- pared gluten may also be substituted for the casein. The sugar is first transformed into a viscous substance which has hitherto been but little studied, and then into lactic acid, large quantities of which may by obtained by arresting the operation at the proper moment; while if it be continued longer, the lactic acid is finally converted into butyric acid, and a mixture of hydrogen and carbonic acid is disengaged. The butyric fermentation is not generally completed until 2 or 3 months, after which the liquid con- tains a mixture of butyrate, lactate, and acetate of lime. The formula of butyric acid being C8II703HO, we have C13H13013=C8H703,H0-f411+4COa. which equation accounts for the evolution of hydrogen and carbonic acid during the butyric fermentation. In order to prepare large quantities of lactic and butyric acid, 3 killog. of sugar are dissolved in 13 killog. of boiling water, to which 15 gm. of tartaric acid have been added, then rotten cheese is added, diluted in sour milk, and 1500 gm. of powdered chalk, the whole is exposed to a temperature of 80° to 95°, and the mass, being shaken from time to time, becomes completely solid in 8 or 10 days. It is then boiled for half an hour with 10 litres of water containing 10 gm. of quick-lime, and after filtering the liquid and evaporating it to the consistence of syrup, it is allowed to crystal- lize. The crystals of lactate of lime being redissolved in 2J times their weight of boiling water, 100 gm. of sulphuric acid diluted with its weight of water, are added, in order to precipitate the lime in the state of sulphate, and isolate the lactic acid; after which the acid liquor, when filtered, is boiled with carbonate of zinc, which forms sulphate and lactate of zinc, a portion of which latter salt separates in crystalline crusts during the cooling of the liquid, while an additional portion is removed by again concentrating it. The lactate of zinc, purified by a second crystallization, is subjected to the action of sulfhydric acid gas, and yields pure lactic acid. The compact mass which has yielded lactic acid, being again left to itself, at a temperature of 98°, becomes liquid and disengages gas; and in 5 or 6 weeks, the new fermentation is terminated. The liquid is then diluted with its weight of water, and a solution of 4 killog. of carbonate of soda is added, which precipitates the lime in the state of carbonate and forms butyrate of soda. The liquor, LACTIC ACID. 573 when filtered, is evaporated until it occupies only a volume of 4 or 5 litres, when 3 kilog. of sulphuric acid diluted with its volume of water are added. The liquid then separates into two layers, the upper one of which, consisting of butyric acid, is removed and brought into contact with chloride of calcium, and distilled. A single operation may yield as much as 1 kilog. of pure butyric acid. Lactic Acid C6TI505,II0. § 1404. Lactic acid, concentrated as much as possible, in vacuo, over sulphuric acid, is a colourless liquid, of a density of 1.22, and soluble in all proportions in water and alcohol. Its composition is represented by the formula CBII505,II0, the equivalent of water being capable of being replaced by 1 equiv. of base; and when subjected to heat it gives off its equivalent of water at about 266°, and is changed into anhydrous lactic acid, CuII505, which is solid, fusible, very slightly soluble in water, but dissolving readily in al- cohol and ether. In contact with water or moist air, it passes slowly into the state of hydrated lactic acid. Anhydrous lactic acid combines with ammoniacal gas, and yields a product of which the formula is NII3,C0II5O5. When heated to 482° lactic acid is further decomposed; and together with other products, a white crystalline substance of the formula C6II404, is formed, which melts at 224.6°, and sublimes without change at about 482°. It combines with ammoniacal gas and forms a compound NII3,C6H404 lactamid, which dissolves with- out change in water and alcohol. The substance ChH404, which has been improperly called anhydrous lactic acid, combines readily with water and reproduces hydrated lactic acid.* The lactates of potassa, soda, and ammonia, are deliquescent, and crystallize with difficulty. Lactate of lime crystallizes in small radiating acic'ulae of the for- mula Ca0,C6II505+oII0, and loses its 5 equiv. of water in vacuo, or at a temperature of 212°. Lactate of zinc ZnO,C6II5Os + 3HO, dissolves in 58 parts of cold, or 6 of boiling water, and bears a temperature of 410° without de- composition. Protolactate of iron Fe0,CaH.05-{-3II0 is prepared by mixing solutions of lactate of ammonia and protochloride of iron, and pre- cipitating by alcohol, or by decomposing lactate of baryta by proto- sulphate of iron. After having separated the sulphate of baryta, alcohol is added to precipitate the lactate of iron in the form of small yellow aciculae. The salt is used in medicine. Lactates of copper and silver are obtained by boiling the carbon- ates of these metals with a solution of lactic acid, and their formulae are CuO,C6II505-f 2IIO, and Ag0,CaII505+2II0. * It is usually called lactide.—J. C. B. 574 LACTIC AND BUTYRIC FERMENTATIONS. Lactic ether C4H50,C6II505 is obtained by distilling 2 parts of dried powdered lactate of lime, with a mixture of 2 parts of anhy- drous alcohol, and 2 parts of concentrated sulphuric acid, the dis- tillation being arrested at the moment the liquid begins to turn brown. The product is rectified over chloride of calcium, and a colourless liquid obtained, having a peculiar odour, a density of 0.866, and boiling at 170°: lactic ether dissolves in water, alcohol, and ether, and is decomposed by the alkalies, yielding alcohol and lactic acid. Butyric Acid C8H703.H0. § 1405. Butyric acid is a colourless liquid, of an extremely dis- agreeable odour, and the smell of rancid butter is owing to the pre- sence of a small quantity of this acid. It solidifies at the tempera- ture of solid carbonic acid, and boils at 327.2°. It dissolves in all proportions in water, alcohol, and spirit of wood, and its density is 0.963, while that of its vapour is 3.09, its equivalent C8H703,IIO, corresponding to 4 vol. of vapour. Butyric acid is inflammable, and chlorine acts on it, yielding two chlorinated butyric acids, of which the formulae are C8H5Cla03,H0 and C8H4C13,Os,HO. Butyrates of potassa, soda, and ammonia, are very soluble in water, and crystallize with difficulty. Butyrate of lime is much less soluble hot than cold, and a solution of the salt, saturated at a low temperature, sets into a mass when heated. The formula of butyrate of baryta, which is deposited from a hot solution, is Ba0,C8lI703+2II0, while that of crystals developed in a cold solution is Ba0,C8II703+4II0, which latter salt melts in its its own water of crystallization. Butyrate of lead is precipitated in the form of an insoluble liquid, which sets after some time. Butyric acid forms a compound ether, wdiich is easily prepared by mixing 100 gm. of butyric acid, 100 gm. of alcohol, and 50 gm. of sulphuric acid, and shaking them for some moments, when a layer of butyric ether forms on the surface of the mixture. It is washed with water, and purified by chloride of calcium. Butyric ether, though but slightly soluble in water, is very soluble in alcohol, and boils at 230°, and its formula is C^HjOjCgHyOg. Ammonia reacts on butyric ether, and produces butyramid jNTIs c8h7o, C8H7Os,HO+NH3=NH2,C8H702+2HO; the butyric ether gradually disappearing, and the aqueous solution, when evaporated, yielding pearly crystals of butyramid, which melts at 239°, and sublimes at a higher temperature without decomposition. Butyrate of lime yields, when heated, an odorous, inflammable liquid, boiling at about 284°, and called butyrone. Its formula is C7H70, and it arises from the following reaction: Ca0,C8II703=Ca0,C02+ C^O. AVOOD SPIllIT. 575 By operating on considerable quantities of butyrate of lime, there is formed, with the butyrone, a more volatile liquid, boiling at 203°, of the formula C8II802, and Avhich has been called butyral. Buty- ral C8II803 is to butyric acid C8II703,H0 what aldehyde C4II402 is to acetic acid C4H303,II0, Avhich comparison is confirmed by the chemical properties of butyral, since it oxidizes in the air, particu- larly Avhen aided by platinum sponge, and is converted into butyric acid. It reduces oxide of silver like aldehyde, the metallic silver forming a coating on the surface of the vessel SPIRIT OF WOOD, OR METHYLIC ALCOHOL, AND THE PRODUCTS DERIVED FROM IT. § 1406. By subjecting wood to distillation, there is obtained, in addition to the gaseous products, an aqueous acid liquor, which con- tains a great number of different substances; that which imparts to it its acidity being acetic acid, the method of the extraction of which has been described (§ 1370). There also exists a volatile, in- flammable liquid, called spirit of wood. The proportion of this liquid varies according to the nature of the wood and the temperature at which the calcination is effected, and it generally reaches 1 per cent, of the whole quantity of fluid. It is mixed with acetone, aldehyde, methylacetic ether, and two volatile substances to which the names of mesite and xylite have been given, and lastly, a pitch-like matter is also found. The liquor is saturated Avith slaked lime, which attacks the acids and a portion of the tarry substances, after which the clarified liquor is decanted and distilled until the first tenth is collected in the receiver. This first product, which contains nearly the whole of the spirit of wood, is again distilled, Avith a small quantity of lime to decompose the methyl- acetic ether, and convert it into spirit of wood. The first portions distilled are alone collected, and by continuing these fractioned dis- tillations, highly concentrated spirit of wood is finally obtained, which, when distilled over lime, yields anhydrous spirit of wood. This is sufficient for all purposes of commerce, but in order to separate the pure principle, methylic alcohol, from it, it is treated with twice its weight of melted and poAvdered chloride of calcium, with which methylic alcohol forms a crystalline compound, resisting a tempera- ture of 212° A\Tithout decomposition. It is heated in a AArater-bath, when the greater portion of the foreign products distils over, and the compound of methylic alcohol Avith chloride of calcium remains. By treating it Avith water, it is destroyed, and the methylic alcohol is set free, and separated by distillation. The product again dis- tilled over quick lime, yields pure and anhydrous methylic alcohol. § 1407. Methylic alcohol is a colourless liquid, of a peculiar 576 METHYLIC ALCOHOL. odour, resembling that of acetic ether, and its density is 0.798, while it boils at 151.7°. Its ebullition in a glass vessel is accom- panied by violent agitation, which renders its distillation difficult, which is avoided by placing a stratum of mercury at the bottom of the vessel. It burns in the air with a flame resembling that of alcohol, and forms a series of compounds so closely resembling those of ordinary alcohol, that it is impossible to separate the study of these two substances, although their origin is very different, on ac- count of which analogy spirit of wrood has been called methylic al- cohol (from, fiiOv, wine, and v^rt, wood.) Its formula is CaH40a, and the density of its vapour being 1.041, its equivalent is represented by 4 vol. of vapour like that of alcohol. Methylic alcohol readily dissolves potassa and soda, and forms, with anhydrous baryta, a crystallizable compound Ba0,C2II408, while the formula of its crystalline compound with chloride of cal- cium is 2 (CaII40,) 2CaCl. Its solvent properties closely resemble those of alcohol, all substances soluble in the latter liquid being equally so in methylic alcohol. ACTION OF SULPHURIC ACID ON METHYLIC ALCOHOL. § 1408. On mixing 2 parts of concentrated sulphuric acid with 1 part of methylic alcohol, a great elevation of temperature ensues, and if the acid liquor be saturated with carbonate of baryta, sulphate of baryta separates, and there remains in solution a salt called sul- phomethylate of baryta, BaO, (C2H30,2S03) which may be obtained in crystals, by evaporating the liquid to the consistence of syrup, and allowing it to rest in a dry vacuum. All the other sulphome- thylates are easily prepared, by double decomposition, from the sulphomethylate of baryta. By carefully decomposing a solution of sulphomethylate of baryta by dilute sulphuric acid, the sulplio- methylic acid is obtained isolated, and its solution exposed for a long time in a dry vacuum, yields small acicular crystals of hydrated sulphomethylic acid. All the sulphomethylates are very soluble in water, and when heated are decomposed into the metallic sulphate which remains, and a compound ether, methylsulphuric ether C3H5 0,S0a, which shall presently be described. § 1409. By mixing 1 part of methylic alcohol with 4 parts of concentrated sulphuric acid, and distilling the mixture, an inflam- mable gas of the formula C2II30 is disengaged, consisting of methy- lic ether, which is to methylic alcohol CaII40a what ordinary ether C4H50 is to alcohol C4II602. The gas thus obtained is, however, always mixed with small quantities of sulphurous and carbonic acids, which are separated by allowing the gas to remain for some time in contact with caustic potassa. Methylic ether is a colourless liquid, of a peculiar etherial smell, and liquid only at a temperature of —22° to —40° ; and its density being 1.61, its formula C31I30 corresponds to 2 vol. of vapour. METHYLIC ETHER. 577 Water dissolves about 37 times its volume of it, and it is still more soluble in ordinary and methylic alcohol. As we have been led by chemical reaction's to write the formula of alcohol C4II50,H0, so also we shall be induced to w'rite that of methylic alcohol C2H30,H0.* § 1410. By distilling 1 part of methylic alcohol with 8 or 10 parts of concentrated sulphuric acid, very little methylic ether is obtained, but an oleaginous liquid distills over, which, when washed several times with water, and then distilled over caustic baryta, presents a composition corresponding to the formula C2H30,S03. It is methylsulphuric ether, that is, a compound ether, formed by the combination of methylic ether with sulphuric acid. The correspond- ing compound C4H50,S03 of the alcohol series has recently been obtained. This product is also obtained by the direct combination of methy- lic ether C2II30 with anhydrous sulphuric acid, the combination being accompanied with great evolution of heat. Methylsulphuric ether is a colourless liquid, of the density 1.324, and which boils at 370.4°; the density of its vapour being 4.37, and its equivalent therefore represented by 2 vol. of vapour. Methylsulphuric ether is slowly decomposed by cold water, but very rapidly by boiling water, the products of decomposition being methylic alcohol C2H30,H0, and sulphomethylic acid C2I130,2S03. Dry ammoniacal gas, and the aqueous solutions of ammonia, de- compose methylsulphuric ether, forming a white crystallizable sub- stance, which has been called sulphomethylam, and also methylsul- phamidic ether, regarding it as a compound ether, formed by a pe- culiar acid, methylsulphaviidic, which has not yet been isolated; the formula of this substance, in fact, may be written C2H30,(NH3S03,S03). § 1411. By introducing anhydrous methylic alcohol and anhy- drous sulphuric acid, separately, into two open tubes entering a very dry bottle, which is then corked, their vapours combine slowly, and an acid is formed, yielding, with baryta, a soluble salt having the same formula is the sulphomethylate of baryta, but differing in its properties It is therefore an isomeric of sulphomethylic acid. § 1412. By causing sulphuric acid, under the most varied circum- stances, to act on methylic alcohol, it has hitherto been impossible to obtain a carburetted hydrogen C3II„ which shall he to methylic ether C2H30, wThat olefiant gas C41I4 is to ether C4H50. * Methylic ether is with more propriety called mether, apd regarded as the oxide of a radical, CaH3, or H(C2H2), which has been isolated, and called methyl. The following series of compounds, called in the text compounds of methylic ether, and methylic acids, should therefore rather be regarded as salts of the oxide of methyl, or mether; the methylic acids being merely acid salts. The names of methylonitric, methyloxalic ether, etc., would then change to re- spectively nitrate of mether, etc.— W. L. F. 578 METHYLIC ALCOHOL. Ethers compounded of Methylic Ether and Methylic Acids. § 1413. Compound methylic ethers are formed under the same circumstances as compound alcoholic ethers, and exhibit the same relations of composition. As in the case of alcohol, two species of combinations of methylic ether with acids are known; neutral com- pounds, which are compound methylic ethers properly so called, and acid compounds, containing a double proportion of acids, and which we shall call methylic acids. Certain acids form both kinds of com- pounds, an example of which has just been shown in sulphuric acid; while others produce only the neutral, and others again only the acid compound. Methylonitric Ether, C2H30,N05. § 1414. The preparation of this substance is not so difficult as that of the nitric ether of the vinic series; since nitric acid of com- merce may be made to react immediately on methylic alcohol, with- out any fear of the tumultuous and complicated reactions which this acid exerts on vinic alcohol. The best method of preparing* methylo- nitric ether consists in heating in a retort a mixture of 1 part of methylic alcohol, 1 part of nitrate of potassa, and 2 parts of con- centrated sulphuric acid, when an etherial liquid is obtained which must be rectified several times over litharge and chloride of calcium. Methylonitric ether is a colourless liquid, of the density 1.182, and which boils at 154.4°; and the density of its vapour being 2.653, its equivalent C3I130,N0S is represented by 4 vol. Methy- lonitric ether detonates with extreme violence at a temperature slightly above its boiling point, and must therefore be handled with great caution. A methylonitrous ether C3H30,N03 would probably be obtained by distilling a mixture of concentrated sulphuric acid and methylic alcohol with nitrate of potassa. Metliylocarbonic Acid C2II30,2C03H0. § 1415. By passing a current of carbonic acid gas through a so- lution of baryta in anhydrous methylic alcohol, a precipitate results in the form of pearl-like spangles, of the formula Ba0(C2H30,2C03), which is the carhomethylate of baryta. The salt is insoluble in methylic alcohol, but dissolves readily in water, being soon decom- posed into carbonate of baryta, carbonic acid and methylic alcohol. Methylocarbonic ether CaH30,C03, has not yet been obtained. Methyloxalic Ether C2H30,C20. § 1416. This product is prepared by distilling a mixture of equal parts of crystallized oxalic acid, concentrated sulphuric acid, and methylic alcohol, when a liquid is obtained which, when allowed to evaporate spontaneously, deposits white crystals of methyloxalic acid. The crystals are dried between tissue paper, and distilled over litharge. METHYLACETIC ETHER. 579 Methyloxalic ether is a solid substance, melting at 123.8°, and boiling at 321.8°. It dissolves in water, alcohol, ether, and methylic ether; and water decomposes it slowly at the ordinary temperature, and rapidly at the boiling point, forming free oxalic acid and me- thylic alcohol. This ether is decomposed by dry ammoniacal gas, and converted into a crystalline substance, of which beautiful crys- tals are obtained by redissolving it in alcohol, and which may be considered as a methyloxamic ether, C2H30,(NII2C302,C303). If a large quantity of ammonia in solution be used, methylic alcohol and oxamid NH2C203 are obtained. Methylacetic Ether C2H30,C4H303. § 1417. It is obtained by distilling 2 parts of methylic alcohol with 1 part of monohydrated acetic acid and 1 part of concentrated sulphuric acid. The product is poured over powdered anhydrous chloride of calcium, and shaken frequently, when, by allowing the liquid to rest, two layers are formed, the upper one of which, when distilled over quicklime to retain the sulphurous acid, and then over chloride of calcium to retain a small quantity of methylic alco- hol, yields pure methylacetic ether. It is a colourless liquid, hav- ing an odour resembling that of acetic ether of the vinic series, and its density is 0.919, while it boils at 136.4°. The density of its vapour being 2.57, its equivalent C2H30,C4II303 is represented by 4 vol. of vapour. It has been shown (§ 1406) that crude spirit of wood always contains a certain quantity of this substance. Boiling water, and the alkaline solutions particularly, decompose it into methylic alcohol and acetic acid; and it dissolves in 2 parts of water, and mixes in all proportions with vinic and methylic alco- hol and with ether. MetJiylocJilorocarbonic Ether C2H30,C203C1. § 1418. This ether is formed under circumstances analogous to those in which the corresponding product of the vinic series is pro- duced, that is, by pouring methylic alcohol into a bottle filled with chlorocarbonic gas COC1. By treating it with water, an oily liquid separates, which is distilled, after being well washed with water, first over chloride of calcium, and then over oxide of lead. It is a colourless liquid, of a suffocating odour. Ammonia dissolved in water decomposes it, chlorohydrate of ammonia and a deliquescent crystalline substance called urethylan being formed; which lat- ter, however, may be considered as methylocarbamic ether, for its formula can be written C2H30,(NH2,C0,C02). Methylobiboracic Ether C3H30,2B03 and Trimethyloboracic Ether 3C3H30,B03. § 1419. By treating melted and finely powdered boracic acid with methylic alcohol, a combination ensues with elevation of temperature; 580 METHYLIC ALCOHOL. and, after driving off the excess of methylic alcohol by heat, there remains as residue a soft, transparent substance, which can be drawn out in threads at the ordinary temperature, consisting of methylo- biboracic ether C2H30,2B03. Water decomposes it immediately into hydrated boracic acid and methylic alcohol. By treating methylic alcohol with chloride of boron, a very vola- tile and colourless liquid is obtained, having a penetrating smell, and the formula is 3C21I30,B03, while its density is 0.955 at 32°, and it boils at 161.6°. The density of its vapour is 3.60. These two compounds burn with a beautiful green flame. Methylosulphocarbonic Ether C2H30,CS2, and Sulphocarbomethylic Acid C2H30,2CS2. § 1420. By pouring sulphide of carbon into caustic potassa, dis- solved in anhydrous amylic alcohol, silky crystals of sulphocarbo- methylate of potassa K0,(C2H30,2CS2) are formed; and a great number of other sulphocarbomethylates are obtained from this salt by double decomposition. If iodine be added to a solution of sulpliocarbomethylate of potassa in methylic alcohol, the temperature rises, while sulfhydric acid and oxide of carbon are disengaged. In addition, iodide of potassium, crystallized sulphur, and a brown oil, which, after two or three rectifications, yields pure methylosul- pliocarbonic ether, are formed. This is an amber-coloured liquid, having a density of 1.143 at 59°, and boiling at about 338° ; and the density of its vapour being 4.266, its equivalent C2II30,CS2 is represented by 2 volumes of vapour. § 1421. By heating in a flask 2 parts of sea-salt with a mixture of 1 part of methylic alcohol and 3 parts of concentrated sulphuric acid, a colourless gas is disengaged, which is to be left for some time in contact with water, to effect the absorption of the mixed sulphurous acid and methylic ether. This gas, which does not liquefy at a cold of —0.4°, is methylochlorohydric ether. Its density is 1.728, and its equivalent C2II3C1 corresponds to 4 volumes of vapour. It burns with a flame edged with green; and water dis- solves about 3 times its volume of it. Metliylochloroliydric Ether C2II3C1.* Metliyliodohydric Ether C2II3I. §1422. It is formed by pouring 8 parts of iodine into 12 or 15 parts of methylic alcohol, and gradually adding 1 part of phosphorus, and then applying heat to distil the liquor. The liquid collected in the receiver is shaken with water, the ether is precipitated, washed * According to tlie more probable theory, this substance would be chloride of methyl.— W. L. F 581 several times with waiter, and then distilled, first over chloride of calcium, and then over oxide of lead. It is a colourless liquid, boil- ing between 104° and 122°; while its density is 2.237 at 69.8°. METHYLIC ETHELS. § 1423. This simple ether, the corresponding one of which in the vinic series is not yet known, is prepared by heating in a retort, methylosulphuric ether C2II30,S03 with fluoride of potassium, or also with fluoride of calcium reduced to an impalpable powder; when a colourless gas is disengaged, of an agreeable etherial smell, burning with a bluish flame, and of which the density is 1.186; while its equivalent C2H3F1 corresponds to 4 volumes. Water dis- solves lj time its volume of it. Methylojiuohydric Ether C2II3F1. Methylocyanohydric Ether C2H3Cy. § 1424. In order to obtain this ether, it is sufficient to distil methylosulphuric ether with cyanide of potassium, or finely pulverized cyanide of mercury; when it is obtained as a liquid, insoluble in water, and very poisonous. Methylosulfhydric Ether C2H3S and its Compounds. § 1425. Methylosulfhydric ether is prepared by passing a current of methylochlrohydric ether C2H3C1 through an alcoholic solution of monosulphide of potassium, heating the liquid, and collecting the distilled products in a well-cooled receiver; after which they are washed with water and distilled over chloride of calcium. Methylosulfhydric ether is a very volatile liquid, of an extremely disagreeable smell, and its density is 0.846 at 69.8°, while it boils at 105.8°. The density of its vapour is 2.115, and its equivalent C2II3S corresponds to 2 volumes of vapour, like methylic ether C2I130. Methylosulfhydric ether is a simple ether,- which forms a great number of compound ethers by combining with electro-negative sulphides ; and the principal of these compound ethers are : §1426. Methylosulfhydric Alcohol C2H3S,HS, or methylic alco- hol C2II30,II0, in which the 2 equivalents of oxygen are replaced by 2 equivalents of sulphur; which is obtained by passing a current of methylochlorohydric ether through an alcoholic solution of sulf- hydrate of sulphide of potassium, and then distilling the mixture. It is also prepared by distilling a mixture of sulphomethylate of potassa K0,(C2II30,2S03) with a solution of sulfhydrate of sulphide of potassium; the distilled product being washed with water, and rectified over chloride of calcium. Methylosulfhydric alcohol, also called methylic mercaptan, is a colourless liquid, of an extremely fetid odour, and very volatile, for it boils at 69.8°. It is decom- posed by contact with red oxide of mercury, and yields a crystal- lized product, in which the sulfhydric acid is replaced by 1 equi- 582 valent of sulphide of mercury HgaS; analogous products being obtained with several other metallic sulphides. § 1427. Sulphocarbomethylosulfhydric Ether C2II3S,CS3 is ob- tained by distilling a concentrated solution of sulphomethylate of lime Ca0,(C2H30,2S03) with a solution, also concentrated, of sulphocarbonate of sulphide of potassium KS,CS2, and rectifying the liquid over chloride of calcium. It is a yellowish liquid, of a density of 1.159 at 64.4°, while it boils at 399.2°. The density of its vapour being 4.650, its equivalent C2II3S,CSa is represented by 2 volumes of vapour: it is methylocarbonic ether C2II30,C03, hitherto unknown, the oxygen of which is replaced by equivalent quantities of sulphur. § 1428. By replacing, in the preparation of methylosulfhydric ether, the alcoholic solution of monosulphide of potassium, by an alcoholic solution of bisulphide of a slightly yellowish liquid is obtained, of an extremely disagreeable and persistent alli- aceous odour; while its density is 1.046 at 64.4°, and it boils at 240.8°. The formula of this substance being C3I13S2, it may be considered as methylosulfhydric ether C3II3S, combined with 1 equivalent of sulphur: the density of its vapour is 3.310, and its equivalent corresponds to 2 volumes of vapour. Lastly, by substituting pentasulphide for the bisulphide of potas- sium, there results a product still more sulphuretted, of which the formula is C2I13S3. METHYLIC ALCOHOL. Protocarburetted Hydrogen C2H4, or Marsh Gras. §1429. Protocarburetted hydrogen evidently belongs to the methylic series, and may be considered as the starting point of this series. By causing chlorine to act on this gas, products are obtained which are identical with those afforded by methylochloro- liydric ether C2H3C1, and it is not to be doubted, although this is not yet proved, that by causing suitable volumes of protocarburetted hydrogen and chlorine to react on each other, methylochlorohydric ether itself will be obtained. Now, methylochlorohydric ether, treated with an alcoholic solution of potassa, yields methylic alco- hol ; and it has been mentioned (§ 1390) that the vinic series may also be regarded as derived from a carburetted hydrogen C4IIc, which is as yet unknown. When vapours of monohydrated acetic acid C4H303,H0 are poured through a glass tube containing platinum-sponge, and heated to 750°, the acetic acid is decomposed into carbonic acid and protocar- buretted hydrogen, C4H303H0=2C02+C3H4. A similar decomposition takes place by heating acetic acid in contact with an excess of alkali; but in that case the carbonic acid remains combined with the alkali, and the protocarburetted hydrogen FORMIC ACID. 583 alone is disengaged. The most economical manner of preparing the gas consists in heating 4 parts of crystallized acetate of soda with 10 parts of an alkaline mixture composed of 2 parts of caustic potassa and 3 parts of quicklime. In order to make the mixture, the 2 parts of potassa are dissolved in a small quantity of water and sprinkled over with the 3 parts of pulverized quicklime; and the paste is then heated to a dull-red to drive off the excess of water. Protocarburetted hydrogen also arises spontaneously from marsh mud (§ 265) and from layers of bituminous coal. It has never been liquefied at any temperature, and its density is 0.559, while its equivalent C31I4 corresponds to 4 vol. of gas, and it burns with a bluish flame, which is much less brilliant than that of bicarburetted hydrogen. PRODUCTS OF THE OXIDATION OF METHYLIC ALCOHOL. Formic Acid C2H03H0. § 1430. Methylic alcohol oxidizes, at the expense of the oxygen of the air, in the presence of platinum-sponge, and, like alcohol, it exchanges, in this case, 2 equiv. of hydrogen for 2 equiv. of oxy- gen,* producing a peculiar acid C2H03,H0, called formic, a large portion of which is, however, destroyed by contact with the platinum- sponge, and, especially if the temperature be elevated, complete com- bustion and the formation of carbonic acid ensue: C2H03,H0+20=2C03+2H0. But formic acid is obtained in a great number of chemical reac- tions, in which certain organic substances are subjected to oxidizing agents; by heating, for example, a mixture of peroxide of manganese and dilute sulphuric acid, with alcohol, sugar, fecula, tartaric acid, etc., a portion of the organic substance being completely converted into water and carbonic acid, while the other is imperfectly oxidized and produces formic acid. When any considerable quantity of formic acid is to be prepared, 2 kilog. of sugar are dissolved in 10 litres of water, and 6 kilog. of sulphuric acid being gradually added, the mixture is poured into the cucurbit of an alembic, at the bottom of which have been placed 6 kilog. of peroxide of manganese. A lively effervescence ensues immediately, owing to the evolution of carbonic acid, and when it lessens, the capital is adjusted and dis- tillation effected, but it is arrested when 5 or 6 litres of liquid are obtained. This liquid, in which the formic acid is concentrated, is * It is more rational to assume, in the case of both acetic and formic acids, that the alcohol takes up 4 equiv. of oxygen and gives off 3 equiv. of water, because the substitution of oxygen for hydrogen in combinations is scarcely admissible. Vinic alcohol C4H602, by taking up 04, becomes C4II606, and, by losing 3HO, as- sumes the formula of acetic acid C4H303-f-aq. In like manner, methylic alcohol C2H40a becomes C2H406 by gaining 04, and is converted into formic acid C,H03-)-aq. by giving off 3HO.— W. L. F. 584 METIIYLIC ALCOHOL. saturated with milk of lime and the formiate of lime crystallized by evaporation. The salt thus forms only crystalline crusts; and by distilling it with more or less concentrated sulphuric acid, formic acid also more or less concentrated is obtained. If formic acid is to be obtained at its maximum of concentration, the formiate of lime must be converted into formiate of lead, by adding acetate of lead to the solution of formiate of lime; when the formiate of lead, being but slightly soluble in cold water, is almost wholly deposited, and may be purified by dissolving it in boiling water, which deposits it, on cooling, in small prismatic crystals. Formiate of lead, well dried, is introduced into a long glass tube, heated by some coals, and through which a current of sulfhydric acid is passed, when sulphide of lead is formed, while mono- hydrated formic acid condenses in the receiver. It is a colourless liquid, of a penetrating and characteristic odour, and it solidifies at a few degrees below 32°, while it boils at 212°. Its density is 1.235, and the density of its vapour being 1.556, its equivalent C2H03,II0 is represented by 4 volumes of vapour. Monohydrated formic acid is highly caustic, and produces blisters on the skin. In combining with water, the first portions of water added elevate its boiling point; with the addition of 20.7 of water, that is 1 equiv., it boils at 222.8°. An excess of concentrated sul- phuric acid decomposes formic acid into oxide of carbon and water. At the boiling point, formic acid reduces several metallic oxides, particularly the oxides of silver and mercury. Formiate of potassa and soda are very soluble and deliquescent. Formiate of baryta dissolves in 4 parts of water, and crystallizes readily; the formula of its crystals being BaO,C2H03. Formiate of lime dissolves in 10 parts of water, and is nearly as soluble in hot as in cold water. Formiate of lead requires 36 to 40 parts of cold water for solu- tion, but dissolves more freely in hot water, and its crystals are anhydrous. By double decomposition, a formiate of silver may be obtained which is destroyed by being boiled with water. § 1431. Formic ether C4II50,C„H03 of the vinic series is obtained by heating a mixture of 7 parts of dry formiate of soda, 10 parts of concentrated sulphuric acid, and 9 parts of alcohol. It is made on a larger scale and cheaply, by mixing, in a large retort, 80 parts of starch, 120 of ordinary alcohol at 0.85, 120 parts of water, 304 of peroxide of manganese, and 240 of concentrated sulphuric acid. Heat is applied gently, and, when the reaction is fully established, the fire is removed, and the sides of the retort cooled with moist cloths, when a stratum of formic ether separates, which is removed and treated with milk of lime to free it from acids, and subse- quently distilled over chloride of calcium. Formic ether is a colourless liquid, of a mild taste, of a density of METHYLAL. 585 0.912, and boiling at 128.1°, which dissolves in 10 parts of water, and mixes in all proportions with alcohol. It should be remarked that formic ether C4H50,C2H03 is isomeric Avith methylacetic ether CaII30,C4II303. Formic ether, treated with chlorine in diffused light, forms a chlorinated ether, of the formula C4H3C120,C2II03, and, by exhausting the action of the chlorine in the sun, a perchlori- nated chloroformic ether C4Cl50,CaC103 is obtained. Methyloformic ether C21I30,C2H03 is prepared in the same man- ner as that of the vinic series, except that spirit of wood is substi- tuted for alcohol, and it is an etherial, very mobile liquid, which boils at about 98.6°. Methylal C6Hs04. § 1432. It has not yet been found possible to obtain aldehyde of the methylic series, the formula of which would be CaII30a. By distilling a mixture of methylic acid and alcohol over peroxide of manganese, there results a mixture of several volatile liquids, in which methyloformic ether and a peculiar liquid, called methylal, predominate. The latter being dissolved in water, and potassa added, the alkali docomposes the methyloformic ether, while the methylal separates in the form of a liquid layer floating on the sur- face, which is purified by distillation over chloride of calcium. Me- thylal boils at 107.6°, and corresponds to acetal. Its formula being C6H504, it may be regarded as resulting from the union of 3 mole- cules of methylic ether, of which one has taken 1 equiv. of oxygen in the place of 1 equiv. of hydrogen.* ACTION OF CHLORINE ON COMPOUNDS OF THE METHYLIC SERIES. Products of the Action of Chlorine on Methylochlorohydric Ether and on Protocarburetted Hydrogen. § 1433. Chlorine acts with more difficulty on chlorohydric ether of the methylic series than on that of the vinic series, the reaction ensuing only when assisted by the direct rays of the sun; and as these products are more volatile, greater care is required in cooling the receivers. The apparatus described (§ 1387) and represented by fig. 680 is used. By maintaining the methylochlorohydric ether in excess, the bottle C, (fig. 680), which should be kept in a refrigerating mixture, receives a very volatile liquid, which should be purified by distilla- tion over concentrated sulphuric acid, and then over quicklime, and which is monochlorinated methylochlorohydric ether CaH3Cla. The odour of this product resembles that of Dutch liquid, and its density * Here again it is unnecessary to assume the highly improbable substitution of oxygen for hydrogen, since the reaction is very simply explained by allowing 3 equiv. of methylic ether C6Hs03 to gain 2 equiv. of oxygen, forming CsHsOs) and then to lose 1 equiv. of water, which gives metliylal C6II804.— W. L. F. 586 METHYLIC ALCOHOL. is 1.344 at 64.4°, while it boils at 86.9°. The density of its vapour being 2.94, its equivalent C2H2C12 is represented by 4 volumes of vapour, like that of methylochlorohydric ether C2H3C1. § 1434. The second product of the action of chlorine on methylo- chlorohydric ether is a liquid having a density of 1.491 at 62.6°, and boiling at 141.8°; the composition of which is represented by the formula C2I1C13, corresponding to 4 vols. of vapour. This is hichlorinated methylochlorohydric ether, more commonly known as chloroform, which name has been given to it because, in contact with an alcoholic solution of potassa, it yields chloride of potassium and fonniate of potassa, CsHC13+4KO=3KC1+KO,C2HOv Chloroform is produced in several other chemical reactions, and particularly when a solution of hypochlorite of lime is made to re- act on alcohol or acetone. This product has been extensively manufactured since the discovery of its power in effecting the insensibility of patients during surgical operations. Chloroform is also obtained by decomposing hydrated chloral C4HC1302,H0 by a solution of potassa, C4HCfl303,H0+KO=C2HC13+KO, C2H03. Lastly, chloroform is produced when the chloracetates are heated in the presence of an excess of hydrated alkali, It is readily and economically prepared, by pouring 35 to 40 litres of water into the cucurbit of an alembic, heating the water to 106°, and adding first 5 kilog. of quicklime, and subsequently 10 kilog. of hypochlorite of lime of commerce; and lastly, by pouring in litre of alcohol at 0.85, and, after having mixed it well, and adjusted the capital, heating the liquid to boiling. As soon as distillation commences, the fire is slackened and the pro- cess allowed to continue spontaneously, when an aqueous liquid condenses in the receiver, at the bottom of which a heavier liquid, chloroform, is formed. It is separated and purified by distillation over chloride of calcium; and the process just described yields about 600 gm. of chloroform. § 1435. Chloroform, subjected to the action of chlorine, in the light of the sun, until chlorohydric acid is no longer disengaged, loses its last equivalent of hydrogen, while perchlorinated methylo- chlorohydric ether C2C14, which is a new chloride of carbon, is formed. This compound is liquid at the ordinary temperature, but at 9.4° solidifies into a pearly crystalline mass; and it boils at 172.4°. Its density is 1.599; the density of its vapour being 5.30, its equivalent is likewise represented by 4 volumes of vapour. § 1436. By exposing to the rays of the sun a bottle containing a K0,C4G1303+K0,H0=2(K0,C02)+C3HC13. CHLOROFORM. 587 mixture of protocarburetted hydrogen, and chlorine in excess, a liquid condenses on the sides, which is a mixture of the various chlorinated methylochlorohydric ethers just described, comprising principally chloroform C4HC13 and chloride of carbon C2C14. The first chlorinated product, methylochlorohydric ether C3II3C1, would probably be obtained by introducing the two gases in an ap- paratus resembling that of fig. 680, maintaining the protocarbu- retted hydrogen in excess, and then passing the gases through a tube cooled by solidified carbonic acid, in order to condense the gaseous ether. In all cases, it is proved that, by the action of chlorine and protocarburetted hydrogen CaH4, the same products are obtained as by the action of chlorine on methylochlorohydric ether C3H3C1, and it is correct to regard this substance as the starting point of the series. Thus, we have Protocarburetted hydrogen C2H4, a non-liquefiable gas. Methylochlorohydric ether C2H3C1, liquefying at a very low temperature. Monochlorinated methylochlorohydric ether C2H2C12, boiling at 86.9°. Bichlorinated methylochlorohydric ether, or chloroform C2HC13, boiling at 141.8°. Perchlorinated methylochlorohydric ether C2C14, boiling at 172.4°. § 1437. But again, it is possible, by operating on chloride of carbon C2C14, and by proper chemical reactions, to substitute hydrogen for the chlorine, and ascend from chloride of carbon to protocarburetted hydrogen, passing through all the intermediate products : in order to prove which, it is sufficient to introduce into a flat-bottomed flask a solution of chloride of carbon in aqueous al- cohol, and then to add an amalgam of potassium. On communi- cating the flask successively with two U-tubes, the first of which is kept at a temperature of about 86°, and the second cooled by a mixture of ice and salt, then with a bulb-apparatus filled with water, and lastly with a conducting-tube which leads the gases into a bell- glass over the water-cistern, and heating the flask, the chloride of carbon is decomposed, chloride of potassium and caustic potassa being formed; and the chlorine abstracted is replaced by hydrogen arising from the decomposition of the water. Bichlorinated methylochlorohydric ether C3HC13 condenses chiefly in the first U-tube, and in the second the monochlorinated methylo- chlorohydric ether C2H3C12, while the water in the bulb-apparatus dissolves the methylochlorohydric ether C2H3C1, which may be sepa- rated by saturating it with chloride of calcium; and lastly, proto- carburetted hydrogen is collected in the bell-glass. This inverse transformation has not hitherto succeeded on the corresponding series of chlorohydric ether of alcohol; but would be 588 particularly interesting, as it would enable the preparation of the carburetted hydrogen C4H6 which is still wanting in the series. METHYLIC ALCOHOL. Bromoform, Iodoform, and Sulphoform. § 1438. By treating alcohol with bromine, a product correspond- ing to chloral is obtained, which is decomposed by alkaline solu- tions, and yields bromoform CsIIBr3. Iodoform C3HI3 is obtained by pouring a solution of caustic po- tassa, or carbonate of potassa, into alcohol saturated with iodine, until the liquid is discoloured; when, by adding a large quantity of water, the iodoform is precipitated in the form of small crystalline spangles, which are purified by redissolving them in alcohol and evaporating the liquid. By distilling 1 part of iodoform with 3 parts of sulphide of mer- cury, a yellow oleaginous liquid is obtained, constituting sulpho- form C3HS3. Action of Chlorine on Methylic Ether C2II30. § 1439. The action of chlorine on methylic ether is excessively violent, even in diffused light; and the experiment, being dangerous, must be carefully conducted, in order to prevent the apparatus from bursting to pieces. Figure 682 represents the apparatus most suit- Fig. 682. able to the production of any considerable quantity of the product. Methylic ether is prepared by beating in a flask A (fig. 682) a mix- ture of 1 part of wood-spirit and 4 parts of concentrated sulphuric ACTION OF CHLORINE ON METHYLIC ETHER. 589 acid; allowing the gas to traverse a first washing-bottle B contain- ing water, then a second bottle C containing a solution of potassa in order to retain the sulphurous and carbonic acids, and lastly, a long tube filled with chloride of calcium to dry the gas. (This tube is not represented in the figure.) The chlorine is prepared in the flask G by the reaction of chlorohydric acid on peroxide of manganese, and is washed in the water of the bottle F, and dried by passing through concentrated sulphuric acid contained in the bottle E. The two gases, which are brought together in the flask D, escape through a refrigerator H, made very cold by ice, into the atmosphere by the opening o. The liquids which condense in the flask D and in the refrigerator H fall into the bottle I, which should be entirely inde- pendent of the apparatus, so that if the latter should burst, the products already obtained will not be lost. The apparatus should be arranged in a well-lighted place, but pro- tected from the direct rays of the sun; and, though the reaction is sometimes long in being established, when once commenced, it con- tinues with great energy. The operator should then regulate the evolution of the two gases with great care : they should meet in such proportion as to destroy each other, immediately, on reaching the flask D; for if one of the gases should flow too freely, as, for example, if the flask were to become coloured by chlorine, which would require a more rapid disengagement of methylic ether, an ex- plosion would inevitably ensue. In order to prevent this accident, the current of chlorine must be lessened by opening one of the w’ashing-bottles E or F, and the ether must be allowed to flow very slowly until the flask D is deprived of colour; after which the gases would be made to flow. The bottle I is found to contain a very volatile liquid, of a suffo- cating odour and exciting to tears, which exhales acid fumes by being decomposed by the moisture of the air. Its density at 68° is 1.315, wdiile it boils at 221°, and cold Avater decomposes it, though slowly. This liquid is monochlorinated methylic ether C3II3C10, the formula of which corresponds to 2 volumes of vapour, like that of methylic ether C2H30, from Avhich it is derived. This product, subjected to the action of chlorine, exchanges 1 equivalent of hydrogen for 1 equivalent of chlorine, and becomes bichlorinated methylic ether, the density of which is 1.606 at 68°, while it boils at about 266° ; its equivalent C3HC130 corresponding likewise to 2 volumes of vapour. Finally, by again exposing this neAV product to the action of chlorine, in the rays of the sun, its last equivalent of hydrogen is replaced by 1 equivalent of chlorine, forming perchlorinated me- thylic ether C2C130, which product has not maintained a state of concentration similar to that of the two preceding, and that of me- thylic ether C2H30, for its equivalent corresponds to 4 volumes of vapour. There has been either a doubling of the original mole- 590 METHYLIC ALCOHOL. cule, or a separation of the molecules, so that the same num- ber of molecular groups now occupy a double space; which change of molecular arrangement is manifested by an anomaly in the boil- ing point. It has always hitherto been observed that when a mole- cular group is modified merely by the substitution of 1 equivalent of chlorine for 1 equivalent of' hydrogen, its boiling point rises; which circumstance is not true for terchlorinated methylic ether, compared with bichlorinated methylic ether ; the boiling point of the latter being 266°, while that of the former is about 212°. Action of Chlorine on Methylosulfhydric Ether. § 1440. Chlorine readily acts on metliylosulfliydric ether, which gradually exchanges its oxygen for equivalent quantities of chlo- rine, and the final product is perchlorinated methylosulfhydric ether C3C13S. Action of Cldorine on the Compound Methylic Ethers. § 1441. A large number of compound ethers of the methylic se- ries can exchange more or less completely their hydrogen for equi- valent quantities of chlorine. Thus methyloxalic ether C2H30,C203 furnishes A bichlorinated methyloxalic ether C2HC120,C203, And a perchlorinated “ “ CSC130,C203. Methylacetic ether C2H30,C4H303 also yields A bichlorinated methylacetic ether C„IIC120,C4II303, And a perchlorinated u .... CaCl30,C4Cl303. It has been shown that formic ether of the vinic series C4H50, C2IIOs presents the same elementary composition as methylacetic ether CaH30,C4II303, although the two substances differ materially in their physical and chemical properties; and the composition of the perchlorinated products of the two ethers should therefore be similar: not only are they so, hut they are identical, constitut- ing one and the same substance, and no longer exhibiting the di- versity of their origin. We have already mentioned an analogous case. Dutch liquid C4II3C1,IIC1 is isomeric with monochlorinated chlorohydric ether C4H4C12, while the two substances differ distinctly in their physical and chemical properties; but when treated with chlo- rine, they both yield the same final product, chloride of carbon C4C16. Methyloformic ether yields with chlorine two chlorinated ethers: Bichlorinated methyloformic ether C2IIC120,C2II03, And perchlorinated “ “ C2C130,C2C103. This last ether is liquid, boils at about 356°, and is isomeric with chlorocarbonic gas COC1; into which it is entirely converted, by passing its vapour into a tube heated to a temperature above 572°. METHYLIC SERIES. 591 Action of Chlorine on Formic Acid. § 1442. No chlorinated formic acid is known, and when mono- hydrated formic acid C2H03H0 is treated with chlorine, the equi- valent of water is always decomposed, chlorohydric and carbonic acids being formed: C2H03,H0+2C1==2HC1+2C02. But it has been shown (§§ 1431 and 1441,) that the formic acid which exists in formic and methyloformic ethers can exchange its hydrogen for chlorine. § 1443. It will be seen from the preceding observations that the compounds of the methylic series may be considered as being pro- duced by the same molecule CaH4, that of protocarburetted hydro- gen, or marsh gas, in which one or several equivalents of hydrogen are replaced by a corresponding number of other elements, such as oxygen, sulphur, chlorine, etc. etc. In order to render this method of generation evident, we have collected into a single table all the known products of the methylic series. TABLE OF COMPOUNDS DERIVED FROM CARBURETTED HYDRO- GEN C2II4, OR FROM METHYLIC ETHER C2II30. Protocarburetted hydrogen, or CaH4 2 vols. Marsh Gas, the starting point of the series. SIMPLE ETHERS. Methylic ether CaH30 2 “ Methylosulfhydric ether CaH„S 2 “ Methylochlorohydric ether CaII3Cl 4 “ Methylobromohydric ether CaH,Br 4 “ Methylodohydric ether CaH3Io 4 “ Methyloliydrocyanic ether CaH3Cy 4 “ Methylosulphohydrocyanic ether CaH3SCy 4 “ COMPOUND ETHERS. Alcohols. Methylic alcohol, or wood-spirit CaH30,H0 4 “ Methylosulfhydric alcohol CaH3S,HS 4 “ Methyloplumbic “ CaH3S,PbS Methylomercurie “ CaH3S,IIgaS. Compound Ethers, properly so called. General formula (A representing the acid) CaH30,A 2 or 4 vols. Methylobiboracic ether CaH30,2B03 Trimethyloboracic “ 3CaH3O.BOs 4 “ Methylic Acids. General formula of methylic acids formed by the monobasic acids A (CaH30-|-H0),2A Formula of the methylic acids produced by the tribasic acids, such as POs,3HO (CaII30-}-2H0),P05 592 METHYLIC SERIES. PRODUCTS DERIVED SUCCESSIVELY FROM METHYLIC ETHER CaII30. 1st. By Oxidation. Methylic ether CaII30 2 vols. Methyal (2CaII30,CaIIa0a) 4 “ Anhydrous formic acid CaH03 unknown. Remains combined with the water formed and yields Hydrated formic acid CaH03,H0 4 “ But corresponding to methylic alcohol CaH30,H0 4 “ 2d. By the Action of Chlorine. Methylic ether C3H3 0 2 “ Monochlorinated methylic ether. ~ CaHaC10 2 “ Bichlorinated “ “ CaHClaO 2 “ Perchlorinated “ “ CaCl3 0 4 “ PRODUCTS DERIVED FROM METIIYLOSULFIIYDRIC ETHER CaII3S. By the Action of Chlorine. Methylosulfhydric ether CaII3S 2 vols. Perchlorinated methylosulfhydric ether CaCl3S. PRODUCTS DERIVED FROM PROTOCARBURETTED HYDROGEN CaH4, OR FROM METHYLOCHLOROIIYDRIC ETHER CaH3Cl. By the Action of Clorine. Protocarburetted hydrogen CaII4 4 vols. Metliylochlorohydric ether CaII3Cl 4 “ Monochlorinated methylochlorohydric ether CaIlaCla 4 “ Bichlorinated do., or chloroform CaHCl3 4 “ Perchlorinated do., “ CaCl4 4 “ PRODUCTS DERIVED FROM METHYLIC ALCOHOL CaH30,H0. lsi. By the Action of Oxygen. Methylic alcohol CaHsO,HO 4 vols. Formic acid CaH03,II0 4 “ 2d. By the Action of Chlorine. Products unknown PRODUCTS DERIVED FROM AQUEOUS METHYLIC ALCOHOL CaH30,H0+H0. By the Action of Chlorine. Formic acid CaHO„HO. An excess of chlorine converts the formic acid, by its oxidizing action, into carbonic acid. Aqueous methylic ether CaII 30-}-2110 yields the same products. METHYLIC SERIES. 593 PRODUCTS DERIVED FROM COMPOUND METHYLIC ETHERS. By the Action of Chlorine. On Methyloxalic ether CaH3 0,Ca 03. Bichlorinated methyloxalic ether CaH ClaO,Ca 03. Perchlorinated “ “ Ca Cl30,Ca 03. On Methylacetic ether CaH3 0,C4H303. Bichlorinated methylacetic ether CaH Cla0,C4H303. Perchlorinated “ “ Ca C130,C4H303. On Methyloformic ether CaH3 0,CaH 03. Bichlorinated methyloformic ether CaH ClaO,CaH 03. Perchlorinated “ “ Ca Cl30,CaC103. § 1444. Chemists have formed, for the methylic series, hypothe- ses analogous to those proposed for the vinic series. Some regard all simple methylic ethers as produced by the combination of the same radical C2Ha, or methylen, with 1 equivalent of oxygen, sul- phur, chlorine, etc. etc., in which case methylic ether becomes a monoliydrate of methylen C2H3,H0, and methylic alcohol its bi- hydrate C2Ha,2HO. This radical is entirely hypothetical, since as yet no earburetted hydrogen of the formula C3Ha is known which yields by direct combination, either with water or with chlorohydric acid, a simple ether of the methylic series; a condition indispensa- ble, neverthless, to enable it to be considered as the radical of the series. Moreover, the methylic and vinic series are so similar that their formula cannot be written in two different ways, and we have incontestably proved (§ 1401) that bicarburetted hydrogen C4H4 could not be considered as pre-existing in the state of a radical in vinic ethers. Other chemists consider methylic ether CaII30 as the oxide of a radical CaHa, which they call methyl, and of which methylochloro- hydric ether is then the chloride; but as methyl is not any better known than is ethyl and methylen, we see no advantage in resorting to hypotheses of these unknown radicals, especially for the methylic series, which may be as easily derived, by means of substitution, from a perfectly well known hydrocarbon, protocarburetted hydro- gen C3H4. We have shown it, in fact, (§ I486,) to be very probable that, by causing chlorine, in proper proportions, to act upon carbu- retted hydrogen C2II4, methylochlorohydric ether C2II3C1 would be obtained: now, the latter is decomposed by contact with alkaline solutions, and yields wood-spirit, whence the whole methylic series may be subsequently derived.* * Referring the reader, on the subject of the radicals of ether and mether, back to the note to \ 1401, (page 568,) it now only remains to describe the radical methyl, the isolation of which renders the correctness of the French theory ex- tremely doubtful. Methyl is given off at the positive pole, in decomposing a concentrated solution of acetate of potassa by a powerful galvanic current, while at the negative pole Methyl CaII3. 594 VEGETABLE ACIDS. OF CERTAIN ACIDS WHICH EXIST IN THE JUICES OF VEGETABLES. § 1445. We shall describe in this chapter certain acids which are found ready formed in the juices of vegetables, and which have not been included in any group of substances of analogous composition, as chemists have succeeded in doing for acetic, formic acid, etc. etc. OXALIC ACID Ca03,II0. § 1446. Of these acids, one of the most important is oxalic, of which the properties were described (§ 259) when treating of the compounds of carbon with oxygen, among which oxalic acid is ranked on account of the composition it presents in anhydrous salts. Oxalic acid is found in a large number of vegetables, which fre- quently, as in the case of sorrel,* owe their acid taste to its presence. In the Black Forest (Southern Germany) it is obtained from certain species of rumex, by pounding the plant in troughs and expressing its juice; after which the residue is moistened with water and ex- pressed a second time. The liquid is clarified with clay, decanted and evaporated to crystallization; when crystals of binoxalate and quadroxalate of potassa, (§ 451,) called in commerce salts of sorrel, are separated. In order to extract the oxalic acid, acetate of lead is poured into a solution of salt of sorrel, when oxalate of lead is precipitated, which is decomposed by sulphuric acid; after which the liquid, on evaporation, yields crystals of oxalic acid C20s,II0 + 2110. The greater part of the oxalic acid now in use in laboratories is prepared by the reaction of nitric acid on sugar, (§ 259.) appear hydrogen and carbonic acid, resulting from the oxidation of the oxalic acid formed, at the expense of an equivalent of water, whence the hydrogen. Acetic acid is considered as a pairling of oxalic acid Ca03 with methyl CaIis» which view is sustained by the decomposition of the acid, ensuing as follows: K0,C4H303+2H0=K0,H0-4-C2H3-(-Ca03-f-II0, or = KO, HO+CaH3+2COa+ H. Methyl is also formed in the decomposition of iodohydric ether by zinc, in pre- sence of water; and in the decomposition of cyanohydric ether (cyanide of ethyl) by potassium. It is a colourless and inodorous gas, almost insoluble in water, soluble in alcohol, and does not liquefy at —0.4°. Its specific gravity being 1.037, its formula CaII3 corresponds to a condensation to 2 volumes. It should be re- garded as H(CalIa), or hydrogen paired with elayl, or olefiant gas. Combinations of methyl with several metalloids and metals have been discovered, but are not yet fully investigated; the only one which is well known being a com- pound of arsenic with 2 equivalents of methyl, or cacodyl, already described, (§1381.) Zincmethyl ZnCaH3 or Zn. P(CaHa) and Phosphuretted methyl P,C6IIS or P,[H(CaHa)]3, corresponding to phosphuretted hydrogen have been obtained. Zincmethyl resem- bles zincethyl; and phosphuretted methyl bears a close analogy to phosphuretted hydrogen.— IF. L. F. * Oxalis acetosella, whence the name.— IF. L. F. MALIC ACID. 595 MALIC ACID CsH40„2H0. § 1447. Malic acid is most widely diffused through the organic kingdom, being found partly free and partly combined with potassa, lime, magnesia, and some organic bases, and giving rise to the acid taste observed in fruits before maturity. Malic acid is generally obtained from the berries of the mountain ash, which are collected before maturity, crushed, and their juice expressed. The juice is clarified by being boiled for a few moments with white of egg and filtered, when acetate of lead is added, which yields a white crystalline precipitate of malate of lead; the salt, however, being always mixed with a small quantity of other organic sub- stances, which are precipitated in combination with the oxide of lead. Malate of lead is nearly insoluble in cold, but readily soluble in boiling water, and is purified by boiling with water the crude malate of lead previously filtered, and rapidly filtering the liquor; when the latter deposits, on cooling, malate of lead in small crysr talline spangles. The mother liquid is again boiled with the residue of the first ebullition, and this is continued until the hot liquor no longer deposits malate of lead on cooling. The foreign plumbic compounds remain in the residue. Crude malate of lead is usually decomposed by sulfhydric acid, (§ 1207,) and the impure malic acid is thus isolated ; after which the solution of malic acid thus obtained is boiled for a few moments, in order to drive off the sulfhydric acid, and then divided into two equal parts. One part, which has been accurately saturated with ammo- nia, is poured into the second part, which remained in the state of free malic acid, which furnishes a solution of bimalate of ammonia, or rather a neutral malate of ammonia and water (NII3,IIO-f IIO), C8II408, wliich is crystallized; and as the salt crystallizes very readily, it is purified by successive crystallizations. If the malate of lead contained tartrate and citrate of lead, as frequently happens, the first crystals deposited by the solution of impure bimalate of ammonia would be bitartrate of ammonia, which is very slightly soluble ; after which the bimalate would crystallize, while the citrate would remain in the mother liquid. In this case, the bimalate of ammonia is again converted into malate of lead, and the salt is again decomposed by sulfhydric acid. The solution of malic acid is evaporated to the consistence of syrup, and then left in vacuo, when it deposits colourlesa crystals of hydrated malic acid, C8II4Os,2IIO, which are deliquescent, and cannot be freed from their water without decomposition. Malic acid is a powerful acid, forming a great -number of salts, and producing in general, with the same base, two salts, the formulae of which, when deprived of their water of crystallization, are 2R0,CsH408, (RO+H0),CsH408, and it is therefore a bibasic acid, as we stated in § 1225. 596 VEGETABLE ACIDS. Alkaline malates are very soluble and deliquescent, which is equally true of the malate of ammonia 2(NH3,H0),C8H408 ; while the malate (NII3,H0 + II0),C8II408, on the contrary, crystallizes readily. Malate of lime crystallizes with 6 equivalents of water of crystallization, andpresents the formula (Ca0 + H0),C8H408 + 6H0. § 1448. Crystallized malic acid melts at 181.4°, and, if kept for some time- at a temperature of 347°, is converted into two new acids, called maleic andparamaleic, which are isomeric, and present the formulae C4H03,II0. Water separates from them, without disen- gagement of gas. If the retort be rapidly heated to 392°, the maleic acid distils over, with very small quantities of paramaleic acid, for, at this temperature, but a small quantity of the latter acid is formed. Distilled maleic acid solidifies in large crystals in the neck of the retort and the receiver, and is very soluble in water and alcohol, its solution not being clouded by limewater, while water of baryta throws down a white precipitate in crystalline spangles, and acetate of lead produces a similar precipitate. The maleates of potassa and soda crystallize readily. The general formula of the dried maleates is RO,C4HOs, showing maleic acid to be monobasic Maleic acid has been found in several vegetables, particularly in the horsetail, (equisetum fluviatile), whence it has also been called equi- setic acid. If maleic acid be heated to only 392°, and be kept for some time at this temperature, the second acid, or paramaleic, is abundantly formed instead of the first. It is much less fusible than maleic acid, for it melts at only about 390°, and sublimes at a higher tempera- ture ; and it is moreover easily distinguished from it by being very slightly soluble in water, 200 parts of water dissolving about 1 part of it. Paramaleic acid produces with oxide of silver, a salt remark- able for its insolubility, and yields, with potassa, soda, and ammonia, easily crystallizable salts. It may be boiled with nitric acid without undergoing any change. The general formula of the paramaleates is R0,C4II03, and that of crystallized paramaleic acid is C4H03II0. Maleic acid is converted into paramaleic acid when it is kept for a long time at a temperature exceeding 302°, while the maleates themselves, heated to 480° or 570°, are converted into paramaleates. Paramaleic acid is also found in vegetables, and having been obtained from fumitory, (fumaria officinalis,) has hence been called fumaric acid. It has also been found in Iceland moss. CITRIC ACID ClsH8011,3H0-f-2H0. § 1449. Citric acid, which exists in the juice of a large number of acid fruits, particularly in lemons, gooseberries, and currants, is generally extracted from lemons, by allowing their juice to ferment spontaneously for some time, when mucilaginous substances sepa- rate from it; after which the liquid is saturated with finely pow- dered chalk, gradually added, so as not to be in excess, and it is boiled. Citrate of lime, being insoluble, is precipitated, and is de- CITRIC ACID. 597 composed by a slight excess of sulphuric acid; and the sulphate of lime being then separated by filtering, the acid liquid is care- fully evaporated, until a crystalline crust begins to form on its sur- face, when it is left to itself. Citric acid crystallizes in large crystals, the presence of a slight excess of sulphuric acid assisting the crystallization. The acid is very soluble in water, for it dis- solves in J of its weight of cold, and f of its weight of boiling water. After a time, its aqueous solutions become mouldy. The formula of citric acid crystallized at the ordinary tempera- ture is CjgHgOjjSHO, while that of the acid dried at 212° is Cl3H5Otl,3HO, the 3 equivalents of water which remain being basic, and replaceable by equivalent quantities of bases. The formula of citrate of silver is 3AgO,C12H5Otl, and a methylocitric ether is known of the formula 3(C2H30),C13H50n. The alkaline citrates are soluble, while those of the alkaline earths and other metallic oxides are generally insoluble, but dis- solve in an excess of citric acid. About 1 per cent, of crystallized citric acid may be obtained from the juice of common currants, by fermenting it with beer- yeast, when the saccharine matter is converted into alcohol, which is separated by distillation; and the residue, being saturated with chalk, yields citrate of lime. § 1450. Citric acid is decomposed by heat, carbonic acid being first disengaged, with oxide of carbon and acetone; while at a higher temperature, an oleaginous substance is formed which dis- tils. If the operation be arrested at the moment of the appear- ance of the oleaginous substance, the residue contains only a very small quantity of unaltered citric acid, and consists almost entirely of a peculiar acid, called aconitic, because it was first found in a vegetable, the aconitum napellus. The composition of this acid C4H03,H0 is the same as that of maleic acid, and its properties are very analogous, while it appears to differ from it in some of its reactions, and seems therefore to be a second isomeric modification of this acid. Aconitic acid melts at about 284°, and distils at 320° ; but the product which passes over is no longer aconitic acid, oleaginous drops, which crystallize on cooling, being formed. The same pro- duct is necessarily obtained by the direct distillation of citric acid. It dissolves in water, and yields an acid liquid depositing crystals on evaporation, which are purified by being redissolved in alcohol or ether. They are formed by a new acid, which has been called pyroaco- nitic and itaconic acid, the formula of which, in the crystallized state, is C5II2Os,HO, while that of itaconate of silver is AgO,CsH303. If itaconic acid be again distilled, it is soon found to change, for the oily drops which condense no longer crystallize by cooling, being formed by a new acid, called citraconic. The same acid may be obtained by means of the crude product yielded by the imme- 598 VEGETABLE ACIDS. diate distillation of citric acid, for which purpose it suffices to distil it a second time in a retort heated in an oil-bath, and to collect separately the products which distil at a temperature beyond 392°. A very fluid, colourless liquid is thus obtained, boiling at 413°, and of which the density is 1.247. Its formula being C5II203, its com- position is consequently the same as that of anhydrous itaconic acid. Exposed to a moist atmosphere, it slowly absorbs the vapour of water, and is converted into a crystalline compound which melts at about 176°, the formula of which is the same as that of crystallized itaconic acid, and their composition is also the same, while itaconic acid melts only at about 320°, and the crystallized acid formed by the combination of anhydrous citraconic acid with water melts at 178°. The two products are therefore merely isomeric. Hydrated citraconic acid yields, by distillation, anhydrous citraconic acid. § 1451. Tartaric is one of the most important of the organic acids, and exists in a great number of fruits, such as grapes, pine- apples, mulberries, and other vegetables. On a large scale it is always made from grape-juice, in which it exists in the state of bi- tartrate of potassa and neutral tartrate of lime, the two salts being in solution; for the first is eminently soluble, and the second, although insoluble in water, dissolves in an acid liquid. When grape-juice is fermented in order to be made into wine, the bitar- trate of potassa and tartrate of lime are slowly precipitated, being insoluble in the alcoholic water, and they form a crust which adheres to the sides of the barrel. This crust, called tartar, is red or white according to the colour of the wine which produces it, and is mixed with many foreign substances. In order to purify this crude tartar, or argol, it is powdered, and boiled for several hours with enough water to dissolve it, after which the liquid is then allowed to cool; when, in the course of a few days, crystals form, which adhere to the sides of the vessel, while the residue is composed chiefly of foreign substances. The crystals, being separated, are redissolved in boil- ing water, while clay and animal black are added, and the boiling liquid is filtered. The latter yields, on cooling, very pure crystals of bitartrate of potassa,' which is the cream of tartar of commerce. In order to extract tartaric acid from cream of tartar, it is dis- solved in about 10 times its weight of boiling water, and finely powdered chalk is gradually added, until effervescence ceases, when the lime has formed, with one-lialf of the tartaric acid, an insoluble tartrate of lime, while the other half of the tartaric acid remains in the liquid in the state of neutral tartrate of potassa. A solution of chloride of calcium is then added, until no more precipitate is thrown down, when the remainder of the tartaric acid is thus sepa- rated in the state of tartrate of lime. The two portions of tartrate of lime are united and decomposed by sulphuric acid diluted with TARTARIC ACID CsH4010)2HO. TARTARIC ACID. 599 3 or 4 times its weight of water, 52 parts of concentrated sulphuric acid being usually taken for 100 parts of cream of tartar, which is a little more than is absolutely necessary to decompose the tartrate of lime. The sulphate of lime being separated by filtering, the acid liquid, evaporated to the consistence of syrup, is then left to itself, in a slightly warm situation to prevent it from becoming too viscous; when it yields beautiful crystals, which are purified by a second crystallization. The acid is largely used in dyeing. Tartaric acid, dissolved in water, exerts rotation to the right, with a specific energy the greater as the proportion of water is larger and the temperature higher. It then divides the planes of polarization of the various simple rays according to the laws pecu- liar to it, and in which it differs from all known substances. These laws are modified, without losing their peculiarity, when it is dis- solved in alcohol or wood-spirit, but disappear completely when it is brought into the presence of alkaline bases or boracic acid, when the phenomena reassume the appearance common to the generality of substances possessing a rotatory power. Tartaric acid is obtained in large and generally well-defined crystals, of the density 1.75. Boiling water dissolves about twice its weight of it, and cold water a little more than its own weight, while alcohol dissolves it more sparingly. The composition of crys- tallized tartaric acid corresponds to the formula C8H6012, which is commonly written C8H4O10,2HO. The two equivalents of water cannot be driven off by heat without injury to the acid, and in the anhydrous tartrates they are replaced by 2 equivalents of the base. The same base generally forms two salts with tartaric acid; the formula of the first, called neutral tartrate, being 21lO,C8II4O10, while that of the second, or bitartrate, is (Ii0-f-II0),C8H4010. These denominations are very erroneous, since the salts, from their constitution, are both neutral, and because, in both cases, the acid is saturated by 2 equivalents of base; with the difference that in the second case, one of the equivalents of base, water, does not saturate the acid as regards its reaction on vegetable colours. From its composition, tartaric acid may be regarded as formed of 1 equiv. of acetic acid and 2 equiv. of oxalic acid, and we have, in fact, C8H4O10,2HO=C4H3O3,HO+2(a2O3,HO). It is actually decomposed in this manner, when heated with alka- lies in excess, at a temperature of 302°. It is a powerful acid, and dissolves several metals with disengage- ment of hydrogen, particularly zinc and iron. It is decomposed by several easily reducible metallic oxides: thus, at the boiling point, peroxide of lead decomposes it into carbonic acid, water, and formic acid; the liquid, on cooling, depositing very pure crystals of formiate of lead. The soluble neutral tartrates generally become less soluble by 600 VEGETABLE ACIDS. the addition of an excess of acid, while the insoluble neutral tartrates dissolve, on the contrary, in an excess of acid. § 1452. Potassa forms 2 tartrates: the neutral, or rather bi- potassic tartrate 2KO,C8II4010-f 2IIO, which dissolves in its own weight of water, and loses by heat its equivalents of Avater of crys- tallization, and the bitartrate, or rather the monopotassie tartrate (KO + riO),C8II4O10, Avhich is cream of tartar. This salt requires for its solution 18 parts of boiling and more than 200 of cold Avater, and it is nearly insoluble in alcohol at 0.85. Its crystals, which are hard and opaque, are decomposed by heat, and yield a mixture of carbonate of potassa and charcoal, or black flux, (§438.) Bitartrate of potassa forms a compound with boracic acid, called soluble cream of tartar, Avhich is generally prepared by dissolving in boiling water 47 J parts of cream of tartar and 15J parts of crys- tallized boracic acid. The liquor, A\Then evaporated, leaves a non- crystalline Avliite mass, insoluble in alcohol, but which dissolves in 1|- part of cold water, or in | part of boiling Avater. The formula of this substance, dried at 212°, is K0,(C8H4010,B03). At 545° it loses 2 equiv. of Avater, becoming K0(C8H208,B03), and the organic compound Avhich it then contains presents no longer the composition AA'hich we have assigned to anhydrous tartaric acid, although Avhen redissolved in hot water it reproduces the original substance. Soda also forms two tartrates, 2NaO,C8II4Ol0+4HO, which readily parts Avith its water in a dry vacuum, and (NaO-f HO),C8II4O10. Ammonia also yields tAvo tartrates, of which the formulae are 2(NIL,HO),C8H4010+IIO, slightly soluble in water, and (NH3IIO + HO),C8H4O10. Lime forms 2 tartrates: the neutral salt 2CaO,C8H4010-f8IIO, which is nearly insoluble in cold water, and is frequently found in beautiful crystals in crude tartar, and the acid tartrate (CaO-f HO), c8H4o10. By saturating cream of tartar with carbonate of soda and crys- tallizing it, a double tartrate of potassa and soda is obtained (KO + NaO),CgII4010+8HO, called Rochelle salt, which is used in me- dicine, and is generally prepared by dissolving in boiling AA'ater 1 part of crystallized carbonate of soda and 1J part of cream of tar- tar, Avhen the salt is obtained in large prismatic crystals. All the tartrates, Avhen dissolved in Avater, exert rotation to the right, Avhile tartrate of lime, dissolved in chlorohydric acid, turns the plane of polarization to the left. Tartar Emetic (K0 + Sb03),C8II4010+2H0. § 1453. Tartar emetic, one of the most valuable medicines used, is a double tartrate of potassa and oxide of antimony, according to the formula (K0 + Sb03),C8lI4010+2H0. It is prepared by boil- TARTARIC ACID. 601 ing in 5 or 6 parts of water equal parts of oxide of antimony and cream of tartar, and then glass of antimony; the oxychloride or subsulphate may he substituted for the oxide. The hot solution, when filtered, deposits colourless crystals, soluble in 2 parts of boil- ing and 14 of cold water, which, when heated to 212°, part with their 2 equiv. of water of crystallization, while, if heated to 442.4°, they lose 2 more equiv., and the remaining product (K0 + Sb03), C81I208 no longer presents the formula of the tartrates, although if it be redissolved in water it reproduces, by crystallization, the original salt, tartar emetic. Acids decompose solutions of tartar emetic, bitartrate of potassa and a basic suit of oxide of antimony being separated. Alkalies and the alkaline earths also decompose them, but this precipitate is frequently not formed for some time, as is the case in potassa and soda; by using an excess of which bases no precipitate is formed, because the oxide of antimony remains dissolved in the alkaline liquid. Ammonia and limewater immediately effect a precipitate. Sulfhydric acid decomposes the solution of tartar emetic, and an orange-coloured precipitate of sulphide of antimony is formed. Tar- tar emetic is decomposed by heat, and, when calcined in a close ves- sel, yields a residue of antimoniuret of potassium, (§ 1017,) while in Marsh’s apparatus it produces abundantly antimonial deposits, (§1016.) By dissolving in boiling water 9 parts of tartar emetic and 4 parts of tartaric acid, evaporating the solution by a gentle heat, and then leaving it to itself, crystals of tartar emetic first separate, and then, by continuing the evaporation, a crystalline compound, efflorescent and very soluble in water, is deposited, the formula of which is (KO+SbO3),2CgH4O10+7HO, corresponding to that of a neutral tartrate. Tartar emetic can also combine with 3 equiv. of bitartrate of potassa, which compound is obtained by dissolving together 10 parts of tartar emetic and 15 of cream of tartar. Lastly, by pouring into a solution of tartar emetic nitrate of silver or acetate of lead, precipitates are obtained which are species of tartars emetic, in which the oxides of silver or lead replace the potassa. Their formulae are (AgO + SbO3),C8H4O10 and (PbO + SbO3),C8H4O10, etc. etc.; and, like tartar emetic, they lose 2 equiv. of water at a high temperature. § 1454. When tartaric acid is rapidly heated in an oil-bath to the temperature of 338°, it fuses without losing any water, while its composition is remarkably modified; for when redissolved in water and combined with the various bases, it yields salts which differ in their forms and solubility from the ordinary tartrates. The name of metatartaric has been given to this modified tartaric acid. The bimetatartrate of ammonia (NH3HO + HO),C8H4O10 is much more Modifications of Tartaric Acid by Heat. 602 VEGETABLE ACIDS. soluble than the bitartrate, and produces crystals of a totally dif- ferent form, and the former salt does not precipitate a solution of chloride of calcium, while the bitartrate does. Boiling converts metatartrates into bitartrates. By maintaining melted tartaric acid for a long time at a tempera- ture of 338° it undergoes a second isomeric modification, and forms an acid called isotartaric acid, which, while exhibiting the same composition as tartaric acid, appears to differ from it by saturating only 1 equiv. of base. Isotartrate of lime (CaO-f HO),C8H4010 dis- solve's readily in cold water, producing a solution behaving perfectly neutral with litmus paper, which, when boiled, becomes acid and deposits crystals of neutral metatartrate of lime. Isotartrate of ammonia is a deliquescent salt, easily converted by heat into the bimetatartrate. By heating tartaric acid rapidly to 356°, it first melts, swells up, loses 12 per cent, of water, and finally solidifies again, forming a substance of the formula C3II4010, which has become insoluble in water, and may be easily separated by washing from the portions which have not yet undergone the transformation. This substance, which has been called anhydrous tartaric acid because it presents the composition of the acid in the anhydrous tartrates, is equally insoluble in alcohol and ether; while, when in contact with water, it is converted successively into the preceding modifications of tar- taric acid, the transformation being very rapid in contact with boil- ing water and the bases. § 1455. By heating tartaric acid to distillation, it undergoes a decomposition which produces two new pyrogenated acids, which have been called pyroracemic and pyrotartaric acid. Pyroracemic acid is chiefly formed when tartaric acid is rapidly distilled at a temperature of 428°. The product, subjected to a second distillation, yields a very acid liquid, consisting of a mixture of pyroracemic and acetic acids, which, when saturated with carbonate of lead, forms soluble acetate of lead, while the pyroracemate of lead remains in the shape of an insoluble precipitate. The preci- pitate is rapidly washed in cold water, suspended in water, and de- composed by a current of sulf hydric acid gas, and the acid solution, when evaporated, is reduced to a syrupy condition without crystal- lizing. Pyroracemic acid forms a great number of salts; the pyroracemate of potassa is deliquescent, while that of soda crystal- lizes readily, and the salts of lime and baryta are soluble in water. Pyroracemate of silver is obtained by double decomposition, and separates in small crystalline spangles of the formula Ag0,C6II305, showing the formula of anhydrous pyroracemic acid as it exists in dry salts to be C6H3Os. The name given to this acid is very im- proper, for it seems to indicate that pyroracemic acid is a special pyrogenated product of racemic acid, which is presently to be described. RACEMIC ACID. 603 If tartaric acid be rapidly heated to about 570° the products of its decomposition differ from those just indicated, and the receiver contains a brown liquid, which is subjected to a second distillation. The first products are collected separately, and the receiver changed when the substance in the retort becomes syrupy. The liquid which then distils sets into a crystalline mass under the receiver of an air-pump, and the crystals are pressed between several folds of tissue-paper, in order to free them from adherent empyreumatic matter, redissolved in water, and, after having discoloured the solu- tion by boiling it with a small quantity of animal black, it is again evaporated, and yields crystals of pure pyrotartaric acid. A much larger proportion of pyrotartaric acid is prepared by subjecting to the action of heat an intimate mixture of tartaric acid and platinum- sponge, or even of powered pumice-stone, the latter substance as- sisting the decomposition, which then takes place at a lower temper- ature. Pyrotartaric acid melts at about 212°, and distils at 356°, while a portion of it is decomposed. It is very soluble in water and alcohol, and its solutions are not precipitated by baryta or lime- water. Pyrotartaric acid is probably a monobasic acid, of which the formula, in anhydrous salts, is CsH303, PARATARTARIC, RACEMIC, OR UYIC ACID CsH.O^HO+HO. § 1456. The acid to which these various names have been given, has only been obtained once, accidentally, in making tartaric acid on a large scale, and never has been since produced. We shall re- tain the name of racemic acid alone. The composition of racemic acid, when dried, is exactly the same as that of tartaric acid, and the composition of the salts it forms with the different bases is also identical with those of the corresponding tartrates, the two acids exhibiting one of the most remarkable examples of isomerism, hut crystallized racemic acid contains 1 equivalent of water more than tartaric acid, which is easily driven off by heat. Racemic acid dif- fers from tartaric acid in the crystalline form and solubility of its salts, and also in its physical properties, particularly in the absence of all rotatory action on the plane of polarization. But we shall soon see that this neutrality is owing to its being the union, in equal weights, of two acids, one of which is tartaric acid itself, and the other an acid which differs from it only by an opposition of he- mihedrism in crystalline forms, and by an equally identical rotatory power, but in an opposite direction. Nevertheless, for the mo- ment, we shall continue to describe the properties of racemic acid as though it were simple, in order to conform to the language adopted. Racemic is much less soluble in water than tartaric acid, and as it only dissolves in 5.7 parts of cold water, it is easily separated from the latter acid by crystallization. The two acids are also dis- 604 VEGETABLE ACIDS. tinguished by the manner in which they behave with limewater: thus, tartaric acid does not form immediately any precipitate in lime water, and a crystalline deposit is not thrown down until after some time, while racemic acid immediately affords a white precipi- tate. By dissolving separately in weak chlorohydric acid, tartrate and racemate of lime, and carefully saturating the two liquids with ammonia, the racemate of lime is immediately precipitated in an opaque crystalline powder, while the tartrate of lime, on the contrary, is slowly deposited in the form of small transparent crystals. Like tartaric acid, racemic acid is a bibasic acid, and forms two salts with potassa, one (KO-f HO,)C8H4O10 corresponding to cream of tartar, and even less soluble than that tartrate, while the other 2KO,C8H4O10 is very soluble. Ammonia yields two salts: (NH3,HO+HO),C8H4O10, which only dissolves in 100 parts of water; and 2(NII3,HO),C8H4010, which is very soluble, and affords beautiful crystals. The salt of soda (NaO -f HO),C8H4O10-f 2HO dissolves in 12 parts of water, while the salt 2NaO,C8H4010 is much more soluble. Racemic, like tartaric acid, forms crystallizable double salts, and produces, with potassa and soda, a double racemate, having the same composition as Rochelle salt, but differing from it in its crys- talline form and in its solubility. Subjected to the action of heat, raceimc acid appears to afford the same modifications as tartaric acid, and pyrogenated acids identical with those produced by the latter substance. Dextro-racemic and Levo-racemic Acid. § 1457. The solution of the neutral racemates of soda, potassa, or ammonia, and even that of a double racemate of potassa and an- timony, exert no rotatory power, and if they be allowed to evaporate spontaneously, the form and all the other physical properties of the crystals progressively precipitated are identical in each, and they are merely distinguished from each other by their size. Such is not the case with double racemates of soda and ammonia, or of soda and potassa. Their solutions are still deprived of rotatory power, but the crystals deposited by each are of two kinds, distin- guished from each other by hemihedral facets in opposite directions. If they are separated according to this character, and each sort dis- solved by itself, two solutions are obtained possessing equal and inverse rotatory powers, so that if they are mixed together in equal quantity, the resulting rotatory power is null, like that of the ori- ginal solution before the separation. As a single sorting, by hand, is never strictly exact, separation may he effected more perfectly by redissolving each sort of crystal separately, and rejecting the first which are deposited. Those sub- TANNIC ACIDS. 605 sequently obtained are generally formed alone, and of a single sort, thus completing the separation. The acid peculiar to each sort of crystal is extracted from its salts in a similar manner as tartaric acid is extracted from the tar- trates. One of the acids exerts rotation toward the right, like tar- taric acid, and with the same special characters of dispersion; and while its chemical composition is the same, it also behaves exactly like it in the presence of boracic acid and the alkaline bases, pro- ducing crystals of exactly the same form. In short, nothing dis- tinguishes it from ordinary tartaric acid; but it is nevertheless, called dextro-racemic acid, in order to recall its origin, and to not decide too hastily on its density. The other acid, extracted from crystals of the opposite form, is identical with tartaric, acid in its ponderable composition, but ex- actly inverse in its rotatory properties. They are exerted toward the left, as those of tartaric acid toward the right, with the same energy, the same laAVS of dispersion, and evincing similar reactions in the presence of the same substances. It has been called levo- racemic acid, and it crystallizes in the same form as tartaric acid, except that its crystals have hemihedral facets in opposite direc- tions. Levo-racemic and dextro-racemic acid being dissolved together in equal weights, combine immediately, and reproduce racemic acid, the mixed solution becoming neutral in polarized light, and the crystals deposited by it exhibiting no distinctive characters. The individual dissymmetry of the two compounds has disappeared in their union, and when combined they are identical with racemic acid which has not been decomposed. TANNIC ACIDS. § 1458. The name of tannin has been given to several sub- stances, probably of different composition, which possess the property of forming insoluble compounds with albumen, gluten, gelatin, fi- brin, the animal tissues in general, and the epidermis and skin of ani- mals. These compounds will not putrefy, and are unchangeable by water; on which properties is founded the process of tanning of skins, to be described at the close of this work. Tannins exist in almost all vegetables, in the bark and leaves of trees, and the seeds of fruits; the oak, chestnut, elm, and willow containing large quantities of it, while it occurs most abundantly in galls, a sort of excrescence which grows on the leaves of the oak when they have been punctured by a certain insect. In order to extract tannin, the galls are finely powdered and introduced into a displacer, (fig. 683,) the neck of which has been previously stopped with a plug of cotton, the powder being heaped upon it, and ordinary ether of commerce poured 606 VEGETABLE ACIDS. on. The tube is corked, and adjusted in a flask, as represented in the figure; when the ether filters slowly through the galls, while the tannin contained in the latter dissolves in the water given off by the ether, a very small portion being dissolved by the ether itself. The liquid which falls into the flask divides into two layers, the inferior stratum, of the consistence of syrup and colour of amber, being a highly concentrated aqueous solution of tannin, while the upper layer is ether, holding in solu- tion a small quantity of tannin and some other substances extracted from the galls. The ether is again poured upon galls, in order to abstract an additional portion of tannin; and the aqueous solution of tannin is shaken several times with pure ether, and then evaporated under the receiver of an air-pump, when a spongy mass, without any appearance of crys- tallization, generally slightly yellowish, remains, consisting of tannin in its greatest state of purity known. It is a spongy, brilliant, very light, generally yellowish substance, hut sometimes is obtained of a perfectly white colour. It dissolves freely in water, and gives it a strongly astringent taste ; and as it reddens litmus and decomposes the carbonates, it is often called tannic acid. Tannin combines with bases, and precipitates the majority of the metallic solutions, the colours of the precipitates being frequently characteristic; whence tannin and an infusion of galls are often used as tests to distinguish various metals from each other. The composition of tannin dried at 248° corresponds to the formula C18II8Ol2, which should probably be written C18H509,3H0 ; for, on pouring a solu- tion of tannin into a boiling solution of acetate of lead and main- taining ebullition for some time, a yellow precipitate of the formula 3Pb0,Cl8II509 is formed. Tannin yields a deep-blue precipitate with sesquisalts of iron, which compound is very important, being the colouring principle of ordinary writing-ink. In order to ink, 1J part of pow- dered galls are boiled for 3 hours with 15 of Avater, filling up the water as it evaporates; after which the liquid is filtered, and 2 parts of gum and 1 part of protosulphate of iron are added, besides frequently a small quantity of a solution of copper. The mixture is frequently shaken, and exposed in open vessels, in order that the protoxide of iron may absorb oxygen from the air and be converted into sesquioxide, Avhich causes the colour of the liquid, at first broAvn, gradually to deepen and become bluish black. Oxidation being arrested at the proper shade, the ink is bottled. This kind of ink contains a large amount of protoxide of iron, at the moment of using it, and the marks Avhich it leaves on paper, being at first pale, turn black when they have absorbed the oxygen necessary for the peroxidation of the iron. Tannin completely precipitates gelatin and albuminous substances Fig. 683. GALLIC ACID. 607 from their solutions; and animal membranes and skins, dipped into a solution of tannin, ultimately abstract all this substance which is incorporated in the membrane, thus rendering it unchangeable and imputrefiable. Tannin combines also with a large number of the mineral acids, and forms ill-defined compounds, soluble in pure water, but very slightly so in an excess of acid. 1459. Gallic acid is always prepared from tannin or galls, and several processes may be adopted. 1. By causing sulphuric or chlorohydric acid, diluted with 8 or 10 times their weight of water, to act on tannin, and boiling the mixture for about 12 hours, taking care to fill up the water as it evaporates, the tannin is almost wholly converted into gallic acid, the greater portion of which crystallizes during the cooling of the liquid. 2. By exhausting powdered galls with cold water, concentrating the filtered liquid by evaporation, and saturating it exactly with caustic potassa. Chlorohydric acid is added to the liquid when cooled, when a deposit of brown crystals of impure gallic acid is precipi- tated, which is dissolved in boiling water; and the hot solution being left for some time in contact with animal black, which removes the colouring matter, the filtered liquid is allowed to cool, when the gallic acid crystallizes in a state of purity. 3. The process usually employed in the preparation of gallic acid is founded on a peculiar and spontaneous fermentation experienced by galls, and by which its tannin is converted into gallic acid. Moistened and powdered galls are left for several months at a tem- perature of 68° to 86°, in an earthen vessel, when the substance becomes covered with small whitish crystals of gallic acid. Toward the close, the substance is allowed to dry, and is treated with boil- ing alcohol, which dissolves the gallic acid alone, and deposits the greater portion of it on cooling. If an extract of galls be substi- tuted for the galls, the transformation of the tannin takes place in the same way, though more slowly; wdiile if a solution of pure tannin be used, the transformation does not ensue. We are hence naturally led to infer that galls contain substances which induce the conver- sion of tannin into gallic acid, and which behave like ferments, since the transformation is arrested by all substances which destroy the fermentation of the yeast. The presence of air does not appear to be necessary, because gallic fermentation of extract of galls takes place even in an hermetically closed vessel. Gallic acid crystallizes in long silky aciculse, which are some- times perfectly white, but more frequently slightly yellowish ; and it is deposited in larger prismatic crystals from an alcoholic or etherial solution. It dissolves in 100 parts of cold and in 3 only Grallic Acid C7H305,H0. 608 VEGETABLE ACIDS. of boiling water; and it neither precipitates gelatin nor attaches itself to animal membranes; thus furnishing a ready method of separating it from tannin. The formula of crystallized gallic acid is C7H305,H0, and it loses 1 equivalent of water at 212°. The acid forms a large number of salts, the composition of which has not yet been sufficiently studied; and therefore chemists are not agreed upon the formula for anhy- drous gallic acid. By dropping an alcoholic solution of potassa into an alcoholic solution of gallic acid, until perfect saturation is effected, white flakes of a salt of the formula KO,3(C7H3Os) are deposited; while an excess of potassa decomposes the gallic acid. By exactly saturating a solution of gallic acid with ammonia, a salt is obtained by evaporation, of which the composition corresponds to the formula (NH3,HO),2C7H3Oj+HO ; while, if only one-half of the ammonia necessary to saturation be added, there results a com- pound, slightly soluble when cold, and corresponding to the formula (NH3,H0),C7H03+C h8o?. The gallate of lead, which is precipitated by pouring a solution of gallic acid into a boiling solution of acetate of lead in excess, forms white flakes, which change, by heat, into yellowish crystalline granules, corresponding to the formula 2Pb0,C7H03. It therefore frequently occurs in the gallates, that the acid in combination with the base presents the formula C7II03, which would seem to indicate that such is the composition of anhydrous gallic acid, and that crystallized gallic acid should be written C7H03,2H0 + HO; one of the equivalents of water being water of crystalliza- tion, while the other two are basic. The aqueous solution of gallic acid remains unchanged in well- closed vessels, but soon becomes mouldy in the air. Gallic acid dissolves in concentrated hot sulphuric acid, forming a red liquid, Avhich, when poured into cold water, yields a red crystalline preci- pitate of the formula C7II204; which new compound differs from crystallized gallic acid only in the loss of 2 equivalents of water. A solution of gallic acid colours sesquisalts of iron of a deep blue; and when the liquid is concentrated, a precipitate of the same colour is formed. Gallic acid precipitates several metals from their solu- tions, particularly silver and gold, which reduction is more easily effected in the light of the sun. § 1460. By heating gallic acid in a retort over an oil-bath, it first loses 1 equivalent of water, and then melts, and if the temperature be raised to 365°, and kept stationary for some time at this point, carbonic acid is disengaged, while a pyrogenated acid, pyrogallic acid C6H303, sublimes in white crystalline spangles, only a small brown residue being left in the retort. The reaction which pro- duces pyrogallic acid is expressed by the following equation: C7Hs09=C0a+C6H303. ELLAGIC ACID. 609 If, on the contrary, the temperature be suddenly raised to 460° or 480°, water and carbonic acid are both disengaged, and a small quantity of pyrogallic acid still sublimes, while the greater portion of the gallic acid is converted into a brown substance, which re- mains in the retort. In its appearance and chemical properties, this acid closely resembles humic and ulmic acids, (§ 1307,) being insoluble in water, but dissolving in alkaline liquids and forming brown solutions, from which acids precipitate the original substance unchanged. This substance has been called metagallic acid, and its composition corresponds to the formula C6II202; the reaction by which it is derived from gallic acid being expressed by the equa- tion, c7h3o5=c6h2o2+co2+iio. Pyrogallic acid may be prepared by carefully heating powdered galls, or still better, its evaporated extract, in an earthen vessel covered with a pasteboard cone, when crystals of the acid sublime on the sides of the cone. Pyrogallic acid, which is very soluble in water, alcohol, and ether, melts at 257°, sublimes at about 410°, and is decomposed at 482° into water and metagallic acid. It turns salts of the protoxide of iron of a deep blue colour, and those of the sesquioxide of an intense red. Ellagic Acid C14H207,H0. § 1461. Extract of galls, exposed for a long time to the air, con- tains, in addition to gallic acid, another acid, insoluble in water, and to which the name of ellagic has been given. This latter acid is extracted from the deposit formed at the bottom of the vessel, by treating it first with boiling water which dissolves the gallic acid, and then with a solution of potassa which dissolves the gallic acid in the state of ellagate of potassa. The alkaline liquid, when eva- porated, deposits the latter salt in the form of small crystalline spangles, insoluble in fresh water, but dissolving readily in an al- kaline liquid. Acids separate ellagic acid in the form of a slightly yelloAvish powder. Ellagic acid is insoluble in water, alcohol, and ether, and its composition corresponds to the formula C14IIsO10. It loses 2 equi- valents of water at 248°, when its formula becomes C14H308. The formula of ellagic acid in combination with bases being C13II207, that of the dried acid is therefore C1402H7,H0, and that of the hydrated acid C14II207,H0 + 2H0. Ellagic acid also occurs in the animal economy, sometimes form- ing concretions known by the name of bezoars. Meconic Acid C14HOn,3HO. § 1462. Meconie acid is extracted from opium. When chloride 610 VEGETABLE ACIDS. of calcium is poured into an infusion of opium, a precipitate of im- pure meconate of lime is formed, which, after being washed succes- sively with water and alcohol, is treated with 20 parts of hot water, to which 3 parts of chlorohydric acid are added, when the filtered liquid deposits, on cooling, acid meconate of lime. The salt is di- gested with the same quantity of hot acidulated water, and, on cool- ing, the meconic acid separates ; but it is generally necessary to re- peat this operation once or twice before obtaining the acid entirely, free from lime. The impure meconic acid may also be combined with potassa, and the meconate of potassa decomposed by chloro- hydric acid, after being purified by crystallization. Meconic acid dissolves in 4 parts of boiling water, from which it is almost wholly deposited, on cooling, in the form of crystalline, pearly white spangles. It is decomposed by long boiling with water, particularly in the presence of chlorohydric acid; carbonic acid being disengaged, while a new acid, called comenic, is formed. It is also destroyed by contact with alkaline liquids, yielding compli- cated products. The composition of crystallized meconic acid is represented by Ci4IIio020, which formula should be written because the 6 equivalents of water of crystallization are driven off at 212°, while the 3 equivalents of basic water may be replaced, either wholly or partly, by bases. In fact, the three following meconates of potassa have been obtained: 8KO,C14HOn, (2K0+H0),CWH011> (KO+2HO),C14HOu. By pouring nitrate of silver into a solution of meconate of am- monia, a yellow precipitate of the formula 3AgO,C14HOu is formed. Meconic acid presents therefore all the characters of a tribasic acid. It produces a beautiful red colour with sesquisalts of iron. § 1463. By boiling meconic acid for some time with acidulated water, it is converted into comenic acid, while carbonic acid is dis- engaged. The formula of comenic acid, is C12H208,2H0, the 2 equi- valents of water being basic, for the formula of comenate of silver is 2Ag0,C12II208. Meconic, by being converted into comenic acid, loses only carbonic acid, according to the equation CmH0u,SH0=2C0,+ CuHs08,2H0. Comcnic acid is also largely formed in the dry distillation of me- conic apid, but it is then mixed with another acid, pyromeconic, into which comenic acid itself is transformed when subjected to another distillation. In order to obtain pure pyromeconic acid, it must be distilled several times; and the formula of the crystallized acid is C10H3Os,HO, while that of pyromeconate of lead is PbO,C10II3O5. The following equation shows how this acid is derived from comenic acid: C12H2O8,2HO=2CO3,C10H3Oi,HO. QUINIC ACID. 611 Comenic and pyrocomenic acids turn sesquisalts of iron of a red colour. § 1464. In celandine, (chelidonium majus,) a plant of the family of the papaveraceae, there is formed a peculiar acid, called chelidonic, which is there combined with lime ; besides malic and fumaric acids. The juice of the plant is expressed and boiled to coagulate the albu- minous substances, when, after having added a small quantity of nitric acid, acetate of lead is poured in until a precipitate no longer forms. The chelidonate of lead is alone precipitated, the malic and fumaric acids remaining in solution on account of the excess of nitric acid. The chelidonate of lead, which is mixed with chelido- nate of lime, is decomposed by sulfhydric acid, and the acid liquor is saturated with lime; after which the chelidonate of lime is crys- tallized several times. The salt is subsequently decomposed by carbonate of ammonia, and the chelidonate of ammonia resulting, by chlorohydric acid; when the chelidonic acid separates in long crystalline aciculae during the cooling of the liquid. The formula of crystallized chelidonic acid is C14H3010 + 51IO, and it loses 3 equivalents of water at 212°. From the composition of its salts it should be regarded as a bibasic acid CHELIDONIC ACID C^O^HO. QUINIC ACID C„HuOtMHO. § 1465. This acid is found in cinchona bark, in the state of qui- nate of lime. The hark is boiled with water acidulated with chlo- rohydric acid, which is then saturated with lime, in excess; when the filtered liquid contains quinate of lime which may be crystal- lized by proper evaporation. The salt is purified by animal black and several successive crystallizations ; and in order to separate the quinic acid from it, 6f- parts of the quinate of lime are heated with 1 of sulphuric acid diluted with 10 of water, when the lime sepa- rates in the state of sulphate of lime; after which alcohol is added to effect its complete precipitation, and the filtered liquid is evapo- rated to the consistence of syrup, when the quinic acid crystallizes in large prisms. The formula of the crystallized acid is C^B^O^IIO; and that of quinate of silver is Ag0,C14Hn0n. Quinic acid, subjected to heat, yields very complex products : they are benzin, benzoic phenic, and salicylous acids, all of which shall subsequently be described; besides a peculiar crystallizable substance of the formula C24Hia08, very soluble in water and alco- hol, and which has been called hydroquinone. Subjected to the action of sulphuric acid and peroxide of manganese, quinic acid yields a volatile product, qumone, of which the formula is C24H808. In order to obtain a small quantity of this product, 100 gm of qui- nic acid are heated gently in a small retort with 400 gm. of per- oxide of manganese and 100 gm. of sulphuric acid previously diluted 612 ORGANIC ALKALIES. Avith one-half of its weight of Avater. A great bubbling ensues in the retort, and a mixture of formic acid and quinone is deposited in the receiver. The latter substance crystallizes in beautiful golden- yelloAV spangles. Quinon is easily sublimed by the same method as camphor, and it has a strong and irritating odour, resembling that of camphor. It dissolves slightly in cold, but more freely in boiling Avater, Avhile its true solvents are alcohol and ether. Chlorine acts powerfully upon it, and gradually abstracts all its hydrogen, Avhich is replaced by an equivalent quantitity of chlorine ; and tAvo crystallized chlori- nated products have thus been separated: sechlorinated quinone C24II2C1608 and 'perchlorinated quinone C^ClgOg. Quinone also gives rise to a great number of interesting products, but their study Avould lead us too far. § 1466. Vegetables contain several other organic acids, named generally after the plant from which they are extracted, but they are as yet only imperfectly known; and several of them are proba- bly identical Avith those already described, for which reason Ave shall not stop to mention them. ORGANIC ALKALIES. § 1467. At the present day a large number of organic substances are known which combine with acids after the manner of mineral bases, forming compounds which exhibit all the characters of salts, and to which the name of organic alkalies, or alkaloids, has been given. Some are found already formed in vegetables, while others are produced by the calcination or other appropriate treat- ment of organic matter. The majority of native alkaloids are ex- tremely poisonous, and rank among the most powerful medicines, which character lends them peculiar importance. All the organic alkalies contain nitrogen and hydrogen, and all, Avith the exception of ammonia, contain carbon; while the majority, in addition, contain oxygen; and lastly, sulphur has been found in some. They all present the remarkable peculiarity which has been described (§ 513) in treating of ammonia; that of combining directly and Avithout decomposition, Avith the hydracids, by forming chlorohy- drates, iodohydrates, etc. etc., and of fixing, in all salts Avhich they form with the oxacids, 1 equiv. of Avater, necessary to the constitu- tion of the salt, and Avhich cannot be driven off without destroying its nature. The alkaloids, like ammonia, are therefore bases only when they have combined with the elements of 1 equiv. of water. QUININ. 613 We shall first describe the alkaloids which exist ready formed in vegetables, and then some of the numerous artificial alkaloids ob- tained in modern days, confining ourselves chiefly to general remarks on the method of their preparation and their properties. The native alkaloids may be divided into two classes: alkaloids volatile without decomposition, and non-volatile alkaloids, each class requiring a special method of extraction. In order to extract those of the first class, the liquid containing them is distilled with potassa or lime, which bases unite with the acid until then com- bined with the alkaloid, while the latter passes over in distillation. The majority of non-volatile alkaloids are very slightly soluble in water, and are prepared by boiling the vegetables containing them with water acidulated with chlorohydric acid, when the alkaloid is dissolved in the state of chlorohydrate, after which the liquid is then saturated with an alkali or with lime, in order to precipi- tate the alkaloid. The deposit is then treated with boiling alco- hol to dissolve the alkaloid, which crystallizes on cooling or by evaporation. NON-VOLATILE NATIVE ALKALOIDS. ALKALOIDS OF THE CINCHONAS. § 1468. The bark of the cinchonas contains two principal alka- loids, to which they owe their medicinal virtue: these are quinia and cinchonin. Three species of cinchona are known in commerce, the yellow, red, and gray; and while quinin predominates in yellow bark, cinchonin is principally found in the gray ; and red bark con- tains nearly equal proportions of quinin and cinchonin. Two other less important alkaloids are also found in the barks, chinoidin and cinchovatin, which are present in very small quantities. Quinin C38H24N204. § 1469. Yellow cinchona is preferred for the manufacture of quinin, to which elfect the bark is bruised and boiled with water containing 15 or 20 per cent, of sulphuric or chlorohydric acid, when the liquid is filtered through a cloth, and milk of lime added until an alkaline reaction is produced with litmus. The deposit formed, which contains the quinin, is squeezed in a press, and the cake resulting treated with boiling alcohol, three-fourths of which being separated by distillation, sulphuric acid is added to the re- mainder until a slight persistent acid reaction is obtained. The liquid is discoloured by animal black, and crystallize when the sulphate of quinin crystallizes first, while the sulphate of cinchonin remains in the mother liquid. By decomposing the sulphate of quinin by ammonia, quinin is obtained in the form of a white pow- der, which, by slow evaporation from an alcoholic solution, is depo- sited in small prismatic crystals. 614 ORGANIC ALKALIES. Quinin has a very bitter taste, requires for its solution 400 parts of cold and 250 of boiling water, and turns litmus blue. Boiling alcohol dissolves one-half of its weight of it, while ether also dis- solves a considerable quantity, and thus furnishes a method of sepa- rating it from cinchonin, which is insoluble in ether. The formula of quinin, crystallized from an aqueous solution, is C38II24N204 + 6IIO, and it loses the 6 equivalents of water at 248°. Quinin, dissolved in alcohol or acidulated water, exerts a rotatory power toward the left, at least at the temperature of 71.6°, the power de- creasing as the temperature rises. Quinin forms crystallizable salts with nearly all the acids, its most important compound being the neutral sulphate, used in medicine as an anti-intermittent. Two sulphates of quinin are known. 1. The neutral sulphate, crystallizing in fine silky aciculse, and very slightly soluble in cold water, of which it requires 750 parts for solution, while it dissolves in 30 parts of boiling water. Its formulae is (C38II24Na04,H0),S03-f-7II0, and it loses its water of crystallization by heat. It exerts rotation toward the left, like the alkali which acts as its base. 2. The acid sulphate, soluble in 10 or 12 parts of cold water, the formula of which is (C38H24N204,H0,)2S03-f 8HO, the water of crystallization being driven off by heat. Cinchonin C38H24N302. § 1470. Cinchonin is prepared either from the mother liquid of sulphate of quinin, or by treating gray cinchona in the manner by which quinin is extracted from yellow cinchona. Cinchonin crys- tallizes readily, and without any water of crystallization, its formula being C38H24NaNa, which differs from that of anhydrous quinin only by containing 2 equiv. of oxygen less. Cinchonin is still less solu- ble in water and alcohol than quinin, while it is insoluble in ether. Salts of cinchonin crystallize readily, and are generally more solu- ble in water than the corresponding salts of quinin. When chlorine is made to act upon a concentrated and hot solu- tion of chlorohydrate of cinchonin, a slightly soluble salt is depo- sited, which, when redissolved in water, and treated with ammonia, forms a precipitate of bichlorinated cinchonin C3sll22Cl2Na02. This substance crystallizes in needles, turns tincture of litmus blue, and forms with acids crystallizable salts, which closely resemble the cor- responding salts produced by ordinary cinchonin, and even appear to be isomorphous with them. In the same way bromine converts cin- chonin into bichlorinated cinchonin C38H22Br2N2Oa. The elementary composition of the bichlorohydrate of bibrominated cinchonin C38H23 BraNaOa,2IICl is the same as that of the bibromohydrate of bichlori- nated cinchonin C38IIa2ClaN3Oa,2HBr, while the turn substances dif- fer essentially from each other, since the former yields with potassa bibrominated cinchonin, and the latter bichlorinated cinchonin. MORPHIN. 615 Cinchonin, dissolved in alcohol or acidulated water, exerts a ro- tatory power toward the right, while that of quinin is toward the left, and the salts of cinchonin also turns to the right, like the al- kali which forms their base, the chlorinated derivatives of the alkali exerting it in the same direction. Cliinoidin. § 1471. The mother liquid of sulphate of quinin, after having deposited its sulphate of cinchonin, may yield a small quantity of sulphate of cliinoidin. Chino'idin is as yet but little known, and from the analyses which have been made of it, it would appear to have the same composition as quinin. Cinchovatin C46H37N303. § 1472. Cinchovatin is found chiefly in the cinchona from Jain, (cinchona ovata,) from which it is extracted by the same process as quinin. It is a substance insoluble in water, and soluble in alcohol, from which it is deposited in crystals of the formula C^II^NaOg.* §1473. On making incisions into the head of the white poppy, a liquid issues from it, which hardens in the air into a brown horn- like mass, constituting opium, the chief part of which is imported from the East, and principally from Smyrna. The poisonous pro- perties of opium are owing to the existence of several alkaloids, the principal of which are morphin, narcotin, and codein; while several others, less important, and only existing in small quantity, are also extracted: thebaina, narcein, pseudomorphin, porphyroxin, and a non-nitrogenous crystalline substance, which does not act the part of a base, and has been called meconin. First quality opium contains about 10 per cent, of morphin and 5 per cent, of narcotin. ALKALOIDS OF OPIUM. Morphin C^B^NOg. § 1474. In order to obtain morphin, the opium, cut into thin slices, is macerated for some time with water, and the substance, when softened, is crushed with an additional quantity of water, squeezed in bags under a press, and the cake subjected to similar treatment. The liquid yielded by this process, being evaporated to the consist- ence of an extract, is again treated with a small quantity of water, which dissolves the salts of morphin, and leaves the greater portion of the narcotin mixed with a brown substance. By testing a small quantity of the liquid, the quantity of ammonia necessary to wholly precipitate this substance is ascertained, while only of this quan- tity is poured into the whole liquid, when the impure morphin is precipitated, carrying with it nearly all the colouring matter. By * Aricin is not mentioned by Regnault, and in fact much uncertainty exists as to the alkaloids in cinchona bark, except quinine and cinchona.—J. C. B. 616 ORGANIC ALKALIES. then adding the balance of the ammonia, nearly pure morphin is precipitated, and is treated with alcohol marking 20° of Baumd, which does not sensibly dissolve the morphin, while it removes almost entirely the resinous matter which adulterates it. The residue is then treated with boiling alcohol at 35° Baumd, which dissolves the morphin and deposits the greater part of it on cooling. Three-fourths of the alcohol are deposited by distillation and the residue yields the balance of the morphin. In order to obtain the base perfectly pure, it is best to redissolve it in weak chloroliydric acid, crystallize the clilorohydrate, and again decompose this salt by ammonia. Morphin readily forms crystals of the formula C34II18N06-f 2IIO, which lose the 2 equiv. of water by an elevation of temperature, and may be heated to 570° without injury. Cold water dissolves about jobo of morphin, and hot water nearly double of that quantity; the solution showing an alkaline reaction with litmus. Weak alco- hol at 20° B. dissolves but very little morphin, while boiling alcohol at 35° B. dissolves of its weight, the greater portion of the mor- phin crystallizing on cooling. It is scarcely soluble in ether, but a concentrated solution of caustic potassa dissolves it without change, by which process the base may be separated from narcotin, the latter being insoluble in alkaline lixivise. Morphin dissolved in acidulated water exerts a rotatory power towTard the left, like its salts. Morphin forms crystallizable salts with acids, soluble in water and alcohol, but insoluble in ether. Chlorohydrate of morphin, which is most important on account of its use in medicine, crystallizes in silky tufts, and dissolves in 1 part of boiling or in 20 parts of cold water. Its formula is C34H18N06,IIC1+6II0, while that of crystal- lized sulphate of morphin is (C34H18N06,H0),S03+6H0. Narcotin C46II25N014. §1475. Narcotin is extracted from tlie residues left after the extraction of morphin from opium by treating them with ether, which dissolves a mixture of narcotin and porphyroxin, the narcotin greatly predominating. Fresh opium may also be treated directly with ether, when the salts of morphin remain in the residue and the ether contains, with the narcotin and porphyroxin, a certain quantity of meconin. The ether being distilled in a water-bath and the residue treated with water, which dissolves the meconin, the narcotin and porphyroxin are finally dissolved in dilute chlorohydric acid. The solution, when evaporated, deposits chlorohydrate of narcotin, while the chlorohydrate of porphyroxin remains in the mother liquid. The chlorohydrate of narcotin, decomposed by am- monia, yields isolated narcotin, which is purified by crystallizing it in alcohol. STRYCHNIN. 617 Narcotin crystallizes in small rhomboidal prisms, melting at 338°, decomposing at about 390°, insoluble in cold water, and only dis- solving in 500 parts of boiling water. Alcohol, when hot, dissolves about of its weight, and ether Narcotin is a much more feeble base than the alkaloids we have hitherto described, since its solutions do not turn to blue the reddened tincture of litmus, although it forms crystallizable salts with acids. The formula of narcotin is N014, while that of the chlorohydrate is Narcotin, dissolved in alcohol or acidulated water, exerts a rotatory power to the right, opposite to that of morphin; the salts of narcotin pos- sessing the same power as the alkali. Codein C34HigN05. §1476. Codein remains in the liquid from which morphin has been precipitated by ammonia, and is extracted by concentrating them through evaporation, adding caustic potassa, and then continu- ing the evaporation to dryness. The residue is treated with ether, which dissolves the codein, and yields, by spontaneous evaporation, large crystals of this substance, which are remarkable for the sharp- ness of their configuration. Codein, which is much more soluble than the other alkaloids of opium, since it dissolves in 80 parts of cold and 20 of boiling water, turns the reddened tincture of litmus blue, and is also highly soluble in alcohol and ether. The formula of code'in, crystallized in water, is C34HigN05-t-2H0, and heat readily drives off' its 2 equiv. of water, while it crystallizes in the anhydrous state from its solutions in ether. Codein has been used for some time in medicine. ALKALOIDS OF STRYCHNOS. Strychnin C42FI22N204 and Brucin C46H2GN208. § 1477. The majority of the genus of strychnos, particularly the bean of St. Ignatius, (strychnos Ignatia,) nux vomica, (strychnos nux vomica,) viper-wood, (strychnos colubrma,) and the upas tieutd, (.strychnos tieute,) contain two alkaloids in various proportions, strychnin and brucin, remarkable for the very poisonous effect they exert on the animal economy. The two bases are generally extracted from nux vomica by boil- ing the powdered nut with water containing its weight of sulphuric acid, expressing the liquid, and precipitating the two bases by hy- drated lime. The deposit is treated with boiling alcohol, which dissolves the strychnin and brucin; and, on cooling, the greater portion of the strychnin crystallizes. The liquid, concentrated by evaporation, yields less pure strychnin, and the brucin crystallizes last. It is necessary to purify these substances by several succes- sive crystallizations. 618 ORGANIC ALKALIES. Strychnin crystallizes readily in octohedrons with rectangular bases, insoluble in water, slightly soluble in alcohol, and presenting the formula C42II23Na04. It forms easily crystallizable salts, and the formula of crystallized chlorohydrate of strychnin is HC1+3HO, while that of the crystallized sulphate is II0),S03. Strychnin, dissolved in acidulated water, exerts a rota- tory power toward the left, like its salts.* Brucin crystallizes in right prisms with a rhombic base, and its formula is C46H26NzOg.+ 8HO; the 8 equiv. of water being given off’ by heat. Water dissolves a small quantity of it, and it is much more soluble in alcohol than strychnin. Concentrated nitric acid produces an intense red colour with brucin, which property dis- tinguishes it from a majority of the other alkaloids. Brucin dis- solved in alcohol, or in water to which no acid has been added, deviates to the left like strychnin, its salts presenting the same behaviour. ALKALOID OF COFFEE AND TEA. § 1478. Coffee and tea contain the same alkaloid, which is called caffein or them, according as it has been extracted from either of these substances, because it was at first supposed that they were not identical. In order to extract caffein from coffee, the bruised coffee-grains are treated with water, and subacetate of lead is poured into the liquid, after which, the deposit being separated, sulfliydric acid is passed through in order to precipitate the excess of lead. The solution being then evaporated, the caffein crystallizes, and is purified by successive crystallizations. Them is extracted in pre- cisely the same manner. Caffein crystallizes in silky aciculas, taking the formula C8H5N202 -)-2HO, while it loses its 2 equivalents of water at 212°, melts at about 356°, and sublimes above 570°. It is soluble in water, alcohol, and ether; and its basic affinities are very feeble, for although it dis- solves in acids, it generally leaves them when the solution is eva- porated. Caffein or Them C8H5N303. VOLATILE NATIVE ALKALOIDS. §1479. Two native alkaloids are now known, which volatilize without change: nicotin, or the alkali of tobacco, and conicin, the alkali of cicuta. Nicotin C20II14N2. § 1480. Certain varieties of tobacco contain 7 or 8 per cent, of nicotin, which is extracted by digesting the tobacco-leaves with * The elementary composition of this most violent poison is, singular enough, identical with that of rye bread, a most wholesome article of food. The natives of Borneo use the juice of the different kinds of strychnos for poisoning their ar- row-heads, the wound of which is generally fatal.— W. L. F. NICOTIN. 619 water, evaporating the infusion to the consistence of an extract, and then treating with alcohol, which is, in its turn, concen- trated, after being decanted. The new extract is treated with potassa, and then shaken with ether, which dissolves the nicotin as well as some foreign substances. Finely powdered oxalic acid is added to the etherial solution, which is to be frequently shaken, when oxalate of nicotin is formed, and precipitated in drops, which are washed several times with water. The oxalate of nicotin being decomposed by potassa, free nicotin is separated by ether. The etherial solution is distilled in a retort over a water-bath, when the greater portion of the ether distils rapidly, while the last particles do not pass over at 212° ; and there exists also a small quantity of ammonia and water, which separate only at a higher temperature. The retort must be kept, for a whole day, at a temperature of 284°, and a feeble current of hydrogen must be passed through it, after which the receiver is changed, and the temperature raised to 356°, in order to distil the nicotin in a current of hydrogen. Nicotin is an oleaginous, limpid, and colourless liquid, smelling slightly of tobacco, and which boils at 473°, but begins to decom- pose at this temperature; so that it is necessary to distil it under feeble pressure, or in a current of hydrogen gas, so as not to be obliged to raise the temperature to a degree at which the elastic force of the vapour is equal to the pressure of the atmosphere. The density of liquid nicotin is 1.048, while the density of its vapour has been found to be 5.607. Nicotin is very soluble in water, which then reacts powerfully alkaline; and caustic potassa precipitates it from its solutions in the form of oleaginous drops, while ether takes it from water and dissolves it in all proportions, alcohol also dis- solving a large quantity of it. It is one of the most powerful poi- sons. Nicotin soon changes in the air, by absorbing oxygen, and is converted into a brown substance of a resinous appearance. The salts of nicotin are in general very soluble, and crystallize with difficulty. The formulae of the sulphate and nitrate of nicotin are (C20H14N2,HO),SO3 and (C20H14N2,HO),NOS, according to which the formula of free nicotin is corresponding to 4 volumes of vapour, like that of ammonia. Nicotin exerts an extremely ener- getic rotatory power toward the left, while its chlorohydrate turns the plane of polarization with the same power toward the right. The various species of tobacco contain very different proportions of nicotin, the following quantities having been found in 100 parts of dry tobacco: Foreign Tobacco. Havana 2.0 Maryland 2.3 Virginia 6.9 French Tobacco. Alsace 3.2 Pas-de-Calais 4.9 Nord 6.6 Lot 8.0 The tobacco which contains most nicotin is the best for the manu- 620 ORGANIC ALKALIES. facture of snuff, since the property possessed by tobacco of stimu- lating the mucous membrane of the nose, is owdng to the pre- sence of nicotin and ammoniacal salts. Conicin C1GH15N § 1481. Conicin is extracted from the seeds of the conium, but it is also found in the leaves and stalk of this plant, previous to its flowering. The bruised seeds being distilled with a solution of potassa, conicin passes over with water and ammonia. The liquid is saturated with sulphuric acid, and evaporated to the consistence of syrup; when, by treating the extract with a mixture of alcohol and ether, the sulphate of conicin is dissolved, while the ammonia- cal sulphate is left. The solution of the sulphate of conicin is then evaporated, and afterward decomposed by caustic potassa; when the conicin arising from this decomposition is decanted, and then left for some time on chloride of calcium, which abstracts its water, after which it is purified by distillation. Conicin is a colourless liquid, having a sharp smell, which imme- diately produces sickness, and its density is 0.89, while it boils at 338°. It is one of the most powerful poisons. Conicin is slightly soluble in water, but dissolves in all proportions in alcohol and ether, its solutions showing a strong alkaline reaction. It rapidly absorbs the oxygen of the air, and then assumes various shades of colour. The salts of conicin are in general deliquescent and not crystalline; and the composition of the alkaloid corresponds to the formula C16H15N. ARTIFICIAL ALKALOIDS. § 1482. Chemists have long since succeeded in preparing a great number of alkaloids, which have not yet been found in vegetables. Almost all these alkaloids are volatile without decomposition, and contain no oxygen; and wdiile some resemble, in their properties, nicotin and conicin, others are so closely analogous to ammonia, that, in a purely philosophical classification of substances, it "would be impossible to separate them from that base. Quinole'in C18H7N. § 1483. Several native organic bases, particularly quinin, cin- chonin, and strychnin, yield, by distillation with potassa, a volatile alkaloid called quinole'in. It is obtained in greatest quantity from cinchonin, by heating in a tubulated retort some fragments of caustic potassa with a small quantity of water, so as to form a pasty solu- tion, and gradually adding powdered cinchonin. It is heated with an alcohol-lamp until the substance appears to be dried, when hydrogen is disengaged, while water passes over, as also an oily substance, which is rectified a second time over potassa. Quinole'in is a colourless oil, of a disagreeable odour, distilling at about 446°, ANILIN. 621 insoluble in cold, and scarcely soluble in boiling water, while alcohol and ether dissolve it freely. It forms crystallizable salts with chlo- rohydric, sulphuric, and nitric acids, and it contains no oxygen, its formula being C18H7N. Quinolein is also found among the products of distillation of coal-tar, and was formerly called leucole. ALKALOIDS DERIVED FROM VARIOUS CARBURETTED HYDROGENS. Anilin C12II7N. § 1484. The majority of the carburetted hydrogens yield, when they are boiled with monohydrated nitric acid, or a mixture of this acid and concentrated sulphuric acid, nitrogenous substances, which result from the substitution of 1 equivalent or 2 equivalents of the compound N04 in the place of 1 or 2 equivalents of hydrogen. Thus, we shall soon see that benzin C12H8, treated with mono- hydrated nitric acid, produces two substances, nitrobenzin C12II5 (N04) and binitrobenzin C13H4(N04)2. These nitrogenous com- pounds yield alkaloids when they are subjected to the action of reducing substances, as e. g. the sulfhydrate of ammonia, or to the action of nascent hydrogen obtained by causing dilute sulphuric acid to act on zinc in contact with the nitrogenous substance. Thus, by the action of the bisulf hydrate of ammonia on nitrobenzin, we obtain an alkaloid, anilin C12H7N, from the following reaction: C12Hs(N04)+6(NH3,2HS)=C12H7N+6S+4H0+6(NH3,HS). By the action of nascent hydrogen, we have C12Hs(N04)+6H=C12H7N+4H0. When binitrobenzin is subjected to the same treatment, there results a second alkaloid, nitranilin C12H0(NO4)N, according to the following reactions: C12H4(N 04)a+6 (NH3,2 H S)=C12H6(N 04)N+6 S +4H 0 +6(NH3, HS),6C12H4(N 04)2+6H=C12H6(N 04)N+4H 0. We shall describe only anilin and nitranilin; the properties of the numerous alkaloids obtained by applying the same processes to other carburetted hydrogens, or substances derived from them, being very similar. Anilin is a colourless liquid, of an agreeable vinous smell, boiling at 359.6°, and dissolving slightly in water, but in all proportions in alcohol and ether. Anilin possesses no rotatory power. Chlo- rine and bromine convert it into chlorinated or brominated sub- stances, modified merely by substitution, and which often retain the basic properties and capacity of saturation of the original anilin. Monochlorinated anilin C12H6C1N, the monohrominated C12H6BrN, and nitranilin C12H6(N04)N, are baseS which form salts as well defined as anilin itself; while the terchlorinated C121I4C13N and terbrominated anilins C12H4Br3N possess no basic properties. 622 ORGANIC ALKALIES. Iodine may also be substituted for hydrogen in anilin, and a moniodinated anilin C12H6IN has been obtained which combines with acids. Cyanogen gives rise to no phenomena of substitution, but combines directly with anilin with the evolution of heat, and produces a new crystallizable base, cyanilin C13H7NCy=C14II7N2, which forms, with the majority of acids, well-defined and crystalli- zable salts. ALKALOIDS DERIVED FROM CYANIC AND CYANURIC ETHERS, PRESENTING A CLOSE ANALOGY WITH AMMONIA. § 1485. We shall subsequently describe, together with some other products of cyanogen, two isomeric compounds of this substance with oxygen, cyanic acid CyO=CaNO, and cyanuric acid Cy303 = c8n3o3, which are readily converted into each other, as will be shown in its place. These acids combine with bases, forming cya- nates and cyanurates. Ethylammonia C4HS(NH2). § 1486. By distilling cyanate of potassa KO,CyO with a solution of sulphovinate of potassa K0,(C4II50,2S03) there is obtained a mixture of cyanic ether C4II50,CyO and cyanuric ether 3C4H50. Cy303, which are easily separated by distillation, the first being very volatile, while the second boils only at a very high tempera- ture. Cyanic ether dissolves in ammonia with disengagement of heat, and the liquid, when evaporated, deposits beautiful prismatic crystals, which are fusible, very soluble in water and alcohol, and of the formula C0IIgN2O3: they result therefrom from the simple combination of 1 equivalent of cyanic ether C4H5O,CyO=C0HsNO3 with 1 equivalent of ammonia NH3. Cyanic and cyanuric ethers, treated with caustic potassa, yield carbonate of potassa and an al- kaloid C4H7N : C4H50, CaN 0+2(KO, HO, =2(K0)C08)+C4H7N. We shall call this alkaloid etJiylammonia, and its formula C4TLN may be written C4II4NH3, considering it as resulting from the com bination of 1 equivalent of ammonia with 1 equivalent of bicarbu- retted hydrogen C4II4, while it may also be written and the alkaloid regarded as belonging to the series of simple ethers. One of the equivalents of hydrogen and carburetted hydrogen C4Hg, the generator of the series, having been replaced by 1 equi- valent of amide (NHg). In order to obtain ethylammonia, cyanic or cyanuric ether is boiled in a distilling apparatus with an excess of potassa, the va- pours being collected in a well-cooled receiver containing a small quantity of water, which takes the ethylammonia in solution, and thus becomes strongly alkaline, with an intense ammoniacal odour, although it does contain a trace of free ammonia. This liquid is saturated with chlorohydric acid and evaporated, when crystals are METIIYLAMMONIA. 623 obtained which dissolve completely in absolute alcohol, and are again deposited, by evaporation, in crystalline lamellae. This compound is chlorohydrate of ethylammonia C4II7N,HC1, and is distinguished from chlorohydrate of ammonia by its solubility in absolute alcohol. The chlorohydrate of ethylammonia, perfectly dried, is mixed with double its weight of quicklime, and introduced into a long tube closed at one end, so as to fill one-half of it; and the other half being filled with fragments of caustic potassa, a disengagement- tube, which enters a flask surrounded by a refrigerating mixture, is adapted to it. Gentle heat being applied, the ethylammonia set free distils, and is condensed in the receiver. It is important to remark that this process exactly resembles that used for obtaining ammonia. Ethylammonia is a colourless, very volatile liquid, boiling at 64.4°, exhaling a very penetrating ammoniacal odour, turning blue the reddened tincture of litmus, and exhibiting a causticity resem- bling that of potassa. When a glass rod moistened with chlorohy- dric acid is brought near it, extremely thick white fumes are pro- duced ; and each drop of acid poured into it produces a hissing at the moment of its mixing with the base. Ethylammonia ignites when brought near to a substance in combustion, and burns with a bluish flame. It mixes with water in all proportions, becoming very hot, and giving rise to a solution of which the basic properties absolutely resemble those of ammonia. A solution of ethylam- monia precipitates, in fact, the salts of magnesia, alumina, manga- nese, iron, bismuth, chrome, uranium, tin, lead, and mercury. Salts of zinc throw down a white precipitate, which redissolves in a large excess of the reagent. Salts of copper produce a bluish white pre- cipitate, readily soluble in an excess of the reagent, furnishing a deep-blue liquid, analogous to that produced by an excess of am- monia, (§1046.) Ethylammonia combines with all the acids, forming crystallizable salts precisely resembling those of ammonia, and it also furnishes compounds analogous to the amides, (§ 514.) In fact, by mixing a solution of ethylammonia with oxalic ether, the mixture becomes cloudy, and alcohol is formed, while acicular crystals of a compound C6116N03=C4H6N,C303 corresponding to oxamide NH3,C303 sepa- rate. Methylammonia C3IISN or C3H3(NH3). § 1487. By boiling methyloeyanic or methylocyanuric ether with a solution of potassa, and collecting the product in a well-cooled receiver containing water, a strongly alkaline solution is obtained, which exhales a very penetrating ammoniacal odour. It is satu- rated with clilorohydric acid, evaporated to dryness, and again treated with boiling alcohol, which deposits, on cooling, pearl-like 624 ORGANIC ALKALIES. crystalline lamellae of chlorohydrate of methylammonia CSI15N,HC1. This salt heated with quicklime, as in the preparation of ammonia and ethylammonia, yields methylammonia, which may be obtained in the form of a colourless liquid by cooling the receiver with a proper refrigerating mixture. Methylammonia is gaseous at the ordinary temperature, and may be collected in bell-glasses over mercury, when it resembles ammoniacal gas so closely as to require peculiar attention to distinguish it from it. Methylammonia liquefies at about 32°, and its odour is strongly ammoniacal, while its density is 1.08, its chemical equivalent C3I1N. corresponding, like that of ammonia, to 4 volumes of gas. Metliyl- ammoniacal gas is the most soluble of all gases known, since, at 53.6°, 1 volume of water dissolves 1040 volumes of it, while at 77° water only takes up 906. Like ammoniacal gas, it is instantane- ously absorbed by charcoal, but it is distinguished from the latter gas by igniting by contact Avith a lighted candle and burning with a yellowish flame. It produces, with metallic solutions, reactions precisely similar to those of ammonia or ethylammonia. Amylammonia C10H13N or C10Hu(NHa). § 1488. The oil of potato-spirit C10H13O3 exhibits, as shall soon he shown, a perfect analogy with vinic and methylic alcohols, in the products which it forms with chemical agents, for which reason it has been called amylic alcohol. If amylocyanic or amylocyanuric ether be distilled with a solution of potassa, carbonate of potassa is obtained, besides a new base, amylammonia C10H13N, which formula may be written C10H10NH3, because carburetted hydrogen C10H10 is, in the amylic series, the analogue of bicarburetted hydrogen in the vinic series. It may be also written C10H11(NI1S), if it be consi- dered as resulting from the replacing of 1 equivalent of hydrogen, in the amylic molecule C10II12, by 1 equivalent of amide (NHa). Amyl is found in solution in the water which has passed over in dis- tillation ; by saturating which with chlorohydric acid, white crys- talline lamellm, soluble in water and alcohol, of chlorohydrate of amylammonia C10H13N,IIC1, are obtained after evaporation. This salt, distilled with quicklime, yields amylammonia in the form of a colourless liquid, of a strong ammoniacal odour, and very soluble in water. Amylammonia precipitates all the metallic salts which are precipi- tated by ammonia; and with solutions of copper, it yields a precipi- tate which dissolves in an excess of the reagent and colours the liquid blue: nevertheless, to effect perfect solution, a larger propor- tion of amylammonia must be used than of ethylammonia or methyl- ammonia. Chloride of silver also dissolves in it, but less readily than in ammonia. Amylammonia forms with acids a great number of crystallizable acids. BUTYRYLAMMONIA. 625 Butyrylammonia CgHnN or C8IIg(NH3). § 1489. Butyrylammonia has not yet been prepared by the gene- ral process which has furnished the foregoing volatile alkaloids; while among the products of distillation of animal substances, several volatile alkaloids have been found, among which one called petinin CJIjjN is distinguished, presenting exactly the composition of buty- rylammonia. The composition of this substance presents, in fact, with that of butyric acid C8II703,H0, the relation which exists be- tween ethylammonia C4H7N and acetic acid C4H303,H0. It is a colourless liquid, of a penetrating ammoniacal odour, and forming well-defined salts with acids. § 1490. The resemblance with ammonia of the last volatile alka- loids which we have described, is as perfect as that observed between potassa and soda; and their composition presents the remarkable peculiarity, that they may be considered as formed by the union of 1 equivalent of ammonia with a carburetted hydrogen. The other volatile alkalies, either native or artificial, which we have described, exhibit a similar grouping in their composition, and should probably be included in a single class, which will, certainly, he subsequently greatly extended. Thus we have, Ammonia* NH3 Methylammonia NH3,C2H2, . Ethylammonia NH3,C4H4, Butyrylammonia NH3,C8H8, Amylammonia NH3,C10H10, Nicotin NH3,C10H4, Anilin NH3,C12H4, Conicin NH3,C16Hia, Quinolein NH3, C18H4. § 1491. In the following chapter we shall describe certain sub- stances found in vegetables, exhibiting no well-marked characters of acidity or alkalinity, and which have hitherto not been attached OF SOME NEUTRAL SUBSTANCES FOUND IN VEGETABLES. * The first five compounds in the above table may be considered as ammonia paired with respectively 0, 1,2, 4, and 5 equivalents of the carburetted hydrogen C2H2, or olefiant gas ; which, according to the theory of pairing, explained in the note to $1401, would fully explain the ammoniacal properties of the paired com- pounds. They may also be regarded, with equal propriety, as ammonias in which 1 equivalent of hydrogen is replaced by 1 equivalent of the radicals methyl, ethyl, butyril, and amyl, respectively; which view has gained much probability by the recent investigations of Frankland and Kolbe.— W. L. F. 626 INDIFFEKENT SUBSTANCES. to any of the great series of organic compounds. These substances being very numerous, Ave shall only mention the most important and those which are best knoAvn. Piperin C34IIlgN06. § 1492. Piperin exists in pepper, and is generally extracted from white pepper, by treating it Avith alcohol. The alcoholic solution is evaporated, the residue treated with an alkaline lye, which dissolves various substances, and leaves the piperin isolated. It is to be puri- fied by several crystallizations in alcohol. Piperin forms colourless prisms, which melt at about 212°, and is slightly soluble in water, but very soluble in alcohol. Acids dissolve it readily, without forming a fixed compound Avith it, and, if they are volatile, they part Avith it Avholly by evaporation, which operation is even effected at the ordinary temperature in vacuo. The composition of piperin corresponds to the formula C34H18N06, showing it to be isomeric with morphin. Picrotoxin C12II705. § 1493. Picrotoxin is the poisonous principle of the coculus Indi- cus, and is obtained by exhausting these berries by alcohol, and evaporating the liquor, when a mixture of picrotoxin with fatty matter remains as a residue. The residue is pressed between folds of tissue-paper, and then redissolved in alcohol, after which the liquor is bleached by animal black, and picrotoxin obtained, by evaporation, in small acicular crystals. Picrotoxin dissolves in 25 parts of boiling water, the greater portion of it being again depo- sited on cooling, while it dissolves readily in alcohol. Picrotoxin does not combine with acids, and it contains no nitrogen, its com- position corresponding to the formula C12H705. Cantharidin C10II6O4. § 1494. Cantharidin, the active principle of cantharides, possesses extremely powerful vesicating properties, and if any portion of the body be exposed to its vapours, swelling accompanied by acute pain immediately ensues. It is obtained by treating powdered can- tharides with alcohol, and evaporating the alcohol, when an aqueous liquid remains, on which floats an oily coat, solidifying on cooling. This coat being dissolved in alcohol and discoloured by animal black, crystals of cantharidin are obtained by evaporation. Can- tharidin contains no nitrogen, and its composition corresponds to the formula C10H6O4; but its equivalent has not yet been deter- mined, as no definite compound of it is known. Cantharidin is insoluble in water, but dissolves readily in alcohol and ether. Asparagin C8H7N305,H0. § 1495. The name of asparagin has been given to a crystallizable substance, first found in the shoots of asparagus, but which also ASPARAGIN. 627 exists in liquorice-root, in marsh-mallow root, comfrey, potatoes, vetches, and several other plants. It is generally prepared by macerating bruised marsh-mallow roots with very clear milk of lime, filtering the liquid, precipitating the dissolved lime by carbonate of ammonia, and evaporating to the consistence of syrup; when, in the course of a few days, granular crystals of impure asparagin separate, which are purified by recrystallization. Asparagin does not originally exist in the seeds of the vetch, but is developed during germination and vegetation, to again disappear at the flowering period. In order to extract it, the plant is cut at the proper season, and the juice expressed and boiled, when albumin- ous substances coagulate and are separated. The liquid being evaporated to the consistence of syrup, and left to itself, deposits crystals of asparagin, which are purified by being washed with cold water and recrystallized several times. Asparagin forms beautiful colourless prismatic crystals, requiring for solution about 60 parts of water, at the ordinary temperature, but dissolving more freely in boiling water. It is not sensibly solu- ble in absolute alcohol or in ether. Its aqueous solution feebly reddens litmus ; and when it is poured into a hot solution of acetate of copper, a beautifully blue precipitate is formed, consisting of a compound with oxide of copper, of the formula Cu0,C8II7N30s'. The formula of asparagin dried at 212° is C8H8N306, which should be written C8II7N20.,II0 ; while the formula of crystallized aspara- gin is C8H7N205,H0+2H0. A solution of pure asparagin, left to itself, remains unchanged for an indefinite length of time, which is not the case if it contains some of the principles which accompany it in the vegetable, when it undergoes a kind of fermentation which converts it into succinate of ammonia. If we observe that 1 equivalent of succinate of am- monia is equal, in its elementary composition, to 1 equivalent of asparagin plus 2 equivalents of water and 2 equivalents of hydrogen^ 2(NH3+HO), C8H406=C8H8N206+2HO+2H, we may admit that asparagin assimilates to itself 2 equivalents of water and 2 equivalents of hydrogen, produced by the putrefaction ensuing in the liquid, which excites a reducing action in nearly all analogous cases. Under the influence of sulphuric and chlorohydric acid, and of nitric free from nitrous acid, asparagin is decomposed into ammonia and anew acid, called aspartic C8H5N06,2H0, which is very slightly soluble in water, but readily so in the acids, with which it afterward parts with difficulty by evaporation. It crystallizes in small pearly leaflets; and may also be obtained by boiling asparagin with a solution of potassa, when ammonia is disengaged, and the liquor contains aspartate of potassa, C8H8N306+2110=C8H5N06,2H0+NH3. 628 INDIFFERENT SUBSTANCES. If asparagin be treated with nitric acid containing nitrous acid, a considerable quantity of bimalate of ammonia (NII3,HO-f HO), C8H408 is formed, nitrogen being disengaged at the same time. Under the influence of the nitric acid, the asparagin is converted into aspartic acid and ammonia, while the ammonia has been con- sumed by the nitrous acid, yielding water and free nitrogen; and the aspartic acid, having combined with 2 equivalents of water in the nascent state, has been changed into bimalate of ammonia, according to the equation, It is proper to observe that aspartic acid and asparagin may be considered as malic acid, united to 1 or 2 equivalents of ammonia NII3; that is, as two amides of malic acid. This view of the con- stitution of these substances is corroborated by the fact that the other amides, such as oxamide, butyramide, etc., yield, with nitric charged with nitrous acid, decompositions analogous to those produced by as- partic acid and asparagin, and are converted into oxalic, butyric acid, etc., with disengagement of nitrogen. C8H.N06,2H0+2H0=(NII„ HO+HO), C8H408. Phloridzin C24II1B04. § 1496. Phloridzin exists in the fresh bark of the apple, pear, plum, and cherry tree, and is generally extracted from the bark of the roots of the apple, by digesting it in weak alcohol, when the phloridzin dissolves and separates by evaporation in silky aciculse, which are purified by recrystallization in alcohol. Boiling water dissolves a large quantity of phloridzin, while, it scarcely retains part of it after cooling; and alcohol dissolves it readily, the solution exerting no reaction on litmus. The solution of phlo- ridzin in alcohol exerts a rotatory power toward the left. It loses water when heated, and is subsequently decomposed at about 392°. Dilute mineral acids dissolve phloridzin when cold, while if heat be applied the liquid becomes clouded, and deposits a new substance, yhloretin C13II705, which is obtained in crystalline lamellae by solu- lution in alcohol. Grlycyrrhizin C36II22012,2H0. § 1497. This name has been given to a sweet substance found in the aqueous extract of liquorice-root, [glycyrrldza glabra,) from which it is extracted by adding to the concentrated liquid almost any acid, which yields a flaky precipitate collecting into a tari’y mass. This substance, when dried, is dissolved in absolute alcohol, which again deposits it, by evaporation, in the form of an amorphous brownish-yellow mass. Glycyrrliizin is hut slightly soluble in cold water, and nearly insoluble when the water contains an acid; while it dissolves freely in absolute alcohol, but is insoluble in ether. Analysis has assigned to it the formula C36H22012,2H0, and its so- lution produces, with acetate of lead, a precipitate of the formula 2Pb0,Cs6H33013. NITRILS. 629 NITRILS. § 1498. By causing anhydrous phosphoric acid to act on the am- moniacal salts formed by the organic acids, or on the corresponding amides, a new class of substances, called nitrils, is obtained, the com- position of which may be represented by cyanhydrates of carburetted hydrogen, and which regenerate, by the action of the alkalies, the acid of the original ammoniacal salt, by seizing on the water and disengaging ammonia. We shall give some examples of their curi- ous reactions. § 1499. By heating crystallized acetate of ammonia with anhydrous phosphoric acid, a liquid is obtained soluble in water in all proportions. In order to purify it, it is first digested over chloride of calcium, and then distilled successively over chloride of calcium and calcined mag- nesia. The liquid, which is called acetonitril,* boils at 170.6°, and its formula C4H3N corresponds to 4 vol. of vapour. In contact with hydrated potassa, ammonia and acetic acid are regenerated : Acetonitril C4H3N. Potassium decomposes it when cold, cyanide of potassium being formed, and a mixture of hydrogen and carburetted hydrogen dis- engaged. Acetonitril appears to be identical with methylocyanohydric ether C2H3,CaN, but alkalies do not act upon it as upon other compound ethers, since they convert it into acetic acid and ammonia. Acetonitril is also produced when acetamide C4II302,NII3 is heated with anhydrous phosphoric acid. Acetamide, which is obtained by treating acetic ether with ammonia, is white, and crystallizes in prismatic aciculse, melting at 172.4°, and boiling at about 428°. Chloracetate of ammonia (NH3, HO), C4C1303 and chloracetamide C4C1302,NH2 furnish, with anhydrous phosphoric acid, perchlori- nated acetonitril C4C13N, which boils at 177.8°, and yields chlora- cetic acid, when the corresponding compound forms acetic acid. C4H3N+4H0=C4H303,H0+NH3. § 1500. The butyrate of ammonia and butyramide, heated with anhydrous phosphoric acid, yield butyronitril C8H7N, an oily liquid, boiling at 245.3°, and which potassium converts into cyamide of potassium, hydrogen, and a new carburetted hydrogen. Its for- mula C8H7N corresponds to 4 vol. of vapour. Butyronitril C8H7N. § 1501. Yaleramide, heated with anhydrous phosphoric acid, pro- duces valeronitril C10H9N,a colourless liquid, boiling at 257°, which is decomposed by potassium, when cold, into cyanide, hydrogen, and a new carburetted hydrogen. Valeronitril, C10HgN. * It may be termed methyocyanhydric acid.—J.C.B. 630 DERIVATIVES OF CYANOGEN. § 1502. Cyanogen is always a product of the decomposition by heat, in the presence of alkalies, of nitrogenous organic substances. Its study, and that of its numerous derivatives, should therefore find a place among substances of the organic kingdom; but its compounds play too considerable a part in chemical processes and are too fre- quently used in the examination of the salts of various metals to allow us to postpone their consideration until the end of the course. These reasons have induced us to describe, in the first part of our course, cyanogen and its compound with hydrogen, cyanohydric acid. We have seen that cyanogen behaves, in its compounds, like the simple metalloid substances, particularly like chlorine, and we have described in detail the principal compounds it forms with the metals, the simple and multiple cyanides, which are very important compounds, both on account of their use in dyeing, and in chemical analysis. It still remains to us to describe the compounds of cya- nogen with several metalloids, chlorine, iodine, oxygen, sulphur, and several more complicated combinations, which present some points of peculiar interest for our chemical theories. PRODUCTS OF CYANOGEN. § 1503. As yet only two compounds of cyanogen with chlorine are known, the elementary composition of which is exactly the same, while their properties are wholly different, one of the compounds being gaseous at the ordinary temperature of our climate, and the other solid and boiling only at about 390°. The gaseous chloride of cyanogen CyCl or C3NC1 is obtained by causing chlorine to act on moist cyanide of mercury, which reaction is expressed by the fol- lowing equation: COMPOUNDS OF CYANOGEN WITH CHLORINE. HgCy+2Cl=HgCl+CyCl. It is also prepared by passing a current of chlorine through a concentrated solution of cyanoliydric acid, when the gaseous chlo- ride of cyanogen remains in solution, and may he disengaged hy gently heating the liquid, the gas being dried hy passing it over chloride of calcium. It is a colourless gas, of a strong odour, caus- ing tears, liquefying at about 10.4°, and solidifying at —0.4°. Thus, this substance passes through three states in a very small change of temperature. Water dissolves about 25 times its vol., and alcohol and ether 50 times its vol. of it. Liquid chloride of cy- anogen soon passes into the solid modification, called solid chloride of cyanogen. If, in fact, it be enclosed in a glass tube hermeti- cally sealed, it undergoes at first no change, and if the tube be broken, it is wholly evolved in the gaseous state, while, in a few days, long prismatic crystals, ultimately occupying the whole mass, will be found to be developed. If the tube be then broken, no gas is CYANURIC ACID. 631 disengaged, and we find only crystals melting at 284°, and boiling at 374°. Solid chloride of cyanogen is directly formed, when an- hydrous prussic acid is poured into a large bottle filled with dry chlorine and exposed to the sun. The density of the vapour of solid chloride of cyanogen is three times greater than that of the gaseous chloride, for which reason the formula CyCl has been as- signed to the gaseous chloride, and the formula Cy3Cl3 to the solid. The equivalents of these substances are therefore represented by 4 gaseous volumes. The two chlorides of cyanogen combine directly with ammoniacal gas, and form solid compounds, of which the formulae are, For the gaseous chloride 2NH3,CyCl. “ solid chloride 3NII3,Cy3Cl3. The first is soluble in water, and the second is insoluble. Two compounds of cyanogen with bromine and iodine are also known. COMPOUNDS OF CYANOGEN WITH OXYGEN. § 1504. Four isomeric compounds of cyanogen and oxygen are known, cyanic acid, cyanuric acid, cyamelide, and fulminic acid, the first two of which appear to present the same relations of constitu- tion as the gaseous and solid chlorides of cyanogen. By digesting solid chloride of cyanogen with water, chlorohydric acid and a solid white substance, cyanuric acid Cy303, are formed: Cy3Cl3+3HO=3HCl+Cy303. The same compound is found under many other circumstances, and particularly when certain substances of animal origin are decom- posed. A solution of the substance in hot water again deposits it, on cooling, in crystals, which are hydrated and present the formula Cy303, 7HO, while, when dried at 212°, the formula becomes Cy3033H0 ; that deposited from a nitric or chlorohydric solution also present- ing the latter composition. The 3 equiv. of water are basic, and may be replaced partially or wholly by an equivalent quantity of base; and, in fact, three series of cyanides are known, of which the general formulae are (R0+2H0),Cy303, (2R0+H0),Cy303, 3R0,Cy303. Cyanuric is therefore a tribasic acid. Cyanuric acid, heated in a small glass retort, passes over wholly in distillation, hut is then deeply changed, for the distilled product forms a very volatile liquid, of an odour resembling concentrated acetic acid, and which reddens litmus and behaves like a powerful acid. Its composition is the same as that of cyanuric acid dried at 212°, but it forms only one series of salts, and should he con- sidered as a monobasic acid. The formula CyO,IIO has been 632 DERIVATIVES OF CYANOGEN. assigned to this acid, called cyanic, and to its salts the general formula RO,CyO. Cyanic acid is spontaneously converted into an isomeric substance, called cyamelide, while the transformation does not take place so long as the cyanic acid is kept at a very low temperature; but, at the ordinary temperature, the liquid soon becomes clouded, while at the same time its temperature rises spontaneously, and it is con- verted into a solid mass, resembling porcelain. This is cyamelide, a wholly neutral substance, insoluble in water, alcohol, and ether, and which reproduces the original cyanic acid by distillation. Cyanic acid may also be transformed, directly, into cyanuric acid, by adding a small quantity of nitric or acetic acid to a concentrated solution of cyanate of potassa, which converts the salt into cyanurate. Cyanic acid may be prepared, directly, in several ways : 1. By passing cyanogen gas through a solution of potassa or car- bonate of potassa, cyanate of potassa and cyanide of potassium are formed, the reaction being similar to that of chlorine on alkaline lixivise, when it converts them into hypochlorites, (§ 450): 2. By heating a mixture of prussiate of potash and nitrate of potassa or peroxide of manganese, when cyanic acid passes over in distillation. The mixture may also be roasted in the air, and then treated with boiling alcohol, which dissolves the cyanate of potassa. 3. By fusing yellow prussiate of potash at a red-heat, and throw- ing litharge into the melted mass as long as the former is reduced. Boiling alcohol then dissolves the cyanate of potassa formed. The fourth isomeric modification of cyanic acid, fulminic acid, is formed under quite peculiar conditions. Mercury or silver being treated with a mixture of alcohol and nitric acid, a very powerful reaction ensues, and various products of the oxidation of alcohol pass into the receiver, among which may be distinguished aldehyde, acetic acid, formic acid, and nitrous, acetic, and formic ethers. A crystalline salt, which is the f ulminate of mercury or silver, is de- posited in the retort. The composition of fulminic acid is the same as that of cyanic and cyanuric acids, hut it is a bibasic acid, the formula of which should be written Cy2Os,2IIO, since it forms, in fact, two series of salts, of which the general formulae are (R0 + H0),Cy203 and 2RO, Cy303. The formulae of the fulminates of mercury and silver are 2Hg0,Cy303and 2Ag0,Cy303; and by treating the fulminate of sil- ver with potassa, only one-half of the silver is precipitated, while a double fulminate, of the formula (Ag0+K0),Cy303, is obtained. The dry fulminates detonate with extreme violence, either by percussion or when heated. Fulminate of mercury is used in the manufacture of percussion caps for firearms. 2KO+2Cy=KO,CyO+KCy. SULPHOCYANIDES. 633 They are prepared on a large scale, by dissolving 1 part of mer- cury in 12 of nitric acid of a density of 1.36, adding to the solution 11 parts of alcohol at 0.80, and then gently heating the mixture in a distilling apparatus, in order to condense the disengaged volatile products, which may be used in another operation. The liquid remaining in the retort deposits the fulminate on cooling. Metallic Sulphocyanides and Sulphocyanohydric Acid. § 1505. By heating to a dull-red an intimate mixture of 2 parts of prussiate of potash and 1 part of sulphur, and then treating it with boiling alcohol, sulphoeyanide of potassium KS,CyS is depo- sited in small crystalline aciculse; and it may be regarded as a cyanate of potassa, in which the oxygen of the acid and the base is replaced by a corresponding quantity of sulphur. A larger quan- tity is obtained by heating 46 parts of prussiate of potash, 17 parts of carbonate of potassa, and 16 of sulphur, and treating the mass with boiling alcohol. If sulphoeyanide of potassium be distilled with phosphoric acid, sulphocyanohydric acid CyS,HS is obtained, a large proportion of which is, however, decomposed. Acetate of lead also be poured into the solution of the sulphoeyanide of potassium, when sulphoeyanide of lead PbS,CyS is precipitated, and is decomposed by sulf hydric acid, a colourless acid liquor, reddening litmus, being formed. Free sulphocyanohydric acid, and the alkaline sulphocyanides, yield, with sesquisalts of iron, precipitates of a blood-red colour, which reaction is often used to detect these salts. By pouring into a solution of an alkaline sulphoeyanide, 6 or 8 times its volume of concentrated chlorohydric acid, a deposit of small white aciculae is formed, which are to be washed with a small quantity of cold water. It is a new acid, called persulphocyanohy- dric, of the formula CySa,HS. This acid may be dissolved in boiling water, and is deposited from it, on cooling, in small crystalline aci- culse. It is a feeble acid, which combines directly, without altera- tion, under certain conditions, while under other conditions it is decomposed. Persulphocyanohydric acid, and sulphocyanohydrate of ammonia, yield, when heated, a great number of new substances, as yet but imperfectly known. 634 ESSENTIAL OILS. ESSENTIAL OILS. § 1506. A large number of volatile substances, possessing gene- rally a powerful and frequently an agreeable odour, adapting them for the toilet, are extracted from vegetables; and the greater por- tion of them are liquid, while some are solid at the ordinary temper- ature. These substances are in general prepared by expressing the juice of the vegetables which contain them, and distilling it with water, when the essential oil passes over with the water, and, as it is generally less volatile than the latter, the proportion which passes over, compared with the quantity of water, is the greater as the difference between the boiling point of water and that of the oil is less. Parts of the vegetables themselves, the flowers for example, are frequently distilled with water, and when the essential oil is lighter than water, the products are collected in a bottle of peculiar shape, (fig. 684,) called a jlorence receiver. The bottle is conical, and has a lateral tube communicating with the bot- tom, and of which the orifice is at a lower level than the mouth a of the bottle. The Avater and oil distilled pass into the bottle through the mouth a, the oil forming the upper stratum; and Avhen the bottle is filled above the level of the orifice c, the water escapes through the lat- ter, and the essential oil floats on its surface, in a layer of a thickness in proportion to the diameter of the neck of the bottle, and which is removed from time to time with a pipette. An ordinary alembic is used for distillation, but the A’egetables subjected to the operation must not be allowed to reach a temperature above 212°, in order to avoid the generation of empyreumatic products, AV'hich, distilling at the same time as the essential oil, would injure its flavour. In order to prevent these accidents, the vegetables are placed in bags, or metallic vessels pierced Avith holes, and kept above the liquid in the cucurbit, in the space traversed by the vapour. As the water Avhich has distilled over with the essential oil gene- rally dissolves a small quantity of it, sufficient to impart to it its odour, it is carefully collected and sold. Thus, Avhile distilling orangc-floAvers with water, a certain quantity of essence of orange- flower collects at the top of the florence receiver, while a Avater, possessing a very agreeable smell, and Avhicli is sold under the name of orange-flower water, is found under it. The quantity of essential oil which exists in the portions of vege- tables subjected to distillation is frequently so small that no sepa- rate oil can be obtained, but only an odoriferous water. The same Fig. 684. TERPENTINE. 635 thing occurs when the boiling point of the essential oil is very high; and in the latter case, the fresh water in the cucurbit is replaced by water saturated with salt, which boils at 230°, and the vessel containing the flowers is suspended in this water; when the tension of the vapour of the oil is necessarily greater in this hotter space, and a larger quantity of it passes over. Some essential oils would be very easily injured by heat, and at other times the flowers in which they exist contain alterable princi- ples, and the distilled oil is far from possessing the odour of the flower. They are then not distilled, and we are satisfied with sepa- rating the oil by dissolving it in a fixed oil, of itself inodorous, poppy-oil for example; for which purpose the flowTers are spread thinly over woollen cloths soaked in poppy-oil, when the cloths are piled on each other, and the whole placed under a press. Essential oils differ materially from each other, both in their com- position and chemical reactions; and, if due regard be paid to the nature of the compounds from which they are derived, we are led to divide them among those series most differing from organic bodies. A great number of oils contain only carbon and hydrogen, while others also contain oxygen, and, lastly, some few contain sulphur. We shall therefore divide them into three groups, and include in the first, those oils which are composed of hydrogen and carbon alone; in the second, those which contain, in addition, oxygen ; and in the third, the sulphuretted essential oils. § 1507. The composition of the greater number of these oils cor- responds to the formula C5H4-, and we therefore here find a great number of isomeric substances, the chemical properties of which are so similar that recourse must be had to very delicate characters to prove their non-identity. The mobility of their molecular constitu- tion is such, that by distilling, or forming them into compounds from which they are subsequently separated, their nature is changed. HYDROCARBURETTED ESSENTIAL OILS. § 1508. This is the most important of the essential oils, on ac- count of its application in the arts, being used in the preparation of varnishes, and, in general, as a solvent for certain substances, which it deposits, by spontaneous evaporation, on the surface of bodies coated with the solution. A viscous substance, called terpentine, consisting essentially of a resin, colophony, or common resin dissolved in oil of terpentine, exudes from the trees of the family of the coniferse, chiefly from the pines. By distilling terpentine with water, the greater portion of the essential oil is carried over by the vapour of water, in which state it still contains a small quantity of resin, partly formed by the oxida- tion of the oil by contact with the air. In order to purify it, it is again distilled with water, dried by leaving it for some time over Essential Oil of Terpentine or Terebethene C20II16. 636 ESSENTIAL OILS. chloride of calcium, and again distilled for the last time by itself, avoiding as much as possible the contact of the air. The essential oil extracted from the various terpentines of com- merce is far from being identical, and appears to vary according to the tree which has produced it. French oil of terpentine, produced by the pinus maritima which grows in the south of France, is a colourless, very volatile liquid, of a characteristic smell and an acrid and burning taste. Its density at 32° is 0.875, wdiile the density of its vapour is 4.76 ; and if it be admitted that its equiva- lent is represented by 4 volumes of vapour, like that of the carbu- retted hydrogen hitherto described, its formula should be written C20II1B. Oil of terpentine, which we shall call, for brevity’s sake, terebenthen,* boils at about 300°, the boiling point being rarely constant. It deviates polarized light to the left, Avhile the various oils differ from each other in the intensity of their rotatory power; some even producing deviation to the right, as the oil extracted from the pinus tada of Carolina, which is chiefly used in England. Moreover, the same terebenthen does not maintain an identical rotatory power when it is subjected to successive distillations, and its molecular constitution appears to be modified by the simple process of distillation ; these modifications being much more decided when the distillation is effected under high pressure, and, conse- quently, at a more elevated temperature. An oil of terpentine having been kept boiling, for several hours, under a pressure of 8 or 10 atmospheres, more than one-lialf of it was converted into an isomeric product which did not boil under 464°. Terebenthen dissolves but slightly in water, communicating to it, however, its characteristic odour; and it dissolves freely in alco- hol, ether, and the fixed oils. It dissolves a large proportion of sulphur, phosphorus, and several organic compounds. § 1509. Terebenthen, left for a long time in contact with wrater, deposits colourless crystals, which have been improperly called hy- drate of terebenthen, because their composition corresponds to the formula C.,0II166HO. A. much larger quantity of this compound is obtained by leaving a mixture of 8 parts of oil of terpentine, 2 parts of ordinary nitric acid, and 1 part of alcohol at 0.80, to itself for several months, during which time it is frequently shaken; when a crystalline magma is formed, which is expressed between tissue-paper, and redissolved in boiling water, from which it is de- posited in small prismatic crystals on cooling. By redissolving it in boiling alcohol, it yields large crystals, which melt at 217.4°, while, at a more elevated temperature, they lose 2 equivalents of water, and form a new hydrate C?0IIi6,4I1O, which distils at about 482° Avithout change. The density of its vapour being 6.26, the equivalent is represented by 2 volumes. * Called Camphine in tlie U. S., when purified by distillation.—J. C. B. TERPENTINE. 637 § 1510. Terebenthen combines readily with chlorohydric acid gas, and absorbs large quantities of it, with elevation of tempera- ture, the saturated liquid depositing crystals, on cooling, varying in proportion according to the nature of the oil, and which are purified by recrystallization in boiling alcohol. The crystals melt at 302°, the substance boiling at about 338°, with partial decomposi- tion ; and its composition corresponds to the formula showing it to be a chlorohydrate of terebenthen, which is times called artificial camphor: it deviates the plane of polariza- tion to the left. The liquid which floats on the crystals, in the preparation of artificial camphor, is itself a liquid chlorohydrate of terebenthen, of the same composition as the solid chlorohydrate, but which does not solidify at any temperature. If solid chlorohydrate of terebenthen be passed over caustic lime heated to redness, a liquid carburetted hydrogen separates from it, having the same composition and boiling point as the ori- ginal terebenthen, but differing from it by exerting no action on polarized light: it has been called camphilen. It also combines with gaseous chlorohydric acid, yielding, at the same time, a solid and a liquid chlorohydrate ; and it is therefore composed of at least two distinct liquids, like terebenthen itself. By decomposing the liquid chlorohydrate of terebenthen by means of lime, an essen- tial oil is separated having no action on polarized light, and yield- ing only liquid chlorohydrate with chlorohydric acid, which new oil has been called terebilen. Bromohydric and iodohydric acids pro- duce compounds similar to those of chlorohydric acid. § 1511. Terebenthen undergoes very curious isomeric modifica- tions by contact with sulphuric acid. By mixing, in a well-cooled flask, oil of terpentine with about dj of its weight of sulphuric acid, and leaving the mixture to itself during 24 hours, shaking it fre- quently, a red and viscous liquid is obtained; and after allowing it to rest for some time, the supernatant oil is decanted, when a black residue, saturated with acid, remains in the flask. If the decanted oil be distilled, a small quantity of sulphurous acid first passes over, and then an essential oil, having the same composition, density, and boiling point as terebenthen, but differing from it in exerting no rotatory povrer on polarized light, and in forming vrith chlorohy- dric acid gas a compound of the formula 2CaoII1B,HCl, which con- sequently contains one-half less chlorohydric acid than the chlo- rohydrate of terebenthen. This essential oil has been called tereben. The essential oil modified by sulphuric acid is not solely com- posed of tereben, and when it has separated by distillation, and the temperature is raised to 590°, a new product is obtained, composed of a viscous oil, which is bleached by being distilled over an alloy of potassium and antimony, (§ ] 017). This liquid is highly dichroic ; light which passes through it normally being colourless, while that 638 ESSENTIAL OILS. obliquely refracted by it, particularly at certain angles of incidence, exhibits a beautiful indigo colour. Its density is 0.940 at 48.2°, and it has no rotatory power. It absorbs chlorohydric acid gas, but without forming any fixed compound, for carbonate of lime readily abstracts the chlorohydric acid. The name of colophen has been given to this gas, the composition of which is the same as that of terebenthen ; and large quantities of it are obtained by the direct distillation of resin. Chlorine acts powerfully on terebenthen and its isomeric com- pounds, chlorohydric acid being disengaged, while a viscous, co- lourless liquid is formed, having the smell of camphor, and which is quadricldorinated terebenthen, its formula being C^H^Cl^ § 1512. Lemon-peel contains an agreeable-smelling essential oil, of an identical composition with terebenthen, and which we shall call citren. It may be extracted by expressing the yellow part of the lemon peel, but it is more generally separated by distilling the peel with water, in which case the smell of the oil is, however, less grateful. Citren boils at about 338°, and its density is 0.847 at 71.6°, while the density of its vapour is the same as that of tere- benthen, for which reason it has received the same formula C20IIl6; but it polarizes to the right. It combines with chlorohydric gas forming a liquid and a solid chlorohydrate having the same composi- tion. These chlorohydrates of citren contain twice as much chlo- rohydric acid as the chlorohydrate of terebenthen, and their for- mulae is therefore C20II1(i,2IlCl. Oil of Lemons, or Citrene CaoII16. Oil of Oranges, or Oil of Neroli C20II16. § 1513. Orange-peel, like lemon-peel, contains an essential oil, to which it owes its fragrance, and of which the formula is the same. It yields, with chlorohydric acid, a solid and a liquid product, of an identical composition with the chlorohydrates of citren; and it polarizes to the right. In the bergamot, in juniper-berries, in the seeds of parsley, and many other vegetables, essential oils of the composition C5ll4 are found, but which are distinguished by certain chemical properties, and by their rotatory powers, from the essential oils just described. Es- sential oils of bergamot, Seville oranges, cedrat, caraway, and limes rotate toward the right. Essential oils of the same composition are obtained in the distillation of several organic substances. Certain kinds of bitumen yield a yellowish liquid, petrolen, which may be made perfectly colourless by distilling it over potassium, and pre- senting the same composition with oil of terpentine. But as it boils at 536°, and the density of its vapour is double, its formula should be written C40H33. CAMPHOR. 639 § 1514. These oils being numerous, and their chemical properties very various, we shall describe only the most important and best known of them. OXYGENATED ESSENTIAL OILS. § 1515. The name of camphors, or stearoptens, has been given to neutral compounds, solid at the ordinary temperature, volatile, hav- ing an odour resembling those of ordinary camphor, and applicable to the same uses. We shall here treat only of the camphor from Japan and that from Borneo. CAMPHORS. § 1516. Japan camphor is extracted from the laurus camphora, the wood of which tree contains it so abundantly that small crystals of it are seen in the fissures. The trunk and branches are split into stiiall pieces and distilled with water in iron boilers, covered with an earthen capital filled with straw or small twigs, on which the cam- phor sublimes and crystallizes in the shape of crude camphor. It is distilled with a small quantity of lime and charcoal in flat-bottomed vessels, resembling those used for the sublimation of chloroliydrate of ammonia, (§ 516,) when the camphor sublimes at the upper part, and forms crystalline, colourless, and transparent masses, such as are found in commerce. At the ordinary temperature, the tension of the vapour of camphor is very feeble, and, nevertheless, it ex- hales an intense and characteristic odour; while, when kept in a close-stoppered bottle, the vapour condenses on its sides, and forms small brilliant crystals, remarkable for their sharpness. Camphor melts at 347°, and boils at about 410°, its density being 0.986, and the density of its vapour 5.32. From its great elasticity it is very difficult to pulverize. Its chemical composition corresponds to the formula C10II8O, which is generally written C20H16O3; its equivalent then corresponding to 4 volumes of vapour. Camphor is slightly soluble in water, hut dissolves more freely in alcohol, ether, and concentrated acetic acid, and it burns with a white and smoky flame. Camphor obtained from the family of the laurels, when dissolved in alcohol, rotates toward the right. Chlorine does not act readily on camphor, hut when dissolved in chloride of phosphorus PC13, and subjected to the action of chlorine, it yields chlorinated camphor C30II10Cl6O3, which is separated from the perchloride of phosphorus by washing it with water and weak solutions of carbonate of potassa. Camphor absorbs chlorohydric acid gas, and yields a colourless liquid of the formula C20II16O2,IICl, which is readily destroyed by water, while camphor separates from it. § 1517. Alkaline solutions exert no action upon camphor, but if its Japan Camphor C30II16030. 640 vapour be passed over potassic lime heated to 750° in a glass tube, an acid called campholic is formed, which combines with the alkaline substance, and which is then separated by dissolving in water and supersaturating with chlorohydric acid. The precipitated cam- phoric acid is dissolved in a mixture of alcohol and ether, from which it separates in crystals, melting at 176°, and boiling at 482°. It is insoluble in water, but very soluble in alcohol and ether. When crystallized, its formula is C20II18O4, or more properly which corresponds to 4 volumes of vapour, for the density of the vapour of campholic acid is 5.9. The formula of campholic acid differs from that of camphor only by containing, in addition, the elements of 1 equiv. of water. The formula of campholate of silver is AgO,C20II1703. Campholate of lime CaO,C20II17O3 is decomposed by heat into carbonate of lime and a peculiar liquid called campholone C19II170. ESSENTIAL OILS. CaO,C20II17O3=CaO,COa+C19II17O. Campholic acid, distilled with anhydrous phosphoric acid, gives off water and carbonic acid, while a carburetted hydrogen C18II16, called campholen, which boils at 275°, is formed. § 1518. Cold nitric acid dissolves camphor, and parts with it when diluted with water, while, by the application of heat, a peculiar acid, called camphoric, is developed. In order to prepare this acid, camphor is boiled for a long time with 10 times its weight of nitric acid, and as the latter distils over, it is collected and poured back into the retort. At the close of the operation, the excess of nitric acid is driven off by evaporation, when the camphoric acid separates in a crystalline mass, which is purified by dissolving it in carbonate of potassa, and again separating it by means of nitric acid. Cam- phoric acid is moderately soluble in boiling water, the greater por- tion of it separating during cooling, while alcohol and ether dissolve it readily. Its composition corresponds to the formula C20II1608; and the camphor, by being converted into camphoric acid, combines therefore with 6 equiv. of oxygen, which it takes from the nitric acid. The formula of camphoric acid should be written C20II14O6, 2IIO, because it is a bibasic acid, and the general formula of its, salts is 2RO,C20H140„. When heated it is decomposed into water and a crystallized substance, boiling at 518°, which, from its com- position C20II14OG, may be regarded as anhydrous camphoric acid. Camphoric acid, dissolved in alcohol, rotates toward the right. § 1519. A species of camphor is extracted from the labiates, which, in its chemical composition, appears identical with the camphor of the laurels, but which rotates toward the left. § 1520. From the dryabalanops camphora exudes a more or less viscous oil, containing a cry stall izable substance, of which the pro- Borneo Camphor C20H1802. CAMPHORS. 641 perties are analogous to those of Japan camphor. It has been called Borneo camphor, and is often found crystallized in old trunks of the tree of the dryabalanops camphora. The camphor imported from Borneo and Sumatra is in small, crystalline, colourless, and trans- parent fragments, insoluble in water, but dissolving freely in alcohol and ether. It melts at about 383°, and boils at about 419°. Bor- neo camphor differs from Japan camphor only by containing 2 ad- ditional equiv. of hydrogen, which are consumed by heating it with nitric acid; the Borneo being converted into Japan camphor. The liquid portion of the essential oil of the dryabcdanops camphora is essentially composed of a liquid carburetted hydrogen C20I116, called borneen, boiling at about 320°, and isomeric with oil of terpentine, similarly to which it polarizes to the left, its rotatory power being much greater. Nitric acid, after some time* and assisted by gentle heat, converts borneen into Japan camphor, probably by the mere absorption of oxygen. Of some other Stearoptens analogous to Camphor. § 1521. Stearoptens, exhibiting properties analogous to the cam- phors, are found in a great number of vegetables; but we shall only mention them, for as yet they possess but little interest, and are but little known. Peppermint contains a stearopten of the formula C20H20O2, called menthen C^Hj, which boils at 325.4°. Oil of mint rotates toward the right. Oil of cedar is composed of a crystallizable substance C32H2802, and a liquid carburetted hydrogen, cedren C3H24, which boils at 478.4°. Oil of absinth, when purified, boils at 399. °2, and rotates to- ward the right; its formula being C20Il16O2, it is isomeric with Japan camphor. The root of elecampane (inula hellenium) contains a wdiite crys- tallizable substance, helenin, very soluble in alcohol and ether, melt- ing at 161.6°, boiling at about 536°, and presenting the formula CM . An essential oil, composed of a liquid portion and a portion which solidifies at 9.5°, is extracted from roses; but the composition of the two substances is not exactly known. Oil of lavender contains a considerable proportion of Japan cam- phor, and a Volatile oil, the essential oil properly so called, which has been used in the arts. Oil of Bitter Almonds C14H602. § 1522, Bitter almonds contain an essential oil, and a non-vola- tile fatty oil, which latter is expressed by subjecting them to pres- sure ; and if the pulp moistened with water be then distilled in an BENZOIC SERIES. 642 ESSENTIAL OILS. alembic, a volatile oil, which falls to the bottom of the receiver, passes over with the water. This is the oil of bitter almonds, mixed with cyanohydric acid and two new substances, benzoine and ben- zoic acid, which shall soon be described. They are separated by distilling the crude oil with lime and protosulphate of iron, reduced to a paste with water; the distilled oil being removed with a pipette, and again distilled in a glass retort, collecting separately the first portions, which contain water. Oil of bitter almonds is a colourless, very fluid liquid, having a peculiar odour resembling that of cyanohydric acid ; and its density is 1.043, while it boils at 348.8°. Water dissolves about of its weight of it, while it is indefinitely soluble in alcohol and ether. Its formula is C14H602, and it exerts no rotatory power. Oil of bitter almonds rapidly absorbs the oxygen of the air, and is converted into benzoic acid Cl4H503,H0, C14He03+ 20=C14H603,H0. Anhydrous benzoic acid is therefore derived from the oil of bitter almonds, by the substitution of 1 equivalent of oxygen in the place of 1 equivalent of hydrogen. Benzoic acid is also formed when oil of bitter almonds is boiled with a solution of potassa; the hydrated potassa converting, at a high temperature, the oil of bitter almonds wholly into benzoic acid, hydrogen being at the same time disen- gaged. Chlorine, in contact with water, effects the transformation in a very short time. § 1528. Dry chlorine acts powerfully on oil of bitter almonds, disengaging chlorohydric acid. When the evolution of the gas has ceased, the liquor is heated to drive off the dissolved chlorine, and a liquid of a penetrating and disagreeable odour is obtained, of the density 1.106, and boiling at 388°, which is monochlorinated oil of bitter almonds C14H5C102. Water, particularly when hot, decom- poses it, forming chlorohydric and benzoic acids: C14H5C102+2H0=C14H503,H0+HC1. It has not yet been ascertained if the oil of bitter almonds forms still more chlorinated products with chlorine. Bromine converts it into monobrominated oil C14II5Br02; and monoiodinated oil C14H5I02. is obtained, crystallized in laminae, by distilling the monochlorinated oil over iodide of potassium. By replacing the iodide of potassium by sulphide of lead, or cyanide of mercury, a mono sulphuretted oil C14H5S02, or a monocyanuretted oil C14H5Cy02, is obtained. Some chemists take a different view of the composition of these various bodies, and admit the existence of an hypothetical radical C14H502, called benzoyl, which, combined with hydrogen, constitutes the oil of bitter almonds C14H502,H, thus forming a hydruret of benzoyl, while benzoic acid is the oxide of benzoyl C14H502,0. The chlori- nated, brominated, cyanuretted, and sulphuretted oils are chlorides, bromides, sulphides, and cyanides of benzoyl. BENZOIC SERIES. 643 §1524. The chlorinated oil of bitter almonds absorbs a large quantity of ammoniacal gas, and is converted into a white crystal- line compound C14H7N03, or benzamide: CuH5C102+2NH3=NH3,HC1+C14H502,NH2. By treating the solid product of the reaction with water, the am- moniacal salt which formed during the operation is dissolved, while the benzamide alone remains, and may be crystallized from its solu- tion in alcohol. The relation of benzamide C14H503,N1I3 with the benzoate of ammonia (NH3,H0),C14II503 is the same as that of sul- phamide S03,NII3 with sulphate of ammonia (NH3,H0),S03. Benzamide dissolves in boiling water, and separates from it, on cooling, in crystals, which melt at 239°, and boil without change at a higher temperature. Benzamide, treated with a cold alkaline lye, undergoes no change, while at the boiling point it yields ben- zoate of potassa and ammonia. Sulphuric acid also decomposes it, sulphate of ammonia and benzoic acid being formed. § 1525. The oil of bitter almonds, kept for several weeks at a temperature of 100° to 120°, with 20 times its volume of an aqueous solution of ammonia, gives rise to a large number of crystals, which are obtained isolated by removing the unaltered oil by ether. They are dissolved in cold alcohol, which, by evaporation, deposits them in a pure state, when their composition is represented by the formula C42H18N3. It has been called hydrobenzamide, and its formation is represented by the following equation: Hydrobenzamide, dissolved in alcohol, is readily converted, by boiling, into ammonia and oil of bitter almonds. If hydrobenzamide be boiled with a solution of caustic potassa, crystalline flakes are formed, which, by recrystallization in alcohol, furnish colourless crystals of the formula C42Ii18N„ like that of the original hydroben- zamide, but which differ from it widely in its properties. This new sub- stance, called amarin, is a true organic base, which forms crystal- lizable salts with the acids. The formula of chlorohydrate of amarin is HO, while that of the nitrate, which is but slightly soluble in water, is 3,C14H602+2NH3=C42H18N2+6HO. (C42H18N2,HO),NOs. § 1526. By adding chlorohydric acid to water which has distilled with the oil of bitter almonds in the preparation of the latter sub- stance, and evaporating it to dryness at a gentle heat, the residue is composed of chlorohydrate of ammonia, and a peculiar substance, called formobenzoylic acid, which is removed by dissolving it in ether, when it is deposited after evaporation in the form of crystal- line spangles, having the smell of bitter almonds and a strongly acid reaction. This substance dissolves readily in water, alco- hol, and ether, aAd its composition corresponds to the formula C16Hs06, or rather C16H705,H0, the equivalent of water being 644 ESSENTIAL OILS. replaced, in the salts, by 1 equivalent of base. The formula of the acid may be written C14IIG02, which would represent it as formed by the combination of 1 equivalent of oil of bitter almonds and 1 equivalent of formic acid; and such, in fact, is the constitu- tion assigned to it by its behaviour in a great number of chemical reactions : thus, with oxidizing reagents, it yields carbonic acid, pro- duced by the combustion of the formic acid and oil of bitter almonds. § 1527. Oil of bitter almonds rapidly absorbs the oxygen of the air, and is converted into benzoic acid C14II503,II0, which same transformation is effected by exposing the oil to oxidizing reagents. Benzoic acid is also extracted from a large number of vegetable and animal substances, in which it generally does not exist already formed, being the product of chemical reactions. In the laboratory it is obtained from the resin of benzoin, by various processes, the most simple of which consists in placing in an earthen or cast-iron capsule 1 kilog. of coarsely powdered benzoin, covering the capsule with a sheet of tissue-paper, the edges of which are pasted to the vessel, and then surmounting it with a pasteboard cone. The cap- sule being heated in a sand-bath for 3 or 4 hours, the vapours of benzoic acid condense on the sides of the cone, after having tra- versed the tissue-paper, which retains a small quantity of the empy- reumatic oily substances, which would injure the product. This process yields very pure benzoic acid, in the form of snow-white crystals of an agreeable odour, but furnishes only a small portion of the acid which the benzoin contains; 1 kilog. of benzoin yielding only 40 gm. of benzoic acid. By the following process, as much as 140 gm. of benzoic acid may be obtained from the same quantity of benzoin. The resin of benzoin, finely powdered, is mixed with of its weight of carbonate of soda, and a sufficient quantity of water to make a liquid paste, which is gently heated for several hours, stirring it continually to prevent the melting of the resin. It is then heated with a larger quantity of water, to dissolve the benzoate of soda, and the benzoic acid is separated by the addition of a proper quantity of sulphuric acid. The resin of benzoin may also be treated with 3 times its weight of alcohol at 0.75, and the benzoic acid saturated with carbonate of soda dissolved in 8 parts of water; and 2 parts of alcohol being finally added, the liquid, when decanted, is distilled in order to separate the greater portion of the alcohol. The resin which was dissolved in the alcoholic liquor separates, while the solution only contains the benzoate of soda, which is decomposed by sulphuric acid, when the benzoic acid separates almost wholly from the liquor when cool. By this method, 1 kilog, of benzoin will yield as much as 180 gm. of benzoic acid. Benzoic Acid Cl4H3C)„HO. BENZOIC SERIES. 645 Benzoic acid crystallizes in lamelloe or in flexible and brilliant silky acicubc ; and it has, of itself, but little odour, while it gene- rally preserves the smell of benzoin, particularly when it has been prepared by simple distillation. It weakly reddens litmus, melts at 248°, and boils at 464°, exhaling copious vapours already at a tem- perature of 800° or 400°. The density of its vapour being 4.27, its equivalent C14II803II0 corresponds to 4 volumes of vapour. It re- quires for its solution 25 parts of boiling and 200 parts of cold water, while it dissolves in 2 parts of alcohol, and is also very solu- ble in ether. The general formula of the benzoates is R0,C14II503. The ben- zoates of potassa, soda, and ammonia, are very soluble in water, and crystallize with difficulty. The benzoate of lime is very soluble in hot water, while cold water retains only about of its weight of it. The benzoate of silver is prepared by double decomposition, by pouring a hot solution of nitrate of silver into a boiling solution of an alkaline benzoate, when the benzoate of silver Ag0,C14H503 is precipitated, during the cooling, in the form of colourless needles. Chlorine acts on benzoic acid when assisted by the rays of the sun, and produces chlorinated benzoic acid, retaining the principal properties and capacity of saturation of free benzoic acid, the same products being obtained by heating benzoic acid with the alkaline hypochlorites or with mixtures of chlorohydric acid and chlorate of potassa. Two chlorinated benzoic acids have been obtained in this manner: Monochlorinated benzoic acid C14H4C103,H0. Terchlorinated “ “ C14H2C1503,H0. Vinobenzoic Ether C4II50,C14H503. ' § 1528. In order to prepare this ether, 2 parts of alcohol, 1 part of ben- zoic acid, and 6 parts of concentrated chlorohydric acid are heated, in a dis- tilling apparatus, the liquid acid which distils being returned several times to the retort; when the benzoic acid is thus almost wholly converted into hen- zoic ether. But it is better to arrange the operation as represented in fig. 685: the mixture is placed over a water-bath in a flask A which is made to commu- nicate with a refrigerator so arranged as to allow the distilled liquid to gra- dually fall back again. The liquid is treated, first with water, and then with a weak solution of carbonate of soda to remove the free benzoic Fig. 685, 646 ESSENTIAL OILS. acid, after which the benzoic ether is dried by digesting it over chloride of calcium. Benzoic ether is a colourless liquid of an oleaginous consistence, boiling at 410°, and of the density 1.054 at 50°. The density of its vapour being 5.41, its equivalent corresponds to 4 volumes of vapour, and it is insoluble in water, but soluble in all proportions in alcohol. § 1529. By replacing, in the preceding operation, vinic by me- thylic alcohol, methylbenzoic ether* is obtained as an oily liquid, boiling at 226.4°. Metliylbenzoic Ether C2H30,C14H50g. § 1530. If vapour of anhydrous sulphuric acid be introduced into a dry and well-cooled flask containing benzoic acid, a semifluid mass is formed, which is afterward treated with water to dissolve the monohydrated sulphuric acid, and a peculiar acid, called sulphoben- zoic, while the benzoic acid is separated unchanged. The acid liquid is saturated with carbonate of baryta, when sulphobenzoate of baryta alone remains in the liquid. By adding chloroliydric acid, crystals of acid sulphobenzoate of baryta (BaO + HO), (C14I1403,S205) separate, which are redissolved in boiling water and again crystallized by cooling. Sulphobenzoic acid may be sepa- rated by decomposing a solution of this salt with sulphuric acid added by drops: it is very soluble in water, remains undecomposed even at 300°, and may be obtained in a crystalline form by evapo- ration. Sulphobenzoic acid forms two series of salts of which the general formulae are 2R0,(C14II403,S30)5 (R0+H0),(C14II40s,S205). It is therefore a bibasic salt. It will be seen that when benzoic acid C14HS03,H0 is treated with anhydrous sulphuric acid, 2 equivalents of the latter enter into the new compound, but only after having parted with 1 equivalent of oxygen, which has formed water with 1 equivalent of hydrogen given off by the benzoic acid; according to the equation Sulphobenzoic Acid (C14H403,S205),2H0. C14Hs03,H0+2S03=(CmH403,S20s),2H0. Nitrobenzoic Acid C14H4(N04)03,H0. § 1531. Dilute nitric acid does not act readily on benzoic acid, * More properly called benzoic mcther.— W. L. F. BENZOIC SERIES. 647 but if the fuming acid be used, and in great excess, the benzoic acid is dissolved with the disengagement of nitrous vapours, and the liquid deposits, on cooling, crystals of nitrobenzoic acid C14II4 (N04)03,H0, which is purified by recrystallizations. Nitrobenzoic acid is but slightly soluble in cold, but much more so in boiling water; and dissolves freely in alcohol and ether. If crystallized into benzoate of lime, it takes the formula CaO, C14H4(N04)03 + 2HO, and that of baryta, Ba0,C14H4(N04)03+4H0. From its composition it may be admitted that the molecule of nitrobenzoic acid C14II4(N04)03,H0 is merely that of benzoic acid C14II503,II0 in which 1 equivalent of hydrogen has been replaced by the compound (N04); and many cases will subsequently be met with in which the same substitution may be admitted. If a current of chlorohydric acid gas be passed through an alco- holic solution of nitrobenzoic acid, nitrobenzoic ether C411.0, C141I4- (NOJOj is formed, which separates in colourless crystals, fusible at 116.6°, and boiling at about 570°. § 1532. By digesting at a gentle heat 1 part of benzoic acid with 12 or 15 parts of a mixture, in equal proportions, of Nordhausen sulphuric acid and fuming nitric acid, we effect the substitution, in the molecule of benzoic acid C14H.03,H0, of 2 equivalents of the compound N04 for 2 equivalents of hydrogen, and obtain binitro- benzoic acid C14H3(N04)203,H0. Binitrobenzoic Acid C14H3(N04)203,H0. Bromobenzoic Acid C14H5Br04,H0. § 1533. By introducing into a very dry bottle benzoate of silver, and bromine contained in an open tube, and leaving it to itself after having closed the bottle, the benzoate of silver absorbs the vapours of bromine, bromide of-silver being formed, while the ben- zoic acid combines, at the same time, with the equivalent of oxygen given off by the silver and with 1 equivalent of bromine. By treating it with ether, only the new acid C14H5Br04,H0, dissolves, which remains in the form of a crystalline mass. It is important to remark that bromobenzoic acid has not preserved the constitution of benzoic acid, but that it is formed by the addition, and not the substitution, of new elements. § 1534. When moist chlorine is passed through oil of bitter almonds, crystals insoluble in water, but very soluble in alcohol, are, after some time, developed in it. The composition of this substance may he represented by the formula (2C14H603,C14H503); 3 mole- cules of the oil being grouped into one, after one of these molecules Benzoate of Oil of Bitter Almonds. 648 ESSENTIAL OILS, has been converted into benzoic acid, by the oxidizing action of the moist chlorine. Its composition would therefore be analogous to that of acetal (§ 1368) and of methylal, (§ 1432.) Benzoin C14II602. § 1535. If crude oil of bitter almonds be shaken with an alco- holic solution of potassa, the oil sets, in a few minutes, into a crys- talline mass; the presence of a certain quantity of cyanohydric acid being necessary to the transformation. The new substance is crystallized by purifying it in alcohol. This substance, to which the name of benzoin has been given, presents exactly the same composition as the oil of bitter almonds, melts at 248°, and may he distilled without change. Though insoluble in cold, it is slightly soluble in boiling water, and rather freely so in alcohol. Melted with hydrate of potassa, it yields benzoate of potassa. If it be left, for a long time, with an aqueous solution of ammonia, a white powder is formed, nearly insoluble in water, alcohol, and ether, which has been called benzoinamide, and presents the formula C42H18Na: it may be supposed to be formed by means of 3 equivalents of ben- zoin 3(Cj4H0O2) and 2 of ammonia, from the equation 3C14H802+2NII3=C42H18N2+6H0. § 1536. Benzoin dissolves when heated with nitric acid, and a new substance of the formula C14II50a, separates after cooling, called benzil, which therefore results by the simple abstraction of 1 equivalent of hydrogen from the benzoin. The same compound is obtained when chlorine is caused to act upon benzoin heated to fusion, when the equivalent of hydrogen is disengaged in the state of chlorohydric acid. Benzil is crystallized by purifying it in al- cohol, and is a slightly yellowish substance, melting at about 194°. Benzil is not changed, even at the boiling point, by an aqueous solution of potassa, while in contact with an alcoholic solution of the same alkali, it abstracts 1 equivalent of water, and is converted into an acid, called benzilic, of the formula which results from the combination of the elements of 2 equivalents of water with 2 equivalents of benzil: C28H1206=2C14HA+2H0. The same acid is formed by heating benzoin with an alcoholic solution of potassa, saturating the hot solution with chlorohydric acid, and allowing it to cool, when benzilic acid is deposited in crys- tals. It melts at 248°, and decomposes at a higher temperature, giving off a certain quantity of benzoic acid. Benzine C12II6 § 1537. When benzoic acid C14II503,H0 is heated with 3 times its weight of hydrate of lime, carbonate of lime is formed, while a BENZOIC SERIES. 649 colourless, very volatile liquid, of the formula C13H6, and called benzine, distils over, which is rectified over quicklime. The reaction is expressed by the equation C14HA,H0=2(Ca0,C03)+C12H6. Benzine is also formed when benzoic acid in vapour is passed through a tube filled with fragments of pumice-stone and heated to redness ; benzine and carbonic acid alone being formed: C14H503,H0=C12H6+2C02. Benzine is also produced by the decomposition of a great number of organic substances by heat: thus, a considerable proportion of it is found in the volatile oils formed in the manufacture of illuminat- ing gas. Benzine boils at 186.8°, and its density is 0.85, while that of its vapour is 2.38, its equivalent corresponding to 4 volumes of vapour. At 32° it sets into a crystalline mass, which melts only at 44.6°; and it is insoluble in water, but very soluble in alcohol and ether. Benzine is easily acted on by dry chlorine, when exposed to the rays of the sun; and if it be poured into a large well-dried bottle, filled with chlorine, and the bottle be exposed to the sun, it becomes filled with white vapours, while the sides are covered with white crystals of the formula C12H6C1. The behaviour of this substance with an alcoholic solution of potassa leads us to write its formula C12H3C1s,3IIC1 ; the solution, in fact, decomposing it by abstracting 3HC1; while, if the liquid be diluted with water, an oily and co- lourless liquid, insoluble in water, and of the formula Cl2II3Cl3, separates, the density of the vapour of which being 6.37, its equiva- lent corresponds to 4 volumes. This is therefore Ur chlorinated benzine, and the crystalline substance formed by the direct action of chlorine on benzine may be regarded as a ter chlorinated triclilo- rohydrate of benzine. This same decomposition of the crystalline compound takes place when it is distilled several times alone, or still better, over lime. Bromine yields with benzine an analogous product C14H3Br3, 3HBr, which, with the alcoholic solution of potassa, also produces terbrominated benzine C14H3Br3. § 1538. Common nitric acid acts but feebly on benzine, while if it be heated with the fuming acid, it dissolves, and an addition of water precipitates from it a yellowish liquid C12H5(N04), nitroben- zine. It may be granted that this substance is formed by the sub- stitution of 1 equivalent of the compound N04 for 1 equivalent of hydrogen of the benzine. Nitrobenzine solidifies at 32°, and melts only at 37.4°, while it boils at 415.4° without change. By causing a large excess of fuming nitric acid to act for a long time on benzine, we can succeed in replacing 2 equivalents of hy- drogen by 2 equivalents of the compound (NOJ, and producing 650 ESSENTIAL OILS. binitrobenzine C12H4(N04)2, which, by the addition of water, is precipitated in the form of a crystalline powder. By crystallization in alcohol, it is obtained in large brilliant lamellae. By subjecting nitrobenzine and binitrobenzine to certain re- ducing agents, they are converted into two very remarkable sub- stances: anilin C12H7N, and nitranilin C12H6(N04)N, which are true volatile organic bases. Sulphobenzinic acid C12H5,S205,HO, and Sulphobenzine C12H5,S02. § 1539. Benzine is not appreciably acted on by ordinary sul- phuric acid, while the anhydrous acid dissolves it with elevation of temperature, a viscous liquid being formed, which, when treated with water, deposits a crystalline precipitate, sulphobenzine, and pro- duces a solution containing, with ordinary sulphuric acid, a new acid, called sulphobenzinic. Sulphobenzine should be purified by crystallization in alcohol, after which it is a colourless substance, melting at 212°, and boiling at about 750°, without change. Its formula is C14H6,S02, and the following equation expresses the reaction which produces it: C13H8+2S03=C12H5,S02+S03,H0. By saturating the acid liquid with carbonate of baryta, the free sulphuric acid is precipitated, and a solution of sulphobenzinate of baryta is obtained. By pouring sulphate of copper into the latter, this salt is converted into sulphobenzinate of copper, which crystal- lizes readily according to the formula CuO,(C12H5,Sa05). When decomposed by sulfhydric acid, it produces isolated sul- phobenzinic acid, a very acid liquid which may by crystallized by evaporation. Benzone C13H50. § 1540. When benzoate of lime is subjected per se, without any addition of an excess of hydrated lime, to the action of heat, with the benzine, two other products are formed: benzone, and a crystal- line substance of which the nature is not yet known. As these two latter substances boil at much higher temperatures than benzine, they are easily separated from it, by heating the mixture to 428°, at which temperature the benzine is wholly volatilized. The residue being cooled to — 4°, nearly all the solid substance is deposited, and the benzone, which remains fluid, may be decanted. Benzone is an oily liquid of the formula C13H50, the reaction from which it arises being expressed by the equation Ca0,C]4Hs03=Ca0,C02+C13HJ0. § 1541. Bitter almonds do not contain the oil of bitter almonds AMYGDALIN C40Ha,N,02a. BENZOIC SERIES. 651 ready formed, but in its stead a very remarkable substance, called amygdalin, which is converted in the oil by the action of a second substance, called emulsin. In order to prepare amygdalin, bitter almonds are subjected to very heavy pressure, when a fatty, colour- less, non-volatile oil exudes, called oil of sweet almonds, because it also exists in this species of almond. The balance of the oil is then removed by treating the crushed cake several times with ether; after which the pulp is boiled twice with alcohol, to dissolve the amyg- dalin, the greater portion of the alcohol being afterward separated by distillation ; when the residue deposits the amygdalin, on cooling, in crystalline lamellae. Amygdalin dissolves readily in water, and is deposited from it in beautiful crystals, of the formula C40II27N3033 + 6110; the 6 equivalents of water being disengaged at 248°. It dissolves freely in boiling alcohol, but is nearly insoluble in cold alcohol. Amygdalin rotates toward the left. When heated with a mixture of peroxide of manganese and sul- phuric acid, it is decomposed into ammonia, carbonic acid, formic acid, and oil of bitter almonds, by which process it yields more than one-half of its weight of oil. § 1542. By pouring into a solution of amygdalin in 10 parts of water, an emulsion of sweet almonds, cyanohydric acid and oil of bitter almonds, readily known by their smell, are immediately formed. The name of synaptase has been given to the active sub- stance effecting the transformation, which exists both in sweet and in bitter almonds. In order to prepare synaptase, sweet almonds, from which the oil has been previously expressed, are treated with water, and to the solution is added, first, acetate of lead in order to precipitate a gummy matter, then acetic acid to coagulate the albumen, and lastly, a large quantity of alcohol, after having pre- cipitated the excess of lead by sulfhydric acid; when synaptase is deposited in flakes, which change, on cooling, into a brittle, gum- like substance. The action of synaptase on amygdalin may be com- pared to that of yeast on sugars, its analogy with the phenomena of fermentation being perfect, while the products of the reaction are complicated, and a considerable quantity of sugar is formed. One part of synaptase is sufficient to decompose 10 parts of amyg- dalin. Synaptase is soluble in water, but it coagulates at 140°, and then loses all its power over amygdalin. In order to produce perfect transformation, the amygdalin must be dissolved in a large quantity of water. From this it will be seen that, in order to prepare the oil of bitter almonds, the pulp must not be immediately distilled with water, but must be digested in the cold, or better still, at a temperature of 86°, long enough to allow the amygdalin to be wholly decomposed by the synaptase. The essential oil and the cyanohydric acid are then separated by distillation. 652 ESSENTIAL OILS. ESSENTIAL OIL OF SPIRAEA ULMARIA, AND THE SALICYLIC SERIES. § 1543. By distilling the flowers of the meadow-sweet [spirsea ulmaria) with water, an essential oil C14II604 is obtained, accompanied by a carburetted hydrogen, isomeric with oil of terpentine, and a crystalline substance analogous to camphor. The oil possesses acid properties, and has hence been called spiroylous acid, and salicylous acid from its correlations with a neutral substance, salicin, which exists in the bark of the willow. Salicin treated with a mixture of sulphuric acid and bichromate of potassa yields, in fact, a large pro- portion of oil of spiraea; and we shall, therefore, commence with the description of this substance, which it is impossible to separate from the series of salicylic products. Salicin C2flH18014. § 1544. In order to prepare salicin, the bark of the willow is ex- hausted by boiling water, and litharge is added to the concentrated solution until the liquid is deprived of colour. The oxide of lead is then partially precipitated by sulphuric acid, the precipitation being finished by sulphide of barium, added by drops to prevent its being in excess. The filtered liquid is evaporated, and then deposits impure salicin, which is purified by dissolving it in water, discolouring it by animal black and recrystallizing it. Salicin crystallizes in white inodorous aciculae of a bitter taste, and without any reaction on vegetable colours. It loses nothing of its weight at 212°, melts at 248°, and is decomposed at a higher temperature. 100 parts of water, at the ordinary temperature, dis- solve 5.6 of salicin, while boiling water dissolves it much more freely, and alcohol also dissolves it, but it is insoluble in ether. Salicin polarizes toward the left. Cold concentrated sulphuric acid dissolves salicin, and it becomes of a blood-red colour; which reaction is a test of salicin in the bark of the willow and poplar tree. Dilute sulphuric and chlorohydric acids decompose salicin at the boiling point into glucose C13II13013, and a resinous substance, called saliretin C14IT602, according to the equation C26Hi8Om— C„HuOI!1+ C14H603. § 1545. Nitric acid forms, with salicin, very various products, ac- cording as it is more or less dilute. If 1 part of salicin be treated with 10 parts of nitric acid at 20° Baumd, and the mixture be left to itself for 1 or 2 days, shaking it frequently to hasten the solu- tion of the salicin, a yellow liquid is obtained, which deposits a white substance, crystallized in small needles, and called helicin. It is very soluble in hot water, but scarcely so in cold, and its formula is Cj6H]6014+3H0, the 3 equiv. of water being given off at 212°, with- out alteration, while it melts at about 347°. A solution of potassa, SALICIC SERIES. 653 baryta, or ammonia decomposes it into glucose and oil of spirrna C14H604: C26H16014+2H0=C12H12012+C14Hb04. Chlorine acts readily upon helicin in the presence of water, form- ing monochlorinatecl helicin which is decomposed by a solution of potassa into glucose ClaII130la, and into monochlorinatecl oil of spirsea C14tI.C104. Monobrominated helicin is prepared in the same manner, and undergoes an analogous transformation with potassa. Beer-yeast and synaptase exert a true fermenting action on heli- cin, decomposing it into glucose and oil of spiraea, and producing an analogous effect on monochlorinated helicin, which they decom- pose into glucose, and monochlorinated oil of spiraea. When the nitric acid is more concentrated, and it is heated, the salicin is converted into oxalic acid, and an acid which we shall describe under the name of picric acid. Chlorine does not act so energetically on salicin except in the presence of water, when chlorinated salicins are formed, which com- bine with a certain quantity of water, and Ave thus have successively Monochlorinated salicin C26H17C10ll+4H0, Bichlorinated “ C fiH16Cl3014+2H0, Trichlorinated “ C26H1SC13014+2H0. Chromic acid, or a mixture of sulphuric acid and bichromate of potassa, converts salicin into salicylous and formic acids. § 1546. Beer-yeast and albuminous substances do not act upon salicin, while synaptase exerts over it a very remarkable power, which should be classed among the phenomena of fermentation, since it decomposes it into glucose, and into a new substance, called saligenin C14H804, according to the reaction 8014+2HO—C12II12012+C14H804. In order to effect this transformation, 50 parts of powdered salicin, diffused in 200 parts of distilled water, are treated with about 3 parts of synaptase, when the whole is introduced into a bottle, which is well shaken, and heated in a water-bath to 104°. In 10 or 12 hours the transformation is completed, and the greater portion of the saligenin is deposited in the form of small rhombohedral crystals. In order to extract the remainder, the liquid is shaken with its volume of ether, which takes the saligenin from the water, and deposits it on evaporation. Glucose remains in the aqueous solution, and may be easily recognised by its optical properties, or by causing it to ferment with yeast. Saligenin dissolves in all proportions in boiling water, but it re- quires 15 parts for solution at the ordinary temperature, and it is very soluble in alcohol and ether, without possessing rotatory power. It melts at 179.6°, while the prolonged action of heat converts it into 654 ESSENTIAL OILS. saliretin, which transformation is also very rapidly effected by dilute mineral acids. A mono, bi, and trichlorinated saligenin has been obtained by causing synaptase to act on mono, bi, and trichlorinated salicin; which fact is remarkable, because it shows that the substitu- tion of chlorine for hydrogen in salicin does not prevent fermenta- tion. Salicylous Acid C14Hs03,H0. § 1547. We have said (§ 1543) that salicylous acid is merely the oil extracted from the flowers of the meadow-sweet, by distillation . with water. It does not exist in them ready formed, for the flowers may be exhausted by alcohol without obtaining a trace of it; but it is produced during the distillation of the flowers with water; probably by a phenomenon of fermentation analogous to that producing oil of bitter almonds, when the pulp of the almond is digested with tepid water. The distillation of the flowers of the meadow-sweet with water yields, in addition to salicylous acid, an essential oil, isomeric with oil of terpentine, and a volatile substance which crystallizes. But by shaking the distilled product with caustic potassa, the sali- cylous acid alone combines with the alkali, and, if the whole be again distilled, the volatile oil and crystalline substance volatilize with the water, while the salicylite of potassa remains in the retort. The salt being decomposed by sulphurous acid, and the distillation re- commenced, the salicylous acid, set free, condenses in the receiver. It is more easy to obtain salicylous acid from salicin by introduc- ing a mixture of 3 parts of the latter substance with 3 parts of bi- chromate of potassa and 24 parts of water into a retort, and shak- ing it frequently until complete solution is effected, when 4J parts of concentrated sulphuric acid, dissolved in 12 parts of water, are added, and the whole is again shaken. Reaction gradually ensues, and when it appears to be terminated, the temperature is gradually raised, and the distilled products are collected in a well-cooled re- ceiver. The latter are composed of an aqueous solution, slightly acid, containing a small quantity of formic acid, and a reddish oil which collects at the bottom of the aqueous liquid. The oil is de- canted and digested for 24 hours over chloride of calcium, and then rectified anew, by which means perfectly pure salicylous acid is obtained. Salicylous acid, or the essential oil of spiraea ulmaria, is a colour- less liquid, assuming a red tinge on exposure to the air, of an odour similar to that of the oil of bitter almonds, and staining the skin yellow, the stains disappearing as rapidly as those of iodine. It boils at 384.8°, and its density at 55.4° is 1.173, while the density of its vapour is 4.27, and its equivalent C14H503,H0 is represented by 4 volumes. It has no rotatory power. It is nearly insoluble in water, but dissolves in all proportions in alcohol and ether; and although its solutions do not redden tincture of litmus, they will SALICIC SEKIES. 655 decompose the alkaline carbonates, even when cold. It is important to remark that the formula and density of vapour of salicylous acid is the same as that of benzoic acid, furnishing a curious example of isomerism. Salicylous acid forms two compounds with potassa; and salicylite of potassa K0,C14H503+2H0 is obtained as a yellow crystalline mass when salicylous acid is added to a concentrated solution of potassa. By dissolving it in absolute alcohol, the salt is deposited in crystalline lamellae of a golden yellow colour. By means of • this salt, the salycylites of baryta, lime, zinc, lead, mercury, and silver can be prepared by double decomposition. The aqueous solu- tion of salicylite of potassa is readily decomposed, and yields formi- ate of potassa and a salt of potassa formed by a black substance C20H8O]0, to which the name of melanic acid has been given. By dissolving salicylate of potassa in hot alcohol, and adding an additional quantity of salicylous acid, the liquid, on cooling, depo- sits colourless aciculae of a salt of the formula (KO-f H0),2C14H503, which may be called bisalicylite of potassa, and is more fixed than the neutral salicylite. Salicylous acid absorbs ammoniacal gas, and is converted into yellow and crystalline salicylite of ammonia (NH3,II0),C14HJ03, the same compound being formed when salicylous acid is dissolved in an aqueous solution of ammonia; while, if the acid be first dissolved in 3 times its volume of alcohol, and ammonia be added by drops, yel- low aciculae are formed, which readily dissolve when the temper- ature is raised. On cooling, the new product is deposited in crystals of a golden yellow colour, with the formula C43H18N206=C42IT14 (NH2)206, ensuing from the following reaction: 3(C14H503, H 0)+2NH3=C42H14(NH2)206+6H0. It has been called salhydramide, and is insoluble in water, even at the boiling point. Salicylous acid absorbs chlorine, even when cold, and the reaction takes place with elevation of temperature, chlorohydric acid being disengaged, and the oil at last becoming solid. By dissolving it in alcohol, crystalline, colourless, and pearly lamellae are deposited, of monochlorinated salicylous acid C14H4C103 + H0, which forms well marked salts, of the general formula R0,C14H4C103, and yields, with ammoniacal gas, monochlorinated salicylamide C42HUC13(NH2)206. Bromine forms a monochlorinated salicylic acid C14H4Br03,H0. If salicylous acid be heated with nitric acid of medium strength, hyponitric acid is disengaged, and the oil is converted into a crys- talline mass, which is purified by dissolving it in boiling water after having washed it with a small quantity of cold water. The solution deposits, by spontaneous evaporation, yellow prismatic crystals of nitrosalicylous acid C14II4(N04)03,H0, which combines with bases, 656 and forms salts possessing detonating properties by an elevation of temperature. ESSENTIAL OILS. Salicylic Acid C14U5Os,HO. § 1548. When salicylous acid is heated with an excess of hydrate of potassa, hydrogen is disengaged; and if the operation be arrested at the moment of the cessation of the evolution of gas, the mass be dissolved in water, and an excess of chlorohydric acid added, crys- tals are precipitated, wdiich are purified by recrystallization from boiling water. They are formed by a new acid, salicylic C14IIAOs, II0,. which arises from the following reaction: C14H503,H0+K0,H0=K0,C14H505+2H. This acid results from the simple combination of 1 equivalent of salicylous acid with 2 equivalents of oxygen. Salicylic acid dissolves in boiling water, but is nearly insoluble in cold water: it dissolves freely in alcohol and ether; volatilizes without change, and then produces crystals resembling those of benzoic acid: it reddens litmus and decomposes the carbonates. It has no action on polarized light. Bromine and chlorine act on it readily, and produce mono and bibrominated, mono and bichlo- rinated salicylic acids. Treated with fuming nitric acid, salicylic acid is converted into a reddish resinoid mass, which is to be washed with cold and dissolved in boiling water: yellowish, fusible, and volatile aciculse, of nitro- salicylic acid C14H4(N04)05,H0 are deposited from the solution. Methylosalicylic Ether C3H30,C14H50s. § 1549. By distilling a mixture of 2 parts of methylic alcohol, 2 parts of salicylic acid, and 1 part of sulphuric acid, this compound ether is readily obtained, as a colourless or slightly yellowish liquid, boiling at 428°, and of the density 1.18 at 50°, the density of its vapour being 5.42, and its equivalent C2H30,C14H505 corresponding to 2 volumes of vapour. It is nearly insoluble in water, but dis- solves readily in alcohol and ether. Methylosalicylic ether exists ready formed in a native essential oil, called wintergrcen, and obtained from the gaultheria procumbens. The oil of gualtheria comes principally from New Jersey, where the plant grows in great abundance. By distilling the oil, there is dis- engaged, first a carburetted hydrogen isomeric with oil of terpen- tine, and subsequently methylosalicylic ether.* Methylosalicylic ether is a true acid, which combines with potassa, forming a salt which crystallizes in pearly spangles. But if an excess of potassa be used, particularly when assisted by heat, the * The interesting discovery of the artificial formation of this substance, by Ca- hours, was first indicated by W. Proctor, of Philadelphia, who first proved that the oil of gaultheria belonged to the salicylic series.—J. C. B. SALIC1C SERIES. 657 ether undergoes the ordinary decomposition of compound ethers, and is converted into alcohol and salicylic acid. Chlorine and bromine readily act on methylosalicylic ether, and yield chlorinated and brominated products: Monochlorinated methylosalicylic ether C2H30,C14H4C10S, Bichlorinated “ “ ......C2H30,C14H3C1205, Monobrominated “ “ C2H30,C14H4Br0s, Bibrominated “ “ C2H30,C14H3Br202. With a hot solution of potassa, these substances are decomposed into methylic alcohol and mono or bichlorinated or brominated salicylic acid. Fuming nitric acid converts methylosalicylic ether into nitrome- thylosalicylic ether C2H30,C14II4(N04,)0J. By introducing into a well-corked bottle 1 volume of methylo- salicylic ether, and 5 or 6 volumes of a concentrated solution of ammonia, the ether disappears after some time, and by then eva- porating the liquid and distilling the residue, a yellow mass is ob- tained, which may be converted into crystalline aciculse, by solution in boiling water. The formula of this substance is C14H5(NH2)04, and it is generated from anhydrous salicylic acid, according to the following equation: C14H505+NH3=C14H5(NH3)04+H0. This substance, which has been called salicylamide, is soluble in boiling water, but nearly insoluble in cold water, and dissolves readily in alcohol and ether. It volatilizes without alteration, and with acids regenerates ammonia and salicylic acid. By causing ammonia, under similar circumstances, to act on chlorinated, bro- minated, or nitric products, derived from methylosalicylic ether, mono and bichlorinated, mono and bibrominated, and nitric salicy- lamides are obtained. Lastly, by allowing methylosalicylic ether to fall on anhydrous lime or baryta, carbonates of these bases, and a new substance C14H802, called anisole, are formed, the reaction being expressed by the following equation : C2H30,C14HA+2Ba0=2(Ba0,C02) + C14H802. Anisole is a colourless, very fluid liquid, of an agreeable aromatic odour, boiling at 302°, insoluble in water, but very soluble in alcohol and ether. Vinosalicylic Ether C4HsO,C14H5Os. § 1550. By distilling a mixture of 2 parts of absolute alcohol, Im- part of salicylic acid, and 1 part of sulphuric acid, we obtain vino- salicylic ether, which, like its analogue of the methylic series, com- bines with bases. It also forms salicylamide with ammonia, and produces, with chlorine, bromine, and nitric acid, chlorinated, bro- 658 ESSENTIAL OILS. minated, and nitric ethers, corresponding to those formed by me- thylosalicylic ether. OIL OF CINNAMON AND THE CINNAMIC SERIES. § 1551. Oil of cinnamon is found in commerce, being imported from Ceylon and China. That from China is more esteemed, be- cause it lias an agreeable smell, peculiar to cinnamon-bark, while the Ceylon oil has a mixed smell of cinnamon and bed-bugs, and its composition appears to be more complicated. By digesting powdered cinnamon-bark with water for 12 hours, and then saturat- ing the water with sea-salt, and subjecting the whole to distillation, a milky water passes over, which deposits an essential oil, of a more or less reddish yellow, and resembling the cinnamon-oils of com- merce. Oils of cinnamon appear to be mixtures of an essential oil, to which the name of hydruret of cinnamyl has been given, and which we shall consider as the oil of cinnamon, properly so called, with other oils which have not yet been studied. The oil of cinna- mon, properly so called, is separated by agitating the oil of cinnamon of commerce with concentrated nitric acid, Avhen, in a few hours, long prismatic crystals are formed, which are separated and pressed between folds of tissue-paper. Water readily decomposes them, and yields an essential oil C13II802, which is regarded as pure oil of cinnamon ; the water then containing nitric acid. The crystals, which may be considered as a nitrate of the oil of cinnamon, pre- sent the formula C18H802,N05-fHO. Pure oil of cinnamon is a colourless, oleaginous liquid, which be- comes perfectly solid with nitric acid, and reproduces the crystalline compound just mentioned. It absorbs chlorohydric acid gas, and forms a compound C18II802,IIC1. Chlorine acts powerfully upon it, and, if its action be exhausted by heat, and the product distilled in a current of chlorine, we obtain white acicular crystals of quadri- chlovinated oil of cinnamon C18II4C1402, called also chlorocinnose. Oil of cinnamon absorbs the oxygen of the air, and is converted into a peculiar substance C18H703,II0, called cinnamic acid, which may be regarded as being derived from the oil ClsII803, by the substitution of 1 equivalent of oxygen for one of hydrogen.* The acid is also formed when oil of cinnamon is treated with hydrate of potassa, hydrogen being disengaged; while, if the action of the potassa be prolonged, benzoate of potassa K0,C14H503 only is found in the liquid. Concentrated boiling nitric acid converts oil of cinnamon into oil of bitter almonds and into nitrobenzoic acid. * This view is certainly incorrect, because oxygen will not replace hydrogen. The oil of cinnamon simply gains 2 equivalents of oxygen, while 1 equivalent of water parts from it and becomes basic.— IF. L. F. CINNAMIC ACID. 659 Cinnamic Acid C18II703,II0. § 1552. We have said that cinnamic acid is formed by the oxida- tion of oil of cinnamon; but it exists already formed in balsams of Tolu and Peru, from which it is generally extracted by running the the balsam of Peru into milk of lime, which is constantly stirred, when the resins of the balsam combine with the lime and produce insoluble compounds. By treating the whole with boiling water, the cinnamate of lime only is dissolved, and crystallizes on the cooling of the liquid; and by decomposing a boiling solution of cinnamate of lime with chlorohydric acid, the cinnamic acid is deposited, on cooling, in the form of pearly, colourless lamellae, which melt at 264.2°, and boil at about 570°. The alkaline and alkalino-earthy cinnamates, are soluble in water, while the majority of the other metallic cinnamates are insoluble; and their general formula is R0,C18H703, when they contain no water of crystallization. By causing chlorohydric acid gas to act on cinnamic acid dis- solved in absolute alcohol or in anhydrous wood-spirit, cinnamic ethers C4H50,C18II703 and C2H30,C18H703 are obtained. By heating 1 part of cinnamic ivith 8 parts of concentrated nitric acid, a spongy mass results, which is to be washed with water, and afterward dissolved in boiling alcohol. The alcoholic liquid depo- sits, on cooling, acicular crystals, fusible at a high temperature, of nitrocinnamic acid C18H6(ISr04)03,H0. Cinnamen C16II8. § 1553. When vapours of cinnamic acid are passed through a glass tube heated to a dull-red, carbonic acid is disengaged, with a carburetted hydrogen, cinnamen C16H8, which condenses in the form of a colourless liquid: C18H703, HO=C16H8+2 C 02. The same substance is obtained by decomposing cinnamate of cop- per by heat, or subjecting to dry distillation certain resins, particularly storax, a kind of balsam found in commerce. The best method of preparing cinnamen consists in mixing 10 kilog. of storax with 3J kilog. of carbonate of soda, and distilling the whole in an alembic with a sufficient quantity of water, when a milky water passes over, which by resting, parts with the cinnamen, which floats on its sur- face. Storax thus yields rather more than of its weight of cin- namen ; and the oil obtained is left for some time on chloride of calcium, and then distilled. Cinnamen is a colourless liquid, of a penetrating odour, of the density 0.95 at 32°, and boiling at 294.8°. When heated to 390° in a glass tube hermetically closed, it is converted into an isomeric substance, metacinnamen, which is solid, and insoluble in water, al- 660 ESSENTIAL OILS. cohol, and ether. Heated to distillation, metacinnamen again passes into the state of cinnamen. Chlorine, when cold, reacts upon cinnamen, and converts it into a viscous fluid, of the formula C16II8C12, but which we shall write C16H7C1,HC1. Distilled over quicklime, or treated with an alcoholic solution of potassa, this compound yields monoclilorinated cinna- men C16H7C1. Monobrominated cinnamen C16H7Br is also ob- tained, as well as its bromoliydrate C16H7Br,HBr. Balsams of Peru. § 1554. Two species of balsam of Peru are found in commerce: a liquid balsam, which alone has been properly studied; and a solid and nearly black balsam, which appears to be a modification of the first. Balsam of Peru is dissolved in alcohol at 96.8°, and an al- coholic solution of potassa added, when the resin contained in the balsam combines with the potassa, with which it forms a compound nearly insoluble in water, while the cinnamate of potassa remains in solution. By diluting the alcoholic liquid with wrater, the cinna- mate of potassa remains in solution, while a complex oil separates, retaining a small quantity of resin. This is treated with oil of naphtha, which leaves the resin, and dissolves the oil; and the latter is cooled in a refrigerating mixture, and treated with weak alcohol, equally cold. An oily portion, which is cinnamein, is thus ex- tracted, and the residue is dissolved in boiling alcohol, which depo- sits a crystalline substance, metacinname'in. Metacinname'in is a solid, very fusible substance, insoluble in water, but readily soluble in alcohol and ether, isomeric with oil of cinnamon, and being changed by hydrate of potassa into cinnamic acid, with disengagement of hydrogen. Cinnamein is a liquid, which does not volatilize without change; and a concentrated solution of potassa decomposes it, by prolonged contact, into cinnamic acid and a new oily liquid, lighter than wa- ter, called peruvin C18H]202. The composition of cinnamein corre- sponds to the formula C54H2608, and it may be represented by 2 equivalents of anhydrous cinnamic acid, and 1 equivalent of peru- vin, according to the equation C54H26O8=2(C18H7O3)+018H12O2, Balsam of Peru may therefore be considered as formed of cinna- mein, metacinname'in, cinnamic acid, and resinous substances. Balsam of Tolu. § 1555. Balsam of Tolu is composed of resin, cinnamic acid, and a carburetted hydrogen, isomeric with oil of terpentine, and called tolen. This balsam, heated with a solution of caustic potassa, yields benzoic acid, which is probably formed at the expense of the resin. Tolen is a colourless liquid, boiling at about 320°. COUMARIN. 661 COUMARIN C18H,04. - § 1556. The name of coumarin has been given to a crystalline odoriferous substance extracted from the Tonka bean, but which appears to exist in the flowers of several plants: thus, its existence has been detected in the flowers of the melilot, and the sweet wood- ruff, called waldmeister by the Germans, who use it in the prepara- tion of an agreeable beverage, called maitrank. Coumarin is pre- pared by digesting bruised Tonka beans with alcohol at 96.8°, when the alcoholic liquor, subjected to distillation, yields a syrupy resi- due, which, on cooling, sets into a crystalline mass. This is dis- solved in boiling water, and the liquid being discoloured by animal black, the coumarin separates in white crystalline aciculge during 'the cooling. Coumarin melts at 122°, and boils at 518°, without any change, and its smell is agreeably aromatic, while its vapours exert a pow- erful action on the brain. It dissolves freely in boiling water, but is almost wholly deposited from it on cooling. It dissolves in cold monohydrated nitric acid, with evolution of heat; and if the liquid be then diluted with water, a cheesy precipitate is formed, which dissolves in boiling alcohol, and separates again, on cooling, in small crystalline aciculae. It is nitrocoumarin C18H5(N04)04, melting at 838°, and then subliming without alteration in white and pearly crystals. If the action of the nitric acid be prolonged, the couma- rin is converted into trinitrophenic acid C12H2(N04)03,H0, which shall hereafter be described. Coumarin dissolves in a weak solution of potassa, and is preci- pitated from it without change when the alkali is saturated with an acid; while, if the solution is concentrated, and it be boiled, adding some pieces of hydrate of potassa, coumaric acid C18II705,II0 is formed; and if the temperature be greatly raised, hydrogen is dis- engaged and salicylic acid formed at the same time. The alkaline substance, treated with water, and then supersaturated with chloro- hydric acid, deposits coumaric acid, wilich is washed with cold wa- ter, to dissolve the salicylic acid which may have been precipitated with it, and then dissolved in ammonia, which leaves the coumarine unchanged. The ammoniacal liquid is boiled to drive off the excess of ammonia, when nitrate of silver is added, effecting a precipitate of coumarate of silver, wdiich, with chlorohydric acid, yields free coumaric acid, removable by means of ether. Coumaric acid is a white crystalline substance, very soluble in alcohol and ether, dissolving freely in boiling, but nearly insoluble in cold water, and melting at about 374°. The general formula of the coumarates is R0,C18H705, from which it will be seen that an- hydrous coumaric acid only differs from coumarin by the addition of 1 equivalent of water. 662 ESSENTIAL OILS. § 1557. By distilling aniseed with water, a slightly yellowish essen- tial oil is obtained, possessing the characteristic odour of the seed, and which, at a low temperature, consolidates almost wholly into a crys- talline mass. This mass is pressed between tissue-paper, when a liquid portion, of which the nature is not yet known, separates ; and it is redissolved in alcohol, which deposits, on evaporation, white crystalline lamellae, fusible at 64.4°, and boiling at about 428°. This substance is called concrete oil of aniseed, and its formula is C20H12O2. When made liquid by heat, it rotates to the left. Oil of aniseed absorbs chlorohydric gas and forms a compound C20II12O2,21ICl; while chlorine acts upon it and produces compounds derived by substitution : thus, A trichlorinated oil C20H9Cl3O2 And a quadrichlorinated oil C20II8Cl4O2 have been separated. With bromine, a tribrominated oil C20H9Br3O2, and, with nitric acid, the binitric oil C20H10(NO4)2O2, have been obtained. When oil of aniseed is heated with dilute nitric acid, a reddish oil falls to the bottom of the acid liquid, by distilling which, after having washed it with water, two substances are collected; one being crystalline, and a new acid, called anisic C16H705,H0; and the other liquid, and consisting of a neutral substance C16H804, to which tHe name of liydruret of anisyle has been given. It will be seen that anisic acid may be considered as resulting from the substitution of 1 equiv. of oxygen for 1 equiv. of hydrogen,* in the molecule of liydruret of anisyl, and there exists, therefore, between these two substances, the same relation as between oil of bitter almonds C14H602 and benzoic acid C,4H503,H0. The mixture of the two substances is treated with a weak solution of potassa, which dissolves the anisic acid, when the liydruret of anisyl is distilled in a current of carbonic acid gas. Hydruret of anisyl is a colourless gas, which absorbs the oxygen of the air, and is converted into anisic acid. Chlorine acts upon it and yields a monochlorinated product C16H7C104. When hydruret anisyl is dropped on melted caustic potassa, hydrogen is disengaged and anisic acid formed. Anisic acid crystallizes in white inodorous needles, which melt at 347°, and volatilize without change, and it dissolves readily in boil- ing water, alcohol, and ether. The general formula of its salts is ro,c16ii7o5. Chlorine and bromine form chlorinated and brominated anisic acids, while nitric acid forms first a nitranisic acid C16II6(N04)0., IIO. OIL OF ANISEED, AND THE ANISIC SERIES. * The hydruret of anisyl takes up 2 equiv. of oxygen and loses 1 equiv. of water, which becomes basic with the acid formed.— W. L. F. ANISEN. 663 and then, if a mixture of fuming nitric and concentrated sul- phuric acid be made to act upon it, it forms trinitranisic acid C16H4(N04)305,H0. Anisic acid yields anisole C14H802 by distilla- tion with caustic baryta: C16II705, HO+2BaO=2(BaO, C 02)+C14H802. Anisen or Benzoen C14H8. § 1558. These names have been given to a carburetted hydrogen C14H8, which is to anisic acid C16II705,H0 what benzin is to benzoic acid C14H503,H0. It is prepared by distilling the resin of balsam of tolu, and collecting the oil, which is again distilled at a temperature not exceeding 284°; the distilled portion being recti- fied several times over caustic potassa, and dried over chloride of calcium. It is a very fluid, colourless liquid, boiling at 226.4°, and its density is 0.87 at 64.4°; while that of its vapour is 3.26, its equivalent C14II8 corresponding therefore to 4 volumes of vapour. Chlorine acts readily upon anisen, and yields Monochlorintated anisen C14H7C1, Trichlorinated “ C14II5C13, Sesquichlorinated “ C14H2C16, as well as the following compounds, which these substances form with chlorohydric acid: C14H5C13,HC1, C14H5C13,2HC1, C14H5C13, 3HC1. § 1559. Nitric acid produces nitranisen C14H7(N04) and bini- tranisen C14H6(N04)2. Nitranisen yields, with sulfhydrate of am- monia, an alkaloid C14H9N which is called toluidin; the reaction being analogous to that which forms anilin with nitrobenzin, (§ 1538,) according to the equation C14H7(N04)+6(NH3,2HS)=C14H9N+6S+4HO+6(NH3,HS). Nitranisen must be dissolved in alcohol, and ammonia and sulf- hydric gas be successively passed through the liquid, which, after being left for some days to itself, and then gently heated, is again subjected to the successive action of ammoniacal and sulfhydric gas, and is finally saturated with chlorohydric acid, and evaporated to one-third, when the residue is distilled with caustic potassa. The toluidin condenses in the receiver in the form of a colourless oil, which, on cooling, sets into a crystalline mass. In order to purify it, oxalic acid is added, and it is treated with alcohol, which dissolves the oxalate of toluidin, and leaves the oxalate of ammonia. Oxa- late of toluidin is decomposed by caustic potassa, and the isolated toluidin coagulates in a crystalline crust on the surface of the liquid. Toluidin melts at 104°, and boils at about 390°, and its salts crystallize readily; their general formula being (C14H9N,IIO)A. 664 ESSENTIAL OILS. OIL OF CUMIN AND THE CUMINIC SERIES. § 1560. Cumin seed,* distilled with water, yields an essential oil composed of carburetted hydrogen C20H14, cymen, and another volatile oil C20II12O2, called cuminole. When oil of cumin is again distilled, the cymen passes over first, at about 392°, which tempera- ture is maintained so long as any thing passes over, when the re- ceiver is changed and the temperature raised by passing a current of carbonic acid gas through the retort: the cuminole then distils. Cuminole is a colourless liquid, having the smell of cumin, and an acrid and burning taste, and it boils at 428°; the density of its vapour being 5.24, and its equivalent C20H12O2 being represented by 4 volumes of vapour. It rapidly absorbs the oxygen of the air, and is converted into cuminic acid C2UHU03,H0, which transformation it readily undergoes when boiled with a concentrated solution of potassa, or when dropped into melted hydrate of potassa; hydrogen being disengaged in the latter case. Oxidizing reagents, such as nitric acid, chlorine in the presence of water, chromic acid, etc., also con- vert cuminole into cuminic acid. Chlorine acts on cuminole when exposed to diffused light, and produces monocldor mated cuminole C20HuC1O2; while bromine forms monobrominated cuminole C20HnBrO2. Cuminic Acid C20HnO3,IIO. § 1561. This acid is generally prepared by melting hydrate of potassa in a retort having a pointed tube fitted to its tubulure, through ■which the crude oil of cumin drops; when the cymen is not acted on, and distils without change, while the cuminole is decomposed by contact with the alkali, being converted into cuminic acid, which remains combined with the potassa. The alkaline mass being dis- solved in water, and heated to ebullition, an excess of chlorohydric acid is added, which precipitates the cuminic acid in flakes; and the latter, redissolved in alcohol, are transformed into beautiful prisma- tic tablets. Cuminic acid melts at a few degrees above 212°, and boils at about 500°, subliming without alteration in crystalline aciculse. Hot water dissolves it slightly, and deposits it entirely on cooling, while it dissolves freely in alcohol and ether. The general formula of the cuminates is RO,C2oHu03. Cymen C20II14. § 1562. We have described (§ 1560) the best method of separat- ing cymen from crude oil of cumin. It is a colourless liquid, of an agreeable odour, resembling that of lemon; it boils'at 347°, and * The seed of cuminum cyminum.— W. L. F. EUGENIC ACID. 665 the density of its vapour is 4.64, its equivalent being represented by 4 volumes of vapour. Nordhausen sulphuric acid dissolves it, and produces a compound acid C20H13,S2O5,HO which forms a solu- ble salt with baryta. ESSENTIAL OIL OF CLOVES, AND THE EUGENIC SERIES. § 1563. Cloves and Jamaica pimento yield, by distillation with water, a yellowish essential oil of a complicated character, for four dis- tinct substances have already been separated from it: a carburuetted hydrogen, isomeric with oil of terpentine; an oxygenated essential oil C20IIuO3,HO, called eugenic acid, because it possesses acid proper- ties ; and two neutral crystalline substances, eugenin and cariophyllin. Water which has been distilled over cloves gradually deposits a substance crystallized in pearly spangles, consisting of eugenin C20H12O4, isomeric with eugenic acid. Crude oil of cloves deposits, after some time, fine colourless aci- cultB of cariophyllin C20H16O2, isomeric with the camphor from the family of the laurels. If crude oil of cloves be mixed with a concentrated solution of potassa, a crystalline mass, of the consistence of butter, is formed, which is separated and distilled with water, when the oil, isomeric with terpentine alone, passes over, while the eugenic acid remains in the residue in the state of eugenate of potassa. The residue is treated with chlorohydric acid, which separates the eugenic acid from it in the form of a colourless, oleaginous liquid, boiling at 473°, which is distilled in a current of carbonic acid gas. Eugenic acid absorbs the oxygen of the air, and is converted into a resinous substance. It forms crystallizable salts with potassa, soda, and lime, of the general formula RO,C20HnO3. OIL OF POTATO-SPIRIT,* OR AMYLIC ALCOHOL C10H1503- § 1564. This oil is obtained when, in the manufacture of alcohol, the liquors resulting from the action of ferment on the fecula of the potato are distilled; and it is also formed in the distillation of cer- tain alcoholic products obtained in the fermentation of the cerealia or of grapes; the oil, therefore, constantly accompanying the pro- ducts of alcoholic fermentation. Toward the close of the distillation of brandy from fecula, the largest proportion of the oil is obtained, when a milky water passes over, on the surface of which, after rest- ing for some time, the oil floats. The composition of this oil is very complicated, and when distilled, it begins to boil at about 185°, while its boiling point rises to 269.6°, at which it remains for some time; the last product, which is collected separately, being almost wholly composed of the essential oil required. It is purified by several rectifications, and the oil which boils exactly at 269.6° should alone be regarded as pure. * Also called /ousel oil.— W. L. F. 666 ESSENTIAL OILS. Oil of potato-spirit is an oily, colourless liquid, of a strong and disagreeable odour and an acrid and burning taste. Its density at 59° is 0.818, while that of its vapour is 3.15, its equivalent C10H12O2 corresponding to 4 volumes. At — 4.0° it solidifies in crystalline leaflets; and it stains paper like the essential oils, but the spot quickly disappears, because the oil volatilizes. Oil of potato-spirit does not ignite at the approach of a burning substance, unless it be at a temperature of 120° or 140°, its vapour supporting com- bustion only at that degree. It is not sensibly soluble in water, but dissolves in all proportions in alcohol and ether. Oil of potato spirit rotates toward the left. A large number of compounds is derived from the oil, so analo- gous to those obtained by means of alcohol and wTood-spirit, that chemists have not hesitated to regard this oil as a true alcohol, to which they have given the name of amylic alcohol. In our subse- quent investigation of these compounds, we shall follow the same order as in those of the vinic and methylic compounds, since their analogy will be thus more easily understood. Action of Sulphuric Acid on Amylic Alcohol. § 1565. By shaking together equal parts of oil of potato-spirit and concentrated sulphuric acid, a brown liquor is formed, which, when saturated with carbonate of baryta, yields sulphate of baryta and a soluble salt of baryta, the solution of which is bleached by animal black. The liquor, when evaporated at a gentle heat, yields small crystalline lamellae of sulphamylate of baryta, of the formula BaO,(C10HuO,2SO3)+3HO, which is decomposed at the boiling point. Its solution, when decomposed by sulphate of potassa, yields, after evaporation and dessication in vacuo, a crystalline resi- due of sulphamylate of potassa KO,(C10HnO,2SO3). If, on the contrary, the baryta be precipitated by sulphuric acid added drop- wise, a solution of free sulphamylic acid is obtained, which, boil- ing readily, decomposes into sulphuric acid and amylic alcohol C10H12O2 or C10HnO,HO. § 1566. If an excess of concentrated sulphuric acid be made to act on amylic alcohol, and it be heated to boiling, we obtain a car- buretted hydrogen C10H10, called amylen, which is to amylic alco- hol C10HnO,HO wdiat olefiant gas C4II4 is to vinic alcohol C4H50, HO. All reagents wdiich abstract water from vinic alcohol modify amylic alcohol in an analogous manner : thus both concentrated and anhydrous phosphoric acid, fluoboric and fluosilicic gases, and chlo- ride of zinc produce the same effect as concentrated sulphuric acid. As the chloride of zinc effects the neatest decomposition, it is gene- rally used in the preparation of pure amylen. Amylic alcohol is heated in a retort, with a solution of chloride of zinc marking 70° on the hydrometer, the retort being frequently shaken while the tem- perature rises: when the oil is finally wholly dissolved, distillation 667 may be begun. The liquid, when distilled, is again rectified in a tubulated retort furnished with a thermometer, and only the most volatile part is collected. Amylen thus obtained is a colourless, very fluid liquid, boiling at 102.2°, and the density of its vapour being 2.45, its equivalent C10H10 corresponds to 4 volumes of vapour, like that of olefiant gas. Amylen can form two isomeric products: paramylen C20H20; and metamylen, of which the formula is C30II30 or C40II40. These two pro- ducts generally arise at the same time as the amylen, and are found in the last products of distillation ; but they may be obtained directly by distilling amylen with chloride of zinc several times successively. Paramylen boils at about 320°, and the density of its vapour is double that of amylen; for which reason its formula has been writ- ten C20H20. Metamylen distils only at 570°; but it probably has not yet been obtained in a state of purity. § 1567. Amylic ether C10HuO has not yet been prepared by the action of sulphuric acid on amylic alcohol; but it has been obtained by causing an alcoholic solution of potassa to act on amylochloro- hydric ether C10HnCl, of which we shall speak presently. It is a colourless liquid, of an agreeable odour, and boiling at 230°. AMYLIC ALCOHOL. Compound Amylic Ethers, and Compound Amylic Acids. § 1568. As yet we are acquainted neither with amylosulphuric ether C10HuO,SO3, nor with amylonitric ether C10HuO,NO5; while an amylonitrous ether C10HuO,NO3 is produced by collecting in amylic alcohol the nitrous vapours which are disengaged when starch is treated with nitric acid. By distillation, the amylonitrous ether separates in the form of a pale, yellow liquid, which is to be washed several times with water, and then with a weak solution of potassa; after which it is dried over chloride of calcium and redis- tilled. It boils at 204.8°, and the density of its vapour is 4.03, so that its equivalent C10HnO,NO3 corresponds to 4 volumes of vapour, like the corresponding product of the vinic series. The same ether is formed when nitric acid is made to act on amylic alcohol; but it is then mixed with various products of oxidation, particularly with valerianic acid and methylic aldehyde. By causing boracic acid, melted and reduced to an impalpable powder, to act on amylic alcohol, exactly under the circumstances which have been described for alcohol, (§ 1248,) there remains a residue of amylobiboracic ether C10HnO,2BO3, solid at a low tem- perature, but assuming at about 248° a viscous consistence resem- bling that of fused glass. This substance resists a temperature of 570° without decomposition, burns with a green flame, and is decom- posed by water. If chloride of boron be made to act on amylic alcohol, an oily liquid is obtained, which boils without change at about 527°, and 668 ESSENTIAL OILS. consists of triamylboracic ether 3C10HuO,BO3. The density of its vapour is 10.55. By dropping amylie alcohol into chloride of silicium, shaking the mixture frequently, then distilling it and collecting only the product which passes over at from 608° to 640°, a liquid is obtained, which is to he purified by several distillations, and which consists of tria- mylosilicic ether 3C10HuO,SiO3. Water decomposes it slowly. Amylacetic ether 3C10IIuO,C4H3O3 is obtained by distilling 1 part of amylie alcohol, 2 parts of acetate of potassa, and 1 part of con- centrated sulphuric acid, the product being washed with an alkaline solution, dried over chloride of calcium, and rectified a last time over litharge. It is a colourless, limpid liquid, of an aromatic odour,* boiling at 257°, and the density of its vapour being 4.46, its equivalent corresponds to 4 volumes of vapour, like the corre- sponding ethers of the vinic and methylic series. Oxalic acid forms two compounds with amylie alcohol, correspond- ing to those which it produces with vinic and methylic alcohols. When amylie alcohol is heated with oxalic acid, a liquor is obtained, which, when saturated with carbonate of lime, yields a soluble salt of lime, the amyloxalate of Ivne, of which the formula of the crys- tals is CaO,(C10II11O,2C2O3)+2IIO ; and a great number of other amyloxalates may be obtained by double decomposition, by means of this salt. If, on the contrary, the mixture of amylie alcohol and oxalic acid be distilled, a liquid is obtained, boiling at 500°, and called amylox- alic ether C10HuO,C2O3, which rotates toward the right, in an oppo- site direction to that of amylie alcohol. This liquid, treated with an aqueous solution of ammonia, yields oxamide; while if ammo- niacal gas be passed through a solution of amyloxalic ether in abso- lute alcohol, a liquid is obtained which deposits, on evaporation, crystals of amyloxamic ether C10HnO,(C4O5NII2). § 1569. We have described (§ 1567) the mode of preparing simple amylic ether C10HnO. Amylochlorohydric ether C10HUC1 is ob- tained by distilling equal parts of perchloride of phosphorus and amylic alcohol, when the product is washed with alkaline water and dried over chloride of calcium. The same substance is also obtained by causing chlorohydric acid to act, for a long time, on the same alcohol; the liquid separating into 3 layers, of which the upper one contains the amylochlorohydric ether. It is a colourless liquid, of an aromatic odour, boiling at 215.6°, and its equivalent corresponds to 4 volumes. Chlorine acts on it, and when its action is exhausted, Simple Ethers of the Amylic Series. * The odour of amylacetic ether closely resembles that of the banana, and it is with this substance that the favourite acidulated banana drops are flavoured.— W. L. F. VALERIANIC ACID. 669 by exposure to the rays of the sun, a chlorinated product, of the formula C10H3C19, is obtained. • By causing 15 parts of amylic alcohol, 8 parts of iodine, and 1 of phosphorus to react at a gentle heat, and then distilling tlie mix- ture, we obtain a liquid, which is to be purified by several washings, drying over chloride of calcium, and redistillation. It is amyliodo- hydric ether C10HnI. By distilling a concentrated solution of sulphamylate of lime and cyanide of potassium, amylocyanohydric ether C10IIuCy is obtained; and chlorohydrate of amylen heated with an alcoholic solution of monosulphide of potassium produces amylosulfhydric ether C10IInS, a colourless liquid, of a very disagreeable odour, and boiling at 402.8°. Its equivalent is represented by 2 volumes of vapour. Sulphamylic alcohol or amylic mercaptan C10HUS,IIS is obtained be distilling amylochlorohydric ether C10HUC1 with an alcoholic solution of sulf hydrate of sulphide of potassium. It is an oleaginous, colourless liquid, of an alliaceous smell; and it boils at 242.6°, while its density at 69.8° is 0.825. In contact with oxide of mercury it yields sulphamylomercurie alcohol C10IIuS,Hg2S. Products of the Oxidation of Amylic Alcohol. § 1570. When amylic alcohol is subjected to oxidizing agencies, it is converted into an acid C10H9O3,HO, called amylic, identical with an acid extract of the valerian root, and called valerianic acid. This acid is to amylic alcohol C10HnO,HO what acetic acid C4H303, HO is to vinic alcohol C4H-0,H0, and what formic acid C2H03,H0 is to methylic alcohol C2H30,H0. An intermediate product, amylic aldehyde C10H10O2, corresponding to the aldehyde of the vinic series, has also been obtained, but it is difficult to isolate it among the pro- ducts of oxidation of amylic alcohol. By heating oil of potato-spirit with a mixture of sulphuric acid and bichromate of potassa, there pass over in distillation valerianic acid C10H9O3,HO and amylovalerianic ether C10HnO,C10H9O3. If it be treated by a solution of potassa, the valerianic acid is dissolved in the state of valerianate of potassa, while the amylovalerianic ether remains, which in its turn may be wholly transformed into valerianic acid, if its vapours be passed over sodic lime. The oil of valerian is, in fact, converted into valerianic acid, when its vapours are passed over sodic lime placed in a flask heated in an oil-bath to a tempera- ture between 400° and 480°; hydi'ogen only being disengaged in the beginning, while toward the close of the operation this gas is accompanied by carburetted hydrogens. The flask is allowed to cool, and is opened under water in order to prevent the access of air; and the substance, diluted with water, is distilled with an excess of sulphuric acid. The liquor collected in the receiver is saturated with carbonate of soda, and the solution evaporated to dryness; and, lastly, the residue is distilled with phosphoric acid, when the vale- 670 rianic acid forms an oily layer on the surface of the water in the receiver. § 1571. In order to extract valerianic acid from valerian root, it is sufficient to distil the root with a large quantity of water acidu- lated by sulphuric acid; a still larger quantity being obtained by using the following mixture:—1 kilog. of valerian root, 100 gr. of sulphuric acid, 60 gm. of bichromate of potassa, and 5 litres of water. This is owing to the fact that valerian contains an essential oil, valerole C12H10O2, which is converted, by oxidizing reagents, into valerianic acid. The distillation should not be commenced until the mixture has macerated for 24 hours. Valerianic or amylic acid is a colourless liquid, having a strong odour of valerian, and the density 0.937 at 62.6°, while it boils at 175°; its equivalent C10H9O3,HO corresponding to 4 volumes of vapour. It dissolves slightly in water, but in all proportions in alcohol and ether. The majority of the valerates are soluble, and the alkaline valerates crystallize with difficulty, while that of baryta forms small brilliant prisms. Valerate of silver is insoluble, and presents the formula AgO,C10H9O3. Valerianic acid is acted on by chlorine, even when protected from direct solar light, and is then converted into tricldorinated valerianic acid C10H6Cl3O3,HO. In order that the reaction may be complete, heat must be applied toward the close, and the current of chlorine must be kept up until no more chlorohydric acid is disengaged. If the action of chlorine be continued in the sun, quadrichlorinated acid C10H5Cl4O3,IIO is obtained. Valerate of baryta, distilled over the fire in a retort, yields a volatile, oleaginous product, which is purified by redistillation, col- lecting only the product which boils at 212°. The formula of this compound is C10H10O2, and it is amylic or valeric aldehyde, which oxidizing reagents readily convert into valerianic acid; the trans- formation being effected even by the oxygen of the air in the pre- sence of platinum-sponge.* ESSENTIAL OILS. ESSENTIAL OIL OF WINE, OR (ENANTHIC ETHER C4H50,C14H1303. § 1572. There exists in wine an essential oil, to which the peculiar odour of wines, called their bouquet, has been chiefly attributed. It consists of a compound vinic ether, containing an acid called oenan- thic (from olvoj, vine, and avdo;, flower.) When large quantities of wine are distilled, an oil volatilizes to- ward the close of the operation, which is a mixture of vincenanthic * Amylic ether is considered as the oxide of a radical amyl C10H1U in the same manner as ether is regarded as oxide of ethyl, which theory has gained much ground since amyl has been actually isolated. Valerianic acid then assumes the formula (C3IL,)C303,H0, or oxalic acid paired with a radical valyl which Kolbe has isolated. See the note to g 1401.— W. L. F. CAOUTCHOUC. 671 ether and free oenanthic acid. As the oenanthic ether is much more volatile than the oenanthic acid, they may be imperfectly sepafated by distillation; the first products being much richer in oenanthic ether. In order to obtain pure oenanthic ether, the crude oil is shaken with a hot solution of carbonate of soda, which dissolves the free oenanthic acid, and toward the close it is heated to ebulli- tion, so that the oenanthic ether may separate more readily and form an oily layer on the surface. After being decanted, and again subjected to the same treatment, it is dried over chloride of calcium and purified by distillation. CEnanthic ether is a colourless liquid, of a very penetrating smell of wine, and an acrid and disagreeable taste. It is insoluble in water, but dissolves readily in alcohol and ether. Its density is 0.862, it boils at 446°, and the density of its vapour is 10.48; its equivalent C4H50,CuII1303, being therefore represented by 2 volumes of vapour. It is easily decomposed by a hot solution of caustic potassa, or soda, yielding alcohol and oenanthic acid which remains combined with the alkali. By decomposing the alkaline oenanthate by dilute sulphuric acid, the oenanthic acid collects on the surface of the liquid in the form of a colourless oil, which is merely washed with hot w'ater, and then dried in vacuo. At the ordinary temperature oenanthic acid has the consistence of butter, while it becomes very fluid at a higher temperature, and boils at about 570°. It does not sensibly dissolve in water, but it nevertheless reddens litmus. Alcohol and ether dissolve it freely. The distilled acid is anhydrous, and presents the formula C14H1303; while, when in contact with water, it abstracts 1 equiv. from it and becomes monohydrated acid C14II1303,H0. By heating to 302° a mixture of 5 parts of sulphovinate of potassa and 1 part of monohy- drated oenanthic acid, a vinoenanthic ether is obtained, which may be purified by a hot solution of carbonate of soda. If a mixture of wood-spirit, concentrated sulphuric acid, and oenanthic acid be heated, methoenanthic ether C2H30,C14H130 is formed. As vinoenanthic ether cannot be detected in the fresh juices of vegetables, it is probably a product of fermentation. CAOUTCHOUC. § 1573. Caoutchouc is contained in the milky juice of several vegetables, where it exists in the form of small globules, suspended in an aqueous liquid, precisely in the same manner as the fatty globules in milk. The chief importations of caoutchouc are from Java and South America; and it is obtained from the siphonia caJmcha and the ficus elastica. The milky sap of these trees con- tains about 30 per cent, of caoutchouc; and when left to itself, the globules of caoutchouc float on the surface, because they are lighter than water, and form a thick cream on it; which separation is more easily effected if the density of the water is increased by sea-salt. 672 ESSENTIAL OILS. In order to collect the caoutchouc, deep incisions are made into the base of the tree producing it, and the liquid which exudes is re- ceived in earthen vessels, whence it is transferred into bottles, which, when hermetically sealed, may be transported and preserved for a long time-without undergoing any change. The greater part of the caoutchouc found in commerce is in the shape of pears, either smooth or covered with marks, and generally of a brown colour. The In- dians make these pears by spreading successive layers of the milky juice, which they coagulate in the sun, over pyriform clay moulds; and when the caoutchouc is of sufficient thickness, they dip the mould in water to soften the earth, which is then emptied through the mouth of the caoutchouc bottle. The brown colour is owing to the deposition of the smoke during its desiccation over fire. Pure caoutchouc must he obtained from the milky juice itself, by mixing it with 4 times its weight of water, and allowing it to rest for 24 hours, when the globules of caoutchouc float on the surface in the form of cream. This cream is removed, and by agitation is suspended with an additional quantity of water, of which the density is increased by a small quantity of sea-salt and clilorohydric acid; when, after some time, the caoutchouc again collects on the surface, and is again removed and washed, and so on, until the water will dis- solve no more of it; after which the substance is compressed between paper and dried under the receiver of an air-pump. Caoutchouc, thus prepared, is a white, elastic substance, of the density 0.925, and containing 87.2 of carbon and 12.8 of hydrogen. All the useful articles of caoutchouc, now so extensively applied in the arts, are manufactured from the pyriform substance, by very various mechanical processes, the description of which would be out of place. The elasticity and impermeability of caoutchouc render it valuable for many purposes in surgery, and it also finds frequent use in the laboratory of the chemist and physicist. It has recently been used for covering cloths and other stuffs, to render them water and air tight. Caoutchouc is hard at a low temperature, hut softens readily by heat, and at 77° possesses great flexibility; while it melts at about 248°, and then forms a viscous liquid, which does not recover its original condition for a very long time. If it be further heated, the liquid becomes more fluid, and remains indefinitely viscous even after cooling. Melted caoutchouc, diluted with a small quantity of some fatty oil, is used for greasing stopcocks. It burns with a' brilliant and very smoky flame; and by heating it to distillation, it is converted into several essential oils, of different volatile powers, and which are themselves modified by redistillation. Caoutchouc is insoluble in water and alcohol, although boiling water softens it and causes it to swell, but without dissolving it. Ether, the essential oils, and sulphide of carbon, on the contrary, dissolve it readily, and form solutions, which deposit, after sponta- 673 ncous evaporation, on the objects to which they have been applied, an elastic and impervious coating of caoutchouc.* RESINS. GUTTA-PERCHA. § 1574. A substance of organic origin has lately been found, closely resembling caoutchouc in its chemical and physical proper- ties, and called gutta-percha, which is used in the fabrication of hands to drive machinery, and several purposes which require great solidity united to a certain degree of flexibility. It is imported from India and China, and is probably the product of some vegeta- ble, although as yet we have no accurate account of its origin. Gutta-percha is of a grayish-white colour, of a consistence resem- bling that of horn, and not at all elastic; but it softens and be- comes more elastic by an increase of temperature, its original hardness returning after cooling. It burns, like caoutchouc, with a brilliant and smoky flame. Water, alcohol, the acid or alkaline liquors, exert no action upon it; but ether and ihe essential oils first soften and then dissolve it. Its elementary composition differs but slightly from caoutchouc, for 87.8 of carbon and 12.2 of hydro- gen have been found in it.f RESINS. §1575. The name of resins has been given to certain solid sub- stances, widely spread among vegetables, and w’hich flow copiously from some of them in the state of solution in the essential oil. Resins are solid, non-volatile, sometimes colourless, most frequently of a yellow or brown tinge; insoluble in water, hut dissolving readily * The discoveries of Goodyear that caoutchouc may be modified in its properties by various processes, termed vulcanizing, are too important to pass over in utter silence. Charles Goodyear, of Connecticut, United States, discovered, by years of patient and laborious experiment, that sulphur heated with caoutchouc produced what he termed a drying effect upon the latter, rendering it more elastic, incapable of becoming hard by frost, insoluble in ether, the essential oils, &c. By a series of highly ingenious mechanical processes, the new fabric was made to imitate paper, every hind of leather, and various kinds of dry goods, still, however, re- taining more or less of the original, valuable properties of the rubber. His more recent improvements consist in imparting to caoutchouc any required degree of hardness between its usually soft state and the hardness and elasticity of ivory, effected by an expansion of his sulphurizing process, and by the addition of mate- rials to the caoutchouc. By this discovery of Goodyear, and through his enter- prise and patient perseverance, a single vegetable product can be made to replace paper, leather, and dry goods, but with greater elasticity and durability,—to re- place whalebone, horn, tortoise-shell, horn, and ivory.—J. C. B. f Gutta-percha is similar in its origin and composition to caoutchouc, and yet presents very different external characters. The hardening effect produced by Goodyear’s sulphuration of caoutchouc seems to convert the latter into a substance resembling gutta-percha in its properties, and enables us to comphrehend how the same class of plants may produce substances of very different external properties. The uses of gutta-percha are rapidly extending.—J. C. B. 674 ESSENTIAL OILS. in absolute alcohol, which frequently deposits them, in the form of crystals, after evaporation. The majority of resins behave like weak acids, and form definite compounds with the alkalies and with other metallic oxides. We shall here describe only the resins of ter- pentine, which have, as yet, been most accurately investigated. When the terpentine which exudes from the pinus maritima is distilled with water, the oil of terpentine distils with the water, while a substance called colophony remains, consisting of three resins, possessing acid properties, and to which the name of pimaric, sylvic, and pinic acid have been given. The elementary composition of these three acids is exactly the same, corresponding to the formula C40H3004=C4oH2903,IIO. Pimaric acid predominates greatly over the other two acid resins, and colophony appears sometimes to be wholly constituted of it. In order to obtain it, powdered colophony is treated several times with a mixture of 5 or 6 parts of alcohol and 1 part of ether, when the sylvic and pinic acids are dissolved, while the greater portion of the pimaric acid remains as a residue, and is purified by being crystallized repeatedly from boiling alcohol. Pimaric acid dissolves very readily in ether, while it requires 10 parts of cold and its own weight of boiling alcohol for solution. It melts at about 257°, and then undergoes an isomeric modification, which is easily recog- nisable by dissolving it in cold alcohol, of which it then only requires 1 part. However, this modification is not fixed, since, after a cer- tain time, the pimaric acid is regenerated, with its original proper- ties, in the alcoholic solution, and the greater portion of it is depo- sited in crystals. Crystallized pimaric acid is after a time spontaneously converted into pinic acid, when it is soluble in its own weight of alcohol, and does not assume any crystalline form. By distilling pimaric acid, an oleaginous substance is condensed and congeals in the neck of the retort; and it is purified by dis- solving it in boiling alcohol, whence it is deposited in the form of crystalline lamellae. This substance is identical with sylvic acid, of which we mentioned the presence in colophony, differing from pimaric acid by its crystalline foiyn, melting at nearly the same temperature of 257°, and dissolving in 8 or 10 times its weight of alcohol. A great number of resins are found in commerce, which are generally called by the name of the vegetable from which they are derived; and the chemical properties of all of them are analogous to those of resins of terpentine. Resins yield by distillation very complicated products: carburet- ted hydrogens, which burn with a brilliant flame, and are used as illuminating gases; besides essential and fixed oils. The following products have been separated: 675 Retinaphtha C14H8, an oil boiling at 226.6°. Retinyl C18II12, “ “ 302.0°. Retinole C12H6, isomeric with benzine, boiling at 464.0°. Retisterin, isomeric with naphthalin, a crystalline substance melt- ing at 149°, and boiling at 617.0°. OIL OF GARLIC. SULPHURETTED ESSENTIAL OILS. § 1576. Only two sulphuretted essential oils are as yet accurately known: oil of mustard, and oil of garlic; while their number will, without doubt, be greatly increased hereafter. OIL OF GARLIC C0II5S. § 1577. This essential oil is obtained by distilling cloves of garlic with water, when an extremely fetid brown-coloured oil passes over, which is decanted, and, after distillation in a salt-water bath, is rec- tified over potassium until it is no longer acted on by this metal. Oil of garlic is a colourless liquid, of a repulsive odour, less dense than water, distilling without alteration, and presenting the formula C6H5S. It has been called sulphide of allyl, because it has been considered as a compound of sulphur with a carburetted hydrogen C6H5, or allyl. This oil throws down precipitates with several metallic solutions: thus, if a concentrated solution of it be mixed with an equally concentrated solution of chloride of mercury, a white precipitate is formed, which, when purified by being washed in alcohol, presents the formula (HgS)2,C6H5S + (HgCl)2,C6H5Cl. When alcoholic solutions of oil of garlic and bichloride of platinum are mixed together, and the liquid is diluted with water, a yellow precipitate is formed, of which the composition corresponds to the formula 3(PtS2,C6H.S)+PtCl2,C6H5Cl. When an alcoholic solution of oil of garlic is added to nitrate of silver, a precipitate of sulphide of silver is obtained, mixed with a white crystalline compound, which is deposited from a solution in boiling water, when kept in the dark, in the form of brilliant white crystals, of a composition corre- sponding to the formula AgO,NO5,C0H5O, which may be considered as formed by the combination of 1 equivalent of nitrate of silver with 1 equivalent of oil of garlic, the equivalent of sulphur in the latter having been replaced by 1 equivalent of oxygen. By treating this crystalline substance with ammonia, the compound C6H50, called oxyde of allyl, is separated, in the form of a volatile, colourless oil, of a disagreeable odour, which combines directly with nitrate of silver, reproducing the crystalline compound of which we have just spoken. 676 ESSENTIAL OILS. OIL OF BLACK MUSTARD C3H5NSs §1578. This oil does not exist already formed in mustard-seed, hut is developed in it, in the presence of water, by a kind of fer- mentation taking place between the substances contained in the seed, to which we shall presently recur. The fatty oil contained in the mustard-seed is extracted by means of a press; when the cake being moistened with water, and left to itself for several hours, the seed, at first inodorous, soon exhales the pungent smell of mustard. It is then distilled with water, when a yellow oil, denser than water, passes over with the aqueous vapours. By a second distillation with water, it loses colour sensibly, but as it still contains foreign substances, it is distilled in a retort furnished with a thermometer, and the liquid which distills below 293° is separated, the temper- ature being arrested at this point, when pure oil of mustard passes over. Oil of mustard is a colourless oil, boiling at 293°, and furnishing vapours which irritate the eyes and nose, and show the density 3.4, its equivalent C8II5NS2 corresponding to 4 volumes of vapour. It is very soluble in alcohol and ether, but insoluble in water, and it exerts no rotatory power. Its formula C8H5NS2 may be written CGIIr)S,C2N,S, which constitutes oil of garlic CcII5S and sulphocya- nogen; and in fact, the constitution of oil of mustard must be thus considered, for if it be treated with monosulphide of potassium, oil of garlic CGII5S is obtained by distillation, while the liquid contains sulphocyanide of potassium. If the vapour of oil of mustard be passed over a mixture of lime and caustic soda, heated to 248°, oxide of allyl CGH.O is obtained, and the residue contains sulpho- cyanides. §1579. Oil of mustard yields, either with ammoniacal gas or with liquid ammonia, a crystallized compound, thiosinammin C8H5NS2NH3, which is a true alkaloid. This substance being re- dissolved in boiling water, the liquor, when bleached by animal black, deposits, by evaporation, the thiosinammin, in the form of pris- matic crystals, of a brilliant white colour. It dissolves in chloro- hydric acid, forming an uncrystallizable compound; while, by adding bichloride of platinum to the solution, a yellow crystalline precipi- tate is formed, of which the formula is (C8H5NS2,NII3),IICl-fPtCl2. Thiosinammin dissolves also in sulphuric, nitric, and acetic acids, but the compounds do not crystallize. When heated with oxide of lead or mercury, it parts wholly with its sulphur, and a new alkaloid C8HGN2, called sinavwiin, is formed: C8H5N S2+NH3+2Pb 0=C8H6N2+2PbS+2H 0. Powdered thiosinammin is mixed with freshly precipitated and moist hydrated protoxide of lead, and is heated over a water-bath 677 until the filtered liquid is no longer blackened by the addition of potassa; after which it is heated several times with boiling alcohol, to dissolve the sinammin, leaving, after evaporation, a syrupy mass in which crystals are developed. Sinammin has a strongly alkaline reaction, but forms only a small number of crystallizable salts and its chlorohydric solution yields, with the bichloride of platinum, a flaky yellow precipitate, of the formula C8H6N2,2HCl+2PtCl2. If oil of mustard be digested with hydrated oxide of lead, until an additional quantity of the oxide ceases to turn black, and it be then treated with boiling water, a new substance C14II12N202, called smapolin, is dissolved, which also possesses basic properties, the reaction from which it arises being expressed by the following equation: MYRONIC ACID. 2 C8H3N S2+6PbO+2H0=C14H12N202+4PbS+2(Pb 0, C 02). Synapolin crystallizes from its aqueous solution in spangles of a grayish lustre, and turns litmus blue, while its solution in chlorohy- dric acid yields a crystalline precipitate with chloride of mercury. Myronic Acid and Myrosin. § 1580. Black mustard-seed contains an acid substance, myronic acid, combined with potassa, which, by the assistance of water and a peculiar ferment, called myrosin, also contained in the seed, is converted into oil of mustard by a peculiar fermentation, called sinapic fermentation. In order to extract the myronate of potassa, black mustard-seed, previously freed from its fatty oil by pressure, is heated with alcohol to 185°; Avhen the ferment, myrosin, in this way coagulates and becomes inactive. The substance is again ex- pressed and heated with tepid water, which dissolves the myronate of potassa; and by adding alcohol to this new solution, some muci- laginous substances are coagulated, when the liquid, after evapora- tion, deposits crystals of myronate of potassa. By pouring tartaric acid into a concentrated solution of myronate of potassa, the greater part of the potassa is precipitated, and a very acid liquor remains, which leaves, after evaporation, an uncrys- tallizable syrupy substance. The composition of myronic acid is unknown. Myrosin is separated by exhausting white mustard-seed with cold water, evaporating the filtered liquid at a low temperature, and adding alcohol, which precipitates the myrosin. Myrosin cannot be extracted from black mustard-seed, because it forms oil of mustard as soon as it is moistened with water. No other known ferment can be substituted for myrosin in the sinapic fermentation. 678 PRODUCTS OF DRY DISTILLATION. OF SOME IMPORTANT PRODUCTS WHICH ARE FORMED DURING THE DISTILLATION OF ORGANIC SUBSTANCES. § 1581. We shall include in this chapter some important sub- stances produced by the distillation of organic matter, which have not yet been, with certainty, appended to any great series. We shall add the native hydrocarburetted essential oils, known under the name of naphtha and petroleum, wdiich probably arise in the same manner from the bosom of the earth. NAPHTHALIN G,0H„. § 1582. This remarkable substance is formed by the decomposition of a great number of organic substances at a high temperature, a considerable quantity of it being produced in the manufacture of illuminating gas from bituminous coal. Adulterated with an oily substance and lampblack, naphthalin is deposited in crystals on the sides of the pipes which convey the gas from the retorts; and it must be removed, from time to time, to prevent their becoming completely choked; and in the laboratory, it is generally extracted from these deposits. The most simple method consists in employing the process described (§ 1527) for the extraction of benzoic acid, by sublimation from the resin of benzoin, the naphthalin thus obtained being nearly pure; and to make it perfectly so, it is dissolved in boiling alcohol, whence it is again deposited, in crystals, on cooling. Naphthalin crystallizes in beautiful rhomboidal laminae, of a white colour and greasy lustre; has a peculiar, very persistent odour; melts at 174.2°, and boils at 413.6°, the density of its vapour being 4.53, and its equivalent C20H8 corresponding to 4 volumes of vapour. Hot water dissolves a very small quantity of it, for water, heated with naphthalin, becomes slightly cloudy on cooling. Alcohol dis- solves one-fourth of its weight of it, while ether and the essential oils dissolve it more freely. §1583. Chlorine acts readily on naphthalin, which first becomes liquid under its action, but again solidifies if it be prolonged. If the substance be then expressed between tissue-paper and crystal- lized in ether, a homogeneous substance of the formula C20H8,C14 is obtained, which may be considered as a combination of 1 equivalent of naphthalin and 4 equivalents of chlorine. The formula of the liquid which precedes the formation of this crystalline compound is C20H8,C12; and it results from the combination of 1 equivalent of naphthalin with 2 equivalents of chlorine. The formula of the crys- talline compound may be written C20H6C12,2IIC1, being considered as a compound of 1 equivalent of bichlorinated naphthalin C20II6C12 with 2 equivalents of chlorohydric acid. In fact, the substance is in this manner decomposed by heat, chlorohydric acid being disen- gaged, while bichlorinated naphthalin C20H6C12 condenses in the form of a colourless liquid. The liquid substance C20H8C12 being also NAPHTHALIN. 679 decomposed by heat into chlorohydric acid, and into monochlori- nated naphthalin C20H7C1; its formula may therefore he written C20H7C1,HC1. These are not the only substances which may be derived from naphthalin by the action of chlorine, since a great numbers of others exist, which are obtained by subjecting the first two to various reagents, or by causing chlorine to act on the pro- ducts they yield by distillation. We shall merely indicate the for- mulae of the principal of these substances: Naphthalin C^Hg, Monochlorinated naphthalin C20H7C1, Bichlorinated “ C20H6C12, Trichlorinated “ C20H5C13, Quadrichlorinated “ C20H4C14, Sesquichlorinated “ C20H2C16, Perchlorinated “ C20C18. With bromine have been obtained Monobrominated naphthalin C20H7Br, Bibrominated “ C20H6Br2, Tribrominated “ C20H5Br3, Quadribrominated “ C20II4Br4. By the successive action of bromine and chlorine, Bromobichlorinated naphthalin C20H5BrCl2, Bibromobichlorinated “ C20H4Br2Cl2, Bromotrichlorinated “ C^H^BrClg, Bibromotrichlorinated “ C20H3Br2Cl3. To which may be added the move complex groupings, considered either as compounds with chlorine or bromine, of the original naph- thalin or chlorinated or brominated naphthalins, or as chlorohydrates of chlorinated naphthalin, from which two ways of examining them we shall write their formulae: C20II8C12 or C20H7C1,HC1, c20h6ci2,ci2 C20H5C13,HC1, C20H6Br2,Cl2 C20H5Br2Cl,HCl, C20H5Br3,Br2 C20H4Br4,HBr. (WA C30HeCl3,2HCl, C20H5C13,2HC1, C20H4Br2Cl2,Br4 C20H2Br4Cl2,2HBr. § 1584. Nitric acid reacts readily on naphthalin at the boiling point, converting it rapidly into an oil which solidifies on cooling, and should be purified by several crystallizations in alcohol. Its 680 PRODUCTS OF DRY DISTILLATION. formula being C20II7(NO4), it may be considered as naphthalin in which 1 equiv. of hydrogen is replaced by 1 equiv. of the compound N04. By continuing the action of the nitric acid, we obtain suc- cessively Binitronaphthalin C20H6(N 04) and Trinitronaphthalin C20II5(NO4)3. By causing sulfhydrate of ammonia to act on an alcoholic solu- tion of mononitronaphthalin C20II7(NO4), an organic base is obtained, naphthalidam C20II9N: C20H7(NO4)+6(NH3,2HS)=C20H9N+4HO+6S4-6(NH3,HS). This substance crystallizes in white needles, melting at 86°, and boiling at about 570°, without alteration, which combine with the acids and form crystallizable salts, the formula of the chlorohydrate being C20II9N,HC1, and that of the sulphate (C20H9N,HO),SO3. Under the same circumstances, binitronaphthalin C20H6(NO4)2, and the trinitronaphthalin C20II5(N 04)3, yield other alkaloids C20H8N2, c20h7n3. . By causing nitric acid to act on chlorinated naphthalins, there re- sult either substitutions of the compound N04for hydrogen, or pro- ducts of oxidation in which the molecule of naphthalin is modified by the substitution of oxygen in the place of hydrogen; and in this manner have been obtained Trichlorinated binitronaphthalin C20H3Cl3(NO4)2, and the products of oxidation: C20H4Cl2O2,O2, C20 C1602,02, C20II5C1 02,04, C20II C1502,05. It will be seen that from no carburetted hydrogen are more numerous products derived than from naphthalin; which probably arises from the fact that no other one has been so carefully examined in this point of view. § 1585. Concentrated sulphuric acid acts readily on naphthalin, and yields acid compounds. By heating naphthalin to about 194° with concentrated sulphuric acid, it dissolves in it, and forms a syrupy liquid, generally reddish, which, when exposed to a moist air, sets in a crystalline mass, readily soluble in water, producing an acid liquid which forms, with carbonate of lead, two salts unequally so- luble in alcohol. The acid of which the salt of lead is more soluble in alcohol is by far the more abundant, and has been called sulpho- naphtlialic acid; the general formula of its dried salt being BO, (C20II7S2Or).) The other acid has received the name of sulphonaph- thic acid, but its composition is not exactly known. By causing concentrated sulphuric acid to act on trichlorinated PARAFFIN. 681 and on quadrichlorinated naphthalin, there result acids perfectly analogous to sulphonaphthalic acid, forming salts of the general formulae, when dried, RO,(C20H4Cl3,S2O5), RO,(C20H3Cl4,S2O5). By substituting anhydrous sulphuric for monohydrated sulphuric acid, two neutral crystallizable substances are obtained in addition to the same acid compounds: sulphonaphthalin, of which the formula is C20H8,SO2, and sulphonaphthalide, the composition of which ap- pears to correspond to the formula C24H10,SO2. These substances are generally accompanied by a red colouring matter, of which the composition is not yet exactly known. Paraffin. § 1586. A small quantity of this substance is found among the products of distillation of bituminous coals, together with a great number of organic substances; and it is concentrated in the sub- stances which volatilize last, when these products are subjected to redistillation. In order to extract it, the substance is heated with concentrated sulphuric acid, which carbonizes the greater portion of the substances mixed with the paraffin, Avhen, if the liquid be allowed to rest, at a temperature of 122° or 140°, the pure paraf- fin forms an oily layer on the surface, which solidifies on cooling. The substance is. expressed several times between tissue-paper, which absorbs the oily portions, and it is purified by solution in boiling alcohol, or in a mixture of alcohol and ether, whence it is deposited, on cooling, in the form of brilliant spangles of a greasy lustre. A large quantity of paraffin may be obtained by distilling a mix- ture of wax and lime, when the oily product which solidifies on cool- ing, after being expressed between tissue-paper, furnishes pure paraf- fin by crystallization in alcohol or in ether. Paraffin melts at 116.6° and boils at about 700°, while, if it is not carefully heated, a portion of it is decomposed and yields gaseous products. It is distinguished by great stability, since concentrated sulphuric acid, at a temperature not exceeding 212°, ordinary nitric acid, and chlorine, exert no action upon it, to which property it owes its name, (from parum affinis.) Paraffin burns in the air with a brilliant flame, and very good candles are made of it. 100 parts of boiling alcohol dissolve about 3.5 of it, nearly all of which is de- posited on cooling. The name of eupione has been given to volatile oils obtained, in greater or less quantity, in the preparation of paraffin, which are mixtures of various carburetted hydrogens, analogous to those con- stituting petroleum. # 682 PRODUCTS OF DRY DISTILLATION. § 1587. These various names are given to a product extracted from coal-tar, by distilling the oily part of the tar and collecting separately the portion which passes over between 300° and 400°. The liquid distilled between these two degrees is shaken several times with a very concentrated solution of caustic potassa, to which fragments of hydrate of potassa are added, when the oil disengages a disagreeable odour, and sets into a crystalline mass. Water being then added, and the whole heated to boiling, the liquid separates into two layers: a light, oily layer, which is removed, and a heavier, aqueous liquid, which is treated with chloroliydric acid. The oil which is thus separated by rising to the surface is decanted, digested over chloride of calcium, and distilled several times. This oil, which is phenic acid, and becomes solid at a low temperature, is also formed in the distillation of salicylic acid with lime, and in that of benzoin. Phenic acid constitutes, at the ordinary temperature, a white crys- talline compound, melting at about 95.0°, and boiling at 370.4°; of the density 1.065 at 64.4°; slightly soluble in water, and dis- solving in all proportions in alcohol and ether. It combines with potassa to a crystalline salt K0,C12H50, and forms analogous com- pounds with baryta and lime. It reduces several metallic salts, par- ticularly the salts of silver and mercury. Chlorine acts readily on phenic acid, and the following phenic acids have thus been obtained: PHENIC ACID, PIIENOLE, OR CARBOLIC ACID CiaIIsO,HO. Bichlorinated C12H3C]20,H0, Trichlorinated C12H2C130,II0. and Bromine forms analogous products. Nitric acid also acts on phenic acid, and yields successively binitrophenic acid C12H3(N04)20,H0, and trinitrophenic acid C12II2 (N04)30,H0; which two products are generally prepared by at- tacking directly, by nitric acid, the portion of oil of coal-tar which distils between 354° and 374°, when a very energetic reaction ensues, furnishing a brown mass, which is washed with cold water and dis- solved in ammoniacal water heated to boiling. The liquid deposits, on cooling, binitrophenate of ammonia, which is to be purified by several crystallizations; and which, by decomposition with chlorohydric acid, yields binitrophenic acid. This acid, which crystallizes in right-angled prisms, with a rectangular base, and of a slightly yel- lowish colour, is suddenly decomposed by heat. It dissolves slightly in boiling water, and is wholly deposited from it on cooling, while alcohol and ether dissolve it largely. Boiling nitric acid acts readily on binitrophenic acid, and con- verts it into trinitrophenic acid C12H2(N04)30,II0, which has been known for a l«ng time under different names; having been called Welter's bitter, nitrocarbonic acid, picric acid, etc. It is obtained 683 by the action of nitric acid on the most diversified organic sub- stances, particularly on nitrogenous substances of animal origin, such as silk, fibrine, and animal tissues. Salicin treated with nitric acid yields a large quantity of trinitrophenic acid, and wTe shall see that it is also obtained in treating indigo by the same acid. It crystallizes in brilliant yellow prisms, is but slightly soluble in cold, but largely so in hot water, while alcohol and ether dissolve it freely. It forms yellow crystallizable salts with bases which detonate when heated. NAPHTHA. CREASOTE C28H1s03. § 1588. A liquid substance, called creasote, and possessing some interest in being used to allay toothache, is extracted from wood-tar and pyroligneous acid, by a long and complicated process. The Vood-tar is distilled until a pitchlike mass alone remains, when the distilled liquid separates in the receiver into three layers, the lower of which, containing the creasote, is saturated with carbonate of soda; after which the supernatant oil is decanted and again dis- tilled ; the first products, which are lighter than wrater, being rejected, while the heavier oil is collected and again distilled. This oil is then shaken several times with a weak and hot solution of phos- phoric acid, washed until it gives off’ no more acid, and treated with an alkaline solution of the density 1.12, when the creasote leaves the oil, and dissolves in the alkaline liquid, which is separated and exposed for some time to the air, to oxidize a foreign substance which discolours the liquid. Lastly, the solution, after being satu- rated with phosphoric acid, is distilled, when the creasote volatilizes with the water and separates in the receiver in the form of an oily layer. Creasote is a colourless, oleaginous liquid, of a penetrating and disagreeable odour and an acrid and burning taste ; cauterizing the organic tisues, coagulating albumen, and preventing the putrefaction of meat. It boils, without change, at about 390°, and is insoluble in water, but readily so in alcohol and ether. It forms, with potassa and soda, crystalline compounds, from which acids separate it without change; and its composition corresponds to the formula C28II1604. An alcoholic solution of creasote is used in medicine. NAPHTHA, OR PETROLEUM. § 1589. In many countries, odoriferous oils exude from the ground, accompanied generally by hot or cold -water, and sometimes by combustible gases; and when such liquids are collected in natural or artificial reservoirs, the oil floats on the surface. The general name of petroleum is given to these oils, the nature of which is evi- dently very diversified, for some of them distil wholly without change, while others leave a considerable residue of fixed oil, which is decomposed by heat. The most abundant springs of petroleum 684 FATS, are in the neighbourhood of Baku in Persia, where jets of com- bustible gas, copious enough to enable the inhabitants to use it for cooking their food, issue simultaneously from fissures in the ground; and some springs of petroleum are also found at Amiano, in the Duchy of Parma. Petroleum is purified by distillation with water, and the product is known in commerce by the name of oil of naphtha, or oil of petroleum . Oil of naphtha, which presents the density of about 0.84, and gives a peculiar odour, contains no oxygen, and appears to be formed by the mixture of several carburetted hydrogens. If it be distilled in a retort furnished with a thermometer, ebullition is found to com- mence when the thermometer marks 250° to 284°, while the temper- ature gradually rises, and the last portions do not distil below 570°. If the products of distillation be collected separately, the most vola- tile is a liquid boiling at about 194°, after which numerous products pass over, boiling at higher and higher temperatures, while it has hitherto been impossible to separate a liquid presenting a constant boiling point, mixtures only having been obtained. The composition of the most volatile products correspond approximately to the formula CH, and they are isomeric with olefiant gas, while the less volatile products contain less hydrogen. The essential oils which form petroleum are remarkable for their resistance to chemical agents, since they are scarcely affected by concentrated sulphuric and nitric acids ; and they are used in the laboratory for the preservation of potassium, (§ 426.) THE FATS. § 1590. The name of fats is commonly assigned to substances of organic origin, liquid or solid, but melting at a very low tempera- ture, which, when spread in a liquid state on paper, render it trans- lucent, and make permanent stains on it, known by the name of grease- spots ; while the chemist defines fats by certain chemical properties, and, particularly, by their manner of composition, as shall subse- quently be shown. Fatty substances are found both in the vegetable and animal kingdoms, and seem to be identical in both; which has led some physiologists to the opinion that animals merely assimilate to them- selves those which exist in vegetables, without their undergoing any chemical change. Although we shall reserve for the close of this work the study of the principal substances constituting the animal eco- nomy, we shall not, in this place, separate the fatty substances of the two kingdoms. Vegetable fats are generally fluid at the ordinary temperature, while several of them coagulate and solidify, more or less perfectly, FATS 685 at a low temperature. They are completely liquid only at a high heat, and at the ordinary temperature possess a certain degree of viscidity, called an oily consistence. The fat of warm-blooded ani- mals is solid, its firmness varying according to the position it occu- pies in the body of the animal; while that of fishes and cold-blooded animals in general is fluid. In plants, fat is found chiefly in the seeds and pericarp of the fruit, in the form of small drops which fill peculiar cells, and also exists in the shape of a waxlike substance * on the surface of the leaves and hark. The proportion existing in seeds is often very considerable: thus, flaxseed contains about 20 per cent, of oil, and rapeseed 35 to 40, while the seed of ricinus communis, which fur- nishes castor-oil, contains as much as 60. The oil is generally ex- tracted merely by expressing the seeds, hut in order to render it more fluid they are heated, and then compressed between hot plates. When the proportion of oil is smaller, fermentation is sometimes resorted to for the destruction of a portion of the organic substances and in order to break up the fruit. Lastly, in the laboratory, sol- vents are sometimes used, chiefly ether, which is then driven off by evaporation. Animal fat may be obtained either mechanically or by the action of heat. In order to purify it in the laboratory, it is generally dis- solved in ether; but it must not be forgotten that this liquid can also dissolve some of the foreign substances mixed with the fat. The melting point of fat varies from 23° to 140°, while at temperatures above 480° they yield copious and very acrid fumes, but do not distil without alteration, whence they are called fixed oils. At an intense heat they are wholly decomposed, and produce gases of great illuminating power. § 1591. Oils generally absorb oxygen from the air, but in very various proportions; and while some absorb but small quantities of it without sensibly changing in appearance, merely acquiring a dis- agreeable smell, when they are said to become rancid, others absorb larger proportions of oxygen, become covered with a coating of a resinous appearance, and are finally completely solidified; and these are called drying-oils, the only ones which can be used in painting. Linseed, nut, hemp, poppy, and castor-oil are drying-oils, while some fish-oils appear to possess the same property. The fat of warm-blooded animals, the oil of almonds, olive-oil, rapeseed-oil, &c. are not drying-oils. The chemical action which produces the solidification of drying- oils is sometimes limited to a simple combination with oxygen; as in the case with linseed-oil, which absorbs large quantities of oxy- gen without disengaging any gas; but more frequently carbonic acid, and sometimes hydrogen, is evolved. Absorption goes on slowly at first, but subsequently becomes more rapid, especially when the oil is spread over a large surface or on porous bodies. Drying-oils 686 FATS dry more quickly when they have been previously boiled with litharge or peroxide of manganese; in which case they contain a small quantity of these metallic oxides in solution. § 1592. The greater part of animal fats is formed of several proximate principles united in indefinite proportions; and of which chemists have distinguished only three: stearin, margarin, and olein. These principles behave, in chemical reactions, like compounds of the same substance, glycerin, with a fatty acid, peculiar to each of these principles. Stearin and margarin, to which beef and mutton fat owe their solidity, are converted into glycerin, and two fatty acids, which are stearic acid for stearin, and margaric acid for margarin ; while olein, to which fats owe their oleaginous character, is trans- formed into glycerin and oleic acid. In several fatty substances, such as butter, we find, in addition, small quantities of peculiar fatty matters, called butyrin, caprin, and caproin, which may be considered as compounds of glycerin with volatile acids, differing in each of these substances, and which have been called butyric, capric, and caproic acids. We have shown that butyric acid is formed in a peculiar fermentation of sugar; and it will now soon be seen that the same acid arises, as also capric and caproic acids, from the ac- tion of nitric acid on stearin, margarin, and olein. The fat of the goat contains, in addition to the ordinary immediate principles, a small quantity of a peculiar fat, called Tiircin, which behaves like a compound of glycerin and a peculiar volatile acid, hircic acid. Lastly, another fatty substance is found in fish-oils, which may be considered as a compound of glycerin and a peculiar acid, called yhocenic, ap- pearing to be identical with valerianic acid. A peculiar fat substance is extracted from the head of the sperm whale, called spermaceti, the constitution of which is very different from that of other animal fats, since it does not contain glycerin, but in its stead another neutral substance, called ethal; while the fat acid which is combined with the ethal has received the name of ethalic acid. Lastly, the various kinds of wax, which should be classed among the fats, from the definition given of the latter, (§ 1590,) differ com- pletely from it in their chemical composition, as shall presently be shown. § 1593. Stearic, margaric, and oleic acids are weak acids, which are displaced from their compounds by a majority of the other acids; and they are insoluble in water, but soluble in alcohol, and very feebly in ether. They are less easily melted than the proxi- mate fatty principles which produced them, and they do not distil without alteration under the ordinary pressure of the atmosphere. They are then decomposed at a temperature above 570°, yielding very complicated products; but they may be distilled in vacuo, be- cause the distillation is then effected at a much lower temperature. § 1594. The chemical operations by which natural fat substances EATS, 687 are converted into glycerin and fat acids are known by the general name of saponification. They are various; and the saponification of fats may be effected either by alkalies or by powerful acids, or by the action of heat alone. If fats be heated to a temperature of 570°, in an apparatus tra- versed by a current of steam, under a pressure inferior to that of the atmosphere, the glycerin is converted into several products soluble in water ; while the fat acids, set free, distil without altera- tion ; thus furnishing an example of saponification by heat alone. The action of hot alkaline lixivise decomposes fats and oils into glycerin, which dissolves in the aqueous liquid, and into fat acids, which combine with the alkali and form salts, commonly called soaps, which are insoluble in the alkaline liquor, but readily dissolve in a sufficient quantity of water. This operation, called saponifi- cation by bases, may be effected not only by alkaline bases, such as potassa, soda, and ammonia, but also by other metallic oxides which possess powerful basic properties, such as baryta, strontia, lime, and the protoxides of lead and zinc. The other metallic oxides no longer produce the saponification of fats, that is, their decom- position into glycerin and fat acids; while they may combine with the isolated fat acids and form insoluble soaps. Water is generated during saponification, for the united weight of the glycerin and fat acids is greater than the weight of the original fat. The neutral alkaline carbonates can also effect the saponification of fats, in which case they part with one-half of their alkali, which produces saponification, while the other half retains all the carbonic acid in the shape of bicarbonate; carbonic acid being disengaged only if heat is applied, because the bicarbonate is then decomposed. Powerful acids, such as sulphuric, also effect the saponification of fats ; and if the proportion of acid be not very great, the fat acid is isolated, the glycerin combining with the animal acid to form a compound acid. If the weight of the mineral acid exceed the half of that of the fat acid, it often combines with the latter, producing sulplioglyceric, sulphostearic, sulphomargaric, and sulpholeic acids. Smaller quantities of sulphuric acid are however sometimes used to purify the oils intended for burning in lamps, in which case the acid selects the foreign substances more easily acted on, contained in the oils, dissolving them, and effecting only an insensible saponification. § 1595. No fatty substance is soluble in water, which does not even moisten them; while they are somewhat soluble in absolute alcohol and wood-spirit, ether and the essential oils dissolving them much more freely. The liquid fats are the best solvents of solid fats. We have seen that natural fats are rarely simple, nearly always mixtures or indefinite compounds of various different fatty substances, which are separated only with the greatest difficulty. When the fat is solid, it is sufficient to melt it, and allow it to cool slowly, to observe in it the forming of solid lumps, the nature of 688 FATS, which differs from the liquid part. So again, certain fatty oils, olive-oil, for example, deposits, by slow cooling, more or less copious flocculi, which differ from the liquid portion; and by expressing these solidified portions between tissue-paper, a large quantity of interstitial liquid oil can be separated, furnishing a mixture of stearin and margarin, adulterated merely with a small quantity of olein. The proportions of stearin and margarin in the substances expressed vary according to the nature of the original fats. When they are yielded by mutton or beef fat, or lard, they are composed almost wholly of stearin; while, if furnished by human fat or olive- oil, they consist chiefly of margarin. These substances may be more perfectly isolated by a proper use of solvents. The immediate fluid constituent of animal fats, olein, is still more difficult to isolate, the oil which flows from the compression of such fats being olein saturated with stearin or margarin. The most fluid vegetable oils are themselves olein, containing more or less stearin and margarin in solution; and by cooling them gradually and de- canting the fluid, a large portion of the solid constituent may be separated; or the oil may also be shaken with alcohol, which dis- solves the olein much more freely than the stearin and margarin, and the alcoholic solution may be evaporated: but all these pro- cesses never effect a perfect separation. It is moreover highly pro- bable that stearin, margarin, and olein are not merely mixed in the majority of fats, and that they are in the state of indefinite com- pounds. Olein does not appear to be identical in the various vegetable oils, since several chemical experiments seem to prove that it differs in the drying and non-drying oils. If, for example, a non-drying oil, such as olive-oil, be agitated with a small quantity of hyponitric acid, or with a solution of subnitrate of mercury, which contains hyponitric acid, the oil becomes completely solid after some time, and is converted into a crystalline substance, elaidin. Drying-oils do not possess this property, which thus furnishes a test, applicable to commercial purposes, of the purity of olive-oil, which is fre- quently adulterated with other vegetable oils, and particularly with poppy-oil. Fat acids which are capable of crystallization may be obtained in a state of purity, and since they at the same time form a great number of definite compounds, their properties and chemical com- position have been more accurately ascertained than those of the fats which furnish them. Nevertheless, uncertainties still exist, on account of the very high value of their chemical equivalents; the smallest errors in analyses corresponding to 1 or several equivalents of simple elements, and sufficing to change the formulae. We shall examine only the most important and most common fatty substances, commencing with the study of glycerin, which is an essential and constant principle of the majority of these substances. GLYCERIN. 689 § 1596. The most simple method of preparing glycerin consists in heating fats with protoxide of lead, in the presence of water, when saponification is soon effected, an insoluble soap of lead being formed, while the glycerin remains dissolved in the water. The aqueous solution is subjected to a current of sulfhydric gas, which precipitates a small quantity of oxide of lead dissolved in it in the state of sulphide; after which it is concentrated at a gentle heat, and the evaporation completed in vacuo. Glycerin, dried in vacuo at 212°, is a syrupy, colourless, inodor- ous liquid, tasting like sugar, from which circumstance it has de- rived its name, (y-Kvxvs, sweet,) insoluble in water, but soluble in all proportions in alcohol and ether. It is decomposed by heat, yielding very complex products; among which is remarked an oily, colourless, extremely disagreeable-smelling liquid, called acrolein, and present- ing the formula C6II402. Oxidizing substances, such as ordinary nitric acid, or a mixture of sulphuric acid and peroxide of manga- nese, form with glycerin, oxalic, formic, and carbonic acids. Chlorine and bromine act on glycerin, and form chlorinated and brominated compounds, which can only be expressed in equivalents by doubling the ordinary formula of glycerin, that is, by writing it C12H14O10,2HO, which furnishes, Glycerin C6H705,H0. Original glycerin C12H14O10,2HO, Trichlorinated “ C^E^ClgOj,,, Tribrominated “ C12HnBr3O10. But it is difficult to decide the question, owing to the want of means of ascertaining the purity of the chlorinated and brominated sub- stances, inasmuch as they do not crystallize. By mixing 2 parts of concentrated sulphuric acid with 1 part of glycerin, combination ensues, with elevation of temperature; and by leaving the mixture to itself for some time, shaking it frequently, an acid compound, sulphoglyceric acid, is produced, which forms soluble salts with lime and oxide of lead; the lime-salt being pre- pared by adding water to the mixture, saturating it with chalk, and filtering to separate the sulphate of lime. The liquor, when evaporated, yields sulphoglycerate of lime, of which the formula, when it is dried at 248° in vacuo, is Ca0(C6H705,2S03), and which dissolves in one-half of its weight in water, but it is insoluble in alcohol and ether. Glycerin also becomes heated when it is mixed with anhydrous or hydrated phosphoric acid; aphosphogly ceric acid, which dissolves in water, being formed. By saturating the liquid with carbonate of baryta, and lastly by caustic baryta, the free phosphoric acid is precipitated in the state of phosphate of baryta, while the liquid contains phosphoglycerate of baryta, which is separated by evapora- 690 FATS. tion. The formula of this salt, dried at 284°, is 2Ba0,(C6II706, PO,). Phosphoglyceric acid has been found ready formed in the yolk of eggs. Sulphoglyceric and phosphoglyceric acids yield a large quantity of acrolein when they are decomposed by heat; which is, in fact, the best method of preparing this substance. Stearin and Stearic Acid, § 1597. The most efficient method of isolating stearin consists in melting talloAv with oil of terpentine, when the oil, after being de- canted, deposits a solid substance on cooling, which is subjected to pressure between the folds of tissue-paper in a press. After being similarly treated several times, it is dissolved in ether, with the as- sistance of heat, when the greater portion of it is again deposited on cooling. The stearin thus obtained is considered as pure. Chemical analysis, added to the knowledge of its products of sapo- nification, have assigned to stearin the formula C142II140O16, which is more properly written (C6H705-f IIO),2C68H6605. Stearin is therefore admitted to be an acid compound, analogous to sulphovinic acid (C4H50,H0)2S03, and formed by the combination of 2 equiv. of stearic acid C68Hff605 with 1 equiv. of glycerin and 1 equiv. of water. Stearin crystallized in ether forms small white lamellae, of a pearly lustre, melting at from 140° to 144°, and setting, on cooling, into a white opake mass, presenting no appearance of crystalliza- tion. It is completely insoluble in water, but dissolves in 8 parts of boiling alcohol, separating from it almost entirely on cooling; while ether dissolves a large proportion of it at the boiling point, but when cooled only retains about § 1598. Stearic acid is an important article of commerce, of which candles, called stearic candles, are made. It is jmepared by sapo- nifying beef or mutton suet by lime: 500 kilog. of suet and 800 litres of water are placed in a wooden vat, holding 2000 litres, and lined with lead, and heated by steam conveyed directly into the vat by means of a circular tube pierced with holes; and when the suet is melted, about 600 litres of a solution of lime, containing 60 kilog. of quicklime, is added, and the mixture is continually stirred. After 6 or 7 hours, the saponification is terminated, and the soap of lime has formed a consistent mass, which becomes very hard on cooling. It is reduced to a fine powder, and decomposed by sulphuric acid, diluted with water, in vats similar to the first, and heated by steam, Avhen the fatty acids, set free, form an oily layer on the surface of the acid liquids. The melted fat is decanted, and washed several times, Avliile hot, Avith Avater charged Avith sulphuric acid, and then with fresh Avater; and it is finally run into tin moulds, forming cakes of 3 or 4 kilogs. STEARIC ACIDS. 691 in weight. This mass, which is still a mixture of stearic, margaric, and oleic acids, is first powerfully compressed when cold, in order to express the greater part of the oleic acid, and then at a tempera- ture of 90° or 100°, to drive out the remainder. The oleic acid thus expressed is of a deep brown colour, and contains nearly all the margaric, besides a certain quantity of stearic acid. The cakes remaining after this compression are again melted, in contact with a dilute solution of sulphuric acid, which removes the last traces of lime from the fatty substance; after which it is freed from the ad- hering acid by washing it in boiling water. It is then poured into moulds, where it becomes solid, and is thus brought into commerce as refined stearic acid, used for the manufacture of candles. § 1599. Large quantities of solid fat acids are now prepared for the manufacture of stearic candles by a very ingenious process, in which saponification by sulphuric acid is combined with distillation of the fat acids, in intensely heated steam, having but little tension. This process enables the use of fats of all kinds, and of the most inferior qualities. The fats, placed in boilers heated by steam, are first treated with a quantity of concentrated sulphuric acid, which varies from 6 to 15 per cent., according to the nature of the fat. The temperature being raised to 212°, and kept at that point for 15 or 20 hours, under constant stirring, the fat acids are set free, and the glycerin is almost wholly converted into sulphoglyceric acid; while the greater portion of the foreign substances are destroyed by the sulphuric acid, yielding carbonaceous residues and products soluble in water. The fat acids are washed with water, and then placed in a distilling apparatus, through which steam heated to about 600° is passed, with an elastic force inferior to that of the atmosphere, when the fat acids distil with the water, and by pressure can be brought into a state fitted for the manufacture of candles. § 1600. Very pure stearic acid may be obtained, for laboratory purposes, by crystallizing the stearic acid of commerce several times in boiling alcohol. Stearic acid yields, by slow cooling, beautiful and pearly crystals, melting at 158°, and at a temperature of 570° giving oft' vapour without alteration. It may be distilled in vacuo, and is completely insoluble in water, but very soluble in boiling alcohol and ether. The formula of crystallized stearic acid is C68II6807, which should be written C68H6605,2II0, since 2 equiv. of a base may be substituted for 2 equiv. of water; showing it, therefore, to be a bibasic acid. The acid forms two salts with potassa: bipotassic stearate 2KO, C68II6605, and monopotassic stearate (K0-fH0),C68H6605.* The former is obtained by treating stearic acid with an equal vTeight of * These salts would with more propriety be called basic and neutral stearates of potassa.— W. L. F. 692 FATS hydrate of potassa, dissolved in 20 parts of water, when the salt remains in the form of clots, which are compressed between tissue- paper. It is then redissolved in 15 or 20 parts of boiling alcohol, and the liquid allowed to cool, when the bipotassic stearate is de- posited in white crystalline lamellse. It dissolves without change in 10 times its weight of water, but, when cold, produces only a mucilaginous liquid, which does not become perfectly fluid and limpid unless it be heated to boiling. When a larger quantity of water is poured into this solution, a clouded, opalizing liquid is obtained, in which a large number of small crystalline spangles of extreme de- licacy swim, and which settle to the bottom of the vessel, if it be allowed to rest. These small crystals constitute monopotassic stea- rate, of which the formula is (KO-fiH0),C68IIgg05. Alcohol does not effect this decomposition in the bipotassic stearate. Soda forms two stearates analogous to those of potassa: stearates of baryta, strontian, and lime, which present the formula 2RO, C6SH6605> are prepared by double decomposition from the bipo- tassic stearate, and are completely insoluble in water. The lead- salt is obtained in the same way, but the stearate of lead used in pharmacy for the making of plasters is prepared by directly sapo- nifying fats by litharge in the presence of water. Spring-wTater is generally hard, and is then unsuitable for washing, owing to the presence of calcareous salts, which decompose the alkaline soaps as they form, and make insoluble soaps; and alkaline soap can only dissolve when the calcareous salts are completely decomposed. Water is rendered fit for washing by adding a small quantity of carbonate of soda, which decomposes the salts of lime. Stearic acid forms vinostearic and methylostearic ethers, which are obtained by dissolving stearic acid in absolute alcohol or wood- spirit, and passing through it a current of chlorohydric acid gas; when the ethers, after being precipitated by wrater and crystallized in alcohol, form white substances of a greasy lustre, and melting at from 86° to 95°. § 1601. By decomposing with acids a soap made of human fat, a mixture of fatty acids is obtained, melting at about 135°, and which is considered as composed solely of margaric and oleic acids. Mar- garic acid is supposed to be produced by the saponification of a sim- ple fat, margarin, but which probably exists in combination with olein. Margaric acid is also formed in the distillation of stearic acid and the fats in general, as well as when the latter are subjected to the action of oxidizing reagents. Chemists are not agreed upon the formula of margaric acid; and while some write it C68H6606, 2HO, a formula which differs from that of stearic acid by 1 equiva- lent of oxygen, others assert that its composition is identical with that of stearic acid. Margaric Acid C68H6606,2II0. OLEIC ACID. 693 The best method of preparing margaric acid consists in saponify- ing human fat or olive-oil by potassa, and pouring acetate of lead into the solution, which yields a precipitate of margarate and oleate of lead. The precipitate being treated several times with ether, which completely dissolves the oleate of lead, and a much smaller proportion of margarate, the remaining margarate of lead is decom- posed by dilute nitric acid, and the margaric acid arising from it is purified by crystallization in alcohol. In its physical properties, margaric closely resembles stearic acid, but it melts at a lower temperature, viz. at 140°. It forms two salts with potassa: the bipotassic margarate 2K0,C68H6606, and the monopotassic marga- rate (KO-f II0),C68H6e06; which are formed under the same circum- stances as the corresponding stearates, and nearly resemble them. Oleic Acid CggH^OgjHO. §1602. In order to separate this acid, oils very rich in olein, such as olive-oil and oil of almonds, are saponified by potassa; when the soap is decomposed by tartaric acid, and the fatty acids which sepa- rate are decanted. The latter are digested in a water-bath with one-half of their weight of finely-powdered oxide of lead, thus form- ing a soap of lead, consisting of both the oleate and the margarate. This soap is digested for 24 hours with twice its volume of ether, which dissolves the oleate, and the etherial liquor being evapo- rated, the oleate of lead is decomposed by chlorohydric acid. The oleic acid thus obtained is, however, not pure, and must be redis- solved in ammonia, precipitated by chloride of barium, and the oleate of baryta must be purified by several crystallizations in boiling alco- hol. Lastly, the oleate of baryta is decomposed by tartaric acid, operating in a bottle perfectly fitted and well corked, to prevent the oleic acid from absorbing the oxygen of the air. Oleic acid is a colourless liquid, solidifying below 53.6°, and insoluble in water, but very soluble in alcohol, ether, and the essen- tial oils. It does not redden litmus, even when dissolved in alcohol; and it readily absorbs oxygen from the air. The formula C36H303, HO, which has generally been assigned to this acid, should probably be doubled and written C72H6606,2H0, in which latter case the acid would be considered as bibasic. Oleic acid is decomposed by heat, but may nevertheless be distilled in vacuo. The products of its decomposition are very various; and a fatty acid, called sebacie, which characterizes oleic acid under these circumstances, is remarked among them. Treated with nitrous acid, oleic acid is easily trans- formed into an isomeric modification, elaidic acid, which sets into a crystalline mass, and which shows a very strong acid reaction. It dissolves in boiling alcohol, and separates partly from it, on cooling, in large crystalline lamellae, which melt only at 111.2°. of ni- trous acid will effect the transformation of oleic acid, but it rapidly increases with the quantity of nitrous acid used. Elaidic acid 694 FATS. oxidizes rapidly in the air, particularly if it be heated to 140° or 160°. The alkaline oleates are readily formed by dissolving oleic acid in alkaline lixivise, or by treating the alkaline carbonates by an alcoholic solution of oleic acid; other metallic oleates being prepared by double decomposition. The formula of oleate of baryta is BaO, A large quantity of water decomposes the alkaline oleates, salts containing a smaller proportion of base being deposited; which decomposition is however less readily effected than in the stearates and margarates. § 1603. When sulphuric acid is made to act on stearin, the latter is decomposed in the same manner as when in contact with the hydrated alkalies; stearic acid being set free, and the glycerin combining with the sulphuric acid to form sulphoglyceric acid. It is as yet unknown what reaction sulphuric acid exerts on margarin or on olein when isolated; the reaction on the natural fats, which are mixtures or compounds of these two substances, and particularly on olive-oil, having hitherto only been studied. When olive-oil is treated with one-half of its weight of concen- trated sulphuric acid, by placing the bottle containing the two sub- stances in a refrigerating mixture, in order to prevent an elevation of temperature, a homogeneous liquid of a viscous consistence is formed, composed of sulphoglyceric acid and two new compound acids, called sulphomargaric and sulpholeic. By adding a great excess of cold sulphuric acid, the sulphomargaric and sulpholeic acids are separated from the sulphoglyceric acid, which remains in solution, while they form an oily coating on the surface, which is removed and washed with a small quantity of water, to free it from the sulphuric acid. These acids dissolve readily in water and alco- hol, and form well-defined salts. Their aqueous solution decom- poses spontaneously in the cold, and more rapidly at the boiling point, into sulphuric acid, and new fat acids, which appear to differ from margaric and oleic acids only by the addition of 1 or more equivalents of water. Margarin yields the three acids, metamar- garic, hydromargaric, and liydromargaritic; while oleic acid fur- nishes but two, metoleic and kydroleic acids. The three acids derived from margarin are solid at the ordinary temperature, meta- margaric acid melting at 122°, hydromargaric at 140°, and hydro- margaritic at 154°; while metoleic and hydroleic acids are oily liquids. All the new fat acids, being insoluble in water, are readily soluble in alcohol and ether. Metoleic and hydroleic acids, carefully heated in a retort, are decomposed, and disengage pure carbonic acid, while, together with some empyreumatic substances, an oily liquid, composed of two iso- meric carburctted hydrogens, presenting the composition of olefiant ACTION OF SULPHURIC ACID ON THE NATURAL FATS. 695 gas, condense in the receiver, and may be separated by distillation at different temperatures. The first, oleen, boils at 131°, has a disagreeable and penetrating odour, and the density of its vapour has been found to be 2.87, while its formula is C12II12, which is represented by 4 volumes of vapour. The second compound, elaen, the formula of which appears to be C18H18, boils at 230°. DECOMPOSITION OF FAT ACIDS. ACTION OF NITRIC ACID ON STEARIC,'MARGARIC, AND OLEIC ACIDS. § 1604. Nitric acid reacts energetically on the fat acids, forming with them very complicated products, among which are some new and highly interesting acids. Since during the first periods of the reaction of nitric on stearic acid the latter is converted into margaric acid, the products afforded by margaric and oleic acids only remain to he described. The ultimate products of the reaction are very complicated, and may he divided into two classes : the volatile acids which condense in the receiver, and the fixed or slightly volatile acids which remain in the retort. We shall here enumerate them with their formula, in order that the curious relation between them may be more easily seen. The fourth column contains the carbu- retted hydrogens from which they may be supposed to be derived by substitution. Volatile Acids. Formic acid C2 H2 04 or C2 H 03,II0 C2 H4 Acetic “ C4 H4 04 C4 H3 Os,HO C4 H6 Acetonic “ C6 H6 04 C6II5 03,II0 C6H8 Butyric “ C8 H8 04 C8 H‘7 03,H0 C8 Hlu Valerianic “ C10H10O4 C10H9 03,H0 C10H12 Caproic “ C12H1204 C12Hu03,H0 C12H14 (Enanthylic “ C14H1404 C14H1303,H0 C14H16 Caprylic “ C16H1604 C16H1503,H0 C1GH18 Pelargonic “ C18H1804 C18H1703,H0 Capric “ W4 C20H19O3,HO C20H22. It will be seen that if the equivalent of basic water be not sepa- rated in the formula, all these acids may be regarded as compounds of 4 equivalents of oxygen with carburetted hydrogen isomeric with olefiant gas. If, on the contrary, the basic water be isolated, they may be regarded as resulting from the substitution of 3 equivalents of oxygen for 3 equivalents of hydrogen in carburetted hydrogens of which the general formula is 02„H2n+2 (n being a whole number :) but only one of these carburetted hydrogens, the protocarbu- retted C2II4, is as yet known with certainty.* * This theory has already been noticed in the note to $ 1401, where it is also shown that the acids in the above table may more properly be considered as oxalic acid paired with one eqviiv. of a carburetted hydrogen of the general 696 The slightly volatile acids which remain in the retort are FATS Succinic acid C8 H6 08 or C8 H4 06,2H0 Adipic “ C12H10O8 C12H8 06,2H0 Pimelic “ C14H1208 C14H10O6,2HO Suberic “ C16H1408 C16H1206,2H0 Sebacic “ C20H18O8 C20H16O6,2HO If we omit the basic water contained in the formula, we shall find all these acids to result from the combination of 8 equivalents of oxygen with the carburetted hydrogens of which the general formula is C2„H2(n_1). § 1605. In order to obtain these various products, it is necessary to operate on a somewhat considerable quantity of oleic acid. The nitric acid should be first introduced by itself into a tubulated retort, and heated to 120° or 140°, the oleic acid being added by small quantities at a time. Violent reaction ensues at each addition; and when all the oleic acid has been poured into the retort, the heat is continued until reaction ceases. The liquid collected in the receiver consists of water containing the most soluble of the volatile acids, such as formic, acetic, acetonic, and butyric acids, covered by an oily layer which contains the valerianic and other acids. The latter is de- canted, saturated with water of baryta, and the various salts of baryta formed are separated by successive crystallizations. The caproate of baryta crystallizes first, and then successively the cenanthylate, the caprylate, the pelargonate, the caprate, and lastly the valerianate of baryta. The more volatile acids, when dissolved in water, are saturated by carbonate of soda, and the solution evaporated; when the first crystals deposited from the cold solution are acetate of soda; while if sulphuric acid be then poured into the mother liquid, an oily layer, composed of butyric and metacetonic acids, is separated. When the slightly volatile acids which remain in the retort are chiefly sought to be obtained, the action of the nitric acid must not be too much prolonged, since a portion of them would then be de- stroyed. The oleic acid is then acted on by double its weight of nitric acid, and the action is continued until no more reddish vapours are disengaged, when a portion of the oleic acid has dis- appeared, being converted into products which dissolve in the aqueous liquid. The supernatant oil is decanted, and again acted on by nitric acid ; this process being continued until it has nearly disappeared, when the slightly volatile acids are found in the watery liquids arising from this treatment. formula, Ca„Hin+1. The substitution of oxygen for hydrogen is in no case admis- sible; and while of the hydrocarbons assumed in the text as the radicals only one is known, several of the formula just mentioned have been isolated, such as methyl C\1IS, ethyl C4H5, valyl C8II9, and amyl C10Ihi-— W. L .F. SUCCINIC ACID. 697 Succinic Acid C8H406,2H0. § 1606. Succinic acid is produced not only by the action of nitric acid on fatty acids, but is also found under other remarkable cir- cumstances. It is generally prepared by distilling amber, a sub- stance of organic origin, sometimes found in strata of lignite, and occurring in large quantities in the alluvial sands of the Baltic. Amber distilled in a glass retort yields an acid water, and empy- reumatic oils, which remain in the paper through which the acid liquid is filtered. The latter being saturated with chlorine in order to destroy some foreign substances, and then evaporated, the suc- cinic acid is deposited in crystals. An aqueous solution of impure asparagin left to itself for some time is converted by a species of fermentation into succinate of ammonia. Impure neutral malate of lime, such as is directly obtained from the berries of the service-tree, left for several months, under a layer of water, in a vessel covered merely by a sheet of paper, undergoes an analogous fermentation, the liquor becoming covered with mucilage, while crystals of hydrated carbonate of lime are deposited on the sides of the vessel, and acicular crystals of succinic acid are developed on the deposit of malate of lime. Succinic acid melts at 365°, boils without alteration at 473°, and may be sublimed at much lower temperatures. Cold water dissolves about | of its weight of it, and boiling water about and it also dissolves in considerable quantity in alcohol, but very slightly in ether. The formula of succinic acid, crystallized in water, is C8H0O8, which is generally written C8H406,2II0, since 2 equiv. of base may be substitued for 2 equiv. of water. At 284° it loses 1 equiv. of water, and after several distillations becomes perfectly anhydrous; its composition then corresponding to the formula C8H406. Nitric acid and chlorine do not sensibly act on succinic acid, while anhydrous sulphuric acid forms a compound acid with it, called sulp ho succinic. Adipic Acid C12H806J2H0. § 1607. This acid is formed by the reaction of nitric on oleic acid, being deposited after the suberic and pimelic acids, which are less soluble. The best method of preparing it consists in boiling, in a large retort furnished with its receiver, tallow with nitric acid of commerce, renewed until the fatty substance has entirely disappeared. The distilled portions are returned to the retort, and the reaction of the nitric acid is continued until crystals appear in the receiver, after which the liquid is concentrated in a water-bath, when it coagulates into a crystalline mass. It is washed, first with concen- trated nitric acid, then with the same acid more diluted, and lastly with fresh water. Treated again with boiling water, it dissolves and deposits, on cooling, very pure crystals of adipic acid. 698 FATS. This acid melts at 266°, may be distilled without alteration, and forms wTell-marked salts, of which the general formula is 2BO, C12II806. When an alcoholic solution of adipic acid is saturated with chlorohydric acid gas, an oil is obtained having the smell of pippin apples, and known by the name of adipic ether 2C4II50,C12H806. Suberic Acid C16H1206,2H0. § 1608. Suberic acid is formed by the action of nitric acid on fats, being the first deposited when the liquid is crystallized; while it has also been directly obtained by causing the same acid to act on cork, which is the most convenient method of preparing it. The rasped cork being boiled with nitric acid of commerce, the acid liquid is con- centrated by distillation, and allowed to cool, when suberic acid is deposited, and may be purified by solution in boiling water and recrystallization. Suberic acid forms small, hard, granular crystals, soluble in about 2 parts of boiling water, which scarcely retains after cooling, while it is very soluble in alcohol and ether, especially at the boiling point. The alkaline suberates are soluble in water, and nitrate of silver effects in their solution a precipitate of suberate of silver, of the formula 2Ag0,C16H1206. By saturating an alcoholic solution of suberic acid with chlorohydric acid gas, vinosuberic ether 2C4II50,C16II1206 is obtained, as an olea- ginous, colourless liquid, which boils at about 500°. Sebacic Acid C20H16O6,2HO. § 1609. It has been mentioned (§ 1602) that sebacic acid is con- stantly formed in the distillation of substances containing olein or oleic acid, and that it is regarded as characteristic of these sub- stances : it is separated by treating the distilled products several times with boiling water. Acetate of lead is poured into the solu- tion, and the salt of lead precipitated is decomposed by sulphuric acid, when the sebacic acid is deposited from the boiling aqueous solution in the form of crystalline, pearly lamellae. This acid melts at 260.6°, distils without alteration, and is slightly soluble in cold, but much more freely in boiling water, while alcohol and ether dis- solve it readily. It forms crystallizable salts with the alkalies of the general formula 2RO,C20H16O6. It produces a compound ether 2C4H5O,C20II16O6 under the same circumstances as the preceding acids.* * The admirable examination of the fats and fat acids by Chevreul was the first investigation which gave an insight into the chemistry of organic compounds. But more recent investigations have developed the singular transformations to which they are subject; such as, the action of sulphuric acid, their oxidation into other acids, &c.— W. L. F. 699 CAPROIC ACID. OF SOME VOLATILE ACIDS EXTRACTED FROM NATURAL FATS. Hircic Acid. § 1610. Hircic acid is obtained by saponifying the fat of the goat by an alkali, and decomposing the soap resulting by tartaric acid; after which the aqueous liquid is separated and distilled, when the hircic acid, being volatile, passes into the receiver. It is saturated with water of baryta, and the hircate of baryta, which is obtained by evaporation, is decomposed by distilling it with sulphuric acid diluted with its weight of water, when the hircic acid forms an oily stratum on the surface of the water which condenses in the receiver. It has a decided goatlike smell, is slightly soluble in water, but easily so in alcohol or ether, and its composition is un- known. Phocenic Acid. § 1611. The oil of the sperm whale and dolphin yields, by saponi- fication, in addition to the ordinary fat acids, a peculiar volatile acid, called phocenic, which appears to be identical with valerianic acid. Caproic, Capric, and Caprylic Acids. § 1612. These three acids are found among the products of the oxidation of oleic by nitric acid, and are also obtained mixed with butyric acid when butter is saponified by the alkalies. It is admitted that butyric, capric, caproic, and caprylic acid in butter are com- bined with glycerin, and form peculiar substances: butyrin, caprin, caproin, and caprylin. In order to prepare these substances, butter is kept for a long time at a temperature approaching its melting point, when a liquid por- tion separates, in which the butyrin, caprin, caproin, and caprylin are principally concentrated. This oily portion is treated, after being decanted, with an equal part of anhydrous alcohol, and shaken frequently; the alcoholic solution leaving by evaporation an oil formed of a mixture of butyrin, caprin, caproin, and caprylin. If, on the contrary, the butyric, capric, and caproic acids are to be isolated, the butter is saponified with an alkali, and the soap decomposed by an aqueous solution of tartaric acid, when the acids sought remain in the watery liquid; which is separated and distilled. The acids, being volatile, pass over, and are then saturated with caustic baryta, and evaporated, which furnishes a mixture of buty- rate, caprate, caprylate, and caproate of baryta. The salts are separated by crystallization, the caprate of baryta being first de- posited, then the caprylate, the caproate, and lastly the butyrate. The acid of each of these salts may be easily separated by distil- ling them with a small excess of sulphuric acid diluted with its 700 FATS. weight of water, when the acid passes into the receiver with the water, and forms an oily coating on its surface. Capric acid is liquid above 62.6°, but" solidifies into crystalline aciculm when the temperature is lower; and it is very slightly solu- ble in water, but readily so in alcohol. The formula of free capric acid is C20II,9O3,IIO, that of the caprates being RO,C20H19O3. Caprylic acid is solid below 57.2°, and boils at about 464°. Water dissolves only a very small quantity of it, even at the boiling point, while it is very soluble in alcohol and ether; and the general formula of the caprylates is R0,C16II1503. Caproic acid is an oily liquid at the ordinary temperature, and does not solidify even at 14°, while it boils at about 410°, and dis- solves in 75 parts of water and in all proportions in alcohol. The general formula of its salts is R0,C12Hn03. These various acids form compound vinic and methylic ethers, which may be obtained by passing chlorohydric acid gas through alcohol or wood-spirit holding the acids in solution. PALM-OIL. § 1618. This oil, which is imported chiefly from Guinea, has, of late years, become an object of great commercial importance. It is gene- rally of a reddish-yellow colour, and melts at a temperature varying from 80° to 86°. It is supposed to be formed of olein, margarin, and a new fatty substance, called palmitin, which is extracted by express- ing the oil and washing the residue several times with alcohol, when the palmitin is isolated and purified by being washed in ether. Palmitin forms crystalline aciculae, melting at 118.4°, but decom- posing at a high temperature; and it is nearly insoluble in alcohol, even at the boiling point, but dissolves largely in ether. Alkalies convert it into glycerin, and into a new acid called 'palmitic. Its composition corresponds to the formula C70H66O8, which is written C6II402,Ce4H6206; the formula of free palmitic acid being C64II6206, 2HO. CASTOR-OIL. § 1614. Castor-oil is extracted from the ricinus communis, and forms a white or somewhat yellowish oil, slightly fluid, which soon becomes rancid in the air. When saponified, it yields glycerin, and three new fatty acids: stearoricinic, called also margaritic, ricinic, and oleoricinic or elaiodic acids. By decomposing, by an acid, soap made with castor-oil, an oil separates, which partially coagulates at the ordinary temperature. The solid part being separated and ex- pressed between bibulous paper, the residue is dissolved in boiling alcohol, when, on cooling, pearly crystalline lamellae of stearoricinic acid separate, which melt only at 266°. The greater portion of the oil which has been separated by expression from the stearori- cinic acid coagulates at 28.4°, and is also separated, by expression SPERMACETI. 701 between tissue-paper, from the portion which remains liquid, when it constitutes l'icinic acid, which melts at 71.6°, and may be distilled without alteration. Lastly, the name of oleoricinic acid has been given to the portion of the acid oil which did not become solid at 28.4°. § 1615. A peculiar fat oil, which, by exposure to the air for a few days, deposits a crystalline substance called spermaceti, is extracted from the brain of the sperm whale. The crystalline mass is ex- pressed to separate the part which remains liquid, and digested in a hot lye of potassa, while the oily fluid is washed several times with boiling water, and poured into crystallizing vessels, in which it solidifies into crystalline masses,’constituting the cakes of spermaceti found in commerce. In order to obtain it in a state of purity, it is necessary to crystallize it several times in alcohol, when it takes the name of cetin. Cetin is a white substance of a crystalline texture, almost inodor- ous, melting at 120.2°, and solidifying, by slow cooling, into a mass composed of large crystalline lamellae. It is insoluble in water, and 100 parts of boiling alcohol dissolve 16 parts of it, but retain only 3 after cooling; while ether and the essential oils dissolve it freely. Its composition corresponds to the formula C32H3202. Spermaceti is saponified by potassa, but it differs from all fat substances we have hitherto described by yielding no glycerin, but in its place another very remarkable neutral substance, called ethal, while the fat acid which combines with the alkali has received the name of ethalic acid. The saponification of spermaceti is much more difficult than that of the other fats, since it can only be effected by a concentrated solu- tion of potassa, assisted by heat, and continued for several days; or better, by melting 2 parts of spermaceti in a capsule and adding 1 part of caustic potassa broken into small pieces, and stirring it con- stantly. After some time, as soon as the substance has become com- pletely solid, it is treated with boiling water and chlorohydric acid, when the ethalic acid separates and forms an oily layer on the sur- face of the liquid. The oil being decanted, and treated in the same manner by potassa, is again saturated with chlorohydric acid, and the oil obtained is heated with hydrated lime, when the ethalic acid alone combines with the lime, leaving the ethal isolated. The latter is removed by boiling alcohol, which is then driven off by distilla- tion, and it is finally crystallized by dissolving it in ether. Ethal melts at 118.4°, crystallizing readily, on cooling, in brilliant lamellae, and it is insoluble in water, but dissolves in all proportions in alcohol and ether. It may be distilled without alteration. Its composition corresponds to the formula C32H3402, and exhibits seve- ral reactions which assimilate it to alcohol and wood-spirit, on which account it has even been called ethalic alcohol. SPERMACETI. 702 FATS § 1616. If a mixture of ethal and concentrated sulphuric acid he heated, stirring it frequently, an acid product is obtained consist- ing of a mixture of pure sulphuric acid and a compound acid, sulph- ethalic acid (C32H330 + II0),2S03, which is to ethal C32H3402 what sulphovinic acid (C4H50-f II0),2S03 is to alcohol C4II602. The acid mass being dissolved in alcohol and saturated with potassa, sulphate of potassa is precipitated, while the sulphethalate of po- tassa (C32II3304-H0),2S03 remains in solution, and crystallizes by evaporating the liquid. By heating in a retort equal volumes of ethal and perchloride of phosphorus, chlorohydric acid is disengaged, and protochloride of phosphorus first distils, then the perchloride, and lastly an oily pro- duct of the composition C32II33C1, which may be regarded as the chlorohydric ether of ethalic alcohol C32II3402. In order to obtain it pure, it should be distilled a second time with perchloride of phosphorus, washed with water, and distilled over a small quantity of quicklime. By heating ethal with 5 or 6 times its weight of potassic lime to a temperature of 410° to 430°, pure hydrogen is disengaged, and ethalic acid C32H3103,H0 is formed, which is to ethalic alcohol C32II3402 what acetic acid C4H303,H0 is to vinic alcohol C4II602. In order- to separate this acid, the alkaline mass is diluted with water and saturated with chlorohydric acid, the ethalic acid separates in the form of flocculi, but always mixed with unaltered ethal. In order to purify it, it is heated with a solution of caustic baryta, which combines with the ethalic acid, after which it is eva- porated to dryness, and the residue treated with alcohol to dissolve the ethal. The residue, which is composed only of ethalate of ba- ryta, is decomposed by chlorohydric acid, while the ethalic acid, set free, is purified by solution in ether. §1617. We have shown (§1615) that spermaceti is converted by saponification into ethal and ethalic acid; and a large quantity of the latter acid may also be obtained by decomposing spermaceti soaps by acids. Ethalic acid melts at about 140°, crystallizing, on cooling, in brilliant aciculse; and it is insoluble in water, hut very soluble in alcohol and ether. The general formula of its salts is 110,(C32II3103). As ethalic acid exists in palm-oil, either isolated or combined with glycerin, it has also received the name of palmitic acid. By distilling ethal several times with anhydrous phosphoric acid, a volatile liquid of the formula C32II32 is obtained, which has been called ceten, and forms in the series of ethalic alcohol the analogue of olefiant gas in the vinic series. This liquid boils at about 527° without alteration, and its formula corresponds to 4 volumes of vapour. WAX. 703 WAX. §1618. Chemists give the name of wax to substances arising from various sources, the type of which, beeswax, will alone occupy our attention, because it is best known ; and we shall omit the other substances produced by vegetables, which frequently resemble ordi- nary wax only in appearance or in physical properties. Wax forms the solid portions of the honeycomb; and when the honey has been removed by expression, the wax is melted with hot water, and washed several times with water, when a yellow substance remains, the smell of which resembles that of honey. By exposing it in large sheets on the grass to the action of moist air and the rays of the sun, the odoriferous and colouring substances are de- stroyed, and white wax remains; the bleaching being more promptly effected by chlorine or the alkaline hypochlorites, and by oxidizing reagents in general. White wax contains less carbon and more oxygen than yellow wax. Bleached wax is translucent to a certain degree, shows a density varying from 0.960 to 0.996, is hard and brittle at 82°, but very malleable at 86°, and melts at about 149°. Boiling alcohol sepa- rates it into, (1) myricin, almost insoluble in boiling alcohol; (2) cerin, also called cerotic acid, soluble in boiling alcohol, but de- posited from it, on cooling, in small crystalline aciculse; and (3) into cerolein, which remains in solution in the alcohol when cooled. The proportions of these substances vary. Wax yields, by distillation, a small quantity of acid water, com- bustible gases, and liquid oils, isomeric with olefiant gas, besides a solid substance, composed essentially of margaric acid and a crys- tallizable substance very analogous to paraffin. By distilling it with lime, yellow oils of complex composition are first obtained, and then a large quantity of the crystalline substance about to be de- scribed. § 1619. When wax is boiled for some time with alcohol, and the liquor allowed to cool, the deposit which is formed is composed chiefly of cerin and myricin, which must be again dissolved in boiling alcohol, until the substance deposited during the cooling of the liquid melts only at 158°. It is redissolved in boiling alcohol, and acetate of lead is added, the precipitate of cerotate of lead being washed, when hot, with alcohol and ether, and then decomposed by acetic acid. The cerotic acid is crystallized by dissolving it in boiling alcohol; and the pure acid, which melts at 172.4°, is insoluble in water. Cerin or Cerotic Acid C54H5404=C54H5303,H0. Myricin. § 1620. Myricin is very slightly soluble in alcohol, 200 parts of boiling alcohol being required to dissolve 1 of it, which is again 704 ORGANIC COLOURING MATTERS. deposited, during the cooling, in white flakes; while it requires about 100 parts of cold ether for solution. It melts at 161.6°, and partly sublimes without change at a higher temperature. Its ele- mentary composition corresponds to the formula C82II9204; and when heated for a long time with a concentrated solution of caustic potassa, it is converted into palmitic acid C92H3103,H0, which re- mains combined with the potassa, and a neutral substance, melissin CG0H62O2, which in its chemical reactions resembles ethal. Cerolein. § 1621. Cerolein, which remains in solution in the cold alcoholic liquor with which wax has been treated, is separated by evaporation from alcohol, and appears as a soft substance, fusible at 84.2°, very soluble in alcohol and cold ether, and reddening litmus. It contains more oxygen than cerin and myricin. ORGANIC COLOURING MATTERS. § 1622. While vegetables contain very various colouring matters, unequally distributed through their various parts, they also fre- quently enclose substances which are colourless, or nearly so, con- stituting a part of the living vegetable, but which acquire very beautiful colours by contact with atmospheric air or the reaction of various chemical agents. Nearly all organic colouring matters change in the air, especially when exposed to the sun, and undergo partial combustion, being converted into colourless substances ; and the quality of the colour- ing matter depends upon the time in which this change is effected. Chemical agents generally modify the shade of organic colouring matters, forming compounds with them or converting them into other substances equally coloured, which properties are frequently applied in dyeing. The metallic oxides especially combine with a great number of colouring matters possessing acid properties; and the majority of the oxides, such as that of alumina, tin, etc., thus form insoluble compounds, exhibiting often very beautiful colours, and which are used, under the name of lakes, for painting in oil and in water-colours. Very porous charcoal, particularly animal black, absorbs the majority of organic colouring matters dissolved in water, without alteration, and again deposits them if a small quantity of alkali be added to the water; woody and animal fibre possessing the same property. Moist chlorine destroys all organic colouring matters, by exerting on them a powerful oxidizing action, owing to the de- composition of water; and sulphurous acid also bleaches them, 705 cither by removing their oxygen, or by combining with the substance without altering it, and thus forming colourless compounds. A large number of reducing substances, such as nascent hydro- gen, sulfhydric acid, the alkaline sulphides, the hydrated protoxides of iron and manganese, etc., bleach colouring matters by abstract- ing their oxygen. We shall here treat only of the organic colouring matters used in dyeing. MADDER. COLOURING MATTERS OF MADDER. § 1623. Madder, (rubia tinctorum,) also known by the name of alizari, is one of the most important dyestuffs, which is extensively cultivated in the Levant and the East Indies, as well as in France, particularly in Alsace and the county of Avignon. Madder con- tains several colouring matters, the majority of which are as yet but imperfectly known; and the plant, while growing, contains only a yellow sap, without any red-colouring principle, the same being true of the root; while, when the latter has been separated from the plant and dried in the air, a red substance is developed which imparts its colour to all the ligneous portions. In dyeing, sometimes crude madder is used, and sometimes that which has undergone several preparations, of which the intention is to reduce the colouring matter to a smaller volume, or to destroy some of the colouring principles, the presence of which affect the shade of the red colour. When ground madder is exhausted by cold water, a yellow colouring matter, or xanthin, very soluble in water, is extracted from it; and if the residue be treated with one-half of its weight of concentrated sulphuric acid heated to 212°, a large portion of the ligneous matter is altered, becoming soluble in water, and, after several washings, yielding a brown substance, easily pulverized after desiccation, and constituting the article known in commerce by the name of garcincin or madder-red. Madder-red contains another colouring matter of a beautiful red hue, called alizarin, mixed with some other colouring principles. When treated with boiling alco- hol, it furnishes a beautifully red solution, which deposits, on eva- poration, a substance of an ochrous yellow colour, and named colorin. Colorin is chiefly formed of alizarin, fatty matters, and a small quan- tity of other colouring matters; and if it be carefully heated, it emits yellow vapours, which condense in the form of bright-red needles, constituting alizarin, mixed merely with a small quantity of empyreumatic oil, from which it may easily be freed by crystal- lizing it in weak alcohol. Alizarin presents all the characters of a definite compound, and its analysis has led to the formula C30H8O4. It forms very fine aciculse of an orange-yellow colour, nearly insoluble in cold water, slightly soluble in boiling water, but very soluble in alcohol. It 706 ORGANIC COLOURING MATTERS. dissolves readily in alkaline lixivige and ammonia, furnishing solu- tions of a violet colour, and yielding bluish precipitates with solu- tions of baryta, strontian, and lime: concentrated sulphuric acid also dissolves it, forming a brown liquid, from which the alizarin is precipitated unchanged upon the addition of water. § 1624. Very variously coloured products have been obtained by different methods of treating madder-root, which, however, do not exhibit the characters of definite substances, and are probably only mixtures. When madder-root, previously washed, is boiled with a concentrated solution of alum, a red liquid is obtained, depositing, on cooling, a brownish-red substance, which is separated, while the filtered liquid is of a pure red, and by the addition of sulphuric acid gradually deposits the colouring matter, a mere trace of it remain- ing in the solution after 24 hours. The precipitate, after being washed, first with weak boiling chlorohydric acid, and then with cold water, is redissolved in alcohol, which solution is evaporated, and the residue treated several times with ether, -when a colouring matter dissolves, called purpurin or madder-purpie, which remains after the evaporation of the ether, in the form of a bright-red pow- der. This substance is insoluble in cold water, but very soluble in boiling water, alcohol, and ether; and its analysis has led to the formula C28H]0O15: but as it has not been obtained in a crystallized form, it is difficult to assert that it is a simple substance. The name of madder-red is given to a colouring matter found in the brown precipitate deposited by a hot decoction of madder, on cooling; which substance sublimes at about 437°, forming crystals of a yellowish red colour, and of a composition corresponding to the formula C20H10O15. By dissolving the colouring matters of madder in a solution of alum, and then adding carbonate of soda, pecipitates of very beau- tiful colour and great stability are obtained, consisting of compounds of alumina with the colouring matters, and called madder-lakes, which are used in painting. § 1625. The name of hematin has been given to the substance to which logwood owes its value as a dyestuff. It is readily ob- tained by making a decoction of powdered logwood, evaporating it to dryness, and treating the residue with alcohol, when hematin is deposited in crystals, varying in depth of colour according to their size, but producing a yellow powder. The aqueous solution of hematin is colourless in the air, but if ammonia be added, it assumes an intense red hue; the substance produced by this reaction being named hematein, which is granular and crystalline, showing a violet- black colour and metallic lustre. It dissolves in water, and turns it of a deep purple colour. Hematein appears to differ from hema- tin by containing 1 equiv. less of water, the formula of dried COLOURING MATTERS OF LOGWOOD. QUERCITRON. 707 hematin being C16H706,H0, and that of hematein C16H6Oi; ; while the formula of hematin crystallized from an aqueous solution is C16H706,H0+2H0. Hematin possesses the properties of a feeble acid, its aqueous solution being precipitated by baryta and acetate of lead. Hema- tate of lead, decomposed by aqueous sulf hydric acid, forms a liquid which deposits nearly colourless crystals of hematin on evaporation. § 1626. The safflower is used in dyeing, and produces colours which vary from a delicate rose to a deep poppy hue. Several colour- ing matters exist in the flowers; and when they are exhausted by water, they yield a yellow colouring matter, useless in dyeing, which combines with bases; the formula of its compound with oxide of lead being 3PbO,C16H10O10. If safflower, exhausted by cold water, be treated with a solution of carbonate of soda, a red solution is obtained, by accurately neu- tralizing which with acetic acid, and dipping cotton into it, the red colouring matter, or carthamin, is precipitated. As soon as the liquid is nearly bleached, the cotton is removed, and treated with water containing of carbonate of soda, when the carthamin dis- solves, and, if citric acid be added to the liquid, is again precipitated in the form of crimson flakes. The precipitate being redissolved in alcohol and evaporated, a deep-green substance is obtained, which changes colour wdien seen in different lights. The formula C14H807 has been assigned to carthamin. COLOURING MATTERS OF SAFFLOWER. § 1627. Decoctions of Brazil or Pernambuco wood are used in dyeing, and produce red colours which are not very permanent. The colouring principle of this wood, called brazilin, has been ob- tained in small orange-coloured crystalline aciculae, soluble in water, alcohol, and ether, but of unknown composition. Brazilin assumes a purple hue on contact with the alkalies, while the action of acid and of ammonia converts it into a new substance, brazilein, which is of a deep purple. BRAZIL OR PERNAMBUCO WOOD. WELD. §1628. Weld (reseda luteola) contains a colouring principle of a beautiful yellow colour, called luteolin, which is extracted by boiling water, and appears as a yellow substance, soluble without decompo- sition, and subliming in small acicuke. It is very slightly soluble in water, and yet the small quantity which dissolves in it is suffi- cient to afford beautiful dyes, remarkable for their stability. § 1629. The name of quercitrin has been given to a colouring principle found in the bark of a certain species of oak, the quercus QUERCITRON. 708 VEGETABLE COLOURING MATTERS. nigra, from which it is extracted by treating the powdered bark with alcohol, precipitating the tannin by gelatin, evaporating the liquid, and dissolving the residue in alcohol and then in water. Quercitrin is a yellow crystalline substance, of the formula C1GH9O10, which dissolves in 100 parts of cold water, and in 4 or 5 of absolute alcohol. ARNOTTO. § 1630. This is the name of a reddish-yellow substance, arising from the fermentation of the bixia orellana, and imported from Brazil, Guiana, and the East Indies. Arnotto contains two dis- tinct colouring matters, one of which is yellow, and soluble in water and alcohol, but very slightly soluble in ether; while the other, which is red, is slightly soluble in water, but highly so in alcohol and ether. § 1631. The name of santalin has been given to the collection of colouring matters of the wood of the pterocarpus santalinus, and it is extracted by treating this wood, ground to powder, by alcohol, when the solution is of a reddish-yellow colour, and leaves, after evaporation, a resinous substance of the same colour. It dissolves in the alkaline lixiviae, and turns them of a violet colour. RED SANDERS. § 1632. A substance used in dyeing, and known by the names of purree and Indian yellow, is imported from China and the Indies, but its origin is unknown. It dissolves in wTater acidulated with chlorohydric acid, while a crystalline substance separates, called euxanthic acid, which forms nearly one-half of the weight of Indian yellow; some foreign substances being precipitated at the same time. In order to prepare pure euxanthic acid, Indian yellow is treated with acetic acid, and acetate of lead is added to the liquid, when euxanthate of lead is precipitated, and may be decomposed by sulf- hydric acid. By boiling the liquid, the euxanthic acid is dissolved, and crystallizes, on cooling, in long, yellow, silky needles, which are readily soluble in alcohol and in ether. Its formula, when dried at 212°, is C42H18022; while, if it be heated still further, the euxan- thic acid melts and evolves vapours which solidify in small crystals, constituting a new substance, euxanthone C42II120]2, which is also ob- tained either by the distillation of euxanthate of lead or by causing concentrated sulphuric or chlorohydric acid to act on euxanthic acid. We have, moreover, INDIAN-YELLOW. C40H12O12+2CO2+6HO. Euxanthone possesses no acid properties. With chlorine, bromine, or nitric acid, euxanthic acid yields products by substitution, with the formulae The clilo- CHLOROPHYLL. 709 rinated and brominated euxanthic acids dissolved in concentrated sulphuric acid, and precipitated by water, yield chlorinated euxan- thone C40H10Cl2O12 or brominated § 1633. Carotin, the red-colouring matter of carrots, is extracted by diluting carrot-juice Avith 4 or 5 times its volume of Avater, and then adding sulphuric acid, Avhich precipitates the colouring matter Avith the albumen and fatty substances. The latter are separated by boiling the precipitate for some time with a solution of caustic potassa, Avhich dissolves them; and the carotin is purified by boiling it with dilute sulphuric acid, and digesting it, first Avith ordinary, and then with absolute alcohol. The substance, Avhen dried, is treated with sulphide of carbon, Avhich dissolves the carotin, after Avhich f of the liquid are separated by distillation, anhydrous alco- hol is added to the residue, and the liquid is exposed to the air, Avhen, after some time, small copper-coloured crystals of pure caro- tin are deposited. Carotin melts at about 338°, but is decomposed at a higher temperature, and it is nearly insoluble in Avater, alcohol, and ether. Its elementary composition is the same as that of oil of terpentine, but no means of ascertaining its equivalent are known. CAROTIN. GREEN AND YELLOW COLOURING MATTER OF LEAVES. § 1634. The green-colouring matter of leaves, or chlorophyll, exists in them but in a very small quantity, and is exceedingly dif- ficult to extract in a state of purity. The best method known con- sists in digesting the leaves for several days with ether; after which the liquid is filtered and evaporated to dryness, when the greater portion of the residue is composed of a substance analogous to wax and of chlorophyll. It is dissolved in boiling alcohol, which deposits, on cooling, the greater part of the wax; and the alcohol being again evaporated, and the residue treated with a smaller proportion of boil- ing alcohol, wax still separates on cooling. The solution is finally evaporated, and the residue treated with concentrated chlorohydric acid, which yields a beautiful green solution. The liquid is satu- rated and filtered, after having introduced some pieces of marble into it, when the chlorophyll, which is rendered insoluble, being precipitated, is washed with weak chlorohydric acid, and then with fresh water. Chlorophyll is insoluble in Avater, but readily soluble in alcohol and ether, and sulphuric and chlorohydric acids dissolve it without change; a large quantity of water precipitating it again. From an analysis made of it, the composition of chlorophyll, dried at 266°, would correspond to the formula C18H9N08. The name of xanthophyll has been given to the yellow-colouring matter of autumnal leaves; but nothing is with certainty known as to its nature. 710 VEGETABLE COLOURING MATTERS. § 1635. The cochineal (