f^?m&y5jP**Tl>*}. '■'i 'ir"'-"; 'Vi;'l k "^ ■■4??': %^y 7- 77/ >*v - % \ EXPLANATIONS OF FIGURE 39, SlDEAM ENGINE. For a full description, see page 325-^332, * ---,—- A.A The Boiler. B.B Fire Place. X.X Flues. C.CSteim Pipe. D.D Steam Box. Y.Y The Piston which works in the Cylinder. E Steam Pipe to convey Steam to force down the Piston F. Steam Pipe to convey Steam to force up the Piston. Note. See Fig. 40 (on next page) for an enlarged plan of the Steam Box, Cylinder, &e. G Pipe from Steam Box to the condenser. H.H The Condenser. V and W Cranks to work the Valve I.I. See Fig. 40. X The Eccentric to work the cranks V and W, U Fly Wheel to equalize the motion of the machinery. L.L Cistern of Cold Water to condense the steam. C Injection Cock to let cold water into the condenser. M.M Air Pump communicating with the bottom of the condenser. N Small Cistern. O Forcing Pump attached to cistern N. P. Q. R. S represents a plan Cwith the exception of one pipe) con- nected with the cistern N. and the forcing pump O ,to ascertain the quantity of water in the boiler—Ris a float always resting on the surface of the water in the boiler. T.T The Lever or Working Beam. 1 Piston rod to work the Piston in the Cylinder. 2 3 4 Bods to work the Pumps. 5 Rod to work the Main Shaft, Fly Wheel, and Eccentric. 6 The Throttle Valve. a.a bed represents an apparatus connected with the Throttle Valve which regulates the quantity of Steam which enters the cylinder from the boiler ; it is called the Governor. e f g h A system of Levers or Rods to cause the parallel motion of the Piston Rod. FIG. 40, Representing the Cylinder and the Pipes connected with the Steam Box upon an enlarged scale. D.D The Steam Box. Z.Z The Cylinder in which the Piston moves. E.E Steam Pipe to convey St -m to force down the Piston. F.F Steam Pipe to convey steam to force up the Piston. Y.Y Piston fitted to work i the Cylinder. G Pipe f. om Steam Box to Condenser. I.I A Hollow Slidirg Valve. C Steam Pipe from the Boiler. 6 Valve. CONVERSATIONS ON CHEMISTRY; IN WHICH THE ELEMENTS OF THAT SCIESMCS ABE FAMILIARLY EXPLAINED, AND AND 38 ENGRAVINGS ON WOOD. THE THIRTEENTH AMERICAN, FROM THE LAST LONDON EDITION, WITH ADDITIONS AND CORRECTIONS. 1—M I) ..... TO WHICH ARE NOW ADDED, EXPLANATIONS OF THE TEXT--DIRECTIONS FOR SIMPLIFYING THE APPARATUS, AND A VOCABULARY OF TERMS—TOGETHER WITH A LIST OF INTERESTING EXPERIMENTS. BY J. L. COMSTOCK, M. D. TOGETHER WITH A NEW AND EXTENSIVE Series of nuiesitiong, 1 BY REV. J. L. BLAKE, A. M. HARTFORD: PUBLISHED BY COOKE AND CO. AND PACKARD AND BUTLER. 1831. Q*D C-?l ; Mnixitt of Cownecttcttt, n*. BE IT REMEMBERED, That on the second day of October, in L. S. the fifty-first year of the Independence of the United States of America, Oliver D. Cooke & Co. of the said District, have deposited in this of- fice the title of a Book, the right whereof they claim as proprietors, in the words following, to wit, " Conversations on Chemistry; in which the elements of that science are familiarly explained and illustrated by experiments, and thirty-eight en- gravings on wood. The tenth American from the eighth London edition, revised, corrected, and enlarged. To which are now added, explanations of the text, direc- tions for simplifying the apparatus, and a vocabulary of terms ; together with a list of interesting experiments. By J. L. Comstock, M. D. Together with a new and extensive Series of Questions, by Rev. J. L. Blake, A. M. In conformity to the act of the Congress of the United States, entitled, " An act for the encourage- ment of learning, by securing the copies of Maps, Charts and Books, to the authors and proprietors of such copies, during the times therein mentioned." CHAS, A. INGERSOLL, Clerk of the District of Connecticut. A true copy of record, examined and sealed by me, CHAS. A. INGERSOLL, Clerk of the District of Connecticut ADVERTISEMENT OF THE AMERICAN "EDITOR. The familiar and agreeable manner in which the " Conversations on Che- mistry" are written, renders this one of the most popular treatises on the sub- ject which has ever appeared. The elegant and easy style, also, in which the authoress has managed to convey scientific instruction is peculiarly adapted to the object of the work. In some respects, however, the English edition may be considered as ob- jectionable. A book designed for the instruction of youth, ought, if possible, to contain none but established principles. Known and allowed facts are always of much higher consequence than theoretical opinions. To youth, particularly, by advancing as truths, doc- trines which have arisen out of a theory not founded on demonstration, we run a chance of inculcating permanent error. In these respects we think that Mrs. Bryant has not been sufficiently guard- ed. The brilliant discoveries of Sir Humphrey Davy, and his known emi- nence as a Chemical Philosopher, seem in many instances to have given his opinions an authority, which, in the mind of the writer, superseded further investigation. Indeed, inferences are sometimes drawn from these opinions which they hardly wan-ant. Under this view of the subject, a part of the notes is designed to guard the pupil against adopting opinions which ho will find either contradicted, or merely examined by most chemical writers. In addition to this, I have made such explanations of the text as I thought would assist the pupil in understanding what he reads. In attempting to make this science popular, and of general utility, it is of great importance that the experiments come within the use of such instru- ments as are easily obtained. I have therefore given such directions on this •ubject, as my former experience as a lecturer, with a small apparatus, taught me to believe would be of service. The list of experiments was chiefly made up without referring to books ; some few of them, however, are copied from Parke, Accum, &c. REMARKS BY THE REV. MR. BLAKE. The questions, in the present edition, are placed at the bottom of the sev- eral pages to which they relate. This plan has been adopted in the Boston edition of Conversations on Natural Philosophy, and is become very popular. The advantages of it are too obvious to escape observation, and, of course, to need being particularized. It, will be seen that the questions are more nu- merous than they were in the two first impressions from this copy. It may be supposed by persons not acquainted with teaching, that they are too numerous, as some of them are repeated in various forms, and others are seemingly un- important. But it is found necessary that scholars should be examined on every page, and upon nearly every paragraph, whether there is any thing very important or not. No small portion of learners will pass over without study, all in which they are not to be questioned. Hence what might be called a system of questions would be quite insufficient. PREFACE. In venturing to offer to the public, and more particularly to the female sex, an introduction to Chemistry, the author, herself a wo- man, conceives that some explanation may be required; and she feels it the more necessary to apologize for the present undertaking, as her knowledge of the subject is but recent, and as she can have no real claims to the title of chemist. On attending for the first time experimental lectures, the author found it almost impossible to derive any clear or satisfactory infor- mation from the rapid demonstrations which are usually, and per- haps necessarily, crowded into popular courses of this kind. ' But frequent opportunities having afterwards occurred of conversing with a friend on the subject of chemistry, and of repeating a variety of experiments, she became better acquainted with the principles of that science, and began to feel highly interested in its pursuits. It was then that she perceived, in attending to the excellent lectures delivered at the Royal Institution, by the present Professor of Che- mistry, the great advantage which her previous knowledge of the subject, slight as it was, gave her over others who had not enjoyed the same means of private instruction. Every fact or experiment attracted her attention, and served to explain some theory to which she was not a total stranger; and she had the gratification to find that the numerous and elegant illustrations, for which that school is so much distinguished, seldom failed to produce on her mind the ef- fect for which they were intended. Hence it was natural to infer, that familiar conversation was, in studies of this kind, a most useful auxiliary source of information ; and more especially to the female sex, whose education is seldom calculated to prepare their minds for abstract ideas, or scientific language. As, however, there are but few women who have access to this mode of instruction; and as the author was not acquainted with any book that could prove a substitute for it, she thought it might be useful for beginners, as well as satisfactory to herself, to trace the steps by which she had acquired her little stock of chemical know- ledge, and to record, in the form of dialogue, those ideas which she had first derived from conversation. But to do this with sufficient method, and to fix upon a mode of arrangement was an object of some difficulty. After much hesita- tion, and a degree of embarrassment, which, probably, the most competent chemical writers have often felt in common with the most superficial, a mode of division was adopted, which, though the most natural, does not always admit of being strictly pursued—it is that of treating first the simplest bodies, and then gradually rising to the most intricate compounds. It is not the author's intention to enter into a minute vindication of this plan. But whatever may be its advantages or inconvenien- ces, the method adopted in this work is such, that a young pupil, who should only recur to it occasionally with a view to procure in- PREFACE. V formation on particular subjects, might often find it obscure or un- satisfactory ; for its various parts are so connected with each other as to form an uninterrupted chain of facts and reasonings, which will appear sufficiently clear and consistent to those only who may have patience to go through the whole work, or have previously devoted some attention to the subject. It will, no doubt, be observed, that in the course of these Conver- sations, remarks are often introduced, which appear much too acute for the young pupils, by whom they are supposed to be made. Of this fault the author is fully aware. But, in order to avoid it, it would have been necessary either to omit a variety of useful illus- trations, or to submit to such minute explanations and frequent repe- titions, as would have rendered the work tedious, and therefore less suited to its intended purpose. In writing these pages the author was more than once checked in her progress, by the apprehension that such an attempt might be considered by some, either as unsuited to the ordinary pursuits of her sex, or ill-justified by her own imperfect knowledge of the sub- ject. But, on the one hand, she felt encouraged by the establish- ment of those public institutions, open to both sexes, for the dissemi- nation of philosophical knowledge, which clearly prove that the general opinion no longer excludes woman from an acquaintance with the elements of science: and, on the other, she flattered her- self, that whilst the impression made upon her mind, by the wonders of Nature, studied in this new point of view, were still fresh and strong, she might perhaps, succeed the better in communicating to others the sentiments she herself experienced. The reader will perceive, in perusing this work, that he is sup- posed to have previously acquired some slight knowledge of Natu- ral Philosophy, a circumstance so desirable, that the author has since the original publication of this work, been induced to offer to the public a small tract, entitled " Conversations on Natural Phi- losophy," in which the most essential rudiments of that science are familiarly explained. 1* CONTENTS, CONVERSATION I. * ON THE GENERAL PRINCIPLES OF CHEMISTRY. 13 Connexion between Chemistry and Natural Philosophy—Improved state of modern Chemistry—Its use in the Arts—The general Ob- jects of Chemistry—Definition of Elementary Bodies—Definition of Decomposition—Integrant and Constituent Particles—Distinction "between Simple and Compound Bodies—Classification of Simple Bodies—Of Chemical Affinity, or Attraction of Composition—Ex- amples of Composition and Decomposition. CONVERSATION II. ON LIGHT AND HEAT. 26 Light and heat capable of being separated—Dr. Herschel's Experi- ments—Phosphorescence—Of Caloric---Its two modifications— Free Caloric—Of the three different states of bodies, solid, fluid, and aeriform—Dilatation of Solid bodies—Pyrometer—Dilatation of Fluids—Thermometer—Dilatation of Elastic Fluids—Air Ther- mometer—Equal diffusion of Caloric—Cold a Negative Quality__ Professor Prevost's Theory of the Radiation of Heat—Professor Pictet's Experiments on the Reflection of Heat—Mr. Leslie's Ex- periments on the radiation of Heat. CONVERSATION III. CONTINUATION OF THE 6UBJECT. 47 Of the different Power of Bodies to conduct Heat—Attempt to ac- count for this power—Count Rumford's opinion respecting the non-conducting power of Fluids—Phenomena of Boiling__Of So- lution and Mixture—Solvent power of Caloric—Of Clouds, Rain Dr. Wells' Theory of Dew, Evaporation, &c.—Influence of At- mospherical Pressure on Evaporation—Ignition. CONVERSATION IV. ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT AND LATENT HEAT. 69 Of Specific Heat—Of the different Capacities of Bodies for Heat__ Specific Heat, not perceptible by the senses—How to be ascertained —Of Latent Heat---Distinction between Latent and Specific Heat—Phenomena attending the Melting of Ice, and the Form- ation of Vapor---Phenomena attending the Formation of Ice CONTENTS. Vll and the Condensation of elastic Fluids—Instances of Condensation, and consequent Disengagement of Heat, produced by Mixtures, by the Slacking of Lime—General Remarks on Latent Heat—Ex- planation of the Phenomena, of Ether boiling, and Water freezing, at the same Temperature—Of the Production of Cold by Evapora- tion. CONVERSATION V. ON THE CHEMICAL AGENCIES OF ELECTRICITIES. 84 Of Positive and Negative Electricity—Galvani's Discoveries—Volta- ic Battery—Electrical Machine—Theory of Voltaic Excitement- Its influence on the Magnetic Needle. CONVERSATION VI. ON OXYGEN AND NITROGEN. 95 The Atmosphere composed of Oxygen and Nitrogen in the state of Gas—Definition of Gas—Distinction between Gas and Vapor— Oxygen essential to Combustion and Respiration—Decomposition of the Atmosphere by Combustion—Nitrogen Gas obtained by this process—Of Oxygenation in General—Of theOxydation of Metals —Oxygen Gas obtained from Oxyd ofManganese—Description of a Water Bath for collecting and preserving Gases—Combustion of Iron Wire in Oxygen Gas—Fixed and Volatile Product of Com- bustion—Patent Lamps—Decomposition of the Atmosphere by Respiration—Recomposition of the Atmosphere. CONVERSATION VII. ON HYDROGEN. 109 Of Hydrogen—Of the Formation of Water by the combustion of Hy- drogen—Of the Decomposition of Water—Detonation of Hydro- gen Gas—Description of Lavoisier's apparatus for the formation of Water—Hydrogen Gas essential to the production of Flame—Music- al tones produced by the Combustion of Hydrogen Gas within a Glass Tube—Combustion of Candles explained—Gas Lights—De- tonation of Hydrogen Gas in Soap Bubbles—Air Balloons—Meteo- rological Phenomena ascribed to Hydrogen Gas—Miner's Lamp. CONVERSATION VIII. ON SULPHUR AND PHOSPHORUS. 126 Natural History of Sulphur—Sublimation—Alembic—Combustion of Sulphur in Atmospheric Air—Of Acidification in general—No- menclatures of Acids—Combustion of Sulphur in Oxygen Gas- Sulphuric Acid—Sulphurous Acid---Decomposition of Sulphur VIU CONTENTS. —Sulphuretted Hydrogen Gas—Harrogate, or Hydrosulphuretted Waters—Phosphorus—Decomposition of Phosphorus—History of its Discovery—Its combustion in Oxygen Gas —Phosphoric Acid— Phosphorous Acid—Eudiometer—Combination of Phosphorus with Sulphur—Phosphoretted Hydrogen Gas—Nomenclature of Binary Compounds—Phosphoret of Lime burning under water. CONVERSATION IX. ON CARBON. 137 Method of obtaining pure Charcoal—Method of making common Charcoal—Pure Carbon not to be obtained by Art—Diamond— Properties of Carbon—Combustion of Carbon—Production of Car- bonic Acid Gas—Carbon susceptible of only one degree of Acidi- fication—Gaseous oxyd of Carbon—Of Seltzer Water, and other Mineral Waters—Effervescence—Decomposition of Water by Car- bon—Of Fixed and Essential Oils—Of the Combustion of Lamps and Candles—Vegetable Acids—Of the power of Carbon to revive Metals. CONVERSATION X. ON METALS. 149 Natural History of Metals—Of Roasting, Smelting, &c.—Oxydation of Metals by the Atmosphere—Change of Colours produced by different degrees of Oxydation—Combustion of Metals—Perfect Metals burnt by Electricity only—Some Metals revived by Carbon and other Combustibles—Perfect Metals revived by Heat alone— Of the Oxydation of certain Metals by the Decomposition of Water —Power of Acids to promote this effect—Oxydation of Metals by Acids—Metallic Neutral Salts—Previous Oxydation of the Metal requisite—Crystallization—Solution distinguished from Dissolu- tion—Five Metals susceptible of Acidification—Meteoric Stones, Alloys, Soldering, Plating, &c.—Of Arsenic, and of the Caustic ef- fects of Oxygen—Of Verdigris, Sympathetic Ink, &c.—Of the New Metals discovered by Sir H. Davy. CONVERSATION XL ON THE ATTRACTION OF COMPOSITION. 171 Of the Laws which regulate the Phenomena of the Attraction of Com- position—1. It takes place only between bodies of a different Na- ture—2. Between the most minute Particles only—3. Between 2, 3,4, or more bodies—Of Compound or Neutral Salts—4. Produ- ces a Change of Temperature—5. The Properties which charac- terise Bodies in their separate state, destroyed by Combination— 6. The force of Attraction estimated by that which is required by the separation of the Constituents—7. Bodies have amongst them- CONTENTS. IX selves different degrees of Attraction-Of simple elective and double elective Attractions—Of quiescent and divellant Forces—Law of definite Proportions—Decomposition of Salts by Voltaic Electri- city. CONVERSATION XIV. ON ALKALIES. 181 Of the Composition and general Properties of the Alkalies—Of the new discovered Alkali of Lithion—Of Potash—Manner of prepar- ing it—Pearlash—Soap—Carbonat of Potash—Chemical Nomen- clature—Solution of potash—Of Glass—Of Nitrat of Potash, or Saltpetre—Effect of Alkalies on Vegetable Colors—Of Soda—Of Ammonia or Volatile Alkali—Muriat of Ammonia— Aminoniacal Gas—Composition of Ammonia—Hartshorn and Sal Volatile— Combustion of Ammoniacal Gas. CONVERSATION XV. ON EARTHS. 191 Composition of the Earths—Of their incombustibility—Form the ba- ses of all Minerals—Their Alkaline Properties—Silex ; its prop- erties and uses in the Arts—Alumine; its uses in Pottery, &c.— Alkaline Earths—Barytes—Lime; its extensive Chemical Prop- erties and uses in the Arts—Magnesia—Strontian. CONVERSATION XVI. ON ACIDS. 202 Nomenclature of the Acids—Of the Classification of Acids—1st Class —Acids of simple and known Radicals, or Mineral Acids-2d Class —Acids of double Radicals, or Vegetable Acids—3d Class—Acids of triple Radicals, or Animal Acids—Of the decomposition of Acids of the 1st Class by Combustible bodies. CONVERSATION XVII. OF THE SULPHURIC AND PHOSPPORIC ACIDS ; OR THE COMBINATIONS OF OXYGEN WITH SULPHUR AND PHOSPHORUS ; AND OF THE SUL- PHATS AND PHOSPHATS. 206 Of the Sulphuric Acid—Combustion of Animal or Vegetable Bodies by this Acid—Method of preparing it—The Sulphurous Acid ob- tained in the form of Gas—May be obtained from Sulphuric Acid —May be reduced to Sulphur—Is absorbable by Water—Destroys Vegetable Colors—Oxyd of Sulphur—Of Salts in general—Sul- phats—Sulphat of Potash, or Sal Polychrest—Cold produced by the melting of Salts—Sulphat of Soda, or Glauber's Salt—Heat X CONTENTS. evolved during the formation of Salts—Crystallization of Salts— Water of Crystallization—Efflorescence and Deliquescence of Salts —Sulphat of Lime, Gypsum, or Plaster of Paris—Sulphat of Mag- nesia—Sulphat of Alumine, or Alum—Sulphat of Iron—Of Ink— Of the Phosphoric and Phosphorous Acids—Phosphorus obtained from bones—Phosphat of Lime. CONVERSATION XVIII. OF THE NITRIC AND CARBONIC ACIDS : OR THE COMBINATION OF OXYGEN WITH NITROGEN AND WITH CARBON, AND OF THE NITRATS AND CAR- BONATS. 214 Nitrogen susceptible of various degrees of Acidification—Of the Nitric Acid—Its nature and Composition discovered by Mr. Cavendish— Obtained from Nitrat of Potash—Aqua Fortis—Nitric Acid may be Converted into Nitrous Acid—Nitric Oxyd Gas—Its Conversion in- to Nitrous acid gas—Used as an Eudiometrical test—Gaseous oxyd of Nitrogen, or exhilarating Gas obtained from Nitrat of Ammonia —Its singular effects on being respired—Nitrats—Of Nitrat of Pot- ash, Nitre or Saltpetre—Of Gunpowder—Causes of Detonation— Decomposition of Nitre—Deflagration—Nitrat of Ammonia—Nitrat of Silver—Of the Carbonic Acid—Formed by the combustion of Carbon—Constitutes a component part of the" Atmosphere—Exha- led in some caverns—Grotto del Cane—Great weight of this Gas— Produced from calcareous stones by Sulphuric Acid—Deleterious effects of this Gas when respired—Sources which keep up a supply of this Gas in the atmosphere—Its effects on vegetation—Of the Carbonats of Lime ; Marble, Chalk, Shells, Spars, and Calcareous Stones. CONVERSATION XIX. ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MURIATIC ACIDS J AND ON MURIATS. 226 On the Boracic Acid—Its decomposition by Sir H. Davy—Its basis Boracium—Its Recomposition—Its uses in the arts—Borax or Bo- rat of Soda—Of the Fluoric Acid—Obtained from Fluor; corrodes siliceous earth; its supposed composition—Fluorine; its supposed basis— Of Muriatic Acid—Obtained from Muriats—Its gaseous form—Is absorbable by water—Its Decomposition—Is susceptible of a stronger degr-e of Oxygenation—Oxygenated Muriatic Acid— Its gaseous form and other properties—Combustion of bodies in this gas—It dissolves Gold—Composition of Aqua Regia—Oxygenated Muriatic Acid destroys all colours—Sir H. Davy's Theory of the nature of Muriatic and Oxymuriatic Acid—Chlorine, used for bleaching and for fumigation—Its offensive smell, &c. Muriats— Muriat of Soda, or common salt—Muriat of Ammonia—Oxygena- ted Muriat of Potash—Detonates with Sulphur, Phosphorus, &c.— Experiments of burning Phosphorus under water by means of this salt and Sulphuric Acid. CONTENTS. XI CONVERSATION XX. ON THE NATURE AND COMPOSITION OF VEGETABLES. 238 Of Organized Bodies—Of the functions of Vegetables—Of the ele- ments of Vegetables—of the materials of Vegetables—Analysis of Vegetables—Of Sap—Mucilage or Gum—Sugar—Manna and Honey—Gluten—Vegetable Oils—Fixed Oils—Linseed, Nut, and Olive Oils—Volatile Oils, forming Essences and perfumes—Cam- phor—Resins and Varnishes—Pitch, Tar, Copal, Mastic, &c.— Gum, Resins—Myrrh, Assafretida, &c.—Caoutchouc, or Gum Elas- tic—Extractive colouring matter ; its use in the arts of dyeing and painting—Tannin ; its use in the art of preparing Leather—Woody Fibre—Vegetable Acids—The Alkalies and Salts contained in Ve- getables. CONVERSATION XXI. ON THE DECOMPOSITION OF VEGETABLES. 254 Of fermentation in general—Of the saccharine fermentation, the pro- duct of which is sugar—Of the vinous fermentation, the product of which is wine—Alcohol, or spirit of wine—Analysis of wine by dis- tillation—Of brandy, rum, arrack, gin, &c.—Tartrit of Potash, or Cream of Tartar—Liquers—Chemical properties of Alcohol—Its combustion—Of Ether—Of the acetous fermentation, the product of which is Vinegar—Fermentation of bread—Of the putrid fermenta- tion, which reduces vegetables to their elements—Spontaneous suc- cession to these fermentations—Of vegetables said to be petrified— Of bitumens; Naphtha, Asphaltum, Jet, Coal, Succin, or Yellow Amber—Of Fossil Wood, Peat and Turf. CONVERSATION XXII. HISTORY OF VEGETATION. 271 Connection between the Vegetable and animal Kingdoms—Of Ma- nures—Of Agriculture—Inexhaustible sources for materials for the purposes of Agriculture—Of sowing Seed—Germination of the Seed—Function of the Leaves of Plants—Effects of Light and air on Vegetation-Effects of water on Vegetation—Effects of Vegetation on the Atmosphere—Formation of Vegetable Mate- rials by the organs of Plants—Vegetable Heat—Of the organs of Plants—Of the Bark, consisting of Epidermis, Parenchyma, and Cortical Layers—Of Alburnum, or wood—Leaves, Flowers, and Seeds—Effects of the season on Vegetation—Vegetation of Ever- greens in the Winter. CONVERSATION XXIII. ON THE COMPOSITION OF ANIMALS. 287 Elements of Animals—Of the principal Materials of Animals, via. Xll ourm/jiuxs. Gelatine, Albumen, Fibrine, Mucus—of Animal Acids—Of Animal Colours, Prussian Blue, Carmine, and Ivory Black. CONVERSATION XXIV. ON THE ANIMAL ECONOMY. Of the principal Animal Organs—Of Bones, Teeth, Horns, Liga- ments, and Cartilage—Of the Muscles, constituting the organs of Motion—Of the Vascular System, for the conveyance of Fluids—Of the Glands for the secretion of Fluids—Of the Nerves, constituting the Organs of Sensation—Of the Cellular substance, which connects the several Organs—Of the Skin. CONVERSATION XXV. ON ANIM.VLISATION, NUTRITION AND RESPIRATION. 302 Digestion—Solvent power of the Gastric Juice—Formation of Chyle —Its Assimilation, or Conversion into Blood—Of Respiiation—Me- chanical Process of Respiration—Chemical process of Respiration— Of the Circulation of the Blood—Of the functions of the arteries, the Veins, and the Heart—Of the Lungs—Effects of Respiration on the Blood. CONVERSATION XXVI. ON ANIMAL HEAT; AND OF VARIOUS ANIMAL PRODUCTIONS. 311 Of the Analogy of Combustion and Respiration—Animal Heat evolv- ed in the Lungs—Animal Heat evolved in the Circulation—Heat produced by Fever—Perspiration—Heat produced by Exercise— Equal temperature of Animals at all Seasons—Power of the Ani- mal body to resist the effects of Heat—Cold produced by Perspira- tion—Respiration of Fish and of Birds—Effects of Respiration on Muscular Strength—Of several Animal Products, viz. Milk, Butter, and Cheese; Spermaceti; Ambergris; Wax; Lac; Silk; Musk; Civet; Castor—Of the Putrid Fermentation—Conclusion. CONVERSATION XXVII. ON THE STEAM-ENGINE. 325 Origin of" the Steam Engine—Marquis of Worcester's Invention— Savaryand Newcomen's Engine—Watt's Double Steai%Engine described—Wolfe's Engine—Advantages derived from the Steam- Engine. CONVERSATIONS ON CHEMISTRY. CONVERSATION I. ON THE GENERAL PRINCIPLES OF CHEMISTRY. Mrs. B. As you have now acquired some elemeutary notions. 3f Natural Philosophy, lam going to propose to you another branch of science, to which I am particularly anxious that you should devote a share of your attention. This is Chemistry, which is so closely connected with Natural Philosophy, that the study of the one must be incomplete without some knowledge of the other ; for, it is obvious that we can derive but a very imperfect idea of bodies from the study of'the general laws by which they are governed, if we remain totally ignorant of their intimate nature. Caroline. To confess the truth, Mrs. B., I am not disposed to form a very favourable idea of chemistry, nor do I expect to derive much entertainment from it. I prefer the sciences which exhibit nature on a graud scale, to those that are confined to the minutias of petty details. Can the studies which we have lately pursued, the general properties of matter, or the revolutions of the heavenly bodies, be compared to the mixing up of a few insignificant drugs? I grant, however, there may be some entertaining experiments in Chemistry, and should not dislike to try some of them ; the distil- ling of lavender, for instance, or rose water.... Mrs. B. I rather imagine, my dear Caroline, that your want of taste for chemistry proceeds from the very limited idea you enter- tain of its object. You confine the chemist's laboratory to the nar- row precincts of the apothecary's and perfumer's shops, whilst it is subservient to an immense variety of other useful purposes. Be- sides, my dear, chemistry is by no mean's confined to works of art. Nature also hasher laboratory, which is.the universe,and there she is incessantly employed in chemical operations. You are surprised, Caroline ; but I assure you that the most wonderful and the most 1. With what other study is that of chemistry closely connected? 2. Why is the study of Natural Philosophy incomplete without that of chemistry ? 3. What does'Mrs. B. consider a chemical laboratory, in its most extended signification ? 2 14 General principles interesting phenomena of nature, and almost all of them produced by chemical powers. What Bergman, in the introduction to his history of chemistry, has said of this science, will give you a more just and enlarged idea of it. The knowledge of nature may be divi- ded, he observes, into three periods. The first is that in which the attention ofmen, is occupied in learning the external forms and characters of objects, and this is called Natural History. In the second, they consider the effect of bodies acting on each other by their mechanical power, as their weight and motion, and this con- stitutes the science of Natural Philosophy. ,The third period is that in which the properties and mutual action of the elementary parts of bodies are investigated. This last is the science of Chem- istry, and I have no doubt you will soon agree with me in think- ing it the most interesting. You may easily conceive, therefore, that without entering into the minute details of practical chemistry, a woman may obtain such a knowledge of the science as will not only throw an interest on the common occurrences of life, but will enlarge the sphere of her ideas, and render the contemplation of nature a source of delight- ful instruction. Caroline. If this is the case, I have certainly been much mista- ken in the notion 1 had formed of chemistry. I own that I thought it was chiefly confined to the knowledge and preparation of medi- cines. Mrs. B. That is only a branch of Chemistry which is called Pharmacy, and though the study of it is, no doubt, of great import- ance to the world at large, it belongs exclusively to professional men, and is therefore the last that 1 should advise you to pursue. Emily. But did not the chemists formerly employ themselves in search of the phiilosopher's stone, or the secret of making gold ?* * The Alchymists had in view three great objects of discovery, viz. 1st. The Elixir nf health ; by the use of which the lives of men might be protracted to any desirable length, or their mortality pre- vented. 2d. The universal solvent, or a liquid which should dis- solve every other substance. This, it was supposed, would lead to the grand discovery. 3d. The making of gold, or finding the phi- losopher's stone. That men of sound and discriminating minds on other subjects should have spent their whole lives in pursuits so chimerical, is to us wonderful indeed. But our wonder ceases in some degree, when we are told that the doctrine of transmutation, &c. was founded on a Theory, which, in the 12th century, was con- sidered as plausible, as we consider many of ours at the present day, viz. That a perfect metal consisted of quicksilver and sulphur; 4. To what author does Mrs. B. allude in her introductory re- marks ? 5. Into how many periods does Bergman divide the knowledge of nature ? 6. What is the first? 7. What is the second ? 8. What is the third? 9. What is that branch of chemistry called Pharmacy? 10. What three great objects had the Alchymists in view? QF CHEMISTRY. 15 Mrs. B. These were a, particular set of misguided philosophers, Who dignified themselves with the name of Alchymists, todistinguish their pursuits from those of the common chemists, whose studies were confined to the knowledge of medicines. But since that period, chemistry has undergone so complete a revolution, that, from an obscure and mysterious art, it is now be- come a regular and beautiful science, to which art is entirely sub- servient. It is true, however, that we are indebted to the Alchy- mists for many very useful discoveries, which sprung from their fruitless attempts to make gold, and which, undoubtedly, have pro- ved of infinitely greater advantage to mankind than all their chi- merical pursuits. The modern chemists, instead of directing their ambition to the vain attempt of producing any of the original substances in nature, rather1 aim at analyzing and imitating her operations, and have sometimes succeeded in forming combinations, or effecting decom- positions, no instances of which occur in the chemistry of Nature. They have little reason to regret their inability to make gold, whilst by their innumerable inventions and discoveries, they have so great- ly stimulated industry and facilitated labour, as prodigiously to in- crease the luxuries as well as the necessaries of life. Emily. But 1 do not understand by what meaos chemistry can facilitate labour ; is not that rather the province of the mechanic ? Mrs. B. There are many ways by which labour may be render- ed more easy independently of mechanics ; but mechanical in- ventions themselves often derive their utility from a chemical prin- ciple. Thus that most wonderful of all machines, the'.,Steam En- gine, could never have been invented without the assistance of chemistry. In agriculture, a chemical knowledge of the nature of soils, and of vegetation.;' is highly useful; and in those arts which relate to the comforts and conveniences of life, it would be endless £o enumerate the advantages which result from the study of this science. ' Caroline. But pray, tell us more precisely in what manner the discoveries of chemists have proved so beneficial to society ? these, when pure and united, formed gold. That all other metals contained a quantity of dross, which prevented the particles of these two substances from uniting. If, therefore, this dross could be got rid of in the other metals, gold would be the result. They believed also, that nature herself favoured this operation. Thus Friar Ro- ger Bacon, in his Mirror of Alchymy, says, " 1 must tell you that nature alwaies intendeth and striueith to the perfection of gold ; but many accidents coming between, change the mettalls," &c. See his Book printed in 1597, chap. ii.—:C. 11. Who were formerly called Alchymists ? 12. Why did they assume this name ? 13. What is the object of modern chemistry ? 14. Can chemistry afford any assistance in manual labour ? 15. What are instances of it ? 16. How is chemistry serviceable in agriculture ? 17. What opinion is said in thenote, to have -prevailed in the 12$ century in relation to metals ? 16: GENERAL PRINCIPLES Mrs. B. That would be an injudicious anticipation ; for youi would not comprehend the nature of such discoveries and useful ap- plications, as well as you will do hereafter. Without a due regard to method, we cannot expect to make any progress in chemistry, I wish to direct your observation chiefly to the chemical opera- tions of Nature ; but those of art are certainly of too high import- ance to pass unnoticed. We shall therefore allow them also some share of our attention. Emily. Well, then, let us now set to work regularly. I am very anxious to begin. Mrs. B. The object of chemistry is to obtain a knowledge of the intimate nature of bodies, and their mutual action on each other. You find, therefore, Caroline, that this is no narrow or confined science, which comprehends every thing material within our sphere. Caroline. On the contrary, it must be inexhaustible ; and I am at a loss to conceive how any proficiency can be made in a science whose objects are so numerous. Mrs.B. If every individual substance were formed of different materials, the study of chemistry would, indeed, be endless; but you must observe that the various bodies in nature, are composed of certain elementary principles, which are not very numerous. Caroline. Yes; 1 know'that all bodies are composed of fire, air, earth, and water; I learnt that many years ago. Mrs. B. But you must now endeavor to forget it. I have al- ready informed you what a great change chemistry has undergone since it has become a regular science. Within these thirty year3 especially, it has experienced an entire revolution, and it is now proved that neither fire, air, earth, nor water, can be called elemen- tary bodies. For an elementary body is one that has never been decomposed, that is to say, separated into other substances; and fire, air, earth, and water, are all of them susceptible of decompo^ sition. Emily. I thought that decomposing a body was dividing" it into its minutest parts. And if so 1 do not understand why an elemen- tary substance is not capable of being decomposed, as well as any other. * Mrs. B. You have misconceived the idea of decomposition ; it is very different from mere division. v The latter simply reduces a body into parts, but the former separates it into the various ingre- dients, or materials* of which it is composed. If we were to take a loaf of bread and separate the several ingredients of which it is made, the flour, the yeast, the salt, and the water, it would be very different from cutting or crumbling the loaf into pieces. Emily. I understand you now very well. To decompose a body 18. To what does Mrs. B. say it is necessary to pay regard in the study of chemistry ? 19. Of what are the various bodies in nature composed ? 20. Of what was it formerly thought they were composed? 21. What is an elementary body ? 22. What is the difference between division and decomposition? 23. What are instances of decomposition? OF CHEMISTRY. 17 is to separate from each other the various elementary substances of which it consists. Caroline. But flour, water, and other materials of bread, accord- ing to your definition, are not elementary substances. Mrs. B. No, my dear; I mentioned bread rather as a familiar comparison to illustrate the idea, than as an example. v The elementary substances of which a body is composed are called the constituent parts of that body ; in decomposing it, there- fore, we separate its constituent parts. If, on the contrary, we di- vide a body by chopping it to pieces, or even by grinding or pound- ing it to the finest powder, each of these small particles will still consist of a portion of the several constituent parts of the whole body : these are called the integrant parts ; do you understand the difference ? Emily. Yes, I think perfectly. We decompose a body into its constituent parts; and divide it into its integrant parts. Mrs. B. Exactly so. If, therefore, a body consists of only one kind of substance, though it may be divided into its integrant parts, it is not possible to decompose it. Such bodies are therefore call- ed simple or elementary, as the}' are the elements of which all other bodies are composed. Compound bodies are such as consist of more than one of these elementary principles. Caroline. But do not fire, air, earth, and water, consist each of them, but of one kind of substance ? Mrs. B. No, my dear: they are every one of them susceptible of being separated into various simple bodies. Instead of four, chemists now reckon no less than .fifty-seven elementary sub- stances. The existence of most of these is established by the clearest experiments ; but, in regard to a few of them, particularly the most subtle agents of nature, heal, light, and electricity, there is yet much uncertainty, and 1 can'only give you the opinion which seems most probably deduced from the latest discoveries. After I have given you a list of the elementary bodies, classed according to their properties, we shall proceed to examine each of them sepa- rately, and then consider them in their combinations with each other. Except the more general agents of nature, heat, light and elec- tricity, it would seem that the simple form of bodies is that of a metal.* Caroline. You astonish me ! I thought the metals were only one * No actual discovery makes this probable. It is supposing that all the gases, as oxygen, hydrogen, &c, as well as phosphorus, sul- phur, and carbon, and several other substances are in part com- posed of a metal, and yet not one among this number are known to have metallic bases.—C. 24. What are the constituent parts of a body ? 25. What are integrant parts of a body ? 26. How may compound bodies be defined? 27. How many elementary substances are there? 23. Concerning which three of them is there much uncertainty ? 29. How is it proposed to examine these elementary substances? 2* 18 GENERAL PRINCIPLES class of minerals, and that there were besides, earths, stones, rocks, acids, alkalies, vapours, fluids, and the whole of the animal and vegetable kingdoms. Mrs. B. You have made a tolerably good enumeration, though I fear not arranged in the most scientific order. All these bodies, however, it is now strongly believed, may be ultimately resolved into metallic substances.* Your surprise at this circumstance is not singular, as the decomposition of some of them, which has been but lately accomplished, has excited the wonder of the whole philo- sophical world. But to return to the list of simple bodies—these being usually found in combination with oxygen, 1 shall class them according to their properties when so combined. This will, I think, facilitate their future investigation. Emily. Pray, what is oxygen ? Mrs. B. A simple body ; at least, one that is supposed to be so, as it has never been decomposed. It is always found united with the negative electricity. It will be one of the first of the elementa- ry bodies, whose properties I shall explain to you, and, as you will soon perceive, it is one of the most important in nature ; but it would be irrelevant to enter upon this subject at present. We must now confine our attention to the enumeration and classifica- tion of the simple bodies in general. They may be arranged as follows : CLASS I. Comprehending the imponderable agents, viz : HEAT OR CALORIC, LIGHT. ELECTRICITY. CLASS II. Comprehending agents capable of uniting with inflammable bodies, and in most instances of effecting their combustion. OXYGEN, CHLORINE, lODIJSE. f * Three of the alkalies only are known to have metallic bases. f A majority of the most learned Chemists, it is believed, bare doubted whether Chlorine and Iodine were supporters of combus- tion, any farther than they contain oxygen.—C. 30. With what are simple bodies usually found in combination? 31. With what are they always found united ? 32. Which of the elementary substances are included in the first class ? 33. What one does the second class include ? 34. What number of the alkalus are known to have mdallic bases ? OF CHEMISTRY. 19 CLASS III. Comprehending bodies capable of uniting with oxygen, and forming with it various compounds- This class may be divided as follows : DIVISION 1. hydrogen, forming water, V DIVISION 2. Bodies forming acids. nitrogen, . . . forming nitric acid. sulphur, . . . . forming sulphuric acid. phosphorus, . . forming phosphoric acid, carbon, .... .forming carbonic acid. boracium, . . . forming boracic acid. fluorium, . . .forming fluoric acid. muriatium, .' . forming muriatic acid. division 3. Metallic bodies forming alkalies. potassium, . . .forming potash. sodium, .... forming soda. ammonium, . . forming ammonia. lithium, . . . forming lithina.* division 4. Metallic bodies forming earths. calcium, or metal forming lime. magnium, .... forming magnesia. barium......forming barytes. strontium, . . .forming strontites. silicium, . . . . forming silex. alumtum, . . . forming alumine. yttrium, . . . .forming yttria. glucium, .... forming glucina. zirconium, . . . forming zirconia.f thornium, . . . forming thorina.% * This fourth alkali was discovered by Mr. Arfundson, a Swedish chemist, so recently as the year 1818. ■}■ Of all these earths three or four only have as yet been distinct- ly decomposed. \ Thorina, a new earth discovered by Berzelius in 1816, in a mineral composed of fluoric acid and cerium. 35. What one makes'the first division of the third class? 36. What ones make the second division of the third class? 37. What ones make the third division of the third class? 38. What ones make the fourth division of the third class? 20 GENERAL PRINCIPLES DIVISION 5. Metals, either naturally metallic, or yielding their oxygen to carbon or to heat alone. SUBDIVISION 1. Malleable Metals. GOLD, COPPER, platina, IRON, PALLADIUM, LEAD, SILVER,* NICKEL, MERCURY,f ZINC, TIN, CADMIUM.J SUBDIV. 2 Brittle Metals. ARSENIC, ANTIMONY, BISMUTH, MANGANESE, SELENIUM,} URANIUM, TELLURIUM COLUMBIUM Or TANTALUM, COBALT, IRIDIUM, TUNGSTEN, OSMIUM, MOLYBDENUM, RHODIUM, TITANIUM, CERIUM.|| CHROME, * These first four metals have commonly been distinguished by the appellation of perfect or noble metals, on account of their pos- sessing the characteristic properties of ductility, malleability, in- alterability, and great specific gravity,, in an eminent degree. f Mercury, in its liquid state, cannot, of course, be called a mal- leable metal. But when frozen, it possesses a considerable degree of malleability. | A metal resembling tin ; which was discovered in 1819, in an ore of zinc, by Mr. Stromeyer. $ Selenium was discovered a few years ago by Berzelius, in the ferruginous pyrites of Fahlun, of Sweden. It has the metallic lus- tre, but it does not conduct electricity, and is but a bad conductor of caloric. It passes to the state of oxide and acid, so that it might perhaps more strictly be classed with sulphur. It may be distin- guished by the smell of its vapour, which is that of horse raddish. || These four or five metallic bodies are placed under this class for the sake o>" arrangement, though some of their properties have not been yet fully investigated. ----------------------------------------------------------------------------------------------------1--------r,-----------------------------.-----------------------.----------------------- 39. What ones make th« first part'bf the fifth division in the third class ? ^ 40. What ones make the second part of the fifth division in the sec- ond class ? 41. Why have gold,platina, palladium, and silver been called perfect or noble metals ? OF CHEMISTRY. 21 Caroline. Ob, what a formidable list ! you will have much to do to explain it, Mrs. B.; for I assure you it is perfectly unintelligible to me, and I think rather perplexes than assists me. Mrs. B. Do not let that alarm you, my dear; I hope that hereaf- ter this classification will appear quite clear, and, so far from per- plexing you, will assist you in arranging your ideas. It would be in vam to attempt forming a division that would appear perfectly clear to a beginner; for you may easily conceive that a chemical division being necessarily founded on properties with which you are almost wholly unacquainted., it is impossible that you should at once be able to understand its meaning or appreciate its utility. But, before we proceed further, it will be necessary to give you some idea of chemical attraction, a power on which the whole sci- ence depends. Chemical Attraction or the Attraction of Composition, consists in the peculiar tendency which bodies of a different nature have to unite with each other. It is by this force that all the compositions, and decompositions are effected. Emily. What is the difference between chemical attraction, and the attraction of cohesion or of aggregation, which you often men- tioned to us in former conversations ? Mrs. B. The attraction of cohesion exists only between particles of the same nature, whether simple or compound ; thus it unites the particles of a piece of metal which is a simple substance, and like- wise the particles of a loaf of bread which is a compound. The at- traction of composition on the contrary, unites and maintains, in a state of combination, particles of a dissimilar nature ; it is this pow- er that forms each of the compound particles of which bread con- sists ; and it is by the attraction of cohesion that all these particles are connected iato a single mass. Emily, The attraction of cohesion, then, is the power which unites the integrant particles of a body ; the attraction of composition that which combines the constituent particles. Is it not so? Mrs. B. Precisely; and observe that the attraction of cohesion unites particles of a similar nature, without changing their original properties ; the result of such an union, therefore, is a body of the same kind as the particles of which it is formed ; whilst the attrac- tion of composition, bjr combining particles of a dissimilar nature, produces compound bodies, quite different from any of their constit- uents. If, for instance, I pour on the piece of copper, contained in this glass, some of this liquid (which is called nitric acid,) for which it has a strong attraction, every particle of the copper will combine with a particle of acid, and together they will form a new body, to- tally different from either the copper or the acid. 42. Why do the divisions in chemical science appear unmeaning to the young student ? 43. What is chemical attraction or the attraction of composition ? 44. What is the difference between chemical attraction and the at- traction of cohesion ? 45. What is the experiment mentioned as illustrating chemical at-r traction ? 46. What will be the result if copper and nitric acid are pqt togeth-: er ? 22 GENERAL PRINCIPLES, Do you observe the internal commotion that already begins to, take place? It is produced by the combination of these two sub- stances,* and yet the acid has in this case to^overcome not only the resistance which the strong cohesion of the particles of copper op- poses to their combination with it, but also to overcome the weight of the copper, which makes it sink to the bottom of the glass, and prevents the acid from having such free access to it as it would if the metal were suspended in the liquid. Emily. The acid seems, however, to overcome both these ob- stacles without difficulty, and appears to be very rapidly dissolving. the copper. Mrs. B. By this means it reduces the copper into more minute parts than could possibly be done by any mechanical power. But as the acid can act only on the surface of the metal, it will be some time before the union of these two bodies will be completed. You may, however, already see how totally different this com- pound is from either of its ingredients. It is neither colorless, like the acid, nor hard, heavy, and yellow like the copper If you tasted it, you would no longer perceive the sourness of the acid. It hasat present the appearance of a blue liquid; but when the union iscom- pleted, and the water with which the acid is diluted, is evaporated, the compound will assume the form of regular crystals of a fine blue color, and perfectly transparent.! Of these I can show you a spe- cimen, as I have prepared some for that purpose. Caroline. How beautiful they are in colour, form, and transpa- rency ! Emily. Nothing can be more striking than this example of chem- ical attraction. Mrs. B. The term attraction has been lately introduced into chemistry as a substitute for the word affinity, to which some chem- ists have objected because it originated in the vague notion that chemical combinations depended upon a certain resemblance, or relationship, between particles that are disposed to unite ; and this * This hardly explains the process. A part of the oxygen of the nitric acid unites with the copper ; and in consequence of this loss of oxygen, the nitric acid is converted into nitrous gas. It is the escape of this gas through the water as it is formed that occasions the commotion.—C. •f- These crystals are more easily obtained from a mixture of sul- phuric with a little nitric acid. J \ Thesecrystals are sulphat of copper, or what is commonly known under the name of blue vitriol.—C. 47. What has the acid in this experiment to overcome ? 48. On what part of a metal can the acid operate in this experi- ment ? 49. What is the appearance of the compound substance thus form- ed of copper and nitric acid ? 50. In the place of what term has chemical attraction been substi- tuted ? 51. What is said in the note to produce the commotion when copper find nitric acid are put together ? 52. What was the objection to the term affinity? OF CHEMISTRY. 23 idea is not only imperfect, but erroneous, as it is generally particles of the most dissimilar nature, that have the greatest tendency to combine. Caroline. Besides there seems to be no advantage in using a va- riety of terms to express the same meaning ; on the contrary, it creates confusion ; and as we are well acquainted with the term At- traction in natural philosophy, we had better adopt it in chemistry likewise. Mrs. B. If you have a clear idea of the meaning, 1 shall leave you at liberty to express it in the terms you prefer. For myself, I confess that 1 think the word Attraction best suited to the gen- eral law that unites the integrant particles of bodies ; and Affinity ^better adapted to that which combines the constituent particles, as it may convey an idea of the preference which some bodies have for others, which the term attraction of composition does not so well express. Emily. So I think; for though that preference may not result from any relationship, or similitude, between the particles (as you » say was once supposed,) yet as it really exists, it ought to be ex- pressed. Mrs. B. Well, let it be agreed that you may use the terms affini- ty, chemical attraction, and attraction of composition, indifferently, provided you recollect that they have all the same meaning. Emily. I do not conceive how bodies can be decomposed by chemical attraction. That this pcwer should be the means of com- posing them is very obvious; but that it should at the same time, produce exactly the contrary effect, appears to me very singular. Mrs. B. To decompose a body is, you know, to separate its con- stituent parts, which, as we have just observed, cannot be done by mechanical means. Emily. No ; because mechanical means separate only the inte- grant particles ; they act merely against the attraction of cohesion, and only divide a compound into smaller parts, Mrs. B. The decomposition of a body is performed by chemical powers. If you present to a body composed of two principles, a third, which has a greater affinity for one of them than the two first have for each other, it will be decomposed, that is, its two principles will be separated by means of the third body. Let us call two in- gredients, of which (he body is composed, A. and B. If we present to it another ingredient C, which has a greater affinity for B than that which unites A and B, it necessarily follows that B will quit A to combine with C. The new ingredient, therefore, has effected a decomposition of the original body A B ; A, has been left alone, and a new compound B, C, has been formed. Emily. We might, I think, use the comparison of two friends, who were very happy in each other's society, till a third disunited them by the preference which one of them gave to the new comer, 53. Why does Mrs. B. prefer the term affinity ? 54. By what means can decomposition be effected ? 55. How can a compound body be decomposed ? 56. What illustration is given of the manner of decomposing a body ? 24 GENERAL PRINCIPLES Mrs. B. Very well. I shall now show you how this takesplacfe in chemistry. Let us suppose that we wish to decompose the compound we have just formed by the combination of the two ingredients, copper and nitric acid ; we may do this by presenting to it a piece of iron, for which the acid has a stronger attraction than for copper; the acid will, consequently, quit the copper to combine with the iron, and the copper will be what the chemists call precipitated, that is to say, it will be thrown down in its separate stale, and re-appear in its simple form. In order to produce this effect, I shall dip the blade of this knife into the fluid, and when I take it out, you will observe that instead of being wetted with a bluish liquid, like that contained in the glass, it will be covered with a thin coat of copper. Caroline. So it is really ! but then is it not the copper instead of the acid, that has combined with the iron blade ? Mrs. B. No; you are deceived by appearances ; it is the acid which combines with the iron, and in so doing, deposites or precipi- tates the copper on the surface of the blade. Emily. But cannot three or more substances combine together, without any of them being precipitated? Mrs. B. That is sometimes the case ; but, in general, the strong- er affinity destroys the weaker ; and it seldom happens that the at- traction of several substances for each other is so equally balanced as to produce such complicated compounds.* Caroline. But pray, Mrs. B., what is the cause of the chemical attraction of bodies for each other ? It appears to me more extraor- dinary or unnatural, if I may use the expression, than the attrac- tion of cohesion, which unites particles of a similar nature. Mrs. B. Chemical attraction may, like that of cohesion or grav- itation, be one of the powers inherent in matter, which, in our present state of knowledge, admits of no other satisfactory expla- nation than an immediate reference to a divine cause. Sir H. Da- vy, however, whose important discoveries have opened such im- proved views in chemistry, has suggested an hypothesis which may * Such compounds are quite numerous. They are called triple salts. Alum is one. It is composed of alumine, potash and sulphu- ric acid. Tartar Emetic is another. It is composed of tartaric acid, potash and antimony.—C 57. How can the substance formed of copper and nitric acid be de- composed ? 58. Why will decomposition take place on tho application of iron ? 59. What is precipitation ? 60. If it is the acid which combines with the iron, why is the iron covered with a thin coat of copper in this experiment f 61. Do more than-two simple substances over unite in forming the same compound ? 62. What are such compounds called ? 63. What am instances of them ? 64. What is'onb of the powers in addition to those mentioned bv .philosophers which may be considered as inherent in bodies? OF CHEMISTRY. 25 ;;hrow great light upon that science. He supposes that there are two kinds of electricity, with one or other of which all bodies are united. These we distinguish by the names of positive and nega- tive electricity ; those bodies are disposed to combine, which pos- sess opposite electricities, as they are brought together by the at- traction which these electricities have for each other. But, whether this hypothesis be altogether founded on truth or not, it is impossi- ble to question the great influence of electricity in chemical com- binations. Emily. So, that we must suppose that the two electricities, al- ways attract each other, and thus compeljhe bodies in which they exist to combine ?* Caroline. And may not this be also the cause of the attraction of cohesion ? Mrs. B. No, for in particles of the same nature, the same elec- tricities must prevail, and it is only the different or opposite elec- tric fluids that attract each other. Caroline. These electricities seem to me to be a kind of chemi- cal spirit which animates the particles of bodies, and draws them together. Emily. If it is known, then, with which of the electricities bod- ies are united, it can be inferred which will, and which will not combine together ? Mrs. B. Certainly.—1 should not omit to mention, that some doubts have been entertained, whether electricity be really a ma- terial ajent, or whether it might not be a power inherent in bod- ies, similar to, or perhaps identical with, attraction. * There seems to be an objection to this theory as explained here. When two bodies,one iu the positive, the other in the negative state of electricity are presented to each other, a mutual attraction takes place, until they touch, or come within the striking distance, so that the electric fluid can pass from the positive to the negative body. When this is effected, they are said to be in a state of equi- librium, or in the same state of electricity, and consequently nei- ther attract nor repel each other. If, therefore, chemical attrac- tion depends on the different electrical states of the particles, we are still at a loss how to account for their adhesion even after they are united. The celebrated Kepler accounted for the affinity of particles by supposing each to have its likings and its antipathies, and the power of choosing accordingly. This theory only wants our belief to make it satisfactory. —C. 65. How many kinds of electricity are there, and what are they called ? 66. What does Mrs B. think has a great influence in effecting chem- ical combinations ? 67. What is said of electricity in the note ? 68. What difficulty arises, if we suppose chemical attraction to de- pend upon the different states of the particles ? 69. How does Kepler account for the affinity of particles ? 70. What doubts does Mrs. B. mention as having been entertained concerning electricity ? 26 LIGHT. Emily. But what, then, would be the electric spark which is vis- ible, and must, therefore, be really material? . Mrs. B. What we call the electric spark, may, Sir H Davy says, be merely the heat and light, or fire produced by the chemical combinations with which these phenomena are always connected. We will hot, however, enter more fully on this important subject at present, but reserve the principal facts which relate to it to a future conversation. Before we part, however, I must recommend you to fix in your memory the names of the simple bodies against our next interview. CONVERSATION II. ON LIGHT AND HEAT, OR CALORIC. Caroline. We have learned by heart the names of all the simple bodies which you have enumerated, and we are now ready to enter on the examination of each of them successively. You will begin, I suppose, with light ? Mrs.B. Respecting the nature of light we have little more than conjectures. It is considered by most philosophers as a real sub- stance immediately emanating from the sun, and from all luminous bodies^ from which it is projected in right lines with prodigious ve- locity. Light, however, being imponderable, it cannot be confined and examined by itself: and therefore it is to the effects it produ- ces on other bodies, rather than to its immediate nature, that we must direct our attention. The connexion between light and heat is very obvious ; indeed, it is such, that it is extremely difficult to examine the one inde- pendently of the other. Emily. But is it possible to separate light from heat ? 1 thought they were onljT different degrees of the same thing, fire. Mm. B. I told you that fire was not now considered as a simple element. Whether light and heat be altogether different agents, or not, 1 cannot pretend to decide : but, in many cases, light may be separated from heat. The first discovery of this was made by a celebrated Swedish chemist, Scheele. Another very striking illus- tration of the separation of heat and light was long after pointed out by Dr. Herschell. This philosopher discovered that these two agents were emitted in the rays of the sun, and the heal was less ■ 71. If electricity is a power inherent in bodies, what would the electric spark be which is visible, and therefore, must be really ma- terial ? 72. What do most philosophers consider light ? 73. With what is light obviously connected ? 74. Can light and heat be separated ? 75. Who first discovered that they are not inseparably connected ? LIGHT. 27 refrangible than light; for, in separating the different coloured rays of light by a prism, (as we did some time ago,) he found that the greatest heat was beyond the spectrum, at a little distance from the red rays, which, you may recollect, are the least refrangible. Emily. I should like to try that experiment. Mrs. B. It is by no means an easy one ; the heat of a ray of light, refracted by a prism, is so small, that it requires a very delicate ther- mometer to distinguish the difference of the degree of heat within and without the spectrum, For in this experiment, the heat is uot totally separated from the light, each coloured ray retaining a cer- tain portion of it, though the greatest part is not sufficiently refrac- ted to fall within the spectrum. Emily. I suppose, then, that those coloured rays which are the least refrangible, retain the greatest quantity of heat ? Mrs. B. They do so. Emily. Though 1 no longer doubt that light and heat can be separated, Dr. Herschell's experiment does not appear to me to af- ford sufficient proof that they are essentially different; for light which you call a simple body, may likewise be divided into the various colored rays. Mrs. B. No doubt there must be some difference in the various coloured rays. Even their chemical powers are different. The blue rays for instance, have the greatest effect in separating oxy- gen from bodies, as was found by Scheele; and there exists also, as Dr. Wollaston has shown, rays more refrangible than the blue, which produce the same chemical effect, and, what is very remark- able, are invisible.* Emily. Do you think it possible that heat may be merely a mod- ification of lignt ? Mrs. B. That is a supposition which, in the present state of nat- ural philosophy, can neither be positively affirmed nor denied. Let us, therefore, instead of discussing theoretical points, be contented with examining what is known respecting the chemical effects of light. v Light is capable of entering into a kind of transitory union with certain substances,. and this is what has been called phospho- rescence. Bodies that are possessed of this property, after being exposed to f:>e sun's rays, appear luminous in the dark. vThe shells offish, the bones of land animals, marble, limestone, and a variety of combinations of earths; are more or less powerfully phosphores- cent. * The violet rays have the power of imparting the magnetic vir- 76. How can they be separated ? 77. Which of the coloured rays refracted by a prism, retain the greatest quantity of heat ? 78. What effect have the blue rays on bodies ? 79. What power have the violet rays asmentinned in the note ? 80. In what does the process consist ? 81. Is light capable of a union with other substances? 82. What is this union called ? 83. With what substances does this union mostly take place,in the production of phosphorescence ? 2S LIGHT. Caroline. I remember being much surprised last summer witHi the phosphorescent appearance of some piecesof rotten wood, which had just been dug out of the ground ; they shone so bright that I at first supposed them to be glow-worms. Emily. And is not the light of a glow worm of a phosphorescent nature ? Mrs. B. It is a very remarkable instance of phosphorescence in living animals; this property, however, is not exclusively possessed by the glow-worm. The insect called the lanthorn-fly which is peculiar to warm climates, emits light as it flies, producing in the dark a remarkably sparkling appearance. But it is more common to see animal matter in a dead state possessed of a phosphorescent quality ; sea-fish is often eminently so.* Emily. I am rather surprised, Mrs. B., that you should hare said so much of the light emitted by phosphorescent bodies, without tak- ing any notice of that which is produced'by burning bodies. Mrs. B. The light emitted by the latter is so intimately connect- ed with the chemical history of combustion, that I must defer all explanation of it till we come to the examination of that process, which is one of the most interesting in chemical science. Emily. I have heard that the sea has sometimes had the appear- ance of being illuminated, and that the light is supposed to proceed from the spawn of fishes floating on its surface. Mrs. B. This light is probably owing to that or some other ani- mal matter. Sea water has been observed to become luminous from the substance of a fresh herring having been immersed in it; and certain insets of the Medusa kind, are known to produce simi- lar effects. But the strongest phosphorescence is produced by chemical com- positions prepared for the purpose, the most common of which con- sists of oyster-shells and sulphur, and is known by the name of Can- ton's Phosphorus.f tue to steel. The process consists in intercepting all the rays ex- cept this, and of throwing this, being first collected into a focus by a lens, on the middle of a needle, and carrying it towards the extrem- ity. • This is to be done many times, and always towards the same extremity. After a while the needle acquires polarity.—C. * The phosphorescence of dead animals is owing to the escape of phosphorus in the form of phosphorelted hydrogen. This is set free from its combination with the substance of the animal by the putre- factive fermentation.—C. t' To prepare this, mix three parts of oyster-shells calcined for an hour and pulverized with one part of sulphur. This is to be rammed into a crucible, which is to be kept at a red heat for one hour. On . 84. What remarkable instances of phosphorescence in living ani- mals are mentioned ? . 85. To what is the phosphorescence of dead animals owing ? . 86. How is it freed from its combination with the substance of the animal ? 87. What is the strongest phosphorescence, or how is it produced? 88. How is this substance prepared ? LIGHT 29 .Light is an agent capable of producing various chemical changes. '■.It is essential to the welfare both of the animal and vegetable king- doms ; for men and plants grow pale and sickly if deprived of its salutary influence. It is likewise remarkable for its property of de- stroying colour, which renders it of great consequence in the pro- cess of bleaching. Emily. Is it not singular thatdight, which in studying optics we were taught to consider as the source and origin of colours, should have also the power of destroying them? Caroline. It is a fact, however, which we every day experience; you know it fades the colours of linens and silks. Emily. Certainly. And I recollect that endive is made to grow white instead of green, by being covered up so as to exclude the light. But by what means does light produce these effects ? Mrs. B. This 1 cannot attempt to explain to you until you have obtained a further knowledge of chemistry. As the chemical pro- perties of light can be accounted for only in their reference to com- pound bodies, it would be useless to detain you any longer on this subject; we may, therefore, pass on to the examination of heat, or caloric, with which we are somewhat better acquainted. Heat and Light may be always distinguished by the different sensations they produce.' Light affects the sense of sight; Caloric that of feeling; the one produces Vision, the other the sensation of Heat. Caloric is found to exist in, a variety of forms or modifications, and I think it will be best to consider it under the two following heads, viz: 1. Free or radiant caloric. 2. Combined caloric. The first, free or radiant caloric, is also called heat of temperature ; it comprehends all heat which is perceptible to the senses, and affects the thermometer. Emily. You mean such as the heat of the sun, of fire, of candles, of stoves; in short, of every thing that burns ? Mrs. B. And likewise of things that do not burn, as, for instance, the warmth of the body ; in a word, all heat that is sensible, what- ever may be its degree, or the source from which it is derived. Caroline. What, then, are the other modifications of caloric ? It exposing some of this to the sun's rays, it absorbs light, and will shine in the dark. This shows that light can be separated from heat.—C. 89. What does this experiment prove? 90. To what is light essential, and what remarkable property has it ? 91. What do optics teach us to consider the source and origin of colours ? . 92. How may light and heat always be distinguished? 93. Under what two heads is caloric considered? 3* 30 FREE CALORIC. must be a strange kind of heat that cannot be perceived by our senses. Mrs. B. None of the modifications of caloric should properly be called heat ; for heat, strictly speaking, is the sensation produced by caloric, on animated bodies ; this word, therefore, in the accurate language of science, should be confined to express the sensation. But custom has adapted it likewise to inanimate matter, and we say, the heat of an oven, the heat of the sun, without any reference to the sensation which they are capable of exciting. It was in order to avoid the confusion, which arose from thus con- founding the cause and effect, that modern chemists adopted the new word caloric, to denote the principle which produces heat; yet they do not always, in compliance with their own language, limit the word heat to the expression of the sensation, since they still fre- quently employ it in reference to the other modifications of caloric which are quite independent of sensation.* Caroline. But you have not yet explained to us what these other modifications of caloric are. Mrs. B. Because you are not acquainted with the properties of free caloric, and you know that we have agreed to proceed with regularity. One of the most remarkable properties of free caloric is its powei of dilating bodies". This fluid is so extremely subtle, that it enters and pervades all bodies whatever, forces itself between their parti- cles, and not only separates them, but frequently drives them asun- der to a considerable distance from each other. It is thus that ca- loric dilates or expands a body so as to make it occupy a greater space than it did before. Emily. The effect it has on bodies, therefore, is directly contrary to that of the attraction of cohesion ; the one draws the particles to- gether, the other drives them asunder. Mrs. B. Precisely. There is a continual struggle between the attraction of aggregation, and the expansive power of caloric; and from the action of these two opposite forces, result all the va- rious forms of matter, or degrees of consistence, from the solid to the. liquid and a-riform state- And, accordingly, we find that mosi bodies are capable of passing from one of these forms to the other * If I touch a body at n higher temperature than my hand, I im- mediately receive a quantity of caloric from it, and at the same in- stant feel the sensation called heat. The caloric, then, is the cause of this sensation, and heat the effect of caloric passing into my hand.— C. 94. What is free or radiant caloric ? 95. What is heat, strictly speaking ? 96. What is the difference between caloric and heat, as the terms are used by chemists ? 97. What illustration of this is given in the note ? 98. What is one of the most remarkable properties of free caloric? 99. What two forces are in direct opposition to each other? 100. From what result all the various forms of matter, or de"rees of consistence in bodies ? FREE CALORIC, 31 merely in consequence of their receiving different quantities of caloric. Caroline. That is very curious; but 1 think 1 understand the reaton of it. If a great quantity of caloric is added to a solid body, it introduces itself between the particles in such a manner, as to overcome, in a considerable degree, the attraction of cohesion; and the body, from a solid, is then converted into a fluid, Mrs. B. This is the case whenever a body is fused or melted ; but if you add caloric to a liquid, can you tell me what is the conse- quence? Caroline. The caloric forces itself in greater abundance between the particles of the fluid, and drives them to such a distance from each other, that their attraction of aggregation is wholly destroyed ; the liquid is then transformed into vapor. Mrs. B. Very well; and this is precisely the case with boiling water, when it is converted into steam or vapor, and with all bodies that assume an aeriform state. Emily. I do not well understand the word aeriform. Mrs.B. Any elastic fluid whatever; whether it be merely va- vonr or permanent air, is called aeriform. But each of these various states, solid, liquid, and aeriform, ad- mit of different degrees of density, or consistence, still arising (chiefly at least) from the different quantities of caloric the bodies contain. Solids are of various degrees of density, from that of gold, to that of a thin jelly. Liquids, from the consistence of melted glue, or melted metals, to that of ether, which is the lightest of all liquids. The different elastic fluids (with which you are not yet acquainted) are susceptible of no less variety in their degrees of density. Emily. But does not every individual body also admit of different degrees of consistence, without changing its state ? Mrs. B. Undoubtedly : and this 1 can immediately show you by a very simple experiment. This piece of iron now exactly fits the frame, or ring, made to receive it; but if heated red hot, it will no longer do so, for its dimensions will be so much increased by the caloric that has penetrated into it, that it will be much too large for the frame. The iron is now red hot: by applying it to the frame, we shall see how much it is dilated. Emily. Considerably so indeed ! I knew that heat had this effect on bodies, but did not imagine that it could be made so con- spicuous. • 101. What causes bodies to pass from one of these forms to the other? 102. How would you explain the manner in which a solid is con- verted into a liquid? 103. If we add caloric to a liquid, what is the consequence ? 104. What is meant by the word aeriform ? 105. From what do the different degrees of density or consistence arise ? 106. Which is the lightest of all liquids? 107. Are the elastic fluids susceptible of various degrees of density ? 108. Do bodies admit of different degrees of consistence without changing their state ? &z FREE CALORIC. Mrs. B. By means of this instrument (called a Pyrometer) we may estimate, in the most exact manner, the various dilatations of any solid body by heat. The hody we are now going to submit to trial is this small iron bar ; 1 fix it to this apparatus, and then Fig. 1. Pyrometer. A A, Bar of metal. 12 3, Lamps burning. B B, Wheel work. C, Index. heat it by lighting the three lamps beneath it ; when the bar ex- pands, it increases in length as well as thickness ; and, as one end communicates with this wheel work, whilst the other end is fixed and immoveable, no sooner does it begin to dilate, than it presses against the wheel work, and sets in motion the index, which points out the degrees of dilatation on the dial plate. Emily. This is, indeed, a very curious instrument ; but I do not understand the use of the wheels; would it not be more simple, and answer the purpose equally well, if the bar in dilating, pressed against the index, and put it in motion without the intervention of the wheels ? Mrs. B. The use of the wheels is merely to multiply the motion, and therefore render the effect of the caloric more obvious ; for if the index moved no more than the bar increased in length, its mo- tion would scarcely be perceptible ; but by means of the wheels, it moves in a much greater proportion, which therefore renders the variations far more conspicuous. By submitting different bodies to the test of the pyrometer, it is found that they are far from dilating in the same proportion. Dif- ferent metals expand in different degrees, and other kinds of solid bodies vary slill more in this respect. But this different suscep- tibility of dilatation is still more remarkable in fluids than in solid bodies as I shall show you. I have here two glass tubes, terminated at one end by large bulbs. We shall fill the bulbs, the one with 109. What experiment proves that they do ? 110. What is the use of the Pyrometer ? 111. How would you explain figure 1 ? 112. What is the use of wheels in this instrument? ♦113. Does caloric expand all bodies in the same degree ? 114. Which are most susceptible of dilatation, fluids or solids? FREE CALORIC. 33 A .A spirit of wine, the other with water. I have colored both liquids, in order that the effect may be more conspicuous. The spirit of wine, you see, dilates by the warmth of my hand as I hold the bulb.* Emily. It certainly does, for 1 see it is rising into the tube. But water it seems, is not so easily affected by heat; for scarcely any change is produced on it by the warmth of the hand. Fig- 2. Mrs. B. True; we shall now plunge the bulbs into hot water, and you will see both liquids rise in the tube; but the spir- it of wine will ascend highest. Caroline. How rapidly it expands! Now it has nearly reached the tube, though the water has hardly begun to rise, Emily, The water now begins to dilate. Are not these glass tubes, with liquids rising within them, very like thermome- ters? Mrs. B. A thermometer is constructed exactly on the same principle, and these tubes require only a scale to answer the ■•; purpose of thermometers; but they would be rather awkward in their dimensions*— The tubes and bulbs of thermometers, though of various sizes, are in general much smaller than these ; the tube too, is jhermeticallyt closed, and the air excluded from it. The fluid most generally used in thermometers, is 'mercury, commonly cat- ses of water in which they areled quicksilver, the dilatations and con- immersed, tractions of which correspond more exact- ly to the additions and subtractions of ca- loric, than those of any other fluid."\ Caroline. Yet I have often seen colored spirit of wine used in thermometers. Mrs. B. The expansions and contractions of that liquid are not quite so uniform as those of mercury ; but incases in which it is B '•' S >~*i A A', Glass bulbs. B B, Glas- * In the absence of the glass tubes terminated by bulbs, procure a pair of tin canisters, three inches high and two wide, soldered up all round. In the middle of the top of each, have inserted a circu- lar tin spout, and into these cement glass tubes about twelve inches high. These will answer every purpose.—C. f The tube is closed by holding the end over a spirit lamp until the glass is melted. This word is derived from Hermes, the Greek name for mercury. He is said to have been the inventer of chenv istry; hence this is sometimes called {he-Hermetic art, and hermet- ically, or chemically closed, is closed by heat or melting.—C. 115. What is the object of figure 2? 116. Whatfluid is generally used in thermometers'1 117. How do the expansions and subtractions of the spirits of wine, compare with those of mercury? 34 FREE CALORIC. not requisite to ascertain the temperature with great precision, spirit of wine will answer the purpose equally well, and indeed in some respects better, as the expansion of the latter is greater, and therefore more conspicuous. This fluid is used likewisejn situations and experiments in which mercury would be frozen ; for mercury becomes a solid body, like a piece of lead or any other metal, at a certain degree of cold ; but no degree of cold has ever been known to freeze spirit of wine.* A thermometer, therefore,, consists of a tube with a bulb, such as you see here, containing a fluid whose degrees of dilatation and contraction are indicated by a scale to which the tube is fixed.-— The degree which indicates the boiling point simply means that when the fluid is sufficiently dilated to rise to this point, the heat is such that water exposed to the same temperature will boil. When on the other hand, the fluid is so much condensed as to sink to the freezing point, we know that water will freeze at that temperature. The extreme points of the scales are not the same in all thermome- ters, hot are the degrees always divided in the same manner. In different countries philosophers have chosen to adopt different scales and divisions. The two thermometers most used are those of Fah- renheit, and Reaumur; the first is generally preferred by the Eng- lish, the latter by the French. Emily. The variety of scale must be very inconvenient, and I should think liable fto occasion confusion when French and Eng- lish experiments are compared. ' Mrs. B. The inconvenience is but very trifling, because the dif- ferent gradations of the scales do not effect the principle upon which thermometers are constructed. When we know, for in- stance, that Fahrenheit's scale is divided into 212 degrees, in which 32° corresponds with the freezing point, and 212° with the point of boiling water; and that Reaumur's is divided only into 80 degrees, in which 0° denotes the freezing point, and 80° that of boiling. water, it is easy to compare the two scales together, and reduce the one into the other. But, for greater convenience, thermome- ters are sometimes constructed with both these scales; one on either side of the tube; so that the correspondence of the different degrees of the two scales is thus instantly seen. Here is one of these scales, (Fig. 3, see next page,) by wihch you can at once per- ceive that each degree of Reaumur's corresponds to 2 1-4 of Fah- renheit's division. But I believe the French have, of late, given the preference to what they call the centigrade scale, in which the space between the freezing and the boiling point is divided into 100 degrees. * Spirit of wine is stated to have been frozen in England by some process which the author has preferred to keep secret.—C. When is spirit of wine used ? 118. How would you describe a thermometer? 119. What two thermometers are mostly used ? 120. How are they graduated? 121. What is the temperature of boiling water ? 122. To what scale have the French been said to have preference ? FREE CALORIC. 35 3oilingl pointi *' Fig- 3. Caroline. That seems to me Thermometer. the most reasonable division, and I cannot guess why the freez- ing point is called 32°, or what advantage is derived from it. Mrs. B. There really is no Boiling advantage in it; and it originat- ing ed in a mistaken opinion of the instrument-maker, Fahrenheit, who first constructed these ther- mometers. He mixed snow and salt together, and produced by that means a degree of cold which he concluded was the great- est possible, and therefore made his scale begin from that point. Between that and boiling water he made 212 degrees, and the freezing point was found to be at 32°. Emily. Are spirit of wine, and mercury, the only liquids used g in the construction of thermome- % ters? «, Mrs. B. I believe they are the js only liquids now in use, though 5 some others, such as linseed oil, would make tolerable thermom- eters ; but for experiments in^ which a very quick and delicate. test of the changes of tempera- ture is required, air is the fluid. sometimes employed. The bulb of air thermometers is filled with common air only, and its expan- sion and contraction are indicat- ed by a small drop of any col- ored liquor, which is suspended within the tube, and moves up, Freesingand down, according as the air point within the bulb and tube expands or contracts. But in general, air thermometers, however sen- sible to changes of temperature, are by no means accurate in their indications. I can however, show you an air thermometer of a very peculiar construction, which is remarkably well adapted for some chemical ^ l«S 10 Freezing point X 123. Why was the freezing point in Fahrenheit's thermometer fix- ed at 32 degrees ? ■ 124. How are thermometers constructed ? 36 FREE CALORIC. experiments, as it is equally delicate and accurate in its indict tions.* Fig. 4. Caroline. It looks like a double thermom- ■Differential Ther- eter reversed, the tube being bent, and hav- mometer. ing a large bulb at each of its extremities. Emily. Why do you call it an air thermom- eter ; the tube contains a colored liquid? Mrs. B. But observe that the bulbs are filled with air, the liquid being confined to a portion of the tube, and answering only the purpose of showing, by its motion in the tube, the comparative dilatation or contraction of the air within the bulbs, which afford an in- dication of their relative temperature. Thus if you beat the bulb A, by the warmth of your hand, the fluid will rise towards the bulb B, and the contrary will happen if you reverse the experiment. But if on the contrary, both tubes are of the same temperature, as is the case now, the col- ie <* ored liquid, suffering an equal pressure on each jj ^ side, no change of level takes place. Caroline. This instrument appears, indeed, uncommonly delicate. The fluid is set in mo- tion by the mere approach of my hand. Mrs. B. You must observe, however, that this thermometer cannot indicate the tem- perature of any particular body, or of the medium in which it is immersed; it serves only to point out the dif- ference of temperature between the two bulbs, when placed under different circumstances.^. For this reason it has been called differ- ential thermometer. Yon will see hereafter to what particular pur- poses this instrument applies. Emily. But do common thermometers indicate the exact quan- tity of caloric contained either in the atmosphere, or in any body with which they are in contact ?f * Students in chemistry may amuse themselves with air ther- mometers of their own construction. Procure a flat vial or ink- stand with a wide mouth ; also, a broken thermometer tube, the bulb being entire. Fit a cork air tight to the vial, and pierce it in the middle with a hot iron to admit the tube. Fill the vial about half full of some coloured liquid. Warm the bulb of the tube by holding it in the hand, and in this state introduce the small end through the cork nearly to the bottom of the vial. The hand be- ing removed from the bulb, the fluid will raise in the tube. The flu- id will afterwards rise or fall as heat is applied to the vial or bulb. —C; f The thermometer indicates the exact quantity of free caloric. 125. What is said of air thermometers in the note? 126. Which figure represents an air thermometer ? 127. Why has the air thermometer been called the differential ther- mometer ? FREE CALORIC. 37 Mrt. B. No : first because there are other modifications of ca- loric which do not affect the thermometer; and,secondly, because the temperature of a body, as indicated by the thermometer, is on- ly relative. When, for instance, the thermometer remains sta- tionary at the freezing point, we know that the atmosphere, (or medium in which it is placed, whatever it may be) is as cold as freezing water; and when it stands at the boiling point, we know that this medium is as hot as boiling water ; but we do not know the positive quantity of heat contained either in freezing or boiling water, any more than we know the real extremes of heat and cold; and consequently we cannot determine that of the body in which the thermometer is placed. Caroline. I do not quite understand this explanation. Mrs. B. Let us compare a thermometer to a well, in which the water rises to different heights, according as it is more or less sup- plied by the spring which feeds it; if the depth of the well is un- fathomable, it must be impossible to know the absolute quantity of water it contains ; yet we can with the greatest accuracy measure the number of feet the water has risen or fallen in the well at any time, and consequently know the precise quantity of its increase or diminution, without having the least knowledge of the whole quantity of water it contains.* Caroline. Now I comprehend it very well; nothing appears to me to explain a thing so clear as a comparison. Emily. But will thermometers bear any degree of heat? Mrs. B. No; for if the temperature were much above the high- est degree marked on the scale of the thermometer, the mercu- ry would burst the tube in an attempt to ascend. And at any rate, no thermometers can be applied to temperatures higher than the boiling point of the liquid used in its construction, 'for the steam, on the liquid beginning to boil, would burst the tube. In furna- ces, or whenever any very high temperature is to be measured, a present at the time and place of the experiment. Thus if a cer- tain quantity of heat is required to raise the mercury 20°, double this quantity will raise it to 409. All bodies contain a quantity of heat not appreciable by the thermometer, or sensible to the touch. This is called fixed or latent heat. This can sometimes be set free, as when we hammer a piece of cold iron it becomes hot. Thus the latent caloric is squeezed out of the iron bj the contraction of its pores under the hammer, and it then becomes free caloric.—C * This passage may be expounded as follows. The unfathoma- ble depth of the well signifies the absolute quantity of caloric, and which the thermometer does not measure; because all bodies 128. Do common thermometers indicate the exact quantity of ca- loric contained either in the atmosphere, or in any body, with which they come in contact ? 129. Why do they not ? 130. What comparison is made between a well and a thermometer? 131. Why might not thermometers be applied to temperatures high- er than the boiling point of the liquid used in their construction ? 4 38 FREE CALORIC. pyrometer, invented by Wedgwood, is used for that purpose. It is made of a certain composition of baked clay, which has the pe- culiar property of contracting by heat, so that the degree of con- traction of this substance indicates the temperature to which it has been exposed. Emily. But is it possible for a body to contract by heat ? I thought that heat dilated all bodies whatever. Mrs. B. This is not an exception to the rule. You must recol- lect that the bulk of the clay is not comnr, reel, whilst hot, with that which it has when cold; but it is fro'm the change which the clay has undergone by having been heated, that the indications of this instrument are derived. This change consists in a beginning fu- sion, which tends to unite the particles of clay more closely, thus rendering it less previous or spongy.* Clay is to be considered as a spongy body, abounding in inter- stices or pores, from its having contained water when soft. These interstices are by heat lessened, and would by extreme beat be en- tirely obliterated. Caroline. And how do you ascertain the degrees of contraction of Wedgwood's pyrometer? Mrs. B. The dimensions of the piece of clay are measured by a scale graduated on the side of a tapered groove, formed in a brass ruler; the more the clay is contracted by the heat, the further it will descend into the narrow part of the tube. Before we quit the subject of expansion, I must observe to you, that, as fluids expand more readily than solids, so elastic fluids, whether air or vapor, are the most expansible of all bodies. It may appear extraordinary, that all elastic fluids whatever, un- dergo the same degree of expansion from equal augmentation of temperature. Emily. I suppose, then, that all elastic fluids are of the same den- sity. Mrs. B. Very far from it; they vary in density, more than ei- ther liquids or solids. The uniformity of their expansibility, which at first may appear singular, is, however, readily accounted for.— For if the different susceptibilities of expansion of bodies arise from their various degrees of attraction of cohesion, no such dif- however cold, still contain caloric. Thus mercury freezes at 40' below zero, but still contains caloric, and so on. The rising and falling of the water signifies the greater or less quantity of free ca- loric as indicated by the thermometer.—C. * According to the calculations of Saussure, the temperature necessary to melt this clay is 1575° Wedgwood, which is a degree of heat greatly beyond our common furnaces. It is therefore most probable that the clay contracts at lower temperatures by the loss of moisture.—C. 132. Do all bodies however cold contain caloric ? 133. In what manner is it that clay appears to contract by heat ? 134. What bodies are most expansible ? 135. Are all elastic fluids equally expanded from equal augmenta- tions of temperature ? 136. Are all elastic fluids of the same density ? FREE CALORIC. 39 ference can be expected in elastic fluids, since in these the attrac- tion of cohesion does not exist, their particles being on the contra- ry possessed of an elastic or repulsive power ; they will therefore all be equally expanded by equal degrees of caloric, t Emily. True; as there is no power opposed to' the expansive force of caloric in elastic bodies, its effect must be the same in all of them. Mrs. B. Let us now proceed to examine the other properties of free caloric. Free caloric always tends to diffuse itself equally ; that is to say, when two bodies are of different temperatures, the warmer gradu- ally parts with its heat to the colder, till they are both brought to the same temperature. Thus, when a thermometer is applied to a hot body, it receives caloric ; when to a cold one, it communicates part of its own caloric, and this communication continues until the thermometer and the body arrive at the same temperature. Emily. Cold, then, is nothing but a negative quality, simply im- plying the absence of heat. Mrs. B. Not the total absence, but a diminution of heat; for we know of no body in which some caloric may not be discovered. Caroline. But when 1 lay my hand on this marble table, I feel it positively cold, and cannot conceive that there is any caloric in it. Mrs. B. The cold you experience consists in the loss of caloric that your hand sustains in an attempt to bring its temperature to an equilibrium with the marble. If you lay a piece of ice upon it, you will find that a contrary effect will take place; the ice will be melted by the heat it abstracts from the marble. Caroline. Is it not in this case the air of the room, which beinff warmer than the marble, melts the ice ? Mrs. B. The air certainly acts on the surface which is exposed to it, but the table melts that part with which it is in contact. Caroline. But why does caloric tend to an equilibrium ? It can- not be on the same principle as other fluids, since it has no weight ? Mrs. B. Very true, Caroline, that is an excellent objection. You might also, with some propriety, object to the term equilibri- um being applied to a body that is without weight; but I know of no expression that would explain my meaning so well. You must consider it, however, in a figurative rather than a literal sense ; its strict meaning is an equal diffusion. We cannot, indeed, well say by what power it diffuses itself equally, though it is not surprising that it should go from the parts which have the most to those which have the least. The subject is best explained by a theory sugges- 137. How then can their uniformity of expansibility be accounted for? 138. How does caloric tend to diffuse itself? 139. How is this illustrated by a thermometer ? • 140. What is cold? 141. Do we know of any substance in which some caloric may not be found ? 142. Why do some bodies feel cold if we lay our hand upon them ? 143. What objection is there to the term equilibrium, when speak- ing of the equal diffusion of caloric ? 40 FREE CALORIC. ted by Professor Prevost of Geneva, which is now, I believe, gen- erally adopted. According to this theory, caloric is composed of particles per- fectly separate from each other, every one of which moves with a rapid velocity in a certain direction. These directions vary as much as imagination can conceive, the result of which is, that there are rays or lines of these particles moving with immense velocity in every possible direction. Caloric is thus universally diffused, so that when any portion of space happens to be in the neighborhood of another, which contains more caloric, the colder portion re- ceives a quantity of calorific rays from the latter, sufficient to re- store an equilibrium of temperature. This radiation does not only take place in free space, but extends also to bodies of every kind.* Thus you may suppose all bodies whatever, constantly radiating ca- loric ; those that are of the same temperature give out and absorb equal quantities, so that no variation of temperature is produced in them; but when one body contains more free caloric than anoth- er,<'the exchange is always in favour of the colder body, until an equilibrium is effected ; this you find to be the case when the mar- ble table cooled your hand, and again when it melted the ice. Caroline. This reciprocal radiation surprises me extremely ; I thought, from what you first said, that the hotter bodies alone emit- ted rays of caloric which were absorbed by the colder ; for it seems unnatural that a hot body should receive any caloric from a cold one, even though it should return a great quantity. Mrs. B. It may at first appear so, but it is no more extraordina- ry than that a candle should send forth rays of light to the sun|, which, you know, must necessarily happen. .Caroline. Well, Mrs. B., I believe that I must give up the point, But I wish 1 could see these rays of caloric ; 1 should then have greater faith in them. Mrs. B. Will you give no credit to any sense but that of sight? You may feel the rays of caloric which you receive from any body of a temperature higher than your own; the loss of the caloric you part with in return, it is true, is not perceptible; for as you gain more than you lose, instead of suffering a diminution you are really making an acquisition of caloric. It is, therefore, bniy when you are parting with it to a body of a lower temperature, that you are sensible of the sensation of cold,because you then sustain an ab- solute loss of caloric. * This is true when applied to inanimate matter. But if.'a live animal is exposed to a degree of heat above the temperature" of its own body, it has the power of resistance ; and though the heat be 100 degrees above that of the animal, it scarcely affects its temper- ature.—C. 144. What is Professor Prevost's theory of caloric ? 145. What remark respecting live animals is made in the note ? 146. Do all bodies constantly radiate caloric ? 147. If one body contains more free caloric than another, what is the consequence ? 148. Does a hot body receive caloric from a cold one ? 149. How does Mrs. B. answer the objection to the reciprocal radi- ation of caloric between bodies of different temperature ? 150. What occasions the sensation of cold? FREE CALORIC. 41 Emily. And in this case we cannot be sensible of the small quan- tity of heat we receive in exchange from the colder body, because it serves only to diminish the loss. Mrs. B. Very well, indeed, Emily. Professor Pictet, of Gene- va, has made some Very interesting experiments, which,prove not only that caloric radiates from all bodies whatever, but that these rays may be reflected, according to the laws of optics, in the same manner as light. ? 1 shall repeat these experiments before you, hav- ing procured mirrors* fit for the purpose ; and it will afford us an opportunity of using the differential thermometer, which is partic- ularly well adapted for these experiments—I place an iron bullet, Fig. 5. Mr. PicteCs Apparatus for the Reflection of Heal. A A, and B B, Concave Mirrors, fixed on stands. C, Heated Bullet, placed in the fo- cus of the Mirror A. D, Thermometer, with its bulb placed in the fo*us of the Mir- ror B. 12 3 4, rays of Caloric radiating from the Bullet, and fijdKng on the Mirror A. 5 6 7 8, the same rays reflected from the Mirror A to the Mirror B. 910 1112, the same rays reflected by the Mirror B, to the Thermometer. about two inches in diameter, and heated to a degree not sufficient to render it luminous, in the focus of this large metallic concave mirror. The rays of heat which fall on this mirror are reflected, agreeably to the property of concave mirrors, in a parallel direc- tion, so as to fall on a similar mirror, which, you see, is placed op- posite to the first, at the distance of about ten feet; thence the rays converge to the focus of the second mirror, in which I place one of the bulbs of this thermometer. Now, observe in what man- ner it is affected by the caloric which is reflected on it from the heated bullet.—The air is dilated in the bulb which we placed in the focus of the mirror, and the liquor rises considerably in the op- posite leg. * Mirrors made of common tinned iron show this experiment very well. Tbey may be 10 or 12 inches in diameter, and about 2 inches deep. They must be planished with a hammer having a convex face, and afterwards polished with a piece of buckskin, and a little whiting.—C. 151. What do Professor Pictet's experiments on caloric prove ? 152. What is the object of figure 5 ? 153. How would you explain the experiment represented in this fig- ure ? 4* 42 FREE CALORIC. Emily. But would not the same effect take place, if the rays of caloric from the heated bullet fell directly on the thermometer, without the assistance of the mirrors ? Mrs. B. The effect would in that case be so trifling, at the dis- tance at which the bullet and the thermometer are from each oth- er, that it would be almost imperceptible. The mirrors, you know, greatly increase the effect, by collecting a large quantity of rays in a focus \ place your hand in the focus of the mirror, and you will find it much hotter there than when you remove it nearer to the bullet. Emily. That is very true; it appears extremely singular to feel the heat diminish in approaching the body from which it proceeds. Caroline. And the mirror which produces so much heat, by con- verging the rays, is itself quite cold. Mrs.B. The same number of rays that are dispersed over the surface of the mirror are collected by it into the focus ; but if you consider how large a surface the mirror presents to the rays, and consequently, how much they are diffused in comparison to what they are at the focus, which is a little more than a point, I think you can no longer wonder that the focus should be so much hotter than the mirror. The principal use of the mirror in this experiment is, to prove that the calorific emanation is reflected in the same manner as light. Caroline. And the result, I think, is very conclusive. Mrs. B. The experiment may be repeated with a wax taper in- stead of the bullet, with a view of separating the light from the caloric. For this purpose a transparent plate of glass must be in- terposed between the mirrors; for light, you know, passes with great facility through glass, whilst the transmission of caloric is almost wholly impeded by it. We shall find, however, in this ex- periment, that some few of the calorific rays pass through the glass together with the light, as the thermometer rises a little; but, as soon as the glass is removed, and free passage left to the caloric, it will rise considerably higher. Emily. This experiment, as well as that of Dr. Herschell's, proves that light and heat may be separated ; for in the latter ex- periment the separation was not perfect, anv more than that of Mr. Pictet. Caroline. I should like to repeat this experiment, with the dif- ference of substituting a cold body instead of a hot one, to see whether cold would not be reflected as well as heat. Mrs. B. That experiment was proposed to Mr. Pictet by an in- credulous philosopher like yourself, and he immediately tried it by substituting a piece of ice in the place of a healed bullet. Caroline. Well, Mrs. B., and what was the result? 154. Why do mirrors increase the effect in this experiment? 155. Why does a metallic mirror feel cold when placed before the fire ? 156. What is the use of the mirror in the experiment ? 157. What substance almost wholly impedes the transmission of caloric ? 158. What does this prove ? 159. What philosopher supposed that cold might be reflected ? FREE CALORIC. 43 Mrs. B. That we shall see ; 1 have procured some ice for the purpose. Emily. The thermometer falls considerably! Caroline. And does not that prove that cold is not merely a nega- tive quality, implying simply an inferior degree of heat ? The cold must bepositive, since it is capable of reflection. Mrs. B. So it first appeared to Mr. Pictet; but upon a little consideration he found that it afforded only an additional proof of the reflection of heat; this I shall endeavour to explain to you. According to Mr. Prevost's theory, we suppose that all bodies whatever radiate caloric ; the thermometer used in these exper- iments, therefore, emit calorific rays in the same manner as any other substance. When its temperature is in equilibrium with that of the surrounding bodies, it receives as much caloric as it parts with, and no change of temperature is produced. But when we introduce a body of a lower temperature, such as a piece of ice, which parts with less caloric than it receives, the consequence is, that its temperature is raised whilst that of the surrounding bodies is proportionally lowered. Emily. If, for instance, I was to bring a large piece of ice into this room, the ice would in time be melted, by absorbing caloric from the general radiation which is going on throughout the room; and as it would contribute very little caloric in return for what is absorbed, the room would necessarily be cooled by it. Mrs. B. Just so ; and as in consequence of the mirrors, a more considerable exchange of rays takes place between the ice and the thermometer, than between these and any of the surrounding bod- ies, the temperature of the thermometer must be more lowered than that of any other adjacent object. Caroline. I confess I do not perfectly understand your explan- ation. Mrs. B. This experiment is exactly similar to that made with the heated bullet f Jor, if we consider the thermometer as the hot body (which it certainly is in comparison to the ice,) you may then easily understand that it is by the loss of the calorific rays which the thermometer sends to the" ice, and not by any. cold rays receiv- ed from it, that the fall of the mercury is occasioned"; for the ice, far from emitting rays of cold, sends forth rays of caloric, which di- minish the loss sustained by the thermometer. Let us say, for instance, that the radiation of the thermometer towards the ice is equal to 10, and that of the ice towards the thermometer to 20 ; the exchange in favor of the ice is as 20 is to 10, or the thermometer absolutely loses 10, whilst the ice gains 10. Caroline. But if the ice actually sends rays of caloric to the thermometer, must not the latter fall still lower when the ice is re- moved ? Mrs. B. No; for the space which the ice occupies, admits rays 160. What did his experiment prove? 161. What is probable respecting the use of the thermometer in this experiment, according to Mr. Prevost's theory ? 1'12. What similarity is there between this experiment and that of tijc iieated bullet ? 163. Since the ice sends rays of caloric to the thermometer, will not the thermometer fall if the ice is removed? 44 FREE CALORIC. from all the surrounding bodies to pass through it; and those being of the same temperature as the thermometer, will not affect it,, be- cause as much heat now returns to the thermometer as radiates from it. , , • 1 *!_• Caroline. I must confess that you have explained this in so satis- factory a manner, that I cannot help being convinced now that cold has no real claim to the rank of a positive being. Mrs. B. Before I conclude the subject of radiation, I must ob- serve to you, that different bodies (or rather surfaces,) possess the power of radiating caloric in very different degrees7> Some curious experiments have been made by Mr. Leslie on this subject, and it was for this purpose that he invented the differ- ential thermometer ; with its assistance he ascertained tha^fblack surfaces radiate most,%lass next, and polished surfaces the least of all. / " , , Emily. Supposing these surfaces, of course, to be all of the same temperature. Mrs. B. Undoubtedly. I will now show you the very ingen- ious apparatus, by means of which he made these experiments. This cubical tin vessel, or cannister, has each of its sides externally covered with different materials ; the one is simply blackened ; the next is covered with white paper; the third with a pane of glass, and in the fourth the polished tin surface remains uncovered. We shall fill this vessel with hot water, so that there can be no doubt but that all its sides will be of the same temperature. Now let us place it in the focus of one of the mirrors, making each of its sides front it in succession. We shall begin with the black sur- Caroline. It makes the thermometer which is in the focus of the other mirror rise considerably. Let us turn the paper surface towards the mirror. The thermometer falls a little, therefore of course, this side cannot emit or radiate so much caloric as the black- ened side. Emily. This is very surprising ; for the sides are exactly of the same size, and must be of the same temperature. But let us try the glass surface. Mrs. B. The thermometer continues falling, and with the plain surface it falls still lower ; these two surfaces therefore radiate less and less. Caroline. I think I have found out the reason of this. Mrs. B. I should be very happy to hear it, for it has not yet, (to my knowledge) been accounted for. * The radiating power of different surfaces may be shown thus. (Take a common half pint tin cup, scour one side bright, and paint or smoke the other blackn Place this in the focus of the mirror, and the thermometer will rfse or fall as its sides are changed.—C. 164. Why will it not? "•^65. Do all surfaces radiate caloric in equal degrees ? 166. What surfaces radiate most caloric, and what ones least ? 167. What illustration is given of the different radiations of differ- ent surfaces ? 168. How is it stated in the note, that the radiating power of different surfaces may be shown ? FREE CALORIC. 45 Caroline. The water within the vessel gradually cools, and the thermometer in consequence gradually falls. Mrs. B. It is true that the wat^^jojs, but certainly in much less proportion than the thermometer^! Beds, as you will perceive if you now change the tin surface fod^Pplack one. Caroline. I was mistaken, cet**p3& ^or *'ie thermometer rises again now that the black surface.frorrrFthe mirror. Mrs. B. And yet the water in the vessel is still cooling, Caro- line. Emily. I am surprised that the tin surface should radiate the least caloric, for a metallic vessel filled with hot water, a silver tea- pot for instance, feels much hotter to the hand than one of black earthen ware. Mrs. B^Th&t is owing to the different power which various bo- dies possessTor conducting caloric,!a property which we shall pres- ently examine. Thus, although/a metallic vessel feels warm to the hand, a vessel of this kind is known to preserve the heat of the liquid within, better than one of any other materials^ it is for this reason that silver tea-pots make better tea than those of earthen- ware. Emily. According to these experiments, light colored dresses, in cold weather, should keep us warmer than black clothes, since the latter radiate so much more than the formers Mrs. B. And that is actually the case. Emily. This property, of different surfaces to radiate in different degrees, appears to me to be at variance with the equilibrium of caloric; since it would imply that those bodies which radiate most must ultimately become coldest. Suppose that we were to vary this experiment, by using two me- tallic vessels full of boiling water, the one blackened, the other not; would not the black one cool the first? Caroline. True: but when they were both brought down to the temperature of the room, the interchange of caloric between the canisters and the other bodies of the room being then equal, their temperature would be the same. Emily. I do not see why that should be the case; for if different surfaces of the same temperature radiate in different degrees when heated, why should they not continue to do so when cooled down to the temperature of the room ? Mrs. B. You have started a difficulty, Emily, which certainly requires explanation. It is found by experiment, that the power of absorption corresponds with, and is proportional to, that of radia- tion ; so that under equal temperatures, bodies compensate for the 169. Why will a silver tea-pot or any metallic vessel filled with hot Water, feel much hotter to the hand than one of black earthen-ware ? 170. Why will a silver tea-pot make better tea than an earthen one ? 171. Why is a light colored dress warmer than a black one in win- ter? 172. And why a light colored one colder than a black in the sum- mer? 173. What difficulty is mentioned respecting the above theory of the radiation of calorfc ? 46 FREE CALORIC. greater loss they sustain in consequence of their greater radiation by their greater absorption ; so that if you were to make your exr periment in an atmosphere heated like toe canisters, to the tempe- rature of boiling water, though it-is true that the canisters would radiate in different degrees, no change of temperature would be produced in them, because they'would each absorb caloric in pro- portion to their respective radiation. Emily. But would not the canisters of boiling water also absorb caloric in different degrees in a room of the common temperature ? Mrs. B. Undoubtedly they would. But the various bodies in the room would not, at a lower temperature, furnish either of the canisters with a sufficiency of caloric to compensate for the loss they undergo; for, suppose a black canister to absorb 400 rays of caloric, whilst the metallic one absorbed only 200; yet if the former radiates 800, whilst the latter radiates only 400, the black canister will be the first cooled down to the temperature of the room. But from the moment the equilibrium of temperature has taken place, the black canister, both receiving and giving out 400 rays, and the metallic one 200, no change of temperature will take place. • Emily. 1 now understand it extremely well. But what becomes of the surplus of calorific rays, which good radiators emit, and bad radiators receive ? they must wander about in search of a resting- place ! Mrs. B. They really do so ; for they are rejected and sent back, or in other words, reflected by the bodies which are bad radiators of caloric; and they are thus transmitted to other bodies which happen to lie in their way, by which they are either absorbed or again reflected, according as the property of reflection, or that of absorption predominates in these bodies. Caroline. I do not well understand the difference between radia- ting and reflecting caloric, for the caloric that is reflected from a body, proceeds from it in straight lines, and may surely be said to radiate from it ? Mrs. B. It is true that there at first appears to be a ri eat analo- gy between radiation and reflection, as they equally com ey the idea of the transmission of caloric. But if you consider a little, you will perceive that when a body radiates caloric, the heat which it emits not only proceeds from,but has its origin in the body itself.; Whilst when a body reflects calo- ric, it parts with none of its own caloric, but only reflects that which it receives from other bodies. Emily. Of this difference we have very striking examples before us,, in the tin vessel of water, and the concave mirrors; the first radiates its own heat, the latter reflect the heat which they receive from other bodies. Caroline. Now that I understand the difference, it no longer 174. If different surfaces of the same temperature radiate in differ- ent degrees when heated, why do they not continue to do so when coofed to the temperature of the room ? 175. What becomes of the surplus of caloric, which good radiators emit and bad ones refuse to receive ? 176. What is the difference between the radiation and reflection of caloric? 177. How would you illustrate this difference by example ? FREE CALORIC. 47 surprises me that bodies which radiate or part with their own calor- ic freely, should not have the power of transmitting with equal fa- cility that which they receive from other bodies. Emily. Yet no body can be said to possess caloric of its own, if all caloric is originally derived from the sun. Mrs. B. When I speak of a body radiating its own caloric, I mean that which it has absorbed and incorporated either immedi- ately from the sun's rays, or through the medium of any other sub- stance: Caroline. It seems natural enough that the power of absorption should be in opposition to that of reflection, for the more caloric a body receives, the less it will reject. Emily. And equally so that the power of radiation should corres- pond with that of absorption. It is, in fact, cause and effect ; for a body cannot radiate heat without having previously absorbed it; just as a spring that is well fed flows abundantly. Mrs. B. Fluids are in general very bad radiators of caloric; and air neither radiates nor absorbs caloric in any sensible degree. We have not yet concluded our observations on free caloric.— But I shall defer, till our next meeting, what I have further to say on this subject. I believe it will afford us ample conversation for another interview. o CONVERSATION III. CONTINUATION OF THE SUBJECT. Mrs. B. In our last conversation, we began to examine the ten- dency of caloric to restore an equilibrium of temperature. This property when once well understood affords the explanation of a great variety of facts which appeared formerly unaccountable.— You must observe, in the first place, that the effect of this tendency is gradually to bring all bodies that are in contact, to the same temperature. Thus the fire which burns in the grate, communi- cates its heat from one object to another, till every part of the room has an equal portion of it. Emily. And yet this book is not so cold as the table on which it lies, though both are at an equal distance from the fire, and actual- ly in contact with each other, so that according to your theory, they should be exactly at the same temperature. Caroline. And the hearth which is much nearer the fire than the carpet, is certainly the colder of the two. Mrs. B. If you ascertain the temperature of these several bodies 178. When we speak of a body radiating its own caloric, what do we mean ? 179. What are very bad radiators of caloric ? 180. Has caloric any effect upon the air? 181. What is the tendency of caloric? , 182. Do all substances at the same temperature feel equally warm or cold ? 48 FREE CALORIC. by a thermometer (which is a much more accurate test than your feeling,) you will find that it is exactly the same. Caroline. But if they are of the same temperature, why should the one feel colder than the other? Mrs. B. The'hearth and the table feel colder than the carpet or the book, because the latter/are not such good conductors of heat as the former. Caloric finds a more easy passage through marble and wood, than through leather and worsted ; the two former will therefore absorb heat more rapidly from your hand, and conse- quently give it a stronger sensation of cold than the two latter, al- though they are all really of the same temperature. Caroline. So, then, the sensation I feel on touching a cold body, is in proportion to the rapidity with which my hand yields its heat to that body. .- \ Mrs.B. Precisely; and; if you lay your hand/successively on every object in the room, you will discover which are good, and which are bad conductors of heat, by the different degrees of cold which you feel. But in order to ascertain this point, it is necessary that the several substances should be of the same temperature, which will not be the case with those that are near the fire, or those that are exposed to a current of cold air from a window or door. Emily. But what is the reason that some bodies are better con- ductors of heat than others ? Mrs. B. This is a point not well ascertained. It has been con- jectured that a certain union or adherence takes place between the caloric and the particles of the body through jwhich it passes; If this adherence be strong, the body detains the heat, and parts with it slowly and reluctantly ; if slight, it propagates it freely and rap- idly. The conducting power of a body is therefore, inversely, as its tendency to unite with caloric. Emily. That is to say, that the best conductors are those that have the least affinity for caloric. Mrs. B. Yes; but the term affinity is objectionable in this case, because, as that word is used to express a chemical attraction, (which can be destroyed only by decomposition,) it cannot be ap- plicable to the slight and transient union that takes place between free caloric and the bodies through which it passes; an union which is so weak, that it constantly yields to the tendency which caloric has to an equilibrium. Now you clearly understand^Jhat the passage of caloric, through bodies that are good conductors, is much more rapid than through those that are bad conductors, and that the former both give and receive it more quickly, and there- 183. Why do they not? 184. What are instances of substances of the same temperature pro- ducing different sensations of heat and cold? 185. To what is the sensation proportional on touching one's hand to a cold body ? 186. How can we ascertain which bodies are good conductors of heat and which are not ? 187. Why are some bodies better conductors of heatthan others? 188. Will caloric pass quickest through good or bad conductors? 189. Which gives it and receives it most readily? FREE CALORIC. • 49 fore, in a given time more abundantly, than bad conductors, which makes them feel either hotter or colder, though they may be in fact, both of the same temperature. Caroline. Yes, I understand it now ; the table and the book lying upon it, being really of the same temperature, would each receive in the same space of time, the same quantity of heat from my hand, were their conducting powers equal; but as the table is the best conductor-.of the two it will absorb the heat from my hand more rapidly, and consequently produce a stronger sensation of cold than the book. Mrs. B. Very well, my dear ; and observe, likewise, that if you were to heat the table and the book an equal number of degrees above the temperature of your body, the table, which before felt the colder, would now feel the hotter of the two; for, as in the first case it took the heat most rapidly from your hand, so now it will im- part heat most rapidly to it. Thus the marble table, which seems to us colder than the mahogany one, will prove the hotter of the two to the ice ; for if it takes heat more rapidly from our hands, which are warmer, it will give out heat more rapidly to the ice, which is colder. Do you understand the reason of these apparent- ly opposite effects ? Emily. Perfectly. A body which is a good conductor of caloric affords it a free passage; so that it penetrates through that body more rapidly than through one which is a bad conductor ; and conse- quently, if it is colder than your hand, you lose more caloric, and if it is hotter you gain more than a bad conductor of the same tem- perature. 9 Mrs. B But you must observe that this is the case only when the conductors are either hotter or colder than your hand ; for, if you/lieat different conductors to the temperature of your bodyJ)they wilf all feel equally warm, since the exchange of caloric between bodies of the same temperature is equal. Now, can you tell me why flannel clothing, which is a very bad conductor of heat, pre- vents our feeling cold ? Caroline. It prevents the cold from penetrating. Mrs. B. But you forget that cold is only a negative quality. Caroline. True, it only prevents the heat of our bodies from es- caping so rapidly as it would otherwise do. Mrs. B. Now you have explained it right; the flannel rather keeps in the heat, than keeps out the cold. Were the atmosphere of a higher temperature than our bodies, it would be equally effica- cious in keeping their temperature at the same degree, as it would prevent the free access of the external heat, by the difficulty with which it conducts it. Emily. This, I think, is very clear. Heat, whether external or internal, cannot easily penetrate flannel; therefore, in cold weather 190. If we lay our hand upon a table and a book both of the same temperature, why does the table produce astroager sensation of cold than the book ? 191. Under what circumstances will good and bad conductors feel equally warm to.our flesh ? 192. Why does flannel clothing prevent our feeling cold ? 193. Under what circumstances, or when would a flannel dress pro- duce a contrary effect in our feelings ? 50 FREE CALORIC. it keeps us warm, and if the weather were hotter than our bodies, it would keep us cool. Mrs. B. The most dense bodies aie, generally speaking, the best conductors of heat; probabljfjbecause the denser the body tho>great- er are the number of points or particles that come in contact with caloric/N At the common temperature of the atmosphere, a piece of metal will feel much colder than a piece of wood, and the latter than a piece of woollen cloth ; this again will feel colder than flan- nel ; and down, which is one of the lightest, is at the same time one of the warmest bodies.* Caroline. This is, I suppose, the reason that the plumage of birds preserves them so effectually from the influence of cold in winter ? Mrs. B. Yes ; but though feathers in general are an excellent preservative against cold, down is a kind of plumage, peculiar to aquatic birds, and covers their chest, which is the part most ex- posed to the water ; for though the surface of the water is not of a lower temperature than the atmosphere, yet it is a better conduc- tor of heat, it feels much colder, consequently the chest of the bi.-d requires a warmer covering than any other part of its body. Be- sides, the breasts of aquatic birds are exposed to cold, not only from the temperature of the water, but also from the velocity with which the breast of the bird strikes against it; and likewise from the rap- id evaporation occasioned in that part by the air against which it strikes, after it has been moistened by dipping from time to time into the water. If you hold a finger of one hand motionless in a glass of water, and at the same time move a finger of the other hand swiftly through water of the same temperature, a different sensation will be soon perceived in the different fingers.f Most animal substances, especially those which Providence has assigned as a covering for animals, such as fur, wool, hair, skin, &c. are bad conductors of heat, and are, on that account, such excellent preservatives against the inclemency of winter, that our warmest apparel is made of these materials. * One reason why fur, down, &c. conduct heat so badly, is, that they contain a large quantity of air, which is a worse conductor than the materials themselves.—C. f The reason seems to be, that the finger, when it is still, warms the water in contact with it ; while the one that is stirring is con- stantly exposed to fresh applications of cold.—C. 194. What bodies are generally considered the best conductors of caloric? ,'■ • 195. Why are dense bodies the best conductors' 196. If the surface of water is not of a lower temperature than the atmosphere, why does it feel colder ? 197. Why are fur, hair, wool, and down, good preservatives against the inclemency of winter? 198. Why are they bad conductors of caloric ? 199. If you hold a finger of one hand motionless in a glass of water, and at the same time move afinger of the other hand swiftly through wa- ter of the same temperature, why is a different sensation produced ? FREE CALORIC. 51 Emily. Wood is, I dare say, not so good a conductor as metal, and it is for that reason, no doubt, that silver tea pots have always wooden handles. Mrs. B. Yes; and it is the facility with which metals conduct caloric that made you suppose that a silver pot radiated more ca- loric than an earthen one. The silver pot is in fact hotter to the hand when in contact with it; but it is because its conducting pow- er more than counterbalances its deficiency in regard to radiation. We have observed that the most dense bodies are in general, the best conductors ; and metals you know, are of that class. Porous bodies, such as the earths, and wood, are worse conductors, chief- ly, I believe, on account of their pores being filled with air ; for air is a remarkably bad conductor. Caroline. It is a very fortunate circumstance that air should be a bad conductor, as it tends to preserve the heat of the body when exposed to cold weather. Mrs. B. It is one of the many benevolent dispensations of Prov- idence, in order to soften the inclemency of the season, and to ren- der almost all climates habitable to man. In fluids of different densities, the power of conducting heat va- ries no less remarkably ; if you dip your band into this vessel full of mercury, you will scarcely conceive that its temperature is not lower than that of the atmosphere. Caroline. Indeed I know not how to believe it, it feels so extreme- ly cold. But we may easily ascertain its true temperature by the thermometer. It is really not colder than the air : the apparent difference then is produced merely by the difference of the conduct- ing power in mercury and in air. Mrs. B. Yes ; hence you may judge how little the sense of feel- ing is to be relied on as a test of the temperatureofbodies, and how necessary a thermometer is for that purpose. It has indeed been doubted whether fluids have the power of con- ducting caloric in the same manner as solid bodies. Count Rum- ford a very few years since, attempted to prove by a variety of ex- periments, that fluids when at rest, were not at all endowed with this property. Caroline. How is that possible, since they are capable of impart- ing cold or heat to us ; for if they did not conduct heat, they would neither take it from, nor give it to us ? Mrs. B. Count Rumford did not mean to say that fluids would not communicate their heat to solid bodies ; but only that heat does Dot pervade fluids, that is to say is not transmitted from one particle of a fluid to another, in the same manner as in solid bodies. Emily. But when you heat a vessel of water over the fire, if the particles of water do not communicate heat to each other, how does the water become hot throughout ? 200. Why does a silver tea-pot feel hotter to the hand than an earthen one ? 201. Why are wood and earths bad conductors of it? 202. Have fluids of different densities the same power of conducting caloric ? 203. Ought the sense of feeling to be relied on as a test of the tem- perature of bodies ? Why ? 52 FREE CALORIC. Mrs. B. By constant agitation. Water, as you have seen, ex- pands by heat, in the same manner as solid bodies ; the heated par- ticles of water, therefore, at the bottom of the vessel, being spe- cifically lighter than the rest of the liquid, and consequently ascend to the surface, where, parting with some of their heat to the colder atmosphere, they are condensed and give way to a fresh succession of heated particles ascending from the bottom, which, having thrown off their heat at the surface, are in their turn displaced.— Thus every particle is successively heated at the bottom, and cool- ed at the surface of the liquid ; but as the fire communicates heat more rapidly than the atmosphere cools the succession of surfaces, the whole of the liquid in time becomes heated. Caroline. This accounts most ingeniously for the propagation of heat upwards. But supposing you were to heat the upper surface of a liquid, the particles being specifically lighter than those below, could not descend ; how therefore would the heat be communica- ted downwards? Mrs. B. If there were no agitation to force the heated surface downwards, Count Rumford assures us that the heat would not de- scend. In proof of this he succeeded in making the upper surface of a vessel of water boil and evaporate, while a cake of ice remain- ed frozen at the bottom.* Caroline. That is very extraordinary indeed ? Mrs. B. It appears so, because we are not accustomed to heat liquids by their upper surface ; but you will understand this theory better if I show you the internal motion that takes place in liquids when they experience a change of temperature. The motion of the liquid itself is indeed invisible from the extreme minuteness of its particles; but if you mix with it any colored dust, or powder, of nearly the same specific gravity as the liquid, you may judge of the internal motion of the latter by that of the colored dust it con- tains.—Do you seethe small pieces of amber moving about in the liquid contained in this phial? Caroline. Yes, perfectly. Mrs. B. We shall now' immerse the phial in a glass of hot water, and the motion of the liquid will be shown by that which it commu- nicates to the amber. Emily. I see two currents, the one rising along the sides of the phial, the other descending in the centre ; but I do not understand the reason of this. * Dr. Thomson says—" All fluids, however, are capable of con- ducting caloric ; for when the source of heat is applied to their surface, the caloric gradually makes its way downwards, and the temperature of every stratum gradually diminishes from the surface to the bottom of the liquid."—C. 204. How are fluids heated, when placed over the fire ? 205. By what experiment did Count Rumford attempt to prova that fluids do not conduct caloric downward ? 206. What was Dr. Thomson's opinion on this subject ? 207. What experiment shows the internal motion that takes place in liquids when they experience a change of temperature ? FREE CALORIC. 53 Mrs. B. The hot water communicates its caloric, through the medium of the phial, to the particles ef the fluid nearest to the glass: these dilate and ascend laterally to the surface, where, in parting with their heat, they are condensed, and in descending, form the central current. Caroline. This is indeed avery clear and satisfactory experiment; but how much slower the currents now move than they did at first! Mrs. B. It is because the circulation of particles has nearly pro- duced an equilibrium of temperatura between the liquid in the glass and that in the phial. Caroline. But these communicate laterally, and I thought that heat in liquids could be propagated only upwards. Mrs. B. You do not take notice that the heat is imparted from one liquid to (he other, through the medium of the phial itself, the external surface of which receives the heat from the water in the glass, whilst its internal surface transmits it to the liquid it contains. Now take the phial out of the hot water, and observe the effect of its cooling. Emily. The currents are reversed ; the external current now descends, and the internal one rises-—1 guess the reason of this change; the phial being in contact with cold air instead of hot wa- ter, the external particles are cooled, instead of being heated;— they therefore descend and force up the central particles, which, being warmer, are consequently lighter. Mrs. B. It is just so ; Count Rumford hence infers, that no alter- ation of temperature can take place in a fluid, without an internal motion of its particles; and as this motion is produced only by the comparative levity of the heated particles, heat cannot be propaga- ted dowowards. But though 1 believe that Count Rumford's theory as to heat being incapable of pervading fluids is not strictly correct, yet there is, no doubt, much truth in his observation, that the communication is materially promoted by a motion of the parts ; and this accounts for the cold that is found to prevail at the bottom of the lakes in Swit- zerland, which are fed by rivers issuing from the snowy Alps, i The water of these rivers being colder, and therefore more densethan that of the lakes, subsides to the bottom, where it cannot be affect- ed by the warmer temperature of the surface) the motion of the waves may communicate this temperature to sbme little depth, but it can descend no further than the agitation extends. Emily. But when the atmosphere is colder than the lake, the colder surface of the water will descend, for the very reason that the warmer will not. Mrs. B. Certainly ; and it is on this account that neither a lake nor any body of water whatever, can be frozen until every particle 208. Why does one of the currents rise along the side of the phial and the other descend in the centre, when the phial is immersed in hot water? 209. If the phial be taken out of the hot water, what will be the ef- fect? 210. What is the reason of this change? . 211. Why does cold prevail at the bottom of the lakes in Switzer- land, which are fed by the rivers issuing from the snowy Alps ? 212. When is a lake or any collection of water frozen ? 54 FREE CAI.ORIC. of the water has risen to the surface to give off its caloric to the colder atmosphere; therefore the deeper a body of water is, the longer will be the time it requires to be frozen. Emily. But if the temperature of the whole body of water be brought down to the freezing point, why is only the surface frozen? Mrs. B./ The temperature of the whole body is lowered, but not to the freezing point. The diminution of heat, as you know, pro- duces a contraction in/ the bulk of fluids, as well as of solids. This effect, however, does not take place in water below the tempera- ture of 40 degrees, which is 8 degrees above the freezing point. At that temperature, therefore, the internal motion, occasioned by the increased specific gravity of the condensed particles ceases; for when the water at the surface no longer condenses, it will no longer descend and leave a fresh surface exposed to the atmosphere ; this surface alone, therefore, will be further exposed to its severity, and will soon be brought down to the freezing point, when it becomes ice, which being a bad conductor of heat, preserves the water be- neath a long time, from being affected by the external cold. Caroline. And the sea does not freeze, I suppose, because its depth is so great, that a frost never lasts long enough to briogdown the lemperature of such a great body of water to 40 degrees ? Mrs. B. That is one reason why the sea, a^ a large mass of water, does not freeze. But, independently of this, salt water does not freeze till it is cooled much below 32 degrees, and with respect to the law of condensation, salt water is an exception, as it condeoses even many degrees below the freezing point. When tbe caloric of fresh water, therefore, is imprisoned by the ice on its surface, the ocean still continues throwing off heat into the atmosphere, which is a most signal dispensation of Providence to moderate the intensi- ty of the cold in winter. Caroline. This theory of the non-conducting power of liquids, does not, I suppose, hold good with respect to air, otherwise the at- mosphere would not be heated by the rays of the sun passing through it? Mrs. B. Nor is it heated in that way. The pure atmosphere is a perfectly transparent medium, which neither radiates, absorbs, nor conducts caloric, but transmits the rays of the sun to us without in any way diminishing their intensity. The air is therefore not more heated, by the sun's rays passing through it, than diamond, glass, water, or any other transparent medium.* Caroline. That is very extraordinary ! Are glass windows not heated then by the sun shining on them? * To show still better that transparent media are not heated by the rays of the sun, throw the focus of a burning lens into a vessel of clear water. No effect on the temperature will be pioduced; but if an opaque body, as a piece of cork, be introduced under the focus, the water at this point instantly begins to boil.—C. 213. Why does water first freeze at the surface? 214. Why does not the surface of the sea freeze? 215. What moderates the intensity of cold in winter? 216. Is the atmosphere heated by the rays of the sun passing through 217. What experiment mentioned in the note, proves that transparent media are not heated by ike rays of the f.m? FREE CALORIC. 55 Mrs.B. No; not if the glass be perfectly transparent. A most convincing proof that glass transmits the rays of the sun without being heated by them, is afforded by the burning lens, which by con- verging the rays to a focus will set combustible bodies on fire, without its own temperature being raised. Emily. Yet, Mrs. B., if 1 hold apiece of glass near the fire, it is almost immediately warmed by it; the glass therefore must retain some of ihe caloric radiated by the fire. Is it that the solar rays alone pass freely through the glass without paying tribute? It seems unaccountable that the radiation of a common fire should have power to do what the sun's rays cannot accomplish. Mrs.B. It is not because the rays from the fire have more power, but rather because they have less, that they heat glass and other transparent bodies. It is true, however, that as you approach the source of beat/the rays being nearer each other, the heat is more condensed, and-can produce effects of which the solar rays, from the great distance of their source, are incapable!^-Thus we should find it impossible to roast a joint of meat by the sun's rays, though it is so easily done by culinary heat. Yet caloric emanated from burning bodies, which is commonly called citlinary heat, has neither the intensity nor the velocity of solar rays. All caloric, we have said, is supposed to proceed originally from the sun ; but after hav- ing been incorporated with terrestrial bodies, and again given out by them, though its nature is not essentially altered, it retains nei- ther the intensity nor the velocity with which it first emanated from that luminary; it has therefore not the power of passing through transparent mediums, such as glass and water, without being par- dally retained by those bodies. Emily. I recollect that in the experiment on the reflection of heat}v the glass screen which*-you interposed between the burning taper and mirror, arrested the rays of caloric, and suffered only those of light to pass through it. Caroline. Glass windows, then, though they cannot be heated by the sun shining on them, may be heated internally by a fire in the room ? But, Mrs. B., since the atmosphere is not warmed by the solar rays passing through it, how does it obtain heat? for all the fires that are burning on the surface of the earth would contribute very little towards warming it- Emily. The radiation of heat is not confined to burning bodies; for all bodies, you know, have that property : therefore, not only every thing upon ihe surface of the earth, but the earth itself, must radiate heat; and this terrestrial caloric, not having, I suppose suf- ficient power to traverse the atmosphere, communicates heat to it. Mrs. B. Your inference is extremely well drawn, Emily ; but the foundation onTwhich it rests is not sound : for the fact is, that ter- restrial or culinary heat, though it cannot pass through the denser transparent mediums, such as glass or water, without loss, travers- es the atmosphere completely ; so that all the heat which the earth 218. What is culinary heat ? 219. Why does fire heat glass, when the sun does not? , 220. To what experiment is allusion here made illustrative of this subject ? 56 FREE CALORIC. radiates, unless it meet with clouds* or any foreign body to inter- cept its passage, passes into the distant regions of the universe. Caroline. What a pity that so much heat should be wasted ! Mrs. B. Before you are tempted to object to any law of nature, reflect whether it may not prove to be one of the numberless dispen- sations of Providence for our good. If all the heat which the earth has received from the sun since the creation,had been accumulated in it, its temperature at this time, would no doubt have been more elevated than any human being could have borne. Caroline. 1 spoke, indeed, very inconsiderately. But, Mrs. B., though the earth, at such a high temperature, might have scorched our feet, we should always have had a cool refreshing air to breathe, since the radiation of the earth does not heat the atmosphere. Emily. The cool air would have afforded but very insufficient refreshment, whilst our bodies were exposed to the burning radia- tion of the earth. Mrs. B. Nor should we have breathed a cool air; for though itjs true that heat is not communicated to the atmosphere by radiation, yet the air is warmed by contact with heated bodies, in the same manner as solids or liquids. The stratum of air which is immedi- ately in contact with the earth is heated by it; it becomes specific- ally lighter, and rises, making way for another stratum of air, which is in its turn heated and carried upwards ; and thus each successive stratum of air is warmed by coming in contact with the earth. Yon may perceive this effect in a sultry day, if you attentively observe the strata of air near the surface of the earth ; they appear in con- stant agitation ; for though it is true the air itself is invisible, yet the sun shining on the vapors floating in it, render them visible, like the amber dust in the water. The temperature of the surface of the earth is therefore the source from whence the atmosphere de- rives its heat, though it is communicated neither by radiation, nor transmitted from one particle of it to another by the conducting power; but every particle of air must come in contact with the earth, in order to receive heat from it. Emily. Wind, then, by agitating the air, should contribute to cool the earth and warm the atmosphere, by bringing a more rapid succession of fresh strata of air in contact with the earth? and yet in general wind feels cooler than still air. Mrs. B. Becausefthe agitation of the air carries off heat from the surface of our bodies more rapidly than still air, by occasioning a greater number of points of contact in a given time. * Every one has observed how oppressive the heat is on a foggy, or cloudy day in the summer. The moisture of the fog absorbs the heat which the earth radiates, and throws it back upon the earth again, and upon us.—C. 221. What becomes of the heat which the earth radiates ? 222. What would be the effect if all the heat which the earth has r ceived from the sun, since the creation, had been accumulated in it? 223. Why in summer, is it particularly hot in cloudv, or fofff weather ? J SJ 224. How is the air heated, if not as been said, by the rays of the si passing through it ? 225. Why is the wind cooling to our bodies? EREE CALORIC. 57 Emily. Since it is from the earth, and not the sun, that the at- mosphere receives its heat, I no longer wonder that elevated regions should be colder than plains and valleys. It was always a subject of astonishment to me, that in ascending a mountain and approach- ing the sun, the air became colder instead of being more heated. Mrs.B. At the distance of about a hundred millions of miles, which we are from the sun, the approach of a few thousand feet makes no sensible difference, whilst it produces a very considerable effect with regard to the warming of the atmosphere at the surface of the earth. Caroline. Yet as the warm air arises from the earth, and the cold air descends to it, I should have supposed that heat would have ac- cumulated in the upper regions of the atmosphere, and that we should have felt the air warmer as we ascended. Mrs.B. The atmosphere you know, diminishes in density, and consequently in weight, as it is more distant from the earth ; the warm air, therefore, rises only till it meets with a stratum of air of its own den-ity ; and it will not ascend into the upper regions of the atmosphere until all the parts beneath have been previously heated. The length of summer, even in warm climates, does not heat the air sufficiently to melt the snow which has accumulated during the win- ter on very high mountains, although they are almost constantly exposed to the heat of the sun's rays, being too much elevated to be often enveloped in clouds. Emily. These explanations are very sat- isfactory ; but allow me to ask you one more question respecting the increased levity of heated liquids. You said that when water was heated over the fire, the particles at the bottom of the vessel ascended as soon a3 heated, in consequence of their specific levity; why does not the same effect con- tinue when the water boils and is converted into steam ? and why does the steam arise from the surface, instead of the bottom of the liquid ? Mrs. B. The steam or vapour does as- cend from the bottom, though it seems to arise from the surface of the liquid. We shall boil some water in this Florence flask, (Eig. 6,) in order that you may be well ac- quainted with the process of ebullition ; you will then see through the glass, that the va- pour rises in bubbles from the bottom. We shall make it boil by means of a lamp, which — is more convenient for this purpose than Boiling water in a flask tfa chimney fire. over a Patent Lamp. J 226. Why is it colder on.high hills and mountains than it is in val- lies, since the former are nearer the sun than the latter, and since al- so it is the nature of the air to rise as it becomes warmed ? 227. What illustration is mentioned to shew that tho air is not heated by the sun's rays passing through it ? 228. Does water boil from the top, or from the bottom of a vessel ? 58 FREE CALORIC. Emily. I see some small bubbles ascend, and a great many appear all over the inside of the flask ; does the water begin to boil already ? Mrs.B. No; what you now see'are bubbles of air, which were either dissolved in the/water, or attached to the inner surface o( the flask, and which,me'mg rarefied by the heat, ascend in the water. Emily. But the heat which rarefies the air inclosed in the water must rarefy the water at the same time ; thefore, if it could remain stationary in the water when both were cold, I do not understand why it should not when both are equally heated. Mrs. B. Air being much less dense than water, is more easily rarefied"; the-former, therefore, expands to a great extent, whilst the latter continues to occupy nearly the same space ; for the wa- ter dilates comparatively but very little without changing its state and becoming vapour. Now that the water in the flask begins to boil, observe what large bubbles rise from the bottom of it. Emily. I see them perfectly ; but I wonder that they have suffi- cient power to force themselves through the water. Caroline. They must rise, you know, from their specific levity.'; Mrs. B. You are right, Caroline, but vapour has not in all li- quids (when brought to the degree of vaporization) the power of overcoming the pressure of the less heated surface. Metals, for in- stance, mercury excepted, evaporate only from the surface; there- fore no vapour will ascend from them till the degree of heat which is necessary to form it has reached the surface ; that is to say, till the whole of the liquid is brought to a state of ebullition. Emily. I have observed that steam, immediately issuing from the spout of a tea kettle, is less visible than at a further distance from it, 37et it must be more dense when it first evaporates, than when it "begins to diffuse itself in the air. Mrs. B. When the steam is first formed, it is so perfectly dissolv- ed by caloric, as to be invisible. In order, however, to understand this, it will be necessary for me to enter into some explanation re- specting the nature of solution. \Solution takes place whenever a body is melted in a fluid".-, In this operation the body is reduced to such a minute state of division by the fluid, as to become invisible in it and to partake of its fluidity; but in common solutions this happens without any decomposition, the body being only divided into its integrant particles by the fluid into which it is melted. Caroline. It is then a mode of destroying the attraction of aggre- gation. __ Mrs.B. Undoubtedly—the two principal solvent fluids are wa- ter and caloric?1, You may have observed that if you melt salt in wa- ter it totally disappears, and the water remains clear and transpa- rent as before ; yet though the union of these bodies appears so perfect, it is not produced by any chemical combination ; both the 229. What causes those bubbles which ascend, and those which gather on the inside of a vessel when water is heating ? 230. Why is air more easily rarefied than water ? 231. When water begins to boil why do large bubbles rise from the bottom ? 232. Has vapour always the power of overcoming the pressure of the less heated surface ? 233. What substances evaporate only from the surface ? 234. When does solution take place ? 235. What are the two principal solvent fluids ? FREE CALORIC. 59 salt and the water remain unchanged ; and if you were to separate them by evaporatingtbe latter, you would find the salt in the same state as before. Emily. I suppose that water is a solvent for solid bodies, and ca- loric for liquids. Mrs. B. Liquids of course can only be converted into vapour by caloric. But the solvent power of this agent is not at all confined to that class of bodies ; a, great variety of solid substances are dis- solved by heat; thus metals, which are insoluble in water, can be dissolved by intense heat, being first fused or converted into a liquid and then rarefied into an invisible vapour. Many other bodies, such as salt, gums, &c. yield to either of these solvents. Caroline. And that, no doubt, is the reason why hot water will melt them so much better than cold water. Mrs. B. It is so. Caloric may, indeed, be considered as having in every instance^ some share in the solution of a body by water, since water, however low its temperature may be, always contains more or less caloric. Emily. Then, perhaps, water owes its solvent power merely to the caloric contained in it. Mrs. B. That, probably, would be carrying the speculation too far ; I should rather think that water and caloric unite their efforts Jo dissolve a body, and that the difficulty or facility of affecting this, depend both on the degree of attraction of aggregation to be over- come) and on the arrangement of the particles which are more or less disposed to be divided and penetrated by the solvent. Emily. But have not all liquids the same solvent power as water ? Mrs. B. The solvent power of other liquids varies according to their nature, and that of the substances submitted to their action.— Most of these solvents, indeed,differ essentially from water, as they do not merely separate the integrant particles of the bodies which they dissolve, but attack their constituent principles by the power of chemical attraction, thus producing a true decomposition.'.These more complicated operations we must consider in another place, and confine our attention at present to the solutions by water and caloric. Caroline. But there are a variety of substances which, when dis- solved in water, make it thick and muddy, and destroy its transpa- rency. Mrs. B. In this case, it is not a solution, but simply a mixture. I sbaf. show you the difference between a solution and a mixture, by putting some common salt into one glass of water, and some pow- der of chalk into another; both these substances are white, but their effect on the water will be very different. Caroline. Very different, indeed ! The salt entirely disappears 236. After salt has been dissolved in water, can they be separated so as to have the salt in the same state, as before it was dissolved ? By what means ? 237. Has caloric any influence in the solution of a body by water? 238. On what does the difficulty or facility of dissolving bodies de- pend ? 239. Have all liquids the same solvent power as water ? 240. How do these solvents differ from water ? 24 J. What is the difference between a solution and a mixture ? 60 FREE CALORIC. and leave the water transparent, whilst the chalk changes it into an opaque liquid like milk. Emilu. And would lumps of chalk and salt produce similar effects on water ? Mrs.B. Yes, but not so rapidly: salt is, indeed, soon melted, though in a lump : but chalk, which doesnot mix so readily with water would require a much greater length of time; I therefore preferred showing you the experiment with both substances reduced to powder, which does not in any respect alter their nature, but fa- cilitates the operation merely by presenting a greater quantity of surface to the water. I must not forget to mention a very curious circumstance respect- ing solution, which is, that a fluid is not nearly so much increased in bulk by holding a body in solution, as it would be, by mere mix- ture with the body. Caroline. How is that possible ? for two bodies cannot exist to- gether in the same space. Mrs. B. Two bodies may, by condensation, occupy less space when in union than when separate, and this 1 can show you by an easy experiment. This phial which contains some salt, I shall fill with water, pour- ing it in quickly, so as not to dissolve much of the salt; and when it is quite full I cork it. If I now shake the phial till the salt is dis- solved, you will observe that it is no longer full. , Caroline. I shall try to add a little more salt. But now you see Mrs. B. the water runs over. Mrs.B. Yes; but observe that the last quantity of salt you put in remains solid at the bottom and displaces the water ; for it has already melted all the salt it is capable|of holding in solution. This is called the point of saturation; and the water in this case is said to be saturated with salt. Emily. I think I now understand the solution of a solid body by water perfectly ; but I have not so clear an idea of the solution of a liquid by caloric. Mrs. B. It is probably of a similar nature; but as caloric is an invisible fluid, its action as a solvent is not so obvious as that of wa- ter. Caloric, we may conceive, dissolves water and converts it in- to vapour by the same process as water dissolves salt; that is to say, the particles of water are so minutely divided by the caloric as to become invisible. Thus, you are now enabled to understand why the vapour of boiling water-hen it first issues from the spout of a kettle is invisible : it is so,(because it is then completely dissolved by caloric. But the air with which it comes in contact, being much colder than the vapor, the latter yields to it a quantity of its caloric. The particles of vapour being thus in a good measure deprived of their solvent, gradually collect, and become visible in the form of steam, which is water in a state of imperfect solution ; and if you were further to deprive it of its caloric, it would return to its original liquid state. 242. Are fluids equally increased in bulk by the solution and the mixture of a solid ? 243. What ■experiment proves that they are not? 244. W hen is a solvent saturated ? 245. Why is vapour less visible on first rising from a liquid, than af- ter having ascended a distance from it ? FREE CALORIC. 61 Caroline. That I understand very well. If you hold a gold plate 'over a tea-urn, the steam issuing from it will be immediately con- verted into drops of water by parting with its caloric to the plate ; but in what state is the steam when it becomes invisible by being diffused in the air ? Mrs. B. It is not merely diffused, but is again dissolved by the air. Emily. The air then, has a solvent power, like water and caloric ? Mrs.B. This was formerly believed to be the case. But it ap- pears from more recent enquiries that the solvent power of the at- mosphere depends solely upon the caloric contained in it.' Sometimes thewatery vapor diffusedin the atmosphere is but imperfectly dis- solverfjias is the case in the formation of clouds and fogs ; but if it gets into a region sufficiently warm, it becomes perfectly invisible. Emily. Can any water be dissolved in the atmosphere without having been previously converted into vapour by boiling? Mrs. B. Unquestionably ; and this constitutes the difference be- tween vaporization and evaporation. Water, when heated to the boiling point, can no longer exist in the form of water, and must necessarily be converted into vapour or steam, whatever may be the state and temperature of the surrounding medium ; this is called vaporization. But the atmosphere, by means of the caloric it con- tains, can take up a certain portion-of water at any temperature, and hold it in a state of solution. This is simply evaporation. Thus the atmosphere is continually carrying off moisture from the sur- face of the earth, until it is saturated with it. Caroline. This is the case, no doubt, when we feci the atmos- phere damp. Mrs. B. On the contrary, when the moisture is well dissolved it occasions no humidity ; it is only wher{ in a state of imperfect solu- tion^ and floating in the atmosphere, in flfe form of watery vapour, thaf it produces dampness. This happens more frequently in win- ter than in summer ; for the lower the temperature of the atmos- phere, the less water it can dissolve ; and in reality it never con- tains so much moisture as in a dry, hot, summer's day. Caroline. You astonish me ; but why, then, is the air so dry in frosty weather, when its temperature is at the lowest? Emily. This, I conjecture, proceeds not so much from the mois- ture being dissolved, as from us being frozen);* is not that the case ? Mrs. B. It is ; and the freezing of the watery vapour\vhich the * In cold climates, where there is not a cloud to be seen, and the sun rises in all his glory, the air is sometimes full of little particles of ice glistening in ever}' direction, and forming a most beautiful spectacle. This is owing to the condensation, and freezing of the particles of water in the air, by the intense cold.—C. 246. Upon what does the solvent power of the atmosphere depend? 247. What causes fogs? 240. What is the difference between vaporation and evaporization ? ' 249. Why does the atmosphere sometimes feel damp ? 250. When does the atmosphere contain most moisture, in summer or winter ? 251. Why is the air so dry in frosty weather ? 252. How is frost produced ? 6 62 FREE CALORIC. atmospheric heat could not dissolve, produces what is called a hoar frost ; for the particles descend in freezing, and attach themselves to whatever they meet with on the surface of the earth. The tendency of free caloric to an equilibrium, together with its solvent power, are likewise connected with the phenomena of rain, ofdew, &c. When most air of a certain temperature happens to pass through a cold region of the atmosphere, it parts with a por- tion of its heat to the surrounding air ; the quality of caloric, there- fore, which served to keep the water in a state of vapour, being di- minished, the'watery particles approach each other, and form them- selves into drops of water, which, being heavier than the atmosphere descend to the earth. There are also other circumstances, and par- ticularly the variation in the weight of the atmosphere, the changes which take place in its electrical state, &c. which may contribute to the formation of rain. This, however, is an intricate subject, into which we cannot more fully enter at present. Emily. In what manner do you account for the formation ofdew: Mrs. B. Dew is a deposition of watery particles or minute drops from the atmosphere, precipitated by the coolness of the evening. Caroline. This precipitation is owing, I suppose, to the cooling of the atmosphere, which prevents its retaining so great a quantity of watery vapour in solution as during the heat of the day. Mrs. B. Such was, from time immemorial, the generally received opinion respecting the cause ofdew ; but it has been very recently proved by a course of ingenious experiments of Dr. Wells, that the deposition ofdew is produced by the cooling of the surface of the earth, which he has shown to take place previously to the cooling of the atmosphere ; for on examining the temperature of a plot of grass just before the dew-fall, he found that it was considerably colder than the air a few feet above it, from which the dew was shortly after precipitated. Emily. But why should the earth cool in the evening sooner than the atmosphere ? Mrs. B. Because it parts with its heat more readily than the air; the earth is an excellent radiator of caloric, whilst the atmosphere does not possess that property, at least in any sensible degree. To- wards evening, therefore, when the solar heat declines, and when after sun-set it entirely ceases, the earth rapidly cools by radiating heat towards the skh s ; whilst the air has no means of parting with its heat but by coming in contact with the cooled surface of the earth, to which it communicates its caloric. Its solvent power be- ing thus reduced, it is unable to retain so large a portion of watery vapour, and deposits those pearly drops which we call dew. Emily. If this be the cause of dew. we need not be apprehensive of receiving any injury from it; for it can be deposited only on sur- faces that are colder than the atmosphere, which is never the case with our bodies. Mrs. B. Very true; yet I would not advise you for this reason t0 253. How is rain formed ?' 254. In what manner do you account for the formation ofdew ? 255. To what is the precipitation owing that takes place in the pro- duction of dew ? 256. Why does the earth cool sooner in the evening than the at- mosphere ? 657. What ill effects may result from dew to health ? FREE CALORIC. 63 be too confident of escaping all the ill effects which may arise from exposure to the dew ; for it may be deposited on your clothes, and chill you afterwards by its evaporation from them. \ Besides, when- ever the dew is copious, there is a chill in the atmosphere which i9 not always safe to encounter. Caroline. Wind,"then, should promote the deposition ofdew, by bringing a more rapid succession of particles of air in contact with the earth, just as it promotes the cooling of the earth and warming of the atmosphere during the heat of the day ? Mrs. B. This may the case in some degree, provided the agita- jjon of the air be not considerable ; for when the wind is strong it is found that less dew is deposited than in calm weather, especial- ly if the atmosphere be loaded with clouds. These accumulations of moisture not only prevent the free radiation of the earth to- wards the upper regions, but themselves radiate towards the earth ; for which reasons much less dew is formed than on fine clear nights when the radiation of the earth passes without obstacle through the atmosphere to the distant regions of space, whence it receives no caloric in exchange. The dew continues to be deposited during the night, and is generally the most abundant towards morning when the contrast between the temperature of the earth, and that of the air is greatest. After sunrise the equilibrium of temperature be- tween those two bodies is gradually restored by the solar rays pass- ing freely through the atmosphere to the earth; and later in the morning the temperature of the earth gains the ascendancy, and gives out caloric to the air by contact, in the same manner as it re- ceives it from the air duriugthe night. Can you lell me, now, why a bottle of wine taken fresh from the cellar (in summer particularly,) will soon be covered with dew ; and even the glasses into which the wine is poured will be mois- tened with a similar vapour ? Emily.-The bottle being colder than the surrounding air, must absorb caloric from it; the moisture, therefore, which that air con- tained, becomes visible, and forms the dew which is deposited on the bottle. Mrs. B. Very well, Emily. Now, Caroline, can you inform me why, in a warm room or close carriage, the contrary effect takes place ; that is to say, that the inside of the windows is covered with vapour? Caroline. I have heard that it proceeds from the breath of those within the room or the carriage ; and I suppose it is occasioned by the windows which, being colder than the breath, deprive it of part of its caloric, and by this means convert it into watery vapour. Mrs. B. You have both explained it extremely well. Bodies at- 258. When does wind promote the deposition ofdew? 259. Why does more dew accumulate in a clear night than when jt is cloudy ? 260. When is the dew most abundant, and why is it then most abundant? 261. Why is a tumbler or bottle filled with cold water covered with moisture in a warm day ? 262. Why in a warm room or in a close carriage does moisture collect on the inside of the windows ? 263. Why does less dew collect on rocks and sands, than on grass, and vegetables ? 04 FREE CALORIC. tract dew in proportion as they are good radiators of caloric, as it ia this quality which reduces their temperature below that of the at- mosphere ; hence we find that little or no dew is deposited on rocks, sand, or water ; while grass and living vegetables, to which it is so highly beneficial, attract it in abundance—another remarkable in- stance of the wise and bountiful dispensations of Providence. Emily. And we may again observe it in the abundance ofdew in summer, and in hot climates, when its cooling effects are so much required; but I do not understand what natural cause increases the dew in hot weather? Mrs. B. The more caloric the earth receives during the day, the. more it will radiate afterwards, and consequently the more rapidly its temperature will be reduced in the evening, in comparison to that of the atmosphere. In the West Indies especially, where the intense heat of the day is strongly contrasted with the coolness of the evening, the dew is prodigiously abundant. During a drought the dew is less plentiful, as the earth is not sufficiently supplied with moisture to be able to saturate the atmosphere. Caroline. I have often observed, Mrs. B„ that when I walk out in frosty weather, with a veil over my face, my breath freezes upon it. Pray what is the reason of that ? Mrs. B. It is because- the cold air immediately seizes on the calo- ric of your breath,;and, by robbing it of its solvent, reduces it to a denser fluid, which is the watery vapour that settles on your veil, and there it continues parting with its caloric till it is brought down to the temperature of the atmosphere, and assumes the form of ice. You may, perhaps, have observed that the breath of animals, or rather the moisture contained in it, is visible in damp weather, or during a frost. In the former ease, the atmosphere being over satu- rated with moisture, can dissolve no more. In the latter, the cold condenses it into visible vapor; and for the same reason the steam arising from water that is warmer than the atmosphere, becomes visible. Have you never taken notice of the vapour rising from your hands after having dipped them into warm water? Caroline. Frequently, especially in frosty weather. Mrs. B. We have already observed that pressure is an obstacle to evaporation : there arc liquids which contain so great a quantity of caloric, and whose particles consequently adhere so slightly to- gether, that they may be rapidly converted into vapour without any elevation of temperature, merely by taking off the weight of the at- mosphere. In such liquids you perceive, it is the pressure of the atmosphere alone that connects their particles, and keeps them in a liquid state. Caroline. I do not well understand why the particles of such flu- ids should be disunited and converted into vapour, without any ele- vation of temperature, in spite of the attraction of cohesion. Mrs. B. It is because the degree of heat at which we usually 264. Why does more dew collect in summer and in cold climates, than in winter and warm climates ? ~ 265. Why is there a small quantity ofdew in a time of drought ? 266. Why is the moisture contained in the breath of animals visi* ble in damp weather, or during a frost ? 267. How are certain liquids, which contain a great degree of calo- ric, conveited into vapour, without any increase of temperature ? FREE CALORIC. 65 observe these fluids is sufficient to overcome their attraction of co- hesion. Ether is of this description ; it will boil and be converted into vapour, at the common temperature of the air, if the pressure of the atmosphere be taken off. Emily. I thought that ether would evaporate without either the pressure of the atmosphere being taken away, or heat applied ; and that it was for that reason so necessary to keep it carefully corked up. Mrs. B. It is true it will evaporate, but without ebullition ; what I am now speaking of is the vaporization of ether, or its conversion into vapour by boiling. I am going to show you how suddenly the ^ther in this phial will be converted into vapour, iby means of the air pump. Observe with what rapidity the bubbres ascend, as I take off the pressure of the atmosphere. Caroline. It positively boils ; how singular, to see a liquid boil without heat! Fig. 7. Pneumatic Pump. Mrs.B. Now I shall place the phial of ether in this glass, which it nearly fills, so as to leave ouly a small space, which 1i fill with water: and in this state I put it again under the re- ceiver.*---You will observe, as 1 exhaust the air from it, that whilst the ether boils, the water freezes ! Caroline. It is in- deed wonderful to see water freeze in con- tact with a boiling flu- id ! Emily. I am at a loss to conceive how the ether can pass to the state of vapour, without an addition of taining water. C. C. Thermometers, one in the caloric. Does it not Ether, the other in the water. contain more caloric in a state of vapour, than in a state of liquidity . * Two pieces of thin glass tubes, sealed at one end, might answer this purpose better. The experiment, however, as here.described, is difficult, and requires a very nice apparatus. But if, instead of phials or lubes, two watch glasses be used, water may be frozen al- most instantly in the same manner. The two glasses were placed over one another, with a few drops of water interposed between them, and the uppermost glass is filled with ether. After working the 268. How can ether be made to boil without the application of ca- I oric ? 269. How is the experiment made ? 6* Fig. 7. Ether evaporated and water frozen in the air pump. A. Phial of ether. B. Glass vessel con- 66 FREE CALORIC. Mrs. B. It certainly does ; for though it is the pressure of Ihe at- mosphere which condenses it into a liquid, it is by forcing out the caloric that belongs to it when in an aeriform state. Emily. You have therefore, two difficulties to explain, Mrs, B. First, whence the ether obtains the caloric necessary to convert it into vapour, when it is relieved from the pressure of the atmosphere; and, secondly, what is the reason that the water in which the bot- tle of ether stands, is frozen ? Caroline. Now, I think I can answer both these questions. The ether obtains the addition of caloric required, from the water in the glass ; and (he loss of the caloric which the latter sustains, is the oc- casion of its freezing. Mrs. B. You are perfectly right ; and if you look at the ther- mometer which I have placed in the water, whilst I am working the pump, you will see that every time bubbles of vapour are produ- ced, the mercury descends ; which proves that the heat of the wa- ter diminishes in proportion as the ether boils. Emily. This I understand now very well; but if the water freezes in consequence of yielding its caloric to the ether, the equilibrium, of heat must in this case be totally destroyed. Yet you have told us, that the exchange of caloric between two bodies of equal tem- perature, was always equal ; how, then, is it that the water, which was originally of the same temperature as the ether, gives out ca- loric to it, till the water is frozen and the ether made to boil? Mrs. B. I suspected that you would make these objections; and in order to remove them, I enclosed two thermometers in theai r- nump ; one of which stands in the glass of water, the other in the phial of ether ; and you may see that the equilibrium of temper- ature is not destroyed ; for as the thermometer descends in the wa- ter, that in the ether sinks in the same manner ; so that both ther- mometers indicate the same temperature, though one of them is in a boiling, the other in a freezing liquid. Emily. The ether, then, becomes colder as it boils ! This is so contrary to common experience, that I confess it astonishes me ex- ceedingly. Caroline. It is, indeed, a most extraordinary circumstance. But pray how do you account for it ? Mrs. B. I cannot satisfy your curiosity at present; for before we can attempt to explain this apparent paradox, it is necessary to become acquainted with the subject of latent heat, and that, I think, we must defer till our next interview. Caroline. I believe, Mrs. B. that you are glad to put off the ex- planation ; for it must be a very difficult point to account for. Mrs. B. 1 hope, however, that I shall do it to your complete sat- isfaction. Emily. But before we part, give me leave to ask you one ques- pump for a minute or two, the glasses are found to adhere strongly together, and a thin layer of ice is seen between them. •270. In what state does ether exist when the pressure of the atmos- phere is taken off ? 271. Why does the evaporation of ether freeze water ? 272. W hat experiment is made with water and ether, and two ther- mometers? FREE CALORIC, 67 tion, Would not water, as well as ether boil with less heat, if de- prived of the pressure of the atmosphere? Mrs. B. Undoubtedly. You must always recollect that there are two forces to overcome, in order to make a liquid boil or evap- orate ;fthe attraction of aggregation, and the weight of the atmos- phere. > On the summit of a high mountain (as M. De Saussure as- certained on Mount Blanc,) much less heat is required to make water boil, than in the plain where the weight of the atmosphere is greater.* Indeed, if the weight of the atmosphere be entirely re- moved by means of a good air pump, and if water be placed in the exhausted receiver, it will evaporate so fast, however cold it may be, as to give it the appearance of boiling from the surface. But without the assistance of the air pump, 1 can show yon a very pret- ty experiment, which proves the effect of the pressure of the at- mosphere in this respect. Observe that this Florence flask is about half full of water, and the upper half of invisible vapor, the water being in the act of boil- ing. 1 take it from the lamp, and cork it carefully—the water, yon see, immediately ceases boiling. I shall now dip the flask into a basin of cold uater.f Caroline. Bat look, Mrs. B. the water begins to boil again, al- though the cold water must rob it more and more of its caloric ! What can be the reason of that? Mrs. B. Let us examine its temperature. You see the ther- mometer immersed in it remains stationary at 180 degrees which is about 30degrees below the boiling point. When I tcok the flask from the lamp. 1 observed to you that the upper part of it was filled with vapor; this being compelled to yield its caloric, to the cold water, was again condensed into water. What then filled the up- per part of the flask ? Emily. Nothing ; for it was too well corked for the air to gain admittance, and therefore, the upper part of the flask must be a vacuum. Mrs. B. The water below, therefore, no longer sustains the pressure of the atmosphere, and will consequently boil at a much lower temperature. Thus you see, though it. had lost many degrees of heat, it began boiling again the instant the vacuum was formed above it. The boiling has now ceased, the temperature of the water * On the top of Mount Blanc, water boiled when heated only to 188 degrees, instead of212 degrees. f The same effect may be produced by wrapping a cold wet lin- nen cloth round the upper part of the flask. In order to show you how much the water cools whilst it is boiling, a thermometer grad- uated on the tube itself, may be introduced into the bottle through the cork.—C. "273. What two forces are to be overcome in order to make a liquid boil or evaporate ? 274. Why does it require the application of less caloric to boilwa- tor on a high mountain than on low land? 275. What is the appearance of water when placed in an exhausted receiver? 276. What experiment is mentioned to show how tho boiling of li- quids is effected by atmospherical pressure ? 63 FREE CALORIC. being still farther reduced ; if it had been ether instead of water, it would haye continued boiling much longer, for ether boils under the usual atmospheric pressure, at a temperature as low as 100 de- grees; and in a vacuum it boils at almost any temperature; but water being a more dense fluid, requires a more considerable quan- tity of caloric to make it evaporate quickly, even when the pres- sure of the atmosphere is removed. Emily. What proportion of vapor can the atmosphere contain in astate of solution. Mrs. B. I do not know whether it has been exactly ascertained by experiment; but at any rate this proportion must vary, accord- ing to the temperature of the atmosphere; for the lower the tem- perature, the smaller must be the proportion of vapor that the at- mosphere can contain. To conclude the subject of free caloric, I should mention Ignition^ by which is meant that emission of light which is produced in bod- ies at a very high temperature, and which is the effect of accumu- lated caloric. Emily. You mean, I suppose, that light which is produced by a burning body. Mrs. B. No; ignition is quiie independent of combustion.— Clay, chalk, and indeed all incombustible substances may be made red hot. When a body burns, the light emitted is the effect of a chemical change which takes place, whilst ignition is the effect of caloric alone, and no other change than that of temperature is pro- duced in the ignited body. All solid bodies, and most liquids, are susceptible of ignition, or in other words, of being heated so as to become luminous ; and it is remarkable that this takes place pretty nearly at the same temper- ature in all bodies, that is, at about 800 degrees of Fahrenheit's scale. Emily. But how can liquids attain so high a temperature, with- out being converted into vapor? Mrs. B. By means of confinement and pressure. Water confi- ned in a strong iron vessel (called Papin's digester;) can have its temperature raised to-upwards of 400 degrees. Sir James Hall has made some very curious experiments on the effect of heat assisted by pressure ; by means of strong gun barrels be succeeded in melt- ing a variety of substances which were considered as infusible; and it is not unlikely that, by similar methods, water itself might be heated to redness. Emily. I am surprised at that; fori thought that the force of steam was such as to destroy almost alll mechanical resistance. Mrs. B. The expansive force of steam is prodigious ; but in or- der to subject water to such a high temperature, it is prevented by confinement from being converted into steam, and the expansion of 277. What proportion of vapor can the atmosphere contain in a state of solution ? * 278. What is meant by ignition ? 279. How does ignition vary from combustion? 280. Are liquids susceptible of ignition? 281. At what temperature dons ignition take place ? • 282. How can tney attain so high a temperature, without being con- verted into vapor ? 283. What experiments were made by Sir James Hall? COMBINED CALORIC. 69 heated water is comparatively trifling. But we have dwelt so long on the subject of free caloric, that we must reserve the other modi- fications of that agent to our next meeting, when we shall endeavor to proceed more rapidly. CONVERSATION IV. ON COMBINED CALORIC, COMPREHENDING SPECIFIC AND LA- TENT HEAT. Mrs B. We are now to examine the other modifications of ca- loric. Caroline. I am vrry curious to know of what nature they can be; for I have no notion of any kind of heat that is not perceptible to the senses. Mrs. B. In order to enable you to understand them, it will be necessary to enter into some previous explanations. It has been discovered by modern chemists, that bodies of a dif- ferent nature, heated to the same temperature, ^lo not contain the same quantity of caloric. Caroline. How could that be ascertained ? Have you not told us that it is impossible to discover the absolute quantity of caloric which bodies contain ? Mrs. B. True; but at the same time 1 said that we were enabled to form a judgment of the proportion which bodies have to each oth- er in this respect. True, it is found that, in order to raise the tem- perature of different bodies the same number of degrees, different quantities of caloric are required for each of them. , If for instance, you place a pound of lead, a pound of chalk, and a pound of milk, in a hot oven, they will be gradually heated to the temperature of the oven ; but the lead will attain it first, the chalk next, and the milk lasO Caroline. That is a natural consequence of their different bulks ; the lead being the smallest body, will be heated soonest, and the milk, which is the largest, will require the longest time. Mrs. B. That explanation will not do; for if the lead be the least in bulk, iroffers also the least surface to the caloric, the quan- tity of heat therefore, which can enter into it in the same space of lime is proportionally smaller. Emily. Why, then, do not the three bodies attain the tempera- ture of the oven at the same time? Mrs. B. It is supposed to be on account of the different capaci- ties of these bodies for caloric. Caroline. What do you mean by the capacity of a body for ca-r loric ? 284. Do bodies of a different nature heated to the same tempera? ture contain equal quantities of caloric? 285. What facts illustrative of this case mentioned of lead, chalk and milk? 70 COMBINED CALORIC. Mrs. B. I mean ^certain disposition of bodies to require more or less caloric for raising their temperature to any degree of heat.+- Perhaps the fact may be thus explained : Let us put as many marbles into this glass as it will contain, and pour sand over them—observe how the sand penetrates and lodg- es between them. We shall now fill another glass with pebbles of various forms—you see that they arrange themselves in a more compact manner than the marbles, which being globular, can touch each other by a single point only. The pebbles, therefore, will not admit so much sand between them ; and consequently one of these glasses will necessarily contain more sand than the other,\ though both of them be equally full. Caroline. This 1 understand perfectly. The marbles and the pebbles represent two bodies of different kinds, and the sand, the caloric contained in them ; and it appears very plain from this com- parison, that, one body may admit of more caloric between its par- ticles than another. Mrs. B. You can no longer be surprised, therefore, that bodies of a different capacity for caloric should require different proportions of that fluid to raise their temperatures equally. Emily. But I do not conceive why the body that contains the most caloric should not be of the highest temperature : that is to say, feel hot in proportion to the quantity of caloric it contains. Mrs. B. The caloric that is employed in filling the capacity of a body is not free caloric ; but is imprisoned as it were, in the body, and is therefore, imperceptible ; for we can feel only the caloric which the body parts with, and not that which it retains. Caroline. It appears to me very extraordinary, that heat should be confined in a body in such a manner as to be imperceptible. Mrs.B. If you lay your hand on a hot body, you feel only the caloric which leaves it, and enters your hand ; for it is impossible that you should be sensible of that which remains in the body. The thermometer in the same manner, is effected only by the free calor- ic which a body transmits to it, and not at all by that which it does not part with. Caroline. 1 begin to understand it ; but I confess that the idea of insensible heat is so new and straDge to me, that it requires some time to render it familiar. Mrs. B. Call it insensible caloric, and the difficulty will appear much less formidable. It is indeed a sort of contradiction to call it heat, when it is so situated as to be incapable of producing that sen- sation. Yet this modification of caloric is commonly called specif- ic heat. Caroline. But it certainly would have been more correct to have called it specific caloric. 286. What is to be understood by the capacity of abody for caloric? 287. How is this fact explained? 288. Why do not bodies that contain most caloric feel hot in pro- portion to the quantity of caloric they contain ? 289. When a body transmits caloric to a thermometer, is the ther- mometer affected by what remains in the body ? . 290. What is the imperceptible heat which bodies contain called ? COMBINED CALORIC. 71 Emily. I do not understand how the term specific applies to this modification of caloric. Mrs. B. It expresses the relative quantity of caloric which dif- ferent species of bodies of the same weight and temperature are ca- pable of containing. This modification is also frequently called heat of capacity, a term perhaps preferable, as it explains better its own meaning. You now understand, I suppose, why the milk and chalk required a longer portion of time than the lead, to raise their temperature to that of the oven ? Emily. Yes; the milk and the chalk having a greater capacity for caloric than the lead, a greater proportion of that fluid became in- sensible in those bodies; and the more slowly, therefore, their temperature was raised. Caroline. But might not this difference proceed from the differ- ent conducting powers of heat in these three bodies, since that which is the best conductor must necessarily attain the temperature of the oven first ? Mrs.B. Very well observed, Caroline. This objection would be insurmountable if we could not, by reversing the experiment, prove lhatvthe milk, the chalk, and the lead actually absorbed different quantities of caloric, and we know that if the different time they took in heating, proceeded merely from their different conducting powers, they would each have acquired an equal quantity of caloric. Caroline. Certainly. But how can you reverse this experiment? Mrs. B. It may be done/by cooling the several bodies to the same degree, in an apparatus adapted to receive and measure the caloric which they give out. Thus, if you plunge them into three equal quantities of water, each at the same temperature, you will be able to judge of the relative quantity of caloric which the three bodies contained, by that, which, in cooling, they communicated to their respective portions of water ; for the same quantity of caloric which they each absorbed to raise their temperature, will abandon them in lowering it; and,on examining the three vessels of water, you will find the one in which you immersed the lead to be the least heated ; thnt which held the chalk will be the next; and that which contained the milk will be heated the most of all. The cel- ebrated Lavoisier has invented a machine to estimate, upon this principle, the specific heat of bodies in a more perfect manner ; but I cannot explain it to you, till you are acquainted with the next modification of caloric. Emily. The more dense a body is, I suppose, the less is its capa- city for caloric ? Mrs. B. This is not always the case with bodies of different na- ture ; iron, for instance, contains more specific heat than tin, though it is more densev This seems to show that specific heat does not merely depend jupon the interstices between the particles; but ' 291. Do all bodies of equal weight contain the same capacity for ca loric ? 292. How is the experiment of the heated lead, chalk, and milk ex- rjlained ? 293. How can we ascertain the capacity of a body for caloric? 294. On what is the capacity of caloric chiefly depending ? 72 COMBINED CALORIC. probably, also upon some peculiar constitution of the bodies, which we do not comprehend. Emily. But, Mrs. B., it would appear to me more proper to com- pare bodies by measure, rather than by weight, in order to estimate their specific heat. Why, for instance should we not compare pints of milk, of chalk, and of lead, rather than pounds of those substan- ces ; for equal weights may be composed of very different quanti- ties. Mrs. B. You are mistaken my dear; equal weights must contain equal quantities of matter; and when we wish to know what is the relative quantity of caloric, which substances of various kinds are capable of containing under the same temperature, we must com- pare equal weights, and not equal bulks of those substances. Bod- ies of the same weight may undoubtedly be of very different di- mensions ; but this does not change their real quantity of matter. A pound of feathers does not contain one atom more than a pound of lead. Caroline. I have another difficulty to propose. It appears to roe that if the temperature of the three bodies in the oven did not rise equally, they would never reach the same degree, the lead would always keep its advantage over the chalk and milk, and would, per- haps, be boiling before the others had attained the temperature of the oven. I think you might as well say that in the course of time, you and I shall be of the same age. Mrs. B. Your comparison is not correct, Caroline. As soon as the lead reached the temperature of the oveD, it would remain sta- tionary ; for it would then give out as much heat as it would^eceive. You should recollect that the exchange of radiating heat, between two bodies of equal temperature, is equal; it would be impossible, therefore, for the lead to accumulate heat after having attained the temperature of the oven , and that of the chalk and milk, therefore, would ultimately arrive at the same standard. Now I fear that this will not hold good with respect to our ages, and that as long as I live, I shall never cease to keep my advantage over you. Emily. I think that I have found a comparison for specific heat, which is very applicable. Suppose that two men of equal weight and bulk, but who require different quantities of food to satisfy their appetites, sit down to dinner, both equally hungry ; the one would consume a much greater quantity" of provisions than the other, in order to be equally satisfied. Mrs. B. Yes, that is very fair; for the quantity of food necessa- ry to satisfy their respective appetites, varies in "the same manner as the quantity of caloric requisite, to raise equally the temperature of different bodies. Emily. The thermometer then, affords no indication of the spe- cific heat of bodies. Mrs. B. None at all; no more than satiety is a test of the quan- "tity>>f food eaten. The thermometer, as I have repeatedly said, can 295. Why are not bodies compared by measure rather than weight to estimate their specific heat? 296. If different bodies have different capacities for caloric, why do they not rise to different temperatures in the same atmosphere ? • 297. Does the thermometer afford any indication of the specific heat of bodies? FREE CALORIC. 73 be affected only by free caloric which alone raises the temperature of bodies. But there is another mode of proving the existence of specific heat, which affords a very satiifactory illustration of that modification.— This, however, I did not enlarge upon before, as I thought it might appear to you rather complicated. If you mix two fluids of different temperatures, let us say the one at 50 degrees, and the other at 100 degrees^of what temperature do you suppose the mixture will be ? Caroline. It will be, no doubt, the medium between the two, that is to say, 75 degrees. Mrs.B. That will be the case if the two bodies happen to have the same capacity for caloric ; but if not, a different result will be obtained. Thus for instance, if you mix together apound of mercu- ry, heated at 50 degrees, and a pound of water heated at 108 degrees, the temperature of the mixture, instead of being 75 degrees will be , 80 degrees; so that the water will have lost only 12 degrees, whilst ^the mercury will have gained 38 degrees, from which you will con- clude that the capacity of mercury for heat is less than that of water. Caroline. I wonder that the mercury should have so little spe- cific heat. Did we not see it was a much better conductor of heat than water? Mrs. B. And it is precisely on that account that its specific heat is less. For since the conductive power of bodies depends, as we have observed before, on their readiness to receive heat and part with it, it is natural to expect that those bodies which are the worst conductors should absorb the most caloric before they are disposed to part with it to other bodies. But let us now proceed lo latent heat. Caroline. And pray, what kind of heat is that? Mrs.B. It is another modification of combined caloric, which is so analagous to Specific heat, that most chemists make no distinc- tion between them ; but Mr. Pictet, in his Essay on Fire, has so clearly discriminated them, that I am induced lo adopt his view of the subject. We therefore call latent heat that portion of insensible caloric which is employed in changing the state of bodies ;that is to say, in converting solids into liquids, or liquids into vapour.— When a body changes its state from solid to liquid, or from liquid to vapour, its expansion occasions a sudden and considerable in- crease of capacity for heat, in consequence of which,it immediately absorbs a quantity of caloric, which becomes fixed'in the body it has transformed ; and as it is perfectly concealed from our senses, it has obtained the name of latent heat. Caroline. I think it would be much more correct to call this mod- ification latent caloric instead of latent heat, since it does not ex- cite the sensation of heat. Mrs. B. This modification of heat was discovered and named by Dr. Black, long before the French chemists introduced the term ca- loric, and we must not presume to change it, as it is still used by 298. What other method is mentioned as proving the existence of specific heat ? 299. What will be the result as to temperature, if mercury heated at 50, and water heated at 100 degrees be mixed together ? 300. Why has mercury so Kttle specific heat ? '361. What is latent caloric ? 302. What does the conversion of a solid to a liquid occasion ? 7 74 COMBINED CALORIC. much better chemists than ourselves. Besides, you are not to sup- pose that the nature of heat is altered by being variously modified: for if latent heat and specific heat do not excite the same sensations as free caloric, it is owing to their being in a state of confinement, which prevents them from acting upon our organs; and conse- quently, as scones they are extricated from the body in which they are imprisoned/they return to their state of free caloric^ Emily. But 1 do not yet clearly see in what respect latent heat differs from specific heat; for they are both of them imprisoned and concealed in bodies. Mrs. B. (Specific heat is that which is employed in filling the ca- pacity of a body for caloric, in the state in which this body actually exists; while latent heat is that which is employed only in affecting a change of stalel) that is, in converting bodies from a solid to a li- quid, or from a liquid to an aeriform state. But I think, that in a general point of view, both these modifications might be compre- hended under the name of:heal of capacity, as in both cases the ca- loric is equally engaged infilling the capacity of bodies. I shall now show you an experiment, which I hope will give you a^clear idea of what is understood by latent heat. . The snow which you see in this phial has been cooled by certain chemical means, (which I cannot well explain to you at present,) to five or six degrees below the freezing point, as you will find in- dicated by the thermometer which is placed in it. We shall expose it to the heat of a lamp, and you will see the thermometer gradual- ly rise, till it reaches the freezing point. , Emily. But there it stops, Mrs. B. and yet the lamp burns just as well as before. Why is not its heat communicated to the thermom- eter? Caroline. And the snow begins to melt; therefore it must be ri- sing above the freezing point. Mrs. B. 'The heat no longer affects the thermometer, because it is wholly employed in converting the ice into water. As the ice melts, the caloric becomes latent in the new formed liquid, and therefore cannot raise its temperature ; and the thermometer will consequently remain stationary, till the whole of the ice be melted. Caroline. Because the conversion of the ice into water being completed, the caloric no longer becomes latent; and therefore the heat which the water now receives raises its temperature, as you find the thermometer indicates. - Emily. But I do not think that the thermometer rises so quickly in the water as it did in the ice, previous to its beginning to melt, though the lamp burns equally well. 303. What is the consequence if latent and specific heat are extri- cated from the body in which they are imprisoned? 304. What is the difference between specific heat and latent heat ? ■ 305. By what name is it thought they may both be called ? 306<7. Why does not the thermometer rise in a warm room when its bulb is in a piece of ice ? 306. In what experiment may be seen the existence of latent heat ? 307. Why does the thermometer begin to rise ns soon as the ice is melted? COMBINED CALORIC. 75 Mrs. B. That isiowing to the different specific heat of ice and water.' The capacity of water for caloric being greater than that of ice, more heat is required to raise its temperature, and therefore the thermometerr rises slower in the water than it did in the ice. Emily. True ; you said that a solid body always increased its ca- pacity for heat by becoming fluid, and this is an instance of it. Mrs. B. Yes ; and the latent heat is that which is absorbed in consequence of the greater capacity which the water has for heat, in comparison to ice. I must now tell you a curious calculation founded on (hat consi- deration. 1 have before observed to you that though the thermo- meter shows us the comparative warmth of bodies, and ^mibles us to determine the same point at different times and places, it gives us no idea of the absolute quantity of heat in any body. We cannot tell how low it ought to fall by the privation of all heat, but an at- tempt has been made to infer it in the following manner. It has been found by experiment, that the capacity of water for heat, when compared with that of ice, is asv!0 to 9 ;. so that, at the same temperature, ice contains one tenth of Caloric less than water. By experiment, also, it is observed, that in order to melt ice, there must be added to it&s much heat as would, if it did not melt it, raise its temperature 140 degrees.? This quantity of heat is, therefore, ab- sorbed, when the ice, by being converted into water, is made to contain one ninth more caloric than it did before. Therefore 140 degrees is a ninth part of the heat contained in ice at 30 degrees ; and the point of zero, or the absolute privation of heat, must conse- quently be 1260 degrees, below 32 degrees.f This mode of investigating so curious a question is ingeni ius, but fts correctness is not yet established by similar calculations for other bodies. The points of absolute cold, indicated by this method in va- rious bodies, are very remote from each other; it is however, possi- ble, that this may arise from some imperfection in the experiments. Caroline. It is indeed very ingenious—but we must now attend to our present experiment. The water begins to boil, and the ther- mometer is again stationary. Mrs. B. Well, Caroline, it is your turn to explain the phenome- non. * That is, water contains 140 degrees of heat more than is indica- ted by the thermometer.—C. f This calculation was made by Dr. Irvine. Dr. Crawford af- terwards placed the real zero at 1500 degrees below the 0 of Fah- renheit, Still later, Mr. Dalton has turned his attention to the same subject. The mean of his experiment places the real zero 6000 degrees below the freezing point. AH this goes to show that very little has yet been demonstrated on this difficult question.—C. 308. Why does the thermometer rise slower in the water than it did in the ice ? 309. Since a thermometer does not indicate the absolute quantity of caloric contained in any body, what is its use ? 310. H®w much latentheat does water contain ? 311. How much heat must be added to ice in order to melt it ? 312. What was proposed by Dr. Crawford, and by Dr. Dalton, as to fixing the real zero ? 76 COMBINED CALORIC. Caroline. It is wonderfully curious ! The caloric is now busy in changing the water into steam, in which it hides itself, and becomes insensible. This is another example of latent heat, producing a change of form. At first it converted a solid body into a liquid, and now it turns the liquid into vapour ! Mrs. B. You see, my dear, how easily you have become acquain- ted with these modifications of insensible heat, which at first ap- peared so unintelligible. If now, we were to reverse these chan- ges, and condense the vapour into water, and the water into ice, the latent heat would re-appear entirely, in the form of free caloric. Emily. Pray do let us see the effect of latent heat returning to its free state. Mrs. B. For the purpose of showing this, we need simply con- duct the vapour through this tube into this vessel of cold water, where it will part with its latent heat and return to its liquid form. Emily. How rapidly the steam heats the water! Mrs. B. That is because it does not merely impart its free caloric to the water, but likewise its latent heat. This method of heating liquids, has been turned to advantage, in several economical estab- lishments. The steam kitchens, which are getting in such gene- ral use, are upon the same principle. The steam isconveyed through a pipe in a similar manner, into the several vessels which contain the provisions to be dressed, where it communicates to them its lat- ent caloric, and returns to the state of water. Count Bumford makes great use of this principle in many of his fire-places : his grand maxim is to avoid all unnecessary waste of caloric, for which purpose he confines the heat in such a manner, that not a particle of it shall unnecessarily escape; and while he economises the free ca- loric, he takes care also to turn the latent heat to advantage. It is thus that he is enabled to produce a degree of heat superior to that which is obtained in common fire-places, though he employs less fuel. Emily. When the advantages of such contrivances are so clear and plain, I cannot understand why they are not universally used. Mrs. B. A long time is always required before innovations, how- ever useful, can be reconciled with the prejudices of the vulgar. Emily. What a pity it is that there should be a prejudice against new inventions ; how much more rapidly the world would improve if such useful discoveries were immediately and universally adopted! Mrs. B. I believe, my dear, that there are as many novelties at- tempted to be introduced, the adoption of which would be prejudi- cial to society, as there are of those which would be beneficial to it. The well informed, though by no means exempt from error, have an unquestionable advantage over the illiterate, in judging what is like- ly or not to prove serviceable ; and therefore' we find the former more ready to adopt such discoveries as promise to be really advan- tageous than the latter, who, having no other test of the value of a novelty but time and experience, at first oppose its introduction.—- ■313. What is that heat called which produces a change of form i bodies ? 314. How may latent heat be converted into free caloric? 315. In what experiment may be seen the effect of latent heat re turning to its free state ? 316. What is the advantage of Count Rumford's improved fire-pla ces ? COMBINED CALORIC. 77 The well informed, however, are frequently disappointed in their most sanguine expectations, and the prejudices of the vulgar, though they often retard the progress of knowledge, yet sometimes, it must be admittted, prevent the propagation of error.—But we are deviating from our subject. We have converted steam into water, and are now to change wa- ter into ice, in order to render the latent heat sensible, as it escapes from the water on its becoming solid. For this purpObe we must produce a degree of cold that will make water freeze. Caroline. That must be very difficult to accomplish in'this warm room. Mrs. B. Not so much as you think. There are certain chemical mixtures which produce a rapid change" from the solid to the fluid state, or the reverse, in the substances combined, in consequence of which change latent heat is either extricated or absorbed. Emily. I do not quite understand you. Mrs. B. This snow and salt which you see me mix together, are melting rapidly ; beat therefore must be absorbed by the mixture, and cold produced. Caroline It feels even colder than ice, and yet the snow is melt- ing. This is very extraordinary. Mrs. B. The cause of the mtense cold of themixture is to be at- tributed'to the change of a solid to a fluid stateA The union of the snow anct'salt produces a new arrangement oTtheir particles, in consequence of which they become liquid ; and the quantity of ca- loric required to effect this change, is seized upon by the mixture whenever it can be obtained. This eagerness of the mixture for caloric, during its liquefaction, is such that it converts part of its own free caloric into latent heat, and it is thus that the tempera- ture is lowered. Emily. Whatever you put in this mixture, therefore, would freeze! Mrs. B. Yes; at least any fluid that is susceptible of freezing at that temperature. 1 have prepared this mixture of salt and snow for the purpose of freez ng the water from which you are desirous of seeing the latent heat escape. I have put a thermometer in the glass of water that is to be frozen, in order that you may see how it cools. Caroline. The thermometer descends, but the heat which the wa- ter is now losing is iis free not its latent heat. Mrs.B. Certainly; it does not part with its latent heat till it changes its state and is converted into ice.' Emily. But here is a very extraordinary circumstance ! The thermometer has fallen below the freezing point, and yet the water is not frozen.* * To make this experiment striking, the glass containing the wa- ter and thermometer ought to be kept perfectly still until the mer- cury sinks below the freezing point. Then agitate the water, or drop 317. How is latent heat rendered sensible? 318. How can water be made to freeze ia a warm room? 319. Why is a mixture of snow and salt so intensely cold? 3^0 When dor>s water pait with its latent heat? 7* 78 COMBINED CALORIC. Mrs. B. That is always the case previous to the freezing of wa- ter when it is in a state of rest. Now it begins to congeal, and you may observe that the thermometer again rises to the freezing point. Caroline. It.appears tome very strange that the thermometer should rise the very moment that the water freezes; for it seems to imply that the water was colder before it froze than when in the act of freezing. Mrs. B It is so; and after our long dissertation on this circum- stance, I did not think it would appear so surprising to you. Re- flect a little, and I think you will discover the reason of it. Caroline. It must be, no doubt, the extraction of latent heat, at the instant the water freezes,1 which raises the temperature. Mrs. B. Certainly ; and if you now examine the thermometer, you will find that its rise was but temporary, and lasted only du- ring the disengagement of the latent heat—now that all the water is frozen, it falls again, and will continue to fall, till the ice and mixture are all of an equal temperature. Emily. And can you show us any experiments, in which liquids, by being mixed, become solid and disengage latent heat ? Mrs. B. I could show you several, but you are not yet sufficiently advanced to understand them well. 1 shall, however, try one, which will afford you a striking instance of the fact. The fluid which you see in this phial, consists of a quantity of a certain salt called muriat of lime, dissolved in water. Now, ifl pour into it a few drops of this other fluid, called sulphuric acid, the whole, or very nearly the whole, will be instantaneously converted into a solid mass. Emily. How white it turns ! I feel the latent heat escaping ; for the bottle is warm, and the fluid is changed lo a solid white sub- stance, like chalk !* Caroline. This is, indeed, the most curious experiment we have seen yvt. But pray what is that white vapor which ascends from the mixture ? Mrs. B. You are not yet enough of a chemist to understand that. But take care, Caroline, do not approach too near it, for it has a very pungent smell. I shall show you another instance, similar to that of the water, which you observee to become warmer as it froze. I have in this phial a solution of a salt called sulphat of soda, or Glauber's salt, made very strong, and corked up when it was hot, and kept without into it a small piece of ice, and it instantly shoots into crystals, and the thermometer rises. — C. * The sulphuric acid, by its stronger affinity for the lime, takes it from the muriatic acid, unites with it, and forms sulphate of lime. The solidity is owing to the insolubility of this last substance in water. The experiment succeeds well, if the water is saturated with the muriate.—C. 321. Why does water become colder before freezing than it is in the act of freezing? 322 What example can you give of liquids becoming solid, by being mixed, and disengaging latent heat? 3 ^3. How is this effect accounted for, in the note? 324. What other instance of the extrication of latent heat is given, w.d how is it produced? COMBINED CALORIC. 79 agitation, till it became cold, as you may feel the phial is. Now when 1 take out the cork, and let the air fall upon it, (for being closed when boiling, there was a vacuum in the upper part,) ob- serve that the salt will suddenly crystallize. Caroline. Surprising ! how beautifully the needles of salt have shot through the whole phial! Mrs. B. Yes, it is very remarkable; but pray do not forget the object of the experiment. Feel how warm the phial has become by the conversion of part of the liquid into a solid. Emily. Quite warm, 1 declare : this is a most curious experiment of the disengagement of latent heat. Mrs. B. Tbe slaking of lime, is another remarkable instance of the extrication of latent heat.| Have you never observed how quicklime smokes, when water'is poured upon it, and how much heat it produces? Caroline. Yes; but I do not understand what change of state takes place in the lime that occasions its giving out latent heat; for the quick-lime, when it is solid, is (if I recollect right,) reduced to powder by this operation, and is, therefore, rather expanded than condensed. Mrs. B. It is from the water, not the lime, that the latent heat is set free. The water incorporates with, and becomes solid in the lime ; in consequence of which the heat, which kept it in a liquid state is disengaged, and escapes in a sensible form. Caroline. I always thought that the heat originated in the lime. It seems very strange that water, and cold water, too, should con- tain so much heat. Emily. After this extrication of caloric, the water must exist in a state of ice in the lime, since it parts with the heat which kept it liquid. Mrs. B. It cannot properly be called ice, since ice implies a degree of cold at least equal to the freezing point. Yet, as water, in combining with lime, gives out more heat than in freezing, it must be in a state of still greater solidity in the lime than it is in the form of ice ; and you may have observed that it does not moisten or liquefy the lime in the smallest degree. Emily. But, Mrs. B. the smoke that rises is white; if it was only pure caloric which escaped, we might feel, but could not see it. Mrs. B. This white vapor is formed by some of the particles of lime in a state of fine dust, which are carried off by the caloric. Emily. In all changes of state, then, a body either absorbs or dis- engages latent heat. Mrs. B. You cannot exactly say absorbs latent heat, as the heat becomes latent only on being confined in the body; but you may say, generally, that bodies in passing from a solid to a liquid form, or from the liquid stale to thai of vapor, absorb heat: and that when the reverse takes place heat is disengaged.* * This rule, if not universal, admits of very few exceptions. 825. What other instance is mentioned of the extrication of latent beat? 326. Whence proceeds the heat in the slaking of lime ? 327. Why is the smoke that rises in the slaking of lime, white ? 328. When do bodies absorb heat? When is heat disengaged? I 80 COMBINED CALORIC. Emily. We can now, I think, account for the ether boiling, and the water freezing in vacuo, at the same temperature-! Mrs. B. Let me hear how you explain it. Emily. The latent heat which the water gave out in freezing, was immediately absorbed by the ether, during its conversion into vapor ; and therefore from a latent state in one liquid, it passes into a latent stale in the other. Mrs. B. But this only partly accounts for the result of the ex- periment: it remains to be explained why the temperature of the ether, while in a state of ebullition, is brought down lo the freezing temperature of water, iritis because the ether, during its evapora- tion, reduces its own temperature, in the same proportion as that of the water by converting its free caloric into latent heat; so that though one liquid boils, and another freezes, their temperatures remain in a state of equilibrium. Emily. But why does not water, as well as ether, reduce its own temperature by evaporating? Mrs. B. The fact is, that it does, though much less rapidly than ether. Thus, for instance, you may often have observed, in the heat of summer, how much any particular spot may be cooled by water- ing, though the water used for that purpose be as warm as the air itself. Indeed so much cold may be produceqYby the mere evapora- tion of water,) that the inhabitants of India, by availing themselves of the most favorable circumstances for this process which their warm climate can afford, namely, the cool of the night, and situations most exposed to the night breeze, succeed in causing water to freeze though the temperature of the air be as high as 60 degrees. ^The water is put into shallow earthen trays, so as to expose an extensive surface to the process of evaporation, and ip the morning, the water is found covered with a thin cake of ice, which js collected in suffi- cient quantity to be used for purposes of luxury?- Car Line. How delicious it must be to drink liquids so ccrld in those tropical climates ! But, Mrs. B. could we not try that ex- periment ? Mrs. B. If we were in the country, I have no doubt but that we should be able to freeze water, by the same means, and under sim- ilar circumstances. But we can do it immediately, upon a small scale, in this very room, in which the thermometer stands at 70 de- grees. For this purpose we need only place some water in a little cup under the receiver of the air-pump Fig. 8. and exhaust the air from it. What will r>e the consequence,Caroline? Caroline. Of course the water wll evaporate more quickly, since there will no longer be an atmospheric pressure on its surface; but will this be sufficient to make the water freeze? Mrs. B. Probably not, because the vapor will not be carried off f See page 65. 329. Why does water freeze and ether boil in vacuo? 330. Why does the ground become cooled by watering in summer, though the water used be as warm as the air itself? 331. How is ice often produced in India, where the temperature is not below 60 degrees? 332. How is water made to freeze under a glass receiver, as illus- trated in figure 8 ? COMBINED CALORIC. 81 fast enough; but this will be accomplished without difficulty if we introduce into the receiver, Fig. 8, in a saucer, or other large shal- low vessel some strong sulphuric acid, a substance which has a great attraction for water, whether in the form of vapour or in the liquid state. This attraction is such thai the acid will instantly ab- sorb the moisture as it rises from the water, so as to make room for Fig. 8. 8. The air pump and receiver for Mr. Leslie's experiment. C. a saucer with sul phuric acid. B. a glass or earthen cup containing water. D. a stand for the cup with its legs made of glass. A. A. Thermometer. the formation of fresh vapour; this will of course hasten the pro" cess, and the cold produced from the rapid evaporation of the wa- ter, will in a few minutes, be sufficient to freeze its surface.* We shall now exhaust the air from the receiver. Emily. Thousands of small bubbles already arise through the water from the internal surface of the cup; what is the reason of this > Mrs.B. These are bubbles of air which were partly attached to the vessel, and partly diffused to the water itself; and they expand and rise in consequence of the atmospheric pressure being removed. Caroline. See, Mrs. B.; the thermometer in the cup is sinking fast; it has already descended to 40 degrees ! Emily. The water now and then violently agitated on the surface as if it were boiling ; and yet the thermometer is descending fast! Mrs. B. You may call it boiling if you please, for this appear- ance is, as well as boiling, owing to the rapid formation of vapour; but here, as you have just observed, it takes place from the surface for it is only when heat is applied to the bottom of the vessel that the vapor is formed there.—Now crystals of ice are actually shooting all over the surface of the water. » This experiment was first devised by Mr. Leslie, and has since been modified in a variety of forms. 333. Whe/i the air is exhausted from the receiver, why do bubbles rise through the water from the internal surface of the cup ? 334. Why does the water appear as if boiling ? 82 COMBINED CALORIC. Caroline. How beautiful it is ! The surface is now entirely fro- zen—but the thermometer remains at 32 degrees. *■ Mrs. B. And so it will, conformably with our doctrine of latent heat, until the whole of the water be frozen ; but it will then again begin to descend lower and lower,, in consequence of the evapora- tion which goes on from the surface of the ice. Emily. This is a most interesting experiment; but it would be still more striking if no sulphuric acid were required. Mrs. B. I will shew you a freezing instrument, contrived by Dr. Wollaston, upon the same principle as Mr. Leslie's experiment, by which water may be frozen by its own evaporation aloue, without the assistance of sulphuric acid. Fig. 9. Dr. Wollaston's Cryophorus. This tube which as you ^___________ see is terminated at each f. extremity by a bulb, one/\ of which is half full of wa-W ter, is internally, perfectly exhausted of air; the consequence of this is, that the water in the bulb, is always much disposed to evaporate. This evaporation, how- ever, does not proceed sufficiently fast to freeze the water ; but if the empty ball be cooled by some artificial means, so as to condense quickly the vapour which rises from the water, the process may be thus so much promoted as to cause the water to freeze in the other ball. Dr. Wollaston has called this instrument Cryophorus. Caroline. So that cold seems to perform here the same part which the sulphuric acid acted in Mr. Leslie's experi- ment ? Mrs. B. Exactly so ; but let us try the exper- iment. Emily. How will you cool the instrument? You have neither ice nor snow. Mrs. B. True; but we have other means of effecting this.* You re- collect what an intense cold can be produced by the evaporation of e- her in an exhausted re- ceiver. We shall in- Fig. 10. No. 3. (Fig. 10.) Dr. Marcet's mode of using the Cryophorus. No 1, and 2, the different parts of .No. 3, seen separate. * This mode of making the experiment was proposed, and the Journal \f^ by Dr> Marcet> in the 34th v°l. of Nicholson's 335. How long will this experiment in the thermometer remain at 32 degrees, or at the freezing point? am al 6i 336. Why will it begin and continue to descend as aoon as all the water is frozen ? 337. What is the object of figures 1, 2, and 3 ? COMBINED CALORIC. 83 close the bulb in this little bag of fine flannel, (Fig. 1.) then soak itin ether, and introduce it into the receiver of the air-pump. (Fig. 3.) For this purpose we shall find it more convenient to u-e a cryo- phorus of this shape, (Pig. 2.) as its elongated bulb passes easily through a brass plate which closes the top of the receiver. If we now exhaust the receiver quickly, you will see in less than a min- ute, the water freeze in the other bulb out of the receiver. Emily. The bulb already looks quite dim, and small drops of wa- ter are condensing on its surface. Caroline. Aud now crystals of ice shoot all over the water. This is, indeed, a very curious experiment! Mrs. B. You will see, some other day, that, by a similar method, even quicksilver may be frozen.. But we cannot at present indulge in any- further digression Having advanced so far on the subject of heat, I may now give you an account of the calorimeter,,'an instrument invented by Lavois- ier, upon the principles just explained, for the purpose of estimating the specific heat of bodies.- It consists of a vessel, the inner surface of which is lined with icei so as to form a sort of hollow globe of ice, in the midst of which the body, whose specific heat is to be as- certained, is placed. The ice absorbs caloric from this body, till it has brought it down to the freezing point; this caloric converts into water a certain portion of ice which runs out through an aperture at the bottom of the machine; and the quantity of ice changed to water is a test of the quantity of caloric which the body has given out in descending from a certain temperature to the freezing point. Caroline. In this apparatus, I suppose, the milk, chalk, and lead, would melt different quantities of ice, in proportion to their differ- ent capacities for caloric. Mrs. B. Certainly ; and thence we are able to ascertain, with precision, their respective capacities for heat. But the calorimeter affords us no more idea of the absolute quantily of heat contained in a body, than the thermometer ; for though by means of it we extricate both the free and combined caloric, yet we extricate (hem only to a certain degree, which is the freezing point; and we know not how much thev contain of either below that point. Emily. According to the theory of latent heat, it appears to me that the weather should be warm when it freezes, andcold in a thaw ; for latent heat is liberated from every substance that it freezes, and such a large supply of heat must warm the atmosphere ; whilst du- ring a thaw, that very quantity of free heat must be taken from the atmosphere and return to a latent state in the bodies which it thaws. Mrs. B. Your observation is very natural; but consider that in a frost the atmosphere is so much colder than the earth, that all the caloric which it takes from the freezing bodies, is insufiicient to raise its temperature above the freezing poirt ; otherwise the frost must cease. But if the quantity of latent heat extricated does not destroy the frost, it serves to moderate the suddenness of the change oftem- ' 338. Can quicksilver be frozen ? 339. What is the calorimeter, and what is its use ? 340. Of what does it consist ? 341. Does the calorimeter indicate the absolute quantity of heat contained in a body ? 342. What effect is produced on the temperature of the atmosphere, by the attraction of latent heat from the winter frosts ? 84 COMBINED CALORIC. perature of the atmosphere, at the commencement both of frost and of a thaw. In the first instance, its extrication diminishes the se- verity of the cold ; and in the latter, its absorption moderates the warmth occasioned by a thaw ; it even sometimes produces a dis- cernible chill, at the breaking up ol fiost. Caroline. But what are the general causes that produce those sudden changes in the weather, especially from hot to cold, which we often experience? Mrs. B. This question would lead us into meteorological discus- sions, to which I am by no means competent. One circumstance, however, we can easily understand. When the air has passed over cold countries, it will probably arrive here at the temperature much below our own, and then it must absorb heat from every object it meets with, which will produce a general fall of temperature. Caroline. But pray, now that we know so much of the effects of heat, will you inform us whether it is really a distinct body, or, as I have heard, a peculiar kind of motion produced in bodies ? Mrs. B. As I have before told you, there is yet much uncertain- ly as to the nature of these subtle agents. But I am inclined to consider heat not as mere motion, but as a_separate substance.— Late experiments, too, appear to make it £ compound body, con- sisting of the two electricities ; and in our next conversation 1 shall inform you of the principal facts upon which that opinion is founded. CONVERSATION V. ON THE CHEMICAL AGENCIES OF ELECTRICITY.* Mrs. B. Before we proceed further, it will be necessary to give you some account of certain properties of electricity, which have of late years been discovered to have an essential connexion with the phenomena of chemistry. Caroline. It is electfucitv1, if 1 recollect right, which comes next in our list of simple substances ? Mrs. B. 1 have placed electricity in that list, rather from the ne- cessity of classing it somewhere, than from any conviction that it has a right to that situation ; for we are as yet so ignorant of its intimate nature, that we are unable to determine, not only whether it is sim- ple or compound, but whether it is in fact a material agent; or, as Sir H. Davy has hinted, whether it may not be merely a property inherent in matter. As, however, it is necessary to adopt some hypothesis for the explanation of the discoveries which this agent has enabled us to make, I have chosen the opinion, at present most prevalent, which supposes the existence of two kinds of electricity, distinguished by the name of positive and negative electricity. * The electricity extracted by the metals is commonly called Galvanism. 343. What is heat now supposed to be ? 344. What subject is to be considered in this conversation ? •345. What are the uncertainties as to the nature of electricity ? 346. How many kinds of electricity are there? 347. What are they called ? ELECTRO-CHEMISTRY. 95 Caroline. Well, I must confess, 1 do not feel nearly so interested in a science in which so much uncertainty prevails as in those which rest upon established principles. I never was fond of elec- tricity, because, however beautiful and curious the phenomena it exhibits may be, the theories, by which they were explained, ap- peared to me so various, so obscure and inadequate, that I always remained dissatisfied.. I was in hopes that the new discoveries in electricity had thrown so great a light on the subject, that every thing respecting it would now have been clearly explained. Mrs. B. That is a point which we are yet far from having attain- ed. But, in spite of the imperfection of our theories, you will be amply repaid by the importance and novelty of the subject. The number of new facts which have already been ascertained, and the immense prospect of discovery which has lately been opened to us, will, I hope, ultimately lead to a perfect elucidation of this branch of natural science ; but at present you must be contented with study- ing the effects, and in some degree explaining the phenomena, with- out aspiring to a precise knowledge of the remote cause of electri- city. You have already obtained some notions of electricity ; in our present conversation, therefore, I shall confine myself lo that part of the science which is of late discovery, aud is more particularly connected with chemistry. It was a trifling and accidental circumstance which first gave rise to this new branch of physical science. Galvani, a professor of nat- ural philosophy at Bologna, being engaged (about 20 years ago) in some experiments on muscular irritability, observed, that when a piece of metal was laid on the nerve of a frog recently dead, whilst the limb supplied by that nerve rested upon some other metal, the limb suddenly moved, on a communication being made betwen the two pieces of metal. Emily. How is this communication made ? Mrs. B. Either by bringing the two metals into contact, or by connecting them by means of a metallic conductor. But without subjecting a frog to any cruel experiments, I can easily make you sensible of this kind of electric action. Here is a piece of zinc, (one of the metals 1 mentioned in the list of elementary bodies)— put it under your tongue, and this piece of silver upon your tongue, and let both the metals project a little beyond the tip of the tongue —very well; now make the projecting parts of the metals touch each other, and you will instantly perceive a peculiar sensation. Emily. Indeed I did ; a singular taste, and I think a degree of heat ; but 1 can hardly describe it. Mrs. B. The action of these two pieces of metal on the tongue is, I believe, precisely similar to that made on the nerve of a frog. I shall not detain you by a detailed account of the theory by which Galvani attempted to explain this fact, as it was soon overturned •348. What is the difference between electricity and Galvanism? 349. From whom did Galvanism receive its name ? 350. What gave rise to the branch of physical science called Galvan- ism? 351. What simple experiment is mentioned, that can be made up on the tongue to illustrate this subject? 86 ELECTRO-CHEMISTRY. by subsequent experiments, which proved that Galvanism (the name this new power had obtained) was nothing more than electricity. fGalvani supposed that the virtue ol this new agent resided in ihe 'nerves of the frog1; but Volta, who prosecuted this subject with much greater success, showed that the phenomena did not depend on the oigans of. the frog, but upon the cicctrical agency of the metais, i of the frc fluence. :nl ogfinc metais, which is.excited hy the moisture of the animaDthe organs of the frog bcingNonly a delicate te=t of the presence of electric in- Caroline. I suppose, then, the saliva of the mouth answers the same purpose as the moisture of a frog, in exciting the electricity of the pieces of silver, and zinc, with which Emily tried the exper- iment on her tongue? Mrs. B. Precisely. It does appear, however, necessary that the fluid used for this purpose should be of animal nature. Water, and acids very much diluted by water, are found to be the most ef- fectual in promuliivr the developcment of electricity in metals; and accordingly the ordinal apparatus which Volta first constructed for this purpose consisted of a pile or succession of pLtes of zinc and copper, each pair of which was connected by pieces of cloth or pa- per impregnated with water; and this instrument, from its original inconvenient structure and limited strength, has gradually arrived at its present state of power and improvement, such as exhibited in the Voltaic battery. In this apparatus, a specimen of which you see before you, the plates of zinc, and copper are soldered together in !>-..-rs. each pair being placed at repulardislan- ces in wooden troughs and the interstices being filled with fluid. Fig. 11. Voltaic Battery. Caroline. Thoagh you wiU not allow us to -^quire info se cause of electricity, may we not ask in what manner the pre- ;. the fluid acts on the metals so as to produce it ? Mrs. B. The action of the fluid on the metals, whether water or acid be used, is entirely of a chemical nature. But whether elec- tricity is excited by this chemical action, or whether it is produced i>y ne contact of the two metals, is a point upon which philosophers do not yet perfectly agree. Ennly. But can the mere contact of two metals, without any in- tei vening fluid, produce electricity ? y ^rs. B. Yes, if they are afterwards separated. It is an establish- •352. How did Galvani account for the moving of the limb on a com- munication being made between the two metals ? ■053. What was the true cause of it ? ■ -354. What metals are used in the production of galvanic action ? 355. Which figure represents a Voltaic battery ? ■ 356 Can galvanism be produced without water ? ELECTRO-CHEMISTRY. 37 ed fact, that when two metals are put in contact, and afterwards separated, that which has the strongest attraction for oxygen ex- hibits signs of positive, the other of negative electricity. Caroline. It seems, then, but reasonable to infer thai the power of the Voltaic battery should arise from the contact of the plates of zinc and copper. Mrs.B. It is upon this principle that Volta and Sir H. Davy explain the phenomena of the pile ; but notwithstanding these two great authorities, many philosophers entertain doubts of the truth of this theory. The chief difficulty which occurs in explaining the phenomena of the Voltaic battery on this principle, is that two such plates show no signs of different slates of electricity whilstin con- tact, but only on being separated after contact. Now, in the Vol- laic battery, those plates that are in contact, always continue so, being soldered together ; and they cannot, therefore, receive a suc- cession of charges. Besides, if we consider the mere disturbance of the balance of electricity by the contact of the plates, as the sole cause of the production of Voltaic electricity, it remains to be ex- plained how this disturbed balance becomes an inexh sustible source of electrical energy, capable of pouring forth a constant and copi- ous supply of electrical fluid, though without any means of replenish- ing itself from other sources. This subject it must beowned, is in- volved in too much obscurity to enable us to speak very decidedly in favor of any theory. But in order to avoid perplexing you with different explanations, I shall confine myself to one which appears to me to be least, encumbered with difficulties, and most likely to accord with truth.* This theory supposes the electricity to be excited by the chemic- al action of the arid on the zinc ; but you are yet such novices in chemistry, that I think it will be necessary to give you some previ- ous explanation of the nature of this action. All metals have a strong attraction for oxygen ; and this element is found in great abundance, both in water and in acids. The ac- tion of the diluted acid on the zinc consists, therefore, in its oxy- gen combining with it, and disssolving its surface. Caroline. In the same manner, I suppose, as we saw an acid dis- solve copper. Mrs. B. Yes ; but in the Voltaic battery, the diluted acid is not strong enough to produce so complete an effect; it acts only on the * This mode of explaining the phenomena of the Voltaic pile is palled the chemical theory of electricity, because it ascribes the cause of these phenomena to certain chemical changes which take place during their appearance. The mode which is here sketched was long since suggested by Dr. Bostock, who has lately, (1818) published " An account of the History and present state of Galvan- ism ;'' which contains a fuller and more complete statement of his opinions and those of other writers on the subject, than any of his former papers. 357. What established fact in galvanic experiments is mentioned ? 358. What two chemists have explained the phenomena of the Vol- taic battery, as proceeding solely from the contact of the two metals i ■ 359. For what have all metals strong attraction ? "50 ELECTRO-CHEMISTRY. surface of the zinc, to which it yields its oxygen, forming upon ft a film or crust, which is a compound of the oxygen and the metal, Emily. Since there is so strong a chemical attraction between oxygen and metals, I suppose they are naturally in different states of electricity. Mrs. B. Yes ; it appears that all metals are united with the pos- itive, and that oxygen is the grand source of the negative electri- city. Caroline. Does not, then, the acid act on the plates of copper, as well as on those of zinc ?* Mrs. B. N'o : for though copper has an affinity for oxygen, it is less strong than that of zinc; and therefore theenergy of the acid is only exerted upon the zinc. It will be best, I believe, in order to render the action of the Vol- taic battery more intelligible, to confine our attention at first to the effect produced on two plates only. (Fig. 12.) If a plate of zinc be placed opposite to one of copper, or Fig. 12. any other metal less attractive of oxygen, and the space Voltaic between them (suppose of half an inch in thickness,) be fil- Battery, led with an acid or any fluid capable of oxydating the zinc, j_ g the oxydated surface will have its capacity for electricity diminished, so that a quantity of electricity will be evolv- ed from that surface. This electricity will be received by the contiguous fluid, by which it will be transmitted to the opposite metallic surface, the copper, which is not ox- ydated, and is therefore disposed to receive it ; so that the copper plate will thus become positive, whilst the zinc plate will be in the negative state. This evolution of electrical fluid, however, will be very limited ; for as these two plates admit of but very little ac-.. cumulation of electricity, and are supposed to have no Communication with other bodies, the action of the acid, and further development of electricity, will be immediately stopped. Emily. This action, I suppose, can no more continue, than that of a common electrical machine, which is not allowed to communi- cate with other bodies ? Mrs. B. Precisely ; the common electrical machine when exci- ted by the friction of the rubber gives out both the positive and negative electricities. (Fig. 13.; The positive, by the rotation of th e glass cylinder, is conveyed into the conductor, whilst the negative goes into the rubber. But unless there is a communication°made between the rubber and the ground, a very inconsiderable quantity * The acid acts upon the copper, but not so strongly as on the zinc. Any two metals, one of which has a stronger attraction for oxygen than the other, will form the galvanic series.—C. 360. What is the grand source of negative electricity ? 361. Why in the Voltaic battery is the energy of the action exerted only upon the zinc ? 362. How would you explain the principle of the Voltaic battervbv Kig. 12 ? J J 363. How would you describe the mode of collecting electricitv in the common electrical machine ? ^ 364. Why must the rubber be connected with the ground? ELECTRO-CHEMISTRY. 89 of electricity can be excited : for the rubber, like the plates of the battery, has too small a capacity to admit of an accumulation of electricity. Unless, therefore, the electricity can pass out of the rubber, it will not continue to go into it, and consequently, no ad- ditional accumulations will take place. Now, as one kind of elec- tricity cannot be gjven out without the other, the developement of the positive electricity is stopped, as well as that of the negative, and the conductor, therefore, cannot receive a succession of charges. FJ"-. 13. Electrical Machine. Fig. 13. A the Cylinder. B the Conductor. R the Rubber. C the Chain. Caroline. But does not the conductor, as well as the rubber, re- quire a communication with the earth, in order to get rid of its electricity? Mrs. B. No; for it is susceptible of receiving and containing a considerable quantity of electricity, as it is much larger than the rubber, and therefore has a greater capacity; and this continued accumulation of electricity in the conductor, is what is called a charge. Emily. But when an electrical machine is furnished with two conductors to receive the two electricities, 1 suppose no communi- cation with the earth is required? Mrs. B. Certainly not, until the two are fully charged : for the two conductors will receive equal quantities of electricity. Caroline. I thought the use of the chain had been to convey the elcctricitvfrom the ground into the machine Mrs. B. That was the idea of Dr. Franklin, who supposed that there was but one kind of electricity, and who by tlie terms posi- tive and negative (which he Gral introduced,) meant onlv different quantities of the same kind of electricity.* The chain was in that * The idea of Dr. Franklin was, that the positive state consisted 3S5 What is called a charge, in the use of the common electrical machine ? 366. What was Dr. Franklin's opinion concerning electricity ? 90 ELECTRO-CHEMISTRY. base suoposed to convey electricity from the ground through the rubber into (he conductor. But as we have adopted the hypothesis of two electricities we must consider the chain as a vehicle to con- duct the negative electricity into the earth. Emily. And are both kinds produced whenever electricity is ex- Mrs. B. Yes, invariably. If you rub a tube of glass with a wool- len cloth, the glass becomes positive, and the cloth negative.11 If, on the contrarv, you excite a stick of sealing- wax by the same means, it is the rubber which becomes positive, and the wax negative. But with regard to the Voltaic battery, in order that the acid may act freely on the zinc, and the two electricities be given out without interruption, some method must be devised, by which the plates may part with their electricities as fast as they receive them. Can you think of any means by which this might be effected ? Emily. Would not two chains or wires, suspended from either place to the ground, conduct the electricities into the earth, and thus answer the purpose ? Mrs. B. It would answer the purpose of carrying off the electri- city, I admit; but recollect, that though it is necessary to find a vent for the electricity, yet we must not lose it, since it is the power we are endeavouring to obtain. Instead, therefore, of conducting it into the ground, let us make the wires from either plate meefi; the two electricities will thus be brought together, and will combine and neutralize each other; and as long as this communication con- tinues, the two plates having a vent for their respective electrici- ties, the action of the acid will go on freely and uninterruptedly. Emily. That is very clear, so far as two plates only are concerned; but I cannot say I understand how the energy of the succession of plates, or rather pairs of plates, of which the Galvanic trough is composed, is propagated and accumulated throughout a battery. in the presence, or accumulation of the electric fluid, and that the negative was merely its absence or diminution. Hence the terms used by him to indicate these states were positive and negative. In this chapter, Mrs. B. has used these terms of the American Philo- sopher improperly, fovplus and minus were never meant to signify two sorts of electricity, but only it presence or absence. W here au- thors have adopted Dufay's theory of two electricities, they have used the term vitreous and resinous.—C. * Most probably, because the glass takes the electric fluid from the cloth. Indeed, we conceive there is about the same reason for believing that the negative stale is the absence of the electric fluid, as there is for believing that cold is the absence of heat.—('. 367. What is the use of the chain in the common electrical machine ? 368. Are negative and positive electricity always produced, when electricity is excited ? 369. What is necessary in the Voltaic battery, that the two electri- cities be given out without interruption ? 370. In what manner do two pieces of wire produce this effect ? ELECTRO-CHEMl STRY. 91 Voltaic Battery. 45 G Mrs. B. In order to show you how the intensity of the electrici- ty is increased by increasing the number of plates, we will exam- ine the action of four plates ; if you understand these, you will readily comprehend that of any number whatever. t r Fie 14 In this figure you will observe that the two central plates are united ; they are soldered together, (as we observed in de- scribing the Voltaic trough,) so as to form but one plate, which offers two different surfaces ; the one of copper, the other of zinc. Now you recollect, that, in explaining the action of two plates, we supposed that a quantity of electricity was evolved from the surface of the first zinc plate, in consequence of the action of the acid, and- was conveyed by the interposed fluid to the copper plate No. 2, which thus became positive. This copper plate communicates its electricity to the contiguous zinc plate, No. 3, in which, conse- quently, some accumulation of electricity takes place. When, therefore, the fluid in the next cell acts upon the zinc plate, elec- tricity is extricated from it in larger quantity, and in a more con- ce«drated form than before. This concentrated electricity is again conveyed by the fluid to the next pair of the plates, No. 4 and 5, when it is further increased by the action of the fluid in the third cell, and so on, to any number of plates, of which the battery may consist, so that the electrical energy will continue to accumulate in proportion to the number of double plates, the first zinc plate of the series being the most negative, and the last copper plate the most positive. Caroline. But does the battery become more and more strongly charged merely by being allowed to stand undisturbed? Mrs. B. No : for the action will soon stop, as was explained be- fore, unless a vent be given to the accumulated electricities. This is easily done, however, by establishing a communication by means of the wires (See Fig. II,) between the two ends of the battery ; these being brought into contact, the two electricities meet and neutralize each other, producing the shock, and other effects of electricity : and the action goes on with renewed energy, being no longer obstructed by the accumulation of the two electricities which impeded its progress. Emily. Is it the union of the two electricities which produces the electric spark ? Mrs. B. Yes ; and it is, I believe, this circumstance which gave rise to Sir FI. Davy's opinion, that caloric may be a compound of the two electricities. Caroline. Yet, surely, caloric is very different from the electoral spark. ? .Mrs. B. The difference may consist, probably, only in intensity : 371. How would you explain figure 14 ? 372. How would you explain figure 14, which represents the Volta- ic battery, so as to produce the electric spark ? - 373. What does Sir H. Davy suppose caloric to be ? D+1+�05+.+/./B 92 ELECTRO-CHEMISTRY for the heat of the electric spark is considerably more intense though confined to a very minute spot, than any heat we can pro- duce b)' other means. Emily. Is it quite certain that the electricity of the Voltaic batte- ry is precisely of the same nature as that of the common electrical machine ? Mrs. B, Undoubtedly ; the shock given to the human body, the spark, the circumstance of the same substances winch are conduct- ors of the one, being also conductors of the other, and of those bod- ies, such as glass and sealing wax, which are non-conductors of the one, being also non-conductors of the other, are striking proofs of it. Besides, Sir H. Davy has shown, in his Lectures, that a Leyden jar, and a common electric battery, can be charged with electricity obtained from a Voltaic battery, the effect produced being perfectly similar to that obtained by a common machine. Dr. Wollaston has likewise proved, (hat similar chemical decom. positions are ethcled by the electric machine and by the Voltaic battery ; and has made other experiments which render it highly probable, that the origin of both electricities is essentially the same, as they show that the rubber of the common electrical machine, like tnezinc in the Vo'tiic battery, produces the two electricities, by combining with oxygen. Caroline. But I do not see whence the rubber obtains oxygen, for there is neither acid nor waterused in Ihe comm-n machine; aaxl I always understood that the eleencity was exciied by (he friction. . Mrs.B. It appears that py friction the rubber obtains oxygen from the atmosphere,!: which is partly composed of that element. The oxygen combines with the amalgam of the rubber, which is of a metallic nature, much in the same way as the oxygen of the acid combines with the zinc in the Voltaic battery, and'it is thus that the two electricities are disengaged Caroline. But if the electricities of both machines are similar, why not use the common machine for chemical decompositions? Mrs. B. Though its effects are similar to those of the Voltaic bat- tery, they are incomparably weaker. Indeed Dr. Wollaston, in using it for chemical decompositions, was obliged to act upon the most minute quantities of matter, and though the result was satis- factory in proving the similarity of its effect to those of the Voltaic battery, these effects were too small in extent to be in any consid- erable degree applicable to chemical decompositions. Ctrolinr. How terrible, then, a shock must be from a Voltaic battery, since it is so much more powerful than an electrical ma- chine. Mrs. B. It is not nearly so formidable as you think ; at least it is -374. How does the degree of heat in the electric spark compare with that produced by other means? 375. What proves that the electricity in the Voltaic battery is of the same nature as that of the common electrical machine ? . 376- "°"' 'I0 the rubber of ^e common electrical machine and the zinc in the Voltac battery produce the same eici-icitics ?. •377. How do. -s the rubber obtain oxygen, in the use of'the common electrical machine? , 3*8. Why is not the common electrical machine used for chemipal decompositions? cnemicai EL ECTRO-CHEMISTR Y. 93 by no means proportional to the chemical effect. The great supe- riority of the Voltaic battery consists in the large quantity of elec- tricity that passes :. but in regard to the rapidity or intensity of the charge, it is greatly surpassed by the common electrical machine. It would seem that the shock or sensation depends chiefly upon the intensity ; whilst, on the contrary, for chemical purposes, it is quantity which is required. In the Voltaic battery, the electricity, though copious, is so weak as not to be able to force its way through the fluid which separates the plates, whilst that of a common ma- chine will pass through any space of water. Caroline. Would it not be possible to increase the intensity of the Voltaic battery till it should equal that of the common machine ? Mrs. B. It can actually be increased till it imitates a weak elec- trical machine, so as to produce a visible spark when accumulated in a Leyden jar. But it can never be raised sufficiently to pass through any considerable extent of air, because of the ready com- munication through the fluids employed. By increasing the number of plates of a battery, you increase its intensity, whilst, by enlarging the dimensions of the plates, you aug- ment its quantity—and as the superiority of the battery over ihe common machine consists entirely in the quantity of electricity pro- duced, it was at first supposed that it was the size, rather than the number of plates that was essential to the augmentation of power. It was, however, found upon trial, that the quantity of electricity pro- duced by the Voltaic battery, even when of a very moderate size, was sufficiently copious, and that the chief advantage in this appa- ratus was obtained by increasing the intensity, which, however, still falls very far short of that of the common machine. I should not omit to mention, that a very splendid, and, at the same time, most powerful battery, was a few years ago, constructed under the direction of Sir H. Davy, which he repeatedly exhibited in his course of electro-chemical lectures. It consists of two thou- sand double plates of zinc and copper, of six square inches in di- mensions, arranged in troughs of Wedgwood-ware, each of which contains twenty of these plates. The troughs are furnished with a contrivance for lifting the plates out of them in a very convenient and expeditious manner.* *A model of this mode of construction is exhibited in (Fig. 15.) Note. In consequence of the discoveries of •404. What causes negative electricity ? 3t<)5] How can combustion separate them ? 39^' How is caloric produced in combustion ? 398.* What is 'the theory of combustion proposed by Berselius.? #8 OXYGEN AND NlTROGEft. ed ; and the two electricities escaping, that is to say, the negative from the oxygen, the positive from the burning body, unite and pro- duce caloric. • Emily. And what becomes of this caloric? Mrs.B. We shall make this piece of dry wood attract oxygen from the atmosphere, and you will see what becomes of the caloric. Caroline. You are joking, Mrs. B.: you do not mean to decom- pose the atmosphere with a piece of dry stick? Mrs. B. Not the whole body of the atmosphere, certainly ; but if we can make this piece of wood attract any quantity of oxygen from it, a proportional quantity of atmospherical air will be decom- posed. Caroline. If wood has so strong an attraction for oxygen, why does it not decompose the atmosphere spontaneously ? Mrs. B. It is found by experience, than an elevation of tempera- ture is require^ for the commencement of the union of the oxygen and the wood. / This elevarfon of temperature was formerly thought to be neces- sary, in order to diminish the cohesive attraction of Ihe wood, and enable the oxygen to penetrate and combine with it more readily. But since the introduction of the new theory of chemical combina- tion, another cause has been assigned, and it is now supposed that the high temperature, by exalting the electrical energies of bodies, and consequently their force of attraction, facilitates their combi- nation. / Emily. If it is true that caloric is composed of the two electrici- ties, an elevation of temperature must necessarily augment the electric energies of bodies. Mrs. B. I doubt whether that would be a necessary consequence; for admitting this composition of caloric, it is only by being decom- posed that electricity can be produced. Sir H. Davy, however, in his numerous experiments, has found it to be an almost invariable rule, that the electrical energies of bodies are increased by eleva- tion of temperature. What means, then, shall we employ to raise the temperature of the wood, so as to enable it to attract oxygen from the atmosphere ? Caroline. Holding it near the fire, I should think, would answer the purpose. Mrs. B. It may, provided you hold it sufficiently close to the fire ; for a very considerable elevation of temperature is required. Caroline. It has actually taken fire ; and yet I did not let it touch the coals, but I held it so very close that I suppose it caught fire merely from the intensity of the heat. ' Mrs- B- Or you might say, in other words, that the caloric which the consequence./ This theory is not well proved, nor ffcnerallv adopted.—C. .• * J 399. If wood has a strong attraction for oxygen, why does it compose the air spontaneously ? 400. Why is it necessary to heat a combustible substance U l Durn ? c |trog ■401. Are the electrical energies of bodies increased by ele^ temperature ? J b . 4)2. Why will a piece of wood when held near the fire, tL' though it does not touch the coals? ot de- e it apjn of j"'n, al- OXYGEN AND NITROGEN; 99 the wood imbibed, so much elevated its temperature, and exalted its electic energy, as to enable it to attract oxygen very rapidly from the atmosphere. Emily. Does the wood absorb oxygen while it is burning ? Mrs. B. Yes ; and the heat and light are produced by the union of the two electricities which are set at liberty, in consequence of the oxygen combining with the wood. Caroline. You astonish me !■ the heat of a burning body proceeds then as much from the atmosphere as from the body itself? Mrs. B. It was supposed that the caloric given out during com- bustion, proceeded entirely, or nearly so, from the decomposition of the oxygen gas; but according to Sir H. Davy's new view of the subject, both the oxygen gas^and the combustible body concur in supplying the heat and light, by the union of their opposite elec- tricities. Emily. 1 have not yet met with any thing in chemistry that has, surprised or delighted me so much as this explanation of combus- tion. I was at first wondering what connexion there could be be- tween the-affinity of a body for oxygen and its combustibility; but I think I understand it now perfectly. Mrs. B. Combustion, then, you see, is nothing more than the rapid combination of a body with oxygen,)atteuded by the disen- gagement of light and heat. Emily. But are there no combustible bodies whose attraction for oxygen is so strong, that they will combine with it, without the ap- plication of heat ? Caroline. That cannot be ; otherwise we should see bodies burn- ing spontaneously. Mrs. B. But there are some instances of this kind, such as'phos- phorus, potassium), and some compound bodies, which I shall here-. after make you acquainted with. These bodies, however, are pre- pared by art, for in general, all the combustions that could occur spontaneously, at the temperature of the atmosphere, have already taken place; therefore new combustions cannot happen without the temperature of the body being raised. Some bodies, however, will burn at a much lower temperature than others. Caroline. But the common way of burning a body is not merely to approach it to one already on fire, but rather to put the one in actual contact with the other, as when I burn this piece of paper by holding it in the flame of the fire. Mrs. B. The closer it is in contact with the source of caloric, the sooner will its temperature be raised to the degree necessary for it to burn. If you hold it near the fire, the same effect will be produced ; but more time will be required, as you found to be the case with the piece of stick. Emily. But why is it not necessary to continue applying caloric throughout the process of combustion, in order to keep up the elec- tric energy of the wood, which is required to enable it to combine with the oxygen ? '403. When a substance burns, what does it absorb ? 404. How are heat and light produced ? 405. What is oombustion ? 406. Why do not bodies burn spontaneously ? *407. What are instances of combustion without a previous increase of temperature ? 100 OXYGEN AND NITROGEN. Mrs. B. The caloric which is gradually produced by the two1 electricities during combustion keeps up the temperature of the burning body ; so that when once combustion has begun, no-further application of caloric is required. Caroline. Since I have learnt this wonderful theory of combus- tion, I cannot help gazing at the fire; and I can scarcely conceive that the heat and light, which I always supposed to proceed entire- ly from the coals, are really produced as much by tbe atmosphere. Emily. When you blow the fire, you increase the combustion, I suppose, by supplying the coals with a greater quantity of oxygen gas. Mrs.B. Certainly; but of course no blowing will produce com-■, bustiow, unless the temperature of the coals be first raised. A sin- ;,' gle spark, however, is sometimes sufficient to produce that effect;::, ' ; for, as I said before, when once combustion has commenced, the-jj.-■' the atmosphere, and obtaining the nitrogen gas in its simple j state; but how do you secure this gas, and prevent it from mixing ■ Fig. 16. with the rest of the atmosphere? Mrst B. It h necessary for this purpose to burn the body within a close vessel, which is easily done.—We shall introduce a small light- ed taper under this glass receiver, which stands in a basin over water, to prevent all communi- cation with the external air.* Caroline. How dim the light burns already .' It is now extinguished* Mrs. B. Can you tell us why it is extinguish- ed ? r., Caroline. Let me consider.—-The receiver was full of atmospherical air; the taper, in Combustion of a» taper * under a receiver. * To make a taper, melt some bees wax, and dip into it a strip of cotton cloth about an inch wide, and before it is cold twist it pretty 408. Why is it not necessary to continue applying caloric through- out the process of combustion, in order to keep up the electric energy of the wood, which is required to enable it to combine with the oxygen ? -409. Why does blowing the fire increase combustion ? 410. Why will fire be sometimes extinguished before all tbe wood is Consumed ? • 411. What three things are necessary to produce combustion ? 412. Why will a burning taper placed under a glass receiver, as in figure 16, soon become extinguished ? OXYGEN AND NITROGEN, 101 burning within it, must have combined with the oxygen contained in that air, and the caloric that was disengaged produced the light of the taper. But when the whole of the oxygen was absorbed, the whole of its electricity was disengaged ; consequently no more ca- loric could be produced^ the taper ceased to burn, and the flame was extinguished. Mrs. B. Your explanation is perfectly correct. Emily. The two constituents of the oxygen gas being thus dis- posed of, what remains under the receiver must be pure nitrogen gas. Mrs. B. There are some circumstances which prevent thenitro- ' ' gen gas thus obtained, from being perfectly pure ; but we may easily try whether the oxygen has disappeared, by putting another . lighted taper under it.—You see hpw instantaneously the flame is ^extinguished, for want of oxygen t6 supply the negative electricity ; required for the formation of caloric ; and were you to put an ani- ' mal under the receiver it would be immediately suffocated. But ■, that is an experiment which I do not think your curiosity will tempt ^fou to try. . Emily. Certainly not. But look, Mrs. B., the receiver is full of a thick white smoke. Is that nitrogen gas ? ♦ Mrs. B. No, my dear; nitrogen gas is perfectly transparent and invisible, like common air. This cloudiness proceeds from a varir ety of exhalations, which arise from the burning taper, the nature of which you cannot yet understand. Caroline. The water in the receiver has now risen a little above ijs level in the basin. What is the reason of this ? Mrs. B. With a moment's reflection, I dare say you would have explained it yourself. The water rises in consequence of the oxy- gen gas within it having been destroyed or rather decomposed, by the combustion of the taper. Caroline. Then why did not the water rise immediately when the oxygen gas was destroyed ? Mrs. B. Because the heat of the taper, whilst burning, occasion- ed a dilatation of the air in the vessel, and a production of carbonic acid, which at first counteracted this effect. Another means of decomposing the atmosphere is the oxygenation of certain metals. This process is very analogous to combustion ; it is, indeed, only a more general term to express the combination of a bpdy with oxvgen. Caroline. In what respect, then, does it differ from combustion? Mrs. B. The combination ofox3'gen in combustion is always ac- hard. Cotton wick does better than the cloth. A quart tumbler makes a good receiver. Two or three inches of (he taper can be fastened to a piece of wire, bent so that it will stand up. Thus the experiment is easily made.—C 413. How long will it burn thus placed under a receiver? 414. What woulr! be the consequence if an animal were placed un- der the receiver ? Why ? 415. What is another method of decomposing the air ? 416. In what respect does oxygenation differ from the decomposi- tion of air by combustion ? 102 OXYGEN AND NITROGEN. companied by a disengagement of light and heat; whilst this cir- cumstance is not a necessary consequence of simple oxygenation. Caroline. But how can a body absorb oxygen without the com- bination of the two electricities which produce caloric ? Mrs. B. Oxygen does not always present itself in a gaseous form ; it is a constituent part of a vast number of bodies, both solid and li- quid, in which it exists in a state of greater density than in the at- mosphere-; and from these bodies it may be obtained without much disengagement of caloric. It may likewise, in some cases, be ab- sorbed from the atmosphere without any sensible production of light and heat; for, if the process be slow the caloric is disengaged in such small quantities and so gradually, that it is not capable of pro- ducing either light or heat. In this case the absorption of oxygen is called oxygenation or oxydation, instead of combustion, as the pro- duction of sensible light and heat is essential to the latter. Emily. I wonder that metals can unite with oxygen ; for, as they are so dense, their attraction of aggregation must be very great; and I should have thought that oxygen could never have penetra- ted such bodies. Mrs. B. Their strong attraction for oxygen counterbalances this obstacle. Most metals, however, require to be made red hot, be- fore they are capable of attracting oxygen in any considerable quantity. By this combination they lose most of their metallic properties, and fall into a kind of powder, formerly called calx, but now much more properly termed an oxyd ; thus we have oxyd of lead, oxyd,of iron, &c* Emilu. And in the Voltaic battery, it is, I suppose, an oxyd of zinc, that is formed by the union of the oxygen with that metais Mrs. B. Yes, it is. Caroline. The word oxyd, then, simply means a metal combined with oxygen. Mrs. B. Yes; but the term is not confined to metals, though chiefly applied to (hem. Any body whatever, that has combined with a certain quantity of oxygen, either by means of oxydation, or combustion, is called an oxyd, and is said to be oxydated or oxy- genated. Emily. Metals, when converted into oxyds, become, I suppose, negative. Mrs. B. Not in general; because in most oxyds tbe positive en- ergy of the metal, more than counterbalances the native energy of the oxygen with which it combines. This black powder is an oxyd of manganese, a metal which has so * Red Lead and Rust of Iron—C. 417. Does oxygen always exist in a gaseous state ? ydttfonr116" 'S the abs°rption of oxy§en called oxygenation, or ox- JvrtSZ^ °XJf?n Penetrate metals' sinc* ^eir attraction of aggregation is so great ? ' 41°,' »??at is the chernical name for red lead and rust of iron ? ' 421. \\ hat is an oxyd ? ' ' notfegative^8 *" * C°mbination ,)f metaIs and °^gen, why are they OXYGEN AND NITROGEN. 103 strong an affinity for oxygen, that it attracts that substance from the atmosphere at any known temperature, it is therefore never found in its metallic form, but always in that of an oxyd, in which state, you see it has very little of the appearance of a metal. It is now heavier than it was before oxydation, in consequence of the ad- ditional weight of the oxygen, with which it has combined. Caroline. I am very ghd to hear that; for I confess I could not help having some doubts whether oxygen was really a substance, as it is not to be obtained in a simple and palpable state; but its weight is, I think, a decisive proof of its being a real body. Mrs. B. It is easy to estimate its weight by separating it from the manganese, and find how much the latter has lost} Emily. But if you can take the oxygen from the metal, shall we not have it in its palpable simple state ? Mrs. B. No; for I can only separate the oxygen from the man- ganese by presenting lo it some other body, for which it has a great- er affinity than for the manganese. Caloric affording the two elec- tricities is decomposed, and one of them uniting with the oxygen, restores it to the aeriform state. Emily. But you said just now, that manganese would attract ox- ygen from the atmosphere in which it is combined with the nega- tive electricity; how, therefore, can the oxygen have a superior affinity for that electricity, since it abandons it to combine with the manganese ? Mrs. B- 1 give you credit for this objection, Emily; and the on- ly answer I can make to it is, that the mutual affinities of metals for oxygen, and of oxygen for electricity, vary at different tempera- tures; a certain degree of heat will, therefore, dispose a metal to combine with oxygen, whilst on the contrary, the former will be compelled to part with the latter, when the temperature is further increased. 1 have put some oxyd of manganese into a retort,* which is an earthen vessel with a bent neck, such as you see here. (See Fig. 17, No. I.) The retort containing the manganese you can- not see, as 1 have enclosed it in this furnace, where it is now red-hot. But, in order to make you sensible of the escape of the gas, which is itself invisible, I have connected the neck of (he retort with this bent tube, the extremity of which is immersed in a vessel of water. (See Fig. 17, No. 2.) Do you see the bubbles of air rise through the Caroline. Perfectly. This, then, is pure oxygen gas? What a pity it should be lost. Could you not preserve it? * To collect oxygen gas, take an oil flask, and having fitted a cork to it, pierce the cork so as to admit a bent glass tube; (the bending is done over a spirit lamp.) Put into the flask some black oxyd of manganese, and pour on sulphuric acid enough to make it into a paste. Then put in the cork and tube.and having connected the other end of the tube, with a receiver, in the tube of water, ap- ply the heat of an Argand lamp.—C. 423. How can it be determined that oxygen has weight? 424. How can oxygen be separated from manganese after having been oxydated ? 425. How may pure oxygen be collected.' 426. How would you describe the experiment represented in fig- ure J 7> 104 OXYGEN AND NITROGEN. Fig. 17. No. 1. A. retort on a stand.—No. 2. A, Furnace. B, Earthen Retort in the fur- nace. C, Water Bath. D, Receiver. E E, Tube conveying the gas from the Retort through the water into the Receiver. F E F, Shelf perforated on which the Receiv- er stands. Mrs. B. We shall collect it in this receiver. For this purpose, you observe, I first fill it with water, in order to exclude the at- mospherical air; and then place it over (he bubbles which issue from the retort, so as to make them rise through the water to the upper part of the receiver. Emily. The bubbles of oxygen gas rise, 1 suppose, from their specific levity ? Mrs.B. Yes; for though oxygen forms rather a heavy gas, it is light compared to water. You see how it gradually displaces the water from the receiver. It is now full of gas, and I may leave it inverted in water on this shelf, where I can keep the gas as long as I choose, for future experiments. This apparatus (which is indis- pensable in all experiments in which gases are concerned) is called a water-bath.* Caroline. It is a very clever contrivance, indeed ; equally simple and useful. How convenient the shelf is for the receiver to rest upon under water, and the holes in it for the gas to pass into the re- ceiver? 1 long to make some experiments with this apparatus. Mrs. B. 1 shall try your skill that way, when you have a little more experience. I am now going to show 3'ou an experiment, which proves, in a very striking manner, how essential oxygen is to combustion. ' You will see that iron itself will burn in this gas, in the most rapid and brilliant manner. * A common large sized wash-tub, with aboard 4 or 5 inches wide fixed through the middle, and about 6 inches from the top, and filled with water, will answer very well for a great variety of ex- periments on the gases.—C. ♦-427. How does the weight of oxygen gas compare with that of wa- ter ? 428. How may the great tendency of oxygen to produce combus- tion, be proved ? OXYGEN AND NITROGEN. 105 Caroline. Really ! I did not know that it was possible to burn iron. Emily. Iron is a simple body, and yo ; know, Caroline, that all simple bodies are naturally positive, and therefore must have an af- finity for oxygen. Mrs. B. Iron will, however, not burn in atmospherical air with- out a very great elevation of temperature ; but it is eminently com- bustible in pure oxygen gas ; and what will surprise you still more, it can be set on fire without any considerable rise of temperature. You see this spiral iron wire.*—1 fasten it at one end to this cork, which is made to fill an opening at the top of the glass receiver. Fig. 18. Emily. I see this opening in the receiver; but it is carefully closed by a ground glass stopper. Mrs. B That is in order to prevent the gas from escaping ; but I shall take out the stop- per, and put in the cork to which the wire hangs. Now I mean to burn this wire in the oxygen gas, but I must fix a small piece of lighted tinder to the extremity of it, in order to give the first impulse to combustion ; for, however powerful oxygen is in promoting combustion, vou must recollect that it cannot , , . -. r . P Combustion of iron wire la take place without some elevation ot tempera- oxygen ga«. ture. I shall now introduce the wire into the receiver, by quickly changing the stoppers. Caroline. Is there no danger of the gas escaping while you change the stoppers ? Mrs. B. Oxygen gas is a little heavier than atmospherical air, therefore it will not mix with it very rapidly ; and if 1 do not leave the opening uncovered, we shall not lose any------- Caroline. Oh, what a brilliant and beautiful flame ! Emily. It is white and dazzling as the sun !—Now a piece of the melted wire drops to the bottom ; I fear it is extinguished : but no, it burns again as bright as ever. Mrs. B. It will burn till the wire is entirely consumed, provided the oxygen is not first expended ; for you know it can burn only while there is oxygen to combine with it. Caroline. I never saw a more beautiful light. My eyes can hardly bear it ! How astonishing to think that all this caloric was contained in the small quantity of gas and iron that was enclosed in the receiver ; and without producing any visible heat! Emily. How wonderfully quick combustion goes on in pureoxy- * The combustion of steel, as a watch spring, is much more vivid than that of iron. This affords a very beautiful experiment, and is easily made after the oxygen is collected. A bottle of white glass of a quart capacity does well as a receiver. An inch of water at tbe bottom will prevent its breaking.—C. 429. Why have all simple bodies an affinity for oxygen ? 430. Will iron burn in oxygen gas without an elevation of tempera- ture ? . 431. Which is lightest, oxygen gas or atmospherical air ? 432. How long will a piece of iron burn in oxygen gas? 106 OXYGEN AND NITROGEN. gen gas ! But pray, are these drops of burnt iron as heavy as the' wire was before ? Mrs. B. They are even heavier J for the iron in burning, has ac- quired exactly the weight of the oxygen which has disappeared, and is now combined with it. It has become an oxyd of iron. Caroline. I do not know what you mean by saying that the oxy- gen has disappeared, Mrs. B. for it was always invisible. Mrs. B. True, my dear ; the expression was incorrect. But though you could not see the oxygen gas, I believe you had no doubt of its presence, as tbe effect it produced on the wire was sufficiently evident. Caroline. Yes, indeed ; yet you know it was the caloric, and not the oxygen gas itself, that dazzled us so much. Mrs. B. You are not quite correct in your turn, in saying the caloric dazzled you; for caloric is invisible; it affects only the sense of feeling ; itywas the light which dazzled/you. Caroline. True; but light and caloric are such constant compan- ions, that it is difficult to separate them, even in idea. Mrs. B. The easier it is to confound them, the more careful yon should be in making the distinction. Caroline. But why has the water now risen and filled part of the receiver ? Mrs. B. Indeed, Caroline, I did not suppose you would have ask- ed such a question ! I dare say, Emily, you can answer it. Emily. Let me reflect . . . The oxygen has combined with the wire ; the caloric has escaped ; consequently nothing can remain in the receiver, and the water will rise to fill the vacuum. Caroline. I wonder that I did not think of that. I wish that we had weighed the wire and the oxygen gas before the combustion ;; we might then have found whether the weight of the oxyd was equal to that of both. Mrs. B. You might try the experiment if you particularly wish- ed it ; but I can assure you that if accurately performed, it never fails to show that the additional weight of the oxyd is precisely equal to that of the oxygen absorbed, whether the process has been a re- al combustion or a simple oxygenation. Caroline. But this cannot be the case with all combustions in general; for when any substance is burnt in the common air, so far from increasing in weight, it is evidently diminished, and sometimes entirely consumed. Mrs. B. But what do you mean by the expreseinnconswme charcoal, and metals, when heated red hotA will attract the oxygen from water, in the same manner as they will from the atmosphere. Caroline. Hydrogen, 1 see, is like nitrogen, a poor dependant friend of oxygen, which is continually forsaken for greater favorites. Mrs. B. The connection, or friendship, as you choose to call it, is much more intimate between oxygen and hydrogen, in the state of water, than between oxygen and nitrogen, in the atmosphere ; for, in the first case^ there is a chemical union and condensation of the two substances ; in the latter, they are simply mixed together in their gaseous stated You will find, however, that in some cases, nitrogen is quite as intimately connected with oxygen, as hydrogen is. But this is foreign to our present subject. Emily. Water, then, is an oxyd, though the atmospherical air is not. Mrs. B. It is not commonly called an oxyd, though, according to our definition, it may, no doubt, be referred to that class of bodies. Caroline. I should like extremely to see water decomposed. Mrs. B. I can gratify your curiosity by a much more easy pro- cess than the oxydation of charcoal or metals ; the decomposition of water by these latter means takes up a great deal of time, and is attended with much trouble; for it is necessary that the charcoal or metal should be made red hot in a furnace, that the water should pass over them in a state of vapour, that the gas formed should be collected over the water bath, &c. In short, it is a very complica- ted operation. But the same effect may be produced with the greatest facility, by tbe action of the Voltaic battery, which this will give me an opportunity of exhibiting. Caroline. 1 am very glad of that, for I longed to see the power of this apparatus in decomposing bodies. Mrs. B. For this purpose, I fill this piece of glass tube with wa- Fig. 18. Apparatus for the decomposition of water by the Voltaic1 Battery. ter, and cork it up at both ends; through one of the corks I intro- duce that wire of the battery, which conveys the positive elec- tricity ; and the 455. What are the means of decomposing water? 456. What is the difference between the union of oxygen and nitro- gen, and the union of oxygen and hydrogen? 457. May water be considered an oxyd ? 458. What is the inconvenience of decomposing water by the oxy- dation of charcoal or metals? 459. How may water be decomposed by the use of the Voltaic bat-= tery ? 112 HYDROGEN. wire which conveys the negative electricity is made lo pass through the other cork, so that the two wires approach each other suffi- ciently near to give out their respective electricities. Caroline. It does not appear to me that you approach the wires so near as you did when you made the battery act by itself. Mrs. B. ■'! Water being a better conductor of electricity than air, the two wires will act on each other at a greater distance in the for- mer, than in the latter case. Emily. Now the electrical effect appears ; I see small bubbles of air emitted from each wire. Mrs. B. Each wire decomposes the water ; the positive by com- bining with its oxygen, which is negative ; the negative by com- bining with its hydrogen, which is positive. Caroline. That is wonderfully curious ! but what are the small bubbles of air ? Mrs. B. Those that appear to proceed from the positive wire, are the result of the decomposition of the water, by that wire. That is to say, the positive electricity having combined with some of the oxygen of the water, the particles of hydrogen which were combin- ed with that portion of oxygen are set at liberty, and appear in the form of small bubbles of gas or air. Emily. And I suppose the negative fluid, having in the same manner combined with some of the hydrogen of the water, the par- ticles of oxygen that were combined with it are set free, and emit- ted in a gaseous form. Mrs. B. Precisely so. But I should not forget to observe, that the wires used in this experiment are made,of platina, a metal which is not capable of combining with oxygen? for otherwise the wire would combine with the oxygen, and the'hydrogen alone would be disengaged. Caroline. But could not water be decomposed without the elec- tric circle being completed? If, for instance, you immersed only the positive wire in the water, would it not combine with the oxygen, and the hydrogen gas be given out? Mrs.B. No; for as you may recollect, the battery cannot act unless the circle be completed; since the positive wire will not give' out its electricity, unless attracted by that of the negative wire. Caroline. I understand it now. But look, Mrs. B., the decompo- sition of the water which has been going on for some time, doesnot sensibly diminish its quantity—what is the reason of that? Mrs. B. Because the quantity decomposed is so extremely small. If you compare the density of water with that of the gases into which it is resolved, you must be aware that a single drop of water is sufficient lo produce thousands of such small bubbles as those you now perceive. Caroline. But in this experiment, we obtain the oxygen and hy- drogen gases mixed together. Is there any means of procuring. the two gases separately ? Mrs. B. They can be collected separately with great ease by •460. Which is the best conductor of electricity, water or air ? 461. What remarkable property has platina ? 462. Why cannot water be decomposed unless the electric circle is completed ? HYDROGEN. 113 modifying a little the experiment. Thus, if instead of one tube, we employ two, as you see here (c, d.) (Fig. 19,) both tubes being clos- Fig. 19- ed at one end, and open at the other; and if after filling these tubes with water, we place them standing in a glass of water(e) with their open end downwards, you will see that the moment we connect the wires (a, b,) which proceed upwards from the interior of each tube, the one with one end of the battery, and the other with the other end, the waterin the tubes will be decomposed ; hydrogen will be given out round the wire in the tube connected with the positive end of the battery, and oxy- gen in (he other, and these gases will be Apparatus for decomposing wa-evoIved exactly in the proportions which ter bwVoltaic Eicctricityfendob-I have before mentioned, namely, two tainiijg the gases separate measures of hydrogen for one of oxygen. We shall now begin the experiment, but it will be some time be- fore any sensible quantity of the gases can be collected. Emily. The decomposition of water in this way, slow as it is, is certainly very wonderful; but I confess that I should be still more gratified, if you could show it us on a larger scale, and by a quicker process. I am sorry that the decomposition of water by charcoal or metals is attended with so much incovenience. Mrs. B. Water may be decomposed by means of metals without any difficulty ; but for this purpose the intervention of an acid is re- quired. Thus, if we add some sulphuric acid (a substance with the nature of which you are not yet acquainted) to the water which the metal is to;decompose, (The acid enables the metal to combine with the oxygen of the water so readilv and abundantly, that no heat is required tohasten the process. Of this I am going to show you an instance. 1 put into (his bottle the water that is to be decomposed, the metal that is to effect that decomposition by combining with the oxygen, and the acid which is to facilitate the combination of tbe metal and the oxygen. You will see with what violence these will act on each other.* * To obtain hydrogen, fit a cork air tight to an oil flask, and pierce it with a burning iron, to admit a tube. The tube may be of glass, lead, or tin, bent to a convenient shanc, and put into the opening made by the hot iron. Pour into the fla'k about a gillof water, and drop into it about an ounce of zinc, granulated by melting, and pouring it into cold water. Then pour in half ah ounce by measure ofsulnrmric acid, and immediately put the cork into its place, and plunge the other end of the tube under a receiver, or large tumbler, filled wi(h water, and inverted in the water bath. The flask grows hot and the gas begins to rise, the instant the acid is poured in; a place therefore must previouslv be prepared to set it; and if nothing better is at hand, a bowl, with a cloth in it. to prevent breaking the flask, and set at a convenient height will do very well.—C. 463. How can water be decomposed so as to procure the two gases separate ? 464. How may water be decomposed by means of iron filings? 10* 114 HYDROGEM. Caroline. But what metal is it that you employ for this purpose? ' Mrs. B. It is iron ; and it is used in the stale of filings, as these „ present a greater surface \o the acid than a solid piece of metal, ' For as it is the surface of tflie metal which is acted upon by the acid, and is disposed to receive the oxygen produced by the decomposi- tion of the water, it necessarily follows that the greater is the sur- face, the more considerable is the effect. Tbe bubbles which are now rising, on the hydrogen gas------• Caroline. How disagreeable it smells! Mrs. B. It is indeed unpleasant, though I believe not particularly hurtful. We shallnot, however, suffer anymore to escape, as it will be wanted for experiments. I shall therefore collect it in a glass receiver, by making it pass through this bent tube, which will conduct ipto the water-bath) (Fig. 20. No. 1.) ' Fig. 20. 1. Apparatus for preparing and collecting hydrogen ga«. 2. Receiver full of hydrogen gas inverted over water. Emily. How very rapidly the gas escapes ! it is perfectly trans- parent, and without any colour whatever. Now the receiver is full. Mrs.B. We shall therefore remove it and substitute another in its place. But you must observe, that when the receiver is full, it is necessary to keep it inverted with the mouth under water, other- wise the gas would escape. And in order that it may not be in the way, I introduce within the bath, under the water, a saucer, into which I slide the receiver, so that it can be taken out of the bath and conveyed any where; the water in the saucer being equally ef- fectual in preventing its escape as that iu the bath. (Fig. 20. No. 2.) Emily. I am quite surprised to see what a large quantity of hy- drogen gas can be produced by so small quantity of water, especial- ly as oxygen is the principal constituent of water. Mrs. B. In weight it i-,; but not in volume. For though the pro- portion, by weight, is. nearly eight parts of oxygen to one of hydro- gen, yet the proportion of the volume of the gases is about one part 465. Why are iron filings, in this experiment, better than a solid piece of metal ? 466. How may hydrogen gas be collected as the water is decom- posed ? ' 467. What are the proportions of oxygen and hydrogen in water? HYDROGEN. 115 of oxygen to two of hydrogen; so much heavier is the former than the latter.* Caroline. But why is the vessel in which the water is decomposed bo hot? As the water changes from a liquid to a gaseous form cold should be produced instead of heat. Mrs.B. No; for if one of the constituents of water is converted into gas, the other becomes solid in combining'with the metal. Emily. In this case, then, neither heat nor cold should be produ- ced ? Mrs. B. True; but observe that the sensible heat which is dis- engaged in this operation, is not owing to the decomposition of the water, but to an extrication of heat produced by the mixture of wa- ter and sulphuric acid. I will mix some water and sulphuric acid together in this glass, that you may feel the surprising quantity of heat which is disengaged by their union—now take hold of the glass. Caroline. Indeed I cannot; it feels as hot as boiling water. I should have imagined there would have been heat enough disenga- ged to have rendered the liquid solid. Mrs. B. As, however, it does not produce that effect, we cannot refer this heat to the modification called latent heat. We may however, I think, consider it as heat of capacity, since the liquid is condensed by its loss ; and if you were to repeat the experiment, in a graduated tube, you would find the two liquids, when mixed, oc- cupy considerable less space than they did separately. But we will reserve this to another opportunity, and attend at present to the hydrogen gas which we have been producing. If I now set the hydrogen gas which is contained in this receiver at liberty all at once, and kindle it as soon as it comes in contact with the atmosphere, by presenting it to a candle, it will so sudden- ly and rapidly decompose the oxygen gas, by combining with its ba- sis) that an explosion, or a detonation, (as chemists commonly call it) will be produced. For this purpose, I need only take up the re- ceiver, and quickly present its open mouth to the candle----so . . Caroline. It produded only a sort of hissing noise, with a vivid flash of light. I had expected a much greater report. Mrs. B. And so it would have been, had the gases been closely confined at the moment they were made to explode. If, for in- stance, we were to put in this bottle a mixture of hydrogen gas and atmospheric air ; and if, after corking the bottle, we should kindle the mixture by a very fine orifice, from the sudden dilatation of the gases at the moment of (heir combination, the bottle must either fly to pieces, or the cork be blown out with considerable violence. Caroline. But in the experiment which we have just seen, if vou did not kindle the hydrogen gas, would it not equally combine with the oxygen ? Mrs. B. Certainly not: for, as 1 have just explained to you, it is necessary that the oxygen and hydrogen gases be burnt together, in order to combine chemically and produce water. * Hydrogen is about 13 times lighter than atmospheric air.—C. 468. How much lighter is hydrogen than cmmon o. 2.) iron filings, water, and sulphuric acid, materials similar to those which we have just used for the same purpose. I shall then cork up the bottle, leaving only a small orifice in the cork, with a piece of glass tube fixed to it, through which the gas will issue in a continued ra- Apid stream. Caroline. I hear already the hissing of the gas through the tube, and I can feel a strong current against my hand. Mrs B. This current I am going to kindle with the candle—see how vividly it burns---- Emily. It burns like a candle with a great flame. But why does this combustion last so much longer nhustMmtnan jn the Jbrmer experiment ? 1. Slow( .of hydrogen gas,-—*. _, _. „,, ApparMus for uiustra- Mrs. B. I he combustion goes on uninterruptedly ting the formation of a« long as the new gas continues to be pioduced.— "oTofV^ntr Now ifl invert this receiver over the flame, you will * The levity of hydrogen is such, that if a vessel be filled with it, and kept inverted, it may be carried about the room without its es- caping. The above experimpnt therefore may be made by bring- ing a small jar, or tumbler of gas over a lighted lamp. — C. 471. Can oxygen and hydrogen combine in any other proportions than to produce water ? 472. What is represented in figure 21 ? 473. How can it be made to burn like a candle ? 474. If an inverted receiver filled with hydrogen gas beheld over the flame of a lamp, what will be seen on its internal surface? HYDROGEN. 117 soon perceive its internal surface covered with a very fine dew, which is pure water.—* Caroline. Yes, indeed ; tbe glass is now quite dim with mois- ture ? How glad I am that we can see the water produced by this combustion. Emily. It is exactly what I was anxious to see ; for 1 confess I was a little incredulous. Mrs. B. If I had not held the glass bell over the flame, the wa- ter would have escaped in the state of vapor, as it did in the former experiment. We have here; of course, obtained but a very small quantity of water ; but the difficulty of procuring a proper appara- tus, with sufficient quantities of gases, prevents my showing it you on a larger scale. The composition of water was discovered about the same period, both by Mr. Cavendish, in this country, and by the celebrated French chemist,, Lavoisier. The latter invented a very perfect and ingenious apparatus, to perform with great accuracy,and upon a large scale, the formation of water by the combination of oxygen, and hydrogen gases. Two tubes, conveying due proportions, the one of oxygen the other of hydrogen gas, are inserted at opposite sides of a large globe of glass previously exhausted of air ; the two streams of gas are kindled within the globe, by the electrical spark, at the point where they come in contact^ they burn together, that is to say, the hydrogen combines with the oxj gen, the caloric is set at liberty, and a quantity of water is produced, exactly, equal in weight to that of the two gases introduced into the globe. Caroline. And what was the greatest quantity of water ever formed in this apparatus? Mrs- B. Several ounces; indeed, very Dearly a pound, if I recol- lect right; but the operation lasted many days. Emily. This experiment must have convinced all the world of the truth of the discovery. Pray if improper proportions of tbe gases were mixed and set fire to, what would be the result? Mrs B. Water would equally be formed, but there would be a residue of either one or other of the gasesi because, as I have al- ready told you, hydrogen and oxygen wiUtiombine only in the pro- portions requisite for the formation of water. Emily. Look, Mrs. B., our experiment with the Voltaic battery, [See Fig. 19,) has made great progress ; a quantity of gas has been formed in each tube, but in one of them there is twice as much as in the other. Mrs. B. Yes ; because, as I said before, water is composed of * The burning of a candle, lamp, wood, &c. always produces wa- ter. The tallow and oil contain hydrogen, andduringcombustion, it unites with the oxygen of the atmosphere. Hold a wide tube over a lamp, and it is soon covered with moisture. Wood contains hydrogen.—C. 475. How is water produced by the burning of a candle, lamp, &c. . 476. What chemists discovered the composition of water ? 477. How would you describe the apparatus invented by Lavoisier for converting oxygen and hydrogen gases into water? 478. What would be the result if other proportions of oxygen and hydrogen gas were mixed than is proper for the production of water? 118 HYDROGEN. two volumes of hydrogen to one of oxygen—and if we should now mix these gases together and set fire to them by an electrical spark, both gases would entirely disappear, and a small quantity of water would be formed. There is another curious effect produced by the combustion of hydrogen gas, which I shall show you, though I must acquaint you first, that I cannot well explain the cause of it. For this purpose, I must put some materials into our apparatus, in order to obtain a stream of hydrogen gas, just as we have done before. Tbe process is already going on, and the gas is rushing through the tube, 1 shall now kindle it with a taper. Emily. It burns exactly as it did before—What is the curious effect which you are mentioning? Mrs. B. Instead of the receiver, by means of which we have just seen the drops of water form, we shall invert over the flame this piece of tube, which is about two feet in length, and one inch indi- (Fig. 22 ) ameter, but you must observe that it is open at both ends. Emily What a strange noise it produces! something like the JEolian harp, but not so sweet. Caroline. It is very singular indeed ; but I think rather too powerful to be pleasing. And is not this sound accounted for? Mrs. B. That the percussion of glass, by a rapid stream of gas, should produce a sound, is not extraor- dinary; but the sound here is so peculiar^that do other gas has a similar effect. Perhaps it is owing to a brisk vibratory motion of the glass occasioned by the succes- sive formation and condensation of small drops of water on the sides of the glass tube, and the air rushing in to replace the vacuum formed.* Caroline. How very much this flame resembles the burning of a candle. Mrs. B. The burning of a candle is produced by much the same means. A great deal of hydrogen is contained in candles, whether of tallow or wax. This hydi ogen be- ing converted into gas by the heat of the candle, com- ,„.,, bines with the oxygen of the atmosphere, and flame and ^*5£35£y water result from the combination.- So that in fact the Apparatus forflameof a candle isowingto the combustion of hydrogen producing har-_as £n erevation of temperature, such as is produced by moDlc sounds by° ,.,,, ., . '■ .,, . ~ „ , •< the combustiouofalighted match or taper, is required to give the first lra- hydrogen ga». pulse to the combustion ; but afterwards it goes on of itself, because the candle finds a supply of caloric in the successive quantities of heat which result from the union of the two electrici- ties given out by the gases during their combustion. But there are other circumstances connected with the combustion of candles and lamps, which I cannot explain to you till you are acquainted with carbon, which is one of their constituent parts. In general, howev- er, whenever you see flame, you may infer, that it is owing to the * This ingenious explanation was first suggested by Dr. Dela- rive. See Journals of the Boyal Institution, vol. i. p. 259. 479. What curious experiment is exhibited in figure 22 ? 480. How is a common candle made to burn? HYDROGEN. 119 formation and burning of hydrogen gas*f; for flamef is the pecu- liar mode of burning hydrogen gas>,which with only one or two ap- parent exceptions, does not belong to any other combustible. Emily. You astonish me ! I understood that flame was the calo- ric produced by the union of the two electricities, in all combus- tions whatever. Mrs. B. Your error proceeded from your vague and incorrect idea of flame ; you have confounded it with the light and caloric in general. Flame always implies caloric, since it is produced by the combustion of hydrogen gas ; but all caloric does not imply flame. Coals, for instance, burn with flame„until all the hydrogen which they contain is evaporated ; but when they afterwards become red hot, much more caloric is disengaged than when they produce flame. Caroline. But the iron wire, which you burnt in oxygen gas, ap- peared to me to emit flame ; yet, as it was a simple metal, it could contain no hydrogen. Mrs. B. It produced a sparkling, dazzling blaze of light, but no real flame. Emily. And what is tbe cause of the regular shape of the flame of a candle f Mrs. B. >The regular stream of hydrogen gas which exhales from its combustible matter. Caroline. But the hydrogen gas must, from its great levity, as- cend into the upper regions of the atmosphere ; why, therefore, does not the flame continue to accompany it ? Mrs. B. The combustion of the hydrogen gas is completed at the point where the flame terminates : it then ceases to be hydrogen gas, as it is converted, by its combination with oxygen, into watery vapor ; but in a state of such minute division as to be invisible. Caroline. I do not understand what is the use of the wick of a candle, since the hydrogen gas burns so well without it. Mrs. B. The (Combustible matter of the candle must be decom- posec£)io order to emit the hydrogen gas ; and the wick is instru- mental in effecting this decomposition. Its combustion first melts the combustible matter, and— Caroline. But, in lamps, the combustible matter is already fluid, and yet they also require wicks. Mrs. B. I am going to add, that afterwards, the burning wick (by the power of capillary attraction) gradually draws up the fluid to the point where combustion lakes place; for you must have ob- served that the wick does not burn quite to the bottom. * Or rather hydro-carbonat, a gas composed of hydrogen and carbon, which will be noticed under the head Carbon. f The candle also contains carbon", which gives brilliancy to the flame, and the product of combination besides flame and water is a quantity of carbonic acid.—C. 481. What is said in the note of the burning of a candle ? 482. What is flame ? 483. How long will coals burn with flame? , 484. To what is the regular shape of the flame of a candle owing ? 485. If the flame of a candle is produced by Hydrogen gas, why » *the wick necessary ? lau HYDROGEN. Caroline. Yes ; but I do not understand why it does not. Mrs. B. Because the air has not so free an access to that part of the wick which is immediately in contact with the candle as to the part just above, so that the heat there is not sufficient to produce its decomposition; the combustion, therefore, begins a little above this point.* Caroline. But, Mrs. B., in those beautiful lights, called gas lights, which are now seen in so many streets, and will, I hope, be soon adopted every where, I can perceive no wick at all. How are these lights managed ? Mrs. B. I am glad you have put me in mind of saying a few words on this very useful and important improvement. In ^his mode of lighting,<4he gas is conveyed to the extremity of a tubfi^where it is kindled and burns as long as the supply continues. There is therefore, no occasion for a wick, or any other fuel whatever. Emily. But how is this gas procured in such large quantities ? Mrs.B. It is obtained from coal, rW distillation. Coal, when exposed to heat in a close vessel, is decomposed; and hydrogen, which is one of its constituents, rises in the state of gas, combined with another of its component parts, carbon, forming a compound gas, called JJydro-Carbonat, 'the nature of which we shall again have an opportunity of noticing when we treat of carbon. This gas, like hydrogen, is perfectly transparent, invisible, and highly inflammable; and, in burning, it emits that vivid light which yon have so often observed. Caroline. And does the process for procuring it require nothing but heating the coals, and conveying the gas through tubes? Mrs. B. Nothing else, except that the gas must be made to pass, immediately at its formation, through two or three large vessels of water,f in which it deposits some other ingredients, and especially water, tar, and oil, which also arise from the distillation of coals. The gas-light apparatus, therefore, consists simply in a large iron vessel, in which the coals are exposed to the heat of a furnace^ some reservoirs of water, in which the gas deposits its impurities, and tubes that convey it to the desired spot, being propelled with uniform velocity through the tubes by means of a certain degree of pressure which is made upon the reservoir. * In the burning of a candle, the reason why combustion does not take place in immediate contact with the tallow, is/That the caloric is here employed in converting a solid into a fluid jas explained in the conversation on free caloric. In the burning of a lamp, if the same thing takes place, it is because the metallic tube through which the wick passes, conducts off the heat.—C. f The gas is passed through one vessel of slacked lime and water to absorb the carbonic acid gas, with which it is always more or less mixed, when first distilled.—C. 486. Why is it that the wick of a candle does not burn to the bottom ? 487. How are gas lights made to burn without wicks? ■ 4b«. What is the gas called, used in lighting the streets of some large cities? - 489. How is it obtained ? 490. Of what does the gas light apparatus consist? HYDROGEN. 121 Emily. What an admirable contrivance ! Do you not think, Mrs. B., that it will soon be universally adopted ? Mrs. B. Most probably ; for the purpose of lighting streets, offi- ces, and public places, it farsurpasses any former invention); but in regard to the interior of private houses, this modeof lighting has not yet been sufficiently tried to know whether it will be found gene- rally desirable, either with respect to economy or convenience. It may, however, be considered as one of the happiest applications of chemistry to the comforts of life ; and there is every reason to sup- pose that it will answer the full extent of public expectation. 1 have another experiment to show you with hydrogen gas, which I think, will entertain you. Have you ever blown bubbles with soap and water? Emily. Yes, often, when I was a child ; and I used to make them float in the air by blowing them upwards. Mrs. B. We shall fill some bubbles with hydrogen gas, jtistead of atmospheric air, and you will see with what ease and rapidity they will ascend, without the assistance of blowing, from the light- ness of the gas.— Will you mix some soap and water, whilst I fill this bladder with the gas contained in the receiver which stands on the shelf in tbe water bath ? Caroline. What is the use of the brass-stopper and turn-cock at the top of the receiver? Mrs. B. It is to afford a passage to the gas, when required. There is, you see, a similar stop-cock fastened to this bladder, which is made to fit on the receiver. I screw them one on the other, and now turn the two cocks, to open a communication between the re- ceiver and the bladder; then, by sliding the receiver off the shelf, and gently sinking into the bath, the water rises in the receiver, and forces the gas into the bladder. (Fig. 23, No. 1.) Caroline. Yes. I see the bladder swell as the water rises in the receiver. Mrs. B. I think that we have already a sufficient quantity in the bladder for our purpose; we must be careful to stop both the cocks before we separate the bladder from the receiver, lest the gas should escape.—Now I must fix a pipe to the stopper of the bladder, and by dipping its mouth into the soap and water, take up a few drops : then I again turn the cock, and squeeze the bladder, in order to force the gas into the soap and water, at the mouth of the pipe. (Fig. 23, No. 2.; Emily. There is a bubble ; but it bursts before it leaves the mouth of the pipe. Mrs. B. We must have patience and try again ; it is not easy to blow bubbles by means of a bladder, as simply with the breath. Caroline. Perhaps there is not soap enough in the water. I should have had warm water ; it would have dissolved the soap better. Emily. Does not some of the gas escape between the bladder and the pipe ? r491. What is said of lighting streets, offices, and public places with this gas? 492. How can bubbles of soap & water be made to float in the air? How can these bubbles be made so as to explode on setting fire to them? (Seepage 123.) 493. What is represented in 23, No. 1 and 2? 122 No. 1/^Apparatus for transferring gases from a Receiver into a bladder. No.2 . Ap- paratus for blowing Soap bubbles. . Mrs. B. No.; they are perfectly air tight; we shall succeed presently, I dare say. Caroline. Now a bubble ascends ; it moves with the rapidity of a balloon. How beautifully it refracts the light. Emily. It has burst against the ceiling—you succeed now won- derfully ; but why do they all ascend and burst against the ceiling? Mrs. B. Hydrogen gas is so much lighter than atmospherical air, that it ascends rapidly with its very light envelope, which is burst by the force with which it strikes the ceiling. Air-balloons are filled with this gas, and if they carry no other weight than their covering, would ascend as rapidly as these bubbles. Caroline. Yet their covering must be much heavier than that of these bubbles ! Mrs. B. Not in proportion to the quantity of gas they contain, I do not know whether you have ever been present at the filling of a large balloon. The apparatus for that purpose is very simple. Its consists of ajoumber of vessels, either jars or barrels,\in which the materials for the formation of the gas are mixed, each of these being furnished with a tube, and communicating with along flexi- ble pipe which conveys the gas into the balloon. Emily. But the fire-balloons which were first invented, and have been since abandoned, on account of their being so dangerousX were constructed, I suppose, on a different principle. Mrs. B. They were filled simply with atmospherical air, consider- ■494. With what are air balloons filled? 495. What is the apparatus for filling a large balloon with hydro- gen gas ? " 496. With what were fire balloons filled? 497. Why were they abandoned? HYDROGEN. 123 ably rarefied by heat; and the necessity of having a fire underneath the balloon, in order to preserve the rarefaction of the air within it, was the circumstance productive of so much danger. If you are not yet tired of experiments, I have another to show you. It consists in'fiUing soap-bubbles with a mixture of hydrogen and oxygen gasesy,in the proportions that form water ; and after- wards setting fire to them. Emily. 1 hey will detonate, I suppose. Mrs. B. Yes, they will. As you have seen the method of trans- ferring the gas from the receiver into the bladder, it is not neces- sary lo repeat it. I have therefore providedfa bladder which con- tains a due proportion of oxygen and hydrogen gases, and we have only to blow bubbles with it./ Caroline. Here is a fine large bubble rising—shall I set fire to it with a candle ? Mrs. B. If you please* Caroline. Heavens, what an explosion !* It was like the report of a gun : I confess it frightened me much. I never should have imagined it could be so loud. Emily. And the flash was as vivid as lightning. Mrs. B. The combination of the two gases takes place during that instant of time that you see the flash, and hear the detonation. Emily. This has a strong resemblance to thunder and lightning.f Mrs. B. These phenomena, however, are generally of an electri- cal nature. Yet various meteorological effects may be attributed to accidental detonations of hydrogen gas in the atmosphere ; for nature abounds with hydrogen; it constitutes a very considerable portion of the whole mass of water belonging to our globe, and from that source almost every body obtains it. It enters into the com- position of all animal substances, andof a great number of minerals*, but it is most abundant in. vegetables.] From this immense variety of bodies it is often spontaneously discharged ; its great levity makes it rise into the superior regions of the atmosphere ; and when, either by an electrical spark, or any casual elevation of tem- perature it takes fire, it may produce such meteors or luminous appearances as are occasionally seen in the atmosphere. Of this kind are probably those broad flashes which we often see on a summer evening, without hearing any detonation. Emily. Every flash, 1 suppose, must produce a quantity of water? Caroline. And this water, naturally, descends in the form of rain. Mrs. B. That probably is often the case, though it is not a neces- * In making this experiment, always be careful to turn the stop- cock, or detach the bubble completely from the pipe before it is set fire to; otherwise a sad accident may happen from the gas taking fire in the bladder.—C. f The report is owing to the air, rushing in to fill the vacuum, caused by the condensation of the two gases, and the heat extrica- ted at the same instant.—C. 498. How can bubbles be made of soap and water so as to explode with a loud report, on setting fire to them ? 499. To what is it said in the note that the report is owing ? "*500. In what substance is hydrogen most abundant? 501. How may heat lightning be accounted for ? 124 HYDROGEN. sary consequence; for the water may be dissolved by the atmos- phere, as it descends towards the lower regions, and remain there in the form of clouds. The application of electrical attraction to chemical phenomena is likely to lead to many very interesting discoveries in meteorology; for electricity evidently acts a most important part in the atmos- phere. This subject, however, is, as yet, not sufficiently developed for me to venture enlarging upon it. The phenomena of the at- mosphere are far from being well understood : and even with the little that is known, I am but imperfectly acquainted. But before we take leave of hydrogen, I must not omit to men- tion to you a most interesting discovery of Sir H. Davy, which is connected with this subject. Caroline. You allude, I suppose, to the new miner's lamp, which has of late been so much talked of. I have long been desirous of knowing what that discovery was, and what purpose it was intend- ed to answer. Mrs. B. It often happens in coal-mines, that quantities of the gas called by chemists hydro carbonat, or by the miners^re damp, (the same from which the gas lights are obtained,) ooze out from the fis- sures in the beds of coal, and fill the cavities in which the men are at work y1 and this gas being inflammable, the consequence is, that when the men approach those places, with a lighted candle, the gas takes fire, and explosions happen, whichdestroy the men and horses employed in that part of the colliery, sometimes in grev' numbers. Emily. What tremendous accidents these must be ! Bat whence does that gas originate? Mrs. B. Being the chief product of the combustion of coal, no wonder that inflammable gas should occasionall}7 appear in situa- tions in which this mineral abounds, since there can be no doubt that processes of combustion are frequently taking place at a great depth under the surface of the earth ; and, therefore, these accu- mulations of gas may arise eithe/from combustions actually going on, or from former combustions, ihe gas having perhaps been con- fined there for ages. Caroline. And how does Sir H. Davy's lamp prevent those dread- ful explosions. Mrs.B. By a contrivance equally simple and ingenious; and one which does no less credit to the philosophical views from which it was deduced, than to the philanthropic motives from which the inquiry sprung. The principle of the lamp is shortly this : It was ascertained two or three years ago, both by Mr. Tenant, and by Sir Humphrey himself, that the combustion of inflammable gas could not be propagated through small tubes ) so that if a jet of an in- flammable gaseous mixture, issuing from a bladder, or any other vessel, through a small tube, be set fire to, it burns at the orifice of the tube, but the flame never penetrates into the vessel. It is upon this fact that Sir Humphrey's safety lamp is founded. Emily. But why does not the flame ever penetrate through the " 502. Is it supposed that the subject of meteorology is well under- stood ? 503. What disastrous effects often happen in coal-mines ? 504i Whence does the hydrogen gas in mines originate ? 505. Upon what discovery of Mr. Tenant and Sir H. Davy was the miner's safety lamp founded ? HYDROGEN. 125 tube into the vessel from which the gas issues, so as to explode at once the whole of the gas ? Mrs. B. Because, no doubt, the inflamed gas is so much cooled in its passage through a small tube as to cease to burn before the combustion reaches the reservoir. Caroline. And how can this principle be applied to the construc- tion of a lamp? Mrs. B. Nothing easier. You need only suppose a lamp enclo- sed all round in glass or horn, but having a number of small open tubes at the bottom, and others at the top, to let the air in and out. Now, if such a lamp or lanthorn be carried into an atmosphere ca- pable of exploding, an explosion or combustion of the gas will take place withintbe lamp ; and although the vent afforded by tfie tubes will save the lamp from burstings yet from the principle just ex- plained, the combustion will not be propagated to the external air through the tubes, so that no farther consequence will ensue. Emily. And is that all the mystery of that valuable lamp ? Mrs. B. No; in the early part of the inquiry, a lamp of this kind was actually proposed ; but it was but a rude sketch compared to its present state of improvement. Sir H. Davy, after a succession of trials, by which he brought his lamp nearer and nearer to per- fection, at last conceived the happy idea that if the lamp were'sur- rounded with a wire-wick or wire-gauze, of a close texture^ instead of glass or horn, the tubular contrivance I have just described would be entirely superseded, fince each of the interstices of the gauze would act as a tube in preventing the propagation of explo- sions : so that this previous metallic covering would answer the va- rious purposes of transparency, of permeability (o air and of pro- tection against explosion. This idea, Sir Humphrey immediately submitted to the test of experiment, and the result has answered his most sanguine expectaiions, both in his laboratory and in the collieries where it has already been extensively tried. And he has now the happiness of thinking that bis invention will probably be the means of saving every year a number of lives, which would have been lost in digging out of the bowels of the earth one of the most valuable necessaries of life Here is one of these lamps, every part of which yi 631. What is sulphur in its pure state ? ■ 532. Can a gas dissolve a solid substance ? 533. How can it be done ? 534. How is it known that the union between hydrogen gas and sulphur is a chemical union ? 535. What is the product of this union? 132 PHOSPHORUS. Mrs. B. Yes; they are naturally impregnated with sulphuretted/" hydrogen gas, and there are many other* springs of the same kind-, which show that this gas must often be formed in the bowels of the earth by spontaneous processes of nature. Caroline. \nd could not such waters be made artificially by im- pregnating common water with this gas ? Mrs.B. Yes ; they can be so well imitated, as perfectly to re- semble the Harrogate waters. Sulphur combines likewise with phosphorus, and with the alka- lies, and alkaline earths, substances with which you are yet unac- quainted. We cannot, therefore, enter into these combinations at present. In our next lesson we shall treat of phosphorus. Emily. May we not begin that subject to day ; this lesson has been so short ? Mrs.B. I have no objection, if you are not tired. What do you say, Caroline ? Caroline. I am as desirous as Emily of prolonging the lesson to- day, especially as we are to enter on a new subject; for I confess that sulphur has not appeared to me so interesting as the other sim- ple bodies. Mrs. B. Perhaps you may find phosphorus more entertaining. You must not, however, be discouraged when you meet with some parts of a study less amusing than others ; it would answer no good purpose to select the most pleasing parts, since if we did not proceed with some method, in order to acquire a general idea of the whole, we could scarcely expect to take interest in any particular subjects. PHOSPHORUS. Phosphorus is considered as a simple body; though, like sulphur, it has been suspected of containing hydrogen. It was not known by the earlier chemists. It was first discovered by. Brandt^ a chemist of Hamburg, whilst employed in researches after the philosopher's stone; but the method of obtaining it remained a secret till it was a second time discovered both by Kunckle and Boyle, in the j ear 1680, You see a specimen of phosphorus in this phial; it is generally moulded intofsmall sticks of a yellowish color; as you find it here. Caroline. I do not understand in what the discovery consisted: there may be a secret method of making an artificial composition; but how can you talk of making a composition which naturally exists? Mrs. B. A body may exist in nature, so closely combined with other substances, as to elude the observation of chemists, or render it extremely difficult to obtain it in its separate state. This is the case with phosphorus, which is so intimately combined with other substances, that its existence remained unnoticed till Brandt dis- covered the means of obtaining it free from other combinations. It is found in all animal substances, and is now chiefly extracted from 536. What is there which shows that this gas is sometimes formed spontaneously inthe bowels of the earth ? . 537. By whom was phosphorus discovered ? ■ 538. What is the appearance of it ? . 539. How is phosphorous obtained ? phosphorus. 133 'bonesjby a chemical process. It exists also in some plants, that bear a strong analogy to animal matter in their chemical composition. Emily. But is it never found in its pure separate state ^ Mrs. B. Never ; and this is the reason why it remained so long undiscovered. Phosphorus is eminently combustible ; it melts and takes fire at the temperature of one hundred degrees, and,absorbs in its com- bustion, nearly once and a half its own weight of oxygen. Caroline. What ! will a pound of phosphorus consume a pound and a half of oxygon)? Mrs. B. So it appears from accurate experiments. I can show you with what violence it combines with oxygen, by burning some of it in that gas. We must manage the experiment in the same man- ner as we did the combustion of sulphur. You see I am obliged to cut this little bit of phosphorus under water, otherwise there would be danger of its taking fire by the heat of my fingers. 1 now put it into the receiver, and kindle it by means of a hot wire. Emily. What a blaze ! I can hardly look at it. I never saw any thing so brilliant. Does it not hurt your eyes, Caroline ? Caroline. Yes ; but still 1 cannot help looking at it. A prodi- gious quantity of oxygen must, indeed, be absorbed, when so much light and caloric are disengaged ! Mrs. B. In the combustion of a pound of phosphorus, a sufficient quantity of caloric is set free, to melt upwards of a hundred pounds of ice ; this has been computed by direct experiments with the ca- lorimeter. Emily. And is the result of this combustion, like that of sulphur, an acid ? ■Mrs. B. Yes;'phosphoric acid. And had we duly proportioned the phosphorus and the oxygen, they would have been completely converted into phosphoric acid, weighing together, in this new state, exactly the sum of their weights separately. Tbe water would have ascended into the receiver, on account of the vacuum formed, and would have filled it entirely. In this case, as in the combustion of sulphur, the acid vapor formed is absorbed and condensed in the water of the receiver. But when this combustion is performed with- out any water or moisture being present, the acid then appears in the form of concrete whitish flakes, which are, however, extremely ready to melt upon the least admission of moisture. Emily. Does phosphorus, in burning in atmospherical air, pro- duce like sulphur, a weaker sort of the same acid? Mrs. B. No ; but it burns in atmospherical air, nearly at the same temperature as in pure oxygen gas; and it is in both cases so strong- ly disposed to combine with the oxygen, that the combustion is per- fect and the product similar : only in atmospherical air, being less rapidly supplied with oxygen, the process is performed in a slow manner. * 540. Why was it for a long time undiscovered ? 54l! At what temperature will it melt and take fire ? .'542'. What proportion of oxygen will phosphorus consume, com- pared with its own weight ? . 543. How much caloric will the combustion ofa pound of phospho- rilfl set Ir6C m 144 What is the result of the combustion of phosphorus? ► 12 134 PHOSPHORUS. Caroline. But is there no method of acidifying phosphorus in a slighter manner, so as to form phosphorus acid ? Mrs. B. Yes, there is. When simply exposed to the atmosphere, phosphorus undergoes a kind of slow combustion at any tempera- ture above zero. Emily. Is not the process in this case rather an oxydation than a combination ? For if the oxygen is too slowly absorbed for a sensi- ble quantity of light and heat to be disengaged, it is not a true com- bustion. Mrs. B. The case is not as you suppose ; a faint light is emitted, which is very discernible in the dark; but the heat evolved is not sufficiently strong to be sensible; a whitish vapour arises from this combustion, which, uniting with water, condenses into liquid phos- phorous acid. Caroline. Is it not very singular that phosphorus should burn at so low a temperature in atmospherical air, whilst it does not burn in pure oxygen without the application of heat? Mrs. B. So it at first appears. But this circumstance seems to be owing to the nitrogen gas of the atmosphere?* This gas dissolves small particles of phosphorus, which being thusminutely divided and diffused in the atmospherical air, combines with the oxygen, and un- dergoes this slow combustion. But the same effect does not take place in oxygen gas, because it is not capable of dissolving phospho- rus ; it is therefore necessary, in this case, that heat should be ap- plied to effect that division of particles, which, in the former in- stance, is produced by the nitrogen. Emily. I have seen letters written with phosphorus, which are invisible by day-light, but may be read in the dark by their own light. They look as if they were written with fire ; yet they do not seem to burn. Mrs. B. But they do really burn ; for it is by their slow combus- tion that the light is emitted ; and phosphorus acid is the result of this combustion. Phosphorus is sometimes used as a test to estimate the purity of atmospherical air. For this purpose, it is burnt in a graduated tube, called an Eudiometer (fig. 26.) and the proportion of oxy- Fig. 26. gen in the air examined is deduced from the quantity of air Eudiometer which the phosphorus absorbs ; for the phosphorus will ab- sorb all the oxygen, and the nitrogen alone will remain. Emily. And the more oxygen is contained in the atmos- phere, the purer, I suppose, it is esteemed ? Mrs. B. Certainly. Phosphorus when melted, combines with a great variety of substances. With sulphur it forms a compound so extremely combustible that it immediately takes fire on coming in contact with the air. It is with this composition that phosphoric matches are prepared which kindle as soon as they are taken out of their case and are exposed to the air. (^) 545. Why will phosphorus burn at so low a temperature in atmos- pherical air, when it does not burn in pure oxygen without the appli- cation of heat? 546. For what is phosphorus sometimes used ? 547. What instrument is used for this purpose, and how is the pu- rity of the air ascertained by it ? 548. How are phosphoric matches made ? PHOSPHORUS. 135 Emily. I have a box of these curious matches ; but I have ob- served that, in very cold weather, they will not take fire without being previously rubbed. Mrs. B. By rubbing them you raise their temperature ; for you know, friction is one of the means of extricating heat. Emily. Will phosphorus, like sulphur, combine with hydrogen gas ? Mrs.B. Yes; and the compound gas which results from this combination has a smell still more fetid than the sulphuretted hy- drogen ; it resembles that of garlic. The phosphorated hydrogen gas has this remarkable peculiarity, that it takes fire spontaneously in the atmosphere at any tempera- ture. It is thus, probably, that are produced those'transient flames or flashes of light, called by the vulgar Will-of-the-Wisp, or, more properly, lgnesfatui, which are often seen in church-yards, and places where the putrefactions of animal matter exhale phosphorus and hydrogen gas. Caroline. Country people, who are so much frightened by those appearances, would be soon reconciled to them if they knew from what a simple cause they proceed. Mrs.B. There are other combinations of phosphorus that have also very singular properties, particularly that which results from its union with lime. Emily. Is there any name to distinguish the combination of two substances, like phosphorus and lime, neither of which are oxygen, and which cannot therefore produce either an oxyd or an acid ? Mrs. B. The names of such combinations are composed from those of their ingredients, merely by a slight change in their termi- nation. Thus, the combination of sulphur with lime is called a sul- phuret, and that of phosphorus, a phosphuret of lime.* This latter * Phosphuret of lime is a very curious substance. To make it, take a thin glass tube, 6 or 8 inches long, and less than half an inch in diameter ; if it is closed at one end, so much the better, but a cork will do. Near the closed end put a piece of phosphorus half an inch long. Then put in by means of a stick or wire, holding the tube horizontally, thirty or forty pieces of newly burned quick lime, about the size of split peas, letting the lowest remain two or three inches from the phosphorus. Then stop the other end of the tube loosely, and place the part containing the quick-lime in a bed of charcoal, so contriving it that a candle or red hot iron can be brought under the part where the phosphorus lies. Kindle a fire by means of bellows, and heat the lime red hot, without melting the phospho- rus, which may be kept cool by a wet rag ; when this is done, bring the'hot iron or candle under the phosphorus, so as to make it pass through the quick lime in the form of vapour. Cork up the phos- phuret of lime for use.—C. * 549. Will phosphorus combine with hydrogen ? 550. What remarkable peculiarity has phosphoretted hydrogen gas ? 551. How is it supposed that the ignes-fatui are produced? • 552. What is the combination of phosphorus with lime, called ? 136 PHOSPHORUS. compound, INwas going to say, has the singular property of decom- posing water, rnerelv by being thrown into it. It effects this by ab- sorbing the oxygen'of water, in consequence of which, bubbles of hydrogen gas ascend, holding in solution a small quantity of phos- phorus, lit /, Emily. These bubbles tben are phosphoretted hydrogen gas ? Mrs. jg. Yes ; and they produce the singular appearance of a flash of fire issuing from water, as the bubbles kindle and detonate on the surface of the water, at the instant that they come m contact with the atmosphere. Caroline. Is not this effect nearly similar to that produced by the combination of phosphorus and sulphur, or, more properly speak- ing, the phosphuret of sulphur ? Mrs. B. Yes; but the phenomenon appears more extraordinary in this case, from the presence of water, and from the gaseous form of the combustible compound. Besides, the experiment surprises by its great simplicitv. You only throw a piece of phosphuret of lime into a glass of water, and bubbles of fire will immediately is- sue from it. Caroline. Cannot we try the experiment ? Mrs.B. Very easily; but we must do it in the open air; for the smell of the phosphoretted hydrogen gas is so extremely fetid, that it would be intolerable in the house;. But before we leave the room, we may produce by another process, some bubbles of the same gas, which are much less offensive. There is in this little glass retort a solution of potash and water; I add to it a small piece of phosphorus. We must now heat the re- tort over the lamp after having engaged its neck under water—you see it begins to boil; in a few minutes bubbles will appear, which take fire and detonate as they issue from the water. Caroline. There is one—and another. How curious it is !—But I do not understand how this is produced. Mrs. B. It is the consequence of a display of affinities too com- plicated, 1 fear, to be made perfectly intelligible to you at present. In a few words, the reciprocal action of the potash, phosphorus, caloric, and water are such, that some of the water is decomposed, and the hydrogen gas thereby formed carries off some minute par- ticles of phosphorus with which it forms phosphoretted hydrogen gas, a compound which spontaneously takes fire at almost any tem- perature. Emily. What is that circular ring of smoke which slowly rises from each bubble after its detonation ? Mrs. B. It consists of water and phosphoric acid in vapor, which are produced by the combustion of hydrogen and phosphorus. ' 553. What singular peculiarity has the phosphoret of lime? - 554. What will be the consequence if a piece of phosphoret of lime is thrown into the water ? 555. Why is it necessary that this experiment be made in the open air? 556. What will be the consequence if phosphorus be added to a so- lution of potash in water, and the whole heated over a fire? CARBON. 137 CONVERSATION IX. ON CARBON. Caroline. To-day, Mrs, B., I believe we are to learn the nature and properties of carbon. This substance is quite new to me ; I never heard it mentioned before. Mrs. B. Not so new as you imagine; for carbon is nothing more Ihanrcharcoal in a state of purity, that is to say, unmixed with any foreign ingredients. Caroline. But charcoal is made by art, Mrs. B-, and how can a body consisting of one simple substance be fabricated? Mrs. B- You again confound the idea of making a simple body with that of separating it from a compound. The chemical proces- ses, by which a simple body is obtained in a state of purity, consist in unmaking the compound^ which it is contained, in order to sep- arate from it the simple substance in question. The method by which charcoal is usually obtained, is, indeed, commonly called making it; but upon examination, you will find this process to con- sist simply in separating it from other substances with which it is found combined in nature. Carbon forms a considerable part of the solid matter of all organ- ized bodies; but it is most abundant in the vegetable creation, and it is chiefly obtained from wood. When the oil and water (which are other constituents of vegetable matter) are evaporated, the black, porous, brittle substance that remains, is charcoal. Caroline. But if he* t be applied to the wood in order to evaporate the oil and water, will not the temperature of charcoal be raised so as to make it burn ? and if it combines with oxygen, can we any longer call it pure? Mrs. B. I was going to add, that, in this operation, the air must be excluded. Caroline. How then can the vapour of oil and water fly off? Mrs. B. In order to produce charcoal in its purest state (which is, even then, but a less imperfect sort of carbon,) the, operation should be performed in an earthen retort.—Heat being applied to the body of the retort, the evaporable part of the wood will escape through its neck, into which no air can penetrate, as long as the heated vapour continues to fill it. And if it be wished to collect these volatile products of the wood, this can easily be done by introducing the neck of the retort into the water bath apparatus, with which you are acquainted. But the preparation of common charcoal, such as is used in kitchens and manufactures, is performed on a much larger scale, and by an easier and less expensive process. Emily. I "have seen the process of making charcoal, The wood is ran»-ed on the ground in a pile of pyramidical form, with a fire underneath; the whole is then covered with clay, a few holes only being left for the circulation of air. ■ 557. What is carbon ? 558. In what consists the chemical process by which a simple body is obtained in a state of purity ? * 559 In what is charcoal found in most abundance ? 12* 138 CARBON. Mrs. B. These holes are closed as soon as the wood is fairly light- ed, so that the combustion is checked, or at least continues but in a very imperfect manner; but the heat produced by it is sufficient to force out and volatilize, through the earthy cover, most part of the oily and watery principles of the wood, although it cannot reduce it to ashes. Emily. Is pure carbon as black as charcoal? Mrs. B. The purest carbon we can prepare is so; but chemists have never yet been able to separate it entirely from hydrogen. Sir H. Davy says, that the most perfect carbon that is prepared by art contains about five per cent, of hydrogen; he is of opinion that if we could obtain it quite free from foreign ingredients, it would be metallic, in common with other simple substances. But there is a form in which charcoal appears, that I dare say will surprise you. This ring, which I wear on my finger, owes its bril- liancy to a small piece of carbon. Caroline. Surely you are jesting, Mrs. B. Emily. I thought your ring was diamond. Mrs. B. It is so. But diamond is nothing more than carbon in a crystallized state. Emily. That is astonishing ! Is it possible to see two things ap- parently more different than diamond and charcoal? Caroline. It is indeed, curious to think that we adorn ourselves with jewels of charcoal ! Mrs. B. There are many other substances, consisting chiefly of carbon, that are remarkably white. > Cotton, for instance, is almost wholly carbon. Caroline. That, I own, I could never have imagined ! But pray, Mrs. B., since it is known of what substance diamond and cotton are composed, why should they not be manufactured, or imitated, by some chemical process, which would render them much cheap- er, and more plentiful than the present mode of obtaining them? Mrs. B. You might as well, my dear, propose that we should make flowers and fruit, nay, perhaps, even animals by a chemical process; for it is known of what these bodies consist, since every thing which we are acquainted with in nature is formed from the va- rious simple substances that we have enumerated. But you must not suppose that a knowledge of the component parts of a body will in every case enable us to imitate it. It is much less difficult to de- compose bodies,' and discover of what materials they are made, than it is to recompose them. * The first of these processes is called analy- sis, the last synthesis. When we are able to ascertain the'natureof a substance by both these methods, so that the result of one confirms that of the other, we obtain the most complete knowledge of it that we are capableof acquiring. This is the case with water, with the atmosphere, with most of the oxyds, acids,and neutral salts, and with 560. How is charcoal in its purest state produced ? 561. What is the common method of producing charcoal? 562. What did Sir H. Davy suppose carbon would be, if free from foreign ingredients ? "563. What does charcoal become on being crystallized ? - 564. What white substance is there consisting chiefly of carbon r 565. What is to be understood by the terms analysis and synthesis as used by chemists? CARBON. 139 many other compounds. But the more complicated combinations of nature, even in the mineral kingdom, are in general beyond our reach, and any attempt to imitate organized bodies must ever prove fruitless; their formation is a secret which rests in the bosom of the Creator. You see, therefore, how vain it would be to attempt to make cotton by chemical means. But, surely, we have no reason to regret our inability in this instance, when nature has so clearly pointed out a method of obtaining it in perfection and abundance. Caroline. I did not imagine that the principle of life could be im- itated by the aid of chemistry; but it did not appear to me absurd to suppose that chemists might attain a perfect imitation of inani- mate nature. Mrs. B. They have succeeded in this point in a variety of instan- ces ; but, as you justly observe, the principle of life, or even the minute and intimate organization of the vegetable kingdom, are se- crets that have almost entirely eluded the researches of philosophers: nor do I imagine that human art will ever be capable of investiga- ting them with complete success. Mrs. B. But diamond, since it consists of one simple, unorgani- zed substance, might be, one would think, perfectly imitable by art. Mrs. B. It is sometimes as much beyond our power to obtain a simple body in a state of perfect purity, as it is to imitate a compli- cated combination; for the operations by which nature separates bodies are frequently as inimitable as those which she uses for their combination. This is the case with carbon; all the efforts for chem- ists to separate it entirely from other substances have been fruitless, and in the purest state in which it can be obtained by art, it still retains a portion of hydrogen, and probably of some other foreign ingredients. We are ignorant of the means which nature employs to crystallize it. It may probably be the work of ages, to purify, arrange, and unite the particles of carbon in the form of a diamond. Here is some charcoal, in the purest state we can procure it; you see that it is a very black, brittle, light, porous substance, entirely destitute of either taste or smell. Heat, without air, produces no alteration in it, as it is not volatile ; but on the contrary, it invari- ably remains at the bottom of the vessel, after all the other parts of the vegetables are evaporated. Emily. Yet carbon is, no doubt, combustible, since you say that charcoal would absorb oxygen, if air were admitted during its pre- paration. Caroline. Unquestionably. Besides, you know,Emily, how much it is used in cooking. But pray what is the reason that charcoal burns without smoke, whilst a wood fire smokes so much? Mrs. B. Because, in the conversion of wood into charcoal, the volatile paitides of tbe former have been evaporated. Caroline. Yet I have frequently seen charcoal burn witb flame; therefore, it must, in that case contain some hydrogen. Mrs. B. You should recollect that charcoal, especially that which is used for common purposes, is not perfectly pure. It generally 566. In what cases is obtained the most perfect knowledge of the nature of compound bodies ? * 567. Have means ever been discovered to crystallize carbon? 568. What is the reason that charcoal burns without smoke ? 140 CARBON. retains some remains of the various other component parts of veg- - etables, and hydrogen particularly* which accounts for the flame in question. „• . Caroline. But what becomes of the carbon itself during its com- bustion? Mrs. B. It gradually combines with the oxygen of the atmos- phere, in the same way as sulphur and phosphorus, and, like those substances, it is converted into a peculiar acid, which flies off in a gaseous form. There is this difference, however, that the acid ii not, in this instance, as in the two cases just mentioned, a mere condensible vapour, but a permanent elas ic fluid, which always remains in the stale of gas, under any pressure and at any tempera- ture. The nature of this acid was first ascertained by Dr. Black, of Edinburgh; and, before the introduction of the new nomencla- ture, it was called fixed air. It is now distinguished by the more appropriate name of carbonic acid gas.' Emily. Carbon, then, can be volatilized by burning, though by heat alone, no such effect is produced ? Mrs. B. Yes; but then it is no longer simple carbon, but an acid of which carbon forms the basis. In this state, carbon retains no | more appearance of solidity or corporeal form than the basis of any other gas. And you may, I think, from this instance, derive a more clear idea of the basis of the oxygen, hydrogen, and nitrogen gases, the existence of which, as real bodies, you seemed to doubt, because they were not to be obtained simply in a solid form. Emily. That is true ; we may conceive the basis of the oxygen and of the other gases, to be solid, heavy substances, like carbon ; but so much expanded by caloric as to become invisible. Caroline. But does not the carbonic acid gas partake of the blackness of charcoal? Mrs. B. Not in the least. Blackness, you know, does not ap- pear to be essential to carbon, and it is pure carbon, and not char- coal, that we must consider as the basis of carbonic acid. We shall make some carbonic acid, and, in order to hasten the process, we shall burn the carbonic in oxygen gas. Emily. Butdojou mean, then, to burn diamond ? Mrs. B. Charcoal will answer the purpose still better, being softer and more easy to inflame ; besides the experiments on dia- mond are rather expensive. Caroline. But is it possible to burn diamond ? Mrs. B. Yes, it is ; and in order to effect this combustion, noth- ing more is required than to apply a sufficient degree of heat by means of the blow-pipe, and of a stream of oxygen gas. Indeed, it is by burning diamond that its chemical nature has been ascertained, 569. From what does the flame in the burning of charcoal proceed ? '570. In the combustion of charcoal what becomes of the carbon? • 571. What is the gas called formed by the combination of carbon and oxygen ? 572. Why does not carbonic acid gas partake of the blackness of charcoal, if prepared from that material ? 573. How has the chemical nature of diamonds been ascertained ? CARBON. 141 It has long been known as a combustible substance, but it is with- in these few years only that the product of its combustion has been proved to be pure carbonic acid. Ibis remarkable discovery is due to Mr. Tennant. Now let us try to make some carbonic acid. Will you Emily, decant some oxygen gas from this large jar into the receiver in which we are to burn the carbon ; and I shall introduce this small piece of charcoal, with a little lighted tinder, which will be neces- sary to give the first impulse to combustion. Emily. I cannot conceive how so small a piece of tinder, and that but just lighted, can raise the temperature of the carbon suffi- ciently to set fire to it; for it can produce scarcely any sensible heat, and it hardly touches the carbon. Mrs. B. The tinder thus kindled has only heat enough to begin its own combustion, which, however, soon becomes so rapid in the oxvgen gas, as to raise the temperature of the charcoal sufficiently for this to burn likewise, as you see is now the case. Emily. 1 am surprised that the combustion ofcarbon is not more brilliant; it does not give out near so much light or caloric as phosphorus, or sulphur. Yet since it combines with so much oxy- gen, why is not a proportional quantity of light and heat disengaged from the decomposition of the oxygen gas, and the union of its elec- tricity with that of the charcoal ? Mrs. B. Is it not surprising that less light and heat should be lib- erated in this than in almost any other combustion, since the ox- ygen, instead of entering into a solid or liquid combination, as it does in the phosphoric and sulphuric acids, is employed in forming another elastic fluid ;; it therefore parts with less of its caloric. Emily. True ; and, on second consideration, it appears on the contrary, surprising that the oxygen should, in its combination with carbon, retain a sufficient portion of caloric to maintain both sub- stances in a gaseous state. Caroline. We may then judge of the degree of solidity in which oxygen is combined in a burnt body, by the quantity of caloric lib- erated during its combustion ? Mrs. B. Yes ; provided that you take into the account the quan- tity of oxygen absorbed by the combustible body, and observe the proportions which the caloric bears to it. Caroline. But why should the water, after the combustion of carbon, rise in the receiver, since the gas within it retains an aeri- form state ? Mrs. B. Because the carbonic acid gas is gradually absorbed by the water; and this effect would be promoted by shaking the re- ccivcr* Emily. The charcoal is now extinguished, though it is not nearly consumed ; it has such an extraordinary avidity for oxygen, I sup- pose, that the receiver did not contain enough to satisfy the whole. Mrs.B. That is certainly the case ; for if the combustion were '574, What is the production of their combustion? 575. Why is so little light and heat disengaged in the combustion of carbon? , 576, Does carbon unite with more than one proportion ol oxygen i 142 CARBON. performed in the exact proportions of 28 parts of carbon to 72 of oxygen, both these ingredients would disappear, and 100 parts of carbonic acid would be produced. Caroline. Carbonic acid must be a very strong acid, since it con- tains so great a proportion of oxygen ? Mrs.B. That is a very natural inference; yet it is erroneous. For the carbonic is the weakest of all the acids. The strength of an acid seems to depend upon the nature of its basis, and its mode of combination, as well as upon the proportion of the acidifying principle. Thesame quantity of oxygen that will convert some bod- ies into strong acids, will only be sufficient simply to oxydate others. Caroline. Since this acid is so weak, I think chemists should have called it the carbonous, instead of the carbonic acid. Emily. But, I suppose, the carbonous acid is still weaker, and is formed by burning carbon in atmospherical air. Mrs. B. It has been lately discovered, that carbon may be con- verted into a gas, by uniting with a small proportion of oxygen ; but as this gas does not possesss any acid properties, it is no more than an oxyd ; it is called gaseous oxyd of carbon. Caroline. Pray is not carbonic acid a very wholesome gas to breathe, as it contains so much oxygen r Mrs.B. On the contrary, it is extremely pernicious. Oxygen, when in a state of combination with other substances, loses, in al- most every instance, its respirable properties, and the salubrious effects which it has on the animal economy when in its unconfined state. Carbonic acid is not only unfit for respiration, but extreme- ly deleterious if taken into the lungs. Emily. You know, Caroline, how very unwholesome the fumes of burning charcoal are reckoned. Caroline. Yes; but to confess the truth, I did not consider that a charcoal fire produced carbonic acid gas.—Can this gas be con- densed into a liquid ? Mrs. B. No : for, as I told you before, it is a permanent elastic fluid. But water can absorb a certain quantity of this gas, and can even be impregnated with it, in a very strong degree, by the assist- ance of agitation and pressure,as 1 am going to show you. I shall decant some carbonic acid gas into this bottle, which I fill first with water, in order to exclude the atmospherical air ; the gas is then introduced through the water, which you see it displaces, for it will not mix with ilin any quantity, unless strongly agitated, or allowed to stand over it for some time. The bottle is now about half full of carbonic acid gas, and the other half is still occupied by the water. By corking the bottle, and then violently shaking it, in this way, 1 can mix the gas and water together. Now will you taste it ? Emily. It has a distinct acid taste. Caroline. Yes, it is sensibly sour, and appears full of little bubbles. Mrs. B. It possesses likewise all the other properties of acid, but 577. On what does the strength of an acid depend ? 578. Why is not carbonic acid good for respiration, since it contains a large quantity of oxygen ? 579. Why are the fumes of burning charcoal reckoned unwhole- some ? 580. How can water be impregnated with carbonic gas ? - 581. What is Seltzer found to be, on analysis? CARBON. 143 of course, in a less degree than the pure carbonic acid gas, as it is so much diluted by water. This is a kind of artificial Seltzer water. By analysing that which is produced by nature, it was found to con- tain scarcely any thing more than common water impregnated with a certain proportion of carbonic acid gas. We are therefore able to imitate it by mixing those proportions of water and carbonic acid. Here, my dear, is an instance in which, by a chemical process, we can exactly copy the operations of nature; for the artificial Seltzer waters can be made in every respect similar to those of nature ; in one point, indeed, the former have an advantage, since they may be prepared stronger or weaker, as occasion requires. Caroline. I thought I had tasted such water before. *li'ut what renders it so brisk and sparkling ? Mrs. B. This sparkling or effervescence, as it is called, is always occasioned by the action of an elastic fluid escaping from a liquid ; in the artificial Seltzer water it is produced by the carbonic acid, which being lighter than the water in which it was strongly conden- sed, flies off with great rapidity the instant the bottle is uncorked; this makes it necessary to drink it immediately. The bubbling that took place in this bottle was but trifling, as the water was but very slightly impregnated with carbonic acid. It requires a partic- ular apparatus to prepare the gaseous artificial mineral waters. Emily. If, then, a bottle of Seltzer water remains for any length of time uncorked, I suppose it returns to the state of common water? Mrs. B. The whole of the carbonic acid gas, or very nearly so, will soon disappear : but there is likewise in Seltzer water a very small quantity of soda, and a few other saline or earthy ingredi- ents, which will remain in the water, though it should be kept un- corked for any length of time. Caroline. I have often heard of people drinking soda-water.— Pray what sort of water is that ? Mrs. B. It is a kind of artificial Seltzer water, holding in solu- tion besides the gaseous acid, a particular saline substance, called soda, which imparts to the water certain medicinal qualities. Caroline. But how can these waters be so wholesome, since car- bonic acid is so pernicious ? Mrs. B. A gas, we may conceive, though very prejudicial to breathe, may be beneficial to the stomach. But it would be of no use to attempt explaining this more fully at present. Caroline. Are waters never impregnated with other gases ? Mrs. B. Yes ; there are several kinds of gaseous waters. I for- got to tell you that waters have, for some years past, been prepared, / impregnated both with oxygen and hydrogen gases'. These are not -an imitatiou of nature, but are altogether obtained by artificial means. They have been lately used medicinally, particularly on the continent, where, I understand, theyhave acquired some reputation. Emily. If I recollect right, Mrs. B., you told us that carbon was " 582. How "is the brisk and sparkling appearance in Seltzer water occasioned ? 583.,What is soda water? 584. How can these waters be wholesome, since carbonic acid is so pernicious? 585. What other gaseous waters have been .prepared, and for what (purpose ? 144 CARBON. capableof decomposing water; the affinity between oxygen andean bon must, therefore, be greater than between oxygen and hydrogen. Mrs. B. Yes ; but this is not tbe case, unless their temperature be raised to a certain degree. It is only when carbon is red-hot, that it is capable of separating the oxygen from the hydrogen. Thus, if a small quantity of water be thrown on a red-hot fire, it will increase rather than extinguish the combustion ; for the coals of wood, (both of which contain a quantity of carbon,) decompose the water, and thus supply the fire both with oxygen and hydrogen gases. If, on the contrary, a large mass of water be thrown over the fire, the diminution of heat thus produced is such, that the com- bustible ,^tter loses the power of decomposing the water, and the fire is extinguished. Emily. I have heard that fire-engines sometimes do more harm than good, and that they actually increase the fire when they can* not throw water enough to extinguish it. It must be owing, no doubt, to the decomposition of the water by the carbon during the conflagration. •Mrs. B. Certainly.—The apparatus which you see here (fig. 27,) Fig. 27. Decomposition of water by Carbon. A. Retort contaimng water. B. Lamp to heat the water. CC. Porcelain tube con- taining Carbon. D, Furnace through which the tube passes. E. Receiver for the gas produced. F, Water bath. may be used to exemplify what we have just said. It consists in a kind of open furnace, through which a porcelain tube, containing charcoal, passes. To one end of the tube is adapted a glass retort with water in it; and the other end communicates with a receiver placed on the water bath. A lamp being applied to the retort, and the water made to boil, the vapor is gradually conveyed through the red-hot charcoal, by which it is decomposed ; and the hydrogen gas, which results from this decomposition, is collected in the re- ceiver. But the hydrogen thus obtained is far from being pure ; it retains in solution a minute portion of carbon and contains also a quantity of carbonic acid. This renders it heavier than pure hy- S0£eni£a8' aDd ?rves J* Some Peculiar properties : it is distinguish- ed by the name ,pf carbonated hydrogen gas.' 587. Why will a small quantity of water thrownupon a nreincrease rather than diminish it? 588. How would you describe'the experiment made by the use of figure 27 ? J ■ 589. What is the gas called produced in the experiment? CARBON. 145 Caroline. And whence does it obtain the carbonic acid that is mixed with it? Emily. I believe I can answer that question, Caroline.—From the union of the oxygen (proceeding from the decomposed water) with the carbon, which, you know, makes carbonic acid. Caroline. True: I should have recollected that.—The product of the decomposition of water by red-hot charcoal therefore, is car- bonated hydrogen gas, and carbonic acid gas. Mrs. B. You are perfectly right, now. Carbon is frequently found combined with hydrogen in a state of solidity, especially in coals, which owe their combustible nature to these two principles. . Emily. Is it t^e hy 'rogery, then, that produces the flame of coals ? Mrs. B. It is so ; and when all the hydrogen is consumed, the carbon continues to burn without flame. But again, as 1 mention- ed when speaking of the gas-lights, the hydrogen gas produced by the burning of coals is not pure; for, during the combustion, par- ticles of carbon are successively volatilized with the hydrogen, with which they form what is called a hydro-carbonal which is the prin- cipal product of the combustion. Carbon is a very bad conductor of beat; for this reason, it is employed (in conjunction with other ingredients) for coating furna- ces and other chemical apparatus. Emily. Pray what is the use of coating furnace's ? Mrs. B. In most cases in which a furnace isvused, it is necessary to produce and preserve a great degree of heat^>for which purpose every possible means are used to prevent the heat from escaping by communicating with other bodies, and this object is attained by coating over the inside of the furnace with a kind of plaster, com- posed of materials that are bad conductors of heat. Carbon, combined with a small quantity of iron, forms a com- pound called plumbago, or black lead, of which pencils are made. This substance, agreeably lo the nomenclature, is a carburet of 'iron. Emily- Why, then, is it called black-lead ? Mrs. B. It is an ancient name gi^en to it by ignorant people, £from its shining metallic appearance'; but it is certainly a most im- proper name for it, as there is not a particle of lead in the composi- tion. There is only one mine of this mineral, which is in Cumber- land.* It is supposed to approach as nearly to pure carbon as the best prepared charcoal does, as it contains only five parts of iron, unadulterated by any other foreign ingredients. There is another carburet of irony in which the iron, though united only to an ex- * She means in England. Black lead is found in a great variety of places in this country.—C. 590. By what is the flame of burning coals occasioned? 591. Why is carbon used for coating furnaces and other chemical apparatus ? " 592. Of what is black lead made ? * 593. Why is it called black lead ? 594. What is steel ? 13 146 CARBON. tremely small proportion of carbon, acquires very remarkable nroDerties : this is steel. , V Caroline. Really ; and yet steel is much harder than ,ron ? Mrs B. But carbon is not ductile like iron, and therefore may render"the steel more brittle, and prevent its bending so easily. Whether it is that the carbon, by introducing itself into the: pores of the iron, and, by filling them makes the metal both harder and heavier'; -or whether this change depends upon some chemical cause, I cannot pretend to decide. But there is a subsequent ope- ration, by which the hardness of steel is very much increased, which simply consists in heating the steel till it is red-hot, and then plungring it into cold water. . . Carbon, besides the combination just mentioned, enters into the composition of a vast number of natural productions: such, for in- stance, as all the various kinds of oils, which result from the com- bination of carbon, hydrogen, and caloric, in various proportions. Emily. I thought that carbon, hydrogen, and caloric, formed car- bonated hydrogen gas. . Mrs. B. That is the case when a small portion of carbonic acid gas is held in solution by hydrogen gas. Different proportions of the same principles, together with the circumstances of their union, produce very different combinations ; of this you will see innumer- able examples. Besides, we are not now talking of gases, but of carbon and hydrogen, combined only with a quantity of caloric, sufficient to bring them to the consistency of oil or fat. Caroline. But oil and fat are not df the same consistence ? Mrs. B. Fat is only congealed oi.U or oil, melted fat. The one requires a little more heat to maintain it in a fluid state than the other. Have you never observed the fat of meat turned to oil by the caloric it has imbibed from the fire ? Emily. Yet oils in general, as salad-oil, and lamp-oil, do not turn to fat when cold ? Mrs. B. Not at the common temperature of the atmosphere, be- cause thev retain too much caloric to congeal at that temperature; but if exposed to a sufficient degree of cold, their latent heat is ex- tricated, and they become solid, fat substances. Have you never seen salad-oil frozen in winter ? Emily. Yes; but it appears to me in that state very different from animal fat. Mrs. B. The essential constituent parts of either vegetable or an- imal oils are the same carbon and hydrogen ;/their variety arises from the different proportions of these substances, and from other accessory ingredients that may be mixed with them. The oil of a whale, and the oil of roses, are, in their essential, constituent parts, the same ; but the one is impregnated with the offensive particlesof animal matter, the other with the delicate perfume of a flower. \ The difference of fixed oils, and volatile or essential oils, consists also in the various proportions of carbon and hydrogen. Fixed oils 595. To what is the hardness of steel owing ? 596. What is the difference between fat and oil ? ■ 597. What are the essential constituent parts of oil ? 598. What is the difference between offensive animal and fragrant vegetable oil ? CARBON. 147 are those which will not evaporate without being decomposed ;• this is the case with all common oils, which contain a greater proportion of carbon than the essential oils. The essential oils (whichvcom- prehend the whole class of essences and perfumes) are lighter Athey contain more equal proportions of carbon and hydrogen, ana are volatilized or evaporated without being decomposed. Emily. When you say that one kind of oil will evaporate, and the other be decomposed, jou mean, I suppose, by the application of heat ? Mrs. B. Not necessarily ; for there are oils that will evaporate slowly at the common temperature of the atmosphere ; but for a more rapid volatilization, or for their decomposition, the assistance of heat is required.* Caroline. 1 shall now remember, I think, that fat and oil are re- ally the same substances both consisting of carbon and hydrogen; that in fixed oils the carbon preponderates, and heat produces a de- composition ; while, in essential oils, the proportion of hydrogen is greater, and heat produces a volatilization only. Emily. I suppose the reason why oil burns so, well in lamps, is because its twoconstituents are so combustible ?) Mrs. B. Cjertainly; the combustion of oil is just the same as that of a candle': if tallow, it is only oil in a concrete state; if wax, or spermaceti, its chief chemical ingredients are still hydrogen and carbon. Emily. I wonder, then, there should be so great a difference be- tween tallow and wax ? Mrs. E. I must again repeat, that the same substances, in differ- ent proportions, produce results that have sometimes scarcely any resemblance to each other. But this is rather a general remark that I wish to impress upon your minds, than one which is applica- ble to the present case ; for tallow and wax are far from being very dissimilar; the chief difference consists in the wax being a purer compound of carbon and hydrogen than the tallow, which retains more of the gross particles of animal matter. The combustion of a candle, and that of a lamp, both produce water and carbonic acid gas. Can you tell me how these are formed ? Emily. Let me reflect . . . Both the candle and lamp burn by means of fixed oil—this is decomposed as the combustion goes on, and the constituent parts of the oil being thus separated, the carbon unites with a portion of oxygen from the atmosphere to form carbo- nic acid gas, whilst the hydrogen combines with another portion of * The volatile or essential oils evaporate when exposed to the air. Hence the odour which oil of lavender, peppermint, &c. give out The animal oils, and what are called expressed oils, as that of castor, &c. do not evaporate. Hence a good test of the purity of essential oil, is, to let a drop fall on paper. If a grease-spot remains after a few minutes, it is adulterated with some fixed oil—C. 599. What are fixed oils ? 600. What are essential oils ? 601. Why will oil burn so well in lamps ? 602. In what does the difference between tallow and wax consist ? 603. How may the adulteration of volatile oil bo detected ? 604. What are the products of the combustion of oils ? 148 CARBON. oxygen and forms with it water.—The products, therefore, of the combustion of oils, are water, and carbonic acid gas. Caroline. But we see neither water nor carbonic acid produced by the combustion of a candle. Mrs. B. The carbonic acid gas you know, is invisible, and the water being in a state of vapour, is so likewise. Emily is perfectly correct in her explanation, and I am very much pleased with it. All the vegetable acids consist of various proportions oFcarbon and hydrogen, acidified by oxygen.J- Gums, sugar, and starch, are likewise composed of these ingredients ; but, as the oxygen which they contain is not sufficient to convert them into acids, they are classed with the oxyds, and called vegetable oxyd. Caroline. I am extremely delighted with all these new ideas ; but, at the same time, I cannot help being apprehensive that I may forget many of them. Mrs. B. I would advise you to take notes, or, what would answer better still, to write down, after every lesson, as much of it as you can recollect. And, in order to give you a little assistance, I shall lend you the heads or index, which I occasionally consult for the sake of preserving some method and arrangement in these conver- sations. Unless you follow some such plan, you cannot expect to retain nearly all that you learn, how great soever be the impress- ion it may make on you at first. Emily. I will certainly follow your advice. Hitherto I have found that I recollected pretty well, what you have taught us ; but the history of carbon is a more extensive subject than any of the simple bodies we have yet examined. Mrs. B. I have little more to say on carbon at present; but hereafter you will see that it performs a considerable part in chem- ical operations. Caroline. That is, I suppose, owing to its entering into the com- position of so great a variety of substances ? Mrs. B. Certainly ; it is the basis, as you have seen, of all vege- table matter; and you will find that it is very essential to the pro- cess of animalization. But in the mineral kingdom, also, particu- larly in its form of carbonic acid, we shall discover it combined with a great variety of substances. In chemical operations, carbon is particularly useful, from its very great attraction for oxygen, as it will absorb this substance from many oxygenated or burnt bodies, and thus de-oxygenate, or unburn them, and restore them to their original combustible state. Caroline. I do not understand how a body can be unburnt, and re- stored to its original state. This piece of tinder, for instance, that has been burnt, if by any means oxygen were extracted from it, would not be restored to its former state of linen ; for its texture is destroyed by burning, and that must be the case with all organized or manufactured substances, as you observed in a former conver- sation. Mrs. B. A compound body is decomposed by combustion in a way which generally precludes the possibility of restoring it to its former state; the oxygen, for instance, does not become fixed in the tinder 605. Of what do the vegetable acids consist ? 606. How does carbon restore oxydated substances to their com- bustible state ? METALS. 149 but it,combines with its volatile parts, and flies off in the shape of gas or watery vapour. You see, therefore, how vain it would be to attempt the recomposition of such bodies. But, with regard to simple bodies, or at least bodies whose component parts are not dis- turbed by the process of oxygenation or deoxygenation, it is often ?ossible to restore them, after combustion, to their original state. 'he metals, for instance, undergo no other alteration by combustion than a combination with oxygen ; therefore, when the oxygen is taken from them, they return to their pure metallic state. But 1 shall say nothing further of this at present, as the metals will furnish ample subject for another morning ; and they are the class of sim- ple bodies that come next under consideration. CONVERSATION X. ON METALS. Mrs. B. The metals, which we are now to examine, are bodies of a very different nature from those which we have hitherto con- sidered. They do not, like the bases of gases, elude the observa- tion of our senses ; for,t they arg the most brilliant, the most pon- derous, and the most palpable substances in nature. Caroline. I doubt, however, whether the metals will appear to us so interesting, and give us so much entertainment, as those myste- rious elements which conceal themselves from our view. Besides, they cannot afford so much novelty: they are bodies with which we are already so well acquainted. Mrs. B. You are not aware, my dear, of the interesting discove- ries which were a few years ago made by Sir H Davy, respecting this class of bodies. By the aid of the Voltaic battery, he has obtained from a variety of substances, metals before unknown, the properties of which are equally new and curious. We shall begin, however, by noticing those metals with which you profess lo be so well acquain- ted. But theacquaintance, you will soon perceive, is but very super- ficial, and I trust you will find both novelty and entertainment in considering the metals in a chemical point of view. To treat of this subject fully, would require a whole course of lectures ; for metals form of themselves a most important branch of practical chemistry. We must, therefore, confine ourselves to a general view of them. These bodies are «eldom)found naturally in their metallic form : they. are generally more or less oxygenated, or combined with sulphur,/ earths, or acids, and are often blended, with each other. They are found buried in the bowels of the earth in most parts of the world, but chiefly in mountainous districts, where the surface of the globe has been disturbed by earthquakes, volcanoes, and other convulsions of nature They are spread in strata or beds, called veins, and these veins are composed of a certain quality of metal, combined with 607. What alteration do metals undergo from combustion ? ' 608. What is the subject of this conversation ? 609. Are metals generally found in their pure metallic state ? 610. In what state are they usually found to exist ? 611. In what places are they chiefly discovered.' 13* 150 METALS. various earthy substances, with which tbey form minerals of differ- ent nature and appearance, which are called ores. Caroline. I now feel quite at home, for my father has a lead mine in Yorkshire, and I have heard a great deal about veins of ore, and of the roasting and smelting of lead ; but, I confess, that I do not understand in what these operations consist. Mrs. B. Roasting is the process by which the volatile parts of the ore are evaporated ; smelting, that by which the pure metal is af- terwards separated from the earthy remains of the ore. This is done by throwing the whole into a furnace, and mixing it with cer- tain substances that will combine with the earthy parts and other foreign ingredients of the ore ; the metal being the heaviest, falls to the bottom, and runs out by proper openings in its pure metallic state. Emily. You told us in a preceding lesson, that metals had a great affinity for oxygen. Do they not, therefore, combine with oxygen, when strongly heated in the furnace, and run out in the state of oxyds ? Mrs. B. No; for the scoriae, or oxyd, which soon forms on the surface of the fused metal, when it is oxydable, ("prevents the air from having any further influence on the mass; so that neither combustion nor oxygenation can take place. Caroline. Are all the metals equally combustible? Mrs. B. No/; their attraction for oxygen varies extremely. There are some that will combine with it only at a very high tem- perature, or by the assistance of acids ; whilst there are others that oxydate spontaneously, and with great rapidity, even at the low- est temperature ; such is, in particular, manganese, which scarce- ly ever exists in the metallic state, as it immediately absorbs oxy- gen on being exposed to the air, and crumbles to an oxyd in the course of a Tew hours. Emily. Is not that the oxyd from which you extracted the oxy- gen gas? Mrs. B. It is : so that, you see, this metal attracts oxygen at at low temperature, aud parts with it when strongly heated. Emily. Is there any other metal that oxydates at the tempera- ture of the atmosphere? Mrs. B. They all do, more or less, excepting gold, silver, and platina. Copper, lead, and iron/oxydafe slowly in the air and cover them- selves with a sort of rust, a process which depends on the gradual conversion of the surface into an oxyd. This rusty surface pre- serves the interior metal from oxydation, as it prevents the air from coming in contact with it. Strictly speaking, however the word rust applies only to the oxyd, which forms on the surface of iron, when exposed to air and moisture, which oxyd appears to be united with a small portion of carbonic acid. 612. How are they refined? 613. What prevents the combustion and oxygenation of metals, when in a state of fusion ? 614. Are all metals equally combustible? 615. To what is their difference in this respect owing? . 616. Do metals oxydate on being exposed to the air? 617. By what is the rust occasioned that takes place on copper and Jron? rr METALS. 151 Emily. When metals oxydate from the atmosphere without an elevation of temperature, some light and heat, I suppose, must be disengaged, though not in sufficient quantities to be sensible. Mrs. B. Undoubtedly } and, indeed, it is not surprising that, in this case, the light and heat should not be sensible, when you Con- sider how extremely slow, and, indeed, how imperfectly, most met- als oxydate by mere exposure to the atmosphere. For the quantity of oxygen with which metals are capable of combining, generally depends upon their temperature ; and the absorption stops at vari- ous points of oxydation, according td the degree to which their tem- perature is raised. Emily. That seems very natural ; for the greater the quantity of caloric introduced into a metal, the more will its positive electricity be exalted, and consequently the stronger will be its affinity for ox- ygen. Mrs B. Certainly. When the metal oxygenates with sufficient rapidity for light and heat to become sensible, combustion actually takes place. But this happens only at very high temperatures, and the product is nevertheless an oxyd ; for though, as 1 have just said, metals wilt combine with different proportions of oxygen, yet with the exception of orily five of them, they are not susceptible of acidification: Metals change color during the different degrees of oxydation which they undergo. Lead, when heated in contact with the at- mosphere, first becomes grey ; if its temperature be then raised, it turns yellow, and a still stronger heat changes it to red. And it is even capable of a stronger degree of oxydation, in which the oxyd is puce colored. Iron becomes successively a green, brown and white oxyd. Copper changes from brown to blue, and lastly green. Emily. Pray, is the white lead with which houses are painted, prepared by oxydating lead ? Mrs. B. Not merely by oxydating, but by being also united with carbonic acid. It is a carbonat of lead. The mere oxyd of lead is called red lead. Litharge is another oxyd of lead, containing less oxygen. Almost all the metallic oxyds are used as paints. The various sorts of ochres consist chiefly of iron more or less oxydated. And it is a remarkable circumstance, that if you burn metals rap- idly, the light or flame they emit during combustion partakes of the colors which the oxyd successively assumes. Caroline. How is that accounted for, Mrs. B., since light does not proceed from the burning body, but from the decomposition of the oxygen gas ? Mrs B. The correspondence of the Color of the light, with that of the oxyd which emits it, is, in all probability, owing to some par- ticles of the metal which are volatilized and carried off by the caloric . 618. Are light and heat disengaged when metals oxydate from the atmosphere, without an elevation of temperature ? 619. Why are they not perceived ? 620. What changes of color do lead, iron, and copper undergo during their different degrees of oxydation? • 621. How is common white lead obtained ? 622. For what purpose are most of the metallic oxyds used ? 623. How are yellow paints or ochres obtained, or of what are they composed ? 152 METALS. Caroline. It is then a sort of metallic gas. Emily. Why is it reckoned so unwholesome to breathe the air of a place where metals are melting ? Mrs. B. Perhaps the notion is too generally entertained. But it is true with respect to lead, and some other noxious metals, because unless care be taken, the particles of the oxyd which are volatili- zed by the heat are inhaled with the breath, and may produce dan- gerous effects. Fig. 28. I must show you some instances of the combus- tion of metals; it would re- quire the heat of a furnace to make them burn in the common air, but if we supply them with a stream of oxygen gas, we may easily accomplish it. Caroline. It will still, I suppose, be necessary in some degree to raise their temperature ? Mrs. B. This, as you shall see, is very easily done, particularly if the experiment be tried upon a small scale. I begin by lighting this piece of char- coal with the candle, and then increase the rapidity of its combustion by blow- ing upon it with a blow- pipe. (Fig. 28, No. 1.) Emily. That I do not understand ; for it is not every kind of air, but merely oxygen gas, that produces combustion.— Now you said that in brea- thing we inspired, but did pot expire oxygen gas.— Why, therefore, should the air which you breathe through the blow-pipe promote the combustion of the charcoa ? Mrs B. Because the /Apparatus for the combustion of metal&by means air. which has but once olBoxygengas.. No. 1. Igniting charcoalAvitha ta-j thromrh the lunirs plr and blow-ptpe. No. 2. Combustion of metals passea uirougn uie lungs, by means of a blow-pipe conveying a stream of IS yet but little altered, a oxygen gas from a gas-holder. small portion only of its ox- ygen being destroyed ; so that a great deal more is gained by in- creasingthe rapidity of the current, by meansdf the blow-pipe, than 624. Why is it reckoned unwholesome to breathe the air of a plaee in which metals are melting ? • 625. What gas produces combustion ? METALS. 153 is lost in consequence of the air passing once through the lungs, as you shall see— Emily. Yes, indeed, it makes the charcoal burn much brighter. Mrs. B. Whilst it is red hot, I shall drop some iron filings on it, and supply them with a current of oxygen gas, by means of this apparatus, (Fig. 28, No. 2,) which consists simply of a closed tin cylindrical vessel, full of oxygen gas, with two apertures and stop- cocks, by one of which a stream of water is thrown into the vessel through a long funnel, whilst by the other the gas is forced out through a blow-pipe adapted to it, as the water gains admittance. Now that I pour water into the funnel, you may hear the gas issu- ing from the blow-pipe. 1 bring the charcoal close to the current, and drop the filings upon it— Caroline. They emit much the same vivid light as the combustion of the iron wire in oxygen gas. Mrs. B. The process is, in fact, the same ; there is only some difference in the mode of conducting it. Let us burn some tin in the same manner—you see that it is equally combustible. Let us now try some copper— Caroline. This burns with a greenish flame; it is, I suppose, owing to the color of the oxyd ? Emily. Pray, shall we not also burn some gold? Mrs. B. That is not in our power, at least, in this way. Gold, silver, and platina, are incapable of being oxydated by the greatest heatjthat we can produce by the common method. It is from this circumstance, that they have been called perfect metals. Even these, however, have an affinity for oxygen ; but their oxydation or combustion can be performed only by means of acids, or by electricity. The spark given out by the Voltaic battery produces at the point of contact, a greater degree of heat than any other process ; and it is at this very high temperature only that the affinity of these metals for oxygen will enable them to act on each other. I am sorry that I cannot show you the combustion of the perfect metals by this process, but it requires a considerable Voltaic battery. You will see these experiments pertormed in the most perfect man- ner, when you attend the chemical lectures of the Royal Institution. But in the mean time I can, without difficulty, show you an ingen- ious apparatus lately contrived for the purpose of producing intense heats, the power of which nearly equals that of the largest Voltaic batteries. It simply consists, you see, in a strong box, made of iron orcopper, (Fig. 29.) to which may be adapted the air syringe or condensing pump, and a stop-cock, terminating in a small orifice similar to that of a blow-pipe. By working the condensing syringe up and down in this manner, a quantity of air is accumulated in the vessel, which may be increased to almost any extent, so that, if we now turn the stop-cock, the condensed air will rush out, forming a jet of considerable force ; and if we place the flame of a lamp in the current, you will see how violently the flame is driven in that direc- 626. What is represented by figure 28 ? • 627. W hat metals have been called perfect ? . 628. Why have they been thus called ? 629. What is represented by figure 29? 154 metals; - Fig. 29. A, the reservoir of condensed air. B, the condensing syringe. C, the bladder for oxygen. D, the moveable jet. Caroline. It seems to be exactly the same effect as that ofa blow- pipe worked by the mouth, only much stronger. Emily. Yes ; and the instalment has this additional advantage, that it does not fatigue the mouth and lungs like the common blow- pipe, and requires no art in blowing. Mrs.B. Unquestionably ; but yet this blow-pipe would be of very limited utility, if its energy and power c«uld not be greatly increased by some other contrivance. Can you imagine any mode of producing such an effect? Emily. Could not the reservoir be charged with pure oxygen instead of common air, as in the case of the gas-holder ? Mrs. B. Undoubtedly ; this is precisely the contrivancel allude to. The vessel need only be supplied with air from a bladder full of oxygen^ instead of the air of the room, and this, you see, may be easily done by screwing the bladderon the upper part of the syringe, so that, in working the syringe, the oxygen gas is forced from the bladder into the condensing vessel. Caroline. With the aid of this small apparatus, therefore, we could obtain the same effects as those we have just produced with the gas- holder, by means of a column of water forcing the gas out of it. Mrs. B. Yes; and much more conveniently so. But there is a mode of using this apparatus, by which more powerful effects still may be obtained. It consists in condensing in the reservoir, not oxygen alone, but a mixture of oxygen and hydrogen in the exact pr6portion in which they unite to produce water; and then kindle '630. How could the reservoir in that figure be supplied with oxygen ? 631. How is the most intense heat produced ? METALS. 155 the jet formed by the mixed gases. The heat disengaged by this combustion, without the help of any lamp, is probably the most in- tense known ; and various effects are said to have been obtained from it which exceed all expectation. Caroline But why should we not try this experiment ? Mrs. B. Because it is not exempt from danger ;* the combustion (notwithstanding various contrivances which have been resorted to with a view to prevent accident) being apt to penetrate into the in- side of the vessel, and lo produce a dangerous and violent explosion. We shall, therefore, now proceed lo our subject. Caroline. I think ypu said the oxyds of metals could be restored to their metallic state^1 ^ Mrs.B. Yes; this'operation is called reviving a metal. Metals are in general capable of being revived by\charcoal,)when heated red hot, charcoal having a greater attraction for oxygen than the metals. You need only, therefore, decompose, or unburn the oxyd by depriving it of its oxygen and the metal will be restored to its pure state. Emily. But will the carbon, by this process, be burnt, and be converted into carbonic acid?j Mrs. B. Certainly. There are other combustible substances to which metals of a high temperature will part with their oxygen. They will also yield it to each other, according to their several de- grees of attraction for it; and if the oxygen goes into a more dense state in the metals which it enters, than it existed in that which it quits, a proportional disengagement of caloric will take place. Caroline. And cannot the oxyds of gold, silver, and platina, which are formed by means of acids or of the electric fluid, be re- stored to their metallic state ? Mrs. B. Yes, they may, and the intervention of a combustible body is not required ;' heat alone will take the oxygen from them, convert it into gas, and revive the metal. Emily. You said that rust was an oxyd of iron ; how is it, then, that water, or merely dampness, produces it, which you know, it very frequently does on steel grates, or any iron instruments ? * Hydrogen and oxygen may be burned together with the most perfect safety by means of the compound blow-pipe, an instrument invented by Prof. Hare, of Philadelphia. Instead'of mixing the gases in the same reservoir, they are kept separate until they meet at the point of combustion. An account of this blow-pipe is given by Prof. Silliman, in his edition of Henry's chemistry, together with a list of experiments made with it on various substances. This was the first notice of any experiment made by burning the two gases together, for the purpose of obtaining au intense heat.—C. ' 632. How may oxygen and hydrogen be burned together with safety 633. W hat is called reviving a metal ? ' 634. By what are metals revived ? 635. What effect is produced on the carbon which is used to revive a metal ? ' 636. Can the oxyds of the perfect metals be restored to their me- tallic state? - 637. By what means? - 156 METALS. Mrs. B. In that case the metal decomposes the water, or damp- i ness (which is nothing but water in a state of vapour,) and obtains the oxygen from itN Caroline. I thought that it was necessary to bring metals to a ve- ry high temperature to enable them to decompose water. Mrs. B. It is so, if it is required that the process should be per- formed rapidly, and if any considerable quantity is to be decompos- ed. Rust, you know, is sometimes months in forming, and then it is only the surface of the metal that is oxydated. Emily. Metals, then, that do not rust, are incapable of spontane- ous oxydation,;either by air or water? Mrs.B. Ye?; and this is the case with the perfect metals, which on that account, preserve their metallic lustre so well. Emily. Are all metals capable of decomposing water, provided their temperature be sufficiently raised ? Mrs. B. No ; a certain degree of attraction is requisite, besides the assistance of heat. Water, you recollect, is composed of oxy- gen and hydrogen ; and, unless the affinity of the metal for oxygen be stronger than that of the hydrogen, it is in vain that we raise its temperature, for it cannot take (he oxygen from the hydrogen.— I, Iron, zinc, tin, and antimony, have a stronger affinity for oxygen than hydrogen has, therefore these four metals are capable of de- composing water. But hydrogen, having an advantage over all the other metals with respect to its affinity for oxygen, it not only with- holds its oxygen from them, but is even capable, under certain cir- cumstances, of taking the oxygen from the oxyds of these metals. Emily. I confess that I do not quite understand why hydrogen can take oxygen from those metals which do not decompose water. Caroline. Now I think I do perfectly. Lead, for instance, will not decompose water, because it hasAiot so strong an attraction for, oxygen as hydrogen has. Well, then, suppose the lead to be in a state of oxyd ; hydrogen'will take the oxyd from the lead, and unite with it to form water, because hydrogen has a stronger attraction than oxygen has for lead, and it is the same with all the other met- als, which do not decompose water. Emily. I understand your explanation, Caroline, very well; aod I imagine that it is because lead cannot decompose water that it is so much employed for pipes for conveying that fluid.* Mrs. B. Certainly ; lead is, on that account, particularly appro- priate to such purposes; whilst, on the contrary, this metal, if it was oxydable by water, would impart to it very noxious qualities, as all oxyds of lead are more or less pernicious. * Lead is capable of decomposing water, and when suffered to stand long in a vessel of this metal, it becomes poisonous. When used merely lo convey water, there is but little danger.—C. 638. If rust is an oxyd of iron, why is it that water or dampness causes it? ■ 639. Do the metals oxydate on being exposed to the air? 640. Why will not the perfect metals rust? 641. What metals are capable of decomposing water? 642. Why cannot all metals decompose water ? METALS. 157 But with regard to the oxydation of metals, the most powerful mode of effecting it is by means of acids. These, you know, con- tain a much greater proportion of oxygen than either air or water ; and will, most of them, easily yield it to metals. Thus, you recollect, the zinc plates of the voltaic battery are ox- ydated by the'acid ;and water, much more effectually than by water alone. Caroline. And I have often observed that if I drop vinegar, lem- on, or any acid on the blade of a knife, or on a pair of scissors, it will immediately produce a spot of rust. Emily. Metals have, then, three ways of obtaining oxygen ; from the atmosphere, from water, and from acids. Mrs. B. The two first you have already witnessed; and 1 shall now show you how metals take the oxygen from an acid. This bot- tle contains nitric acid ; I shall pour some of it over this piece of copper leaf. Caroline. Oh, what a disagreeable smell! Emily. And what is it that produces the effervescence, and that thick yellow yapour ? , Mrs. B. It is the acid,jwhich, being abandoned by the greatest part of its oxygen, is converted iuto a weaker acid, which escapes in the form of gas. Caroline. And whence proceeds this heat ? Mrs. B. Indeed, Caroline, I think you might now be able to an- swer that question yourself. Caroline. Perhaps it is that the oxygen enters into the metal in a more solid state than it existed in the acid, in consequence of which caloric is disengaged. Mrs. B. If the combination of (he oxygen and the metal results from the union of their opposite electricities, of course caloric must be given out. Emily. The effervescence is over ; therefore I suppose that the metal is now oxydated. Mrs. B. Yes ; but there is another important connexion between metals and acids, with which I must now make you acquainted. Metals, when in a state of oxyds, are capable of being dissolved by acids. In this operation they enter into a chemical combination with the acid, and form an entirely new compound. Caroline. But what difference is there between the oxydation and the dissolution of the metal by an acid ? Mrs. B. In the first place, the metal merely combines with a por. tion of oxygen taken from the acid, which is thus partly deoxygen. ated, as in the instance you have just seen ; in the second case the metal, after being previously oxydated, is actually dissolved in the ' 643. What is the most powerful mode of oxydating metals ? •644. From what do metals obtain oxygen ? • 645. When a metal dissolves an acid, what causes the efferves- cence ? 646. To what is the heat owing when a metal is dissolved in acid ? 647. What state must a metal be in before it can be dissolved by an acid ? 648. How can a metal then be dissolved ? 649. What is the difference between the oxydation and the dissolu- tion of a metal by an acid ? 14 158 METALS. acid, and enters into a chemical combination with it, without produ- cing any further decomposition or effervescence. This complete combination of an oxyd and an acid forms a peculiar and important class of compound salts. Emily. The difference between an oxyd and a compound salt, therefore, is very obvious ; the one consists of a metal and oxygen, the other of'an oxyd and an acid. • Mrs. B. Very well ; and you will be careful to remember that the metals are incapable of entering into this combination with acids, unless they are previously oxydated ; therefore whenever you bring a metal in contact with an acid, it will be first oxydated, and after- wards dissolved, provided that there be a sufficient quantity of acid for both operations. There are some metals, however, whose solution is more easily ac- complished by diluting the acid in water; and the metal will, inthis case, be oxydated, not by the acid, but by the water, which it will decompose. But in proportion as the oxygen of the water oxydates the surface of the metal, the acid combines with it, washes it off, and leaves a fresh surface fur the oxygen to act upon ; then other coats of oxyd are successively formed, and rapidly dissolved by the acid, which continues combining with the new formed surfaces of oxyd till the whole of the metal is dissolved. During this process, the hy- drogen gas of the water is disengaged, and flies off with efferves- cence. Emily. Was not this the manner in which the sulphuric acid as- sisted the iron filings in decomposing water? Mrs. B. Exactly ; and it is thus that several metals, which are incapable alone of decomposing water, are enabled to doit by the assistance of an acid, which, by continually washing off the cover- ing ofoxydAas it is formed, prepares a fresh surface of metal to act upon the water. Caroline. The acid here seems to act a part not very different from that of a scrubbing brush. But pray, would not this be a good method of cleansing metallic utensils? Mrs.B. Yes; on some occasions a weak acid, as vinegar, is used for cleaning copper. Iron plates, too, are freed from the rust on their surface by diluted muriatic acid, previous to their being cov- ered with tin. You must femember, however, that in this modeof cleaning metals, the acid should be quickly afterwards wiped off, otherwise it will produce fresh oxyd* Caroline. Let us watch the dissolution of the copper in the nitric acid ; for I am very impatient to see the salt that is to return from it. The mixture is now of a beautiful blue colour ; but there is no appearance of the formation of a salt; it seems to be a tedious ope- ration. Mrs. B. The crystallization of the salt requires some length of time to be completed; if, however, you are too impatient, 1 can ea- sily show you a metallic salt already formed. Caroline. But that would not satisfy my curiosity half so well as one of our own manufacturing. Mrs. B. It is one of our own preparing that I mean to show you. When we decomposed water a few days since, by the oxydation of 650. What is the difference between a compound salt and an oxyd ? 651. Why are acids good in cleaning rust from metals ? f, >2. What caution is necessary in cleaning metals by acids ? METALS. 159 iron filings through the assistance of sulphuric acid, in what did the process consist ? Caroline. In proportion as the water yielded its oxygen to the iron, the acid combined with the new formed oxyd, and the hydro- gen escaped alone. Mrs. B. Very well; the result, therefore, was a compound ?alt, formed by the combination of sulphuric acid with oxygen of iron. It still remains in the Vessel in which the experiment was performed. Fetch it, and we shall examine it. Emily. What a variety of processes the decomposition of water, by a metal and an acid, implies : 1st, the decomposition of the wa- ter ; 2dly, the oxydation of the metal; and 3dly, the formation of a compound salt. \ Caroline. Here it is, Mrs. B. What beautiful green crystals ! But we do not perceive any crystals in the solution of copper in ni- trous acid. Mrs. B. Because the salt i« now suspended in the wafer which the nitrous acid contains, and will remain so till it is deposited, in consequence of rest and cooling. Emily. I am surprised that a body so opaque as iron can be con- verted into such transparent crystals. , Mrs. B. It is the union with the acid fchat produces the transpa- rency ; for if the pure metal were melted, and afterwards permitted to cool and crystallize, it would be found just as opaque as before. Emily. I do not understand the exact meaning of crystallization. Mrs. B. You recollect that when a solid body is dissolved, either by water or caloric, it is not decomposed : but that its integrant parts are only suspended in the solvent. When the solution is made in water, the integrant particles of the body will, on the water being evaporated, again unite into a solid mass, by the force of their mu- tual attraction. But when the body is dissolved by caloric alone; nothing more is necessary, in order to make its particles re-unite, than to reduce its temperature. And, in general, if the solvent, whether water or caloric, be slowly separated by evaporation or by cooling, and care taken that the particles be not agitated during their re-union, they will arrange themselves in regular masses, each individual substance assuming a peculiar form or arrangement: and this is what is called crystallization. Emily. Crystallization, therefore, is simply there-union of the particles of a solid body which has been dissolved in a fluid.* Mrs. B. That is a very good definition of it. But 1 must not forget to observe, that heat and water may unite their solvent pow- ers, and in this case, crystallization may be hastened by cooling, as well as by evaporating the liquid. Caroline. But if the body dissolved is of a volatile nature, will it not evaporate with the fluid ? * Not exactly, because the particles of the fluid make a part of the crystal. Crystallization is/that process by which the particles of bodies unite to form solids, of certain, and regular shapesTy-C. 653. What processes does the decomposition of water by a metal and an acid imply ? ' 654. What causes crystallized iron to be transparent ? a. What is crystallization ? 160 METALS. Mrs. B. A crystallized body held in solution only by water is scarcely ever so volatile as the fluid itself; and care must be taken to manage the heat so that it may be sufficient to evaporate the water only. I should not omit also to mention that bodies, in crystallizing from their watery solution, always retain 6 small portion of water, which remains confined in the crystal,)in a solid form, and does not re-ap- pear unless the body loses its-crystalline state. This is called the water of crystallization. But you must observe, that whilst a body may be separated from its solution in water or caloric simply by cooling or by evaporation, an acid can be taken from a metal with which it is combined only by stronger affinities, which produce a decomposition. Emily. Are the perfect metals susceptible of being dissolved and converted into compound salts by acids ? Mrs. B. Gold is acted upon by only one acid, the oxygenated muriatic, a very remarkable acid, which, when it is in its most con- centrated state, dissolves gold or any other metal, by burning them rapidly. i Gold can,i it is true, be dissolved likewise by a mixture of two acids, commonly called aqua regia; but this mixed solvent derives that property from containing the peculiar acid which I have just mentioned. Platina is also acted upon by this acid only ; silver is dissolved by nitric acid. Caroline. I think you said that some of the metals might be so strongly oxydated as to become acid ? Mrs. B. There are five metals', arsenic, molybdean, chrome, tungsten, and columbium^which are susceptible of combining with a sufficient quantity of oxygen to be converted into acids. Caroline. Acids are connected with metals in such a variety of ways, that I am afraid of some confusion in remembering them. In the first place, acids will yield their oxygen to metals. Secondly, they will combine with them in their state of oxyds, to form com- pound salts ; and lastly, several of the metals are themselves sus- ceptible of acidification. Mrs. B. Very well; but though metals have so great an affinity for acids, it is not with that class of bodies alone that they will com- bine. They are most of them, in their simple state, capable of uni- ting with sulphur, with phosphorus, with carbon, and with each other ; these combinations, according to the nomenclature which was explained to you on a former occasion, are called sulphurels, phosphorets, carburets, fyc. The metallic phosphorets offer nothing very remarkable. The sulphurets form the peculiar kind of mineral called pyrites, from which certain kind of mineral waters, as those of Harrogate, derive 655. What is the water of crystallization? 656. Are the perfect metals susceptible of being dissolved and con- verted into compound salts by acids ? 657. Can any of the metals combine with so great a quantity of oxygen as to become acids ? • 658. With what other substances besides acids, will metals com- bine? • 659. What are the combinations of the metals with each other call- ed? METALS. 161 their chief chemical properties. In this combination, the sulphur* together with the iron, have so strong an attraction for oxygen, that they both obtain it from the air and from water, and by condensing it in a solid form, produce the heat which raises the temperature of the water in such a remarkable degree. Emily. But if pyrites obtain oxygen from water, that water must suffer a decomposition, and hydrogen gas be evolved. Mrs. B. That is actually the case iu the hot springs alluded to, which give out an extremely fetid gas, composed of hydrogen, im- pregnated with sulphur. Caroline. If I recollect right, steel and plumbago) which you mentioned in the last lesson, are both carburets of iron. Mrs. B. Yes ; and they are the only carburets of much conse- quence. A curious combination of metals has lately very much attracted the attention of the scientific world : I mean the meteoric stones which fall from the atmosphere. They consist principally of native Of pure iron, which is never found in that state in the bowels of the earth ;* and 'contain also a small quantity of nickel and chrome, a combination likewise new in the mineral kingdom. These circumstances have led many scientific persons to believe that those substances have fallen from the moon, or some other planet, while others are ofopinion either that they are formed in the atmosphere, or are projected into it by some unknown volcano, on the surface of our globe. J Caroline. I have heard much of these stones, but I believe many people are of opinion that they are formed on the surface of the earth, and laugh at their pretended celestial origin. Mrs. B. Tbe fact of their falling is so well ascertained that I think no person who has at all investigated the subject, can now entertain any doubt of it. Specimens of these stones have been dis- covered in all parts of the world, and to each of them some tradition or story of its fall has been found connected. And as the analysis of all those specimens afford precisely the same results, there is strong * This seems to be a mistake. Several localities of native iron, found in veins,, are pointed out by authors. In several instances large blocks of native iron have been found on the surface of the earth;—One found by Prof. Pallas in Siberia, weighed 1600 lbs; Another found in South America, is said to weigh 30,000 lbs. &c. These have been suspected to be of meteoric origin, though nothing is known which makes this certain, i hose stones which are known beyond a doubt to have fallen from the atmosphere, have a very dif- ferent composition. These generally contain the following ingre- dients, viz. iron, nickel, chrome, oxide of iron, sulphur, silex, lime, mag- nesia, and alumine. The iron rarely amounts to a quarter of the whole. Accounts are recorded of the falling of stones, sulphur, &c. in every age since the Christian era, and in almost every part of the world.—C. "660. What are the most important carburets ? 661. Of what do the meteoric stones which have attracted so much attention from the scientific world< consist ? 662. What opinions have been entertained as to the origin of these stones ? 14* 162 METALS. reason to conjecturelhat they all proceed from the same source. It is to Mr. Howard that philosophers are indebted for having first analysed these stones, and directed their attention to this interest- ing subject. Mrs. B. But pray, Mrs. B., how can solid masses of iron and nickel be formed from the atmosphere, which consists of the two airs, nitrogen and oxygen ? Mrs. B. I really do not see how they could, and think it much more probable that they fall from the moon, or some other celestial body.—But we must not suffer this digression to take up too much of our time. The combinations of metals with each other are called alloys; thus brass is an alloy of copper andzinc ; bronze of copper and tin,&c, Emily. And is not pewter also a combination of metal ? Mrs. B. It is. The pewter made in this country is mostly com- posed of tin, with a very small proportion of zinc and leack Caroline. Block-tin is a kind of pewter, I believe ? Mrs.B. Properly speaking, block-tin means tin in blocks, or square massive ingots ; but in the sense in which it is used by ig. norant workmen, it is iron plated with tin, which renders it more du- rable, as tin will not so easily rust. Tin alote, however, would be too soft a mcSal to be worked for common use, and all tin vessels and utensils are in fact made of plates of iron, thinly coated with tin, which prevents the iron from rusting. Caroline. Say rather oxydaling. Mrs. B.—Rust, is a word that ought to be exploded in chemistry. Mrs. B. Take care, however, not to introduce the word oxydate instead of rust, in general conversation ; for you would probably not be understood, and you might be suspected" of affectation. Metals differ very much in their affinitv for each other; some will not unite at all, others readily combine together, and on thia properly of metals the art otsoldering depends. Emily. What is soldering ? Mrs. B. It is joining two pieces of metal together, by a more fu- sible metal interposed between them. Thus tin is a solder for lead; brass, gold, or silver, are solder for iron, &c. Caroline. And is not plating metals something of the same nature ? Mrs. B. In the operation of plating, two metals are united, one being covered with the other, but without the intervention of a third : iron or copper may thus be covered with gold or silver. iLmily. Mercury appears to me of a verv different nature from the other metals. Mrs.B. One of its greatest peculiarities is, that it retains a fluid state at the temperature of the atmosphere. All metals are fusible at different degrees of heat, and they have likewise each the proper- ty of freezing or becoming solid at a certain fixed temperature— 663. Who first analysed these stones? alt S^tT thu6 combinati°ns of metals with each other called? bb5. Oi what is brass an alloy ? 666. Of what is pewter composed ? 667. What is block-tin? - 668. On what does the art of soldering depend ? Metals. 163 Mercury congeals only at seventy-two degrees below the freezing point. Emily. That is to say, that in order to freeze. It requires a tem- perature of seventy-two degrees colder than that at which water freezes. Mrs. B. Exactly so. Caroline. But is the temperature of the atmosphere ever so low as that? Mrs. B. Yes, often in Siberia; but happily never in this part of the globe. Here, however, mercury may be congealed by artifi- cial cold; I mean such intense cold as can be produced by some chemical mixtures or by the rapid evaporation of ether under the air pump.* Caroline. And can mercury be made to boil and evaporate? Mrs.B. Yes, like any other liquid; only it requires a much greater degree of heat. At the temperature of six hundred de- grees, it begins to boil ano evaporate like water. Mercury combines with gold, silver, tin, and with several other metals; and, if mixed with any of them in a sufficient proportion, it penetrates the solid metal, softens it, loses its own fluidity, and forms an'amalgam,^which is the name given to the combination of any metal with mercury, forming a substance more or less solid, according as the mercury or the other metal predominates. Emily. In the list of metals there are some whose names I have never before heard mentioned; Mrs. B. Besides those which SirH. DaVyhas obtained, there are several that have been recently discovered, whose properties are yet but little known, as for instance, titanium, which was discover- ed by the Rev. Mr. Gregor in the tin-mines of Cornwall; colum- bium or tantalium, which has lately been discovered by Mr. Hatch- ett; andosmium, iridium, palladium, and rhodium, all of which Dr. Wollaston and Mr. Tenant found mixed in minute quantities with crude platina, and the distinct existence of which thev proved by curious and delicate experiments. More recently still Professor Berzelius has discovered in a pyritic ore, at Fahlun, in Sweden, a metallic substance, which he has called selenium, and which has the singular peculiarity of assuming the form of a yellow gas when heated in close vessels. In some of its properties this substance seems to hold a medium between the combustibles and the metals. It bears in particular a strong analogy to sulphur. Caroline. Arsenic has been mentioned amongst the metals; I had no notion that it belonged to that class of bodies, for I had never seen it but as a powder, and never thought of it but as a most dead- ly poison. " Mrs. B. In its pure metallic state, I believe it is not so poisonous; but it has such a great affinity for oxygen, that it absorbs it from the atmosphere at its natural temperature; you have seen it therefore, * By a process analogous to that described, page 81 of this work. 669. At what temperature will mercury congeal ? •b70. At what temperature will it boil and evaporate? 671. What is the combination of metal with mercury called ? 672. What metals have been recently discovered ? ,.673. What is the natural state of arsenic? 164 METALS* only in its state of oxyd, when, from its combination with oxygen, it has acquired its very poisonous properties. Caroline. Is it possible that oxygen can impart poisonous quali- ties? That valuable substance which produces light and fire, and which all bodies in nature are so eager to obtain? Mrs. B. Most of the metallic oxyds are poisonous, and derive this property from their union with oxygen. The white lead, so much used in paint, owes its pernicious effects to oxygen. In gen- eral, oxygen, in a concrete state, appears to be particularly destruc- tive in its effects on flesh or any animal matter; and those oxyds are most caustic that have an'acrid, burning taste, which proceeds from the metal having but a slight affinity for oxygen, and therefore easily yielding to the flesh, which it corrodes and destroys. Emily. What is the meaning of the word caustic, which you have just used? Mrs. B. It expresses that property which some bodies possess, of disorganizing and destroying animal matter, by operating a kind of combustion, or at least a chemical decomposition. You must often have heard of caustic used to burn warts, or other animal excres- cences ; most of these bodies owe their destructive power to the ox- ygen with which they are combined. The common caustic called lunar caustic, is a compound formed by the union of nitric acid and silver; and it is supposed to owe its caustic qualities to the oxygen contained in the nitric acid. Caroline. But, pray, are not acids still more caustic than oxydsj as they contain a greater proportion of oxygen ? *i Mrs. B. Some of the acids are; but the caustic property of a bo- dy depends not only upon the quantity of oxygen which it contains, but also upon its slight affinity for that principle, and tbe consequent facility with which it yields it. Emily. Is not this destructive property of oxygen accounted for? Mrs. B. It proceeds probably from the strong attraction of oxy- gen for hydrogen ^ for if the one rapidly absorb the other from the animal fibre, a disorganization of the substance must ensue. Emily. Caustics are, then, very properly said to burn the flesh, since the combination of oxygen and hydrogen is an actual com- bustion. Caroline. Now, I think, this effect would be more properly term- ed an oxydation, as there is no disengagement of light and heat. Mrs. B. But there really is a sensation of heat produced % the action of caustics. Emily. If oxygen is so caustic, why does not that which is con- tained in the atmosphere.burn us? Mrs. B. Because it is in a gaseous state,/and has a greater at- traction for its electricity than for the hydrogen of our bodies. Be- sides, should the air be slightly caustic, We are in a great measure sheltered from its effects by the skin: you know how much a wound, however trifling, smarts on being exposed to it. 674. From what do metals derive their poisonous properties? 675. What is a caustic ? 676. On what does the caustic property of a body depend ? 677. How is this destructive property of oxygen accounted for' ' 678. If oxygen is of a caustic tendency, why does not that burn ue, which is contained in the atmosphere ? METALS* 165 Caroline. It is a curious idea, however, that we should live in a slow fire. But, if the air was caustic, would it not have an acrid taste ? Mrs. B. It possibly may have such a taste; though in so slight a degree, that custom has rendered it insensible. Caroline. And why is not water caustic ? When I dip my hand into water, though cold, it ought to burn me from the caustic na- ture of its oxvgen ? Mrs.B. Your hand does not decompose the water; the oxygen in that state is much better supplied with hydrogen/than it would be by animal matter, and. if its causticity depend on its affinity for that principle, it will be very far from quitting its state of water to act upon your hand. You must not forget that oxyds are caustic in proportion as the oxygen adheres slightly to them. Emily. Since the oxyd of arsenic is poisonous, its acid, I suppose, is fully as much so? Mrs. B. Yes, it is one of the strongest poisons in nature. Emily. There is a poison called verdigris, which forms on brass and copper when not kept very clean ; and this I have heard, is an objection to these metals being made into kitchen utensils. Is this poison likewise occasioned by oxygen? Mrs. B. It is produced by the intervention of oxygen, for verdi- gris is a compound salt formed by the union of vinegar and copper; it is a beautiful green color, and much used in painting. . Emily. But,, I believe;, verdigris is often formed on copper when no vinegar hj8 been in contact with it. "' Mrs B. Not real verdigris, but other salts, somewhat resembling it, may be produced by the action of other acids on copper. The solution of copper in nitric acid, if evaporated, affords a salt which produces an effect on tin that will surprise you, and I have prepared some from thesojutiou we made before, that I might show it to you. 1 shall first sprinkle some water on this piece of tinfoil, and then some of the salt.-^-Now observe that I fold it up suddenly, and press it into one lump. Caroline. What a prodigious vapor issues from it—and sparks of fire, I declare! Mrs. B. 1 thought it would surprise you. The effect, however, I dare say you could account for, since it is merely the consequence of the oxygen of the salt rapidly entering into a closer combination with the tin. There is also a beautiful green salt too curious to be omitted ; it is produced by the combination of cobalt with muriatic acid, which has the singular property of forming what is called sympathetic ink. Characters written with this solution are invisible when cold, but when a gentle heat is applied, they assume a fine bluish green col- or. Caroline. 1 think one might draw very curious landscapes with the assistance of this ink; 1 would first make a water color draw- * 679. W hy is not water caustic ? 680. What is verdigris ? 681. What experiment is made with a piece of tin-foil and a solu- tion of copper in nitric acid ? 682. What is called sympathetic ink ? • 683. What are the peculiarities of this ink ? 166 METALS. ing of a winter scene, in which the trees would be leafless, and the grass scarcely green ; 1 would then trace all the verdure with the invisible ink, and whenever I chose to create spring, I should hold it before the fire, and its warmth would cover the landscape with a rich verdure. Airs. B. That will be a very amusing experiment, and I advise you by all means to try it. Before we part, I must introduce to your acquaintance the curi- ous metals which Sir H. Davy has recently discovered. The histo- ry of these extraordinary bodies is yet so much in its infancy that I shall confine myself to a very short account of them ; it is more important to point out to you the vast, and apparently inexhaustible field of research which has been thrown open to our view by Sir H. Davy's memorable discoveries, than to enter into a minute account of particular bodies or experiments. Caroline. But I have heard that these discoveries, however splen- did and extraordinary, are not very likely to prove of any great benefit to the world, as they are rather objects of curiosity than of use. Mrs. B. Such may be the illiberal conclusions of the ignorant and narrow-minded ; but those who can duly estimate the advanta- ges of enlarging the sphere of science, must be convinced that the acquisition of every new fact, however unconnected it may at first appear with practical utility, must ultimately prove beneficial to mankind. But these remarks are scarcely applicable to the pres- ent subject; for some of tbe new metals have already proved emi- nently useful as chemical agents, and are likely soon to be employed in the arts. For the enumeration of these metals, I must refer you to our list of simple bodies; they are derived from the alkalies, the earths, and three of the acids, all of which had been hitherto con- sidered as undecompoundable, or simple bodies. When Sir H. Davy first turned his attention to the effects of the Voltaic battery, he tried its power on a variety of compound bodies, and gradually brought to light a number of new and interesting facts, which led tbe way to more important discoveries. It would be highly interesting to trace his steps in this new department of science, but it would lead us too far from our principal object. A general view of his most remarbable discoveries is all that 1 can aim at or that you could, at present, understand. The facility with which compound bodies yielded to the Voltaic electricity, induced him to make a trial of its effects on substances hitherto considered as simple, but which he suspected of being com- pound, and his researches were soon crowned with the most com- plete success. The body which he first submitted to the Voltaic battery, and S2 ? "h™^* beuD decomP°sed, was one of the fixed alkalies called potash. This substance gave out an elastic fluid at the pos- itive wire which was ascertained to be oxygen, and at the negative wire, small globules of a ■very high metallic lustre, very similar in ' 684. What induced Sir H. Davy to try the effects of the Voltaic bat- tery on substances till then considered simple' -685. What was the first substance whieh he submitted to the Vol- T3.1 c DcLttcry ♦ ' 686. What was the effect ? METALS. 167 appearance to mercury; thus proving that potash, which had hith- erto been considered as a simple incombustible body, was in fact, a metallic oxyd ; , and that its incombustibility proceeded from its being already combined with oxygen. Emily. I suppose the wires used in this experiment were of pla- tina, as they were when you decomposed water ; for if of iron, the oxygen would have been combined with the wire, instead of appear- ing in the form of gas. Mrs. B. Certainly; the metal however, would equally have been disengaged. Sir H. Davy has distinguished this new substance by the name of potassium, which is derived from that of the alkali, from which it is procured. I have some small pieces of it in this phial, but you have already seen it, as it is the metal which we burnt in contact with sulphur. Emily. What is the liquid in which you keep it? Mrs. B. It is naptha, a bituminous liquid, with which I shall hereafter make you acquainted. 11 is almost the only fluid in which potassium can be preserved, as it contains no oxygen, and this metal has so powerful an attraction for oxygen, that it will not only absorb it from the air, but likewise from water, or any bod}' what- ever, that contains it. Emily. This, then, is one of the bodies that oxydates spontane- ously without the application of heat. Mrs. B. Yes: and it has this remarkable peculiarity, that it at- tracts oxygen much more rapidly from water than from air; so that wberj thrown into water Jhowever cold, it actually bursts into flame. I shall now throw a small piece, about the size of a pin's head, on this drop of water. Caroline. It instantaneously exploded, producing a little flash of light! This is, indeed, a most curious substance! Mrs. B. By its combustion it is re-converted into potash ; and as potash is now decidedly a compound body, I shall not enter into any of its properties till we have completed our review of the sim- ple bodies ; but we may here make a few observations on its basis, potassium. If this substance is left in contact with air, it rapidly returns to the state of potash, with a disengagement of heat, but without any flash of light. Emily. But is it not very singular that it should burn better in water than in air? Caroline. I do not think so ; for if the attraction of potassium for oxygen is so strong, that it finds no more difficulty in separating it from the hydrogen in water, than in absorbing it from the air, it will no doubt, be more amply and rapidly supplied by water than by air. Mrs. B. That cannot, however, be precisely the reason, for when potassium is introduced under water, without contact of air, the combustion is not so rapid, and, indeed, in that case there is no lu- minous appearance; but a violent action takes place, much beat is excited, the potash is regenerated and hydrogen gas is evolved. • 687. What did this prove ? .688. What is this new substance called? k689. What fluid contains no oxygen? • 690. What remarkable peculiarity has potassium ? 691. How may potassium be recomposed? 692. What will be the result if potassium is put under water with- out being in contact with air? 168 METALS. Potassium is so eminently combustible, that instead of requiring, like other metals, an elevation of temperature, it will burn rapidly in contact with water, even below the freezing point. This you may witness by throwing a piece on this lump of ice. Caroline. It again exploded with flame, and has made a deep hole in the ice. Mrs.B. This hole contains a solution of potash : for the alkali being extremely soluble, disappears in the water the instant it is produced. Its presence, however, may be easily ascertained, alka- lies having the properties of changing paper, stained with tumeric, to a red color; if you dip one end of this slip of paper into the hole in the ice, you will see it change color ; and the same, if you wet it with the drop of water in which the first piece of potassium was burnt. Caroline. It has indeed changed the paper from yellow to red. Mrs. B. This metal will burn likewise, in carbonic acid gas, a gas that has always been supposed incapable of supporting combus- tion, as we were unacquainted with any substance that had a great- er attraction for oxygen than carbon. ) Potassium, however, readi- ly decomposes this gas by absorbing its oxygen, as I shall show you. This retort is filled with carbonic acid gas. . I will put a small piece of potassium in it; but for this combustion a slight elevation of temperature is required, for which purpose I shall hold the retort over the lamp. Caroline. Now it has taken fire and burns with violence ! It has burst the retort. Mrs. B. Here is a piece of regenerated potash; can you tell me why it has become so black? Emily. No doubt it is blackened by the carbon, which, when its oxygen entered iuto combination with the potassium,, was deposited on its surface. Mrs. B. You are right. This metal is perfectly fluid at the tem- perature of one hundred degrees; at fifty degrees it is solid, but soft and malleable; at tbirty-two degrees it is hard and brittle, and its fracture exhibits an appearance of confused crystallization. It is scarcely more than half as heavy as water; its specific gravity be- ing about six, when water is reckoned at ten; so that this metal is actually lighter than any known fluid, even than ether. Potassium combines with sulphur and phosphorus, forming sul- phurets and phosphorets ; it likewise forms alloys with several met- als, and amalgamates with mercury. Emily. But can a sufficient quantity of potassium be obtained, by means of the Voltaic battery, to admit of all its properties and rela- tions to other bodies, beiog satisfactorily ascertained ? *S"j / 5°.te.a8,,yj. but J must not neglect to inform you that a method of obtaining this metal in considerable quantities, has since been discovered. Two eminent French chemists, Thenard and Gay Lussac, stimulated by the triumph which Sir H. Daw hadob- - 693. At how low a temperature will potassium burn in contact with water ? • 694. Why, until the discovery of potassium, had carbonic acid gas been considered incapable of supporting combustion ? 695. How does potassium decompose this gas ? 696. What metal is lighter than any known fluid ? METALS. 169 tained, attempted to separate potassium from its combination with oxygen by common chemical means, and without the aid of elec- tricity. They caused red hot potash in a state of fusion, to filter through iron turnings in an iron tube, heated to whiteness. Their experiment was crowned with tbe most complete success; more potassium was obtained by a single operation, than could have been collected in many weeks by the most diligent use of the Voltaic battery. Emily. In this experiment, I suppose the oxygen quitted its com- bination with the potassium, to unite with the iron turnings? Mrs. B. Exactly so; and thus the potassium was obtained in its simple state. From that time it has become a most convenient and powerful instrument of deoxygenation in chemical experiments.— This important improvement engrafted on Sir H. Davy's previous discoveries, served but to add to his glory, since the facts which he had established, when possessed only of a few atoms of this curious substance, and the accuracy of his analytical statements were all confirmed, when an opportunity occurred of repeating his exper- iments upon this substance, which can now be obtained in unlimit- ed quantities. Caroline. What a satisfaction Sir H. Davy must have felt, when by an effort of genius, he succeeded in bringing to light, and actu- ally giving existence to these curious bodies, which without him, might perhaps have ever remained concealed from our view ! Mrs. B. The next substance which Sir H. Davy submitted to the influence of the Voltaic battery, waslSoda^he other fixed alkali, whicb/yielded to the same powers of decomposition ; from this alkali too, almetallic substance was obtained, very analagous in its prop- erties to that which had been discovered in potash ; Sir H. Davy has called it sodium. It is rather heavier than potassium, though con- siderably lighter than water; it is not so easily fusible as potassium. Encouraged by these extraordinary results, Sir H. Davy next performed a series of beautiful experiments on Jlmmania, or the vol- atile alkali, which, from analogy, he was led to suspect, might also contain oxygen. This he soon ascertained to be the fact, but he has not yet succeeded in obtaining the basis of ammonia in a sepa- rate state : it is from analogy, and from the power which the volatile alkali has, in its gaseous form, to oxydate iron, and also from the amalgams which can be obtained from ammonia by various process- es, that the proofs of alkali being also a metallic oxyd are deduced. Thus, then, the three alkalies, two of which had always been con- sidered as simple bodies, have now lost all claim to that title, and I have accordingly classed the alkalies amongst the compounds, whose properties I shall treat of in a future conversation. Emily. What are the other newly discovered metals which you have alluded to in your list of simple bodies? 697. How may potassium be obtained in large quantities ? "698. In the experiment for obtaining potassium, why did the oxygen quit that substance ? ' 699. What was the next substance submitted to the influence of the Voltaic battery ? - 700. What was the effect ? • 701. What is the substance produced by the decomposition of Soda called ? 15 170 METALS. Mrs. B. They are the metals of the earth which became next the object of Sir H. Davy's researches; these bodies had never yet been decomposed, though they were strongly suspected, not only of being compounds, but of being metallic oxyds. From the circumstance of their incombustibility, it was conjectured with some plausibility, that they might possibly be bodies that had been already burnt. Caroline. And metals, when oxydated, become, to all appear- ance, a kind of earthy substance: Mrs. B. Thffy have besides,'several features of resemblance with metallic oxyds,* Sir H. Davy hnd, therefore, great reason to be sanguine in his expectations of decomposing them, and he was not disappointed. He could not, however, succeed in obtaining the basis of the earths in a pure separate state ; but metallic alloys were formed with other metals, which sufficiently proved the ex- istence of the metallic basis of the earths. The last class of new metallic bodies which Sir H. Davy discov- ered, was obtamedfarom the three undecompounded acids, the bora- cic, the fluoric, andMhe muriatic acids ; but as you are entirely un- acquainted with these bodies, I shall reserve the account of their decomposition, till we come to treat of their properties as acids. Thus in the course of two years, by the unparalleled exertions of a single individual, chemical science has assumed a new aspect. Bodies have been brought to light which the human eye never be- fore beheld, and which might have remained eternally concealed under their impenetrable disguise. It is impossible, at the present period, to appreciate, to their full extent, the consequences which science or the arts may derive from these discoveries; we may, however, anticipate the most important results. In chemical analysis, we are now in possession of more energetic agents of decomposition than were ever before known. In geology, new views are opened, which will probably operate a revolution in that obscure and difficult science. It is already pro- ved that all the earths, and, in fact, the solid surface of this globe, are metallic bodies-mineralized by oxygen, and as our planet has been calculated to be considerably more dense upon tbe whole than it is on the surface, it is more reasonable to Suppose that the inte- rior of the earth is composed'of a metallic mass, the surface of which only has been mineralized by the atmosphere. The eruption of volcanoes, those stupendous problems of nature, admit now of an easy explanation.* For if the bowels of the earth are the grand recess of these newly discovered inflammable bodies, whenever water penetrates into them, combustions and explosions * It is always easy to form a theory. / But an explanation of these " stupendous problems of nature,'' we believe has not yet been de- monstrated to the satisfaction of all, though great learning and im- 702. What peculiarities have the new metals, discovered by Sir H. Davy ? 703. What reason had Sir H. Davy for supposing the metals might be decomposed ? • 704. What are earths supposed to be ? 705. What is supposed to form the principal interior part of our globe ? ON THE ATTRACTION OP COMPOSITION. 171 roust take place; and it is remarkable that the lava which is thrown out, is thevery kind of substance which might be expected to result from these combustions.^/ I must now take my leave of you ; we have had a very long con- versation to-day, and I hope you will be able to recollect what you have learnt. At our next interview, we shall enter on a new sub- ject. CONVERSATION XIII. ON THE ATTRACTION OF COMPOSITION. Mrs. B. Having completed our examination of the simple or el- ementary bodies, we are now to proceed to those of a compound nature; but, before we enter on this extensive subject, it will be necessary to make you acquainted with the principal laws by which chemical combinations are governed. You recollect, 1 hope, what we formerly said of the nature of the attraction of composition, or chemical attraction, or affinity, as it is also called. Emily. Yes, I think, perfectly ; it is the attraction that subsists between bodies of a different nature, which occasions them to com- bine and form a compound, when they corm? in contact; and, ac- cording to Sir IT. Davy's opinion, this effect is produced by the at- traction of the opposite electricities, which prevailed in bodies of different kinds. Airs. B. Very well; your definition comprehends the first law of chemical attraction, which is, that it lakes place only between bo- dies of a different nature ; as, for instance, between an acid and an aiksli; between oxygen and a metal, &c. Caroline. That we understand of course; for the attraction be- tween particles of a similar nature is that of aggregation, or cohe- sion, which is independent of any chemical power. Mrs. B. The second law of chemical attraction, is, that it lakes place only between the most minute particles of bodies; therefore the mense labor has been bestowed on the subject. If the "easy ex- planation" is founded on the data here proposed, viz. that the solid surface of our globe consists of nothing except metals and oxygen, such a theory in the present state of knowledge, must chiefly con- sist of supposition piled on supposition; there being as yet no proof that the crust of the earth is formed onlv of these two elements.—: C. r706. How are volcanoes accounted for? '707. What do you understand by the attraction of composition ? "708. What cause does Sir H. Davy assign for the attraction be- tween bodies of a different nature ? "709. What is the first law of chemical attraction ? 710. What is the attraction between particles of a similar nature palled ? • 711. What the second law of chemical attraction ? 172 ON THE ATTRACTION more you divide the particles of the bodies to be combined, the more readily they act upon each other. Caroline. That is again a circumstance which we might have in- ferred ; for the finer the particles of the two substances are, the more easily and perfectly they will come in contact with each oth- er, which must greatly facilitate their union. It was for this pur- pose, you said, that you used iron filings, in preference to wires or pieces of iron, for the decomposition of water. Mrs.B. It was once supposed (hat no mechanical power could divide bodies into particles sufficiently minute for them to act on each other ; and that, in order to produce the extreme division re- quisite for a chemical action, one, if not both of the bodies, should be in a fluid state. There are, however, a few instances in which two solid bodies, very finely pulverized, exert a chemical action or* one another;* but such exceptions to the general rule are very rare indeed. Emily. In all the combinations that we have hitherto seen, one of the constituents has, I believe, been either liquid or aeriform.— In combustion, for instance, the oxygen is taken from the atmos- phere, in which it existed in a state of gas ; and whenever we have seen acids combine with metals or with alkalies, they were either in a liquid or an aeriform stafte. Mrs. B. The third law of cftemical attraction is, That it can take place between two, three, four, or even a greater number of bodies^ Caroline. Oxyds and acids are bodies composed of two constitu- ents, but I recollect no instance of the combination of a greater number of principles. Mrs. B- The compound salts, formed by the union of the metals with acids, are composed of three principles. And there are salts »- formed by the combination of the alkalies with the earths which are of a similar description. Caroline. Are they of the same kind as the metallic salts? Alrs.B. Yes; they are very analogous in their nature, although different in many oftheir properties. ( A methodical nomenclature, similar to that of the acids, has been adopted for the compound salts. Each individual salt derives its name from its constituent parts, so that every name implies a know- ledge of the composition of the salt. ^ f The-three alkalies, the alkaline earths, and the metals,) are called 1 salifiable bases or radicals, and the acids/Ratifying principles. The name of each salt is composed both of that of the acid and the salifi- able base; and it terminates j^n at or it acording to the degree of the oxygenation of the acid.' Thus, for instance, all thost salts which are formed by the combination of sulphuric acid with any of the salifiable bases, are called su/phats, and the name of the radical is * This is the case with muriate of ammonia and quick lime.—C. "712. What is necessary in order that chemical action take place be- tween different bodies? 713. What the third law of chemical attraction? 714. How are compound salts formed? 715. What are called salifiable bases or ladicals? 716. What are called salifying principles ? 717. How do salts ending in ate differ from those ending in ete ? OF COMPOSITION* 173 added for the specific distinction of the salt; if it be potash, it will compose a sulphat of potash; if ammonia, sulphat of ammonia, &c. Emily. The crystals which we obtained from the combination of iron and sulphuric acid were therefore called sulphat of iron. Airs. B. Precisely ; and those which we prepared by dissolving copper in nitric acid, nitrat of copper, and so on. But this is not all; ifthesaltbe formed by that kind of acids which.ends in out, (which you know indicates a less degree of oxygenation) the termi- nation of the name of the salt will be in it, as sulphit qf potash, sul- pliit of ammonia, &c. Emily. There must bean immense number of compound salts, Bince there is so great a variety of salifiable radicals, as well as of salifying principles. Mrs. B. Their real number cannot be ascertained, since it in- creases every day. But we must not proceed further in the inves- tigation of the compound salts, until we have completed the exami- nation of the nature of the ingredients of which they are composed. The fourth law of chemical attraction is, that a change of temper- ature always takes place at the moment of combination? This arises from the extrication of the two electricities) in the form of caloric, which always occurs when bodies unite; and also sometimes in part from a change of capacity in the bodies for heat, which always takes place when the combination is attended with an increase of density, but more especially when the compound passes from the liquid to the solid form. I shall now show vou a striking-instance of a change of temperature from chemical union, merely by pouring some ni- trous acid on this small quantity of oil of turpentineVthe oil will in- stantly combine with the oxygen of the acid, and produce a consid- erable change of temperature. Caroline. What a blaze! The temperature of the oil and the acid must be greatly raised, indeed, to procure such a violent com- bustion. Airs. B. There is, however, a peculiarity in this combustion, which is, that the oxygen, instead of being derived from the atmos- pheric air alone, is principally supplied by the acid itself. Emily. And are not all combustions instances of the change of temperature produced by the chemical combination of two bodies? Mrs.B. Undoubtedly; when oxygen loses its gaseous form, in order to combine with a solid body, it becomes condensed, and the caloric evolved produces the elevation of temperature. The spe- cific gravity of bodies is at tbe same time altered by chemical com- bination ; for in consequence of a change of capacity for heat, a change of density must be produced. Caroline. That was the case with the sulphuric acid and water, which, by being mixed together, gave out a great deal of heat, and increased in density. '718. How do acids ending in ic differ from those ending in ousi '719. What is the fourth law of chemical attraction? .720. From what does the change of temperature arise? 721. What is an instance of increase of temperature from chemical union ? 722. Is the specific gravity of bodies affected by chemical combina- tion ? 15* 174 ON THE ATTRACTION Mrs. B. The fifth law of chemical attraction is, that the proper- ties which characterize bodies, when separate, are altered or destroyed by their combination. \ Caroline. Certainly ; what, for instance, can be so differentfrom water, as the hydrogen and oxygen gases ? Emily. Or what more unlike sulphat of iron, than iron or sulphu- ric acid ? Mrs. B. Every chemical combination is an illustration of this rule. But let us proceed— The sixth law is, that the force of chemical affinity between the con- stituents of a body, is estimated by that which is required for their sepa- ration. This force is not always proportional to the facility with which bodies unite; for manganese, for instance, which you know, is so much disposed to unite with oxygen, that it is never found in a metallic state, yields it more easily than any other metal. Emily. But, Mrs. B., you speak of estimating the force of attrac- tion between bodies, by the force required to separate them; bow can you measure these forces? Alrsi B. They cannot be precisely measured, but they are com- paratively ascertained by experiment, and can be represented by numbers which express, at least by approximation, the relative de- grees of attraction. The seventh law is, that bodies have amongst themselves different degrees of attraction. Upon this law, (which you may have discover- ed yourselves, long since,) the whole science of chemistry dependSj for it is by means of the various degrees of affinity which bodies have for each other, that all the chemical compositions and decom- positions are effected. Every chemical fact or experiment is an instance of the same kind ; and whenever the decomposition of a body is performed by the addition of any single new substance, it is said to be effected by simple elective attractions. But it often happens that no simple substance will decompose a body, and that in order lo effect this, you must offer to the compound a body which is itself composed of two, or sometimes three principles, which would not, each separately, perform the decomposition. In this case there are two new compounds formed in consequence of a reciprocal decom- position and recomposition. All instances of this kind are called double elective attractions. Caroline. 1 confess I do not understand this clearly. Mrs. B. You will easily comprehend it, by the assistance of this diagram, in which the reciprocal forces of attraction are represent- ed by numbers: 723. What is the fifth law of chemical attraction ? 724. What is the sixth law of chemical attraction ? * 725. What is the seventh law of chemical attraction ? "* 726. Upon what does the whole science of chemistry depend ? 727. What is a simple elective attraction ? ""28. What is a double elective attraction ? OF COMPOSITION. 175 Original Compound. Sulphat of Soda. Result. Nitrat -5 of Soda. Soda 8 Sulphuric Acid : Result. 7 Divellent 2 Attractions 6-13 }- Sulphat of Lime. Nitric Acid 4 Lime 12 Original Compound. , Nitrate of Lime. We here suppose that we are to decompose sulphat of soda ; that is, to separate the acid from the alkali : if for this purpose, we add some lime, in order to make it combine with the acid, we shall fail in our attempt, because the soda and the sulphuric acid attract each other by a force which is superior, and, (by the way of supposition] is represented by the number 8 ; while the lime tends to unite with this acid by an affinity equal only to the number 6. It is plain, therefore, that the sulphat of soda will not be decomposed, since a force equal to 8 cannot be overcome by a force equal only to 6. Caroline. So far, this appears very clear. Mrs. B. If on the other hand we endeavour to decompose this salt by nitric acid, which tends to combine with soda, we shall be equally unsuccessful, as nitric acid tends to unite with the alkali by a force equal only to 7. In neither of these cases of simple elective attraction, therefore, can we accomplish our purpose. But let us previously combine together the lime and nitric acid, so as to form a nitrate of lime, a compound salt, the constituents of which are united by a power equal to 4. If then we present this compound to the sulphat of so- da, a decomposition will ensue, because the sum of the forces which tend to preserve the two salts in their actual state is not equal to that of the forces which tend to decompose them, and to form new combinations. The nitric acid, therefore, will combine with the soda, and the sulphuric acid with the lime.* * Suppose we say thus. The sulphuric acid attracts soda with a stronger force than it does lime, and soda has a stronger affinity for sulphuric acid than it has for nitric acidi It is plain, then, that nei- ther lime nor nitric acid alone will decompose the sulphat of soda. Now if we unite the nitric acid and lime, we form nitrate of lime.— 729. What is represented in the diagram ? 730. What is said in the note of the subject of this diagram ? 176 ON THE ATTRACTION Caroline. I understand you now very well. This double effect takes place because ihe numbers 8 and 4, which represent the de- grees of attraction of the constituents of the two original salts, make a sum less than the numbers 7 and 6, which represent the degrees of attraction of the two new compounds that will in conse- quence be formed. Mrs. B. Precisely so. Caroline. But what is the meaning of quiescent and divellent for- ces, which are written in the diagram ? Mrs. B. Quiescent forces are those which tend to preserve com- pounds in a state of rest, or such as they actually are; divellent forces, those which tend to destroy that state of combination, and to form new compounds. These are the principal circumstances relative to the doctrine of chemical attractions, which have been laid down as rules by mod- em chemists : a few others might be mentioned respecting the same theory, but of less importance, and such as would take us too far from our plan. I shomd however, not omit to menlion that Mr. Berthollet, a celebrated French chemist, has questioned the uni- form operation of elective attraction, and has advanced the opinion that, m chemical combinations, tbe changes which take place and the proportions in which bodiescombin^ depend not only upon the affinities, but also, in sonxe degree, on "Hie respective qualities of the substances concerned,) on the heat applied during the process, and some other circumstances, Caroline. In that case, I suppose there would hardly be two com- pounds exactly similar, though composed of tbe same materials? Mrs. R. On the contrary it is found that a remarkable uniformity prevails/,as to proportions,• between the ingredients of bodies of similar composition) Thus water, as you may recollect to have seen in a former corfversation, is composed of two volumes of hy- drogen gas to one of oxygen, and this is always found to be precise- ly the proportion of its constituents, frcm whatever source the wa- ter be derived. The same uniformity prevails wilh regard to the various salts; the acid and alkali, in each kind of salt, being always found to combine in the same proportions. Sometimes, it is true, the same acid, and the same alkali are capable of making two dis- tinct kinds of salts ; but in all these cases it is found that, one of the salts contains just twice, or in some instances, thrice as much acid, or alkali, as the other.*) But the nitric acid has not so strong an affinity for the lime as it has for soda. On mixing the two salts in solution therefore, the nitric acid quits the lime, und combines with the soda. This leaves the sulphuric acid and the lime free and uncombined ; they then unite and form sulphat of lime___C. * The student already understands, that in chemical combinations the union takes place only between the particles, or atoms, of sub- 731. What are quiescent forces ? 732. What are divellent forces? 733. What was the opinion of Berthollet upon chemical combina- tions ? 734. What remarkable uniformity is found to exist in chemical combinations ? OF COMPOSITION. 177 Emily. If the proportion in which these bodies combine are so constant, and so welt defined, how can Mr. Berthollet's remark be reconciled with this uniform system of combination ? Atrs. B. Great as that philosopher's authority is in chemistry, it is now generally supposed that his doubts on this subject were in a great degree, groundless, and that the exceptions he has observed in the laws of definite proportions, have been only apparent, and may be accounted for consistently with those laws. Emily. I think I now understand this law of definite proportions very well, so far as it regards the gases, such as oxygen and hydro- gen, in the instance you have just mentioned ; but in the case of acids and alkalies, when the bodies are either liquid or solid, 1 do not conceive how their bulks or volumes can be measured in order to ascertain the proportion in which they combine. Mrs. B. Your question is quite in point; the fact is, that the law of combination by volume, does not prevail in regard to liquids and solids. In these we must leave the circumstance of bulk entirely out of consideration. It is to their weight that we must attend, in determining the proportions in which they combine ; and accord- ingly, if we take the combining substance in a state of perfect puri- ty, and ascertain with great accuracy, once for all, the proportions by weight, in which they unite, we shall find that in every other in- stance in which these substances have an opportunity of combining, they will unite in the same proportions, and in no other—unless it be in such proportions that one of the bodies shall be in weight, ex- actly double, triple, or quadruple what it was in the former combi- nation. stances. These atoms it is supposed, are invisible, being the ulti- mate particles of which bodies are composed. In chemical com- binations, then, where substances are capable of uniting in only one proportion, this must be atom to atom. Thus oxygen and hydrogen unite only in the proportions of 100 of the former to 750*of the lat- ter by weight. Here an atom of oxygen unites to an atom of hy- drogen, to form water ; but the atoms of oxygen are seven and a half times heavier than those of hydrogen. When substances unite in several proportions, the second and third are always multiples of the first. Thus 100 parts of manga- uese will unite to 14, 28, 42, or 56 of oxygen, but not with any in- termediate quantity, as with 12, 20, 60, &c. This law of definite proportions, so far as is known, holds good, where the resulting compound differs widely from either of the substances of which it is composed, as in the salts, compound minerals, &c. The theory of definite proportions is explained by supposing that a substanee which we shall call A, unites with another substance, B, atom to atom, and that this forms a certain compound. When they unite in the second proportion, two atoms of B, unite to one of A, and this forms another compound, and so on, until the atoms of A, can unite to no more of B.—C. 735. In what proportion do oxygen and hydrogen unite to form wa- ter ? 736. How much heavier is oxygen than hydrogen ? 737. When acids and alkalies unite in several proportions, what re- lation do these proportions bear to each other ? 178 ON THE ATTRACTION Caroline. This requires a good deal of attention to be well under- stood ; and I should like to have it illustrated by some particular example of these different combinations. Mrs. B. Nothing easier than to satisfy you in this respect. For instance, with regard to bulk, nitrogen gas is capable of combining with oxygen gas in different proportions ; thus one volume of ni- trogen, by combining with one volume of oxygen, forms the sub- stance called nitrous gas ; with two volumes of oxygen, it forms ni- trous acid gas, &c. And with regard to solids and liquids, the pro- portions of which are estimated by weight, I may mention, as an example, the case of the salt called sulphat of potash, in which a given weight of potash may combine with two different proportions of sulphuric acid ; but the quantity of acid in one case is exactly double what it is in the other. Emily. And pray what can be the cause of this singular uniform- ity in the law of combination ? Mrs. B. Philosophers have not been able to give us any decisive information upon this point; but they have attempted to explain it in the following manner ; since chemical combination takes place between the most minute particles of bodies, may we not suppose that the smallest particles or portions in which bodies combine, (and which we may call chemical atoms) are capable of uniting together one to one, or sometimes one to two, or one to three, &c, but that they cannot combine in any intermediate proportion. Emily. But if an atom was broken into two, an intermediate com? bination would be obtained' Mrs.B. Yes; but the nature of the atom is incompatible with the idea of any farther division; since the chemical atom is the smallest quantity which chemistry can obtain, and such as no me- chanic means can poossibly subdivide. , Caroline. And pray, what is the use of all this doctrine of defii nite proportions ? Mn.B. It ts very considerable ; fcr it csabres chemists to form tables, by which they can see at one glance the composition of all the bodies which have been accurately analyzed, and ascertain in an instant what quantity of one body will be necessary to decom- pose a certain quantity of another ; and in general, such tables serve to present, in one view, the result of any chemical decom- positions, and the quantities of the new compounds formed; by which means, a considerable saving of labour is gained, either in enabling us to calculate beforehand the results of any manufacturing opera- tions ; or in estimating those obtained in analytical processes. But 1 perceive the subject is becoming rather too intricate for us. We must not run the risk of entering into difficulties which might con- fuse your ideas, and throw more obscurity than interest upon this, abstruse part of the philosophy of chemistry.* * This would have been the proper place for mentioning Dr. Wollaston's scale of chemical equivalents ; but the subject has been thought to imply some considerations not sufficiently elementary for the purpose of this book. It may, however, be just mentioned, that the principal object of this scale is to give a tabular view of the proportions in which the several acids and bases combine in forming their respective salts, and Likewise to indicate the equivalent com- pounds which result from their decomposition. The great utility qf OF COMPOSITION. 179 'Caroline. Pray, Mrs. B., can you decompose a salt by means of ■electricity, in the same way as we decompose water? Airs. B. Undoubtedly ; and I am glad this question occurred to you, because it gives me an opportunity of showing you some very interesting experiments on the subject. If we dissolve a quantity, however small, of any salt in a glass of water, and if we plunge into it the extremities of the wires, which proceed from the two ends of the Voltaic battery, the salt will be gradually decomposed, the acid being attracted; by the positive; and the alkaii by the negative wire. V Emily. But how can you render that decomposition perceptible? Mrs. B. By placing in contact with the extremities of each wire, in the solution, pieces of paper stained with certain vegetable co- lours, which are altered by the contact of ao acid or an alkali.— Thus this blue vegetable preparation called litmus, becomes red when touched by an acid ; and the juice of violets becomes green by the contact of an alkali. Butthe experimentcan be made in a much more distinct manner, by receiving the extremeties of the wires into different vessels, so that the alkali shall appear in one vessel, and the acid in the other.' Caroline. But then the voltaic circle will not be completed; how can the effect be produced ? Mrs. B. You are right"; I ought to have added that the two ves- sels must be connected together by some interposed substance, ca- pable of conducting electricity. A piece of moistened cotton wick answers this purpose very well. You see that the cotton has one Fig. 31. €3 C3 Instances of chemical decomposition by the Voltaic Battery. end immersed in one glass, and the other end in the other, so as t° establish a communication between any fluids contained in them- this scale, and the peculiar properties which it possesses, though not very easily described, mav be readily understood on inspecting the instrument, which should'be in thehands of every chemical student. 738. Can a salt be decomposed by means of electricity ? 739. When a salt is decomposed by Galvanism, at which pole does the acid appear? 740. How would you explain Fig. 31 ? 180 ON THE ATTRACTION We shall now put into each of these glasses a little glauber salt, or sulphat of soda, (which consists of an acid and alkali.) and then we shall fill the glasses with water, which will dissolve the salt. Let us now connect the glasses by means of the wires, (e. d.) with the two ends of the battery thus .... Caroline. The wires are already giving out small bubbles: is this owing to the decomposition of the salt? Airs, JB, No ; these are bubbles produced by the decomposition ofthe water, as you saw in the former experiment. In order to render the separation of the acid from the alkali, visible, I pour into the glass (a) which is connected with the positive wire, t. few drops of a solution of litmus, which the least quantity of acid iurns red; and in the other glass (b) which is connected with the negative wire, I pour a few drops of the juice of violets. . . . Emily. The blue solution is already turning red all around the wire. Caroline. And the violet solution is beginning to turn green.— This is indeed very singular I Airs. B. You will be still more astonished when we vary the ex- periment in this manner. These three glasses (f,g, h,) are, as Fig. 32. - in the former instance, con- nected together by wetted cot- ton,*but the middle one con- tains a saline solution, the two others containing only distilled water, coloured as before by vegetable infusions. Yet on making the connection with the battery, tbe alkali will ap- pear in the negative glass, (h) and the acid in the positive Instances of chemical decomposition by £lass> (O though neither of the Voltaic Battery. them contained any saline matter. Emily. So that the acid and alkali must be conveyed right and left from the central glass, into the other glasses by means of the connecting moistened cotton? Mrs. B. Exactly so, and you may render the experiment still more striking by putting into thecentral glass, (k,j an alkaline so- Fig. 33. lution, the glauber salt being placed iuto the ne- gative glass, (1,) and the positive glass, (i,) con- taining only water. The acid will be attracted by the positive wire, (m,] and will actually appear in the vessel, (i,) after ■ . r v. i j ..- . x. „ , , passing through the al- Instances of chemical decomposition by the Voltaic Battery. . ,• ° i .• ° n \ -.1. ,kahne solution, (k) with- out combining with it, although, you know acids and alkalies are so much disposed to combine. But this conversation has already 741. How will you explain the experiment illustrated in Fig. 32? 742. How willyou explain the experiment illustrated in Fig. 33? ALKALIES. 181 much exceeded our usual limits, and we cannot enlarge more upon this interesting subject at present. CONVERSATION XIV. ON ALKALIES. Mrs. B. Having now given j ou some idea of the laws by which chemical attractions are governed, we may proceed to the examina- tion of bodies which are formed in consequence of these attractions. The first class of compounds that present themselves to our notice. in our gradual ascent to the most complicated combinations, are bo- dies composed of'only two principles. Thesulphurets, phosphorets, carburets, Sfc. are of this description ; but the most numerous and important of these compounds are the combinations of oxygen with the various simple substances with which it has a tendency to unite. Of these you have already acquired some knowledge, but it will be necessary to enter into further particulars respecting the nature and properties of those most deserving our notice. Of this class are the ^alkalies and the earths,* which we shall successively examine. We shall first take a view of the alkalies, of which there are three. viz. potash, soda, and ammo.ma. The two first are called fixed al- kalies,* because they exist in a solid format the temperature of the atmosphere, ami require a great heat to be Volatilized. They consist as you already know of metallic bases combined with oxygen.} In potash, the proportions-are about eighty-six parts of potassium, to fourteen of oxygen', and in soda, seventy-seven parts of sodium to twenty-three of oxygen. The third alkali, ammonia, has been dis- tinguished by the name of volatile alkali, because its natural form is that of gas.; Its composition is of a more complicated nature, of which we shall speak hereafter. Some of the earths bear so strong a resemblance in their proper- ties to the alkalies, that it is difficult to know under which head to place them. The celebrated French chemist, Fourcroy, has classed * It has already been stated that a third fixed alkali has lately been discovered by Mr. Arfvredson, which has been called tithion. It was first found in a Swedish mineral called petalite ; but has since been detected in some other minerals. Though this alkali resembles pot- ash and soda in its general properties, yet it has decidedly an alka- line substance of its own, capable of forming different salts with the acids, and having in particular the property of combining with much greater proportions of acid than the other alkalies. 743. What is the first class of compounds which present themselves to our notice ? 744. What are instances of this description ? 745. What are the alkalies ? 746. Why are potash and soda called fixed alkalies ? 747. Of what do the fixed alkalies consist? 748. Why is ammonia called volatile? 16 182 POTASIT. two of them (barytes and strontites) with the alkalies; but as lime and magnesia have almost an equal title to that rank, 1 think it bet- ter not to separate them, and therefore have adopted the common method of classing them with the earths, and of distinguishing them bv the name of alkaline earths. , The general properties of alkalies are/an acrid burning taste, a pungent smell, and a caustic action on (he skin and tleshj Caroline. 1 wonder they should be caustic, Mrs. B., srrrce they contain so little oxygen. . . , Mrs. B. Whatever substanc/has an affinity for any one of the constituents of animal matterY sufficiently powerful to decompose it, is entitled to the appellatidrrtf caustic. The alka.es, in their pure state have a very strong attraction for water, for hydrogen, and for carbon, which you know, are the constituent principles of oil, and it is chiefly by absorbing these substances from animal matter that they effect its decomposition; for, when diluted with a sufficient quantity of water, or combined with any oily substance, they lose their causticity. , _ But to return to the general properties ol alkalies—they change, as we have already seen, the color of syrup of violets, and other blue vegetable infusions to green^ and have, in general, a very great tendency to unite with acids, although the respective qualities of these two clastes of bodies form a remarkable contrast. We shall examine the result of the combination of acids and alka- lies more particularly hereafter. It will be sufficient at present to inform you, that wheneve(acids are brought in contact with alka- lies or alkaline earths) they unite with a remarkable eagerness, and form compounds perfectly different from either of their constitu- ents ; these bodies are called neutral or compound salts. The dry white powder which you see in this phial is pure caustic potash; it is very difficult to preserve it in this state, as it attracts, with extreme avidity the moisture from the atmosphere, and if the air were not perfectly excluded, it would, in a very'short time, be actually meltedV Emily. It is then, I suppose, always found in a liquid state ? Mrs. B. No ; it exists in nature in a great variety of forms and combinations, but it is never found in its pure separate state ; it is combined with carbonic acid, with which it exists in every part of the vegetable kingdom, and is most commonly obtained from the ashes of vegetables, which are the residue that remains after all the other parts have been volatilized by combustion. Caroline. But you once said, that after all the volatile parts of a vegetable were evaporated, the substance that remained was char- coal ? Mrs. B. lam surprised that you should still confound the processes of volatilization and combustion. In order to procure charcoal, we evaporate such parts as can be reduced to vapour by the operation 749. What are the general properties of alkalies? 750. On what does the caustic property of alkalies depend ? 751. To what color do the alkalies change the vegetable blues ? 752. How are neutral or compound salts formed ? "53. What would be the consequence if cauetic potash were not se- cluded from the air ? POTASH. 183 of heat alone; but when we burn the vegetable, we burn the car- bon also, and convert it into carbonic acid gas. Caroline. That is true ; I hope I shall make no more mistakes in my favorite theory of combustion. Mrs. B Potash derives its name from the pots in which the ve- getables, from which it was obtained, used formerly to be burnt; the alkali remained mixed with the ashes at the bottoiri, and was thence called potash. Emily. The ashes of a wood fire, then, are potash, since they are vegetable ashes ? Mrs. B. They always contain more or less^tash, but are very far from consisting of that substance alone, as^they aie a mixture of various earths and salts which remain after the combustion of ve- getables, and from which it is not easy to separate the alkali in its pure form. The process by which potash is obtained, even in the imperfect state in which it is used in the arts, is much more com- plicated than simple combustion. It was once deemed impossible to separate it entirely from all foreign substances, and it is only in chemical laboratories that it is to be met with in the state of purity in which you find it in this phial. Wood-ashes are, however, valua- ble for the alkali which they contain, and are used for some pur- poses without any further preparation. Purified in a certain de- gree, they make what is commonly called pearl ash, which is of great; efficacy in taking out grease, in washing linen, &c; for pot- ash combines readily with oil or fatWith which it forms a compound well-known to you under the namerof soap. Caroline. Really! Then I should think it would be better to wash all linen with pearl-ash than with soap, as in the latter case, the al- kali being already combined with oil, must be less efficacious in ex- tracting grease. Mrs. B. Its effects would betoo powerful on fine linen, and would injure its texture ; pWarl-ash is therefore only used for that which is of a strong, coarse kind. For the same reason, you cannot wash your hands with plain potash ; but, when mixed with oil in the form of soap, it is soft as well as cleansing, and is therefore much better adapted to the purpose. Caustic potosh, as we already observed, acts on the skin, and ani- mal fibre, in virtue of its attraction for water and oil, and converts all animal matter into a kind of saponaceous jelly. Emily. Are vegetables the only source from which potash can be derived ? . . Mrs. B. No : for though far most abundant in vegetables, it is by no means confined to that class of bodies, being found also on the surface of the earth, mixed with various minerals, especially with earths and stones, whence it is supposed to be conveyed in vege- tables by the roots of the plant. It is also met with, though in very 754. From what is potash obtained ? 755. From what is the term potash derived ? 756. Of what do wood-ashes consist? 757. How will soap assist in cleansing clothes from grease or oil ? 758. Why may not pearl-ash be used for the purpose, without be- ing made into soap ? 759. Is potash confined to vegetables ? 184 POTASH. small quantities in some animal substances. The most common state of potash is thattof carbonat; 1 suppose you undersiand whatthatis? Emily. I believe so ; though I do not recollect that jou ever mentioned the word before. If I am not mistaken, it must/be a com- pound salt, formed by the union of carbonic acid with potash. Mrs.B. Very true ; you see how admirably the nomenclature of modern chemistry is adapted to assist the memory ; when you hear the name of a compound, you necessarily learn what are its consti- tuent parts ; and when you are acquainted with these constituents, you can immediately name the compound which they form. Caroline. Pray how were bodies arranged and distinguished be- fore this nomenclature was introduced ? Mrs.B. Chemistry was then a much more difficult study; for every substance had an arbitrary name^-which it derived from the person who discovered it, as Glauber's salts for instance ; or from some other circumstance relative to it, though quite unconnected with its real nature as potash. These names have been retained for some of the simple bodies; for as this class is not numerous, and therefore can easily be re- membered, it has not been thought necessary to change (hem^l Emily. Yet 1 think it would have rendered the new nomenclature more complete to have methodized the names of the elementary, as of the compound bodies, though it could not have been done in the same manner. But the names of the simple substances might have indicated their nature, or, at least, some of their principal proper- ties ; and if, like the acids and compound salts, all the simple bodies had a similar termination, they would have been immediately known as such. So complete and regular a nomenclature would, I think, have given a clearer and more comprehensive view of chemistry than the present, which is a medley of old and new terms. Mrs. B. But you are not aware of the difficulty of introducing into science an entire set of new terms; it obliges all teachers and professors to go to school again, and if some of the old names, that are least exceptionable, were not left as an introduction to the new ones, few people would have had industry and perseverance enough to submit to the study of a completely new language ; and the infe- rior classes of artists, who can only act from habit and routine, would at least for a time, have felt material inconvenience from a total change of their habitual terms. From these considerations, Lavoi- sier and his colleagues, who invented the new nomenclature, thought it most prudent to leave a few links of the old chain, in order to con- nect it with the new one. Besides, you may easily conceive the in- convenience which might arise from giving a regular nomenclature to substances, the simple nature of which is always uncertain ; for the new names might, perhaps, have proved to have been founded in 760. What is the most common state of potash? 761. W hat is carbonat ? 762. How were bodies arranged and distinguished before the new nomenclature was introduced ? 763. Why have the old chemical names been retained ? 764. What inconvenience might arise from giving a regular nomen- clature to substances, the nature of which is uncertain? POTASH. 185 error. And, indeed, cautious as the inventors of the modern chem- ical language have been, it has already been found necessary to modify it in many respects. In those few cases, however, in which new terms have been adopted to designate simple bodies, those names have been so contrived as to indicate one of the chief prop- erties of the body in question ; this is the case with oxygen, which, as I explained to you, signifies generator of acids ; and hydrogen generator of water.* If all the elementary bodies had a similar ter- mination as you propose, it would be necessary to change the name of any that might hereafter be found of a compound nature, which would be very inconvenient in this age of discovery. But to return to the alkalies. We shall now try to melt some of this caustic potash in a little water, as a circumstance occurs du- ring its solution very worthy of observation. Do you feel the heat that is produced ? Caroline. Yes, I do ; but is not this directly contrary to our the- ory of latent heat, according to which heat is disengaged when fluids become solid) and cold produced when solids are melted ? Mrs. B. The latter is really the case, in all solutions ; and if the solution of caustic alkalies seems to make an exception to the rule, it does not, 1 believe, form any solid objection to the theory. The matter may be explained thus : When water first comes in contact with the potash, it produces an effect similar to the slacking of lime, that is, tbe water is solidified in combining with the potash, and thus loses its latent heat; this is the heat that you now feel, and which is therefore, produced not by the melting of the solid, but by the solidification of the fluid. But when there is more water than the potash can absorb and solidify, the latter then yields to the solvent power of the water ; and if we do not perceive the cold produced by its melting, it is because it is counter-balanced by the heat pre- viously disengaged.f A very remarkable property of potash is the formation of glass by its fusion with siliceous earthy You are not yet acquainted with this last substance, further than its being in the list of simple bodies. It is sufficient for the present, that you should know that sand" and flint are chiefly composed of it; alone, it is infusible, but mixed with *It may here be observed, that even with regard to these two bodies, the nomenclature is become exceptionable, since it is now found that oxygen is one of the constituents of alkalies as well as of acid, and in particular of the muriatic. f This defence of the general theory, however plausible, is liable to some obvious objections. The phenomenon might perhaps be better accounted for, by supposing that a solution of alkali in water has less capacity for heat than either water or alkali in their sepa- rate state. 765. In the few cases where new names have been adopted to desig- nate simple substances, how have these names been contrived ? 766. What interesting circumstance occurs if caustic potash is melt- ed in water. 767. How is glass made ? . " 768. If caustic potash is put in water, why is heat disengaged ? 16* 186 POTASH. potash, it melts when exposed to the heat of a furnace, combines with the alkali and runs into glass. Caroline. Who would ever have supposed that the same substance which converts transparent oil into such an opaque body as soap, should transform that opaque substance, sand, ioto transparent glass ? Mrs. B. The transparency or opacity of bodies, does not, I con- ceive, depend so much on their intimate nature, as upon the ar- rangement of their particles ; we cannot have a more striking in- stance of this, than is afforded by the different states of carbon, which, though it commonly appears in the form of a black, opaque body, sometimes assumes the most dazzjing transparent form in nature, that of diamond, which, you recollect, is carbon, which in all probability, derives its beautiful transparency from the peculiar arrangement of its particles during their crystallization. Emily. I never should have supposed that the formation of glass was so simple a procees as you describe it. Mrs. B. It is by no means an easy operation to make perfect glass ; for if the sand or flint from which the siliceous earth is ob- tained, be mixed with any metallic particles, or other subtance, which cannot be vitrified, the glass will be discolored, or defaced, by opaque specks. Caroline. That 1 suppose, is the reason why objects so often ap- pear irregular and distorted through a common glass window. Mrs.B. This species of imperfection proceeds, I believe, from another cause. It is extremely difficult to prevent the lower part of the vessels, in which the materials of glass are fused, from con- taining a more dense vitreous matter than the upper; on account of the heavier ingredients falling to the bottom. When this happens, it occasions the appearance of veins or waves in the glass, from the difference of density in its several parts, which produces an irregu- lar refraction of the rays of light which pass through it. Another species of imperfection sometimes arises from the fusion not being continued for a length of time sufficient to combine the two ingredients completely, or from the due proportion of potash and silex (which are as two tc/one) not being carefully observed ; the glass, in those cases, will be liable to alteration from tbe action of the air, of salts, and especially of acids which will effect its de- composition by combining with the potash, and forming compound salts. Emily. What an extremely useful substance potash is ! Airs B. Besides the great importance of potash in the manufac- tures of glass and soap, it is of very considerable utility in many of the other arts, and its combinations with several acids, particular- ly the nitric, with which it forms saltpetre. 769. On what does the opacity of bodies depend ? 770. To what does a diamond owe its transparency ? 771. What is the occasion of the veins or waves discovered on some glass p 772. What other imperfection sometimes occurs in the making of glass ? 773. Of what does saltpetre consist ? AMMONIA. 187 Caroline. Then saltpetre must be a nitrat of potash. But we are not yet acquainted with the nitric acid. Mrs. B. We shall therefore defer entering into the particulars of these combinations till we come to a general review ofthe compound salts. In order to avoid confusion, it will be better at present to confine ourselves to the alkalies. Emily. Cannot you show us the change of colour which you said the alkalies produced on blue vegetable infusions ? Mrs. B. Yes, very easily. 1 shall dip a piece of white paper into this syrup of violets, which, you see, is of a deep blue, and dyes the paper of the same colour. As soon as it is dry, we shaft dip it into a solution of potash, which, though itself colourless, will turn the paper green.* Caroline. So it has, indeed ! And do the other alkalies produce a similar effect? Mrs. B. Exactly the same.—We may now proceed to soda, which, however important, will detain us but a very short time ; as in all its general properties it very strongly resembles potash; in- deed, so great is their similitude, that they have been long confound- ed, and they can now scarcely be distinguished, except by the dif- ference ofthe salts which they form with acids. The great source of this alkali is the sea, where, combined with a peculiar acid, it forms the salt with which the waters of the ocean are so strongly impregnated. Emily. Is not that the common table salt ? Mrs. B. The very same; but again we must postpone entering into the particulars of this interesting combination, till we treat of the neutral salts. Soda may be obtained from common salt; but the easiest and most usual method of procuring it is by the combus- tion of marine plants, an operation perfectly analagous to that by which potash is obtained from vegetables. Emily. From what does soda derive its name ? Mrs. B. From a planf?called by us soda, and by the Arabs kali, which affords"-it in great abundance. Kali has, indeed, given its name to the alkalies in general. Caroline. Does soda form glass and soap in the same manner as potash ? * A very pretty experiment on the change of colours may be made as follows: Make a tincture, by pouring boiling water on red cabbage and let it stand a while. Put it into a phial. The colour will be purple. Take two wine glasses, and into one put a tew drops of sulphuric acid, and into the other the same quantity of a strong solution of potash. So little of either will do, that the glasses may be inverted for a moment. Then pour the tincture into each, and the one containing the acid will appear of a most beautiful red, and the other as beautiful a green.—C. 774. What is the chemical name of saltpetre? 775. How may blue vegetable colours be turned green ? 776*. How does soda differ from potash ? 777. What is the great source of soda ? 778. How may soda be obtained ? 779. From what does soda derive its name ? 188 AMMONIAk- Mrs. B.' Yes, it does ; it is of equal importance in the arts, and is even preferred to potash for some purposes; but you will not be able to distinguish their properties, till we examine the compound salts which they form with acids; we must therefore leave soda for the present, and proceed to ammonia, or the volatile alkali. Emily. I long to hear something of this alkali; is it not of the same nature as hartshorn ? Mrs. B. Yes, it is, as you will see bye-and-bye. This alkali is seldom found in nature in its pure state; it is most commonly ex- tracted from a compound salt, called sal. ammoniac, which was for- merly imported from Ammonia, a region of Lybia, from which both these salts and the alkali derive their names. The* crystals contain- ed in this bottle are specimens of this salt, which consist of a combi- nation of ammonia and muriatic acid. Caroline. Then it should be c&Wei muriat of ammonia ;• for though I am ignorant what muriatic acid is, yet I know that its combina- tion with ammonia cannot but be so called ; and I am surprised to see sal. ammoniac inscribed on the label. Airs. B. That is the name by which it has been so long known, that the modern chemists have not yet succeeded in banishing it alto- gether; and it is still sold under that name by druggists, though by scientific chemists it is more properly called muriat of ammonia. Caroline. Both the popular and common name should be inscribed on labels—this would soon introduce the new nomenclature. Emily. By what means can the ammonia be separated from the muriatic acid ? Airs. B. By!cnemical attractions^ but this operation is too com- plicated for you to understand till you are better acquainted with the agency of affinities. Emily. And when extracted from the salt, what kind of sub- stance is ammonia ? Mrs. B. Its natural form, at the temperature of the atmosphere, when free from combination, is that of gas ; and in this state it is called ammoniacalgas. But it mixes very readily with water, and can be thus obtained in a liquid formi Caroline. You said that ammonia'was more complicated in its composition than the other alkalies; pray of what principles does it consist ? Mrs. B. It was discovered a few years since, by Berthollet, a cel- ebrated French chemist, that it consisted of aboutpne part of hydro- gen to four parts of nitrogejji Having heated arrimoniacal gas un- der a receiver, by causing the electrical spark to pass repeatedly through it, he found that it increased considerably in bulk, lost all its alkaline properties, and was actually converted into hydrogen and nitrogen gases ; and from the latest and most accurate experiments 780. Can glass and soap be formed from soda as well as from potash ? 781. From what does ammonia derive its name? 782. From what is it mostly obtained? 783. What is the proper chemical name of this volatile alkali ? 784. How can ammonia be separated from muriatic acid ? 785. How is ammoniacal gas obtained? 786. Under what form does it appear when pure ? 737. Of what principles does ammonia consist? AttMONIA. 189 the proportions appear to be, one volume of nitrogen gas, to three of oxygen gas.* _...-, Caroline. Ammonia, therefore, has pot, like the two other alka- lies, a metallic basis. Airs. B. It is believed that it has, though it is extremely difficult to reconcile that idea with what I have just stated of its chemical nature. But the fact is, that although this supposed metallic basis of ammonia has never been obtaineddistinct and separate, yet both Professor Berzehus of Stockholm, and Sir H. Davy, have suc- ceeded in forming a combination of mercury with the basis of am- monia which has so much the appearance of an amalgam, that it strongly corroborates the idea of ammonia having a metallic basis.f But these theoretical points are full of oitticulties and doubts, and it would be useless to dwell any longer upon them. Let us therefore return to the properties of volatile alkali. Am- moniarjal gas is considerably lighter llriu oxygen gas, and only about^half the weight of atmospherical airj It possesses most of the properties ofthe fixed alkalies; but c^not be of so much use in the arts on account of its volatile nature. It is, therefore, never employed in the manufacture of glass, but it forms soar) with oils equally as well as potash and soda; it resemb,', s them likewise in its strong attraction for water;'for which rea^cn it can be collected in a receiver over mercury only Caroline. I do not understand this. Mrs. B. Do you recollect the meihod whi- ,as used to collect gasses in a glass receiver over water? Caroline. Perfectly. Mrs. B. Ammoniacal gas has so strorg a tendency to unite with water, that instead of passing through that duic\ it would be in- stantaneously absorbed by it. ( We can therefore neither use water for that purpose nor any other liquid of which water is a component part; so that in order to collect thisgas, we are obliged to have re- course to mercury, (a liquid which has no action upon it,) and a mer- curial bath is used instead of a water bath, such as we employed on former occasions. Water impregnated with this gas*is nothing more than the fluid which you mentioned at the beginning ofthe conver- sation—hartshorn ; it is the ammoniacal gas escaping from the wa- ter which gives it so powerful a smell. J * It ought to be hydrogen gas.—C f This amalgam is easily obtained, by placing a globule of mercu- ry upon a piece of muriat, or carbonat of ammonia, and electrifying this globule by the Voltaic battery. The globule instantly begins to expand to three or four times its former size, and becomes much less fluid, though without losing its metallic lustre, a change which is ascribed to the metallic basis of ammonia uniting with the mercu- ry. This is an extremely curious experiment. X To obtain ammoniacal gas, mix together equal parts of muriate of ammonia, and dry burnt lime; after pulverizing each separately, 788. Has ammonia a metallic basis ? 789. What is the specific gravity of ammoniacal gas? 790. How does ammonia resemble potash and soda-? 791. Why cannot ammonia be collected in a receiver over water ? 792. What is hartshorn ? 190 AMMONIA-. Emily. But there is no appearance of effervescence iu hartshorn. Mrs. B. Because the particles of gas that rise from the water are too subtle and minute fortheir effect to be visible. Water diminishes in density, by being impregnated with ammoni- acal gas J and this augmentation of bulk increases its capacity for caloric. Emily. In making hartshorn, then, or impregnating water, with ammonia, heat must be absorbed and cold produced ? Mrs. B. That effect would lake place if it was not counteracted by another circumstance; the gas is liquefied by incorporating with the water, and gives out its latent heat. The condensation of the gas .more than counterbalances the expansion of the water- therefore, upon the whole, heat is produced. But if you dissolve ammoniacal gas with ice or snow, cold is produced.—Can you ac- count far that? Emily. The gas in being condensed into a liquid, must give out heat; and on the other hand, the snow or ice in being rarefied into a liquid, must absorb heat; so that between the opposite ef- fects, I should have supposed the original temperature would have been preserved. Mrs. B. But you haye forgotten to take into the account the i rarefaction ofthe water, (or melted ice,) by the impregnation ofthe • gas, and this is the cause of the cold which is ultimately produced. Caroline. Is the sal volatile (the smell of which so strongly re- sembles hartshorn) likewise a preparation of ammonia? Airs. B. It is carbonat of ammonia dissolved in water; and which in its concrete state, is commonly called salts of hartshorn. Am- monia is caustic, like the fixed alkalies, as you may judge by the pungent effects of hartshorn, which cannot betaken internally, nor applied to delicate external parts, without being plentifully diluted rub them together in a mortar; put them into a retort, and apply the heat of a lamp. Or, the common spirit of sal ammoniac may be heated in a retort in the same way. To collect and retain the gas without a mercurial bath,-fix a receiver or bottle in an inverted po- sition,Nand connect to the retort a tube, which introduce up into the receiver, so that it nearly reaches the bottom. As the gas comes over, its levity is such, that it fills the upper part of the re- ceiver first, gradually driving out the air, and taking its place. To keep it for any considerable time, the receiver must be stopped. A pretty experiment may be made by introducing up into the receiver with the ammonia, some muriatic gas. Both gasses are invisible until they are brought together, when they unite, forming a dense white cloud, and fall down in the solid form of muriat of ammonia. The muriatic gas is obtained by pouring sulphuric acid on common salt, and applying the heat of a lamp. It may be sent up into the receiver in the way above described, or ammonia.—C. 793. What change is produced on water by being impregnated with ammoniacal gas ? 794. Why is cold produced if ammoniacal gas is dissolved with snow or ice ? 795. How can ammoniacal gas be retained for experiments without a mercurial bath ? 796. What is sal volatile? EARTHS. 191 with water.—Oil and acids are very excellent antidotes for alkaline poisons; can you guess why? Caroline. Perhaps, because the oil combines with alkali^and forms soap, and thus destroys its caustic properties; and the acid converts it into a compound salt, which, I suppose, is not so perni- cious as caustic alkali. Mrs. B. Precisely so. Ammoniacal gas, if it be mixed with atmospherical air, and a burning taper repeatedly plunged into it, will burn with a large flame of a peculiar yellow color. Emily. But, pray, tell me, can ammonia be procured from this Lybian salt only ? Airs. B. So far from it, that it is contained in, and may be ex- tracted from, all animal substtnces whatever. Hydrogen and ni- trogen are two ofthe chief constituents of animal matter; it is there- fore not surprising that they should occasionally meet and combine in those proportions that compose ammonia. But this alkali is more frequently generated by the spontaneous decomposition of ani- mal substances; the hydrogen and nitrogen gases that arise from putrefied bodies combine and form the volatile alkali. Muriat of ammonia, instead of being exclusively brought from Lybia, as it originally was, is now chiefly prepared in Europe, by chemical processes. Ammonia, although principally extracted from this salt, can also be produced by a great variety of other sub- stances. The horns of cattle, especially those of deer, yield it in abundance, and it is from this circumstance that a solution of am- monia in water has been called hartshorn. It may likewise be pro- cured from wool, flesh, and bones ; in a word, any animal substance whatever, yields it by decemposition. We shall now lay aside the alkalies, however important the sub- ject may be, till we treat of their cembination with acids. The next time we meet we shall examine the earths. CONVERSATION XV. ON EARTHS. Airs. B. The earths, which we are to-day to examine, are nine in number. SILEX, STRONTITES,* * There is less evidence that these four earths are composed of metallic bases than there is in the case of ammonia, which it will be ' 797. Why are oils and acids good antidotes for alkaline poisons? 798. From what can ammonia be procured ? 799. What are the chief constituents of animal matter ? 800. Why has a solution of ammonia in water been called hartshorn? 801. How many earths are there ? 802. What are their names? 192 EARTHS. ALUMINE, YTTRIA, BARYTES,* GLTJClNA, ^ LIME,* ZIRCONIA. MAGNESIA, The last three are of late discovery; their properties are but imperfectly known ; and as they have not yet been applied .to use, it will be unnecessary to enter into any particulars respecting them. We shall confine our remarks, therefore, to the first five. They are composed, as you have already learnt, of a metallic basis combined with oxygen); and from this circumstance are incombustible. Caroline.'Yet Thave seen turf burnt in the country, and it makes an excellent fire; the earth becomes red hot, and produces a very great quantity of heat. Airs. B. It is not the earth that burns, my dear, but the roots, grass, and other remnants of vegetables that are intermixed with it. The caloric, which is produced by the combustion of these sub- stances, makes the earth red hot, and this being a bad conductor of heat, i-etains its caloric a long tim.eV""and were you to examine it wherfcool, )ou would find that it had not absorbed one particle of oxygen, nor suffered any alteration from the fire. Earth is how- ever, from the circumstance just mentioned, an excellent radiator of heat, and owes its utility, when mixed with fuel, solely to that properly. It is in this point of view that Count Rumford has re- commended balls of incombustible substances to be arranged in fire- places, and mixed with the coals, by which means the caloric dis- engaged by the combustion of the latter is more perfectly reflected into the room, and an expense of fi\el is saved. Emily. I expected that the lists of earths would be much more considerable. When I think ofthe immense variety of soils, I am astonished that there is not a greater number of earths to form them. Mrs. B. You might, indeed, almost confine that number to four; for barytes, strontites, and the others,of late discovery, act but so small a part in this great theatre, that they cannot be reckoned as essential to the general formation of the globe: And you must not coufine your idea of earths to the formation ofsoil; for rock, mar- ble, chalk, slate, sand, flint, and all kinds of stones, from the pre- cious jewels to the commonest pebbles; in a word, all the immense remembered, was supposed to have formed an amalgam with mer- cury, and on this account was supposed to have had a metallic ba- sis. Ofthe other earths no one except Dr. Clarke, of Cambridge, Eng., has pretended to offer any but conjectural evidence of their metallic nature. This gentleman, on subjecting them to the heat of the blow-pipe, charged with oxygen and hydrogen, was led to be- lieve he had obtained their metallic bases. But as his experiments have been repeated at the Royal Institution without success, it is now understood that the Dr. must have been mistaken.—C. 803. Of what are the earths composed ? 804. Why are the earths incombustible ? 805. Why then is turf used for fuel in some countries ? 806. Why is the earth a good radiator of heat ? 807. What is said of barytes and strontites, as constituting a part of the globe ? EARTHS. 193 variety of mineral products, may be referred to some of these earths, either in a simple state, or combined the one with the other, or blended with other ingredjents. Caroline, i Precious stones composed of eai th ! That seems very difficult to conceive. /, Emily. Is it more extraordinary than that (he most precious of all jewels, diamond, should be composed of carbon ? But diamond forms an exception, Mrs. B.; for, though a stone, it is not composed of earth. Airs. B. I did not specify the exception, as 1 knew you were so well acquainted with it. Besides, I would call a diamond a mineral rather than a stone, as the latter teim always implies the presence of some earth. Caroline. I cannot conceive how such coarse materials can be converted into such beautiful productions. Mrs. B. We are very far from understanding all the secret re- sources of nature ; but I do not think'lhe spontaneous formation of the crystals, which we call precious stones, one ofthe most difficult phenomena to comprehend. By the slow and regular work of ages, perhaps of hundreds of ages, these earths may be gradually dissolved by water, and as gradually deposited by their solvent in the undisturbed process of crystallization. The regular arrangement of their particles, during their re-union in a solid mass, gives them that brilliancy, transpa- rency, and beauty, for which they are so much admired ; and ren- ders them in appearance so totally different from their rude and primitive ingredients. Caroline. But how does it happen that they are spontaneously dissolved, arid afterwards crystallized? Mrs. B. The scarcity of mo.'iy kinds of crystals, as rubies, eme- ralds, topazes, &c, shows that/lufir formation is not an operation very easily carried on\ in nature, fi'it cannot you imagine that wheiv/water holding in solution some oarticles of earth filters through the crevices of hills or mountains, and at length dripples into some cavern, each successive drop may be slowly evaporated. leaving behind it the particle of earth which it held in solution A You know that crystallization is more regular and perfect, in pro-* portion as the evaporation of the solvent is slow and uniform ; na- ture therefore, who knows no limit of time, has, in all works of this kind, an infinite advantage over any artist who attempts to imitate such productions. Emily. 1 can now conceive that the arrangement ofthe particles of earth during crystallization, may be such as to occasion transpa- rency, by admitting free passage to the rays of light; but I cannot understand why crystallized earths should assume such beautiful colors as most of them do. Sapphire, for instance, is of a celestial blue ; ruby, a deep red ; topaz, a brilliant yellow ? 808. What valuable substance do the earths composd ? 809. Is it deemed difficult to understand the spontaneous formation, of crystal ? 810. What does the scarcity of many kinds of crystals show ? 811. How may it be supposed that they are formed ? 194 EARTHS. Mrs. B. Nothing is more simple than to suppose that the ar- rangement of their particles is such, as to transmit some of the colored rays of light, and reflect others, in which case 4he stone must appear of the colour of the rays which it reflects. )But be- sides, it frequently happens that the colour of a stone is owing to a mixture of some metallic matter. Caroline. Pray, are the different kinds of precious stones each composed of one individual earth, or are they formed of a combina- tion of several earths ? Airs. B. A great variety of materials enters into the composition of most of them ; not only several earths, but sometimes salts and metals. The earths, however, in their simple state, frequently form very beautiful crystals; and, indeed, it is in that state only that they can be obtained perfectly pure. , Emily. Is not the Derbyshire spar produced by the crystalliza- tion of earths, in the way you have just explained ? I have been in some of the subterraneous caverns where it is found, which are similar to those you have described. Airs. B. Yes; but this spar is a very imperfect specimen of crystallization ;* it consists of a variety of ingredients confusedly blended together, as you may judge by its opacity, and by the va- rious colours apd appearances which it exhibits. But, in examining the earths in their most perfect and agreeable form, we must not lose sight of that state in which they are com- monly found, and which, if less pleasing to the eye, is far more in- teresting by its utility. All the earths are more or less endowed with alkaline proper- ties ; but there are four, barytes, magnesia, lime, and strontites^ which are called alkaline earths^ because they possess those quali- ties in so great a degreey, as to entitle them, in most respects, to the rank of alkalies. They combine and form compound salts with acids, in the same way as alkalies ; they are like them, susceptible of a considerable degree of causticity, and are acted upon inasimi- lar manner by chemical tests.—The remaining earths, si lex and alumine, with one or two others of late discovery, are in some de- gree more earthy, that is to say, they possess more completely the properties common to all the earths, which .are insipidity, dryness, unalterableness in the fire, infusibility, &c. Caroline. Yet, did you not tell us that silex, or siliceous earth, when mixed with an alkali, was fusible, and run into glass \ Airs. B. Yes, my dear; but the characteristic properties of earths, * The Derbyshire spar is composed of lime zndfluoric acidl hence it is called fluute of lime. The colours are owing to intermixture with metallic oxides. It is a very beautiful mineral, and instead of being opaque, it is generally translucent, or nearly transparent.—C 812. Whence may it be supposed they receive their beautiful col- ors ? 813. What is an instance of simple earths in a state of crystalli- zation ? 814. What is the composition of Derbyshire spar ? 815. What are alkaline earths ? 816. Why are they so called ? 817. What properties are common to all earths? SILEX. 195 which I have mentioned, are to be considered as belonging to them in a state of purity only; a state in which they are very seldom to he met with in nature. Besides these general properties, each earth bas its own specific characters, by which it is distinguished from any other substance. Let us thefefore review them separately. Silex, or silica, abounds inJlint, sand, sand-stone, agate, jas- [ier^ &c.; it forms the basis of many precious stones, and particu- arly of those which strike fire with steel. It is, rough to the touch, scratches and wears away metals; it is acted upon by no acid but the fluoric, and it is not soluble in water by any known process ; but nature certainly dissolves it by means with which we are unac- quainted, and thus produces a variety of sileceous crystals, and amongst these, rock crystal, which is the purest specimen of this earth. Silex appears to have been intended by Providence to form the solid basis of the globe, to serve as the foundation for the origi- nal mountains, and give them that hardness and durability which has enabled them to resist the various revolutions which the surface of the earth has successively undergone. From these mountains siliceous rocks have, during the course of ages, been gradually de- tached by torrents of water, and brought down in fragments; these, in the violence and rapidity of their descent, are sometimes crum- bled to sand, and in this state form the beds of rivers and ofthe sea, chiefly composed of siliceous materials. Sometimes the fragments are broken without being pulverized by their fall, and assume the form of pebbles, which gradually become rounded and polished. Emily. Pray, what is the true color of silex, which forms such a variety of different colored substances ? Sand is brown, flint is nearly black, and precious stones are of all colors. Mrs. B. Pure silex, such as is found only in the chemist's labora- tory, is perfectly white, >and the various colors which it assumes in the different substances you have just mentioned, proceed from the different ingredients with which it is mixed in them. Caroline. I wonder that silex is not more valuable, since it forms the basis of so many precious stones.* Mrs. B. You must not forget that the value we set upon precious stones depends in a great measure upon the scarcity with which nature affords them ; for were those productions either common or perfectly imitable by art, they would no longer, notwithstanding their beauty, be so highly esteemed. But the real value of siliceous earth in many of the most useful arts, is very extensive. Mixed with clay,; it forms the basis of all the various kinds of earthen ware, from the most common utensils to the most refined ornaments. Emily. And we must recollect its importance in the formation of glass with potash. Mrs. B. Nor should we omit to mention, likewise, many other * The bases of some ofthe most costly gems, as sapphire, fubyj and topaz, are alumine.—C. 818. In what is silex chiefly found ? 819. What is the purest specimen of silex? 820. What is the color of silex? 821. Upon what does the value of precious stones depend ? 822. For what important uses is silex chiefly valuable ? 196 ALUMINE. important uses of silex, such as being the chief ingredient of some of the most durable cement, of mortar, &c. I said before that siliceous earth combined with no acid but the fluoric; it is for this reason that glass is liable to be attacked by that acid only, which, from its strong affinity to silex, forces that substance from its combination with tbe potash, and thus destroys tbe glass; We shall now hasten to proceed to the other eartbs, for I am ra- ther apprehensive of your growing weary of this pari of our subject. Caroline. I confess that the history of the earths is not quite so entertaining as that ofthe simple substances. Airs. B. Perhaps not; but it is absolutely indispensable that you should know something of them; for£ they form the basis of so many interesing and important compounds,Mhat their total omis- sion would throw great obscurity on our general outline of chemi- cal science. We shall however, review them in as cursory a man- ner as the subject can admit of. v Alumine derives its name from a compound salt oalled a/um, of which it forms ihe basis. Caroline. But it ought to be just the contrary, Mrs. B.; the sim- ple body should give instead of taking, its name from the compound. Mrs. B. That is true ; but as the compound salt was known long before its basis was discovered, it was very natural that when the earth was at length separated from the acid, it should derive its name from the compound from which it was obtained. However, to remove your scruples, we will call the salt according to the new nomenclature, sulphat of alumine. From this combination, alu- mine may be obtained in its pure state; it is then soft to the touch, makes a paste with water, and hardens in the fire. In nature it is found chiefly in clay,t which contains a considerable proportion of this earth; it is very abundant in fullers' earth, slate, and a variety of other mineral productions. There is indeed scarcely any mine- ral substance more useful to mankind than alumine. In the stale of clay, it forms large strata of the earth, gives consistency to the soil of valleys, and of all low and damp spots, such as swamps and marshes. The beds of lakes, ponds, and springs, are almost en- tirely of clay ; instead of allowing ofthe filtration of water, as sand does, it forms an impt netrable bottom, and by this means water is accumulated in the c: verns ofthe earth, producing those reservoirs whence springs issue, and spout out at the surface. Emilu. 1 always tl ought that these subterraneous reservoirs of water were bedded by some hard stone, or rock, which the water could not penetrate. Airs. B. That is ni t the case; for in the course of time water would penetrate, or wear away silex, or any other kind of stone, whde it is effectually stopped by clay, or alumine. The solid compact soils such as are fit for corn, owe their consist- 823. How, and why does the fluoric acid destroy glass ? 824. Why is it necessary to understand the nature ofthe earths ? 825. From what does alumine derive its name? 826. What is the sulphat of alumine ? 827. In what is alumine chiefly found? 828. In what kind of soil does it occur mo'st abundantly ? BARYTES. 197 ence'in a great measure to alumine ; this earth is therefore used to improve sandy or chalky soils, which do not retain a sufficient quan- tity of water for the purpose of vegetation. Alumine is the most essential ingredient in all potteries. It en- ters into the composition of brick, as well as that ofthe finest porce- lain : the addition of silex and water hardens it, renders it suscep- tible of a degree of vitrification, and makes it perfectly fit for its va- rious purposes. Caroline. I can scarcely conceive that brick and china should be made of the same meterials. Mrs B. Brick consists almost entirely of baked clay ; but a cer- tain proportion of silex is essential to the formation of earthen or Btone ware. In the common potteries sand is used for that purpose ; a more pure silex is,* I believe, necessary for the composition of porcelain, as well as a finer kind of clay ; and these materials are* no doubt, more carefully prepared, and curiously wrought in the one case than in the other. Porcelain owes Ks beautiful semi-trans- parency 10 a commencement of vitrification. Emily. But the commonest earthenware, though not transparent, is covered with a kind of glazing. Airs. B. That precaution is equally necessary for use as for beau- ty, as the ware would be liable to be spoiled and corroded by a va- riety of substances, if not covered wiih a coating of this kind. In porcelain it consists of enamel, which is a fine white opaque glass, formed of metallic oxy 's, sands, salts, and such other materials as are susceptible of vitriiioation. The glazing of common earthen- ware is made chiefly of oxyd of lead, or sometimes merely of salt, which, when thinly spread over earthen vessels, will, at a certain heat, run into opaque glass. Caroline. And of what nature are the colours which are used for painting porcelain ? Mrs. B. They are all composed of metallic oxyds ; so that these colours, instead of receiving injury from the application of fire, are strengthened and developed by its action, which causes them to un- dergo different degrees of oxydation. Alumine and silex are not only often combined by art but they have in nature a very strong tendency to unite, and are found com- bined, in different proportions, in various gems and other minerals. Indeed, many ofthe precious stones, such as ruby, oriental sap- phire, amethyst,f &. consist chiefly of alumine. We may now proceed to the alkaline earths; I shall say but a few words on barytes, as it is hardly ever used, except in chemical * Porcelain clay, of which china ware is made, is found among granite rocks, and seems to owe its origin to the decomposition of a mineral called fields par. Its composition is silex and alumine, si- lex being the predominant ingredient.—C. f The amethyst is almost entirely composed of silex.—C. 829. What is the use of alumine for purposes of vegetation ? 830. What is the use of it in works of art ? 831. To what is the transparency of porcelain owing ? 832. Of what is the glazing of common earthen-ware made r 833. What is the nature ofthe colours which are used for painting porcelain ? 17* 198 LIME. laboratories. It is remarkable for its great weight, and its strong alkaline properties, such as destroying animal substances, turning ereen some blue vegetable dolours, and showing a powerful attrac- tion for acids ;i this last property it possesses to such a degree, par- ticularly with regard to the sulphuric acid that it will always de- tect its presence in any substance or combination whatever, by lift. mediately uniting with it, and forming a sulphat of barytes. This renders it a very valuable chemical test. It is found pretty abun- dantly in nature in the stale of carbonat* from which the pure earth can be easily separated. . . The next earth we have to consider is Lime. This is a substance of too great and general importance to be passed over so lightly as the I .st. . . . . Lime is strongly alkaline. In nature it is not met with in its simple state as its affinity for water and carbonic acid is so great that u is always found combined with these substances, with which it forms the common lime stone; but it is separated in the kiln from these ingredients, which f re volatilized whenever a sufficient de- gree of heat is applied. Emily. Pure lime, then, is nothing but lime stone, whicn has been deprived, in the kiln, of its water and carbonic acid*? M rs. B. Precisely : in this state it is called quick Zime,.anditisso caustic, that it is < apabl; of decomposing the dead bodies of animals very rapidly, without their undergoing the process of putrefaction. I have here some quick lime, which is kept carefully corked up in a botle to prevent the access of the air ; for were it all exposed to the atmosphere, it would absorbsboth mo:sture and carbonic acid gas from it, and be soon slaked.\ Here is also some lime stone— we shall pour a little water on each, and observe the effects that result from it. Caroline. How the quick-lime hisses ? It is become excessively bot ! — It swells, and now it bursts and crumbles to powdeiyyvhile the water appears to produce no kind of alteration on the lime- stone. ,," Airs. B. Because the lime stone is already saturated with water, whiht the quick I me, which has been deprived of it io the kiln, combines with it with very great avidity, and produces this prodi- gious disengagement of heal, the cause of which I formerly explain- ed to you ; do you recollect it ? Emily. Yes; you said that the heat did not proceed from the lime * The native rarbrmat or barytes is a rare mineral. It is a viru- lent poison. The sulphat of barytes is found in considerable abun- dance.—C. 834. For what is barytes remarkable ? 835. For what is it valuable ? 836. Where is it abundantly found ? 837. What is the reason that lime is not found in its simple state ? 83ii. flow does lime-stone differ from pure lime ? 839. What effect will quick lime have upon the dead bodies of ani- mals ? fi4 '. What effect docs the air produce on quick lime ? 841. VVhat effect has water on it? 842 Why will not water have an effect on lime-stone as well as upon quick lime ? BARYTES. 199 but from the water which was solidified, and thus parted with its heat of liquidity. Mrs. B. Very well. If we continue to add successive quantities of water to the lime, after being slaked and crumbled, as vou see, it will then gradually be diffused in the water, till it will at length be dissolved in it, and entirely disappear ; but for this purpose it requires no less than 700 times its weight of water. This solution is called lime water* Caroline. How very small, then, is the proportion of lime dissol- ved ! Mrs. B. Barytes is also of very difficult solution ; but it is much more soluble in the state of crystals. The liquid contained in this bottle i3 lime water: it is often used as a medicine, chiefly. 1 believe, for the purpose of combining with, and nentraliz ng the superabun- dant acid which it meets with in the stomach. Emily. I am surprised that it is so perfectly clear : it does not at all partake of the whiteness of the lime. Mrs. li. Have yon forgotten that, in solutions, the rolid body is so minutely subdivided by the fluid as to become invisible, and there- fore, will not, in the least degree, impair the transparency ofthe solvent ? I said that the attraction of lime for carbonic acid was so strong, that it would absorb it from the atmo phere. We may see this effect by exposing a glass of lime-water to th<> air; the lime will ihen sep- arate fiom the water, combine with the carbonic acid, and re-ap- fiear on the surface in the form of a white film, which ?\s carbonat of ime commonly called chalk. Caroline. Chalk is, then, a compound salt ! I never should have supposed that those immense beds of chalk, that we see in many part* ofthe country were a salt. Now the white film begins to ap- pear on the surface ofthe water : but it is far from resembling hard solid chalk. Airs. B. That is owing to its state of extreme division : in a lit- tle time it will collect into a more compact mass, and subside at tbe bottom of the glass.# Ifyou breathe into lime-water, the carbonic acid, which is mixed with the air that you cxpiie. will produce the same effect- It is an experiment v.ry easilv made:—I shall pour some lime water into this glass tube, and by breathing repeatedly into it, you will soon perceive a precipitation of chalk. * To make lime-waterCtake a piece of well burned lime, about the size of a hen's egg, put it into an earthen dish, and sprinkle wa- ter on it, till it falls into powder : Then pour on two quarts of boil- ing water, and st r it several times, after the lime has settled ; pour off the clear water and cork it for use.—C. _________ 843. Why is heat disengaged when water is put upon quicklime? 844. How much water docs it take to dissolve lime? 845. Is Barytes easily dissolved in water? 846. Why does not lime water partake ofthe whiteness of lime? k 847. For what has lime a very strong attraction ? 84M. Why does a white film collect on the surface of lime-water on being exposed to the air ? . 849. Why will lime water turn white ifyou breathe into it. 200 LIME. Emily. 1 see already a small white cloud formed. Mrs. B. It is composed of minute particles of chalk ; at present it floats in the water, but it will soon subside. Carbonat of lime,\ or chalk, you see, is insoluble in water, since the lime which was dissolved re-appears when converted into chalk; but you must take notice of a very singular circumstance, which is, that chalk is soluble in water impregnated with carbonic acid. Caroline. It is very curious, indeed, that carbonic acid and gas should render lime soluble in one instance and insoluble in the other! Mrs. B. I have here a bottle of Seltzer water, which you know, is strongly impregnated with carbonic acid ; let us pour a little of it into a glass of lime-water. You see that it immediately forms a precipitation ofcarbonat oflime ? Emily. Yes, a white cloud appears. Mrs. B. I shall now pour an additional quantity of the Seltzer water into the lime-water.— Emily. How singular ! The cloud is re-dissolved, and the liquid is again transparent. Mrs. B. All the mystery depends upon this circumstance, that carbonat oflime is soluble in carbonic acid, whilst it is insoluble in water ; the first quantity of carbonic acid, therefore, which I intro- duced into the lime-water, was employed in forming the carbonat oflime, which remained visible, until an additional quantity of car- bonic acid dissolved it. Thus, you see, when the lime and carbonic acid are in proper proportions to form chalk, the white cloud ap- pears ; but when the ac id predominates, the chalk is no sooner form- ed than it is dissolved. Caroline: That is now the Case ; but let us try whether a further addition of lime-water will again precipitate the chalk. Emily. It does, indeed ! The cloud re appears, because, I sup- pose, there is now no more of the carbonic acid than is necessary to form chalk; and, in order to dissolve the chalk, a superabun- dance of acid is required. Mrs. B. We have, I think, carried this experiment far enough; every repetition would but exhibit the same appearance. Lime combines With most of the acids, to which the carbonic (as being the weakest) readily yields it; but these combinations we shall have an opportunity of noticing more particularly hereafter. It unites with phosphorus, and with sulphur, in their simple state ; in short,-of all the earths, lime is that which nature employs most frequently, and most abundantly, in its innumerable combinations. It is the basis of a'l calcareous earths and stones; we find it like- wise in the animal and vegetable crealions. Emily. And in the arts is not lime of very great utility? Mrs. B. Scarcely any substance more so ; you know that it is a 850. What is the chemical name of chalk? 851 What is the process of making lime-water ? 852. How may chalk be dissolved ? 853. What will be ihe result if Seltzer water be poured into lime- water? 854. What is the basis of all calcareous earths and stones? 855. Of what use is lime in the arts ? MAGNESIA. 201 most essential, requisite in building, as it constitutes the basis of all cements, such as mortar, stucco, plaster, fcc. Lime is also of infinite importance in agriculture ; it lightens and warms soils that are too cold and compact, in consequence of too great a proportion of clay. But it would be endless to enumerate tbe various purposes for which it is employed ; and you know enough of it to form some idea of its importance; we shall therefore, now proceed to the third alkaline earth, magnesia. Caroline. 1 am already pretty well acquainted with that earth; it is a medicine. Mrs. B. It is in the state of carbonatxthat magnesia is usually employed medicinally ; it then differs but'little in appearance from its simple form, which is that of a very fine light white powdet. It dissolves in 2000 times its weight of water, but forms with acids ex- tremely soluble salts. It has not so great an attraction for acids as lime, and consequently yields them to the latter. It is found in a great variety of mineral combinations, such as slate, mica, amian- thus ; and more particularly in a certain lime stone, which has been discovered by Mr. Tennant to contain it in very great quantities. It does not attract and solidify water, like lime; but when mixed with water and exposed to the atmosphere, it slowlyabsorbs carbon- ic acid from the latter, and thus loses its causticity. Its chief use in medicine is, like that of lime, derived from its readiness to com- bine with, and neutralize, the acid which it meets with in the sto- mach. Emily. Yet, you said that it was taken in the state of carbonat, in which case, it has already combined with an acid ? Mrs. B. Yes ; but the carbonic is the last of all the acids in the order of affinities ; it will therefore yield the magnesia to any of the others. It is, however, frequently taken in its caustic state as a re- medy for flatulence. Combined with sulphuric acid, magnesia forms another and more powerfhl medicine commonly called Epsom salt. Caroline. And properly, sulphat of magnesia, 1 suppose ? Pray, how did it obtain the name of Epsom salt ? Mrs. B. Because there is a spring in the neighborhood of Epsom which contains this salt in great abundance. The last alkaline earth which we have to mention is strontian, or sbontites, discovered by Dr. Hope a few years ago. It so strongly resembles barytes in its properties, and is so sparingly found in nature, and of so little use in the arts, that it will not be necessary to enter into any particulars respecting it. One of the remarkable characteristic properties of strontites is, that its salts, when dissolved in spirits of wine, tinge the flame a deep red, or blood color. 856. Of what use is lime in agriculture? 857. What is the simple form of magnesia? 858. Does it attract water ? 859. What is its chief use in medicine ? 860. In what state is it used in medicine ' 861. What does it form combined with sulphuric acid? 86?. Why is the sulphat of magnesia called Epsom salt? 863. Is strontian of any use ? 864. What is one ofthe remarkable properties of strontities ? 202 ACIDS. CONVERSATION XVI. ON ACIDS. Mrs. B. We may now proceed to the acids. Ofthe metallic ox- yds, you have already acquired some general notions. This subject though highly interesting in its details, is not of sufficient impor- tance to our concise view of chemistry, to be particularly treated of; but it is absolutely necessary that you should be better acquainted with the acids, and likewise with their combinations with the alka- lies, which form the triple compounds, called neutral salts. This class of acids is characterized by very distinct properties. They all change blue vegetable infusions to a red color ; they are more or less sour to the taste; and have a general tendency to com- bine with the earths, alkalies and metallic oxyds.) You have, I believe, a clear idea of the nomenclature by which the base (or radical) ofthe acid, and the various degrees of acidifi- cation, are expressed ? Emily. Yes, I think so ; the acid is distinguished by the name of its base, and its degree of oxydation, that is, the quantity of oxygen it contains, by the termination of that name in oils, or ic; thus sul- phureous acid, is that formed from ihe smallest proportion of oxygen combined with sulphur^sulphuric .'acid is that which results front the combination of sulphur with tbe greatest quantity of oxygen. Mrs. B. A still greater latitude may, in many cases, be allowed to the proportions of oxygen that can be combined with acidifiable radicals: for several of these radicalsfare susceptible of uniting with a quantity of oxygen so small as to be insufficient to give them the properties of acids; in these casesytherefore, they are converted in- to oxyds. Such issulphurV whicl{. by exposure to the atmosphere with a degree of heat inadequate to produce inflammation, absorbs a small proportion of oxygen, which colors it red or browrj} This, therefore, may be considered as the first degree of oxygenation of sulphur ; the 2d converts it into sulphureous acid y the 3d into the sulphuric acid; and4thly, if it was found capable of combining with a still larger proportion of oxygen, it would then be termed super- oxygenated sulphuric acid. Emily. Are these various degrees of oxygenation common to all the acids ? Airs. B. No ; they vary much in this respect; some are suscep- tible of only one degree of oxygenation : others of two or three; there are but very few that will admit of more. 865. What is an acid ? 866. How are acids distinguished ? 867. What is meant by the radical of an acid ? 868. What substance unites to the radical to form an acid ? 869. How does the language of chemistry distinguish the stronger from the weaker acid ? 870. What term is used to denote the first degree of oxygenation ? 871. When a radical unites with another proportion of oxygen af- ter that denoted by ic, what term is used ? 872. Are all acids susceptible ofthe same degree of oxygenation ? ACIDS. 203 Caroline. The modern nomenclature must be of immense ad- vantage in pointing out so easily the nature of the acids, and their various degrees of oxygenation. Airs. B. Till lately many of the acids had not been decomposed ; but analogy afforded so strong a proof of their compound nature, that 1 could never reconcile myself to classing them with the sim- ple bodies, though this division has been adopted by several chem- ical writers. At present the muriatic and the fluoric are the only acids which have not had their bases distinctly separated. Caroline. We have heard of a great variety of acids; Pray how many are there in all ? Mrs. B. I believe there are reckoned at present thirty-fouivand their number is constantly increasing as the science improves ; but the most important, and those to which we shall almost entirely confine our attention, are but few. I shall, however, give you a general view of the whole; and then we shall more particularly ex- amine those that are the most essential. This class of bodi.es was formerly divided into mineral, vegetable and animal acids, according to the substances from which they were commonly obtained. Caroline. That, I should think, must have been an excellent ar- rangement; why was it altered? Mrs. B. Because, in many cases it produced confusion. In which class, for instance, would you place carbonic acid? Caroline. Now I perceive the difficulty. I should be at a loss where to place it, as you have told us that it exists in the animal, vegetable and mineral kingdoms. Emily. There would be the same*objection with respect to phos- phoric, which though obtained chiefly from bones, can also, you said, be found in quantities in stones, and likewise in some plants. Airs. B. You see, therefore, the propriety of changing this mode of classification. These objections do not exist in the present no- menclature ; for the composition and nature of each individual acid is in some degree pointed out, instead of the class of bodies from which it is extracted; and, with regard to the more general divi- sion of acids, they are classed under these three heads: First. Acids of known or supposed simple bases, which are form- ed by the union of these bases with oxygen. They are the follow- ing: 873. How many acids are there ? 874. How were acids formerly divided ? 875. What objection was there to this division? 876. Under how many general heads or divisions are acids at pre sent d1&.cgq •* 8T7. What kind of acids make the first class ? 204 ACIDS. The Sulphuric Carbonic Nitric Phosphoric Arsenical Tungsltnic Alolybdenic Boracic Fluoric Alurialic }-Acids of known and simple bases. This class comprehends the most anciently known and most im- portant acids. The sulphuric, nitric, and muriatic, were formerly, and are still frequently called mineral acids. 2dly. Acids that have double or binary radicals, and which con- sequently consist of triple combinations. These are the vegetable acids, whose common radical is a compound of hydrogen and carbonj Caroline. But if the basis of all the vegetable acids be the same it should form but one acid ; it may indeed combine with different proportions of oxygen, but the nature ofthe acid must be the same. Mrs. B. The only difference that exists in the bases of vegetable acids, is the various proportions of hydrogen and carbon from which they are severally composed. But this is enough to produce a number of acids apparently very dissimilar. That they do not however, differ essentially, is proved by their susceptibility of being converted into each other, by the addition or subtraction of a por- tion of hydrogen or carbon. The names of these acids are, The Acetic Oxalic Tartarous Citric Malic Gallic }■ Acids of double bases, being of vegetable origin. Mucous Benzoic Succinic Camphoric Suberic ' The 3d class of acids consists of those which have triple radicals, and are therefore of a still more compound nature. This class com- prehends the animal acids, which are, The Lactic Prussic Formic Bombic Sebacic Zoonic Li'hic Y Acids of triple bases, or animal acids. 878. What are their names ? 879. What ones of this class are called mineral acids ? 880. What ones make the second division? 881. What is the common radical of vegetable acids ? 882. What is the difference in the bases of vegetable acids ? 883. What are the names of the vegetable acids ? 884. What ones make the third division of acids? 8.85. Name the acids with triple radicals. ACIDS. 205 1 have given you this summary account or enumeration of the acids, as you may find it more satisfactory to have at once an out- line or a general notion ofthe extent of the subject : but we shall now confine ourselves to the first class, which requires our more immediate attention ; and defer the few remarks which we shall have lo make on the others, till we treat of the .chemistry ofthe an- imal and vegetable kingdoms. The acids of simple and known radicals are in most instances ca- pable of being decomposed by combustible bodies, to which'they yield their oxygen.j If, for instance, I pour a drop of sulphuric acid on this piece of iron, it will produce a spot of rust; you know what it is? Caroline. Yes ; it is an oxyd, formed by the oxygen of the acid combining with the iron. Mrs. B. In this case you see the sulphur deposits the oxygen by which it was acidified on the metal ? And again, if we pour some acid on a compound combustible substance, (we shall try it on this piece of wood) it will combine with one or more of the constituents of that substance, and occasion a decomposition. Emily. It has changed the color of the wood to black. How is that? Airs. E. The oxygen deposited by the acid has burnt it; you know that wood in burning becomes black before it is reduced to ashes. Whether it derives the oxygen which burns it from the at- mosphere, or from any other source, the chemical effect on the wood is the same. In the case of real combustion,, wood becomes black, because it is reduced to the state of charcoal by the evapo- ration of its other constituents. But can you tell me the reason why wood turns black when burnt by the application ofan acid ? Caroline. First tell me what are the ingredients of wood ? Airs. B. Hydrogen and carbon) are the chief constituents of wood, as of all other vegetable substances. Caroline, Well, then, I suppose that the oxygen ofthe acid com- bines with the hydrogen of the wood, to form water; and that the carbon of the wood, remaining alone appears of its usual black col- our. Mrs. B. Very well indeed, my dear ; that is certainly the most plausible explanation. Emily. Would not this be a good method of making charcoal ? Airs. B. It would be an extremely expensive, and I believe very imperfect method ; for the action of the acid on the wood, and the heat produced by it, are far from sufficient to deprive the wood of all itsevaporable parts. Caroline. What is the reason that vinegar, lemon, and the acid of fruits, do not produce this effect on the wood? Airs. B. They are vegetable acids whose bases are composed of ■886. How can acids of simple radicals be decomposed ? 887. If a drop of sulphuric acid falls on a piece of iron, why does it produce rust ? 888. Why does acid turn wood black? 899. Why does wood become blackin real combustion? 890. What are the chief constituents of wood ? 891. Why does not vinegar, lemon, and the other vegetable acid* produce the same effect on wood ? 206 OF THE SULPHURIC hvdrogen and carbon ; the oxygen, therefore, will not be disposed to quit this radical, where it is already united with hydrogen. The strongest of these may, perhaps, yield a little of tehir oxygen to the wood, and produce a stain upon it, but the carbon will not be suffi- ciently uncovered to assume its black colour, Indeed, the several mineral acids themselves possess this power of charring wood in very different degrees. Emily. Cannot vegetable acids be decomposed, by any combus- tibles ? Mrs. B. No : because their radical is composed of two substan- cesVhich have a greater attraction for oxygen than any known bo- dy.' ' Caroline.—And are those strong acids, which burn and decom- pose wood, capable of producing similar effects on the skin and flesh of animals ? Mrs. B. Yes; all the mineral acids, and one of them more es- pecially, possess powerful caustic qualities. They actually corrode and destroy the skin and flesh ; but they do not produce upon these 7 exactly the same alteration they do on wood, probably because (' there is a great proportion of nilrogenVnd other substances in ani- ^ inal matter, which prevents the separation of carbon from being so conspicuous. CONVERSATION XVII. OF THE SULPHURIC AND PHOSPHORIC ACIDS *, OR THE "COM- BINATIONS OF OXYGEN WITH SULPHUR AND PHOSPHORUS ; AND OF THE SULPHATS AND PHOSPHATS. Airs. B. In addition to the general survey which we have taken of acids, I think you will find it interesting to examine individually, a few of the most important of them, and likewise some of their principal combinations with the alkalies, alkaline earths, and metals. The first of these acids, in point of importance, is the sulphuric, formerly called oil of vitriol. Caroline. 1 have known it a long time by that name, but had nc idea that it was the same fluid as sulphuric acid. What resemblance or connection can there be between oil of vitriol and this acid? Mrs. B. Vitriol is the common name for sulphat of iron, a salt which is formed by the combination of sulphuric acid and iron : the sulphuric acid was formerly obtained by distillation from this sain, and it very naturally received its name from the substance which afforded it. 892. Why cannot vegetable acids be decomposed by combusti- bles ? 893. Do the mineral acids have the same effect on the skin and flesh of animals as on wood? 894. If they do not what is the reason ? 895. What i3 the proper chemical name of oil of vitriol ? 896. Why was it called oil of vitriol? AND SULPHURIC ACIDS. 207 Caroline. But it is still usually called oil of vitriol ? Airs. B. Yes : a sufficient length of time has not yet elapsed, since the invention of the new nomenclature, for it lo be generally disseminated ; but as it is adopted by all scientific chemists, there is every reason to suppose that it will gradually become universal. When I received this bottle from tbe chemists, oil of vitriol was in- scribed on the label; but as I knew you were very punctillious in regard to the nomenclature, I changed it and substituted the words sulphuric acid. Emily. This acid has neither colour nor smell, but it appears much thicker than water. Mrs.B. It is nearly twice as heavy as water, and has, you see, an oily consistence. Caroline. And it is probably from this circumstance that it has been called an oil; for it can have no real claim to that name, as it does not contain either hydrogen or carbon, which are the essential constituents of oil. Mrs. B. Certainly, and therefore, it would be the more absurd to retain a name which owed its origin to such a mistaken analogy. Sulphuric acid, in its purest state would probably be a concrete substance, but its attraction for water is such, that it is impossible to obtain that acid perfectly free from it: it is therefore, always seen in a liquid form, such as you here find it. One of the most striking properties of sulphuric acid is that of evolving a considera- ble quantity of heat when mixed with water ; this I have already shown you. Emily. Yes, 1 recollect it; but what was the degree of heat pro- duced by that mixture ? Airs. B. The thermometer may be raised by it 300 degrees, which is considerably above the temperature of boiling water. Caroline. Then the water may be made to boil in that mixture I Airs. B. Nothing more easy, provided that you employ sufficient quantities of acid and of water, and in the due proportions. The greatest heat is produced by a mixture of one part of water to four of the acid ; we shall make a mixture of these proportions, and im- merse in it this thin glass tube, which is full of water. Caroline. The vessel feels extremely hot, but the water does not boil yet. Mrs. B. You must allow some time for the heat to penetrate the tube, and raise the temperature of the water to the boiling point— Caroline. Now it boils—ami with increasing violence. Mrs.B. But it will not continue boiling long: for the mixture gives out heat only while the particles of the water and the acid are mutually penetrating each other; as soon as the new arrangement 897. What is the colour and smell of this acid ? 898. What is its weight ? 899. What would sulphuric acid be in its purest state ? 900. What is the consequence qf mixing it with water ? 901. What is one of its most striking properties ? 902. How high may a thermometer be raised by it ? 903. In what proportions must sulphuric acid and water be mixed in order to produce the greatest degree of heat ? 904. Why does the mixture of Bulphuric acid and water give out heat only for so short a time ? 208 OF THE SULPHURIC of these particles is affected, the mixture will gradually cool, anrl the water return to its former temperature. You have seen the manner in which sulphuric acid decomposes all combustible substances, whether animal, vegetable, or mineral, and burns them by means of its oxygen ? Caroline. I have very unintentionally repeated the experiment on my gown, by letting a drop of the acid fall upon it, and it has made a stain, which I suppose will never wash out. Mrs. B. No, certainly ; for before you can put it into water, the spot will become a hole, as the acid has literally burnt the muslin. Caroline. So it has indeed ! Well, I will fasten the stopper, and put the bottle away, for it is a dangerous substance,—Oh, now I have done worse still, for I have spill some on my hand ! Mrs. B. It is then burned, as well as your gown, for you know that oxygen destroys animal as well as vegetable matter; and as far as the decomposition ofthe skin of your finger is effected, there is no remedy ; but by washing it immediately in water, you will di- lute the acid, and prevent any further injury. Caroline. It feels extremely hot, I assure yon. Airs. B. You have now learned by experience, how cautiously this acid must be used. You will soon become acquainted with another acid, the nitric, which, though it produces less heat on the skin, destroys it still quicker, and makes upon it an indelible stain., You should never handle any substances of this kind without pre- viously dipping your fingers into water, which will weaken their caustic effect. But, since you will not repeat the experiment, I must put in the stopper, for the acid attracts the moisture from the atmosphere, which would destroy its strength and purity. Emily. Pray, how can sulphuric acid be extracted from sulphat of iron by distillation ? Mrs. B. The process of distillation, you know consists in sepa- rating substances from one another by means of their different de- grees of volatility, and by the introduction of a new chemical agent, caloric. Thus, if sulphat of iron be exposed in a retort to a proper degree of heat, it will be decomposed, and the sulphuric acid will be volatilized. Emily. But now that the process for forming acids, by the com- bustion of their radicals is known, why should not this-method be used for making sulphuric acid ? Airs. B. This is actually done in most manufactures ; but the Usual method of preparing sulphuric acid does not consist in burn- ing the sulphur in oxygen gas (as we formerly did by way of ex- periment,) but in heating it together with another substance, nitre, which yields oxygen in sufficient abundance to render the combus- tion in common air rapid and complete. Caroline. This substance, then, answers the same purpose as ox- ygen gas ? Airs. B. Exactly. In manufactures the combustion is performed in a leaden chamber, with water at the bottom, to receive the va- por and assist its condensation. The combustion is however, never so perfect but that a quantity of sulphureous acid is formed at the 905. How does sulphuric acid compare with nitric acid ? 906. In what consists the process of distillation ? 907. How is sulphuric acid obtained ? AND SULPHUREOUS ACIDS. 209 same time; for, ifyou recollect that the sulphureous acid, accord- ing to the chemical nomenclature, differs fiom the sulphuric only by containing less oxygen. From its own powerful properties, and from the various combina- tions into which it enters, sulphuric acid is of great importance in many ofthe arts. It is used also in medicine in a state of great dilution; for were it taken internally, in a concentrated state, it would prove a most dangerous poison. Caroline. 1 am sure it would burn the throat and stomach. Mrs. B. Can jou think of any thing that would prove an antidote to this poison ? Caroline. A large draught of water to dilute it. Mrs. B. That would certainly weaken the caustic power of the acid, but it would increase the heat to an intolerable degree. Do you recollect nothing that would destroy its deleterious properties more effectually ? Emily. An Alkali might, by combining with it; but then a pure alkali is i'v If a poibon, on account of its causticity. Mrs. B. There is no necessity that the alkali should be caustic. Soap, in which it is combined with oil ;\or magnesia, either in tbe state of carbonat, or mixed with water,jwould prove the best anti- dote. Emily. In those cases then, I suppose, the potash and the mag- nesia would quit their combinations to form salts with the sulphuric acid? Airs. B. Precisely. We may now make a few observations on the sulphureous acid, which we have found to be the product of sulphur slowly and im- perfectly burnt. This acid is distinguished by its pungent smell, and its gaseous form. Caroline. Its aeriform state is, I suppose, owing to the smaller proportion of oxygen, which renders it lighter than sulphuric acid ? Mrs. B. Probably ; for by adding oxygen to the weaker acid, it may be converted into the stronger kind. But this change of state may also be connected with a change of affinity with regard to caloric. Emily. And may sulphureous acid be obtained from sulphuric acid by a diminution of oxygen ?v Mrs. B. Yes ; it can be done by bringing any combustible sub- stance in contact with the acid. This decomposition is most easily performed by some of the acids ; these absorb a portion of the oxy- gen from the sulphuric acid, which is thus converted into the sul- phureous, and flics off in its gaseous form. Caroline. And cannot the sulphureous acid itself be decomposed and reduced to sulphur? Mrs. B. Yes ; if this gas be heated in contact with charcoal, the oxygen of the gas will combine with it, and the pure sulphur'will be regenerated 908. How does sulphureous acid differ fiom sulphuric? 909. What would prove the'best remedy to a person who had swal- lowed sulphuric acid ? 910. How may sulphureous acid be obtained ? 911. How can the sulphuric acid be changed to the sulphureous? 912. How can sulphureous acid be reduced to sulphur? 18* 210 OF THE SULPHUREOUS ACID. Sulphureous acid is readily absorbed by water; and in this liquid "state if. is found particularly useful in bleaching linen and woollen cloths^ and is much used in manufactures for those purposes. I can show you its effect in destroying colours, by taking out vegeta- ble stains—I think I see a spot on your gown, Emily, on Which we may try the experiment. Emily. It is the stain of mulberries : but I shall be almost afraid of exposing my gown to ihe experiment, after seeing the effect which the sulphuric acid produced on that of Caroline— Airs. B. There is no such danger from the sulphureous; but the experiment must be made with great caution, fordnring the forma- tion of sulphureous acid by combustion, there is always some sul- vphoric produced. Caroline. But where is your sulphureous acid? Airs. B. We may easily prepare some ourselves, simply by buro- ing a match ; we must first wet the stain with water, and how bold it in this way, at a distance over the lighted match; the vapour that arises from it is sulphureous acid, and the stain, you see, grad- ually disappears. Emilu. I have frequently taken out stains by this means, with- out understanding the nature of the process. But why is it neces- sary to wet the stain before it is exposed to the acid fumes? Mrs. B. The moisture attracts and absorbs the sulphureous acid; and it serves likewise to dilute any particles of sulphuric acid which might injure the linen. Sulphur appears to be susceptible of a third combination of oxy- gen in which the proportion of the latter is too small to render the sulphur acid. It acquires this slight oxygenation by mere exposure to the atmosphere, without any application of heatv; in this case the sulphur does not change its natural form, but is inly discolour- ed, being changed to red or brown, a state in which it may be con- sidered an oxyd of sulphur. Before we take leave of the sulphuric acid, we shall say a few words of its principal combinations. It unites with all the alkalies, alkaline earths and metals, to form compound salts. Caroline. Pray, give me leave to interrupt you for a moment: you have never mentioned any other salts than the compound or neutral salts ; is there no other kind? Airs. B. The term salt has been used, from time immemorial, as a kind of a general name for any substance that has savour, odour, is soluble in water, and crystallizable, whether it be of an acid, an alkaline or compound nature ; but the compound salts alone retain that appellation in modern chemistry. The most important ofthe salts formed by the combinations of the sulphuric acid, are, fir t, sulphat of potash, formerly called sal poly chrest: tb.s is a very bitter salt, much used in medicine ; it is found in the ashes of most vegetables, but it may be prepared artificially by the immediate combination of sulphuric acid and potash. This 913. What important use is made of this acid ? 914. What is the easiest process for making this acid ? 915. How would you describe a third combination of sulphur with oxygen? 9i6. With what does sulphuric acid unite? 917. What is the meaning ofthe term salt ? OF THE SULPHATS. 211 salt is easily soluble in boiling water. Solubility is, indeed, a prop- erty common to all salts ; and they always produce cold in melting. Emily. That must be owing to the caloric which they absorb in passing from a solid to a fluid form. Airs. B. That is, certainly, the most probable explanation. Sulphat of Soda, commonly called^Glauber's salt, is another me- dicinal salt, which is still more bitter than the preceding. We must prepare some of these compounds, that you may observe the phe- nomena which take place during their formation. We need only f pour some sulphuric acid over the soda which I have put into this glass. Caroline. What an amazing heat is disengaged!—I thought you said that cold was produced by the melting of salts ? Airs. B. But you must observe that we are now making not melt- ing a salt. Heat is disengaged during the formation of compound salts, and a faint light is also emitted, which may sometimes be per- ceived in the dark. Emily. And is this heat and light produced by the union of the opposite electricities ofthe alkali and the acid? Mrs. B. No doubt it is, if that theory be true. Caroline. The union of an acid and an alkali is then an actual combustion? Mrs. B. Not precisely, though there is certainly much analogy in these processes. Caroline. Will this sulphat of soda become solid? Airs. B. We have not, I suppose, mixed the acid and the alkali in the exact proportions which are required for the formation of the salt, otherwise the mixture would have been almost immediate- ly changed to a solid mass; but in order to obtain it in crystals, as you see it in this bottle, it would be necessary first to dilute il with water, and afterwards to evaporate the water, during which opera- lion the salt would gradually crystallize. Caroline. But of what use is the addition of water, if it is after- wards to be evaporated ? Mrs. B. When suspended in water, the acid and the alkali are more at liberty to act ou each other, their union is more complete, and the salt assumes the regular form of crystals during the slow evaporation of its solvent. Sulphat of soda liquefies bv heat and effloresces in the air. Emily. Pray what is the meaning ofthe word effloresces ? I do not recollect yeur having mentioned it before. Mrs. B.. A salt is said to effloresce when it loses its water of crys- tallization on being exposed to the atmosphere, and is thus gradual- ly converted into a dry powder; you may observe that these crys- tals of snlphat of soda are far from possessing the transparency which belongs to their crystalline state; they are covered with a white powder, occasioned' by their having been exposed to the at- mosphere, which has deprived their surface of its lustre, by absorb- ing its water of crystallization. Salts are, in general either efflor- escent or deliquescent; this latter property is precisely the reverse o« 918. Why do the salts produce cold in melting ? 919.' By what name is the sulphat of soda called? 920 How can sulphat of soda be formed? 021 AV hat is the signification of the word effloresces ? 212 OF THE SULPHATS. the former; that is to say, deliquescent salts absorb water from the atmosphere^and are moistened and gradually melted by it. Muriat oflime is an instance of great deliquescence. Emily. But are there no salts that have the same degree of at- traction for water as the atmosphere, and that will consequently not be affected by it ? Mrs. B. Yes: there are many such salts, as, for instance, com- mon salt, sulphat of magnesia, and a vatiety of others. Sulphat oflime is very frequently met with in nature, and consti- tutes the well known substance called gypsum or plaster ofparis., Sulphat of magnesia, commonly called Epsom salt is another very bitter medicine, which is obtained from sea-water and from several springs, or may be prepared by the direct combination of its ingre- dientsi We have formerly mentioned sulphat of alumine as constituting the common alum ; it is found in nature chiefly in the neighborhood of volcanoes, and is particularly useful in the arts, from its strong astringent qualities. It is chiefly employed by dyers and calico- printers, to fix colors; and is used also in the manufactures of some kinds of leather. Sulphuric acid combines also with the metals. Caroline. One of these combinations, sulphat of iron, we are al- ready well acquainted with. Mrs. B. This is the most important metallic salt formed by sul- phuric acid, and the only one which we shall here notice. It is of great use in the arts; and in medicine, it affords a very valuable tonic; it is of this salt that most of those preparations called steel medicines are composed Caroline. But does any carbon enter into these compositions to form steel ? Mrs.B. Not an atom; they are, therefore, very improperly call- ed steel; but it is ihe vulgar appellation, and medical men them- selves often comply with the general custom. Sulphat of iron may be prepared, as you have seen, by dissolving iron in sulphuric acid: but is generally obtained from the natural production called Pyrites,/ which being asulphuret of iron, requires only exposure to the atmosphere to be oxydated, in order to form the salt; this, therefore, is much the most easy way of procuring it on a large scale. Emily. I am surprised lo find that bo'h acids and compound salts are generally obtained from their various combinations, rather than from the immediate union of their ingredients. Alrs.B. Were the simple bodies always at hand, their combina- tions would naturally r>e the most convenient method of forming compounds; but you must consider that, in most instances, there is great difficulty and expense in obtaining the simple ingredient from 922. What is the signification ofthe word deliquescent ? 923. What substance is frequently found in nature the sulphat oflime ? 924. From what is sulphat of magnesia obtained? 925. Where is the sulphat of alumine chiefly found ? 926. For what purpose is it used ? 927. From what is the sulphat of iron obtained? 928. How is sulphat of iron manufactured in the large waj OF THE SULPHATS. 213 their combinations; it is, therefore, often more expedient to procure compounds from the decomposition of other compounds. But, to return to the sulphat of iron. There is a certain vegetable acid cal- \edtgallic acid, which has the remarkable property of precipitating this salt black—I shall pour a few drops of the gallic acid into this solution of sulphat of ironl- Caroline. It is become as black as ink ! Airs. B. And it is ink in reality. Common writing ink is a pre- cipitate of sulphat of iron by gallic acid ; the black color is owing to the formation of gallat of iron, which being insoluble, remains suspended in the fluid. This acid has also the property of altering the color of iron in its metallic state. You may frequently see its effect on the blade of a knife, that has been used to cut certain kinds of fruits. Caroline. True; and that is, perhaps, the reason that a silver knife is preferred to cut fruits: the gallic acid, I suppose, does not act upon silver.— Is this acid found in all fruits? Airs. B. It is contained, more or less, in the rind of most fruits and roots, especially the raddish, which, if scraped with a steel or iron knife, has its deep red color changed into a deep purple, the knife being at the same time blackened. But the vegetable substance in which the gallic acid most abounds, \s.nutgall,\ a kind of ex- cresence that grows on oaks, and from which the acid is commonly obtained for its various purposes. Mrs. B. We now come to the phosphoric and phosphorous acids. In treating of phosphorus, you have seen how these acids may be obtained from it by combustion. Emily. Yes ; but I should be much surprised if it was the usual method of obtaining them, since it is so very difficult to procure phosphorus in its pure state. Mrs. B. You are right, my dear; tbe phosphoric acid, for gene- ral purposes, is extracted from bones, in which it is contained in the state ot phosphat of lime; from this salt the phosphoric acid is sepa- rated by means of the sulphuric, which combines with the lime. In its pure state, phosphoric acid is either liquid or solid, according to its degree of concentration. Among the salts formed by this acid, phosphat of lime is the only one that affords much interest; and this, we have always observed, constitutes the basis of all bones. It is also found in very small quantities in some vegetables. 929. How may the sulphat of iron be turned black ? 930. Why is a knife turned black in cutting fruit? 931. In what vegetable substance does gallic acid mostly abound ? 932. Where is the phosphat oflime found? 214 ON THE NITRIC CONVERSATION XVIII. OF THE NITRIC AND CARBONIC ACIDS ; OR THE COMBINATIONS OF OXYGEN WITH NITROGFN AND CARBON ; AND OF THE NITRATS AND CARBON ATS. Airs. B. I am almost afraid of introducing the subject ofthe m- tric acid, as 1 am sure that I shall be blamed by Caroline for not having made her acquainted with it before. Caroline. Why so, Mrs. B. ? . . . Airs. B. Because you have long known its radical, which is ni- trogen, or azote; and in treating of that element, Ididnoteven hint that it was the basis of an acid. Caroline. And what could be your reason for not mentioning this acid sooner? Mrs. B. I do not know whether you will think the reason suffi- ciently good to acquit me; but the omission, I assure you, did not proceed from negligence. You may recollect that nitrogen was one ofthe first simple bodies which we examined ; you were then igno- rant ofthe theory of combustion, which I believe was, for the first time mentioned in that lesson ; and therefore it would have been in vain, at any time, to have attempted to explain the nature and formation of acids. Caroline. 1 wonder, however, that it never occurred to us to in- quire whether nitrogen could be acidified ; for, as we knew it was classed among the combustible bodies, it was natural to suppose (hat it might produce an acid. Mrs. B. That is not a necessary consequence; for it might com- bine with oxygen only in the degree requisite to form an oxyd. But you will find that nitrogen is susceptible of various degrees of oxygenation, some of which convert it merely into an oxyd, and others give it all the acid properties. ' The acids, resulting from the combination; of oxygen and nitro- gen, are called the nitrous and nitric acids, We will begin with the nitric, in which nitrogen is in the highest state of oxygenation, This acid has so powerful an attraction for water that it has never been obtained perfectly free from it. But water may be so strongly impregnated with it as to form an exceedingly powerful acid solu- tion. Here is a bottle of this acid, which you see is quite limpid. Caroline. What a strong offensive smell it has! Mrs, B. This acid contains a greater abundance of oxygen than any other ; but it retains it with very little force. Emily, Then it must be a powerful caustic, both from the facility with which it parts with its oxygen, and the quantity which itaffords, 933. What is the radical of nitric acid ? 934. What acids are formed by the combination of nitrogen and ox- ygen ? 935. How does nitric acid naturally exist? 936. How does this compare with other acids as to the quantity of oxygon contained in it? 937, To what is the great causticity of nitric acid owing? AND NITROUS ACID&. 215 Mrs. B. Very well, Emily; both causes and effects are exactly such as you describe ; nitric acid burns and destroys all kinds of organized matter. It even sets fire to some of the most combustible substances. We shall pour a little of it over this piece of dry warm charcoal*—you see it inflames it immediately ; it would do the same with oil of turpentine, phosphorus, and several other very combustible bodies. This shows you how easily this acid is decom- posed by combustible bodies,teince these effects must depend upon the absorption of its oxygen. ' Nitric acid has been used in the arts from time immemorial; but it is only within these twenty-five years that its chemical nature has been ascertained. The celebrated Mr. Cavendish discovered that it consisted of about 10 parts of nitrogen and 25 of oxygen, f These principles, in their gaseous state, combine at a high temperature; and this may be effected by repeatedly passing the electoral spark through a mixture ofthe two gases. Emily. The nitrogen and oxygen gases, of which the atmosphere is composed, do not combine I suppose, because their temperature is not sufficiently elevated. Caroline. But in a thunderstorm, when the lightning repeatedly passes through them, may it not produce nitric acid? We should be in a strange situation, if a violent storm should at once convert the atmosphere into nitric acid. Mrs.B. There is no danger of it, my dear; the lightningi can af- fect but a very small portion ofthe atmosphere, and though it were occasionally to produce a little nitric acid, it never could happen to such an extent as to be perceivable. Emily. But bow could the nitric acid be known, and used, before the method of combining its constituent was discovered? Mrs. B. Previous to that period the nitric acid was obtained, and it is indeed still extracted, for the common purposes of art, from the compound salt which it forms with the pot-ash, commonly Caroline. Why is it so called? Pray, Mrs. B., let these old un- meaning names be entirely given up, by us at least; and let us call this salt nitrat of pot-ash. * To inflame charcoal, a stronger acid than that sold at the shops is necessary. The experiment with oil, turpentine, and phospho- rus, succeeds, if about a sixth part of sulph. acid is added to the ni- tric acid. The experiment with the turpentine requires caution. The vial containing the acid must be tied to a stick, a yard or two long, the operator pouring it into a small quantity of the turpentine standing at a distance.—C. f The proportion stated by Sir H. Davy, in his Chemical Re- searches, is as 1 to 2,389. 938. What is the reason why nitric acid inflames charcoal, oil of tur- pentine, &c? 939. What are the proportions of oxygen and nitrogen in nitric 940. What is the reason that the oxygen and nitrogen of which the atmosphere is composed, do not combine and form nitric acid ? 941. Why doesnot lightning produce this elevation of temperature ? 216 ON THE NITRIC Mrs. B~ With all my heart; but it is necessary that I should, at least, mention the old names, and more especially those which are yet in common use; otherwise, when you meet with them, you would not be able to understand their meaning. Emily. And how is the acid obtained from this salt? Mrs.B. By the intervention of sulphuric acid, which combines with the pot-ash, and sets tbe nitric acid at liberty. This I can easily show you, by mixing some nitrat of potash and sulphuric acid in this retort, and heating it over a lamp; the nitric acid will come over in the form of vapor, which we shall collect in a glass bell, This acid diluted in water, is commonly called aquafortis,' if Car- oline will allow me to mention that name. Caroline. 1 have often heard that aqua fortis will dissolve almost all metals; it is no doubt because it yields its oxygen so easily. Mrs. B. Yes; and from thispowerful solvent property, U deriv- ed the name of aqua fortis, or strong water. Do you not recollect, that we oxydated, and afterwards dissolved, some copper in this acid ? Emily. If I remember right, the nitrat of copper was the first in- stance you gave us of a compound salt. Caroline. Can the nitric acid be completely decomposed and con- verted into nitrogen and oxygen? Emily. That cannot be the case, Caroline; since the acid can be decomposed only by the combination of its constituents with other bodies. Airs. B. True; but caloric is sufficient for this purpose. \ By making the acid pass through a red hot porcelain tuber, it is decomposed; the nitrogen and oxygen regain the caloric which they had lost in combining, and are thus both restored to their gas- eous state. The nitric acid may also be partly decomposed, and is by this means converted into nitrous acid. Caroline. This conversion must be easily effected, as the oxygen is so slightly combined with the nitrogen. Mrs. B. The partial decomposition of nitric acid is readily ef- fected by most metals; but it is sufficient to expose the nitric acid to a very strong light to make it give out oxygen gas, and thus be converted into nitrous acid. This latter acid appears in various de- grees of strength, according to the proportions of nitrous acid gas and water of which it is composed: the strongest is a vellow color, as you see in this bottle. Caroline. How it fumes when the stopper is taken out! Airs. B. The acid exists naturally in a gaseous state, and is here so strongly concentrated in water, that it is constantly escaping. Here .is another bottle of nitrous acid, which, you see, is of an or- ange red; this acid is weaker, that is, contains a smaller quantity of the acid gas; and w.th a still less proportion of the gas it is of an Ifo S,°uW iS "I1"0 add obtained f™m the nitrate of potash? 2S" wua!?S tuC common name of nitric acid diluted in water? 944. What is the propriety ofthe name aquafortis' 945. How may nitric acid be decomposed ? 946. How can nitrous acid be formed? 947. How may the color of water be affected by the different dot- itions of nitrous acid with which it is combined ? ai«erent por AND ^NITROUS ACIDS. 217 olive green color, as it appears in this third bottle. In short, the weaker the acid, the deeper is its color. ^ Nitrous acid acts still more powerfully on some inflammable sub- stances than the nitric. Emily. I am surprised at that, as it contains less oxygen. Airs B. But, on the other hand, it parts with its oxygen much more readily ; you may recollect that we once inflamed oil with this acid. The next combinations of nitrogen and oxygen form only oxyds of nitrogen, the first of which is commonly called nitrous air ; or more properly nitric oxyd gas.* This may be obtained from nitric acid, py exposing the latter to the action of metals, as in dissolving them it does not yield the whole of its oxygen, but retains a portion of this principle sufficient to convert it into this peculiar gas, a spe- cimen of which I have prepared, and preserved with this inverted glass bell. Emily. It is a perfectly invisible elastic fluid. Mrs. B. Yes; and it may be kept any length of time in this manner over water, \ as it is not, like the nitric and nitrous acids, absorbable by it. It is rather heavier than atmospherical air, and is incapable of supporting either combustion or respiration. 1 am going to incline the glass gently on one side, so as to let some ofthe gas escape— Emily. How very curious!—It produces orange fumes like the nitrous acid! that is "the more extraordinary, as tbe gas within the glass is perfectly invisible. Airs. B. It would give me much pleasure ifyou could make out the reason of this curious change, without requiring any further explanation. Caroline. It seems, by the color and smell, as if it were convert- ed into nitrous acid gas; yet that cannot be, unless it combines with more oxygen ; and how can it obtain oxygen the very instant it escapes from the glass? Emily. From the atmosphere, no doubt. Is it not so, Mrs. B. ? Airs. B. You have guessed it; as soon as it comes in contact with the atmosphere, it absorbs from it the additional quantity of oxygen, necessary to convert it into nitrous acid gas. And, if I now remove the bottle entirely from the water, so as to bring at once the whole of the gas in contact with the atmosphere, this conversion will ap- pear still morfi striking. Emily. Look, Caroline, the whole capacity of the bottle is in- stantly tinged of an orange color! Airs. B. Thus you see, it is the most easy process imaginable to * To procure nitrous air, put into a retort some filings, or shav- ings of copper, on which pour nitric acid, diluted with four or five parts of water; then apply the heat of a lamp, and receive the gas in the usual way, over water.—C. 948. Why does nitrous acid act more powerfully on some inflam- mable substances than nitric acid ? 949. How can nitrous air, or nitric oxyd gas be obtained ? 950. How can this gas be preserved ? 951 How can nitrous oxyd gas be converted into nitrous acid gas ? 19 2ly OF THE NITRIC oonvert nitrous oxyd gas, into nitrous acid gas. Tbe property ofa^ tracting oxygen ifrom the atmosphere, without any elevation of tem- perature, has occasioned this gaseous oxyd being used as a test, for ascertaining the degreeof purity of the atmosphere, lamgoingto show you how it is applied to this purpose.—You see this graduated glass tube, which is closed at one end, (see fig. 30,) I first fill it with water, and then introduce a certain measure of nitrous gas, which, not being absorbable by water, passes through it, and occupies the upper part of the tube. I must now add rather above two-thirds of oxygen gas, which will just be sufficient to convert the nitrous oxyd gas into nitrous acid gas. , Caroline. So it has !—I saw it turn of an orange color; but it im- mediately afterwards disappeared entirely, and the water, you see, has risen, and almost filled the tube. Airs. B. That is because tbe acid gas is absorbable by water, and in proportion as the gas impregnates the water, the latter rises in the tube. When the oxygen gas is very pure, and the required proportion of nitrous oxyd gas very exact, the whole is absorbed by the water ; but if any other gas be mixed with the oxygen, instead of combining with the nitrous oxygen, it will remain and occupy the upper part ofthe tube : or if tbe gasses be not in the due proportion, there will be a residue of that which predominates. Before we leave this subject, I must not forget to remark that nitrous acid may be formed, by dissolving Ditrous oxyd gas in nitric acid. This so- lution may be effected simply, by making bubbles of nitrous oxyd gas pass through nitric acid. Emily. That is to say that nitrogen at its highest degree of oxy- genation, being mixed with nitrogen at its lowest degree of oxy- genation, will produce a kind of intermediate substance, which is nitrous acid. Airs. B. You have stated the fact with great precision.—There are various other methods of preparing nitrous oxyd, and of obtain- ing it from compound bodies ; but it is not necessary to enter into these particulars. It remains for me only to mention another curi- ous modification of oxygenated nitrogen, which has been distinguish- ed by the name of gaseous oxyd of nitrogen,' It is but lately that this gas has been accurately examined, and its properties have been investigated chiefly by Sir H. Davy. It has obtained also the name of exhilarating gas, from the very singular property which that gentleman has discovered in it, of elevating the animal spirits, when inhaled into the lungs, to a degree sometimes resembling delirium or intoxication. & Caroline. It is respirable, then ? Mrs.B. It can scarcely be called respirable, as it would not sup- port hie for any length of time; but it may be breathed for a few moments without any other effects, than the singular exhilaration of spirits 1 have just mentioned. It affects different people, however, lnavery different manner. Some become violent, even outrageous, 952. On what principle can nitrous air be applied, to test the purif ot the atmosphere ? 953. What is the process? 954. By what other name is the exhilarating gas called > 955. And why is it called exhilarating gas? AND NITROUS ACIDS. ' 219 others experience a languorattended with faintness ; but most agree in opinion, that the sensations it excites are extremely pleasant. Caroline. I thought 1 should like to try it—how do you breathe it ?■ Mrs. B. By collecting the gas in a bladder, to which a short tube with a stop-cock, is adapted ; this is applied to the mouth with one hand, whilst the nostrils are kept closed with the other, in order that the common air may have no access. You then alternately inspire, and expire the gas, till you perceive its effects. But I cannot con- sent to your making the experiment; for the nerves are sometimes unpleasantly affected by it, and I would not run any risk of that kind. Emily. 1 should like, at least, to see some body breathe it; but pray by what means is this curious gas obtained ? Airs. B. It is procured from nitrat of ammonia,f an artificial salt, which yields this gas on the application of a gentle heat. I have put some of the salt into a retort, and by the aid of the lamp the gas will be extracted.— Caroline. Bubbles of air begin to escape through the neck ofthe retort into the water apparatus; will you not collect them ? Mrs. B. The gas that first comes over need not be preserved, as it consists of little more than common air that was in the retort ; * To make nitrate of ammonia, take some nitric acid, or aqua fortis—dilute it with four or five quarts of water ; put it into a shal- low earthen dish, and throw in pieces of carbonate of ammonia, un- til the effervescence ceases.) Evaporate about one third of the liquor by a gentle heat, and set \{ away to crystallize. The crystals are long strained prisms. To procure the nitrous oxide or exhilarating gas, and to try its effect by respiration, the following simple appa- ratus may be used, where a better is not at hand. Put some nitrate of ammonia into an oil flask, having first fitted to it a cork, and glass tube, bent so as to go under the receiver in the water bath. Then apply the gentle heat of a lamp. For a receiver, fill a large jug with water, and invert it in the water bath ; having fitted to the jug a cork, having two holes made through it with a burning iron ; into one of these holes put a glass tube open at both ends, and nearly long enough to reach the bottom of the jug. ( Provide a large bladder furnished witb a short tube tied to it. W hen the jug is nearly filled with the gas, remove and set it upright, by passing the hand under its mouth—then put in the cork and tube, the other opening in the cork being closed. When you wish to breathe the gas, take the stopper out ofthe cork, and pass in the tube attached to the bladder. Then by means of a small tun- nel, pour water into the jug through the long tube, until it drives out gas enough to fill the bladder, Mrs, B. describes the manner of breathing it. Caution. Let the gas stand an hour or two over water before it is breathed—C. 956. How is this gas breathed ? 957. How is this gas obtained ? 958. When do chemical decompositions and combinations lake place^ during the formation of this gas from nitrate of ammonia? 959, What caution is necessary before it is breathed ? 220 OF THE NITRIC besides there is always in this experiment, a quantity of watery va- por which must come away before the nitrous oxyd appears. Emily. Watery vapor? Whence does that proceed? There is no water in nitrat of ammonia? Airs. B. You must recollect that there is in every salt a quantity of water of crystallization which may be evaporated by heat alone. But, besides this, water is actually generated in this experiment, as you will see presently. First tell me, what are the constituent parts of nitrat of ammonia? Emily. Ammonia, and nitric acid\; this salt, therefore, Gontains three different elements, nitrogen and'hydrogen, which produce the ammonia; and oxygen, which, with nitrogen, forms the acid. Mrs. B. Well then, in this process the ammonia is decomposed: the hydrogen quits the nitrogen to combine wi'h some of the oxygen of the nitric acid, and forms with it the waterv vapor which is now coming over. When that is effected, what will you expect to find? Emily. Nitrous acid instead of nitric acid, and nitrogen instead of ammonia. Mrs. B. Exactly so ; and the; nitrous acid and nitrogenlcombine and form the gaseous oxyd of nitrogen, in which the proportion of oxygen is 37 parts to 63 of nitrogen. You may have observed, that for a little wbile no bubbles of air have come over, and we have perceived only a stream of vapor condensing as it issued into (he water.—Now bubbles of airagain make their appearance, and I imagine that by this time all tbe wa- tery vapor is come away, and that we may begin to collect the gas. We may try whether it is pure,(by filling a phial with it,'and plung- ing a taper in it*—yes, it will do now, for the taper burns brighter than in the common air, and with a greenish flame. Caroline. But how is that ? I thought no gas would support com- bustion but oxygen or chlorine. Mrs- B. Or any gas that contains oxygen, and is ready to yield it, which is the case with this in a considerable degree ; it is not therefore, surprising that it should accelerate the combustion ofthe taper. You see that the gas is now produced in great abundance; we shall collect a large quantity of it, and I dare say that we shall find some of the family who will be curious to make the experiment of respiring it. Whilst this process is going on, we may take a gene- ral survey of the most important combinations of the nitric and ni- trous acids with the alkalies. The first of these is nitrat of potash, commonly called nitre, or saltpetre Caroline. Is not that the salt with which gunpowder is made ? Airs. B. Yes. Gunpowder is a-mixture of five parts of nitrat to one of sulphur, and one of charcoal.—Nitre, from its great propor- 960. What are constituent parts of nitrat of ammonia? 961. What is the process of making nitrous oxide ? 962. Haw is the gaseous oxide of nitrogen formed? 963. How can it be determined when it is pure ? 964. What is the common name of nitrat of potash ? 965. Of what is gunpowder made? AND NITROUS ACIDS. 221 tion of oxygen, ant! from the facility with which it yields it; it is the basis of the most detonating compositions. Emily. But what is the cause of the violent detonation of gun- powder when set on fire ? Mrs. B. Detonation may proceed from two causes; the sudden formation or destruction of an elastic fluid. In the first case, when either a solid or liquid is instantaneously converted into an elastic fluid, the prodigious and sudden expansion ofthe body strikes the air with great violence, and this concussion produces the sound call- ed detonation. Caroline. That I comprehend very well; but how can a similar effect be produced by the destruction of a gas ? Mrs. B. A gas can be destroyed only by condensing it to a liquid or solid state; when this takes place suddenly, the gas, in assuming a new and compact form, produces a vacuum, into which the sur- rounding air rushes with great impetuosity ; and it is by that rapid and violent motion that the sound is produced. - In all detonations, therefore, gases are either suddenly formed or destroyed. In that of gunpowder, can you tell me which of these two circumstances takes place? Emily. As gunpowder is a solid, it must, of course, produce the gases in its detonation ; but how I cannot tell. Airs. B. The constituents of gunpowder, when heated to a cer- tain degree, enter into a number of new combinations, and are in- stantaneously converted into a variety of gases, the sudden explo- sion of which gives rise to the detonation. Caroline. And in what instance does the destruction or condensa- tion of gases produce detonation ? Mrs. B. I can give you one with which you are well acquainted ; the sudden combination of trie oxygen and hydrogen gases. Caroline. True ; I recollect perfectly that hydrogen detonates with oxygen when the two gases are converted into water. Airs. B. But let us return to the nitrat of potash. This salt is decomposed when exposed to heat, and mixed with any combusti- ble body, such as carbon, sulphur, or metals', these substances oxy- dating rapidly at the expense ofthe nitrat. 1 must show you an in- stance of this. I expose to the fire some ofthe salt in a small iron ladle, and when it is sufficiently heated, add to it some powdered charcoal: this will attract tbe oxygen from the salt, and be con- verted into carbcnic acid. Emily. But what occasions that crackling noise, and those vivid flashes that accompany it ? Airs. B. The rapidity with which the carbonic acid gas is formed, occasions a succession of detonations, which, together with the emission of flame, is called deflagration. Nitrat of ammonia we have already noticed, on account of the gaseous oxyd of nitrogen which is obtained from it. 966. VVhy is nitre the basis of most detonating compositions? 967. What is the cause ofthe detonation of gunpowder, when fire is set to it ? 968. What causes the detonation when a gas is destroyed ? 969. In what instances does the destruction or condensation of gases produce detonation ? 970. When is the nitrat of potash decomposed? 19* 222 CARBONIC ACID. Nitrdt of silver, fa the lunar caustic, so remarkable for its de- stroying animal fibre, for which purpose it is often used by sur- geons. We have said so much on former occasions, on the mode in which caustrcs act on animal matter, that I shall not detain you any longer dn this subject. We now come to /carbonic acid, which we have already had many opportunities of noticing. You recollect that this acid may be formed by the combustion of carbon, whether in its imperfect state of charcoal, or in its purest form of diamond. And it is not ■necessary, for this purpose, to burn the carbon in oxygen gas, as we 'did in the preceding lecture ; for jounced only light a piece of charcoal, and suspend it under a receiver on the water bath. Tbe charcoal will soon be extinguished, and the air in the receiver will be found mixed with carbonic acid. The process, however, is much more expeditious if the combustion be performed in pure ox- ygen gas. Caroline. But bow can you separate the carbonic acid, obtained in this manner, from the air with which it is mixed ? Mrs.B. The readiest mode is to introduce under the receiver a quantity of caustic lime, or caustic alkali, which soon attracts the whole carbonic acid to form a carbonat. The alkali is found in- creased in weight, and the volume of the air is diminished by a quantity equal to that of the carbonic acid which was mixed with it. Emily. Pray, is there no method of obtaining pure carbon from carbonic acid ? Mrs. B. For a long time it was supposed that carbonic acid was not decompoundable; but Mr. Tennant discovered, a few years ago, that this acid may be decomposed by burning phosphorus in a closed vessel with carbonat of soda or carbonat of lime ; the phosphorus absorbs the oxygen from the carbonat, whiUt the carbon is separa- ted in the form of a black powder. This decomposition, however, is not affected simply by the attraction of the phosphorus for oxygen, since it is weaker than that of charcoal ; but the attraction of the alkali or lime for the phosphoric acid, unites its power at the same time. Caroline. Cannot we make the experiment ? Mrs. B. Not easily ; it requires being performed with extreme nicety, in order to obtain any sensible quantity of carbon, and the experiment is much too delicate for me to attempt it. But there can be no doubt ofthe accuracy of Mr. Tennant's results ; and all chemists now agree that one hundred parts of carbonic aqid gas consists of about twenty-eight parts of carbon to seventy-twotyox- ygen gas. But if you recollect, we decomposed carbonic acid' gas, the other day, by burning potassium in it. Caroline. True, so we did; and found the carbon precipitated on tbe resienerated potash. Mrs.B. Carbonic acid gas is found very abundantly in nature; it is supposed to form about one thousandth part of the atmosphere-, 971. What is nitrat of silver? 972. What gas is produced by the burning of charcoal in oxygen gas? 973. How is carbonic acid formed ? 974. And how can carbon be obtained from carbonic acid ? 975. What portion of the atmosphere does this gas form ? 976. How is the carbonic acid gas in the atmosphere produced ? CARBONIC ACID. 223 and is constantly produced by the respiration of animals ; it exists in a great variety of combinations, and is exhaled from many natu- ral decompositions. It is contained in a stale of great purity in certain caves, such as the Grotto del Cane, near Naples. Emily. 1 recollect having read an account of that grotto, and of the cruel experiments made on the poor dogs, to gratify the curios- ity of strangers. But I understood that the vapor exhaled by the cave was ca 11 ed fixed air. Mrs. B. That is the name by which carbonic acid was known before its chemical composition was discovered. This gas is more destructive of life than any other ; and if the poor animals that are submitted to its effects are not plunged into cold water as soon as they become senseless, they do not recover. It extinguishes flame instantaneously. I have collected some in this glass, which I will pour over the candle.* Caroline. This is extremely singular—it seems to extinguish the light as it were by enchantment, as the gas is invisible. 1 never should have imagined that gas could have been poured like a liquid. Airs. B. It can be done with carbonic acid only, as no other gas is sufficiently heavy to be susceptible of being poured out in the atmospherical air, without mixing with it. Emily. Pray, by what means did you obtain this gas? Mrs. B. I procured it from marble., Carbonic acid gas has so strong an attraction for all the alkalies and alkaline earths, that these are always found in nature in the state of carbonats. Com- bined with lime, this acid forms chalk j which may be considered as the basis of all kinds of marbles, and calcareous stones. From these substances carbonic acid is easily separated, as it adheres so slight- ly to its combinations, that the carbonats are all decomposable by any of the other acids. I can easily show you how I obtained this gas ; I poured some diluted sulphuric acid over pulverized marble in this bottle, (the same which we used the other day to prepare hydrogen gas,) and the gas escaped through the tube connected with it; the operation still continues, as you may perceive— Emily. Yes. it does ; there is a great fermentation in the glass vessel. What singular commotion is excited by the sulphuric acid taking possession of the lime, and driving out the carbonic acid ? Caroline. But did the carbonic acid exist in a gaseous state in the marble ? Mrs. B. Certainly not; the acid, when in a state of combina- tion is capable of existing in a solid form. Caroline. Whence, then, does it obtain the caloric necessary to convert it into gas? * Merely pouring it over a candle will not extinguish it. Put a short piece of candle, or taper, into tbe bottom of a deep tumbler, and then pour in the gas, and the flame goes out as quickly as though you poured in water.—C. 977. By what name was this known before its chemical composi- tion was discovered ? g78. By what means is this gas procured for experiment? 979. Of what is chalk formed ? 080. What is the basis of all kinds of marble and calcareous earths? »8l! How may carbonic acid be obtained from marble? 224 CARBONIC ACID. Mrs. B. It may be supplied in this case from tbe mixture of sul, phuric acid and water, which produces an evolution of heat, even greater than is required for the purpose ; since as you may per- ceive by touching the glass vessel, a considerable quantity of the caloric disengaged becomes sensible. But a supply of caloric may be obtained also from a diminution of capacity for heat, occasioned by the new combination which takes place ; and, indeed, this must be the case when other acids are employed for the disengagement of carbonic acid gas, which do not, like the sulphuric, produce heat on being mixed with water. Carbonic acid may likewise be dis- engaged from its combinations by heat alone, which restores it to its gaseous staVe. Caroline. It appears to me very extraordinary that the same gas which is produced by the burning of wood and coal should exist also in such bodies as marble and chalk, which are incombustible substances. Airs. B. I will not answer that objection, Caroline, because I think I can put you in the way of doing it yourself. Is carbonic acid combustible ? Caroline. Why, no—because it is a body which has been already burnt ;* it is carbon only, and not the acid that is combustible. Mrs. B. Well, and what inference do you draw from this ? Caroline. That carbonic acid cannot render the bodies with which it is united combustible; but that simple carbon does, and that it ia in this elementary state that it exists in wood, coals, and a great va- riety of other combustible bodies. Indeed, Mrs. B., you are very ungenerous; you are not satisfied with convincing me that my ob- jections are frivolous, but you oblige me to prove them so myself. Mrs. B. You must confess, however, that I make ample amends for the detection of error, when 1 enable you to discover the truth. You understand, now, I hope, that carbonic acid is equally produ- ced by the decomposition of chalk, or by,the combustion of charcoal. These processes are certainly of a very different nature ; in the first case the acid is already formed, and requires nothing more than heat to restore it to its gaseous state ; whilst in the latter, the acid is actually made by the process of combustion. Caroline. I understand it now, perfectly. But 1 have just been thinking of another difficulty, which 1 hope, you will excuse my not being able to remove myself. How does the immense quantity of calcareous earth, which is spread all over the globe, obtain the carbonic acid with which it is combined ? Mrs. B. The question is, indeed, not very easy to answer ; but I * Not burnt in the common acceptation ofthe word. The carbon is already united to oxygen, and therefore has no affinity for it. In the artificial production of carbonic acid, the carbon is burnt.—C. 962. Whence does carbonic acid obtain the caloric necessarv to co« vert it into gas ? J 983. Will carbonic acid render a body combustible 3 884. It might be thought that carbonic acid could not be obtained answered?11068 S° *" Cha'k and rarbon-bow « *» objection 985. How do the processes of obtaining carbonic acid from the de- composition of chalk, and the combustion of charcoal differ ? CARBONIC ACID. 225 conceive that the general carbonization of calcareous matter may have been/the effect of a general combustion* occasioned by some revolution of our globe, and producing an immense supply of car- bonic acid, with which the calcareous matter became impiegnated ; or that this may have been effected by a gradual absorption of car- bonic acid from the atmosphere. But this would lead us to discus- sions which we cannot indulge in, without deviating too much from our subject. Emily. How does it happen that we do not perceive the perni- cious effects of the carbonic acid which is floating in the atmosphere? Mrs. B. Because ofthe stateof the very great dilution in which it exists there. But can you tell me, Emily, what are the sources which keep the atmosphere constantly supplied with this acid ? Emily. I suppose the combustion of wood, coals, and other sub- stances that contain carbon.. Airs. B. And also, the breath of animals.\ Caroline. The breath of animals? I thought you said that the gas was not at all respirable, but on the contrary, extremely poison- ous. Mrs.B. So it is; but although animals cannot breathe in carbo- .nicacid gas, yet in the process of respiration, they have the power of forming this gas in their lungs ; so that the air which we expire, or reject from the lungs, always contains a certain proportion of carbonic acid, which is much greater than that which is commonly found in the atmosphere. Caroline. But what is it that renders carbonic acid such a deadly poison ? , Airs. B. The manner in which this gas destroys hfe, seems to be merely by preventing the access of respirable air >; for carbonic acid gas,"unless very much diluted with common air, does not pen- etrate into the lungs, as the windpipe actually contracts and refuses it admittance —But we must dismiss the subject at present, as we shall have an opportunity of speaking of respiration much more fully when we come io the chemical functions of animals. Emily. Is carbonic acid as destructive to the life of vegetables as it is to that of animals ? Airs. B. lfa vegetable be completely immersed in it, 1 believe it generally proves fatal to it ; but mixed in certain proportions with atmospherical air, it is, on the contrary, very favourable to vegeta- tion. * This idea is at random. We cannot account for the origin of carbonic acid in its native state, any better than we can for oxygen. It cannot be the product of combustion, since it existed before the growth of combustible materials.—C.__________________ 986. How does marble and calcareous earth obtain its great quan- tity of carbonic acid ? . . 9B7. Why do we not experience the pernicious efiects ot the car- bonic'acid in the atmosphere? 988 How is the atmosphere supplied with this acid? 989! Why is carbonic acid gas destructive to animal life ? 990. What effect does it have on vegetation? 226 BORACIC ACID. You remember, I suppose, our mentioning the mineral waters^ both natural and artificial, which contain carbonic acid gas ? Caroline. You mean the Seltzer water ? Airs. B. That is one of those which are most used ; there are, however, a variety of others into which carbonic acid enters as an ingredient; all these waters are usually distinguished by the name of acidulous or'gaseous mineral waters. The class of salts called carbonats, is the most numerous in nature; we must pass over them in a very cursory manner, as the subject is far too extensive for us to enter on it in detail. The state of carbo- nat is the natural state of a vast number of minerals, and particu- larly of the alkalies and alkaline earths, as they have so great an attraction for the carbonic acid, that they are almost always found combined with it; and you may recollect that it is only by separa- ting them from this acid, that they acquire causticity and those striking qualities which I have formerly described. All marbles, chalks, shells, calcareous spars, and limestones of every description, are neutral salts, in which lime, their common basis, has lost all its characteristic properties. Emily. But if all these various substances are formed by the un- ion of lime with carbonic acid, whence arises their diversity of form and appearance? Mrs.B. Both from the different proportions-of their component parts, and from a variety of foreign ingredients iwhich may occa- sionally be blended with them ; the veins and colours of marbles, for instance, proceed from a mixture of metallic substances; silex and alumine also frequently enter into these combinations. The vari- ous carbonats, therefore, which 1 have enumerated, cannot be con-. sidered as pure and unadulterated neutral salts, although they cer-» tainly belong lo that class of bodies. CONVERSATION XIX* ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MU- RIATIC ACIDS ; AND ON MURIATS.— ON IODINE AND IODIC ACID. Airs. B. We now come to the three remaining acids with simple bases, the compound nature of which, though long suspected, has been but recently proved. The chief of these is the muriatic : but 991. What are the waters called, into which this gas enters as an ingredient ? 992. W hat are the salts formed by the acid of this gas ? 993. How extensive is this class of salts, and under what forms do they chiefly occur in nature ? 994. If lime is the common basis of marbles, chalks, shells, calcare- ous spars, and lime stones, why is there such a diversity in their form and appearance ? 995. From what do the veins and colours of marble proceed ? BORACIC ACID. 227 \ shall first describe the two others, as their bases have been ob- tained more distinctly than that of the muriatic acid. You may recollect 1 mentioned the boracic acid. This is found very sparingly in some parts of Europe, but for the use of manufac- tures we have always received it from the remote country of Thi- bet, where it is found iu some lakes, combined with Soda. It is easily separated from the soda by sulphuric acid, and appears in the form of shining scales, as you see here. Caroline. I am glad to meet with an acid which we need not be afraid to touch ; for I perceive from your keeping it in a piece of paper, that it is more innooent than our late acquaintance, the sul- phuric and nitric acids. Mrs.B. Certainly; but being more inert, you will not find its properties so interesting. However, its decomposition, aud the brilliant spectacle it affords when its basis again unites with oxy- gen, atones for its want of other striking qualities. Sir H. Davy succeeded in decomposing the boracic acid, (which had till then, been considered as undecompoundable,) by vari- ous methods. On exposing this acid to the Voltaic battery, the positive wire gave out oxygen, and on the negative wire was depos- ited a black substanoe^in appearance resembling charcoal. This was the basis ofthe acid, which Sir II. Davy has called Boracium or Boron. The same substance was obtained in more considerable quantities by exposing the acid to a great heat in an iron gun barrel. A third method of decomposing the boracic acid consisted in burn- ing potassium in contact with it in vacuo. The potassium attracts the oxygen from the acid, and leaves its basis in a separate state. The recomposition of this acid I shall show you by burning some of its basis which you see here, in a retort full of oxygen gas. The heat of a candle is all that is required for this combustion. 'Emily. The light is astonishingly brilliant, and what beautiful sparks it throws out! Airs. B. The result of this combustion is the boracic acid, the nature of which, you see, is proved, both by analytic and synthetic means. Its basis has not, it is true, a metallic appearance; but it makes very hard alloys with other metals. Emily. But pray, Mrs. B. for what purpose is the boracic acid used in manufactures ? Mrs. B. Its principal use is in conjunction with soda, that is, in the state of borat of soda, which in the arts is commonly called bo- rax. This salt has a peculiar power of dissolving metallic oxyds, and of promoting the fusion of substances capable of being melted ; it is accordingly employed in various metallic arts; it is used, for example, to remove the oxyd from the surface of metals, and is oh$ ten employed in the assaying of metallic ores. Let us now proceed to the fluoric acid. This acid is obtained from a substance which is found frequently in mines, and particu- 996. Where is the boracic acid obtained ? 997. What is the composition of borax ? 998. What is the basis of this acid ? 999. For what purpose is the boracic acid used in manufactures iJOOO. From what is the fluoric acid obtained ? 228 FLUORIC ACID. Iarly in those of Derbyshire, called fiuor, a name which it acquired from the circumstance of its being used to render the ores of met- als more fluid when heated. Caroline. Pray, is not this the Derbyshire spar, of which so many ornaments are made ? Mrs. B. The same ; but though it has long been employed for a variety of purposes, its nature was unknown until Scheele, the great Swedish chemist, discovered that it consisted of lime united with a peculiar acid, which obtained the name offluoric acid. It is easily separated from* the lime by the sulphuric acid, and unless condensed in water, ascends in the form of gas. A very peculiar property of this acid, is its union with siliceous earths, which I have already mentioned. If the distillation of this acid is performed in glass ves- selsy-they are corroded Aand the siliceous part of the glass comes overpmited with the gas ; if water is then admitted, part ofthe silex is deposited, as you may observe in the jar. Caroline. I see white flakes forming on the surface of the water; is that silex ? Mrs. B. Yes, it is. This power of corroding glass has been used for engraving, or rather etching upon it. The glass is first cover- ed with a coat of wax, through which the figures to be engraved are to be scratched with-a pin ; then pouring the fluoric acid over the wax, it corrodes the glass where the scratches have been made. Caroline. I Should like to have a bottle of this acid to make en- gravings.* Airs. B. But you could not have it in a glass bottle ; for in that case, the acid would be saturated with silex, and incapable of exe- cuting an engraving ; the same thing would happen were the acid kept in a vessel of porcelain or earthenware ; this acid must there- fore be both prepared and preserved io vessels of silver. ^ If it be distilled from fluorspar andvitrolic acid, in silver or lead- en vessels, the receiver being kept very cold during the distillation, it assumes the form of a dense fluid, and in that state is the most in- tensely corrosive substance known. This seems to be the acid * A bottle of fluoric acid is not easily obtained. To make etch- ings on glass, first cover the glass with a thin coat of bees wax.— This is done by warming it over a lamp, and passing the wax over the surface. Then make the drawing by cutting through the wax, quite down to the glass. To do the etching in the small way, take a lead or tin cup, and on the bottom place about a table.spoonful of pulverized fluor spar, and on this pour sulphuric acid enough to moisten it—place the glass on the cup as a cover, with the side to be etched downward—then set the cup in warm water, or warm the bottom over a lamp, taking care not to melt the wax. In 15 or 20 minutes or more, the etching will be done. In this way, draw- ings are easily and beautifully made on glass.—C. 1001. From what does it derive its name ? 1002. By what other name is this acid called ? 1003. Of what does it consist ? 1004. What singular effect does it have on glass ? 1005. How could you describe the method of etching on glass' 1006. In what kind of vessels may it be preserved ? MURIATIC ACID. 229 bined with a little water. It maybe called hydrofluic acid ; and SirH. Davy has been led, from late experiments on the subject, to consider pure fluoric acid as a compound of a certain unknown principle, which he calls fluorine, with hydrogen. Sir H. Davy has also attempted to decompose the fluoric acid by burning potassium in contact with it; but he has not yet been able by this or any other method, to obtain its basis in a distinct separate state. We shall conclude our account of the acids with that of the mu- riatic acid, which is, perhaps, the most curious and interesting of all of them. It is found in nature combined with soda, lime, and magnesia. Aluriat of soda is the common sea salt; and from this substance the acid is usually disengaged by means of the sulphuric acid. The natural state ofthe muriatic acid is that of an invisible, permanent gas, at the common temperature ofthe atmosphere ; but it has a remarkable strong attraction for water, and assumes the form of a whitish cloud whenever it meets any moisture to combine with. This acid is remarkable for its peculiar and very pungent smell, and possesses, in a powerful degree, mo-t of the acid proper- ties. Here is a bottle containing muriatic acid in a liquid state. Caroline. And how is it liquefied? Airs. B. By impregnating water with it; its strong attraction for water makes it very easy to obtain it in a liquid form. Now, if I open the vial, you may observe a kind of vapour rising from it, which is muriatic acid gas, of itself invisible, but made apparent by combining with the moisture ofthe atmosphere. Emily. Have you not any ofthe pure muriatic acid gas ? Airs. B. This jar is full of that acid in its gaseous state—it is inverted over mercury instead of water, because, being absorbable by water, this gas cannot be confined by it.—I shall now raise the jar a little on one side, and suffer some of the gas to escape. You see that it immediately becomes visible in the form of a cloud. Emily. It must be, no doubt, from its uniting with the moisture of the atmosphere, that it is converted into this dewy vapour,. Mrs. B. Certainly : and for the same reason, that is to '^a^,/its extreme eagerness to unite with water, this gas will cause snowed melt as rapidly as an intense fire. v- This acid proved much more refractory, when Sir H. Davy at* tempted to decompose it, than the other two undecomposed acids. , It is singular that potassium will burn in muriatic acid, and be con- verted into potash, without decomposing the acid, and the result of this combustion is a muriat of potash ; for the potash as soon as it is regenerated, combines with tbe muriatic acid. Caroline. But how can the potash be regenerated if the muriatic acid does not oxydate the potassium ? Airs. B. The potassium in this process, obtains oxygen from the moisture with which the muriatic acid is alw^a^scombined, and, ac- -----------------:^m>------ 1007. What did Sir H. Davy call this acid?'-- - 1008. Where is muriatic acid found ? 1009. What is the natural state ? 1010. How is it liquefied ? 1011. How can this gas be confined without a mercurial bath ? 1012. What effect will muriatic acid gas have on snow ? 1013. Why will it melt snow ? 20 230 OXY-MURIATIC ACID. cordingly, hydrogen, resulting from the decomposition ofthe mois- ture, is invariably evolved. Emily. But why not make these experiments with dry muriatic acid ? Airs. B. Dry acids cannot be acted on by the Voltaic battery, be- cause acids are non-conductors of electricity! unless moistened. In the course of a number of experiments, which Sir H. Davy made upon acids in a state of dryness, he observed that the presence of water appeared always necessary to develope the acid properties, so that acids are not even capable of reddening vegetable blues if they have been carefully deprived of moisture. This remarkable cir- cumstance led him to suspect, that water, instead of oxygen, may be the acidifying principle ; but this he threw out rather as a conjec- ture than as an established point. Sir H. Davy obtained very curious results from burning potassi- um in a mixture of phosphorus and muriatic acid, and also ofsul- * phur and muriatic acid ; the/latter detonates with great violence. All his experiments, however, failed in presenting to his view the basis ofthe muriatic acid, of which he was in search ; and he was at last induced to form an opinion respecting the nature of this acid, which 1 shall presently explain. Emily. Is this.acid susceptible of different degrees of oxygenation? Mrs. B. Yes ;.for though it cannot bedeoxygenated, yet we may add oxjgen to it. Caroline. Why, then, is not the least degree of oxygenation of the acid called the muritous, and the higher degree the muriatic acid ? Mrs. B. Because, instead of becoming, like other acids, more dense, and more acid by an addition of oxygen, it is rendered, on the contrary, more volatile, more pungent, but less acid, and less ab- sorbable by water. These circumstances, therefore, seem to indi- cate the propriety of making an exception to the nomenclature. The highest degree of oxygenation of this acid has been distinguish- ed by the additional epithet of oxygenated, or, for the sake of brevi- ty, oxy, so that it is called oxygenated or oxy-muriatic acid. This likewise exists in a gaseous forrrtlat the temperature of the atmos- phere ; it is also susceptible of bqmg absorbed by water, and can be congealed, or solidified, by a certain degree of cold. Emily. And how do you obtain the oxy-muriatic acid? Mrs. B. In various ways ; but it may be most conveniently ob- tained by distilling liquid muriatic acid over oxyd of manganese, which supplies the acid with the additional oxygen. One part of the acid being put into a retort, with two parts of the oxyd of manga- nese, and tbe heat of a lamp applied, the gas is soon disengaged, anj 1014. Why cannot dry acids be acted on by the Voltaic battery ? 1015. What is the basis of muriatic acid ? 1016. Is this acid capable of combining with different proportions of oxygen ? 1017. Why is not the least degree of oxygenation called the muria- tous acid ? 1018. What is the highest degree of oxygenation of this acid called: 1019. How is the oxy-muriatic acid obtained? OXY-MURIATIC ACID. 231 may be received over water, as it is but sparingly absorbed by it. 1 have collected some in this jar—* Caroline. It is not invisible, like the generality of gases ; for it is of a yellowish color. Airs. B. The muriatic acid extinguishes flame, whilst, on the contrary, the oxy-muriatic makes the flame larger, and gives it a dark red color. Can you account for this difference in the two acids ? Emily. Yes, I think so; the muriatic acid will not supply the flame with the oxygen necessary for its support 5 but when this acid is further oxygenated, it will part with its additional quantity of oxygen, and in this way support combustion.f/ Mrs. B. This is exactly the case: indeed the oxygen added to the muriatic acid, adheres so slightly to it, that it is separated by mere exposure to the sun's rays; This acid is'decomposed also by combustible bodies, many of which it burns, and actually inflames, without any previous increase of temperature. Caroline. That is extraordinary indeed ! I hope you mean to in- dulge us with some of these experiments? Airs. B. I have prepared several glass jars of oxy-muriatic acid gas for that purpose. In the first we shall introduce some Dutch gold leaf.—Do you observe that it takes fire ? Emily. Yes, indeed it does—how wonderful it is! It became im- mediately red hot, but was soon smothered in a thick vapor. Caroline. What a disagreeable smell! Mrs. B. We shall try the same experiment with phosphorus in another jar of this acid. You had better keep your handkerchief to your nose when 1 open it—now let us drop into it this little piece of phosphorus— Caroline. It burns really; and almost as brilliantly as in oxy^es gas! But what is most extraordinary, these combustions take place without the metal or phosphorus being previously lighted, or even in the least heated. Mrs. B. All these curious effects are^owing to the very great fa- cility with which this acid yields oxygen to such bodies as are strongly disposed to combine with it.^ It appears extraordinary in- deed to see bodies, and metals in particular, melted down and in- flamed by a gas, without any increase of temperature, either of the gas or ofthe combustible. The phenomenon, however, is, you see, well accounted for. Emily. Why did you burn a piece of Dutch gold leaf rather than a piece of any other metal ? Mrs. B. Because, in the first place, it is a composition of metals * Breathing only a few bubbles ofthe gas is attended with bad— sometimes with dangerous consequences. The young chemist, therefore, had better not undertake to make it.—C. f According to this new theory of chlorine, as will be explained at the end of this conversation, this combustion is effected in con- sequence of the union of chlorine (or oxy-muriatic acid) with the hydrogen of the combustible body. 1020. Why will the muriatic acid extinguish flame, and oxy-muriat- ic acid make it larger, giving it a dark red color ? 1021. Why will some combustible bodies burn in this acid without any previous increase of temperature? 232 OXY-MURIATIC ACID. (consisting chiefly of copper) which burns readily ; and I use a thin metallic leaf in preference to a lump of metal, because it offers to the action of the gas but a small quantity of matter under a large surface. Filings, or shavings, would answer the purpose nearly as well ; but a lump, of metal, though the surface would oxydate with great rapidity, would not take fire. Pure gold is not inflamed by oxy-muriatic acid gas, but it is rapidly oxydated, and dissolved by it; indeed, this acid is the only one that will dissolve gold. Emily. This, I suppose, is what is commonly called aqua regia, ' which you know is the only thing that will act upon gold. / Mrs. B. This is not exactly the case either ; for aqua regia is composed of a mixture of muriatic acid and nitric acid.—But, in fact, the result of this mixture is the formation of oxy-muriatic acid, as the«muriatic acid oxygenates itself at the expense of the nitric ; this mixture, therefore, though it bears the name of nitro- muriatic acid, acts on gold merely in v'irtue of the oxy-muriatic acid which it contains. Sulphur, volatile oils, and many other substances, will burn in the same manner in oxy-muriatic acid gas ; but I have not prepared a sufficient quantity of it, to show combustion of all these bodies. Caroline. There are several jars ofthe gas yet remaining. Mrs. B. We must reserve these for future experiments. The oxy-muriatic acid does not, like other acids, redden the blue vege- table colours ; but it totally destroys all colour, and turns vegetables perfectly white. Let us collect some vegetable substances to put into this glass, which is full of gas. Emily. Here is a sprig of myrtle— Caroline. And here some colored paper— Mrs. B. We shall also put in this piece of scarlet riband, and a rose— Emily. Their colours begin to fade immediately. But how does the gas produce this effect ? Mrs. B. The oxygen combines with the colouring matter of these substances, and destroys it; that is to say, destroys the property which these colours had of reflecting only one kind of rays, and ren- ders them capable of reflecting them all, which, you know, will make them appear white. Old prints may be cleaned by this acid, for the paper will be whitened without injury to the impression, as printer's ink is made of materials (oil and lamp black) which are not acted on by acids. This property ofthe oxy-muriatic acid has lately been employed in manufactures in a variety of bleaching processes ; but for these purposes the gas must be dissolved in water, as the acid is thus ren- dered much milder and less powerful in its effects; for in a gaseous, 1022. By what acid is gold oxydated and dissolved ? 1023. Why does a mixture of nitric and muriatic acids dissolve gold, when neither of them will do it alone ? 1024. What effect does the oxy-muriatic acid have on vegetable co- lours ? 1025. Why does it produce this effect ? 1026. Why is it, that the paper of old prints may be cleansed by this acid, without any injury to the impression ? 1027. Of what use is the oxy-muriatic acid in manufactures? OXY-MURIATIC ACID. 233 state, it would destroy the texture, as well as the color of the sub- stance submitted to its action. Caroline. Look at the things which we put into the gas; they have now entirely lost their color! Mrs. B. The effect of the acid is almost completed ; and if we were to examine the quantity that remains, we should find it lo con- sist chiefly of muriatic acid. The Oxy-muriatic acid has been used to purify the air in fever hospitals and prisons, as it burns and destroys putrid effluvia of every kind. The infection of the small-pox is likewise destroyed by this gas, and matter that has been submitted to its influence will no lon- ger generate that disorder. Caroline. Indeed, I think the remedy must be nearly as bad as the disease; the oxy-muriatic acid has such a dreadfully suffocating smell. Mrs. B. It is certainly extremely offensive: but by keeping the mouth shut, and welting the nostrils with liquid ammonia, in order to neutralize the vapor as it reaches the nose, its prejudicial effects may be in some degree prevented. At any rate, however, this mode of disinfection can hardly be used in places that are inhabited. And as the vapor of nitric acid, which is scarcely less efficacious for this purpose, is not at all prejudicial, it is usually preferred on such occasions. Caroline. You have not told us yet what is Sir Hi Davy's new opinion respecting the nature of muriatic acid to which you alluded a few minutes ago? Mrs. B. True : I avoided noticing it then, because you could not have understood it without some previous knowledge of the oxy- muriatic acid, which 1 have but just introduced to your acquaint- ance. Sir H. Davy's idea is, that muriatic acid, instead of being a com- pound, .consisting of an unknown basis and oxygen, is formed by the union of oxy-muriatic gas with hydrogen. Emily. Have you not told us just now that oxy-muriatic gas was itself a compound of muriatic acid and oxygen ? Airs. Bi Yes ; but according to Sir H. Davy's hypothesis, oxy- muriatic gas is considered as a simple body, which contains no oxy- gen—as a substance of its own kind, which has a great analogy to oxygen in most of its properties, though in others it differs entirely from it. According to this view of the subject, the name of oxy- muriatic acid can no longer be proper, and therefore, Sir H; Davy has adopted that of ehlorine, or chlorine gas, a name which is sim- ply expressive of its greenish color ; and in compliance with that philosopher's theory, we have placed chlorine in our table among the simple bodies. Caroline. But what was Sir H. Davy's reason for adopting an opinion so contrary to that which had hitherto prevailed ? Mrs. B. There are many circumstances which are favorable to the new doctrine; but the clearest and simplest fact in its support is, 1028. For what medicinal purposes has it been used ? 1029. How may the inconvenience ofthe oxy-mUriatic acid be pre- vented ? 1030. What does Sir H. Davy suppose muriatic acid to be? 1031. Why is oxy-muriatic acid lately called chlorine ? 20* 234 MURIATS. that if hydrogen gas and oxy-muriatic gas be mixed together, both these gases disappear, and muriatic acid gas is formed. Emily. That seems to be a complete proof; is it not considered as perfectly conclusive ? Mrs. B. Not so decisive as it appears at first sight; because it is argued by those who still incline to the old doctrine, that muriatic acid gas, however dry it may be, always contains a certain quantity of water, which is supposed essential to its formation. So that, in the experiment just mentioned, this water is supplied by the union of the hydrogen gas with the oxygen ofthe oxy-muriatic acid ; and therefore the mixture resolves itself into the base of muriatic acid and water, that is, muriatic acid gas. Caroline. I think the old theory must be the true one; for other- wise how could you explain the formation of oxy-muriatic gas, from a mixture of muriatic acid and oxyd of manganese? Mrs. B. Very easily; you need only suppose that in this process the muriatic acid is decomposed ; its hydrogen unites with the oxy- gen of the manganese to form water and the chlorine appears in its separate state. Emily. But how can you explain the various combustions which take place in oxy-muriatic gas, ifyou consider it as containing no oxygen ? Airs. B. We need only suppose that combustion is the result of intense chemical action ;* so that chlorine, like oxygen, is combin- ing with bodies, forms compounds which have less capacity for ca- loric than their constituent principles, and, therefore, caloric is evolved at the moment of their combination. Emily. If, then, we may explain every thing by either theory, to which of the two shall we give the preference ? Airs. B. It will, perhaps, be better to wait for more decisive proofs, if such can be obtained, before we decide positively Upon the subject. The new doctrine has certainly gained ground very rapid- ly, and may be considered as generally established ; but a few com- petent judges will refuse their assent to it, and until that theory is established beyond all doubt, it may be as well for us still occasion' ally to use the language to which chemists have long been accus- tomed. But let us proceed to the examination of salts formed by muriatic acid. Among the compound salts formed by muriatic acid the murial of soda, or common salt, is the most interesting.f The uses and pro- * "Intense chemical action," neither explains the process, nor indeed conveys to the mind any definite idea. The views of Sir H. Davy on the composition of chlorine, arecombatted by many ofthe first chemists in England, as well as in this country. The inquisi- tive reader may become acquainted with the grounds of dispute on both sides by referring to Cooper's edition of Thompson's chemis- try—C. r v f According to Sir H. Davy's view ofthe nature ofthe muriatic and oxy-muriatic acids, dry muriat of soda is a compound of sodium 1032. What are the reasons for supposing that chlorine is not a sim- ple substance? 1033. How are the combustions in oxy-muriatic acid explained, if it does not contain oxygen? 1034. What is said on the subject in the note? MURtATS. 235 perties of this salt are too well known to require much comment. Besides the pleasant flavor it imparts to the food, it is very whole- some when not used to excess, as it assists in the process of digestion. Sea-water is the great source from which muriat of soda is ex- tracted by evaporation. But it is also found in large solid masses in the bowels ofthe earth, in England, and in many other parts of the world. Emily. 1 thought that salts, when solid, were always in the state of crystals; but the common table salt is in the form of a coarse white powder. Mrs. B. Crystallization depends, as you may recollect, on the slow and regular re-union of particles dissolved in a fluid ; common sea-salt is only in a state of imperfect crystallization, because the process by which it is prepared is not favourable to the formation of regular crystals. But if you dissolve it, and afterwards evapo- rate the water slowly, you will obtain a regular crystallization. Alurial of ammonia is another combination of this acid, which we have already mentioned as the principal source from which ammo- nia is derived. I can at once show you the formation of this salt by the immediate combination of muriatic acid with ammonia. These two glass jars contain, the one muriatic acid gas, the other ammoniacal gas, both of which are perfectly invisible—now, if 1 mix them together, you see they immediately form an opaque white cloud, like smoke. If a thermometer was placed in the jar in which these gases are mixed, you would perceive that some heat is at the same time produced. Emily. The effects of chemical combinations are, indeed, won- derful!—How extraordinary it is that two invisible bodies should become visible by their union ! Airs. B. This strikes you with astonishment, because it is a phe- nomenon which nature seldom exhibits to our view ; but the most common of her operations are as wonderful, and it is their frequen- cy only that prevents our regarding them with equal admiration. What would be more surprising, for instance, than combustion, were it not rendered familiar by custom ? Emily. That is true. But pray, Mrs. B., is this white cloud the salt that produces ammonia ? How different it is from the solid mu- riat of ammonia which you once showed us! Mrs. B. It is the same substance, which first appears in the state of vapor, but will soon be condensed by cooling against the sides of the jar, in the form fcf very minute crystals. We now proceed to the oxy-murials. In this class of salts the oxy- muriat of potash* is the most worthy of our attention, for its striking and chlorine, for it may be formed by the direct combination of oxy- muriatic gas and sodium. In his opinion, therefore, what we com- monly call muriat of soda, contains neither soda nor muriatic acid. * Oxy-muriat of potash is prepared by passing chlorine through a solution of potash in water. The process is long and difficult—C. 1035. Where is the muriat of soda obtained ? 1036. On what does crystallization depend ? 1037. Why is common salt in a state of imperfect crystallization ? 1038. Of what is the muriat of ammonia a combination ? 1039. What two gases, when mixed, form muriat of ammonia ? 236 OXY-MURIATS. properties. The acid, in this state of combination, contains a still greater proportion of oxygen than when alone. Caroline. But how can the oxy-muriatic acid acquire an increase of oxygen by combining with potash ? Mrs. B. It does not reallv acquire an additional quantity of oxy- gen, but it loses some of the muriatic acid, which produces the same effect, as the acid which remains is proportionably super-oxy- genated. If this salt be mixed, and merely rubbed together with sulphur, phosphorus, charcoal, or indeed any other combustible, it explodes strongly. Caroline. Like gun-powder, I suppose, it is suddenly converted into elastic fluids ?t Alrs.B. Yes: but with this remarkable difference, that no in- crease of temperature, any further than is produced by gentle fric- tion, is required in this instance. Can you tell me what gases are generated by the detonation of this salt with charcoal ? Emily. Let me consider,..... ..The oxy-muriatic acid parts with its excess of oxygen to the charcoal, by which means it is convert- ed into muriatic acid gas; whilst the charcoal, being burnt by the oxygen, is changed to carbonic acid gas. What becomes of the potash 1 cannot tell. Mrs. B. That is a fixed product which remains in tbe vessel. Caroline. But since the potash does not enter into the new combi- nations, I do not understand what use it is in this operation. Would not the oxy-muriatic acid and the charcoal produce the same effect without it ? Airs. B. No; because chlorine (or oxy-muriatic acid) does not unite with charcoal, unless oxygen be added to it, and this oxygen is supplied by the potash. I mean to show you this experiment, but I would advise you not to repeat it alone; for if care be not taken to mix only very small quantities at a time, the detonation will be extremely violent, and may be attended with dangerous effects. You see I mix an exceed- ing small quantity of salt with a little powdered charcoals in this Wedgwood mortar, and rub them together with the pestle— Caroline. Heavens ! How can such a loud explosion be produced by so small a quantity of matter ? Mrs. B. You must consider that an extremely small quantity of solid substance may produce a very great volume of gases; and it is the sudden evolution of these which occasions the sound. * According to Sir H. Davy's new views, just explained, oxy- muriatof potash is a compound of chlorine with oxygen and oxyd of potassium. 1040. What are the peculiar properties of oxy-muriat of potash ? 1041. Why will the oxy-muriat of potash explode if mixed and rub- bed together with sulphur, phosphorus, charcoal, or any other combus- tible substance ? 1042. What gases are generated by the detonation of this salt with charcoal ? 1043. Why would not the same effect be produced by the oxy-mu- riatic acid and charcoal without the potash ? OXY-MURIATS. 237 Emily. Would not oxy-muriat of potash make stronger gun-pow- der than nitrat of potash ? • ^lrs'P' Yes » but the preparation, as well as the use of this salt, is attended with so much danger, that is never employed for that purpose. Caroline. There is no cause to regret it, I think ; for the com- mon gun-powder is quite sufficiently destructive. Mrs.B. I can show you a very curious experiment with this salt; but it must again be on condition that you will never attempt to re- peat it by yourselves. I throw, a small piece of phosphorus into this glass of water : then a little oxy-muriat of potash ; and lastly, I pour in, (by means of this funnel, so as to bring it in contact with the two other ingredients at the bottom ofthe glass) a small quanti- ty of sulphuric acid— Caroline. This is indeed, a beautiful experiment! The phospho- rus takes fire and burns from the bottom of the water. Emily. How wonderful it is to see flame bursting out under wa- ter, and rising through it! Pray, bow is this accounted for? Mrs. B. Cannot you find it out, Caroline ? Emily. Stop—1 think I can explain it. Is it not because Hhe sulphuric acid decomposes the salt by combining with the potash, so as to liberate the oxy muriatic acid gas by which the phosphorus is set on fire ? Mrs. B. Very well, Emily ; and with a little more reflection you would have discovered another concurring circumstance, which is, that an increase of temperature is produced in the mixture of the sulphuric acid and water, which assists in promoting the combus- tion of the phosphorus. I must, before we part, introduce to your acquaintance the newly discovered substance, iodine, which you may recollect we placed next to oxygen and chlorine in our table of simple bodies. Caroline. Is this also a body capable of maintaining combustion like oxygen and chlorine ? Mrs. B. It is ; and although it does not so generally disengage light and heat from inflammable bodies, as oxygen and chlorine do, yet it is capable of combining with most of them; and sometimes, as in the instance of potassium and phosphorus, the combination is attended with an actual appearance of light and heat. Caroline. But what sort of substance is iodine? what is its form and colour? Airs. B. It is a very singular body in many respects. At the or- dinary temperature ofthe atmosphere, it commonly appears in the form of bluish-black crystalline scales, such as you see in this tube. Caroline. They shine like black lead, and some of the scales have the shape of lozenges. Airs. B. That is actually the form which the crystals of iodine 1044. From what may a stronger gun-powder than that now usedbe made ? 1045. Why is it not used ? 1046. How may phosphorus be set on fire in water ? 1047. Why is this effect produced ? 1048. How does iodine differ from oxygen and chlorine ? 1049. How does iodine appear ? 238 COMPOSITION often assume. But if we heat them gently by holding the tube over the flame of a candle, see what a change takes place in them. Caroline. How curious ! They seem to melt, and the tube im- mediately fills with the beautiful violet vapour. But look, Mrs.B., the same scales are now appearing at the other end ofthe tube. Mrs. B. This is, in fact, a sublimation of iodine, from one part of the tube, to another ; but with this remarkable peculiarity, that while in the gaseous state, iodine assumes that bright violet colour, which as you may already perceive, it loses as the tube cools, and the substance resumes its usual solid form. It is from the violet colour of the gas that iodine has obtained its name. Caroline. But how is this curious substance obtained ? Mrs. B. It is found in the ley of ashes, of sea-weeds, after the soda has been separated by crystallization ; and it is disengaged by means of sulphuric acid, which expels it from the alkaline ley in the form of a violet gas, which may be collected and condensed in the way which you have just seen. This interesting discovery was made in the year 1812, by M. Courtios, a manufacturer of saltpetre, at Paris. Caroline. And pray, Mrs. B., what is the proof of iodine being a simple body ? Mrs. B. It is considered as a simple body, both because it is not capable of being resolved into other ingredients^; and because it is itself capable of combining with other bodies, in a manner analo- gous to oxygen and chlorine. The most curious of these combina- tions is that which it forms with hydrogen gas, the result of which is a peculiar gaseous acid. Caroline. Just as chlorine and hydrogen gas form muriatic acid. In this respect chlorine and iodine seem to bear a strong analogy to each other. Mrs.B. That is indeed the case ; so that if the theory ofthe con- stitution of either of these two bodies be true, it must be true also in regard to the other; if erroneous in the one, the theory must fall in both. But it is now time to conclude ; we have examined such of the acids and salts as I conceived would appear to you most interesting. I shall not enter into any particulars respecting the metallic acids, as they offer nothing sufficiently striking for our present purpose. CONVERSATION XX. ON THE NATURE AND COMPOSITION OF VEGETABLES. Mrs. B. We have hitherto treated only ofthe simplest combina- tion of elements, such as alkalies, earths, acids, compound salts, 1050. How can you show the violet coloured gas ? 1051. From what does iodine obtain its name ? 1052. How is iodine obtained ? 1053. Why is iodine reckoned a simple body ? 1054. In what respect do chlorine and iodine resemble each other ? . 1055. What are the simplest combinations of elements ? OF VEGETABLES. 239 stones, &c. all of which belong to the mineral kingdom. It is time now to turn our attention to a more complicated class of compounds, that of organized bodies, which will furnish us with a new source of instruction and amusement Emily. Bv organized bodies, I suppose you mean the vegetable and animal creation ? 1 have, however, but a very vague idea of the word organization, but 1 have often wished to know more pre- cisely what it means. Mrs. B. Organized bodies are such as are endowed by nature with various parts, peculiarly constructed and adapted to perform certain functions connected with life. Thus you may observe, that mineral compounds are formed by the simple effect of mechanical or chemical attraction, and may appear to some to be, in a great measure, the productions of chance : whilst organized bodies bear the most striking and impressive marks of design, and are eminent- ly distinguished by that unknown principle, called life, from which the various organs derive the power of exercising their respective functions. Caroline. But in what manner does life enable these organs to perform their several functions ? Airs. B. That is a mystery which I fear is enveloped in such profound darkness, that there is very little hopes of our ever being able to unfold" it. We must content ourselves with examining the effect of this principle ; as for the cause we have been able only to give it a name, without attaching any other meaning to it than the vague and unsatisfactory idea of an unknown agent. Caroline. And yet I think I can form a very clear idea of life. Mrs. B. Pray let me hear how you would define it ? Caroline. It is, perhaps, more easy to conceive, than to express- let me consider—Is not life the power which enables both the ani- mal and the vegetable creation to perform the various functions which nature has assigned to them ? Mrs. B. 1 have nothing to object to your definition; but you will allow me to observe, that you have only mentioned the effects which the unknown cause produces, without giving us any notion ofthe cause itself. Emily. Yes, Caroline, you have told us what life does, but you have not told us what it is. Airs. B. We may study its operations ; but we should puzzle ourselves to no purpose by attempting to form an idea of its real nature. . We shall begin with examining its effects in the vegetable world, which constitutes the simplest class of organized bodies ; these we shall find distinguished from the mineral creation, not only by their more complicated nature, but by the power which they possess with- in themselves, of forming new chemical arrangements of their con- stituent parts, by means of appropriate organs. Thus, though all vegetables are ultimately composed of hydrogen, carbon, and oxy- gen, (with a few other occasional ingredients,) they separate and 1056. What are organized bodies ? 1057. How do they differ from inorganic matter? 1058. What is life in its philosophical acceptation ? 1059. What is the simplest class of organized bodies ? 1060. Of what are vegetables mostly composed ? 240 COMPOSITION combine these principles, by their various organs, in a thousand ways, and form, with them, different kinds of juices and solid parts, which exist ready made in vegetables, and may, therefore, be con- sidered as their immediate materials. These are, Sap, Resins, Mucilage, Gum Resins, Sugar, Balsams, Fecula, Caoutchouc, Gluten, Extractive Coloring Alatler, Fixed Oil, Tannin, Volatile Oil, Woody Fibre. Camphor, Vegetable acids, c\c. Caroline. What a long list of names! I did not suppose that a vegetable was composed of half so many ingredients. Mrs. B. You must not imagine that every one of these materi- als is formed in each individual plant. I only mean to say, that they are all derived exclusively from the vegetable kingdom. Emily. But does each particular part of the plant, such as the root, the bark, the stem, the seeds, and leaves, consist of one of these ingredients only, or of several of them combined together ? Mrs. B. I believe there is no part of a plant which can be said to consist solely of any one particular ingredient ; a certain number of vegetable materials must always be combined for the formation of any particular part, (of a seed for instance,) and these combina- tions are carried on by sets of vessels, or minute organs, which se- lect from other parts, and bring together the several principles re- quired for the developement and growth of those particular parts which they are intended to form and to maintain. Emily. And are not these combinations always regulated by the laws of chemical attraction ? Airs. B. No doubt; the organs of plants cannot force principles to combine which have no attraction for each other : nor can they compel superior attractions to yield to those of inferior power; they probably act rather mechanically, by bringing into contact such principles, and in such proportions, as will, by their chemical com- bination, form the various vegetable products. Caroline. We may then consider each of these organs as a curi- ously constructed apparatus, adapted for the performance of a vari- ety of chemical processes. Mrs. B. Exactly so. As long as the plant lives and thrives, the carbon, hydrogen, and oxygen, (the chief constituents of its imme- diate materials,) are so balanced and connected together, that they are not susceptible of entering into other combinations ; but no sooner does death take place, than this state of equilibrium is de- stroyed and new combinations produced. 1061. What are the ingredients of vegetables ? 1062. Is it to be supposed that all these ingredients exist in a single vegetable ? 1063. And does any vegetable or any part of one consist solely of a single one of these ingredients ? . 1064. By what are the combinations in the vegetable kingdom reg- ulated ? e s 1C65. How may the organs of plants be considered ? OF VEGETABLES. 241 !Emily. But why should death destroy it ? for these principles must remain in the same proportions, and consequently, I should suppose, in the same order of attractions ? Airs. B. You must remember, that in the vegetable, as well as in the animal kingdom, it is by the principle of life that the organs are enabled to act; when deprived of that agent or stimulus, their power ceases, and an order of attractions succeeds, similar to that which would take place'in mineral or unorganized matter. Emily. It is this order of attractions, I suppose, that destroys the organization ofthe plant after death ; for if the same combinations still continued to prevail, the plant would always remain in the state in which it died. Airs. B. And that, you know, is never the case ; plants may be partially preserved for some time after death, by drying; but in the natural course of events they all return to the state of simple ele- ments ; a wise and admirable dispensation of Providence, by which dead plants are rendered fit to enrich the soil, and become subser- vient to the nourishment of living vegetables. Caroline. But we are talking of the dissolution of plants, before we have examined them in their living state. Mrs. B. That is true, my dear. But I wished to give you a gen- eral idea of the nature of vegetation, before we entered into par- ticulars. Besides, it is not so irrelevant as you suppose to talk of vegetables in their dead state, since we cannot analyze them with- out destroying life ; and it is only by hastening to submit them to examination, immediately after they have ceased to live, that we can anticipate their natural decomposition. There are two kinds of analysis of which vegetables are susceptible ; first, that which separates them into their immediate materials, such as sap, resin, mucilage, &e; secondly, that which decomposes them into their primitive elements, as carbon, hydrogen, and oxygen. Emily. Is there not a third kind of analysis of plants, which con- sists in separating their various parts, as the stem, the leaves, and the several organs ofthe flower I Mrs. B. That, my dear, is rather the department ofthe botanist; we shall consider these different parts of plants only, as the organs by which the various secretions or separations are performed; but we must first examine the nature of these secretions. The sap is the principal material of vegetables, since it contains the ingredients that nourish every part of the plant. The basis of this juice, which the roots suck up from the soil, is water ; this holds in solution the various other ingredients required by the several parts ofthe plant, which are gradually secreted from the sap by the different organs appropriated to that purpose, as it passes them in circulating through the plant. Mucus or mucilage, is a vegetable substance, which, like all the 1066. Why should death destroy vegetable combinations ? 1067. What is an admirably wise dispensation of Providence in re- gard to the nature of plants ? . 1068. Of how many kinds of analysis are vegetables susceptible ? 1069. What is the first? 1070. What is the second r - 1071. What is the principal material of vegetables? 1072. What is the basis of this juice ? 21 242 UUM.I'OSITIOJN others, is secreted from the sap ; when in excess, it exudes from the trees, in the form of gum. Caroline. Is that the gum so frequently used instead of paste or glue ? Mrs. B. It is : almost all fruit trees yield some sort of gum, but that most commonly used in the arts is obtained from a species of acacia-tree, in Arabia, and is called gum arable ; it forms the chief nourishment ofthe natives of those parts, who obtain it in great quantities from incisions which they make in the trees. Caroline. I did not know that gum was eatable. Mrs. B. There is an account of a whole ship's company being saved from starving, by feeding on the cargo, which was gum Sen- egal. I should not, however, imagine, that it would be either a pleasant, or a particularly eligible diet to those who have not, from their birth, been accustomed to it. It is, however, frequently ta- ken medicinally, and considered as very nourishing. Several kinds of vegetable acids may be obtained, by particular processes, from gum or mucilage, the principal of which is called the mucous acid. Sugar is not found in its simple state in plants, but is always mix- ed with gum, sap, or other ingredients: this saccharine matter is to be met with in every vegetable, but abounds most in roots, fruits, and particularly in the sugar cane. Emily. If all vegetables contain sugar, why is it extracted ex- clusively from the sugar cane ? Airs. B. Because it is both most abundant in that plant, and most easily obtained from it. Besides, the sugars produced by oth- er vegetables differ a little in their nature. During the late troubles in the West Indies, when Europe was but imperfectly supplied with sugar, several attempts were made to extract it from other vegetables, and very good sugar was obtain- ed from parsnips and from carrots ; but the process was too expen- sive to carry this enterprize to any extent Caroline. I should think that sugar might be more easily obtain- ed from sweet fruits, such as figs, dates, &c. Airs. B. Probably ; but it would be still more expensive, from tbe high price of those fruits, and it would not be exactly like com- mon sugar.* Emily. Pray, in what manner is sugar obtained from the sugar- cane ? * Some foreign chemists (MM. Kirkoff, Braconnot, &c. have found that if starch be boiled for a long time in water containing one fortieth part of sulphuric acid, and evaporated down to a cer- tain consistence, the solution of starch concretes, in cooling, into a solid brownish mass, which has the taste and other general proper- ties of sugar. During this process, no gas is disengaged, and the acid is not decomposed. * 1073. What is the mucilage of vegetables ? 1074. What uses are made of mucilage or gum ? • 1075. In what state does sugar naturally exist? 1108. From what is camphor obtained? . 1109. Is camphor obtained in other plants? 1L10. What is the method of obtaining it ? 1111. What remarkable peculiarity has camphor ? • 1112. What are resins? OF VEGETABLES. 249 pal, mastic and frankincense, are also of this class of vegetable sub- stances. Emily. Is it of these resins that the mastic and copal varnishes so much used in painting are made ? Mrs. B. Yes. Dissolved either in oil or in alcohol, resins form varnishes. From these solutions they may be precipitated by wa- ter, in which they are insoluble. This \ can easily show you. If you will pour some water into this glass^of mastic varnish, it will combine with the alcohol in which the resin is dissolved, and the lat- ter will be precipitated in the form of a white cloud., Emily. It is so. And yet how is it that pictures or drawings, var- nished with this solution, may safely be washed with water? Airs. B. As the varnish dries, the alcohol evaporates, and the dry varnish or resin which remains, not being soluble in water, will not be acted on by it. There is a class of compound resins, called gum resins, which are precisely what their name denotes, that is lo say, resins, combined with mucilage. Myrrh aud assafoetida are of this description. Caroline. Is it possible that a substance of so disagreeable a smell as assafoetida can be formed from a volatile oil ? Mrs. B. The odor of volatile oils is by no means always grateful. Onions and garlic derive their smell from volatile oils, as well as roses and lavender. There is still another form under which volatile oils present them- selves, which is that of balsams. These consist of resinous juices combined with a peculiar acid, called the benzoic acid. Balsams appear to have been originally volatile oils,* the oxygenation of which, has converted one part into a resin, and the other part into an acid, which combined together, form a balsam ; such are the balsams of Peru, Tolu, &c. We shall now take leave of the oils and their various modifica- tions, and proceed to the next vegetable substance which is caout- chouc. This is a white, milky, glutinous fluid, which acquires consis- tence and blackens in drying, in which state it forms the substance with which you are so well acquainted, under the name of gum- plastic • Caroline. I am suprised to hear that gum-elastic was ever white, or ever fluid ! And from what vegetable is it procured ? Mrs.B. It is obtained from two or three different species of trees in the East Indies, and South America, by making incisions in the stem The juice is collected as it trickles from these incisions, and moulds of clay, in the form of little bottles of gum elastio, are dipped * This is an erroneous idea. Balsams are original and peculiar substances, and consist chiefly of resinous matter in a semifluid state. The benzoic acid is most probably formed during the pro- cess by which it is obtained.—C. *1113. What are the most common resins? 1M4. Of what are mastic and copal varnishes made ? 1115. What will be the consequenoes if water be poured into a ves- sel containing mastic varnish ? -1116. What are gum resins? 1117. What are balsams ? 1118. From what is caoutchouc obtained? 1119. What are its uses? 250 COMPOSITION into it. A layer of this juice adheres to the clay and dries on it; and several layers are successively added by repeating this till the bottle is of sufficient thickness. It is then beaten to break down, the clay which is easily shaken out. The natives of the countries where this substance is produced, sometimes make shoes and boots of it by a similar process, and they are said to be extremely pleas- ant and serviceable, both from their elasticity, and their being wa- ter-proof. The substance which comes next in our enumeration of the im- mediate ingredients of vegetables, is extractive matter. This is a term which, in a general sense, may be applied to any substance extracted from vegetables ; but it is more particularly understood to relate to the extractive coloring matter of plants. A great variety of colors are prepared from the vegetable kingdom, both for the purposes of painting and of dying; all the colors called lakes are of this description ; but they are less durable than mineral colors, for by long exposure to the atmosphere, they either darken or turn yellow. Emily. I know that in painting the lakes are reckoned far less durable colors than the ochres ; but what is the reason of it ? Mrs. B. The change which takes place in vegetable colors is owing chiefly to the oxygen of the atmosphere slowly burning their hydrogen, and leaving in some measure, the blackness of the car- bon exposed. Such change cannot take place in ochre, which, is altogether a mineral substance. Vegetable colors have a stronger affinity for animal than for veg- etable substances ; and this is supposed to be owing to a small quan- tity of nitrogen, which they contain. Thus, silk and worsted, will take a much finer vegetable dye than linen and cotton. Caroline. Dying, then, is quite a chemical process ? Airs. B. Undoubtedly. The condition required to form a good dye is, that the coloring matter should be precipitated, or fixed, on the substance to be dyed, and should form a compound not soluble in tie liquids to which it would probably be exposed.. Thus, for in- stance, printed or dyed linens or cottons must be able lo resist the action of soap and water, to which they must necessarily be subject in washing ; and woollens and silks should withstand the action of grease and acids, to which they may accidentally be exposed. Caroline. But if linen and cotton have not a sufficient affinity for coloring matter, how are they made to resist the action of washing, which they always do when they are well printed? Airs. B. When the substance to be dyed has either no affinity for the coloring matter, or not sufficient power to retain it, the com- bination is effected or strengthened, by the intervention of a third substance called a mordant or basis. The mordant must have a * 1120. What is the extractive matter of vegetables ? 4121. What are the colors prepared from vegetables ? 1122. To what is the change which takes place in vegetable colors owing ? • 1123. Why have vegetable colors a stronger affinity for animal than, for vegetable substances ? 1124. V\ hat is necessary that vegetable colors be durable ? H25. What are mordants and their uses ? OF VEGETABLES. 251 •strong affinity both for the coloring matter and the substance dyed, by which means it causes them to combine and adhere together. Caroline. And what are the substances that perform the office of thus reconciling the two adverse parties? Mrs. B. The most common mordant is sulphat of alumine, or alum. Oxyds of tin and iron in the state of compound salts, are likewise used for that purpose. Tannin is another vegetable ingredient of great importance in the arts. It is obtained chiefly from the bark of trees; but it is found also in nut-galls, and in some other vegetables. Emily. Is that the substance commonly called tan, which is used in hot-houses ? Mrs.B. Tan is the prepared bark in which the peculiar sub- stance, tannin is contained. But the use of tan in hot-houses is of much less importance than the operation of tanning, by which skin is converted into leather. Emily. Pray how is this operation performed ? Mrs. B. Various methods are employed for this purpose, which all consist in exposing skin to the action of tannin, or of substan- ces containing this principle in sufficient quantities, and disposed to yield it to the skin. The most usual way is to infuse coarsely powdered oak bark in water, and to keep the skin immersed in this infusion for a certain length of time. During this process, which is slow and gradual, the skin is found to have increased in weight, and to have acquired a considerable tenacity and impermeability to water. This effect may be much accelerated by using strong satu- rations of the tanning principle, (which can be extracted from bark) instead of employing the bark itself. But this quick mode of prep- aration does not appear to make equally good leather. Tannin is contained in a great variety of astringent vegetable substances, as galls, the rose tree, and wine; but it is no where so plentiful as in bark. All these substances yield it to water, from which it may be precipated by a solution of isinglass or glue, with which it strongly unites, and formsan insoluble compound. Hence its valuable property of combining with skin (which consists chief- ly of glue,) and of enabling it to resist the action of water. Emily. Might we not see that effect by pouring a little melted isinglass into a glass of wine, which you say contains tannin? Airs. B. Yes. I have prepared a solution of isinglass for that very purpose. Do you observe the thick, muddy precipitate? That is the tannin combined with the isinglass. Caroline. This precipitate must then be of the same nature as the leather? Airs. B. It is composed of the same ingredients; but the organi- zation and texture of the skin being wanting, it has neither the consistence nor the tenacity ofthe leather. 1126. What substances are commonly used as mordants ? '1127. From what is tannin obtained? 1128. What are its uses? 1129. What is the process of converting skins into leather, by the 'use of tanning? 1130. Why does tanning canse skins on being changed to leather, lto be impervious to water? *H31. How does a solution of isinglass in water differ from leather? 252 COMPOSITION Caroline. One might suppose that men who drink large quautr- ties of red wine, stand a chance of having the coats of their stom- achs converted into leather, since tannin has so strong an affinity for skin. Airs. B. It is not impossible but that the coats of their stomachs may be, in some measure, tanned or hardened by the constant use of this liquor; but you must remember that where a number of other chemical agents are concerned, and above all, where life ex- ists, no certain chemical inference can be drawn. I must not dismiss this subject, without mentioning a recent dis- covery of Mr. Hatchett, which relates to it This gentleman found that a substance very similar to tannin, possessing all its leading properties, and actually capable of tanning leather, may be produ- ced by exposing carbon, or any substance containing carbonaceous matter, whether vegetable, animal, or mineral, to the action of ni- tric acid.* Caroline. And is not this discovery likely to be of use lo manu- factures ? Mrs. B. That is very doubtful, because tannin thus artificially prepared, must probably always be more expensive than that which is obtained from bark. But the fact is extremely curious, as it af- fords one of those very rare instances of chemistry being able to imitate the proximate principles of organized bodies. The last of the vegetable materials is woody fibre—it is the hard- est part of plants. The chief source from which this substance is derived, is wood, but it is also contained, more or less, in every sol- id part ofthe plant It forms a kind of skeleton of the part to which it belongs and retains its shape after all the other materials have disappeared. It consists chiefly of carbon united with a small por- tion of salts, and the other constituents common to all vegetables. Emily. It is of woody fibre then, that the common charcoal is made? Mrs. B. Yes. Charcoal, as you may recollect, is obtained from wood by the separation of all its evaporable parts. Before we take leave of the vegetable materials, it will be proper at least to enumerate the several vegetable acids which we either have had or may have occasion to mention. I believe I formerly told you that their basis or radical, was uniformly composed by hy- drogen and carbon, and that their difference consisted only in the various proportions of oxygen which they contained. * To make artificial tannin, Mr. Hatchett used 100 grains of char- coal with 500 of nitric acid, diluted with twice its weight of water. This mixture was heated, and then suffered to digest for two days; more acid was then added, and the digestion continued until the charcoal was dissolved. This solution being evaporated to dryness, leaves a dark brown mass. This is the tannin in question. Its taste is bitter and highly astringent___C 4132. What discovery was made by Mr. Hatchett ? 1133. How did he prepare artificial tannin? • 1134. What is woody fibre ? 1135. Of what does it chiefly consist ? 1136. From what is charcoal made? OF VEGETABLES. 253 The following are the names of the vegetable acids : The Alucous acid obtained from gum or mucilage ; Suberic, - from cork; Camphoric, - from camphor; Benzoic, - from balsams; Gallic, - from galls, bark, &c. Malic, - from ripe fruits; Citric, - from lemon juice; Oxalic, • from sorrel ; Succinic, - from amber ; Tartarous, - from tartrit of potash; Acetic, - from vinegar. They are all decomposable by heat, soluble in water, and turn ve- getable blue colors red. The succinic, the tartarous, and the ace- tous acids, are the productions of the decomposition of vegetables ; we shall, therefore, reserve their examination for a future period. The oxalic acid, distilled from sorrel, is the highest term of vege- table acidification ; for, if more oxygen be added to it, it loses its vegetable nature, and is resolved into carbonic acid and water ; therefore, though all the other acids may be converted into the ox- alic by au addition of oxygen, the oxalic itself is not susceptible of a further degree of oxygenation : nor can it be made by any chem- ical processes, to return to a state of lower acidification.* To conclude this subject, I have only to add a few words on the gallic acid. Caroline. Is not this the same acid before mentioned which forms ink, by precipitatiag sulphat of iron from its solution ? Mrs. B. Yes. Though it is usually extracted from galls, on ac- count of its being most abundant in that vegetable substance, it may also be obtained from a great variety of plants. It constitutes what is called the astringent principle of vegetables ; it is generally combined with tannin, and you will find that an infusion of tea, cof- fee, bark, red wine, or any vegetable substance that contains the astringent principle, will make a black precipitate with a solution of sulphat of" iron. Caroline. But pray what are galls? Airs. B. They are excrescences which grow on the bark ot young * Oxalic acid may be formed artificially. Put one ounce of white sugar, powdered, into a retort, and pour on three ounces of rntnc acid. When the solution is over, make the liquor boil, and when it acquires a reddish brown color, add three ounces more of nitric acid. Continue the boiling until the fumes cease and the color of the liquor vanishes. Then let the liquor be poured into a wide ves- sel, and on cooling, white slender crystals will be formed. These are oxalic acid.—C. 1137. What are the names of the vegetable acids ? 1138 What is the composition ofthe basis of these acids ? 1139 What general quality have all vegetable acids ? 1140.' What is the highest term ofvegetable acidification? J141 What acid is called the astringent principle of vegetables ? 1142. From what is it usually extracted ? 1143. What are the galls that yield this acid ? 254 DECOMPOSITION oaks, and are occasioned by an insect which wounds the bark of trees, and lays its egg in the aperture. The lacerated vessels ofthe tree then discharge their contents, and form an excrescence, which affords a defensive covering for these eggs. The insect, when come to life, first feeds on this excrescence, and sometime afterwards eats its way out, as it appears from a hole which is formed in all gall- nuts that no longer contain an insect It is in'hot climates only that strongly astringent gall-nuts are found ; those which are used for the purpose of making ink are brought from Aleppo. Emily. But are not the oak apples which grow on the leaves of the oak in this country of a similar nature ? Airs. B. Yes; only they are an inferior species of galls, contain- ing less ofthe astringent principle, and therefore less applicable to useful purposes. Caroline. Are the vegetable acids never found but in their pure uncombined state ? Airs. B. By no means ; on the contrary, they are frequently met with in the state of compound salts ; these, however, are in general not fully saturated with the salifiable bases, so that the acid predom- inates; and in this state they are called acidulous salts. Of this kind is the salt called cream of tartar. Caroline. Is not the salt of lemon commonly used to take out inkspots, and stains, of this nature ? Airs. B. No ; that salt consists of the oxalic acid combined with a little potash. It is found in that state in sorrel. Caroline. And pray how does it take out ink-spots? Airs. B. By uniting with the iron, and rendering it soluble in water. Besides the vegetable materials which we have enumerated, a variety of other substances, common to the three kingdoms, are found in vegetables, such as potash, which was formerly supposed to belong exclusively to plants, and was, in consequence, called vegetable alkali. Sulphur, phosphorus, earths, and a variety of metallic oxyds, are also found iu vegetables, but only in small quantities. And we meet sometimes with neutral salts, formed by the combination of these idgredients. CONVERSATION XXI. ON THE DECOMPOSITION OF VEGETABLES. Caroline. The account which you have given us Mrs. B., of the materials of vegetables, is, doubtless, very instructive ; but it does 1144. In what climates are strongly astringent gall-nuts found? ■ 1145. Are the vegetable acids never found but in their pure uncom- bined state ? 1146. How does the oxalic acid remove ink-spots? 1147. What substances common to the three kingdoms are found in vegetables ? OF VEGETABLES. 255 not completely satisfy my curiosity. I wish to know how plants ob- tain the principles from which their various materials are formed ; b; what means these are converted into vegetable matter, and how they are connected with the life ofthe plant. Mrs. B. This implies nothing else than a complete history of the chemistry and physiology of vegetation, subjects on which we have yet but very imperfect notions. Still 1 hope that I shall be able in some measure, to satisfy your curiosity. But, in order to render the subject more intelligible, I must first make you acquainted with the various changes which vegetables undergo, when the vital power no longer enables them to resist the commou laws of chemical at- traction. The composition of vegetables being more complicated than that of minerals, the former more readily undergo chemical changes than the latter ; for the greater the variety of attractions, the more easily is the equilibrium destroyed, and a new order of combinations introduced. Emily. I am surprised that vegetables should be so easily suscep- tible of decomposition ; for the preservation of the vegetable king- dom is certainly far more important than that of minerals. Mrs. B. You must consider, on the other hand, how much more easily the former is renewed than the latter. The decomposition of the vegetable takes place only after the death of the plant, which, in the common course of nature, happens when it has yielded fruit and seeds to propagate its species, if, instead of thus finishing its career, each plant was to retain its form and vegetable state, it would become a useless burden to the earth and its inhabitants. When vegetables, therefore, cease to be productive, they cease to live, and nature then begins her process of decomposition, in order to resolve them into their chemical constituents, hydrogen, carbon and oxygen ; those simple and primitive ingredients, which she keeps in store for all her combinations. Emily. But since no system of combination can be destroyed ex- cept by the establishment of another order of attractions, how can the decomposition of vegetables reduce them to their simple ele- ments ? Airs. B. It is a very long process, during which a variety of new combinations are successively established, and successively destroy- ed ; but, in each of these changes, the ingredients of vegetable matter tend to unite in a more simple order of compounds, till they are at length brought to their elementary state, or, at least, to their most simple order of combinations. Thus you will find that vege- tables are in the end almost entirely reduced to water and carbonic acid; the hydrogen and carbon dividing the oxygen between them so as to form with it these two substances But the variety of inter- mediate combinations that take place during the several stages of • 1148. Why do vegetables more readily undergo chemical changes than minerals? 1149. When do vegetables become decomposed ? 1150. Into what are vegetables reduced by decomposition ? 1151. Since no system of combination can be destroyed, except by the establishment of another order of attractions, how can the decom- position of vegetables reduce them to their simple elements ? 256 DECOMPOSITION the decomposition of vegetables, present us with a new set of com- pounds, well worthy of our examination. Caroline. How is it possible that vegetables, while putrefying, should produce any thing worthy of observation ? Mrs. B. They are susceptible of undergoing certain changes be- fore they arrive at the state of putrefaction, which is the final term of decomposition ; and of these changes we avail ourselves for par- ticular and important purposes. But, in order to make you under- stand this subject, which is of considerable importance, I must ex- plain it more in detail. The decomposition of vegetables is always attended by a violent internal motion, produced by the disunion of one order of particles, and the combination of another. This is called fermentation. There are several periods at which this process stops, so that a state of rest appears to be restored, and the new order of compounds fair- ly established. But, unless means be used to secure these new combinations in their actual state, their duration will be but tran- sient, and a new fermentation will take place, by which the com- pound last formed will be destroyed ; and another, and less complex will succeed. Emily. The fermentations, then, appear to he only the succes- sive steps by which a vegetable descends to its final dissolution. Mrs. B. Precisely so. Your definition is perfectly correct. Caroline. And how many fermentations, or new arrangements, does a vegetable undergo before it is reduced to its simple ingredi- ents? Mrs.B. Chemists do not exactly agree in this point; but there are, I think, four distinct fermentations, or periods, at which the de- composition of vegetable matter stops and changes its course. But every kind of vegetable matter is not equally susceptible of under- going all these fermentations. There are likewise several circumstances required to produce fermentation. Water, and a certain degree of beat are both essen- tial to this process, in order to separate the particles, and thus weak- en their force of cohesion, that the new chemical affinities may be brought into action. Caroline. In frozen climates, then, how can the spontaneous de- composition of vegetables take place ? Mrs. B. It certainly cannot; and, accordingly, we find scarcely any vestiges of vegetation where a constant frost prevails. Caroline. One would imagine that, on tbe contrary, such spots would be covered with vegetables ; for since they cannot be decom- posed, their number must always increase. Airs. B. But, my dear, heat and water are quite as essential to the formation of vegetables, as they are to their decomposition. Be- sides, it is from the dead vegetables, reduced to their elementary principles, that the rising generation is supplied with sustenance. No young plant, therefore, can grow, unless its predecessors contri- bute both to its formation and support ; and these not only furnish 1152. What is the prdcess called, that disunites and decomposes the elements of vegetables ? 1153. What are the fermentations ? 1154. How many kinds of fermentation are there ? 1155. What is necessary to produce fermentation ? OF VEGETABLES. 257 the seed from which the new plant springs, but likewise the food by which it is nourished. Caroline. Under the torrid zone, therefore, where water is never frozen, and the heat is very great, both the processes of vegetation and of fermentation must, I suppose, be extremely rapid ? Mrs. B. Not so much as you imagine; for in such climates great part ofthe water which is required for these processes is in an aeri- form state, which is scarcely more conducive either to the growth or formation of vegetables than that of ice. In those latitudes, there- fore, it is only in low, damp situations, sheltered by woods from the sun's rays, that the smaller tribes of vegetables can grow and thrive during the dry season, as dead vegetables seldom retain water enough to produce fermentation, but are, on the contrary, soon dried up by the heat of the sun, which enables them to resist that process ; so that it is not till the fall of the autumnal rains (which are very violent in such climates,) that spontaneous fermentation can take place. The several fermentations derive their names from their principal products. The first is called the saccharine fermentation, because its product is sugar. Caroline. But sugar, you have told us, is found in all vegetables ; it cannot, therefore, be the product of their decomposition. Airs. B. It is true that this fermentation is not confined to the decomposition of vegetables, as it continually takes place during their life ; and, indeed, this circumstance has till lately prevented it from being considered as one of the fermentations, and the forma- tion of sugar, whether in living or dead vegetable matter, is so evi- dently a new compound, proceeding from the destruction ofthe pre- vious order of combinations, and essential to the subsequent fer- mentations, that it is now, I believe, generally esteemed the first step, or necessary preliminary to decomposition, if not an actual commencement of that process; Caroline. 1 recollect your hinting to us that sugar was supposed not to be secreted from the sap, in the same manner as mucilage, fecula, oil, and the other ingredients of vegetables. Mrs. B. It is rather from these materials, than from the sap itself, that sugar is formed ; and it is developed at particular periods, as you may observe in fruits, which become sweet in ripening, some- times even after they have been gathered. Life therefore is not essential to the formation of sugar, whilst, on the contrary, muci- lage, fecula, and the other vegetable materials that are secreted from the sap by appropriate organs, whose powers immediately de- pend on the vital principle, cannot be produced but during the ex- istence of that principle. . Emily. The ripening of fruits is then their first step to destruc- tion as well as their last towards perfection ? Mrs. B. Exactly. A process analogous to the saccharine fer- 1157. What in the torrid zone prevents the processes of vegetation and fermentation from being rapid .> - _•-.„• , 1158. From what do the several fermentations derive their names? I 159! Why is the fiistofthem called a saccharine fermentation ? 1I6O. Why was not sugar formerly considered a fermentation? 1161. Why is it at present considered a fermentation ? 1162* From what parts of vegetables is sugar formed ? 22* 258 DECOMPOSITION mentation takes place also during the cooking of certain vegetables; This is the case with parsnips, carrots, potatoes, &c., in which sweet- ness is developed by heat and moisture; and we know that if we carry the process a little farther, a more complete decomposition would ensue. The same process takes place also in seeds previous to their sprouting. ■ ■ Caroline. How do you reconcile this to your theory, Mrs. B. ? Can you suppose that decomposition is the necessary precursor of life? . , _ _ Mrs. B. That is indeed the case. The materials of Ihe seed must be decomposed, and the seed disorganized, before a plant can sprout from it. Seeds, besides the embryo plant, contain (as we have al- ready observed) fecula, oil, and a little mucilage. These substan- ces are destined for the nourishment of the future plant; but they undergo some change before they can be fit for this function. The seeds, when buried in the earth, with a certain degree of moisture and of temperature, absorb water, which dilates them, separates their particles, and introduces a new order of attractions, of which sugar is the product The substance of the seed is thus softened, sweetened, and converted into a sort of white, milky pulp, fit for the nourishment of the embryo plant. The saccharine fermentation of seeds is artificially produced, for the purpose of making malt, by the following process:—A quantity of barley is first soaked in water for two or three days : the water being afterwards drained off, the grain heats spontaneously, swells, bursts, sweetens, shows a disposition to germinate, and actually sprouts to the length of an inch, when the process is stopped by put- ting it into a kiln, where it is well dried at a genlle heat. In this state it is crisp and friable, end constitutes the substance called malt\ which is the principal ingredient of beer. Emily. But 1 hope you will tell us how malt is made into beer? Airs. B. Certainly ; but I must first explain to you the nature of the second fermentation, which is essential to that operation. This is called the vinous fermentation, because its product is wine. Emily. How very differerrt the decomposition of vegetables is from what 1 had imagined ! The products of their disorganization appear almost superior to those which they yield during their state of life and perfection. Airs. B. And do you not, at the same time, admire the beautiful economy of Nature, which, whether she creates, or whether she destroys, directs all her operations to some useful and benevolent purpose?—It appears that the saccharine fermentation is extremely favorable, if not absolutely essential, as a previous step, to the vinous fermentation ; so that if sugar be not developed during the life of the plant, the saccharine fermentation must be artificially produced be- * 1163. What process analogous to saccharine fermentation takes place during the cooking of certain vegetables ? 1164. Flow would you describe this fermentation in seeds prior to germination? 1165. How is saccharine fermentation exhibited in the making of malt? 1166. Why is the second fermentation called vinous ? 1167. Why does barley resist the vinous fermentation until it has gone through the saccharine? of vegetables; 259 fore the vinous fermentation can take place. This is the case with barley, which does not yield any sugar until it is made into malt; and it is in that state only that it is susceptible of undergoing the vinous fermentation by which it is converted into beer. Caroline. But if the product ofthe vinous fermentation is always wine, beer cannot have undergone that process, for beer is certain- ly not wine. Mrs. B. Chemically speaking, beer may be considered as the wine of grain. For it is the product of the fermentation of malt, just as wine is that of the fermentation of grapes, or other fruits. The consequence of the vinous fermentation is the decomposition of the saccharine matter, and the formation of a spiritous liquor frorrj the constituents of the sugar. But in order to promote this ferment- ation, not only water and a certain degree of heat are necessary, but some other vegetable ingredients, besides the sugar, a3 fecula, mu- cilage, acids, salts, extractive matter, &c, all of which seem to con- tribute to this process, and give to the liquor its peculiar taste. Emily. It is, perhaps, for this reason, lhat wine is not obtained from the fermentation of pure sugar; but that fruits are chosen for that purpose, as they contain not only sugar, but likewise the other vegetable ingredients which promote the vinous fermentation, and give the peculiar flavor. Mrs. B. Certainly. And you must observe, also, that the relative quantity of sugar is not the only circumstance to be considered in the choice of vegetable juices for the formation of wine ; otherwise the sugar-cane would be best adapted for lhat purpose. It is rather tbe manner and proportion in which the sugar is mixed with other vegetable ingredients that influences the production and qualities of wine. And it is found that the juice of the grape not only yields the most considerable proportion of wine, but that it likewise; affords it of the most grateful flavor. Emily. I have seen a vintage in Switzerland, and I do not re- collect that heat was applied, or water added, lo produce the fer- mentation ofthe grapes. Mrs. B. The common temperature of the atmosphere in the cel- lars in which the juice of the grape is fermented is sufficiently warm for this purpose; and as the juice contains an ample supply of water, there is no occasion for any additiou of it. But when fermentation is produced in dry malt, a quantity of water must necessarily be added. Emily. But what are precisely the changes that happen during the vinous fermentation? Airs. B. The sugar is decomposed, and its constituents are re- combined into two new substances; the one a peculiar liquid sub- stance, called alcohol or spirit of wine, which remains in the fluid; the other, carbonic acid gas, which escapes during the fermentation. Wine, therefore, as 1 before observed, in a general point of view may be considered as a liquid, of which alcohol constitutes the essen- • 1168. W hat is the consequence of the vinous fermentation ? 1169. What is necessary to produce this fermentation ? 1170. Why are grapes chosen for wine instead of pure sugar? 1171. What is to be considered in the choice of vegetable juices for the formation of wine ? 1172. W hat are the changes that happen during the vinous ferment- ation ? 266 DECOMPOSITION tial part. And tbe variety of streugth and flavor of the different kinds of wine, are to be attributed to the different qualities of the fruits, from which they are obtained, independently ofthe sugar. Caroline. 1 am astonished to hear that so powerful a liquid as spir- it of wine should be obtained from so mild a substance as sugar. Mrs. B. Can you tell me in what the principal difference con- sists between alcohol and sugar? Caroline. Let me reflect;—Sugar consists of carbon, hydrogen, and oxygen. If carbonic acid be subtracted from it, during the for- mation of alcohol, the latter will contain less carbon and oxygen than sugar does; therefore hydrogen must be the prevailing prin- ciple of alcohol. Mrs. B. It is exactly so. And this very large proportion of hy- drogen accounts for the lightness and combustible property of alco- hol, and of spirits in general, all of which consist of alcohol various- ly modified. Emily. And can sugar be recomposed from the combination of alcohol and carbonic acid' Mrs. B. Chemists have never been able to succeed in effecting this; but from analogy I should suppose such a recomposition possi- ble. Let us now observe more particularly, the phenomena that take place during the vinous fermentation. At the commencement Of this process, "heat is ievolved^and the liquor swells considerably from the formation of the carbonic acid, which is disengaged in such prodigious quantities as would be fatal to any person who should unawares inspire it; an accident which has sometimes happened. If the fermentation be stopped by putting the liquor into barrels, before the whole ofthe carbonic acid is evolved, the wine is brisk, like Champagne, from the carbonic acid imprisoned in it, and it tastes sweet, like cider, from the sugar not being completely de- composed. Emily. But 1 do not understand why heat should be evolved during this operation. For, as there is a considerable formation of gas in which a proportionable quantity of heat must become in- sensible, I should have imagined that cold, rather than heat, would have been produced. Alrs.B. It appears so on first consideration ; but you must recol- lect that fermentation is a complicated chemical pt ocess ; and that, during the decompositions and recompositions attending it, a quan- tity of chemical heat may bedisengaged, sufficient both to develope the gas, and to effect an increase of temperature. When the fer- mentation is completed, the liquid coojs and subsides, the efferves- ence, ceases, and the thick, sweet, sticky juice of the fruit, is con- verted into a clear, transparent, spiritous liquor, called wine. Emily. How much I regret hot having been acquainted with the nature of the vinous fermentation, when I had an opportunity of seeing the process. Alrs.B. You have an easy method of satisfying yourself in that 1173. What is the principal difference between sugar and alcohol? * 1174. Can sugar be recomposed by the combination of alcohol and carbonic acid ? 1175. What takes place at the commencement of the vinous fer- mentation ? '1176. Why is Champagne wine so brisk? 1177. What process is analagous to the making of wine? OF VEGETABLES. 261 respect by observing the process of brewing, which in every essen- tial circumstance, is similar to that of making wine, and is really a very curious chemical operation. Although we cannot actually make wine at this moment, it will be easy to show you the mode of analyzing it. This is done by distil- lation. When wine of any kind is submitted to this operation, it is found to contain brandy, water, tartar, attractive coloring matter and some vegetable acids. I have put a little Port wine into this alembic of glass, & (Fig. 24.) on placingthelamp under it, you will soon see the spirit and water succes- sively comeover.— Emily. But you do not mention al- cohol amongst the products ofthe dis- tillation of wine ; and yet that is its most essential in- gredient. Mrs. B. The al- cohol is contained in the brandy which is now coming over and dropping from the still. Brandy is nothing more than a mixture of alco- hol and water; and in order to obtain the alcohol pure, . we must again dis- A- Alembic—b. Lamp.—c. w«. til it from brandy. Caroline. 1 have just taken a drop on my finger; it tastes like strong brandy, but it is without color, whilst brandy is of a deep yellow. Mrs. B. It is not so naturally ; in its pure state, brandy is color- less, and it obtains the yellow tint you observe, by extracting the coloring matter from the new oaken casks in which it is kept. But if it does not acquire the usual tinge in this way, it is the custom to color the brandy used in this country artificially with a little burnt sugar, in order to give it the appearance of having been long kept Caroline. And is rum also distilled from wine? Airs. B. By no means; it is distilled from the sugar cane, a plant which contains so great a quantity of sugar, that it yields more al- cohol than almost any other vegetable. After the juice of the cane has been pressed out for making sugar, what still remains in the bruised cane is extracted by water, and this watery solution of su- gar is fermented, and produces rum. When wine is distilled what is the product? What is brandy ? From what does brandy obtain its coloring. From what and how is rum distilled ? 1178. 1179. 1180. 1181. 262 DECOMPOSITION The spiritous liquor called arack is in a similar manner distilled from the product ofthe vinous fermentation of rice. Emily. But rice has no sweetness; does it contain any sugar? Mrs. B. Like barley, and most other seeds, it is insipid until it has undergone the saccharine fermentation ; and this, you must re- collect, is always a previousstep to the vinous fermentation in those vegetables in which sugar is not already formed. Brandy may, in the same manner, be obtained from malt. Caroline. You mean from beer, I suppose; for the malt must have previously undergone the vinous fermentation. Mrs. B. Beer is not precisely the product ofthe vinous ferment- ation of malt. For hops are a necessary ingredient for the forma- tion of that liquor ; whilst brandy is distilled from pure fermented malt. But brandy, no doubt, might be distilled from beer, as well as from any other liquor that has undergone the vinous fermenta- tion : for since the basis of brandy is alcohol, it may be obtained from any liquid that contains that spirituous substance. Emily. And pray, from what vegetable is the favorite spirit of the lower orders of the people, gin, extracted ? Airs. B. The spirit (which is the same in all fermented liquors; may be obtained from any kind of grain; but the peculiar flavor which distinguishes gin is "that, of juniper berries, which aredistilled together with the grain,, I think the brandy contained in the wine which we are distilling, must, by this time, be all come over. Yes—taste the liquid that is now dropping from the alembic. Caroline. It is perfectly insipid, like water. Mrs. B. It is water, which as I was telling you, is the second product of wine, and comes over after all the spirit, which is the lightest part, is distilled. The tartar, and extractive coloring mat- ter we shall find in a solid form at the bottom ofthe alembic. Emily. They look very much like the lees of wine. Mrs. B. And in manv respects, they are of a similar nature, for lees of wine consist chiefly of tartrit of potash ; a salt which exists in the juice ofthe grape, and in many other vegetables, and is de- veloped only by the vinous fermentation. During this operation, it is precipitated, and deposits itself on the internal surface of the cask in which the wine is contained. It is much used in medicine, and in various arts, particularly dying, under the name of cream of tar- tar, and it is from this salt lhat the tartarous acid is obtained. Caroline. But the medicinal cream of tartar is in appearance, quite different from those dark colored dregs ; it is perfectly colorless. Mrs. B. Because it consists ofthe pure salts only, in its crystal- lized form; whilst in the instance before us, it is mixed with the deep colored extractive matter, and other foreign ingredients. Emily. Pray, cannot we now obtain pure alcohol from the bran- dy \vhich we have distilled ? Mrs.B. We might; but the process would be tedious; for in order to obtain alcohol perfectly free from water, it is necessary to distil, or, as the distillers call it, rectify it several times. You must 1182. From what and how is gin distilled? 1183. What is the origin ofthe cream of tartar? . 1184. From what may alcohol be obtained? OF VEGETABLES. 263 therefore, allow me to produce a bottle of alcohol that has been thus purified. This is a very important ingredient, which has many striking properties, besides its forming the basis of all spiritous liquors. Emily. It is alcohol, 1 suppose, that produces intoxication ? Mrs.B. Certainly; but the stimulus and momentary energv it gives to the system, and the intoxication it occasions when taken in excess, are circumstances not yet accounted for. Caroline. 1 thought that it produced these effects by increasing the rapidity of the circulation of the blood ; for drinking wine or spirits, I have heard always quickens the pulse. Alrs.B. No doubt; the spirit by stimulating the nerves increases the action of the muscles ; and the heart, which is one o f the strong- est muscular organs, beats with augmented vigor, and propels the blood with accelerated quickness. After such a strong excitation the frame naturally suffers a proportional degree of depression, so that a state of debility and languor, is the invariable consequence of intoxication. But though these circumstances are well ascer- tained, they are far from explaining why alcohol should produce such effects. Emily. Liqueurs are the only kind of spirits which I think plea- sant. Pray, of what do they consist? Mrs. B. They are composed of alcohol, sweetened with syrup, and flavored with volatile oil. The different kinds of odoriferous spiritous waters are likewise solutions of volatile oil in alcohol, as lavender water, eau de Co- logne, &c. The chemical properties of alcohol are important and numerous. It is one of the most powerful chemical agents, and is particularly useful in dissolving a variety of substances, which are soluble nei- ther by water nor heat. Emily. We have seen it dissolve copal and mastic to form var- nishes; and these resins are certainly not soluble in water, since water precipitates them from their solution in alcohol. Mrs. B. I am happy to find that you recollect these circumstan- ces so well. The same experiment affords also an instance of an- other property of alcohol,—its tendency to unite with water; for the resin is precipitated in consequence of losing the alcohol, which abandons it from its preference for water. It is attended also, as you may recollect, with the same peculiar circumstance of a dis- engagement of heat, and consequent diminution of bulk, which we have supposed to be produced by a mechanical penetration of par- ticles, by which latent heat is forced out. Alcohol unites thus readily not only with resins and with water, but with oils and balsams; these compounds form the extensive class of elixirs, tinctures, quintessences, &c Emily. I suppose that alcohol must be highly combustible, since it contains so large a proportion of hydrogen. 1185. What is the intoxicating principle in spiritous liquors? 1186. How does it produce this effect? 1187 What are the different kinds cf odoriferous spiritous waters ? 1 lb8 What are some ofthe most peculiar uses of alcohol ? 1189 Why are brandy and other spiritous liquors so combustible. 265 DECOMPOSITION Airs. B. Extremely so; and it will burn at a very moderate temperature. Caroline. I have often seen both brandy and spirit of wine burnt; they produce a great deal of flame, but not a proportional quantity of heat, and no smoke whatever. Mrs. B. The last circumstance arises from their combustion be- ing complete ; and the disproportion between the flame and heat shows you that these are by no means synonymous. The great quantity of flame proceeds from the combustion ofthe hydrogen, to which you know that manner of burning is peculiar.— Have you not remarked also, that brandy and alcohol will burn without wick?—they take fire at so low a temperature, that this assistance is not required to concentrate the heat and volatilize the fluid. Caroline. I have sometimes seen brandy burnt by merely heating it in a spoon. Airs. B. The rapidity of the combustion of alcohol, may, how- ever, be prodigiously increased by first volatilizing. An ingenious instrument has been constructed on this principle to answer the purpose of a blow-pipe, which may be used for melting glass, or other chemical purposes. It consists of a small metallic vessel, (fig. 35.) of a spherical shape, Fig. 35. which contains the alpo- Alcohol Blowpipe. hoi, and is heated by the lamp beneath it; as soon as the alcohol is vola- tilized, it passes thro1 the spout of the vessel, and issues just above the wick of the lamp which immediately sets fire to the stream of vapour, as 1 shall show you.* Emily. With what amazing violence it burns! The flame of alcohol, in the state of vapour, is, I fancy, much hotter than when the D. The lamp.—E. The vessel in which the Alcohol spirit is merelv burnt 's boiling.—F. Safety valve.—G. The inflamed jet or in a sooon steam of alcohol directed towards the glass tube H. Mrs. B. Yes; because in this way the combustion goes on much quicker, and, of course, the heat is proportionally increased.—Ob- * A spirit lamp, which answers very well for bending small glass tubes, may be constructed by almost any one. Take a low vial with a wide mouth, fit a cork to it, and pierce the cork to admit a piece of glass tube, the bore of which is about the size of a large 1190. Why is no smoke produced when brandy or spirit of wine i* burnt ? 1191. Why will brandy and alcohol burn without a wick? 1192. How would you describe the experiment represented in fig. 3 35? 1193. How would you describe the spirit lamp? OF VEGETABLES. 265 serve its effect on this small glass tube, the middle of which 1 pre- sent to the extremity of the flame, where the heat is greatest. Caroline. The glass, in that spot, is become red hot, and bends from its own weight. Mrs. B. 1 have now drawn it asunder, and am going to blow a ball at one ofthe heated ends ; but I must previously close it up and flatten it with this littlu metallic instrument, otherwise the breatii would pass through the tube without dilating any part ofit. —Now Caroline, will you blow strongly into the tube whilst the closed end is red hot ? Emily. You blow too hard; for the ball suddenly dilated to a great size, and then burst into pieces. Mrs. B. You will be more expert another time; but I must cau- tion 3'ou, should you ever use this blow pipe, to be very careful that the combustion of the alcohol does not go on with too great vio- lence, for I have seen the flame sometimes dart out with such force as to reach the opposite wall ofthe room, and set the paint on fire. There is however, no danger ofthe vessel bursting, as it is provi- ded with a safety tube, which affords an additional vent for the va- pour of alcohol when required. The products of the combustion of alcohol consist in a great pro- portion of water, and a small quantity of carbonic acid. There is no smoke or fixed remains whatever.—How do you account for that, Emily ? Emily. I suppose that the oxygen which the alcohol absorbs in burning, converts its hydrogen into water, and its carbon into car- bonic acid gas, and thus it is completely consumed. Alrs.B. Very well.—Ether, the lightest of all fluids, and wilh which you are well acquainted, is obtained from alcohol, of which it forms the lightest and most volatile part. Emily. Ether, then, is to alcohol, what alcohol is to brandy. Mrs.B- No; there is an essential difference. In order to ob- tain alcohol from brandy, you need only deprive the latter of its water ; but for the formation of ether, the alcohol must be decom- posed, and one of its constituents partly subtracted. 1 leave you to guess which of them it is. Emily. It cannot be hydrogen, as ether is more volatile than al- cohol, and hydrogen is the lightest of all its ingredients : nor do I suppose that it can be oxvgen, as alcohol contains so small a pro- portion of that principle ; "it is therefore, most probably, carbon, a diminution of which would not fail to render the new compound more volatile. .,„,,, r .i Mrs B You are perfectly right. The formation of ether con- sists simply in subtracting from the alcohol a certain proportion of carbon ; this is effected by the action ofthe sulphuric, nitric, or mu- e-oose-quill. Let the tube rise an inch or two above the cork- pass some cotton wick through the tube-then fill the vial with al- cohol, and put the cork and tube in .heir places. The lamp is then ready.—C. ' 1194. What is the composition of alcohol? 1195. From what is ether obtained? 1196. How does it differ from alcohol ? 1197 In what does the formation of ether consist ? 23 266 DECOMPOSITION riatic acids, on alcohol. The acid and carbon remain at the bot- tom of the vessel, whilst the decarbonized alcohol flies off in the form of a condensable vapor, which is elher. Ether is the most iuflammable of all fluids, and burns al so low a temperature that the heat evolved during its combustion is more than is required for its support, so that a quantity of ether is vola- tilized, which takes fire, and gradually increases the violence o. the combustion. Sir Humphrey Davy has lately discovered a very singular fact re- specting the vapor of ether. If a few drops of ether be poured in- to a wine glass, and a fine platina wire, heated almost to redness, be held suspended in the glass, close to the surface of the ether, the wire soon becomes intensely red hot, and remains so for any length of time. We may easily try the experiment Caroline. How very curious ! The wire is almost white hot, and a pungent smell rises from the glass. Pray how is this accounted for? Airs. B. This is owing to a very peculiar property ofthe vapor of ether, and indeed of many other combustible gaseous bodies. At a certain temperature lower than lhat of ignition, these vapors un- dergo a slow and imperfect combustion, which does not give rise, iu any sensible degree, to the phenomena of light and flame, and yet extricates a quantity of caloric sufficient to re-act upon the wire, and make it red hot, and the wire in its turn keeps up tbe ef- fect as long as the emission of vapor continues. This singular effect, which is also produced by the alcohol, may be rendered more striking, and kept up for an indefinite length of time, by rolling a few coils of platina wire, of the diameter of from about I-60th to l-70th of an inch, round the wick of a spirit-lamp. If this lamp be lighted for a moment, and blown out again, the wire, after ceasing for an instant to be luminous, becomes red hot again, though the lamp is extinguished, and remains glowing vividly, till the whole ofthe spirit contained in the lamp has been evaporated and consumed in this peculiar manner. Caroline. This is extremely curious. But why should notan iron or silver wire produce the same effect ? Airs. B. Because either iron or silver, being much better con- ductors of heat than platina, the heat is carried off too fast by those metals to allow the accumulation of caloric necessary to produce the effect in question. Ether is so light that it evaporates at the common temperature of the atmosphere ; it is therefore necessary to keep it confined by a well ground glass stopper. No degree of cold known has ever irozen it.* * Ether freezes and shoots into crystals, at 46? below the zero of Fahrenheit.—C. ■ 1198. What is the most inflammable of all bodies ? 1199. What singular effect has Sir H. Davy lately discovered re- specting the vapour of ether ? 1200. How may this effect be rendered more striking ? 1201. Why would not an iron or silver wire produce the same ef- fect ? 1202. At what degree of cold will ether freeze ? OF VEGETABLES. 267 Caroline. Is it not often taken medicinally? Mrs. B. Yes; it is one ofthe most effectual antispasmodic medi- cines, and the quickness of its effects, as such, probably depends, on its being instantly concerted into vapor by the heat of the stomach, through the in'ervention of which it acts on the nervous system. But the frequent use of ether, like that of spiritous liquors, becomes prejudicial, and, if taken to excess, it produces effects similar to those of intoxication. We may now take our leave ofthe vinous fermentation, of which, I hope, you have acquired a clear idea: as well as of the several products that are derived from it. Caroline. Though this process appears, at first sight, so much complicated, it may, I think, be summed up in a few words, as it con-ists in the conversion of sugar and fermentable bodies into al- cohol and carbonic acid, which gives rise both to the formation of wine, and of all kinds of spiritous liquors. Airs. B. We shall now proceed to the acetous fermentation, which is thus called, because it converts wine into vinegar, by the forma- tion of the acetous acid, which is the basis or radical of vinegar. Caroline. But is not the acidifying principle ofthe acetous acid the same as that of all other acids, oxygen ? Airs. B. Certainly : and on that account the contact of air is es- sential to this fermentation, as it affords the necessary supply of oxygen. Vinegar, in order to obtain pure acetous acid from it, must be distilled and rectified by certain processes. Emily, But pray, Mrs. B., is not the acetous acid frequently formed without this fermentation taking place? Is it not, for in- stance, contained in acid fruits, and in every substance that be- comes sour? Airs. B. No, not in fruits ; you confound it with the citric, the malic, the oxalic, and other vegetable acids, to which living vege- tables owe their acidity. But whenever a vegetable substance turns sour, after it has ceased to live, the acetous acid is developed by means of the acetous fermentation, in which the substance ad- vances a step towards its final decomposition. Amongst the various instances of acetous fermentation that of bread is usually classed. Caroline. But the fermentation of bread is produced by yeast; how does that effect it ? Mrs. B. It is found by experience that any substance that has already undergone a fermentation, will readily excite it in one that is susceptible of that process. If, for instance, you mix a little vine- -gar with wine, that is intended to be acidified, it will absorb oxygen more rapidly, and the process be completed much sooner than if left to ferment spontaneously. Thus yeast, which is a product of the fermentation of beer, is used to excite and accelerate tbe fermenta- 1203. How may the process of the vinous fermentation be ex- pressed in a few words ? 12i'4 Why is the third fermentation called acetous? 1205^ Why is the contact of air necessary to produce the acetous feri206.aWhat is the reason that wine, or cider, when corked tight, fines not turn to vinegar ? 1207. How is the fermentation of bread produced by yeast ? 268 DECOMPOSITION tion of malt, which is to be converted into beer, as well as that of paste, which is to be made into bread. Caroline. But if bread undergoes the acetous fermentation, why is it not sour ? Mrs. B. It acquires a certain savour which corrects the heavy insipidity of flour, and may be reckoned a first degree of acidifica- tion, or if the process were carried further, the bread would become decidedly acid. There are, however, some chemists who do not consider the fer- mentation of bread as being ofthe acetous kind, but suppose, that it is a process of fermentation peculiar to that substance. The putridfermentation is the final operation of Nature and her last step towards reducing organized bodies to their simplest combi- nations. All vegetables spontaneously undergo this fermentation after death, provided there be a sufficient degree of heat and mois- ture, together with access of air; for it is well known that dead plants may be preserved by drying, or by the toial exclusion of air. Caroline. Bui do dead plants undergo the other fermentations previous to this last; or do they immediately suffer the putrid fer- mentation ? Airs. B. That depends on a variety of circumstances, such as the degreesof temperature and of moisture, the nature of the plant itself, &c. But ifyou were carefully to follow and examine the decompo- sition of plants from their death to their final dissolution, you would generally find a sweetness developed in the seeds, and aspiritous fla- vour in the fruits (which have undergone tbe saccharine fermenta- tion,) previous to the totaldisorganization and separation of the parts. Emily. 1 have sometimes remarked a kind of spiritous taste in fruits that were over ripe, especially oranges, and this was just be- fore they became rotien. Airs B. It was Iben the vinous fermentation, which had succeed- ed the saccharine, and had you tollowed up thesechanges attentive- ly, you would probably have found the spiritous taste followed by acidity, previous lo the fruit passing to the state of putrefaction, When the leaves fall from the trees in the autumn, they do not (if there is no great moisture in the atmosphere) immediately undergo a decomposition, but are first dried and withered; as soon, howev- er, as the rain sets in, fermentation commences, their gaseous pro- ducts are imperceptibly evolved into (he atmosphere, and their fix- ed remains mixed with their kindred earth. Wood, when exposed to moisture, also undergoes the putrid fer- mentation, and becomes rotten. Emily. But I have heard lhat \hedr>, rot, which is so liable to de- stroy the beams of houses, is prevented by a current of air ; and yet you said that the air was essential to the putrid fermentation ? Airs. B. True ; but it must not be in such a proportion to the moisture as to dissolve the latter, and this isgenerally the case when 1208. Why then is it not sour ? • 1209. What is the final fermentation in reducing organized bodies to their simplest combinations? 1210. What is mentioned of oranges, and other over-ripe fruit, as illustrating the above principle of fermentation ? 1211. What is said of the fermentation of leaves ? * 1212. How may the dry rot be prevented ? OF VEGETABLES. 269 the rotting of wood is prevented or stopped by the free access of air. What is commonly called dry rot, however, is not, I believe, a true process of putrefaction. It is supposed to depend on a peculiar kind of vegetation, which by feeding on the wood gradually destroys it. Sti aw and all other kinds of vegetable matter undergo the putrid fermentation more rapidly when mixed with animal matter. Much heat is evolved during this process, and a variety of volatile products are disengaged, as carbonic acid and hydrogen gas, the latter of which is frequently either sulphurated or phosphorated. When all these gases have been evolved, the fixed products, consisting of carbon, small quantities of salts, potash, &c. form a kind of veget- able earth, which makes very fine manure, as it is composed of those elements which form the immediate materials of plants. Caroline. Pray are not vegetables sometimes preserved from de- composition by petrifaction ?'* I have seen very curious specimensof petrified vegetables, in which state they perfectly preserve their form and organization, though in appearance they are changed to stone. Mrs. B. That is a kind of metamorphosis, which, now that you are tolerably well versed in the history of mineral and vegetable substances, 1 leave to your judgment to explain. Do you imagine that vegetables can be converted into stone? Emily. No, certainly ; but they might, perhaps, be changed lo a substance in appearance resembling stone. Mrs B. It is not so, however, with the substances that are call- ed petrified vegetables; for these are really stone, and generally of the hardest kind, often consisting chiefly of silex. The case is this : when a vegetable is buried under water, or wet in earth, it is slow- ly and gradually decomposed. As each successive particle of the vegetable is destroyed, its place is supplied by a particle of silicious earth, conveyed thither by the water In the course of time the vegetable is entirely destroyed, but thesilex has completely repla- ced it, having assumed its form and apparent texture, as if the ve- getable itself were changed to stone. Caroline. That is very curious ! and I suppose that petrified an- imal substances are of the same nature ? Mrs. B. Precisely. It is equally impossible for either animal or vegetable"substance's to be converted into stone. They may be re- duced, as we find they are, by decomposition, to their constituent elements, but cannot be changed to elements which do not enter into their composition. ^^^ * Pitrefactions are of two kinds, viz. siliceous, when flinty parti- cles take the place of the original substance, and calcareous where the substance appears to be changPdI to lime-stone. The first kind gives fire with steel, and the other effervesces with acids.—O. 1213 On what is the dry rot supposed to depend ? 1214' Why will animal matter, mixed with straw and other veg- etable s'ubstances, hasten fermentation ? 121-3 What are vegetable petrifactions . 1216 How are vegetable petrifactions formed? M2I7! [low many kinds of petrifactions are there? 1.18 What are they called, and what are their properties , 23* 270 DECOMPOSITION OF VEGETABLES. There are, however, circumstances which frequently prevent the regular and final decomposition of vegetables: as for instance, when they are buried either in the sea or in the earth, wheie ihey cannot undergo the purtid fermentation for want of air. In these cases they are subject to a peculiar change, by which they are convert- ed into a new class ot compounds called bitumens. Caroline. These are substances 1 never heard of before. Airs. B. You will find, however, that some of them are very fa- miliar to you. Bii umens are vegetables so far decomposed as to re- tain no organic appearance ; but their origin is easily delected by their oily nature, their combustibiliy, the products ol their analy- sis, and the impression of the forms of leaves, grains, fibres of wood, and even ofaninuls, which they frequently bear. They are sometimes of an oily, liquid consistence, as the sub- stance called naptha,* in which we preserved potassium; it is a fine transparent, colorless fluid, that issues out of clays in some parts of Persia. But more frequently bitumens are solid, as asphallum, a smooth, hard, brittle substance, which easily melts, and forms, in its liquid state, a beautiful dark brown color for oil painting. Jet, which is of a still harder texture, is a peculiar bitumen, susceptible of so fin3 a polish, that it is used for many ornamental purposes. Coal isal^o a bituminous substance, to the composition of which both Ihe m neral and animal.kingdoms seem to concur. This most useful mineral appears to consist chiefly of vegetable matter, mix- ed with the remains of marine animals and marine salts, and occa- sionally containing a quantity of sulphuret of iron, commonly call- ed p\ rites. Emily It is, 1 suppose, the earthy, the metallic, and the saline par's of coals, that compose Ihe cinders or fixed products of their combustion; whilst the hydrogen and carbon, which they derive from vegetables, constitute their volatile products. Caroline. Pray is not coke, (which I have heard is much used in some manufactures,) also a bituminous substance ? Airs. B. No; it is a kind of fuel artificially prepared from coals. It consists, of coals reduced to a substance analogous to charcoal by the evaporation of their bituminous parts. Coke, therefore, is com- posed of carbon, with some earthy and saline ingredients. Succin, or yellow amber, is a bitumen which the ancients called eleclrum, from whence the word electricity is derived, as that sub- stance is peculiarly, and was once supposed to be exclusively elec- tric. It is found either deeply buried in the bowels ofthe earth, or * Naptha appears to be the only fluid in which oxygen does not exist; hence its property of preserving potassium which has so strong an affinity for oxygen as to absorb it from all o'.her fluids. It however loses this property by exposure to the atmosphere, pro- bably, because it absorbs a small quantity of air, or moisture. It is again restored by distillation.—C. 12' 9. What are bitumens, and how are they formed ? 1220. What is asphallum ? ' 1221. What is jet? 1222. What is coal? 1223. How does coke differ from coal ? • 1224. What is yellow amber? VEGETATION; 271 floating oh the sea, and is supposed to be a resinous body which has been acted on by sulphuric ac d, as its analysis shows it to Consist of an oil and an acid. The oil is called oil of amber: the acid the sucannic. Emily. That oil I have sometimes used in painting, as it is reck' oned to change less than the other kinds of oil. Airs. B. The last class of vegetable substances that have chang- ed their nature are fossil-wood, peat, and turf. These are compos- ed of wood and roots of shrubs, that are partly decomposed by being exposed to moisture under ground, and yet in some measure, pre- serve their form and organic appearance. The peat, or black earth ofthe moors, retains but few vestiges of the roots to which it owes its richness and combustibility, these substances being in the course of time, reduced to the state of vegetable earth. But in turf the roots of plants are still discernible, and it equally answers the pur- pose of fuel. It is the combustible used by the poor in heathy countries, which supply it abundantly. It is too late this morning to enter into the history of vegetation, We shall reserve the subject, therefore, to our next interview, when I expect that it will furnish us with ample matter for another conversation; CONVERSATION XXII* HISTORY OF VEGETATION. Mrs. B. The vegetable kingdom may be considered as the link which unites the mineral and animal creation into one common chain of beings; for ii is throUgh the means of vegetation alone lhat mineral substances are introduced into the animal system; since, generally speaking, it is.from vegetables that all animals ultimate- ly derive their sustenance. Caroline. I do not understand that; the human species subsist as much on animal as on vegetable food. Airs. B. That is true; but you do not consider that those that live on animal food derive their sustenance equally, though not so immediately, from vegetables. The meat which we eat is formed from the herbs ofthe field, and the prey of carniverous animals pro- ceeds either directly or indirectly from the same source. It is, therefore, through this channel, that the simple elements become a part of the animal frame. We should in vain attempt to derive nourishment from carbon, hydrogen, and oxygen, either in their separate state or combined in the mineral kingdom ; for it is only . 1225. Where is it found ? 1226. What are fossil-wood, peat and turf? 1227! Why does naptha preserve potassium? 1228. What is considered as uniting the mineral and animal •reation? .,,.,- 2 > 1229 From whence do all animals der.ve their sustenance ? 1230! In what state are carbon, hydrogen, and oxygen capable of affording nourishment ? 272 VEGETATION. by being united in the form of vegetable combination that they be- come capable of conveying nourishment. Emily. Vegetation, then, seems to be the method which Nature employs to prepare the food of animals? Mrs. B. That is certainly its principal object. The vegetable creation does not exhibit more wisdom in that .idmirable system of organization, by which it is enabled to answer iis own immediate ends of preservation, nutrition and propagation, than in its grand and ultimate object of forming those arrangemc nts and combina- tions of principles, which are so well adapted for tbe nourishment of animals,. Emily. But I am very curious to know whence vegetables ob- tain those principles which form their immediate materials? Mrs. B. This is a point on which we are yet so much in the dark that I cannot hope fully to satisfy your curiosity ; but what little I know on this subject, 1 shall endeavor to explain 10 you The soil which at first view, appears to be the element of vegeta- bles, is found on a closer investigation, to be li tie more than tbe channel through which they receive their nourishment; sothalitis very possible to rear plants without any earth or soil.* * The opinion that water is the only food of plants, was adopted by the learned on this subject in the 17th century : and many ex- periments were made which seemed to prove that this was the truth. Among others was a famous one by Van Hehnont, which for a long time was supposed to have established the point beyond all doubt. He planted a willow which weighed five pounds, in an earthen vessel containing 200lbs. of dried earth. This vessel was sunk into the ground, and the tree was watered, sometimes with distilled, and sometimes with rain water. At the end of five years the willow weighed 169lbs.; and on weighing the soil, dried as before, it was found to have lost only two ounces. Thus the willow had gained l64lbs., and yet its food had been only water. The induction from this experiment was obvious. Plants live on pure water. This. therefore, was the general opinion until the progress of chemistry detected its fallacy. Bergman, in 1763, showed by some experiments, that the water which Van Hel- mont had used, contained as much earth as could exist in the tree at the end of the five years ; a pound of water contained about a grain of earth. So that this experiment by no means proved that the willow lived on water alone. Since this time a great variety of experiments have been made for the purpose of deciding what was the food of plants. In the course of these it has been found, that although seeds do vegetate in pure distilled water, yet the plant is weakly and finally dies before the fruit is matured. It is pretty eertain, then, that earth is absolutely necessary to the growth of plants, and that a part of their food is taken from the soil. Indeed, the well known fact that a soil is worn out by along succes- 1231. Do vegetables receive their chief aliment from the soil in which they grow ? 1232. What experiment was made byllelmonl lo ascertain the nour- ishment of vegetables ? • 1233. What will be the condition of plants in pure water only ? VEGETATION. 273 Caroline. Of that we have an instance in the hyacinth and other bulbous roots, which will grow and blossom beautifully in glasses of water. Rut I confess I should think it would be difficult to rear trees in a similar manner. Mrs. B. No doubt it would, as it is the burying ofthe roots in the earth that supports the stem of the tree. But this office, be-ides that of affoidin^ a vehicle for food, is far the most important part which the earthy portion ofthe soil performs in the process of ve- getation ; for we can discover by analysis, bul an extremely small proportion of earth in vegetable compounds. Cai dine. But if earths do nol afford nourishment, why is it ne- cessary to be so attentive to the preparation of the so 1 ? Airs. B. In order to impart lo it those qualities which render it a proper vehicle for the food of the plant. Waler is IheChief nour- ishment of vegetables ; if, therefore, the soil be too sandy, it will not retain a quantity of water sufficient to supply the rools ofthe plants. If, on the contrary, it abounds loo much with clay, the water will lodge in such quantities a- to threaten a decomposition ofthe roots. Calcareous soils are, upon the whole, the most favorable to the growlh of plants: soils are, therefore, usually improved by chalk, which you may recollect, is carbonat oflime. Different vegetables however, require different kinds of soils. Thus, rice demands a most retentive soil; potatoes, a soft sandy soil; wheat, a firm and r'ich soil. Forest trees grow beter in fine sand, than in a stiff clay ; and a light ferruginous soil is best suited to fruit trees. Caroline. But pray what is the use of manuring the soil? Airs. B. Manure consists of all kinds of substances whether of vegetable or animal origin, which have undergone the putrid fer- sion of crops, and finally becomes steril unless manured, is good proof that plants do absorb something from it. Saussure has shown that this is the fact, and also that the earth, which is always found in plants, is of the same kind as that on which they grow. Thus trees growing in a granitic soil,contain a large proportion of silica, while those growing in calcareous soil, contain little silica, but a great proportion of calcareous earth In addition to what plants absorb from the ground, there is no doubt but they obtain a part of their nourishment from water and air. Some experiments made at Berlin, show that wheat barley, Sue. contain a quantity of earth though fed only on distilled water. From the air, plants absorb carbonic acid gas. The carbon they retain, which forms the greatest part of their bulk. The oxygen is emitted and goes to purify the atmosphere. Thus it is seen that plants obtain their food from the earth, from water, and from the air.—C. 1234. What facts did Suassure discover relating to this subject ? * 1235. Whence do plants derive their food ? 1236. If earths do not afford nourishment, why is it necessary to be so particular in enriching the soil ? 1237. What is the nourishment of vegetables i 1238. What is the consequence to vegetables if the soil is too 1239. What if it abounds too much with clay ? 274 VEGETATION. mentation, and are consequently decomposed, or nearly so, into their elementary principles. And it is requisite that these vegeta- ble matters should be in a state of decay, or, approaching decompo- sition. The addition of calcareous earth, in the state of chalk or lime, is beneficial to such soils, as it accelerates the dissolution of vegetable bodies. Now I ask you, what is the utility of supplying the soil with these decomposed substances? Caroline. It is, I suppose, in order to furnish vegetables with the principles which enter into their composition. For manures not only contain carbon, hydrogen and oxygen, but by their decompo- sition supply the soil with these principles in their elementary form.* Mrs. B Undoubtedly ; and it is for this reason that the finest crops are produced in fields that were formerly covered with woods, because their soil is composed of a rich mould, a kind of vegetable earth which abounds in those principles. Emily. This accounts for the plentifulness of the crops produced in America, where the country was, but a few years since, covered with wood. Caroline. But how is it that animal substances are reckoned to produce the best manure? Does it not appear much more natural that the decomposed elements of vegetables should be the most ap- propriate to the formation of new vegetables ? Mrs. B. The addition of a much greater proportion of nitrogen, which constitutes the chief difference between animal and veget- able matter, renders the composition ofthe former more complica- ted and consequently more favorable to decomposition. Indeed the use of animal substance is chiefly to give the first im- pulse to the fermentation of the vegetable ingredients that enter in- to the composition of manures. The manure of a farm yard is of that description; but there is scarcely any substance susceptible of undergoing the putrid fermentation, that will make good manure. The heat produced by the fermentation of manure is another cir- cumstance which is extremely favorable to vegetation; yet this heat would be too great if the manure was laid on the ground dur- ing the height of fermentation ; it is used in this state only for hot- beds to produce melons, cucumbers, and such vegetables as require a very high temperature. Caroline. A difficulty has just occurred to me which I do not know how to remove. Since all organized bodies are, in the com- mon course of nature ultimately reduced to their elementary state, they must necessarily in that state enrich the soil, and afford food for vegetation. How is it, then, that agriculture, which cannot in- crease the quantity of those elements that are required to manure theearth, can increase its produce so wonderfully, as is found to be the case in all cultivated countries? * But what is the use of all this, if " water is the chief nourish- ment of vegetables ?''—C. 1240. What is the use of decomposed substances as is found in manure ? »1241. Why are the best crops produced on new lands, or where they weie recently covered with wood? 1242. Why do animal substances make the best manure ? VEGETATION. 275 Airs. B. It is by suffering none of these decaying bodies lo be dispersed and wasted, but in applying them duly to the soil.: It is also by a judicious preparation of the soil, which consists in fitting it either for the general purposes of vegetation, or for that of the particular seed which is to be sown. Thus, if the soil be too wet, it may be drained ; if too loose and sandy it may be rendered more consistent and retentive of water by Ihe addition of clay or loam ; it may be enriched by chalk, or any kind of calcareous earth. On soils thus improved, manures will act with double efficacy ; and if attention be paid to spread them on the ground at a proper season ofthe year, to mix them with the soil, so that they may be general- ly diffused through it, to destroy the weeds which might appropri- ate these nutritive principles to their own use, to remove the stones which would impede the growth of the plant, we may obtain a pro- duce an hundred fold more abundant than the earth would sponta- neously supply. Emily. VVe have a very striking instance of this in the scanty produce of uncultivated commons, compared to the rich crops of meadows which are occasionally manured. Caroline. But, Mrs. B., though experience daily proves the ad- vantages of cultivation, there is still a difficulty which I cannot get over. A certain quantity of elementary principles exist in nature, which it is not in the power of man either to augment or diminish. Of these principles you have taught us that both the animal and ve- getable creation are composed. Now the more of them is taken up by the vegetable kingdom, the less it would seem will remain for animals; and therefore the more populous the earth becomes, the less it will produce. Alrs.B. Your reasoning is very plausible; but experience ev- ery where contradicts the inference you would draw from it; since we find that the animal and vegetable kingdoms instead of thriving as you would suppose, at each other's expense, always increase and multiply together. For you should recollect that animals can derive the elements of which they are formed only through the me- dium of vegetables. And you must allow that your conclusion would be valid only if every particle of the several principles that could possibly be spared from other purposes, were employed in the animal and vegetable creations. Now we have reason to be- lieve that a much greater proportion of these principles than is re- quired for such purposes, remains either in an elementary state, or engaged in a less useful mode of combination in the mineral king- dom. Possessed of such immense resources as the atmosphere and the waters afford us, for oxygen, hydrogen and carbon, so far from being in danger of working up all our simple materials, we cannot suppose that we shall ever bring agriculture lo such a degree of per- fection as to require the whole of what these resources could supply. Nature, however, in thus furnishingus with an inexhaustible stock 1243. How is it that agriculture, which cannot increase the quanti- ty of those elements that are required to manure the earth, so greatly increase its vegetable products? . 1244. Of what are the vegetable and animal creation composed ? 1245. What objection is made to the principle stated for the increase of vegetable productions? 1246. How is this objection answered ? 276 VEGETATION. of raw materials, leaves it in some measure to the ingenuity of man to appropriate them to his own purposes. But, like a kind parent, she stimulates him to exertion, by setting the example, and point- ing out the way. For jt is on the operations of nature that all the improvements of art are founded. The art of agriculture consists, therefore, in discovering ihe readiest method of obtaining ihe seve- ral principles, either from their grand sources, air and water, or from the decomposition of organized bodies; and in appropriating them in the besl manner lothe purposes of vegetation. Emily. But, among the sources of nutritive principles, I am sur- prised that you do not mention the eartlritself, as it contains abun- dance of coals, which are chiefly composed of carbon. Mrs. B. Though coals abound in carbon, they cannot on ac- count of their hardness and impermeable texture, be immediately subservient to the purposes Df vegetation; and, we find, on the con- trary, lhat coal districts are generally barren. Emily. No; but by their combustion, carbonic acid is produced; and this entering into various combinations on the surface of the earth, may, perhaps, assist in promoting vegetation. Mrs. B. Probably it may in some degree; but at any rate, the quantity of nourishment which vegetables may derive from that source can be but very trifling, and must entirely depend on local circumstances. Caroline. Perhaps the smoky atmosphere of London is the cause of vegetation being so forward and so rich in its vicinity ? Alrs.B. I rather believe that this circumstance proceeds from the very ample supply of manure, assisted, perhaps, by the warmth and shelter, which the town affords. Far from attributing anj good to the smoky atmosphere of London, I confess I like to anticipate the time when we shall have made such progress in the art of managing com- bustion that every particle of carbon will be consumed, and the smoke destroyed at the moment of its production. We may then expect to have the satisfaction of seeing the atmosphere of London as clear as that of the country. But to return to our subject; lhope that you are now convinced that we shall not easily experience a deficiency of nutritive elerents to fertilize the earth, and thai pro- vided we are but industrious in applying them to the best advan- tage by improving the art of agriculture, no limits can be assigned to the fruits that we may expect to reap from our labors. Caroline. Yes: I am perfectly satisfied in that respect, and lean assure you that I feel already much more interested in the progress and improvement of agriculture. Emily. I have frequently thought that the culture of the land was not considered as a concern of sufficient importance. Manufactures always lake the lead; and health and innocence are frequently sa- crificed to the prospect of a more profitable employment. It has often grieved me to see the poor manufacturers crowded together 1247. In what does the art of agriculture consist? 1248. Why cannot coals be immediately subservient to the purpo- ses of vegetation ? '■ 1249. Is there any occasion to apprehend a deficiency of nutritive •lements to fertilize the earth ? - 1250. What objection is made to manufactures ? VEGETATION. 277 m close rooms, and confined for the whole day to the most uniform and sedentary employment, instead of being engaged in that inno- cent and salutary kind of labor, which Nature seems to have as- signed to man for the immediate acquirement of comfort, and for the preservation of his existence. I am sure that you agree with me, in thinking so, Mrs. B. Mrs. B. I am entirely of your opinion, my dear, in regard to tbe importance of agriculture ; but as the conveniences of life, which we are all enjoying, are not derived merely from the soil I am far from wishing to depreciate manufactures. Besides, as the labor of one man is sufficient to produce food for several, those whose in- dustry is not required in tillage must do something in return for the food that is provided for them. They exchange, consequently, the accommodations for the necessaries of life. Thus the carpenter and the weaver lodge and clothe the peasant, who supplies them with their daily bread. The greater stock of provisions, therefore which the husbandman produces, the greater is the quantity of accommo- dation which the artificer prepares. Such are the happy effects which naturally result from civilized society. It would be wiser, therefore, to endeavour to improve the situation of those who are engaged in manufactures, than to indulge in vain declamations on the hardships to which they are too frequently exposed. But we must not yet take our leave ofthe subject of agriculture ; we have prepared the soil, it remains for us now to sow the seed.— In this operation, we must be careful not to bury it too deep in the ground, as ihe access of air is absolutely necessary to its germina- tion ; the earth must, therefore, lie loose and light over it, in order that the air may penetrate. Hence the use of ploughing and dig- ging, harrowing and raking, &c. A certain degree of heat and moisture, such as usually takes place in the spring, is likewise ne- cessary. Caroline. One would imagine you were going to describe the decomposition of an old plant, rather than the formation of a new one ; for you have enumerated all the requisites of fermentation. Airs. B. Do you forget, my dear, that the young plant derives its existence from the destruction ofthe seed, and thai it is actually by the saccharine fermentation that the latter is decomposed ? Caroline. True; I wonder that I did not recollect that. The tem- perature and moisture required for the germination of the seed is then employed in producing the saccharine fermentation within it? Mrs. B. Certainly. But, in order to understand the nature of germination, you should be acquainted with the different parts of which the seed is composed. The external covering or envelope contains, besides the germ ofthe future plant, the substance which is to constitute its first nourishment; this substance which is call- ed the parenchyma, consists of fecula, mucilage, and oil, as we for- merly observed. 1251. For how many persons can one man in agricultural labour produce food ? 1252. Why is this a reason for encouraging manufactures ? 1253. What is the use of ploughing, digging, harrowing, raking, &c, in agriculture.? 278 VEGETATION. The seed is generally divided into two compartments called lobes, or cotyledons, as is exemplified by this bean, (Fig. 36,)—the dark (Fig. 36.) coloured kind of string which divides the lobes is ^-^. >*-v called tbe radicle, as it forms the root ofthe plant, fT \j ^V and it is from a contiguous substance, called plu- W Pif) // mu/a, which is enclosed within the lobes, that the \\ III/ (j stem arises.—The figure and size ofthe seed depend M \fl JJ very much upon the cotyledons; these vary in num- \^/V^' ber in different seeds; some have only one, as ) wheat, oats, barley, and all the grasses ; some have three, others six. But most seeds, as for instance, all the varieties of beans, have two cotyledons. When the seed is buried in the earth,atany temperature above40 degrees, it imbibes water, which softerts and swells the lobes ; it then absorbs oxygen, which com- bines with some of its carbon, and is returned in the form of car- bonic acid. This loss of carbon increases the comparative propor- tion of hydrogen and oxygen in seed, and excites the saccharine fermentation by which the parenchymatious matter is converted into a kind of sweet emulsion. In this form it is carried into the radicle by vessels appropriated to that purpose ; and in the mean- time, the fermentation having caused the seed to burst, the cotyle- dons areVent asunder, the radicle strikes into the ground and be- comes the root of the plant, and hence the fermented liquid is con- veyed to tbe plumula, whose vessels have been previously distended by the heat of the fermentation. The plumula being thus swelled, as it were, by the emulsive fluid, raises itself and springs up to the surface ofthe earth, bearing with it the cotyledons, which, as soon as they come in contact with the air, spread themselves, and are transformed into leaves.—If we go into the garden, we shall prob- ably find some seeds in the state in which I have described. Emily. Here are some little lupines that are just making their appearance above ground. Mrs. B. We shall take up several of them to observe their differ- ent degress of progress in vegetation. Here is one that has but recently burst its envelope—do you see the Utile radicle striking downwards ? (Fig. 37, No. I.) In this the plumula is not yet visi- ble. But here is another in a greater state of forwardness—the plumula, or stem, has risen out of the ground, and the cotyledons are converted! into seed-leaves* (Fig. 37, No. 2.) Caroline. These leaves are very thick and clumsy, and, unlike the other leaves, which I perceive are just beginning to appear. Mrs. B. It is because they retain the remains of the parenchyma, with which they still continue to nourish the young plant, as it has not yet sufficient roots and strength to provide for its sustinence from the soil. But, in this third lupine, (Fig. 37, No. 3.) the radicle had sunk deep into the earth, and sent out several shoots, each of J 254. What part ofthe seed is called cotyledons ? 1255. Wrhatpart is called radicle? 1256. What part is called plumula? ; 1257. At what temperature will seeds germinate ? 1258. How would you describe the process of germination ia seeds ? 1259. What do Nos. 1 and 2 of Fig. 37, represent ? ,1260. What does No. 3, in Fig. 37, represent? VEGETATION. 279 which is furnished with a mouth to suck up nourish- ment from the soili the func- tion of the original leaves, therefore, being no longer re- quired, they are gradually de- caying, and the plumula is be- come a regular stem, shoot- ing out small branches, and I spreading its foliage. ' Emily. There seems to be a very stnkinganalogy between a seed and an egg; both require an elevation of temperatu re to be brought to life; both at first supply with alimenttheorgan- ized being which they pro- duce; and as this has attained sufficient strength to procure its own nourishment, the egg- shell breaks whilst in the plant the seed leaves fall off. Airs. B. There is certainly ksome resemblance between these processes ; and when Fig. 36 and 37, No. 1. A B, Cotyledon. C,y0u become acquainted with Envelope. D, Radicle. Fig. 37,No. 21. A B, j y cnemistry J0U wjjl Cotyledons. C, Plumula. D,Radicle. Fig.37* ".. ,a _t;* il milh ;,E No. 3. A B, Cotyledon. C,Plumula. D.Radiclefrequently be struck with its analogy to that «f the vegeta- ble kingdom As soon as the young plant feeds, from the soil, it requires the assistance of leaves, which are the organs by which it throws off its super-abundant fluid ; this secretion is much more plentiful in the vegetable than in the animal creation, and the great extent of sur- face of the foliage of plants is admirably calculated for carrying it on in sufficient quantities. This transpired fluid consists of little more than water. The sap, by this process, is converted into a liquid of greater consistence, which is fit to be assimilated to its several parts. ... . , •, . Emily. Vegetation, then, must be essentially injured by destroy- ing the leaves of the plant Mrs. B. Undoubtedly ; it not only diminishes the transpiration, but also the absorption by the roots;; for the quantity of sap ab- sorbed is always in proportion to the quantity of fluid thrown off by transpiration. You see, therefore, the necessity that a young plant should unfold its leaves as soon as it begins to derive its nourish- ment from the soil; and, accordingly, you will find that those lupines which have dropped their seed-leaves, and are no longer 1261. What purposes do the leaves of vegetables answer during their growth ? .-«*_, j 1262. What will be the injury to vegetation if the leaves are de- stroyed ? 280 VEGETATION. fed by the parenchyma, have spread their foliage, in order to per- form the office just described. But 1 should inform you that this function of transpiration seems to be confined to the upper surface of the leaves, whilst on the con- trary, the lower surface, which is more rough and uneven, andfurr nished with a kind of hair or down, is destined to absorb moisture^ or such other ingredients as the plant derives from the atmosphere. As soon as a young plant makes its appearance above ground, light, as well as air, bee mes necessary to its preservation. Light is essential to the developement of the colors, and to the thriving of the plant. You may have often observed what a predilection vegetables had for the light. If you make any plants grow in a room, ihey all spread their leaves and extend their branches to- wards the windows. Caroline. And many plants close up their flowers as soon as it is dark. Emily. But may not this be owing to the cold and dampness of the evening air? Mrs. B. That does not appear to be the case; for in a course of curious experiments, made by Mr. Senebier of Geneva, on plants which he reared by lamp-light, he found that the fluwers closed their petals whenever the lamps were extinguished. Emily. But, pray, why is air essenTial to vegetation? Plants do not breathe it like animals. Mrs. B. At leasl not in the same manner ; but they certainly derive some principles from the atmosphere, and yield others to it. Indeed, it is chiefly owing to the action of the atmosphere, and the vegetable kingdom on each other, that the air continues always fit for respiration. But you will understand this better when I have explained ihe effect of water on plants. i have said lhat water forms the chief nourishment of plants; it is the basis not only of the sap, but of all the vegetable juices. > Wa- ter is the vehicle which carries into the plant the various salts and other ingredients required for the formation and support of thevege- table s) stem. Nor is this all; part of the water itself is decomposed by the organs ofthe plant; the hydrogen becomes a constituent part of oil, of extract, of coloring matter, &c., whilst a portion of the oxygen enters into the formation of mucilage, of fecula, of sugar, and of vegetable acids. But the greater part of the oxygen proceed- ing from the decomposition of the water is converted into a gase- ous state by the caloric disengaged from the hydrogen during its condensation in the formation of the vegetable materials. In this state (he oxygen is transpired by the leaves of plants when exposed to the sun's rays. Thus you find that the decomposition of water, by the organs of the plant, is not only a means of supplying it with its chief ingredient, hydrogen, but at the same time of replenishing the atmosphere with oxygen, a principle which requires continual renovation, to make up for the great consumption of it occasioned 1263. How does the under side of leaves differ from the upper side? 1264. Of what use is light in the growth of vegetables ? 1265 Of what use is air in vegetation ? 1266. How are the various salts and other ingredients required for ihe formation and support of the vegetable system carried into plants ? VKGETATION. 281 by the numerous oxygenations, combustions, and respirations, that are constantly'taking place on the surface of the globe.* Emily. What a striking instance ol the harmony of nature' Mrs B. And how admirable the design of Providence, who makes every different part of the creation thus contribute to the support and renovation of each other? But the intercourse of the vegetable and animal kingdoms, through the medium of the atmosphere extends -till furthcr.C Ani- mals, in breathing, not only consume the oxygen of the air, huf load it with carbonic acid, which, if accumulated in the almost here, would in a short time, render it to'ally unfit for respiration Here Ihe vegetable kingdom again interferes ; it atlracts and decomposes the carbonic acid, retains the carbon for its own purposes and re- turns the oxygen for ours.f Caroline. How interesting this is! I do not know a more beauti- ful illustration of the wisdom which is displayeil in tbe laws of na- ture. Airs. B. Faint and imperfect as are the ideas which our limited perceptions enable us to form of divine wisdom, still they cuinot fail to inspire us with awe and admiration. What, then, would be our feelings, were the complete system of nature at once displayed before us! So magnificent a scene would probably be too great for our limited compi ehension ; and it is, no doubt, among the wise dis- * The foregoing paragraph might mislead the student. Indeed it seems to have been written without regard to proper authorities. For instance, there is no proof that water is decomposed by the or- gans of plants ; nor is il in the least degree probable that the oxy- gen emitted by them owes its gaseous state, to the caloric set free by the condensation of hydrogen. Authors on this subject agree that the thickest veil covers the process by which the sap is con- verted into the several parts ofthe plant. But it has been demon- strated, that most, if not all the oxygen emitted by Ihe leaves, is obtained by the decomposition of air, instead of water, as here stated. If leaves are exposed to the rays of the sun, while under common water, Ihey emit oxygen. But if the water is first deprived of its air, by an air pump, or by boiling, not a particle of oxygen is emit- ted. Now, atmospheric air, always contains a quantity of carbonic acid gas, and experiments show, that plants give out oxygen in some proportion to the quantity of this gas contained in the water. The fact ihen seems to be, that plants absorb carbonic acid, that this is decomposed by gome unknown process; the plant retaining the carbon, while the oxygen is given out.—C. fit is a curious fact, demonstrated by experiments, that'the leaves of plants perform different offices at different pc.i iods of the 24 hours. During the day they give out water, absorb carbonic acid, and emit oxygen gas; but during the night they absorb wa- ter, and oxygen gas, and give out carbonic acid.—C. 1267. How do animal and vegetable life mutually support each oth- er? 1268. What curious fact is staled ofthe leaves of vegetables in the note / 1269. Whatin the organization of nature is particularly suited to the rational powers of man ? 24* •282 VEGETATION. pensation of Providence, to veil the splendor of a glory with which we should be overpowered. But it is well suited to a rational being ? to explore step by step, the works of }he creation, to endeavor to connect ihem into harmonious systems'; and, in a word, to Irace, in the chain of beings, the kindred ties and benevolent design which unites its various links, and secures its preservation. Caroline. But of what nature are the organs of plants which are endued with such wonderful powers? Mrs B. They are so minute that their structure, as well as the mode in which they perform their functions, generally elude our ex- amination ; but we miy consider them as so many vessels or appa- ratus appiopriated to perform, with the assistance of the principle of life, certain chemical processes, by means of which these vegeta- ble-compounds aie generated. We may, however, trace the tan- nin, resins, gums, mucilage, and some other vegetable materials, in the organized arrangement of plants, in which they form the bark, the wood, ihe leaves, flowers, and seeds. The bark is composed ofthe epidermis, the parenchyma, and the cortical layers. The epidermis is the exterial covering ofthe plant.) It is a thin transparent membrane, consisting of a number of slender fibres, crossing each other, and foiming a kind of net work. When of a white glossy nature, as in several species of trees, in the steins of corn and of seeds, it is composed of a thin coaling of silicious earth, which accounts for the strength and hardness of those long and slen- der stems. Sir IT. Dav) was led to the discovery of Ihe silicious nature ofthe epideimis of such plants, by observing the singular phenomenon of sparks of fire emitted by ihe collision of ralan canes with which two boys were fighting in a dark room. On analysing the epidermis of the cane, he found it to be almost entirely siliceous.* Caroline. With iron, then, a cane 1 suppose, will strike fire very easily? A.rs. B. 1 understand that it will —In evergreens the epidermis is mostly resinous, and in some few plapts is formed of wax. The resin, from its want of affinity 'or water, tends to preserve the plant from the destructive eff't cts of violent rains, severe climates, or in- clement seasons, to which this species of vegetables is peculiarly exposed. Emily Resin must preserve wood just like a varnish, as it is the essential ingredient of varnishes. Mrs. B. Yes ; and by this means it prevents, likewise, all unne- cessary expenditure of moisture. The parenchyma is immediately beneath the epidermis; it is that * In the scouring rush, [Equisetum hyema/e) the siliceousepider-' mis is still more obvious. If di awn across a piece of soft metal, as silver or copper, it cuts it like a fiie. It even makes an impression on the hardest steel.—C. 1270. Of what is bark composed ? 1271. What is the epidermis? 1272. In what manner was Sir H. Davy led to discover the silice- ous nature of the epidermis of particular plants? 1273. How does resin tend to preserve the plant? 1274. What is the parenchyma? VEGETATION. 283 green rind which appears when you strip a branch of any tree or shrub of its external coat of bark. The parenchyma is not confin- ed to ihe stem or branches, but extends over every part of the plant. It forms the green matter of ihe leaves, and is composed of tubes filled with a peculiar juice. The cortical layers are immediately in contact with the wood; they abound wiih lannin and gallic acid, and consist of small ves- sels through which the sap descends after being elaborated in the leaves. The cortical layers are annually renewed, the old bark being converted into wood. Airs. B. That function is performed by the tubes of the albernum or wood, which is immediately beneath the cortical layets. Ihe wood is composed of woody fibre mintage and resin The fibres are disponed in two ways: some of them longitudinally, aid these form what is called the silver grain of the wi od. The others which are concentric, are called the spurious grain. These last are dispos- ed in layers, from the number of which the age of the tree may be compi.led, a new one being produced annually hy the conversion of the bark into'wood. The oldest and consequently most internal part ofthe albernum, is called heart wood; it appears to be dead, at least no vital functions are discernible in it. It i* through the tubes of the living albernum that the sap rises These, therefore spread into ihe leaves, and there commui.icate with the ex remities of the ves- sels of thecorlical lasers, into which they pour their contents. Caroline. Of what use, then, are the tubesof the parenchj ma, since neither the ascending nor descending sap passes throuph them ? Mrs. B. They arc supposed to perform the important function of secre ing from the sap the peculiar juices from which the plant more immediately derives its nourishment. /These juices are very conspicuous, as the vessels which contain them are much larger lhan those through which the sap circulates. The peculiar juices of plants differ much in their nature, not only in different species of vegetables, but frequently in different parts ofthe same individ- ual plant; they are sometimes saccharine, as in the sugar-cane, sometimes resinous as in fm and evergreens, sometimes of a milky appearance, as in the laurel. Emily. I have often obsei ved, lhat in breaking a young shoot, or in bruising a leaf of laurel, a milky juice will ooze out in great abundance. .. _ Airs. B. And it is by making incisions in the bark, that pitch, tar, and turpentine* are obtained from fir trees. The durability of this species of wood is chiefly owing 10 the resinous nature of its peculiar ' * Turpentine is obtained as described in the text But tar and - pitch are obtained bv a very different method. A conical cavity u duff in the earth, at the bottom of which is placed a reservoir. Over this is piled billets of fir-wood, forming a large pile The pile is covered with turf to smother the fire which is kindled at the lop. As the wood is heated, and gradually converted into charcoal, the tar is 1275. Through what does the sap ascend? 1276. Of what is the wood composed? 1277 How are the fibres disposed ? 1278 Of what use are the tubes ofthe parenchyma? 1279 How may pitch, tar, and turpentine be obtained ? 284 VEGETATION. juices. The volatile oils have, in a great measure, the same preserv- ative effects, as they defend the parts with which they are connect- ed, from the attack of insects. This tribe seems to have as great an aversion to perfumes, as the human species have delight in them. They scarcely ever attack any odoriferous parts of plants, and it is not uncommon to see every leaf of a tree destroyed by a blight, whilst tiie blossoms remain untouched. Cedar, sandal, and all aro- matic woods, are, on this account, of great durability. Emily. But the wood of the oak, which is so much esteemed for its durability, has, I believe, no smell. Does it derive this quality from its hardness alone? Mrs.B Not entirely ; for the chesnut, though considerably hard- er and firmer than the oak, is not so lasting. The durability ofthe oak, is, I believe, in a great measure, owingto its having very lit- tle heart wood, the albernum preserving its vital functions longer than in other trees. Caroline. If incisions are made into the albernum and cortical layers, may not the ascending and descending sap be»procured in the same manner as the peculiar juice is from the vessel ofthe pa- renchyma? Mrs. B. Yes; but in order to obtain specimens of these fluids, in any quantity, the experiment must be made in the spring, when the sap circulates with the greatest energy. For this purpose a small bent glass tube should be introduced into the incision, through which the sap may flow without mixing with any of the other juices ofthe tree. From the bark the -ap will flow much more plentiful- ly than from the wood, as the ascending sap is much more liquid, more abundant, and more rapid in its motion, than that which de- scends; for the latter having been deprived by the operation of the leaves of a considerable part of its moisture, contains a much great- er proportion of solid matter, whicli retards its motion. It does not appear (hat there is any excess of descending sap, as none ever ex- udes from the roots of plants; this process, therefore, seems to be carried on only in proportion to the wants of the plant, and the sap descends no further, and in no greater quantity than is required to nourish the several organs. Therefore, though the sap rises and descends in the plant, it does not appear to undergo a real circula- tion. The last of the organs of plants, is the^ouier, or blossom, which driven out, and runs into the cavity, and finally into the reservoir. Tar is a mixture of resin,empyreumalic oil, charcoal, and acetic acid. The color is derived from ihe charcoal. Pitch is made by boiling tar, by which its more volatile parts are driven off—C. 1280. On what are the durability of cedar, sandal, and all aroma- tic woodn depending? 1281. On what is the durability of oak depending? 1282. Of what is tar said in the note to consist ? 1283. At what time in the year does the sap circulate with most en- ergy ? 1284. Why will sap flow more plentifully from the bark than from the wood ? 1285. What is the ultimate purpose of nature in the vegetable cre- ation ? VEGETATION. 285 produces the fruits and seed. These may be considered as the ulti- mate purpose of nature in the vegetable creation. From fruits and seeds animals derive both a pleniiful source of immediate nourish- ment, and an ample provision for the re-production of the same means of subsistence. The seed which forms the final product of mature plants, we have already examined, as constituting the first rudiments of future ve- getation. These are the principal organs of vegetation, by means of which the several chemical processes which are carried on during the life of the plant are performed. Emily. But how are the several principles which enter into the composition of vegetables, so combined by the organs of the plant, as to be converted into vegetable matter? Airs. B. By chemical processes, no doubt; but the apparatus in which they are performed, is so extremely minute as completely to elude our examination. We can form an opinion, therefore, only by the result of these operations. The sap is evidently composed of water, absorbed by the roots and holding in solution the various principles which it derives from the soil. From the roots the sap ascends through the tubes of the alburnum into the slem, and thence branches out to every exirem- ity of the plant Together with the sap circulates a certain quan- tity of carbonic acid, which is gradually disengaged from the for- mer by the internal heat ofthe plant. Caroline. What? have vegetables a peculiar heat, analogous to animal heat ? Mrs. B. It is a circumstance that has long been suspected ; but late experiments have decided beyond a doubt that vegetable heat is considerably above lhat of unorganized matter in winter, and be- low it in summer. The wood of a tree in its interior, is about sixty degrees when the thermometer is at seventy or eighty degrees in the air. And the bark, though so much exposed, is seldom below forty in winter. It is from the sap after it has been elaborated by tbe leaves, that vegetables derive their nourishment; in its progress through the plant from the leaves to the roots, it deposits in the several sets of vessels with which it communicates, the materials on which the growth and nourishment of each plant depends. It is thus that the various peculiar juices, saccharine, oily, mucous, acid, and color- ing, are formed ; as also the more solid parts fecula, woody-fibre, tannin, resins, concrete salts; in a word all the immediate materi- als of vegetables, as well as the organized parts of plants, which lat- ter, besides the power of secreting these from the sap, for the gen- eral purpose ofthe plant, have also that of applying them to their own particular nourishment. Emily. But why should the process of vegetation take place only 1286 How are the several principles which enter into the compo- sition of vegetables so combined by the organs of the plant as to be converted into vegetable matter? 1287. How does the temperature of vegetables compare with that of unorganized matter? 1288. How arc the several pieces as well as more solid parts ol ve- getables formed ? 286 VEGETATION. at one season of the year, whilst a total inaction prevails during the other ? N Airs. B.\ Heat is such an important chemical agent, that its ef- fect as such, might perhaps alone, account for the impulse which the S ring gives to vegetation. But, in order to explain the me- chanism of that operation, it has been supposed that the warmth of spring dilales the vessels of plants, and produces a kind of vacuum, into which the sap (which had remained in a slate of inaction in the trunk during the winter) rises; this is followed by the ascent ofthe sap contained in the mots, and room is thus made for fresh sap, which the roots in their turn pump up from the soil. This process goes on till the plant blossoms and bears fruit, which terminates its summer career; but when the cold weather sets in, the fibres and vessels contract, the leaves wither, and are no longer able to per- form their office of transpiration; and as this secretion stops, the roots cease to absorb sap from the soil. If the plant be an annual, its life then terminates; if not, it remains in a state of torpid inac- tion during the winter, or the only internal motion that takes place is that of a small quantity of resinous juice, which slowly rises from the stern into the branches, and enlarges their buds duringthe win- ter. Caroline. Yet, in evergreens vegetation must continue through- out the year. Airs. B. Yes; but in winter it goes on in a very imperfect man- ner, compared to the vegetation of spring and summer. We have dwelt much longer on the history of vegetable chemis- try than I had intended; but we have at length, 1 think, brought the subject to a conclusion. Caroline. I rather wonder that you did not reserve the account ofthe fermentations for the conclusion; for the decomposition of vegetables naturally follows their death, and can hardly, it seems, be introduced with so much propriety at any other period. Airs. B. It is difficult to determine at what point precisely it may be most eligible to enter on the history of vegetation y every part ofthe subject is so closely connected, and forms such an uninter- rupted chain, that it is by no means easy to divide it. Had I begun with the germination of the seed, which, at first view seems to be the most proper arrangement, I could not have explained the na- ture and fermentation of tbe seed, or have described the changes which manure must undergo, in order to yield the vegetable ele- ments. To understand the nature of germination, it is necessary, I think, previously to decompose the parent plant, in order to be- come acquainted with ihe materials required for that purpose. I hope, therefore, lhat, upon second consideration, you will find that the order which I have adopted, though apparently less correct, is, in fact, the best calculated for the elucidation of the subject. 1289. Why should the process of vegetation take place onlv in warm weather ? J 1290 What is the condition of vegetables called evergreens, in the season of winter? 1291. Why was not the fermentation of vegetables reserved for the eoncluding part of what is said on this subject ? ou-irGsiTj.OjN Of AmjaALS* 287 CONVERSATION XXIII. ON THE COMPOSITION OE ANIMALS. Mrs. B. We have now come to the last branch of chemistry, ■which comprehends the most complicated order of compound be- ings. This is the animal creation, the history of which, cannot but excite the highest degree of curiosity and interest, though we often fail in attempting to explain the laws by which it is governed. Emily. But since all animals ultimately derive their nourish- ment from vegetables, the chemistry of this order of beings must consist merely in the conversion of vegetable into animal matter. Airs. B. Very true; but the manner in which this is effected is, in a great measure, concealed from our observation. This process is called animalization, and is performed by peculiar organs. The difference of the animal and vegetable kingdoms does not,however, depend merely on a different arrangement of combinations. A new principle abounds in the animal kingdom, which is but rarely and in very small quantities found in vegetables; this is nitrogen. There is likewise in animal substances a greater and more constant proportion of phosphoric acid, and other saline matters. But these are not essential to the formation of animal matter. Caroline. Animal compounds contain, then, four fundamental principles; oxygen, hydrogen, carbon and nitrogen. Airs. B. Yes ; and these form the immediate materials of ani- mals, which me gelatine, albumen, and fibrine.* Emily. Are those all ? I am surprised that animals should be composed of fewer kinds of materials than vegetables ; for they ap- pear much more complicated in their organization. Mrs. B. Their organization is certainly more perfect and intri- cate, and the ingredients that occasionally enter into their compo- sition are more numerous. But notwithstanding the wonderful variety observable in the texture ofthe animal organs, we find that the original compounds, from which all the varieties of animal mat- ter are derived, may be reduced to the three heads just mentioned. Animal substances being the most complicated of all natural com- pounds, are most easily susceptible of decomposition, as the scale of attractions increases in proportion to the number of constituent principles. Their analysis is however, both difficult and imper- fect ; for as they cannot be examined in their living state, and are liable to alteration immediately after death, it is probable that when submitted to the investigation of a chemist they are always * These are the principal ingredients of the soft parts. But in addition to these, animal substances contain coloring matter, of blood, mucous, sulphur, phosphorus, earths, alkalies, oils, acids, re- sins, and several others, which it is unnecessary to specify.—C. 1292. What forms the subject of the 23d conversation ? 1293. What is animalization ?( 1294 What do animal compounds contain? 1295* What are the immediate materials of animals? 1296.' On what account is the analysis of animal compounds dita- Keult and imperfect ? 288 COMPOSITION more or less altered in their combinations and properties, from what they were, whilst they made part ofthe living animal. Emily: The mere diminution of temperature, which they experi- ence by the privation of animal heat, must I should suppose, be suf- ficient to derange the order of attractions, that existed during life. Airs. B. That is one of the causes, no doubt; but there are many other circumstances which prevent us from studying the na- ture of living animal substances. We must, therefore, in a con- siderable degree, confine our researches to the phenomena of these compounds in their inanimate state. These three kinds of animal matter, gelatine, albumen, and fibrine, form the basis of all the various parts of the animal system; either solid, as the skin, flesh, nerves, membranes, cartilages, and bones; or fluid, blood, chyle, mi/k,mucous, the gastric and pancre- atic juices, bile, perspiration, saliva, tears, ts at- traction either for the menstruum or for the matter which was before held in solution. , Precipitation. That chemical process by which bodies dissolved, mixed, or suspended in a fluid, are separated from that fluid, and made to gravitate to the bottom of the vessel. Prussiutes. ---alts formed by the combination of any base with prussic acid. Putrefaction. The last fermentative process of nature, by which organized bodies are decomposed so as to separate their principles, for the purpose of reuniting them by future attractions, in the production of new composi- Pyriles. An abundant mineral found on the English coasts, and elsewhere. "some are sulphurels of iron, and others sulphurels of copper, with a portion of alumine and silex. The former are worked for the sake of the sulphur, and the latter for sulphur and copper. They are also called Marcasitei and Fire-stone. ... , . ________martial. That species of pyrites which contains iron for its basis. See a full account of these minerals in Henckel's Pyntologia. Pyrometer. An instrument invented by M r. Wedgwood for ascertaining the degrees of heat in furnaces and intense fires. See Philosophical transac- tions, vol. lxii. and lxiv. and Chemical Catech. ,., . Pyrophori. Compound substances which heat of themselves, and take fire on the admission of atmospheric air. See an account of a variety fgP™ ments with these compositions in Wiegleb's Chemistry, 4to. p.622.&c. Q. Quartz. A name given to a variety of siliceous earths mixed with a small portion of lime or alumine. Mr. Kirwan confines the term to.the purer kind of silex. Rock crystal and the amethyst are species ot quartz. R. Radicals. A chemical term for Elements of bodies ; which see. ________compound. When the base of an acid is composed of two or more substances" it is said that the acid is formed of a cornpound^d^h fhe sulphuric acid is formed with a simple radical; but the vegetable acids, which have radicals composed of hydrogen and carbon, are said to oe acids with compound radicals. , i;„„;,i= ns test* Reagents. Substances which are added to mineral waters or liquids as testt to discover their nature and composition _ _„__... of Dre. Receivers. Globular glass vessels adapted to ^.an%Xv^^ serving and condensing the volatile matter rawed in ^I^ion it ^ Rectification, is nothing more than the re-d.st.lhng a liquid to render it more pure, or more concentrated, by abs racting a part of it only. ReZct'ion. The restoration of metallic oxideB to Aeirong^d state of met als ; which is usually effected by means of faJc°±*™{*™eolhcT metair_, Refining. The process of separating the perfect metals from other meiaiu. substances, by what is called cupelhuion. containing cold water, RS„/l3^,^rS^, signifies a pure metallic substance, freed from all extraneous matters 0f bodies are prevented from ^Sin t£K£_?"ft '.t.S S-wing „ cfc -.hich _. been called the repulsive power. ti either spontaneously or Resins Vegetable•J^J^^Z'^l^ 4^ ^a' R by fire. 1 heir t amcter »> ^' h j union WIth oxygen. kST i^eSrthfshap'e S"a Pea^, with its, neck bent dowwards, 340 A VOCABULARY used in distillation; the extremity of which neck fits into that of another bottle, called a receiver. Rock-crystal. Crystallized silex. s. Saccholates. Salts formed by the combination of any base with saccholac- tic acid. Salifiable bases. All the metals, alkalies and earths, which are capable of combining with acids, and forming salts, are called salifiable bases. Saline. Partaking of the properties of salt. Salts, neutral. A class of substanees formed by the combination to satura- tion of an acid with an alkali, an earth, or other salifiable base. ----triple. Salts formed by the combination of an acid with two bases or radicals. The tartrate of soda and potass (Rochelle salt) is an instance of this kind of combination. Soponaceous. A term applied to any substance which is of the nature or appearance of soap. Saturation. The act of impregnating a fluid with another substanoe, till no more can be received or imbibed. A fluid which holds as much of any substance as it can dissolve, is said to be saturated with that substance. A solid may in the same way be saturated with a fluid. Sebates. Salts formed by the combination of any base with sebacic acid. Semi-metal. A name formerly given to those metals, which, if exposed to the fire, are neither malleable, ductile, nor fixed. It is a term not used by modern chemists. Siliceous earths. A term used to describe a variety of natural substances, which are composed chiefly of silex ; as quartz, flint, sand, &c. Simple substances. Synonymous with Elements; which see. Smelting. The operation of fusing ores for the purpose of separating the metals they contain, from the sulphur and arsenic with which they are mineralized, and also from "other heterogeneous matter. Solution. The perfect union of a solid substance with a fluid. Salts dis- solved in water are proper examples of solution. Spars. A name formerly given to various crystallized stones ; such as the fluor spar, the adamantine spar, &c. These natural substances are now distinguished by names which denote the nature of each. Stalactites. Certain concretions of calcareous earth, found suspended like icicles in caverns. They are formed by the oozing of water through the crevices, charged with this kind of earth. Steatites. A kind of stone composed of silex, iron, and magnesia. Also called French chalk, Spanish chalk, and soap-rock. Sub-salts. Salts with less acid than is sufficient to neutralize their radicals. Suberates. Salts formed by the combination of any base with the suberic acid. Sublimation. A process whereby certain volatile substances are raised by heat, and again condensed by cold into a solid form. Flowers of sulphur are made in this way. The soot of our common fires is a familiar instance of this process. Succinates. Salts formed by the combination of any base with succinic acid. Sulphates. Salts formed by the combination of any base with the sulphuric acid. Sulphites. Salts formed by the combination of any base with the sulphurous acid. Sulphures and Sulphurets. Combination of alkalies, or metals with sulphur. Sulphuretted. A substance is said to be sulphuretted when it is combined with sulphur. Thus we say sulphuretted hydrogen, &e. Super-salts. Salts with an excess of acid, as the supertartrate of potass. Synthesis. W hen a body is examined by dividing it into its component parts, it is called analysis ; but when we attempt to prove the nature of a sub- stance by the union of its principles, the operation is called synthesis. T. Tartrates. Salts formed by the combination of any base with the acid of tartar. Temperature. The absolute quantity of free caloric which is attached to any body, occasions the degree of temperature of that body. OF CHEMICAL TERMS. 341 Test. That part of a cupel which is impregnated with litharge in the opera- tion o. refining lead. It is also the name of whatever is employed in chem- ical experiments to detect the ingredients of any composition. Test-papers. Papers impregnated with certain chemical re-agents ; such as litmus, turmeric, radish, e two fluids, a chemic- al combination takes place between their particles, in consequence of which caloric is extricated at the same time their bulk is dimin- ished. This also illustrates Dr. Black's law, that when substances pass from a rarer to a denser state, caloric is given out. If one measure of sulphuric acid, and one of water, be mixed together, the mixture will not again fill the measure twice. See p. 77. 10. To produce nitrogen, take a bell glass or large tumbler and invert it over a short taper, set in a shallow dish of water. The ta- per burns until it absorbs all the oxygen contained in the air under •the bell glass. What remains is nitrogen. If now, a lighted taper be put under the bell glass, it will be instantly extinguished, show- ing the absolute necessity af oxygen for the support of combustion. ■Hee p. 100. II. The formation of water by the burning of hydrogen maybe 344 EXPERIMENTS. shown thus: Take a Florence flask and pour into it half a pint Of water, then put in about an ounce of granulated zinc, or the same quantity of iron filings, and then pour in half an ounce by measure of sulphuric acid. Have ready a cork, pierced with a burning iron, and the stem of a tobacco pipe passed through the aperture. After putting in (he acid, put the cork in its place, and fix the flask up- right by setting it in a bowl, surrounded by a cloth to make it stand up and prevent its breaking. As the hydrogen is formed, it issues through the stem of the tobacco pipe, at the end of which it is to be fixed. If now a glass tube two or three feet long, and an inch or two wide be passed on to the stem so as to include the flame within its bore, the tube, in a few moments will be covered on the inside with moisture. Fee p. 109. If the orifice of the tube is quite small at the end where the gas is fired, the above experiment serves to produce the musical tones — Sec p. 118. 12. An exhibition of gas light my be made as follows : Into the bowl of a common tabacco pipe put a piece of mineral, or what is called sea-coal, and cover the coal closely with clay. When the clay is dry, place the bowl in the fire and heat it slowly. In a few minutes the gas, called carbureltcd hydrogen will issue from the end of the pipe stem ; set fire to it with a candle, and it will burn with a beautiful bright flame. .This is the gas with which the streets, factories, &c. are lighted in many of the .European cities. In the absence of mineral coal, a walnut, small piece of pine knot, or butternut meat, &c. may take the place of coal. See p. 120. 13. The following gives an example ofthe manner in which sul- phuric acid is formed. Mix with a small quantity of the flowers of sulphur, about one fifth part of finely pulverized nitre. Make a stand by hollowin"- with a hammer a large button, and attaching wire to" the eye, for feet, so that the button will be two inches high; or, by any other means, place the sulphur and nitre about this height in a shallow dish, containing an inch or two of water. Set fire lo the mixture with a hot iron, and immediately invert over it a bell glass, or large tumbler. The sulphur as it burns, absorbs oxygen from the air contained under the bell glass, in a proportion which would consti- tute sulphurows acid. At the same time, the heat which this pro- cess occasions, compels the nitre lo give out another proportion of oxygen, which is absorbed by the sulphurous acid, and this addi- tional quantity of oxygen constitutes sulphuric acid. Seep. 130. 14. Take three parts of nitre, two ofpotash, and one of sulphur, and mix them intimately, by rubbing in a mortar. This compound is called fulminating powder. On placing a little of it on a shovel over a hot fire, it explodes with great violence, and with a peculiarly stunning report. The combustion of pliosphurMed hydrogen in oxygen gas, af- fords one of the most striking and beautiful among chemical exper- iments. It is done as follows; Take some phosphuret oflime, wrap k in a paper and push it under a vessel, as a widemouthed vial, filled with water, and inverted on the shelf of the water bath. As soon as the water penet rates through the paper so as to wet the phosphuret of lime, bubbles of phosphuretted hydrogen begin to rise up through the water. While this is going on, fill a strong glass vessel as a tumbler, or a piece of thick-glass tube stopped at one end, with ox- EXPERIMENTS. 345 gen gas. Invert this also on the shelf of the water bath. When the phosphuretted hydrogen is collected, take the vessel containing it in one hand, and that containing the oxygen in the other ; bring the mouth of the former, by sinking it deeper in the water, under the edge ofthe latter vessel, then by carefully depressing the bot- k!!i?i the vessel containing the phosphuretted hydrogen, let up a bubble at a time into the oxygen gas. If this experiment is made in a darkened room, the flashes of light appear asto-aishmg-lv vivid and beautiful. See p. 135. 16. Take six or eight grains of oxy-muriate of potash, put it into a mortar and drop in with it about a grain of solid phosphorus, cut into two or three parts ; then rub them together with a pestle.— Very violent detonations are produced by these small quantities. It is best, therefore, not to use more than is here mentioned at a time. The hand, holding the pestle, ought always to be protected With a glove or handkerchief. 17. To make liquid phosphorus, take an ounce vial and half fill it with olive oil, put into the oil a piece of phosphorus ofthe size of a pea ; gradually heat the bottom of the vial, until the phosphorus is melted, taking care to keep the thumb on the mouth ; then cork it air tight. If this vial is first sh»ken, and then the cork be taken out, it becomes luminous, first near tbe mouth and gradually down to the oil, at the bottom. The light which a bottle prepared in this way gives, particularly if warmed, by holding it in the hand, is suf- ficient to tell the hour of night by a watch. This luminous ap- pearance, when the cork is removed, is owing to the union of the oxygen ofthe atmosphere with the phosphorus. It is slow combus- tion, attended with light, and most probably with some heat. 18. If drawings be made on silk with a solution of nitrate of sil- ver, and the silk first moistened, is exposed to a stream of hydro- gen gas, or in any other way exposed to the action of this gas, the metal is instantly revived, and the silk is covered with figures of silver.—See p. 155. 19. If a few drops of a solution of nitrate of silver in water, be placed on a bright surface of copper, the silver is revived, and gives the copper a brilliant white coat of that metal. This is explained on the principle of affinity. The copper has a stronger attraction for the acid which composes a part ofthe nitrate of silver, than the silver itself has. Therefore it attracts the acid from the silver, in consequence of which this is received, and at the same time pre- cipitated on the copper. See p 155. 20. Take a little of the white arsenic of the shops, and mix it with some finely ground charcoal; put the mixture into a small glass tube closed at one end, and expose the part where the mixture is to a moderate degree of heat gradually raised ; the arsenic will be received, and will attach itself to the upper part of the tube, giv- ing it a brilliant metallic coat like quick silver. The arsenic may be preserved in this state by stopping up the tube. See p. 155. 21. Dissolve a tea-spoonful of sugar of lead in a quart of rain water. Put this into a decanter, or white glass bottle, and suspend in it b'v means of a string, a piece of zinc. The zinc decomposes tbe acetate of lead by depriving it of its oxygen; the consequence is, that the lead is precipitated in the metallic state, on and around the zinc, and forms a brilliant tree of metal. 22. Pour a solution of nitrate of sifver into a glass vessel, and >m* 30 346 EXPERIMENTS. merse a few slips of copper in it. In a short time, a portion of cop- per will be dissolved, and all the silver precipitated in a metallic form. If the solution which now contains copper be decanted into another glass, and pieces of iron added lo it, this metal will then be dissolved, and the copper precipitated, yielding a striking instance of peculiar affinities. Seep. 176. 23. Ivory may be coated with silver by the following process; Make a strong solution of nitrate of silver in pure water ; into this immerse a piece of ivory until it turns yellow ; then take it out and immediately plunge it into a vessel of distilled water exposed to the direct rays of the sun until it turns black. On rubbing it gently it will appear covered with a brilliant coat of silver resembling a bar of that metal. This curious effect is owing to the solar light which decomposes the nitrate of silver, by taking the oxygen from it, which flies off in the form of oxygen g*as. 24. Through a vessel of lime water, recently made, pass bubbles of carbonic acid gas by means of a bladder and tube, the lime water instantly becomes white and turbid, and finally deposits a quantity of carbonate of lime in the form of powdered chalk. If now the wa- ter be evaporated, a white powder remains which effervesces with acids. If this powder is put into a retort, and sulphuric acid diluted with water, is poured upon it, the beak ofthe retort being undera vessel filled with water, the carbonic acid is again obtained, and the salt remaining in the retort will be sulphate of lime or gypsum. 25. Mix one part of nitric acid with 5 or 6 parts of water in a vial; into this put some copper filings, and in a few moments pour off the liquid ; it will be colourless. If now there be added some liquid ammonia, another colourless fluid, the mixture becomes of an in- tense and beautiful blue. Hence ammonia is a most delicate test for the presence of copper, with which it strikes a deep blue colour. See p. 187. 26. Put into a vial of pure water a few drops of the tincture of nut galls, made by steeping the galls in water; into another vial of pure water put a grain or two of the sulphate of iron. If these colour- less fluids are mixed, they instantly become black. Tincture of galls is a most delicate test for the presence of iron, with which it strikes a black. These two substances form the basis of ink. See p. 187. 27. Take two small glass jars, or tumblers, and fill one with car- Ionic acid gas, and the other with oxygen gas. Have them set up- right with a cover on each. If a lighted taper be plunged into the vessel containing the carbonic acid, it is ext inguished instantly; but if it is immediately plunged into the other jar containing the oxy- gen, it is as instantly lighted with a sort of explosion. See p. 236. 28. Put eight or ten grains of oxy muriate of potash into a tea-cup, and then pour in two or three drachms of alcohol.—If now about two drachms of sulphuric acid is added, the mixture begins to dart forth little balls of blue fire, and in a minute or two the whole bursts into flame. The alcohol is inflamed by the chlorine which is set free from the salt, in consequence of the combination which takes place between the potash and the sulphuric acid. See p. 236. 29. Into a glass tube half an inch or an inch wide, two or three inches long, with a bulb at the end, put a grain or two of iodine. Warm the tube, (but not at that part where the iodine is,) and im- mediately cork it tight; the tube remains colourless, there being EXPERIMENTS. 347 only a few little specks here and there. If at anytime the tube be warmed at that part where the iodine is, it is insrantly filled with a gas of a most beautiful violet colour. If care is taken to keep the tube well closed, so that the iodine does not escape, when it lakes the form of gas, this effect will always be produced whenever the tube is warmed. A tube with two bulbs, like what is called a pulse glass, containing the iodine hermetically sealed, would be better. Such a little apparatus would be quite a curiosity to those who know nothing of the nature of iodine. See p. 238. 30. Write on paper with a solution of the nitrat of silver, taking care not to have it so strong as to destroy the paper. So long as it is kept in the dark, or if the paper be closely folded, the writing re- mains invisible ; but on exposure to the rays of the sun the charac- ters turn yellow, and finally bjack, so that they are perfectly legible. Mr. Accum says, that this' change of color is owing to the par- tial reduction of the oxide of silver, from the light expelling a por- tion of its oxygen ; the oxyde therefore approaches lo the metallic state; for when the blackness is examined with a deep, or power- ful magnifier, the particles of metal may be distinctly seen. 31. Write on paper with a dilute solution of common sugar of lead ; the writing will remain invisible. But on moistening the lines with a pencil, or feather dipped in water impregnated with sulphuretted hydrogen, the metal is revived, and the letters appear in metallic brilliancy. The author above cited, says, that in this instance, the hydrogen ofthe sulphuretted hydrogen gas, abstracts the oxygen from the ox- ide of lead, and causes it to re-approach to the metallic state ; at the same time, the sulphur of the sulphuretted hydrogen gas com- bines with the metal thus regenerated, and converts it into a sul- phuret which exhibits the metallic color. 32. Write on paper with a solution of the sulphate of copper. If this is strong, the writing will be of a faint green color; if weak, the characters are invisible. On holding the paper over a vessel containing some liquid of ammonia, or if it be exposed to the action of this gas in any other way, the writing assumes a beautiful blue color. On exposing the paper to the sun, the color disappears, be- cause the ammonia evaporates. 33. Put a small piece of phosphorus into a crucible, cover it closely with common chalk, so as to fill the crucible. Let another crucible be inverted upon it, and both subjected to the fire. When the whole has become perfectly red hot, remove them from the fire, and when cold, the carbonic acid ofthe chalk will have been de- composed, and the Black Charcoal, the basis of the acid, may be easilv nerceived amongst the materials. „,.,,., , 34 f nto a large glass jar inverted upon a flat brick tile and con- taining near its top** branch of fresh rosemary, or any other such hnb moistened with water, introduce a flat, thick piece of heated iron on which place some gum benzoin in gross powder. The ben- zoic'ac"d in consequence of the heat, will be separated and ascend fn white fumes, which will at length condense, and forrna mos beautiful appearance upon the leaves of the vegetable. This will serve as an example of Sublimation. i_u-._ %S Mix a little acetate of lead with an equal portion of sulphate „f>inc both in fine powder; stir them together with a piece of 'r wood and noPchemicalchange will be perceptible; but if 348- EXPERIMEATS. they be rubbed together in a mortar, the two solids will operate on each other; an intimate union will take place, and a fluid will be produced. If alum or Glauber salt be used instead of sulphate of zinc, the experiment will be equally successful. 36. If the leaves of a plant, fresh gathered, be placed in the sun, very pure oxygen gas may be collected. 37. Put a little fresh calcined magnesia in a tea-cup upon the hearth, and suddenly pour over it as much concentrated sulphuric acid as will cover the magnesia. In an instant sparks will be thrown out, and the mixture will become completely ignited. 38. If a few pounds of a mixture of iron filings and sulphur be made in paste with water, and buried in the ground for a few hours, the water will be decomposed with so much rapidity, that combus- tion and flame will be the consequence. 39. For want of a proper glass vessel, a table spoonful of ether may be put into a moistened bladder, and the neck of the bladder closely tied. If hot water be then poured upon it, the ether will expand, and the bladder become inflated. 40. Procure a phial with a glass stopper accurately ground into it; introduce a few copper filings, then entirely fill it wiih liquid ammonia, and stop the phial so as to exclude all atmospheric air. If left in this state, no solution of the copper will be effected. But if the bottle be afterwards left open for some time, and then stopped, the metal will dissolve, and the solution will be colorless. Let the stopper be now taken out, and the fluid will become blue, beginning at the surface, and spreading gradually through the whole. If this blue solution has not been too long exposed to the air, and fresh cop- per filings be put in, again stopping the bottle, the fluid will once more be deprived of its color, which it will recover only by the re- admission of air. These effects may thus be repeatedly produced. 41. If a spoonful of good alcohol and a little boracic acid be stir- red together in a tea-cup, and then set on fire, they will produce a beautiful green flame. 42. Alloy a piece of silver with a portion of lead, place the alloy upon a piece of charcoal, attach a blow-pipe to a gasometer, charg- ed with oxygen gas, light the charcoal first with a bit of paper, and keep up the heat by pressing upon the machine. When the metals get into complete fusion, the lead will begin to burn, and very soon will be all dissipated in a white smoke, leaving the silver in a state of purity. This experiment is designed to show the fixity of the noble metals. 43. Burn a piece of iron wire in a deflagrating jar of oxygen gas, and suffer it to burn till it goes out of itself. If a lighted wax taper be now let down into the gas, this will burn in it for some time, and then become extinguished. If ignited sulphur be now introduced this will also burn for a limited time. Lastly introduce a morsel of phosphorus, and combustion will also follow in like manner. These experiments show the relative combustibility of different substances. 44. Drop a piece of phosphorus, about the size of a pea into a tumbler of hot water, and from a bladder, furnished with a stop cock, force a stream of oxygen gas directly upon it. This will afford the most brilliant combustion under water that can be imagined. 45. Take an amalgam of lead and mercury, and another amal- gam of bismuth, let these two solid amalgams be mixed by triture, and they will instantly become fluid. INDEX. 349 46. Into distilled water drop a little spiritous solution of soap, no chemical effect will be perceived ; but if some of the same solution be added to hard water, a milkmess will immediately be produced, more or less, according to the degree of its impurity. This is a good method of ascertaining the purity of spring waten 47. To silver copper or brass.—Clean the article intended to be silvered, by means of dilute nitric acid, or by scouring it with a mixture of common salt and alum. When ii is perfectly bright, moisten a little ofthe powder, known in commerce by the name of silvering powder, with water, and rub it for some time on the per^ fectly clean surface of copper, or brass, which will become covered with a coat of metallic silven, It may afterwards be polished with soft leather. The silvering powder-is prepared in the following manner: Dis- solve some silver in nitric acid, and put pieces of copper into the so- lution ; this will throw down the silver in a state of metallic powder; Take fifteen or twenty grains of this powder, and mix with it two drachms of acidulous tartarite of potash, the same quantity of com- mon salt, and half a drachm of alum. Another method : Precipi- tate silver from its solution in nitric acid by copper, as before ; to half an ounce of this silver, add common salt and muriate of ammo- nia, of each two ounces, and one drachm of corrosive sublimate; rub them together, and make them into a pa^te with water. With this, copper utensils intended to be silvered, that have been previ- ously boiled with acidulous tartarite of potash and alum, are to be rubbed ; after which they are to be made red hot and polished. 48. To prove that the air ofthe a mosohere always contains car- bonic acid. This may be shown by simply pouring any quantity of barytic water, or lime water, repeatedly from one vessel into an- other. The barytic water when deprived of the contact of air, is perfectly transparent; but it instantly becomes milky, and a white Erecipitate, which is carbonate of barytes, is deposited, when rought into contact with it for a few minutes only. The quantity of carbonic acid contained in the atmosphere, sel- dom varies except in the immediate vicinity of places where respi- ration and combustion are going on in the large way, and is about one hundredth part. A Agate, 195 Agriculture, 274 Absorbent vessels, 298 Air, 95 Absorption of caloric, 40, 45 Albumen, 287 Acetic acid. 252, 253 Alburnum, 283 Acetous fermentation,267 Alchemists, 15 acid 253 Alcohol, or spirit of wine, 259 Acidulous gaseous mineral wa- Alembic, 127 ters 226 Alkalies, 181 salts "54 Alkaline earths, 182, 194 Acids, 202 ~ Alloys, 162 Aeriform 31 Alum, or sulphat of alumine, 196, Affinity* 23, 174 212 350 INDEX. Alumine, 196 Alumium, 19 Amalgam, 163 Ambergris, 320 Amethyst, 197 Amianthus, 201 Ammonia, or volatile alkali, 169 181, 188 Ammoniacal gas, 188 how obtained, 191 Analysis, 138 of vegetables, 241 Animals, 288 Animal acids, 292 colors, 294 heat. 311 oil, 292 Animalization, 287, 295 Antidotes, 191 Antimony, 20 Aqua fortis, 216 regia, 160 Arrak, 262 Argand's lamp, 107 Arsenic, 20, 163, 165 Arteries, 298 Arterial blood, 306, 308 Asphaltum, 270 Assafoetida, 249 Assimilation, 297 Astringent principle, 253 Atmosphere 61, 95, 108 Atmospherical air, 95 Attraction of aggregation, or co- hesion, 21, 171 Attraction of composition, 23. 171 Azote, or nitrogen, 214 Azotic gas, 95 B Balsams, 249 Balloons, 122 Bark, 282 Barytes, 192, 197 Basis of acids, 204 gases, 30 salts, 172 Beer, 258 Benzoic acid, 204, 253 Bile, 303 Birds 297 Bismuth, 20' Bitumens, 270 Black lead, or plumbago, 145 Bleaching, 210 Blow-pipe, 140, 153 Blood, 303, 305 Blood-vessels, 309 Boiling water, 67 Bombic acid, 292, 204 Bones, 295 Borncic acid, 204, 226 Boracium, 19 227 Borat of soda, 227 Brandy, 261 Brass, 162 Bread, 224 Bricks, 197 Brittle metals, 20 Bronze, 162 Butter, 318 Butter-milk, 318 C Calcareous earths, 224 stones, 223 Calcium, 20 Caloric, 29 absorption of, 46 conductors of, 48 combined, 69 expansive power of, 30j 31 equilibrium of, 39 reflection of, 46 radiation of, 40, 43 solvent power of, 59 capacity for, 70 Calorimeter, 83 Calx, 102 Camphor, 240 Camphoric acid, 204, 258 Caoutchouc, 240, 249 Carbonats, 226 Carbonat of ammonia, 2S0 lead, 150 lime, 199 magnesia, 201 potash, 184 Carbonated hydrogen gas, 144 Carbon, 137 Carbonic acid, 142 Carburet of iron, 145 Carmine, 294 Cartilage, 297 Castor.321 Cellular membrane, 300 Caustics. 164 Chalk, 199, 226 Charcoal. 137 Cheese, 320 Chemical attraction, 91 Chemistry, 13 INDEXi 351 Chest, 304 China, 197 Chlorine, 18 Chrome, 20 Chyle, 298 Chyme, 303 Citric acid, 204, 253 Circulation ofthe blood, 205 Civet, 321 Clay, 38 Coke, 270 Coal, 270 Cobalt, 20 Cochineal, 274 Cold, 40 from evaporation, 80 Colours of metallic oxyds, 151 Columbium, 20 Combined Caloric, 69 Combustion, 99 volatile products of, 107 fixed products of, 107 of alcohol, 263 of ammoniacal gas, 188 of boraccium, 227 by oxy-muriatic acid, or chlorine, 231 of carbon, 140 of coals, 119, 145 of charcoal, by nitric acid, 215 of candles. 118, 147 Of diamonds, 140 of ether, 266 of hydrogen, 109,116 of iron, 105 of metals, 152 of oils, 147 of oil of turpentine by ni- trous acid, 215 of phosphorus, 133 ofsulphur, 128 of potassium, 168 Compound bodies, 17 or neutral salts, 182 Conductors of heat, 44 solids, 50 fluids, 51 Count Rumford's theory, 51 Constituent parts, 17 Copper, 20, 165 Copal, 249 Cortical layers, 282 Cotyledons, or lobe, 278 Cream, 318 Cream of tartar, or tartrit of pot- ash, 263 Cryophorus, 82 Crystallization, 159 Cucurbit, 127 Culinary heat, 55 Curd, 319 Culicle, or epidermis, 300 Cyanogen, 293 D Decomposition, 16 of atmospherical air, 98, 100 of water, by the Voltaic battery, 112 of salts by the Voltaic bat- tery, 179 of water by metals, 113 by carbon,144 of vegetables, 254 of potash, 168 'of soda. 169 of ammonia, 169 ofthe boracic acid, 227 of the fluoric acid, 228 of the muriatic acid, 229 Deflagration, 221 Definite proportions, 177 Deliquescence, 211 Detonation 115, 123 Dew. 62 Diamond, 138 Diaphragm, 304 Digestion. 302 Dissolution of metals, 87, 167 Distillation. 127, 208 of red wine, 261 Divellent forces, 176 Division, 16 Drying oils 246 Dyeing. 250 E Earths, 181 Earthen ware, 197 Effervescence, 157 Effloresrence, 211 Elastic fluids. 31 Electricity, 86, 90, 92 Electric machine, 88 Electo-magnetism, 94 Elective attraction, 174 Elementary bodies, 17 Elixirs, tinctures, or quintessen- ces, 263 352 INDEX. Enamel, 197 Epidermis of vegetables, 282 of animals, 300 Epsom salts, 201 Equilibrium of calorid, 39 Essences, 147, 247 Essential or volatile oils, 147 247 Ether, 65, 265 Evaporation, 61 Evergreens^ 286 Eudiometer, 134 Expansion of caloric, 30 Extractive colouring matter, 250 F Falling stones, 161 Fat, 318 Feathers, 296 Fecula, 244 Fermentation, 356 Fibrine, 287, 292 Fire, 16,26 Fish, 316 Fixed air, or carbonic acid, 140, 233 alkalies, 121 oils, 146,245 products of combustion* 106 Flame, 119 Flint, 185, 195 Flower of blossom, 284 Fluoric acid, 228 Fluorium, or Fluorine,28, 229 Formic acid, 292 Fossil wood, 271 Frankincense, 249 Free or radiant caloric, or heat of temperature, 29 Freezing mixtures, 77 by evaporation, 65, 80 Frost, 62 Fruit, 285 Fuller's earth, 196 Furnace, 145, 150 G Galls, 253 Gallat, of iron, 213 Gallic acid, 213, 253 Galvanism, 85 Gas. 95 Gas-lights, 120 Gaseous oxyd of carbon, nitro- gen, 142,217 Gastric juice, 302 Gelatine, Or jelly, 287, 288 Germination, 277 Gin, 262 Glands, 295, 299 Glass, 185 Glauber's salts, or sulphat of soda 184 Glazing, 197 Glucium, 19 Glue, 189 Gluten, 244 Gold, 20, 160 Gum, 242 arabic, 242 elastic, or caoutchonc, 249 resins, 249 Gunpowder, 221 Gypsum, or Plaster of Paris, or sulphat oflime, 212 H Hair, 299 Harrogate water, 132 Hartshorn, 188, 190 Heart, 305 wood, 283 Heat, 26 of capacity, 71, 74 of temperature, 29 Honey, 244 Horns, 289 Hydro-carbonat, 124, 146 Hydrogen, 109 gas, 110 I&J Jasper, 195 Ice, 83 Jelly, 289 Jet, 270 Ignes fatui, 135 Ignition, 68 Imponderable agents, 18 Inflammable air, 109 Ink,213 Insects, 254 Integrant part3, 17 Iodine, 109j 237 Iridium, 20 Iron, 20, 150,161 Isinglass, 289 Ivory black, 294 K Kali, 187 Koumiss, 320 L Lac, 321 INDEX. 353 Lactic acid, 292, 320 Lakes, colours, 250 Lamp without flame, 107, 322 Latent heat, 73 Lavender water, 263 Lead, 20, 151, 156 Leather, 25i, 291 Leaves, 280 Life, 239 Ligaments, 296 Light, 18 Lightning, 215 Lime, 198 water, 199 Limestone, 198 Linseed oil, 246 Liqueurs, 263. Liver, 299. Lobes, 278, 309. Lunar caustic, or nitrat of sil- ver, 164, 222 Lungs, 307, 309 Lymph, 298 Lymphatic vessels, 293 M Magnetic needle, 94 Magnesia, 201 Magnium, 19. Malic acid, 204, 253 Malt, 258 Malleable metals, 20 Manganese, 20, 150 Manna, 241 Manure, 274 Marble, 226 Marine acid, or muriatic acid, 229 Mastic, 249, 263 Materials of animals, 287 of vegetables, 239 Mercury, 20, 162 new mode of freezing, 83, 163 Metallic acids, 1 60 oxyds, 150 Metals, 149 Meteoric stones, 161 Mica, 201 Milk, 288, 299 Minerals, 150 Mineral waters, 143 acids, 203 Miner's lamp, 125 Mixture, t-0 Molybdena, 20, 160 Mordant, 250 Mortar, 201 Mucilage, 241 Mucous acid, 204, 241 membrane, 300 Muriatic acid, or marine acid, 229 Muriats, 234 Muriat of ammonia, 188,23^ lime, 78" soda, or common salt, 187, 234 potash, 235 Muriatum, 19 Muscles of animals, 295 Musk, 321 Myrrh, 249 N Naptha, 270 Negative electricitj', 25, 84, 88 Nerves, 299 . Neutral, or compound salts, 202 Nickel, 20, 161 Nitre, or nitrat of potash, or salt- petre, 215, 224 Nitric acid, 214 Nitrogen, or azote, 96 gas, 96 Nitro-muriatic acid, or aqua re- gia, 160 Nitrous acid gas, 217 air, or nitric oxyd gas, 218 Nitrats, 221 Nitrat of copper, 165 ammonia, 219, 221 potash, or nitre, or salt- petre, 215 silver, or lunar caustic, 222 Nomenclature of acids, 202 compound salts, 172 Nomenclature of other binary compounds, 135 Nut-galls, 213 Nut-oil, 245 Nutrition, 295 O Ochres, 151 Oils, 146, 247 Oil of amber, 271 vitriol, or sulphuric acid, 206 Olive-oil, 245 Ores, 150 Organized bodies, 239 354 INDEX. Organs of animals, 299 , vegetables, 239 Osmium, 20, 163 Oxalic acid, 204, 253 Oxyds, 102, 157 Oxyd of manganese, 105 iron, 102 lead, 151 sulphur, 201 Oxydation, or oxygenation, 157 Oxygen, 18, 129 gas, or vital air, 95 Oxy-muriatic acid, 230 Oxy-muriats, 235 Oxy-muriat of potash, 235 P Palladium, 20, 163 Papin's digester, 290 Parenchyma, 277,283 Particles, 21 Pearl-ash, 183 Peat, 271 Peculiar juice of plants, 283 Perfect metals, 20, 153 Perfumes, 247 Perspiration, 310 Petrifaction, 269 Pewter, 162 Pharmacy, 14 Phosphat oflime, 213 Phosphorated hydrogen gas, 135 Phosphoresence, 28 Phosphoric acid, 213 Phosphorus 132 acid, 213 Phosphoret of lime, 135 sulphur, 136 Pitch, 248 Plaster, 201 Platina, 20, 153 Platina ignited by a lamp with- out a flame, 322 Plating, 162 Plumbago, or black lead, 161 Plumula, 278 Porcelain, 197 Positive electricity, 25, 84, 38 Potassium, 168 Pottery, 197 Potash, 182 Precipitate, 24 Pressure of the atmosphere, 67, 68 Printer's Ink, 232 Prussiat of iron, or Prussian blue, 294 potash, 293 Prussic acid, 293 Putrid fermentation, 263, 321 Pyrites, 212, 161 Pyrometer, 32 Q Quicklime, 198 Quiescent forces, 176 R Radiation of caloric, 89 Prevost's theory, 40 Piclet's explanations, 4 Leslie's illustrations, 44. Radicals, 202, 206. Radicle, or root, 278 Rain, 62 Rancidity, 246 Rectification, 262 Reflection of caloric, 40,44 Reptiles, 317 Resins, 248 Respiration, 300, 303 Reviving of metals, 156 Rhodium, 20, 163 Roasting metals, 150 Rock crystal, 195 Ruby, 193 Rum, 261 Rust, 150, '.55 S Saccharine fermentation, 257 Sal ammoniac, or muriat of am- monia, 188 polychrest, or sulphat of potash, 210 volatile, or carbonat of am- monia, 190 Salifiable basis, 172 Salifying principles, 172 Saltpetre, or nitre, or nitrat of potash, 220 Salt, 210 Sand, 195 Sandstone, 195 Sap of plants, 257, 241, 283 Sapphire, 193 Saturation, 60 Seas, temperature of, 54 Sebacic acid, 246 Secretions, 292 Seeds of plants, 258, 285 Seltzer water, 143, 200 Senses, 300 INDEX. 355 Silex, or silicia, 195, 191 Silicium, 19 Silk, 321 Silver, 153. Simple bodies, 18 Size, 269 Skin, 288 Slacking of lime, 300 Slate, 196 Smelting metals, 150 Smoke, 107 Soap,183 Soda, 187,169 water, 143 Sodium, 19, 169 Soils, 273 Soldering, 162 Solubility, 211 Solution, 58 by the air, 61 of potash, 185 Specific heat, 70 Spermaceti, 320 Spirits, 261 Spirit lamp, 364 Starch-Sugar, 242 Steam, 68, 76 Steel, 146 Stomach, 302 Stones, 193 Stucco, 201 Strontites, 201 Strontium, 19 Suberic acid, 204, 253 Sublimation, 127 Succin, or yellow amber, 271 Succinic acid, 204, 253 Sugar, 240, 269 of milk, 319 Sulphats, 211 Super-oxygenated sulphuric acid, 202 Sulphat of alumine, or alum, 196,212 barytes, 198 iron,212 lime, or gypsum, or plas- ter of Paris, 212 magnesia, or Epsom salt, 201,212 potash, or salt polychrest, 210 soda, or Glauber's salts 21 Sulphur, 126 Sulphur, flowers of, 127 Sulphurated hydrogen gas, 131 Sulphurets, 160 Sulphureousacid, 130,208 Sulphuric acid, 207 Sympathetic ink, 165 Synthesit, 13U T Tan, 251 Tannin, 251 Tar, 243 Tartarous acid, 253 Tartrit of potash, 254 Teeth, 296 Tellurium, 20 Temperature, 29 Thaw, 85 Thermometers, 34, 35 Fahrenheit's, 34 Reaummer's, 34 Centrigrade, 34 air, 35 differential, 36 Thunder, 123 Tin, 20 Titanium, 20, 163 Turf, 270 Turpentine, 173 Transpiration of plants, 279 TuDgsten, 20, ItO V Vapour, 68,76, 266 Vaporization, 61 Varnishes, 249 Vegetables, 238 Vegetable acid, 240, 148 colors, 250 heat, 285 oils. 244 Veins, 101, 306 Venous blood, 306, 308 Ventricles, 307 Verdigris, 165 Vessels, 298 Vinegar, 267 Vinous fermentation, 258 Vital air, or oxygen gas, 96 Vitrol. or sulphat of iron, 206 Volatile oils, 240, 244, 247 products of combustion, 106 alkali, 181, 188 Voltaic battery, 86,149,153,166, 179 U Uranium, 20 356 INDEX. W Water, 109, 113 decomposition of, by elec- tricity, 113 condensation of, 54 of the sea, 54 boiling, 58 solution by, 58 of crystallization, 159 Wax, 320, 245 Whey, 318 Wine, 258 Wood, 283 Woody fibre, 240, 252 Wool, 296 Y Yeast, 267 Yttria, 192 Yttrium, 19 Z Zinc, 19 Zicornia, 192 Zincornium, 19 Zoonic acid, 204, 292; £ 'n:L % v ^ "*-*"£■ / // // 7 iC ": t ■/- ■'4 4 ■'?■ > V: ■-Q''. r ;;^>^ ^r I . •w & ■# :* '35*! ^ ^Hi,.''-'^ I#.M &>: \s 0i && 95^ $1 i_fc^l Si