V V * \ Boston Medical Library Association, V 19 boylsto'iKplace * ■ y \ Received./:....... .......>^..... SURGEON GENERAL'S OFFICE LIBRARY. Section,..............______________ !;i).(.'.sn.\ ii « r u SYSTEM OF THEORETICAL AND PRACTICAL CHEMISTRY. IN TWO VOLUMES, WITH PLATES. BY FREDRICK ACCUM, OPERATIVE CHEMIST, LECTURER ON PRACTICAL CHEMISTRY, AND ON MINERALOGY AND PHARMACY ; LATE CHEMICAL OPERATOR IN THE ROYAL INSTITUTION OF GREAT BRITAIN. FROM THE IMPROVED LONDON EDITION. V0LUME;I- LiB"ii\iiY 1 | ■■ ■ y ■- m ;; ..hi-.- QAL'S OFFICE | MV.-31HW1. PHILADELPHIA : \ r) I *) 0 PUBLISHED BY KIMBER & CONRAb, f NO. 93, MARKET STREET. SOLD ALSO BY J. P. PARKE; J. HUMPHREYS; HOPKINS & EARLE M. CAREY; AND B. & T. KITE. 1808. Hrowu & Mn-vilt. Piititii PREFACE. 11, Old Compton-street, Soho. THE following treatise has been composed for the in- struction of such as are actually unacquainted with chemi- cal science ; and with that view I have followed such an arrangement of the subjects, as appeared best calculated to afford a clear and permanent knowledge of their re- lations and consequences. As the proofs of chemistry are grounded upon an ap- peal to the senses, I have in the first place described some experiments, which are easy to be performed, and particularly adapted to exhibit the general nature of chemical action. But mere facts do not constitute a science. The rea- soning faculty must be exerted to dispose them in the order of cause and effect; first by the method called ana- lysis, and afterwards in that of synthesis: which last may be considered as including those tentative processes of the mind called hypotheses, which in natural science are rendered legitimate by experiment. IV PREFACE. To announce those generalities which have been de- duced from the analytical labours of former philoso- phers, and constitute the theory of the science ; to ex- hibit the conditions of the mutual actions of bodies ; and to place the student upon an eminence whence he may contemplate the phenomena with advantage, and in ma- ny cases foretel events with certainty ; require a display of the nature of chemical attraction, or affinity, and of heat. I have distinctly stated the laws of affinity in the synthetical form, and have then proceeded to illustrate those laws, by a series of experiments sufficiently strik- ing, to interest the mind and fix the doctrine in the memory. The same method is adopted with regard to heat and light; which, together with attraction and re- pulsion, constitute the causes of every chemical change. These positions and their illustrative proofs are immedi- ately followed by the classification of the simple or unde- compounded bodies, with their attributes, affections, or habitudes ; which latter are proved experimentally. The gases and the theory of their formation are next considered ; their characteristic properties are detailed ; the processes for obtaining them described; and a va- riety of the most appropriate experiments explained, by applying the general doctrines to each particular fact. Among these important first lines of chemistry, the formation of water; the production of various acids ; the nature of the air we breathe ; eudiometry; combus- tion ; and many phenomena of the utmost magnitude and value present themselves, and are elucidated by ex- periments. PREFACE. V The metals, alcalies, earths, &c. next succeed, and are treated in the same manner by direct reference to the facts they afford during chemical examination. The natural history of each, and their obvious physical and chemical properties, are first stated; then follow the means of obtaining them; and lastly, their physico- chemical properties are shown, by a series of experi- ments. A similar method pervades the whole of the work. I have endeavoured experimentally to unfold all the fundamental truths of the science. I have proceeded from first notions step by step; from generals to particulars; from premises to conclusions; deducing causes from their effects, and effects from their causes, in order to maintain a systematic connection between the several parts of the whole, and to recall to the memory all the changes which bodies are susceptible of in their mutual actions. I am persuaded this cannot be better done than by de- termining their properties by experiments under different circumstances. Hence the same facts are exhibited under various forms and relations, in order to oblige the mind to re-consider the same phenomena in different lights. It is perhaps needless to state, that I have availed my- self of all the authors who have cultivated and enriched this science. In many instances I found perspicuity of style and precision of detail, on which I could not hope to make improvements; and in such cases I have not scrupled to transcribe whatever answered my purpose. VI PREFACE. But I have faithfully quoted my authorities, and render- ed honour to whom honour is due. They who are familiar with the science will neverthe- less observe that I have done more than borrow from others. I have corrected errors which are found even in the works of modern authors of eminence; particu- larly in respect to the practical part of many processes. I have facilitated many operations; I have advanced a variety of new experiments, and pointed out such par- ticulars in the performance of others as I have found in the course of my profession to be superior to those in general use. The directions for performing chemical experiments, and the explanations in general, may be considered by some readers as top minute: but I am fully convinced that chemistry cannot be learned without actually ap- plying to the operative part of the science. It is obvi- ous that success must greatly depend on minute and clear instructions: this method of teaching cannot therefore be deemed trifling. I have indeed written for begin- ners ; but accuracy and precision are so far from being faults, that they are more acceptable even to proficients, than that loose descriptive method which leaves the whole detail of quantities, order, and operation, to be supplied by the trials of the reader himself. FREDRICK ACCUM. London, 1803. PREFACE TO THE SECOND LONDON EDITION. 11, Compton-streety Soho, I HAVE carefully revised the second edition of this work; the discoveries which have offered themselves in the field of chemical science are inserted, some new plates have been added exhibiting a variety of chemical instruments useful to the operative chemist, and no labour has been spared to render the present edition worthy of the distinguished approbation which this work has met with, amongst the chemical public. FREDRICK ACCUM. London, Jan. 1, 1807. CONTENTS OF THE FIRST VOLUME. PART I. Page Sect. I. DEFINITION OF CHEMISTRY l Methr \ of obtaining chemical operations General nature of chemistry - - 2 II. Subjects and importance of chemistry . 4 III. History of chemistry ... 7 PART II. HISTORY OF GEOLOGY Sect. I. Preliminary observations II. Theory of Burnet . III. Theory of Woodward IV. Theory of Whiston V. Theory of Hutchinson VI. Theory of Moro . VII. Theory of Le Cat . VIII. Theory of Maillet . IX. Theory of Buffon . X. Theory of Raspe XI. Theory of Worthington XII. Theory of Whitehurst XIII. Theory of De Luc XIV. Theory of Milne XV. Theory of Dr. Hutton XVI. Theorv of Williams 14 16 17 18 20 21 22 23 24 25 26 27 28 30 31 VOL. I. B A CONTENTS. Page Sect. XVII. Theory of Delametherie . • 33 XVIII. Theory of Howard ... 34 XIX. Theory of Bertrand ... 35 XX. Theory of Kirwan . • • 36 PART III. NATURAL HISTORY OF THE EARTH 40 PART IV. SIMPLE SUBSTANCES. Sect. I. Nature of simple bodies . . 45 II. Classification of simple substances 46 PART V. NATURE OF CHEMICAL ACTION. Sect. I. Instances of chemical action - 49 Experiments I, II, III, IV, V, VI, VII . . . 49—52 PART VI. ATTRACTION. Axiom of attraction ... 54 Sect. I. Proofs of the energy of attraction 55 Experiments, I, II, III, IV, V, VI, VII. . . . 55—57 II. Division of attraction . . 59 PART VII. REPULSION. Axiom of repulsion ... 60 Sect. I. Proofs of the energy of repulsion 61 Experiments I, II, III, IV, V. 61—62 Inferences ..... 63 PART VIII. THEORY OF CORPUSCULAR ATTRACTION. Sect. I. Instances of corpuscular attraction 65 Experiment I.....ib contents. XI Page Sect. II. Measurement of corpuscular attraction 65 General laws of corpuscular attraction 66 Law I. ..... ib Experiments I, II, III. . 67 Law II......68 Law III......69 PART IX. CHEMICAL AFFINITY: OR, AFFINITY OF COMPOSITION. Sect. I. II. 70 71 Chemical affinity Instances of chemical affinity Experiments I, II, III, IV, V, VI, VII. . . • 71—73 III. General laws of chemical affinity 74 IV. Experimental proofs of the laws of chemical affinity Law I. Proofs of law I. Experiments I, II. III. Law II. Proofs of law II. Experiment I, II. . Law III. • Proofs of law III. Experiments I, II, III, IV, V, VI..... Law IV. . Proofs of law IV. Experiment I, II. Law V. Proofs of law V. Law VI. . . Proofs of law VT. Experiments I, II, III, IV, V, VI. Law VII. Proofs of law VII. Experiments I, II, III. Law VIII. Proofs of law VIII. • Experiment I. ib 75 ib 76 ib ib 77 ib ib 78—79 ib ib 80 81 ib ib 82 82—83 83 84 84—85 85 86 ib xii contents. PART X. HEAT, OR CALORIC. Tag* Sect. I. Theories of heat ... 88 Nature and theorems of heat . 90 II. Methods of exciting and collecting heat 91 1. Production of heat by percussion ib 2. Production of heat by friction 92 3. Production of heat by chemical action 93 4. Solar heat .... 94 5. Production of heat by the electric spark by galvanism . . 95 III. General effects of heat . . ib Expansive property of heat . ib 1. Expansion of fluid bodies by heat 96 Experiment I. ib 2. Expansion of aeriform bodies by heat ib Experiment I. ib Nature of the air thermometer . 97 3. Expansion of solid bodies by heat 99 Experiment I. . . . ib Inferences ..... ib IV. Measurement of heat . . 100 Nature of the thermometer . 101 Nature of the differential thermometer 102 Nature of the pyrometer - . 104 V. Exceptions to the expansion by heat 105 VI. Equal distribution of heat . . 106 VII. Propagation of heat, &c. . • 107 Experiment I, II. . . 108—110 VIII. Theory of caloric of fluidity . 113 Experiment I, II. . 114—115 Production of artificial cold . 115 Tables of freezing mixtures . 116 IX. Conversion of solids and fluids into the aeriform or gazeous state . 119 Conversion of solids into the gaze- ous state . . . .120 Experiment I. . . . . ib X. Conversions of fluids into the gaze- ous state ..... ib Experiments I, II, III, IV. . 121 contents. xiii Page Sect. XI. Capacity of bodies for containing heat 125 Experiment I, II, III. 125—126 XII. Radiation of caloric . . . 127 Experiment . . . . 130 PART XL LIGHT. Sect. I. Nature oflight . . . . 137 1- Explanation of certain terms oflight 138 2. Sources of light . . . 139 II. Physical properties of light • . ib 1. Velocity of light ... ib 2. Momentum of light . . . 142 3. Light moves in straight lines . 143 Experiment I. ... ib 4. Reflection of light ... ib Experiments II, III. . . 144 5. Inflection of light . . . 145 Experiments I, II, III. . 146, 147 6. Refraction of light ... ib Experiments I, II, III. . ." 148 III. Analysis of light by the prism . 149 Experiments I, II, III. . 149, 150 IV. Theory of colours . . . . 152 Experiment I. . . . 153 V. Chemical properties of light . . 156 1. Effects of light on vegetables . ib Experiment I. . . . 157 2. Effects of light on animals . . 158 3. Effects of light on metalic oxids . 159 Experiments I, II, III. . . 160 4. Effects of light on acids . . 163 Experiments I, II. . . ib VI. Combination oflight with different bodies 164 Solar phosphori .... ib Phosphoric substances which become luminous by attraction . . 167 Experiment I. . . . 168 Photometer.....169 II. . III. - PART XII. OXIGEN . HIDROGEN . NITROGEN . 172 173 174 xiv contents. PART XIII. SULPHUR. Page Sect. I. Natural history of sulphur . . 176 Physical properties of sulphur . 177 Method of obtaining sulphur . 179 II. Experimental proofs of the properties of sulphur . . . . . 180 Experiment I, II, III, IV, V. 181—183 Combination of sulphur with metals ib Experiment I, II, III, IV, V, VI, VII, VIII. . . 183—185 Combination of sulphur with alcalies 186 Experiments I, II, III, IV, V, VI, ... . 187, 188 Combination of sulphur with earths 189 Experiments I, II. . . ib Combination of sulphur with carbon and phosphorus .... ib Experiment . . . . 190 PART XIV. PHOSPHORUS. Sect. I. Natural history of phosphorus . 192 Physical properties of phosphorus . ib Methods of obtaining phosphorus . 193 Methods of purifying and moulding phosphorus . . . . 195' II. Experimental proofs of the properties of phosphorus . . . . 196 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X, XI. 196—201 Combination of phosphorus with metals 202 Experiments I, II, III, IV, V, VI, VII, VIII. . . 202—204 Combination of phosphorus with alcalies ib Experiments I, II, III. . 204, 205 Combination of phosphorus with carbon ib PART XV. DIAMOND, OR PURE CARBON. Sect. I. Natural history of diamond . . 207 Physical properties of diamond . 210 II. Proofs of the combustibility of diamond 211 CONTENTS. XV PART XVI. NATURE AND FORMATION OF GASES. Page Sect. I. Nature, of gases . . • . 217 Formation of gases . . . 218 Experiment I. 219 Pneumatic apparatus . . . 220 II. Methods of collecting gases, and trans- ferring them from one vessel to an- other .....221 Experiment I. ib Classification of gases . . . 222 PART XVII. OXIGEN GAS. Sect. I. Properties of oxigen gas . . 224 Methods of obtaining oxi gen gas . 225 Experiments I, II, III, IV. 225—227 II. Experimental proofs of the properties of oxigen gas .... 228 Experiment I. ... ib Decomposition of oxigen gas by bodies destitute of metallic properties ib Experiment II, III, IV. 228—230 Decomposition of oxigen gas by me- tallic substances . . . 231 Experiment I, II, III, IV. 231—233 Decomposition of oxigen gas by vari- ous other substances . . ib Experiments I, II, III, IV, V, VI. . . . 233—234 PART XVIII. HIDROGEN GAS. Sect. I. Properties of hidrogen gas . . 235 Methods of obtaining hidrogen gas 236 Rationale of the processes . . 237 II. Experimental proofs of the properties of hidrogen gas .... 239 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII. 239—244 XVI CONTENTS. PART XIX. NITROGEN GAS. Page 246 247 248 Sect. I. Properties of nitrogen gas Methods of obtaining nitrogen gas . Rationale of the processes II. Experimental proofs of the properties of nitrogen gas .... ib Experiments I, II, III, IV, V, VI.....248—250 PART XX. ATMOSPHERIC AIR. Sect. I. Mechanical examination ofatmospheric air 251 Experiment I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII.....252—255 Specific weight of atmospheric air 256 Elasticity of atmospheric air . 257 Invisibility of atmospheric air . ib Dilatability of atmospheric air . 258 Experiment I. ib II. Chemical examination ofatmospheric air 259 Analysis of atmospheric air . . 260 Experiments I, II, III. . 260, 261 III. Eudiometry.....262 Priestley's eudiometer . . . 263 Scheele's ditto .... 264 De Marti's ditto .... ib Humbolt's ditto .... 265 Seguin's ditto .... 266 Bertholet's ditto .... ib Davy's ditto.....267 General remarks .... 268 PART XXI. CARBONIC ACID GAS. Sect. I. Properties of carbonic acid gas . 271 Methods of obtaining carbonic acid gas 272 Rationale of the processes . . ib II. Experimental proofs of the properties of carbonic acid gas . . . 274 Experiments I, II, III, IV, V, VI, VII, VIII, IX. 274—278 CONTENTS. xvii PART XXIL LIGHT CARBONATED HIDROGEN GAS. Page Sect. I. Properties of light carbonated hidrogen gas 279 Methods of obtaining light carbonated hidrogen gas .... 280 Rationale of the processes . . ib II. Experimental proofs of the properties of light carbonated hidrogen gas . 281 Experiments I, II, III, IV. 282, 283 PART XXIII. HEAVY CARBONATED HIDROGEN GAS. Sect. I. Properties ofheavy carbonated hidrogen gas 284 Methods of obtaining heavy carbonated hidrogen gas .... 285 Rationale of the processes .. . 286 II. Experimental proofs of the properties of heavy carbonated hidrogen gas . 287 Experiments I, II. . . . 288 PART XXIV. GAZEOUS OXID OF CARBON. Sect. I. Properties of gazeous oxid of carbon 290 Methods of obtaining gazeousoxid of carbon 291 Rationale of the processes . . 292 Inferences ..... 293 PART XXV. SULPHURATED HIDROGEN GAS. Sect. I. Properties of sulphurated hidrogen gas 295 Methods of obtaining sulphurated hi- drogen gas ..... 296 Rationale of the processes . . 297 II. Experimental proofs of the properties of sulphurated hidrogen gas . . 298 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X. . 299—301 VOL. I. c XVlll CONTENTS. PART XXVI. PHOSPHORATED HIDROGEN GAS. Page Sect. I. Properties of phosphorated hidrogen gas 303 Methods of obtaining phosphorated hi- drogen gas ..... 304 Rationale of the processes . . ib II. Experimental proofs of the properties of phosphorated hidrogen gas . 305 Experiments I, II, III, IV, V, VI, VII.....305—309 PART XXVII. NITROUS GAS. Sect. I. Properties of nitrous gas . . 310 Methods of obtaining nitrous gas . 311 Rationale of the processes . . ib II. Experimental proofs of the properties of nitrous gas . . . . . 312 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII.....312—319 PART XXVIII. GAZEOUS OXID OF NITROGEN. Sect. I. Properties of gazeous oxid of nitrogen 321 Methods of obtaining gazeous oxid of nitrogen ..... 322 Rationale of the processes . . 324 II. Experimental proofs of the properties of gazeous oxid of nitrogen . 328 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII, XIV. . . 328—334 Inferences . . . . . 334 PART XXIX. AMMONIA. Sect. I. Properties of ammonia . . . 336 Methods of obtaining ammonia. . 337 contents. X1X Page Rationale of the processes . . 338 Sect. II. Experimental proofs of the properties of ammonia .... ib Experiments I, II, HI, IV, V, VI, VII, VIII, IX, X. 338—342 PART XXX. SULPHUREOUS ACID GAS. Sect. I. Properties of sulphureous acid gas . 344 Methods of obtaining sulphureous acid gas......345. Rationale of the processes . • 346 II. Experimental proofs of the properties of sulphureous acid gas . • 1U Experiments I, II, III, IV, V, VI, VII, VIII, IX, X. 346—350 PART XXXI. MURIATIC ACID GAS. Sect. I. Properties of muriatic acid gas . 351 Methods of obtaining muriatic acid gas ib Rationale of the processes . • 352 II. Experimental proofs of the properties of muriatic acid gas . . . 353 Experiments 1,11,111, IV, V. 353—355 PART XXXII. OXIGENATED MURIATIC ACID GAS. Sect. I. Properties of oxigenated muriatic acid gas ....'. . 356 Methods of obtaining oxigenated mu- riatic acid gas .... 357 Rationale of the processes . . 358 II. Experimental proofs of the properties of oxigenated muriatic acid gas . 358 Experiments I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII, XIV. 358—361 XX contents. PART XXXIII. FLUORIC ACID GAS. p»e* Sect. I. Properties of fluoric acid gas . . 365 Methods of obtaining fluoric acid gas 366 Rationale of the processes . • ib II. Experimental proofs of the properties of fluoric acid gas lD Experiments I, II, III, IV, V. 366—368 Phosphorated carbonated hidrogen gas . 369 PART XXXIV. THEORIES OF COMBUSTION. Sect. I. Lavoisier's theory of combustion . 371 II. Thomson's theory of combustion . 378 A SYSTEM OF THEORETICAL AND PRACTICAL CHEMISTRY. PART I. SECT I. DEFINITION OF CHEMISTRY. CHEMISTRY is that department of physical sci- ence the object of which is to investigate and account for the intimate changes produced in all bodies in nature by the mutual action of their parts upon each other; by means of which their physical properties are altered, and their individuality destroyed. METHOD OF PERFORMING CHEMICAL OPERATIONS. In examining the changes which take place in natural bodies, chemistry employs either simple observation or operative experiment. It either observes the processes which are incessantly taking place in the great laboratory of nature, or institutes, on purpose for this or that inves- tigation, new processes of its own. When we observe how water is converted into ice, and ice into water; how metallic substances lose their lustre in 2 General Nature of Chemistry. the open air; we then acquire chemical knowledge by simple observation. When, again, we kindle a fire, that we may see its action upon some combustible or incombus- tible body; when we immerse a solid into a fluid, that we may learn whether the solid will be dissolved or not, in consequence of the immersion; in these and other such cases we investigate chemical truth by experiments. Of the chemical knowledge acquired by simple obser- vation every man possesses more or less ; and a very con- siderable knowledge of the chemical changes of bodies may indeed be thus obtained. But mere unassisted ob- servation is ever so inaccurate, so subject to accident, and so little capable of accomplishing any continuous and con- nected plan, that chemical inquiries almost always as- sume the form of experiment. The artificial arrangement, or method which chemistry employs to favour the mutual action of bodies, consists in the proper application of those substances to each other which experience has taught us are best calculated to pro- duce certain changes, that, in many cases, would other- wise be too minute to affect the senses individually. Those operations themselves are called chemical PROCESSES, OPERATIONS, Or EXPERIMENTS. GENERAL NATURE OF CHEMISTRY. The processes of chemistry have been usually repre- sented as either analytical or synthetical. Analysis, which is synonimous with decomposition, expresses the separation of the principles of a compound body. Synthesis denotes the reproduction of compound substances from simple bodies. Analysis is divided into simple or perfect, and into com- plex or imperfect, analysis. It is called simple or perfect when, by means of synthesis, we can re-produce a body with the very substances which were the products of the analy- sis. It is complex or imperfect, when this cannot be effect- ed. Simple analysis is the surest proof of the truth of chemical investigation : it is the most useful, and also the most rare, in all our artificial processes. From this cursory account of the nature of the processes of chemistry, it becomes obvious that the whole art of the science consists in promoting the mutual actions of bodies General Nature of Chemistry. 3 on each other, and carefully observing the phenomena that takes place. It must not be forgotten that these two methods do continually take place in the grand opera- tions of nature, of which the chemist is only an imitator. The operations all depend on certain laws established between bodies, and require nothing more in order to their being rendered active than that the bodies should be placed into such situations as enable them to exercise their action. These important truths require to be ma- turely weighed and considered by the student who intends to embark in chemical pursuits. Chemistry, therefore, consists in a detail of those facts which are founded on experiments and observations. Its basis is EXPERIENCE : from this, by regular con- clusions, it deduces a THEORY, and connects a series of accurately established facts into a certain order, called a SYSTEM. It follows from this that the evidence of chemical truth is, strictly speaking, only probable, not absolutely certain. This probability, however, is so much the greater, as the experiments on which the observations are founded are more numerous, and have been more accurately per- formed. All possible exceptions, then, being made, we may venture to consider the results which offer them- selves as true, till other facts are furnished, which by a more extensive and complete induction prove their fal- lacy. It has been thus, by simple experiments and observa- tion, that the science is become enriched with a store of facts. These facts have been gradually connected to- gether, and arranged in such order as appeared most pro- per for exhibiting their reciprocal relation to each other ; and at the same time for referring them to a smaller number of general heads, in order to consult them with the least difficulty, and to trace the laws that regulate them. SECT. II. SUBJECTS AND IMPORTANCE OF CHEMISTRY. CHEMISTRY, in its connexion with the operations of nature and the existence of man, is highly worthy of an accurate examination. It unfolds the causes of many important phenomena; it enables us to reason concerning those properties of bodies which most immediately con- cern us, and to predict their alterations; and it develops to us sublime views of the order and harmony belonging to the different parts of our system. This branch of science has been slowly formed, in consequence of minute observations made upon natural events, and of experiments in which natural agents have been placed in new relations: and though much has been done, much remains to be effected. The facts already ascertained are nevertheless sufficient to prove, that all the different known substances belonging to our globe are subjected to certain and invariable chemical laws, and that the most extensive and important chemical changes are continually taking place in the solid substance of the earth, the ocean, and in the atmosphere. All material bodies are therefore the subjects of che- mical research. The solid matters composing the terres- trial mass of the globe we inhabit; the aqueous fluids which penetrate its cavities, or float about its surface ; the more subtile gazeous matter circumfused around it; the agencies of heat, light, and other imponderable sub- stances expanded through space; are subjects for the chemical philosopher. The events which chemistry holds out are equal to, and perhaps more important than, those which belong to me- chanical philosophy. It extends itself into the province of active life. It is the nursing mother and guide of in- numerable important arts. The arts of dyeing, bleach- ing, tanning, glass and porcelain-making, printing, the working of metals, &c. are purely chemical arts. They depend so much on that science, they are so combined Subjects and Importance of Chemistry. 5 with its proper existence and its advancement, that all the steps which it makes in the knowledge of bodies, all the discoveries with which it is daily enriched, are so many new acquisitions for these arts : it perpetually improves them, adds to their processes, and creates new ones. Agriculture can only be rationally improved by calling in the assistance of the chemical philosopher; for it is che- mistry which explains the phenomena of vegetation, germination, the growth, the ripening, and the death of plants. To the public economist chemistry presents a trea- sure of useful information. By means of this science alone can he expect to attack with success the destroying pes- tilence, so far as it is an object of human prevention, and to guard against other evils to which the state of the elements give rise. To the domestic economist this science abounds with pleasing and wholesome lessons. It enables him to make a proper choice of meats and drinks ; it directs him to those measures with respect to aliment, cookery, cloth- ing, and respiration, which have the best tendency to promote health, enjoyment, and cheapness of living; and it sets him on his guard against unseen evils, to which those who are ignorant of its laws are continually exposed. The gardener, whose employments are more curious than those of the farmer, equally needs its assistance. The nature of the different manures necessary for the various kinds of vegetables, the influence of light, the different temperatures, the quantity of moisture, the preservation of seeds, roots, plants, &c. are all founded upon chemi- cal principles. Chemistry likewise directs the labours of the husband- man. In the dairy, milk cannot be kept sweet and fresh, butter cannot be made, cheese cannot be prepared, with- out a skill founded wholly upon chemical principles. The culinary art, for preparing wholesome and nu- tritious food ; and the method of preserving bacon, hams, and other animal and vegetable substances ; is entirely chemical. The whole process of the vintage; the art of the brewer and distiller ; the preparation of cyder, perry, home-made wines, &c. vinegar, &c. ; all depend upon chemical principles. vol. j. D 6 Subjects and Importance of Chemistry* To the rural economist this science furnishes prin- ciples and agents of inestimable value. It teaches him the food of plants; the choice and use of manures ; and the best means of promoting the vigour, growth, productive- ness, and preservation, of the various vegetable tribes. In medicine and pharmacy great benefits have been derived from the discoveries of chemical philosophers. To the physician this science is of the greatest value. He learns from it to compound his medicines, to disarm poisons of their force, to adjust remedies to diseases, and to adopt general means of preserving health. The chemist begins his inquiries where those of the na- tural historian and those of the natural philosopher termi- nate. The first of these examines bodies, in order to arrange them into certain classes, genera, and species : the second investigates the general properties of objects, such as their density, elasticity, figure, &c. and calculates the relative forces of their mechanical actions. The chemist,however, goes further:...he looks into the more intimate structure of substances ; he separates their heterogeneous particles from each other; he resolves them further into their simple or elementary substances, and examines their nature and properties when in a detached or simple state. He thus learns their reciprocal relation to each other, and becomes enabled to re-combine them • • in proportions different from those in which they were united by nature, in order to form new and useful com- pounds, which nature herself does not produce. But chemistry is not only valuable as an art which sup- plies many of our wants, our comforts, and luxuries : its objects are sublime and beautiful in another point of view ...it removes the veil from the fabric of nature, and makes us acquainted with all the phenomena which happen around us...it affords pleasure to the senses, and calls into action a laudable curiosity, which characterises the minds of those who ^re of a scientific turn; exciting at the same time a spirit of rational inquiry, which is capable of producing the most beautiful and striking phenomena, well calculated to serve as an instructive and rational amusement. SECT. Ill HISTORY OF CHEMISTRY. FROM what has been already stated, it becomes obvi- ous that chemistry may be considered both as a science and as an art :....as a science, it may be said to be of modern date ; but as an art, it must be coeval with the earliest exercise of the industry of man; for many operations now considered chemical certainly must owe their invention to the immediate wants of society. The method of kindling fires, the arts of baking bread, moulding clays and burn- ing them into pottery, extracting metals from their ores, the methods of working them, and various other pro- cesses, were certainly known to the antediluvians. If we attempt to trace its birth as a science, we find it ori- ginating in fables and obscurity ; nor indeed could we de- rive any chemical advantage if it were possible to dispel the cloud by which it is enveloped. Whether Tubal-Cain, who is stated to have been a worker in metals in the time of Abraham; whether Noah, who made wine and bricks, and who preserved the requi- site stores of provisions in the ark, during the deluge ; whether Moses, who burnt the golden calf of the Israelites; or whether Cleopatra, who is said to have dissolved a pearl; understood chemistry, are questions, important perhaps to the antiquarian, but of little value to the chemist. It is more plausible to suppose that a science so much de- pending on the state of the arts, the civilization of man, and the experience of ages, could not possibly exist in such a remote time. But as it would be in some respect unpardonable for those who devote themselves to the study of chemistry to be utterly unacquainted with its history, we shall shortly notice the outlines of this history, and fix the dates of the progressive discoveries of our pre- decessors which led to the establishment of the science. The Israelites acquired their information in Egypt. It was there that Moses learnt the properties of metals, the method of extracting oils, the preparation of odoriferous 8 History of Chemistry. gums and perfumes, the solution of gold, the dyeing of linen, the making of wine, vinegar, the art of gilding, and the fabrication of pottery, soap, &c. The Phoenicians were the first who applied themselves to the examination of the effect of different bodies upon each other, which maybe called chemical. They invented the art of tinging garments with a purple-coloured matter, produced by a species of shell-fish. They manufactured glass, with which they traded; artificial gems, perfumes, and odoriferous balsams. They also invented the art of preserving the fruits of various plants and vegetables. Iti China, even in these remote ages, the inhabitants were acquainted with nitre, gun-powder, borax, alum, verdegris, sulphur, mercurial-ointment, various pigments, dyes for linen and silk, and with the art of making paper. They also manufactured porcelain, and different other kinds of pottery; they made a variety of metallic com- pounds. The use of wax was known to them, and was very well applied. From this account of the state of the arts we may be permitted to consider the Chinese, according to Guignes, as an Egyptian colony. The Carthaginians, who. were a colony of the Phoe- nicians, learnt their arts ; but the priests in whose hands the learning was retained, handed them to their succes- sors veiled in hieroglyphic mystery. The Grecians derived their arts depending upon che- mical principles from the Phoenicians. They practised all the inventions of their predecessors successfully. It is natural that the obvious difference or changes of the bodies that surround us could not escape the notice of a people of so philosophical a turn of mind as the Gre- cians : hence both Aristotle and Empedocles taught the doctrine of the four supposed elements, air, earth, fire, and water. The Romans, a people always at war and victorious, were not distinguished among the nations of the ancient world as discoverers in the arts, or inventors in science. After having conquered and subjugated almost all the civi- lized parts of the earth, they arduously cultivated the arts of their masters, the Grecians. They understood the art of making excellent wines and ardent spirit: they knevr the application of manures; they prepared incombustible History of Chemistry. 9 cloth for wrapping up the dead bodies which were destined to be burnt, in order to preserve their ashes distinct from those of the funeral pile : they moulded clays, and con- verted them, by burning, into different kinds of pottery; they were also acquainted with almost all the metals, and the methods of coining them: they were skilled in the culinary art ; their cooks invented delicious sauces,* as luxuries for their table: and the remains of their aque- ducts, and other works of architecture, evince the incom- parable perfection of their cements. But all the arts, the sciences, and literature of the Ro- mans and Greeks, were destined to sink into oblivion. Hosts of barbarian conquerors descended upon them from the North ; the energies of civilization withered at their touch, and its works were destroyed before them. During all this epocha of war and desolation chemistry acquired only a few facts, without connection and with- out order. Driven as it were from Europe, the arts obtained an asylum with the Arabians ; who improved many, and applied them to medicine. The attachment of this nation to magic, and their inclination for the marvellous, soon increased the mysteries in which the arts were then al- ready involved; and hence alchemy, or the art of trans- muting base metals into gold, took its rise. This hap- pened about the commencement of the fourth century. As this delusive dream of the imagination held out a bait to avarice, it soon acquired a train of followers. In- toxicated with the idea of the boundless wealth that would reward success, the great object was the philosopher's stone, and the possibility of the discovery of an universal medicine, which should cure every disease, and give im- mortal health and life to embodied man. The research was pursued with an ardour which no disappointment could damp, and the mania spread from one country to another. In Egypt it attracted the attention of the go- vernment. Dioclesian, apprehensive that the dreams of the alchemists might be realised, ordered all their books to be burnt, in order that he might subdue them with more facility. After this period the alchemists were strongly opposed by several able and learned men. They were considered as people who held intercourse with malevolent spirits. 10 History of Chemistry. Roger Bacon, the alchemist, who is supposed to be the inventor of gun-powder, was excommunicated by the pope and imprisoned ten years, for supposed dealings with the devil; and Paracelsus was thought to have an evil spirit confined in the pommel of his sword. Indeed, many of the adherents of alchemy endeavoured to enforce the,belief of charms and spells. Paracelsus, the most im- petuous man, who in ostentation and lies surpassed all his predecessor alchemists, promised immortality in this world to his followers ; but his premature death, which happened in 1541, exposed his vanity, and blasted all their hopes. It would surpass our limits were we to give a circum- stantial detail of the state of the chemical arts at that pe- riod. It will be readily conjectured, that, owing to the great numbers of experiments which were performed amongst the alchemists, many valuable discoveries must have been made unintentionally. The alchemists actually collected a rich store of important chemical facts ; and if they did not succeed in drawing gold from their furnaces, they produced those materials on which the true doctrine of chemistry was afterwards erected. If we were to fix the existence of chemistry in the arts which it elucidated, it is evident that this science would have preceded every other; that Egypt would have been its cradle; and that it had been cultivated for time im- memorial in China. Vinegar was the only acid then known : amongst the salts they treated only of sea-salt, ammoniac, verdegris, alum, and soda; which latter was called nitre. They dis- tinguished no earth but lime and clay. Sulphur and bitu- men were the only inflammable matters employed. They worked seven ductile metals ; the brittle metals were un- known. There were no real experiments made in chemis- try ; so that among the whole of these facts we perceive nothing more than the infancy of the art: there neither was nor could be any scientific system, for as yet the sci- ence of chemistry did not exist. At the end of the seventeenth century chemistry began to assume a scientific form. The scattered chemical facts which the alchemist had discovered were collected, ar- ranged, andjreduced to principles. History of Chemistry. 11 The first chemical writer that excites our notice is Becher. This man collected all the facts which were noticed before him, and pointed out many important ob- jects to which the researches of chemists ought to be di- rected. The publication of his Physica Subterranea, in 1669, forms a very important sera in the history of che- mistry. At that period chemistry escaped for ever from the trammels of alchemy, and became the rudiments of the science which we find at present. Becher distin- guished himself so highly by his chemical knowledge as to cause the names of all former theorists to be forgotten, after having laid the fo\indation of the famous system of phlogiston. He died in the year 1682. Soon after his death arose one of his pupils, whose name was Stahl. He simplified and improved the doctrine of his master so much that he made it entirely his own ; and accordingly it has been known ever since by the name of the Stahlean Theory. He was the first who had a clear notion of chemical union, and gives many instances of double elective attractions. His writings have done him immortal honour, and ranked him amongst the first charac- ters of the age in which he lived. He died in the year 1704. Ever since the death of these chemists chemistry has been cultivated with success. Men of eminence have appeared every where ; discoveries have been multiplied which led to numerous important facts. The names of Margraaf, Scheele, Bergman, Baume, Rouelle, &c. will remain distinguished in the annals of chemical science. The spirit of chemical inquiry which these philosophers had infused summoned on a sudden into action the facul- ties of the most learned men of Europe. Several of the invisible agents which form so important a part in the economy of nature, were discovered. Dr. Priestley dis- covered, in 1777, various aerial fluids, formerly totally unknown to chemists; Dr. Black traced the laws of latent heat, and discovered the carbonic acid. The sci- ence of electricity was as it were created, the thunder was taken from the clouds, and the properties of the atmosphere were examined with accuracy. All these new discoveries embarrassed the votaries of the doctrine of Stahl; and the conclusions to which they led were of such a nature as to puzzle and to contradict many of the laws of the science. It was requisite to take 12 History of Chemistry. but one step further that the doctrine of phlogiston might be exploded for ever. This was left to Lavoisier. Lavoisier, endowed by nature with the most happy genius for science, and favoured by his own princely for- tune and the liberal bounty of the French government, instituted a series of ingenious and accurate experiments, the result of which proved to demonstration that the theory of phlogiston was founded in error. His experi- ments were repeated, under every diversity of circum- stances, by all the philosophers of Europe: his reason- ings and inferences were vigorously attacked by the de- fenders of the phlogistic theory; a kind of chemical war was thus kindled in the republic of letters, which was carried on with great animosity; and posterity will see with regret men of undoubted genius at times divesting themselves of the armour of truth and candour, and en- deavouring to serve their party and stab their adverse fellow-labourers with darts steeped in the poison of calumny and falsehood. These things have passed away: the contest has been productive of good effects, which infinitely surpass the bad ones: it has occasioned an accu- mulation of facts, produced a rigid examination of the- ories and opinions, introduced accuracy in chemical ex- periments, and given that tone and vigour to the cultiva- tors of chemistry which have brought to light the most sublime and unlooked for truths. The principles of Lavoisier have triumphed, and are now taught in all the schools of Europe: his opponents have become his disciples; and thus he has erected the luminous and beautiful theory of chemistry which all the chemists of Europe have now adopted. What a pity that the sanguinary tyranny of Robespierre should not even have spared this man ! who perished on the 7th of May, 1794, under the axe of the guillotine. Thus chemistry is become an entirely new science. It is no longer confined to the laboratory of the arts : it has extended its flight to the sublimest heights of philosophy, and pursues paths formerly regarded as impenetrable mysteries. Placed for ever in the elevated rank it now holds, rich with all its new conquests, it is become the science most adapted to the sublime speculations of. philo- sophy, the most useful in advancing all the operations of History ef Chemistry. 13 the arts, and the most rational for scientific amusement. Exact in its process, sure in its results, varied in its ope- rations, without limits in its applications and its views, severe and geometrical in its reasoning, there is scarcely any human occupation which it does not enlighten, and upon the perfection of which it may not have great influ- ence. It bestows enjoyment to every class of individu- als : and who would not be ambitious of becoming ac- quainted with a science which enlightens almost every species of human knowledge ? Amongst the number of philosophers who have since that time cultivated and enriched the new theory of che- mistry with discoveries which will for ever give immor- tality to their names, we have to notice Aikin, Babing- ton, Bancroft, Beddoes, Blagden, Cavendish, Chenevix, Chrichton, Cruickshank, Davy, lord Dundonald, lord Dundas, Fordyce, Garnett, Hatchett, Henry, Higgins, Hope, Howard, Kirwan, bishop of Llandaff, Murray, Nicholson, Pearson, Tenant, Tilloch, Thomson, Wedg- wood, and Wollaston; Achard, Crell, Gilbert, Gren, Goetling, Humbold, Hermbstaedt, Klaproth, Lowitz, Richter, Scherer, Tromsdorf, Westrumb, Wiegleb; Ber- tholet, Chaptal, Fourcroy, Lagrange, Guiton, Van Mons, •Proust, Sequin, Vauquelin, &c. &c. VOL. I. THEORIES OF GEOLOGY. PART II. SECT. I. THE material universe presents itself to an enlarg- ed human observation as an immense assemblage of sys- tems within systems, each complete in itself, yet con- nected, by numberless relations, with all around it ; a larger still including a less, till all nature is, in this last grand result, comprehended in—one whole. The laws of this vast universe can be studied by us on- ly in its inferior subdivisions. We conceive of it as sub- divided into planetary systems. Comets are the only agents of combination among these systems with which we have any tolerable acquaintance. It is from the con- sideration of the appearances of that particular system to which our earth belongs that all our science concerning the laws of material nature is derived. When we con- fine our views to the globe we inhabit, we discover a vast variety of substances which may well excite our curiosity and arrest our attention. We perceive our earth to be a solid globe, composed of an assemblage of substances considerably fixed, and not to be destroyed without a considerable force of impulse. We observe a large part of it covered with an ocean, and numberless streams of cold liquid matter tending with great activity to inces- sant motion. Around this earth and water, to a great but unknown height, is circumfused an atmosphere of an impalpable gazeous fluid, intermingled with portions of every solid Theories of* Geology. 15 or aqueous matter that by an extreme comminution is capable of suspension in this aerial fluid. Different opinions have been formed concerning the question, in what manner our earth was brought into the present distribution of its parts. An origination of this globe out of a chaos was the general belief of the ancients. Moses, in the beginning of the Pentateuch, gives an account of a series of succes- sive changes, which he represents as the first which took place, from the moment'at which matter was made subject to the laws it now obeys to that aera at which it was finally fit for the residence and support of animals, and had living inhabitants, brute and human, placed upon it. In modern times, different classes of speculatists have attempted to investigate the circumstances which must have attended the origin of it. Divines have endeavoured to justify the account of Moses, by an appeal to the present laws of nature: but Burnet and others have been easily convicted of supposing primaeval states of things utterly incompatible with these . laws. Chemists have conceived that the origin of the earth, in its present form, is from a general liquidity of its whole matter: others again have attributed it to the action of fire. Astronomers have been persuaded that it was owing to the action of some comet, or to an altered arrange- ment of the planets. Others have conceived the idea of a world perhaps without beginning, but by the action of internal fires, with volcanic orifices, continually lacerated, undermined, and subverted, with the constant rise of a new earth, the residue and product from those fires, by which the for- mer was demolished. Others, again, have fancied a continual flitting of the ocean around the globe ; by which that which was lately land becomes now the bottom of the sea, and that which is now covered by the sea is again to become land. These fanciful opinions, to say nothing of the impious nature of some of them, have generally rather resembled philosophical dreams than the conceptions of waking and sober reason. Their authors, in forming them, have been too often guided by imagination more than judgment; and 16 Theories of Geology. have laboured rather to support a favourite hypothesis than to consult the voice of authentic history, or patiently to examine the materials and structure of the fabric which they undertook to describe. It may, however, not be improper to take a brief review of some of the more conspicuous among the great number which, at different periods and in different parts of the world, have been received by philosophers. SECT. II. THEORY OF BURNET. THE first theory of geology which deserves to be no- ticed is that of the rev. Dr. Thomas Burnet.* This ce- lebrated theorist was a man of genius and taste ; and his work, if it do not command the assent of the philosophic mind, will be found to display much learning, and a very vigorous imagination. According to Dr. Burnet the earth was first a fluid heterogeneous mass. The heaviest parts descended and formed a solid body. The waters took their station round this body, and all lighter fluids rose above the water. Thus, between the coat of air and that of water a coat of oily matter was interposed. But as the air was then full of impurities, and contained great quantities of earthly particles, these gradually sub- sided and rested upon the stratum of oil, and composed a crust of earth mixed with oleaginous matter. This crust was the first inhabitable part of the earth; ai.d was level and uniform, without mountains, seas, or other inequali- ties. In this state it remained about sixteen centuries, when the heat of the sun, gradually drying the crust, produced, at first, superficial fissures or cracks; but, in process of time, these fissures became deeper, and increas- ed so much, that at last they entirely penetrated the crust. Immediately the whole split in pieces, and fell into the abyss of waters which it had formerly surrounded. This wonderful event was the universal Deluge. These • Telluris Theoria Sacra. This work was first published in 1680 in the Latin language. It was afterwards translated by the autlior, and published in two parts in 1683 and 1690. Theories of Geology. 17 masses of indurated earthy matter, in falling into the abyss, carried along with them vast quantities of air, by the force of which they dashed against each other, accu- mulated, and divided in so irregular a manner, that great cavities, filled with air, were left between them. The waters gradually opened passages into these cavities, and in proportion as the cavities were filled with water, parts of the crust began to discover themselves in the most elevated places. At last the waters appeared no where but in those extensive valleys which contained the ocean. Thus our ocean is a part of the ancient abyss; the rest of it remains in the internal cavities, with which the sea has still a communication. Islands and rocks are the small fragments, and continents the large masses, of the ante- diluvian crust: and as the rupture and fall of the mass were sudden and confused, the present surface of the earth is full of corresponding confusion and irregularity.* SECT. ill. THEORY OF WOODWARD. THIS " elegant romance" of Burnet was succeeded by the work of his countryman, Mr. Woodward, who, in 1695, published Essays towards a Natural History of the Earth, and terrestrial bodies. Though he possessed much more knowledge of mi- nerals than his predecessor, and on this account had greatly the advantage of him, he produced a work far less ingenious and interesting. He also proceeded on the supposition of the Mosaic history being true, and ascribed the present aspect of our globe to the influence of the general deluge. He supposed that all the substances of which the earth is composed were once in a state of so- lution ; that this solution took place at the flood ; that on the gradual retiring of the waters the various substances held in solution, or suspended in them, subsided in distinct strata, according to their specific gravities; and that these are arranged horizontally, one over the other, like the coats of an onion. As this theory was soon found * Sullivan's Vieiu of Nature, vol. i. letter 6 18 Theories of Geology. to contradict some of the plainest and most unquestionable facts which geologists observed, it has had few admirers, and its refutation has been usually considered as obvious and easy. SECT. IV. THEORY OF WHISTON. IN 1696 Mr. William Whiston, a man of uncommon acuteness, and of still greater learning, published a New Theory of the Earth, from its original to the consummation of all things. He supposed the earth, in the beginning, to be an uninhabitable Comet, subject to such alternate extremes of heat and cold, that its matter, being some- times liquefied and sometimes frozen, was in the form of a chaos, or an abyss surrounded with utter darkness. This chaos was the atmosphere of the comet, composed of heterogeneous materials, having its centre occupied with a globular, hot, solid nucleus, of about two thou- sand leagues diameter. Such was the condition of the earth before the period described by Moses at the time of creation. The first day of the creation every material in this rude mass began to be arranged according to its specific gravity. The heavy fluids sank down, and left to the earthy, watery, and aerial substances, the supe- rior regions. Round the solid nucleus is placed the heavy fluid, which descended first, and formed the great abyss, upon which the earth floats, as a cork upon quick- silver. The great abyss is formed of two concentric circles ; the interior being the heavy fluid ; and the su- perior, water; upon which last, the earth, or the crust we inhabit, is immediately formed. So that, according to this theorist, the globe is composed of a number of coats or shells, one within the other, of different materials, and of different densities. The air, the lightest sub- stance of all, surrounds the outer coat; and the rays of the sun, making their way through the atmosphere, pro- duced the light which Moses tells us first obeyed the di- vine command. The hills and valleys are formed by the mass of which they consist pressing with greater or Theories of Geology. 19 less weight upon the inner coat of the earth; those parts which are heaviest sinking lowest into the subjacent fluid, and making vallies, and those which are lightest rising higher and forming mountains. Such Mr. Whiston supposed to be the state of the globe we inhabit before the Deluge. Owing to the superior heat, at that time, of the central parts, which have been ever since cooling, the earth was more fruitful and popu- lous anterior to that event than since. The greater vigour of the genfal principle was more friendly to animal and vegetable life. But as all the advantages of plenty and lon- gevity which this circumstance produced were productive only of moral evil, it pleased God to testify his displea- sure against sin, by bringing a flood upon a guilty world. The flood was produced, as this theorist supposed, in the following manner. A Comet, descending in the plane of the ecliptic to its perihelion, made a near approach to the earth. The approximation of so large a body raised such a strong tide, and produced such powerful com- motion in the abyss concealed under the external crust, that the latter was broken, and the waters which had been before pent up, burst forth with great violence, and were the principal means of producing the deluge. In aid of this, he had recourse to another supposition, which was, that the comet, while it passed so near the earth as to produce these effects by the force of attraction, also in- volved our globe in its atmosphere and tail for a consi- derable time, and deposited vast quantities of vapours on its surface, which produced violent and long-continued rains; and, finally, that this vast body of waters was re- moved by a mighty wind, which dried up a large por- tion, and forced the rest into the abyss from which it had been drawn, leaving only enough to form the ocean and rivers which we now behold. 20 Theories of Geology. SECT. V. THEORY OF HUTCHINSONV AT an early period of the eighteenth century, the celebrated John Hutchinson formed a theory of the earth, which he professed to derive from Scripture.* He sup- posed, that, when the earth was first created, the terres- trial matter was entirely dissolved in the aqueous, form- ing a thick, muddy, chaotic mass ; that the figure of this mass was spherical, and on the outside of this sphere lay a body of gross dark air ; that within the sphere of earth and water was an immense cavity, called by Moses the deep; that this internal cavity was filled with air of a kind similar to that on the outside ; that on the creation of light the internal air received elasticity sufficient to force its way through the external covering ; that imme- diately on this, the water descended, filled up the void, and left the earth in a form similar to that which it bears at present; that when it pleased God to destroy mankind by a flood, he caused, by his own miraculous agency, such a pressure of the atmosphere on the surface of the earth, that a large portion of it was forced into the inter- nal cavity which it had formerly occupied, and expelled the waters from it with great violence, spreading them over the surface ; that the shell of the earth was by this means utterly dissolved, and reduced to its original state of fluidity ; and that, after the divine purposes were an- swered by the deluge, the globe, by a process similar to that which at first took place, was restored to the form which it now bears. * This theory was enlarged and commented upon by Mr. Catcot, a follower of Hutchinson, who, in 1768, published a volume on the subject. Theories of Geology. 21 SECT. VI. THEORY OF MORO. IN the year 1740 the abbe Moro, of Italy, published a theory of the earth, which he chiefly derived from the works of Ray, of the preceding centuiy. He supposed that the surface of the earth, as we now behold it, and especially the mountainous parts, arose originally from the bottom of the ocean. At first, according to him, these mountains contained neither strata of shells nor any organ- ized fossils ; but by means of subterranean conflagrations, earthquakes, and volcanoes, these substances were thrown up in confused heaps, after which they successively sub- sided according to their different specific gravities, and thereby necessarily disposed themselves in different strata. He also maintained that these submarine eruptions, while they threw up huge and irregular masses of matter, also ingulfed marine plants and animals of every kind, which subsided in like manner, and thus formed new mountains, and new beds of stones, sand, metals, and other minerals, intermingled with the remains of vegetable and animal bodies, all which remained under the sea till some new agitation threw them above its surface. He supposed that the waters by which the earth was originally over- flown subsided by degrees,the dryland first appearing in places adjacent to that where the first man and animals were placed at the creation ; that the land extended itself gradually, a considerable time elapsing before the waters had returned into their proper bed, during which time the shell-fish, multiplying in great abundance, were uni- versally distributed by the waters of the sea ; and that when the bottom of the sea was raised up by the earth- quakes that accompanied the deluge, and formed the mountains, whole beds of such shells were thrown up, and distributed as we now behold them. VOL. T. r 22 Th co r i es of Geo logy. SECT. VII THEORY OF LE CAT. ABOUT the year 1744 M. le Cat, a philosopher of France, proposed a theory of the earth differing f'om all which had preceded it. According to him, in the beginning, the substance whence metals, stones, earths, and other mineral bodies were to be formed, was a soft mass, consisting of a kind of mud. The earth was a globe, or regular spheroid, and its surface was uniform and free from hills and vallies. The sun and moon were afterwards created. The fluid which covered the mud became agitated by the flux and reflux to which it was subjected by attraction, and the mud was variously and violently moved. This agitation increasing, part of the mud became exposed, and dried. Continents were thus formed. The materials of the earth being compact and solid, the sea continually excavated its bed; and from the continual retreat of it, and the exca- vation of the earth, this globe is doomed to be at last so perfectly undermined as to produce a confluence of the sea from hemisphere to hemisphere. The earth becoming thus hollow, and its shell being gradually extenuated, will at length fall to pieces ; a new chaos will be formed, the fabric will be again revived, as at first; and a periodical dissolution ard renovation take place. Le Cat professed to believe the sacred scriptures, and discovered an anxi- ous desire to show that his theory was consistent with them ; but the best judges among his contemporaries, and since that period, have pronounced it equally inconsistent with the structure and phenomena of our globe, and with the Mosaic history. Theories of Geology. 23 SECT. VIII. THEORY OF MAILLET. ABOUT the year 1750 appeared the Telliamed of M. Maillet, a French writer of some note. He taught, that the earth was once w holly covered with water, which, by means of strong currents, raised in its bosom all those mountains which different countries bear on their sur- face ; that this water has been ever since gradually dimi- nishing, and will continue to diminish until it shall be quite absorbed; that our globe, being then set on fire, will become a sun, and have various planets revolving in its vortex, till its igneous particles being consumed, it will be extinguished; that then it will roll through the immensity of space, without any regular motion, till it is again covered with watery particles, collected from other planets, when it will fix in the vortex of a new sun, and again go through the same course of motions and changes, being supplied with fresh inhabitants, resembling those by which it is tenanted at present; that the earth has probably been undergoing revolutions of this kind from all eternity, and will continue to go through a succession of them without end. This atheistical and absurd theory, if it deserve the name, not more hostile to reve- lation than to all sound philosophy, seems to have gained but few adherents, and but little celebrity. SECT. IX. THEORY OF BUFFON. AFTER M. Maillet, his countryman, the count de Buffon, formed a new theory of the earth, which has been much celebrated, and, notwithstanding its incon- sistency with revelation, and the visionary absurdities 24 Theories of Geology. which it involves, has gained many advocates and ad- mirers.—According to this ingenious theorist, a comet falling into the body of the sun with great force, struck from its surface a large mass of liquid fire. The comet communicated to. this fragment, thus driven off from the sun, a violent impulsive force, which it still retains. This fragment forms the globe we inhabit. It assumed its present figure when in a fluid state. As the heated mass gradually cooled, the vapours which surrounded it con- densed, fell down in the form of water upon the surface, depositing at the same time a slimy substance, mixed with sulphur and salts, part of which was carried by the waters into the perpendicular fissures of the strata, and produced metals; the rest remaining on the surface, and giving rise to vegetable mould, with more or less of ani- mal and vegetable particles. Thus the interior parts of the globe were originally composed of vitrified matter, and they continue so at present. Above these were placed those bodies which the fire had reduced to the smallest particles, as sands, which are only portions of glass, and above these pumice stones, and the dross of melted matter, which gave rise to different clays. The whole was covered with water to the depth of five or six hundred feet. This water deposited a stratum of mud, mixed with all those materials which are capable of being sublimed or exhaled by fire, and the air was formed of the most subtile vapours, which, from their levity, rose above the waters. Such are the outlines of a theory bold and plausible, as might have been expected from the mind of its author, but unsubstantial and deceptive. Its manifest object is to exclude the agency of a Divine Architect, and to re- present a world begun and perfected merely by the operation of natural undesigning causes. That it cannot be reconciled with the sacred history, will appear evident on the slightest inspection ; and that it involves the grossest philosophical absurdities has been clearly shown bv succeeding geologists. Theories of Geology, 2S SECT. X. THEORY OF RASPE. M. de Button's theory was warmly opposed, soon after its publication, by Raspe, a geologist of Germany.* He also opposed the theory of Moro before mentioned, though he considered it as approaching much nearer the truth than the ingenious fable of the French naturalist. He insisted, that the opinion of continents and moun- tains having been thrown up from the bottom of the ocean, solely by submarine conflagrations and volcanoes, was abundantly refuted by close observation. He contended, likewise, that in veins of sand, marble, chalk, and slate, there are found no indications of a burning soil, but ra- ther of a sediment disposed by the agitation of the sea. Accordingly, he maintained, that the strata, of which the shell or surface of the earth is composed, were ori- ginally formed at the bottom of the sea, by the constant agitation of the waters, and the continual production of plants and shells; that the subterraneous explosions and earthquakes, breaking through the bottom of the sea, not only formed banks, hills, and submarine mountains, of its broken parts, but also frequently raised up such large portions of the bed of the ocean, with its incumbent strata, as to form islands and dry mountains. At some times, as he supposed, the presence of so large a body of water caused it to break through the cavities made by previous eruptions, and at other times the violence of the subterraneous explosions was so great as to remove moun- tains from one place to another; while the heat of the internal fires causing these explosions was so intense as to melt, calcine, or vitrify, all adjacent substances. • Specimen Historic Naturalis Globi Terraquxi.—Autore Rudolph* Erico Raspe. 8vo, I.eipsic, 1763. i6 Theories of Geology. SECT. XI. THEORY OF WORTHINGTON. IN 1773, Dr. William Worthington published a theory,* in which great learning and piety, and a consi- i derable share of ingenuity, are combined. He main- tained that the earth, in its primitive state, was plain and uniform; and that all mountains, and every thing irre- gular and rugged in the surface of it, are the result of the curse pronounced on the ground after the fall ; that the melancholy lapse of our first parents was immediate- ly followed by earthquakes, and every species ol convul- sion, which produced these dreadful effects in the sur- face of our earth; that the antediluvian earth greatly abounded with water, much more than at present, and that the greatest quantity of it was collected about the poles ; that at first the poles of the earth were erect, and at right angles with the plane of the equa or ; that the centre of the earth was then the centre of gravity ; that the deluge was produced by the centre of gravity being removed twenty-three degrees and a half nearer to one of the poles, which, led to a corresponding deviation of the poles from their former position, and thus threw the great body of water accumulated round them on those parts of the earth where little had existed before, and by these means drowned them. This event he supposed, increased the irregularity of the earth's surface, and pro- duced many of those phenomena, which so plainly esta- blish the reality of the general deluge. * Scripture Theory of the Earth, 8vo, 1773. Theories of Geology. 27 SECT. XII. THEORY-OF WHITEHURST. ANOTHER British theorist, of still more celebrated name, published a new system of geology in 1778. This was Mr. Whitehurst, a gentleman of respectable talents and information, and whose theory has attracted consider- able attention*. Mr. Whitehurst supposes, that not only this globe, but the whole of the planetary system, was once in a state of fluidity, and that the earth acquired its oblate spheroidical form by revolving round its axis in that state. In this fluid state, the component parts of the earth were suspended in one general undivided mass, u without form and void." These parts were endued with a variety of principles or laws of elective attraction, though equally and universally governed by the same law of gravitation. 1 hey were heterogeneous ; and by their attraction progressively formed a habitable world. As the component parts of the chaos successively sepa- rated, the sea universally prevailed over the earth ; and this would have continued to be the case had it not been for the sun and moon, which wrere coeval with the earth, and by their attractive influence interfered with the regular subsiding of the solid matter, which was going on. As the separation of the solids and fluids increased, the former were moved from place to place, without re- gularity ; and hence the sea became unequally deep. These inequalities daily becoming greater, in process of time dry land was formed, and divided the sea ; islands gradually appeared, like sand-banks above the water, ami at length became firm, dry, and fit for the reception of the animal and vegetable kingdoms. He supposed that mountains and continents were not primary productions of nature, but of a very distant period from the creation; that they are the effects of subterranean fires and cmmo- * An Inquiry into the Original State and Formation of the Earth, Sec. by John Whitehurst, F. R. S. 1778. 28 Theories of Geology. tion* and were produced when the strata of the earth had acquired their greatest degree of firmness and cohe- sion, and when the testaceous matter had assumed a stony hardness. And, finally, that the marine shells found in various places, on and below the surface of the earth, were for the most part generated, lived and died, in the places in which they are found; that they were not brought from distant regions, as some have supposed ; and consequently, that these beds of shells, &c. were ori- ginally the bottom of the ocean. SECT. XIII. THEORY OF DE LUC. TWO or three years after the appearance of Mr. Whitehurst's publication, M. de Luc, of Geneva, dissa- tisfied with all the numerous theories which had been proposed, offered another, which has occupied consider- able attention in the scientific world.* He supposes that the ocean once covered our continents; that the bottom of the old ocean was full of mountains, which neither the waters, nor any other cause known to us, formed, and which he therefore calls primordial. These mountains rose above the surface of the waters, and formed islands. These islands, and the ancient continents, were fruitful and well peopled; and the ancient sea had tides, currents, and tempests, as the present ocean. These powers acting upon the soft matters which are known to have formed the bottom of the ancient ocean, produced accumulations of calcareous substances, which, in process of time, became more or less mixed with marine bodies. The rivers, in the mean while, carried from the land into the sea scattered remains of animal and vegetable productions; the sea itself washed them from its coasts into its bosom ; and these materials, transported by currents, became a * Lettres Physiques et Morales sur VHistoire de la Terre et de I'Hoin- ine, &c. by J. A. de Luc, 8vo, 5 torn. 1780. This theory, as to its princi pal outlines, was first suggested by Mr. Edward King; but was after- wards much extended and improved by M. de Luc. Theories of Geology. 29 secondary soil upon its primordial bottom. Fires and elastic fluids, formed by fermentations, made various openings in the bottom of the ocean, whence proceeded torrents of liquid suustances and lava ; which gave rise to the volcanic mountains observable on the surface of our continents. The continents which existed in a state of population and fertility, w hiie the sea covered those which we now inhabit, though they did not form a solid mass, but were, properly speaking, vaults, which covered im- mense caverns, maintained their elevation above the level oi the ocean by the strength of their pillars ; which being of primordial matter, were solid and stable: but the changes which the subterranean fires produced at the bottom oi the ancient sea opened passages for its waters into the interior of the earth ; the fermentation produced by this irruption shook the pillars of the primitive earth ; which sinking into its caverns, the old continents disap- peared, and their surface descending below the level of the waters, a general inundation ensued. This was the general deluge : the sea now covered all the globe, except the islands of its ancient bottom, which increased in num- ber and magnitude, until the weight of the water added to that of the superior vaults, crushed the inferior ones, and deepened more and more the new bed of the ocean; so that, at last, by a motion rapid, but not violent, all the waters retired from their former bed, and left our conti- nents dry. Secondary mountains, and other irregularities, were afterwards formed by volcanic commotions and ma- ritime currents and convulsions. This learned theorist professes a firm belief in revela- tion ; and insists that all the principal lines in the Mosaic history are confirmed, and none of them contradicted, by the most attentive survey of the globe. h may well be questioned, however, whether some parts of his theory can be reconciled with the sacred records ; and they are precisely those parts which it is most difficult to reconcile with reason and sound philosophy. VOL. I. 30 Theories of Geology'• SECT. XIV. THEORY OF MILNE. NEXT to the theory of M. de Luc appears that of Mr. Milne; which, though less celebrated, is by no means unworthy of notice.* This gentleman declares himself a warm friend to revelation, and professes to have formed a system in strict conformity with the sacred history. In some respects he agrees with Mr. Whitehurst; in others, he adopts the opinions of M. de Luc ; while, with regard to a third class of his doctrines, he claims to be original: he supposes that the earth, immediately after the fall, and in consequence of the divine curse pronounced against it, underwent a total change, by means of the elementary fire lodged at that time near its centre; and that hence arose the irregularities which now appear in the earth's surface. SECT. XV. THEORY OF DR. HUTTON. THE theory of Milne was followed by that of Dr. James Hutton, of Edinburgh, which has been much more distinguished, and excited incomparably more at- tention. Dr. Hutton thinks,! tnat a^ our rocks and strata have been formed by subsidence under the waters of a former ocean, from the decay of a former earth, carried down to the sea by land floods; that the strata at * A Course of Physico-Theoligical Lectures on the State of the World, from the Creation to the Deluge, by Robert Milne, A. M. 8vo, 1786. f Theory of the Earth; or, an Investigation of the Laws observable in the Composition, Dissolution, and Restoration, of Land upon the Earth, by James Hutton, M. D. F. R. S.E. This memoir is contained in the Trans- actions of the Royal Society of Edinburgh, vol. i. Theories of Geology. 31 the bottom of the ocean were brought into fusion by subterraneous fires, and consolidated by subsequent con- gelation ; that these strata were forced up, and made to form islands and continents by similar agency; that the shells and other exuvite of animals, gradually collected and incorporated with these strata, make about a fourth part of our solid ground ; and that the foregoing ope- rations, viz. the waste of old land, the formation of new under the ocean, and the elevation of the strata now forming there into future dry land, are a progressive work of nature, which always did, and always will go on, forming world after world in perpetual succession. Con- sequently, according to this theory, the continents which we now inhabit must, in process of time, be worn away and destroyed, and others be forced up to supply their place. The length of time to be allowed for this suc- cessive destruction and reproduction, Dr. Hutton sup- poses to be far greater than is generally imagined. His system, therefore, is to be arranged, of course, among those which are hostile tq the sacred history; and the best judges have pronounced it equally hostile to the principles of probability, to the results of the ablest ob- servations on the mineral kingdom, and to the dictates of rational philosophy. It has been suggested, that this doctrine of the igniform origin of our globe appears to be drawn from the theory of M. Buffon, with the difference of perpetually reno- vating powers, having no determinate commencement, instead of a once slowly forming and now gradually de- caying principle. Dr. Hutton, indeed, does not attribute the fusion of terrestrial substances to the state in which this planet issued from the sun, but to subterraneous fires and furnaces, coeval with it, and still existing undiminished.* * Howard's Thoughts on the Globe, &c. 32 Theories of Geology. SECT. XVI. THEORY OF WILLIAMS. IN 1790 appeared a new theory of the earth, by Mr. John Williams, a mineralogist, of respectable character, which, though it has not acquired much celebrity, is en- titled to a transient notice in the present sketch.* Mr. Williams supposes, that the superficial parts of the earth were originally mixed with water into a fluid or chaotic mass. All the regular strata were formed by the flow of the tides successively spreading out the deposited matters on a large horizontal plane. The granites and other stones, which he does not consider as stratified, subsided when the water was in some degree of rest, as at the highest of the tides, or where local obstructions pro- duced stagnation. When the whole surface was in a fluid state, the tides, necessarily rose to a prodigious height, several miles higher than the tops of any of our moun- tains. The mountains of granite, which are uniform throughout, must have subsided in one tide. The tides were highest, and had their resting places on the two opposite parts of the globe, which are now the continents ; and their direction, on different parts of the globe, was such as we now fini'. that of the strata to be. He main- tained, further, that the interior body of the earth was formed in the same manner, prior to the superficial parts. From various causes, it was full of inequalities : it con- tained much water both in the composition of the not yet consolidated strata and in separate cavities ; so that when the superficial strata were laid between the tides, and the ocean began to retreat into its present bed, the weight of these superincumbent strata forced out the water imprison- ed below them: these strata themselves, as yet soft and flex- ible, were, in many cases, b?nt and broken : cracks were occasioned by their contraction in drying; which cracks * Natural History of the Mineral Kingdom,, &c. bv John Williams, 2 vols. 8vo 1790. Theories of Geology. 33 were increased by the inclination of the strata iv different ways, and were widest at the top; and the whole solid matter diminishing in bulk, as it became dry, high tides still overflowed it, and poured extraneous stony matter into the fissures. On these principles he explains all the t declivities, ruptures, interruptions, and irregularities, which we now behold. The larger grains and fragments found in the composition of our rocks, a? d all those bodies which are of a similar structure, and not crystal- lized, were once in distinct strata, though not now to be found in that state. This he considers as one of the many evidences which our earth every where affords of the general deluge. By the high tides and violent agi- tation of the diluvian waters, the primitive strata, which had never before felt any rain, were loosened, torn asunder, and ground down by attrition against each other, and all the superficial parts of the earth reduced again to a chaos. When the waters began to abate, the larger stony particles and fragments subsided first, and formed the compound rocks and beds of sand ; and the finer and lighter sediment was spread, by the tides, into strata of different consistency. SECT. XVII. THEORY OF DELAMETHERIE. • THE next theory entitled to notice is that of M. Delametherie, of France, which has been, of late, very fashionable in that country, and produced considerable discussion.* He supposes thst the external crust of our globe was formed in the bosom of the waters, from which it emerged in a state not very different from its present appearance. The crust, after its formation, un- derwent a variety of small alterations, from local causes. The waters surpas-ed the highest mountains; in other words, they were at least three thousand toises above their present level. All mountains, vallies, and plains, Thiorie de la Terre, 8vo, 5 torn. Paris, 1797. This large work em- braces much extraneous matter. The fourth and filth volumes contain the author's theory. 34 Theories of Geology. were formed by crystallization amidst the waters. The materials which formed them were truly dissolved ; but as they would require much more water for solution than is now to be found, it is evident that most of the waters of the primitive seas have disappeared. He thinks, that these have chiefly retreated into the bowels of the earth : that cavities were formed there at the time of the crys- tallization of the globe, which were at first filled with elastic fluids ; but the water afterwards finding its way into them, became lodged there : that some caverns have been formed by subterraneous fires, but that the most powerful cause of them has been the refrigeration of our globe; and that, though the surface of the earth has been brought to its present state by the action of water, it may, at the first moment of its formation, have under- gone a very great degree of heat, as happens to a comet passing near the sun. In the formation of this theory, M. Delametherie dis- covered considerable ingenuity and great learning. He can scarcely, however, be-called an original writer: Voigt had held the doctrine of the aqueous crystalliza- tion of strata before him ; and, indeed, the greater part of his system is made up of parts collected from different theorists. This is generally considered as one of those theories which are hostile to revelation. SECT. XVIII. THEORY OF HOWARD. OF a very different character is the theory of Mr. Howard, who about the same time published his opinions on this subject.* ^This gentleman is a firm believer in revelation, and his theory is intended to be perfectly consistent with the sacred history. He supposes that the elements of all material sub- stances wese originally in a confused mass, called the abyss, without motion or animation ; and that the present • Thoughts on the Structure of the Globe, and the Scriptural History of the Earth, and of Mankind, &c. by Philip Howard, Esq. 4to, London, 1797. Theories of Geology. 35 order of things was gradually, and at different intervals, drawn from it, by means of laws impressed by the power of the Creator. The earth, of which we now behold the ruins, was originally constructed with its pol^s perpen- dicular to the equator ; the centre of gravity was the cen- tre of the globe ; and the year consisted of three hundred and sixty days. At that time, the irregularities of the earth's surface being less considerable, and the distribu- tion of land and sea being more equal, the atmosphere was more temperate and salubrious, and, of course, the life of man was prolonged greatly beyond its present li- mits. The termination of this " golden age" might have been effected by the proximity of a Comet condens- ing the vapours of the atmosphere and attracting the sub- terraneous waters, which, bursting through the exterior surface, precipitated indiscriminate portions of the prim- itive earth into the cavities below. The more perfect consolidation of the globe in the southern hemisphere changed the centre of gravity, which produced a propor- tionate deviation from the plane of the equator. The ocean did not, at once, however, sink to its present level. The posterior accession of waters from seas hitherto in- land may have crushed down other inferior vaults, and finally settled its lowest degradations. As the land be- came thus elevated above the bed of the ocean, the cold became more intense, the vicissitudes of climate were more severely felt, and the life of man suffered a pro- portionate abbreviation. SECT. XIX. THEORY OF BERTRAND. MR. Howard was succeeded by M. P. Bertrand, of France, who next proposed a theory, much less philoso- phical, and in every /espect unworthy of a sober mind.* This theory though exhibited and defended with some talents, may be considered as the most wild, and as in- volving the most palpable opposition to every received * Nouveaux Principes de Giologie, par P. Bertrand, 8tc. 8vo. Paris, 1798. 36 Theories of Geology. principle, that has yet been presented to the public. In- deed, its unreasonableness and extravagance are so great, that it seems to have attracted but little respectful atten- tion among any class of philosophers. SECT. XX. THEORY OF KIRWAN. THE last person to be mentioned, as having adven- tured in this ample field of speculation and inquiry, is Mr. Kirwan. This gentleman with that learning which has enabled him to prosecute his numerous investigations in so enlightened a manner, with that judgment and penetration which render his inquiries so valuable, and with that spirit of patient and accurate observation which is so indispensably necessary to a successful development of this subject, has framed a theory of the earth, which is perhaps the most rational and probable extant.* Mr. Kirwan believes that the superficial parts of the globe were originally in a soft liquid state, proceeding from solution in water heated at least to 33°, and possibly much higher : that this menstruum held in solution all the different earths ; the metallic, the semimetallic, the saline, and the inflammable substances: that in this fluid its solid contents coalesced and crystallized, according to the laws of elective attraction; thatthtse were deposited in strata according to the predominant proportion of the ingredients: that by this crystallization of these immense masses a prodigious quantity of heat must have been generated, and increased by the decomposition of the water intercepted in the precipitated ferruginous particles, and by the disengagement of inflammable air, even to incandescence; the oxigen uniting with the inflammable air, and bursting into flame ; that this stupendous confla- gration must have rent and split to an unknown extent the solid basis on which the chaotic fluid rested: that from the heated chaotic fluid must have been extricated the oxigen and orotic airs, which gradually formed the * Geological Essays, by Richard Kirwan, Esq. F. R. S. &c. 8vo, 1799. Theories of Geology. 37 atmosphere : that from the union of oxygen wTith ignited carbon proceeded the carbonic acid, the absorption of which, as the chaotic fluid cooled, occasioned the crys- tallization and deposition of calcareous earth. Mr. Kirwan also believes, that the immense masses thus crystallized and deposited formed the primitive mountains ; that the formation of plains took place from the subsequent depo- sition of matters less disposed to crystallize in the intervals of distant mountains ; that the level of the ocean gradually subsided, leaving large" and elevated tracts of land unco- vered ; that the creation of fishes was subsequent to the emersion of the land; that after this retreat of the sea, the earth soon became covered with vegetables and peopled with animals^ being in every respect fitted to receive them ; that the gradual retreat of the waters con- tinued until a few centuries before the general deluge ; that this event was occasioned by a miraculous effusion of water both from the clouds and from the great abyss—the latter originating in and proceeding from the great south- ern ocean below the equator, and thence rushing on to the northern hemisphere, spreading over the arctic region, and descending again southward ; that duringthis elemen- tal conflict, the carbonaceous and bituminous matter ran into masses no longer suspensible in water, and formed strata of coal; and that other substances, by the combina- tion or decomposition of their respective materials, formed various other kinds of mineral bodies, as basaltic masses, calcedonies, spars, cifc. That the inequalitiy of declivity exhibited by the sides or flanks of mountains, in every part of the globe, had any regard to the points of the compass, seems to have been first remarked by the celebrated Swedish geologist, Tilas.* He supposes that this fact is connected with the ori- ginal structure of our globe ; that it proves that mountains are not mere fortuitous eruptions (as some, within a few years past, have confidently advanced) and that it fur- nishes a powerful argument in favour of the Mosaic ac- count of the creation, deluge, Scc.f But, although there has been in modern times (as ap- pears from the foregoing pages) a wonderful variety of • See Memoirs of Stockholm, for 1760. f See Transactions of the Royal Irish Academy, vol.vii. VOL. I. H 38 Theories of Geology. fanciful productions; under the name of geological the ories, we are by no means to imagine that nothing has been usefully done in this department of natural history. Amidst all the splendid rubbish with which it has been incumbered, some precious treasures have been brought to light. Amidst the speculations which have darkened counsel, large additions have been made to our knowledge of this important subject. These may be briefly summed up in the following particulars. The materials for the formation of a correct and ra- tional theory of the earth have been greatly augmented during the last age. Enlightened mineralogists, practical miners, and patient chemical experimenters, have been engaged, throughout the century, in making accurate ob- servations ; in visiting foreign countries ; in exploring the bowels of the earth ; in comparing the strata of every por- tion of the globe ; in examining their form, direction, ex- tension, and connexion ; in analysing their component parts; and in collecting a multitude of facts, which have -all tended to throw light on the origin and history of our planet. By means of the useful discoveries which these inquirers have made, we are furnished with weapons for beating down false theories, and with information en- abling us to pursue our investigations further, and with more advantage. Difficulties have been lately removed which were once supposed1, by some, to militate strongly against the possi- bility of a general Deluge. Early geologists, for want of accurate information, supposed that all the waters of the globe were not sufficient to cover the whole earth to such a depth as the sacred historian describes. It was assert- ed that the mean depth of the ocean, did not exceed a quarter of a mile, and that only half of the surface of the globe was covered by it. On these data Dr. Keil com- puted, that twenty-eight oceans would be requisite to co- ver the whole earth to the height of four miles, which he judged to be that of the highest mountains ; a quan- tity, which, at that time, was utterly denied to exist. But further progress in mathematical and physical knowledge has since shown, that the different seas and oceans contain at \ezstforty-eight times as much water as they were sup- posed to do, and much more than enough for the extent ascribed to the deluge in the sacred history.* * Kirwan's Geological Essays, pp 66, 67. Theories of Geology. 3* While difficulties which were supposed to render the deluge impossible have been removed by the investigations of modern philosophers, many facts have been, at the same time, brought to light, showing the probability, and even certainty^ of that mighty inundation. In every valley and mountain, support for revelation has been found. Marine shells have been discovered in situations so elevated, and under circumstances so remarkable, as to prove that they were left there by a flood extending over the whole globe; and what confirms this conclusion is, that shells peculiar to different shores and climates verv distant from each other have been found in promiscuous heaps, plainly showing that they could have been brought together only by an extensive inundation. The bones of elephants and of rhinoceroses have been found, in a multi- tude of instances, far distant from the regions in which they are found to live, and where, from the nature of the climate, they could never exist in the living state : and between the climates which they might have inhabited, and the places, in which they are now found, too many nlountains intervene to suppose them carried thither by any other means than a general deluge.* The most pa- tient and accurate examinations of detached mineral sub- stances, and of the strata of the globe, which late inquir- ers have made, afford every reason to believe that the earth was for a considerable time wholly overflowed with water. And, to crown all, as voyagers and travellers have explored new regions of the earth, they have found, every where, the indications of geological pheno- mena confirmed and supported by the notices of tra- dition. Accordingly, it is very remarkable that a great majority of modern theorists have embraced the Neptu- nian doctrines; and even such of them as rejected the Mosaic account of the deluge have been compelled to seek for other means of immerging the present conti- nents in the ocean. Finally, the researches of modern geologists have given abundant confirmation to the sacred history, not only with respect to the general deluge, but also with regard < o the age of the earth. * Kirwan's Geological Essay:, p 54, et seq. NATURAL HISTORY OF THE EARTH. PART III. SECT. I. THE natural division of triis globe of ours is into sea and land; about three-fourths of it being occupied by water, although probably no where to a depth compara- tively very considerable. The remaining fourth consists of land, elevated more or less above the level of the sea, interspersed in some parts with small collections of water, at various heights, and, in a few instances, somewhat lower .than the surface of the main ocean. The internal constitution of the earth is little known. The deepest excavations that have been made by human art do not exceed 2400 feet, or less than half a mile ; which is a very short distance indeed when compared with the diameter of the earth, which is about 7947 English miles: so that whatever lies below that depth is to us utterly unknown. The substances which have been extracted from those excavations are not in general of a nature different from those which in some particular places have been found immediately upon the surface. These substances are in general arranged in strata, vari- ously inclined to the horizon, and of a thickness not very equal. Some indeed have supposed that they follow each other, in a certain order, almost throughout the globe ; but this opinion appears to rest on slight foundations. The mean density of the earth, deduced from the ob- servations made by Dr. Maskelyne on the sides of Sche- hallien, an insulated mountain in Perthshire, is 4-y, rec- Natural History of the Earth. 41 zoning water, as usual, the standard of comparison. Mr. Cavendish has lately assigned a greater quantity, or about 5±, from a very elegant experiment on the principle of torsion, which Coulomb employed so successfully in a va- riety of delicate researches. Perhaps the true proportion would be found to lie between these limits. The observa- tions of Dr. Maskelyne, however skilfully conducted by that eminent astronomer, were performed under the most unfavourable circumstances, in a foggy climate, and a rainy season. And Mr. Cavendish's experiment was not perhaps made on a scale sufficient to afford very great precision. Nor is it at all improbable, that the apparent force of attraction was in some degree augmented by a slight infusion of magnetic virtue ; for the masses of lead which discovered their mutual appetency might yet con- tain a certain admixture of iron, in a state of such in- timate combination as to resist the action of chemical solvents. We are disposed to think that, instead of selecting a conical hill with a view to ascertain the deviation of the plummet, it would be more eligible to place the observer successively on the opposite sides of a narrow vale, bounded by two ranges of lofty mountains which run from east to west. Those stations would be very com- modious for determining the altitude of a star, and their true distance could be found trigonometrically with the utmost exactness. The mountains themselves might be surveyed by considering them as composed of a number of parallel and vertical slices, formed by planes, in the di- rection of the meridian. The best scene that I am ac- quainted with for attempting these operations is in the Up- per Valais, where the Rhone holds a westerly course; and the enormous Alps, in a double chain, having more than a mile of perpendicular height, approach at their lower flanks perhaps within two or three miles. The surface of the earth, as well sea as land, is occu- pied by innumerable individuals, constituting an immense variety of distinct species of animated and inanimated beings, comprehended in the three grand divisions of na- tural bodies, which have been emphatically called the three kingdoms of nature, viz. the mineral, the vegetable, and the animal kingdom. This division is no doubt of great advantage in the methods of natural history; but 4- Natural History of the Earth. if we consider this branch of knowledge with a chemical eye, we must observe that this division has the inconve- nience of not including a variety of bodies, which, by their mass, and by their vast influence, act a very impor- tant part in the operations of nature, viz. light, caloric, the air of the atmosphere. The above grand divisions may nevertheless be followed by the chemist with advantage. The mineral kingdom consists of such substances as are composed of particles united, either without any regular form, or by accretion only. Vegetables are all those organized bodies which derive their existence, by seeds or otherwise, from a parent stock. They grow by an enlargement of parts, have a cer- tain period of life or existence, and are attached to a parti- cular part of the soil, from which they derive the greatest part of their nourishment by superficial absorption only. Animals are all those self-moving, organized, bodies, of which the human being forms one species. They receive their food in an internal cavity, constituting a stomach. Minerals have growth only, but not always; vegetables grow and live also ; but animals have sensation, as well as life and increase of magnitude. Mineralogy is so nearly allied to chemistry, that it can- not well be understood without a previous knowledge of that science. Vegetables present a spectacle very inte- resting by its variety, and by its elegance ; but the philo- sophy of vegetation appears to be little diversified, and less understood. Some slight difference in the apparatus, by which the fruits and seeds are prepared for multi- plying the individuals of each species, have formed the oasis of the very excellent artificial system of Linnaeus. But the class cryptogamia is separated by a more natural distinction, the preparation of the seed being less con- spicuous, and in some cases scarcely intelligible, though in others an analogy with more perfect vegetables is perceptible; yet on the whole the class appears to form one of the connecting links between the three kingdoms. The herbs, palms, shrubs, and trees, which constitute the numerous genera of flowering vegetables, exhibit the greatest diversity in the forms and dispositions of the or- gans of fructification. And some of them indicate, upon particular irritation, a sensibility ^vhich seems to imitate the muscular motions of animals. In general, every ve Natural History of the Earth. 43 <;etable may be considered as a congeries of vessels, in which, by some unknown means, the aqueous fluids, im- bibed by the roots, are subjected to peculiar chemical ac- tions, and exposed in the leaves to the influence of the light and air, so as to be rendered fit for becoming consti- tuent parts of the plant, or of t^e peculiar substances con- tained in its various parts. A considerable portion of the bulk of all animals is also composed of tubular vessels, which originate in a heart, propelling through the arteries, which also co-operate with it, either a colourless transparent fluid, or a red blood, into the extremities of the veins, through which it again returns to the origin of its motion. Insects, and the vermes, or worms, have colourless juices, little warmer than the sur- rounding medium; but insects have legs furnished with joints, and worms at most have nothing but simple ten- tacula in the place of legs. Fishes have cold red blood, which is exposed to the influence of the air dissolved in water, by means of their gills. The amphibia receive the air into their lungs, but their blood is like that of fishes ; and in both classes the heart has only two cavities, while that of animals with warm blood has four. Of these, the oviparous are birds, and are generally covered with feathers; the viviparous are either quadrupeds or ceta- ceous animals, and are furnished with organs for suck- ling their young. The more perfect animals are informed of the qualities of external objects by the senses of touch, taste, smell, hearing, and vision. A few quadrupeds are incapable of seeing. Insects appear to want the organs of smell; but it is not impossible that their attennae may answer the pur- pose of hearing: in a particular stage of their existence, most of their senses appear to be inactive. Many of the vermes are totally destitute of sight, and some of all the organs of sense. The food, when received by the mouth, is subjected, in the more perfect animals, to mastication, and then enters the stomach; but in ruminating cattle it is first lodged in a peculiar receptacle, and more completely masticated at leisure. In the stomach, it undergoes digestion, and be- ing mixed with the bile and other juices, becomes fit for the separation of the chyle by the absorbents of the intes- tines. The chyle is thrown into the veins, and passes 44 Natural History of the Earth. through the heart with the blood into the lungs, to be there mixed with it, and perhaps to be animalised; while the blood receives from the air a supply of oxygen, and emits some superfluous carbonic matter. Returning to the heart, the blood is distributed thence to every part of the system, supplying nourishment throughout, while the glands and arteries secrete from it such fluids as are be- come redundant, and such as are required for particular purposes. In these processes, heat is probably evolved. The muscles are furnished by the blood with a store of the unknown principle by which they are rendered capable of contracting, for locomotion or for other purposes, in obedience to the influence of the mind, transmitted by the nerves ; and the brain and nervous system in general are sustained by means of the vascular circulation, in a fit state for transmitting the impressions on the senses to the im- mediate seat of thought and memory in the sensorium ; and for conveying the dictates of the mind, and of the will, to the muscular parts of the whole frame. In what manner these reciprocal impressions are trans- mitted by the nerves, has never yet been determined : but it has long been conjectured, that the medium of commu- nication may bear a considerable analogy to the electrical agency; and late experiments appear to have added new weight to the opinion. Indeed nothing can be more fit to constitute a connecting link between material and imma- terial beings, than some modification of a fluid which cer- tainly differs very considerably in its essence from the common gross matter of the universe, and which perhaps pervades, without interruption, the expanse of immea- surable space. When the knowledge of these various subjects was not very extensive, all the known particulars could be easily arranged under the general title of natural philosophy; but the progress of civilization of man, and the unre- mitted attention which has been bestowed upon them, particularly within our own time, has increased the num- ber of useful discoveries to such a degree, as to render the capacity of one man inadequate to the comprehension of the whole stock of knowledge. Hence to chemistry is allotted the explanation of those changes or events that are effected in the component parts of liodies by their mutual action upon each other, and which are not accomA panied by sensible motion. SIMPLE SUBSTANCES. PART IV. SECT. I. NATURE OF SIMPLE BODIES. IN every age there have been certain substances con- sidered by the philosophers of the day as simple bodies or elemt nts, of which every thing else has been suppos- ed to be compounded. But what have been enumerated by the philosophers of one age as elements, have been afterwards proved by those of another to be com- pounds ; and as the science of chemistry has been im- proved, we have discovered the means of analyzing or decomposing what was previously conceived to be sim- ple. Thus water, and air, from time immemorial to a very late date, were allowed by all philosophers to be two of the elements of nature: modern chemists have, how- ever, decomposed both fluids, and detected with accura- cy the ingredients of which they are formed, and even the proportion in which these are combined. For many ages past, earth, air, fire, and water, have been considered the four elements of which the globe we inhabit was formed. Chemistry now teaches, that there are many kinds of earths, and many kinds of air, perfectly distinct from each other. It teaches that fire is a simple substance ; and that water is a compound. This premised, simple bodies consist of particles which cannot be further separated into others of a more simple nature, or reproduced by artificial means. The true cha- racter of them is immutability of properties, unity, and similarity. It does not follow from this that these bodies are ab- solutely simple ; on the contrary, it is very possible that VOL. t. t 46 Classification of Simple Substances. they are compound. It cannot be doubted that, as the science advances towards perfection, many of them will be found so. Very probably a new set of simple bodies will offer itself, of which we are at present ignorant. These again may perhaps be decomposed, till at last, when the science has reached the highest degree of per- fection, those really elementary substances will come into view, of which all bodies are ultimately composed. Whenever this shall happen, the list of simple substances will probably be reduced to a much smaller number than at present; till this however does take place, we are entitled to consider them as simple substances, according to the present state of our knowledge. Their number amounts now to fifty, including those unconfinable agents called heat and light. They may be conveniently arranged in the following order. SECT. II. CLASSIFICATION OF SIMPLE SUBSTANCES. DIVISION I. SIMPLE SUBSTANCES PRODUCIBLE BY ART- 2 IMPONDERABLE SUBSTANCES. Light Caloric. PONDERABLE SUBSTANCES. 3 Combustible bodies destitute of metallic properties, Sulphur Phosphorus Diamond. Classification of Simple Substances. 47 28 Combustible bodies, possessing metallic properties, called METALS. Platina Cobalt Gold Silver Uranium Titanium Copper Iron Columbium Chrome Lead Tin Zinc Molybdena Tungsten Arsenic Mercury Tellurium Tantalium Cerium Antimony Bismuth Palladium Rhodium Manganese Nickel Iridium Osmium. IMCOMBUSTIBLE BODIES. 6 EARTHS. Silex Alumine Glucine Zircon Yttria Magnesia. 5 ALCALIES. Potash Soda Barytes Strontia Lime. DIVISION II. 6 SUBSTANCES NOT YET PRODUCIBLE BY ART, BUT ANALOGICALLY CONSIDER- ED AS SIMPLE. Oxigen Nitrogen 48 Classification of Simple Substances. Hidrogen Muriatic radical Fluoric radical Boracic radical. Such are the bodies which the corpuscular theory con- siders as simple, and to which chemical writers have giv- en the appellation of radicals. Some can only be exhi- bited to our view in their simple state; others, on the contrary, have not yet been successfully exhibited experi- mentally, uninsulated. Their existence can nevertheless be inferred from the analogy of certain general and well- established facts. The impossibility of producing them arises no doubt from their great tendency to unite with other substances, and from the opportunity they meet with at every separation. X NATltfeE' -^ OF CHEMICAL ACTION. PART V. THE different actions which result from the proper application of the bodies enumerated before, when either in a simple state or when combined together, are founded on certain agencies inherent in all matter. This we take for granted, and consider as a fact ; without pretending to explain how bodies came to be possessed of these agen- cies, or how they are capable of exeiting it. Philosophers therefore express the unknown causes which produce these changes, by the metaphors of at- traction and repulsion. Before we attempt to give an explanation of these terms, we shall endeavour to exemplify what is under- stood by chemical action in general. We therefore flatter ourselves that the following simple facts intended for that purpose will not he deemed frivolous ; our chief object being to advance in this place some palpable, positive, and negative proofs, which show, that whenever chemical ac- tion takes place, the properties of bodies become altered, and their individuality destroyed. (? jO Instances of Chemical Action. LSECT. i. INSTANCES OF CHEMICAL ACTION. Experiment I. * LET a small portion of marble or chalk, reduced to powder, be diffused in a quantity of water, the marble presented to the water will fall to the bottom of the ves- sel and remain unaltered. On shaking up the whole, a white turbid mixture will be formed, but on letting it stand undisturbed, the marble will again fall to the bot- tom, and the supernatant fluid remain transparent ana unaltered. In this case no chemical action has taken place, for nei- ther the properties of the marble nor the water are altered if examined chemically. Experiment II. If we let fall a like quantity of marble or chalk into an- other fluid, called an acid ; for instance, into vinegar, or nitric, muriatic, or sulphuric acid ; the effect then will be different: a violent action will take place the instant they come into contact, the marble will gradually disappear in these fluids and become more or less dissolved, and a transparent solution will be obtained. In this case a chemical action has taken place between the bodies brought into the sphere of action, for the pro- perties of both the substances can no longer be distin- guished, their appearances are more or less altered, and their individuality destroyed. Rem ark....Chemical action is reciprocal. It cannot be said that the acid acts on the marble, or the marble on the acid ; convenience of expression has permitted the whole of the action to be attributed, without misconcep- tion, to one of the substances, when the effect of the ac- tion is to be examined instead of the action itself; hence we say, vinegar acts upon marble, water acts upon salt, Sec. It were to be wished that the action of different bodies upon each other could be referred to a few general laws3 Instances of Chemical Action. si so as to be enabled to. foretel beforehand the changes which would result, in every possible circumstance. This would save us the trouble of learning in detail an immense number of insulated facts, which at present are necessary for the practice of the science. Experiment III. It is a well known fact, that if oil and water are added to each other they will not mix, because no sensible che- mical action takes place between them under such cir- cumstances ; but if we add to the oil and water a sufficient quantity of another substance, called an alcali—for in- stance, potash or soda—the oil, the water, and the alcali, will then unite and form a saponaceous compound, which has a milky appearance, and renders water opaque. A chemical action has then taken place between them; for the properties of the oil, the water, and the potash, are lost, and a compound possessing new properties has been formed. Experiment IV. If we put into a phial equal quantities of oil of turpen- tine, highly rectified alcohol, and a concentrated solution of carbonate of potash, and shake them together, no che- mical change takes place ; the different fluids will ap- parently mix, but on suffering them to stand undisturbed, they will separate again, and arrange themselves into dis- tinct spherules. The heaviest fluid will sink with the greatest celerity^ and they will place themselves over each other according to their specific gravities. Three different fluids -which do not mix, but constantly remain separate, ■will thus be contained in one phial. In this instance, therefore, no chemical action takes place between the bodies presented to each other. But if we bring the same substances into contact with others of a different nature, the case will be different, for violent chemical actions will ensue under favourable circumstances; for instance, Experiment V. Accension of oil of turpentine, by the affusion of nitrous acid. If we put into a tea-cup about one table-spoonful of oil of turpentine, and add to it double that quantity of 52 Instances of Chemical Action, very concentrated nitrous acid, a violent action takes' place, and fire and flame will be produced. Remark...As it is our duty to point out such experi- ments as may prove unsafe to those who never applied their hands to the practical part of chemistry, we must re- mark, that in performing this experiment care should be taken to avoid dangerous events ; for the cup is sometimes shattered to pieces, and the mixture is thrown about in all directions to a considerable distance ; it is therefore ne- cessary to fasten the vessel containing the nitrous acid to the end of a long stick, in order that the operator may be at a distance when the accension takes place, which hap- pens the instant the acid comes into contact with the oil. Experiment VI. Production of heat (sufficient to make water boil J by the mixture of sulphuric acid and alcohol or water. If half an ale-glassful of sulphuric acid of commerce be hastily mingled with half that quantity of alcohol or Water, the mixture instantly becomes so hot as to render the glass insupportable to the hands. A small quantity of water contained in a thin glass tube may be made to boil, when immersed in it for a few minutes only. Remark...Great caution is likewise necessary in mak- ing this experiment, lest the glass should crack from the sudden heat, and throw the mixture about, to the mani- fest danger of the operator. The safest method is to mix the two fluids gradually ; by this means the heat is produced slowly; Avhereas if both fluids are at once mingled together, the heat is almost instantaneous, and rises considerably above that of boiling water. Experiment VII. ( Production of Sulphate of Potash. If a concentrated solution, carbonate of potash, be mingled with sulphuric acid, the two fluids unite, a very brisk effervescence takes place, and a solid mass of salt (sulphate of potash) will be produced. These experiments, which shall be more fully consi- dered hereafter, are merely advanced to prove that the Instances of Chemical Action. 53 individuality of different substances becomes destroyed, that is to say, that a chemical action takes place when they are presented to each other under such circumstan- ces as experience has taught us are necessary to produce such effects. The conditions, or artificial arrangements requisite for that purpose, resolve themselves into the general operations of chemistry. vol. 1. K ATTRACTION. PART VI. THE terms attraction and repulsion, in the language of modern philosophers, are employed merely as the ex- pression of the general facts, that the masses or particles of matter have a tendency to approach to, or to recede from, one another, and to unite to, or repel, each other, under certain circumstances. Hence the following AXIOM OF ATTRACTION. All bodies whatever have a tendency or power to at- tract each other more or less ; they search as it were, and make efforts, when left to themselves, to approach one another in order to unite, or to come into apparent con- tact. This energy is called the power of attraction. This attraction is mutual; it extends to indefinite dis- tances. All bodies whatever, as well as their component elementary particles, are endued with it. It is not anni- hilated, at how great a distance soever we suppose them to be placed from each other ; neither does it disappear, though they be arranged ever so near each other. The nature of this reciprocal attraction, or at least the cause which produces it, is altogether unknown to us. Whether it be inherent in all matter, or whether it be the consequence of some other agent, are questions be- f . yond the reach of human understanding; because we ' have no means of deciding the point, we are absolutely unable to judge of the simplicity of Nature. We have but a few imperfect glimpses here and there ; and from the few points which we see and understand, we are not able Proofs of the Energy of Attraction. 53 to form plausible conjectures concerning the whole ma- chinery by which her operations are carried on. Superior beings perhaps smile at our theories, as we smile on the reasoning of a child ; and were the veil with which her Operations are covered suddenly withdrawn, we ourselves in all probability would be equally astonished and con- founded at the wide difference between our theories and the real power by which the machinery of the universe is governed. SECT. I. PROOFS OF THE ENERGY OF ATTRACTION. THAT the power of attraction really exists is obvi- ous from the slightest view of the phenomena of nature. It is proved with mathematical certainty that the celestial bodies, which constitute the solar system, are urged to- wards each other by a force which preserves them in their orbits. It is further proved beyond any doubt, that this planetary attraction is possessed not only by the heavenly bodies as wholes, but that it also extends to the smaller particles of which they are formed, as may be evinced by means of the following experiments: Experiment I. If we place two or more globules of mercury on a dry glass or earthen plate, and push them gently towards each other, the globules will attract each other, and form one mass or sphere, greater in bulk, but precisely the same in nature. Experiment II. If a plate of clean glass, perfectly dry, be laid on a large globule of mercury, the globule, notwithstanding the pressure applied to it, continues to preserve its spherical form; if we gradually charge the plate with weights care- fully, the globule will be depressed and become thinner and thinner; but if we again remove the weights from the 56 Proofs of the Energy of Attraction. plate, the mercury will instantly recover its globular figure, and push up the glas9 before it. In both these experiments we see that there exists an attraction between the particles of mercury ; in the first, the globules which are in contact with the plate of glass leave this substance completely, they attract each other, and form a sphere greater in bulk. A mere inert fluid would in any case retain the figure it once possessed. It could not be endued with a globular form unless a real reciprocal attraction among its particles took place, which in the latter experiment is still more striking, for it there is not only superior to gravitation, but actually over- comes an external force. Experiment III. If a glass tube of a fine bore be immersed in water, contained in any vessel, the fluid will ascend to a certain height within the tube above its level, and its elevation in several tubes of different sizes will be reciprocally as the diameter of their bores. This kind of attraction, which takes place as well in vacuo as in the open air, has been called capillary attraction. It is this attraction which causes water to rise in sponge, cloth, sugar, sand, &c. for all these substances may be considered as fine tubes in which the fluid ascends. Remark...The ascension of fluids in glass tubes of a fine bore succeeds best when the inside of the tube has been previously moistened, which may conveniently be done by blowing through it with the mouth. And if the water be coloured with a little red or black ink its ascension will be more obvious, particularly if the tube be held against a sheet of white paper. Experiment IV. If two plates of glass, previously wetted, be made to meet on one side, and be kept open at the other, at a small distance, by the interposition of a shilling, or any other thin substance, and then immersed in water, the fluid will ascend between the two plates unequally. Its upper sur- face will form a curve, in which the'heights of the several points above the surface of the fluid will be to one another reciprocallv, as their perpendicular distance from the line Proofs of the Energy of Attraction, :>7 in which the plates meet. The ratio of this attraction is, therefore, as the squares of the increments with which the plates open. Here, then, we have two other instances that an attrac- tion prevails among the particles of bodies. For in both cases part of the fluid has left the contiguous mass, con- trary to the laws of gravitation. It is drawn up, as it were, or attracted, by the tube or plate of glass. Experiment V. •> If we immerse a piece of tin, lead, bismuth, silver, or gold, in mercury, and draw it out again immediately, the mercury will attract the metal, and the latter will carry with it a portion of the former, which will stick to it so obstinately as to be inseparable by mere friction. There exists, therefore, an attraction between the dif- ferent metals brought in contact with each other. Experiment VI. If we let fall into water a lump of sugar or salt, the particles of the water attract those af the sugar with a greater force than the last particles attract each other; they are therefore gradually carried off by the water, that is to say, the sugar is gradually dissolved. The particles of the solid thus dis solved, are each of them surrounded and combined with a certain number of the particles of the fluid; hence they must be arranged in the liquid in regular order, and at regular distances from each. Experiment VII. If a small stick be dipped in water, or any other fluid, and drawn out again, a drop will be found hanging at the end of it in a spherical form. The drop is spherical, be- cause each particle of the fluid exerts an equal force in every direction, drawing other particles towards it on every side as far as its power extends. Thus the very formation of drops obviously demon- strates that there must exist a cause which produces that effect. This cannot be gravity, for, agreeable to experi- ence, that is rather an obstacle to the formation of drops : since, by the weight of the particles, large globules rest- •*»'8 Proofs of the Energy of Attraction. ing on solid bodies are flattened, and their regular spheri- cal form prevented. To explain this phenomenon there remains only the power of attraction, acting between the particles of the liquid body ; for if it is supposed that the particles of a substance reciprocally attract each other with equal force, and their aptitude for being moved upon one another be great enough to overcome any impediment to their mo- tion, it follows, by the principles of mechanics, that the equilibrium of the attractive forces can only take place when the mass has received a globular form. Hence it is that all liquid bodies assume a spherical figure when suffered to fall through the air, or form drops. Whether the attractions of gravitation, or magnetism^ of electricity, and of cohesion, be or be not considered as essentially the same, is not our business to consider here circumstantially; there is difference enough between them to allow a very accurate examination of each. We merely consider attraction as an unknown power, by which all bodies are urged towards each other as an agent, which acts constantly and uniformly in all times and places, and which is always diminishing the distances between bodies. It is obvious that the distances of bodies are of two kinds, either sensible or insensible; consequently the changes pro- duced by attraction must be either sensible or insensible. Hence the attraction of bodies naturally divides itself into two classes; those wKSch act at sensible distances, and those which act at insensible distances. The attractions be- longing to the first class must be as numerous as there are bodies situated at sensible distances; but it has been as- certained that they may be all reduced to three different heads, viz, gravitation, electricity, and magnetism. The first belongs to all matter, and therefore is universal: the other two are only partial, or confined to certain sets of bodies. The first extends to the greatest .distances to which bodies are placed from each other: how far elec- tricity extends, has not been ascertained. Magnetism ex- tends, at least, as far as the semi-diameter of the earth. All bodies possess gravity; and it is supposed that the two other attractions are confined to certain subtile fluids which constitute a part of all those bodies which exhibit the attractions of electricity and magnetism. This may be so, but it has not and scarcely can be demonstrated. Division of Attraction. 50 SECT. II. DIVISION OF ATTRACTION. THOUGH we are unable to discover the cause of the mutual attraction, experience has proved to us that this agency follows certain conditions or laws ; for similar phenomena always present themselves whenever the cir- cumstances of experiment are the same. Observation has taught us that the particles of bodies are of two kinds, either homogeneous or heterogeneous. By homogeneous particles, chemists understand particles composed of the same body ; thus all particles oi sulphur, &c. are homogeneous particles. By heterogeneous par- ticles, chemists mean particles which compose different bodies ; thus a particle of sulphur and a particle of mer- cury are heterogeneous particles. In the early periods, when chemists perceived that the force here considered opposed their operations, being ha- bituated to explain the effects they observed by certain relations, or analogies, which they supposed to exist be- tween bodies, they gave different appellations, to express this agency. The first agency is still called by physical writers corpuscular attraction, or attraction of aggrega- tion; molecular attraction ; attraction, of cohesiont ox the cohesive power. The latter is termed chemical attraction, chemical af- finity, or affinity of composition. But before we consi- der this subject any further, we shall give an idea of what has been called repulsion. REPULSION. PART VII. IT was mentioned before (page 54) that all matter pos* sesses, besides attraction, another power which is in con- stant opposition to the former. This agency, which is equally powerful and equally obvious, acts an important part in the phenomena of nature, and is called the power of repulsion. It is not less interesting to the chemical philo- sopher, than the powers of attraction. AXIOM OF REPULSION. All bodies are endowed with a certain power, whose constant tendency is to oppose their approach towards each other, or to remove the particles of matter to a greater distance. SECT. I PROOFS OF THE ENERGY OF REPULSION. THAT there exists a force which opposes the approach of bodies towards each other is evident from numberless facts. Nt wton has shown that when a convex lens is put upon a flat glass, it remains at a distance of the T£T part of an inch, and a very considerable pressure is required to dimi- Proofs of the Energy of Repulsion. 61 nish this distance; nor does any force which can be ap- plied bring them into actual mathematical contact; a force may indeed be applied sufficient to break the glasses into pieces, but it may be demonstrated that it does not diminish their distance much beyond the y^. part of an inch. There is, therefore, a repulsive force, which pre- vents the two glasses from touching each other. There exists, therefore, a repulsion between bodies ; this repulsion takes place while they are yet at a distance from each other; and it opposes their approach towards each other. The cause, or the nature, of this force is equally in- scrutable with that of attraction, but its existence is un- doubted ; it increases, so far as has been ascertained, in- versely as the square of the distance, consequently at the point of contact it is infinite. The following experiments will serve to prove the energy of repulsion more fully. Experiment I. We have seen (experiment III. p. 56) that when a glass tube is immersed in water, the fluid is attracted by the glass and drawn up into the tube; but if we substitute mercury instead of water we shall find a different effect. If a glass tube of a large bore be immersed in this fluid it does not rise, but the surface of the mercury is consi- derably below the level of that which surrounds it. In this case, therefore, a repulsion takes place between the glass and the mercury, which is even considerably greater than the attraction existing between the particles of the mercury, and hence the latter cannot rise in the tube, but is repelled, and becomes depressed. Experiment II. When we present the north pole of a magnet, A, to the same pole of another magnet, B, suspended on a pivot, and at liberty to move, the magnet B will recede as the other approaches ; and by following it with A, at a pro- per distance, it may be made to turn round on its pivot with considerable velocity. In this case there is evidently some agency which op- VOL. i. l 62 Proofs of the Energy of Repulsion. poses the approach of the north poles of A and B, which acts as an antagonist, and causes the moveable magnet to retire before the other- There is, therefore, a repulsion between the two magnets, a repulsion which increases with the power of the magnets; which may be made so great, that all the force of a strong man is insufficient to make the two north poles touch each other. The same repulsion is equally obvious in electrical bodies ; for in- stance, Experiment III. If two small cork balls be suspended from a body with silk threads so as to touch one another, and if we charge the body in the usual manner with electricity, the two cork balls separate from each other, and stand at a distance pro- portional to the quantity of electricity with which the body is charged; the balls, of course, repel each other. Experiment IV. If we rub over the surface of a sheet of paper the fine dust of lycopodium or puff-ball, and then let water iall on it in small quantities, the water will instantly be repelled, and form itself into distinct drops which do not touch the lycopodium, but roll over it with uncommon rapidity. That the drops do not touch the lycopodium, but are actually kept at a distance above it, is obvious from the copious reflection of white light. Experiment V. If the surface of water contained in a basin be covered over with lycopodium, a solid substance deposited at the bottom of the fluid may be taken out of it with the hand without wetting it. In this case the repulsion is so pow- erful as to defend the hand completely from the contact of the fluid. INFERENCES. The various substances which compose the globe are therefore subject on the one hand to a general law which tends to unite them together, and on the other hand to another agent which tends to disunite, or to remove them to a greater distance. Hence it is impossible to produce Proofs of the Energy of Repulsion. 63 any change whatever in bodies without interrupting these respective agencjes. The great business of the chemist is to examine the changes arising from these agencies, and to trace the laws by which they are regulated. In doing this he investi- gates the operations of nature, and endeavours to point out their dependencies on one another. For that pur- pose he places different bodies in contact with each other under -a diversity of circumstances, and observes the phenomena which accompany their action. He endea- vours to trace the conditions under which they are pro- duced, and examines the properties of the new compounds; thus making them subservient to the improvement of the arts, and rendering them the ministers of our necessities, eomforts, and enjoyments. CORPUSCULAR ATTRACTION, OR, ATTRACTION OF AGGREGATION. PART VIII. CORPUSCULAR attraction, or attraction of cohe- sion or aggregation, is that power by means of which the "imilar particles of bodies attract each other and become united into one mass, without changing, in the least, the chemical properties they possessed before their union. The bodies may be in a solid, fluid, or aeriform state. Corpuscular attraction is different in different bodies. It is always in an inverse ratio to the power of repulsion, or the quantity of caloric interposed between the particles of the acting bodies. It becomes obvious from this, that the agency of cor- puscular attraction consists in a mere successive and con- stant accumulation of similar particles into one mass; and that it produces adherence of surface, or apparent contact in the ratio of the surfaces. This force is inherent in all the particles of all bodies (caloric and light perhaps excepted) we never find the particles of bodies in a detached state, but constantly in masses of greater or smaller magnitude, made up of an indefinite number of particles united together by virtue of the force of cohesion. Measurement of Corpuscular Attraction. 65 SECT. I. INSTANCES OF CORPUSCULAR ATTRACTION. THE simplest case of the exertion of corpuscular at* traction is that where two bodies, placed in mutual con- tact with each other, form a direct union, without chang- ing their chemical properties. Experiment I. If different particles of sulphur be melted together, they form an uniform mass or whole, the particles of which are held together by virtue of the power of corpuscular attraction, but the properties of the body are not altered. The same effect takes place when pieces of the same metal, or particles of resin, wax, &c. are united in a simi- lar manner. Innumerable other instances might be advanced, were not the subject obvious to every one. MEASUREMENT OF CORPUSCULAR ATTRACTION. The force of corpuscular attraction in solid bodies may be measured by the force or weight necessary to demolish it. Thus, if a rod of metal, glass, wood, &c. be suspend- ed in a perpendicular direction, and weights be attached to its lower extremity, till the rod is broken by them, the weight attached to the rod just before it broke is the measure of the cohesive force of the rod. It is also expsessed by comparing it with other bodies: thus it is said that a ruby is softer than a diamond, but harder than the hardest steel, because with it the steel may be scratched, but not the diamond. Various experiments have been instituted for the pur- pose of determining the force requisite fo disunite solids from contiguous fluids, to disunite solids from contiguous solids, and to break or to disunite the continuity of a given solid. But the circumstances of temperature, purity 66 General Laws of Corpuscular Attraction. of the bodies, equality of size, surface, &c. render such experiments subject to a considerable uncertainty. It has been found that wires of the following metals, drawn through the same hole, one tenth of an inch in di- ameter, and fastened with one end to a hook, whilst weights were suspended to the other extremity, could not be broken by any force less than the annexed weights. Lead.............29r| Tin .... '.......... 49H Copper............299i | Brass.............360 ^poundsi Silver.............370 | Iron..............450 Gold.............500 j SECT. II. GENERAL LAWS OF CORPUSCULAR ATTRACTION. Law I. The agency of corpuscular attraction acts only at insensible distances ; its force increases as the distance of the bodies presented to each other decreases, and as the surfaces af apparent contact are more numerous. Experiment I. IF from each of two leaden bullets a piece be cut off with a sharp knife, and if then the two bullets be pressed with their flat bright surfaces against each other (giving them a little twist) they will be found to adhere so firmly to each other, that sometimes the weight of fifty pounds will hardly be sufficient to separate them. When sepa- rated, a considerable degree of roughness will be found on their surfaces. The adhesion of the two bullets is certainly not owing to the pressure of the surrounding medium ; for in the first place the pressure of the atmosphere is by no means so great as to produce that degree of adhesion between such small surfates; and, in the second place, the two bullets thus prepared are found to adhere as firmly in va- cuo as they do in air. General Laws of Corpuscular Attraction. 67 Experiment II. For similar reasons, two plates of glass wetted with a little water, to fill up their inequalities, when laid toge- ther, will cohere ; and two pieces of marble or brass, hav- ing each a flat, smooth, and well polished surface, when moistened and split upon each other, with a gentle pres- sure, will unite, and a considerable force is required to separate them. But if the two substances placed together be not sufficiently smooth or polished, it will be in vain to try to cause them to adhere together; for this reason, that the particles touch each other only in a few points: whereas, on the contrary, the particles of the former flat and smooth surfaces touch each other in many points. It has been noticed, that a silk-worm's thread can be in- terposed, but not two. Experiment III. If two brass polished and perfectly flat surfaces, about three inches in diameter, be rubbed over with grease, and put together in a pretty hot state, they will, when cold, adhere to each other so firmly, as to require nearly five hundred pounds weight to disunite them. It must be observed, however, that in these cases where something is interposed between the two surfaces, the ad- hesion seems to take place not between the surfaces of the two solids so much as between each of those surfaces and the interposed substance : lor, in the first place, it seems strange that two surfaces should have a greater at- traction to each other, when something is interposed, than otherwise; and, secondly, it has been found that the degree of cohesion differs, according as different substan- ces are interposed between the very substances of the same solids. It is on this account that carpenters, when they intend to glue pieces of wood together, plane the surfaces per- fectly smooth, before they apply the glue ; and that the surfaces of metals are scraped clean before they are sol- dered, &c. Hence the corpuscular attraction always vanishes when- ever the distance is measurable, and becomes exceedingly great whenever the distance is exceedingly diminished ; but the particular rate which this power follows is still 68 General Laws of Corpuscular Attraction. unknown, as we have no method of measuring either the distance at which it acts or its relative intensity. 1 he force of gravity decreases inversely as the squares of the distance But the attraction of cohesion decreases much faster: for instance, if a force of a thousand pounds weight be required to break a certain solid, and if then the broken parts be placed contiguous to each other, and so closely that the eye cannot discern the fracture, 11 will be found that they may be separated with the utmost facility. Law ll...Corpuscular attraction acts differently in differ- ent bodies ; according to the degree of force with which it acts between the particles of matter, the bodies appear under different forms. 1. It is on this account that rock-crystal, flint, dia- mond and various other precious stones, are extremely hard; for the corpuscular attraction unites the particles of these bodies with a great degree of force. Hence a considerable mechanical effort is necessary to disunite them. 2. In blocks of marble, chalk, lime-stone, &c, the par- ticles are held together with a force considerably less. In these bodies it prevents all relative motion among the par- ticles themselves, and hence the motion of one particle is followed by the motion of the whole mass; or if that is impossible, the cohesion is destroyed altogether, and the piece breaks. 3. The integrant parts of wax, tallow, suet, or lard, may be made to change their situations, with a less degree of force than the former. Every genus of those aggregations comprehends a great number of species or degrees of solidity, softness, and liquidity. In these substances the motion of one particle of the body is not necessarily followed by that of all the rest; neither does that motion destroy the cohesion, nor break them. 4. The particles of water, spirit, and ether, move or slide over each other very readily^ hence their resistance is considerably less. 5. And lastly, vapours, the air of the atmosphere, and all the gases, yield to the slightest possible impulse. General Laws of Corpuscular Attraction. 69 Law III. Corpuscular attraction may be annihilated by every effort which tends to separate the particles of bodies. This law has, in truth, no relation to any chemical principle, but that of the destruction of aggregation. It is easy to imagine, that in order to produce this last effect nothing else is required to be done but to apply force greater than the agency of aggregation. It need hardly be mentioned that all mechanical forces, such as grinding, cutting, filing, rasping, pounding, break- ing, &c. are of this nature. In all these cases, the power applied must be more than equal to the force of corpuscular attraction; and as it was stated before that the corpuscular attraction acts with dif- ferent degrees of energy between the particles of different bodies, so different degrees of force are necessary to de- stroy that corpuscular attraction in different bodies. The art of chemistry, in the different means it employs to demolish the aggregation of bodies, has really for its ob- jects to cause these bodies to pass from the state of physi- cal subjects (that is to say, subjects of which the mechani- cal philosophy can ascertain their properties) to that of chemical subjects, on which this science may be consi- dered as no longer operating. VOL. I, M CHEMICAL AFFINITY, OR AFFINITY OF COMPOSITION. PART IX. SECT. I. CHEMICAL AFFINITY. AFFINTY of composition, or chemical affinity, is that power, by means of which the particles of bodies, whe- ther simple or compound, attract each other so intimately as to produce an uniform whole, totally inseparable by mechanical efforts, and whose characteristic properties are often different, and sometimes contrary to those of its constituent parts. It is obvious from this, that the particles of those bodies which are united by virtue of chemical affinity form not a mere aggregate, but an entirely new body, which can only be altered by the action of another chemical power. In considering this kind of affinity, it will be necessary to state, In what manner it takes place between the particles of different bodies; In what proportion they are capable of combining; Under what conditions; With what degree of force they unite ; And what takes place when a variety of different sub- stances are made to act upon each other at the same time, under certain circumstances and in different proportions. Instances of Chemical Affinity. 71 Hence affinity of composition is of greater importance than corpuscular attraction, or affinity of aggregation, for it takes place in all the complex operations of chemistry. These topics will form the subject of the following sec- tions. SECT. II. INSTANCES OF CHEMICAL AFFINITY. TO prove that chemical affinity acts differently from attraction of aggregation; that it takes place between the ultimate constituent parts of bodies; and that it produces substances possessing properties frequently very different, and sometimes contrary, to those of the constituent parts ; the following experiments may serve. Experiment I. Formation of sulphuret of mercury. Put into a crucible, placed in a coal fire, equal parts by weight of sulphur and mercury; stir the two substances together for a few minutes, and when the sulphur is melted pour the contents out on a marble slab, or piece of glass previously warmed and greased. The substance obtained by this means is a sulphuret of mercury, in which the mercury and sulphur are united by virtue of chemical affinity : for the compound has nei- ther the colour, the splendour, the inflammability, the volatility, nor the specific gravity, of either of its consti- tuent parts ; nor can the sulphur and mercury be separat- ed by mechanical means : they are therefore chemically united. Experiment II. Two malleable and ductile metals form a brittle alloy. If we melt together tWo very malleable and ductile me- tals—for instance, tin and iron—in equal quantities, the compound produced will have totally lost the properties 72 Instances of Chemical Affinity. which its constituent parts possessed before their union , for the alloy formed will be a brittle metal, which may easily be broken with the blow of a hammer. Experiment III. Blue fluids become changed into red or green, green ones into crimson or purple, tyc. Put two or three teaspoonfuls of an aqueous infusion of red cabbage, or syrup of violets, into a wine-glass of wa- ter ; mix it well and put half the mixture into another glass. By adding a few drops of sulphuric acid to one of the glasses, and stirring it, the bl.:e will be changed to a crimson; and by adding an alcali, for instance potash, to the other glass, the blue fluid will be changed into a green. If we drop carefully down the sides of the glass into the green obtained in this experiment a few drops of sul- phuric acid, crimson will be perceived at the bottom, pur- ple in the middle, and green at the top. On adding a little alcali to the other glass, containing the crimson, these colours will appear in an inverted order. Experiment IV. Two inodorous bodies evolve a very pungent smelling gas. C Production of ammonia. J When equal parts of muriate of ammonia and slaked lime, both substances destitute of odour, are intimately blended in a stone mortar, a very pungent gas (ammonia) becomes evolved. Experiment V. Two odorous and pungent bodies produce a compound destitute of odour. (Formation of muriate of ammonia.) Water impregnated with ammonia and concentrated muriatic acid, both fluids of a strong odour, when mixed together in proper proportions, instantly lose their odour, and form a fluid void of smell (muriate of ammonia. J General Laws of Chemical Affinity. 73 Experiment VI, Two fluid bodies produce a solid when mingled together. (Formation of sulpha*" of lime.) Into a saturated solution of muriate of lime let fall grad-ally concentrated sulphuric acid; a quantity of pun- gent vapour will become disengaged (muriatic acid gas), and from the two fluids will thus be produced an almost solid compound, called sulphate of lime. Experiment VII. Two solid bodies produce a fluid by mere mixture. Let equal parts of fresh crystallized acetite of lead and acidulous sulphate of alumine and potash be rubbed to- gether intimately in a stone mortar; the saline mixture will soon become soft, and lastly fluid. A like effect is produced by treating in a similar man- ner equal parts of crystallized nitrate of ammonia and sulphate of soda. A solid alloy of mercury and bismuth, and another composed of lead and mercury, on being triturated to- gether instantly become fluid. It is obvious from this, that when chemical combina- tion takes place, the compound which is formed does not possess prop rties merely intermediate between those of its component parts, but has acquired others more or less new. This,'however, does not hold good in all cases. There are various combinations in which the properties of bodies are only slightly altered. SECT. III. GENERAL LAWS OF CHEMICAL AFFINITY. OBSERVATION has shown that affinity of composi- tion offers certain invariable phenomena, which, being founded on a great number of facts, are regarded by che- mists as laws, and may be reduced under the following heads : 74 Proofs of the Laws of Chemical Affinity. Law I.—Chemical affinity can exert its action between a number of bodies, simple or compound, and unite them che- mically into one whole. Law II.__The efficacy of chemical affinity is in an in- verse ratio to that of corpuscular attraction. • Law III.—The agency of chemical affinity is influenc- ed by temperature; its action is either accelerated, retard- ed, prevented, or rendered efficacious. Law IV.—Chemical affinity is accompanied by a change of temperature at the instant of its action. Law V.—The agency of chemical affinity existing be- tween two or more bodies may be dormant, until it is called into action by the interposition of another body which fre- quently exerts no energy upon any of them in a separate state. Law VI.—The ratio of the energy of chemical affinity acting between various bodies is different in different sub- stances. Law VII.— The agency of chemical affinity is either limited or unlimited in certain bodies; in other words, che- mical affinity is capable of uniting bodies in definite or in indefinite proportions. Law VIII.—The energy of the chemical affinity of dif- ferent bodies is modified in proportion to the ponderable quantities of the bodies placed within the sphere of action. Such are the leading laws which regulate the affinity of composition ; they may be demonstrated by means of the following experiments. SECT. IV. EXPERIMENTAL PROOFS OF THE LAWS OF CHEMICAL AFFINITY. Law I.—Chemical affinity can exert its action between a number of bodies, simple or compound, and unite them chemically into one whole. PROOFS OF LAW I. THERE are an infinite variety of compounds, consist- ing of three, four, five, or more simple substances in nature; and art can also effect combinations in which Proofs of the Laws of Chemical Affinity. 75 there are many simple bodies chemically united into one whole. It frequently happens that various separate bodies pre- sented to each other in a fluid unite and form a single mass, which possesses all the characters of an homogene- ous compound, and which retains these characters till its composition has been altered by chemical means. A considerable number of triple salts are known, which consist of three different substances; for instance, the common alum of commerce consists of sulphuric acid united to alumine and potash or soda. The salt formerly called microcosmic salt, or phosphate of soda and ammo- nia, consists of phosphoric acid united to soda and ammo- nia, &c. When the oxigenated muriate of mercury is precipitated by the precise quantity of carbonate of soda which is requisite to effect its decomposition, the precipi- tate obtained contains muriatic acid, carbonic acid, and oxid of mercury in excess. It is a well known fact, that two, three, or more metals may be fused together so as to produce compounds whose properties are widely different from those of the consti- tuent parts. Experiment I. Fusible alloys which melt in boiling water. Melt together, in an iron ladle or crucible, eight parts of bismuth, five of lead, and three of tin ; the fusibility of the metals will thus be altered, for the alloy melts at 212° Fahr. A spoon, or any other utensil, formed of this com- pound, will therefore melt in water kept boiling. If in a similar manner an alloy be made of lead, tin, bismuth, and mercury, their proportions being two, three, five, and one, the compound produced melts at a heat even less than that of boiling water. A composition of lead, zinc, and bismuth, in equal parts, may be kept in fusion upon paper over a lamp. Experiment II. Put into a teacup one ounce of alcohol, and add to it ten grains of hyper-oxigenised muriate of potash. If to fii Proofs of the Laws of Chemical Affinity. this mixture a quarter of an ounce of concentrated sul- phuric acid be added a violent action ensues, and the fluid bursts into flame. Experiment III. If we triturate together, in a warm mortar, three parts by weight of very dry nitrate of potash, two of cfjrbonate V.'O: of potash, and one of sulphur, a powder is obtained, of which a few grains, when laid on a knife and held over the candle, first fuses, and then explodes with a loud re- port. A drachm of it put into a shovel and held over the fire makes a noise as loud as a cannon, and indents the shovel as if it had received a violent blow. It is known by the name oi fulminating powder. Law II. The efficacy of chemical affinity is in an in- verse ratio to that of corpuscular attraction. PROOFS OF LAW II. It was mentioned before, that the cohesion of the par- ticles of a body is owing to the mutual attraction existing between them. It is this force which must be overcome by the action of a substance which has a tendency to combine with those particles chemically. The affinity of composition therefore does not become stronger as the affinity of aggregation becomes weaker, it becomes only more efficacious ; the absolute powers remain the same; the effect produced by that agency increases, because the resistance opposed to it decreases. * Remark-...It is from this law that it was formerly in- ferred, that some, or at least one, of the bodies should be in a state of fluidity. This, however, is by no means ne- cessary. It is in general true, that the weaker the attrac- tion of aggreg tion is, the more easily the affinity of com- bination takes place, as may be evinced by means of the following experiments : Proofs of the Laws of Chemical Ajjinity. 77 Experiment I. Let any quantity of dry corbonate of soda and tarta- reous acid be mingled together, and put the mixture into a wine-glass; no chemical change will be produced : but if water be added, or either of the salts be previously dissolved, a violent effervescence ensues, and a chemical union is obtained. The water added is of use merely to overcome the re- sistance which arises from the cohesion of the particles of the salts intended to be brought into the sphere of action, or to increase their mutual contact. Experiment II. If crystallized sulphate of alumine, or sulphate of soda. and acetite of lead are brought into contact with each other, the individuality of these bodies will not be de- stroyed, that is to say, no chemical change will take place; but if they be intimately rubbed together in a mortar, the two solids will act upon each other, and form a fluid. It is obvious, therefore, that in order to facilitate chemical affinity, the attraction of aggregation must be broken; the bodies intended to be chemically united must not be presented to each other in their mass of contact, but mechanically divided, or reduced to the smallest moleculse possible. Hence liquids combine with more facility than solids, or even than a solid and a liquid ; and in like manner va- pours combine with rapidity and ease. Law III. The agency of affinity of composition is influ- enced by temperature. Its action is either accelerated, retarded, prevented^ or rendered efficacious. PROOFS OF LAW III. Experiment I. If we mingle equal parts of sulphur and carbonate of potash, and leave the mixture for any length of time, no VOL. I. v 73 Proofs of the Laws of Chemical Ajinitij. change will take place ; but if we increase the tempera ture or heat the mixture, a union will be obtained. Experiment II. If we expose phosphorus in an open vessel to the ac- tion of the atmosphere, a chemical union will take place between the phosphorus and one of the constituent parts of the atmosphere, namely, the oxigen gas ; the phos- phorus will gradually (but very slowly) disappear, and become converted into a fluid, called phosphoric acid. But if we heat the vessel containing the phosphorus-, the latter will take fire, and become converted into a yel- lowish white substance, which in a short time is chang- ed into an acid analogous to the former. Experiment III. If equal quantities of muriate of ammonia and carbon- ate of magnesia are mixed with six or eight parts of wa- ter, and suffered to stand for some time exposed to the ordinary temperature of the atmosphere, a mutual de- composition of the two salts will take place. For if the mixture and the fluid which passes are left to evaporate spontaneously, muriate of magnesia and carbonate of am moniawillbe obtained. On. the contrary, Experiment IV. If equal quantities of muriate of magnesia and carbon- ate of ammonia be exposed to a temperature of 200° in about four parts of water, the products obtained are mu- riate of ammonia and carbonate of magnesia. Experiment V. If muriate of soda and sulphate of magnesia be mix- ed together in any proportion, and exposed to a tempera- ture below zero, they decompose each other, and muriate of magnesia and sulphate of soda are formed ; but no de- composition takes place at a temperature above 30°. Muriate of soda, and acidulous sulphate of alumine and potash, exhibit precisely the same phenomena. ■Proofs of the Laws of Chemical Affinity. 73 * \ Experiment VI. If ardent spirit and a solution of salt in water be mixed cogether, the compound formed is a. real chemical union ; but if we carefully heat the fluid, the caloric applied will be divided between the three ingredients, according to their respective affinities; the union will be broken, for the ardent spirits will first become volatilized, and the union of the salt and water remain unaltered. On in- creasing the temperature, the water will escape in the form of vapour, and the salt will be left behind. There are numerous cases in which an increase of tem- perature is essentially necessary to determine bodies to unite. If mercury be exposed to oxigen gas, at the com- mon temperature of the atmosphere, the corpuscular at- traction subsisting between its particles is sufficient to pre- vent^combination : but if the mercury be heated to a cer- tain degree, the force which kept its particles united will become annihilated, and it then combines with the oxigen which is present. Again, if the oxid of mercury thus formed be exposed to a higher degree of temperature, the union is demo- lished, and the quicksilver reappears in its metallic state. Hence it is obvious that the action of caloric favours the union of the oxigen and mercury, in consequence of the dimunition of the mutual affinity of the parts; but at length, by augmenting this difference, it again breaks the union, or renders the combination impossible. That increased temperature augments the powers of chemical union the solutions of salt and water afford in- stances. A larger quantity of salt is soluble in a given quantity of water at a high than at a low temperature, and this •larger quantity of salt is again separated by cooling. ♦ •Law IV. Chemical affinity is accompanied by a change of temperature at the instant of its action. The truth of this principle will be perceived bv apply- ing experiment to theory. 80 Proofs of the Laws of Chemical AjjinitXj. PROOFS OF LAW IV. Experiment I. Prsduction of heat, by the combination of dense acids, alcalies, &?c. with water. We have mentioned already (page 52) that when two parts of concentrated sulphuric acid and ardent spirit are mingled together, the mixture in a few minutes becomes so hot as to render the vessel insupportable to the hands. If four parts of sulphuric acid of commerce and one part by weight of water be mixed together, each at the temperature of 50°, the mixture immediately acquires a temperature of about 300°. All the dense acids, ammonia, and ardent spirit, when mixed with water, have the property of raising its tem- perature remarkably : and the same is the case when al- calies are introduced into concentrated acids. On the contrary, in many instances cold is produced. Experiment II. Production of extreme degrees of cold. Take one ounce and a half of muriate of ammonia, and a like quantity of nitrate of potash; reduce each of these salts separately to powder, and blend them intimately to- gether : having done this, mix them gradually in a glass basin, or other thin glass vessel, with four ounces of water. The result will be, that the cold produced sinks a thermo- meter immersed in it to 36° Fahr. A new addition of the same quantity of salts will cool it to 14°, which there- fore will freeze water in a glass tube that is immersed in it, without the use of snow or ice. If the water employ- ed in a first process be used to reduce other water and salts to the temperature of about 32°, and these be appli- ed to the performance of a second experiment, the tem- perature may be lowered to 4° below 0°. A number of experiments have lately been made to produce artificial cold by means of such freezing mix- tures. The most complete set of this kind are those of Pepys, Lowitz, and Walker. They shall be noticed in :he next part of this worjc. Proofs of the Laws of Chemical Affnity. 8t Law V. The agency of chemical affinity between two or more bodies may lie dormant, until it is called into ac- tion by the interposition of another body, xvhich fre- quently exerts no energy upon them in a separate state. From this law originates what was formerly called dis- posing affinity, or that case in which two or more bodies are incapable of uniting, until the agency is called into action by the addition of a third body, which exerts no sensible affinity upon either of them. This may be proved in the following manner. PROOFS OF LAW V. Water is a compound of hidrogen and oxigen; phos- phorus is a simple body, according to our present state of knowledge. If these be presented to each other, no che- mical union will take place; but if we add to them an al- cali, and then apply heat, the water will become decom- posed ; that is to say, part of the phosphorus will unite to the oxigen of the water and form phosphoric acid, and the other part will be dissolved in the hidrogen gas and appear as phosphorated hidrogen. Here the alcali acts as the substance requisite to favour the mutual action, or to give the disposing affinity. If iron and water be brought into contact with each other, no perceptible change will be produced; but if a little sulphuric acid be added to the water and iron, a vio- lent effervescence takes place, the water becomes decom- posed, hidrogen gas will be evolved, and the iron become dissolved in the acid. In this case the sulphuric acid is the condition neces- sary to accelerate the chemical action. These experiments will be more fully considered here- after. Law VI. The ratio of the energy of chemical affnity acting between various bodies is different in different substances. This is the most important law of chemical attraction. As beginners will find it rather difficult to understand what passes in this more complicated agency, we shall «2 Proofs of the Laws of Chemical Affinity. •shortly remark, that the combination which is effected ber tween two or more bodies, by virtue of the affinity of composition, becomes broken whenever we present to the compound another body, which has an attraction to one of the constituent parts of the compound, superior to that attraction by which they were held together: the bodies, therefore, between which the strongest attraction prevails combine, and the rest are disengaged. PROOFS OF LAW VI. Experiment I. If muriatic acid be poured either on pure barytes or on its carbonate, the barytes will be dissolved, and the com- pound will be muriate of barytes, which compound is held together by the force of affinity existing between the mu- riatic acid and the barytes. On letting fall into this so- lution a few drops of sulphuric acid, an immediate change of principles takes place ; the whole quantity of the muri- atic acid which was combined with the barytea becomes disengaged; and the sulphuric acid unites to the barytes with a force equal to their affinity, minus that of the mu- riatic acid. Experiment II. If pure silver be dissolved in nitric acid, the silver will remain united to the acid till another body is presented to it which has a greater force of attraction to one of the constituent parts of the compound : for instance, if mer- cury be added to this solution of silver, the mercury will be dissolved, and the silver becomes precipitated or dis- engaged. The supernatant fluid will then be a solution. of mercury in nitric acid. Experiment III. If to the before-obtained solution of mercury in nitric acid a piece of sheet lead be presented, the lead will be dissolved, and the mercury become precipitated. Thf fluid will then be a solution of lead in nitric acid. Proofs of the Laws of Chemical Affnity. Experiment IV. If in this solution of lead a thin slice of copper be sus- pended, the copper will be dissolved, and the lead will be- come disengaged. The fluid now is a solution of copper in nitric acid. Experiment V. If in this solution of copper a thin sheet of iron be kept immersed, the iron will be dissolved, and the copper be- come precipitated. The fluid now is a solution of iron in nitric acid. Experiment VI. If to this solution of iron a piece of zinc be presented, the zinc will be dissolved, and the iron become precipi- tated. The solution then consists of zinc and nitric acid. Remarks....It appears nevertheless, from Berthollet's Treatise, as we shall see directly, that in almost all cases of elective affinity, there is not a total transfer of the base, but that a division is made between the two opposite at- tracting substances, in a compound ratio of the relative force of affinity and quantity of each; that, in many cases, the excess of quantity may supply the difficiency of force, and therefore that the mass must be carefully taken into consideration. Law VII. The agency of chemical affinity is either li- mited or unlimited; in other words, chemical affnity is capable of uniting bodies in definite or in indefinite pro- portions. Experience has convinced us, that in all bodies there are certain precise limits of combinations beyond which their action cannot pass, namely, a minimum and a maxi- mum ; it remains still to be ascertained how bodies can combine'within these limits. If we attend to what is known at present, we are forced to acknowledg that this law comprehends several modi ft- 84 Proofs of the Laws of Chemical Affinity. cations, which may be arranged under the following classes. 1. Chemical affinity unites several bodies in any pro- portion whatsoever; their combination is therefore un- limited : for instance, PROOFS OF LAW VII. Experiment I. If water and ardent spirit be mingled together in any quantity, a chemical combination ensues, for the com- pound obtained has always a specific gravity different from the mean specific gravity of the fluids combined. Its bulk is likewise not the arithmetical mean of the fluids in a separate state. The same is the case when liquid acids and water, or acids and ardent spirit, are combined together. 2. Chemical affinity combines several bodies to a cer- tain extent or maximum only. To this class belong all those bodies which are capabh of (what is called) saturation. Experiment II. If we take a quantity of any of the dense acids diluted with water—for instance sulphuric acid—and let fall into it a solution of an alcali—for example soda—by a little at a time, and examine the mixture after every addition of the alcali, we find for a considerable time it will exhibit the properties of an acid, it will have a sour taste, and convert vegetable blue colours into red; but if we continue to add greater quantities of soda, these acid properties will gra- dually diminish, and at last disappear altogether. At that point the combination is at an end, it has reached its maximum in this case; for if we continue to add more alcali, the mixture will gradually acquire alcalint proper- ties; it will convert blue vegetables into green; it will have an urinous or alcaline taste, &c. These properties will become stronger the greater the quantity of the soda is which is added. Proofs of the Laws of Chemical Affinity. 85 Experiment III. Take muriatic acid, and let fall into it gradually car- bonate of lime or magnesia: an effervescence will take place ; for a chemical union ensues between the acid and the lime, or magnesia, and the carbonic acid, the other constituent part of these bodies, becomes disengaged. But if we continue the addition of the lime or magnesia until it produces no further effervescence, no chemical union will be obtained, the lime will fall to the bottom unalter- ed, for the combination is at its maximum. It is on this account that water can only dissolve a cer- tain quantity of salt; ardent spirit, a certain quantity of resin, &c. The union of oxigen and hidrogen belongs likewise to this class. 3. Chemical affinity is capable of uniting different bo- dies in two, three, or more proportions; each of these combinations produces compounds possessing peculiar properties. This peculiarity of combination is highly important. It is owing to this circumstance that both nature and art produce substances of the same principles, only com- bined in different proportions, which possess peculiar properties widely different from each other. Law VIII.—The energy of the chemical affinity of dif- ferent bodies is modified in proportion to the ponderable quantities of the substances placed within the sphere of action. It is obvious from this, that the denomination of elec- tive affinity is erroneous; since it supposes the union of one entire substance with another in preference to a third. But this is not the case; a mere division of action takes place in instances of this kind; that is to say, the substances act according to the quantity existing within the sphere of activity. The excess of quantity is capable of compensating for the deficiency of the force of affinity. When, therefore, a compound body of two substances is acted on by a third, that part of a compound which is the subject of combination is divided between the two re- maining, not only in proportion to their respective de- vol. i. o 86 Proofs of the Laws of Chemical Affinity. grees of affinity, but also according to their ponderable quantities; so that by varying this in either, the effect produced will be varied. Thus Berthollet has proved, that in all cases a large quantity of a body is capable of abstracting a portion of another from a small portion of a third, how weak soever the affinity between the first and second of these bodies may be, and how strong soever the affinity between the second and third. Thus potash is capable of abstracting part of the acid from oxalate of lime, phosphate of lime, and carbonate of lime. Soda and lime decompose par- tially sulphate of potash. Nitric acid subtracts part of the base^from oxalate of lime, &c. The following experiment, advanced by Berthollet, will prove this more clearly. PROOFS OF LAW VIII. Experiment I. If equal parts by weight of sulphate of barytes and pot- ash be boiled in a small quantity of water to dryness, it will be found that the sulphuric acid has been divided be- tween the two bases in the compound ratio of their mass and their force of affinity. The greater part of the sul- phate of barytes will be found undecomposed ; a small quantity of barytes will be found at liberty ; most of the potash will also be uncombined ; but a certain portion will be united with the sulphuric acid which the barytes has lost in the form of sulphate of potash. It is not merely in the instance stated here that this division of one body between two others, according to their respective masses and affinities, takes place, there being scarcely any example to the contrary. And as the affinities of bodies vary with their masses, it is obvious, that when we speak of the affinities of bo- dies, we ought to consider them as always acting in cer- tain determinate proportions. Inferences....All th« tables of affinities, which have so much engaged the attention of the moderns, and which are deceitful under the appearance of accuracy, are there- fore merely comparative approximations to truth; for they have been constructed upon the supposition that dif- Proofs of the Laws of Chemical Affnity. . 8T terent substances possess different absolute degrees of affinity to each other, capable of producing the decompo- sitions and combinations which offer themselves, inde- pendently of the proportions of the bodies presented to each other. On the contrary, to determine the elective affinity of different bodies to each other, it is requisite to inquire what are the phenomena which they offer when presented to each other, in different proportions ? These phenomena have hitherto been little attended to ; nor has much attention been paid to other particular circumstances which appear capable of influencing the agency of affinity in general, namely, the action of light, electricity, galva- nism, &c. When these, and the before-mentioned discovery of Berthollet for determining the relative strength of affinity, are more attended to, they will probably lead to conse- quences of the greatest importance. It will oblige che- mists to attend more closely to the reciprocal action of bodies on each other under different circumstances; and the result must be, the discovery of several laws which will greatly facilitate the acquisition and the advancement of the science. The rapid progress which chemistry has lately made, the multiplicity of its researches, and the scrupulous accura- cy of observation with which experiments are now con- ducted, afford us every reason to hope that this will soon be accomplished.. HEAT, OR CALORIC. PART X. HE AT and cold are perceptions of which we acquire the ideas from the senses; they indicate only a certain state in which we find ourselves, independent of any ex- terior object. But as these sensations are for the most part produced by bodies around us, We consider them as causes, and, judging by appearances, we apply the terms hot or cold to the substances themselves; calling those bodies hot which produce in us the sensation of heat, and those co/*/which communicate the contrary sensation. This ambiguity, though of little consequence in the common affairs of human life, has led unavoidably to confusion and perplexity in philosophical discussions. It was to prevent this that the framers of the new nomen- clature adopted the word caloric, which denotes that which produces the sensation of heat. SECT. I. THEORIES OF HEAT. TWO opinions have long divided the philosophical world concerning the nature of heat. 1. The one is, that the cause which produces the sen- sation of heat is a real or distinct substance, universally pervading nature, penetrating the particles or pores of all bodies with more or less facility, and in different quantities. This substance, if applied to our system in a greater proportion than it already contains, warms it, as we call Theories of Heat. 8$ it, or produces the sensation of heat; and hence it has been called caloric or calorific. 2. The other theory concerning heat is, that the cause which produces that sensation is not a separate or self- existing substance ; but that it is merely like gravity a property of matter; and that it consists in a specific or peculiar motion, or vibration of the particles of bodies. The arguments in favour of the first theory have been principly deduced from the evolution and absorption of heat during chemical combinations; those of the latter are chiefly founded on the production of heat by friction. For it has been observed, that whatever is capable of pro- ducing motion in the particles of any mass of matter ex- cites heat. Count Rumford* and Professor Davyf have paid uncommon attention to this fact, and proved, that heat continues to be evolved from a body subjected to friction, so long as it is applied, and the texture or form of the body be not altered. All the effects of heat, according to this theory, depend therefore entirely on the vibratory motion of the particles of bodies. According as this is more or less intense, a higher or lower temperature is produced ; and as it pre- dominates over, is nearly equal, or inferior to the at- traction of cohesion, bodies exist in the gazeous, fluid, or solid state. Different bodies are susceptible of it in different de- grees, and receive and communicate it with different ce- lerity. From the generation, communication, and ab- straction of this repulsive motion under these laws, all the phenomena ascribed to heat are explicable. Each of these theories has been supported by the most able philosophers, and given occasion to the most im- portant disputes in which chemists have been engaged; and have contributed in a very particular manner to the advancement of the science. The obscurity of the sub- ject, however, is such that both parties have been able to advance the most plausible arguments. Setting aside all inquiries concerning the merits of these different doctrines, we shall confine ourselves to the general effects which heat produces on different * Rumford's Essays, vol. iii. t Davy's Essay in Beddoes's Medical Contributions 90 v Solar Heat. bodies. For the phenomena which it presents, and theii relation to each other, may be investigated with sufficient precision, though the materiality or immateriality of heat may remain unknown to us. NATURE AND THEOREMS OF HEAT. This premised, those who consider heat as matter, as- sert that caloric exists in two states, namely in combina- tion, and in a radiant state or at liberty. In the first state it is not sensible to our organs, nor indicated by the thermometer; it forms a constituent part of the body ; but it may be brought back to the state of radiant or sensible heat. In this state it affects animals with the sensation of heat. It therefore has been called sensible or free heat, or fire ; and is synonymous with un- combined caloric, thermometrical caloric, caloric of tem- perature, interposed caloric, &c. expressions now pretty generally superseded. From the diversity of opinions among chemists re- specting the nature of caloric several other expressions have been introduced, which it is proper to notice. For instance, by specific heat is understood the relative quan- tities of caloric contained in equal weights of different bodies at the same temperature. Latent heat is the ex- pression used to denote that quantity of caloric which a body absorbs when changing its form. It is, however, more properly called caloric of fluidity. The disposition or property by which different bodies contain certain quantities of caloric, at any temperature, is termed their capacity for heat. By the expression of absolute heat is understood the whole quantity of caloric which anybody contains. These terms shall be more fully considered hereafter. Before we proceed further we shall briefly notice the various methods of exciting heat, and then endeavour to examine its general properties. Productions of Heat. <*1 SECT. II. METHODS OF EXCITING AND COLLECTING HEAT. OF the different methods of exciting heat, the follow- ing are the most usual. 1. PRODUCTION OF HEAT BY PERCUSSION. OR COLLISION. This method of producing heat is the simplest, and therefore it is generally made use of in the common pur- poses of life for obtaining fire. When a piece of hardened steel is struck with a flint, some particles of the metal are scraped away from the mass, and so violent is the heat which follows the stroke, that it melts and vitrifies them. If the fragments of steel are caught upon paper and viewed with a micro- scope, most of them will be found perfect spherules, and very highly polished. Their sphericity demonstrates that they have been in a fluid state, and the polish upon their surface shows them to be vitrified. This evolution of heat by percussion, seems to be the consequence of a permanent or temporary condensation of the body struck. Mr. Dalton* has proved that when air is suddenly con- densed, a thermometer surrounded bv it rises several de- grees. Mr. Mollett was the first who observed that a small piece of linen, rolled up, takes fire when put into the narrow canal in which the lower extremity of a pump for condensing air generally terminates.! Mr. North- moore has inflamed phosphorus by condensed oxigen gas. 2. PRODUCTION OF HEAT BY COMPRESSION OR FRICTION. Heat may likewise be excited by mere friction. Wood •rubbed against wood, or against any hard body; metal * Manchester Memoirs, v. W5. t Phi!. Map. xtv 364 92 Production of Heat by Friction. rubbed against metal, or against any other body ; in short, solid bodies rubbed against each other are thereby heated, often so far as to become red hot. The natives of New Holland are said to produce fire in this manner with great facility, and spread it in a wonderful manner. For that purpose they take two pieces of dry wood, one is a stick about eight or nine inches long, and the other piece is flat; the stick they shape into an obtuse point at one end, and pressing it upon the other piece, they turn it very nimbly by holding it between both hands as we do a chocolate mill, often shifting their hands up and then moving them down upon it, in order to increase the pressure as much as possible. By this method they get fire in a few minutes, and from the smallest spark they increase it with great speed and dexterity. If the irons at the axis of a coach-wheel are applied to each other without the interposition of some unctuous matter to keep them from immediate contact, they will become so hot when the carriage runs swiftly along as to set the wood on fire; and the fore wheels being smallest and niaking most revolutions in a given time will be most in danger. The same will happen to mill-work or to any other machinery. It is no uncommon practice in this country for black- smiths to use a plate of iron as an extemporaneous sub- stitute for a tinder-box; for it may be hammered on an anvil till it becomes red hot, and will fire a brimstone match. A strong man who strikes quick, and keeps turning the iron so that both sides may be equally exposed to the force of the hammer, will perform this in less time than would be expected. If in the coldest season one dense iron plate be laid on another, and pressed together by a weight, and then rubbed upon each other by reciprocal motions, they will gradually grow so hot, as, in a short time, to emit sparks, and at last become ignited. It is not necessary that the substances should be very hard, a cord rubbed backwards and forwards swiftly against a post or a tree will take fire. Count Rumford* and professor Pictetf have made • Nicholson's Journal (4th edit.), vol. ii. p. 106. t Pictet's Essais sur le Feu, chap. ix. Production of Heat by Chemical Action. 93 some very ingenious and valuable experiments concerning the heat evolved by friction. It is asserted, that heat may be produced by friction where there is absolutely no oxigen gas whatever ; so that in these cases it cannot be derived from the decom- position of that gas. This has made several persons su- spect that heat is not the effect of a pe' uliar substance, called caloric, but that it is only a peculiar motion or vibration of the particles of bodies. It must, how- ever, be considered, that there is no friction which does not produce compression, viz. a contraction of the bulk of the bodies concerned, at least for a time, and there- fore that the caloric is squeezed or forced out of the bodies themselves, and being communicated to the sur- rounding bodies, produces the usual signs of heat. What very much corroborates this assertion is, that substances which are not compressible, are not heated by mechanical force; thus a flint will only be broken, but a piece of metal will be heated by the strokes of a hammer. Thus, also, we may place any weight upon a quantity of water without altering its temperature, because the com- pressibility of that fluid is almost nothing; but if we ptace an additional weight upon a quantity of air, the bulk of that fluid will be contracted, and its temperature will be raised by the compression. 3. PRODUCTION OF HEAT BY CHEMICAL ACTION. To this belongs the heat produced by combustion. There are besides this many chemical processes wherein rapid chemical action takes place accompanied with a de- velopment of heat, or fire and flame. Instances of this kind have been noticed already, page 51. More striking experiments will be given in the progress of this work. It has been remarked, that whenever a mixture of two or more bodies is attended with heat, the bulk of that mixture is less than the sum of the bulk of the separate ingredients, viz. a compression or concentration takes place, which is accompanied with a development of caloric ; viz. if 100 grains of alcohol, of ,0,825 specific gravity, occupy a space equal to 100, at a temperature of vot.. i. v 94 Solar Heat. 60° Fahr. and 100 grains of water, at the same temper* ature, occupy a volume equal to 82,5, the volume of these two fluids, after being mingled and reduced to the original temperature, viz. 60°, will be 177,41 ; a dimintr- tion of bulk equal to 5,09 has therefore taken place. The specific weight of the mixture is ,0,93,002. 4. SOLAR HEAT. It is well known that every lens, whether convex or plano-convex, will collect by refraction the rays of the sun dispersed over its surface into one point or focus, and produce the most astonishing effects. Dr. Herschell has discovered, that there are rays emit- ted from the sun which have not the power of illuminat- ing or producing vision ; and that these are the rays which produce the heat of the solar light, besides others which have a deoxidating power. Consequently heat is emitted from the sun in rays; but the%e rays are not the same with the rays of light, as shall be more fully proved hereafter. The direct rays of the sun on the same spot of the sur- face of the earth are more or less hot according to the time of the year, clearness of the atmosphere, state of the wind, and the colour, together with the quality of the spot. On this island, and in the hottest time of the summer, the direct rays of the sun seldom raise the thermometer so high as 110°. In other climates, especially within the tropics, they raise the thermometer considerably higher, viz. 20 or 30, or as it is said, even 40° higher than 110. But we must not believe the idle stories of their melting lead, or even of their setting fire to gunpowder. No sensible heat is known to be derived from any other celestial body. The moon, indeed, on account of the great light it reflects on the earth, might be expected to communicate some degree of heat; but though that light, concentrated by a large concave mirror, has been thrown upon the most sensible thermometers, yet I am not certain that it ever affected them. A great many calculations have been made concerning the proportion between the light which we receive directly from tlu 'Solar Heat. 95 *un, and that which is reflected to us from the moon; from which it appears that the latter is several hundred times less dense than the former; and the heat of both is supposed to be in the same proportion. 5. PRODUCTION OF HEAT BY THE ELEC- TRIC SPARK, AND BY GALVANISM. The effects of electricity are too well known in this point of view to need any description. Galvanism has of late become a powerful instrument for the purpose of exciting heat. Not only easily inflam- mable substances, such as phosphorus, sulphur, &c. have been fired, but likewise gold, silver, copper, tin, and the rest of the metals, have been burnt by means of galvan- ism, as was shown by professor Davy in his lectures at the theatre of the Royal Institution in 1801. Such are the principal methods of exciting heat. We shall now endeavour to examine experimentally the effects which heat produces upon bodies in general. SECT. III. GENERAL EFFECTS OF HEAT. EXPANSIVE PROPERTY OF HEAT. THIS is the first and most obvious effect which heat produces on bodies. Experience has taught us, that at all times when bodies become hot they increase in bulk. The bodies experience a dilatation which is greater in proportion to the accumulation of caloric, or, in other words, to the intensity of the heat. This is a general law which holds good as long as the bodies have suffered no change either in their combination or the quantity of their chemical principles. This power which heat possesses consists therefore in a constant tendency to separate the particles of bodies. Hence philosophers consider heat as the repulsive power ^o Expansion of Bodies. which acts upon alb bodies whatever, and which is in constant opposition to he power of attraction. The phenomena which result from these mutual actions seem as it were the secret springs of nature. Heat, how- ever, does not expand all bodies equally, and we are still ignorant of the laws which it follows. 1. EXPANSION OF FLUID BODIES BY HEAT. Experiment I. Take a glass globe, with a long slender neck called a bolt head, fill it up to the neck with water, ardent spirit, or any other fluid which may be coloured with red or black ink, in order to be more visible, and then immerse the globe of the instrument in a vessel of hot water; the incl ded fluid will instantly begin to mount into the neck. If it be taken out of the water and brought near the fire, it will ascend more and more in proportion as it becomes heated ; but upon removing it from the source of heat, it will sink again: a clear proof that caloric dilates it, so as to make it occupy more space when hot than when cold. These experiments may therefore serve as a de- monstration that heat expands fluid bodies. It appears that liquids of the least density expand most with the same temperature. Thus hidrogen gas dilates more with the same degree of heat than atmospheric air; atmospheric air more than sulphuric ether; ether more than ardent spirit; ardent spirit more than oil; oil more than water ; water more than acids ; and acids more than mercury. But if we compare the periods of time neces- sary for each fluid to acquire the maximum of rarefaction it is susceptible of, there is no law to guide us yet known. 2. EXPANSION OF AERIFORM BODIES BY HEAT. Experiment I. . The expansion of air, or any other gaseous fluid, may be evinced in the following manner: let a glass retort be supported on the ring of the lamp furnace, so as to suffer ;he neck of it to dip into a bason of water; if heat be now General Effects of Heat. 97 applied to the retort by means of the lamp, the confined air in the retort will expand, and bubbles of air will pass through the water. NATURE OF THE AIR-THERMOMETER, OR MANOMETER. This instrument, in which the expansion of air is tried, has been called manometer, but in truth it is only an air- thermometer, and though rather larger, it is not, how- ever, unlike the common thermometer, viz. it consists of a tube five or six feet long, having a bulb at one end and open at the other. The bore of the tube is about a 20th of an inch in diameter. A small quantity of quicksilver is placed in some part of the cavity of the tube, and the expansion of the air of the bulb, when heated, forces the quicksilver to move towards the open end of the tube. The degree of heat to which the manometer is exposed, is measured by means of a thermometer; the quantity of expansion of the air is ascertained by gauging the mano- meter, and making marks on the tube, which marks may indicate parts of the cavity of the tube that are propor- tional to the capacity of the manometer, as, for instance, lOOths or lOOOths, &c. By placing the manometer horizontal or vertical, either with the bulb downwards or the bulb upwards, the air in it may be either left of the natural density, or it may be condensed, or, lastly, it may be rarified; for when the manometer is horizontal, the quicksilver does neither press upon the air of the manometer, nor on that of the atmosphere ; when the bulb is downwards the quicksilver presses upon the air of the manometer: and when the bulb is upwards, the quicksilver presses against, and counteracts, in some measure, the gravity of the atmos- phere. Hence this pressure and this rarefaction of the air within the manometer may be increased to any re- quired degree by increasing the quantity of the quicksil- ver within the tube; and thus the expansibility of com- mon, or of condensed, or of rarified, air may be tried. The expansion of air by the same degrees of heat, differs according to its density, and to the quantity of" moisture it contains; nor are the increments of its bulk proportional to the degrees of temperature. 98 General Effects of Heat. If appears from Colonel Roy's very numerous experi, ments,* that 1000 parts of air, of the density of the com- mon atmosphere, at 0° of heat, become 1484,21 at 212°, viz. are expanded 484,21 by 212° of heat. 1000 parts of air loaded with 2\ atmospheres, are ex- panded 434 of those parts by 212° of heat. 1000 parts of air pressed only with |- of an atmosphere, are expanded nearly 484 of those parts by 212° of heat. 1000 parts of air pressed with | of an atmosphere are expanded about 141 parts by 180° of heat, viz. from the freezing to the boiling point. " From these last experiments," says Colonel Roy, " it " would seem, that the particles of air may be so far re- " moved from each other, by the diminution of pressure, " as to lose a very great part of their elastic force." The above-mentioned expansions are by no means re- gular ; viz. they are not proportional to the number of degrees of heat. The maximum of expansion takes place between 52° and 72°, and the minimum is constantly at the boiling point of water. Moist air expands vastly more than dry air, especially when it approaches the boiling point of water; so that be- tween 192° and 212°, moist air expands about 8 or 9 times as much as dry air in similar circumstances. On the expansibility of air is founded Schmidt's pyro- meter. Let atmospheric air be freed from moisture by caustic alcalis, or other bodies, and included in a vessel of platina. This vessel A (fig. 3, pi. VI.) which may be made of any convenient size, is connected with the tube BB, of as fine a bore as possible. This tube is also made of platina, and reaches into a vessel C, which is filled with water up to e e, and into this the tube is fixed air-tight. Out of the vessel C rises a glass cylinder G hermetically sealed, in- cluding a thermometer, and a graduated tube F F is se- cured into the vessel C in a similar manner. Experiment II. If a bladder be partly filled with air, and the neck of it closely tied, so as to prevent the inclosed air from * Philosophical Transactions, vol. Ixvii. art. xxsiv. General Effects of Heat. 99 escaping, be held near a fire, the air will soon begin to occupy more space, and the bladder will become gradually distended ; on continuing the expansion of the air by in- creasing the heat, the bladder will burst with a loud re- port. 3. EXPANSION OF SOLID BODIES BY HEAT. Experiment I. If we take a bar of iron six inches long, and put it into a fire till it becomes red-hot, and then measure it in this state accurately, it will be found ^ of an inch longer than it was before; that is, about 120th part of the whole. That the metal is proportionably expanded in breadth, will be seen by trying to pass it through an aperture which it fitted exactly when cold, but which will not admit it when red-hot. The bar is therefore increased in length and diameter. To discover the minutest changes of expansion by heat, and the relative properties thereof, instruments have been contrived called pyrometers, the sensibility of which is so delicate as to shew the expansion from 73717 t0 tWW of an inch. INFERENCES. It is owing to this expansion of metals that the motion of time pieces is rendered erroneous; but the ingenuity of artists has discovered methods of obviating this inac- curacy, by employing the greater expansion of one metal to counteract the expansion of another ; this is effected in what is called the gridiron pendulum. Upon the same principle a particular construction of watches has been contrived. The expansion of metals is likewise one of the principal reasons that clocks and watches vary in winter and sum- mer, when worn in the pocket, or exposed to the open air, or when carried into a hotter or a colder climate. For the number of the vibrations of the pendulum, are always in the sub-duplicate ratio of its length, and as the length is changed by heat and cold, the times of vibration will be also changed. The quantity of alteration, when considered 100 Measurement of Heat. in a single vibration, is exceedingly small, but when they are often repeated it will be very sensible. An alteration of one thousandth part in the time of a single vibration of a pendulum which beats seconds, will make a change of eighty-six whole vibrations in twenty-four hours. As different metals expand differently with the same degree of heat; such musical instruments, therefore, whose parts are to maintain a constant true portion, should never be strung with different metals. It is on this account that harpsichords, &c. are out of tune by a change of temperature. Bodies which are brittle, or which want flexibility, crack or break if suddenly heated or cooled. This like- wise depends upon the expansive force of heat, stretching the surface to which it is applied, while the other parts not being equally heated, do not expand in the same ratio, and are therefore torn asunder, or break. Hem thin vessels stand heat better than thick ones. SECT. iv. MEASUREMENT OF HEAT. Upon the expansive property of heat, which we hav; considered before, is founded its arti.xial measurement. Various means have been therefore employed to assist the imperfection of our sensations in judging of the different degrees of heat, for our feelings unaided afford but very inaccurate information concerning this matter ; they indi- cate the presence of h^at,only when the bodies presented to them are hotter than the actual temperature of our organs of feeling. When those bodies are precisely of the same temperature with our body, which we make the standard of comparison, we then are not sensible of the presence of heat in them. When their temperature is less hot than that of our bodies, their contact gives us what is called the sensation of cold. The effects of heat upon material bodies in general which are easily visible to us, afford more precise and de- terminate indications of the intensity, that can be derived from our feelings alone. The ingenuity of the philoso- Nature of the Thermometer. 101 pher and artist has therefore furnished us with instru- ments for measuring the relative heat or temperature of bodies. These instruments are called thermometers and pyrometers. By these all degrees are measurable, from the slightest to that of the most intense heat. NATURE OF THE THERMOMETER. A thermometer is a hollow tube of glass, hermetically sealed and blown at one end in the shape of a hollow globe. The bulb and part of the tube are filled with mer- cury, which is the only fluid which expands equally. When we immerse the bulb of the thermometer in a hot body, the mercury expands, and of course rises in the tube ; but when we plunge it into a cold body, the mer- cury contracts and of course falls in the tube. The rising of the mercury indicates, therefore, an in- crease of heat; its falling, a diminution of it; and the quantity which it rises or falls, denotes the proportion of increase or diminution. To facilitate observation, the tube is divided into a number of equal parts called degrees. Further, if we plunge a thermometer ever so often in- to melting snow or ice, it will always stand at the same point. Hence we learn that snow or ice always begins to melt at the same temperature. If we plunge a thermometer repeatedly into water kept boiling, we find that the mercury rises up to a certain point. This is therefore the point at which water always boils, provided the pressure of the atmosphere be the same. There are four different thermometers used at present in Europe, differing from each other in the number of degrees into which the space between the freezing and boiling points is divided. These are Fahrenheit's, Reau- mur's, Celsius's, and Delisle's. The thermometer uniformly used in Britain is Fahren- heit's : in this the freezing point is fixed at 32° ; the boil- ing point at 212° above 0P, or the part at which both the ascending and descending series of numbers commence. In the thermometer which was first constructed by Reaumur, the scale is divided into a smaller number of degrees upon the same length, and contains not more than 80° between the freezing and the boiling points. The Ireezing point is fixed in this thermometer precisely at 0°, VOT.. T. Q_ 102 Nature of the Differential Thermometer. the term between the ascending and the descending series of numbers. 100 is the number of the degrees between the freezing and the boiling points in the scale of Celsius ; which has been introduce^ into France since the revolu- tion under the name of,the centigrade thermometer; and the freezing point-is in this as in the thermometer of Reaumur fixed at 0°. One degree in the scale of Fahren- heit appears from this account to ibe equal to | of a degree on that of Reaumur, and to | of a degree on that of Celsius. The space in Delisle's thermometer between the freez- ing and boiling points is divided into 150°, but the gradua- tion begins at the boiling point and increases towards the freezing point. The boiling point is marked 0, the freez- ing point 150°. Hence 180 F. = 153 D. or 6 F. = 5 D. To reduce the degrees of Delisle's thermometer under the boiling point to those of Fahrenheit ; we have F. = 212 — J- D.; to reduce those above the boilingpoint F. = 212 + f D. Upon the knowledge of this proportion it is easy for the student to reduce the degrees of any of these thermometers into the degrees of. any other of them. For chemical purposes the ball and part of the tube should project some way below the graduated seats, in order that they may be placed in liquids, mixtures, &c. NATURE OF THE DIFFERENTIAL THER- MOMETER. This instrument, for which we are indebted to Mr. Leslie, is calculated for measuring the minutest variation of temperature. Mr. Leslie's differential thermometer consists of two glass tubes, each terminating in a small bulb of the same dimensions, joined by the blow-pipe, and bent in the form of an U, a small portion of dark-coloured liquor (sulphuric acid, tinged red with carmine) having previously been introduced into one of the balls. By managing the included air with the heat of the hand, this red liquor is made to stand at the point required of the opposite tube. This is the Zero of a scale fastened to that tube, and divided into equal parts above and below nothing. The instrument is then fixed upright on a stand. It is manifest, that when the liquor is at rest, or points at zero, the column is pressed opposite ways by two Nature of the Pyrometer. 103 portions of air, equal in elasticity, and containing equal quantities of caloric. Whatever heat, then, may be ap- plied to the whole instrument, provided both bulbs re- ceive it in the same degree, the liquor must remain at rest. But if the one ball receives the slightest excess of tem- perature, the air which it contains will be proportionably expanded, and will push the liquid against the air in the other bulb with a force, as the difference between the temperatures of those two portions of air. The equi- librium, in short, will be destroyed, and the fluid will rise in the opposite tube. The degrees of the scale through which it passes will mark the successive augmentations in the temperature of the ball, which is exposed to the greatest heat. This instrument, therefore, is truly a ba- lance of extreme delicacy, for comparing the tempera- tures with which its two scales may be loaded. NATURE OF THE PYROMETER. To measure those higher degrees of heat to which the thermometer cannot be applied, there have been other instruments invented by different philosophers; these are called pyrometers. The, most celebrated instrument of this kind, and which has been adopted into general use, is that invented by the late ingenious Mr. Wedgwood. This instrument is also sufficiently simple. It consists of two pieces of brass fixed on a plate so as to be ^ of an inch asunder at one end, and Jz at the other: a scale is marked upon them, which is divided into 240 equal parts, each -^ of an inch ; and with this his gauge are fur-" nished a sufficient number of pieces of baked clay, which must have been prepared in a red heat, and must be of given dimensions. These pieces of clay, thus prepared, are first to be applied cold, to the rule of the gauge, that there may no mistake take place in regard to their dimen- sions. Then any one of them is to be exposed to the heat which is to be measured, till it shall have been completely penetrated by it. It is then removed and applied to the gauge. The difference between its former and its present dimensions will shew how much it has shrunk ; and will, consequently, indicate to what degree the intensity of the heat to which it was exposed amounted. 104 Nature of the Pyrometer. High temperatures can thus be ascertained with accu- racy. Each degree of Wedgwood's pyrometer is equal to 130° of Fahrenheit's. Guyton has lately invented a pyrometer for measuring the highest degrees of heat of our furnaces, consisting of a lever of platina moved by the expansion of a bar of the Same metal, the whole being supported on a mass of baked clay. It consists of a rod of platina placed horizontally in a groove formed in a cake of white clay highly baked. This plate is supported at one of its extremities on the part of the mass which terminates the groove ; the other end presses against a bended lever, whose longest arm forms an index to a graduated arc ; so that the change of position of this index indicates the expansion produced on the plate of metal by the heat. The cake of clay having been highly baked, leaves no cause to apprehend any contraction; and the expansion which may take place during the ignition will only affect the very small distance between the axis of motion of the index and the point of contact of the plate, that is to say, in such a manner as rather to diminish the effect than to increase it. All the parts of this instrument being of platina, nei- ther fusion nor oxidation is to be apprehended. With respect to its dimensions, the author conceives that, in order to render the use of it commodious and ac- curate, they should be reduced to such as may be neces- sary to obtain sensible variations; it will then be render- ed commodious by the facility with which it may be placed under a muffle or an inverted crucible, Sec. and accurate, because the probabilities of any accidental inequalities of the heat willbe diminished, which it is impossible to avoid to a certain extent, even in the midst of a large mass of fire. The variations will be sufficiently perceptible, if we can not only estimate, but correctly determine expansions of the 200th part of a millimetre (about the 500th part of an inch) these the author obtains by the proportions of the instrument which he has himself adopted. The rod or plate of expansion is 45 millimetres (one inch and three quarters) in length, 5 in width (one fifth of an inch) and 2 in thickness (one thirteenth of an inch.) The arm of the bended lever, which presses against thr Exceptions to the Expansion by Heat. 105 end of this rod, is 25 millimetres in length ; (rather 2i, or about one ninth of an inch) and the arm at right an- gles to it, or the index, which traverses on the graduated arc, is 50 millimetres in length (one inch ar-d eight tenths) or twenty times the length of the other. The space tra- versed by the displacing of the small arm will be thus in- creased in the proportion of 1 to 20. As the long arm or index carries a nonius which di- vides each degree on the graduated arc into ten parts, we can distinctly observe the 200th of one of those measures (referred to the bar itself.) Lastly : as the decimal division of an arc of a circle of 50 millimetres radius, gives only 7#8538 deci-millimetres for one of its degrees, it is evident, then, that we may measure an expansion of 0*078538 deci-millimetres, or of the 5730th part of the length of the radius. In order to prevent the position of the index from be- ing changed in removing the instrument from the fur- nace, a plate of platina is fixed so as to form a spring against its extremity. The author has commenced a series of experiments to determine the range of this pyrometer, to compare it with the pyrometric pieces of Wedgwood, and so to shew the degree of confidence it merits, the methods of using, and the cases in which it may be usefully employed in philo- sophical researches, and in the arts. SECT. V. EXCEPTIONS TO THE EXPANSION BY HEAT. PHILOSOPHERS have noticed a few exceptions to the law of heat expanding bodies. For instance, water when cooled down to the freezing point, instead of con- tracting on the further deprivation of heat, actually ex- pands. Another seeming exception is manifested in alumine or clay; others occur in the case of cast-iron, and various other metals. Alumine contracts on being heated, and cast-iron, bismuth, kc. when fully fused are more dense than when solid ; for as soon as they become so they de- crease in density : they expand in the act of cooling ; and 106 Equal Distribution of Heat. hence the sharpness of figures upon iron which has been cast in moulds, compared to that of other metals. Some philosophers have persuaded themselves that these exceptions are only apparent, but not really true. They say when water freezes, it assumes a crystalline form, the crystals cross each other and cause numerous vacuities, and thus the ice occupies more space. The same is the case with fused iron, bismuth, and zinc. The contraction of clay is owing to the loss of water, of which it loses a part at every increased degree of temperature hitherto tried : there is, therefore, a loss of matter ; and a reduction of volume must follow. Mr. Tilloch* has published a brief examination of the received doctrines respecting heat and caloric, in which these truths are more fully considered, together with many other interesting facts relative to the received no- tions of heat. SECT. VI. EQUAL DISTRIBUTION OF HEAT. IT was stated before that all bodies are permeable to iieat, and that it has a constant tendency to diffuse itself over matter till an equilibrium of temperature is established. It is impossible to accumulate it in any body beyond a cer- tain degree, or to preserve it in that accumulated state. If, therefore, a number of bodies of different tempera- tures are placed in contact with each other, they will all at a certain time acquire a temperature which is the mean temperature of the different substances ; the caloric of the hottest body will diffuse itself among those which are heated in a less degree till they have all acquired a certain temperature. Thus, if a bar of iron which has been made red-hot be kept in the open air, it does not retain the heat which it had received, but becomes gradually colder and colder, till it arrives at the temperature of the bodies in its neighbourhood. On the other hand, if we cool down the iron bar by keeping it for some time covered with * Philosophical Magazine, May, 1800, p. 78. Propagation of Heat. 107 snow, and then carry it into a warm room, it does not retain its low temperature, but becomes gradually hotter till it acquires the temperature of the room. It is there- fore obvious that in the one instance the temperature is lowered, and in the other that it is raised. These changes of temperature occupy a longer or a shorter time according to the nature of the body, but they always take place at last. This law itself is indeed fami- liar to every one: when we wish to heat a body we carry it towards the fire ; when we wish to cool it we surround it by cold bodies. This distribution of heat takes place even through the Torricelian vacuum, and it is evidently owing to its re- pulsive power, which constantly tends to an equilibrium SECT. VII. PROPAGATION OF HEAT. WE have seen in the last section that when bodies of higher temperature than others are brought into contact with each other, the heat is propagated from the first to the second, or the colder body deprives the warmer of its excess of heat. We shall now see that some bodies do so much more quickly than others. Through some bodies caloric passes with undiminished velocity; through others its passage is prodigiously retarded. This disposition of bodies of admitting under equal circumstances the refrigeration of a heated body within a shorter or a longer time, is called the power of conducting heat; and a body is said to be a better or worse conductor of heat, as it allows the refrigeration to go on quicker or slower. Those bodies, therefore, which possess the pro- perty of letting heat pass with facility are called good con- ductors; those through which it passes with difficulty are called badconductors ; and those through which it does not seem to pass at all are called non-conductors : thus we say in the common language, some bodies are xvarm or capable of preserving warmth; and from this arises the great difference in the sensations excited by different bodies, when applied at the same temperature to our organs of 108 Propagation of Heat. feeling. Hence if we immerse our hand in mercury wc feel a greater sensation of cold than when we immerse it in water, and a piece of metal appears to be much colder than a piece of wood, though their temperatures when examined by means of the thermometer are precisely the same. It is probable that all solids conduct heat in some degree, though they differ very much in their conducting power. Metals are the best conductors of heat; but the conduct- ing powers of these substances are by no means equal. Stones seem to be the next best conductors. Glass con- ducts heat very slowly; wood and charcoal still slower; and feathers, silk, wool, and hair, are still worse con- ductors than any of the substances yet mentioned. The best conductors of electricity and galvanism are also the best conductors of heat. Experiment I. Take a number of straight wires of equal diameters and lengths, but of different metals, for instance, gold, silver, copper, iron, &c. cover each of them with a thin coat of wax or tallow, and plunge their extremities into water kept boiling, or into melted lead. The melting of the coat of wax will shew that caloric is more quickly transmitted through some metals than others. It is on this account, also, that the end of a glass rod may be kept red-hot for a long time, or even melted with- out any inconvenience to the hand which holds the other extremity; though a similar metallic rod heated in the same manner would very soon become too hot to be held. The preceding observations apply only to the conduct- ing power of solids. With respect to fluids, two opinions are at present entertained ; one which considers them as capable of conducting caloric, though very imperfectly; the other which supposes them absolutely impermeable to this power. Count Ru#nford was the first who endeavored to prove that fluids in general, and aeriform bodies, convey heat on a different pr jiciple from that observed in solids. Accord- ing to this philosopher, caloric is propagated through fluids solely by the successive and actual application of the fluid Propagation of Heat. 109 to the heated part, and the portion so heated gives none of its caloric to the rest of the mass. Although the particles of any fluid individually can receive heat from other bodies, or communicate it to them, yet among these parti- cles themselves, all interchange and communication of heat is absolutely impossible. Fluids, therefore, according to count Rumford, are perfectly non-conductors of heat. It may appear at first sight that fluids are conductors, for they^can be heated as well as solids, and heated too con- siderably without sensibly changing their state of exist- ence. But fluids differ from solids in one essential parti- cular : their particles are at full liberty to move among themselves, and they obey the smallest impulse; while the particles of solids, from the very nature o. these bodies, are fixed and stationary. One of the changes which caloric produces is, as stated' before, expansion, or increase of bulk; and this increase is attended with a proportional diminution of specific gravity. Therefore, whenever caloric combines with a stratum of particles, the whole stratum becomes specifically lighter than the other parti- cles. This produces a change of situation in solids ; but in fluids, if the heated stratum happens to be below the other strata, it is pressed upwards by them, and being at liberty to move, it changes its place and is urged up to the surface. In fluids, then, it makes a very great difference to what part of the body the source of heat is applied. If it be made to act at the highest stratum of all, or to the surface of the liquid, the caloric can only make its way down- wards, as through solids, by the conducting power of the fluid; but if it be applied to the lowest stratum, it makes its way upwards independent of that conducting power, in consequence of the fluidity of the body, and the expan- sion of the heated particles. The lowest stratum, as soon as it combines with a dose of caloric, becomes specifically lighter and ascends. New particles approach the source of heat; combine with it in their turn, and are displaced. In this manner all the particles come one after another to the source of heat; of course the whole of them are heated in a very short time, and the caloric is carried^ al- most at once to much greater distances in fluids than in any solid whatever. Fluids, therefore, have the property VOL. I. R 11. 110 Propagation of Heat. of carrying or transporting caloric ; in consequence of which they acquire heat, independent altogether of any conducting power, according to count Rumford's theory, and hence all fluids are considered by him, as stated be- fore, in a similar respect as absolutely non-conductors of ca- loric. They can receive it from substances, and can give it to other bodies, but no particle can either receive it from, or give it to, another particle. Before a fluid, therefore, can be heated or cooled, every particle, as stated before, must go individually to the very substance from which it receives, or to which it gives, caloric. Heat being there- fore only propagated in fluids in consequence of the inter- nal motion of their particles which transport the heat; the more rapid ihese motions are, the more rapid is the communication of heat. The cause of these motions is the change in the specific gravity of the fluid, occasioned by the change of temperature, and the rapidity is in pro- portion to the change of the specific gravity of the liquid by any given change of temperature. The following ex- periment has been advanced to illustrate these facts. Experiment II. Take a thin glass tube, eight or ten inches long, and about an inch in diameter. Pour into the bottom part for about the depth of one inch, a little water coloured with Brazil- wood or litmus, and then fill up the tube with common water, extremely gently, so as to keep the two strata quite distinct from each other. Having done this, heat the bottom part of the tube over a lamp, the coloured infusion will then ascend and gradually tinge the whole fluid ; the water in the upper part of the tube may be made to boil, but the colouring matter will remain at the bottom undis- turbed. The heat cannot act downwards to make it as- cend. By thus being able to make the upper part of a fluid boil, without heating the bottom part, water may be kept boiling for a considerable time in a glass tube over ice without melting it. Other experiments illustrating the same principle may be found in Count Rumford's Essays, especially in essay the 7th, 1797. Pr opagation of Heat. Ill The results of his experiments, which are contained in the above essay, are highly interesting ; but experiments. lately made on the same subject, have sufficiently con- vinced us, that the Count's position is founded in error; they do not prove that fluids are non-conductors, but rather the contrary: all liquids whatever are capable of conducting caloric. When the source of heat is applied to their surface, the caloric gradually makes its way down- wards, and the temperature of every stratum gradually diminishes from the surface to the bottom of the liquid. The increase of temperature, in this case, is not owing to the carrying power of the fluid. By that power, caloric may, indeed, make its way upwards through fluids, but certainly not downwards. Liquids, then, are conductors of caloric. This, however, will become more evident from the following experiments made by Dr. Thompson and Mr. Murray, and Mr. Dalton. That liquids are conductors of caloric, Dr. Thompson proved in the following manner. The liquid whose con- ducting power was to be ascertained, was poured into a glass vessel till it filled it about half way ; then a hot li- quid of a less specific gravity was poured over it. Ther- mometers were placed at the surface, in the centre, and at the bottom of the cold liquid ; if these rose, it followed that the liquid was a conductor, because the caloric made its way downwards. For instance, to examine the con- ducting power of mercury, a glass jar was half filled with that metal, and boiling water then poured over it. The thermometer at the surface began immediately to rise, then the thermometer at the centre, and lastly that at the bottom. The first rose to 118°, the second to 90°, the third to 86° : the first reached its maximum in 1', the second in 15', the third in 25'. The conducting power of water was tried in the same manner, only hot oil was poured over it. A variety of precautions were necessary to ensure accuracy ; but for these we refer the reader to the experiments themselves, which are detailed in Nichol- son's Journal.* These facts have been since confirmed by a very ingeni- ously contrived and convincing experiment made by Mr • Nicholson's Journal, iv, 9 29 112 Propagation of Heat. Murray. To prevent the possibility of any heat being conducted by the apparatus, he employed a vessel of ice, which is incapable of conducting any degree "of heat greater than 32°. In this vessel Mr. Murray made experiments of the same nature with those just mentioned, and the result was the same. The thermometer constantly rose upon the application of a hot body to the surface of the liquid in which the thermometer was standing.* Mr. Dalton has likewise published lately a set of experiments almost exactly of the same nature with Dr. Thompson's, and with the same result. From the date affixed to his paper we learn, that his experiments had been made, and an account of them read to the Manchester Society just about the same time that Dr. Thompson was drawing up an account of his ; though they were not published till about two years after.f Fluids, then, so far as experiments have been made, are conductors of caloric as well as solids. Hence it fol- lows that all bodies with which we are acquainted are capable of conducting caloric. i On the bad conducting power of different bodies is founded the well-known facts, that of the different sub- stances used in clothing, hares fur and eider-down are the warmest; next to these, beavers fur, raw silk, sheeps wool, cotton-wool, and, lastly, lint or the scrapings of fine linen. In fur the air interposed among its particles is so engaged as not to be driven away by the heat communi- cated thereto by the animal body ; not being easily dis- placed, it becomes a barrier to defend the animal body from the external cold. Hence it is obvious that those skins are warmest which have the finest, longest, and thickest fur ; and that the furs of the beaver, otter, and other like quadrupeds which live much in the water, and the feathers of water-fowl, are capable of confining the heat of those animals in win- ter, notwithstanding the coldness of the water which they frequent. Bears, and various other animals, inhabitants of cold climates, which do not often take the water, have their fur much thicker on their backs than on their bellies. * Manchester Memoirs, V. f Ibid. 8vo, 1 Theory of Caloric of Fluidity, or latent Heat. 113 The snow, as a light porous body, which covers the surface of the earth in winter in high latitudes, is doubt- less designed as a garment to defend it against the pierc- ing winds from the polar regions which prevail during the cold season. Without dwelling further upon the philosophy of this truth, we"must briefly remark that the happy application of this law satisfactorily elucidates some of the most in- teresting facts of the economy of nature. SECT. VIII. THEORY OF CALORIC OF FLUIDITY, OR LATENT HEAT. THERE are some bodies which, when submitted to the action of caloric, dilate to such a degree, and the power of aggregation subsisting among their particles is so much destroyed and removed to such a distance by the interposition of caloric, that they slide over each other in every direction, and therefore appear in a fluid state. This phenomenon is ca\\ed fusion. Bodies thus rendered fluid by means of caloric are said to be fused, or melted; and those that are subject to it are called fusible. The greater number of solid bodies may, by the appli- cation of heat, be converted into fluids, and most proba- bly all would be so were we able to excite a sufficient de- gree of heat. Thus metals may be fused ; sulphur, resin, phosphorus, may be melted ; ice may be converted into water, &c. Those bodies which cannot be rendered fluid by any degree of heat hitherto known are calledfixed, or infusible. If the effects of heat under certain circumstances be carried still further than is necessary to render bodies fluid, vaporization begins ; the bodies then become con- verted into the vaporous or gazeous state. Vaporization, however, does not always require a previous fusion. Some- bodies are capable of being converted into the vaporous 114 Theory of Caloric of Fluidity, or latent Heat. state without previously becoming fluid, and others can- not be volatilized at any temperature hitherto known. Fluidity is, therefore, by no means essential to any spe- cies of matter, but always depends on the presence of a quantity of caloric. Solidity is the natural state of all bo- dies, and there can be no doubt that every fluid is capa- ble of being rendered solid by a due reduction of tem- perature ; and every solid may be fused by the agency of caloric, if the latter do not decompose them at a tempe- rature inferior to that which would be necessary for their fusion. CALORIC OF FLUIDITY. Dr. Black was the first who proved that whenever ca- loric combines with a solid body, the body becomes heat- ed only until it is rendered fluid ; or that whenever it has acquired the fluid state its temperature remains station- ary, though caloric is continued to be added to it. The same is the case when fluids are converted into the aeri- form or vaporous state. From these facts the laws of latent heat have been in- ferred. The theory may be illustrated by means of the following experiments: Experiment I. If a lump of ice at alow temperature, suppose at 22°, be brought into a warm room, it will become gradually less cold, as may be discovered by means of a thermometer. After a very short time it will reach the temperature of 32° (the freezing point) but there it stops. The ice then begins to melt; but the process goes on very slowly. During the whole of that time its temperature continues at 32° : and, as it is constantly surrounded by warm air, we have reason to believe that caloric is constantly enter- ing into it; yet it does not become hotter till it is changed into water. Ice, therefore, is converted into water by a quantity of caloric uniting with it. It has been found by calculation that one pound of ice in melting absorbs 140° of caloric, the temperature of the water produced still remaining at 32°. This fact may be proved in a direct manner. Production of Artificial Cold. 115 Experiment II. Take one pound of ice at 32° reduced to a coarse pow- der ; put it into a wooden bowl, and pour over it gradu- ally one pound of water heated to 172° ; all the ice will become melted, and the temperature of the whole fluid, if examined by a thermometer, will be 32° : 140° of ca- loric are therefore lost, and it is this quantity which was requisite to convert the ice into water. This caloric has been called latent caloric, or rather caloric of fluidity ; because its presence is not measurable by the thermometer. Dr. Black has also ascertained by experiment, that the fluidity of melted wax, tallow, spermaceti, metals, &c. is owing to the same cause, and Ladriani proved that this is the case with sulphur, alum, nitrate of potash, &c. We consider it therefore as a general law, that when- ever a solid is converted into a fluid, it combines with caloric, and that is the cause of fluidity. On the sudden transition of solids into fluids is found- ed the well known PRODUCTION OF ARTIFICIAL COLD, BY MEANS OF FRIGORIFIC MIXTURES. A number of experiments have been lately made by different philosophers, in order to produce artificial cold. And as these methods are often employed in chemistry with a view to expose bodies to the influence of very low temperatures, we shall enumerate the different substan- ces which may be made use of for that purpose, and the degrees of cold which they are capable of producing. We are indebted for them to Pepys, Walker, and Lowitz. 116 Table of Freezing Mixtures. TABLE OF FREEZING MIXTURES. Mixtures. Thermometer sinks Muriate of ammonia. 5 parts Nitrate of potash . . 5 From 50° to 10°. Muriate of ammonia - 5 parts Nitrate of potash . . 5 Sulphate of soda ... 8 From 50° to 4°. Sulphate of soda . . 3 parts Diluted nitric acid . 2 From 50° to 3°. Sulphate of soda . . 8 parts Muriatic acid .... 5 From 50° to 0°. Muriate of soda . . 1 From 32° to 0°. Snow or pounded ice 2 parts Muriate of soda . . 1 From 0° to — 5°. Snow or pounded ice 1 part Muriate of soda . . 5 Muriate of ammonia & Nitrate of potash . . 5 From — 5°to—18°. Table of Freezing Mixtures continued. 117 TABLE OF FREEZING MIXTURES CONTINUED. Mixtures. Thermometer sinks Snow or pounded ice 12 parts Muriate of soda . . 5 Nitrate of ammonia 5 From—18° to—25°. Snow and Diluted nitric acid From 0° to —46°. Muriate of lime . . 3 parts From 32° to —50°. From 32° to—51°. Diluted sulphuric acid 1 Diluted nitric acid . 1 From —10° to—56°. Diluted sulphuric acid 1 From 20° to —60°. Muriate of lime . . . 2 parts From 0° to —66°. Muriate of lime . . 3 parts From —40° to —73°. '.OT.. I. 118 Table of Freezing Mixtures continued. TABLE OF FREEZING MIXTURES CONTINUED. Mixtures. Thermometer sinks Dilut. sulphuric acid 10 parts From—68° to—91°. Nitrate of ammonia 1 part From 50° to 4°* Nitrate of ammonia . 1 part Carbonate of soda . 1 From 50° to 3°. Sulphate of soda . . 6 parts Muriate of ammonia 4 Nitrate of potash . . 2 Diluted nitric acid . 4 From 50° to 10°. Sulphate of soda . . 6 parts Nitrate of ammonia 5 Diluted nitric acid . 4 From 50° to 14°. Phosphate of soda . 9 parts Diluted nitric acid . 4 From 50° to 12°. Phosphate of soda . 9 parts Nitrate of ammonia 6 Diluted nitric acid . 4 From 50° to 21°. Sulphate of soda . . 5 parts Diluted sulphuric acid 4 From 50° to 3°. Conversion of Solids and Fluids into the Gazeous State. 119 MANAGEMENT OF THE PRECEDING MIXTURES FOR PRODUCING COLD. To produce the effects before stated, the salts must be reduced to powder, and contain their full quantity of water of crystallization. The vessel in which the freezing mix- ture is made should be very thin, and just large enough to hold it; and the materials should be mixed together as expeditiously as possible, taking care to stir the mixture at the same time with a rod of glass or wood. In order to obtain the full effect, the materials ought to be first cooled to the temperature marked in the table, by introducing them into some of the other frigorific mixtures, and then mingling them together in a similar mixture. If, Tor instance, we wish to produce = —46°, the snow and diluted nitric acid ought to be cooled down to 0°, by putting the vessel which contains each of them into the fifth freezing mixture in the above table before they are mingled together. If a more intense cold be required, the materials to produce it are to be brought to the proper temperature by being previously placed in the second freezing mixture. This process is to be continued till the required degree of cold has been procured. SECT. IX. CONVERSION OF SOLIDS AND FLUIDS INTO THE AERIFORM OR GAZEOUS STATE. WE have seen before that in order to render solids fluid, a certain quantity of caloric is necessary, which combines with the body, and therefore cannot be measured by the thermometer; we shall now endeavour to prove, that the same holds good in respect to the conversion of solids or fluids into the vaporous or gazeous state. 120 Conversion of Fluids into the Gazeous State. CONVERSION OF SOLIDS INTO THE GAZE- OUS STATE. Experiment I. Take a small quantity of carbonate of ammonia, in- troduce it into a retort, the neck of which is directed under a cylinder filled with mercury and inverted in a bason of the same fluid. On applying heat to the body of the retort, the carbonate of ammonia will be volatilized, it will expel the mercury out of the cylinder, and become an invisible gas, and would remain so, if its temperature was not lowered. The same is the case with benzoic acid, camphor, and various other substances. SECT. X. CONVERSION OF FLUIDS INTO THE GAZE- OUS STATE. ALL fluid may, by the application of heat, be convert- ed into an aeriform elastic state. When we consider water in a boiling state, we find that this fluid, when examined by the thermometer, is not hotter after boiling several hours than when it began to boil, though to maintain it boiling a brisk fire must neces- sarily, be kept up. What then, we may ask, becomes of the wasted caloric ? It is not perceptible in the water, nor is it manifested by the steam ; for the steam, if not com- pressed, upon examination, is found not to be hotter than boiling water. The caloric is therefore absorbed by the steam ; and although what is so absorbed is absolutely necessary for the conversion of water into the form of steam, it does not increase its temperature, and is there- fore not appreciable by the thermometer. This conclusion is further strengthened by the heat given out by steam on its being condensed by cold. This is particularly manifested in the condensation of this fluid in the process of distilling, where, upon examining the Conversion of Fluids into the Gazeous State. 121 refrigeratory, it will be found that a much greater quan- tity of caloric is communicated to it than could possibly have been transmitted by the caloric which was sensibly acting before the condensation. This may be easily ascer- tained by observing the quantity of caloric communicated to the water in the refrigeratory of a still, by any given quantity of liquor that passes over it. 1. The boiling points of different fluids are influenced by atmospheric pressure. The boiling point, or the conversion of fluids into gases or vapours, always takes place at certain temperatures, which is different in different fluids, provided the pres- sure of the atmosphere be the same. Experiment I. Put any quantity of sulphuric ether into a Florence flask, suspend a thermometer in it, and hold the flask over an Argand's lamp ; the ether will immediately begin to boil, and the thermometer will indicate 98°, if the ether has been highly rectified. Experiment II. If highly rectified ardent spirit is heated in a similar manner, the thermometer will rise to 176°, and there remain stationary. Experiment III. If water is substituted, it will rise to 212°. Experiment IV. If strong nitrous acid of commerce be made use of, it will be found to boil at 248° ;—sulphuric acid at 546° ;— and mercury and linseed-oil at 600°, &c. 2. The boiling point of fluids is retarded by pressure. Mr. Watt heated water under a strong pressure to 400°. Yet still, when^the pressure was removed, only part of the water was converted into vapour; and the tempera- * ire of this vapour, as well as that of the remaining fluid, 122 Conversion of Fluids into the Gazeous State. was no more than 212°. There were therefore 188° of caloric suddenly lost. This caloric was carried off by the steam. Now as only about } of the water was converted into steam, that steam must contain not only its own 188°, but also the 188° lost by each of the other four parts ; that is to say, it must contain 188° X 5, or about 940°. Steam, therefore, is water combined with at least 940° of caloric, the presence of which is not indicated by the thermometer. 3. When pressure is removed from the surface of bodies, their conversion into the gazeous state is greatly faci- litated, or their boiling point is lowered. In proof of this the following experiments may serve. Experiment I. Let a small bottle be filled with highly rectified sul- phuric ether, and a piece of wetted bladder be tied over its orifice around its neck. Transfer it under the receiv- er of an air-pump, and take away the superincumbent pressure of the air in the receiver. When the exhaustion is complete, pierce the bladder by means of a pointed sliding wire, passing through a collar of leather which covers the upper opening of the receiver. Having done this, the ether will instantly begin to boil, and become converted into an invisible gazeous fluid. Experiment II. Take a small retort or Florence flask, fill it one half or less with water, and make it boil over a lamp : when kept briskly boiling for about five minutes, cork the mouth of the retort as expeditiously as possible, and remove it from the lamp. The water, on being removed from the source of heat, will keep boiling for a few minutes; and when the ebullition begins to slacken, it may be renewed by dipping the retort into cold water. The water during boiling becomes converted into va- pour : this vapour expels the air of the vessel, and occupies its place: on diminishing the heat, it condenses ; when I Artificial Refrigeration. 123 the retort is stopped, a partial vacuum is formed, the pressure becomes diminished, and a less degree of heat is sufficient to cause an ebullition. For the same reason, water may be made to boil under the exhausted receiver at 94° Fahr. or even at a much lower degree; alcohol at 56°, and ether at — 20°. On the conversion of fluids into gases is founded the following experiment : Experiment III. To freeze water by means of sulphuric ether. Take a thin glass tube, four or five inches long and about two or three eighths of an inch in diameter, and a two ounce botde, furnished with a capillary tube fitted to its neck. In order to make ice, pour a litde water into the tube; taking care not to wet the outside, nor to leave it moist. Having done this, let a stream of sulphuric ether fall through the capillary tube upon that part of it containing the water, which by this means will be converted into ice in a few minutes; and this it will do even near a fire, or in the midst of summer. If the glass tube containing the water be exposed to the brisk thorough air or free draught of an open window, a large quantity of water may be frozen in a shorter time: and if a thin spiral wire be introduced previous to the congelation of the water, the ice will adhere to it, and may thus be drawn out conveniendy. A person might be easily frozen to death during very warm weather, by merely pouring upon his body for some time sulphuric ether, and keeping him exposed to a tho- rough draught of air. ARTIFICIAL REFRIGERATION. The cooling or refrigeration of rooms in the summer season by sprinkling them with water, becomes likewise obvious on this account. The method of making ice artificially in the East Indies Depends on the same principle. The icermakers at Benares dig pits in large open plains, the bottom of which 124 Artificial Refrigeration. they strew with sugar canes, or dried stems of maize or Indian corn. Upon this bed they place a number of un- glazed pans, made of so porous an earth that ihe water penetrates through their whole substance. These pans are filled towards evening, in the winter season, with water that has boiled, and left in that situation till morning, when more or less ice is found in them, according to the temperature of the air; there being more formed in dry and warm weather than in that which is cloudy, though it may be colder to the human body. Every thing in this process is calculated to produce cold by evaporation; the beds on which the pans are placed suffer the air to have a free passage to their bottoms ; and the pans constantly oozing out water to their external sur- face, are cooled by the evaporation of it. In Spain they use a kind of earthen jars, called buxaros, which are only half-baked ; the earth of which is so por- ous, that the outside is kept moist by the water which filters through it, and though placed in the sun, the water in the jar becomes as cold as ice.* It is a common practice in China to cool wine or other liquors by wrapping the bottle in a wet cloth, and hang- ing it up in the sun. The water in the cloth becomes converted into vapour, and thus cold is produced. The blacks in Senegambia have a similar method of cooling water, by filling tanned leather bags with it, which they hang up in the sun ; the water oozes more or less through the leather, so as to keep the outward surface wet, which, by its quick and continued evaporation, cools the water remarkably. The winds on the borders of the Persian Gulph are" often so scorching, that travellers are suddenly suffocated unless they cover their heads with a wet cloth ; if this be too wet they immediately feel an intolerable cold, which would prove fatal if the moisture was not speedily dissi- pated by the heat. If a cold vessel is brought into a warm room, particu- larly where many people are assembled, the outside of it will soon become covered with a sort of dew. Before some changes of weather the stone pavements, * Twiss's Travels through Portugal and Spain. Similar jars are now made in this couatry. Capacity of Bodies for containing Heat. 125 the walls of a house, the balustrades of staircases, and other solid objects, feel clammy and damp. In frosty nights, when the air abroad is colder than the air within, the dampness of this air, for the same reason, settles on the glass panes of the windows, and is there frozen into curious and beautiful figures. Thus fogs and dews take place, and in the higher re- gions clouds are formed from the condensed vapour. The still greater condensation produces mists and rain. SECT. XI. CAPACITY OF BODIES FOR CONTAINING HEAT. THE property which different bodies possess of con- taining at the same temperature, and in equal quantities, either of mass or bulk, unequal quantities of heat, is called their capacity for heat. The capacities of bodies for heat are therefore considered as great or small in the ratio as their temperatures are either raised or lowered by the addition or diminished by the deprivation of equal quantities of heat. In homogeneous bodies the quantities of caloric which they contain are in the ratio of their temperature and quantity of mass ; for instance, when equal quantities of water, oil, or mercury, of unequal temperatures, are mingled together, the temperature of the whole will be the arithmetical mean between the temperatures of the two quantities that had been mixed together. It is a self- evident truth that this should be the case; for the parti- cles of different portions of the same substance being alike, their effects must be equal. For instance, Experiment I. Mix a pound of water at 172° with a pound at 32u, half the excess of heat in the hot water will quit it, to go over into the colder portion : thus the hot water will be cooled 70°, and the cold will receive 70° of temperature ; therefore 172—70, or 32 + 70 = 102 will give the heat Vol.. I. T 126 Capacity of Bodies for containing Heat. of the mixture. To attain the arithmetical mean very exactly, several precautions however are necessary.* When heterogeneous bodies of different temperatures are mixed together, the temperature produced is never the arithmetical mean of the two original temperatures. In order to ascertain the comparative quantities of heat of different bodies, equal weights of them are mingled together; the experiments for this purpose being in ge- neral more easily executed than those by which they are compared from equal bulks. Experiment II. If one pound of mercury heated to 110° Fahr. be added to one pound of water of 44° the temperature of the blended fluids will not be changed to 77°, as it would be if the surplus of heat were divided among those fluids in the proportion of their quantities. It will be found on examination to be only 47°. Experiment III. On the contrary, if the pound of mercury be heated to 44° and the water to 110°, then, on stirring them to- gether, the common temperature will be 107°. Hence, if the q icksilver loses by this distribution 63° of caloric, an equal weight of water gains only 3° from this loss of 63° of heat. And on the contrary, if the water loses 3° the mercury gains 63°. When instead of comparing the quantities of caloric which equal weights of different bodies contain, we com- pare the quantities in equal volumes, we still find that the same difference takes place. Thus it is found by experi- ment, that. the quantity of caloric necessary to raise the temperature of a given volume of water any number of degrees is to that necessary to raise an equal volume of mercury the same number of degrees as 2 to 1. This is therefore the proportion between the comparative quan- tities of caloric which these two bodies contain, estimated by their volumes; and similar differences exist with re- spect to every other kind of matter. * Crawford on Animal Heat, p. 95, kc. Radiation of Caloric. 127 From the nature of the experiments by which the quantities of caloric which bodies contain are ascertained, it is evident that we discover merely the comparative, not the absolute, quantities. Hence water has been chosen as a standard, to which other bodies may be referred: its capacity is stated as the arbitrary term of 1000, and with this the capacities of other bodies are compared. It need not be told that pains have been taken to esti- mate on these experiments that portion of heat which diffuses itself into the air, or into the vessel where the mercury and water are blended together. As, however, such valuations cannot be made with complete accuracy, the numbers stated above are only an approximation to truth. SECT. XII. RADIATION OF CALORIC. CALORIC is thrown off or radiates from heated bo- dies in right lines, and moves through space with incon- ceivable velocity. It is retarded in its passage by atmos- pheric air, by colourless fluids, glass, and other transpa- rent bodies. For if a glass mirror be placed before a fire, the mirror transmits the rays of light, but not the rays of heat. If a plate of glass, talc, or glass vessel filled with water, be suddenly interposed between the fire and the eye, the rays of light pass through it, but the rays of caloric are considerably retarded in its passage ; for no heat is per- ceived until the interposed substance is saturated with heat, or has reached its maximum. It then ceases to in- tercept the rays of caloric, and allows them to pass as freely as the rays of light. It has been lately shewn by Dr. Herschelthat the rays of caloric are refrangible, »but less so than the rays of light ; and the same philosopher has also proved by ex- periment, that it is not only the rays of caloric emitted by the sun which are refrangible, but likewise the rays emitted by common fires, by candles, by heated iron, and even by hot water. Whether the rays of caloric are differently refracted in different mediums has not yet been ascertained. We 128 Radiation of Caloric. are certain, however, that they are refracted by all trans- parent bodies which have been employed as burning glas- ses. The rays of caloric are also reflected by polished surfaces, in the same manner as the rays oflight. This was long ago noticed by Lambert, Saussure, Scheele, Pictet, and lately by Dr. Herschel. Professor Pictet placed two concave metallic mirrors opposite to each other, at the distance of about twelve feet. When a hot body, an iron bullet for instance, was placed in the focus of the one, and a mercurial thermome- ter in that of the other, a substance radiated from the bullet: it passed with incalculable velocity through the air, it was reflected from the mirrors, it became concen- trated, and influenced the thermometer placed in the focus according to the degree of its concentration. An iron ball two inches in diameter, heated so that it was not luminous in the dark, raised the thermometer not less than ten and a half degrees of Reaumur's scale, in six minutes. A lighted candle occasioned a rise in the thermometer nearly the same. A Florence flask containing two ounces and three drachms of boiling water raised Farenheit's thermometer three degress. He blackened the bulb of his thermome- ter, and found that it was more speedily influenced by the radiation than before, and that it rose to a greater height. M. Pictet discovered another very singular fact; viz. the apparent radiation of cold. When, instead of a heat- ed body, a Florence flask full of ice or snow is placed in the focus of one of the mirrors, the thermometer placed in the focus of the other immediately descends, and as- cends again whenever the cold body is removed. This phenomenon may be explained on the supposition that from every body at every temperature caloric radiates, but in less quantity as the tefhperaturefis low ; so that in the above experiment, the thermometer gives out more caloric by radiation than it receives from the body in the opposite focus, and therefore its temperature is lowered. Or as Pictet has supposed, when a number of bodies near to each other have the same temperature, there is no radiation of caloric, because in all of them it exists in a s'ate of equal tension; but as soon as a body at on inferior Radiation of Caloric. 129 temperature is introduced, the balance of tension is bro- ken, and caloric begins to radiate from all of them till the temperature of that body is raised to an equality with theirs. In the above experiment, therefore, the placing the snow or ice in the focus of the mirror causes the ra- diation of caloricyVom the thermometer, and hence the diminution of temperature which it suffers. These experiments have been lately repeated by Dr. Young and Professor Davy, at the Theatre of the Royal Institution. These gentlemen inflamed phosphorus by reflected caloric, and proved that the heat thus excited was very sensible to the organs of feeling. Mr. Leslie* has lately made a number of experiments on this subject, which are highly interesting. He used a variety of reflectors, carefully constructed of block-tin, and chiefly of the elliptical form. Sometimes he found the parabolic curvature convenient, especially when the reflection was made at considerable distances. The heat was given out from cubical boxes of plain and polished tin, with an orifice at the top, through which water of va- rious temperatures was introduced, and a common mer- curial thermometer occasionally placed in that fluid, to note the progress of its cooling. When the radiation of cold was to be tried, the canisters were filled with ice or snow. The differential thermometer being placed so that the ball containing the red liquor was in the focus of the speculum, and the canister being filled with boiling water the red liquor rose to a certain height, and then began to fall in proportion as the water cooled. A similar effect, though in the contrary direction, was produced by a canister filled with ice; and, in every case, the motion of the red liquor, above or below the point of equilibrium, was exactly proportional to the difference between the temperatures of the canister and the surrounding air. If different substances were applied to the canister while giving out heat, the degree of its emission suffered very- singular changes. If one side of the canister was coated with lamp-black, another with writing paper, a third with crown glass, and the fourth left bare, or covered with tin- foil—the differential thermometer rose to 100, 98, 90, and 12 respectively, when these four sides were exposed to the speculum in succession. The metal surface, then, gave out heat about eight times less copiously than the * Leslie on Heat. 130 Radiation of Caloric. other three substances. Bv coating the focal ball of the differential thermometer with tin-foil, it was found to re- ceive about five times less heat from any side of the can- ister than when it was exposed bare in the focus ; and by coating the surface of a concave glass mirror, first with black pigment, then with tin-foil, and lastly exposing it bare to the heating bod)-, it was found that the glass re- flected very little heat, the pigment none at all, and the tin-foil ten times more than the glass. The metallic sur- face, then, has about five times less power of absorbing heat, eight times less power of emitting it, and ten times greater power of reflecting it, than the glass. If between the canister and the reflector was placed a frame, over which were stretched, successively, tin-foil, glass and paper, the communication of heat or cold was altogether stopped by the first; at least so little passes, that the differential thermometer was not sensibly affect- ed, while the glass only stopped four-fifths, and the paper not so much. The metallic screen, too, produced this effect, however near the canister it was placed, provided the separation was only sensible. The other two sub- stances interrupted the communication more and more the nearer they were placed to the canister, but always per- mitted a large portion of the heat or cold to pass. If, in- stead of one screen, or a screen composed of only one substance, a combination of these wras interposed, a very remarkable illustration of the general fact was obtained. The combinations used by Mr. Leslie were, plates of glass, coated with tin-foil on one side, and plates of tin, coated in like manner with lamp-black. These he either placed in contact, so that their similar sides touched ; or at a distance from each other, with their similar sides facing. He denominates the combination of glass and tin-foil the experimentum crucis. We conceive that of the tin-foil and lamp-black better entitled to this appellation. Experiment I. Cause two sheets of tin about ten inches square to be hammered quite flat and smooth, and paint one side of each with a thin coat of lamp-black. Arrange the appa- ratus as usual, and, having joined together the tin-plates with their clear surfaces touching, fix them to a vertical frame : the liquor of the differential thermometer will rise Radiation of Caloric. 131 23 degrees. Invert the position of the plates, so that the blackened sides come into contact; it will now sink down to zero. Remove either of the plates, and the liquor will again mount near four degrees. It is truly pleasing, says Mr. Leslie, to witness this varied spectacle, where the changes succeed each other as if performed by the fancied operation of magic. But those transitions, and even the measures of the diversified effects, are the necessary re- sults of the principles already established. Compare the case where both the external surfaces of the screen arc metallic with that in which they are covered with pigment. On the one side it receives five times less heat, and this heat is propagated with eight times less energy from the other. By the joint influence of those circumstances, therefore, its effect is 40 times less; which corresponds to about half a degree, a quantity scarcely distinguishable. When the screen consists only of a single plate blackened on the one side, the diminished effect is a mean between the receptive and the projecting powers, or 6£ times smaller than where both surfaces are painted. This en- feebled impression is consequently equal to about four degrees. The experimental inquiries of Mr. Leslie, which were directed particularly to the radiation of heat, its connec- tion with the spaces through which it is propagated, the direction in which it moves, the projecting power of the heated body, and connection which subsists between it and the nature of the projecting surface, are highly im- portant. The canister being placed successively at different dis- tances from the reflector, the effects of its removal, upon the differential thermometer in the focus, were noted; and an allowance was made for the changes in the focal length. It was found, in general, that the total corrected effects were inversely as the distances of the canister. This obstruction evidently cannot arise from the loss of heat in the atmosphere ; for that cause would produce a diminu- tion in\ much more rapid series. To prove that the irre- gularity of the reflecting surface has no share in the phe- nomenon, Mr. Leslie shews that a concave glass speculum reflects the heat of a charcoal fire with an energy in- versely as its distance. The diminution, then, can onl\ 1,2 Radiation of Caloric. be owing to an imperfect reflection; and this was well demonstrated, by increasing the size of the canister, in such a proportion to its increased distance from the re- flector, that it always subtended an equal angle there. Making the same correction as before, for the variation of focal length, the total effect of the removal upon the differential thermometer was found to be nothing more than might fairly be ascribed to the inaccuracy unavoida- ble in such delicate experiments. Hence the capital in- ference is drawn, that the impulses, by which heat and cold are propagated between distant objects, do not suf- fer any sensible diminution of strength from the length of their progress through the atmosphere. A very remarkable aberration is observed to take place in the reflection of heat. When the flame of a taper is withdrawn above two inches from the axis of the reflec- tor, its image vanishes entirely from the focal ball of the differential thermometer. But the heated canister may be removed seven inches from the axis, before its im- pression on the instrument ceases to be distinguishable. Mr. Leslie gives us no computation of the extent of this penumbra of heat (if the expression may be used) he only explains the law by which the lateral motion of the heated body, from the reflector's axis, diminishes the total effect of the reflection upon the thermometer. The distance of the canister being proportioned to the series 1, 2, 3—7, the rise of the thermometer is as the powers of \, whose exponents are the triangular numbers, 1, 3, &x. He al ;o finds, by experiment, what he pretends is also a deduction from the aberration just now described, that the maxi- mum of the effect produced by reflection is not in the focus, but nearer the speculum. His experiment is quite conclusive. The thermometer being at 58° in the optical focus, it rose to 80° half an inch nearer the reflector; and, half an inch beyond the focus, fell to 25°. The heat is therefore more diffused over equal spaces beyond the focus than between the focus and reflector. If the side of the canister is turned gradually round, while its axis remains fixed in the axis of the reflector, the thermometer is less and less affected, as the radiating surface is more inclined from the perpendicular. Nothing can be simpler than the method adopted by Mr. Leslie Radiation of Caloric. 133 for ascertaining the law of this diminution. He placed a sliding screen between the canister and the reflector, and adjusted the slit so, that the radiating surface, at every part of its motion round its axis, subtended the same an- gle as the reflector. There was scarcely any effect pro- duced upon the thermometer by the revolution of the ca- nister. In like manner a cylindrical canister produces the same rise in the thermometer with a cubical one of an equal base and altitude ; and from these, and other experiments founded upon the same principle, we may conclude, that the total action of a heated surface is equal to that of its orthographic projection, or proportional to the sine of its inclination. Mr. Leslie having ascertained that bodies differ veiy widely in their power of projecting, absorbing, and re- flecting heat, found that the chemical qualities of the heating surface have a considerable influence upon its projecting power; the effect of tin being 12, iron or steel operates as 15, mercury above 20. All oxydes acquire a greater action as they recede from the metallic state. Lead being as 19 ; when tarnished by exposure to the air, it becomes as 45, while minium is as 80. Sealing- wax and rosin are nearly equal to paper, and ice is as 85. The polish of the radiating surface diminishes its action, where that is not naturally great. The roughening of glass does not heighten its projecting power ; but that of tin is doubled by covering it with furrows. This singular ef- fect cannot be owing to the greater surface which the roughened metal exposes ; for the increase of surface is precisely counterbalanced by the increase of obliquity; and, moreover, it is found that the addition of cross fur- rows, by striatingthe surface in the other direction, nearly destroys the effect of the first operation. The thickness of the radiating surface greatly affects its powers of ac- tion. A thin film of isinglass produces a radiation as 26 ; a thick one as 42 : but wnen the thickness exceeds the thousandth part of an inch, any subsequent increase does not augment its action. Mr. Leslie thinks that the difference in projective power, which is observable in several of the cases above noticed, may be resolved into the variations of the bodies with respect to hardness and softness. He reasons this matter with his wonted inge- VOL. I. 'T 134 Radiation of Caloric. nuitv, and shews that the addition of moisture, and still more the addition of a mucilaginous substance, consider- ably augments the action of a surface painted black. 1 he quality of colour is the last to which our attention is di- rected, and Mr. Leslie seems disposed to doubt whether it exerts any influence at all in modifying the projective and absorbent powers of bodies ; a point which he con- ceives is incapable of strict solution, because a change of colour must always be attended with an alteration in the structure of the substance : and, rigorously speaking, this is no doubt true. But there is one mode of inducing a change of colour, by means of a change in the body's struc- ture, which is known, and for which allowance may be made by our author's experiments; we allude to the scoriae on the surface of metals, from slight oxydation. If the oxydation is found always to augment the metal's action, as different metals assume different hues in the beginning of the process, a comparison of several, in this respect, will enable us to estimate how far colour operates. Perhaps even the change induced upon the substance of vegetable tinctures, by weak, acidulous, and alcaline solutions, is so little proportionate to the alter- ations which their colours undergo in the mixture, that an approximation might be obtained from experiments with paper dyed in this manner. Mr. Leslie repeated several branches of this inquiry, te ascertain the various reflecting powers of different sur- faces. Those which absorbed and projected heat most co- piously were, in general, found to reflect least, though by no means in a reciprocal proportion. Glass reflecting as 10, tin-foil reflected as 85, lead as 60, steel as 70: tin-foil shining with mercury as 50, and brass as 100. A tin re- flector had its power reduced to one tenth, by being stri- ated in one direction, although this operation did not at all change the limits of its focus. A coat of tallow re- duced the powers of the deflector to one twelfth ; a coat of olive oil to two fifths; a coat of isinglass to three tenths, but, as it dried and became thinner, only to seven tenths: a thin iridescent coating reduced the reflection only to four fifths. The general rule then holds good, that the reflecting powers of bodies bear some inverse ratio to their absorbent and projecthe powers ; although Radiation of Caloric. 135 so many circumstances unite in modifying the proportion, that we are unable, as yet, to express it by one universal law. It is therefore evident that caloric is thrown off from bodies in rays, which are invisible, or incapable of excit- ing vision, but which are capable of exciting heat. These invisible rays of caloric are propagated in right lines, with extreme velocity, and are capable of the laws of reflection and refraction. The heating agency, however, is different in the dif- ferent coloured rays of the prismatic spectrum. Accord- ing to Dr. Herschel's experiments, it follows inversely the order of the refTangibility of the rays of light. The least refrangible possessing it in the greatest degree. Sir Henry Englefield has lately made a series of expe- riments on the same subject, from which we learn that a thermometer having its ball blackened rose when placed in the blue ray of the prismatic spectrum in 3' from 55° to 56° ; in the green, in 3' from 54° to 58° ; in the yellow, in 3' from 56° to 62° ; in the full red, in 2|' from 56° to 72° ; in the confines of the red, in 2£' from 58° to 73^ ; and quite out of the visible light, in 2\' from 61° to 79°. Between.each of the observations, the thermometer was placed in the shade so long as to sink it below the heat to which it had risen in the preceding observation ; of course its rise above that point could only be the effect of the ray to which it was exposed. It was continued in the focus long after it had ceased to rise; therefore the heats given are the greatest effects of the several rays on the thermometer in each observation. A thermometer placed constantly in the shade near the apparatus was found scarcely to vary during the experiments. Sir Henry made other experiments with thermometers with naked balls, and with others whose balls were painted white ; for which we refer the reader to the interesting paper of the baronet,* from which the above experiments are transcribed. The coloured rays emitted from the sun and combus- tible bodies, since they excite heat and vision, must con- sist of a mixture of heat-making rays and rays of light. And as the rays of heat and light accompany each othei * Journals of the Royal Institution, No. x, p. 202. 130 Radiation of Caloric. when emitted from luminous bodies, the velocity with which the rays of caloric move must be equal to that of light; and hence its particles must be equally minute. The}T differ however in this particular, that the rays of light produce the sensation of vision, and possess certain chemical properties, whilst in those of caloric the pecu- liar agency of heat resides. LIGHT. PART XI. THE difference, in the day time, of what we perceive when our eyes are open and when our eyes are shut is produced by what is called light. The privation oflight is called darkness. It is this light which informs us of the presence of ob- jects which are not near enough to touch our bodies, or which do not affect any of our other senses. Hence the blind must judge of the presence of the particular objects by the sound, or by the smell, or by the touch, &c. but not by means of light. In short, light does not sensibly affect any other part of our frame, besides the eyes. The nature of light has occupied much of the attention of thinking men, and numerous opinions have been en- tertained concerning it. It has been sometimes consi- dered as a distinct substance, at other times as a quality ; sometimes as a cause, frequently as an effect: by some it has been considered as a compound, by others as a sim- ple substance. Philosophers of the present day are not agreed as to the independent existence of light, or the cause by which we see. This is not the place for discussing the respective me- rits of all the ingenious hoypotheses which have been ad- vanced concerning this subject: we shall assume the doctrine of those who admit the independent existence of light, not only because it is more generally received, but js also best calculated to explain its ihemiral properties. 138 Nature of Light. SECT. I. NATURE OF LIGHT IN GENERAL. LIGHT is that which proceeds from any body produc- ing the sensation of vision, or perception of other bodies, by depicting an image of external objects on the retina of the eye. Hence it announces to animals the presence of the bodies which surround them, and enables thejn to dis- tinguish these bodies into transparent, opaque, and co- loured. These properties are so essentially connected with the presence of light, that bodies lose them in the dark, and become undistinguishable. Light is regarded by philosophers as a substance con- sisting of a vast number of exceedingly small particles, which are actually projected from luminous bodies, and which probably never return again to the body from which they were emitted. They have a determinate size ; they are at a certain distance from each other; they move with a certain velo- city, and have a certain momentum. They are univer- sally expanded through space ; they exert peculiar actions ; and are obedient to the laws of attraction, and other pro- perties of matter. Several remarkable discoveries made in astronomy, and in other branches of natural philosophy, give us some ideas concerning the size, distance, velocity, Sec. of the particles of light. 1. EXPLANATION OF CERTAIN TERMS OF LIGHT. In order to facilitate the doctrine of light, we shall shortly explain a few terms made use of by philosophers when treating of it; namely: A ray of light is an indefinitely small portion of light as it comes from a luminous body. A medium is a body which affords a passage for the rays of light. A beam oflight is a body of parallel rays. I Physical Properties of Light. 139 A pencil of light, or a pencil of rays of light, is a body of diverging or converging rays. Converging rays are rays which tend to a common point. Diverging rays are those which come from a point, and continually separate as they proceed. The rays of light are parallel, when the lines which they describe are so. The radiant point is the point from which diverging rays proceed. . The focus is the point to which the converging rays are directed. 2. SOURCES OF LIGHT. Light is emitted from the sun, the fixed stars, and other luminous bodies. It is produced by percussion, during electrization, combustion, and in various other chemical processes. Why the sun and stars are constantly emitting light, is a question which probably will for ever baffle human un- derstanding ; at any rate, it is not connected with che- mistry. The light emitted during combustion, or chemical ac- tion, exists previously, either combined with the combus- tible body or with the substance which supports the com- bustion. The light emitted during percussion and elec- trization, &c. is foreign to our subject. SECT. II. PHYSICAL PROPERTIES OF LIGHT. l. VELOCITv OF LIGHT. THE velocity of light is much greater than that of sound; for the flash of a gun fired at a considerable dis tance is seen before the report is heard. The clap of thunder is not heard till some time after the lightning has been seen, except the phenomenon take? place at no great distance. 140 Physical Properties of Light. The motion of light is so very rapid, that in all common experiments it appears to be instantaneous. Its velocity cannot be measured between the tops of the most distant mountains that are visible from each other. Astronomers have, nevertheless, found that it may be measured when it moves between some of the heavenly bodies. For by the eclipses of Jupiter's satellites, it appears that it takes 8 minutes and 13 seconds in passing across the semidia- meter of the earth's orbit. From these accurate investi- gations they have deduced that light moves at the astonish- ing rate of about 167,000 geographical miles in one second, or that it passes from the sun to the earth in little more than eight minutes; and nevertheless, according to geome- tricians, light, from its departure from the nearest of the fixed stars, which is, in truth, at least four hundred thou- sand times more remote than the sun, is near six years in its progress to our eyes ; so that a star placed at that dis- tance would be still visible for six years after its destruc- tion, supposing that process to take place. How grand and sublime are the meditations suggested by this object on the immensity of space, the boundless extent of the universe, the vast number of globes which traverse through it, and the duration of time which they measure in their silent march! The velocity of light was first noticed by Roemer, and afterwards determined and established by Dr. Bradley's ingenious theory on the aberration of the lights of the fixed stars. The principles on which this discovery is founded may be familiarly explained as follows : Suppose a tube to be erected perpendicular to the hori- zon at a time when it rains, the drops falling perpendicu- larly down, and suppose the diameter of the tube to be such as to admit but one drop at a time: then it is plain, that if a drop of water enter the orifice of the tube it will fall to the bottom without touching its sides. But if the tube, without altering its perpendicularity, be moved along in the direction of the horizon, any drop that enters will strike against one of its sides, and none will pass clearly through while the motion continues, unless the upper end of the tube be also inclined towards the part to which its motion is directed. Physical Properties of Light. 141 Thus, if a b represent the horizon, c d the perpendi- cular tube, and g D the course of a drop of rain: then, if c d be mov- ed towards a, k while the drop is falling with- in the tube, it is evident that the inner surface of the tube, which is situated towards b, will be carried against the drop, and prevent its arriving at the bottom without touching. But if the inclined tube e c be moved with a similar motion to that of the drop from e to D, in the time that the drop moves from c to D, the lower orifice of the tube and the drop will be found at d at the same instant; and the velocity of the drop will be expressed by c D, and that of the tube by e d. The same reasoning holds good, if instead of drops of rain we suppose particles of light, and a telescope instead of a tube. For to an observer, who through the tube q d views the vastly distant object G, if the motion of light be instantaneous, or infinitely swift, no finite motion of c D, its position being unaltered, can prevent its being visible ; since, by the supposition, the light which enters at c will arrive at D before c D can have moved at all. But if light be propagated in time, and the observer be carried by a motion similar, as to acceleration, to that of light, the tube must be inclined to the ray in an angle, whose sine is to the sine of c e d, or the angle the tube makes with the line of the observer's motion, as the velocity of the observer is to the velocity oflight. For in the trian- gle d c e, the sides d e and d c, which express these veloci- ties, are as the sines of their opposite angles. Hence if the angle of the inclination of the tube to the ray of light, to- gether with the velocity and direction of the observer's motion, be known, the velocity oflight may be determined. The velocity of light is uniform in the same medium, however it may be excited ; either because the corpuscle;: vor. i. x, 142 Physical Properties of Light. are emitted by a peculiar repulsive force, acting equally in all bodies and in all directions, and known only by this effect; or simply, because a homogeneous fluid propa- gates all impulses with a constant velocity. 2. MOMENTUM AND MAGNITUDE OF THE PARTICLESOF LIGHT. The velocity of light being thus ascertained, we should be enabled to form some notion of the magnitude of the particles of light, if we were in possession of good ob- servations on the effect of their momentum. For example; it is found that a ball from a cannon at its first discharge flies with a velocity of about a mile in eight seconds, and would therefore arrive at the sun in thirty-two years, supposing it to move with unremitted celerity. Now light moves through that space in about eight minutes, which is two million times faster. But the forces with which bodies move are as their masses multiplied by their velocities : if, therefore, the particles oflight were equal in mass to the two-millionth part of a grain of sand, we should be no more able to endure their impulse than that of sand when shot point-blank from the mouth of a cannon.* How much less must therefore be the particles of light, which make no sensible impression upon so delicate an organ as the eye. From some imperfect experiments made by throwing the focus of a concave mirror on the extremity of a very delicate beam, nicely suspended, by which means a slight motion was given to the beam, it was deduced that the light thus collected had a searchable momentum. Now from the weight of the beam, and from the motion which was communicated to it by the impulse of light (if that was the real cause of its motion) also from the above- mentioned velocity of light, it was calculated that the matter contained in the light which was thrown upon the end of the above-mentioned beam during one second of time, and which was collected from a reflecting surface of about four square feet, amounted to no more than one twelve-hundred-millionth part of a grain.f * Nicholson's Introd. to Natural Philosophy, vol. i. p. 256. t Priestley's History of Discoyeries on Light, Vision, &c. Period VI Sect. I. chap. iii. Physical Properties of Light. 14- .5. LIGHT MOVES IN STRAIGHT LINES. Whenever light passes through a space occupied by a medium of uniform density, it describes right lines in all directions. Because all undisturbed motion is rectilinear; or because, in a homogeneous and highly elastic medium, all undulations are transmitted rectilinearly. It is well known that if a portion of a beam of light be intercepted by any body, the shadow of that body will be bounded by right lines, passing from the luminous body, and meeting the lines which terminate the opaque body. Experiment I. Darken a room into which the sun shines, and only admit the light by a small hole in the window-shutter; and place opposite to the hole a board or screen. If we look at the screen, we observe thereon a picture of all the exterior objects which are opposite to the hole in all their natural colours: these colours are faintly depicted; the images of the objects that are stationary, as houses, trees, &c. are likewise fixed or stationary in the picture ; whilst the images of those that are in motion, as those of horses, carriages, &c. are seen to move. If we place our eye in this ray, we find that our eye, the light, and the hole are in one and the same straight line. Which is a clear proof that light is emitted in straight lines, by the luminous bodies. It is equally obvious from light finding no passage through bent or crooked tubes. 4. REFLECTION OF LIGHT. Another property of the rays of light is their refiexi- bility, or disposition of being turned back into the medi- um in which they moved with a certain obliquity, so that the light is driven back, without coming into contact with the matter which repels it. The ray is then said to be refected. The angle of re- flection is always equal to the angle of incidence. 144 Physical Properties of Light. Experiment II. To prove that the angle of refection is equal to the angle of incidence. There are several ways of measuring the angles of in- cidence and of reflection ; but the following is one of the easiest: Let ab cbe a se- micircle, divided into twice 90 de- grees ; a b repre- sents the section of a flat reflector. Co- ver the surface of 4-V.:n M^.n f*4-s-..« «..:.l« ^fc^a m'»Mr.'iim'ffiiU''>l*'fo»iiW''''«?''!'''''''"'iJnpHTi"if"Lar} mis renecioi wnn paper, excepting a very small circular spot, as at d. Place this semicircle perpendicularly upon the reflector, and with its centre in the middle of the uncovered spot doi. the reflector. This being done, fix a pin, or other small object, close to the edge of the semicircle, for instance, at e, the 50th degree ; then move your eye along the side af c of the semicircle, and you will perceive the object e reflected by the reflector d only when the eye is at /, viz. at the 50th degree of the quadrant af c; whence it becomes evident that the angle of reflection c df is equal to the angle of incidence f d c. When a ray of light falls upon a polished medium, for instance, a plate of glass, or mirror with a certain obli- quity, it does not enter the glass at all, but is reflected when it approaches its surface. When a ray of light enters other transparent media, it continues to move on till it comes to the opposite surface ; but then, instead of passing through, it bends, and passes out again at the same surface at which it entered, just as a ball would do if made to strike obliquely against a floor. Experiment III. Let a beam of solar light pass into a darkened room through a hole in the window-shutter ; at that part of the floor where the beam oflight falls place a looking-glass, Inflection of Light. 145 and then throw some hair-powder into the air, in order to render the beam of light more visible. We shall then see that the beam is reflected back into the air, and that the inclination of the reflected beam is exactly the same as that of the incidental one. The common experiment of children casting the light of the sun, by means of a looking-glass, into various di- stant places, also illustrates this property. If we direct our eyes towards certain polished surfaces, we frequently see in them the appearances of objects which are situated in places quite different from those in which we see them. Thus: an eye at c, j± directed towards the flat and polished surface tj of which A b is the sec- tion, will perceive the exact figure, colour, &c. of a body which actual- ly stands at d, but which will appear as if it stood at e ; it is therefore evi- dent that the light which proceeds from d falls upon the surface A b, and thence it comes in another direc- tion, f c, to the eye at c. Now the surface a, b, which thus sends back the light, is called the reflected light; whereas the light from the object D, to the reflecting sur- face, is called the incident light. The angle which the incident light makes with the per- pendicular to the reflecting surface at the point of inci- dence, viz. the angle D F G, is called the angle of incidence. The angle which the reflected light makes with the same perpendicular, viz. the angle c f g, is called the angle of refraction. But some authors call the angle dja the angle of incidence, and the angle c f b, the angle of refraction. 5. INFLECTION OF LIGHT. When a ray oflight passes within a certain distance of the surface of a body, parallel to which it is moving, it is attracted, or bent towards, it, so as to form apparently a 146 Inflection of Light. rectilinear angle at that place. This bending or inflec- tion of the rays of light, by passing not through, but near, the surface, is caused by an attractive power to which light is obedient. It is called therefore the inflec- tion of light. It has also been called diffraction. Experiment I. Admit a beam of light into a dark room, through a round hole in the window-shutter, and place at the spot on the floor where it falls a sheet of paper; the rays of light will there form a round luminous spot. But if we bring two penknives, with their edges towards each other, on opposite sides of the hole, and make them approach each other gradually, the luminous spot will dilate itself on the sides of the knives ; indicating that those rays which are nearest the edges of the knives have been drawn from their former direction towards the knives. This property of light is called infection. The edge of an- other thin plate of metal produces the same effect. Experiment II. If we let abeam of light pass into a dark room through a narrow slit made in a window-shutter, not above -fa part of an inch broad, the beam of light will be split into two, and leave a dark space in the middle ; it will there- fore be attracted by both sides of the slit. Experiment III. The shadow of a small body, as a hair, a thread, &c. placed in a beam of the sun's light, will be much broader than it ought to be if the rays of light passed by these bodies in right lines, or without being attracted by them. For example : a hair whose breadth was the 280th part of an inch, being held in this light, at the distance of about twelve feet from a hole of the breadth of the 42d part of an inch, did cast a shadow which, at the distance of four inches from the hair, was the 60th part of an inch broad, that is, ab.ove four times broader than the hair; and at the distance of ten feet was the eighth part of an inch broad, that is, 35 times broader. Refraction of Light. 147 The phenomena which relate to the inflection of light, not appearing to be reduceable to one general principle, were particularly examined under a considerable variety of circumstances by sir Isaac Newton : yet his observa- tions were not quite correct, nor was his hypothetical ex- planation very plausible. Subsequent experiments and observations have reduced the phenomena of inflection to a single principle, namely, to the attraction of bodies to- wards light; which attraction becomes conspicuous when the rays of light pass within a certain distance of their surfaces. Besides their being bent, the rays of light are likewise separated into colours by the vicinity of bodies, and this produces the singular phenomena of the colour- ed fringes that accompany the inflection. 6. REFRACTION OF LIGHT. When a ray of light passes through the same medium, or when it passes perpendicularly from one medium into another, it continues to move on, without changing its di- rection. But the case is different when it passes oblique- ly from one medium into another of a different density ; it is then bent from its first direction, and assumes a new one ; it is said to be refracted. When it passes into a den- ser medium it is refracted towards the perpendicular; but when it passes into a rarer medium it is refractedyrom the perpendicular. The denser the medium the more the rays are bent, and approach to a perpendicular let fall upon its surface. This, however, must always be understood of the rays which fall obliquely upon these media; for those rays which fall perpendicularly do not suffer any deviation: refraction only takes place when the rays fall obliquely, and is so much greater as their angle of incidence is more oblique. After having taken the new direction, the ray again proceeds invariably in a straight line, till it meets with a different medium, when it is again turned out of its course. On this account it is that objects seen under water appear out of their true place. 148 Refraction of Light. Experiment I. Let'a lighted candle be placed on the side of a vessel full of water abcd, so as to cast a shadow on the side of the vessel upon the bottom: the edge of the shadow does not come to e, so as to form a straight line ebg, but will be found somewhere else, as at f, and f b Gwill form an angle at the surface of the water; which proves beyond a doubt that the light which proceeds from the candle is refracted, viz. bent at the surface of the water. This will become equally obvious from the following experiments: Experiment II. Take an empty bason, and on the bottom fix marks at a small distance from each other ; then take it into a dark room, and let in a ray of light: where this ray falls upon the floor place the bason, so that its marked diameter may point from the window, and so that the beam of light may fall on the mark most distant from the window. Having done this, when the bason is filled with water the beam which before fell upon the most distant mark will now, by the refractive power of the 'water, be turned out of its straight course, and will fall two, three, or more marks nearer to the centre of the bason. This may be more clearly proved in the following manner: Experiment III. Let a small bright object be laid upon the bottom of a cylindrical vessel n b a l at c, so that a ray passing in a right line from the remote edge of p the object to the eye at s will be in- Q j tercepted by the edge of the vessel, S or that the first ray which is not in- tercepted passes in the direction o n c above the eye. While the eye continues in the same situation, if the vessel be filled with water the object will become visible, that is, the ray which passed from the remote edge of the ob- f Analysis of Light by the Prism. 149 ject in a right line c n o by the vessel on entering the air is refracted into the direction n s towards the eye, or • from the perpendicular P N A. It is upon the reflection and refraction of light that the whole science of optics principally depends ; for'f the, rays of light were neither reflexible nor refrangible we should be deprived of telescopes, microscopes, spectacles, and a number of other optical instruments. SECT. III. ANALYSIS OF LIGHT BY THE PRISlft. *# EVERY ray oflight consists of seven parts ; the first of these seven parts of the ray excites upon our organs of sight the sensation which we call red, the second ex- cites the .sensation called orange, the third yellow, the fourth green, the fifth blue, the sixth indigo, and the se- venth violet. None of these seven parts of a ray oflight can be fur- ther decomposed ; they always produce the same colour, on which account they are called original or primitive colours. Experiment I. To prove that light consists of these primitive colours, let a ray of it fall through a hole in a window-shutter into a darkened room ; and place a glass prism parallel to the horizon with its axis perpendicular, so as to receive the beam of light. On turning the prism slowly about its axis, we perceive that the refracted light on the opposite wall first descends and then ascends between the ascent and descent; that is, where the spectrum is stationary the prism is to be fixed. The beam of light now passes into the prism, and is there refracted into its primitive rays, viz. the lower ex- tremity of the spectrum is red, above this is placed the VOL. I Y + * 150 Analysis of Light by the Prism orange, afterwards the yellow, then the green, the blue, the indigo, and lastly the violet, which is placed in the upper part of the image. The instance of the separation of the primary colours oflight which seems most remarkable is that of the rain- bow. It is formed in general by the reflection of the rays of the sun's light, from the drops of falling rain; though frequently it appears amongst the waves of the sea, whose heads or tops are blown by the wind into small drops ; and it is sometimes seen on the ground, when the sun shines, in a very thick dew. Cascades and fountains whose waters are, in their fall, divided into drops, exhi- bit rain-bows to a spectator, if properly situated during the time of the* sun's shining ; and water blown violently _^from ^e mouth of an observer whose back is turned to- wards the sun never fails to produce the same pheno- menon. This appearance is also seen by moon-light, though sel- dom vivid enough to render the colours distinguishable ; and the artificial rainbow may be produced even by can- dle-light, on the water which is ejected by a small foun- tain or jet d'eau : all these are of the same nature as the analysis of light by the prisms. The colours observable on soap-bubbles, and the halos which sometimes surround the moon, are also referable to the refrangibility of the rays of light. Various methods have been tried for the purpose of rendering the colours of the prismatic spectrum distinct or unmixed with each other, but none as yet has been attended with complete success: the following method seems to be the best approximation. Experiment II. Let the light of the sun pass through a hole of the f^ of an inch into a dark room; and placing a screen at a little distance (for instance, 6 inches) within the room, let the middlemost part of that light pass through a smaller hole in^he screen; the object of which is to prevent, in great measure, the indefinite light, or penumbra on the sides of the prismatic spectrum. Let that light fall per- pendicularly upon a convex lens, at the distance of about 10 feet, by which means an image well defined of the Analysis of Light by the Prism. 151 sun will be formed upon a screen placed at a proper dis- tance from the lens : but if a prism be placed close to the lens, so that the light, after having passed through the lens, mav pass through and be refracted by the prism, then a coloured spectrum well defined will be formed* upon the screen. If small bodies be placed in the different colours of the prismatic spectrum, they will appear of the same colour, fed in the red light, green in the green light, &c. The decomposition effected by means of the prism has therefore been called an analysis of light. These coloured rays differ from each other in reflexi- bility, refrangibility, and inflexibility. The red is the most refrangible, the violet the least; the others are re- frangible in the following order, namely, orange, yellow, green, blue, indigo, and violet. Newton ascertained by actual measurement, that if the whole of the spectrum be divided into 360 parts, then the red will occupy 45 of these parts, the orange 27, the yellow 48, the green 60, the blue 60, the indigo 40, and the violet 80. Dr. Herschel has lately proved* that the rays of light differ in their power of illuminating objects. The rays towards the middle of the spectrum possess the greatest illuminating powers, and those at the extremity the least; the illuminating power of the rays gradually diminishes from the middle of the spectrum towards its extremities. Experiment III. That the rays of light differ in their illuminating power may be evinced by letting equal portions of each of them fall on a minute object; a printed page, for instance, which will not be seen distinctly at the same distance when illuminated by each. We must stand nearer the object when it is illuminated by the violet; we see dis- tinctly at a somewhat greater distance when the object is illuminated by the indigo ray, at a greater when by the blue, at a still greater when by the deep green, and at the greatest of all when by the lightest green, or deepest yellow: we must stand nearer when the object is en- lightened by the orange ray, and still nearer when by the red. Philosoph. Trans. 1800, p. 255. • 152 Theory of Colours. It has been supposed that three of the prismatic colours, the red, yellow, and blue, were simple ; and that the other four were formed each of the two contiguous ones; that is, the orange from the red and yellow, the green from the yellow and blue, the indigo from the blue and violet, and the violet from the indigo and red: but this supposition has not been satisfactorily proved. SECT. IV. THEORY OF COLOURS. LANGUAGE being invented chiefly for the expres- sion of ordinary events that do not require any great pre- cision, it very frequently happens that the same word is used to denote very different things. It is proper to re- mark, that the word colour is thus used. If the word be used to denote the sensation or idea excited in the mind, it is sufficiently obvious that it cannot be sufficiently used to denote that attribute by which bodies are able, by re- flecting the rays of light, to produce the sensation ; and still less ought it to be used to imply that quality the va- rious kinds of light possess of producing the sensation when separated from each other, either by reflection from bodies or otherwise. It may, however, be allowed to use the terms coloured rays, or coloured bodies; though the sensation of colour, the specific properties of the rays and of the reflecting bodies, are undoubtedly things very dif- ferent from each other. Having, therefore, so far considered the na' re and effects of light, and seen that it is subject, like other mat- ters, to the laws of attraction and repulsion, and that it may be analysed by means of the prism into several rays of different tints, we shall now endeavour to prove, that from the nature of these different tints arises that variety of shades which paints the face of nature. Hence it is, that whatever pleasure we derive from the beauty of colouring is owing to the different refrangibility of light, each object sending back to our eyes those rays which the peculiar structure of its surface is best adapted Theory of Colours. 153 to reflect. In this sense, the blushing beauties of the rose, and the modest blue of the violet, may be consider- ed as not in the objects themselves, but in the light that adorns them in those robes. The colours of all natural bodies depend on this re- frangibility of light; they may be considered as prisms, which decompose or rather divide the light. Some reflect the rays without producing any change, and these are white; others absorb them all, and are therefore black. The greater or less affinity of the several rays with va- rious bodies is no doubt the cause that when a pencil of light falls upon a body some rays enter into it, whilst others are reflected ; and it is this which affords the diversity of colours and the prodigious variety of shades under which bodies appear to our eyes : and thus are formed the pellucid stream, the green sea, the white froth, the dark pool, the azure sky, the varying colours of the pigeon's neck, the opal, the mother-of-pearl, the silk called changeable, &c. and hence the white colour of the European, the copper colour of the American, and black colour of the Negro. The changes of colours which are produced by mix- tures, by boiling, heating, pounding, &c. are so common and so remarkable, as to come within every body's notice. The following chemical production of colours will, per- haps, not be unacceptable to some readers. Experiment I. Production of various colours by the mere mixture of colourless fluids. For this purpose the following articles are necessary. No. 1. A solution of acetite of lead, prepared by dis- solving two drams of acetite of lead in twelve ounces of distilled water, and afterwards filtering the solution. 2. A solution of carbonate of potash, obtained by dis- solving three ounces of carbonate of potash in twelve of water, and proceeding as before. 3. A solution of corrosive muriate of mercury, con- sisting of twenty grains of corrosive muriate of mercury dissolved in twelve ounces of water. 154 Theory of Colours, 4. A solution of sulphate of iron, produced by dissolv- ing two ounces of sulphate of iron in twelve of water. 5. Acidulous solution of sulphate of iron, composed of an ounce of sulphate of iron and twelve of water, mixed with an ounce of the next solution, No. 6. 6, One ounce of sulphuric acid, mingled with twelve of water. 7. One dram of crystallized acetite of copper, dissolv- ed in twelve ounces of water, with the addition of one dram of nitric acid. 8. Concentrated liquid ammonia. 9. Sulphureous acid. 10. Tincture of roses, prepared by infusing red rose leaves in sulphureous acid. 11. Tincture of red-cabbage leaves, prepared in the same manner. 12. Tincture of galls, obtained by digesting half an ounce of gall-nuts in twelve ounces of water, and adding one dram of nitric acid to the filtered solution. 13. Diluted solution of prussiate of potash. 14. A solution of nitrate of mercury, obtained by dis- solving one dram of mercury in half an ounce of mode- rately strong nitric acid, mingling the solution with an ounce of water. By merely mixing these colourless fluids, the following tints are produced. Milk-white....Mix. three parts of No. 1 with one of No.2. Yellow....¥ our parts of No. 14, and one of No. 2. Orange....Four parts of No. 3 with one of No. 2. If No. 6 be added, the orange colour disappears, and the whole returns to its limpid state. Carmine....A. few drops of No. 6 with No. 10. This colour disappears on adding No. 9. Blood-red....A. few drops of No. 6 with No. 11. This liquid becomes again colourless on adding No. 9. Grass-green....Three parts of No. 10 with one of No. I. On adding No. 6, the mixture turns to red ; a few drops of No. 9 destroy this colour, and the fluid returns to its former limpid state. Light-green....Three parts of No. 11 with one of No. 1. Ultraviarine-blue....Three parts of No. 7 with one of No. 8. It becomes again colourless by adding No. 6. Dark-blue....Three parts of No. 11 with one of No. 2, the addition of No. 6 changes it to ruby-red. Theory of Colours. 155 Prussian-blue....By mixing equal quantities of No. 5 and No. 13. Violet....Equal quantities of No. 7 and No. 11. Pitch-black....Three parts of No. 11 with one of No. 4. Ink-black....Three parts of No. 12 with one of No. 4. It is again rendered limpid by No. 6 ; and No. 13 turns it blue. For these amusing experiments we are indebted to Mr. Tielebein. WHITENESS, The most curious composition of light is that of white- ness. There is no one sort of rays which can alone ex- hibit this colour: it is always compound, and to its com- position all the aforesaid primary colours are necessary. It is the most surprising composition, an assemblage of all the colours of the prism, in union in a due proportion. Whiteness therefore, or the solar light, is always compound; it is produced by a copious reflection of the rays of all sorts of colours. A spinning top painted on the surface with the colours of the spectrum of the prism may serve to prove this. On spinning the top, it revolves rapidly on its axis ; while it is so revolving, none of the colours can possibly be dis- tinguished singly, but the whole appears white; this whiteness will be greater in proportion as the primitive colours are brighter. BLACKNESS, On the contrary, is produced by a total absorption of the incidental light, which being stopped or absorbed in the body is not reflected outwards, but refracted within; hence it is lost, and produces darkness. Such are the principal physical properties of light. Optical writers may be consulted for a great number of curious and useful deductions made from these principles and applied to the doctrine of vision, the nature of colours, the construction of mirrors, and other instruments, nof immediately within the province of chemistrv. 156 Effects of Light on Vegetables. SECT. V. CHEMICAL PROPERTIES OF LIGHT. THE chemical effects of light have much engaged the attention of philosophers. Its influence upon animal, vegetable, and other substances, shall form the subject of the following heads. 1. EFFECTS OF LIGHT ON VEGETABLES. Every body knows that most of the discous flowers fol- low the sun in his course ; that they attend him to his evening retreat, and meet his rising lustre in the morning with the same unerring law. It is also well known that the change of position in the leaves of plants at different periods of the day is entirely owing to the agency oflight, and that plants which grow in windows in the inside of houses are, as it were, solicitous to turn their leaves to- wards the light. Natural philosophers have long been aware of the influence of light on vegetation. It was first observed that plants growing in the shade, or darkness, are pale and without colour. The term etiolation has been givefl to this phenomenon, and the plants in which it takes place are said to be etiolated'or blanched. Gardeners avail them- selves of the knowlege of this fact to furnish our tables with white and tender vegetables. When the plants have attained a certain height, they compress the leaves, by tying them together, and by these means (or by laying earth over them) deprive them of the contact of light: and thus it is that our white celery, lettuce, cabbages, endive, &c. are obtained. For the same reason wood is white under the green bark ; roots are less coloured than plants, some of them alter their taste, &c. they even acquire a deleterious quality when suffered to grow exposed to light. Potatoes are of this kind. Herbs that grow beneath stones, or in places utterly dark, are white, soft, aqueous, and of a mild and insipid taste. The more plants are exposed to the light, the more colour they acquire. Though plants are capable of being nourished exceedingly well in perfect ob- Effects of Light on Vegetables. 157 scurity, and in that state they even grow much more rapidly than in the sun (provided the air that surrounds them is fit for vegetation,) they are colourless, and unfit for use. Professor Davy* assures us that red rose-trees carefully excluded from light produced roses almost white. He likewise ascertained that this flower owes its colour to light entering into its composition ; that pink, orange, and yellow flowers imbibe a smaller proportion of light than red ones, and that white flowers contain no light. But vegetables are not only indebted to the light for their colour: taste and odour are likewise derived from the same source. Light contributes greatly to the maturity of fruits and seeds. This seems to be the cause why under the burning sun of Africa vegetables are in general more odoriferous, of a stronger taste, and more abounding with resin. From the same cause it happens that hot climates seem to be the native countries of perfumes, odoriferous fruits, and aromatic resins. The action of light is so powerful on the organism of vegetables, as to cause them to pour forth torrents of pure air from the surface of their leaves into the atmosphere, while exposed to the sun ; whereas, on the contrary, when in the shade they emit an air of a noxious quality. Experiment I. Take a few handfuls of fresh gathered leaves of mint, cabbage, or any other plant; place them in a bell-glass filled with fresh water, and invert it into a bason with the same fluid. If the whole be then exposed to the direct rays of the sun, small air bubbles will appear on the sur- face of the leaves, which gradually grow larger, and at last detach themselves and become collected at the sur- face of the water. This is oxigen gas. All plants do not emit this air with the same facility: there are some which yield it the moment the sun acts upon them, as the leaves of the jacobosa or ^igwort, of lavender, peppermint, and some other aromatic plants. The leaves afford more air when attached to the plant than * Beddoes's Physical and Medical Contributions, p. 790. 701.. r. 7. 158 Effects of Light on Animals. when gathered; the quantity is also greater the fresher and sounder they are, and if full grown and collected during dry weather. Green plants afford more air than those which are of a yellowish or white colour. Green fruits afford likewise oxigen gas; but it is not so plenti- fully furnished by those which are ripe. The nasturtium indicum, in the space of a few hours, gives out more air than is equal to the bulk of all its leaves. On the contrary, if a like bell-glass, prepared in the same manner, be kept in the dark, another kind of air will be disengaged, of an opposite quality. The method of collecting and examining these gases will be shewn hereafter, and the philosophy of their production will then be more fully pointed out. There is not a substance which, in well-closed glass vessels, and exposed to the sun's light, does not experi- . ence some alteration. Camphor kept in glass bottles exposed to light crystal- lizes or vegetates into the most beautiful symmetrical figures, on that side of the glass which is exposed to the light. Yellow wax exposed to the light loses its colour, and becomes bleached. Gum guaiacum, reduced to powder, becomes green on exposure to light. Vegetable colours, such as those of saffron, logwood, &c. become pale or white, &c. 2. EFFECTS OF LIGHT ON ANIMALS. The human being is equally dependent on the influ- ence of light. Animals in general droop when deprived of light; they become unhealthy, and even sometimes die. When a man has been long confined in a dark dungeon (though well aired) his whole complexion becomes sallow, pus- tules filled with aqueous humours break out on his skin, and the person who has thus been deprived of light be- comes languid, and frequently dropsical. Worms, grubs, and caterpillars, which live in the earth, or in wood, are of a whitish colour ; moths, and other in- sects of the night, are likewise distinguishable from those which fly by day, by the want of brilliancy in their colour. Effects of Light on Metallic Oxids. 159 The difference between those insects in northern and southern parts is still more obvious. The parts of fish which are exposed to light, as the back, fins, &c. are uniformly coloured; but the bellv, which is deprived of light, is white in all of them. Birds which inhabit the tropical countreys have much brighter plumage than those of the north. Those parts of the birds which are not exposed to the light are uni- formly pale. The feathers on the belly of a bird are generally pale or white ; the back which is exposed to the light, is almost always coloured ; the breast which is par- ticularly exposed to light in most birds, is brighter than the belly. Butterflies, and various other animals of equatorial countreys, are brighter coloured than those of the polar regions. Some of the northern animals are even darker in summer, and paler in winter. 3. EFFECTS OF LIGHT ON METALLIC OXIDS. Experiment I. Effect oflight on muriate of silver. Dissolve pure silver in nitric acid, and add to it muri- atic acid, a decomposition will take place ; for the muri- atic acid, having a stronger affinity to silver than the nitric acid, will unite to it, and fall to the bottom as an insoluble compound called muriate of silver. Separate this muriate by pouring the whole on a filter as quick as possible, and expose it still wet to the light, on a plate of white glass, on the lower side of which black paper has been pasted : at the end of some hours it will be seen that the light has exercised no action but at the surface, where the muriate will be found blackened, or re-approaching to the metallic state ; while at the place where the light did not fall there will be no alteration. Mr. T. Wedgwood has availed himself of the property which light exercises upon the metallic oxids for copy- ing paintings upon glass, and making profiles of figures by the mere agency of light upon nitrate of silver, in the following manner :;': * Journals of the Royal Institution, No 9, p- 171 160 Effects of Light on Metallic Oxid*. Experiment II. Let white paper or leather be covered with a solution of nitrate of silver, place it behind a painting on glass, and expose it to the solar light; the rays emitted through the differently painted surfaces will produce distinct tints of brown or black, sensibly differing in intensity, accord- ing to the shades of the picture ; and where the light is unaltered the colour of the nitrate becomes deepest. When the shadow of any figure is thrown upon the prepared surface, the part concealed by it remains white, and the other parts speedily become dark. For copying paintings on glass, the solution should he applied on leather ; and in this case it is more readily acted upon than when paper is used. After the colour has been once fixed upon the leather or paper, it cannot be removed by the application of water, or water and soap, and it is in a high degree permanent. The copy of a painting, or the profile, immediately af- ter being taken, must be kept in an obscure place. It may indeed be examined in the shade, but, in this case, the ex- posure should be only for a few minutes ; by the light of candles or lamps, as commonly employed, it is not sensi- bly affected. No attempts that have been made to prevent the un- coloured parts of the copy or profile from being acted up- on by .light have as yet been successful. They have been covered with a thin coating of fine varnish, but this has not destroyed their susceptibility of becoming coloured; and even after repeated washings, sufficient of the active part of the saline matter will still adhere to the white parts of the leather or paper to cause them to become dark when exposed to the rays of the sun. Besides the applications of this method of copying that have been just mentioned, there are many others. And it will be useful for making delineations of all such objects as are possessed of a texture partly opaque and partly transparent. The woody fibres of leaves, and the wings of insects, may be pretty accurately represented by means of it; and in this case, it is only necessary to cause the direct solar light to pass through them, and to receive the shadows upon prepared leather. Effects of Light on Metallic Oxids. 161 When the solar rays are ^passed through a print and thrown upon prepared paper, the unshaded parts are slow- ly copied ; but the lights transmitted by the shaded parts are seldom so definite as to form a distinct resemblance of them by producing different intensiti'es of colour. Professor Davy has found, that the images of small objects produced by means of the solar microscope may be copied without difficulty on prepared paper. This will probably be a useful application of the method ; that it may be employed successfully-, however, it is necessary that the paper be placed at a small distance from the lens. With regard to the preparation of the solution, this gentlemanjfound the best proportions those of one part of nitrate to about ten of water. In this case, the quantity of the salt applied to the leather or paper will be sufficient to enable it to become tinged, without affecting its com- position, or injuring its texture. Count Rumtord has made some valuable experiments concerning the chemical properties that have been attri- buted to light.* This philosopher observed, that white ribands wetted in a diluted aqueous solution of muriate of gold, and exposed wet to the action of the sun's direct rays, soon become tinged of a beautiful crimson colour. Magnesia wetted with a solution of muriate of gold, and exposed wet to the action of the sun's rays, soon changes to a purple, and afterwards to a deep crimson colour. But if the riband or magnesia, after being so wetted, be dried in a dark place, and then exposed in a dry state to the sun's rays, their colour will not be sensibly changed by the action of the light. The following method of silvering ivory, which we shall transcribe from the count's paper,f is extremely beau- tiful, and may become a valuable acquisition to the arts. Experiment III. Take a slip of ivory, immerse it in a diluted solution of pure nitrate of silver, and suffer it to be immersed till the ivory has acquired a bright yellow colour; then take it out of the solution, and immerse it in a tumbler of pure * Rnmford's Philosoph. Papers, vol i, 1802. p. 22-. 11. c p. 36? 162 Effects of Light on Metallic Oxids. water, and immediately expose it, in the water, to the direct rays of a bright sun. After the ivory has been thus exposed for about two or three hours to the action of the sun's light, it will appear black ; but on rubbing it a lit- tle, the black surface will become changed into a metallic one, resembling a slip of fine silver. Although this coating of revived metal is extremely thin, yet if the ivory be well impregnated with the nitrate of silver the solution will penetrate to a considerable depth, and as fast as the silver wears off from the surface of the ivory, the oxid below it becoming uncovered, and exposed to the light, a new coating of revived metal will be formed to replace it, and the surface of the ivory will not lose its metallic appearance. The Count further observes, that this method of silver- ing ivory, which is not only expeditious, but very econo- mical, might, no doubt, be employed with advantage in many cases, for ornamental purposes. The process is certainly curious and beautiful, when considered merely as a philosophical experiment. All metallic oxids, but especially those of mercury,. bismuth, lead, silver, and gold, become of a deeper colour, by exposure to the sun ; some of them become perfectly revived, others only partially, as may be seen by observ- ing various painters' colours, preserved in powder, and exposed to the light, in the windows of colour-shops. The yellow oxid of mercury, the acetate and muriate, are very soon affected by light. The black oxid of mercury, obtained by pouring am- monia copiously into a neutral solution of sulphate of mercury (or rather on dry sulphate) exposed to the rays oflight, becomes readily converted into fluid quicksilver. The yellow oxid of tungsten, if exposed to light, loses weight and becomes blue. Green prussiate of iron exposed to the solar light be- comes also blue. The rose-coloured solution of sulphate of manganese becomes colourless when kept exposed to the light, and regains its colour when removed into the dark. Effects of Light on Acids. 163 4. EFFECTS OF LIGHT ON ACIDS. Experiment I. Decomposition of nitric acid by light. If a white glass bottle be half filled with concentrated nitric acid, and exposed to the rays of the sun, at the end of some days the white acid will be converted into an orange-coloured and fuming one, and the bottle will be- come filled with red vapours. If the bottle be now car- ried into a dark place and suffered to remain there for some time, the red vapours will gradually diminish, and the acid return to its primitive or colourless state. Nitric acid, as we shall see hereafter, consists of the basis of two aeriform fluids, called nitrogen and oxigen. The acid in this instance loses part of its oxigen, which unites with the light, and forms oxigen gas ; hence the acid becomes more volatile, and fuming. This experiment succeeds best with highly concentrat- ed acid, exposed to the light in bottles only half filled. If oxigenated muriatic acid be exposed to the light, oxigen gas may easily be obtained, in the following man- ner, in considerable quantity. Experiment II. Decomposition of oxigenated muriatic acid by light. Put concentrated oxigenated muriatic acid into a bottle, and fit to it a bent glass tube, one end of which pierces the cork of the bottle, and the other end reaches under a bell or receiver, filled with and inverted in a bason of water, care being taken that the tube does not touch the acid ; the light falling directly on the acid, decomposes it, and a part of the oxigen of the acid becomes disengaged in the gaseous form, and passes into the receiver. Thus, there remains no doubt that light acts chemically on various substances. We have seen that incombustible bodies, such as oxids of metals, become combustible when exposed to the light; that acids are decomposed by its contact; that various other substances change their na- ture ; that vegetables acquire colour, odour, taste, and in- 164 Sulphuret of Barytes, or Bolognian Phosphorus. flammability : whereas, on the contrary, deprived oflight they remain pale and insipid, and are what is called etio- lated, or blanched. Light therefore enters into the composition of bodies ; and its effects are so considerable, that the skilful operator ought to be constantly aware of the influence it may have upon the products submitted to his investigation. SECT. VI. COMBINATION OF LIGHT WITH DIFFER- ENT BODIES. PHILOSOPHERS have ascertained that various bo- dies, if exposed to light either at a high or low tempera- ture, combine with it and emit it again, without altera- tion, under certain circumstances. Substances of this kind have been called SOLAR PHOSPHORI, or substances which shine in the dark without emitting heat, after having been exposed to the light. The world is stocked with an immense variety of bodies of this kind. All terrestrial objects not only possess a power of absorbing light, but they likewise emit it again. The eyes of cats, owls, and several other animals, are constructed so as to collect light, to enable them to find their food in the dark. Water condensed into the form of ice or snow, emits light remarkably. This accounts for the light afforded by snow, even when the heavens are involved in extreme darkness. The snow on the ground absorbs light, by being exposed to it all the day, and emits a considerable'quantity again in the dark. The principal bodies of this kind are the following: Bolognian phosphorus....The process for preparing this phosphorus is as follows: pieces of sulphate of barytes are first made red-hot, for a few minutes, in a covered crucible, placed in the middle of a fire, and then left to cool. When cold they are pulverized in a stone mortar, md sifted. This powder is formed into a paste with a Sulphate of Lime, or Canton's Phosphorus. 16.> Tittle mucilage of gum arabic, and divided into cakes, cylinders, or pieces of the thickness of a quarter of an inch. Those pieces are dried in a moderate heat, and then exposed, by degrees, to a more violent heat, among charcoal, in a strong drawing wind-furnace. As soon as the coals are half consumed, the furnace must be filled a second time, and the phosphorus be left undisturbed. When the coals are quite consumed, the ashes must be carefully blown off with a pair of bellows, and the phos- phorus is found at the bottom of the grate. These phosphoric stones exposed for a few minutes to the light, shine when taken into the dark like burning coals. Even immersed in water, they emit the same glow- ing light. Not only this phosphorus, but likewise all other phosphori of this class, lose their luminous proper- ty gradually, which they however regain on being heat- ed a second time. Ration ale....During the process of preparing the Bo- lognian phosphorus, a partial decomposition of the sul- phuric acid of the sulphate of barytes takes place. The ignited charcoal, at a high temperature, has a greater affinity to the oxigen of the sulphuric acid than the sul- phur has; it therefore attracts it, and forms carbonic acid gas : part of the sulphur of the sulphuric acid becomes thus separated ; it unites to the pure barytes, and forms sulphuret of barytes, which seems in this union more dis- posed to decompose oxigen gas than when single. The phenomenon is therefore to be considered analogous to a slow combustion of the sulphur ; the extrication of ca- loric, during each instant of observation, being too in- considerable to be appreciable either by the senses or by the thermometer. Canton's phosphorus....To prepare this phosphorus, take some oyster shells ; calcine them, by keeping them in a good coal-fire, for about an hour. Then let the purest part of the lime so obtained be broken into pieces (not powdered). To three parts of it, add one of flowers of sulphur, and place the whole in layers, in a crucible, tightly. Let it then be placed in the middle of a fire, where it must be kept red hot for an hour at least; it may then be removed to cool. When it is cold, select tin- brightest part, which, if good, will shine in the dark. This is to be kept in a wide-mouthed glass phial, well closed. VOL. I. a a 166 Nitrate of Lirrte, or Baldwins Phosphorus. This is Canton's phosphorus. The quantity of light which a little of it gives, when brought into a dark room, after it has been exposed for a few minutes to the sun, or even day-light, is sufficient to shew the hour by a watch, if the eyes have been previously kept shut a minute or two. Rationale....Analogous to the former. Baldwin's phosphorus....is a combination of nitric acid with lime, obtained by dissolving carbonate of lime in nitric acid, and evaporating the solution in an earthen vessel to dryness. This solid salt is then to be rammed into a crucible, which is placed in the middle of a good fire, where it is to be kept till the whole mass becomes liquid. As soon as the mass has fused about eight mi- nutes, the crucible is to be removed, and its contents pour- ed out into an iron pot, previously heated. This mass, when still hot, is to be preserved from the contact of the air in a well-stopped phial. Baldwin's phosphorus, when well prepared, shines with a beautiful white light, after having been exposed to the sun for a few hours. Modern observations have made \is acquainted with several other bodies which possess the property of shin- ing, after having been exposed to an elevated tempera- ture. We know that not only all neutral salts with a base of barytes belong to this class, but also many other substances, namely, diamonds, and several precious gems, magnesia, carbonate of magnesia, sulphate and carbonate of lime, alumine earth, sulphate of potash, sulphate of strontian, some metallic oxids, cotton wool, appatite, zeo- lite, &c. display the same phenomena. The combination of fluoric acid with lime, commonly called fluor spar or fluate of lime, is remarkable on ac- count of its property of shining in the dark, at an elevated temperature only. When the phosphoric fluor spar is re- duced to a fine powder, and placed in contact with any bo- dy, heated to about 212° Fahr. though not ignited, and afterwards taken into a dark place, it shines with a phos- phoric light. By this means may be performed writings, drawings, &c. «^pon an iron or copper plate, with a thin mucilage of gum arabic, or with white of egg, and strewing over it some fine powdered fluate of lime. When this is dry, all the superfluous powder must be carefully blown off, and the plate removed over a gentle coal fire. As soon Muriate of Lime, or Homberg's Phosphorus. 167 as it is heated the delineated objects become luminous, and opaque again when the plate becomes cold. Not only lapis lazuli, several kinds of stones, &c. be- come luminous in a high temperature ; but also Dr. Ma- rum observed, that a phosphoric light is discernible in expressed oils and animal fats, when heated to 450° Fahr. PHOSPHORIC SUBSTANCES WHICH BECOME LU- MINOUS BY ATTRITION OR PERCUSSION. The most celebrated and most anciently known body of this kind is called Homberg's phosphorus....Homberg's process for ob- taining this phosphorus is as follows : One part of pow- dered muriate of ammonia is mixed with two of powder- ed lime, introduced into a red-hot crucible, and kept hot till the mixture becomes liquid. As soon as the mass has been fused for a few minutes, it is poured out into a heated iron pot, broken into pieces, and preserved in a well-stopped phial. This substance has the property of emitting a phospho* ric light, when struck or excited with a hard sharp body in the dark. When a red hot poker is dipped into the fused substance, and rubbed after it is cool with another piece of metal, it becomes luminous, and gives out phos- phoric sparks and light. This phosphorus is obtained more conveniently, as well as at less expence, when that portion of muriate of lime which remains in the retort, after the decomposition of muriate ammonia by lime, is melted, and then exposed for some minutes to such a degree of heat as is sufficient to melt the surface of a green glass matrass ; it acquires the property of giving fire with steel, and emits phospho- ric sparks and flashes of light in a high degree. Those kind of phosphori or substances which give a perceptible sparkling light by attrition or percussion, with- out having been exposed either to the solar light or fire, are likewise numerous. Flints, and several other siliceous stones, struck against one another, appear luminous in the dark, some through the whole mass, others only on the sidestruck upon. Tremolit, phosphate of lime, black-jack, and other stones of this genus, become luminous or yield 168 Muriate of Lime, or Homberg's Phosphorus. phosphoric light in the dark, when struck with a sharp in- strument. Gum elemi, various resins, and sugar, emit a perceptible light by attrition or percussion, without hav- ing been exposed to light or heat. Mr. T. Wedgwood* has published an excellent paper on the light produced by attrition. Mr. Coatesf of Clifton observed, that if two pieces of bonnet-cane were rubbed together in the dark, light was liberated. Professor Davy, who pursued this experiment, found that all canes of this kind when briskly rubbed to- gether produce sparks of white light, which are more vi- vid on collision. But the most perfect phosphorus of this class is sub- borate of soda. Two pieces of this salt stuck one against another, or a swift blow with any sharp instrument upon it, produces such a flash of white light, as none of the before-mentioned substances are capable of giving. Other substances again emit light on immersion into acids. Mr. Westrumbi. observed, that when fresh prepared magnesia is thrown into concentrated sulphuric acid, light is liberated, which produces an appearance similar to that known by the name of red heat. Experiment I. To perform this experiment, about two scruples or one drachm of magnesia, recently freed from carbonic acid by heat, must be put into a tea-cup, and half an ounce of highly concentrated sulphuric acid poured over it at once, so as to cover the magnesia. A prodigious quantity of vapour is instantly extricated; sparks are thrown about, and the mixture becomes ignited. Mr. Westrumb ob- served, that coloured (or partly deoxigenized) sulphuric acid answered the purpose better than when the acid was colourless. During the combination of lime with muriatic acid, and of dry potash or soda with sulphuric acid, a white light is uniformly perceived. * Philosopli. Trans. 1792. t Nicholson's Journal, May, 1799, p. 56. \ Crell's Chemic. Annals, 1784, p. 432 Nature of the Photometer. 169 Various animal and vegetable substances likewise emit light, under peculiar conditions only. Fish, and several other marine animals, both in a living state and when dead, possess this property ; as instances of the first may be mentioned the shell-fish calledpholas, the medusa phos- phorea, and various other mollusca. In the class of insects are many which emit light very copiously, particularly several species oifulgora, or lantern fly; and oilampyris, or glow-worm: also the scolopendra electrica, and a species of crab, called cancer fulgens. Rotten wood is well known to emit light spontane- ously. Peat earth has the same property. The flesh of quadrupeds has also been observed to emit light. The softest parts become often totally phosphoric; it appears in this state as if sprinkled over with gems. Upon touching the brilliant luminous particles they come off, and appear almost liquid. The medullary substance of the brain of human beings, or rather the nervous system in general, is said to possess this property in a high degree : it is this particularly which gives rise to those phosphorescent lights frequently observed in anatomical theatres. Citizen Cabarris, who read a memoir on this subject before the national institute, remarks, that a variety of observations have made him conclude, that the quantity of phosphorescent matter after death bears some proportion to the activity of the nervous system during life. Dr. Hulme has made some interesting experiments on the light which is spontaneously emitted from various bodies. He believes (as is highly probable) that the light is a constituent part of many animals, particularly of the marine fishes; that it maybe separated, collected, and ren- dered permanent for some time by peculiar processes, for which we refer our reader to the interesting, curious, and well-conducted experiments enumerated in his paper.* NATURE OF THE PHOTOMETER. In order to measure the relative intensity of light emit- ted by luminous bodies, various kinds of contrivances, call • Philosph. Trans. 1800, p. 161. 170 Nature of the Photometer. ed photometers, have been contrived. The most perfect instruments of that kind are the photometer of count Rumford and that of Mr. Leslie. Count Rumford's me- thod of measuring the comparative intensity of two lights, is to place the two lights at such distances from a given plane, that the shadows cast by them appear equally dark; and since the intensity of light must obviously decrease as the square of the distance increases, it be- comes easy to calculate from the distance determined the original density of the lights compared. The Count found by means of his photometer, that the saving in the quan- tity of oil consumed by an Argand's lamp, compared with one of the common construction with a riband wick, amounted to about 15 per cent, in the production of an equal quantity of light. He also ascertained, than an Argand's lamp of the common size well trimmed, and burning with its greatest brilliancy, emitted about as much light as ten common wax candles, each three-quarters of an inch in diameter; and that the light of a good wax candle varies from 100 to about 60: if, namely, such a candle when newly snuffed, and burning with its greatest brilliancy, emits a quantity of light = 100, its light will be reduced to 20, and even as low as 16, when it is suffer- ed to burn very dim for want of being snuffed. The loss of light emitted by a tallow candle under similar circum- stances was found to be much greater. A particular ac- count of the principles on which count Rumford's pho- tometer is founded, together with some masterly draw- ings of the instrument, may be found in count Rumford's work,* from which these data have been copied. The ratio of the intensities of luminous bodies, for in- stance, two candles of unequal size, may also be measured with tolerable accuracy, by placing them at different distances from a given object, until that object casts two shadows of equal density or darkness; or by observing when two equal objects appeared to be equally illuminated, each by one of the luminous objects; for then the pro- portion of the intensities of their lights was reckoned to be as that of the square of distances : for instance, if two equal objects appear to be equally illuminated, when one of them is three feet from a tallow candle, and when the * Rumford's Philosophical Papers, 1802, p. 270, Nature of the Photometer. 171 other is nine feet from a wax candle, then it is concluded that the intensity of the light of the tallow is to that of the wax candle as 9 to 81. Thus far we have examined the two imponderable sub- stances diffused through space, namely caloric and light. They have been considered by different philosophers as substances whose particles mutually repel each other, for thev are never found cohering together. They agree in many of their properties : they radiate from hot or luminous bodies with inconceivable velocity ; they are transmitted, reflected, and refracted, by different substances ; while they have the property of combining with others. Caloric, we have seen, is the cause of the sensation of heat; it produces expansion, is the cause of fluidity, &c. Light, on the other hand, produces the sensation of vision, and is the cause of colours. Both substances do not affect the ponderability of bodies. All attempts to weigh them have hitherto been in vain ; they have there- fore been called imponderable substances : if they are absolutely imponderous, is left to the determination of the more successful labours of future inquirers. SUBSTANCES NOT YET PRODUCIBLE BY ART, BUT ANALOGICALLY CONSIDERED AS SIMPLE. PART X. SECT. I. OXIGEN. AS the two agents which have formed the subject of our last inquiry may be considered as the great instru- ments of analysis and synthesis in the phenomena of na- ture ; so likewise will those substances which will form the subjects of the present part, though long unknown, or ill understood to men, prove no less interesting, entitled to our attention. They afford to our art instruments and means not less important, and necessary to be known. Oxigen, though long concealed from chemists, and as it were eluding the ancient methods of analysis in their possession ; though it be an independent substance very distinct from every other, it is not easy to give a clear notion or precise definition of this body, because this sub- stance, existing sometimes in a solid and sometimes in an aeriform state, is never distinctly perceptible to the hu- man senses, but in combination. Nevertheless, it can be weighed and measured, combined and disengaged. We know it only in hs combination, by its effects. Nature never presents it solitary ; chemists do not know how to insulate it. We are therefore obliged to consider it at first as an abstract being, or metaphysical entity. when we wish to avoid speaking of its combinations. Hidrogen. 173 Oxigen is absorbable by combustible bodies, and converts most of them into acids. This is, in fact, one of the most characteristic properties of this body, first discover- ed by Dr. Priesdey in the year 1774. It is an indispen- sable condition of combustion, uniting itself always to bodies which burn, augmenting their weight and chang- ing their properties. It may be disengaged in the state of oxigen gas from burnt bodies, by a joint accumulation of caloric and light. It is highly necessary for the respi- ration of animals, and for the support of plants. It ex- ists universally dispersed through nature, and in a consti- tuent part of atmospheric air, of water, of acids, and of all bodies of the animal and vegetable kingdoms. One of the most remarkable combinations into which it is capable of entering, is that which it forms with light and caloric. The nature of that mysterious union has not been ascertained ; but it is certain that in that state it constitutes the gazeous fluid called oxigen gas, which it will be more proper to consider hereafter. The combination of oxigen with different bases, is called oxigenation, oxigenisement, oxidation, or oxidise- ment. SECT. II. HIDROGEN. HIDROGEN is another substance not perceptible to our sensations in a separate state ; but its existence is not at all the less certain. Though we cannot exhibit it ex- perimentally uncombined, we can pursue it while it passes out of one combination into another: we cannot indeed arrest it on its passage ; but we never fail to discover it, at least if we use the proper chemical means, when it pre- sents itself to our notice in a new compound. Hidrogen, as its name expresses, is one of the consti- tuent elements of water. Its existence was unknown till lately. It is plentifully distributed in nature, and acts a very considerable part in the processes of the animal and vegetable economy. It is one of the ingredients in the mixtures of bitumen, of oils, fats, ardent spirit, ether, and in fact of all the proximate component parts of all animal vol. i. * h 174 Nitrogen. and vegetable bodies. It forms a constituent part of all animal and vegetable acids. It is one of the bases of am- monia, and of various other compound gases. It possesses so great an affinity with caloric, that it can only exist in the state of gas : it is consequently impos- sible to procure it in the concrete or liquid state, inde- pendent of combination. Solid hidrogen, therefore, united to caloric and light, forms hidrogen gas, which will be noticed in its proper place. SECT. III. NITROGEN. NITROGEN or Azote is another simple body in the same condition with regard to us as hidrogen and oxigen. It is very abundant in nature, though not producible alone or in an insulated state. It is not distinctly perceptible to the human senses, however aided by instruments. We know it only in its combination. But the reality of its existence is unquestionable ; since we can mark its pas- sage out of one combination into another ; since we know the laws of chemical attraction to which it is subject; since we discern the piecise character of those simple sub- stances with which it is combinable, and can distinguish the nature of the new compounds which the combination produces. The separate existence and peculiar nature of this substance were first discovered by Dr. Rutherford. It is the radical principle of our atmospheric air, and other gazeous substances, and forms a constituent part of ani- mal and vegetable substances. It is a component part of the'nitric acid, and of ammonia. It probably enters into the formation of alcalies, and it is considered by some as a real alcali gen or alcalizing principle, in opposition to oxigen, which, as we have noticed before, is the prin- ciple of acidity. One of the most remarkable combina- tions into which nitrogen is known to enter, is that which takes place between it and light and caloric. The com- pound thus produced is called nitrogen gas, which shall be treated of in a farther part of this work. Nitrogen. 175 We have noticed these three substances here separate- ly, because they act so very important a part in all the phenomena of chemistry, that it is requisite to have some previous notion of them before we proceed any further. They shall be more circumstantially described hereafter, together with the rest of the bodes envimerated before in the table of simple substances. COMBUSTIBLE BODIES, DESTITUTE OF METALLIC PROPERTIES. SULPHUR. PART XL SECT. I. NATURAL HISTORY OF SULPHUR. SULPHUR, which is also known by the name of brim- stone, is the only simple combustible substance which nature offers pure and in abundance. It was the first known of all. It was on this substance that the ingenious Stahl most particularly established his theory of phlogis- ton, which has governed the schools during a century. In general, sulphur, even considered as a principal subject in chemistry, has been at all times one of those which have participated the most in the different changes which the science has experienced, and concerning which philo- sophers have been more particularly employed. Sulphur is consequently a body whose combinations are the most numerous, and, at present, the best understood. It is found abundantly in the earth, and exists external- ly in depositions, in sublimed incrustations, and on the surface of certain waters, principally near burning volca- nos. It is found combined with many metals. It exists in vegetable substances, and has lately been discovered by Mr. Carlisle in the albumen of eggs.* Sulphur in the mineral kingdom is either in a loose powder, or compact and crystallized ; and then either de- tached or in veins. It is found in the greatest plenty in * Nicholson's Journal, August, 1801, p. 178. Physical Properties of Sulphur. 177 the neighbourhood of volcanos or pseudo-volcanos, whe- ther modern or extinct, as at Solfatara, &c. and is deposited as a crust on stones contiguous to them, either crystallized or amorphous. It is frequently met with in mineral wa- ters, and in caverns adjacent to volcanos ; sometimes also in coal-mines. It is found in combination with most of the metals. When united to iron it forms the mineral call- ed martial pyrites, or sulphur pyrites. All the ores known by the name oi pyrites, of which there are a vast variety, are combinations of sulphur with different metals ; and hence the names of copper, tin, arsenical, &c. pyrites. It exists likewise in combination with alumine and lime ; it then constitutes different kinds of schistus, or alum ores. It occurs cdmmonly in masses in gypsum and marls. It is sometimes found in veins that traverse primitive rocks. It occurs also in nests in lime-stone. Very lately the celebrated and enterprising Prussian traveller Von Humboldt has discovered a bed composed of sulphur and quartz, in a mountain of micaceous slate.* Sulphur is found in Europe, at Baaden in Austria, at Lauenstein in Hanover, at Artern in Thuringia, Schwartz- walde in Swabia, at Jura in Switzerland, Lothringen in France, in the mountains of Grenada, Andalusia, and Conil, near Cadiz, in Spain. What is called by mineralogists volcanic sulphur oc- eurs only in volcanic countries; where it is found in greater or smaller quantity amongst lava, Solfatara, n« the vicinity of Vesuvius, &c. PHYSICAL PROPERTIES OF SULPHUR. Sulphur is a combustible, dry, and exceedingly brittle body, of a pale lemon-yellow colour. Its specific gravity is 1.990. It is destitute of odour, except when rubbed or heated. It is of a peculiar faint taste. It frequently crystal- lizes in entire or truncated octahedra, or in needles. If a piece of sulphur of a considerable size be very gently heated ; as for example, by holding it in the hand and squeezing it firmly ; it breaks to pieces with a crackling noise. It is a non-conductor of electricity, and hence it becomes electric by friction. When heated, it first softem * Annales «.lu Museum National 178 Method of obtaining Sulphur. before5 it melts, and its fusion commerces at 184° Fahr.; at 28&'vit becomes volatilized, and takes fire at 302°. In the beginning of fusion it is very fluid, but by continuing the heat it grows tough, and its colour changes to a red- dish brown. If in this condition it be poured into water, it remains as soft as wax, and yields to any impression. In time, however, it hardens again, and recovers its former consistence. It unites with most of the earths and with all alcalies, with muriatic acid, and becomes soluble, when thus com- bined, in water. It unites to most of the metals, and renders them brittle and fusible. It is soluble in oils; water takes up a minute quantity, as does ardent spirit and ether by means of heat. It dissolves in hidrogen gas, and unites to phosphorus by fusion. Sulphur, like all combustible bodies, burns in proportion to the quantity of oxigen which combines with it. If melted sulphur be exposed in the open air to an increase of heat, it takes fire, and burns with a blue flame and suffocating vapour. The result of this combustion is sulphureous acid. According to the slow or rapid com- bustion, it absorbs different quantities of oxigen, and the produced acid differs in its properties. Sulphur heated in a close vessel sublimes without alteration. It is not changed by exposure to air. It is attacked by the nitric acid when poured on it in its fused state. METHOD OF OBTAINING SULPHUR. A prodigious quantity of sulphur is obtained from Sol- fatara, in Italy. This volcanic country every where ex- hibits marks of the agency of subterraneous fires: almost all the ground is bare and white ; and is every where sensibly warmer than the atmosphere, in the greatest heat of summer ; so that the feet of persons walking there are burnt through their shoes. It is impossible not to observe the sulphur; for a sulphureous vapour which rises through different apertures is every where perceptible, and gives reason to believe that there is a subterraneous fire under- neath from which that vapour proceeds. From pyrites sulphur is extracted in the large way by the following process : Method of purifying Sulphur. 179 Pyrites is broken into small pieces, and put into large earthen tubes, which are exposed to the heat of a furnace. A square vessel of cast-iron, containing water, is connect- ed as a receiver with the tube in the furnace. The action of the fire proceeds, and the sulphur being thus melted is gradually accumulated on the water in the receiver. It is then removed from this receiver, and melted in large iron ladles ; in consequence of which, the earthy parts with which it was contaminated are made to sub- side to the bottom of the ladle, leaving the putrified sul- phur above. It is then again melted, and suffered to cool gradually, in order to free it from the rest of the impuri- ties. It is then tolerably pure, and constitutes the sul- phur we meet with in large masses or lumps in the market. In order to form it into rolls, it is again melted and poured into cylindrical wooden moulds : in these it takes the form in which we usually see it in commerce, as roll sulphur. Flowers of sulphur, as they are called, are formed by subliming purified sulphur with a gentle heat in close rooms, where the sublimed sulphur is collected ; though the article met with in general, under that name, is no- thing but sulphur finely powdered. METHOD OF PURIFYING SULPHUR. Take one part of flowers of sulphur, boil it in twenty- parts of distilled water in a glass vessel for about a quarter of an hour; let the sulphur subside, decant the water: and then wash the sulphur repeatedly in distilled water; hav- ing done this, pour over it three parts of pure nitro-muri- atic acid, diluted with one part of distilled water; boil it again in a glass vessel for about a quarter of an hour, decant the acid, and wash the sulphur in distilled water till the fluid passes tasteless, or till it does not change the blue colour of tincture of cabbage, or litmus. The sul- phur thus carefully treated is PURE SULPHUR, fit for philosophical experiments. We shall now endeavour to prove some of the before- stated properties of sulphur. 180 Proofs of the Properties of Sulphur. SECT. II. EXPERIMENTAL PROOFS OF THE PRO- PERTIES OF SULPHUR. Experiment I. Slow combustion of sulphur. PUT some threads previously dipped in sulphur into a cup or other vessel floating on water. Set fire to the threads, and cover the whole with an inverted glass re- ceiver. The threads will continue to burn for some time, and the whole receiver will become filled with a dense white vapour. The water will ascend into the receiver. The whole is then to be left till the vessel is become again transparent. If the water be now examined, it will have a suffocating odour and taste. It will turn the blue co- lour of litmus paper red, and exhibit all the other signs that an acid has been formed. Ration ale...The sulphur, being a simple body, has at an elevated temperature a great affinity to oxigen; it therefore attracts it from the atmospheric air, and thus becomes converted, by slow combustion, into sulphure- ous acid gas, which is absorbed by water. The volume of air within the receiver being diminished, is the cause of the ascent of the fluid. This experiment may perhaps be more conveniently performed by covering burning sulphur contained in a crucible with a large receiver, and then placing the ap- paratus in a broad dish, and surrounding it with water. Experiment II. Rapid combustion of sulphur. Take a large receiver, or any other round-bellied bottle with a wide orifice, containing a little water ; fit a bung Slow Combustion of Sulphur. 181 to close it, and fasten to this bung an iron or copper spoon, containing a mixture of one part of nitrate of potash and six of sulphur, blenued together. Set fire to the mixture and introduce it expeditiously into the vessel, taking care to close the mouth accurately. In this case, the combus- tion will go on very rapidly, and the water at the bottom of the vessel will become sour, but without possessing much suffocating odour. Rationale....In this experiment the combustion is not slow, but on the contrary very rapid ; for the nitric acid of the nitrate of potash is decomposed, and furnishes oxigen gas, into which the sulphur is plunged the instant of its inflammation. It therefore absorbs a much greater quantity of oxigen, and furnishes sulphuric acid, different in properties from the former, which is not completely oxigenated, and therefore is pungent and volatile. Experiment III. Sulphur is soluble in ardent spirit only in a state of extreme comminution. If a piece of sulphur be left in contact with ardent spirit for any length of time, the spirit will not act upon it; but if we present the sulphur in its smallest division to the spirit, an union will then take place. To perform this experiment, put pounded sulphur into a mattrass furnished with an alembic; suspend within it a cup or wide-mouthed bottle containing very strong ar- dent spirit, then put on the alembic, and adjust a phial to the beak ; lute well the joinings, and heat the lamp. The sulphur and spirit will now meet in a state of va- pour, and the fluid which distils over will contain sulphur in solution. To prove that sulphur is dissolved in the spirit, water may be added : the spirit will unite to the water, and the sulphur be precipitated. This furnishes an instance that chemical attraction takes place only between the minutest parts of bodies. (Ser page 46.) vol.. i. r. c 182 Action of Caloric on Sulphur. Experiment IV. Sulphur is soluble in sulphuric ether. Take one part of sulphur reduced to a fine powder, put it into a bottle, and pour over it eight of sulphuric ether; suffer the mixture to stand for some days, taking care to agitate it frequently. On decanting the supernatant fluid, the presence of sulphur may be proved, as stated before. Experiment V. Action of caloric on Sulphur. If sulphur be put in a crucible placed among burning coals, it will soon enter into fusion. This first fusion is liquid ; but if it be kept longer over the fire it becomes tenacious, very thick, and dark coloured. When poured into water in this state, it will be as soft as wax, and may be easily worked into any form between the fingers, in- stead of being solid or brittle, as sulphur is in common. Sulphur in this state may be employed with advantage as a paste for taking impressions from seals and engraved stones. It is this property of sulphur of which Mr. Tassie has availed himself to furnish elegant impressions of antique gems. It is supposed that sulphur rendered tenacious and co- loured by fusion has combined with a portion of oxigen; and hence Fourcroy has^iven it the name of oxid of sul- phur. According to Dr. Thompson it contains 2.4 per cent. of oxigen. Dr. Thompson was unable to produce this change in the appearance of sulphur by heating it in a flat dish, where nothing impeded the volatilization, though he kept it melted in a glass capsule on sand heated to 250° for ten hours together.* But the change took place in a short time when a considerable quantity of sulphur was kept melted in a crucible ; and the greater the quantity of sul- phur employed the sooner the change took place, and the more complete it was effected. Dr. Irvine asserts that * Nicholson's Journal, Oct. 1803, p. 102 t Combination of Sulphur with Metals. 183 the shape of the vessel does not influence the thickening of sulphur by heat, provided enough of heat is employed ;* and that the effect never fails to appear if the sulphur be exposed to the proper temperature necessary to produce this change. Dr. Irvine found that this thickening be- gins at 320° Fahr. and continues, and even increases, to the temperature of 530°, and even 550° at least. If melted sulphur be withdrawn from the fire as soon as it is completely melted, and left to cool slowly, its parts assume a regular symmetrical arrangement, dispos- ed in needles, which form a crystallization of sulphur. If the vessel in which the sulphur is kept melting be covered with another vessel, and the air be excluded by luting, flowers of sulphur will be obtained in the upper vessel. As it seldom happens that there is not a small quantity of sulphur burnt in this process, the sublimed sulphur is usually in a slight degree acid ; hence the acid should be removed by ablution. COMBINATION OF SULPHUR WITH METALS. Sulphur and iron have a great attraction to each other: the iron becomes of easy fusion and brittle by this union. Experiment I. Formation of sulphuret of iron. If a bar of iron be heated to perfect whiteness and then touched with a roll of sulphur, the two bodies combine, and drop down together in a fluid state, forming sulphu- ret of iron, a compound of the same nature as the native iron pyrites. By this method a piece of iron rolled out very thin mav be apparently melted in the hand, by putting it, when heated to whiteness, upon a thick piece of solid sulphur. Remark...At is necessary that this experiment be per- formed under a chimney, or in a place where there is a current of air, to carry off the suffocating vapours. If three parts of iron filings and one of powdered sul- phur be mingled together, and the mixture be introduced in a Florence flask, placed over the lamp furnace, and * Irvine's Essays on Chemical Subjects. 184 Combination of Sulphur with Metals, gradually heated, it first begins to melt, but afterwards takes fire and burns vividly. The result is a brownish black sulphuret, weighing three ounces and six drachms. Experiment II. Sulphuret of arsenic. If one part of sulphur and three of arsenic, both re- duced to powder, be melted together in a covered cruci- ble, a reddish yellow vitreous mass is obtained, which is a true sulphuret of arsenic. It is a perfect imitation of the native red sulphuret of arsenic, or realger. It may be formed also by heating together the white acid of arsenic and sulphur. Experiment III. Sulphuret of lead. To obtain this compound, let five parts of lead be fus- ed, and add gradually, by little at a time, two parts of sulphur, taking care to cover the crucible carefully. The compound thus obtained i" sulphuret of lead. It greatly resembles the native sulphuret. Experiment IV. Sulphuret of tin. This sulphuret may be produced by fusing together three ounces of tin and one of sulphur. It crystallizes in leaves. Its colour is lead grayr. Experiment V. Sulphuret of antimony. Sulphur combines easily with antimony, and forms a compound greatly resembling the native sulphuret of an- timony. To produce this sulphuret, let four parts of an- timony and one of .sulphur be hastily fused together in a covered crucible, and suffer the mass to cool slowly. It crystallizes in needles. Its colour is a brilliant gray. Combination of Sulphur with Metals. i 85 Experiment VI. Sulphuret of silver. To obtain this sulphuret, let thin plates of silver and sulphur be laid alternately in a crucible ; press them well together, and remove the crucible into a coal fire. As soon as the crucible has acquired a bright red heat the sulphur will have combined with the silver, and a true sulphuret of silver is the result. This sulphuret is of a deep violet colour: it is brittle, but capable of being cut with a knife. It is much more fusible than silver. Experiment VII. Sulphuret of bismuth. If we heat together equal parts of bismuth and sulphur, both reduced to powder, in a crucible, the mixture fuses' and on being suffered to cool, a grayish black sulphuret of bismuth is obtained, beautifully crystallized in needles,and frequently tinged with the most brilliant deep blue and red colours. The crystallization is best effected by suf- fering the surface of the fused bismuth to cool and be- come solid, then piercing the solid crust, and letting the portion which is still liquid run off, whereby a kind of cavity is formed, lined with the most brilliant needles, and which, when sawed through longitudinally, presents a crystalline mass worthy of being placed in valuable collec- tions amongst the most beautiful productions of art. This sulphuret of bismuth is much more difficult of fusion than bismuth itself. Indeed, in forming the com- pound, we soon perceive that the fusion of the metal is retarded, and that, in order to fuse it, much more heat must be employed than would be necessary if the metnl were by itself. Experiment VIII. Sulphuret of Copper. (Accensicn of sulphur and metals. J The union of sulphur with copper and other metals, at a low temperature, is attended with some remarkable phe- nomena. In order to exhibit this experiment, mix three 186 Combination of Sulphur with Alcalies. parts of copper filings and one of sulphur reduced to powder intimately together: introduce this mixture into a glass tube or Florence flask, and heat it gradually over a lamp or coal fire. After the mixture has been heated to a certain degree, it begins to swell, and a small ignited spark becomes first visible at the bottom of the glass ves- sel, which increases in size, exhibiting a combustion more rapid than that of iron and sulphur, mentioned before. A society of Dutch chemists, consisting of Messrs. Dieman, Pacts, Van Troostwyk, and others, were the first who observed this phenomenon. They introduced filings of copper with different pro- portions of sulphur into small glass phials, from which common air was excluded; being in some cases filled with carbonic acid gas, or nitrogen gas, and in others with water or mercury. Whenever the phial was heated under any of these cir- cumstances, the mixture began to swell, the metal always became red hot, and in some cases real inflammation took place, notwithstanding the exclusion of oxigen gas. The proportions that produced most ignition or flame were forty parts of copper and fifteen of sulphur. Tin and sulphur succeeded in the same proportion. Lead and sulphur, the proportions being as forty-five of the former and fifteen of the latter. Zinc and sulphur, in the same proportion, burned with explosion. Mercury, antimony, and cobalt, could not be made to inflame with sulphur. These experiments succeed equally well in the Torri- cellian vacuum. COMBINATION OF SULPHUR WITH ALCALIES. Alcalies and sulphur have a great affinity to each other in the dry as well as in the humid way. Experiment I. Preparation of sulphuret of potash. If four parts of carbonate of potash be melted by a mo- derate heat, with three of sulpl rr, in a covered crucible, Combination of Sulphur with Alcalies. 187 a mass is obtained which after cooling exhibits a liver- brown colour. It is called sulphuret of potash. It may also be produced by mixing four parts of sul- phate of potash with one of charcoal powder, and exposing this mixture in a crucible to a bright-red heat for about one hour. Sulphuret of soda may be formed in a like manner, by melting together five parts of carbonate of soda, freed from its water of crystallization, with three of sulphur. Experiment II. Sulphuret of barytes. If two parts of barytes and one of sulphur be mixed to- gether, and the mixture be heated in a crucible for about half an hour, or till it fuses, a reddish yellow mass is ob- tained void of odour, which is sulphuret of barytes. It may likewise be obtained from the native sulphate of barytes. See Barytes. Experiment III. Sulphuret of strontia. If three parts of strontia and one of sulphur be gradu- ally heated till it melts, the compound obtained is sulphu- ret of strontia. Sulphuret of strontia may also be produced by heating sulphate of strontia in contact with charcoal powder. See Barytes. Experiment IV. Sulphuret of lime. That sulphur combines with lime may be proved by mingling one part of sulphur with two of powdered lime, and heating the mixture in a covered crucible for at least half an hour, or until no blue flame appears on the surface. The compound thus obtained is sulphuret of lime. In preparing this compound, care should be taken that both 188 Combination of Sulphur with Earths. the ingredients be very finely powdered, and intimately blended together. The mixture should not be rammed tight in the crucible, but loosely introduced ; whereas, on the contrary, the whole is otherwise apt to be blown out of the vessel, as soon as the mixture becomes red hot. Experiment V. Preparation of sulphuret of ammonia. Ammonia also combines with sulphur. Sulphuret of ammonia may be obtained in the following manner: Two parts of finely-powdered lime are put into a dry retort; upon this one part of muriate of ammonia, well mingled by trituration with one-third part of sulphur, is poured, and the whole mingled together by shaking. The charged retort is then placed in a sand-heat; a receiver, containing a little water, is adapted, and the distillation carried on very slowly. The fluid which passes over on increasing the heat is sulphuret of ammonia : it is of a deep yellow colour, a volatile and disagreeable odour, and fumes strongly in contact with air. In order to obtain sulphuret of ammonia very fuming, the first fluid which passes over must be kept separate ; for it is only this which is smoking, by reason of its containing some un- combined ammonia. In other respects its properties are like the former combinations of sulphur with alcalies. Its volatility renders it capable of restoring oxidated metals to the metallic state, as may be evinced hi the following Experiment VI. Dissolve some crystallized nitrate of silver, free from excess of acid, in a sufficient quantity of distilled water; dilute the solution with water, till writings performed with it on paper are invisible when dry. If this writing be exposed to the vapour of the sulphuret of ammonia, it will become visible'with the brilliancy of silver. Rationale....The sulphuret of ammonia gives out sulphurated hidrogen gas at the ordinary temperature of the atmosphere: on coining into contact'with the solution Combination of Sulphur with Carbon and Phosphorus, 189 of silver, the hidrogen attacks the oxigen of the silver and forms water, and the metal becomes revived, which then unites with the ammonia and sulphur, in order to form a sulphurated ammoniuret of silver. COMBINATION OF SULPHUR WITH EARTHS Experiment I. Sulphuret of magnesia Is best prepared in the following manner: one part of charcoal powder is to be mixed with six of sulphate of magnesia ; the mixture is then reduced to dryness, and ignited gradually. RATioNALE....Sulphate of magnesia consists of sulphu- ric acid and magnesia. At a high temperature the sulphuric acid becomes decomposed by the charcoal which unites to its oxigen in order to be converted into carbonic acid gas, and sulphur is produced. The carbonic acid gas flies off, and the sulphur unites to the magnesia. Care must be taken not to ignite this sulphuret too much, for the sulphur seems to adhere to the magnesia very feebly. In the same manner allumine maybe united to sulphur. Experiment II. Sulphuret of alumine. See Pyrophorus. COMBINATION OF SULPHUR WITH CAR- BON AND PHOSPHORUS. Till lately it was supposed that sulphur does not com- bine with carbon; but Messrs. Desorms and Clement, two French chemists, who have paid particular attention to the properties of carbon, have lately announced a method of combining them in the following manner. VOL. i. d d 190 Combination of Sulphur with Carbon and Phosphorus. Experiment I. Fill a porcelain or earthenware tube with well-burnt charcoal, and make it pass through the openings of the universal furnace (see universal furnace J in such a way that one end shall be considerably elevated above the other. To the other end lute a wide glass tube, of such a length and shape that its end can be plunged to the bot- tom of a bottle of water. To the elevated extremity of the tube adapt another glass tube filled with small pieces of sulphur, and secured at the farther end, so that the sul- phur may be pushed forwards by means of a wire, with- out allowing the inside of the tube to communicate with the external air. Heat the porcelain tube, and conse- quently the charcoal which it contains, to redness, and continue the heat till air bubbles cease to come from the charcoal; then push the sulphur slowly, and piece after piece into the earthen tube. A substance will then soon be delivered by the glass tube, which condenses un- der the water in the bottle into a liquid. This liquid is a combination of carbon and sulphur, and hence it has been called carburet of sulphur. This carburet of sulphur is transparent and colourless when pure, but very frequently it has a greenish yellow tinge. Its taste is pungent, and its odour very peculiar and penetrating. Its specific gravity is 1.3. It does not mix with water. When put into the receiver of an air- pump, and the air exhausted, it rises in bubbles through the water, and assumes the form of a gas. The same change takes place when it is introduced into the top of a barometer tube ; but it is again condensed into a liquid, when the tube is immersed under mercury. Carburet of sulphur burns easily, like alcohol and many other fluids. During the combustion it emits a sulphu- reous odour. Sulphur is deposited, and charcoal remains behind. When a little of it is put into a bottle filled with oxigen gas, it dissolves in it, and assumes the gaze- ous state. If a burning taper be applied to the mouth of the bottle, this mixture burns instantaneously, and with an explosion so violent as to endanger the vessel. It as- Combination of Sulphur xvith Carbon and Phosphorus, 191 sumes the gazeous form in the same way when placed in contact with atmospheric air. This mixture does not detonate when kindled, but burns quietly. Carburet of sulphur dissolves phosphorus readily ; it dissolves like- wise a small portion of sulphur, but it has no action whatever on charcoal.* The combination of sulphur with phosphorus will br considered in the next part. ' Ann. de Chim. 42,1> PHOSPHORUS. PART XII. SECT. I. NATURAL HISTORY OF PHOSPHORUS. PHOSPHORUS is the next simple body we have to consider ; it has never been found pure in nature. It is always met with united to oxigen, or in the state of phos- phoric acid : in that state it exists very plentifully, and is combined to different animal, vegetable, and mineral sub- stances. PHYSICAL PROPERTIES OF PHOSPHORUS. Phosphorus is a flesh-coloured or yellowish semi-trans- parent substance, of the consistence of wax, but brittle during frost. In atmospheric air it is luminous at com- mon temperatures, without emitting heat. It has a rough disagreeable taste, and its odour resembles that of garlic. Its specific gravity is 2.033, water being 1.000. Phos- phorus crystallizes in laminae, in needles, or elongated octahedra. Exposed to the light it becomes covered with a crust, which is first white, next orange, and at last red. It becomes liquid at a temperature of 99° Fahr. It has a strong attraction for metallic oxids. It takes fire spontaneously, and burns rapidly in the open air at 122* Fahr. with a brilliant white flame, and becomes con- verted into phosphoric acid. It is volatilized at 554° Fahr. It is soluble in caustic alcalies by the assistance of heat. Expressed and essential oils, take up a small quantity, and Methods of obtaining Phosphorus. 193 are rendered luminous. Sulphuric ether, nitric ether, and ardent spirit, dissolve it sparingly in the cold. It combines with lime, strontia, barytes, sulphur, charcoal, and with metals. It is soluble in hidrogen gas, and de- composes nitric acid and metallic solutions. It acts strongly, and frequently like poison, on living animals. METHODS OF OBTAINING PHOSPHORUS. For some time phosphorus was made in very inconsi- derable quantities, and by a tedious and disagreeable pro- cess, consisting in evaporating considerable quantities of urine, and decomposing them by various means. The following processes now employed are more easy and expeditious. 1. GIOBERT'S PROCESS. According to this method phosphorus may be obtained without any offensive preparation. It consists in pouring a concentrated solution of nitrate of lead, by a little at a time, into a quantity of urine until no more cloudiness is produced by a further addition of the solution. The mix- ture is then to be diluted with soft water, and suffered to stand undisturbed: when the precipitate has fullv sub- sided, the clear fluid is to be separated. The precipitate is formed into a paste with charcoal powder, the mass dried gradually in an earthen pan, and submitted to dis- tillation. Rationale....The phosphoric acid of the urine unites to the lead of the nitrate of lead, and the nitric acid joins to the ammonia and soda of the urine ; hence phosphate of lead and nitrate of soda and ammonia are formed. The former, being insoluble, falls to the bottom, and the latter salt remains in the super-natant fluid. On adding char- coal to the phosphate of lead, and exposing it to a high temperature, the union is again broken: the phosphoric acid becomes decomposed, its oxigen unites to the char- coal and forms carbonic acid gas, which flies off during the distillation ; the phosphorus appears in its simple state, and the metal is left behind in the retort, together with the super-abundant quantity of charcoal. 194 Methods of obtaining Phosphorus. 2. NICOLA'S PROCESS. Take a quantity of bones of adult animals, burn them to whiteness in an open fire, and reduce them to a fine powder. Upon three pounds of this powder, after having been put into a matrass, there may be poured one pound of concentrated sulphuric acid of commerce ; four or five pounds of water must be afterwards added by degrees, to assist the action of the acid. During the whole process the operator must place himself and the vessel so that the fumes of the mixture may be blown from him. The whole is then to be left in a gently heated sand-bath for about twelve hours or more, taking care to supply the loss of water which happens by evaporation. The next day a large quantity of water must be added, the clear liquor afterwards decanted, and the rest strained through a cloth or sieve. The residuary matter is to be edulcorated by repeated affusions of cold water, till it passes tasteless. The water which has been used to wash out the adhering acid is mixed with the before decanted or strained liquor, and the whole fluid is gradually evaported in a flat earthen bason to the consistence of syrup. It is then to be mixed with four ounces of charcoal powder, and submitted to distillation in an earthen retort. Instead of applying a receiver, the neck of the retort may be immersed in a bason of water to a small depth, and the phosphorus as it comes over will fall in drops to the bottom. Rationale....The first part of the process consists in destroying the gelatine of the bones, by the action of heat. They then consist of phosphate of lime, mixed with a very little carbonate of lime. In the second part of' the pro- cess, the phosphate of lime is decomposed by the sul- phuric acid : this decomposition is, however, only partial. The sulphuric acid combines with part of the lime, and forms an insoluble sulphate of lime. The phosphoric acid, separated from that portion of lime, immediately combines with the rest of the phosphate, and produces a super-phosphate of lime, which is no further decom- posable by sulphuric acid. The super-phosphate of lime thus formed is soluble in water, but as the sulphate of lime with which it is mixed concretes into a very thick or solid mass, it is in Methods of moulding Phosphorus into Cylinders, 195 some measure defended from the action of the water; hence a large quantity of water is necessary to dilute the mass. It is from this super-phosphate of lime that the phosphorus is obtained. The charcoal at an elevated temperature takes the oxigen from the phosphoric acid, and hence the phosphorus passes over. Three pounds of bones yield l^oz. and 30 grs. of phosphorus, if the process be well conducted. METHOD OF PURIFYING PHOSPHORUS. Phosphorus obtained in either manner is of a dirty blackish colour, and soiled, with a certain quantity of charcoal and oxid of phosphorus, which gives it that ap- pearance. In order to purify it, it must be put into a piece of chamois leather, and closely tied up in it. The whole is then immersed in a vessel of hot water; the phosphorus melts, and may be pressed through the lea- ther, taking care to keep it under the water. It is better, however, to purify phosphorus by a second distillation. Dr. Higgins purified it by means of hidrogen gas.* METHODS OF MOULDING PHOSPHORUS INTO CYLINDERS. In order to form phosphorus into sticks, a funnel with a long neck may be used, the lower orifice of which is closed with a cork: the funnel is then to be filled with water, and phosphorus put in it; and this being plunjged into boiling water, the heat communicated to the funnel melts the phosphorus, which runs into the neck, and ac- quires that form. The funnel is then removed into a vessel of cold water; and when it is thoroughly cooled, the cork is taken out and the phosphorus thrust out of its mould with a piece of wood, and then preserved in water. Pelletier invented another method, which is as follows : Take a few tubes of any length, the apertures of which are of such a size that they can be exactly closed with the extremity of the finger. Melt the phosphorus in boiling * Minutes of the Society for Philosoph. Exper. &c. 9 196 Proofs of the Properties of Phosphorus. water, and apply to it one of the ends of the tube, while you hold the other in your mouth ; make a short inspira- tion, that the phosphorus may ascend a little way in the tube ; stop the inspiration when the phosphorus has risen a sufficient height, and close the extremity of the tube with the fore finger, and immerse it in a bason of cold water. The phosphorus will soon become fixed, and by a slight shake may be separated from the tube. The combustibility and luminous property of phospho- rus have given birth to various amusing experiments; which we shall insert, for they are well calculated to evince some of its characteristic properties in a pleasing manner. SECT. II. EXPERIMENTAL PROOFS OF THE PRO- PERTIES OF PHOSPHORUS. Experiment I. Phosphorus burns at the common temperatures of the atmosphere. LUMINOUS CHARACTERS. TH AT phosphorus burns at the usual temperature is obvious by writing with a cylinder of it upon black paper, or upon any other smooth surface. The writing appears luminous in the dark, as if on fire: the fiery appearance vanishes by blowing on the object, but becomes visible again in a few seconds. If the writing is performed upon the purple coloured paper of this country, the traces appear red in the day- light after the luminous appearance has ceased. Rat ion ale....The phosphorus has been converted into phosphoric acid, which changes the blue vegetable colour of the paper to red : the light evinces the combustion of the phosphorus. Proofs of the Properties of Phosphorus. 197 Rem ark.... It is necessary to place the cylinder of phosphorus in a quill or metallic pencil case, in order that it may be removed from the hands, if it should take fire ; which may happen, particularly in hot weather. A cup or bason of water should likewise be near at hand to plunge it into, to prevent accidents. Experiment II. Phosphorus takes fire by the application of a very gentle heat. Introduce a few pieces of phosphorus, of the size of a pin's head, into tow or cotton, and wrap the cotton round a phial, or glass cylinder; on filling the phial with hot water, the phosphorus inflames and sets fire to the cotton. Experiment III. Accension of phosphorus by friction. Fold up in a piece of brown paper a few grains of phos- phorus, and rub it against any hard body, or between the paper itself; the phosphorus inflames and sets the paper on fire. A few grains of phosphorus rubbed in a mortar with iron filings, take fire instantly. Rationale....The friction applied in these experi- ments raises the temperature of the phosphorus ; it then attracts the oxigen from the atmosphere rapidly, in or- der to become converted into phosphoric acid, and the heat and light both of the phosphorus and oxigen gas are set free. Rem ark....It is curious that written paper inflames more readily than paperwhichhasnot been written upon. Straw and wood are extremely difficult to be fired by burning phosphorus, they become only converted into charcoal ; but sulphur, cotton, ardent spirit, ether, and essential oils, take fire by it readily. Experiment IV. A phosphoric fire-bottle. Take a small thin phial, heat it gradually in a ladle full vol. i. e e 198 Proofs of the Properties of Phosphorus. 'of sand, and introduce into it a few grains of phosphorus ; the phial is then to be loosely stopped, and left undis- turbed for a few minutes : small quantities of phosphorus are thus repeatedly added until the phial is full. Another method of preparing this phosphoric bottle consists in heating two parts of phosphorus and one of lime mixt together in a loosely stopped phial for about half an hour. To use this fire-bottle, a common match or small bit of wood tipped with sulphur is introduced into the phial, turned round and quickly drawn out, which causes the phosphorus to take fire as soon as it comes out of the bottle. Phosphoric fire-bottles may also be prepared by adding to melted phosphorus under water one sixteenth of sul- phur. This compound is so inflammable that if a minute quantity be taken out of the bottle with a match, and rubbed upon a cork, it inflames instantly, and fires the match. Experiment V. Phosphoric tapers. lake a glass tube, about four inches long and one line wide, closed at one end. A small quantity of phosphorus is to be introduced into the tube, and pushed to its ex- tremity with an iron wire, after which a taper covered at one end with wax is put into it; the open end of the tube is then hermetically sealed, and the other plunged into hot water. The phosphorus melts and fixes as it cools upon die taper. A line is then drawn by means of a diamond or file at one-third of the tuba. To use these tapers, the tube is broken at the marked line ; and when it is quickly drawn out, it takes fire, and burns rapidly. Experiment VI. Phosphorized ether. If phosphorus be dissolved in rectified sulphuric ether, and poured into a decanter, at the bottom of which is a little water, a brilliant light is disengaged, which passes with a serpentine motion along the surface of the fluid. Proofs of the Properties of Phosphorus. 199 The air within the vessel becomes luminous, and remains for some time in this state. 1. If the decanter be unstopped, and air blown into it, the luminous vapour disappears: but if the mixture be again agitated,"several luminous points are seen at its sur- face, the air of the decanter becomes again phosphores- cent, and this may be renewed until the whole of the ether has been decomposed. 2. If a feather be dipped in water, and in this state be plunged into phosphorized ether, at the moment of con- tact of the two fluids, a sudden light spreads through the air, and very perceptible flashes are seen (in a dark place) to issue from time to time out of the mouth of the phial. 3. When a lump of fine loaf-sugar is wetted with phos- phorized ether, and thrown into a bason of water, the whole of the surface will be illuminated ; by gently blow- ing it, beautiful undulations are formed, greatly resem- bling the fiery appearance of the sea. All these experiments with phosphorated ether succeed best if the water be a little warm. Rationale....The phosphorized ether is decomposed on coming in contact with a large quantity of water; the water unites with the ether; the phosphorus being then presented to the air, burns, and exhibits the luminous appearance. Phosphorized ether is best prepared by suffering sul- phuric ether to stand for some weeks over a considerable quantity of phosphorous in a well-stopped phial. Experiment VIL Liquid Phosphorus. When phosphorus is dissolved in oils, it forms what is called liquid phosphorus. The best method of preparing it, is to heat very gently one part of phosphorus with six of oil of olives. The oil thus charged with phosphorus must be kept in a bottle, well corked. It may also be pre- pared by rubbing in a mortar one part of phosphorus with one-sixteenth of sulphur and a small quantity of olive oil, until a perfect homogeneous mass is obtained, and then adding gradually more oil to effect a solution. Liquid phosphorus has the property of becoming luminous in tlv ^00 Proofs of the Properties of Phospttorus. dark as soon as the phial containing it is unstopped, and opaque again when the phial is corked. It may serve for showing the hour of the night, by holding a pocket-watch against the bottle when unstopped. It may likewise be used for forming luminous writings, or drawings, by means of a small brush. It may also be rubbed on the face^ hands, &c. to make them appear luminous, without in- jury. Liquid phosphorus may likewise be prepared by tritu- rating phosphorus in a stone mortar, vv ith oil of cloves. This method is expensive. Experiment VIII. Accension of phosphorus by means of sulphuric acid and •water. Melt over a slow fire, in a cup, gallipot, or phial, con- taining a table-spoonful of water, a small quantity of phos- phorus ; as soon as the water boils, pour into it about one drachm of concentrated sulphuric acid. In a few minutes the surface of the mixture becomes filled with luminous vapours, a considerable ebullition takes place, accom- panied with a hissing noise, which increases gradually until the mixture takes fire, with a smart explosion. Lit- tle fire-balls and stars \\ ill be thrown out in all directions, and the whole will boil very high. T'ATioNALE....This accension of phosphorus is owing " to :ie heat evolved by the mixture of the acid and water. Remark....To perform the experiment with safety, the vessel containing the water and r. . lted phosphorus should be fastened to the end of a long stick, in order that the operator may be at a sufficient distance when the explosion takes place, as it frequently happens that the vessels are dashed to pieces the moment the mixture is made, and the whole is thrown about to a considerable distance. Experiment IX. Phosphorus precipitates copper in a metallic state. Put into a concentrated solution of nitrate, or sulphate of copper, a cylinder of phosphorus, and leave it undis- turbed for at least twenty-four hours. The phosphorus Proofs of the Properties of Phosphorus. 201 will precipitate the copper, and by that means become co- vered with a stratum of brilliant metallic copper. Rationale....The phosphorus has a stronger affinity for oxigen than copper has ; it therefore deoxidizes the solution of this metal, and the copper re-iippears in its metallic state. M. Schnaubert has lately examined the action of phos- phorus in metallic solutions,* from which it appears that the solutions of gold, silver, mercury, lead, tin, and manganese, are all deoxidized by phosphorus, and that, when reduced, in many cases again unites to another por- tion of the phosphorus, forming phosphurets, as is the case in the deoxidizement of the solutions of silver, mer- cury, and tin. Experiment X. A luminous fluid which throws out flashes oflight. Water boiled with a little phosphorus for a few minutes, and preserved in a well-corked phial, becomes luminous in the dark. Long cylinders of glass, filbd two-thirds with this solution a little warmed, and then agitated, dis- charge flashes of light in all directions into the air. Rationale....Part of the phosphorus is dissolved by the water, and remains in combination with it so long as this fluid is at rest, but becomes disengaged when the water is agitated; it then burns, and exhibits the lumi- nous appearance. Experiment XL Phosphorized mercury May be prepared by dissolving phosphorus by tritura- tion in a mortar, in as little oil of cloves as possible, and then uniting this mixture to mercury, by a continual agitation. Long cylinders filled with this compound become lu- minous when shaken in the dark. Rationale....A simple spontaneous combustion of minutely divided phosphorus. * Goetling's Fascbenbucb, 1804, v. i. p. 99. 202 Combination of Phosphorus with Metals. COMBINATION OF PHOSPHORUS WITH METALS. Experiment I, Phosphuret of arsenic. Phosphuret of arsenic may be obtained in the follow- ing manner: Take two parts of metallic arsenic, reduce it to an impalpable powder, put it into a Florence flask, and pour over it six of water, and then add one of phos- phorus. Place the flask over the lamp-furnace, and apply a gentle heat for at least three hours, taking care to sup- ply the water as it evaporates. The phosphuret of arse- nic thus obtained is of a brilliant gray colour ; it may be freed from the adhering or superfluous phosphorus, by squeezing it through a fine muslin, under the surface of heated water. Experiment II. Phosphuret of copper. To obtain phosphuret of copper, let the finest copper wire that can be obtained be coiled up into a ball, and heated to redness in a crucible, and then let fall on it pieces of phosphorus, until the copper melts. The phos- phuret thus obtained is of a yellowish white colour: on being broke, it exhibits a crystalline appearance. It soon loses its lustre on exposure to the air, and becomes black. Experiment III. Phosphuret of gold. This compound may be obtained in a similar manner, by letting fall pieces of phosphorus on fine gold wire, heated to whiteness, expeditiously covering the crucible the moment the phosphorus has reached the gold wire. Phosphuret of gold is of a brass-yellow colour. It is very brittle, and exhibits, on being broken, needle-shaped crystalst Combination of Phosphorus with Metals. 203 Experiment IV. Phosphuret of iron. To obtain this phosphuret, let fine iron wire be heated as before, and drop into the crucible pieces of phosphorus of the size of a pea, until an union is effected, which may be known by the wire melting down suddenly. The pro- perties of this phosphuret have not yet been examined. Experiment V. Phosphuret of lead. Phosphuret of lead may be prepared by melting lead in a crucible, and then adding to it phosphorus in small quantities at a time. By the first addition of phosphorus, the lead acquires consistence ; but on increasing the heat, and continuing the addition, the whole becomes again fluid, which is the criterion that the process is at an end. It is of a silver white, but soon tarnishes on exposure to air. Experiment VI. Phosphuret of nickel. Phosphuret of nickel may be formed by melting nickel, and letting fall on it phosphorus. The union is very dif- ficult to be obtained: one part of nickel requires about eleven of phosphorus. The phosphuret obtained fuses more easily than nickel. It is a white crystalline sub- stance ; its properties have not yet been examined. Experiment VII. Phosphuret of silver. Phosphuret of silver is best prepared by heating to red- ness, in a crucible, fine silver, rolled out as thin as writ- ing paper, and then letting fall on it phosphorus, in small quantities at a time, until the fresh added portion of phos- phorus combines with the ignited silver. Phosphuret of silver is of a white colour, and of a granulated texture. It is very hard, and soon tarnishes on exposure to air. 204 Combination of Phosphorus with Alcalies. Experiment VIII. Phosphuret of cobalt May be formed by heating to redness, in a crucible, cobalt, broken into pieces of the size of a split pea, and then adding to it gradually pieces of phosphorus of the same size, until the cobalt fuses. Phosphuret of cobalt is of a reddish-white colour: it is very brittle, and fuses more easily than cobalt. COMBINATION OF PHOSPHORUS WITH ALCALIES. Experiment I. Preparation of phosphuret of lime. Take an earthen or glass tube, about one foot long and three-quarters of an inch in diameter, and closed at one end : put into this one ounce of phosphorus^ cut into pieces of the size of a pea, and freed, by means of blotting- paper, from the adhering water; then introduce into the tube three ounces of fresh burnt lime of the size of split peas, and stop the other opening of the tube loosely with a chalk stopper, to prevent the access of air. Having done this, heat to redness that part of the tube -which contains the lime, by means of charcoal: when the lime maybe sup- posed to be ignited, apply heat to the part containing the phosphorus, so as to sublime it, and to bring the vapour of it into contact with the ignited lime. The lime and phos- phorus will now unite and fo m a mixture of a reddish- brown colour, which is phosphuret of lime. This pre- paration has the property of making fire rise out of wa- ter, when small pieces of it are dropt into it. Rationale....'! he phenomenon is owing to a decom- position of water at the common temperature, which shall be more fully treated on under the article phosphorized ' hidrogen gas. Rem ark....If a glass tube be made use of for preparing phosphuret of lime, that part of the tube which is heated (which ma\ conveniently be done by passing it through the universal furnace, or through a chafing dish, filled with ignited charcoal) should be coated with clay, or Combination of Phosphorus with Carbon. 205 loam, in order to secure it from breaking during the process. Phosphuret of lime may also be prepared, according to Von Mons,** in the following manner: Fill a small glass matrass two-thirds with carbonate of lime in powder: put it into a sand-bath, and expose it to a heat sufficient to drive off the carbonic acid. Towards the end of the process introduce gradually a third part of phosphorus, taking care to keep the lime in a red heat. The phosphorus melts, but is prevented from burning by the remains of carbonic acid which is disengaged from the lime. When the whole of the phosphorus is introduced. shut up the matrass with a stopper provided with a valve to let gas escape, but permit none to enter, and let the fire be immediately withdrawn. When quite cold the phos- phuret is to be put in a dry bottle. Experiment II. Phosphuret of barytes. To prepare phosphuret of barytes, introduce into an earthen tube, closed at one end, first, one part of phos- phorus, and then add two of fresh prepared barytes, and proceed as directed before. Phosphuret of barytes is of a brownish yellow colour: it also causes phosphorized hidrogen gas to be evolved when thrown into water. Experiment III. Phosphuret of strontia. Phosphuret of strontia may be obtained in a similar manner. COMBINATION OF PHOSPHORUS WITH CARBON. Phosphorus is also capable of combining with carbon, or rather with charcoal. This compound, which has received the name oi phosphuret of carbon, was first examined by Mr. Proust. It is the red substance which remains behind when new made phosphorus is strained through chamou- * Journal de Chim. iii. 75. VOL. I. k f 206 Combination of Phosphorus with Carbon. leather. In order to separate from it a small quantity of phosphorus, which it contains in excess, it should be put into a retort, and exposed for some time to a moderate heat. What remains behind in the retort is the pure phosphuret of carbon. It is a light flaky powder, of a lively orange red, without taste or odour. When heated in the open air, it burns rapidly, and a quantity of char- coal remains behind. When the retort in which it is formed is heated red hot, the phosphorus comes over, and the charcoal remains behind.* This phosphuret of carbon may also be obtained by putting a few grains of phosphorus in a silver spoon, and then heating the spoon, to cause the phosphorus to burn. After the combustion of the phosphorus has ceased, a red trace will be observed in the spoon, which is carburet of phosphorus ; hence the pure phosphorus always contains a portion of this compound, from which it cannot be freed by any process yet known. * Ann. de Chim. xxxiv. 44. DIAMOND, OR PURE CARBON. PART XIII. SECT. II. NATURAL HISTORY OF DIAMOND. IT appears at first extraordinary .nat the diamond, which has been so long placed in the rank of precious stones, or crystallized gems ; that the diamond, one ^f the hardest bodies in nature, should at present be reckon- ed in the class of combustible bodies, next to sulphur and phosphorus. It is nevertheless entitled to this place, as will be seen presently. The diamond, which was well known to the ancients, is principally found in the western peninsula of India, on the coast of Coromandel, in the kingdoms of Golconda and Visapour, in the island of Borneo, and in the Brazils. Diamonds are generally found bedded in yellow ochre, or dispersed among rocks of free-stone or quartz, and sometimes in the beds of running waters. It is not known whether there is any rock where the diamonds are found which has some of the properties of these bodies, or which has served as a matrix for their formation. They do not lie in clusters; but are always found detached, at a greater or less distance, .'hose mines which yield large diamonds frequently do not contain above one in a quarter of an acre ; those that yield small diamonds contain a greater number in the same space. There are about twenty-three :u» Natural History of Diamond. diamond mines in Golconda, and fifteen in Visapour. The depth of these mines is commonly three or four fathoms. The miners can seldom dig deeper, on account of the wa- ter, which they have no method of removing. In one of the Golconda mines, they are obliged to dig through rock five or six feet deep, before they come to the stratum of earth in which the diamonds are deposited. They work through this rock with great difficulty, as they seem to be altogether unacquainted with the use of gunpowder in mining. They, however, in some measure supply its place by lighting a large fire on that part of the rock through which they intend to pass: when the heat has penetrated the rock to a sufficient depth they split it, by throwing cold water upon it. .Diamonds, when taken out of the earth, are incrusted with an exterior earthy covering, under which is another, consisting of carbonate of lime. This earthy incrustation covers them so perfectly, that it is with the utmost difficulty that they can be distin- guished from an indurated iron ore. It adheres so strongly to them, upon many occasions, that it cannot be got off but by grinding or rubbing them against one another. From this, as well as from the foreign matter that is frequently found in the centre of diamonds, it would appear that they were once in a soft or fluid state, or that it was not till long after their first formation that they acquired that hard- ness for which they are so much valued. In consequence of the diamond, when bedded in the earth, having so lit- tle of the lustre by which it is easily distinguished in its polished state, it is necessary to examine the earth in which they lie with the utmost attention. In order to render this as easy as possible, the lighter earths, and those parts that approach in quality to common mould, are removed by agitating the whole in water, and pour- ing off immediately the muddy fluid. As the diamond is among the heaviest of the earthy and stony substances, there is little danger of its being carried off in this man- ner. Those parts which are not carried off by the water are dried in the sun, and carefully examined. Every thing that has the smallest resemblance to the diamond is rubbed against the common kinds of stone. If it does not discover itself to the satisfaction of the miners by this method, they strike it with violence against a hard body, and sometimes with the iron instrument with which Physical Properties of Diamond. 209 they work. By this imprudent method many of the finest diamonds have such cracks or flaws in them that their value is greatly diminished. In the Brazils it is supposed that diamonds might be obtained in greater quantities than at present, if the suf- ficient working of the diamond mines was not prohibited, in order to prevent that diminution of their commercial value which a greater abundance of them might occasion. Rem ark....Brazilian diamonds are in commercial esti- mation inferior to the oriental ones. In the rough, diamonds are worth two pounds sterling the carat, or four grains, provided they are without blemish. The expence of cutting and polishing amounts to. about four pounds more. The value, however, is far above what is now stated when they become considerable in size. The usual method of calculating the value of diamonds is by squaring the number of carats, and then multiplying the amount by the price of a single carat: thus, suppos- ing one carat to be £2, a diamond of 8 carats is worth £128, being 8x8X2. The famous Pigot diamond weighs 188^ grains. The following very remarkable diamonds, with regard to size and value, may be noticed. 1. That which is in the possession of the Great Mogul; its weight is 279 carats, and is valued at six millions of florins, about £540,000 sterling. 2. That belonging to the Grand-duke of Tuscany weighs 139 carats, and is valued at one million of florins, about £90,000 sterling. 3. That in the possession of the King of Portugal weighs 215 carats. 4. The diamond which the Stadtholder Pitt sold to the Duke of Orleans, for the King of France, for 1,500,000 livres. Its weight is 547 grains ; and there was one in the crown of the late King of France, of 106 carats. 5. Mr. Gregor Saffraz, of the family of Gogia Minarian, was in possession of a diamond from the East Indies, weighing 779 grains. And, 6. The rough, diamond from Brazil, in the possession of the King of Portugal, weighs 1680 carats. This is tlv largest diamond known. 210 Physical Properties of Diamond. PHYSICAL PROPERTIES OF DIAMOND. Diamond is always crystallized ; but sometimes so im- perfectly, that at first sight it might appear amorphous. The figure of the diamond when perfect is an eight-sided prism. There are also cubical, flat, and round diamonds. It is the oriental diamond which crystallizes into octo- hedra, and exhibits all the varieties of this primitive figure. The diamond of Brazil crystallizes into dodecahedra. The texture of the diamond is lamellated, for it maybe split or cleft with an instrument of well-tempered steel, by a swift blow in a particular direction. There arc, however, some diamonds which do not appear to be form- ed of lamina;, but of twisted and interwoven fibres, like those of knots in wood. These exceed the others great- ly in hardness; they cannot be cut or polished, and are therefore called by the lapidaries diamonds of nature. The diamond is one of the hardest bodies known. It resists the most highly tempered steel file, which circum- stance renders it necessary to attack it with diamond powder. It takes an exquisite and lasting polish. It has a great refractive power; and hence its lustre, when cut into the form of a regular solid, is uncommonly great. It sparkles with all the splendour of the rainbow, princi- pally when its effects are multiplied by cutting, and the number of the polished facets with which it is enclosed. The usual colour of diamonds is a light gray, often in- clining to yellow, at times lemon colour, violet, or black, seldomer rose-red, and still more rarely green or blue, but more frequently pale brown. The purest diamonds are perfectly transparent. The colourless diamond has a spe- cific gravity which is in proportion to that of water as 3.512 to 1.000, according to Brisson. This varies, how- ever, considerably. When rubbed it becomes positively electric, even before it has been cut by the lapidary. Diamond is not acted upon by acids,.or by any chemi- cal agent, oxigen excepted; and this requires a very grent increase of temperature to produce any effect. It then burns with flame and decrepitation. The diamond burns by a strong heat, even in common air, with a sensible flame, like other combustible lx>dies. Proofs of the Combustibility of Diamond. 211 attracting oxigen, and becoming wholly converted into carbonic acid gas during that process. It combines with iron by fusion, and converts it, like common charcoal, into steel; but diamond requires much more oxigen to burn in than common charcoal doe s, and even then it consumes but slowly, and ceases to burn the instant its temperature is lowered. It is considered by modern chemists as PURE CRYS- TALLIZED CARBON. SECT. II. PROOFS OF THE COMBUSTIBILITY OF DIAMOND. THE combustibility of the diamond is a phenomenon sufficiently interesting to induce us to give an extract of the principal experiments which have served to advance our knowledge upon this subject. The emperor Francis I. exposed to a vehement heat the value of six thousand florins in diamonds and rubies ; the diamonds disappeared, but the rubies remained unal- tered. These experiments were repeated ; and it was ascertained that the diamond lost its polish, scaled off^ and was dissipated. The Grand-duke of Tuscany, in 1694, caused experi- ments to be made by Averoni and Targioni, by the mir- ror of Tschirnhausen, and the diamond disappeared in a few minutes. These experiments were repeated by the French che- mists, Darcet, Cadet, Lavoisier, &c. with equal success. The details of their experiments may be seen in the vo» lumes of the Academy of Sciences, and the Journal de Physique for the year 1772. Macquer took notice that the diamond dilated, swelled, and burnt with a blue flame. Ladriani* mentions an experiment, in which the diamond was fixed to the end of a small iron wire, which was heated red hot, and plunged into a vessel filled with oxigen gas. The com- bustion of the iron communicated itself to the diamond, * Annales de Chiro. torn. xi. p. 156. 212 Proofs of the Combustibility of Diamond. which burnt in this gas with a very bright flame. This experiment, however, did not succeed with the diamond of Brazil. Lavoisier and Cadet proved that the combustion of the diamond, in close vessels, like all other combustible bodies, ceased as soon as the oxigen was exhausted, and that it only burnt in proportion to the oxigen presented to it. De Saussure burnt a diamond by means of the blow- pipe. But as the sole object of all the former experiments was to ascertain the combustibility of the diamond, no attention was paid to the products it afforded during the process ; and it still remained to be determined whether the diamond was a distinct substance, or one of the known inflammable bodies. No attempt was made to decide this question, till Lavoisier, in 1777, undertook a series of experiments for this purpose. He exposed the diamond to a large lens, -and was thus enabled to burn it in a close glass vessel. He observed that the air, in which the diamond had been burnt, became absorbed by wrater ; that it disturbed lime- water ; and that the precipitate obtained was soluble in acids with effervescence. Carbonic acid had therefore been formed. As nothing was present but diamond and oxigen, and as carbonic acid gas consists of charcoal, oxigen, and caloric, the diamond and oxigen must have been converted by caloric into the state of carbonic acid gas ; and hence the diamond must have been charcoal. The diamond is therefore a combustible body, which burns in the same manner in oxigen gas as charcoal does. This strict and accurate consequence is deduced from all the experiments which can be imagined to acquire a per- fect demonstration. But that the diamond was charcoal in its pure and crystallized state was left to the determin- ation of modern chemists. Guyton-Morveau applied the solar heat, by means of a great lens, to a diamond placed in a china cup, and sur- rounded in a proper apparatus, with a confined quantity of oxigen gas. In one experiment the diamond exhibited, first, ablack point at the angle directly struck by the solar rays ; after this, it soon became completely black, and of a coaly ap- pearance ; the instant afterwards, brilliant and as it were Proofs of the Combustibility of Diamond. 213 boiling points were distinctly perceived on the black ground. It now began to diminish in size, and in a short time no more than one-fourth was remaining. It was then withdrawn. It was without any marked sharp angles or edges, but still very white, and of a beautiful transparen- cy. The diamond was a second time heated with the solar rays, and in twenty minutes entirely consumed\vith- out any residue. During this operation the same pheno- mena were observed. A solution of barytes was then introduced over the mercury, confining the air in which the diamond had been consumed. It became immediately milky, the vo- lume of the gas diminished, and carbonate of barytes was formed. In this process a greater quantity of carbonic acid was obtained than would have been produced had the dia- mond been in the same state as common charcoal: for one part of charcoal absorbs during combustion 2.527 of oxigen, and produces 3.575 of carbonic acid ; but one part of diamond absorbs somewhat more than four parts of oxigen, and produces five of carbonic acid. The diamond of which Guiton effected the complete combustion was a native octohedral crystal. It burned in a temperature of about 90 pyrometrical degrees, which in the scale of Wedgwood constitutes a difference of from 183° to 1765°. We are likewise indebted to Dr. Smithson Tennant for some excellent experiments on the nature of the diamond. His paper of which we shall give an abstract, is in the Philosophical Transactions for 1797. Dr. Tennant has taught us a method of effecting the combustion of the diamond in a much easier manner than that stated above. He has proved that, by means of nitrate of potash, the combustion maybe accomplished in a moderate heat. The Dr. procured a tube of gold, which having one end closed, served as a retort, to which a glass tube was adapted, in order to collect the air produced. To be cer- tain that the gold vessel was perfectly closed, and that it did not contain any thing which could occasion the pro- duction of carbonic acid, some nitrate of potash was heat- ed and decomposed in it, and afterwards washed out with water. The solution was examined, but did not exhibit any appearance of carbonic acid. vol. i, g g 214 Proofs of the Combustibility of Diamond. The diamond was then burnt in this vessel by means of nitrate of potash. When it was thus destroyed, the sub- stance which remained precipitated lime from lime-water; and on the addition of acids, afforded carbonic acid gas and nitrous gas, and therefore consisted of nitrate of pot- ash partly decomposed, and carbonate of potash. In order to estimate the quantity of carbonic acid which might be obtained from a given quantity of diamonds, two grains and a half of small diamonds were put into the golden tube, with a quarter of an ounce of nitrate of pot- ash, the whole was then kept in a strong red heat for about an hour and a half. After the tube had grown cold again, the contents were dissolved in water, consequently the diamonds had been destroyed. In order to ascertain the quantity of carbonic acid, the contents which had been dissolved were decomposed by muriate of lime: hence muriate of potash and carbonate of lime were obtained. This carbonate of lime was sepa- rated from the supernatant muriate of potash, and intro- duced into a glass globe, having a tube annexed to it. This globe and tube were then filled with mercury, and in- verted in a vessel containing the same fluid. The lime by that means was made to occupy the very top of the tube. It now remained to separate the carbonic acid from the lime: it was therefore mixed with muriatic acid ; by this means, 10.3 ounce measures of carbonic acid gas, or nearly 9.166 grains, were separated; but, according to the experiments of Lavoisier, this gas is composed of 72 parts of oxigen and 28 of carbon: 9.166 grains, therefore, contain 2.56 grains of carbon, which is almost the weight of the dia- mond consumed ; and hence it follows, that it was com- posed of, pure carbon, or the pure acidifiable basis of the carbonic acid. The combustion of the diamond is effected at three dif- ferent temperatures. At the first and least elevated tem- perature the diamond assumes a gray and black colour: this is the first degree of oxidation ; it is the state of the plumbago and of the antracolite, or incombustible pit- coal. At the second degree of temperature there is anew. slow, and successive combination of oxigen; it then con- stitutes the habitual state of our charcoal. Proofs of the Combustibility of Diamond. 215 . Supposing, therefore, we could operate with sufficient precision to take from the surface of the diamond the black matter in proportion as it formed, during our ex- periment for burning it, we should undoubtedly convert the whole diamond into charcoal. At the third degree of combustion the diamond is wholly converted into carbonic acid gas, as we have shown before. Guy ton Moveau has likewise converted soft iron into cast steel, by means of the diamond, in the following manner:* A cavity was bored in a block of soft iron, and a stopper fitted to it of the same metal. Into the cavity was put a diamond, with some filings of the block of iron, to fill the remaining space, after which the stopper was driven in. In this state the whole was put into a crucible, and this placed into another. The space between the two crucibles was filled with pure siliceous sand. The exter- nal crucible was well closed and luted, and the whole ex- posed to the strong ignition of a blast-furnace, by which the metal was fused completely; the diamond disappear- ed, and the iron was thus converted into steel. After all this, it will no doubt be demanded how it happens that the pure carbon or diamond is so scarce, whilst, when combined with oxigen, in the state of char- coal it is so abundantly dispersed through nature? We obtain by our chemical decompositions of bodies charcoal and not diamond. No chemist speaks of our exhaling diamond by respiration, but many of charcoal, or at least carbonic acid. To any disbelief of this matter it must be answered, that iron exists every where, under every form, except in the state of perfect purity, or uninsulated ; for the ex- istence of pure native iron is still doubtful. The wonder consists, therefore, only in the difference between facts and our opinions ; it vanishes in proportion as we disco- ver and appropriate the powers of nature to produce the same effects. After these considerations of the facts now discovered regarding the diamond, the mind naturally turns itself to the possibility of forming diamonds by artificial processes. It cannot be said that this discovery, if made, would be o! * Annates de Chim. xxxi. p. 328 216 Proofs of the Combustibility of Diamond. any great advantage to mankind. It is difficult to con ceive to what use this substance could be generally ap- plied ; and though the mention of a method of making diamonds might possibly procure a handsome fortune to the inventor, a publication of the process would infallibly lessen the value of diamonds so prodigiously, that the manufacture would considerably sink in value. If what has been advanced before be right, there is no want of materials from which diamonds might be made. All na- ture abounds with charcoal, or its combinations; whole mountains, nay kingdoms, are composed of chalk and limestone, in which diamonds ought to be contained in astonishing abundance. But, plentiful as this principle may be, there appears at present no likely method of ob- taining it pure or uninsulated. The diamond is advantageously used, on account of its excessive hardness, to engrave on hard stones and glass, or to cut them into convenient pieces. It is also used as an ornament. The extreme hardness, the labour of cut- ting and polishing it, together with its rarity, render it precious without the assistance of the caprice of fashion. Before we proceed farther in the description of simple substances, it will be necessary to illustrate the nature and production of gases, together with their properties; for the agency of these bodies produces so considerable a number of the phenomena which distinguish some bodies from others, that without a previous acquaintance with them a great number of the experiments illustrative of the properties of simple substances would be unintelli- gible. NATURE AND FORMATION OF GASES. PART XIV. SECT. I. NATURE OF GASES. .-* BY the word gases we distinguish permanently elastic aeriform fluids, or substances which have the appearance of air; that is to say, they are transparent, elastic, ponder- able, invisible,* and not condensible into a liquid or solid state by any degree of cold hitherto known. Some of the gases exist in nature, without the aid of art, and may therefore be collected; others, on the con- trary, are only producible by artificial means. All gases are combinations of certain substances, reduc- ed to the gazeous form by the addition of caloric and light. It is therefore necessary to distinguish in every gas the matter of heat which acted the part of a solvent, and the substance which forms the basis of the gas. Gases are not contained in those substances from which we ob- tain them in the state of gas, but owe their formation to the expansive property of caloric. The bases of some gases are known to us, and may be exhibited in an uncombined state ; others again are not producible by art. * Oxigenated muriatic acid gas, and nitrous acid gas, are the only exceptions to this rule. 218 Formation of Gase.s. FORMATION OF GASES. It has been mentioned before, that the different forms under which bodies appear depend upon a certain quantity of caloric chemically combined with them. The very formation of gases corroborates this truth. Their pro- duction totally depends upon the combination of particular substances with caloric j and those we call permanently elastic are only so because we cannot so far reduce their temperature as to dispose them to part with it; otherwise they would undoubtedly become fluid or solid. Water, for instance, is a solid substance in all degrees below 32° of Fahrenheit's scale; above this temperature it combines with caloric and becomes a fluid. It retains its fluidity under the ordinary pressure of the atmosphere, till its temperature is augmented to 212°. It then com- bines with a larger portion of caloric, and is converted apparently into gas, or at least into elastic vapour; in which state it would continue if the temperature of our atmo- sphere was above 212°. Gases are therefore solid sub- stances, between the particles of which a repulsion is established by the quantity of caloric. But as in the gazeous water or steam the caloric is retained with but little force, on account of its quitting the water when the vapour is merely exposed to a lower temperature, we do not admit steam amongst the class of gazes, or permanent aeriform elastic fluids. In gases, caloric is united by a very forcible affinity, and no dimi- nution of temperature or pressure that has ever yet been effected can separate it from them. Thus the air of our atmosphere in the most intense cold still remains in the aeriform state; and hence is derived the essential cha- racters of gases, namely, that they shall remain aeriform, under all variations of pressure and temperatures. In the modern nomenclature, the name of every sub- stance existing in the aeriform state is derived from its solid base; and the term gas is used to denote its existence in this state. In order to illustrate the formation of gases, or to show in what manner caloric is combined with them, the fol lowing experiment may serve. Pneumatic Apparatus. 219 Experiment I. Put into a retort, capable of holding half a pint of wa- ter, two ounces of muriate of soda (common salt) pour on it half its weight of sulphuric acid, and apply the heat of a lamp ; a great quantity of gas is produced, which might be collected and retained over mercury. But to serve the purpose of this experiment, let it pass through a glass re- ceiver, having two openings, into one of which the neck of the retort passes, whilst from the other a bent tube proceeds, which ends in a vessel of water. Before clos- ing the apparatus, let a thermometer be included in the receiver, to show the temperature of the gas. It will be found that the mercury in the thermometer rises only a few degrees, whereas the water in the vessel which re- ceives the bent tube will soon become boiling hot. RATioNALE....Common salt consists of muriatic acid united to soda; on presenting sulphuric acid to it a de- composition takes place. The sulphuric acid unites by virtue of its greater affinity to the soda, and forms sul- phate of soda, or Glauber's salt; the muriatic acid be- comes therefore disengaged, and takes the gazeous form, in which it is capable of existing in our temperature. To trace the caloric during this experiment, as was our ob- ject, we must remark, that it first flows from the lamp to the disengaged muriatic acid, and converts it into gas; but the heat thus expended is chemically united, and there- fore not appreciable by the thermometer. The caloric, however, is again evolved, when the muriatic acid gas is condensed by the water with which it forms liquid mu- riatic acid. In this experiment we therefore trace caloric in a che- mical combination producing gas; and from this union we again trace it in fire or sensible heat. Such in general is the cause of the formation and fixa- tion of gases. It may be further observed, that each of these fluids loses or suffers the "disengagement of differ- ent quantities of heat, as it becomes more or less solid in its new combination, or as that combination is capable of retaining more or less specific heat. PNEUMATIC APPARATUS. The discovery of aeriform or gazeous fluids has occa- sioned the necessity of some peculiar instruments, by 220 Method of collecting Gases. means of which those substances may be conveniently collected and submitted to examination. The principal ones for that purpose are styled the pneumatic apparatus. THE PNEUMATIC RESERVOIR OR CISTERN Is made either of wood or strong sheet-iron tinned, ja- panned, or painted. A trough of about two feet long, six- teen inches wide, and fifteen high, has been found to be sufficient for most experiments. Two or three inches * below its brim, a horizontal shelf is fastened, in dimen- sion about half Or one-third part of the width of the trough. In this shelf are several holes: these holes must be made in the centre of a small excavation, shaped like a funnel, which is formed in the lower part of the shelf. This trough is filled with water sufficient to cover the shelf to the height of an inch. The use of this shelf is to support receivers, jars, or bell-glasses, which, being previously filled with water, are placed invertedly, their open end turned down upon the above-mentioned holes, through which the gases, conveyed there and directed by means of the funnel-shaped exca- vations, rise in the form of air-bubbles into the receiver. When the gazeous fluids are capable of being absorbed by water, as is the case with some of them, the trough must be filled with mercury. The price and gravity of this fluid make it an object of convenience and economy, that the trough should be smaller than when water is used. A mercurial trough is best cut in marble, free-stone, or a solid block of wood. A trough about 12 inches long, 3 inches wide, and 4 deep, is sufficient for all pri- vate experiments. SECT. II. METHOD OF COLLECTING GASES AND TRANSFERRING THEM FROM ONE VESSEL TO ANOTHER. PREVIOUS to undertaking experiments on gases, it may be well for the unexperienced operator to accustom Methods of collecting Gases. 221 himself to the dexterous management of collecting and transferring common air. Experiment I. Methods of transmitting air from one vessel to another. If we are desirous of transferring air from one vessel to another it is necessary that the vessel destined to re- ceive it be full of water, or some fluid heavier than air. For that purpose, take a wide-mouthed bell-glass or re- ceiver, plunge it under the water in the trough in order to fill it, then raise it with the mouth downwards, and place it on the shelf of the trough, so as to cover one or more of the holes in it. It will now be full of water, and continue so as long as the mouth remains below the surface of the fluid in the cistern; for in this case the water is sustained in the ves- sel by the pressure of the atmosphere, in the same man- ner as the mercury is sustained in the barometer. It may without difficulty be imagined, that if common air (or any other fluid resembling common air in lightness and elasticity) be suffered to enter the inverted vessel filled with water, it will rise to the upper part on account of its levity, and the surface of the water will subside. To ex- emplify this, take a glass or any other vessel, in that state which is usually called empty, and plunge it into the water with its mouth downwards, scarce any of it will enter the glass, because its entrance is opposed by the elasticity of the included air; but if the vessel be turned with its mouth upwards, it immediately fills, and the air rises in bubbles to the surface. If this operation be performed under one of the jars or receivers which are filled with water, and placed upon the perforated shelf, the air will ascend in bubbles as before; but, instead of escaping, it will be caught in the upper part of the jar, and expel part of the water it contains. In this manner we see that air may be emptied out of one vessel into another by a kind of inverted pouring ; by which means it is made to ascend from the lower to the upper vessel. When the receiving vessel has a nar- row neck, the air may be poured in a similar manner through an inverted funnel inserted in its mouth. vol. i. h h ~~~ Classification of Gases. If the air is to be transferred from a vessel that is stop- ped like a bottle, the bottle must be unstopped with its ori- fice downwards in the water, and then inclined in such a manner that its neck may come under the perforated ex- cavation of the shelf. The gas will escape from the bot- tle ; and, passing into the vessel destined to receive it, will ascend in it in the form of bubbles. In whatever manner this operation is performed, the necessity of the excavation in the lower part of the shelf may be readily conceived. It is, as mentioned before, destined to collect the gas which escapes from the vessel, and direct it in its passage towards the vessel adapted to receive it. Without this excavation, the gas, instead of proceeding to the place of its destination, would be dis- persed and lost. The vessels or receivers for collecting the disengaged gases should be glass cylinders, jars, or bell-glasses of various sizes ; some of them should be open at both ends, others should be fitted with necks at the top, ground per- fectly level, in order that they may be stopped by ground flat pieces of metal, glass, slate, &c. others should be fur- nished with ground stoppers ; some should be graduated into cubic inches, and subdivided into decimal or other equi-distant parts. Besides these, common glass bottles, tumblers, &c. may be used. CLASSIFICATION OF GASES. All the elastic aeriform fluids with which we are hither- to acquainted are generally divided by systematic writers into two classes ; namely, those that are respirable and ca- pable of maintaining combustion, and those that are not respirable and incapable of maintaining combustion. Thie division indeed has its advantage ; but the term respira- ble, in its physicological application, has been very dif- ferently employed by different writers. Sometimes by the respirability of a gas has been meant its power of sup- porting life, when repeatedly applied to the blood in the lungs. At other times all gases have been considered re- spirable which were capable of introduction into the lungs by voluntary efforts, without any relation to their vitality. Classification of Gases. 223 In the last case the word respirable seems to us most pro- perly employed, and in this sense it will be used hereafter. Non-respirable gases are those which, when applied to the external organs of respiration, stimulate the muscles of the epiglottis in such a manner, as to keep it perfectlv close on the glottis ; thus preventing the smallest particle of gas from entering into the bronchia, in spite of volun- tary exertions. Of respirable gases, or those which are capable of be- ing taken into the lungs by voluntary efforts, according to their conditions, only one has the power of uniformly supporting life, namely, atmospheric air: other gases, when respired, sooner or later impair the health of the human constitution, or perhaps occasion death, but in different modes. Some gases effect no positive change in the blood; ani- mals immersed in it die of a disease produced by the pri- vation of atmospheric air, analagous to that occasioned by their submersion in water. Others again produce some positive change in.the blood, as appears from the experiments of Dr. Beddoes and Professor Davy. They seem to render it incapable of supplying the nervous and muscular fibres with principles essential to sensibility and irritability. These gases, therefore destroy animal life on a different principle. It is obvious, therefore, that the above classification does not hold good in all respects, but is capable of mis- leading the student. We shall not divide the gases we are going to treat of into different classes, for we do not see the advantage which can arise from any division; we shall therefore examine first those which are simple, the bases of which cannot be exhibited in an insulated state, namely, oxigen, nitrogen, and hidrogen gas. We shall then consider the combination of these gases with each other, in order to understand some of the most important phenomena in which they are concerned, together with the rest of those gases, of which the bases may be exhi- bited experimentally. OXIGEN GAS. PART XV. SECT. I. PROPERTIES OF OXIGEN GAS. OXIGEN gas is an elastic invisible fluid, like com- mon air, capable of indefinite expansion and compression. It has neither taste nor odour, nor does it show any tra- ces of an acid, Its specific gravity, as determined by Kirwan, is 0.00135, that of water'being 1.0000; it is therefore 740 times lighter than the same bulk of water. Its weight is to atmospheric air as 1103 to 1000. 116 cubic inches of oxigen gas weigh 39.38 grains. It is not ab- sorbed by water, but entirely absorbable by combustible bodies, which at the same time disengage its caloric and light, producing in consequence a strong heat and flame. It rekindles almost extinct combustible bodies ; it is indis- pensable to respiration, and is the cause of animal heat; it hastens germination ; it combines with every combus- tible body, with all the metals, and with the greater number of vegetable and animal substances; it is consi- dered as the cause of acidity, and from this last property is derived the name oxigen, a word denoting the origin of acidity. The act of its combining with bodies is called oxidation (oxidiZement) or oxigsnation (oxigenizement) and the bodies with which it is combined are called oxids. Oxigen gas is the chief basis of the pneumatic doctrine of chemistry. Methods of obtaining Oxigen Gas. 22S METHODS OF OBTAINING OXIGEN GAS. We are at present acquainted with a great number of bodies from which we tnay, by art, produce oxigen gas. It is most amply obtained from the oxids of manganese or mercury, from nitrate of potash, from the green leaves of vegetables, and from oxigenized muriate of potash, or soda. Besides these, there are a great many other sub- stances from which oxigen gas may be procured. Experiment I. To obtain oxigen gas from oxigenized muriate of potash. In order to procure oxigen gas in a state of great purity, pure oxigenized muriate of potash must be made use of. With this view, put some of the salt into a small earthen or glass retort, the neck of which is placed under the shelf of the pneumatic trough filled with water, and heat the retort by means of a lamp. The salt begins to melt, and oxigen gas will be obtained in abundance and of great purity, which may be collected and preserved over water. Rationale....Oxigenized muriate of potash consists of oxigenized muriatic acid and potash : at an elevated tem- perature a decomposition of the oxigenized muriatic acid takes place: its oxigen unites to the caloric, and forms oxigen gas. The oxigenized acid becomes therefore con- verted into simple muriatic acid, which remains in the retort united to the potash, in the form of muriate of potash. Experiment II. fo obtain oxigen gas from green leaves of vegetables. Oxigen gas may likewise be obtained from the green leaves of vegetables. For this purpose fill a bell-glass with water, introduce fresh gathered green leaves into it, and^place the bell or receiver inverted in a vessel containing the same fluid; 226 Methods of obtaining Oxigen Gas. expose the apparatus to the rays of the sun, and very pure oxigen gas will be liberated. The emission of oxigen gas is proportioned to the vigour of the plant and the vivacity of the light: the quantity differs in different plants, and under different conditions. (See page 157.) Rationale....It is an established fact, that plants de- compose water, and probably carbonic acid, which serve for their nourishment; they absorb the hidrogen and car- bon of these fluids, disengaging part of the oxigen in a state of purity. Light, however, favours this decompo- sition greatly; it seems to serve for melting the oxigen, and thus forms it into oxigen gas: in proportion as it becomes disengaged, the hidrogen becomes fixed in the vegetable, and combines partly with the carbon and partly with the oxigen, to form the oil, &c. of the vegetable. Experiment III. To obtain oxigen gas from nitrate of potash. Nitrate of potash is another substance frequently made use of for obtaining oxigen gas, in the following manner: Take any quantity of this salt, introduce it into an earthen or coated glass retort, and fit to it a tube, which must be plunged into the pneumatic trough under the receiver filled with water. When the apparatus has been properly adjusted, heat the retort gradually till it becomes red-hot, the oxigen gas will then be disengaged rapidly. The gas obtained in this way is also very pure, especially if the last portion be kept separate. Rationale....Nitrate of potash consists of nitric acid and potash. Nitric acid consists again of oxigen and nitrogen. On exposing the salt to ignition, a partial decomposition of the acid takes place ; the greatest part of the oxigen of the nitric acid unites to caloric, and appears under the form of oxigen gas. The other part remains attached to the potash in the state of nitrous acid. The residue in the retort is therefore nitrate of potash, if the process has been carefully conducted. Remark....If too much heat be applied, particularly towards the end of the process, a total decomposition of Methods of obtaining Oxigen Gas. 227 the nitric acid takes place ; the oxigen gas in that case will therefore be mingled with nitrogen gas. The weight of the two gases when collected will be found to correspond very exactly with the weight of the acid which had been decomposed: the residue then left in the retort is potash. Experiment IV. To obtain oxigen from black oxid of manganese. Black oxid of manganese, however, is generally made use of for obtaining oxigen gas, on account of its cheap- ness. This native oxid is reduced to a coarse powder; a stone, or rather an iron retort, to which a conducting tube has been fitted, is then charged with it and heated. As soon as the retort becomes ignited, oxigen gas is obtained plentifully. Rationale....Black oxid of manganese is the metal called manganese fully saturated with oxigen, together with many earthy impurities : on applying heat, part of the solid oxigen quits the metal, and unites to caloric, in order to form oxigen gas ,• the remainder of the oxigen remains united to the metal with a forcible affinity; the metal therefore reapproaches to the metallic state, or is found in the state of a gray oxid of manganese. One pound of the best manganese yields upwards of 1400 cubic inches of oxigen gas, nearly pure. If sul- phuric acid be previously added to the manganese, the gas is produced by a less heat and in a larger quantity; a glass retort may then be used, and the heat of a lamp is suffi- cient. Red oxid of mercury yields oxigen gas in a manner similar to that of manganese. Rationale....This oxid consists likewise of solid oxi- gen and mercury, the combination of which takes place on exposing mercury to a heat of about 610° Fahr. At this degree it attracts oxigen, and becomes converted into an oxid; but if the temperature be increased to about 1000° the attraction of oxigen is changed. The oxigen then attracts the caloric stronger than it did the mercu- ry ; it therefore abandons it and forms oxigen gas. The mercury then reappears in its metallic state. (See p. 79.) * ^ Red oxid of lead yields oxigen gas on the same principle. 228 Proofs of the Properties of Oxigen Gas. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF OXIGEN GAS. Experiment I. Oxigen gas is not absorbed by water. Let a cylindrical bell-glass be filled with oxigen gas, and agitate it in contact with water: the gas will not sensibly diminish in bulk, which is a proof that water does not absorb oxigen. It may, however, be made to com- bine with it, by means of artificial pressure. DECOMPOSITION OF OXIGEN GAS, BY BODIES DESTITUTE OF METALLIC PROPERTIES. Experiment II. Combustion of Phosphorus in oxigen gas. Fill a bell-glass or receiver with oxigen gas, confine it by mereury, and introduce a piece of phosphorus through' the quicksilver, which immediately will rise to the surface of it; then set fire to the phosphorus, by means of a crooked heated iron wire, introduced so as to touch it without disturbing the vessel. It will burn with a very brilliant flame. A considerable quantity of caloric and light will be liberated, and the whole inside of the glass will be covered with a white flaky crust, which will be found to be phosphoric acid ; and the mercury will have ascended considerably. Rationale....This experiment proves that a decompo- sition of the oxigen gas has taken place. The phosphorus ?.t ' a certain degree of heat is capable of decomposing this gas; it attracts its ponderable base the oxigen, and becomes converted into phosphoric acid; the light and heat, which kept the oxigen in a gazeous state, together with those of the phosphorus, are then disengaged in the form of fire. Proofs of the Properties of Oxigen Gas. 229 If the phosphorus is weighed before the experiment, and the quantity of oxigen gas has been also ascertained, the weight of the produced acid will be found equal to the sum of the weights of the phosphorus consumed and oxigen absorbed, if the experiment has been conducted carefully. Forty grains of phosphorus absorb generally sixty-five of oxigen. If the oxigen gas be pure, the residuum after com- bustion is as pure as the gas employed : this proves that nothing could escape from the phosphorus capable of altering the purity of the oxigen gas, and that the only action of the phosphorus is to separate the oxigen from the caloric with which it was before united. This property of being convertible into an acid belongs to all combustible bodies: hence the combination of oxigen with such a body is called oxigenation, or oxigenisement. Experiment III. Combustion of sulphur in oxigen gas. This experiment is best performed by filling a large receiver with oxigen gas in the water-apparatus, and removing it by means of a flat dish into the«#.ercurial trough, taking care to leave a little water over the mercury. When this is done, put a small piece of sulphur into a copper ladle, set fire to it by means of a candle and blow- pipe, and introduce it into the gas. The sulphur will burn with a beautiful blue flame: when the fumes have disap- peared, the water over the mercury will be found to have an acid taste ; it will turn blue vegetable colours red, and effervesce with carbonated alcalies. It is therefore an acid; and, as it is composed of sulphur and oxigen, it is called sulphuric acid. If the respective quantities of gas, sulphur, and water, have been previously ascertained, the water will be found to have increased in weight, as much as the sum of the weights of the sulphur and oxigen consumed. Rationale.....Sulphur is a simple combustible body, which possesses the property of decomposing oxigen gas at a high temperature, by attracting the oxigen from the caloric with which it was combined, in order to be con- verted into sulphuric acid. vol. i. i i Proofs of the Properties of Oxigen Gas. Experiment IV. Combustion of charcoal in oxigen gas. The oxigenation of charcoal may be effected like that of phosphorus, in the receiver placed over mercury. But as the heat of the red hot iron is not sufficient to ignite the charcoal, a small piece of tinder, with a minute particle of phosphorus, are brought in contact with it; these being set on fire will kindle the charcoal, which then will burn, and throw out scintillating sparks in all directions. After the combustion ceases, it will be found that the elastic.fluid under the receiver has not disappeared, as was the case in the former experiments ; but that a new pecu- liar kind of gas is formed. This air is unfit for respiration, and incapable of maintaining combustion. It is greatly absorbed by cold water, and vanishes by lime-water, barytic-water, or by other alcalies, which first are rendered turbid, and prove it to be an acid, consisting of charcoal and oxigen; hence it is called carbonic acid gas. Whatever quantity of gas remains after the absorption by alcalies is that portion of oxigen gas which has escaped the action of the charcoal during the combustion. Rationale....The charcoal in this case likewise effects a decomposition of the oxigen gas. When charcoal is ignited, its affinity for oxigen is stronger than that of caloric ; it therefore unites to it, and forms carbonic acid, which assumes the gazeous state at the temperature of our atmosphere. Part of the light and heat becomes liberated, and appears under the form of fire. DECOMPOSITION OF OXIGEN GAS BY ME- TALLIC SUBSTANCES. Oxigen has likewise a great affinity for another kind of combustible bodies, we mean those called metals; parti- cularly when heated to a certain degree. All metallic bodies, except gold, silver, and platina, have the pro- perty of decomposing oxigen gas, by attracting its ponder- able base (the solid oxigen) from the caloric and light, which kept it in its gazeous state. They then lose their properties and approach to the acid state. Proofs of the Properties of Oxigen Gas. 231 Experiment I. Combustion of arsenic in oxigen gast and production of arseneous acid. Put into a copper ladle a piece of metallic arsenic, having previously affixed to it a small bit of wood or charcoal. Set fire to the charcoal by means of the blow- pipe, and quickly introduce it into the gas. The charcoal being inflamed, it will communicate the combustion to the arsenic, which will burn with a beautiful white flame. The receiver will become filled with dense white fumes, and a coat of arsenic will gradually cover the whole inside of the receiver. When the combustion has ceased, or when all the arsenic is burnt, let the receiver be moved out of the water-trough. A coat of white powder will be observed floating on the water, which is arseneous acid. This may be collected, and added to that adhering to the sides of the receiver. Rationale....Arsenic is a simple combustible body; on being presented under these circumstances to oxigen gas, it attracts the basis of it, with which it unites, and forms arseneous acid. Experiment II. Combustion of iron in oxigen gas> This experiment may be exhibited in the mo6t conve- nient manner as follows: a glass receiver, with a narrow open neck, must be provided. It may be closed at the top with a cork, or a rough-ground flat piece of glass or metal. It is to be filled with water and put upon the shelf of the pneumatic trough. Oxigen gas is then conveyed into it in the usual manner. When the receiver is filled with gas, a shallow bason or dish with water must be brought near it, so that the receiver may be removed with the gas, and easily slid into the bason. The gas is thus confined by the water, and the receiver may be removed to any convenient place. Iron wire of about ^ of an inch in diameter must be coiled tightly round a stick of wood or glass, of about half an inch in diameter; the stick 232 Proofs of the Properties of Ogixen Gas. is then withdrawn, and the wire will form a length of spiral rings. This wire, extended to about the inside length of the receiver, must be fixed in a cork, so that it may hang vertically, and may be readily introduced at the top of the receiver, and kept, by means of the cork, firm therein: at the other extremity of the wire, a little thread dipped in sulphur, or a piece of wood, is to be fixed. The thread or wood is then lighted, and the wire quickly introduced into the receiver ; an intense deflagration of the wire immediately takes place, throwing out a num- ber of brilliant sparks, ascending in a spiral direction, - J with a beautiful sun-like body, giving in a darkened room a luminous appearance inconceivably striking. 1 If we examine the weight of the iron after combustion, we find it augmented in proportion to the quantity of ] oxigen it has absorbed. It has at the same time lost its metallic splendour, and obtained properties different from those it possessed before. The use of the heat employed for the first ignition is to j separate the particles of the metal from each other, and to diminish the attraction of cohesion or aggregation. i RATioNALE....The iron, when heated to a certain de- \ gree, decomposes the oxigen gas : the equilibrium of the attraction subsisting between the caloric and solid oxigen j being interrupted, it is acted upon by two separate and opposite forces, that of the attraction for caloric to remain 1 in the gazeous state, and that exerted by the metal: the latter power being greater, it unites with it, and gives out at the same time its caloric and light. The new substance ■■* produced, consisting of oxigen and iron, is called oxid of • iron. It is not an acid, but it is changed to an interme- \ diate substance, approaching to the acid state, though not possessing all the requisite properties. Experiment III. Combustion of zinc in oxigen gas. Take some turnings of zinc, form a ball of them, and affix it to a copper wire ; insert a small bit of phosphorus or charcoal into the ball, set fire to it, and introduce it quickly into a receiver filled with oxigen gas ; the zinc will thus take fire, and burn with a beautiful green flame surrounded by a white one. Proofs of the Properties of Oxigen Gas. 233 Rationale....This experiment is analogous to the former: the zinc unites to the oxigen of the gas at an elevated temperature, and the result is an oxid of zinc. Experiment IV. If a current of oxigen gas be conveyed to filings or turnings of metals, they will burn with great rapidity. For this purpose, fill » large bladder, or better fill the gazometer, with oxigen gas, and adapt to the bladder, or to the stop-cock of the gazometer, a tube ; by pressing the bladder, or by pressing down the ball of the gazometer, and ejecting the gas on a piece of excavated ignited char- coal, into which filings of metal have ben put, the metal will burn rapidly. The filings which exhibit the most brilliant appearance are those of zinc, copper, antimony, iron, and steel. DECOMPOSITION OF OXIGEN GAS BY VARIOUS OTHER SUBSTANCES. Experiment I. If a lighted wax taper fixed to an iron wire or ladle be let down into a vessel filled with oxigen gas, it will burn with great splendour. If the taper be blown out, and let down into the vessel of gas while the snuff remains red- hot, it instantly rekindles with a slight explosion, and burns vividly. Experiment II. A piece of the bark of charcoal, fastened to a copper wire ignited, and then immersed in the gas, throws out brilliant sparks. Experiment III. A mixture of nitrate of strontia and charcoal powder, previously ignited, burns with a rose-coloured fame. Experiment IV. ith oxigen. It has been with great plausibility conjectured, that de. tonations in the air, or claps of thunder, are similar ef- fects of the combustion of hidrogen and oxigen gas; and that the rain which falls so copiously at the time of thun- der-storms is owing to a sudden formation of water in the atmosphere, from the rapid combustion of the hidrogen and oxigen gases fired by an electric spark. The diminution or hidrogen and oxigen gases by their bases may also be shown in the following manner. Experiment XII. Fill a tall jar with oxigen gas, and fill also with hidro- gen gas a bladder, furnished with a stop-cock, and with a long brass pipe like the letter S, and drawn out to a fine point. On pressing the bladder a stream of gas will issue from the pipe, which may be set fire to, and brought cau- tiously under the inverted jar of oxigen gas. By this in- tercourse the stream of oxigen gas will be burnt in a con- Proofs of the Properties of Hidrogen Gas. 245 fixed portion of oxigen gas : by continuing the combustion a sufficient time, the water will rise gradually within the jar. On the first impression of the heat indeed a. small quan- tity of gas will escape from the jar, which will render it difficult to ascertain what degree of absorption actually takes place. But this loss may be prevented by using a jar, with a neck at the top, to which a compressed blad- der is firmly tied. The expanded air, instead of escaping through the water, will now enter the bladder at the top ; and when the experiment is closed and the vessels have cooled, it may be ascertained, by pressing out the gas from the bladder, what quantity of oxigen gas has been consumed. When this experiment is made with the sub- stitution of common air for oxigen gas, a diminution takes place, but much less considerable, viz. not amount- ing to one-sixth of the original bulk of the gases. Rationale.... The disappearance of the gases depends on the union of their bases, which takes place during the state of ignition, and forms water, as has been noticed already. • Though hidrogen gas unites with oxigen gas only by the effect of combustion, exerted by the contact of an in • flamed body, yet the hidrogen contained in a great num- ber of combinations, even solid, combines probably in va- rious ways hitherto unknown to us, and produces differ- ent with different bodies. It has been mentioned before that hidrogen gas kills an- imals when immersed in it; but this gas is not itself de- structive to animal life. Scheele first inspired it several times successively without danger, and almost without uneasiness. Other chemists and philosophers have since repeated this experiment with success. Pilatre de Rozier breathed hidrogen gas six or seven times from a bladder without inconvenience. VOL. I. NITROGEN GAS. PART XVII. SECT. I. PROPERTIES OF NITROGEN GAS. NITROGEN gas, or azotic gas, as it is also called, is not possessed of any remarkable property capable of cha- racterizing it; but is principally distinguished by certain negative qualities, namely: it is extremely hurtful to respiration, and quickly kills animals ;* plants thrive and even flourish in it; it has no sensible taste ; it neither reddens blue vegetable colours, nor precipitates lime or barytic-water; its weight is to common air as .985 to l.OOO. No combustible substance burns in nitrogen gas; but it is capable of combustion in combination with oxi- gen gas when exposed to the action of the electric spark : it is not absorbable by water; it is capable of dissolving sulphur,phosphorus, and charcoal, in minute quantities; it unites to hidrogen under certain conditions, and con- stitutes with it ammonia. When united to oxigen in dif- ferent proportions it produces atmospheric iir, gazeous oxid of azote or nitrogen, nitrous gas, nitrous acid, and ni- tric acid; it is a component part of all animal substances, and communicates to them their most distinctive cha- racters : it was discovered by Dr. Rutherford of Edin- burgh. * Hence the name azote, which signifies « destructive to life," from a and 1,<>>a- Methods of obtaining Nitrogen Gas. 247 Nitrogen gas has been found by Priestley in the Bath waters, and by Pearson in the Buxton waters. METHODS OF OBTAINING NITROGEN GAS. Nitrogen gas may be obtained by various means : for instance, it has been long since ascertained that air, which has served the purposes of combustion and respiration, is no longer proper for these uses. Chemists have avail- ed themselves of this circumstance, in order to obtain ni- trogen gas in the following manner. 1. Make a quantity of sulphuret of potash or sulphuret of iron into a paste with water, and place the mixture in a saucer or plate over water, on a stand raised above the fluid ; then invert over it a jar or bell-glass, and allow this to stand for a day or two. The air contained in the bell- glass will gradually diminish, as will appear from the ascent of the water, until only about three fourths of its original bulk remain. When no further diminution takes place, the vessel containing the sulphuret must be removed, and the re- maining air will be found to be nitrogen gas. Rationale....The moistened sulphuret of potash has a great affinity to oxigen; it attracts and separates it from the atmospheric air, and the nitrogen gas is left behind; the sulphur is during the experiment converted into sul- phuric acid, which unites to the alcali, and forms sulphate of potash. The water with which the sulphuret is moister - ed likewise undergoes a decomposition, as shall be more fully proved in another place. 2. Nitrogen gas may likewise be obtained from fresh animal substances. For this purpose cut a piece of lean muscular flesh into small pieces, introduce them into a retort, and pour over them nitric acid of commerce, di- luted with double its bulk of water. If the heat of a lamp be then gently applied the gas will be speedily obtained. Rationale....Animal substances are composed of ni- trogen, carbon, hidrogen, and oxigen. On adding nitric acid the equilibrium of the respective affinities is destroy- ed, the nitrogen gas becoming separated. That the nitric acid does not furnish the nitrogen gas is obvious, from its saturating after its action as large a 248 Proofs of the Properties of Nitrogen Gas. quantity of alcali as before; consequently it could not have suffered any alteration. REMARK....The fibrous part of animal matter is that which affords the most nitrogen gas ; next to this, all the concretive parts, such as the clot of blood ; next to that, albuminous matter, such as the serum and white of eggs, cheese : gelatinous substances afford the least. 3. Nitrogen gas may likewise be obtained by causing oxigenated muriatic acid gas to be received in a vessel containing liquid ammonia. Rationale....Ammonia consists of hidrogen and ni- trogen. The hidro. en of the ammonia unites to the oxigen of the oxigenated muriatic acid, and forms water; heat is evolved, the nitrogen becomes free, and the oxi- genated muriatic acid becomes converted into simple mu- riatic acid. Other methods of obtaining nitrogen gas will be given in the next part. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF NITROGEN GAS. Experiment I. Nitrogen gas is not absorbable by -water. TAKE a long glass tube, divided into equal measures, which are distinguished by marks made with a diamond or file; send up into it any quantity of nitrogen gas; on agitating it strongly over water no absorption will take place, the volume of the air will not be sensibly dimi- nished. Experiment II. Nitrogen gas does not exhibit signs of acidity. Fill a receiver with pure nitrogen gas, and introduce therein a piece of litmus paper, or a small quantity of Proofs of the Properties of Nitrogen Gas. 249 tincture of red cabbage, no change of colour will be pro- duced in either of them ; the gas therefore cannot be acid. Experiment III. Nitrogen gas does not maintain combustion, and is fatal to animal life. This may be proved by plunging a lighted taper into a glass filled with this gas; the taper will be immediately extinguished. If a small animal, such as a mouse or bird, be immersed in the gas, it instantly dies. Experiment IV. Nitrogen gas is capable of combustion with oxigen, at * high temperature. Take a barometer tube, the diameter of which is about the sixth part of an inch. Shut one of its ends with a cork, through the middle of which passes a small wire, with a ball of metal at each end. Fill the tube with mer- cury, and invert it into a bason of this fluid. Throw up into the tube as much of a mixture of 13 parts of nitro- gen gas and 87 parts of oxigen gas as will fill three inches. Through this gas, by means of the wire in the cork, pass a number of electric sparks ; the volume of the gas gra- dually diminishes, and in its place will be found nitric acid. Experiment V. A mixture of nitrogen gas and oxigen gas produces arti- ficial atmospheric air. Introduce into a bell-glass filled with water four parts of nitrogen gas and one of oxigen gas: after shaking the mixture well together, an air will be formed greatly re- sembling that of our atmosphere ; for if a lighted taper, or any other burning substance, be plunged into this fluid, it will burn in the same manner as it does in atmospheric air; it may be breathed with safety, and animals confined in it will live as long as in an equal quantity of atmosphe- ric air. * 250 Proofs of the Properties of Nitrogen Gas. REMARK....Though we are not capable of producing in this manner an air absolutely the same as that of the atmosphere, the fault is not to be attributed to oiujignor- ance of the quantity and quality of the gazeous bases, but to a difference in their union: in the atmosphere the union of the two gases is a true chemical combination, but in our experiments the mass of the formed air is a mere mechanical nature. Experiment VI. Nitrogen gas does not precipitate lime from lime-water. This may be proved by putting a quantity of lime-wa- ter into a tube filled with the gas, and shaking it. The transparency of the lime-water will not be injured. ATMOSPHERIC AIR. PART XVIII. THE whole globe of the earth is surrounded by, or is involved in, a fluid, called air, which though not perceiv- ed by our eyes is however manifested in various ways. Whatever has been hitherto stated relative to the dif- ferent kinds of aeriform fluids is chiefly important, be- cause the knowledge' of them is necessary to enable us to comprehend the nature of the air or gazeous fluid in which we are plunged the moment we are born, and in which we exist. This fluid which surrounds the earth to a consi- derable but unknown height above its surface is called THE ATMOSPHERE. As fishes are surrounded by water, and live and move in water, so are we human beings, and all other animals, surrounded by air, and live and move in air. A fish which is taken out of the water will die in a short time : and a human being, or any animal, taken out of the aeriai fluid, will in general die much sooner. Water gravitates towards the centre of the earth, and so does air. Hence as a fish or any body in water is pressed on every side by that fluid, so are other animals, &c. pressed on every side by the surface of air, and this pressure (as will be shewn hereafter) is very considerable. As the progressive motion of water from one place to- wards another is called a current of water, so the pro- gressive motion of the air is called in general wind. which according to the different velocities of that fluid is more particularly specified by the appellation of breeze. gentle wind, gale, &c. t 252 Gravity of Atmospheric Air. In treating of the different aeriform fluids which have hitherto been the subject of our consideration, it was ne- cessary in some measure to anticipate the present, and to intimate that the air of our atmosphere is not, as was for- merly supposed, a simple or homogeneous fluid, but that in reality it is composed of two distinct fluids, called oxigen gas and nitrogen gas. Strictly speaking, the air of our atmosphere is however not so simple a substance as to be formed only of two in- gredients. Besides the two bodies of which it is compos- ed, it contains a small portion of another gazeous fluid, called carbonic acid. It is also well known that a large portion of water is generally contained in the atmosphere, besides a great va- riety of substances which are subject to evaporation, and which are capable of existing in an aeriform state at the usual temperature. SECT. I: MECHANICAL EXAMINATION OF ATMOS- PHERIC AIR. BY mechanical examination we would be understood to mean such properties as are connected with sensible changes of motion, and which indicate the presence and agency of moving or mechanical powers. They are there- fore strictly the subject of mathematical discussion ; ad- mitting of measure, number, and direction ; notions in- deed purely mathematical. But as those mechanical pro- perties characterize, or are peculiar to all kinds of elastic aeriform or gazeous fluids, no objection occurs to us against the propriety of considering th< m here briefly. The mechanical properties of atmospheric air are GRAVITY, ELASTICITY, INDIVISIBILITY,and DILATABILITY. GRAVITY OF ATMOSPHSRIC AIR. Experiment I. To prove the weight of the air, a pair of common bellows may serve; thus, for instance, if we stop the * Gravity of Atmospheric Air. +5± nozzle and secure the valve-hole closely,having first blown or squeezed all the air out of them, we shall find that a considerable force is requisite for separating the boards. They are kept together by the pressure of the air, which surrounds them, in the same manner as if they were im- mersed in water. Experiment II. In like manner, if we stop the end of a syringe, after its piston has been pressed down qu te to the bottom, and then endeavour to draw it up, we shall find a considerable force necessary, viz about 15 pounds for every square inch of the section of the syringe. Exerting this force, we can draw up the piston and hold it there ; but the mo- ment we cease pulling, the piston rushes down again. We feel something as it were drawing in the piston, but it is solely the weight of the incumbent i.ir pressing it: and this obtains in every position of the syringe ; because the air is a fluid, and presses in every direction; nay, it presses on the syringe as well as on the piston; for if the piston b - suspended by its ring on a nail, it will re- quire a wi ight to draw down the syringe equal to that which is necessary to draw up the piston, and as soon as the syringe is freed from the weight it will spring up to its place again. That the air presses equally in all directions becomes obvious f-om the following experiments: Experiment III. In a tall phial let an orifice be made about three inches from the bottom : stop this orifice. Through a cork in the neck of the phial, insert along tube open at each end, and let the lower end be below the orifice in the side ot the phial. The mouth of the phial being closed up : bout the tube, pour water into the tube till it is full. Upon opening the orifice, the water will be discharged, till its surface in the tube is level with the orifice ; after which it will cease to flow, because the external lateral pressure of the air balances the perpendicular pressure upon th-: water in the tube. vol. J. ?i ni '254 Gravity of Atmospheric Air. Experiment IV. If a conical wine-glass be entirely filled with water, and covered with a flat piece of paper j on inverting the glass, the water will be kept from falling by the upward pressure of the air. Experiment V. If a vessel be perforated with small holes at the bottom, but closed at the top, the upward pressure of the air will keep water within the vessel, as will appear by successive- ly stopping and unstopping a small hole in the top. The pressure of the air may be shown by means of the air-pump. Experiment VI. Let the air be exhausted from a glass receiver placed on the pump, the vessel will be held fast by the pressure of the external air. Experiment VII. Let a small receiver be placed under a large one, and both be exhausted ; the larger will be held fast, while the small one, being protected from the pressure of the air, may be easily moved. Experiment VIII. If the hand be placed upon a small open vessel, in such a manner as to close its upper orifice, it will be held down with great force, if the vessel be exhausted. Experiment IX. If the mouth of an open receiver be closely covered With a piece of bladder, and then exhausted, the super- incumbent air will burst the bladder with a loud report. In a similar situation, a thin plate of glass may be broken. Experiment X. If i glass bulb with a long nc ek filled with water be put inverted into a vessel of the same fluid, placed under a receiver, and the latter be exhausted, on re-admitting the air, its pressure upon the surface of the water in the vessel will cause the fluid to rise up in the bulb. Gravity of Atmospheric Air, 255 Experiment XI. If on a plate, called a transferrer, the air be exhausted from a long receiver, and then water be admitted through a pipe by means of a stop-cock, the water will be pressed up, and form a fountain. Experiment XII. If the air be exhausted from a vessel, and by means of a cock kept so, and the vessel be weighed while it is empty, and again weighed when the air is re-admitted; the differ- ence will be the weight of the quantity of air the vessel -ontains. Experiment XIII. Fill a glass tube, about three feet long, and closed at one end, with mercury; then insert the open end in a cup or vessel of the same fluid. The mercury in the tube will be kept suspended, by the pressure of the external air on the surface of that which is on the open cup: when this pressure is removed by placing them under a receiver, and exhausting it, the mercury in the tube will sink, and rise again on re-admitting the air. On the gravity of the air depends the ascent of water in pumps, syphons, &c. and the phenomena of the barometer. The weight of the air compresses all fluids, and resists their dilatation ; it opposes the evaporation of fluids, &c. The gravity of the air resists the dilatation of the ani- mal fluids; for the blood often bursts through the skin, or from the lungs, on the top of high mountains, occasion- ing hemorrhages, &c. because the air is there considerably lighter than near the level of the sea. /• By the pressure of the air the sucking of animals, the art of cupping, and many other phenomena, are explained, too numerous to be noticed here. The operation of sucking \n general consists in removing the pressure of the atmosphere from a certain part of the surface, whilst that pressure is at liberty to act on some other part of the surface ; in consequence of which, the fluid is forced to ascend where the pressure has been removed or diminished. 256 Specific Weight of Atmospheric Air. If a man apply his mouth to the aperture of a bottle full of liquor, and holding his head straight up, he will not be able to suck any liquor out of it; but if a hole be opened at the bottom of the bottle, then the liq or maybe sucked out of it. And the same effect will take place if an open tube be set with one end in water, and a man apply his mouth to the other end, and suck. The mechanical part of the operation is as follows: by enlarging his chest, the man rarefies the air, and of course diminishes its pressure on the liquor which is immediately under the tube ; in consequence of which, the press"re of the atmosphere on the surface of the surrounding liquor forces it to ascend into the tube. Thus the doctrine of the gravity and pressure of the air being established, by the most unexceptionable evi- dence, we are erititled to assume, a priori, all its legitimate consequences. SPECIFIC WEIGHT OF ATMOSPHERIC AIR. A bulk of atmospheric air that is equal to an English quart, when taken near the level of the sea, and at about 50 Fahr. weighs at a medium about 16 grains, and the same bulk of ram-water at the same temperature weighs about 14621 grains. Hence rain-water is about 914 times specifically heavier than air. The pressure of the air is equal to about 15 pounds troy on every square inch, and this pressure is the same in every direction. A square mile contains 27,878,400 square feet. The earth's surface in round numbers is 200,000,000 square milrs, and therefore the pressure of the atmosphere circumfused about the whole surface of the earth is 12"',043,468",800,0O0',O00,00O pounds. The surface of a middle-sized man is about 14 square feet; he sustains therefore a weight of air that is equal at a medium to about 30,240 pounds troy, or 24,h821 pounds avoirdupois nearly, or 1777 stone and 4 pounds, or 11 tons, 2 cwt. \8\ lbs. Though our body supports such an enormous weight, we need not wonder at the freedom with which we tra- verse this atmosphere. We see fish move with as great ease in a much more dense and more ponderous fluid. We are not sensible of the weight of the air, on account Invisibility of Air. 257 of its being equally applied on every side, besides, that we have been accustomed to support it from our earliest in- fancy. Sensations to which we have at all times been habituated are not felt; we can perceive no difference where we have no standard to judge of variations. ELASTICITY OF ATMOSPHERIC AIR. That the air is an elastic fluid, or capable of compression and expansion, may be proved by a great number of ex- periments. In fact the elasticity or spring of the air pro- duces the same effect as the pressure, because the pressure is equal to the compressing force ; for if it were less, it is clear it would yield and be more compressed ; were it greater, it would not be so much reduced ; for action and re-action are always equal. The air-gun, the effects of which are generally known, illustrates the elasticity of the air, and shows the com- pression it is susceptible of. A foot-ball or bladder filled with air rebounds from any hard body. The elasticity of the air is also proved by fish and other animals. The former have received from nature various means of action ; among these is an air-bladder, which they contract or dilate at pleasure, and by this double property they ascend or descend in the water. INVISIBILITY OF AIR. The invisibility of air suggests the vulgar idea X>i its being nothing; but it must be considered that transpar- ent bodies, such as let the rays of light pass freely through them, cannot be seen. Thus water, glass, air, &c, cannot be perceived by an eye, which is entirely surrounded bv any of them. And even when that is not the case, we can only perceive those substances by the heterogeneous bodies which they may happen to contain, or by the refraction, inflection, &c. of the rays of light at their surfaces ; hence, when such bodies are absolutely pure, and their surfaces are removed from our sight, so that we cannot observe the bending of the rays of light at those surfaces, then it is impossible to discern the bodies themselves. 258 Dilatability of Air. If a glass botde entirely filled with perfect transparent water be situated against a dark place, so that no objecM may be seen through it, a person who looks directly at it will not be able to say whether the bottle be full of water or not. A fish, or man in water, will feel the water, but cannot see it. The particles which are seen moving about T"hen light passes through a hole in a room other- wise dark, are not the particles of air, but they are particles of dust, &c which float in the air. Hence, Atmospheric air when confined in vessels is absolutely invisible, and cannot be distinguished from the glass which contains it. It owes this property, as stated before, to the ready passage it affords to the rays of light, which are refracted without being reflected, and it is therefore des- titute of colour ; though some philosophers have per- suaded themselves that they discovered large masses of it to be of a blue colour, as is the case in the sky, or in view- ing extensive landscapes. But this is certainly a mistake ; the blue colour is occasioned by the vapours which are always mixed with the air, and which have the property of reflecting the blue rays more copiously than any other. It appears, from the very accurate observations of Saus- sure, that the colour of the sky acquires a deeper shade in proportion as it is viewed from a more elevated situa- tion.* Consequently at a certain height the blue will disappear altogether, and the sky appear black, that is to say it will reflect no light at all. DILATABILITY OF AIR. We have noticed already7 (page 98) that if a flaccid or half-blown bladder be exposed to the action of caloric, the air will be dilated so as to burst the'bladder. Experiment I. To the bottom of a hollow glass-ball let an open bended tube be affixed. Let the lower part of the bended tube be filled with mercury ; the external surface will be pressed by the weight of the atmosphere, and the air en- » Journal de Physique, March 1777, and Saussure's Voyages dans leg Alpes. Chemical Examination of Atmospheric Air, 259 closed in the ball of the tube by means of the mercury will be equally pressed by the spring of the air within the vessel. If the ball be immersed in boiling water, the in- creased elasticity of the included air will raise the mer- cury in the tube. REMARK....The theory of the Mongolfiers depends on the rarefaction of the air. In this case a given volume of atmospheric air is rarefied by heat, and kept separated from the common mass by a hollow vessel of cloth. This rarefied space may therefore be considered as consisting of a mass of air of greater levity than atmospheric air. It must therefore make an effort to rise in it. SECT. II. CHEMICAL EXAMINATION OF ATMOSPHE- RIC AIR. CHEMISTRY affords two general methods of investi- gating the constituent parts of bodies, Analysis and Syn- thesis ; that both of ^hese methods can be applied in the investigation of the nature of atmospheric air we shall endeavour to prove. From some ingenious experiments Lavoisier has de- monstrated, as stated already, that the air of our atmos- phere is not a simple homogeneous fluid, but consists of two elastic aeriform bodies, possessing very different pro- perties ; one of which is capable of supporting combustion and animallife,called oxigen gas, and the other is destruc- tive to animals and extinguishes fire, called nitrogen gas. The atmosphere contains some other gazeous fluids, or bodies capable of being dissolved or suspended in it, but in small quantities. Late experiments seem to have prov- ed that a minute quantity of carbonic acid is always con- tained in the air, for alkalies become effervescent; stron- tia, barytic, and lime-waters, acquire a pellicle on being exposed a sufficient time to the action of the air, even up- on the highest mountains. Water is likewise always found in the atmosphere, but the quantity of these mat- ters is extremely minute ; and experiments are still want- ing to prove satisfactorily that carbonic acid gas and water are always and every where present ii: our atmosphere. The former constituents must therefore be considered a? the two- substances of which atmospheric air is composed. 260 Analysis of Atmospheric Air. Sincethe nitrogen gas of the atmospheric air cannot be separated by any substance with which chemists are ac- quainted, the analvsis 01 air can only be attempted by ex- posing it to the action of those bodies which have the pro- perty of abstracting its oxigen. The oxigen gas being separated, the nitrogen is left behind, and the proportion of oxigen may be ascertained by the diminution of bulk, which once known, it is easy to determine the exact re- lative quantity of the component parts. ANALYSIS OF ATMOSPHERIC AIR. Experiment I. Fasten a straight piece of wax taper, about four inches long, upon a cork, then take an empty wine bottle, and hold it by the neck in an inverted position; light the taper, and introduce it quickly into the mouth of the bottle ; push in the cork in order to prevent the entrance of any air from without. The flame of the taper will burn well at first, but in a few mimites it will contract, grow dim, and at last be extinguished. If now the taper be quickly withdrawn, the mouth of the bottle being closed with the thumb, and the taper lighted again and introduced into the bottle, it will be immediately extinguished. On introducing the bottle in an inverted position into a bason of water, and then withdrawing the cork, the water will ascend into the bottle and fill the place of the air which has been lost. The following experiment will further illustrate this fact. Experiment II. Take a Florence flask, holding about a pint, put into it three or four grains of phosphorus, and cork it air-tight. Having done this, heat it gradually over a lamp. As soon as the phosphorus has been heated to a certain degree it takes fire, burning with a flame and a dense white smoke; but as it soon ceases to burn, heat the vesstl again, after it has cooled, to try if any more combustion will take place ; lastly, let the flask cool. If the vessel was perfectly dry, the inside of V ,vill be Analysis of Atmospheric Air. 261 lined with a white coating, but if it was moist this coating will be dissolved into a fluid (phosphoric acid.) After every thing has returned to its former tempera- ture, plunge the flask inverted under water and draw out the cork ; the water will ascend in it: hence a portion of the air it contained has disappeared. The water which has risen shows what quantity of air has been lost, if its cubic contents be compared with that of the whole vessel. The portion of air thus vanished will in general amount to about one-fifth of the whole that had been submitted to the experiment. If the flask, after the phosphorus was enclosed in it, be accurately weighed, and again after the combustion has taken place, no difference of weight will be found. The water forced up into the vessel changes the blue tincture of cabbage-juice to red ; an evident proof'of the presence of an acid. The remaining air is unfit for burning phosphorus or other bodies; animals are likewise suffocated in it. Rationale....Phosphorus is a simple body ; on being heated it analyses the atmospheric air, that is to say, the equilibrium of the affinity subsisting between the com- pound parts of the air, namely, the oxigen and the nitro- gen, is broken, on account of the phosphorus having a greater attraction for the oxigen than the nitrogen has, it therefore unites to it, and becomes by this addition con- verted into an acid, called phosphoric acid: the other part of the atmosptiere remains behind. The light and heat which are liberated during the combustion arise both from the oxigen gas and the phosphorus. Experiment III. Take a piece of lead or any other material considera- bly heavier than water, fasten into it perpendicularly metal wires of different lengths ; affix tapers to the extremities of these wires, and place the stand in the middle of a flat dish or bason half filled with water. Then light the tapers (which should differ in height five or six inches) and cover the whole with a tall cylindrical glass receiver. The tapers will burn duringthe first few minutes all alike, but after some time the highest one wili~a«sume a-bJue vol. i. n n 262 Eudiometry. colour, and the last be extinguished, and the crater in the dish will begin to rise ; the next taper in height will then burn dull and go out, and the others will be extinguished in succession. The water will rise at the same time con- siderably up into the glas. Rationale....The philosophy of this experiment is analogous to the former. The burning bodies effect in the confined quantity of atmospheric air a real analysis. They absorb the oxigen it contains and divest it of this princi- ple, leaving the nitrogen gas behind. Combustion there- fore consists in the absorption of oxigen gas by a combus- tible body, the basis of the oxigen being absorbed, and the caloric set at liberty. SECT. III. EUDIOMETRY, OR METHODS OF ASCER- TAINING THE PURITY OF AT- MOSPHERIC AIR. NO sooner was the composition of the atmosphere known, than it became an inquiry of importance to find out a method of ascertaing with facility and precision the relative quantity of oxigen gas contained in a given bulk of atmospheric air. The instruments in which the oxigen gas of a deter- mined quantity of air was ascertained, received the name of EUDIOMETERS, because they were considered as measurers of the purity of air. They are however more properly called OXIMETERS. The eudiometers proposed by different chemists are the following: 1. PRIESTLEY'S EUDIOMETER. The first eudiometer was made in consequence of Dr. Priestley's discovery, that when nitrous gas is mixed with atmospheric air over water, the bulk of the mixture diminishes rapidly, in consequence of the combination of the gas with the oxigen of the air, and the absorption of the nitric acid thus formed by the water. When nitrous gas is mixed with nitrogen gas, no dimi- nution takes place ; but when it is mixed with oxigen gas Scheele's Eudiometer. 263 in proper proportions, the absorption is complete. Hence it is evident, that in all cases of a mixture of these two gases, the diminution will be proportional to the quantity of the oxigen. Of course it will indicate the proportion of oxigen in . r; and by mixing it with different portions of air, it will indicate the different quantities of oxigen which they contain, provided the component parts of air be susceptible of variation. Dr. Priestley's method was to mix together equal bulks of air and nitrous gas in a low jar, and then trans- fer the mixture into a narrow graduated glass tube about three feet long, in order to measure the diminution of bulk. He expressed this diminution by the number of hundredth parts remaining. Thus, suppose he had mixed together equal parts of nitrous gas and air, and that the sum total was 200 (or 2.00) : suppose the residuum when measured in the graduated tube to amount to 104 (or 1.04) and of course that 96 parts of the whole had disap- peared, he denoted the purity of the airthus tried by 104. Remark....This method of analysing air by means of nitrous gas is liable to many errors. For the water over which the experiment is made, may contain more or less carbonic acid, atmospheric air, or other heterogeneous substance. 1'he nitrous gas is not always of the same composition, and is partly absorbed by the nitrous acid which is formed; the figure of the vessel and many other circumstances are capable of occasioning considerabhrdif- ferences in the results. Fontana, Cavendish, Ladriani, Magellan, Von Hum- bolt, and Dr. Falconer, have made series of laborious experiments to bring the test of nitrous gas to a state of complete accuracy; but notwithstanding the exertions of these philosophers, the methods of analysing air by means of nitrous gas are liable to so many anomalies, that we think it unnecessary to give a particular description of the differtit instruments invented by them. 2. SCHEELE'S EUDIOMETER Is merely a graduated glass cylinder, containing a given quantity of air, exposed to a mixture of iron filings and sulphur formed into a paste with water. The sub- stances may be made use of in the following manner : 264 De Marti's Eudiometer. / Make a quantity of sulphur in powder, and iron filings, into a paste with water, and place the mixture in a saucer or plate, over water, on a stand raised above the fluid; then invert over it a graduated bell-glass, and allow this to stand for a day or two. The air contained in the bell- glass will gradually diminish, as will appear from the as- cent of the water. When no further diminution takes place, the vessel con- taining the mixture must be removed, and the remaining air will be found to be nitrogen gas, which was contained in that quantity of atmospheric air. Rationale....The moistened sulphur and iron have great affinity to oxigen ; they attract and separate it from the atmospheric air, and the nitrogen gas is left behind; the sulphur during the experiment is converted into sul- phuric acid, which unites to the alcali and forms sulphate of potash. The air which is exposed to moistened iron and sul- phur gradually becomes diminished, on account of its oxigen combining with a portion of the sulphur which becomes converted into sulphuric acid, and its nitrogen remains behind. The quantity of oxigen contained in the air examined becomes thus obvious, by the diminution of bulk which the volume of air submitted to examination has undergone. Remark....The only error to which this method is li- able, is that the sulphuric acid which is formed acts on the iron and produces hidrogen gas, which joins to the nitrogen remaining after the absorption, and occasions an incorrect result; and hence it is that the absorption amounts in general to 0.27 parts, although the true quan- tity of oxigen is no more than from 0.21 to 0.22. 3. DE MARTI'S EUDIOMETER. f De Marti obviated the errors to which the method of Scheele was liable. He availed himself for that purpose of a hidrogenated sulphuret, formed by boiling sulphur and liquid potash, or lime-water, together. These sub- stances, when newly prepared, have the property of ab- sorbing a minute portion of nitrogen gas; but they lose this property when saturated with that gas, which is HumboWs Eudiometer, 265 easily effected by agitating them for a few minutes in contact with a small portion of atmospheric air. The apparatus is merely a glass tube, ten inches long, and rather less than half an inch in diameter, open at one end, and hermetically sealed at the other. The close end is divided into 100 equal parts, having an in- terval of one line between each division. The use of this tube is to measure the portion of air to be employed in the experiment. The tube is filled with water, and by allowing the water to run out gradually while the tube is inverted, and the open end kept shut with the finger, the graduated part is exacdy filled with air. These hundred parts of air are introduced into a glass bottle filled with liquid sulphuret of lime previously saturated with nitrogen gas, and capable of holding from two to four times the bulk of the air introduced. The bottle is then to be closed with a ground glass stopper, and agi- tated for five minutes. After this the stopper is to be withdrawn while the mouth of the phial is under water; and for the greater accuracy, it may be closed and agi- tated again. Lastly, the air is to be again transferred to the graduated glass tube, in order to ascertain the di- minution of its bulk.* 4. HUMBOLT'S EUDIOMETER, Consists in decomposing.a definite quantity of atmos- pheric air by means of the combustion of phosphorus, after which the portion of gas which remains must be measured. Take a glass cylinder closed at the top, and whose capa- city must be measured into sufficiently small portions by a graduated scale fixed on it. If the instrument be des- tined solely for examining atmospheric air, it will be sufficient to apply the scale from the orifice of the cy- linder down to about half its length, or to sketch that scale on a slip of paper pasted on the outside of the tube, and to varnish it over with a transparent varnish. This half of the eudiometrical tube is divided into fifty equidistant parts, which in this case indicate hundredth parts of the whole capacity of the instrument. * Journ.de Phys.LII.176. 266 Bertholefs Eudiometer. Into this vessel full of atmospheric air 'put a piece of dry phosphorus (one grain to every twelve cubic inches) close it air-tight and heat it gradually, first thesides near the bottom and afterwards the bottom itself. The phos- phorus will take fire and bum rapidly. After everything is cold, invert the mouth of the eudiometer-tube into a bason of water or mercury, and withdraw the cork. The water will ascend in proportion to the loss of oxigen gas the air has sustained, and thus its quantity may be ascertained. Analogous to this is 5. SEGUIN'S EUDIOMETER, Which consists of a glass tube of about one inch in dia- meter, and eight or ten inches high, closed at the upper extremity. It is filled with mercury, and kept inverted in this fluid in the mercurial trough. A small bit of phosphorus is introduced into it, which, on account of its specific gravity beting less than that of mercury, will rise up in it to the top. The phosphorus is then melted by means of a red-hot poker, or burning coal applied to the outside of the tube. When the phosphorus is liqui- fied, small portions of air destined to be examined, and which have been previously measured in a vessel gradu- ated to the cubic inch or into grains, are introduced into the tube. As soon as the air which is sent up reaches the phosphorus, a combustion wiL take place and the mercu- ry will rise again. The combustion continues till the end of the operation; but for the greater exactness, Mr. Se- guin directs the residuum to be heated strongly. When cold, it is introduced into a small vessel, whose capacity has been ascertained at the same time as that of the pre- ceding. The difference of the two volumes gives the quantity of the oxigen gas contained in the air subjected to examination. Remark....The objection to which this eudi.ometer is liable will be noticed in the next, which is said to be an improvement of this. 6. BERTHOLET'S EUDIOMETER. Instead of the rapid combustion of phosphorus, Ber- Davy's Eudiometer. 267 tholet has substituted its spontaneous combustion, which absorbs the oxigen of atmospheric air completely, and when the quantity of air operated on is small, the process is accomplished in a short time. Bertholet's apparatus consists of a narrow graduated glass tube, containing the air to be examined, into which is introuduced a cylinder or stick of phosphorus support- ed upon a glass rod, while the tube stands inverted in wa- ter. The phosphorus should be nearly as long as the tube. Immediately after the introduction of the phos- phorus, white vapours are formed which fill the tube, these vapours gradually descend and become absorbed by the water. When no more white vapours appear, the process is at an end, for all the oxigen gas which was pre- sent in the confined quantity of air, has united with the phosphorus; the residuum is the quantity of nitrogen of the air submitted to examination. REMARK....This eudiometer, though excellent of the kind, is nevertheless not absolutely to be depended upon ; for as soon as the absorption of oxigen is completed, the nitrogen gas exercises an action upon thr phosphorus, and thus its bulk becomes increased. It has been ascertained that the volume of nitrogen gas is increased to -fa part; consequently the bulk of the residuum diminished by ^ gives us the bulk of the nitrogen gas of the air examined; which bulk subtracted from the original mass of air, gives us the proportion of oxigen gas contained in it. The same allowance must be made in the eudiometer of Seguin. 7. DAVY'S EUDIOMETER. Until very lately the preceding processes were the me- thods of determining the relative proportions of the two gases which compose our atmosphere. Some of these methods, though very ingenious, are so extremely slow in their action, that it is difficult to ascer- tain the precise time at which the operation ceases. Others have frequently involved inaccuracies not easily removed. The eudiometer we are now going to describe is not only free from these objections, but the result it offers is always constant, it requires little address, and is very ex- 268 General Remarks. peditious; the apparatus is portable, simple, and conve- nient. Take a small glass tube graduated into one hundred equidistant parts ; fill this tube with the air to be exa- mined, and plunge it into a bottle or any other conveni- ent vessel, containing a concentrated solution of green muriate or sulphate of iron, strongly impregnated with nitrous gas. All that is necessary to be done is to move the tube in the solution a little backwards and forwards; under these circumstances the oxigen gas contained in the air will be rapidly absorbed; and condensed by the ni- trous gas in the solution, in the form of nitrous acid. N. B. The state of the greatest absorption must be marked, as the mixture afterwards emits a little gas which would alter the result. This circumstance depends upon the slow decomposi- tion of the nitrous acid (formed during the experiment) by the green oxid of iron, and the consequent production pf a small quantity of aeriform fluid (chiefly nitrous gas) which having no affinity with the red muriate, or sulphate of iron, produced by the combination of oxigen, is gra- dually evolved, and mingled with the residual nitrogen gas. The impregnated solution with green muriate is more rapid in its operation than the solution with green sul- phate. In cases when these salts cannot be obtained in a state of absolute purity, the common sulphate of iron of commerce may be employed. One cubic inch of mode- rately strong impregnated solution is capable of absorbing five or six cubic inches of oxigen in common processes; but the same quantity must never be employed for more than one experiment. GENERAL REMARKS. In all these different methods of analysing air, it is ne- cessary to operate on air of a determinate density, and to take care that the residuum be neither more condensed nor dilated than the air was when first operated on. If these things are not attended to, no dependence whatever can be placed upon the result of the experiment*, how carefully soever they may have been performed. It is General Remarks, 269 therefore necessary to place the air before and after the examination into water of the same temperature. If this and several other little circumstances have been attended to, for instance a change in the height of the barometer, &c. we find that air is composed of 0.22 of oxigen gas, and 0.78 of nitrogen gas by bulk. But as the weight of these two gases is not exactly the same, the proportion of the component parts by weight will differ a little ; for as the specific gravity of oxigen gas is to that of nitrogen gas as 135 : 115, it follows that 100 parts of air are compos- ed by weight of about 74 nitrogen gas 26 oxigen gas 100 The air of this metropolis, examined by means of Davy's eudiometer, I found in all the different seasons of the year to contain 0.21 of oxigen ; and the same was the case with air taken at Islington and Highgate, in the solitary cells in Cold-bath-fields prison, on the River Thames, and at Brighton. But the quantity of water contained in a given bulk of air from these places differed considerably. Having thus ascertained the nature and the proportion of the component parts of air, it remains only to i quire in what manner these component parts are united. Are they merely mixed together mechanically, or are they combined chemically ? Is air a mechanical mixture or a chemical compound ? Philosophers seem at first to have adopted the former of these opinions, if we except Scheele, who always considered air as a chemical compound. But the supposition that air is a mechanical mixture, by no means agrees with the phenomena which it exhibiis. If the two gases were only mixed together, as their specific gravity is different, it is scarcely possible that they would be uniformly mixed in every part of the atmosphere. Since therefore air is in all places composed of the same ingredients, exactly in the same proportions, it follows that its component parts are not only mixed, but actually combined. When substances differing in specific gravity combine together, the specific gravity of the compound '15 usually greater than the mean. This holds good also with respect to air. The specific gravity, by calculation, amounts only to 0.00119, whereas it actually is 0.0012. vol. 1. 00 270 General Remarks. We must therefore consider air as a chemical compound. Hence the reason that it is in all cases the same, notwith- standing the numerous decomposing processes to which it is subjected. The breathing of animals, combustion, and a thousand other operations, are constantly abstract- ing its oxigen, and decomposing it. The air thus decom- posed or vitiated, no doubt, ascends in the atmosphere, and is again, by some unknown process, re-converted in- to atmospheric air. But the nature of these changes is at present concealed under an impenetrable veil. CARBONIC ACID GAS. PART XIX. SECT. I. CARBONIC acid gas is the first elastic aeriform fluid that was known. We find that the ancients were in some measure acquainted with it. Van Helmont called it the gas of Must, or of the vintage, or gas sylvestre. We are indebted to Dr. Black of Edinburgh for the knowledge of some of the most remarkable properties of this fluid. In the year 1755 he discovered the affinity between this gas and the alcalies: and Bergman, in 1772, proved that it was an acid. PROPERTIES OF CARBONIC ACID GAS. Carbonic acid gas is invisible. It extinguishes flame. It is fatal to animal life. It exerts powerful effects on living vegetables. Its state is pungent and acid. Its energy, as an acid, is but feeble, although distinct and certain. Neither light nor caloric seems to produce any distinct ef- fect upon it, except that the latter dilates it. It mixes without combining with oxigen gas. It unites with water 272 Methods oj obtaining Carbonic Acid Gas. slowly. These two fluids, after considerable agitation, at last combine, and form a sub-acid fluid. The colder the water, and the greater the pressure applied, the more carbonic acid gas will be absorbed. The water impreg- nated with it sparkles upon agitation ; it has a pungent, acidulous taste, and reddens tincture of litmus. Heat again disengages the gas from the water. This gas pre- cipitates lime, strontia, and barytes, from their solutions in water. It is greedily attracted by all the alcalies. It undergoes no alteration by light. Its specific weight is to that of atmospheric air as 1500 to 1000. It may be poured out of one vessel into another. It is not acted upon by oxigen, nor is it altered by any of the simple combustible bodies at common temperatures ; but phos- phorus, iron, and lime, are capable of decomposing it when assisted by heat. METHODS OF OBTAINING CARBONIC ACID GAS. Of all the gases, carbonic acid gas is that, perhaps, which is diffused in the greatest abundance throughout nature. It is found in three different states : 1st, In that of gas; 2dly, In that of mixture ; and 3dly, In that of combination. The various processes of obtaining it are the following: 1. Put into a common gas-bottle, or retort, a little marble, chalk, or lime-stone, and pour on it sulphuric acid, diluted with about six times its weight of water; an effervescence will ensue, and carbonic acid gas will be li- berated, which those who have an opportunity may col- lect over mercury ; but a mercurial apparatus is not ab- solutely necessary, since the gas may be collected over water, if it is to be used immediately when procured. Rationale....In this instance the carbonic acid is dis- engaged from the state of combination, and reduced to the aeriform state of gas. The marble, lime-stone, or chalk, consists of this acid and lime ; on presenting to it sulphuric acid, a decomposition takes place : the sulphu- ric acid has a greater affinity to the lime than the carbonic acid has ; it therefore unites to it, and forms sulphate of lime, disengaging at the same time the carbonic acid iv the state of gas at the temperature of our atmosphere. Methods of obtaining Carbonic Acid Gas. 273 Remark....Carbonic acid gas may in this manner be disengaged from all its combinations with alcalies; by using indifferently any other dense acid, possessing a superior affinity to the alcali in the common acceptation of the word. 2. It may likewise be obtained from the same substan- ces by the action of caloric. For this purpose reduce marble or chalk to powder, introduce it into a gun-barrel, which must be placed across the universal furnace, adapt a bent tube to its lower extremity, and insert it below a receiver in the pneumatic apparatus. Maintain a strong heat till the bar- rel is brought to a state of ignition, and at that tempera- ture carbonic acid gas will be liberated in abundance. Rationale....In this case a decomposition of the mar- ble or carbonate of Kme takes place, on account of the action of caloric, which at a high temperature breaks the affinity of the carbonic acid and lime ; it unites with the first, and leaves the lime behind in that state which is generally called quick-lime. 3. Carbonic acid gas may also be obtained by burning charcoal in oxigen gas. We have already mentioned this, but we shall here give directions how it is best effected. Take a bell-glass, filled with oxigen gas, resting inverted in a bason of mercury; pass up into it some bits of new- made charcoal, with some touch paper affixed to them; set fire to them by means of a lens collecting the sun's rays, and carbonic acid will be produced by the combus- tion of the charcoal. The rationale of this experiment has been given, page 230. Carbonic acid gas is often found occupying the lower parts of mines, caverns, tombs, and such other subterra- neous places as contain materials for producing it. It is called choke, or chalk-dam. The grotto del Cane, near Naples, has long been famous for the quantity of carbonic acid gas produced there, which runs out at the opening like a stream of water. The quantity of carbonic acid gas generated in this cavern is so great, that a dog or any other animal is immediately killed if his nose be thrust into it. The carbonic acid, existing naturally in a state of gas, maybe collected by filling bottles with water and empty- 274 Proofs of the Properties of Carbonic Acid Gas. ing them in the atmosphere of this gas; the gas takes the place of the water, and fills the bottles, which must then be corked. Carbonic acid gas is likewise formed during ferment- ation ; on account of its great weight, it occupies the apparently empty space, or upper part of the vessel in which the fermenting process is going on. It may in this case be collected in a manner similar to that above. Carbonic acid gas is also obtained during the reduction of metallic oxids, and during the deflagration of nitrates with combustible bodies, as shall be noticed in another part of this work. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF CARBONIC ACID GAS. Experiment I. Carbonic acid gas is unfit for combustion. TO prove this, set a vessel filled with this gas with its mouth upwards, and let down a lighted candle ; the candle will be immediately extinguished, and the smoke remain- ing in the gas will render its surface visible, which by agitation may be thrown into undulating waves. The following experiment will shew this property in a pleasing manner. Experiment II. Take three glass tubes, of equal heights, and fill the first with atmospheric air, the second with carbonic acid gas, and the third with oxigen gas ; plunge successively, and with swiftness, a lighted taper into these three tubes; first into that containing atmospheric air, then into the tube filled with carbonic acid gas, and lastly into that filled Proofs of the Properties of Carbonic Acid Gas. 275 with oxigen gas. In the tube filled with atmospheric air the taper will burn with its usual brightness ; in that filled with carbonic acid gas, the flume will be suddenly extin- guished, but the glowing wick will be re-lighted in the tube containing oxigen gas, and burn with a dazzling splendour. RATioNALE....This experiment confirms a fact already established; namely, that oxigen gas is much fitter ior combustion than atmospheric ait ; and is also a most com- plete proof that carbonic acid gas extinguishes light. Remark....This property of carbonic acid gas may be advantageously made use of to learn whether the air m a newly sunk well, in subterraneous caverns, pits, mines, vaults, cellars, and the like, may be approached without danger. Experiment III. Carbonic acid gas is fatal to animal life. Put a mouse or other small animal into a vessel filled with this gas, and cover the vessel, to prevent the contact of atmospheric air. The animal will die in a minute or two. Remark....It is this gas which has produced so many fatal accidents, at the opening of cellars or vau'ts, in which wine, cider, or beer, has been suffered to ferment. The famous lake of Averno, where Virgil placed the entrance of hell, yields so large a quantity of carbonic acid gas, that birds cannot fly close over it with impunity. Experiment IV. Carbonic acid gas is heavier than atmospheric air. Let a long glass tube proceeding from a gas-bottle in which carbonic acid gas is disengaged be twice bent at right angles. Let the open erd of the longest leg reach to the bottom of a jar, perfectly dry within, and standing with its mouth uppermost. The carbonic acid disengaged will expel the atmospheric air from the jar, on account of its greater specific gravity. When the jar is filled with the gas (which may be known by a lighted candle being 276 Proof* of the Properties of Carbonic Acid Gas. instantly extinguished in it a little below the brim) take another jar of rather a smaller size, and place at the bot- tom of it a lighted taper or a small animal, and pour the invisible contents of the first jar into the second (in the same manner as if water was poured) the candle will be immediately extinguished, or the animal will die ; though the eye is incapable of perceiving any thing poured upon them capable of producing this effect. Experiment V. Carbonic acid gas is absorbable by water. Fill ajar partly with this gas, and let it stand for some hours over water; an absorption will gradually take place, till at last none of the gas remains. If this be repeated, with this difference, that the jar be shaken strongly, a very rapid diminutiom will take place. Remark....Water may be charged with upwards of three times its own bulk of carbonic acid gas, if pressure be applied. The water thus impregnated has a very brisk and pleasant taste. Various kinds of apparatus are em- ployed for this purpose. A machine has been invented by Dr. Nooth, and improved by Parker and Magellan, which is convenient and ingenious ; but it is impossible to impregnate water by its means with more than half its own bulk of carbonic acid gas. The valve of this ma- chine is the most defective, and renders it extremely apt to break: for the capillary tube does not admit the air through it, unless there be a considerable quantity condensed in the lower vessel, and the condensation is apt to burst the vessel. Other apparatus, more simple, have been invent- ed by different persons, descriptions of which may be found in Scherer's Journal der Chimie; in the Transac- tions of the Manchester Philosophical Society ; and in Bouillon La Grange's Manual of Chemistry, vol. I. p. 93. Cider, perry, ale, champaign, &c. owe their briskness to the carbonic acid gas which they contain, and which becomes rapidly disengaged in order to assume the gaze- ous form, on removing the cork of the bottle ; it is this also which produces froth, &c. Proofs of the Properties of Carbonic Acid Gas. 277 Experiment VI. Carbonic acid gas when combined with water possesses acid t properties. This may be shewn by dipping into water saturated with carbonic acid gas a piece of litmus paper, or by mix- ing with it about an equal quantity of infusion of cabbage. The blue colour of the paper or infusion will be changed to red. Experiment VII. Carbonic acid gas precipitates lime, barytic, and strontia water. Let the stream of carbonic acid gas, as it proceeds from the disengaging vessel, pass into either of these solutions, the fluid, though perfectly transparent before, will instantly grow turbid, and carbonate of lime, barytes, or strontia, will be formed. If equal measures of water impregnated with carbonic acid gas, and either of the above solutions be mixed, a similar effect will be produced. Experiment VIII. Carbonic acid gas exerts powerful effects on living vegetables. Water impregnated with carbonic acid gas proves highly nutritive, when applied to the roots of plants. But, on the contrary, carbonic acid gas applied as an at- mosphere, by confining living vegetables in it, proves in- jurious to the health of the plants, especially in the shade. This may be proved by confining a small plant in a vessel filled with the gas. The plant will soon decay and die. Rationale....In the first case, where water is present, the carbonic acid is decomposed, the carbonaceous prin- ciple fixes itself into the vegetable, becoming a compo- nent part of it, the oxigen which held the carbon in solu- tion is therefore disengaged in a gazeous state. In the latter instance no such effect takes place. vol. i. p p 278 Proofs of the Properties of Carbonic Acid Gas. Experiment IX. Carbonic acid gas is rapidly absorbed by alcalies. Fill a tube with this gas over water, and when full i* vert it in a cup containing a concentrated solution of pot- ash, or any other alcali; the solution will rise in the tube, and if the gas be very pure will fill it entiiely. Rationale....This absorption of the gas is owing to the alcali uniting with the carbonic acid gas, and forming with it a saline compound, called carbonate of potash. LIGHT CARBONATED HIDROGEN GAS. PART XX. SECT. I. IT was mentioned before that hidrogen gas has the property of dissolving various substances in minute quan- tities, such as carbon, sulphur, phosphorus, &c. The na- ture of the gas now under consideration furnishes an in- stance of this kind. Light carbonated hidrogen gas is hidrogen gas holding charcoal in solution. There are several combinations of this kind of gas obtained by different processes, which differ in their properties, and in the proportion of their constituent principles. PROPERTIES OF LIGHT CARBONATED HIDROGEN GAS. Light carbonated hidrogen gas has a fetid odour It is neither absorbed nor altered by water. It is inflammable, and burns with a denser and deeper coloured flame than hidrogen gas. It is unalterable by acids or alcalies, and by water. Its specific gravity is greater than that of hi- drogen gas, or that of common air. Its combustion with a due proportion of oxigen gas is productive of water and carbonic acid. When passed through melted sulphur, it becomes converted into sulphurated hidrogen gas, and charcoal is deposited. Electrization dilates it permanently to a little more than twice its original bulk. The air thus ~80 Light carbonated Hidrogen Gas. expanded requires a greater quantity of oxigen to decom- pose it than the same quantity of gas not dilated by elec- tricity ; 100 cubic inches of pure carbonated hidrogen gas weigh from 16 to 21 grains. METHODS OF OBTAINING LIGHT CARBON- ATED HIDROGEN GAS. Light carbonated hidrogen gas may be obtained from animal, vegetable, or mineral substances. Nature pro- duces it ready formed in marshes and ditches, on the sur- face of putrid water, in burying-places, common-sewers, and in those situations where putrid animal and vegeta- ble matters are accumulated. It is also generated in the intestinal canal of living animals. 1. Light carbonated hidrogen gas may be plentifully procured from most stagnant waters: to do this fill a wide-mouthed bottle with the water, and keep it inverted therein, with a funnel in its neck ; then with a stick stir the mud at the bottom just under the funnel in the bot- tle, so as to let the bubbles of air which rise from the mud enter into the bottle ; when, by thus stirring the mud in various places, and catching the air in the bottle, it is fil- led, it must be corked under water. 2. It may also be obtained during the distillation of animal and vegetable matters. For instance, Let shavings of wood or saw-dust be put into a retort, and begin the distillation with a gentle heat, increasing it gradually till the retort becomes red-hot; a great quantity of gas will be liberated, which may be caught over water. On examining this gas, it will be found to consist of car- bonic acid gas and carbonated hidrogen gas. In order to obtain the latter in a state of purity, the whole must be mixed with lime-water, or with a caustic alcaline solu- tion. The carbonic acid gas will be absorbed, and the carbonated hidrogen gas left behind in a pure state. Rationale....The production of this gas in this man- ner is the result of a partial analysis of the wood : it proves that wood contains solid hidrogen, carbon, and oxigen. When the intensity of the heat has reached a certain degree, a part of the charcoal unites with part of the oxigen, and produces carbonic acid, which by means of Light carbonated Hidrogen Gas. 281 caloric is melted into the gazeous state, and forms carbo- nic acid gas ; at the same time, a part of the hidrogen ofv the wood combines with another portion of carbon and caloric, and forms carbonated hidrogen gas. Remark....The flame of burning wood, &c. is the in- flamed carbonated hidrogen gas, liberated on the applica- tion of caloric to such bodies. 3. Charcoal is in general made use of for obtaining light carbonated hidrogen gas. For this purpose, put some moistened charcoal into an earthen retort, apply heat, and increase it till the retort becomes ignited; gas will be evolved, consisting partly of carbonic acid gas, and partly of light carbonated hidrogen gas, which may be separated as before. Rationale....In this case a decomposition of the water, takes place, by means of the charcoal. The oxigen for- sakes its hidrogen, and unites to part of the charcoal at this temperature, and forms carbonic acid gas, in conjunc- tion with caloric ; the liberated hidrogen, assisted by caloric, dissolves another portion of the charcoal, and forms with it light carbonated hidrogen gas. 4. Light carbonated hidrogen gas may be formed in a direct manner by dissolving charcoal in hidrogen gas. This may be effected by directing the rays of the sun, collected in the focus of a mirror, upon a small piece of charcoal placed on mercury, in a receiver filled with hi- drogen gas. SECT. II. EXPERIMENTAL PROOFS OF THE PRO- PERTIES OF LIGHT CARBONATED HIDROGEN GAS. Experiment I. Light carbonated hidrogen gas is inflammable. THIS may be shown by filling a tumbler, or any wide- mouthed vessel, with this gas, and setting fire to it, by means of a lighted taper. It may likewise be shown by burning it in the manner directed for burning hidrogen gas. The colour of the flame of this gas is of a deepei blue than that of hidrogen gas. 282 Light carbonated Hidrogen Gas. Experiment II. Light carbonated hidrogen gas is heavier than hidrogen gas. Soap bubbles blown in it do not ascend like those filled with hidrogen gas, but descend like those filled with common air. Ajar filled with carbonated hidrogen gas, held inverted for a few minutes, exchanges its Contents for common air. Experiment III. Decomposition of light carbonated hidrogen gas, by means of oxigen gas. Mr. Cruikshank found (Nicholson's Journal, April, 1801) that six measures of carbonated hidrogen gas ob- tained from moistened charcoal, when mixed with four of pure oxigen gas, over mercury, exploded violently by the electric spark, and became augmented to 12£ measures, or that there was an increase of 24 measures nearly. On admitting lime-water, the volume diminished rather more than two measures; the residue amounted to 10£, on which nitrous gas had no effect. Two measures of the residuary gas fired with one of oxigen became reduced to one, which was carbonic acid gas. Hence the whole re- siduary gas would require about 5^ measures of oxigen to saturate it, and produce 5 measures of carbonic acid gas. Experiment IV. Decomposition of light carbonated hidrogen gas, by means of oxigenated muriatic acid gas. The effects of the oxigenized muriatic acid gas upon all the hidro-carbonates is remarkable. Mr. Cruikshank observed, that if the pure oxigenized muriatic acid gas be mixed with these kinds of gases over water, although no action should be perceptible at first, yet in twenty-four hours a complete decomposition and change of principles takes place. For instance, introduce into a bottle filled with and in- verted over water one measure of pure light carbonated Light carbonated Hidrogen Gas, 283 hidrogen gas well washed, mixed with two measures of fresh-prepared pure oxigenized muriatic acid gas. On the first contact of the oxigenized muriatic acid gas, a white cloud and some diminution will be perceived, which will soon cease. The bottle must then be stopped, and suffered to remain inverted in water for about twenty-four hours. If the bottle be then uncorked under water, this fluid will instantly ascend into it, and the gas will occupy about .43 parts of a measure, the diminution being 2.57 measures. On mixing the residuary gas with lime-water, .09 parts more become absorbed. Rationale....The results obtained in this experiment with the pure light carbonated hidrogen gas are very easily understood; for it is evident that the oxigenized muriatic acid gas gives out its excess of oxigen to the car- bon and hidrogen of the inflammable gas from a superior affinity; in consequence of which, we have no less than four new compounds. Part of the oxigen of the oxigen- ized muriatic acid gas joins to the hidrogen of the car- bonated hidrogen gas, and forms water; another part unites to the charcoal, and produces carbonic acid gas; a still less quantity combines with another portion of char- coal, and forms gazeous oxid of carbon; and the oxigen- ized muriatic acid gas, by thus losing its excess of oxigen, becomes converted into simple muriatic acid gas. Rem ark....According to Mr. Cruik shank's experi- ments, 100 cubic inches of light carbonated hidrogen gas, obtained from wetted charcoal, weighed 14.5 grains; they required 66 cubic inches (22.4 grains) of oxigen to saturate them. The compound yielded 40 cubic inches (19 grains) of carbonic acid, and nine grains of water. Hence this gas consists of nearly 4 of carbon, 1.3 of hi- drogen, and 9 of water. HEAVY CARBONATED HIDROGEN GAS. PART XXL SECT. I. THIS gas was first brought into notice by a society of Dutch chemists, consisting of Deiman, Troostwyk, Bond, and Laurenburgh. They observed in this gas the particular property, that when it was combined with oxi- genated muriatic acid gas in a certain proportion the elas- tic form of both fluids became destroyed, and an oil was produced ; for which reason the}' called it olefiant gas. .PROPERTIES OF HEAVY CARBONATED HIDROGEN GAS. Heavy carbonated hidrogen gas is not absorbed or altered by water. Its weight compared with common air is as 909 to 1000. It has a disagreeable fetid odour, dif- ferent from that of light carbonated hidrogen gas. It burns with a strong compact flame, similar to that of a resinous oil. When mixed with oxigenized muriatic acid gas its bulk is diminished, and an oil is formed. When the mixture of these two gases is fired, a quantity of char- coal is immediately deposited in the form of fine soot. Sulphuric, sulphureous, nitric, nitrous, and muriatic acids do not act upon it; neither does nitrous gas, nor any of the fixed alcalies. Ammonia adds to its volume without Heavy carbonated Hidrogen Gas. 285 occasioning any other change. Phosphorus heated in it even to fusion does not affect it. When made to pass through an ignited glass tube, it does not diminish in vo- lume, but loses the property of forming oil with oxigen- ized muriatic acid gas. Electric shocks passed through it dilate, and likewise deprive it of this property. When passed through an ignited porcelain tube, it affords hidro- gen gas, mingled with carbonic acid, and carbon is depo- sited. When passed through a tube with sulphur in fu- sion, sulphurated hidrogen gas is obtained, and charcoal deposited. When burnt with oxigen gas, or when passed through a red-hot tube filled with oxid of manganese, carbonic acid gas is formed. METHODS OF OBTAINING HEAVY CAR- BONATED HIDROGEN GAS. Heavy carbonated hidrogen gas is obtained by decom- posing alcohol by sulphuric acid at high temperatures. It is also obtained in abundance when alcohol or ether is passed through a red-hot earthen tube. Sulphuric ether, mixed with sulphuric acid, and subjected to heat, also affords it, but in a less pure state. The Dutch chemists observed, that if the vapour of ardent spirit or ether be made to pass through a glass tube, over the component parts of the earthen tube, namely, alumine and silex, this gas was also produced, or by passing it through a red-hot tube of pipe-clay. In order to obtain this gas, the following method may- serve : Let four parts of concentrated sulphuric acid and one of highly rectified ardent spirit be mingled together gra- dually in a glass retort, heat will be developed, the mix- ture will become brown, and heavy carbonated hidrogen gas will be extricated by the application of heat. When a moderate heat is applied, the action is very violent, and the gas is liberated very copiously, and may be received over water. The gas obtained is always mixed with a considerable quantity of sulphureous acid gas, from which it may be freed by agitating it in contact with lime-water, or a solu- tion of potash. vol. i. Q_ q 286 Heavy carbonated Hidrogen Gas. Remark....In this operation the heat ought to be re- gulated with great care, and the retort holding the mix- ture ought to be very capacious, otherwise the matter will be forced over into the receiver. The heat of a can- dle or lamp is sufficient. Numerous experiments by different chemists have proved, that this species of carbonated hidrogen gas con- tains a larger quantity of carbon in solution than the for- mer. This becomes obvious from the gas losing the property of forming oil, by being made to pass through an ignited tube ; for it then deposits charcoal, and becomes converted into light carbonated hidrogen gas. The Dutch philosophers suppose, that the disposition to form oil depends on the proximity of the constituent moleculae of the gas; and the loss of this property they suppose to be owing to the separation of these moleculae, by the introduction of a greater quantity of caloric. Heavy carbonated hidrogen gas, they say, is converted into light carbonated hidrogen gas whenever a process is executed which increases the distance subsisting between its component parts. In this way the attraction between the particles of the hidrogen and-carbon is diminished, which happens whenever the gas is made to pass through ignited tubes, capable of acquiring a high temperature, or by strongly electrifying it. Either heavy or light carbonated hidrogen gas may therefore be obtained indiscriminately from the'same sub- stances, namely ether or ardent spirit. Their difference arises from the different methods of treating these fluids, and is constantly reducible to this ; that in forming the first gas a less quantity of caloric acts upon the mass, and a compound is formed, in which the hidrogen and char- coal are more concentrated, and more disposed to form oil by the addition of oxigen ; whereas by more strongly heating the ardent spirit or ether, they become more completely decomposed; their constituent parts are re- moved to a greater distance, by a greater proportion of caloric being introduced between them; and the simul- taneous attraction, which might be disposed to foian oil with oxigen, is so far diminished, that they are no longer capable of that transition, therefore no oil can be formed. Hence we perceive, likewise, why the specific gravity of the heavy carbonated hidrogen gas, when it loses it- property of forming oil, becomes diminished. Heavy carbonated Hidrogen Gas. 287 We do not however agree with the Dutch chemists that either the alumine, silex, or earthen tube serves to form this gas, as they assert, while glass tubes only afford the common carbonated hidrogen gas. These different effects certainly do not arise from the causes which are as- signed to them. They seem to arise from a less degree of heat having been applied in all the cases where the heavy carbonated hidrogen gas was produced, and a greater degree in all those which present the light carbon- ated hidrogen gas. Mr. Nicholson observed,* that when ardent spirit is burnt in the lamp of Argand, and the lower aperture or air-passage of the lamp is kept open, the flame of the spirit is as usual faint and bluish, resembling that of car- bonated hidrogen gas ; but if the air-passage be obstructed, by slowly applying the palm of the hand, or any more suitable obstacle, the flame becomes more and more lu- minous, like that of oil, until in the progress of obstruction the aperture is so much closed that the combustion begins to decay for want of air. By a proper adjustment of the aperture, the spirit may be made to burn with a constant luminous white internal flame. In this case the tempera- ture is precisely such as to produce the olefiant gas. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF HEAVY CARBONATED HIDROGEN GAS. THE properties of this gas being similar to those of the other hidro-carbonates, it is unnecessary to exhibit expe- rimental proofs of them ; those already advanced under the head of light carbonated hidrogen gas will explain them all, with the exception of its characteristic property of producing oil with oxigenized muriatic acid gas, which shall be inserted here, with a few other interesting re- marks. • Journal of Natural Philosophy, &c. May, 1797, p. 55. 288 Heavy carbonated Hidrogen Gas. Experiment I. Production of oil by the mixture of heavy carbonated hi- drogen gas with oxigenated muriatic acid gas. Take a glass tube, send up into it three parts oi fresh prepared heavy carbonated hidrogen gas, and add to it gradually four parts oi fresh prepared oxigenized muriatic acid gas. After each addition of the gas, shake the mix- ture ; an absorption will take place, caloric will be liber- ated, and the tube will become filled with white vapours. When the gases have totally disappeared, an oil of a pearl gray colour will be deposited. This oil is heavier than water, its odour is agreeable and penetrating, its taste is rather sweet; it becomes yel- low by exposure to air. Experiment II. Conversion of heavy carbonated hidrogen gas into light carbonated hidrogen by combustion with oxigen gas. Let equal parts of fresh prepared heavy carbonated hidrogen gas and oxigen gas be mingled together in a detonating tube, and a spark be passed through it, a mo- mentary expansion will take place, the tube will become lined with a fine black soot of charcoal, and the heavy carbonated hidrogen gas will thus be converted into light carbonated hidrogen gas. Mr. Cruikshank found that 100 cubic inches of carbon- ated hidrogen gas, obtained from alcohol, weighed 16 grains: it required 118 cubic inches of oxigen to saturate it, and produced 75 cubic inches of carbonic acid. This gas therefore consists of 7 carbon, 1.9 hidrogen, and 7 water. The same quantity of gas obtained from ether weighed 20 grains : it required for saturation 170 cubic inches of oxigen, and produced 108 of carbonic acid. Hence this gas consisted of 9 carbon, 3 hidrogen, and 8 water. One hundred cubic inches of carbonated hidrogen gas, obtained from camphor, weighed 21 grains. They con- sumed 176 cubic inches of oxigen, and produced 116 of Heavy carbonated Hidrogen Gas. 289 carbonic acid; this gas consisted therefore of 11 carbon, 2 + hidrogen, and 8 or 9 water. In the preceding estimate, the weight of 100 cubic inches of common air, under the mean pressure of the atmosphere, and at the temperature of 55°, is estimated at 31 grains. The quantity of carbon in carbonic acid at ^ of the whole nearly, and the proportion of oxigen to hidrogen in water as about 85 to 15. From the result of these experiments we perceive that the carbonated hidrogen gases obtained from various sub- stances differ in their composition. This has given rise to the next species of gas. GAZEOUS OXID OF CARBON. PART XXII. GAZEOUS oxid of carbon was first described by Dr. Priestley, who mistook it for a hidro-carbonate. With the true nature of it we have been only lately acquainted. It was first proved to be a peculiar gas by Mr. Cruikshank of Woolwich, who made it known to us, as such, in April 1801, through the medium of Nichol- son's Journal for that month. Several additional pro- perties of this gas were soon afterwards noticed by De- sormes, Clement, and others. Gazeous oxid of carbon forms an intermediate substance between the pure hidro- carbonates and carbonic acid gas ; but not being possess- ed of acid properties, Mr. Cruikshank has called it, con- formable to the rules of the chemical nomenclature, gaze- ous oxid of carbon, for it consists of oxigen and carbon rendered gazeous by caloric. Though the gazeous oxid of carbon has some of the properties peculiar to the common hkfro-carbonates, the following characteristic properties sufficiently prove that none of those at present known are similar to it. We are therefore entitled to consider it as a gas peculiar to itself. SECT. I. PROPERTIES OF GAZEOUS OXID OF CARBON. GAZEOUSoxid of carbon is considerably lighter than any of the hidro-carbonates. It is lighter than common Methods of obtaining Gazeous Oxid of Carbon. 291 air in the proportion of 22 to 23. When mingled with common air and ignited, it does not explode, but burns with a lambent blue flame, and the product is carbonic acid. It is very little absorbable by water ; it is void of taste and odour. A mixture of 20 parts of gazeous oxid of carbon and 8 of oxigen gas, fired over mercury by electricity, diminishes to a volume equal to about 18 or 19 parts, which is carbonic acid gas. It contains neither water nor the basis of that fluid. It is exceedingly noxious ; animals die in it instantly ; when breathed for a few minutes only, it produces giddiness and fainting. Neither light, heat, nor electricity have any effect upon it. When equal quantities of gazeous oxid of carbon and hidrogen gas are passed through a red-hot glass tube, the tube is lined with charcoal, water is formed, and an excess of hidrogen makes its escape. If a piece of iron be put into the tube, it is oxidated, but not converted into steel. Neither nitrogen gas nor sulphur have any action on it, even at high temperatures. It is capable of dissolving a minute quantity of charcoal, and increases in bulk. It dissolves phosphorus, and acquires the property of burning with a yellow flame. The alcalies have no effect on this gas. It is not altered when passed with ammonia through an ignited tube. When the red oxid of mercury is heated in it, a commencement of reduction takes place. Neither sulphuric, nitric, nor nitro-mu- riatic acids alter it, when passed with it through a red- hot tube. Four parts of oxigenized muriatic acid gas left with one of carbonic acid gas decompose it completely. Nitrous gas has no effect upon it. When mixed with sulphurated hidrogen gas, and passed through a red-hot tube, sulphur is deposited, and sulphurated hidrogen gas remains mixed with gazeous oxid of carbon. METHODS OF OBTAINING GAZEOUS OXID OF CARBON. Gazeous oxid of carbon may be obtained by a decom- position of carbonic acid at high temperatures, by means of various fixed substances which have a considerable affinity to oxigen. This may be done by distilling a mix- ture of charcoal with any of the metallic oxids, or by 292 Methods of obtaining Gazeous Oxid of Carbon. exposing to a strong red heat a mixture of carbonate of lime or barytes, and filings of iron, zinc, &c. The method of obtaining the gazeous oxid of carbon in a state of purity, recommended by Mr. Cruikshank, is the following: 1. Take one part of chalk, previously exposed to alow red heat for about ten minutes. Mix it with an equal quantity of perfectly dry filings of zinc ; let the mixture be introduced into a retort, and expose it to a heat gra- dually increased. As soon as the retort becomes of a dull red heat, gas will be disengaged in great abundance. The gas which comes over first is carbonic acid gas ; but as soon as the retort becomes thoroughly ignited, pure gazeous oxid of carbon is liberated in a prodigious quan- tity, which may be collected in the usual manner over water. Rationale....In this process a decomposition of the carbonic acid of the chalk takes place in its nascent state. The zinc robs the carbonic acid of part of its oxigen at a high temperature, and becomes to a certain degree oxid- ated. The carbonic acid, by being thus deprived of part of its oxigen, becomes converted into a new inflammable gas, called gazeous oxid of carbon. Remark....Upon the whole, therefore, we have to consider this gas as holding the same relation to pure hidro-carbonates and carbonic acid gas which nitrous gas or nitrous oxid does to pure nitrogen and nitrous acid. Tin, and probably various other metals, when mingled with charcoal, are capable of producing gazeous oxid of carbon in a similar manner. 2. Gazeous oxid of carbon may also be obtained in the following manner: Take equal quantities of scales of iron separated in forg- ing (black oxid of iron) and charcoal powder previously heated to redness; mix them together; introduce the mixture into a coated glass retort or gun-barrel, and apply heat gradually ; as soon as the retort becomes of a dull red heat, gas is produced in great abundance. It consists of about one part of carbonic acid gas and four of gazeous oxid of carbon. In order to separate the carbonic acid gas, it must be suffered to stand over lime diffused through wa- ter, or agitated with lime-water; the carbonic acid gas will be absorbed, and what remains behind is pure inflammable Methods of obtaining Gazeous Oxid of Carbon. 293 gazeous oxid of carbon : or this trouble may be saved, by letting the gas, as it is disengaged, pass through lime, formed into a very thin paste with water. The carbonic acid combines with the lime; but the gazeous oxid of carbon passes through it unaltered. Rationale....The production of gazeous oxid of car- bon in this manner is in some respects analogous to the former. The black oxid of iron parts with a portion of its oxigen, which joins to the carbon to form the gazeous oxid, and another partis liberated in the form of carbonic acid gas. The black oxid of iron therefore re-approaches to the metallic state. A mixture of charcoal and oxid of zinc, red oxid of copper, semi-vitreous oxid of lead, black oxid of manga- nese, and the rest of the metallic oxids capable of endur- ing a red heat, on being treated with charcoal, also yields carbonic acid gas and gazeoub oxid of carbon. Those oxids which retain their oxigen most obstinately yield most of the latter, and those which part with it readily afford most carbonic acid gas. The latter comes over chiefly at the beginning, and the former towards the end of the process. Inferences....From these various facts there can no longer remain any doubt but that the carbonic acid, under certain elevations of temperature, may be decomposed by any fixed substance having a considerable affinity with oxigen; and that, with regard to the metals, those succeed the best which have the greatest attraction for acids or oxigen, as is the case with zinc. Upon the whole we may conclude, that there are but two distinct combina- tions of carbon and oxigen capable of assuming and main- taining the form of gas : for although the gazeous oxid of carbon may be obtained in a great variety of ways, by direct composition, as well as during the decomposition of the carbonic acid ; yet when pure it is exactly the same substance, having the same specific gravity, requiring the same portion of oxigen to saturate it, and producing the same quantity of carbonic acid, as Mr. Cruikshank* has sufficiently proved experimentally. * Nicholson's Journal, Sept. 1801, p. 210. VOL. I. r r 294 Methods of obtaining Gazeous Oxid of Carbon. One hundred cubic, inches of gazeous oxid of carbon,, obtained from iron filings and carbonate of lime or bary- tes, previously ignited, according to Mr. Cruikshank, weigh 30 grains. They require 40 cubic inches (13.6 grains) of oxigen for saturation, and form 92 cubic inches (43.2 grains) of carbonic acid, andno water is produced. Hence the 100 cubic inches of gazeous oxid of carbon consist of 21 + oxigen 8.6 carbon. One hundred cubic inches of the same gas, obtained from charcoal and metallic oxids, weigh 30 grains : they require 44 cubic inches (15 grains) of oxigen for satura- tion, and yield 76 cubic inches (35.5 grains) of carbonic acid, and afford (on account of the hidrogen contained in the charcoal) about 8 grains of water. Hence this gas consists of about 15 oxigen, 7 carbon, 1 -f- hidrogen, and an uncertain quantity oi water. Rem ark....The quantity of oxigen in the gazeous ox- ids Mr. Cruikshank estimated thus : In the first instance, for example, we find that 30 grains of the oxid, combined with 13.6 grains of oxigen, produced 43.3 grains of car- bonic acid. This acid consists of 8.6 grains of carbon and 34.6 of oxigen nearly; but the quantity of oxigen employed in the experiment was only 13.6 grains ; hence the difference between 34.6 and 13.6 or 21 grains must have been originally contained in the oxid. It would therefore appear that the gazeous oxids in their purest state consist of oxigen and carbon, in the proportion of 21 to 9 nearly, combined with caloric. Upon the whole we consider, as mentioned before, the gazeous oxid of carbon as holding the same relation to the pure hidro-carbonates and carbonic acid which nitrous gas or nitrous oxid does to pure nitrogen and* nitrous acid. SULPHURATED HIDROGEN GAS. PART XXIII. ^ SECT. I. PROPJERTIES OF SULPHURATED HIDRO- GEN GAS. SULPHURATED hidrogen gas possesses the pro- perties of an acid; for, when absorbed by water, its solution reddens vegetable blues; it combines also with alcalies, earths, and with several metallic oxids. Sulphu- rated hidrogen gas possesses an extremely offensive odour, resembling that of putrid eggs. It kills animals, and ex- tinguishes burning bodies. When mixed with oxigen gas, or atmospheric air, it is inflammable. Mingled with nitrous gas, it burns with a yellowish green flame. It is decomposed by ammonia, by oxigenized muriatic acid gas, and by sulphureous acid gas. It has a strong action on the greater number of metallic oxids. Its specific gravity to common air is as 1106 to 1000. It is composed, ac- cording to Thenart,of 70.857 sulphur and 29.143 hidro- gen. It has the property of dissolving a small quantity of phosphorus. METHODS OF OBTAINING SULPHURATED HIDROGEN GAS. 1. Take dry sulphuret of potash, put it into a tubulated retort, lodged in a sand bath, or supported over a lamp.; 296 Methods of obtaining sulphurated Hidrogen Gas. direct the neck of the retort under a receiver placed in the pneumatic trough: then pour gradually upon the sulphuret dilutedj sulphuric or muriatic acid; a violent effervescence will take place, and sulphurated hidrogen gas will be liberated. . When no more gas is produced spontaneously, urge the mixture with heat by degrees till it boils, and gas will again be liberated abundantly. The water made use of for receiving it should be heated to about 80° or 90° : at this temperature it dissolves little of the gas; whereas, if cold water be made use of, a vast quantity of it is absorbed. Rationale....Though sulphur makes no alteration on water, which proves that sulphur has less attraction for oxigen thah hidrogen has ; yet if sulphur be united to an alcali, this combination decomposes water whenever it comes in contact with it, though the alcali itself has no attraction either for oxigen or hidrogen. The formation of this gas explains this truth. On adding the sulphuret of potash to tne water, this fluid be- comes decomposed, part of the sulphur robs it of its oxi- gen, and forms with it sulphuric acid ; this generated acid unites to part of the alcali, and forms sulphate of potash. The liberated hidrogen dissolves another part of the sul- phur, and forms with it sulphurated hidrogen ; the basis of this gas, which is retained by the separated portion of the alcali. The sulphuric acid added now extricates it from the alcali, and makes it fly off in the form of gas. The mixture in the retort therefore contains an alcaline sulphure properly so called, or the simple combination of sulphur with alcali ; sulphate of potash, and lastly, sul- phurated hidrogen gas dissolved in the alcaline sulphure, or an hidrogenated sulphuret. Remark....Diluted muriatic acid is best adapted for the production of sulphurated hidrogen gas from alcaline sulphurets. If nitric acid be made use of, it must be much diluted. Sulphuric acid yields little gas, unless as- sisted by heat. When the proportion of sulphur in the sulphuret exceeds that of the alcali, the dense sulphuric acid poured upon it^emits sulphuric acid gas much loaded with sulphur. All the rest of the acids maybe made use of for decomposing the sulphurets. 2. When iron and sulphur are united together, they afford a large quantity of sulphurated hidrogen gas on Methods of obtaining sulphurated Hidrogen Gas. 297 submitting them to the action of heat, in contact with water. Melt together in a crucible equal parts of iron filings and sulphur; the product is a black brittle mass called sulphuret of iron. Reduce this to powder, and put it with a little water into a tubulated retort; add diluted muriatic acid, and apply a gentle heat, till no more gas is disengaged. Rationale....The philosophy of this experiment is analogous to the former. Part of the oxigen of the water unites to part of the sulphur, and forms sulphuric acid; another part oxidates the iron, which dissolved by the acid forms sulphate of iron: the hidrogen of the water unites to another part of the sulphur, and forms sulphurated hidrogen, which becomes gazeous by the addition of caloric. 3. Sulphurated hidrogen gas may also be obtained by heating an alcaline sulphuret, with the addition of water, without the affusion of an acid. Rationale....In this case the water is also decompos- ed ; its hidrogen unites Avith part of the sulphur, and forms sulphurated hidrogen; the oxigen of the water unites with another part of the sulphur and produces sulphuric acid, which joins to the alcali, and forms a sulphate. The sulphurated hidrogen becomes disengaged by heat in the gazeous form. 4. Sulphurated hidrogen gas may be obtained by pass- ing hidrogen gas through sulphur in a state of fusion. For this purpose put sulphur into a gun-barrel, Or Wedgwood's tube, and place it across a furnace; fit to the lower extremity a bent glass tube, which goes under a re- ceiver placed in the pneumatic trough, and adapt to the upper extremity a tubulated retort, or other apparatus proper for producing hidrogen gas. The sulphur must then be heated, and when melted, and the hidrogen gas evolved, must be made to pass over it; which in this manner will dissolve part of the sulphur, and become con- verted into sulphurated hidrogen gas. 5. It may likewise be procured in a direct manner : for that purpose let a small quantity of sulphur be inclosed in ajar full of hidrogen gas, and melt it by means of a burning glass. a 298 Properties of sulphurated Hidrogen Gas. REMARK....This method does not succeed except the hidrogen gas be as dry as possible; for its affinity to sul- phur is weakened in proportion to its moisture. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER. TIES OF SULPHURATED HIDROGEN GAS. Experiment I. Sulphurated hidrogen gas is absorbed by water. FILL a bottle with sulphurated hidrogen gas, and keep it inverted in a bason of cold water : an absorption will take place, which may be accelerated by agitation. The water which has absorbed a quantity has the fetid odour of the gas. It is not decomposed by exposure to the air; but the gas is gradually separated and carried off without decomposition. Water impregnated with sulphurated hidrogen gas slightly reddens blue vegetable colours. Remark....It is this gas which gives to the mineral waters of Harrogate and Aix-la-Chapelle their peculiar smell. Such waters may therefore be artificially imitat- ed by impregnating pure water with this gas, and adding the other constituent parts to it. Experiment II. Sulphurated hidrogen gas is inflammable in contact with oxigen gas. Mix equal parts of sulphurated hidrogen gas and oxi- gen gas over water, and apply a lighted taper ; a smart detonation will take place, and both gases will disap- pear. Rationale....Part of the oxigen unites to the hi- drogen of the sulphurated hidrogen gas; another part joins to the sulphur suspended in thi< gas: hence the products after combustion are sulphureous acid and water. Properties of Sulphurated Hidrogen Gas. 299 Experiment III. Sulphurated hidrogen gas mingled with nitrous gas burns with a yellowish-green fame. If three parts of sulphurated hidrogen gas be mixed with two of nitrous gas, the mixture maybe inflamed,and burns with a yellowish-green flame ; the vessel becomes lined with a coat of sulphur. Rationale....The explanation of these phenomena are analogous to the rationale of the next experiment. Experiment IV. Sulphurated hidrogen gas is decomposed by atmospheric air. Introduce into a bell-glass, half filled with sulphurated hidrogen gas, an equal quantity of atmospheric air ; a di- minution will take place, sulphur will be precipitated, and nitrogen be left behind. Rationale....The oxigen of the atmospheric air has a greater affinity for hidrogen than the sulphur of the sul- phurated hidrogen gas has; they therefore unite and form water, and the sulphur becomes deposited. REMARK....On this principle it is that water holding sulphurated hidrogen gas in solution lets fall sulphur on exposure to the open air ; and hence arises the sulphur seen deposited in the channels, and in the neighbourhood of sulphurated, or, as they are commonly called, hepatic waters. Experiment V. Sulphurated hidrogen gas becomes quickly absorbed by alcaline solutions. This may be proved by filling a tube with the gas, and inverting it in a bason containing some concentrated so- lution of potash. The gas will be absorbed, and the potash will acquire colour, odour, and other peculiar properties. 300 Properties of Sulphurated Hidrogen Gas. This combination is called hidro-sulphuret of potash, it is a true saline compound. Remark....Hitherto only the alcalies and some of the earths have been combined with sulphurated hidrogen gas. These compounds are colourless while kept in close vessels, but when exposed to air they soon acquire colour. This change is produced by the decomposition of part of the sulphurated hidrogen gas by the air. The hidrogen combines with the oxigen of the air, and forms water ; while the sulphur is disengaged, and thus darkens the colour. The sulphurated hidrogen gas »..iay again be expelled from these combinations in the same ratio it had been absorbed, by the addition of an acid. It may also be dis- engaged by heat. Experiment VI. Sulphurated hidrogen gas and sulphureous acid gas decompose each other. When sulphurated hidrogen gas and sulphureous acid gas are mingled together over mercury, the volume of the gases becomes diminished, and sulphur is deposited on the sides of the vessel in a considerable quantity. When these gases are dissolved in water, they mutually undergo the same decomposition. If suitable quantities are taken, the odour of both fluids disappears instantly. Rationale....The hidrogen of the sulphurated hidro- gen gas has a greater affinity for the oxigen of the sulphu- reous acid gas thaiylhe sulphur has ; they therefore unite and form water, anWthe sulphur of both is deposited. Rem ark....If concentrated nitrous acid be poured co- piously into water holding sulphurated hidrogen gas in solution, sulphur is likewise deposited. Hence nitrous acid is used as a test to detect the presence of sulphurat- ed hidrogen gas in hepatized waters. Experiment Vll. Combination of sulphurated hidrogen gas and ammonia. Fill a glass jar with fresh prepared sulphurated hidrogen gas, confined over mercury, and add to it gradually am- Properties of Sulphurated Hidrogen Gas. moniacal gas ; a dense white vapour will instantly appear; both gases will vanish; and a white saline compound wili be formed, being hidrogtenated sulphuret of ammonia. Experiment VIII. Oxigenized muriatic acid gas and sulphurated hidrogen gas likewise decompose each. Fill a cylindrical vessel over water with oxigenized muriatic acid gas, keep it over that fluid, and mingle it with sulphurated hidrogen gas; at the instant the gases come in contact with each other their bulk will be dimi- nished, and the vessel become lined with sulphur. Rationale....The oxigen of the oxigenized muriatic acid gas unites partly to the sulphurated hidrogen, and partly to the sulphur dissolved in that gas ; hence water and sulphuric acid are formed: the oxigenized muriatic acid gas being robbed of its oxigen becomes converted into simple muriatic acid, and the sulphur which escaped the action of the oxigen is precipitated. Experiment IX. Decomposition of sulphurated hidrogen gas by the electric spark. Fill a detonating tube over water with sulphurated hidrogen gas, and pass the electric spark through it; the volume of the gas will become dimkiished, and sulphur be precipitated. Experiment X. Sulphurated hidrogen gas acts strongly on the greater number of metallic oxids. Dip a slip of paper into a solution of silver, lead, bis- muth, mercury, tin, &c. and expose it to the action of sulphurated hidrogen gas, the paper will instantly become blackened. Writings performed with these solutions are invisible when dry, but become visible when immers- ed in a bottle filled with this gas. VOL. I. S fi 302 Properties of Sulphurated Hidrogen Gas. Rationale....In this instance the hidrogen of the gas abstracts the oxigen from these bodies, and causes them to re-approach to the metallic state; at the same time, the sulphur contained in the gas combines with the metal thus regenerated, and converts it into a sul- phuret. PHOSPHORATED HIDROGEN GAS. PART XXIV. SECT. I. WE are indebted to M. Gengembre for the discovery of this gas, which differs from the hidro-carbonates in nothing but the nature of the combustible substance sus- pended in the hidrogen gas. Phosphorated hidrogen gas consists of phosphorus dis- solved in hidrogen gas. PROPERTIES OF PHOSPHORATED HIDRO- GEN GAS. Phosphorated hidrogen gas is the most combustible substance in nature. It is particularly distinguished from all other gases, by the property of taking fire immediately when brought in contact with att^flfcpheric air. When mixed with oxigen gas, or with oxigenated muriatic acid gas, it burns with great vehemence. When bubbles of it are suffered to pass through water, they explode in succession as they reach the surface of this fluid. It has an insupportable odour, similar to that of putrid fish. It is partly absorbable by distilled water freed from atmos- pheric air at low temperatures. Distilled water absorbs about one-fourth, arid gives it out again without alteration by heat. Water containing atmospheric air decomposes it, when suffered to stand with it for some time. When exposed to vivid light, it deposits phosphorus in a crys- talline form. 304 Phosphorated Hidrogen Gas. METHODS OF OBTAINING PHOSPHORAT- ED HIDROGEN GAS. 1. Take a small retort, put into it one part of phos- phorus and ten of a concentrated solution of potash or so- da ; make the mixture boil, and receive the liberated gas over mercury; or, if it be intended for immediate use, it may be collected over water. Rationale....In this experiment a decomposition of the water takes place. Its oxigen unites to part of the phosphorus, and forms phosphoric acid, which joins to the potash, and forms phosphate of potash. The liberated hidrogen dissolves another part of the phosphorus, and becomes converted into phosphorated hidrogen gas. Rem ark....In thus preparing this gas, the body of the retort should be filled as nearly as possible with the mix- ture ; otherwise the first portion of gas which is produced inflames in the retort; a vacuum is formed; and the water forced up into the retort, and endangers the bursting of it. 2. Phosphorated hidrogen gas is also obtained, if by a direct exposure to a strong heat we effect a combina- tion of phosphorus and lime, and then throw this com- pound into water ; a great quantity of phosphorated hi- drogen gas will soon be formed, and may be obtained in the usual manner over water or mercury. Rationale....The production of phosphorated hidro- gen gas in this manner is analogous to the first, with the only difference that here the decomposition of the water takes place at common temperatures. 3. PhosphoratedjJ|idrogen gas may also be obtained, according to Davy,Tn the following manner: Let water be decomposed in the usual manner, by means of zinc and sulphuric acid, and add to the mixture a quantity of phosphorus. The hidrogen evolved will dissolve part of the phosphorus ; phosphorated hidrogen gas will be produced, and take fire at the surface of the fluid, so long as the decomposition of the water is made, with considerable rapidity. But the gas produced in this process burns with a more lambent flame than that ob- tained in the usual manner, probably on account of con- taining a larger quantity of hidrogen. The experiment is * Nicholson's Journal, April 1802. Phosphorated Hidrogen Gas. 305 nevertheless brilliant; for the gas is disengaged in small bubbles, which cover the whole surface of the fluid; they disengage themselves rapidly, new ones are produced, and the whole fluid resembles a well of fire. Remark....For the success of this experiment, it is es- sential that the water, during the action of its decompo- sition, be considerably heated, which may be effected by a copious addition of sulphuric acid, and that the phospho- rus be present ir a considerable quantity. Half a part of phosphorus cut into small pieces, one of granulated zinc, three of concentrated sulphuric acid, and five of water, answer this purpose exceedingly well. Phosphorated hidrogen gas is also produced by nature. The air which burns at the surface of certain springs, and forms what is called burning springs and the ignis fatui (Jack o'lanterns) which glide along burying-grounds, or places where animal matters are putrifying, consist of hidrogen gas, holding phosphorus in solution. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF PHOSPHORATED HIDROGEN GAS. Experiment I. Phosphorated hidrogen gas takes fire on coming into con- tact with atmospherismgir. THIS may be evinced by charging a small retort with potash, phosphorus, and water, in the manner mentioned before, applying heat and dipping the mouth of the retort into a bason of water. The bubbLs of air which come from the retort and pass through the water will burst with a slight explosion, and produce flashes of fire in the cir- cumambient air; a circular dense white smoke rises hori- zontally like a ring, enlarging itself continually, and form- ing a sort of corona extremely beautiful if the air be per- fectly tranquil. The finest effect is produced wThen the flashes of gas succeed each other but slowlv. 306 Phosphorated Hidrogen Gas. RATioNALE....We have noticed before that phospho- rated hidrogen gas is nothing but hidrogen gas holding phosphorus in solution. When this gazeous fluid is pre- sented to the atmospheric air or oxigen gas, the minutely- divided phosphorus rapidly attracts oxigen and kindles, setting fire at the same time to the hidrogen gas in con- tact with atmospheric air, and hence phosphoric acid and water are formed. The circular crown of white smoke which rises after the explosion of the gas, originates from the coat of water which enveloped the bubble of the gas ; this water, toge- ther with what is formed during the explosion, is sud- denly converted into vapour, it unites to the phosphoric acid produced, and thus constitutes the circular crown of smoke which rises like a ring. If a wide-mouthed phial be filled with phosphorated hidrogen gas and left in that situation over mercury, the gas will take fire when suffered to escape into the air by inclining the phial. REMARK....This last is a hazardous experiment: the phial is often burst to pieces ; it is therefore necessary to surround it with a cloth, in order to avoid dangerous events. An elastic gum bottle may be used for this pur- pose with safety. Experiment II. Accension of phosphorated hidrogen gas by means of oxigen gas. Fill a receive r^th oxigen gas, and convey into it a few bubbles of phosphorated hidrogen ga;^ At the in- stant of the union of the gases, a brilliant flash of fire takes place, accompanied with a report. The rationale of this experiment is analogous to the former. Remark....Great caution is necessary in performing this experiment. The dilatation of the gases which takes place during the explosion is so great that the vessel is apt to be blown to pieces. Not more than a single small bubble of the phosphorated hidrogen gas should be con- veyed into the oxigen gas at once, except the receiver be made of very thick glass. Phosphorated Hidrogen Gas. 307 Experiment III. Accension of phosphorated hidrogen gas, by means of oxigenized muriatic acid gas. If fresh-prepared phosphorated hidrogen gas and oxi- genized muriatic acid gas are mingled together over mer- cury, a considerable detonation takes place, accompanied with a lambent green flame and dense white vapour. Rationale....All that happened in the last experi- ments takes place in this instance. The oxigenized mu- riatic acid is robbed of its oxigen, and becomes converted into simple muriatic acid gas; and water and phosphoric! acid are produced. The evolved heat inflames the phos- phorus which was dissolved in the gas. Rem ark....For the success of this experiment it is es- sential that both gases are fresh prepared. The receiver in which the mixture is made should be very strong, in . order to guard against accidents. Experiment IV. Phosphorated hidrogen gas burns with a green light in nascent oxigenized muriatic acid gas, under the surface of water. Put into an ale-glass, or Florence flask, one part of phosphuret of lime, broken into pieces of the size of a pea (not in small fragments or in powderjand add to it half apart of oxigenated muriate of potash. Fill the vessel with water, and bring carefully into contact with the ma- terials at the bottom of the fluid three or four parts of con- centrated sulphuric acid. This may be most conveni- ently done, by letting the acid fall through a long-necked funnel, reaching to the bottom of the vessel, or by caus- ing it to pass down the sides of it. As soon as the de- composition of the water and that of the oxigenated mu- riate takes place, flashes of fire dart from the surface of the fluid, and the phosphuret illuminates the bottom of the vessel with a beautiful green light. 308 Phosphorated Hidrogen Gas. Experiment V. A riband or piece of silk, impregnated with a solution of muriate of gold, may be gilt by the action of phosphorated hidrogen gas. Take a silk riband, wet it thoroughly with a solution of muriate of gold, and expose it over mercury to the ac- tion of phosphorated hidrogen gas for a few days; the riband in this situation will become covered with gold. The gilding is so permanent that it will bear washing. Rationale....The hidrogen of the phosphorated hi- drogen gas unites to part of the oxid of gold dissolved in the acid, and forms water. The phosphorus thus sepa- rated unites to another part of the oxigen, and produces phosphoric acid. The gold therefore on losing its oxi- gen totally becomes reduced to the metallic state, and at- taches itself by virtue of a strong molecular attraction to the riband. Remark....One part of the crystallized muriate of gold dissolved in eighteen parts of distilled water, seems to answer this purpose extremely well. If the gilding be repeated a second, or even a third, time, its lustre becomes extremely beautiful. Experiment VI. Phosphorated hidrogen gas and sulphureous acid gas decompose each other. Let phosphorated hidrogen gas and sulphureous acid gas, both obtained over mercury, be mingled together, the two gases will lose their elasticity ; plates of yellow mat- ter are deposited on the sides of the vessel, which take fire on hot iron, first in the manner of phosphorus, and after- wards with the characters of sulphur. Rationale....It follows from this experiment that the hidrogen is the only substance which combines with the oxigen in these circumstances, since the gases lose their fluidity and deposit respectively the sulphur and phospho- rus contained in them. Phosphorated Hidrogen Gas. 309 Experiment VII. Phosphorated hidrogen gas is decomposed by vivid light. Though phosphorated hidrogen gas may be kept over mercury in the dark for any length of time unaltered, this is not the case if the gas be exposed to light. If a bottle filled with this gas be painted partly black, or surrounded with black paper, and then exposed to the light of the sun, the union of the phosphorus and hidrogen will be broken, and the phosphorus will be found crystallized at those parts through which the rays of light were suffered to pass, and the hidrogen gass will be left behind. vol *. T t NITROUS GAS. PART XXV. SECT. I. THE name of nitrous gas is given to an aeriform fluid, consisting of a certain quantity of nitrogen gas and oxi- gen ; first described by Priestley, but in some measure known before to Hales. PROPERTIES OF NITROUS GAS. Nitrous gas is an elastic colourless fluid, having no sensible taste: it is neither acid nor alcaline; it is ex- ceedingly hurtful to animals, producing instant suffoca- tion whenever they attempt to breathe it. The greater number of combustible bodies refuse to burn in it. It is nevertheless capable of supporting the combustion of some of these bodies. Phosphorus burns in nitrous gas when introduced into it in a state of inflammation; pyrophorus takes fire in it spontaneously. It is not decomposable by water; though 100 cubic inches of this fluid, when freed from air, absorb about 11.8 cubic inches of gas. This solution is void of taste ; it does not redden blue vegetable colours; the gas is expelled again when the water is made to boil or suf- fered to freeze. It has no action on nitrogen gas even when assisted by heat. It is decomposed by several me- tals at high temperatures. Methods of obtaining Nitrous Gas. 311 Its specific gravity, when perfectly pure, is to that of atmospheric air as 1.093 to 1. Ardent spirit, saccharine matters, hidro carbonates, sul- phureous acid, and phosphorus, have no action on it. It is not sensibly changed by the action of light. Heat dilates it. It rapidly combines with oxigen gas at common tem- peratures, and converts it into nitrous acid. Atmospheric air produces the same effect, but with less intensity. It is absorbable by green sulphate, muriate, and nitrate of iron, and decomposable by alcaline, terrene, and metallic sul- phurets, and other bodies that have a strong affinity for oxigen; but is not capable of combining with them che- mically, so as to form saline compounds. From the greatest number of bodies which absorb it, it maybe again expelled by the application of heat. It communicates to flame a greenish colour before ex- tinguishing it; when mixed with hidrogen gas it acquires the property of burning with a green flame. It is absor- bable by nitric acid, and renders it fuming. When exposed to the action of caloric in an ignited por- celain tube, it experiences no alteration; but when electric sparks are made to pass through it, it is decomposed and converted into nitrous acid, and nitrogen gas. Phospfiibrus does not shine in it. It is composed of 56 parts of oxigen, and 44 nitrogen. METHODS OF OBTAINING NITROUS GAS. 1. Put into a small proof or retort some copper wire, or pieces of the same metal, and pour on it nitric acid of commerce diluted with water; an effervescence takes place, and nitrous gas will be produced. After having suffered the gas to escape for a few minutes on account of the atmospheric air contained in the retort, collect the gas in the water apparatus as usual. In order to obtain the gas in a pure state, it must then be shook for some time in contact with water. Rationale....We have seen before that water was decomposed on bringing in contact with it a metal and an acid; but here the case is different; the water in this instance suffers no alteration, on the contrary, the acid undergoes a partial decomposition; the metal 312 Methods of obtaining Nitrous Gas. robs the nitric acid of the greatest part of its oxigen, and becomes oxidated ; the remainder of the acid having lost so much of its oxigen, becomes thereby so altered, that at the usual temperature it can exist no longer in the liquid state, but instantly expands, and assumes the form of gas; ceasing at the same time to act as an acid, and exhibiting different properties. Instead of presenting copper to nitric acid, iron, zinc, mercury, or silver, may be made use of. The metals best suited for the production of nitrous gas are silver, mercury, and copper. 2. Nitrous gas may likewise be obtained by synthesis. This method of obtaining it we owe to Dr. Milner of Cambridge. In the'middle of an earthen tube about 20 inches long, and | wide, open at both ends, put as much coarsely-pow- dered manganese as is sufficient nearly to fill it. Let this tube traverse the universal furnace. To one end of the tube lute a retort containing water strongly impregnated with ammonia, and to the other adapt a bent glass tube which passes into the pneumatic trough. Let a fire be kinged in the furnace, and when the manganese may be supposed to be red-hot apply a gentle heat to the retort, and drive over it the vapour of the ammonia; the conse- quence will be that nitrous gas will be delivered at one end of the tube, at the time that the ammonia enters the other end; and this effect does not take place without the presence of the alcali. Rationale....Ammonia consists of hidrogen and ni- trogen : its hidrogen combines with the oxigen which is given out by the ignited manganese, and forms water; its nitrogen unites at the same time to another portion of the oxigen, and constitutes the nitrous gas. Remark....There is a cause of deception in this ex- periment, against which the operator ought to be on his guard, lest he should conclude no nitrous gas is formed, when in reality there is a considerable quantity. The ammonia, notwithstanding every precaution, will frequently pass over undecomposed. If the receiver in the pneumatic trough is filled with water, great part of this will indeed be presently absorbed, but still some portion of it will mix with the nitrous gas formed in the process. Upon admitting the atmospheric Proofs of the Properties of Nitrous Gas. 313 air, the nitrous gas will become decomposed, and the red nitrous fumes instantly unite with the alcali. The receiver is presently filled with white clouds of nitrate of ammonia; and in this manner a wrong conclusion may ea- sily be drawn from the want of the orange colour of the nitrous fumes. A considerable quantity of nitrous gas may have been formed, and yet no orange colour appear, owing to this circumstance ; and therefore it is easy to understand how a small quantity of nitrous gas may be most effectually disguised by the same cause. Dr. Milner* also obtained nitrous gas, by passing am- moniacal gas over sulphate of iron deprived of its water of crystallization. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF NITROUS GAS. Experiment I. Nitrous gas decomposes atmospheric air. IT was mentioned before that nitrous gas greedily at- tracts oxigen of the atmospheric air. We shall demon- strate this fact, and show at the same time that during this union an acid is produced. Pass up into a cylindrical glass vessel, over water, about one measure of nitrous gas and two of common air; the two fluids will speedily unite, red fumes will be produced, and the volume of the two combined gases will be dimi- nished. A considerable degree of heat will be perceived, the water will rise in the cylinder and absorb the red va- pours. When the two gases have been mixed in due proportion, nothing remains at last but the nitrogen gas of the atmospheric air. Usually 16 measures of common air are requisite to destroy completely 7\ measures of nitrous gas, this however varies according to the purity of the airs. Rationale....The nitrous gas in this experiment de- composes the atmospheric air; it takes the oxigen from the nitrogen gas, unites with it, and forms nitrous acid; * Phil. Trans. LXXIX. p. 300 3H4 Proofs of the Properties of Nitrous Gas. tlhe nitrogen is therefore left behind ; the heat which is generated is the caloric which kept the gases in solution, vfhich now becomes liberated. If instead of atmospheric air oxigen gas be substituted, this phenomenon will be still more striking. If a pint of pure oxigen gas be mixed with two of nitrous gas, the redness will be much greater, and the volume of the gases almost entirely disappear. Remark....Upon the property which nitrous gas has of absorbing the oxigen of the atmosphere, Priestley and Fontana founded the construction of their eudiometers already mentioned. Experiment II. Proofs that an acid is produced during the mixture of ni- trous gas and atmospheric air or oxigen gas. Paste a slip of litmus paper within a glass jar, near the bottom, and into the jar, filled with and inverted in water, pass as much nitrous gas, previously well washed, as will displace the fluid below the level of the paper ; the blue colour of the paper will remain unaltered, but on send- ing up atmospheric air, or oxigen gas, it will immediately change its blue colour to red. A sure proof that an acid has been formed. That it is nitrous acid which is produced by the union of nitrous gas, and oxigen gas may be evinced in the fol- lowing Experiment III. Into a jar filled with and inverted over mercury put a small quantity of solution of pure potash, and afterwards measures of oxigen and nitrous gases separately and in proper proportion as long as an absorption takes place. On removing the solution from the jar and evaporating it in a glass bason, crystals of salt will be formed, which exhibit all the properties of nitrate of potash. Experiment IV. Nitrous gas is absorbed by nitric acid, to which it gives new characters. Let nitrous gas pass as it is liberated from the materials Proofs of the Properties of Nitrous Gas. 315 which afford it into a bottle containing colourless nitric acid; the acid will first become yellow, then green, next orange-coloured, and at last dark olive-coloured and fuming. RATiONALE....The change of colour depends on the absorption of different quantities of nitrogen gas. Priestley found that 100 parts of nitric acid of a moderate strength absorbed in two'days 90.29 of nitrous gas. He informs us that when about seven parts were absorbed, the acid as- sumed an orange-colour; when eighteen parts were ab- sorbed, a green colour; and that when the 90.29 were combined it became red and fuming. Remark....If the olive-coloured acid be diluted with water, it becomes blue ; the orange-coloured when united with water becomes emerald-green; and a large quantity of water renders either of them colourless. Experiment V. Nitrous gas which has been absorbed by nitric acid may, be expelled again from this fluid. This may be shewn by gently heating the acid coloured in the before-going experiment till it becomes limpid. In this experiment light should be excluded. RATiONALE....The nitrous gas absorbed by the acid has a greater affinity for caloric than the nitric acid has; this property therefore is here employed for disengaging the nitrous gas which rendered the acid fuming. Experiment VI. Nitrous gas tinges the fame of burning bodies green. Fill a wide-mouthed bottle with a mixture of one part of nitrous gas, and four of hidrogen gas; set fire to it with a lighted taper, and the mixture will burn with a green flame. If a lighted taper be immersed in nitrous gas, it exhibits a green flame before the taper becomes extin- guished. 316 Proofs of the Properties of Nitrous Gas. Experiment VII. Nitrous gas is unfit for'maintaining the combustion of the greater number of burning bodies. Fill a receiver with nitrous gas, and let down into it a burning taper; the taper will instantly be extinguished: the same thing will happen to ardent spirit, oils, &c. though burning with a vivid flame. That nitrous gas however is capable of supporting the combustion of other bodies will be obvious from the fol- lowing experiments: Experiment VIII. Accension of pyrophorus in nitrous gas. Place some new-made pyrophorus in a copper spoon, and introduce it into a receiver filled with nitrous gas; the pyrophorus will instantly take fire, and the volume of the gas will become diminished. RATioNALE....The pyrophorus effects a real analysis of the gas, it subtracts its oxigen, and leaves its nitrogen behind; hence if the remaining air be examined it will be found that it renders lime or barytic water turbid, and that it undergoes no further diminution when mingled with oxigen gas; it is therefore a mixture of carbonic acid and nitrogen gas. Experiment IX. Nitrous gas maintains the combustion of phosphorus when introduced in a state of actual inflammation. Though phosphorus may be fused and even sublimed in nitrous gas without producing the slightest luminous appearance, if the gas be perfectly pure ; yet if a bit of phosphorus be placed in a copper ladle, then inflamed and introduced into the gas when in a state of actual in- flammation, it burns with almost as much brilliancy as in oxigen gas. Proofs of the Properties of Nitrous Gas. 317 Rationale....The rationale of this experiment proves that at the heat of ignition, phosphorus is capable of dis- turbing the equilibrium of the affinity subsisting between oxigen and nitrogen in nitrous gas, on which account it attracts the former from the nitrous gas, and leaves the latter behind. Experiment X. Nitrous gas inflames charcoal when introduced in a state of ignition. If a piece of charcoal thoroughly ignited be introduced into nitrous gas there will also be a vivid inflammation ; this experiment may likewise be performed by setting fire to the charcoal confined in nitrous gas by means of a burning lens. Rationale....The charcoal at the temperature of ig- nition decomposes the nitrous gas by subtracting its oxi- gen ; hence carbonic acid is formed, which maybe evin- ced by admitting to the residuary gas a solution of bary- tes, strontia, or lime in water. Experiment XL Nitrous gas is absorbed by green muriate, sulphate, and nitrate of iron. A very concentrated solution of pure green muriate of iron (prepared by dissolving iron filings perfectly free from rust in muriatic acid, evaporating the solution brisk- ly, and preserving it from the contact ofatmospheric air) is extremely well calculated to ascertain the quantity of nitrogen gas contained in a given quantity of nitrous gas in an easy manner. To prove the absorption of nitrous gas by this means, it is only necessary to agitate in a graduated tube a quan- tity of the gas in contact with the solution ; the green so- lution of iron will soon assume a brown colour, the gas will be diminished, and the solution ascend into the tube. A solution of pure green sulphate of iron (prepared by dissolving clean iron filings in sulphuric acid, and thfn vol. i. u u 318 Proofs of the Properties of Nitrous Gas. agitating the solution in contact with sulphurated hidro- gen gas) answers the same purpose. Pale green nitrate of iron may likewise be used with advantage. Rationale....The absorption of the nitrous gas, by means of these solutions, takes place without any decom- position of it at common temperatures. It depends mere- ly on an equilibrium of affinity produced by the following simple attractions. 1. That of green oxid of iron for the oxigen of nitrous gas and water. 2. That of the hidrogen of the water for the nitrogen of the nitrous gas ; and, 3. That of the principles of the sulphuric acid for ni- trogen and hidrogen. Remark....That this is the true cause of the absorption professer Davy has sufficiently proved in his Research- es, p. 176. Vauquelin and Hui.ibolthave been mistaken with regard to its nature; * the products they obtained must have arisen from the exposure of their impregnated solution to the atmosphere. The absorption of nitrous gas by means of these solu- tions of iron is proportionable to the degree of the con- centration of the solution. Seventy-five cubic inches of concentrated solution of muriate of iron absorb about 18 of nitrous gas. Sulphate of iron absorbs only one half of this quantity; the gas absorbed may be expelled again by heat. Nitrous gas (according to Davy) is also absorbed by me-ms of white prussiate of iron, in contact with water ; by sulphate of tin; sulphate and muriate of zinc at the minimum of oxidation ; and probably by many other me- tallic solutions hitherto not tried. In fact, whenever the metals capable of decomposing water exist in solution at their minimum of oxidation, the affinities exerted by them on nitrous gas and water will be such as to produce combinations ; the powers of metal- lic solutions to combine with nitrous gas at common tem- peratures, as well as to decompose it at higher tempera- tures, Davy supposes to be probably in the ratio of the affinity of the metallic oxids they contain for oxigen. * Annates de Chimie, torn. 88, p. 187. Proofs of the Properties of Nitrous Gas. Experiment XII. Decomposition of nitrous gas by nascent hidrogen gas. When nitrous gas is exposed to wetted iron filings, a diminution of its volume slowly takes place; the iron be- comes oxidated, and ammonia is formed. For performing this experiment, wetted iron filings may be exposed oh a shallow dish or plate supported by a stand to the action of the gas contained in a broad receiv- er ; the vessel containing the iron filings may next be removed by withdrawing it through the water, and the remaining gas may be made the subject of experiment. This decomposition of nitrous gas is more quickly effected by putting plates of iron into a solution of nitrate of copper. Rationale....The water in contact with the iron is decomposed by virtue of the affinity subsisting between its oxigen and the iron. Its hidrogen, with a portion of oxigen, at the same, time attracts the nitrogen of the ni- trous gas, and produces water, ammonia, and nitrous oxid. Rem a rk.—That the iron is not oxidated in this process at the expence of the oxigen of the nitrous gas becomes obvious, when we consider that water is essentially ne- cessary to produce the decomposition; for dry iron filings effect no change whatever in nitrous gas at the usual temperatures. Alcaline sulphurets moistened with water, put into a vessel filled with nitrous gas, decompose it in a short time ; the remaining gas is no longer reddened by the contact of air, the greatest part is nitrous oxid. Experiment XIII. Nitrous gas is decomposed by exposure to zinc and water. When nitrous gas is exposed, to a lage surface of zinc in contact with water, it will be slowly converted into nitrous oxid; at the same time that ammonia is generated and white oxid of zinc is formed, if the process is suffer- ed to go on for a considerable time. 320 Proofs of the Properties of Nitrous Gas. Rationale....These phenomena depend, like the for- mer, upon the decomposition of water by the affinities of part of the oxigen and nitrous gas, for its hidrogen to form ammoni and water. Rem ark....Zinc placed in contact with water, and confined, by mercury, decomposes it, as Davy observed, at common temperatures. But zinc, when perfectly dry, does n-'t in the slightest degree act upon nitrous gas. Van Marum remarked that tin, lead, iron, and mercury, were all oxidated by taking the electric spark in contact with nitrous gas. Davy, who has made the greatest num- ber of experiments concerning the nature of nitrous gas, considers the analysis of it by charcoal as affording data best calculated for determining the respective quantities of nitrogen and oxigen in a given bulk of nitrous gas, and correcting it by mean calculations derived from the de- composition of nitrous ga"s by pyrophorus and hidrogen, and its conversion into nitrous oxid, concluded that 100 grains of nitrous gas are composed of 55.95 of oxigen and 44.05 of nitrogen gas; or taking away decimals of 56. oxigen and 44. nitrogen gas. This estimation agrees very well with the mean proportions of Priestley's experiments. But as Priestley never ascertained the absolute purity of the gas he made use of, and probably employed different kinds, indifferent experiments, it is impossible to fix on any one from which accurate conclusions can i;e drawn. Lavoisier's estimation of the respective quantities of oxigen and nitrogen gas entering into the composition of nitrous gas has been generally adopted. He supposed 64 parts of nitrous gas to be composed of 43^ of oxigen and 20| of nitrogen gas. The difference between this and Davy's account is very great indeed; but Davy* has pointed out many sources of error in the experiments of this great man concerning the decomposition of nitrate of potash by charcoal, which were fundamental to his ac- count of the composition of this gas. * Researches chemical and philosophical, 1800, Div. 1. GAZEOUS OXID OF NITROGEN; OR NITROUS OXID. PART XXVI. THE combination of nitrogen and oxigen, which we considered before under the name of nitrous gas, does not constitute the first degree of oxigenation of nitrogen; there is another degree below this. This combination was formerly called dephlogisticated nitrous gas, but now ga- zeous oxid of nitrogen, or nitrous oxid. It was first dis- covered by Priestley. Its nature and properties have since been investigated (though not very accurately) by a society of Dutch chemists. Professor Davy has examined with uncommon accu- racy the formation and properties of all the substances concerned in its production. He has detected the sources of error in the experiments of Priestley and the Dutch chemists, and to him We are indebted for a thorough knowledge of this gas. We shall therefore exhihit the philosophy of this gazeous fluid as we find it in his re- searches concerning the nitrous oxid. SECT. I. PROPERTIES OF GAZEOUS OXID OF NITROGEN. GAZEOUS oxid of nitrogen exists in the form of permanent gas. A candle burns with a brilliant flame and crackling noise in it; before its extinction the white inner flame becomes surrounded with a blue one. 322 Properties of Gazeous Oxid of Nitrogen. Phosphorus introduced into it, in a state oi actual inflam- mation, burns with increased splendour, as in oxigen gas. Sulphur introduced into it when burning with a feeble blue flame is instantly extinguished ; but when in a state oi vivid inflammation, it burns with a rose-coloured flame. Ignited charcoal burns in it more brilliantly than in at- mospheric air. Iron wire, with a small piece of wood af- fixed to it when inflamed, and introduced into a vessel filled with this gas, burns vehemently, and throws out bright scintillating sparks. No combustible body how- ever burns in it, unless it be previously brought to a state of vivid inflammation. Hence sulphur may be melted, and even sublimed in it; phosphorus may be liquefied in it without undergoing combustion. Nitrous oxid is pretty rapidly absorbed by water that has been boiled ; a quantity of gas equal to rather more than half the bulk of the wa- ter may be thus made to disappear ; the water acquires a sweetish taste, but its other properties do not differ per- ceptibly from common water. The whole of the gas may be expelled again by heat. It does not change blue ve- getable colours. It has a distinctly sweet taste, and a faint but agreeable odour. It undergoes no diminution when mingled with oxigen or nitrous gas. Most of the liquid inflammable bodies, such as ether, alcohol, volatile and fat oils, absorb it rapidly and in great quantity. Acids exert but little action on it. The affinity of the neutro- saline solutions for gazeous oxid of nitrogen is very fee- ble. Green muriate and green sulphate of iron, whether holding nitrous gas in solution or not, do not act upon it. None of the gases, when mingled with it, suffer any per- ceptible change at common temperatures ; the muriatic and sulphureous acid gases excepted, which undergo a slight expansion. Alcalies freed from carbonic acid ex- posed in the dry or solid form have no action upon it; they may however be made to combine with it in the na- scent state, and then constitute saline compounds of a pe- culiar nature. These combinations deflagrate when heat- ed with charcoal, and are decomposed by acids ; the ga- zeous oxid of nitrogen being disengaged. It undergoes no change whatever from the simple effect of light. The action of the electric spark for a long while continued, converts it into a gas analogous to atmospheric air and ni- trous acid ; the same is the case when it is made to pass Methods ofobtdining Gazeous Oxid of Nitrogen. 323 through an ignited earthen tube. It explodes with hidro- gen in a variety of proportions at very high temperatures; for instance, when electric sparks are made to pass through the mixture. Sulphurated hidrogen, heavy and light carbonated hidrogen gases, and gazeous oxid of carbon, likewise burn with it when a red heat is applied. 100 parts by weight of nitrous oxid contain 36.7 of oxigen and 63.3 of nitrogen; 100 cubic inches weigh 50grains at 55° temperature and 30 atmospheric pressure. Ani- mals when wholly confined in gazeous oxid of nitrogen give no signs of uneasiness for some moments, but they soon become restless and die. When gazeous oxid of nitrogen is mingled with atmospheric air, and then re- ceived into the lungs, it generates highly pleasurable sen- sations ; the effects it produces on the animal system are eminently distinguished from every other chemical agent. It excites every fibre to action, and rouses the faculties of the mind, inducing a state of great exhilaration, an irre- sistible propensity to laughter, a rapid flow of vivid ideas, and unusual vigour and fitness for muscular exertions, in some respects resembling those attendant on the plea- santest period of intoxication, without any subsequent languor, depression of nervous energy, or disagret ^ble feelings; but more generally followed by vigour, an\,a pleasurable disposition to exertion, which gradually sub- sides. Such are the properties which characterize the nitrous oxid. The Dutch chemists and some French and German philosophers assert* that it cannot be respired; that burn- ing phosphorus, sulphur, and charcoal, are extinguished in it, &c. It is probable they did not examine it in a state of purity, for it is otherwise difficult to account for these and many other erroneous opinions. METHODS OF OBTAINING GAZEOUS OXID OF NITROGEN. Gazeous oxid of nitrogen is produced when substances Having a strong affinity with oxigen are brought into * Gren's Principles of Chemistry, 1800. Scherer's Introduction to the Knowledge of Gazeous Bodies, 1801. 324 Methods of obtaining Gazeous Oxid of Nitrogen. contact with nitric acid, or with nitrous gas. It may therefore be obtained by various processes, in which nitrous gas or nitric acid is decomposed by substances capable of attracting the greater part of their oxigen. The most commodious and expeditious, as well as the cheapest mode of obtaining it, is by decomposing nitrate of ammonia, at a certain temperature, in the following manner. 1. Introduce into a glass retort some nitrate of ammo- nia, and apply the heat of an Argand's lamp ; the salt will soon liquefy, and when it begins to boil, gas will be evolv- ed. Increase the heat gradually till the body and neck of the retort become filled with a semi-transparent milky- white vapour. In this state the temperature of the fused nitrate is between 340° and 480°. After the decompo- sition has proceeded for a few minutes, so that the gas evolved quickly enlarges the flame of a taper held near the orifice of the retort, it may be collected over water, care being taken during the whole process never to suffer the temperature of the fused nitrate to rise above 500° Fahr. which may be easily judged of, from the density of the vapours in the retort, and from the quiet ebullition of thgp'iused nitrate ; for if the heat be increased beyond this r/fintthe vapours in the retort acquire a reddish and more transparent appearance ; and the fused nitrate begins to rise, and occupy twice the bulk it did before. The ni- trous oxid after its generation is allowed to stand over water for at least six hours, and is then fit for respiration or other experiments. Rationale....Nitrate of ammonia consists of nitric acid and ammonia; nitric acid is composed of nitrous gas and oxigen ; and ammonia consists of hidrogen and nitrogen. At a temperature of about 480° the attractions of hidrogen for nitrogen in ammonia, and that of nitrous gas for oxigen in nitric acid, are diminished; while, on the contrary, the attractions of the hidrogen of ammonia for the oxigen of the nitric acid, and that of the remaining nitrogen of the ammonia for the nitrous gas of the nitric acid, are increased: hence all the former affinities are broken, and new ones produced, namely ; the hidrogen of the ammonia attracts the oxigen of the nitric acid, the result of which is water'; the nitrogen of the ammonia combines with the liberated nitrous gas, and forms nitrous Production of Gazeous Oxid of Nitrogen. 325 oxid. The water and nitrous oxid produced probably ex- ist in binary combination in the aeriform state at the temperature of the decomposition. Such is the philosophy of the production of gazeous oxid of nitrogen, by decomposing nitrate of ammonia at that temperature, given by Davy. To illustrate this complicated play of affinity more fully, the following sketch may not be deemed superfluous. DIAGRAM, EXHIBITING THE PRODUCTION OF GAZEOUS OXID OF NITROGEN, BY DECOMPOSING NITRATE OF AMMONIA AT 480° FAHK. (U to 2 r* •t o e CO O p CO Nitric Acid. O NITRATE OF AMMONIA. J Ammonia. o a » N 2 CD o c "I o CO Oq O a o ~> Remark....Professor Davy has likewise pointed out, that when the heat employed for decomposing nitrate of ammonia is raised above the before-stated temperature, another play of affinities takes place; the attractions of nitrogen and hidrogen for each other, and of oxigen for nitrous gas, are still more diminished, whilst that of nitro- gen for nitrous gas is totally destroyed, and that of hidro- VOL. i. xx 326 Production of Gazeous Oxid of Nitrogen. gen for oxigen increased to a greater extent. A new at- traction likewise takes place, namely, that of nitrous gas for nitric acid to form nitrous vapour,* and a new arrange- ment of principles is rapidly produced: the nitrogen of the ammonia having no affinity for any of the single prin- ciples at this temperature, enters into no binary compound; the oxigen of the nitric acid forms water with the hidro- gen", and the nitrous gas combines with the nitric acid to form nitrous vapour. All these substances most probably exist in combination at the temperature of their production ; and at a lower temperature assume the form of nitrous acid, nitrous gas, nitrogen, and water; and hence we see the necessity of not heating the nitrate of ammonia above the before- stated temperature. On account of the rapid absorption of gazeous oxid of nitrogen by water, it is economical to preserve the fluid which has been used to confine this gas, and to make use of it for collecting other quantities of it. In order to hasten its production, the nitrate of ammonia may be pre- viously freed from its water of crystallization by gently fusing it in a glass of Wedgwood's bason for a few mi- nutes, and then keeping it for use in a well-stopped bottle. 2. Nitrous oxid may likewise be obtained by exposing common nitrous gas to alcaline sulphites, particularly to sulphite of potash containing its full quantity of water of crystallization. The nitrous oxid produced from nitrous gas by sulphite of potash, has all the properties of that ge- nerated from the decomposition of nitrate of ammonia. Rationale....The conversion of nitrous gas into ni- trous oxid by these bodies, depends on the abstraction of a portion of its oxigen by the greater affinity of the sul- phite presented to it. The nitrogen and remaining oxi- gen assume a more condensed state of existence, and con- stitute nitrous oxid. 3. Nitrous oxid may also be obtained by mingling to- gether nitrous gas and sulphurated hidrogen gas. The volume of gases in this case is diminised, sulphur depo- sited, ammonia, water, and nitrous oxid are formed. Rationale....The change of principles which takes place in this experiment depends upon the combination of the hidrogen of the sulphurated hidrogen gas with dif- • Hence the reddish vapour in the retort, stated before, p. 324. Production of Gazeous Oxid of Nitrogen. 327 ferent portions of the oxigen and nitrogen of the nitrous gas, to form water and ammonia, and to deposit sulphur. The remaining oxigen and nitrogen being left in due pro- portion to constitute nitrous oxid. Remark.....This singular exertion of attractions by a simple body appears highly improbable, a priori ; but the formation of ammonia, and the non-oxigenation of the sulphur, elucidate the fact. In performing this experi- ment, care should be taken that the gases should be ren- dered as dry as possible ; for the presence of water consi- derably retards the decomposition. 4. Nitrous oxid may also be produced by presenting alcaline sulphurets to nitrous gas. Davy observed that a solution of sulphuret of strontia or barytes answers this purpose best. Rationale....This decomposition of nitrous gas is not solely produced by7 the abstraction of oxigen from the . nitrous gas to form sulphuric acid. It depends equally on the decomposition of the sulphurated hidrogen dis- solved in the solution or liberated from it. In this pro- cess sulphur is deposited, and sulphuric acid formed. 5. Nitrous oxid is obtained in many circumstances si- milar to those in which nitrous gas is produced. Dr. Priestley found that nitrous oxid was evolved, together with nitrous gas, during the solution of iron, tin, and zinc, in nitric acid. Rationale.....It is difficult to ascertain the exact rationale of these processes, for very complicated agencies of affinities take place. Either the nascent hidrogen aris- ing from the decomposition of the water by the rnetallic substance may combine with portions of the oxigen and nitrogen of the nitrous gas ; and thus by forming water and ammonia, convert it into nitrous oxid ; or the me- tallic substance may attract at the same time oxigen from the water and nitrous gas, whilst the nascent hidrogen of the water seizes upon a portion of the nitrogen of the nitrous gas to form ammonia. The analogy between thi^ process and the decomposition of nitrous gas by sulphurat- ed hidrogen, render the first opinion most probable. Such are the principal methods of obtaining nitrous oxid. There are no reasons, Davy thinks, for supposing that nitrous oxid is formed in any of the processes ot nature ; and the nice equilibrium of affinitv hv which it is 328 Proofs of the Properties of Gazeous Oxid of Nitrogen. constituted forbids us to hope for the power of composing it from its simple principles. We must be content to produce it artificially. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF GAZEOUS OXID OF NITROGEN. Experiment I. Gazeous oxid of nitrogen is rapidly absorbed by water. FILL a glass cylinder or graduated tube with water previously boiled, and invert it in a bason of the same fluid. Having done this, send up into it a quantity of nitrous oxid, and mark the level of the water in the cylin- der. Then agitate it for a few minutes in the water, and the bulk of the gas will be seen considerably diminishing. Water may thus be made to absorb about one half of its own bulk of gazeous oxid of nitrogen. On boiling the water, the gas which was absorbed will be liberated, possessing all its former properties. If nitrous oxid be repeatedly exposed to water, the residual gas will be the common air previously contained in the water, and from which it can in no case be perfectly freed by ebullition; this air becomes separated on ac- count of the greater affinity of water for nitrous oxid. The quantity of common air thus produced generally amounts to about TV part of the volume of water. The absorption of nitrous oxid by the inflammable fluids enumerated before may be evinced in a similar manner. Experiment II. Combustible bodies do not burn in gazeous oxid of nitro- gen, except xvhen in a state of actual inflammation. Fill ajar over mercury with gazeous oxid of nitrogen, and keep it over that fluid ; introduce into it a small piece Proofs of the Properties of Gazeous Oxid of Nitrogen. 329 of sulphur, camphor, or phosphorus, and touch these sub- stances with a bent wire heated to a dull redness. The sulphur, camphor, or phosphorus, will melt, and conti- nuing the heat may even be made to sublime in the gas, but no accension will take place. But that the gas is capable of maintaining the combus- tion of inflammable substances becomes evident from the following facts. Experiment III. Combustion of the taper in gazeous oxid of nitrogen. Immerse a lighted taper into a jar filled with nitrous oxid. The flame of the taper will become instantly larger; it will first burn with a brilliant white flame, and sparkle as in oxigen gas. As the combustion goes on, the lustre of the flame diminishes; it gradually lengthens, and becomes surrounded with a pale blue cone of light, from the apex of which much unburnt charcoal is thrown off in the form of smoke. The flame continues double to the end of the process. Experiment IV. Combustion of phosphorus in gazeous oxid of nitrogen. Put a piece of phosphorus of the size of a pea into a copper ladle, set fire to the phosphorus with a match, and quickly introduce it into a jar filled with the gas. The phosphorus will continue to burn with a splendour nearly equal to that in oxigen gas. The accension of phosphorus may likewise be evinced in the following manner. Experiment V. Fill a strong glass cylinder over mercury, one-eighth full of gazeous oxid of nitrogen ; send up into it a few 330 Proofs of the Properties of Gazeous Oxid of Nitrogen. grains of phosphorus, heat abent iron wire white-hot, and introduce it quickly through the mercury to touch the phosphorus, which thus will take fire instantly with a considerable detonation. Remark....Thisexperiment requires caution: the cy- linder in which the phosphorus is inflamed should be very strong. The gazeous oxid employed should not exceed one-eighth of the capacity of the jar. The wire for the inflammation ought to be very well curved, so as to be expeditiously introduced into the jar, and capable of being quickly withdrawn. We have witnessed several acci- dents where the detonating jar burst during this expe- riment. Another very successful method is as follows. Experiment VI. Let the jar containing the gazeous oxid of nitrogen be placed over mercury ; introduce the phosphorus in a small tube containing oxigen gas, so balanced as to swim on the surface of the mercury without communicating with the gazeous oxid. The phosphorus is then fired in the oxigen gas with an ignited iron wire ; by which, at the moment of combustion, the tube containing it must be raised into the gazeous oxid, and thus the combustion continues. Experiment VII. Sulphur burning with a feeble blue flame becomes instantly extinguished in gazeous oxid of nitrogen. Put a piece of sulphur into a copper ladle, set fire to it by means of a candle, and when it begins to burn with a blue feeble flame, introduce it into ajar filled with gazeous oxid of nitrogen. The sulphur will be extinguished the instant it is plunged into the gas. But that sulphur may be made to burn in it becomes obvious from the following Experiment VIII. Sulphur in a state of vivid inflammation burns with a rose-coloured fame in gazeous oxid of nitrogen. Dip a slip of copper into melted sulphur ; when cold set fire to it, and when in an actual state of combustion Proofs of the Properties of Gazeous Oxid of Nitrogen. 3 31 introduce it into ajar filled with the gas, it will continue burning with a beautiful flame very much enlarged and of a vivid rose-colour. This experiment may be more accurately performed in the same manner as the inflammation of phosphorus ; namely, by introducing it into the small vessel filled with oxigen gas, and igniting it by means of the heated wire. Experiment IX. Detonation of gazeous oxid of nitrogen with carbonated hidrogen gas. Nitrous oxid and carbonated hidrogen gas possess no action on each other except at high temperatures. But when mingled together in certain proportions and expos- ed to the electric spark, a new arrangement of their prin- ciples takes place. This mayr be proved in the follow- ing manner. Mingle together in a detonating tube 35 parts of gaze- ous oxid of nitrogen, and 15 of carbonated hidrogen gas. On passing the electric spark through it, the inflammation will be very vivid, and the light produced, bright red. After the explosion, the space occupied by the gases will be about 60. When 22 parts of nitrous oxid and 20 of hidro-carbo- nate are exploded, the residue fills a space equal to 45. If strontia water be brought into contact with the gas after the detonation, a white precipitate is instantlyform- ed and a diminution takes place. On presenting nitrous gas to this residue, the gas again becomes diminished. Rationale....Reasoning from analogy, there can be little doubt but that when carbonated hidrogen gas is in- flamed with excess of gazeous oxid of nitrogen, it will be only partially decomposed or converted into nitrogen, nitrous acid, and atmospheric air. Experiment X. Gazeous oxid of nitrogen and phosphorated hidrogen gas detonate likewise. Phosphorated hidrogen gas, and gazeous oxid of nitro- gen, exert no action upon each other at common tempe- 322 Proofs of the Properties of Gazeous Oxid of Nitrogen. ratures ; but that they may be made to act upon each other at a very high temperature the following experi- ments will prove. 1. Mix ten grain measures of phosphorated hidrogen gas and 52 of gazeous oxid of nitrogen in a graduated detonating tube, and pass the electric spark through it. A very vivid inflammation will take place, and the tube will be filled with white vapour. The volume of the gas left behind will fill a space nearly equal to 60. On agitating this fluid in contact with water no absorption will take place. On admitting niitrous gas a diminution ensues. Rationale....It appears from this experiment that when a small quantity of phosphorated hidrogen gas is inflamed with gazeous oxid of nitrogen, both the phos- phorus and hidrogen are consumed ; whilst the supera- bundant gazeous oxid is converted into nitrous acid and atmospheric air by the ignition ; or a certain quantity is partially decomposed into atmospheric air by the com- bination of a portion of its oxigen with the combus- tible gas. 2. Twenty-five parts of gazeous oxid of nitrogen, mingled with 10 of phosphorated hidrogen gas, may like- wise be inflamed. After the detonation, white dense va- pours become visible, and the gas left occupies a space equal to 25. The residuary gas is not absorbable by wa- ter : on admitting a solution of green sulphate of iron, or prussiate of potash, no blue or green precipitate is pro- duced ; but if 25 parts of nitrous gas are mingled with it, the result will be 50. Rationale....From this experiment we learn that when phosphorated hidrogen gas and gazeous oxid are to each other as 25 to 10, they both disappear, whilst nitro- gen is evolved, and water and phosphoric acid produc- ed. Reasoning concerning the composition of gazeous oxid of nitrogen from this result, we should conclude that it was composed of about 38 oxigen and 62 nitrogen. 3. Ten grain measures of gazeous oxid, mingled with 20 of phosphorated hidrogen gas, cannot be inflamed. 4. Twenty-five of gazeous oxid of nitrogen with 20 of phosphorated hidrogen gas inflame readily. The gas Proofs of the Properties of Gazeous Qxid of Nitrogen. 333 after detonation is likewise opaque, and fills a space equal to about 45. The residue is not miscible with water • no white fumes are produced by admitting oxigen gas. Rationale....Here we are taught that the affinity of phosphorus for the oxigen of gazeous oxid of nitrogen is stronger than that of hidrogen at the temperature of ignition; so that when phosphorated hidrogen gas is mingled with a quantity of gazeous oxid of nitrogen, not containing sufficient oxigen to burn both its constituent parts, the phosphorus only is consumed, and the hidrogen is liberated. Experiment XL Combustion of charcoal in gazeous oxid of nitrogen. This experiment is best performed by introducing a small piece of charcoal into ajar filled with nitrous oxid, confined by mercury, and then applying the focus of a burning lens. The charcoal will thus take fire, and burn vividly. It may likewise be performed by fixing a piece of well- burnt charcoal to a copper wire, igniting the charcoal com- pletely, and introducing it into the gas. Experiment XII. Combustion of iron in gazeous oxid of nitrogen. The experiment may be performed in a manner similar to the combustion of iron in oxigen gas, or more accu- rately, by setting fire to the touch-wood affixed to the wire by means of a burning glass. Experiment XIII. Combustion of zinc in gazeous oxid of nitrogen. Take shavings of zinc, form them into a ball, in the mid- dle of which a few grains of phosphorus must be included ; affix the ball of zinc shavings to a copper wire, set fire to vol. i. y y 334 Proofs of the Properties of Gazeous Oxid of Nitrogen. the phosphorus, and introduce it into a receiver filled with the gas. The zinc will thus be made to burn with a beautiful white flame, surrounded by a green one, and dense white vapours of oxid of zinc will fill the receiver. Experiment XIV. Accension of pyrophorus in gazeous oxid of nitrogen. Pyrophorus, which readily inflames in nitrous gas and in atmospheric air at a low temperature, requires for its combustion in nitrous oxid a much greater degree of heat. It will not burn in it even at 212°. In order to inflame pyrophorus in gazeous oxid of nitrogen over mercury, the wire must be strongly heated, but not ignited. The pyrophorus then takes fire, and burns with a splendid white light, greatly resembling that produced in oxigen gas. ' INFERENCES. From the preceding experiments it becomes evident that the inflammable bodies in general require for their combustion in gazeous oxid of nitrogen much higher temperatures than those in which they burn in oxigen gas or atmospheric air. When intensely heated, they ♦decom- pose it with the production of much heat and light, and become oxigenized. During the combustion of solid or fluid bodies producing flame in it, nitric acid is generated, and that probably from a new arrangement of principles analogous to those stated before. Likewise, when gazeous oxid of nitrogen in excess is decomposed by inflam- mable gases, nitrogen acid, and sometimes a gas analo- gous to common air, is produced, doubtless from the same cause. Pyrophorus is the only body that inflames in gazeous oxid of nitrogen below the temperature of ignition. Phosphorus burns in it with a blue flame, probably forming with it only phosphorus acid a little above a dull red heat; but when heated more intensely, phosphoric ucid is produced. Proofs of the Properties of Gazeous Oxid of Nitrogen. 335 Charcoal, sulphur, iron, and the compound inflamma- ble bodies, decompose this gas only at temperatures equal to or above that of ignition, probably each at a dif- ferent temperature. - The double flame produced during the combustion of charcoal depends on the production of nitrous acid formed during the process ; for it may be produced by plunging the taper into common air containing nitrous acid vapour, or in a mixture of gazeous oxid of nitrogen and nitrogen gas, through which nitrous acid has been diffused. It is never perceived in the combustion till much nitrous acid is formed. If a taper be suffered to burn in a mixture of equal parts of gazeous oxid of nitrogen and nitrogen gas, it burns at first with a flame nearly the same as that of a candle in common air, whitish yellow. Before its extinc- tion the interior white flame and exterior blue one are perceived. Nitrous oxid is therefore a gas unalterable in its con- stitution at temperatures below ignition. It is composed of oxigen and nitrogen, existing most probably in the most intimate union which those substances are capable of assuming. For it is unalterable by those bodies which are capable of attracting oxigen from nitrous gas and ni- trous acid at common temperatures. The properties of nitrous oxid approach to those of acids. AMMONIA, OR AMMONIACAL GAS. PART XXVII. SECT. I. THIS gas was first discovered by Dr. Priestley. It is composed of hidrogen and nitrogen, rendered gazeous by the addition of caloric. , PROPERTIES OF AMMONIA. i Ammonia gas has a strong and very pungent odour. It extinguishes flame, yet it increases the magnitude of the flame of a taper before extinction, producing a pale yellow colour round its edge. Animals cannot breathe it without death ensuing. It is lighter than atmospheric air, in the proportion of three to five. It tinges yellow vegetable colours brown, and blue ones green. It is ra- pidly absorbed by cold water; by ardent spirit, essential oils, ether, charcoal, sponge, bits of linen cloth, and all porous bodies. When a piece of ice is brought in contact with this gas, it melts and absorbs the gas, while at the same time its temperature is diminished. It has no effect upon oxigen gas while cold; but when made to pass with it through an ignited tube, it detonates, and becomes decomposed. The same is the case with common air. It is also de- composed by phosphorus at high temperatures. Methods of obtaining Ammonia. 337 It does not explode when mixed with hidrogen gas. Nitrogen gas has no effect upon it. Atmospheric air does not combine with it at common temperatures, but only mixes with and dilutes it. When made to pass through ignited charcoal, it forms with it a substance called prussic acid. If brought into contact with acid gases, both gases lose their gazeous form and become concrete. It has no sensible action on earths, or on the salino-terrene sub- stances. It combines readily with acids, and unites to sulphur when both are in a state of vapour. It reduces oxids of metals to their metallic state, and is decomposed by them. It is also decomposed by electrization and by oxigenized muriatic acid gas, &c. When exposed to the temperature of — 46° it crystallizes, and when suddenly cooled down to — 68° it assumes a gelatinous appearance, and has scarcely any odour.* METHODS OF OBTAINING AMMONIA. 1. Mix together equal quantities of muriate of ammonia and lime, separately powdered ; introduce them into a gas-bottle or retort, apply the heat of a lamp, and receive the gas over mercury. Rationale....Muriate of ammonia consists of muriatic acid and ammonia; on adding lime to it a decomposition takes place, the muriatic acid quits the ammonia and unites to the lime, in order to form muriate of lime, which remains in the retort, and the ammonia flies off in the state of gas. Rem ark....In order to obtain the gas in a state of purity, it is essentially necessary that a considerable quantity of the gas first disengaged be suffered to escape, on account of the common air contained in the distilling vessel and in the interstices of the ingredients. 2. Ammonia may likewise be obtained by heating the liquid ammonia of the shops (water of pure ammonia, Pharm. Lond.J in a retort placed in communication with the mercurial pneumatic trough. Fourcroy arid Vauquelin, Ann. de Chim. XXIX. p. 289. 338 Proofs of the Properties of Ammonia. Rationale.....The ammonia contained in this liquid combines with caloric, assumes the form of ammoniacal gas, and parts with the water to which it was united. Remark.....The temperature of the fluid must not be carried so high as to cause the water to be converted into vapour, or, if this cannot well be avoided, a small vessel should be interposed between the retort and the receiver; which, when kept cool, may serve to condense the aqueous vapour which is formed, and cause the ammoniacal gas to pass in a very pure and dry state. Ammonia is likewise produced during the spontaneous decomposition of animal and vegetable substances; in these cases it did not pre-exist in them ready formed, but is gene- rated by the union of the hidrogen and nitrogen contain- ed in them. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF AMMONIA. Experiment I. Ammonia is absorbed by water, ardent spirit, Ztfc. INTRODUCE into a jar filled with ammonia standing over mercury a little water, ardent spirit, or a piece of moistened sponge, paper, &c. In whichever manner the experiment is made there will be an absorption; the gas becomes absorbed, and the mercury rises in the jar so as to fill it entirely, provided the gas be sufficiently pure. If water be presented to this gas in the state of ice, it melts rapidly. Remark.....Water which has absorbed the gas acquire;- its peculiar odour, and constitutes what is called liquid ammonia, or, more properly, solution of ammonia in wa- ter. From this fluid the gas may be again liberated by heat. Experiment II. ximmonia extinguishes light, but increases the magnitude of the flame before its extinction. A burning taper dipt several times successively into a Proofs of the Properties of Ammonia. 339 bottle filled with ammonia is extinguished every time, but before its extinction the flame is enlarged by the ad- dition of another one of a pale yellow colour, and at length this light flame will extend from the top of the vessel to the bottom. If the lighted taper be only presented to the mouth of a vessel filled with ammonia, the yellowish flame will rise considerably higher than that of the taper. Experiment III. Ammonia is lighter than atmospheric air. Let ajar filled with ammonia be placed with its mouth upwards, and left in that situation for a few minutes ; it will be found to have exchanged its contents for common air, which, being heavier, descends and displaces the gas. Experiment IV. Ammonia is heavier than hidrogen gas. Put a quantity of hidrogen gas into a long tube ; add to it half the quantity of ammonia, and to this a like quan- tity of muriatic acid gas. The two latter gases will com- bine and form a white cloud (muriate of ammonia) but the cloud will not rise within the space occupied by the hidrogen gas ; consequently the latter had kept its place below the other without mixing with it. That the ammonia is lighter than the muriatic acid gas is shown from the formation of the white cloud on their mixture ; for it begins at the bottom, and gradually reaches the top when the muriatic acid gas is last added ; but when the ammonia is presented to the muriatic acid gas, the whole becomes cloudy immediately. Experiment V. Ammonia tinges yellow vegetable colours brown, and blue ones green. 1 his mav be shown by pasting a piece of paper coloured yellow with turmqric, or blue with cabbage-juice, into the 340 Proofs of the Properties of Ammonia. top of a receiver, and exposing it to the action of the gas. The first will soon become brown, and the latter green. The same effect may be produced by holding the pa- pers over a bottle filled with water impregnated with am- monia* Experiment VI. Carbonic acid gas and ammonia readily unite and form carbonate of ammonia. Fill a vessel with carbonic acid gas over mercury, and add ammonia ; a white vapour will instantly be formed, heat becomes evolved, the gases disappear, and carbonate of ammonia crystallizes on the inside of the vessel. Experiment VII. Ammonia becomes decomposed by oxigenized muriatic acid gas at common temperatures. Mix in a receiver over mercury two parts of oxigeniz- ed muriatic acid gas with one part, by measure, of ammo- nia. When these two bodies come in contact, a brisk de- tonation is produced, accompanied with a yellowish light; the two gases decrease in volume, and there is formed a portion of solid matter (muriate of ammonia) which ad- heres to the sides of the vessel. The gas which remains has no odour like ammonia, nor colour like muriatic acid gas. It is not dissolved in water, nor does it maintain combustion ; it is therefore nitrogen gas. In the bottom of the vessel there is found a clear and transparent liquid, which is water holding a certain quantity of the muriate of ammonia in solution. Rationale....Ammonia consists of nitrogen and hi- drogen dissolved in caloric. Oxigenized muriatic acid gas consists of muriatic acid, oxigen, and caloric. On bring- ing the two gases into contact, a reciprocal decomposition takes place. The oxigen of the oxigenized muriatic acid gas combines with the hidrogen of the ammonia, and forms water; while the nitrogen, the other component part of the ammonia, becomes disengaged. The oxige- Proofs of the Properties of Ammonia. 341 nized muriatic acid gas having lost its oxigen, becomes converted into simple muriatic acid gas, part of it unites to part of the ammonia (which in this experiment is present in too large a quantity to be wholly decomposed) and forms with it muriate of ammonia. The explosion, heat, and light, originate from the liberated caloric which kept the gases in their aeriform state. Remark....If a smaller portion of ammonia is added to the above quantity of oxigenized muriatic acid gas, its decomposition will be complete, and no muriate of am- monia be produced. The results then are only muriatic acid and water. The same facts may be shown in the following man- ner : Experiment VIII. Fill four-fifths of a long glass tube with strong oxige- nized muriatic acid, and the remaining fifth with water strongly impregnated with ammonia, and invert it in a saucer of water. The ammonia, on ace unt of its light- ness, will pass through the oxigenized muriatic acid ; but by thus passing, a strong effervescence is produced, the elastic fluid by which it is occasioned collects in the up- per part of the tube, and a portion diffuses itself in the vessel. The gas disengaged will be found to be ni- trogen. Rationale....The explanation of this experiment is analogous to the former. Experiment IX. Decomposition of ammonia by means of black oxidof man- ganese at a high temperature. If ammonia be made to pass over pounded black oxid of manganese brought to a red heat in a Wedgwood's tube, connected, by means of another glass tube, with an empty bottle immersed in cold water or ice, abundance of red vapours will soon be produced, and these will be suc- ceeded by white ones, condensing in the bottle into a bright transparent fluid, which has a pungent saline vol. i. z z 342 Proofs of the Properties of Ammonia. taste. If this liquid be distilled to dryness by a gentle heat, the product will be water. The residue in the retort is of a white colour. It fuses in the fire, detonates on ignited coals, and produces vapours of nitric acid by the affusion of sulphuric acid, or ammonia when saturated with lime. It is therefore nitrate of ammonia. The black oxid of manganese has changed its colour, being turned to a pale brown, and no longer gives oxigen gas by the addition of heat. RATiONALE....In this experiment the hidrogen of the ammonia unites to part of the oxigen given out by the "black oxid of manganese, and forms water. The nitrogen of the ammonia unites to another part of the oxigen, and produces nitric acid; this joins to a quantity of undecomposed ammonia, and forms nitrate of ammonia. Experiment X. Decomposition of ammonia by the electric spark. For this purpose take a detonating tube, admit into it about a cubic inch of ammonia and pass through it a suc- cession of electric discharges. When about 200 strong shocks have traversed the gas, it will have increased three times its original bulk. On admitting a small quantity of water, the gas will not, as before, be completely absorbed by this fluid, but a part will remain. Hence it appears that the gas has undergone a decomposition, and on exa- mination it will be found that the chemical union of the hidrogen and nitrogen has been broken, and that they are only mechanically mixed. SULPHUREOUS ACID GAS. PART XXVIII. SEVERAL philosophers have paid attention to the properties of this gas and its combinations ; but Berthollet was the first who published an accurate account of it, which Fourcroy and Vauquelin have lately investigated still more completely. Their paper (of which we have made use) is inserted in the Annalesde Chimie, II. 54, and copied into Nicholson's Journal, vol. I. p. 313. We have seen before, that when sulphur is united to oxigen it forms an acid. When the quantity of oxigen is sufficient to oxigenate a given quantity of sulphur completely, the result is a perfect acid, called sulphuric acid. We shall now see that if a less quantity of oxigen is made use of, the result is an imperfect acid, capable of taking the gazeous state. To this gazeous fluid we give the name of sulphureous acid gas. It becomes obvious from this, that sulphureous acid gas has the same relation to sulphuric acid as phosphorus acid has to the phos- phoric acid. At least this gas occupies the middle place between sulphur and sulphuric acid, which will be more evident when we shall speak of the formation of acids. 344 Properties of Sulphureous Acid Gas. SECT. I. PROPERTIES OF SULPHUREOUS ACID GAS. SULPHUREOUS acid gas is a permanently elastic aeriform fluid at the ordinary pressure and temperature of our atmosphere. Its odour is strong and suffocating. It cannot maintain combustion, nor the respiration of animals. Its weight is more than double that of atmos- pheric air. Its specific gravity, according to Bergman, is 0.00246, and 0.00251 according to Lavoisier. It is not inflammable. One hundred cubic inches of it weigh nearly 63 grains. It is composed, according to Fourcroy, of 85 sulphur and 15 oxigen. It is acid ; it first reddens and then destroys the greater part of the vegetable colours. It exerts little action on the metals, and has a weak attrac- tion to alcalies and earths. It has the property of whiten- ing silk, and giving it a lustre. Priestley, Bergman, Ber- thollet, &c. say, ihat at high temperatures it deposits sulphur; but Fourcroy and Vauquelin, in consequence of some new experiments, deny this assertion. Phosphorus has no action upon it. Its attraction for oxigen when dry, at the common temperature, is very feeble ; but if the smallest quantity of moisture be present, the union of the two gases is much favoured. At high temperatures the combination is more speedily effected. When a mixture of sulphureous acid gas and oxigen gas is made to pass through an ignited tube, the two gases combine, and sul- phuric acid is formed. When passed into water cooled down to the freezing point, the union is very rapid. Water cooled to 40 degrees absorbs one third part of its weight of sulphureous acid gas. It speedily melts ice. Water saturated with it may be frozen without parting with its gas; but when water which has been saturated with ft is exposed to heat, it is filled with a vast number of bubbles, which continually increase and rise to the sur- face ; these bubbles are the gas separating from it. It is ab- sorbed by oil, ether, and sulphuric acid ; the latter when saturated with it acquires the property of emitting fumes when exposed to air ; its colour is altered to a yellowish Methods of obtaining Sulphureous Acid Gas. 345 brown, and its odour is penetrating, like that of the gas. When the acid thus saturated with the gas is exposed to a few degrees below the freezing point, it congeals or freezes into a crystalline mass. The same happens when submitted to distillation. It decomposes nitric and oxi- genized muriatic acid, and dissolves camphor. Sulphu- reous acid gas and hidrogen gas have no action upon each other at common temperatures, but if they are passed through an ignited tube, a decomposition is effected. Charcoal likewise decomposes sulphureous acid gas at a high temperature. Monge and Clouet affirm, that by ex- treme artificial cold and a strong pressure exerted at the same time, they rendered sulphureous acid gas fluid. METHODS OF OBTAINING SULPHUREOUS ACID GAS. 1. Take one part of mercury and four of concentrated sulphuric acid ; put them into a glass retort connected with the pneumatic quicksilver-trough, and apply the heat of a lamp to the mixture till it boils. On continuing the heat after the mercury has been acted upon, sulphu- reous acid gas will be obtained in abundance. Rationale....In this case a partial decomposition of the sulphuric acid takes place. The mercury abstracts part of its oxigen, and becomes converted into an oxid ; the sulphuric acid, in consequence of the loss of oxigen, becomes converted into sulphureous acid, which takes the gazeous form at the common temperature. 2. Sulphureous acid gas may likewise be obtained by the slow combustion of sulphur. Put pounded sulphur into a shallow earthen dish or crucible ; melt and set fire to it; and when it is completely inflamed, cover it with a large bell-glass perfectly dry ; remove the whole on a dish, and surround the apparatus with mercury. The sulphur will burn for some time, and the bell-glass will be filled with white vapour. When the vapour has subsided, the gas may be transfer- red as usual. Rationale....During the burning of the sulphur in a confined quantity of atmospheric air, it absorbs the oxigen contained in it; this however not being sufficient 346 Proofs of the Properties of Sulphureous Acid Gas. . to oxigenate the sulphur completely, the result is an im- perfect aeriform acid, or sulphureous acid gas. 3. Sulphureous acid gas may also be obtained by de- composing sulphite of potash or soda, either by heat alone, or by the affusion of acids. 4. If charcoal be moistened with sulphuric acid, and then exposed to distillation, the products are carbonic acid gas and sulphureous acid gas. Rationale....During this operation the charcoal at- tracts part of the oxigen of the sulphuric acid, and forms carbonic acid gas. The sulphuric acid is therefore partly de-oxidated, and becomes converted into sulphureous acid gas. 5. Sulphureous acid gas is likewise formed by distil- ling sulphur with the oxids of mercury, lead, tin, man- ganese, &c. Rationale....In these processes the sulphur attracts the oxigen of the metallic oxids and becomes converted into sulphureous acid gas, while the oxids are partially restored to the metallic state. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF SULPHUREOUS ACID GAS. Experiment I. Sulphureous acid gas is heavier than atmospheric air, and does not maintain combustion. THIS may be shown by dipping a lighted candle suc- cessively into a jar filled with this gas. The candle will be extinguished every time, though the jar filled with it continues exposed to the air. Experiment II. Sulphureous acid gas is rapidly absorbed by water. Fill a cylinder with the gas over mercury, and send up into it a little water. The gas will instantly become diminished, and the mercury rises up in the vessel. Proofs of the Properties of Sulphureous Acid Gas. 347 The absorption of this gas may likewise be shown by dipping the neck of the retort, in which it is disengaged, into a bason of cold water. REMARK....The combination of sulphureous acid gas with water cooled artificially takes place with such rapi- dity, that not a single bubbleof it rises to the top until the water is saturated. If ice be present in the water, it melts rapidly. The water at this temperature increases almost one seventh part in weight. The saturated water when exposed to a temperature of about 65° or 70° Fahr. becomes filled with a multitude of small bubbles, which continually increase and rise to the surface. This may be shown in the following Experiment III. Disengagement of sulphureous acid gas from water satu- rated with it. Take a bottle filled with water completely saturated with sulphureous acid gas at a low temperature, plunge it into a bason of hot water and uncork it; an infinite num- ber of small bubbles will instantaneously be extricated, the water in the bottle will appear to boil with great ra- pidity and lose most of its gas. Rationale....The sulphureous acid gas contained in the water is capable of remaining in combination with this fluid at low temperatures; but by the addition of ca- loric, becomes converted into the state of gas, which flies off, and occasions the apparent ebullition. Remark....Water that has absorbed sulphureous acid gas is to be looked upon as liquid sulphureous acid. It possesses the peculiar odour of the gas and an acid taste. At first it only reddens blue vegetable colours, but at last totally destroys them. The infusion of rose-leaves and several other vegetable pigments lose all their colour by it instantly. Experiment IV. Sulphureous acid gas and oxigen gas do not act upon each other at a low temperature without the intervention of a fluid. To two parts of sulphureous acid gas, prepared in the mercurial apparatus, add one part of oxigen gas ; no per- 348 Proofs of the Properties of Sulphureous Acid Gas. ceptible union will take place even after some months: but if a small quantity of water be added to the mixture an absorption gradually takes place, the volume of the gases becomes diminished, and sulphuric acid is formed. Remark....The water presented acts as an interme- diate body to favour the union of the two gases. Its great attraction for the sulphureous acid gas enables the oxigen to unite to it in order to convert it into sulphuric acid. Experiment V. Sulphureous acid gas and oxigen gas readily act upon each other at high temperatures. In the last experiment we have seen that the two gases have no action upon each other at common temperatures, unless by the intervention of water; but if we transmit a mixture of sulphureous acid gas and oxigen gas through an ignited earthen tube placed across a furnace, very dense white fumes are formed, which become converted into liquid sulphuric acid, and may be collected in a vessel placed for that purpose at the other extremity of the tube. Ration ale....The oxigen gas at this temperature yields its orxigen to the sulphureous acid gas, and converts it into sulphuric acid, which it is only capable of doing in a direct manner at that temperature. Experiment VI. Hidrogen gas has no action upon sulphureous acid gas in the cold, but decomposes it at high temperatures. When we mingle together hidrogen gas and sulphure- ous acid gas at common temperatures, there is no action; but if we transmit a mixture of three parts of hidrogen gas and one of sulphureous acid gas through aWedgwood's tube in a state of ignition, sulphurated hidrogen gas will be evolved, and sulphur deposited at the extremity of the tube, opposite to that through which the gas is made to pass. Proofs of the Properties of Sulphureous Acid Gas. 349 RATiONALE....Part of the hidrogen at such a tempera- ture unites to the oxigen of the sulphureous acid gas to form water, the sulphur is consequently left uncombined ■ another part (or at least the excess) of the hidrogen dis- solves a portion of the sulphur, and becomes converted into sulphurated hidrogen gas. Rem ARK....The two last experiments are well calculated to demonstrate the nature of sulphureous acid gas. In the first it became changed into sulphuric acid by the addition of oxigen at a high temperature : in the other, hidrogen gas decomposes the sulphureous acid gas at the same temperature, by taking from it that portion of oxigen which kept it acid, and the sulphur is dis- engaged. Experiment VII. Formation of sulphate of ammonia by mingling sulphu- reous acid gas and ammoniacal gas. Let sulphureous acid gas be mixed with ammoniacal gas over mercury ; a beautiful white cloud will be formed by their combination, heat is liberated, and both gases gradually assume the solid state, forming sulphate of am- monia. If the gases have been pure, the mercury rises almost to the top of the vessel. If the sulphureous acid gas be presented to the ammo- niacal gas, the cloud is formed ut the bottom, and gra- dually rises to the top ; but if the ammoniacal gas be pour- ed in last, the cloud rises immediately to the top. These consequences naturally result from the ammoniacal gas being the lightest. Rationale.. .The white cloud formed in this expe- riment is sulphate of ammonia, which originates from the strong attraction these gases have for each other. The caloric which kept them in the gazeous state being set free produces the heat evolved during this union. Experiment VIII. Sulphuric acid saturated with sulphureous acid gas ac- quires a concrete form. When sulphureous acid gas is made to pass into sulphu- ric acid cooled by a f rigorific mixture, the gas is for a con • vol. i. 3 A 350 Proofs of the Properties of Sulphureous Acid Gas. siderable time absorbed by the acid, which at last acquires a solid form. The solid acid has no very perceptible odour. If part of it be laid upon a plate of glass, it exhibits an effervescence, like that occasioned by the decompo- sition of carbonate of lime by the affusion of a weak acid. It soon after becomes liquid and very odorous. Remark....We have therefore a concrete sulphuric acid, formed by the addition of sulphureous acid gas. Nitrous gas is also said to possess the same property. There is no doubt but that other concrete modi- fications occasioned by other gases will be discovered hereafter. Experiment IX Decomposition of sulphureous acid gas by charcoal. When sulphureous acid gas is passed through a tube containing ignited charcoal, carbonic acid gas and sulphur- ated hidrogen gas are obtained, and the inner surface of the tube is lined with sulphur. Rationale...i.The charcoal at the temperature of ignition takes the oxigen from the sulphureous acid gas, and forms with it carbonic acid gas ; the sulphur therefore becomes precipitated. The sulphurated hi- drogen gas arises from a portion of water contained in the charcoal. Experiment X. Decomposition of sulphureous acid gas by muriate of tin. Fill a cylinder with sulphureous acid gas, and pass up into it fresh prepared concentrated muriate of tin, the volume of the gas will soon become diminished, and sulphur be deposited. Rationale....The oxid of tin robs the sulphureous acid gas of its oxigen, and becomes converted into oxige- nated muriate of tin, and the sulphur deprived of its oxigen is deposited. MURIATIC ACID GAS. PART XXIX. SECT. I. THE basis of this gas is still unknown. The presence of oxigen has not been even demonstrated in it, and it is only by analogy that we may venture to suppose it instru- mental in this acid gas. Some philosophers have lately persuaded themselves that it is an oxid of hidrogen. The experiments hitherto advanced are, however, not suffi- cient to prove this assertion. PROPERTIES OF MURIATIC ACID GAS. Muriatic acid gas has a very pungent and suffocating odour, which excites coughing. It is readily absorbed by water, by ardent spirit, ether, fat, and essential oils, melted wax, phosphorus, and many other bodies. It is a true acid. It suffocates animals, and is so very caustic as to excoriate the skm. It extinguishes alighted taper, the flame of which becomes green, or rather light blue, at the upper part of its disk. Light has no effect upon it. Caloric rarefies it. It is heavier than common air. The specific gravity of the former is to that of the latter as 1.750 to 1.000. When brought into contact with atmospheric air, or oxigen gas, it forms a white cloud. Ice is melted by it as speedily as if thrown into the fire. It unites to alcaline and ter- rene substances, and forms with them new compounds. It has no action on siliceous earths. It combines with alumine and magnesia. It absorbs oxigen when in the 352 Methods of obtaining Muriatic Acid Gas. state of gas feebly, though there are methods of uniting them readily. If ammoniacal gas be mixed with it and heat applied, both gases lose their gazeous form in a mo- ment, and are transformed to a concrete salt. Carbonic acid gas, nitrogen gas, gazeous oxid of nitrogen, sul- phurated hidrogen gis, and carbonated hidrogen gas, have no action upon it. It has never been found in a disen- gaged state in nature. When electric explosions are made to pass through it, its bulk is diminished, and hidrogen gas is evolved. These changes are owing to a quantity of water contained in the gas, and cease when it is deprived of moisture, as has been proved by Mr. Henry.* METHODS OF OBTAINING MURIATIC ACID GAS. 1. Muriatic acid gas may be obtained by decomposing muriate of soda by means of sulphuric acid. For this pur- pose, put into a tubulated retort two parts of very dry mu- riate of soda, and pour on it very gradually one part of con- centrated sulphuric acid. A violent action takes place, and muriatic acid gas becomes liberated, which must be collected over mercury in the usual manner. Rationale.....The sulphuric acid has a greater affinity for the soda than the muriatic acid has ; it therefore unites to it, and forms sulphate of soda. The muriatic acid being liberated takes the gazeous form, and appears as muriatic acid gas. Remark.....As"this decomposition takes place very rapidly, it is not necessary to apply heat until the disen- gagement of the gas begins to slacken, after which the further extrication may be assisted by the heat of a lamp. 2. Muriatic acid gas may likewise be obtained by ex- pelling ;t from its combination with water. For this purpose put concentrated muriatic acid into a retort, immerse the beak of it under a receiver placed in a mercurial pneumatic trough, and filled with that metal. On exposing the acid to a gentle heat, muriatic acid gas * Nicholson's Journal, vol. IV. p. 209. Proofs of the Properties of Muriatic Acid Gas* 353 will be obtained. If the process be very carefully man- aged, nothing but water remains in the retort. 3. Muriatic acid gas is likewise produced by putting any quantity of liquid muriatic acid into a long glass tube and adding to it about one-third or one-fourth, by mea- sure, of concentrated sulphuric acid. A viblent efferves- cence takes place, and the whole tube becomes filled with dense white Vapours, which are muriatic acid gas, con- densed again by means of the moisture in the atmosphere. The sulphuric acid added to the muriatic acid, deprives the latter of part of its water ; a combination and pene- tration of the two liquids take place, and caloric is evolv- ed, contributing to render the gas aeriform, which is thus forced to escape. This experiment proves that the affinity of sulphuric acid for water is greater than that of muriatic acid. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF MURIATIC ACID. Experiment I. Muriatic acid gas is readily absorbed by water. Fill a receiver with muriatic acid gas, and introduce into it a little water; the gas will speedily be absorbed, and the fluid exibit all the properties of muriatic acid. The absorption may also be shown by disengaging the gas in a retort, and dipping the neck into a bason of wa- ter, or letting it pass into a receiver moistened with a small quantity of this fluid. Rem ark....Water when charged as highly as possible with this gas, forms the ordinary muriatic acid in a liquid state. Ten grains of water are capable of absorbing 10 grains of the gas. The solution thus obtained occupies the space of 13.3 of water nearly. Water heated absorbs it with difficulty. The colder the water the more it absorbs. 354 Proofs of the Properties of Muriatic Acid Gas. Experiment II. Muriatic acid gas melts ice speedily. This experiment may be shown by passing the current of muriatic acid gas as it is disengaged into a vessel filled with ice, broken into small pieces. The ice will melt as rapidly as if heat were applied. RATiONALE....The rapid liquefaction depends on the vast quantity of caloric which is evolved by the gas when returning from the gazeous to the liquid state, which be- comes absorbed by the ice, and melts it. Experiment III. Muriatic acid gas when brought into contact with air . forms white clouds. If a wide-mouthed bottle be half filled with muriatic acid gas, and atmospheric air be admitted, by removing it from the mercury over which it was charged, the whole vessel will be instantly filled with dense white vapours, and a considerable degree of heat will be produced. Rationale....The vapours are occasioned by the moisture in the air, to which the muriatic acid gas unites, in order to become converted into liquid muriatic acid, abandoning at the same time its combined caloric, which becoming free produces the heat. Remark....The more humid the air, the denser the vapours are on presenting muriatic acid gas to it, and for that reason they are never, produced on the summits of mountains or other places where the air is very dry. This production of white vapour is therefore a sure sign of the humidity of the air. Experiment IV. Formation of muriate of ammonia by mingling muriatic acid gas and ammonia. If muriatic acid gas and ammonia be mingled together in a cylinder over mercury, the mixture becomes in- Proofs of the Properties of Muriatic Acid Gas. 355 stantly heated, and a white cloud is formed. The mercu- ry rises, and muriate of ammonia will be formed, which crystallizes on the internal surface of the receiver, during the subsiding of the white vapour. If the two gases are very pure and perfectly dry, they completely disappear, and the disengagement of caloric is considerable. RATioNALE....The production of the muriate of am- monia is owing to the attraction of the bases of the two gases to each other being greater than that of the caloric which kept them in the gazeous state; they therefore abandon the caloric, unite, and form a solid combination called muriate of ammonia. Experiment V. Muriatic acid gas extinguishes the flame of burning bodies; first enlarging it by the addition of a green or bluish circumambient flame. If a lighted taper be let down into a receiver filled with muriatic acid gas, the flame will be extinguished; but be- fore its extinction it will be enlarged by a green or bluish circumambient flame. Remark....This curious phenomenon has not yet been satisfactorily explained. OXIGENIZED MURIATIC ACID GAS. PART XXX. SECT. I. WHEN the muriatic acid gas before mentioned be- comes combined with a certain quantity of oxigen, the result is an expansible gazeous fluid, to which chemists have given the name of oxigenized muriatic acid gas. PROPERTIES OF OXIGENIZED MURIATIC ACID GAS. Oxigenized muriatic acid gas possesses an uncommonly pungent and suffocating odour. It is absolutely and in every respect non-respirable ; animals immersed in it die instantly. It is absorbable by water, and forms with it what is called liquid oxigenized muriatic acid. When water is saturated with it, the compound crystallizes at low temperatures. Oxigenized muriatic acid gas is not invisible, but has a yellow-greenish colour. It is capable of maintaining and exciting combustion in many cases. Phosphorus, charcoal, red sulphuret of mercury, sulphuret of antimony, bismuth, iron, zinc, copper, gold, arsenic, cobalt, tin, lead, and several other combustible bodies, take fire spontaneously when introduced into it. It is heavier than atmospheric air. It weakens and reddens the flame of a taper, but does not extinguish it. It decom- Methods of obtaining Oxigenized Muriatic Acid Gas. 357 poses ammonia. It thickens fat oils. It detonates with hidrogen gas. Nitrous gas immediately produces a cloud of reddish vapour with it. It is likewise decomposed by sulphurated, phosphorated, and carbonated hidrogen gases. It is not altered by exposure to light, and passes unaltered through an ignited porcelain tube. It discolours stuffs, and totally destroys most of the vegetable colours, rendering them white. It also bleaches yellow wax, &c. METHODS OF OBTAINING OXIGENIZED MURIATIC ACID GAS. 1. Put into a retort one part of powdered black oxid of manganese and three or four of concentrated muriatic acid ; connect the retort with a pneumatic trough, and receive the gas ovvr water* in the usual manner. When no more gas is liberated, apply the heat of the lamp, and gas will be produced abundantly, which may be kept in bottles with ground glass stoppers. Rationale....The oxid of manganese yields up part of its oxigen to part of the muriatic acid, which becomes converted into oxigenated muriatic acid gas ; the oxid of manganese being thus partly de-oxidated, is dissolved in the remaining quantity of the muriatic acid, which is left in the retort as muriate of manganese. Rem ark....The retort containing the mixture should not be filled above one-third; for the fluid on the appli- cation of heat swells, and is otherwise very apt to be forced over into the neck of the retort. 2. Oxigenized muriatic acid gas may likewise be ob- tained in an indirect manner, by decomposing muriate of soda in contact with black oxid of manganese. For that purpose mix eight parts, by weight, of muriate of soda with three of powdered oxid of manganese, put the mix- ture into a tubulated retort, and pour upon it gradually four parts of sulphuric acid, diluted previously with three of water, and which has been suffered to cool after dilu- tion. On applying a gentle heat, gas will be produced as before. * Though mercury is generally made use of in this process, water answers the purpose better. VOL. I. 3 B • 356 Proofs of the Properties of Rationale....In this operation the sulphuric acid acts on the muriate of soda, to the base of which it unites ; the muriatic acid formed by this union attacks the oxid of manganese ; one part of it combines with the oxigen, and another with the oxid brought nearer to the metallic state; and the result is sulphate of soda and muriate of man- ganese, which remain in the distilling vessel; and oxige- nized muriatic acid, which passes in the state of gas at common temperatures. Rem arks....In preparing this gas great care should be taken that, it does not escape into the apartment in any considerable quantity ; as it acts violently on the pituitous membrane, occasions a defluxion of th^ brain, blunts the senses of smell and taste, produces head-ach, and proves extreireiy injurious to health. Pelletier fell a sacrifice in attempting to breathe it, a consumption was the consequence, which proved fatal. Liquid ammonia is the remedy best calculated to check its effects, when accidentally set at liberty in places where it is prepared. The film of water which adheres to the inner side of the vessel filled with oxigenized muriatic acid gas crys- tallizes in the form of yellow spangltrs, if the tempera- ture is near the freezing point. If a considerable quanti* ty of gas be thus condensed, care must be taken to keep it at a low temperature, for as soon as it becomes heated it expands, and endangers the bursting of the vessel. SECT. II. EXPERIMENTAL PROOFS OF THE PROPER- TIES OF OXIGENIZED MURIATIC ACID GAS. Experiment I. Oxigenized muriatic acid gas is absorbed by tvater. FILL a phial with oxigenized muriatic acid gas, and agitate it strongly in contact with water ; a rapid absorp- tion takes place, and the water will ascend in the phial. Oxigenized Muriatic Acid Gas. 35$ It acquires the colour and odour of the gas, and the pro- perty of discharging vegetable colours. Experiment II. Oxigenized muriatic acid gas destroys vegetable colours and renders them white. Fill a vessel with oxigenized muriatic acid gas, and introduce into it a sprig of mint, a rose, &c. Its colour will soon be destroyed, and the gas diminished. All flowers of variegated colours and green leaves of plants are in time rendered white by it; and no alcali is capable of restoring their colour. Rationale.. ..This effect can be ascribed only to the absorption of oxigen. This gas, which contains it in ex- cess, gives up a part of it, which vegetable substances absorb with avidity ; and by this absorption lose their colour: the oxigenized muriatic acid gas then becomes converted into common muriatic acid gas. Remark.....It is this property which induced a new method of bleaching, which has proved completely suc- cessful. The advantages which result from this applica- tion of the oxigenized muriatic acid, either in the gazeous or the liquid state, have accelerated the process of whiten- ing thread, cotton, linen, wax, &c. to a really surprising degree, in every season of the year, and can be justly appreciated by commercial people only, who experience its beneficial effects from the quick circulation of their capitals. Experiment III. Bleaching of linen, calico, &c. by oxigenized muriatic acid gas. Suspend some unbleached calico or linen, moistened with water, in ajar filled with oxigenized muriatic acid gas. The natural colour of the stuff will soon begin to fade, and at last totally disappear. If different coloured patterns of calico or printed cot- ton be immersed for a few minutes into the gas, their colours will soon be destroyed, except those which are yellow. 360 Proofs of the Properties of Experiment IV. Oxigenized muriatic acid gas supports flame. Though oxigenized muriatic acid gas is exceedingly noxious to life, it does not extinguish combustion. If a burning taper affixed to a wire be immersed in it, the taper burns of a red colour, and more vividly than in atmospheric air ; a great quantity of smoke is emitted at the same time. Experiment V. Spontaneous accension of metals in oxigenized muriatic acid gas. Fill a tall receiver furnished with a ground stopper with oxigenized muriatic acid gas, over water, and let fall into it copper beaten out into a thin leaf (Dutch gold). The copper leaf before it reaches the bottom of the receiver will burn with a pale green light. Gold leaf may be burnt in a similar manner. Fine copper wire when heated to redness also takes fire when introduced into the gas in that state. Other metals may be inflamed in oxigenated muriatic acid gas in the following manner. Experiment VI. Fill a tall bell-glass, furnished with a stopper, or cork, at the top, with oxigenized muriatic acid gas, and throw into it, in small quantities, either some antimony or arsenic reduced to fine powder. The metal introduced will in- stantly inflame, and appear like a shower of fire. Tin, cobalt, bismuth, nickel, copper, &c. reduced to a fine powder, may be inflamed in a similar manner. Rationale....The metals presented to the oxigenized muriatic acid gas rapidly subtract its oxigen, and become converted into oxids ; the combined light and heat of both the gas and the metal are disengaged, and appear under the form of fire ; and the oxigenized muriatic acid gas returns to the state of simple muriatic acid gas. Oxigenized Muriatic Acid Gas. 361 Remark....To succeed well in making these experi- ments, it is necessary that the metal should be reduced to a fine powder, and employed in the proportion of a grain to two or three cubic inches of gas. The gas made use of should be perfecdy fresh prepared. If the gas be warmed a little, the phenomena never fail. Iron, lead, and zinc, are more difficult to inflame than any of the for- mer ; it frequently happens that they remain unaltered at the bottom of the vessel for some time, but on a sudden the accension takes place. Nickel, arsenic, and bismuth, are the metals which are most readily inflamed, and which burn most brilliantly. Experiment VII. Spontaneous accension of phosphorus in oxigenized muri- atic acid gas. Put a piece of phosphorus, dried on blotting-paper, in- to a copper ladle, and introduce it into a jar filled with oxigenized muriatic acid gas; the phosphorus will in- stantly kindle, and burn with a greenish white light. Rationale....The phosphorus unites with the oxigen of the oxigenized muriatic acid gas, and becomes con- verted into phosphoric acid; the oxigenized muriatic acid gas, by thus losing its oxigen, returns to the state of muriatic acid gas. Experiment VIII. Spontaneous accension of sulphur in oxigenized muriatic acid gas. If a piece of sulphur be presented to oxigenized mu- riatic acid gas, no action ensues ; but if we melt a little sulphur in a ladle, and then introduce it in a state of per- fect liquidity into a jar filled with this gas, the sulphur takes fire, and burns rapidly. 362 Proofs of the Properties of RATioNALE....The explanation of this experiment is analogous to the former; the sulphur decomposes the oxigenized muriatic acid gas, and becomes converted into sulphuric acid: but before that effect can take place, the attraction of cohesion of the particles of sulphur must be demolished, that is to say, the sulphur must be rendered fluid, which was not necessary with phosphorus. Experiment IX. Spontaneous accension of metallic sulphurets by oxigen- ized muriatic acid gas. Sulphuret of antimony reduced to a fine powder, and introduced into the gas, in the same manner as was di- rected for the accension of the metals, will also take fire. A similar effect is produced by this gas on sulphuret of mercury, iron, &c. A variety of other combustible substances may also be mflamed by presenting them to oxigenized muriatic acid gas in its nascent state, as was first shown by professor Davy.* Experiment X. Accension of ether, alcohol, or oil of turpentine, by oxigen- ized, muriatic acid gas in its nascent state. Put into a wine-glass one part of oxigenated muriate of potash perfectly dry, and pour on it two or three of co- lourless sulphuric acid of commerce; a violent action will take place, and oxigenized muriatic acid gas be .evolved. If, during the extrication of this gas, one part of sulphuric ether, alcohol, or oil of turpentine, be suffered to fall into the gas, an accension takes place, accompanied with a crackling noise. Remark....In this manner not only all the inflamma- ble fluid bodies, but likewise most of the solids, such as camphor, resin, tallow, pitch, elastic gum, &c. may easily be inflamed. * Nicholson's Journal, April 1802, p. 296 Oxigenized Muriatic Acid Gas. 363 Experiment XI. Accension of expressed oils at the surface of water bu oxigenized muriatic acid gas. Put into a glass cylinder one part of oxigenated muriate of potash; add to it hree or four of water, and half a prrt of oil of olives, or of linseed. On adding to it four or five parts of concentrated sulphuric acid, a violent action takes place, much charcoal becomes deposited, and a mul- titude of ignited sparks pass through the black fluid, ex- hibiting a beautiful phenomenon. On adding an additional quantit of oxigenated muriate of potash and sulphuric acid, the whole mass takes fire, and burns with a dense yellow flame. Experiment XII. Accension of phosphorus in oxigenized muriatic acid ga\ under the surface of water. Let fall into a wine-glass, or rather into a long cylinder, two-thirds filled with water, one part of phosphorus, and two of oxigenated muriate of potash. On adding to this mixture gradually three or four parts of sulphuric or nitric acid, the phosphorus takes fire, and burns vividly under the surface of the fluid: on agitating the mixture, streams of ignited sparks pass through the water rapidly. Rem ark....This and the two preceding experiments require caution. The operator ought to be distant during the affusion of the acids, or the addition of the combusti- ble body, which are sometimes thrown out of the vessel to a considerable distance. Experiment XIII. Nitrous gas and oxigenized muriatic acid gas readily unite and produce nitro-muriatic acid. This may be shown by sending up into a receiver filled with oxigenized muriatic acid gas bubbles of nitrous gas ; 364 Proofs of the Properties, Wc. the mixture becomes warm, reddish fumes appear, and nitro-muriatic acid is produced. Rationale....The nitrous gas takes part of the oxigen from the oxigenized muriatic acid gas, and becomes converted into nitrous acid ; it then unites to the oxi- genated muriatic acid gas, and forms . ' \ ~S.1t HI -V' ^;l; • V& '% ,,.";>■#- .'.'»*£*--/' ^-'■'#■: r-;-."