^V-eV ARMY MEDICAL LIBRARY WASHINGTON Founded 1836 Fobm 113c, W. D.. 8. G. O. »<"0 3—10543 (Revised June 1 a. 1936) A SYSTEM OF CHEMISTRY, IN FOUR VOLUMES. '>. Hi BY THOMAS THOMSON, M,D. F.R.S.L. AND E.F.L.S. FELLOW OF THE GEOLOGICAL SOCIETT, OF THE WERNEBIAN NATURAL BISTORT SOCIETY, OF THE IMPERIAL MEDICO-CHIRURGICAL ACADEMY OF PETERSBURG, OF THE LITERARY AND PHILOSOPHICAL SOCIETY OF NEW-YORK, ETC. FROM THE FIFTH LONDON EDITION, WITH NOTES, BY THOMAS COOPER, M.D. PROFESSOR OF CHEMISTRY AND MINERALOGY IN THE FACULTY OF ARTS OF THE UNIVERSITY OF PENNSYLVANIA. **7 „-on Gen/'- , T V r- — " C f iy> VOL. I. -1^2117.^. PHILADELPHIA: PRINTED AND PUBLISHED BY ABRAHAM SMALL, JVb. 112, Chesnut Street. 4818, EASTERN DISTRICT OF PENNSYLVANIA, TO WIT: Be it remembered, That on the twenty-third day of July, in the forty-third year of the Independence of the United States of America, A. D. 1818, THOMAS [L. S.] CLARK, of the said district, hath deposited in this office the title of a book, the right whereof he claims as proprietor, in the words following, to wit: A System of Chemistry, in four volumes. By Thomas Thomson, M.D. F R.S.L. and E.F.L.S. Felloe of the Geological Society, of the Wernerian Natural History So- ciety, of the Imperial Medieo-Chirurgical Academy of Petersburg, of the Literary and Philosophical Society of New-York, etc. From the fifth London Edition, with Notes, by Thomas Cooper, M.D. Professor of Chemistry and Mineralogy in the Faculty of Arts of the University of Pennsylvania. In conformity to the act of the congress of the United States, intituled, " An Act for the Encouragement of Learning, by securing the copies of maps, charts, and books, to the au- thors and proprietors of such copies, during the times therein mentioned."—And also to the act, entitled, "An act supplementary to an act, entitled, " An act for the encoui-agement of learning, by securing the copies of maps, charts, and books, to the authors and proprietors of such copies during the times therein mentioned," and extending the benefits thereof to the arts of designing, engraving, and etching historical and other prints." D. CALDWELL, • Clerk of the Eastern District of Pennsylvania. PREFACE. Several circumstances, which it is unnecessary to state to the public, have retarded the appearance of this Edition much longer than was expected or wished for by the Author. Meanwhile the Science of Chemistry has been advancing with unprecedented rapidity; and in consequence of the introduction of the atomic theory and the improvements in analytical preci- sion, which were the natural consequences of that introduction, it has assumed a regularity and simplicity that could hardly have been anticipated. This revolution, together with the great number of new ideas and new names that have been in- troduced, in consequence of Davy's new views respecting the nature of chlorine and muriatic acid, of the discovery of iodine, and of the knowledge of cyanogen and its compounds by the sagacity of Gay-Lussac, had thrown a certain degree of obscu- rity over the science, and had given it that unsettled and fluc- tuating appearance, which is apt to discourage those who are commencing the study. I thought it necessary, in consequence of these great changes and improvements, to new model this Edition entirely. Indeed almost the whole of the first two volumes, which contain the elementary part of trie science, has been written anew. I have been at great pains to introduce every new fact, as far as I was acquainted with it, and to present the science to my readers in its most recent state. The work has passed so rapidly through the press, that it has been unnecessary to add any appendix whatever, no facts of sufficient1 importance, of which I was ignorant when we began to print, having come to my know- ledge since, except such as I was able to introduce at least nearly into their proper places. Thus the thorina of Berzelius was unknown to me when the chapter on simple combustibles in the first volume was printing; but I was still able to place it at the end of that chapter. Morphia of Sertiirner was unknown to me while treating of the alkalies; but I have been able at least to place it among the vegetable principles; where it must always continue to figure. IV PREFACE. Considerable difference of opinion exists at present respect* ing the nomenclature of the numerous class of new substances that have been lately introduced into Chemistry. Sir Humphry Davy has invented a nomenclature of his own; but I am not aware that he has obtained hitherto any followers in this coun- try; unless Dr. Davy and Mr. Brande constitute exceptions to the observation. Professor Berzelius, of Stockholm, has given another nomenclature to the public; and he seems to be follow- ed by the Swedish chemists; and a few of his terms appear to have made their way into Germany. A third nomenclature has been contrived by M. Gay-Lussac, and it would appear that it has been adopted by the greater number, if not the whole, of the French chemists. The names, which I have adopted, are all exactly conformable to the laws laid down by Lavoisier,and his associates, when they published the new chemical nomen- clature. They merely constitute an extension of that nomen- clature, and seem to apply so happily to the present state of the science, that I entertain sanguine hopes that they will be found to suit not merely the English language, but that they will be easily intelligible to scientific chemists in every country of Eu- rope. Concerning the arrangement which I have adopted, it ap- pears unnecessary to say much. It is merely an improvement of the arrangement followed in the preceding Editions of this Work. And it appears to me to be better adapted to convey a clear idea of the present state of the science in all its bearings to the tyro, who is just commencing the study of Chemistry, than any other that I have yet seen. Mistakes and defects, the consequence of want of sufficient information, may no doubt still be detected in this edition; but I trust that the reader will give me credit when I assure him that they are wholly involuntary; and that neither expense nor pains were spared to avoid them as much as possible. London, October 1, 1817. PREFACE OF THE EDITOR. Four Systems of Chemistry have been published in Eng- land, each of them possessing considerable merit. Accum's, Henry's, Murray's, and Thomson's. Accum's and Henry's are each in two volumes, Murray's in four, and the last edition of Thomson's, (that which precedes the fifth London) in five. Of these Systems, Dr. Thomson's seems ultimately to have obtained the greatest share of public approbation; not only in England but on the European continent; where it has been re- garded as an excellent summary of chemical facts and doctrines, so delivered, as to form a proper compendium of the science to be put at once into the hands of a student ignorant of the ele- ments of Chemistry. It was a happy combination of chemical facts and chemical doctrines ; very extensively applied to the useful purposes of medicine, the arts, and manufactures. Since the fourth edition of this work was published, such a number of new facts have been ascertained, and so many new views and doctrines have been proposed, by the increasing number and increasing ardour of chemical votaries, that the science has assumed almost a new character: former explana- tions have been considered as inadmissible, and exploded; and other theories, founded upon other arrangements, with an op- pressive inundation of new terms and phrases, have rendered a modern digest of chemical science absolutely essential to the student. Such a digest, in conformity to public expectation, Dr. Thomson has presented to us, in this his new edition of the System of Chemistry. Almost every page of the present edition exhibits some dis- sonance from the former; so that we may almost exclaim in the language of Scripture, " old things are done away, and all things have become new." Whether novelty in this case, be likely to shew itself synonimous with improvement, remains, I appre- hend, yet to be ascertained: but whatever may be the name that innovation shall ultimately receive, no student can enter upon the study of chemistry in the present day, without inform- VI PREFACE. ing himself upon the very important facts and controversies which the last ten years has pressed upon the chemical world; and of which, I know no compendious digest, but the book now offered to the public. It will be useless to pass in review here, all the novelties of the present edition, which have induced me to comply with a request, to write a few explanatory notes upon it: explanations which, I am well persuaded, are necessary for a student to con- sider, before he adopts, with implicit deference, the doctrines that mark the present era of chemical science. The leading features of the modem improvements are, 1. A more full developement and illustration of the atomic theory, and the doctrine of definite proportions. 2. The placing of chlorine, fluorine, and iodine, in the same rank with oxygen as supporters of combustion. 3. The introduction of the earths into the class of metals. 4. The introduction of silex as an acid, and of hydrogen as an acidifying principle. Upon each of these, I would venture to premise a few re- marks, although at the hazard of repetition. 1. Of the Atomic Theory.—There can be no reasonable doubt about the propriety of adopting practically the opinion, that substances extraneous to us, are the causes and sources of our sensations : that these substances are made up principally of particles apparently homogeneous; but which in fact are composed of particles different in properties, and more simple: that all compound bodies are composed ultimately of particles which admit of no further division or analysis; and which are not only with respect to our knowledge, but which are in them- selves, and absolutely, indivisible, and indecomposable. If we do not admit this, we must take for granted that the particles of matter are divisible and decomposable actually, and not merely ex hypothesi, ad infinitum : a proposition which seems too ab- surd to be practically admitted. We must therefore admit the existence of simple undecomposable particles, atoms, monads, or molecules, (by whatever name they may be designated) whereof, in different proportions, all the other particles and masses of matter, of whatever kind, are formed and composed. Here then, the foundations of the atomic theory are laid ; and I presume it will thus far be generally admitted. Suppose the size, the weight, or any other property of these particles, or these particles themselves, to be designated for the purpose of illustration by numbers; as, \ \ °3 % and so forth : PREFACE. Vli then it is manifest, that the doctrine of definite proportions must take place in chemical combination; for as by the datum, the particle d for instance, is indivisible, then its exponent the number 4, must be indivisible also; and two particles dd must be represented, not by 5, 6, or 7, but by the number 8 only; and dec by 10, and so forth. Admitting this—and admitting also, that too many cases of coincidence of fact with the doctrine, occur, to induce us to believe that coincidence accidental—I think we have admitted almost as much as the present state of chemical knowledge will authorise us to admit. And although I do not pretend to deny that the attempt to illustrate the theory of indivisible atoms and definite proportions by an appeal to experiment, is very desirable in distinct treatises or memoirs, until the truth shall be settled upon an immoveable basis, yet I think that it occupies far more than its due share in the present elementary work—that in many instances undue pressure is used by Dr. Thomson, to bring his facts in contact with his theory—that the whole of the illustrations are propounded so abstrusely, as to deter ordinary readers from the study—and to leave an im- pression of difficulty, and uncertainty, likely to do much harm to the progress of the science—that undue stress is kVl upon its present importance, whether considered as facilitating the study of the science, or its application to the objects of com- mon life—and although I have endeavoured from Dr. Prout's papers to furnish some steps of the ladder on which Dr. Thomson has mounted, there still remains an appearance of esoteric mystery in his illustrations and calculations, that may well induce the reader to suppose they are meant only for the initiated. I have endeavoured to make some of them more readily intelligible; but I cannot help thinking that they might in great part have been dispensed with, in an elementary pub- lication. 2. With respect to Chlorine, Iodine, and Fluorine.—The whole of Sir Humphry Davy's doctrine respecting the simple nature of chlorine, so well caculated to throw confusion among all our most established notions of chemical theory, has been implicitly adopted by Dr. Thomson, without one intimation of the disputable character of this theory, or any account or even notice of the experiments of Drs. Bostock, Trail, and Murray. This is, 1 apprehend, a culpable neglect on the part of Dr. Thomson; who ought to have informed us, that men of science in his own country were far from adopting implicidy the doc- vm PREFACE. trines he has taken for granted as settled; and to have inform- ed us briefly, of the facts upon which that doctrine was dis- puted. I think in this omission, he has done injustice to men of great eminence among his cotemporaries; as indeed he did to Dr. Higgins, by omitting that gentleman as the first proposer of the atomic theory: an omission which does no credit to Dr. Thomson, or to his friend Mr. Dalton, who certainly ought to have noticed the prior claims of Dr. Higgins, to be found in his "Comparative View" of the phlogistic and anti-phlogistic theories of Chemistry-, that occasioned so much discussion a few years ago. Since Dr. Thomson published this edition, the experiments of Dr. Murray, and Dr. Ure of Glasgow, seem to me to have completely overthrown the whole system of Sir Humphry Davy on the subject of chlorine; and to have restored the old fashioned explanation of Berthollet; which is likely to prove itself, as true, as it is plain and intelligible. For the same reason that chlorine seems to combine with oxygen during the process of procuring it, so may iodine and fluorine: and we are likely to be brought back to the elegant simplicity of the Lavoiserian doctrine, that the only supporter of combustion is oxygen; a change by which, if it can be sup- ported, little will be lost. I have endeavoured to state the argument on both sides, in a way intelligible to the students for whose perusal this edition is designed: and it is manifest, that Dr. Thomson's view of the subject would not be .perfectly correct, though Sir Hum- phry Davy's notions thereon should be considered as true; for even in that case, the modern doctrine ought not to have been stated and propounded in such a way as to itf&uce the reader to suppose, that it had been adopted without opposition. 3. As to the introduction of the Earths among the Metals.-^- I have seen and made potassium too often, not to be aware of the metallic appearance of that substance—of its apparent amalgamation with mercury—of its attraction for oxygen, and the probability that caustic potash is the oxide of potassium. But these characters are not peculiar to these metalloids: the lustre of pyrites and of the Chinese yellow orpiment is as me- tallic and as brilliant as potassium; but for accuracy's sake, let us settle what we mean by a metal, before we call these substances metals. Hitherto, the leading feature of a metal has been its weight; but the alkaline metalloids are the lightest of all solids—hitherto, the oxide of a metal has been deemed with- PREFACE. ix out a contradictory instance, lighter than the metal itself; here it is heavier—hitherto we have found every metal apt to com- bine and form an alloy with almost every other metal: in the present instance we can hardly yet say it has alloyed with any thing but mercury. I am not prepared to deny any of the facts stated, but in an elementary work we should alter our definitions at least to suit the case. 4. The acid character of silex, and tlw acidifying charactei- of hydrogen.—I have the same observation to make on this head. Let us alter our definitions, and I agree that silex is an acid. But while people will persuade themselves that acids are sour to the taste, they will not understand the mystery of calling a piece of flint an acid. I hold the talents and industry of Berzelius and Sir H. Davy in high respect: they are men eminent for their ingenuity in devising, their skill in conduct- ing, their patience in pursuing, and their acuteness in deducing conclusions from experiments; but each of them has contrived to acquire a reputation, in which a love of novelty and paradox seems somewhat to intermingle. But I wrould speak with great deference, of men who have done so much, so well. With respect to the acidifying character of hydrogen, I am not yet prepared to regard it as irrevocably settled: even though Dr. Murray, in his late paper on the theory of chlorine (Edinb. 5th Jan. 1818), seems willing to suppose that the elements of water, and not water itself, enters into the chemical constitution of muriatic acid ; and that the water obtained is formed during the process of obtaining it. The theory is ingenious : but I see nothing that ise^ned by substituting ternary for binary combinations. T^gjPRs are as well explained on the latter, as on the former tHS^y ; and till new facts inexplicable on the old doctrine be dis^bvered, I see no good reason for embracing a new one. With respect to sulphureted hydrogen, (the hydrothionic acid), and cyanogen, their acid characters are so dubious, that Dr. Murray certainly talks in too strong language when he says in his late memoir that sulphur forms with hydrogen a sub- stance unequivocally acid. It takes away the colour of paper blued by Litmus, but without turning it red. That it com- bines with alkalies, is no more than sulphur does without the aid of hydrogen; unless indeed water be decomposed during the combination. But a part of the sulphur in obtaining sul- phureted hydrogen, may well be oxygenated by the atmosphe- ric air contained in the water employed during the process of Vol. I. B X PREFACE. making this gas—or even a part of the water itself may be de- composed and furnish its oxygen. These are difficulties in the way of the modern theory, which must be surmounted before Dr. Murray's opinions find full credit. No investigation of them has yet taken place to my knowledge. The same may be said of cyanogen and the other hydrogen acids. Are we sure that the water employed has not furnished oxygen in one or other of the ways just suggested? The perusal of Dr. Mur- ray's very important Experiments on muriatic acid gas, and his Observations on muriatic acid and on some subjects of chemical theory, which arrived while this preface was at the press, has led me to make these observations, which otherwise might better have appeared perhaps in the form of notes. On some or all of these points, Dr. Thomson's work re- quired notes of explanation, notes of doubt, and notes of con- tradiction. Notes also of addition, where new facts worth registering have occurred since its publication. I have en- deavoured to supply these to the best of my ability, though sparingly.* After all, this System of Chemistry is not only the work of one of our most skilful chemists, and ablest com- pilers, but it is also the only compilation which gives us the present views—the modern facts and doctrines of the science: nor are we likely soon to receive another unlessfrom the same hand, when the additions of some future years of investigation shall require a new summary of the facts. Among the im- provements devoutly to be wished, is some regular system of nomenclature, less abstruse than the present one; for if every student of chemistry and mineralogy hereafter is required to be a profound Greek scholar, I fear the votaries of this most en- gaging science will be often deterred from the pursuit: and we shall be inundated elsewhere as we are threatened to be in this country, with theories fabricated not in the Laboratory but the Lexicon. I make no apology for differing in opinion from my author. His well earned reputation will not be shaken by these remarks, even in my own opinion. The most able men are liable to error, and acknowledge it generally with a promptitude in direct proportion to their real merit. THOMAS COOPER, M. D. , * In classing the new minerals, not having hnd the opportunity of seeing them, I have lieen compelled to take their chemical analysis as furnishing the only analogy I could ven- ture to follow. CONTENTS. {£J* IN the present Edition the Tables of Contents have been enlarged by placing in them the marginal notes of the last London Edition. This will more perfectly answer the object of reference. CONTENTS OF VOLUME I. PAGE 17 17 18 INTRODUCTION, Study of Nature, Mechanical Philosophy, Chemistry, Alchymists, Universal medieine, - PART 1.—Principles of Chemistry, - Book I.—Of Simple Sub- stances, Division I.—Of Impon- derable Bodies, Chap. I— Of Light, 1. Its velocity, 2. Refraction, 3. Reflection, 4. Opacity & transparency, 29 5. Double refraction, 29 6. Polarization, - 29 7. Decomposable into se- ven rays, 10. Illuminating power of each, 11. Light enters bodies, 12. Combines with them, 13. Colour explained, 14. Produces changes on bodies, contains deoxidizing rays not colorific, 16. Possesses three pecu- liar properties, 17,18,19,20. Sources of light, Chap. U.—Of Heat, Sect. 1.—Nature of Ca- loric, ... 1. Rays of, 2 and 3. Is refracted and reflected, 4. Polarization of, ' - 5. Imponderable, §11— Of the Motion of J feat, i. Radiation of heat, 1. Effect of the surface in cooling, . This effect greatest in still air, - - 46 . Differential thermome- ter, - - 46 Radiation, as the differ- ence between the temperature of the hot body and air, 47 , Effect on the thermo- meter inversely as the distance from the reflector, - 47 . 'Radiation proportion- al to the sine of the inclination of the hot surface of the reflector, - 48 Radiating power of dif- ferent bodies, 48 This power increased, in metals,- by tar- nishing or scratch- ing, - - 49 Increasesor diminishes as the thickness of the coat increases, 49 . Surfaces radiate and absorb heat in the same proportion, 50 12. Reflection inversely as radiation, reflect- ing power of vari- ous bodies, - 50 14. Radiation takes place only in elastic me- diums, but is dimi- nished by rarefac- tion, 52 15. A screen effects the radiation of heat, 1st, by its distance from the hot can- ister; 2d, by its thickness; and 3d, b; th<- nature of its s bs . nee, - 53 Conduction of heat, 5j PAGE 2, 3, 4. Conducting power explained, 5. Has a limit, - 8. All solids conductors, 9 andlO. Fluids carry ca- loric, 11. Relative conducting powers of bodies, 12, 1.3, 14, 15. Of metals, stones, glass, woods, 60 16. Relative conducting [towers of liquids, 61 17. Of gases, - - 61 ^ III.—Of the equal distri- bution of temperature, I. Contiguous bodies as- sume the same temperature, - 2. Law of the heating and cooling of bodies, i. Of the equilibrium of heat, 5. Hypothesis of Pictet, fi. OfPrevost, - § IV.—Of the effects of Caloric, i. Changes in bulk, expansion, - 1. Differs in different bo- dies, 2. Expansion of gases, table of expansion of air, 3. Expansion of liquids, 4. Increases with the temperature, Unconnected with their density, - 6. Dilatation of liquids, Expansion of solid bo- dies, Nature of the thermo- meter, different ones used, Exceptions to expansion, 77 10. Maximum density of water at 40°, - 77 62 63 64 65 05 67 67 67 67 68 69 69 70 70 70 76 Xll CONTENTS. PAGE table of expansion of water, - - 78 11. Many liquids expand in crystallizing, ex- pansion of ice, 80 12. Some bodies contract iu freezing, - 81 ii. Changes in the state of bodies, 81 iii. Conversion of solids into liquids, - - 82 1. Takes place at a parti cular.temperature, 82 2. Table of melting points, 83 3. Water cooled under the freezing point, 4. Freezing of saline so- lutions, - - 83 5. Freezing of strong a cids, - - 84 6. Dlack's opinion, that fluidity is occasion- ed by latent heat, 86 proved by experiment, 87 latent heat of water, 89 7. Latent heat of other bodies, 90 8. Softness and ductility owing to the same cause, - - 90 2. Some bodies become vapour at all tem- peratures, others not, - - 91 3. Pioiling explained, 91 4. Boiling points, 5. vary with the pressure, 92 6. Elasticity of vapour, $■! table of elasticity of steam 93 7. Elasticity of other va pours, - - 94 9. Vapours are liquids combined with ca- loric, - - 95 iii. Gases supposed to be liquids combined with caloric, - 9" 1. Condensed by cold, 2. and pressure, - 97 3. Objections to this opi nion, - - 98 iii. Changes in composition, 98 caloric decomposes bodies, - - 98 § V. Of the quantity of Caloric in bodies, 99 i. Of the specific caloric of bodies, - 99 table of specific heats, 103 1. General results, 106 ii. Of the absolute quanti- ty of heat in bodies, 107 1. Hypothesis of Dr. Ir- PAGE ascribed to frigorific particles, - 113 their existence dis- proved - - 113 apparent reflection of cold, - - 114 of freezing mixtures, 114 table of frigorific mix- tures without ice, 115 do. with ice, - 116 do. combinations of frigorific mixtures, 117 VI. (>/ the sources of Cafcr'i.; - - IIS i. The sun, nature of, 118 I. Solar rays heat opaque bodies in propor- tion to the darkness of their colour, ll'J 2. Heat produced by the rays of the sun, 120 By burning glasses, 120 ii. Combustion, - - 121 Hooke's theory of, a- dopted'by Mayow, 122 different theories of, (note) - 122 Theory of Stall!, 123 Modified by Priestley, 124 7,8. By Crawford and Kirwan, - - 124 Refuted by Lavoisier, 125 II. Theory of Lavoisier, 12G Difference between oxygenizement and combustion, - 127 14. Difficulty respecting the origin of the heat and light - 15. Removed bv Brugna- telli, . " - 16. Bodies divided into supporters, com- bustibles, and in- combustibles, - .'0. Combustibles contain light, t:.ble of heat produ- ced by combustion 133 ii. Percussion, heat pro- duced by, Condensation dimin ishes specific calo- ric, Why heat is occasion ed by percussion, Friction, heat produ- ced "by, analogy between ca- loric and electri- . e'ty, Mixture changes tem- perature, I. Water necessary, 128 128 129 130 134 137 137 1.SS 141 PAGE Solidification of water evolves heat, - 144 vi. Electricity, heat pro- duced by - 144 Effect of, on metals, 144 Heat evolved by an electric discharge, 145 Berzelius' theory of combustion, - 146 Chap. III.—Of Electricity, 147 Two electric fluids vi- . treousand resinous, 148 Attraction ci repulsion, 149 Conductor and non- conductors, - 149 Excitement, - 149 Conductors, - - 150 Distribution of elec- tricity, - - 150 8. Origin of galvanism, 151 galvanic pile, - 152 chemical decomposi- tion, - - 153 law of Berzelius, 153 discoveries of Davy, 154 Division II.— Of Ponde- rable Bodies, - 155 Chap. 1.—Of Simple Sup- porters ofCombustiwi, 155 controversies respect- ing, - - 155 hi.—Of Oxygen, - 161 method of procuring it, - - - 161 1. Propertiesof oxygen, 163 2. Specific gra\ity, - 163 3. Supports flame and 4. life, - - - 164 5. Exists in the atmos- phere, - - 164 8. Combination with wa- ter, - - 165 §11. Of Chlorine,. - 165 Properties, - - 166 2. Specific gravity, - 166 3. Destroys colours, 167 4. Supports, combustion, : but 5. destroys kte, 167 6. Absorbed byrwater, 167 9. Combines with four doses of oxygen, I. Protoxide of, 2. Deutoxide of, 3. Chloric acid, 4. Perchloric acid, § III. Of Iodine, I. Preparation, 2. Properties, - 6. Iodides, 8. Irnlic acirl, 9. Chloriodic acid, vine, 7. Dalton'b hypothesis, iii. Of cold, 107.3. Increase of density 111 evolves boat, the 11;->| coutrarv cold. 143 168 168 170 171 172 ^ 173 173 174 174 175 176 78 78 preparation, . 179, properties, - - 180 theory of fluorine, 180 1. Proofs of its e u 1 nee, 181 10. Combines with starch. i; §IV. Of Fluorine, - 1; CONTENTS. X1U PAGE Chap. U.—Of Simple In- combustibles, - 183 § 1.-0/ Azote, - 183 1. Component part of the atmosphere, - 184 2. Weight, 3. absorbs wa- ter, - - 184 4. Absorption by water, 185 ii. Combiues with oxygen, 185 1. Forms nitrous acid, 185 2. Two oxides of azote, 186 3. Gaseous oxide, - 187 4. Nitrous and nitric acid, 188 5. Hyponitrousacid, 189 iii. Chloride of azote, 189 iv. Iodide of azote, - 191 attempts to decom pose azote, - 192 Chap. IH.— Of Simple Combustibles, - 192 i. Arrangement, - 193 Geivcs I.---AcicKftable Combustibles, §1.— Of Hydrogen, - 1. Its properties,«. •weight, 195 3. Action on combustibles, 4. on animals, 195 5. Not absorbable, - 195 ii. Combustible. Forms water with oxygen, 196 iii. With chlorine, muria- tic acid - - 197 iv. With iodine, hydrio- dic acid, - - 197 v. With fluorine, fluoric acid - - 198 vi. With azote, ammonia, 199 §11.—Of Carbon, - 200 method of preparin_ 1. properties, - 200 3. Absorbs gases, - 201 4. Plumbago, - - 202 5. Diamond, - - 202 ii. Combustion of carbon, page 217 219 220 223 224 224 5. Composition of silica 7. Fluoslicic acid, § V.—Of Phosphorus, Properties, - A poison, Union with oxygen, Burns when exposed to the air, - 224 Soluble in oxygen gas, 224 Converted by combus- tion to an acid, 224 Phosphorous acid, 226 Hypophosphorous acid, 226 Ox ide of phosphorus, 227 PAGE i. How obtained, proper ties, - . 258 ii. Oxides, - . 259 iv. Alloys, - - 259 general remarks, 259 1. Weight of the atoms, 260 2. Compounds with oxy- gen, - - 260 With chlorine, - 261 4. With iodine, 5. fluorine, 261 Genus II.---Alkalifiable Combustibles, - 262 Properties of metals, 262 Family I. iii. Union with chlorine, 228 § \.—Of Potassium, 194 194 Protochloride of phos- phorus, - - 228 3. Perchloride of phos- phorus, - - 229 iv. Union with iodine, 230 1. Protiodide, 2. periodide, 230 vi. Soluble in azote, vii. Combines with hydro gen, I. Hydroguret, 2. Bihydroguret, viii. Phosphuret of carbon, 234 235 235 264 265 265 267 236 236 carbonic acid, - 204 4. Carbonic oxide, - 205 iii. Phosgene gas - 205 vi. Cyanogen, - - 207 1. Olefiantgas, - - 207 2. Chloric ether, - 208 4. Carbureted hydrogen, 209 5. Gas from vegetable bodies and pit coal, 210 6. Affinity of carbon for oxvgen, - § III— Of Boron, - 1. Preparation, 2. Properties, - 3. Boracic acid, - 213 4. Chloride, - - 214 6. Fluoboric acid - 214 8. Borureted hydrogen, 215 10. Union with metals, 215 § IV.—Of Silicon, - 216 1. Silica, - - - 216 2. Decomposition of, 217 4. Properties of silicon, 21 §VI.—Of Sulphur, 1. Properties, - 2. Action of heat, flow- ers of sulphur, 3. Capable of crystalliz- ing, .. Combines with oxygen, 236 I. Converted by oombus tiou into an acid, Sulphurous acid, Sulphuric acid, 5. Sulphurs, 6. Lac sulphuris, iii. Chloride of sulphur, iv. Iodide of sulphur, vi. Sulphureted hydrogen, 242 vii. Sulphuret of carbon, 244 ix. Combination of sulphur with phosphorus, 246 § VII.—Of Arsenic, 1. Properties, ii. Oxides, 1. Protoxide, 2. Peroxide or arsenic acid, - - 250 iii. Chloride, - - 251 . Iodide, - - 252 . Arsenureted hydrogen gas, - - 252 viii. Phosphuret, - 253 1. Making potash, 2. Properties of potash, 3. Decomposition of pot ash, - - 267 ii. Oxides of potassinra, 268 I. Composition of potash, 268 230 2. Peroxide of potassium, 269 iii. Chloride of potassium, 269 iv. Iodide of potassium, 270 vi. Hydruret, - - 271 viii. Phosphuret, ix. sul- phuret, x. arseniu- ret, - - 272 § II.—Of Sodium, - 273 formation of sodium, 274 231 231 233 237 237 238 240 241 241 242 248 249 249 249 211 211 212 ... 212ix. Sulphuret, realgar, or- piment, - - 253 § VIII.—0/ Tellurium, 25 i 255 255 256 256 256 258 1. Properties, Oxide, . Chloride, Iodide, , Tellureted hydrogen gas, §IX.—0/ Osmium, - Oxides, - - 274 Soda, - - - 274 Peroxide, - - 275 Chloride, - - 275 iii. Iodide, - - 277 vi. Phosphuret, - 277 vii. Sulphuret, - - 278 viii. Arseniuret, - 278 ix. Alloy with potassium, 278 § lH.—Calcium, - 279 I and 2. Lime, - - 279 discovery of calcium, 279 ii. Lime, - 280 iii. Chloride, - - 281 iv. Iodide, - - 282 §rV.—Of Barium, 283 barytes, - - 283 decomposition,' - 284 I. Composition of barytes, 285 Peroxide, - - 286 iii. Chloride, - - 286 iv. Iodide - - 288 § V.— Of Strontium, 288 ii. Composition of stron- tian, - - 290 iii. Chloride, - - 290 iv. Iodide, - - 291 v. Affinities, - - 292 § VI.—Of .Magnesium, 292 ii. Composition of mag- nesia, - - 293 iii. Chloride, - - 293 iv. Iodide, - - 295 Fami lt II. . - 295 §1. Of Yttrium, - 295 preparation of yttria, 296 composition of, - 297 xjv CONTENTS. PAGE) PAGE § 11—0/ Glucinum, 297ji. Properties, - - 337 ii. Composition of glucina, 298>ii. Oxides, 1. protoxide, 337 §HI.—Of Aluminum, 299 2. Peroxide, - - 338 preparation of alumi- iv. Sulphuret, - - 338 na, - - 299Family IV. §'I.—Zinc, 339 ii. Composition of alumina, 300 i. Properties, - - 340 301 ii. Oxides, - - 341 342 304 304 306 307 307 310 § IV.—Of Zirconium, preparation of zirco- nia, - - 301 Family HI. § I.—0//ron,303 1. Properties, - - 303 ii. Combinations with oxy- gen, 1. Black oxide, 2. Peroxide, 3. Tempering of steel, 1. Protochloride of iron, 2. Perchloride, iv. Iodide, 1. Cast iron, 2. Malleable iron, 3. Steel, --- 6. Natural steel; of ce- mentation, - 313 cast, - - - 314 7. Subcarburets of iron, 314 vii. Boruret, viii. silicuret, ix. phosphuret, 315 v.—1. Protosulphuret of iron, - - 316 2. Persulphuret, - 317 xi. Alloys with arsenic, 319 xii. Affinities, § 11.—Of JYtckel, - reduction ot, i. Properties, ii. Oxides, 1. Protoxide, 2. peroxide, 323 iii. Chloride, vi. carburet, 324 viii. Phosphuret, ix. sul- phuret, - - 324 x. Alloy with arsenic, 324 xi. With iron, - 325 $ 111—0/ Cobalt, - 1, 2, &c. Properties, ii. Oxides, 1. protoxide, '2. Peroxide, iii. Chloride, v. Phosphuret, vi. sulphu ret, viii. Alloy with iron, § IV.—Of .Manganese, Properties, ii. Oxides, iii. Chloride, iv. iodide, viii- Phosphuret, ix. sul- phuret, - - 343 x. Alloys with arsenic, xii. potassium and so- dium, xiv. iron, xv. nickel, - - 341 § II.—0/ Lead, - 344 1, 2, he. Properties, 345 ii. Oxides, 1. yellow oxide, 345 308,2. Peroxide, - - 346 308:3. R»d oxide - - 347 309 4. Cupellation, - 348 309,5. Refining lead, litharge, 348 348 319 320 321 322 322 325 326 326 327 327 49 350 351 351 352 352 353 356 357 327 328 328 329 329 330 331 331 ii. Oxides, 1. Protoxide, 2. Peroxide, iii. Chloride, vi. Carburet, viii. phos- phuret, ix. sulphu- ret, - - 332 xi. Alloys with iron, 333 § V—Of Cerium, - 333 i. Reduction, - - 334 ii. Oxides, - - 335 iv. Carburet, v. phosphu- ret, vi. sulphuret, 335 § VI.—0/ Urunium, 336 iii. Chloride of lead, Iodide, vi. Phosphuret, vii. sul- phuret, - viii. Alloys with arsenic, ix. with potassium and sodium, xi. iron, xii. cobalt, xv. Zinc, xvi bismuth §111.— Of Tin, i. &C Properties, ii Oxides, 1. grey oxide, White oxide, iii. Chloride, I protochlo- ride, 2. perchloride, 354 iv. Iodide, vi. phosphuret, 355 Sulphurets, 1. proto- sulphuret, 2. per- sulphuret, Alloys with arsenic, ix. with potassium and sodium, With iron, xii. cobalt, xiii. Zii.e, \;k. bis- muth, xvi. lead, >5S § IV.—Of Copper, - 35! 1X2, &c. "Properties, 359 ii. Oxides, - - 360 1. Protoxide, 2. peroxide, 361 iii. Chlorides, 1. protoch- loride, - - 362 2. Perchloride, - 363 iv. Iodide, vi. phosphu- ret, vii. sulphuret, 363 viii. Alloys with arsenic, ix. with potassium and sodium, - 564 With iron, xi. nickel, xiii. manganese, xv. zinc, xvi. With bismuth, xvii. lead, xviii. With tin, § V.—Of Bismuth, - 1, 2, &c. Properties, ii. Oxides, PAUE iii. Chloride, iv. iodide, vi. sulphuret, - 371 § VI.— Of Mercury, 372 1,2, &c. Properties, 372 ii. Oxides, 1. protoxide, 373 Red oxide, - - 374 iii. Chlorides, - - 374 I. Perchloride - 375 Protochloride, - S77 ii. Iodide, - - 378 vi. Phosphuret, vii. sul- phurets, I proto, 2 - 397 381 382 •■83 383 :?34 386 388 389 389 390 390 391 per - viii. Amalgams with arse- nic, ix. with tellu- rium, x. with pot- assium and sodium, xii. iron, xv. bis- muth, Lead, xvii. tin, xviii. copper, - § VII.—Of Silver, - 349|l, 2, &c. Properties, ii. Oxide, iii. chloride, iv. Iodide, vi phosphuiet, vii. sulphuret, viii. Alloys with arsenic, ix. iron, xi cobalt, 387 xiii. With zinc, xiv. bis- muth, xv. lead, xvi copper, - xvii. With tin, xviii. amal- gam, Family V., § I.—Of Gold, 1, 2, &c. Properties, Oxides, 1. Peroxide, 2. protoxide, 392 v. Phosphuret, vi. sulphu- ret, - - 393 Alloys with arsenic, viii. potassium and sodium, x. iron, 394 With nickel, xii. co- balt, xiii. manga- nese, xv. zinc, 395 xvi. Wth bismuth, 396 xvii. \A ;.d lead, - 397 xviii. With tin, xix. cop- per, xx. With mercury, xxi. silver, § II.—O/ Platinum, 1. History of, purification, I, &c. Properties, ii. Oxides, 1; Protoxide, 2. peroxide, 404 iii. Chlorides, v. phos- phurets, 1. proto- phosphuret, - 405 2. Perphosphuret, vi. sul- phurets, 1. proto- sulphuret, 2. deuto- sulphuret, 3. per- sulphuret, - 400 vii. Alloys with arsenic, 365 366 367 369 369 370 398 400 401 401 402 403 403 CONTENTS. XV PAGE viS. potassium and sodium, x, iron, xii. zinc, - - 407 xiii. Bismuth, xiv. lead, xv. tin, xvi. cop- per, xyii. copper and zinc, - 408 xviii. Mercury, xix. sil ver, - - 409 xx. Gold, - - 410 § HI.—0/ Palladium, 411 1, &c. Properties, ii. ox- ides, v. Sulphuret, vi. alloys, with 1 gold and 2 platinum, 3 silver, 4 copper, 5 lead, 6 tin, 7 bismuth, 8 iron, § IV.—Rhodium, i. Preparation, ii. Oxides, 1. protoxide, 2. deutoxide, 3. pe- PAGE 4. Table of chlorides, 421 5. Table of iodides, 6. of 422 423 424 411 412 413 413 413 roxide, - - 414 v. Alloys, - - 415 § V.—Of Iridium, - 416 preparation, - 416 i. Properties, ii. oxides, 417 iv. Alloys, - - 418 weight of an atom of each of the metals of the second ge- nus, - - 418 table of general pro' perties of 2d genus, 419 3. Table of oxides, - 420 sulphurets 7. Alloys, tables of, Genus IU.---Intermedi- ate Combustibles, - 425 § I.—Of Antimony, - 426 1, &c. Properties, ii. ox ides, - - 427 1. Protoxide, - - 418 2. Hfeutoxide, • - 429 3. Antimonic acid, chloride, - 430 iv. Iodide, vi. phosphu- ret, vii. sulphuret, 431 viii. Alloys with arsenic, ix. Potassium and sodium, x. iron, xii. zinc, xiii. bismuth, xiv. lead, xv. tin, xvi. copper, - 332 xvii. Mercury, xviii. sil- ver, xix. gold, xx. platinum, - 43. H—Of Chromium, 433 Properties, ii oxides, 1. protoxide, 2. deu- ' toxide, 3. chromic acid, - - 435 § III —Of Molybdenum, 436 how procured, - 437 Properties, ii. oxides, 1 protoxide, 2. mo- lybdous acid, mo- PAGE lybdic acid, - 438 iv. Sulphuret of, - 439 v. Alloys with arsenic, vii. iron, viii. nickel, ix. cobalt, x. manga- nese, xi. zinc, xii. bismuth, - 440 xiii. With lead, xiv. tin, xv. copper, xvii. silver, - - 441 xviii. With gold, xix. pla- tinum, - - 442 § IV.—Of Tungsten, 442 1, &c. Properties, ii. ox- ides, 1. protoxide, 443 2. Tungstic acid or per- oxide, - - 444 iv. Sulphuret, v. alloys, 445 § V.—Of Columbium, or Tantalum, - - 446 Preparation, ii. oxides, 447 iv. Alloys with iron, v. tungsten, - 448 VI.— Of Titanium, 449 Oxides, 1. protoxide, 2. deutoxide, 3. pe- roxide, iii. 2. phos- phuret, iv. alloys, 450 table of properties of 3d genus of metals, 451 table of oxides, - 451 § VII.—0/ Thorinum, 452 Appendix, on the atomic theory, - - 457 A SYSTEM OF CHEMISTRY. AS soon as man begins to think and to reason, the different objects which surround him on all sides naturally engage his at- tention. He cannot fail to be struck with their number, diversity, and beauty; and naturally feels a desire to be better acquainted with their properties and uses. If he reflect also that he himself is altogether dependent upon these objects, not merely for his plea- sures and comforts, but for his very existence ; this desire must become irresistible. Hence that curiosity, that eager thirst for knowledge, which animates and distinguishes generous minds. Natural objects present themselves to our view in two different ways; for we may consider them either as separate individuals, or as connected together and depending on each other. In the first case we contemplate nature as in a state of rest, and consider ob- jects merely as they resemble one another, or as they differ from one another: in the second we examine the mutual action of sub- stances on each other, and the changes produced by that action. The first of these views of objects is distinguished by the name of Natural History; the second, by that of Science. Natural science then is an account of the events which take place in the material world. But every event, or, which is the same thing, every change in bodies, indicates motion; for we cannot conceive change, unless at the same time we suppose motion. Science then is in fact an account of the different motions to which bodies are subjected, in consequence of their mutual action on each other. Now bodies vary exceedingly in their distances from each other. Some, as the planets, are separated by many millions of miles; while others, as the particles of which water is composed, are so near each other, that we cannot, by our senses at least, perceive any distance between them ; and only discover, by means of cer- tain properties which they possess, that they are not in actual con- tact. But the quantity of change or of motion, produced by the mutual action of bodies on each other, must depend, in seme mea- Voi.. I. C 18 INTRODUCTION. sure at least upon their distance from each other; if that distance be great enough to be perceived by the eye, and consequently to admit of accurate measurement, every change in it will also be perceptible, and will admit of measurement. But when the dis- tance between two bodies is too small to be perceptible by our sen- ses, it is evident that no change in that distance can be percepti- ble ; and consequently every relative motion in such bodies must be insensible. Science, therefore, naturally divides itself into two great branch- es : the first, comprehending all those natural events which are ac- companied by sensible motions ; the second, all those which are not accompanied by sensible motions. The first of these branches has been long distinguished in Britain by the name of Natural Phi- losophy, and of late by the more proper appellation of Mechanical Philosophy. The second is known by the name of Chemistry. Chemistry, then, is that science which treats of those events or changes in natural bodies, which are not accompanied by sensi- ble motions. Chemical events are equally numerous and fully as important as those which belong to Mechanical Philosophy; for the science com- prehends under it almost all the changes in natural objects with which we are more immediately connected, and in which we have the greatest interest. Chemistry, therefore, is highly worthy of our attention, not merely for its own sake, because it increases our know- ledge, and gives us the noblest display of the wisdom and goodness of the author of nature ; but because it adds to our resources by ex- tending our dominion over the material world ; and is therefore cal- culated to promote our enjoyment and increase our power. As a science, it is intimately connected with all the phenomena of nature ; the causes of rain, snow, hail, dew, wind, earthquakes, even the changes of the seasons, can never be explored with any chance of success while we are ignorant of chemistry ; and the ve- getation of plants and some of the most important functions of ani- mals, have received all their illustration from the same source. No study can give us more exalted ideas of the wisdom and goodness of the Great First Cause than this, which shows us every where the most astonishing effects produced by the most simple, though adequate means; and displays to our view the great care which has every where been taken to secure the comfort and happiness of every living creature. As an art, it is intimately connected with all our manufactures. The glass blower, the potter, the smith and every other worker in metals, the tanner, the soap maker the dver the bleacher, are really practical chemists j and the most essential improvements have been introduced into all these arts by the pro- gress which chemistry has made as a science. Agriculture can only be improved by calling in the assistance of chemistry: and the advantages which medicine has derived from the same source are too obvious to be pointed out. INTRODUCTION. 19 The word Chemistry seems to be of Egyptian origin, and to have been originally equivalent to our phrase natural philosophy in its most extensive sense. In process of time it seems to have ac- quired a more limited signification, and to have been confined to the art ofxvorking metals.* This gradual change was, no doubt, owing to the great importance attached by the ancients to the art of working metals. The founders and improvers of it were con- sidered as the greatest benefactors of the human race; statues and temples were consecrated to their honour; the} were even raised above the level of humanity, and enrolled among the number of the Gods. How long the word chemistry retained this new signification it is impossible to say; but in the third century we find it used in a much more limited sense, signifying the art of making gold and silver. The cause of this new limitation, and the origin of the opi- nion that gold can be made by art, are equally unknown. Chemis- try, in this new sense, seems to have been cultivated, with consi- derable eagerness in Egypt and Greece; to have passed from the Greeks to the Arabians, and by the followers of the Caliphs to have been introduced into the west of Europe. Those who professed it gradually assumed the form of a sect under the name of Alchy- mists; a term which is supposed to be merely the word chemist with the Arabian article al prefixed.} The alchymists laid it down as a principle, that the substances which compose gold exist in all metals, contaminated indeed with various impurities, but capable, by a proper purification, of being brought to a perfect state. The great object of their researches was to find out the means of producing this change, and, conse- quently, of converting the baser metals into gold. The substance which possessed this wonderful property they called lapis philoso- phorum, " the philosophers' stone ;" and man}' of them boasted that they were in possession of that grand instrument. Chemistry, as the term was used by the alchymists, signified the art of making the philosophers' stone. They affirmed that this art was above the human capacity, and that it was made known by God to those happy sages only whom he peculiarly favoured. The for- tunate few, who were acquainted with the philosophers' stone, cal- led themselves adepti, " adepts ;" that is, persons who had got pos- session of the secret: this secret they pretended that they were not at liberty to reveal; affirming that dire misfortune would fall * Our English word physician has undergone a similar change. •J- I am indebted for the following etymology to my friend, the Rev. Mr. Holme, of St. Peter's, Cambridge, who was supplied with it by the Rev. Mr. Palmer, Professor of Arabic in that University. " Al-chemv, or more properly Al-kemt, the knowledge of the sub- stance or composition of bodies, so named from the substantive \^&\JJ> , (Kiyamon), that is, the substance or constitution of any thing, from the root ^^O, (Kama). See Golius Lexicon." 20 INTRODUCTION. upon that man's head who ventured to disclose it to any of the sons of men without the clearest tokens of the divine authority. In consequence of these notions, the alchymists made it a rule to keep themselves as private as possible. They concealed, with the greatest care, their opinions, their knowledge, and their pursuits. In their communications with each other, they adopted a mystical and metaphorical language, and employed peculiar figures and signs that their writings might be understood by the adepts only, and might be unintelligible to common readers. Notwithstanding all these obstacles, a great number of alchymistical books made their appearance in the dark ages ; many of them under the real names of the authors; but a still greater number under feigned titles, or ascribed to the celebrated sages of antiquity. How far alchymy had proceeded among the ancients, or whether it had even assumed the form of a sect, cannot be ascertained. Traces of it appear among the Arabians, who turned their atten- tion to literature soon after the conquests of the Caliphs, and who communicated to our barbarous ancestors the sacred seeds of sci- ence. The principal chemical writers among the Arabians, were Geber and Avicenna; and in their writings, at least such of them as I have had an opportunity of perusing, there appears but little of that mysticism and enigma which afterwards assumed a syste- matic form. The alchymists seem to have been established in the west of Eu- rope so early, at least, as the 10th century. Between the 11th and 15th centuries alchymy was in its most flourishing state. The wri- ters who appeared during that period were sufficiently numerous, and very different from each other in their style and abilities. Some of their books are nearly unintelligible, and bear a stronger resem- blance to the reveries of madmen than to the sober investigations of philosophers. Others, if we make allowance for their metapho- rical style, are written with comparative plainness, display consi- derable acuteness, and indicate a pretty extensive acquaintance with natural objects. They often reason with great precision, though generally from mistaken principles; and it is frequently easy enough to see the accuracy of their experiments, and even to trace the par- ticular circumstance which led to their wrong conclusions. The principal alchymists who flourished during the dark ages, and whose names deserve to be recorded, either on account of their discoveries, or of the influence which their writings and example had in determining the public taste, were Albertus Magnus, Roger Bacon, Arnoldus de Villa Nova, Raymond Lully, and the two Isaacs of Holland.* * Albertus Magnus was a German ecclesiastic. He was born in the year 1205 and died in 1280. His works are numerous; but the most curious of them is his tract entitled J)e Alchimin, which contains a distinct view of the state of chemistry in the 13th century. Roger Bacon was born in the county of Somerset, in England, in 1224. His merit is too well known to require any panegyric. The greater number of his chemical writings are studiously obscure; but he generally furnishes us with a key for their explanation. S»me INTRODUCTION. 21 The writings of the greater number of alchymists are remarkable for nothing but obscurity and absurdity. They all boast that they are in possession of the philosophers' stone; they all profess to com- municate the method of making it; but their language is enigma- tical, that they may be understood by those adepts only who are favoured with illumination from heaven. Their writings in those benighted ages of ignorance gained implicit credit; and the covetous were filled with the ridiculous desire of enriching themselves by means of the discoveries which they pretended to communicate. This laid the unwary open to the tricks of a set of impostors, who went about the world affirming that they were in possession of the philosophers' stone, and offering to communicate it to others for a suitable reward. Thus they contrived to get possession of a sum of money; and afterwards they either made off with their booty, or tired out the patience of their pupils by tedious, expensive, and ruinous processes. It was against these men that Erasmus and Ben Jonson directed their well known satires, entitled " The Al- chymist." The tricks of these impostors gradually exasperated mankind against the whole fraternity of alchymists. Books appear- ed against them in all quarters, which the art of printing, just in- vented, enabled the authors to spread with facility; the wits of the age directed against them the shafts of their ridicule; men of science endeavoured to point out the infinite difficulty, if not the impracticability of the art; men of learning showed that it had never been understood; and men in authority endeavoured, by laws and punishments, to guard their subjects from the talons of alchymistical impostors. ^ Chemists had for ages hinted at the importance of discovering a universal remedy, which should be capable of curing, and even of preventing, all diseases; and several of them had asserted that this remedy was to be found in the philosophers' stone; which not only converted baser metals into gold, but possessed also the most sovereign virtue, was capable of curing all diseases in an instant, and even of prolonging life to an indefinite length, and of con- ferring on the adepts the gift of immortality on earth. This notion gradually gained ground; and the word chemistry, in consequence, at length acquired a more extensive signification, and implied not only the art of making gold, but the art also of preparing the uni- versal medicine.* of them exhibit a wonderfully enlightened mind for the age in which he wrote: his tract De Mirabili Potestate Artis et Naturx would have done honour to Lord Bacon himself. Arnoldus de Villa Nova is believed to have been born in Provence, about the year 1240. His reputation was very high; but all of his writings that I have examined are so obscure as to be generally unintelligible. Raymond Lully was born at Barcelona, in 1235. His writings are fully as obscure as those of Arnold. It is not known at what period the Isaacs of Holland lived, though it is supposed to hare been in the 13th century. Their writings are perfectly plain. • The first man who formally applied chemistry to medicine was Basil Valentine, who is said to have been born in 1394, and to have been a Benedictine Monk at Erford in Ger- 22 INTRODUCTION. Just about the time that the first of these branches was falling into discredit, the second, and with it the study of chemistry, ac- quired an unparalleled degree of celebrity, and attracted the atten- tion of all Europe. This was owing to the appearance of Theo- phrastus Paracelsus. This extraordinary man, who was born in 1493, near Zurich in Switzerland, was, in the 34th year of his age, after a number of whimsical adventures, which had raised his re- putation to a great height, appointed by the magistrates of Basil to deliver lectures in their city; and thus was the first public Pro- fessor of chemistry in Europe. In two years he quarrelled with the magistrates, and left the city; and, after running through a complete career of absurdity and debauchery, died at Salzburg, in the 47th year of his age. The character of this extraordinary man is universally known. That he was an impostor, and boasted of secrets which he did not possess, cannot be denied; that he stole many opinions and even facts from others, is equally true: his arrogance was unsupportable, his bombast ridiculous, and his whole life a continued tissue of blunders and vice. At the same time it must be acknowledged that his talents were great, and that his labours were not entirely useless. He contributed not a little to dethrone Galen and Avi- cenna, who at that time ruled over medicine with absolute power, and to restore Hippocrates, and the patient observers of nature, to that chair from which they ought never to have risen. He certainly gave chemistry an eclat which it did not before possess; and this must have induced many of those laborious men who succeeded him to turn their attention to the science. Nor ought we to forget that by carrying his speculations concerning the philosophers' stone and the Universal Medicine to the utmost height of absurdity, and by exemplifying in his own person their emptiness and uselessness, he undoubtedly contributed more than any man to their disgrace and subsequent banishment from the science. Van Helmont, who was born in 1577, may be considered as the last of the alchymists. His death completed the disgrace of the Universal Medicine. His contemporaries,* and those who imme- diately succeeded him, if we except Crollius and a few other blind admirers of Paracelsus, attended only to the improvement of che- mistry. The chief of them were Agricola, Beguin, Glaser, Er- kern, Glauber, Kunkel, Boyle, &c. The foundations of the alchymistical system being thus shaken many. His Cvrrus TriumpliaUs Antimonii is the most famous of his treatises. In it he celebrates the virtues of antimoniid medicines, of which he was the original discoverer. It was written in German ; but there is an elegant Latin translation by Kirkringius. * I do not mean that he was the only alchymistof his time; but the only man of eminence who published on the subject. Mr. William Oughtred the mathematician, for example was an alchymist. He used to talk much of the maiden earth for the philosophers' stone' It was made of the harshest clear water that he could get, which he let stand to petrify and evaporated by simmering, " His son Ben," says Mr. Aubrey, « tended his furnaces.' He told me that his father would sometimes say that he could make the stone." Aubrey^ Lives of Eminent Men. Vol. ii. p. 474. INTRODUCTION. 23 the facts which had been ascertained soon became a heap of rub- bish, and chemistry was left without any fixed principle, and des- titute of an object. It was then that a man appeared passionately devoted to the study, and thoroughly acquainted with all the facts; who, by a happy hypothesis, connected them together, pointed out the proper objects of chemistry, and demonstrated the impor- tant purposes to which it might be applied. This man was Bec- cher. He accomplished the arduous task in his Physica Subterra- nea, printed at Francfort in 1669. The publication of this book forms a very important era in the history of chemistry. It then escaped for ever from the trammels of alchymy, and became the rudiments of the science which we find it at present. Ernest Stahl, the editor of the Physica Subterranea, adopted, soon after Beccher's death, the theory of his master; but he sim- plified it and improved it so much, that he made it entirely his own: and accordingly it has been ever since distinguished by the name of the Stahlian theory. Ever since the days of Stahl, chemistry has been cultivated with ardour in Germany and the north; and the illustrious philosophers of these countries have contributed highly towards its progress and its rapid improvement. The most deservedly celebrated of these are Margraff, Bergman, Scheele, Klaproth, Bucholz, Berzelius, &c. In France, soon after the establishment of the Academy of Sci- ences, in 1666, Homberg, Lemery, and Geoffroy, acquired cele- brity by their chemical experiments and discoveries; and after the new modelling of the academy, chemistry became the peculiar ob- ject of a part of that illustrious body. Rouelle, who was made Professor of Chemistry in Paris about the year 1745, contrived to infuse his own enthusiasm into the whole body of French literary men; and from that moment chemistry became the fashionable stu- dy. Men of eminence arose every where, discoveries multiplied, the spirit pervaded the whole nation, extended itself over Italy, and appeared even in Spain. But the most eminent among the French chemists was Lavoisier, who fell a victim to the fury of the Revolu- tion, and died on the scaffold in the year 1794. After the death of Boyle and of some other of the earlier mem- bers of the Royal Society, little attention was paid to chemistry in Britain, except by a small number of individuals. The spirit which Newton had infused for the mathematical science was so great, that it drew within its vortex almost every man of emi- nence in Britain. But when Dr. Cullen became Professor of Che- mistry in Edinburgh, in 1756, he kindled a flame of enthusiasm among the students, which was soon spread far and wide by the subsequent discoveries of Black, Cavendish, and Priestley; and meeting with the kindred fires which were already burning in France, Germany, Sweden, and Italy, the science of chemistry burst forth at once with unexampled lustre. Hence, the rapid pro- gress which it has made during the last 50 years, the universal a^ 24 INTRODUCTION. tention which it has excited, and the unexpected light which it has thrown on several of the most important arts and manufactures. The object of this work is to exhibit as complete a view as pos- sible of the present state of chemistry; and to trace at the same time its gradual progress from its first rude dawnings as a science, to the improved state which it has now attained. By thus blending the history with the science, the facts will be more easily remem- bered, as well as better understood; and we shall at the same time pay that tribute of respect to which the illustrious improvers of it are justly entitled. A complete account of the present state of chemistry must in- clude not merely a detail of the science of chemistry strictly so call- ed, but likewise the application of that science to substances as they exist in nature, constituting the mineral, vegetable, and animal kingdom. This work, therefore, will be divided into two parts. The first will comprehend the science of chemistry properly so called, the second will consist of a chemical examination oe NATURE. PART I. PRINCIPLES OF CHEMISTRY. THE object of chemistry is to ascertain the ingredients of which bodies are composed; to examine the compounds formed by the combination of these ingredients, and to investigate the nature of the power which produces these combinations. The science therefore naturally divides itself into three parts:— 1. A description of the component parts of bodies, or of simple sub- stances as they are called. 2. A description of the compound bo- dies formed by the union of simple substances. 3. An account of the nature of the power which produces these combinations. This power is known in chemistry by the name of Affinity. These three particulars will form the subject of the three following books. BOOK I. OF SIMPLE SUBSTANCES. By simple substances is not meant what the ancient philosophers called elements of bodies, or particles of matter incapable of farther diminution or division. They signify merely bodies which have not been decompounded, and which no phenomenon, hitherto ob- served, indicate to be compounds. Very possibly the bodies which we reckon simple may be real compounds; but till this has actually been proved we have no right to suppose it. Were we acquainted with all the elements of bodies, and with all the combinations of which these elements are capable, the science of chemistry would be perfect. But at present this is very far from being the case. The simple substances at present known amount to about 50, and naturally divide themselves into two classes. Those which belong to the first class are of too subtle a nature to be confined in any of the vessels which we possess. They cannot therefore be exhibited in a separate state, and their existence is merely inferred from certain phenomena exhibited by the second class of bodies in pecu- liar circumstances. Thev do not sensibly affect the most delicate Vol. I. D 26 IMPONDERABLE BODIES. f dSJwJn 1 balance, and therefore have received the name of imponderable bodies. The second class of bodies may be confined in proper ves- sels, may be exhibited in a separate state, their weight and other properties may be determined. They have received the name ot ponderable bodies. It will be exceedingly convenient to consider these two classes separately. We shall place the imponderable bodies first, because during the account of them we shall have an opportunity of introducing several general facts and doctrines which will serve to elucidate the other departments of chemistry. DIVISION I. OF IMPONDERABLE BODIES. The imponderable bodies at present supposed to exist are four in number; namely, light, heat, electricity, and magnetism. The first three of these are intimately connected with chemistry, and appear to be the agents in many of the most important phenomena connected with the science. But as magnetism has no known con- nexion with chemistry, it cannot with propriety claim a place in this work. CHAPTER I. OF LIGHT. Every person is acquainted with the light of the sun, the light of a candle, and other burning bodies; and every one knows that it is by means of light that bodies are rendered visible. Concerning the nature of this light, two different theories have been advanced by philosophers. Huygens considered it as a subtle fluid filling space, and rendering bodies visible by the undulations into which it is thrown. According to his theory, when the sun rises it agitates this fluid, the undulations gradually extend them- selves, and at last, striking against our eye, we see the sun. This opinion of Huygens was adopted also by Euler, who exhausted the whole of his consummate mathematical skill in its defence. The rest of philosophers, with Newton at their head, consider light as a substance consisting of small particles constantly separat- ing from luminous bodies, moving in straight lines, and rendering bodies luminous by passing from them and entering the eye. New- ton endeavoured to establish this theory on the firm basis of mathe- Chap. I.] * light. 27 matical demonstration; by showing that all the phenomena of light may be mathematically deduced from it. Huygens and Euler, on the contrary, attempted to support their hypotheses, rather by start- ing objections to the theory of Newton, than by bringing forward direct proofs. Their objections, even if valid, instead of establish- ing their own opinions, would prove only that the phenomena of light are ncjt completely understood; a truth which no man will re- fuse to acknowledge, whatever side of the question he adopts. Newton and his disciples, on the contrary, have endeavoured to show, that the known phenomena of light are inconsistent with the undulations of a fluid,* and that on such a supposition there can be no such thing as darkness at all. They have also brought forward a great number of direct arguments, which it has been impossible to answer, in support of their theory. The Newtonian theory there- fore is much more probable than the other. But without attempting to canvass the merits of these different hypotheses, let us proceed to state the properties of light. 1. It was first demonstrated by Roemer,| a Danish philosopher, that light takes about eight minutes in moving across one half of the earth's orbit;:): consequently it moves at the rate of nearly * [It is not necessaiy that the impulse given to light by the action of the sun, or of luminous bodies, should produce an undulating motion: it is just as easy to conceive an impulse that Shall produce rectilinear motion.—C] f Phil. Trans, xii. 83. * [2 Smith's Optics, Art. 1120. Roemer's method is this. Let 5 be the sun, a, b, c, the annual orbit of the earth, /Jupiter, e,f, g, h, the orbit of the innermost satellite, the properest for this inquiry, by reason of the quickness of its revolution; and let this satellite en- ter th» shadow of Jupiter at^, and emerge from it at h. Now sup- posing the earth at b, some time before the last quadrature, let an emersion of this satellite be observed at A; then if the earth con- tinued in the same place, we should see the next emersion at the end of 24 hours and an half, this being supposed the exact time in which this satellite revolves to the shadow. Likewise if the earth continued at the same place b during any number of revolutions, sup- pose 30, we should see an emersion at the expiration of 30 times 24 1-2 hours. But the earth in that time being really transferred from b to c, farther from Jupiter, it follows, if light requires time for its propagation, that this emersion will be perceived later at c than it would have been at b, and that to 30 times 24 1-2 hours, we must add the time which the light takes up in describing the space k c, the difference of b h and h c. 1121. On the contraiy, towards the other quadrature, whilst the earth in going from d to a, is approaching towards Jupiter, the emersions of the satellite at^ should be perceived sooner at a than they would be, had the earth remained at d. 1122. Now these retardations of the emersions in going from Jupiter, and acceleration of the immersions in going towards him, have been often found to amount to above ten minutes; and from the most accurate consideration of them it is concluded that light de- scribes a line k c equal to the semidiameter of the earth's annual orbit, nearly in half a quarter of an hour. The motion of Jupiter in his orbit during the earth's passage from b to c and from d to a, is considered in that conclusion; and it is at last agreed by astronomers that these equations, of the times of these eclipses, cannot be accounted for either by any inequality in the motion of the satellite, or by any eccentricity or inclination of its orbit; and lastly, that the three other satellites require the same equations of the times of their eclipses.—Phil. Trans, vol. 1. abrid. p. 422. Mr. Bradley's reasoning on the velocity of light trom the parallax of the fixed stars may be found in the same book, art. 1196.—C] 26 IMPONDERABLE BODIES. 9 division l! 200,000 miles in a second. The discovery of Roemer has been still farther confirmed and elucidated by Dr. Bradley's very inge- nious theory of the aberration of the light of the fixed stars.* 2. While a ray of light is passing through the same medium, or when it passes perpendicularly from one medium to another, it continues to move without changing its direction; but when it passes obliquely from one medium to another of a different density, it always bends a little from its old direction, and assumes a new one. It is then said to be refracted. When it passes into a denser medium, it is refracted towards the perpendicular; but when it passes into a rarer medium, it is refracted from the perpendicular. In general, the quantity of refraction is proportional to the density of the medium; but if the medium be combustible, the refraction is greater than it would otherwise be.f In the same medium the sines of the angles of incidence and of refraction have always the same ratio to each other. It has been the general opinion of philosophers since the days of Newton, that the refractive power of the same body in different states is proportional to its density. But M. M. Arago and Petit have lately shown by a set of experiments, that when a liquid body is converted into vapour, its refractive power diminishes at a greater rate than its density. Thus the refractive power of sulphu- ret of carbon, while liquid, when compared to that of air, is a little greater than 3 ; while that of the same substance in the state of va- pour, being likewise referred to air, does not surpass 2. The liquids tried by these philosophers were sulphuret of carbon, sulphuric ether, and muriatic ether4 This newly discovered fact, constitutes one of the strongest objections to the Newtonian theory of light that has yet been advanced. 3. When a ray of light enters a transparent medium, as a plate of glass, with a certain obliquity, it continues to move on till it comes to the opposite surface of the glass; but then, instead of passing through the glass, 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 the floor. The ray is then said to be re- fected. The angle of reflection is always equal to the angle of in- cidence. When the surface of a medium is polished, as glass or mirrors, oblique rays do not enter them at all, but are reflected when they approach the surface of the body. All surfaces are capable of reflecting a greater or smaller number of oblique rays. Rays are only reflected at surfaces. Newton has explained these phenomena by supposing an attrac- tion to exist between light and the medium through which it is * Phil. Trans, xxxv. 637, and xiv. 1. [2 Smith's Optics, ub. sup. and S. pravesand's Phys. Elem. Math. lib. ii. cap. 1. p. 708.—C.] ■\ It was the knowledge of this law that led Newton to suspect the diamond to be com. bustible, and water to contain a combustible ingredient.—Optics, p. 72. % Ann. de Chimie et Physique, i. 1. Chap. I.] LIGHT. 29 moving, the medium towards which it is approaching, or the bo- dies in its neighbourhood. 4. Some substances, as water, are transparent, or allow light tq pass freely*through them; other, as iron, are opaque, or allow no light to pass through them. Now, it can scarcely be doubted that the component particles of all bodies are far enough distant from each other to allow the free transmission of light; consequently opacity and transparency must depend, not upon the distance of the particles of bodies, but upon something else. Newton has shown, that transparency can only be explained by supposing the particles of transparent bodies uniformly arranged and of equal density. When a ray of light enters such a body, being attracted equally in every direction, it is in the same state as if it were not attracted at all, and therefore passes through the body without ob- struction. In opaque bodies, on the contrary, the particles are either not uniformly arranged, or they are of unequal density. Hence the ray is unequally attracted, obliged constantly to change its direction, and cannot therefore make its way through the body. 5. When a ray of light passes through a crystallized body, pro- vided the primitive form of the crystal be neither a cube nor a re- gular octahedron, it is split into two distinct rays, one of which is refracted in the ordinary way, while the other suffers an extraor- dinary refraction. Hence, when an object is viewed through such a crystal it appears double. Such bodies are said to refract doubly. The laws of this double refraction were first accurately explained by Huygens. Calcareous spar is one of the substances which pos- sesses this property in the most striking degree. 6. If a ray of light fall upon a polished surface of glass at an an- gle of incidence of 35° 25', it will be reflected in a straight line, making the angle of reflection equal to the angle of incidence. Let us suppose another plate of glass to be so placed that the reflected ray will fall upon it likewise at an angle of 35° 25'. The second plate may be turned round its axis without varying the angle which it makes with the ray that falls upon it. A very curious circum- stance may be observed as this second glass is turned round. Sup- pose the two planes of reflection to be parallel to each other, in that case the ray of light is reflected from the second glass in the same manner as from the first glass. Let the second glass be now turn- ed round a quadrant of a circle, so as to make the planes of re- flection perpendicular to each other. Now the whole of the ray will pass through the second glass, and none of it will be reflected. Turn the second glass round another quadrant of a circle, so as to make the reflecting planes again parallel, the ray will now be re- flected by the second glass as at first. When the second glass is turned round three quadrants, the whole light will be again trans- mitted, and none of it reflected. Thus, when the reflecting planes are parallel, the light is reflected ; but when they are perpendicu- lar the light is transmitted. We see that the light can penetrate 30 IMPONDERABLE BODIES. c BOOK I. £ DIVISION 1. through the glass when in one position; but not when in another. Malus, who first observed this curious fact, accounted for it by supposing that the light had bent into another position, just as a needle does when acted upon by a magnet. He therefore called this property of light its polarization. Since his death, the pheno- mena of the polarization of light have been examined with much assiduity, and many new facts discovered by M. M. Biot and Arago, and by Dr. Brewster. 7. When a ray of light is made to pass through a triangular prism, and received upon a sheet of white paper, the image, or spectrum as it is called, instead of being circular, is oblong, and terminated by semicircular arches. In this case the refraction of light is increased considerably by the figure of the prism. Conse- quently if light consists of a congeries of rays differing in refrangi- bility, they will be separated from each other: the least refrangi- ble occupying the luminous circle which the ray would have form- ed had it not been for the prismatic form of the glass; the others going to a greater or smaller distance from this circle, according to their refrangibility. The oblong figure of the spectrum is a proof that light consists of rays differently refrangible: and as the spec- trum exhibits seven colours, these rays have been reduced under se- ven classes. The colours are in the following order; Red, Orange, Yellow, Green, Blue, Indigo, Violet. The red is the least refrangible, the violet the most; the others are refrangible in the order in which they have been named. 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; orange, 27; yellow, 48; green, 60; blue, 60; indigo, 40; violet, 80. But they have been since observed to differ somewhat in their relative lengths in the spectrum, according to the refracting medium. 8. These coloured rays differ from each other in reflexibility and inflexibility, precisely as they do in refrangibility: the red rays being least reflexible and inflexible, the violet most, and the rest according to their order in the prismatic spectrum. 9. Every one of these coloured rays is permanent; not being affected nor altered by any number of refractions or reflections. The properties of light now enumerated constitute the object of the science called Optics. They prove, in the most decisive man- ner, that light is attracted by other bodies; and not only attracted, but attracted unequally. For combustible bodies, provided all other things be equal, refract light more powerfully than other bo- dies, and consequently attract light more powerfully. But it is variation, in point of strength, which consitutes the characteristic mark of chemical affinity. Hence it follows that the attraction which subsists between light and other bodies does not differ from chemical affinity. The importance of this remark will be seen hereafter. 10. The rays of light differ in their power of illuminating objects: Chap. L] LIGHT. 31 For if an equal portion of each of these rays, one after another, be made to illuminate a minute object, a printed page for instance, it will not be seen distinctly at the same distance when illuminated by each. We must stand nearest the object when it is illuminated by the violet: we see distinctly 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 enlightened by the orange ray, and still nearer when by the red. Thus it appears that the rays towards the middle of the spectrum possess the greatest illumina- ting power, and those at the extremity the least; and that the illu- minating power of the rays gradually diminishes from the middle of the spectrum towards its extremities. For these facts we are indebted to the experiments of Dr. Herschel.* 11. Light is capable of entering into bodies and remaining in them, and of being afterwards extricated without any alteration. Father Beccaria, and several other philosophers, have shown us, by their experiments, that there are a great many substances which become luminous after being exposed to the light.f This property was discovered by carrying them instantly from the light into a dark place, or by darkening the chamber in which they are expo- sed. Most of these substances, indeed, lose their property in a very short time, but they recover it again on being exposed to the light; and this may be repeated as often as we please. We are indebted to Mr. Canton for some very interesting experiments on this subject, and for discovering a composition which possesses this property in a remarkable degree.^: He calcined some common oyster shells in a good coal fire for half an hour, and then pounded and sifted the purest part of them. Three parts of this powder were mixed with one part of the flowers of sulphur, and rammed into a crucible which was kept red hot for an hour. The brightest parts of the mixture were then scraped off, and kept for use in a dry phial well stopped.^ When this composition is exposed for a few seconds to the light, it becomes sufficiently luminous to enable a person to distinguish the hour on a watch by it. After some time it ceases to shine, but recovers this property on being again expo- sed to the light. Light then is not only acted upon by other bodies, but it is capable of uniting with them, and afterwards leaving them without any change. It is well known that light is emitted during combustion; and it has been objected to this conclusion, that these bodies are luminous only from a slow and imperceptible combustion. But surely com- * Phil. Trans. 1800, p. 255. f Ibid- lxL 212- * Ibid-lvi"' 337- § Dr. Higgins has added considerable improvements to the method of preparing Canton's pyrophorus. He stratifies the oyster shells and sulphur in a crucible without pounding them; and after exposing theih to the proper heat, they are put into phials furnished with ground stoppers. 32 IMPONDERABLE BODIES. fnmsYoxI bustion cannot be suspected in many of Father Beccaria's experi- ments, when we reflect that one of the bodies on which they were made was his own hand, and that many of the others were altoge- ther incombustible; and the phenomena observed by Canton are also incompatible with the notion of combustion. His pyrophorus shone only in consequence of being exposed to light, and lost that property by being kept in the dark. It is not exposure to light which causes substances capable of combustion at the temperature of the atmosphere to become luminous, but exposure to air. If the same temperature continues, they do not cease to shine till they are consumed; and if they cease, it is not the application of light, but of caloric, which renders them again luminous: but Canton's py- rophorus, on the contrary, when it had lost its property of shining, did not recover it by the application of heat, except it was accom- panied by light. The only effect which heat had was to increase the separation of light from the pyrophorus, and of course to shorten the duration of its luminousness. Two glass globes hermetically sealed, containing each some of this pyrophorus, were exposed to the light and carried into a dark room. One of them, on being im- mersed in a basin of boiling water, became much brighter than the other, but in ten minutes it ceased to give out light: the other re- mained visible for more than two hours. After having been kept in the dark for two days, they were both plunged into a basin of hot water: the pyrophorus which had been in the water formerly did not shine, but the other became luminous, and continued to give out light for a considerable time. Neither of them afterwards shone by the application of hot water; but when brought near to an iron heated so as scarcely to be visible in the dark, they suddenly gave out their remaining light, and never shone more by the same treat- ment : but when exposed a second time to the light, they exhibited over again precisely the same phenomena; even a lighted candle and electricity communicated some light to them. Surely these facts are altogether incompatible with combustion, and fully suffi- cient to convince us that light alone was the agent, and that it had actually entered into the luminous bodies. It has been questioned, indeed, whether the light emitted by pyrophori be the same with that to which they are exposed. Mr. Wilson has proved, that in many cases at least it is different; and in particular that on many pyrophori the blue rays have a greater effect than any other, and that they cause an extrication of red light. Mr. de Grosser has shown the same thing with regard to the dia- mond, which is a natural pyrophorus.* Still, however, it cannot be questioned that the luminousness of these bodies is owing to exposure to light, and that the phenomenon is not connected with combustion. 12. But light does not only enter into bodies, it also combines * Jour, de Phvs. xx. 270. Chap. I.] LIGHT. 3o. with them, and constitutes one of their component parts. That this is the case, has been rendered very evident by a set of experi- ments made long ago by Mr. Canton,* and repeated and carried a great deal farther by Dr. Hulme.f It has been long known that different kinds of meat and fish, just when they are beginning to putrify, become luminous in the dark, and of course give out light. This is the case in particular with the whiting, the herring, and the mackerel. When four drachms of either of these are put into a phial containing two ounces of sea water, or of pure water holding in solu- tion | a drachm of common salt, or two drachms of sulphate of mag- nesia, if the phial be put into a dark place, a luminous ring appears on the surface of the liquid within three days, and the whole liquid, when agitated, becomes luminous, and continues in that state for some time. When these liquids are frozen, the light disappears, but is again emitted as soon as they are thawed. A moderate heat in- creases the luminousness, but a boiling heat extinguishes it altoge- ther. The light is extinguished also bv water, lime water, water impregnated with carbonic acid gas, or sulphureted hydrogen gas, fermented liquors, spirituous liquors, acids, alkalies, and water sa- turated with a variety of salts, as sal-ammoniac, common salt, sul- phate of magnesia: but the light appears again when these solu- tions are diluted with water. This light produces no sensible effect on the thermometer.:): After these experiments, it can scarcely be denied that light constitutes a component part of these sub- stances, and that it is the first of the constituent parts which makes its escape when the substance containing it is beginning to be de- composed. 13. Almost all bodies have the property of absorbing light, though they do not all emit it again like the pyrophori and animal bodies. But they by no means absorb all the rays indiscriminately : some absorb one coloured ray, others another, while they reflect the rest. This is the cause of the different colours of bodies. A red body, for instance, reflects the red rays, while it absorbs the rest; a green reflects the green rays, and perhaps also the blue and the yel- low, and absorbs the rest. A white body reflects all the rays, and absorbs none ; while a black body, on the contrary, absorbs all the rays, and reflects none. The different colours of bodies, then, de- pend upon the affinity of each for particular rays, and its want of affinity for the others. 14. The absorption of light by bodies produces very sensible changes in them. Plants, for instance, may be made to vegetate tolerably well in the dark; but in that case their colour is always white, they have scarcely any taste, and contain but a very small proportion of combustible matter. In a very short time, however, * Phil. Trans, lix. 446. t Ibid- 180°- P- 16L * The same experiments succeed with Canton's pyrophorus, as Dr. Hulme has shown, Vol. L E 34 IMPONDERABLE BODIES. y BOOK 1 £ DlVlSiOV 1 after their exposure to light, their colour becomes green,* their taste is rendered much more intense, and the quantity of combusti- ble matter is considerably increased. These changes are very ob- vious, and they depend incontestibly upon the agency of light. Ano- ther very remarkable instance of the agency of light is the reduc- tion of the metallic oxides. The red oxide of mercury and of lead become much lighter when exposed to the sun; and the white salts of silver, in the same situation, soon become black, and the oxide is reduced.f The oxide of gold may be reduced in the same man- ner. Light, then, has the property of separating oxygen from se- veral of the oxides. Scheele, who'first attended accurately to these facts, observed also, that the violet ray reduced the oxide of silver sooner than any of the other rays ;\ and Sennebier has ascertained, that the same ray has the greatest effect in producing the green co- lour of plants.§ Berthollet observed, that during the reduction of the oxides, a quantity of oxygen gas makes its escape.|| It was supposed till lately, that those reductions of metallic oxides were produced by the colorific rays of light; but Messrs. Wollaston, Ritter, and Bockmann, have ascertained, that chloride of silver is blackened most rapidly when it is placed beyond the violet ray, and entirely out of the prismatic spectrum. These observations have been confirmed by M. Berard. He found that the chemical intensity was greatest at the violet end of the spectrum, and that it extended a little beyond that extremity. When he left substances exposed for a certain time to the action of each ray, he observed sensible effects, though with an intensity con- tinually decreasing in the indigo and blue rays. Hence it is very probable that if he had been in possession of more sensible re- actives^} he would have observed analogous effects, but still more feeble, in the other rays. He concentrated, by means of a lens, all that part of the spectrum which extends from the green to the ex- treme violet; and likewise, by means of another lens, all that por- tion which extends from the green to the extremity of the red. The last pencil formed a white point so brilliant that the eye was scarcely able to endure it; yet the chloride of silver remained ex- * [Hence the process of etiolation, or blanching, used by gardeners; as when they tie up their lettuces, or earth up their celery, to whiten the internal part. It has lately been foi;nd at Paris, that the edible mushroom grows more luxuriantly in situations not much exposed to light —C] f [In the medico-chirurgical transactions for 1816, p. 284—290, are some cases,furnished by Dr. Albers of Bremen, and Dr. Roget of London, of persons whose skin acquired a per- manent blue tinge from persisting in a long course of pills formed of crumb of bread and lunar caustic, which is the fused uitrat of silver. The colour in one case was deepened by exposure to light.—C.] # On Fire, p. 78 and 98. § Mem. Phisico-chim. ii. 72. H Jour, de Phys. xxix. 81. When muriate of silver is exposed to the solar light, it blackens almost instantaneously. In that case it is not oxygen gas which is emitted but muriatic acid, as has been observed also by Berthollet. See Jour, de Phys. lvi. 80. ^ He employed chloride of silver, which becomes black; guaiac, which passes from yel- low to green, as Dr. Wollaston first observed; and a mixture of chlorine and hydrogen which detonate when exposed to light, as Dalton and Gay-Lussac and Thenard ascertained! Chap. I.] LIGHT. 35 posed to it two hours without undergoing any sensible alteration. But when exposed to the first pencil, which was much less bright and less hot, it was blackened in less than six minutes.* 15. M. Morichini, Professor of Chemistry at Rome, announced, in 1813, that when steel needles are exposed to the action of the violet ray of light they become magnetic.f But when these experi- ments were carefully repeated by Professor Configliachi of Pavia,:£ and by M. Berard of Montpellier,§ they did not succeed. Hence we may conclude that Morichini deceived himself by using needles already possessed of magnetic properties. 16. Such are the properties of light as far as they have been ex- amined. They are sufficient to induce us to believe that it is a body, and that it possesses many qualities in common with other bodies. It is attracted by them, and combines with them precisely as other bodies do. But it is distinguished from all the substances hitherto described, by possessing three peculiar properties, of which they are destitute. The first of these properties is the power which it has of exciting in us the sensation of vision, by moving from the object seen, and entering the eye. The phenomena of colours, and the prismatic spectrum, indicate the existence of seven different species of light; but to what the difference of these species is owing, has not been ascertained. We are altogether ignorant of the component parts of every one of these species. The second peculiar property of light is the prodigious velocity with which it moves whenever it is separated from any body with which it was formerly combined. This velocity, which is but little less than 200,000 miles in a second,|| it acquires in a moment; and it seems to acquire it too in all cases, whatever the body be from which it separates. The third, and not the least singular of its peculiar properties, is, that its particles are never found cohering together, so as to form masses of any sensible magnitude. This difference between light and other bodies can only be accounted for by supposing that its particles repel each other. This seems to constitute the grand dis- tinction between light and the bodies hitherto described. Its par- ticles repel each other,^} while the particles of the other bodies at- * Annals of Philosophy, ii. 165. f Gilbert's Annalen der Physick, xlvi. 367. t Ibid. p. 337. § Annals of Pilosophy, iv. 228. H [See p. 27, note of the editor.—C] \ [It is very possible that the particles of light repel each other. The following sugges- tions, however, bear upon this point. 1. The phenomena of mirrors and of lenses, where light, as well as caloric, is so highly concentrated. The attractions of the substances where- ot these instruments are formed, are manifestly stronger, than the repulsive spheres that surround the particles of heat and caloric: analogous to this is the electricity accumulated round a main conductor. The repulsive force then, cannot be very strong. 2. By the con« elusions drawn by Roemer from the immersion of Jupiter's satellites, and by Bradley from the parallax of the fixed stars, the velocity of light is about '200,000 miles per second of time. When this is compared with M. D'Arcet's experiments on the continuous sensation pro- duced by a ray of light, it will appear, that there may be continuous vision, though the parti- cles of light be 20,000 miles from each other; a distance which renders repulsion between 36 IMPONDERABLE BODIES. C BOOK I £ DIVISION 1. tract each other; and accordingly are found cohering together in masses of more or less magnitude. 17. It now only remains to consider the different methods by which light may be procured ; or, to speak more precisely, the different sources from which light is emitted in a visible form. These sources are four: 1. The sun and stars; 2. Combustion; 3. Heat; and 4. Percussion. The light emitted by the sun is familiarly known by the names of sunshine and light of day. The light of the stars, as has been ascertained, possesses precisely the same properties. With respect to the cause why the sun and stars are constantly emitting light, the question will probably for ever baffle the human understanding; at any rate, it is not considered as connected with the science ol chemistry. 18. Light is emitted in every case of combustion. Now combus- tion, as far at least as regards simple combustibles and metals, is the act of combination of the combustible with a supporter. Con- sequently the light which is emitted during combustion must have existed previously combined either with the combustible or with the supporter. But this subject will be resumed in the next chap- ter, where the nature of combustion will be particularly considered. 19. If heat be applied to bodies, and continually increased, there is a certain temperature at which, when they arrive, they become luminous. No fact is more familiar than this; so well known in- deed is it, that little attention has been paid to it. When a body becomes luminous by being heated in a fire, it is said in common language to be red hot. As far as experiments have been made upon this subject, it appears that all bodies which are capable of enduring the requisite degree of heat without decomposition or volatilization begin to emit light at precisely the same temperature. The first person who examined this subject with attention was Sir Isaac Newton. He ascertained, by a very ingenious set of experi- ments, first published in 1701, that iron is just visible in the dark when heated to 635°;* that it shines strongly in the dark when raised to the temperature of 752°; that it is luminous in the twilight just after sunset when heated to 884°; and that when it shines, even in broad day-light, its temperature is above 1000°. From the ex- periments of Muschenbroeck and others, it appears, that what in common language is called a red heat, commences about the tem- perature of 800°. the luminous particles inadequate to account for this effect. The impression on the optic nerve remains, according to D'A reel's experiment, from 4 g0 to 4A0th part of a minute. He made a luminous point (a hot coal) revolve with that velocity which was barely sufficient to keep up a continuous circular image; which he found could not be done unless it revolved in 8 or 9 thirds of a minute. Priestley's History of Light and Colours, 634. Indeed all bodies repel each other, for as heat expandsandcold contracts all bodies their particles are not in contact really, though seemingly to us, they are so.—C.] * Dr. Irvine has shown that this point is rather too low. For mercury, which he found to boil at 672°, does not become the least luminous at that temperature. Irvine's Essays, p. 32. Chap. I.] light. 37 A red hot body continues to shine for some time after it has been taken from the fire and put into a dark place. The constant acces- sion, then, either of light or heat, is not necessary for the shining of bodies: but if a red hot body be blown upon by a strong cur- rent of air, it immediately ceases to shine.* Consequently the moment the temperature of a body is diminished by a certain num- ber of degrees, it ceases to be luminous. Whenever a body reaches the proper temperature, it becomes luminous, independent of any contact of air; for a piece of iron wire becomes red hot while immersed in melted lead.fi; To this general law there is one remarkable exception. It does not appear that the gases become luminous even at a much higher temperature. The following ingenious experiment of Mr. T. Wedgewood seems to set the truth of this exception in a very clear point of view. He took an earthen ware tube, bent so in the mid- dle that it could be sunk, and make several turns in a large cruci- ble, which was filled with sand. To one end of this tube was fixed a pair of bellows; at the other end was a globular vessel, in which was a passage, furnished with a valve to allow air to pass out, but none to enter. There was another opening in this globular vessel filled with glass, that one might see what was going on within. The crucible was put into a fire; and after the sand had become red hot, air was blown through the earthen tube by means of the bellows. This air, after passing through the red hot sand, came into the globular vessel. It did not shine; but when a piece of gold wire was hung at that part of the vessel where the earthen ware tube entered, it became faintly luminous: a proof that though the air was not luminous, it had been hot enough to raise other bo- dies to the shining temperature. 20. The last of the sources of light is percussion. It is well known, that when flint and steel are smartly struck against each other, a spark always makes its appearance, which is capable of set- ting fire to tinder or to gunpowder. The spark in this case, as was long ago ascertained by Dr. Hooke, is a small particle of the iron, which is driven off, and catches fire during its passage through the air. This, therefore, and all similar cases, belong to the class of combustion. But light often makes its appearance when two bo- dies are struck against each other, when we are certain that no such thing as combustion can happen, because both the bodies are in- combustible. Thus, for instance, sparks are emitted, when two quartz stones are struck smartly against each other, and light is emitted when they are rubbed against each other. The experiment succeeds equally well under water. Many other hard stones also emit sparks in the same circumstances. * T. Wedgewood, Phil. Trans. 1792. t Id-Ibid- % [All species of fuel used, is vegetable matter: during the combustion, light previously combined with the vegetable during its living state, is set free: may not the light thus set free from the fuel, be absorbed by the heated metal, and occasion its luminous appear- ance?—C.] 38 IMPONDERABLE BODIES. {Bms?raL If they be often made to emit sparks above a sheet of white pa- per, there are found upon it a number of small black bodies, not very unlike the eggs of flies. These bodies are hard but friable, and when rubbed on the paper leave a black stain. When viewed with a microscope, they seem to have been melted. Muriatic acid changes their colour to a green, as it does that of lavas.* These substances evidently produced the sparks by being heated red hot. Lamanon supposes that they are particles of quartz combined with oxygen. Were that the case, the phenomenon would be precisely similar to that which is produced by the collision of flint and steel. That they are particles of quartz cannot be doubted; but to sup- pose them combined with oxygen is contrary to all experience; for these stones never show any disposition to combine with oxygenf even when exposed to the most violent heat. La Metherie made experiments on purpose to see whether Lamanon's opinion was well founded; but they all turned out unfavourable to it. And Monge ascertained, that the particles described by Lamanon were pure crystal unaltered, with a quantity of black powder adhe- ring to them. He concludes, accordingly, that these fragments had been raised to so high a temperature during their passage through the air, that they set fire to all the minute bodies that came in their way4 The emission of the light is accompanied by a very pecu- liar smell, having some analogy to that of burning sulphur, or more nearly to burning gunpowder. CHAPTER II. OF HEAT. Nothing is more familiar to us than heat; to attempt therefore to define it is unnecessary. When we say that a person feels heat, that a stone is hot, the expressions are understood without difficul- ty ; yet in each of these propositions, the word he at has a distinct meaning. In the one, it signifies the sensation of heat; in the other, the cause of that sensation. This ambiguity, though of little consequence in common life, may lead in philosophical discussions to confusion and perplexity. It was to prevent this that the word caloric has been chosen to signify the cause of heat. When I put my hand on a hot stone, I experience a certain sensation, which I call the sensation of heat; the cause of this sensation is caloric. * Lamanon, Jour, de Phys. 1785. -j- [This seems contradictory to the fact stated in page 254 post, where silica (or quartz) is stated to consist of 100 parts silicon as a base, and 102, 245 oxygen.—C] ± Ann. de Chim. xvi 206. Chap. II.] HEAT. 39 As the phenomena in which caloric is concerned are the mostf intricate and interesting in chemistry; as the study of them has contributed in a very particular manner to the advancement ot the science: as they involve some of those parts of it which are still exceedingly obscure, and which have given occasion to the most important disputes in which chemists have been engaged-4hcy na- turally lay claim to a very particular attention. I shall divide this chapter into six sections: the first will be occupied with the nature of caloric; in the second, I shall consider its propagati on through bodies; in the third, its distribution; in the fourth, the effects which it produces on bodies; in the fifth, the quantity of it which exists in bodies; and in the sixth, the different sources from which it is obtained. SECTION I. NATURE OF CALORIC. Concerning the nature of caloric, there are two opinions which have divided philosophers ever since they turned their attention to the subiect. Some suppose that caloric, like gravity, is merely a property of matter, and that it consists, some how or other, in a peculiar vibration of its particles; others, on the contrary, think that it is a distinct substance. Each of these opinions has been supported by the greatest philosophers; and till lately the obscu- rity of the subject has been such, that both sides have been able to produce exceedingly plausible and forcible arguments. The recent improvements, however, in this branch of chemistry, have gradu- ally rendered the latter opinion more probable than the former: and a discovery, made by Dr. Herschel, has at last nearly put an end to the dispute, by demonstrating, that we have the same reason tor considering heat to be a substance, as we have for believing light to be material. 1 Dr. Herschel had been employed in making observations on the sun by means of telescopes. To prevent the inconvenience arising from the heat, he used coloured glasses; but these glasses, when they were deep enough coloured to intercept the light,very soon cracked and broke in pieces. This circumstance induced him to examine the heating power of the different coloured rays. He made each of them in its turn fall upon the bulb of a thermometer, near which two other thermometers were placed to serve as a standard. The number of degrees, which the thermometer expo- sed to the coloured ray rose above the other two thermometers, in- dicated the heating power of that ray. He found that the most 40 IMPONDERABLE BODIES. J nmaira i'" refrangible rays have the least heating power; and that the heating power gradually increases as the refrangibility diminishes. The violet ray therefore has the smallest heating power, and the red ray the greatest. Dr. Herschel found that the heating power of the violet, green, and red rays, are to each other as the following numbers: Violet =16; Green = 22*4; Red = 55. It struck Dr. Herchel as remarkable, that the illuminating power . and the heating power of the rays follow such different laws. The first exists in greatest perfection in the middle of the spectrum, and diminishes as we approach either extremity; but the second in- creases constantly from the violet end, and is greatest at the red end. This led him to suspect that perhaps the heating power does not stop at the end of the visible spectrum, but is continued beyond it. He placed the thermometer completely beyond the boundary of the red ray, but still in the line of the spectrum; and it rose still higher-than it had done when exposed to the red ray. On shifting the thermometer still farther, it continued to rise; and the rise did not reach its maximum till the thermometer was half an inch be- yond the utmost extremity of the red ray. When shifted still farther, it sunk a little; but the power of heating was 'sensible at the distance of 1 h inch from the red ray.* These important experiments were repeated and confirmed by Sir Henry Englefield,f in the year 1802. The apparatus was very different from that of. Dr. Herschel, and contrived on purpose to obviate certain objections which had been made to the conclusion drawn by him. The bulbs of the thermometers used were mostly blackened. The following Table exhibits the result obtained in one of these experiments. Thermemeter in the blue ray rose in 3' from 55° to 56° green . 3 . 54 . 58 yellow . 3 . 56 . 62 full red . 2$ . 56 . 72 confines of red 2$ . 58 . 73 £ beyond the visible light 22 . 61 . 79 The thermometer, with its bulb blackened, rose much more when placed in the same circumstances, than the thermometer whose bulb was either naked or whitened with paint. This will be appa- rent from the following table: * Phil. Trans. 1800, p. 437. t Journal of the Royal Institution, i. 202. Chap. II.] HEAT. 41 Time. From To Red ray Black therm. White therm. 3' 58° 55 61° 58 Dark Black therm. White therm. 3 59 58 64 58J Confines of red Black therm. White therm. 3 59 57h 71 60* Both Dr. Herschel and Sir Henry Englefield take notice of a faint blush of red, of a semioval form, visible when the rays beyond the red end of the spectrum were collected by a lense. In the year 1807, Professor Wiinsch, at Frankfort on the Oder, published a set of experiments upon the same subject,* which turned out somewhat different from those of Dr. Herschel. He found that the thermometer was not affected when placed either above or below the spectrum. But the rise of temperature was not proportional to the light given by the ray. The blue ray he found gave the most light; but produced the least heat of any of the rays, the violet excepted. When the prism was filled with alcohol, oil of turpentine, or water, the yellow ray raised the thermometer highest; when a prism of green glass was used, the red ray pro- duced most heat: and finally, when a yellow glass prism was used, the colourless tail at the border of the red ray produced the most heat. Professor Wiinsch is one of those philosophers who believe that the solar light is only divisible into three coloured rays, and the principal object of his elaborate paper seems to be to show that the heating power of the rays confirm his peculiar hypothesis. It was examined at great length by Ritter, whose opinions were dif- ferent.! But it is unnecessary to discuss that point here, because, the experiments of Wiinsch, though they do not exactly coincide with those of Herschel, are not however inconsistent with them. The experiments of Herschel were again repeated and confirmed by M. Berard in 1813. He was possessed of'an excellent apparatus for the purpose, and his observations appear to have been made with sufficient care. He found, as Herschel had done, that the heating power of the rays decreases from the red to the violet end of the spectrum. It is greatest at the extremity of the red ray while the thermometer is still plunged in the spectrum. When he placed the thermometer quite beyond the visible spectrum in the spot where Herschel fixed the maximum of heat, its elevation above * Versuche nber die •vermeinte Sonderung des Lichts der Sonnenstrahlen von der Wdrme dersetben, published in the Der Gesellschaft natnr forschender freundf zu Berlin Magazinfur die neuesten entdeckungen in dergcsammten naturkunde. Vol. i. p. 207. ■j- Gehlen's Journal fur die Chemie, Physik und Mineralogie, vi. 033. Vol. I. F 42 IMPONDERABLE BODIES. £ mourns L that of the ambient air was only |th of what it had been in the red ray itself.* These experiments are sufficient to convince us that the calorific and colorific power of the rays of light follow quite different laws. Whether two different species of rays exist in the solar spectrum as some have supposed, namely, rays of light, and rays of heat; or whether certain unknown changes in the velocity or in some other quality of light give it the power of producing heat, are questions which the limited state of our knowledge does not enable us to de- termine. Some late experiments of Delaroche seem rather favour- able to the latter opinion. He found that the higher the tempera- ture of a hot body was raised, the greater was the quantity of rays of heat which became capable of penetrating through a plate of glass.f 2. The rays of caloric are refracted by transparent bodies just as the rays of light. We see, too, that, like the rays of light, they differ in their refrangibility; that some of them are as refrangible as the violet rays, but that the greater number of them are less re- frangible than the red rays. 3. The rays of caloric are reflected by polished surfaces in the same manner as the rays of light. This was shown long ago by Scheele, who even ascertained that the angle of their reflection is equal to the angle of their incidence. Mr. Pictet also had made a set of very ingenious experiments on this subject, about the year 1790, which led to the same conclusion.^: He placed two concave mirrors of tin, of nine inches focus, at the distance of 12 feet 2 in- ches from one another. In the focus of one of them he placed a ball of iron two inches in diameter, heated so as not to be visible in the dark; in the other was. placed the bulb of a thermometer. In six minutes the thermometer rose 22°. A lighted candle, which was substituted for the ball of iron, produced nearly the same effect. In this case both light and heat appeared to act. In order to sepa- rate them, he interposed between the two mirrors a plate of clear glass. The thermometer sunk in nine minutes 14°: and when the glass was again removed, it rose in seven minutes about 12°; yet the light which fell on the thermometer did not seem at all dimi- nished by the glass. 'Mr. Pictet therefore concluded, that the ca- loric had been reflected by the mirror, and that it had been the cause of the rise of the thermometer. In another experiment, a glass matrass was substituted for the iron ball, nearly of the same diameter with it, and containing 2044 grains of boiling water. Two minutes after a thick screen of silk, which had been interposed be- tween the two mirrors, was removed, the thermometer rose from 47° to 501°, and descended again the moment the matrass was re- moved from the focus. * Annals of Philosophy, ii. 163. -j- Ibid. ii. 100. t A similar set of experiments had been made by Mr. King as early as 1785 : See his Morsels of Criticism, vol. i. Chap. II.] heat. 43 The mirrors of tin were now placed at the distance of 90 inches from each other; the matrass with the boiling water in one of the foci, and a very sensible air thermometer in the other, every degree of which was equal to about -jLth of a degree of Fahrenheit. Ex- actly in the middle space between the two mirrors there was placed a very thin common glass mirror, suspended in such a manner that either side could be turned towards the matrass. When the polish- ed side of this mirror was turned to the matrass, the thermometer rose only 0.5°; but when the side covered with tinfoil, and which had been blackened with ink and smoke, was turned towards the matrass, the thermometer rose 3.50°. In another experiment, when • the polished side of the mirror was turned to the matrass, the ther- mometer rose 3°, when the other side, 9.2°. On rubbing off the tinfoil, and repeating the experiment, the thermometer rose 18°. On substituting for the glass mirror a piece of thin white paste- board of the same dimensions with it, the thermometer rose 10°.* 4. Berard has shown by a set of well contrived experiments that the rays of heat are capable of polarization equally with the rays of light.f 5. As heat radiates from luminous bodies like light, and without any sensible diminution of their weight, it is reasonable to con- clude that its particles must be equally minute. Therefore neither the addition of caloric nor its abstraction can sensibly affect the weight of bodies. As this follows necessarily as a consequence from Dr. Herschel's experiments, were it possible to prove by ex- periment that caloric affects the weight of bodies, the theory found- ed on Dr. Herschel's discoveries would be overturned: but such deductions have been drawn from the experiments of De Luc,! Fordyce,§ Morveau,|j and Chausier.^y According to these philoso- phers, bodies become absolutely lighter by being heated. The ex- periment of Fordyce, which seems to have been made with the greatest care, was conducted in the following manner: He took a glass globe three inches in diameter, with a short neck, and weighing 451 grains; poured into it about 1700 grains of water from the New River, London, and then sealed it hermeti- cally. The whole weighed 2150^ grains at the temperature of 32 degrees. It was put for 20 minutes into a freezing mixture of snow and salt till some of it was frozen; it was then, after being wiped first with a dry linen cloth, next with clean washed dry leather, im- mediately weighed, and found to be J-th of a grain heavier than before. This was repeated exactly in the same manner five differ- ent times. At each, more of the water was frozen, and more weight gained. When the whole water was frozen, it was T3Tths of a grain heavier than it had been when fluid. A thermometer applied to the globe stood at 10°. When allowed to remain till the thermo- * Pictet, sur le Feu, chap. iii. t Annals of Philosophy, ii. 164. j: Sur les Modif. de PAtmosph. 4 Phil. Trans. 1785, p. 361. || Jour, de Phys. 1785, Oct. 7 Jour, de Scavans, 1785, p. 493. 44 IMPONDERABLE BODIE9. 5 BOOK I. £ DIVISION 1. meter rose to 32°, it weighed TVhs °f a gram more than it did at the same temperature when fluid. It will be seen afterwards that ice contains less heat than water of the same temperature with it." The balance used was nice enough to mark T-6^Tth part of a grain. This subject had attracted the attention of Lavoisier, and his ex- periments, which were published in the Memoirs of the French Academy for 1783, led him to conclude that the weight of bodies is not altered by heating or cooling them, and consequently that caloric produces no sensible change on the weight of bodies. Count Rumford's experiments on the same subject, which were made * about the year 1797, are equally decisive. He repeated the experi- ment of Dr. Fordyce with the most scrupulous caution; and de- monstrated that neither the addition nor the abstraction of heat makes any sensible alteration in the weight of bodies.* 6. Caloric agrees with light in another property no less peculiar. Its particles are never found cohering together in masses; and whenever they are forcibly accumulated, they fly off in all direc- tions, and separate from each other with inconceivable rapidity.! This property necessarily supposes the existence of a mutual replil- sion between the particles of caloric. Thus it appears that caloric and light resemble each other in a great number of properties. Both are emitted from the sun in rays with a very great velocity; both of them are refracted by transpa- rent bodies, and reflected by polished surfaces; both of them con- sist of particles which mutually repel each other, and which pro- duce no sensible effect upon the weight of other bodies. They differ, however, in this particular: light produces in us the sensa- tion of vision; caloric, on the contrary, the sensation of heat. Whether this difference be sufficient to constitute light and heat two specifically distinct bodies; or whether they be merely modi- fications of one and the same body are questions which the present state of our knowledge does not enable us fully to answer. SECTION II. OF THE MOTION OF HEAT. From the preceding account of the nature of caloric, we learn that it is capable, like light, of radiating in all directions from the surfaces of bodies; and that when thus radiated, it moves with a very considerable velocity. Like light, too, it is liable to be ab- sorbed when it impinges against the surfaces of bodies. When it • Phil. Trans. 1799, p. 179. + [The heat produced in the focus of a burning mirror, or a burning lens, seems to furnish t difficulty in this case.—C.] Chap. II.] heat. 45 has thus entered, it is capable of making its way through all bodies; but its motion in this case is comparatively slow. In that case it is icod to be conducted through bodies. Heat then moves at two very c ~. r<-nt rates. 1. By radiation. 2. By conduction. It will be f.■■, opcr to consider each of these separately. 1. Radiation of Heat. When bodies artificially heated are exposed to the open air, they immediately begin to emit heat, and continue to do so till they be- come nearly of the temperature of the surrounding atmosphere. That different substances when placed in this situation cool down with very different degrees of rapidity, could not have escaptd the most careless observer; but the influence of the surface of the hot body in accelerating or retarding the cooling process, was not sus- pected till lately. For this curious and important part of the doc- trine of heat, we are indebted to the sagacity of Mr. Leslie, who has already brought it to a great degree of perfection. His Inqui- ry into the Nature of Heat, published in 1804, contains a great number * of original experiments and views on this subject. It is remark- able, that a few weeks after the publication of this work, a disserta- tion by Courtt Rumford on the same subject, and containing similar experiments, appeared in the Philosophical Transactions. In the year 1813, a paper on the subject containing some important addi- tions to the experiments of Mr. Leslie was published by M. Dela- roche of Geneva.* ^ 1. Mr. Lesijp filted with hot water a thin globe of bright tin, four inches in, diameter, having a narrow neck, and placed it on a slender.frame in a warm room without a fire. The thermometer inserted in this globe sunk half way from the original temperature of the water to that of the room in 156 minutes. The same expe- riment was repeated, but the outside of the globe was now covered with a thin coat of lamp black. The time elapsed in cooling to the same temperature as in the last case was now only 81 minutes.! Here the rate of cooling was nearly doubled; yet the only differ- ence was the thin covering of lamp black. Nothing can afford a more striking proof than this of the effect of the surface of the hot body on the rate of its cooling. Count Rumford took two thin cylindrical brass vessels of the same size and shape, filled them both with hot water of the same temperature, and clothed the one with a covering of Irish linen, but left the other naked. The naked vessel cooled ten degrees in 55 minutes, but the one covered with linen cooled ten degrees in 36$ minutes.! In this experiment, the linen produced a similar * Annals of Philosophy, ii. 100. f Leslie's Inquiry into the Nature of Heat, p. 268. % Nicholson's Jour. is. 60. 46 IMPONDERABLE BODIES. S n0°K }' {_ DIVISION 1. effect with the lamp black in the preceding. Instead of retarding the escape of heat, as might have been expected, they produced the contrary effect. The same acceleration took place when the cy- linder was coated with a thin covering of glue, of black or white paint, or when it was smoked with a candle. 2. The variation in the rate of cooling occasioned by coating the hot vessel with different substances is greatest when the air of the room in which the experiments are made is perfectly still. The difference diminishes when the atmosphere is agitated, and in very strong winds it disappears almost entirely. Thus two globes of tin, one bright, the other covered with lamp black, being filled with hot water, and exposed to winds of various degrees of violence, were found by Mr. Leslie to lose half their heat in the following times :* Cleaned Globe. Blackened Globe. In a gentle gale......44' 35' In a pretty strong breeze . 23' 20$' In a vehement wind .... 9*5' 9' This is sufficient to convince us, that the effect of the lamp black in accelerating cooling cannot be owing to any power which it has of conducting heat, and communicating it to the air, but to the pro- perty which it has of radiating heat (to use the common expression) fr in a greater degree than clear metallic bodies. That this is in. reality the case is easily shown. 3. When a canister of tin, of a cubic shape and considerable size, is placed at the distance of a foot or two from a concave mirror of bright polished tin, having a delicate thermometer in the focus, the thermometer experiences a certain elevation. If the canister be coated with lamp black, the thermometer rises much higher than when the metal is left bright. Here we perceive that more heat radiates from the lamp black than the clear metal; since the eleva- tion of the thermometer is in some degree the measure of the ra- diation. A common thermometer does not answer well in similar experiments, because it is affected by every change of temperature in the room in which the experiments are made. But Mr. Leslie has invented another, to which we are indebted for all the preci- sion that has been introduced into the subject. He has distinguish- ed it by the name of the differential thermometer. It was employ- ed also by Count Rumford in his researches. This thermometer consists of a small glass tube bent into the shape of the letter U, and terminating at each extremity in a small hollow ball, nearly of the same size; the tube contains a little sul- phuric acid tinged red with carmine, and sufficient to fill the great- est part of it. The glass balls are full of air, and both communi- cate with the intermediate tube. To one of the legs of the tube is affixed a small ivory scale divided into 100 degrees; and the sul- phuric acid is so disposed, that in the graduated leg its upper sur- * Inquiry into the Nature of Heat, p. 271. Chap. II.] heat. 47 face stands opposite to the part of the scale marked 0. The glass ball attached to the leg of the instrument to which the scale is at- tached, is, by way of distinction, called the focal ball. Suppose this thermometer brought into a warm room, the heat will act equally upon both balls, and expanding the included air equally in each, the liquor in the tube will remain stationary. But suppose the focal ball exposed to heat while the other ball is not;. in that case the air included in the focal ball will expand, while that in the other is not affected. It will therefore press more upon the li- quid in the tube, which will of course advance towards the cold ball, and therefore the liquid will rise in the tube above 0, and the rise will be proportional to the degree of heat applied to the focal ball. This thermometer, therefore, is peculiarly adapted for ascertaining the degree of heat accumulated in a particular point, while the surrounding atmosphere is but little affected, as happens in the focus of a reflecting mirror. No change in the temperature of the room in which the instrument is kept is indicated by it, while the slightest alteration in the spot where the focal ball is placed is immediately announced by it. In making experiments on the radiation of heat, Mr. Leslie em- ployed hollow tin cubes, varying in size from three inches to ten, filled with hot water, and placed before a tin reflector, having the differential thermometer in the focus. The reflector employed was of the parabolic figure, and about 14 inches in diameter. This apparatus afforded the means of ascertaining the effect of different surfaces in radiating heat. It was only necessary to coat the sur- face of the canister with the various substances whose radiating properties were to be tried, and expose it, thus coated and filled with hot water, before the reflector. The heat radiated in each case would be collected into the focus where the focal ball of the differential thermometer was placed, and the rise of this instru- ment would indicate the proportional radiation of each surface. These experiments were conducted with much address. The fol- lowing are the principal results obtained. 4. When the nature and position of the canister is the same, the rise of the differential thermometer is always proportional to the difference between the temperature of the hot canister and that of the air in the room in which the experiment is made.* 5. When the temperature of the canister is the same, the effect upon the differential thermometer diminishes as the distance of the canister increases from the reflector, the focal ball being always understood to be placed in the focus of the mirror. Thus if the rise of the thermometer, when the canister was three feet from the mirror; be denoted by 100, it will amount only to 57 when the ca- nister is removed to six feet. On substituting a glass mirror for the reflector, and a charcoal fire for the canister, when the fire was • Leslie, p. 14 48 IMPONDERABLE BODIES. I BOOK I. DIVISION 1. at the distance of 10 feet the thermometer rose 37*, and at the dis- tance of 30 feet it rose 21°*. From Mr. Leslie's experiments it follows, that the effect on the thermometer is very nearly" inversely proportional to the distance of the canister from the reflector. He found likewise that when canisters of different sizes were used, heated to the same point, and placed at such distances that they all subtended the same angle at the reflector; in that case the ef- fect of each upon the differential thermometer was nearly the same. Thus a canister of 3 inches at 3 feet distance raised the thermometer 4 inches - 4 feet ...... 6 inches - 6 feet ....•• 10 inches - 10 feet ...... 50* 54 57 59 From these experiments we learn, that the effect of the canister upon the thermometer is nearly proportional to the angle which it subtends, and likewise that the heat radiated from the canister suffers no sensible diminution during its passage through the air. 6. Heat radiates from the surface of hot bodies in all directions; but from Mr. Leslie's experiments we learn, that the radiation is most copious in the direction perpendicular to the surface of the hot body. When the canister is placed in an oblique position to the reflector, the effect diminishes, and the diminution increases with the obliquity of the canister. Mr. Leslie has shown, that the effect in all positions is proportional to the visual magnitude of the canister as seen from the reflector, or to its orthographic projection. Hence the action of the heated surface is proportional to the sine of its inclination to the reflector. Such are the effects of the temperature, the distance, and posi- tion of the canister with respect to the reflector. None of these, except the first, occasion any variation in the quantity of heat ra- diated, but merely in that portion of it which is collected by the mirror and sent to the focal ball; but the case is different when the surface of the canister itself is altered. 7. Mr. Leslie ascertained the power of different substances to radiate, by applying them in succession to a side of the canister, and observing what effect was produced upon the differential thermo- meter. The following table exhibits the relative power of the dif- ferent substances tried by that philosopher, expressed by the eleva- tion of the differential thermometer produced. Lampblack .... 100 Water by estimate . 100-f Writing paper . . .98 Rosin......96 Sealing wax .... 95 Crown glass .... 90 China ink.....88 Ice.......85 " Leslie, p. 51. Chap. II.} HEAT. 49 Minium.....80 Isinglass.....80 Plumbago . ... 75 Tarnished lead ... 45 Mercury.....20+ Cleanlead.....19 Iron polished . . . . 15 Tin plate.....12 Gold, silver, copper . . 12 From this table it appears, that the metals radiate much worse than other substances, and that tin plate is one of the feeblest of the metallic bodies tried. Lamp black radiates more than eight times as much as this last metal, and crown glass 7-5 times as much. 8. Such are the radiating powers of different substances. But even when the substance continues the same, the radiation is very considerably modified by apparently trifling alterations on its sur- face. Thus metals radiate more imperfectly than other bodies; but this imperfection depends upon the brightness and smoothness of their surface. When, by exposure to the air, the metal acquires that tarnish which is usually ascribed at present to oxidizement, the power of radiating heat is greatly increased. Thus it appears from the preceding table, that the radiating power of lead while bright is only 19; but when its surface becomes tarnished, its radiating power becomes no less than 45. The same change happens to tin, and to all the metals tried. When the smoothness of the surface is destroyed by scratching the metal, its radiating power is increased. Thus if the effect of a bright side of the canister be 12, it will be raised to 22 by rubbing the side in one direction with a bit of fine sand paper.* But when the surface is rubbed across with sand paper, so as to form a new set of furrows intersecting the former ones, the radiating power is again somewhat diminished. 9. The radiating power of the different substances examined was ascertained by applying a thin covering of each to one of the sides of the canister. Now this coat may vary in thickness in any given degree. It becomes a question of some importance to ascertain, whether the radiating power is influenced by the thickness to a given extent, or whether it continues the same whatever be the thickness of the covering coat. This question Mr. Leslie has like- wise resolved. On a bright side of a canister he spread a thin coat of liquified jelly, and four times the quantity upon another side; both dried into very thin films. The effect of the thinnest film was 38, that of the other 54. In this case the effect increased with the thickness of the coat. The augmentation goes on till the thick- ness of the coat of jelly amounts to about p^th °^ an mcn J after which it remains stationary. When a surface of the canister was rubbed with olive oil, the effect was 51: a thicker coat of oil produced an effect of 59. Thus it appears that when a metallic surface is covered with a coat of jelly or oil, the effect is propor- tional to the thickness of the coat, till this thickness amounts to a Vol. I. * Leslie, p. 81. 50 IMPONDERABLE BODIES. 5 n00K [• <> DIVISION 1. certain quantity; but when a vitreous surface is covered by very thin coats of metal, no such change is perceived. A canister was employed, one of the sides of which was a glass plate. Upon this plate were applied, in succession, very fine coats of gold, silver, and copper leaf. But notwithstanding their thinness, the effect was only 12, or the same that would have been produced by a thick coat of these very metals. But when glass enamelled with gold is used, the effect is somewhat increased; a proof that varying the thickness of the metallic coats would have the same effect as vary- ing the thickness of jelly, provided they could be procured of suf- ficient tenuity.* As long as an increase of thickness alters the radiating power of the coat, it is obvious that the surface of the canister below exerts a certain degree of energy. And the action exerted by metallic bodies appears to be greater than that exerted by vitreous bodies. 10. Such are all the circumstances connected with the radiating surface hitherto observed, which influence its power. For hitherto it has been impossible to ascertain the efficacy of hardness and soft- ness, or of colour, upon radiation; though it appears, from Mr. Leslie's experiments, not unlikely that softness has a tendency to promote radiation.! But as the effect, as far at least as measured by the differential thermometer, depends not only upon the radiat- ing surface, but likewise upon the surface of the focal ball, and likewise of the reflector; it will be necessary also to consider the modifications produced by alterations in the surface of these bodies. This inquiry, for which, like the preceding, we are indebted to Mr. Leslie, will throw considerable light on the nature of radiation. 11. When the focal ball is in its natural state, that is to say, when its surface is vitreous, it has been already observed, that the side of the hot canister coated with lamp black raises the thermometer 100°. If the experiment be repeated, covering the focal ball with a smooth surface of tinfoil, instead of rising to 100°, the thermome- ter will only indicate 2C°. A bright side of the canister will raise the thermometer, when the focal ball is naked, 12°; but when the ball is covered with tinfoil, the elevation will not exceed 2\ de- grees.! From these experiments it is obvious, that metal not only radiates heat worse than glass, but likewise that it is not nearly so capable of imbibing it when the rays strike against its surface. If the surface of the tinfoil be furrowed by rubbing it with sand paper, the effect produced when the focal ball is exposed in the focus will be considerably increased.^ It has been already observed that the radiating power of tin is likewise increased by scratching it. These facts entitled us to conclude, that those surfaces which radiate heat most powerfully, likewise absorb it most abundantly when it impinges against them. 12. The very contrary holds with respect to the reflectors as * Leslie, p. 110. t Ibid- P- 90- * Ibid- P- 19- § Ibid. p. 81. Chap. II.] heat. 51 might indeed have been expected. Those surfaces which radiate heat best, reflect it worst; while the weakest radiating surfaces are the most powerful reflectors. Metals of course are much better reflectors than glass. When a glass mirror was used instead of the tin reflector, the differential thermometer rose only one degree; upon coating the surface of the mirror with lamb black, all effect was destroyed; when covered with a sheet of tinfoil the effect was 10°* To compare the relative intensity of different substances as re- flectors, Mr. Leslie placed thin smooth plates of the substances to be tried before the principal reflector, and nearer than the proper focus. A new reflection was produced, and the rays were collected in a focus as much nearer the reflector than the plate as the old fo- cus was farther distant. The comparative power of the different substances tried was as follows :f— Lead .... 60 Tinfoil softened by mercury 10 Glass .... 10 Ditto coated with wax or oil 5 Brass Silver Tinfoil Block-tin Steel . 100 90 85 80 70 When the polish of the reflector is destroyed by rubbing it with sand paper, the effect is very much diminished. When the reflector is coated over with a solution of jelly, the effect is diminished in proportion as the thickness of the coat increases, till its diameter amounts to —^ th part of an inch. The following table exhibits the intensity of the reflector coated with jelly of various degrees of thickness.! Thickness of coat. Effect. Naked reflector.....127 98 93 87 61 39 29 21 15 400000 1 160 6 6 0 50000 ___1__ 26000 10000 __1 500"0" 5 000 1 1606 All these phenomena are precisely what might have been ex- pected, on the supposition that the intensity of reflection is inverse- ly that of radiation. Mr. Leslie has shown that it is the anterior surface of reflectors only that acts. For when a glass mirror is employed, its power is not altered by scraping off the tin from its back, nor by grinding the posterior surface with sand or emery.§ 13. Such are the phenomena of the radiation of heat as far as the radiating surface, the reflector, and the focal ball are concern- ed. It cannot be doubted from them, that heat is actually radia- ted from different surfaces, and that bodies vary considerably in * Leslie, p. 20. f Ibid. p. 98. * Ibid. p. 106. § Ibid. p. 21. IMPONDERABLE BODIES. { BOOK I DIVISION 1. their radiating power. We have seen also that substances differ no less from each other in their power of reflecting heat, and that the intensity of the latter power is always the inverse of the inten- sity of the. former. Before we can be able to form a judgment ot the way in which the heat is conveyed in these cases, it will be ne- cessary to examine the effect of the different mediums in which the radiation may take place, and the obstructions occasioned by put- ting different substances between the radiating surface and the re- flector. Both of these points have been examined by Mr. Leslie with his usual acuteness. . 14. In all common cases, the medium through which the heat is radiated is the air; and from Mr. Leslie's experiments it appears, that no sensible radiation can be observed when the canister, re- flector, and differential thermometer, are plunged into- water. Hence he concludes, that no radiation takes place except when the radiating body is surrounded with an elastic medium. But the ex- periments which he adduces are scarcely sufficient to decide the point. Substances cool so fast when plunged into water, that there is scarcely time for the thermometer to be affected; and, besides, the heat could scarcely accumulate in the focal ball in such quan- tity as to occasion a sensible rise. Heat radiates through all the gaseous bodies tried; and from Mr. Leslie's experiments, it does not appear that the rate of radia- tion is much influenced by altering the surrounding medium. The rate is the same, at least, in air and hydrogen gas; and oxygen and azotic gas appear to have the same properties in this respect as air. Mr. Leslie has shown also that the rarefaction of the sur- rounding air diminishes somewhat the radiating energy of sur- faces ; but the radiation diminishes at different rates in different gases. The following table, calculated from his trials, shows, ac- cording to him, the diminution of the power of radiation in air and hydrogen gas of different degrees of rarity. S5 a £ Q >* 00 to 0* CO CO to to k*5 (O CO to to 00 o to O 00 1ft to Vi £ J •* CO Vi to vi CO o Vi o to 00 o • Vi •* to 00 CO Vi pi < c x, o Oi to co to •*• •* to to o to «o o 00 o 00 >o to o to Vi eo 00 •* Vi CO Vi o Vi .2 K J •* t^ CO CO us o k«5 •* to CO CO 00 o •* Rarity. CH Tf 1 to 1 eo 1 •* to 00 T—1 to Vi O l-H Chap. II.] heat. 53 Such is the effect of different mediums as far as they have been examined by Mr. Leslie; but the experiments on which his con- clusions were founded would require to be repeated. 15. When a substance is interposed by way of screen between the hot canister and the reflector, the effect is either diminished or destroyed altogether, according to circumstances. These circum- stances have been examined by Mr. Leslie with great sagacity. Indeed, the developement of the effect of screens constitutes per- haps the most curious and important part of his whole work. A screen may affect the radiation of heat three ways: 1. By its dis- tance from the hot canister; 2. By its thickness: and, 3. By the nature of the substance of which it is composed. Let us take a view of each of these in succession. First, From all Mr. Leslie's trials, it appears that a screen di- minishes the effect of radiation upon the differential thermometer situated in the focus of the reflector, in proportion to its distance from the canister. When placed very near the canister, the effect is comparatively small; but it increases rapidly as the screen is drawn away from the canister; so that the elevation of the differential thermometer is soon prevented altogether. When the canister is at the distance of three feet from the reflector, if the side painted with lamp black produce an effect equivalent to 100, this effect upon interposing a pane of glass at the distance of two inches from the . canister will be diminished to 20. When the pane is advanced slowly forward towards the reflector, the effect of the radiation gradually diminishes; and when it has got to the distance of one foot from the screen, the radiation is completely intercepted,* Second, When a screen of thin deal board is used instead of the pane of glass, and placed at the distance of two inches from the canister, the radiation is diminished, and the diminution is pro- portional to the thickness of the board. With a board \ inch thick the effect is 20 . . . . | inch ... 15 . . . . 1 inch ... 9 Thus the radiation diminishes very slowly as the thickness increa- ses.! Third, When a sheet of tinfoil is substituted for the glass pane, and put into the same position, the effect, instead of 20, is reduced to 0; and this happens however thin the tinfoil is; even gold leaf of the thickness of 7ooVoo tn Part of ^ mcni though pervious to light, completely stops the progress of radiating heat. When a sheet of writing paper is substituted for tinfoil, the effect is 23.! Thus it appears, that substances vary considerably from each other in their property of intercepting radiating heat; and likewise that the power of intercepting heat is inversely as the power of radia- ting it. Those substances which radiate most heat, intercept the * Leslie, p. 28. f Ibid. p. 38. * Ibid. 54 IMPONDERABLE BODIES. $Dmsio»L, least of it when in the situation of screens; and those which radi- ate the least heat, on the contrary', intercept the most. But it was formerly observed, that the power of absorbing heat was the same with that of radiating it. Hence those substances which absorb least heat are the most powerful interceptors of it, and the contrary. These facts lead naturally to the opinion, that the property of absorbing heat depends upon the surface of the substance which is interposed as a screen; an opinion which Mr. Leslie has estab- lished by the following experiments. He took two panes of glass, and coated one side of each with tinfoil, leaving the other side bare. These two panes were pressed together; the tinned side of each being outmost, and applied as a screen at two inches distance from the canister. The whole of the rays of heat appeared to be inter- cepted, for the thermometer was not acted upon at all. But when the glass side of the screen was outmost, the effect of radiation was equivalent to 18. Here we find the very same screen, in the very same position, intercepting very different proportions of the radi- ated heat, according to the nature of its external surface. When the tin was outmost, the whole heat was stopped; but when the glass was outmost, about |th passed on to the reflector. The effect was analogous when two sheets of tin, each painted on one side with a thin coat of lamp black, were employed as a screen, and placed two inches from the canister. Pressed together, and having their metal sides outmost, the radiation produced no effect upon the thermometer; but when the blackened sides were outmost, the effect was equivalent to 23. When only one of the plates is used, and its blackened side turned to the canister, the effect is equal to 4. If the two plates be used with their blackened sides outmost, and at the distance of two inches from each other, all effect is des- troyed.* 16. But the subsequent experiments of M. De la Roche have somewhat modified the consequences which appeared to follow from the very ingenious experiments of Leslie, and show a much greater analogy between the radiation of light and heat than that philosopher had supposed. De la Roche found that radiant heat in some cases passes directly through glass: that the quantity of radiant heat which passes directly through glass is so much great- er relative to the whole heat emitted in the same direction, as the temperature of the source of heat is more elevated: that calorific rays, which have already passed through a screen of glass, experi- ence in passing through a second glass screen of a similar nature a much smaller diminution of their intensity than they did in passing through the first screen: that rays emitted by a hot body differ from each other in their faculty of passing through glass: that a thick glass, though as much or more permeable to light than a thin glass of a worse quality, allows a much smaller quantity of radiant * Leslie, p. 35. Chap. II.] HEAT. heat to pass; but the difference is so much the less as the tempera- ture of the radiating source is more elevated: and that the quantity of heat which a hot body yields in a given time by radiation to a cold body situated at a distance, increases, cceteris paribus, in a greater ratio than the excess of temperature of the first body above the second.* These experiments of De la Roche, supposing them correct, de- stroy the conclusions deduced from Mr. Leslie's observations, that there is an essential difference between the radiation of light and of heat. There would appear on the contrary to be a close analogy between them. The hypothesis of Mr. Leslie that the radiation of heat is owing to aerial vibrations, similar to the propagation of sound, cannot be admitted, because it is inconsistent with the ex- periments of De la Roche. It would not be surprising if the power of producing heat and light were properties of the same substance. It may produce light when acting with a certain intensity, or when the particles follow each other at certain limited intervals. When these intervals are changed heat may be produced. It is even con- ceivable that those rays which are invisible to our eyes, and which therefore we are accustomed to consider as pure caloric, may pro- duce an illuminating effect upon the eyes of some other animals. II. Conduction of Heat. 1. If we put the end of a bar of iron, 20 inches long, into a com- mon fire, while a thermometer is attached to the other extremity, 4 minutes elapse before the thermometer begins to ascend, and 15 minutes by the time it has risen 15°. In this case, the caloric takes 4 minutes to pass through a bar of iron 20 inches long. When ca- loric passes in this slow manner, it is said to be conducted through bodies. It is in this manner that it usually passes through non- elastic bodies; and though it often moves by radiation through elastic media, yet we shall find afterwards that it is capable of be- ing conducted through them likewise. 2. As the velocity of caloric, when it is conducted through bo- dies, is greatly retarded, it is clear that it does not move through them without restraint. It must be detained for some time by the particles of the conducting body, and consequently must be at- tracted by them. Hence it follows that there is an affinity or at- traction between caloric and every conductor. It is in consequence of this affinity that it is conducted through the body. 3. Bodies then conduct caloric in consequence of their affinity for it, and the property which they have of combining indefinitely with additional doses of it. Hence the reason of the slowness of the process, or, which is the same thing, of the long time neces- sary to heat or to cool a body. The process consists in an almost infinite number of repeated compositions and decompositions. f Annals of Philosophy, ii. 100. 56 IMPONDERABLE BODIES. 5 division!'. 4. We see, too, that when heat is applied to one extremity of a body, the temperature of the strata of that body must diminish equably, according to their distance from the source of heat. Every person must have observed that this is always the case. If, for instance, we pass our hand along an iron rod, one end of which is held in the fire, we shall perceive its temperature gradually di- minishing from the end in the fire, which is hottest, to the other extremity, which is coldest. Hence the measure of the heat trans- mitted must always be proportional to the excess of temperature communicated to that side of the conductor which is nearest the source of heat. 5. The passage of caloric through a body by its conducting power must have a limit; and that limit depends upon the number of doses of caloric with which the stratum of the body nearest the source of heat is capable of combining. If the length of a body be so great that the strata of which it is composed exceed the number of doses of caloric with which a stratum is capable of combining, it is clear that caloric cannot possibly be conducted through the body; that is to say, the strata farthest distant from the source of heat cannot receive any increase of temperature. This limit depends, in all cases, upon the quantity of caloric with which a body is ca- pable of combining before it changes its state. All bodies, as far as we know at present, are capable of combining indefinitely with caloric; but the greater number, after the addition of a certain num- ber of doses, change their state. Thus ice, after combining with a certain quantity of caloric, is changed into water, which is con- verted in its turn to steam by the addition of more caloric. Metals also, when heated to a certain degree, melt, are volatilized, and oxidated: wood and most other combustibles catch fire, and are dissipated. Now whenever as much caloric has combined with the first stratum of a body as it can receive without changing its state, it is evident that no more caloric can enter the body; because the next dose will dissipate the first stratum. 6. As to the rate at which bodies conduct caloric, that depends upon the specific nature of each particular body; the best conduc- tors conducting most rapidly, and to the greatest distance. The goodness of bodies as conductors appears to be in some measure dependent upon their density: but not altogether, as the specific affinity of each for caloric must have considerable influence. When bodies are arranged into sets, we may lay it down as a general rule that the densest sets conduct at the greatest rate. Thus the metals conduct at a greater rate than any other bodies. But in considering the individuals of a set, it is not always the densest that conducts best. 7. As bodies conduct caloric in consequence of their affinity for it,* and as all bodies have an affinity for caloric, it follows as a con- * [It is just as likely that bodies conduct caloric because they have no affinity for it. The heat that permeates a i>ody does not combine with it. We know as yet nothing of the cause of conducting power.—C.) Ghap. II.] LIGHT. 57 sequence, that all bodies must be conductors, unless their conduct- ing power be counteracted by some other property. If a body, for instance, were of such a nature that a single dose of caloric sufficed to produce a change in its state, it is evident that it could not con- duct caloric; because every row of particles, as soon as it had com- bined with a dose of caloric, would change its place, and could not therefore communicate caloric to the strata behind it. 8. All solids are conductors;* because all solids are capable of combining with various doses of caloric before they change their state. This is the case in a very remarkable degree with all earthy and stony bodies; it is the case also with metals, with vegetables, and with animal matters. This, however, must be understood with certain limitations. All bodies are indeed conductors; but they are not conductors in all situations. Most solids are conductors at the common temperature of the atmosphere; but when heated to the temperature at which they change their state, they are no longer conductors. Thus at the temperature of 60° sulphur is a conductor; but when heated to 218°, or the point at which it melts or is volatilized, it is no longer a conductor. In the same manner ice conducts caloric when at the temperature of 20°, or any other degree below the freezing point; but ice at 32° is not a conductor, because the addition of caloric causes it to change its state. 9. With respect to liquids and gaseous bodies, it would appear at first sight that they also are all conductors; for they can be heat- ed as well as solids, and heated too considerably without sensibly changing their state. But fluids differ from solids in one essential particular: their particles are at full liberty to move among them- selves, and they dbey the smallest impulse; while the particles of solids, from the very nature of these bodies, are fixed and stationary. One of the changes which caloric produces on bodies is expansion, or increase of bulk; and this increase is attended with a propor- tional diminution of specific gravity. Therefore, whenever caloric combines with a stratum of particles, the whole stratum becomes specifically lighter than the other particles. This produces no 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 buoyed up to the surface of the fluid. In fluids, then, it makes a very great difference to what part of the body the source of heat is applied. If it be applied to the high- est stratum of all, or to the surface of the liquid, the caloric can only make its way downwards, as through solids, by the conduct- ing 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 expansion of the * [Perfectly dry vegetables are very bad conductors: so is dry charcoal. It can hardly be said to be a conductor of caloric—C] Vol. I. H 58 IMPONDERABLE BODIES. JdmSS« 1 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 caloric 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 of carrying or transporting caloric; in consequence of which they acquire heat independent altogether of any conducting power. 10. The carrying power of fluids was first accurately examined by count Rumford. This ingenious philosopher was so struck with it the first time he observed it, that he was led to conclude, that it is by means of it alone that fluids acquire heat, and that they are altogether destitute of the property of conducting caloric. In a set of experiments on the communication of heat, he made use of thermometers of an uncommon size. Having exposed one of these (the bulb of which was near four inches in diameter) filled with al- cohol to as great a heat as it could support, he placed it in a win- dow to cool, where the sun happened to be shining. Some parti- cles of dust had by accident been mixed with the alcohol: these being illuminated by the sun, became perfectly visible, and disco- vered that the whole liquid in the tube of the thermometer was in a most rapid motion, running swiftly in opposite directions upwards and downwards at the same time. The ascending current occupied the axis, the descending current the sides of the tube. When the sides of the tube were cooled by means of ice, the velocity of both currents was accelerated. It diminished as the liquid cooled; and when it had acquired the temperature of the room, the motion ceased altogether. This experiment was repeated with linseed oil, and the result was precisely the same. These currents were evi- dently produced by the particles of the liquid going individually to the sides of the tube, and giving out their caloric. The moment they did so, their specific gravity being increased, they fell to the bottom, and of course pushed up the warmer part of the fluid, which was thus forced to ascend along the axis of the tube. Having reached the top of the tube, the particles gave out part of their ca- loric, became specifically heavier, and tumbled in their turn to the bottom. As these internal motions of fluids can only be discovered by mixing with them bodies of the same specific gravity with them- selves, and as there is hardly any substance of the same specific gravity with water which is not soluble in it, Count Rumford had recourse to the following ingenious method of ascertaining whether that fluid also followed the same law. The specific gravity of wa- ter is increased considerably by dissolving any salt in it; he added therefore, potash to water till its specific gravity was exactly equal to that of amber, a substance but very little heavier than pure wa- Chap. II.] LIGHT. 59 ter. A number of small pieces of amber were then mixed with this solution, and the whole put into a glass globe with a long neck, which, on being heated and exposed to cool, exhibited exacdy the same phenomena with the other fluids. A change of temperature, amounting only to a very few degrees, was sufficient to set the cur- rents a-flowing; and a motion might at any time be produced by applying a hot or a cold body to any part of the vessel. When a hot body was applied, that part of the fluid nearest it ascended; but it descended on the application of a cold body. These observations naturally led Count Rumford to examine whether the heating and cooling of fluids be not very much retard- ed by every thing which diminishes the fluidity of these bodies. He took a large linseed-oil thermometer with a copper bulb and glass tube: the bulb was placed exactly in the centre of a brass cylinder; so that there was a void space between them all around 0*25175 of an inch thick. The thermometer was kept in its place by means of four wooden pins projecting from the sides and bottom of the cy- linder, and by the tube of it passing through the cork stopper of the cylinder. This cylinder was filled with pure water, then held in melting snow till the thermometer fell to 32°, and immediately plunged into a vessel of boiling water. The thermometer rose from 32° to 200° in 597". It is obvious that all the caloric which served to raise the thermometer must have made its way through the wa- ter in the cylinder. The experiment was repeated exactly in the same manner; but the water in the cylinder, which amounted to 2276 grains, had 192 grains of starch boiled in it, which rendered it much less fluid. The thermometer now took 1109" to rise from 32° to 200°. The same experiment was again repeated with the same quantity of pure water, having 192 grains of eiderdown mixed with it, which would merely tend to embarrass the motion of the parti- cles. A quantity of stewed apples were also in another experiment put into the cylinder. These substances retarded the rate of cool- ing rather more than the starch. Now the starch and eiderdown diminished the fluidity of the water. It follows from these experiments, that " the more com- pletely the internal motions of a liquid are impeded, the longer is that liquid before it acquires a given temperature." Therefore, when heat is applied to liquids, they acquire the greatest part of their temperature, in common cases, by their carrying power. If liquids then be conductors, their conducting power is but small when compared with their carrying power. All liquids, however, are capable of conducting caloric; for when the source of heat is applied to their surface, the caloric gra- dually makes its way downwards,* and the temperature of every * [Very slowly. Fill a glass tube of about a quarter of an inch diameter, and 9 inches long, one third full of common water: carefully introduce without mixing, one third more of water coloured by litmus or cochineal. Hold the coloured part over the flame of a spirit lamp till the water boils. The uncoloured water will long remain undisturbed; at least till 60 IMPONDERABLE BODIES. J JJSS51" 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 liquid. By that power caloric may in- deed make its way upwards through liquids, but certainly not downwards. Liquids, then, are conductors of caloric. 11. If we take a bar of iron and a piece of stone of equal dimen- sions, and, putting one end of each into the fire, apply either ther- mometers or our hands to the other, we shall find the extremity of the iron sensibly hot long before that of the stone. Caloric there- fore is not conducted through all bodies with the same celerity and ease. Those that allow it to pass with facility, are called good con - ductors; those through which it passes with difficulty, are called bad conductors. The experiments hitherto made on this subject are too few to ena- ble us to determine with precision the rate at which different bodies conduct caloric. The subject, however, is of considerable import- ance, and deserves a thorough investigation. 12. Metals are the best conductors of caloric of all the solids hitherto tried. The conducting powers of all, however, are not equal. Dr. Ingenhousz procured cylinders of several metals exact- ly of the same size, and having coated them with wax, he plunged their ends into hot water, and judged of the conducting power of each by the length of wax-coating melted. From these experi- ments he concluded, that the conducting powers of the metals which he examined were in the following order.* Silver, Gold, rp. PP 'I nearly equal, Platinum,""] ct f £>much inferior to the others. Lead, J 13. Next to metals, stones seem to be the best conductors ; but this property varies considerably in different stones. Bricks are much worse conductors than most stones. 14. Glass seems not to differ much from stones in its conducting power. Like them, it is a bad conductor. This is the reason that it is so apt to crack on being suddenly^ heated or cooled. One part of it, receiving or parting with its caloric before the rest, ex- pands or contracts, and destroys the cohesion. 15. Next to these come dried woods. Mr. Meyer! has made a set of experiments on the conducting power of a considerable num- ber of woods. The result may be seen in the following table, in which the conducting power of water is supposed = 1. the whole tube becomes heated. Again, apply the flame to the bottom of the tube; the liquors will be mixed in a minute's time, the uncoloured water will ascend, the coloured will descend.—C.] * Jour, de Phys. 1789, p. 68. f [Hence the practice of annealing glass: that is, putting it while hot, immediately after being formed into the requin-d shape, into an oven strongly heated, where the glass remains till it becomes cold, by slow degrees.—C.] i Ann. de Chim. xxx. 32. Chap. II.] LIGHT. 61 Conducting Power. = 1*00 Bodies. Water .... Diaspyrus ebenum Pyrus malus . Fraxinus excelsior . Fagus sylvatica Carpinus betulus Prunus domestica . Ulmus .... Quercus robur pedunculata Pyrus communis Betula alba Quercus robur sessilis Pinus picea Betula alnus . Pinus sylvestris Pinus abies Tilea Europaea Charcoal is also a bad conductor: of Morveau, its conducting power is to that of fine sand : : 2 : 3.* Feathers, silk, wool, and hair, are still worse conductors than any of the substances yet mentioned. This is the reason that they an- swer well for articles of clothing. They do not allow the heat of the body to be carried off by the cold external air. Count Rum- ford has made a very ingenious set of experiments on the conduct- ing power of these substances.! He ascertained that their con- ducting power is inversely as the fineness of their texture. 16. The conducting power of liquid bodies has not been exami- ned with any degree of precision. I find by experiment, that the relative conducting powers of mercury, water, and linseed oil, are as follows: 2*17 2-74 3*08 3«21 3«23 3.25 3*25 3-26 3*32 3»41 3-63 3-75 3-84 3«86 3-89 3«90 according to the experiments I. Equal Bulks. II. Eojjal Weights. Water . . = 1 Water . . . = 1 Mercury . . = 2 Mercury . . =4*8 Linseed oil . . =1.111 Linseed oil . = 1*085 17. With respect to gaseous bodies, it is well known that bodies cool much more slowly in them than in liquids. But as the cool- ing of hot bodies in gases is produced by a variety of causes be- sides the conducting power of these fluids, it is difficult to form an estimate of their relative intensities as conductors from the time that elapses during the cooling of bodies in them. Count Rum- ford found that a thermometer cooled nearly four times as fast in water as in air of the same temperature; but no fair inference can be drawn from that experiment, as it is known that the rate of cool- ing varies with the temperature much more in water than in air.! * Ibid. xxvi. 825, ! Phi. Trans. 1792. $ Phil. Trans. 1786. 62 IMPONDERABLE BODIES. S B°OK 1 ^divisiojtI. The same philosopher ascertained, that rarefaction diminished the conducting power of air, and that hot bodies cool slowest of all in a Torricellian vacuum. Mr. Leslie was enabled, by the delicacy of his instruments, to examine the conducting power of gases with more precision than had been previously done. The following are the facts which he ascertained. The conducting power of all gases is diminished by rarefaction. He has endeavoured to deduce from his experiments, that the con- ducting power of air is nearly proportional to the fifth root of its density. But Mr. Dalton has rendered it probable that it varies nearly as the cube root of its density. Vapours of all kinds, and every thing that has a tendency to di- late air, diminish its conducting power. The conducting powers of common air, oxygen, and azote, are nearly equal. The conducting power of carbonic acid gas is rather inferior to that of air; but bodies cool in hydrogen gas more than twice as fast as in common air. By analysing the process of cool- ing, and ascertaining that the radiation is the same in air and hy- drogen gas, Mr. Leslie has rendered it probable that the conduct- ing power of this gas is four times as great as that of air.* Mr. Dalton has lately investigated the rate of cooling of hot bodies in different gases. He filled a strong phial with the gas to be examined; introduced into it a delicate thermometer through a perforated cork, and observed the time it took to cool 15° or 20°. The following table exhibits the result of his trials.! Gases. Time of Cooling. Carbonic acid, 112" Sulphureted hydrogen, "\ Nitrous oxide, L 4 100-f defiant gas, J Common air,"} Oxygen, L . 100 Azotic gas, J Nitrous gas, 90 Gas from pit-coal, 70 Hydrogen gas 40 SECTION III. OF THE EQUAL DISTRIBUTION OP TEMPERATURE. We have seen, in the preceding Section, that caloric is capable of moving through all bodies, though with different degrees of facility. The consequence of this property is a tendency which it * Leslie's. Inquiry into the Nature of Heat, p. 473. t Dalton's New System of Chemical Philosophy, p. U7, Chap. II.] LIGHT. 63 has to distribute itself among all contiguous bodies in such a man- ner, that the thermometer indicates the same temperature in all. 1. We can easily increase the temperature of bodies, whenever we choose, by exposing them to the action of our artificial fires. Thus a bar of iron may be made red hot by keeping it a sufficient time in a common fire: but if we take it from the fire, and expose it to the open air, it does not retain the heat which it had received; but becomes gradually colder and colder, till it arrives at the tem- perature 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 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. Thus it appears that no body can retain its high temperature while surrounded by colder bodies, nor its low temperature while it is surrounded by hotter bodies. The caloric, however combined at first, gradually distributes itself in such a manner, that all contiguous bodies, when examined by the thermometer, indicate the same temperature. These changes oc- cupy a longer or a shorter time, according to the size or the nature of the body; but they always take place at last. This law is familiar to every person. When we wish to heat any thing, we carry it towards the fire; when we wish to cool it, we surround it by cold bodies. The caloric in this last case is not lost; it is merely distributed equally through the bodies. When a num- ber of substances are mixed together, some of them cold and some of them hot, they all acquire the same temperature; and this new temperature is a mean of all the first temperatures of the sub- stances. Those which were hot become colder, and those which were cold become hotter. This property of caloric has been called by philosophers the equilibrium of caloric; but it might with greater propriety be denominated, the equal distribution of temperature. 2. From the experiments of Kraft and Richmann,* made with much precision, and upon a great number of bodies, the following general conclusion has been drawn. " When a body is suspended in a medium of a temperature different from its own, the difference between the temperature of the body and the medium diminishes in a geometrical ratio, while the time increases in an arithmetical ratio." Or, u In given small times the heat lost is always propor- tional to the heat remaining in the body." This law had been first suggested by Sir Isaac Newton, who calculated by means of it several temperatures above the scale of thermometers. From the late experiments of Delaroche, which seem to have been made with very great care, it appears that this law is only an approximation to the truth. At all temperatures below 212° it is sufficiently near; but the error increases as the temperature aug- ments, and at last becomes very great. » Nov. Comm. Petrop. i. 195. 64 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. The caloric which leaves hot bodies till they are reduced to the temperature of the substances around them, is partly conducted away by the surrounding medium, partly abstracted by currents produced in that medium (supposing it fluid), and partly radiates from the surface of the hot body. The process of cooling, both in air and in water, has heen analysed with much address and suc- cess by Mr. Leslie, though he has neglected to notice the labours of his predecessors in that investigation. The following facts have been ascertained. The effect of the conducting power depends upon the medium, and is therefore constant, supposing the temperatures and the me- dium constant; but it gradually diminishes as the temperature of the hot body approaches that of the medium. The effect of* radiation depends upon the surface of the hot body, and is therefore constant when the same surface is heated to the same degree: but, like the conducting power, it diminishes as the hot body approaches to the temperature of the medium. That portion of the medium which is in contact with the hot body, receiving a certain portion of its heat, acquires a different density, and in consequence gives place to a new portion, which, being heated in its turn, follows the preceding portion; and in this manner a current is produced, which very much accelerates the rate of cooling. It is obvious, that the velocity of this current will be the greater the higher the temperature of the hot body is. Hence the effect of these artificial currents will diminish as the temperature of the hot body approaches that of the medium. If these currents be artificially increased, it is obvious that the rate of cooling will be proportionably accelerated. Hence the effect of winds in cooling hot bodies. From Mr. Leslie's experi- ments it appears that, other things being the same, the rate of cool- ing is always proportional to the velocity of the current, or, which is the same thing, to the velocity with which the hot body moves through the cold medium. Thus a hot ball, that in calm air cooled down a certain number of degrees in 120', when moved in the same air with different velocities, lost the same quantity of heat in times which diminished as the velocity increased, as will be obvious from the following table: Velocity. Time of cooling. 6f feet per second . . 60' 20 ...... 30 60......12 When the ordinary influence of cooling is deducted, the accelera- tion of cooling in these degrees is found' to increase exactly as the velocity.* 4. As soon as it was discovered that contiguous bodies assume the same temperature, various attempts were made by philosophers to account for the fact. De Mairan, and other writers in the ear- * Leslie, p. 281. Chap. II.] HEAT. 65 lier part of the 18th century, explained it, by supposing that caloric is a fluid which pervades all space, and that bodies merely float in it as a sponge does in water, without having any affinity for it what- ever. The consequence of all this was a constant tendency to an equality of density. Of course, if too much caloric is accumula- ted in one body, it must flow out; if too little, it must flow in till the equality of density be restored. . This hypothesis is inconsistent with the phenomena which it is intended to explain. Were it true, all bodies ought to heat and to cool with the same facility; and the heat ought to continue as long in the focus of a burning glass as in a globe of gold of the same di- ameter. It is equally inconsistent with the nature of caloric; which has been shown in the first section of this chapter to be a body very different from the hypothetical fluid of De Mairan. 5. Another explanation of the equal distribution of temperature, and a much more ingenious one, was proposed by Mr. Pictet. Ac- cording to this philosopher, when .caloric is accumulated in any body, the repulsion between its particles is increased, because the distance between them is diminished. Accordingly they repel each other; and this causes them to fly off in every direction, and to continue to separate till they are opposed by caloric in other bo- dies of the same relative density with themselves, which, by re- pelling them in its turn, compels them to continue where they are. The equal distribution of temperature therefore depends on the ba- lancing of two opposite forces : the repulsion between the particles of caloric in the body, which tends to diminish the temperature; and the repulsion between the caloric of the body and the surround- ing caloric, which tends to raise the temperature. When the first force is greater than the second, as is the case when the tempera- ture of a body is higher than that of the surrounding bodies, the caloric flies off, and the body becomes colder. When the last force is stronger than the first, as is the case when a body is colder than those which are around it, the particles of its caloric are obliged to approach nearer each other, new caloric enters to occupy the space which they had left, and the body becomes hotter. When the two forces are equal, the bodies are said to be of the same temperature, and no change takes place.* But this theory, notwithstanding its ingenuity, is inconsistent with the phenomena of the heating and cooling of bodies, and has accordingly been abandoned by the ingenious author himself. 6. The opinion at present most generally received, and which accounts for the phenomena in the most satisfactory manner, is that of Prevost, first published in the Journal de Physique for 1791, in an essay on the equilibrium of caloric; and afterwards detailed at greater length in his Recherches sur la Chaleur.] It was soon after adopted by Mr. Pictet,! an(^ was applied by Prevost with much ad- * See Pictet, sur le Feu, chap. i. f Geneva, 1792. i Biblioth. Bi-itan. iv. 30. Vol. I. I 66 IMPONDERABLE BODIES. C BOOK I ^DIVISIOX 1 dress to the experiments of Herschel and Pictet.* According to him, caloric is a discrete fluid, each particle of which moves with enormous velocity when in a state of liberty. Hot bodies emit ca- lorific rays in all directions; but its particles are at such a distance from each other, that various currents may cross each other with- out disturbing one another, as is the case with light. The conse- quence of this must be, that if we suppose two neighbouring spaces in which caloric abounds, there must be a continual exchange of caloric between these two spaces. If it abounds equally in each, the interchanges will balance each other, and the temperature will conti- nue the same. If one contains more than the other, the exchanges must be unequal; and by a continual repetition of this inequality, the equilibrium of temperature must be restored between them. If we suppose a body placed in a medium hotter than itself, and the temperature of that medium constant, we may consider the ca- loric of the medium as consisting of two parts; one equal to that of the body, the other equal to the difference between the tempera- ture of the two. The first part'may be left out of view, as its ra- diations will be counterbalanced by those of the body. The excess alone requires consideration ; and relatively to that excess the body is absolutely cold, or contains no caloric whatever. If we suppose that in one second the body receives -j^th of this excess, at the end of the first second the excess will be only ^Vtns. One tenth of this excess will pass into the body during the next second, and the ex- cess will be reduced to ^ of T9T, or (T%)2. At the end of the third second, the excess will be (y^)3; at the end of the fourth, (A)4> and so on: the time increasing in an arithmetical ratio, while the excess diminishes in a geometrical ratio, according to Richmann's rule. Such is a sketch of Prevost's theory. It is founded altogether upon the radiation of caloric, and leaves the effect of the conduct- ing power of bodies out of sight. The reality of the radiation can- not be doubted; and it is exceedingly probable that the equal dis- tribution of temperature is the consequence of it. Were caloric merely conducted, its progress would be excessively slow, and in- deed absolute equality of temperature would scarcely ever take place. At the same time, it must be allowed that this property of bodies has very considerable influence in regulating the time which elapses before the temperature of contiguous bodies is brought to equality; and in so far as Mr. Prevost's hypothesis overlooks this circumstance, which obviously depends upon the affinity existing between caloric and other bodies, it must be considered as im- perfect. * Phil. Trans. 1802, p. 403. Chap. II.] HEAT. 67 SECTION IV. OF THE EFFECTS OF CALORIC. Having in the preceding Sections considered the nature of ca- loric, the manner in which it moves through other bodies, and dis- tributes itself among them; let us now examine, in the next place, the effects which it produces upon other bodies, either by entering into them or separating from them. The knowledge of these effects we shall find of the greatest importance, both on account of the im- mense additional power which it puts into our possession, and of the facility with which it enables us to comprehend and explain many of the most important phenomena of nature. The effects which caloric produces on bodies may be arranged under three heads, namely, 1. Changes in bulk; 2. Changes in state; and, 3. Changes in combination. Let us consider these three sets of changes in their order. I. Of Changes in Bulk. It may be laid down as a general rule to which there is no known exception, that every addition or abstraction of caloric makes a corresponding change in the bulk of the body which has been sub- jected to this alteration in the quantity of its heat. In general the addition of heat increases the bulk of a body, and the abstraction of it diminishes its bulk: but this is not uniformly the case, though the exceptions are not numerous. Indeed these exceptions are not only confined to a very small number of bodies, but even in them they do not hold, except at certain particular temperatures; while at all other temperatures these bodies are increased in bulk when heated, and diminished in bulk by being cooled. We may there- fore consider expansion as one of the most general effects of heat. It is certainly one of the most important, as it has furnished us with the means of measuring all the others. Let us, in the first place, consider the phenomena of expansion, and then turn our attention to the exceptions which have been observed, 1. Though all bodies are expanded by heat and contracted by cold, and this expansion in the same body is always proportional to some function of the quantity of caloric added or abstracted; yet the absolute expansion or contraction has been found to differ ex- ceedingly in different bodies. In general, the expansion of gaseous bodies is greatest of all; that of liquids is much smaller, and that of solids is smallest of all. Thus, 100 cubic inches of atmospherig air, by being heated from the temperature of 32° to that of 212% are increased to 137*5 cubic inches; while the same augmentation of temperature only makes 100 cubic inches of water assume the 68 IMPONDERABLE BODIES. $ B°0K »- £ DIVISION 1 bulk of 104-5 cubic inches: and 100 cubic inches of iron, when heated from 32° to 212°, assume a bulk scarcely exceeding lOO'l cubic inches. From this example, we see that the expansion of air is more than eight times greater than that of water; and the ex- pansion of water about 45 times greater than that of iron. 2. An accurate knowledge of the expansion of gaseous bodies being frequently of great importance in chemical researches, many experiments have been made to ascertain it; yet, till lately, the problem was unsolved. The results of philosophers were so va- rious and discordant, that it was impossible to form any opinion on the subject. This was owing to the want of sufficient care in ex- cluding water from the vessels in which the expansion of the gases was measured. The heat which was applied converted portions of this water into vapour, which, mixing with the gas, totally disgui- sed the real changes in bulk which it had undergone. To this circumstance we are to ascribe the difference in the determinations of Deluc, General Roy, Saussure, Divernois, &c. Fortunately this point has lately engaged the attention of two very ingenious and precise philosophers; and their experiments, made with the proper precautions, have solved the problem. The experiments of Mr. Dalton of Manchester, were read to the Philosophical Society of Manchester in October 1801, and published early in 1802.* To him therefore the honour of the discovery of the law of the dila- tation of gaseous bodies is due : for Mr. Gay Lussac did not pub- lish his dissertation on the expansion of the gases! ^ more than six months after. Mr. Dalton's experiments are distinguished by a simplicity of apparatus, which adds greatly to their value, as it puts it in the power of others to repeat them without difficulty. It consists merely of a glass tube, open at one end, and divided into equal parts; the gas to be examined was introduced into it after being properly dried, and the tube is filled with mercury at the open end to a given point; heat is then applied, and the dilatation is observed by the quantity of mercury which is pushed out. Mr. Gay Lussac's apparatus is more complicated but equally precise; and as his experiments were made on larger bulks of air, their coincidence with those of Mr. Dalton adds considerably to the confidence which may be placed in the results. From the experiments of these philosophers it follows, that all gaseous bodies whatever undergo the same expansion by the same addition of heat, supposing them placed in the same circumstances. It is sufficient, then, to ascertain the law of expansion observed by any one gaseous body, in order to know the exact rate of dilatation of them all. Now, from the experiments of Gay Lussac we learn that air, by being heated from 32° to 212°, expands from 100 to 137*5 parts: the increase of bulk for 180° is then 37«5 parts- or supposing the bulk at 32° to be unity, the increase is equal to 0«375 * Manchester Memoirs, v. 593 f Ann. deChim.3cliii.13r Chap. II.] heat. 6.9 parts: this gives us 0«00208, or -j^th part, for the expansion of air for 1° of the thermometer. Mr. Dalton found that 100 parts of air, by being heated from 55° to 212°, expanded to 132«5'parts: this gives us an expansion of 0*00207, or ^^jd part, for 1°; which dif- fers as little from the determination of Lussac as can be expected in experiments of such delicacy. From the experiments of Gay Lussac it appears that the steam of water, and the vapour of ether, undergo the same dilatation with air when the same addition is made to their temperature. We may conclude, then, that all elastic fluids expand equally and uni- formly by heat. The following table gives us nearly the bulk of a given quantity of air at all temperatures from 32° to 212*. Temp. Bulk. Temp. 1 Bulk. Temp. Bulk. Temp. Bulk. 32° looqooo 53o 1043749 73° 1085416 93° 1127083 33 1002083 54 1045833 74 1087499 94 1129166 34 1004166 55 104791'' 75 1089383 95 1131249 35 1006249 56 1049999 76 1091666 96 1133333 36 1008333 57 1052083 77 1093749 97 1135416 37 1010416 58 105416 78 1095833 98 1137499 38 1012499 59 1056249 79 1097916 99 1139583 39 1014583 60 1058333 80 1099999 100 1141666 40 1016666 61 1060416 81 1102083 110 1162499 41 1018749 62 1062499 82 1104166 120 1183333 42 1020833 63 1064583 83 1106249 130 1204166 43 1022916 64 1066666 84 1108333 140 1224999 44 1024759 65 1068749 85 1110416 150 1245833 45 1027083 66 1070833 86 1112499 160 1266666 46 1029166 67 1072916 87 1114583 170 1287499 47 1031249 68 1074999 88 1116666 180 1308333 48 1033333 69 J 077083 89 1118749 190 1329166 49 1035416 70 1079166 90 1120833 200 1349999 50 1037499 71 1081249 91 1122916 210 1370833 51 1039583 72 1083333 92 1124999 212 1374999 52 1041666 3. The expansion of liquid bodies differs from that of the elas- tic fluids, not only in quantity, but in the want of uniformity with which they expand when equal additions are made to the tempera- ture of each. This difference seems to depend upon the fixity or volatility of the component parts of the liquid bodies; for, in gene- ral, those liquids expand most by a given addition of heat, whose boiling temperatures are lowest, or which contain in them an ingre- dient which readily assumes the gaseous form. Thus mercury expands much less when heated to a given temperature than water, which boils at a heat much inferior to mercury; and alcohol is much more expanded than water, because its boiling temperature is lower. In like manner, nitric acid is much more expanded than 70 IMPONDERABLE BODIES. f Di^2?f; sulphuric acid; not only because its boiling point is lower, but be- cause a portion of it has a tendency to assume the form of an elas- tic fluid. " This rule holds at least in all the liquids whose expan- sion I have hitherto tried. We may consider it therefore as a pretty general fact, that the higher the temperature necessary to cause a liquid to boil, the smaller the expansion is, which is pro- duced by the addition of a degree of heat; or, in other words, the expansibility of liquids is nearly inversely as their boiling tem- perature. 4. Another circumstance respecting the expansion of liquids de- serves particular attention: the expansibility of every one seems to increase with the temperature ; or, in other words, the nearer a li- quid is to the temperature at which it boils, the greater is the ex- pansion produced by the addition of a degree of caloric: and, on the other hand, the farther it is from the boiling temperature, the smaller is the increase of bulk produced by the addition of a degree of caloric. Hence it happens, that the expansion of those liquids approaches nearest to equability whose boiling temperatures are highest; or, to speak more precisely, the ratio of the expansibility increases the more slowly the higher the boiling temperature is. 5. These observations are sufficient to show us, that the expan- sion of liquids is altogether unconnected with their density. It de- pends upon the quantity of heat necessary to cause them to boil, and to convert them into elastic fluids. But we are altogether ignorant at present of the reason why different liquids require different tem- peratures to produce this change. 6. The following table exhibits the dilatation of various liquids from the temperature of 32° to that of 212°, supposing their bulk at 32 to be 1. Muriatic acid* (sp. gr. 1*137) Nitric acid* fsp. gr. 1*40) Sulphuric acid* (sp. gr. 1*85) Alcohol* ... Water* - Water saturated with common salt* Sulphuric ether* Fixed oils* - Oil of turpentine* Mercury* - Mercury! - - - Mercury! - Mercury§ - Mercury|| ... Doctor Young has observed that if we denote a degree of Fah- renheit's thermometer by f, the expansion of water, reckoning either * Dalton, New System of Chemical Philosophy, i. 36. f Lord Charles Cavendish. * General Roy. § Haellstroem, Gilbert's Annaien, xvii. 107. ) Lalande and Delisle, Ibid. p. 102. 0-0600 ss 1 TT 0*1100 ^s 1 0*0600 zss 1 TT 0*1100 = 1 s7 0-0466 = l 0.0500 =: 2V 0*0700 =: T*t 0*0800 = 1 IS? 0*0700 = 1 TT 0*0200 = i J1S 0-01872 = TT 0*0168 = l 0*0175$ = i 0*0150 ^ ■^ Chap. II.] HEAT. 71 way from 39*, is nearly represented by .0000022 f2—00000000435 f3. He gives the following table of the expansion of this liquid from the experiments of Gilpin and Kirwan.* Expansion Expansion Temp. i--------------- Observed. >.------x Calculated. Temp. r—---------- Observed. -------^ Calculated. 30° Gilpin •00020 •00Q18 74° Gilpin •00251 •00251 32 G •00012 •00011 79 G •00321 •00326 34 G •00006 •00005 90 G •00491 •00513 39 G •00000 •00000 100 G •00692 •00720 44 G •00006 •00005 102 Kirwan-00760 •00763 48 G •00018 •00018 122 K •01258 •01264 49 G •00022 •00022 142 K •01833 •01859 34 G •00049 •00048 162 K •02481 •02512 59 G •00086 •00084 182 K •03198 •03219 64 G •00133 •00130 202 K •04005 ■03961 69 G •00188 •00186 212 K •04333 •04332 The following table exhibits the degrees marked upon thermo- meters filled with different liquids at the same temperature as de- termined by the experiments of De Luc! The tubes containing these liquids were of glass ; but as he does not mention their capa- cities, nor the value of a degree, the table does not enable us to de- termine the expansion of the liquids used. Mercury. Olive oil. Essential oil of camomile. Essential oil of thyme. Alcohol ca-pable of set-ting fire to gunpowder. Water satu-rated with common salt. Water. 80° 80° 80° 80° 80° 80° 80° 75 74*6 74*7 T4-3 73*8 74'1 71-0 70 69*4 69'5 68-8 67-8 68*4 62*0 65 64*4 64-3 63-5 61-9 62*6 53*5 60 59*3 59-1 58-3 56-2 57*1 45-8 55 54*2 53-9 53*3 50-7 51*7 38-5 50 49*2 48-8 48-3 45«3 46.6 32-0 45 44-0 48-6 43-4 40-2 41-2 26*1 40 39*2 38-6 38-4 35-1 36*3 20*5 35 34*2 33-6 33-5 30-3 31*3 15-9 30 29«3 28-7 28-6 25-6 26-5 11-2 25 24-3 23*8 23-8 21-0 21*9 7*5 20 19*3 18*9 19-0 16-5 17*3 41 15 14-4 14*1 14«2 12-2 12*8 1-6 10 9-5 9-3 9-4 7*9 8-4 0*2 5 4-7 4-6 4-r 3-9 4-2 0-4 0 0 0 0-0 0-0 0-0 0-0 0*0 -5 -3-9 -4*1 -10 -7*7 -8*0 * Young's Lectures on Natural Philosophy ii. 392. ! Rechercb.es sur les Modifications de 1'Atmosphere, i. 271. -*2 IMPONDERABLE BODIES. f mv^o* l'' In these thermometers O denotes the temperature at which water freezes, 80° the temperature at which it boils. Gay Lussac* has lately turned his attention to the phenomena of the expansion of liquids. The following table exhibits the result of his researches. He supposes the volume of each of the liquids at its boiling temperature to be 1000. The table represents the con- tractions which each liquid experienced when cooled down every five degrees centigrade below its boiling point. The temperatures at which the different liquids tried boiled were as follows : Water - - 212° I Sulphuret of carbon 116-1 Alcohol - - 173*14 J Sulphuric ether - 96*2 Temper-ature. Water. Contractions. Alcohol. Contractions Sulphuret ot carbon. Contractions. Ether. Contractions. 0° 0-00 0-00 0*00 0*00 5 3*34 5.55 6*14 8*15 10 6-61 11-43 12*01 16*17 15 10*50 17-51 17*98 24-16 20 13*15 24-34 23*80 31*83 25 16-06 29-15 29-65 39*14 30 18-85 34-74 35.06 46*42 35 21*52 40*28 40*48 52*06 40 24*10 45*68 45*77 58-77 45 26-50 50*85 51*08 65-48 50 28*56 56-02 56*28 72-01 55 30*60 61-01 61*14 78-38 60 32*42 65*96 66-21 65 34*02 70-74 70 35-47 75*48 75 36-70 80*11 From the preceding table it appears that alcohol and sulphuret of carbon undergo the same dilatation. Gay Lussac has shown that they likewise form the same volume of vapour when exposed to a boiling temperature. Alcohol forms 488-3 its volume of vapour. Sulphuret of carbon 491-1 its volume of vapour. 7. The expansion of solid bodies is so small that many precau- tions are necessary to measure it with precision. So far as obser- vation has gone it is equable. In this respect resembling the ex- pansion of the gases. I shall introduce here in the first place the table of the expansion of different solid bodies from 32° to 212° as determined by Lavoisier and Laplace, in 1782. The experiments seem to have been made with very great care. They were suppos- ed to have been lost; but have lately been recovered and published by Biot.! * Ann. de Cliim. et Phys. ii. 130. t Traite de Physique, i. 158. Chap. II.] HEAT. 73 Length of a rule at Dilatation Substances tried. 21'2" which at 32S in vulgar is 1,0(KXXKXX). fractions. Glass of Saint Gobain ; 1,00089089 . l 1 1'2 iE Glass tube without lead 1,0©087572 . • TT1-* Ditto . 1,00089760 . 1 ill* Dutb 1,00091751 . 1 1090 English flint glass 1,00081166 . • T2T5" French glass with lead 1,00087199 . l__ ' TT4 7 Copper 1,00172244 . TiT Copper , 1,00171222 . I T8~T Brass . 1,00186671 . ■ rh Brass 1.00188971 . i 5 2"9 Hammered iron .1,00122045 . 1 "STTi Iron wire 1,00123504 . . 1 "§"12 Hard steel 1,00107875 . 1' T2"T Soft steel 1,00107956 . l T2~?" Tempered steel 1,00123956 . . TftfT Lead . 1,00284836 . . l 35 1 Malacca tin . 1,00193765 . TTB" Tin from Falmouth 1,00217298 . •1 462 Cupelled silver 1,00190974 . 1 IT* Silver, Paris standard 1,00190868 . i 524 Pure gold 1,00146606 . 1 6~8"2~ Gold, Paris standard, not softened 1,00155155 . . 1 645 Ditto, softened 1,00151361 . 1 TST In the year 1754, Mr. Smeaton published a set of experiments on the expansion of different substances measured by means of a very ingenious instrument of his own invention, described by him in the Philosophical Transactions for that year.* The following table shows the expansions which the different substances tried, undergo from 32° to 212° supposing the original bulk to be 1. White glass barometer tube 0*00083 Antimony - 0*001083 Blistered steel - 0*001125 Hard steel - 0*001225 Iron - - - 0*001258 Bismuth ------ 0*001392 Copper hammered - - - - 0*001700 Copper, 8 parts mixed with tin 1 0*0018166 Brass, 16 parts with tin 1 0*001908 Brass wire - 0*001933 Speculum metal - 0*001933 Spelter solder, viz. brass 2, zinc 1 0*002058 * Phil. Trans. 1754, p. 598. Vol. I. K 74 IMPONDERABLE BODIES. BOOK 1. DIVISION 1. 0*002283 0*002483 0*002508 0*002692 0*002867 0*002942 0*003011 Fine pewter..... Grain tin - Soft solder, viz. lead 2, tin 1 - Zinc, 8 with tin 1, a little hammered Lead ------ Zinc ------ Zinc hammered 5 inch per foot The following table exhibits the dilatations of different sub- stances as determined by General Roy, the accuracy of whose ex- periments is well known. Glass tube - Glass rod - Cast-iron prism - Steel rod - - ■ Brass scale, supposed from Hamburg English plate brass rod English plate brass trough In the following table I shall give the result of the trials of some other artists and philosophers on the expansion of some other bodies, reckoning as usual the bulk at 32° to be 1. The expansion given is from 32° to 212°. 0*00077615 0*00080787 0-0011094 0-0011447 0*0018554 0*001875 0*0018928 Steel Silver Copper - lion wire Platinum Platinum Palladium Iron 0*0011899. 0-0020826. 0*0019188. 0.0014401. 0*0009918. 0*00085655. 0*0010. 0*001446. Troughton. Troughton. Troughton. Troughton. Troughton. Borda. Wollaston. Haellstroem. The expansion of glass being frequently an important point in experiment has been examined with great care. But different kinds of glass differ so much from each other that no general rule can be laid down. Lavoisier and Laplace found that it was the less dilatable by heat the more lead it contained.*! Several deter- minations will be found in the preceding tables, and I shall add some more here. Ramsden found the expansion between 32° and 212° of a solid glass rod 0*0096944, and that of a glass tube 0*0093138. De Luc's experiments on the expansion of thermome- ter and barometer tubes may be seen in the following table. Temp. Bulk. Temp. Bulk. Temp. Bulk. 32° 100000 100° 100023 167° 100056 50 100006 120 100033 190 100069 70 100014 150 100044- 212 100083 * Biot. Traite de Physique, i. 157. ! [From the finer kind of barometer tubes, I have procured by powdering Uie glass and mixing it with a small quantity of charcoal, from l-5th to l-4th its weight of metallic lead. The lead exists in. the glass in the state of an oxyd.—C.] Chap. II.] heat. 75 8. The property which bodies possess of expanding, when heat is applied to them, has furnished us with an instrument for mea- suring the relative temperatures of bodies. This instrument is the thermometer. A thermometer is merely a hollow tube of glass, hermetically sealed, and blown at one end into a hollow globe or bulb. The bulb and part of the tube are filled with mercury. When the bulb is plunged into a hot body, the mercury expands, and of course rises in the tube; but when it is plunged into a cold body, the mercury contracts, and^£course falls in the tube. The rising of the mercury indicates a^^ncrease of heat; its falling a diminution of it; and the quantity which it rises and falls indicates the proportion of increase or diminution. To facilitate observa- tion, the tube is divided into a number of equal parts called degrees. The thermometer, to which we are indebted for almost all the knowledge respecting caloric which we possess, was invented about the beginning of the 17th century; and is supposed by some to have been first thought of by Sanctorio, the celebrated founder of statical medicine. The first rude thermometer was improved by the Florentine academicians and by Mr. Boyle; but it was Sir Isaac Newton who rendered it really useful, by pointing out the method of constructing thermometers capable of being compared together. If we plunge a thermometer ever so often into melting snow, it will always stand at the same point. Hence we learn that snow always begins to melt at the same temperature. Dr. Hooke ob- served also, that if we plunge a thermometer ever so often into boiling water, it always stands at the same point, provided the pressure of the atmosphere be the same; consequently water (other things being the same) always boils at the same temperature. If therefore we plunge a new made thermometer into melting snow, and mark the point at which the mercury stands in the tube; then plunge it into boiling water, and mark the new point at which the mercury stands; then divide the portion of the tube between the two marks into any number of equal parts, suppose 100, calling the freezing point 0, and the boiling point 100;—every other thermo- meter constructed in a similar manner will stand at the same de- gree with the first thermometer, when both are applied to a body of the same temperature. All such thermometers therefore may be compared together, and the scale may be extended to any length both above the boiling point and below the freezing point. Newton first pointed out the method of making comparable ther- mometers ;* but the practical part of the art was greatly simplified by Mr. Fahrenheit of Amsterdam and Dr. Martine of St. An- drew's.! From the different methods followed by philosophical instrument makers in determining the boiling point, it was found, that thermometers very seldom agreed with each other, and that * Phil. Trans. Abr. iv. i. \ On the Construction and Graduation of Thermometers. 76 IMPONDERABLE BODIES. f nSrVs^ 1. they often deviated several degrees from the truth. This induced Mr. Cavendish to suggest to the Royal Society the importance of publishing rules for constructing these very useful instruments. A committee of the society was accordingly appointed to consider the subject. This committee published a most valuable set of direc- tions, which may be consulted in the Philosophical Transactions.* The most important of these directions is, to expose the whole of the tube as well as the ball of the thermometer to steam, when the boiling water point is to be determined. They recommend this to be done when the barometer sWds at 29*8 inches. Mercury is the liquid which answers best for thermometers, be- cause its expansion is most equable, owing to the great distance from its boiling and freezing points. There are four different ther- mometers used at present in Europe, differing from one another in the number of degrees into which the space between the freezing and boiling points is divided. These are Fahrenheit's, Celsius's, Reaumur's, and De Lisle's. Fahrenheit's thermometer is used in Britain. The space be- tween the boiling and freezing points is divided into 180°: but the scale begins at the temperature produced by mixing together snow and common salt, which is 32° below the freezing point; of course the freezing point is marked 32°, and the boiling point 212°.! The thermometer of Celsius is used in Sweden; it has been used also in France since the Revolution, under the name of the ther- mometre centigrade. In it the space between the freezing and boil- ing points is divided into 100°. The freezing point is marked 0, the boiling point 100°.! The thermometer known by the name of Reaumur, which was in fact constructed by De Luc, was used in France before the Revo- lution. In it the space between the boiling and freezing points is divided into 80°. The freezing point is marked 0, the boiling point 80°.$ De Lisle's thermometer is used in Russia. The space between the boiling and freezing points is divided into 150°: but the gradu- ation begins at the boiling point, and increases towards the freez- ing point. The boiling point is marked 0, the freezing point 150°.|| * Phil. Trans. 1777, p. 816. ! This is the thermometer always used throughout this Work, unless when some other is particularly mentioned. \ Consequently the degrees of Fahrenheit are to those of Celsius, as 180 : 100 = 18 : 10= 9 : 5. That is, 9° of Fahrenheit are equal to 5° of Celsius. Therefore, to reduce the 9 C degrees of Celsius to those of Fahrenheit, we have F=-----(- 32. § Consequently 180 F = 80 R, or 18 F = 8 R, or 9 F = 4 R; therefore F = 9R i 32. | Hence 180 F = 150 D, or 6 F= 5 D. To reduce the degrees of De Lisle's thermo- meter under the boiling point to those of Fahrenheit, we have F= 212------; to reduce 5 r ri those above the boiling point, F = 212 -f----• Chap. II.] HEAT. 77 9. Having now considered the phenomena and laws of expan- sion as far as they are understood, it will be proper to state the "ex- ceptions to this general effect of heat, or the cases in which expan- sion is produced, not by an increase, but by a diminution of tem- perature. These exceptions may be divided into two classes. The first class comprehends certain liquid bodies which have a maxi- mum of density corresponding with a certain temperature; and which,, if they be heated above that temperature, or cooled down below it, undergo in both cases an expansion or increase of bulk. The second class comprehends certain liquids which suddenly be- come solid when cooled down to a certain temperature; and this solidification is accompanied by an increase of bulk. 10. Water furnishes a remarkable example of the first class of bodies. This liquid is at its maximum of density when nearly at the temperature of 40°. If it be cooled down below 40°, it expands as the temperature diminishes; if it be heated above 40°, it in like manner expands as the temperature increases. Thus two opposite effects are produced by heat upon water, according to the tempera- ture of that liquid. From 40° to 32°, and downwards, heat dimi- nishes the bulk of water; but from 40° to 212°, and upwards, it in- creases its bulk. Such is the opinion at present received by most persons, and which is considered as the result of the most exact experiments. The facts which led to this conclusion were first observed by the Florentine academicians. An account of their experiments was published in the Philosophical Transactions for 1670.* They filled with water a glass ball, terminating in a narrow graduated neck, and plunged it into a mixture of snow and salt. The water started suddenly up into the neck, in consequence of the construction of the vessel, and slowly subsided again as the cold affected it. After a certain interval it began to rise again, and continued to ascend slowly and equably, till some portion of it shot into ice, when it sprung up at once with the greatest velocity. The attention of the Royal Society was soon afterwards called to this remarkable expan- sion by Dr. Croune, who, in 1683, exhibited an experiment simi- lar to that of the Florentine philosophers, and concluded from it, that water begins to be expanded by cold at a certain temperature above the freezing point. Dr. Hooke objected to this conclusion, and ascribed the apparent expansion of the water to the contraction of the vessel in which the experiment was made. This induced them to cool the glass previously in a freezing mixture, and then to fill it with water. The effect, notwithstanding this precaution, was the same as before.! Mr. De Luc was the first who attempted to ascertain the exact temperature at which this expansion by cold begins. He placed it at 41°, and estimated the expansion as nearly equal, when water is heated or cooled the same number of degrees * Phil. Trans. No. 66, or vol. v. p. 2020. Abridgement, i. 540. f Birche's Hist, of the Royal Society, iv. 253. 78 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. above or below 41°. He made his experiments in glass thermome- ter-tubes, and neglected to make the correction necessary for the contraction of the glass ; but in a set of experiments by Sir Charles Blagden and Mr. Gilpin, made about the year 1790, this correc- tion was attended to. Water was weighed in a glass bottle at every degree of temperature from 32° to 100°, and its specific gravity as- certained. They fixed the maximum of density at 39°, and found the same expansion very nearly by the same change of temperature either above or below 39°. The followihg table exhibits the bulk of water at the corresponding degrees on both sides of 39°, accord- ing to their experiments.* Specific Gra-vity. Bulk of Wa-ter. Temper-ature. Bulk of Wa-ter. Sp. Gravity of Ditto. 100000 39 1 -00000 1-00000 00 38 37 36 35 34 33 32 40 41 42 43 44 45 46 00 1-00000 0-99999 01 01 0-99999 0-99998 02 02 0*99998 0-99996 04 04 0-99996 0-99994 06 06 0*99994 0*99991 08 08 0*99991 0*99988 12 12 0*99988 Mr. Dalton, in a set of experiments published in 1802, obtained nearly the same result as De Luc. He placed the maximum den- sity at 42-5°, not making any correction for the contraction of the glass; and observed, as Blagden had done before him, that the ex- pansion is the same on both sides of the maximum point, when the change of temperature is the same, and continues however low down the water be cooled, provided it be not frozen.! All these experiments had been made by cooling water in glass vessels; but when the French were forming their new weights and measures, the subject was investigated by Lefebvre-Gineau in a different manner. A determinate bulk of water at a given tempe- rature was chosen for the foundation of their weights. To obtain it, a cylinder of copper, about nine French inches long, and as many in diameter, was made, and its bulk measured with the ut- most possible exactness. This cylinder was weighed in water of various temperatures. Thus was obtained the weight of a quantity * Phil. Trans. 1792, p. 428. ! Manchester Mem. v. 374. Chap. II.] heat. 79 of water equal to the bulk of the cylinder; and this, corrected by the alteration of the bulk of the cylinder itself from heat or cold, gave the density of water at the temperatures tried. The result was, that the density of the water constantly increased till the tem- perature of 40°, below which it as constantly diminished.* These experiments seem to have been made about the year 1795. More lately a set of experiments was tried by Haellstroem exactly in the same way; but he substituted a cylinder of glass for the one of me- tal. The result which he obtained was the same. The necessary corrections being made, he found the maximum density of water lie between 4° and 5° of Celsius, or nearly at 40° of Fahrenheit.! Still more lately, a set of experiments have been published by Dr. Hope, which lead to the same result in a different way. He employed tall cylindrical glass jars filled with water of different temperatures, and having thermometers at their top and bottom. The result was as follows; 1. When water was at 32°, and exposed to air of 61°, the bottom thermometer rose fastest till the water be- came of 38°, then the top rose fastest. Just the reverse happened when the water was 53°, and exposed to the cold water surrounding the vessel; the top thermometer was highest till the water cooled down to 40°, then the bottom one was highest. Hence it was in- ferred, that water when heated towards 40° sunk down, and above 40° rose to the top, and vice versa. 2. When a freezing mixture was applied to the top of the glass cylinder (temp, of air 41°), and continued even for several days, the bottom thermometer never fell below 39°; but when the freezing mixture was applied to the bot- tom, the top thermometer fell to 34° as soon as the bottom one. Hence it was inferred, that water when cooled below 39° cannot sink, but easily ascends. 3. When the water in the cylinder was at 32°, and warm water applied to the middle of the vessel, the bottom thermometer rose to 39* before the top one was affected; but when the water in the cylinder was at 39-5°, and cold was applied to the middle of the vessel, the top thermometer cooled down to 33° be- fore the bottom one was affected.! Count Rumford has lately published a set of experiments con- ducted nearly on the same principles with those of Dr. Hope, and leading to the same results. They are contrived with his usual in- genuity ; but as they are of posterior date, and add nothing to the facts above stated, I do not think it necessary to detail them.§ Dr. Hope's experiments and those of Count Rumford coincide with- those above related, in fixing the maximum density of water at be- tween 39° and 40°. Such are the experiments by which this very curious and impor- tant fact seems perfectly established. The mean of them all makes * Jour, de Phys. xlix. 171; and Hauy's Traite de Physique, i. 55. and 181. ! Gilbert's Annalen der Physik, xvii. 207. t See Edin. Trans, vol. vi. The paper was published before October 1804 § See Nicholson's Journal, xi. 228. Aug. 1805 80 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. the point at which the specific gravity of water is a maximum 39-81°. We may therefore without much risk of error consider it in round numbers as 40°, which was the temperature selected by the French Philosophers when they fixed their new standard of weights and measures. 11. That class of bodies which undergo an expansion when they change from a liquid to a solid body by the diminution of tempera- ture, is very numerous. Not only water when converted into ice undergoes such an expansion, but all bodies which by cooling as- sume the form of crystals. The prodigious force with which water expands in the act of freezing has been long known to philosophers. Glass bottles filled with water are commonly broken in pieces when the water freezes. The Florentine academicians burst a brass globe, whose cavity was an inch in diameter, by filling it with water and freezing it. The force necessary for this effect was calculated by Muschenbroeck at 27720 lbs. But the most complete set of experiments on the ex- pansive force of freezing water are those made by Major Williams at Quebec, and published in the second volume of the Edinburgh Transactions. This expansion has been explained by supposing it the consequence of a tendency which water, in consolidating, is observed to have to arrange its particles in one determinate manner, so as to form prismatic crystals, crossing each other at angles of 60° and 120°. The force with which they arrange themselves in this manner must be enormous, since it enables small quantities of water to overcome so great mechanical pressures. I tried various methods to ascertain the specific gravity of ice at 32°: the one which succeeded best was, to dilute spirits of wine with water till a mass of solid ice put into it remained in any part of the liquid without either sinking or rising. I found the specific gravity of such a liquid to be 0-92; which of course is the specific gravity of ice, supposing the specific gravity of water at 60° to be 1. This is an expansion much greater than water experiences even when heated to 212°. We see from this, that water, when converted into ice, no longer observes an equable expansion, but undergoes a very rapid and considerable augmentation of bulk (from crystallization.) The same expansion is observed during the crystallization of most of the salts; all of them at least which shoot into prismatic forms. Hence the reason that the glass vessels in which such li- quids are left usually break to pieces when the crystals are formed. A number of experiments on this subject have been published by Mr. Vauquelin.* Several of the metals have the property of expanding at the mo- ment of their becoming solid. Reaumur was the first philosopher who examined this point. Of all the metallic bodies that he tried, he found only three that expanded, while all the rest contracted on becoming solid. These three were, cast iron, bismuth^ and anti- * Ann. deChim. xiv. 286. Chap. II.] heat. 81 mony.* Hence the precision with which cast iron takes the im- pression of the mould. [Hence the use of antimony to the type- founder.—C] This expansion of these bodies cannot be considered as an ex- ception to the general fact, that bodies increase in bulk when heat is added to them ; for the expansion is the consequence, not of the diminution of heat, but of the change in their state from liquids to solids, and the new arrangement of their particles which accom- panies or constitutes that change [i. e. their tendency to crystal- lization.—C] 12. It must be observed, however, that all bodies do not expand when they become solid. There are a considerable number which diminish in bulk ; and in these the rate of diminution in most cases is rather increased by solidification. When liquid bodies are con- verted into solids, they either form prismatic crystals, or they form a mass in which no regularity of arrangement can be perceived. In the first case, expansion accompanies solidification: in the second place, contraction accompanies it. Water and all the salts furnish instances of the first, and tallow and oils are examples of the se- cond. In these last bodies the solidification does not take place instantaneously, as in water and salts, but slowly and gradually; they first become viscid, and at last quite solid. Most of the oils when they solidify, form very regular spheres. The same thing happens to honey and to some of the metals, as mercury, which Mr. Cavendish has shown from his own experiments, and those of Mr. Macnab, to lose about ^-d of its bulk in the act of solidification.! When sulphuric acid congeals, it does not perceptibly expand, nor does it in the least alter its appearance. Sulphuric acid, of the specific gravity 1-8, may be cooled down in thermometer tubes to - 36° before it freezes; and during the whole process it conti- nually contracts. At -36©, or about that temperature, it freezes; but its appearance is so little altered, that I could not satisfy myself whether or not the liquid was frozen till I broke the tube. It was perfectly solid, and displayed no appearance of crystallization. On • the other hand, cast iron expands in the act of congealing. II. Changes in the State of Bodies. All substances in nature, as far as we are acquainted with them, occur in one or other of the three following states; namely, the state of solids, of liquids, or of elastic fluids or vapours. It has been ascertained, that in a vast number of cases, the same sub- stance is capable of existing successively in each of these states. Thus sulphur is usually a solid body; but when heated to 218°, it is converted into a liquid; and at a still higher temperature (about V * Mem. Par. 1726, p. 273. Berthollett's Statique Chimique, ii. 348. f Phil. Trans. 1783, p. 23. Vol. I. L 82 IMPONDERABLE BODIES. C BOOK I £ DIVISION 1. 570°,) it assumes the form of an elastic vapour of a deep brown colour. Thus also water in our climate is usually a liquid; but when cooled down to 32°, it is converted into a solid body, and at 212° it assumes the form of an elastic fluid. All solid bodies, a very small number excepted, may be convert- ed into liquids by heating them sufficiently; and, on the other hand, every liquid is convertible into a solid body by exposing it to a sufficient degree of cold. All liquid bodies may, by heating them, be converted into elastic fluids, and a great many solids are capa- ble of undergoing the same change; and, lastly, the numben of elastic fluids which by cold are condensible into liquids or solids is by no means inconsiderable. These facts have led philosophers to form this general conclusion, " That all bodies, if placed in a tem- perature sufficiently low, would assume a solid form ; that all solids become liquids when sufficiently heated; and that all liquids, when exposed to a certain temperature, assume the form of elastic fluids." The state of bodies then depends upon the temperature in which they are placed; in the lowest temperatures they are all solid, in higher temperatures they are converted" into liquids, and in the high- est of all they become elastic fluids. The particular temperatures at which bodies undergo those changes, are exceedingly various, but they are always constant for the same bodies. Thus we see that heat produces changes on the state of bodies, converting them -all, first into liquids, and then into elastic fluids. I. When solid bodies are converted by heat into liquids, the change in some cases takes place at once. There is no interval be- tween solidity and liquidity ; but in other cases a very gradual change may be perceived: the solid becomes first soft, and it pas- ses slowly through all the degrees of softness, till at last it becomes perfectly fluid. The conversion of ice into water is an instance of the first change ; for in that substance there is no intervening state between solidity and fluidity. The melting of glass, of wax, and of tallow, exhibits instances of the second kind of change, for these bodies pass through every possible degree of softness before they terminate in perfect fluidity. In general, those solid bodies which crystallize or assume regular prismatic figures have no interval be- tween solidity and fluidity; while those that do not usually assume such shapes have the property of appearing successively in all the intermediate states. 1. Solid bodies never begin to assume a liquid form till they are heated to a certain temperature: this temperature is constant in all. In the first class of bodies it is very well defined: but in the second class, though it is equally constant, the exact temperature of fluidity cannot be pointed out with such precision, on account of the infi- nite number of shades of softness through which the bodies pass before *Hiey acquire their greatest possible fluidity. But even in these bodies we can easily ascertain, that the same temperature al- ways produces the same degree of fluidity. The temperatures at Chap. II.] heat. S3 which this change from solidity to liquidity takes place receive dif- ferent names according to the usual state of the body thus chang- ed. When the body is usually observed in a liquid state, we call the temperature at which it assumes the form of a solid its freezing point, or congealing point. Thus the temperature in which water becomes ice is called the freezing point of water; on the other hand, when the body is usually in the state of a solid, we call the temperature at which it liquifies its melting point: thus 218° is the melting point of sulphur; 442° the melting point of tin. 2. The following table contains a list of the melting points of a considerable number of solid bodies : Substance. Ice Milk Vinegar Blood Oil of Bergamot Wines Substance. Lead Melting Point 612° Bismuth - - 476 Tin - 442 Sulphur - - 218 Wax - 142* Spermaceti Phosphorus Tallow 112 108 92 Oil of anise - 50 Olive oil - - 36 Oil of turpentine Mercury - Liquid ammonia Ether Melting Point. 32 30 28 25 23 20 14 — 39 — 46 — 46 3. Though the freezing point of water be 32°, yet it may be cooled down in favourable circumstances considerably below that temperature, before it begins to shoot into crystals. Experiments were made on this subject by Mairan and Fahrenheit; but it is to Sir Charles Blagden that we are indebted for the fullest investiga- tion of it. He succeeded in cooling water down to 22° before it froze, by exposing it slowly to the action of freezing mixtures. The experiment succeeds best when the water tried is freed from air. It ought also to be transparent; for opaque bodies floating in it cause it to shoot into crystals when only a few degrees below the freezing point. When a piece of ice is thrown into water thus cooled, it causes it instantly to shoot out into crystals. The same effect is produced by throwing the liquid into a tremulous motion; but not by stirring it. It freezes also when cooled down too sud- denly.! 4. When salts are dissolved in water, it is well known that its freezing point is in most cases lowered. Thus sea-water does not freeze so readily as pure water. The experiments of Sir Charles Blagden have given us the point at which a considerable number of these solutions congeal. The result of his trials may be seen in the following table. The first column contains the names of the salts ; the second the quantity of salt, by weight, dissolved in 100 parts of water ; and the third, the freezing point of the solution.! * Bleached wax, 155°. Nicholson. ± See Phil. Trans. 1788, p. 277. f BlagdeD, Phil. Trans. 1788, p. 125. Names of Salts. Common salt Proportion 25. Sal ammoniac - 20 Rochelle salt 50 Sulphate of magnesia Nitre - 41-6 12-5 Sulphate of iron 41-6 Sulphate of zinc 53-3 34- IMPONDERABLE BODIES. S BOOK I. £ DIVISION 1. Freezing point. 4 8 21 25-5 26 28 28-6 From this table it appears that common salt is by far the most effi- cacious in lowering the freezing point of water. A solution of 25 parts of salt in 100 of water freezes at 4°. These solutions, like pure water, may be cooled down considerably below their freezing point without congealing; and in that case the congelation is pro- duced by means of ice just as in common water, though more slowly. When the proportion of the same salt held in solution by water is varied, it follows from Sir Charles Blagden's experiments, that the freezing point is.always proportional to the quantity of the salt. For instance, if the addition of ^th of salt to water lowers its freez- ing point 10 degrees, the addition of -^ths will lower it 20°. Hence, knowing from the preceding table the effect produced by a given proportion of a salt, it is easy to calculate what the effect of any other proportion will be. The following table exhibits the freezing points of solutions of different quantities of common salt in 100 parts of water, as ascertained by Blagden's trials, and the same points calculated on the supposition that the effect is as the propor- tion of salt. Quantity of salt Freezing point r» 1. i i *• to 100 of water. by experiments. Do. by calculation. 3-12 - - 28 -f - - 28-5 4-16 - - 27-5 - - 27-3 6-25 - - 25-5 - - 25 10-00 - - 21-5 - - 20-75 12-80 - - 18-5 - - 17-6 16-1 - - 13-5 - - 14 20 9-5 9-8 22-2 - - 7-2 - 7 25 - - 4 - - 4 5. The strong acids, namely, sulphuric and nitric, which are in reality compounds containing various proportions of water accord- ing to their strength, have been shown by Mr. Cavendish, from the experiments of Mr. Macnab, to vary in a remarkable manner in their point of congelation according to circumstances. The fol- lowing are the most important points respecting the freezing of these bodies that have been ascertained. When these acids diluted with water are exposed to cold the weakest part freezes, while a stronger portion remains liquid ; so that by the action of cold they are separated into two portions dif- fering very much in strength. This has been termed,by Mr. Ca- vendish the aqueous congelation of these bodies. Chap. II.] HEAT. 85 When they are very much diluted, the whole mixture, when ex- posed to cold, undergoes the aqueous congelation; and in that case, it appears from Blagden's experiments, that the freezing point of water is lowered by mixing it with acid rather in a greater ratio than the increase of the acid. The following table exhibits the freezing point of mixtures of various weights of sulphuric acid, ot the density 1-837 (temperature 62°), and of nitric acid ot the den- sity 1-454, with 100 parts of water. SULPHURIC ACID. NITRIC ACID. Proportion Freezing Proportion F^!!™* ofacid. point. ofacid. pomt. 10 - - 24-5 - - 10 - - 22 20 - - 12-5 - - 20 - - 10-5 25 - - 7-5 - - 23-4 - - 7* The concentrated acids themselves undergo congelation when exposed to a sufficient degree of cold; but each of them has a par- ticular strength at which it congeals most readily. When either stronger or weaker, the cold must be increased. The following table, calculated by Mr. Cavendish from Mr. Macnab's experi- ments, exhibits the freezing points of nitric acid of various de- grees of strength.! Strength. Freezing point. Difference. 568 - - —45-5 - - +15*4 538 - - —30-1 - - +12 508 - - —18-1 - " + 8'7 478 — 9-4 - - + 5-3 448 - — 4-1 - - +1*7 418 - - — 2-4 - - — 1*8 388 - — 4-2 - - — S-5 358 - - — 9-7 - . — 8 328 - - —17-7 - - —10 298 - - —27-7 The following table exhibits the freezing points of sulphuric acid of various strengths.! Strength. Freezing point. 977 - - - - + 1 918 - —26 846 +42 758 —*5 Mr. Keir had previously ascertained that sulphuric acid of the specific gravity 1-780 (at 60°) freezes most easily, requiring only the temperature of 46°. This agrees nearly with the preceding ex- periments, as Mr. Cavendish informs us that sulphuric acidot that specific gravity is of the strength 848. From the preceding table • Phil. Trans. 1788, p. 308. ! The strength is indicated by the quantity of marble necessary to saturate 1000 parts of : acid. Phil. Trans. 1788, p. 174. Ibid. p. 181. 86 IMPONDERABLE BODIES. C BOOK I. £ DIVISION I. we see, that besides this strength of easiest freezing, sulphuric acid has another point of contrary flexure at a superior strength; beyond this, if the strength be increased, the cold necessary to produce congelation begins again to diminish. 6. Before Dr. Black began to deliver his chemical lectures in Glasgow in 1757, it was universally supposed that solids were con- verted into liquids by a small addition of heat after they have been once raised to the melting point, and that they returned again to the solid state on a very- small diminution of the quantity of heat necessary to keep them at that temperature. An attentive view of the phenomena of liquefaction and solidification gradually led this sagacious philosopher to observe their inconsistence with the then received opinions, and to form another, which he verified by di- rect experiments; and drew up an account of his theory, and the proofs of it, which was read to a literary society in Glasgow on April 23,1762 ;* and every year after he gave a detailed account of the whole doctrine in his lectures. The opinion which he formed was, that when a solid body is converted into a liquid, a much greater quantity of heat enters into it than is perceptible immediately after by the thermometer. This great quantity of heat does not make the body apparently warmer, but it must be thrown into it in order to convert it into a liquid; and this great addition of heat is the principal and most immediate cause of the fluidity induced. On the other hand, when a liquid body assumes the form of a solid, a very great quantity of heat leaves it without sensibly diminishing its temperature; and the state of solidity cannot be induced without the abstraction of this great quantity of heat. Or, in other words, whenever a solid is converted into a fluid, it combines with a certain dose of caloric without any augmentation of its temperature; and it is this dose of caloric which occasions the change of the solid into a fluid. When the fluid is converted again into a solid, the dose of caloric leaves it without any diminution of its temperature; and it is this abstraction which occasions the change. Thus the combination of a certain dose of caloric with ice causes it to become water, and the abstraction of a certain dose of caloric from water causes it to become ice. Water, then, is.a compound of ice and caloric ; and in general, all fluids are combinations of the solid to which they may be converted by cold and a certain dose of caloric. Such is the opinion concerning the cause of fluidity, taught by Dr. Black as early as 1762. Its truth was established by the fol- lowing experiments: First. If a lump of ice, at the temperature of 22®, be brought into a warm room, in a very short time it is heated to 32°, the freezing point. It then begins to melt; but the process goes on ve- ry slowly, and several hours elapse before the whole ice is melted. During the whole of that time its temperature continues at 32°; * Black's Lectures, preface, p. 38. Chap. II.] HEAT. 87 yet as it is constantly surrounded by warm air, we have reason to believe that caloric is constantly entering into it. Now as none of this caloric is indicated by the thermometer, what becomes of it, unless it has combined with that portion of the ice which is convert- ed into water, and unless it is the cause of the melting of the ice I Dr. Black took two thin globular glasses four inches in diame- ter, and very nearly of the same weight. Both were filled with water ; the contents of the one were frozen into a solid mass of ice, the contents of the other were cooled down to 33°; the two glasses were then supended in a large room at a distance from all other bodies, the temperature of the air being 47°. In half an hour the thermometer placed in the water glass rose from 33° to 40°, or seven degrees; the ice was at first four or five degrees colder than melting snow; but in a few minutes the thermometer applied to it stood at 32°. The instant of time when it reached that tempera- ture was noted, and the whole left undisturbed for ten hours and a half. At the end of that time the whole ice was melted, except a very small spongy mass, which floated at the top and disappeared in a few minutes. The temperature of the ice-water was 40°. Thus 10£ hours were necessary to melt the ice and raise the product to the temperature of 40°. During all this time it must have been receiving heat with the same celerity as the water glass received it during the first half-hour. The whole quantity re- ceived then was 21 times 7, or 147°; but its temperature was only 40°: therefore 139 or 140 degrees had been absorbed by the melt- ing ice, and remained concealed in the water into which it had been converted, its presence not being indicated by the thermometer.* That heat is actually entering into the ice, is easily ascertained by placing the hand or a thermometer under the vessel containing it. A current of cold air may be perceived descending from it during the whole time of the process. But it will be said, perhaps, that the heat which enters into the ice does not remain there, but is altogether destroyed. This opinion is refuted by the following experiment. Second. If, when the thermometer is at 22°, we expose a vessel full of water at 52° to the open air, and beside it another vessel full of brine at the same temperature, with thermometers in each ; we shall find that both of them gradually lose caloric, and are cooled down to 32°. After this the brine (which does not freeze till cool- ed down to 4°) continues to cool without interruption, and gradually reaches 22°, the temperature of the air; but the pure water remains stationary at 32°. It freezes indeed, but very slowly; and during the whole process its temperature is 32°. Now, why should the one liquid refuse all of a sudden to give out caloric, and not the other ? Is it not much more probable that the water, as it freezes, gradually gives out the heat which it had absorbed during its li- quefaction ; and that this evolution maintains the temperature of * Black's Lectures, i. 120. 88 IMPONDERABLE BODIES. S »OOK L £ DIVISION 1. the water at 32°, notwithstanding what it parts with to the air dur- ing the whole process ? We may easily satisfy ourselves that the water while congealing is constantly imparting heat to the sur- rounding air; for a delicate thermometer suspended above it is con- standy affected by an ascending stream of air less cold than the air around.* The following experiment, first made by Fahrenheit, and afterwards often repeated by Dr. Black and others, affords a palpa- ble evidence, that such an evolution of caloric actually takes place during Congelation. Third. If when the air is at 22w, we expose to it a quantity of water in a tall beer glass, with a thermometer in it and covered, the water gradually cools down to 22° without freezing. It is therefore 10Q below the freezing point. Things being in this situation, if the water be shaken, part of it instantly freezes into a spongy mass, and the temperature of the whole instantly rises to the freezing point; so that the water has acquired ten degrees of caloric in an instant. Now, whence came these ten degrees? Is it not evident that they must have come from that part of the water which was frozen, and consequently that water in the act of freez- ing gives out caloric ? From a good many experiments which I have made on water in these circumstances, I have found reason to conclude, that the quantity of ice which forms suddenly on the agitation of water, cooled down below the freezing point, bears always a constant ratio to the coldness of the liquid before agitation. Thus I find that when water is cooled down to 22°, very nearly -^ of the whole freezes;! when the previous temperature is 27°, about ^ of the whole freezes. I have not been able to make satisfactory experi- ments in temperatures lower than 22°; but from analogy I con- clude, that for every five degrees of diminution of temperature be- low the freezing point, without congelation, ^ of the liquid freezes suddenly on agitation. Therefore, if water could be cooled down 28 times five degrees below 32° without congelation, the whole would congeal instantaneously on agitation, and the temperature of the ice would be 32°. Now it deserves attention, that 5 X 28 = 140, gives us precisely the quantity of heat which, according to Dr. Black's experiments, enters into ice in order to convert it into water. Hence it follows, that in all cases when water is cooled down below 32°, it loses a portion of the caloric which is necessary to constitute its liquidity. The instant that such water is agitated, one portion of the liquid seizes upon the quantity of caloric in which it is deficient at the expense of another portion which of course becomes ice. Thus when water is cooled down to 22° every particle of it wants 10° of the caloric necessary to keep it in a state of liquidity. Thirteen parts of it seize ten degrees each from the fourteenth part. These thirteen of course acquire the temperature of 32°; and the other part being deprived of 10 X 13 * Black's Lectures, i. 127. ! A medium of several experiments. Chap. II.] heat. 89 = 130, which with the ten degrees that it had lost before constitute 140°, or the whole of the caloric necessary to keep it flufd, assumes of consequence the form of ice. Fourth. If these experiments should not be considered as suffi- cient to warrant Dr. Black's conclusion, the following, for which we are indebted to the same philosopher, puts the truth of his opi- nion beyond the reach of dispute. He mixed together given weights of ice at 32° and water at 190° of temperature. The ice was melted in a few seconds, and the temperature produced was 53<». The weight of the ice was 119 half-drachms;—that of the hot water 135—of the mixture 254—of the glass vessel 16. Six- teen parts of glass have the same effect in heating cold bodies as eight parts of equally hot water. Therefore, instead of the 16 half- drachms of glass, eight of water may be substituted, which makes the hot water amount to 143 half-drachms. In this experiment there were 158 degrees of heat contained in the hot water to be divided between the ice and water. Had they been divided equally, and had the whole been afterwards sensible to the thermometer, the water would have retained £|| parts of this heat, and the ice would have received 1L| parts. That is to say, the water would have retained 86°, and the ice would have receiv- ed 72°: and the temperature after mixture would have been 104°. But the temperature by experiment is found to be only 53°; the hot water lost 137°, and the ice only received an addition of tem- perature equal to 21°. But the loss of 18° of temperature in the water is equivalent to the gain of 21° in the ice. Therefore 158« — 18° = 140° of heat have disappeared altogether from the hot water. These 140° must have entered into the ice, and converted it into water without raising its temperature.* In the same manner, if we take any quantity of ice, or (which is the same thing) snow at 32° and mix it with an equal weight of water at 172°, the snow instantly melts, and the temperature of the mixture is only'32°. Here the water is cooled 140°, while the temperature of *he snow is not increased at all; so that 140° of ca- loric have disappeared. They must have combined with the snow ; but they have only melted it without increasing its tempe- rature. Hence it follows irresistibly, that ice, when it is converted into water, absorbs and combines with caloric. It is rather difficult to ascertain the precise number of degrees of heat that disappear during the melting of ice. Hence different statements have been given. Mr. Cavendish, who informs us that he discovered the fact before he was aware that it was taught by Dr.,Black, states them at 150Q ; Wilke at 130°*; Black at 140°; and Lavoisier and Laplace, at 135°. The mean of the whole is ve- ry nearly 140°. Water, then, after being cooled down to 32°, cannot freeze till * Black's Lectures, i. 123. ! Phil. Trans. 1783, p. 313. Vol. I. u4*. M 90 IMPONDERABLE BODIES. 5?°?* J" DIVISION 1. it has parted with 140° of caloric : and ice, after being heated to 32°, cann6t melt till it has absorbed 140° of caloric. This is the cause of the extreme slowness of these operations. With regard to water, then, there can be no doubt that it owes its fluidity to the caloric which it contains, and that the caloric necessary to give flu- idity to ice is equal to 140°. To the quantity of caloric which thus occasions the fluidity of solid bodies by combining with them, Dr. Black gave the name of latent heat, because its presence is not indicated by the ther- mometer: a term sufficiently expressive, but other philosophers have rather chosen to call it caloric of fluidity. Dr. Black and his friends ascertained also, by experiment, that the fluidity of melted wax, tallow, spermaceti, metals, is owing to the same cause. Landriani proved that this is the case with sul- phur, alum, nitre, and several of the metals;* and it has been found to be the case with every substance hitherto examined. We may consider it therefore as a general law, that whenever a solid is converted into a fluid, it combines with caloric, and that this is the cause of its fluidity. 7. The only experiments to determine the latent heat of other bodies besides water, that have been hitherto published, are those of Dr. Irvine! and his son Mr. William Irvine.! The following table exhibits the result of their trials. Bodies. Latent heat. Do. reduced to the specific heat of water. Sulphur 143-68 - 27-14 Spermaceti - 145 Lead 162 - 5-6 Bees wax - 175 Zinc 493 - 48-3 Tin 500 - 33 Bismuth 550 - 23-25 The latent heat of spermaceti, wax, and tin, were determined by Dr. Irvine, that of the rest by his son. The latent heat in the se- cond column expresses the degrees by which it would have increas- ed the temperature of each of the bodies respectively when solid, except in the case of spermaceti and wax; in them it expresses the increase of temperature which would have been produced upon -them while fluid. 8. Dr. Black has rendered it exceedingly probable also, or rather he has proved by his experiments and observations, that the soft- ness of such bodies as are rendered plastic by heat depends upon a quantity of latent heat which combines with them. Metals also owe their malleability and ductility to the same cause. Hence the reason that they become hot and brittle when hammered. II. Thus it appears, that the conversion of solids into liquids is * Jour, de Phys. xxv. tt Black's Lectures, i. 187. 4 Nicholson's Jour. ix. 45. Chap. II.] HEAT. 9t occasioned by the combination of a dose of caloric with the solid. But there is another change of state still more remarkable, to which bodies are liable when exposed to the action of heat. Almost all liquids, when raised to a certain temperature, gradually assume the form of an elastic fluid, invisible like air, and possessed of the same mechanical properties. Thus water, by boiling, is converted into steam, an invisible fluid, 1800 times more bulky than water, and as elastic as air. These fluids retain their elastic form as long as their temperature remains sufficiently high; but when cooled down again, they lose that form, and are converted into liquids. All liquids, and even a considerable number of solids, are capable of undergoing this change when sufficiently heated. 2. With respect to the temperatures at which liquids undergo this change, they may be all arranged under two divisions. There are some liquids which are gradually converted into elastic fluids at every temperature; while others again never begin to assume that change till their temperature reaches a certain point. Water is a well known example of the first class of bodies. If an open vessel, filled with water, be carefully examined, we find that the water diminishes in bulk day after day, and at last disappears alto- gether. If the experiment be made in a vessel sufficiently large, and previously exhausted of air, we shall find that the water will fill the vessel in the state of invisible vapour, in whatever tempe- rature it be placed; alcohol likewise, and ether and volatile oils, gradually assume the form of an elastic fluid in all temperatures. But sulphuric acid and the fixed oils never begin to assume the form of vapour till they are raised to a certain temperature. Though left in open vessels they lose no perceptible weight; neither does sulphuric acid lose any weight though kept ever so long in the temperature of boiling water. When liquids gradually assume the form of elastic fluids in all temperatures, they are said to evaporate spontaneously. The second class of liquids want that property altogether. 3. When all other circumstances are the same, the evaporation of liquids increases with their temperature; and after they are heated to a certain temperature, they assume the form of elastic fluids with great rapidity. If the heat be applied to the bottom of the vessel containing the liquids, as is usually the case, after the whole liquid has acquired this temperature, those particles of it which are next the bottom become an elastic fluid first: they rise up, as they are formed, through the liquid, like air-bubbles, and throw the whole into violent agitation. The liquid is then said to boil. Every particular liquid has a fixed point at which this boiling commences (other things being the same); and this is called the boiling point of the liquid. Thus water begins to boil when-heated to 212°. It is remarkable, that after a liquid has begun to boil, it never becomes any hotter, however strong the fire be to which it is 92 IMPONDERABLE BODIES. BOOK I. DIVISION 1 Bodies. Boiling Point. Muriate of lime 264! Sulphuric acid (sp. gr. 1-849) 605* Phosphorus 554 Sulphur - 570 Linseed oil 600 Mercury - 656 exposed. A strong heat indeed makes it boil more rapidly, but does not increase its temperature. This was first observed by Dr. Hooke. 4. The following table contains the boiling point of a number of liquids. o .. Boiling Bod,eS- Point* Sulphuric ether - - 96° Sulphuret of carbon - 116 Ammonia - - 140* Alcohol - - - 173 Water - 212 Nitric acid of 1-54 - 175* Nitric acid (sp. gr. 1-42) 248 Carbonate of potash - 260! j 5. It was observed, when treating of the melting point of solids, that it is capable of being varied considerably by altering the situ- ation of the body. Thus water may be cooled down considerably lower than 32° without freezing. The boiling point is still less fixed, depending entirely on the degree of pressure to which the liquid to be boiled is exposed. If we diminish the pressure, the liquid boils at a lower temperature; if we increase it, a higher temperature is necessary to produce ebullition. From the experi- ments of Professor Robison, it appears that, in a vacuum, all liquids boil about 124° lower than in the open air, under a pressure of 30 inches of mercury; therefore water would boil in vacuo at 88° and alcohol at 49°. In a Papin's digester, the temperature of water may be raised to 300°, or even 400°, without ebullition: but the instant that this great pressure is removed, the boiling commences with prodigious violence. 6. The elasticity of all the elastic fluids into which liquids are converted by heat, increases with the temperature ; and the vapour formed, when the liquid boils in the open air, possesses an elasti- city just equal to that of air, or capable at a medium of balancing a column of mercury 30 inches high. The following very important table, drawn up by Mr. Dalton§ from his own experiments, exhi- bits the elasticity of steam or the vapour of water of every tem- perature, from -40° to 325°. The elasticities of all the tempera- tures from 32° to 212° were ascertained by experiment; the rest were calculated by observing the rate at which the elasticity in- creased or diminished according to the temperature. * DaltQn. •* By my trials. ! When so much concentrated as to become nearly solid 280°. § Manchester Memoirs, v. 559. Chap. II.] HEAT. 93 Table of the Elasticity of Steam. 6 3 s ft £ Force of Vap. in inches of Mercuiy. 9 1 n p. gl s o v &..£§ •229 1 I a i. *Z . "5 8 t? IB "3 3 • S.Sfc £.£S •940 i V p. £ H a. at >* . 2 e «« fri.ES 3-33 5 Lc 41 £ 41 h i Force of Vap. in inches of Mercury. -40° •013 36° 120° 162° 9-91 -30 i -020 37 •237 J 79 •971 121 3-42 163 10-15 -20 •030 38 •245 80 1.00 122 3»50 164 10-41 -10 •043 39 •254 81 1-04 123 3-59 165 10-68 40 •263 •273 82 1-07 MO 124 3-69 3-79 166 167 10-96 11*25 0 •064 41 83 125 1 •066 42 •283 84 M4 126 3-89 168 11-54 • 2 •068 43 •294 85 1-17 127 4-00 169 11-83 3 •071 44 •305 86 1-21 128 411 170 12-13 4 •074 45 •316 87 1-24 129 4-22 171 12-43 5 •076 46 •328 88 1-28 130 4-34 172 12-73 6 •079 ■ 47 •339 89 1-32 131 4-47 173 13-02 7 •082 48 •351 90 1-36 132 4-60 174 13-32 8 •085 49 •363 91 1-40 133 4-73 175 13-62 9 •087 50 •375 92 1-44 134 4-86 176 13-92 10 •090 51 •388 93 1-48 135 5-00 177 14-22 11 •093 52 •401 94 1-53 136 5-14 178 14-52 12 •096 53 •415 95 1-56 137 5-29 179 14-83 13 •100 54 •429 96 1-63 138 5'44 180 15-15 14 •104 55 •443 97 1-68 139 5-59 181 15-50 15 •108 56 •458 98 1-74 140 5-74 182 15-86 16 •112 57 •474 99 1-80 141 5-90 183 16-23 17 •116 58 •490 100 1-86 142 6-05 184 16-61 18 120 59 •507 101 1-92 143 6-21 185 1700 19 •124 60 •524 102 1-98 144 6-37 1 186 17-40 20 •129 61 •542 103 2-04 145 6-53 ! 187 17-80 21 •134 62 •560 104 2-11 146 6-70 : 188 18-20 22 •139 63 •578 105 2-18 147 6-87 j 189 18-60 23 •144 64 •597 106 2-25 148 7-05 | 190 1900 24 •150 65 .616 107 2-32 149 7-23 191 19-42 25 •156 66 •635 108 2-39 150 7-42 j 192 19-86 26 •162 67 •655 109 2-46 151 7-61 ; 193 20-32 27 ■168 68 •676 110 2-53 152 7-81 194 20-77 28 •174 69 •698 111 2-60 \B3 8-01 195 21-22 29 •180 70 •721 112 2-68 154 8-20 196 21-68 30 •186 71 •745 113 2-76 155 8-40 197 22-13 31 •193 72 73 74 •770 •796 •823 114 115 116 2»84 2-92 3*00 156 157 158 8.60 8-81 9-02 198 199 200 22-69 23-16 23-64 32 •200 33 •207 75 •851 117 3-08 159 9«24 201 24-12 34 •214 76 •880 118 316 160 9-46 202 24-61 35 •221 77 •910 119 3-25 161 | 9-68 203 25-10 "H IMPONDERABLE BODIES. Table continued. 6 ■~ a z & s « Force of Vap. in inches of Mercury. 4 U S a u 4 P. £ h Force of Vap. in inclus of Mercury. 5 * c P. £ c-1 ! Force of Vap in inches of Mercury. 1 4. P. e • Force of Vii p. in inches of Mercury. 11 2 p. E 1' Force of Vap. in inches of Mercury. 204° 25-61 228° 40-30 253° 61-00 278° 86-50 302° 114-15 205 26-13 229 41-02 254 61-92 279 87-631 303 115-32 206 26-66 230 41-75 255 62-85 280 88-75 304 116-50 207 27-20 231 42-49 256 63-76 281 89-87 305 117*68 208 27-74 232 43-^4 257 64-82 282 90-99 306 118*86 209 28-29 233 44-on 258 65-78 283 92-11 307 120-03 210 28-84 234 44-78 259 66-75 284 93-23 308 121-20 211 29-41 235 45-58 260 67-73 285 94-35 309 122-37 212 30-00 236 46-39 261 68-72 286 95-48 310 123-53 —— ..____ 237 47-20 262 69-72 287 96-64 311 124-69 213 30-60 238 48-02 263 70-73 288 97*80 312 125-85 214 31-21 239 48-84 264 71-74 289 98-96 313 127-00 215 31-83 240 49-67 265 72-76 290 100-12 314 128-15 216 32*46 241 50-50 266 73-77 291 101-28 315 129-29 217 33-09 242 51*34 267 74-79 292 102-45 316 130-43 218 33-72 243 52-18 268 75-80 293 103-63 317 131-57 219 34-35 244 53-03 269 76-82 294 104-80 318 132-72 220* 34-99 245 53.88 270 77-85 295 105-97 319 133-86 221 35*63 246 54-68 271 78-89 296 107-14 320 135-00 222 36-25 247 55-54 272 79-94 297 108-31 321 136-14 223 36-88 248 56-42 273 80-98 298 109-48 322 137-28 224 37-53 249 57-31 274 82-01 299 110-64 323 138-42 225 38-20 250 58-21 275 83-13 300 111-81 324 139-56 226 38-89 251 59-12 276 84-35 301 112-98 325 140»70 227 39-59 252 60-05 277 85-47 7. Mr. Dalton has shown, that if we consider the expansion of mercury as according to the square of the temperature, then the force# of vapour increases in a geometrical progression, by equal increments of temperature, reckoning these increments upon his new thermometric scale. The ratio of the progression he finds to be 1-321. In like manner thje force of the vapour of ether increases in a geometrical progression, the ratio of which is 1-2278. But the increase of the force of the vapour of alcohol, of the specific gra- vity 0-87, he finds to be irregular. He has drawn as a conclusion from his experiments, that the vapour of all pure liquids increases in force in a geometrical progression to the temperature, but the ratio is different in different fluids. The vapour of alcohol differs from this law, because it is in reality a mixture of two distinct va- pours, namely, that of water, and that of alcohol. 8. The specific gravity of different vapours differs according to Chap. IL] heat. - 95 the nature of the liquid from which they proceed. The following table shows the boiling points of various liquids, and the specific gravity of the vapours which they form as far as the subject has been hitherto investigated. ■'SSC^' B0i,inS Point Water - - - 0-6235* - - - 212° Hydrocyanic vapour 0-9476* ... 79.7 Alcohol - - - 1-603* - - - 173 Muriatic ether - 2-219J 52 Sulphuric ether - 2*586* - - . 96 Sulphuret of carbon 2*6447* - - 116 Oil of turpentine - 5*013* - - - 314+ Hydriodic ether - 5-4749* - - - 148 9. Such are the phenomena of the conversion of liquids into elastic fluids. Dr. Black applied his theory of latent heat to this conversion with great sagacity, and demonstrated that it is owing to the very same cause as the conversion of solids into liquids; namely, to the combination of a certain dose of caloric with the liquid without any increase of temperature. The truth of this very important point was established by the following experiments. First. When a vessel of water is put upon the fire, the water gradually becomes hotter till it reaches 212»; afterwards its tem- perature is not increased. Now caloric must be constantly entering from the fire and combining with the water. But as the water does not become hotter, the caloric must combine with that part of it which flies off in the form of steam: but the temperature of the steam is only 212°: therefore the caloric combined with it does not increase its temperature. We must conclude, then, that the change of water to steam is owing to the combination of this caloric ; for it produces no other change. Dr. Black put some water in a tin-plate vessel upon a red hot iron. The water was of the temperature 50°: in four minutes it began to boil, and in 20 minutes it was all boiled off. During the first four minutes it had received 162°, or 40£° per minute. If we suppose that it received as much per minute during the whole pro- cess of boiling, the caloric which entered into the water and con- verted it into steam would amount to 40$ X 20 = 810°.§ This caloric is not indicated by the thermometer, for the temperature of steam is only 212° ; therefore Dr. Black called it latent heat. Second. Water may be heated in a Papin's digester to 400° without boiling: because the steam is forcibly compressed, and prevented from making its escape. If the mouth of the vessel be suddenly opened while things are in this state, part of the water rushes out in the form of steam, but the greater part still remains * Gay Lussac, Ann. de Chim. xci. p. 95,150.—-Aim. de China, et Phys. i. 218. \ Thenard. Mem. D'Arcueil, i. 121. * By my experiment. 4 Black's Lectures, i. 157. 96 . IMPONDERABLE BODIES. 5 B°°K I. £ DIVISION 1. in the form of water, and its temperature instantly sinks to 212° ; consequently 188° of caloric have suddenly disappeared. This caloric must have been carried off by the steam. Now as only about |th of the water is 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. This experiment was first made by Dr. Black, and afterwards, with more precision, by Mr. Watt. Third. When hot liquids are put under the receiver of an air pump, and the air is suddenly drawn off, the liquids boil, and their temperature sinks with great rapidity a considerable number of de- grees. Thus water, however hot at first, is very soon reduced to the temperature of 70°; and ether becomes suddenly so cold that it freezes water placed round the vessel which contains it. In these cases the vapour undoubtedly carries off the heat of the liquid; but the temperature of the vapour is never greater than that of the liquid itself: the heat therefore must combine with the vapour, and become latent. Fourth. If one part of steam at 212* be mixed with nine parts by weight of water at 62°, the steam instantly assumes the form of water, and the temperature after mixture is 178-6*; consequent- ly each of the nine parts of water has received 116-6° of ca- loric ; consequently the steam has lost 9 X 116-6° = 1049-4° of ca- loric. But as the temperature of the steam is diminished by 33-3°, we must subtract this sum. There will remain rather more than 1000°, which is the quantity of caloric which existed in the steam without increasing its temperature. This experiment cannot be made directly; but it may be made by passing a given weight of steam through a metallic worm, surrounded by a given weight of water. The heat acquired by the water indicates the caloric which the steam gives out during its condensation. From the experi- ments of Mr. Watt made in this manner, it appears that the latent heat of steam amounts to 940°. The experiments of Mr. Lavoisier make it rather more than 1000°. According to Rumford it amounts to 1040-8°.* The latent heat of the vapour of boiling alcohol ac- cording to the same experimenter is between 477° and 500°.f * [Place a tin can of the following form on a dry piece of ✓"----v ^^—*^. cork as a bad conductor. It is better that the surface of the tin I>*__--1 yS^~~) > should be very clean and bright. It should hold about a pint / \y///!/ ( I and a quarter. It will weigh about 4 oz.,or 5 oz.-at the atraost. / y^ ^—' Put into it 16 oz. by measure, or one pound by weight, of pure / \ water, of the common temperature of the room; and into a ^^ , ^ small retort, 1 oz. measure of the same water. Note the temperature. Boil away all the water in the retort, by means of a small chaffing dish or a patent lamp. Then note the ac- cession of temperature communicated to the water and the tin can, by thus converting 1 oz. of water into steam. Suppose the water weighed 16 oz., and the tin can weighed 4 oz. and the original temperature being 50° of Fahrenheit, it is raised by the steam to the tempera- ture of 100°. Then here isan accession of 50° of heat communicated to each of 20 oz. of water and tin, by the latent heat of 1 oz. of water, which in such case will be 1000 besidt the heat communicated to the beak of the retort, through which the steam passes.__CJ f Gilbert's Annalen, xiv. 312. Chap. II.] HEAT. 97 By the experiments of Dr. Black and his friends, it was ascer- tained, that not only water, but all other liquids during their con- version into vapour, combine with a dose of caloric, without any change of temperature ; and that every kind of elastic fluid, during its conversion into a liquid, gives out a portion of caloric without any change of temperature. Dr. Black's law, then, is very general, and comprehends every change in the state of a body. The cause of the conversion of a solid into a liquid is the combination of the solid with caloric ; that of the conversion of a liquid into an elastic fluid is the combina-ion of the liquid with caloric. Liquids are solids combined with caloric ; elastic fluids are liquids combined with caloric. This law, in its most general form, may be stated as follows : whenever a body changes its state, it either combines with caloric, or separates from caloric. No person will dispute that this is one of the most important dis- coveries hitherto made in chemistry. Science seems indebted for it entirely to the sagacity of Dr. Black. Other philosophers indeed have laid claim to it; but these claims are either without any founda- tion, or their notions may be traced to Dr. Black's lectures, or their opinions originated many years posterior to the public explanation of Dr. Black's theory in the chemical chairs of Glasgow and Edinburgh. III. A very considerable number of bodies, both solids and li- quids, may be converted into elastic fluids by heat; and as long as the temperature continues sufficiently high, they retain all the me- chanical properties of gaseous bodies. It is exceedingly probable, that if we could command a heat sufficiently intense, the same change might be produced on all bodies in nature. This accord- ingly is the opinion at present admitted by philosophers. But if all bodies are convertible into elastic fluids by heat, it is exceeding- ly probable, that all elastic fluids in their turn might be converted into solids or liquids, if we could expose them to a low enough temperature. In that case, all the gases must be supposed to owe their elasticity to a certain dose of caloric : they must be consider- ed as compounds of caloric with a solid or liquid body. This opi- nion was first stated by Amontons ; and it was supported, with much ingenuity, both by Dr. Black and by Lavoisier and his associates. It is at present the prevailing opinion ; and it is certainly support- ed not only by analogy, but by several very striking facts. 1. If its truth be admitted, we must consider all the gases as capable of losing their elasticity by depriving them of their heat: they differ merely from the vapours in the great cold which is ne- cessary to produce this change. Now the fact is, that several ot the gases may be condensed into liquids by lowering their tempe- ratures. Ammoniacal gas condenses into a liquid at — 45?. None of the other gases have been hitherto condensed. 2. It is well known that the condensation of vapours is greatly assisted by pressure ; but the effect of pressure diminishes as the Vol.. I, N 98 IMPONDERABLE BODIES. C BOOK I ^onisiox 1. temperature of vapours increases. It is very likely that pressure would also contribute to assist the condensation of gases. It has been tried without effect indeed in several of them. Thus air has been condensed till it was heavier than water; yet it showed no disposition to lose its elasticity. But this may be ascribed to the high temperature at which the experiment was made relative to the point at which air would lose its elasticity. 3. At the same time it cannot be denied, that there are several phenomena scarcely reconcileable to this constitution of the gases, ingenious and plausible as it is. One of the most striking is the sudden solidification which ensues when certain gases are mixed together. Thus when ammoniacal gas and muriatic acid gas are mixed, the product is a solid salt: yet the heat evolved is very in- considerable, if we compare it with the difficulty of condensing these gases separately, and the great cold which they endure before losing their elasticity. In other cases, too, gaseous bodies unite, and form a new gas, which retains its elasticity as powerfully as ever. Thus oxygen gas and nitrous gas combined form a new gas, namely, nitric acid, which is permanent till it comes into contact with some body on which it can act. III. Changes in Composition. Caloric not only increases the bulk of bodies, and changes their state from solids to liquids and from liquids to elastic fluids; but its action decomposes a great number of bodies altogether, either into their elements, or it causes these elements to combine in a dif- ferent manner. Thus when ammonia is heated to redness, it is resolved into azotic and hydrogen gases. Alcohol, by the same heat, is converted into carbureted hydrogen and water. 1. This decomposition is in many cases owing to the difference between the volatility of the ingredients of a compound. Thus when weak spirits, or a combination of alcohol and water, are heat- ed, the alcohol separates, because it is more volatile than the water. 2. In general, the compounds which are but little or not at all affected by heat, are those bodies which have been formed by com- bustion. Thus water is not decomposed by any heat which can be applied to it; neither are phosphoric or carbonic acids. 3. Almost all the combinations into which oxygen enters without having occasioned combustion, are decomposable by heat. This is the case with nitric acid, and many of the metallic oxides. 4. All bodies that contain combustibles as component parts are decomposed by heat. Perhaps the metallic alloys are exceptions to this rule; at least it is not in our power to apply a temperature high enough to produce their decomposition, except in a few cases. 5. When two combustible ingredients and likewise oxygen occur together in bodies, they are always very easily decomposed by heat. This is the case with the greater number of animal and vegetable substances. Chap. II.] HEAT. 99 But it is unnecessary to enlarge any farther on this subject, as no satisfactory theory can be given. The decompositions will all be noticed in describing the different compounds which are to pc- cupy our attention in the subsequent part of this work. SECTION V. OF THE QUANTITY OF CALORIC BODIES. Having, in the second section of this chapter, shown that calo- ric is capable of moving through all bodies; and in ihe third, that it gradually diffuses itself through all contiguous bodies in such a manner that they assume the same temperature—the next point of discussion which presented itself was the quantity of caloric in bo- dies. When different bodies have the same temperature, do they contain the same quantity of caloric in bodies ? When different bo- dies have the same temperature, do they contain the same quanti- ty of caloric ? Is the same quantity necessary to produce the same change of temperature in all bodies ? What is the point at which a thermometer would stand if it were plunged into a body deprived of heat altogether ? or what is the commencement of the scale of temperature ? But these questions could not be examined with any chance of success while we were ignorant of the effects which calo- ric produces on bodies; because it is by these effects alone that the quantity of caloric in bodies is measured. This rendered it neces- sary for us to employ the fourth section in the examination of these effects. Let us now apply the knowledge which we have acquired to the investigation of the quantity of caloric in bodies. This in- vestigation naturally divides itself into three parts: 1. The rela- tive quantities of caloric in bodies, or the quantities in each ne- cessary to produce a given change of temperature. This is usually termed specific caloric. 2. The absolute quantity of caloric which exists in bodies. 3. The phenomena of cold, or the absence of ca- loric. These three topics shall be examined in order. I. Of the Specific Caloric of Bodies. If equal weights of water and spermaceti oil, at different tempe- ratures, be mixed together and agitated, it is natural to expect that the mixture would acquire the mean temperature. Suppose, for instance, that the temperature of the water were 100°, and that of the oil 50°, it is reasonable to suppose that the water would be cool- ed 25° and the oil heated 25°, and that the temperature after the mixture would be 75°. But when the experiment is tried, the re- sult is very far from answering this apparently reasonable expecta- tion : for the temperature after mixture is 83|°; consequently the 100 IMPONDERABLE BODIES. C BOOK i £ DIVISION 1. water has only lost 16|, while the oil has gained 33$. On the other hand, if we mix together equal weights of water at 50°, and oil at 100°, the temperature, after agitation, will be only 66J, so that the oil has given out 33£, and the water has received only 16|. This experiment demonstrates that the same quantity of caloric is not required to raise spermaceti oil a given number of degrees which is necessary to raise water the same number. The quantity of caloric which raises the oil 12f, raises water only 6 J.; consequently the ca- loric which raises the temperature of water 1° will raise that of the same weight of spermaceti oil 2°. If other substances be tried in the same manner, it will be found that they all differ from each other in the quantity of caloric -which is necessary to heat each of them to a given temperature; some re- quiring more than the same weight of water would do, others less j but every one requires a quantity peculiar to itself. Now the quan- tity of caloric which a body requires, in order to be heated to a certain temperature, (one degree for instance,) is called the speci- fic caloric of that body. We do not indeed know the absolute quan- tity of caloric which is required to produce a certain degree of heat in any body; but if the unknown quantity necessary to heat water (one degree for instance) be made = 1, we can determine, by ex- periment, how much more, or much less caloric other bodies re- quire to be heated the same number of degrees. Thus if we find by trial that the quantity of caloric which heats water 1°, heats the same weight of spermaceti oil 2°, it follows, that the specific calo- ric of water is two times greater than that of the oil; therefore if the specific caloric of water = 1, that of spermaceti oil must be = 0-5. In this manner may the specific caloric of all bodies be found. That the specific caloric of bodies is different, was first pointed out by Dr. Black in his lectures at Glasgow between 1760 and 1765.* Dr. Irvine afterwards investigated the subject between 1765 and 1770;f and Dr. Crawford published a great number of experiments on it in his Treatise on Heat. These three philoso- phers denoted this property by the phrase capacity of bodies for heat. But Professor Wilcke of Stockholm, who published the first set of experiments on the subject, introduced the term specific caloric; which has been generally adopted, because the phrase capacity for caloric is liable to ambiguity, and has introduced con- fusion into this subject.:}: The experiments of Mr. Wilcke were first published in the Stockholm Transactions for 1781.§ The manner in which they * Black's Lectures, i. 504. -j- n,;^ i The term specific caloric has been employed in a different sense by Seguin. He used it for the whole caloric which a body contains. § Mr. Wilcke quotes Klingenstjerna as the author who first started the doctrine of the difference between the specific heat of bodies. Kongl. Vetenskups Academiens nya hand- Ungar, torn. ii. for 1781, p. 49. I have been informed by the late Professor Robison that Wilcke's information was first got from a Swedish gentleman, who attended Dr. Black's lectures about 1770. But I do not know on what evidence he founded his statement. Chap. II.] HEAT. 101 were conducted is exceedingly ingenious, and they furnish us with the specific caloric of many of the metals. The metal on which the experiment was to be made was first weighed accurately (generally one pound was taken), and then being suspended by a thread, was plunged into a large vessel of tin-plate, filled with boiling water, and kept there till it acquired a certain temperature, which was ascertained by a thermometer. Into another small box of tin-plate exactly as much water at 32* was put as equalled the weight of the metal. Into this vessel the metal was plunged, and suspended in it so as not to touch its sides or bottom; and the degree of heat, the moment the metal and water were reduced to the same tem- perature, was marked by a very accurate thermometer. From the change of temperature, he deduced, by an ingenious calculation, the specific caloric of the metal, that of water being considered as unity. Next, in point of time, and not inferior in ingenious contrivances to ensure accuracy, were the experiments of Dr. Crawford, made by mixing together bodies of different temperatures. These were published in his Treatise on Heat. In the first edition many errors had crept into his deductions, from his not attending to the chemi- cal changes produced by mixing many of the subjects of his experi- ments. These were corrected by his subsequent experiments, and the corrections inserted in his second edition. The method which he employed was essentially the same with that which had been at first suggested by Dr. Black. Two substances of different tem- peratures were mixed uniformly; and the change of temperature produced on each by the mixture was considered as inversely pro- portional to its specific caloric* To the labours of this ingenious experimenter we are indebted for some of the most remarkable facts respecting specific caloric that are yet known.f Several experiments on the specific caloric of bodies were made also by Lavoisier and Laplace, which from the well-known ac- curacy of these philosophers cannot but be very valuable. Their method was extremely simple and ingenious; it was first suggested by Mr. Laplace. An instrument was contrived, to which Lavoisier gave the name of calorimeter. It consists of three cir- * The specific caloric of water being considered as I, the formula was as follows: Let the quantity of water (which usually constituted one of the substances mixed) be W, and its temperature w. Let the quantity of the other body, whose specific caloric is to be ascer- tained, be B, and its temperature b. Let the temperature after mixture be m. The specific caloric of B is t, I---==; or, when the water is the hotter of the bodies mixed, the spe* X b — m cine caloric of B is W *J°„ ~ZJ1 Sec Black's Lectures, i. 506. B Xm~ZTl f To form an adequate notion of the delicacy of Dr. Crawford's experiments, it will be necessary to peruse his own account of the precautions to which he had recourse. See his Experiments on Animal Heat and Combustion, p. 96. Seguin, in his Essay on Heat Ann de Chun, m. 148, has done little else than translate Crawford. 102 IMPONDERABLE BODIES. C BOOK I. £nmsiox l. cular vessels nearly inscribed into each other, so as to form three different apartments, one within the other. These three we shall call the interior, middle, and external cavities. The interior cavity into which the substances submitted to experiment are put, is com- posed of a grating or cage of iron wire, supported by several iron bars. Its opening or mouth is covered by a lid, which is composed of the same materials. The middle cavity is filled with ice. This ice is supported by a grate, and under the grate is placed a sieve. The external cavity is also filled with ice. We have remarked al- ready, that no caloric can pass through ice at 32.° It can enter ice, indeed, but it remains in it, and is employed in melting it. The quantity of ice melted, then, is a measure of the caloric which has entered into the ice. The exterior and middle cavities being filled with ice,fell the water is allowed to drain away, and the temperature of the interior cavity to come down to 32°. Then the substance, the specific caloric of which is to be ascertained, is heated a certain number of degrees, suppose to 212°, and immediately put into the interior cavity inclosed in a thin vessel. As it cools, it melts the ice in the middle cavity. In proportion as it melts, the water runs through the grate and sieve, and falls through the conical funnel and the tube into a vessel placed below to receive it. The external cavity is filled with ice, in order to prevent the external air from approaching the ice in the middle cavity, and melting part of it. The water produced from it is carried off through a pipe. The external air ought never to be below 32°, nor above 41°. In the first case, the ice in the middle cavity might be cooled too low; in the last, a current of air passes through the machine, and carries off some of the caloric. By putting various substances at the same temperature into this machine, and observing how much ice each of them melted in cooling down to 32°, it was easy to ascertain the specific caloric of each. Thus if water, in cooling from 212° to 32°, melted one pound of ice, and spermaceti oil 0-5 of a pound; the specific caloric of water was one, and that of the oil 0-5. This ap- pears by far the simplest method of making experiments on this subject, and must also be the most accurate, provided we can be certain that all the melted snow falls into the receiver. But from an experiment of Mr. Wedgewood, one would be apt to conclude that this does not happen. He found that the melted ice, so far from flowing out, actually froze again, and choked up the passage. A table of the specific caloric of various bodies was likewise drawn up by Mr. Kirwan, and published by Magellan in his Trea- tise on Heat. Mr. Meyer published a set of experiments on the specific caloric of dried woods; and Mr. Leslie, in his Essay on Heat, has given us the result of his experiments on various bodies. The experiments of Meyer were made by ascertaining the rate of cooling of the same bulks of different bodies. From this he de- duced their conducting power for heat; and he considered the spe- cific caloric as the reciprocal of the product of the conducting power Chap. II.] HEAT. 103 multiplied into the specific gravity of the body.* Mr. Leslie like- wise made his observations by ascertaining the time that various bodies of equal bulks took up in cooling in the same circumstances. He then multiplied the proportional numbers thus got into the spe- cific gravity of the various bodies tried.f Mr. Dalton has also turned his attention to this important sub- ject, and has published a table of the specific heats of different bo- dies. His method was similar to that employed by Leslie j and Mr. Dalton informs us that he found that method susceptible of considerable precision. Count Rumford, who had attached himself in a particular man- ner to the science of heat, likewise made some experiments on the specific heat of various bodies. But his results differ very much from those of the other experimenters, that have turned their at- tention to the subject and are probably not so accurate.^ In the year 1813, a most elaborate set of experiments was pub- lished by Delaroche and Berard on the specific heat of gaseous bo- dies—a subject which had occupied the particular attention of Crawford, and likewise of Lavoisier and Laplace. But the methods employed by these philosophers had not acquired the confidence of chemists. The process of Delaroche and Berard was somewhat difficult of execution ; but seems in skilful hands to be susceptible of considerable precision, and as far as appears, the experiments were conducted with the utmost care.§ The following table exhibits a view of the specific heats of vari* ous bodies as they have been determined by the different experi- ments hitherto made: I. GASES REFERRED TO AIR.[| Same bulk. Same weight. Air - 10000 1-0000 Hydrogen -Carbonic acid 0-9033 1-2583 12-3401 0-8280 Oxygen Azote Oxide of azote -Olefient gas Carbonic oxide - 0-9765 10000 1-3503 - . 1-5530 10340 0-8848 10318 0-8878 1-5763 1-0805 * Let L be the conducting power, A the specific caloric, and M the specific gravity. ■ According to Meyer we have A = __ * See Ann. de Chim. xxx. 46. LM f See Leslie on Heat, p. 240. t His mode of making the experiment may be seen in the Philosophical Magazine, xliii, 212, or in Gilbert's Annalen, xiv. 306. § See Ann. de Chim. Ixxxv. 72, or annals of Philosophy, ii. 134. (] Delaroche and Berard. Annals of Philosophy, ii. 291. 104 IMPONDERABLE BODIES. GASES REFERRED TO WATER.51 Water Air Hydrogen Carbonic acid Oxygen Azote Oxide of azote . Olefiant gas Carbonic oxide Aqueous vapour II. WATER. Same weight. 1-0000 0-2669 3-2936 0-2210 0-2361 0-2754 0-2369 0-4207 0-2884 0-8470 Sp. Caloric Ice Water Steam "10-9000J 8000(a) 1-0000 1-5500* III. SALINE SOLUTIONS. } Carbonate of am monia Sulphuret of ammo nia (0-818) Sulphate of magne sia Water Common Salt Water Ditto (1-197) Nitre 1 "I Water 8 J Nitre 11 Water 3 J Carbonate of pot ash (1-30) Muriate of am- monia Water Tartar Water - 237-3 Sulphate of iron Water - 2 Sulphate of soda 1 Water - 2-9 } 1} l t 1-5J 1 \ 2-5 J } 0-851f 0-95(D) 0-994+. 0-844+ 0-832+ 0-78(D) 0-8167+, 0-646J 0-75(D) 0-798+, 0-734+. 0-765+. 0-728+. Alum - 1 Water - 2-9 Nitric acid 94 Lime - 1 Ditto (1-40.) Solution of br. sugar Ditto (1-17) : BOOK 7. nivisio.N 1. Sp. Caloric. 0-649+ 0-6189+ 0-62(D) 0-086+ 0-77(D) IV. ACIDS AND ALKALIES. Vinegar - - 0-92(D) 'pale 0-844+ (1-20) 0-76(D) acid ^-2989>{ 0.62$ 0-66(D) 0-5 76f 0-63(D) 0-680J 0-60(D) 0-758+, Nitric 1-30 (1-355) 1(1-36) C{^5232)- (1-885) (1-872) 1-844 (1-87) Sulph. { Do. 4. Water 5 Do. 4. do. 3 Do. equal bulks Acetic acid (1-056) Potash (1-346) Amm* (S9I8) 0-429f 0-34 (L) 0-35(D) 0-3345+. 0-333(a) 0-6631+ 0-6031| 0-52(D) 0-66(D) 0-759J f 0-708f \ 1-03(D) V. INFLAMMABLE LIOJJIDS r Alcohol< (0-817) (0-853) (0-818) (-848) CO- to- l-086f 0-930(a) 0-70(D) 0-6666* 0-64(L) 0-602* 0-58978|| 0-54993|j 76(D) 0-66(D) 54329|, Delaroche and Berard. Annals of Philosophy, ii. 432. Chap. II.] HEAT. 105 Oil of olives Linseed oil Spermaceti oil Oil of turpentine Naphtha Spermaceti - Ditto fluid Sp. Caloric. fO-718f \ 0-50(L) LO-43 9|| f 0-528f \ 0-45l92|| ( 0-5000* j 0-52(D) {0*472+ 0-400(a) 0-33856|| 0-415l9|| 0-399f 0-320(a) Betula alba Wheat Elm Quercus robur pe- dunculata Prunus domestica Dyaspyrus ebenum Barley Oats Pit-coal Charcoal Cinders VI. ANIMAL FLUIDS. Arterial blood Venous blood Cow's milk J* 1-0300* { 0-913(b) f 0-8928* \ 0-903(b) f 0-9999* 10-98(D) VII. ANIMAL SOLIDS. Ox-hide with hair - 0*7870* Lungs of a sheep - 0*7690* Lean of ox-beef - 0-7400* VIII. VEGETABLE SOLIDS. Pinus sylvestris Pinus abies Tilea Europaa Pinus picea Pyrus malus Betula alnus Cotton Quercus robur sessilis Fraxinus excelsior Pyrus communis Rice - Horse beans Dust of the pine tree Peas - Fagus Sylvatica Carpinus betulus - Vol. I. 0-65^ 0-60^ 0-62^ 0*585} 0-57fl 0*535} 0-53 0-515J 0-51fi 0*505} 0-5060* 0-5020* 0-5000* 0-4920* 0-495J 0-485| Sp. Caloric. • 0*485| 0*4770* 0*475| 0-4551 0-4451 0*435} 0-4210* 0-4160* 0-28(D) 0*2777* 0*2631* 0*1923* { { IX. EARTHY BODIES, STONEWARE, AND GLASS. Hydrate of lime Chalk Quicklime Ashes of pit-coal Ashes of elm Agate (2*648) Stoneware Crown glass Crystal Swedish glass (2- Flint glass X. Sulphur Muriate of soda { 0*40(D) 0-27(D) 0-2564* rO-30(D) ■J 0-2229* [0-2168+, - 0-1855* 0-1402* 0-195$ - 0-l95f 0-200(a) 0-1929+. 386) 0-187§ 0-l9(D) 0-174f 0-l9(D) 0-183+ 0-23(D) { { XI. METALS. Platinum Iron (7*876) Brass (8-356) 0-13(a) 0-143(a> 0-13(D) 0-125+. 0-1269* J>126$ {0-1123* 0-116$ O-ll(D) O 106 Copper (8-784) Sheet iron Gun metal Nickel Zinc (7-154) Silver C10'001 Tin Antimony IMPONDERABLE BODIES. Sp. Caloric. {0-1111* 0-11 0-11 {0-0 0-1 0-1 Gold Lead (6-107) (19-040) (11-456) 14$ (D) 0-1099} o-nooy o-iO(D) 0-0943* 102$ 0(D) f 0-082$ 10-08(D) -0*068f 0*0704* 0*07(D) 0-060$ rO'086f J 0*0645* ] 0*063$ L0*06(D) J 0*050$ |o*05(D) ■0*050f 0*0352* 0*042$ Bismuth (9*861) Mercury c BOOK i. £DIVISI05 1. Sp. Caloric. J 0*043$ \ 0*04(D) 0.033J 0*0357=* 0-0290+. 0*0496(D) XII. OXIDES. Oxide of iron Rust of iron Ditto nearly free from f . air - 1 White oxide of an- ~| tim. washed J Do. nearly freed from 1 air - - J Oxide of copper do. Oxide of lead and tin Oxide of zinc, do. Oxide of tin nearly") freed from air J Yellow oxide of lead, do. } 0*320f 0-2500* 0.1666* 0*220f 0-2272* 0-1666* 0-2272* 0-102f 0-1369* 0-0990* 0-096J 0-0680* 0-068J (L) Leslie i (a) Irvine, _0*04(D) * Crawford; -J- Kirwan; + Lavoisier and Laplace; § Wilke; f Meyer; || Count Rumford; (D) Dalto-i, New System of Chemical Philosophy, p. 6'2. Essays, p. 84 and 88. (b) John Davy, Phil. Trans. 1814, p. 59J. The following are the most important points respecting the spe- cific caloric of bodies hitherto investigated. 1. Dr. Crawford made a great many experiments relative to the specific caloric of bodies at different temperatures, and the result of them was, that it is nearly permanent in the same body, while that body remains in the same state. His reasoning is founded upon two suppositions, neither of which have been sufficiently proved: 1. That the mercurial thermometer is an accurate measure of heat; 2. That heat does not unite chemically to bodies. With these data he shows, that the specific caloric of water does not vary at differ- ent temperatures. And finally, by mixing bodies at various tempe- ratures with water, he established the permanency of their specific calorics.* As this reasoning is founded on inadmissible supposi- tions, it is not quite legitimate. Mr. Dalton has lately endeavour- ed to show that the specific heat of all bodies increases with their temperature : and his reasoning, though not quite conclusive, is at least very plausible and probable. 2. Whenever a body changes its state, its specific caloric changes at the same time, according to the following law. When a solid * Crawford on Heat, p. 33. Chap. II.] heat. . 107 becomes a liquid, or a liquid an elastic fluid, the specific caloric in- creases; when an elastic fluid becomes a liquid, or a liquid a solid, the specific caloric diminishes. This very important discovery was made by Dr. Irvine, and ap'plied by him, with much sagacity, to the explanation of a great variety of curious and important phenomena. 3. The specific caloric of bodies is increased by combining them with oxygen. Thus the specific caloric of metallic oxides is greater than that of metals, and of acids than of their bases. This fact was discovered by Dr. Crawford, and constituted the foundation of his theorv of animal heat. 4. The specific caloric of oxygen is diminished when it enters into combination with inflammable bodies. This was also establish- ed by Dr. Crawford, though not in a manner quite so satisfactory.* II. Of the Absolute Quantity of Heat in Bodies. Thus we see that the relative quantity of caloric is very different in different bodies, even when they are of the same temperature by the test of the thermometer. It is obvious, therefore, that the ther- mometer is nqt capable of indicating the quantity of caloric contain- ed in bodies: since, not to mention the specific caloric, the presence of the caloric which occasions fluidity is not indicated by it at all. Thus steam at 212° contains 1000° more caloric than water at 212°, 5Tet the temperature of each is the same. Is there then any method of ascertaining the absolute quantity of caloric which a body con- tains ? At what degree would a thermometer stand (supposing the thermometer capable of measuring so low,) were the body to which it is applied totally deprived of caloric ? or, What degree of the thermometer corresponds to the real zero ? The first person, at least since men began to think accurately on the subject, who conceived the possibility of determining this ques- tion, was Dr. Irvine of Glasgow. He invented a theorem, in order to ascertain the real zero, which has, I know not for what reason, been ascribed by several writers to Mr. Kirwan. 1. It is obvious, that if the specific caloric of bodies continues the same at all temperatures, the absolute quantity of caloric in bodies must be proportional to the specific caloric. Thus if the specific caloric of spermaceti oil be only half of that of water, water must contain twice as much caloric as spermaceti oil of the same temperature. Let us suppose both bodies to be totally deprived of caloric, and that we apply to them a thermometer, the zero point of which indicates absolute cold or a total deprivation of heat. To [I see no reason whatever for the names specific heat, or, caloric of capacity; or for supposing that the substance caloric, has not, like all other substances, it own peculiar affini- ties ; combining with one substance in'one proportion, with another in another. Sensible heat, or caloric of temperature, seems to be caloric -mVrec/with a body—pervading its pores: latent heat, is caloric chemically combined with a body; and of course its properties will be merged, until by chemical decomposition of the compound thus formed, the caloric becomes separated, and exhibits again its characteristic properties. Thus muriatic acid in common salt is latent; when set free bv sulphuric acid taking its place, it becomes sepsible. Such seems to be the case with caloric—-C.] 108 IMPONDERABLE BODIES. C B00K1 £ MTISION 1. raise the oil and water one degree, we must throw in a certain quantity of heat, and twice as much heat will be necessary to pro- duce the effect upon the water as on the oil. To produce a tem- perature of two degrees, the same rule must be observed; and so on for three, four, and any number of degrees. Thus at all tem- peratures the water would contain twice as much caloric as the oil. 2. This supposition, that the specific caloric of bodies continues the same at all temperatures, was the foundation of Dr. Irvine's reasoning. He had ascertained, that when a body changes from a solid to a liquid, its specific caloric at the same time increases; and that the same increase is observable when a liquid is converted into an elastic fluid. The constancy of the specific caloric of bodies, on which he founded his theory, was true only while they remained in the same state. He supposed likewise, that when a solid body is converted into a liquid, the caloric absorbed without any increase of temperature, or the latent heat, is merely the consequence of the increase of the specific caloric of the body. Thus when ice is con- verted into water, 140° of caloric are absorbed, because the specific caloric of water is so much greater than that of ice, as to require 140° additional of caloric to preserve the same temperature which it had when its specific caloric was less. The same supposition accounted for the absorption of caloric when liquids are converted into elastic fluids. 3. Dr. Irvine's theory of the absolute caloric of bodies depend- ed upon these two opinions, which he considered as first principles. The first gave him the ratio of the absolute calorics of bodies; the second, the difference between two absolute calorics. Having these data, it was easy to calculate the absolute quantity of caloric in any body whatever. Thus let us suppose that the specific calo- ric of water is to that of ice as 10 to 9, and that when ice is convert- ed into water the quantity of caloric absorbed is 140°. Let us call the absolute quantity of caloric in ice at 32° x, it is obvious that the ab- solute caloric in water at 32° is = x -f-140°. We have then the ab- solute caloric of ice = x, that of water = x + 140. But these quan- tities are to each other as 10 to 9. Therefore we have this propor- tion 10 : 9 :: x + 140 : x. By multiplying the extremes and means we get this equation 10 x = 9 x + 1260, fron which we deduce x = 1260. Thus we obtain the absolute quantity of caloric in ice of 32°, and find it to amount to 1260. Water at 32° of course contains 1400 degrees of caloric. Or, to state the proposition differently; as the specific caloric of water is to that of ice as 10 to 9 it is ob- vious that the 140 degrees of heat which are evolved when water is frozen are equal to ^th of the whole heat in the water. There- fore the heat of the water is equal to 140 X 10, or 1400. Such was the ingenious method proposed by Dr. Irvine for as- certaining the real zero, or the degree at which a thermometer would stand when plunged into a body altogether destitute of ca- loric. We see, that by the above calculation it would be with re- gard to ice 1260 degrees below 32° of Fahrenheit's scale, or 1298 Chap. II.] HEAT. 109 degrees below 0. Dr. Crawford, however, who made his experi- ments upon a different set of bodies, places the real zero at 1500* below 0 of Fahrenheit. Mr. Dalton, who has also turned his at- tention to the same question, has found the mean of his experiments to give 6000° below the freezing point as the real zero.* 4. Unfortunately the truth of the principles on which this theory of Dr. Irvine is founded is by no means established. The first pro- position, " that the specific caloric of bodies continues the same at all temperatures," has by no means been ascertained by experi- ments ; so far from it, that the very contrary has been proved by Dr. Irvine himself to hold in the case of spermaceti and wax, and has been observed by Crawford in other cases.f But even if it did hold at all temperatures while bodies continue in the same state, still as every change of state is confessedly attended with a corres- ponding change of specific caloric, we have no right to affirm that the specific caloric is proportional to the absolute caloric. For in- stance, though the specific caloric of ice be to that of water as 9 to 10, it does not follow that their absolute calorics bear the same pro- portion : nor can any reason be assigned for supposing that this ratio ought to hold, unless we suppose that caloric is incapable of uniting chemically to bodies; in which case indeed it might be admitted. 5. The second proposition, namely, that the caloric absorbed by a body, during its change of state, is merely owing to the change of the specific caloric of the body, is equally unsupported by direct proof, and indeed cannot be admitted, if we allow that caloric is capable of combining chemically with bodies. It assigns no reason for the change of state which the body has undergone, while the theory of Dr. Black accounts for that change. The 940 degrees of heat which disappear when water becomes steam, according to Dr. Irvine, are merely the consequence of the increased specific caloric of steam above that of water. But why does water become steam, and why does it show a tendency to absorb heat before it has ac- tually become steam; a tendency causing it to exert a force which at last overcomes the most powerful obstacles ? If the change be produced by the combination of heat, as all the phenomena announce, then the hypothesis of Irvine is inadmissible. Accordingly, both Irvine and Crawford laid it down as an axiom, that heat is incapa- ble of combining with bodies4 6. Another set of phenomena from which Dr. Irvine drew his conclusions is more susceptible of investigation. When bodies unite together chemically, a change of temperature is almost con- stantly produced; the compound either giving out heat or absorb- ing it. Dr. Irvine ascertained, by a variety of experiments, that the combination is attended with a similar change in the specific heat of the compound.$ When the specific caloric increases, the • New System of Chemical Philosophy, p. 97. t 0n Heat» P- 478- ± [See note to page 107.—C] § Crawford on Heat, p. 455. 110 IMPONDERABLE BODIES. £»™*l compound generates cold; when the specific caloric diminishes, heat is evolved. He inferred, in consequence of his opinion formerly explained, that the heat evolved or absorbed in th&e cases was proportional to the change of specific caloric, and the consequence of that change. Hence it was easy, knowing the specific caloric of two bodies be- fore combination, the specific caloric of the compound, and the heat evolved or absorbed, to ascertain upon that hyphothesis the absolute heat of the body. For example, let the specific caloric of two bodies before combination be = 2, and after it = 1, it is ob- vious, that during combination they must have parted with half of their absolute heat. Let the heat evolved be 700; then we know that the whole heat contained in the bodies is twice 700, or 1400. Suppose equal weights of the two bodies, A, B, to be combined together; let the specific caloric of A be C, and that of B, c; and let the specific caloric after combination be K 4. k, then, according to Dr. Irvine, we have C + c — K + k : K + k :: I = the heat evolved : S = absolute heat, Hence we have S = -—-—el .. C _L c — K — k. If the weights of the bodies combined be not equal, then let Q be the weight of A, and q that of B ; we have as before, C Q + c q — KQ + ^:kQ + ^::/:S. Hence S = CQ ^^Q-fcg. This hypothesis can be true only on the supposition that the quan- tity S, found by mixing substances together in different propor- tions, turns out always the same quantity. If it does not, the opinion falls to the ground. Thus if we mix together various pro- portions of water and concentrated sulphuric acid, the heat evolved at each trial, compared with the change of the specific caloric, ought to give us the same value of S. But from the experiments that have been made upon this subject, it does not appear that any such constant value of S is observed. The experiments indeed of Gadolin approach somewhat to it, but those of Lavoisier and La- place are very anomalous, as will appear from the following statement. From the experiments of Lavoisier and Laplace on a mixture of water and quicklime, in the proportion of 9 to 16, it follows that the real zero is 3428° below O. From their experiments on a mixture of four parts of sulphuric acid and three parts of water, it follows that the real zero is 7262° below 0. Their experiments on a mixture of four parts of sulphuric acid and five of water place it at 2598° below O. Their experiments on 9£ parts of nitric acid and one of lime 1 RftQ place it at____ below 32°, = -f 23837°.* -0-01783 The mean result of Gadolin's experiments on mixtures of sul- phuric acid and water place it at 2300° below 0. * See Seguin, Ann. de Chim. v. 231. Chap. II.] heat. HI Mr. Dalton's results vary from 4150° to 11000°; the mean of the whole places the real zero at 6150° below 32°.* Dr. Irvine's own experiments led him to fix the real zero at 900° below O. Dr. Crawford, from his experiments, placed it at 1500° below 0. These results differ from one another so enormously, and the last of those obtained by Lavoisier and Laplace, which places the real zero far above a red heat, is so absurd, that if we suppose them accurate, they are alone sufficient to convince us that the data on which they are founded are not true. Nor can the hypothesis be maintained till the anomalies which they exhibit be accounted for. 7. Another method of determining the absolute quantity of ca- loric in bodies has been lately proposed by Mr. Dalton,f a philoso- pher whose ingenuity and sagacity leave him inferior to none that have hitherto turned their attention to this difficult subject. He supposes that the repulsion which exists between the particles of elastic fluids is occasioned by the caloric with which these particles are combined, and that it is always proportional to the absolute quantity of calo ic so combined. Now the diameter of the sphere over which the influence of a particle extends is the measure of the repulsion, and it is proportional to the cube root of the whole mass. The repulsion exerted by the particles of an elastic fluid, at differ- ent temperatures, is proportional to the cube root of the bulk of the fluid in these temperatures. Therefore, according to this hypothe- sis, the absolute quantity of caloric in elastic fluids, at different temperatures, is proportional to the cube roots of these bulks at these temperatures. To give an example: the bulk of air at 55° being 1000, its bulk at 212° is 1325: therefore the absolute heat in air at 55° is to its heat at 212° as ^1000 to ^/1325, or nearly as 10 to 11. Let us call the absolute heat of air at 55° x; then the absolute heat of air at 212° is x -f- 157. This gives us the following proportion ; 10 : 11 :: x : x + 157. Hence 11**10*+ 1570, and x = 1570. Thus we obtain 1570 for the absolute heat in air at 55". Subtracting these 55 degrees, we have 1515° below 0 for the point of real zero.J Such is the hypothesis of Mr. Dalton ; and the result which he obtained corresponds pretty nearly with Dr. Crawford's deductions from some of his experiments: but if it be applied to other tempe- ratures, no such exact coincidence will be observed, as has been very well shown by an anonymous writer in Nicholson's Journal.^ It appears from the examples there produced, that the higher the temperature at which the comparison is made, the lower is the point obtained for the commencement of the scale of heat. But Mr. Dalton Conceives that this is owing to the thermometer not being an accurate measure of the scale of temperature ;|| for when the * New System of Chemical Philosophy, p. 97. f Manchester Memoirs, v. * Manchester Memoirs, v. 601. § 1803, vol. iv. 223. |] Ibid. v. 34. 112 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. temperature is corrected by Deluc's experiments, the anomaly in one of the instances disappears. This hypothesis of Mr. Dalton is founded on a supposition which, though it cannot be demonstrated, is nevertheless exceedingly pro- bable to a certain extent: for if elastic fluids owe their peculiar fluidity' to heat, and if their increase of elasticity be proportional to their increase of heat, I do not see how it can be denied that the repulsion between the particles of these bodies is proportional to the caloric combined with them; not, however, to the whole of their caloric, but to that portion of it only which occasions their elasticity, and which increases their elasticity. It is at present believed that the abstraction of heat is capable of converting elastic fluids into liquids, and even into solids. Mr. Dalton himself is a supporter of this opinion, which, in the present state of our knowledge, scarcely admits of dispute. But the particles of liquids and solids do not repel one another, but possess a contrary property; they attract one another; yet they all confessedly contain a great deal of heat. Were we then to convert elastic fluids into liquids, by abstracting heat from them, we should deprive their particles of the repulsive force which they exert, and yet leave a considerable quantity of caloric in them.. It is not the whole of the caloric, then, which is combined with the particles of elastic fluids, that occasions their repulsion, but only a part of it. Now surely it will not be said, that the repulsive force q£ the particles of elastic fluids is proportional to that caloric which has no effect in producing the repulsion, and which would remain in combination, though that repulsion were annihilated. It can only be proportional to that portion of the ca- loric which occasions repulsion. Mr. Dalton's hypothesis, then, only enables us to find out the quantity of caloric which occasions the elastic fluidity of the bodies in question, and by no means the whole of the caloric which they contain, unless they were supposed to continue in the state of elastic fluids till deprived of all the heat which they contain except the last particle: which is a supposition that cannot be made. It does not even give us any precise notion of the caloric of elastic fluidity, unless we ascertain the specific ca- loric of the body in question; and after we have done so, reduce the degrees of caloric of fluidity to a known standard, as to the number of degrees which they would raise the temperature of wa- ter, supposing it not to change its state. This indeed is absolutely necessary in all cases when we wish to speak definitely of the real zero: For as more heat is necessary to raise one body a certain number of degrees than to produce the same change on another, suppose we were to deprive these bodies altogether of heat and then to raise them both to a certain temperature, the number of degrees of heat added to both would be equal; yet the absolute quantity of heat added to both would be very unequal. The term real zero can have no meaning whatever, as far as it alludes to the quantity of heat in bodies, unless we always refer to some particular body, as water, and make it o»'r standard. Chap. II.] HEAT. 113 III. Of Cold. Having pointed out the methods of ascertaining the relative quan- tity of heat in bodies of the same temperature, and explained the various hypotheses respecting their absolute heats, it remains for us only to make a few observations on the abstraction of heat from bodies, or on what in common language is called cold. When ca- loric combines with our own bodies, or separates from them, we experience, in the first case, the sensation oi heat; in the second, of cold. When I put my hand upon a hot iron, part of the caloric leaves the iron, and enters my hand; this produces the sensation of heat. On the contrary, when I put my hand upon a lump of ice, the caloric rapidly leaves my hand, and combines with the ice; this produces the sensation of cold. The sensation of heat is occasion- ed by caloric passing into our bodies. The sensation of cold by caloric passing out of our bodies. We say that a body is hot when it communicates caloric to the surrounding bodies ; we call it cold when it absorbs caloric from other bodies. The strength of the sensations of heat and cold depends upon the rapidity with which the caloric enters or leaves our bodies ; and this rapidity is propor- tional to the difference of the temperature between our bodies and the hot or cold substance, and to the conducting power of that sub- stance. The higher the temperature of a body is, the stronger a sensation of heat does it communicate ; and the lower the tempera- ture, the stronger a sensation of cold: and when the temperature is the same, the sensations depend upon the conducting power of the substance. Thus what in common language is called cold, is nothing else than the absence of the usual quantity of caloric. When we say that a substance is cold, we mean merely that it contains less caloric than usual, or that its temperature is lower than that of our bodies. There have been philosophers, however, who maintained that cold is produced, not by the abstraction of caloric merely, but the addition of a positive something, of a peculiar body endowed with specific qualities. This was maintained by Muschenbroek and De Mairan, and seems to have been the general opinion of philosophers about the commencement of the 18th century. According to them, cold is a substance of a saline nature, very much resembling nitre, constantly floating in the air, and wafted about by the wind in very minute corpuscles, to which they gave the name offrigorific particles. They were induced to adopt this hypothesis, because they could not otherwise account for the freezing of water. According to- them, these frigorific particles insinuate themselves like wedges be- tween the molecules of water, destroy their mobility, and thus con- vert water into ice. Dr. Black, by discovering the cause of the freezing of water, banished the frigorific particles from the regions of philosophy ; because the advocates for them never brought any other proof for their existence than the convenience with which Vol. I. P 114? IMPONDERABLE BODIES. 5 BO°K I £ DIVISION 1. they accounted for certain appearances. Of course, as soon as these appearances were explained without their use, every reason for supposing their existence was destroyed. The only fact which gives any countenance to the opinion that Cold is a body, has been furnished by the following very curious experiment of Mr. Pictet.* Two concave tin mirrors being placed at the distance of 10$ feet from each other, a very delicate air ther- mometer was put into one of the foci, and a glass matrass full of snow into the other. The thermometer sunk several degrees, and rose again when the matrass was removed. When nitric acid was poured upon the snow (which increases the cold), the thermometer sunk 5° or 6° lower. Here cold seems to have been emitted by the snow, and reflected by the mirrors to the thermometer, which could not happen unless cold were a substance. But this curious experiment is explained in a satisfactory manner, by applying to it Prevost's theory of radiant heat. We see from that theory that the fall of the thermometer is really owing to a, smaller proportion than usual of heat being radiated. A very great degree of cold may be produced by mixing together different solids, which suddenly become liquid. The cause of this has been already explained. But as such mixtures are often em- ployed in chemistry, in order to be able to expose bodies to the in- fluence of a low temperature, it will be worth while to enumerate the different substances which may be employed for that purpose, and the degree of cold which each of them is capable of producing. The first person who made experiments on freezing mixtures was Fahrenheit. But the subject was much more completely investi- gated by Mr. Walker in various papers published in the Philoso- phical Transactions from 1787 to 1801. Several curious additions have been made by Professor Lowitz, particularly the introduction of muriate of lime, which produces a very great degree of cold when mixed with snow. + The experiments of Lowitz have been repeated and extended by Mr. Walker.+. The result of all these experiments may be* seen in the following tables, which I transcribe from a paper with which I have been favoured by Mr. Walker. * This experiment, or at least a similar one, was made long ago, and is found in the Es- - .„„ . ,-...-, __*---------upon a very i„v^ ,..« mometer of 400 degrees, placed m its focus. The truth is, it immediately began to subside; but, by reason of the nearness of the ice, it was doubtful whether the director reflected rays of cold were more efficacious: upon this account, we thought of covering the glass and (whatever may be the cause) the spirit of wine did indeed presently begin to rise: for all this, we dare not be positive hut there might be some other cause thereof besides the ■want of the reflection from the glass, since we were deficient in making all the trials l j„k„. .. j ■ " t- "»-------T---.— —--m. spectabilis res mean debet, opposuent.accedat candela per aertm usque ad oculos tit illoscalore et lumine offen- der hoc autem mirabilius erit, ut calor, ita figus reflectitur, si eo loco, nix obiiciatur si oculum retigent, to — 3°. 53 Sulphate of soda . 6 Muriate of ammonia . 4 Nitrate of potash . 2 Diluted nitric acid . 4 From 4- 50° to — 10° 60 Sulphate of soda . 6 Nitrate of ammonia . 5 Diluted nitric acid . 4 From -f 50° to — 14° 64 Phosphate of soda . 9 Diluted nitric acid . 4 From -f 50° to — 12°. 62 Phosphate of soda . 9 Nitrate of ammonia . 6 piluted nitric acid . 4 From -f 50° to — 21° 71 Sulphate of soda . 8 Muriatic acid . . 5 From + 50° to 0°. 50 Sulphate of soda . 5 Diluted sulphuric acid . 4 From -f 50° to 4- 3°. 47 N. B. If the materials are mixed at a warmer temperature than that expressed in the. table, the effect will be proportionably jreater; thus, if the ntost powerful of these mixtut^s be made, when the air is t 85*, it will sink the thermometer to f 2*. 116 IMPONDERABLE BODIES. c book r £ DIVISION 1. TABLE II. Frigorific Mixtures with Ice. Mixtures. Thermometer sinks. Degree of cold pro-duced. Parts. Snow, or pounded ice . 2 Muriate of soda . 1 v. § 4 to — 5°. # Snow, or pounded ice . 5 Muriate of soda . 2 Muriate of ammonia . 1 to — 12°. # Snow, or pounded ice . 24 Muriate of soda . 10 Muriate of ammonia . 5 Nitrate of potash . 5 to — 18°. # Snow, or pounded ice . 12 Muriate of soda . 5 Nitrate of ammonia . 5 to — 25°. # Snow ... 3 Diluted sulphuric acid 2 From + 32° to — 23°. 55 Snow ... 8 Muriatic acid .* . 5 From 4- 32° to — 27©. 59 Snow ... 7 Diluted nitric acid . 4 From 4- 32° to — 30°. 62 Snow ... 4 Muriate of lime . 5 From + 32° to — 40°. 72 Snow . . . 2 Chryst. muriate of lime 3 From 4- 32° to — 50°. 82 Snow ... 3 Potash ... 4 From 4- 32* to — 51°. 83 Chap. II.] heat. 117 TABLE III. Combinations of Frigorific Mixtures. Mixtures. Thermometer sinks. Degree of cold pro-duced. Parts. Phosphate of soda . 5 Nitrate of ammonia . 3 Diluted nitric acid . 4 From 0° to — 34°. 34 Phosphate of soda . 3 Nitrate of ammonia . 2 Diluted mixed acids . 4 From — 34° to — 50°. 16 Snow ... 3 Diluted nitric acid . 2 From 0° to — 46°. 46 Snow ... 8 Diluted sulphuric acid 3 1 Diluted nitric acid . 3 J From— 10° to — 56«». 46 Snow ... 1 Diluted sulphuric acid 1 From — 20° to — 60<». 40 Snow ... 3 Muriate of lime . . 4 From 4- 20° to — 48°. 68 Snow ... 3 Muriate of lime . 4 From 4.10«» to — 54°. 64 Snow ... 2 Muriate of lime . 3 From — 15° to — 68°. 53 • Snow ... 1 Chryst. muriate of lime 2 From 0° to -— 66°. 66 Snow . . • 1 Chryst. muriate of lime 3 From — 40° to — 73°. 33 Snow ... 8 Diluted sulphuric acid 10 From — 68° to —- 91°. 23 118 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. In order to produce these effects, the salts employed must be fresh crystallized, and newly reduced to a very fine powder. The vessels in which the freezing mixture is made should be very thin, and just large enough to hold it, and the materials should be mixed together as quickly as possible. The materials to be employed in order to produce great cold ought to be first reduced to the tempe- rature marked in the table, by placing them in some of the other freezing mixtures; and then they are to be mixed together in a si- milar freezing mixture. If, for instance, we wish to produce a cold = — 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 first freezing mixture in the second table before they are mixed together. If a still greater cold is required, the materials to pro- duce it are to be brought to the proper temperature by being pre- viously placed in the second freezing mixture. This process is to be continued till the required degree of cold has been procured.* SECTION VI. OF THE SOURCES OF CALORIC. Having in the preceding Sections examined the nature, proper- ties, and effects of caloric, as far as the subject has been hitherto in- vestigated, it now only remains for us to consider the different me- thods by which caloric may be evolved or made sensible, or the different sources from which it may be obtained. These sources may be reduced to six: It radiates constantly from the sun; it is evolved during combustion; and it is extricated in many cases by percussion, friction, mixture, and electricity. The sources of heat, then, are the sun, combustion, percussion, friction, mixture, elec- tricity. Let us consider each of these sources in the order in which we have enumerated them. I. The Sun. The sun, which constitutes as it were the vital part of the whole solar system, is an immense globe, whose diameter has been ascer- tained by astronomers to be no less than 888,246 miles, and which contains about 333,928 times as much matter as the earth. Philo- sophers long supposed that this immense globe of matter was un- dergoing a violent combustion; and to this cause they ascribed the immense quantity of light and heat which are constantly separating from it. But the observations of Dr. Herschel render it probable that this opinion is erroneous. + From these observations it ap- * Walker, Phil. Trans. 1795. t Phil. Trans. 1801, p. 265. Chap. II.] HEAT. 119 pears, that the sun is a solid opaque globe, similar to the earth or other planets, and surrounded by an atmosphere of great density and extent. In this atmosphere there float two regions of clouds: the lowermost of the two is opaque and similar to the clouds which form in our atmosphere; but the higher region of clouds is lumi- nous, and emits the immense quantity of light to which the splen- dour of the sun is owing. It appears, too, that these luminous clouds are subject to various changes both in quantity and lustre. Hence Dr. Herschel draws as a consequence, that the quantity of heat and light emitted by the sun varies in different seasons; and he supposes that this is one of the chief sources of the difference between the temperatures of different years. 1. When the solar rays strike transparent bodies, they produce very little effect; but opaque bodies are heated by them. Hence it follows that transparent bodies allow these rays to pass through them; but that they are detained, at least in part, by opaque bodies. The deeper the colour of the opaque body, the greater is the rise of temperature which it experiences from exposure to the sun's rays. It has been long known, that when coloured bodies are ex- posed to the light of the sun or of combustible bodies, their tem- perature is raised in proportion to the darkness of their colour. To ascertain this point, Dr. Hooke made a curious set of experi- ments, which were repeated long after by Dr. Franklin* This philosopher exposed upon snow pieces of cloth of different colours (white, red, blue, black) to the light of the sun, and found that they sunk deeper, and consequently acquired heat, in proportion to the darkness of their colour. This experiment has been re- peated with, more precision by Davy. He exposed to the light six equal pieces of copper painted white, yellow, red, green, blue, and black, in such a manner that only one side of the pieces was illu- minated. To the dark side of each was attached a bit of cerate, which melted when heated to 70°. The cerate attached to the blackened copper became first fluid, that attached to the blue next, then that attached to the green and red, then that to the yellow, and last of all, that attached to the white.* Now it is well known that dark coloured bodies, even when equally exposed to the light, reflect less of it than those which are light coloured; but since the same quantity falls upon each, it is evident that dark-coloured bo- dies must absorb and retain more of it than those which are light- coloured. That such an absorption actually takes place is evident from the following experiment. Mr. Thomas Wedgewood placed two lumps of luminous or phosphorescent marble on a piece of iron heated just under redness. One of the lumps of marble which was blackened over gave out no light; the other gave out a great deal. On being exposed a second time* in the same manner, a faint light was seen to proceed from the clean marble, but none at all could be perceivedto come from the other. The black was now wiped off, * Beddoe's Contributions, p. 4. f20 IMPONDERABLE BODIES. S B0°KL £llIVI8ION 1. and both the lumps of marble were again placed on the hot iron: The one that had been blackened gave out just as little light as the other.* In this case, the light which ought to have proceeded from the luminous marble disappeared: it must therefore have been stopped in its passage out, and retained by the black paint. Now black substances are those which absorb the most light, and they are the bodies which are most heated by exposure to light. Cavallo observed, that a thermometer with its bulb blackened stands higher than one which had its bulb clean, when exposed to the light of the sun, the light of day, or the light of alamp.f Mr. Pictet made the same observation, and took care to ascertain, that when the two thermometers were allowed to remain for some time in a dark place, they acquired precisely the same height. He observed, too, that when both thermometers had been raised a certain number of de- grees, the clean one fell a good deal faster than the other4 2. The temperature produced in bodies by the direct action of the sun's rays seldom exceeds 120°; but a much higher tempera- ture would be produced if we were to prevent the heat communi- cated from being carried off by the surrounding bodies. Mr. Saussure made a little box lined with fine dry cork, the surface of which was charred to make it black and spongy, in order that it might absorb the greatest possible quantity of the sun's rays, and be as bad a conductor of caloric as possible. It was covered with a thin glass plate. When this box was set in the sun's rays, a ther- mometer laid in the bottom of it rose in a few minutes to 221°; while the temperature of the atmosphere was only 75°.§ Professor Robison constructed an apparatus of the same kind, employing three very thin vessels of flint glass, which transmit more caloric than any of the other species of glass. They were of the same shape, arched above, with an interval of-j. inch between them. They were set on a cork base prepared like Saussure's, and placed on down contained in a pasteboard cylinder. With this apparatus the thermometer rose often in a clear summer day to 230°, and once to 237°. Even when set before a bright fire, the thermometer rose to 212°.|J S. Such is the temperature produced by the direct rays of the sun. But when its rays are concentrated by a burning-glass, they are capable of setting fire to combustibles with ease, and even of producing a temperature at least as great, if not greater, than what can be procured by the most violent and best conducted fires. In order to produce this effect, however, they must be directed upon some body capable of absorbing and retaining them; for when they are concentrated upon transparent bodies, or upon fluids, mere air for instance, they produce little or no effect whatever. * Phil. Trans. 1792. | Phil- Trans-17*0- t Sur le Feu, chap. iv. § Voyages sur les Alpes, ii. 932. fl Black's Lectures, i. 547. When the apparatus was carried to a damp cellar before the glasses were put in their places, so that the air within was moist, the thermometer never rose above 208p. Hence Dr. Robinson concluded, the moist air conducts better than dry • a conclusion fully confirmed by the subsequent experiments of Count Rumford. ' Chap. II.] HEAT. 121 Count Rumford has shown by direct experiment, that the heating power of the solar rays is not increased by concentrating them into a focus, but that the intensity of their action is occasioned by a greater number of them being brought to bear upon the same point at once.* 4. These facts, which have been long known, induced philoso- phers to infer, that the fixation of light in bodies always raises their temperature. On the other hand, it was known that the fixation of a certain quantity of caloric always occasions the appearance of light; for When bodies are raised to a certain temperature they al- ways become red hot. Hence it was concluded that light and ca- loric reciprocally evolve each other; and this was explained by sup- posing that they have the property of repelling each other. But some of the recent experiments related in a preceding part of this chapter seem to render it rather probable that heat and light are modifications of the same matter, and that it is susceptible, by means which at present we are incapable of fully appreciating, of as- suming either the modification to which we give the name of light, or that which we call heat. II. Combustion. There is perhaps no phenomenon more wonderful in itself, more interesting on account of its utility, or which has more closely oc- cupied the attention of chemists, than combustion. When a stone or a brick is heated, it undergoes no change except an augmentation of temperature; and when left to itself, it soon cools again and be- comes as at first. But with combustible bodies the case is very different. When heated to a certain degree in the open air, they suddenly become much hotter of themselves, continue for a consi- derable time intensely hot, sending out a copious stream of caloric and light to the surrounding bodies. This emission, after a certain period, begins to diminish, and at last ceases altogether. The com- bustible has now undergone a most complete change; it is convert- ed into a substance possessing very different properties, and no longer capable of combustion. Thus when charcoal is kept for some time at the temperature of about 800°, it kindles, becomes in- tensely hot, and continues to emit light and caloric for a long time. When the emission ceases, the charcoal has all disappeared, except an inconsiderable residuum of ashes; being almost entirely convert- ed into carbonic acid gas, which makes its escape unless the expe- riment be conducted in proper vessels. If it be collected, it is found to exceed greatly in weight the whole of the charcoal consumed. 1. The first attempt to explain combustion was crude and unsa- tisfactory. A certain elementary body, called fire, was supposed to exist, possessed of the property of devouring certain other bo- dies, and converting them into itself. When we set fire to a grate * Jour, de Phys. lxi. 32. Vol. I. Q 122 IMPONDERABLE BODIES. JdwS!?* 1 full of charcoal, we bring, according to this hypothesis, a small por- tion of the element of fire, which immediately begins to devour the charcoal, and to convert it into fire. Whatever part of the charcoal is not fit for being the food of fire is left behind in the form of ashes. 2. A much more ingenious and satisfactory hypothesis was pro- posed in 1665 by Dr. Hooke. According to this extraordinary man, there exists in common air a certain substance which is like, if not the very same with, that which is fixed in saltpetre. This substance has the property of dissolving all combustibles ; but only when their temperature is considerably raised. The solution takes place with such rapidity, that it occasions both heat and light; which in his opinion are mere motions. The dissolved substance is part- ly in the state of air, partly coagulated in a liquid or solid form. The quantity of this solvent present in a given bulk of air is incom- parably less than in the same bulk of saltpetr^. Hence the reason that a combustible continues burning but for a short time in a given bulk of air: the solvent is soon saturated, and then of course the combustion is at an end. Hence also the reason that combustion succeeds best when there is a constant supply of fresh air, and that it may be greatly accelerated by forcing in air with bellows.* f About ten years after the publication of Hooke's Micrographiat his theory was adopted by Mayow, without acknowledgment, in a tract which he published at Oxford on saltpetre.^ We are indebt- ed to him for a number of very ingenious and important experi- ments, in which he anticipated several modern chemical philoso- phers ; but his reasoning is for the most part absurd, and the addi- tions which he made to the theory of Hooke are exceedingly extra- vagant. To the solvent of Hooke he gives the name of spiritus nitro-aereus. It consists, he supposes, of very minute particles, which are constantly at variance with the particles of combustibles, and from their quarrels all the changes of things proceed. Fire consists in the rapid motion of these particles, heat in their less rapid motion. The sun is merely nitro-aerial particles moving with great rapidity. They fill all space. Their motion becomes • Hook's Micrographia, p. 103. See also his Lampas. ■J- [It may be worth while to enumerate the progress of opinion relating to the phenome- na of neat and combustion. 1st. Fire devoured »he substance. Albertus Magnus. 2d. Heat dissolves the substance consumed. Hooke. 3d. Violent friction and agitation between the substance acted on, and something contain- ed in the air nitro-aerial particles. Mayow. This is not very unlike Mr. Brande's notion, that combustion is owing to intense chemical action, 8 Brande's Journ. 306. 4th. Violent gyratory motions. Stahl. Scheele. Davy. 5th. Setting free combined light. Macauer. 6th. Setting free ether. Newton. 7th. Heat and light evolved from oxygen in which they were latent. Crawford. 8th. Ascribed to hydrogen or phlogiston by Kirwan and Priestley. 9th. The absorption and fixation by chemical affinity of oxygen gas. Lavoisier. 10th. I consider it as owing to the latent heat set free, when oxygen combines with carbon, or with hydrogen; this last gas, when liquified, or solidified, gives out more caloric than the oxygen that combines with it. The light is latent in the carbon and in the hydrogen, and on combustion is given out.—C.] i De Sal-nitro et Spiritu Nitro-aereo. Chap. II.] heat. 123 more languid according to their distance from the sun; and when they approach near the earth, they become pointed, and constitute cold.* 3. The attention of chemical philosophers was soon drawn away from the theory of Hooke and Mayow to one of a very different kind, first proposed by Beccher, but new-modelled by his disciple Stahl with so much skill, arranged in such an elegant systematic form, and furnished with such numerous, appropriate, and con- vincing illustrations, that it almost instantly caught the fancy, raised Stahl to the highest rank among philosophers, and constituted him the founder of the Stahlian theory of combustion. According to Stahl, all combustible substances contain in them a certain body, known by the name of Phlogiston, to which they owe their combustibility. This substance is precisely the same in all combustibles. These bodies of course owe their diversity to other ingredients which they contain, and with which the phlogis- ton is combined. Combustion, and all its attendant phenomena, depend upon the separation and dissipation of this principle: and when it is once separated, the remainder of the body is incombusti- ble. Phlogiston, according to Stahl, is peculiarly disposed to be affected by a violent whirling motion. The heat and the light, which make their appearance during combustion, are merely two proper- ties of phlogiston when in this state of violent agitation. 4. The celebrated Macquer was one of the first persons who perceived a striking defect in this theory of Stahl. Sir Isaac New- ton had proved that light is a body; it was absurd, therefore, to make it a mere property of phlogiston or the element of fire. Mac- quer accordingly considered phlogiston as nothing else but light fixed in bodies. This opinion was embraced by a great number of the most distinguished chemists; and many ingenious arguments were brought forward to prove its truth. But if phlogiston be only light fixed in bodies, whence comes the heat that manifests itself during combustion? Is this heat merely a property of light ? Dr. Black proved that heat is capable of combining with, or becoming fixed in bodies which are not combustible, as in ice or water: and concluded of course, that it is not a property but a body. This obliged philosophers to take another view of the nature of phlogiston. 5. According to them, there exists a peculiar matter, extremely subtile, capable of penetrating the densest bodies, astonishingly elastic, and the cause of heat, light, magnetism, electricity, and even of gravitation. This matter, the ether of Hooke and New- ton, is also the substance called phlogiston, which exists in a fixed * Though Mayow's theory was not original, and though his additions to it be absurd, his tract displays great genius, and contains a vast number of new views, which have been fully confirmed by the recent discoveries in chemistry. He pointed out the cause of the increase of weight in metals when calcined; he ascertained the changes produced upon air by respira- tion and combustion; and employed in his researches an apparatus similar to the present pneumatic apparatus of chemists. Perhaps the most curious part of the whole treatise is his fourteenth chapter, in which he displays a much more accurate knowledge of affinities, than any of his contemporaries, or even successors for many years. 124 IMPONDERABLE BODIES. C BOOK I (_ niviMON 1. state in combustible bodies. When set at liberty, it gives to the substances called caloric and light those peculiar motions which produce in us the sensations of heat and light. Hence the appear- ance of caloric and light in every case of combustion ; hence, too, the reason that a body after combustion is heavier than it was be- fore j for as phlogiston is itself the cause of gravitation, it would be absurd to suppose that it possesses gravitation. It is more reason- able to consider it as endowed with a principle of levity. 6. Some time after this last modification of the phlogistic theory, Dr. Priestley, who was rapidly extending the boundaries of pneu- matic chemistry, repeated many experiments formerly made on combustion by Hooke, Mayow, Boyle, and Hales, besides adding many of his own. He soon found, as they had done before him, that the air in which combustibles had been suffered to burn till they were extinguished, had undergone a very remarkable change; for no combustible would afterwards burn in it, and no animal could breathe it without suffocation. He concluded that this change was owing to phlogiston; that the air had combined with that substance; and that air is necessary to combustion, by attracting the phlogiston, for which it has a strong affinity. If so, the origin of the heat and light which appear during combustion remains to be accounted for; since phlogiston, if it separates from the combustible merely by combining with air, cannot surely act upon those bodies in whatso- ever state we may suppose them. 7. The celebrated Dr. Crawford was the first person who at- tempted to solve this difficulty, by applying to the theory of com- bustion Dr. Black's doctrine of latent heat. According to him, the phlogiston of the combustible combines during combustion with the air, and at the same time separates the caloric and light with which that fluid had been previously united. The heat and the light, then, which appear during combustion, exist previously in the air. This theory was very different from Stahl's, and certainly a great deal more satisfactory. But still the question, What is phlogiston ? remained to be answered. 8. Mr. Kirwan, who had already raised himself to the first rank among chemical philosophers, by many ingenious investigations of some of the most difficult parts of the science, attempted to answer this question, and to prove that phlogiston is the same with hydro- gen. This opinion, which Mr. Kirwan informs us was first sug- gested by the discoveries of Dr. Priestley, met with a verv fa- vourable reception from the chemical world, and was adopted either in its full extent, or with certain modifications, by Bergman Mor- veau, Crell, Wiegleb, Westrumb, Hermbstadt, Karsten, Bewley, Priestley, and Delametherie. The object of Mr. Kirwan was to prove, that hydrogen exists as a component part of every combus- tible body; that during combustion it separates from the combus- tible body, and combines with the oxygen of the air. This he at- Chap. II.] HEAT. 125 tempted in a treatise published on purpose, entitled, An Essay on Phlogiston and the Constitution of Acids.* 9. During these different modifications of the Stahlian theory, the illustrious Lavoisier was assiduously occupied in studying the phenomena of combustion. He seems to have attached himself to this subject, and to have seen the defects of the prevailing theory as early as 1770. The first precise notions, however, of what might be the real nature of combustion, were suggested to him by Bayen's paper on the oxides of mercury, which he heard read before the Academy of Sciences in 1774. These first notions, or rather con- jectures, he pursued with unwearied industry, assisted by the nu- merous discoveries which were pouring in from all quarters ; and by a long series of the most laborious and accurate experiments and disquisitions ever exhibited in chemistry, he fully established the existence of this general law—". In every case of combustion, oxy- gen combines with the burning body." This noble discovery, the fruit of genius, industry, and penetration, has reflected new light on every branch of chemistry, has connected and explained a vast number of facts formerly insulated and inexplicable, and has new- modelled the whole, and moulded it into the form of a science. After Mr. Lavoisier had convinced himself of the existence of this general law, and had published his proofs to the world, it was some time before he was able to gain a single convert, notwith- standing his unwearied assiduity, and the great weight which his talents, his reputation, his fortune, and his situation naturally gave him. At last Mr. Berthollet, at a meeting of the Academy of * I have omitted, in the historical view given in the text, the hypothesis published in 177" by Mr. Scheele, one of the most extraordinary men that ever existed. When very young, he was bound apprentice, to an apothecary at Gottenburgh, where he first felt the impulse of that genius which afterwards made him so conspicuous. He durst not indeed de- vote himself openly to chemical experiments; but he contrived to make himself master of that science by devoting those hours to study which were assigned him for sleep. He after- wards went to Sweden, and settled as an apothecary at Koping. Here Bergman first found him, saw his merit, and encouraged it, adopted his opinions, defended him with zeal, and took upon himself the charge of publishing his treatises. Eucouraged and excited by this magnanimous conduct, the genius of Scheele, though unassisted by education or wealth, burst forth with astonishing lustre; and atanage when most philosophers are only rising into notice, he had finished a career of discoveries which have no parallel in the annals of che- mistry. Whoever wishes to behold ingenuity combined with simplicity, whoever wishes to see the inexhaustible resources of chemical analysis; whoever wishes for a model in che- mical researches—has only to peruse and to study the works of Scheele. In 1777, Scheele published a treatise, entitled Chemical Experiments on Air and Fire, which perhaps exhibits a more striking display of the extent of his genius than all his other publications put together. After a vast number of experiments, conducted with astonishing ingenuity, he concluded, that caloric is composed of a certain quantity of oxygen combined with phlogiston; that radiant heat, a substance which he supposed capable of being propa- gated in straight lines like light, and not capable of combining with air, is composed of oxy- gen united with a greater quantity of phlogiston, and light of oxygen united with a still greater quantity. He supposed, too, that the difference between the rays depends upon the quantity of phlogiston: the red, accordingto him, contains the least; the violet the most phlogiston. By phlogiston, Mr. Scheele seems to have meant hydrogen. It is needless therefore to examine his theory, as it is now known that the combination of hydrogen and exygen forms not caloric but water. The whole fabric, therefore, has tumbled to the ground; but the importance of the materials will always be admired, and the ruins of the structure must remain eternal monuments of the genius of the builder. 126 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. Sciences in 1785, solemnly renounced his old opinions, and declar- ed himself a convert. Mr. Fourcroy, professor of chemistry in Paris, followed his example. And in 1787, Morveau, during a visit to Paris, was prevailed upon to relinquish his former opinions, and embrace those of Lavoisier and his friends. The example of these celebrated men was soon followed by all the young chemists of France. Mr. Lavoisier's explanation of combustion depends upon the two laws discovered by himself and Dr. Black. When a combustible body is raised to a certain temperature, it begins to combine with the oxygen of the atmosphere, and this oxygen during its combi- nation lets go the caloric and light with which it was combined' while in the gaseous state. Hence their appearance during every combustion. Hence also the change which the combustible under- goes in consequence of combustion. Thus Lavoisier explained combustion without having recourse to phlogiston; a principle merely supposed to exist, because com- bustion could not be explained without it. No chemist had been able to exhibit phlogiston in a separate state, or to give any proof of its existence, excepting only its conveniency in explaining com- bustion. The proof of its existence consisted entirely in the im- possibility of explaining combustion without it. Mr. Lavoisier, therefore, by giving a satisfactory explanation of combustion with- out having recourse to phlogiston, proved that there was no reason for supposing any such principle at all to exist. 10. But the hypothesis of Mr. Kirwan, who made phlogiston the same with hydrogen, was not overturned by this explanation, because there could be no doubt that such a substance as hydrogen actually exists. But hydrogen, if it be phlogiston, must consti- tute a component part of every combustible, and it must separate from the combustible in every case of combustion. These were points, accordingly, which Mr. Kirwan undertook to prove. If he failed, or if the very contrary of his suppositions holds in fact, his hypothesis of course fell to the ground. Lavoisier and his associates saw at once the important uses which might be made of Mr. Kirwan's essay. By refuting an hypothesis which had been embraced by the most respectable chemists in Eu- rope, their cause would receive an eclat which would make it irre- sistible. Accordingly the essay was translated into French, and each of the sections into which it was divided was accompanied by a refutation. Four of the sections were rtfuted by Lavoisier, three by Berthollet, three by Fourcroy, two by Morveau, and one by Monge. And, to do the French chemists justice, never was there a refutation more complete. Mr. Kirwan himself, with that tandour which distinguishes superior minds, gave up his opinion as untenable, and declared himself a convert to the opinion of La- voisier. 11. Thus Mr. Lavoisier destroyed the existence of phlogiston Chap. II.] heat. 127 altogether, and established a theory of combustion almost precise- ly similar to that which had been proposed long ago by Dr. Hooke. The theory of Hooke is only expressed in general terms; that of Lavoisier is much more particular. The first was a hypothesis or fortunate conjecture which the infant state of the science did not enable him to verify; whereas Lavoisier was led to his conclusions by accurate experiments and a train of ingenious and masterly de- ductions. ^ t . . . . According to the theory of Lavoisier, which is now almost ge- nerally received, and considered by chemists a full explanation of the phenomena, combustion consists in two things: first, a decom- position; second, a combination. The oxygen of the atmosphere being in the state of gas, is combined with caloric and light. Du- ring combustion this gas is decomposed, its caloric and light escape, while its base combines with the combustible and forms the pro- duct. This product is incombustible; because its base, being al- ready saturated with oxygen, cannot combine with any more. Such is a short historical detail of the improvements gradually introdu- ced into this interesting part of the science of chemistry. Let us now take a more particular view of the subject. 12. By combustion is meant a total change in the nature of com- bustible bodies, accompanied by the copious emission of heat and light. Every theory of combustion must account for these two things; namely, the change which the body undergoes, and the, emission of heat and light which accompanies this change. 13. Mr. Lavoisier explained completely the first of these pheno- mena, by demonstrating, that in all cases* oxygen combines with the burning body; and that the substance which remains behind, after combustion, is the compound formed of the combustible body and oxygen. But he did not succeed so well in accounting for the heat and the light which are evolved during combustion. Indeed this part of the subject was in a great measure overlooked by him. The combination of oxygen was considered as the important and essential part of the process. Hence his followers considered the terms oxygenizement and combustion as synonymous: but this was improper; because oxygen often unites to bodies without any ex- trication of heat or light. In this way it unites to azote, chlorine, and mercury ? but the extrication of heat and light is considered as essential to combustion in common language. The union of oxygen without that extrication is very different from its union when accompanied by it, both in the phenomena and in the pro- duct ; they ought therefore to be distinguished. I employ the term combustion in this work in its usual acceptation. * [How does this accord with the statement in this voj. that there are four supporters of combustion ? Mr. Brande, 8 Journ. of Sc. and the Arts S06, observes, that heat is given out in the formation ol some sulphurets and phosphurets: and that the only cause that in the present state of our knowledge can be assigned for the phenomena of heat and light, is intense che- mical action. But this explains nothing. It seems to me, that the theory of Lavoisier will ultimately maintain its ground; but the contradictions of Dr. Thomson still remain.—C] 128 IMPONDERABLE BODIES. S BOOK I. ^ DIVISION 1. 14. To account for the emission of heat and light, which consti- tutes a part of combustion, Mr. Lavoisier had recourse to the theory of Dr. Crawford. The heat and the light was combined with the oxygen gas, and separated from it, when that gas united to the combustible body. But this explanation, though it answers pretty well in common cases, fails altogether in others. Heat and light were supposed to be combined with the oxygen of the atmo- sphere, because it is in a gaseous state; and to separate from it, because it loses its gaseous state. But as violent combustions take place when the oxygen employed is solid or liquid, as when it is in the state of a gas. Thus if nitric acid be poured upon linseed oil, or oil of turpentine, a very rapid combustion takes place, and abun- dance of caloric and light is emitted. Here the oxygen forms a part of the liquid nitric acid, and is already combined with azote; or, according to the language of the French chemists, the azote has undergone combustion. Now, in this case, the oxygen is not only in a liquid state, but it has also undergone the change produced by combustion. So that oxygen is capable of giving out caloric and light, not only when liquid, but even after combustion; which is directly contrary to the theory. Farther; gunpowder, when kindled, burns with great rapidity in close vessels, or under an exhausted receiver. This substance is composed of nitre, charcoal, and sulphur: the two last of which ingredients are combustible: the first supplies the oxygen, being composed of nitric acid and potash. Here the oxygen is not only already combined with azote, but forms a component part of a so- lid; yet a greater quantity of caloric and light is emitted during the combustion, and almost the whole product of the combustion is in the state of gas. This appears doubly inconsistent with the theory; for the caloric and light must be supposed to be emitted from a solid body during its conversion into gas, which ought to require more caloric and light for its existence in the gaseous state than the solid itself contained. 15. Mr. Brugnatelli, the celebrated professor of chemistry at Pavia, seems to have been the first who saw this objection in its proper light.* He has endeavoured to obviate it in the following manner: according to this very acute philosopher, the substance commonly called oxygen combines with bodies in two states: 1. Retaining the greatest part of the caloric and light with which it is ttombined, when in the state of gas; 2. After having let go all the caloric and light with which it was combined. In the first state he gives it the name of thermoxygen; in the second, of oxygen. Ther- moxygen exists as a component part, not only of gaseous bodies, but also of several liquids and solids. It is only in those cases where thermoxygen is a component part of liquids or solids that Galoric and light are emitted. All metals, according to him, com- * Berthollet, in a note upon this passage in the first edition of this Work, informs us that the subject had been examined long before the period assigued hi the text. See Joui-n. de Phys. bt. 289. Chap. II.] HEAT. 129 bine with thermoxygen; those substances, on the contrary, which by combustion are converted into acids, combine with oxygen.* This ingenious theory obviates the objection completely, provided its truth can be established in a satisfactory manner. But as the evidence for it rests almost entirely upon its convenience in ex- plaining several difficult points in the phenomena of combustion, we must consider it rather in the light of an ingenious conjecture than as a theory fully established.! 16. All bodies in nature, as far as combustion is concerned, maj be divided into three classes; namely, supporters, combustibles, and incombustibles. By supporters I mean substances which are not themselves, strictly speaking, capable of undergoing combustion; but their presence is absolutely necessary, in order that this process may take place. Combustibles and incombustibles require no definition. The simple supporters at present known are three in number;] namely,—Oxygen,—Chlorine,—Iodine. The compounds which these three bodies make with each other and with azote are likewise supporters. 17. The combustibles are of three kinds; namely, simple, com- pound; and oxides, chlorides and iodides. The simple are the fol- lowing, 1. Hydrogen, 2. Carbon, 3. Boron, 4. Silicon, 5. Phosphorus, 6. Sulphur, 7. The metals. The compounds are the various bodies formed by the union of these simple substances with each other. The combustible oxides consist chiefly of combinations of hydrogen, carbon and azote with oxygen without undergoing combustion, and they constitute the chief bodies found in the vegetable and animal kingdoms. 18. During combustion, the supporter (supposing it simple, or, if compound, the oxygen, chlorine, or iodine, excluding the base) always unites with the combustible, and forms with it a new sub- stance, which I shall call a. product of combustion. Hence the rea- son of the change which combustibles undergo by combustion. Now every product is either, 1. an acid; 2. an oxide ; 3. a chlo- ride ; or 4. an iodide. 19. As light and heat are always emitted during combustion, but never when a supporter combines with a combustible without combustion, it is natural to suppose that the supporters contain either the one or the other of these bodies or both of them. I am disposed to believe that the supporters contain caloric, * Ann. de Chim. xxi. 182. f The reader will find this theory very fully detailed in the Journal de Chimie of Van Mons, vols. 2d and 3d. I avoid entering into particulars, because I can perceive no evidence whatever for the truth of most of the assertions which constitute this theory. [t Reasons will be assigned, to shew, that there is in reality only one supporter of com- bustion.—C] Vol. I. R 130 IMPONDEBABLE BODIES. 5 BOOK I. £ DIVISION 1. while that body in other cases is wanting, or at least not present in sufficient quantity. Mv reason for this opinion is that the caloric which is evolved during combustion is always proportional to the quantity of supporter which combines with the burning body; but this is by no means the case with respect to light. Thus hydrogen combines with more oxygen than any other body; and it is known that the heat produced by the combustion of hydrogen is greater than can be produced by any other method; yet the light is barely perceptible. 20. It was long the general opinion of chemists, that light exists in a fixed state in all combustible bodies. The discoveries of La- voisier induced the greater number of them to give up this opinion, on the supposition that combustion could be explained in a satisfac- tory manner without it. Indeed the followers of that illustrious philosopher considered it as incumbent upon them to oppose it with all their might; because the fixed light, which had been supposed to constitute a part of combustibles, had been unfortunately deno- minated phlogiston; a term which they considered as incompatible with truth. The hypothesis, however, was occasionally revived; first by Richter and Delametherie, and afterwards in a more for- mal manner by Gren. But little attention has been paid to it in this country till lately. That the light exists combined with the combustible, will appear probable, if we recollect that the quantity which appears during combustion depends altogether upon the combustible. Phospho- rus emits a vast quantity, charcoal a smaller, and hydrogen the smallest of all; yet the quantity of oxygen which combines with the combustible during these processes, is greatest in those cases where the light is smallest. Besides, the colour of the light de- pends in all cases upon the combustible that burns ; a circumstance which could scarcely be supposed to take place unless the light were separated from the combustible. It is well known, too, that when vegetables are made to grow in the dark, no combustible substan- ces are formed in them; the presence of light being absolutely ne- cessary for the formation of these substances. These facts, and se- veral others which might be enumerated, give a considerable de- gree of probability to the opinion that light constitutes a component part of all combustible substances: but they by no means amount to a decisive proof: nor indeed would it be easy to answer all the objections which might be started against this opinion. At the same time, it will be allowed that none of these objections to which I allude amount to a positive proof of the falsehood of the hypo- thesis. It is always a proof of the difficulty of an investigation, and of the little progress which has been made in it, when plausi- ble arguments can be brought forward on both sides of the question. 21. Were we to suppose that the supporters contain caloric as a component part, while combustibles contain light, it would not be difficult to explain what takes place during combustion. The com- Chap. II.] HEAT. 131 ponent parts of the supporters are two: namely, 1. A base; 2. Ca- loric. The component parts of combustibles are likewise two: namely, 1. A base; 2. Light. During combustion the base of the supporter combines with the base of the combustible, and forms the product; while at the same time the caloric of the supporter com- bines with the light of the combustible, and the compound flies off in the form of fire. Thus combustion is a double decomposition; the supporter and combustible divide themselves each into two por- tions, which combine in pairs; the one compound is the product, and the other the fire which escapes. Hence the reason that the oxygen of products is unfit for com- bustion. It wants its caloric. Hence the reason that combustion does not take place when oxygen combines with products or with the base of supporters. These bodies contain no light. The ca- loric of the oxygen of course is not separated, and no fire appears. And this oxygen still retaining its caloric, is capable of producing combustion whenever a body is presented which contains light, and whose base has an affinity for oxygen. Hence also the reason why a combustible alone can restore combustibility to the base of a pro- duct. In all such cases a double decomposition takes place. The oxygen of the product combines with the base of the combustible while the light of the combustible combines with the base of the product. 22. But the application of this theory to the phenomena of com- bustion is so obvious, that it requires no particular explanation. It enables us to explain, with equal facility, some curious phenomena which occur during the formation of the sulphurets and phosphurets. Sulphur and, phosphorus combine with the metals and with some of the earths. The combination is not formed without the assistance of heat. This melts the sulphur and phosphorus. At the instant of their com- bination with the metallic or earthy bases, the compound becomes solid, and at the same time suddenly acquires a strong red heat, which continues for some time. In this case the sulphur and phosphorus act the part of a supporter; for they are melted, and therefore contain a great deal of caloric: the metal or earth acts the part of a combustible ; for both contain light as a component part. The instant of combination, the sulphur or phosphorus com- bines with the metal or earth; while the caloric of the one, uniting to the light of the other, flies off in the form of fire. The process therefore may be called semicombustion, indicating by the term that it possesses precisely one half of the characteristic marks of com- bustion. 23. Whenever a supporter enters into a more intimate combina- tion with a combustible than before, combustion is the consequence. This phenomenon appears in several of the metallic oxides, and has been lately particularly attended to by Berzelius,* Thus green oxide of chromium when heated to redness takes fire an0*73 34*121 0*94 34*556 Chap. II.] BEAT. 135 III. Percussion. It is well known that heat is produced by the percussion of hard bodies against each other. When a piece of iron is smartly and quickly struck with a hammer, it becomes red hot; and the produc- tion of sparks by the collision of flint and steel is too familiar a fact to require being mentioned. No heat, however, has ever been ob- served to follow the percussion of liquids, nor of soft bodies which easily yield to the stroke. 1. This evolution of caloric by percussion seems to be the con- sequence of a permanent or temporary condensation of the body struck. The specific gavity of iron before hammering is 7*788 ; after being hammered, 7*840: that of platinum before hammering is 19*50; after it, 21*65. 2. Now condensation seems always to evolve caloric; at least this is the case in those bodies in which we can produce a remark - ble and permanent diminution of bulk. When muriatic acid gas is absorbed by water, the liquid soon rises to the temperature of 100°; and a still higher temperature is produced when ammoniacal gas and muriatic acid gas concrete into a solid salt. When lime- stone is dissolved in sulphuric acid, a considerable heat is pro- duced, notwithstanding the great quantity of carbonic acid which is set at liberty. And if we use pure lime instead of limestone, a very violent heat takes place. Now in this case the acid and the water which it contains are converted partly from liquids to solids, and the bulk is much diminished. It is known also, that when air is suddenly condensed, a thermometer surrounded by it rises se- veral degrees.* From the suddenness of the rise in this case, Mr. Dalton has shown that a much greater heat is evolved than is in- dicated by the thermometer. From his experiments it follows, that when air is suddenly condensed to half its bulk, its tempera- ture is raised 50 degrees.f The same change takes place when air is suddenly admitted into a vacuum. It cannot be doubted that a much greater rise of temperature than 50 degrees is occasioned by the condensation of air. The experiment first made by Mollet, but which has long been familiar to chemists, shows this in a Con- vincing manner. If a piece of tinder be put into the extremity of a syringe, and the air be suddenly condensed upon it, the tinder catches fire4 On the other hand, when a body is suddenly rarefied, its tem- perature is lowered. Mr. Dalton has shown, that by pumping the air out of a receiver, its temperature sinks also 50°.§ Berthollet, Pictet, and Biot, have made a set of experiments, to ascertain the quantity of heat evolved when ductile metals are sud- denly struck forcibly, as when they are stamped in the process of coining. The experiments were made upon pieces of gold, silver, * Darwin, Phil. Trans. 1788. f Manchester Memoirs, v. 515. * Pictet, Phil. Mag. xiv. 364. § Ibid. v. 515. 136 IMPONDERABLE BODIES. 5 B0°K I. £ DIVISION 1. and copper, of the same size and shape, and care was taken that all the parts of the apparatus had acquired the same temperature be- fore the experiments began. Copper evolved most heat, silver was next in order, and gold evolved the least. The first blow evolved the most heat, and it diminished gradually, and after the third blow was hardly perceptible. The heat acquired was estimated by throwing the piece of metal struck into a quantity of water, and ascertaining the change of temperature which the water underwent. The following table exhibits the increase of temperature, expe- rienced by two pieces of copper by three successive blows; , ^ ni fist Piece - 17*44° 1st Blow 12d piece .... 2o.80 1st Piece - 7*30 1st Piece - 1-90 2d Piece - - - - 1*46 2d Blow , 3d Blow | The whole quantity of heat evolved by each of these pieces of copper is nearly the same ; that from the first piece being 26*64°, and that from the second 25*95°. The following table exhibits the heat evolved from two pieces of silver treated in the same way. , , ni f 1st Piece - 6*19° 1st Blow < _ , n. „ „~ \ 2d Piece - 7*30 ., „, f 1st Piece - 5*85 2d Blow 12d piece .... 2.14 1st Piece - 2*76 3d Blow -» 2d Piece - 2*02 { Total evolved form the 1st piece - - 14*74 Ditto from the 2d - - - - 11*46 The change in the specific gravity which the metals underwent, was found to be proportional to the heat thus evolved, as appears from the following table, deduced from their experiments. The specific gravities were taken at the temperature of 46*5°. Specific gravity of gold 19*2357 Ditto annealed 19*2240 Ditto struck - - 19.2487 Specific gravity of silver 10*4667 Ditto annealed - 10*4465 Ditto struck - - 10*4838 Specific gravity of copper 8*8529 Ditto struck - - 8*8898 Ditto struck a 2d time 8*9081 From these experiments it is obvious, that the heat evolved when metals are struck is owing to the condensation, and proportional to the condensation. Hence, when they can no longer be conden- sed, they cease to evolve heat. These philosophers observed, du- ring their experiments, that heat or cold is propagated much more rapidly, from one piece of metal to another, when they are struck, than when they are simply placed in contact.* * Mem. d'Arcueil, iL p. 441. Chap. II.] HEAT. 137 3. It is not difficult to see why condensation should occasion the evolution of caloric, and rarefaction the contrary. When the par- ticles of a body are forced nearer each other, the repulsive power of the caloric combined with them is increased, and consequently a part of it will be apt to fly off. Now, after a bar of iron has been heated by the hammer, it is much harder and brittler than before. It must then have become denser, and consequently must have parted with caloric. It is an additional confirmation of this, that the same bar cannot be heated a second time by percussion until it has been exposed for some time to a red heat. It is too brittle, and flies to pieces under the hammer. Now brittleness seems in most cases owing to the absence of the usual quantity of caloric. Glass unannealed, or, which is the same thing, that has been cooled very quickly, is always extremely brittle. When glass is in a state of fusion, there is a vast quantity of caloric accumulated in it, the re- pulsion between the particles of which must of course be very great; so great indeed, that they would be disposed to fly off in every direction with inconceivable velocity, were they not confined by an unusually great quantity of caloric in the surrounding bo- dies : consequently if this surrounding caloric be removed, the ca- loric of the glass flies off at once, and more caloric will leave the glass than otherwise would leave it, because the velocity of the particles must be greatly increased. Probably then the brittleness of glass is owing to the deficiency of caloric ; and we can scarcely doubt that the brittleness of iron is owing to the same cause, if we recollect that it is removed by the application of new caloric. 4. It deserves attention, too, that condensation diminishes the specific caloric of bodies. After one of the clay pieces used in Wedgewood's thermometer has been heated to 120°, it is reduced to one half of its former bulk, though it has lost only two grains of its weight, and its specific caloric is at the same time diminish- ed one third.* But we can hardly conceive the specific caloric of a body to be diminished without an evolution of caloric taking place at the same time. 5. These observations are sufficient to explain why caloric is evolved by percussion. It is forced out from the particles of the body struck with which it was formerly combined. But a part of the caloric which is evolved after percussion often originates in another manner. By condensation, as much caloric is evolved as is sufficient to raise the temperature of some of the particles of the body high enough to enable it to combine with the oxygen of the atmosphere. The combination actually takes place, and a great quantity of additional caloric is separated by the decomposition of the gas. That this happens during the collision of flint and steel cannot be doubted; for the sparks produced are merely small pieces of iron heated red hot by uniting with oxygen during their passage through the air, as any one may convince himself by actually exa- • T. Wedgewood, Phil. Trans. 1792. Vol. I. S 138 IMPONDERABLE BODIES. S BOOK I £ DIVISION 1 mining them. Mr. Hawksbee* and others have shown, that iron produces no sparks in the vacuum of an air pump; but Mr. Kirwan affirms, that they are produced under common spring water. It is not easy to account for the emission of caloric on the per- cussion of two incombustibles. In the last chapter, mention was made of the light emitted during the percussion of two stones of quartz, flint, felspar, or any other equally hard. Caloric is also emitted during this percussion, as is evident from the whole of the phenomenon. Mr. T. Wedgewood found, that a piece of window- glass, when brought in contact with a revolving wheel of grit, be- came red hot at its point of contact, and gave off particles which set fire to gunpowder and to hydrogen gas.f We must either sup. pose that all the caloric is produced by mere condensation, which is not probable, or acknowledge that we cannot explain the pheno- menon. This is almost the only instance of the evolution of calo- ric and light where the agency of a supporter cannot be demon- strated or even rendered probable. The luminous appearance which follows the percussion of cer- tain bodies in vacuo, or in bodies which are not capable of support- ing combustion, seems to be connected with electricity; for all such bodies are electrics. They are frequently also phosphores- cent ; which property may likewise contribute to the effect.i. IV. Friction. Caloric is not only evolved by percussion, but also by friction. Fires are often kindled by rubbing pieces of dry wood smartly against one another. It is well known that heavy-loaded carts sometimes take fire by the friction between the axle-tree and the wheel. Now in what manner is the caloric evolved or accumula- ted by friction? Not by increasing the densiiv of the bodies rub- bed against each other, as happens in cases of percussion; for heat is produced by rubbing soft bodies against each other; the density of which therefore cannot be increased by that means, as any one may convince himself by rubbing his hand smartly against his coat. It is true, indeed, that heat is not produced by the friction of li- quids ; but then they are too yielding to be subjected to strong friction. It is not owing to the specific caloric of the rubbed bo- dies decreasing; for Count Rumford found that there was no sen- sible decrease,^ nor, if there were a decrease, would it be sufficient to account for the vast quantity of heat which is sometimes pro- duced by friction. Count Rumford took a cannon cast solid and rough as it came from the foundry; he caused its extremity to be cut off, and form- ed, in that part, a solid cylinder attached to the cannon 71 inches in diameter and 9T87 inches long. It remained joined to the rest of * T. Wedgewood, Phil. Trans, xxiv. 21C5. f Phil- Trans. 1792, p. 45. $ Jour, of the Royal Instit. i. 264. § Nicholson's Journal, ii. 106. Chap. II.] heat. 139 the metal by a small cylindrical neck. In this cylinder a hole was bored 3*7 inches in diameter and 7*2 inches in length. Into this hole was put a blunt steel borer, which by means of horses was made to rub against its bottom; at the same time a small hole was made in the cylinder perpendicular to the bore, and ending in the solid part a little beyond the end of the bore. This was for intro- ducing a thermometer to measure the heat of the cylinder. The cylinder was wrapt round with flannel to keep in the heat. The borer pressed against the bottom of the hole with a force equal to about 10,0O0lbs. avoirdupois, and the cylinder was turned round at the rate of 32 times in a minute. At the beginning of the experiment the temperature of the cylinder was 60°; at the end of 30 minutes, when it had made 960 revolutions, its temperature was 130°. The quantity of metallic dust or scales produced by this friction amount- ed to 837 grains. Now, if we were to suppose that all the caloric was evolved from these scales, as they amounted to just -g-V-f part of the cylinder, they must have given out 948° to raise the cylinder 1°, and consequently 66,360° to raise it 70° or to 130°, which is cer- tainly incredible.* Neither is the caloric evolved during friction owing to the com- bination of oxygen with the bodies themselves, or any part of them. By means of a piece of clock-work, Mr. Pictet made small cups (fixed on the axis of one of the wheels,) to move round with con- siderable rapidity, and he made various substances rub against the outsides of these cups, while the bulb of a very delicate thermome- ter placed within them marked the heat produced. The whole machine was of a size sufficiently small to be introduced into the receiver of an air-pump. By means of this machine a piece of adamantine spar was made to rub against a steel cup in air: sparks were produced in great abundance during the whole time, but the thermometer did not rise. The same experiment was repeated in the exhausted receiver of an air-pump (the manometer standing at four lines;) no sparks were produced, but a kind of phosphoric light was visible in the dark. The thermometer did not rise. A piece of brass being made to rub in the same manner against a much smaller brass cup in air, the thermometer (which almost filled the cup) rose 0*3°, but did not begin to rise till the friction was over. This shows us that the motion produced in the air carried off the caloric as it was evolved. In the exhausted receiver it began to rise the moment the friction began, and rose in all 1*2°. When a bit of wood was made to rub against the brass cup in the air, the thermometer rose 0*7°, and on substituting also a wooden cup it rose 2*1°, and in the exhausted receiver 2*4°, and in air condensed to li atmospheres it rose 0-5°.f If these experiments be not thought conclusive, I have others to relate, which will not leave a doubt that the heat produced by fric- tion is not connected with the decomposition of oxygen gas. Count Xieholson's Journal, ii. 106. t Pictet, sur le Feu, ch. ix. 140 IMPONDERABLE BODIES. C BOOKt £ DIVISION 1. Rumford contrived, with his usual ingenuity, to inclose the cylin- der above described in a wooden box filled with water, which effec- tually excluded all air, as the cylinder itself and the borer were sur- rounded with water, and at the same time did not impede the mo- tion of the instrument. The quantity of water amounted to 18*77lbs. avoirdupois, and at the beginning of the experiment was at the temperature of 60°. After the cylinder had revolved for an hour at the rate of 32 times in a minute, the temperature of the water was 107°; in 30 minutes more it was 178* ; and in two hours and 30 minutes after the experiment began, the water actually boil- ed. According to the computation of Count Rumford, the caloric produced would have been sufficient to heat 26*58 lbs. avoirdupois of ice-cold water boiling hot; and it would have required nine wax candles of a moderate size, burning with a clear flame all the time the experiment lasted, to have produced as much heat. In this experiment all access of water into the hole of the cylinder where the friction took place was prevented. But in another ex- periment, the result of which was precisely the same, the water was allowed free access.* The experiments of Rumford were repeated and diversified by M. Haldot. He contrived an apparatus by which two bodies could be pressed against each other by means of a spring, while one of them turned round with the velocity of 32*8 inches per second. The friction took place in a strong box containing 216 cubic inches of water. The results obtained so nearly resemble those of Count Rumford that it is unnecessary to enter into particular details. The rubber was brass. When the metal rubbed was zinc the heat evolved was greatest; brass and lead afforded equal heat, but less than zinc; tin produced only £ths of the heat evolved during the friction of lead. When the pressure was quadrupled the heat evolved became seven times greater than before. When the rubber was rough it produced but half as much heat as when smooth. When the ap- paratus was surrounded by bad conductors of heat, or by non-con- ductors of electricity, the quantity of heat evolved was diminished.! The caloric, then, which appears in consequence of friction, is neither produced by an increase of the density, nor by an alteration m the specific caloric of the substances exposed to friction, nor is it owing to the decomposition of the oxygen of the atmosphere— Whence then is it derived? This question cannot at present be an- swered : but this is no reason for concluding, with Count Rumford, that there is no such substance as caloric at all, but that it is merely a peculiar kind of motion; because the facts mentioned in the pre- ceding part of this chapter cannot be easily reconciled to such a supposition. Were it possible to prove that the accumulation of caloric by friction is incompatible with its being a substance, in that case Count Rumford's conclusion would be a fair one; but this surely has not been done. We are certainly not yet sufficiently • Nicholson's Journal, ii. 106. t lb"'- xxvi- 30- Chap. II.] heat. 141 acquainted with the laws of the motion of caloric, to be able to affirm with certainty that friction cannot cause it to accumulate in the bodies rubbed. This we know at least to be the case with elec- tricity. Nobody has been hitherto able to demonstrate in what manner it is accumulated by friction; and yet this has not been thought a sufficient reason to deny its existence. Indeed there seems to be a very close analogy between caloric and electric matter. Both of them tend to diffuse tliemselves equally, both of them dilate bodies, both of them fuse metals, and both of them kindle combustible substances. Mr. Achard has proved, that electricity can be substituted for caloric even in those cases where its agency seems peculiarly necessary; for he found, that by constantly supplying a certain quantity of the electric fluid, eggs could be hatched just as when they are kept at the tempera- ture of 103°. An accident indeed prevented the chickens from actually coming out; but they were formed and living, and within two days of bursting their shell. Electricity has also a great deal of influence on the heating and cooling of bodies. Mr. Pictet ex- hausted a glass globe, the capacity of which was 1200*199 cubic inches, till the manometer within it stood at 1*75 lines. In the middle of this globe was suspended a thermometer, which hung from the top of a glass rod fixed at the bottom of the globe, and going almost to its top. Opposite to the bulb of this thermometer two lighted candles were placed, the rays of which, by means of two concave mirrors, were concentrated on the bulb. The candles and the globe were placed on the same board, which was supported by a non-conductor of electricity. Two feet and. a half from the globe there was an electrifying machine, which communicated with a brass ring at the mouth of the globe by means of a metallic con- ductor. This machine was kept working during the whole time of the experiment; and consequently a quantity of electric matter was constantly passing into the globe, which, in the language of Pictet, formed an atmosphere not only within it, but at some dis- tance round, as was evident from the imperfect manner in which the candles burned. When the experiment began, the thermometer stood at 49*8<». It rose to 70*2° in 732". The same experiment was repeated, but no electric matter thrown in; the thermometer rose from 49*8* to 70*2° in 1050"; so that the electricity hastened the heating almost a third. In the first experiment the thermometer rose only to 71*3°, but in the second it rose to 77°. This difference was doubdess owing to the candles burning better in the second than the first experiment; for in other two experiments made ex- actly in the same manner, the maximum was equal both when there was and was not electric matter present. These experiments were repeated with this difference, that the candles were now insulated, by placing their candlesticks in vessels of varnished glass. The thermometer rose in the electrical vacuum from 52*2° to 74*7° in 1050"; in the simple vacuum in 965". In the electrical vacuum 142 IMPONDERABLE BODIES. C BOOK f. "l DIVISION 1. the thermometer rose to 77°; in the simple vacuum to 86°. It fol- lows from these experiments, that when the globe and the candles communicated with each other, electricity hastened the heating of the thermometer; but that when they were insulated separately, it retarded it.* One would be apt to suspect the agency of electricity in the following experiment of Mr. Pictet: into one of the brass cups formerly described a small quantity of cotton was put to pre- vent the bulb of the thermometer from being broken. As the cup turned round, two or three fibres of the cotton rubbed against the bulb, and without any other friction the thermometer rose five or six degrees. A greater quantity of cotton being made to rub against the bulb, the thermometer rose 15°.f I do not mean to draw any other conclusion from these facts, than that electricity is very often concerned in the heating of bo- dies, and that probably some such agent is employed in accumula- ting the heat produced by friction. Supposing that electricity is actually a substance, and taking it for granted that it is different from caloric, does it not in all probability contain caloric as \^ell as all other bodies ? Has it not a tendency to accumulate in anybodies by friction, whether conductors or non-conductors ? May it not then be accumulated in those bodies which are rubbed against one another? or, if they are good conductors, may it not pass through them during the friction in great quantities ? May it not part with some of its caloric to these bodies, either on account of their greater affinity or some other cause ? and may not this be the source of the caloric which appears during friction ? V. Mixture. It is well known that in a vast number of cases, when two sub- stances enter into a chemical union, a change of temperature takes place. In some instances the mixture becomes colder than before, while in others it becomes much hotter. In the third division of the preceding section, a very copious list has been given of the first set of mixtures. It remains for us to consider the nature of the second set, and to endeavour, if possible, to ascertain the cause of the change of temperature. 1. It deserves particular attention, that water constitutes an es- sential part of almost all mixtures in which a change of temperature takes place. The most remarkable exceptions to this rule are some of the gaseous bodies, which when united together constitute a solid body, as ammoniacal and muriatic acid gases. At the instant of union a very considerable heat is evolved. But even these gas- eous bodies contain a considerable proportion of water, which in all probability contributes not a little to the effect. 2. In many cases the particular change of temperature which is produced by mixture depends upon the proportion of water pre- * Pictet sur le Feu, chap. vi. t 1*>"** chap. ix. Chap. II.] HEAT. 143 viously combined with one of the ingredients ; for the same ingre- dients are capable either of producing heat or cold according to that propo.tion. It has been ascertained by the experiments of Mr. Lowitz and Mr. Walker that, when salts which contain a great deal of water in their composition, as carbonate of .soda, sulphate of soda, muriate of lime, &c. are dissolved in water, the temperature sinks considerably; and the fall is proportional to the rapidity of the solution. But when the same salts, previously deprived of ' their water by exposure to heat, are dissolved, the temperature of the mixture rises considerably, (because the water they combine with, gives out its latent heat on being thus combined). 3. It may be laid down as a rule to which there are few excep- tions, that when the compound formed by the union of two bodies is more fluid or dense than the mean fluidity or density of the two bodies.before mixture, then the temperature sinks; but when the fluidity or the density of the new compound is less than that of the two bodies before mixture, the temperature rises ; and the rise is pretty nearly proportional to the difference. Thus when snow and common salt are mixed together, they gradually melt, and assume the form of a liquid. During the whole process of melting, the temperature Continues at zero or lower ; but whenever the solution is completed, the temperature rises. On the other hand, when spirits and water are mixed tcgether, a condensation takes place; for the specific gravity is greater than the mean. Accordingly the mixture becomes hot. When four parts of sulphuric acid and one part of water are mixed together, the density is very much increas- ed ; accordingly the temperature of the mixture suddenly rises to about 300°. 4. We now see the reason why those salts which contain water in abundance produce cold during their solution: the water, while it constituted a part of them, was in a solid state ; but when the salt is dissolved, it becomes liquid. Since these salts, if they be depriv- ed of their water, produce heat during their solution, it cannot be doubted that the water, before it dissolves them, combines first with them, so as to form a solid, or at least a solution of consider- ably greater density. From the experiments of Gay Lussac it appears still more clear- ly that the evolution of heat or cold in such cases depends upon the change of the water from a state of solidity to a state of liquidity, or vice versa. He mixed together a solution of nitrate of ammo- nia of the specific gravity 1-302 at the temperature of 61-3° with water in the proportion of 44-05 of the former and 33-76 of the lat- ter. The temperature of the mixture sunk 8-9°, yet the density in- creased. For the mean density would have been 1-151, while the density of the mixture was 1159. This acute experimenter men- tions several similar examples; though in none of them was the ab- sorption of heat so great as in the instance which I have selected.* • Ann. de Chim. et Phys. i. 214. 144 IMPONDERABLE BODIES. C BOOK 1 £ DIVISION 1 5. Whenever water is solidified, a considerable proportion of the heat is evolved. Hence the reason that a great deal of heat is pro- duced by sprinkling water upon quicklime. A portion of the water combines with the lime, and forms with it a dry powder totally des- titute of fluidity. For the the same reason heat is produced when quicklime is thrown into sulphuric acid. 6. The whole of these phenomena, and likewise the evolution of heat during putrefaction and fermentation, are sufficiently explained by Dr. Black's theory of latent heat. Fluidity, in all cases, is pro- duced by the combination of caloric with the body that becomes fluid. Hence a mixture, when it becomes fluid, must absorb calo- ric ; which is the same as saying that it must produce cold. On the other hand, when a fluid body becomes solid,heat must be evolved; because a fluid can only become solid by parting with its caloric of fluidity. But the application of the theory to all cases of changes in temperature by mixture is so obvious, that it is quite unnecessa- ry to give any farther illustration. 7. In most combinations which evolve heat or cold, a change takes place in the specific caloric of the bodies combined. To this change Dr. Irvine ascribed the whole of the heat or cold evolved. Though he appears to me to have carried this doctrine too far, the change must doubtless be allowed to have considerable effect. VI. Electricity. 1. It is well known that when an excited body is discharged through air, there always appears a very bright flash of light, fa- miliarly known by the name of the spark. This spark when suffi- ciently strong, produces all the effects of heat. It fuses the most refractory metals, and sets fire to gunpowder, to alcohol, and other combustible bodies. Hence, it is obvious, that electricity evolves both heat and light. Indeed the quantity of heat produced by the action of a large galvanic battery is nearly as intense as that produ- ced by the most powerful burning glasses, or by the combustion of a mixture of oxygen and hydrogen gases. This is clearly shown by the experiments of Mr. Children with his magnificent galvanic apparatus.* 2. The effects which electricity produces upon metallic bodies seem to be inversely as their powers of conducting electricity. The best conductors are least injured by its action, and the worst con- ductors are most injured. Van Marumf made the full charge of a battery, charged by the Teylerian machine, to pass through wires fe of an inch in diameter, and consisting of different metals in suc- cession. The following table exhibits the length of each wire melt- ed by the discharge. * Phil. Trans. 1815, p. 363. j- Premiere continuation det experiences faites par ie moyen de la machine electrique Teylerienne. Chap. II.} heat. 145 Inches. Inches. Silver Copper y 0-25 Brass Lead wire - - - 120 Tin - - - - 120 Iron - 5 Gold - 3h By equal discharges of the battery. A wire of iron, -fa inch in diameter, was melted the length of 16 ----------silver, -fa inch in diameter, (partly melted, partly reduced to small bits) - - - 8-5 ---------copper, -^ inch in diameter, (not melted) - 0-25 ---------brass, T^ inch in diameter, (partly melted, partly reduced to small bits) - - - 12 Now it appears from the experiments of Van Marum, that cop- per is a much better conductor of electricity than brass or iron. When electrical shocks are made to pass through a good con- ductor, a thermometer placed in the conductor does not rise. Van Marum made a stream of electric matter pass to the bulb of a ther- mometer ; it rose from 80° to 100°. In the vacuum of an air pump, a thermometer in the same circumstances rose to 120°. Being placed in oxygen gas and in azotic gas, both rarefied to the same degree, the rise of the thermometer was the same.* Mr. Children's experiments, with his powerful galvanic battery, were more susceptible of accuracy than those of Van Marum, owing to the uninterrupted,flow of the electrical current. Hence, in all probability, they are more to be depended on. From the length of metallic wires brought into fusion by this battery, it would appear that the order of the metals as conductors of electricity is as follows.f—*• Silver—2. Zinc—3. Gold—4. Copper—5. Iron— 6. Platinum. It is very remarkable, that when metals are ignited by electricity, they remain longer red hot than when the same effect is induced by a common fire. It would be difficult by a common fire to ignite a wire of zinc. But this may be readily done by means of a gal- vanic battery. 3. Whenever two bodies in different electrical states, the one plus, the other minus, are brought near each other, so as to pro- duce a discharge and destroy the excitement, heat is always evolv- ed. What is the cause, of this heat ? By those who consider the two states of electricity as two distinct fluids, this question is con- sidered as capable of a ready answer. Heat, say they, is formed by the union of the two electricities. While separate, they produce the phenomena of electricity; but when united, they lose their electrical-properties, and constitute heat. The British philosophers, however, who do not admit of the existence of negative electricity as a distinct substance, but consider it as the consequence of a body being deprived of the usual dose of electricity which it possesses • Phil. Mag. viii. 193. | Phil- Trans. 1815, p. 367. Vol. I. T 146 IMPONDERABLE BODIES. J rmsnjN l when in a neutral state, have not been able to answer the question in a satisfactory manner. 4. Berzelius has contrived a theory of combustion and of che- mical affinity, which has a very plausible appearance, and which has been embraced, either entirely or with some modifications, by several of the most eminent chemists of the present day. Accord- ing to him, all bodies which have an affinity for each other are in two opposite states of electricity, and the more intensely each is excited, the stronger is their affinity for each other. When they unite, these opposite electricities are neutralized either in part or entirely, and the neutralization produces the phenomena of com- bustion, namely, the extrication of heat and light. If we were to modify this theory by adopting the French hypothesis, that resinous electricity is a distinct fluid as well as vitreous electricity; and if we were to suppose farther, that the union of these two electricities constitutes the body, which is capable, according to circumstances, of assuming the form of heat or of light; in that case the phenomena of combustion would admit of a simple and com- plete explanation.* The hypothesis is plausible; but it cannot be adopted with safety till Berzelius's theory of chemical affinity be better demonstrated than has hitherto been possible. That every body in nature has a peculiar permanent electrical state which it never loses, except by combining with another body, and that bo- dies which combine are always in opposite states of electricity, may rather, in most cases, be considered as an assertion than a de- duction from the phenomena. Oxygen and chlorine, for example, are two bodies which are conceived to be always negatively elec- tric. Phosphorus and sulphur, with which they unite, are positive. Let it be admitted that these consequences are legitimately deduced from the galvanic experiments of Berzelius, confirmed by Davy. Oxygen and chlorine are capable of uniting and of forming per- manent compounds. This I consider as inconsistent with Berze- lius's doctrine of chemical affinity, taken in its broadest extent. The reason of the union, he says, is, that the oxygen is much more intensely negative than the chlorine. But if negative electricity be a peculiar fluid, the particles of which repel each other, I do not see how bodies charged with it can unite; or at any rate, the union destroys the hypothesis that chemical affinity depends upon the different electrical states of bodies. The subject will require a much closer examination than it has hitherto met with, before the theory of Berzelius can be either adopted or rejected. * [The phenomena of electricity can be so well explained by the presence or absence of one fluid—its accumulation or defect—that to introduce two fluids, is to admit oT more oauses than are necessary to explain the phenomena.—C.] Chap. III.] HEAT. 147 CHAPTER III. Of Electricity. If we rub a piece of sealing wax or a glass tube with a woollen cloth, or the fur from the back of a cat, and then bring into its neighbourhood very small fragments of paper, or the down of fea- thers, we shall find that these minute bodies will be attracted by it, will adhere for some time to its surface, and then be again repelled. This property, which certain bodies acquire by friction, was ob- served by the ancients. Amber was the substance in which it was principally distinguished. Now the Greek name for amber is ■Aix7/>er. On that account the property received the name of electricity. Several other bodies were observed to possess electrical properties by Gilbert and Boyle. But Mr. Stephen Grey, of the Royal So- ciety of London, was probably the first person who made the sub- ject a serious and continued study. He began his electrical expe- riments in the year 1720, and continued them till the period of his death in 1736. He found that certain bodies could be rendered electric by friction while others could not. Glass, resin, sulphur, silk, wool, hair, paper, &c. belong to the first class of bodies; me- tals, and most liquids, to the second. When a glass tube is excited (the name by which the electric state is denoted by electricians) by friction, if it be brought within a certain distance of a metallic rod, however long, the rod acquires the property of attracting light bo- dies, provided it be suspended by silk threads or hair; but not if it be suspended by linen or metal. He found that the same was the case with liquids. But glass, resin, and the other bodies capable of being excited by friction, do not acquire this property when placed near a body in an electric state. Those bodies capable of being excited by friction, Mr. Gray called electrics, the others were non-electrics. Those bodies which become electric by being placed in the neighbourhood of an excited body, he called conductors; those which do not, he called non-conductors. The electrics he found were all non-conductors; while the non-electrics were all con- ductors. The electrics or non-conductors must be employed to sus- pend or insulate metals when they are to receive and retain elec- tricity : the conductors or non-electrics will not answer that purpose. M. Dufay, a French philosopher of considerable celebrity, turn- ed his attention to electricity, seemingly in consequence of the ex- periments of Gray; and in the year 1734 published a paper in the Philosophical Transactions* containing two capital discoveries ; the second of which may be considered as constituting the foundation stone of the science of electricity. 1. When an excited body is placed in the neighbourhood of a light body in its natural state, it attracts the body, and continues to attract it till it has acquired a Phil. Trans, vol. xxxviii. p. 258. He published eight dissertations on electricity, in the Memoirs of tin: French Acadetnv of Sciences. 148 IMPONDERABLE BODIES. S B00K t £ division I. state of excitement. It then repels it. As soon as the light body has lost its electricity by coming in contract with some body in its natural state, it is again attracted, and becoming a second time elec- tric, is repelled as before. So that excited bodies attract bodies in their natural state, but repel them when excited. 2. There are two kinds of electricity; the first belonging to glass, rock crystal, pre- cious stones, hair, and wool; the second to amber, copal, lac, silk, thread, paper, resins, &c. The first kind he called vitreous electri- city, the second resinous electricity. When bodies possess the same kind of electricity, they repel each other; when they possess different kinds of electricity, they attract each other. These discoveries excited the universal attention of philosophers. The science was cultivated with assiduity in every part of Europe, and likewise in America, and has been gradually brought to its present state. The two most distinguished electricians after the two that have been mentioned, are, perhaps, Franklin and Volta. The first discovered the identity of thunder and electricity, and contrived an ingenious theory, which united all the facts, and afford- ed a plausible explanation of the phenomena. The second dis- covered that conductors when brought in contact acquire different electric states, and was led by this discovery to contrive the Vol- taic pile, which has been so important an instrument of investiga- tion in the hands of chemists. Electricity contains so vast a col- lection of facts, that it would be impossible to detail them in the present work; and even if it were possible it would be improper, because the greater part of them have no connxtion with the science of chemistry. I propose, hereafter, to treat of the science of electricity in a separate work. At present I shall merely give such a sketch of the theory as will enable the reader to appreciate the electrical experiments which now constitute an indispensable part of every system of chemistry. 1. Electricity may be conceived to be produced by the agency of a subtile fluid, of such a nature that no quantity of it which we can accumulate in bodies is capable of producing any perceptible effect upon the most delicate balance. The electric fluid then, supposing it to exist, is imponderable. Dufay's original opinion that there exist two kinds of electric fluids, the vitreous and resinous, seems to me to correspond better with all the phenomena, and to lead to fewer perplexing consequences than the theory afterwards sub- stituted for it by Dr. Franklin. According to him bodies may be excited two ways, either by adding to them a superabundant quan- tity of electricity, or by depriving them of a portion of what they naturally contain. When in the first state, he said that they were electrified positively or plus; when in the second state, he said that they were electrified negatively or minus. When they contain their usual quantity of the fluid they exhibit no signs of electricity, in that case they are said to be neutral. Franklin's positive elec- tricity is the same with the vitreous electricity of Dufay; while his negative electricity is the resinous electricity of Dufay. This Chap. III.] ELECTRICITY. 149 theory of Franklin was put into a mathematical dress by Epinus and Cavendish, and has been almost universally adopted both in Great Britain and on the continent. But the recent discoveries made in the science, by the invention of the Voltaic pile, seem to me to agree much better with the theory of Dufay than with that of Franklin; I shall therefore adopt it in preference in the present sketch.* 2. From the experiments of Coulomb we are entitled to infer that the vitreous electricity attracts the resinous with a force in- versely as the square of the distance. But the particles of the vi- treous electricity repel each other with a force inversely as the square of the distance, and the same law holds with the particles of the resinous electricity. 3. When the two electricities are combined together they neu- tralise each other, and in that case the body containing them exhi- bits no sign of electricity. But when the two electricities are sepa- rated from each other, and accumulated either in different bodies or in different parts of the same body, in such cases, the bodies so circumstanced exhibit signs of electricity, by attracting or repelling light bodies, and are then said to be in a state of excitement. 4. Through some substances the electric fluids are capable of passing with great facility ; while through other bodies they pass with considerable difficulty or not at all. The first set of bodies are called conductors, the second non-conductors. All metals are conductors; so is charcoal, and plumbago, and most liquids. Glass, resins, sulphur, diamond, phosphorus, pre- cious stones, silk, hair, wool, are non-conductors. 5. When two bodies are rubbed against each other, the two elec- tricities are separated from each other by the friction; one of them is accumulated in one of the bodies, and the other in the other. Hence both bodies become excited, the one possessing vitreous and the other resinous electricity. If the bodies be conductors, this state cannot continue for an instant, unless they be insulated ; but if the bodies be non-conductors the state possesses some perma- nence. Hence non-conductors alone in ordinary cases can be ex- cited. It is on this account that they have received the name of electrics. When the substances contained in the following table are rubbed against each other, the one that stands first in the list acquires the vitreous electricity, and the one that follows it ac- quires the resinous electricity. Thus the fur of a cat becomes vi- treously electric against whatever substance it is rubbed,, while rough glass becomes resinously electric when rubbed against any body in the table, except sulphur. Feathers when rubbed against wool become resinously electric; but they become vitreously elec- tric when rubbed against wood. • [There seems to be no more reason for introducing two different electric fluids, than for introducing one fluid to account for heat, and another to account for cold. Again, both the vitreous and U*e resinous electricities may b« made apparent in the same piece of glass. 150 IMPONDERABLE BODIES. C BOOK I. £ DIVISION 1. The fur of a cat. Wood. Lac. Polished glass. Paper. Rough glass. Woollen cloth. Silk. Sulphur. Feathers. 6. The electricities when separated from each other are capable of moving through conductors with inconceivable velocity. It ap- pears from the experiments of Sir William Watson, and the other members of the Royal Society, who accompanied him, that the charge of a leyden phial passed through a metallic wire several miles in length, (12276 feet) with a degree of velocity so great, that no perceptible time was seen to elapse between completing the circuit and receiving the shock.* Mr. Cavendish however ascer- tained that iron wire conducts 400 millions of times better than pure water; that sea water containing one-thirtieth of salt conducts 100 times better than pure water, and that a saturated solution of salt conducts 720 times better than pure water.f The following table exhibits a list of the different conductors, arranged according to their goodness, as far as that has been ascertained. The higher in the table the substance occurs, the better a conductor it is. Animal fluids. Acids. Saline solutions. Earths and soft stones. Glass filled with boiling water. Smoke. Steam or vapour. An imperfect vacuum. Hot air. 7. In what way the electric fluids are retained in bodies has not been yet made out in a satisfactory manner. But the air, which is itself a non-conductor, seems to be a principal agent. At least it is known that bodies cannot be excited in vacuo, the electricity making its escape as soon as evolved. 8. The electric fluid appears to spread itself over the surface of bodies. For the quantity which can be accumulated in a body is always proportional to its surface. If a hollow metallic sphere and a solid metallic sphere of the same diameter be both equally charged with electricity, the quantity accumulated in the hollow sphere will be just as great as that accumulated in the solid sphere. M. Poisson has lately reduced to calculation the manner in which electricity is distributed on the surface of bodies. If the body electrified be a sphere, the fluid will be of an equal thickness over every part of the surface. If the body be an ellipsoid, the electri- city will be thickest at the extremities of the larger axis, and thin- nest at the extremities of the smaller axis. The whole fluid will Gold. Charcoal. Silver. Hot water. Copper. Cold water. Brass. Liquids, excepting oils. Platinum. Red-hot glass. Iron. Melted resin. Tin. Flame. Mercury. Ice, not too cold. Lead. Metalline salts. Other metals. Salts in general. Metallic ores. * Phil. Trans. 1748, p. 49, and 491. t !"«•• 1776, p. 196. Chap. III.] ELECTRICITY. 151 assume the form of an ellipsoidal shell, regulated by these laws. In every case the exterior surface of the electric fluid is the same with that of the body; the problem is always reduced to finding the form of the interior surface. If two excited spheres be in contact, the point of contact is neutral, and the greatest quantity of elec- tricity is accumulated in each sphere at the point which is farthest remote from the point of contact. The quantity of electricity in each increases from the point of contact to the maximum point, ac- cording to laws which depend upon the relative diameters of the two spheres, and which have been determined by M. Poisson in a variety of cases. Thus in the case of two spheres, the diameter of the first of which was to that of the second as 1 to 2, the relative thickness of the electricities at the following points from the place of contact was as follows : 30° - - Insensible, j 90 - - 10000 60 - - 0-5563 | 180 - - 1-3535 When the conducting body, in which electricity is accumulated, terminates in a sharp point, the accumulation of electricity at the point is much greater than if the extremity were hemispherical. Hence the reason why a pointed body discharges electricity more readily than a rounded body. Hence the superior advantage of points at the extremity of thunder rods. 8. If an insulated plate of zinc be placed upon an insulated plate of copper, and then withdrawn, if we examine the state of the electricity of each by means of Volta's condenser, we shall find that both are in a state of excitement, and that the electricity of the zinc is vitreous, and that of the copper resinous. This fact was discovered by Volta when he repeated the experiments of Galvani on frogs, about the year 1791, and it induced him to conclude, that what Galvani termed animal electricity, was brought about by the agency of common electricity. Galvani found out by accident that if the crural nerve and the muscles of the leg of a frog be laid bare, if we place a piece of zinc upon the nerve, and a piece of copper upon the muscle, and while the two pieces of metal are in this po- sition make them touch each other, the leg of the frog is immedi- ately thrown into violent convulsions. Galvani conceived that the convulsions were produced by means of a fluid, which he called animal electri ity, which in his opinion was lodged in the nerve and conveyed to the muscles by means of the metals. Volta as- cribed them to the electricity evolved by the contact of the two metals, and which, though small, was sufficient to produce sensible effects upon organs of so delicate a nature. After meditating upon the subject for about nine years, he discovered that if about 40 or 50 pieces of zinc, and as many of copper be procured, each about the size of a half-crown piece, together with as many round pieces of cloth impregnated with a saturated solution of common salt, and if these be piled up upon each other in the following order, 1. A zinc plate. 4. A zinc plate. 7. A zinc plate. 2. A copper plate. 5. A copper plate. 8. A copper plate. o a -:----c „,_u c A _:„_ of ^^ Q> A p.ece of doth 152 IMPONDERABLE BODIES. S BO°K I. £ mvision 1. In this way you proceed till all the plates have been piled up in order with a piece of cloth between each pair. The cloth should be of a somewhat smaller diameter than the metallic plates, and care should be taken not to soak it with so much of the liquid that any of it will be squeezed out by the weight of the plates placed above it. If each pair of zinc and copper plates be soldered toge- ther so much the better. Care must be taken (supposing them sol- dered) that the plates be so placed in the pile, that the same metal is always undermost in each pair. Volta discovered that a pile, constructed in this way, furnishes a continued stream of electricity for a considerable time. He published a description of this new apparatus in the Philosophical Transactions for 1800. It became immediately celebrated in every part of Europe under the name of the Galvanic or Voltaic pile. Mr. Cruickshanks, of Woolwich, soon after substituted a trough of wood for the pile. It was made water tight, and covered within with pitch ; and the pairs of plates, previously soldered together, were cemented at small distances from each other, so as to leave a cell between each. These cells were filled with water holding some salt in solution, or impregnated with about a thirtieth part of its weight of sulphuric, nitric, or mu- riatic acids. More lately an improvement has been introduced into these troughs, which adds considerably to the convenience of the experi- menter, and at the same time increases the energy of the apparatus. The troughs are made of stoneware, with a sufficient number of stoneware diaphragms, dividing them into the requisite number of cells. The metallic plates are square, and a slip of metal of the shape of the letter U is made to join each pair, by one end being soldered to the extremity of a zinc plate, and the other end to the extremity of a copper plate. One of these plates is dipped in- to one cell, and the other into the contiguous cell, while the metallic slip that unites them passes over the diaphragm that divides the two cells. All the plates thus united together are fixed to a metallic rod above, so that they may be lifted out of the trough altogether, either by the hand, or, if too heavy for the hand, by means of a pully properly placed for the pur- pose. This structure will be understood by inspecting the annexed figure. Volta at first constructed his piles of pieces of metal about the size of half crowns; but it was afterwards ascertained, that the energy of the pile, at least as far as chemical phenomena are con- Chap. III.] ELECTRICITY. 153 cerned, increases in proportion to the size of the pieces. At present they are usually made of a diameter amounting to 4, 6, or 8 inches. Indeed, Mr. Children constructed one, each plate of which was 6 feet long and about 4 broad. Several of these troughs are often joined together in experiment. The apparatus is then called a Galvanic or Voltaic battery. Suppose a pile constructed according to Volta's method. If a condenser be applied to that end of it in which the zinc plate is, we shall find that it is charged with vitreous electricity. By the same method we shall find that the electricity of the copper end is resinous. If we moisten our fingers, and apply those of one hand to the zinc end of the pile, upon touching the copper end with the other hand, we receive a shock, the violence of which is always proportional to the number of pairs of plates in the pile. When they amount to several hundreds, the shock is so violent as to be painful. Even in that case, if three or four people take hold of each other's hands, and form a chain, and if the two persons at the extremities touch each an end of the pile, they alone feel the shock, while the intermediate persons are sensible of nothing. When one person'touches the two ends of the pile with his two hands, he feels the shock much more violently in his arms than in any other part of his body. If a wire of gold or platinum be fixed to each extremity of the pile, and the other extremity be introduced into a glass containing water, and so placed that the ends of the wires approach near each other, but do not touch, a stream of gas will be perceived to flow from each wire, and the gas from the wire, proceeding from the negative or resinous end of the pile, is twice as great as that pro- ceeding from the other wire. If these gases be collected in se- parate vessels, it will bewfound that the gas proceeding from the negative wire is hydrogen, and the gas from the positive wire oxy- gen, exactly in the proportion that they exist in water. Hence it is inferred that they are produced by the decomposition of the water. This important fact was first observed by Messrs. Nichol- son and Carlise. It was soon after observed, that the galvanic pile is capable of decomposing many other substances besides water. Ammonia, sulphuric acid, nitric acid, and different metalline salts were sub- jected to its action, and decomposed in a similar way. When the wires proceeding from the two poles of the pile are of iron, copper, or any other metal except platinum or gold, hydrogen gas proceeds as usual from the negative wire, but no gas is extricated from the positive wire, the wire however is speedily encrusted with a coat of oxide. It is easy to see what happens in this case, the oxygen instead of being extricated, combines with the wire, and converts it into an oxide. About the year 1803, a capital discovery, respecting the action of the galvanic battery in decomposing bodies, was made by Berze- Vol.I. U 154 IMPONDERABLE BODIES. C BOOK!. £ DIVISION l. lius and Hisinger.* They tried its effect upon a great variety of salts and other compound bodies, and found that when they were decomposed, they observed the following law: Oxygen and acids are accumulated round the positive pole; -while hydrogen alkalies, earths, and metals, are accumulated round the negative pole. Acids and bases may be made to pass through a considerable column of water, and even to cross each other, in order to accumulate round the poles to which they are respectively attracted. From this general law, Berzelius deduced as a c. nsequence, that the decom- positions were owing to the attractions existing between the bodies and the respective electricities. He afterwards generalized the subject still farther, or rather he adopted the opinion advanced by Sir Humphry Davy, that chemical affinity is identical with electri- cal attractions ; that bodies which unite chemically possess different kinds of electricity; that oxygen and acids are always resinously electric, while hydrogen, alkalies, earths, and metals, are always vitreously electric. Hence the reason, why the one set is attracted by the negative pole and the other by the positive. Sir Humphry Davy took up the subject where Berzelius and Hisinger laid it down. His celebrated dissertation for which Bona- parte's galvanic prize was awarded to him, contains merely a veri- fication of the law discovered by Berzelius and Hisinger. He afterwards went a step farther. According to him bodies con- tinue united, because they are in different electrical states. If we can bring them into a similar state by making them both positive, or both negative, they will repel each other, and of course be de- composed. The galvanic battery produces this effect, if it be suffi- . ciently powerful. Hence in his opinion, we have only to expose any compound whatever to the action of a sufficiently powerful galvanic battery, and it will be decomposed. He applied this theory to the decomposition of the fixed alkalies, and succeeded, showing them to be compounds of oxygen and a metallic basis. He tried the earths by the same means. Some gave traces of decom- position, while others resisted the most powerful battery which it was in his power to apply. The preceding short sketch will enable the reader to understand the galvanic experiments, when I have occasion to introduce them in the subsequent parts of this work. I shall not enter here into any- theory of the pile, nor discuss the respective opinions on the subject advanced by Volta and Berzelius, neither shall I describe the electric column of Deluc and Zamboni, nor the secondary piles of Ritter. These and many other topics will find their place in another "work, which I intend to publish hereafter on Electricity and Galvanism. In the present work, I think, they would be im- properly introduced, as they would divert our attention too long from the proper phenomena of chemistry. * The paper containing these experiments was first published by Gehlen in 1803runder the following title; Vei-suche, betreffend die wirkung der electrischen Saule auf Salze und auf einige von ihren Rasen. Gehlen's Neues Allgefneines Journal der Chemie, i. 115. It was afterwards published in Swedish by Berzelius himself, in the first volume of the Af handlingar, printed at Stockholm in 155 DIVISION II. OF PONDERABLE BODIES. The ponderable bodies at present known amount to 49. They may be arranged under the three following heads. 1. Supporters of combustion—2. Incombustibles—3. Combusti- bles. These classes of bodies will be treated of in their order in the three following chapters. CHAPTER I. OF SIMPLE SUPPORTERS OF COMBUSTION. The term supporter of combustion I apply to those substances which must be present before combustible bodies will burn. Thus a candle will not burn unless it be supplied with a sufficient quan- tity of common air. Common air, then, is a supporter of combus- tion. But we are acquainted with several other substances besides common air which answer the same purpose, and the term sup- porter is applied to them all. By simple supporters we understand such of those bodies as have not hitherto been decompounded. We are at present acquainted with three supporters of combus- tion that have not hitherto been decomposed. The existence of a fourth has been suspect^| by M. Ampere, and its existence ren- dered probable by the ingenuity of Sir Humphry Davy. These four bodies have been distinguished by the following names. 1. Oxygen—2. Chlorine—3. Iodine—4. Fluorine. [As this is a very important part of Dr. Thomson's System of Chemistry, wherein I think he has adopted Sir Humphrey Davy's opinions far too implicitly, and with a strange neglect of the very serious objections that lay against it, I think it necessary to present to the reader, the present state of the controversy; which I appre- hend is far from being favourable to the opinions adopted in this system of chemistry7. When Scheele first discovered the gas now called chlorine (a very appropriate name, from the green tinge it assumes) he sus- pected it was not a compound, but a simple substance. When this gas was afterwards examined, and its properties investigated by Berthollet, he considered it as a compound of oxygen with muria- tic acid gas; and the proportions usually assigned to it, (though in this, as in other cases, chemists differed in opinion as to the de- tails) were 77*65 mur. ac. gas, and 22-35 per cent, oxygen. Hen. 156 SUPPORTERS OF COMBUSTION. C BOOK I. £ DIVISION li. Che. 465. 6th edit. The arguments in support of its being a com- pound of these two gases, are in brief, as follows : 1. Chlorine is never produced, but by treating muriatic acid with substances containing oxygen ; as red lead, manganese, &c.; which part with their oxygen, during the process. 2. This gas is possess- ed of all the properties which may be expected from an union of oxygen with muriatic acid gas. 3. When water saturated with chlorine, is exposed to the sun's light, oxygen is separated, and common muriatic acid gas and water are formed in the vessel. 4. It has the same effect as oxygen in destroying (not changing) vegetable colours; hence the bleachers substitute it in all cases for exposure to air. 5. When used to destroy vegetable colours, the oxygen alone is separated in the process; for after the process, common muriatic acid remains. 6. The mode of forming it is analogous to other combinations of oxygen: when nitrogen, or sulphur, or phosphorus, or sugar, or arsenic, or molybdena, are treated with substances that give out oxygen, the substances are deoxyded, and (as every chemist agrees) the oxygen combines with the substances so treated. These, and other numerous analogies, would lead us to apply the same reasoning to the formation of chlorine (and indeed to iodine and fluorine). On the other hand, it is urged by Sir H. Davy, and those who coincide in opinion with him, that this gas, chlorine, is a simple substance: because, 1. Common muriatic acid gas is formed by detonating together equal volumes of chlorine and hydrogen: after which the bulk of the gases remain the same; whereas, if chlorine contained oxygen, water would have been formed, and the bulk of the gases would have been diminished in proportion to die quantity of water thus formed. Hence, muriatic acid gas, ancrTiot chlorine, is the com- pound ; and consists of equal volumes of chlorine and of hydrogen. 2. Metals form compounds with chlorine, many of which are de- composed by water, and afford muriatic acid gas and metallic oxide: the decomposed water furnishing hydrogen to the chlorine to form common muriatic acid gas, and oxygen to the metal, to form the oxide. 3. When the alkaline and earthy metals (or metal- loids rather) of potash, soda, calcia, &c—-or when mercury, tin, zinc, or iron, are heated in common muriatic acid gas, hydrogen in quantity equal to half the volume of the muriatic acid gas, ap- pears free; and the compounds are such as would have been pro- duced by uniting these metals at once to chlorine. The hydrogen produced is the same in quantity whether the muriatic acid gas had been previously exposed to deliquescent salts, or whether made from liquid muriatic acid. Hence it does not proceed from the decomposition of any water hygrometrically mixed with the muria- tic acid gas employed; nor can it proceed from the decomposition of any water chemically combined with the muriatic acid gas; be- cause there is no proof that this gas contains any such. 4. When metallic oxidesare acted upon by chlorine, oxygen is evolved—and Chap. I.] SUPPORTERS OF COMBUSTION. 157 when acted upon by muriatic acid, water is produced: the oxygen produced, when acted upon by chlorine, is exactly the quantity pre- viously contained in the metallic oxide; and the water produced contains the same quantity of oxygen that the metallic oxide con- tained. 5. Chlorine is not decomposed by red hot charcoal, which usually separates oxygen from every other substance containing it. 6. When tin is combined with chlorine, no oxide of tin is produced by saturating the chlorine with ammonia. 7. When phosphorus is treated with chlorine, a peculiar substance is formed: not the same as when muriatic acid gas is added to phosphoric acid. 8. When this compound is neutralized with ammonia, the product is not muriate of ammonia and phosphoric acid, but an indecomposable, ternary substance. 9. When chlorine and hydrogen are detonated, no water is produced. 10. When chlorine and steam are trans- mitted through a red hot tube, the water is decomposed, its oxygen is evolved, and common muriatic acid is formed by the hydrogen of the water combining with the chlorine. 11. The specific gra- vity of muriatic acid gas is intermediate between the specific gra- vities of hydrogen and chlorine. 12. Finally, if chlorine cannot by analysis be decomposed into muriatic acid gas and oxygen, there is no sufficient evidence to a chemist that it is a compound formed out of these gases. To these arguments, several theoretical objections are stated in two papers signed T. D. in 28 Nicholson's Journ. In 29 Nich. Journ. 190, Mr. Murray of Edinburgh, takes up the subject in opposition to Davy. He states, that the circumstance of charcoal not acting upon chlorine, is as much a difficulty on Mr. Davy's hypothesis, as on M. Berthollet's; for as chlorine is a sup- porter of combustion, it ought to act on so combustible a substance as red hot charcoal: but he shews by direct experiment, that carbo- nic acid gas is actually produced from carbonic oxide and chlorine; which he says could not be the case, unless chlorine had furnished the acidifying dose of oxygen to carbonic oxide. Mr. Murray afterward, in contradiction to the Messrs. Davy's, insists that the explosion produced between chlorine and hydrogen, forms water by the union of the hydrogen to the oxygen of the chlorine, and that this water combines chemically with the original muriatic gas re- maining: and as the Messrs. Davy's had strenuously denied that muriatic acid gas contained any water whatever in chemical union, he undertakes to shew that it does, as an experimentum crucis. He proceeds thus. There can be no suspicion of water existing in ammoniacal gas when well dried by passing it through hot muriate of lime: for as ammoniacal gas consists only of nitrogen and hy- drogen, it contains nothing out of which water can be formed; to the presence whereof, oxygen is indispensible. He then forms muriate of ammonia by combining muriatic acid gas with ammo- niacal gas, both previously made as dry as possible by means of hot muriate of lime, which is known to imbibe moisture with more avidity than almost any other substance. He then distilled the 158 SUPPORTERS OF COMBUSTION. S ^00\^ I £ DIVISION 2 muriate of ammonia so produced, and obtained from it manifest signs of water. This water could not have proceeded from the ammoniacal gas; it must therefore have proceeded from the mu- riatic acid gas; this gas, then, contains water, not hygrometrically —mechanically mixed like moist vapour in the atmosphere—but' chemically combined. To ihese experiments Mr. J. Davy replied in 31 Nichols. Journ. 314, stating that the water thus produced was owing to an inaccu- racy in conducting the process; for that the materials being trans- ferred and exposed to the atmosphere during the experiment, the water that appeared was probably no other than what had been im- bibed from the atmosphere ; inasmuch as no water could be pro- cured from the sal ammoniac thus formed, when the combination was made, the salt transferred, and the distillation conducted with- out access to the atmosphere. This experiment was not only made by Mr. J. Davy, but was also shewn publicly by Sir H. Davy, in his Lectures at the Royal Institute. Dr. Bostock, and Dr. Trail of Liverpool, however, (supplement to 31 Nich. Jour.) repeated Mr. Murray's experiment, with the required precaution of exclud- ing the atmosphere, and they found, contrary to Messrs. Davy's experience, that the muriate of ammonia, formed as above men- tioned, did afford water. In 32 Nich. Jour. 185, Mr. Murray again repeats his experiment excluding the atmosphere, and procures water: he also exposed dry muriate of ammonia for some time to the atmosphere, and found that it had gained no accession of weight by imbibing any atmospheric moisture. So rested this controversy until August or September 1817: for in the Phil. Mag. for Sept. 1817, page 231, Dr. Ure, of Glasgow, is said " to have lately finished a very elaborate series of experi- " ments on the controversial subject of chlorine. Their principal ** object was, to ascertain whether water, or its elements, existed in " or could be obtained from muriate of ammonia. He has perfectly " succeeded in obtaining water from the dry, recently sublimed " salt, by methods quite unobjectionable. The vapour of such " muriate of ammonia being transmitted through laminae of pure " silver, copper, and iron, ignited in glass tubes, water and hydro- " gen were copiously evolved, while the pure metals were convert- " ed into metallic muriates. This fact is decisive in the Doctor's *' opinion of the great chemical controversy relative to chlorine and " muriatic acid, and seems clearly to establish the former theory of " Berthollet and Lavoisier, in opposition to that more lately ad- " vanced by Sir H. Davy, with such apparent cogency of argument " as to have led almost all the chemists of Europe to embrace his " opinion. The details of the experiments have been for some time " communicated to a distinguished member of the Royal Society, " and will speedily be laid before the public. This decomposition .' of the salt by the metals at an elevated temperature, is analagous t' to the decomposition of potash in ignited gun barrels by Gay .< Lussac and Thenard." Of these experiments (not being then Chap. I.] SUPPORTERS OF COMBUSTION. 159 fully detailed) Dr. Thomson seems to have taken no notice; for his preface to this System of Chemistry is dated October 1817. On Monday the 15th of last December, a paper was read before the Royal Society of Edinburgh, by Dr. Murray, containing a se- ries of experiments made with all possible precautions in addition to, and confirmation of, those of Dr. Ure, the professor of che- mistry at Glasgow. Water was in these cases indisputably pro- cured from the decomposition of dry muriate of ammonia made with every precaution that could be taken to exclude extraneous moisture. This is the last account of the controversy that has reached this country, Dr. Murray's experiments being noticed only in the Phil. Mag. for Dec. 1817, page 457, and this note being written the 1st of March 1818. I consider these experiments fatal to the whole theory of Sir H. Davy, herein adopted by Dr. Thom- son ; for they enable us to account for the water formed by the hydrogen exploded with the oxygen of the chlorine. To me, they seem also fatal to the theory that constitutes iodine and fluorine supporters of combustion; for iodine is always procured by means of some substance that gives out its oxygen in the process: and fluorine is so indecisively ranked' in this class, as to form but a slight difficulty (vide sect. 4, chap. i. of this division). Oxygen alone then, seems likely to be reinstated as the exclusive supporter of combustion.—C] [Since writing the above the following notice of Dr. Murray's Paper relative to this sub- ject has been received. See Tilloch's Phil. Mag. for Jan. 1818, voL li. p. 60. •'Jan. 12, 1818. The continuation of Dr. Murray's Paper on Muriatic Acid was read. In the preceding part ofitthe results of experiments had been stated, whence it appeared that from the action of metals on muriatic acid gas water is deposited. This is a result obviously incompatible with the doctrine in which chlorine is considered as a simple substance, since, according to that doctrine, muriatic acid gas is the real acid, altogether free from water. As the opposite doctrine holds the existence of combined water in the gas to the account of a fourth of its weight, a portion of this may be supposed to be liberated by the action of the metal. A difficulty however presents itself even on this view of the subject. The action consists in the acid enabling the metal to decompose the water and combine yith its oxygen; with the oxide thus formed the acid unites, and no water remains to be debited, since none is liberated from its combination with the acid, but what is spent in the rxidation of the me- tal. The products therefore ought to be the same on this hypothesis a» on the other, name- ly, a dry muriate or chloride, and hydrogen gas. " It was shown that the water obtained in the experiments could p>t be derived from hygro- metric vapour; that it could not be accounted for from the supposition of a portion of water beiug combined with the acid in the gas beyond that which is strictly essential to its consti- tution;—and that it could not be ascribed to any lower degre* of oxidation of the metal being established. One explanation remained, that it might arte from the formation of a super- muriate, the quantity of water combined with the quanhty of acid, which forms a neutral muriate, being sufficient for the oxidation of the metal; so that if an additional portion of acid entered into the combination, the water of this might be liberated. It was accordingly found that the products in all these cases were sensibly acid, and this even when any source offal- lacy, from a subversion of ihe combination by thr agency of water, was ob< iatid. In the se- quel another explanation was suggested on a different view of the subject, if this should not be considered as sufficient. . " Dr. Murray considered the results of these experiments as confirming, in addition to what he had before done, the fallacy of the opinion in which chlorine is regarded as a simple substance, which, with hydrogen, forms muriatic acid. The opposite opinion, that it is a compound of muriatic acid with oxygen, and that muriatic gas is a compouud of muriatic acid and water, might be held to be established; and it undoubtedly may be maintained. But he has presented a different view of the subject, as being more conformable to the present State of chemical theory. "The progress of chemical discovery has shown that oxygen cannot be regarded as exclu^ 160 SUPPORTERS OF COMBUSTION. 5 BOOK f. £ DIVISION 2. sively the principle which communicates acidity. The same property is in different cases communicated by hydrogen ; and this fact he regards as affording the only argument of any weight in support of the new theory of chlorine. " When water is obtained from muriatic acid gas, it does not necessarily follow that it has pre-existed in the state of water. It is equally possible, dpriori, that the elements of water may have existed in the gas. On this view oxymuriatic acid will be a binary compound of a radical at present unknown with oxygen, and muriatic acid a ternary compound of the same radical with oxvgen and hydrogen. And when muriatic acid gas is formed from the mutual action of oxymuriatic gas and hydrogen, it is simply from the hydrogen entering into the combii.ation. In the processes by which watei- is obtained from it, the water is formed by its hydrogen and part of its oxygen entering into union. The same view he extends to the other acids which have been supposed to contain combined water. Sulphurous acid is the proper binary compound of sulphur and oxygen; sulphuric acid is a ternary compound of sulphur, oxygen, and hydrogen; and nitric acid is a ternary compound of nitrogen, oxygen, and hydrogen. " While each of these elements, oxygen and hydrogen, communicates acidity, their com- bined action seems to do so in a still higher degree. Sulphur with hydrogen forms a weak acid ;—with oxygen another acid somewhat stronger ;■*— with oxygen and hydrogen one of still greater power. Nitrogen with hydrogen forms a compound having no acidity ; with oxygen in two proportions it forms oxides; with oxygen and hydrogen a powerful acid. Carbon with hydrogen forms compounds which are not acid; with oxygen in one proportion it forms an oxide, in another a weak acid; with oxygen and hydrogen the different vegetable acids which are of much superior strength. " This explains the apparent anomaly which appeared in the old doctrine with regard te oxymuriatic acid, that it is a weaker acid than the muriatic, though it has received an addi- tional portion of oxygen. It is so precisely as sulphurous acid is weaker than sulphuric. The proper points of resemblance are the sulphurous acid with the oxymuriatic, and the sulphu- ric with the muriatic. It was shown that oxymuriatic acid has a stricter analogy to sulphu- rous acid than to any other body; and that any deviation from this analogy arises from the large proportion of oxygen which the former contains. «• The relations of iodine, the analogy of which in some respects to those of chlorine has chiefly given predominance to the new doctrine, with regard to the latter accords perfectly with these views. The nature of the compounds of inflammable bodies with chlorine ac- cords also better with them than with either of the other doctrines. And they serve to ex- plain a number of other facts connected with the action of acids and their combinations. They afford for example a solution of the difficulty which gave rise to the investigation—that of the production of water in the action of metals on muriatic acid gas. " Dr. M. extended the same view to the constitution of the alkalies. Alkalinity is as well as acidity a result of the agency of oxygen,—the fixed alkalies, the earths, and metallic oxides, all of vhich contain oxygen as a common element, forming a series in which there is no well defined %e of separation. Ammonia stands insulated; it contains no oxygen, yet its alkaline proportie" are energetic, an anomaly which has led generally to the belief that oxygen must exist in on« or other of its constituent principles. It may be explained, however, on a very different pritniple. As hydrogen like oxygen communicates acidity, so it may like oxygen give rise to alkalinity. Ammonia therefore will be a compound, of which nitrogen is the base, deriving its alkaline quality from hydrogen ; and hence stands in the same relation to the other alkalis tint sulphuretted hydrogen does to the acids. If the claim of the newly- discovered principle^ opium to the rank of an alkali be established, it may stand in the same relation to the otters that prussic acid or some of the vegetable acids do to the acids. " The fixed alkalies, barytes, strontites, and lime have been supposed to contain combined water essential to them in *jeir insulated form. It is probable that the elements of water rather exist in direct combination with their metallic base: that potash, for example, is a ter- nary compound of potassium, «xygen, and hydrogen; and thus the entire class will exhibit the same relations as the class ol acids, some being compounds of a base with oxygen, am- monia a compound of a base with tydrogen, and potash, soda, etc. compounds of a base with oxygen and hydrogen; and these last, like the analogous order among the acids, exceed the others in power. When an acid and alkali unite, the hydrogen of both is expended in form- ing water. The neutral salts, according to these views, will therefore be either sur-com- pounds of two binary compounds, one of the radical of the acid, the other of the radical of the base with oxygen, or they are ternary compounds of the two radicals with oxygen. The latter is the more probable opinion." Dr. Thomson, in the Annals of Philosophy for January and February, 1818, has no- ticed these papers of Dr. Ure and Dr. Murray, and given a similar abridgment of the latter. Whether any attempt will be made to contradict the facts, or to reconcile the reasonings with the modern doctrine of chlorine being a simple substance, the editor cannot know; the periodical numbers of Dr. Tilloch and Dr. Thomson having arrived just before the former part of this note was struck off,—C] Chap. I.] OXYGEN. 161 They act so important a part in chemistry, that it is proper to become acquainted with them as early as possible. I shall treat of them in order in the four following sections. SECTION I. OF OXYGEN. Oxygen may be obtained by the following process i Procure an iron bottle of the shape A, and capable of holding rather more than an English pint. To the mouth of this bottle an iron tube bent like B, is to be fitted by grinding. A gun barrel de- prived of its butt-end an- swers the purpose very well. Into the bottle put any quan- tity of the black oxide of manganese* in powder; fix the iron tube into its mouth, and the joining must be air tight; then put the bottle into a common fire, and surround it on all sides with burning coals. The extremity of the tube must be plunged under the surface of the water with which the vessel C is filled. This vessel may be of wood or of japanned tin plate. It has a wooden shelf running along two of its sides, about three inches below the top, and an inch under the sur- face of the water. In one part of this shelf there is a slit, into which the extremity of the iron tube plunges. The heat of the fire expels the greatest part of the air contained in the bottle. It may be perceived bubbling up through the water of the vessel C from the extremity of the iron tube. At first the air bubbles come over in torrents; but after having continued for some time they cease altogether. Meanwhile the bottle is becoming gradually hotter. When it is obscurely red the air bubbles make their ap- pearance again, and become more abundant as the heat increases. This is the signal for placing the glass jar D, open at the lower ex- tremity, previously filled with water, so as to be exactly over the open end of $he gun-barrel. The air bubbles ascend to the top of * This substance shall be afterwards described. It is now very well known in Britain, as it is in common use with bleachers and several other manufacturers, from whom it may be easily procured. [In America, the most convenient material, is nitre; such as it exists when purified for the use of the gunpowder makers; that is, freed from common salt and me- chanical impurities. The heat should he gradually raised, till the oxygen comes over, and then rather diminished than increased. Small portions should be collected during the first part of the process, and tried with a taper, before the receiver be adapted. Manganese often furnishes much carbonic acid.—C] Vol. I. X 162 SUPPORTERS OF COMBUSTION. i BOOK T. __ DIVISION 2. the glass jar D, and gradually displace all the water. The glass jar D then appears to be empty, but is in fact filled with air. It may be removed in the following manner: slide it away a little from the gun-barrel, and then dipping any flat dish into the water below it, raise it on the dish, and bear it away. The dish must be allowed to retain a quantity of water in it, to prevent the air from escaping (see E.) Another jar may then be filled with air in the same manner; and this process may be continued either till the manganese ceases to give out air, or till as many jarfuls have been obtained as are required.* This method of obtaining and confi- ning air was first invented by Dr. Mayow, and afterwards much improved by Dr. Hales. All the airs obtained by this or any other process, or, to speak more properly, all the airs differing in their properties from the air of the atmosphere, have, in order to distin- guish them from it, been called gases; and this name we shall af- terwards employ, f Oxygen gas may be obtained likewise by the following process: D represents a wooden trough, the inside of which is lined with lead or tinned copper. C is the cavity of the trough, which ought to be a foot deep. It is to be filled with water at least an inch about the shelf AB, which runs along the inside of it, about three inches from the top. In the body of the trough, which may be called the cistern, the jars destined to hold gas are to be' filled with water, and then to be lifted! and placed inverted upon the shelf at B. This trough, which was invented by Dr. Priestley, has been called by the French chemists the pneumatico-chemical, or simply pneu- matic apparatus, and is extremely useful in all experiments in which gases are concerned. Into the glass vessel E put a quantity of the black oxide of manganese in powder, and pour over it as much of that liquid which in commerce is called oil of vitriol, and in che- mistry sulphuric acid, as is sufficient to form the whole into a thin paste. Then insert into the mouth of the vessel the glass tube F, so closely that no air can escape except through the tube. This may * For a more exact description of this and similar apparatus, the reader is referred to Lavoisier's Elements of Chemistry, and Priestley on Airs, mid above all to Mr. Watt's de- scription of a pneumatic apparatus, in Beddoes' Considerations on Factitious Airs. [A better reference would be to Henry's or Accum's Chemistry, which are common in America.__C.l \ The word gas was first introduced into chemistry by Van Helmont. He seems to have intended to denote by it every thing which is driven off from bodies in the state of va- pour by heat. He divides gases into five classes. " Nescivit, inquam, schola Galenica hac- tenus differentiam inter gas ventosum (quod mere aer est, id est, ventus per syderum bias commotus,) gas pingue; gas siccum, quod sublimatum dicitur; gas fuliginosum, sive endi- micuro; et gas sylvestre, sive incoeroibile, quod in corpus cogi non potest visibi'le." Van Helmont de Flatibus, § 4. Macqaer seems to have introduced the word into the language of modern chemistry. 25 Chap. I.] OXYGEN. 163 be done either by grinding, or by covering the joining with a little glazier's putty, and then laying over it slips of bladder or linen dipped in glue or in a mixture of the white of eggs and quicklime. The whole must be made fast with cord.* The end of the tube F is then to be plunged into the pneumatic apparatus D, and the jar G, previously filled with water, to be placed over it on the shelf. The whole apparatus being fixed in that situation, the glass vessel E is to be heated by means of a lamp or a candle. A quantity of oxygen gas rushes along the tube F, and fills the jar G. As soon as the jar is filled, it may be slid to another part of the shelf, and other jars substituted in its place, till as much gas has been obtain- ed as is wanted. The last of the these methods of obtaining oxy- gen gas was discovered by Scheele,f the first by Dr. Priestley.!: The gas which we have obtained by the above processes was discovered by Dr. Priestley on the 1st of August, 1774, and called by him dephlogisticated air. Mr. Scheele of Sweden discovered it before 1777, without any previous knowledge of what Dr. Priest- ley had done; he gave it the name of empyreal air.§ Condorcet gave it first the name of vital air ; and Mr. Lavoisier afterwards called it oxygen gas; a name which is now generally received, and which we shall adopt. 1. Oxygen gas is colourless, and invisible like common air. Like it, too, it is elastic, and capable of indefinite expansion and com- pression. It has no perceptible taste, and when pure is destitute of smell. 2. Oxygen gas is somewhat heavier than common air. If we reckon the specific gravity of common air 1*000, then the specific gravity of oxygen gas, according to different experimenters, is as follows:—1*103 Kirwan||.—1-114 Saussure.^j—1*1088 Allen and Pepys.** The mean of these experiments gives us 1*1088, which is certainly very near the truth. I am disposed to consider the specific gravity deduced by Dr. Prout, from considerations which I cannot explain here, as in all probability still more correct, name- * This process, by which the joinings of vessels are made air-tight, is called luting, and the substances used for that purpose are called lutes. The lute most commonly used by chemists, when the vessels are exposed to heat, is fat lute, made by beating together in a mortar fine clay and boiled linseed oil. Bees wax, melted with about one-eighth part of turpentine, answers very well, when the vessels are not exposed to heat. The accuracy of chemical experiments depends almost entirely in many cases upon securing the joiuings pro- perly with luting. The operation is always tedious; and some practice is necessary before one can succeed in luting accurately. Some very good directions are given by Lavoisier. See his Elements, Part iii. chap. 7. In many cases luting may be avoided altogether by using glass-vessels properly fitted to each other by grinding them with emery. [Lctes.—Paste of linseed meal. Slacked lime sifted through muslin into common paste. It is convenient to smear linen or strips of paper with these pastes, and tie them on with thread. Loam beat up with molasses forms a lute that bears great heat.—C ] | On Air and Fire, p. 43. Engl. Trans. t Priestley on Air, ii. 154. § Scheele on Air and Fire, p. 34. Engl. Trans. II On phlogiston, p. 25. Lavoisier, Biot, and Arago, give the same specific gravity. H Ann. de Chim. Ixxi. '260. ** On the quantity of carbon in carbonic acid. Phil. Trans. 1807. 164 SUPPORTERS OF COMBUSTION. 5 BOOK I. £nrvisiow2. ly, 1-1111.* On that supposition 100 cubic inches of this gas at the temperature of 60°, and when the barometer stands at 30 inches, will weigh 33*888 grains. At the same temperature, and under the same pressure, 100 cubic inches of common air will weigh 30*5 grains.f 3. If a lighted taper be let down into a phial filled with oxygen gas, it burns with such splendour that the eye can scarcely bear the glare of light, and at the same time produces a much greater heat than when burning in common air. It is well known that a candle put into a well-closed jar filled with common air is extinguished in a few seconds. This is the case also with a candle inclosed in oxy- gen gas ; but it burns much longer in an equal quantity of that gas than of common air. 4. It was proved long ago by Boyle, that animals cannot live without air, and by Mayow that they cannot breathe the same air for any length of time without suffocation. Dr. Priestley and se- veral other philosophers have shown us, that animals live much longer in the same quantity of oxygen gas than of common air. Count Morozzo placed a number of sparrows, one after another, in a glass bell filled with common air, and inverted over water. H. M. H. M. The first sparrow lived 3 O I The third - 0 1 The second - - O 3 | He filled the same glass with oxygen gas, and repeated the ex- periment. H. M. H. M. The first sparrow lived 5 23 The sixth 0 47 The second - 2 10 The seventh 0 27 The third - - 1 30 The eighth 0 30 The fourth - - 1 10 The ninth 0 22 The fifth - - 0 30 The tenth 0 21 He then put in two together; the one died in 20 minutes, but the Other lived an hour longer. 5. It has been ascertained by experiments, which shall be after- wards related, that the atmospherical air contains 21 parts in the hundred (in bulk) of oxygen gas; and that no substance will burn in common air previously deprived of all the oxygen gas which it contains. But combustibles burn with great splendour in oxygen gas, or in other gases to which oxygen has been added. 6. It has been proved also, by many experiments, that no breath- ing animal can live for a moment in any air or gas which does not contain oxygen mixed with it. Oxygen gas, then, is absolutely ne- cessary for respiration. 7. When substances are burnt in oxygen gas, or in any other gas • Annals of Philosophy, vi. 322. *f This determination results from the experiments of Sir George Stuckburgh, which appear to have been made with great precision. Chap. I.] CHLORINE. 165 containing oxygen, if the air be examined after the combustion, we shall find that a great part of the oxygen has disappeared. If charr coal, for instance, be burnt in oxygen gas, there will be found, in- stead of part of the oxygen, another very different gas, known by the name of carbonic acid gas. The oxygen in this case combines with the combustible body. The new compound formed is called an oxide, or sometimes an acid. Exactly the same thing takes place when air is respired by animals; part of the oxygen gas disappears, and its place is occupied by substances possessed of very different properties. 8. Oxygen gas is not sensibly absorbed by water, though jarfuls of it be left in contact with that liquid. It has been ascertained, however, that water does in reality absorb a small portion of it, though not enough to.occasion any perceptible diminution in the bulk of the gas. When water is freed from all air by boiling and the action of the air pump, Dr. Henry ascertained, that 100 cubic inches of it will imbibe 3-55 inches of oxygen gas.* Saussure found that water, in the same circumstances, absorbs 6*5 cubic inches of this gas.f But Mr. Dalton has rendered it probable that Saussure's estimate is considerably above the truth4 SECTION II. OF CHLORINE. Cblorine may be obtained by the following method: Put into a small glass retort a quantity of the black oxide of manganese in powder, and pour over it as much of the common muria- tic acid of the shops as will make the whole into a very thin paste. Then plunge the beak of the retort into the water trough, and place over it a stout glass phial capable of holding about a quart, previously filled with water. Apply the heat of a lamp to the bottom of the retort. A gas is extricated which enters into the mouth of the inverted phial, displaces the water and fills it. As soon as the phial is full it is to be withdrawn and its mouth carefully stopped with a glass stopper, accurately ground so as to fit, and which must be previous- ly provided. Other phials may be then substituted and filled in succession till the requisite quantity of gas is obtained. This gas is chlorine. This substance was discovered by Mr. Scheele, and an account of it published by him in the Memoirs of the Swedish Academy of Sciences, for 1774, in his celebrated paper on manganese, which • Phil. Trans. 1803, p. 174. t Annals of PUosophy, vi. 340. $ Annals of Philosophy, vii, 213. 166 SUPPORTERS OF COMBUSTION. 5" BOOK I. £ DIVISION 2. had occupied him for three years.* He gave it the name of de- phlogisticated muriatic acid, considering it as muriatic acid de- prived of phlogiston. Berthollet made a set of experiments on it, about the year 1785, which were published in the Memoirs of the French Academy of Sciences. He considered himself to have proved that it is a compound of muriatic acid and oxygen; an opinion which was soon after adopted by the chemical world in general. On that account it received the name of oxygenized muria- tic acid, which was afterwards contracted by Mr. Kirwan to oxy- muriatic acid. The experiments of Scheele and Berthollet were repeated and varied by all the eminent chemists of the time. But the first great addition to the discoveries of these philosophers was . made by Gay-Lussac and Thenard, and published by them, in 1811, in the second volume of their Recherches Ppysico-chemique, p. 94. They showed that the opinion that oxymuriatic acid contains no oxygen might be supported. But at the same time assigned their reasons for considering the old opinion as well founded. An ab- stract of these important experiments had been published however in 1809.f These experiments drew the attention of Sir Humphry Davy to the subject, and he soon after communicated a paper to the Royal Society to show that no oxygen gas could be separated from oxymuriatic acid, nor any proof produced that it contained oxygen. This paper was published in the Philosophical Transac- tions for 1810.| This was speedily followed by another paper upon the same subject.^ He drew as a conclusion that oxymuria-i tic acid is an undecompounded substance; on that account he ap- plied to it the new name chlorine, from the yellow colour which it possesses. At present, this name is almost generally adopted by chemists. Few chemists were disposed at first to accede to the opinion of Davy. But subsequent discoveries have greatly aug- mented the weight of his reasoning, and, at present, his view of the subject is almost universally adopted.|| Chlorine possesses the following properties. 1. It is a gaseous body and possesses the mechanical properties of common air. Its colour is greenish yellow. Its odour is ex- ceedingly strong and suffocating, exactly similar to that of aqua regia, or the well known mixture of nitric and muriatic acid. When a person is obliged to inspire the fumes of chlorine, it pro- duces a most insufferable sensation of suffocation, occasions a vio- lent cough with much expectoration, which continues for some time, and brings on a very great degree of debility. Its taste is astringent. 2. The specific gravity of chlorine gas, according to the expe- riments of Gay-Lussac and Thenard, is 2-4700 ;^j according to Davy it is 2-395. Dr. Prout, guided by theoretic reasons, which * Memoires de Chymie de M. C. W. Scheele, i. 67. f Memoires d'Arcueil, ii. 295. * P. 231. § Phil. Trans. 1811, p. 1. H [See note p. 155.—C.] *, Recherches physico-chemique, ii 125. Chap. I.] CHLORINE. 167 cannot be stated here, conside s 2-500 as probably the true specific gravity, and with this opinion I am disposed to agree. In all these cases the specific gravity of air is reckoned 1*000. Supposing the true specific gravity to be 2-5, then 100 cubic inches of it will weigh 76*25 grains at the temperature of 60° and when the baro- meter stands at 30 inches. 3. When any vegetable, blue colour, is exposed to the action of chlorine, it is immediately destroyed and cannot afterwards be re- stored by any method whatever. Indeed chlorine possesses the property of destroying all vegetable colours, and of rendering co- loured bodies white. This property was first observed by Scheele. The knowledge of it induced Berthollet to propose the introduction of chlorine into the practice of bleaching. This suggestion has been successfully adopted in Great Britain and Ireland. At pre- sent all the great bleaching works, in this country, employ chlorine as the grand whitening agent. For the first introduction of it we are indebted to Mr. Watt.* 4. If a lighted taper be plunged into a phial filled with chlorine gas, it continues to burn with a low red flame, emitting much smoke but giving out but little light. If a piece of phosphorus be put into this gas it takes fire of its own accord, burning with a pale yellow- ish green light. Antimony, likewise arsenic, zinc, iron, and se- veral other metals, take fire of their own accord when plunged into chlorine, and burn with considerable splendour. During all these cases of combustion the quantity of chlorine diminishes, and if the portion of combustible be sufficient the gas disappears altogether. The combustible is totally altered in its appearance and converted into a new substance, which has received the name of chloride. This chloride is a compound of the combustible substance and the chlorine. 5. If an animal be plunged in an atmosphere of chlorine, so as to be obliged to breathe it in a pure state, it dies almost instantly. This gas then is incapable of supporting animal life. In this respect it differs entirely from oxygen gas. 6. Water absorbs this gas with considerable rapidity, provided the gas be pure; but much more slowly when it is mixed with air or any other foreign gas. According to the experiments of Dalton, one volume of water at the ordinary temperature, and under the common pressure, absorbs two volumes of chlorine gas.f The wa- ter acquires the greenish yellow colour, the disagreeable smell, the astringent taste, and the whitening qualities of the gas itself. 7. When chlorine in combination with any other body is exposed to the action of the galvanic battery, the compound is decomposed and the chlorine is deposited at the positive pole, while the other substance is deposited at the negative pole. The only probable ex- * See Annals of Philosophy, viii. 1. [See a far better account in all respects in i Parke's Essays, page 47,48.—C.] t Dalton's New System of Chemistry, ii. 298. 168 SUPPORTERS OF COMBUSTION. C BOOK I. £ DIVISION 2. ception to this rule is when chlorine and oxygen are in combina- tion ; in such a case it is reasonable to believe that the oxygen would be given off at the positive pole, and the chlorine at the ne- gative pole, but I am not certain whether the experiment has been tried. At high temperatures chlorine displaces oxygen from its combination with many of the metals and unites with them itself. 8. Chlorine gas may be exposed to a very high temperature by passing it through a white hot porcelain tube, without experiencing any change. 9. Chlorine has the property of combining with oxygen, and of forming four distinct substances, which have been particularly ex- amined. We cannot form the combination directly. All these compounds are obtained by means of a salt first prepared and de- scribed by Berthollet. It was long distinguished by the name of hyperoxymuriate of potash, a name which has been recently changed into chlorate of potash. It is obtained by dissolving a quantity of the common potash of the shops in water, and causing a current of chlorine gas to pass through the solution as long as it continues to be absorbed. After some time flat rhomboidal crystals possess- ing considerable lustre are deposited; these crystals constitute the salt in question. Let us explain the way in which the different com- pounds of oxygen and chlorine may be obtained from it. 1. When this salt is put into a small glass flask and muriatic acid poured over it, an effervescence takes place and a greenish yellow gas is extricated in abundance. If the muriatic acid be diluted with water, and the quantity of salt with which it is mixed be con- siderable in proportion to that of the acid, and if a very gentle heat only be employed, a gas is extricated very slowly, which may be recived in small glass jars standing over mercury. After the gas has been prepared in this manner, it is better to allow it to re- main for 24 hours in contact with the mercury. For, as originally prepared, it always contains a good deal of chlorine gas mixed with it, which disguises and greatly injures its properties. Mercury has the property of absorbing and uniting with chlorine, while it does not actxipon the new gas. It therefore gradually removes the chlo- rine and leaves the new gas in a state of purity. The new gas prepared in the way just described was discovered, in 1811, by Sir Humphry Davy, who gave it the name of euchlo- rine* But it will be better to distinguish it by the appellation of protoxide of chlorine, indicating by that name, that it is a com- pound of chlorine with the smallest quantity of oxygen with which it is capable of combining. It possesses the following properties. Its colour is much more intense and more yellow than that of chlorine. When contained in a small glass tube it still appears of a very lively yellow, whereas chlorine, in the same circumstances, would scarcely be visible. Its smell resembles that of burnt sugar, mixed, however, with • Phil Trans. 1811, p. 155. Chap. I.J CHLORINE. 169 the odour of chlorine. In all probability this last odour is owing to the presence of a small portion of this gas. For it is extremely difficult to free it completely from chlorine. When a moderate heat is applied to a vessel filled with protoxide of chlorine an explosion takes place, and the gas is decomposed into a mixture of chlorine and oxygen gas. A very gentle heat is sufficient to produce this decomposition, sometimes even the heat of the hand will do it. The explosion is but feeble. According to the experiments of Davy, five volumes of protoxide of chlorine become six when decomposed, and the decomposed gas is a. mix- ture of two volumes of chlorine and one volume of oxygen.* Hence it is composed by weight of fChlorine - 5*000 - 81*82 - 100 - 4*50 Oxygen - 1*111 - 18-18 - 22*22 - 1*00 100-00 Now if we make 1*00 represent the weight of the smallest par- ticle of oxygen which can unite with a body, we shall find after- wards that the smallest quantity of chlorine that can combine with a body will be represented by 4-5. Hence we may conclude that protoxide of chlorine is a compound of one atom of chlorine and one atom of oxygen. From the preceding data it follows that the specific gravity of protoxide of chlorine is 2*407, supposing the specific gravity of air to be 14 This gas destroys vegetable colours, as well as chlorine ; but it first gives blue colours a tint of red. Several substances, as phosphorus, take fire when they come in contact with protoxide of chlorine, and occasion an explosion. Water absorbs eight times its volume of this gas, and acquires an orange colour, and the peculiar smell of the gas. * Phil. Trans. 1811, p. 157. t [These numbers will be found proportionate to one another in the same line. But as Dr. Thomson relies on Dr. Prout's calculations in the 6th volume of the Annals of Philoso- phy, I find it absolutely necessary to insert those calculations at the end of this volume; which will furnish the required formulae.—C.] $ [That is, the specific gravity of chlorine when compared with common air being 2-5 and ot oxygen 1-1111, as stated in page 167 from Dr. Prout—and as the protoxide of chlo- rine, according to Dr. Thomson, consists of two volumes of chlorine and one of oxygen, as Stated iii page 168, then Specific gravity of chlorine - - - 2-5 1 --------oxygen .... l -1 111 3-6111 The half of this would be the mean specific gravity, if the compound consisted only of one part chlorine and one part oxygen: but it consists of two parts chlorine and one part oxygen: therefore divide 3-6111 by three and multiply the quotient by two, and you will arrive at the specific gravity of chlorine alone: thus 3 CH1 = 1-2037 X 2 = 2-4074. But in producing this result, no notice is taken of the condensation of six volumes into 5, which in my opinion should enter into the calculation. Throughout this book, the number assigned as the weight of an atom of oxygen, the standard of comparison, is, L—C.] Vol. I. Y 170 SUPPORTERS OF COMBUSTION. $ BOOK I. £ DIVISION '2. 2. The deutoxide of chlorine* was discovered about the same time by Sir Humphry Davy and Count Von Stadion, of Vienna; but Davy's account of it was published sooner than that of Count Von Stadion.f The method of obtaining it is as follows : mix to- gether a small quantity (not more than 50 grains) of chlorate of potash in powder with sulphuric acid, till the whole forms a dry paste, which will have an orange colour. Put this paste into a small glass retort, and plunge the belly of the retort into hot water, and keep it in that position for some time, taking care that the tem- perature of the water never becomes so high as 212°. A bright yellowish green gas separates from the paste, which must be re- ceived in small glass jars standing over mercury. - This gas con- stitutes the deutoxide of chlorine. It possesses the following pro- perties. Its colour is a still brighter yellowish green than that of protoxide of chlorine. Its smell is peculiar and aromatic, without any mix- ture of the smell of chlorine. Water absorbs, at least, seven times its volume of this gas. The solution is deep yellow, and has an as- tringent and corrosive taste, leaving a disagreeable and lasting im- pression on the tongue. It destroys moist vegetable blues without previously reddening them. It does not act upon mercury, nor upon any of the combustible substances, tried by Davy, except phosphorus ; which, when introduced into the gas occasions an ex- plosion, and burns with great brilliancy. When heated to the temperature of 212° it explodes with more violence than protoxide of chlorine, giving out much light. Two volumes of deutoxide of chlorine when thus exploded are convert- ed into three volumes, consisting of a mixture of two volumes of oxygen and one volume of chlorine.:): Hence it is composed by weight of Chlorine - 2-5 - 52*94 - 100 - 4*50 Oxygen - 2-222 - 47-06 - 88-88 - 4*00 10000 Now as the weight of an atom of chlorine was represented by 4-5, and that of an atom of oxygen by one, we see from the last column of the preceding table that the deutoxide of chlorine is composed of one atom of chlorine combined with four atoms of oxygen.§ From the preceding data it is obvious that the specific gravity of * [If Dr. Ure and Dr. Murray be well founded in their late experiments, chlorine will be the protoxide of muriatic acid gas; and the gas here mentioned will be the tritoxide.—C] ■J- Davy's account is published in the Philosophical Transactions for 1815, p. 214. Count Von Stadion's in Gilbert's Annalen der Physik, Iii. 179, published in February, 1816. * Davy, Phil. Trans. 1815, p. 216, and Gay Lussac, Ann. de Chim. et Phys. i. 220. § According to Count Von Stadion its constituents are two volumes chlorine and three volumes oxygen. This would make it a compound of one atom chlorine and three atoms oxygen. But the properties of the substance described by the Count differ so much from those of the gas examined by Davy that it is probable they are distinct substances. The rea- der will find an account of uie properties of the deutoxide of chlorine of Count Von Stadion in the Annals of Philosophy, vol. ix. p. 22. Chap. I.J CHLORINE. 171 deutoxide of chlorine must be 2-361, supposing that of common air to be 100.* 3. The third compound of chlorine and oxygen is called chloric acid. It was first obtained in a separate state by M. Gay Lussac. It is the acid which exists in chlorate of potash. His method of obtaining it in a separate state was as follows: he prepared chlorate of barytes by the method pointed out by Mr. Chenevix, which will be described in a subsequent part of this work. This salt was dis- solved in water, and dilute sulphuric acid cautiously added to it as long as any precipitate continued to fall. By this method all the barytes was removed from the liquid without adding any excess of sulphuric acid, so that on filtring nothing remained but chloric acid held in solution by the water. This acid possesses the following properties-! It has no sensible smell. Its solution in water is colourless, and it reddens vegetable blues without destroying them. Light does not decompose it. It may be concentrated by a gentle heat without undergoing decomposition, and without being volatilized along with the water. When concentrated it has somewhat of an oily consis- tency. When heated it is partly decomposed into chlorine and oxy- gen, and partly volatilized without alteration. Muriatic acid de- composes it in the same manner without the necessity of applying heat. It combines with the different bases and forms the genus of salts called chlorates, to be described in a subsequent part of this work. When 100 parts of dry chlorate of potash are exposed to a red heat in a retort, a quantity of oxygen gas is driven off, which weighs 38*88 parts. The residue, weighing 61*12 parts, is a compound of 32*196 of potassium and 28-924 of chlorine4 But 32-196 of po- tassium require, in order to be converted into potash (in which state they existed in the salt,) 6*576 of the oxygen. There re- main 32-304 of oxygen, which must have been combined with 28*924 of chlorine, and this compound must have constituted chloric acid. According to this statement chloric acid is composed of Chlorine - 28*924 - 47*24 - 4-50 Oxygen - 32-304 - 52-76 - 5-02 10000 We see from the last column that it is a compound of one atom of chlorine and five atoms of oxygen. For the weight of an atom of chlorine is 4-5, and that of an atom of oxygen one.§ [As these numbers designate two volumes of the deutoxide, the specific gravity will be 2-5 -f- 2-222 =_____ = 2361. The protoxide containing a greater proportion of the hea- vier p;.rt of the compound, will of course have a greater specific gravity, and therefore it turns out to be 2-407 as stated in page 169.—C ] f Gay Lussac, Annals of Philosophy, vi. 129. + That this is the case will be shown in a subsequent part of this work. The evidence would not be understood here, if it were given. § Sir H Davy considers chloric acid as a compound of one atom chlorine and six atoms •xygen. The reason is that he believes the potash to exist in the salt in the state of potas- 172 SUPPORTERS OF COMBUSTION. S BOOK I. £ DIVISIONS. 4. The fourth compound of chlorine and oxygen is likewise an acid. We may distinguish it bv the name of perchloric acid. It was lately discovered by Count Von Stadion, and may be obtained in the following manner. When the deutoxide of chlorine is extricated from a mixture of sulphuric acid and chlorate of potash, a peculiar salt is formed which remains behind in the retort. We obtain this salt best when we use three or four grains of strong sulphuric acid for every grain of chlorate of potash employed. After the first violent action of the acid is at an end, heat is to be applied and continued till the yellow colour of the mass disappear. The salt formed in this way is mixed with bisulphate of potash,* which may be separated by a second crystallization. The purified salt possesses the following properties. It is quite neutral,f is not altered by exposure to the air, and has a weak taste similar to that of muriate of potash.:}: It dissolves in considerable quantity in boiling water; but water of the tempera- ture 60°, dissolves only yjth of its weight of it. In alcohol it is quite insoluble. Its crystals are elongated octahedrons similar to the primitive form of sulphate of lead, and resembling the variety which has two prismatic faces between the pyramids.^ It detonates feebly when triturated in a mortar with sulphur. When heated to the temperature of 412° it is decomposed and converted into chlo- ride of potassium]] and oxygen gas. When it is mixed with its own weight of sulphuric acid and exposed to a heat of 280° in a retort, it is decomposed, and the acid which it-contains may be distilled over. The acid may likewise be formed artificially by exposing deutoxide of chlorine to voltaic electricity in an apparatus construc- ted with platinum wires. According to the experiments of Count Von Stadion when this salt is exposed to heat it yields 45*92 parts of oxygen gas, and there remain 54-08 parts of chloride of potas- sium. Now 54*08 of chloride of potassium are composed of— Potassium 28*49—Chlorine 25*59. But 28-49 parts of potassium require 5*819 parts of oxygen in order to be converted into potash. There remain 40*1 parts of oxygen. According to this result per- chloric acid is composed of Chlorine - 25*59 - 38*96 - 4-500 Oxygen - 40*1 - 61-04 - 7-012 100*00 sium, and therefore adds the other atom of oxygen, which we have supposed in the text to be united to the potassium, to the chlorine. * A salt which will be described in a subsequent part of this work. \ That is to say it does not affect the colour of vegetable blues. $ Or chloride of potassium, a substance to be described in a subsequent part of this work. § This variety is called plomb sulphate' semi ptismi by Haiiy, and is figured by him in his 69th plate, figure 73. || A combination of chlorine/ and potassium. Chap. I.] iodine. 1^3 Hence it appears that this acid is a compound of one atom of chlo- rine and seven atoms of oxygen.* Thus it appears that the four compounds of chlorine and oxygen are composed as follows. Chlorine. Oxygen. 1. Protoxide of chlorine - - 1 atom + 1 atom 2. Deutoxide of chlorine - - 1 +4 3. Chloric acid - - - - 1 +5 4. Perchloric acid 1 +7 ■ But if we were to take Count Von Stadion's analysis of deutoxide of chlorine as exact, it would be a compound of one atom chlorine with three atoms oxygen; and in that case all the compounds would consist of-on atom of chlorine united with an odd number of atoms ijf oxygen. SECTION III. OF IODINE. This substance was discovered, I conceive, in the year 1811 by M. Courtois, saltpetre manufacturer at Paris. After ascertaining some of its properties he gave a quantity of it to M. Clement, who undertook to prosecute the investigation. On the 6th of December 1813, M. Clement announced its existence to the Institute of Paris, and at the same time described some of its most remarkable pro- perties. The investigation of it was immediately undertaken by M. Gay Lussac, and prosecuted with his accustomed activity and sagacity. Sir H. Davy, who was at that time at Paris, began like- wise to make experiments upon it, and his results were made known to the Royal Society before any of Gay Lussac's papers were pub- • lished, though the French chemist affirms that he preceded the British philosopher in demonstrating the peculiar nature of this substance. To these two gentlemen, especially to M. Gay Lussac, we are indebted for our knowledge of most of the facts which have been ascertained respecting this singular substance. 1. Iodine may be obtained by the following process. Reduce a quantity of kelp to powder, and digest it in water till every thing soluble is taken up. Then filter the solution and evaporate it tiU all the crystals of common salt that can be obtained have separated from it. Mix the mother liquor with sulphuric acid, and boil for some time.f Put the liquid into a small retort or flask, and mix it with as much black oxide of manganese as you have added of sul- • Gilbert's Annalen derPhysik,lii. 213. ■J- By this means a great quantity of muriatic acid and of sulphureted hydrogen, which impede the collection of the iodine, are previously removed. 174 SUPPORTERS OF COMBUSTION. S BOOK I. £ nivisioN 2. phuric acid. Apply heat. A violet coloured vapour immediately arises, which is to be driven into a proper receiver, against the sides of which it condenses into a black brilliant matter. This substance is the iodine. The process just described was first proposed by Dr. Wollaston. Waste soaper's ley (provided kelp has been used for soap making) may be employed instead of the solution of kelp. French kelp, it would seem, is much richer in iodine than the kelp of Great Britain.* 2. Iodine thus obtained is a solid substance of a greyish black colour and the metallic lustre, having very much the appearance of native sulphuret of antimony. It is usually in scales of a greater or smaller size; but it may be obtained in crystals. And Dr. Wollaston has ascertained that its primitive form is an octahedron, somewhat similar to the primitive form of sulphur. The axes of this octahedron are to each other, as nearly as can be determined, as the numbers, 2, 3, and 4.f Its specific gravity at 62h° is 4*948.1. The smell of iodine is disagreeable and very similar to that of chlorine, though not nearly so strong. Its taste is acrid and hot, and continues for a long time in the mouth. Orfila has shown that when taken internally it possesses poisonous qualities.$ 3. Like chlorine it possesses the property of destroying vegeta- ble colours; though it acts with much less intensity. It stains the hand of a deep yellow colour; but the stain in a short time disap- pears. Paper receives a permanent reddish brown stain, and is at last corroded by it. 4. It melts when heated to the temperature of 224£°, and is vola- tilized under the common pressure of the atmosphere when raised to the temperature of 351 i°.|| But if it be mixed with water and the liquid boiled, it may be distilled over with the water. When converted into vapour it has a very intense and very beautiful vio- let colour. It was from this colour that Gay Lussac imposed on it the name of iode^\, which Sir Humphry Davy changed into iodine§ as better suited to our language. Its specific gravity when in the state of vapour is 8-678.** 5. When iodine is thrown into water the liquid acquires an orange yellow colour and the peculiar small of iodine. But it con- tinues tasteless, and holds in solution only about ^p-th part of its weight of iodine.ff It is more soluble in alcohol, and still more in sulphuric ether.ff 6. If a quantity of iodine be put into a thin glass tube shut at one end and a bit of phosphorus be thrown on it, the two substances * [All the iodine on sale in London hitherto (Feb. 1818) has been imported from Paris, as I am informed.—C] f Annals of Philosophy, v. 237. i Gay Lussac, Ann. de Chim. xci. 7. § Toxicologic generate, torn. i. partie ii. p. 290. [Orfila's book must not be implicitly relied on. Read his account of Fox Glove.—C.] R Gay Lussac, Ann. de Chim. xci. 7. He fixes the temperature between 347° and 356". 1 From /»ind Fire, in which his analysis is contained, was not published till 1777. His experiments were no doubt made some years before, but we do not know their exact date. 2. Azotic gas is invisible and elastic like common air, which it resembles in its mechanical properties. It has no smell. Its spe- cific gravity, according to Biot and Arago, is 0*9691 ;|| according to Kirwan it is 0*985 ;^J according to Lavoisier 0*978 j** air as usual being reckoned one. I am disposed to adopt the number 0*9722 as fixed upon by Dr. Prout, from theoretical considerations which I cannot explain here.ff If this last estimate be correct, 100 cubic inches of it, at the temperature of 60°, and when the barometer stands at 30 inches, will weigh 29*652 grains. 3. It cannot be breathed by animals without suffocation. If obliged to breath it they die very soon, precisely as they .would do if plunged under water. Hence the term azote given to this sub- stance by the French chemists, which signifies " destructive of life."!} No combustible will burn in it. Hence the reason that a candle * The method of obtaining this gas will be described in a subsequent part of this section. ■f See his thesis De Aere Mephitico, published in 1772.—" Sed aer salubris et purus res- pirationem animali non modo ex parte fit mephiticus, sed et aliam indolis sui 2. —Azote, 40 volumes or 2.—Oxygen, 20 volumes or 1.—condensed into 40 volumes. Hence its specific gravity ought to be 1*5277. Now M. Colin found it 1-5204,* which almost corresponds with the calculated gravity. It is composed by weight of Azote - - 0*9722X2 - - 1*75 Oxygen - - 1*111 - - 1*00 But 1*75 is the weight of an atom of azote, and 1 the weight of an atom of oxygen. Hence it follows, that this gas is composed of 1 atom azote, -|- 1 atom oxygen, or it is a protoxide of azote. 4. Nitric acid can only be procured in quantities fiom the salt, called saltpetre or nitre, which is collected in great abundance from the surface of the earth. When this salt is mixed with sulphuric acid and heated in a retort, the nitric acid distils over, and may be collected in a proper receiver. Saltpetre melts in a low heat, and may be kept in that temperature without any alteration. But if the heat be increased, a quantity of oxygen gas is disengaged. If saltpetre which has been kept for some time in such a temperature, be dissolved in water, and the liquid mixed with acetic acid, red fumes are disengaged. But no such phenomenon takes place, if saltpetre be used that has not been subjected to such a process. The cause of this phenomenon was first explained by Scheele. The nitric acid in the saltpetre is altered by the heat, and it is converted into another acid, possessed of a much weaker affinity for potash than nitric acid has. Hence the reason, that it is disengaged by acetic acid, and flies off in the state of red fumes. As oxygen gas is driven off by the heat, the new acid was considered as possess- ing less oxygen than nitric acid, and was in consequence distin- guished by the name of nitrous acid. If we dissolve lead in nitric acid, evaporate the solution to dryness, reduce it to powder, dry it as completely as possible, and then expose it to heat in a small re- tort fitted with a receiver, an orange-coloured liquid is obtained, which was first observed by Berzelius; but was particularly exa- mined by Gay-Lussacf and afterwards by Dulong4 Its specific gravity is 1-451, and it boils at the temperature 82°. Its taste is exceedingly acid, and when mixed with water, an effervescence takes place, and nitrous gas is evolved. Dulong analized it, by passing it through red hot iron, or copper wire, and collecting the gaseous product. The metal increased in weight by absorbing oxygen, and the gas was azote, very nearly in a state of purity. Hence it follows, that it is composed of azote and oxygen, and that it contains no water. The result of an experiment of which he gives us the details,^ is that the acid is composed of • Ann. de Chim. et Phys. i. 218. f Ibid. i. 405. { Ibid. ii. 317. § The acid experimented on weighed 7-985 grammes = 122-54 grains. The oxygen which united to the metal was 5-66 gram. = 87-41 grains. But 3 82 cubic inches of hydrogen gas appeared indicating - - 0-65gr.oxy. H'-nce the oxygen from the acid was ..---. 86-76 grains. The azotic gas evolved was 1-96 litres at 52°. It contained 3-22 per cent *TJf hydrogen gas. Deducting this, the azote makes 115-76 cubic iuehesat 32° = 122 5 cubic inches at'60<>. These weigh.....36-33 grains. See Ann. de Chim. et Phys. ii. 320. -Chap. II.] AZOTE. 18& Azote - - 36*33 - - 1-75 Oxygen - - 86-76 - - 4*178 These numbers do not differ much from those determined by Gay-Lussac, who found, that 100 volumes of oxygen gas could be united with 200 volumes of nitrous gas, and that thus united they constituted nitrous acid.* According to this statement, nitrous acid is composed of 1 volume azote + 2 volumes oxygen, or by weight of Azote - - 0*9722 - - 1-75 Oxygen - - 2*2222 - - 4 Hence we see that nitrous acid is a compound of 1 atom azote and of 4 atoms oxygen. 5. Gav-Lussac concludes from his experiments, that 100 volumes of oxygen gas may be likewise made to unite with 400 volumes of nitrous gas. The compound according to him is an acid, which has hitherto been overlooked by chemists, and to which he has given the name of pernitrous acid.] We see that it must be com- posed of 200 volumes of azote united to 300 volumes of oxygen, or in weight of Azote - - 1*9444 - - 1-75 Oxygen - - 3*3333 - - 3*00 So that it must be a compound of 1 atom azote, and 3 atoms oxy- gen. But as this acid has never been obtained in a separate state, nor ever observed united to a base, its existence is still in some measure hypothetical. Thus, we have five compounds of azote and oxygen; namely, Azote. Oxygen. 1. Protoxide of azote composed of 1 atom -f 1 atom 2. Deutoxide of azote - - 1 +2 3. Hyponitrous acid 1 +3 4. Nitrous acid 1 +4 5. Nitric acid - - 1 +5 III. Azote has the property likewise of combining with chlo- rine, and of forming a very singular compound, to which we may give the name of chloride of azote. It seems to have been discovered about the beginning of 1812, by M. Dulong, who did not however publish any thing on the sub- ject, having been deterred by two severe accidents, which prevent- ed him from completing his investigation. In September 1812, Sir H. Davy received a letter from M. Ampere, in which he men- tions the discovery, without saying any thing about the mode of preparing it. This information roused his curiosity, and induced him to set about a series of experiments in order to obtain it. But before he had proceeded far, Mr. Children put him in mind of an oily substance, that had been observed about a year before by Mr. Burton, at Cambridge, when he passed a current of chlorine through a solution of nitrate ammonia. This information enabled Davy to • Ann. de Chira. et Phys. i. 401. t Ann. de Chim. et Phys. i. 400. Hyponitrous acid would be a better name. 190 SIMPLE INCOMBUSTIBLES. S BOOK I* ^nivision 2. procure the substance, and to investigate its properties.* A very- numerous set of experiments was made upon it about the same time, by Messrs. Porrett, Wilson, and Rupert Kirk.f There was lastly an abridgement of Dulong's original paper, drawn up and publish- ed by Thenard and Berthollet.:): The chloride of azote may be procured in the following manner. Dissolve in water of about 110°, a quantity of nitrate of ammo- nia, or sal ammoniac, so as to make a moderately st ong, but not saturated solution. Put it into a flat dish, and invert over it a phial or cylindrical glass jar, previously filled with chlorine gas. The gas is slowly absorbed; a yellowish oily looking matter col- lects on the surface of the liquid within the jar, and gradually falls to the bottom. It is the chloride of azote. Care must be taken not to collect more at one time than a globule or two; and no experi- ments ought to be made upon a quantity of it, exceeding a grain in weight. For the explosions which it occasions are so violent as to be dangerous, unless the quantity employed be very small. Chlo- ride of azote possesses the following properties. Its colour is nearly similar to that of olive oil. It is as transpa- rent, and has little or none of the adhesiveness of oils. Its smell is peculiar and strong, though not so disagreeable nor injurious to the lungs, as that of chlorine.^ It is very volatile, and is soon dissi- pated when left in the open air. It may be distilled over at 160° without danger; but is partially decomposed by the heat. The temperature of 200° only increases the rapidity of its evaporation; but when heated to 212°, it explodes with prodigious violence. In a vacuum it is converted into vapour, and is again condensed into a liquid when the pressure of the atmosphere is restored. If this vapour be heated sufficiently, it explodes with as much violence as the liquid itself.|| The specific gravity of chloride of azote is 1*653.5| When exposed to cold, the water in contact with it con- geals at about 40°, but it remains fluid itself, though exposed to the cold produced by a mixture of ice and muriate of lime.** When left in water it speedily disappears, while a quantity of azotic gas is disengaged. When put into strong muriatic acid, a quantity of gas is extricated, considerably exceeding the whole weight of the chloride. This gas is chlorine; muriate of ammonia remains in the solution. When chloride of azote comes in contact with phosphorus or oils, a violent detonation immediately takes place ; the effect is so instantaneous and so great, that it has not been possible to collect the products. Messrs. Porrett, Wilson, and Rupert Kirk, brought 125 different substances in contact with it. The following were the only ones which caused it to explode.f f * Davy. Phil. Trans. 1813, p. 1 and 242. | Nicholson's Journal, xxxiv. 180 and 276. March and April 1813. i Ann. de Chim. lxxxvi. 37. § Davy compares it to the smell of phozgene gas: || Porrett, Wilson, and Rupert Kirk. 1 Davy. ** Davy. This temperature was probably as low as •— 40°. f\ Nicholson's Journal, xxxiv. 277. Chap. II.] AZOTE. 191 Olive oil. Camphoreted olive oil. Sulphureted olive oil. Oil of turpentine. Oil of tar. Oil of amber. Oil of petroleum. Oil of orange peel. Naphtha. Soap of silver. Soap of mercury. Soap of copper. Soap of lead. Soap of manganese. Fused potash. Solution of pure am- monia. Phosphureted hy- drogen gas. Nitrous gas. S uper-sulphureted hydrogen. Phosphorus. Phosphuret of lime. Caoutchouc. Myrrh. Phosphureted cam- phor. Palm oil. Ambergris. Whale oil. Linseed oil. Metals, resins, sugar, and most of the gases did not explode with this substance. M. Dulong placed chloride of azote in contact with pieces of copper. The chloride disappeared, azotic gas was disengaged, and there was formed a solution of muriate of copper.* From this experiment it follows, that the substance is a compound of azote and chlorine. Davy found, that when it was exploded in an ex- hausted vessel, the only products were chlorine and azote.f This farther corroborates the nature of its constituents. When made to act upon mercury, a mixture of calomel and corrosive sublimate^ is formed, and azote disengaged. In one experiment 0*7 grain of the chloride produced 49 grain measures, or 0*193 cubic inch of azote. This quantity weighs 0*057 grain. According to this es- timate the chloride is composed of azote 57 - 1*75—chlorine 643 - 19*74. Supposing it a compound of 4 atoms chlorine, and 1 atom azote, its constituents would be azote 1*75—chlorine 4*5 X 4 = 18. The volumes of chlorine and azote according to the preceding ex- periment, are azote 19—chlorine 81. If we suppose that the whole azote was not obtained, as is very probable ; we may state the volumes at azote 20—chlorine 80. This would make the chloride exactly a compound of 1 atom azote and 4 atoms chlorine. Davy made several other experi- ments, which all corroborate this supposition and render it highly probable. IV. Azote has the property likewise of combining with iodine, and of forming a compound which may be called iodide of azote. It was discovered by M. Courtois, and may be prepared in the following manner. Put a quantity of iodine into a solution of ammonia in water. It is gradually converted into a brownish black matter which is the iodide of azote. When left in the open air it gradually flies off in vapour without leaving any residue. It detonates with great violence when slight- » Ann. de Chim. lxxxvi. 59. f P1"'- Trans. 1813, p. 244. * These are compounds of mercury and chlorine. 192 SIMPLE COMBUSTIBLES. 5 BOOK I. £ division2. ly touched, or when heated. If the detonation be performed in an exhausted glass vessel the only products are azotic gas and iodine.* Hence it is obvious that it is composed of these two substances. The attempts which have been made to determine the proportion of the constituents of this substance have not succeeded. Gay- Lussac calculates from theory! that it is a compound of one atom of azote and three atoms of iodine, or by weight of—Azote, 1*75 —Iodine, 15*625 x 3 = 46*875. But the basis of this theoretical calculation is quite uncertain. From the fact that chloride of azote is a compound of 1 atom azote -j- 4 atoms chlorine, we see that it is not a general law that azote combines with other bodies in the proportion of one to three atoms. Various attempts have been made to decompose azote, and to reduce it into simpler elements; but hitherto these attempts have not been attended with success. Berzelius has endeavoured by an ingenious process of reasoning to show that it is a compound of oxygen and an unknown substance, to which he has given the name of nitricum.\ But his reasoning, being founded upon a supposed law§ which has been since found not to hold in many cases, cannot be admitted as valid. Mr. Miers published a numer of ingenious experiments in order to show that azote is a compound of oxygen and hydrogen.j) These experiments are of a very curious nature: but it would be requisite that they should be repeated with more exactness and on a greater scale, before we can venture to draw any consequences from them. There is a third set of experiments on an amalgam made by exposing mercury to the action of galvanism in contact with a moist ammoniacal salt. I shall give a particular account of these experiments in a subsequent part of this work. They appeared to me at first to demonstrate the compound nature of azote. But, upon considering the subject with greater attention, I think it would be hazardous at present to draw any such conclu- sion from them. Upon the whole, then, as no sufficient proof has yet been adduced that azote is a compound, we must continue t» class it among the simple bodies. CHAPTER III. OF SIMPLE COMBUSTIBLES. By combustible is understood substances which have the property of uniting with the supporters of combustion, and of emitting light and heat whenever that union is rapid. There are at present 43 such substances known. It is of great importance to reduce these * Davy, Phil. Trans. 1814, p. 86. t Ann- de Chim. xci. 30. \ Annals of Philosophy, ii. 276. § That, in all neutral salts, the oxygen in the acid is a multiple by a whole number of the oxygen in the base. \ Annals of Philosophy, iii.-364, and iv. 180, 260. Chap. III.] SIMPLE COMBUSTIBLES. 193 substances into distinct genera. The present method of confound- ing every thing under the name of metal has introduced much con- fusion into the science. I conceive they may be very conveniently classed under the three following genera. I. Bodies forming acids by uniting with the supporters of com- bustion or with hydrogen. The substances belonging to this genus are the eight following.* 1. Hydrogen 3. Boron 5. Phosphorus 7. Arsenic 2. Carbon 4. Silicon 6. Sulphur 8. Tellurium. All these bodies, except arsenic and tellurium, have been hitherto classed apart from the metals under the name of simple combustibles. II. Bodies forming alkalies or bases capable of constituting neu- tral salts with acids, by uniting with the supporters of combustion. These bodies are 28 in number. They are all metals, and may be arranged under five families or groups. I. FAMILY. III. FAMILY. V. FAMILY. 1. Potassium 1. Iron 1. Gold 2. Sodium 2. Nickel 2. Platinum 3. Calcium 3. Cobalt 3. Palladium 4. Barium 4. Manganese 4. Rhodium 5. Strontium 5. Cerium 5. Iridium. 6. Magnesium. II. FAMILY. 6. Uranium. IV. FAMILY. 1. Yttrium 1. Zinc 2. Glucinum 2. Lead 3. Aluminum 3. Tin 4. Zirconium. 4. Copper 5. Bismuth 6. Mercury 7. Silver. III. Bodies producing by their union with the supporters of combustion imperfect acids or substances intermediate between acids and alkalies. These bodies are six in number, and belong all to the class of metals. 1. Antimony 3. Molybdenum 5. Columbium or tantalum 2. Chromium 4. Tungsten 6. Titanium.f * I class along with them likewise osmium from analogy. It has not beeu sufficiently examined to enable us to decide where it ought to be placed. f [Upon this arrangement it will be proper to observe, 1st. 'That whether hydrogen be acidinable, depends on the truth of the theory which the author has adopted respecting the constitution of chlorine and muriatic acid gas. There is, as yet, no proof that hydrogen is acidinable. 2. It is imposssible to force any oxide of silicon into the class of acids, according to the de- finition given of acids in vol. ii. which it is worth while to consult on this occasion. 3. It seems to me a strange perversion of language to class 18 of the metals, iron, gold, silver, copper, lead, tin, &c. fete, among the alkalies. 4. It is even yet extremely dubious whether the alkalies, with a metallic appearance, Vol. I. B b 194 SIMPLE COMBUSTIBLES. 5 noOK T £ nivision 2. The description of these different bodies will occupy the following sections. Genus I. Acidifiable Combustibles. Every one of these combustibles, except the first, can be exhi- bited in a solid state. But they all become gaseous by uniting either with hydrogen or with a supporter of combustion. SECTION I. OF HYDROGEN. Hydrogen may be procured by the following process.* Into a retort having an opening at Af put one part of iron filings; then shut the opening A with a cork, through which a hole has been previously drilled by means of a round file, and the bent funnel B passed through it. Care must be taken that the funnel and cork fit the retort so as to be air-tight. Plunge the beak of the retort C under water; then pour through the bent funnel two parts of sulphuric acid previously diluted with four times its bulk of water. Immediately the mixture begins to boil or effervesce with violence, and air-bubbles rush abundantly from the beak of the retort. Allow them to escape for a little, till you suppose that the common air which previously filled the retort has been displaced by the newly generated air. Then place an in- (metalloids) ought to be ranked as metals; for, 1st. They want the characteristic weight of metals. 2. They are extremely soluble iu water. 3. Their oxides are heavier than the substance before it be oxided. Properties that, until Sir H. Davy forced these substances into company with metals, metals were never allowed to possess. 4. Dr. Clarke's experi- ments at Cambridge on the metallization of the earths, have obtained but little credit in London: 8 Brande's Journ. 317. Again, his 3d genus consists of bodies that are intermediate between acids and alkalies, a description hitherto usually applied to neutral salts; but no one who has procured the acids, so called, of chrome, molybdena, and tungsten, can doubt of the propriety of classing them amo'ig acids according to the usual meaning affixed hitherto by chemists to that word. To class silicon among the acidifiable bases, and to reject chrome, is indeed a classification that facts will not justify. The whole of this arrangement appears to me to be formed on considerations too theore- tical : they may possibly be verified by future experiments, but they are not to be taken for granted in the present state of our knowledge, especially in an elementary system of the science of chemistry.—C.^ * [I see no necessity for this safety tube marked B. Put into a common retort, some iron filings, turnings, or small nails; or still better, some granulated zinc: pour on them some oil of vitriol of commerce, previously diluted with about four or five times its bulk of water; the retort should not be above half full. Let the effervescence proceed till all the common air is expelled : then place the beak of the retort under a receiver; that is, a cylin- drical glass jar filled with water, and inverted in water on the shelf of the common pneu- matic trough.—C] \ Such retorts are called tubulated hy chemists: Chap. III.] HYDROGEN*. 195 verted jar on the pneumatic shelf over the beak of the retort. The bubbles rise in abundance and soon fill the jar. The gas obtained by this process is called hydrogen gas. It was formerly called in- flammable air, and by some chemists phlogiston. It may be procured also in great abundance by causing the steam of water to pass through a red hot iron tube. This gas being some- times emitted in considerable quantities from the surface ot the earth in mines * had occasionallv attracted the notice of observers.* Mavow,i Boyle,§ and Hales, procured it in considerable quanti- ties,' and noted a few of its mechanical properties. Its combusti- bility was known about the beginning of the 18th century, and was often exhibited as a curiosity.|| But Mr. Cavendish ought to be considered as its real discoverer; since it was he who first examin- ed it, who pointed out the difference between it and atmospheric air, and who ascertained the greatest number of its properties.^ They were afterwards more fully investigated by Priestley, Scheele, Sennebier, and Volta. • 1. Hydrogen gas, like air, is invisible and elastic, and capable of indefinite compression and dilatation. When prepared by the first process it has a disagreeable smell, similar to the odour evolv- ed when two flint stones are rubbed against each other. This smell must be ascribed to some foreign body held in solution by the gas ; for the hydrogen procured by passing steam through red hot iron tubes has no smell. 2. It is the lightest gaseous body with which we are acquaint- ed.' If the specific gravity of common air be reckoned 1*000, the specific gravitv of hydrogen gas, as described by Biot and Arago, is 0*0732.** Dr. Prout has shown from the specific gravity of am- moniacal gas, which is composed of three volumes of hydrogen and one of azote condensed into two volumes, that its specific gra- vity must be 0*0694.ff According to this estimate 100 cubic inches of hydrogen gas, when the temperature is 60° and the barometer stands at 30 inches, weigh 2*117 grains. 3. All burning substances are immediately extinguished by being plunged into this gas. It is incapable therefore of supporting combustion. 4. When animals are obliged to breathe it, they soon die. The death is occasioned merely by depriving the animal of oxygen. The animal dies precisely as it would do if plunged under water. 5. Hydrogen gas' is not sensibly absorbed by water, though left for some time in contact with it. When water is previously de- prived of all its air by boiling, 100 cubic inches of it imbibe 1*53 * [The gas thus emitud is not hydrogen, but carburetted hydrogen.— C] t See an instance related in Phil. Trans. Abr. i. 169. .„.,„,... „, *TractatusQuinque,p. 163. , 1-i T- ^ wk y Cramer's Elementa Doc.masia, i. 45. This book was published in 1739.—W.isserberg relates a story of an accidental explosion which terrified Protessor Jacquin s operator. VVasserberg'sInstitutionesChemia, i. 184. ,. .... .„ •T Phil Trans. 1766, vol. lvi. p. 141. *# Mem. de l'Inst.t. 1806, p. 320. i f Annals of Philosophy, vi. 322. 196 SIMPLE COMBUSTIBLES. 5 B00K - £ DIVISION J. inches of hydrogen gas at the temperature of 60°.* According to Saussure v. ur absorbs 4*6 per cent, of hydrogen gas and alcohol 5*1 per cent.f II. If a phial be filled with hydrogen gas, and a lighted candle be brought to its mouth, the gas will take lire, and burn gradually till it is all consumed. If the hydrogen gas be pure, the flame is of a yellowish white colour; but if the gas hold any substance in solution, which is often the case, the flame is tinged of different co- lours, according to the substance. It is most usually reddish. A red hot iron likewise sets fire to hydrogen gas. From my experi- ments it follows, that the temperature at which the gas takes fire is about 1000°. If pure oxygen and hydrogen gas be mixed together, they re- main unaltered ; but if a lighted taper be brought into contact with them, or an electric spark be made to pass through them, they burn with astonishing rapidity, and produce a violent explosion. If these two gases be mixed in the proportion of one part in bulk of oxygen gas and two parts of hydrogen gas, they explode over water without leaving any visible residuum ; the vessel in which they were contained (provided the gases were pure) being completely filled with water. This important experiment was made by Scheele ;\ but for want of a proper apparatus he was not able to draw the proper consequences. Mr. Cavendish made the experiment in dry glass vessels with all that precision and sagacity which characterise his philosophical labours, and ascertained, that after the combus- tion there was always deposited a quantity of water equal in weight to the two gases which disappeared. Hence he concluded that the two gases had combined and formed this water. This inference was amply confirmed by the subsequent experiments of Lavoisier and his friends. Water, then, is a compound of oxygen and hy- drogen, united in the proportion of one volume of oxygen to two volumes of hydrogen. But the specific gravity of oxygen gas is 1-1 111, and that of hydrogen gas 0*0694. So that oxygen gas is 16 times heavier than hydrogen gas.§ Therefore water is composed by weight of oxygen|| 8-1---hydrogen 1-0*125. If therefore we suppose water to be composed of one atom of oxygen and one atom of hydrogen, and represent the weight of an atom of oxygen by 1, the weight of an atom of hydrogen will be 0-125.^| If 100 measures of air be mixed with 42 measures of hydrogen, and an electric spark passed through the mixture, a detonation takes place, and the residual gas amounts to 79 volumes, and is * Henry, Phil. Trans. 1803, p. 274. f Annals of Philosophy, vi. 340. + Scheele on Air and Fir.;, p. 57; and Crell's Annals, iii. 101. Eng. Trans. § [These numbers are taken from Dr. Prout's paper, which 1 insert at the end of this volume.—C.] || [This would be stated more intelligibly thus, oxygen 16 - 8 - 1—hydrogen 2-1 - 0125.—C] T [There is no reason to believe, as yet, that oxygen and hydrogen combine in any other proportion Dr. Thomson, after Dr. Prout, corrects the common relative weights of these two substances in water, from 85 and 15, to 80 and 10, or 8 and 1.—C] Chap. III.] HYDROGEN. 19f pure azotic gas. This shows us that air is a compound of 21 oxy- gen and 79 azotic gas. For the 42 measures of hydrogen require just 21 measures of oxygen to convert them into water. This ex- periment is often used to ascertain the purity of hydrogen gas. Mix any quantity of hydrogen gas with its bulk of oxygen, and fire it by means of an electric spark j note the diminution of bulk that takes place; two thirds of that diminution is hydrogen. Suppose we mix 20 measures of hydrogen and 20 of oxygen, and fire them by means of electricity. Suppose the residual gas after the expe- riment 10 measures. Thirty measures have disappeared. Two thirds of that or 20 measures were hydrogen. Therefore in such a case the hydrogen examined would be considered as pure. III. Hydrogen has the property also of combining with chlorine gas. The compound formed is known by the name of muriatic acid. [Qu. for the reasons advanced, p. 155.—C] If equal volumes of chlorine and hydrogen be put into a glass tube and exposed to the direct rays of the sun, an explosion takes place. This curious fact was first observed by Gay-Lussac and Thenard.* When two equal glass vessels, ground so as to fit each other and filled, the one with dry chlorine and the other with hy- drogen, are placed in contact and exposed to the light of day, but not to sunshine, the yellow colour gradually disappears and the mixture becomes colourless. If it be now examined it will be found converted into pure muriatic acid gas, equal in bulk to the volume of the two gases before combination.! Hence it follows that this gas is a compound of chlorine and hydrogen. The expe- riments which led to this conclusion were first made by Gay-Lussac and Thenard. But the consequence was first drawn by Sir Hum- phry Davy, who thus revived the original opinion of Scheele, the discoveref of chlorine gas. Muriatic acid, called hydrochloric acid by Gay-Lussac, is a gas- eous body, invisible and elastic like common air, and having a pe- culiar smell and a very sour taste. Water absorbs it with great avidity, so that it can be preserved only over mercury. No com- bustible body will burn in it: and it destroys life instantly when an attempt is made to breathe it. Indeed it cannot be drawn into the lungs; the glottis being spasmodically shut whenever it comes in contact with this gas. Its specific gravity is the mean of that of chlorine and hydro- gen, or 1-2847. Hence 100 cubic inches of it weigh 39-162 grains. Its constituents are as follows: Hydrogen - 0*125 - 1 . Chlorine - 4*5 - 36 IV. Hydrogen combines with iodine, and forms a compound which has received the name of hydriodic acid. It seems to have * Recherches Physico-Chimiques, ii. 129. The discovery was likewise made by Dalton. who communicated it to me by letter before the publication above quoted appeared. f Ibid. p. 148. 198 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION 2. been first discovered by M. Clement; but its nature and proper- ties were first investigated by Davy* and Gay-Lussac.f It may be obtained by mixing together four parts of iodine and one part of phosphorus, moistening the compound with water and heating it in a small retort. A gas comes over which must be re- ceived over mercury. This gas is hydriodic acid. It is colourless and elastic like common air. It has a smell simi- lar to that of muriatic acid and a very acid taste. Its specific gravity, according to the experiments of Gay-Lussac, is 4*443.1; The real specific gravity ought to be 4*3749, which is the mean be- tween the specific gravity of iodine vapour and hydrogen gas. Hence at the temperature of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 133*434 grains. When this acid is left in contact with mercury it is decomposed, the mercury combines with the iodine and forms an iodide, while a quantity of hydrogen gas is disengaged exactly equal to half the bulk of the hydriodic acid gas. It is decomposed likewise by chlorine, muriatic acid is formed and the iodine is deposited. These experiments leave no doubt about its composition. It con- sists of one volume of vapour of iodine united to one volume of hydrogen gas without any change of bulk. Hence it is composed by weight of Iodine •- - 8*6804 - - 16*625 Hydrogen - - 0-0694 - - 0*125 We see from this that it is composed of an atom of iodine united to an atom of hydrogen. Water absorbs this acid with avidity. When exposed to a heat below 262° the water is driven off and the acid becomes concentra- ted. In this way its specific gravity may be increased to 1*7. At 262° the acid boils and may be distilled over. It readily dissolves iodine, and becomes of a darker colour. It becomes dark colour- ed also by exposure to the air, being partly decomposed. V. Hydrogen has the property of combining with fluorine, and forming a very powerful a.cid known by the name of fluoric acid.§ This acid, in a state of purity, was first made known to che- mists by Gay-Lussac and Thenard.|| It is obtained by putting a mixture of pure fluor spar and sulphuric acid into a retort of lead and silver, and distilling into a leaden or silver receiver. Fluoric acid is a colourless liquid, of the specific gravity 1-0609. It smokes strongly when exposed to the air. It acts with prodi- gious energy upon the skin. The smallest speck occasioning sores. We are not acquainted with the proportions in which the consti- tuents of this acid are combined. If we conclude from an analogy * Phil. Trans. 1814, p. 74. t Ann- de Chim- xci- 9- * Ann- de Chim. xci. 16. § [May not the hydrogen combine with part of the oxygen of these acids and form wa- ter? The acid properties of muriatic acid gas, are lessened or rendered latent, by the dose of oxygen that converts it into chlorine; and when this oxygen is abstracted from chlorine by hydrogen, the acid properties of the muriatic acid gas are developed.—C] || Recherches PhysicO'Chimiques, ii. 2. Chap. III.] HYDROGEN". 199 that it is a compound of an atom of hydrogen and an atom of fluo- rine, its proportions will be 1 of hydrogen to 16 of fluorine. For an atom of fluorine seems to weigh two. According to this notion fluoric acid will be composed of Hydrogen - - - 0125 - - - 1 Fluorine - - - 2*000 - 16 The affinity of hydrogen for the supporters of combustion is in the following order:—Hydrogen—Oxygen—Chlorine—Iodine. Oxygen separates hydrogen from chlorine and iodine; while chlo- rine separates it from iodine. VI. Hydrogen has the property of combining with azote and of forming a gaseous substance distinguished by the name of ammonia. This substance was unknown to the ancients. It seems to have been discovered by the Arabian chemists; though we are ignorant who the discoverer was. When animal substances are distilled, a white saline substance is obtained, having a strong and peculiar odour, to which the name of hartshorn and volatile alkali were given. This salt is a compound of ammonia and another gaseous substance called carbonic acid. The method of obtaining it is de- scribed by Basil Valentine. If this salt or sal ammoniac be mixed with twice its weight of quicklimer put into a flask and exposed to the heat of a lamp, a gas comes over which must be received over mercury, and which is ammoniacal gas. This gas was first disco- vered by Dr. Priestley. Its composition was first ascertained by Scheele. Berthollet determined it by pretty correct experiments. The subsequent experiments of Henry, A. Berthollet, and Davy, ascertained the proportion of the constituents with rigid accuracy. Ammoniacal gas is transparent and colourless, and possesses the mechanical properties of air. Its smell is very pungent; though rather agreeable when sufficiently diluted. Its taste is acrid and caustic, and if drawn into the mouth it corrodes the skin. Ani- mals cannot breathe it without death. When mixed with oxygen gas, and an electric spark passed through the mixture, it detonates, as was first discovered by Dr. Henry. It converts vegetable blues into green. Its specific gravity is 0*590. Hence at the tempera- ture of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 18 grains. Water absorbs 780 times its bulk of this gas, and is converted into liquid ammonia, a substance very much employed in chemical experiments. When this liquid is heated to 130° the ammonia se- parates in the form of gas. When electric sparks are passed for a considerable time through dry ammoniacal gas its bulk is just doubled, and it is completely decomposed. The new gaseous product consists of a mixture of three volumes of hydrogen gas and one volume of azotic gas. It is obvious from this that ammonia is composed of three volumes of hydrogen and one volume of azote compressed into two volumes. Hence its constituents by weight are 20° SIMPLE COMBUSTIBLES. 5 "OOK I. £ DIVISION 2, Hydrogen - 0*1947 - 0-125 + 3 - 1 Azote - 0-9722 - 1*75 - 4f Thus we see that ammonia is a compound of three atoms of hydro- gen and one atom of azote. Hence the weight of an atom of it is 2*125.* SECTION II. OF CARBON. If a piece of wood be put into a crucible, well covered with sand, and kept red hot for some time, it is converted into a black shining brittle substance, without either taste or smell, well known under the name of charcoal. Its properties are nearly the same from whatever wood it has been obtained, provided it be exposed for an hour in a covered crucible to the heat of a forge.f i. 1. Charcoal is insoluble in water. It is not affected (provided that all air and moisture be excluded) by the most violent heat which can be applied, excepting only that it is rendered much harder and more brilliant.^ It is an excellent conductor of electricity, and possesses besides a number of singular properties, which render it of considerable im- portance. It is much less liable to putrefy or rot .than wood, and is not therefore so apt to decay by age. This property has been long known. It was customary among the ancients to char the outside of those stakes which were to be driven into the ground or placed in water, in order to preserve the wood from spoiling. New-made charcoal, by being rolled up in clothes which have con- tracted a disagreeable odour, effectually detroys it. When boiled with meat beginning to putrefy, it takes away the bad taint. It is perhaps the best teeth powder known. Mr. Lowitz of Peters- burgh has shown, that it may be used with advantage to purify a great variety of substances.|j * [Yet Dr Prout, whom our author is so well inclined to follow, says, " Thus ammonia has been stated to be composed of one atom of azote and three of hydrogen; whereas, it is evidently composed of one atom of azote and only one and a half of hydrogen ,which are con- densed into two volumes, equal therefore to one atom." Annals of Phil. v. 6, p. 330. I fear we are not yet ripe for substituting arithmetical deductions in the place of accurate experi- ments.—C.lj | Unless that precaution be attended to, the properties of charcoal differ considerably. t [A new method of making charcoal of an uniform quality has lately been introduced among the manufacturers of gunpowder, for which a Mr. Kurtz has taken out | | a patent. Thi; billets to be charred are put into a sheet-iron chest which i has a cover that fits tight, and a tube that descends nearly to the bottom : thus Fire is at first applied underneath; the whole mass of wood is kept perpetu- ally immersed in vapour always of the same temperature, because it can only I-------1 make its escape from the bottom, as is evident. Hence one piece cannot be more charred than another. When the vapour ceases to escape, and nothing comes out of the tube but carburetted hydrogen, the process is stopped.—C.J § This property was well known to the older chemists. See Hoffmann's Observationes Phvsico-Chymicse Selectiores, p. 298. || See upon the properties of charcoal the experiments of Lowitz, Crell'a Annals, ii. 16$. Engl. Trans, and of Kels, ibid. iii. 270. Chap. III.] CARBON. 201 When putrid water at sea is mixed with about |th of its weight of charcoal powder it is rendered quite fresh, and a much smaller quantity of charcoal will serve if the precaution be taken to add a little sulphuric acid previously to the water. If the water casks be charred before they are filled with water, the liquid remains good in them for years. This precaution ought always to be taken for long sea voyages. The same precaution when attended to for wine casks will be found very much to improve the quality of the wine.* 2. New-made charcoal absorbs moisture with avidity. Messrs. Allen and Pepys found, that when left for a day in the open air, it increased in weight about 12| per cent. The greatest part of this increase was owing to moisture which it emitted again copiously when exposed under mercury to the heat of 214°.f 3. When freed from the air which it may contain, either by heat or by being placed under an exhausted receiver, it has the property of absorbing a certain quantity of any gaseous body in which it may be placed. Lametherie made some experiments on this subject many years ago4 Count Morozzo made many curi- ous observations on the quantity of different gases absorbed by charcoal.^ These were varied and extended still farther by Messrs. Rouppe and Van Noorden of Rotterdam.|| But the most complete and satisfactory set of experiments on the absorption of gases, by charcoal, has been made by M. Theodore de Saussure.^J His method was to heat the bit of charcoal red hot, to plunge it while in that state under mercuiy, and then to introduce it when cold into the gas to be examined. He always employed box wood char- coal. The following table exhibits the bulk of the various gases absorbed by a volume of charcoal reckoned one. Volumes. Volumes. Ammoniacal gas - 90 Muriatic acid - 85 Sulphurous acid - 65 Sulphureted hydrogen 55 Nitrous oxide - 40 Carbonic acid 35 Olefiant gas - - 35 Carbonic oxide - 9*42 Oxygen - - 9*25 Azote - - 7*5 Oxy-carbureted hydrogen**5* Hydrogen - - 1*75 The absoption of all these gases terminated at the end of 24 hours, and was not increased by allowing the charcoal to remain in contact with the gas. From Saussure's experiments it seems clear that this absorption of the gases, by charcoal, is analagous to the capillary attraction of liquids by very small tubes. When charcoal already saturated with any gas is put into another gas, it gives out a portion of the gas already absorbed, and absorbs a portion of the new gas. The proportions vary according to the relative absorbability of the two gases. • Berthollet, Ann. de Chim. lix. 96; and xciii. 150. | Allen and Pepys on the quantity of carbon in carbonic acid. Phil. Trans. 1807. * Jour, de Phys. xxx. 309. § Jour, de Phys. 1783, p. 376. Nicholson's Journal, ix, 255, and x, 12. II Ann. de Chim. xxxii. 3. *J Annals of Philosophy, vi. 241 and 331. ** Gas from moist charcoal of the specific gravity 0-3326. Vol. I. C c 202 SIMPLE COMBUSTIBLES. $ noOK 1 \ DIVISION 2. 4. There is a substance found native, in different parts of the world, that possesses most of the properties of charcoal. This sub- stance is known by the name of plumbago, graphite, black lead. It is employed for making pencils, for making crucibles, and for rubbing bright the surface of cast iron utensils. It serves likewise to diminish friction when interposed between rubbing surfaces. The finest specimens of this mineral are found in the celebrated mine of Barrow dale, in the county of Cumberland. This mine has been worked since the time of Queen Elizabeth, and is said to be the only one which supplies plumbago of sufficient purity to be made into pencils. Pencils of this substance existed in 1565, as they are mentioned by Conrade Gesner in his book on fossils pub- lished that year. But the nature of plumbago was first determined by Scheele in his experiments on plumbago, published in the Me- moirs of the Stockholm Academy, for 1779. Dr. Lewis, indeed, had previously made some considerable advances towards the results obtained by Scheele.* Plumbago is a mineral of a dark steel grey colour, and a metallic lustre ; it is soft and has a greasy feel; it leaves a dark coloured line when drawn along paper; it is a conductor of electricity. When kept red hot it gradually wastes away in the open air, and it burns with great splendour when thrown into red hot saltpetre. The diamond is another substance which possesses many of the properties of charcoal, though it differs from it in others. It is the hardest and most beautiful of all the precious stones. Hitherto it has been found only in India and Brazil. It is always crystallized, and usually of a small size. The figure of its crystal is the octa- hedron, but the faces are usually curved, and the most common figure is a kind of 48 sided figure; the faces are curved, and the whole figure approaches somewhat to a sphere. Its specific gra- vity is about 3*5. It is a non-conductor of electricity. This mineral was long considered as incombustible. But New- ton, from its property of refracting light so powerfully, conjectured that it was capable of burning. This conjecture was verified in 1694, in the presence of Cosmo III. Grand Duke of Tuscany. By- means of a burning glass the Florentine Academicians consumed several diamonds.f In 1751, Francis I. Emperor of Germany, witnessed the destruction of several more diamonds in the heat of a furnace4 These experiments were repeated by Darcet, Rouelle, Macquer, Cadet, and Lavoisier, who proved that the diamond was not merely evaporated but actually burnt, and that if air was ex- cluded it underwent no change.^ Mr. Lavoisier prosecuted these experiments with his usual pre- * Philosophical Commerce of the Arts, p. 326. IGiornale de Litterati d'ltalia, Tom. viii. Art. 9. The experiments were performed verani. \ Das Neueste aus der enmuthigen gelehrsamkeit. Aus das Jalir, 1751, S. 540. § Mem. Par. 1766,1770, 1771,1772. Chap. III.] CARBON. 203 cision ; burnt diamonds in close vessels by means of powerful burning glasses; ascertained that, during their combustion, carbo- nic acid gas is formed; and that in this respect there is a striking analogy between them and charcoal, as well as in the affinity of both when heated in close vessels.* A very high temperature is not necessary for the combustion of the diamond. Sir George Mackenzie ascertained that they burn in a mufflef when heated to the temperature of 14° of Wedge wood's pyrometer ; a heat con- siderably less than is necessary to melt silver.:}: When raised to this temperature they waste pretty fast, burning with a low flame, and increasing somewhat in bulk ; their surface too is often cover- ed with a crust of charcoal, especially when they are consumed in close vessels by means of burning glasses.^ v In 1785, Guyton-Morveau found that the diamond is combus- tible when dropped into melted nitre ; that it burns without leaving any residuum, and in a manner analogous to charcoal.|| Mr. Smith- son Tennant repeated this experiment with precision in 1797. Into a tube of gold'he put 120 grains of nitre, and 2*5 grains of dia- mond, and kept the mixture in a red heat for half an hour. The diamond was consumed by the oxygen, which red-hot nitre al- ways gives out. The carbonic acid formed was taken up by means of lime, and afterwards separated from the lime and measured. It occupied the bulk in one experiment of 10*3 ounces of water, and in another of 10*1: the mean is equal to 19-36 inches of carbonic acid, which have been ascertained to weigh nearly nine grains. But nine grains of carbonic acid, by Lavoisier's experiments, con- tain almost exactly 2-5 grains of carbon, which was the original weight of the diamond.^ Thus Mr. Tennant ascertained, that the whole of the diamond, like charcoal, is converted by combustion into carbonic acid gas. As the proportion of carbonic acid formed by the combustion of diamond is very nearly the same according to Tennant's experi- ment, as what would have been yielded by the same weight of good charcoal; it ought to follow, that diamond and charcoal con- sist both of exactly the same constituents. But when we consi- der the very different properties of the two substances, we feel a strong repugnance to embrace this conclusion. The experiments of Lavoisier were repeated in 1800 by Mor- veau ; but his experiments were inaccurate, as was afterwards ad- mitted by himself; his consequences, of course, are entitled to no attention. The combustion of the diamond in oxygen gas was re- peated in 1807, with every requisite precaution, by Messrs. Al- len and Pepys, and their results agree very nearly with those of Tennant.** It has been repeated still more lately by Sir H. Davy, * Lavoisier's Opuscules, ii. as quoted by Macquer. Diet. i. 337. "I" A muffle is a kind of small earthen-ware oven, open at one end, and fitted into a furnace. $ Nicholson's Quarto Jour. iv. 104. § Macquer and Lavoisier. Macquer"s Diet Ibid. || Encyc. Method. Chim. i. 742. «J Phil. Trans. 1797, p. 123. *• Ibid. 1807. 204 SIMPLE COMBUSTIBLES. S "OOK * ^DIVIMON 2. with nearly the same result.* It seems, therefore, demonstrated-', that the diamond and charcoal are composed of very nearly the same basis. II. When charcoal is heated to about 800° in the open air it be- comes red hot, and continues to burn (supposing it pure) till it is wholly consumed. But the air in which the combustion has been carried on has altered its properties very considerably, for it has become so noxious to animals that they cannot breathe it without death. If small pieces of dry charcoal be placed upon a pedestal, in a glass jar filled with oxygen gas, and standing over mercury, they may be kindled by means of a burning glass, and consumed. The bulk of the gas is not sensibly altered by this combustion, but its properties are greatly changed. A great part of it will be found converted into a new gas quite different from oxygen. This new gas is easily detected by letting up lime water into the jar: the lime water becomes milky, and absorbs and condenses all the new-form- ed gas. This new gas has received the name of carbonic acid. Mr. Lavoisier ascertained, by a very laborious set of experiments, that it is precisely equal in weight to the charcoal and oxygen which disappeared during the combustion. Hence he concluded, that carbonic acid is a compound of charcoal and oxygen, and that the combustion of charcoal is nothing else than its combination with oxygen.f 2. As oxygen gas may be converted into carbonic acid gas by burning charcoal in it without undergoing any change of bulk ; it is obvious that we shall obtain the quantity of carbon contained in carbonic acid gas, by subtracting the specific gravity of oxygen from that of carbonic acid. By carbon is meant the pure basis of charcoal, free from all the hydrogen and earthy or metallic parti- cles which charcoal usually contains. Now, according to the ex- periments of Arago and Biot, the specific gravity of carbonic acid gas is 1-5196.± We shall consider the true specific gravity as 1-527, which differs very little from the preceding estimation. The spe- cific gravity of oxygen gas is 1-111. Therefore carbonic acid is composed of Oxygen - 1*111 - 1*000 - 72-73 Carbon - 0-416 - 0-375 - 27-27 100-00 3. When chlorine is passed through charcoal, previously expos- ed to the strongest heat that can be raised in a furnace, a portion of it is converted into muriatic acid.§ Hence it follows that charcoal, however carefully made, always contains a small portion of hydro- gen from which it cannot be freed by heat. Davy found that when charcoal or plumbago were burnt in dry oxygen gas, there was al- ways an evident deposition of moisture.)) -Hence it is obvious that * Phil. Trans. 1814, p. 557. | Mem. Par. 1781, p. 448. * Mem. de l'lnst 1806, p. 320. § Gay-Lussac & Thenard. ReclierchesPhysico-Chim.ii.98. || Phil. Trans. 18l4,p. 56$, Chap. III.] CARBON. 205 jriumbago, likewise, contains a minute quantity of hydrogen in its composition. When diamond is burnt nothing is formed but pure carbonic acid gas.* 4. When a mixture of equal parts of iron filings and chalk, both made previously as dry as possible, are exposed to a red heat in an iron retort, there is disengaged a great quantity of gas, consisting partly of carbonic acid, and partly of a species of heavy inflamma- ble air. When the carbonic acid is separated by means of lime- water, the inflammable gas obtained is in a state of great purity. It was first procured by Dr. Priestley ; but for our knowledge of its constituents and its properties, we are indebted to the ingenious ex- periments of Mr. Cruikshanks. Clement and Desormes, Morveau and Berthollet, examined it also soon after with equal address and success. The name carbonic oxide gas has been given it by che- mists, and Cruikshanks has shown that it is a compound of oxygen and carbon. This gas possesses the mechanical properties of air. Its specific gravity, according to Cruikshanks, is 0*956, that of air being 1-000. We shall consider its true specific gravity as 0*972. In that case 100 cubic inches of it will weigh 29*652 grains, when the barome- ter stands at 30 inches and the temperature is 60°. It burns with a deep blue flame and gives out but little light. When mixed with oxygen gas, and an electric spark passed through the mixture, it detonates: 100 measures of it require for complete com- bustion 50 measures of oxygen gas, and the product is 100 mea- sures of carbonic acid gas.f Hence it follows that ft contains just half the oxygen that exists in the same volume of carbonic acid gas. It is therefore composed of Oxygen - 0*555 - 1*000 - 57*14 Carbon - 0*416 - 0-750 - 42-86 If we compare this table with that which exhibits the composi- tion of carbonic acid, we shall find that the constituents of these two bodies are in the following proportions : Carbon. Oxygen. Carbonic oxide composed of - - 0*75 -f- 1 Carbonic acid - - - - 0*75 + 2 If, therefore, one denote the weight of an atom of oxygen, 0*75 will be the weight of an atom of carbon ; and carbonic oxide will be a compound of one atom carbon -f- one atom oxygen, and carbonic acid of one atom carbon -f- two atoms oxygen. III. Carbon does not combine with chlorine; but chlorine has the property of combining with carbonic oxide, and of forming a gaseous compound, which has received the name of phosgene gas. It was discovered by Dr. John Davy, to whom we are indebted for every thing at present known respecting its properties.^: The method of procuring it is»as follows. • Davy. Phil. Trans. 1814, p. 565. f Gay-Lusaac Mem. d'ArcueiL ii.218. * Phil. Trans. 1812, p. 144. 206 SIMPLE COMBUSTIBLES. S B0°** £ mvisiov2 Into a glass flask, previously exhausted of air and well dried, in% troduce equal volumes of carbonic oxide and chlorine gases, both well dried by being left in contact with fused chloride of calcium.* Expose this mixture to sunshine for about a quarter of an hour. The colour of the chlorine disappears, and the volume of the mix- ture .diminishes one half. The new gas, thus formed, is phosgene gas. # It is colourless, and possesses the mechanical properties of com- mon air. It possesses a strong smell, which has been compared to what would be produced by a mixture of the odours of chlorine and ammonia. It is more disagreeable and suffocating than that of chlorine, and'affects the eyes in a peculiar manner, producing a rapid flow of tears, and occasioning painful sensations. It posses- ses the properties of an acid, reddening vegetable blues, and com- bining with, and neutralizing, four times its volume of ammoniacal gas. When tin, zinc, antimony, or arsenic, are heated in this gas, they decompose it, absorbing the chlorine and setting at liberty the carbonic oxide. Water decomposes it, and converts it. into muri- atic acid and carbonic acid. As it is composed of equal volumes of chlorine and carbonic oxide gases, reduced to half their original bulk, it is obvious that its specific gravity must be equal to that of these two gases united together, or 3-472. So that at the temperature of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 105*896 grains. Its constituents by weight, are, Chlorin'e - - 2*5 - - 4*5 Carbonic oxide - 0*972 - - 1*75 That is to say, of one atom chlorine and one atom carbonic oxide. Or its composition may be thus stated:—Chlorine 4-5— Oxygen 1*0—Carbon 0-75. Or an atom of carbon united to an atom of chlorine, and an atom of oxygen. So that it is analogous to carbonic acid. Carbonic acid is a compound of ope atom carbon, united to two atoms of a supporter. Phosgene gas is the same. Only there are two dis- tinct supporters. The atom of chlorine in it replaces one of the atoms of oxygen in the carbonic acid. The term chloro-carbonic acid, or chloroxy-carbonic acid, would be applied to it with greater propriety than phosgene gas. Of these I consider the first to be the best. IV. Carbon has not the property of combining with iodine. It would be curious to know whether iodine be capable, like chlorine, of uniting with carbonic oxide, and of forming iodo-carbonic acid. Sir H. Davy tried the expeiiment, but could not succeed in form- ing any combination.! V. Nothing is known respecting the combination of carbon and fluorine. * [Muriat of Lime.—C] t pWL Trans. 1814, p. 50j. Chap. III.] CARBON. 207 0 VI. Carbon has the property of combining with azote, and of forming a curious compound, which was discovered by Gay-Lus- sac in 1815, and to which he has given the name of cyanogen.* It is easily obtained by exposing dry prussiate of mercury in a small retort, to a heat rather under redness: the salt blackens, and a gaseous fluid is extricated in abundance: it must be received over me*ury. This gas is cyanogen. This gas is**colourless, and possesses the mechanical properties of common air. Its smell is quite peculiar, and excessively strong and disagreeable. Its specific gravity as determined by Gay-Lus- sac is 1*8064. I am disposed to consider 1*8042 as the true num- ber. On that supposition 100 cubic inches of it, at the temperature of 60°, and when the barometer stands at 30 inches, will weigh 55*028 grains. It is inflammable, and burns with a purplish blue flame.f It is not decomposed by exposure to a red heat. Water dissolves 4^ times its volume, and alcohol 23 times its volume of this gas. It reddens tincture of litmus. Phosphorus, sulphur, and iodine, may be volatilized in it without alteration. Potassium burns in it and absorbs it. For complete combustion it requires twice its volume of oxygen. The products are twice its volume of carbonic acid, and its own volume of azotic gas. Hence it is ob- viously composed of two volumes carbon and one volume azote, condensed into one volume, or by weight of Azote - - 0-9722 - - 1-75 Carbon - - 0-832 - - 0*75 x 2 = 1*5 Or of two atoms of carbon united to one atom of azote. VII. Carbon combines with hydrogen in two proportions, and forms two compounds which have received the names of olefiant gas and carbureted hydrogen. The terms hydroguret of carbon, and bihydroguret of carbon, would be more systematic. 1. Olefiant gas was discovered in 1796 by the associated Dutch- chemists Bondt, Dieman, Van Troostwick, and Lauwerenburg4 Some experiments were afterwards made upon it by Cruikshanks, Berthollet, and Dr. Henry; and its composition was accurately in- vestigated by Mr. Dalton. I published a set of experiments on it in 1811.$ About the same time an analysis of it was published by M. Theodore de Saussure.|) It is easily obtained by mixing together in a retort four parts of sulphuric acid, and one part of alcohol, and applying the heat of a lamp while the beak of the retort is plunged into a water trough* A gas comes over in abundance, which may be received in glass jars inverted over water. Olefiant gas, thus prepared, is invisible, and possesses the me- chanical properties of common air. It is destitute both of taste • Ann. de Chim. xcv. 172. f [Hence its name of Cyanogen from kuav@' blue.-C] $ Their Memoir was published in the Jour, de Phys. xiv. 178', and an abstract of it 1n the Ann. de Chim. xxi. 48. § Memoirs of the Wernerian Natural History Societv, i. 504. H Ann. de Chim. lxxvii. 57. 208 SIMPLE COMBUSTIBLES. S BOOK J. £ DIVISION 2. and smell. Its specific gravity, according to my experiments, % 0*9745 ;* according to Saussure, it is 0*9852.f From theory its specific gravity should be 0*974, which almost agreeing with my determination, I shall consider as correct. Hence at the tempera- ture of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 29*72 grains. This gas burns with greater splen- dour than any other known gas, and detonates very loudly when mixed with thrice its bulk of oxygen gas, and an electrical spark is passed through it. It requires for its complete combustion three times its volume of oxygen gas, and produces, when burnt, twice its volume of carbonic acid gas. The only other product is water. Now two of the three volumes of oxygen gas must have gone to the formation of carbonic acid. The remaining volume must have gone to the formation of water, and it must have combined with a quantity of hydrogen, which in an uncombined state would have amounted to two volumes. Hence (supposing each volume to be a cubic inch) olefiant gas is composed by weight of Carbon - 0*832 - 0*75 - 6 - 100 Hydrogen - 0*1388 - 0*125 - 1 - 16*66 That is to say, it is composed of an atom of carbon, and an atom of hydrogen, united together. Water, according to the experiments of Mr. Dalton, absorbs one twelfth of its bulk of olefiant gas 4 According to Saussure, 100 cubic inches of water absorb 15*3 cubic inches of olefiant gas.$ 2. When olefiant gas and chlorine gas are placed in contact with each other, a diminution of bulk takes place, and a liquid substance is formed which has somewhat the appearance of an oil, when the condensation takes place over water. The formation of this sub- stance was first observed by the Dutch chemists, and it induced them to contrive the term olefiant gas for the hydroguret of carbon. I examined this compound in 1810, and ascertained that it is a compound of olefiant gas and chlorine.|| Its properties and com- position were still more accurately investigated in 1816, by M. M. Robiquet and Colin.^f It is formed by the union of equal volumes of chlorine and ofefiant gas. If a current of the two gases from separate vessels meet in a large glass globular vessel, they combine and form the liquid in question, which collects at the bottom of the globe. To render it pure there must be rather an excess of olefiant gas. When there is an excess of chlorine, the liquid absorbs it, acquires a greenish colour and acid properties. But it may be rendered pure by washing it with a little water, and then distilling it off chloride of calcium. It is limpid and colourless like water, has an agreea- ble smell similar to that of muriatic ether, and a peculiar, sharp, * Memoirs of the Wernerian Society, i. 516. "J" Ann. de Chim. lxxviii. 63. * Phil. Mag. xxiv. 15. § Annals of Philosophy, vi. 340. || Memoirs of the Wernerian Society, i. 516. •J Ann. de Chim. et Phys. i. S37, and ii. 206. Chap. III.] CARBON. 209 sweetish, agreeable taste. Its specific gravity at 45° is 1-2201, the specific gravity of water being 1. It boils at 152°. At the tem- perature of 49°, its vapour is capable of supporting a column of mercury 24*66 inches in length. The specific gravity of this va- pour is 3*4434, that of air being 1. Now the specific gravity of chlorine and olefiant gas, added together, make 3*474. Hence it is obvious that this body is formed by a volume of chlorine and a volume of olefiant gas, condensed each into half its volume. Hence its constituents by weight are, Chlorine 2*5 - 4*5 - 100 Olefiant gas 0*974 - 0*875X2 38*88 Hence it appears, that it is a compound of one atom of chlorine, and two atoms of olefiant gas. Or its composition may be stated in this manner : chlorine 1 atom = 4*50 - 18—carbon 2 atoms = 1-50 - 6—hydrogen 2 atoms = 0*25 - 1. This liquid burns with a green flame, giving out copious fumes of muriatic acid and much soot. It is decomposed by being pass- ed through a red hot porcelain tube, and converted into muriatic acid, and an inflammable gas, containing hydrogen and carbon; while a copious deposite of charcoal is made in the tube. The in- flammable gas appears to contain no other constituent but carbon and hydrogen. The liquid is decomposed, likewise, when passed through red hot oxide of copper. There is some reason for believing that the different substances called ethers consist of olefiant gas, united either to water, or to an acid, or to a supporter of combustion. Supposing this opinion well founded, the liquid just described ought to be called chloric ether, 3. From an experiment made by Sir H. Davy, there is reason to suspect, that iodine combines with olefiant gas. A reddish brown volatile fluid was formed which did not possess acid pro- perties.* It is not unlikely that this liquid is the same with re- gard to hydriodic ether, that chloric ether is to muriatic ether. 4. Carbureted hydrogen, or bihydroguret of carbon, the other compound of hydrogen and carbon, is a gaseous substance which exhales in hot weather from stagnant water, especially ditches in the neighbourhood of towns. This gas was examined by Dr. Priestley and by Mr. Cruikshanks. But it was Mr. Dalton who first determined its composition with accuracy. I published a set of experiments on it in 181 l.f It may be collected by attaching a large glass phial to a piece of wood, so that it shall float on the surface of the stagnant water, with its mouth just under the surface. Into this mouth should be fixed a funnel (a piece of stout oiled paper will answer). Fill the phial with water, and set it afloat with its mouth undermost. Then stir the mud at the bottom of the pond or ditch. Air bubbles rise in abundance, and soon fill the phial. The gas, thus collected, should be washed with a solution of potash, or with lime water, in • Phil. Trans. 1814, p. 504. t Memoirs of the Wernerian Society, i. 506. Vol. I. D d 21CT SIMPLE COMBTTSTILES. S BOOK 1. £ DIVISION 2. order to separate a quantity of carbonic acid with which it is mix- ed. It usually contains, also, some common air. But I shall sup- pose it pure in the following description. Carbureted hydrogen, thus obtained, is colourless, and possesses the mechanical properties of common air. It has neither taste nor smell. Its specific gravity is 0-555. Hence at the temperature of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 16-99 grains. When a jet of it issuing from a tube is kindled in the open air, it burns with a yellow flame, giving out a good deal of light. When mixed with oxygen gas, and when an electrical spark is passed through the mixture, it detonates with considerable violence. It does^not burn unless the bulk of the oxy- gen rather exceeds its own bulk ; and it ceases to burn when the oxygen is more than 2% times its own bulk. If we mix it with com- mon air, it burns if it amounts to ^th of the air, and it ceases to burn if it exceeds ith of the air. In all proportions between these two extremes, it burns with violence. For complete combustion it requires twice its volume of oxygen gas, and produces exactiy its own volume of carhonir acid gas. The only remaining product is water. Now it is obvious that one-half of the oxygen went to the formation of carbonic acid, and the other half to the formation of water. This last portion must have combined with a quantity of hydrogen which, if it had been in an uncombined state, would have amounted to twice the volume of the original gas. Therefore carbureted hydrogen is composed by weight of Carbon - 0*416 - - 0-750 - 3 Hydrogen - 0-0694 x 2 - 0-125x2- 1 Hence, it is evident that, in this compound there are united one atom of carbon and two atoms of hydrogen. It is, therefore, a bihydroguret of carbon. The gas which exhales in such abundance in some coal mines, and which has been long the dread of miners, under the name of fire damp, is pure carbureted hydrogen. This was ascertained by Dr. Henry in 1807;* and Sir H. Davy, who repeated his experi- ments in 1815, came to the same conclusion.! 5. When moist charcoal, wood, pit-coal, or almost any animal or vegetable substance, is distilled in a retort, abundance of in- flammable gases are extricated. They differ very much in their specific gravity, in\he colour of their flame, and in the quantity of oxygen gas which they require for combustion, according to the degree of heat applied, the substance distilled, and the period of the distillation in which the gases are collected. Many experiments have been made on these gases, especially by Berthollet, Henry, Dalton, Saussure, and myself. They seem to be all mixtures of two, three, or four gases, according to circumstances. These gases are hydrogen, bihydroguret of carbon, carbonic oxide, and hydroguret of carbon. On that account the term oxycarbureted • Nicholson's Journal, xix. 149. tPhil- Trans. 1816, p. 1- Chap. III.] isuttun. 211 hydrogen, which has been applied to them by Berthollet and Saus- sure, and by the French chemists in general, does not seem to be very appropriate, and is altogether unnecessary. That the gas js in question are mixtures is obvious from this circumstance, that you never find any two of them exactly like one another. They are perpetually varying in their specific gravity, and in the quan- tity of oxygen necessary to consume them. Now this could not be the case if they were true chemical compounds. The gas, from pit coal, which is now employed for illuminating the streets and for lighting manufactures, appears, from the ex- periments of Dr. Henry, to consist chiefly of bihydroguret of car- bon, mixed with some hydroguret of carbon, and probably some carbonic oxide.* Mr. Murdoch, of Birmingham, was the person who first thought of this very useful application of coal gas.f 6. It is difficult to determine whether carbon or hydrogen have the strongest affinity for oxygen. Their affinity for each other in- terferes, and promotes the decomposition of those bodies to which they are applied. When red-hot charcoal is plunged into water, the liquid is decomposed; but bihydroguret of carbon is formed, so that this is not a case of the simple displacement of hydrogen by carbon? Hydrogen has the property of decomposing carbonic acid gas at a red heat. But in this case, also, the phenomena are com- plicated ; for the acid is not completely decomposed, but merely reduced to carbonic oxide. The opinion at present entertained by chemists is, that hydrogen has a stronger affinity for oxygen than carbon has; but this opinion is not supported by any facts that can be considered as decisive. SECTION III. OF BORON. The saline substance called borax has been long familiar to Eu- ropean artists, being employed to facilitate the fusion of the pre- cious metals, and in the formation of artificial imitations of the precious stones. It comes from the East Indies, and is said to be found chiefly in certain lakes in Thibet and China. The word bo- rax occurs first in the writings of Geber, an Arabian chemist of the tenth century. In the year 1702, Homberg, by distilling a mixture of borax and green vitriol, obtained a peculiar substance in small white shining plates, which he called sedative or narcotic salt, and which was considered as an efficacious remedy in con- tinued fevers.*. Lemery, the younger, in the year 1727, found * Nicholson's Journal, xi. 73. t.l^r- Murdoch appears to have discovered the gas in 1792, but did not apply it to the lighting of apartments until 1798. M. Le Bon applied this gas to that purpose, in Paris, in 1797.—Cooper on gas lights, 189.] t Histoire de l'Aoad. 1702, p. 50. 212 SIMPIE COMBUSTIBLES. C BOOK I. £ DIVISION 2. that this substance could be separated from borax by the mineral acids.* In 1731, Geofroy ascertained that sedative salt gave a green colour to the flame of alcohol, and that borax contains in it the same alkaline substance that constitutes the basis of common saluf In the year 1752, Baron demonstrated by satisfactory ex- periments, that borax is composed of sedative salt and soda.i. Se- dative salt was found to possess the properties of an acid: it was therefore called boracic acid. But the composition of this acid re- mained altogether unknown. Crell, indeed, published a set of ex- periments on it in the year 1800, in which he endeavoured to show, that its basis was a substance very similar to charcoal in its proper- ties.§ But when his experiments were repeated by Sir H. Davy, they did not succeed. Davy, in the year 1807, exposed a quantity of boracic acid to the action of the galvanic battery, and observed that a black matter was deposited upon the negative wire, which he considered as the basis of this acid, but he did not prosecute the discovery farther at the time. In the summer of 1808, MM. Gay-Lussac and Thenard succeeded in decomposing this acid by heating it in a copper tube along with potassium. They examined the properties of its base, to which the name of boron has been given, and published a detailed account of its properties.j| • Davy, in 1809, decomposed the acid by the process of the French che- mists, and published, likewise, an account of the properties of bo- ron.^j Boron may be obtained by the following process. 1. One part of pure boracic acid, previously melted and reduced to powder, is to be mixed with two parts of potassium** and the mixture put into a copper, or iron tube, and gradually heated till it is slightly red, and kept in that state for some minutes. At the temperature of 300° the decomposition begins, and the mixture becomes intensely red hot, as may be perceived by making the ex- periment in a glass tube. When the tube is cold, the matter in it is to be washed out with water, the potash formed is to be neutral- ized with muriatic acid, and the whole thrown upon a filter. The boron remains upon the filter. It may be washed and dried in a moderate heat.ff Boron, thus prepared, possesses the following properties. 2. It is a powder of an olive brown colour, without either taste or smell. In close vessels it may be exposed to the most violent heat that can be raised, without undergoing any other change, ex- cept an increase of density. When first prepared it does not sink • Mem. Par. 1728, p. 273. f Mem- Pl»r 1732, p. 398. $ Savans Etrangers, ii. 412. § Ann. de Chim. xxxv. 202. || Mem. d'Arcueil, ii. 311, and afterwards in Recherches Physico-chimiques, i. 276. •f Phil. Trans. 1809. ** A metallic body to be described in a subsequent section of this chapter. \\ A better way of obtaining it is to put the liquid containing the boron into a glass ves- sol, to allow the boron to subside, and then to draw off the liquid with a syphon. Water is then to be poured on, the boron allowed to subside, and the liquid again drawn off. This process is repeated till the water comes off quite clear. The boron may now be put into a glass capsule, and dried by a moderate heat Chap. III.] BORON. 213 in sulphuric acid of the density 1-844; but after being thus exposed to a violent heat, it sinks rapidly in that acid. It is insoluble in water, alcohol, ether, and oils, whether cold or hot. It does not decompose water even when heated in that liquid to the tempera- ture of 176°. Probably at a red heat the decomposition would take place. Boron is a non-conductor of electricity. 3. Boron is not altered in common air, or oxygen gas, at the or- dinary temperature of the atmosphere; but when raised to a heat not quite so high as 600°, it takes fire and burns with great splen- dour, absorbing at the same time oxygen. By this combustion, a portion of the boron is converted into boracic acid, which undergo- ing fusion coats the boron, and keeping it from coming in contact with the oxygen, puts an end to the combustion. If this boracic acid be washed off, the boron will burn again, but requires a high- er temperature. A great number of successive combustions and washings are requisite, in order to convert the whole of the boron into boracic acid. Several experiments have been made to deter- mine the quantity of oxygen which combines with boron, and con- verts it into boracic acid; but none of them seem entitled to much confidence. Gay-Lussac and Thenard acidified a portion of boron by heating it in nitric acid. Five parts of boron, by this process, were converted into 7-5 parts of boracic acid.* According to this statement, boracic acid is composed of boron - - 100 - - 2—oxygen 50 - - 1; but they do not put much confidence in its accuracy. Davy found that when 30 grains of potassium were converted into potash 2-375 grains of boron were evolved.f Now 30 grains of potassium require six grains of oxygen to convert them into pot- ash. If we suppose the whole of this to have been in combination with the boron, it will follow that boracic acid is composed of boron 2*375 - - 2—oxygen 6 - - 5*05. The difference between this and the preceding result is enormous. But it is obvious that this mode of experimenting is liable to great uncertainty. As hydrogen gas is given out during the decomposi- tion of the boracic acid by potassium, it is clear that all the oxygen in the potash was not derived from the decomposed acid. Besides it is very unlikely that the whole of the boron could be collected and weighed. Davy found that one grain of boron when converted into boracic acid absorbed 5.125 cubic inches of oxygen gas4 Now 5*125 cubic inches of oxygen gas weigh 1*74 grain. According to this estimate boracic acid is composed of boron 1 - - 2—oxygen I.74 . _ 3.48. This mode of experimenting is probably better than the preceding, but the experiment was made on so small a scale, and agrees so ill with the two others just stated, that we can- not put full confidence in it. There is another method by which we can acquire tolerably cor- rect ideas respecting the proportion of the constituents of this acid. * Recherches Physico-chimiques, i. 307. \ Davy's Lecture on some new Analytical Researches on the Nature of certain Bodies, p. 43. Phil. Trass. 1809. * Ibid. p. 44. 214 SIMPLE C0MBUSTIBEE9. 5 BOOK I. £ DIVISION 2. Berzelius ascertained* by experiment, that boracic acid and ammo- nia combine with each other in the portion of boracic acid 37*95— ammonia 30*32. Now the weight of an atom of ammonia is 2*125, and in neutral compounds one atom of ammonia is found united to one atom of acid. But 30-32 : 37-95 :: 2*125 : 2-66. So that 2-66 represents the weight of an atom of boracic acid. This acid is a compound of boron and oxygen, and it must consist of one atom of boron, united either to one or to two atoms of oxygen. From the observations of Davy there is reason to conclude that the black matter which appears when boron is imperfectly burnt is an oxide of boron. In that case boron in boracic acid must be combined with two atoms of oxygen. But the weight of two atoms of oxy- gen is two. Therefore boracic acid must be composed of boronf 0*66 - -0*33 - - 1—oxygen 2*00 - - 1*00- - 3. This deduction, which, is probably near the truth, agrees best with the first experiment ot Davy. We see from it that the weight of an atom of boron is 0-664 The principal source of uncertainty is the difficulty of mak- ing a correct analysis of borate of ammonia. But from the precau- tions taken by Berzelius, there is reason to believe that the error must be inconsiderable. 4. When boron is introduced into chlorine gas, it takes fire and burns with a brilliant white flame. A white substance coats the vessel in which the experiment is made, and the boron is covered with a white substance, which by washing yields boracic acid.§ It is probable that the substance thus formed is a chloride of boront But it has not hitherto been examined. 5. We do not know whether boron be capable of combining with iodine; no experiments having been hitherto made on the ■subject. 6. Boron has the property of combining with fluorine, and of forming with it a powerful acid to which the name of fiuoboric acid has been given. It was discovered by Gay-Lussac and Thenard in 1808, who published a detailed account of its properties.|| Some additional facts respecting it were afterwards published by Dr. John Davy.ff It may be procured by the following process. Mix together in a retort one part of finely pounded fused bo- racic acid, two parts of fluor spar in powder, and 12 parts of sul- phuric acid. Apply the heat of a lamp. A gas comes over which * Annals of Philosophy, iii. 57. ■j- [In general remarks, No. 1. it is stated as 0-875. I repeat, the time has not yet arriv- ed when we may place full confidence in any of these calculations.—C.] $ From the composition of hydrate of boracic acid (which will be given when treating of that acid) compared with that of borate of ammonia, there is reason for believing that the true weight of an atom of boracic acid is 2-875. Hence an atom of boron weighs 0-875, and boracic acid is composed of boron 0-875 - - 100—oxygen 2- - - 228-57. § Davy's Lecture on some new Analytical Researches on the Nature of certain Bodies, p. 41. Phil. Trans. 1809. Gay-Lussac and Thenard affirm that boron does not burn in dry chlo- rine gas. Recherches Physico-chimiques, i. 303. Is this difference to be ascribed to the pre- sence of water in Davy's chlorine ? I can hardly believe it. H Mem. d'Arcueil, ii. 317. And Recherches Pbyaco*chiiniqties, ii. 87. 1 Phil. Trans. 1812, p. 365. Chap. HI.] boron. 215 must be collected over mercury. It is fluoboric acid gas. For this process we are indebted to Dr. John Davy. Fluoboric acid thus obtained is colourless, and possesses the mechanical properties of common air. Its smell is similar to that of muriatic acid, and it has an exceedingly acid taste. It instantly gives a red colour to vegetable blues. Its specific gravity, as de- termined by Dr. Davy, is 2-3709. Hence at the temperature of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 72*312 grains. Water, according to Dr. Davy, absorbs 700 times its volume of this gas. The liquid thus obtained is of the specific gravity 1*77. Hence it follows that a cubic inch of water when saturated with this gas is expanded to 1-697 cubic inch. This liquid acid has a certain degree of viscidity, similar to that of sulphuric acid; and, like it, requires a high temperature to cause it to boil. It smokes at first, and gives out about the fifth part of the gas which it contains, but no more, when heated; like sulphuric acid it chars animal and vegetable substances. It forms also an ' ether when distilled with alcohol. It combines with the different bases, and forms salts called fluoborates. It may be passed over red hot iron without undergoing any change. But potassium burns in it and appears to be converted into fluoride of potassium, while boron is disengaged. Sulphuric acid has the property of absorb- ing it in considerable quantities. 7. Davy did not succeed in his attempts to unite boron with azotic gas.* 8. He was equally unsuccessful when he heated boron in hydro- gen. But Gmelin appears to have obtained borureted hydrogen gas by the following process. He mixed together four parts of iron filings and one part of boracic acid, and exposed the mixture to a strong heat for half an hour in a crucible. The fused mass was dissolved in diluted muriatic acid. An effervescence took place, and borureted hydrogen gas was extricated.f This gas had the smell of common hydrogen gas from iron, mixed with some- what of the smell of garlic. When kindled it burned with a red- dish yellow flame surrounded by a green border, and white fumes made their appearance in the vessel in which the-combustion took place. These were the only characters by which the presence of boron was indicated. Gmelin neither determined the specific gravity of the gas nor made an analysis of it. His experiments therefore are sufficient only to show us that borureted hydrogen gas may be formed. His gas seems to have been pure hydrogen mix- ed with only a small proportion of borureted hydrogen. 9. Boron, as far as we know at present, does not combine with carbon. 10. Descotilsi. has shown that it combines with iron, and his * Davy's Lecture on some new Analytical Researches on the Nature of certain Bodies, p. 42, Phil. Trans. 1809. f Schweigger's Journal, xv. 246. * Recherches Physico-chimiques. i. 306. 216 SIMPLE COMBUSTIBLES. S BOOK I. ^mvisiox %. experiments have been verified by Gmelin.* Davy has found that it has the property of combining with potassium,! and forming a grey metallic mass. But as far as the experiment has been hither- to tried, it does not unite with any of the other metals. 11. Its affinity for oxygen appears to be greater than either that of hydrogen or carbon. Accordingly at a red heat it decomposes water and carbonic acid. Indeed it has a stronger affinity for oxy- gen than any of the acidifiable bases, unless silicon constitute an exception. Accordingly it separates oxygen from all of them wher assisted by a sufficiently high temperature. SECTION IV. OF SILICON. There is a rock, which occurs in great abundance in the primi- tive mountains, sometimes forming immense beds, or even whole mountains: sometimes mixed with other stony bodies, as in granite. This rock is known by the name of quartz. As this stone and se- veral others which resemble it, as flint, calcedony, &c. have the property of melting into a glass when strongly heated with potash or soda, they were classed together by mineralogists under the name of vitrifiable stones. Mr. Pott, who first described the pro- perties of these minerals in 1746, gave them the name of siliceous stones, supposing them all chiefly composed of a peculiar earth called siliceous earth or silica. This earth was known to Glauber, who describes the method of obtaining it from quartz. But it was long before its properties were accurately ascertained. Geoffroy endeavoured to prove that it might be converted into lime,! anc* Pott,§ and Baume,|j that it might be converted into alumina: but these assertions were refuted by Cartheuser,*fl Scheele,** and Berg- man, jf To this last chemist we are indebted for the first accurate description of the properties of silica.\\ 1. Silica is the most common ingredient in stony bodies, and exists in them, combined with various earths and metallic oxides. Mr. Smithson§§ suggested that in these compounds the silica per- forms the function of an acid; an opinion which has been demon- strated in a satisfactory manner by Berzelius.|j|| It is easily obtain- ed pure by fusing quartz or flint with twice its weight of potash in a silver crucible, dissolving the compound formed in water, super- saturating the liquid with muriatic acid, and evaporating it slowly * Schweigger*s Journal, xv. 245. f Davy, ubi supra, p. 45. * Mem. Par. 1746, p. 286. § Lithogeogn. p. iii. Preface. || Man. de Chim. 1 Miner. Abb. ** Scheele, i. 191. \\ Sur les Terres Geoponiques; Opusc. v. 59. # Ibid. ii. 86. §§ Phil. Trans. 1811, p. 176. |!| Attempt to establish a pure Scientific System of Mineralogy, p, 27, and the sequel- Chap. III.] SILICON. 217 to dryness. When concentrated to a certain extent, the liquid as- sumes the form of jelly. The dry residue is to be well washed with water and then dried. It is a white powder, without taste or smell; but feeling gritty between the teeth. It is not sensibly soluble in water, owing to its great cohesive power. But when the compound of silica and pot- ash is dissolved in water, and diluted with a sufficient quantity of that liquid, the silica cannot be precipitated from it by any addition of acid: snowing that in this state of division it is in reality solu- ble in water. 2. Sir H. Davy, after having succeeded in decomposing the fixed alkalies and alkaline earths by the action of the galvanic battery, was naturally led to try the effects of the same powerful agent upon silica. But his experiments were not attended with success.* But the analogy between silica and other bodies containing oxygen is so great, that it was universally considered as a compound of oxy- gen and a combustible base. Berzelius succeeded in separating this basis from silica, and uniting it to iron ;f and his experiments were successfully repeated by Professor Stromeyer.f. About the end of 1813, Sir H. Davy succeeded in obtaining the basis of silica in a separate state, although he was not able to collect it and exa- mine its properties in detail.^ The base of silica has been usually considered as a metal, and called silicium. But as there is not the smallest evidence for its metallic nature, and as it bears a close re- semblance to boron and carbon, it is better to class it along with these bodies, and to give it the name of silicon. 3. Davy decomposed silica, by passing potassium in excess through it in a platinum tube. The potassium was converted into potash, through which was scattered the silicon under the form of a dark-coloured powder. 4. Silicon seems capable of bearing a very high temperature without undergoing any change. In this respect it resembles boron and carbon. Potash seems to dissolve a portion of it, and the so- lution acquires an olive colour. Silicon has the property of de- composing water, and of being converted into silica when it comes in contact with that body. Hence it was impossible to wash off the potash and obtain it in a separate state. 5. Silicon readily unites with oxygen, and is converted into silica. The object of the experiments of Berzelius and Stromeyer was to determine the quantity of oxygen which exists in silica. They mixed together iron filings from the purest iron that could be pro- cured, silica, and charcoal,|| in the proportions of 3 iron, 1*5 ^ilica, and 0*66 charcoal.- . This mixture was put into a covered * Phil. Trans. 1808. f Afhandlingar i Fysik, Kemi och Mineralogi, iii. 117. Published in 1810. \ Gilbert's Annalen, xxxvii. 335, and xxxviii. 321. Published in 1811. § Phil. Trans. 1814, p. 67. U Stromeyer used lamp black to get rid of the alkali which charcoal contains. Vol. I. E e 218 SIMPLE INCOMBUSTIBLES. $ BOOK 1. I DIVISIONS. crucible, and exposed for an hour to the greatest heat that could be raised in a blast furnace. By this means a combination of iron, silicon, and carbon, was formed. It was in the state of globules that had undergone complete fusion. When freed from the char- coal they were white and ductile, unless when they contained a great proportion of carbon. When dissolved in muriatic acid they gave put a greater proportion of hydrogen gas than the same weight of pure iron would have furnished. A substance remained undissolved, which retained the form of the globules, and which was silica, still mixed with some iron and carbon, from which it was separated by repeated calcination and digestion in muriatic acid. According to Stromeyer's experiments, the globules con- taining most silicon were composed of Iron 85*3528 Silicon 9*2679 Carbon 5*3793 100*0000 and the globules that contained the least silicon where composed of Iron 96*1780 Silicon 2*2124 Carbon 1*6096 100*0000* The specific gravity of the iron was considerably reduced by combining it with silicon. The specific gravity of the iron em- ployed by Stromeyer was 7*8285. The specific gravity of the alloy was never higher than 7*3241, nor lower than 6-7777. Its specific gravity was inversely as the proportion of silicon which it contained. There could be no doubt, that in the alloy the silicon existed in a state of purity; but when the compound was dissolved in muri- atic acid, the silicon combined with oxygen and was converted into silica. Both Berzelius and Stromeyer endeavoured to determine the quantity of oxyrgen which unites with silicon, and converts it into silica, by decomposing a given weight of the alloy, and then weighing each of the constituents separately. The excess of weight was considered to be the oxygen which had united with the silicon. This method would answer, if these experiments could be perform- ed with rigid accuracy. But where an error amounting only to a small fraction of a grain would make a very material difference in the result, it is impossible to have much confidence in the conclu- sions. According to the experiments of Berzelius silica is com- posed of Silicon - 54-66 to 52-25 - 53-455 - 100 Oxygen- 45*34 to 47-75 - 46*555 - 87-09 100*00 100*00 100.000 * Gilbert's Annalen, xxxviii. 330. Chap. III.] silicon. 219 According to Stromeyer, silica is composed of Silicon - - 46-0069 - 100 Oxygen - 53*9931 - 117*4 100*0000 The mean of these two sets of experiments gives us silica com- posed of Silicon 100—Oxygen 102*245. Davy found that more than three parts of potassium were re- quired to decompose one part of silica.* If we could be certain, that the whole of the oxygen that converts the potassium into pot- ash is derived from the silica, it would follow from this experi- ment, that 100 parts of silica contain at least 60 of oxygen. Upon the whole, I conceive, that at present we may consider silica with- out any material error, as containing exactly half its weight of oxygen. From the analogy of carbonic acid and boracic acid, it is not improbable, that it consists of one atom of silicon united to two atoms of oxygen. In that case an atom of silicon would weigh two. But the natural silicates point out two as the weight of an atom of silica. Therefore silica must contain only one atom of oxyTgen, and an atom of silicon can weigh only one. 6. Nothing is known respecting the action of silicon on chlorine and iodine. No experiments having been hitherto made on the subject. 7. Silica has the property of combining with fluorine, and of forming a compound, which has received the name of iilicated fluoric acid. But the term fiuosilicic acid being more systematic, and being preferable in other respects, we shall make choice of it. Fiuosilicic acid was first discovered by Scheele.f It was after- wards obtained in the gaseous state by Dr. Priestley, and many of its properties investigated.^ A valuable set of experiments was published on it in 1812, by Dr. John Davy.§ To obtain this gas we have only to put a mixture of equal quan- tities of pounded fluor spar and glass into a retort, and to pour over it sulphuric acid in sufficient quantity to convert the whole into a paste. On the application of a gentle heat, the gas comes over in abundance, and may be collected in glass jars standing over mercury. Fiuosilicic acid gas is colourless, and possesses the mechanical properties of common air. It has a smell similar to muriatic acid, a very acid taste, and occasions a white smoke when it is allowed to escape into the atmosphere. It changes vegetable blues to red. No animal can breathe it, and no combustible will burn in it. Its specific gravity as determined by the experiments of Dr. John Davy is 3-5735.(| Hence at the temperature of 60°, and when the baro- meter stands at 30 inches, 100 cubic inches of it weigh 108-992 grains. • Phil. Trans. 1814, p. 67. \ Scheele's Memoires de Chimie, i. 24. * Priestley on Air, ii. 339. § Phil. Trana. 1812, p. 352. g Ibid. p. 354. 220 SIMPLE COMBUSTIBLES. C BOOKL £ mviMo.N 2. Dr. John Davy found that water was capable of absorbing 263 times its bulk of this gas. But as water has the property of de- composing it and of precipitating silica, this circumstance doubtless diminishes the action of the liquid. From other circumstances, he concludes that water absorbs as much of this gas as of muriatic acid gas. In that case water will be capable of absorbing 515 times its bulk of this gas. Dr. J. Davy analysed this gas by passing it into liquid ammonia, which has the property of throwing down the whole of the silicon that it contains in the state of silica. From 40 cubic inches of the gas, he procured 27*2 grains of silica. Now 40 cubic inches weigh 43*597 grains. Hence he concluded that the gas is composed of Silica - 27*2 - 62*4 - 165-88 Fluoric acid 16*397 - 37-6 - 100*00 But if this acid be a compound of silicon and fluorine, as has been rendered probable by Sir H. Davy, then in order to have its composition, we must subtract the oxygen from the silica, and add it to the fluoric acid, in order to convert it into fluorine. The acid will then be composed of Silicon - 13*6 - 100 Fluorine - 29*997 - 220*6 If the weight of an atom of silicon be a little le«s than one, and that of fluorine a little more than two, as is probably the case, it will follow from this analysis, that fluosilicic acid is a compound of one atom of silicon and one atom of fluorine. When fluosilicic acid gas comes in contact with water, it is ab- sorbed by that liquid, and at the same time deposites a portion of its silicon in the state of silica. From the experiments of Dr. J. Davy it appears that 44 cubic inches of the gas when thus absorb- ed by water deposit 7*33 grains of silica, equivalent to 3.665 grains of silicon. Now 44 cubic inches of fluosilicic acid gas weigh 47*956 grains, and must be composed of silicon 14-96—fluorine 32*996. Hence the acid portion absorbed by the water must be composed of Silicon - - 11-295 - - 100 Fluorine - - 32*996 - - 292*1 Which perhaps may be two atoms of silicon united to three atoms of fluorine. But on this obscure subject nothing better than con- jecture can be at present offered. SECTION V. OF PHOSPHORUS. Phosphorus may be procured by the following process : Let a quantity of bones be burnt, or, as it is termed in chemistry, calcined, Chap. III.] PHOSPHORUS. 221 till they cease to smoke, or to give out any odour, and let them afterwards be reduced to a fine powder. Put 100 parts of this powder into a basin of porcelain or stoneware, dilute it with four times its weight of water, and then add gradually (stirring the mixture after every addition) 40 parts of sulphuric acid. The mixture becomes hot, and a vast number of air bubbles are extri- cated.* Leave the mixture in this state for 24 hours; taking care to stir it well every now and then with a glass or porcelain rod to enable the acid to act upon the powder, f The whole is now to be poured on a filter of cloth; the liquid which runs through the filter is to be received in a porcelain basin; and the white powder which remains on the filter, after pure water has been poured on it repeatedly, and allowed to strain into the porcelain basin below, being of no use, may be thrown away. Into the liquid contained in the porcelain basin, which has a very acid taste, nitrate of lead,:}: dissolved in water, is to be poured slowly; a white powder immediately falls to the bottom: the ni- trate of lead must be added as long as any of this powder continues to be formed. Throw the whole upon a filter. The white powder which remains upon the filter is to be well washed, allowed to dry, and then mixed with about one-sixth of its weight of charcoal powder. This mixture is to be put into an earthenware retort. The retort is to be put into a furnace, and the beak of it plunged into a vessel of water, so as to be just under the surface. Heat is now to be applied gradually till the retort be heated to whiteness. A vast number of air-bubbles issue from the beak of the retort, some of which take fire when they come to the surface of the water. At last there drops out a substance which has the appearance of melt- ed wax, and which congeals under the water. This substance is phosphorus. It was accidentally discovered by Brandt, a chemist of Ham- burgh, in the year 1669,§ as he was attempting to extract from human urine a liquid capable of converting silver into gold. He showed a specimen of it to Kunkel, a German chemist of conside- rable eminence, who mentioned the fact as a piece of news to one Kraft, a friend of his at Dresden. Kraft immediately repaired to Hamburgh, and purchased the secret from Brandt for 200 dollars, exacting from him at the same time a promise not to reveal it to any other person. Soon after, he exhibited his phosphorus publicly in Britain and France, expecting doubtless that it would make his fortune. Kunkel, who had mentioned to Kraft his intention of getting possession of the process, being vexed at the treacherous • The copious emission of air-bubbles is called in chemistry effervescence. f Fourcroy and Vauquelin, Mem. de l'lnst. ii. 282. i A salt to be described in a subsequent part of this Work. It answers better than acetate of lead, as was first pointed out by Giobert, and more lately by Mr. Hume. See Giobert's process, Ann. de Chim. xii. 15. and Phil. Mag. xx. 160. § Homberg, Mem. Par. x. 84. An account of it is published in the Philosophical Trans* actions for 1681, first by Sturmius, and then by Dr. Slare. 222 SIMPLE COMBUSTIBLES. S BOOK I. £ DIVISION t. conduct of his friend, attempted to discover it himself; and about. the year 1674 he succeeded, though he only knew from Brandt that urine was the substance from which phosphorus had been pro- cured.* Accordingly he is always reckoned, and deservedly too, as one of the discoverers of phosphorus. Boyle likewise discovered phosphorus. Leibnitz indeed af- firms, that Kraft taught Bode the whole process, and Kraft de-. claredthe same thing to Stahl. But surely the assertion of a deal- er in secrets, and one who had deceived his own friend, on which the whole of this story is founded, cannot be put in competition with the affirmation of a man like Boyle, who was not only one of the greatest philosophers, but likewise one of the most virtuous men of his age; and he positively assures us, that he made the discovery without being previously acquainted with the process.! Mr. Boyle revealed the process to his assistant Godfrey Hank- witz, a London apothecary, who continued for many years to sup- ply all Europe with phosphorus. Hence it was known to chemists by the name of English phosphorus.]. Other chemists, indeed, had attempted to produce it, but seemingly without success,^ till in 1737 a stranger appeared in Paris, and offered to make phospho- rus. The French government granted him a reward for commu- nicating his process. Hellot, Dufay, Geoffroy, and Duhamel, saw him execute it with success ; and Hellot published a very full ac- count of it in the Memoirs of the French Academy for 1737.|| It consisted in evaporating putrid urine to dryness, heating the inspissated residue to redness, washing it with water to extract the salts, drying it, and then raising it gradually in stoneware retorts to the greatest intensity of heat. It was disgustingly tedious, very expensive, and yielded but a small quantity of produce. The ce- lebrated Margraf, who informs us that he had devoted himself at a very early period to the investigation of phosphorus, soon after published a much more expeditious and productive process; for the first hint of which he was indebted to Henkel. It consisted in mixing a salt consisting chiefly of lead with the inspissated urine. He even found that urine contained a peculiar salt,^} which yielded phosphorus when heated with charcoal.** In the year 1769, Gahn, a Swedish chemist, discovered that phosphorus is contained in bones ;ff and Scheele, very soon after, invented a process for obtaining it from them. Phosphorus is now generally procured in that manner. The process described in the beginning of this Section is that of Fourcroy and Vauquelin. The * This is Kunkel's own account. See his Laboratorium Chymicum, p. 660. See also Wiegleb's Geschichte des Wachsthums und der Erfindungen in der Chemie, vol. i.jp. 41. f Boyle's Works abridged by Shaw, iii. 174. + See Hoffman's experiments on it, published in 1742 in his Observat. Phys. Chym. Select, p. 304. § Stahl's Fundament. Chym. ii. 58. || Mem. Par. 1737, p. 342. *3 Known at that time by the name of fusible salt of urine, now called phosphate of ammonia. ** Miscel. Berolin, 1740, vi. 54.; and Mem. Acad. Berlin, 1746, p. 84; and Margraf's Opsc. i. 30. ft" Bergman's Notes on Scheffer, p. 208. I quote the edition of 1796. Chap. III.] phosphorus. 223 usual process followed by manufacturers of phosphorus is an im- provement on that of Scheele. Soon after the discovery of phosphorus, many experiments on it were made by Slare and Boyle. Hoffman published a dissertation on it, containing some curious facts, in 1722; but Margraf was the first who investigated its effects upon other bodies, and the nature of the combinations which it forms. The subject was resumed by Pelletier, and continued with much industry and success. Lavoi- sier's experiments were still more important, and constitute indeed a memorable era in chemical science. Many important experiments on phosphorus have been made still more lately by Davy, and by Gay-Lussac and Thenard. The- nard* and Vogelf have made researches on the red powder which remains when phosphorus is burnt, and upon the changes produ- ced on it by the action of light. Dulong^: and Berzelius^ have examined its combination with oxygen; while I have made some experiments on the compounds which it forms with hydrogen.|| 1. Phosphorus is usually of a light amber colour and semi-trans- parent ; though when carefully prepared \t is nearly colourless and transparent.^} When kept some time in water, it becomes opaque externally, and then has a great resemblance to white wax. Its consistence is nearly that of wax. It may be cut with a knife, or twisted to pieces with the fingers. It is insoluble in water. Its mean specific gravity is 1*770. 2. It melts, according to Pelletier, when heated to 99°.** In my trials I found that a temperature of 108° was requisite to produce complete fusion. Care must be taken to keep phosphorus under water when melted; for it is so combustible, that it cannot easily be melted in the open air without taking fire. When phosphorus is newly prepared, it is always dirty, being mixed with a quantity of charcoal dust and other impurities. These impurities may be separated by melting it under water, and then squeezing it through a piece of clean shamois leather. It may be formed into sticks, by putting it into a glass funnel with a long tube, stopped at the bottom with a cork, and plunging the whole under warm water. The phos- phorus melts, and assumes the shape of the tube. When cold, it may be easily pushed out with a bit of wood. If air be excluded, phosphorus evaporates at 219°, and boils at 554°.ff 3. Phosphorus is dissolved in a small proportion by alcohol, ether, and oils. The solutions are transparent. When the alcohol or ether is mixed with water, the phosphorus separates and burns • Ann. de Chim. xxxvi. 109. "j- Ibid. xxxv. 225. * Ann. de Chim. et Phys. ii. 141. § Ibid. p. 151, 218, and 329. ' II Annals of Philosophy, viii. 87. *t Thenard informs us that when melted and then suddenly cooled, it becomes quite black. But again resumes its original appearance when kept melted for a short time. Ann. de Chim. lxxi. p. 109. There seems to have been something peculiar about the phosphorus which he employed. ** Jour, de Phys. xxxv. 380. tt Pelletier, Jour, de Phys. xxxv. 381. 224 SIMPLE COMBUSTIBLES. S BOOK I. ^DIVISION 2. on the surface of the liquid. When the oily solution of phospho- rus is poured upon paper and carried into a dark room, it shines vividly, provided the temperature be above 60°. But at lower temperatures the light is scarcely perceptible. 4. When used internally, it is poisonous.* In very small quan- tities (as one fourth of a grain,) when very minutely divided, it is said by Leroi to be very efficacious in restoring and establishing the force of young persons exhausted by sensual indulgence ;f that is, I suppose, in exciting the venereal appetite.i. II. Phosphorus has the property of combining with oxygen at least in four proportions, and of forming four compounds, which have received the following names. 1. Oxide of phosphorus. 3. Phosphorous acid. 2. Hypophosphorus acid. 4. Phosphoric acid. 1. When phosphorus is exposed to the atmosphere, it emits a white smoke, which has the smell of garlic, and is luminous in the dark. This smoke is more abundant the higher the temperature is, and is occasioned by the gradual combustion of the phosphorus, which at last disappears altogether. 2. When a bit of phosphorus is put into a glass jar filled with oxygen gas, part of the phosphorus is dissolved by the gas at the temperature of 60°; but the phosphorus does not become luminous unless its temperature be raised to 80°.§ Hence we learn, that phosphorus burns at a lower temperature in common air than in oxygen gas. This slow combustion of phosphorus, at the common temperature of the atmosphere, renders it necessary to keep phos- phorus in phials filled with water. The water should be previous- ly boiled to expel a little air, which that liquid usually contains. The phials should be kept in a dark place; for when phosphorus is exposed to the light, it soon becomes of a white colour, which gradually changes to a dark brown. 3. When heated to 148°, phosphorus takes fire and burns with a very bright flame, and gives out a great quantity of white smoke, which is luminous in the dark; at the same time it emits an odour which has some resemblance to that of garlic. It leaves no resi- duum ; but the white smoke, when collected, is found to be an acid. Stahl considered this acid as the muriatic. According to him, phosphorus is composed of mu iatic acid and phlogiston, and the combustion of it is merely the separation of phlogiston. He even declared that, to make phosphorus, nothing more is necessary than to combine muriatic acid and phlogiston.|| These assertions having gained implicit credit, the composition and nature of phosphorus were considered as completely under- stood, till Margraf of Berlin published his experiments in the year * Ann. de Chim. xxvii. 87. ] Nicholson's Journal, iii. 85. i [It seems to have been of use in typhoid disorders.—C.] § Fourcroy and Vauquelin, Ann. de Chim. xxi. 196. § Stahl's Three Hundred Experiments. Chap. III.] PHOSPHORUS. 225 1740. He attempted to produce phosphorus by combining together phlogiston and muriatic acid: but all his attempts failed, and he was obliged to give up the combination as impracticable. On ex- amining the acid produced during the combustion of phosphorus, he found that its properties were very different from those of mu- riatic acid. It was therefore a distinct substance.* The name of phosphoric acid was given to it; and it was concluded that phos- phorus is composed of this acid united to phlogiston. But it was observed by Margraf, that phosphoric acid is heavier than the phosphorus from which it was produced ; and Boyle had long before shown that phosphorus would not burn except when in contact with air. These facts were sufficient to prove the inac- curacy of the theory concerning the composition of phosphorus; but they remained themselves unaccounted for, till Lavoisier published those celebrated experiments which threw so much light on the nature and composition of acids.f He exhausted a glass globe of air by means of an air-pump; and after weighing it accurately, he filled it with oxygen gas, and intro- duced into it 100 grains of phosphorus. The globe was furnished with a stop-cock, by which oxygen gas could be admitted at plea- sure. He set fire to the phosphorus by means of a burning glass. The combustion was extremely rapid, accompanied by a bright flame and much heat. Large quantities of white flakes attached themselves to the inner surface of the globe, and rendered it opaque; and these at last became so abundant, that notwithstand- ing the constant supply of oxygen gas the phosphorus was extin- guished. The globe, after being allowed to cool, was again weigh- ed before it was opened. The quantity of oxygen employed dur- ing the experiment was ascertained, and the phosphorus, which still remained unchanged, accurately weighed. The white flakes, which were nothing else than pure phosphoric acid, were found exactly equal to the weights of the phosphorus and oxygen which had disappeared during the process. Phosphoric acid therefore must have been formed by the combination of these two bodies; for the absolute weight of all the substances together was the same after the process as before it4 Lavoisier drew, as a conclusion, from his experiments that phosphoric acid is composed of 100 phosphorus and 154 parts of oxygen. But his mode of experimenting was not sufficiently pre- cise to merit confidence. Rose endeavoured to obtain more ac- curate results by acidifying phosphorus by means of nitric acid. According to him phosphoric acid is composed of 100 phosphorus and 114-75 oxygen.§ But this mode of experimenting is worse than that employed by Lavoisier. I have repeated Rose's experi- ment at least a dozen of times, and no two results coincided with • Margraf's Opusc. i. 56. t Mem- Par- 17~8 and 1780. t Lavoisier's Chemistry, Part I. chap. v. § Gehlen's Journal fur die Chemie, Physik und Miaeralogie, ii. 309. Vol. I. F f 226 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION it each other. But there is another method by which we can obtain the composition of this acid with considerable accuracy, by exa- mining the composition of the neutral salts which it forms with the different bases. It will be seen in a subsequent part of this work that the numbers which represent the weight of an atom of each of the following bodies are Yellow oxide of lead 14 Barytes - - - 9*75 Soda - - - 4 Lime - - - 3*625 From the analyses of Berzelius, and my own analyses, it follows that the neutral salts formed of these bases and phosphoric acid are composed as follows: Phosphate of lead. Phosphate of barytes. Acid - 100 - 4*45 Acid - 100 - 4-54 Base - 314 - 14 Base - 214-46 - 9*75 Phosphate of soda. Phosphate of lime. Acid - 100 - 4-57 Acid - 100 - 4-53 Base 87 - 4 Base - 80 - 3*625 In these little tables the number above the weight of an atom of the base represents the weight of an atom of phosphoric acid. Now the greatest of these numbers is 4*57, and the smallest of them is 4*45. The mean of the whole four is 4*527, which must be very nearly the true weight of an atom of phosphoric acid. We shall therefore take 4*5 as representing that weight. It will appear in a subsequent part of this section that 1*5 represents the weight of an atom of phosphorus; therefore phosphoric acid must be a com- pound of Phosphorus - 1*5 - 100 Oxygen - 3 - 200 Probably the reason why the quantity of oxygen found experimen- tally to combine with phosphorus is so small, has been that the whole phosphorus was not converted into phosphoric acid. 4. Phosphorus acid was first obtained in a state of purity by Sir H. Davy. When phosphorus is made to pass through corrosive sublimate* a liquid is obtained which was first discovered by Gay- Lussac and Thenard, and which Davy showed to be a protochlo- ride of phosphorus. When this liquid is mixed with water it is decomposed and converted into muriatic acid and phosphorous acid. The muriatic acid is driven off by a moderate heat, and pure phosphorous acid remains behind, combined with some water.f It will appear in a subsequent part of this section that phosphorous acid is composed of 1*5 phosphorus and 2 oxygen. Hence its con- stituents are—Phosphorus, 100—Oxygen, 133|. 5. Hypophosphorus acid was discovered in 1816 by Dulong4 When phosphorus is united to lime or barytes it forms a well known compound called phosphuret of lime or of barytes, which will be described hereafter. When these compounds are thrown into wa- * A substance which will be described in a subsequent section. t Phil. Trans. 1812, p. 407. * Ann. de Chim. et Phys. ii. 141. Chap. III.] PHOSPHORUS. 227 ter that liquid is decomposed, two acids are formed by the com- bination of the oxygen of the water with a portion of the phospho- rus ; while another portion of the phosphorus unites to the hydro- gen and flies off in the state of gas. The two acids are the phos- phoric and hypophosphorous, both of which combine with the lime or barytes, forming phosphate and hypophosphite of lime or barytes. The first of these salts is insoluble in water; but the second dis-« solves in that liquid. M. Dulong put a quantity of phosphuret of barytes into water. After the evolution of phosphureted hydrogen gas was at an end, he filtered the liquid. It then contained a quan- tity of hypophosphite of barytes in solution. Into this solution he dropt cautiously sulphuric acid as long as any precipitate fell. By this means he threw down the whole of the barytes without adding any excess of sulphuric acid. The clear liquid being decanted off consisted of a solution of hypophosphorous acid in water. Dulong endeavoured to determine the composition of this acid by convert- ing it into phosphoric acid by the action of chlorine. He considers it as composed of—Phosphorus, 100—Oxygen, 37*44—But his method does not seem susceptible of much precision, and indeed is too complicated for accuracy. I have little doubt, from experi- ments to be related in a subsequent part of this section, that hypo- phosphorous acid is composed of Phosphorus - 1*5 - 100 Oxygen - - 1 - 66*66 Thus the three acids of, phosphorus are composed as follows: Phosphorus. Oxygen. Hypophosphorous acid - - 1*5 - 1 Phosphorous acid - - - 1*5 - 2 Phosphoric acid - - - 1*5 - 3 Or the" first consists of one atom phosphorus united to one atom oxygen; the second of one atom phosphorus united to two atoms oxygen; and the third of one atom phosphorus- united to three atoms oxygen. 6. Though pure phosphorus does not take fire till it be heated to 141°, it is nevertheless true, that we meet with phosphorus which burns at much lower temperatures. The heat of the hand often makes it burn vividly; nay, it sometimes takes fire when merely exposed to the atmosphere. In all these cases the phosphorus has undergone a change. It is believed at present, that this increase of combustibility is owing to a small quantity of oxygen with which the phosphorus has combined. Hence, in this state, it is distin- guished by the name of oxide of phosphorus. When a little phos- phorus is exposed in a long narrow glass tube to the heat of boiling water, it continues moderately luminous, and gradually rises up in the state of a white vapour, which lines the tubes. This vapour is the oxide of phosphorus. This oxide has the appearance of fine white flakes, which cohere together, and is more bulky than the original phosphorus. When slightly heated it takes fire, and burns 228 SIMPLE COMBUSTIBLES. 5 BOOK I, £DIVISlC» 2. brilliantly. Exposed to the air, it attracts moisture with avidity, and is converted into an acid liquor.* When a little phosphorus is thus oxidized in a small tin box by heating it, the oxide acquires the property of taking fire when exposed to the air. In this state it is often used to light candles under the name of phosphoric matches; the phosphorus being sometimes mixed with a little oil, sometimes with sulphur. When phosphorus is long acted bn by water, it is covered at last with a white crust, which is also considered as an oxide of phos- phorus; but it differs considerably from the oxide just described. It is brittle, less fusible, and much less combustible than phospho- rus itself.-)- Phosphorus, when newly prepared, usually contains some of this last oxide of phosphorus mixed with it; but it may be easily separated by plunging the mass into water heated to about 100°. The phosphorus melts, while the oxide remains unchanged, and swims upon the surface of the melted phosphorus. The red substance formed when phosphorus burns in a confined place, and which remains behind after combustion in glass jars, is also considered as an oxide of phosphorus. All these bodies con- tain very little oxygen. I have endeavoured to determine the pro- portion, but my attempts were not attended with success. III. Phosphorus has the property of uniting in two proportions with chlorine, and of forming two compounds, which have received the names of protochloride and perchloride of phosphorus.^: 1. When phosphorus is introduced into chlorine gas it takes fire and burns with a pale bluish white flame, giving out but little light. A white matter sublimes and coats the inside of the glass vessel. If the quantity of phosphorus be considerable there is formed at the same time towards the end of the combustion a small quantity of liquid. The combustion of phosphorus in chlorine had been re- peated a great number of times by almost every chemist ever since the discovery of chlorine gas. But nobody thought of examining the nature of the products till Sir H. Davy advanced the theory that chlorine is a simple body. 2. The protochloride of phosphorus was first prepared in quanti- ties, and examined by Gay-Lussac and Thenard.^ But Davy first ascertained its constituent parts.|| It is easily obtained by passing phosphorus through corrosive sublimate heated in a glass or por- celain tube. The method is to take a glass tube shut at one end, to put into its bottom a quantity of phosphorus, and then to fill up a considerable part of the tube with corrosive sublimate. Heat the portion of the tube containing the sublimate; then, by applying a few bits of red hot charcoal to the extremity of the tube cause the phosphorus to pass in vapour through the sublimate. A bent * Steinacher, Ann. de Chim.xlvii. 104. -J- Ibid. i- Sir H. Davy has given to these bodies the names of phosphorane and phosphorana. But his momenclature has not been adopted by chemists. See Phil. Trans. 1812, p. 412. § Recherches Physico-chimiques, ii. 98,176. H Phil. Trans. 1812, p. 406. Chap. III.] PHOSPHORUS. 229 tube must be luted to the other extremity of the glass tube, which must pass into a proper receiver. A liquid collects in this re- ceiver, which is the protochloride of phosphorus. This liquid is colourless like water, smokes strongly when it comes into the atmosphere, and has an acid and very caustic taste. Its specific gravity is 1*45.* It may be kept in close vessels with- out alteration. But in the open air it is speedily dissipated, leav- ing behind it a quantity of phosphorus. It has the property of dis- solving phosphorus. *When paper is dipped into this solution and exposed to the air it speedily evaporates, leaving a quantity of phosphorus which soon takes fire and burns the paper. It was in this state that it was first obtained by Gay-Lussac and Thenard. When dropped into water it is converted into muriatic and phos- phorus acids. This liquid by evaporation furnishes a thick fluid, which crystallizes on cooling and forms transparent parallejopipe- dons. These crystals are compounds of phosphorus acid and wa- ter. When these crystals are distilled in close vessels they give out a gas which is a compound of hydrogen and phosphorus, and which mav be called bihidroguret of phosphorus. Phosphoric acid remains behind in the retort. From Davy's experiments it fol- lows, that these crystals are composed of 4 parts phosphorus acid and 1 part of water.f He endeavoured to ascertain the composi- tion of protochloride of phosphorus by dissolving a given quantity of it in water, and throwing down the muriatic acid formed by means of nitrate of silver. 13-6 grains of protochloride treated in this way gave 43 grains of horn silver4 Now 43 grains of horn silver contain 10*62 grains of chlorine. Hence the protochloride is composed of Chlorine - 10*62 - 5*34 - 4*5 Phosphorus - 2*98 - 1*5- - 1*26 This analysis shows us that the protochloride is a compound of 1 atom chlorine and 1 atom phosphorus. But the numbers which we have fixed upon for the weight of an atom of chlorine (4*5) and of phosphorus (1*5) do not correspond well with the experiment of Davy. Had the quantity of horn silver been only 41^- instead of 43 grains, the experiment would have tallied exactly with our num- bers. Now this is an error that might have been, easily committed in an experiment made upon so small a scale. 3. The perchloride of phosphorus may be formed by burning phosphorus in dry chlorine gas, in the proportion of one grain of the former to about 12 cubic inches of the latter. It is a snow- white substance, exceedingly volatile, rising at a temperature below that of boiling water. Under pressure it may be fused, and then crystallizes in prisms that are transparent. When thrown into water it acts with great violence, the water is decomposed, and phosphoric acid and muriatic acid formed. It seems to possess • Davy, Phil. Trans. 1812, p. 40G. f H>id. p. 408. t Ibid. p. 407. 230 SIMPLE COMBUSTIBLES. $ BOOK I. £ DIVISION 2. acid properties, for its vapour reddens paper stained blue with litmus, and burns when lighted in the open air. When passed through a red hot tube with oxygen gas it is decomposed, phos- phoric acid being formed and chlorine disengaged. From the ex- periments of Davy, to whom we are indebted for all the preceding facts, it follows that 1*5 grain of phosphorus, when converted into perchloride, combines with 10 grains of chorine.* Hence we see that it is a compound of 1 atom phosphorus and 2 atoms chlorine. If our numbers for the weight of an atom of phosphorus (1-5) and of chlorine (4*5) be accurate, then it ought to be a compound of—- Phosphorus 1-5—Chlorine 4*5 X 2 *= 9—Now this differs but lit- tle from the results obtained by Davy. IV. Phosphorus has the property of combining in two propor- tions with iodine, and of forming two compounds, which may be called protiodide of phosphorus and periodide of phosphorus. These substances were first mentioned by Sir H. Davy ;| but for the first accurate examination of them we are indebted to Gay-Lussac.:}: 1. When one part of phosphorus and 10*41 parts of iodine are mixed together in a thin glass tube they unite with great rapidity, producing much heat but no light. The compound is a solid body of a reddish brown colour. It melts at 212° and is volatilized when the temperature is raised somewhat higher. When thrown into water it dissolves, and is converted into hydriodic acid and phos- phorous acid.§ This compound is obviously composed of Phosphorus - - 1 - - 1*5 Iodine - - - 10*41 - - 15-625 Or of one atom of phosphorus and one atom iodine. It is there- fore a protiodide of phosphorus. 2. When 1 part of phosphorus and 20-82 parts of iodine are mixed together, they cpmbine likewise with violence and the evo- lution of a great deal of heat. The compound formed is black, and melts at the temperature of 115°. It dissolves in water with great heat, but the solution usually has a dark colour; owing, I believe, to the whole of the phosphorus not entering into combina- tion. The consequence is an excess of iodine which is dissolved by the hydriodic acid formed. For, in my trials, there always re- mained a small portion of phosphorus undissolved after the action of the water. This compound, supposing it in the proportions above stated, is composed of Phosphorus - 1 - 1*5 Iodine - - 20-82 - 15*625 X 2 = 31*25 Or it is composed of 1 atom phosphorus united to 2 atoms iodine. V. Nothing is known respecting the combination of phos'phorus and fluorine. J_ VI. Phosphorus plunged into azotic gas is dissolved in a small * PhiL Trans. 1812, p. 406. + Ibid. 1814, p. 79. * Ann. de Chim. xci. p. 9. *j Gay-Lussac's proportions are 1 phosphorus and 8 iodine. But this is too small a pro- portion of iodine, as 1 find by experiment To this I ascribe the phosphureted hydrogen gas which exhaled in his experiments. Chap. III.] PHOSPHORUS. 231 proportion. Its bulk is increased about •&,* and phosphureted azotic gas is the result. When this gas is mixed with oxy gen gas, it becomes luminous, in consequence of the combustion of the dis- solved phosphorus. The combustion is most rapid when bubbles of phosphureted azotic gas aredet up into a jar full of oxygen gas. When phosphureted oxygen gas, and phosphureted azotic gas, are mixed together, no light is produced, even at the temperature of 82°.f VII. Phosphorus combines with hydrogen in two proportions and forms, two gaseous compounds which have received the names of phosphureted hydrogen and hydrophosphoric gas. But the terms hydroguret of phosphorus and bihydroguret of phosphorus would be more systematic. 1. Phosphureted hydrogen gas, the first of these compounds, was discovered in 1783 by M. Gengembre, while heating a mixture of liquid potash and phosphorus in a small retort. He made some experiments on this remarkable gas, and published an account of its properties.:): Some experiments were made upon it in 1786 by Mr. Kirwan,§ who discovered it without being aware that it had been already made known to chemists by M. Gengembre. In 1791, M. Raymond pointed out a method of preparing it in greater quan- tities by heating a mixture of phosphorus and quicklime. || And, in 1799, he described the properties of a solution of this gas in water.^j Mr. Dalton, in his New System of Chemical Philosophy, published in 1810, gives an account of a set of experiments to which he subjected it in order to determine its nature and composition.** And, in 1816,1 published a set of experiments which 1 had made on it.ff 2. Phosphureted hydrogen may be obtained pure by the follow- ing process : Fill a small retort with water, acidulated by muriatic acid, and then throw into it a quantity of phosphuret of lime in lumps. Plunge the beak of the retort under water, and place over it an inverted jar filled with that liquid. Phosphureted hydrogen gas is extricated in considerable quantity and soon fills the glass jar. Half an ounce of phosphuret of lime yields about 70 cubic inches of this gas.:)4 * Berthollet. -J- Fourcroy and Vauquelin, Ana. de Chim. xxi. 199- i Memoiresdes Savans Etrangers, x. 651. § Phil. Trans. 1786, p. 118. || Ann. de Chim. x. 19. *I B>id. xxxv. 225. •* Vol. II. p. 457. jf Annals of Philosophy, viii. 87. it [This is a troublesome and expensive mode of procuring it; for it is not easy to make good phosphuret of lime, or in other than small quantities. Into a small glass retort capable of holding about a quarter of a pint, put a moderately strong solution of caustic potash, the causticum commune of the shops: let the solution fill the retort about three parts full: put in about a quarter of an inch of the common sticks of phosphorus: it is not necessary to cut it. Let the retort be fastened on a wooden stand and a lamp heat applied under the retort. The beak of the retort should be immersed in a hot solution of potash in a basin, so that when the gas ceases for a short time to come over, the retort may not break by means of cold water filling the vacuum. In this way the gas is easily and sal'eiv procured. Mr. John Dalton (Ann. of Phil.forJan. 1818, p. 8.1 observes, that the phosphureted hydro- gen is not obtained pure by this means, if the phosphuret of lime has been exposed for a few hours to the atmosphere, in which case, the gas procured will contain from 50 to 80 per cent, of free hydrogen. The pure phosphureted hydrogen, may be separated by liquid oxy- muriat of lime, and the hydrogen left behind.—C.j ^S> 232 SIMPLE COMBUSTIBLES. £ BOOK L £ nrvisiox 2. 3. Phosphureted hydrogen gas is colourless and possesses the mechanical properties of air. It has a smell similar to that of onions, and an exceedingly bitter taste. It may be kept in pure water without alteration ; but in water containing common air it soon loses a portion of its phosphorus, and its properties are alter- ed in consequence. Its specific gravity is 0-9022. Hence at the temperature of 60°, and when the barometer stands at 30 inches, 100 cubic inches of it weigh 27*517 grains. When electric sparics are passed through this gas for some time the phosphorus is deposited, and pure hydrogen gas remains. . But the volume of the gas is not altered by this process. Hence it fol- lows that phosphureted hydrogen gas consists of hydrogen gas, holding a quantity of phosphorus in solution. This quantity is discovered by subtracting the specific gravity of hydrogen gas from that of phosphureted hydrogen. Specific gravity of phosphureted hydrogen 0*9022 -----------------hydrogen gas - - 0*0694 Phosphorus.....= 0*8328 Therefore phosphureted hydrogen gas is composed of hydrogen 694 or 1—phosphorus 8328 or 12 ; so that phosphureted hydro- gen contains ^th of its weight of hydrogen and -f4tns OI" phospho- rus. Now, if we reckon the weight of an atom of hydrogen 0*125, and that of an atom of phosphorus 1*5 ; it is obvious that phosphu- reted hydrogen is composed of 1 atom hydrogen and 1 atom phos- phorus, for *125 X 12 = 1*5. When phosphureted hydrogen comes in contact with common air, it takes fire and burns with great splendour. Yet in a narrow tube it may be mixed with oxygen gas without undergoing sponta- neous combustion. But it is deprived of its phosphorus without undergoing any alteration in its bulk. For complete combustion, it requires either 1 volume of oxygen gas or H volume.* In both cases the two gases over water disappear altogether. Now half a volume of the oxygen gas, in both cases, must unite to the hydro- gen and form water. So that the phosphorus, in phosphorated hy- drogen, combines either with \ volume or with 1 volume of oxygen gas. In the first case, I suppose that hypophosphorous acid is form- ed : In the second case, phosphorous acid. When a volume of phosphureted hydrogen gas is mixed with 3 volumes of nitrous gas, and an electric spark passed through the mixture, a detonation takes place, and there remains 1 \ volume of azotic gas. Now nitrous gas contains half its bulk of oxygen. Therefore, in this case, the phosphureted hydrogen has combined * [According to Dalton, Ann. of Ph. Jan. 1818, p. 8, it requires two volumes of oxygen. Phosphoric acid and water are formed. Water absorbs | th of the pure gas. This gas ex- plodes when mixed with z\ \olumes (not 3, as Thomson says) of nitrous gas, when an elec- tric spark is passed through it, or when a bubble of oxygen is let up to the mixed gases. Dalton.—C] Chap. III.] PHOSPHORUS. 233 with lh volume of oxygen. If these two gases be mixed over wa- ter and a bubble of oxygen gas be let up to them, a detonation im- mediately takes place. When 1 volume of phosphureted hydrogen is mixed with 3 vol- umes of protoxide of azote, and an electric spark passed through the mixture, a detonation takes place, and there remains 3 volumes of azotic gas. But protoxide of azote is composed of 1 volume of azote -f half a volume of oxygen condensed into 1 volume ; so that 3 volumes, if decomposed, would constitute 3 volumes of azote and 1 i volume of oxygen gas. Hence, in this case also, phosphu- reted hydrogen has combined with li volume of oxygen. When phosphureted hydrogen gas is mixed with chlorine gas, it burns with a greenish yellow flame; and when the two gases are mixed in the proportion of 1 volume of the former to 3 of the lat- ter, they disappear entirely, being converted into muriatic acid, and a brown matter which speedily dissolves in water, and which is doubtless a bichloride of phosphorus. When iodine is heated in phosphureted hydrogen gas, iodide of phosphorus is formed, and probably hydriodic acid; for when wa- ter is present the bulk of the gas diminishes 1 third. Water, according to the experiments of Dr. Henry, dissolves rather more than 2 per cent, of this gas. The water acquires a yel- low colour, an intensely bitter taste, and a smell similar to that of the gas. It produces no alteration on vegetable blues, but preci- pitates silver, mercury, and copper, from their solutions, of a dark colour. 4. Hydrophosphoric gas or bihydroguret of phosphorus was first particularly examined by Sir H. Davy, in 1812.* He obtained it by heating crystallized phosphorous acid. It may be procured, also, by exposing phosphureted hydrogen to the di- rect rays of the sun. A quantity of phosphorus is deposited, and the gas is changed into bihydroguret of phosphorus. This gas is colourless, and possesses the mechanical properties of common air. Its smell is similar to that of phosphureted hy- drogen, but not so disagreeable. When sulphur is sublimed in this gas the volume is doubled, and 2 volumes of sulphurated hy- drogen gas are formed. When potassium is heated in it, the vol- ume is also doubled. The potassium combines with phosphorus, and the residual gas is pure hydrogen. Hence it is obvious that it is a compound of two volumes of hydrogen gas, united with the same quantity of phosphorus that exists in a volume of phosphu- reted hydrogen gas, and condensed into 1 volume. Hence its composition must be, phosphorus 12 - - 1*5—hydrogen 2 - - 0*125 x 2. Thus we see that it is a compound of 1 atom phospho- rus and 2 atoms hydrogen. It is obvious, also, that its specific gravity must be fcqual to the * Phil. Trans. 1812, p. 406. Vol. I. G g -34 .SIMPLE COMBUSTIBLES. S BOOK 4. £ nivisiox 2. specific gravity of phosphureted hydrogen gas, added to that of hydrogen gas, or 0*9022 -f 0*0694 = 0-9716. Sir Humphry Davy found it 0*87. But his experiment was made upon a small scale, and only once repeated. Hence an error of ^ can hardly be con- sidered as excessive. This gas does not burn spontaneously when it comes into com- mon air or oxygen gas; but if it be mixed with oxygen and heated to 300°* it explodes. 1 volume of this gas requires either 1 h or 2 volumes of oxygen gas for complete combustion. If the first pro- portion be used, some phosphorus is apt to be precipitated. Now as the gas contains 2 volumes of hydrogen, it is obvious that 1 volume of the oxygen goes to the formation of water. The remain- ing 5, or 1 volume of oxygen, must have united with the phospho- rus. Now this is just the quantity which the phosphorus in a volume of phosphureted hydrogen gas requires. Hence the reason for estimating the quantity of phosphorus in a volume of hydrogu- ret, and bihydroguret of phophorus as the same. When mixed with chlorine gas it burns spontaneously with a white flame. According to Davy, 1 volume of bihydroguret of phosphorus requires 4 volumes of chlorine gas for complete com- bustion. Two of these volumes uniting to the hydrogen go to the formation of muriatic acid. The other two must combine with the phosphorus, and form a perchloride of phosphorus which would be speedily converted into muriatic acid and phosphoric acid, by de- composing water. So that the products, in this case, are precise- ly the same as when phosphureted hydrogen is burnt in chlorine. According to Davy, water absorbs ^.th of its volume of this gas. So that the absorbability of this gas and olefiant gas, by water, is the same. Thus we have two compounds of phosphorus and hydrogen, com- posed as follows, Phosphorus. Hydrogen. Hydroguret of phosphorus of 1 atom -+- 1 atom Bihydroguret of phosphorus of 1 -f 2 VIII. Phosphorus has the property likewise of uniting with carbon, and of forming a compound, called phosphuret of carbon. Its existence was first recognised by M. Proust. He gave that name to the red substance which remains when new made phos- phorus is strained through shamois leather.f It is not improbable that this red substance may frequently contain phosphuret of car- bon, especially as the same assertion has been subsequently made by Thenard4 But I have never been able to find any such sub- stance in it.§ The experiments of Vogel appear to have been equally unsuccessful.|| But I have never failed to procure it by the following method. * Davy. -j- Ann. de Chim. xxxiv. 44. t Ann. de Chim. lxxxi. 109. § Twice indeed on distilling this substance I obtained a residue of charcoal. ButI never could succeed in obtaining the phosphuret in a separate state. | Ann. de Chim. lxxxv. 225. Chap. III.] SULPHUR. 235 Allow phosphuret of lime to remain in water till it has given out all the phosphureted hydrogen gas which it is capable of evolving. Then add to the liquid a considerable excess of muriatic acid, agi- tate for a few moments, and throw the whole upon a filter. Phos- phuret of carbon will remain upon the filter. Let it be properly washed and dried. Phosphuret of carbon thus obtained is a soft powder of a dirty lemon yellow colour, without either taste or smell. When left in the open air it very slowly imbibes moisture, emits the smell of carbureted hydrogen, and acquires an acid taste. Hence it decom- poses the water which it absorbs, and its phosphorus is slowly converted into phosphorous acid. It does not melt when heated; nor is it altered, though kept in a temperature higher than that of boiling water. It burns below a red heat, and when heated to red- ness, gradually gives out its phosphorus. The charcoal remains behind in the state of a black matter, being prevented from burn- ing by a coating of phosphoric acid with which it is covered. When the powder is thrown over the fire in small quantities at a time, it burns in beautiful flashes. It is composed of 1 atom phosphorus, and 1 atom carbon, or by weight of Phosphorus - 1*5 - 200 Carbon - 0*75 - 100 The substance, when distilled, gives no traces of water.* IX. Nothing is known respecting the combination of phosphorus with boron and silicon. SECTION VI. OF SULPHUR. Sulphur, distinguished also by the name of brimstone, was known in the earliest ages. Considerable quantities of it are found native, especially in the neighbourhood of volcanoes, and it is procured in abundance by subjecting the mineral called pyrites to distillation. The ancients used it in medicine, and its fumes were employed in bleaching wool.f 1. Sulphur is a hard brittle substance, commonly of a greenish yellow colour, without any smell, and of a weak though percepti- ble taste. It is a non-conductor of electricity, and of course becomes elec- tric by friction. Its specific gravity is 1*990. The specific gravity of native sulphur is 2*03324 Sulphur undergoes no change by being allowed to remain ex- posed to the open air. When thrown into water, it does not melt • Annals of Philosophy, viii. 157. t Pl^y, lib. xxxv. c. 15. * Brisson. Lavoisier's Elements, p. 577. 236 SIMPLE COMBUSTIBLES. 5 BOOK I. I nmsioN -. as common salt does, but falls to the bottom, and remains there unchanged: It is therefore insoluble in water. 2. If a considerable piece of sulphur be exposed to a sudden though gentle heat, by holding it in the hand, for instance, it breaks to pieces with a crackling noise. When sulphur is heated to the temperature of about 170", it rises up in the form of a fine powder, which may be easily collected in a proper vessel. This powder is called fiowers of sulphur.* When substances fly off in this manner on the application of a moderate heat, they are called volatile; and the process itself, by which they are raised, is called volatilization. When heated to the temperature of about 218° of Fahrenheit's thermometer, it melts and becomes as liquid as water. If this experiment be made in a thin glass vessel, of an egg shape, and having a narrow mouth,f the vessel may be placed upon burning coals without much risk of breaking it. The strong heat soon causes the sulphur to boil, and converts it into a brown coloured vapour, which fills the vessel, and issues with considerable force out from its mouth. 3. There are a great many bodies which, after being dissolved in water or melted by heat, are capable of assuming certain regular figures. If a quantity of common salt, for instance, be dissolved in water, and that fluid, by the application of a moderate heat, be made to fly off in the form of steam; or, in other words, if the wa- ter be slowly evaporated, the salt will fall to the bottom of the vessel in cubes. These regular figures are called crystals. Now sulphur is capable of crystallizing. If it be melted, and, as soon as its sur- face begins to congeal, the liquid sulphur beneath be poured out, the internal cavity will exhibit long needle-shaped crystals of an octahedral figure. This method of crystallizing sulphur was con- trived by Rouelle. If the experiment be made in a glass vessel, or upon a flat plate of iron, the crystals will be perceived beginning to shoot when the temperature sinks to 220°. Sulphur is frequently found native in fine large crystals. The primitive form of the crystals is an octahedron, with scalene triangular faces. It consists of two pyramids joined together, base to base. These bases con- stitute a rhomboid, the longer diagonal of which is to the shorter, as 5 to 4. The perpendicular drawn from the centre of this rhom- boid to the edge is to the height of the pyramid as 1 to 34 4. Alcohol dissolves a small portion of sulphur. So does sul- phuric ether and oils. II. Sulphur combines, at least, in two proportions with oxygen, and forms two compounds which have been long known, and which have received the names of sulphurous and sulphuric acids. * It is only in this state that sulphur is to be foflnd in commerce tolerably pure. Boll sulphur usually contains a considerable portion of foreign bodies. ■(• Such vessels are usually called receivers or flasks by chemists. i Hauy's Mineralogie, iii. 278. Chap. III.] 9ULPHUR. 237 1. When sulphur is heated to the temperature of 560' in the ©pen air, it takes fire spontaneously, and burns with a pale blue flame, and at the same time emits a great quantity of fumes of a very strong suffocating odour. When set on fire, and then plunged into a jar full of oxygen gas, it burns with a bright violet coloured flame, and at the same time emits a vast quantity of fumes. If the heat be continued long enough, the sulphur burns all away without leaving any ashes or residuum. If the fumes be collected, they are found to consist of sulphurous acid. By combustion, then, sulphur is converted into acid. This fact was known several centuries ago; but no intelligible explanation was given of it till the time of Stahl. According to him, sulphur is a compound of sulphuric acid and phlogiston. By combustion the phlogiston is driven off, and the acid remains behind. The experiments by which he endeavoured to establish these opinions were long considered as satisfactory. But it was observed that sulphur will not burn unless air be present, and that sulphuric acid is heavier than the sulphur from which it was produced. These facts were incompatible with the hypothesis of Stahl. Lavoisier first explained them by showing that, during combustion, sulphur unites with the oxygen of the air, and that the acid formed is exactly equal to the weight of the sulphur and oxy- gen which disappeared. Hence he concluded that the acid formed is a compound of these two bodies—an opinion which is now uni- versally acceded to. 2. Sulphurous acid is formed, when sulphur is burnt, either in the open air, or in oxygen gas. But the best way to procure it in quantities, is to heat a mixture of sulphuric acid and mercury in a small retort, and receive the gaseous product over mercury. This gas is sulphurous acid. This acid was first examined by Stahl, who gave it the name of phlogisticated sulphuric acid. Scheele in 1774 pointed out a me- thod of procuring it in quantities.* Dr. Priestley, about the same time, obtained it in the gaseous form, and ascertained many of its properties.! Berthollet examined it in 1782 and 17894 Fourcroy and Vauquelin published a detailed set of experiments on it in 1797.§ Some experiments on it by me were published in 1803.|j Sulphurous acid gas is colourless, and possesses the mechanical properties of common air. Its smell is exceedingly suffocating and disagreeable, being precisely similar to the smell of burning sul- phur. Its taste is intensely acid and sulphureous. It converts vegetable blues to red, and then gradually destroys them. Its spe- cific gravity, according to Davy's experiments, is 2*2293 .♦fl If we suppose it composed of a volume of vapour of sulphur, and a vo- lume of oxygen gas, condensed into one volume, its specific gravity ought to be 2*2222. Hence 100 cubic inches of it at the tempera- • Scheele's Memoires de Chymie, i. 43. f Priestley on Air, ii. 295. $ Mem. Par. 1782, and Ann. de Chim. ii. 54. § Ann. de Chim. xxiv. 229. j| Nicholson's Journal, vi. 93. H Phil. Trans. 1812, p. 412. 238 SIMPLE COMBUSTIBLES. S BOOK ? £ DIVISION 2. ture of 60% and when the barometer stands at 30 inches, will weigh 67*771 grains. Water absorbs 33 times its bulk of this gas, according to my experiments; but according to Theodore de Saussure, that liquid takes up 43-78 times its bulk of it.* I ascertained, by experiment, that the quantity of oxygen in sulphurous acid is ^ of that in sulphuric acid.f Now we shall see immediately that sulphuric acid is composed of 100 sulphur -f- 150 oxygen. Hence it follows that sulphurous acid is composed of 100 sulphur -f 100 oxygen. There is another experiment which de- monstrates, in a very satisfactory manner, the composition of this acid. Sulphureted hydrogen is a gas which will be described in the subsequent part of this section. It contains its volume of hydrogen, holding a quantity of sulphur in solution. Now a volume of this gas requires 1\ volume of oxygen for complete combustion. The substances formed are water and sulphurous acid. The half vo- lume of the oxygen goes to the formation of water, and combines with the hydrogen. The one volume of oxygen combines with all the sulphur, and forms sulphurous acid. The sulphur, in a volume of sulphureted hydrogen, is obtained by subtracting the specific gravity of hydrogen gas from that of sulphureted hydrogen. Sp. gravity of sulphureted hydrogen - - 1*180 ——---------hydrogen gas - 0*069 Sulphur in the gas - - - - = 1*111 But the specific gravity of oxygen gas is 1-111. Hence it follows that sulphurous acid is composed of—-Sulphur 1*111 or 1—Oxy- gen 1*111 or 1. 3. Sulphuric acid is obtained by burning a mixture of 7 parts sulphur and 1 part nitre, in large chambers lined with lead. By this combustion, sulphurous acid and nitrous gas are formed. The nitrous gas absorbs oxygen from the atmosphere, and is converted into nitrous acid. Both the acids are absorbed by water. The nitrous acid gives out part of its oxygen to the sulphurous acid, and converts it into sulphuric acid, and being reduced to the state of nitrous gas again flies off, unites to oxygen, is converted into nitrous acid, and absorbed by the water. This process goes on till the whole of the sulphurous acid is converted into sulphuric acid4 The water, thus acidulated, is evaporated in leaden vessels to a certain point. The evaporation is then continued in glass retorts, till the acid acquires the requisite degree of strength. By this evaporation a very considerable portion of the water is driven off. But by this process, sulphuric acid cannot be deprived of the whole of its water. This acid was discovered in the middle ages, either by the Ara- * Annals of Philosophy, vi. 340. t Nicholson's Journal, vi. 95. + Clement and Desorraes. Ann. de Chim. lix. 329—Dalton, New System of Chemical Philosophy, ii. 396—Davy, Elements of Chemical Philosophy, p. 276. Chap. III.] SULPHUR. 239 bian chemists, or the alchemists. But nothing is known respect- ing the exact period of the discovery. It is mentioned by Basil Valentine, who wrote in the early part of the fifteenth century. It was long procured by distilling green vitriol, and this process is still followed in Germany. Sulphur and nitre were afterward* burnt under a glass bell, and the product evaporated: hence it was called oleum sulphuris per campanam. Dr. Roebuck first contrived the method of making it in leaden chambers, and established the original manufactory at Prestonpans, in Scotland. Sulphuric acid is colourless like water. It has somewhat of a glutinous consistency: is destitute of smell, but has an exceedingly acid taste. It speedily chars animal and vegetable substances, when placed in contact with them. It converts vegetable blues to red. Acid, of the specific gravity 1*85, boils, according to Mr. Dalton, at the temperature of 620°. The boiling point diminishes with the strength. Acid, of the specific gravity 1*780, boils at 435°, and acid, of the specific gravity 1*650, at 350°.* Many experiments have been made to determine the proportion of oxygen contained in sulphuric acid. It is unnecessary to state the old trials of Berthollet, Trommsdorf, Lavoisier, Chenevix, and Thenard, because they are very inaccurate. Bucholz, Klaproth, and Richter, approach much nearer to the truth. Their estimates are as follows: Bucholz 100 sulphur -f 135-3 oxygen. Klaproth 100 -f 138-1 Richter 100 + 138*1 Berzelius made a set of experiments, with every attention to ac- curacy, on purpose to determine this point. He found that 10 parts of sulphuret of lead, when boiled in nitric acid, were converted into 12*645 parts of sulphate of lead. Now sulphate of lead is a compound of 10 sulphuric acid, -f-28 yellow oxide of lead. There- fore the 12*6450 of sulphate of lead formed, are composed of, Yel- low oxide of lead 9-3174—Sulphuric acid 3-3276. In this experiment both the lead and the sulphur had united with oxygen. But Berzelius has shown, that yellow oxide of lead contains —th of its weight of oxygen. Now yyth of 9*3174 is 0*6655. If we subtract this quantity from 2*645, the whole in- crease which the sulphuret acquired, there will remain 1*9795, in- dicating the quantity of oxygen which exists in 3*3276 parts of sul- phuric acid.f Therefore sulphuric acid is composed of—Sulphur 1-3485 or 100—Oxygen 1*9795 or 146*85. These numbers are much nearer the truth than those of preced- ing experimenters. But it is easy to show, that the quantity of oxy- gen, thus stated by Berzelius, is a little below the truth. Most of the metals have the property of uniting either with oxygen or sul- phur, constituting with the one oxides, with the other sulphurets. Now the weight of sulphur, necessary to convert any metal into a * Dalton's New System of Chemical Philosophy, ii. 404. f Ann. de Chim. lxxviii. 21. 240 SIMPLE COMBUSTIBLES. $" BOOK I. £ DIVISION 2. protosulphuret, is just double the weight of oxygen necessasy to convert the same metal into a protoxide. From this it follows, that the weight of an atom of sulphur, is exactly twice that of an atom of oxygen. Most of the sulphates have been analysed with great care. The following table represents the component parts of some of these salts: Sulphate of lead. Sulphate of barytes. Sulphate of potash. • Acid 10 - 5 Acid 100 - 5*02 Acid 42*2 - 5-05 Base 28 - 14 Base 194 - 9-75 Base 50-1 - 6 Sulphate of lime. Sulphate of copper. Sulphate of soda. Acid 100 - 5*006 Acid 100 - 5 Acid 100 - 5-07 Base 72*41 - 3*625 Base 200 - 10 Base 78*82 - 4 The second set of numbers, after the bases, represent the weights of the atoms of the different bases. For these weights are as follows: Yellow oxide of lead - 14 Lime - 3-625 Barytes - - 9-75 Black oxide of copper 10 Potash - - 6 Soda - - 4 The numbers above these represent the weight of an atom of sulphuric acid, resulting from the analysis of the salt. Now these numbers agree very nearly with each other, and the mean of the whole of them is 5*024. Is it not evident from this, that 5 is the number which represents the weight of an atom of sulphuric acid ? It must be composed of—Sulphur 2, or 1 atom—Oxygen 3, or 3 atoms. Sulphuric acid, then, is composed of—Sulphur 100—Oxygen 150. Proportions which differ but little from Berzelius' analysis. The error is probably owing to a minute quantity of the sulphuret of lead having been carried off by the nitric acid fumes. 4. Thus we see that the two acid combinations of sulphur are composed as follows: Sulphur. Oxygen. Sulphur. Oxygen. Sulphurous acid 100 + 100 or 1 atom + 2 atoms. Sulphuric acid 100 + 150 or 1 +3 We shall see afterwards that sulphur is capable of combining with one atom of oxygen^ and of forming an acid, which has not hither- to been obtained in a separate state; but which may be distinguish- ed by the name of hyposulphurous acid. 5. If sulphur be kept melted in an open vessel, it becomes gra- dually thick and viscid. When in this state, if it be poured into a basin of water, it will be found to be of a red colour, and as soft as wax. In this state it is employed to take off impressions from seals and medals. These casts are known in this country by the name of sulphurs. When exposed to the air for a few days, the sulphur soon recovers its original brittleness, but it retains its red eolour. This substance, when newly made, has a violet colour; it has a fibrous texture j its specific gravity is 2*325 ; it is tough, and has a straw colour when pounded. This substance has Chap. III.] SULPHUR. 241 been considered as an oxide of sulphur. But it produces the same quantity of sulphuric acid as common sulphur, and sulphur undergoes the same change in its appearance, even when oxygen and common air are carefully excluded. We cannot therefore consider it as an oxide. 6. When sulphur is first obtained by precipitation from any liquid that holds it in solution, it is always of a white colour, which gradually changes to greenish yellow when the sulphur is exposed to the open air. This substance has been considered as an oxide of sulphur by some. But if this white powder, or lac sulphuris, as it is called, be exposed to a low heat in a retort, it soon acquires the colour of common sulphur ; and, at the same time, a quantit} of water is deposited in the beak of the retort. On the other hand, when a little water is dropped into melted sulphur, the portion in contact with the water immediately assumes the white colour of lac sulphuris. If common sulphur be sublimed into a vessel filled with the vapour of water, we obtain lac sulphuris of the usual whiteness, instead of the common flowers of sulphur. These facts prove that lac sulphuris is a compound of sulphur and water. Hence we may conclude that greenish yellow is the natural colour of sulphur. Whiteness indicates the presence of water.* III. Sulphur combines readilv with chlorine, and forms a li- quid compound which has received the name of chloride of sulphur. This substance was first described by me in 1804.f It was examin- ed by'M. Berthollet Junior in 18074 ancl D>r Mr* Buchols in 1810.$ It is easily obtained by passing a current of chlorine gas through flowers of sulphur. It may be obtained also, as Davy first observ- ed, by heating sulphur in a dry glass vessel filled with chlorine gas. It is a liquid of a brownish red colour when seen by reflected light; but appears yellowish green when seen by transmitted light. Its smell is strong and somewhat similar to that of sea plants, or which we perceive when walking along the sea shore. The eyes when exposed to it are filled with tears and acquire the same pain- ful feeling as when exposed to wood or peat smoke. The taste is acid, hot, and bitter, affecting the throat with a painful tickling. It does not change the colour of dry litmus paper; but if the paper be moist it immediately becomes red. I found the specific gravity 1.623. But Berthollet found it 1*7 and Bucholz 1*699. We must therefore consider 1*7 as the true gravity. It readily dissolves sul- phur, and acquires a brown colour. It dissolves phosphorus with facility. The solution has a fine amber colour and is permanent. Chloride of sulphur smokes violently in the open air and soon flies off, leaving crystals of sulphur if it contains that substance in solu- tion. When dropped into water it is decomposed, sulphur being evolved. When dropped into nitric acid a violent effervescence is produced, and sulphuric acid formed. * Nicholson's Journal, vi. 102. f Ibid. p. 104. t Mem. d'Arcueil, i. 161 § Gehlen's Journal, fur die Chemie, Physik und Mineralome, ix. 172. Vol. I. H h 242 SIMPLE COMBUSTIBLES. 5 BOOK I. J DIVISION 2. According to Davy 10 grains of sulphur absorb 30 cubic inches or 22*875 grains of chlorine. Hence it is composed of Sulphur 1 - - 2 Chlorine - - 2*2875 - 4*575 It is evident from this that it is a compound of 1 atom sulphur and 1 atom chlorine. Had the absorption been 29*5 instead of 30 cubic inches, the chloride would have been composed of 2 sulphur -f 4*5 chlorine. Now as the glass in which the experiment was made had a metallic stop-cock, some of the chlorine would be absorbed by it. IV. Sulphur has the property of combining with iodine, and of forming a compound which has been called iodide of sulphur. It was first discovered by Gay-Lussac* It is easily formed by mixing together the two constituents in a glass tube and exposing them to a heat sufficient to melt the sul- phur. This iodide is greyish black, and has a radiated structure like that of sulphuret of antimony. When distilled with water io- dine is disengaged. When heated sufficiently to produce fusion a portion of the iodine is likewise disengaged. This iodide has not hitherto been analysed. But from analogy we may conclude that it is composed of 1 atom iodine -f 1 atom sulphur, or by weight of Sulphur 2 100 Iodine - - 15*625 - 781*25 V. Nothing is known respecting the combination of sulphur with fluorine. Neither has it been hitherto possible to form a compound of sulphur and azote. VI. Sulphur has the property of combining with hydrogen, and of forming a gaseous compound which has received the name of sulphureted hydrogen gas. Gay-Lussac has given it the name of hydro sulphuric acid. That such a gas existed, and that it was inflammable, had been observed by Rouelle ;f but its properties and composition were first investigated by Scheele in 1777, who must therefore be considered as the real discoverer of it4 Bergman, in 1778, detailed its pro- perties at greater length,^ having examined it probably after read- ing the experiments of Scheele. In 1786, Mr. Kirwan published a copious and ingenious set of experiments on it.|| The Dutch che- mists examined it in 1792,fj and in 1794, Berthollet, with his usual sagacity, still further developed its properties ;** and since that time several important facts respecting it have been ascertained by Proust and Thenard. Berzelius published an elaborate analysis of it in 1807; If and * Ann. de Chim. xci. 22. f lacquer's Diet. i. 520. \ Scheele on Air and Fire, p. 186. Eng. Trans. § See his Treatise on Hot Mineral Waters, Opusc. i. 233. and Eng. Trans, i. 290. I Phil. Trans. 1786. p. 118. T Ann. de Chim. xiv. 294. ** Ibid. xxv. 233. ff Af handlingar i Fjsik, Kemioch Mineralogi, ii. 78. Chap. III.] SULPHUR. 243 Gay-Lussac, Thenard,* and Sir H. Davy,f have ascertained seve- ral of its properties with precision. It may be obtained by pouring diluted sulphuric or muriatic acids on a mixture of three parts iron filings and two parts sulphur melted together in a crucible. But when procured in this way it is always mixed with hydrogen gas. It may be obtained quite pure by digesting sulphuret of antimony in powder in muriatic acid. It is colourless, and possesses the mechanical properties of air. It has a strong fetid smell, not unlike that of rotten eggs. It does not support combustion, nor can animals breathe it without suffo- cation. Its specific gravity, according to the experiments of Gay- Lussac and Thenard, is 1-19124 According to Sir H. Davy it is 1*1967. I conceive that its true specific gravity is 1-180. Sup- posing this to be its gravity, then 100 cubic inches of it, when the barometer stands at 30 inches, and when the temperature is 60°, will weigh 35*89 grains. This gas is rapidly absorbed by water. According to Dr. Henry 100 cubic inches of this liquid absorb, at the temperature of 50°, 108 cubic inches of sulphureted hydrogen.§ But the gas must have been impure. Theodore de Saussure found that 100 cubic inches of water absorb 253 cubic inches of pure sulphureted hy- drogen gas.|| Alcohol of the specific gravity 0*84 absorbs, ac- cording to the same chemist, 6-06 times its volume of gas. Mr. Higgins has shown likewise that it dissolves in ether. The water thus impregnated is colourless, but it has the smell of the gas, and a sweetish nauseous taste. It converts vegetable blue colours to red, and has many other properties analogous to those of acids. When the liquid is exposed to the open air the gas gradually makes its escape. When sulphureted hydrogen gas is set on fire, it burns with a bluish red flame, and at the same time deposits a quantity of sul- phur. When the electric spark is passed through it, sulphur is de- posited, but its bulk is scarcely altered.fj It deposits sulphur also when agitated with nitric acid, or when that acid is dropped into water impregnated with it.** When mixed with common air it burns rapidly but does not explode. When mixed with its own bulk of oxygen gas, and fired by electricity, an explosion is produ- ced, and no sulphur deposited; but the inside of the glass is moist- ened with water. For complete combustion it requires 1 h volume of oxygen gas. It is converted into water and sulphurous acid. The half volume of the oxygen goes to the formation of water, and the whole volume to the formation of sulphurous acid. When electrical sparks are made to pass for a long time through this gas the whole sulphur is deposited, and the bulk of the gas is * Phil Trans. 1812, p. 41J "j" Recherches Physico-chimiques, i. 191. $ Ibid. § Phil. Trans. 1803, p. 27i. II Annals of Philosophy, vi. 340. 1 Austin, Phil. Trans. 1788, p. 385. ** Scheele, on Air and File, p. 190. 244 SIMPLE COMBUSTIBLES. S B00K *• £ DIVISION 2. not altered; but it is converted into pure hydrogen gas. When sulphur is strongly heated in hydrogen gas a quantity of sulphu- reted hydrogen gas is formed: but the bulk of* the gas is not al- tered. It is obvious from these facts that it consists of hydrogen gas, holding a quantity of sulphur in solution. To determine its composition we have only to subtract the specific gravity of hy* drogen gas from that of sulphureted hydrogen gas. The remain- der will give us the weight of sulphur. Specific gravity of sulphureted hydrogen gas - 1*180 ----------------hydrogen gas - 0-069 Sulphur - - - =1*111 Hence it is composed by weight of Sulphur - 1111 - 2 Hydrogen - 0*0694 - 0*125 Or of an atom of sulphur united to an atom of hydrogen. When sulphureted hydrogen gas and sulphurous acid gas are mixed together, they mutually decompose each other, as was first observed by Berthollet. VII. Sulphur has the property of combining with carbon, and of forming a very remarkable compound, distinguished by the name of sulphuret of carbon. The phenomena which take place when sulphur is brought in contact with red hot charcoal were first observed by Messrs. Cle- ment and Desormes, during a set of experiments on charcoal. The process which they followed was this: fill a porcelain tube with charcoal, and make it pass through a furnace in, such a way that one end shall be considerably elevated above the other. To the lower extremity lute a wide glass tube, of such a length and shape that its end can be plunged to the bottom of a bottle of water. To the elevated extremity lute another wide glass tube filled with small bits of sulphur, and secured at the further end, so that the sulphur may be pushed forward by means of a wire, without allow- ing the inside of the tube to communicate with the external air. Heat the porcelain tube, and consequently 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 porcelain tube. A substance passes through the glass tube, and condenses under the water of the bottle into a liquid.* This liquid was obtained by Lampadius in 1796, while distilling a mixture of pyrites and charcoal, and described by him under the name of alcohol of sulphur.] From a later and more detailed set of experiments on it, he drew, as a conclusion, that it is a com- pound of sulphur and hydrogen.:}: But Clement and Desormes considered it as a compound of sulphur and charcoal; and inform * Ann. de Chim. xiii. 13C. f CrelPs Annals, 1796, ii. 136. * Gehlen's Jour. ii. 192. Chap. III.] SULPHUR. 245 us, that when it is exposed to evaporate in open vessels, a portion of charcoal remains behind. Berthollet Junior, who made some experiments on it, adopted the opinion of Lampadius.* But the subject was resumed by Cluzel,f who published an elaborate set of experiments on it in 1812. Berthollet, Thenard, and Vauquelin, who were appointed, by the French Institute to examine Ouzel's paper, repeated some of his experiments, and drew, as a conclu- sion, that the liquid in question is a compound of about 15 carbon and 85 sulphur.f Soon after a very complete set of experiments on it were published by Professor Berzelius, and Dr. Marcet.§ Their results almost exactly agreed with those of the French che- mists, and leave no doubt that this liquid is a compound of sulphur and carbon, and that it contains no other ingredient. Sulphuret of carbon, when prepared by the process of Clement and Desormes, has at first a yellow colour, owing to an excess of sulphur which it contains. But when rectified, by being distilled in a retort at a temperature not exceeding 110°, it is obtained in a state of purity. Sulphuret of carbon is a liquid as transparent and colourless as water. Its taste is acrid, pungent, and somewhat aromatic. Its smell is nauseous and fetid, though quite peculiar. Its specific gravity, according to Berzelius and Marcet is 1 '272,11 according to Cluzel 1-263,^| the specific gravity of water being 1. Its expan- sive force at the temperature of 63-5° is equal to a pressure of 7*36 inches of mercury. So that air, to which it is admitted' at that temperature, will be dilated by about i of its volume.** It boils briskly at a temperature between 105° and 110°. It does not con- geal when cooled down to — 60°. It is one of the most volatile liquids known, and produces a greater degree of cold, by its eva- poration, than any other substance. The bulb of a thermometer being enveloped in fine lint, dipped in this liquid, and suspended in the air, sinks from 60° to about zero. If it be introduced under the receiver of an air-pump, and the receiver rapidly exhausted, the thermometer will sink to — 82° in less than two minutes.f f Sulphuret of carbon takes fire in the open air, at a temperature scarcely exceeding that at which mercury boils. It burns with a blue flame, giving out the smell of sulphurous acid. Its vapour detonates when mixed with oxygen gas, and an electric spark is passed through it. The products are sulphurous acid and carbo- nic acid, and carbonic oxide, if the oxygen be in small proportion j but if six or seven times the bulk of the vapour, the whole of the carbon is converted into carbonic acid. Sulphuret of carbon is scarcely soluble in water, but alcohol and ether dissolve it readily. Ether is capable of taking up three times its bulk of this liquid without becoming turbid. It readily unites * Mem. d'Arcueil, i. 304. f Ann. de Chim. lxxxiv. 72, 113. * Ibid. Ixxxiii. 252. § Phil. Trans. 1813, p. 171. || Ibid. p. 175. *fl Ann. de Chim. Ixxxiv. 83. ** Berzelius**Marcet,Phil.Trans. 1813, p. 175. ft Marcet, Phil.Trans. 1813,p. 252, 246 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION J. with chloride of azote, and prevents that liquid from detonating, when it comes in contact with oils or phosphorus.* When passed through red-hot copper, it combines with that me- tal, forming a carbosulphuret of metal. By this method, Berthollet, Thenard, and Vauquelin, succeeded in ascertaining its composi- tion. When passed very slowly through red oxide of iron, it is also completely decomposed, and converted partly into sulphuret of iron, and partly into sulphurous acid and carbonic acid gases. By this process, Berzelius succeeded in decomposing it, and as- certained it to be a compound of Sulphur - - 84*83 - - 100*00 Carbon - - 15-17 - - 17*89 This result almost coincides with that of the French chemists. Now we have found that an atom of sulphur weighs 2 and an atom of carbon 0*75. On the supposition that sulphuret of carbon is a compound of 2 atoms sulphur, and 1 atom carbon, its constituents would be Sulphur 4 84*21 - 100 Carbon - 0*75 - 15-79 - 18*75 But these numbers approach so nearly to Berzelius' analysis, that we may safely consider them as exact. The liquid then is in fact a bisulphuret of carbon. It is not improbable that a sulphuret of carbon may likewise be formed. VIII. We do not know whether sulphur combines with boron and silicon: no experiments on the subject having been hitherto made. IX. Sulphur and phosphorus readily combine with each other, as was first ascertained by Margraf.f Pelletier afterwards examined the combination with care.f Some curious observations were pub- lished on the formation of this compound by Mr. Accum ;§ and soon after the circumstances under which it takes place were ex- plained with precision by Dr. Briggs.|| All that is necessary is to mix the two substances together, and apply a degree of heat sufficient to melt them, as Pelletier first ob- served. The compound has a yellowish white colour, and a crys- tallized appearance.*^ The combination may be obtained by heat- ing the mixture in a glass tube, having its mouth properly secured from the air. The sulphuret of phosphorus, thus prepared, is more combustible than phosphorus. If it be set on fire by means of a hot wire, allowed to burn for a little, and then extinguished by ex- cluding the air, the phosphorus, and perhaps the sulphur, seem to be oxidized, and the mixture acquires the property of taking fire spontaneously as soon as it comes in contact with air.** The combination may be procured also by putting the two bodies * Berzelius and Marcet, Phil. Trans. 1813, p. 175. -j- Opusc. i. 11. i Jour, de Phys. xxxv. 382. § Nicholson, vi. )j Ibid. vii. 58. *3 Briggs, Nicholson, vii. 58. ** Briggs,Ibid. Chap. III.] sulphur. 247 into a retort, or flask, filled with water, and applying heat cautious- ly and slowly. They combine together gradually as soon as the phosphorus is melted. It is necessary to apply the heat cautiously, because the sulphuret of phosphorus has the property of decom- posing water, as had been observed by Margraf, and ascertained by Pelletier. The rate of decomposition increases very rapidly with the temperature, a portion of the two combustibles being converted into acids by uniting to the oxygen: the hydrogen at the moment of its evolution unites with sulphur and phosphorus, and forms sulphureted and phosphureted gases. This evolution, at the boiling temperature, is so rapid as to occasion violent explosions.*f The sulphuret of phosphorus may be distilled over without de- composition. Indeed it was by distillation that Margraf first ob- tained it. Sulphur and phosphorus, by combining, acquire a con- siderable tendency to liquidity; and this tendency is a maximum when the two bodies are combined in equal proportions. The fol- lowing table exhibits the result of Pelletier's experiments on the temperatures at which the compound becomes solid when the sub- stances are united in various proportions.! 8 Phosphorus") , wwo 1 Sulphur j ^geals at 77 8 Phosphorus-) at59< 2 bulphur J 8 Phosphorus 1 ^ __0 a c i u V . . at 50 4 bulphur J 8 Phosphorus 1 , . . .„ _ 0 , s y congeals at 41 8 Sulphur J ° 4 Phosphorus") 'M.';0 8 Sulphur J 2| Phosphorus") atQQ.50 8 Sulphur J From Pelletier's experiments it is probable, that the most inti- mate combination of phosphorus and sulphur consists of 1 atom of sulphur and 1 atom of phosphorus, or by weight of Sulphur 2 - - 4 100 Phosphorus - 1*5 - -3 - - 75 But they doubtless combine in other proportions.^ * [I have had it explode in my hand, by the mere heat of my hand.—C.] f [By a paper of Mr. Faraday's, in 8 Brande's Journal, 361, it should appear, that the best mode of combining phosphorus with sulphur is the following: boil some distilled water to get rid completely of any air it may contain; then put into the boiling water 8 parts of phosphorus, and let it melt therein : then add 4 parts of sulphur, and wait till they are in- corporated. It had best be done in an open phial placed in some vessel where an explosion may take place with impunity. When cold, add some ammonia and wash the substance by shaking the phial. Then transfer the substance into fresh water previously boiled and cork the phial. The combination of phosphorus and sulphur, which at first is of a reddish brown colour, becomes of a light yellow after washing with ammoniated water. On repeating Mr. Faraday's experiment, I find it succeeds best in the proportions of three phosphorus to two sulphur.—C.] t Ann. de Chim. iv. 10. § [Concentrated sulphuric acid, that is, oil of vitriol of commerce, of specific gravity 1-85 at 60 of Fah. combines with water with violent heat and condensation. According to Dr. Ure the greatest condensation is when 73 parts of oil of vitriol are mixed with 27 parts (by weight) of water. In this case 100 parts in volume, become 9214 parts. 8 Brande's Journ. 298.—C.] 24& SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIV1SIOX2. SECTION VII. OF ARSENIC. I. The word arsenic (*ks,"*i»') occurs first in the works of Di- oscorides, and of some other authors who wrote about the begin- ning of the Christian era. It denotes in their works the same sub- stance which Aristotle had called **« P' U tt Recherches Physico-chimiques, i. 107. 268 SIMPLE COMBUSTIBLES. $ BOOK I. (DIVISION 2. Potassium is white, and it has the metallic lustre as completely as silver or mercury. At the temperature of 50° it is a soft and malleable solid. Its fluidity becomes perfect at 136£, and at 32° it is hard and brittle, and when broken in fragments exhibits a crys- talline structure. Nearly a red heat is required to convert it into Vapour. Its specific gravity at 60° is 0-86507, so that it is lighter than water. It is an excellent conductor of electricity and of heat. II. When potassium is exposed to the air, it absorbs oxygen, and is covered with a crust of potash in a few minutes. This crust ab- sorbs water, which is rapidly decomposed, and in a short time the whole becomes a saturated solution of potash. When heated in oxygen gas to the temperature at which it begins to evaporate, it burns with a brilliant white light producing intense heat. When thrown upon the surface of water it decomposes that liquid with rapidity, and the hydrogen gas evolved, carrying with it small particles of the meta!, takes fire in the air, and communicating the combustion to the potassium, the whole burns "with a kind of ex- plosion. Potassium combines with two proportions of oxygen, and forms two compounds, which have received the names of potash and peroxide of potassium. 1. Potassium is converted into potash when put into water. That liquid is decomposed, giving out hydrogen gas, while its oxy- gen unites to the potassium and converts it into potash. Accord- ing to the experiments of Gay-Lussac and Thenard 34*177 grains of potassium when put into water, evolve 40*655 cubic inches of hydrogen gas at the temperature of 59°, and when the barometer stands at 29-351 inches.* Hence*^ under a pressure of 30 inches of mercury, the quantity of gas evolved would have been 39-776 cubic inches. According to this experiment, 100 grains of potas- sium, when converted into potash in water, occasions the evolution of 116*38 cubic inches of hydrogen gas. Consequently the potas- sium must have united with a quantity of oxygen equivalent to 58*19 cubic inches. But 58*19 cubic inches weigh 19*72 grains. According to this experiment, potash is composed of—Potassium 100—Oxygen 19-72.| Berzelius took an amalgam of potassium, decomposed it by wa- ter, saturated the potash by muriatic acid, and then determined its quantity by weighing the salt which he had thus formed. The loss of weight of the amalgam gave him the quantity of potassium. This weight, subtracted from that of the potash, gave the quantity of oxygen with which it had combined. The result of his experi- ments gave him potash, composed of 100 potassium -f 20*525 oxy- gen ;* but which he afterwards corrected to the following num- bers :§—Potassium 100—Oxygen 20*45. " Recherches Physico-chimiques, i. 117. ■f [Before these calculations can be admitted, it is necessary to shew that when potassium decomposes water, it unites to oxygen only, and not to water. This has never been shewn to my knowledge; and therefore I consider potassium simply as potash free from moisture. —C.] * Ann. de Chim. Ixxx. 245. § Annals of Philosophy, iii. 360. Chap. III.] POTASSIUM. 269 Now the mean of these two sets of experiments gives us potash composed of—Potassium 100—Oxygen 20-08. Hence, I think, we may without hesitation adopt the following as the true propor- tions in which the constituents of potash combine:—Potassium 100 —Oxygen 20. If we consider potash as a compound of 1 atom potassium and 1 atom oxvgen, and nothing appears contrary to this supposition; then it follows that the weight of an atom of potassium is 5, and that of an atom of potash 6: 6 accordingly is the equivalent num- ber according to which potash enters into all combinations. 2 The peroxide of potassium was discovered in 1810, by tjay- Lussac and Thenard. It is formed by heating potassium in a sxlass iar filled with oxygen gas. A vivid combustion takes place, and a great deal of oxygen gas is absorbed. From the experiments of Gay-Lussac and Thenard, it appears that 100 grains of potas- sium, when thus burnt, are capable of absorbing 177 cubic inches of oxygen gas. Hence this peroxide is composed of—Potassium 100 or 5—Oxygen 60 or 3—So that it is a compound of 1 atom potassium and 3 atoms oxygen. This peroxide is a solid body of a yellow colour. It fuses when exposed to a temperature higher than is requisite to fuse common caustic potash. On cooling, it crystallizes in plates. When put into water it effervesces, and is reduced to the state of potash, giv- ing out the excess of oxygen which it contained. When brought in contact with phosphorus, sulphur, and carbon, combustion takes place when the temperature is raised; these bodies are acidified, and the acids formed unite to the potash. When surrounded with hydrogen and heated, that gas is absorbed without the appearance of light, and much water is formed. In like manuer, sulphurous acid, and protoxide of azote, are acidified when it is heated in them. Ammonia is decomposed, water being formed and azotic gas disengaged.* 3. Gay-Lussac and Thenard describe a third oxide of potassium containing less oxygen than potash. But they have produced no evidence that it is any thing else than a mixture of potassium and potash, f III. Potassium combines readily with chlorine, and forms a compound called chloride of potassium. When potassium is introduced into chlorine gas, it burns with a brilliant red flame, the chlorine is absorbed, and the whole is con- verted into a white saline mass. This substance is chloride of pot- assium. If potash be heated in chlorine gas its oxygen is disen- gaged, while the chlorine is absorbed and takes its place. It ap- pears from this experiment, which was made by Davy, that at a red heat potassium has a stronger affinity for chlorine than it has for oxygen. 1. Chloride of potassium has been long known to chemists. It • Recherches Physico-chimiques, i. 129. f Ibid. p. 12£. 270 SIMPLE COMBUSTIBLES. S BOOK 1. £ DIVISION 2. was formerly distinguished by the names of febrifuge or digestive salt of Sylvius; and Boerhaave called it regenerated sea salt. The French chemists gave it the name of muriate of potash, which it retained till its true nature was pointed out by Sir Humphry Davy. That gentleman proposed to distinguish it by the term potassanet but I consider the name which I have given it as more systematic, and therefore preferable. 2. It is easily obtained by saturating potash with muriatic acid, and exposing the compound formed to a red heat. At that tem- perature, it seems the oxygen of the potash unites with the hydro- gen of the acid, and converts it into water while the potassium and chlorine remain united. 3. This chloride is white, and seems to crystallize in cubes. Its taste is somewhat similar to that of common salt, but more inclined to bitter. Its specific gravity is 1-836. When boiled in water it dissolves in 1*7 times its weight of that liquid.* It requires thrice its weight of cold water.f But this difference is not sufficient to enable us to obtain regular crystals, by allowing a saturated boiling solution of it to cool. Regular crystals can only be obtained by abandoning the solution to spontaneous evaporation. It suffers but little alteration in the air. It is not sensibly soluble in alcohol. Many accurate experiments have been made on the composition of this salt, on the supposition that it is a compound of muriatic acid and potash. The most accurate of these are the three follow- ing: Acid 35:}: - 35*85$ - 36|j Base 65 - 64*15 - 64 Total 100 100* 100 The last two of these analyses almost coincide. If we correct them by depriving the potash of its oxygen, and adding the amount to the acid, we shall find the composition of the chloride Berzelius. Kirwan. Chlorine 48*114 - 48 Potassium 53*46 - 53*333 Now, if we suppose it a compound of 1 atom chlorine and 1 atom potassium, its constituents will be Chlorine 4*5 - 48*6 - 90 Potassium 5 - 54 - 100 Now these numbers coincide so nearly with the preceding analy- sis, that we can have no doubt about their accuracy. IV. Potassium combines readily with iodine, and forms a com- pound which we shall call iodide of potassium. When the vapour of iodine comes in contact with potassium the * Wenzel's Verwandtschaft, p. 310. t Bergman, Opusc. i. 134. t Wenzel's Verwandtschaft, p. 100. § Berzelius, Ann. de Chim. bxvii. M- II Kirwan, Nicholson's Quarto Journal, iii. 21$. Chap. III.] potassium. 271 metal takes fire and burns with a violet coloured flame, while the iodine is absorbed. The compound melts, and is volatilized at a temperature below redness. On cooling it crystallizes, and assumes a pearly lustre. It dissolves readily in water, and the solution does not alter vegetable blues. This iodide has not been analysed; but there can be little doubt that it consists of an atom of iodine com- bined with an atom of potassium, or of Iodine - 15*625 - - 100 Potassium 5-000 - - 32 V. Nothing is known respecting the combination of potassium with fluorine. It does not appear capable of uniting with azote. VI. When potassium is heated in hydrogen gas a portion of it is volatilized, and remains mixed with the gas. The hydrogen, in consequence, acquires the power of burning spontaneously when mixed with common air or oxygen gas. But if the gas be kept it speedily deposits the potassium, and is reduced to its ordinary state. We cannot, therefore, consider this as a gaseous compound of potassium and hydrogen. When potassium is heated in hydrogen gas, there is a particular temperature intermediate between a red heat and the common tem- perature of the air, at which the metal absorbs the gas and is con- verted into a hydruret. This hydruret has a grey colour, and is destitute of the metallic lustre. It is infusible, and does not burn spontaneously either in common air or oxygen gas. In water it is converted into potash, and the hydrogen which it contains is disen- gaged along with what proceeds from the water decomposed.* According to Gay-Lussac and Thenard, to whom we are indebted for the discovery of this hydruret, the quantity of hydrogen which potassium absorbs is rather more than }th of what it disengages from water when converted into potash. Now 100 grains of potassium evolve from water 116*4 cubic inches of hydrogen. The fourth part of 116*4 is 29-1. But 29*1 cubic inches of hydrogen gas weigh 0*616 grain. So that hydruret of potassium is composed of Potassium 100 5 Hydrogen 0*616 - - 0*0308 But 0*0308 X 4 = 0*1232, which is nearly equivalent to the weight of an atom of hydrogen. We have reason, therefore, to conclude that this hydruret is a compound of 4 atoms potassium and 1 atom hydrogen. If so, its constituents are Potassium 5 - - 100 Hydrogen 0*03125 - 0*625 According to this statement 100 grains of potassium, in order to be converted into a hydruret, must absorb 29*5 cubic inches of hy- drogen. But this I consider as in reality £th of the hydrogen which potassium disengages from water when it is converted into potash. * Recherches Physico-chimiques, i. 176. 272 SIMPLE COMBUSTIBLES. S B00K '■ £ DIVISION 2. VII. We are not acquainted with any combination which potas- sium forms with carbon, boron, or silicon. VIII. When potassium is heated in contact with phosphorus, a combination takes place with the evolution of a weak light. The phosphuret formed has a chocolate colour, and is similar in ap- pearance to phosphuret of lime. It burns in the open air, and when thrown into water a kind of detonation takes place in consequence of the rapid evolution of phosphureted hydrogen gas. If we sup- pose this phosphuret a compound of one atom potassium and 1 atom phosphorus, its composition will be Potassium - 5 - 100 Phosphorus - 1*5 - 30 IX.* Potassium combines with sulphur with great energy when the two substances are heated together. A violent combustion accompanies their union. This sulphuret has a dark grey colour. When thrown into water it acts upon that liquid with violence, producing sulphureted hydrogen gas. When heated in the air it burns brilliantly, and is converted into sulphate of potash. From this experiment it follows that this sulphuret is composed of 1 atom potassium and 1 atom sulphur, or of Potassium 5 100 Sulphur 2 40 X. Arsenic combines readily with potassium by the application of a moderate heat. Light is evolved during the combination. This arseniuret has a brown colour, and little of the metallic lustre. When put into water much less hydrogen gas is evolved than would have appeared if the potassium had not been alloyed with the arsenic. The reason is, that a portion of it remains combined with the arsenic, forming a solid hydruret of arsenic.f XI. The alloy of potassium and tellurium has not been examined. Potassium has so great an affinity for oxygen that it separates that body from every one of the combustible substances belonging to the preceding genus. The order of its affinities for the suppor- ters of combustion at a red heat are as follows:—Potassium—Chlo- rine—Iodine—Oxygen. Of the simple acidifiable combustibles it has the strongest affinity for sulphur. Phosphorus comes next, and then hydrogen. * [From an account of a paper of Vauquelin, in 8 Brande's Journ. 375, it appears, that the combinations of sulphur with the alkaline oxides, are proportionate to the quantities of oxy- gen, with which these alkalies can unite: and thus a perfect resemblance is established be- tween the acids and sulphur, in this respect. In the dry way, in 100 parts, there are Pot- ash 47-8; Sulphur 52-7; Soda 38; Sulphur 62; Lime 74; Sulphur 26. In the moist way, Lime 60; Sulphur 40; Barytes 65-5; Sulphur 34-5. 100 parts of Sulphat barytes contain 34 acid J 100 parts of Drv sulphat lime contain 58 acid Sulphuret barytes - 34>sulp. | Sulphuret lime - 63 sulp. Dry sulphat soda - 64 acid j Dry sulphat potash - 47 acid Sulphuret soda - 62 sulp. | Sulphuret potash - 52-7 sulp. C] t Gay-Lussac and Thenard. Recherches Physieo-ehimiques, i. 224. Chap. III.] SODIUM. 273 SECTION II. OF SODIUM. Soda, called also fossil or mineral alkali,* because it was thought peculiar to the mineral kingdom, was known to the ancients (though not in a state of purity) under the names of *■ £ DIVISION 2. is to be diluted with water, dissolved in muriatic acid, and the so- lution evaporated to dryness. The residuum is to be mixed with a great quantity of water, and the whole thrown on a filter. The silica, which constitutes more than half the weight of the stone, remains behind; but the glucina and the other earths, being com- bined with muriatic acid, remain in solution. Precipitate them by means of carbonate of potash. Wash the precipitate, and then dissolve it in sulphuric acid. Add to the solution sulphate of pot- ash; evaporate it to the proper consistency, and set it by to crys- tallize. Alum crystals gradually form. When as many of these as possible have been obtained, pour intu the liquid carbonate of ammonia in excess, then filter, and boil the liquid for some time. A white powder gradually appears, which is glucina. Glucina, thus obtained, is a soft light white powder, without either taste or smell; which has the property of adhering strongly to the tongue. It has no action on vegetable colours. Its specific gravity is 2*976.* It is insoluble in water, but forms with a small quantity of that liquid a paste which has a certain degree of ductility. It does not combine with oxygen nor with any of the simple combustibles; but sulphureted hydrogen dissolves it, and forms with it a hydrosul- phuret, similar to other hydrosulphurets in its properties.! Glucina is soluble in the liquid fixed alkalies, in which it agrees with alumina. It is insoluble in ammonia, but soluble in carbonate of ammonia, in which respect it agrees with yttria; but it is about five times more soluble in carbonate of ammonia than that earth. It combines with all the acids and forms with them sweet-tasted salts,! as is the case also with yttria. II. From the experiments of Sir H. Davy there is reason to con- clude that glucina like yttria is a metallic oxide. When heated with potassium that metal is converted into potash, and grey me- tallic-looking particles are observed mixed with the potash, which when put into water slowly evolve hydrogen gas and are converted into glucina. According to the experiments of Berzelius,§ sulphate of glucina is composed as follows, Acid - 100 - 5 Glucina - 64*1 - 3-205 Hence the equivalent number for glucina is 3*25. Farther, 64 glucina must contain 20 parts of oxygen, therefore it is composed of Glucinum - 44 - 100 Oxygen - 20 - 45*45 If we divide the number 3.25 in the proportion of 100 : 45 we ob tain glucina composed of • Ekeberg, Ann. de Chim. xliii. 277. t Fourcroy, ii. 159. $ Hence the name glucina, from yxmoc, srmeet. § Attempt to establish a pure scientific system of Mineralogy, p. 13*i. Chap. III.] aluminum. 299 Glucinum - - - 2*25 - - - 100 Oxygen - 1*00 - 44*4 Hence we see.that glucina is composed of 1 atom glucinum and 1 atom oxygen, and that the weight of an atom of glucinum is 2-25. SECTION III. . OF ALUMINUM. Alum is a salt which was well known to the ancients, and em- ployed by them in dyeing, but they were ignorant of its compo- nent parts. The alchymists discovered that it is composed of sul- phuric acid and an earth; but the nature of this earth was long un- known. Stahl and Neuman supposed it to be lime; but in 1728 Geoffroy junior proved this to be a mistake, and demonstrated, that the earth of alum constitutes a part of clay.* In 1754, Mar- graff showed that the basis of alum is an earth of a peculiar nature, different from every other; an earth which is an essential ingredi- ent in clays, and gives them their peculiar properties.! Hence this earth was called argil; but Morveau afterwards gave it the name of alumina, because it is obtained in the state of greatest purity from alum. The properties of alumina were still farther examined by Macquer in 1758 and 1762,! by Bergman in 1767 and 1771,$ and by Scheele in 1776 ;|| not to mention several other chemists who have contributed to the complete investigation of this sub- stance. A very ingenious treatise on it was published by Saussure junior in 1801.^f Alumina may be obtained by the following process: Dissolve alum in water, and add to the solution ammonia as long as any precipitate is formed. Decant off the fluid part, and wash the pre- cipitate in a large quantity of water, and then allow it to dry. The substance thus obtained is alumina ; not however in a state of abso- lute purity, for it still retains a portion of the sulphuric acid with which it was combined in the alum. But it may be rendered tole- rably pure, provided it has been deprived of all the potash by care- ful washing, if we expose it to a strong heat in a platinum cruci- ble. For at a high temperature the sulphuric acid may be driven off almost completely. The earth thus obtained assumes two very different appearances according to the way in which the precipitation has been conduct- ed. If the earthy salt be dissolved in as little water as possible, the alumina has the appearance of a white earth, light, friable, very • Mem. Par. 1728, p. 303. f Mem. Berlin, 1754 and 1759. Margraff, ii. 1. * Mem. Paris. § Bergman, i. 287, and v. 71. H Scheele, i. 191, French Transl. *J Jour, de Phys. Iii. 280, 300 SIMPLE COMBUSTIBLES. C BOOK I. £i>ivi8ion2. spongy, and attaching itself strongly to the tongue. In this state Saussure distinguishes it by the name of spongy alumina. But if the salt has been dissolved in a great quantity of water, the alumina is obtained in a brittle transparent yellow-coloured mass, splitting in pieces like roll sulphur when held in the hand. Its fracture is smooth and conchoidal; it does not adhere to the tongue, and has not the common appearance of an earthy body. In this state Saussure gives it the name of gelatinous alumina.* Alumina has little tase: when pure, it has no smell; but if it contains oxide of iron, which it often does, it emits a peculiar smell when breathed upon, known by the name of earthy smell.] This smell is very perceptible in common clays. The specific gravity of alumina is 2*00.! When heat is applied to alumina it gradually loses weight, in consequence of the evaporation of a quantity of water with which, in its usual state, it is combined; at the same time its bulk is con- siderably diminished. The spongy alumina parts with its mois- ture very readily, but the gelatinous retains it very strongly. Spon- gy alumina, when exposed to a red heat, loses 0.58 parts of its weight; gelatinous, only 0-43 : Spongy alumina loses no more than 0-58 when exposed to a heat of 130° Wedgewood; gelatinous in the same temperature loses but 0*4825. Yet Saussure has shown that both species, after being dried in the temperature of 60°, contain equal proportions of water.§ Davy was naturally led by his previous discoveries to consider alumina as a metallic oxide. His experiments leave little doubt on the subject, though he did not succeed in obtaining the metal in a separate state. When potassium is passed through alumina heated to whiteness, a considerable proportion of it is converted into pot- ash, and grey metallic particles are perceived in the mass, which effervesce in water and are converted into alumina. When a glo- bule of iron is fused by galvanism in contact with moist alumina it forms an alloy with aluminum. It effervesces slowly in water, being covered with a white powder.|| To this metallic basis Davy gave the name of aluminum. II. According to the experiments of Berzelius^j sulphate of alu- mina is composed of Sulphuric acid - 100 - - 5 Alumina - - 42*722 - 2*115 From this experiment it follows that the equivalent number for alumina is 2-115. We shall consider it as 2-125. Farther, 42*722 parts of alumina must contain 20 parts of oxygen. Hence alumina is composed of—Aluminum 22-722—Oxygen 20. Or, dividing 2-125 in the proportion of these numbers, its constituents are, * Jour, de Phys. Iii. 290. ! Saussure, Jour, de Ph>s. Iii. 287. % Kirwan's Miner, i. 1. § Jour, de Pitvg. Hi 287. | Elements of Chemical Philosophy, p. 355, 5 Ann. de Chim. lxxxii. 14. Chap. III.] ZIRCONIUM. 301 Aluminum - 1-125 - 100 Oxygen - 1 - - 28-8 Hence it appears that alumina is a compound of 1 atom aluminum and 1 atom oxygen, and that an atom of aluminum-weighs 1*125. SECTION IV. OF ZIRCONIUM. Among the precious stones which come from the island of Cey- lon, there is one called jargon* or zircon, which is possessed of the following properties: Its colour is various ; grey, greenish-white, yellowish, reddish- brown, and violet. It is often crystallized, either in right-angular quadrangular prisms surmounted with pyramids, or octahedrons consisting of double quadrangular pyramids. It has generally a good deal of lustre, at least internally. It is mostly semitranspa- rent. Its hardness is from 10 to 16 : its specific gravity from 4*416 to 4-7-! It loses scarcely any of its weight in a melting heat; for Kla- proth, who analysed it in 1789, found that 300 grains, after remain- ing in it for an hour and a half, were only ith of a grain lighter than at first.! Neither was it attacked either by muriatic or sul- phuric acid, even when assisted by heat. At last, by calcining it with a large quantity of soda, he dissolved it in muriatic acid, and found that 100 parts of it contained 31*5 of silica, 0-5 of a mixture of nickel and iron, and 68 of a new earth, possessed of peculiar properties, which has received the name of zirconia, from the mineral in which it was detected. Owing probably to the scarcity of the zircon, nobody attempted to repeat the analysis of Klaproth, or to verify his discovery. In 1795 he published his analysis of the hyacinth, another mineral from the same island, in which he also detected a large proportion of zirconia, expressing his hopes that it would induce chemists to turn their attention to the sub- ject.§ This analysis induced Guyton Morveau, in 1796, to examine the hyacinths of Expailly in France. They proved similar to the hyacinths of Ceylon, and contained the proportion of zirconia indi- cated by Klaproth.|| These experiments were soon after repeated, and the nature of the new earth still further examined by Vauque- lin.^ Zirconia has hitherto been found only in the zircon and hya- • [The silversmiths and jewellers call the transparent stones with which French and Genevan watches are frequently ornamented, jargoons: they are white hyacinths.—C] ! Kirwan's Miner, i. 333. * Jour, de Phys. xxxvi. 180. § Beitrage, i. 231. U Ann. de Chim. xxi. 72. *J Ann. de Chim. xxii. 158, and Jour, de Min. An. v. 97. 302 SIMPLE COMBUSTIBLES. S BOOK I. £ DIVISION 2. cinth. It may be obtained pure by the following process : reduce the mineral to powder, mix it with thrice its weight of potash, and fuse it in a crucible. Wash the mass in pure water till the whole of the potash is extracted; then dissolve the residuum as far as possible in diluted muriatic acid. Boil the solution to precipitate any silica which may have been dissolved; then filter, and add a quantity of potash. The zirconia precipitates in the state of a fine powder. Zirconia, thus prepared, has the form of a fine white powder, which feels somewhat harsh when rubbed between the fingers. It has neither taste nor odour. It is infusible before the blowpipe* but when heated violently in a charcoal crucible, it undergoes a kind of imperfect fusion, acquires a grey colour, and something of the appearance of porcelain. In this state it is very hard, its speci- fic gravity is 4-3, and it is no longer soluble in acids. Zirconia is insoluble in water: but it has a considerable affinity for that liquid. When dried slowly, after being precipitated from a solution, it retains about the third of its weight of water, and assumes a yellow colour, and a certain degree of transparency, which gives it a great resemblance to gum arabic* It does not combine with oxygen, azote, or the simple combusti- bles ; but it has a strong affinity for several metallic oxides, espe- cially for oxide of iron, from which it is very difficult to sepa- rate it. i It is insoluble in liquid alkalies, neither can it be fused along with them by means of heat; but it is soluble in alkaline carbo- nates. Davy subjected zirconia to the same experiments as the other earths described in the three preceding sections, and obtained the same evidence for its metallic nature. To the metallic basis he gave the name of zirconium. As no very accurate analyses of the salts, containing a basis of zirconia, have been hitherto made, we have no good data for de- termining its equivalent number, and for deducing from it its com- position. The analyses published by Klaproth and Vauquelin lead us to consider its equivalent number as 5*625. And to suppose it composed of Zirconium - 4*625 - 100 Oxygen 1 23*78 These numbers may be employed as approximations till better data enable us to determine the point with more precision. FAMILY III. This family includes under it six substances, all of which are of a metallic nature; namely: 1. Iron 3. Cobalt 5. Cerium 2. Nickel 4. Manganese 6. Uranium. * Vauquelin, Ann. de Chim. xxii. 158. Chap. III.] iBoiff. 303 They are distinguished from the other metals comprehended under this genus by two properties. 1. Their oxides cannot be reduced to the metallic state by the most violent heat which can be applied. 2. When dissolved in an acid they cannot be precipitated in the metallic state by plunging into the solution a rod composed of any other metal. SECTION I. OF IRON. Iron, the most abundant and most useful of all the metals, was neither known so early, nor wrought so easily, as gold, silver, and copper. For its discovery we must have recourse to the nations of the east, among whom, indeed, almost all the arts and sciences first sprung up. The writings of Moses (who was born about 1635 years before Christ) furnish us with the amplest proof at how early a period it was known in Egypt and Phoenicia. He mentions furnaces for working iron,* ores from which it was extracted:! and tells us, that swords,! knives,§ axes,|| and tools for cutting stone,^] were then made of that metal. How many ages before the birth of Moses iron must have been discovered in these countries, we may perhaps conceive, if we reflect, that the knowledge of iron was brought over from Phrygia to Greece by the Dactyli,** who settled in Crete during the reign of Minos I. about 1431 years be- fore Christ; yet during the Trojan war, which happened 200 years after that period, iron was in such high estimation, that Achilles proposed a ball of it as one of his prizes during the games which he celebrated in honour of Patroclus. At that period none of their weapons were formed of iron. Now if the Greeks in 200 years had made so little progress in an art which they learned from others, how long must it have taken the Egyptians, Phrygians, Chalybes,. or whatever nation first discovered the art of working iron, to have made that progress in it which we find they had done in the days of Moses? 1. Iron is of a bluish white colour; and, when polished has a great deal of brilliancy. It has a styptic taste, and emits a smell when rubbed. 2. Its hardness exceeds most of the metals; and it may be ren- dered harder than most bodies when converted into steel. Its spe- cific gravity varies from 7*6 to 7*8.!! * Deut. iv. 20. -j- Ibid. viii. 9. * Numb. xxxv. 16. § Levit. i. 17. U Deut. xviii. 5. *f Ibid, xxvii. 5. •• Hesiod, as quoted by Pliny, lib. vii. c. 57. ff Kirwan's Min. ii. 155. Dr. Shaw states the specific gravity of iron at 7-645 Shaw's Boyle, ii. 345. Brisson at 7-788. Mr. Hatchettfou.id a specimen 7-700. On the JMovsof Gold, p. 66. Swedenburgh states it at 7-817. According to Muaelwnbrwlt hammered 304 SIMPLE COMBUSTIBLES. $ BOOK I. £ DIVISION f. 3. It is attracted bv the magnet or loadstone, and is itself the substance which constitutes the loadstone. But when iron is per- fectly pure, it retains the magnetic virtue for a very short time. 4. It is malleable in every temperature, and its malleability in- creases in proportion as the temperature augments ; but it cannot be hammered out nearly so thin as gold or silver, or even copper. Its ductility, however, is more perfect; for it may be drawn out into wire as fine, at least, as a human hair. Its tenacity is such, that an iron wire, 0*078 of an inch in diameter, is capable of sup- porting 549*25 lbs. avoirdupois without breaking.* 5. When heated to about 158° Wedgewood, as Sir George M'Kenzie has ascertained,! it melts. This temperature being nearly the highest to which it can be raised, it has been impossible to ascertain the point at which this melted metal begins to boil and to evaporate. Neither has the form of its crystals been examined: but it is well known' that the texture of iron is fibrous ; that is, it appears when broken to be composed of a number of fibres or strings bundled together. II. When exposed to the air, its surface is soon tarnished, and it is gradually changed into a brown or yellow powder, well known under the name of rust. This change takes place more rapidly if the atmosphere be moist. It is occasioned by the gradual combi- nation of the iron with the oxygen of the atmosphere, for which it has a very strong affinity. Iron has a strong affinity for oxygen. It decomposes water at the common temperature of the air slowly, and almost impercepti- ble. But at a red heat the decomposition goes on with rapidity ; pure hydrogen gas being evolved in abundance. It is even capable of decomposing potassium when assisted by a sufficiently high tem- perature. When iron wire,! having a little cotton tied to its ex- tremity, is plunged into oxygen gas while the cotton is in flames, it takes fire and burns with great brilliancy. As far as is known at present, iron combines with only two pro- portions of oxygen, and forms two oxides, the protoxide and the peroxide. The protoxide is black, but the peroxide is red. 1. The black oxide of iron may be obtained by three different processes ; 1. By keeping iron filings a sufficient time in water at the temperature of 70°. The oxide thus formed is a black powder, formerly much used in medicine under the name of martial ethiops, and seems to have been first examined by Lemeri.§ 2. By burn- iron softened by heat is of the specific gravity 7-600; the same hammered hot, becomes 7-7633; and the same hammered cold, becomes 7 875. Wasserberg, i. 168. * Sickingen, Ann de Chim. xxv. 9. English iron only supports a weight 348-38 lbs. Sec Annals of Philosophy, vii. 320. f Nicholson's 4to Jour. iv. 109. * [Fine harpsichord wire.—C.] § The best process is that of De Roover. He exposes a paste formed of iron filings and water to the open air in a stoneware vessel; the paste becomes hot, and the water disap- pears. It is then moistened again, and the process repeated till the whole is oxidized. The mass is then pounded, and the powder is heated in an iron vessel till it is perfectly dry, stir- ring it constantly. See Ann. de Chim. xliv. 329. Chap. III.] IRON. 305 ing iron wire in oxygen gas. The wire as it burns is melted, and falls in drops to the bottom of the vessel, which ought to be cover- ed with water, and to be of copper. These metallic drops are brit- tle, very hard, and blackish, but retain the metallic lustre. They were examined by Lavoisier, and found precisely the same with martial ethiops.* They owe their lustre to the fusion which they underwent. 3. By dissolving iron in sulphuric acid, and pour- ing potash into the solution. A green powder falls to the bottom, which assumes the appearance of martial ethiops when dried quick- ly in close vessels. This oxide, when pure, is a black tasteless powder, insoluble in water; but soluble in acids, forming solutions of a pale green co- lour and a sweetish astringent taste. It is capable of combining with water,! and the compound has a dirty greenish colour; but the water is very easily driven off. Many experiments have been made to determine the proportion of oxygen which this oxide con- tains. The following table exhibits the results obtained by the dif- ferent experimenters. Proust! - 100 iron + 28 oxygen Hassenfratz§ 100 +29 Bucholz|| ... 100 +29-87 Berzelius^f 100 + 29*57 Thomson** 100 +28 Gay-Lussac!! 100 + 28*3 Mean of the whole 100 + 28*78 In order to be able to judge of the accuracy of these numbers, let us examine some of the salts into which this oxide enters. According to the experiments of Berzelius, sulphate of iron is composed of Sulphuric acid - - 100 - - 5 Protoxide of iron - - 88 - - 4-4 From this we see that the equivalent number for protoxide of iron is 4*4. Let us take it at 4-5, which would suppose the salt a compound of 100 acid + 90 oxide. Farther, 90 protoxide of iron must contain 20 of oxygen. Hence it is a compound of Iron 79 100 Oxygen 20 28*57 Thus we obtain 28*57 for the quantity of oxygen which unites with 100 of iron in order to constitute protoxide of iron. If we divide the number 4*5 in the proportion of 79 : 20 we obtain the protoxide composed of * Ann. deChim. i. 19. | [Distilled water does not appear to act on a polished needle.—C.] * Ann. de Chim. xxiii. 85. § Ibid. lxix. 152. || Gehlen's Journal fur die Chimie und Physik, iii. 711. His experiments gave only 29-09. But he considers the number in the text as the true one. t Annals of Philosophy, iii. 356. Ann. de Chim. Ixxviii. 240. •* Annals of Philosophy. ft Ann. de Chim. Ixxx. 163. Vol. I. Qq 306 SIMPLE COMBUSTIBLES. 5 BOOK 1 £ DIVISION -. Iron 3.5 100 Oxygen i-o 2«->7 We see from this that the protoxide is a compound of 1 atom iron and 1 atom oxygen, and that an atom of iron weighs 3-5. 2. The peroxide of iron may by formed by keeping iron filings red hot in an open vessel, and agitating them constantly till they are converted into a dark red powder. This oxide was formerly called saffron of Mars. Common rust of iron is merely this oxide combined with carbonic acid gas. The red oxide may be obtained also by exposing for a long time a diluted solution of iron in sul- phuric acid to the atmosphere, and then dropping into it an alkali, by which the oxide is precipitated. This oxide, when pure, has a fine red colour, bordering on crim- son. It has frequently a shade of yellow or brown, owing to causes not well understood; but probably from the presence of some foreign body. It is tasteless, and insoluble in water ; but it dissolves in acids, though not so readily as the protoxide, and forms brownish or yellowish solutions having a sweetish and as- tringent taste. From the experiments recently made on the constitution of this oxide, there can be no doubt that it is a compound of 100 iron + 28*57 X I3 oxygen = 42*955. From the experiments of Berzelius it appears that the persulphate of iron is composed of—Sulphuric acid 100—Peroxide of iron 65*5. This approaches very nearly to Acid 100 - - - 5 Oxide - - - 66*6 3>3 The equivalent number we perceive is 3*. This appears at first sight absurd. The peroxide contains more oxygen than the pro- toxide, and yet its equivalent is less. But let us suppose it a com- pound of 2 atoms iron 3 atoms oxygen.—Then the weight will be 3'5 + 3*5 + 3 = 10. Let us suppose the persulphate a com- pound of 3 atoms sulphuric acid and 1 atom peroxide. Then we have its composition Acid - 100 - 5 X 3 = 15 Oxide - 66*6 - 10 Now this is what I consider to be the true constitution of this salt, and the true nature of the peroxide. We thus get rid of the anomaly of the red oxide being a compound of 1 atom iron + 1 \ atom oxygen. If we get rid of this anomaly, by supposing the black oxide of iron to contain 2 atoms and the red oxide 3 atoms of oxy- gen, we represent these oxides by numbers which do not corres- pond with their equivalents, and which cannot, therefore, be cor- rect. 3. I do not notice here the new oxides of iron announced by Thenard* and Gay-Lussac;! because I do not think that these chemists have succeeded in establishing their existence. * Ana. de Chim. lvi. 59. ! Ibid. Ixxx. 164. Chap. III.] IRON. 307 Cutting instruments of steel, after being finished, are hardened by heating them to a cherry red, and then plunging them into a cold liquid. After this hardening, it is absolutely necessary to soften them a little, or to temper them as it is called, in order to obtain a fine and durable edge. This is done by heating them till some particular colour appear on their surface. The usual way is to keep them in oil, heated to a particular temperature, till the re- quisite colours appear. Now these colours follow one another in regular suceession according to the temperature. Between 430° and 450°, the instrument assumes a very pale yellowish tinge: at 460°, the colour is a straw yellow, and the instrument has the usual temper of pen-knives, razors, and other fine edge tools. The co- lour gradually deepens as the temperature rises higher, and at 500° becomes a bright brownish metallic yellow. As the heat increases, the surface is successively yellow, brown, red, and purple, to 580°, when it becomes of a uniform deep blue, like that of watch-springs.* The blue gradually weakens to a water colour, which is the last shade distinguishable before the instrument becomes red hot.! That these different shades of colour are owing to the oxidizement of the surface becomes evident from a mode of ornamenting sword- blades, knives, &c. long practised in Sheffield. Flowers, and va- rious other ornaments, are painted on the blade with an oily com- position. It is then subjected to the requisite heat for tempering it. The colour of the blade is altered in every part except where it is covered with the paint. When the paint is taken off the orna- ments appear of the natural colour of polished steel, and of course are easily distinguishable. Sir H. Davy, in consequence of a letter from Mr. Stoddart, found that when steel is heated in hydrogen gas it does not change its colour as it does when tempered in the usual way-! From these facts it is obvious that the changes of colour are owing to the oxidizement of the surface of the iron. Whether the changes be owing to alterations in the thickness of the coat of oxide or to the formation of various proportions of the two oxides we have no data to determine. III. Iron combines readily with chlorine, and forms two com- pounds, which we shall call protochloride and perchloride of iron. 1. The protochloride may be formed by dissolving iron in mu- riatic acid, evaporating the solution to dryness, and exposing the dry mass to a red heat in such a manner as to exclude the action of air on it. It was first described by Dr. John Davy,§ Protochloride of iron has a grey but variegated colour and a metallic splendour. Its texture is lamellated. When heated to redness it melts, but is not volatilized. It is imperfectly soluble in water, and the solution yields crystals of green muriate of iron. According to the analysis of Dr. John Davy,|| it is composed of • See the curious experiments of Mr. Stoddart, as related by Mr. Nicholson. Nichol- son's Quarto Jour. iv. 129- ! Lewis, Newman s Chem. p. 79. i Annals of Philosophy, i. 131. § Phil- Trans 1812, p. 181. || Phil. Trans. 1812, p. 182. 308 SIMPLE COMBUSTIBLES. 5 B°OK l- £ DIVISION "2. Chlorine - 53*43 - 100 - 4-5 Iron - - 46.57 - 87-16 - 3-9 100-00 From this analysis we see that the protochloride is a compound of 1 atom chlorine + 1 atom iron. The accurate proportions, ac- cording to the numbers formerly ascertained for the atoms of these bodies, are as follows: Chlorine - - 4*5 - - 100 Iron 3-5 77-7 2. The perchloride of iron was first described by Sir H. Davy,* and afterwards more particularly examined by Dr. John Davy.! It may be obtained by burning iron wire in chlorine gas, or by evaporating the red muriate of iron to dryness, and heating it in a tube with a narrow orifice. It is a substance of a bright brown co- lour, with a lustre approaching that of iron ore from the isle of Elba. It is volatilized by a moderate heat, and forms minute bril- liant crystals, the shape of which has not been determined. It dis- solves completely in water, and the solution constitutes red mu- riate of iron. According to the analysis of Dr. Davy, it is com- posed of Chlorine - 64*9 - 100 - 4*5 X 2 Iron - - 35-1 - 54*08 - 4*86 If it be a compound of 2 atoms chlorine and 1 atom iron, of which there seems no doubt, then its composition should be Chlorine - - 9 - - 100 Iron - - 3*5 - - 38*8 These numbers do not agree with the results obtained by Dr. John Davy: but if we consider that his analysis was the first, and that it was upon a minute scale, we shall not be surprised at this want of coincidence. IV. Iron combines readily with iodine. We know at present only one iodide of this metal. It was first mentioned by Sir H. Davy and afterwards was more minutely described by Gay-Lussac. It may be formed by heating iron in contact with vapour of io- dine. It is a brown substance which fuses at a red heat. It dis- solves in water and forms a light green solution consisting without doubt of hydriodate of iron. It has not been analysed. But it is probably composed of 1 atom iodine united to 1 atom iron, or by weight of Iodine - - 15*625 - - 100 Iron - - 3'5 - 22-4 Analogy leads to the opinion that there exists likewise a perio- dide of iron, though it has not hitherto been observed. V. We know nothing respecting the action of fluorine on iron. * Phil. Trans. 1811, p. 23. ! Ibid. 1812, p. 181. Chap. III.] IRON. 309 Azote does not seem capable of uniting with iron. Neither does it appear to form any permanent combination with hydrogen. VI. Iron has the property of combining with carbon and the compound constitutes the very important modifications of iron known by the names of cast iron and steel. There are a great many varieties of iron, which artists distin- guish by particular names; but all of them may be reduced under one or other of the three following classes—Cast Iron, Wrought or Soft Iron, and Steel. 1. Cast Iron, or Pig Iron, is the name of this metal when first extracted from its ores. The ores from which iron is usually ob- tained are composed of oxide of iron and clay. The object of the manufacturer is to reduce the oxide to the metallic state, and to separate all the clay with which it is combined. These two ob- jects are accomplished at once, by mixing the ore reduced to small pieces with a certain portion of limestone and of charcoal, and sub- jecting the whole to a very violent heat in furnaces constructed for the purpose. The charcoal absorbs the oxygen of the oxide, flies off in the state of carbonic acid gas, and leaves the iron in the me- tallic state; the lime combines with the clay, and both together run into fusion, and form a kind of fluid glass; the iron is also melted by the violence of the heat, and being heavier than the glass, falls down, and is collected at the bottom of the furnace. Thus the contents of the furnace are separated into two portions; the glass swims at the surface, and the iron rests at the bottom. A hole at the lower part of the furnace is now opened, and the iron allow- ed to flow out into moulds prepared for its reception. The cast iron thus obtained is distinguished by manufacturers into different kinds, from its colour and other qualities. The three following are the most remarkable of these varieties: 1st, White cast iron, which is extremely hard and brittle, and appears to be composed of a congeries of small crystals. It can neither be filed, bored, nor bent, and is very apt to break when suddenly heated or cooled. 2d, Grey or mottled cast iron, so called from the inequality of its colour. Its texture is granulated. It is much softer, and less brittle, than the last variety, and may be cut, bored, and turned on the lathe. Artillery is made of it. 3d, Black cast iron, is the most unequal in its texture, the most fusible, and least cohesive of the three.* Cast iron melts when heated to about 130° Wedgewood. Its specific gravity varies from 7*2 to 7*6. It contracts considerably when it comes into fusion. It is converted into soft, or malleable iron, by a process which is considered as a refinement of it; and hence the furnace in which the operation is performed is called a finery. 2. This was usually done in this country by keeping the iron * Black's Lectures, ii. 495. 310 SIMPLE COMBUSTIBLES. S BOOK I. £ DIVISION 2. melted for a considerable time in a bed of charcoal and ashes, and the scori* of iron, and then forging it repeatedly till it became com- pact and malleable. The process varies considerably in different countries, according to the nature of the fuel, and of the ore from which the iron was obtained ; and the quality of the iron obtained is equally various. Mr. Cort, about 25 years ago, proposed a new method, which succeeded in converting every kind of cast iron into malleable iron of the best quality. The cast iron is melted in a re- verberatory furnace by means of the flame of the combustibles, which is made to play upon its surface. While melted, it is con- stantly stirred by a workman, that every part of it may be exposed to the air. In about an hour the hottest part of the mass begins to heave and swell, and to emit a lambent blue flame. This continues nearly an hour; and by that time the conversion is completed. The heaving is evidently produced by the emission of an elastic fluid.* As the process advances, the iron gradually acquires more consistency; and at last, notwithstanding the continuance of the heat, it congeals altogether. It is then taken while hot, and hammered violently by means of a heavy hammer driven by machinery. This not only makes the particles of iron approach nearer each other, but drives away several impurities which would otherwise continue at- tached to the iron. This constitutes the foundation of the puddling process now universally practised in our manufactories. In this state it is the substance described in this Section under the name of iron. As it has never yet been decomposed, it is con- sidered at present when pure as a simple body; but it has seldom or never been found without some small mixture of foreign sub- stances. These substances are either some of the other metals, or oxygen, carbon, silicon, or phosphorus. 3. When small pieces of iron are stratified in a close crucible, with a sufficient quantity of charcoal powder, and kept in a strong red heat for eight or ten hdurs, they are converted into steel,! which is distinguished from iron by the following properties. It is so hard as to be unmalleable while cold, or at least it ac- quires that property by being immersed while ignited into a cold liquid: for this immersion, though it has no effect upon iron, adds greatly to the hardness of steel. It is brittle, resists the file, cuts glass, affords sparks with flint, and retains the magnetic virtue for any length of time. It loses this hardness by being ignited and cooled very slowly. It melts at above 130° Wedgewood. It is malleable when red hot, but scarce- ly so when raised to a white heat. It may be hammered out into much thinner plates than iron. It is more sonorous ; and its spe- cific gravity, when hammered, is greater than that of iron, varying from 7*78 to 7-84. By being repeatedly ignited in an open vessel, and hammered, it becomes wrought iron.] • Beddoes, Phil. Trans. 1791. ! This process is called cementation. t Dr. Pearson on Wootz, Phil. Trans. Chap. III.] IRON. 311 4. These different kinds of iron have been long known, and the converting of them into each other has been practised in very re- mote ages. Many attempts have been made to explain the manner in which this conversion is accomplished. According to Pliny, steel owes its peculiar properties chiefly to the water into which it is plunged in order to be cooled.* Beccher supposed that fire was the only agent; that it entered into the iron, and converted it into steel. Reaumur was the first who attended accurately to the pro- cess ; and his numerous experiments contributed much to elucidate the subject. He supposed that iron is converted into steel by com- bining with saline and oily or sulphureous particles, and that these are introduced by the fire. But it was the analysis of Bergman, published in 1781, that first paved the way to the explanation of the nature of these different species of iron.! By dissolving in diluted sulphuric acid 100 parts of cast iron, he obtained, at an average, 42 ounce measures of hydrogen gas; from 100 parts of steel he obtained 48 ounce measures; and from 100 parts of wrought iron, 50 ounce measures. From 100 parts of cast iron he obtained, at an average, 2*2 of plumbago, or 1^; from 100 parts of steel, 0-5, or ^j and from 100 parts of wrought iron, 0*12, or ^4 From this analysis he concluded, that cast iron con- tains the least phlogiston, steei more, and wrought iron most of all; for the hydrogen gas was at that time considered as an indication of phlogiston contained in the metal. He concluded, too, that cast iron and steel differ from pure iron in containing plumbago. Mr. Grig- non, in his notes on this analysis, endeavoured to prove, that plum- bago is not essentially a part of cast iron and steel, but that it was merely accidentally present. But Bergman, after considering his objections, wrote to Morveau on the 18th November 1783, " I will acknowledge my mistake whenever Mr. Grignon sends me a single bit of cast iron or steel which does not contain plumbago; and I beg of you, my dear friend, to endeavour to discover some such, and to send them to me ; for if I am wrong, I wish to be unde- ceived as soon as possible."§ This was almost the last action of the illustrious Bergman. He died a few months after at the age of 49, leaving behind him a most brilliant reputation, which no man ever more deservedly acquired. His industry, his indefatigable—his astonishing industry, would alone have contributed much to esta- blish his name; his extensive knowledge would alone have attract- ed the attention of philosophers; his ingenuity, penetration, and accurate judgment, would alone have secured their applause ; and his candour and love of truth procured him the confidence and the esteem of the world.—But all these qualities were united in Berg- man, and conspired to form one of the noblest characters that ever adorned human nature. • Pliny, lib. xxxiv. 14. ! Opusc. iii. 1. $ Scheele had previously observed, that plumbago is obtained when some kinds of iron arc dissolved in sulphuric acid. See his Dissertation on Plumbago. 4 Morveau, Eucyc. Method. Chim. i- 448. 312 SIMPLE COMBUSTIBLES. J BOOK I. £ DIVISION 2. The experiments of Bergman were repeated, varied, and extend- ed, by Vandermonde, Monge, and Berthollet, who published an admirable dissertation on the subject in the Memoirs of the French Academy for 1786. These philosophers, by an ingenious applica- tion of the theoretical discoveries of Mr. Lavoisier and his associ- ates, were enabled to explain the nature of these three substances in a satisfactory manner. By their experiments, together with the subsequent ones of Clouet, Vauquelin, and Morveau, the follow- ing facts have been established. Wrought iron is a simple substance, and if perfectly pure would contain nothing but iron. Steel is iron combined with a small portion of carbon, and has been for that reason called carbureted iron. The proportion of car- bon has not been ascertained with much precision. From the an- alysis of Vauquelin, it amounts at an average, to T^ part.* That steel is composed of iron combined with carbon, has been still farther confirmed by Morveau, who formed steel by combin- ing together directly iron and diamond. At the suggestion of Clouet, he enclosed a diamond in a small crucible of pure iron, and exposed it completely covered up in a common crucible to a suffi- cient heat. The diamond disappeared, and the iron was converted into steel. The diamond weighed 907 parts, the iron 57,800, and the steel obtained 56,384; so that 2,313 parts of the iron had been lost in the operation.! From this experiment it follows, that steel contains about ^ of its weight of carbon. This experiment was objected to by Mr. Mushet; but the objections were refuted by Sir George M'Kenzie.! Rinman, long ago, pointed out a method by which steel may be distinguished from iron. When a little diluted nitric acid is dropt upon a plate of steel, allowed to remain a few minutes, and then washed off, it leaves behind it a black spot; whereas the spot form- ed by nitric acid on iron is whitish green. We can easily see the reason of the black spot: it is owing to the carbon of the iron which is left undissolved by the acid. Cast iron is iron combined with a still greater proportion of car- bon than is necessary for forming steel. The quantity has not yet been ascertained with precision: Mr. Clouet makes it amount to |th of the iron. The blackness of the colour, and the fusibility of cast iron, are proportional to the quantity of carbon which it contains. Cast iron is almost always contaminated with foreign ingredients; These are chiefly oxide of iron, phosphuret of iron, and silicon.^ * Ann. de Chim. xxii. 1. ! Ibid. xxxi. 328. i Nicholson's Journal, iv. 103. § A specimen of very pure cast iron analysed by Berzelius, yielded Iron (with silicon and magnesium) .... 91-53 Manganese --------- 4-57 Carbon.........390 10000 The silicon was j a per cent the magnesium -yth of a per eent. Afhandlingar, iii. 152. Chap. III.] IRON. 313 5. It is easy to see why iron is obtained from its ore in the state of cast iron. The quantity of charcoal, along with which the ore is fused, is so great, that the iron has an opportunity of satu- rating itself with it. The conversion of cast iron into wrought iron is effected by burn- ing away the charcoal, and depriving the iron wholly of oxygen: this is accomplished by heating it violently while exposed to the air.* Mr. Clouet has found, that when cast iron is mixed with 3th of its weight of black oxide of iron, and heated violently, it is equally converted into pure iron. The oxygen of the oxide, and the carbon of the cast iron, combine, and leave the iron in a state of purity.! The common method of refining cast iron is nothing else than this process of Clouet, as has been pointed out by Dr. Black. A considerable quantity of the iron, (about |d) is scorified or con- verted into black oxide of iron, known when melted by the name of finery cinder.% This being mixed with the melted iron, and the heat increased, the oxide acts upon the carbon, and both mu- tually decompose each other. The nicety of the operation depends on knowing how far to carry the calcination of the iion, that there may be just sufficient to consume the whole of the carbon. Much more, however, is actually formed in the large manufactories. 6. The conversion of iron into steel is effected by combining it with carbon. This combination is performed in the large way by three different processes, and the products are distinguished by the names of natural steel, steel of cementation, and cast steel. Natural steel is obtained from the ore by converting it first into cast iron, and then exposing the cast iron to a violent heat in a fur- nace while its surface is covered with a mass of melted scoriae five or six inches deep. Part of the carbon is supposed to combine with the oxygen which cast iron contains, and to fly off in the state of carbonic acid gas. The remainder combines with the pure iron and constitutes it steely This steel is inferior to the other species; its quality is not the same throughout, it is softer, and not so apt to break ; and as the process by which it is obtained is less expen- sive, it is sold at a lower price than the other species. Steel of cementation is made by stratifying bars of pure iron and charcoal powder alternately in large earthen troughs or cruci- bles, the mouths of which are carefully closed up with clay. These troughs are put into a furnace, and kept sufficiently hot till the bars of iron are converted into steel, which usually requires eight or ten days.|| This process was invented, or at least first practised to any extent, in Britain. The bars of steel thus formed, are known * A detailed account of the process used at Sheffield for converting cast iron into pure iron has been published by Mr. Collier in the 5th volume of the Manchester Memoirs, p. 111. ! Jour, de Min. An. vii. p. 8. * The French name for this is laitier. § A detailed account of this process, as performed in different iron works, may be seen in the Jour, de Min. No. iv. p. 3. || The process is described at large by Mr. Collier in the Manchester Memoirs, v. 117. Vol. I. R r 31*4 SIMPLE COMBUSTIBLES. C BOOK I £ divisio* 2. in this country by the name of blistered steeL, because their surface is covered here and there with a kind of blister of the metal, as if an elastic fluid had been confined in different parts of it. VV hen drawn out into smaller bars by the hammer, it receives the name of tilted steel, from the hammer employed. When broken to pieces, and welded repeatedly in a furnace, and then drawn out into bars, it is called German or shear steel.* Steel of cementation has a fine .grain, is equal, harder, and more elastic than natural steel. Cast steel is the most valuable of all, as its texture is most com- pact, and it admits of the finest polish. It is used for razors, sur- geons' instruments, and other similar purposes. It is more fusible than common steel, and for that reason cannot be welded with iron: it melts before it can be heated high enough. The method of mak- ing it was discovered about 1750 by Mr. Huntsman of Sheffield. The process was for some time kept secret; but it is now well known in this country, and other manufacturers succeed in it equally well with the original discoverer. It consists in fusing blistered. steel in a close crucible, mixed with a certain proportion of pound- ed glass and charcoal powder. It may be formed also, according to the experiments of Clouet, by melting together 30 parts of iron, 1 part of charcoal, and 1 part of pounded glass; or by surround- ing iron in a crucible with a mixture of equal parts of chalk and clay, and heating the crucible gradually to a white heat, and keep- ing it a sufficient time in that state. \ The carbon, according to Clouet, is obtained by the decomposition of the carbonic acid, which exists abundantly in the chalk ; one part of the iron combin- ing with the oxygen of this acid, while the other part combines with the carbon.! But the subsequent experiments of Mr. Mushet have rendered it very probable that this theory is erroneous, and that the steel obtained by Clouet was owing to some other unob- served circumstance : for when he repeated it with all possible pre- cision, he obtained only iron which had been melted, and thereby altered in its texture and appearance, but not converted into steel.§ From the experiments of Clouet, it does not appear that the pre- sence of glass is necessary to constitute cast steel; the only essen- tial ingredients seem to be iron and carbon: but the quantity of carbon is greater than in common steel, and this seems to constitute the difference between these two substances. • 7. From the preceding detail, it is obvious that iron and carbon are capable of combining together in a variety of different propor- tions. When the carbon exceeds, the compound is carburet of iron or plumbago. When the iron exceeds, the compound is steel or cast iron in various states, according to the proportion. All these compounds may be considered as subcarburets of iron. The most complete detail of experiments on these various compounds which have appeared in this country are those of Mr. Mushet, published • Collier, Manchester Memoirs, v. 117. t Jour, de Min. An. vii. 3. * Guytoa and Darcet, Ibid. As. vi. 709. § PhiL Mag. xii. 27. Chap. III.] IRON. 315 in the Philosophical Magazine. This ingenious practical chemist has observed, that the hardness of iron increases«\vith the propor- tion of charcoal with which it combines, till the carbon amounts to about fa of the whole mass. The hardness is then a maximum; thfr metal acquires the colour of silver, loses its granulated appear- ance, and assumes a crystallized form. If more carbon be added to the compound, the hardness diminishes in proportion to its quantity.* The following table, by the same ingenious chemist, exhibits the proportion of charcoal which disappeared during the conversion of iron to the different varieties of subcarburet known in commerce.! T|7 Soft cast steel -fa White cast iron i^r Common cast steel fa Mottled cast iron fa The same, but harder Jy Black cast iron. fa The same, too hard for drawing 8. The substance described in a preceding section under the name of plumbago, has been usually considered as a carburet of iron. But this opinion cannot be maintained by any plausible ar- guments. According to the analysis of Allen and Pepys, it is com- posed of—Carbon 95—Iron 5. Now if an atom of carbon weigh 0*75 and an atom of iron 3*5, it must follow that it consists of about 100 atoms of carbon, united to only 1 atom of iron. But such a combination cannot be con- ceived. It is much more probable that the small proportion of iron is only mechanically mixed. VII. From the experiments of Descotils! and GmelimJ we leam, that iron is capable of combining with boron. The boruret. was formed by fusing a mixture of iron filings and boracic acid in a covered crucible. It constituted a ductile mass of a silver white colour. VIII. From the experiments, of Berzelius and Stromeyer, it appears that silicon may be combined with iron. It is even pro- bable, from Berzelius' observations, that some kinds of iron may owe their peculiar qualities to the silicon which they contain. Silicuret of iron is of a silver white colour and ductile. It requires heat before it dissolves in sulphuric acid. When dissolved in acids it leaves a quantity of silica, constituting a porous mass of the size of the silicuret dissolved. Nothing is known respecting the pro- portions of iron and silicon, capable of uniting. IX. Iron readily unites with phosphorus, and forms a phosphuret of iron. 1. Phosphuret of iron may be formed by fusing in a crucible 16 parts of phosphoric glass, 16 parts of iron, and half a part of char- coal powder. It is magnetic, very brittle, and appears white when broken. When exposed to a strong heat, it melts, and the phos- • Phil. Mag. xiii. 138. + Ibid. xiii. p. 142. ■- Recherches Physico-chimiques, i. 306. § Sehweigger's Journal, xv. 246. 316 SIMPLE COMBUSTIBLES. S BOOK l- { nivisov 2. phorus is dissipated.* It may be formed also by melting together equal parts of pjtosphoric glass and iron filings. Part of the iron combines with the oxvgen of the phosphoric glass, and is vitrified; the rest forms the phosphuret, which sinks to the bottom of the crucible. It mav be formed also by dropping small bits of phos- phorus into iron filings heated red hot.! The proportions of the in- gredients of this phosphuret have not yet been determined. It was first discovered and examined by Bergman, who took it for a new metal, and gave it the name of siderum. 2. There is a particular kind of iron known by the name of cold short iron, because it is brittle when cold, though' it be malleable when hot. Bergman! was employed at Upsala in examining the cause of this property, while Meyer§ was occupied at Stetin with the same investigation; and both of them discovered, nearly at the same time, that by means of sulphuric acid, a white powder could be separated from this kind of iron, which by the usual process they converted into a metal of a dark steel grey exceedingly brittle, and not very soluble in acids. Its specific gravity was 6.700; it was not so fusible as copper; and when combined with iron rendered it cold short. Both of them concluded that this substance was a new metal. Bergman gave it the name of siderum, and Meyer of hy- drosiderum. But Klaproth soon after, recollecting that the salt composed of phosphoric acid and iron bore a great resemblance to the white powder obtained from cold short iron, suspected the pre- sence of phosphorus in this new metal. To decide the point, he combined phosphoric acid and iron, and obtained, by heating it in a crucible along with charcoal powder,|| a substance exactly resem- bling the ne^w metal.^j Meyer, when Klaproth communicated to him this discover}-, informed him that he had already satisfied him- self, by a more accurate examination, that siderum contained phos- phoric acid.** Soon after this, Scheele actually decomposed the white powder obtained from cold short iron, and thereby demon- strated that it is composed of phosphoric acid and iron.!! The siderum of Bergman, however, is composed of phosphorus and iron, or it is phosphuret of iron ; the phosphoric acid being de- prived of its oxygen during the reduction.]] X. Iron combines with two proportions of sulphur, and forms protosulphuret and persulphuret of iron, compounds which are usually distinguished among mineralogists by the names of magne- tic pyrites and cubic pyrites. 1. Protosulphuret of iron or magnetic pyrites, is found native in considerable quantity. Its colour is that of bronze. It has a me- * Pelletier, Ann. de Chim. i. 105. ! Ibid. xiii. 113. % Opusc. iii. 109. § Schriften der Berliner Gesellsch. Naturf. Freunde, 1780, ii. 334, and iii. 380. I This process in chemistry is called reduction. *J Crell's Annals, 1784, i. 390. ** Ibid. i. 195. ff Crell, i. 112, E-,g. Tram. %% Rinman has shown that the brittleness and bad qualities of cold short iron may be re- moved by heating it strongly with limestone, aud with this the experiments of Levavasseur correspond. See Ann. de Chim. xiii. 831. Chap. III.] IRON. 317 tallic lustre; but its powder is blackish grey. Its specific gravity is 4*518. It strikes fire with steel, and easily melts when heated. Mr. Hatchett found it composed of 63 iron and 37 sulphur, which agrees almost exactly with the analysis of Proust. He is of opinion that the iron is not altogether in the metallic state, but contains about Tlj. part of its weight of oxygen.* This sulphuret dissolves readily in sulphuric and muriatic acids, emitting abundance of sulphureted hydrogen. When heated with nitric acid, a considerable portion of the sulphur is separated-! If we suppose it a compound of 1 atom iron 4- 1 atom sulphur, its constituents will be, Iron - 3-5 - - 100 Sulphur - 2 - - 57*1 Now the result of Hatchett's analysis is,—Iron 100—Sulphur 58-73. Here we see the coincidence is very close. 2. Per sulphuret of iron, or cubic pyrites, is of a yellow colour, and has the metallic lustre. It is brittle, and sufficiently hard to strike fire with steel. Its specific gravity is about 4*5. It usually crystallizes in cubes. When heated it is decomposed. In the open air the sulphur takes fire: in close vessels filled with charcoal, part of the sulphur is volatilized; and a black substance remains, retaining the original form of the mineral, but falling to powder on the slightest touch. Mr. Proust has demonstrated that this black substance is protosulphuret of iron. Pyrites, according to him, when thus treated, gives out 0*20 parts of sulphur, and 0*80 parts of sulphuret remain behind.! Hence pyrites is composed of—80 protosulphuret of iron—20 sulphur. But this method is not susceptible of great accuracy. Mr. Hatchett subjected various specimens of pyrites to analysis with that precision for which he is distinguished. The following table exhibits a view of the results which he obtained :§ Pyrites. Specific gravity. 1 Constituents. i Iron. Sulphur. Total. 1st In dodecahedrons 4*830 47*85 52*15 100 2d Striated cubes ! 47-50 42*50 100 3d Smooth cubes " 4-831 47*30 52*70 100 4th Radiated 4*698 46*40 53*60 100 5th Smaller do. Mean 4-775 45*66 54-34 100 46*94 53*06 100 • Hatchett's Analysis of Magnetical Pyrites, Phil. Trans. 1804. t Hatchett, ibid. * Jour, de Phys. Lui. 89. § Hatchett, Phi). Trans. 1804, 318 SIMPLE COMBUSTIBLES. f BOOK I. £ DIVISION 3. If we suppose the persulphuret of iron to be a compound of 1 atom iron with 2 atoms sulphur, then its constituents will be Iron - 3*5 - - 100 Sulphur - 4 - - 114-2 Now the mean of Mr. Hatchett's analyses, just stated, gives us, —-Iron 100—Sulphur 113. Here the coincidence between the experimental and theoretical result is still greater than is the case with protosulphuret of iron. As the deviations in the two cases are on opposite sides, the mean of both would come still nearer the truth. This is sufficient to convince us that on the supposition of perfect precision the differ- ences would vanish altogether. Protosulphuret of iron is not only attracted by the magnet, but may be itself converted into a magnet by the usual methods ; but persulphuret is not in the least obedient to the magnet, neither is it susceptible of the magnetic virtues.* It has been long known that pure iron is not susceptible of retain- ing the properties of a magnet; but steel, when once magnetized, continues permanently magnetic. Now steel, as we shall see im* mediately, is a combination of iron and carbon. When the propor- tion of carbon united to iron is increased to a certain proportion, as in plumbago, the iron loses the property of being acted on by the magnet,' The addition of a certain portion of sulphur likewise renders iron susceptible of becoming a permanent magnet. The sulphur may amount to 46 per cent, without destroying this pro- perty ; but when it is increased to 52 per cent, the magnetism va- nishes completely. Iron may be made permanendy magnetic also when united to phosphorous; but whether the magnetism disap- pears when the proportion of phosphorus is increased, has not been ascertained. Thus it appears that pure iron is not susceptible of permanent magnetism. United to a portion of carbon, it forms a compound more or less brittle, soluble in muriatic acid, and susceptible of magnetic impregnation. Saturated with carbon, it becomes brit- tle, insoluble in muriatic acid, and destitute of magnetic properties. Iron, united to a portion of sulphur, forms a brittle compound, soluble in muriatic acid, and susceptible of magnetic impregnation. Saturated with sulphur, the compound becomes brittle, insoluble in muriatic acid, and destitute of magnetic properties. Iron, united to phosphorus, is brittle, and susceptible of magnetic impregnation in a great degree, and in all probability, by saturation, would lose its magnetic properties altogether. For these facts, which are of the utmost importance, we are in- debted to Mr. Hatchett, who was led to the discovery of them by his experiments on magnetic pyrites. " Speaking generally of the carburets, sulphurets, and phosphurets of iron, I have no doubt," • Hatchett, Phil. Trane. 1804. Chap. III.] IRON. 319 says this sagacious philosopher, " but that, by accurate experi- ments, we shall find that a certain proportion of the ingredients of each constitutes a maximum in the magnetical power of these three bodies. When this maximum has been ascertained, it would be proper to compare the relative magnetical power of steel (which hitherto has alone been employed to form artificial magnets) with that of sulphuret and phosphuret of iron; each being first ex- amined in the form of a single mass or bar of equal weight, and afterwards in the state of compound magnets, formed like the large horse-shoe magnets, by the separate arrangement of an equal num- ber of bars of the same substance in a box of brass. " The effects of the above compound magnets should then be tried against others, composed of bars of the three different sub- stances, various in number, and in the mode of arrangement; and lastly, it would be interesting to make a series of experiments on chemical compounds, formed by uniting different proportions of carbon, sulphur, and phosphorus, with one and the same mass of iron. These quadruple compounds, which, according to the mo- dern chemical nomenclature, may be called carburo-sulphuro phos- purets, or phosphuro-sulphuro carburets, &c. of iron, are as yet un- known as to their chemical properties, and may also, by the inves- tigation of their magnetical properties, afford some curious results. At any rate, an unexplored field of extensive research appears to be opened, which possibly may furnish important additions to the history of magnetism; a branch of science which of late years has been but little augmented, and which, amidst the present rapid progress of human knowledge, remains immersed in considerable obscurity." XL Iron and arsenic may be alloyed by fusion. The alloy is ' white and brittle, and may be crystallized. It is found native, and is known among mineralogists by the name of mispickel. Iron is capable of combining with more than its own weight of arsenic* XII. We are not acquainted with the combination of iron and tellurium. It combines with potassium and sodium; but its alloys with these metals have not-been particularly observed. We know nothing of its combinations with the metals of the alakaline earths and earths proper. At present it would be difficult to determine the order of the affinities of the simple combustibles for oxygen. Iron has the pro- perty, when assisted by heat, of depriving potassium and sodium of their oxygen. But potassium and sodium are equally capable of reducing the oxides of iron to the metallic state. Again, iron at a red heat rapidly decomposes water and separates the hydrogen gas. Here it would seem that iron has a stronger affinity for oxygen than hydrogen gas. But, on the other hand, when oxide of iron is surrounded with hydrogen gas, and heated, it is rapidly converted • Bergman, ii. 281. 320 SIMPLE COMBUSTIBLES. S B00K *• £DIVISIO> '-. into the metallic state while abundance of water is formed. Here the affinities of the different bases for oxygen seem to have alter- nately the preponderance Various other examples might easily be given. Thev show sufficiently that our present opinions respect- ing affinity are bv no means accurate. The order of the affinities of the simple supporters for iron is as follows : Iron—Chlorine- Oxygen*—Iodine. SECTION II. OF NICKEL. There is found in different parts of Germany a heavy mineral of a reddish brown colour, not unlike copper. When exposed to the air, it gradually loses its lustre, becomes at first brownish, and is at last covered with green spots. It was at first taken for an ore of copper; but as none of that metal can be extracted from it, the miners give it the name of Kupfernickel, or " false copper." Hierne, who may be considered as the father of the Swedish chemists, is the first person who mentions this mineral. He gives a description of it in a book published by him in 1694, on the art of detecting metals. It was generally considered by mineralogists as an ore of copper, till it was examined by the celebrated Cronstedt. He con- cluded from his experiments, which were published in the Stock- holm Transactions for 1751 and 1754, that it contained a new me- tal, to which he gave the name of nickel. This opinion was embraced by all the Swedes, and indeed by the greater number of chemical philosophers. Some, however, par- ticularly Sage and Monnet, affirmed that it contained no new me- tal, but merely a compound of various known metals, which could be separated from each other by the usual processes. These asser- tions induced Bergman to undertake a very laborious course of ex- periments, in order, if possible, to obtain nickel in a state of puri- tv ; for Cronstedt had not been able to separate a quantity of arse- nic, cobalt, and iron, which adhered to it with much obstinacy. These experiments, which were published in 1775,] fully confirm- ed the conclusions of Cronstedt. Bergman has shown that nickel possesses peculiar properties; and that it can neither be reduced to anv other metal, nor formed artificially by any combination of metals. It must therefore be considered as a peculiar metal. It may possibly be a compound, and so may likewise many other me- tals ; but we must admit every thing to be a peculiar body which * It would appear from Davy's experiments that the peroxide of iron retains oxygen more obstinatelv than the protoxide. For the red oxide was not decomposed by chlorine, though the black oxide was. See Phil.Trans. 1811, p. 25. ! Bergman, ii. 231. Chap. III.] NICKEL. 321 has peculiar properties, and we must admit every body to be sim- ple till some proof be actually produced that it is a compound; otherwise we forsake the road of science, and get into the regions of fancy and romance. Nickel is rather a scarce mineral, and it occurs always in com- bination with several other metals, from which it is exceedingly dif- ficult to separate it. These metals disguise its properties, and ac- count in some measure for the hesitation with which it was admit- ted as a peculiar metal. Since the great improvements that have been introduced into the art of analysing minerals, chemists of emi- nence have bestowed much pains upon this metal, and a variety of processes have been published for procuring it in a state of purity. For the brittle metal that is sold under the name of nickel contains abundance of iron and arsenic, and some cobalt, copper, and bis- muth. The first set of experiments, after those of Bergman, made expressly to purify nickel, are those of the School of Mines of Pa- ris, of which Fourcroy has published an abstract.* Their method was tedious and incomplete. Since the publication of these expe- riments, no less than eight other processes have been proposed by chemists, all of them ingenious, and attended each with peculiar advantages and inconveniences.! In the year 1804 an elaborate paper on nickel was published by Richter,! and in the year 1811 an excellent set of experiments on this metal and its combinations was published by Tupputi.§ About the same time an elaborate analysis of its oxides was made by Rothoff.|| Tupputi's mode of obtaining pure nickel is as follows. The im- pure metallic substance to be met with in commerce called speiss, is to be reduced to powder and digested in 2 2 times its weight of nitric acid diluted with an equal weight of water. When the ac- tion is at an end, filter the solution in order to get rid of a quantity of arsenious acid which exists in it in the state of a powder. Eva- porate the liquid to ith of its bulk; more crystals of arsenious acid will fall; let them be separated by a filter. Then into the liquid, still hot, drop by degrees a solution of carbonate of soda till the precipitate which falls begins to assume a green colour.*f| Then filter the liquid, dilute it with a good deal of water, and add an excess of acid, and pass through it a current of sulphureted hy- drogen gas in order to precipitate the whole of the arsenic. It falls in the state of yellow flocks. When it has been all thrown down, filter again and add a sufficient quantity of potash to precipitate * Discours Preliminaire, p. 117. ! Mr. Philips published a process in Phil. Mag. xvi. 312; Proust another in Jour, de Phys. Ivii. 169; Thenard another, in Ann.de Chim. I. 117; Bucholz another, in Gehlen's Jour. ii. 282, and iii. 201; Richter a fifth, Ibid, iii. 244; and Proust a sixth, Ann. de Chim. Ix. 275. \ Gehlen's Journal, iii. 244. § Ann. de Chim. Ixxviii. 133. || Bcrzelius's Liirboki kemien, ii. 311. 1 There first falls arseniate of iron in yellowish-white flocks, then arseniate of cobalt la rose-red flocks mixed with arseniate of copper and some arseniate of manganese. Vol. I. S s 322 SIMPLE COMBUSTIBLES. $ BOOK 1. £ DIVISION 2. the oxide of nickel which now remains combined with nitric acid. Mix this oxide with 3 per cent, of resin, make it into a paste with oil, and expose it to the most violent heat of a forge in a charcoal crucible. A metallic button of pure nickel will be obtained. But a much shorter process may be employed to procure nickel in a state of very considerable purity. Dissolve speiss in sulphuric acid by adding the quantity of nitric acid necessary to produce the solution. Concentrate this solution and set it aside. Fine green crystals of sulphate of nickel make their appearance. Proceed in this manner till you have obtained a sufficient quantity of crystals of sulphate of nickel. Dissolve these crystals in water and crys- tallize them a second time. If they be now dissolved in water, and decomposed by an alkali, pure oxide of nickel will fall. It may be reduced as above to the metallic state. I. Nickel, when pure, is of a fine white colour resembling silver; and, like that metal, it leaves a white trace when rubbed upon the polished surface of a hard stone.* It is rather softer than iron. Its specific gravity, according to Richter, after being melted, is 8*279; but when hammered, it be- comes 8-666.! But Tourte found the specific gravity of Richter's nickel 8-402, and when strongly hammered it was as high as 8*932.! According to Tuputi, when fused it is 8*380, and after being ham- mered it is as high as 8*820.§ It is malleable both cold and hot; and may without difficulty be hammered out into plates not exceeding the jfo part of an inch in thickness.j) It is attracted by the magnet. Like steel, it may be converted into a magnet; and in that state points to the north when freely suspended precisely as a common magnetic needle.^f According to Lampadius, its magnetic energy is to that of iron as 35 to 55.** It requires for fusion a temperature at least equal to 160° Wedge- wood-!! It has not hitherto been crystallized. It is not altered by exposure to the air, nor by keeping it under water.!! From the experiments of Tuputi, it appears that preparations of nickel possess poisonous qualities.§§ II. Nickel, when moderately heated, is soon tarnished; and from the observations of Tourte, it appears that it runs through nearly the same changes of colour that steel does when tempered. It becomes first light-yellow, then deep-yellow, light violet-blue, • Fourcroy, Discours Preliminaire, p. 117. ] Gehlen's Jour. iii. 352. $ Gehlen's Journal, fiir die Chemie, Physick und Mineralogie, vii. 444. From Lam- padius'experiments it appears that this nickel contained cobalt and arsenic. Tromsdorf's Journal, xvi. 49, as quoted by Tuputi. § Ann. de Chim. lxxviii. 140. II Richter, Gehlen's Jour. iii. 252. ♦J Bergman, Klaproth, Fourcroy, Richter, he.—Mr. Chenevix had announced a method of procuring nickel which was not magnetic; but he afterwards ascertained, that it owed this peculiarity to the presence of arsenic. ** Annals of Philosophy, v. 62. !! Bergman, ii. 269. According to Richter, its melting point is as high as tbat of manga- nese. Tuputi thinks it rather lower. +* Richter, Ibid. §§ Ann. de Chim. lxxx. 188. Chap. III.] NICKEL. 323 and last of all greyish-blue.* It is capable of combining with two proportions of oxygen, and of forming two oxides. The protoxide is blackish ash grey, the peroxide black. 1. By exposure to heat, however long continued, Tuputi was not able to oxidize this metal completely. The protoxide is easily pro- cured by dissolving nickel in nitric acid, throwing it down by pot- ash, and after washing the precipitate, drying it and heating it to redness. We have four sets of experiments to determine the quantity of oxgen in this oxide. The following table exhibits the results. Proust! - 100 nickel + 26 oxygen Richter!, - 100 - +28*2 Tuputi§ - 100 - + 27 Rothoff|| - 100-4- 27-255 Klaprothff 100 - + 32*5 To determine which of these numbers is most correct, let us ex- amine the composition of sulphate of nickel. This salt, according to the experiments of Tuputi, is composed of Sulphuric acid - 100 - 5 Protoxide of nickel 87*26 - 4*362 We see that according to this analysis the equivalent number for protoxide of nickel is 4*362. We may consider it without sensible error as 4*375. On this supposition (considering it as a compound of 1 atom metal + 1 atom oxygen) it will consist of—Nickel 100 —Oxygen 29*63. This agrees best with the determination of Richter, which there- fore appears to be nearest the truth. The weight of an atom of nickel is 3*375. This oxide is tasteless, soluble in die acids, and forms with them a grass-green solution. It is soluble also in ammonia, and the so- lution, according to Richter, is pale blue. 2. The peroxide of nickel was first examined by Thenard. It may be formed by causing a current of chlorine gas to pass through water holding protoxide of nickel suspended in it; a portion is dissolved, and the rest acquires a black colour. This oxide is so- luble in ammonia as well as the last; but the solution is accompa- nied with effervescence, owing to the decomposition of a part of the ammonia by the combination of its hydrogen with part of the oxygen of the oxide. A similar effervescence accompanies its so- lution in acids, occasioned by the separation of a portion of its oxygen in the state of gas.** From the experiments of Rothoff, it appears that this oxide contains lh times as much oxygen as the protoxide. Hence it is a compound of—Nickel 100—Oxygen A.A..A A C • Gehlen's Journal, fur die Chemie, Physik, 8sc. vii. 443. f Ann- <*e Chim. Ix. 272. t Gehlen's Journal, iii. 258. § Ann de Chim. lxxviii. 144. II Berzelius Larbok i Kemien ii. 311, *f Ann. de Chim. lxxxv. 68. '* Thenard, Ann. de Chim. 1.125. 324 SIMPLE COMBUSTIBLES. S BOOK I. £ DIVISION 2. To get rid of the anomaly of the half atom we must consider it as a compound of 2 atoms of nickel and 3 atoms of oxygen. Hence its weight will be 9*75. From Thenard's experiments it does not appear to be capable of combining with acids without giving out its excess of oxygen, and being reduced to the state of a protoxide. III. Nickel does not burn when introduced into chlorine gas. Its oxide is not altered though heated to redness in that gas.* But the chloride of nickel may be formed by leaving nickel in contact with chlorine gas, or by subliming dry muriate of nickel. It is an olive-coloured substance, the properties of which have not been examined. IV. The iodide of nickel is still unknown. , V. We are not acquainted with the compound of nickel and fluorine. It does not appear to unite with azote or hydrogen. VI. According to Tuputi nickel always contains a portion of carbon when prepared bv the process described at the commence- ment of this section. When dissolved in acids it leaves this car- bon in the state of charcoal. VII. We are not acquainted with any combination of nickel with boron or silicon. VIII. Phosphuret of nickel may be formed either by fusing nickel along with phosphoric glass, or by dropping phosphorus into it while red-hot. It is of a white colour; and, when broke, it ex- hibits the appearance of very slender prisms collected together. When heated, the phosphorus burns, and the metal is oxidated. It is composed of 83 parts of nickel and 17 of phosphorus-! The nickel, however, on which this experiment was made, was not pure. According to Lampadius it is composed of 100 nickel + 15 phos- phorus, or 3 atoms nickel 4- 1 atom phosphorus. It is tin-white, ac- cording to him, and has the metallic lustre. It is moderately hard and very brittle. Its fracture, is foliated, and it is not attracted by the magnet.! IX. Cronstedt found that sulphuret of nickel may be easily form- ed by fusion. The sulphuret which he obtained was yellow and hard, with small sparkling facets; but the nickel which he employ- ed was impure. Lampadius describes it as yellowish-white, or similar in appear- ance to copper nickel. It is not attracted by the magnet. It was composed of 100 nickel + 10 sulphur.§ This would be a com- pound of 6 atoms nickel and 1 atom sulphur. But no doubt it'was incomplete. X. Nickel combines readily with arsenic, and indeed is seldom found without being more or less contaminated by that metal. The compound has a shade of red, considerable hardness, and a specific gravity considerably under the mean. It is not magnetic. Arse- • Davy, Phil. Trans. 1811, p. 25. ] Pelletier, Ann. de Chim. xiii. 13$. * Annals of Philosophy, iv. 63. § Ibid. Chap. III.] COBALT. 325 nic possesses the curious property of destroying the magnetic virtue of iron, and all other metals susceptible of that virtue. XI. We are ignorant of the alloys which nickel is capable of forming with tellurium, the metallic bases of the fixed alkalies, al- kaline earths and earths proper. It combines readily with iron; but the properties of the alloy have not been examined. Accord- ing to Lampadius an alloy of 5 parts nickel and 2 parts iron is mo, derately hard, quite malleable, and has the colour of steel.* SECTION III. OF COBALT. I. A mineral called cobalt,] of a grey colour, and very heavy, has been used in different parts of Europe, since the 15th century, to tinge glass of a blue colour. But the nature of this mineral was altogether unknown till it was examined by Brandt in 1733. This celebrated Swedish chemist obtained from it a new metal, to which he gave the name of cobalt.] Lehmann published a very full ac- count of everything relating to this metal in 1761.$ Bergman confirmed and extended the discovery of Brandt in different dis- sertations published in the year 1780.|| Scarcely any farther addi- tion was made to our knowledge of this metal till 1798, when a paper on it was published by Mr. Tassaert.'fl In the year 1800, a new set of experiments were made upon it by the School of Mines at Paris, in order to procure it perfectly pure, and to ascertain its pro- perties when in that state.** In 1802, a new series of trials was published by Thenard, which throw considerable light on its com- * Annals of Philosophy, v. 62. ! The word cobalt seems to be derived from cobalus, which was the name of a spirit that. according to the superstitious notions of the times, haunted mines, destroyed the labours of the miners, and often gave them a great deal of unnecessary trouble. The miners probably gave this name to the mineral out of joke, because it thwarted them as much as the suppos- ed spirit, by exciting false hopes, and rendering their labour often fruitless; for as it was not known at first to what use the mineral could be applied, it was thrown aside as useless. It was once customary in Germany to introduce into the church-service a prayer that God would preserve miners and their works from kobalts and spirits. See Beckmau's History of Inventions, ii. 362. Mathesiifs, in his tenth sermon, where he speaks of cadmia fossilis (probably cobalt ore), says, " Ye miners call it cobolt; the Germans call the black devil and the old devil's whores and hags, old and black kobel, which by their witchcraft do injury to people and to their cattle." Lehmann, Paw, Oelaval, and several other philosophers, have supposed that smalt (oxide of cobalt melted with glass and pounded) was known to the ancients, and used to tinge the beautiful blue glass still visible in some of their works; but we learn from Gmelin, who ana- lysed some of these pieces of glass, that they owe their blue colour, not to the presence of co- balt, but of iron. According to Lehmann, cobalt ore was first used to tinge glass blue by Christopher Schu- rer, a glassmaker at Platten, about the year 1540. + Acta Upsal. 1733 and 1742. § Cadmialogia, oder Geschichte des Farben-Kobolds, || Opusc. ii. 444, 501, and iv. 371. 1 Ann. de Chim. xxviii. 101. '• Fourcroy, Discours Preliminaire, p. 114. 326 SIMPLE COMBUSTIBLES. $ BOOK I. I DIVISION 2. binations with oxygen.* And in 1806, Mr. Proust published a set of experiments upon the same subject.! Considerable attention has been lately paid to the purification of this metal; but hitherto no one seems to have been fortunate enough to hit upon a method altogether free from objections.! 1. Cobalt is of a grey colour with a shade of red, and by no means brilliant. Its texture varies according to the heat employ- ed in fusing it. Sometimes it is composed of plates, sometimes of grains, and sometimes of small fibres adhering to each other.§ It has scarcely any taste or smell. 2. It is rather soft. Its specific gravity according to Tassaert, is 8*5384.|) According to Lampadius it is 8-7.JJ 3. It is brittle, and easily reduced to powder; but if we believe Leonhardi, it is somewhat malleable when red-hot. Its tenacity is unknown. 4. When heated to the temperature of 130° Wedgewood, it melts; but no heat which we can produce is sufficient to cause it to evaporate. When cooled slowly in a crucible, if the vessel be in- clined the moment the surface of the metal congeals, it may be ob- tained crystallized in irregular prisms.** 5. Like iron,- it is attracted by the magnet; and, from the ex- periments of Wenzel, it appears that it may be converted into a magnet precisely similar in its properties to the common magnetic needle. II. When exposed to the air it undergoes no change; neither is it altered when kept under water. Its affinity for oxygen is not sufficiently strong to occasion a decomposition of the water. When kept red hot in an open vessel, it gradually imbibes oxy- gen, and is converted into a powder, at first blue, but which gradu- ally becomes deeper and deeper, till at last it becomes black, or rather of so deep a blue that it appears to the eye black. If the heat be very violent, the cobalt takes fire and burns with a red flame. Cobalt combines with two proportions of oxygen and forms two oxides. The protoxide has a blue colour, but the peroxide is black. 1. The protoxide of cobalt may be obtained by dissolving cobalt in nitric acid, and precipitating the cobalt from the solution by means of potash. The precipitate has a blue colour, but when dried in the open air it gradually becomes black. This black pow- der is to be kept for half an hour in that degree of heat known to manufacturers of iron utensils by the name of cherry-red. This heat expels the oxygen which it had absorbed in drying, and con- » Ann. de Chim. xiii. 210. ] Ibid. Ix. 260. * See Richter, Gehlen's Jour. ii. 53; Bucholz, ibid. Hi. 201; Philips, PhiL Mag. xvi. 312. § L'Ecole des Mines. II Ann. de Chim. xxviii. 99. •f As quoted by Berzelius; Larboki Kemien, ii. 295. Bergman and the V'rench che- mists, and Hatchett, state the specific gravity as 7-7; but their specimens wer*- obviously Impure. ** Fourcroy, v. 137. Chap. III.] COBALT. * 327 verts it into a fine blue colour. This oxide dissolves in acids with- out effervesence. The solution of it in muriatic acid, if concen- trated, is green; but if diluted with water, it is red. Its solution in sulphuric and nitric acids is always of a red colour.* This oxide has been analysed by Proust and Rothoff. The following are the results which they obtained: Proust! - 100 cobalt 4- 19*8 oxygen Rothoff! 100 - + 27*3 From the experiments of Rothoff it appears that when the pe- roxide of cobalt is converted into the protoxide it gives out 9*7 of oxygen. Hence we see that the oxygen in the two oxides are as the numbers 2 to 3. This last analysis, which seems susceptible of considerable precision, would make the protoxide of cobalt a compound of Cobalt 100—Oxygen 27*36. From this it would appear that the weight of an atom of cobalt is 3-625; on this supposition (which must be very near the truth) the protoxide of cobalt is composed of Cobalt - - 3*625 - - 100 Oxygen 1 - - 27*58 2. When the protoxide of cobalt, newly precipitated from an acid, is dried by heating it in the open air, it assumes a flea-brown colour, which gradually deepens till at last it becomes black. This is the peroxide of cobalt. It dissolves with effervescence in mu- riatic acid, and a great quantity of chlorine gas is exhaled. From the experiments of Rothoff, combined with the preceding deter- mination of the composition of the protoxide, it follows, that the peroxide is composed of—Cobalt 100—-Oxygen 36*77. To reconcile this proportion with the atomic theory, we must consider this oxide as a compound of 2 atoms cobalt and 3 atoms oxygen. On this supposition its weight will be 10*250. III. Cobalt burns when gently heated in chlorine gas. The compound formed is a chloride which has not been examined. IV. The iodide of cobalt has not been examined. Neither are we acquainted with its action on fluorine. It does not appear capa- ble of combining with azote or hydrogen. We know no com- pound which it forms with carbon, boron, or silicon. V. Phosphuret of cobalt may be formed by heating the metal red hot, and then gradually dropping in small bits of phosphorus. It contains about -^th of phosphorus. It is white and brittle; and when exposed to the air, soon loses its metallic lustre. The phos- phorus is separated by heat, and the cobalt is at the same time oxi- dated. This phosphuret is much more fusible than pure cobalt.^ VI. Cobalt cannot be combined with sulphur by fusion. But sulphuret of cobalt may be formed by melting the metal along with sulphur previously combined with potash. It has a yellowish • Ann. de Chim. xiii. 21S. ] Ibid. lx. 267. t Annals of Philosophy, iii. 356. § Pelletier, Ann. de Chim. xiii. 134. 328 SIMPLE COMBUSTIBLES. $ BOOK I. £ DIVISION S. white colour, displays the rudiments of crystals, and can scarcely be decomposed by heat. The sulphuret of cobalt, according to Proust, may be formed by heating together the oxide of cobalt and sulphur. According to his experiments* it is composed of—Cobalt 100—Sulphur 39-86.— But he does not place much confidence in the accuracy of his ex- periments. If the sulphuret of cobalt be a compound of 1 atom cobalt + 1 atom sulphur, its constituents will be Cobalt - - 3*625 - - 100 Sulphur 2- - - 55*16 VII. We are not acquainted with the alloys which cobalt forms with arsenic, tellurium, the metallic bases of the fixed alkalies, of the alkaline earths, and earths proper. VIII. The alloy of iron and cobalt is very hard, and not easily broken. Cobalt generally contains some iron, from which it is with great difficulty separated. SECTION IV. OF MANGANESE. The dark grey or brown mineral called manganese, in Latin magnesia (according to Boyle from its resemblance to the magnet,) has been long known and used in the manufacture of glass. A mine of it was discovered in England by Boyle. A few experiments were made upon this mineral by Glauber in 1656,! and by Waiz in 1705 ;! but chemists in general seem to have paid but very little attention to it. The greater number of mineralogists, though much puzzled what to make of it, agreed in placing it among iron ores : but Pott, who published the first chemical examination of this mineral in 1740, having ascertained that it often contains scarcely any iron, Cronstedt, in his System of Mineralogy, which appeared in 1758, assigned it a place of its own, on the supposition that it consisted chiefly of a peculiar earth. Rinman examined it anew in 1765 ;§ and in the year 1770 Kaim published at Vienna a set of experiments, in order to prove that a peculiar metal might be extracted from it.|| The same idea had struck Bergman about the same time, and induced him to request of Scheele, in 1771, to undertake an examination of manganese. Scheele's dissertation on it, which appeared in 1774, is a master-piece of analysis, and contains some of the most important discoveries of modern chemis- try. Bergman himself published a dissertation on it the same year; in which he demonstrates, that the mineral, then called manganese, is a metallic oxide.^f He accordingly made several * Ann. de Chim. ix. 272. ] Prosperilas Germania. * Weigleb's Geschichte, i. 127. § Mem. Stockholm, 1765, p. 235. I De Metallis dubiis, p. 48. *J Opusc. ii. 201. Chap. III.] MANGANESE. 329 attempts to reduce it, but without success; the whole mass either assuming the form of scoriae, or yielding only small separate glo- bules attracted by the magnet. This difficulty of fusion led him to suspect, that the metal he was in ques^t of bore a strong analogy to platinum. In the mean time, Dr. Gahn, who was making experi- ments on the same mineral, actually succeeded in reducing it by the following process: He lined a crucible with charcoal powder mois- tened with water, put into it some of the mineral formed into a ball by means of oil, then filled up the crucible with charcoal pow- der, luted another crucible over it, and exposed the whole for about an hour to a very intense heat. At the bottom of the cruci- ble was found a metallic button, or rather a number of small me- tallic globules, equal in weight to one-third of the mineral employ- ed.* It is easy to see by what means this reduction was accom- plished. The charcoal attracted the oxygen from the oxide, and the metal remained behind. The metal obtained, which is called manganese, was farther examined by Ilseman in 1782, Hielm in 1785, and Bindheim in 1789. An elaborate and extensive set of experiments on this metal and its combinations was published by Dr. John in 1807.! 1. Manganese, when pure, is of a greyish-white colour, like cast iron, and has a good deal of brilliancy. Its texture is granular. It has neither taste nor smell. It is softer than cast iron and may be filed. Its specific gravity is 8*013.! 2. It is very brittle; of course it can neither be hammered nor drawn out into wire. Its tenacity is unknown. Its fracture is un- even and its texture fine granular. 3. It requires, according to Morveau, the temperature of 160" Wedgewood to melt it; it is therefore somewhat less fusible than iron. 4. When pure it is not attracted by the magnet, even when in powder; but a very small quantity of iron gives it the magnetic property. II. Manganese, when exposed to the air, attracts oxygen with considerable rapidity. It soon loses its lustre, and becomes grey, violet, brown, and at last black. These changes take place still more rapidly if the metal be heated in an open vessel. When thrown into water it decomposes that liquid with considerable ra- pidity. The hydrogen extricated has a smell of assafcetida, owing it is supposed to a small portion of the metal which it carries up with it. Three sets of experiments have been made to determine the oxides which this metal forms. According to John it forms three oxides, the green, the brown, and the black. The green is obtained by dissolving the metal in acids and precipitating it by an alkali, or by leaving it a sufficient time in water. The black or peroxide • Bergman, H. 211. ! Gehlen's Journal fur die Chemie und Physik, iii. 452. + John, Gehlen's Journal, iii. 460. Vol. I. T t 330 SIMPLE COMBUSTIBLES. $ ROOK I £ DIVISION '2. is found native in abundance. The brown is obtained by exposing the black for some time to a red heat. According to him these oxides are composed as follows : Green - - 100 manganese -f- 15 oxygen Brown 100 - 4-25 Black 100 - +40 Berzelius, partly from his own experiments and partly from those of John, reckons five oxides. The first is grey and is obtained by keeping metallic manganese for some time in a phial with a cork stopper. The second is green and is obtained by keeping manga- nese in water. The third by dissolving manganese in acids; the fourth by calcining the nitrate of manganese; while the fifth or pe- roxide exists in nature.* According to him these oxides are com- posed as follows : 1 - 100 metal + 7-0266 4 - 100 metal + 42*16 2-100 - + 14-0533 5 - 100 - + 56*213 3-100 - + 28*1070 Sir H. Davy obtained two oxides of manganese,! the olive and the brown, which he found composed as follows : Olive - - 100 metal + 26*58 Brown - - 100 - + 39*82 Dr. John acknowledges that his analyses of these oxides is by no means to be depended on. Berzelius's statements are rather theoretical than experimental. He even doubts of the existence of his first oxide, the only one he examined; and he has advanced no proof that there exists any difference between his second and third oxide. The existence of the green oxide of John cannot be doubt- ed. It constitutes the bases of the different salts of manganese. The existence of the black oxide is equally certain, as it occurs na- tive in such abundance. When the black oxide is heated to redness a brown powder remains, which constitutes the intermediate oxide of John. But when we attempt to dissolve this powder in acids it is immediately separated into the green and the black oxides of manganese. Hence it would seem to be merely a mixture or com- bination of these two oxides. At present therefore we have evi- dence of the existence of only two oxides of manganese; the pro- toxide which combines with acids and forms the common salts of manganese, and the peroxide which exists native. 1. To determine the composition of the protoxide the best way seems to be to have recourse to the salts into which it enters. Ac- cording to Dr. John, sulphate of manganese is composed of * Sulphuric acid - - 100 - 5 Protoxide - - - 92-06 4*6 Carbonate of manganese according to the same chemist is com- posed of * Ann. de Chim. lxxxiii. 169. f Elements of Chemical Philosophy, p. 367. Chap. III.] MANGANESE. 331 Carbonic acid - - 100 - 2*75 Protoxide - - - 163*46 4*495 By the first of these salts we see that the equivalent number for protoxide of manganese is 4*6; by the second it is 4*495. We may therefore take 4*5 as the true equivalent without falling into any great error. Hence it is evident that protoxide of manganese is composed of Manganese - 3*5 - 100 Oxygen 1 - 28*75 This very nearly coincides with Berzelius' third oxide. And in reality his third oxide is the protoxide of manganese. The protoxide of manganese is an olive green powder, which when exposed to the air' speedily attracts oxygen and becomes black. When combined with carbonic acid it constitutes a white powder. 2. The peroxide of manganese is found native in abundance par- ticularly in Devonshire near Exeter. When pure it has a radiated texture and a dark steel-grey colour, with considerable lustre and beauty. It is brittle and very soft, soiling the fingers. Its specific gravity is about 4*7563. When heated to redness it gives out ra- ther more than the tenth part of its weight of oxygen gas, and is converted into a brown powder destitute of metallic lustre. This oxide has never been accurately analysed. Berzelius states its com- position from theoretical considerations to be—Manganese 100— Oxygen 56-213. If we suppose the quantity of oxygen which it contains to be exactly double the oxygen in the protoxide, which from the facts respecting it already known there is every reason to consider as its composition, then it must be a compound of—Man- ganese 100—Oxygen 57-5. And the weight of an atom of it will be 5-5. III. As far as is known at present manganese combines with chlorine in only one proportion. The chloride of manganese was first described by Dr. John Davy. He obtained it by dissolving the black oxide of manganese in muriatic acid, evaporating the so- lution to dryness and exposing the white salt that remains to a red heat in a glass tube with a very narrow orifice. It is a substance of a pure delicate light pink colour and of a lamellar texture, con- sisting of broad thin plates. It melts at a red heat without altera- tion in close vessels; but in the open air it is decomposed, muriatic acid being given out and oxide of manganese remaining. When left in an open vessel it deliquesces and is converted into muriate of manganese. According to Dr. John Davy's experiments it is composed of Chlorine .54-100 - 4*5 Manganese - 46 - 85*18 - 3*83 This does not correspond exactly with the weight of an atom of manganese as determined from Dr. John's analyses of the sulphate 332 SIMPLE COMBUSTIBLES. C BOOK». £ mvisiokS. and carbonate of manganese. I should not be surprised if the real weight of an atom of manganese were 3-75. But this must be left for the decision of future experiments. IV. No experiments have been hitherto made on the combina- tions of manganese and iodine. V. We are ignorant of the action of fluorine on manganese. It does not combine with azote nor hydrogen. VI. It appears capable of combining with carbon. This com- pound is formed occasionally in iron founderies. And in this country it is known by the name of Keesh. It occurs occasionally in small cavities in the mass of cast iron, and seems to be th-. re- sult of crystallizing during the cooling of the mass. It is compo- sed of thin scales having the lustre and appearance of steel; but very brittle. It was considered as plumbago; but Dr. Wollaston examined it and found that acids have the property of separating ' from it a little iron. The residuum he found a compound of car- bon and manganese. It is therefore a carburet of that metal. VII. We do not know any comp und of manganese with boron or silicon. VIII. Phosphorus may be combined with manganese by melting together equal parts of the metal and of phosphoric glass ; or by dropping phosphorus upon red hot manganese. The phosphuret of manganese is of a white colour, brittle, granulated, disposed to crystallize, not altered by exposure to the air, and more fusible than manganese. When heated the phosphorus burns, and the metal is oxidized.* IX. Bergman did not succeed in his attempt to combine manga- nese with sulphur; but he formed a sulphureted oxide of manga- nese, by combining eight parts of the black oxide with three parts of sulphur. It is of a green colour, and gives out sulphureted hy- drogen gas when acted on by acids.j It cannot be doubted, how- ever, that sulphur is capable of combining with manganese; for Proust has found native sulphuret of manganese in that ore of tel- lurium which is known by the name of gold ore of Nagyag.! Vauquelin likewise succeeded in combining sulphur with man- ganese, by heating them together. According to his experiments, the sulphuret of manganese is composed of Manganese - 74-5 - 100 Sulphur - 25-5 - 34-22 100*0$ From this analysis it is reasonable to conclude, that sulphuret of manganese is composed of 2 atoms manganese and 1 atom sulphur. On this supposition its constituents are Manganese - 7 - 100 Sulphur - 2 - 28*57 * Pelletier, Ann. de Chim. xiii. 137. ! Bergman, ii. 221. * Jour, de Phys. Ivi. I. h Ann. des Mus. d'Hist. Nat 159. Chap. III.] CERIUM. 333 X. We are not acquainted with the alloys which manganese is capable of forming with arsenic, tellurium, the metallic bases of the fixed alkalies, alkaline earths, and earths proper. XI. It combines readily with iron; indeed it has scarcely ever been found quite free from some mixture of that metal. Manga- nese gives iron a white colour, and renders it brittle. From Berzelius' experiments we learn, that manganese enters as a constituent into cast iron. XII. We do not know the alloys of manganese with nickel and cobalt. SECTION V. OF CERIUM. In the year 1750 there was discovered, in the copper mine of Bastnas at Ridderhytta, in Westmannland, in Sweden, a mine- ral which, from its great weight, was for some time confounded with tungsten. This mineral is opaque, of a flesh colour, with va- rious shades of intensity, and very rarely yellow. Its streak is greyish white, and when pounded it becomes reddish grey. It is compact, with a fine splintery fracture, and fragments of no deter- minate form; moderately hard; its specific gravity, according to Cronstedt, 4*988,* according to Klaproth 4-660,! according to Messrs. Hisinger and Berzelius, from 4-489 to'4-6194 This min- eral was first examined by M. D'Elhuyar: the result of whose analysis was published by Bergman in 1784.§ It ascertained that the mineral in question contained no tungsten. No farther attention was paid to this mineral till Klaproth pub- lished an analysis of it in 1804, under the name of Ochroits,]] and announced that it contained a new earth, to which he gave the name of ochroita. He sent a specimen of this new product to Vau- quelin, who made a few experiments on it, but hesitated whether to consider ochroita as an earth or a metallic oxide.^\ Meanwhile the mineral had undergone a still more complete examination in Swe- den by Hisinger and Berzelius, who gave it the name of cerit; de- tected in it a peculiar substance, which they considered as a metallic oxide, and to which they gave the name of cerium, from the planet Ceres, lately discovered by Piazzi.** But the attempts of these chemists to reduce the supposed oxide to the metallic state were unsuccessful. Nor were the subsequent trials of Gahn, to reduce it by violent heat along with charcoal, or to alloy it with other metals, attended with greater success-!! Vauquelin re-examined • Gehlen's Jour. ii. 305. f Ibid. * Ibid. ii. 398. § Opusc. vi. 108. || Gehlen's Jour. ii. 203. *J Ann. de Chim. 1. 140. ** Gehlen's Jour. ii. 297. !! Gehlen's Jour. iii. 217. 334 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. it more lately; but his attempts have been only partially success- ful.* They demonstrate, however, that the substance in question is a metal; though from its refractory nature, and its volatility, only minute globules of it were obtained. In 1814 a new set of experiments on it were published by Lau- gier.! He appears to have reduced it to the metallic state, but, instead of the pure metal, obtained only a carburet. Hisinger had previously endeavoured to determine the composition of its oxides.! To obtain the metal, the combination of oxide of cerium with tartaric acid was mixed with some lamp-black and oil, and expo- sed to the violent heat of a forge in a crucible lined with charcoal, and inclosed in another filled with sand. Only a small metallic button was obtained, not exceeding the fiftieth part of the oxide of cerium exposed to heat. It was white, brittle, dissolved with great difficulty in nitro-muriatic acid, and proved a mixture of iron and cerium. Another attempt to obtain the metal by heating 'its tartrate in a porcelain retort was not more successful. Most of it was dissipated, small globules only remaining, which proved as be- fore a mixture of cerium and iron.§ Laugier has shown that oxalic acid precipitates the whole of the oxide of cerium, and thus separates it from iron. He employed the oxide from the oxalate and exposed it to a strong heat made up into a paste with oil. He affirms that it is not volatile. But an experiment made in Mr. Children's laboratory demonstrates the contrary. Oxalate of cerium, which I had prepared, was exposed to the. heat of a furnace, urged by bellows in a crucible of charcoal: it was completely volatilized.|| I. To procure oxide of cerium in a state of purity, the Swedish chemists employed the following method: The mineral was re- duced to a fine powder, and digested in nitric acid till every thing soluble was taken up. The solution being decanted off is evaporat- ed to dryness, and the residue dissolved in water. Into this solu- tion ammonia is poured, till every thing precipitable by means of it is thrown down. This precipitate being well washed is re-dissolv- ed in nitric acid ; the acid is neutralized ; and then tartrate of pot- ash*^ is added to the solution. The precipitate which is separated being heated to redness, and well washed with vinegar, and dried, is pure oxide of cerium.** 1. When first procured it has a white colour, but when heated to redness it becomes reddish brown. 2. When made into a paste with oil, and heated in a charcoal crucible, it loses weight. When urged by a strong fire on char- coal, it does not melt, but continues in powder. It exhibited, however, brilliant particles, and dissolved in muriatic acid, disen- * Ann.de Chim. iv. 28. ] Ann. de Chim. Ixxxix. 317. t Memoirs of the Stockholm Academy for 1813, and Annals of Philosophy, iv. 355. § Ann. de Chim. liv. 59. I Annals of Philosophy, ii. 147. •J A salt to he described hereafter. *• Gehlen's Jour. ii. 401. C^hap. III.] CERIUM. 335 gaging at first sulphureted hydrogen, and afterwards pure hydro- gen gas.* II. According to the experiments of Vauquelin and Hisinger, this metal combines with 2 portions of oxygen. The protoxide is white, the peroxide reddish brown. Hisinger endeavoured to de- termine the proportion of oxygen which these oxides contain by a careful analysis of some of the salts which they form. The per- oxide contains lh times as much oxygen as the protoxide. The protoxide, according to him, is composed of—Cerium 100—Oxy- gen 17-41. The peroxide of—Cerium 100—Oxygen 26*115. From Hisinger's experiments it appears, that the equivalent number for protoxide of cerium is 6-75, and that it is a compound of 1 atom cerium + 1 atom oxygen. On this supposition it is composed of Cerium - 575 - - 100 Oxygen - 1 - 17*39 We must suppose peroxide of cerium a compound of 2 atoms cerium + 3 atoms oxygen. According to this supposition the weight of an atom of it will be 14*5. III. We are not acquainted with any combination of cerium with chlorine, fluorine, azote, or hydrogen. IV. From the experiments of Laugier, it appears capable of combining with carbon. He obtained the carburet by heating pro- toxide of cerium, made into a paste with oil, surrounded with char- coal in a retort. The carburet was a black matter which took fire spontaneously when exposed to the air.! V. When a stick of phosphorus was put into a solution of cerium in muriatic acid, and kept for some days on a stove, the bottom and sides of the vessel were covered with a white precipitate, and the phosphorus was covered with a hard brown crust, which was tenacious, and shone in the dark. When heated it took fire, and left a small quantity of oxide of cerium. But this experiment did not succeed when repeated-! VI. Hydro-sulphuret of ammonia throws down cerium at first ot a brown colour, but it becomes deep green as we continue to add the re-agent. The precipitate when dried becomes bright green. When heated it burns, and leaves the yellow oxide of cerium ; but the colour of the precipitate varies according to the state ol the cerium held in solution.^ VII. The attempt made by Gahn to unite cerium with lead did not succeed, and hitherto no other combination of it with metals has been tried, if we except the alloy of cerium and iron obtained by Vauquelin. • Hisinger and Berzelius, Gehlen's Jour. ii. 401. ! Ann de Chim. lxxxix. 317. i Hisinger and Berzelius, Ann. de Chim. liv. 46. § Hisinger and Berzelius, ibid. With Vauquelin the result was different. The pre- cipitate which be obtained was white, and contained no sulphureted hydrogen. 336 SIMPLE COMBUSTIBLES. $ BOOK 1 £ DIVISION - SECTION VI. OF URANIUM. I. There is a mineral found in the George Wagsfort mine at Johan-Georganstadt, in Saxony, partly in a pure or unmixed state, and parth" stratified with other kinds of stones and earths. The first variety is of a blackish colour, inclining to a dark iron grey, of a moderate splendor, a close texture, and when broken presents a somewhat even, and (in the smallest particles) a conchoidal surface. It is quite opaque, tolerably hard, and on being pounded yields a black powder. Its specific gravity is about 7-500. The second sort is distinguished by a finer black colour, with here and there a reddish cast: by a stronger lustre, not unlike that of pitcoal; by an inferior hardness ; and by a shade of green, which tinges its black colpur when it is reduted to powder.* This fossil was called pechblende; and mineralogists, misled by the name,! nac* taken it for an ore of zinc, till Werner, convinced from its texture, hardness, and specific gravity, that it was not a blende, placed it among the ores of iron. Afterwards he suspected that it contained timgsten; and this conjecture was seemingly con- firmed by the experiments of some German mineralogists, publish- ed in the Miners'Journal. But Klaproth examined this ore in 1789, and found that it consists chiefly of sulphur, combined with a peculiar metal, to which he gave the name of uranium.] Uranium was afterwards examined by Richter, and more lately an elaborate set of experiments has been published on it by Bu- cholz.§ To obtain uranium from its ore, the mineral is to be treated with nitric acid, which dissolves the metallic portion, and leaves the greater part of the foreign bodies. The solution usually contains iron, copper, and lime as well as uranium. By evaporating it to dryness, and exposing the dry mass to a moderately strong heat, the iron is rendered insoluble, while the other ingredients are taken up bv distilled water. Ammonia poured into this solution, and digested in it for some time, retains the copper, but throws down the uranium. The precipitate is to be well washed with ammonia till the liquid comes off colourless ; it is then to be dissolved in nitric acid, concentrated by evaporation, and set by to crystallize. The green coloured crystals that form are to be picked out, dried on blotting paper, dissolved in water, and the liquid again crys- tallized. By this means the whole of the lime, should any be pre- * Klaproth, Crell's Jour. Engl. Transl. i. 126. ! Blende is the name given to ores of zinc. + From Uranus (Oi/g*v«?), the name given by Mr. Bode to the new planet discovered by Herschel; which name the German astronomers have adopted. Mr. Klaproth called the metal at first uranite; but he afteiwards changed that name lor uranium. § Gehlen's Journal, b. 17. Chap. III.] UKANIUM. 337 sent, is gradually left behind, and the crystals consist at last of pure oxide of uranium, united to nitric acid. They are to be ex- posed to a red heat; a yellow powder remains, which is oxide of uranium. This powder is to be mixed with a small quantity of charcoal powder, and exposed to a violent heat. By this method it is reduced to the metallic state.* 1. Hitherto uranium has not been obtained in masses of any con- siderable size; the heat requisite to melt it being much greater than can be raised in furnaces. It follows, from the trials of Bu- cholz, that no flux is of any service in facilitating the fusion of this metal; that its refractoriness does not, as Richter suspected, proceed from the presence of iron; that charcoal powder, when mixed in a large proportion, obstructs the success; and that we accomplish our purpose best when the oxide is mixed with a por- tion of charcoal not exceeding ^th of the weight. This mixture is to be inclosed in a charcoal crucible, to exclude the air, and ex- posed to the strongest heat that can be raised. Klaproth, in a heat of 170° Wedgewood, obtained a porous metallic mass, firmly co- hering; and Bucholz procured it nearly in the same state. 2. Its colour, when thus obtained, is iron-grey; it has conside- rable lustre, and is soft enough to yield to the file. Its malleability and ductility are of course unknown. Its specific gravity, in Kla- proth's trials, was only 8-100. But Bucholz obtained it as high as 9-000. II. From the experiments of Bucholz, together with those of Schoubert! we learn, that uranium combines with 2 doses of oxy- gen. The protoxide is greyish-black; but the peroxide is yellow. 1. When uranium is heated to redness in an open vessel, it un- dergoes a species of combustion, glowing like a live coal, and is soon converted into a greyish black powder, which undergoes no farther change, though the heat be continued. This powder is the protoxide of uranium. According to the experiments of Bucholz, this oxide is composed of—Uranium 100—Oxygen 5-17.! But Schoubert, from the muriate of uranium, has calculated the composition of the protoxide as follows :—Uranium 100—Oxygen 6*3 73.§ As the experiments of Schoijbert were made with care, and his method is susceptible of greater precision than that of Bucholz, we shall take his estimate as the most correct. If the protoxide be a compound of 1 atom metal + 1 atom oxygen, then the weight of an atom of uranium will be 15*691. We shall consider 15*625 as the correct number. We have in that case protoxide of uranium composed of * See Klaproth's Beitrage, ii. 476, Eng. Trans, and Bucholz, Gehlen's Jour. iv. 19. | Berzelius' Attempt to establish a pure scientific system of Mineralogy, p. 118. 4 Gehlen's Journal, iv. 35. § Berzelius' Attempt to establish a pure scientific system of Mineralogy, p. 118. Vol. I. Uu 338 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION 8. Uranium - - 15*625 - 100 Oxygen 1 6*4 2. When uranium or its protoxide is dissolved in nitric acid, and the solution is treated with an alkali, the metal is precipitated in the state of a peroxide. The same perpxide is procured bv pre- cipitating uranium from sulphuric or muriatic acids, and exposing it while moist to the air. The peroxide thus obtained, when well washed and dried, is yellow, tasteless, and insoluble in water. When treated with muriatic acid, it dissolves with effervescence, chlorine acid gas being disengaged. According to the experiments of Schoubert it follows, that this oxide contains li times as much oxygen as the protoxide. It is composed therefore of—Uranium 100—Oxygen 9*6. If we consider it as a compound of 2 atoms uranium and 3 atoms oxygen, an atom of it will weigh 34*25. III. We are unacquainted with the compounds which uranium makes with chlorine, iodine, and fluorine. It does not appear capable of uniting with azote nor hydrogen. We are acquainted with no compounds which it forms with carbon, boron, silicon, and phosphorus. IV. Klaproth mixed the peroxide of uranium with twice its weight of sulphur, and heated it in a retort till most of the sulphur was driven off. The residuum was a blackish brown compact mass. By increasing the heat, the whole of the sulphur was driven off, and the uranium remained in the metallic state in the form of a black heavy coarse powder.* Bucholz's experiments, though made in a different way, led nearly to the same result. He boiled a mix- ture of sulphur and oxide of uranium in an alkaline solution to dry- ness, heated the residue to redness, and then treated it with dis- tilled water. A blackish brown powder remained behind, and small needles of a red colour appeared in the solution. In one trial, the compound which he obtained gave out some sulphureted hydrogen when dissolved in muriatic acid. This is a proof that it was not a sulphureted oxide, but a sulphuret of uranium.! V. Nothing is known respecting the combinations of uranium with the other metals; Bulcholz having been hitherto prevented from making any experiments on that part of the subject, by the want of a sufficient quantity of uranium. family IV. The substances belonging to this family are the following seven: 1. Zinc 3. Tin 5. Bismuth 7. Silver. 2. Lead 4. Copper 6. Mercury. They are all metals, and have been long known, and are in com- mon use for the purposes to which metals are applied. They are precipitated from their solutions in acids in the metallic state in * Beitrage, ii. 213. ! Gehlen's Jour. iv. 47. Chap. III.] zinc 339 the order according to which they are placed in the preceding table. Zinc precipitates all the others, but is not itself precipitated by any of them. Lead precipitates all except zinc. Tin all ex- cept zinc and lead. Copper precipitates only bismuth, mercury, and silver; and mercury precipitates only silver. Silver is preci- pitated by all the rest, but does not itself precipitate any of the •thers. SECTION I. OF ZINC. I. The ancients were acquainted with a mineral to which they gave the name of Cadmia, from Cadmus, who first taught the Greeks to use it. They knew that when melted with copper it formed brass; and that when burnt a white spongy kind of ashes was volatilized, which they used in medicine.* This mineral contained a good deal of zinc ; and yet there is no proof remain- ing that the ancients were acquainted with that metal*! It is first mentioned in the writings of Albertus Magnus, who died in 1£80; but whether he had seen it is not clear, as he gives it the name of marcasite of gold, which implies, one would think, that it had a yellow colour-! The word zinc occurs first in the writings of Paracelsus, who died in 1541. He informs us very gravely, that it is a metal, and not a metal, and that it consists chiefly of the ashes of copper.§ This metal has also been called spelter. • Pliny, lib. xxxiv. cap. 2 and 10. t Grignon indeed says, that something like it was discovered in the ruins of an ancient Roman city in Champagne; but the substance which he took for it was not examined with any accuracy. It is impossible therefore to draw any inference whatever from his assertion. Bulletin de Fouilles d'une Ville Romaine, p. 11. * The passages in which he mentions it are as follows: They prove I think, incontesti- bly, that it was not the metal, but the ores of the metal, witli which Albertus was acquaint- ed De Mineral, lib. ii. cap. 11. " Marchasita, sive marchasida ut quidam dicunt, est lapis in substantia, et habet multas-species, quare colorem accipit cujuslibet metalh et s.c dicitur marchasita argentea et aurea, et sic dicitur aliis. Metallum tamen quod colorat cum nou distillat ab ipso, sed evaporat in ignem, et sic relinquitur cinis mutilis, et hie lapis notus est anud alchymicos.et in multis locis veniuntur." ... PLib. iii. cap. 10. " JEs autem invenitur in venis lapidis, et quod est apud locum qui die,- turGoselaria est purissimum et optimum, ettoti subtanf.se lapid.s incorporatum, ita quod totus lapis est sicut marchasita aurea, et profundatum est melius ex eo quod P™. Lib. v. cap. 5. « Dicimus igitur quod marchasita dupl.cera habet in sui ^at.onesub- stantiam,arg^ntivivi silicet morl^ Ipsam habere sulphureitatem comperimus manifesto exper.ent.a. Namcu™ subl matur, ex ilia emanat substantia sulphurea manifeste comburens. Et s.ne subhmatione similiter ^^^fiijni^ non suscipit il.am priusquam .nnammatione> sulphuris inflammetur.etardeat V-m vero argenti vivi substantiam mamfestatur habere ens.blw ter. Nam albedinera prastat Veneri meri argenti, quemadmodum et ipsum argen urn vivum.et colorem in ipsius sublimatione cxlestium prastare, et lucid.mem man.lestam metallicam habere videmus, qua certum reddunt arUficem Alchimis, dlam has substantias continere in race sua." § See vol. vi. of his Works in quarto. 340 SIMPLE COMBUSTIBLES. 5 BOOK I £ division 2. Zinc has never been found in Europe in a state of purity, and it was long before a method was discovered of extracting it from its ore.* Henkel pointed out one in 1721 ; Von Swab obtained it by distillation in 1742 ; and Margraff published a process in the Ber- lin Memoirs in 1746.! At present there are three works in this country in which zinc is extracted from its ore ; two in the neigh- bourhood of Bristol, and one at Swansey. The ore (sulphuret of zinc) is roasted and reduced to powder, mixed with charcoal, and exposed to a strong heat in large closed clay pots. The zinc is re- duced, and gradually drops down through an iron tube issuing from the bottom of the pot, and falls into a vessel of water. The zinc is afterwards melted and cast into ingots. A considerable quantity of zinc is yearly exported from Britain, chiefly to the north of Europe.! 1. Zinc is of a brilliant white colour, with a shade of blue, and is composed of a number of thin plates adhering together. When this metal is rubbed for some time between the fingers, they ac- quire a peculiar taste, and emit a very perceptible smell. 2. It. is rather soft; when rubbed upon the fingers it tinges them of a black colour. The specific gravity of melted zinc varies from 6-861 to 7-1 ;§ the lightest being esteemed the purest. When ham- mered it becomes as high as 7*1908.|| 3. This metal forms as it were the limit between the brittle and the malleable metals. Its malleability is by no means to be com- pared with that of copper, lead, or tin ; yet it is not brittle, like an- timony or arsenic. When struck with a hammer, it does not break, but yields, and becomes somewhat flatter; and by a cautious and equal pressure, it may be reduced to pretty thin plates, which are supple and elastic, but cannot be folded without breaking. This property of zinc was first ascertained by Mr. Sage.^j When heat- ed somewhat above 212°, it becomes very malleable. It may be beat at pleasure without breaking, and hammered out into thin plates. When carefully annealed, it may (it is said) be passed through rollers. It may be very readily turned on the lathe. When heated to about 400°, it becomes so brittle that it may be re- duced to powder in a mortar. 4. It possesses a certain degree of ductility, and may with care be drawn out into wire.** Its tenacity, from the experiments of Muschenbroeck, is such, that a wire whose diameter is equal to ^th of an inch is capable of supporting a weight of about 26 lbs.!! * The real discoverer of this method appears to have been Dr. Isaac Lawson. See Pott, iii. diss. 7, and Watson's Chemical Essays. ! Bergman, ii. 309. t See an account of the manufacture of this metal in Watson's Chem. Essays, iv. 1. § Brisson and Dr. Lewis. A specimen of Goslar zinc was found by Dr. Watson of the specific gravity 6-953; Bristol zinc 7-028. Chemical Essays, iv. 41. A specimen of zinc tried by Mr. Hatchett was 7-065. On die Alloys of Gold, p. 67. 0 Brisson. t Jour, de Min. An. v. 595. ** Black's Lectures, ii. 583. ■j-J- He found a rod of an inch diameter to support 2600 lbs. Now if the cohesion increase as the square of the diameter, the strength of a wire of l-10th inch will not differ much from that assigned in the text. Chap. III.] zinc. 341 5. When heated to the temperature of about 680°,* it melts; and if the heat be increased, it evaporates, and may be easily distilled over in close vessels. When allowed to cool slowly, it crystallizes in small bundles of quadrangular prisms, disposed in all directions. If they are exposed to the air while hot, they assume a blue change- able colour.! II. When exposed to the air, its lustre is soon tarnished, but it scarcely undergoes any other change. When kept under water, its surface soon becomes black, the water is slowly decomposed, hy- drogen gas is emitted, and the oxygen combines with the metal. If the heat be increased, the decomposition goes on more rapidly; and if the steam of water is made to pass over zinc at a very high temperature, it is decomposed with great rapidity.! When zinc is kept melted in an open vessel, its surface is soon covered with a grey coloured pellicle, in consequence of its combi- nation with oxygen. When this pellicle is removed, another soon succeeds it; and in this manner may the whole of the zinc be oxi- dized. When these pellicles are heated and agitated in an open vessel, they soon assume the form of a grey powder, often having a shade of yellow. This powder has been called the grey oxide of zinc. When zinc is raised to a strong red heat in an open vessel, it takes fire, and burns with a brilliant white flame, and at the same time emits a vast quantity of very light white flakes. These are merely an oxide of zinc. This oxide was well known to the an- cients. Dioscorides describes the method of preparing it. The ancients called it pompholyx : the early chemists gave it the name of nihil album, lana philosophica, and flowers of zinc. Dioscorides compares it to wool.§ Zinc combines with only one proportion of oxygen. The oxide of zinc is a tasteless, white powder, rather light and insoluble in water. It is used as a paint and answers very well as a water co- lour. It combines readily with acids and forms neutral salts. Many careful experiments have been made to determine the com- position of this oxide. The following table exhibits the results ob- tained by the different experimenters : Proustj) 100 metal + 25 I Gay-Lussac** 100 metal + 24*4 Berzelius^ 100 . . . +24-4 j Thomson!! 100 .. . +24*16 We perceive a great coincidence in all these experiments. If the oxide of zinc be a compound of 1 atom.metal + 1 atom oxy- gen, then according to Proust's determination an atom of zinc will weigh 4. According to the determination of Berzelius and Gay- Lussac its weight will be 4*098. According to mine it will be 4*139. We may take 4-125 as sufficiently near the truth. The reduction of the oxides of zinc is an operation of difficulty • Black's Lectures, ii. 583. ! Mongez. * £avoisier, Mem. Par. 1781, p. 274. § Ef/ov rokv7reu n^tfAimrm, V. 85, p. 352. || Ann. de Chim. xxxv. 51. 1 Ibid. Uxvii. 84. •• Ibid. Ixxx. 170. f\ Annals of Philosophy, ii. 410. 342 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION 2. in consequence of the strong affinity which exists between zinc and oxygen, and the consequent tendency of the zinc after reduction to unite with oxygen. It must be mixed with charcoal, and exposed to a strong heat in vessels which screen it from the contact of the external air. III. Zinc combines readily with chlorine and forms a chloride of zinc. This metal takes fire in chlorine gas and the chloride is formed. It may be obtained by dissolving zinc in muriatic acid, evaporating the solution to dryness, and exposing it to a red heat in a glass tube with a narrow orifice. When obtained by distilling a mixture of zinc filings and corrosive sublimate it was formerly distinguished by the name of butter of zinc. When obtained in this way it sublimes readily when heated, and crystallizes in nee- dles. But Dr. John Davy assures us that when the chloride is formed by heating the muriate in a glass tube it does not sublime even at a red heat; but remains in a state of fusion. When ex- posed to the air it very speedily deliquesces. According to the analysis of Dr. John Davy* it is composed of Chlorine - - 50 - - 100 Zinc ... 50 - - 100 . If we suppose it composed of an atom of chlorine and an atom of zinc, its constituents should be Chlorine 4-5 - - 100 Zinc - - - 4*125 - - 91*6 IV. Zinc readily combines with iodine by heat. The iodide has a white colour. It is easily volatilized and crystallizes in fine qua- drangular prisms. It deliquesces in the air and is very soluble in water. The solution is colourless and does not crystallize. This solution contains a combination of hydriodic acid and oxide of zinc. Hence the iodide must decompose water. Gay-Lussac has shown that this iodide is a compound of 1 atom iodine + 1 atom zinc; or by weight of Iodine - - 15-625 - - 100 Zinc - - 4*125 - - 26*52 V. We are not acquainted with any combination of zinc and fluorine. It does not combine with azote, nor hydrogen. VI. Hydrogen gas procured from zinc by means of diluted sul- phuric acid, when burnt, produced a certain portion of carbonic acid. Hence it was inferred that it contained originally some car- bureted hydrogen.! As the zinc dissolves, a black powder makes its appearance in the solution. This black powder the French chemists affirm to be plumbago, and to its presence they ascribe the cause of the formation of carbureted hydrogen ; but this opinion has not been verified by accurate experiments, and is indeed un- likely to be true.! • Phil. Trans. 1812, p. 125.* ! See the experiments of Fourcroy, Vauquelin, and Seguin, Ann. de Chim. viii. 230. ± Proust h» ascertained, that this black powder is often not carburet ef iron, bat a mix* Chap. III.] «INC. 343 VII. We are not acquainted with any compound of zinc and boron, or silicon. VIII. Zinc may be combined with phosphorus, by dropping small bits of phosphorus into it while in a state of fusion. Pelletier, to whom we are indebted for the experiment, added also a little re- sin, to prevent the oxidation of the zinc. Phosphuret of zinc is of a white colour, a metallic splendour, but resembles lead more than zinc. It is somewhat malleable. When hammered or filed, it emits the odour of phosphorus. When exposed to a strong heat, it burns like zinc* Phosphorus combines also with the oxide of zinc; a compound which Margraff had obtained during his experiments on phospho- rus. When 12 parts of oxide of zinc, 12 parts of phosphoric glass, and 2 parts of charcoal powder, are distilled in an earthenware re- tort, and a strong heat applied, a metallic substance sublimes of a silver-white colour, which when broken has a vitreous appearance. This, according to Pelletier, is phosphureted oxide of zinc. When heated by the blowpipe, the phosphorus burns, and leaves behind a glass, transparent while in fusion, but opaque after cooling.! Phosphureted oxide of zinc is obtained also when 2 parts of zinc and 1 part of phosphorus are distilled in an earthen retort. The products are, 1. Zinc; 2. Oxide of zinc; 3. A red sublimate, which is phosphureted oxide of zinc; 4. Needleform crystals, of a metallic brilliancy and a bluish colour. These also Pelletier con- siders as phosphureted oxide of zinc! IX. Sulphur cannot be artificially combined with zinc; but when melted with the oxide of zinc, a combination is formed, as was first discovered by Dehne in 1781.§ The experiment was after- wards repeated by Morveau.|| A similar compound is formed when sulphureted hydrogen, in combination with an alkali, is dropped into a solution of zinc. It is at first white, but becomes darker on drying. It was considered by chemists as sulphur united to the oxide of zinc; but experiment does not confirm the opinion. The zinc seems to be in the metallic state. Mr. Edmond Davy found that when the vapour of sulphur was passed over zinc in fusion, a yellowish compound was obtained similar in appearance to blende. One of the most common ores of zinc is a foliated mineral, usually of a brown colour, called blende; tasteless, insoluble in wa- ter, and of a specific gravity about 4. Bergman showed that this ore consisted chiefly of zinc and sulphur. Chemists were disposed to consider it as a sulphureted oxide of zinc, in consequence chiefly of the experiments of Morveau, above referred to; but the analy- ture of arsenic, copper, and lead. Ann. de Chim. xxxv. 51. On separating this black now- der and drying it, I found that it assumed an olive-green colour. It proved in all rav trials to be a mixture of copper and lead. * Ann. de Chim. xiii. 129. | Pelletier, Ann. de Chim. xiii. 128. * Ann. de Chim. xiii. 125! § Chem. Jour. p. 46, and Crell's Annals, 1786, i. 7. B Mem. de l'Acad. de Dijon, 1788. 344 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. ses of Bergman were inconsistent with this notion. Proust gave it as his opinion, that blende is essentially a compound of zinc in the metallic state with sulphur.* This opinion is now universally admitted to be the true one. By a careful analysis of yellow blende, I found it (abstracting some iron) a compound of—Zinc 100— Sulphur 48*84.! Hence we see that it is a compound of 1 atom zinc + 1 atom sulphur. X. Zinc may be combined with arsenic by distilling a mixture of it and of arsenious acid.! This alloy, according to Bergman, is composed of four parts of zinc and one of arsenic XI. We are not acquainted with the alloy of zinc and tellurium. XII. Zinc maybe alloyed with potassium by heat; but the alloy is difficult to form on account of the volatility of the potassium. It has the colour of pounded zinc It is gradually destroyed in the air, effervesces in water, and still more violently in acids.§ With sodium it is easily alloyed in a cherry-red heat. The co- lour of the alloy is bluish-grey. It is brittle, and of a foliated tex- ture. It is destroyed in the air, and effervesces in water and in acids.|| XIII. We are not acquainted with the alloys which zinc forms with the metals of the alkaline earths and earths proper. XIV. It is difficult to combine zinc with iron, because the heat necessary to melt the latter metal dissipates the former. The alloy, according to Lewis, when formed, is hard, somewhat malleable, and of a white colour approaching to that of silver.♦{[ Malouin has shown that zinc may be used instead of tin to cover iron plates : a proof that there is an affinity between the two metals.** XV. Zinc does not appear capable of combining with nickel by fusion.!! Neither does it combine with cobalt by fusion. We are not acquainted with the alloys which zinc may be capa- ble of forming with manganese, cerium, and uranium. SECTION II. OF LEAD. Lead appears to have been very early known. It is mentioned several times by Moses. The ancients seem to have considered it as nearly related to tin. * Jour, de Phys. Ivi. 79. ! Annals of Philosophy, iv. 92. + Malouin. § Gay-Lussac and Thenard, Recherches Physico-chimiques, i. 221. || Ibid. i. 243. 1 Neuman's Chem. p. 69. ** Mem. Par. 1742. 1"! The Chinese, however, seem to be in possession of some mrthod of combining these metals: for, according to Engestroem, the puk-fong, or white copper, is composed of cop- per, nickel, and zinc. The zinc amounts to seven-sixteeuths of the whole, and the propor- tions of the copper and nickel are to each other as five to thirteen. Mem. Stock. 1776. Chap. III.] LEAD. * 345 1. Lead is of a bluish white colour; and when newly melted is very bright, but it soon becomes tarnished by exposure to the air. It has scarcely any taste, but emits on friction a peculiar smell. It stains paper or the fingers of a bluish colour. When taken inter- nally it acts as a poison. 2. It is one of* the softest of the metals, its specific gravity is 11*3523.* Its specific gravity is not increased by hammering; so far from it, that Muschenbroeck found lead when drawn out into a wire, or long hammered, actually diminished in its specific gra- vity. A specimen at first of the specific gravity 11*479, being drawn out into a fine wire, was of the specific gravity 11*317; and on being hammered, it became 11*2187; yet its tenacity was nearly tripled;! Guyton Morveau on repeating this experiment found the result as stated. But he found likewise that he could increase the specific gravity of lead, by hammering it, confined in a mould so that it had not liberty to expand. 3. It is very malleable, and may be reduced to thin plates by the hammer; it may be also drawn out into wire, but its ductility is not great. Its tenacity is such, that a lead wire ^*7 inch dia- meter is capable of supporting only 18-4 pounds without breaking. 4. From the experiments Mr. Crichton of Glasgow we learn that lead melts when heated to the temperature 612°4 When a very strong heat is applied the metal boils and evaporates. If it be cooled slowly, it crystallizes. The Abbe Mongez obtained it in quadrangular pyramids, lying on one of their sides. Each py- ramid was composed, as it were, of three layers. Pajot obtained it in the form of a polyhedron with 32 sides, formed by the con- course of six quadrangular pyramids.^ II. When exposed to the air it soon loses its lustre, and acquires first a dirty grey colour, and at last its surface becomes almost white. This is owing to its gradual combination with oxygen, and conversion into an oxide. But this conversion is exceedingly slow; the external crust of oxide, which forms first, preserving the rest of the metal for a long time from the action of the air. Water has no direct action upon lead; but it facilitates the ac- tion of the external air: for, when lead is exposed to the air, and kept constantly wet, it is oxidated much more rapidly than it other- wise would be. Hence the reason of the white crust which ap- pears upon the sides of leaden vessels containing water, just at ther place where the upper surface of the water usually terminates. Lead unites with oxygen in three portions, and forms the pro- toxide of lead, which is yellow; the peroxide, which is brown; and the red oxide, which seems to be a compound of the yellow and the brown. 1. The protoxide or yellow oxide of lead, which has been longest * Brisson. Fahrenheit found it 11-3500, Phil. Trans. 1724. Vol. xxxiii. p. 114. I found a specimen of milled lead 11-407 at the temperature of 64*. VWasserberg, i. 441. $ Phil. Mag. xvi. 49. § Jour, de Phys. xxxviii. 53. OL. I* X X 346 * SIMPLE COMBUSTIBLES. $ R°OK *• £ nivisiovS. known, and most carefully examined, may be obtained by dissolv- ing lead in a sufficient quantity of nitric acid, so as to form a colourless solution, and then supersaturating it with carbonate of potash. A white poSvder falls, which when dried, and heated nearly to redness, assumes a yellow colour. It is pure yellow oxide of lead. This oxide is tasteless, insoluble in water, but soluble in potash and in acids. It readily melts when heated, and forms a yellow, semi-transparent, brittle, hard glass. In violent heats a portion of it is dissipated. When kept heated in the open air, its surface becomes brick red. Various careful experiments have been made in order to deter- mine with accuracy the-composition of this oxide. I consider the results obtained by Bucholz and Berzelius, especially the last, as very near the truth. These are as follows: Bucholz* - - - 100 lead + 8 oxygen Berzelius! 100 +7*7 Let us consider the yellow oxide of lead as a compound of 100 lead + 7*692 oxygen, which does not differ materially from the determination of Berzelius. In that case, if it be a combination of 1 atom, metal with 1 atom oxygen, its constitution will be Lead - - 13 - - 100 Oxygen - 1 7-692 The weight of an atom of lead will be 13, and of an atom of pro- toxide 14. When lead is kept melted in an open vessel, its surface is soon covered with a grey coloured pellicle. When this pellicle is re- moved, another succeeds it; and by continuing the heat, the whole of the lead may soon be converted into this substance. If these pellicles be heated and agitated for a short time in an open vessel, they assume the form of a greenish yellow powder. Mr. Proust has shown that this powder is a mixture of yellow oxide and a portion of lead in the metallic state. It owes its green colour to the blue and yellow powders which are mixed in it. If we con- tinue to expose this powder to heat for some time longer in an open vessel, it absorbs more oxygen, assumes a yellow colour, and is then known in commerce by the name of massicot. The reason of this change is obvious: the metallic portion of the powder gradual- ly absorbs oxygen, and the whole of course is converted into yel- low oxide. When thin plates of lead are exposed to the vapour of warm vinegar, they are gradually corroded, and converted into a heavy white powder, used as a paint, and called "white lead. This pow- der used formerly to be considered as a peculiar oxide of lead; but it is now known that it is a compound of the yellow oxide and car- bonic acid. 2. If nitric acid, of the specific gravity 1-260, be poured upon the red lead, 185 parts of the oxide are dissolved ; but 15 parts re- • Gehlen's Journal, v. 259. t Ann- de Chim. lxxviii. 11, and lxxix. 121. Chap. III.] LEAD. 347 main in the state of a black or rather deep brown powder.* This is the peroxide or brown oxide of lead, first discovered by Scheele. The best method of preparing it is the following, which was pointed out by Proust, and afterwards still farther improved by Vauque- lin : Put a quantity of red oxide of lead into a vessel partly filled with water, and make chlorine gas pass into it. The oxide be- comes deeper and deeper coloured, and is at last dissolved. Pour. potash into the solution, and the brown oxide of lead precipitates. By this process 68 parts of brown oxide may be obtained for every 100 of red oxide employed.! . This oxide is a tasteless powder of a flea-brown colour, and very fine and light. It is not acted on by sulphuric or nitric acids. From muriatic acid it absorbs hydrogen, and converts it into chlo- rine. When heated it gives out the half of its oxygen and is con- verted into yellow oxide.! Hence it is obvious that the peroxide of lead is a compound of 1 atom lead + 2 atoms oxygen, or by weight of Lead - 13 - - lOO Oxygen - 2 - - 15*384 3. If massicot, ground to a fine powder, be put into a furnace, and constantly stirred while the flame of the burning coals plays against its surface, it is in about 48 hours converted into a beautiful rod powder, known by the name of minium or red lead.§ This pow- der, which is likewise used as a paint and for various other pur- poses, is the red oxide of lead. Red lead is a tasteless powder, of an intense red colour, often inclining to orange, and very heavy ; its specific gravity, according to Muschenbroeck, being 8*940. It loses no sensible weight in a heat of 400°; but when heated to redness, it gives out oxygen gas, and gradually runs into a dark brown glass of considerable hard- ness. By this treatment it loses from four to seven parts in the hundred of its weight, and a part of the lead is reduced to the me- tallic state. Red lead does not appear to combine with acids. Many acids indeed act upon it, but they reduce it in the first place to the state of yellow oxide. It appears from the analysis of Berzelius that the red lead of commerce is mixed with yellow oxide, with sulphate of lead, mu- riate of lead, and silica. When separated from all these foreign bodies he found it a compound of—Lead 100—Oxygen 11*08.|| It is obvious then that it contains 1 h times as much oxygen as the protoxide. We have two ways of viewing this substance. It may be considered as a compound of 2 atoms of lead and 3 atoms of oxygen, or as a compound of 1 atom of protoxide and 1 atom of peroxide. Which .ever of these views we take, it is evident that • Scheele, i. 113, and Proust, Ann. de Chim. xxiii. 98. ! Fourcroy, iv. 91. \ Berzelius, Ann. de Chim. lxxviii. 16; § See an account of the method of manufacturing red lead in Watson's Chemical Es- says, iii. 338. || Berzelius, Ann. de Chim. lxxviii. 14. 348 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION 2. its weight will be the same. It must be twice the weight of an atom of lead + 3 atoms of oxygen ; or 29. As red lead does not combine with any other substance without undergoing decomposi- tion, its nature is not of much importance in a chemical point of view. But every person may convince himself by an examination of the salts into which yellow oxide of lead enters that its equiva- lent number is 14. It must therefore be a protoxide. Now I am not aware of any other means of reconciling the composition of the oxides of lead with this number but the two suppositions just made, one or other of them therefore must be admitted. 4. All the oxides of lead are very easily converted into glass: and in that state they oxidize and combine with almost all the other metals except gold, platinum, silver, and the metals recently disco- vered in crude platina. This property renders lead exceedingly useful in separating gold and silver from the baser metals with which they happen to be contaminated. The gold or silver to be purified is melted along with lead, and kept for some time in that state in a flat cup, called a cupel, made of burnt bones, and the ashes of wood. The lead is gradually vitrified, and sinks into the cupel, carrying along with it all the metals which were mixed with the silver and gold, and leaving these metals in the cupel in a state of purity. This process is called Cupellation. 5. Lead when first extracted from its ore always contains a cer- tain portion of silver, variable, according to the ore, from a few grains to 20 ounces or more in the fodder. When the silver con- tained in lead is sufficient to repay the expense, it is usual to sepa- rate it; and the process is known by .the name of refining the lead. The lead is placed gradually upon a very large flat dish called a test, made by heating a mixture of burnt bones and fern ashes into an iron hoop, and scooping out the surface to a certain depth. Being acted upon by the flame of the furnace, it gradually assumes a kind of a vitriform state, and is blown off the test, or sinks into it, while the silver remains unaltered. The lead by this process is converted into the substance called litharge. As it is thrown off in a melted state, the litharge at first coheres in masses, but it gra- dually falls down by exposure to the air, and then consists of fine scales, partly red and partly of a golden-yellow. It consists of yellow oxide of lead combined with a certain portion of carbonic acid.* III. When lead is introduced into chlorine gas it does not burn; but it absorbs the gas, and is converted into chloride of lead. This substance is easily obtained by mixing a solution of nitrate of lead with a solution of common salt. A precipitate falls, consisting of small, white, silky crystals. When these crystals are heated they melt, and are converted into pure chloride of lead. This com- * Some improvements in the method of separating silver from lead by cupellation may be seen in a disseration by Duharoel, published in the 3d Vol. of the Memoirs de I'lnstitute, p. 406. They had been previously practised in this country. Chap, in.] LEAD. 349 pound was formerly distinguished by the name of plumbum cor- neum, or horn lead. It is a semi-transparent greyish-white mass, having some resemblance to horn in appearance. When heated in the open air it partly evaporates in a white smoke ; but when the access of air is excluded, it remains fixed at a red heat. Accord- ing to the analysis of Dr. John Davy,* it is composed of Chlorine - 25*78 - 100 - 4-5 Lead r 74.22 - 287-88 - 12-955 100-00 From this analysis (which is very nearly accurate) it is obvious that the chloride of lead is a compound of 1 atom chlorine and 1 atom lead. IV. Lead combines readily with iodine when the two substances are heated together. The iodide of lead has a fine yellow colour. It is precipitated whenever a hydriodate is dropped into a solution containing lead. It is insoluble in water. It has not been analys- ed ; but there can be no doubt that it is a compound of 1 atom io- dine -j- 1 atom lead. Of course it must be composed of—Iodine 15*625—Lead 13*. V. We are ignorant of the action of fluorine upon lead. Lead does not combine with azote, hydrogen, or carbon. No combina- tion of it with boron, or silicon, is known. VI. Phosphuret of lead may be formed by mixing together equal parts of filings of lead and phosphoric glass, and then fusing them in a crucible. It may be cut with a knife, but separates into plates when hammered. It is of a silver-white colour with a shade of blue, but it soon tarnishes when exposed to the air. This phosphu- ret may also be formed by dropping phosphorus into melted lead. It is composed of about 12 parts of phosphorus and 88 of lead.! If we suppose it a compound of 1 atom lead + 1 atom phosphorus, it would consist of 88 lead + 10 phosphorus, which agrees sufficient- ly well with Pelletier's analysis. VII. Sulphuret of lead may be formed, either by stratifying its two component parts and melting them in a crucible, or by dropping sulphur at intervals on melted lead. The sulphuret of lead is brit- tle, brilliant, of a deep blue-grey colour, and much less fusible than lead. These two substances are often found naturally combined; the compound is then called galena, and is usually crystallized in cubes. The specific gravity varies somewhat, but is not much be- low 7. Lead appears capable of uniting with two different proportions of sulphur. With the minimum it forms sulphuret of lead, which is the common galena of mineralogists. There can be no doubt, from the experiments of Berzelius and others, that it is a compound of 1 atom lead + l atom sulphur, or by weight of Lead 13 100 Sulphur - 2 - - 15*384 • Phil. Trans. 1812, p. 185. t Pelletier, Ann. de Chim, xiii. 114- 350 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION '- Besides this common sulphuret of lead there occurs another oc- casionally, lighter in colour, and more brilliant, which burns in the flame of a candle, or when put upon burning coals, emitting a blue flame. It contains, at least, 25 per cent, or ith of its weight of sulphur. It is, therefore, a bisulphuret of lead. This variety has not hitherto been noticed by mineralogists, neither has it been made artificially by chemists. VIII. Lead and arsenic may be combined by fusion. The alloy is brittle, dark-coloured, and composed of plates. Lead takes up £th of its weight of arsenic* IX. Lead may be easily alloyed with potassium. The two me- tals unite when the heat is raised sufficiently high to fuse the lead. The alloy is very fusible and brittle. Its texture is fine granular. When exposed to the air it is speedily destroyed. It effervesces in water. The potassium is converted into potash, and the lead re- mains unaltered-! The alloy of lead and sodium may be formed in the same man- ner. This alloy has some ductility. It is fine granular, and has a bluish-grey colour, and is nearly as fusible as lead. When exposed to the air, or placed under water, the sodium is speedily converted into soda, and the lead separates unaltered.! X. We do not know the alloys which lead forms with the me- tallic bases of the alkaline earths and earths proper. XI. The older chemists affirm, that iron is not taken up by melt- ed lead at any temperature whatever, but that it constantly swims upon the surface. Muschenbroeck, however, succeeded in uniting by fusion 400 parts of iron with 134 parts of lead, and formed a hard alloy, whose tenacity was not h of that of pure iron. The specific gravity of an alloy of ten iron and one lead, according to him, is 4*250.§ The experiments of Guyton Morveau have proved, that when the two metals are melted together, two distinct alloys are formed. At the bottom is found a button of lead containing a little iron; above is the iron combined with a small portion of lead.|| XII. Lead cannot readily be combined with nickel by fusion. XIII. It was supposed formerly that cobalt does not combine with lead by fusion ; for upon melting equal parts of lead and co- balt together, both metals are found separate, the lead at the bot- tom and the cobalt above. Indeed, when this cobalt is melted with iron, it appears that it had combined with a little lead: for the iron combines with the cobalt, and the lead is separated.^ But Gmelin has shown that the alloy may be formed. He put cobalt in powder within plates of lead, and covered them with charcoal to exclude the air. He then applied heat to the crucibles containing the mix- tures. Equal parts of lead and cobalt produced an alloy, in which the metals appeared pretty uniformly distributed, though in some * Bergman. ] Gay-Lussac and Thenard, Recherches Physico-ehimiques, L 218. t Ibid. i. 241. § Wasserberg, i. 212. B Ann. de Chim. lvii. 47. 1 Gellert, p. 137. Chap. III.] tin. 351 cases the lead predominated. It was brittle, received a better po- lish than lead, which metal it resembled rather than cobalt; its spe- cific gravity was 8*12. Two parts of lead and one of cobalt pro- duced an uniform mixture, more like cobalt than lead, very little malleable, and softer than the last. Its specific gravity was 8*28. Four parts of lead and one of cobalt formed an alloy still brittle, and having the fracture of cobalt, but the polish of lead. It was harder than lead. Six parts of lead and one of cobalt formed an alloy more malleable, and harder than lead. Its specific gravity was 9*65. Eight parts of lead and one of cobalt was still harder than lead, and it received a better polish. It was as malleable as lead. Its specific gravity was 9-78,* XIV. We do not know the alloys which lead forms with manga- nese, cerium, and uranium. XV. The alloy of lead and zinc has been examined by Walle- rius, Gellert, Muschenbroeck, and-Gmelin. This last chemist suc- ceeded in forming the alloy by fusion. He put some s^iet into the mixture, and covered the crucible, in order to prevent the evapora- tion of the zinc When the zinc exceeded the lead very much, the alloyvwas malleable, and much harder than lead. A mixture of two parts of zinc and one of lead formed an alloy more ductile and harder than the last. A mixture of equal parts of zinc and lead formed an alloy differing little in ductility and colour from lead; but it was harder, and more susceptible of polish, and much more sonorous. When the mixture contained a smaller quantity of zinc, it still approached nearer the ductility and colour of lead, but it continued harder, more sonorous, and susceptible of polish, till the proportions approached to 1 of zinc and 16 pf lead, when the alloy differed from the last metal only in being somewhat harder.! XVI. The alloy of bismuth and lead is brittle; its colour is nearly that of bismuth; its texture lamellar; and its specific gra- vity greater than the mean. According to Muschenbroeck, the specific gravity of an alloy of equal parts bismuth and silver is 10*70974 SECTION III. OF TIN. Tin was known to the ancients in the most remote ages. The Phoenicians procured it from Spain§ and from Britain, with which nations they carried on a very lucrative commerce. At how early a period they imported this metal we may easily conceive, if we recollect that it was in common use in the time of Moses.|| • Ann. de Chim xix. 357. ! ftid. ix. 95. t Wasserberg, i. 160. § Pliny, lib. iv. cap. 34, and lib. xxxiv. cap. 47. H Numbers xxxi. 22^ 352 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. 1. This metal "has a fine white colour like silver; and when fresh, its brilliancy is very great. It has a slightly disagreeable taste, and emits a peculiar smell when rubbed. 2. Its hardness is between that of gold and lead. Its specific gravity is 7*291; after hammering, 7*299.* 3. It is very malleable: tin leaf, or tinfoil as it is called, is about jfa^ part of an inch thick, and it might he beat out into leaves as thin again if such were wanted for the purposes of art. Its ductility and tenacity are much inferior to that of most of the metals known to the ancients. A tin wire 0*078 inch in diameter is capable of supporting a weight of 34-7 pounds only without breaking.! Tin is very flexible, and produces a remarkable crack- ling noise when bended. 4. When heated to the temperature of 442°! it melts; but a very violent heat is necessary to cause it to evaporate. When cooled slowly, it may be obtained crystallized in the form of a rhomboidal prism.§ II. When exposed to the air it very soon loses its lustre, and assumes a greyish-black colour, but undergoes no farther change ; neither is it sensibly altered by being kept under cold water; but when the steam of water is made to pass over red hot tin, it is de- composed, the tin is oxidated, and hydrogen gas is evolved.|| When tin is melted in an open vessel, its surface becomes very soon covered with a grey powder, which is an oxide of the metal. If the heat be continued, the colour of the powder gradually changes, and at last it becomes yellow. When tin is heated very violently in an open vessel, it takes fire, and is converted into a white oxide, which may be obtained in crystals. The first correct experiments on the oxides of tin were made by Proust.^} The subject was afterwards investigated by Dr. John Davy,** Berzelius,!! anc* Gay-Lussac!! It forms two oxides. The protoxide has a grey or black colour; but when combined with wa- ter is white. The protoxide is yellow, and in certain circumstances transparent, and nearly white. 1. The grey oxide is formed when tin is exposed to a moderate heat for some time; but in that case it is never pure. It may, how- ever, be obtained in a state of purity by the following method: Dissolve tin in muriatic acid, either by means of heat, or by adding a little nitric acid occasionally. When the solution is completed, add to it an excess of potash; a white powder falls, but is partly taken up again. But the remainder, on standing, assumes a dark- grey colour, and even a metallic lustre; this remainder is pure grey oxide of tin.§§ The white powder, first precipitated, is the hydrate * Brisson. ! Morveau, Ann. de Chim. Ixxi. 223. * Crichton, Phil. Mag. xv. 147. § Pagot, Jour, de Phys. xxxviii. 52. II Bouillon La Grange, Ann. de Chim. xxxv. 208. Gay-Lussac, Ibid. lxxx. 170. *J Ann. de Chim. xxviii. 213. •* Phil. Trans. 1812, p. 194. !! Nicholson's Journal, xxxv. 122. *t Ann. deChim. lxxx. 170. §§ See Proust, uii supra, smd Berthollet, junior, Statique Chimique, ii. 457. Chap. III.] Tiar. 353 of the protoxide. When heated, it gives out its water, and be- comes dark-grey, or nearly black. This protoxide is a tasteless powder, soluble in both acids and alkalies. When heated it takes fire, and burns like tinder, and is converted into peroxide. When in a state of solution, it absorbs oxygen with avidity, and is con- verted into peroxide. The following table exhibits the composi- tion of this oxide, according to the most accurate experiments hitherto made: Tin. Oxygen. Gay-Lussac - - 100 + 13*5 John Davy - - 100 13*55 Berzelius - - 100 13*6 These experiments almost coincide. Supposing the protoxide •f tin to be a compound of 1 atom' tin + 1 atom oxygen; it fol- lows that an atom of tin weighs 7-375. For on that supposition we have protoxide of tin composed of Tin - - 7-375 - - 100 Oxygen 1 13*55 which is the mean of the preceding experiments. 2. The peroxide may be obtained by heating tin in concentrated nitric acid. A violent effervescence ensues, and the whole of the tin is converted into a white powder, which is deposited at the bot- tom of the vessel. When heated so as to drive off all the acid and water, it assumes a yellow colour. When tin filings and r.ed oxide of mercury are heated together, the peroxide of tin is obtained of a white colour; but in every other respect it possesses the proper- ties of common peroxide of tin.* This oxide does not dissolve in muriatic acid, but it forms a combination with it which is soluble in water. In the same way when digested with potash it combines with that alkali, and the compound dissolves in water. When this solution is evaporated it leaves a yellow jelly, again soluble in water. It appears also to combine with sulphuric acid though the compound does not dis- solve in water, because that liquid unites in preference with the acid. When this oxide is exposed to a red heat it is no longer dissolved by acids or water. The same property is observable in most metallic oxides. Thus the peroxide of tin is capable both of acting the part of an acid and of a salifiable base.. But the union which it forms both with acids and bases is very weak, since heat alone is sufficient to separate it again. The following table exhibits the composition of the peroxide of tin according to the most accu- rate experiments hitherto made: Tin. Tin. Berzelius 100 + 27-2 Klaproth 100 + 27*64 Gay-Lussac 100 + 27*2 John Davy 100 + 27*64 • Berzelius, Nicholson's Journal, xxxv. 130. Vol. I. Y y 354 SIMPLE COMBUSTIBLES. S BOOK I. (DIVISION 2, These experiments very nearly coincide, though not quite so nearly as those on the protoxide. There cannot be a doubt from them that the peroxide of tin contains twice as much oxygen as the protoxide, or that it is a compound of 1 atom tin + 2 atoms oxy- gen. Hence it contains Tin - - 7*375 - - 100 Oxygen - - 2 - - 27*1 Numbers which almost agree with the analyses of Berzelius and Gay-Lussac. 3. Both Proust and Berzelius have endeavoured to prove the existence of a third oxide of tin. The opinion of Proust has been refuted by the experiments of Dr. John Davy. Berzelius' evi- dences are quite unsatisfactory. He conceives that an intermediate oxide exists in the Liquor of Libavius, yet when he separated this oxide he found it possessed of precisely the same properties as the peroxide.* III. Dr. John Davy has shown that tin combines with two pro- portions of chlorine, and forms 2 chlorides, which he has examined and analysed. 1. Protochloride of tin may be formed by heating together an amalgam of tin and calomel, or by evaporating to dryness the pro- tomuriate of tin and fusing the residue in a close vessel. It has a grey colour, a resinous lustre and fracture, and takes fire when heated in chlorine gas, and is converted into perchloride of tin. In close vessels it may be fused at a heat rather below redness without decomposition; but when strongly heated it seems to be partially decomposed. Water converts it into muriate of tin. It is com- posed, according to Dr. John Davy's experiments, of—Tin 100— Chlorine 60-71! 2. The perchloride of tin has been long known under the name of fuming liquor of Libavius, because it was discovered by Liba- vius, a chemist of the 16th century. It is usually prepared by mixing together an amalgam of tin and corrosive sublimate, and distilling with a very moderate heat. The proportions that answer best according to Sulze, are 6 parts of tin, 1 part of mercury, and 33 parts of corrosive sublimate.! The distillation is to be con- ducted with a very moderate heat. At first a colourless liquid passes into the receiver, consisting chiefly of water: then the fum- ing liquor rushes all at once into the receiver in the state of a white vapour. John Davy found that the perchloride of tin may be pre- pared, likewise, by mixing a concentrated permuriate of tin with sulphuric acid, and distilling with a gentle heat. It is formed, likewise, when tin is introduced into chlorine gas. The metal catches fire and perchloride sublimes. Fuming liquor of Libavius is a colourless liquid like water and very fluid. When exposed to the air it smokes with great vio» • See Nicholson's Journal, xxxv. 124. t Pha- Trans. 1812,177. * Gehlen's Journal, iv. 438. Chap. III.] TIN. 355 lence, owing, as Adet first showed, to its avidity for moisture. When 1 part of water and 3 parts of fuming muriate are mixed together, the mixture condenses into a solid mass. Hence the rea- son that crystals appear on the surface of this liquor, when kept in a phial, with a common cork stopper. It gradually imbibes mois- ture from the air and crystallizes in consequence. These crystals fall to the bottom of the liquor and remain unaltered. Dr. Davy found that this liquor acts with great violence on oil of turpentine. In one case, indeed, it set the oil on fire. According to his ex- periments perchloride of tin is composed of—Tin 100—Chlorine 140*44.* If we suppose the chloride of tin to be a compound of 1 atom metal + 1 atom chlorine, and the bichloride a compound of 1 atom metal + 2 atoms chlorine, as must undoubtedly be the case, their composition will be as follows : Chloride. I Bichloride. Tin - - 100 I Tin - - 100 Chlorine - - 61*01 | Chlorine - - 122*02 The chloride agrees very well with the analysis of John Davy, but the bichloride not so well. The difference is probably owing to the difficulty of obtaining the bichloride in a state of purity. It has the property of dissolving tin, and the bichloride which he analysed, might have contained a little of that metal in solution. IV. Iodine combines readily with tin when the melted metal is brought in contact with the vapour of this supporter. The iodide has a dirty orange colour, and is very fusible. Water decomposes it completely, converting it into hydriodic acid and oxide of tin. When tin and iodine are heated together under water, they act upon each other, and are converted respectively into hydriodic acid and oxide of tin.! This iodide has not been analysed, but it is probably composed of 1 atom metal + 1 atom iodine, or of— Tin 7*375—Iodine 15*625. Analogy would lead us to suppose that 2 iodides of tin exist. V. The action of fluorine on tin is unknown. Probably tin does not combine with azote nor with hydrogen. We do not know any compound which tin is capable of forming with carbon, boron, or silicon. VI. Phosphuret of tin may be formed by melting in a crucible equal parts of filings of tin and phosphoric glass. Tin has a greater affinity for oxygen than phosphorus has. Part of the metal there- fore combines with the oxygen of the glass during the fusion, and flies off in the state of an oxide, and the rest of the tin combines with the phosphorus. The phosphuret of tin may be cut with a knife; it extends under the hammer, but separates in lamina. When newly cut, it has the colour of silver; its filings resemble those of lead. When these filings are thrown on burning coals, the phosphorus takes fire. This phosphuret may likewise be formed * Phil. Trans. 1812, p. 177. ! Gay-Lussac, Ann. de Chim. xci. 26. 356" SIMPLE COMBUSTIBLES. C BOOK I. (DIVHIOS 2. by dropping phosphorus gradually into melted tin. According t» Pelletier, to whose experiments we are indebted for the knowledge of all the phosphurets, it is composed of about 85 parts of tin and 15 of phosphorus.* Margraff also formed this phosphuret, but he was ignorant of its composition. VII. Tin combines with 2 proportions of sulphur, and forms 2 sulphurets, both of which have been long known. 1. Sulphuret of tin may be formed by fusing tin and sulphur together, reducing the compound formed to powder, mixing it with sulphur, fusing it a second time, and keeping the temperature suf- ficiently high to volatilize the superfluous sulphur. It has the co- lour of lead, the metallic lustre, and is capable of crystallizing. When dissolved in concentrated muriatic acid it is totally convert- ed into oxide of tin and sulphureted hydrogen gas. Its constitu- ents according to the most accurate experiments hitherto made, are as follows : Tin. Tin. Bergman! 100 - - - - + 25 J John Davy§ 100------h 27*3 Proust! 100--------r- 25 I Berzelius|| 100------h 27*234 There can be no doubt that this sulphuret is a compound of 1 atom tin + 1 atom sulphur, and that it is composed by weight of Tin - - 7*375 - - 100 Sulphur - 2 - - 27*1 Numbers which coincide very nearly with the analyses of John Davy and Berzelius. 2. Persulphuret of tin has been long known in chemistry under the name of aurum mosaicum or musivum, mosaic gold. I do not know when it was discovered, but Kunkel gives a formula for pre- paring it. In the year 1771 Mr. Woulfe rectified the old process and proposed the following method of making this substance, which is much cheaper than the old one. Mix together 12 parts tin, 7 parts sulphur, 3 parts mercury, and 3 parts sal ammoniac. Expose the mixture to a strong heat for eight hours in a black lead crucible, to the top of which an aludel is luted. The mosaic gold sublimes.^} In the year 1792 Pelletier published a set of experi- ments on this compound, and showed that it might be prepared by heating together in a retort a mixture of equal parts of sulphur and oxide of tin. Sulphurous acid and sulphur are disengaged, and mosaic gold remains.** Before the appearance of this dissertation it had been the general opinion of chemists that mosaic gold is a compound of tin and sulphur. But Pelletier endeavoured to show that the tin was in the state of an oxide. Proust published a va- luable set of experiments on it in 1805 in his paper on tin.!! Ac- cording to him it is a combination of sulphur and an oxide of tin, containing less oxygen than the protoxide above described. This * Ann. de Chim. xiii. 116. f Opusc. iii. 157. i Nicholson's Journal, xiv. 41 § Phil. Trans. 181 , p. 199. II Nicholson's Journal, xxxv. 162. 1 Phil. Trans. 1771, p. 114. ** Ann. deChira. xiii. 280. f! Nicholson's Journal, xiv. 42. Chap. III.] tin. 357 opinion was rectified in 1812 by Dr. John Davy, who demon- strated that this substance is a compound of tin and sulphur,* and thus restored the old chemical theory. Berzelius has also ex- amined this compound, and has come to a similar conclusion.! Hence there can be no doubt that it is really a sulphuret of tin. Mosaic gold when pure is in the form of light scales which readily adhere to other bodies and which have the colour of gold. When heated it gives out a portion of sulphur and is converted into common sulphuret of tin. It is insoluble in water and alcohol, and is not acted upon either by muriatic or nitric acids. But when nitromuriatic acid is boiled on it we gradually decompose and dis- solve it. Potash ley dissolves it when assisted by heat. The so- lution has a green colour. When an acid is poured into the solu- tion a yellow powder is precipitated, which according to Proust is a hydrosulphuret of tin. Mosaic gold according to the analysis of John Davy and Berzelius is composed as follows : Tin. John Davy - 100 + 56*25 sulphur. Berzelius - 100 + 52-3 If we suppose it a compound of 1 atom tin + 2 atoms sulphur, its composition will be Tin - 100 - - 7-375 Sulphur - 54-2 - . - 4 Now this is exactly the mean of the two preceding analyses. 3. Berzelius believes in the existence of another sulphuret of tin containing li times the quantity of sulphur in the protosulphuret. But I have no doubt that the compound described by him, which I have myself obtained many years ago while engaged in preparing mosaic gold, is merely a mixture of protosulphuret and persulphu- ret, or in other words a persulphuret partially decomposed. VIII. Tin and arsenic may be alloyed by fusion. The alloy is white, harder, and more sonorous than tin, and brittle, unless the proportion of arsenic be very small. An alloy, composed of 15 parts of tin and one of arsenic, crystallizes in large plates like bis- muth ; it is more brittle than zinc, and more infusible than tin. The arsenic may be separated by long exposure of the alloy to heat in the open air.! IX. Tin and potassium are easily alloyed by heating them toge- ther. A weak light is emitted at the instant ofcombination. The alloy is brittle, not so white as tin, and pretty fusible. It is speedily destroyed either in the air or under water by the conversion of the potassium into potash.^ During the combination of sodium and tin no light is disengaged. This alloy possesses similar properties as the alloy of tin and po- tassium, but it is less fusible than tin.|| X. We are unacquainted with the alloys which tin forms with the metallic bases of the alkaline earths and earths proper. • Phil. Trans. 1812, p. 199. ! Nicholson's Journal, xxxv. 165. + Bay en. § Gay-Lussac and Thenard, Recherches Physico-chimiques, i. 220. || Ibid. p. 24d. 358 -SIMPLE COMBUSTIBLES. f BOOK J. £ DIVISION 2. XI. Tin does not combine readily with iron. An alloy, how- ever, may be formed, by fusing them in a close crucible, complete- ly covered from the external air. We are indebted to Bergman for the most precise experiments on this alloy. When the two metals were fused together, he always obtained two distinct alloys: the first, composed of 21 parts of tin and 1 part of iron ; the second, of 2 parts of iron and 1 part of tin. The first was very malleable, harder than tin, and not so brilliant; the second but moderately malleable, and too hard to yield to the knife.* The formation of tin plate is a sufficient proof of the affinity be- tween these two metals. This very useful alloy, known in Scot- land by the name of white iron, is formed by dipping into melted tin thin plates of iron, thoroughly cleaned by rubbing them with sand, and then steeping them 24 hours in water acidulated by bran or sulphuric acid. The tin not only covers the surface of the iron, but penetrates it completely, and gives the whole a white colour. It is usual to add about J^-th of copper to the tin, to prevent it from forming too thick a coat upon the iron.! XII. The alloy of tin and cobalt is of a light violet colour, and formed of small grains. XIII. Tin and zinc may be easily combined by fusion. The alloy is much harder than zinc, much stronger than tin, and still ductile. This alloy, it is said, is often the principal ingredient in the compound called pewter. XIV. Bismuth and tin unite readily. A small portion of bis- muth increases the brightness, hardness, and sonorousness of tin: it often enters into the composition of pewter, though never in Britain. Equal parts of tin and bismuth form an alloy that melts at 280°: eight parts of tin and one of bismuth melt at 390°: two parts of tin and one of bismuth at 330°4 XV. When eight parts of bismuth, five of lead, and three of tin, are melted together, a white coloured alloy is obtained, which melts at the temperature of 212°, and therefore remains melted under boiling water. XVI. Lead and tin may be combined in any proportion by fusion. This alloy is harder, and possesses much more tenacity than tin^ Muschenbroeck informs us that these qualities are a maximum when the alloy is composed of three parts of tin and one of lead. The presence of the tin seems to prevent in a great measure the noxious qualities of the lead from becoming sensible when food is dressed in vessels of this mixture. This mixture is often employed to tin copper vessels, and the noxious nature of lead having raised a suspicion, that such vessels when employed to dress acid food, might prove injurious to the health, Mr. Proust was employed by the Spanish government to examine the subject. The result of his experiments was, that * Bergman, iii. 471. t See Watson's Chem. Essays, iv. 191. J Dr. Lewis, Neuman's Chem. p. 111. Chap. III.] COPPER.. 359 vinegar and lemon juice, when boiled long in such vessels, dissolve a small portion of tin, but no lead, the presence of the former metal uniformly preventing the latter from being acted on. The vessels of course are innocent.* The specific gravity of this alloy increases with the lead, as might be expected. Hence the proportion of the two metals in such alloys may be estimated nearly from the specific gravity, as will appear from the following table, drawn up by Dr. Watson from his own experiments-! Tin. Lead. Sp. grav. Tin. Lead. Sp. grav. 0 100 11-270 5 1 7*645 100 0 7*170 3 1 7*940 32 1 7-321 2 1 8*160 16 1 7-438 1 1 8*817 8 1 7*560 What is called in this country ley pewter is often scarcely any thing else than this alloy.! Tinfoil, too, almost always is a compound of tin and lead. This alloy, in the proportion of two parts of lead and one of tin, is more soluble than either of the metals separately. It is accordingly used by plumbers as a solder. SECTION IV. OF COPPER. If we except gold and silver, copper seems to have been more early known than any other metal. In the first ages of the world, before the method of working iron was discovered, copper was the principal ingredient in all domestic utensils and instruments of war. Even during the Trojan war, as we learn from Homer, the combatants had no other armour but what was made of bronze, which is a mixture of copper and tin. The word copper is derived from the island of Cyprus, where it was first discovered, or at least wrought to any extent, by the Greeks. 1. This metal is of a fine red colour, and has a great deal of brilliancy. Its taste is styptic and nauseous ; and the hands, when rubbed for some time on it, acquire a peculiar and disagreeable odour. 2. It is harder than silver. Its specific gravity varies according to its state. Lewis found the specific gravity of the finest copper * Ann. de Chim. lvii. 73. ! Chemical Essays, iv. 165. $ There are three kinds of pewter in common use; namely, plate, trifle, and ley. The plate pewter is used for plates and dishes; the trifle chiefly for pints and quarts; and the ley metal for wine measures, &c. Their relative specific gravities are as follows: Plate, 7-248; trifle, 7-359; ley,7963. The best pewter is said to consist of 100 tin and 17 antimony. See Watson's Chemical Essays, iv. 167. 360 SIMPLE COMBUSTIBLES. S. BOOK I. £ DIVISION 2. he could procure 8*830.* Mr. Hatchett found the finest granulated Swedish copper 8*895.! At *s probable that the specimens which have been found of inferior • gravity were not quite pure.! Cron- stedt states the specific gravity of Japan copper at 9*000.§ 3. Its malleability is great: it may be hammered out into leaves so thin as to be blown about by the slightest breeze. Its ductility is also considerable. Its tenacity is such that a copper wire 0*078 inch in diameter is capable of supporting 302*26 lbs. avoirdupois without breaking.|| 4. When heated to the temperature of 27° Wedgewood, or, ac- cording to the calculation of Mortimer,^ to 1450° Fahrenheit, it melts; and if the heat be increased, it evaporates in visible fumes. While in fusion it appears on the surface of a bluish green, nearly like that of melted gold.** When allowed to cool slowly, it as- sumes a crystalline form. The Abbe Mongez, to whom we owe many valuable experiments on the crystallization of metals, ob- tained it in quadrangular pyramids, often inserted into one another. II. Copper is not altered by water: It is incapable of decom- posing it even at a red heat, unless air have free access to it at the same time; in that case the surface of the metal becomes oxidized. Every one must have remarked, that when water is kept in a cop- per vessel, a green crust of verdigris, as it is called, is formed on that part of the vessel which is in contact with the surface of the water. When copper is exposed to the air, its surface is gradually tar- nished ; it becomes brown, and is at last covered with a dark green crust. This crust consists of oxide of copper combined with car- bonic acid gas. At the common temperature of the air, this oxi- dizement of copper goes on but slowly; but when a plate of metal is heated red hot, it is covered in a few minutes, with a crust of oxide, which separates spontaneously in small scales when the plate is allowed to cool. The copper plate contracts considerably on cooling, but the crust of oxide contracts but very little; it is there- fore broken to pieces and thrown off, when the plate contracts un- der it. Any quantity of this oxide may be obtained by heating a plate of copper and plunging it alternately in cold water. The scales fall down to the bottom of the water. When copper is kept t* Neuman's Chemistry, p. 61. Fahrenheit had found it 8-834. Phil. Trans. 1724, vol- xxxiii. p. 114. ! On the Alloys of Gold, p. 50. It would have been heavier had it been hammered 01' Colled. Bergman states the specific gravity of Swedish copper at 9-3243. Opusc. ii. 263. i The following are the results of Mr. Hatchett's trials: Finest granulated Swedish copper, ... 8-895 Do. Swedish dollar do......8-799 Do. sheet British do. .....8-785 Fine granulated British do. - 8-607 § I have had an opportunity of taking the specific gravity of Chinese copper, and found it the same as European. Hence I am inclined to suspect that Cronstedt's number is inac- curate. || Sickengen, Ann. deChim. xxv. 9. *fl Phil. Trans, xliv. 672. ** Dr. Lewis, Neuman's Chemistry, p. 61. Chap. lll.J COPPER. 361 heated below redness, its surface gradually assumes beautifully va- riegated shades of orange, yellow, and blue. Thin plates of it are used in this state to ornament children's toys. In a violent heat, or when copper is exposed to a stream of oxy- gen and hydrogen gas, the metal takes fire and burns with great brilliancy, emitting a lively green light of such intensity that the eye can scarcely bear the glare. The product is an oxide of copper. There are two oxides of copper at present known; and it does not appear that the metal is capable of being exhibited in combina- tion with more than two doses of oxygen. The protoxide is found native of a red colour, but when formed artificially it is a fine orange; but the peroxide is black, though in combination it assumes various shades of blue, green, and brown. 1. The protoxide of copper was first observed by Proust; but we are indebted to Mr. Chenevix, who found it native in Cornwall, for the investigation of its properties. It may be prepared by mix- ing together 57'5 parts of Jblack oxide of copper, and 50 parts of copper reduced to a fine powder by precipitating it from muriatic acid by an iron plate. This mixture is to be triturated in a mortar, and put with muriatic acid into a well-stopped phial. Heat is dis- engaged, and almost all the copper is dissolved. When potash is dropped into this solution, the oxide of copper is precipitated orange. But the easiest process is to dissolve any quantity of cop- per in muriatic acid by means of heat. The green liquid thus ob- tained is to be put into a phial, together with some pieces of rolled copper, and the whole is to be corked up closely. The green co- lour gradually disappears; the liquid becomes dark brown and opaque ; and a number of dirty white crystals, like grains of sand, are gradually deposited. When this liquid, or the crystals, are thrown into a solution of potash, the orange coloured oxide preci- pitates in abundance. According to the experiments of Chenevix this oxide is composed of 100 copper + 13 oxygen.* But Berze- lius who examined it more lately with scrupulous accuracy obtain- ed as a result,!—Copper 100—Oxygen 12*5. If we suppose it a compound of 1 atom copper + 1 atom oxygen, then an atom of copper will weigh 8, and protoxide of copper is composed of— Copper 8—Oxygen 1. v 2. The peroxide of copper is easily procured pure from the scales which are formed upon the surface of red hot copper. These scales have a violet red colour, owing to the presence of a little metallic copper upon their under surface; but when kept for some time red hot in an open vessel, they become black, and are then pure peroxide of copper. The same oxide may be obtained by dissolving copper in sulphuric or nitric acid, precipitating by means of potash, and then heating the precipitate sufficiently to drive off any water which it may retain. This oxide is a tasteless black powder without any lustre. It dissolves in acids without efferves- * Phil. Trans. 1806, p. 227. ! Ann. de Chim. Ixxviii. 107. Vol. I. 7, z 362 SIMPLE COMBUSTIBLE*;. 5 BOOK I. 2.DIV1S10X 2. cence, and forms green or blue coloured solutions according to the acid. This oxide according to the analyses of Proust* is com- posed of—Copper 100—Oxygen 25. The analysis of Berzelius! agrees precisely with this. It is obvious therefore that it is a com- pound of 1 atom copper and 2 atoms oxygen, or it consists of— Copper 8 - - 100 Oxygen - - - 2 25 The oxides of copper are easily reduced to the metallic state when heated along with charcoal, oils, or other fatty bodies; and even with some of the metals, especially zinc. III. When copper filings are introduced into chlorine gas they take fire, a fixed yellowish substance is formed, while a portion sublimes in the state of a yellowish brown powder. The first of these compounds is a protochloride of copper; the second a per- chloride. 1. The protochloride may be formed by heating a mixture of two parts of corrosive sublimate and one part of copper. Boyle obtained it in this way and published an account of it in 1666 in his treatise on the origin of forms and qualities,] under the name of rosin of copper. Proust obtained it by mixing protomuriate of tin with a solution of copper in muriatic acid. He procured a white salt to which he gave the name of muriate of copper.^ Che- nevix found afterwards that this salt is formed when equal weights of black oxide of copper, and copper in powder, are mixed toge- ther and then acted upon by muriatic acid in a close vessel.|| Proust obtained it likewise by distilling green muriate of copper. A greyish mass remained in the retort, which was protochloride of copper. It is obtained also when a plate of copper is plunged into a botde filled with green muriate of copper. The green colour gradually disappears and small white crystals are deposited, which consist of protochloride of copper.fj Protochloride of copper when pure has an amber colour and a certain degree of translucency. It melts at a heat just below red- ness. In close vessels it is not decomposed nor sublimed by a strong red heat, but in the open air it is dissipated in white fumes. It is insoluble in water. But dissolves in nitric acid without effer- vescence. In muriatic acid it dissolves without effervescence, and is precipitated again unaltered by water. Potash throws down protoxide of copper. According to the analysis of Dr. John Davy,** it is composed of Copper - 64 - 100 - - 8 Chlorine - 36 - 56-25 - 4*5 Thus we see that it is a compound of 1 atom chlorine + 1 atom copper. • Ann de Chim. xxxii. 26. ! Ibid, lxxviii. 107. * Shaw's Boyle, i. 252, 255. § Ann. de Chim. xxviii. 218. II Phil. Trans. 1801, p. 237. 1 Jour, de Phys. Ii. 181. *• Phil. Trans. 1812, p. 170. Chap. III.] COPPER. 363 2. The perchloride of copper may be obtained by evaporating the green muriate to dryness in a temperature not exceeding 400°. It has a brownish yellow colour and is pulverulent. When exposed to the air it absorbs moisture, and becomes first white and then green. Heat decomposes it driving off a portion of the chlorine and converting it into protochloride. According to the analysis of Dr. John Davy* it is composed of Copper - 47 - 100 - 8 Chlorine - 53 - 112-76 - 9*02 Thus we see that the perchloride of copper is a compound of 1 atom copper and 2 atoms chlorine. IV. Copper may be combined with iodine by heating the two substances together. Analogy would lead us to suppose that two iodides of this metal exist. But no experiments have hitherto been made on the subject. The only iodide known is of a dark brown colour. It may be obtained by dropping a hydriodate of potash into a solution of copper in an acid. This iodide is insoluble in water. It is probably a compound of 1 atom copper + 1 atom iodine, or of—Copper 8—Iodine 15*625. V. We do not know the action of fluorine on copper. Copper does not combine, so far as is known, with azote, hydrogen, carbon, boron, or silicon. VI. Mr. Pelletier formed phosphuret of copper by melting to- gether 16 parts of copper, 16 parts of phosphoric glass, and 1 part of charcoal.! Margraff was the first person who formed this phos- phuret. His method was to distil phosphorus and oxide of copper together. It is formed most easily by projecting phosporus into red hot copper. It is of a white colour ; and, according to Pelle- tier, is composed of 20 parts of phosphorus and 80 of copper.! This phosphuret is harder than iron. It is not ductile, and yet cannot easily be pulverised. Its specific gravity is 7*1220. It crystallizes in four sided prisms.^ It is much m .re fusible than copper. When exposed to the air, it loses its lustre, becomes black, falls to pieces; the copper is oxidated, and the phosphorus converted into phosphoric acid. When heated sufficiently, the phosphorus burns, and leaves the copper under the form of black scoriae.|j Sage has shown that this compound does not easily part with the w*hole of its phosporus, though frequently melted, but retains about a twelfth. In this state it may be considered as a sub-phosphuret. It is more fusible than copper, and has the hardness, the grain, and the colour of steel, and admits of an equally fine polish.4^ VII. When equal parts of sulphur and copper are stratified al- ternately in a crucible, they melt and combine at a red heat. Sul- phuret of copper, thus obtained, is a brittle mass, of a black or • Phil. Trans. 1812, p. 170. t Ann- de Chim- '■ 74* * Ann. de Chim. xiii. 3. § S^> Jour- de Phys- xxxvili- «*• B Fourcroy, vi. 252. K Nicholson's Jour. ix. 268. 364 SIMPLE COMBUSTIBLES. 5 BOOK I.. £ DIVISION 2. very deep blue-grey colour, and much more fusible than copper. The same compound may be formed by mixing copper filings and sulphur together, and making them into a paste with water, or even by merely mixing them together without any water, and al- lowing them to remain a sufficient time exposed to the air, as I have ascertained by experiment. If 8 parts by weight of copper filings, mixed with 3 parts of flowers of sulphur, be put into a glass receiver, and placed upon burning coals, the mixture first melts, then a kind of explosion takes place ; it becomes red hot; and when taken from the fire, con- tinues to glow for some time like a live coal. If we now examine it, we find it converted into sulphuret of copper. This curious ex- periment was first made by the associated Dutch chemists, Die- man, Troostwyk, Niewland, Bondt, and Laurenburg, in 1793*. They found that the combustion succeeds best when the substances are mixed in the proportions mentioned above; that it succeeds equally, however pure and dry the sulphur and copper be, and whatever air be present in the glass vessel, whether common air, or oxygen gas, or hydrogen, or azotic gas, or even when the receiver is filled with water or mercury. It is not easy to determine the composition of this sulphuret by directly combining copper and sulphur. It would seem that the copper unites with a portion of oxygen as well as sulphur, which makes the increase of weight greater than it ought to be. The following are the most accurate experiments hitherto made on this compound: Copper. Sulphur. Copper. Sulphur. Proust!......78 +22 or 8 + 2*25 Vauquelin!------ 78'69 + 21'31 8 + 2*166 Berzelius§------10 + 2*56 8 + 2-048 We see that the sulphuret of copper is a compound of 1 atom metal + 1 atom sulphur. Berzelius' experiment comes the near- est to the truth; though the augmentation of weight is about 2\ per cent, greater than it ought to have been. VIII. Copper may be combined with arsenic by fusing them to- gether in a close crucible, while their surface is covered with com- mon salt to prevent the action of the air, which would oxidize the arsenic. This alloy is white and brittle, and is used for a variety of purposes ; but it is usual to add to it a little tin or bismuth. It is known by the names of "white copper and white tombac. When the quantity of arsenic is small, the alloy is both ductile and mal- leable.|| IX. Davy ascertained the fact that copper may be alloyed with potassium and sodium, and that the alloys formed decompose water. But their properties have not been particularly investi- gated. • Jour, de Min. No. ii. 85. $ Ann. du Mus. d'Hist. Nat. xvii. 16. | Neuman's Chem. p. 144. f Ann. de Chim. xxxviii. 872. § Ann. de Chim. lxxv'ui. 105. Chap. III.] COPPER. 365 We are not acquainted with the alloys which copper forms with the metallic bases of the alkaline earths and earths proper. X. Iron may be united to copper by fusion, but not without con- siderable difficulty. The alloy has been applied to no use. It is of a grey colour, has but little ductility, and is much less fusible than coppen Thenard has ascertained, that it is attracted by the magnet, even when the iron constitutes only ^th of the alloy.* Mr. Levavasseur has published some observations, which render it pro- bable that the variety of iron called hot short iron, because it is brittle when red-hot, sometimes owes its peculiarities to the pre- sence of copper. This variety possesses a greater degree of tena- city than common iron, and therefore answers better for some pur- poses. It may be hammered when white hot. As soon as it cools, so far as to assume a brown colour, the forging must be stopped till it becomes of an obscure cherry-red, and then it may be continued till the iron is quite cold.! XI. With nickel copper forms a white hard brittle alloy, easily oxidized when exposed to the air. XII. The alloy of copper and cobalt is unknown. XIII. Manganese unites readily with copper. The compound, according to Bergman, is very malleable, its colour is red, and it sometimes becomes green by age. Gmelin made a number of ex- periments to see whether this alloy could be formed by fusing the black oxide of manganese along with copper. He partly succeeded, and proposed to substitute this alloy instead of the alloy of copper and arsenic, which is used in the arts-! XIV. The alloys of copper with cerium and uranium are un- known. XV. Zinc combines readily with copper, and forms one ot the most useful of all the metallic alloys. The metals are usually com- bined together by mixing granulated copper, a native oxide of zinc called calamine, and a proper proportion of charcoal in powder. The heat is kept up for five or six hours, and then raised sufficient- ly high to melt the compound. It is afterwards poured into a mould of granite edged round with iron, and cast into plates. This compound is usually known in this country by the name of brass. The metals are capable of uniting in various proportions, and ac- cording to them, the colour and other qualities of the brass vary also. According to Dr. Lewis, who made a large set of experi- ments on the subject, a very small portion of zinc dilutes the co- lour of copper, and renders it pale; when the copper has imbibed one-twelfth of its weight the colour inclines to yellow. The yel- lowness increases with the zinc, till the weight of that metal in the alloy equals the copper. Beyond this point, if the zinc be in- creased, the alloy becomes paler and paler, and at last white.§ The proportion of zinc imbibed by the copper varies m different a r-k:™ 1 lai + Ann. de Chim. xiii. 183. J ^ngen Commenl11787, vol. ix. P. 75. \ Neuman's Chem. p. 65: 366 SIMPLE COMBUSTIBLES. S BOOK I. (DIVISIONS. manufactories according to the process, and the purposes to which the brass is to be applied. In some of the British manufactories the brass made contains jd of its weight of zinc. In Germany and Sweden, at least if the statements of Swedenburg be accurate, the proportion of zinc varies from |th to £th of the copper.* It is obvious that the most intimate and complete alloy will con- sist of 2 parts of copper by weight, and 1| part of zinc, which is equivalent to 1 atom of each metal. This is British*brass. Dutch brass, which answers so much better for the purposes of watch- makers, &c. appears to be a compound of 2 atoms copper and 1 atom zinc. Brass is much more fusible than copper; it is malleable while cold, unless the portion of zinc be excessive ; but when heated it becomes brittle. It is ductile, may be drawn out into fine wire, and is much tougher than copper, according to the experiments of Muschenbroeck. According to Gellert, its specific gravity is greater than the mean. It varies considerably according to the proportion of zinc. Dr. Watson found a specimen of plate brass from Bristol 8*441 :! while Brisson makes common cast brass only 7*824. Brass may be readily turned upon the lathe, and in* deed works more kindly than any other metal. When zinc in the metallic state is melted with copper or brass, the alloy is known by the names of pinchbeck, prince's metal, Prince Rupert's metal, &c. The proportion of zinc is equally variable in this alloy as in brass; sometimes amounting nearly to one-half of the whole, and at other times much less. The colour of pinch- beck approaches more nearly to that of gold, but it is brittle, or at least much less malleable than brass. Brass was known, and very much valued, by the ancients. They used an ore of zinc to form it, which they called cadmia. Dr. Watson has proved that it was to brass which they gave the name of orichalcum.] Their as was copper, or rather bronze.§ XVI. Copper forms with bismuth a brittle alloy of a pale red colour, and a specific gravity exactly the mean of that of the two metals alloyed.|| XVII. Copper does not unite with melted lead till the fire is raised so high as to make the lead boil and smoke, and of a bright red heat. When pieces of copper are thrown in at that tempera- ture, they soon disappear. The alloy thus formed is of a grey co- lour, brittle when cold, and of a granular texture.^I According to • Wasserberg, i. 267. !Chem. Essays, iv. 58. + Manchester Transactions, vol. ii. p. 47 § The ancients do not seem to have known accurately the difference between copper, brass, and bronze. Hence the confusion observable in their names. They considered brass as only a more valuable kind of copper, and therefore often used the word a* indifferently to denote either. It was not till a late period that mineralogists began to make the distinction. They called copper vhich combines with sulphur if it be present. Many experiments have been made to determine the composi- tion of this salt on the supposition that it is a compound of muriatic acid and red oxide of mercury. The following table exhibits the most accurate of these results. Chenevix. Rose.* g~oTat ZM* Muriatic acid 18 - 18-5 - 18*8 - 19*5 Peroxide - 82 - 81-5 - 81-2 - 80*5 100 100*0 100*0 1000 If we correct these so as to make them correspond with the real composition of the perchloride, we obtain the following numbers : Chenevix. Rose. ^^otf Zaboada' Chlorine - 24-07 - 24*53 - 24-81 - 25*46 Mercury - 75*93 - 75*47 - 75*19 - 74*54 100*00 100-00 100*00 100*00 If we consider corrosive sublimate as a compound of 1 atom mer- cury -f 2 atoms chlorine, its constituents will be Chlorine - 9 - 26*47 Mercury - 25 - 73*53 100-00 * Verwandtschaft, p. 310. ! [To distinguish corrosive sublimate from calomel: pour a drop of liquid ammonia on a few grains of each salt: the sublimate remains unite, the calomel turns black.—C.] * Gehlen's Journal, vi. 28. § Ann. de Chim. Ut. 124. | Jour, de Pbys. Ix. 383. Chap. III.] mercury; 377 We see from this that the analysis of Zaboada is nearest the truth, though even he reckons the proportion of mercury rather too high. 2. Chloride of mercury is usually distinguished by the names of calomel and mercurius dulcis. I am ignorant who the original dis- coverer of it was. It seems to have been prepared by the alchy- mists ; yet Crollius, so late as the beginning of the 17th century, speaks of it as a grand secret and mystery: but Beguin made the process public in 1608 in his Tirocinium Chemicum, in which he describes the salt under the name of draco mitigatus.* The processes for preparing it, which are numerous, have been described by Bergman. The most usual is to triturate four parts of perchloride of mercury with three parts of running mercury in a glass mortar, till the mercury is killed, as the apothecaries term it; that is to say, till no globules of the metal can be perceived; and the whole is converted into a homogeneous mass. This mix- ture is put into a matrass, and exposed to a sufficient heat in a sand bath. The chloride is sublimed ; mixed, however, usually with a little perchloride, which is either removed by repeated sublimations and triturations, or by washing the salt well with water. It may be prepared also in the humid way, by a process first suggested by Scheele, but corrected by Mr. Chenevix. Scheele's method is to form a nitrate of mercury by dissolving as much mercury as possible in a given quantity of boiling nitric acid. A quantity of common salt, equal to half the weight of the mercury used, is then dissolved in boiling water, and the boiling nitrate is cautiously poured into it. A white precipitate falls, which is to be edulcorated with water till the liquid comes off with- out any taste, and then dried upon a filter.! Chenevix has shown that in order to obtain the chloride by this process quite free from all mixture of subnitrate, it is necessary to mix the solution of com- mon salt with some muriatic acid. Chloride of mercury is usually in the state of a dull white mass; but when slowly sublimed, it crystallizes in four-sided prisms, ter- minated by pyramids. It has very little taste, is not poisonous, but only slightly purgative. Its specific gravity is 7*1758.! It is scarcely soluble, requiring, according to Rouelle, 1152 parts of boil- ing water to dissolve it. When exposed to the air, it gradually becomes deeper coloured. When rubbed in the dark, it phosphoresces, as Scheele discovered. A stronger heat is required to sublime it than is necessary for the sublimation of perchloride. Chlorine gas converts it into perchlo*. ride ; and the same change is produced by subliming it with one part of common salt and two parts of sulphate of iron. Nitric acid * It has been known also by a variety of other names; such as, sublimatum dulce, aquila alba, aquila mitigata, manna metallorum, panchymogogum minerale, panchymogogut quev* cetanus. ! Scheele, i. 221. * Hassenfratz, Ann. de Chim. xxviii. 12. Vol. I. 3 B 378 SIMPLE C0MBU9TIBLES. C BOOK I. (_ DIVISION 2. dissolves it readily, and much nitrous gas is evolved, as Berthollet has shown, and the salt is converted into a perchloride.* Mr. Chenevix employed the following method to ascertain the composition of this salt. He dissolved 100 parts of it in nitric acid, and precipitated the acid by nitrate of silver. The precipi- tate obtained indicated 11*5 muriatic acid. The oxide obtained was 88*5. Zaboada followed nearly the same plan. The precipi- tate, by means of nitrate of silver indicated 10*6 of muriatic acid. Muriate of tin threw down 85 grains of pure mercury. The fol- lowing is the result of the analysis of these two chemists : Zaboada. Chenevix. Acid - 10*6 - 11*5 Protoxide - 89*4 - 88-5 Total 100 100 When we correct these results according to the true constitution of this chloride, we obtain Zaboada. Chenevix. Chloride - 14*04 - 14*9 Mercury - 85*96 - 85*1 100*00 100*0 If we suppose it a compound of 1 atom mercury -f 1 atom chlo- rine, its composition will be Chlorine - 4-5 -> 15-25 Mercury - 25 - 84*75 100*00 Now Chenevix's analysis corresponds with these numbers very nearly. There can be no doubt then that the composition of these two chlorides is as follows :! Protochloride. Perchloride. Mercury 1 atom - 100 Mercury 1 atom - 100 Chlorine 1 atom - • 18 Chlorine 2 atoms - 36 IV. Iodine combines readily with mercury. Nothing more is necessary than to place the two bodies in contact. They speedily unite. Iodide of mercury is formed likewise when a hydriodate is dropped into a solution of mercury in an acid. According to Gay-Lussac there are two iodides of mercury. The protiodide has a yellow colour, the periodide is a beautiful red, which may be em- ployed as a paint. They are both insoluble in water. They are decomposed by nitric acid. The first, as Gay-Lussac ascertained, is a compound of 1 atom mercury -f- 1 atom iodine ; the second of 1 atom mercury -f 2 atoms iodine. Hence their composition is as follows: * [Because the nitric acid being decomposed oxygenates the muriatic acid of the calomel; the salt then becomes an oxymuriat of mercury: that is, corrosive sublimate.—C.] t See Davy's observations and experiments, Phil. Trans. 1811, p. 26. C hap. III.] mercury. 37Q Protiodide of mercury. Periodide of mercury. Mercury - 25 - 100 Mercury - 25 - ' 100 Iodine - 15*625 - 62*5 Iodine - 31*25 - 125 V. We do not know the action of fluorine on mercury. This metal does not unite with azote, hydrogen, carbon, boron, or silicon. VI. Mr. Pelletier, after several unsuccessful attempts to com- bine phosphorus and mercury, at last succeeded by distilling a mixture of red oxide of mercury and phosphorus. Part of the phosphorus combined with the oxygen of* the oxide, and was con- verted into an acid ; the rest combined with the mercury. He ob- served, that the mercury was converted into a black powder before it combined with the phosphorus. On making the experiment, I found that phosphorus combines very readily with the black oxide of mercury, when melted along with it in a retort filled with hy- drogen gas to prevent the combustion of the phosphorus. Phos- phuret of mercury is of a black colour, of a pretty solid consistence, and capable of being cut with a knife. ' When exposed to the air, it exhales vapours of phosphorus.* VII. Mercury combines with two proportions of sulphur and forms two sulphurets. The protosulphuret is black but the per- sulphuret is red. 1. When two parts of sulphur and one of mercury are triturated together in a mortar, the mercury gradually disappears, and the whole assumes the form of a black powder, formerly called ethiops, mineral. It is scarcely possible by this process to combine the sulphur and mercury so completely, that small globules of the me- tal may not be detected by a microscope. When mercury is added slowly to its own weight of melted sulphur, and the mixture is constantly stirred, the same black compound is formed. It may be obtained very readily likewise by passing a current of sulphureted hydrogen gas through an acid solution of mercury. The black sulphuret is precipitated abundantly. According to Guibourt run- ning mercury may be pressed out of the sulphuret prepared in this way.! This sulphuret according to him is composed of Mercury - - 100 • - - - 25 Sulphur - - 8-2 - - - 2*05 Hence it is obviously a compound of 1 atom mercury -+- 1 atom sulphur. 2. When ethiops mineral is heated red-hot, it sublimes; and if a proper vessel be placed to receive it, a cake is obtained of a fine red colour. This cake was formerly called cinnabar ; and when reduced to a fine powder, is well known in commerce under the name of vermilion.] • Ann. de Chim. xiii. 122. t Ann. de Chim. et Phys. i. 424. T The word vermilion is derived from the French word vermeil, which comes trom ver- miculus or vermiculum: names given in the middle ages to the kermes or coccus illicis, well known as a red dye. Vermilion originally signified the red dye of the kermes. See Beckman's History of Discoveries, ii. 180. 380 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION '2. This sulphuret of mercury has a scarlet colour, more or less beautiful, according to the mode of preparing it. Its specific gra- vity is about 10. It is tasteless, insoluble in water, and in muriatic acid, and not altered by exposure to the air. When heated suffi- ciently, it takes fire, and burns with a blue flame. When mixed with half its weight of iron filings, and distilled in a stoneware re- tort, the sulphur combines with the iron, and the mercury passes into the receiver, which ought to contain water. By this process mercury may be obtained in a state of purity. The use of this sulphuret of mercury as a paint is well known.* Cinnabar may be prepared by various other processes. One of the simplest of these is the following, lately discovered by Mr. Kirchoff. When 300 grains of mercury and 68 of sulphur, with a few drops of solution of potash to moisten them, are triturated for some time in a porcelain cup by means of a glass pestle, ethiops mineral is produced. Add to this 160 grains of potash dissolved in as much water. Heat the vessel containing the ingredients over the flame of a candle, and continue the trituration without inter- ruption during the heating. In proportion as the liquid evaporates, add clear water from time to time, so that the oxide may be con- stantly covered to the depth of near an inch. The trituration must be continued about two hours ; at the end of which time the mix- ture begins to change from its original black colour to a brown, which usuaily happens when a large part of the fluid is evaporated. It then passes very rapidly to a red. No more water is to be add- ed ; but the trituration is to be continued without interruption. When the mass has acquired the consistence of a jelly, the red co- lour becomes more and more bright, with an incredible degree of quickness. The instant the colour has acquired its utmost beauty, the heat must be withdrawn, otherwise the red passes to a dirty brown. Count de Moussin Pouschkin has discovered, that its passing to a brown colour may be prevented by taking it from the fire as soon as it has acquired a red colour, and placing it for two or three days in a gentle heat, taking caie to add a few drops of water, and to agitate the mixture from time to time. During this exposure the red colour gradually improves, and at last becomes excellent. He discovered also, that when this sulphuret is exposed to a strong heat, it becomes instantly brown, and then passes into a dark violet; when taken from the fire, it passes instantly to a beau- tiful carmine red-! The persulphuret according to the experiments of Proust! *s composed of—Mercury 100—Sulphur 17*64. According to Guibourt§ it is a compound of Mercury - - 100 - - 25 Sulphur - - 16 - - 4 * See a description of the process of making it by Paysse, Ann. de Chim. Ii. 196; and by Tuckert, ibid. iv. 25. ! Nicholson's Journal, ii. 1. * Jour, dc Phys. liii. 92. 4 Ann. de Chim. et Phys. i. 425: Chap. III.] MERCURY. 381 This last analysis is accurate. We see from it that the persul- phuret of mercury is a compound of 1 atom mercury -f 2 atoms sulphur. VII. Mercury may be amalgamated with arsenic by keeping them for some hours over the fire, constantly agitating the mixture. The amalgam is grey-coloured, and composed of 5 parts of mer- cury and 1 of arsenic* IX. Mercury may be amalgamated with tellurium by trituration. X. Mercury may be readily amalgamated with potassium and 6bdium, either by heat or by simply placing the two bodies in con- tact. Considerable heat is evolved during the combination. The amalgam is solid, unless the proportion of potassium or sodium be very small. It crystallizes and has a white colour like that of mer- cury. The potassium or sodium is speedily converted into alkali in the open air or under water.! XI. Mercury has been amalgamated with the metallic bases of the alkaline earths, by Seebeck, Berzelius, and Davy. But these amalgams have not been examined. We are unacquainted with the compounds which mercury is capable of forming with the bases of the earths proper. XII. Iron is not acted on by mercury: accordingly this last me- tal is usually kept in vessels of iron. Mr. Arthur Aiken, how- ever, has shown that these two metals may be combined together. To form an amalgam of iron, he triturates together iron filings and the amalgam of the metal called zinc, and adds to the mixture a solution of iron in muriatic acid. By kneading this mixture, and heating it, the iron and mercury which combine together gradually assume the metallic lustre.! XIII. Mercury does not combine with nickel, or cobalt, or man- ganese. We are ignorant of the action of this metal on cerium and uranium. XIV. The amalgam of zinc was examined by Malouin. Ac- cording to him, it is formed most readily by pouring mercury upon zinc, heated so as to char paper, but not to burn it. Its consistence varies with the proportion of zinc. Eight parts zinc, and 1 mer- cury, form a white very brittle compound. One zinc and 2\ mer- cury form an alloy, which, when melted and cooled slowly, crys- tallizes. This amalgam is used to promote the excitement of elec- tric machines.^ XV. Mercury combines readily with bismuth, either by triturat- ing the metals together, or by pouring 2 parts of hot mercury into 1 part of melted bismuth. This amalgam is at first soft, but it be- comes gradually hard. When melted and cooled slowly, it crys- tallizes. When the quantity of mercury exceeds the bismuth considera- * Bergman, ii. 281. f Gay-Lussac and Thenard, Recherches physico-chimiques, i. 2t2. * Phil. Mag. xiii. 416. § It was first recommended for that purpose by Dr. Higgins. See Phil. Trans. 1778, p. 861. 382 SIMPLE COMBUSTIBLES. S BO()K •• I bivisiov 2, bly, the amalgam remains fluid, and has the property of dissolving lead, and rendering it also fluid. This curious fact was first de- scribed by Beccher, who affirmed that a mixture of 3 parts mer- cury, 1 lead, and 1 bismuth, form a perfectly fluid amalgam. This triple compound may be filtered through shamois leather without decomposition. Mercury is sometimes adulterated with these me- tals ,- but the imposition may be easily detected, not only by the specific gravity of the mercury, which is too small, but because it drags a tail, as the workmen say; that is, when a drop of it is agitated on a plain surface, the drop does not remain spherical, but part of it adheres to the surface, as if it were not completely fluid, or as if it were inclosed in a thin pellicle. This amalgam is used hot for silvering glass balls. XV. Mercury amalgamates readily with lead in any proportion, either by triturating with lead filings, or by pouring it upon melted lead. The amalgam is white and brilliant, and when the quantity of lead is sufficient, assumes a solid form. It is capable of crys- tallizing. The crystals are composed of 1 part of lead and 1% of mercury.* XVII. Mercury dissolves tin very readily cold; and these me- tals may be combined in any proportion by pouring mercury into melted tin. The amalgam of tin, when composed of 3 parts of mercury and 1 of tin, crystallizes in the form of cubes, according to Daubenton; but, according to Sage, in grey brilliant square plates, thin towards the edges, and attached to each other, so that the cavities between them are polygonal. This alloy is used in silvering the backs of looking glasses. A sheet of tinfoil is spread upon a table, and mercury rubbed upon it with a hare's foot, till the two metals incorporate; then a plate of glass is slid over it, and kept down with weights. The excess of mercury is driven off, and in a short time the tinfoil adheres to the glass and converts it into a mirror.! XVIII. Mercury acts but feebly upon copper, and does not dis- solve it while cold; but if a small stream of melted copper be cau- tiously poured into mercury heated nearly to the boiling point, the two metals combine and form a soft white amalgam.! Boyle point- ed out the following method, which succeeds very well: triturate together 2 parts of mercury, 2\ parts of verdigris, and 1 part of common salt, with some acetous acid, and keep them for some time over a moderate fire, stirring them constantly, and supplying acid as it evaporates; then wash the amalgam and pour it into a mould; it is at first nearly fluid, but in a few hours it crystallizes and becomes quite solid.§ This amalgam may be formed also by keeping plates of copper in a solution of mercury in nitric acid. * Dijon Academicians. ! See Watson's Chem. Essays, p. 240. Dr. Watson has rendered it probable that the art of forming mirrors by coating glass with a plate of metal was known at least as early as the irstcentury. | Lewis, Neuman** Chem. p. 65. *j Shaw's Boyle, i. 343. Chap. III.] SILVER. 38-3 The plate is soon impregnated with mercury. The amalgam of copper is of a white colour, and so soft at first that it takes the most delicate impressions; but it soon becomes harder when exposed to the air. It is easily decomposed by heat; the mercury evaporates, and leaves the copper. SECTION VII. OF SILVER. I. Silver seems to have been known almost as early as gold, which was probably the first metal employed by man. 1. It is a metal of a fine white colour with a shade of yellow, without either taste or smell; and in point of brilliancy is inferior to none of the metallic bodies, if we except polished steel. 2. It is softer than copper, but harder than gold. When melted, its specific gravity is 10-474;* when hammered, 10*510.! 3. In malleability it is inferior to none of the metals, if we ex- cept gold. It may be beat out into leaves only ^0J66i inch thick. Its ductility is equally remarkable: it may be drawn out into a wire much finer than a human hair ; so fine indeed, that a single grain of silver may be extended about 400 feet in length. 4. Its tenacity is such, that a wire of silver 0.078 inch in diame- ter is capable of supporting a weight of 187*13 lbs. avoirdupois without breaking.! 5. Silver melts when it is heated completely red hot; and while melted its brilliancy is much increased. According to the calcula- tion of Mortimer and Bergman, its fusing point is 1000° of Fah- renheit. Dr. Kennedy ascertained, that the temperature at which it melts corresponds to 22° of Wedgewood's pyrometer.^ If the heat be increased after the silver is melted, the liquid metal boils, and may be volatilized ; but a very strong and long-continued heat is necessary. Gasto Claveus kept an ounce of silver melted in a glass-house furnace for two months, and found, by weighing it, that it had sustained a loss of J^-th of its weight.|| Vauquelin however found that when placed upon charcoal, urged by a current of oxy- gen gas, the silver was volatilized in a visible smoke.^ When cooled slowly, its surface exhibits the appearance of crys- tals ; and if the liquid part of the metal be poured out as soon as * Brisson and Hatchett. Fahrenheit found it 10-481. Phil. Trans. 1724, vol. xxxiii. p. 114. I found pure silver melted and slowly cooled of the specific gravity 10-3946; when hammered it became 10-4177 ; when rolled out into a plate it became 10-4812. Nicholson's Jour. xiv. 397. ! According to Brisson. Muschenbroeck found the specific gravity of hammered silver 10-500. Dr. Lewis makes it no less than 10-980. Phil. Cora. p. 549. i Ann. de Chim. xxv. 9. § Sir James Hall, Nicholson's Jour. ix. 99*. If Theatrum Chem. ii. 17. J Ann. de Chim. Ixxxix. 239. 384 SIMPLE COMBUSTIBLES. C BOOK 1. ( DIVISION 2 0 *■ the surface congeals, pretty large crystals of silver may be obtain- ed. By this method Tillet and Mongez junior, obtained it in four- sided pyramids, both insulated and in groups. II. Silver is not oxidized by exposure to the air: it gradually indeed loses its lustre, and becomes tarnished; but this is owing to a different cause. Neither is it altered by being kept under wa- ter. But if it be kept for a long time melted in an open vessel, it gradually attracts oxygen from the atmosphere, and is converted into an oxide. This experiment was first made by Junker, who converted a quantity of silver into a vitriform oxide.* It was af- terwards confirmed by Macquer and Darcet. Macquer, by expos- ing silver 20 times successively to the heat of a porcelain furnace, obtained a glass] of an olive green colour.! Nay, if the heat be sufficient, the silver even takes fire, and burns like other combus- tible bodies. Van Marum made electric sparks from his powerful Teylerian machine pass through a silver wire; the wire exhibited a greenish white flame, and was dissipated into smoke. Before a stream of oxygen and hydrogen gas, it burns rapidly with a light green flame. By means of the galvanic battery it may be burnt with great brilliancy. The oxide of silver, obtained by means of heat, is of an olive colour. When silver is dissolved in nitric acid, and precipitated by lime water, it falls to the bottom under the form of a powder of a dark olive-brown colour. This oxide is tasteless. It is insoluble in water, but readily soluble in nitric acid. When heated to red- ness it is reduced to the metallic state. The following table ex- hibits the composition of this oxide, according to the experiments of different chemists Klaproth.§ Proust.|| Berzelius.*! Davy.»» Thomson.ft Silver - 100 - 100 - 100 - 100 - 100 Oxygen - 12*36 - 9-5 - 7*44 - 7*3 - 7*291 We may, I conceive, without deviating from the truth, consider this oxide as a compound of—Silver 100—Oxygen 7-272. In that case, if we suppose it a compound of 1 atom silver 4- 1 atom oxygen, an atom of silver will weigh 13*75 and an atom of oxide of silver 14*75. III. Silver does not burn when heated in chlorine gas; but it gradually absorbs the gas, and is converted into the well known compound called formerly horn silver, and more lately distinguish- ed by the name of muriate of silver. Sir H. Davy first showed that it is a chloride of silver. This chloride is easily obtained by dissolving silver in nitric acid, and mixing the solution with a solution of common salt. A * Junker's Conspectus Chem. i. 887. t Metallic oxides, after fusion, are called glass, because they acquire a good deal of re- semblance, in some particulars, to common glass. $ Macquer' Dictionary, ii. 571. § Beitrage, iii. 199. II Nicholson's Journal, xv. 375. *J Ann. de Chim. Ixxix. 132. An inference from the analysis of sulphuret of silver. ** Elements of Chemical Philosophy, p. 444. !! Airoals of Philosophy, iv. 13. Chap. III.] SILVER. 385 copious curdy precipitate falls. When this precipitate is washed and dried it constitutes pure chloride of silver. This chloride is one of the most insoluble substances known: According to Monnet it requires no less than 3072 parts of water to dissolve it. When exposed to the air, it gradually acquires a purple colour. When exposed to a heat of about 500°, it melts, and assumes, on cooling, the form of a grey-coloured semitransparent mass, having some resemblance to horn, and for that reason called luna cornea. A strong heat sublimes it, as Margraff ascertained.* When heated strongly in an earthen crucible, it passes through al- together, and is lost in the fire; but when mixed with about four times its weight of fixed alkali, formed into a ball with a little wa- ter, and melted rapidly in a crucible well lined with alkali, the sil- ver is reduced, and obtained in a state of purity. Considerable caution is necessary in conducting this experiment. The easiest way of obtaining the silver is, by boiling the chloride in an iron pot with water and pieces of iron. The chloride of silver is soluble in ammonia. The alkaline car- bonates decompose it, but not the pure alkalies ; neither is it de- composed by any of the acids. Several of the metals, when fused along with it, separate the silver in its metallic state ; but it is al- ways alloyed with a little of the metal employed. Copper, iron, lead, tin, zinc, antimony, and bismuth, have been used for that purpose.} If the solution of this salt in ammonia be mixed with running mercury, the silver gradually separates, combines with the mercury, and forms the crystals usually distinguished by the name of arbor Diance. Margraff recommends this amalgamation as the best method of procuring pure silver. This salt dissolves in muri- atic acid, and by that means may be obtained in octahedral crys- tals. When the ammoniacal solution of this salt is heated, fulmi- nating silver is precipitated.! All substances containing hydrogen have the property of removing the chlorine, but no other bodies. Considerable pains have been taken to ascertain the constituents of this chloride correctly, because it is by means of it that the dif- ferent muriates are analysed. The following table exhibits the result of the most accurate trials hitherto made, on the supposition that the chloride is a compound of muriatic acid and oxide of silver: Proust.§ Rose.|| Berzelius.^ Marcet.** Gay-Lussae.ff Muriatic acid - 18 - 18-28 - 18*7 - 19-05 - - 19*28 Oxide of silver- 82 - 81*72 - 81*3 - 80-95 - - 80*72 100 100-00 100*0 100*00 100*00 * Opusc i 265. Proust affirms that this sublimation stops after the salt is in complete fusion ! Margraff, Ibid. * Proust, Nicholson's Jour. xv. 369. § Jour, de Phys, xlix. 221. || Gehlen's Journal, vi. 29. 1 A,,n- de Cbim- *J«V»'- **-*• •* Nicholson's Journal, xx 30. •H- As quoted by Dr. Henry, Chemistry, vol. n. p. 77. I do not know where Gay-Lus- sac's experiments were published. In Ann. de Chim, xci. 100, he adopts the analysis of Berzelius. Vol. I. 3 C 386 SIMPLE COMBUSTIBLES. J BOOK 1. ^nivisioN 2. When these results are corrected according to the true composi- tion of the chloride, we obtain the following numbers. Proust. Rose. Berzelius. Marcet. Gay-Lussac. J.Davy.• Chlorine - - 23-55 - 23*82 - 24-21 - 24*53 - 24-75 - 24*5 Silver - - - 76*45 - 76*18 - 75*79 - 75*47 - 75*25 - 75-5 100-00 100*00 100*00 100*00 100-00 100*0 If we consider this chloride as a compound of 1 atom silver and 1 atom chlorine, its constituents will be Chlorine----4*5 - - - 24*66 Silver - - - - 13-75 - - 75*34 100*00 This is almost the exact mean of the analyses of Gay-Lussac and Marcet, which in consequence we must consider as the most accu- rate. IV. The iodide of silver is easily obtained by dropping a hy- driodate into nitrate of silver. A greenish yellow curdy precipi- tate falls having a good deal of resemblance to chloride of silver. It melts at a low red heat and assumes a reddish colour. When exposed to light its colour is altered more rapidly than even that of chloride of silver. It is insoluble in water and easily decomposed when heated with potash. It has not been analysed ; but there can be no doubt that it is a compound of 1 atom silver 4. 1 atom iodine, or by weight of—Silver 13*75—Iodine 15*625. V. We are unacquainted with the action of fluorine on silver. This metal does not combine with azote, hydrogen, carbon, boron, or silicon. VI. Silver was first combined with phosphorus by Mr. Pelletier. If one ounce of silver, one ounce of phosphoric glass, and two drachms of charcoal, be mixed together, and heated in a crucible, phosphuret of silver is formed. It is of a white colour, and appears granulated, or as it were crystallized. It breaks under the ham- mer, but may be cut with a knife. It is composed of 4 parts of silver and 1 of phosphorus. Heat decomposes it by separating the phosphorus.! Pelletier has observed that silver in fusion is capa- ble of combining with more phosphorus than solid silver ; for when phosphuret of silver is formed by projecting phosphorus into melt- ed silver, after the crucible is taken from the fire, a quantity of phosphorus is emitted the moment the metal congeals.! VII. When thin plates of silver and sulphur are laid alternately above each other in a crucible, they melt readily in a low red heat, and form sulphuret of silver. It is of a black or very deep violet colour; capable of being cut with a knife; often crystallized in small needles; and much more fusible than silver. If sufficient heat be applied, the sulphur is slowly volatilized, and the metal remains behind in a state of purity. This compound frequently • Phil. Trans. 181*, p. 172. \ Pelletier, Ann.de Chim. i. 73. $ Ann. de Chim. xiii. 110. Chap. III.] silver. 387 occurs native. It has a dark grey colour, a metallic lustre, and the softness, flexibility, and malleability of lead. Ics specific gravity is about 7-2. The following table exhibits the most correct experi- ments on the composition of this sulphuret hitherto made: Klaproth* Vauquelin-! Berzelius.^ Silver - - 100 - 100 - 100 Sulphur - - 17*64 - 14*59 - 14*9 It is obvious from these analyses that sulphuret of silver is a compound of 1 atom silver + 1 atom sulphur. The correct com- position according to that supposition is Silver - - 13*75 - 100 Sulphur - - 2 - 14-544 From this it appears that Vauquelin's analysis is the most cor- rect. It is well known that when silver is long exposed to the air, espe- cially in frequented places, as churches, theatres, &c. it acquires a covering of a violet colour, which deprives it of its lustre and mal- leability. This covering which forms a thin layer, can only be de- tached from the silver by bending it, or breaking it in pieces with a hammer. It was examined by Mr. Proust, and found to be sul- phuret of silver.^ VIII. Melted silver takes up ^th of arsenic.|| The alloy is brittle, yellow-coloured, and useless. IX. The alloy of silver and iron has not been examined by mo- dern chemists. According to Wallerius, the metals unite readily by fusion, and when the quantity of each is equal, the alloy has the colour of silver, but it is harder; it is very ductile, and is attract- ed by the magnet.*^ Morveau** has shown, that when this alloy is kept in fusion, the metals separate from each other according to their specific gravity, forming two buttons, exceedingly distinct. Neither of these, however, is in a state of purity. The silver re- tains a little iron, which makes it obedient to the magnet. Coulomb has shown, that the proportion of iron which remains in the silver amounts to -y^th Part- The iron, on the other hand, retains about fa of its weight of silver; which gives it an excessive hard- ness and compactness of structure, of which pure iron is destitute-!! X. Silver does not unite with nickel by fusion. XI. When 2 parts of cobalt and 1 of silver are melted together, the two metals are obtained separately after the process: the silver at the bottom of the crucible, and the cobalt above it. Each of them, however, has absorbed a small portion of the other metal: for the silver is brittle and dark coloured, while the cobalt is whiter than usual-!! XII. We are ignorant of the alloys of silver with manganese, cerium, and uranium. * Beitrage, i. 162. ! Ann. du Muse. d'Hist. Nat. xvii. 16. $ Ann. de Chim. Ixxix. 131. § Ann. de Chim. i. 142. II Bergman, ii. 281. •J Wasserberg, i. 156. »* Jour, de Phys. 1788. ft" Ann. de Chim. xliii. 47. tt Gellert, p. 137. 388 SIMPLE COMBUSTIBLES. S book ■• • ^DIVISION 2. XIII. Silver unites to zinc with facility, and produces a brittle alloy of a bluish white colour, and a granular texture. Its specific gravity, according to Gellert, is greater than the mean. When an alloy of 11 zinc and 1 silver is sublimed in open vessels, the whole of the silver arises along with the flowers of zinc* XIV. Bismuth combines readily with silver by fusion. The alloy is britde; its colour is nearly that of bismuth; its texture la- mellar; and its specific gravity greater than the mean. According to Muschenbroeck, the specific gravity of an alloy of equal parts bismuth and silver is 10-7097.! XV. Melted lead dissolves a great portion of silver at a slightly red-heat. The alloy is very brittle:] its colour approaches to that of lead; and, according to Kraft, its specific gravity is greater than the mean density of the two metals united. The tenacity of silver, according to the experiments of Muschenbroeck, is diminished by the addition of lead. This alloy is easily decomposed, and the lead separated by cupellation. XV I. Silver is easily alloyed with copper by fusion. The com- pound is harder and more sonorous than silver, and retains its white colour even when the proportion of copper exceeds one-half. The hardness is a maximum when the copper amounts to one-fifth of the silver. The standard or sterling silver of Britain, of which coin is made, is a compound of 12-£ silver and one copper. Its specific gravity after simple fusion is 10*200.§ By calculation it should be 10*351. Hence it follows that the alloy expands, as is the case with gold when united to copper.|| The specific gravity of Paris standard silver, composed of 137 parts silver and seven cop- per, according to Brisson, is 10*1752; but by hammering, it be- comes as high as 10*3765. The French silver coin, at least during the old government, was not nearly so fine, being composed of 261 parts of silver and 27 of copper, or one part of copper alloyed with 9A of silver. Its specific gravity, according to Brisson, was 10*0476; but after being coined, it became as high as 10-4077. The Austrian silver coin, according to Wasserberg, contains ^fa of copper.^] The * Wasserberg, i. 160. f I|li(i- * Lewis, Neuman's Chem. p. 57. § Cavallo's Nat. Phil. ii. 76. Dr Shaw makes it 10-535 after hammering, as it appears from his table. Shaw s Boyle, ii. 345. || I find the specific gravity of our new silver (1817) 10-3121. The weight of a shilling is 87-55 grains. *I V\ asserberg, i. 155. The following table exhibits the composition of different Euro- pean coins, according to my experiments. Alloy >er Weight of silver, that of , cent the copper being 1. British - • 7-5 - 125 Dutch 8 • 11-5 French - 9 . 101 Austrian 9-5 ■ 9-5 Sardinian . 9-5 . 95 Spanish C10-5 £ 15-5 - . 8-5 5-5 Portuguese - 11 - 8 Danish 12 - 7-3 Swiss - 21 - 3-8 . Russian 24 . 3-6 Hamburgh • 50 - 1 Chap. III.] SILVER. 389 silver coin of the ancients was nearly pure, and appears not to have been mixed with alloy. This seems to be the case also with coins of the East-Indies; at least a rupee which I analysed contained only fa part of copper; a proportion so small that it can scarcely be supposed to have been added on purpose. A pound of standard silver is coined into 62 shillings.* XVII. The alloy of silver and tin is very brittle and hard. It was examined by Kraft and Muschenbroeck. According to them, one part of tin and four of silver form a compound as hard as bronze. The addition of more tin softens the alloy. It has a gra- nular appearance, and is easily oxidized. According to Gellert, these metals contract in uniting.! Mr. Hatchett found that silver made standard by tin was brittle, and did not ring well.! XVIII. The amalgam of silver is easily formed by throwing pieces of red hot silver into mercury heated till it begins to smoke. It forms dendritical crystals, which, according to the Dijon acade- micians, contain eight parts of mercury and one of silver. It is of a white colour, and is always of a soft consistence. Its specific gravity is greater than the mean of the two metals. Gellert has even remarked, that when thrown in pure mercury, it sinks to the bottom of that liquid.^ When heated sufficiently, the mercury is volatilized, and the silver remains behind pure. This amalgam is sometimes employed, like that of gold, to cover the surfaces of the inferior metals with a thin coat of silver. FAMILY v. This family contains the five following metallic bodies.—1. Gold —2. Platinum—3. Palladium—4. Rhodium—5. Iridium. They all require a strong heat to fuse them; they are all insolu- ble in nitric acid, and their oxides are reducible to the metallic state by the application of mere heat. The first column of this table gives the supposed proportion of alloy in 100 parts of the respective coin; the second gives the weight of silver contained in each coin, on the suppo- sition that the weight of the copper with which the silver is alloyed is always 1. Nicholson's Jour. xiv. 409. • [In the coin of the United States, 1485 parts of pure silver are alloyed with 179 parts of pure copper, and make 1664 parts of standard silver, of which 15 ounces are equal in value to one ounce of standard gold. So that I lb. or 12 oz. standard silver, containing M) oz. 14dwts. bfa gr. pure silvi r. The standard gold consists of eleven parts pure gold, and one part ot" an alloy; which consists of equal parts of silver and copper.—C] ! Metallurgic Chem. p. 140. t On the Alloys of Gold, p. 33. § Gellcrt's Metallurgic Chemistry, 142. 390 SIMPLE COMBUSTIBLES. SECTION I. OF GOLD. Gold seems to have been known from the very beginning of the world. Its properties and its scarcity have rendered it more valua- ble than any other metal.* 1. It is of an orange-red, or reddish-yellow colour, and has no perceptible taste or smell. Its lustre is considerable, yielding only to that of platinum, steel, silver, and mercury. 2. It is rather softer than silver. Its specific gravity is 19*3.! 3. No other substance is equal to it in ductility and malleability. It may be beaten out into leaves so thin, that one grain of gold will cover 56| square inches. These leaves are only ftgS'06"6 of an inch thick. But the gold leaf with which silver wire is covered has only T^ of that thickness. An ounce of gold upon silver wire is capable of being extended more than 1300 miles in length.! 4. Its tenacity is considerable ; though in this respect it yields to iron, copper, platinum, and silver. From the experiments of Sickingen, it appears that a gold wire 0-078 inch in diameter is capable of supporting a weight of 150.07 lbs. avoirdupois, without breaking.^ 5. It melts at 32° of Wedgewood's pyrometer.|| When melted, it assumes a bright bluish-green colour. It expands in the act of fusion, and consequently contracts while becoming solid more than most metals; a circumstance which renders it less proper for cast- ing into moulds.^} It requires a very violent heat to volatilize it; it is therefore, to use a chemical term, exceedingly fixed. Gasto Claveus informs * The fullest treatise on gold hitherto published is that by Dr. Lewis in his Philosophical Commerce of the Arts. The account of gold in Wasserberg's Institutiones Chemise, vol. i. is, a great part of it at least, nearly a translation of Dr. Lewis; but it contains likewise seve- ral discoveries of posterior date, chiefly made by Bergman. Mr. Hatchett's Experiments and Observations on the Alloys, Specific Gravity, and comparative wear of Gold, published in the Phil. Trans, for 1803, are of the utmost importance, on account of the care with which they were made, and the many mistaken notions which they have enabled us to rec- tify. Proust published a valuable paper on gold in the Journal de Physique. It was after- wards examined by Vauquelin; (Ann.de Chim. lxxvii. 321), Oberkamp, (Ibid. lxxx. 140), and Berzelius, (Ibid, lxxxiii. 166.) ! The specific gravity of gold varies somewhat according to its state, that being heaviest which has been hammered or rolled. Dr. Lewis informs us that he found, on many different trials, the specific gravity of pure gold, well hammered, between 19-300 and 19-400. The 6pecific gravity of one mass which he specifics was 19-376, (Philosophical Commerce of the Arts, p. 41). Brisson found the specific gravity of another specimen of fine gold, hammer- ed, 19-361. Mr. Hatchett tried gold of 23 carats 3$ grains, (or gold containing 1-96 of al- loy) ; its specific gravity was 19-277. * See Shaw's Boyle, i. 404, and Lewis's Phliosoph. Commerce of the Arts, p. 44. § Ann. de Chim. xxv. 9. || According to the calculation of the Dijon academicians, it melts at 1298$ Fahrenheit; according to Mortimer, at 1301°. •J Lewis's Philosophical Commerce, p. 67. C BOOK I. \ DIVISION 2. Chap. III.] gold. 391 us that he put an ounce of pure gold in an earthen vessel, into that part of a glass-house furnace where the glass is kept constantly melted, and kept it in a state of fusion for two months, yet it did not lose the smallest portion of its weight.* Kunkel relates a similar experiment attended with the same result;! neither did gold lose any perceptible weight, after being exposed for some hours to the utmost heat of Mr. Parker's lens.! Homberg, how- ever, observed, that when a very small portion of gold is kept in a violent heat, part of it is volatilized.^ This observation was con- firmed by Macquer, who observed the metal rising in fumes to the height of five or six inches, and attaching itself to a plate of silver, which it gilded very sensibly ;|J and Mr. Lavoisier observed the very same thing when a piece of silver was held over gold melted by a fire blown by oxygen gas, which produces a much greater heat than common air.^j After fusion, it is capable of assuming a crystalline form. Tillet and Mongez obtained it in short quadrangular pyramidal crystals. 6. Gold is not in the least altered by being kept exposed to the air; it does not even lose its lustre. Neither has water the smallest action upon it. II. It is capable, however, of combining with oxygen, and even of undergoing combustion in particular circumstances. The result- ing compound is an oxide of gold. Gold must be raised to a very high temperature before it is capable of abstracting oxygen from common air. It may be kept red hot almost any length of time without any such change. Homberg, however, observed, that when placed in the focus of Tschirnhaus's burning-glass, a little of it was converted into a purple-coloured oxide; and the truth of his observations was confirmed by the subsequent experiments of Macquer with the very same burning-glass.** But the portion of oxide formed in these trials is too small to admit of being exa- mined. Electricity furnishes a method of oxidizing it in greater quantity. If a narrow slip of gold leaf be put, with both ends hanging out a little, between two glass plates tied together, and a strong elec- trical explosion be passed through it, the gold leaf is missing in se- veral places, and the glass is tinged of a purple colour by the por- tion of the metal which has been oxidized. This curious experi- ment was first made by Dr. Franklin ;!! it was confirmed in 1773 by Camus. The reality of the oxidizement of gold by electricity was disputed by some philosophers, but it has been put beyond the reach of doubt by the experiments of Van Marum. When he made electric sparks from the powerful Teylerian machine pass through a gold wire suspended in the air, it took fire, burnt with a • •« Nee minimum de pondere decidisse conspexi." Gastonis Clavei Apologia Argyro- poeise et Chrysopoese adversus Thomam Erastum, Theatrum Chemicum ii. 17. t Lewis, Philosophical Commerce, p. 70. * Kirwan's Mineralogy, i. 92. § Mem. Par. 1702, p 147. II Dictionaire de Chimie,ii. 148. »f Kirwan's Min ii. 92. ** Diet. ii. 153. ff- Lewis's Philosoph. Cora.me.roe, p. 175. This work was published in 170S 392 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. green-coloured flame, and was completely dissipated in fumes, which, when collected, proved to be a purple-coloured oxide of gold. This combustion, according to Van Marum, succeeded not only in common air, but also when the wire was suspended in hy- drogen gas, and other gases which are not capable of supporting combustion. The combustion of gold is now easily effected by ex- posing gold leaf to the action of the galvanic battery. I have made it burn with great brilliancy, and a green-coloured flame, by exposing a gold wire to the action of a stream of oxygen and hydro- gen gas mixed together and burning. Now, in all cases of com- bustion, the gold is oxidized. We are acquainted only with two oxides of gold. The protoxide has a green colour, the peroxide is reddish-brown. 1. Of these the peroxide is most easily procured ; it is, there- fore, best known. It may be procured in the following manner: 1 part of nitric and 4 of muriatic acid are mixed together, and pour- ed upon gold: an effervescence takes place, the gold is gradually dissolved, and the liquid assumes a yellow colour.* Let this solu- tion be rendered as neutral as possible by cautiously evaporating it to dryness, and re-dissolving it in water. Into the solution pour a quantity of potash, and then heat the liquid. A voluminous pre- cipitate gradually appears. It must be carefully washed with water and dried. In this state it is a reddish-brown powder, tasteless and insoluble in water, but readily soluble in muriatic acid. When ex- posed to even a moderate heat, it is deprived of its oxygen, and re- duced to the metallic state. The following table exhibits the com- position of this oxide, according to the most accurate experiments hitherto made: Bergman.! Proust.^ Oberkampf.§ Berzelius. U Gold 100 - 100 - 100 - 100 Oxygen 9*889 - 8*57 - 10*01 - 12*077 2. When the permuriate of gold is heated till it ceases to give out chlorine gas, a straw-yellow mass remains which is insoluble in cold water, and which is a protomuriate of gold. When this sub- stance is treated with caustic potash a green-coloured powder is separated, which is protoxide of gold. In a short time this protoxide divides itself into two parts. One-third deprives the other two- thirds of the whole of their oxygen and becomes peroxide, while the two-thirds*are reduced to the metallic state.^f From this it is obvious that the peroxide of gold contains only one-third of the oxygen which exists in the peroxide. If, therefore, we adopt Ber- zelius's analysis of the peroxide as most correct, it follows that p o- toxide of gold is composed of—Gold 100—Oxygen 4*026. If we take the quantity of oxygen which unites with 100 gold at * [Linen rags dipt in this solution, dried and burnt to tinder, are used (moistened with a solution of common salt) to give a slight gilding to silver. The flame of the rug when burn- ing, is a beautiful green ; which is also the colour of the finest and thinnest leaf gold when held up to the light—C.] t Opusc. ii. 201. \ Nicholson's Journal, xiv. 238, 324. \ Ann de Chim. lxxx. 155. fl Ibid, lxxxiii. 166. •J Berzelius, Ann. de Chim. lxxxiii. 166. Chap. III.] GOLD, 393 4*02 ; and suppose the protoxide a compound of 1 atom gold 4- 1 atom oxygen, then the weight of an atom of gold will be 24-875, the weight of an atom of protoxide will be 25*875, and the weight of an atom of peroxide 27-875. We have no means of verifying these numbers, as we are not in possession of accurate analyses of any of the salts of gold.* 3. Berzelius thinks that there exists an intermediate oxide, which constitutes a component part of the purple of Cassius. But he has not established its existence by decisive experiments. III. We are not in possession of any accurate experiments either respecting the chloride, iodide, or fluoride of gold. IV. Gold does not unite with azote, hydrogen, carbon, boron, or silicon. V. Margraff failed in his attempts to unite gold with phosphorus;! but Pelletier was fortunate enough to succeed by melting together in a crucible half an ounce of gold and an ounce of phosphoric glass,! surrounded with charcoal. The phosphuret of gold thus produced was brittle, whiter than gold, and had a crystallized appearance. It was composed of 23 parts of gold and one of phosphorus.§ He formed the same compound by dropping small pieces of phospho- rus into gold in fusion.|| By the application of a sufficient heat, the phosphorus is dissipated and the gold remains. Oberkampf formed phosphuret of gold by precipitating muriate of gold by means of water impregnated with phosphureted hydrogen gas. VI. Sulphur, even when assisted by heat, has no action on gold whatever ; nor is it ever found naturally combined with sulphur, as is the case with most of the other metals ; yet it can scarcely be doubted that sulphur exercises some action on gold, though but a small one : for when an alkaline hydro-sulphuret<\\ is dropped into a solution of gold, a black powder falls to the bottom, which is found to consist of gold and sulphur; and when potash, sulphur, and gold, are heated together, and the mixture boiled in water, a con- siderable portion of gold is* dissolved, as Stahl first discovered. Three parts of sulphur, and three of potash, are sufficient to dis- solve one of gold. The solution has a yellow colour. When an acid is dropped into it, the gold falls down, united to the sulphur in the state of a reddish powder, which becomes gradually black.** The composition of this sulphuret has been investigated by Bxx- cholz!!and Oberkampf-!! The following are the results which they obtained: Bucholz. Oberkampf. Gold - 100 - 100 Sulphur - 21-95 - 24*39 * I think it probable that the equivalent number for peroxide of gold is 9^25 ! Opusc. i. 2. * Phosphoric acid evaporated to dryness, and then fused. \ BTuil^^undersmo'd a combination of sulphureie^hydrogen and an alkali These compounds will be described hereafter. ** Stahl's Opusc Chjnrc -Phys.Med. p. 606 |! Beitrage, iii. 171. ** A1"1- de Ch,ra'lxxx* 1**« Vol. I. 3 D 394 SIMPLE COMBUSTIBLES. $ ROOK 1. £ DIVISION t. The analysis of Oberkampf nearly agrees with Berzelius' esti- mate of the composition of the peroxide of gold. The two, there- fore, serve to confirm each other. VII. There appears to be a strong affinity between gold and ar- senic : but in consequence of the great volatility of the latter metal, it is difficult to unite them by fusion. Bergman succeeded in mak- ing gold take up ^th of its weight of arsenic* Mr. Hatchett added 453 grains of arsenic to 5307 grains of melted gold, and, stirring the whole rapidly with an iron rod, poured the mixture into an iron mould. Only six grains of the arsenic were retained; so that the alloy contained only ^fjth of arsenic. It had the colour of fine gold; and though brittle, yet it bent in some measure before it broke. When once united to gold, arsenic is not easily expelled by heat. Mr. Hatchett discovered that gold readily imbibes, and combines with, arsenic, when heated to redness. A plate of gold was exposed red hot to the fumes of arsenic by suspending it near the top of a dome, made by luting one crucible inverted over ano- ther. In the lower crucible some arsenic was put, and the whole exposed to a common fire for about 15 minutes. The arsenic had acte*d on the gold, and combined with its surface. The alloy being very fusible had dropped off as it formed, leaving the gold thinner, but quite smooth. The alloy of gold and arsenic formed a button in the undermost crucible. This button had a grey colour, and was extremely brittle.! VIII. Potassium and sodium may readily be combined with gold by heat, as Davy ascertained. The alloys are destroyed in the open air, or when put into water. IX. We are not acquainted with the action of gold on, the metal- lic bases of the alkaline earths or earths proper. X. Iron unites very readily with gold by fusion in all its states of soft iron, cast iron, and steel. The alloy was examined by Mr. Hatchett, who found it remarkably ductile when composed of 11 gold and 1 iron. It was easily rolled into plates, cut into blocks, and stamped into coin, without its being necessary to anneal it. The colour was a pale yellowish-grey approaching to a dull white; its specific gravity was 16-885. The bulk of the metals before fusion was 2799; after their union the bulk was 2843. Hence they suffer an expansion, as had been previously noticed by Gel- lert. Suppose the bulk before union to have been 1000, after union it becomes 1014*7.! This alloy is harder than gold. Dr. Lewis even says that it is fit for making edge-tools ; but in that case the proportion of iron was doubtless increased. When the iron is three or four times the quantity of gold, the alloy, according to Dr. Lewis, has the colour of silver :§ according to Wallerius it still continues magnetic.|j Gold answers well as a solder for iron. • Opusc. n. 281. J On the Alloys of Gold, p. 7. $ Ibid. p. 37 § Phil. Com. p. 85. 11 Wasserberg, i. 115. Chap. III.] 60LD. 395 XI. Mr. Hatchett melted a mixture of 11 gold and 1 nickel, and obtained an alloy of the colour of fine brass. It was brittle, and broke with a coarse-grained earthy fracture. The specific gravity of the gold was 19*172 ; of the nickel 7*8; that of the alloy 17-068. The bulk of the metals before fusion was 2792, after fusion 2812. Hence they suffered an expansion. Had their bulk before fusion been 1000, after fusion it would have become 1007. When the proportion of nickel is diminished, and copper substituted for it, the brittleness of the alloy gradually diminishes, and its colour ap- proaches to that of gold. The expansion, as was to be expected, increases with the proportion of copper introduced.* XII. Mr. Hatchett melted together 11 parts of gold and 1 part of cobalt. The alloy was of a dull yellow colour, very brittle, and the fracture exhibited an earthy grain. Its specific gravity was 17*112. The bulk of the metals before fusion being 1000, after fusion, became 1001. Hence they experienced a very small de- gree of expansion. The brittleness of gold alloyed with cobalt con- tinues when the cobalt does not exceed T^th of the whole ; but when it is reduced below that proportion, the gold becomes some- what ductile.! XIII. We are indebted to Mr. Hatchett for some curious ex- periments on the alloy of manganese and gold. Olive oil was re- peatedly mixed and burned with blauk oxide of manganese, after which a piece of gold was imbedded in the oxide, placed in a cru- cible lined with charcoal, and well luted. The crucible was expo- sed for three hours to a strong heat. By this means a portion of manganese was reduced and combined with the gold. The alloy was externally of a pale yellowish-grey colour, with a considerable lustre, almost equal to that of polished steel. It was very hard, and possessed some ductility. The fracture was coarse, very spongy, and of a reddish-grey colour. It was not altered by ex- posure to the air. From the analysis of Mr. Bingley, the alloy was found to vary in the proportion of manganese from £th to -Jth of the whole. It is more difficult of fusion than gold. When kept melted with access of air, the whole manganese is oxidized, and swims on the surface. The manganese may be separated by cu- pellation with lead.! XIV. The alloys of gold with uranium and cerium are unknown. XV. Zinc may be united to gold in any proportion by fusion. The alloy is the whiter and the more brittle the greater quantky of zinc it contains. An alloy, consisting of equal parts of these metals, is verv hard and white, receives a fine polish, and does not tarnish readily. It has, therefore, been proposed by Mr. Hellot§ as very proper for the specula of telescopes. Mr. Hatchett united, 11 part's of gold and 1 of zinc. The alloy was of a pale grt: nish-vellow like brass, and very brittle. Its specific gravity- was 16*93>. The bulk of the metals'before union was 1000; after • Hatch, tt on the Alloys of Gold, p. 21. ! Ibid. p. 19. + ibid. p. 22. $ Mem. Acad. Par. 1735. 396 SIMPLE COMBUSTIBLES. C BOOK I. ^ division 2> it, 997 nearly. Hence the union is accompanied with a small de- gree of contraction. The brittleness continued though the zinc was reduced to ^th of the alloy, ^ths of copper being added to reduce the gold to the standard value. Even the fumes of zinc near melted gold are sufficient to render the ptecious metal brittle.* Hellot affirms, that when 1 part of gold is alloyed with 7 of zinc, if the zinc be elevated in the state of flowers, the whole of the gold rises along with it. XVI. Gold combines very readily with bismuth by fusion. An alloy composed of 11 gold and 1 bismuth was found by Hatchett to have a greenish yellow colour, like bad brass. It was very brit- tle, and had a fine grained earthy fracture. Its specific gravity was 18*038. The bulk of the metals before fusion was 1000, after it only 988. They had suffered, therefore, a considerable contrac- tion. The properties of the alloy continued nearly the same when the bismuth amounted to ^th of the compound; the requisite quan- tity of copper to reduce the gold to standard being added. When the bismuth was diminished beyond this proportion, thr colour of the alloy became nearly that of gold; but its brittleness continued even when the bismuth did not exceed W^th °f tne mass. As the proportion of bismuth diminished, and that of the copper increased (the gold being always standard), the contraction disappeared, and an expansion took place, which was soon much greater than when copper alone was need to alloy the gold. This curious progression will appear evident from the following table.! Metals. Grains.' Specific gra-vity of alloy. Bulk before fusion. Do. after. Change of bulk. Gold Bismuth 442 38 18*038 1000 988 —12 Gold Copper Bismuth 442 30 8 17*302 1000 1018 + 18 Gold Copper Bismuth 442 34 4 16*846 1000 1044 +44 Gold Copper Bismuth 442 37-5 0*5 16*780 1000 1047 +47 Gold Copper Bismuth 442 37-75 0*25 17*495 1000 1027 +27 * Hatchett on the Alloys of Gold, p. 17. ! The specific gravity of the gold was 19-172 (it was 23 carats 8-j grains fine), of tfie bismuth 9-822, of the copper 8-895. Chap. III.] GOLD. 397 So great is the tendency of bismuth to give brittleness to gold, that the precious metal is deprived of its ductility, merely by keep- ing it, while in fusion, near bismuth raised to the same tempera- ture.* XVII. When 11 parts of gold are melted with one of lead, an alloy is formed, which has externally the colour of gold, but is ra- ther more pale. It is exceedingly brittle, breaking like glass, and exhibiting a fine-grained fracture, of a pale brown colour, without any metallic lustre, and having the appearance of porcelain. The brittleness continues even when the proportion of lead is so far diminished that it amounts only to -r-gV^th of the alloy. Even the fumes of lead are sufficient to destroy the ductility of gold. The specific gravity of the alloy of 11 gold and 1 lead is 18-080, which is somewhat less than the mean; so that the metals undergo an ex- pansion. This expansion increases as the lead diminishes (the gold remaining the same, and the deficiency being supplied by cop- per), and becomes a maximum when the lead amounts only to gf^th of the alloy. The following table exhibits a view of this remarka- ble expansion: Metals. Grains. Specific gra-vity of alloy. Bulk before union. Do. after. Expansion. Gold Lead 442 38 18*080 1000 1005 5 Gold Lead Copper 442 19 19 17*765 1000 1005 6 Gold Copper Lead 442 30 8 17-312 1000 1022 22 Gold Copper Lead 442 34 4 17032 1000 1035 35 Gold Copper Lead 442 37*5 0*5 16*627 1000 1057 57 Gold Copper Lead 442 37*75 0*25 17*039 1000 1031 31] • See Hatchet*, on the Alloys of Gold, p. 26. f !*»«•• P- 29 »hd 67. 398 SIMPLE COMBUSTIBLES. f B00K '• £nivisiox 2. XVIII. Tin unites readily with gold by fusion, and was sup- posed by the older chemists to have the property of communicating brittleness to the alloy in how small a portion soever it was united to the precious metal; but later and more precise experiments have shown that this opinion was ill founded. The mistake was first removed by Mr. Alchorne, in a set of experiments on this alloy published in the Philosophical Transactions for 1784; and these have been amply confirmed by the subsequent trials of Mr. Hatch- ett. An alloy of 11 gold and 1 tin has a very pale whitish colour; brittle when thick; but when cast thin, it bends easily, but breaks when passed between rollers. The fracture is fine grained, and has an earthy appearance. The specific gravity of this alloy was 17*307. The bulk of the two metals before fusion being reckoned * 1000, after fusion, it was reduced to 981 ; so that the metals con- tract very considerably by uniting together.* When gold was made standard by equal parts of tin and copper, an alloy was ob- tained of a pale yellow colour, and brittle; but when the tin amounted only to^ of the whole, the alloy was perfectly ductile.! Indeed, from the experiments of Mr. Alchorne, we learn, that when gold is alloyed with no more than 7Vtn °f tm> *l retains its ductility sufficiently to be rolled and stamped in the usual way. But Mr. Tillet showed, as was indeed to have been expected, that when heated to redness, it falls to pieces, owing to the fusion of the tin. Both of these facts have been confirmed by the late expe- riments of Mr. Bingley. He found that an alloy of gold with ^th of tin, when annealed in a red heat, just visible by day-light, which is equal to 5° of Wedgewood, was quite ductile, and capable of being worked into any form ; but when heated to a cherry red, or to 10° Wedgewood, blisters began to appear on the surface of the bar; its edges curled up; and at last it lost its continuity, and fell into a dark-coloured mass with little of the metallic lustre.! XIX. The alloy of gold and copper is easily formed by melting the two metals together. This alloy is much used, because copper has the property of increasing the hardness of gold without injuring its colour. Indeed a little copper heightens the colour of gold without diminishing its ductility. This alloy is moVe fusible than gold, and is therefore used as a solder for that precious metal.§ Copper increases likewise the hardness of gold. According to Muschenbroeck, the hardness of this alloy is a maximum when it is composed of 7 parts of gold and 1 of copper.|| Gold alloyed with -V-d of pure copper by Mr. Hatchett, was perfectly ductile, and of a fine yellow colour, inclining to red. Its specific gravity was 17*157. This was below the mean. Hence the metals had suffered an expansion. Their bulk before union was 2732, after union 2798. So that 916| of gold and 83* of copper when united, » Hatchett, on the Alloys of Gold, p. 32. ] Hatchett, Ibid. 4 Ibid. ^ Wasserberg, i. 112. I.Ibid. Chap. III.] GOLD. 399 instead of occupying the space of 1000, as would happen were there no expansion, become 1024.* Gold coin, sterling or standard gold, consists of pure gold al- loyed with ^th of some other metal.! The metal used is always either copper or silver, or a mixture of both, as is most common in British coin. Now it appears that when gold is made standard by a mixture of equal weights of silver and copper, that the expansion is greater than when the copper alone is used, though the specific gravity of gold alloyed with silver differs but little from the mean. The specific gravity of gold alloyed with -jTth of silver and -j^th of copper was 17*344. The bulk of the metals before combination was 2700; after it 27674 We learn from the experiments of Mr. Hatchett that our standard gold suffers less from friction than pure gold, or gold made standard by any other metal besides silver and copper; and that the stamp is not so liable to be obliterated as in * Hatchett on the Alloys of Gold, p. 66. The gold was already alloyed with l-96th of copper; the expansion, had the gold been pure, would have been greater. For the spe- cific gravity of an alloy of 11 gold and 1 copper, (supposing the specific gravity of gold 19-3, of copper 8-9), should be by calculation 17-58. Its real specific gravity is only 17-157. f [According to the standard regulations of the British mint, 1 lb. troy weight of gold, consists of 11 oz. of pure gold and 1 oz. ofcopper: it used to be coined into 44-j guineas; it now yields 46^ of the new gold coin, called sovereigns, of which 934 weigh 20 lbs. troy weight The lb. standard of silver, consists of 11 oz. 2 dwt. pure silver, and 18 dwt. copper and is coined into 66 shillings sterling. , The quantity of precious metals annually raised from the mines, amounts to about 10i millions sterling, of which -j millions are gold, and 8 millions are silver. Of the gold, 2,300,000 is from America, and about 200,000 from Europe, Asia, and Africa. Of the silver, 7 millions come from America, and 1 million from the other parts of the globe. 8 Brande's Journal, 246. I have good authority for stating, that the amount of gold used up and consumed in works of art in the United States, is about 40,000 dollars worth yearly:' and the amount of silver so used and consumed, about 500,000dollars worth yearly. This is independent of all Eu- ropean importation of gold and silver leaf, and gilt and plated goods.—C] i The first guineas coined were made standard by silver, afterwards copper was added to make up for the deficiency of the alloy; and as the proportion of the silver and copper varies, the specific gravity of our gold coin is various also. The specific gravity of gold made standard by silver is - - - 17-927 copper - - - 17-157 silver and copper - - 17-344 The following trials made by Mr. Hatchett will show the specific gravity of our coius in different reigns. Reign. Date. Specific gravity. Charles II. a five-guinea piece - - lfi8l 17-825. James II. a two-guinea piece - - 1687 17-634. William III. a five-guinea piece - - 1701 17-710. George I. a quarter-guinea - - 1718 16-894. George U. a guinea - 1735 17-637. ---------- a two-guinea piece - - 1740 17-848. George 111. a one guinea - - 1761 17-737. a one guinea a one guinea 1766 17-655. 1774 17-726. a one guinea - - 1775 17-698. a one guinea - - 1776 17-iS6. a one guinea - - 1777 17750. a one guinea - - l^ 17-20?. a one guinea - - 1786 17-465. a one guinea - 1788 17-418. 400 SIMPLE COMBUSTIBLES. S B00K1. £nivisio> 2. pure gold. It therefore answers better for coin. A pound of standard gold is coined into 442 guineas.* XX. The amalgam of gold is formed very readily, because there is a very strong affinity between the two metals. If a bit of gold be dipped into mercury, its surface, by combining with mercury, becomes as white as silver. The easiest way of forming this amalgam is to throw small pieces of red-hot gold into mercury heated till it begins to smoke. The proportions of the ingredients are not determinable, because they combine in any proportion. This amalgam is of a silvery whiteness. By squeezing it -through leather, the excess of mercury may be separated, and a soft white amalgam obtained, which gradually becomes solid, and consists of about 1 part of mercury to 2 of gold. It melts at a moderate temperature ; and in a heat below redness the mercury evaporates, and leaves the gold in a state of purity. It is much used in gild- ing. The amalgam is spread upon the metal, which is to be gilt; and then by the application of a gentle and equal heat, the mercury is driven off, and the gold left adhering to the metallic surface; this surface is then rubbed with a brass wire brush under water, and afterwards burnished.!! XXI. When silver and gold are kept melted together, they com- bine, and form an alloy composed, as Homberg ascertained, of 1 part of silver and 5 of gold. He kept equal parts, of gold and sil- ver in gentle fusion for a quarter of an hour, and found, on break- ing the crucible, two masses, the uppermost of which was pure silver, the undermost the whole gold combined with \ of silver. Silver, however, may be melted with gold in almost any propor- tion ; and if the proper precautions be employed, the two metals remain combined together. The alloy of gold and silver is harder and more sonorous than gold. Its hardness is a maximum when the alloy contains 2 parts of gold and 1 of silver.^ The density of these metals is a little di- minished,|| and the colour of the gold is much altered, even when the proportion of the silver is small; 1 part of silver produces a Reign. Date. Specific gravity. George III. five guineas - - 1793 17-712. ---------- ten half-guineas - - 1801 17-750. ----------15 seven-shilling pieces (a) - 1802 17-793. (a) Supposing guineas, half-guineas, and seven-shilling pieces, to be made from the same metal, there is reason to expect (in a given comparative sum of each) aii increase of specific gravity in the smaller coins, as a natural consequence of rolling, punching, annealing, blanch- ing, milling, and stamping; the effects of which must become more evident in proportion to the number of the small pieces required to form a given sum of the larger coins. The average specific gravity of our gold coin, at the present time, may probably be esti- mated at 17-724. * [For the standard gold of the United States, see p. 389.—C.] ! Gellert's Metallurgic Chemistry, 375, and Lewis, Phil. Com. p. 75. * [It is absolutely necessary, for the preservation of health, to have a chimney with'a strong draught, artificially made in it, over the evaporating mercury : also, a glass screen interposed between the workmen and the fire. II" these precautions be not taken, death en- sues in no long time.—C.] § Muschenbroek. I Hatchett. Chap. III.] PLATINUM. 401 sensible whiteness in 20 parts of gold. The colour is not only pale, but it has also a very sensible greenish tinge, as if the.light reflected by the silver passed through a very thin covering of gold. This alloy, being more fusible than gold, is employed to solder pieces of that metal together. SECTION II. OF PLATINUM. Gold, the metal just described, was known in the earliest ages, and has been always in high estimation, on account of its scarcity, beauty, ductility, and indestructibility. But platinum, though perhaps inferior in few of these qualities, and certainly far superior in others, was unknown in Europe, as a distinct metal, before the year 1749.* I. It has hitherto been found only in America, in Choco in Peru, and in the mine of Santa Fe, near Carthagena. Vauquelin has lately discovered it in considerable quantity in the silver mines of Guadalcanal, in the province of Estremadura in Spain.! The workmen of the American mines must no doubt have been early acquainted with it; and indeed some of its properties are obscure- ly mentioned by some of the writers of the 16th century. Mr. Charles Wood, assay-master in Jamaica, saw it in the West Indies about the year 1741. He gave some specimens of it to Dr. Brown- rigg, who presented it to the Royal Society in 1750. In 1748 it was noticed by Don Antonio de Ulloa, a Spanish mathematician, who, in 1735, had accompanied the French academicians to Peru • Father Cortinovis, indeed, has attempted to prove that this metal was the electrum of the ancients. See the Chemical Annals of Brugnatelli, 1790. That the electrum of the an- cients was a metal, and a very valuable one, is evident from many of the ancient writers, particularly Homer. The following lines of Claudian are alone sufficient to prove it: "Atria cinxit ebur, trabibus solidatur ahenis " Culmen et in celsas surgunt electro columnas." L. I. v. 164. Pliny gives us an account of it in his Natural History. He informs us that it was a com- position of silver and gold ; and that by candle-light it shone with more splendour than sil- ver. The ancients made cups, statues, and columns of it. Now, had it been our platinum, is it not rather extraordinary that no traces of a metal, whbh must have been pretty abun- dant, should be perceptible in any part of the old continent ? As the passage of Pliny contains the fullest account of electrum to be found in any ancient author, I shall give it in his own words, that every one may have it in his power to judge whether or not the description will apply to the platinum of the moderns. « Omni auro inest argentum vario pondere.—Ubicunque quinta argenti poi-Uo est, elec- trum vocatur. Scrobes ea: reperiuntur in Canaliensi. Fit et cura electrum argento addito. Quod si quintam portionem excessit incudibus non restit.t Et electro auctontas, Homero teste, qui Menelai regiam auro, electro, argento, ebore fulgere tradit. Minerva templum habet Lindos insula Rhodiorum in quo Helena sacravit calicem ex electro.—Electri natura est ad lucernarum lu.nina clarius argento splendere. Quod est natiyum et venenadepreheu- dit. Namque discurrunt in calicibus arcus coelestibus similes cum igneo stridore, et gemma ratione prxdicuin "'—Lib. xxxiii. cap. iv. VAnn. de China. Ix. 317. ot. I. 3 E 402 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. in their voyage to measure a degree of the meridian. A paper on it was published by Mr. Wood in the 44th volume of the Philoso- phical Transactions for 1749 and 1750. Dr. Lewis began a set of experiments on it in 1749, the result of which was published in four papers in the Philosophical Transactions for 1754, and after- wards two other papers were added.* These experiments de- monstrate its peculiar nature and its remarkable properties. In 1752, Scheffer of Sweden published a dissertation on this metal, remarkable for its precision, if we consider the small quanity of ore on which he had to work, which was not more than 40 grains. The experiments of Lewis were repeated, and many curious addi- tions made to them by Margraff in 1757.! These dissertations having been translated into French, drew the attention of the che- mists of that country, and induced Macquer and Baume! to make a set of experiments on platinum, which were soon followed by the experiments of Buffon, Tillet, and Morveau ;§ Sickengen,|| Berg- man,^ Lavoisier,** and more lately Mussin Puschkin,!! and Mor- veau ;!! and several other chemists of eminence have added to our knowledge of this mineral. But the experiments of Berzelius§§ and Edmond Davy|||| have added most to our knowledge of its combinations. Crude platina comes from America in small flat grains of a sil- very lustre. In this state it is exceedingly impure, containing, either mechanically mixed, or chemically united, no less than nine other metals; but it may be reduced nearly to a state of purity by the following process. Disssolve the grains in concentrated nitro- muriatic acid with as little heat as possible. Decant the solution from the black matter which resists the action of the acid. Drop into it a solution of sal ammoniac. An orange yellow-coloured precipitate falls to the bottom. Wash this precipitate ; and when dry, expose it to a heat slowly raised to redness in a porcelain cru- cible. The powder which remains is platinum nearly pure. By redissolving it in nitro-muriatic acid, and repeating the whole pro- cess, it may be made still purer. When these grains are wrapt up in a thin plate of platinum, heated to redness, and cautiously ham- mered, they unite, and the whole may be formed into an in- got.^*** * Phil. Trans, xlviii. 638, and 1. 148. See also Phil. Com. p. 443, for a full detail of all the experiments on this metal made before 1763. ! Mem. Berlin, 1757, p. 31, and Margraff's Opusc. ii. 226. $ Mem. Par. 1758, p. 119. § Jour, de Phys. iii. 234. |) Macquer's Dictionary. *fl Opusc, ii. 166. ** Ann. de Chim. v. 137. !! Ann. de Chim. xxiv. 205. # Ibid. xxv. 3. §§ Ibid, lxxxiii. 167. |||| Phil. Mag. xl. 27,209,263, 350. 11 Phil. Mag. xxi. 175. *** [To manufacture Platinum—Boil the ore in grains in dilute muriatic acid; wash them; dissolve in aqua regia (or nitro-muriatic acid of three-fourths muriatic and one-fourth nitric, previously freed from sulphuric acid by barytes); precipitate gradually and cautiously by means of a solution of sal ammoniac containing no iron—this must be previously ascertained. Let the orange-coloured precipitate tall at intervals; when a reddish-coloured precipitate begins to fall, stop—this is pallsidium. Upon which see particularly Mr. Cloud's paper oa these metals, in the 6th vol. of the Am. Phil. Trans, old series. Chap. III.] platinum. 403 1. Platinum, thus obtained, is of a white colour like silver, but not so bright.* It has no taste nor smell. 2. Its hardness is intermediate between that of copper and iron. Its specific gravity when reduced from the ammonio-muriate by heat is 21*47. By hammering it may be increased 3|o-th ; so that its maximum specific gravity is 21*5313.! 3. It is exceedingly ductile and malleable ; it may be hammer- ed out into very thin plates, and drawn into wires not exceed- mg TsVo- mcn in diameter. In these properties it is probably infe- rior to gold, but it seems to surpass all the other metals. 4. Its tenacity is such, that a wire of platinum 0*078 inch in dia- meter is capable of supporting a weight of 274-31 lbs. avoirdupois without breaking.! 5. It is one of the most infusible of all metals, and cannot be melted in any quantity at least, by the strongest artificial heat which can be produced. Macquer and Baume melted small particles of it by means of a blow-pipe, and Lavoisier by exposing them on red hot charcoal to a stream of oxygen gas.§ It may indeed be melted without difficulty when combined or mixed with other bodies, but then it is not in a state of purity. Pieces of platinum, when heat- ed to whiteness, may be welded together by hammering in the same manner as hot iron. 6. This metal is not in the smallest degree altered by the action of air or water. II. It cannot be combined with oxygen and converted into an oxide by the strongest artificial heat of our furnaces. Platinum, indeed, in the state in which it is brought from America, may be partially oxidized by exposure to a violent heat, as numerous ex- periments have proved ; but in that state it is not pure, but com- bined with a quantity of iron. It cannot be doubted, however, that if we could subject it to a sufficient heat, platinum would burn, and be oxidized like other metals : for when Van Marum exposed a wire of platinum to the action of his powerful electrica^ It is not necessary to wash the precipitate, for water will dissolve it. Dry it; expose it in a crucible under a muffle to a strong heat, to drive off and decompose the acids combined with the platinum ; collect the metallic-grey powder; place it by a little at a time in a hol- low steel mould; press itgraduallv bv means of a powerful screw: a layer of about half an inch at a time ; when the hollow of the mould is full, apply the whole force of the screw. Then take the spongy mass to a blacksmith's forge ; heat it to a full white heat, and ham- mer it into the form you wish. When it is to be fashioned into any shape, it should be given to a skilful hammer-man, and gradually formed, annealing it every now and then to prevent its cracking, which will happen, if some skill and patience be not applied. When all the orange-coloured precipitate has been thrown down, the solution still con- tains palladium, and the black undissolved powder, iridium and osmium. If small cuttings or clippings of platinum be stratified in the mould with the grey powder, they may be made to unite by strong pressure, so as to bear welding at the forge.—C] * To this colour it owes its name. Plata, in Spanish, is " silver;" and platina, " little silver " was the name first given to the metal. • Bergman changed that name into platinum, that the Latin names of all the metals might have the same termination and gender. It had been, however, called platinum by Linnseus long before. ! Dr. Wollaston. * Morveau, Ann. de Chim. xxv. 7. § Dr. Clarke,by meansof his oxygen and hydrogen gas blow-pipe, melted piecesof pla^ tinum weighing 100 grains. 404 SIMPLE COMBUSTIBWES. C BOOK I. ^nivisio.v 2. machine, it burnt with a faint white flame, and was dissipated into a species of dust, which proved to be the oxide of platinum. By putting a platinum wire into the flame produced by the combustion of hydrogen gas mixed with oxygen, I caused it to burn with all the brilliancy of iron wire, and to emit sparks in abundance. At present only two oxides of platinum are known ; the protoxide has a black Colour, but the peroxide is dark brown or grey. 1. The protoxide may be obtained by pouring a neutral solution of mercury into a dilute solution of muriate of platinum in hot water. A dense powder precipitates, varying in colour from deep brown to yellow and sometimes olive-green. It is a mixture of calomel and protoxide of platinum. It must be carefully washed and dried and then exposed to a heat just sufficient to volatilize the calomel. A deep black powder remains which is the protoxide. One hundred grains of it when heated to redness give off 12h cubic inches of oxygen gas and are reduced to the metallic state. When heated with lamp-black it gives out the same proportion of carbo- nic acid and is reduced to the metallic state. Mr. Cooper to whom we are indebted for the discovery of this oxide found that it might be heated strongly when mixed with enamellers' flux without being reduced. On this account he considers it as a valuable addition to the colours of enamellers.* From the preceding experiments it follows, that, protoxide of platinum is composed of—Platinum 100 —Oxygen 4*423. Hence an atom of platinum must weigh 22*625, and an atom of protoxide of platinum 23*625. 2. The peroxide of platinum appears to be a compound of 1 atom metal and 3 atoms oxygen, or to be a tritoxide. No accurate account of it has been hitherto published. But Mr. Edmond Davy has ascertained that when his fulminating platinum is treated with nitric acid and heated cautiously a grey oxide remains, which he concludes from his experiments to be composed of—Platinum 100 —Oxygen 11*86. Berzelius endeavoured to obtain the peroxide of platinum by the following process. He decomposed the muriate by adding an excess of sulphuric acid. This excess was distilled off and the sulphate of platinum decomposed by caustic potash add- ed in slight excess. The peroxide separates in the form of a light yellowish-brown bulky powder. When this powder is heated it becomes dark brown, almost black, and gives out water. When the peroxide of platinum is exposed to a high temperature it is re- duced to the metallic state giving out oxygen gas. It dissolves in the fixed alkalies both when caustic and when in the state of car- bonates. It combines likewise with lime, strontium, and barytes. This is the oxide which constitutes the base of the platinum salts-! According to the experiments of Berzelius it contains twice as much oxygen as the protoxide. It is therefore a compound of— Platinum 100—Oxygen 16*494. The mean of Berzelius' numbers and those of Edmond Davy would give 14*177 for the oxygen in * Royal Institution Journal, iii. 119. ! Berzelius, Larbok i Kemien, ii. 422. Chap. IH.J PLATINUM. 405 the peroxide. Now this does not differ much from 13-269 the quantity of oxygen, which would be requisite to form a tritoxide. III. Platinum does not take fire when introduced into chlorine gas ; but it slowly imbibes the gas and is converted into a chloride. Mr. Edmond Davy, to whom we are indebted for all the facts re- specting this combination at present known, is of opinion that there are two chlorides of platinum. The protochloride is soluble in water and has not been much examined. The perchloride is an in- soluble powder. But the existence of this last only has been clear- ly made out.* To obtain this chloride pure platinum is to be boiled in strong muriatic acid adding occasionally a little nitric acid. The solution is to be evaporated to dryness and then digested with a little mu- riatic acid which is likewise to be driven off. The dry mass is to be cautiously heated nearly to redness and boiled with a considerable quantity of water. Being now dried it is pure chloride of platinum. Its colour is dull olive brown or green. It has rather a harsh feel; but is destitute of taste and smell. It is infusible. It does not appear to be altered by exposure to the atmosphere and it is scarcely soluble in water. When heated to redness the chlorine is driven off and pure platinum remains. It is slightly soluble in boiling muriatic acid but it is insoluble in nitric, sulphuric, phos- phoric, and acetic acids. When boiled in potash ley a black pow- der is obtained which yields both oxygen and chlorine by heat-! When it is heated with sulphur or phosphorus, chlorides of sulphur and phosphorus are obtained and phosphorus or sulphuret of plati- num. According to the experiments of Mr. Edmond Davy, the chloride of platinum is composed of Platinum - 100 or nearly 12*125 Chlorine - 37*93 - 4*5 From this analysis we see that it is a compound of 1 atom plati- num 4- 2 atoms chlorine. The soluble chloride, if it be really dis- tinct, must be the protochloride. IV. The iodide of platinum has not been examined. We are ignorant of the action of fluorine on this metal. It does not combine with azote, hydrogen, carbon, boron, or silicon. V. It unites in two proportions with phosphorus. For our knowledge of these two combinations we are indebted to Mr. Ed- mond Davy-! . , , , . 1 Protophosphuret of platinum may be obtained by heating phosphorus and platinum in an exhausted glass tube At a tem- perature considerably below redness they combine with vivid igni- tion and flame. Protophosphuret of platinum has a bluish-grey colour. When it has undergone fusion its lustre is little inferior to that of lead. It crystallizes in cubes. Its specific gravity while porous is 6. It is destitute of taste and smell. It is a non-con- • Phil. Mag. xl. 271. ! Is not this the protoxide of Berzelius? * Phil. Mag. xl. 32. 406 SIMPLE COMBUSTIBLES. £ HOOK 1. £ division 2. ductor of electricity. When strongly heated on platinum it unites with the metal which it perforates with holes. According to the experiments of Mr. Edmond Davy it is composed of—Platinum 100—Phosphorus 21*21. 2. Perphosphuret of platinum is obtained by heating together ammonio-muriate of platinum with about two-thirds of its weight of phosphorus in small bits in a retort over mercury. Towards the end of the experiment the retort should be heated to a dull red to expel every thing volatile. The perphosphuret of platinum has an iron grey colour and a slight metallic lustre. It stains the fir.gers or paper, but the lustre is inferior to that communicated by per- sulphuret of platinum. Specific gravity 5*28. It is destitute of taste and smell, and is a nonconductor of electricity. When heated it becomes ignited and diminishes in bulk without changing its colour. According to the experiments of Mr. Edmond Davy, it is composed of—Platinum 100—Phosphorus 42-85*. VI. Platinum combines with three proportions of sulphur. For the investigation of these compounds also we are indebted to Mr. Edmond Davy.! 1. Protosulphuret of platinum was formed by mixing equal weights of sulphur and platinum in an exhausted glass tube and heating them together. Towards the end of the process the mass was heated nearly to redness to expel every thing volatile. Proto- sulphuret of platinum thus formed is of a dull bluish grey colour. Its lustre is earthy ; but when rubbed on paper it leaves a metallic stain. Its feel is rather harsh. It has no smell or taste. Its spe- cific gravity is 6*2. It is a nonconductor of electricity. It is de- composed when heated with zinc filings. According to the analy- sis of Mr. Edmond Davy, its constituents are—Platinum 100— Sulphur 19-04. 2. Deutosulphuret of platinum is obtained by precipitating pla- tinum from its solution by sulphureted hydrogen gas, and heating the precipitate which falls in close vessels. It is a tasteless loose powder, of a bluish black colour, staining paper and the fingers like black lead. It is composed of—Platinum 100—Sulphur 28*21.! 3. Persulphuret of platinum is obtained by heating a mixture of 3 parts of ammonio-muriate of platinum and 2 parts of sulphur in a glass retort over mercury. The mixture must be gradually heated to redness and continued for some time in that heat till every thing volatile be expelled. It has a dark iron grey colour approaching to black. When in lumps it has a slight metallic lus- tre. It has a soft feel and when rubbed on paper leaves a stain si- milar to that of black lead. Its specific gravity is 3*5. It is a non- conductor of electricity. It does not melt though exposed to a very * The analyses of these two phosphurets agree very well with each other, but they do not correspond with the numbers which we have adopted for the weight of an atom of phos- phorus and platinum. ! Phil. Mag. xl. 27, 219. * Phil. Mag. xl. 219. Chap. III.] PLATINUM. 4Q7 strong heat. When heated with zinc filings combustion takes place and sulphuret of zinc is formed. When heated to redness in the open air the sulphur is expelled and pure platinum remains. According to the analysis of Mr. Edmond Davy, its constituents are—Platinum 100—Sulphur 38*8. The sulphur in these three compounds is as the numbers 1, 1§, 2. Hence the first should be a compound of 1 atom platinum and 1 atom sulphur, the second of 2 atoms platinum and 3 atoms sul- phur, and the third of 1 atom platinum and 2 atoms sulphur. But the numbers do not correspond with the weight of an atom of pla- tinum as deduced from the experiments hitherto made on the sub- ject. Hence it is probable that this number is incorrect. We can- not venture to determine the weight of an atom of phosphorus from these experiments of Mr. Edmond Davy, because the num- bers for the phosphurets and sulphurets do not accord with each other. VII. The alloy of arsenic and platinum was first examined by Scheffer, and afterwards by Dr. Lewis. The addition of white oxide of arsenic causes strongly heated platinum to melt; but the mixture does not flow thin, and cannot be poured out of the cruci- ble. The alloy is brittle and of a grey colour. The arsenic is mostly expelled in a strong heat, leaving the platinum in the state of a spongy mass.* VIII. Platinum unites with potassium and sodium with igni- tion, as Sir H. Davy first ascertained. The alloy is decomposed by the action of air or water.! IX. We are ignorant of the alloys which platinum is capable of forming with the metallic bases of the alkaline earths and earths proper. X. Platinum is usually found alloyed with iron. Dr. Lewis did not succeed in his attempts to unite these metals by fusion, but he melted together cast iron and crude platina, and likewise steel and crude platina. The alloy was excessively hard, very tough, and possessed some ductility when the iron was about |ths of the alloy. The specific gravity greatly exceeded the mean; the platina having destroyed the property which cast iron has of expanding when it becomes solid. This alloy, after being kept ten years, was very little tarnished. At a red heat it was brittle, and appeared, when broken, to be composed of black grains, without any metallic lustre.J: XI. We are unacquainted with the alloys which platinum forms with nickel, cobalt, manganese, uranium, and cerium. XII. Dr. Lewis found that platinum unites with the fumes of zinc reduced from its ore, and acquires about £d of additional weight. The two metals very readily melt, even when the zinc * Phil. Com. p. 515. . + f Platinum is acted on by the caustic alkalies in a red heat, hence it will not answer to be usal as a vessel for analysis when caustic potass or soda is to be exposed in it to this heat.—C] t PbiL Com. p. 534, aud 551. 408 SIMPLE COMBUSTIBLES. $ BOOK I. £ DIVISION 2. does not exceed Ith of the platinum. The alloy is very brittle, of a bluish white colour, and much harder than zinc. One twentieth of platinum destroys the malleability of zinc, and £th of zinc ren- ders platinum brittle.* ^ XIII. Bismuth and platinum readily melt and combine when ex- posed rapidly to a strong heat. Dr. Lewis fused the metals in va- rious proportions, from 1 of bismuth to 24 with 1 of platinum. The alloys were all as brittle, and nearly as soft as bismuth; and when broken, the fracture had a foliated appearance. When this alloy is exposed to the air, it assumes a purple, violet, or blue co- lour. The bismuth can scarcely be separated by heat.! XIV. Dr. Lewis fused crude platina and lead together in vari- ous proportions ; a violent heat was necessary to enable the lead to take up the platinum. Hence a portion of the lead was dissipated. The alloys had a fibrous or leafy texture, and soon acquired a pur- ple colour when exposed to the air. When equal parts of the me- tals were used, the alloy was very hard and brittle; and these qualities diminished with the proportion of platinum. When the alloys were melted again, a portion of the platinum subsided-! Many experiments have been made with this alloy, in order, if possible, to purify platinum from other metals by cupellation, as is done successfully with silver and gold. But scarcely any of the experiments have succeeded; because platinum requires a much more violent heat to keep it in fusion than, can be easily given.§ XV. From the experiments of Dr. Lewis we learn, that tin and platinum readily melt, and form an alloy which is brittle and dark coloured when the proportions of the two metals are equal, and continue so till the platinum amounts only to * th of the alloy; after this the ductility and white colour increase as the proportion of platinum diminishes. When this alloy is kept, its surface gradu- ally tarnishes and becomes yellow, but not so readily if it has been polished.) | XVI. Platinum may be alloyed with copper by fusion, but a strong heat is necessary. The alloy is ductile, hard, takes a fine polish, and is not liable to tarnish. This alloy has been employed with advantage for composing the mirrors of reflecting telescopes.- The platinum dilutes the colour of the copper very much, and even destroys it, unless it be used sparingly. For the experiments made upon it we are indebted to Dr.Lewis.^j Strauss has lately proposed a method of coating copper vessels with platinum instead of tin; it consists in rubbing an amalgam of platinum over the copper, and then exposing it to the proper heat.** XVII. Mr. Cooper has formed an alloy of 7 parts platinum, 16 copper, and 1 zinc, that has much the appearance of pure gold. The copper and platinum are first fused with the usual precautions * Phil. Com. p. 520. ! Ibid. p. 509, 573. $ Ibid. p. 512. § Ibid. p. 561. D Ibid. p. 510. 11bid. p. 529,. •• Nicholson's Journal, ix. 303- Chap. III.] PLATINUM. 409 of covering the metals with charcoal and adding a flux of borax. When it is in perfect fusion it is removed from the fire, the zinc is added, and the mixture stirred. This alloy is very ductile, is not oxydized by exposure to the air, and is not dissolved by nitric acid except at a boiling heat.* XVIII. Dr. Lewis attempted to form an amalgam of platinum, but succeeded only imperfectly, as was the case also with Schef- fer.! Guyton Morveau succeeded by means of heat. He fixed a small cylinder of platinum at the bottom of a tall glass vessel, and covered it with mercury. The vessel was then placed in a sand- bath, and the mercury kept constantly boiling. The mercury gra- dually combined with the platinum ; the weight of the cylinder was doubled, and it became brittle. When heated strongly, the mer- cury evaporated, and left the platinum partly oxidated. It is re- markable that the platinum, notwithstanding its superior specific gravity, always swam upon the surface of the mercury, so that Morveau was under the necessity of fixing it down-! The simplest and easiest way of combining platinum and mer- cury was pointed out by Muschin Pushkin. It consists in tritura- ting with mercury the fine powder obtained by precipitating plati- num from nitro-muriatic acid by sal ammoniac, and exposing the precipitate'to a graduated heat. Some trituration is necessary to produce the commencement of combination; but when once it be- gins it goes on rapidly. Small quantities of the platinum and mer- cury are to be added alternately till the proper portion of amalgam is procured. The excess of mercury is then separated by squeez- ing it through leather. The amalgam obtained is of a fine silvery whiteness, and does not tarnish by keeping. At first it is soft, but gradually acquires hardness. It adheres readily to the surface of glass, and converts it into a smooth mirror. XIX. When silver and platinum are fused together (for which a very strong heat is necessary), they form a mixture, not so duc- tile as silver, but harder and less white. The two metals are sepa- rated by keeping them for some time in the state of fusion ; the platinum sinking to the bottom from its weight. This circumstance would induce one to suppose that there is very little affinity be- tween them* Indeed Dr. Lewis found, that when the two metals were melted together, they sputtered up as if there were a kind of repugnance between them. The difficulty of uniting them was no- ticed also by Scheffer.§ * Journal of the Royal Institution, iii. 119. . ! Lewis, Phil. Com. p. 508 * Ann de Chim. xxv. 12.—This was doubtless owing to the strong cohesion which ex- ists between the particles of mercury. If you lay a large mass of platinum upon the sur- face of mercury, it sinks directly on account of its weight; but a small slip (a platinum wire, for instance) swims, being unable to overcome the cohesion of the mercury. However, if you plunge it to the bottom, it remains there in sonsequence of its superior weight. It heat be now applied to the bottom of the vessel, the wire comes again to the surface being buoyed up by the hot mercury, to which it has begun to adhere. These facts explam tire seeming anomaly observed by Morveau. § Lewis's Philosoph. Commerce, p. 522. Vol. I. 3 F 410 SIMPLE COMBUSTIBLES. C BOOK I (DIVISION 2. XX. Dr. Lewis found that gold united with platinum when they were melted together in a strong heat. He employed only crude platina; but Vauquelin, Hatchett, and Klaproth, have since exa- mined the properties of the alloy of pure platinum and gold.* To form the alloy, it is necessary to fuse the metals with a strong heat, otherwise the platinum is only dispersed through the gold. When gold is alloyed with this metal, its colour is remarkably injured; the alloy having the appearance of bell-metal, or rather of tarnished silver. Dr. Lewis found, that when the platinum amounted only to |th, the alloy had nothing of the colour of gold; even -^d part of platinum greatly injured the colour of the gold. The alloy formed by Mr. Hatchett of nearly 11 parts of gold to 1 of platinum, had the colour of tarnished silver. It was very ductile and elastic. From Klaproth we learn, that if the platinum exceed Tyth of the gold, the colour of the alloy is much paler than gold; but if it be under -j-^th, the colour of the gold is not sensibly altered. Neither is there any alteration in the ductility of the gold. Platinum may be alloyed with a considerable proportion of gold without sensibly altering its colour. Thus an alloy of 1 part of platinum with 4 parts of* gold can scarcely be distinguished in appearance from pure pla- tinum. The colour of gold does not become predominant till it constitutes eight-ninths of the alloy.! From these facts it follows, that gold cannot be alloyed with -j^th of its weight of platinum, without easily detecting the fraud by the debasement of the colour; and Vauquelin has shown, that when the platinum does not exceed ^th, it may be completely separated from gold by rolling out the alloy into thin plates, and digesting it in nitric acid. The platinuth is taken up by the acid while the gold remains. But if the quantity of platinum exceeds tVth, it cannot be separated completely by that method.! SECTION III. OF PALLADIUM. This metal was discovered by Dr. Wollaston in 1803, and the first account of its properties circulated without any intimation of the discoverer, or the source whence the metal was obtained. It was examined by Mr. Chenevix, who endeavoured to show that it was a compound of platinum and mercury. But his attempt was unsuccessful. Soon after Dr. Wollaston announced that he was the discoverer of palladium, and that he had obtained it from crude platinum. It has been since examined by M. Vauquelin,§ and a set of experiments on its oxide has been published by Berzelius.|| * Vauquelin, Manuel de l'Essayeur, p. 44.—Hatchett, on the Alloys of Gold, kc. Phil. Trans. 1803.—Klaproth, Journal de Chimie,iv. 29. t Klaproth, Journal de Chimie, iv. 29. * Manuel de l'Essayeur, p. 48. § Ann. deChim. Ixxxviii. 167. I Annals of Philosophy, iii. 354. Chap. III.] PALLADIUM. 411 Dr. Wollaston separated palladium from .crude platina by the following process: Dissolve crude platina in nitro-muriatic acid, and into the solu- tion, previously freed from any excess of acid, drop a quantity of prussiate of mercury.* In a short time the liquid becomes muddy, and a pale yellowish-white matter falls down. This precipitate, washed, dried, and exposed to a strong heat, leaves a white matter, which is palladium.! By heating it with sulphur and borax it may be obtained in the state of a metallic button, which will bear ham- mering or rolling. 1. Palladium thus obtained is a white metal, which, when po*j lished, bears a very close rsemblance to platinum. 2. It is rather harder than wrought iron. Its specific gravity varies according to the state in which it is exhibited. When com- pletely fused, Mr. Chenevix found it 11*871 ; but some of the pieces exposed to sale were as low as 10-972. Dr. Wollaston states it as varying from 11*3 to 11*8. Vauquelin obtained it when rolled as high as 12 and a small fraction. This nearly agrees with an experiment of Mr. Lowry who found it 12*148. 3. It seems to be as malleable as platinum itself. It possesses but little elasticity, breaks with a fibrous fracture, and appears of a crystallized texture. 4. It is not altered by exposure to the air. It requires a very violent heat to fuse it. Mr. Chenevix succeeded in melting it, but was not in possession of the means of estimating the temperature. Vauquelin fused it on charcoal by a jet of oxygen gas. When the heat was continued the metal boiled and burnt, throwing out bril- liant sparks. A portion of the metal which escaped the combustion was dissipated and condensed on the surface of the charcoal in very small grains. Platinum melted in the same way does not burn like palladium, which shows that this last metal is more vola- tile and more combustible. II. When strongly heated its surface assumes a blue colour; but by increasing the temperature the original lustre is again re- stored. This blue colour is doubtless a commencement of oxidize- ment. Berzelius was able to obtain only 1 oxide of palladium. He formed it by heating palladium filings in a platinum crucible, along with caustic potash and a little nitre. The oxide has a ches- nut-brown colour and readily dissolves in muriatic acid. Accord- ing to the experiments of Berzelius it is composed of—Palladium 100—Oxygen 14*209. Vauquelin found that when this oxide is reduced to the metallic state by being heated to redness it loses 20 per cent, of its weight. But we are not certain that it had been previously deprived of all its water. If we suppose this oxide to be a compound of 1 atom palladium and 1 atom oxygen, and to consist of 100 palladium -f 14*285 oxygen, the weight of an atom of palladium will be 7, and the weight of oxide of palladium 8. • A salt to be described in a subsequent part of this work. f Wollaston on the Discovery of Palladium, Phil. Trans. 1805: 412 SIMPLE COMBUSTIBLES. C BOOK I. £M1 1SI0N 2. III. The chloride,^iodide, and fluoride of palladium are still un- known. IV. It is not probable that palladium combines with azote, hy- drogen, carbon, boron, or silicon. The phosphuret of palladium has not been examined. V. Palladium unites very readily to sulphur. When it is strong- ly heated, the addition of a little sulphur causes it to run into fusion immediately, and the sulphuret continues in a liquid state till it be only obscurely red hot. Sulphuret of palladium is rather paler than the pure metal, and is extremely brittle. By means of heat and air, the sulphur may be gradually dissipated, and the metal obtained in a state of purity. According to the experiments of Vauquelin the sulphuret of palladium is a compound of—palla- dium 100—Sulphur 24. If we suppose the analysis of the oxide of palladium by Berze- lius to be correct, 100 palladium ought to combine with 28$ sul- phur. VI. Mr. Chenevix alloyed palladium with various metals. The following are the results which he obtained. 1. *■ Equal parts of palladium and gold were melted together in a crucible. The colour of the alloy obtained was grey: its hard- ness about equal to that of wrought iron. It yielded to the ham- mer ; but was less ductile than each metal separate, and broke by repeated percussions. Its fracture was coarse-grained, and bore marks of crystallization. Its specific gravity was 11*079. 2. " Equal parts of platinum and palladium entered into fusion at a heat not much superior to that which was capable of fusing palladium alone. In colour and hardness this alloy resembled the former; but it was rather less malleable. Its specific gravity I found to be 15*141. 3. " Palladium alloyed with an equal weight of silver, gave a but- ton of the same colour as the preceding alloys. This was harder than silver, but not so hard as wrought iron; and its polished sur- face was somewhat like platina, but whiter. Its specific gravity was 11*290. 4. " The alloy of equal parts of palladium and copper was a lit- tle more yellow than any of the preceding alloys, and broke more easily. It was harder than wrought iron; and by the file, assumed rather a leaden colour, specific gravity 10.392. 5. •• Lead increases the fusibility of palladium. An alloy of these metals, but in unknown proportions, was of a grey colour, and its fracture was fine-grained. It was superior to all the former in hardness, but was extremely brittle. I found its specific gravity to be 12-000. 6. " Equal parts of palladium and tin gave a greyish button, in- ferior in hardness to wrought iron, and extremely brittle. Its frac- ture was compact and fine-grained. Specific gravity 8*175. 7. " With an equal weight of bismuth, palladium gave a button still more brittle, and nearly as hard as steel. Its colour was greys Chap. III.] RHODIUM. 413 but when reduced to powder it was much darker. Its specific gravity I found to be 12*587. 8. " Iron, when alloyed with palladium, tends much to diminish its specific gravity, and renders it brittle. Arsenic increases the fusibility of palladium, and renders it extremely brittle."* SECTION IV. OF RHODIUM. Rhodium was discovered by Dr. Wollaston in 1804. While Mr. Smithson Tennant was engaged in the examination of the black powder that remains undissolved when crude platina is treated with nitro-muriatic acid, Dr. Wollaston produced soda-muriate of rhodium, and presented it to Mr. Tennant as containing one of the new substances of which he was in quest. Mr. Tennant soon sa- tisfied himself that it was quite different from his new metals. Upon this, Dr. Wollaston investigated its properties, and gave it the name of rhodium. I. It may be procured from crude platina by the following me- thod of Wollaston: The platina was freed from mercury by exposure to a red heat, and from gold and other impurities by digestion in a small quantity of dilute nitro-muriatic acid in a moderate sand heat, till the acid was saturated, and the whole was dissolved, except a shining black powder, from which the solution was separated. A solution of sal ammoniac in hot water was poured into this, solution, in order to separate the platinum ; the greatest part of which was precipitated in the form of a yellow powder. Into the solution thus freed from its platinum, a piece of clear zinc was immersed, and allowed to remain till it ceased to produce any farther effect. By the zinc a black powder was thrown down, which was washed and treated with very dilute nitric acid in a gentle heat, in order to dissolve some copper and lead with which it was contaminated. It was then washed and digested in dilute nitro-muriatic acid till the greater part was dissolved. To this solution some common salt was added. The whole was then gently evaporated to dryness, and the resi- duum washed repeatedly with small quantities of alcohol till it came off nearly colourless. By this means two metallic oxides are washed off in combination with common salt, namely, the oxides of platinum and palladium. There remained behind a deep red-coloured substance, consisting of the oxide of rhodium united to common salt. By solution in water and gradual evapo- • See Chenevix's Enquiries concerning the Nature of a Metallic Substance called Pal- ladium, Phil. Trans. 1803; and Wollaston's Paper on a New Metal found in Crude Platina-, libid. 1804; and on the Discovery of Palladium, Ibid, 1805. From these, most of the facts contained in this Section have been extracted. 414 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2" ration, it forms rhomboidal crystals of a deep-red colour, whose acute angles are about 75°. When these crystals are dissolved in water, and a plate of zinc immersed in the solution, a black pow- der precipitates ; which being strongly heated with borax becomes white, and assumes a metallic lustre. In this state it is rhodium. From Wollaston's analysis it follows, that crude platina contains about 1 part in 250 of rhodium. 1. Rhodium, thus obtained, is of a white colour, not much differ- ing from that of platinum. Its specific gravity, according to Mr. Lowry, is 10*649. It is brittle, and requires a much higher tem- perature to fuse it than any other metal, unless iridium be an ex- ception. Vauquelin was unable to fuse it on charcoal, though the combustion was increased by a jet of oxygen gas. Dr. Wollaston has never been able to fuse it so completely as to obtain it in a solid mass free from cavities. Its fracture is granular, and in hardness it appears fully equal to iron. It has the remarkable property of being insoluble in all acids. II. From the experiments of Berzelius upon this metal, we learn that it is capable qf combining with three proportions of oxygen. The protoxide is black, the deutoxide brown, and the peroxide red. 1. The protoxide is obtained by reducing rhodium to powder, and exposing it to a moderate red heat in an open vessel. It slowly combines with oxygen, and is converted into protoxide. Its colour is black, and it is destitute of metallic lustre. When heated with tallow, or sugar, it is reduced with detonation to the metallic state. It is insoluble in acids. According to the experiments of Berze- lius, this oxide is composed of—Rhodium 100—Oxygen 6-71.* 2. Deutoxide of rhodium is obtained by calcining rhodium in powder with caustic potash and a little saltpetre. The alkali is re- moved by water; and if any portion of metal remain it is separated by levigation. The oxide thus obtained is light and flea-coloured, and retains between 15 and 16 per cent, of potash. Sulphuric acid separates the potash, but leaves the oxide untouched. This oxide combines readily with alkaline substances, but scarcely with acids. According to the calculation of Berzelius, the deutoxide of rho- dium is composed of—Rhodium 100—Oxygen 13-42. 3. The peroxide of rhodium is obtained by precipitating soda- muriate of rhodium with caustic potash. A red powder falls, which is a compound of peroxide of rhodium and water. When heated, it gives out its water, and assumes a darker colour. At a heat below redness it takes fire, gives out part of its oxygen, and is converted into protoxide. This oxide, like the protoxide, has the property of combining with acids, and forming salts. Berzelius, without having analysed it, supposes that it contains three times the quantity of oxygen in the protoxide, or that it is a compound of—Rhodium'100—Oxygen 20*13.! If we suppose the protoxide of rhodium to be a compound of 1 * This proportion is an inference from the supposed composition «f the muriate of rho- dium. ! Annals of Philosophy, iii. 252. Chap. III.] RHODIUM. 415 atom rhodium and 1 atom oxygen, and that it consists of 100 rho- dium united to 6*66 oxygen, which comes sufficiently near Berze- lius' calculation, then the weight of an atom of rhodium will be 15. III. Rhodium has been too imperfectly examined to enable us to state the compounds which it forms with the other supporters of combustion. IV. Rhodium unites readily with sulphur, and, like palladium, is rendered fusible by it; so also is it with arsenic. The arsenic Or sulphur may be expelled by means of heat; but the metallic button obtained does not become malleable. V. The following are the results of the experiments made byDr. Wollaston to alloy rhodium with other metals. " It nnites readily with all metals that have been tried, except- ing mercury ; and with gold or silver it forms very malleable al- loys, that are not oxidized by a high degree of heat, but become irrcrusted with a black oxide when very slowly cooled. " When 4 parts of gold are united with 1 of rhodium, although the alloy may assume a rounded form under the blow-pipe, yet it seems to be more in the state of an amalgam than in complete fusion. 9 " When 6 parts of gold are alloyed with one of rhodium, the compound may be perfectly fused, but requires far more heat than fine gold. There is no circumstance in which rhodium differs more from platina than in the colour of this alloy, which might be taken for fine gold by any one who is not very much accustomed to discriminate the different qualities of gold. On the contrary, the colour of an alloy containing the same proportion of platina differs but little from that of platina. This was originally observed by Dr. Lewis. 4 The colour was still so dull and pale, that the com- pound (5 to 1) could scarcely be judged by the eye to contain any gold.'* " I find that palladium resembles platina in this property of de- stroying the colour of a large quantity of gold. When 1 part of palladium is united to 6 of gold, the alloy is nearly white. " When I endeavoured to dissolve an alloy of silver or of gold with rhodium, the rhodium remained untouched by either nitric or nitro-muriatic acids; and when rhodium had been fused with arsenic or with sulphur, or when merely heated by itself, it was re- duced to the same state of insolubility. But when 1 part of rho- dium had been fused with 3 parts of bismuth, of copper, or*of lead, each of these alloys could be dissolved completely in a mixture of 2 parts, by measure, of muriatic acid with 1 of nitric. With the two former metals, the proportion of the acids to each other seemed not to be of so much consequence as with lead; but the lead ap- peared on another account preferable, as it was most easily sepa- rated when reduced to an insoluble muriate by evaporation. The muriate of rhodium had then the same colour and properties as • Lewis's Phil. Com. p. 526. 416 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION 2. when formed from the yellow oxide precipitated from the original salt."* SECTION V. OF IRIDIUM. This metal was discovered by Mr. Smithson Tennant in 1803; but before he communicated the result of his experiments, a disser- tation was published on it by Descotils in the Annales de Chimie, who had made the same discovery; and the subject was afterwards prosecuted more in detail by Vauquelin and Fourcroy. When crude platina is dissolved in nitro-muriatic acid, especial- ly if the acid be dilute, and only a moderate heat applied, there remains behind a quantity of black shining powder in small scales, which preceding chemists had mistaken for black lead. Mr. Ten- nant examined these scales, found their specific gravity to be 10-7, and that they consisted of two unknown metals united together. The first of these metals he called iridium, from the variety of co- lours which its solutions exhibit; »to the second he gave the name of osmium, from the peculiar smell by wnich its oxides are distin- guished. Dr. Wollaston discovered, that in crude platina there exists another substance very similar to the grains of platina in appear- ance, but differing altogether in its properties. It consists of flat white grains, often distinctly foliated. They are not soluble in any acid, and their specific gravity is no less than 19*25, which is higher than that of any other mineral; the grains of platina by the trials of this accurate chemist not exceeding 17-5. These metallic grains are separated when the platina is dissolved in nitro-muriatic acid. Dr. Wollaston has ascertained them to be a compound of iridium and osmium. They are, therefore, of the same nature with the black powder examined by Mr. Tennant. To separate the two metals from each other, the black powder is to be heated to redness in a silver crucible with its own weight of potash, and kept in that state for some time. The potash is then to be dissolved off by water. A solution is obtained of deep orange- colour. The portion of powder that remains undissolved is to be digested in muriatic acid. The acid becomes first blue, then olive- green, and lastly deep-red. The residual powder, which has re- sisted the action of these agents, is to be treated alternately with potash and muriatic acid, till the whole of it is dissolved. By this process two solutions are obtained: first, the alkaline solution, of a deep orange-colour, which consists chiefly of the potash united to the oxide of osmium; second, the acid solution, of a deep red, which consists chiefly of the muriatic acid united to the oxide of iridium. * Sec Dr. Wollaston's paper, Phil. Trans. 1804, from which all the facts contained in this Section have been extracted. Chap. III.] iridium. 417 I. By evaporating this last solution to dryness, dissolving the residuum in water, and evaporating again, octahedral crystals are obtained, consisting of muriatic acid united to oxide of iridium, 1 hese crystals being dissolved in water, give a deep red solution, from which the iridium may be precipitated in the state of a black powder by putting into the liquid a plate of zinc or iron, or indeed any metal, except gold and platinum. When heat is applied to this powder it becomes white, and assumes the metallic lustre. In this state it is pure iridium. The metal may be obtained also by ex- posing the octahedral crystals to a strong heat. It has the appearance of platinum, and seems to resist the action of heat at least as strongly as that metal; for neither the French chemists nor Mr. Tennant were able to fuse it. Vauquelin has lately succeeded in fusing a little of it, and found it possessed of a certain degree of ductility.* Mr. Children has succeeded in fusing it by means of his immense galvanic battery, and found its specific gravity 18*68.! As the globule was porous, it is obvious that this is considerably under the truth. It resists the action of all acids, even the nitro-muriatic, almost completely; much more than three hundred parts being necessary of that acid to dissolve one of iridium.! II. The affinity between iridium and oxygen seems to be very weak; but, like all other metals, it unites with that principle. The phenomena of its solution in muriatic acid indicate that it is capable of uniting with at least two doses of oxygen, and of forming two oxides. The first solution is a deep blue. In that state it seems to be united to a minimum of oxygen; by diluting the solution with water it becomes green. By digesting the blue solution in an open vessel, or by adding nitric acid, it becomes dark red. In this state the metal appears to be united to a maximum of oxygen. Most of the metals destroy the colour of these solutions by de- priving the iridium of its oxygen, and throwing it down in the metallic state. The infusion of galls and the prussiate of potash likewise destroy the colour, but occasion no precipitate. The al- kalies precipitate the oxide of iridium, but retain a portion of it in solution. We neither know the composition nor the number of its oxides. Neither have any experiments been made on its compounds with chlorine, iodine, or fluorine. III. It is probable that it does not combine with azote, hydro- gen, carbon, boron, or silicon. Its combination with phosphorus has not been examined. Vauquelin formed a sulphuret of iridium by heating a mixture of ammonio-muriate of iridium and sulphur. The sulphuret formed was a black powder composed of—Iridium 100—Sulphur 33*3.$ If we suppose this sulphuret a compound of 1 atom iridium and • Ann de Chim. Ixxxix. 240. t Phil- Trans. 1815, p. 370. * Fourcroy and Vauquelin, Ann. de Chim. 1. 22. § Ann. de Chim. Ixxxix. 236. Vol. I. 3 G - 418 SIMPLE COMBUSTIBLES. C BOOK I. £ DIVISION t. 1 atom sulphur, it will follow that the weight of an atom of iridium is 6. IV. The following are the results of Mr. Tennant's experiments to alloy iridium with the metals: " It does not combine with arsenic. Lead easily unites with it: but is separated by cupellation, leaving the iridium upon the cupel as a coarse black powder. Copper forms with it a very malleable alloy, which, after cupellation with the addition of lead, left a small proportion of the iridium, but much less than in the former case. Silver may be united with it, and the compound remains perfectly malleable. The iridium was not separated from it by cupellation, but occasioned on the surface a dark and tarnished hue. It ap- peared not to be perfectly combined with the silver, but merely diffused through the substance of it in the state of a fine powder. Gold alloyed with iridium is not freed from it by cupellation, nor by quartation with silver. The compound was malleable, and did not differ much in colour from pure gold ; though the proportion of alloy was very considerable. If the gold or silver is dissolved, the iridium is left in the form of a black powder."* Vauquelin has more lately alloyed this metal with lead, copper, and tin. All these alloys were malleable and the hardness of the dif- ferent metals was greatly increased by the addition of the iridium.! Thus we have finished the description of the second genus of simple combustibles. It includes 28 substances, all of which are metals, though the first ten have such a disposition to unite with oxygen, that it is with difficulty they can be preserved in the me- tallic state. Indeed the earths proper have not yet been reduced to metals. The weight of an atom of each of these substances, as it has been deduced from the combinations into which they enter, is as follows: Potassium 5 Iron 3*5 Bismuth 8*875 Sodium 3 Nickel 3*375 Mercury 25 Calcium 2-625 Cobalt 3-625 Silver 13-75 Barium 8*75 Manganese 3*5 Gold 24*875 Strontium 5>5 Cerium 5-75 Platinum 22*625 Magnesium 1*5 Uranium 15*625 Palladium 7 Yttrium 4 Zinc 4125 Rhodium 15 Glucinum 2*25 Lead 13 Iridium 6 Aluminum 1-125 Tin 7*375 Zirconium 4-625? Copper 8 * See Mr. Tennant's paper on Two Metals found in the Powder remaining after the Solution of Platina, Phil. Trans. 1804. Descotils did not succeed in obtaiuining it in a se- parate state; but he showed that the red colour which the precipitates of platinum some- times assume is owing to the presence of iridium. See his paper, Ann. de Chim. xlviii. 153. Fourcroy and Vauquelin confounded together the properties of osmium and iridium, ascrib- ing both to one metal; to which they have given the name of ptene. See Ann. de Chim, xlix. 177, and 1. 5,. ! Ann. de Chim. Ixxxix. 237. Chap. III.] SIMPLE COMBUSTIBLES. 419 But the weights of the atoms of the last 5 metals must be consi- dered as still imperfectly known; because the salts which their oxides form are of so peculiar a nature that it has not been hitherto possible to analyse them with sufficient exactness to determine the equivalent numbers for these oxides. The following table exhibits the colour, specific gravity, hard- ness, fusibility, and tenacity of the different metals belonging to this genus as far as these properties have been ascertained. Meliing point. Metals. Colour. Hardness. Sp. Gravity. Fahren-heit. Wedge-wood. Tenacity. Potassium White 4 0-86507 136*5° __ _ Sodium White 4 0*97223 194 -- — Calcium White — — — — -- Borium White Strontium White Magnesium White Yttrium Grey ? Glucinum Grey ? Aluminum Grey ? Zirconium Iron Grey 9 7*8 — 158° 549*25 Nickel White 8-5 8*82 — 160+ — Cobalt Grey 6 8-7 — 130 — Manganese Grey 8 8*013 — 160 — Cerium White ? Uranium Grey 8 9 — 170+ — Zinc White 6*5 7*1908 680° — 109*8 Bismuth -1 Reddish 1 white J 7 " 9*822 476 — 20*1 Tin White 6 7*299 442 — 34-7 Lead Blue 55 11*352 612 — 27-7 Copper Red 7-5 8*895 — 27 302*26 Mercurv White 0 13*568 39 — — Silver White 7 10-510 — 22 187*13 Gold Yellow 6*5 19*361 — 32 150*07 Platinum White 8 21*5313 — 170+ 274*31 Palladium White 9 12-148 — 170+ — Rhodium White 9 10*649 — 180+ — Iridium White 9 18*68+ 1 — 180+ — 3. The following table exhibits the different combinations which these metals are capable of forming with oxygen. The oxides dis- tinguished by the mark * are those which combine most readily with acids, and form neutral salts. The oxygen is the quantity by weight which combines with 100 metal. 420 SIMPLE COMBUSTIBLES. c BOOK I. £ DIVISION 2. Weight of Metals. Oxides. Colour. Oxygen. an atom of oxide. Potassium { 1# 2 White Yellow 20 60 6 8 Sodium { 1# 2 White Yellow 33*3 50 4 9 Calcium 1# White 38-39 3*625 Borium { 1# 2 White 11*42 9*75 Strontium 1* White 18*18 6-5 Magnesium 1* White 66-6 2*5 Yttrium 1* White 25 5 Glucinum 1# White 44*4 3*25 Aluminum 1# White 88-8 2*125 Zirconium 1* White 23*78? 5*625 ? Iron { 1# Black 28*75 4*5 2 Red 43*12 10 Nickel { 1*. Grey 29*63 4*375 2 Black 44*445 9*75 Cobalt { 1# 2 Blue Black 27-58 36-77 4*625 10-25 { 1# Green 28*75 4*5 Manganese 2 Black 57-5 5 5 f 1# White 17-39 6-75 Cerium { 2 ("Reddish ") \ brown J 26*04 14-5 Uranium { 1# f Greyish ") I black J 6*4 16-625 1 2 Yellow 9*6 34*25 Zinc 1# White 24*24 4.125 Bismuth 1* Yellow 11*2672 9-875 r 1* Yellow 7*692 14 Lead \ 2 Red 11*538 29 I 3 Brown 15*384 15 Tin { 1# Black 13*55 8-375 2 Yellow 27-1 9*375 Copper { 1 2* Red Black 12*5 25 9 10 Mercury { 1* 2* Black Red 4 8 26 27 Silver 1* Olive 7*272 14*75 r 1 Green 4*02 25*875 Gold { 2* f Reddish \ \ brown J 12-06 27*875 Platinum {] 1 2* Black Brown 4*419 13*257 23*625 25*625 Chap. III.] . CHLOBIDES. 421 Metals. Oxides. Colour. Oxygen. Weight of an atom of oxide. Palladium 1* Brown 14-285 8 f 1 Black 6*666 16 Rhodium < 2 Brown 13*333 17 1 3* Red 20 18 Iridium 7? These oxides amount to about 47 in number; but not more than 28 or 29 have the property of neutralizing acids, and forming neu- tral salts. 4. The chlorides of these metals have been but imperfectly exa- mined. The following table exhibits such of them as we are at present acquainted with: Chlorine Weight of an Metals. Chlorides. Colour. united to 100 atom of chlo- metal. ride. Potassium White 90 9*5 Sodium White 150 7-5 Calcium White 171-42 7*125 Barium White 51-42 13*25 Strontium White 69*23 11 Magnesium White 300 6 Yttrium White Glucinum White Aluminum White Zirconium White Iron I Grey 128*37 8 2 Brown 256.74 12*5 Nickel Olive Cobalt Manganese Pink Cerium Uranium Zinc White 112*5 8*625 Bismuth Grey 50-7 13-375 Lead White 34*61 17*5 { Grey 61*01 11*875 Tin Liquid 122*02 16*375 { { White 56*25 12-5 Copper Yellow 112*5 17 White 18 29.5 Mercury White 36 34 Silver Grey 32-73 18-25 Platinum Green 19-88 27*125 422 SIMPLE COMBUSTIBLES, , S BOOK I. — ^ £ DIVISION 2. The chlorides of the 5th family of metals, \vith the exception of that of platinum, have not hitherto been examined. 5. The iodides are still more imperfectly known than the chlo- rides. The following table exhibits the composition of such of them as we are acquainted with: Metals. Iodides. Colour. Iodine combin-ing with 100 metal. Weight of an atom of iodide. Potassium 1 White 312*5 20*625 Sodium 1 White 18*625 Calcium 1 White 18*250 Barium 1 White 24*375 Strontium 1 White 21125 Iron 1 Brown 19*125 Zinc 1 White 390-6 19-625 Bismuth 1 Orange 24*5 Lead 1 Yellow 28*625 Tin 1 Orange Copper 1 Brown 23*625 Mercury I 1 2 Yellow Red 62-5 125 40*625 56*25 Silver • { 1 f Greenish-") \ yellow J 29*375 6. Of the acidifiable combustibles there are four which seem capable of uniting with most of the metals belonging to this genus; I mean phosphorus, sulphur, arsenic, and tellurium. Carbon is known to combine with three metals only; namely,—Iron—Nickel —Manganese. The phosphurets have been too imperfectly examined to warrant any general statements respecting their composition. The following table exhibits the sulphurets, as far as we are ac- quainted with them: Sulphur Weight of Metals. Sulphurets. Colour. Sp. gravity. united to 100 metal. an atom of sulphuret. Potassium Grey 40 7 Sodium Grey 66*6 5 Iron p g CO s c o B '+3 a < u In -a O O u C cs C ea c o *o Gold B-— B—- B B— M B Platinum B B B B— Silver B— B— B B B Mercury B B B O O O Palladium tf____ B Rhodium Potassium B B B Sodium B B B 1 Copper B= B— M M S Iron B+ B4- B B S B Nickel B B4- B S Tin M M?+ B B Lead M— M— B B s Zinc o B+ B O O o GENUS III. INTERMEDIATE COMBUSTIBLES. The substances belonging to this genus may be considered as in- termediate between the first and the second genus. They differ from those of the second genus, by forming compounds with oxy- gen which do not neutralize acids ; and from those of the first ge- nus, by not entering into any gaseous combinations. They agree with the bodies of the first genus because their oxides possess acid properties. They agree with the bodies of the second genus be- cause these acids are but imperfectly soluble in water and act with but little energy upon animal and vegetable bodies. Vol. I. 3H 426 SIMPLE COMBUSTIBLES. < BOOK; I. £nivisio'IMSlON f. temperature that could be raised in a forge for six hours. The mass, after cooling, consisted of three distinct layers. The centre consisted of brilliant needles, similar in appearance to black oxide of manganese in its crystallized state. The surface consisted of a very thin brown coat, similar to the oxide of copper. Between these two layers there was a third, full of cavities, and having the yellow colour of gold. This last Laugier considered as titanium in the metallic state. It has considerable lustre. It is brittle, but in thin plates has considerable elasticity. It is highly infusible.* II. When exposed to the air, it tarnishes, and is easily oxidized by heat, assuming a blue colour. It detonates when thrown into red-hot nitre.! It seems capable of forming three different oxides; namely, the blue or purple, the red, and the ■white. 1. The protoxide, which is of a blue or purple colour, is formed when titanium is exposed hot to the open air, evidently in conse- quence of the absorption of oxygen. 2. The deutoxide or red oxide is found native. It is often crys- tallized in four-sided prisms ; its specific gravity is about 4*2 ; and it is hard enough to scratch glass. When heated it becomes brown, and when urged by a very violent fire, some of it is volatilized. When heated sufficiently along with charcoal, it is reduced to the metallic state. 3. The peroxide or white oxide may be obtained by fusing the red oxide in a crucible with four times its weight of potash, and dissolving the whole in water. A white powdci soon precipitates, which is the white oxide of titanium. Vauquelin and Hecht have shown that it is composed of 89 parts of red oxide and 11 parts of oxygen. III. 1. Titanium does not seem to be capable of combining with sulphur.! 2. Phosphuret of titanium has been formed by Mr. Chenevix by the following process. He put a mixture of charcoal, phosphate of titanium (phosphoric acid combined with oxide of titanium) and a little borax, into a double crucible, well luted, and exposed it to the heat of a forge. A gentle heat was first applied, which was gradually raised for three quarters of an hour, and maintained for half an hour as high as possible. The phosphuret of titanium was found in the crucible in the form of a metallic button. It is of a pale-white colour, brittle, and granular; and does not melt before the blow-pipe.§ IV. Vauquelin and Hecht attempted to combine it with silver, copper, lead, and arsenic, but without success. But they combined it with iron, and formed an alloy of a grey colour, interspersed Mrith yellow-coloured brilliant particles. This alloy they were not able to fuse. The other properties of this untractable metal are still unknown. * Nicholson's Journal, vi. 62. t Lampadius, Nicholson's Jour. vi. 62. * Gregor. § Nicholson's Jour. v. 134-. Chap. III.] TITANIUM. 451 Such are the properties of this genus of bodies as far as they have been hitherto investigated. 1. The following table exhibits some of the most striking charac- ters of these bodies. Colour. Hardness. Sp. Gravity. Melting point. VVeight of an atom. Metals. Fahren-heit. Wedge-wood. Antimony White 6*5 6*712 810° 5*625 Chromium White 9? 5*9 170o-f 3*5 Molybdenum White 8*611 170'-}- 6 Tungsten White 9 17*4 170*+ 12 Columbium Grey 8 5*61+ 170°+ 18 Titanium Yellow 170°+ 18? 2. The following table exhibits the compounds which these me- tals form with oxygen as far as they have been examined. Metals. Oxides. Colour. Oxygen j Weight of an united to 100 atom of rae-metal. j tallic oxide. Antimony 1 2 3 Grey White ■' Yellow 17*778 23*7 35-556 Chromium 1 2 3 Green Brown Red 87-72 6-5 Molybdenum 1 2 3 Brown Blue White 16-6 33-3 50 7 8 9 Tungsten 1 2 1 Brown Yellow 16*6 25 14 15 Columbium White 5-5 19 Titanium 1 2 3 Blue Red White 19? 20? 21? 452 SIMPLE COMBUSTIBLES. 5 BOOK I. £ DIVISION 2 3. Neither the chlorides nor iodides of these metals (if we except antimony) have been examined. Neither have many experiments been made on their compounds with the acidifiable and alkalifiable combustibles. The few facts which have been ascertained will be found in the preceding Sections. Any recapitulation here seems unnecessary. SECTION VII. OF THORINUM. This metal should have been placed in the second family of the alkalifiable combustibles immediately after zirconium. But as it has only become known to the chemical world since that part of the volume was printed, I am under the necessity of placing it here. It was discovered in 1815 by Professor Berzelius, while engaged in the analysis of the gadolinite of Korarvet. But as he obtained it only in very small quantity, and as it was detected only in one specimen, he did not mention it in his paper on gadolinite publish- ed in the fourth volume of the Af handlingar. But in the summer of 1816, while engaged with Assessor Gahn in examining the mi- nerals in the neighbourhood of Fahlun, he found it again in two new minerals, the deutofluate of cerium and the double fluate of ce- rium and yttria. But it was only occasionally present in these mi- nerals as had been the case in the gadolinite of Korarvet; and all of it which Berzelius obtained did not amount to quite 7i grains. He printed however in the fifth volume of the Af handlingar a de- scription of its properties as far as he was able to ascertain them; and from that paper I have extracted the following account.* The oxide only of this new metal has been obtained, and as it is white and incapable of being reduced by means of charcoal, it agrees in its properties with the earths. On that account Berzelius has distinguished this oxide by the name of thorina, and classed it along with zirconia. Thorina may be obtained from the minerals containing protoxide of cerium and yttria, by the following process. Precipitate the iron by means of succinate of ammonia. Thorina indeed when alone is precipitated by that salt; but this is not the case when it is mixed with the other bodies that exist in the fluates of cerium and yttria. After the iron is removed, precipitate the cerium by means of sul- phate of potash. Ammonia now precipitates the thorina mixed with yttria. Dissolve them in muriatic acid. Evaporate the so- lution to dryness, and pour boiling water on the residue, which will dissolve the greatest part of the yttria, but not the whole. Re- dissolve the residue in muriatic or nitric acid, and evaporate till it * A translation of the paper will be found in the Annals of Philosophy, ix. 452. Chap. III.] THORINUM. 453 becomes as exactly neutral as possible. Then pour water upon it and boil it for an instant. The thorina precipitates and the solution contains a disengaged acid. If we saturate this acid and boil a second time, an additional portion of thorina precipitates. Thorina, when separated by the filter, has the appearance of a gelatinous, semitransparent mass. When washed and dried it be- comes white, absorbs carbonic acid, and dissolves with effervescense in acids. Though calcined it retains its white colour ; and when the heat to which it is exposed is only moderate, it continues rea- dily soluble in muriatic acid. But after exposure to a violent heat, it requires to be digested in strong muriatic acid in order to obtain a solution of it. This solution has a yellowish colour; but it be- comes colourless when diluted with water. If it be mixed with yttria it dissolves more readily after having been exposed to heat. The neutral solutions of thorina have a purely astringent taste, which is neither sweet, nor saline, nor bitter, nor metallic. In this property it agrees with zirconia, and differs from all the other earths. When dissolved in sulphuric acid with a slight excess of acid and subjected to evaporation, it yields transparent crystals, which are not altered by exposure to the air, and which have a strong styptic taste. The mother water remaining after the formation of these crystals, retains but very little thorina. When the crystals are put into water they are decomposed. A subsulphate precipitates and a supersulphate remains in solution. When this solution is boiled it lets fall no precipitate. Sulphate of potash occasions no precipitate when added to this solution or to the muriate of thorina. Thorina dissolves readily in nitric acid, unless it has been ex- posed to a red heat. In that case nitric acid dissolves it only in consequence of long boiling. The solution does not crystallize, but forms a mucilaginous mass which becomes more liquid by ex- posure to the air, and which when evaporated by a moderate heat leaves a white, opaque mass, similar to enamel, in a great measure insoluble in water. When the neutral solution is boiled a great por- tion of the earth is precipitated. A slight calcination leaves the earth with its white colour, so that we discover no evidence of a higher degree of oxidizement. Thorina dissolves in muriatic acid in the same way as in nitric. The solution does not crystallize. When evaporated by a mode- rate heat it is converted into a syrupy mass, which does not deli- quesce in the air; but dries, becomes white like enamel, and after- wards dissolves only in very small quantity in water, leaving a sub- salt undissolved. When the muriate, not too acid, is diluted with water and boiled, the greatest part of the thorina is precipitated. When the nitrate or muriate of thorina is evaporated by a strong heat, it leaves on the edges of the vessel a white opaque film, having the appearance of enamel. It appears very distinctly when the li- 4^4 SIMPLE COMBUSTIBLES. 5 BOOK I. C division 2. quid is made to pass over the inside of the glass. This is a very characteristic mark of this earth. Thorina combines eagerly with carbonic acid. The precipitates produced by caustic ammonia, or by boiling the neutral solutions of the earth, absorb carbonic acid from the air while drying. The alkaline carbonates precipitate the earth combined with the whole of their acid. Thorina is precipitated by oxalate of ammonia in the state of a white, bulky matter, insoluble in water and in caustic alkalies. Tartrate of ammonia throws down a white precipitate, which re- dissolves at first and does not become permanent till a sufficient quantity of the salt has been added. This precipitate is redis- solved by caustic ammonia. Boiling drives off the ammonia, but the earth is not precipitated till the liquid has been concentrated to a certain degree by evaporation. It then precipitates under the form of a gelatinous mass, almost transparent. Citrate of ammonia does not occasion any precipitate, not even when caustic ammonia is added to it. But if the liquid be boiled, the earth precipitates in proportion as the ammonia evaporates. Benzoate of ammonia produces a white bulky precipitate. Succinate of ammonia occasions a precipitate, which is imme- diately redissolved. If a sufficient quantity be added to prevent the precipitate from redissolving, and if we attempt to redissolve it by pouring in water, it is decomposed and remains in a great measure undissolved, under the form of a salt with excess of base, while the liquid contains the greatest part of the acid united to a small portion of the earth. Ferrocyanate of potash throws down a white precipitate, which is redissolved by muriatic acid. Caustic potash and ammonia have no action on newly precipitated thorina, not even at a boiling temperature. Liquid carbonate of potash or carbonate of ammonia dissolves a small portion of it, which precipitates again when the alkali is super- saturated with an acid, and then neutralized by caustic ammonia. But this earth is much less soluble in the alkaline carbonates than any of the other earths. When exposed in a charcoal crucible to a heat at which tantalum is reduced, it underwent no change in its properties, excepting that it contracted in its dimensions and acquired a small degree of translucency. It does not fuse before the blow-pipe. With borax it melts into a transparent glass, which when exposed to the ex- terior flame becomes opaque and milky. With phosphate of soda it fuses into a transparent pearl. It is infusible with soda. When soaked with a solution of cobalt it becomes greyish-brown. It differs from alumina by its insolubility in hydrate of potash; from yttria, by its purely astringent taste without sweetness, and by the property which its solutions possess of being precipitated by Chap. III.] THORINUM. 455 boiling when they do not contain too great an excess of acid. It differs from zirconia by the following properties. 1. After being heated to redness it is still capable of being dissolved in acids. 2. Sulphate of potash does not precipitate it from its solutions, while it precipitates zirconia from a solution, containing even a considerable excess of acid. 3. It is precipitated by oxalate of ammonia, which is not the case with zirconia. 4. Sulphate of thorina crystallizes readily, while sulphate of zirconia, supposing it free from alkali, forms, when dried, a gelatinous transparent mass, without any tendency to crystallization. APPENDIX. [As Dr. Thomson seems to rely greatly on Dr. Prout's calcula- tions in 6 Ann. of Phil. 321, it seems desirable to give here, Dr. Thomson's and Dr. Prout's views of the atomic theory, that no- thing may be wanting to render Dr. Thomson's calculations and the principles he has adopted, intelligible. I have, therefore, thought it right to insert in this Appendix, Dr. Thomson's view of the atomic theory, his remarks on Dr. Prout's memoir, and the memoir itself.—C] No. I. 4)n the Proportions in which Bodies Combine Chemically.—By Dr. Thomson, from 5 Ann. of Phil. p. 8. That the ultimate particles of matter consist of atoms, incapable of farther subdivision, is an opinion which has been pretty generally received among philosophers ever since the time of the Greeks; and since the establishment of the Newtonian philosophy this opinion has become almost universal. That substances always enter into che- mical combination, in determinate proportions which never vary, has been known ever since chemists acquired the art of analysing bodies. Thus carbonate of lime, wherever, or in whatever state, it occurs, is always a compound of 43*2 carbonic acid and 57*8 lime; and sulphate of barytes, of 34*5 sulphuric acid and 65-5 barytes. In like manner, the yellow oxide of lead is always a compound of 100 lead and 7-7 oxygen ; and red oxide of mercury, of 100 mer- cury and 8 oxygen. Sulphuric acid is always composed of three parts of oxygen and two parts of sulphur; and carbonic acid, of 2000 oxygen and 751 carbon. This law is universally admitted by chemists ; and, indeed, the more rigorously it has been examined the more conspicuous and decided have become the proofs in its favour. Even Berthollet, who seems to be an enemy to the atomic theory in the abstract, has admitted that all known compounds unite in determinate proportions ; and has endeavoured to recon- cile this fact to his own opinions by several highly ingenious, and some rather whimsical, arguments. The few exceptions which he was able to muster up against the law have all disappeared before the more rigid and exact examination of modern analyses. Mr. Dalton was the first person who ventured to account for this fixedness in chemical proportions. According to him, it is the atoms of bodies that unite together.* One atom of a body, a, • [The atomic theory was first stated and explained by Dr. Bryan Higgins, in 1789, as Sir H. Davy acknowledges, Elem. of Chem. Phil. p. 60.—C] Vol. I. 3M 458 APPENDIX. [No. I. unites with one atom of a body, b, or with two atoms of it, or with three, four, &c. atoms of it. The union of one atom of a with one atom of b produces one compound, the union of one atom of a with two atoms of b produces another compound, and so on. Each of these compounds, of course, must consist of the same proportions, because the weight of every atom of the same body must of neces- sity be the same. We have no means of demonstrating the number of atoms which unite together in this manner in every compound; we must, there- fore, have recourse to conjecture. If two bodies unite only in one 'proportion, it is reasonable to conclude that they unite atom to atom. Hence it is most likely that water is composed of one atom of oxygen and one atom of hydrogen; oxide of silver, of one atom silver and one atom oxygen; and oxide of zinc, of one atom zinc and one atom oxygen. When a body has the property of uniting with various doses of oxygen, we can then determine the number of atoms which con- stitute the compounds. Thus manganese unites with four doses of oxygen; and supposing the manganese to be represented by 100, the oxygen of each respective oxide is represented by the numbers 14, 28, 42, 56; but these numbers are to each other as the num- bers one, two, three, four. Hence the first oxide is composed of one atom manganese and one atom oxygen; the second, of one atom manganese and two atoms oxygen; the third, of one atom manganese and three atoms oxygen; and the fourth, of one atom manganese and four atoms oxygen. In like manner, as mercury combines with two doses of oxygen, and forms two oxides, the first composed of 100 mercury and four oxygen, and the second of 100 mercury and eight oxygen, it is obvious that the first must be a compound of one atom mercury and one atom oxygen, and the se- cond of one atom mercury and two atoms oxygen. Nor is there any difficulty with respect to iron. There are two oxides of that metal: the first composed of 100 iron and 28 oxy- gen ; the second of 100 iron and 42 oxygen. Now as 28 is to 42 as two to three, it follows that the first is a compound of one atom iron and two atoms oxygen; the second, of one atom iron and three atoms oxygen. The same rule holds good with respect to the oxides of nickel and cobalt. If. we know the number of atoms of which a body is combined, and the proportion of the constituents, there is no difficulty in de- termining the proportional weight of the atoms of which it is com- posed. Thus if water be composed of one atom of oxygen and one atom of hydrogen, and if the weight of the oxygen in water is to that of the hydrogen as 7h to one, then it follows that the weight of an atom of oxygen is to that of an atom of hydrogen as 7h to one. If black oxide of mercury be composed of one atom of mer- cuiy and one atom of oxygen, and if it be composed of 100 mercu- ry and four oxygen, then an atom of mercury is to the weight of an No. I.] APPENDIX. 459 atom of oxygen as 100 to four, or as 25 to one. If black oxide of iron be composed of one atom iron and two atoms oxygen, and if it consist of 100 iron and 28 oxygen, then an atom of iron is to an atom of oxygen as 100 to 14, or as 7*142 to one. Such is the me- thod of determining the weight of an atom of the different sub- stances upon which experiment has hitherto been made. The ad- vantage of such a knowledge is immense; because it gives us the proportions in which the different substances unite together, and even enables us to calculate the proportional constituents of all compound bodies, independent of experiment, and with more ac- curacy than would result from experiments unless conducted with uncommon precautions. Hitherto the only persons who have written upon the subject of chemical atoms are Mr. Dalton, Sir Humphry Davy, Dr. Berze- lius, Dr. Wollaston, and myself. Mr. Dalton made choice of hy- drogen as his unit, because it is the lightest of all the atoms ; and Sir H. Davy has followed his example. But as oxygen enters into a much greater number of compounds than any other body, it was chosen by Dr. Wollaston and Dr. Berzelius as the most convenient unit; and in the tables of atoms which I have published in the dif- ferent volumes of the Annals of Philosophy, I have followed their example. Berzelius considers an atom of oxygen to weigh 100, Wollaston makes it weigh 10, and I myself make its weight one. The reader will perceive that these three numbers are the same, the only difference being the position of the decimal point. The person who has hitherto made the greatest number of expe- riments upon this important subject is Dr. Berzelius ; and he has considered himself as entitled, by the results which he has obtain- ed, to establish two propositions which he considers as axioms or chemical first principles, and which have a prodigious influence on the whole doctrine. These axioms are the following:— 1. In all compounds of inorganic matter one of the constituents is always in the state of a single atom. According to this axiom, no inorganic compound is ever composed of two atoms of a united with three atoms of b, or of three atoms of a united with four atoms of b, &c.; but always of one atom of a united with one, two, three, four, &c. atoms of b. This axiom, if it hj^j>£>o(L which Berze- Kus thinks it will-greatly simplifies tnTdoctrineof atomic combi- nation, as far as inorganic bodies are concerned, and reduces the whole to a state of elementary facility. 2. When an acid unites to a base, the oxygen in the acid is al- ways a multiple of the oxygen in the base by a whole number, and generally by the number denoting the atoms of oxygen in the acid. Thus sulphuric acid contains three atoms of oxygen: 100 parts of it contain 60 oxygen; and 100 parts of sulphuric acid combine with, and saturate, a quantity of base which contains 20 oxygen. Now 20 multiplied by three, the number pf atoms ©f oxygen in 460 APPENDIX. [No. I. sulphuric acid, makes 60 the quantity of oxygen in 100 of sulphu- ric acid. Such are the two axioms of Berzelius, which he has made the foundation of his whole reasoning, and from which he has deduced his rules for determining the proportion of oxygen in bodies, and the number of atoms of which they are composed. If they hold good, and hitherto they have answered wonderfully well, they must be admitted to be of the utmost importance, and to give a facility and elegance to our chemical investigations which could scarcely have been looked for. Mr. Dalton, the founder of the atomic theory, has not adopted either of these axioms. At the same time he has not advanced any fact in opposition to them; but only that there is nothing in the atomic theory which necessarily leads to their adoption. This is doubtless true. The axioms are merely empyrical, and deductions from analyses. Yet if they hold in all the analyses hitherto made, we cannot well refuse them a good deal of generality ; and the best mode of proceeding seems to be to admit them till some exception to them be discovered. Berzelius, considering the atomic theory to labour under difficul- ties, which in the present state of our knowledge we are not able to surmount, has substituted in its place another, which he conceives to be easier and simpler. This may be called the theory of volumes. He conceives bodies to be all in the gaseous state, and embraces the opinion of Gay-Lussac, that gaseous bodies always unite in vo- lumes that are aliquot parts of each other. One volume of one body always unites with one, two, three, &c. volumes of another. How this alteration, which consists merely in the substitution of the word volume for atom, simplifies the atomic theory, or removes any of the difficulties under which it labours, is, I own, beyond my compre- hension. But Berzelius has deserved so well of chemistry, that he may be indulged in any innocent whim which produces no de- terioration. I should take up too much room were I here to give a table of the weights of the atoms of bodies. I must satisfy myself with re- ferring to the different papers which I have inserted in the Annals of Philosophy on the subject, to the paper of Berzelius in the third volume of the Annals, in which will be found his table of the weights of an atom of the simple substances, and to Dr. Wollas- ton's scale of chemical equivalents. The weights given in these three different tables do not always coincide with each other; but in general a very near approach to coincidence will be perceived. In some cases the weights that I have assigned are half those given by Berzelius. The reason of this is obvious; and the circumstance can occasion no difficulty or ambiguity. No. II.] APPENDIX. 462 No. II. On the Relation between the Specific Gravities of Bodies in their Gaseous State and the Weights of their Atoms.—Ann. Phil. 6. The author of the following essay submits it to the public with the greatest diffidence; for though he has taken the utmost pains to arrive at the truth, yet he has not that confidence in his abilities as an experimentalist as to induce him to dictate to others far supe- rior to himself in chemical acquirements and fame. He trusts, however, that its importance will be seen, and that some one will undertake to examine it, and thus verify or refute its conclusions. If these should be proved erroneous, still new facts may be brought to light, or old ones better established, by the investigation; but if they should be verified, a new and interesting light will be thrown upon the whole science of chemistry. It will perhaps be necessary to premise that the observations about to be offered are chiefly founded on the doctrine of volumes as first generalized by M. Gay-Lussac ; and which, as far as the author is aware at least, is now universally admitted by chemists. On the Specific Gravities of the Elementary Gases. 1. Oxygen and Azote.—Chemists do not appear to have consi- dered atmospheric air in the light of a compound formed upon che- mical principles, or at least little stress has been laid upon this cir- cumstance. It has, however, been long known to be constituted by ♦bulk of four volumes of azote and one volume of oxygen; and if we*" consider the atom of oxygen as 10, and the atom of azote as 17*5, it will be found by weight to consist of one atom of oxygen* and two atoms of azote, or per cent, of—Oxygen 22*22f—Azote 77-77. Hence, then, it must be considered in the light of a pure chemi- cal compound; and indeed nothing but this supposition will account for its uniformity all over the world, as demonstrated by numerous experiments. From these data the specific gravities of oxygen and * [Two atoms of azote =35 One atom of oxygen =10 45 45 100 — 22-222 = 77-777. The numbers 10 and 17-5 are adopted from Wollaston's table of equivalents.—C.] + [These numbers seem substituted to make out the supposition of common air consist; ing of two atoms of azote and one of oxygen. The most accurate experiments seem to rest on 21 as the proportion of oxygen and 79 nitrogen or azote.—C] 462 APPENDIX. [No. II. azote (atmospheric air being 1*000) will be found to be,*—Oxygen 1*1111—Azote -9722. 2 Hydrogen.—The specific gravity of hydrogen, on account of its great levity, and the obstinacy with which it retains water, has always been considered as the most difficult to take of any other gas. These obstacles made me (to speak in the first person) des- pair of arriving at a more just conclusion than had been before ob- tained by the usual process of weighing; and it occurred to me that its specific gravity might be much more accurately obtained by cal- culation from the specific gravity of a denser compound into which it entered in a known proportion. Ammoniacal gas appeared to be the best suited to my purpose, as its specific gravity had been taken with great care by Sir H. Davy, and the chance of error had been much diminished from the slight difference between its sp. gr. and that of steam. Moreover, Biot and Arrago had obtained almost precisely,the same result as Sir H. Davy. The sp. gr. of ammonia, * Let x = sp. gr. of oxygen. 22-22 = a y = sp. gi. of azote. 77-77 = b Then 5 5 And x : 4 y :: a: b. 4 ay (*)Hence 5 — iy = -—■ And «/= •j-^-5-3 = -9722. And x= 5 — 4i/= 1-11111. (*) [Some intermediate steps of the equation, which Dr. Prout has abbreviated, would perhaps make the calculation easier to a young algebraist. x : iy :: a : b. Then, the product of the extremes multiplied together, equal the product of the means, i.«. xb = Aay x= b But it has been found before, that *+4y=l,hence 5 X-)- 4y= 5, and x — 5 — 4 y, but 4<*V. r — 4 y _ -—£- because it is equal to x 5 6 — 46«/= iay 5 6 = iay + *by 4 au-j- 4 6v ■ . , , . = v, and 4o + 4 6^ "' 56 ,. v . ^ -.---r —r-, = v, or -which is the same 4 a + 4 b 3' 5b , a ia-\- 4 b •9722, therefore 4a + 46 y = -9722, and x= 5 — 4 y, or 1*1111. ——C] No. II.] APPENDIX. 463 according to Sir H. Davy, is -590164, atmospheric air* being 1-000. vV e shall consider it as -5902; and this we are authorised in doing, as Biot and Arrago state it somewhat higher than Sir H. Davy. Now ammonia consists of three volumes of hydrogen and one vo- lume of azote condensed into two volumes. Hence the sp. gr. of hydrogen will be found to be *0694,* atmospheric air being 1*0000. It will be also observed that the sp. gr. of oxygen as obtained above is just 16 times that of hydrogen as now ascertained, and the sp. gr. ©f azote just 14 times.f 3. Chlorine.-—The specific gravity of muriatic acid, according to Sir H. Davy's experiments, which coincide exactly with those of Biot and Arrago, is 1*278. Now if we suppose this sp. gr. to be erroneous in the same proportion that we found the sp. gr. of oxy- gen and azote to be above, (which, though not rigidly accurate, may yet be fairly done, since the experiments were conducted in A similar manner), the sp. gr. of this gas will come out about 1*2845 ;] and since it is a compound of one volume chlorine and one volume hydrogen, the specific gravity of chlorine will be found by calcula- tion to be 2*5.§ Dr. Thomson states, that he has found 2*483 to be near the truth,|| and Gay-Lussac almost coincides with him.^] Hence there is every reason for concluding that the sp. gr. of chlo- rine does not differ much from 2-5. On this supposition, the sp. gr. of chlorine will be found exactly 36 times that of hydrogen. On the Specific Gravities of Elementary Substances in a Gaseous State, that do not at ordinary Temperatures exist in that State. 1. Iodine.—I had some reason to suspect that M. Gay-Lussac had in his excellent memoir rated the Aveight of an atom of this substance somewhat too high; and in order to prove this, 50 grains of iodine, which had been distilled from lime, were digested with 30 grs. of very pure lamellated zinc. The solution formed was transparent and colourless; and it was'found that 12-9 grains of zinc had been dissolved. 100 parts of iodine, therefore, according to this experiment, will combine with 25*8 parts of zinc, and the weight of an atom of iodine will be 155,** zinc being supposed to be * Let x= sp. gr. of hydrogen. „,, 3 x + -9722 Then---------- = -5902. 1-1804—-9722 Hence x =-------------= -0694. f 1 Hill _---0694 = 16. And -9722 -=- -0694 = 14. i As 1104: 1-11111 :: 1-278 : 1-286. And as -969 : -9722 :: 1-278 : 1-283. The mean of these is 1-2845. § Let x = sp. gr. of chlorine. Then—^----= 12845. And x = 2-569 — -0694 = 2-5 very nearly. [| Annals of Philosophy, iv. p. 13. 1 Ibid. vi. p. 126. •* As 85-8 ; 100 :* 40: 155. According to experiment 8th, stated below, the weight of 464 APPENDIX. [No. II. 40. From these data, the sp. gr. of iodine in a state of gas will be found by calculation to be 8-611111, or exacdy 124 times that of hydrogen.* 2. Carbon.—I assume the weight of an atom of carbon at 7-5. Hence the sp. gr. of a volume of it in a state of gas will be found by calculation to be *4166, or exactly 12 times that of hydrogen. 3. Sulphur.—The weight of an atom of sulphur is 20. Hence the specific gravity of its gas is the same as that of oxygen, or 1*1111, and consequently just 16 times that of hydrogen. 4. Phosphorus.—I have made many experiments in order to as- certain the weight of an atom of this substance ; but after all, have not been able to satisfy myself, and want of leisure will not permit me to pursue the subject further at present. The results I have obtained approached nearly to those given by Dr. Wollaston, which I am therefore satisfied are correct, or nearly so, and which fix phosphorus at about 17-5, and phosphoric acid at 37-5,f and these numbers at present I adopt. 5. Calcium.—Dr. Marcet found carbonate of lime composed of 43-9 carbonic acid and 56-1 lime4 Hence as 43*9 : 56*1 :: 27*5 : 35-1, or 35 very nearly ; and 35 — 10 = 25, for the atom of cal- cium. The sp. gr. of a volume of its gas will therefore be 1-3888, or exactly 20 times that of hydrogen. 6. Sodium.—100 grains of dilute muriatic acid dissolved 18*6 grs. of carbonate of lime, and the same quantity of the same dilute acid dissolved only 8*2 grs. of carbonate of lime, after there had been previously added 30 grs. of a very pure crystallized subcarbo- nate of soda. Hence 30 grs. of crystallized subcarbonate of soda are equivalent to 10*4 grs. of carbonate of lime, and as 10*4 : 30 :: 62*5 : 180. Now 100 grs. of crystallized subcarbonate of soda were found by application of heat to lose 62*5 of water. Hence 180 grs. of the same salt contain 112*5 water, equal to 10 atoms, and 67*5 dry subcarbonate of soda, and 67*5 — 27*5 =40 for the atom of soda, and 40 — 10 = 30 for the atom of sodium. Hence a volume of it in a gaseous state will weigh 1*6666, or exactly 24 times that of hydrogen. 7. Iron.—100 grs. of dilute muriatic acid dissolved as before 18*6 grs. of carbonate of lime, and the same quantity of the same an atom of zinc is 40. Dr. Thomson makes it 40.9, which differs very little. See Annals of Philosophy, iv. p. 94. * One volume of hydrogen combines with only half a volume of oxygen, but with a whole volume of gaseous iodine, according to M. Gay-Lussac. The ratio in volume, therefore, be- tween oxygen and iodine is as £ to 1, and the ratio in weight is as 1 to 15-5. Now -5555, the densitv of half a volume of oxygen, multiplied by 15-5, gives 8-61111, and 8-61111 -4- -06944 = 124. Or, generally, to find the sp. gr. of any substance in a state of gas, we have only to multiply half the sp. gr. of oxygen by the weight of the atom of the substances with respect to oxygen. See Annals of Philosophy, v. p. 105. ] Some of my experiments approached nearer to 20 phosphorus and 40 phosphoric acid. * I quote on the authority of Dr. Thomson, Annals of Philosophy, iii. p. 376. Dr. Wol- laston makes it somewhat different, or that carbonate of lime consists of 43-7 acid and 56-3 lime. Phil. Trims, civ. p. 8. No. II.] APPENDIX. 465 acid dissolved 10*45 of iron. Hence as 18*6 : 10*45 :: 62-5 : 35*1, or for the sake of analogy, 35, the weight of an atom of iron. The sp. gr. of a volume of this metal in a gaseous state will be 1-9444, or exactly 28 times that of hydrogen. 8. Zinc.—100 grs. of the "same dilute acid dissolved, as belore, 18*6 of carbonate of lime and 11*85 of zinc. Hence as 18-6 : 11*85 : : 62-5 : 39-82, the weight of the atom of zinc, considered from analogy to be 40. Hence the sp. gr. of a volume of it in a gaseous state will be 2-222, or exactly 32 times that of hydrogen. 9. Potassium.—100 grs. of the same dilute acid dissolved, as be- fore, 18*6 carbonate of lime ; but after the addition of 20 grs. of su- per-carbonate of potash, only 8*7 carbonate of lime. Hence 20 grs. of super-carbonate of potash are equivalent to 9*9 carbonate ot lime; and as 9*9 : 20 :: 62*5 : 126*26, the weight of the atom of su- per-carbonate of potash. Now 126*26 — 55 + 11*25 = 60, the weight of the atom of potash, and 60 — 10 = 50, the weight of the atom of potassium. Hence a volume of it in a state of gas will weigh 2-7777, or exactly 40 times as much as hydrogen. 10. Barytium.—100 grs. of the same dilute acid dissolved exact- ly 'as much again of carbonate of barytes as of carbonate of lime. Hence the weight of the atom of carbonate of barytes is 125 ; and 125 — 27-5 = 97*5, the weight of the atom of barytes, and 97-5 _ 10 = 87*5, the weight of the atom of barytium. The sp. gr. therefore,^ of a volume of its gas will be 4-8611, or exactly 70 times that of hydrogen. With respect to the above experiments, I may add, that they were made with the greatest possible attention to accuracy, and most of them"were many times repeated with almost precisely the same results. The following tables exhibit a general view of the above results, and at the same time the proportions, both in volume and weight, in which they unite with oxygen and hydrogen : also the weights of other substances, which have not been rigidly examined, are here stated from analogy. Vol. I. 3N TABLE I.—Elementary Substances. — a -a— c ' 4 •c 0) •a * ■c • J= © JD 'v o *s 60 * be o. °a 3 CO si O . o §3 2 °* A .. o CU CO s<-. s . --.^ w Name. 1 a. d i o .E 0/ S Is' "••if . 'v il Wt. of atom 1 being 10, ft riment m O a . CO Sp. gr. atmos being 1, fr riment. Wt. in grs. o inches. Bi Therm. 60 — 0 Observations. Hydrogen . 1 1 1-25 1-32 •06944 •073 a 2118 2-23 a Dr. Thomson. See Annals of Philosophy, i. 177. b Dr. Wollaston, from Biot and Arrago. Phil. Trans, civ. Carbon . . 6 6 7-5 7-54A •4166 — 12-708 — 20. Dr. Thomson makes it 7-51. Annals of Philoso- phy, ii. 42. Azote . . 14 14 17*5 17-54 •9722 •969 c 29-65-.' !9.56 c Dr. W. from Biot and Arraeo. d Dr. W. from Berzelius and nose. Phosphorus 14 14 17 5 17-4J •9722 — 29-652 — Oxygen . . Sulphur. . 16 8 10 10 11111 1 104e 33-888 J3.672 e Dr. Thomson, from a mean of several experiments. 16 ! 16 20 20/ 11111 — 3.3-888 — /Dr. W. from Berzelius. Calcium. . 20 ' SO 25 25-46> 29-1 h 1 3888 — 42-36 — g Dr. VV. from experiment. h Dr. W. from Davy. Sodium . . 24 : 24 30 1-6666 — 50832 — Iron . . . 528 ' 28 35 34-5 i 1-9444 — 59-302 — i Dr. W. from Thenard and Berzelius. Zinc . . . 32 j 32 40 41 k 2-222 — G7777 — k Dr. W. from Gay-Lussac. Chlorine 36 j 36 ! 45 441/ 2-5 2481m 76248 "~• 1 Dr. W. from Berzelius. m Quoted from Dr. Thomson. Annals' of Philosophy, iv. 13. Potassium . 40 t 40 50 49-1 n 2-7777 — 84-72 _ n Dr. W. from Berzelius. Barytium . 70 70 87-5 S7o 4-8611 — 148-26 — o Dr. W. from Berzelius and Klain-oth. Iodine . . 124 U4 155 156 21/; 8-6111 — 262-632 — p Gay-Lussac. Ann. de Chim. xci. 5. TABLE II.—Combinations with Oxygen. Name. 6 3 £ ^ on fi 1 "• O e -^ • 0 c . *o = 6 ! S> 0.0 ii Wt. ot atom, ox. being 10, from exper. Sp. gr. atmos. air being 1. Sp. gr. atmos. air being 1, from exper. Wt.oflOOcu. in. Bar. 30. Ther. 60. a P. O X is u. O A CO . = s o> a t> O No. of vol. af-ter combina-tion. g'5 5 * Observations. Water . . . Carbonic oxide Nitrous oxide Atmospheric air Phosphorous acid Oxide of sulphur? Euchlorine Lime . . . 9 14 22 14-4 44 28 9 14 22 36 44 28 11 -26 7-5 27-5 45 55 35 11 32 17-54 35-46 •625 •9722 1-5277 1-000' 3-0555 1-9444 ■6896 . •956 6 1-614c 1000 2-409 e 19-06-i 29-652 46-596 30-5 93-192 59-304 21 -033 29-16 49-227 30-5 d 73-474 ■5 ox -f- 1 hyd ■5 ox -j- 1 ca •5 ox 4" « az ■5 ox 4" 2 az •5 ox -f- 1 ph? •5 ox 4~ 1 sul? •5 ox 4" * ch •5 ox 4" 1 iod •5 ox -|- 1 cal be. 1 1 1 2-5 1? 1 ox f 1 hyd 1 ox 4~ * car 1 ox -f 1 az 1 ox 4" 2 az 1 ox 4- * ph? 1 ox 4~ * sul? 1 ox 4~ 1 ch 1 ox 4~ * i°d 1 ox 4~ 1 cal be. a i rales, Ur. Thomson, Annals, i. \7T. b Ciuickshaucks, quoted by Thomson. c Sir H.Davy. ' d Sir G. S. Evelyn. e Sir H. Davy. Carbonic acid Nitrous gas Phosphoric acid Sulphurous acid 22 15 30 32 22 30 30 32 27-5 37-5 37-5 40 27-54 37-4 1-5277 1-0416 2-0832 2-2222 \-S\*g 1-0388 h 2193 i 46-596 31 -77 63-54 67-777 46-313 31-684 66-89 1 ox + 1 hy/ 1 ox + 1 car I ox 4- 1 az 1 ox 4~ ' ph 1 ox -j- * sul 1 ox 4" 1 °h I ox 4" 1 iod be. 1 2 1 2 ox + 1 hyd 2 ox 4- 1 car 2 ox 4" 1 »z 2 ox 4- 1 ph 2 ox 4" 1 sul 2 ox 4- 1 ch 2 ox 4" 1 ioii be. J 1 his and all higher combinations of hy-drogen with oxygen are unknown. if Saussure. k Berard. i Sir H. Davy. Nitrous acid . Sulphuric acid 38 40 38 40 54 76 164 47-5 50 67-5 95 205 50 2-6388 2-7777 2-427 k 80-484 84-72 740234 1-5 ox + 1 car 1-5 ox -j- 1 az 1-5 ox 4- 1 ph 1-5 ox 4" 1 sul 1-5 ox 4" 1 ch 1-5 ox 4" 1 iod be. 1 1 3 ox + 1 car 3 ox 4~ !• az 3 ox 4~ 1 ph 3 ox 4" 1 sul 3 ox -+- 1 ch 2 ox 4~ 1 iod be. e Sir H. Davy. Nitric acid . . Chloric acid . Iodic acid . . 54 76 164 67-54 3-75 5-2777 11-3883 — 114-372 160-968 347-352 2-5 ox -J- 1 car 2-5 ox 4- 1 az 2-5 ox 4~ 1 ph 2-5 ox 4~ 1 sul 2-5 ox 4- 1 ch 2-5 ox 4,- 1 iod be. 1 1 1 5 ox -f- 1 car 5 ox 4" 1 az 5 ox -f- 1 ph 5 ox 4~ 1 sul 5 ox 4~ 1 ch 5 ox 4" 1 iod be r ■ J See Gay-Lussac's memoir on iodine *\ above referred to. TABLE III.—Compounds with Hydrogen. Name. on c "3 XI 6 V X? So a. CO c on 2 •a >-. Xi i o • •s.s . 0. .*"' -o 4 7 17 37 125 17 26 27 62 s a> bo x" o i o . «2 '■s °° S , 'v Wt. of atom, oxygen being 10, from expe-riment. '5 o ■c 4) Xi a. o e . ^5 T . to &■§ en •5555 •9722 1-1805 1-284 4-3402 •5902ri 1-8055 ■9374 2-1527 » IF 4» .a & - X 41 41 -is tf o 2£ . cXw •_ = c OD-7" 4* w 4i e CO •5555a •9740a I 177 1-278 4-34634 •5900 I-8064e •9360e 2-lllle -g d s to . i.' ot* o 2d o C C5 16-990 29-65': 36-006 39 183 132-37.> 18 003 55-06^ 28-593 65-659 XI o .£ *i c s 5 o -r §1 •s a j.8 4) a _3 O t* c 4) a 3 5 » u u "es o 5 > .5 as O £ . 41 41 Pi ,n C0 "S 4) a ii w Observations. Carbureted hydrogen Olefiant gas . . . Sulphureted hydrogen Muriatic acid . . Hydriodic acid . . Ammonia .... Cyanogen .... Hydrocyanic acid . Chloro-cyanic acid . 8 14 17 185 62-5 8-5 26 13-5 31 5-8-75 21 -25 46-25 156-25 21-25 32-5 33 75 77-5 5-09 8-86 21-32 45-42 157-53 21-5 c 32-52 33-846 16999 29-72 .55-89 ;8-979 18-000 1 hyd -J- -5ear l hyd 4" 1 car 1 hyd 4" 1 sul 1 hyd 4- 1 chl 1 hyd -f- 1 iod 3 hyd -f- I az 2 car -J- 1 az I cya -j~ *■ hy 1 cya 4~ 1 c^' •5 •5 1 2 2 2 1 2 2 l hyd -f- -5car 1 hyd -|" * °ar 1 hyd 4" * sul I hyd + 1 chl I hyd 4" l iotl 3 hyd 4" * az 2 car +1 az I cya 4" * az 1 cya 4" * chl £a Dr. Thomson. b Gay-Lussac. c Dr. Woll \ston. d Sir H. Duy. 7 e Gav-Lussac. Ann. de J Chim. Aug. 1815. No. II.] APPENDIX. 469 TABLE IV.—Substances stated from Analogy, but of which we are yet uncertain. Name. Aluminum Magnesium Chromium Nickel Cobalt . Tellurium Copper . Strontium Arsenic . Molybdenum Manganese Tin ' . . Bismuth . Antimony Cerium . Uranium Tungsten Platinum Mercury Lead . . Silver . Rhodium Titanium Gold . . 12 18 28 28 32 32 48 48 48 56 60 72 88 92 96 96 96 100 104 108 ICO 144 200 •J c 8 12 18 28 28 32 32 48 48 48 56 60 72 88 92 96 96 96 100 104 10 15 22-5 35 35 40 40 60 60 60 70 75 90 110 115 120 120 120 125 130 -a a 2