THE DISCOVERY THE COMPOSITION OF WATER. BDINBCBCH : FBIXTED Bt T CONSTABLE, PB1STEB TO HBB MAJESTT. I CORRESPONDENCE OF THE LATE JAMES WATT ON fflS DISCOVERY OF THE THEORY OF THE COMPOSITION OF WATER. WITH A LETTER FROM HIS SON. EDITED WITH INTRODUCTORY REMARKS AND AN APPENDIX BY JAMES PATRICK MUIRHEAD, ESQ. F. R. S. E. LONDON: JOHN MURRAY. EDINBURGH: WILLIAM BLACKWOOD AND SONS. M.DCCC.XLVI. '. .'.-'.-" ' CONTENTS. Page Letter from James Watt, Esq. to the Editor, i Introductory Remarks, by the Editor, . . . xvii Summary of the History of the progress towards the discovery, and of the discovery itself, . . cxxiii Extracts from the late Mr. Watt's Correspondence re- specting his discovery of the theory of the compo- sition of Water, 3 Translation of a Letter from Dr. Blagden, Sec. R.S.L., to Dr. Lorenz Crell, ... 71 APPENDIX : No. I. Thoughts on the constituent parts of water and of dephlogisticated air ; with an account of some experiments on that subject. In a letter from Mr. James Watt, Engineer, to Mr. De Luc, F.R.S. . 77 No. II. Sequel to the Thoughts on the constituent parts of water and of dephlogisticated air, in a sub- sequent letter from Mr. James Watt, Engineer, to Mr. De Luc, F.R.S., 106 No. III. Experiments on Air. By Henry Cavendish, Esq., F.R.S. and S.A Ill 610846 CONTENTS. Pa s e No. IV. Memoire ou 1'on prouve par la decomposition de 1'eau, que ce fluide n'est point une substance simple, et qu'il y a plusieurs moyens d'obtenir en grand 1'air inflammable qui y entre comme principe constituant. Par MM. Meusnier et Lavoisier, . 151 No. V. Memoire dans lequel on a pour objet de prouver que 1'eau n'est point une substance simple, un ele- ment proprement dit, mais qu'elle est susceptible de decomposition et de recomposition. Par M. La- voisier, 171 No. VI. Memoire sur le resultat de 1'inflammation du Gaz inflammable et de 1'air dephlogistique dans des vaisseaux clos. Par M. Monge, . . . 205 No. VII. Extract from the Translation of M. Arago's Historical Eloge of James Watt, relative to the dis- covery of the composition of water, . . . 221 No. VIII. Historical Note on the discovery of the theory of the composition of water. By the Right Hon. Henry Lord Brougham, F.R.S., and Member of the National Institute of France, . . . 242 No. IX. Extract from the Comptes Rendus Hebdoma- daires des Seances de 1'Academie des Sciences, . 260 LETTER FROM JAMES WATT, ESQ. TO THE EDITOR. ASTON HAIL, February 5, 1846. MY DEAR SIR, You have satisfied me that the time has now arrived for the publication of the documents in my possession, relative to my Father's discovery of the Theory of the Composition of Water. After the testimony borne by M. Arago in his Eloge, and by Lord Brougham in his Historical Note appended to it, I deemed such publication not neces- sary, and certainly not urgent. My opinion was in no degree affected by the weak declamation of the Rev. W. Vernon Harcourt, at the meeting of the British Association at Birmingham in 1839, which, shortly afterwards, met with just exposure and rebuke in the Notes to your Translation of the Eloge,* (page 114), and was treated as it deserved by MM. Arago and Dumas, in the Memoirs of the Institute of France. The Diary of Mr. Cavendish, subsequently * London. John Murray, 1839. H LETTER FROM MR. WATT TO THE EDITOR. printed by the same Reverend gentleman, appeared to me too obviously inconclusive to call for any com- ment ; although it has since received one from a far abler pen than mine.* It had, however, always been my intention, when retirement from business and active pursuits should permit the requisite leisure, that such a publication should form an amusement and occupation of my later years ; perhaps accompanied by another volume, containing the Specifications of my Father's various ' Mechanical Patents, which so materially contributed to the development of our national industry and re- sources ; and also a volume of his Reports on subjects of Civil Engineering, which, though now obsolete, would add to the history of that important art, and mark the accuracy and talent of a young self-taught engineer, then fully estimated by his great precursor, Smeaton. Some of the infirmities of age have, how- over, come upon me more suddenly than I had taken into my account ; and now render it difficult for me to peruse written or printed documents. I therefore, willingly and gratefully, resign to your friendly care the editing of my father's correspondence, the origi- nals of which you have minutely examined. As a question of evidence, this falls peculiarly within the sphere of your pursuits, and I am satisfied it could not be placed in better hands. * See Lord Brougham's Lives of Men of Letters and Science, vol. i. p. 400. LETTER FROM MR, WATT TO THE EDITOR, 111 That correspondence commences about the close of the year 1 782, and is continued throughout 1 783, and part of 1784. Although I was at that period too young and uninformed to be able to appreciate the whole merit of his discovery, I well recollect his conversations with his philosophical friends, and the sentiments he expressed in regard to it. He early directed my attention, both at home and abroad, to Natural Philosophy and Chemistry; and on my re- turn from the Continent in 1 794, when he and Mr. Boulton took me into partnership, together with the late Mr. Robinson Boulton, and my late brother Gre- gory, I was tolerably versed in the facts and doc- trines of the new system of chemistry, which the able writings and generalization of Lavoisier had caused to be commonly received. The old nomen- clature was supplanted by the new, although Dr. Priestley, who had just retired to the United States, as well as Mr. Keir and some others, formed brilliant exceptions to the universality of its adoption. When the theory of the composition of water was spoken of in the presence of my father, he calmly but uniformly sustained his claim to its discovery ; and once, on my hinting that it was passed over by some writers, and not correctly given by others, he observed, that hav- ing done all that he and his friends considered requi- site to place it upon record, by the note affixed to his paper of 26th November 1 783, in the Philosophical Transactions, the accuracy of which had never been IV LKTTER FROM MR. WATT TO THE EDITOR. questioned, he should leave posterity to decide. The important, though vague testimony of Dr., after- wards Sir Charles Blagden, was published in Crell's Ghemische Annalen for 1786; consequently in the lifetime of Cavendish and Lavoisier ; and was never contradicted, nor in any way impeached. When I met with it, I shewed it to my father ; who, although he no longer felt any warm interest in the question, was amused by the skill of the narrator. After be- coming in 1 785 a Fellow of the Royal Society, he formed the personal acquaintance of Mr. Cavendish, and lived upon good terms with him. I well remem- ber his introducing me, at one of the meetings of the Society, to that highly-gifted and singular man. When upon my father's death, in August 1819, I became possessed of his papers, I found copies of all his letters taken by his copying machine, arranged in volumes, and carefully preserved; and the letters of his correspondents relating to this subject, tied up together, along with the press copies of his letters to Dr. Priestley of 26th April 1783, and to Mr. De Luc of 26th November 1 783 ; and I was gratified to find that the documents he had left contained proofs so ample, satisfactory, and conclusive. I then shewed the whole to my friend and neigh- bour, the late Mr. John Corrie, the President of the Philosophical Society of Birmingham, whose literary and scientific attainments are well known, and highly estimated ; and who strongly expressed an opinion LETTER FROM MR. WATT TO THE EDITOR. concurrent with my own. In the summer of 1820, having occasion to visit Scotland in the performance of some of my duties as my father's executor, I, on my passage through Manchester, consulted the late Dr. William Henry, whose knowledge of the history and practice of chemistry is undisputed ; referring him to all the printed authorities, and acquainting him generally with the corroborative proofs in my father's correspondence. The former were sufficient to convince him, as appeared from a letter which I received from him at Edinburgh ; where I had men- tioned the subject to Dr. Hope, and Dr. (now Sir David) Brewster, whose opinions, however, differed from my own, and from those of Mr. Cqrrie and Dr. Henry.* But a farther examination entirely confirmed my own conviction of my father's priority ; and I was restrained from giving to the public at that time the whole of the documents now first printed, only by the constant avocations of the business of which I had then assumed the management, and by my own dislike to appear as an author. In the year 1823, on being applied to by Mr. Mac- vey Napier, as editor of the Encyclopaedia Britannica. * Dr. Henry afterwards, in the years 1835 and 1836, called upon me and inspected the original correspondence, which had the natu- ral effect of strengthening the opinion he had formed and expressed in 1820 ; and upon the latter occasion he mentioned his intention of writing a history of Chemistry, in which he said he should do justice to my father's claims to the priority. vi LETTER FROM MR. WATT TO THE EDITOR. for a short life of my father, in the Supplement then publishing, I inserted in the memoir the following statement, which, from the whole of the facts, since ascertained, not having been known to me, was ne- cessarily somewhat imperfect. " Chemical studies engaged much of his attention " during his busiest time ; and at the very period " when he was most engaged in perfecting his rotative " engines, and in managing a business become con- " siderable, and, from its novelty, requiring close at- " tention, he entered deeply into the investigations " then in progress relative to the constitution and " properties of the different gases. Early in 1 783, " he was led, by the experiments of his friend and " neighbour, Dr. Priestley, to the important conclu- " sion, that water is a compound of dephlogisticated " and inflammable airs (as they were then called,) " deprived of their latent or elementary heat, and " he was the first to make known this theory. This " was done in a letter to Dr. Priestley, dated the 2Gth " April 1783, in which he states the Doctor's ex- " periments to have come in aid of some prior notions " of his own, and supports his conclusions by original " experiments. That letter Dr. Priestley received in ' London, and, after shewing it to several members " of the Royal Society, he delivered it to Sir Joseph " Banks, with a request that it might be read at some " of the public meetings of the Society ; but before " that could be complied with, Mr. Watt, having heard LETTER FR01I MR. WATT TO THE EDITOR. Vll " of some new experiments made by Dr. Priestley, " begged that the reading might be delayed. Those " new experiments soon afterwards proved to have " been delusive ; and Mr. Watt sent a revised edition " of his letter to Mr. De Luc, on the 26th November " of the same year, which was not read to the Society " until the 29th April 1784, and appears in the Phi- " losophical Transactions for that year, under the title " of ' Thoughts on the Constituent Parts of Water " ' and of Dephlogisticated Air, with an Account of " ' some Experiments on that Subject.' In the in- " terim, on the 15th January 1784, a paper by Mr. " Cavendish had been read, containing his ' Experi- " ' ments on the Combustion of the Dephlogisticated " ' and Inflammable Airs,' and drawing the same in- " ference as Mr. Watt, with this difference only, that " he did not admit elementary heat into his expla- " nation. He refers in it to his knowledge of Mr. " Watt's paper, and states his own experiments to " have been made in 1781, and mentioned to Dr. " Priestley ; but he does not say at what period he " formed his conclusions : he only mentions that a ' friend of his had, in the summer of 1783, given M. " Lavoisier some account of his experiments, as well " as of the conclusion drawn from them. It is quite " certain that Mr. Watt had never heard of them ; " and Dr. Blagden has stated, that he mentioned at " Paris the opinions of both the English philosophers, " which were not admitted without hesitation, nor viii LETTER FROM MR. WATT TO THE EDITOR. " until the French chemists had satisfied themselves " by experiments of their own." To this was appended a note to the following effect : " There is a confusion of dates in the ac- " counts of this affair. Mr. Watt's letter to Mr. De " Luc, in the Philosophical Transactions, appears " dated 26th November 1784, which is evidently an " error of the press. Mr. Cavendish, in his letter, "read 15th January 1784, speaks of Mr. Watt's " paper as ' lately read before the Society,' whereas " the paper itself purports to have been read on the " 29th April 1784. This we cannot explain." What was then unintelligible to me has since been explained by Lord Brougham's discovery, that the passage citing my father's paper, had been interpo- lated by Dr. Blagden at a period subsequent to that at which Mr. Cavendish's paper was read. It cannot escape observation, that it is the only passage in that paper in which Mr. Watt's name is even mentioned. It is now, also, well known that another extraordi- nary error of the press was committed, in the nume- rous separate copies of his paper circulated by Mr. Cavendish, in which that paper was said to have been " read at the Royal Society, January 15, 1783 ;" it having been in fact read there January 15, 1784. On the 18th of June 1824, a public meeting was held at Freemason's Hall, for the purpose of erecting a monument as a tribute of national gratitude to my father; at which many of the most distinguished states- LETTER FROM MR. WATT TO THE EDITOR. IX men of the day attended, and the Earl of Liverpool, who presided, announced that the King had graciously commanded him to put down his Majesty's name as heading the subscription. A Committee having been appointed, of which Mr. Charles Hampden Tur- ner, the attached and zealous friend both of my father and myself, was chairman, the execution of the colos- sal statue, now erected in Westminster Abbey, was confided to the late Sir Francis Chantrey, and an in- scription for it was written by Lord Brougham. In September of the same year, Sir Humphry Davy paid me a visit, and remained with me a few days. I then showed him the Life I had written for the Encyclo- paedia Britannica, of which the- editor had sent me some detached copies. I directed his attention to what is there said on my father's claim to the dis- covery of the theory of the composition of water ; but the facts stated appeared to be new to him, or, if known at all before, to have been forgotten, or not to have been considered. I mentioned my desire to do justice, and inquired if he knew of any papers left by Mr. Cavendish, from which the date of his conclusions might be ascertained ; but he was ignorant of the ex- istence of any such papers. I then laid before him the press copies of my father's letters, and the origi- nal ones of his correspondents, which he read over with much interest, and appeared exceedingly struck with their contents. He expressed concern at the effect which their publication must produce, (a con- b X LETTER PROM MR. WATT TO THE EDITOR. cern not unnaturally proceeding from his known attachment to Mr. Cavendish,) and he did not then, or at our subsequent meeting in 1826, endeavour to lessen their force, or to call in question the deductions resulting from their perusal. In the last conversa- tion I had with him here on the subject, he said he thought that my father's theory, admitting the latent heat, would prove correct. Year after year of a life of business had passed away, without my finding leisure to resume the sub- ject, when, in May 1833, I received notice from M. Arago of his having been directed, as Perpetual Se- cretary of the Academy of Sciences at Paris, to write an Eloge of my father, and he requested some details of his life. These were given ; and, in the autumn of 1834, M. Arago paid me a visit, in order to collect further materials, and to make himself acquainted with the scenes of my father's later life. He afterwards extended his journey to the earlier ones in Scotland. Finding, upon conversing with M. Arago, that he had studied and made himself master of my father's improvements on the steam-engine, I inquired whether he had also paid attention to the origin of the theory of the composition of water. He answered in the affir- mative, and said he had satisfied himself, by a peru- sal of the published documents, of my father's right to the priority. I then showed him the press copies of my father's letters, and the originals of those of his correspondents, which put the seal on his conviction, LETTER FROM MR. WATT TO THE EDITOR. XI and he requested permission to make use of them in his intended memoir, urging that, in justice to my father's memory, and as a matter of history, I ought not to withhold them. In consequence, I arranged them in chronological order for his use, accompanied by such brief explanations and remarks as occurred to me. His Eloge was read to the Institute on the 8th De- cember 1834, and although some parts of the personal history were subsequently corrected and added to, the portion relative to the composition of water ex- perienced no alteration. In the summer of 1834, I called the attention of Lord Brougham, who was then Lord Chancellor, and had undertaken to write the inscription for the monu- ment in Westminster Abbey, to the Memoirs in the Philosophical Transactions, and the papers I had col- lected and transcribed, with a request that he would examine them with the discrimination of a lawyer, and the impartiality of a judge. After having given them his attentive perusal, he suggested the propriety of an inquiry whether Mr. Cavendish had left any papers, as these might throw light on the precise pe- riod when his conclusions were formed. His Lord- ship wrote to the Duke of Devonshire, as representa- tive of Mr. Cavendish, and received for reply, that all Mr. Cavendish's papers were in the hands of Mr. Hud- son, who was arranging them for publication ; and His Grace most handsomely gave me permission to Xll LETTER FROM MR. WATT TO THE EDITOR. inspect them. I, however, felt it a matter of delicacy to become a witness in a cause, where I must, as the representative of my father, be considered a party ; and I requested those two very competent and unex- ceptionable gentlemen, Mr. Charles Hatchett and Mr. W. T. Brande, the former of whom had been a friend both of Mr. Cavendish and of my father, to under- take the examination, which they both promised to do. Mr. Hatchett reported to me that he had found nothing whatever to indicate the period when Mr. Cavendish's conclusion was formed. Mr. Brande fur- ther carefully searched the books of the Royal So-' ciety, and expressed his opinion that the records which he there found were " satisfactory as to the " priority of Mr. Watt's claims ; in short, leave no- " thing further to be said against them." Lord Brougham also suggested an examination of the original papers preserved in the archives of the Royal Society, which he undertook himself : he then discovered the interpolations in the Memoir of Mr. Cavendish, in the hand-writing of Sir C. Blagden, with which, from frequent correspondence with him, he was himself familiar ; and thus threw light on what was before unintelligible. At his Lordship's request I afterwards accompanied him to Somerset House, and saw the documents confirming his state- ment. M. Arago's Eloge is published in the Memoirs of the Institute, and in the Annuaire du Bureau de LETTER FROM MR. WATT TO THE EDITOR. X11I Longitudes for 1839, accompanied by the paper of Lord Brougham, with Notes, which I added, at his Lordship's request, and which he desired to be printed along with it. The reader will find all these in the Appendix to your translation. To those who may wish to form a just apprecia- tion of the circumstances in which this correspon- dence took place, and of the merit that attaches to my father for the discovery it records, I beg to state, in the words of the great master of the English tongue, that " it was written, not in the soft obscuri- " ties of retirement, or under the shelter of academick " bowers ; but amidst inconvenience and distraction, " in sickness and in sorrow." About the beginning of the year, when the cor- respondence commences, he had returned from plan- ning and superintending the erection of his steam en- gines, during a long sojourn in Cornwall, where he had been much harassed by attempts to pirate his improvements ; and he was, through the greater part of the subsequent period, laboriously engaged in making out drawings and descriptions for the long specifications of his three great patents for mecha- nical improvements and inventions, taken out in the years 1781, 1782, and 1784, besides giving the con- stant attention necessary to the concerns of a nascent manufactory, and himself writing volumes of other letters on business, which alone would have furnished full employment even to an industrious intellect. XIV LETTER FROM MR. WATT TO THE EDITOR. His mind had been greatly affected by his unavoid- able absence from the death-bed of his aged father ; and during the greater part of the time, I well re- member seeing him suffer under most acute sick head- aches, sitting by the fire-side for hours together, with his head leaning on his elbow, and scarcely able to give utterance to his thoughts.* It was unquestion- ably the busiest, as Avell as the most anxious, period of his life, and fraught with the most important re- sults. I need not attempt to do justice to them, for time has sanctioned the judgment of his contempo- raries, who had done it already. The principals and witnesses whose names appear in the correspondence have long departed this life. M. Lavoisier in 1794, Dr. Black in 1799, Dr. Priestley in 1804, Mr. Cavendish in 1810, Mr. Kirwan in 1812, Mr. De Luc in 1817, Mr. Watt in 1819, Dr. Blagden and Sir Joseph Banks in 1820. The historical facts must therefore now be sought for in the contemporary memoirs, published by themselves or others, and in the documents they have left. Inquiry was made of Dr. Priestley's son (since dead) as to his father's papers in I 783-4. He supposed them to have been burned at the time of the Birmingham riots in 1791, which was confirmed by a search he caused to be * To show the state of his own feelings, there are inserted in the Correspondence extracts from his letters to his confidential friend and brother-in-law, Mr. Hamilton, of date 3d January and 18th February, 1783. LETTER FROM MR. WATT TO THE EDITOR. XV made in America. My father's letters and papers, and the letters of his friends, which, as already men- tioned, have fortunately been preserved, are still in my possession, and all that seemed material are copied in this publication. They are authenticated beyond the reach of doubt, to which, as you have inspected and perused them all, and collated the originals with the copies furnished to M. Arago and Lord Brougham, you can now add your own tes- timony. Should their publication produce any unpleasant sensation in the minds of the friends of Mr. Caven- dish, they will, I trust, do me the justice to admit, that it has been neither hastily nor prematurely brought forward, and that it would now be a dere- liction of duty not to produce evidence so creditable to my father, both as a philosopher and as a man. Let me also hope that the Rev. Mr. Harcourt, and other gentlemen who may be placed in a similar elevation, may thus receive a caution, how they abuse functions, the exercise of which is expected to combine talents for historical research with scientific attainments, and impartiality of judgment with com- petency of knowledge. Mr. Harcourt may plead that he had not seen this correspondence. I think it ap- pears equally probable that he has little examined the published documents, from which Lord Brougham principally draws his conclusions, and which alone were sufficient in the first place to satisfy M. Arago. XVI LETTER FROM MK. WATT TO THE EDITOR. These remarks are called for by the late desperate attempt in the Quarterly Review, a Journal generally most respectable, to gain for Mr. Harcourt a scientific reputation, (undeserved, so far as I know,) by fulsome panegyric, misrepresentation of facts, additional blun- ders, and reckless assertions. Such of these as con- cern M. Arago and Lord Brougham may safely be left to the retribution that awaits them. To those which concern myself I shall not condescend to reply otherwise than by the above narrative, and the an- nexed documents. Having thus accomplished what I feel to be pecu- liarly incumbent on myself, I must now confide to you the superintendence and editorship of the pub- lication, accompanied by such further narrative, re- marks, and illustrations, as may appear to you to be necessary ; and I entertain a full conviction that the publication, when completed, will form a permanent record of my father's merit in that great discovery, as well as place the claims of others in their just light. Believe me, My dear Sir, Truly yours, JAMES WATT. INTRODUCTORY REMARKS THE EDITOR. THE admiration which the discoveries and inven- tions of the late James Watt won from the greatest masters of intellectual power, could be surpassed only by the readiness with which men acknowledged his singular modesty, benevolence, and worth. From many, that welcome commendation came early in his career ; by others, it was bestowed when " time and " reflection had contributed to enhance their esti- " mate of Mr. Watt's extraordinary merits." * But by few indeed was it tardily offered from none coldly or reluctantly extorted ; and when his useful and blameless life came at last to a close, all deplored the loss of one of the greatest benefactors that had ever blessed his country and the world. How large a tribute of national gratitude was due to genius and industry which had long been so labo- rious, and had at last become so triumphant, the greatest statesmen, philosophers, and orators of Britain * Mr. C. H. Turner's Preface to the Report of the Speeches de- livered at Freemasons' Hall, 18th June 1824. See Translation of Arago's Eloge, p. 183. XV111 INTRODUCTORY REMARKS have proudly and eloquently told. The variety of their sentiments, the opposition of their politics, the diversity of their paths all were disregarded in the endeavour to do honour to merits of which they showed themselves justly sensible. The fame thus liberally accorded, must not be con- sidered as having been gained solely by the combi- nation of rare virtues, with those creative powers which first discovered, and then supplied, the capacity for improvement in the steam-engine. Mr. Watt's prin- cipal inventions connected with that machine, with all their prodigious results, were founded on the at- tentive observation of great philosophical truths ; and the economy of fuel, increase of productive power, and saving of animal labour, which gradually ensued, all originated in the sagacious and careful thought with which he investigated the nature and properties of heat. Other very material improvements in the construction of the engine were effected by changes in the mode of communicating, directing, or regulat- ing the force generated ; and by the efforts of a mind prolific of mechanical expedients, and perfectly con- versant with practical details, the double engine, the beautiful parallel motion, the crank, the sun arid planet wheels, the application of the governor, the float, the indicator, the smokeless furnace, and many other ingenious devices, were no less successfully exe- cuted than they had been felicitously conceived. But the surprising powers of Mr. Watt's intellect were not limited to one set of subjects, nor was he, in his course of invention, content to travel only by one path, however arduous or untrodden. lie ap- BY THE EDITOR. XIX peared to roam at large over every field of science and learning, exploring them all ; and to be confined by nothing less expanded than the horizon of his own enlarged views. The systems, which he first brought into effective operation, of heating by steam, and bleaching by chlorine, are instances of his numerous contributions to the practical arts and comforts of his country ; his extensive reading and acquaintance with languages, his accurate study of both the prin- ciples and practice of some of the more difficult parts of law, his knowledge, which " overflowed on all sub- jects,"* were such as to astonish the most gifted and energetic students of literature ; while the press for copying letters, the machine for reducing and copy- ing statuary, the musical instruments -J- which, though without a natural ear for music, he skilfully con- structed even his neat drawings and faultless calli- graphy still exist, to prove how fertile in resources, how universal in acquirements, how thoughtful even in its amusements, w r as his patient and industrious mind. The department of physical science with which, next to mechanics, he may be said to have been at one time most familiar, and which long continued in some measure to occupy his leisure hours, was Che- mistry. With what success he studied it, we know from the testimony of the most eminent among his contemporaries who directed their attention especially * Sir Walter Scott, in his Preface to " the Monastery." t Of these, we know of at least four kinds ; an organ, seolian harp, guitar, and flute. The organ was constructed by Mr. Watt for his friend, Dr. Black, and presented to him. XX INTRODUCTORY REMARKS to that subject, and many of whom were his frequent correspondents. " He was equally distinguished," said the late illustrious President of the Royal Society, Sir Humphry Davy, " as a natural philosopher and a " chemist, and his inventions demonstrate his pro- " found knowledge of those sciences." * The numerous experiments which he made with a view to the attain- ment of the great principles of which he was in search, are further commended by the same accom- plished and able judge, as diiScult, delicate, and re- fined. It is stated in the Memoirs of his friend and neigh- bour, the celebrated botanist Dr. Withering, that " in " his estimation, Mr. Watt's abilities and acquire- " ments placed him next, if not superior, to New- " ton ;"f a judgment dictated, no doubt, by the kind partiality of a friend, but shewing the estimation in which Mr. Watt's talents were held by an able and discerning man of science. How intently he watched the phenomena, how deeply he penetrated into the causes of chemical action, might be conceived from his friend Robison's description of him as " a philoso- " pher in the most exalted sense of the word, Avho " never could be satisfied with a conjectural know- " ledge of any subject, and who grudged no labour nor " study to acquire certainty in his researches." j The highest merit certainly attaches to his chemical dis- coveries, and deep interest must be felt by all who * Speech in 1824. Translation of Arago's Eloge, p. 191. t Tracts and Memoir of Dr. Withering, by his Son, 1822. Vol. i. p. 46. 1 Preface to Black's Lectures. BY THE EDITOR. XXI attend to the history of their origin and progress, from the fact that he was in this, as in almost every other part of learning, self-taught. He has himself, on one of the very few occasions on which he ever made public any of his writings through the medium of the press, (almost all the others being only com- munications to the Royal Society, which were ordered to be printed,) taken pains to correct the statements of Professor Robison on this point. That gentle- man, in dedicating to him his edition of Dr. Black's Lectures, called him Dr. Black's pupil, declared that he had attended two courses of his lectures, and even alluded to his professing to owe his improvements on the steam-engine to the instructions he had received from that eminent teacher. This, however, is alto- gether erroneous; and Mr. Watt has lamented* that the necessary avocations of his business at that time prevented his attending either Dr. Black's or any other lectures. But he repeatedly acknowledged the information and pleasure he derived from the con- versation of that enlightened philosopher, as well as from the friendship of such men as Robert Simson and Dr. Dick, both distinguished cultivators of kin- dred branches of natural knowledge. It was not till 1774 that he left his residence in Glasgow, the scene of his early studies and struggles, where his merits had been recognised and fostered by patrons of deserved eminence and the most kindly feelings, and where he had first conceived those felici- * See his Preface to his edition of Dr. Robison's Articles, Steam and Steam-Engine. XX11 INTRODUCTORY REMARKS tous ideas which afterwards became so honourably and inseparably associated with his name. In establishing himself at Soho,* he retained his habits of intimate cor- respondence with Dr. Black, who had then, for more than twenty years, made known his discovery of car- bonic acid gas, and for at least sixteen had annually explained his theory of latent heat in his lectures, in which, also, for the first time, he developed the doc- trine of the capacities of bodies for heat, (or that of specific heat ;) and who, after spending ten years of academical labour in the University of Glasgow, had, in 1766, accepted that chair in Edinburgh, which for thirty years longer he continued to render famous.f In a work, the object of which is to cause justice to be done to Mr. Watt's claims to a great chemical discovery, we have much pleasure in being able, on indisputable authority, to attribute the public an- nouncement of his illustrious friend's theory of latent heat to a period considerably earlier than has been * The celebrated manufactory situated within a mile or two of Birmingham. t Dr. Ferguson, as quoted by Robison in his Preface to the Lec- tures, and repeated, among many others, by Lord Brougham, says that Dr. Black died on the 26th November 1799. But we have now before us Dr. Black's last letter to Mr. Watt, which was written on the 2d December of that year ; which is indorsed by Mr. Watt, " his last " letter," and in which he mentions that he had been slightly unwell, but was then better. In fact, on the 1 1 th December, Professor Robison wrote to Mr. Watt, that his much respected friend had died on the Friday preceding, viz. the 6th December. Ferguson also says, that he died in the seventy-first year of his age ; but he really died in his seventy-second year, for in a letter to Mr. Watt of 8th April 1 798, he writes " I have now finished my seventieth year." BY THE EDITOR. XX111 named, even by Dr. Black's zealous admirer and pupil, Lord Brougham. His Lordship says that Dr. Black meditated on that theory, investigated it by experi- ment, and taught it in his lectures, at least as early as 1 763. But the following extract from his letter to Mr. Watt, of 15th May 1780, furnishes information more precise, and which, as assigning with certainty a much earlier date to so admirable a discovery, can- not fail to interest the scientific world. " I began," says the Doctor, " to give the doctrine of latent heat " in my lectures at Glasgow, in the winter 1757-58, " which I believe was the first winter of my lecturing " there, or, if I did not give it that winter, I certainly "gave it in the 1758-59, and I have delivered it " every year since that time in my winter lectures, " which I continued to give at Glasgow until winter " 1766-67, when I began to lecture in Edinburgh." In the same letter he mentions by name many distinguished foreigners, as well as natives of this country, who had attended some of the earliest courses of his lectures, and had then heard his explanations of that remarkable theory; adding, that about 1760-61, or soon after, he read a paper on the subject, in the Philosophical or University Club at Glasgow, and thus concluding : " I could bring a " multitude of other evidences to prove the early date " of my doctrines on this subject." We need hardly observe, that none who are duly aware of the modesty and carelessness of fame, the scrupulous veracity, and exact observation of facts, which distinguished that truly learned and excellent person, can imagine any other kind of evidence more convincing than his own XXIV INTRODUCTORY REMARKS testimony. After the publication of so decisive a record, further exposure of the attempts which have of late been made to rob Dr. Black of his great and well-earned glory' is wholly superfluous.* Priestley, who in the year 1774, had effected by far the most remarkable and brilliant of his numerous discoveries, (that, viz. of oxygen gas,) came in 1 780 to Birmingham ; where he afterwards usually resided, till driven away from that place in 1791, by the vio- lence of a riotous mob, under the influence of reli- gious and political exasperation. During the whole of his stay in that neighbourhood, which has been well described as at that period " a region of rare " talents," he was on terms of habitual and friendly intercourse with Mr. Watt, frequently conversing with him on those scientific subjects which were of the greatest interest to them both ; and we find him pub- licly acknowledging the pleasure he derived from such congenial society.-f- It is impossible to conceive a more complete con- trast than was presented by the mode of philoso- phising adopted by Black and Priestley respectively. The one, calm and reflective, conducted his experi- ments often with such simple apparatus as came * Preposterous pretensions have also been, by insinuation, set up for Cavendish to the discovery of the same theory ; pretensions which are quite unfounded. See p. 30 of the Birmingham Address of the Rev. W. V. Harcourt ; in whom Mr. Cavendish has certainly found a most injudicious defender. We can duly respect Mr. Cavendish's fame, and praise his chemical skill ; but we cannot undertake to save him from his friends, nor to approve of their indiscriminate and unreasonable eulogies. t Philosophical Transactions, 1783, p. 416. BY THE EDITOR. XXV readiest to his hand, but always with studied neat- ness, accuracy, and success ; carefully watching every step of the well-considered process, and deducing, with all the force of exact demonstration, either the overthrow of some long-settled belief, or the descrip- tion of a new substance, or the establishment on solid foundations of a theory altogether unsuspected by any other inquirer ; his conclusions being as much distinguished for their originality, beauty, and use- fulness, as any thing to be found in the whole history of inductive research. The other, with warm zeal and untiring perseverance, but with little idea of order, and an imperfect acquaintance with the true first principles of science, contrived experiments of infinite number and variety, observed them with lively interest, and often with a just perception ; and mi- nutely recorded the smallest particulars, which in their progress he noticed, if not always for his own advantage, yet certainly for the great benefit of others. But to the higher objects of philosophical inquiry and generalisation, he was little accustomed to apply the many great and luminous truths which he was the first to make known ; and in more than one instance he even plunged deep into error, which some of his contemporaries, neither better informed on other points, nor gifted with superior powers of observation, were able to avoid. It is curious to find his well-known candour thus expressing his own views of the manner in which scientific research ought to be conducted, at a period nearly twenty years after he had received the Copley medal for his inquiries into several kinds of air, and had, almost at XXVI INTRODUCTORY REMARKS the same time, completed his grand and undisputed discovery of oxygen gas : " I do not think it at all degrading to the business " of experimental philosophy, to compare it, as I often " do, to the diversion of hunting, where it sometimes " happens that those who have beat the ground the " most, and are consequently the best acquainted with " it, weary themselves without starting any game, " when it may fall in the way of a mere passenger ; so " that there is but little room for boasting in the most " successful termination of the chase." * His metaphor reminds us of the jocose observation, said to have been addressed by Sir Isaac Newton to Dr. Barrow, who complained that he had occupied all the ground of new discovery : " Beat the bushes : there is still " plenty of game to be raised."f But the proceedings of the other two great experimental inquirers whom we have named, were nothing like this ; and we may perhaps question the propriety of applying language which conveys the idea of something vague and even fortuitous, to that system which Bacon first illustri- ously taught, and w r hich Black and Watt so worthily exemplified ; by which the present age has been guided to very many of the more remote and occult parts of nature, with the same certainty and safety, with which the compass has directed the course of navigation to the discovery of new regions of the globe. It cannot, however, be said that Priestley either derived small amusement from his quest of the game * See the Preface to his Abridgement of the " Experiments on " Air," in three vols. 1790, p. 21. t Works of Sir Humphry Davy, edited by his Brother, vol. vii. p. 124. BY THE EDITOR. XXY11 to which he alludes, or failed of brilliant success in that exciting chase, which he followed with enthusi- astic ardour. It is equally true that he greatly con- tributed to its popularity with others. But, though he could not fairly be called uncertain in his aim, he occasionally abandoned the main pursuit to follow some deceptive appearance in another track ; and had often to submit, which he always did with perfect frankness and good-nature, to see his competitors triumph where he himself had failed. No more apposite or memorable instance of the truth of these remarks could be found, than in the discovery of which we are about to recount the history; where he stedfastly opposed a theory which was in great measure founded on one of his own experiments, but in which, even after it had received the most ample confirmation from the results of further inquiry, and had been adopted by nearly all the most eminent chemists of the day, he never could be induced to believe.* Before proceeding to the history, as it appears in the following correspondence, of the manner in which Mr. Watt was more immediately led to form and state in writing, his conclusions respecting the composition of water, which had previously always been looked upon as an element or simple substance, it is proper that we should shortly relate the steps which had been taken, before the year 1783, towards a more ac- curate knowledge of its real nature. If this must of necessity lead us to recapitulate some of the informa- * Among the latest of his publications was " The Doctrine of " Phlogiston Established, and that of the Decomposition of Water " Refuted." Northumberland, 1800. XXV111 INTRODUCTORY REMARKS tion, which has already been laid before the public by the learned labours of M. Arago and Lord Brougham, we shall at least gain the advantage of being able to present at one view, and with brevity, several parti- culars which have been hitherto a good deal dispersed, and are on that account not easy of reference. The first observation of the moisture which is formed when inflammable air or hydrogen gas is burnt in common air, was made by M. Macquer, an excellent French physician and chemist, whose good sense and judicious experiments rendered great service to sci- ence, at a time when few minds had as yet shaken oft any of the fetters of the old philosophy. In that edi- tion of his Dictionnaire de Chimie which was pub- lished in 1778, and of which his translator, Mr. Keir, says, that it had been much esteemed, and had per- haps contributed more to the diffusion of chemical knowledge than any other book, (and which, as well as its author, was always spoken of by Dr. Black with the greatest respect,) he details, under the article Inflammable Gas, many experiments on its combus- tion, which were made in 1776-7, and in which he was assisted by M. Sigaud de Lafond. " I assured " myself also," he says, " by placing a saucer of white " porcelain in the flame of inflammable gas burning " tranquilly at the orifice of a bottle, that the flame is " not accompanied by any fuliginous smoke ; for that " part of the saucer which the flame licked, remained " perfectly white ; it was only moistened by small " drops of a liquor as clear as water, and which, in fact, " appeared to us to be only pure water."* The pheno- * Dictionnaire de Chymie, torn, ii., p. 314 ; ed. Neuchatel, 1789. BY THE EDITOR. XXIX menon was certainly a remarkable one, and its ob- servation appears now, as it did to Lavoisier in 1783,* to have nearly approximated to a most inter- esting inquiry, which might, indeed, have ended in the discovery afterwards so famous. But Macquer drew no conclusion from it, takes no further notice of it, and seems not even to have hazarded a specula- tion on its cause. He also mentions the combustion of mixtures both of inflammable gas and common air, and of inflam- mable gas and dephlogisticated air or oxygen gas : and describes the explosion by which it was in both cases attended ; that being, however, very much more violent in the latter case than in the former. He seems to have fired the airs in glass vessels, but al- though on one occasion he speaks of having done so in close vessels, it is evident from his further account of the experiment, that the vessel employed had a narrow aperture, to which a lighted match was ap- plied. Volta, in a letter dated 10th December 1776, which is printed in Dr. Priestley's third volume,-f- says, that he then fired inflammable air by the simple electric spark. The next considerable step in the progress towards the grand discovery, was made by an English chemist and philosophical lecturer, Mr. Warltire, whose mode of conducting his experiments on the combustion of gases was highly creditable to his ingenuity. He fired * Lavoisier, Memoires de 1' Academic for 1781, printed in 1784, j>. 469. t Priestley's Experiments on Air, &c., 1781, vol. iii. p. 381. XXX INTRODUCTORY REMARKS a mixture of common and inflammable airs in a close metal flask or globe, by the electric spark ; and, his object being to ascertain " whether heat was heavy " or not," he says, " I always accurately balanced the " flask of common air, then found the difference of " weight after the inflammable air had been intro- " duced, that I might be certain I had confined the " proper proportion of each. The electric spark having " passed through them, the flask became hot, and was " cooled by exposing it to the common air of the room ; " it was then hung up again to the balance." Mr. Warltire adds, that in his experiments of this sort, he always found a small loss of weight, but not con- stantly the same ; the vessel held three wine pints, and weighed fourteen ounces, and the average loss which he thought he detected, was only two grains. These experiments are detailed in a letter dated Birmingham, 18th April 1781, which was addressed to Dr. Priestley, and published by him in the appen- dix to the second volume of his " Experiments and " Observations relating to various branches of Natural " Philosophy; with a continuation of the Observations " on Air;" printed at Birmingham in 1 781.* From the * Mr. Warltire's letter is given by Dr. Priestley as follows : " A letter from Mr. John Warltire, Lecturer in Natural Philosophy, on " the firing of inflammable air in dose vessels. " BIRMINGHAM, 18(A April 1781. " SIR, I had long entertained an opinion that it might be de- " tennined whether heat is heavy or not, by firing inflammable air, " mixed with common air, and applying them to a nice balance ; but " as I conceived the danger of passing the electric spark through so '' combustible a mixture in a close vessel to be greater than it is, I BY THE EDITOR. XXXI same letter it appears, that Priestley was the first to fire air in a close glass vessel, and to observe a depo- sit of water ; but that Warltire, on repeating the same " was deterred from making the experiment, till, being encouraged " by you, I procured a copper ball, or flask, which holds three wine " pints, the weight 14 oz., with a screw stopper adapted to it, and " began with small quantities of inflammable and large quantities of " common air, which were fired without the least danger. " I then increased the bulk of the inflammable air to half that of " the common air, which, when fired, made the flask very warm to " my hand ; and every time I applied a long glass tube, fastened to " the pipe of a pair of bellows, to blow the phlogisticated air out of " the flask, I observed a smoke escape along with it. I also fired the " air when the flask was under water, and did not observe anything " escape when I perceived the heat against my hand with which I " kept the ball from rising. When the stopper was unscrewed, the " external air always rushed into the vessel containing the phlogis- " ticated air with some violence. " The method I usually practise to mix the airs in any proportion, " is accurately to fill a measure with inflammable air, and rest it in " a tub, with its rim barely under water, hanging over the edge of a " shelf, so far as to admit one leg of an inverted syphon, the other " leg being closed, but afterwards opened, and the copper flask in- < " verted upon it, but closed with its stopper when the measure of air , K " has been plunged under water, to force it out through the syphon. " I have sometimes exhausted the common air to admit the inflam- " mable air into the flask, but I do not find that that circumstance " produces any difference in the result of the main experiment. " My next object was to adjust the balance in such a manner as " that I could always be certain to weigh to less than a grain when " it was loaded with the flask and its counterpoise, and I con- " stantly examined it at the beginning and end of every experiment. " The apparatus being adjusted, I proceeded to make the experiment " I had in view, and always accurately balanced the flask of common " air, then found the difference of weight after the inflammable air " was introduced, that I might be certain I had confined the proper " proportion of each, the electric spark having passed through them " the flask became hot, and was cooled by exposing it to the common XXX11 INTRODUCTORY REMARKS experiment, obtained the same result. " I have fired " air in glass vessels," says Mr. Warltire, " since I saw " you venture to do it, and have observed, as you " did, that though the glass was clean and dry before, " yet after firing the air, it became dewy, and was " lined with a sooty substance." Dr. Priestley adds, that Mr. Warltire, " the moment he saw the moisture " on the inside of the close glass vessel in which I " afterwards fired the inflammable air, said that it con- " firmed an opinion he had long entertained, viz., that " air of the room ; it was then hung up again to the balance, and a " loss of weight was always found, but not constantly the same ; upon " an average it was about two grains. " I have fired air in glass vessels since I saw you venture to do it " and have observed, as you did, that though the glass was clean and " dry before, yet, after firing the air, it became dewy, and was lined " with a sooty substance. " If you think these experiments worth communicating to your " philosophical acquaintance, it may be depended upon that the cir- " cumstances appeared to me as I have represented them, whatever " they may be found to prove. " I am, with great esteem, " Your humble servant, " JOHN WABLTIRE." On this letter Dr. Priestley makes the following remarks : " The preceding article, though coming too late to be printed to- " gether with the rest of the volume, and to be noticed in the con- " tents of it, I have thought proper to insert on account of the re- " markable facts it exhibits. " Dr. Withering and myself were present when the mixture of " common air and inflammable air was fired repeatedly in the close " copper vessel, and we observed that, notwithstanding all the pre- " cautions we could think of, the vessel certainly weighed less after " the explosion than it had done before. I do not think, however, " that so very bold an opinion as that of the latent heat of bodies BY THE EDITOE. XXxiii " common air deposits its moisture when phlogisti- " cated ; " both inquirers being evidently impressed with the belief that the dew was nothing else than the mechanical deposit of the moisture dispersed in common air. It is remarkable enough, as an instance of the con- fusion which the least inattention must introduce into the history of such discoveries, and of the consequent importance of exact accuracy as to all their most mi- " contributing to their weight, should be received without more ex- " periments, and made upon a still larger scale. If it be confirmed, " it will no doubt be thought to be a fact of a very remarkable na- " ture, and will do the greatest honour to the sagacity of Mr. Warl- " tire. " I must add, that the moment he saw the moisture on the inside " of the close glass vessel, in which I afterwards fired the inflam- " mable air, he said that it confirmed an opinion he had long enter- " tained, viz., that common air deposits its moisture when it is phlo- " gisticated. With me it was a mere random experiment, made to " entertain a few philosophical friends, who had formed themselves " into a private society, of which they had done me the honour to ' make me a member. " After we had fired the mixture of common and inflammable air, " we did the same with dephlogisticated and inflammable air ; and " though, in this case, the light was much more intense, and the heat " much greater, the explosion was not so violent, but that a glass " tube about an inch in diameter, and not exceeding one tenth of an '' inch in thickness, bore it without injury. Nor shall we wonder at " this, when we consider that the expansion of air by heat does not " go beyond four or five times its bulk. It is evident, however, from " this experiment, that little is to be expected from the firing of in- " flammable air in comparison with the effects of gunpowder ; be- " sides, that after firing of inflammable air, there is a great diminu- " tion of the bulk of air, whereas in the firing of gunpowder there " is a production of air." PRIESTLEY'S Experiments and Observations, &c. Birmingham, 1781. Vol. ii. p. * 395. e XXXIV INTRODUCTORY REMARKS nute particulars, that Mr. Watt inadvertently stated * that he believed Mr. Cavendish was the first who ob- served the dewy deposit ; thereby assigning to him too much merit in place of too little. Mr. Cavendishf expressly states Mr. Warltire to have observed it. Mr. WarltireJ states Dr. Priestley to have observed it ; while, ultimately, the mere observation of the moisture must be referred to Macquer, who also first ascer- tained it to be pure water. But this point may be said to have excited no controversy, which has been limited to the question, who first explained the real cause of the formation of the water, by drawing and stating the conclusion that water is composed of two gases, which unite in the process of their combustion, or explosion. To that question, accordingly, we shall now confine our attention, and see who was in point of fact the first to make public that theory, after having formed it altogether independently of the ideas of others. On the publication of Dr. Priestley's work in 1 781, Mr. Cavendish proceeded in July of that year, and at subsequent times, to examine Mr. Warltire's expe- riment, (the object of which, it will be remembered, was to determine whether heat was ponderable,) fre- * See his Note, Phil. Trans, for 1784, p. 332. It is proper, how- ever, to observe, that the note is not in Mr. Watt's original draft, nor in the press copy of the letter in his own writing, sent to Mr. De Luc, of 26th November 1783 ; but is added at the bottom in pencil, in his own hand. t Phil. Trans. 1784, pp. 126, 127. J In his letter, cited above. Dictionnaire de Chymie ; Memoires de 1' Academic for 1781, p. 489 ; Arago, Eloge of Watt, p. 98 ; ante, p. xxviii. BY THE EDITOR. XXXV quentlj repeating it, with changes in some parts of the apparatus, and in the mode of preparation of the airs employed. He fired mixtures both of common and inflammable air, and of inflammable and dephlo- gisticated air, varying the proportions of each ; and, as was to be expected, not uniformly obtaining quite the same results. For, although he always observed, as Priestley and Warltire had done before him, that a dew was deposited, or, as he calls it, condensed, on the sides of the vessel in which the airs were fired, and though he applied more accurate measurement to the airs, and some tests to the " liquor condensed," he sometimes observed a slight loss of weight, some- times none at all. In one instance, he found that " the weight seemed to be diminished two-tenths on " firing, and one-tenth more on standing."* Mr. Cavendish's journal, or collection of laboratory notes, in which the details of all these experiments were entered, has been preserved among his papers. The whole of those papers were accurately examined, his Grace the Duke of Devonshire having granted permission, for the purpose of ascertaining whether any of them contained anything indicative of the dates of Mr. Cavendish's conclusions, respecting the theory of the formation of water by the combustion of hydrogen and oxygen gases ; but Mr. Charles Hat- chett " could not find anything in them which refer- " red to any date connected with the time when Mr. " Cavendish probably first conceived his theory ;"f * MS. Journal. t Letter to the present Mr. James Watt, 16th April 1835. XXXVI INTRODUCTORY REMARKS and another gentleman, Mr. Hudson, in whose hands the papers had been placed by the Duke of Devonshire, and who minutely investigated them with every wish to discover some support to the claims which had been put forth on behalf of Mr. Cavendish, said, " I " do not find in these journals of the experiments any- " thing more than the simple statement of the facts, " without any casual mention of theoretical opinions."* This material fact has since been placed beyond the possibility of doubt, by the publication of the journal in question ; in the whole course of which Mr. Ca- vendish does not make a single inquiry into the cause of the appearance of the water, nor indicate the most remote suspicion of its real origin ; never using any expressions which could imply an union of the two airs, or which are inconsistent with the notion which Warltire and Priestley had entertained, of a mere me- chanical deposit of the water. We are fully borne out in this assertion by the opinion of Lord Brougham, who says, " I must add, having read the full publica- " tion with fac-similes, Mr. Harcourtf has now clearly " proved one thing, and it is really of some importance. " He has made it appear, that in all Mr. Cavendish's * Letter to Mr. Hatchett, 15th April 1835. In the continuation of his letter, Mr. Hudson supposes that there could be " no doubt" of Mr. Cavendish having then also formed his theory. We should sup- pose so too : if the theory had then occurred to him. That is THE im- portant step ; of which there is not a particle of evidence. After the theory had been stated by Mr. Watt, it may to Mr. Hudson appear to have been easy. The story of Columbus and the egg is exactly in point. t The Reverend Gentleman who, with a curious infelicity for his own purpose, gave to the public the journal in question. "Amicus " Cavendish, sed magis arnica veritas /" BY THE EDITOR. XXXV'ii " diaries, and notes of his experiments, not an intima- " tion occurs of the composition of water having been " inferred by him from those experiments earlier " than Mr. Watt's paper of spring 1783."* This fact further receives great confirmation from all that Mr. Cavendish has himself stated on the sub- ject. His Paper, in which his conclusions are con- tained, was not read to the Royal Society till the 15th of January 1784 ; and although in July 1784, when the Philosophical Transactions for that year were printed, he said that his experiments (made in 1781,) had been mentioned to Dr. Priestley, he does not name the precise time, nor even the year, when the experi- ments were so communicated. He does not say that any conclusion was, along with them, mentioned or even hinted at. He does not even say at what time he himself first drew any conclusion on the matter. But in a continuation of the same passage he says, " during the last summer, [1783] also, a friend of " mine gave some account of them to M. Lavoisier, as " well as of the conclusion drawn from them, that de- " phlogisticated air is only water deprived of phlogis- " ton." This passage was not contained in Mr. Caven- dish's paper, as originally written, presented, arid read to the Society; and it was afterwards added, not in Mr. Cavendish's handwriting, but in that of Dr. (afterwards Sir Charles) Blagden, who was the friend referred to ; but being printed in the body of the paper, without any explanation as to its separate authorship, and, of course with the knowledge and * Lives of Men of Letters and Science, vol. i. p. 401. XXXV111 INTRODUCTORY REMARKS approval of Mr. Cavendish, that gentleman is to be held as making the statement contained in it, and the whole passage must be taken as part of his Paper. And (what is a most material proof of Mr. Caven- dish never having made any communication of the theory) Dr. Priestley, who, in his Paper dated 21st April 1 783, and read 26th June of the same year, alludes to one experiment of Mr. Cavendish as being known to him, says not a word of any theory which that gentleman had founded upon it; but, on the contrary, was in evident ignorance of any conclusion such as that which Mr. Cavendish, nearly a year later, communicated to the Eoyal Society. " It is clear," says Lavoisier, * " that Dr. Priestley has formed water " without suspecting it." It will presently be seen that his first intelligence of any idea being entertained that water is a compound body, came from Mr. Watt, and was received by him not only with surprise, as being entirely novel, but also with incredulity, as being quite erroneous. The real state of the case is very well explained by him in his Paper, read 24th February 1785, and printed in the Philosophical Transactions for that year, where he says, " Mr. Watt " concluded from some experiments of which I gave " an account to the Society, and also from some ob- " servations of his own, that water consists of dephlo- " gisticated and inflammable air, in which Mr. Caven- " dish and M. Lavoisier concur with him."f There is thus no statement put on record by Mr. Cavendish, so far as we have yet gone, of his conclu- * Memoires de 1'Academie for 1781, p. 479. t Phil. Trans, for 1785, p. 280. BY THE EDITOR. XXxix sions having been either drawn by himself, or made known to a single human being, previous to the sum- mer of 1 783 ; while the only intimation to be derived from the printed papers in the Philosophical Trans- actions, of his having drawn his conclusions at even so early a period, is contained in the above passage, which was written by Blagden, interpolated after the paper had been read in January 1784, and then adopted by Cavendish. It is, further, apparent from the very title of his Paper, "Experiments on Air," that the composition of water was not the principal object to which Mr. Cavendish's attention had been directed. In this respect, his Paper presents an obvious contrast to that of Mr. Watt, which bears the much more une- quivocal title of " Thoughts on the Constituent Parts " of Water, and of Dephlogisticated Air ;" and of which the great object is to maintain that doctrine of the composition of water which is distinctly stated in its outset. Moreover, some of the expressions used by Mr. Cavendish in further treating of the subject, are marked by no small ambiguity, and even incon- sistency ; for his theory is thus expressed in his own Paper : " From what has been said there seems the " utmost reason to think, that dephlogisticated air is " only water deprived of its phlogiston, and that in- " flammable air, as was before said, is either phlogisti- " cated water, or else pure phlogiston ; but in all pro- " bability the former." Now, besides the strange sup- position as to inflammable air being phlogisticated water, which shows that Mr. Cavendish had then no xl INTRODUCTORY REMARKS very clear ideas on the subject of water being com- posed of oxygen and hydrogen, it is evident that he here omits entirely the consideration of latent heat ; an omission which he even attempts to justify in one of the passages interpolated by Blagden.* But it is well known to every one acquainted with the first principles of chemical science even as it was taught in the days of Black and it was indisputably fami- liar to Mr. Watt, that no aeriform fluid can be convert- ed into a liquid, nor any liquid into a solid, without the evolution of heat, previously latent. This essen- tial part of the process, Mr. Cavendish's theory does not embrace. But without it, no theory on the sub- ject can be complete. It will presently be seen, that Mr. Watt's theory took fully into account this most important principle, without which, no conversion from the aeriform to the liquid state can possibly take place ; and without which, therefore, Mr. Cavendish's theory was quite inadequate to explain the facts observed. We have the authority of one of the best informed practical and theoretical chemists of this country, for declaring that " ideas exactly similar to those of Mr 1 . " Watt are entertained by the most distinguished phi- " losophers of the present day." " Dr. Black," says Professor Graham of University College, " made it " appear probable, that metals owe their malleability " and ductility to a quantity of latent heat combined " with them."f And the learned Professor carries the same doctrine further ; where, in referring to change * Phil. Trans., p. 140. t Elements of Chemistry, p. 42. BY THE EDITOR. xli in the physical condition, and crystalline configura- tion of bodies, without any alteration in their ponder- able constituents, he says, " The loss of heat observed " will afford all the explanation necessary, if heat be " admitted as a constituent of bodies, equally essential " as their ponderable elements."* This may serve as another illustration of the masterly grasp of Mr. Watt's comprehensive mind, which could so early fore- see all that subsequent inquiry has fully confirmed. M. Lavoisier, in his celebrated Memoir, admits that a partial communication was made by Blagden, to him and some other members of the French Aca- demy, when, on the 24th of June 1 783, along with M. La Place, he tried the experiment which they re- ported to the Academy on the following day. " He " informed us," says Lavoisier, " that Mr. Cavendish " had already attempted to burn inflammable air in " close vessels, and that he had obtained a very sensi- " ble quantity of water." He thus confines the com- munication within very narrow limits ; for neither the experiment nor the result, as thus reported, was any thing more than had been effected by Warltire and Priestley. Evidently he did not intend to admit that he knew of any conclusion as to the real origin of the water having been drawn by Cavendish ; for in a subsequent part of the same memoir, he takes to his coadjutor and himself the credit of drawing such conclusion : " we did not hesitate to conclude from it, " that water is not a simple substance, and that it is " composed, weight for weight, of inflammable air, and * Elements of Chemistry, p. 154. xlii INTRODUCTORY REMARKS " of vital air." He adds also, that they were then ig- norant, and did not learn for some days, that M. Monge was occupied on the same subject. It may be observed in passing, that as compared with Lavoisier and Cavendish, sufficient justice does not appear to have been done by writers on this sub- ject, to the valuable labours of Monge. It is true, that when we consider the whole contents of his Paper, which includes some deductions both hesitating and obscure, and even, so far as we can judge, incorrect ; and recollect the comparatively late period at which it was first given to the world, in the Memoirs of the Academy, we find it impossible, without showing an undue excess of favour to his memory, to rank him, in respect either of the precision, or of the early date of his conclusions, along with any of the other three great philosophers who have been candidates in either country, for the credit of the discovery. But his experiments, performed in the laboratory of the School at Mezieres, were on a great scale ; and are admitted by Lavoisier and Meus- nier,* to have been conducted with a very exact appa- ratus, and the most scrupulous attention. They are described in his Paper in the Memoirs of the Aca- demy for 1783, printed in 1786; it is not stated when that Paper was read, but a note mentions that they were made in June and July, and repeated in October 1783, in ignorance of those of Cavendish in England, which were on a smaller scale, and of those of Lavoisier and La Place at Paris, which were made * Me'moires de 1'Acade'mie for 1781, pp. 269, 270. BY THE EDITOR. xliii with an apparatus not fitted to attain so great exact- ness. Lavoisier and Monge thus declare their mutual ignorance of each other's proceedings : but Monge has never been accused, and may safely be acquitted, while the other has been frequently, and with too much justice, convicted, of concealing previous know- ledge of other men's proceedings, in order to increase the estimated amount of his own merits. The want of any date for either the authorship or the reading of M. Monge's paper, between the end of the year 1 783, in which his experiments were made, and that part of 1786 in which it was printed, leaves us in doubt as to how far he may have profited by the lights which were during that interval thrown upon the subject. Certainly his words, as there given, are very similar to those of Mr. Watt's letter of April 1 783, hereafter to be particularly noticed. " It fol- " lows," says Monge, " from this experiment, that when " we detonate inflammable gas and dephlogisticated " gas, each considered as pure, we obtain no other re- " suit than pure water, the matter of heat, and that " of light." But his conclusions, as further explained in the same paper, are less clear and decided than Mr. Watt's, or than those of Lavoisier and Cavendish ; for he hesitates whether to consider water as not a simple substance, or fire as a compound one, and is encum- bered with the uncertainty of an alternative theory ; either of different substances being held in solu- tion by the fluid of fire considered as a common sol- vent, and combining to produce water ; or else, of the two gases being solutions of water in different elastic fluids, which quit the water they held in solu- xliv INTRODUCTORY REMARKS tiou, iii order to combine and form the fluid of fire and light, which escapes through the sides of the vessel in which the detonation takes place. Lavoisier's paper having been in part read in No- vember 1783, was afterwards published with addi- tions, which are not specifically distinguished from the original memoir, but are said to refer to the labour undertaken in common with M. Meusnier relative to the same subject. The volume in which it appears was printed in 1 784, and is known in the series of the Memoires de I' Academic as that for 1781. It ar- rived in this country after Mr. Cavendish's paper had been read on 15th January 1784, but before it was printed in July of that year ; and it is alluded to in another addition to Mr. Cavendish's paper, which was unquestionably made after its arrival in England, and in which the theory of the composition of water is more clearly stated than it had been by him previous to the enunciation and exposition of it by the en- lightened French chemist.* A point of internal evi- dence that seems to fix within very narrow bounds the period at which that volume of the French Me- moirs was printed, is, that Lavoisier therein speaks of Blagden as " aujourd'hui Secretaire de la Societe " Royale de Londres ;" an office to which he was not appointed till the 5th of May 1 784. Now, there can be little doubt, that the passage al- ready cited, in which Blagden, in his own hand, but in Cavendish's name, detailed his communication to Lavoisier, was written to supply the imperfect ad- * Phil. Trans, pp. 150-153. BY THE EDITOR. xlv mission of the French author, and to prevent those inferences as to priority of the theory, which other- wise might have been drawn from it, in favour of La- voisier. Considering the object thus manifestly in view, here, if anywhere, we ought to look for an ex- plicit statement of the earliest date at which Mr. Ca- vendish's theory could be said to have been formed, which, at that time, there was no difficulty in ascer- taining, and there could have been little in establish- ing ; and we are fairly entitled to hold, that the ear- liest date consistent with the fact would be assigned, if not by the author of the paper, at least by his zealous and assiduous friend who is so much mixed up with the transaction. All this we say, on the sup- position, that the question as to priority had arisen merely between Lavoisier and Cavendish : for that is the whole length that our statement has as yet gone. We shall presently see whether other circumstances had not in the meantime arisen, which called still more loudly for that full, clear, and precise declara- tion which was to have been expected ; and which was absolutely indispensable, in order to authenticate for the theory which Mr. Cavendish stated to the Royal Society on the 15th January 1784, an earlier date than its publication on that day could ensure. Mr. Watt, in whose neighbourhood Dr. Priestley says he had " the happiness to be situated," and with whom, as has been mentioned, he was on habits of friendship and frequent intercourse, had, previous to 1 783, for many years entertained an opinion that air was a modification of water ; and that, if steam could be made red-hot, so that all its latent heat should be xlvi INTRODUCTORY REMARKS converted into sensible heat, either the steam would he converted into permanent air, or some other change would take place in its constitution. So early as 1 3th December 1 782, he talks of processes " by which," he says, " I now believe air is generated from water ;" using the expression, " if this process contains no de- " ception, here is an effectual account of many phe- " nomena, and one element dismissed from the list."* Being thus, even at that time, prepared to expect that water was, in some way or other, convertible into air, he directed his attention to Dr. Priestley's experiment, which he thus accurately relates : " He " puts dry dephlogisticated air and dry inflammable " air into a close vessel, and kindles them by electricity. " No air remains, at least if the two were pure, but he " finds on the sides of the vessel a quantity of water " equal in weight to the air employed." f In less than a month after he thus mentions his knowledge of that experiment, we find him writing to Dr. Black that he " believes he has found out the cause of the * Mr. Watt to Mr. De Luc, 13th December 1782. As frequent re- ference will be made to the correspondence of Mr. Watt, printed in a subsequent part of this volume, we are happy to be able to record the very perfect condition in which, on a minute inspection, we find that correspondence to have been preserved ; and which, fortunately, leaves nothing to be regretted on the score of mutilation or destruc- tion. The copies of Mr. Watt's own letters, taken by his copying- machine, are still in excellent preservation ; and, although in several of them the ink has become somewhat pale, it is nowhere so faint as to be illegible. They had been carefully pasted by the late Mr. Watt, in the order of their dates, into a large folio volume, in which they still remain. t To his brother-in-law, Mr. Gilbert Hamilton, 26th March 1783. BY THE EDITOR, xlvii " conversion of water into air ;"* and giving the very words in which, both on that day, and a few days later, he stated his conclusions in the letter to Dr. Priestley, which he desired might be read to the Royal Society. The same conclusions are given in other letters written nearly at the same time ; but nowhere are they more clearly, briefly, or forcibly stated, than in that to Mr. Gilbert Hamilton of the 22d of April, where, after a short enumeration of FACTS, beginning with the result of Dr. Priestley's experiment, follow these DEDUCTIONS. " Pure inflammable air is phlogiston itself. " Dephlogisticated air is water deprived ofitsphlo- " giston, and united to latent heat. " Water is dephlogisticated air deprived of part of its " latent heat, and united to a large dose of phlogiston." In writing to Mr. De Luc, four days afterwards, " These," says Mr. Watt, " seem bold propositions, " but I think they follow from the present state of the " experiments ; and if I were at leisure to write a book " on the subject, I think I could prove that no experi- " ment hitherto made contradicts them, and that the " greater number of experiments affirm them."f To others of his correspondents he announced his theory in similar terms. To Mr. Smeaton, writing that he has " attempted to demolish two of the most ancient ele- " ments air and water ;"J and to Mr. Fry, giving particular directions for the production of water and of [dephlogisticated] air, concluding thus : " The ingre- " dients of water are pure air and phlogiston, united * 21st April 1783. t 26th April 1783. J 27th April 1783. xlviii INTRODUCTORY REMARKS " in a state of ignition, and deprived of much elenicn- ' tary heat."* It will be remembered, that in the letter to Mr. Hamilton he had shown his belief to be, that pure inflammable air and phlogiston were exactly synonymous ; and it is very remarkable, that the proportions of the two gases which lie directs to be fired, viz., of pure air one pail, and of inflammable air two parts, by measure, are exactly those which chemists of the present day would employ. It appears from the letter to Dr. Black of the 2 ] st of April, that Mr. Watt had, on that day, written his letter to Dr. Priestley, to be read by him to the Royal Society ; but on the 26th he informs Mr. De Luc, that having observed some inaccuracies of style in that letter, he had removed them, and would send the Doctor a corrected copy in a day or two, which he accordingly did on the 28th ; the corrected letter, (the same that was afterwards embodied verbatim in the letter to Mr. De Luc, printed in the Philoso- phical Transactions,) being dated 26th April, and containing, almost at its very commencement, the fol- lowing passages : " The same ingenious philosopher mixed together " certain proportions of pure dry dephlogisticated air " and of pure dry inflammable air in a strong glass " vessel, closely shut, and then set them on fire by " means of the electric spark. The first effect was " the appearance of red heat or inflammation in the " airs, which was soon followed by the glass vessel " becoming hot. The heat gradually pervaded the * 28th April 1783. BY THE EDITOR. xlix " glass, and was dissipated in the circumambient air, " and as the glass grew cool, a mist or visible vapour " appeared in it, which was condensed on the glass " in the form of moisture or dew. When the glass " was cooled to the temperature of the atmosphere, " if the vessel was opened, with its mouth immersed " in water or mercury, so much of these liquids entered, " as was sufficient to fill the glass within about ?J B th " part of its whole contents ; and this small residuum " may safely be concluded to have been occasioned " by some impurity in one or both kinds of air. The " moisture adhering to the glass, after these deflagra- " tions, being wiped off, or sucked up, by a small " piece of sponge paper, first carefully weighed, was " found to be exactly, or very nearly, equal in weight " to the airs employed. In some experiments, but " not in all, a small quantity of a sooty-like matter " was found adhering to the inside of the glass. The " whole quantity of sooty-like matter was too small " to be an object of consideration, particularly as it " did not occur in all the experiments. " Let us now consider what obviously happens in the " case of the deflagration of the inflammable and de- " phlogisticated air. These two kinds of air unite with " violence; they become red-hot, and upon cooling " totally disappear. When the vessel is cooled a quan- " tity of water is found in it equal to the weight of " the air employed. The water is then the only re- " maining product of the process, and water, light, " and heat, are all the products. "Are we not, then, authorised to conclude that water " is composed of dephlogisticated air and phlogiston, 9 1 INTRODUCTORY REMARKS " deprived of part of their latent or elementary heat ; " that dephlogisticated or pure air is composed of water " deprived of its phlogiston, and united to elementary " heat and light ; and that the latter are contained in " it in a latent state, so as not to be sensible to the tJier- " mometer or to the eye ; and if light be only a modifi- " cation of heat, or a circumstance attending it, or a " component part of the inflammable air, then pure or " dephlogisticated air is composed of water deprived " of its phlogiston and united to elementary heat."* In enclosing it, Mr. Watt adds, " As to myself, the " more I consider what I have said, I am the more " satisfied with it, as I find none of the facts repug- " nant." Thus was announced, for the first time, and with as much confidence as its eminent author thought it became any philosophical inquirer to feel, when prosecuting his researches into new parts of science, one of the most wonderful discoveries that are re- corded in its annals ; of startling novelty, of admir- able simplicity, leading to consequences of an im- portance and grandeur perhaps unparalleled, except by those which have attended other exertions of the same inventive mind ; or by those which, emanating from a kindred intellect, have immortalized the name of Newton. It has been justly termed the commence- ment of a new era, the dawn of a new day, in physi- cal inquiry, the real foundation of the new system of chemistry. The language in which this new and * See the same passages, printed in the Philosophical Transactions for 1784, pp. 331-333. BY THE EDITOR. li astonishing truth was expressed, though plain and perfectly unpretending, is so clear, precise, and just, that Mr. Cavendish accomplished chemist and per- spicuous writer as he was could vary scarcely a single word of it, and that not for the better, when nine months later he made it public as his own : while M. Lavoisier, when he too, after it had been explained to him by Blagden, " invented it himself, " and read a paper on the subject to the Royal Aca- " demy of Sciences,"* altered only the terras which Mr. Watt had employed to express the two gases, viz. dephlogisticated air and inflammable air, or phlo- giston, for their equivalents in his new nomenclature, viz. oxygen and hydrogen ; their equivalents, that is to say, in the sense in which Mr. Watt had used them. " This letter," as is stated in Mr. Watt's Note published in the Philosophical Transactions, " Dr. " Priestley received at London, and after showing it " to several members of the Royal Society, he delivered " it to Sir Joseph Banks, the President, with a request " that it might be read at some of the public meetings " of the Society."! Had that been then done as requested, there can- not be a doubt in the mind of any one at all fitted to form an impartial opinion on the subject, that all possibility of controversy as to priority in the disco- very must have been effectually prevented. It is true, that, judging from what actually occurred, it is difficult to say, even in that case, what use might * Mr. Watt to Mr. Fry, 15th May 1784. t Philosophical Transactions, 1784, p. 330. Note. Hi INTRODUCTORY REMARKS have been made of the private perusal with which " several members of the Royal Society" were fa- voured. Lavoisier in France might even then have displayed that culpable want of a due acknow- ledgment of the aid he derived from others, which is so frequently to be deplored in the long series of his most interesting, able, and elegant memoirs. Cavendish in England might still have failed to exemplify that generous liberality, which ought to have noticed with eulogy, or, at least, to have named with exact justice, a philosophical discoverer who had thus preceded him in the same path. But both of those illustrious chemists would, at all events, have been in that case peremptorily debarred from openly taking credit for either priority or novelty in the announcement of their theory ; and it would have been still harder for Cavendish or his friend even to have pretended as for Lavoisier it is absolutely impossi- ble to establish a right to the claim of independent originality. But, as it happened, the public reading which had been so requested by Mr. Watt did not take place at that time. " Before that could be complied with/' the note continues, " the author, having heard of Dr. " Priestley's new experiments, begged that the reading " might be delayed." The delay was, in some small measure, unfortunate for the scientific renown of Mr. Watt ; because competitors thereafter stepped in, and sought to appropriate that discovery of which the world had not yet heard, and which, at that time, must have been by all allowed to be honestly, solely, and honourably his own. But the misfortune BY THE EDITOR. liii is infinitely increased if we consider it as having, with some writers, led to doubts, seriously affecting the reputation of those competitors ; as adding to the reproach which one of them had, to the sorrow of science, already justly incurred in similar matters ; and as leaving on the fame of the other what must at least be termed a shade of suspicion. The new experiments alluded to in the note, Priest- ley had announced in these terms : " Behold with " surprise and indignation the figure of an apparatus " that has utterly ruined your beautiful hypothesis," * giving a rough sketch with his pen of the apparatus employed. But Mr. Watt immediately and unhesi- tatingly replied, " I deny that your experiment ruins " my hypothesis. It is not founded on so brittle a " basis as an earthen retort, nor on its converting " water into air. I founded it on the other facts, and " was obliged to stretch it a good deal before it would " fit this experiment. * * * I maintain my " hypothesis until it shall be shewn that the water " formed after the explosion of the pure and inflam- " mable airs, has some other origin."f So to Mr. De Luc : " I do not see Dr. Priestley's experiment " in the same light that he does. It does not dis- " prove my theory. * * My assertion was simply, " that air," [i. e. dephlogisticated air, or oxygen, which was also commonly called vital air, pure air, or ^ simply a>,] " was water deprived of its phlogiston, " and united to heat, which I grounded on the * Dr. Priestley to Mr. Watt, 29th April 1783. t Mr. Watt to Dr. Priestley, 2d May 1783. liv INTRODUCTORY REMARKS " decomposition of air by inflammation with inflam- ' mable air, the residuum, or product of which, is " only water and heat."* Even when writing to Dr. Black that he had withdrawn his paper, he adds, " I " have not given up my theory." f But he did withdraw, or rather reserve the public reading of his paper, till he should further examine the new experiments which were said to be hostile to the doctrine which it unfolded ; and also, as he adds with his usual modesty, because he was " informed that that " theory was considered too bold, and not sufficiently " supported by facts." \ " Mr. Watt then wished," as it is more fully expressed in a work published shortly afterwards, " that the letter should not be " read at the public meeting of the Society, because " he learned that his theory was thought too bold, " or that a substance such as water, till then con- " sidered as of the nature of an element, was there " placed in the class of compounds." || But the letter itself, after being read by many members, remained in the custody of the President till the day when it was read to the Society, 22d April 1 784, as is well ascertained from Mr. Watt's letter to Blagden of 27th May 1784. On the upright and unsuspecting philosopher, whose diffidence of his own admirable judgment, and " re- " spect for the opinions of others where he thought " they might merit it," had led him thus to delay what * To Mr. De Luc, 18th May 1783. t To Dr. Black, 23d June 1783. t Mr. Watt to Sir Joseph Banks, 12th April 1784. I De Luc, Meteorologie, torn. ii. p. 216. 1786. BY THE EDITOR. Iv lie calls " the first attempt he had made to lay any " thing before the public," a new and unpleasant light was destined soon to break. But in the meantime, having by additional experiments still further satis- fied himself of the correctness of his theory, in which he had never been able to detect error, and the truth of which he now held to be abundantly confirmed, he proceeded, towards the end of November, tranquilly to occupy himself in preparing a more full statement of it, to be sent to his friend De Luc, for the purpose of being read to the Royal Society. By the 1st of December, however, we find that he had received accounts of an occurrence which appeared to stand much in need of explanation ; and which, after that had been obtained, proved in some respects little to the credit of those concerned. " M. Lavoisier," he writes, " has read a memoir opening a theory very " similar to mine on the composition of water; in- " deed, so similar, that I cannot help suspecting he " has heard of the theory I ventured to form on that ' subject, as I know that some notice of it was sent " to France."* To this conjecture, Mr. Kirwan was able, in his reply, to add the most positive assurance. " M. " Lavoisier," he writes, "certainly learned your theory " from Dr. Blagden, who first had it from Mr. Ca- " vendish, and afterwards from your letter to Dr. " Priestley, which he heard read, and explained the " whole minutely to M. Lavoisier last July." [June.jf * To Mr Kirwan, 1st December 1783. t Mr. Kirwan to Mr. Watt, 13th December 1783. Ivi INTRODUCTORY REMARKS The letter was, of course, well known to Dr. Priest- ley, who received it, perused it, and at once occupied himself in answering it, and to Sir Joseph Banks, in whose hands it long remained. But that it was also read by many other members of the Royal Society, though not then at a public meeting of the body, there cannot be any manner of doubt. For we have not only the direct statement of Mr. Watt to that effect, published in the Philosophical Transactions in 1 784, under the direct superintendence of Dr. Blag- den, and repeated by Mr. De Luc in 1786,* but we have Blagden admitting his own knowledge of the paper, both in the statement which he says he made to Lavoisier in June, and in his letter which Crell printed in 1 786, of which we shall presently have much more to say. Mr. Kirwan's letter completes the demon- stration of Blagden having acquired a minute know- ledge of the paper, some time at least before he went to Paris, which was not later than the beginning of June.f It also appears very probable, (as it was clearly meant by Kirwan, and understood by Mr. Watt), that the first account of Mr. Watt's theory which Blagden ever received, he had from Cavendish. For the words are, " Lavoisier learned your theory " from Dr. Blagden, who first had it from Mr. Caven- " dish, and afterwards from your letter to Dr. Priest- " ley, which he heard read." The theory there spoken of is not said to have been one which had been formed by Cavendish, or which merely bore some * Meteorologie, vol. ii. p. 216. t We know, from a private letter of Blagden's, that on the llth of June he had been in Paris for several days. BY THE EDITOR. Ivii resemblance, whether general or close, to that of Mr. Watt; it is Mr. Watt's own theory alone that is spoken of the same that Blagden more minutely studied when he read the paper in which it was ex- plained, but which he first appears to have heard of from Cavendish's report. Such is the only natural and obvious sense of Blagden's words, as reported by Kirwan ; and, though it is by no means essential to our argument to insist upon it, they are almost in- capable of any other interpretation. We are, however, perfectly justified in asserting that two such theories, so novel and strange as to be then deemed incredible, could scarcely have come to any man of science, or even any pretender to scientific knowledge, first from one discoverer and then from another, both within the same month perhaps on the same day, without eliciting some observation on so marvellous a coincidence, some further explanation some parti- cular inquiry, as to the time and manner of the theory being announced, or formed, by each discoverer re- spectively. Still more strongly does this remark apply, from the circumstance of Blagden being well acquainted with Cavendish's proceedings. If the theories had then been distinct, but if Mr. Watt's so much resembled another previously formed, as to be spoken of and treated as the same, would Blagden have had no wonder to express, no disap- pointment to feel, at his patron having been both rivalled in the formation of it, and certainly antici- pated in the announcement 1 Would he have had no explanation to offer no priority to attempt to sus- tain no originality to claim for Mr. Cavendish, h mil INTRODUCTORY REMAKKS even if that gentleman was unwilling to do so for himself ? We repeat it : the only theory alluded to here, is, so far as appears, that which Mr. Watt conceived, and which he alone had as yet committed to writing. Such was evidently Mr. Watt's own view of the meaning of Mr. Kirwan's communica- tion ; and we are, however unwillingly, compelled to admit that the first part of the great engineer's reflections on the tidings sent by Kirwan may have been applicable in other quarters than that to which he then directed it. " You see," he says, " from " the above, that it is possible for a philosopher to " be disingenuous. For M. Lavoisier had heard of " my theory before he formed his, or before he tried " the experiment of burning dephlogisticated and " inflammable airs together, and saw the product was " water."* Mr. De Luc having gone to Paris in December, 1783, and there passed the month of January, 1784, returned to England in February, when his letters to Mr. Watt were resumed. In the meantime, on the 15th January, Mr. Cavendish had read to the Royal Society the first part of his celebrated " Experiments " on Air," of which the second part was read on the 2d of June, 1 785. In one of Mr. De Luc's letters, dated 1st March, 1784, he mentions that he had heard some particulars of the paper which Mr. Caven- dish had read, but nothing concerning the conclusions stated in it as to the composition of water appears to have been then reported to him. The imperfect * Mr. Watt to Mr. De Luc, 30th December, 1783. BY THE EDITOR. lix account which he thus received came from Dr. Blag- den. As the paper, however, was said to have in- cluded a thorough examination of the combustion of the two airs, he requested Mr. Cavendish's permission to see it, which was granted. The consternation into which he was thrown on perusing it for the first time is well depicted in the close of the same letter : " Being at this point of " my letter, I have received Mr. Cavendish's paper, " and have read it ! ! . . . . Expect something " that will astonish you as soon as I can write to you. "... Meanwhile, tell no one. . . . In " short, he expounds and proves your system, word for " word, and makes no mention whatever of you." The fact, however surprising, and whatever infer- ences may be drawn from it, was literally true. In the whole of that paper, as Mr. De Luc saw it, and as it had been read at the Royal Society, the learned chemist who had so carefully prepared it, had never once named James Watt, whose theory on the same subject had become " known to all the active mem- " bers" of the same Royal Society for nearly nine months ; had been announced and confirmed at Paris for nearly seven months, and was confessedly all the while minutely familiar to Blagden, the chosen friend and constant companion of Cavendish, professing to be engaged in the same pursuits with him, and who certainly was, as De Luc has elsewhere said, " in- " formed of all his experiments, as well as of those " of Dr. Priestley, and of the ideas of Mr. Watt." Mr. De Luc, in his letter of the 1st March, had pro- mised an analsisy of Cavendish's paper, and on the Ix INTRODUCTORY REMARKS same day began a long transcript of its principal parts, which he finished on the 4th March, and sent to Mr. Watt in a letter, which showed that, on a fur- ther examination, his amazement had not subsided. Having endeavoured, in some degree, to defend La- voisier and La Place from the charge of le Plagiat, he says " But that which is, on the other hand, per- " fectly clear, precise, astonishing, is the memoir of Mr. " Cavendish. Your own terms, in your letter of April " to Dr. Priestley, given as something new, by some one " who must have known that letter, which ICHX i-i/mi'ii. to " all the active members of the Royal Society to Dr. " Blagden above all, (for he said he had spoken of it to " Messrs. Lavoisier and La Place,) who well knew Mr. " Cavendish's memoir, both before it was read to the " Royal Society, and at its reading, and who conversed " with me about it, as I told you in my last me, whom " he knows to be your zealous friend." After strongly recommending caution, De Luc says " It is yet pos- " sible that Mr. Cavendish does not think he is pillaging " you, however probable it is that he does so ; " giving as his reasons for desiring to entertain so charitable a hope, that Cavendish had not objected to let him peruse his paper, and also the character which both Cavendish and Blagden had previously maintained. The force of the first of these considerations is much diminished, when we remember, that the paper in question had already been made public to a great extent by being read at the Royal Society, and was, besides, soon to be printed in the Philoso- phical Transactions : so that there could be no pos- sibility of keeping it secret, had that been desired. BY THE EDITOR. Ixi And the character of Mr. Cavendish was clearly no excuse for the entire suppression of Mr. Watt's name in his paper ; a defect which was afterwards, in Blag- den's interpolation, most inadequately remedied ; and which must ever remain a reproach both to Cavendish and to his companion Blagden, whose early and inti- mate knowledge of Mr. Watt's letter to Priestley has been so completely proved. In the very delicate and disagreeable circumstances which had thus occurred, Mr. De Luc suggested two modes of proceeding ; the one, to suffer in silence the injustice which he could not but feel had been done, in which case he engaged to print the letters to Dr. Priestley and himself, with their dates, in a work he was then preparing ; the other, to make the matter more public, by requesting Sir Joseph Banks to cause both the letters to be read to the Royal Society. In recommending the former, the too discreet philoso- pher used these words : " I should almost advise it, " considering that, in your position of drawing from " your discoveries practical consequences for your for- " tune, you must avoid making yourself des jaloux." He had yet to learn the full extent of the manly virtue of his friend ; who, while he declined to make any attack upon Mr. Cavendish, admitting, perhaps with a somewhat extravagant liberality, that it was " baijsly possible" that he might not have heard of his theory, still spoke in a strain of honest indigna- tion of the plagiarism which he felt there was too much room to believe had been effected, of the wound which his scientific fame had been made to suffer, and of the hardship of being thus anticipated in the first Ixii INTRODUCTORY REMARKS attempt he had made to lay anything before the pub- lic. " As to what you say," he wrote, " about making " myself desjaloux, that idea would weigh little ; for, " were I convinced I had had foul play, if I did not " assert my right, it would either be from a contempt " for the modicum of reputation which would result " from such a theory, from a conviction in my own " mind that I was their superior, or from an indolence " that makes it more easy for me to bear wrongs, " than to seek redress. In point of interest, so far as " connected with money, that would be no bar : for " though I am dependent on the favour of the public, " I am not on Mr. C. or his friends, and could despise " the united power of the illustrious house of Caven- " dish, as Mr. Fox calls them."* What followed may be very briefly told : " He " states his intention of being in London in the ensuing " week, and nis opinion, that the reading of his letter " to the Royal Society will be the proper step to be " taken. He accordingly went there, waited upon " the President of the lloyal Society, Sir Joseph " Banks, was received with all the courtesy and just " feeling which distinguished that most honourable " man, and it was settled, that both the letter to Dr. " Priestley of 26th. April 1783, and that to Mr. De " Luc of 26th November 1 783, should be successively " read. The former was done on the 22d, and the " latter on the 29th April 1784 ;"f and it is said by * Mr. Watt to Mr. De Luc, 6th March 1784. t Note by the present Mr. James Watt, added to Lord Brougham's Historical Note. See Translation of Arago's Eloge, p. 164. BY THE EDITOR. Ixiii Sir Joseph Banks, that " both appeared to meet with " great approbation from large meetings of Fellows." * Both of the letters were ordered by the Committee of Papers to be printed, and it was arranged that the best form in which that could be done, in order to avoid repetition, was by incorporating the first with the second, which was accordingly the plan adopted ; " but," as the note in the Philosophical Transactions bears, " to authenticate the date of the author's ideas, " the parts of it which are contained in the present " letter are marked with double commas." Blagden became Secretary of the Royal Society on the 5th of May 1 784 ; and to him, in virtue of his office, was entrusted the superintendence of the print- ing of Mr. Watt's paper. In his letters on that sub- ject, he appeared perfectly willing to attend with care to the publication ; and in one of them offered, should Mr. Watt desire it, to send him the proof-sheets for correction. Mr. Watt, residing at a distance from town, declined his offer ; a resolution which he had afterwards reason to regret ; for the consequence has been, that in his paper, as it stands in the Philoso- phical Transactions, there is a very inexcusable error of tJie press. The date of the letter to Mr. De Luc, which we have just seen was 26th November 1 783, is there given as 26th November 1784. It is true that the date of the reading of the paper is rightly given, and therefore that error might not always mis- lead ; but, considering all that had previously oc- curred, it was of great importance that every date * Sir Joseph Banka to Mr. Watt, llth May 1784. Ixiv INTRODUCTORY REMARKS establishing Mr. Watt's priority should be accurately printed, and what we shall in this instance call care- lessness, cannot well be freed from blame. But this is not all. Of Mr. Cavendish's Paper there were a number of separate copies thrown off, which were widely circulated throughout Europe by himself and his friends, before the seventy-fourth volume of the Philosophical Transactions, in which it was to be contained, made its appearance. These also, it is pre- sumed, had been printed under the superintendence of Dr. Blagden, and of Mr. Cavendish. They all bear on their title page, that Mr. Cavendish's paper was "read at the Royal Society, January 15, 1783." Moreover, the true date, 1 784, which is placed at the head of that paper as it stands in the Philosophical Transactions, is not given at all in those separate copies. It is said by Mr. Harcourt, that in one instance, more than a year afterwards, (when the error, had already been propagated in most of the scientific Journals of the Continent, and when also the Philoso- phical Transactions with the true date of the reading of the Paper had come into circulation,) Mr. Caven- dish desired that it might be corrected.* We have no desire to take from him the credit of having done so in that instance. But the error continued long after- * The above is the only new fact which that reverend gentleman, among all his petty cavillings and prolix sophistry, has disclosed ; excepting, indeed, the additional and very important evidence which his publication of the Diary afibrds, of Mr. Cavendish's conclusions not having been drawn till after those of Mr. Watt had been made known. BY THE EDITOR. Ixv wards to have its natural, unjust effect. For Cuvier, writing at the distance of four and twenty years from the circulation of the erroneous date, has distinctly said, " The experiment of Mr. Cavendish dates from 1781 ; " th'e reading of his Memoir, from January 1783;" and gives Cavendish the precedence over Lavoisier in their respective published memoirs, making the latter supe- rior only in having discarded the hypothesis of phlo- giston."* In his Eloge of Cavendish,-f- it is true, he alters 1783 to 1784, observing that three years had been occupied " in establishing that great pheno- " menon ;" but still his readers are left without the means of knowing which of the two dates is the right one. Numerous as are Cuvier's errors on such points, yet his illustrious name, and the charms of the dic- tion in which he clothes the history of philosophy and philosophic men, have led him to be cited by many as a safe authority ; and Mr. Harcourt, who, as will presently be seen, himself practises such inaccuracies with a fatal facility, seems to think lightly of their effect. But this only the more deeply impresses us with the sacred obligation of scrupulously recording matters of fact in subjects of controversy, and makes us more sensible of the inestimable value of rigid ac- curacy. Every one must admit, that after the series of events which we have now detailed after the zealous attempts to establish priority which had been made by two of the three great claimants for * Rapport Historique, 1808, p. 57. t Memoires de 1'Academie, for 1811, p. cxxxiii ; and, in the separate edition of Cuvier's Eloges Historiques, tome ii. p. 87. i Ixvi INTRODUCTORY REMARKS the honour of the discovery, and the public state- ment which had been put on record by the third, (which, being uncontradicted, might be deemed de- cisive,) it was, truly, most unfortunate that any thing should occur, which could give to any of the pro- ceedings, even in appearance, a character not alto- gether consistent with justice. It was at least a piece of most singular negligence, on the part of the Secretary to the Royal Society who super- intended the printing, that those Papers should have been circulated with a double error in their dates ; that the tendency, if not the effect, of both the errors should have been, to take the priority from Watt, and to give it to Cavendish ; and that of all the errors which the printer might have committed, he should have happened to select precisely those which were best fitted to effect that object. When M. Arago exclaimed, after mentioning the same cir- cumstance, " God forbid that I should, by these re- " marks, intend to cast any imputation on the literary " probity of those illustrious philosophers ; they only " prove that, on the subject of discoveries, the strict- " est justice is all that can be expected from a rival, " or a competitor, however high his reputation may " already be,"* we must confess that he well de- serves to receive credit, for restraining within the bounds of those moderate words, the expression of a strong and just indignation. An additional argument certainly arises from the remarkable fact, that Cavendish appears never to have * Eloge of Watt, p. 106. BY THE EDITOR. Ixvii made any observation on Mr. Watt's chronological note, when it was printed with his Paper by the Royal Society ; nor ever to have confessed his know- ledge of the real time at which Mr. Watt made either his first or his second communication, or of that at which he thus knew that his conclusions were drawn. But we have not yet done with either the history of the discovery, or the share which Dr. Blagden took in it as an auxiliary and historian. Finding that Lavoisier still maintained some claim, and seeing from the note appended to Mr. Watt's Paper, and from the total want of -any statement as to the chronology of Cavendish's conclusions, that Mr. Watt stood dis- tinctly recorded as the first discoverer, notwithstand- ing the inexplicable awkwardness of the typographical errors, he thought proper to write the letter to Crell, printed two years later in his Journal, which is given at full length at p. 71 of this volume. Blagden there says : " I can certainly give you the best account of the " little dispute about the first discoverer of the arti- " ficial generation of water, as I was the principal " instrument through which the first news of the disco- " very that had been already made was communicated " to M. Lavoisier. The following is a short statement " of the history. In the spring of 1 783, Mr. Caven- " dish communicated to me, and other members of " the Royal Society, his particular friends, the result " of some experiments with which he had for a long " time been occupied. He showed us that out of " them he must draw the conclusion, that dephlogis- " ticated air was nothing else than water deprived Ixviii INTRODUCTORY REMARKS " of its phlogiston, and, vice versa, that water was " dephlogisticated air united with phlogiston. About " the same time the news was brought to London that " Mr. Watt of Birmingham had been induced, by " some observations, to form a similar opinion. Soon " after this I went to Paris, and in the company of " M. Lavoisier and of some other members of the " Royal Academy of Sciences, I gave some account " of these new experiments, and of the opinions " founded upon them. * * * But those con- " elusions opened the way to M. Lavoisier's present " theory. * * * He was induced to institute " such experiments solely by the accounts he received " from me, and of our English experiments, and he " really discovered nothing but what had before been " pointed out to him to have been previously made " out and demonstrated in England." Now, before examining the history which this letter gives of the discovery, it is to be observed that it pro- fesses to have been written in order to give the best account of the dispute about the first discoverer. And from the relations in which Blagden had always stood to Cavendish, and the obligations which he owed him, he cannot be suspected of under-stating any claims which he might have been able to establish for that gentleman to the possession of so great an honour. Bearing this in mind, and taking the statement as we find it, an extraordinary fact which meets us at the outset is, that it does not contain any distinct allegation of Cavendish having been the first disco- verer ; although it does positively assert that he was prior to Lavoisier, and appears to aim at having it BY THE EDITOR. Ixix understood that he was prior also to Mr. Watt. Even the time at which Cavendish is reported to have communicated to his friends of the Royal Society his experiments and their results, and " showed that " out of them he must draw the conclusion," is only noted in the most general way, as " in the Spring of " 1 783." But we know that Mr. Watt's conclusions, on the other hand, were actually formed, reduced to writing, (which Cavendish's confessedly were not), and known to many members of the Royal Society, also " in the Spring of 1 783 ;" and Blagden, though he was well aware of all these circumstances, and professes to give " the best account," and was natu- rally desirous of gaining the credit of the priority for his patron, does not even state that Cavendish's verbal communication preceded his knowledge of Mr. Watt's written conclusions. But further, no time has ever yet been stated, either by Cavendish or Blagden, at which the former really drew his conclusions; which are thus never heard of as having been even imagined by him till " the Spring of 1783 ;" and in the absence of all such assertion by either of those gentlemen, or by any one else who was acquainted with the circum- stances, it is impossible, in common fairness to the other parties concerned, to attribute his conclusions to an earlier period than that which, however vaguely, is so assigned to them. Again, if Mr. Cavendish, at the time of making his communication to his friends, was ignorant of Mr. Watt's conclusions, of which, even according to Blagden, " the news was brought to London about INTRODUCTORY REMARKS " the same time," why does not Blagden, in his claim of priority, make any assertion to that effect ? Would he not have done so if he could, and is it not a per- fectly fair inference from the fact of his not having done so, that he knew he could not ] If, on the contrary, Cavendish was then in the knowledge of Mr. Watt's conclusions, why did he not, in order to assert any claim for himself, not only to priority, but even to originality, mention in his ver- bal communication to his friends, that he had drawn his own conclusions, or rather, had seen " that he must draw them" for that is the more circuitous way in which Blagden puts it before he had heard of those of Mr. Watt, and independent of them \ Failing any statement of the time not during which he had been occupied with his experiments, for that proves nothing but at which he had first drawn the particular conclusion from them, that " dephlogis- " ticated air is in reality nothing but dephlogisticated " water, or water deprived of its phlogiston," he could claim no priority, except as against a discoverer, the date of whose discovery could be proved to be subsequent to that communication to his friends, the members of the Royal Society. But only a vague approximation being attempted to the date of his communication, and no better or earlier one being even suggested as that of his conclusions (and that, too, in " the best account" that could be given of his claims, published in his own lifetime, and written by one who well knew the necessity there was for the greatest possible minuteness and precision of chrono- logical record) and no later period being assigned as BY THE EDITOR. Ixxi that of his knowledge of Mr. Watt's conclusions, the inference is both just and inevitable, that neither Cavendish, nor Blagden on his behalf, could establish any priority as against Mr. Watt. It was comparatively an easy matter to assert it for one or both of the English philosophers as against Lavoisier, for that chemist, on his own shewing, could not claim even for his experiment, an earlier date than the 24th of June 1 783 ; and, had his been the only competition which Cavendish had to appre- hend, " the Spring" might have been held a sufficient anticipation ; when taken in connexion with what Blagden states, and Lavoisier partially admits, to have passed at Paris. Still, even in that case, Blagden's way of speaking must have appeared to all accurate inquirers very negligent, very unsuitable to the nicety of the subject, and very unfit for the purposes of care- ful scientific history. But when the question concerns the conclusions of Mr. Watt, which had been stated not verbally, nor at an uncertain date, nor only to his own private and particular friends, but in writing, on the 21st and subsequent days of April, to many members and the President of the Royal Society; and which, before this letter of Blagden's was written, had been printed in the Philosophical Transactions, under Blagden's immediate eye and sole superintendence, with a note emphatically and fully " authenticating the date of " the author's ideas" it would be utterly absurd to found any claim, or even any argument in support of a claim, on an expression so indeterminate as that of " the Spring." Ixxii INTRODUCTORY REMARKS Was it early in the Spring, or late in the Spring ? Was it in February, or in March, or in April \ We apprehend that neither Mr. Cavendish nor Dr. Blag- den would have thanked us for the supposition, that it might possibly have been in May. But " questions " as to priority," says M. Arago, " may depend" not only on years, and on seasons, and on months but " on weeks, on days, on hours, on minutes." In what week, on what day of the month, was the important disclosure made by Mr. Cavendish ? To bring the matter to a short issue ; was it not after a certain letter, of date the 26th of April 1 783, had been re- ceived by Dr. Priestley at London, shewn to " several " members of the Royal Society," nay, read and mi- nutely studied by Dr. Blagden, (for that is proved by his own admission to Kirwan,) and then delivered to Sir Joseph Banks the President ? Blagden could not, surely, have so soon forgotten all the circumstances which attended so important a communication ; he must at least have remembered whether, when it came from Mr. Cavendish, it was no longer graced with the freshness and interest of novelty ; and whether it was not an echo of some- thing else which had come to London and his ears " about tlie same time'' Of two theories so nearly identical, he surely could have recollected, without much difficult reflection, which he had heard first; the memory which was so retentive as to the pro- ceedings at Paris, where Lavoisier was concerned, could not well have been oblivious as to the occur- rences in London, where Mr. Watt's communication excited so much attention, had been intimately known BY THE EDITOR. Ixxiii to Blagden himself, had gained most honourable ap- plause from many learned persons, and stood recorded in the books of the Royal Society as the first an- nouncement of the discovery of the compound nature of water. When Mr. Watt's conclusions were first made known, and that to all the active members of the Royal Society, they laughed at them, says De Luc, as at the explanation of the golden tooth; so great was their wonder, so strong their disbelief. But Mr. Cavendish's friends are not said by Blagden to have testified any surprise, or any incredulity ; yet " the " conclusions," as Lord Brougham has truly said, " are " identical," with the single difference as to heat, in which respect the discoveries of modern che- mists have shewn that Mr. Watt's had greatly the advantage. But the novelty was gone, and the disbelieving wonder had ceased. When Blagden says only, that both communications were made in " the Spring," and " about the same time," he claims for his patron no priority; he is content to insinuate for him only a very questionable sort of independence in the discovery ; nay more, for that is the result to which the evidence brings it, he can for Mr. Caven- dish, as against Mr. Watt, neither claim priority, nor establish independence. In Mr. Cavendish's paper as first written, and as read on the 15th January 1784, he made no mention whatever of Mr. Watt's theory. Yet it appears from this letter to Crell, that Blagden was not uninformed at a much earlier period, (viz. the Spring of 1 783,) of Mr. Watt having formed " an opinion" similar to that of Cavendish ; he confesses that " the news was brought k Ixxiv INTRODUCTORY REMARKS " to London" in the same spring; that he knew it, at latest, before - " covery, is assigned to Mr. Watt." Sir Humphry Davy does not say a word of any " discovery imply - " ing an inference" having been made by Cavendish, nor of any inference at all having been drawn by him. Neither does he say, that Mr. Watt's reason- ing and conclusion " required to be confirmed, to con- " stitute a discovery." Dr. Davy's commentary strongly reminds us of what we once heard asserted, viz. that he might have been supposed to knoiv some- thing of his late brother's opinions, if he had not taken the pains to show the world that he did not. With a quiet disregard alike of the difficulties of the case, and of the evidence which helps to remove them, which cannot well be surpassed, he goes on to say " Mr. Cavendish, in 1781, made the experiments " showing that water is the true product of the com- " bustion of oxygen and hydrogen ; and drew the in- " ference that water is composed of oxygen and hy- BY THE EDITOR. cxvi] " drogen." Of course, this pro ratione voluntas mode of proceeding would reduce the whole inquiry to the greatest possible simplicity ; the only disadvantage of it being, that it can be used, at the same time, with equal justice, and equal success, on both sides of any given question.* Sir David Brewster, in an article in the Edinburgh Review, f in which he reviewed the Eloge of M. Arago, first of all stated that " chemists of our own " and foreign countries had, by acts of omission, de- " prived Mr. Watt of a merit to which he is clearly " entitled," and then, " established," as he says, " on " the authority of printed documents, the priority of " Mr. Watt's hypothesis, to the experiments and de- " ductions of Cavendish ;" and " obtained," as it is repeated, " for Mr. Watt's hypothesis a decided " priority, or, to use Lord Brougham's words, showed " that he was the first to reduce the theory of com- " position to writing." He then went on to attempt to lessen the merit of the priority, so established by himself to his own satisfaction ; borrowing his prin- cipal support from the modest expressions which Mr. Watt himself used in the matter. The caution with which Mr. Watt thought it pro- per to speak, he has himself well described in his Paper, J as " the diffidence which ought to accompany " every attempt to account for the phenomena of na- * Sir Humphry Davy's latest and best informed opinion has been given at pp. ix. x. of this volume. t In January 1840. The article has been publicly acknowledged by Sir David. % Phil. Trans., 1784, p. 357. CXV111 INTRODUCTORY REMARKS " ture, on other principles, than those which are com- " monly received by philosophers in general." We have yet to learn that any inquirer into the causes of phenomena previously unexplained, could with pro- priety either recommend or adopt a greater degree of boldness in assertion, respecting subjects of which the difficulty could be considered as at all analogous. And we may suppose, that when Sir David Brewster shall be satisfied, by the perusal of the correspond- ence now first published, that Mr. Watt's theory was with him much more than mere conjecture or bare hypothesis, that he was never shaken in his confi- dence in it, and positively refused to doubt, much more to abandon it, even after examining the expe- riments on which Priestley denied it he may modify his opinion to one more consistent with the facts, and more liberal of praise to the first discoverer. Had Mr. Watt's statement as to the date of his conclusions ever been called in question, or had he, like Mr. Cavendish, left no precise chronologi- cal statement at all ; had we been now forced to collect from other quarters, and for the first time, the facts on both sides of a disputed question, and to decide the cause according to the preponderance of such secondary evidence, a chief consideration might have been, the peculiarities of character and disposi- tion of the two principal parties. Even as matters now stand, with a priority of publication really in- contestable, placed on record in the registers of the most learned body in the kingdom, and uncontra- dicted during the lives of any of the parties, while it is by no means our wish to lessen the high repu- BY THE EDITOR. CX1X tation which Mr. Cavendish maintained, (however much that may have been exaggerated by the indis- criminate eulogy of Cuvier and others) we may be forgiven if we dwell with pride on some characteris- tics of Mr. Watt, in which he was surpassed by no man, and could certainly have been equalled by few ; which are not without a very important and obvious bearing on a question like the present. The Earl of Liverpool, when Prime Minister of England, after publicly declaring that on his personal knowledge he could aver, that a more amiable and excellent man in all the relations of life never existed, amply enlarged on the simplicity of his character, the absence in him of every thing like presumption and ostentation, and his unwillingness to obtrude himself not only upon the great and powerful, but even on those branches of the scientific world to which he more immediately belonged.* An orator and states- man still more distinguished, after mentioning that he had the happiness of knowing Mr. Watt for many years, in the intercourse of private life, said that those who were admitted to his society would readily allow, that any thing more pure, more candid, more simple, more scrupulously loving of justice, than the whole habits of his life and conversation proved him to be, was never known : " There was one quality, which " most honourably distinguished him from too many " inventors, and was worthy of all imitation he was " not only entirely free from jealousy, but he exer- " cised a careful and scrupulous self-denial, and was * Speeches at Freemason's Hall, 18th June 1824. Translation of Arago's Eloge, p. 189. CXX INTRODUCTORY REMARKS " anxious not to appear, even by accident, as appro- " priating to himself that which he thought belonged " to others. * * The only jealousy I have known " him to betray, was with respect to others ; in the " nice adjustment he was fond of giving to the claims " of inventors. Justly prizing scientific discovery " above all other possessions, he deemed the title to " it so sacred, that you might hear him arguing by " the hour to settle disputed rights ; and if you ever " perceived his temper ruffled, it was when one man's " invention was claimed by, or given to another ; or " when a clumsy adulation pressed upon himself that " which he knew to be not his own." 45 ' It is no derogation from his excellence, that he was at the same time not unconscious of " just pride, " founded on great talents and great services ; that " pride, which the most exalted and most worthy can " justly indulge." f But his exemplary mind bor- rowed an additional grace from his habitual restraint of all such emotions ; and we shall never forget the noble animation with which one of our most gifted and venerable Poets,! a f ter having pointedly censured the unhappy passion for notoriety by which he conceived that some scientific men of the present day were too much actuated, fervently exclaimed " It was not so, " that NEWTON made his discoveries, the grandest ever " known ; nor that WATT made his, the most bene- " ficial to mankind : I look upon him, considering * Lord Brougham's Speech, printed with the Translation of Ara- go's Eloge, pp. 216-218. f Sir E. Peel, in the House of Commons, 23d January 1846. J Mr. Wordsworth, in September 1840. BY THE EDITOR. CXX1 " both the magnitude and the universality of his ge- " nius, as perhaps the most extraordinary man that " this country ever produced ; he never sought dis- " play, but was content to work in that quietness and " humility, both of spirit and of outward circum- " stances, in which alone all that is truly great and " good was ever done." Such is his enviable reputation as a man; such his fame as a philosopher. And it is interesting in a high degree to remark, that for him, who had so fully subdued to the use of man the gigantic power of STEAM, it was also reserved to unfold its com- pound nature and elemental principles : as if on this subject there were to be nothing which, his researches did not touch nothing which they touched that they did not adorn. That to his thoughtful sagacity is due the glory of having first made that remarkable step in the progress of science, cannot admit of a reasonable doubt. Had Mr. Watt's discovery of the theory of the composition of water been, like very many of his inventions, directly available for the increase of his own wealth, and, as such, protected by a patent, most certainly no case has been made out, on the part of Mr. Cavendish, of such public use, or prior invention, as could have invalidated that patent. But, is honour to be meted out with a less liberal hand, or guarded with less jealous care, than those pecuniary rewards, which the true philosopher does not covet, and which few men would with equal ardour desire \ Are learned Societies, or the individual followers and friends of Science, to be guided by less exact principles of CXX11 INTRODUCTORY REMARKS BY THE EDITOR. justice, in their award of praise to a first inventor, than those impartial Tribunals where, in similar cases, but with other interests at stake, the great improver of the steam-engine found his rights vindicated, and his inventions sacredly protected, by the strong arm of the Law \ " Vilius argentum est auro, virtutibus aurum. " O cives, cives ! quaerenda pecunia primum est, " Virtus post nummos ?"* The result of the evidence on the whole case, as far as Mr. Watt's priority is concerned, we shall briefly express in these propositions, which certainly do not assume more than we have already proved ; and of which every one who has been accustomed to the ex- actness of legal inquiries into matters of disputed dis- covery, will acknowledge the force. First, that Mr. Watt formed the original idea in his own mind, and thus was A DISCOVERER of the true theory of the composition of water. Secondly, that being a discoverer, he was also THE FIRST PUBLISHER of that true theory. Thirdly, that being both a discoverer, and also the first publisher, he must therefore be held to be " THE " TRUE AND FIRST INVENTOR THEREOF."f * Hor. Epist. I. i. 52. t See Godson on Patents, pp. 27-30. The term " Inventor" is, of course, here used in the legal sense, of " one that has found out " something new." END OF THE INTRODUCTORY REMARKS. SUMMARY THE HISTORY OF THE PROGRESS TOWARDS THE DISCOVERY, AND OF THE DISCOVERY ITSELF. 1776. Volta fires inflammable air by the electric spark. 1776-77. Macquer explodes mixtures of inflammable and common airs, and of inflammable and dephlogisticated airs, (but not by the electric spark,) in glass vessels, not close. He makes his observation of the moisture formed when inflammable air is burned in common air, and of that moisture -being pure water. 1778. Macquer publishes his observations. 1781. Before the 1 8th of April, Mr. Warltire, being en- couraged by Dr. Priestley, fires, by the electric spark, a mixture of common and inflammable air in a close CXX1V SUMMARY OF THE HISTORY metal flask, weighing the vessel before and after the explosion, observing the dewy deposit, and finding only a very trifling loss of weight. Dr. Priestley fires mixtures of common and inflam- mable airs, and of inflammable and dephlogisticated airs, in a close glass vessel, and observes a deposit of water on the sides of the vessel. Mr. Warltire repeats Dr. Priestley's experiment in the close glass vessel, and confirms his observation of the dewy deposit. In July, after the publication of Dr. Priestley's and Mr. Warltire's experiments, Mr. Cavendish repeats them. No conclusion as to the real origin of the water, published by Mr. Cavendish ; nor communicated to any individual, nor contained in the Journal and Note* of his experiments ; nor alleged by himself, nor by any one else, to have been then drawn by him. 1782. 13th December. Mr. Watt, in writing to Mr. De Luc and Dr. Black, mentions an opinion which he had held for many years, that air was a modifica- tion of water ; and that if all the latent heat of steam could be turned into sensible heat, the constitution of the steam would be essentially changed, and it would become air. 1783. " Dr. Priestley having put dry dephlogisticated air " and dry inflammable air into a close [glass] vessel, " and kindled them by the electric spark, finds on the OF THE DISCOVERY. CXXV " sides of the vessel a quantity of water equal in " weight to the air employed." 26th March. Mr. Watt mentions as new to him, that experiment of Dr. Priestley's. 21st April. -Mr. Watt states in his letters, both to Dr. Priestley and to Dr. Black, his conclusions, viz. : " that water is composed of dephlogisticated and in- " flammable air, or phlogiston, deprived of part of " their latent heat ; and that dephlogisticated or pure " air is composed of water deprived of its phlogiston, " and united to heat and light." He requests his let- ter to Dr. Priestley to be read to the Royal Society. 26th April. Mr. Watt having re-written his let- ter of the 21st, sends it to Dr. Priestley, who re- ceives it in London shows it to several members of the Royal Society, among whom was Mr. Caven- dish's intimate friend, Dr. Blagden, and then deli- vers it to Sir Joseph Banks the President, for the purpose of being publicly read to the Society. Prior to the 23d of June, Mr. Watt requests the public reading of his paper to be delayed till he should examine new experiments, said by Dr. Priest- ley to contradict his theory. 24th June. MM. Lavoisier and La Place perform their experiment at Paris, at which Blagden is pre- sent. They are informed, as Lavoisier says, of Mr. Cavendish having burned the two airs and obtained water ; as Blagden says, of the conclusions of Watt and Cavendish (this being the first time that any conclusion of Mr. Cavendish on the subject is referred to by any one.) 25th June. MM. Lavoisier and La Place give an CXXV1 SUMMARY OF THE HISTORY account of their experiment to the Academy of Sciences, and Lavoisier states the conclusion as to the compound nature of water, to have been drawn by La Place and himself. June and July. M. Monge performs his experi- ments at Mezieres ; and repeats them in October. Martinmas. M. Lavoisier reads to the Academy of Sciences his memoir on the composition of water. 2Gth November. Mr. Watt being fully satisfied of the correctness of his theory, and hearing that Lavoisier was passing it off as his own, repeats it in his letter to Mr. De Luc, which he requests may be read to the Royal Society. No conclusion published, nor known to have been committed to writing, nor alleged (excepting by Dr. Blagden,) to have been drawn by Mr. Cavendish. 1784. 15th January. In his paper read to the Royal Society this day, Mr. Cavendish, for the first time, states publicly in writing, and in his own person, his conclusions as to the compound nature of water ; coinciding generally with those of Mr. Watt, but omitting the consideration of latent heat, as well as the mention of Mr. Watt's name. March. Mr. Watt, finding that in Mr. Caven- dish's paper his own theory had been fully explained and proved, and his name excluded, expresses his in- dignation, and takes immediate steps for having his own letters, of 26th April and 26th November 1 783, read at the Royal Society, with their true dates. 21st April. MM. Meusnier and Lavoisier read OF THE DISCOVERY. CXXvii to the Academy of Sciences their memoir on the decomposition of water, which is printed in the same year. 22d April Mr. Watt's first letter, which had till now remained in the custody of the President, is, ac- cording to his request, read at the Royal Society. 29th April. His second letter is also read. Both letters are ordered to be printed in the Philosophical Transactions. 5th May. Dr. Blagden is appointed Secretary to the Royal Society, and is entrusted with the superin- tendence of the printing of both of Mr. Watt's let- ters, to be embodied in one paper, with marks dis- tinguishing each from the other. June ? M. Lavoisier's memoir is printed with additions. July. Mr. Watt's paper is printed, under the sole superintendence of Dr. Blagden, and with the errone- ous date of 1784 instead 0/1783. Mr. Cavendish's paper is printed ; the separate copies, with the erro- neous date of 1 783 instead of 1 784 ; and the paper itself containing two interpolations, made by Dr. Blagden some months after it had been read to the Society. In one of these, Mr. Watt's name is for the first time mentioned as if by Mr. Cavendish, and his theory alluded to as his own. 1786. The paper of M. Monge is printed ; no date be- ing mentioned at which it had been read. END OF THE SUMMARY. EXTRACTS FROM MR. WATT'S CORRESPONDENCE RESPECTING THE THEORY OF THE COMPOSITION OF WATER. EXTRACTS MR. WATTS PEIVATE CORRESPONDENCE RESPECTING HIS DISCOVERY OF THE THEORY OF THE COMPOSITION OF WATER, &C. DK. PRIESTLEY TO MR. WATT. Fairhill, Birmingham, 8th Dec. 1782. I HAVE the pleasure to inform you that I readily convert water into a permanent air, by first combin- ing it with quicklime, and then exposing it to a red heat. This, I believe, agrees with your idea on the subject. I have not, though, much merit, as I had only random expectations from exposing volatile sub- stances in general to a red heat, when combined with other substances, in imitation of the method of converting the acids into air, when combined with the calces of metals, or with alkaline bodies. When I have the pleasure of seeing you, I will inform you what kind of air I get, and what quantity, &c. Yours sincerely, JOSEPH PRIESTLEY. 4 EXTRACTS FROM EXTRACT MR. WATT TO MR. DE LUC. Birmingham, 13th Dec. 1782. * * - Dr. Priestley has made a most surprising disco- covery, which seems to confirm my theory of water's undergoing some very remarkable change at the point where all its latent heat would be changed into sensible heat, which must follow from the diminution of the latent heat, as the sensible heat increases, pro- bably at or near 1200 of Fahrenheit. The Doctor took a quantity of very caustic quick- lime (calx viva) from which he had driven all the fixed air by means of violent heat ; he poured upon this quicklime one ounce of water, and put the lime after it had absorbed the water into an earthen re- tort, and subjected it to a strong heat. He placed a balloon between the retort and the receiver. On the application of heat, air began to come over, and continued to do so until he got a quantity equal in weight to the ounce of water, viz. 800 oz. measures. The balloon remained quite cold, and was perfectly dry, without any appearance of moisture. The air so produced contained a little fixed air, but the greatest part of it was nearly of the nature of atmospheric air, only somewhat more phlogisti- cated. I have observed several other processes by which I now believe air is generated from" water, some of which I shall mention to you when I have the plea- MR. WATT'S CORRESPONDENCE. 5 sure of seeing you. If this process contains no de- ception, here is an effectual account of many pheno- mena, and one element dismissed from the list. With the greatest regard and esteem, I remain, Dear Sir, your obliged friend, JAMES WATT. EXTRACT MB. WATT TO DR. BLACK. Birmingham, 13th Dec. 1782. Mr. De Luc was here lately, and told me that he was now writing something on heat, and on the nature of elastic fluids, and begged I would explain to him some of my experiments and theories of that fluid, which I complied with in part, but could not do so without first explaining your theories of latent heat, of which he wanted to know more than I could tell him, or chose to do without your consent. He is a man of great modesty and most engaging manners ; is a great admirer of you from what he has heard of your discoveries ; thinks you have been ill-used by Dr. Crawford and other people who have endeavoured to rob you of the merit of your disco- veries, and wishes to be made able to do you justice ; as he will take upon himself the trouble of being the editor of whatever you please to communicate, either as received directly from yourself, or through me. If, therefore, you should chuse to communicate any thing, I think you may depend on his doing you jus- tice, in publishing as yours whatever you claim. If it is not agreeable to you to furnish any materi- 6 EXTRACTS FROM als, I shall only explain to him more fully your doc- trine of the latent heat of steam ; but, in doing that, I know not how to avoid mixing what may have been the suggestions of my own mind, with what I have learned from you, which I would [not] wish to do, as my suggestions may do your theory no honour. What I mean to tell him that I think my own, is, the trying the experiment on the latent heat in vacuo, and finding it to be greater than under the pressure of the atmosphere ; the experiments to ascertain the different degrees of heat at which water boils under different pressures ; the expansion which steam in its perfect state receives from heat ; and the experiments on the bulk of water when converted into steam ; together with a theory which I have de- vised, which accounts for the boiling heat of water not following a geometrical progression ; and shewing that, as steam parts with its latent heat as it acquires sensible heat, or is more compressed, that when it arrives at a certain point it will have no latent heat, and may, under proper compression, be an elas- tic fluid nearly as specifically heavy as water ; at which point I conceive it will again change its state and become something else than steam or water. My opinion has been that it would then become air ; which many things had led me to conclude, and which is confirmed by an experiment which Dr. Priestley made the other day, in his usual way of groping about. As he had succeeded in turning the acids into air by heat only, he wanted to try what water would become in like circumstances. He under- MR. WATT'S CORRESPONDENCE. 7 saturated some very caustic lime with an ounce of water, and subjected it to a white heat, in an earthen retort. He fixed a balloon between the re- ceiver and the retort. No water or moisture came over, but a quantity of air, equal in weight to the water, viz., 800 oz. measures, a very small part of which was fixed air, and the rest of the nature of atmospheric air, but rather more phlogisticated. He has repeated the experiment with the same results. Mr. Keir also presents his compliments to you. He is going to publish a new edition of his Diction- ary, and makes the same request that Mr. De Luc does, as he must now say something on the subject of heat, which he formerly declined, hoping you would have done it yourself. He wishes to have his information from the fountain-head, and to give to Csesar the things that are Caesar's. In relation to those things which I look upon as my own, if you think my title to any of them bad, I will cheerfully resign it if you claim it ; and shall at all events own that I have built my house on the foundation of your theory of latent heat, and that I owe a just way of thinking on these subjects to you. Mr. De Luc will be here again about the middle of February ; and I wish, as soon as proves conve- nient, that you would give me a few hints how you would have me act in the matter, as I have it much at heart to do what would prove most agreeable to you in it. It will also give me great pleasure to hear of your health, and also of that of all my good friends with you, to whom I beg to be remembered. My own 8 EXTRACTS FROM health is, as it used to be, none of the best, and I think my vexations increase faster than my wealth. I remain, dear Doctor, most affectionately yours, JAMES WATT. DR. PRIESTLEY TO MR. WATT. Fairhill, 26th Dec. 1782. I have the pleasure to inform you that I now con- vert water into air without combining it with lime or any thing else, with less than a boiling heat, in the greatest quantity and with the least possible trouble or expense. The air is of the purity of that of the atmosphere, and, I think, without any mixture of fixed air. The method will surprise you more than the effect, but that I may give you the pleasure of speculating on the subject, I shall defer the communication of the hocus pocus of it, till you give me the pleasure of your company at Fairhill. I have other curious things to shew you. Yours sincerely, JOSEPH PRIESTLEY. EXTRACT MR. WATT TO MR. HAMILTON. Birmingham, January 3, 1783. My spirits have been so much affected by one thing and another, and my headaches have been so frequent and of such long continuance, that there have scarcely been two days in the week, this long time, that I have been tolerably well ; and even at MR. WATT'S CORRESPONDENCE. 9 those times my head stupid and confused. This, united to the necessity of writing such letters of business as required immediate answers, and con- triving many things which were to be contrived, has made me put off from day to day everything I could. As you know the keenness of my sensibility, you can conceive how much these various accidents have af- fected me. This is the first day of a clear head I have had this fortnight; I dare not strain it too much. UR. BLACK TO MB. WATT. Edinburgh, 30th January 1763. MY DEAR WATT, There is nothing I meet with now, that gives me so much pleasure as your letters, excepting those parts of them in which you mention your health and your vexations ; w^hen I come to these I exclaim, " Good God, why cannot I find the " philosopher's stone, that I may be enabled to relieve " my friends from their diseases and their distresses!" But though I feel a painful sympathy with you on such occasions, I wish to hear everything that relates to you, and I would beg of you to write to me more particularly on this very subject, were I not sensible that it would give you a great deal of trouble to ex- plain such matters to me, and in the busy restless state of your mind, to add to your trouble would be unpardonable ; as I am persuaded that nothing would conduce so much to your relief and better health, than relaxation, and ease, and amusement. You may, how- ever, give me a few lines when you have any new experiment or discoveries, such as you mention, to B 10 EXTRACTS FROM communicate ; early knowledge of these things being of some consequence to me. I have thought upon your conversation with Mr. De Luc and am very much flattered by his opinion of me, as I have a very high opinion of his genius and abilities ; nor have I the smallest doubt of his candour, or any suspicion that he would fail to do me ample justice were he to be the editor of what I have done on the subject of heat."' But I assure you I have already prepared a part of that subject for publication, and that I am re- solved next summer to prepare the rest, and give it to the world such as it is. This is my fixed resolu- * As there was afterwards a good deal of discussion in regard to this very point, (on which, however, we must decline entering,) it is but just to the memory of Mr. De Luc to relate the manner in which that was terminated. Professor Robison, in his edition of Dr. Black's Lectures, (%enly accused Mr. De Luc of having published Dr. Black's discovery of latent heat without due acknowledgment, and even of his having claimed it as entirely his own. That accu- sation was fully noticed and commented on in the Edinburgh Review for October 1803 ; the Reviewer at the same time expressing a wish, that some friend of the Genevese philosopher would step forward, to clear him from so foul a charge. Mr. De Luc was at that time on the Continent, and long remained ignorant of the attack which had been made upon him. It is much to he lamented, that he was deprived of the opportunity of receiving a full retractation, by the death of Dr. Robison ; which occurred some months previous to his return to England. But in April 1805, Mr. De Luc addressed a very full explanation of the whole matter to the conductors of the Edinburgh Review, which they published in that Journal for July of the same year ; and " in which," said they, " we think he exculpates himself completely from the imputation " which was rather rashly thrown upon him in Dr. Robison's edition " of Dr. Black's Lectures, and repeated by us in our review of that " publication." Edinburgh Review, vol. vi. p. 501. ED. MR. WATT S CORRESPONDENCE. 1 1 tion, and I am sorry that it is inconsistent with the friendly offer of Mr. De Luc. It gives me also particular concern that I cannot gratify Mr. Keir in this matter, to whom I reckon myself under great obligation. But, perhaps, the in- convenience to both of these gentlemen will not be great, even if they should choose to see what I have to say before they publish. It will delay their pub- lications only some months, or, at most, one year, supposing that they were nearly ready at present. As for what you have done on these subjects, you have certainly a right to communicate it to the pub- lic in what manner you please ; but I think you ought to do it in such a manner as to derive from it some profit, as well as reputation ; and if you choose to make it a part of my publication, I shall certainly think myself bound to give you a share of what I make by it, proportioned to the number of pages which it fills ; and I shall willingly either receive it from you in your own composition, or express it myself as well as I can ; in which case it will be necessary that I pay you a visit, or that we have a meeting somehow or other. Having thus answered the principal part of your letter, I can only, for the present, return you my thanks for the rest, which contains very curious mat- ter, and some of it appearing to me very surprising ; but I have no time to spare just now ; adieu, then, and present my best compliments to Mrs. Watt. I am, my dear Friend, Yours most affectionately, JOSEPH BLACK. 12 EXTRACTS FROM EXTRACT MR. DE LUC TO MR. WATT. Londres, le 31 Jan- 1783. J'ai commence pendant mon court sejour a Paris, ce que j'ai a coeur de faire ; c'est qu'on vous connoisse comme vous le meritez. Je me suis done beaucoup entretenu de vous, et de vos experiences et inven- tions ; et ayant reconnu qu'il importe de publier promptement quelque chose sur les fluides elastiques complexes, soit composes de substances purement graves, et de fluides subtils, j'ai tout arrange pour la production d'une premiere partie experimentale sur cet objet, dans lequel je desire extremement de faire entrer le recit des experiences que vous voulez bien faire en ma presence. Les chimistes de Paris, s'occupent beaucoup au- jourd'hui de la chaleur, et des modifications de ces transmissions ; des grands mathematiciens se joignent a eux ; car la theorie de ces transmissions ou com- munications donnent lieu a de fort beaux problemes. MM. Lavoisier et De La Place entr' autres sont en grand travail et publieront. Enfin il est certain, qu'on commence a fouiller vivement dans les vraies bases de la Physique ; ainsi je vous prie, mon cher Mon- sieur, de vous preter a y cooperer, car vous y pouvez beaucoup. Je finis done, en vous assurant, qu' on ne peut etre avec plus de consideration que je le suis. mon cher Monsieur, Votre tres humble et tres obeissant serviteur. J. A. DE Luc. MR. WATT S CORRESPONDENCE. J 3 EXTRACT MK. WATT TO DR. BLACK. Birmingham, 3d February 1 783. [Mr. Watt, in the early part of this letter, refers to his preceding one of 13th December, and states that he has received no answer, and goes on to say,] which makes me fear that I have been too pre- suming in my request. I hope, however, that you will impute it to the desire I have to set your fame in the light it merits, and which, I think, you have neglected too long. For my own part, I have little ambition or desire to publish any of the few experi- ments I have made ; but I find myself so set upon by many of my friends to do it, that I cannot longer resist their importunities ; though neither my health nor leisure enable me to repeat the experiments with the necessary attention. One thing prompts me more than any other, which is, that we have been so beset with plagiaries, that if I had not a very good me- mory of my doing it, their impudent assertions would lead me to doubt whether I was the author of any improvements on the steam-engine ; and the ill-will of those we have most essentially served, whether such improvements have not been highly prejudicial to the commonwealth. * * -;:- -si- Mr. De Luc writes his book in French, and pub- lishes it at Paris ; and as he is an author who will be read by all men of philosophical learning there, I look upon it as a good opportunity. v- ;:- -:;- Dr. Priestley has been going on with his experi- 14 EXTRACTS FROM merits on turning water into air, and has discovered many facts which seem in some degree contradictory to each other. He finds the mixture of quicklime and water heated in a glass vessel gives no air, only water ; but that water alone, put into the stone- ware retort, gives air in great quantities, even the eighth part of its weight. That olive oil, or oil of turpen- tine, in that earthen retort, produces very pure in- flammable air. That water being put, into a gun- barrel, and distilled over slowly, gives no air ; but on being confined by a cock, and let out by puffs, it produces much air ; which agrees with my theory, and also coincides with what I have observed in steam-engines. In some cases I have seen the tenth of the bulk of the water, of air extricated or made from it. Hoping to hear from you soon, I am, &c. Most affectionately yours, JAMES WATT. EXTRACT MR. WATT TO MR. DE LUC. 3d February 1783. * -::- * * I have written to Dr. Black to try if he would favour us with any communication, but have received no answer yet ; and fear that, as he is now in the mid- dle of his course of lectures, he will use that as a cover to his inertia. I thank you most sincerely for the pains you have taken at Paris in my behalf, and wish to be able to prove deserving of it. ME. WATTS CORRESPONDENCE. 15 DR. BLACK TO MB. WATT. Edinburgh, 13th February 1783. MY DEAR WATT, I received yours of the 3d in- stant, and, by observing the dates, I see that you would receive my answer to your former, two or three days after you wrote it. In my last I acquainted you that it is my fixed resolution to publish next summer. At present, I am so much occupied with the busiest part of my course and other matters, that I cannot do any thing in that business. What you tell me in your last gives me a different notion of Mr. De Luc's intention from that I had formed before. I had imagined that he meant to publish in England, and in the English language. His intention to publish in France, and in the French language, makes a considerable differ- ence ; and if it was in my power to sit down just now and give him an esquisse of what I have done, and mean soon to publish, on heat, I should do it with pleasure ; and I think it is very proper for you to give him a short account of your discoveries and spe- culations, and particularly to assert, clearly and fully, your sole right to the honour of the improvements on the steam-engine. And there is one advantage which will attend this method of publication. Mr. De Luc will naturally mention your discoveries with a pro- per degree of esteem for their value and ingenuity ; whereas, were you to be the first publisher of them yourself, you would do it in such a cold and modest manner, that blockheads would conclude there was nothing in it, and rogues would afterwards, by mak- 16 EXTEACTS FROM ing trifling variations, vamp off the greater part of it as their own, and assume the whole merit to them- selves. I am greatly obliged to you for your philoso- phical news, and I assure you, that the friends you mention here remember you always with the greatest affection and esteem. * * % -si- Farewell, my dear friend, and believe me most af- fectionately yours, JOSEPH BLACK. EXTRACT MB. WATT TO MR. GILBERT HAMILTON. 18th February, 1783. % ft -A % Dr. Priestley finds that when he confines the steam of water in a gun-barrel, and lets it out at intervals, it produces air, but does not if suffered to distil without pressure. He finds that in a copper tube, water treated in the same way produces very little or any air, and has never been able to pro- duce it in glass vessels. While any water remains in the gun-barrel, the air is about the goodness of atmospheric air ; but as soon as all the water is dis- tilled, there comes the common inflammable air. As to my own health, it is as usual ; headaches frequent, listlessness, confusion of head, and inacti- vity constant, or nearly so. I remain, dear Sir, yours affectionately, JAMES WATT. MB. WATT'S CORRESPONDENCE. 17 NOTE LEFT BY DR. PRIESTLEY AT MR. WATTES HOUSE. March, 1783. Dr. Priestley has called to inform Mr. Watt, that by an improvement in his process, he now gets readily 500 ounce measures of air, quite as good as that of the atmosphere, from an ounce of water. He also col- lects the water that escapes through the pores of the retort, and finds that the weight of this and of the air together, are very nearly the weight of the original water. The water so collected serves for making fresh air, as well as fresh water. EXTRACT MR. WATT TO MR. GILBERT HAMILTON. 26th March, 1783. * * * -X- Dr. Priestley makes fixed air from dephlogisticated and inflammable air, in the following manner. He takes mere, precip. ruber. which yields only dephlo- gisticated air; and iron, which yields only inflammable air, and heats them together. They produce only fixed air. He puts dry dephlogisticated air and dry inflammable air into a close vessel, and kindles them by electricity. No air remains, at least if the two were pure ; but he finds on the side of the vessel a quantity of water, equal in weight to the air em- ployed. Yours affectionately, JAMES WATT. EXTRACT MR. WATT TO MR. DE LUC. llth April, 1783. # * * # I have the pleasure of informing you that Dr. c 18 EXTRACTS FROM Priestley, who goes to London soon, has made some more discoveries on the production of air from water. EXTRACT MB. WATT TO DR. BLACK. 21st April, 1783. [In the early part of this letter Mr. Watt acknow- ledges the receipt of two letters from Dr. Black, of 30th January and 13th February 1783 ; which have been already given. Mr. Watt again urges him to publish his discoveries. He states that Mr. De Luc had been staying for ten days with him, making experiments on latent heat ; the result of which was, that the sum of the latent and sensible heat was always equal. He then continues : ] I have not yet begun to put my sentiments into writing. I shall consider it a great honour, to have the little I have been able to add to your doctrines, published along with them. As to any share of the profit, it would be a shame for me to think of selling your doctrines, which I learnt from you ; and all I can do in that way will be but a small recompense for the many obligations you have laid me under. It will give me great pleasure to see you here, and I hope you will put your proposal in practice ; but let me know the time you can come, that I may be dis- engaged as much as possible from worldly concerns. Dr. Priestley has made many more experiments on the conversion of water into air, and I believe I have found out the cause of it ; which I have put in the form of a letter to him, which will be read at the Royal Society, with his paper on the subject. It is MR. WATTS CORRESPONDENCE. 19 briefly this : 1st, By reducing metals in inflammable air, he finds they absorb it, and that the residuum of ten ounces out of the hundred is still the same sort of inflammable air ; therefore inflammable air is the thing called phlogiston. 2dly, When quite dry pure inflammable air, and quite dry pure dephlogisticated air, are fired by the electric spark in a close glass vessel, he finds, after the vessel is cold, a quantity of water adhering to the vessel, equal, or very nearly equal, to the weight of the whole air ; and when he opens the vessel under water, or mercury, it is filled within zee part of its whole contents, which remain- der is phlogisticated air, probably contained as an im- purity in the other airs. 3dly, When he exposes to heat porous earthen retorts, previously soaked in water, or makes steam pass slowly through a red-hot tobacco pipe, the water or steam is converted into air, either entirely or in great part, according as the process is conducted. This conversion does not take place when the water is contained in metalline or glass vessels, and only in a small degree when the water is im- bibed by clay inclosed in a glass vessel ; and the con- version goes on much less rapidly when the earthen vessel is immersed in heated quicksilver. In the deflagration of the inflammable and dephlo- gisticated airs, the airs unite with violence, become red hot, and, on cooling, totally disappear. The only fixed matter which remains, is water; and water, light, and heat, are all the products. Are we not then authorized to conclude, that water is composed of dephlogisticated and inflammable air, or phlogis- ton, deprived of part of their latent heat ; and that 20 EXTRACTS FROM dephlogisticated, or pure air, is composed of water deprived of its phlogiston, and united to heat and light ; and if light be only a modification of heat, or a component part of phlogiston, then pure air con- sists of water deprived of its phlogiston and of latent heat? [Some farther explanations of the phenomena fol- low here, which it does not appear necessary to ex- tract, as they are more fully developed in the letter to Dr. Priestley of 26th April 1783, printed in the Philosophical Transactions.] EXTRACT MR. WATT TO MR. GILBERT HAMILTON. Birmingham, 22d April 1783. K- * -:'r Dr. Priestley has made many discoveries lately in relation to the conversion of water into air; and I have from them made out what water is made of, and what air is made of; which theory I have given him in a letter to be read at the Royal Society, along with the accounts of his discoveries. It is briefly as follows : Facts. 1st, Pure dry dephlogisticated air and pure dry inflammable air fired together, leave no re- siduum, except a small quantity of water equal to their weight. 2d, Pure inflammable air reduces calces of metals, and is absorbed by them. The residuum, after nine- tenths was absorbed, was still inflammable air. 3d, All substances which produce inflammable air, are substances which contain some water firmly united to them, and have some principle which is known to MR. WATT S CORRESPONDENCE. 21 attract phlogiston strongly. (Example nitre, alum, gypsum, calces of metals, &c.) tth, Porous earthen vessels imbibed with water, and slowly heated, produce air, if the process is well performed, equal in weight to the water. Deductions. Pure inflammable air is phlogiston itself. Dephlogisticated air is water deprived of its phlo- giston, and united to latent heat. Water is dephlogisticated air deprived of part of its latent heat, and united to a large dose of phlogis- ton. The acid of the neutral salts take the phlogis- ton of the water, and convert it into something else ; and the fire gives the latent heat. [Mr. Watt's letter to Dr. Priestley, dated 26th April 1783, gives the statement of his theory; to be read at the Royal Society, at the same time as Dr. Priest- ley's paper, containing the experiments upon which that theory was in great measure founded. Dr. Priestley's paper was addressed by him to Sir Joseph Banks on the 21st April 1783, and was read on the 26th June 1 783. Dr. Priestley went to London about the former period, and had Mr. Watt's paper sent to him there ; as appears from the following letter.] EXTRACT MR. WATT TO MR. DE LUC. Birmingham, 26th April 1783. * * -5C- * I fancy that before you receive this, you will have 22 EXTRACTS FROM seen Dr. Priestley, and heard the account of his new discoveries in the air way, and of my attempt to give a reason or theory for the conversion of water into air. Lest you should not have seen him, I shall just mention what I attempt to prove from his experi- ments. 1st, That dephlogisticated air is composed of wa- ter deprived of its phlogiston, and united to latent or elementary heat and light. 2dly, That water is composed of pure air, deprived of a great part of its latent heat, and united to phlo- giston. 3e%, That nitre and other salts attract the phlo- giston from water; and, by the assistance of heat, convert it into air. Uhly, That clay vessels attract the phlogiston from water, and transmit it from particle to particle, until it comes to the outside, where they give it to the external air. 5thly, That air attracts phlogiston from clay, par- tially from the acid of nitre, and perfectly from vi- triolic acid. These seem bold propositions, but I think they follow from the present state of the experiments ; and, if I were at leisure to write a book on the sub- ject, I think I could prove that no experiment hither- to made contradicts them, and that the greater num- ber of experiments affirm them. Since the Doctor's departure, I have observed some inaccuracies of style which I wish to correct (if the Society should do me the honour to publish it) and also some ambi- guity concerning the decomposition of nitrous air, ME. WATT'S CORRESPONDENCE. 23 which I have removed, and shall send him a cor- rected copy in a day or two. EXTRACT MR. WATT TO MR. SMEATON. 27th April 1783. * * * -s;- By the help of Dr. Priestley's experiments, I have attempted to demolish two of the most ancient ele- ments (air and water) ; a third, (fire), has been de- stroyed for some time, but in return we have made two or three more. For particulars I refer you to a letter of mine to Dr. Priestley, which he was to do me the honour to read to the Royal Society. MR. WATT TO DR. PRIESTLEY IN LONDON. Birmingham, 28th April 173. DEAR SIR, Having discovered some inaccuracies in language, and some inconsistencies in the theore- tical essay I sent you, I have made out another copy, which I shall be obliged to you to put in the place of that formerly sent you, and to return the former to me when you return here. Dr. Withering has read it, and approves of it. I have also shewn it to Mr. Keir, who thinks it ingenious, but adheres to his former opinion, that some acid enters into the com- position of air; which theory I cannot make to ac- count for the phenomena in question. As to my- self, the more I consider what I have said, I am the more satisfied with it, as I find none of the facts re- 24 EXTRACTS FROM pugnant. I shall be glad to hear from you at your convenience, and remain, dear Sir, yours sincerely, JAMES WATT. EXTRACT MR. W-ATT TO MR. FRY OF BRISTOL. 28th April, 1783. -::- # -5? * Dr. Priestley, as you observe, converts water into air, and air into water, and I have found out the reason of all these wonders, and also what air is made of, and what water is made of; for they are not simple elements. I have written a paper on the sub- ject, and sent it with Dr. Priestley's to the Royal Society. It is too long to give you even an abstract of it, but if you will forgive me the reasoning, I will add the receipt below for making both these elements. To make Water. R. Of pure air and of phlogiston Q.S., or if you wish to be very exact, of pure air one part, of phlogiston, in a fluid form, two parts, by measure. Put them into a strong glass vessel, which admits of being shut quite close ; mix them, fire them with the electric spark ; they will explode, and throw out their elementary heat. Give that time to escape, and you will find the water, (equal in weight to the air), adhering to the sides of the vessel. Keep it in a phial close corked for use. To make Air. Take pure water Q. V., deprive it of its phlogiston by any practicable method, add elementary heat Q.S. and distil. You will obtain pure air, to be pre- served as above. MR. WATT S CORRESPONDENCE. 25 The ingredients of air are water deprived of its phlogiston, and united to much elementary heat ; and the ingredients of water are pure air and phlogiston, united in a state of ignition, and deprived of much elementary heat. Now, I have given you somewhat to ruminate upon, and my head aches much. I remain, Dear Sir, your obliged friend, JAMES WATT. DR. PRIESTLEY TO MR. WATT. London, 29th April 1783. DEAR SIR, Behold with surprise and with indig- nation the figure of an appara- tus that has utterly ruined your beautiful hypothesis, and has rendered some weeks of my labour in working, thinking, and writing, almost useless. In order to ascertain the effect of heating the moist clay in an earthen retort, on the external air, I put the retort within a glass receiver, standing in a basin of water, and with good luting made the junc- ture air-tight at a. Then throwing the heat of Mr. Parker's excellent lens upon the bulb, within the re- ceiver, air was collected very copiously at b, and the water ascended within the receiver. This looked like a phlogistication of the internal air ; but the process went on till more than three-quarters of the internal D 26 EXTRACTS FROM air disappeared, and I believe it would all have gone farther, if the water had not almost covered the bulb of the retort. The process then stopping, I found I had got about as much air as was missing in the receiver It was, however, a little better than the air of the atmos- phere, and the remainder of the air within the re- ceiver was a little worse, but only a mere trifle. It is, therefore, a new hydraulic engine, but on what principle it acts, I know not. It is more within your province than mine. You must convene the Club,""" and give me your joint opinion. Before this experiment I had fully satisfied Mr. Kirwan of the reality of the conversion. He, and many others, saw the simple experiment (with the retort in the fire) with astonishment. With my best respects to Mrs. Watt, and also all our Club, I am, Dear Sir, yours sincerely, J. PRIESTLEY. P.S. I have just received yours. MR. WATT TO DE. PRIESTLEY. Birmingham, 2d May 1783. DEAR SIR, I received yours of the 29th to-day. I deny that your experiment ruins my hypothesis. It is not founded on so brittle a basis as an earthen retort, nor ou its converting water into air ; I founded * The Lunar Society ; so called because the members met every month at the full of the moon. See Translation of Arago's Eloge, p. 93. ED. MR. WATT'S CORRESPONDENCE. 27 it on the other facts, and was obliged to stretch it a good deal before it would fit this experiment. I am not, however, quite clear that even this new experiment overturns any thing ; (not even that great law of Nature, which says, that all fluids fly from the side on which they are most pressed, towards that where they find least resistance.) I say, perhaps, (but I say it feebly) the air of the receiver was changed into fixed air, and absorbed by the water in the receiver. Let it be tried what happens when the solar receiver is filled with dephlogisticated air what happens when filled with fixed air and what with phlogisticated. Will you find these different species unchanged in the second receiver ? But if, after all, this should account for the production of common air from water, where did the dephlogisticated air come from, which was produced by spirit of nitre and by vitriolic acid passing through the red-hot tobacco pipe, or the inflammable air produced from spirit of wine, and oils, or the air from the vola- tile alkali 1 Some of these, or indeed any of them, could not be got in such quantities from the atmo- sphere. I maintain my hypothesis, until it shall be shewn that the water, found after the explosion of pure and inflammable air, has some other origin; nor shall I believe that air is a child of acids, or rather a modi- fication of them, until such acids can be found after the decomposition of it. I have many experiments to propose to you to help to bring out the truth, which I think is certainly to be got at, and a fair analysis made of the two fluids. Qucere, does the 28 EXTRACTS FROM imbibed water remain in the solar receiver, or is it impelled into the other in the form of steam ? I have read Scheele since I saw you, and found several things to confirm my hypothesis. I shall take the first opportunity to communicate your letter to the Club, but in the meantime hope to be furnished with some more facts from you, with any philosophical news the town produces at pre- sent. I remain, Dear Sir, Yours sincerely, JAMES WATT. MR. DE LUC TO MR. WATT. Londres, le 8 Mai 1783. Bien oblige, mon cher Monsieur, de votre bonne lettre du 26me Avril. Elle m'a fait grand plaisir par le succes de vos machines ;* et elle m'en auroit fait beaucoup par vos idees chimiques, si le Dr. Priestley lui-meme ne croyoit pas avoir renverse, d'un seul coup, toutes ses experiences precedentes par une nouvelle, du moins quant a la conclusion qu'il faisoit de I' Air. " We are undone" me dit il, en entrant un matin dans ma chambre. Et la dessus il m'expliqua, ce que vous savez deja sans doute, qu'ayant lutte sa cor- nue de terre en haut d'un recipient plein d'air, trem- pant dans le mercure, et ayant fait tomber sur elle le foyer de la lentille de Mr. Parker, il avoit vu feau sortir de sa cornue en dehors, et couler le long * Rotative Steam-Engines. ED. MR. WATT'S CORRESPONDENCE. 29 des parois du recipient, et en meme terns le mercure y raonter ; preuve que 1'air passoit de quelque ma- niere dans la cornue, et alloit par son col dans le Vase ou il plongeoit. Qu'au lieu de 1'air atmo- spherique, il avoit mis de 1'air inflammable autour de sa cornue dans le recipient ; que 1'eau etoit venue prendre la place de cet air, qu'il avoit recueilli pur par le col de la cornue. Je vous marque toujours cela, mon cher Monsieur, en cas que le Dr. n'eut pas pu en ecrire a Birming- ham, et pour que vous y reflechissiez de votre cote. EXTRACT MR. WATT TO MR. DE LUC. Birmingham, 18th May 1783. Your kind letter of the 8th I received last Sunday, and would have answered sooner, but have been de- molished for a whole week by a fever and sore throat, from both which I am now recovered. I do not see Dr. Priestley's new experiment in the same light that he does. It does not disprove my theory; it only shows that that experiment does not require it, or rather does not admit the application of it. My assertion was simply, that air was water deprived of its phlogiston, and united to heat; which I grounded on the decomposition of air by inflamma- tion with inflammable air, the residuum, or product of which, is only water and heat : 2dly, on the facts, that in all cases wherein dephlogisticated air is ob- tained by distillation, some one of the principles has a great attraction for phlogiston, and that water is 30 EXTRACTS FROM also contained as another constituent part of these substances. The water remaining after inflammation is not in the least acid, which must be the case if the air was formed of the acid part of the substances. In most of the experiments, the substances from which the air was detached become phlogisticated, the metallic calces are reduced, and the vitriolic acid is converted into vitriolic acid air, which is known to be one of the combinations of that acid with phlogiston. When you calcine metals in pure air, water is al- ways produced. There are many other facts which coincide in furnishing similar proofs. EXTRACT MR. WATT TO DR. BLACK. Birmingham, 23d June 1783. * * -;c- -;;- I wrote you last month, * giving you an account of some curious experiments of Dr. Priestley's, and a theory I had formed to account for the production of dephlogisticated air ; which I supposed to be water deprived of phlogiston, and united to heat, and men- tioning that I had written a short paper on this sub- ject, to be presented to the Royal Society. Since that time I have not had the pleasure of hearing from you. I have withdrawn my paper from the Royal So- ciety, on account of an ugly experiment the said Dr. Priestley tried at my desire, and which renders the * Mr. Watt alludes to his letter of 21st April 1783. ED. MR. WATT'S CORRESPONDENCE. 31 theory useless in so far as relates to the change of water into air by means of porous earthen vessels. [Mr. Watt here enters into the details of the experi- ment, for which see Dr. Priestley's letter of 29th April, p. 25.] I have not given up my theory, though neither it, nor any other known one will account for this experiment. EXTRACT MB. WATT TO MR. DE LUC. Birmingham, 26th June 1783. 5V -::- -s:- % Dr. Priestley, by using very pure nitre, has obtain- ed 787 ounce measures of dephlogisticated air from two ounces of nitre, measure of the test with two equal measures of nitrous air, 1.25. I have examin- ed the residuum which he sent me of a former dis- tillation of nitre, and found that the greatest part, say four-fifths of the acid, still remained united to the alkali; but that part of it was highly phlogisticated, and could be separated in the form of nitrous acid, by the muriatic acid, or even by vinegar, neither of which would have acted upon nitre in its common state. I have distilled the nitre of magnesia, and also the calcareous nitre ; and I have obtained again, as near as I could determine, all the acid, besides a quantity of pure air. The acid in these cases comes over highly phlogisticated, however much it might be freed from that principle beforehand. 32 EXTRACTS FROM EXTRACT MB. WATT TO DR. BLACK. Birmingham, 25th September 1783. DEAR DOCTOR, I have long expected the pleasure of a letter from you, but have had none, except a few lines by the Marquis de Biancourt.* Mr. de Luc, who is here, desires his compliments to you, and has sent along with this, MM. Lavoisier and La Place's Me"moire upon heat, which is a very weh 1 written paper, though not free from objections. It is a present to you from the authors ; who, I think, might have done you the justice to have mentioned your name in it ; but this, and much more, you bring on yourself by not publishing your discoveries. I think, so far as I can see into the matter, that Dr. Irvine's doctrines, and Dr. Crawford's, of capacity, will fall to the ground, and your original theory of latent, or essential heat, be established. * -;:- -:i- -x- [Mr. de Luc paid a visit to Mr. Watt in Septem- ber, October, and November, 1783, and Mr. Watt appears then to have determined to send a revised copy of his memoir, through him, to the Royal So- ciety. On the 25th November he writes to Mr. de Luc that he was then engaged upon it ; and on the 30th November he writes, that he had sent it the day before.] EXTRACT MR. WATT TO MR. KIRWAN IN LONDON. Birmingham, 2Cth Nov. 1783. *- * * # I have lately tried some farther experiments on * Quaere, Liancourt ? MR. WATT'S CORRESPONDENCE. 33 dephlogisticated air. I took 1 oz. pure nitre, and distilled from it, in a coated flint glass retort, 50 oz. measures of air. The air was received in 50 oz. of water, which became slightly acid. The air smelt of phlogisticated nitrous acid, and I could not free it from the smell by washing. The residuum was alkaline, but on being dissolved in the receiving wa- ter, the mixture was nearly neutral, and became per- fectly so, by the addition of 10 grains of a dilute nitrous acid 105 grains of which contained the acid of 60 grains of nitre consequently the 10 grains contained about 2 grains of real nitrous acid, by your experiments. There was therefore 34 oz. mea- sures""" of air produced, and only 2 grains of acid lost. I attribute part of the loss to the pungent gas mixed with the air, and part to some of the alkali of the glass, which was set free by its solution in the nitre. I could not determine the loss of weight in the nitre and retort, because some of the coating stuck too fast to be got off, particularly as the retort cracked into a hundred pieces in cooling. This is the fourth experiment which has given nearly the same results ; but I shall go on with some variations. The experiments of yours which I was comparing, were those on the quantity of phlogiston in fixed air. You make it 14 per cent., and MM. Lavoisier and La Place, 9 per cent. I am now completing my pa- per on those subjects, at least as far as my present facts permit. I shall send it to Mr. De Luc when * It will be seen from Mr. Watt's next letter to Mr. Kirwan, that 34 oz. measures were here a mistake for 34 grains' weight. ED. E 34 EXTRACTS FROM done, when I shall be obliged to you to read it. 1 have discovered a more accurate test of alkalis and acids than Litmus ; of which I shall send you some if it continues to please me. EXTRACT MK. KIRWAN TO MR. WATT. London, 29th Nov. 1783. * * -X- * As to your experiment on the decomposition of nitre I shall make some remarks. 1st, From an oz. of nitre you obtained only 50 oz. measures of air, equal to 94.75 cubic inches. But Dr. Priestley ob- tained, from the same quantity of nitre, from 393 to 406 oz. measures. How is this to be explained 1 It is probable he operated in an earthen, as you have done in a glass retort. The greater part of the nitre was therefore undecomposed in your experiment, and in effect your 50 oz. measures, if consisting of pure dephlogisticated air, weighed but 39,795 grains. You cannot be sure that the whole of the alkalized part of their residuum was saturated by 2 grains of real nitrous acid, because part of the alkali united to the silex of the glass, and, consequently, you can- not infer that the dephlogisticated air should, ac- cording to me, proceed from 2 grains of nitrous acid ; but if, indeed, you had obtained after the sa- turation 1 oz. of pure crystallized nitre, then you might be sure of the inference ; but this, I believe, will not happen. That dephlogisticated air contains a large proportion of water, I do not deny. Why ME. WATT'S CORRESPONDENCE. 35 you infer that 2 grains of real acid afford 34 oz. measures* of air, I do not understand. As Mr. Lavois- ier does not acknowledge the existence of phlogiston, I pray you tell me why you infer, that he says fixed air contains 9 per cent, of it? It is probable he says some- thing tantamount ; but, as I am now busied about mi- neralogy, I do not recollect where. I shall be much obliged to you for informing me of your new test of acids and alkalis ; and am, with great esteem, &c., E. KIRWAN. EXTRACT MB. WATT TO MR. DK LUC. Birmingham, Nov. 30, 1783. # * * -;;- I was at Dr. Priestley's last night. He thinks, as I do, that Mr. Lavoisier, having heard some imperfect account of the paper I wrote in the Spring, has run away with the idea, and made up a memoir hastily, without any satisfactory proofs. How that may be, I cannot take on me to say ; but if you will read the 47th and 48th pages of Mr. De La Place's and h ; s Memoir on Heat, you will be convinced that they had no such ideas then, as they speak clearly of the nitrous acid being converted into air. I, therefore, put the query to you of the propriety of sending my letter to pass through their hands to be printed ; for even if this theory is Mr. Lavoisier's own, I am vain enough to think that he may get some hints from my letter, which may enable him to make experiments, and to * Mr. Watt has here written on Mr. Kirwan's letter, " This is a mistake." ED. 36 EXTRACTS FROM improve his theory, and produce a memoir to the Academy before my letter can be printed, which may be so much superior as to eclipse my poor perform- ance, and sink it into utter oblivion ; nay, worse, I may be condemned as a plagiary, for I certainly can- not be heard in opposition to an Academician and a Financier. But, after all, I may be doing Mr. Lavoisier injustice. I see it, on the one hand, so dim- cult to satisfy those nice chemists, and, on the other hand, so difficult to be allowed even the honour of the discovery, that I am nearly discouraged, either from publishing at all, or trying any more experi- ments ; as it seems to be losing my labour and pro- curing myself disquiet. EXTRACT MR. WATT TO MR. KIRWAN. Birmingham, 1st Dec. 17B3. I would not delay a minute to answer such part of your objections as I can. Imo, I only took from the ounce of nitre 50 ounce measures of air, in order to prevent the action of nitre on the retort, which would have been sufficient to destroy it, had I used more heat ; as it was, that action was very trifling. I have no reason to think that my nitre would have yielded less air than Dr. P.'s, if the vessel could have retained it, and the heat had been raised to the same degree ; the greater part of the nitre was, therefore, undecomposed. 2do, I allow that the alkali of the nitre did act upon the glass ; but, as glass is com- posed of alkali as well as earth, and the earthy mat- ter was precipitated, I rather suppose that the nitre MR. WATT S CORRESPONDENCE. 37 was made more alkaline, by the addition of the alkali of that part of the glass which it decomposed. 3fio, I did not attempt the obtaining the nitre in a crys- tallized form, because the quantity of water was large, and the nitrous acid, or at least part of it, was a little phlogisticated, and would have left the alkali during the evaporation. I shall, however, attempt it the next experiment I try. kthly, All the inference I draw from your experiment is, that the acid of 5.7 grains nitre is about two grains, and that quantity of acid is all that was wanting to saturate the nitre of my experiment, in which 34 grains weight of de- phlogisticated air was produced. If I wrote 34 ounce measures, it was a mistake ; I meant 34 grains; which is the weight I make the dephlogisticated air at the specific gravity of r ^ of that of water ; whether that specific gravity is right or not I cannot say, as I have never weighed it. Whether M. Lavoisier acknowledges phlogiston yet, I cannot say ; but in the 45th page of his and M. La Place's memoir on heat, they say that 3.3167 ounces of dephlogisticated air, formed 3.6715 of fixed air; so that to 9 parts of de- phlogisticated air, was added 1 part of a certain prin- ciple furnished by the charcoal, which was the basis of fixed air. Now, I infer that this principle was no other than phlogiston. By an attentive perusal of the same passage, you will find there is f of an ounce of charcoal, of which they give no account. What became of it? For only J ounce entered into the composition of the fixed air, and 1 ounce was consumed. Mr. Lavoisier has read a memoir, opening a theory 38 EXTRACTS FROM very similar to mine, on the composition of water ; indeed, so similar, that I cannot help suspecting he has heard of the theory I ventured to form on that subject, as I know that some notice of it was sent to France. He does not seem, however, to have been more fortunate in his proofs of it than I have been. * EXTRACT MR. DE LUC TO MR. WATT. Windsor, 7th Dec. 1783. v- -is- ?:- * J'ai reu tout a la fois votre me"moire en deux pa- quets, et la lettre qui 1'a sum. # * * * Je ne puis pas encore vous dire precisement ce que je pense des details ; le language chimique ne m'etant pas bien familier. J'en jugerai mieux en traduisant ; et, chemin faisant, je noterai les questions que je voudrois vous faire, pour aj outer quelques petits eclair- cissemens aux endroits ou d'autres physiciens, non chymistes pratiques, pourroient etre arretes comme moi. Mais, quant a 1'ensemble, j'ose vous donner courage. II y a un ensemble de faits, si beaux, si concluans, qui me plaisent tant, oui tant, que si votre systeme n'est pas absolument la verite, il en est bien pres ; et c'est beaucoup, dans un moment comme celui-ci. J'ose esperer qu'entre nous deux nous met- trons les tetes en travail. x- * * * MR. WATT'S CORRESPONDENCE. 39 EXTRACT MR. KIRWAN TO MB. WATT. London, 13th Dec. 1783. * # -i'c I am still of opinion that much of the alkali re- mains with the silex of the glass, as you know that flint glass contains only iVth of its weight of alkali, and I'o-ths of its weight of silex, which is capable of combining with much more alkali. I readily allow that the acid of 5.7 grains of nitre is only about two grains, but surely 34 grains of dephlogisticated air cannot proceed from 5.7 of nitre. Mr. Lavoisier certainly learned your theory from Dr. Blagden, who first had it from Mr. Cavendish, and afterwards from your letter to Dr. Priestley, which he heard read, and explained the whole mi- nutely to Mr. Lavoisier last July.* This he autho- rized me to tell you. As for Mr. Lavoisier's conver- sion of dephlogisticated air into fixed, by charcoal, it is too inaccurate to rely on. He does not tell us how good his dephlogisticated air was, nor does he take notice that charcoal itself contains in general much fixed air. I am much obliged to you for your test liquor, and shall send for it immediately. I am, Sir, with great esteem, &c. &c., R. KIRWAN. EXTRACT MR. WATT TO MR. DE LUC. Birmingham, 30th Dec. 1783. * * * * I should have written to you before now, on the * A mistake of Mr. Kirwan's for June. ED. 40 EXTRACTS FROM subject of dephlogisticated air, but, though I have tried several very laborious experiments, I have not obtained any thing more satisfactory than what I have already sent you ; and think the matter, in so far as relates to its production from nitre, still extremely uncertain, and I have great doubts of the propriety of publishing any more than what is interwoven in your letters to M. De La Place. The following is an extract from a letter from Mr. Kirwan to me. [Here follows a copy of that part of Mr. Kirwan's letter of 13th December, given above, p. 38, commencing " Mr. " Lavoisier," and ending " fixed air."] You see from the above, that it is possible for a philosopher to be disingenuous. For Mr. Lavoisier had heard of my theory before he formed his, or before he tried the experiment of burning dephlogis- ticated and inflammable air together, and saw the product was water. As to the proofs he pretends to give of his hypothesis, I am pretty certain they are not facts. He has, therefore, run away with a thing he does not understand. I will not imitate him in that ; for if another experiment or two I mean to try do not give more certainty, I think it will be better to content myself with opening the theory, without adducing any controvertible experiments. EXTRACT MB. DE LCC TO MR. WATT. Londres, le 9" Fcvr., 1784. K V: % -/- Je me persuade, que cette doctrine des capacites, prises pour unique cause des phenomenes de chaleur ME. WATTS CORRESPONDENCE. 41 produite ou perdue, est une chimere, fondee sur des illusions. II en est bien autrement de votre systeme, mon cher ami ; car au contraire, plus j'y reflechis, plus je me persuade que vous avez trouve la verite, et qu'il ne faut que du terns et de la patience, pour le deter- miner plus surement, et lever les objections. Prenez done courage, je vous en prie ; ne vous laissez pas degouter par les difficultes. Si vous ne trouvez pas encore des faits decisifs, aucun fait ne vous est con- traire ; et ce qui semble d'abord ne pas repondre a vos idees, dans les experiences que vous avez faites, peut s'expliquer de bien des manieres. * % # -;;- Malgre ce que vous marque Mr. Kirwan, je ne saurois accuser MM. Lavoisier et La Place de vous avoir copie ; non seulement parcequ'ils ne parlent point comme vous, mais parcequ'en fait, ce qu'ils disent aujourd'hui, Mr. De La Place me 1'a ecrit dans le mois de Juin. Voici d'abord ce qu'ils me di- soient dans une lettre du 28me; "nous avons repete*, " ces jours derniers, Mr. Lavoisier et moi, devant " Mr. Blagden et plusieurs autres personnes, 1'expe- " rience de Mr. Cavendish sur la conversion en eau des " airs dephlogistique et inflammable, par leur com- " bustion ; avec cette difference, que nous les avons " fait bruler sans le secours de 1'etincelle electrique, " en faisant concourir deux courants, 1'un de Tair pur, " 1'autre de Tair inflammable. Nous avons obtenu " de cette maniere plus de 2^ gros d'eau pure, ou " au moins qui n'avoit aucun caractere d'acidite, et " qui etoit insipide au gout ; mais nous ne savons F 42 EXTRACTS FROM " pas encore, si cette quantite d'eau represente le " poids des airs consumes ; c'est une experience a " recommencer avec toute 1'attention possible, et qui " me paroit de la plus grande importance." Vos queries sur un objet aussi obscur, et en meme terns si important, auront le caractere de celles de NEWTON. EXTRACT ME. WATT TO MR. DE LUC. Birmingham, 22d Feby. 1784. # * % # I must still differ from you in regard to Mr. Lavoisier's knowledge of my theory before he even made his experiments ; because, according to Mr. La Place's letter to you, Dr. Blagden was present when those gentlemen tried the experiment ; and, as Dr. Blagden had not only heard of my theory, but had read with attention the paper which I drew up for the Royal Society, it was certainly natural for him to mention it ; and I can easily conceive Mr. Kirwan, or Dr. Blagden himself, writing, or saying, July for June. Of this matter you can easily satisfy yourself from Dr. Blagden. The matter is not, how- ever, of much importance, though it somewhat takes off from the new gloss of my idea, and may with many lose me the honour of it, if it can convey any, which I somewhat doubt of. EXTRACT MR. DE LOC TO MR. WATT. Londres, le l er . Mars, 1784. * * * -;: Mr. Cavendish a fait lire un long memoire a la MR. WATT'S CORRESPONDENCE. 43 Socie"te Royale, ou il traite a fond le sujet de la com- bustion des deux airs, par des experiences et des raisonnemens. II est fort contraire a la doctrine des capacities ; ainsi il ne soutient surement pas ce systeme. Mais il est contraire aussi, a celle du feu latent a notre mauiere, parcequ'il ne conceit \&chaleur, que comme un mouvement dans les particules propres des corps, &c., doctrine que vous connoissez. Dans ce memoire il nie la formation d'aucun air fixe dans la combustion, et soutient que celui qu'on trouve apres la combustion, est sorti des substances combus- tibles. Le Dr. Blagden, son ami, de qui je tiens ces details, etoit de cette opinion, malgre un autre me- moire de Mr. Kirwan, lu aussi deja a la Socie"te Royale, dans lequel il refute cette partie du memoire de Mr. Cavendish. * * * Je ne vais guere a la Socie'te' Royale, ainsi je n'ai pas ou'i la lecture de ces deux memoires ; mais j'ai de- mande a Mr. Cavendish la permission de voir le sien, et je compte de voir les deux dans quelques jours ; apres quoi je vous ecrirai. Etant ici de ma lettre, jai reu le memoire de Mr. Cavendish, et j e 1'ailu! ! .... Attendez-vous a quel- que chose qui vous etonnera des que je pourrai vous ecrire. Mais ce ne pourra etre que dans quelques jours ; car j'aurai beaucoup de travail a faire pour vous rendre compte de ce que j'ai lu et que je relirai. .... En attendant ne dites rien a personne Je vous quitte pour y travailler ; sansfafon. J. A. D. L. En bref, on expose et prouve votre systeme, mot pour mot, et on ne dit rien de vous. 44 EXTRACTS FROM EXTRACT MR. DE LUC TO MR. WATT. Londres, commence le I" Mars, termine le 4 do. 171J4. Dans ma lettre qui va a la poste pour vous, mon cher Monsieur, je n'ai laisse en arriere qu'un article de votre derniere, et c'est celui qui regarde le Playiat. Je ne puis point non plus etre d'accord avec vous, sur ce que MM. Lavoisier et De La Place vous out copie. Je conviens qu'ils le pouvoient, parceque le Dr. Blagden etoit a Paris lorsque Mr. De La Place m'ecrivit la lettre dont je vous ai fait mention. Mais, je le repete, ce qu'il dit dans cette lettre, et ce qu'ils ont dit de plus dans leur m&noire posterieur ; n'est point de tout votre systeme ; ce n'est absolu- ment que 1'expression du fait tout pur ; ainsi n'en prenez absolument aucun souci. Mais ce qui est tout autrement clair, precis, eton- nant, est le memoire de Mr. Cavendish. Nospropres termes, dans votre lettre d'Avril au Dr. Priestley, donne pour quelque chose de nouveau, par quelqu'un qui doit connoitre cette lettre, connue de tons les membres actifs de la Societe Royale : du Dr. Blag- den surtout, (puisqu'il dit en avoir parle a MM. La- voisier et De La Place), qui a eu pleine connoissance du memoire de Mr. Cavendish avant qu'il fut lii a la Societe Royale, et a sa lecture ; et qui m'en a entretenu, comme je vous le disois dans ma prece- dente, moi qu'il sait etre votre ami zele". Mais gar- dons tout cela entre vous et moi. Nous sommes trop occupes, 1'un et 1'autre, pour avoir des tracasseries, et par consequent pour entamer rien de polemique, ni de bouche, ni par ecrit. Je vous re"ponds d 'assurer votre date; cela me convient mieux a moi, comme JIR. WATT'S CORRESPONDENCE. 45 tiers, qu'a vous-meme : et pour vous, tout comme pour moi, je le ferai sans heurter personne de front ; ce serout les consequences des faits simples, qui feront justice. L'essentiel done, est que vous preniez courage, sur votre propre terrein ; et je crois que le memoire de Mr. Cavendish contribuera a vous en donner. Ce memoire ayant e'te lue a la Societe Royale, et etant sans doute destine a l'impression, je ne me fais aucun scrupule de 1'extraire pour vous et pour moi. J'ecri- rai en Fra^ois ce qui ne sera qu'extrait, et en Anglois ce qui sera copie litteralement. [Here follows a long transcript, with remarks on sundry parts of Mr. Cavendish's memoir.] Tel est, mon cher Monsieur, 1'essentiel de ce me- moire, dans lequel le fond de votre systeme se trouve en propres termes, quoiqu'il y manque 1'addition du FEU. Maintenant, reflechissons entre nous sur ce singulier eVenement, pour ne prendre aucune reso- lution a la legere. II est encore possible que Mr. Cavendish ne croit pas vous piller, quelque probable qu'il soit qu'il le fait. Son caractere semble plaider d'abord pour la premiere opinion ; et voici copie d'un billet de sa part, en re- ponse au mien, qui semble fortifier cette idee. " Mr. " Cavendish, &c. . . . Saw Mr. Planta yester- " day, and informed him that he had no objection to " his lending the paper to Mr. de Luc, and is glad " to hear that he is preparing a work on these sub- " jects." C'est par le Dr. Blagden qu'il sait cela ; le Dr. Blagden sait ma liaison intime avec vous ; com- 46 EXTRACTS FROM ment 1'un et 1'autre, s'ils pensoient seulement a vous, en exposant ce systeme, verroient ils tranquille- ment ce memoire passer sitot entre mes mains ? L'explication la plus naturelle que je puisse dormer de ce paradoxe, est, que lors de votre lettre au Dr. Priestley en Avril dernier, comme elle etoit destine e a expliquer un fait pretendu, dont 1'equivoque venoit d'etre trouvee, on n'y fit pas attention. Mais que quelque ide"e vague peut en etre reste dans 1'esprit de Mr. Cavendish, qui ensuite aura germe et produit ce m&noire. Alors done, il est encore plus certain, que MM. Lavoisier et De La Place ne vous ont pas pille ; et que tout ce que le Dr. Blagden a pu leur dire la-dessus, est les proce'de's pour la combustion des deux airs, et 1'eau qui en resultoit, sans parler de votre systeme. Car s'il connoissoit reellement votre systeme, il faudroit supposer et a lui, et a Mr. Caven- dish, un caractere que personne de ma connoissance ne leur suppose. Maintenant que faut il faire 1 II va bien sans dire, que dans mon ouvrage je ferai 1'histoire de votre de- couverte, avec sa date et celles de vos autres lettres sur ce sujet ; et, si vous vous contentez de cela, je n'ai pas de doute, que vous n'ayez toute la gloire de 1'invention sans autre appareil. Je vous le conseil- lerois presque ; vu, que dans votre position, de tirer de vos decouvertes des consequences pratiques pour votre fortune, il faut eviter de vous faire des jaloux. Si toute fois vous vouliez que cette affaire s'eclair- cit plutot, je crois que le plus court seroit que je re- misse de votre part une lettre au Chevalier Banks, par laquelle vous lui diriez, qu'apprenant que la Socie'te' MR. WATT S CORRESPONDENCE. 47 Royale est occupee des experiences sur fair, vous le priez, s'il le juge a propos, d'y faire lire deux lettres ; 1'une que vous ecrivites au Dr. Priestley a telle date, et 1'autre a moi a telle date, (celle que je dois tra- duire) comme ayant beaucoup de rapport au sujet traite. Je ne crois pas qu'il peut refuser cela ; et per- sonne n'auroit a s'en plaindre. Soit que vous preniez ce dernier parti, ou le pre- mier, sachez, s'il vous plait, du Dr. Priestley, si votre lettre d'Avril fut lue a la socie'te' assemblee, ou de qui au moms elle fut connue. Je sais qu'elle fut connue ; et qu'on en rit, au cause de la circonstance que vous expliquiez la dent d'or ; et que je dis alors, rira bien qui rira le dernier. J'ai le memoire de Mr. Kirwan. II est fort in- teressant, comme vous pensez bien ; et il n'y a rien centre nous ; meme il est pour nous : je vous en en- verrai un extrait, comme de celui de Mr. Caven- dish ; mais ne parlez, s'il vous plait, ni de 1'un, ni de 1'autre. Seulement vous pouvez bien dire au Dr. Priestley, en lui demandant les circoustances ci- dessus, que les deux memoires ont e"te" lu, et leur sujet general. Peut-etre lui-meme en sait-il quel- que chose, et vous en parlera-t-il le premier. ME. WATT TO MR. DE LUC. Birmingham, 6th March, 1784. DEAR SIR, You have laid me under a debt which I cannot repay, at least at present. I mean I can- not pay your two long and kind letters in like coin ; 48 EXTRACTS FROM and, perhaps, may never pay them at all. I mean, however, to be in London next week, where your de- mands on my person shall be answered, and to which time I must refer particulars, having much business as disagreeable, but of another nature than the plagiarism of Mr. C., pressing hard upon me. On the slight glance I have been able to give your extract of the paper, I think his theory very differ- ent from mine ; which of the two is the right I can- not say ; his is more likely to be so, as he has made many more experiments, and, consequently, has more facts to argue upon. I by no means wish to make any illiberal attack on Mr. C. It is barely possible he may have heard nothing of my theory ; but, as the Frenchman said when he found a man in bed with his wife, " / sus- " pect something." As to what you say of making myself " des " jaloux," that idea would weigh little ; for, were I convinced I had had foul play, if I did not assert my right, it would either be from a contempt of the mo- dicum of reputation which could result from such a theory ; from the conviction in my own mind that I was their superior ; or from an indolence, that makes it easier to me to bear wrongs, than to seek redress. In point of interest, in so far as connected with money, that would be no bar; for, though I am de- pendent on the favour of the public, I am not on Mr. C. or his friends ; and could despise the united power of the illustrious house of Cavendish, as Mr. Fox calls them. . You may, perhaps, be surprised to find so much MR. WATT'S CORRESPONDENCE. 49 pride in my character. It does not seem very com- patible with the diffidence that attends my conduct in general. I am diffident, because I am seldom certain that I am in the right, and because I pay re- spect to the opinions of others, where I think they may merit it. At present, je me sens un pen blesse; it seems hard, that in the first attempt I have made to lay any thing before the public, I should be thus anticipated. It will make me cautious how I take the trouble of preparing any thing for them another time. I defer coming to any resolution till I see you ; but, at present, I think reading the letters at the Royal Society to be the proper step. I ask your pardon for the egotism of this letter, and remain, Most truly yours, JAMES WATT. [Mr. Watt at this time, or in the following week, went to London, and saw Sir Joseph Banks. All that can be collected of what passed must be deduced from the following letters.] EXTBACT MB. WATT TO MB. DE LUC. Birmingham, 4th April, 1784. * * -ir # Sir Joseph Banks called on me in London, on Monday or Tuesday, and left a note, asking me to have my letters on Air read to the Society, and pro- mising to take care there should be no mistake. In the very civil manner in which he has requested it I cannot avoid complying with it, if they can be G 50 EXTRACTS FROM published in the volume now in the press, or at least the first of them, with some proper notes which I shall transmit. I, however, leave the affair wholly to you, and beg you would call and settle it with him. If you give the first letter to be read imme- diately, please alter the phrase where, speaking of the composition of nitrous air, I say, " I suppose it " to be nitrous acid super-saturated with phlogiston," to nitrous acid not fully saturated with phlogiston. I shall with first possible convenience make the necessary alterations on the second letter, so as to make it follow the first properly, and add some ex- planatory notes concerning the processes, still re- taining the original form of a letter to you. EXTRACT ME. DB LUC TO MR. WATT. Londres, 1e JOme Avril, 1784. * * * -SC- J'ai vu le Chevalier Banks au sujet du billet qu'il avoit laisse pour vous : il ne m'a pas paru qu'il at- tachat pour lui aucun interet a la lecture de ces let- tres, mais seulement qu'il les feroit surement lire si vous le desirez, disant positivement que cela depend de vous. Quant a. la condition de les inserer dans le premier volume qui paroitra, vous savez que cela de- pend du Comite, et non pas de lui. Ainsi, faites ex- actement ce que vous jugerez a propos, et parlez lui en, en lui envoyant ce que vous avez dessein de lui envoyer sur le Test. Mais si vous souhaitez que ces lettres soient lues, envoyez moi d'avance la nouvelle edition de celle que vous m'aviez ecrite le 26. Novem- MR. WATT'S CORRESPONDENCE. 51 bre, en y mettant la meme date ; aim que la traduc- tion que j'en ferai, soit d'accord avec ce qui sera lu a la societe. J'ai corrige la phrase dans la lettre au Dr. Priestley. EXTRACT MB. WATT TO ME. DE LUC. Birmingham, April 12th, 1784. * % * * In relation to Sir Joseph Banks, he wants the paper to be read, not, as you observe, because he is attached to me, but because he feels as a slight put upon the Society the withdrawing it ; and perhaps thinks his own honour a little called in question, which I do not wish him to think, as he has always behaved in a friendly manner towards us. For my own part, I would rather that the matter had been left to take its course in your publication ; but, after the reading of this paper of Mr. Caven- dish's, and being civilly requested to publish in the same channel, I think it would savour a little of re- sentment and cowardice to decline it any farther. I know very well that the insertion depends on the Committee, but he can influence them ; and if he does not, there is nothing lost. I have still my reme- dy. At all events, I shall certainly send the letter to yourself through your own hands, and, I assure you, I should have been much better pleased that you had been the President and members of the Society who should publish it ; but circumstances compel me to give it to the other, and I hope it will answer your end as well, after they have had their will of it. 52 EXTRACTS FROM MR. WATT TO SIR JOSEPH BANKS. Birmingham, 12th April, 1784. SIK, I intended to have done myself the honour of writing to you sooner, but caught cold in my jour- ney home ; which, with a quantity of business which had fallen behind in my absence, has prevented me from writing some necessary explanations of the me- thod of conducting the experiments I made last sum- mer, on dephlogisticated air, an account of which is contained in my letter to Mr. De Luc of November 26th, which I intend shall be soon laid before you. I desired Mr. De Luc to do me the favour to return to you my letter to Dr. Priestley on that sub- ject, begging the favour of you to present it to the Royal Society, and to inform them of my reasons for withdrawing it last year ; which were, in the first place, my having attempted in that letter to account for the (apparent) conversion of water into air, by ex- posing it to heat in porous earthen vessels ; which Dr. Priestley soon after discovered to be no real conver- sion, but an exchange of air for water or steam : and, secondly, my being informed that that theory was considered too bold, and not sufficiently supported by facts. These reasons made me think it prudent to delay the publication, until I should have consi- dered it more maturely, and have made some expe- riments to determine the truth, or falsehood of it. I have since that time made several experiments, (an account of which you will find in my letter to Mr. De Luc,) and have considered the theory in every view which occurred to me, without being able to find any fallacy in it ; and as similar theories have MR. WATT'S CORRESPONDENCE. 53 since been, as I am informed, supported by philoso- phers of first-rate abilities, the second objection seems to be removed. I hope, therefore, that the Royal Society will excuse my troubling them with laying before them my letter to Dr. Priestley unaltered, and also that to Mr. De Luc, which contains some addi- tional reasoning, and an account of some of the expe- riments I have made ; and that they will also excuse the defects of my style, which must naturally be con- cluded to savour more of the mechanic than of the philosopher. It will add much to the obligations I have already received from you, if you will, as soon as you judge it proper, present my letter to Dr. Priestley to the Soci- ety ; and, as soon as I get the postscript to the letter to Mr. De Luc finished, I shall beg the favour of him to send it to you. Mr. Boulton joins in presenting our respectful com- pliments to you; and I remain, with much respect and esteem, &c. JAMES WATT. SIB JOSEPH BANKS TO MR. WATT. Soho Square, London, 15th April, 1784. DEAR SIR, On the receipt of your favor, I wrote immediately to Mr. De Luc, requesting him to deliver to me your letter to Dr. Priestley. If I receive it before next Thursday, (the day on which the Royal Society resume their meetings,) I will certainly pre- sent it to them, either at that or their next meeting. I beg to thank you for your intention of communi- cating to them your letter to Mr. De Luc, concerning 54 EXTRACTS FROM the method you have taken, of conducting your ex- periments on dephlogisticated air ; and venture, at the same time, to assure you, that the communica- tions you are pleased to make, will ever be welcome to that body, as long as I have the honour to preside over it. The sooner I receive it, the better I shall like it, as I wish to have both your letters appear in the next volume of the Philosophical Transactions. I beg my best compliments to Mr. Boulton, and that you will believe me, your faithful servant, Jos. BANKS. EXTKACT MB. WATT TO MB. DE LUC. Birmingham, April 17th, 1784. X * * * I have just now received a letter from Sir Joseph Banks, wherein he says, that in consequence of my last, he had written to you for the letter to Dr. Priestley ; and that if he received it before Thursday next, he would certainly present it to the Society, either that day, or at their next meeting. He also promises to use his endeavours, to have both the let- ters published in the next volume of the Transactions. I have not been able to finish the postscript, but have added some notes, and have made some alterations on the first and last page of the letter, which I con- ceived to be necessary in the present circumstances, and to make it more suitable to the place where it is now to appear. The note on the left hand page, relating to Mr. Kirwan, I have left loose, because I am not quite certain what it was he said about in- flammable air, and have not the volume of the Trans- MR. WATT'S CORRESPONDENCE. 55 actions wherein he mentions it. I think it is either the last, or the last but one. If, on examination, you find I am right, leave it as it is ; if not, take it away. It is in the same paper wherein he treats of the quantity of phlogiston in fixed and nitrous airs. I should be sorry you should take the trouble of making an entire fresh transla- tion ; I see no need for it, and I think you need not publish both the letters. It may suffice if you pub- lish the second, and mark by commas (") the passages which formed part of the first letter, after giving the history of that letter. However, do as you think proper ; I am sure you have my reputation in the matter more at heart than I have myself, and it vexes me exceedingly to cause you so much trouble. I should have sent the postscript, but a headache yesterday disabled me, and to-morrow I must set out for Shropshire, from which I shall not return for a week at least. As soon as I return, I shall finish and send you the postscript, in the form of a letter of the present date. Meanwhile, I shall thank you to for- ward the new copy of the letter, which I send by to- morrow's coach, to Sir Joseph Banks, as soon as you have made the necessary alterations and additions to the copy you have. I have mentioned to Sir Joseph that there are a few alterations, and where they are, and have told him that you will show him the origi- nal letter, if doubts should arise concerning the date of any part of it ; but shall be obliged to you, in such case, to take care they do not read or print the wrong copy. 56 EXTRACTS FROM MR. WATT TO SIB JOSEPH BANKS. Birmingham, 17th April, 1784. DEAR SIR, I have just received your obliging fa- vour of the 1 5th. I have not been able yet to finish the postscript to my letter of 26th November to Mr. De Luc, and shall be obliged to delay it for a week, as I shall be absent on a journey into Shropshire. I have, however, revised the letter itself, and by this post send a corrected copy to him, which he will de- liver to you. The principal alterations I have made are, the retrenching some superfluous phrases in the first page, and some part at the end of the last page, which was complimentary to MM. Lavoisier and De La Place, to the former of whom I certainly owe nothing. I have also added some notes, on the left hand pages; which, being in my own hand-writing, are sufficiently distinguished. I thought it right to apprize you of these alterations, lest it should be said by anybody, that the letter was fabricated at a later date than it bears. If anything of that kind should be started, Mr. De Luc can produce the original, in my own handwriting, which can be compared with this present copy. Mr. Kirwan also has a copy, which he took from one I lent him when in town. As I have not been able to finish the postscript in time to add it to the letter, I mean to write it in the form of an explanatory letter, which may follow the other at any date, and it shall be my first care after I return from my journey. Indeed, I should have finished it yesterday, but was seized with an unlucky headache, which prevented me. I cannot sufficiently thank you for the trouble you ME. WATT'S CORRESPONDENCE. 57 take in this matter, and beg you will believe me to remain, with due respect, dear Sir, Your most obliged humble Servant, JAMES WATT. SIR JOSEPH BANKS TO MR. WATT. Soho Square, London, 23d April, 1784. DEAR SIR, Your letter to Dr. Priestley of April 21, 1783, was read to the Royal Society last night. Yours to Mr. De Luc I have received, and shall bring it into reading as soon as I can do it. Probably, on Thursday, May 6th ; of which I give you this notice, that you may, if convenient, send me the postscript in time to follow in immediate succession. A paper of Dr. Withering's was also read, which the Society seemed to approve much. It contained experiments on various kinds of Terra Ponderosa. Dr. Priestley is here, and in good health and spirits. How much the Royal Society, and the world at large, are indebted in point of science to the town of Bir- mingham, I need not declare, after mentioning him. That you are at last induced to make it the convey- ance of your discoveries, gives, I frankly confess, no little pleasure to Your faithful and obedient Servant, Jos. BANKS. MR. WATT TO SIR JOSEPH BANKS. Birmingham, 2d May, 1784. DEAR SIR, I received your very obliging infor- mation, of my letter to Dr. Priestley having been read H 58 EXTRACTS FROM before the Royal Society, and have this day sent the sequel of the letter to Mr. De Luc to him, with a de- sire that he would send it to you as soon as he could. From my late absences from home, and the neces- sary attention to business since I returned, it is but a hasty compilation ; and, if I had not judged the few things it contained, necessary to be explained to most of those who may be disposed to try experiments on the same subject, and that, therefore, it should attend the former letters, I should not have sent it until I had been able to put it into a better dress. I must, therefore, beg your and the Royal Society's pardon for its defects, and hope your and their excuse for troubb'ng you so much with my ideas on these subjects, I remain, with great esteem and respect, dear Sir, Your much obliged and obedient humble Servant, JAMES WATT. EXTRACT MR. WATT TO MR. DE LUC. Birmingham, 2d May, 1784. DEAR SIR, I send you enclosed the sequel to my letter on dephlogisticated air; which, after all the delay, is hastily and badly composed. The fact is, that the subject begins now to wear out of my mind, and I have not time to refresh my memory by fresh expe- riments, as I have had no leisure hours since I saw you. * * * * I am hurried to be in time for the packet, so must conclude with begging you to send the enclosed to Sir Joseph as soon as you can, as he advises me he means to bring forward the other letter to be read on Thursday next. SIR. WATTS CORRESPONDENCE. 59 MR. WATT TO SIR JOSEPH BANKS. Birmingham, May 5, 1784. DEAR SIR, I had the honour of writing to you on Sunday last, informing you that I had sent to Mr. De Luc the sequel of my letter to him on dephlogisticated air; since which, having been stupified by headaches, I have not been able to revise the letter till to-day, when I perceived an obscurity, in the wording of the passage where I mention, that litmus is no test of the saturation of the phlogisticated nitrous acid by alka- lies ; the words which follow should run thus " for " the infusion of litmus added to stick a mixture will " turn red, &c." The words I have under-scored, are what I wish to be inserted instead of " mixt with it," which at pre- sent stands in the letter. The passage is about two- thirds down the second page. I am quite ashamed to be so troublesome, but hope you will excuse ; and I remain, &c. JAMES WATT. EXTRACT SIR JOSEPH BANKS TO MR. WATT. Soho Square, llth May, 1784. DEAR SIR, Your paper commenced reading to the Royal Society on Thursday se'nnight ; and last Thursday the postscript was read. Both appeared to meet with great approbation from large meetings of Fellows. On Friday I received your favour, requesting a small alteration to be made in the postscript, which I have delivered to Dr. Blagden, our new Secretary, 60 EXTRACTS FROM who has undertaken that it shall be made before the papers are printed. [The sequel of this letter com- municated an account of some experiments by M. Lavoisier, on a mode of making inflammable air by passing the steam of water through a red-hot iron tube.] EXTRACT MB. DE LUC TO MR. WATT. Londres, le 12me Mai, 1784. Je suis charme du parti que vous aviez pris d'au- thentiquer vos lettres, et leurs dates ; et le Chevalier Banks s'y est prete volontiers. La lettre au Dr. Priestley fut lue pendant son sejour ici ; et celle du 26. Novembre a moi, ainsi que votre addition, durent etre lues Jeudi dernier. Je n'ai pas voulu les garder pour corriger ma copie de la premiere, et tirer copie de la seconde ; preferant qu'elles furent lues d'abord, et de les r'avoir ensuite. [The rest of this letter contains some remarks on M. Lavoisier's experi- ment, mentioned by Sir J. Banks ; on a supposed in- vention of a new steam engine, by Kempelen ; and on private matters.] EXTRACT MR. WATT TO MR. DE LUC. Birmingham, Hth May, 1784. Sir Joseph Banks has behaved with great civility and kindness in the affair of the letters. I had a letter from him the other day, advising they were all read. * I cannot be sufficiently thankful for the daily instances you give me of your friendship and regard to our interest, which is the more flattering as coming from you. MR. WATT'S CORRESPONDENCE. 61 It is such consolations as experiencing the regard of the worthy few, which make the bitter pill of life palatable. It is the next thing to self-approbation, and to sensible minds a necessary appendage to it, for without it, self-approbation cannot properly exist. EXTRACT ME. WATT TO MR. FEY OF BRISTOL. Birmingham, 15th May, 1784. SC- % * * The papers which I mentioned to you that I had writ- ten, on the composition of water and dephlogisticated air, have been read at the Royal Society ; I am told, with applause. If they are printed, I shall do myself the pleasure to send you a copy. But I have had the honour, like other great men, to have had my ideas pirated. Soon after I wrote my first paper on the subject, Dr. Blagden explained my theory to M. Lavoisier at Paris ; and soon after that, M. Lavoi- sier invented it himself, and read a paper on the subject to the Royal Academy of Sciences. Since that, Mr. Cavendish has read a paper to the Royal Society on the same idea, without making the least mention of me. The one is a French Financier ; and the other a member of the illustrious house of Caven- dish, worth above 100,000,'"" and does not spend 1000 per year. Rich men may do mean actions. May you and I always persevere in our integrity, and despise such doings. Adieu, my worthy friend ! JAMES WATT. * Mr. Watt probably meant to say 1,000,000. ED. 62 EXTRACTS FROM MR. WATT TO SIR JOSEPH BANKS. Birmingham, 21st May, 1784. [Sends him a paper on a new method of preparing tests for acids and alkalies, to be laid before the Royal Society. Makes some comments on M. La- voisier's experiments on the production of inflam- mable air in the iron tube, &c.] DR. BLAGDEN TO MR. WATT. London, May 25, 1784. SIR, The Committee of Papers have ordered your two letters and postscript, on the production of air from water, to be printed ; subject to your judgment, as to the best form under which they can appear. I am, therefore, to request that you would inform me, whether your first letter to Dr. Priestley, dated April 26th, 1 783, should be published entire as it is, or be incorporated into the second or corrected letter, bear- ing date the 26th of November 1783. The only rea- son for suggesting this latter method is, that the opi- nions are most digested in that second letter ; and to avoid repetitions. The advantage of publishing the first letter at full length would be, to shew the exact state of your sentiments on that subject at a certain period. It is absolutely at your option to decide upon whichever of those methods you shall prefer. Should your choice fall upon that of incorporating the two letters, I must request you to let me know what parts of the former you choose to be struck out, and how the remainder is to be placed ; and, at the same time, be so good as to send me what you think MR. WATT'S CORRESPONDENCE. 63 the properest title to be inserted before these papers in the Transactions. I have the honour to be, Sir, Your obedient humble servant, C. BLAGDEN. P.S. Sir Joseph Banks has just received your ac- count of a new Test for acids and alkalies ; which shall be read to the Royal Society next Thursday. In 2 of your paper on the Test, there is an expres- sion " putrid acid fermentation." Is it to stand so, or do you mean " putrid and acid V EXTRACT MB. WATT TO DR. BLAGDEN. Birmingham, 27th May, 1784. SIR, My only reason for wishing my letter to Dr. Priestley to be read before the Royal Society, was to shew them what my ideas on the subject were, at the time it was written. On some other accounts, I would rather have wished it to be suppressed. I therefore would propose, if it meets the appro- bation of the gentlemen of the Committee of Papers, that that letter should be wholly left out ; and that in place of it, a note should be added to the second paragraphs of the letter to Mr. De Luc, following the words, " April 26th, 1783," to the following pur- port : " Which letter Dr. Priestley received at Lon- " don ; and, after shewing it to several members of " the Royal Society, he delivered it to Sir Joseph " Banks the President, with a request that it might " be read at some of the public meetings of the So- " ciety ; but, before that could be complied with, the 64 EXTRACTS FROM " author, having heard of Dr. Priestley's new experi- " ments, begged that the reading might be delayed. " The letter, therefore, remained in the custody of " the President until - ; when, at the author's re- " quest, it was read before the Society. It has been " judged unnecessary to print that letter, as the " essential parts of it are repeated, almost verbatim, " in this letter to Mr. De Luc ; but to authenticate " the date of the author's ideas, the parts of it which " are contained in the present letter are marked with " double commas." As I have marked some passages in my letter to Mr. De Luc with double commas, by way of directing the reader's attention to my conclusions, it will be necessary by this new arrangement to print those passages in italics, to distinguish them from the quo- tations. I am very sorry to give you the trouble of collating the two letters, and of marking off the pas- sages wherein the same ideas are expressed in each ; but I must beg it of you as a favour, as it will come with more propriety from the hand of the Secretary to the Royal Society, than from mine. If you shall judge it to be proper to insert upon the margin, the dates of my experiments mentioned in my letter to Mr. De Luc, they are as follows, $ 7th May, 1783, 8th June, I 9th July, 3d, 10th July, 4th, 12th Nov. 1st, f 13th Nov. 22d. I am really at a loss what title to give the paper, but propose the following; " Thoughts (conjectures) " on the constituent parts of water, and of dephlogisti- " cated air ; with an account of some experiments on " that subject." I am much obliged to you for your MR. WATT'S CORRESPONDENCE. 65 correction of the Test paper. It should be " putrid " and acid fermentation." It undergoes both in a high degree, if we may judge of its putrescence by the smell, and of the acidity by the colour of the liquor. I beg the favour of you to return my thanks to the gentlemen of the Committee of Papers, for the honour they do me in ordering my communication to be printed ; and that you would also accept of my thanks for your obliging letter, communicating their intentions. I remain, with sincere esteem, your most obliged humble servant, JAMES WATT. EXTRACT DR. BLACK TO MR WATT. May 28th, 1784. MY DEAR FRIEND, The great length of time during which I have been your debtor requires some apology from me. It has been occasioned by the following circumstances. I had made you a promise that I should, in the course of last summer, prepare some of my lectures for the press. When the sum- mer came, I found myself so much worn out with my winter's labours, and in such bad health, with a cough, and defluxion from my breast, that I was quite unfit to sit down to serious business ; and during the rest of that season I had other things, in the way of College and other business, which broke my time, and took up my attention in such a manner that I got nothing done. All this while I was ashamed to write to you, after the promise I had made. In the beginning of last winter, when it became i 66 EXTRACTS FROM necessary to drop for some time all thoughts of such undertakings, I sat down to write to you, but some- thing prevented me from finishing my letter, and it remains unfinished to this day. In short, I feel that I am unfit to come under such engagements. I have not sufficient activity and spirits to be sure of fulfilling them ; and they are a load on my mind, which in- creases my disability. I received Lavoisier's and De La Place's Memoir.""" Their method for measuring quantities of heat is ingenious, but they have not used it with accuracy in some cases ; and there is reason to suspect, from Mr. Wedgewood's experiments in this way, that it cannot be practised with exactness. I am told it was contrived by La Place. Be so good as to return my best compliments to Mr. De Luc, and many thanks for his trouble and attention to me. it * -:: * Few things have given me so much pleasure, as the opportunity I had, in the beginning of winter, to form an acquaintance with Mr. Boulton. His connexion with you had raised a strong desire in me to be acquainted with him ; and I found so much reason to be satisfied that the connexion is a fortunate and a comfortable one, that I was made happy on your account, as well as in forming a friendship with a man of so much merit and worth. Present my most respectful compliments to him, and be assured that I ever am, my dear friend, Yours most faithfully, JOSEPH BLACK. * "Memoire sur la Chaleur, par MM. Lavoisier et De La Place," dated 18th June, 1783, and printed in the Memoirea de 1' Academic for 1780. MR. WATT'S CORRESPONDENCE. 67" EXTRACT MR. WATT TO PROFESSOR ROBISON. Birmingham, May 31st, 1784. -;:- .;- -;;- * I have lately, through the importunity of my friends, been prevailed upon to have read before the Royal Society of London, a paper containing a new hypothesis on the constituent parts of water and of dephlogisticated air, which has so far met their appro- bation as to be ordered to be printed. It may seem rather bold in me to commence my publications in science by a new theory ; and my natural timidity and diffidence would certainly have prevented me, if Mr. Lavoisier in France, having learned something about it from Dr. Blagden, had not adopted it as his own, and Mr. Cavendish, a year after the broaching of mine, had not published one of the same kind. EXTRACT MR. WATT TO MR. DE LUC. Birmingham, June 6th, 1784. * > -:c- The Committee of Papers referred it to me to de- cide, whether I would have both the letters printed. But I preferred to print only the one to you ; to mark with double commas the parts of it which were con- tained in the letter to Dr. Priestley ; to add a note giving a short history of that letter, and certifying that it had been seen by many of the members, and left in the possession of the President until it was read ; and to print the conclusions, which I had marked with double commas, in italics. 68 EXTRACTS FROM DR. BLAGDEN TO MR. WATT. London, 9th August 1784. DEAR SIR, Your paper is now going to be printed. I have marked off the similar parts, &c., according to your request, as well as I could make them out ; but, if it would be any satisfaction to you, the proof-sheets shall be sent to Birmingham for your correction. Whatever separate copies you may choose to have, send your order to Mr. Nichols, the printer, Red Lion Court, Fleet Street. * * * * Should you determine to have the proof-sheets sent down to you, let me know it as soon as you can ; otherwise you need not give yourself the trouble of answering this letter. Your paper on the test-liquor, &c., will be printed, I believe, toward the end of this month. I am, Sir, your obedient humble servant, C. BLAODEN. MR. WATT TO DR. BLAGDKN. Birmingham, llth August 1784. DEAR SIR, I am very much obliged to you for the attention you have been pleased to bestow on my paper on dephlogisticated air. I have no desire to see the proof-sheets, as I am satisfied that you would mark off with propriety the passages in the second letter which were mentioned in the first, and also that you are much more capable of correcting any grammatical errors, or inaccuracies of style, than I am ; and that favour I take the liberty to request of you, so far as it can be done consistently with your own convenience, and in the correction of a proof-sheet. MR, WATT'S CORRESPONDENCE. 69 Mr. De Luc did me the favour to write to you lately, requesting that you would desire the printer to print fifty separate copies of my paper, which liberty I hope you will excuse. Mr. De Luc is still here, and desires to join in compliments to you. I remain, with respect, dear Sir, your obliged humble servant, JAMES WATT. EXTRACT MR. WATT TO DK. BLACK. Birmingham, llth Nov. 1784. DEAR DOCTOR, I sent you lately a copy of the paper on dephlogisticated air, which I communicated to the Royal Society, and which will be printed in the next volume of their Transactions. It is far from being well written, but I am every day more and more satisfied that the doctrines it contains are true, however bold they appeared at first. My bad health, and my avocations, prevented me from sitting close at it, or thinking continuedly on the subject ; it should therefore be considered as a parcel of de- tached scraps, rather than -any attempt at system; which made me put it into the form of a letter. EXTRACT M. P1CTET OF GENEVA TO MR. 1>E LUC. Geneve, le 9. Mai 1785. ~/f 'if '/- 'if Aux experiences de M. Watt, pour le dire en passant, j'avois et j'ai encore la foi la plus implicite, en meme terns que j'en aime et admire la belle et simple Theorie. Je 1'ai exposee de mon mieux dans 70 EXTRACTS, ETC. mon cours, et il m' a paru qu' elle seduisoit la plu- part de ines auditeurs. Son fils, comme vous le savez sans doute, a suivi mes lecons avec beaucoup d'assiduite et d'attention. Lui et M. votre neveu etoient des modeles a cet egard. EXTRACT MB. WATT TO MR. DE LUC. Birmingham, 27th June 1786. # -::- * -/- It seems odd, but in the detached memoirs of Mr. Cavendish and myself, on the Composition of Water, they should be both wrong dated. Mr. Cavendish's dated, " read January 1 783," when it was read Janu- ary 1 784,* and my letter to Dr. Priestley,f dated April 1784, when it was written April 1783. END OF THE EXTRACTS FROM MR. WATT'S CORRESPONDENCE. * This refers to the copies of Mr. Cavendish's memoir for private circulation, which were circulated by him before the publication of the seventy-fourth volume of the Transactions for 1784, having on their title-page this date, " Read at the Royal Society, January. 15, " 1783." The date at the head of the paper itself is rightly given in the Philosophical Transactions, but omitted in those copies. ED. t It is not the letter to Dr. Priestley, but that to Mr. De Luc, which is misdated in the Philosophical Transactions, being there dated " 26th Nov. 1784," when the real date was 1783. That letter to Dr. Priestley, written and dated 26th April 1783, was read at the Royal Society 22d April 1784. The letter to Mr. De Luc was written and dated 26th November 1783, and was read at the Royal Society 29th April 1784. ED. TRANSLATION OF A LETTER FROM DR. BLAGDEN, SEC. R. S. L., TO DR. LORENZ CRELL. NOT DATED. * I can certainly give you the best account of the little dispute about the first discoverer of the artifi- cial generation of water, as I was the principal in- strument through which the first news of the disco- very that had been already made was communicated to Mr. Lavoisier. The following is a short statement of the history : In the Spring ("Fruhjahr") of 1783, Mr. Cavendish communicated to me and other members of the Royal Society, his particular friends, the result of some ex- periments with which he had for a long time been occupied. He showed us, that, out of them, he must draw the conclusion, that dephlogisticated air was nothing else than water deprived of its phlogiston ; and, vice versd, that water was dephlogisticated air united with phlogiston. About the same time (" um " dieselbe Zeit") the news was brought to London, that Mr. Watt of Birmingham had been induced by some * Published in Crell's " Chemischc Annalen," Helmstadt u. Leip- zig, 1786, pp. 58-61. E. 72 LETTER FROM DR. BLAGDEN observations, to form ("fassen") a similar opinion. Soon after tin's (" bald darauf") I went to Paris, and in the company of Mr. Lavoisier, and of some other members of the lloyal Academy of Sciences, I gave some account of these new experiments, and of the opinions founded upon them. They replied that they had already heard something of these experi- ments ; and, particularly, that Dr. Priestley had re- peated them. They did not doubt, that in such man- ner a considerable quantity of water might be ob- tained ; but they felt convinced that it did not come near to the weight of the two species of air employed ; on which account it was not to be regarded as water formed or produced out of the two kinds of air, but was already contained in, and united with the airs, and deposited in their combustion. This opinion was held by Mr. Lavoisier, as well as by the rest of the gentlemen, who conferred on the subject ; but, as the experiment itself appeared to them very remarkable in all points of view, they unanimously requested Mr. Lavoisier, who possessed all the necessary prepara- tions ("Vorrichtungen") to repeat the experiment on a somewhat larger scale, as early as possible. This desire he complied with on the 24th June 1 783, (as he relates in the latest volume of the Paris Memoirs.) From Mr. Lavoisier's own account of his experiment, it sufficiently appears, that at that period he had not yet formed the opinion, that water was composed of dephlogisticated and inflammable airs ; for he ex- pected that a sort of acid would be produced by their union. In general, Mr. Lavoisier cannot be convict- ed of having advanced any thing contrary to truth ; TO DR. CRELL. 73 but it can still less be denied, that he concealed a part of the truth. For he should have acknowledged that I had, some days before, apprized him of Mr. Caven- dish's experiments ; instead of which, the expression " il nous apprit," gives rise to the idea that I had not informed him earlier than that very day. In like manner, Mr. Lavoisier has passed over a very re- markable circumstance, namely, that the experiment was made in consequence of what I had informed him of. He should likewise have stated in his pub- lication, not only that Mr. Cavendish had obtained " une quantite d'eau tres sensible," but that the water was equal to the weight of the two airs added toge- ther. Moreover, he should have added, that I had made him acquainted with Messrs. Cavendish and Watt's conclusions ; namely, that water, and not an acid or any other substance, (" Wesen"), arose from the combustion of the inflammable and dephlogisticated airs. But those conclusions opened the way to Mr. Lavoisier's present theory, which perfectly agrees with that of Mr. Cavendish ; only that Mr. Lavoisier accommodates it to his old theory, which banishes phlogiston. Mr. Monge's experiments, (of which Mr. Lavoisier speaks as if made about the same time,) were really not made until pretty long, I believe at least two months, later than Mr. Lavoisier's own, and were undertaken on receiving information of them. The course of all this history will clearly convince you, that Mr. Lavoisier, (instead of being led to the discovery, by following up the experiments which he and Mr. Bucquet had commenced in 1777,) was in- duced to institute again such experiments, solely by K 74 LETTER FROM DK. BLAGDEN. the account he received from me, and of our English experiments ; and that he really discovered nothing, but what had before been pointed out to him to have been previously made out, and demonstrated in England. END OP DR. HLAODEN S LETTER TO Dli. t'KKLI.. APPENDIX. APPENDIX. No. I. THOUGHTS ON THE CONSTITUENT PARTS OP WATER AND OF DEPHLOGISTICATED AIR ; WITH AN ACCOUNT OF SOME EXPERIMENTS ON THAT SUBJECT. IN A LETTER FROM MR. JAMES WATT, ENGINEER, TO MR. DE LUC, F. R.S.* Read April 29, 1784. Birmingham, November 26, 1783. DEAR SIR, In compliance with your desire, I send you an account of the hypothesis I have ventured to form on the probable causes of the production of water from the deflagration of a mixture of dephlogis- ticated and inflammable airs, in some of our friend Dr. Priestley's experiments. I feel much reluctance to lay my thoughts on these subjects before the public in their present indigested * Reprinted from the Philosophical Transactions, vol. Ixxiv. for 1784, p. 329 to 353 ; the erroneous date of 1784 being now correct- ed to 1783, and the paper thus resuming its rightful precedence of that of Mr. Cavendish, hereafter also reprinted. In all the papers now reprinted, the numbering of the pages of that volume of the Phi- losophical Transactions in w hich they are to be found, is preserved, and is placed within brackets. ED. 78 MR. WATT'S FIRST PAPER IN THE state, and without having been able to bring them to the test of such experiments as would confirm or re- fute them ; and should, therefore, have delayed the publication of them until these experiments had been made, if you, Sir, and some other of my philosophical friends, had not thought them as plausible as any other conjectures which have been formed on the subject ; and that though they should not be verified by further experiments, or approved of by men of science in general, they may perhaps merit a discus- sion, and give rise to experiments which may throw light on so important a subject. I first thought of this way of solving the pheno- mena in endeavouring to account for an experiment of Dr. Priestley's, [330] wherein water appeared to be converted into air ; and I communicated my sen- timents in a letter addressed to him, dated April 26, 1783,* with a request that he would do me the honour to lay them before the Royal Society ; but as, before he had an opportunity of doing me that favour, he found, in the prosecution of his experiments, that * This letter Dr. Priestley received at London ; and, after show- ing it to several Members of the Royal Society, he delivered it to Sir Joseph Banks, the President, with a request that it might be read at some of the public meetings of the Society ; but before that could be complied with, the author, having heard of Dr. Priestley's new experiments, begged that the meeting might be delayed. The letter, therefore, was reserved until the 22d of April last ; when, at the author's request, it was read before the Society. It has been judged unnecessary to print that letter, as the essential parts of it are repeated, almost verbatim, in this letter to Mr. De Luc ; but, to authenticate the date of the author's ideas, the parts of it which are contained in the present letter are marked with double commas. PHILOSOPHICAL TRANSACTIONS. 79 the apparent conversion of water into air, by expos- ing it to heat in porous earthen vessels, was not a real transmutation, but an exchange of the elastic fluid for the liquid, in some manner not yet accounted for ; therefore, as my theory was no ways applicable to the explaining these experiments, I thought proper to delay its publication, that I might examine the sub- ject more deliberately, which my other avocations have prevented me from doing to this time. 1. It has been known for some time that inflam- mable air contained much phlogiston ; and Dr. Priest- ley has found, by some experiments made lately, that it " is either wholly pure phlogiston, or at least that " it contains no apparent mixture of any other mat- " ter." (In my opinion, however, it contains a small quantity of water, and much elementary [331] heat.)* " He found, that by exposing the calces of metals to the " solar rays, concentrated by a lens, in a vessel con- " taining inflammable air only, the calces of the softer " metals were reduced to their metallic state ;" and that the inflammable air was absorbed in proportion as they became phlogisticated ; and, by continually supplying the vessel with inflammable air, as it was absorbed, he found, that out of 101 ounce measures, which he had put into the vessel, 99 ounce measures were absorbed by the calces, and only two ounce * Previous to Dr. Priestley's making these experiments, Mr. Kir- wan had proved, by very ingenious deductions from other facts, that inflammable air was, in all probability, the real phlogiston, in an aerial form. These arguments were perfectly convincing to me ; but it seems more proper to rest that part of the present hypothesis on the direct experiment. 80 .MR. WATT'S FIRST PAPER IN THE measures remained, which, upon examination, he found to be nearly of the same quality the whole quantity had been of before the experiment, and to be still capable of deflagrating in conjunction with atmospheric or with dephlogisticated air. Therefore, as so great a quantity of inflammable air had been absorbed by the metallic calces ; the effect of reducing them to their metallic state had been produced ; and the small remaining portion was still unchanged, at least had suffered no change which might not be attri- buted to its original want of purity ; it was reasonable to conclude, that inflammable air must be the pure phlo- giston, or the matter which reduced the calces to metals. 2. " The same ingenious philosopher mixed toge- " ther certain proportions of pure dry dephlogisti- " cated air, and of pure dry inflammable air in a " strong vessel, closely shut, and then set them on " fire by means of the electric spark," in the same manner as is done in the inflammable air pistol. " The first effect was the appearance of red heat or " inflammation [332] in the airs, which was soon fol- " lowed by the glass vessel becoming hot. The heat " gradually pervaded the glass, and was dissipated " in the circumambient air, and as the glass grew " cool, a mist or visible vapour appeared in it, which " was condensed on the glass in the form of moisture " or dew.* When the glass was cooled to the tem- * I believe that Mr. Cavendish was the first who discovered that the combustion of dephlogisticated and inflammable air produced moisture on the sides of the glass in which they were fired. [This note was not in the original draft, nor in the press copy of the letter as sent to Mr. De Luc ; but was afterwards added in pencil. ED.] PHILOSOPHICAL TRANSACTIONS. 81 " perature of the atmosphere, if the vessel was opened " with its mouth immersed in water or mercury, so " much of these liquids entered as was sufficient to " fill the glass within about zandth part of its whole " contents ; and this small residuum may safely be " concluded to have been occasioned by some impu- " rity in one or both kinds of air. The moisture ad- " hering to the glass after these deflagrations, being " wiped off, or sucked up by a small piece of sponge " paper, first carefully weighed, was found to be " exactly, or very nearly, equal in weight to the airs " employed." " In some experiments, but not in all, a small " quantity of a sooty-like matter was found adhering " to the inside of the glass," the origin of which is not yet investigated ; but Dr. Priestley thinks that it arises from some minute grains of the mercury that was used in order to fill the glass with the air, which, being super-phlogisticated by the inflammable air, assumed that appearance ; but, from whatever cause it proceeded, " the whole quantity of sooty-like " matter was too small to be an object of considera- " tion, particularly as it did not occur in all the ex- " periments." I am obliged to your friendship for the account of the experiments which have been lately made at Paris on this subject, [333] with large quantities of these two kinds of air, by which the essential point seems to be clearly proved, that the deflagration or union of dephlogisticated and inflammable air, by means of ignition, produces a quantity of water equal in weight to the airs ; and that the water thus pro- L 82 MR. WATT'S FIRST PAPER IN THE duced, appeared, by ever y test, to be pure water. As I am not furnished with any particulars of the man- ner of making the experiment, I can make no obser- vations on it, only that, from the character you give me of the gentlemen who made it, there is no reason to doubt of its being made with all necessary pre- cautions and accuracy, which was further secured by the large quantities of the two airs consumed. 3. " Let us now consider what obviously happens in " the case of the deflagration of the inflammable and " dephlogisticated air. These two kinds of air unite " with violence, they become red-hot, and upon cool- " ing, totally disappear. When the vessel is cooled, "a quantity of water is found in it equal to the " weight of the air employed. This water is then the " only remaining product of the process, and water, " light, and heat, are all the products," unless there be some other matter set free which escapes our senses. " Are we not then authorized to conclude, that water " is composed of dephlogisticated air and phlogiston, " deprived of part of their latent or elementary heat ; " that dephlogisticated or pure air is composed of " water deprived of its phlogiston, and united to ele- " mentary heat and light ; and that the latter are con- " tained in it in a latent state, so as not to be sensible " to the thermometer or to the eye ; and if light be " only a modification of heat, or a circumstance at- " tending it, or a component part of the inflammable " air, then pure or dephlogisticated air is composed " of water deprived of its phlogiston and united to " elementary heat ?" [334] PHILOSOPHICAL TRANSACTIONS. 83 4. "It appears that dephlogisticated water," or, which may be a better name for the basis of water and air, the element you call humor, " has a more " powerful attraction for phlogiston than it has for " latent heat, but that it cannot unite with it, at least " not to the point of saturation, or to the total expul- " sion of the heat, unless it be first made red-hot," or nearly so. " The electric spark heats a portion of it " red-hot, the attraction between the humor and the " phlogiston takes place, and the heat which is let " loose from this first portion heats a second, which " operates in a like manner on the adjoining parti- " cles, and so continually, until the whole is heated " red-hot and decomposed." Why this attraction does not take place to the same degree in the com- mon temperature of the atmosphere, is a question I am not yet able to solve ; but it appears, that, in some circumstances, " dephlogisticated air can unite, " in certain degrees, with phlogiston, without being " changed into water." Thus Dr. Priestley has found, that by taking clean filings of iron, which alone pro- duce only inflammable air of the purest kind, and mercurius caldnatus per se, which gives only the purest dephlogisticated air, and exposing them to heat in the same vessel, he obtained neither dephlo- gisticated nor inflammable air, " but in their place " fixed air." Yet it is well known, that a mixture of dephlogisticated and inflammable air will remain for years in close vessels in the common heat of the atmosphere, without suffering any change, the mix- ture being as capable of deflagration at the end of that time as it was when first shut up. These facts 84 MB. WATT'S FIRST TAPER IN THE the Doctor accounts for, by supposing that the two kinds of air, when formed at the same time in the same vessel, can unite in their nascent state ; but that, when fully formed, they are incapable of acting upon one another, unless they are [335] first set in motion by external heat. " Phlogisticated air seems " also to be another composition of phlogiston and " dephlogisticated air ;" but in what proportions they are united, or by what means, is still unknown. It appears to me to be very probable, that fixed air con- tains a greater quantity of phlogiston than phlogisti- cated air does, because it has a greater specific gra- vity, and because it has more affinity with water. 5. " For many years I have entertained an opi- " nion, that air was a modification of water, which " was originally founded on the facts, that in most " cases wherein air was actually made," which should be distinguished from those wherein it is only ex- tricated from substances containing it in their pores, or otherwise united to them in the state of air, " the " substances were such as were known to contain " water as one of their constituent parts, yet no water " was obtained in the processes," except what was known to be only loosely connected with them, such as the water of the crystallization of salts. " This " opinion arose from a discovery," that the latent heat contained in steam diminished in proportion as the sensible heat of the water from which it was produc- ed increased ; or, in other words, " that the latent " heat of steam was less when it was produced under " a greater pressure, or in a more dense state, and " greater when it was produced under a less pressure, PHILOSOPHICAL TRANSACTIONS. 85 " or in a less dense state ; which led me to conclude, " that when a very great degree of heat was neces- " sary for the production of the steam, the latent heat " would be wholly changed into sensible heat ; and " that, in such cases, the steam itself might suffer " some remarkable change. I now abandon this " opinion in so far as relates to the change of water " into air, as I think that may be accounted for on " better principles." [336] 6. "In every case, wherein dephlogisticated air " has been produced, substances have been employed, " some of whose constituent parts have a strong at- " traction for phlogiston, and, as it would appear, a " stronger attraction for that substance than humor " has ; they should, therefore, dephlogisticate the " water" or fixed air, and the humor thus set free should unite to the matter of fire and light, and be- come pure air. Dephlogisticated air is produced in great abundance from melted nitre. " The acid of " nitre has a greater attraction for phlogiston than " any other substance is known to have ; and it is " also certain that nitre, besides its water of crystal- " lization, contains a quantity of water as one of its " elementary parts, which water adheres to the other " parts of the nitre, with a force sufficient to enable " it to sustain a red heat. When the nitre is melted, " or made red-hot, the acid acts upon the water, and " dephlogisticates it ; and the fire supplies the humor " with the due quantity of heat to constitute it air, " under which form it immediately issues. It is not " easy to tell what becomes of the acid of nitre and " phlogiston, which are supposed to be united," as 86 MR. WATT'S FIRST PAPER IN THE they seem to be lost in the process. Dr. Priestley has lately made some experiments, with a view to ascertain this point. He distilled dephlogisticated air from pure nitre, in an earthen retort glazed within and without. He employed 2 oz. = 960 grains of nitre : the retort was placed in an air fur- nace, and, by means of an intense heat, he obtained from the nitre in one experiment 787, and in another experiment 800 ounce measures of dephlogisticated air ; and he found that, upon weighing the retort and nitre before and after the process, they had suf- fered a loss of weight equal to the weight of the air, and to the water of crystallization of the nitre, but nothing more. He remarked that the air had a pun- gent [337] smell, which he could not divest it of by washing ; and that the water in which the air was received had become slightly acid. I examined a portion of this water, which he was so kind as to send me, and found by it that the whole of the receiving water had contained the acid belonging to 2 drams = 120 grains of nitre. I also examined the residuum and the retort in which the distillation had been per- formed, and found the residuum highly alkaline, yet containing a minute quantity of phlogisticated nitrous acid. It had acted considerably upon the retort, and had dissolved a part of it, which was deposited in the form of a brownish powder, when the saline part was dissolved in water. This earthy powder I have not yet thoroughly examined, but have no doubt that it principally consists of the earth of the retort. This experiment, and all others tried in earthen ves- sels, leave us still at a loss to determine what becomes PHILOSOPHICAL TRANSACTIONS. 87 of the acid and phlogiston. They seem either to re- main mixed with the air, in the form of an incoerci- ble gas ; or to unite with the alkali or with the earth of the retort, in some manner so as not to be easily separated from them ; or else they are imbibed by the retorts themselves, which are sufficiently porous to admit of such a supposition. A II that appears to be conclusive from this experi- ment is, that above one half of the weight of the nitre was obtained in the form of dephlogisticated air ; and that the residuum still contained some nitrous acid united to phlogiston. 7. Finding that the action of the nitre on the re- tort tended to prevent any accurate examination of the products, I had recourse to combinations of the nitrous acid with earths from which the dephlogisti- cated air is obtained with less heat than from nitre itself. As these processes have been particularly de- scribed by Dr. Priestley, by Mr. Scheele, and others, I [338] shall not enter into any detail of them ; but shall mention the general phenomena which I ob- served, and which relate to the present subject. The earths I used were magnesia alba, calcareous earth, and minium or the red calx of lead. I dis- solved them in the respective experiments in nitrous acid dephlogisticated by boiling, and diluted with proper proportions of water. I made use of glass re- torts, coated with clay ; and I received the air in glass vessels, whose mouths were immersed in a glazed earthen bason, containing the smallest quan- tity of water that could be used for the purpose. As soon as the retort was heated a little above the heat 88 MR. WATT'S FIRST PAPER IN THE of boiling water, the solutions began to distil watery vapours containing nitrous acid. Soon after these vapours ceased, yellow fumes, and in some of the cases dark red fumes began to appear in the neck of the retort ; and at the same time there was a pro- duction of dephlogisticated air, which was greater in quantity from some of these mixtures than from others, but continued in all of them until the sub- stances were reduced to dryness. I found in the receiving water, &c., very nearly the whole of the ni- trous acid used for their solution, but highly phlogis- ticated, so as to emit nitrous air by the application of heat ; and there is reason to believe, that with more precaution the whole might have been obtained. 8. As the quantity of dephlogisticated air produc- ed by these processes did not form a sufficient part of the whole weight, to enable me to judge whether any of the real acid entered into the composition of the air obtained, I ceased to pursue them further, having learned from them the fact, that however much the acid and the earths were dephlogisticated before the solution, the acid always became highly phlogisti- cated in the process. [339] In order to examine whether this phlogiston was furnished by the earths, some dephlogisticated nitrous acid was distilled from minium till no more acid or air came over. More of the same acid was added to the minium as soon as it was cold, and the distilla- tion repeated, which produced the same appearance of red fumes and dephlogisticated air. This opera- tion was repeated a third time on the same minium, without any sensible variation in the phenomena. PHILOSOPHICAL TRANSACTIONS. 8.9 The process should have been still farther repeated, but the retort broke about the end of the third distil- lation. The quantity of minium used was 1 20 grains, and the quantity of nitrous acid added each time was 240 grains, of such strength that it could dissolve half its weight of mercury by means of heat. It appears from this experiment, that unless minium be supposed to consist principally of phlogiston, the source of the phlogiston, thus obtained, was either the nitrous acid itself, or the water with which it was di- luted ; or else that it came through the retort with the light, for the retort was in this case red-hot before any air was produced ; yet this latter conclusion does not appear very satisfactory, when it is considered, that in the process wherein the earth made use of was magnesia, the retort was not red-hot, or very ob- scurely so, in any part of the process ; and by no means luminous, when the yellow and red fumes first made their appearance. 9. As the principal point in view was to determine whether any part of the acid entered into the com- position of the air, I resolved to employ 'some sub- stance which would part with the acid in a moderate heat, and also give larger quantities of air than had been obtained in the former processes. Mercury was thought a proper substance for this purpose. 240 grains of mercury were put into a glass retort with 480 grains [340] of diluted dephlogisticated nitrous acid, which was the quantity necessary to dissolve the whole of the mercury, a gentle heat was applied, and as soon as the common air contained in the retort was dissipated, a vessel was placed to receive the H 90 MR. WATT'S FIRST PAPER IN THE nitrous air proceeding from the solution, which was 16 ounce measures. When it had ceased to give nitrous air, the neck of the retort became hot from the watery steams of the acid. The air receiver was taken away, and a common receiver was luted on, with a little water in it, to condense the vapours, and a quantity of dilute, but highly phlogisticated, acid was caught in the receiver. When the watery va- pours had nearly come over, and yellow fumes ap- peared in the neck of the retort, the common receiver was removed, and the air receiver replaced ; about four ounces of very strong nitrous air passed up im- mediately, the fumes in the retort became red, and dephlogisticated air passed up, which, uniting with the nitrous air in the receiver, produced red fumes in the receiver ; and the two kinds of air acting upon one another, their bulk was reduced to half of an ounce measure. At this period the fumes in the retort were of a dark red colour, and dephlogisticated air was produced very fast. After a short time, some orange-coloured sublimate appeared in the upper part of the retort, and extended a little way along its neck, the red colour of the fumes gradually dis- appeared, and the neck of the retort become quite clear. At the same time that this happened, small globules of mercury appeared in the neck of the retort, and accumulated there until they ran down in drops. The production of the air was now very rapid, and accompanied with much of the w r hite cloud or powdery matter, which passed up with the air into the receiver, and mixed with the water, but did not dissolve in it. After giving about 36 ounce PHILOSOPHICAL TRANSACTIONS. 91 measures of dephlogisticated air, [341] it suddenly ceased to give any more ; and the retort being cooled, the bulb was found to be quite empty, except- ing a small quantity of black powder, which, on being rubbed on the hand, proved to be mostly running mercury. The orange-coloured sublimate was wash- ed out of the neck of the retort, and what running mercury was in it was separated, and added to that which had run down into the basin among the water. The whole fluid mercury, when dried, weighed 218 grains ; therefore 22 grains remained in the form of sublimate, which, I believe, would also have been re- duced if I could have applied heat in a proper man- ner to the neck of the retort, as some of it to which heat could be applied, disappeared. 10. The 16 ounce measures of nitrous air, which had been produced in the solution of the mercury, and had remained confined by water in the receiver, was converted into nitrous acid by the gradual admis- sion of common air, and was taken up by the water ; this water was added to that in the bason, which had served to receive the dephlogisticated air. The whole quantity was about two quarts, was very acid to the taste, and sparkling with nitrous air. It was im- mediately put into bottles, and well corked, until it had lost the heat gained in the operation. In order to determine the quantity of acid in the receiving water and in the sublimate, I dissolved, first, alkali of tartar in water, and filtered the solution. 352 grains of this alkaline solution saturated 120 grains of the nitrous acid I had employed to dissolve the mercury, and 1395 grains of the same alkaline solu- 92 ME, WATT'S FIRST PAPER IN THE tion saturated the orange-coloured precipitate, and all the acid liquor obtained from the process : therefore we have the proportion as 352 : 120 :: 1395 : 475, from which it appears, that all the acid employed was recovered again in the form of acid, excepting only five grains ; [342] a smaller quantity than what might reasonably be supposed to be lost in the pro- cess by the extreme volatility of the nitrous air. In order to ascertain the exact point of saturation, slips of paper, stained by the juice of the petals of the scarlet rose, were employed, which were the nicest test I could procure, as litmus will not show the point of saturation of any liquor containing much phlogis- ticated nitrous acid, or even fixed air, but will turn red, and show it to be acid, when the test of those leaves, violets, and some other of the like kind, will turn green in the same liquor, and show it to be alkaline. But the exact point of saturation of so dilute a liquor is so very difficult to ascertain, that an error might easily be committed, notwithstanding the attention bestowed upon it. Supposing this ex- periment to be unexceptionable, the conclusions which may be drawn from it are very favourable to the hypothesis I endeavour to support. Thirty-six ounce measures of dephlogisticated air were obtained, and only five grains of a weak nitrous acid were lost in the process. Two hundred and eighteen grains of mercury out of two hundred and forty were revived, and all the dephlogisticated nitrous acid employed is found to be highly phlogisticated in the process. It appears that the nitrous acid does not enter into the composition of dephlogisticated air; it seems only to PHILOSOPHICAL TRANSACTIONS. 93 serve to absorb phlogiston from the watery part of the mercurial nitre. , 11. As this last process proved very tedious and complicated on account of the necessity of ascertain- ing the quantity of acid in the receiving water, by means of an alkali which afforded a double source of error in the point of saturation, I resolved to try the distillation of dephlogisticated air from cubic nitre in a glass vessel, and to draw from it only such a quantity of air as it would yield without acting much upon the retort, which latter circumstance is [343] essentially necessary to be attended to. An ounce of the crystals of mineral alkali were dissolved in nitrous acid, and the mixture brought to an exact saturation by the test of litmus ; 30 ounce measures of air were distilled from it, which, during the latter part of the process, was accompanied with slightly yellow fumes ; the receiving water was found to be acid, and the residuum alkaline. The residuum being dissolved in the receiving water, the solution was neutral, or very nearly so, by every test ; for in this case litmus might be used, as the acid was very slightly phlogis- ticated. On adding a few drops of a very dilute nitrous acid, the tests showed the liquor to be acid. 1 2. Encouraged by the success of this experiment, I took an ounce = 480 grains of pure common nitre, and put it into a flint-glass retort, coated, which was placed in a furnace. It began to give air about the time it became red-hot, and during the latter part of the process this air was accompanied with yellowish fumes. I stopped the process when it had produced 50 ounce measures of air. The receiving water, and 94 MR. WATT'S FIRST PAPER IN THE particularly the air, had a strong but peculiar smell of nitrous acid. The air was well washed with the re- ceiving water, but was not freed from the smell. The receiving water, which was 50 ounces, was slightly acid, and the residuum alkaline. I dissolved the latter in the former, and found the mixture alkaline, 10 grains of weak nitrous acid were added to it, which saturated it, and 105 grains of this spirit of nitre was found to contain the acid of 60 grains of nitre ; there- fore the 10 grains contained the acid of 5-7 grains of nitre, which, by Mr. Kirwan's experiments, is equal to two grains of real nitrous acid. We have, therefore, 34 grains weight of dephlogisticated air produced, and only two grains of real acid missing; and it is not [344] certain that this quantity was destroyed, because some portion of the glass of the retort was dissolved by the nitre, and some part of the materials employed in making the glass being alkali, we may conclude that the alkali of the nitre would be augmented by the alkali of that part of the glass it had dissolved. As the glass cracked into small pieces on cooling, and some part of the coating adhered firmly to it, the quantity of the glass that was dissolved could not be ascertained. From this experiment it appears, that if any of the acid of the nitre enters into the compo- sition of the dephlogisticated air, it is a very small part; and it rather seems that the acid, or part of it, unites itself so firmly to the phlogiston as to lose its attraction for water. 13. " The vitriolic salts also yield dephlogisticated " air by heat ; and in these cases the dephlogisti- " cated air is always attended with a large quantity PHILOSOPHICAL TRANSACTIONS. 95 " of vitriolic acid air or sulphureous vapour," even when the salts used are not known to contain any phlogistic matter. Mr. Scheele mentions his having obtained dephlogisticated air from manganese dis- solved in acid of phosphorus, and also from the arsenical acid ; from whence it appears that these acids, or perhaps any acid which can bear a red heat, can concur to the production of dephlogisticated air. It is necessary to remark, that no experiments have been yet published showing that deplilogisticated air can be produced from salts formed by the muriatic acid. The acids which produce salts suitable for this purpose have all a strong affinity with phlogiston ; and the marine acid has either a very small affinity with it, or else is already saturated with it, at least so far saturated as not to be able to attract it from the humor. 14. " The dephlogisticated air obtained from the " pure calces of metals may be attributed to the " calces themselves, attracting the phlogiston from " water which they have imbibed from [345] the " atmosphere, or from dephlogisticating the fixed air " which they are known to contain." It is very probable that the dephlogisticated air extruded from growing vegetables may be owing to their dephlogisticating the water they grow in ; but it appears more probable that the plants have a power of dephlogisticating the fixed or phlogisticated air of the atmosphere. " When dephlogisticated and nitrous air are mixed, " the dephlogisticated air seizes part of the phlo- " giston of the nitrous air." The water contained in 96 MR. WATT'S FIRST PAPER IN THE the nitrous air, and the other part of the phlogiston, unite with the nitrous acid, which then assumes a liquid form, or at least that of a dense vapour ; " and " that part of the latent heat of the two airs not " essential to the new combination is set at liberty."* In the combustion of sulphur the same thing happens, but in a greater degree ; for the vitriolic acid having a much weaker attraction for phlogiston than air has, abandons it almost entirely to the latter, which is thereby converted into water, and in that form attracts the vitriolic acid, and reduces it to a liquid state. The same reasoning may be applied to the combustion of phosphorus, which is attended with similar effects. [346] 15. I shall not make, at present, any further de- ductions from what I myself consider still in the light of a conjectural hypothesis, which I have, per- haps, dwelt upon too long already. I shall only beg your attention to some general reasoning on the subject, which, however, may possibly serve more to show the uncertainty of other systems on the con- stituent parts of air, than the certainty of this. Some of those systems supposed dephlogisticated air to be * I cannot take upon me to determine, from any facts which have come to my knowledge, whether any part of the dephlogisticated air employed in this experiment is turned into fixed air ; but I am rather inclined to think that some part is, because the quantity of heat, which is separated by the union of the two airs, does not seem to be so great as that which is separated when the dephlogisticated air is wholly changed into water ; yet some water appears to be formed, because, when the mixture is made over mercury, the solution of the mercury in the nitrous acid assumes a crystallized form, which, however, may be due to the watery part of the nitrous air. PHILOSOPHICAL TRANSACTIONS. 97 composed of an acid and something else, some say phlogiston. If an acid enters into the composition of it, why does not that acid appear again when the air is decomposed, by means of inflammable air and heat 1 And why is the water which is the product of this process pure water 1 And if an acid forms one of its constituent parts, why has nobody been able to detect any difference in the dephlogisticated air, made by the help of different acids, when com- pared with one another, or with the air extruded by vegetables \ These airs, of such different origins, appeal 1 to be exactly the same. And if phlogiston be a constituent part of air, why does it attract phlogiston with such avidity 1 Some have, on the other hand, contended that air is composed of earth, united to acids, or phlogiston, or to both, or to some other matter. Here we must ask, what earth it is which is one of the component parts of air ? All earths which will unite with the nitrous or vitriolic acids, and with some others, such as the phosphoric and the arsenical acids, will serve as bases for the formation of air, and the air produced from all of them appears by every test to be the same, when freed from accidental impurities. To this argument it is answered, that it is not any particular species of earth which is the basis of air, but elementary or simple earth, .which is contained in all of them. If this were the [347] matter of fact, would not that earth be found after the decomposition of the air ? Mr. Scheele has formed an hypothesis on this sub- ject, in which he supposes heat to be composed of dephlogisticated air united to phlogiston, and that H 98 MR. WATT'S FIRST PAPER IN THE this combination is sufficiently subtile to pass through glass vessels. He affirms, that the nitrous and other acids, when in an ignited state, attract the phlogiston from the heat, and set the dephlogisticated air at liberty ; but he does not seem to have been more successful than myself in explaining what becomes of the acid of nitre and phlogiston in the case of the decomposition of nitre by heat. And since we know, from the late experiments, that water is a composition of air, or, more properly, humor and phlogiston, his whole theory must fall to the ground, unless that fact be otherwise accounted for, which it does not seem easy to do. 16. To return to the experiment of the deflagra- tion of dephlogisticated and inflammable air, " it " appears from the two airs becoming red-hot on " their union, that the quantity of heat contained in " one or both of them is much greater than that " contained in steam, because, for the first moments " after the explosion, the water deposited by the air " remains in the form of steam, and consequently " retains the latent heat due to that modification of " water. This matter may be easily examined by " firing the mixture of dephlogisticated and inflam- " mable air in a vessel immersed in another vessel " containing a given quantity of water of a known " heat, and after the vessel in which the deflagration " is performed is come to the same temperature with " the water in which it is immersed, by examining " how much heat that water has gained, which being " divided by the quantity of water produced by the " decomposition of the airs, will give the whole quan- PHILOSOPHICAL TRANSACTIONS. 99 " tity of elementary [348] or latent heat which that " water had contained, both as air and as steam ; " and if from that quantity we deduct the latent ' ; heat of the steam, the remainder will be the latent " or elementary heat contained more in air than in " steam." This experiment may be made more com- pletely by means of the excellent apparatus which MM. Lavoisier and De La Place have contrived for similar purposes. Until direct experiments are made, we may con- clude, from those which have been made by the gentlemen just named, on the decompositions of air by burning phosphorus and charcoal, that the heat extricated during the combustion of inflammable and dephlogisticated air is much greater than it appears to be ; for they found that one Paris ounce ( = 576 Parisian grains) of dephlogisticated air, when decom- posed by burning phosphorus, melted 68,634 ounces of ice ; and as, according to another of their experi- ments, ice, upon being melted, absorbs 135 of heat, by Fahrenheit's scale, each ounce of air gave out 68,634 x 135 == 9265,590 ; that is to say, a quan- tity of heat which would have heated an ounce of water, or any other matter which has the same capacity for receiving heat as water has, from 32 to 9265^: a surprising quantity! (It is to be. under- stood that all the latent heats mentioned herein are compared with the capacity of water.) And when an ounce of dephlogisticated air was changed into fixed air, by burning charcoal, or by the breathing of animals, it melted 29,547 ounces of ice; conse- quently we have 29,547 x 135 = 3988,845, the 100 MR. WATT'S FIRST PAPER IN THE quantity of heat which an ounce of dephlogisticated air loses when it is changed into fixed air. By the heat extricated during the detonation of one ounce of nitre with one ounce of sulphur, 32 ounces of ice were melted ; and, by the experiment I have men- tioned of Dr. Priestley's (6,) it appears that [349] nitre can produce one-half of its weight of dephlogis- ticated air. When the nitre and sulphur are kindled, the dephlogisticated air of the nitre unites with the phlogiston of the sulphur, and sets its acid free, which immediately unites to the alkali of the nitre, and produces vitriolated tartar. The dephlogisticated air, united to the phlogiston, is turned into water, part of which is absorbed by the vitriolated tartar, and part is dissipated in the form of vapours, or unites to the nitrous air, or other air produced in the process. As half an ounce of dephlogisticated air is, in this process, united by inflammation to a quantity of phlogiston sufficient to saturate it, and no fixed air is produced, it should melt a quantity of ice equal to the half of what was melted by the combination of an ounce of air with phlogiston in burning phos- phorus, that is, it should melt 34,317 ounces of ice ; and we find, by MM. Lavoisier and De La Place's experiment, that it actually melted 32 ounces of ice : the small difference may be accounted for by sup- posing that the heat produced by the combustion might not be quite so great as that Dr. Priestley em- ployed in his experiment, or that the nitre might be less pure, and consequently not so much air formed. The two facts, however, agree near enough to permit us to conclude that dephlogisticated air, in uniting to PHILOSOPHICAL TRANSACTIONS. 101 the phlogiston of sulphur, produces as much heat as it does in uniting with the phlogiston of phosphorus. 17. According to Dr. Priestley's experiments, de- phlogisticated air unites completely with about twice its bulk of the inflammable air from metals. The inflammable air being supposed to be wholly phlogis- ton, and being 9 ' 8 of the weight of an equal bulk of dephlogisticated air, and being double in quantity, will be ^Tg of the weight of the dephlogisticated air [350] it unites with. Therefore one ounce (576 grains) of dephlogisticated air, will require 120 grains of inflammable air, or phlogiston, to convert it into water. And supposing the heat extricated by the union of dephlogisticated and inflammable air to be equal to that extricated by the burning of phos- phorus, we shall find that the union of 120 grains of inflammable air with 576 grains of dephlogisticated air, extricates 9265 of heat. 18. In the experiment on the deflagration of nitre with charcoal, by MM. Lavoisier and De La Place, an ounce of nitre and one-third of an ounce of char- coal melted twelve ounces of ice. Supposing the ounce of nitre to have produced half an ounce of de- phlogisticated air, it ought to have consumed 0,1507 ounces of charcoal, and should have melted 14,773 ounces of ice ; and I suppose it fell short of its effect by the heat not being sufficiently intense to decom- pose the nitre perfectly. 1 9. By the above gentlemen's experiment an ounce of charcoal required for its combustion 3,3167 ounces of dephlogisticated air, and produced 3,6715 ounces of fixed air ; therefore there was united to each ounce 102 MR. WATT'S FIRST PAPER IN THE of air, when changed into fixed air, 61,5 grains of phlogiston, and 3988 of heat were extracted. It ap- pears by these facts that the union of phlogiston, in different proportions, with dephlogisticated air, does not extricate proportional quantities of heat. For the addition of 61,5 grains produces 3988, and the union of 120 grains produces 9265. This difference may arise from a mistake in supposing the specific gravity of the inflammable air Dr. Priestley employed to have been only ^ of that of dephlogisticated air; for if it be supposed that its specific gravity was a little more than ^ of that of the dephlogisticated air, then equal additions of phlogiston would [351] have produced equal quantities of heat :* this matter should there- fore be put to the test of experiment, by deflagrating dephlogisticated air with inflammable air of a known specific gravity, or by finding how much dephlogisti- cated air is necessary for the combustion of an ounce of sulphur, the quantity of phlogiston in which has been accurately determined by Mr. Kirwan ; or by finding the quantity of phlogiston in phosphorus, the quantity of dephlogisticated air necessary for its de- composition being known from MM. Lavoisier and De La Place's experiments. * Or it may arise from my being mistaken, in supposing that the same quantity of heat is disengaged by the union of dephlogisticated air with phlogiston, in the form of inflammable air, as is by its union with the phlogiston of phosphorus or sulphur ; and there appears to be some reason why there should not ; because in these latter cases the water, being united to the acids, cannot retain so much elemen- tary heat as it can do when left in the form of pure water, which is the case when the inflammable air is used. PHILOSOPHICAL TRANSACTIONS. 103 On considering these latter gentlemen's experi- ments on the combustion of charcoal, a difficulty arises to know what became of the remainder of the ounce of charcoal ; for the dephlogisticated air, in becoming fixed air, gained only the weight of 0,3548, or about ^ of an ounce ; about f of an ounce are therefore unaccounted for. The weight of the ashes of an ounce of charcoal is very inconsiderable ; and, by some experiments of Dr. Priestley's, charcoal, when freed from fixed air, and other air which it imbibes from the atmosphere, is almost wholly con- vertible into phlogiston. The cause of this apparent loss of matter, I doubt not, these gentlemen can ex- plain satisfactorily, arid very probably in such a man- ner as will throw other lights on the subject. [352] It is also worthy of inquiry, whether all the amaz- ing quantity of heat let loose in these experiments was contained in the dephlogisticated air ; or whether the greatest portion of it was not contained in the phlogiston or inflammable air. If it was all contained in the dephlogisticated air, " the general rule is not "fact, that elastic fluids are enlarged in their dimen- " sions in proportion to the quantity of heat they con- " tain;" because, then, inflammable air, which is ten times the bulk of dephlogisticated air, must be sup- posed to contain no heat at all ; " and it is known, " from some -experiments of my friend Dr. Black's, " and some of my own, that the steam of boiling " water, whose latent and sensible heat are only " 1100, reckoning from 60, or temperate, is more " than twice the bulk of an equal weight of dephlo- " gisticated air." It seems, however, reasonable to 104 MR. WATT'S FIRST PAPER IN THE suppose, that the greater quantity of heat should be contained in the rarer fluid. It may be alleged, that in proportion to the quan- tity of phlogiston that is contained in any fluid, the quantity of heat is lessened. But if we reason by analogy, the attraction of the particles of matter to one another in other cases is increased by phlogis- ton, and " bodies are thereby rendered specifically " heavier ;" and we know of no other substance be- sides heat which can be supposed to separate the particles of inflammable air, and to endow it with so very great an elastic power, and so small a specific gravity. On the other hand, if a great quantity of elementary heat be allowed to be contained in in- flammable air, on account of its bulk, the same reason- ing cannot hold good in respect to the phlogiston of phosphorus, sulphur, charcoal, &c. But all these sub- stances contain other matters besides phlogiston and heat. The acids in the sulphur [353] and phospho- rus, and the alkali and earth in charcoal, may attract the phlogiston so powerfully that the heat they contain may not be able to overcome the adhesion of their particles, until, by the eifect of external heat, they are once removed to such a distance from one another as to be out of the sphere of that kind of attraction.* If it be found to be a constant fact, that equal additions of phlogiston to dephlogisticated air do not extricate equal quantities of heat, that may afford the means of finding the quantities of heat contained * On the whole, this question seems to involve so many difficulties that it cannot be cleared up without many new experiments. PHILOSOPHICAL TRANSACTIONS. 10.5 in phlogiston and dephlogisticated air respectively, and solve the problem. Many other ideas on these subjects present them- selves ; but I am not bold enough to trouble you, or the public, with any speculations but such as I think are supported by uncontroverted facts. I must therefore bring this long letter to a con- clusion, and leave to others the future prosecution of a subject which, however engaging, my necessary avocations prevent me from pursuing. I cannot however conclude, without acknowledging my obli- gations to Dr. Priestley, who has given me every information and assistance in his power, in the course of my inquiries, with that candour and liberality of sentiment which distinguish his character. I return you my thanks for the obliging attention you have paid to this hypothesis ; and remain, with much esteem, &c. JAMES WATT. 106 SEQUEL TO MB. WATT'S FIRST PAPER No. II. SEQUEL TO THE THOUGHTS ON THE CONSTITUENT PARTS OF WATER AND DEPHLOGISTICATED AIR. IN A SUB- SEQUENT LETTER FROM MR. JAMES WATT, ENGINEER, TO MR. DE LUC, F.R.S.* Read May 6, 1784. Birmingham, April 30, 1784. DEAR SIR, On reconsidering the subject of my letter to you of the 26th of November last, I think it necessary to resume the subject, in order to men- tion some necessary cautions to those who may choose to repeat the experiments mentioned there, and to point out some circumstances that may cause varia- tions in the results. In experiments where the dephlogisticated air is to be distilled from common or cubic nitre, these salts should be purified as perfectly as possible, both from other salts and from phlogistic matter of any kind ; otherwise they will produce some nitrous air, or yel- low fumes, which will lessen the quantity, and, per- haps, debase the quality of the dephlogisticated air. If the nitre is perfectly pure, no yellow fumes are * Reprinted from the Philosophical Transactions, vol. Ixxiv. for 1784, p. 354 to 357. IN THE PHILOSOPHICAL TKAKSACTIONS. 107 perceptible, until the alkaline part begins to act upon the glass of the retort, and even then they are very slightly yellow. When earthen retorts are used, and a large quan- tity of air is drawn from the nitre, it acts very much upon the retort, dissolves a great part of it, and be- comes very alkaline, retaining only a small part of its acid, at least only a small part which [355] can be made appear in any of the known forms of that acid ; and unless retorts can be obtained of a true apyrous and compact porcelain, I should prefer glass retorts, properly coated, for making experiments for the present purpose. In some of my experiments the nitre was left in the retort placed in a furnace, so that it took an hour or more to cool. In these cases there was always a deficience of the acid part, which seemed, from some appearances on the coating, either to have penetrated the hot and soft glass, by passing from particle to particle, or to have escaped by small cracks which happened in the retort during the cooling. There was the least deficience of the acid when the distil- lation was performed as quickly as was practicable, and the retort was removed from the fire immediately after the operation was finished. In order to shorten the duration of the experiment, and consequently to lessen the action of the nitre on the retort, it is ad- visable not to distil above 50 ounce measures of de- phlogisticated air from an ounce of nitre. The ex- periment has succeeded best when the retort was placed in a charcoal fire in a chafing-dish or open furnace ; because it is easy in that case to stop the 108 SEQUEL TO MR. WATT'S FIRST PAPER operation, and to withdraw the retort at the proper period. When the dephlogisticated air is distilled from the nitre of mercury, the solution should be performed in the retort itself, and the nitrous air produced by the solution should be caught in a proper receiver, and decomposed by the gradual admission of common air through water ; and the water, which thus becomes impregnated with the acid of the nitrous air, should be added after the process to the water through which the dephlogisticated air has passed. When the solution ceases to give any more nitrous air, the point of the tube of the retort should be raised out of the water ; otherwise, by the condensation of the [356] watery and acid vapours which follow, a par- tial exhaustion will take place, and the receiving water will rise up into the retort and break it, or at least spoil the experiment. A common receiver, such as is used in distilling spirit of nitre, should be ap- plied, with a little water in it, to receive the acid steam ; and it should be kept as cool as can conve- niently be done, as these fumes are very volatile. This receiver should remain as long as the fumes are colourless ; but when they appear, in the neck of the retort, of a yellow colour, it is a mark that the mer- curial nitre will immediately produce dephlogisticated air ; the receiver should then be withdrawn, and an apparatus placed to receive the air. The rest of the process has been sufficiently explained in my former letter. The phlogisticated nitrous acid, saturated by an alkali, will not crystallize ; and, if exposed to evapo- IX THE PHILOSOPHICAL TRANSACTIONS. 109 ration, even in the heat of the air, will become alka- line again, which shows the weakness of its affinity with alkalies when dissolved in water ;* a farther proof of which is, that it is expelled from them by all the acids, even by vinegar, (which fact has been ob- served by Mr. Scheele.) I have observed that litmus is no test of the saturation of this acid by alkalies ; for the infusion of litmus added to such a mixture will turn red, when the liquor appears to be highly alkaline, by its turning the infusions of violets, rose leaves, and most other red juices, green. This does not proceed from the infusion of litmus being more sensible to the presence of acids than other tests ; for I have lately discovered a test liquor (the preparation of which I mean to publish soon) which is more sen- sible to the presence of acids [357] than litmus is ; but which turns green in the same solution of phlogisti- cated nitre that turns litmus red. The unavoidable little accidents which have at- tended these experiments, and which tend to render their results dubious, have prevented me from rely- ing on them as full proofs of the position that no acid enters into the composition of dephlogisticated air ; though they give great probability to the sup- position. I have, therefore, explained the whole of the hypothesis and experiments with the diffidence which ought to accompany every attempt to account for the phenomena of nature on other principles than * You have informed me that Mr. Cavendish has also observed this fact ; and that he has mentioned it in a paper lately read before the Royal Society ; but I had observed the fact previous to my knowledge of his paper. 110 SEQUEL TO MB. WATT'S FIRST PAPER. those which are commonly received by philosophers in general. And in pursuance of the same motives it is proper to mention, that the alkali employed to saturate the phlogisticated nitrous acid, was always that of tartar which is partly mild ; and I have not examined whether highly phlogisticated nitrous acid can perfectly expel fixed air from an alkali, though I know no fact which proves the contrary. It should also be examined, whether the same quantity of real nitrous acid is requisite to saturate a given quantity of alkali, when the acid is phlogisticated, as is neces- sary when it is dephlogisticated. As I am informed that you have done me the ho- nour to communicate my former letter on this sub- ject to the Royal Society, I shall be obliged to you to do me the same favour in respect to the present let- ter, if you judge that it merits it. I remain, &c. JAMES WATT. CAVENDISH'S EXPERIMENTS ON AIR. Ill No. III. EXPERIMENTS ON AIR. BY HENRY CAVENDISH, ESQ., F.R.S. & S.A.*~ Read Jan. 15, 1784. THE following experiments were made principally with a view to find out the cause of the diminution which common air is well known to suffer by all the various ways in which it is phlogisticated, and to discover what becomes of the air thus lost or con- densed ; and as they seem not only to determine this point, but also to throw great light on the con- stitution and manner of production of dephlogisticat- ed air, I hope they may be not unworthy the accept- ance of this Society. Many gentlemen have supposed that fixed air is either generated or separated from atmospheric air by phlogistication, and that the observed diminution is owing to this cause ; my first experiments, there- fore, were made in order to ascertain whether any fixed air is really produced thereby. Now, it must * Reprinted from the Philosophical Transactions, vol. Ixxiv. for 1784, p. 119 to 153. The two interpolations by Dr. Blagden, and an addition by Mr. Cavendish, all made after the Paper itself had been read in January 1784, are now marked by being placed within brackets. ED. 112 CAVENDISH'S EXPERIMENTS ON AIR. be observed, that as all animal and vegetable sub- stances contain fixed air, and yield it by burning, distillation, or putrefaction, nothing can be concluded from experiments in which the air is phlogisticated by them. The only methods I know, which are not liable to objection, are by the calcination of metals, the burning of sulphur or phosphorus, the mixture of nitrous air, and the explosion of inflammable air. Perhaps it may be supposed, that I ought to add to these the electric spark; but I [120] think it much most likely, that the phlogistication of the air, and production of fixed air, in this process, is owing to the burning of some inflammable matter in the apparatus. When the spark is taken from a solution of tournsol, the burning of the tournsol may produce this effect ; when it is taken from lime-water, the burning of some foulness adhering to the tube, or perhaps of some in- flammable matter contained in the lime, may have the same effect ; and when quicksilver or metallic knobs are used, the calcination of them may contri- bute to the phlogistication of the air, though not to the production of fixed air. There is no reason to think that any fixed air is produced by the first method of phlogistication. Dr. Priestley never found lime-water to become turbid by the calcination of metals over it :* Mr. Lavoisier also found only a very slight and scarce perceptible tur- bid appearance, without any precipitation, to take place when lime-water was shaken in a glass vessel full of the air in which lead had been calcined ; and * Experiments on Air, vol. i. p. 137. CAVENDISH S EXPERIMENTS ON AIR. 1J3 even this small diminution of transparency in the lime-water might very likely arise, not from fixed air, but only from its being fouled by particles of the calcined metal, which we are told adhered in some places to the glass. This want of turbidity has been attributed to the fixed air uniting to the metallic calx, in preference to the lime ; but there is no rea- son for supposing that the calx contained any fixed air ; for I do not know that any one has extracted it from calces prepared in this manner ; and though most metallic calces prepared over the fire, or by long exposure to the atmosphere, where they are in con- tact with fixed air, contain that substance, it by no means follows that they must [121] do so when pre- pared by methods in which they are not in contact with it. Dr. Priestley also observed, that quicksilver, fouled by the addition of lead or tin, deposits a powder by agitation and exposure to the air, which consists in great measure of the calx of the imperfect metal. He found too some powder of this kind to contain fixed air ;* but it is by no means clear that this air was produced by the phlogistication of the air in which the quicksilver was shaken ; as the powder was not prepared on purpose, but was procured from quick- silver fouled by having been used in various experi- ments, and may therefore have contained other im- purities besides the metallic calces. I never heard of any fixed air being produced by the burning of sulphur or phosphorus ; but it has * Exper. in Nat. PhU. Vol. i. p. 144. P 114 CAVENDISH'S EXPERIMENTS ON AIR. been asserted, and commonly believed, that lime water is rendered cloudy by a mixture of common and nitrous air ; which, if true, would be a convincing proof that on mixing those two substances some fixed air is either generated or separated ; I therefore examined this carefully. Now it must be observed, that as common air usually contains a little fixed air, which is no essential part of it, but is easily separat- ed by lime water ; and as nitrous air may also con- tain fixed air, either if the metal from which it is procured be rusty, or if the water of the vessel in which it is caught contain calcareous earth, suspend- ed by fixed air, as most waters do, it is proper first to free both airs from it by previously washing them with lime water.* Now I found, by repeated [122] experiments, that if the lime water was clean, and the two airs were previously washed with that substance, not the least cloud was produced, either immediately on mixing them, or on suffering them to stand up- wards of an hour, though it appeared by the thick clouds which were produced in the lime water, by breathing through it after the experiment was finish- ed, that it was more than sufficient to saturate the aqd formed by the decomposition of the nitrous air, * Though fixed air is absorbed in considerable quantity by water, as I showed in Phil. Trans., vol. Ivi., yet it is not easy to deprive com- mon air of all the fixed [122] air contained in it by means of water. On shaking a mixture of ten parts of common air, and one of fixed air, with more than an equal bulk of distilled water, not more than half of the fixed air was absorbed, and on transferring the air into fresh distilled water, only half the remainder was absorbed, as ap- peared by the diminution which it still suffered on adding lime water. CAVENDISH'S EXPERIMENTS ON AIR. 115 and consequently that if any fixed air had been pro- duced, it must have become visible. Once indeed I found a small cloud to be formed on the surface, after the mixture had stood a few minutes. In this experiment the lime water was not quite clean ; but whether the cloud was owing to this circumstance, or to the air's having not been properly washed, I can- not pretend to say. Neither does any fixed air seem to be produced by the explosion of the inflammable air obtained from metals, with either common or dephlogisticated air. This I tried by putting a little lime water into a glass globe, fitted with a brass cock, so as to make it air- tight, and an apparatus for firing air by electricity. This globe was exhausted by an air-pump, and the two airs, which had been previously washed with lime water, let in, and suffered to remain some time, to show whether they would affect the lime water, and then fired by electricity. The event was, that not the least cloud was produced in the lime-water, when the inflammable air was mixed with common air, and [123] only a very slight one, or rather dimi- nution of transparency, when it was combined with dephlogisticated air. This, however, seemed not to be produced by fixed air ; as it appeared instantly after the explosion, and did not increase on standing, and was spread uniformly through the liquor; whereas if it had been owing to fixed air, it would have taken up some short time before it appeared, and would have begun first at the surface, as was the case in the above-mentioned experiment with nitrous air. What it was really owing to I cannot pretend to say ; but 116 CAVENDISH'S EXPERIMENTS ON AIR. if it did proceed from fixed air it would show that only an excessively minute quantity was produced.* On the whole, though it is not improbable that fixed air may be generated in some chymical processes, yet it seems certain that it is not the general effect of phlogisticating air, and that the diminution of com- mon air is by no means owing to the generation or separation of fixed air from it. As there seemed great reason to think, from Dr. Priestley's experiments, that the nitrous and vitriolic acids were convertible into dephlogisticated air, I tried whether the dephlogisticated part of common air might not, by phlogistication, be changed into nitrous or vitriolic acid. For this purpose I impreg- nated some milk of lime with the fumes of burning sulphur, by putting a little of it into a large glass re- ceiver, and burning sulphur therein, taking care to keep the mouth of the receiver stopt till the fumes were all absorbed ; after which the air of the receiver was changed, and more sulphur burnt in it as before, and the process repeated till 122 grains of sulphur were consumed. The milk of lime was then filtered and evaporated, but it yielded no nitrous salt, nor any other substance except selenite ; so that no sen- sible quantity of air was changed [124] into nitrous acid. It must be observed, that as the vitriolic acid produced by the burning sulphur is changed by its union with the lime into selenite, which is very little soluble in water, a very small quantity of nitrous salt, * Dr. Priestley also found no fixed air to be produced by the ex- plosion of inflammable and common air. Vol. v. p. 124. CAVENDISH'S EXPERIMENTS ON AIE. 117 or any other substance which is soluble in water, would have been perceived. I also tried whether any nitrous acid was produc- ed by phlogisticating common air with liver of sul- phur ; for this purpose I made a solution of flowers of sulphur by boiling it with lime, and put a little of it into a large receiver, and shook it frequently, changing now and then the air, till the yellow colour of the solution was quite gone ; a sign that all the sulphur was by the loss of its phlogiston, turned into vitriolic acid, and united to the lime, or precipitated ; the liquor was then filtered and evaporated, but it yielded not the least nitrous salt. The experiment was repeated in nearly the same manner with dephlogisticated air procured from red precipitate ; but not the least nitrous acid was ob- tained. It is well known that common selenite is very little soluble in water ; whereas that procured in the two last experiments was very soluble, and even crystal- lized readily, and was intensely bitter ; this, how- ever, appeared to be owing merely to the acid with which it was formed being very much phlogisticated ; for on evaporating it to dryness, and exposing it to the air for a few days, it became much less soluble, so that on adding water to it not much dissolved ; and by repeating this process once or twice, it seem- ed to become not more soluble than selenite made in the common manner. This solubility of the selenite caused some trouble in trying the experiment ; for while it continued much soluble it would have been impossible to have 118 CAVENDISH'S EXPERIMENTS ON AIR. distinguished a small mixture of nitrous salt ; but by the above-mentioned process I was able to [125] dis- tinguish as small a proportion as if the selenite had been originally no more soluble than usual. The nature of the neutral salts made with the phlogisticated vitriolic and nitrous acids has not been much examined by the chymists, though it seems well worth their attention ; and it is likely that many besides the foregoing may differ remarkably from those made with the same acids in their common state. Nitre formed with the phlogisticated nitrous acid has been found to differ considerably from com- mon nitre, as well as Sal Polychrest from vitriolated tartar. In order to try whether any vitriolic acid was pro- duced by the phlogistication of air, I impregnated fifty ounces of distilled water with the fumes pro- duced on mixing fifty-two ounce measures of nitrous air with a quantity of common air sufficient to de- compound it. This was done by filling a bottle with some of this water, and inverting it into a bason of the same, and then, by a syphon, letting in as much nitrous air as filled it half-full ; after which common air was added slowly by the same syphon, till all the nitrous air was decompounded. When this was done, the distilled water was further impregnated in the same manner till the whole of the above-mentioned quantity of nitrous air was employed. This impreg- nated water, which was very sensibly acid to the taste, was distilled in a glass retort. The first run- nings were very acid, and smelt pungent, being nitrous acid much phlogisticated ; what came next had no CAVENDISH S EXPERIMENTS ON AIR. 119 sensible taste or smell ; but the last runnings were very acid, and consisted of nitrous acid not phlogis- ticated. Scarce any sediment was left behind. These different parcels of distilled liquor were then exactly saturated with salt of tartar, and evaporated ; they yielded 87i grains of nitre, which, as far as I could perceive, was unmixed with vitriolated tartar or any [126] other substance, and consequently no sensible quantity of the common air with which the nitrous air was mixed was turned into vitriolic acid. It appears, from this experiment, that nitrous air contains as much acid as 2f times its weight of salt- petre ; for fifty-two ounce measures of nitrous air weigh 32 grains, and, as was before said, yield as much acid as is contained in 87 grains of saltpetre; so that the acid in nitrous air is in a remarkably con- centrated state, and I believe more than H times as much so as the strongest spirit of nitre ever pre- pared. Having now mentioned the unsuccessful attempts I made to find out what becomes of the air lost by phlogistication, I proceed to some experiments, which serve really to explain the matter. In Dr. Priestley's last volume of experiments is re- lated an experiment of Mr. Warltire's, in which it is said that, on firing a mixture of common and inflam- mable air by electricity in a close copper vessel hold- ing about three pints, a loss of weight was always perceived, on an average about two grains, though the vessel was stopt in such a manner that no air could escape by the explosion. It is also related that on repeating the experiment in glass vessels, the in- 120 CAVENDISH'S EXPERIMENTS ON AIR. side of the glass, though clean and dry before, im- mediately became dewy ; which confirmed an opi- nion he had long entertained, that common air de- posits its moisture by phlogistication. As the latter experiment seemed likely to throw great light on the subject I had in view, I thought it well worth examin- ing more closely. The first experiment also, if there was no mistake in it, would be very extraordinary and curious ; but it did not succeed with me ; for though the vessel I used held more than Mr. Warl- tire's, namely 24,000 grains of water, and though the experiment [127] was repeated several times with different proportions of common and inflammable air, I could never perceive a loss of weight of more than one-fifth of a grain, and commonly none at all. It must be observed, however, that though there were some of the experiments in which it seemed to dimi- nish a little in weight, there were none in which it increased.* In all the experiments the inside of the glass globe became dewy, as observed by Mr. Warltire ; but not the least sooty matter could be perceived. Care was taken in all of them to find how much the air was di- minished by the explosion, and to observe its test. The result is as follows : the bulk of the inflamma- ble air being expressed in decimals of the common air * Dr. Priestley, I am informed, has since found the experiment not to succeed. CAVENDISH S EXPERIMENTS ON AIR. 121 Common air. Inflammable air. Diminution. Air remain- ing after the explosion. Test of this air in first method. Standard. 1,241 ,686 1,555 ,055 ,0 1 1,055 ,642 1,413 ,063 ,0 ,706 ,647 1,059 ,066 ,0 ,423 ,612 ,811 ,097 ,03 ,331 ,476 ,855 ,339 ,27 ,206 ,294 ,912 ,048 ,58 In these experiments the inflammable air was pro- cured from zinc, as it was in all my experiments ex- cept where otherwise expressed : but I made two more experiments, to try whether there was any dif- ference between the air from zinc and that from iron, the quantity of inflammable air being the same in both, namely, 0,331 of the common ; but I could not find any difference to be depended on between the two kinds of air, [128] either in the diminution which they suffered by the explosion, or the test of the burnt air. From the fourth experiment it appears, that 423 measures of inflammable air are nearly sufficient to completely phlogisticate 1000 of common air ; and that the bulk of the air remaining after the explosion is then very little more than four-fifths of the common air employed ; so that as common air cannot be re- duced to a much less bulk than that by any method of phlogistication, we may safely conclude, that when they are mixed in this proportion, and exploded, al- most all the inflammable air, and about one-fifth part of the common air, lose their elasticity, and are con- densed into the dew which lines the glass. Q 122 CAVENDISH'S EXPERIMENTS ON AIR. The better to examine the nature of this dew, 500,000 grain measures of inflammable air were burnt with about 2| times that quantity of common air, and the burnt air made to pass through a glass cylinder eight feet long and three-quarters of an inch in dia- meter, in order to deposit the dew. The two airs were conveyed slowly into this cylinder by separate copper pipes, passing through a brass plate which stopped up the end of the cylinder ; and as neither inflammable nor common air can burn by themselves, there was no danger of the flame spreading into the magazines from which they were conveyed. Each of these magazines consisted of a large tin vessel, invert- ed into another vessel just big enough to receive it. The inner vessel communicated with the copper pipe, and the air was forced out of it by pouring water into the outer vessel ; and in order that the quantity of common air expelled should be 2^ times that of the inflammable, the water was let into the outer vessels by two holes in the bottom of the same tin pan, the hole which conveyed the water into that vessel in [129] which the common air was confined, being 2 times as big as the other. In trying the experiment, the magazines being first filled with their respective airs, the glass cylinder was taken off, and water let, by the two holes, into the outer vessels, till the airs began to issue from the ends of the copper pipes ; they were then set on fire by a candle, and the cylinder put on again in its place. By this means upwards of 135 grains of water were condensed in the cylinder, which had no taste nor smell, and which left no sensible sediment CAVENDISH'S EXPERIMENTS ON AIR. 123 when evaporated to dryness ; neither did it yield any pungent smell during the evaporation ; in short, it seemed pure water. In my first experiment, the cylinder near that part where the air was fired was a little tinged with sooty matter, but very slightly so ; and that little seemed to proceed from the putty with which the apparatus was luted, and which was heated by the flame ; for in another experiment, in which it was contrived so that the luting should not be much heated, scarce any sooty tinge could be perceived. By the experiments with the globe it appeared, that when inflammable and common air are exploded in a proper proportion, almost all the inflammable air, and near one-fifth of the common air, lose their elas- ticity, and are condensed into dew. And by this experiment it appears that this dew is plain water, and consequently that almost all the inflammable air, and about one-fifth of the common air, are turned into pure water. In order to examine the nature of the matter con- densed on firing a mixture of dephlogisticated and inflammable air, I took a glass globe, holding 8800 grain measures, furnished with a brass cock and an apparatus for firing air by electricity. This globe was well exhausted by an air-pump, and then filled with [130] a mixture of inflammable and dephlogis- ticated air, by shutting the cock, fastening a bent glass tube to its mouth, and letting up the end of it into a glass jar inverted into water, and containing a mixture of 19,500 grain measures of dephlogisticated air, and 37,000 of inflammable ; so that, upon open- 124 CAVENDISH'S EXPERIMENTS ON AIR. ing the cock, some of this mixed air rushed through the bent tube, and filled the globe.* The cock was then shut, and the included air fired by electricity, by which means almost all of it lost its elasticity. The cock was then again opened, so as to let in more of the same air, to supply the place of that destroyed by the explosion, which was again fired, and the operation continued till almost the whole of the mixture was let into the globe and exploded. By this means, though the globe held not more than the sixth part of the mixture, almost the whole of it was exploded therein, without any fresh exhaustion of the globe. As I was desirous to try the quantity and test of this burnt air, without letting any water into the globe, which would have prevented my examining the nature of the condensed matter, I took a larger globe, furnished also with a stop cock, exhausted it by an air-pump, and screwed it on upon the cock of the former globe ; upon which, by opening both cocks, the air rushed out of the smaller globe into the larger, till it became of equal density in both ; then, by shutting the cock of the larger globe, un- screwing it again from the former, and opening it under water, I was enabled to find the quantity of the burnt air in it ; and consequently, as the propor- tion which the contents of the two globes bore to each other was [131] known, could tell the quantity * In order to prevent any water from getting into this tube, while dipped under water to let it up into the glass jar, a bit of wax was stuck upon the end of it, which was rubbed oft' when raised above the surface of the water. CAVENDISH S EXPERIMENTS ON AIR. 125 of burnt air in the small globe before the communi- cation was made between them. By this means the whole quantity of the burnt air was found to be 2950 grain measures ; its standard was 1,85. The liquor condensed in the globe, in weight about 30 grains, was sensibly acid to the taste, and by saturation with fixed alkali, and evaporation, yielded near two grains of nitre ; so that it consisted of water united to a small quantity of nitrous acid. No sooty matter was deposited in the globe. The dephlogis- ticated air used in this experiment was procured from red precipitate, that is, from a solution of quick- silver in spirit of nitre distilled till it acquires a red colour. As it was suspected that the acid contained in the condensed liquor was no essential part of the dephlo- gisticated air, but was owing to some acid vapour which came over in making it and had not been absorbed by the water, the experiment was repeated in the same manner, with some more of the same air, which had been previously washed with water, by keeping it a day or two in a bottle with some water, and shaking it frequently ; whereas that used in the preceding experiment had never passed through water, except in preparing it. The condensed liquor was still acid. The experiment was also repeated with dephlogis- ticated air, procured from red lead by means of oil of vitriol ; the liquor condensed was acid, but by an accident I was prevented from determining the nature of the acid. I also procured some dcphlogisticated air from the 126 CAVENDISH'S EXPERIMENTS ON AIR. leaves of plants, in the manner of Doctors Ingenhousz and Priestley, and exploded it with inflammable air as before ; the condensed liquor still continued acid, and of the nitrous kind. [132] In all these experiments the proportion of inflam- mable air was such that the burnt air was not much phlogisticated ; and it was observed, that the less phlo- gisticated it was the more acid was the condensed liquor. I therefore made another experiment, with some more of the same air from plants, in which the proportion of inflammable air was greater, so that the burnt air was almost completely phlogisticated, its standard being ^. The condensed liquor was then not at all acid, but seemed pure water : so that it appears, that with this kind of dephlogisticated air, the condensed liquor is not at all acid, when the two airs are mixed in such a proportion that the burnt air is almost completely phlogisticated, but is con- siderably so when it is not much phlogisticated. In order to see whether the same thing would obtain with air procured from red precipitate, I made two more experiments with that kind of air, the air in both being taken from the same bottle, and the experiment tried in the same manner, except that the proportions of inflammable air were different. In the first, in which the burnt air was almost completely phlogisticated, the condensed liquor was not at all acid. In the second, in which its standard was 1,86, that is, not much phlogisticated, it was considerably acid ; so that with this air, as well as with that from plants, the condensed liquor contains, or is entirely free from, acid, according as the burnt air is less or CAVENDISH'S EXPERIMENTS ON AIR. 127 more phlogisticated ; and there can be little doubt but that the same rule obtains with any other kind of dephlogisticated air. In order to see whether the acid, formed by the explosion of dephlogisticated air obtained by means of the vitriolic acid, would also be of the nitrous kind, I procured some air from turbith mineral, and exploded it with inflammable air, the [133] propor- tion being such that the burnt air was not much phlogisticated. The condensed liquor manifested an acidity, which appeared, by saturation with a solution of salt of tartar, to be of the nitrous kind ; and it was found, by the addition of some terra ponderosa salita, to contain little or no vitriolic acid. When inflammable air was exploded with common air, in such a proportion that the standard of the burnt air was about 3^ , the condensed liquor was not in the least acid. There is no difference, however, in this respect between common air and dephlogis- ticated air mixed with phlogisticated in such a pro- portion as to reduce it to the standard of common air ; for some dephlogisticated air from red precipi- tate, being reduced to this standard by the addition of perfectly phlogisticated air, and then exploded with the same proportion of inflammable air as the common air was in the foregoing experiment, the condensed liquor was not in the least acid. From the foregoing experiments it appears, that when a mixture of inflammable and dephlogisticated air is exploded in such proportion that the burnt air is not much phlogisticated, the condensed liquor con- tains a little acid, which is always of the nitrous kind, 128 CAVENDISH'S EXPERIMENTS ON AIE. whatever substance the dephlogisticated air is pro- cured from ; but if the proportion be such that the burnt air is almost entirely phlogisticated, the con- densed liquor is not at all acid, but seems pure water, without any addition whatever ; and as, when they are mixed in that proportion, very little air remains after the explosion, almost the whole being condensed, it follows, that almost the whole of the inflammable and dephlogisticated air is converted into pure water. It is not easy, indeed, to determine from these ex- periments what proportion the burnt air, remaining after the explosions, bore to the dephlogisticated air employed, as neither the [134] small nor the large globe could be perfectly exhausted of air, and there was no saying with exactness what quantity was left in them ; but in most of them, after allowing for this uncertainty, the true quantity of burnt air seemed not more than r~th of the dephlogisticated air em- ployed, or ^th of the mixture. It seems, however, unnecessary to determine this point exactly, as the quantity is so small, that there can be little doubt but that it proceeds only from the impurities mixed with the dephlogisticated and inflammable air, and consequently that, if those airs could be obtained perfectly pure, the whole would be condensed. With respect to common air, and dephlogisticated air reduced by the addition of phlogisticated air to the standard of common air, the case is different ; as the liquor condensed in exploding them with in- flammable air, I believe I may say in any proportion, is not at all acid ; perhaps, because if they are mixed in such a proportion as that the burnt air is not CAVENDISH S EXPERIMENTS ON AIR. 129 much phlogisticated, the explosion is too weak, and not accompanied with sufficient heat. [All the foregoing experiments, on the explosion of inflammable air with common and dephlogisticated airs, except those which relate to the cause of the acid found in the water, were made in the summer of the year 1781, and were mentioned by me to Dr. Priestley, who in consequence of it made some ex- periments of the same kind, as he relates in a paper printed in the preceding volume of the Transactions. During the last summer also, a friend of mine gave some account of them to M. Lavoisier, as well as of the conclusion drawn from them, that dephlogis- ticated air is only water deprived of phlogiston ; but at that time so far was M. Lavoisier from think- ing any such opinion warranted, that, till he was pre- vailed [135] upon to repeat the experiment himself, he found some difficulty in believing that nearly the whole of the two airs could be converted into water. It is remarkable that neither of these gentlemen found any acid in the water produced by the com- bustion, which might proceed from the latter having burnt the two airs in a different manner from what I did ; and from the former having used a different kind of inflammable air, namely, that from charcoal, and perhaps having used a greater proportion of it.*] Before I enter into the cause of these phenomena, it will be proper to take notice, that phlogisticated air appears to be nothing else than the nitrous acid united to phlogiston ; for when nitre is deflagrated * Interpolation by Dr. Blagdcn, after the paper had been read. ED. E 130 CAVENDISH'S EXPERIMENTS ON AIR, with charcoal, the acid is almost entirely converted into this kind of air. That the acid is entirely con- verted into air, appears from the common process for making what is called clyssus of nitre ; for if the nitre and charcoal are dry, scarce any thing is found in the vessels prepared for condensing the fumes ; but if they are moist a little liquor is collected, which is nothing but the water contained in the materials, impregnated with a little volatile alkali, proceeding in all probability from the imperfectly burnt charcoal, and a little fixed alkali, consisting of some of the alkalized nitre carried over by the heat and watery vapours. As far as I .can perceive, too, at present, the air into which much the greatest part of the acid is converted, differs in no respect from common air phlogisticated. A small part of the acid, however, is turned into nitrous air, and the whole is mixed with a good deal of fixed, and perhaps a little inflam- mable air, both proceeding from the charcoal. It is well known, that the nitrous acid is also con- verted by phlogistication into nitrous air, in which respect there seems a [136] considerable analogy between that and the vitriolic acid ; for the vitriolic acid when united to a smaller proportion of phlogis- ton, forms the volatile sulphureous acid and vitriolic acid air, both of which, by exposure to the atmo- sphere, lose their phlogiston, though not very fast, and are turned back into vitriolic acid, but, when united to a greater proportion of phlogiston, it forms sulphur, which shows no signs of acidity, unless a small degree of affinity to alkalies can be called so, and in which the phlogiston is more strongly adherent, CAVENDISH'S EXPERIMENTS ON AIR. 131 so that it does not fly off when exposed to the air, unless assisted by a heat sufficient to set it on fire. In like manner, the nitrous acid, united to a certain quantity of phlogiston, forms nitrous fumes and nitrous air, which readily quit their phlogiston to common air ; but when united to a different, in all probability a larger quantity, it forms phlogisticated air, which shows no signs of acidity, and is still less disposed to part with its phlogiston than sulphur. This being premised, there seem two ways by which the phenomena of the acid found in the con- densed liquor may be explained ; first, by supposing that dephlogisticated air contains a little nitrous acid, which enters into it as one of its component parts, and that this acid, when the inflammable air is in a sufficient proportion, unites to the phlogiston, and is turned into phlogisticated air, but does not when the inflammable air is in too small a proportion ; and, secondly, by supposing that there is no nitrous acid mixed with, or entering into the composition of, de- phlogisticated air, but that, when this air is in a suf- ficient proportion, part of the phlogisticated air with which it is debased is, by the strong affinity of phlo- giston to dephlogisticated air, deprived of its phlo- giston and turned into nitrous acid ; whereas, when the dephlogisticated air is not more than sufficient to consume the inflammable air, [137] none then remains to deprive the phlogisticated air of its phlogiston, and turn it into acid. If the latter explanation be true, I think we must allow that dephlogisticated air is in reality nothing but dephlogisticated water, or water deprived of its 132 CAVENDISH'S EXPERIMENTS ON AIR. phlogiston ; or, in other words, that water consists of dephlogisticated air united to phlogiston ; and that inflammable air is either pure phlogiston, as Dr. Priestley and Mr. Kirwan suppose, or else water united to phlogiston ;* since, according to this sup- position, these two substances united together form pure water. On the other hand, if the first expla- nation be true, we must suppose that dephlogisticated air consists of water united to a little nitrous acid and deprived of its phlogiston ; but still the nitrous acid in it must make only a very small part of the whole, [138] as it is found that the phlogisticated * Either of these suppositions will agree equally well with the follow- ing experiments ; but the latter seems to me much the most likely. What principally makes me think so is, that common or dephlo- gisticated air do not absorb phlogiston from inflammable air, unless assisted by a red heat, whereas they absorb the phlogiston of nitrous air, liver of sulphur, and many other substances, without that assist- ance ; and it seems inexplicable, that they should refuse to unite to pure phlogiston, when they are able to extract it from substances to which it has an affinity ; that is, that they should overcome the affinity of phlogiston to other substances, and extract it from them, when they will not even unite to it when presented to them. On the other hand, I know no experiment which shows inflammable air to be pure phlogiston rather than an union of it with water, unless it be Dr. Priestley's experiment of expelling inflammable air from iron by heat alone. I am not sufficiently acquainted with the circumstances of that experiment to argue with certainty about it ; but I think it much more likely that the inflammable air was formed by the union of the phlogiston of the iron filings with the water dispersed among them, or contained in the retort or other vessel in which it was heated ; and in all probability this was the cause of the separation of the phlogiston, as iron seems not disposed to part with its phlo- giston by heat alone, without being assisted by the air or some other substance. CAVENDISH S EXPERIMENTS ON AIR. 133 air, which it is converted into, is very small in com- parison of the dephlogisticated air. I think the second of these explanations seems much the most likely ; as it was found that the acid in the condensed liquor was of the nitrous kind, not only when the dephlogisticated air was prepared from red precipitate, but also when it was procured from plants or from turhith mineral ; and it seems not likely, that air procured from plants, and still less likely that air procured from a solution of mercury in oil of vitriol, should contain any nitrous acid. Another strong argument in favour of this opinion is, that dephlogisticated air yields no nitrous acid when phlogisticated by liver of sulphur ; for if this air contains nitrous acid, and yields it when phlogis- ticated by explosion with inflammable air, it is very extraordinary that it should not do so when phlogis- ticated by other means. But what forms a stronger, and, I think, almost decisive argument in favour of this explanation is, that when the dephlogisticated air is very pure, the condensed liquor is made much more strongly acid by mixing the air to be exploded with a little phlo- gisticated air, as appears by the following experi- ments. A mixture of 18,500 grain measures of inflammable air with 9750 of dephlogisticated air procured from red precipitate were exploded in the usual manner ; after which, a mixture of the same quantities of the same dephlogisticated and inflammable air, with the addition of 2500 of air phlogisticated by iron filings and sulphur, was treated in the same manner. The 134 CAVENDISH'S EXPERIMENTS ON AIR. condensed liquor, in both experiments, was acid, but that in the latter evidently more so, as appeared also by saturating each of them separately with marble powder, and precipitating [139] the earth by fixed alkali, the precipitate of the second experiment weigh- ing one-fifth of a grain, and that of the first being several times less. The standard of the burnt air in the first experiment was 1,86, and in the second only 0,9. It must be observed, that all circumstances were the same in these two experiments, except that in the latter the air to be exploded was mixed with some phlogisticated air, and that in consequence the burnt air was more phlogisticated than in the former ; and from what has been before said, it appears that this latter circumstance ought rather to have made the condensed liquor less acid ; and yet it was found to be much more so, which shows strongly that it was the phlogisticated air which furnished the acid. As a further confirmation of this point, these two comparative experiments were repeated with a little variation, namely, in the first experiment there was first let into the globe 1500 of dephlogisticated air, and then the mixture, consisting of 12,200 of dephlo- gisticated air, and 25,900 of inflammable, was let in at different times as usual. In the second experi- ment, besides the 1500 of dephlogisticated air first let in, there was also admitted 2500 of phlogisticated air, after which the mixture, consisting of the same quantities of dephlogisticated and inflammable air as before, was let in as usual. The condensed liquor of the second experiment was about three times as acid CAVENDISH'S EXPERIMENTS ON AIR. 135 as that of the first, as it required 119 grains of a diluted solution of salt of tartar to saturate it, and the other only 37. The standard of the burnt air was 0,78 in the second experiment, and 1,96 in the first. The intention of previously letting in some dephlo- gisticated air in the two last experiments was, that the condensed liquor [140] was expected to become more acid thereby, as proved actually to be the case. In the first of these two experiments, in order that the air to be exploded should be as free as possible from common air, the globe was first filled with a mixture of dephlogisticated and inflammable air, it was then exhausted, and the air to be exploded let in ; by which means, though the globe was not per- fectly exhausted, very little common air could be left in it. In the first set of experiments this circum- stance was not attended to, and the purity of the dephlogisticated air was forgot to be examined in both sets. From what has been said there seems the utmost reason to think that dephlogisticated air is only water deprived of its phlogiston, and that inflammable air, as was before said, is either phlogisticated water or else pure phlogiston ; but in all probability the former. [As Mr. Watt, in a paper lately read before this Society, supposes water to consist of dephlogisticated air and phlogiston deprived of part of their latent heat, whereas I take no notice of the latter circum- stance, it may be proper to mention in a few words the reason of this apparent difference between us. If there be any such thing as elementary heat, it must be allowed that what Mr. Watt says is true ; 136 CAVENDISH'S EXPERIMENTS ON AIR. but by the same rule \ve ought to say, that the di- luted mineral acids consist of the concentrated acids united to water and deprived of part of their latent heat ; that solutions of sal ammoniac, and most other neutral salts, consist of the salt united to water and elementary heat ; and a similar language ought to be used in speaking of almost all chemical combinations, as there are very few which are not attended with some increase or diminution of heat. Now, I have chosen to avoid this form of speaking [141] both because I think it more likely that there is no such thing as elementary heat, and because saying so in this instance, without using similar expressions in speaking of other chemical unions, would be impro- per, and would lead to false ideas ; and it may even admit of doubt, whether the doing it in general would not cause more trouble and perplexity than it is worth.*] There is the utmost reason to think that dephlo- gisticated and phlogisticated air, as M. Lavoisier and Scheele suppose, are quite distinct substances, and not differing only in their degree of phlogis- tication ; and that common air is a mixture of the two ; for if the dephlogisticated air is pretty pure, almost the whole of it loses its elasticity by phlogis- tication, and, as appears by the foregoing experi- ments, is turned into water, instead of being con- verted into phlogisticated air. In most of the fore- going experiments, at least y-ths of the whole was * Second interpolation by Dr. Blagden, after the paper had been read. Ei>. CAVENDISH'S EXPERIMENTS ON AIR. 137 turned into water ; and by treating some dephlo- gisticated air with liver of sulphur, I have reduced it to less than s'cth of its original bulk, and other persons I believe have reduced it to a still less bulk ; so that there seems the utmost reason to suppose that the small residuum which remains after its phlo- gistication proceeds only from the impurities mixed with it. It was just said, that some dephlogisticated air was reduced by liver of sulphur to sVth of its original bulk ; the standard of this air was 4,8, and conse- quently the standard of perfectly pure dephlogisti- cated air should be very nearly 5, which is a confir- mation of the foregoing opinion ; for if the standard of pure dephlogisticated air is 5, common air must, according to this opinion, contain one-fifth of it, and therefore ought to lose one-fifth of its bulk by phlogistication, which is what it is actually found to lose. [142] From what has been said, it follows, that instead of saying air is phlogisticated or dephlogisticated by any means, it would be more strictly just to say, it is deprived of, or receives, an addition of dephlogis- ticated air ; but as the other expression is convenient, and can scarcely be considered as improper, I shall still frequently make use of it in the remainder of this paper. There seemed great reason to think, from Dr. Priestley's experiments, that both the nitrous and vitriolic acids were convertible into dephlogisticated air, as that air is procured in the greatest quantity from substances containing those acids, especially the 138 CAVENDISH'S EXPERIMENTS ON AIR. former. The foregoing experiments, however, seem to show that no part of the acid is converted into dephlogisticated air, and that their use in preparing it is owing only to the great power which they pos- sess of depriving bodies of their phlogiston. A strong confirmation of this is, that red precipitate, which is one of the substances yielding dephlogisticated air in the greatest quantity, and which is prepared by means of the nitrous acid, contains in reality no acid. This I found by grinding 400 grains of it with spirits of sal ammoniac, and keeping them together for some days in a bottle, taking care to shake them fre- quently. The red colour of the precipitate was ren- dered pale, but not entirely destroyed ; being then washed with water and filtered, the clear liquor yielded on evaporation not the least ammoniacal salt. It is natural to think, that if any nitrous acid had been contained in the red precipitate, it would have united to the volatile alkali and have formed ammo- niacal nitre, and would have been perceived on evapo- ration ; but in order to determine more certainly whether this would be the case, I dried some of the same solution of quicksilver from which the red pre- cipitate was prepared with a less heat, so that it acquired only an orange [143] colour, and treated the same quantity of it with volatile alkali in the same manner as before. It immediately caused an effervescence, changed the colour to grey, and yielded 52 grains of ammoniacal nitre. There is the utmost reason to think, therefore, that red precipitate con- tains no nitrous acid ; and consequently that, in pro- curing dephlogisticated air from it, no acid is con- CAVENDISH'S EXPERIMENTS ON AIR. 139 verted into air ; and it is reasonable to conclude, therefore, that no such change is produced in pro- curing it from any other substance. It remains to consider in what manner these acids act in producing dephlogisticated air. The way in which the nitrous acid acts, in the production of it from red precipitate, seems to be as follows. On distilling the mixture of quicksilver and spirit of nitre, the acid comes over, loaded with phlogiston, in the form of nitrous vapour, and continues to do so till the remain- ing matter acquires its full red colour, by which time all the nitrous acid is driven over, but some of the watery part still remains behind, and adheres strongly to the quicksilver ; so that the red precipitate may be considered, either as quicksilver deprived of part of its phlogiston, and united to a certain portion of water, or as quicksilver united to dephlogisticated air ;* after which, on further increasing the heat, the water in it rises deprived of its phlogiston, that is, in the form of dephlogisticated [144] air, and at the same time the quicksilver distils over in its me- tallic form. It is justly remarked by Dr. Priestley, that the solution of quicksilver does not begin to * Unless we were much better acquainted than we are with the manner in which different substances are united together in com- pound bodies, it would be ridiculous to say, that it is the quicksilver in the red precipitate which is deprived of its phlogiston, and not the water, or that it is the water and not the quicksilver ; all that we can say is, that red precipitate consists of quicksilver and water, one or both of which are deprived of part of their phlogiston. In like manner, during the preparation of the red precipitate, it is certain that the acid absorbs phlogiston, either from the quicksilver or the water ; but we are by no means authorised to say from which. 140 CAVENDISH'S EXPERIMENTS ON AIR. yield dephlogisticated air till it acquires its red colour. Mercurius calcinatus appears to be only quicksilver which has absorbed dephlogisticated air from the at- mosphere during its preparation ; accordingly, by giving it a sufficient heat, the dephlogisticated air is driven off, and the quicksilver acquires its original form. It seems, therefore, that mercurius calcinatus and red precipitate, though prepared in a different manner, are very nearly the same thing. From what has been said it follows, that red pre- cipitate and mercurius calcinatus contain as much phlogiston as the quicksilver they are prepared from ; but yet, as uniting dephlogisticated air to a metal comes to the same thing as depriving it of part of its phlogiston and adding water to it, the quicksilver may still be considered as deprived of its phlogiston ; but the imperfect metals seem not only to absorb de- phlogisticated air during their calcination, but also to be really deprived of part of their phlogiston, as they do not acquire their metallic form by driving off the dephlogisticated air. In procuring dephlogisticated air from nitre, the acia acts in a different manner, as, upon heating the nitre red hot, the dephlogisticated air rises mixed with a little nitrous acid, and at the same time the acid remaining in the nitre becomes very much phlo- gisticated ; which shows that the acid absorbs phlo- giston from the water in the nitre, and becomes phlo- gisticated, while the water is thereby turned into de- phlogisticated air. On distilling 3155 grains of nitre in an unglazed earthen retort, it yielded 256,000 CAVENDISH'S EXPERIMENTS ON AIR. 141 grain measures of dephlogisticated air,* the [145] standard of different parts of which varied from 3 to 3,65, but at a medium was 3,35. The matter re- maining in the retort dissolved readily in water, and tasted alkaline and caustic. On adding diluted spirit of nitre to the solution, strong red fumes were pro- duced ; a sign that the acid in it was very much phlogisticated, as no fumes whatever would have been produced on adding the same acid to a solution of common nitre ; that part of the solution also which was supersaturated with acid became blue ; a colour which the diluted nitrous acid is known to assume when much phlogisticated. The solution, when satu- rated with this acid, lost its alkaline and caustic taste, but yet tasted very different from true nitre, seeming as if it had been mixed with sea-salt, and also requir- ed much less water to dissolve it ; but on exposing it for some days to the air, and adding fresh acid as fast as by the flying off of the fumes the alkali predo- minated, it became true nitre, unmixed, as far as I could perceive, with any other salt.f It has been remarked, that the dephlogisticated air procured from nitre is less pure than that from red precipitate and many other substances, which * This is about eighty-one grain measures from one grain of nitre ; and the [145] weight of the dephlogisticated air, supposing it 800 times lighter than water, is one-tenth of that of the nitre. In all probability it would have yielded a much greater quantity of air, if a greater heat had been applied. t This phlogistication of the acid in nitre by heat has been ob- served by Mr. Scheele ; see his experiments on air and fire, p. 45, English translation. 142 CAVENDISH'S EXPERIMENTS ON AIR. may perhaps proceed from unglazed earthen retorts having been commonly used for this purpose, and which, conformably to Dr. Priestley's discovery, may possibly absorb some common air from without, and emit it along with the dephlogisticated air ; but if it should be found that the dephlogisticated air procur- ed from nitre in glass or glazed earthen vessels is also impure, it would seem to show that part of [146] the acid in the nitre is turned into phlogisticated air, by absorbing phlogiston from the watery part. From what has been said it appears, that there is a considerable difference in the manner in which the acid acts in the production of dephlogisticated air from red precipitate and from nitre ; in the former case the acid comes over first, leaving the remaining substance deprived of part of its phlogiston ; in the latter the dephlogisticated air comes first, leaving the acid loaded with the phlogiston of the water from which it was formed. On distilling a mixture of quicksilver and oil of vitriol to dryness, part of the acid comes over, loaded with phlogiston, in the form of volatile sulphureous agid and vitriolic acid air ; so that the remaining white mass may be considered as consisting of quick- silver deprived of its phlogiston, and united to a cer- tain proportion of acid and water, or of plain quick- silver united to a certain proportion of acid and de- phlogisticated air. Accordingly, on urging this white mass with a more violent heat, the dephlogisticated air comes over, and at the same time part of the quicksilver rises in its metallic form, and also part of the white mass, united in all probability to a greater CAVENDISH S EXPERIMENTS ON AIR. 143 proportion of acid than before, sublimes ; so that the rationale of the production of dephlogisticated air from turbith mineral, and from red precipitate, are nearly similar. True turbith mineral consists of the above-men- tioned white mass, well washed with water, by which means it acquires a yellow colour, and contains much less acid than the unwashed mass. Accordingly, it seems likely, that on exposing this to heat, less of it should sublime without being decompounded, and con- sequently that more dephlogisticated air should be procured from it than from the unwashed mass. [147] This is an instance that the superabundant vitrio- lic acid may, in some cases, be better extracted from the base it is* united to by water than by heat. Vi- triolated tartar is another instance ; for, if vitriolated tartar be mixed with oil of vitriol and exposed even to a pretty strong red heat, the mass will be very acid ; but if this mass is dissolved in water, and eva- porated, the crystals will be not sensibly so. In all probability, the vitriolic acid acts in the same manner in the production of dephlogisticated air from alum, as the nitrous does in its production from nitre ; that is, the watery part comes over first in the form of dephlogisticated air, leaving the acid charged with its phlogiston. Whether this is also the case with regard to green and blue vitriol, or whether in them the acid does not rather act in the same manner as in turbith mineral, I cannot pretend to say, but I think the latter more likely. There is another way by which dephlogisticated air has been found to be produced in great quantities, 144 CAVENDISH'S EXPERIMENTS ON AIR. namely, the growth of vegetables exposed to the sun or day-light ; the rationale of which, in all probabi- lity is, that plants, when assisted by the light, deprive part of the water sucked up by their roots of its phlo- giston, and turn it into dephlogisticated air, while the phlogiston unites to, and forms part of, the sub- stance of the plant. There are many circumstances which show, that light has a remarkable power in enabling one body to absorb phlogiston from another. Mr. Senebier has observed, that the green tincture procured from the leaves of vegetables by spirit of wine, quickly loses its colour when exposed to the sun in a bottle not more than one-third part full, but does not do so in the dark, or if the bottle is quite full of the tincture, or if the air in it [148] is phlogisticated ; whence it is natural to conclude, that the light enables the de- phlogisticated part of the air to absorb phlogiston from the tincture ; and this appears to be really the case, as I find that the air in the bottle is consider- ably phlogisticated thereby. Dephlogisticated spirit of nitre also acquires a yellow colour, and becomes phlogisticated by exposure to the sun's rays ;* and I find on trial that the air in the bottle in which it is * If spirit of nitre is distilled with a very gentle heat, the part which conies over is high coloured and fuming, and that which re- mains behind is quite colourless, and fumes much less than other ni- trous acid of the same strength, and the fumes are colourless. This is called dephlogisticated spirit of nitre, as it appears to be really de- prived of phlogiston by the process. The manner of preparing it, as well as its property of regaining its yellow colour by exposure to the light, is mentioned by Mr. Scheele in the Stockholm Memoirs, 1774. CAVENDISH S EXPERIMENTS ON AIR. 145 contained becomes dephlogisticated, or in other words, receives an increase of dephlogisticated air, which shows that the change in the acid is not owing to the sun's rays communicating phlogiston to it, but to their enabling it to absorb phlogiston from the water contained in it, and thereby to produce dephlogisti- cated air. Mr. Scheele also found, that the dark colour acquired by luna cornea on exposure to the light, is owing to part of the silver being revived ; and that gold, dissolved in aqua regia, and deprived by distillation of the nitrous and superfluous marine acid, is revived by the same means ; and there is the utmost reason to think, that, in both cases, the re- vival of the metal is owing to its absorbing phlogis- ton from the water. Vegetables seem to consist almost entirely of fixed and phlogisticated air, united to a large proportion of phlogiston and some water, since by burning in the open air, in which their phlogiston unites to the de- phlogisticated part of the atmosphere, and forms [149] water, they seem to be reduced almost entirely to water and those two kinds of air. Now plants grow- ing in water without earth, can receive nourishment only from the water and air, and must therefore, in all probability, absorb their phlogiston from the water. It is known also that plants growing in the dark do not thrive well, and grow in a very different manner from what they do when exposed to the light. From what has been said, it seems likely that the use of light in promoting the growth of plants and the production of dephlogisticated air from them, is, 146 CAVENDISH'S EXPERIMENTS ox AIK. that it enables them to absorb phlogiston from the water. To this it may perhaps be objected, that though plants do not thrive well in the dark, yet they do grow, and should therefore, according to this hy- pothesis, absorb water from the atmosphere, and yield dephlogisticated air, which they have not been found to do. But we have no proof that they grew at all in any of those cases in which they were found not to yield dephlogisticated air ; for though they will grow in the dark, yet their vegetative powers may perhaps at first be entirely checked by it, espe- cially considering the unnatural situation in which they must be placed in such experiments. Perhaps two plants growing in the dark may be able to absorb phlogiston from water not much impregnated with dephlogisticated air, but not from water strongly im- pregnated with it ; and consequently, when kept under water in the dark, may perhaps at first yield some dephlogisticated air, which, instead of rising to the surface, may be absorbed by the water, and, be- fore the water is so much impregnated as to suffer any to escape, the plant may cease to vegetate unless the water is changed. Unless, therefore, it could be shown that plants growing in the dark, in water alone, will increase in size, without yielding dephlogisticated [150] air, and without the water becoming more im- pregnated with it than before, no objection can be drawn from thence. Mr. Senebier finds that plants yield much more dephlogisticated air in distilled water impregnated with fixed air, than in plain distilled water, which is perfectly conformable to the above-mentioned hypo- CAVENDISH'S EXPERIMENTS ON AIR. 147 thesis ; for as fixed air is a principal constituent part of vegetable substances, it is reasonable to suppose that the work of vegetation will go on better in water containing this substance, than in other water. '""[There are several memoirs of Mr. Lavoisier pub- lished by the Academy of Sciences, in which he en- tirely discards phlogiston, and explains those pheno- mena which have been usually attributed to the loss or attraction of that substance, by the absorption or expulsion of dephlogisticated air ; and as not only the foregoing experiments, but most other phenomena of nature, seem explicable as well, or nearly as well, upon this as upon the commonly believed principle of phlogiston, it may be proper briefly to mention in what manner I would explain them on this principle, and why I have adhered to the other. In doing this, I shall not conform strictly to his theory, but shall make such additions and alterations as seem to suit it best to the phenomena ; the more so, as the fore- going experiments may, perhaps, induce the author himself to think some such additions proper. According to this hypothesis, we must suppose, that water consists of inflammable air united to de- phlogisticated air ; that nitrous air, vitriolic acid air, and the phosphoric acid, are also combinations of phlogisticated air, sulphur, and phosphorus, with de- phlogisticated air ; and that the two former, by a fur- ther addition of the same substance, are reduced to the common [151] nitrous and vitriolic acids; that * Addition by Mr. Cavendish after the paper had been read. ED. 148 CAVENDISH'S EXPERIMENTS ON AIR. the metallic calces consist of the metals themselves united to the same substance, commonly, however, with a mixture of fixed air ; that on exposing the calces of the perfect metals to a sufficient heat, all the dephlogisticated air is driven off, and the calces are restored to their metallic form ; but as the calces of the imperfect metals are vitrified by heat, instead of recovering the metallic form, it should seem as if all the dephlogisticated air could not be driven off from them by heat alone. In like manner, according to this hypothesis, the rationale of the production of de- phlogisticated air from red precipitate is, that during the solution of the quicksilver in the acid, and the subsequent calcination, the acid is decompounded, and quits part of its dephlogisticated air to the quick- silver, whereby it comes over in the form of nitrous air, and leaves the quicksilver behind united to de- phlogisticated air, which, by a further increase of heat, is driven off, while the quicksilver reassumes its metallic form. In procuring dephlogisticated air from nitre, the acid is also decompounded ; but with this difference, that it suffers some of its dephlogisticated air to escape, while it remains united to the alkali itself, in the form of phlogisticated nitrous acid. As to the production of dephlogisticated air from plants, it may be said, that vegetable substances consist chiefly of various combinations of three different bases, one of which, when united to dephlogisticated air, forms water, another fixed air, and the third phlo- gisticated air ; and that by means of vegetation each of these substances are decomposed, and yield their dephlogisticated air ; and that in burning they again CAVENDISH'S EXPERIMENTS ON AIR. 149 acquire dephlogisticated air, and are restored to their pristine form. It seems, therefore, from what has been said, as if the phenomena of nature might be explained very well on this principle [152] without the help of phlo- giston ; and indeed, as adding dephlogisticated air to a body comes to the same thing as depriving it of its phlogiston and adding water to it, and as there are, perhaps, no bodies entirely destitute of water, and as I know no way by which phlogiston can be transferred from one body to another, without leav- ing it uncertain whether water is not at the same time transferred, it will be very difficult to determine by experiment which of these opinions is the truest ; but as the commonly received principle of phlogiston explains all phenomena, at least as well as Mr. La- voisier's, I have adhered to that. There is one cir- cumstance also, which though it may appear to many not to have much force, I own has some weight with me ; it is, that as plants seem to draw their nourish- ment almost entirely from water and fixed and phlo- gisticated air, and are restored back to those sub- stances by burning, it seems reasonable to conclude, that notwithstanding their infinite variety they con- sist almost entirely of various combinations of water and fixed and phlogisticated air, united according to one of these opinions to phlogiston, and deprived ac- cording to the other of dephlogisticated air, so that, according to the latter opinion, the substance of a plant is less compounded than a mixture of those bodies into which it is resolved by burning ; and it is 150 CAVENDISH'S EXPERIMENTS ON AIR. more reasonable to look for great variety in the more compound than in the more simple substance. Another thing which Mr. Lavoisier endeavours to prove is, that dephlogisticated air is the acidifying principle. From what has been explained it appears, that this is no more than saying, that acids lose their acidity by uniting to phlogiston, which, with re- gard to the nitrous, vitriolic, phosphoric, and arsenical acids, is certainly true. The same tiling I believe, may be said of the acid of sugar ; and Mr. Lavoisier's experiment is a [153] strong confirmation of Berg- man's opinion, that none of the spirit of nitre enters into the composition of the acid, but that it only serves to deprive the sugar of part of its phlogiston. But as to the marine acid and acid of tartar, it does not appear that they are capable of losing their acidity by any union with phlogiston. It is to be remarked also, that the acids of sugar and tartar, and in all probability almost all the vegetable and animal acids are by burning reduced to fixed and phlogisticated air and water, and therefore contain more phlogiston, or less dephlogisticated air than those three sub- stances.] MEMOIRE. 151 No. IV. MEMOIRE OU L'ON PEOTTVE PAR LA DECOMPOSITION DE L'EAU, QUE CE FLUIDE N'EST POINT UNE SUBSTANCE SIMPLE, ET QF'lL Y A PLUSIEURS MOYENS D'OBTENIR EN GRAND L J AIR INFLAMMABLE QUI Y ENTRE COMME PRINCIPE CONSTITUANT. PAR MM. MEUSNIER ET LA- VOISIER.* Lule 21 Avril 1784. DEPUIS qu'on connoit 1'experience dans laquelle un melange d'air inflammable et d'air de'phlogistique', fait suivant les proportions convenables, ne produit en brulant que de 1'eau tres-pure, a peu-pres gale en poids a celui des deux airs re"unis, il etoit difficile de ne pas reconnoitre dans cette production d'eau, une preuve presque eVidente que ce fluide, mis de tout temps au rang des substances simples, est reellement un corps compose" ; et que les deux airs, du melange desquels il resulte, en fournissent les principes consti- tuans. M. Lavoisier en tira cette consequence dans uri Me'moire qu'il lut a la derniere seance publique de cette Academic, en annoncant avec M. de la Place qu'ils avoient les premiers obtenu ainsi une quantite * Reprinted from the Me'inoires de 1'Academie des Sciences for 1781, (printed in 1784), pp. 269 to 283. 152 MEMOIRE PAR d'eau assez considerable pour la soumettre a quelques epreuves chimiques ;* et en admettant quelqu'exac- titude dans la determination du poids des airs em- ploye's dans cette experience, on ne voit pas comment il seroit possible de 1'infirmer : on a cependant eleve des doutes sur cette reduction entiere de deux fluides aeriformes en eau ; et malgre les soins apportes par M. Lavoisier, pour assurer, autant qu'il est possible, la precision d'une experience aussi delicate ; malgre la conformite du resultat obtenu a peu-pres en meme temps par M. Monge, [270] dans le laboratoire de 1'Ecole de Mezieres, avec un appareil tres-exact et les attentions les plus scrupuleuses, quelques personnes ont cru pouvoir attribuer 1'eau qui provient de cette operation, a 1'humidite dissoute par les airs, et privee de soutien au moment de leur combustion. Mais sans parler du peu de proportion d'une cause aussi legere avec la quantite d'eau dont il faut expliquer 1'origine, si les airs eux-memes n'y entroient pour rien, il resteroit a trouver quel est le produit reel de leur combustion ; et puisqu'en en brulant des volumes considerables, on n'obtient autre chose que cette eau tres-pure qu'on voit couler de toutes parts, il s'ensuit * Ce Memoire se trouve dans ce meme volume. C'est par erreur qu'il a ete imprime posterieurement a celui-ci. [Notwithstanding this note, and a similar one which is printed with M. Lavoisier's sub- sequent Memoir, at p. 171, these two Memoirs have been allowed to retain here the same relative place which they occupy in the Me moires de 1' Academic for 1781. For although M. Lavoisier's paper was in part read before that by him and M. Meusnier, yet much of it contains express allusions to that other, and was therefore written later in order of time ; and we have in the Memoires, as printed, no means of determining precisely the extent of the additions. ED.] MM. MEUSNIER ET LAVOISIER. 153 que meme en admettant une erreur grossiere clans la comparaison du poids des airs avec celui de 1'eau qui se manifesto, 1'explication qu'on vient de rappeler se- roit encore sujette aux difficulty's les plus fortes. C'est au reste la multitude des faits, bien plutot que le raisonnement, qui doit e"tablir toute espece de theorie nouvelle, et c'est la voie que nous avons prise dans le travail dont nous allons rendre compte, il est le fruit des recherches recentes auxquelles M. Lavoi- sier et moi avons eu occasion de nous livrer sur la production de 1'air inflammable ; et voyant deja tant de raisons de croire que c'est dans 1'eau que la Nature a depose tout celui dont elle fait usage pour ses di- verses combinaisons, ayant e"prouve" qu'en le tirant des corps plus composes, il est toujours altere par le melange des substances qui servoient a le fixer, nous ne pouvions etre mieux conduits a le chercher directe- rnent dans ce fluide si abondant. La question qu'il s'agissoit de resoudre e"toit done de decomposer 1'eau, en lui pre"sentant des intermedes capables de s'unir a 1'un de ses principes constituans, et tendans a cette union avec une force superieure a celle qui lie ces principes entr'eux : et puisqu'il etoit si naturel de penser qu'outre 1'air inflammable, 1'eau contient encore 1'air de"phlogistique que nous avions vu contribuer a sa formation, il falloit chercher a en separer ce dernier par le moyen des corps avec les- quels on lui connoit une grande affinite ; [271] c'etoit done parmi les corps combustibles et les metaux cal- cinables que nous pouvions esperer de trouver les agens propres a operer cette decomposition. M. Lavoisier, conduit par ces principes, avoit deja u 154 MEMOIEE PAR tente" un melange dont il rendit compte dans le M6- moire que je viens de citer, et avoit reussi par ce moyen a obtenir de 1'air inflammable. De la limaille de fer et de 1'eau mises en petite quantite dans la partie superieure d'une cloche pleine de mercure, n'avoient pas tarde a laisser degager ce fluide aeri- forme, qui au bout de quelques jours devint assez abondant pour en essayer la combustion, et le fer, cal- cine alors, annoii9oit une absorption d'air dephlogis- tique, qu'il ne pouvoit avoir tire que de 1'eau dans laquelle il etoit plonge. Cette experience dans laquelle M. Lavoisier avoit opere une vraie decomposition de 1'eau, n'etoit cepen- dant pas exempte de toute difficult^, et quoiqu'il cut employe de 1'eau distillee, la petitesse du volume de 1'air inflammable ainsi obtenu, pouvoit peut-etre don- ner encore lieu aux objections qu'on a etablies sur la supposition ou cette eau n'eut pas ete parfaitement pure. II manquoit en effet quelque chose a ce pre- cede" ; et puisque la matiere de feu paroit un element si essentiel a la formation de tous les Guides elasti- ques, qu'elle est presque toujours absorbee dans les ex- periences qui en produisent, et degagee quand ils se condensent ; puisque sur-tout il s'en fait une produc- tion si considerable lorsque les deux airs qui consti- tuent 1'eau, la reforment par leur combustion ; et qu'enfin les metaux calcinables de meme que les com- bustibles ne deviennent sensiblement alterables par 1'air de'phlogistique qu'a 1'aide d'une temperature tres- e"levee, il n'est pas e"tonnant qu'une operation, dans laquelle on n'employoit d'autre chaleur que celle de 1'atmosphere, eut un effet si lent et si peu marque. MM. MEUSNIER ET LAVOISIER. 155 La decomposition do 1'eau exige done, pour se faire rapidement, le concours d'une chaleur considerable, et c'est une condition principale que nous avions a rem- plir ; mais la difficulte de donncr a 1'eau une chaleur au-dessus du degre de son ebullition, e'toit [272] encore un obstacle a nos vues ; et ce n'est qu'en la prenant deja reduite en vapours, que nous avons pu la porter jusqu'a 1'etat d'incandescence auquel nous presumions qu'il e'toit necessaire de 1'amener. D'apres ces considerations, 1'appareil necessaire se presente de lui-meme et n'exigeroit pas une longue description ; mais quelqu'interessantes qu'aient e*te" pour nous les premieres epreuves que nous en avons faites, et dont M. Berthollet a bien voulu etre temoin et cooperateur, les bornes de ce Memoire ne nous per- mettent pas d'entrer a ce sujet dans le detail qu'elles exigeroient, et nous passerons rapidement aux expe"- riences plus concluantes que nous nous sommes em- presses de tenter des que notre appareil eut acquis successivement le degre de perfection necessaire. Nous dirons seulement qu'en faisant passer dans un tube de fer incandescent, soit de 1'eau en vapeurs fournie par une cornue a laquelle il etoit ajuste", soit de 1'eau versee goutte a goutte an moyen d'un robinet ouvert imperceptiblement, et qui se vaporisant de meme des qu'elle commen^oit a atteindre la partie rouge du fer, e"toit egalement forcee, en la parcourant en entier, d'acquerir au passage le meme degre" de chaleur, nous avons constamment obtenu de grandes quantites d'air inflammable : que cet air pre"sentoit. dans son inflammation et dans sa detonation avec 1'air dephlogistique, tous les phenomenes qui carac- 156 MEMOIRE PAR teVisent celui qu'on obtient par la dissolution de quel- ques metaux dans Tacide vitriolique : qu'il avoit de meme une odeur tres-marquee ; mais que n'offrant rien de semblable & celle de 1'acide sulfureux qu'on demele dans 1'air inflammable ordinaire, celui-ci se rapprochoit infiniment plus de ce que les Chimistes ont nomme empyreume : que sa pesanteur specifique de"terminee avec des instrumens tres-delicats, s'est toujours trouvee d'autant moindre que 1'air atmo- spherique qui rernplissoit originairement 1'appareil, s'y est mele en moindre proportion par rapport au volume total de 1'air inflammable qu'on a fabrique a chaque experience, et que pour peu qu'on en [273] produise un volume decuple de la capacite des vaiss- eaux qu'on emploie, on 1'obtient au moins neuf fois plus leger que celui de 1'atmosphere : qu'enfin le tube de fer soumis a cette operation, eprouve successive- ment une alteration considerable qui le rend de moins en moins propre & degager 1'air inflammable : que 1'operation Eprouve par cette raison, un rallentisse- ment gradxie jusqu'a ce qu'elle cesse enfin totalement, et qu'alors le fer calcine* inte'rieurement se trouve con- verti sur une grande epaisseur en une matiere sin- guliere que nous decrirons plus bas, et qui annonce sa combinaison avec 1'air de'phlogistique' qu'il devoit en- lever a 1'eau, pour mettre 1'air inflammable en liberte. Ces experiences expliquent done 1'observation faite assez re"cemment, que le fer rouge eteint dans 1'eau, de- gage de 1'air inflammable ; en le plongeant au-dessous d'une cloche renverse"e et pleine d'eau, on voit en efiet ce gaz se rassembler dans la partie supe>ieure de la cloche, et on lui trouve toutes les proprie"tes de celui MM. MEITSNIER ET LAVOISIER. 157 que nous venons de d<3crire : cette espece d'epreuve est meme extremement commode pour connoitre sur le champ les diverses substances qui peuvent produire le meme effet, et nous nous en sommes servis dans cette vue : nous allons encore rendre un compte suc- cinct de ces tentatives ge"nerales. II etoit en effet bien essentiel de verifier si les sub- stances calcinables ou combustibles sont les seules qui puissent decomposer 1'eau comme la the'orie 1'indi- quoit ; et il etoit egalement inteYessant de determiner si elles ont toutes cette propriete : nous avons en consequence soumis a 1'experience de 1'extinction dans 1'eau un assez grand nombre de corps incandescens, principalement des substances metalliques : celles qui sont facilement fusibles ont te mises dans des creu- sets, avec lesquels nous les avons plongees, et toutes ces dpreuves ont e*te d'accord avec la theorie que nous avons exposee. Ainsi, 1'or et 1'argent, metaux parfaits, qui ne sont susceptibles d'aucune calcination, pris en masses considerables du poids de trente et qua- rante-cinq marcs, et plonge"s presque [247] fondans, n'ont point fourni d'air inflammable : des cailloux rougis, des creusets vides, substances egalement de- nuees d'affmite pour 1'air deplilogistique, n'ont de'gage', comme les premiers, qu'un air incombustible en tres- petite quantite, que tout annonce etre celui que 1'eau tient naturellement en dissolution. Le cuivre rouge, quoique calcinable, a eu le m&tne sort ; n'ayant pas sans doute avec 1'air de'phlogistique' le degre d'affinite* suffisante pour le separer de 1'air inflammable, et il est bien remarquable que, dissous par 1'acide vitrioli- que, il n'en fournit pas non plus ; mais le zinc qui 158 MESIOIRE PAR a cet egard se comporte comme le fer, a donne aussi comme lui de 1'air inflammable par son contact avec 1'eau : le charbon vegetal et le charbon de terre, plonge"s brulans, en ont e"galement fourni, quoiqu'on les cut e"puises par une longue combustion de tout celui qu'ils pouvoient donner par la seule chaleur ; et il faut bien que 1'eau soit essentielle a ces divers phe- nomenes, puisque rimmersiou dans le mercure ne pro- duit rien de semblable : quant a 1'etain et au regule d'antimoine, ils ont constamment occasion^ des ex- plosions si fortes que les cloches ont ete brise"es avec eclat, et ils nous ont appris a ne plus tenter ces sortes d'epreuves qu'avec des precautions particulieres. En meme temps que nous voyions la theorie qui nous guidoit se confirmer de plus en plus, nous veni- ons d'acquerir par ces dernieres experiences une con- noissance precieuse pour la pratique, en apprenant qu'un me'tal commun dans les Arts, tel que le cuivre rouge, qui peut, apres le fer, supporter la plus grande chaleur, n'eprouve aucune alteration dc la part de 1'eau, dans l'e"tat d'incandescence. Si en effet ce metal se fut calcine" comme le fer, on n'auroit pu fa- briquer pour ces sortes d'experiences que des appareils exposes a une prompte destruction, et les recherches exp^rimentales y auroient presque autant perdu que les usages auxquels on appliquera les nouvelles me- thodes qui re"sultent de ce travail pour la fabrication de 1'air inflammable ; car le verre ou les poteries sont infiniment trop fragiles pour etre employes en [275] grand a des operations de ce genre, et Ton sait d'ail- leurs que ces dernieres ne sont plus inperme'ables a 1'air, des qu'elles sont echaufie'es au point de devenir MM. MEUSNIER ET LAVOISIER. 159 rouges. C'cst done de cuivre que doivent etre faits par la suite les appareils que Ton destinera a ces sor- tes de decompositions de 1'eau, et Ton y renfermera les substances que Ton jugera pouvoir y employer ; nous cherchames en consequence a nous procurer des tubes de ce metal, coules d'une seule piece et sans soudure, mais I'empressement, bien naturel dans des recherches aussi neuves, nous engagea & continuer les notres avec les tubes de fer que nous avions sous la main. II ne s'agissoit plus alors de chercher de nouvelles metliodes pour fabriquer 1'air inflammable, nous nous voyions en possession d'une theorie feconde, de la- quelle derive une multitude de ces moyens ; mais plus cette theorie cadroit avec les epreuves que nous avions deja faites, plus nous devions 1'examiner seVerement, et multiplier pour cela les experiences de poids et de mesure, sans lesquels la Physique ni la Chimie ne peuvent plus guere rien admettre. Nous cherchames done d'abord a constater si en mesurant exactement toute 1'eau qu'on fait passer dans 1'appareil que nous avons indique, et recueillant de meme celle qui se condense, apres en avoir par- couru toute la longueur, il se trouveroit entre ces deux quantites une difference notable qu'on put attribuer a 1'eau decomposee qui auroit ainsi change de nature : ainsi, au lieu de faire aboutir immediatement le tube de fer a 1'appareil pneumato-chimique, nous interpo- sames un serpentin environne" d'eau froide, et 1'eau qui se condensoit dans ce refrigerent, etoit versee dans un flacon tubule, d'ou les produits aeriformes se rendoient, comme a 1'ordinaire, sous le cloches de 160 MEMOIRE PAR 1'appareil par un conduit particulier applique" a la tu- bulure du flacon. La Planche jointe a ce Memoire, donne une ide"e complete de toute cette disposition ; on y voit en detail 1'entonnoir qui verse 1'eau goutte a goutte, a 1'aide d'un robinet qui en traverse la queue, le tube de fer ou elle passe ensuite, le brasier qui [276] 1'echauffe, le serpentin, le recipient, et enfin la cloche ou est recueilli 1'air inflammable : il est pres- que inutile d'observer que toutes les jointures de cet appareil e"toient herme"tiquement ferm^es par des kits, de 1'exactitude desquels on s'est assure" avec le plus grand soin. Plusieurs Membres de 1'Acade'mie voulurent bien etre te"moins de cette experience importante, il en re- sulta cent vingt-cinq pintes d'air inflammable, et il s'en fallut trois onces un gros que 1'eau re9ue au sor- tir de 1'appareil n'egalat cello que 1'entonnoir superieur y avoit verse"e ; ce deficit, beaucoup trop considerable pour qu'on put 1'attribuer a 1'humidite qui avoit du mouiller I'inteYieur de la machine, annonce done qu'- une certaine quantite d'eau e"toit vraimeut disparue, et avoit contribue" a former 1'air inflammable ainsi obtenu : cet air fut peso" avec la plus scrupuleuse at- tention, il etoit neuf fois et demi plus leger que 1'air atmospherique, et le volume total qui en avoit etc" produit, pesoit par consequent quatre gros et quel- ques grains : il est a remarquer que c'est, a quelques grains pres, le sixieme de la quantite" d'eau que nous avons vu s'etre dissipee, et que cette proportion est aussi pre'cise'ment celle qui resulte de 1'exp^rience capitale dans laquelle on forme de 1'eau par la com- bustion des deux airs. MM. MEUSNIEK ET LAVOISIER. 161 Une seconde experience faite avec le meme canou, dans la vue de la calciner entierement, a encore fourni soixante-une pintes d'air inflammable, avec une deper- dition d'eau d'une once sept gros, dont la sixieme partie etoit encore, a quelques grains pres, egale au poids total du gaz degage. On avoit reussi parfaitement a preserver ce tube de fer de 1'action de 1'air exterieur, par des envelop- pes et des luts d'argile arranges avec soin ; il se cassa neanmoins avec facilite" quand on voulut en visiter 1'interieur, et a 1'exception d'une couche tres-mince de fer doux qui le couvroit par dehors, il se trouva converti tout entier en une matiere qui n'avoit plus du fer que la couleur, mais elle presentoit un grain compost de facettes brillantes qui lui donnoient quelque [277] ressemblance avec la mine de fer spe"- culaire ; la surface interieure paroissoit meme etre devenue d'autant plus fusible, qu'elle etoit plus satu- re"e d'air dephlogistique", et formoit ainsi sur un tiers de ligne d'epaisseur une doublure lisse et brillante, sur laquelle le burin ni la lime ne mordoient plus, tandis que les parties plus eloignees du centre, pre- sentoient un grain plus ine"gal et comme rempli de petites cavites : 1'aimant attire d'autant moins les dif- ferentes parties de cette matiere, qu'elles sont plus voisines de 1'etat de la doublure interieure, mais son action paroit devoir etre toujours sensible : enfin le metal avoit considerablement augmente de volume en e"prouvant ce changement, puisque le calibre interieur. fut reduit de sept lignes a quatre, sans que le dia- metre exterieur eut chang^. Cette substance eprouvee par les acides, ne donne x 162 MEMOIRS PAR plus aucune espece de gaz, il en reste meme une quan- tite considerable qui demeure indissoluble ; et quoi- qu'ayant beaucoup de rapport avec le fer calcine par 1'air dephlogistiqu^ qui se trouve dans Fair libre, c'est cependant, a beaucoup d'egards, une matiere nouvelle qui nitrite 1'attention des Chimistes. Independamment des connoissances acquises dans ces derniers temps, sur la cause de la calcination des metaux, tout annon^oit done dans cet etat du fer, 1'admission d'une substance etrangere qui en avoit augmente le volume et change 1'organisation : il fal- loit bien en effet que les cinq sixiemes du poids de 1'eau qui nous manquoit, eussent ete employes, et leur union avec le metal e"toit la seule destination qu'on put leur attribuer, puisqu'il n'y a point dans la Na- ture de deperdition proprement dite ; mais la persua- sion ou nous e'tions que notre tube de fer seroit cal- cine par dehors, nous ayant fait negligcr de le peser avant Foperation, nous ne pumes acque"rir de cette consequence une confirmation directe que son evi- dence ne pouvoit nous empecher de desirer. Nous entreprirnes done une nouvelle experience, dont 1'objet etoit de constater si le fer augmente de poids quand [278] il se calcine par le contact de 1'eau, comme quand il se calcine dans Fair libre ou dans Fair dephlogistique". C'etoit d'ailleurs le moyen le plus direct de repondre a Fobjection qu'on pour- roit peut-etre encore faire centre la decomposition de Feau, en attribuant tout Fair inflammable que nous avons obtenu, au metal qui Fauroit fourni, et non a Feau de laquelle nous croyons qu'il provient : dans cette maniere de voir, le fer perdant un de ses princi- MM. MEUSNIER ET LAVOISIER. 163 pes, diminueroit de poids, tandis que dans la the"orie que nous avons adoptee il doit au contraire augmenter. Cette experience e"toit done la plus propre a decider la question d'unc maniere definitive. N'ayant pu encore obtenir aucun des tubes de cuivre rouge que nous avions demandes afin d'y in- troduire un morceau de fer d'un poids connu et d- termine scrupuleusement, nous cherchames au moins a en faire une sorte d'imitation avec un nouveau tube de fer dans lequel nous fimes appliquer une feuille de cuivre rouge qui lui servoit de doublure : nous ne pumes a la verite" fermer exactement la jointure lon- gitudinale, parce qu'il n'y a point de soudure qui ne soit trop fusible pour le degre de clialeur que nous avions intention de produire ; mais si nous ne pr6- servames pas en entier le fer du canon de 1'action de 1'eau en vapeurs, nous diminuames au moins de beau- coup cette action e"trangere a notre objet present. Nous introduisimes dans cet appareil une baguette de fer plate, roulee sur elle-meme comme le filet d'une vis, et occupant ainsi une longueur de 18 pouces ; et pour eYiter que, devenue plus fusible, elle n'adherat a la doublure de cuivre, nous la mimes dans un canal de meme metal, avec lequel nous devions la retirer avec facilite quand 1'operation seroit finie : notre baguette de fer pesoit exactement deux onces cinq gros qua- rante-sept grains. Cette operation consomma une once cinq gros cin- quante-quatre grains d'eau, et produisit cinquante- trois pintes d'air inflammable : la baguette de fer cal- cinee par 1'eau, avoit [279] e"prouve a sa surface une sorte de fusion, qui en avoit arrondi les aretes, et son 164 ilEMOIRE PAR poids se trouva augmente de deux gros cinquante- quatre grains, comme notre the'orie le demandoit. Cette augmentation de poids fait presque un septieme du total, mais nous nous sommes assures qu'il restoit encore dans cette baguette une grande quantite de fer non calcine", qui en formoit le noyau, que le reste e"toit compose de differentes couches ine"galement cal- cinees, de sorte que n'etant pas a beaucoup pres sa- turee d'air dephlogistique, elle ne peut scrvir a deter- miner la vraie dose de cette saturation, mais il paroit qu'elle ne doit pas 6tre e"loigne"e de celle qu'on ob- serve dans le fer calcine" par 1'air libre, qui augmente d'environ un quart de son poids. Apres avoir ainsi vane" les experiences pour con- stater les phenomenes que presente le concours du fer et de 1'eau dans l'e"tat d'incandescence, et en avoir tire des preuves demonstratives, que 1'eau ne fournit 1'air inflammable, qu'autant qu'elle depose 1'air de- phlogistique dont elle contient encore la base, nous resolumes de prendre cette theorie pour toutes ses consequences, et d'etablir, en les verifiant, autant d'ex- pe"riences confirmatives : ainsi, voyant, par ce qui precede, que le fer a plus d'affinite avec 1'air dephlo- gistiqu^, que celui-ci n'en a pour 1'air inflammable, puisqu'il les se"pare Tun de 1'autre en decomposant 1'eau ; sachant d'ailleurs par 1'operation la plus com- mune en Metallurgie, que le principe du charbon a plus