The Life of the Honble Henry Cavendish

"The proceeding quotation contains the account of the first conclusion that was drawn concerning the compound nature of water, and the possibility of producing it out of hydrogen, and the oxygen contained in air."

"Cavendish solved the problem... and whilst he avoided the confusion in which it involved others, he built upon it an additional great discovery. After ascertaining that the appearance of nitric acid was not dependent on the source from which the oxygen was prepared, and that the acid did not show itself unless more than a combining measure of oxygen was detonated with the hydrogen, he traced its production to the presence in the [eudiometer] of a little nitrogen, derived from the atmospheric air which had originally filled it, or had become mingled with the hydrogen and oxygen during their preparation or collection. He... verified this conclusion, by showing that the artificial addition of nitrogen to hydrogen, mixed with more than one-half its volume of oxygen, increased the amount of nitric acid produced at each detonation, and on the other hand, that if the hydrogen instead of the oxygen was in excess, no nitric acid appeared, although nitrogen was present."

"By the performance of an immense number of elaborate experiments, Cavendish succeeded in perfecting a process, by means of which he could employ so as to occasion a constant amount of contraction, when mixed with different portions of the same specimen of air. Having certified this, he applied his method to the determination of the two important questions: Is the atmosphere constant in composition? And if so, what is its composition?"

"Having demonstrated... that the lost gas was accounted for, and remained in the produced liquid, he proceeded to investigate the nature of the latter. The globe explosions yielded too small a quantity of liquid for a full analysis. He burned together, accordingly, by direct combustion, a large volume of hydrogen with 2 1/2 times that quantity of common air within a glass cylinder, and collected the liquid produced. This he found to be without taste, or smell, or action on colouring matter, and to leave no sediment on evaporation; in short... "it seemed pure water," and his... conclusion... "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.""

"His brain seems to have been but a calculating engine; his eyes inlets of vision, not fountains of tears; his hands instruments of manipulation which never trembled with emotion, or were clasped together in adoration, thanksgiving, or despair; his heart only an anatomical organ, necessary for of the circulation of the blood."

"Comparatively little is known concerning the personal history of [Cavendish]. Nor is there much hope now that more may be gleaned. It may be doubted, indeed, whether there is much more to learn, for apart from his scientific achievements, his life was singularly uneventful. He lived a solitary, secluded existence, and, despite his rank, and, in his later years, his great wealth, he deliberately refrained from any attempts to exercise the slightest social influence. He left no personal records, and few of his letters seem to have been preserved, possibly because few were written. Such as are known relate almost exclusively to matters of science and are otherwise of very slight human interest. All the knowledge of him we possess is based upon the fragmentary notices of a few contemporaries, principally Thomas Young, Thomas Thomson of Glasgow, Sir Humphry Davy, and Lord Brougham. Their accounts, together with the reminiscences of others who had a certain small measure of personal acquaintance with him, or were able to communicate hearsay information concerning his character, habits and mode of life, have been brought together by the late Dr George Wilson, of Edinburgh, whose Life of the Honble Henry Cavendish, written at the request of the Cavendish Society, and published in 1851, still remains the only authoritative biography of the philosopher."

"To discover what became of the lost air was a question which, in 1777, greatly interested... chemists... and Cavendish's attention was specially directed to the problem, by the researches of Scheele on this point... Priestley and Lavoisier had, contemporaneously with Scheele, investigated the same subject; and all three had made some progress, especially Lavoisier, in explaining the problem."

"The instruments... ', or measurers of the goodness of the air; the object of the analyst being to determine the freedom of the air from phlogiston, which rendered it bad in proportion to the amount of it present."

"The protracted eudiometrical enquiry... taught Cavendish... the maximum amount of diminution... one-fifth of the original volume of the air... was the dephlogisticated part, or pure air (oxygen), of the atmosphere, which disappeared during combustion, so that he was now fully prepared to enquire what had become of the lost oxygen. His account... forms the first series of his Experiments on Air... read to the Royal Society in January 1784... a year after the paper on the New Eudiometer..."

"Cavendish... unhesitatingly concluded, that in the circumstances described, "almost all the inflammable air, and about one-fifth part of the common air, lose their elasticity and are condensed into the dew which lines the glass.""

"The general conclusion to which Cavendish came concerning the nature of water, was in his own words, "that water consists of dephlogisticated air united with phlogiston;" and as dephlogisticated air was his term for oxygen, and phlogiston his term for , this... corresponds to the modern view of the nature of water introduced by Lavoisier. The two views cannot be considered identical, yet this is certain, that Cavendish was the first who consciously converted hydrogen and oxygen into water, and taught that it consisted of them."

"All that needed for its apprehension, more than the pure intellect, or required the exercise of fancy, imagination, affection, or faith, was distasteful to Cavendish. An intellectual head thinking, a pair of wonderfully acute eyes observing, and a pair of very skilful hands experimenting or recording, are all that I realise in reading his memorials."

"Cavendish did not stand aloof from other men in a proud or supercilious spirit, refusing to count them his fellows. He felt himself separated from them by a great gulf, which neither they nor he could bridge over, and across which it was vain to stretch hands or exchange greetings. A sense of isolation from his brethren, made him shrink from their society and avoid their presence, but he did so as one conscious of an infirmity, not boasting of an excellence."

"He could not sing for them a sweet song, or create a "thing of beauty" which should be "a joy for ever," or touch their hearts, or fire their spirits, or deepen their reverence or their fervour. He was not a Poet, a Priest, or a Prophet, but only a cold, clear, Intelligence, raying down pure white light, which brightened everything on which it fell, but warmed nothing—a Star of at least the second, if not of the first magnitude, in the Intellectual Firmament."

"[P]hlogiston was held to be a material and therefore ponderable substance, so that its escape from a combustible should have caused the latter to diminish in weight; yet the metals and phosphorus were known to increase in weight by combustion. Thus the lameness of the phlogiston hypothesis was betrayed at its first step, and it had to be furnished with a crutch, in the shape of an assumption that it was a principle of levity, so that a body containing it weighed less than if it were absent, before it could move a step further. Many of the Phlogistians... did not adopt this assumption... but they ignored the phenomenon of increased weight... and stood in the anomalous position of professors of a Quantitative Science, who should weigh and measure... and yet had put aside the balance as a useless thing."

"The discovery of oxygen, of , and of other gases, and the experiments which Priestley, Scheele, and Lavoisier had been assiduously making for some years, had directed... attention... to the fact, that air not only became irrespirable and unable to support combustion when exposed to the action of burning inflammables, but... underwent a diminution in volume, so that a portion of it was to appearance lost."

"He had proceeded but a short way in his attempt to discover what became of the air apparently lost during combustion, when he was arrested in his researches by the necessity... of ascertaining the quantitative composition of atmospheric air."

"[N]itrous gas... can combine with oxygen in various proportions, according to the mode in which it is mixed with air... Priestley... and the great majority of his contemporaries were either ignorant or heedless of this fact... travelling from place to place, analysing what they called the good air and the bad air of different localities, and coming to the most extravagant conclusions as to the relative purity of specimens... in which... modern analysis would fail to detect any difference."

"[T]he atmosphere had long occupied his attention. So far back as 1766 he had imperfectly analysed it, by observing the loudness... which it gave when detonated with . This device might be called an Acoustic Eudiometer."

"He concludes this paper with an estimate of... the information which the eudiometer supplies, which he shows to be very much smaller than the majority of his contemporaries imagined. His views in this respect... are another monument to the caution and sagacity with which he kept himself free from the prejudices of his time, and anticipated conclusions which were not generally accepted till a recent period."

"[I]n his paper on , of 1766, he had represented this gas as itself phlogiston. He now experimented accordingly upon it, not as an individual combustible which would yield a certain product, but as the phlogiston... in all combustibles, and the product of whose combustion would represent the universal product of combustion."

"[T]here was exactly the same weight of matter in the globe after the explosion as before, but the oxygen originally present in the air, and twice its volume of the hydrogen which had been mixed with it, had disappeared as gases, and were replaced by a volume of liquid, which... exactly equalled them in weight."

"This startling phenomenon, on which the chemistry of the period could throw no light... led not only Priestley, but even La Place astray; and it was probably ignorance of the phenomenon on the part of Watt and Lavoisier, which saved them from being entangled in difficulties in their investigation into the nature of water."

"In this way he demonstrated that the only product of the combustion of pure hydrogen and oxygen is pure water; but he was further led to a view of the composition of nitric acid, which he carried out in the second series of his experiments on air, and which secures to him the honour of being the discoverer of the composition of nitric acid, as well as of that of water."

"His identification, however, of and phlogiston, and his inheritance of the prejudices of the early phlogiston school, led him to the erroneous conclusion that every combustible contains hydrogen, and that the deoxidation of air and the oxidation of combustibles, are invariably accompanied by the production of water. In this respect he erred, but we may forgive the discoverer of so great a truth as that of the composition of water, for over-estimating its importance. To this, and to the other points glanced at in this sketch of the first series of experiments on air, I have referred fully in the abstract of the paper, and in the chapters devoted to the discussion of the Water Controversy."

"It only remains that I offer very briefly my own estimate of the character of the Philosopher. Morally it was a blank, and can be described only by a series of negations. He did not love; he did not hate; he did not hope; he did not fear; he did not worship as others do. He separated himself from his fellow men, and apparently from God. There was nothing earnest, enthusiastic, heroic, or chivalrous in his nature, and as little was there anything mean, grovelling, or ignoble. He was almost passionless."

"Yet, if such a being, who reversed the maxim nihil humani me alienum puto [nothing human is foreign to me], cannot be loved, as little can he be abhorred or despised. He was, in spite of the atrophy or non development of many of the faculties which are found in those in whom the "elements are kindly mixed," as truly a genius as the mere poets, painters, and musicians, with small intellects, and hearts and large imaginations, to whom the world is so willing to bend the knee."

"He is more to be wondered at than blamed."

"He was like a deaf mute sitting apart from a circle, whose looks and gestures show that they are uttering and listening to music and eloquence, in producing or welcoming which he can be no sharer. Wisely, therefore, he dwelt apart, and bidding the world farewell, took the self imposed vows of a Scientific Anchorite, and, like the Monks of old, shut himself up within his cell. It was a kingdom sufficient for him, and from its narrow window he saw as much of the Universe as he cared to see. It had a throne also, and from it he dispensed royal gifts to his brethren."

"He was one of the unthanked benefactors of his race, who was patiently teaching and serving mankind, whilst they were shrinking from his coldness, or mocking his peculiarities."

"The doctrine of phlogiston... [i]nstead of being treated as a doubtful hypothesis... was employed as a perfect theory; and phenomena at variance with it were either wilfully overlooked, or compelled to adjust themselves to its Procrustean bed."

"A true hypothesis, or one in the main, true, is always found capable of explaining more than it professed or expected to explain. But the phlogiston hypothesis transgressed its own self-imposed conditions, and failed to explain the most simple and essential phenomena of combustion. Thus its presence in bodies was held to confer upon them combustibility, yet when transferred from a blazing combustible to air, instead of rendering the latter inflammable, and changing it into a gas which could be kindled, it changed it into one which was totally incombustible and at once extinguished flame; for phlogisticated air in its simplest form was our ."

"That a burning body changed the quality of the air around it, whilst itself undergoing a complete change of properties, had not escaped the attention of the phlogistians. Beccher and Stahl, although they made no investigation into the nature of the change which air underwent when it supported combustion, were aware that a limited quantity of air in which a combustible had burned till it was extinguished, could not a second time support combustion, a fact... of universal belief from the earliest times."

"Such, then, was the crude and clumsy hypothesis which was recognised as a fundamental law of all chemistry, at the period when Cavendish commenced his Experiments on Air. Their object was to ascertain what Beccher and Stahl should have ascertained before they promulgated their hypothesis, viz., what change does combustion effect upon air."

"When those researches commenced, air was universally reputed to be a simple or elementary body. It was liable, according to the phlogistians, to vitiation, by the addition to it of phlogiston, so that it was referred to as being more or less phlogisticated, according to the degree of its power to support respiration and combustion."

"When oxygen was discovered by Priestley and Scheele, it was regarded by them as air altogether respirable, and exhibiting a maximum power of supporting combustion, because it was quite free from phlogiston. It was named accordingly de-phlogisticated air, and for a season the atmosphere was referred to as consisting of two parts, a "dephlogisticated part" and a "phlogisticated part," which differed... only in degree. By-and-by those parts were regarded as differing in kind, not merely in degree; the dephlogisticated part, or dephlogisticated air, being our oxygen, and the phlogisticated part or air, our . Cavendish's enquiry began before this later view became general."

"The problem which originally interested him... If any combustible, such as , , or a candle, was allowed to burn till it went out, in a portion of air confined over water, the volume of the air was observed to diminish as the combustion proceeded, and at its close the water was found to have risen through about a fifth of the space originally occupied by the air."

"[[[Henry Cavendish|H]e]] published in 1783, and, like all his other papers, the modest title... An Account of a New , conveyed a very imperfect idea of its contents. ...[I]t is ostensibly devoted to the explanation of an instrument for determining the proportion of oxygen in air, by observing the contraction which followed its mixture with a given volume of . Priestley, the first investigator of the properties of nitric oxide, had devised this process, but was too inaccurate a manipulator to make good use of it."

"He came to the conclusion which all subsequent observations have confirmed, that no sensible difference can be detected by Eudiometrical analysis between the purity of different specimens of atmospheric air. It was universally such "that the quantity of pure air in common air is 10/48" or... the per centage by volume of oxygen in air is 20.83. This... is remarkable... accuracy, when we consider how totally the great majority, not only of Cavendish's contemporaries, but also his successors, even among living philosophers, failed to obtain any constant results with nitric oxide eudiometers."

"Cavendish is... the discoverer of the constant composition of the atmosphere, and its first accurate analyst."

"Whilst engaged also in the enquiry... we have been discussing, he checked the results obtained with , by observing the diminution which air underwent when exposed to dissolved in water, and when exploded with in a shut vessel by means of the electric spark. The apparatus last referred to is... Cavendish's Eudiometer, and... in connexion with the discovery of the composition of water, has been selected by the Cavendish Society as their emblem, and placed on the title-page of their publications."

"Cavendish... never named this instrument a Eudiometer, nor was it his device, but Volta's. The Society's emblem represents the instrument as it is constructed at the present day, not as it was used by Cavendish."

"When he commenced... researches, he found an opinion prevailing, that the production of fixed air, or , is the invariable result of what he called the phlogistication, and we should call the deoxidation, of atmospheric air. He readily disproved... this view, and also of another notion, that nitric, or sulphuric acid was produced in those circumstances; and having disposed of these erroneous opinions, he proceeded to observe with great care, what was the product of the combustion of in air and in ."

"Priestley, and... Mr. [John] Warltire, had already experimented on this... with a detonating globe of the same kind as... Cavendish's Eudiometer. Their experiments were made partly in metallic, partly in glass vessels, and when employing the latter, they observed a deposition of moisture follow each explosion, but Priestley paid no attention to this... and Warltire referred it to the condensation of water which had been diffused in the state of vapour through the gases. ...Cavendish ...from the first appears to have anticipated that in the deposited water would be found the oxygen, which disappeared during the combustion of hydrogen in air, and the explanation of the diminution in volume which attended the vitiation of air."

"He first employed and air, varying their relative proportion, till he ascertained that ratio in which, after their explosion in a shut vessel, the air was found diminished one-fifth, whilst the residual air was free from oxygen, and possessed the properties of ."

"In place of the oxygen which had thus disappeared, and a volume of hydrogen twice as great which had burned along with it, there was found a certain amount of liquid. The globe, moreover, had remained shut during the experiment, so that nothing had been allowed to escape, and nothing ponderable had been lost, for the vessel was found to weigh the same after the electric spark had passed, as before the explosion."

"Cavendish proceeded to try whether free oxygen, if detonated with hydrogen, would in like manner yield water. ... [I]t was only necessary to fill the globe with a mixture of one volume of oxygen and two of hydrogen, and to explode it by the electric spark, to secure the entire conversion of the contents of the globe into water. Cavendish came as near this result, as a slight mistake in the adjustment of the combining volumes of hydrogen and oxygen, and the limits of error in such an experiment, at the period when it was made... permitted."

"[A]n unexpected and perplexing phenomenon showed itself. The liquid instead of being pure water, was found in certain cases to consist in addition of an acid, which analysis proved to be the nitric, and a long and difficult investigation had to be prosecuted into the source of this acid, the composition of which... was totally unknown in 1784."

"Cavendish discovered for himself, and announced with admirable clearness, the fundamental laws of specific heat; and collected, probably before any one else, tables of the specific heats of various bodies."

"[H]ad [these researches] been made public in 1764 or 1765, they would have given Cavendish chronological precedence to Black in some of his discoveries, and equality of merit in others. They would have entitled him... to rank above Black's pupils and imitators... as Irvine, Crawford, and Wilcke."