The Life of the Honble Henry Cavendish

The Life of the Hon^ble Henry Cavendish Including Abstracts of His More Important Papers, and a Critical Inquiry into the Claims of all the Alleged Dicsoverers of the Composition of Water by George Wilson, M.D., F.R.D.E. Lecturer on Chemistry, Edinburgh, was published in 1851. It was written at the request of the Cavendish Society, and contains an authoritative biography of Henry Cavendish, a general sketch of his scientific researches and discoveries, as well as a discussion supporting Cavendish as the discoverer of the chemical composition of water. Wilson quotes Cavendish's words, "that water consists of dephlogisticated air united with phlogiston;" and argues that Cavendish demonstrated by experiments that water is united by the elastic airs (i.e., gases) oxygen and hydrogen being fixed by the chemical reaction of combustion, into liquid water. At the time of publication, there was a lively debate on this matter known as the Water Controversy, between the supporters of James Watt and those of Cavendish.

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Preface

During the enforced leisure of a long illness, I commenced, in 1842, to collect materials for a projected work on the lives of the Chemists of Great Britain, in which Cavendish should occupy a prominent place; and I had made some progress in my task when the Cavendish Society was founded.

When... at the call of the Society, I... turned my attention solely to the works and character of the Honourable Henry Cavendish, circumstances had occurred which gave him an importance in the eyes of the lettered public, such as no other chemist at the time possessed. He prosecuted zealously and successfully so many branches of knowledge, that the students of nearly all the physical sciences may consider him as an illustrious brother...

[H]is memory has been specially honoured by chemists, among whom Sir Humphry Davy, Faraday, and Thomas Thomson have been foremost.

I have written this volume as a student of chemistry... I have dwelt less upon Cavendish's purely physical researches, than I should have done had I been free to expatiate upon his merits as a natural philosopher. His physical researches, however, especially those on electricity and on the density of the earth, have not been overlooked in the succeeding pages; and the value of these memoirs is... fully appreciated by men of science...

I have given prominence, accordingly, to his discoveries in chemistry, and in the science of heat, but especially to the former. It has been impossible to do otherwise. ...Cavendish has been the occasion of the keenest controversy that has interested chemists for a long time, and much of this volume is occupied with... Who discovered the composition of water,—Cavendish, Watt, or Lavoisier?

[C]harges of plagiarism, and of unfair dealing towards each other, have been brought against the rivals, nor have their friends and acquaintances escaped reproach, including the entire Royal Society...

I have undertaken... a delicate and difficult task, in writing a work which compels me to pass under review the judgments of men of such note in science and letters as Arago, Dumas, Brougham, Brewster, Jeffrey, Harcourt, Whewell, and Peacock, at whose feet I have been accustomed to sit as a humble disciple.

The reputation of Lavoisier, and of Watt, is as sacred a thing in my eyes as that of Cavendish; and I should be the first to regret if the tone of this work should seem at variance with the catholic spirit of esteem for all great philosophers...

Whilst... I have endeavoured to be impartial, and to make the biography a faithful sketch, not a eulogy, I have deemed it an essential part of my duty as a biographer to vindicate the moral character of Cavendish from even the shadow of suspicion. It has been impossible to do this, without censuring those who have called his good name in question.

If in uttering censure I have forgotten what is due to great authorities in literature and in science, even when they are in error, I shall deserve and bow to reproof; but if I have only reluctantly fulfilled an imperative though invidious duty, and have justified my censures by showing that they are deserved, I shall hope to be vindicated at the hands of my readers.

In 1845, Mr. Muirhead, the able editor of "the Correspondence of the late James Watt on his discovery of the theory of the Composition of Water,"... and by that gentleman, the most zealous of Watt's defenders, and the most unhesitating of Cavendish's assailants, I had everything that could be said in favour of Watt urged upon me in the strongest terms.
- Reference: Correspondence of the Late James Watt on his Discovery of the Theory of the Composition of Water (1846) ed., James Patrick Muirhead.

The publication, also, of the Watt Correspondence in 1846, led to my obtaining the friendship of the late lamented Lord Jeffrey. He had known and esteemed Watt, and he welcomed the publication of the Watt Correspondence, as furnishing a becoming occasion for exalting the honour of his old friend.

Before his Lordship published his judgment on the rival claims of Cavendish and Watt in the Edinburgh Review for 1848, I had many conversations with him... Chemistry was a science in which he had always taken great interest... With his estimate of the relative merits of Cavendish and Watt I could not concur, and he listened to my earnest defence... with all the frank courtesy and love of fair dealing which so eminently characterized him.

Against Cavendish he entertained no animosity or prejudice, and he was most willing to praise him; but he thought that Watt had been wronged... so that he pressed me with all the arguments which... might be urged in favour of his great client... and I defended Cavendish in the strongest terms which courtesy sanctioned.

My zeal in Cavendish's cause made no difference in Lord Jeffrey's kindly dealings towards me, and he was the first in whose hands I purposed to place this volume, in which many of his conclusions are called in question.

After Lord Jeffrey's decease, the Rev. William Vernon Harcourt, the ablest of Cavendish's defenders... furnished me with his estimate of the position in which Cavendish's claims were placed by the publications in favour of Watt... since 1846. ...I owe to him an introduction to the Earl of Burlington, who placed at my disposal the whole of Cavendish's papers in his possession, and obtained for me much information concerning his illustrious ancestor's personal history.

The papers on Electricity which Cavendish left behind him, are at present in the hands of that accomplished Electrician, Sir W. Snow Harris, who, in the kindest manner, drew up for me an abstract of them, accompanied by a commentary.

I have thus had access to many unpublished documents, which are fitted to throw light on Cavendish's merits and his personality...

[T]he Rev. Dr. Vaughan, of Manchester, has permitted me to make any use I pleased of papers contributed to the British Quarterly Review, in which I published, in 1845, a short biographical sketch of Cavendish.

[S]ince the publication of the Watt Correspondence, in 1846, the only lengthened notices... in reference to Cavendish, have been Sir David Brewster's Article in the North British Review for 1847, and Lord Jeffrey's Paper in the Edinburgh Review for 1848. Both of these writers pronounce against Cavendish, and refer to the Watt Correspondence as decisive of the merits of Watt; but... from the following pages... the admirers of Cavendish have every reason to congratulate themselves on the publication of the "Correspondence;"... for... it furnishes the most decisive evidence in favour of Cavendish, and as such I have constantly quoted from it.

Ch II. General Sketch of Cavendish's Scientific Researches and Discoveries.

He was an excellent mathematician, electrician, astronomer, meteorologist, and geologist, and a chemist equally learned and original. In the fullest sense of the term, indeed, he was a natural philosopher, and had he published during his lifetime all the researches which he completed, his reputation would have been much wider and more varied even than it was.

Cavendish... dealt with his discoveries as with his great wealth, and allowed the larger part of them to lie unused in his repositories.

His published papers, accordingly, give but an imperfect notion of the great extent of ground over which he travelled in the course of his investigations, and of the success with which he explored it.

[A]s chemistry is concerned, Mr. Harcourt has left little to be done in this matter by his analyses of the Cavendish MSS.
- See Letter to Henry Lord Brougham, F.R.S. &c., Containing Remarks on Certain Statements in his Lives of Black, Watt and Cavendish (1846)

[H]e could, with the greatest ease, change his subject of study, and that he was in the constant practice of carrying on together, widely dissimilar enquiries.

Cavendish's life is so barren of incident, that with the solitary exception of the Controversy concerning the discovery of the composition of Water, almost no connexion can be traced between the events of his history and the researches which he prosecuted.

Cavendish did not give to the world his earliest researches. He probably kept many back. Two lengthened investigations, at least, the one chemical, the other physical, were completed and laid aside, in a condition ready for publication, before he commenced contributing to the Transactions of the Royal Society of London, in which all his papers were published.

Experiments on Arsenic... experiments... are as early... as 1764... [T]he paper... contains an elaborate enquiry into the differences between regulus of Arsenic (Metallic Arsenic), white Arsenic (Arsenious Acid, AsO₃), and Arsenical Acid (Arsenic Acid, AsO₅). The properties... are described with no little accuracy. ...Cavendish ...held arsenic acid to be "more thoroughly deprived of its phlogiston" than arsenious acid; and the latter to bear a similar relation to metallic arsenic. ...[Equivalently] arsenic acid contains more oxygen than arsenious acid, and the latter more than metallic arsenic, which we know to be the case. The paper, is otherwise remarkable for its speculations on the nature of the "red fumes," (nitrous acid, produced by the action of the air on nitric oxide) which attended the action of nitric acid on arsenious acid, and for its discussion of the theory of the solution of metals in acids, and the reduction of the former by heat and inflammable matter.

Cavendish engaged in an extensive series of Experiments on Heat... [W]e must go back... into 1764, for the commencement of the researches... They were written out for a friend... but were not publicly referred to till some nineteen years after... when certain of the results were quoted in a paper published in 1783, on the Congelation of Quicksilver.

[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.

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.

With scarcely any knowledge... of what Black had done towards the exposition of the laws of Latent Heat, and guiding himself by a totally different theory, as to its relation to solidity and liquidity, Cavendish investigated... the evolution of heat which attends the solidification of Liquids, and the condensation of Gases or Vapours, and the converse "generation of Cold," as he styled it, which accompanies the liquefaction of Solids and the Vaporisation of Liquids.

Cavendish's earliest public contribution to science was... his paper on Factitious Airs, published in the Transactions of the Royal Society for 1766. It consisted of three parts: a fourth, which was not published, remains in a state of perfect completion, ready for the press, among his papers. It was evidently intended to be read to the Royal Society, for it contains a reference to the "Former Experiments read to this Society." ...since ...published by the Rev. W. V. Harcourt.
- Reference: Three Papers, containing Experiments on factitious Air, by the Hon Henry Cavendish, F.R.S., Received May 12, 1766, Read May 29, Nov. 6, and Nov. 13, 1766, Philosophical Transactions, Vol. 56, XIX, p. 141.

Those four papers... are occupied with the discussion of the properties of Hydrogen, Carbonic Acid, and the gases evolved during the fermentation, putrefaction, and destructive distillation of vegetable and animal matters. They contain the first distinct exposition of the properties of hydrogen, and the first full account of those of carbonic acid, besides investigations into the combining proportion of the latter, and the properties of carbonates. They recount also the first successful attempt to determine the differences in density which characterise the gases, and suggest the probability of there being more kinds than one of inflammable air.

A paper which was published by Cavendish in the Philosophical Transactions for 1767, may be considered as an extension of the research into the properties of carbonic acid. It is occupied with an account of the Analysis of one of the London pump waters (... of Rathbone Place), which was remarkable for the quantity of calcareous earth which it deposited when boiled.

Cavendish showed that the earth was originally retained in solution by carbonic acid, which the boiling dissipated, so as to allow the earth to precipitate. The other constituents of the water were determined also, and the whole research is curious as one of the earliest tolerably successful attempts to analyse a natural water.

Abstracts of [the above] papers are given in the sequel... I refer to them... as showing the prominent position which Cavendish took... as a discoverer in chemistry.

He may be counted the third in order of time among the four great English pneumatic chemists of the eighteenth century, the other three being Hales, Black, and Priestley.

Hales was the earliest enquirer into the properties of elastic fluids, and, without injustice to his illustrious predecessors, the immediate disciples of Bacon, and early contemporaries of Newton, who had made some progress in investigating the properties of the gases, he may be called the father of pneumatic chemistry in England.

His great merit was to point out that elastic fluids may be obtained from an immense variety of organic and inorganic substances, of which they are as important constituents as the solids or liquids which may be separated from them.

Hales did not recognise, unless very imperfectly, that those elastic fluids were chemically unlike, and specifically distinct, so that he spoke of them as if essentially identical with each other and with the atmosphere; and had no other name for them than simply air. His writings belong to the first third of the preceding century.

Black, appeared a little after the middle of the century, and by his celebrated essay on Magnesia Alba, demonstrated that there existed at least one gas totally distinct from the atmosphere, and able by its addition to bodies, or its removal from them, to alter immensely their physical and chemical properties.

Black thus rose to a higher discovery than that reached by Hales. The latter had shown that the most solid stone might owe half or more of its weight to the presence of an imprisoned or solidified air; but he had paid little or no attention to the effect which the removal of this air had in altering the chemical properties of the substance from which it had been extracted.

Black demonstrated that the fixed or solidified air did not merely increase the bulk and weight of the solid, but determined in a most striking manner its chemical properties, so that a substance which, when saturated with a peculiar air, was a bland, innocuous insoluble powder, or crystalline solid, became by the expulsion of this air soluble, caustic, and corrosive; and the difference between marble or chalk on the one hand, and quicklime on the other, was shown to be entirely dependent on the presence or absence of the gas, which Black named fixed air, and we name Carbonic Acid.

Twelve years after the publication of Black's paper, namely in 1766, Cavendish published the first of the essays we have been considering. He took up the investigation of fixed air where Black and his pupils had left it, and examined in particular its properties when free, on which Black had published scarcely anything.

Thus far Cavendish appears rather as the follower of Black than as an independent observer, although... his investigation of the properties of free Carbonic Acid was equally original and accurate. He struck out, however... a new path... and added to the solitary fixed air, a second gas equally distinct from it and from atmospheric air in properties. This was Hydrogen, of which Cavendish cannot be called the discoverer, for many of his predecessors, Boyle among others, had encountered it; but no chemist had carefully examined its properties, or at least had described them.

His predecessors... knew only as much about the gas as a navigator who merely touches at a strange island, knows of its geography and various products, to whom we cannot deny the merit of being its discoverer, although we often assign much more credit to some later visitor who surveys and describes the new territory.

The mere discovery of hydrogen was no great feat; for the most random experimenter, who, with or without purpose, handled the more powerful reagents, was likely to encounter a phenomenon of which the conditions are so simple as the evolution of hydrogen from the contact of iron and an acid; and the ready and explosive combustion of the gas when it meets flame could not fail to attract the attention of the most heedless observer.

[A]mong Cavendish's predecessors backwards through several centuries, there were many who could assert equally good claims to be called the discoverers of hydrogen, of which, nevertheless, they knew exceedingly little. Cavendish did not claim to be one of them, but he could claim a merit which was much greater.

Boyle, Mayow, and Brownrigg had preceded him in showing how gases may be collected, but no one had given an example of the mode of examining them.

Cavendish's examination, accordingly, of the properties of carbonic acid and hydrogen, has all the interest that attaches to the first demonstration of a method of pursuing a novel investigation. It is easy to look back from our thoroughly appointed laboratories, filled with the apparatus which some ninety years have added to the chemist's instruments... and to criticise and depreciate the methods and results it records; and this has been done largely and unreasonably.

[I]f we consider how much more genius is requisite for the devising of an apparatus or method of research which is quite new than is needed for its indefinite extension and improvement, and if we further judge the experimenter of 1766, not by his successors of 1840 or 1850, but by his contemporaries, we shall not hesitate to assign a very high rank to Cavendish, as one of the earliest investigators of the chemical properties of the gases.

We find him... collecting the elastic fluids on which he experimented, with various precautions to secure their purity, observing carefully from how many different sources they could be procured with identical properties, and determining with numerical precision the relative volumes yielded by different processes. The questions of their permanent elasticity, their solubility in different liquids, their combustibility or power to support combustion, their specific gravity, and likewise their combining equivalent, were all carefully enquired into.

The apparatus employed, though deficient in delicacy according to modern standards, was unexceptionable in principle, and wherever... possible, was made to yield quantitative results, so that this earliest analyst of the gases introduced the principle of rendering all descriptions of phenomena as precise as possible, and endeavoured... to attach a numerical value to each. We... have done little more in later times than extend, improve, and... perfect Cavendish's processes for the analysis of gases, and that we differ from him more in our mode of interpreting certain of the phenomena... than we do in our methods...

[H]e mistook... the source of the hydrogen... procured... from the solution of iron, zinc, and tin, in sulphuric and muriatic acids, and referred it to the metals in which he supposed it to exist in a peculiar state of combination.

Water at this time... was supposed to be an element, and the composition of all the acids was unknown. No gas had been certainly traced to a liquid as its source, otherwise than as dissolved in it like carbonic acid in a mineral water; whilst Hales and Black had shown that the most fixed and solid bodies might yield from their very substance large volumes of elastic fluid.

[T]his may have been one reason which induced Cavendish to suppose that the hydrogen came out of the metal rather than out of the liquid. ...[T]he belief common to him with the majority of his contemporaries, [was] that the metals contained a peculiar combustible principle named phlogiston. This Cavendish supposed to abandon the metal, and, assuming the form of an elastic fluid, to show itself as the inflammable air.

Hydrogen was... the first of the combustible gases examined, and for many years... great confusion existed in the mind of chemists as to the number and nature of the different inflammable elastic fluids; nor did this begin to cease till the composition of water and of carbonic acid was ascertained.

Cavendish... had clearer views on this... than most of his fellow chemists. He ascertained that vegetable and animal matters, by putrefaction and destructive distillation, yielded inflammable air. He was not aware of its exact nature, but he satisfied himself by the test of specific gravity, and the volume of common air required for its combustion, that it was not identical with Hydrogen, which accordingly he distinguished as the "inflammable air from metals." He further observed that "the nature of the inflammable air was not quite the same" from animal as from vegetable substances. [H]e turned these observations to excellent account in the researches which led him to the discovery of the composition of water.

Between the years 1767 and 1783, Cavendish did not appear before the public as an author on any subject directly connected with chemistry, but... he continued to prosecute chemical enquiries.

Among his papers is one on which he himself has written, "communicated to Dr. Priestley," the contents of which are referred to by the latter in his account of Experiments and Observations made in and before the year 1772... The paper... has been printed by Mr. Harcourt, and is... one of the earliest distinct accounts of nitrogen. Cavendish prepared it by passing atmospheric air repeatedly through red hot charcoal, and removing the carbonic acid produced, by caustic potash.

He gives the following description of it: "The specific gravity of this air was found to differ very little from that of common air; of the two, it seemed rather lighter. It extinguished flame, and rendered common air unfit for making bodies burn in the same manner as fixed air, but in a less degree, as a candle which burnt about 80” in pure common air, and which went out immediately in common air mixed with 6/55 of fixed air, burnt about 26” in common air mixed with the same portion of this burnt air."

Cavendish gave no special name to nitrogen, which he referred to generally as mephitic air. It was afterwards minutely described by Lavoisier and Scheele, and was distinguished by Priestley and his contemporaries, by the name phlogisticated air.

The quotation adduced above, shows incontestably that Cavendish discovered nitrogen for himself, and had ascertained with great precision its chief properties; but in the absence of precise dates, I hesitate to adopt Mr. Harcourt's conclusions, that the paper from which I have quoted contains "the first clear description of nitrogen as a distinct gas."

Dr. Rutherford, of Edinburgh, the reputed discoverer of nitrogen, published his Thesis De Aere Mephitico, in 1772. His process for procuring the gas, for which he had the same general term as Cavendish, viz., mephitic air, resembled that of the latter chemist, except that he employed atmospheric air vitiated by respiration, not by combustion. This he passed through caustic potash, and tested by lime-water, which it did not precipitate, whilst it possessed the power of extinguishing life and flame.

The dates of publication, or announcement, of Cavendish and Rutherford's observations, are thus the same, whilst the dates of their experiments are uncertain. We cannot in these circumstances give precedence to the former, but it is certain that he was an independent discoverer of nitrogen.

In 1771 he published the elaborate paper on the theory of the principle phenomena of electricity, which appears in the Philosophical Transactions for that year. In 1776 appeared... his Attempts to imitate the effects of the Torpedo. ...[T]he singular power which the torpedo possesses, of benumbing those that touch it, had been referred with great ingenuity and force of argument, by Walsh and others, to its possessing the means of discharging electricity at will. Cavendish... tried whether he could not successfully imitate the effects of the living fish, by a piece of apparatus constructed in imitation of it, and placed in connection with a friction electrical machine and a Leyden battery. He succeeded... all doubts as to the identity of the torpedinal benumbing power, with common electricity, were removed.

Faraday, among others, have borne testimony to the light which was thrown upon every department of electrical enquiry, by Cavendish's demonstration... Faraday found the theory which Cavendish suggested, sufficient to explain the curious and apparently contradictory voltaic phenomena which he observed so late as 1833. ...In none of his essays does Cavendish appear to greater advantage than in this.

[T]he Royal Society... selected... [Cavendish] in 1776 to describe the meteorological instruments which were made use of... The Society had commenced in 1773 recording their observations with the thermometer, barometer, rain-guage, hygrometer, variation-compass, and dipping needle, and Cavendish was applied to, to give an account of these. His father, Lord Charles Cavendish, had devoted himself to meteorology, and had paid special attention to the improvement of the thermometer and barometer... That [Henry] had paid great attention... to the thermometer... is certain from his unpublished papers on heat of 1764 and 1765... The most important part of this paper is his description of the best method of accurately graduating thermometers... found specially referred to in the abstract of his papers on Heat.

1777 or perhaps... 1778, marks the period when he commenced his most important chemical researches... Experiments on Air... carried on with frequent, and sometimes long interruptions till 1788, and no part... was published till 1783. They led to the discovery of the constant quantitative composition of the atmosphere, the compound nature of water, and the composition of nitric acid.

In 1783... Cavendish published his first paper on heat, embodying some of the results he obtained in 1764 in reference to the freezing or solidifying point of liquids. [T]he papers on heat... are three... 1783, 1786, and 1788. All of them refer to congelation; the first to that of quicksilver, the second and third to... mineral acids and... alcohol [respectively]. ...They are all... commentaries upon observations made in North America by officers of the Hudson Bay Company on the effect of great natural cold, assisted by powerful freezing mixtures in congealing mercury, nitric acid, oil of vitriol, and spirits of wine. These observations were made under Cavendish's directions, and at his cost...

The most important of these papers was that on the freezing of quicksilver. This metal... was frozen in a thermometer in 1759... by Professor Braun, of Petersburgh, who observed that its congelation was accompanied by a descent of the mercury, through many hundred degrees, and came to the conclusion that the freezing point of the metal was some 300° or 400° below Farhenheit's zero, but was unable to determine the exact point of congelation.

Braun confounded two phenomena. The one of these was the contraction which accompanies the cooling of liquid mercury; the other the further contraction which attends its solidification. The contraction due to both these causes [was] exaggerated by the peculiarities which attend the freezing of mercury in capillary tubes... To his conclusion the majority of the natural philosophers of Europe assented, but... Cavendish and Black... by independent researches, suggested the same way of ascertaining the true freezing point of mercury... This method... was put in practice by Governor Hutchins at Albany Fort, Hudson Bay... The result was, that the freezing point of mercury is not more than 39° or 40° below Fahrenheit's zero... Mr. Hutchins's observations were not made till 1782, but the directions by which he was guided had been laid down by Cavendish in 1764 and 1765.

The experiments on air... supplied materials for four papers, besides leading to the observation of many phenomena which were never made public. ...In the interval which elapsed between the publication of Cavendish's first chemical papers and [these]... Priestley, the fourth of the great English pneumatic chemists, had appeared... while Scheele... and Lavoisier... besides other less distinguished observers had effected the discovery of nearly all the gases known to... the present... and their study engrossed the attention of every chemist.

[T]he relation of the atmosphere to combustion demanded explanation, and the nature of the change which the air underwent when inflammables, burned within confined portions of it, deprived it of the power of further supporting combustion. At this problem all the active chemists of Europe were now working, but with very unequal success, owing to the false theory of combustion which the majority espoused, and the erroneous opinions which were current concerning the constitution of atmospheric air.

Boyle, Hooke and Mayow in England, and Rey in France, besides other early disciples of the school of Bacon, understood the true nature of combustion in air much better than the immediate predecessors of Lavoisier. The former held as we do, that a burning body is literally fed by the air, and they apprehended with considerable clearness, that burning combustibles add something to themselves from the atmosphere. Some of these observers were also well aware that combustibles are converted by combustion into substances possessing greater weight than the original inflammable.

In an evil day... Beccher and Stahl, two men of unquestionable genius, devised a theory of combustion which led all chemistry astray for half a century. According to their view combustion consisted in the emission from the combustible of a peculiar fiery principle, to which the name phlogiston was given. It was present in all inflammables, however different their appearance and properties. When they burned, it passed out of them into the air which surrounded them, and by its loss they became changed in character and quite incombustible; but if phlogiston was restored to them, they recovered their original appearance and properties, among the rest, their combustibility.

Much has been said by the historians of chemistry in praise of this theory as having served, in spite of its inaccuracy, to guide chemistry to great results, at a time when the science was not ripe for a juster theory. From this statement I must totally dissent. Its devisers assuredly were men of rare gifts, and their theory, welcomed by their fellows and immediate successors as a great boon to the science, exerted for some forty or fifty years a strange fascination over all the chemists of Europe. These forty years, however, were like those spent by the Israelites in the wilderness, after their glimpse of the Promised Land.

Had Stahl and Beccher carried out the conclusions which the early disciples of Bacon had imperfectly announced, we should not have waited till the close of the eighteenth century, and the advent of Lavoisier, for the true interpretation of the nature of combustion. A Joshua would have been found some half a century sooner, and the goodly land which the chemists cultivate, would exhibit a much wider extent of fertile territory than it does at the present day.

[N]o service can be rendered to the cause of truth by affecting to deny that, especially in the early history of the sciences, we find long periods of total stagnation, and the tide even ebbing, when by our calculations it should have overflowed.

Stahl's theory of phlogiston was not a refined speculation. It scarcely deserves to be called a scientific hypothesis. It really amounted to nothing more than the assertion, that a body was combustible because it contained something combustible; which was equivalent to the identical proposition that a body burned because it burned. This declaration instead of being a refinement of philosophy, to which only a man of science could reach, was but the reduction to terms, of a vulgar belief. It was a poetical, rather than a scientific thought; for the natural tendency of every untrained imaginative mind, as we see in children, and in the early history of all nations, is to impute every manifestation of power, to the presence in the body manifesting it, of some inner principle more or less self-sustaining, and resembling a living or vital agent.

The same spirit, which made the Greeks people the winds and the waves, the rivers and the trees, with gods; which makes the savage regard the compass needle as animated; and the child demand to see in some visible shape, the motive principle of a watch or moving toy; led the Chemists of the seventeenth and eighteenth centuries to declare that a candle burned because it contained a burning principle.

I have sometimes thought that this theory was in part occasioned by the spectacle of the sun and other heavenly bodies unceasingly emitting heat and light. I have found, however, no reference to this striking phenomenon in the writings of the phlogistians; and however much the unbroken radiance of the sun might justify a popular belief in the power of combustibles simply to emit light, it could never justify the assertion of this even as a probable truth, for this would have been to explain one mystery by another.

Whilst poetry might have welcomed the doctrine that a blazing body throws off light and heat, as a bell utters a sound, or a flower exhales an odour, that science could only accept it as an hypothesis of no great likelihood or high value, and which at all events required at once to be tested, as to its utility as an interpreter of known phenomena, and a guide to the discovery of new ones.

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 nitrogen.

[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.

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.

The discovery of oxygen, of nitric oxide, 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.

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.

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 nitrogen. Cavendish's enquiry began before this later view became general.

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.

The problem which originally interested him... If any combustible, such as hydrogen, phosphorus, 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.

[H]e published in 1783, and, like all his other papers, the modest title... An Account of a New Eudiometer, 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 nitric oxide. 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.
- A source: An Account of a New Eudiometer. Read (Jan. 16, 1783) Philosophical Transactions Vol. 73, 1783, p. 106, in The Scientific Papers of the Honourable Henry Cavendish (1921) Vol. 2, p. 127.

[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.

The instruments... Eudiometers, 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.

By the performance of an immense number of elaborate experiments, Cavendish succeeded in perfecting a process, by means of which he could employ nitric oxide 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?

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.

[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 hydrogen. This device might be called an Acoustic Eudiometer.

Whilst engaged also in the enquiry... we have been discussing, he checked the results obtained with nitric oxide, by observing the diminution which air underwent when exposed to liver of sulphur dissolved in water, and when exploded with hydrogen 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.

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.

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...

When he commenced... researches, he found an opinion prevailing, that the production of fixed air, or carbonic acid, 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 hydrogen in air and in oxygen.

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.
- Footnote: The instrument which Volta introduced for firing explosive mixtures of gas, by means of the electric spark, and which still bears the name of Volta's Eudiometer, was a tube or cylinder open at one end. I do not know whether Volta ever employed a shut globe, but Priestley and Warltire certainly did before Cavendish, as he freely acknowledged, and they... as well as Watt, referred the device to Volta, so that it must be regretted that this apparatus has been called Cavendish's Eudiometer, especially as Monge used an exactly similar apparatus, which he also refers to Volta. It is the admirable use which Cavendish made of the detonating globe, not the devising of it, which justifies its employment as the Cavendish Society's symbol. The instrument itself might, perhaps, best be called, without reference to any one's name, the Spark Eudiometer.

[I]n his paper on hydrogen, 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.

He first employed hydrogen 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 nitrogen.

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.

[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.

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."

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."

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 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.

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.

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.

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.

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 hydrogen, 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.

His identification, however, of hydrogen 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.

Ch. IV. Concluding Events of Cavendish's Life.

—Estimate of his Moral and Intellectual Character.

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.

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.

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.

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.

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 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.

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.

About The Life...

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 Hon^ble Henry Cavendish, written at the request of the Cavendish Society, and published in 1851, still remains the only authoritative biography of the philosopher.
- Thomas Edward Thorpe, Introduction to The Scientific Papers of the Honourable Henry Cavendish (1921) Volume 2, p. 1.

External links

Archive.org
- The Life of the Honble Henry Cavendish by George Wilson, M.D., F.R.D.E. Lecturer on Chemistry, Edinburgh (1851)