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ESSAYS IN HISTORICAL CHEMISTRY 
 
E SSAYS 
 
 IN 
 
 HISTORICAL CHEMISTRY 
 
 BY 
 
 T. E. THORPE 
 
 PH.D., B.SC. VICT., SC.D. DUEL., F.R.S. 
 
 PROFESSOR OF CHEMISTRY IN THE ROYAL COLLEGE OK SCIENCE, 
 SOUTH KENSINGTON, LONDON. 
 
 ^SE 
 OF THE 
 :VERSITY 
 
 ILontJon 
 
 MACMILLAN AND CO. 
 
 AND NEW YORK 
 1894 
 
 All r'ujhts reserved 
 

IVE T RSITT) ' 
 OF ^X 
 
 PREFACE 
 
 THIS book consists mainly of lectures and addresses given 
 at various times, and to audiences of very different type, 
 during the last eighteen or twenty years. These essays 
 in historical chemistry are now put together with the object 
 of showing how the labours of some of the greatest masters 
 of chemical science have contributed to its development. 
 The book has no pretensions to be considered a history of 
 chemistry, even of the time over which its narratives extend. 
 Many honoured names as Black, Dalton, Davy, Berzelius, 
 Liebig, Hofmann that ought, in all fitness, to find a fuller 
 notice in such a series of biographical sketches, are only 
 incidentally mentioned. The only excuse I can advance is, 
 that it has not as yet been my good fortune to be in a 
 position to offer an account of their labours. 
 
 The greater number of the sketches in the present volume 
 have already been seen in print ; but in arranging them for 
 republication I have not hesitated to make such alterations 
 and corrections as seemed necessary or desirable in view 
 of their appearance in a connected series. Certain of the 
 
vi Preface 
 
 lectures, when delivered, were illustrated by experiments 
 of which mention was made in the accounts originally pub- 
 lished. It seemed useless to retain these references, and 
 they have consequently been omitted. The lectures, too, 
 for an obvious reason, have been arranged in historical 
 sequence, and not in the order in which they were written 
 or delivered. Hence, in some cases, it happens that what 
 now appear as successive chapters have in reality been com- 
 posed at wide intervals of time, and addressed to audiences 
 of very dissimilar character. Although, as stated, a certain 
 amount of pruning has been done, there are occasional re- 
 petitions; possibly also a few inconsistent statements may 
 be detected on comparing the earlier with the later essays 
 more, I trust, in matters of opinion than of fact. This is 
 almost inevitable, unless some portions had been recast, or, 
 to a greater or less extent, rewritten which, as the essays 
 are, to all intents and purposes, reprints, I did not feel 
 justified in doing. It is to be expected that the wider 
 knowledge which should follow upon twenty years of reading 
 and study would modify, or possibly even altogether change, 
 the impressions of the earlier time. 
 
 My thanks are due to the Proprietors and Editors of the 
 Contemporary and Fortnightly Reviews for permission to include 
 certain articles which have appeared in those periodicals. 
 I am also indebted to the Council of the British Association 
 for the Advancement of Science for permission to reprint 
 the Presidential Address delivered to the Chemical Section 
 of the Association at the meeting in Leeds in 1890. Messrs. 
 
Preface vii 
 
 Macmillan and the Editor have allowed me to make use of 
 certain articles contributed to Nature; the Managers of 
 the Royal Institution have permitted me to reprint the 
 lecture on Wohler; the Council of the Chemical Society, 
 that on Kopp ; and the Council of the Philosophical Society 
 of Glasgow, the Graham Lecture, given in 1887. Lastly, 
 I have to thank Mr. John Heywood, the publisher of the 
 Manchester Science Lectures, for granting me permission 
 to make use of the lectures on Priestley and Cavendish. 
 
 FALMOUTH, Christmas 1893. 
 
 OF THE 
 
 UNIVERSITY 
 CALIFORNIA 
 
CONTENTS 
 
 i 
 
 EGBERT BOYLE 
 
 PAGE 
 
 (One of the Free Evening Lectures delivered in connection with the 
 Loan Collection of Scientific Apparatus at South Kensington 
 in 1876) ........ 1 
 
 II 
 
 JOSEPH PRIESTLEY 
 
 (A Lecture delivered in the Hulme Town Hall, Manchester, on 
 
 18th November 1874 . Manchester Science Lectures) . . 28 
 
 III 
 
 CARL WILHELM SCHEELE 
 
 (An Address to the Owens College Chemical Society, at the Opening 
 Meeting, 24th October 1893 ; subsequently published in the 
 Fortnightly Revieiv] . . . . . .53 
 
 IV 
 
 HENRY CAVENDISH 
 
 (A Lecture delivered in the Hulme Town Hall, Manchester, 24th 
 
 November 1875. Manchester Science Lectures) . . 70 
 
x Contents 
 
 V 
 
 
 
 ANTOINE-LAURENT LAVOISIER 
 
 (Contemporary Review, December 1890) 
 
 VI 
 
 PRIESTLEY, CAVENDISH, LAVOISIER, AND LA REVOLUTION 
 CHIMIQUE 
 
 (The Presidential Address to the Chemical Section of the British 
 
 Association for the Advancement of Science, Leeds, 1890) . 110 
 
 ADDENDUM 
 
 (M. Berth elot and the Address to the Chemical Section of the 
 
 British Association at Leeds, 1890) . . . .134 
 
 VII 
 
 MICHAEL FARADAY 
 
 (A Review of Dr. Bence Jones's Life and Letters of Faraday. 
 
 Manchester Guardian, 1870) ..... 142 
 
 VIII 
 
 THOMAS GRAHAM 
 
 (A Lecture (with additions) delivered in the Yorkshire College, 
 
 Leeds, introductory to the Evening Class Session, 1877-78) . 160 
 
 The Third Triennial Graham Lecture, delivered to the Philosophical 
 
 Society of Glasgow in Anderson's College, 16th March 1887 . 217 
 
Contents xi 
 
 IX 
 
 FRIEDRICH WOHLER 
 
 PAGE 
 
 (A Lecture delivered at the Royal Institution on Friday Evening, 
 
 15th February 1884 . . . . . .236 
 
 X 
 
 JEAN BAPTISTE ANDRE DUMAS 
 
 (A Lecture delivered to the Royal Dublin Society, March 1885) . 258 
 
 XI 
 
 HERMANN Korr 
 
 (Memorial Lecture delivered to the Fellows of the Chemical Society, 
 20th February 1893 ; published in the Transactions of the 
 Chemical Society, 1893) . . . . . . 299 
 
 XII 
 DMITRI IVANOWITSH MENDELEEFF 
 
 ("Scientific Worthies," No. x\vL Nature, 1889) . . . 350 
 
 XIII 
 
 THE RISE AND DEVELOPMENT OF SYNTHETICAL CHEMISTRY 
 
 (The Presidential Address to the Sutton Coldfield Institute, 1892 ; 
 
 subsequently published in the Fortnightly Review] . . 366 
 
EGBERT BOYLE 
 
 ONE OF THE FREE EVENING LECTURES DELIVERED IN CONNECTION 
 WITH THE LOAN COLLECTION OF SCIENTIFIC APPARATUS AT SOUTH 
 KENSINGTON IN 1876. 
 
 FROM whatever point of view we may regard it, the period 
 which began with the restoration of the House of Stuart 
 and ended with its downfall is one of the most extraordinary 
 in our history. It is a period of paradoxes. The reign 
 of Charles II. is at once one of the worst and one of the 
 brightest epochs in our annals. Never were the resources 
 of this country so recklessly wasted; never was it more 
 wretchedly governed. At home, public morality and political 
 virtue were at their lowest ebb. Abroad, the foreign policy 
 of the power which the firmness of Oliver had made to be 
 everywhere respected was the subject of derision in even the 
 smallest of German courts. The boys of Amsterdam, who, 
 as Macaulay tells us, ran along the canals, when the great 
 Protector was no more, shouting for joy that the Devil was 
 dead, had as men the gratification of helping De Winter to 
 burn our arsenals, and of insulting Tilbury, sacred to the 
 memory of Elizabeth, and of one of the proudest moments 
 of our national existence. On the other hand, at no former 
 period were such mighty legislative reforms enacted ; blow 
 after blow was aimed at and made its mark upon spiritual 
 
 B 
 
Robert Boyle 
 
 tyranny and territorial aggression ; and the Church was made 
 to admit, with Praed's good old Dr. Brown, 
 
 That if a man's belief is bad, 
 
 It will not be improved by burning. 
 
 If our literature was debased by the ribaldry of a crowd of 
 dramatists and poetasters, it was purified arid ennobled by 
 the sublime genius of Milton and the brilliant fancy of 
 Dryden. 
 
 Times so rich in incongruities, the times of Clarendon, 
 Halifax, Hale, Russell, Milton, and Jeremy Taylor; and of 
 Buckingham, Sunderland, Jeffreys, Gates, and the Duchess of 
 Portsmouth, have been the wonder and the despair of his- 
 torians. The inquiry how, under such untoward circumstances, 
 such a marvellous progress was possible, was a riddle which it 
 has been left to our own age to solve. This movement was the 
 effect of that vague and indefinable force we call the spirit of the 
 age ; and the spirit of that age, as it has been laid bare to us by 
 the searching anatomy of the author of the History of Civilisation 
 in England, was a sceptical, inquiring, reforming spirit. It per- 
 vaded every department of knowledge and of intellectual energy. 
 It was rife in theology, in politics, in philosophy, and eventually 
 in science. This spirit may be said to have infused itself in 
 science with the appearance in 1661 of a little octavo volume 
 from an Oxford printing press : it came forth without apy 
 preparatory bustle, anonymously and undedicated. But in its 
 revolt against mere authority, in its disdain of old-world 
 notions, and in its ill-concealed contempt for the schoolmen, 
 it so exactly caught and expressed the spirit of the time that 
 it instantly arrested the attention of the learned world, and 
 not only of the small world of the virtuosi, but of that infinitely 
 larger public of thinking men who felt a growing impatience 
 of the dogmas of the schools. The book was entitled the 
 " Sceptical Chymist : or Chemico Physical Doubts and Para- 
 doxes touching the Experiments, whereby vulgar Spagyrists 
 
Robert Boyle 
 
 are wont to endeavour to evince their Salt, Sulphur, and 
 Mercury to be the true Principles of Things." There was not 
 much in such a title to attract the common public, nor were 
 its merits as a piece of literary workmanship of a very high 
 order; nevertheless, the book was eagerly bought up, and 
 its popularity was such as to attract even the attention of 
 foreigners visiting London, and no fewer than ten Latin 
 editions of it appeared on the Continent. Who was the 
 author 1 ? was in everybody's mouth. Men declared that the 
 mantle of the great lawgiver who, as Cowley sung, had seen, 
 as from the summit of Pisgah, the land which he was not per- 
 mitted to enter, had fallen upon him. The writer was soon 
 identified as a young nobleman, the youngest son of an Irish 
 peer, who the year before had ventured abroad a treatise on 
 the elastic power of the air, in which he exploded the notion 
 of a Fuga Vacui, and for doing which he had drawn down 
 upon himself the trenchant wrath of the author of the 
 Leviathan Hobbes of Malmesbury, the last man of note in 
 England who did battle for the Plenists. 
 
 This young nobleman was called the Honourable Robert 
 Boyle : he was the seventh son and the fourteenth child of the 
 Great Earl of Cork, and was born at Lismore, in the county 
 of Waterford, on 25th January 1626. His father, Richard 
 Boyle, a younger son of the younger branch of a Hertford- 
 shire family, which could trace its ancestry back to the times 
 of Edward the Confessor, despairing of employment at home, 
 had resolved to push his fortunes in Ireland, and at twenty-two 
 years of age found himself in Dublin with no other worldly 
 possessions than a taffety doublet and a pair of black velvet 
 breeches laced, a new Milan fustian suit, two cloaks and com- 
 petent linen, a couple of tokens, a trusty rapier and dagger, 
 and twenty -seven pounds three shillings in ready money. 
 From these inconsiderable beginnings he built, as his son 
 relates with pride, so plentiful and so eminent a fortune that 
 his prosperity found many admirers but few parallels. Of 
 
 TFTHF 
 
Robert Boyle 
 
 the mother of Kobert Boyle we learn little beyond that she 
 was the daughter of Sir Geoffrey Fenton, Principal Secretary 
 of State for Ireland, that she wanted not beauty, and was 
 rich in virtue. She died when her youngest son was only a 
 few years old, and he tells us that he ever counted it among 
 the chief misfortunes of his life that he. knew not her that 
 gave it him. When eight years of age he was sent to Eton, 
 at which time Sir Henry Wotton was Provost : a fine gentle- 
 man himself, and well skilled in the art of making others so. 
 Here the studious sickly boy with his uncouth Irish manners, 
 his stuttering speech, and his roving habits, must have been 
 sorely tried had he not fallen into good hands : as it was, 
 Eton and Sir Henry were ever pleasant memories to him. It 
 might have been otherwise, however, for through a stupid 
 mistake of a careless apothecary he had nearly lost his life ; 
 which accident, he said, made him long after apprehend more 
 from the physicians than from the disease, and was possibly 
 the occasion that made him so inquisitively apply himself to 
 the study of physic that he might have the less need of them 
 that profess it. Years after he himself was nominated to the 
 Provostship by Charles II., but his objection to take orders, 
 in spite of the advice of Clarendon, overcame his inclination 
 to accept an office to which his habits and associations dis- 
 posed him. At the age of twelve he was sent with an elder 
 brother to the Continent, where he remained for six years. 
 The good old earl his father died in the midst of the troubles 
 occasioned by the insurrection in Ireland, and Boyle with 
 great difficulty found his way back to England and to his 
 manor at Stalbridge, in Dorsetshire, which had descended to 
 him. Here he lived in great retirement throughout the 
 unhappy times which culminated in the death of Charles I, 
 seeking in his books and in his laboratory some diversion 
 from the contemplation of the miseries of his country. At 
 about this time Boyle became a member of what its promoters 
 pleasantly termed the Invisible College, an assembly of learned 
 
Robert Boyle 
 
 and curious gentlemen who applied themselves to the study 
 of experimental science, or, as it was then called, the New 
 Philosophy. The little band included John Wallis, the 
 mathematician ; John Wilkins, afterwards Bishop of Chester ; 
 Jonathan Goddard, Warden of Merton; Samuel Foster, Pro- 
 fessor of Astronomy at Gresham College ; and Theodore Haak, 
 a German resident in London, who appears to have first sug- 
 gested the meetings. These were held weekly at each other's 
 lodgings in London or at Gresham College, " to discourse and 
 consider of philosophical inquiries and such as related there- 
 unto (precluding matters of theology and State affairs)." A 
 certain portion of the company removed to Oxford, and, 
 continuing the meetings, were joined by Seth Ward, after- 
 wards Bishop of Salisbury ; Ralph Bathurst, President of 
 Trinity College, Oxford ; Dr., afterwards Sir William, Petty ; 
 Thomas Willis, and others. Boyle followed in 1654, and 
 thereafter the philosophers met at his lodging, with Crosse, 
 an apothecary, for the convenience of inspecting drugs. The 
 Oxford section, however, always seemed to regard their 
 Gresham brethren as constituting the parent society, and 
 from time to time they journeyed up to London for the 
 purpose of attending the meetings at the College. Out of 
 such beginnings grew the Royal Society of London for 
 Improving Natural Knowledge, incorporated by Charles II. 
 in 1663; and in the charter Boyle is named as one of the 
 council. The growth of the new philosophy excited the 
 jealousy and anger of those who affected to see in the ascendency 
 of the Baconian method the subversion of everything that 
 was orderly and of good repute. Religion, they cried, was 
 being undermined ; civil law was gone ; the empire of reason 
 and of all true learning was at an end. Bishops anathematised ; 
 Hobbes, who certainly had scant affection for the clergy, 
 thundered ; Butler lampooned. Boyle was earnestly solicited 
 to leave the society. " I beseech you, sir," writes one of his 
 correspondents, " consider the mischief it hath occasioned in 
 
Robert Boyle 
 
 this once flourishing kingdom, and if you have any sense, not 
 only of the glory and religion, but even of the being of your 
 native country, abandon that constitution. It is too much 
 that you contribute to its advancement and repute : the only 
 reparation you can make for that fatal error is to desert it 
 betimes. Do not you apprehend that all the inconveniences 
 that have befallen the land, all the debauchery of the gentry 
 (which ariseth from that pious and prudent breeding, which 
 was and ought to have been continued) will be charged on 
 your account ? ... It will be impossible for you to preserve 
 your esteem but by a seasonable relinquishing of these 
 impertinents." The writer, Henry Stubbe, a physician of 
 repute, was one of those unquiet spirits of which the times 
 were fertile : he was formerly a Student of Christ Church and 
 Keeper in the Bodleian Library, where he wrote several tracts ; 
 his Essay on the Good Old Times was pardonable, but his 
 Apology for the Quakers was too much for the patience of the 
 University, and he lost his position in Oxford. At the time 
 of the outcry against the Eoyal Society Stubbe made himself 
 the champion of his faculty, the majority of whom condemned 
 Sydenham for believing that the new-fangled philosophy and 
 physic might have something good in common, and he fell 
 foul of Glanvill, Rector of Bath, who had followed Sprat in 
 lauding the institution and objects of the society, in his 
 characteristic fashion. The controversy raged with no little 
 fury and bitterness, and hard knocks were freely given and 
 returned, as was the manner of the time. Fate decreed, how- 
 ever, that Glanvill should have the last word, for his adversary 
 being accidentally drowned near Bath, it fell to the rector's lot 
 to preach his funeral sermon. And let us hope that he saw in it, 
 as the French say, a grand opportunity for holding his tongue. 
 But the Eoyal Society, notwithstanding the rough usage of 
 its youth, continued to grow and prosper, and people began 
 even to see that it might be of use to them in their day and 
 generation. The Great Plague of 1665 and the Great Fire of 
 
Robert Boyle 
 
 1666 gave the Society an opportunity, and much of what was 
 good in the arrangement in the new city was the result of 
 their deliberations and counsel. Science became even fashion- 
 able. The King set up a laboratory, and amused himself by 
 making weather observations with the newly-invented baro- 
 scope ; the fine ladies of his court marvelled at the properties 
 of the phosphorus (of so curious an origin), which Mr. Kraffts 
 had brought from Germany; and the gentlemen at Will's 
 conversed of the Vacuo Boyliano and the spring of air. More- 
 over, many of the matters upon which the learned world at 
 that time disputed were, when stated in intelligible terms, of 
 common interest. One of the points about which people 
 wrangled, when reduced to a plain issue, was this : Is a 
 vacuum possible ; that is, can a space absolutely void of 
 matter be obtained? A few years before a very learned 
 Frenchman, Rene Des Cartes, had asserted that, as according 
 to his thinking, the universe was absolutely full, it was im- 
 possible even to conceive of the existence of a vacuum ; and 
 such was his subtlety and logic that many other learned 
 persons came to be of his opinion. But when men began to 
 use their hands and eyes as well as their reason in attempting 
 to get at nature's secrets, doubts arose whether the expla- 
 nations and hypotheses of the gown -men were not rather 
 strained, and for the most part unsatisfactory. For example, 
 the manner in which Mr. Hobbes explained the action of the 
 watering-pot would scarcely commend itself to the readers of 
 his Dialogus Physicus de Natura Aeris:"H a gardener's 
 watering-pot be filled with water, the hole at the top being 
 stopped, the water will not flow out at any of the holes in the 
 bottom ; but if the finger be removed to let in the air above, 
 it will run out at them all, and as soon as the finger is applied 
 to it again the water will suddenly and totally be stayed 
 again from running out. The cause whereof seems to be no 
 other but this, that the water cannot, by its natural endeavour 
 to descend, drive down the air below it, because there is no 
 
8 Robert Boyle 
 
 place for it [the air] to go into, unless either by thrusting 
 away the next contiguous air it proceed by continual endea- 
 vour to the hole at the top, where it may enter and succeed 
 in the place of the water that floweth out, or else by resisting 
 the endeavour of the water downwards penetrate the same, 
 and pass up through it." 
 
 Unfortunately for the Plenists, as Mr. Hobbes and the 
 Cartesians came to be called, there were some awkward facts 
 which did not seem to agree at all with the notion of the 
 plentitude of the world. There was the fact that if a tube, 
 say 35 feet long, closed at one end and open at the other, 
 be completely filled with water and inverted with the open 
 end under water, the level of the water in the tube will sink 
 a few feet that is, the water-column will not exceed some 32 
 or 33 feet in length, measured from the level of the liquid in 
 the cistern. Moreover, if the experiment be repeated with 
 quicksilver, which is more than thirteen times heavier than 
 water, bulk for bulk, the height of the quicksilver column will 
 be only one-thirteenth of that of the water. And there was 
 this particularly awkward fact, that if the tube containing 
 the quicksilver be carried up a high tower, as did Claudio 
 Bereguardi up the leaning tower of Pisa, or up a mountain, as 
 did Perrier some four or five years later in France, or as Mr. 
 Kichard Townley did up one of the Lancashire hills, the space 
 above the mercury became much greater as the summit was 
 approached, and became less again as the descent was made. 
 Curious persons naturally asked why the mercury behaved in 
 this way, and what was in the space above the level of the 
 liquid 1 If the world were actually as full as an egg, the 
 existence of these apparently empty spaces was certainly very 
 perplexing. It was not at all clear why nature should be so 
 partial in her likings and dislikings as to put up with a much 
 bigger space from the mercury than she would from the water, 
 and it seemed rather irrational for her to hate a vacuum less 
 at the top of a mountain than at the bottom. 
 
Robert Boyle 
 
 It was about this time that Boyle published in the form of 
 a letter to his nephew, Lord Dungarvan, his "New Experiments 
 Physico-Mechanical touching the Spring of Air and its Effects, 
 made for the most part in a new Pneumatical Engine." Shortly 
 after Boyle had turned his attention to physical science he 
 heard of a book " published by the industrious Jesuit 
 Schottus, wherein it was related how that that ingenious 
 gentleman, Otto Gericke, Consul of Magdeburg^ had lately 
 practised in Germany a way of emptying glass vessels by 
 sucking out the air at the mouth of the vessel plunged under 
 water." Boyle at once recognised that important results 
 might be expected to follow the study of the phenomena of 
 the air's rarefaction, but he also saw that such results could 
 scarcely be furnished by Yon Guericke's method. He accord- 
 ingly sought to devise a more perfect form of instrument, and 
 with the assistance of Robert Hooke, a man of remarkable 
 inventive powers, he, about the year 1658, contrived his 
 " Pnuematical Engine." 
 
 It consisted of a large pear-shaped vessel holding about 
 thirty wine-quarts, fitted with a stopper at the top and con- 
 nected at the bottom with a brass cylinder in which was a 
 piston worked by a rack and pinion. Between the glass 
 vessel, "which we," says Boyle, "with the glassmen shall 
 often call a receiver for its affinity to the large vessels of 
 that name used by chemists," was a stopcock which was 
 alternately opened and closed as the piston was worked 
 up and down, the air from the cylinder being allowed to 
 escape through a small hole at the top, temporarily closed by 
 a stopper. The mode of working the pump will be obvious. 
 " By the repetition of the motion of the sucker [piston] upward 
 and downward, and by opportunely turning the key [of the 
 stopcock] and stopping the valve [the brass peg inserted into 
 the cylinder] as occasion requires, more or less air may be 
 sucked out of the receiver according to the exigency of the 
 experiment and the intention of him that makes it." 
 
 CF THF 
 
io Robert Boyle 
 
 Before describing his experiments in detail Boyle proceeds 
 to " insinuate that notion by which it seems likely that most 
 if not all of them will prove explicable, namely, that there is 
 a spring or elastical power in the air we live in. By which 
 elater or spring of the air, that which I mean is this : that our 
 air either consists of, or at least abounds with, parts of such a 
 nature, that in case they be bent or compressed by the 
 weight of the incumbent part of the atmosphere, or by any 
 other body, they do endeavour, as much as in them lieth, to 
 free themselves from that pressure, by bearing against the 
 contiguous bodies that keep them bent ; and, as soon as those 
 bodies are removed, or reduced to give them way by presently 
 unbending and stretching out themselves, either quite, or so 
 far forth as the contiguous bodies that resist them will per- 
 mit, and thereby expanding the whole parcel of air these 
 elastical bodies compose." Boyle pictured to himself this pro- 
 cess of unbending and stretching by considering the air near 
 the earth to be " such a heap of little bodies lying one upon 
 another as may be resembled to a fleece of wool. For this (to 
 omit other likenesses betwixt them) consists of many slender 
 and flexible hairs; each of which may indeed, like a little 
 spring, be easily bent or rolled up; but will also, like a 
 spring, be still endeavouring to stretch itself out again. For 
 though both these hairs, and the aerial corpuscles to which we 
 liken them, do easily yield to external pressures ; yet each of 
 them (by virtue of its structure) is endowed with a power or 
 principle of self -dilatation ; by virtue whereof, though the 
 hairs may, by a man's hand, be bent and crowded closer, and 
 into a narrower room than suits best with the nature of the 
 body ; yet, whilst the compression lasts, there is in the fleece 
 they compose an endeavour outwards, whereby it continually 
 thrusts against the hand that opposes its expansion. And 
 upon the removal of the external pressure, by opening the 
 hand more or less, the compressed wool doth, as it were, spon- 
 taneously expand or display itself towards the recovery of its 
 
i Robert Boyle 1 1 
 
 more loose and free condition, till the fleece hath either 
 regained its former dimensions, or at least approached them 
 as near as the compressing hand (perchance not quite opened) 
 will permit." 
 
 This passage illustrates in a remarkable manner the 
 mechanical turn of Boyle's mind, and the extreme caution 
 with which he invariably expressed his opinions. Humboldt, 
 indeed, calls him " the cautious and doubting Robert Boyle." 
 He was well aware that other modes of explaining the elas- 
 ticity of the air were possible, and, in fact, he cites that of 
 Descartes, that the air is nothing but a heap of small flexible 
 particles raised by the sun's heat "into that fluid and subtle 
 and ethereal body which surrounds the earth; and by the 
 restless agitation of that celestial matter, wherein those par- 
 ticles swim, are so whirled round that each corpuscle endea- 
 vours to beat off all others from coming within the little 
 sphere requisite to its motion about its own centre ; and in 
 case any, by intruding into that sphere, shall oppose its free 
 rotation to expel or drive it away." The vehement agitation 
 which the particles receive from the fluid aether that swiftly 
 flows between and whirls about each of them, as the eddying 
 stream about the corks, not only keeps them separated, but 
 also makes them hit against and knock away each other, and 
 consequently require more room than they would need if com- 
 pressed. After all, there is a certain resemblance in this to 
 our modern notions of the constitution of a gas. On the 
 whole, Boyle is inclined to his own hypothesis, but he is un- 
 willing, as he says, "to declare peremptorily for either of 
 them against the other"; for "to determine whether the 
 motion of restitution in bodies proceed from this, that the 
 parts of a body of a peculiar structure are put into motion by 
 the bending of the spring, or from the endeavour of some 
 subtle ambient body whose passage may be stopped or ob- 
 structed, or else its pressure unequally resisted by reason 
 of the new shape or magnitude, which the bending of a 
 
1 2 Robert Boyle 
 
 spring may give the pores of it : to determine this, I say, 
 seems to me a matter of more difficulty than at first sight one 
 would easily imagine it." 
 
 Boyle had a perfectly clear conception of the materiality 
 of air, and he attempted on several occasions to determine its 
 weight, although it is remarkable that he who was so familiar 
 with the principle of Archimedes that a body weighed in a 
 fluid loses of its weight an amount equal to that of the bulk 
 of fluid displaced, should have made the experiment by 
 weighing bladders first empty and then inflated with air. 
 Indeed, he himself was the first to show that a bladder con- 
 taining air and counterpoised with metallic weights appears to 
 weigh more in vacua than in the air ; and the familiar experi- 
 ment in which the cork ball seems to increase in weight when 
 placed in the exhausted receiver was first devised by him. 
 
 "Taking it for granted then," he goes on to say, "that the 
 air is not devoid of weight, it will not be uneasy to conceive 
 that that part of the atmosphere wherein we live, being the 
 lower part of it, the corpuscles that compose it are very 
 much compressed by the weight of all those of the like 
 nature that are directly over them ; that is, of all the particles 
 of air that being piled up upon them, reach to the top of the 
 atmosphere." He then recalls to mind the observation that 
 tjie mercurial column in the barometer stands lower at the 
 top of a mountain than at the bottom, " of which the reason 
 seems manifestly enough to be this, that upon the tops of high 
 mountains the air, which bears against the restagnant quick- 
 silver, is less pressed by the less ponderous incumbent air." 
 He next disposes of the possible objection that the air thus 
 strongly compressed by the superincumbent atmosphere 
 should yet yield readily to the motion even of little flies and 
 feathers, by demonstrating " that it is the equal pressure of 
 the air on all sides upon the bodies that are in it, which 
 causeth the easy cession of its parts, which may be argued 
 from hence ; that if by the help of our engine the air be but 
 
Robert Boyle 1 3 
 
 in great part, though not totally, drawn away from one side 
 of a body without being drawn away from the other, he that 
 shall think to move that body to and fro, as easily as before, 
 will find himself much mistaken." To demonstrate this 
 Boyle was wont to tie a partially inflated bladder to the 
 stopper of the receiver, and to desire a bystander to lift up 
 the stopper after the receiver was partly exhausted : it was 
 "pleasant to see," he says, "how men will marvel that so 
 light a body, filled at most with but air, should so forcibly 
 draw down their hands, as if it were filled with some very 
 ponderous thing." The distention of the bladder, in con- 
 sequence of the expansion of the included air, as the rarefac- 
 "tion in the receiver proceeded, affords him an additional 
 proof of the force of the spring of air. He proceeds to point 
 out that the force of this spring may be augmented by heat : 
 " the elastical power of the same quantity of air may be as 
 well increased by the agitation of the aerial particles (whether 
 only moving them more swiftly and scattering them, or also 
 extending or stretching them out, I determine not) within an 
 every way inclosing and yet yielding body ; as displayed by 
 the withdrawing of the air that pressed it without. For we 
 found that a bladder but moderately filled with air and 
 strongly tied, being awhile held near the fire, not only grew 
 exceedingly turgid and hard, but afterwards being brought 
 nearer to the fire suddenly broke with so loud and vehement 
 a noise as stunned those that were by, and made us for a 
 while after almost deaf." The connection of these phenomena 
 singularly impressed Boyle ; and he says that it deserves 
 "deliberate speculation." During the two centuries which 
 have elapsed since then many men have given this matter a 
 vast amount of "deliberate speculation," with the result 
 of showing that this connection is even more intimate than 
 Boyle, with all his prevision, could have dreamt of. 
 
 The relation of the air to combustion, and the nature 
 of flame, attracted much attention from Boyle, and he 
 
14 Robert Boyle 
 
 frequently returned to these subjects in the course of his 
 work. His observations on the burning of candles in a 
 partial vacuum are worth mention for the evidence they 
 afford of the care with which he noted even the minutest 
 phenomena attending an experiment. After proving that 
 the flame is extinguished long before the exhaustion is com- 
 plete, he goes on to say "that these things were further 
 observable, that after the two or three first exsuctions of the 
 air, the flame (except at the very top) appeared exceedingly 
 blue, and receded more and more from the tallow, till at 
 length it appeared to possess only the very top of the wick, 
 and there it went out." These phenomena, apparently so 
 trivial, are now recognised as of importance in connection 
 with the theory of illuminating flames. Boyle next proceeds 
 to what he evidently regards as a great experimentum crucis, 
 " whereof," he says, " the satisfactory trial was the principal 
 fruit I promised myself from our engine " : it related to the 
 behaviour of a barometer in the exhausted receiver. After 
 carefully fitting the barometer into the receiver, so that the 
 outer air could not press down upon the surface of the metal 
 in the cistern, he drew down the sucker, and found to his 
 delight that the mercury fell within the tube and continued 
 to fall so long as the pump was worked until it was only an 
 inch or so from the level of that in the cistern : on readmitting 
 the air the mercury was impelled up again to its original 
 position in the tube. The importance of this observation was 
 obvious, and all Oxford came to see an experiment which 
 afforded such a signal confirmation of the truth of the specula- 
 tions of Galileo and Pascal. It now occurred to Boyle to try 
 what relation existed between the height of the mercurial 
 column and the number of suctions made by the pump, for he 
 had observed that the first sucks caused a far more rapid 
 decrease in the height than the last. Boyle, we see, is now 
 on the verge of the great discovery which has made his name 
 familiar to every schoolboy in this country. It is worth 
 
Robert Boyle \ 5 
 
 noticing that it was in all probability the accident of the mode 
 of construction of his engine, and the fact that each suction 
 drew out a determinate bulk of air, that induced him to 
 attempt to determine the relation between the pressure and 
 volume of the air. He was forced, however, to abandon the 
 attempt at this time, for he found that with the apparatus in 
 its present form he was unable to make observations accurate 
 enough to reduce them to any hypothesis. "Yet," he adds, 
 " would we not discourage any from attempting it, since if it 
 could be reduced to a certainty it is probable that the dis- 
 covery would not be unuseful." 
 
 He is now forced to confront the ever-recurring question 
 Is there a vacuum ? and accordingly he proceeds to take the 
 arguments of the Plenists to pieces. What proof, he asks, do 
 they offer of the existence of that subtle ethereal matter which 
 they say must exist in the space above the mercury. Why 
 must exist? Because, they answer, there cannot be a void. 
 And there cannot be a void because extension is the only 
 nature of a body, and to say a space is devoid of body is, to 
 the schoolmen, a contradiction in adjecto. The matter is, in 
 fact, reduced to a question of metaphysics, and Boyle gives it 
 up, " finding it very difficult either to satisfy naturalists with 
 this Cartesian notion of a body, or to manifest wherein it is 
 erroneous." The truth is, Boyle was hampered by his cor- 
 puscular notions, or he would assuredly have gone over to the 
 Vacuists. He puts his candles and his bladders into his 
 receivers, and however completely he may pump out the air, 
 the things are none the less visible, and he asks Can it be 
 seriously imagined that light can be conveyed from an object 
 without some vehicle to convey it ? 
 
 He then substituted water for mercury, and repeated the 
 experiment. As the rarefaction proceeded, he was struck 
 with the appearance of a multitude of air bubbles within the 
 liquid. The origin of this air puzzled him greatly. Was the 
 water turned into air, or was the air pre-existent and latitant 
 
1 6 Robert Boyle 
 
 in the water? On the whole, he inclines to the latter sup- 
 position, but mainly for the reason that all experience showed 
 that water was elementary, indestructible, and inconvertible. 
 He argues the matter at such length that he is constrained to 
 apologise for his prolixity in treating of such empty things as 
 bubbles ; yet he does not fail to point the moral " that there 
 are very many things in nature that we disdainingly overlook 
 as obvious or despicable, each of which would exercise our 
 understandings, if not pose them too, if we would but attentively 
 enough consider it, and not superficially contemplate it, but 
 attempt satisfactorily to explicate the nature of it." 
 
 -The idea that the air was the medium by which sound is 
 ordinarily conveyed was familiar enough to the philosophers 
 of the seventeenth century, and Boyle furnishes a proof of the 
 fact by the observation that the ticking of a watch placed in 
 the receiver became inaudible when the air was withdrawn. 
 
 The mode of action of the syphon next engages his attention, 
 and he proceeds to inquire what must be the height of the 
 atmosphere on the assumption that it has the same density at 
 all points that it possesses on the earth's surface. He has 
 completed the proof that the pressure of the air supported the 
 mercurial column ; his problem was to determine how much 
 heavier mercury is than air, bulk for bulk ; he would thus be 
 able to calculate the height of a column of air, of the density 
 of that on the earth's surface, required to balance a mercurial 
 column of equal base and of 30 inches in height. Boyle 
 unfortunately considered that the ratio of the weights of equal 
 bulks of water and air was known with sufficient accuracy in 
 his day, and after a discussion of all the observations with 
 which he was acquainted, he concludes that water may be 
 considered to be 1000 times heavier than air, which we now 
 know to be greatly in excess of the truth. He proceeds, 
 then, to inquire how much heavier mercury is than water, but 
 the observations of his predecessors on this point are so dis- 
 cordant that he feels himself obliged to re -determine the 
 
Robert Boyle 1 7 
 
 relation, firstly by observing the heights of counterbalancing 
 columns of mercury and water in a U-shaped tube, and, 
 secondly, by the method now adopted as the most accurate 
 of all modes of estimating the specific gravities of liquids. 
 By the first method he found that mercury is 13'7, by the 
 second 13 '68 times heavier than water: no very great dis- 
 parity from the number 13 '6 which we now adopt. From 
 these data Boyle calculated that the atmosphere must be 
 between six and seven miles high, on the supposition that it 
 has the same density throughout that it has on the surface of 
 the earth : in reality on the same assumption, it is only 
 between five and six miles high. Boyle was perfectly aware 
 that this result was, in a sense, fictitious, but he shows that 
 it was not without value as demonstrating what must be the 
 minimum height of the atmosphere : it proved that the con- 
 jectures of Kepler and others that the air could not extend 
 beyond a couple of miles or so from the earth's surface were 
 certainly erroneous. 
 
 The main fact that air is related to life was of course as 
 well understood in those days as it is now, but very little was 
 known of the theory of respiration. Boyle made many 
 experiments with his air-engine to elucidate this matter, and 
 I am really afraid, in these anti-vivisection days, to tell you 
 how many cats, mice, sparrows, fishes, tadpoles, and snails 
 fell victims to his zeal. Not that he inflicted needless suffer- 
 ing, for Boyle was the most tender-hearted of men ; if he has 
 occasion to confine a mouse all night in one of his receivers, 
 he places him near the fire, and consoles him with a bit of 
 cheese, that he may be as comfortable as circumstances will 
 permit ; a lusty and pugnacious sparrow makes such a resolute 
 stand for existence that Boyle is fain to let him go ; and the 
 intercession of a lady is quite sufficient to deprive a certain 
 kitten of the honour and glory of settling an important query * 
 concerning respiration. yV 
 
 The last experiment which Boyle narrates is one of the 
 
 c 
 
 i- 
 
 v 
 Y 
 
1 8 Robert Boyle 
 
 'most important and striking in the whole series, since by 
 means of it he demonstrated how dependent is the boiling- 
 point of a liquid upon the atmospheric pressure. Having 
 boiled some water " a pretty while that by the heat it might 
 be freed from the latitant air," he placed it, whilst still hot, 
 within the receiver, when, on exhaustion, it again began to 
 boil "as if it had stood over a very quick fire. . . . Once, 
 when the air had been drawn out, the liquor did, upon a 
 single exsuction, boil so long with prodigiously vast bubbles 
 that the effervescence lasted almost as long as was requisite 
 for the rehearsing of a Pater Noster. This experiment, he 
 says, seems to teach that the air by its stronger or weaker 
 pressure may very much modify (as the schoolmen speak) 
 divers of the operations of that vehement and tumultuous 
 agitation of the small parts of bodies, wherein the nature of 
 
 \j heat seems chiefly, if not solely, to consist." 
 
 Such is a very rapid and a very imperfect summary of this 
 
 -"' great work. I have purposely quoted very largely from it, 
 for I wished to show you, in Boyle's own words, how wonder- 
 fully near much of the philosophy of the seventeenth century 
 is to that which we are too apt to regard as the outcome of 
 the nineteenth. It is impossible to exaggerate the importance 
 of Boyle's labours ; they served to give a marvellous sharpness 
 to the notions of that time concerning the materiality of the 
 air and of the phenomena which depend upon its elasticity. 
 The work exhibits in an eminent degree Boyle's character as 
 an investigator, his quick perception and receptive mind, his 
 great power of co-ordination, his insight, his logic, his patient 
 care and scrupulous accuracy. It exhibits, too, his weakness ; 
 for it must be admitted that it is wanting in that grasp of 
 principle and faculty of generalisation which we see in the 
 work of the illustrious author of the Novum Organum. It 
 lacks, too, the ForscherUick and power of divination so 
 characteristic of the genius of Newton. But to say that 
 Boyle is only inferior to Bacon and Newton is to assign 
 
Robert Boyle 1 9 
 
 him one of the first niches in the Walhalla of the heroes of 
 science. 
 
 But Boyle's work, as I have before hinted, was not allowed 
 to go forth unchallenged; and the Elaterists were quickly 
 taken to task, on the one hand by one Franciscus Linus, and 
 on the other by a far more important personage Thomas 
 Hobbes, of Malmesbury. Hobbes has been styled the subtlest 
 dialectician of his time, and a master of precise and luminous 
 language; too frequently, however, that language lost more 
 in elegance than it gained in force. Hobbes, although not a 
 professed Peripatetic or a Cartesian, was a very pronounced 
 Plenist. He utterly failed to see any virtue in the new 
 philosophy, and the disparagement of the Gresham set, or- 
 " the experimentarian philosophers," as he sneeringly called 
 them, was the chief design of his Dialogus Physicus de Natura 
 Aeris, the book in which he attempts to write down Boyle 
 and his work. Boyle hated contention; but he and his 
 friends felt that the new doctrines were at stake. It is 
 unnecessary for me to take up your time by examining Mr. 
 Hobbes's arguments or Boyle's refutation of them ; it is 
 sufficient to say that Mr. Hobbes, who had, with singular 
 indiscretion, laid himself open by quoting Vespasian's law, 
 "That it is unlawful to give ill language first, but civil and lawful 
 to return it" was taught politeness and much sound philosophy. 
 The world will willingly let the Dialogus die, or remember it 
 only in connection with Boyle's Examen of it. 
 
 We cannot however so summarily dismiss Franciscus 
 Linus. Linus sets out to prove that the mercury in the Tor- 
 ricellian experiment is upheld not by the pressure of the air 
 but by a certain nondescript internal cord ; and Boyle under- 
 takes to show that this hypothesis of an internal funiculus, 
 which he remarks, with quiet humour, "seems to some more 
 difficult to conceive than any of the phenomena in controversy 
 is to be explained without it, is 'partly precarious, partly 
 unintelligible, partly insufficient, and besides needless.'" 
 
2o Robert Boyle 
 
 Indeed the matter is scarcely worth mention except for the 
 circumstance that it gave an occasion to Boyle to return to 
 the question, which we have seen had already interested him, 
 of the relation between the volume and the pressure of the air. 
 n the answer to Linus he gives two new experiments touch- 
 ing the measure of the force of the spring of air compressed 
 and dilated. The account of these memorable experiments 
 must be given in Boyle's own words " We took then a long 
 glass tube, which, by a dexterous hand and the help of a 
 lamp, was in such a manner crooked at the bottom, that the 
 part turned up was almost parallel to the rest of the tube, 
 and the orifice of this shorter leg of the syphon (if I may 
 so call the whole instrument) being hermetically sealed, the 
 length of it was divided into inches (each of which was sub- 
 divided into eight parts) by a straight list of paper, which, 
 containing those divisions, was carefully pasted all along it. 
 Then putting in as much quicksilver as served to fill the arch 
 or bended part of the syphon, that the mercury standing in a 
 level might reach in the one leg to the bottom of the 
 divided paper, and just to the same height or horizontal line 
 in the other, we took care, by frequently inclining the tube, 
 so that the air might freely pass from one leg into the other 
 by the sides of the mercury (we took, I say, care), that 
 the air at last included in the shorter cylinder should be of 
 the same laxity with the rest of the air about it. This done, 
 we began to pour quicksilver into the longer leg of the 
 syphon, which, by its weight pressing up that in the shorter 
 leg, did by degrees straighten the included air ; and continu- 
 ing this pouring in of quicksilver till the air in the shorter leg 
 was by condensation reduced to take up but half the space it 
 possessed (I say possessed, not filled) before, we cast our eyes 
 upon the longer leg of the glass, upon which we likewise 
 pasted a list of paper carefully divided into inches and parts, 
 and we observed, not without delight and satisfaction, that 
 the quicksilver in that longer part of the tube was 29 inches 
 
Robert Boyle 2 1 
 
 higher than the other. Now that this observation does both 
 very well agree with and confirm our hypothesis, will be 
 easily discerned by him that takes notice what we teach : and 
 Monsieur Pascal and our English friend's [Mr. Townley's] 
 experiments prove, that the greater the weight is that leans 
 upon the air, the more forcible is its endeavour of dilatation, 
 and consequently its power of resistance (as other springs are 
 stronger when bent by greater weights). For this being 
 considered, it will appear to agree rarely well with the 
 hypothesis, that as according to it the air in that degree of 
 density, and correspondent measure of resistance, to which 
 the weight of the incumbent atmosphere had brought it, was 
 unable to counterbalance and resist the pressure of a mer- 
 curial cylinder of about 29 inches, as we are taught by the 
 Torricellian experiment ; so here the same air being brought 
 to a degree of density about twice as great as that it had 
 before, obtains a spring twice as strong as formerly. As may 
 appear by its being able to sustain or resist a cylinder of 
 29 inches in the longer tube, together with the weight of the 
 atmospherical cylinder that leaned upon those 29 inches of 
 mercury ; and, as we just now inferred from the Torricellian 
 experiment, was equivalent to them." 
 
 At this stage of the experiments the tube broke, and it 
 was only after several mischances that Boyle was able to com- 
 plete his observations. 
 
 He then proceeded to the converse experiment that is, to 
 determine the spring of rarefied air. A tube, about 6 feet in 
 length, and sealed at one end, was nearly filled with mercury, 
 and into it was placed "a slender glass pipe of about the 
 bigness of a swan's quill, and open at both ends ; all along 
 of which was pasted a narrow list of paper, divided into 
 inches and half-quarters. This slender pipe being thrust 
 down into the greater tube almost filled with quicksilver, the 
 glass helped to make it swell to the top of the tube ; and the 
 quicksilver getting in at the lower orifice of the pipe filled it 
 
22 Robert Boyle 
 
 up till the mercury included in that was near about a level 
 with the surface of the surrounding mercury in the tube. 
 There being, as near as we could guess, little more than an 
 inch of the slender pipe left above the surface of the restag- 
 nant mercury, and consequently unfilled therewith, the promi- 
 nent orifice was carefully closed with sealing-wax melted ; 
 after which the pipe was let alone for a while that the air, 
 dilated a little by the heat of the wax, might, upon refrigera- 
 tion, be reduced to its wonted density. And then we observed, 
 by the help of the above-mentioned list of paper, whether we 
 had not included somewhat more or somewhat less than an inch 
 of air ; and in either case we were fain to rectify the error by 
 a small hole made (with a heated pin) in the wax, and after- 
 wards closed up again. Having thus included a just inch of 
 air, we lifted up the slender pipe by degrees, till the air was 
 dilated to an inch, an inch and a half, two inches, etc., and 
 observed in inches and eighths the length of the mercurial 
 cylinder, which, at each degree of the air's expansion, was 
 impelled above the surface of the restagnant mercury in the 
 tube. The observations being ended, we presently made the 
 Torricellian experiment with the above-mentioned great tube 
 of 6 feet long, that we might know the height of the mer- 
 curial cylinder for that particular day and hour, which height 
 we found to be 29f inches." 
 
 Such were the experiments, simple and easily made, which 
 led Boyle to the recognition of the great law which bears his 
 name a law which is so far from being "unuseful" that it is 
 recognised by the physicist as of the first importance. And 
 yet in spite of the thoroughness with whic{i Boyle did the 
 work, and in spite, too, of the precision with which he stated 
 his results, the attempt has not been wanting to deprive him 
 of the whole merit of this discovery, and there is scarcely a 
 text-book of physics or chemistry on the Continent, or at 
 least in France, in which his name is mentioned in connection 
 with the matter : abroad they prefer to ascribe the glory to 
 
Robert Boyle 
 
 the Abbe Mariotte, although Mariotte's treatise, De la Nature 
 de I' Air, in which he enunciates the law, was not printed until 
 seventeen years after Boyle had published his reply to Linus. 
 " The results of the two series of experiments here de- 
 tailed are given in the following tables : 
 
 A TABLE OF THE CONDENSATION OF THE AIR 
 
 I/ 
 
 I/ 
 
 
 
 
 
 
 A 
 
 A 
 
 B 
 
 C 
 
 D 
 
 
 
 48 
 
 12 
 
 00. 
 
 
 29 T \ 
 
 29 r \ 
 
 46 
 
 114 
 
 OlyV 
 
 
 30 T ^- 
 
 30A 
 
 44 
 
 11 
 
 021f 
 
 
 31rl 
 
 3111 
 
 42 
 
 10i 
 
 04 T 6 ^- 
 
 
 33i\ 
 
 33y 
 
 40 
 
 w 
 
 06/%. 
 
 
 35 T 5 75- 
 
 35 
 
 38 
 
 94 
 
 07ii 
 
 
 37 
 
 361f 
 
 36 
 
 9 
 
 IQy^j 
 
 
 39^ 
 
 38|- 
 
 34 
 
 84 
 
 12i 8 <j 
 
 
 41^.0. 
 
 41yy 
 
 32 
 
 8 
 
 15yV 
 
 CO 
 
 44fV 
 
 43H 
 
 30 
 
 74 
 
 171.5. 
 
 P^ 
 
 47 T V 
 
 46f 
 
 28 
 
 7 
 
 21^ 
 
 g 
 
 50 T 5 ff 
 
 50 
 
 26 
 
 65 
 
 25 T 8 ff 
 
 -t|33 
 
 54 T \ 
 
 53ft 
 
 24 
 
 6 
 
 29 H 
 
 <M 
 
 58H 
 
 58| 
 
 23 
 
 51 
 
 32^ 
 
 O 
 
 61^ 
 
 60^-f 
 
 22 
 
 64 
 
 
 *& 
 
 64^ 
 
 63 T T 
 
 21 
 
 5* 
 
 37lf 
 
 T! 
 
 67rtr 
 
 66| 
 
 20 
 
 5 
 
 41 T 9 ^ 
 
 << 
 
 701^ 
 
 70 
 
 19 
 
 4x 
 
 45 
 
 
 74% 
 
 7311 
 
 18 
 
 44 
 
 48H 
 
 
 77H 
 
 77| 
 
 17 
 
 41 
 
 53H 
 
 
 821f 
 
 82x7" 
 
 16 
 
 4 
 
 58^ 
 
 
 87f|- 
 
 87| 
 
 15 
 
 3| 
 
 631f 
 
 
 93 T V 
 
 93^ 
 
 14 
 
 
 
 
 100^ 
 
 99f 
 
 13 
 
 3* 
 
 78H 
 
 
 
 107 T 7 3 
 
 12 
 
 3 
 
 88 T V 
 
 
 117A 
 
 H6| 
 
 A A The number of equal spaces in the shorter leg that contain the 
 same parcel of air diversely extended. 
 
 B The height of the mercurial cylinder in the longer leg that com- 
 pressed the air into those dimensions. 
 
 C The height of the mercurial cylinder that counterbalanced the 
 pressure of the atmosphere. 
 
 D The aggregate of the two last columns, B and C, exhibiting the 
 pressure sustained by the included air. 
 
 E What that pressure should be according to the hypothesis that 
 supposes the pressure and expansion to be in reciprocal proportion. 
 
2 4 
 
 Robert Boyle 
 
 A TABLE OF THE RAREFACTION OF THE AIR 
 
 A 
 
 B 
 
 C 
 
 D 
 
 E 
 
 1 
 
 00 
 
 
 29f 
 
 29| 
 
 1* 
 
 10| 
 
 
 19* 
 
 19} 
 
 2 
 
 15f 
 
 
 u| 
 
 Hi 
 
 3 
 
 20f 
 
 
 91 
 
 9i-| 
 
 4 
 
 22f 
 
 2 
 
 7* 
 
 7A 
 
 5 
 
 24i 
 
 P> 
 
 3 
 
 5* 
 
 5^ 
 
 6 
 
 24* 
 
 Q 
 
 *i 
 
 4H 
 
 7 
 
 26| 
 
 MW 
 01 
 
 4f 
 
 s 
 
 8 
 
 26$ 
 
 CM 
 
 si 
 
 311 
 
 9 
 
 26f 
 
 1 
 
 3f 
 
 SH 
 
 10 
 
 26| 
 
 
 
 3 
 
 2f| 
 
 12 
 14 
 
 27i 
 27| 
 
 1 
 
 o 
 
 2f 
 
 2f 
 
 2H 
 
 2i 
 
 16 
 
 27| 
 
 I 
 
 2^ 
 
 111 
 
 13 
 
 27| 
 
 -+-* 
 
 
 
 H 
 
 1 
 
 20 
 
 28 
 
 
 
 If 
 
 1A 
 
 24 
 
 28f 
 
 
 If 
 
 ill 
 
 28 
 
 28| 
 
 
 If 
 
 1A 
 
 32 
 
 28$ 
 
 
 H 
 
 OHi 
 
 A The number of equal spaces at tlie top of the tube that contained 
 the same parcel of air. 
 
 B The height of the mercurial cylinder that, together with the spring 
 of the included air, counterbalanced the pressure of the atmosphere. 
 
 C The pressure of the atmosphere. 
 
 D The complement of B to C exhibiting the pressure sustained by 
 the included air. 
 
 E What that pressure should be according to the hypothesis." 
 
 It would be quite impossible for me, in the time which 
 remains, to attempt to go over, however superficially, the 
 whole ground of Boyle's work, although there is much in it of 
 special interest in the present time, as, for example, his papers 
 on the Saltness of the Sea, and the Nature of the Sea's Bottom ; 
 and his Essay of the Intestine Motions of the Particles of Quiescent 
 Solids wherein the absolute Rest of Bodies is called in question. He 
 was perhaps the earliest to draw attention to the desirability 
 of studying the forms of crystals, and his paper on the Figures 
 of Salts contains many curious observations ; in his Experi- 
 ments about the Superficial Figures of Fluids, especially of Liquors 
 
Robert Boyle 25 
 
 contiguous to other Liquors, he breaks ground which has taxed 
 the energies of our greatest mathematicians. His Treatise on 
 Gold abounds with striking and original experiments : thus he 
 demonstrates the expansive power of freezing water by burst- 
 ing a gun-barrel filled with water and securely plugged, by 
 placing it in a mixture of snow and salt, a freezing mixture 
 which he himself brought into use in England. His Essays on 
 the Usefulness of Experimental Natural Philosophy were of the 
 greatest service in his time in furthering the cause of science 
 by showing how the material interests of civilisation may be 
 promoted by its study ; and, lastly, his tract on Unsucceeding 
 Experiments must have been as the wine of gladness and the 
 oil of consolation to many a despondent virtuoso. His fame 
 and his social position made Boyle's personal influence very 
 considerable, and his house (or rather that of his sister, with 
 whom he lived, for he was never married), was constantly 
 besieged by a crowd of patentees and inventors, who sought 
 his aid in bringing their schemes to the notice of the Govern- 
 ment or the King : he was thus the means of introducing into 
 the marine a method of obtaining fresh water from sea-water, 
 not very dissimilar to that which we owe to the late Dr. 
 Normandy : this method, I need scarcely add, is not that 
 of the ingenious youth who (whisper it not in the shades of 
 Burlington Gardens !) gravely proposed to obtain fresh water 
 from salt water by letting it stand and skimming it ! 
 
 Boyle was a religious man, in the best sense of that 
 term, and his theological writings form no inconsiderable 
 portion of his works. But we fear that Carneades and 
 Eleutherius have made more stir, and, possibly, have done 
 not less good in the world, than Lindamor and Eusebius. 
 The Christian Virtuoso and the Seraphic Love, and possibly 
 Swift's merciless Pious Meditation on a Broomstick in the style of 
 the Honourable Mr. Boyle, have done more to perpetuate the 
 Occasional Reflections than the Occasional Reflections have done 
 for themselves. 
 
 OF THE 
 
 v EHSITT 
 
26 Robert Boyle 
 
 Boyle was born in the year in which Bacon died : and 
 Boyle's place in the history of science is that of the first 
 true exponent of the Baconian method, and the Sceptical 
 Chymist is his greatest work. This book probably contains 
 a greater number of well-authenticated facts than is to be found 
 in any other chemical treatise of its day. Many of these 
 originated with Boyle, as, for example, the isolation of methyl 
 alcohol from the products of the destructive distillation of 
 wood, and that of acetone, which he prepared by heating the 
 acetates of lead and lime. 
 
 But the greater merit of this work consists in its determined 
 attack on the authority of the Peripatetics and the Paracelsians. 
 Not that he is blind to the services of the Spagyrists : " the 
 devisers and embracers of the hypothesis of the tria prima have 
 done the commonwealth of learning some service by helping to 
 destroy that excessive esteem or rather veneration, wherewith 
 the doctrine of the four elements was almost as generally as 
 undeservedly understood ! The Peripatetics, thinking it more 
 high and philosophical to discover truth a priori than a posteriori, 
 scorn the experimental method as descending to the capacities 
 of such as can only be taught by their senses : the dialectical 
 subtleties of the schoolmen much more declare the wit of him 
 that uses them than increase the knowledge or remove the 
 doubts of sober lovers of truth." Boyle is very severe upon 
 the affected mysticism of the Spagyrists. They may be as 
 obscure as they like about their elixir, and the rest of their 
 grand arcana, " yet when they pretend to teach the general 
 principles of natural philosophers, this equivocal way of writing 
 is not to be endured. For in such speculative inquiries where 
 the naked knowledge of the truth is the thing principally 
 aimed at, what does he teach me worth thanks, that does not, 
 if he can, make his notion intelligible to me, but by mystical 
 terms and ambiguous phrases darkens what he should clear 
 up, and makes me add the trouble of guessing at the sense of 
 what he equivocally expresses, to that of learning the truth of 
 
Robert Boyle 27 
 
 what he seems to deliver." Boyle indeed does not scruple to 
 say that the reason why the Spagyrists wrote so obscurely of 
 their three great principles was, that not having clear and 
 distinct notions of them themselves they could not write 
 otherwise than confusedly of what they had confusedly appre- 
 hended : they could scarcely keep themselves from being con- 
 futed but by keeping themselves from being clearly understood 
 home thrusts which must have made many a Helmontiair 
 wince. The effect of such hard hitting is made evident on 
 the most superficial comparison of the general style of chemical 
 treatises immediately preceding Boyle's time with those pub- 
 lished towards the close of the seventeenth century. 
 
 The Sceptical Chymist sealed the fate of the doctrine of the 
 tria prima, and before the close of the century the Paracelsians 
 were as much out of date as a Phlogistian would be to-day. 
 Boyle indeed seems to incline to the belief that all matter is 
 compounded of one primordial substance in other words that 
 all matters are merely modifications of the materia prima and 
 how closely he was in accord with the modern spirit is manifest 
 in this remarkable passage : "I am apt to think that men will 
 never be able to explain the phenomena of nature, while they 
 endeavour to deduce them only from the presence and pro- 
 portions of such or such material ingredients, and consider 
 such ingredients or elements as bodies in a state of rest; 
 whereas indeed the greatest part of the affections of matter, 
 and consequently of the phenomena of nature, seem to depend 
 upon the motion and contrivance of the small parts of bodies." 
 
II 
 
 JOSEPH PEIESTLEY 
 
 A LECTURE, DELIVERED IN THE HULME TOWN HALL, MANCHESTER, ON 
 18TH NOVEMBER 1874. MANCHESTER SCIENCE LECTURES. 
 
 THOSE of you who read newspapers will, probably, not have 
 forgotten that on the 1st of August of this present year 
 (1874) a great gathering took place at Birmingham to do 
 honour to Joseph Priestley, one of that band of scientific 
 worthies which made the reign of George III. memorable in 
 the annals of science. On that day Professor Huxley (than 
 whom no one is better qualified to appreciate the whole out- 
 come of Priestley's life, or better able to set forth the singular 
 force and beauty of his character) uncovered a statue which 
 the friends of science and of liberal thought had raised to the 
 memory of the philosopher. Birmingham, however, was not 
 the only town in England, nor were Englishmen the only 
 people, that did homage to the memory of Priestley on that 
 day. The lovers of science in Leeds, near to which place he 
 was born, assembled in public meeting ; and the chemists of 
 America, to which country he was driven by the political and 
 theological bigotry of his own people, met together at his 
 grave in a quiet little town on the banks of the Susquehanna 
 river. 
 
 My object this evening is to give you some account of the 
 labours of this philosopher, whose services in the cause of 
 
IT Joseph Priestley 29 
 
 truth, and whose sacrifices in the struggle for freedom of 
 thought, were, seventy years after his death, thus gratefully 
 recognised. 
 
 But the very richness of my material is a source of em- 
 barrassment ; for Priestley was a man of so many and such 
 diverse acquirements 
 
 A man so various, that he seemed to be 
 Not one, but all mankind's epitome ; 
 
 his energy and power of application were so great, the range 
 of his work so wide, that to attempt to do full justice to 
 the many-sidedness of the man and of his labours would re- 
 quire me to inflict on you, not one lecture alone, but a whole 
 series. You may form some conception of his marvellous 
 mental activity, when I tell you that, as appears from the 
 catalogue drawn up by his son after his death, he published 
 no fewer than 108 works. Among them we have two volumes 
 On the History and Present State of Discoveries relating to Vision, 
 Light) and Colours; next, two volumes of Disquisitions relat- 
 ing to Matter and Spirit ; A Course of Lectures on Oratory and 
 Criticism; A General History of the Christian Church, in six 
 volumes ; The Doctrine of Phlogiston Established ; A Treatise on 
 Civil Government ; six volumes of Experiments on Different Kinds 
 of Air ; A Harmony of the Evangelists in Greek; A Familiar 
 Introduction to the Theory and Practice of Perspective ; and Tlie 
 Pediments of English Grammar, Adapted to the Use of Schools. 
 And this formidable development of the cacoethes scribendi 
 came, as he tells us, by a practice of abstracting sermons and 
 writing much in verse. 
 
 Some particulars of the life of this extraordinary man may 
 be interesting to you. He was born in 1733, at Fieldhead, a 
 hamlet of some half-dozen houses, about six miles from Leeds. 
 The old home of the Priestleys was pulled down some years 
 ago. It was described by one who pointed out its site to me, 
 and who remembered it well, as a little house of three small 
 
30 Joseph Priestley u 
 
 rooms, built of stone and slated with flags. Jonas Priestley, 
 the father, was a cloth-dresser by trade. Of the mother but 
 little is known beyond that she was the daughter of a farmer 
 living near Wakefield. She died when Priestley was only 
 seven years old, and he was taken charge of by his aunt, a 
 Mrs. Keighley, a pious and excellent woman, in a good position, 
 but who, as he tells us, " knew no other use of wealth, or of 
 talents of any kind, than to do good." The boy was of a 
 weakly consumptive habit, one consequence of which was 
 seen in the desultory character of his early education. But 
 his home-life with his aunt must have done much to make up 
 for the deficiencies of his school training. She encouraged 
 him in his fondness for books, and as her house was the resort 
 of all the dissenting clergymen in the district without dis- 
 tinction, young Priestley was constantly brought in contact 
 with men of culture and of liberal thought, and several of 
 them seem to have made a lasting impression on his vigorous 
 mind. Still, the gloomy Calvinism under which he was 
 brought up, and the frequent talk of experiences and of new 
 births to which he listened, had its effect upon the sensitive 
 mind in the weakly frame. Years afterwards he wrote of 
 this period : "I felt occasionally such distress of mind as it is 
 not in my power to describe, and which I still look back upon 
 with horror. Notwithstanding I had nothing very material 
 to reproach myself with, I often concluded that God had 
 forsaken me, and that mine was like the case of Francis Spira, 
 to whom, as he imagined, repentance and salvation were denied. 
 In that state of mind I remember reading the account of the 
 man in the iron cage in The Pilgrim's Progress with the greatest 
 perturbation." But the strengthening intellect was not slow 
 to recover its ascendency ; and Priestley could afterwards 
 write, in his characteristic way of always looking at the sunny 
 side of every circumstance : "I even think it an advantage to 
 me, and am truly thankful for it, that my health received the 
 check that it did when I was young ; since a muscular habit 
 
ii Joseph Priestley 31 
 
 from high health, and strong spirits, are not, I think, in general 
 accompanied with that sensibility of mind which is both favour- 
 able to piety and to speculative pursuits." 
 
 Priestley was destined by his aunt for the ministry, but her 
 views which were his also were for a time interfered with 
 by his continued ill-health. Eventually he was sent to the 
 Dissenting Academy at Daventry, which the labours of the 
 good and learned Dr. Doddridge had brought into repute. 
 Of the three years he spent there Priestley ever spoke with 
 peculiar satisfaction. The system of study was congenial to 
 his independent and inquisitive mind, for the freest inquiry 
 on every article of theological orthodoxy and heresy was 
 warmly encouraged, and every vexed question was in turn 
 handled by the teachers, who took opposite sides in con- 
 troversy, and incited their students to discussion. If training 
 such as this laid the foundation of the successes of Priestley's 
 after-life, it was also, and in no less degree, the source of much 
 of his misfortune. His first charge, on leaving Daventry, was at 
 Needham Market, in Suffolk ; but his congregation did not 
 like his Arianism, nor the stuttering way in which he told 
 them of it, and they almost deserted him. Driven to extrem- 
 ities, he issued proposals to teach the classics and mathe- 
 matics for half-a-guinea a quarter, and to board the pupils 
 in his house for twelve guineas a year. This scheme not 
 answering, he next turned his attention to popular science, 
 and commenced with a course of twelve lectures on " The 
 Use of the Globes," from which he barely got enough to pay 
 for his globes. Although he keenly felt the effects of what 
 he terms his "low despised situation," Priestley never lost 
 heart or hope. He could even say of his impediment in 
 speech, that, like St Paul's " thorn in the flesh," it was not 
 without its use. "Without some such check as this," he 
 writes, "I might have been disputatious in company, or 
 might have been seduced by the love of popular applause 
 as a preacher; whereas my conversation and my delivery 
 
32 Joseph Priestley 
 
 having nothing in them that was generally striking, I hope 
 I have been more attentive to qualifications of a superior 
 kind." 
 
 Years afterwards, on being invited to preach in the district 
 when he had raised himself to some degree of notice in the 
 world, the same people crowded to hear him ; and though his 
 elocution was not much improved they professed to admire 
 one of the same discourses they had formerly despised. 
 
 From Needham he passed on to Nantwich, in Cheshire, 
 where he found himself in more congenial society, and in 
 better circumstances, so that he was able to buy books and 
 a few philosophical instruments. Not that philosophy here 
 occupied the whole of his leisure, for he tells us that he 
 betook himself to music, and learned to play on the English 
 flute, as the easiest instrument. Music he recommends to all 
 studious persons ; and it will be better for them, he says, if, 
 like himself, they should have no very fine ear or exquisite 
 taste, as by this means they will be more easily pleased, 
 and be less apt to be offended when the performances they 
 hear are but indifferent. In 1761 he was invited to Warring- 
 ton, as " tutor in the languages " in the Dissenting Academy 
 in that town. Here he taught Latin, Greek, Hebrew, French, 
 and Italian ; and delivered courses of lectures on Logic, on 
 Elocution, on the Theory of Language, on Oratory and 
 Criticism, on History and General Policy, on Civil Law, and 
 on Anatomy. About this time, too, he made the friendship 
 of Benjamin Franklin a friendship which constitutes a 
 turning-point in Priestley's career, for Franklin encouraged 
 his leaning towards philosophical pursuits, warmly recom- 
 mending him to undertake his proposed History of Electricity, 
 and furnishing him with books for the purpose. In connec- 
 tion with this work, he made a number of original observations 
 in electricity, on account of which the book was favourably 
 received ; its author was made a Fellow of the Royal 
 Society, and a Doctor of Laws of Edinburgh University. 
 
ii Joseph Priestley 33 
 
 Priestley by this time was married, but seeing no prospect of 
 providing for his family at Warrington, he accepted an 
 invitation to take charge of a congregation in Leeds, and 
 thither he removed in 1767. Having leisure, he redoubled 
 his attention to experimental philosophy, and began that 
 brilliant series of discoveries by which others were to accom- 
 plish the overthrow of that system of chemical philosophy of 
 which he considered himself the special champion. "But," 
 writes Priestley, " the only person in Leeds who gave much 
 attention to my experiments was Mr Hey, a surgeon. . .*. 
 When I left Leeds he begged off me the earthen trough in 
 which I had made all my experiments on air while I was 
 there. It was such an one as is there commonly used for 
 washing linen." 
 
 In 1772 Lord Shelburne wished for a "literary companion," 
 and Priestley was induced to accept the office by the offer of 
 a good salary, a house and other appointments, together with 
 an annuity at the end of the engagement. Fortunately for 
 science, his lordship had scarcely any duties for his literary 
 companion to perform, and Priestley was thus able to give 
 most of his time to the continuation of his chemical work. 
 He remained with Lord Shelburne seven years. 
 
 He then settled in Birmingham, and accepted the charge 
 of a congregation which he characterises as the most liberal 
 in England. He was now nearly sixty years of age, free 
 from embarrassment of every kind, and happy in the friend- 
 ship of such men as Boulton and Watt, the engineers ; Wedg- 
 wood the potter ; Keir, Withering, Darwin, and the Galtons. 
 He had ample leisure for his work, and no lack of encourage- 
 ment and substantial help when needed. The picture of his 
 life which he draws at this time indicates his serenity of 
 mind and his sense of rest. He is thankful to that good 
 Providence which always took more care of him than he ever 
 took of himself, and he esteems it a singular happiness to 
 have lived in an age and country in which he had been at 
 
 D 
 
34 Joseph Priestley u 
 
 full liberty both to investigate, and, by preaching and writ- 
 ing, to propagate religious truth. This calm, however, was 
 but the presage of a great storm, and it burst over the old 
 philosopher during the loud strife of party passion which 
 agitated this country at the outbreak of the French Kevolu- 
 tion. On the occasion of a public dinner on the anniversary 
 of the taking of the Bastile, at which dinner Priestley was 
 not present, and with which it does not appear that he had 
 anything to do, a mob attacked and wrecked, in the name of 
 " Church and King," the chapels and houses of the Dissenters 
 in the town. The full fury of the rising seemed to be 
 concentrated upon Priestley, and he and his family barely 
 escaped with their lives, leaving library, papers, and instru- 
 ments to the tender mercies of the insane crowd, who speedily 
 demolished what had been the labour and fruit of years. 
 Priestley with difficulty got to London, but so uncertain was 
 the temper of the time that his friends forcibly kept him in 
 hiding for some weeks. His appeal for redress met with 
 but a tardy acknowledgment, and the recompense which 
 he eventually received was absurdly disproportionate to his 
 disastrous experience of what Mr. Pitt was pleased to call 
 "the effervescence of the public mind." His sons, disgusted 
 with the justice which he received, left the country, and 
 eventually settled in America. Although he himself was not 
 without a position, for he was invited to minister to a large 
 congregation at Hackney before he had been many months in 
 London, and his friends vied with each other in rendering 
 him help, his situation was still hazardous : his scientific 
 brethren turned their backs upon him, his servants feared to 
 remain with him, and the tradespeople declined to have his 
 custom. At length he determined to follow his sons. Before 
 he left he wrote these remarkable words : " I cannot refrain 
 from repeating again, that I leave my native country with 
 real regret, never expecting to find anywhere else society so 
 suited to my disposition and habits, such friends as I have 
 
ii Joseph Priestley 35 
 
 here (whose attachment has been more than a balance to all 
 the abuse I have met with from others), and especially to 
 replace one particular Christian friend, in whose absence 
 I shall, for some time at least, find all the world a blank. 
 Still less can I expect to resume my favourite pursuits with 
 anything like the advantages I enjoy here. In leaving this 
 country I also abandon a source of maintenance which I can 
 but ill bear to lose. I can, however, truly say that I leave 
 it without any resentment or ill-will. On the contrary, I 
 sincerely wish my countrymen all happiness ; and when the 
 time for reflection (which my absence may accelerate) shall 
 come, they will, I am confident, do me more justice. They 
 will be convinced that every suspicion they have been led to 
 entertain to my disadvantage has been ill-founded, and that I 
 have even some claim to their gratitude and esteem. In this 
 case I shall look with satisfaction to the time when, if my life 
 be prolonged, I may visit my friends in this country ; and 
 perhaps I may, notwithstanding my removal for the present, 
 find a grave (as I believe is naturally the wish of every man) 
 in the land that gave me birth." He never returned. His 
 sons had settled at Northumberland, a little town placed in 
 one of the most beautiful spots on the Susquehanna. Here, 
 surrounding himself with books and taking but little interest 
 in the politics of the country, he occupied himself to the last 
 with philosophy and his beloved theology ; steadily refusing 
 to become naturalized, although the expediency of such a step 
 was frequently pressed upon him, saying that "as he had been 
 born and lived an Englishman he would die one, let what 
 might be the consequence." 
 
 Priestley is mainly remembered by his theological contro- 
 versies and his contributions to the history of pneumatic 
 chemistry. I have nothing to tell you of his merits as a 
 controversialist, except to say that some of his argumentative 
 pieces are among the most forcible and best written of his 
 literary productions. It is on his chemical work that his 
 
36 Joseph Priestley \\ 
 
 reputation will ultimately rest : this will continue to hand 
 down his name when all traces of his other labours are lost. 
 He has frequently been styled the Father of Pneumatic 
 Chemistry ; and although we may question the propriety of 
 the appellation when we call to mind the labours of Van 
 Helmont, of Boyle, and of Hales, there is no doubt that 
 Priestley did more to extend our knowledge of gaseous bodies 
 than any preceding or successive investigator. 
 
 Priestley was born just as Stahl, the author of what is 
 known in the history of chemistry as the Phlogistic Theory, had 
 run out his course. To this theory, handed down as it seemed 
 to his especial keeping, Priestley unswervingly adhered. But, 
 by a strange perversity of fate, the very discoveries which he 
 brought forward as the strongest proofs of the soundness of 
 the Phlogistic doctrine have conduced, perhaps more than any 
 other set of facts, to its destruction. Let me attempt to give 
 you some other notion of this Phlogistic Theory. A piece 
 of wood burns : a piece of stone does not. Why is this 1 
 "Because," answers Stahl, "the wood contains a peculiar 
 principle the principle of inflammability : the stone does not. 
 Coal, charcoal, wax, oil, phosphorus, sulphur in short, all 
 combustible bodies contain this principle in common : to this 
 principle (which, indeed, I regard as a material substance) I 
 give the name of Phlogiston. I regard all combustible bodies, 
 therefore, as compounds, and one of their constituents is this 
 phlogiston : the differences which we observe in combustible 
 substances depend partly upon the proportion of the phlogiston 
 they contain, and partly upon the nature of the other con- 
 stituents. When a body burns if parts with its phlogiston ; 
 and all the phenomena of combustion the heat, the light, 
 and the flame are due to the violent expulsion of that 
 substance. This phlogiston lies at the basis of all chemical 
 change : all chemical reactions are so many manifestations of 
 parts played by phlogiston." If zinc be strongly heated it 
 takes fire and burns with a beautiful greenish flame, and 
 
ii Joseph Priestley 37 
 
 a white or yellowish - white substance remains behind. 
 "Phlogiston," says Stahl, "is here making its escape. Zinc 
 is composed of phlogiston and the white earthy powder 
 which I term calx of zinc which now becomes visible." If I 
 melt some lead, and keep it well stirred, it gradually becomes 
 converted into a powder, first of a yellow and ultimately of 
 a beautiful red colour. Phlogiston has thus been gradually 
 expelled, its expulsion having been promoted by stirring the 
 mass, and the calx of lead the other constituent of the metal 
 becomes evident. To remake the metal it is merely neces- 
 sary to impart phlogiston to the calx, and any substance 
 that will give up its phlogiston may be employed for that 
 purpose. If the red lead or the calx of zinc be heated with 
 wood or charcoal, or resin, or phosphorus, or sulphur, the 
 respective metals will be regenerated. Too much of the 
 phlogiston, however, will destroy the metallic nature of the 
 lead or the zinc. If we employ an excess of phosphorus or 
 sulphur (bodies very rich in phlogiston, as their excessive 
 inflammability shows) the metals will combine with the 
 superabundant phlogiston and lose their metallic character. 
 
 I told you that in heating the lead the calx had, to begin 
 with, a yellow colour, and that it only became red by the pro- 
 longed action of the fire. The change in the colour affords a 
 measure of the rate of the expulsion of the phlogiston. When 
 in the yellow stage the calx has not parted with the whole of 
 the phlogiston : as we continue to heat it more phlogiston is 
 expelled, and the mass becomes red. So, too, if, in perform- 
 ing the reverse operation, we add an insufficient amount of 
 phlogiston, the red calx is not converted into metal it is 
 only brought back to the yellow stage. In some such manner 
 as this the Stahlian doctrine attempted to account for the 
 colours of substances. 
 
 We all know that if a candle is burnt in a limited amount 
 of air the flame will shortly be extinguished, although no 
 change apparently takes place in the air. This was explained, 
 
38 Joseph Priestley \\ 
 
 according to Stahl's doctrine, by supposing that air had an 
 affinity for phlogiston, and that in the act of combustion the 
 phlogiston was transferred from the candle to the air. 
 Gradually, however, the limited amount of air becomes 
 saturated with phlogiston that is wholly phlogisticated and 
 combustion accordingly ceases. In like manner, if a mouse is 
 placed in a confined volume of air, after a time it experiences 
 difficulty in breathing and eventually is suffocated, although 
 the bulk of the air remains the same. The act of breathing, 
 therefore, is nothing else than the transference of phlogiston 
 from the animal to the air, which gradually becomes phlogisti- 
 cated and is thereby unable to support respiration. To this 
 doctrine of phlogiston, originally broached as a theory of com- 
 bustion and gradually extended into a theory of chemistry, 
 nearly every European chemist for upwards of half a century 
 after its author's death gave an implicit adherence. 
 
 Priestley, whilst at Leeds, lived near a brewery : it was 
 this circumstance that first directed his attention to chemical 
 matters. He had read of fixed air, the gas which we now style 
 carbon dioxide or carbonic acid ; and being desirous of making 
 himself acquainted with its properties, he took advantage of 
 the fermentative process in which it is abundantly formed to 
 procure some. Priestley at this time had little or no know- 
 ledge of chemistry ; he was possessed of no apparatus, and 
 had scarcely the means of procuring any. But these very 
 circumstances were the sources of his success, since he was 
 under the necessity of devising original processes and ap- 
 pliances suited to his narrow means and peculiar views. " If," 
 he says, " I had been previously accustomed to the usual 
 chemical processes I should not have so easily thought of any 
 other, and without new modes of operation I should hardly 
 have discovered anything materially new." One of the 
 earliest pieces of apparatus which he devised is the well- 
 known pneumatic trough a simple enough piece of chemical 
 furniture certainly, but one that required a considerable amount 
 
ii Joseph Priestley 39 
 
 of experimenting with before it took its present shape. In 
 his experiments with fixed air he observed that this gas con- 
 ferred "a pleasant acidulous taste " on water, so that he was 
 able in two or three minutes to make a " glass of exceedingly 
 pleasant sparkling water, which could hardly be distinguished 
 from very good Pyrmont, or rather seltzer water." He like- 
 wise observed that " the pressure of the atmosphere assists 
 very considerably in keeping fixed air confined in water. . . . 
 I do not doubt, therefore, but that, by the help of a con- 
 densing engine, water might be much more highly impregnated 
 with the virtues of the Pyrmont spring; and it would not be 
 difficult to contrive a method of doing it." Priestley here 
 throws out the idea of the manufacture of "soda water "- 
 "a service," says Mr. Huxley, "to naturally, and still more 
 to artificially, thirsty souls, which those whose parched throats 
 and hot heads are cooled by morning draughts of that 
 beverage, cannot too gratefully acknowledge." 
 
 Priestley was next attracted by the singular properties of 
 hydrogen, or inflammable air, as it was then termed a gas 
 which had already been made the subject of an elaborate 
 memoir by Mr. Cavendish. Cavendish was inclined to sup- 
 pose that inflammable air was phlogiston in the free state 
 an opinion contrary to the belief of Stahl and his immediate 
 followers, who imagined that phlogiston was a solid earthy 
 volatile substance. In order to get some clue as to the 
 nature of this protean body, Priestley placed a quantity of 
 minium or the calx of lead that is, lead from which the 
 phlogiston has been expelled within a tall cylinder, filled 
 with inflammable air, and standing over water. He then 
 proceeded to heat the calx by means of a burning lens a 
 method which he constantly employed, and which materially 
 assisted him to many of his discoveries. Let us give the 
 result in his own words : "As soon as the minium was dry, 
 by means of the heat thrown upon it, I observed that it 
 became black, and then ran in the form of perfect lead ; at 
 
40 Joseph Priestley \\ 
 
 the same time that the air diminished at a great rate, the 
 water ascending within the receiver. I viewed this process 
 with the most eager and pleasing expectation of the result, 
 having at that time no fixed opinion on the subject ; and 
 therefore I could not tell except by actual trial whether the 
 air was decomposing in the process, so that some other kind 
 of air would be left, or whether it would be absorbed in toto. 
 The former I thought the more probable, as if there was any 
 such thing as phlogiston, inflammable air, I imagined, con- 
 sisted of it and something else. However, I was then satisfied 
 that it would be in my power to determine, in a very satisfac- 
 tory manner, whether the phlogiston in inflammable air had 
 any base or not ; and if it had, what that base was. For, 
 seeing the metal to be actually revived, and that in a 
 considerable quantity, at the same time that the air was 
 diminished, I could not doubt but that the calx was actually 
 imbibing something from the air; and from its effects in 
 making the calx into metal, it could be no other than that 
 to which chemists had unanimously given the name of 
 
 This experiment he repeated with every precaution, and in 
 every conceivable manner varying the nature of the calx, 
 sometimes taking the calx of tin, of bismuth, of mercury, of 
 silver, of iron, and of copper and sometimes making the 
 experiment over quicksilver instead of water. He found that 
 the inflammable air was totally absorbed ; and, accordingly, 
 he concludes "that phlogiston is the same thing as inflam- 
 mable air, and is contained in a combined state in metals, just 
 as fixed air is contained in chalk and other calcareous sub- 
 stances : both being equally capable of being expelled again 
 in the form of air." 
 
 Priestley then proceeded to determine the amount of the 
 phlogiston which must be contained in the various metals, 
 by ascertaining the quantity of, inflammable air taken up by 
 their calces. He found that 1 oz. of lead was revived by the 
 
Joseph Priestley 41 
 
 absorption of 108 oz. measures of inflammable air, and 1 oz. 
 of tin by the absorption of 377 oz. measures. Let me direct 
 your attention for a moment to these numbers, since they 
 afford us a ready means, of determining the degree of accuracy 
 with which Priestley made his observations. The 108 oz. 
 measures of hydrogen required to revive the 1 oz. of lead are 
 equivalent to 204' 1 cubic inches, and weigh, at the ordinary 
 temperature, about 4*4 grains. Now, the most refined processes 
 of modern chemical analysis have shown that the weight of 
 hydrogen required to regenerate 1 oz. of lead from the yellow 
 calx is 4 '6 grains no great disparity, after all, from Priest- 
 ley's result. The 377 oz. measures of hydrogen required to 
 revive 1 'oz. of tin would weigh about 15- 4 grains; modern 
 chemistry says that the exact quantity needed is 16*3 grains. 
 Priestley was here on the verge of a great discovery a 
 'discovery which, in the first place, would have given a crush- 
 ing blow to Stahl's doctrine and which, in the second, might 
 have ended in the determination of a fact of no less magnitude 
 than the true composition of water. But his phlogistic ideas 
 rendered him blind to the full significance of his results. He 
 was prepossessed with the notion that by phlogisticating the 
 calx it gained in weight, and that the weight of the metal 
 formed must be equal to the weight of the calx plus that of the 
 phlogiston absorbed. He tells us that he frequently attempted 
 to ascertain the weight of the inflammable air in the calx, " so 
 as to prove that it had acquired an addition of weight by 
 being metallized," but the result never came out in accordance 
 with the theory. This, he satisfies himself, must be due to 
 part of the calx subliming, and part being dissolved by the 
 mercury ; and he concludes, " that were it possible to procure 
 a perfect calx, no part of which should be sublimed and 
 dispersed by the heat necessary to be made use of in the 
 process, I should not doubt but that the quantity of inflam- 
 mable air imbibed by it would sufficiently add to its weight." 
 Every sound phlogistian for at least a quarter of a century 
 
42 Joseph Priestley 
 
 after Stahl's death believed that when a metal was calcined 
 the calx must weigh less than the metal : for had not phlogis- 
 ton been expelled ? There were indeed certain vague rumours 
 that various people had found it otherwise : Boyle had made 
 some experiments with tin; a French surgeon named Key 
 had experimented upon lead ; and an obscure alchemist called 
 Sulzbach had recorded some observations upon mercury ; but 
 then these people had not had the good fortune to work in the 
 light of the phlogistic doctrine, or they were sceptics who 
 were justly punished for their unbelief by their false results. 
 But about Priestley's time it gradually dawned upon the 
 phlogistians that the sceptics and ignorant people might be 
 right after all, for some of their own trusted number had 
 condescended to repeat the experiments which so obstinately 
 refused to chime in with the established order of things, and 
 found, doubtless to their dismay, that it could no longer be 
 gainsayed that a metal by calcination gained in weight. 
 But the phlogistians were not going to see their beautiful 
 superstructure a theory in which all the parts seemed to fit so 
 nicely brought ignominiously down by the trivial weight of 
 such a fact as this. We concede, said they, that we have been in 
 error respecting the precise nature of phlogiston : it cannot be 
 the gross earthy substance that Stahl had taught us to believe 
 in. It is plainly something far more etherealised a sort of 
 invisible, imponderable ether the very principle of levity, in 
 fact, a principle so very light that so far from adding to the 
 weight of bodies with which it combines, it actually makes 
 them lighter than they were before ! It seems scarcely 
 credible, but this was precisely the position taken up by a 
 large section of the phlogistians ; not by all of them, however, 
 for some were sagacious enough to see that a theory which 
 needed a hypothesis of this character to bolster it up must be 
 rapidly on the wane. " Of late," writes Priestley, " it has been 
 the opinion of many celebrated chemists, Mr. Lavoisier among 
 others, that the whole doctrine of phlogiston is founded on 
 
ii Joseph Priestley 43 
 
 mistake. The arguments in favour of this opinion, especially 
 those which are drawn from the experiments Mr. Lavoisier 
 made on mercury, 1 are so specious that I own I was myself much 
 inclined to adopt it." . And Priestley assuredly would have 
 adopted it if he could only have looked at the results of his 
 experiments otherwise than through the fogs of his prejudices. 
 He would have grasped the fact that with the disappearance 
 of ponderable inflammable air (for light as it is it could not 
 have been the principle of levity), the calx lost weight, and by 
 much more than the weight of the inflammable air. This fact 
 once properly laid hold of might have explained the origin of 
 that water which he distinctly noted as being produced in his 
 trials over mercury. In one of his experiments he heated a 
 quantity of the calx of mercury in inflammable air, and although, 
 as he tells us, " the gas was previously well dried with fixed 
 ammoniac," water was found in sufficient quantity. "This 
 experiment," he goes on to say, "may be thought to be 
 favourable to the hypothesis of water being composed of 
 fixed and inflammable air : as all water was carefully excluded, 
 and yet a sufficient quantity was found in the process." But 
 to the notion of the compound nature of water he attaches no 
 weight. The water he supposes came either from the calx or, 
 which he thinks more probable, from the inflammable air 
 that it was in fact essential to the constitution of the gas ; an 
 opinion which became a conviction when he observed how fre- 
 quently water was formed in processes in which the inflam- 
 mable air played a part. 
 
 When steam is driven through a red-hot iron tube inflam- 
 mable air, the phlogiston of Priestley and Cavendish, is 
 produced in abundance a fact first observed by Lavoisier; 
 but then, as Priestley says, " Mr. Lavoisier is well known to 
 maintain that there is no such thing as what has been called 
 phlogiston; affirming inflammable air to be nothing else but 
 one of the elements or constituent parts of water. As to 
 1 A repetition of the experiments of Sulzbacli. 
 
44 Joseph Priestley \\ 
 
 myself, I was a long time of opinion that his conclusion was 
 just, and that the inflammable air was really furnished by 
 the water being decomposed in the process. But though I 
 continued to be of this opinion for some time, the frequent 
 repetition of the experiments, with the light which Mr. Watt's 
 observations threw upon them, satisfied me, at length, that 
 the inflammable air came from the iron." The arrangement 
 which Priestley made use of in these experiments is identical 
 with that which we use on our lecture tables to-day for the 
 same purpose. Steam is driven through an iron tube heated 
 to redness, and the inflammable air is collected in one of 
 Priestley's pneumatic troughs. " Of the many experiments 
 which I made with iron," says Priestley, "I shall content 
 myself with reciting the following results. With the addition 
 of 267 grains to a quantity of iron, and the loss of 336 grains 
 of water, I procured 840 ounce measures of inflammable air ; 
 and with the addition of 140 grains to another quantity of iron, 
 and the consumption of 254 grains of water, I got 420 ounce 
 measures of air." These numbers again serve to test the 
 accuracy of Priestley's work. In the first experiment the iron 
 gained 267 grains, and the yield of inflammable air was 840 
 ounce measures. 840 ounce measures of hydrogen, at the 
 ordinary temperature, weigh 34'3 grains ; that is, the gain of 
 the iron was 7f times the weight of the inflammable air. 
 Assuming, then, with Lavoisier, that water is a compound, and 
 that one constituent is fixed by the iron and the other makes 
 its escape as inflammable air, it would follow from Priestley's 
 experiment that water is composed of 7f parts by weight 
 of the substance fixed by iron, united to 1 part by weight of 
 inflammable air. Modern science has completely established 
 the correctness of Lavoisier's opinion, and disproved that of 
 Priestley, but it has added little, even with all its elaborate 
 processes of quantitative analysis, to the results of Priestley's 
 trials. Water is composed of oxygen the substance fixed by 
 the iron and inflammable air, or hydrogen ; and the propor- 
 
ii Joseph Priestley 45 
 
 tion by weight of the former gas to the latter is almost 
 exactly as 7 '9 to 1. 
 
 Acting upon some remarks by Mr. Cavendish, Priestley 
 was led to study the action of aqua fortis, or " nitrous acid," 
 as it was then called, upon the metals. Trying first upon 
 brass, and then upon copper, he obtained a gas to which he 
 gave the name of nitrous air, but which is now called nitric 
 oxide. " One of the most conspicuous properties of this kind 
 of air is the great diminution of any quantity of common 
 air with which it is mixed, attended with a turbid red, or 
 deep orange colour, and a considerable heat. . . . The diminu- 
 tion of a mixture of this and common air is not an equal 
 diminution of both the kinds . . . but of one-fourth of the 
 common air, and as much of the nitrous air as is necessary to 
 produce that effect. ... I hardly know any experiment that 
 is more adapted to amaze and surprise than this is, which 
 exhibits a quantity of air, which, as it were, devours a 
 quantity of another kind of air half as large as itself, and yet 
 is so far from gaining any addition to its bulk, that it is 
 considerably diminished by it. It is exceedingly remarkable 
 that this effervescence and diminution, occasioned by the 
 mixture of nitrous air, is peculiar to common air, or air fit for 
 respiration, and, as far as I can judge from a great number of 
 observations, is at least very nearly, if not exactly, in pro- 
 portion to its fitness for this purpose ; so that by this means 
 the goodness of air may be distinguished much more accu- 
 rately than it can be done by putting mice, or any other 
 animals, to breathe in it." Upon this principle Priestley devised 
 a method of measuring the quality of air. A small phial, termed 
 the air measure, about an ounce in capacity, was filled with the 
 air to be examined, which was then transferred to a jar about- 
 1J inches in diameter, previously filled with water. The air 
 measure was then filled with the nitrous air and emptied into 
 the jar containing the air to be analysed. The mixture was 
 allowed to stand for about two minutes, and was then trans- 
 
46 Joseph Priestley 
 
 ferred to a glass tube about two feet long and one-third of an 
 inch wide, graduated in terms of the air measure, and divided 
 into tenths and hundredth parts. The volume of the residual 
 gas was then read off, care being taken to immerse the tube to 
 such a depth in the trough that the water in the inside and on 
 the outside was on the same level. The result was expressed 
 in measures and parts of a measure : thus, if on mixing equal 
 volumes of common air and nitrous air the residual volume was 
 one measure and two-tenths of a measure, the standard of the 
 air was said to be 1 '2. 
 
 With this instrument Priestley attempted to measure the 
 difference between good air and that which was reputed to be 
 unwholesome; but, although he compared the worst air he 
 could get from manufactories, from coalpits, and from the 
 holds of ships, with the best country air, he was unable to 
 perceive any difference ; and he was satisfied, therefore, " that 
 air may be very offensive to the nostrils, probably hurtful to 
 the lungs (and, perhaps, also in consequence of the presence 
 of phlogistic matter in it), without the phlogiston being so far 
 incorporated with it as to be discoverable by the mixture of 
 nitrous air. ... I have frequently taken the open air in the 
 most exposed places in the country, at different times of the 
 year and in different states of the weather, etc., but never found 
 the difference so great as the inaccuracy arising from the 
 method of making the trial might easily amount to or excel." 
 Other experimenters, less conscientious than Priestley, found 
 the differences they sought for ; but the researches of Bunsen, 
 of Eegnault, and of Dr. Angus Smith, made with all the 
 precision of modern gasometric analysis, have shown that the 
 atmosphere is wonderfully constant in composition, and thatj 
 although there are variations, they are infinitely beyond the 
 cognisance of the nitrous air test. 
 
 A second observation by Mr. Cavendish led Priestley to 
 another discovery. Cavendish, in the course of the work on 
 inflammable air to which I have alluded, attempted to prepare 
 
ii JosepJi Priestley 47 
 
 that gas by acting on copper with spirit of salt, or " marine 
 acid," as it was then commonly called. Instead of the wished- 
 for result, he procured " a much more remarkable kind of air, 
 viz., one that lost its elasticity by coming in contact with 
 water." By substituting quicksilver for water in his trough, 
 Priestley obtained this air in quantity, and examined its 
 properties. He quickly found that the copper played no part 
 in the process of making the gas, for on heating the acid alone 
 he procured it just as readily. "So that," he says, "this 
 remarkable kind of air is, in fact, nothing more than the 
 vapour, or fumes of spirit of salt, which appear to be of such 
 a nature that they are not liable to be condensed by cold, like 
 the vapour of water and other fluids ; and therefore may be 
 very properly called an acid air, or more restrictively, the 
 tnarine acid air" Spirit of salt, or, as chemists also term it, 
 hydrochloric acid, is therefore nothing else than a solution of 
 Priestley's marine acid air in water. 
 
 This discovery induced Priestley to try the same experi- 
 ment with other acids, and, among them, with oil of vitriol. 
 But he says, "I got no air from the oil of vitriol by any 
 application of heat. But in attempting to procure it, I got it 
 by means of mercury in a manner that I little expected, and I 
 paid pretty dearly for the discovery it occasioned. Despairing 
 to get any air from the longer application of my candles, I 
 withdrew them ; but before I could disengage the phial from 
 the vessel of quicksilver, a little of it passed through the tube 
 into the hot acid, when instantly it was all filled with dense 
 white fumes, a prodigious quantity of air was generated, the 
 tube through which it was transmitted was broken into many 
 pieces (I suppose by the heat that was suddenly produced), 
 and part of the hot acid being spilled upon my hand burned 
 it terribly, so that the effect of it is visible to this day. The 
 inside of the phial was coated with a white saline substance, 
 and the smell that issued from it was extremely suffocating. 
 . . . Not discouraged by the disagreeable accident above 
 
48 Joseph Priestley 
 
 mentioned, the next day I put a little quicksilver into the 
 phial along with the oil of vitriol, when, before it was boiling 
 hot, air issued plentifully from it." The new gas with which 
 Priestley was rewarded for his pain and perseverance he 
 termed vitriolic acid air : it is now known as sulphur dioxide, 
 and is precisely the same substance which is produced on 
 burning brimstone in the air. You have doubtless all noticed 
 its formation on striking an old-fashioned lucifer match. 
 
 I daresay many of you have seen the beautiful etchings 
 made upon glass by means of hydrofluoric acid an acid first 
 obtained by a contemporary of Priestley, named Scheele a 
 poor Swedish apothecary, and one of the greatest chemists 
 of the last century. Glass, as you are doubtless aware, is a 
 mixture of sand or silica, lime, alkali, and occasionally red 
 lead. The hydrofluoric acid acts upon the glass by seizing 
 upon the silica and forming with it a gaseous substance termed 
 by chemists fluoride of silicon. This fluoride of silicon was 
 obtained by Priestley by heating a mixture of fluor spar, or 
 Derbyshire spar, with oil of vitriol in a glass vessel. When 
 this gas (which he termed fluor acid air) is led into water it is 
 instantly decomposed, and silica is reproduced. The forma- 
 tion of this silica constitutes a very striking experiment ; so 
 much so, that, says Priestley, " I have met with few persons 
 who are soon weary of looking at it, and some could sit by it 
 almost a whole hour and be agreeably amused all the time." 
 
 I doubt not that you are all familiar with that pungent, 
 tear-exciting liquid termed by the apothecaries " spirits of 
 hartshorn," or ammonia. This substance has been known for 
 a very long time : its name, " ammonia," is derived from the 
 circumstance that it was prepared, ages ago, by the Arabs in 
 the desert near the temple of Jupiter Ammon. Now, although 
 this liquid has been known for some thousands of years, it 
 required Priestley to tell us that its peculiar properties were 
 due to a gas held in solution. Priestley treated the spirit of 
 hartshorn as he had treated the spirit of salt, and he presently 
 
ii Joseph Priestley 49 
 
 found that a great quantity of a transparent and, apparently, 
 permanent air was discharged from it. He ascertained all 
 the more striking attributes of this "alkaline air," as he 
 termed it; among others, its solubility in water and its 
 inflammability. He next proceeded to determine its com- 
 position by passing electric sparks through it, and he found 
 that, after passing the sparks until no further increase of bulk 
 could be observed, the gas was ultimately trebled in volume, 
 and that no part of it was soluble in water. The gas, in fact, 
 had been decomposed into its constituents into hydrogen (the 
 presence of which Priestley recognised), and into nitrogen, 
 which he calls phlogisticated air, and which, he says, is con- 
 tained to the extent of one-fourth of the bulk of the mixture. 
 He then tried the action of the alkaline air upon the airs which 
 he had previously discovered, and notably upon the " marine 
 acid air," as he had " a notion that these two airs, being of 
 opposite natures, might compose a neutral air, and perhaps the 
 very same thing with common air. But the moment that 
 these two kinds of air came into contact a beautiful white 
 cloud was formed, and there appeared to be formed a solid 
 white salt, which was found to be the common sal ammoniac, or 
 the marine acid united to the volatile alkali." 
 
 If by some evil chance the cold and damp of this coming 
 winter should drive some of you to the dentist, and if after 
 seating you in that awful chair and harrowing your distracted 
 nerves with the sight of his murderous tools, he humanely 
 offers to send you to sleep with his nitrous oxide, by all means let 
 him, and, when you wake with the sweet consciousness that 
 "it is all over," give a passing benediction to the memory of 
 Priestley, for he first told us of the existence of that gas. 
 
 If, too, as you draw up to the fire "betwixt the gloaming 
 and the mirk" of these dull, cold November days, and note 
 the little blue flame playing round the red-hot coals, think 
 kindly of Priestley, for he first told us of the nature of that 
 flame when in the exile to which our forefathers drove him, 
 
5O Joseph Priestley \\ 
 
 The crowning work of Priestley's life was, however, the 
 discovery of that gas which he termed dephlogisticated air, but 
 to which Lavoisier, who swept away all the jargon of the 
 Phlogistic doctrine, gave the name of Oxygen. The manner 
 of this discovery is characteristic of much of Priestley's work. 
 " It furnishes," he says, " a striking illustration of the truth of 
 a remark which I have more than once made in my philo- 
 sophical writings, and which can hardly be too often repeated, 
 as it tends greatly to encourage philosophical investigations ; 
 viz., that more is owing to what we call chance, that is, 
 philosophically speaking, to the observation of events arising 
 from unknown causes, than to any proper design or preconceived 
 theory in this business." The accident of possessing a burning 
 glass " of considerable force " led Priestley to try the effect of 
 the heat of the sun upon various substances contained in tubes 
 filled with mercury, and standing over the mercurial trough. 
 " With this apparatus, after a variety of other experiments, 
 an account of which will be found in its proper place, on the 
 1st of August 1774 I endeavoured to extract air from mercurius 
 cakinatus per se that is, calx of mercury, and I presently found 
 that, by means of this lens, air was expelled from it very 
 readily. Having got about three or four times as much as the 
 bulk of my materials, I admitted water to it, and found that 
 it was not imbibed by it. But what surprised me more than 
 I can well express was, that a candle burned in this air with 
 a remarkably vigorous flame, very much like that enlarged 
 flame with which a candle burns in nitrous gas exposed to 
 iron or liver of sulphur [that is, his nitrous oxide gas] ; but as 
 I had got nothing like this remarkable appearance from any 
 kind of air besides this particular modification of nitrous air, 
 and I knew no nitrous air was used in the preparation of 
 mercurius cakinatus, I was utterly at a loss how to account for 
 it." His astonishment was still further increased when he 
 found that, tested with his nitrous air, the new gas was actually 
 better than common air, and that mice would live longer in it 
 
ii Joseph Priestley 51 
 
 than in an equal bulk of that air. He had the curiosity to 
 breathe it himself. " The feeling of it to my lungs was not 
 sensibly different from that of common air ; but I fancied that 
 my breast felt peculiarly light and easy for some time after- 
 wards. Who can tell but that in time this pure air may 
 become a fashionable article in luxury 1 ? Hitherto only two 
 mice and myself have had the privilege of breathing it. ... 
 But, perhaps, we may also infer from these experiments, that 
 though pure dephlogisticated air might be very useful as a 
 medicine, it might not be so proper for us in the usual healthy 
 state of the body ; for, as a candle burns out much faster in 
 dephlogisticated than in common air, so we might, as may be 
 said, live out too fast, and the animal powers be too soon 
 exhausted in this pure kind of air. A moralist, at least, may 
 say, that the air which nature has provided for us is as good 
 as we deserve." 
 
 Priestley at length got to the conclusion that common air 
 was no longer a "simple elementary substance, indestructible and 
 unalterable," but that it was composed of 1 volume of his new 
 air and 4 volumes of phlogisticated air. This new air, he con- 
 cluded, was devoid of phlogiston hence the term "dephlo- 
 gisticated air," but that in the processes of respiration and 
 combustion phlogiston was imparted to it. Priestley found 
 that he could obtain this air from the calx of lead as well as 
 from the calx of mercury, and this fact, he says, " confirmed 
 me more in my suspicion that the mercurius calcinatus must 
 have got the property of yielding this kind of air from the 
 atmosphere, the process by which that preparation, and this 
 of red lead, is made being similar. As I never make the 
 least secret of anything that I observe, I mentioned this 
 experiment also, as well as those with the mercurius calcinatus, 
 to all my philosophical acquaintances at Paris and elsewhere, 
 having no idea at that time to what these remarkable facts 
 would lead." The knowledge which Priestley, as he tells us, 
 imparted to the French chemists was used by them- with 
 
52 Joseph Priestley 
 
 crushing effect against his favourite theory. The discovery 
 of oxygen was the deathblow to phlogiston. Here was the 
 thing which had been groped for for years, and which many 
 men had even stumbled over in the searching, but had never 
 grasped. Priestley indeed grasped it, but he failed to see the 
 magnitude and true importance of what he had found. It 
 was far otherwise with Lavoisier. He at once recognised in 
 Priestley's new air the one fact needed to complete the 
 overthrow of Stahl's doctrine ; and now every stronghold of 
 phlogistonism was in turn made to yield. Priestley, however, 
 never surrendered, even when nearly every phlogistian but he 
 had given up the fight or gone over to the enemy. When age 
 compelled him to leave his laboratory he continued to serve 
 the old cause in his study, and almost his last publication was 
 his Doctrine of Phlogiston Established. His own life, indeed, 
 affords an exemplification of the truth of his own words, that 
 "we may take a maxim so strongly for granted, that the 
 plainest evidence of sense will not entirely change, and often 
 hardly modify, our persuasions; and the more ingenious a 
 man is, the more effectually he is entangled in his errors, his 
 ingenuity only helping him to deceive himself by evading the 
 force of truth." 
 
Ill 
 
 CARL WILHELM SCHEELE 
 
 AN ADDKESS TO THE OWENS COLLEGE CHEMICAL SOCIETY, AT THE 
 OPENING MEETING, 24ra OCTOBER 1893 ; SUBSEQUENTLY PUBLISHED 
 IN THE FORTNIGHTLY REVIEW. 
 
 IN the personal history of learning there are few more striking 
 or, in a sense, more romantic figures than the chemist Scheele. 
 " La vie de M. Scheele," wrote Vicq d'Azyr, " offre 1'exemple 
 d'un savant modeste qui, dedaignant tout eclat, eut le courage 
 de vivre obscur ; dont le zele n'eut pas besoin d'etre excite par 
 la louange, et qui, connu des gens de 1'art, mais presque ignore 
 de son siecle, avoit rendu son nom immortel lorsqu'il n'avoit 
 pas encore de celebrite." 1 An obscure apothecary, living a 
 solitary sedentary life in a small town on the shore of a 
 Scandinavian lake, hampered by poverty and harassed by 
 debt, hypochondriacal, and, at times, the victim of the most 
 depressing melancholy he yet succeeded by the sheer force 
 of his genius as an experimentalist, and under the influence of 
 a passion which defied difficulty and triumphed over despair, 
 in changing the entire aspect of a science. No man ever 
 served chemistry more loyally or with a purer, nobler, more 
 disinterested devotion than Scheele. "Diese edel Wissen- 
 schaft," he wrote to his friend Gahn, "ist mein Auge." The 
 pursuit of truth for its own sake with no thought of worldly 
 
 1 filoges historiques, vol. ii. p. 19. 
 
Ill 
 
 54 Carl Wilhelm Scheele 
 
 gain or reward was to him the supreme object of his exist- 
 ence and the highest form of his religion. The cause of 
 science was, indeed, as sacred to him as if it were that of a 
 martyr, and he gave up his life to her service with a martyr's 
 spirit of patience, self-sacrifice, and humility. 
 
 But although Scheele's name is associated with some of the 
 most remarkable discoveries of the eighteenth century, and of 
 which the value was quickly recognised by his contemporaries, 
 comparatively little is known of his personal characteristics, 
 of his habits of work, or of the nature of his surroundings. 
 Practically the only mental picture of him that we have 
 hitherto been able to form is to be derived from the memorial 
 notice of him by Sjosten, the Secretary of the Stockholm 
 Academy of Sciences, which appears in the Proceedings of the 
 Academy for 1799, that is thirteen years after Scheele's death. 
 Sjosten was not a chemist, and was otherwise unfitted to judge 
 of the merit and true proportion of Scheele's work. He 
 appears to have obtained his information from materials 
 collected by his predecessor in office, Johan Carl Wilcke, 
 whose name is honourably known in the .history of science 
 from his connection with the discovery of latent heat. On 
 the death of Scheele, Wilcke placed his papers and laboratory 
 notes in the charge of the Academy, which subsequently came 
 into possession of Scheele's correspondence with Retzius, Gahn, 
 and Hjelm. From this rich material, together with a collection 
 of letters to Bergmann, preserved in the University of Upsala, 
 Wilcke conceived the idea of preparing an account of Scheele's 
 life and labours which should set forth the origin and chrono- 
 logical history of his investigations, and so exhibit his true 
 relations as a discoverer to his great contemporaries, Cavendish, 
 Priestley, and Lavoisier. Unfortunately the realisation of this 
 project was frustrated by Wilcke's death. Thanks, however, 
 to the piety and patriotism of Baron Nordenskiold this valuable 
 collection of letters and laboratory memoranda has now been 
 given to the world, and the historian of chemistry is at length 
 
in Carl Wilhelm Scheele 55 
 
 in a position to determine much in Scheele's life that has 
 hitherto been doubtful and obscure. 1 
 
 M. Nordenskiold has been materially aided in his work by 
 the Lars Hiertas minne Trust, and, above all, by the zeal of 
 Mme. Elin Bergsten, who undertook not only to transcribe 
 the letters, which are difficult to read on account of their 
 archaic style and antiquated language and the constant em- 
 ployment in them of an obsolete nomenclature, but also to 
 decipher the laboratory notes, which are for the most part 
 rough jottings of experimental results put together by means 
 of contractions and a system of symbols wellnigh as illegible 
 as that of the alchemists. 
 
 The handsome well-printed volume which embodies the 
 results of so much patient and conscientious labour has 
 appeared at a timely moment; indeed, no more fitting 
 memorial of the one hundred and fiftieth anniversary of the 
 birth of the great Swedish chemist could be conceived than the 
 publication of a work which fixes for all time, without question 
 or cavil, his true relation to his epoch, and his place in the 
 history of scientific discovery. Scheele, who took little 
 thought for his own fame, owes much to women ; for, it is 
 worth noting, Mme. Bergsten is not the first of her sex who 
 has striven to perpetuate his genius. It was through Mme. 
 Picardet, the wife of a magistrate at Dijon, that France first 
 gained a knowledge of his memoirs. Instigated by De 
 Morveau, she learned German and Swedish solely for the 
 purpose of translating Scheele's papers. 
 
 Carl Wilhelm Scheele was born on 9th December 1742, at 
 Stralsund, at that time the capital of Swedish Pomerania. He 
 was the seventh child in a family of eleven. His father, Joachim 
 Christian Scheele, was a merchant of some note in Stralsund. 
 He came of a good stock, branches of which had occupied 
 
 1 Carl Wilhelm Sclieele : Nachgelassene Brief e und Aufzeichnungen. 
 Herausgegeben von A. E. Nordenskiold. Stockholm: Verlag von P. A. 
 Norstedt & Soner. 
 
56 Carl Wilhelm Scheele \\\ 
 
 important positions in North Germany as far back as the 
 fifteenth and sixteenth centuries. One member became Bishop 
 of Liibeck, and another distinguished himself as an admiral in the 
 Swedish service in the time of Charles XL A female connection 
 of the family, Anna Scheele, was the mother of Wilcke, the 
 Secretary of the Swedish Academy of Sciences, whose name has 
 already been mentioned as having projected a biography of his 
 illustrious relative. The Stralsund merchant was apparently not 
 in a position to afford his sons the advantages of a university 
 training. Carl Wilhelm was placed at a private school in his 
 native town, and after having acquired a fair knowledge of 
 Latin he passed on to the gymnasium. He seems to have 
 been a thoughtful, studious boy, remarkable among his fellows 
 for diligence and for the ease and rapidity with which he 
 accomplished his school tasks. The bent of his mind towards 
 science would appear to have manifested itself even at this 
 time ; at all events, he then acquired that facility in writing 
 chemical symbols which characterised his letters and memo- 
 randa, and the apothecary Cornelius, who gave him instruction 
 in reading pharmaceutical receipts and prescriptions, has 
 testified to his aptitude for chemical study and speculation. 
 It is not improbable, however, that the course of his inclina- 
 tion may have been, to some extent, directed from home. His 
 eldest brother, Johann Martin, had been apprenticed to an 
 apothecary in Gothenburg named Bauch, but had died whilst 
 Carl Wilhelm was at school. Three years afterwards, that is 
 when fourteen years of age, he too was apprenticed to Bauch. 
 The Gothenburg apothecary seems to have been an honest, 
 even-handed man, who, to judge from the inventory of his 
 possessions in the archives of the Rathhaus of the town, 
 followed his calling in a worthy, liberal-minded fashion. In 
 Bauch's laboratory Scheele made the practical acquaintance of 
 nearly all the pharmaceutical and chemical products of his 
 time. He had also access to such standard works as 
 Neumann's Prcelediones Chemicce, Lemery's Cours de Chimie, 
 
in Carl Wilhelm Scheele 57 
 
 Bcerhaave's Elementa Chemicce, Kunckel's Laboratorium 
 Chymicum, and Rothe's Anleitung zur Chymie. ! Nor was he 
 slow to avail himself of his opportunities. Bauch, in letters to 
 the Stralsund home, fears for the health of his young charge, 
 who devotes hours which should be given to sleep either to 
 the study of books which are beyond his years, or to the 
 making of experiments that would tax the skill of his older 
 fellow-apprentices. Kunckel's Laboratorium and Neumann's 
 Chymie seem, indeed, to have been his chief instructors in 
 practical chemistry, and it was by diligently repeating the 
 experiments contained in these books that he laid the founda- 
 tions of the manipulative skill and analytical dexterity on 
 which his success as an investigator ultimately rested. 
 
 In 1765 Bauch, then an old man, sold his business, and 
 Scheele, now twenty-three years of age, took service with 
 Kjellstrom, an apothecary in Malmo, with whom he remained 
 about a couple of years. 
 
 Kjellstrom has recorded his opinion of his young assistant, 
 but it is from his fellow-worker and friend Retzius that we 
 derive the most vivid conception of Scheele at this period of 
 his career. Anders Johan Retzius was of the same age as 
 Scheele, and, like hirn, began life as a pharmacist. Eventually 
 he attached himself to the University of Lund, as director of 
 its Museum and Botanical Garden, and died at Stockholm in 
 1821, the last survivor of the Phlogistic School of Chemists. 
 In a communication found amongst Wilcke's papers Retzius 
 thus records his impressions of Scheele : 
 
 His genius was wholly concerned with physical science. He 
 had absolutely no interest in any other. . . . Although possessing 
 an excellent memory, it seemed only fitted to retain matters relating 
 to chemistry. 
 
 " One science only will one genius fit," says Pope. ^ 
 
 During his stay at Malino he bought as many books as his small 
 pay enabled him to procure. These he would read once or twice 
 
58 Carl Wilhelm Scheele \\\ 
 
 through, when he would remember all that he desired to recall, 
 and never again consulted them. Without systematic training and 
 with no inclination to generalise, he occupied himself mainly with 
 experiments. During the time of his apprenticeship at Gothenburg 
 he worked without plan and for no other purpose than to note 
 phenomena ; these he could remember perfectly. Eleven years' 
 continuous exercise in the art of experimenting had enabled him to 
 collect such a store of facts that few could compare with him in 
 this respect. In addition he gained a readiness in devising and 
 executing experiments such as is rarely seen. He made all kinds 
 of experiments without reference to any system or pre-arranged 
 plan. He was thus enabled to learn what no doctrinaire could 
 possibly acquire, since working by no formulated principles he 
 observed much and discovered much that the doctrinaire would 
 consider impossible, inasmuch as it was opposed to his theories. I 
 once persuaded him during his stay at Malm 6 to keep a journal of 
 his experiments, and, on seeing it, I was amazed, not only at the 
 great number he made, but also at his extraordinary aptitude for 
 the art. 
 
 In 1768 Scheele removed to Stockholm, where he superin- 
 tended the shop of an apothecary named Scharenberg. Here 
 his opportunities for experimenting were considerably re- 
 stricted. However, a window with a sunny aspect close to 
 his place of work enabled him to make the novel and 
 important observation that different parts of the solar 
 spectrum influence the decomposition of silver chloride in 
 very different degrees. It was at about this time that his name 
 first appears in chemical literature as a discoverer. With his 
 friend Retzius he undertook the examination of cream of 
 tartar, and succeeded in isolating, for the first time, its 
 characteristic acid, the properties of which he carefully 
 studied, and from which he was enabled to conclude that it 
 differed from all acids up to that time known. 
 
 This, however, was not the first attempt made by Scheele 
 to contribute to the literature of science. Retzius tells us 
 that he had forwarded to the Academy an account of an 
 inquiry into the nature of the so-called Globuli martiales, a 
 pharmaceutical preparation made by boiling finely-divided 
 
in Carl Wilhelm Scheele 59 
 
 iron with a solution of cream of tartar. The paper was, for 
 the most part, a description of experiments ; it was un- 
 methodically put together, and was without definite theoretical 
 result. It was referred to Bergmann by the Academy, and 
 as his opinion was adverse, it was never published, and was 
 ultimately lost. From Scheele's correspondence with Gahn, 
 and from the laboratory memoranda which have now been 
 published, we are able to glean an idea of the contents of this 
 memoir. Some of the observations were unquestionably new 
 and not without importance. Thus Scheele found that 
 hydrogen was evolved by the contact of organic acids with 
 iron, and he describes an apparatus by which this gas may be 
 obtained by the action of water alone on iron filings. The 
 theoretical value of these facts will be obvious from the 
 circumstance that Cavendish, at that time the recognised 
 authority on hydrogen, or inflammable air, as it was then 
 termed, had stated in his classical papers on " Factitious Air," 
 published in the Philosophical Transactions for 1766 : "I know 
 of only three metallic substances, namely, zinc, iron, and tin, 
 that generate inflammable air by solution in acids, and those 
 only by solution in the diluted vitriolic acid, or spirit of 
 salt." 
 
 Nor was Scheele more fortunate with his second contribu- 
 tion " Chemical Experiments with Sal-acetosellse " [acid potas- 
 sium oxalate], which he sent to the Academy in 1768. The 
 paper was read, but was not published again through the 
 intervention of Bergmann. It is doubtful if Bergmann at this 
 time had any personal knowledge of Scheele ; at all events, it 
 is impossible to suppose that he was in any way influenced 
 by animosity. The " hochedelgeborner Herr Professor" to 
 whom Scheele a year or two afterwards subscribed himself as 
 his " dienstschuldigster Knecht," and with whom he was to 
 live in the closest bonds of sympathy and mutual esteem, 
 although one of the most cultivated men of his age, and 
 distinguished by the breadth of his knowledge, which ranged 
 
60 Carl Wilhelm Scheele \\\ 
 
 over zoological, physical, and cosmographical science, had at 
 this period little acquaintance with experimental chemistry. 
 It is hardly to be wondered at, therefore, that the crude 
 essays of the unknown apothecary's assistant, who, like 
 Addison's clubfellow, was somewhat awkward at putting 
 his talents within the observation of such as should take notice 
 of them, should have failed to commend themselves to the 
 critical judgment and refined taste of the homo multarum 
 literarum, noted for the grace and polish of his style. There 
 is reason to believe that these disappointments reacted upon 
 the sensitive nature of Scheele, and that the rejection of 
 his papers by the Academy, together with the uncongenial 
 nature of his position in Stockholm, induced him to leave the 
 capital in order to accept employment as a laborant in the 
 pharmacy of Lokk at Upsala. Whatever may have been the 
 real grounds for the change, there is no question that it was 
 attended with the most beneficial results on Scheele's fortunes. 
 To begin with, he was brought into personal contact with 
 Bergmann. This rapprochement was due to Gahn, who had 
 made Scheele's acquaintance in Stockholm, and who had 
 been greatly impressed with the power and capacity of the 
 young apothecary. It is said that Bergmann, unable to 
 explain the change that nitre experiences when it is strongly 
 heated, whereby it is converted into the deliquescent potas- 
 sium nitrite, and evolves a ruddy gas when treated with oil of 
 vitriol, was led by Gahn to consult Scheele, to whom the 
 phenomena and their cause were well known. According to 
 Eetzius, the properties of the so-called Salpeterluft, as the 
 ruddy gas came to be termed, were ascertained by Scheele 
 when at Malmo, and were known to him long before any- 
 thing had been written on the subject. This meeting laid the 
 foundation of a warm and active friendship which ended only 
 with Bergmann's death a friendship, too, which was of the 
 greatest service to science. "It would be difficult to say," 
 wrote Retzius, " which of the two, Scheele or Bergmann, was 
 
in Carl Wilhelm Scheele 61 
 
 the teacher or the taught. Bergmann, without a doubt, re- 
 ceived the greater part of his practical instruction from Scheele, 
 whilst Scheele owed to Bergmann the wider knowledge of his 
 later years." It was at Bergmann's instigation that Scheele 
 undertook the epoch-making investigation of magnesia nigra, 
 the Braunstein or pyrolusite of the German mineralogist, the 
 " wad " of the English miner, whereby he not only showed 
 that this substance contained a metal hitherto unknown, but 
 also incidentally discovered oxygen, chlorine, and baryta. It 
 may seem remarkable that Scheele, with his tastes and 
 aptitudes, should not have followed the example of his friend 
 Retzius, and have abandoned pharmacy for an academic 
 career. M. Nordenskiold finds an explanation in the assump- 
 tion that the Zunftgeist of the time would not permit of the 
 introduction of the studiosus pharmacice within the academic 
 circle. It is doubtful, however, whether Scheele was at all 
 fitted, either by temperament or training, for an academic 
 career, and as schools of chemistry were at that time consti- 
 tuted it is certain that he would have gained little by the 
 change. Chemical laboratories were seldom to be found at 
 the universities, even at the largest, and the chemical pre- 
 lections of the period were, for the most part, dull and 
 formal disquisitions unenlivened by a single experimental 
 illustration. On the other hand, the pharmacist at that time 
 had a right to the appellation which, in this country at least, 
 he now too frequently usurps. He was a practical chemist 
 in the real sense of the term, and his laboratory was of more 
 importance to him than his shop. 
 
 Whilst with Lokk, Scheele seems to have had abundant op- 
 portunity for the prosecution of his inquiries. It was at Upsala 
 that he collected the greater part of the experimental material 
 for his great work on Air and Fire. The correspondence and 
 laboratory memoranda which M. Nordenskiold has given to the 
 world show that prior to 1773, that is at least a year before the 
 date of Priestley's discovery, Scheele liad prepared oxygen from the 
 
62 Carl Wilhelm Scheele \\\ 
 
 carbonates of silver and mercury, from mercuric oxide, nitre and 
 magnesium nitrate, and by the distillation of a mixture of man- 
 ganese oxide and arsenic acid. It was at Upsala, too, that he 
 began and finished his work on manganese, chlorine, and 
 baryta ; he also demonstrated the acidic character of silica and 
 the chemical nature of magnesia, microcosmic salt, and oxalic 
 acid. 
 
 On 4th February 1775, when thirty-two years of age, 
 Scheele was made a member of the Swedish Academy of 
 Sciences, a distinction never accorded, either before or since, 
 to a student of pharmacy. In the following year he was 
 appointed, by the Medical College, provisor of the pharmacy at 
 Koping, a small town on the north shore of Lake Malar, as 
 successor to Hinrich Pohls, whose privilege, in conformity with 
 Swedish law, had passed, on his death, to his young widow, 
 Sara Margaretha Sonneman. Scheele now seemed to himself 
 to have reached the goal of his aspirations ; he had at length, 
 he thought, obtained an independent position with the pros- 
 pect of a fairly lucrative business, and he would now be able 
 to follow his cherished projects under conditions of com- 
 parative ease and comfort. " Oh, how happy I am," he wrote"^ 
 to Gahn, "with never a care about eating or drinking or / 
 dwelling ! " The quiet peaceful life he saw before him I 
 was to be consecrated to science. "There is no delight," I 
 he wrote, "like that which springs from a discovery; it is / 
 a joy that gladdens the heart." 
 
 But the haven of rest was not yet won. The young 
 academician, rich in honour, was poor in means, and unlooked- 
 for difficulties arose respecting the transfer of the lease. The 
 widow and her father were exacting, and other provisors came 
 forward who understood the art of money-getting better than 
 Scheele. Scheele's letters seldom contain allusions to his 
 private affairs, but the half-dozen lines in which he makes 
 mention to Gahn and to Bergmann of his disappointment 
 show how deeply he felt it. Offers of assistance came from 
 
Ill 
 
 Carl Wilhelm Scheele 63 
 
 all sides. Gahn invited him to Fahlun ; Bergmann wished 
 him to return to Upsala : "Es fallt uns beiden schwer uns 
 von einander zu trennen," he had written at the prospect of 
 the change to Koping. The suggestion was publicly made 
 that he should be " chemicus regius " in the capital. He had 
 even invitations from abroad. D'Alembert, in a letter to 
 Frederick II., suggested that he should be called to Berlin. 
 " J'ai appris," he wrote, " il y a peu de temps qu'il y avait a 
 Stockholm un tres habile chimiste, nomme M. Scheele 
 Membre de 1' Academic des Sciences de cette ville, et qui, sans 
 m'etre d'ailleurs connu, me paroit fort estim6 par les plus 
 habiles chimistes de la France." Among Wilcke's papers was 
 found a letter from the brother, Fr. Christian Scheele, from 
 which it appears that Scheele actually did receive an invita- 
 tion to Berlin with a salary of 1200 reich-thalers. Crell, 
 the editor of the well-known Neue Entdeckungen and Annolen 
 in which many of Scheele's papers first appeared, stated that 
 inducements were even held out to him by the English 
 ministry. It is difficult to know upon what basis this state- 
 ment rests. Thomson, the author of the History of Chemistry, 
 in mentioning the circumstance expresses his doubts as to its 
 truth, and states that he made inquiries of Sir Joseph Banks, 
 Cavendish, and Kirwan, but none of them had ever heard of 
 the matter. Indeed, it is intrinsically improbable. " I am 
 utterly at a loss," says Thomson, "to conceive what one 
 individual in any of the ministries of George III. was either 
 acquainted with the science of chemistry or at all interested 
 in its progress. ... If any such project ever existed it 
 must have been an idea which struck some man of science 
 that such a proposal to a man of Scheele's eminence would 
 redound to the credit of the country. But that such a 
 project should have been broached by a British ministry or by 
 any man of great political influence, is an opinion that no 
 person would adopt who has paid any attention to the 
 history of Great Britain since the Revolution to the present 
 
64 Carl Wilhelm Scheele \\\ 
 
 time." However this may be, there is one name that suggests 
 itself as the possible author of such a project, and that is 
 Lord Shelburne. Had Thomson been able to question Priest- 
 ley on the subject, the real ground for Crell's statement might 
 have been elicited. 
 
 But Scheele's love of quiet and retirement was too deep- 
 seated to allow him to exchange Koping for a foreign capital. 
 Even if he should be forced to leave the little town, Lokk 
 was ready to take him back to Upsala. His yearning for 
 independence and for the tranquil life which Koping had 
 seemed to promise held him there. " One needs not to eat 
 more than enough," he wrote to Bergmann, " and if I can find 
 my bread in Koping there is no occasion to seek it else- 
 where." Other influences, too, were at work. The burghers 
 of the place and the gentry of the neighbourhood combined 
 to induce him to remain. The former, mindful, as they said, 
 of the reproach that in parting with Scheele they would be. 
 neglectful of the benefit, no less than of the honour, to the 
 town, declared their intention of dealing with no other 
 apothecary ; whilst the latter, headed by the principal man of 
 the province, expressed their willingness to move for a new 
 privilege, so as to enable him to start an independent business. 
 This remarkable exhibition of popular sympathy at length 
 compelled the Sonnemans to accept the young provisor, and 
 Scheele was duly installed at Koping. But herein fortune 
 showed herself even less kind than is her wont. Scheele, 
 after all, had gathered Dead Sea fruit. Instead of the pros- 
 perous, well-ordered business he had been led to expect, he 
 found little but debts and discomfort. Such a blow would 
 have crushed a weaker man. He accepted his lot uncomplain- 
 ingly; we search in vain amongst the letters for a word 
 of railing or accusation. Scheele, in truth, had been schooled 
 in adversity, and many a hard and bitter lesson had taught 
 him how to grapple with it. Patiently, and with a tenacity 
 of purpose which is well-nigh sublime in its heroic self- 
 
in Carl Wilhelm Scheele 65 
 
 abnegation, he deliberately set himself to retrieve the fallen 
 fortunes of the widow's estate. 
 
 For years his life was a continual struggle with privation, 
 relieved to some extent by an annual grant of 100 rix-thalers, 
 which the Academy, at Bergmann's instigation, made him in 
 1 777. In the previous year he acquired full possession of the 
 pharmacy, and the last of the widow's debts was at length 
 paid. The tide had now turned. In 1782 his circumstances 
 had so far improved that he was able to build himself a new 
 house, with a good and well-furnished laboratory. If not rich 
 he had at least a sufficiency ; a modest competency was, indeed, 
 all he desired, for Scheele was one of those men whose riches 
 consist, not in the abundance of their possessions, but in the 
 fewness of their personal wants. He was now in the prime 
 of life, and in the full maturity of his mental vigour. His 
 scientific position was assured, and his name was mentioned 
 with honour and respect in every intellectual centre in 
 Europe. Many years of scientific activity were, in all human 
 probability, before him. Although never of robust health, he 
 had been fairly free from illness up to his thirty-fifth year, 
 when he contracted rheumatism from working, in the rigour 
 of a Scandinavian winter, in the outhouse which at that time 
 did duty as his laboratory. During the autumn of 1785 he 
 suffered greatly, not only from rheumatism, "the natural 
 heritage," he says, " of all apothecaries," but from a weariness 
 and dejection even harder to bear. He still worked on, how- 
 ever. In the early part of 1786 he sent a memoir to the 
 Academy on gallic acid. In the March of the same year he 
 was studying the action of light on nitric acid. " I will repeat 
 the experiments," he wrote, " during the coming summer. We 
 shall then see what will come of them." That summer never 
 came to Scheele. The rheumatism brought other disorders in 
 its train, and he instinctively felt that his end was near. 
 Some time before his fatal illness he had formed the resolution 
 of marrying the widow Pohl, who, together with his sister, 
 
 F 
 
66 Carl Wilhelm S cheek m 
 
 who died in 1780, had kept house for him at Koping. On 
 his deathbed he carried out this project, that he might leave 
 to her once more the business he had striven so manfully to 
 preserve. Two days afterwards 21st May 1786 he died, in 
 the forty-third year of his age. The brave man who had 
 struggled with such unflinching courage in the storms of fate 
 had conquered but to die. A new promisor quickly appeared, 
 and within a few months the widow was again a wife. 
 
 The true history of Scheele's life is, after all, to be found 
 in his works. "What we call a genius," said Pope, "is hard 
 .to be distinguished by a man himself from a strong inclination." 
 Scheele himself would have been the first to admit that his 
 strongest inclination was to experiment, and the rest of the 
 world has said that herein lay his genius. His old master, 
 Kjellstrb'm, has recorded that such phrases as "Das kann 
 sein"; " Das ist nicht richtig " ; "Das werde ich untersuchen," 
 were ever on his lips as he pored over the chemical literature 
 of his time. This incessant mental activity was fruitful in 
 investigations in every department of chemistry. We owe to 
 Scheele our first knowledge of chlorine and of the individuality 
 of manganese and baryta. He was an independent discoverer 
 of oxygen, ammonia, and hydrochloric acid gas. He dis- 
 covered also hydrofluoric, nitro-sulphonic, molybdic, tungstic, 
 and arsenic acids among the inorganic acids ; and lactic, gallic, 
 pyrogallic, oxalic, citric, tartaric, malic, mucic, and uric among 
 the organic acids. He isolated glycerin and milk - sugar ; 
 determined the nature of microcosmic salt, borax, and Prussian 
 blue, and prepared hydrocyanic acid. He demonstrated that 
 plumbago is nothing but carbon associated with more or less 
 iron, and that the black powder left on solution of cast iron 
 in mineral acids is essentially the same substance. He ascer- 
 tained the' chemical nature of sulphuretted hydrogen, dis- 
 covered arsenetted hydrogen, and the green arsenical pigment 
 which is associated with his name. He invented new processes 
 for preparing ether, powder of algaroth, phosphorus, calomel, 
 
in Carl Wilhelm Scheele 67 
 
 and magnesia alba. His services to quantitative chemistry 
 included the discovery of ferrous "ammonium sulphate, and 
 of the methods still in use for the analytical separation of 
 iron and manganese, and for the decomposition of mineral 
 silicates by fusion with alkaline carbonates. 
 
 To Scheele, however, the greatest work of his life was his 
 memoir on " Air and Fire," which appeared in 1777, and which, 
 on account of its relations to the chemical theory of that time, 
 attracted universal attention, and was translated into almost 
 every European language. The chief part of the experimental 
 material for this work, as is proved by the correspondence 
 and laboratory memoranda now published, was collected 
 partly in Malmo and Stockholm that is, before the autumn of 
 1770, and partly during the earlier portion of his stay in 
 IJpsala that is, prior to 1773. These dates are important in 
 view of Scheele's relations as a discoverer to Priestley and 
 Lavoisier. A number of circumstances, and more especially 
 the dilatoriness of the publisher Swederus, retarded the 
 appearance of the book. From the letters to Gahn it appears 
 that the manuscript was sent to the printer towards the close 
 of 1775, but nearly two years elapsed before the work was 
 made public. Scheele, in several of his letters complains 
 bitterly of the delay. In August 1776 he wrote to Berg- 
 mann : "I have thought for some time back, and I am now 
 more than ever convinced, that the greater number of my 
 laborious experiments on fire will be repeated, possibly in a 
 somewhat different manner, by others, and that their work 
 will be published sooner than my own, which is concerned 
 also with air. It will then be said that my experiments are 
 taken, it may be in a slightly altered form, from their writings. 
 I have to thank Swederus for all this." No imputation of 
 plagiarism was ever brought against Scheele. The whole 
 conduct of his life was proof indeed against even a suspicion 
 of unfair dealing. Although on occasions he could show that 
 he had the mens sibi conscia recti, and could manifest a proper 
 
68 Carl Wilhelm Scheele 
 
 assurance in his own vindication, he was singularly unselfish 
 and unworldly. With all Priestley's candour and sense of 
 rectitude, he had Cavendish's indifference to fame and his 
 contempt for notoriety. It can hardly be doubted, however, 
 that had Scheele's work appeared in 1775 he himself would 
 have occupied a still higher position in the estimation of his 
 contemporaries, and that it would not have been left to 
 posterity to assign him his true place in the history of scientific 
 discovery. 
 
 It is impossible to read this, or indeed any other of Scheele's 
 memoirs, without being impressed by his extraordinary insight, 
 which at times amounted almost to divination, and by the way 
 in which he instinctively seizes on what is essential and steers 
 his way among the rocks and shoals of contradictory and con- 
 flicting observations. No man was more staunchly loyal to 
 the facts of his experiments, however strongly these might tell 
 against an antecedent or congenial hypothesis. "Es ist ja 
 nur die Wahrheit," he wrote to Hjelm, " welche wir wissen 
 wollen, und welch ein herrliches Gefiihl ist es nicht, sie 
 erforscht zu haben." Had these facts been worked out by 
 their discoverer in the spirit of quantitative accuracy so 
 characteristic of his contemporary Cavendish, they would 
 inevitably have undermined phlogistonism, even if they would 
 not have effected its overthrow, before the advent of Lavoisier. 
 As it was, other heads and other hands made use of them to 
 demolish the theory by which their author could alone explain 
 them, and to which he vainly imagined they lent so strong a 
 support. It is, perhaps, idle to speculate on the causes which 
 prevented Scheele from recognising the full significance of his 
 work. It may be that from the lack of mathematical training 
 the quantitative aspects of chemistry had few attractions for 
 him, but it is equally probable that the peculiar character of 
 his inquiries may have been determined by the circumstances 
 of his position, by his poverty, and by the want of the refined 
 and costly apparatus needed for quantitative research. But 
 
in Carl Wilhelm Scheele 69 
 
 surmises, as Scheele himself said, cannot determine anything 
 with certainty. It must be admitted that he was wanting in 
 the faculty of co-ordination, grasp of principle, and power of 
 generalisation, that so strikingly characterise Lavoisier; and 
 his greatest investigation, whilst it testifies to his genius as an 
 experimentalist, reveals, no less clearly, his weakness as a 
 theorist. But when every legitimate deduction has been 
 made, Scheele's work, with all its shortcomings and limita- 
 tions, stamps him as the greatest chemical discoverer of his 
 age. His story constitutes, indeed, one of the most striking 
 examples of what may be achieved by the diligent cultivation 
 of a single natural gift. 
 
IV 
 
 HENRY CAVENDISH 
 
 A LECTURE DELIVERED IN THE HULME TOWN HALL, MANCHESTER, 
 ON 24ra NOVEMBER 1875. MANCHESTER SCIENCE LECTURES. 
 
 WHEN I had the honour to appear here on a former occasion 
 I gave you some account of the life and labours of a famous 
 Yorkshire philosopher, Joseph Priestley, one of the most 
 illustrious of that remarkable band of learned men which 
 did so much to make the reign of George III. what Lord 
 Brougham was wont to declare it to be the Augustan age of 
 modern history. 
 
 To-night I shall venture to offer you a brief notice of the 
 character and work of another and equally illustrious member 
 of that band Henry Cavendish. These two men had, 
 however, little in common beyond their zeal for science; 
 indeed, it is scarcely possible to conceive of a stronger contrast 
 than that which their personal histories afford. Priestley, 
 the son of a poor cloth -dresser, was ardent, impulsive, 
 ingenuous fond of the strife of words, never so happy, 
 indeed, as when, Ishmael-like, his hand was against everybody 
 and everybody's hand was against him. Cavendish, a scion 
 of a great house, was cold, retiring, reticent, passively selfish, 
 a confirmed misogynist, a hater of noise and bustle. It was 
 said of him that he probably uttered fewer words in the 
 course of his fourscore years than any man who ever lived so 
 
IV 
 
 Henry Cavendish 71 
 
 long not even excepting the monks of La Trappe. Priestley 
 delighted in literary composition ; his pen was ever busy ; he 
 published more than a hundred works on subjects of the most 
 extraordinary diversity, turning them off with an ease and 
 rapidity which even the most prolific of lady novelists might 
 envy. Cavendish, although he wrote much, printed fewer 
 pages than Priestley did books ; his morbid shyness, and his 
 horror of publicity, compelled him to keep back his scientific 
 memoirs even when he had prepared them for publication. 
 
 But that you may the better frame for yourselves some 
 conception of the manner of man Cavendish was, let me 
 attempt to sketch for you a scene in which he might have 
 played a part. That there is nothing opposed to truth in it 
 you may readily determine for yourselves, if what I say to- 
 night may so far interest you in Cavendish as to lead you to 
 read his life as written by Dr. Wilson or by Lord Brougham. 
 Imagine, then, you are in the London of ninety years ago : it 
 is night, and you are standing before an old-fashioned house 
 in what is now a very unfashionable square. It is evident 
 from the lights in the windows and the bustle before the door 
 that there is a dinner party or some social meeting in the 
 house. A couple of chairmen have deposited a portly gentle- 
 man, with a large frill, on the step, and two or three lumber- 
 ing vehicles, having set down their charges, are rattling away 
 over the rough stones into the obscurity of the dimly -lighted 
 street. My knowledge of London ninety years ago is so vague 
 that I must ask you to complete the picture for yourselves by 
 throwing in any other accessories which may occur to you as 
 giving it a strong eighteenth century flavour, such as a few 
 link-boys, a solitary watchman, an oil lamp or two, and a 
 plentiful sprinkling of puddles and mud. You are informed 
 that the house belongs to Sir Joseph Banks, who is the 
 President of the Eoyal Society of London, and that the 
 occasion is one of his weekly conversaziones. The portly 
 visitor, with the large frill, makes his way upstairs, to the 
 
72 Henry Cavendish 
 
 IV 
 
 evident embarrassment of a thin, middle-aged gentleman in 
 an old-fashioned Court dress of faded violet and a knocker- 
 tailed periwig, who is moving uneasily about on the landing, 
 manifestly afraid to face the assembly. The approach of the 
 gentleman on the stairs, however, drives him into the room. 
 He shuffles quickly from place to place, his manner is 
 awkward ; his face betrays a nervous irritation of mind, and 
 he appears annoyed if looked at. It is the Honourable Mr. 
 Cavendish. Finding himself close to a group, evidently, from 
 the appearance which their faces wear, speaking of a deeply- 
 important matter, he draws near to listen. They are talking 
 of a rumour of some grave disaster which has befallen my 
 Lord Cornwallis and his troops, who it would seem have been 
 circumvented in some unexpected manner by the machinations 
 of that arch-rebel Washington. Mr. Cavendish is scarcely 
 interested, and he moves aside to catch something concerning, 
 it may be, some fresh eccentricity of poor Lord George 
 Gordon, or perhaps some account of the troubles of the 
 unhappy Mr. Watt, the engineer, who, it is being said, is 
 fighting tooth and nail to defend his just rights from a set 
 of unprincipled rogues who pirate his inventions. None of 
 these matters is sufficiently moving to detain him. But his 
 manner quickly alters when he overhears the mention of the 
 name of Mr. Herschel. Mr. Herschel is a musician at Bath, 
 who employs his leisure in constructing big telescopes, with 
 one of which he has just discovered a new planet. Mr. 
 Cavendish is greatly interested ; he listens with marked 
 attention ; he is even about to put a question, and begins in 
 a nervous, hesitating manner, and in a thin, shrill voice, when 
 his eye catches that of a stranger ; he is instantly silent, and 
 retires in great haste, for he has a horror of a strange face. 
 The portly gentleman with the large frill espies him, and 
 comes up with a foreign gentleman, who is formally introduced 
 to Mr. Cavendish. Mr. Cavendish is assured by the portly 
 gentleman that his foreign friend is particularly desirous to 
 
IV 
 
 Henry Cavendish 73 
 
 make the acquaintance of a philosopher so profound and 
 so universally celebrated all of which is confirmed by the 
 foreign gentleman, who adds that it was, indeed, his chief 
 reason for coming to London, that he might see and converse 
 with one of the greatest ornaments of Britain, and one of the 
 most illustrious philosophers of that or any other age. Mr. 
 Cavendish is speechless ; he is overwhelmed with confusion, 
 until, seeing an opening in the crowd, he darts through it with 
 all possible speed, and, reaching his carriage, is driven home. 
 His house is precisely such as you would expect from one of 
 his habits and disposition ; it is made up of laboratories and 
 workshops, and very little is set apart for personal comfort. 
 The principal laboratory is in what the builder intended to 
 be the drawing-room ; in an adjoining chamber is a forge ; 
 and the upper apartments are turned into an astronomical 
 observatory. Mr. Cavendish rarely did violence to his love 
 of solitude by asking any one to his house. If a friend 
 chanced to dine with him he was invariably treated to a leg 
 of mutton, and nothing else. We are told that on one 
 occasion, three or four guests being expected, he was asked 
 what was to be got for dinner. He replied with the 
 customary formula, "A leg of mutton." "But," said the 
 servant, " that will not be enough for five." " Then get two 
 legs," was his answer. During the latter part of his life 
 Mr. Cavendish was immensely rich. At the time of his 
 death he was said to be worth a million and a quarter, and 
 was the largest holder of Bank Stock in England. But he 
 who was said to be the most wealthy of learned men, and the 
 most learned of wealthy men, seemed quite indifferent to his 
 riches. There is a well-known story of his threatening to 
 remove his money out of the hands of his bankers if, as he 
 said, they continued to plague him about it. Cavendish, as 
 you may suppose, could never be induced to sit for his 
 portrait ; but an artist, who was bent upon having it, managed 
 to get near his subject unobserved, and first sketching the 
 
74 Henry Cavendish iv 
 
 three-cornered hat, and then the great-coat, he patiently 
 watched his opportunity and inserted the profile between 
 them. This, I believe, is the only known or authentic portrait 
 of Cavendish. 
 
 The life of such a man is, as you may well imagine, nearly 
 devoid of incident. There is but little more of his personal 
 history to tell, except that he was the son of Lord Charles 
 Cavendish, that he was born at Nice in 1731, and that he 
 died in London in 1810. He died as he had lived, voluntarily 
 severing every tie of human sympathy. When he found 
 himself near his end, he called his servant to his bedside, and 
 said, "Mind what I say I am going to die. When I am 
 dead, but not till then, go to Lord George Cavendish and tell 
 him Go ! " The dying man wished to be alone, and the ser- 
 vant, who hesitated to leave him, was ordered from the room. 
 In half an hour he returned to find that his master had turned 
 his face to the wall, and quietly passed away. 
 
 There is nothing lovable in such a character ; on the other 
 hand, there is nothing in it that is despicable. This passion- 
 less man, whose moral character seemed almost a blank, had a 
 marvellously clear intelligence, and a range of mental vision 
 second to none of his age. In extent of acquirements, and in 
 profundity of learning, he was unsurpassed by any of his 
 contemporaries. His published work, although of the highest 
 order, gives a very incomplete idea of his powers. He left 
 behind him a mass of papers which indicate that he was far 
 in advance of the science of his time. His memoirs on heat 
 and electricity contain the germs of discoveries, if not actual 
 discoveries, which are commonly associated with the names of 
 subsequent investigators. He was an accomplished practical 
 astronomer and a profound mathematician. His knowledge 
 of the calculus and the manner in which he handled it have 
 been described as masterly. 
 
 Science is indebted to a learned Scotch professor of the last 
 century Dr. Black for the discovery of certain fundamental 
 
iv Henry Cavendish 75 
 
 laws of heat ; and the elucidation of these laws seems to have 
 been the subject of Cavendish's earliest inquiries. One of the 
 problems he set himself to solve, in the course of these investiga- 
 tions, was whether our mercurial thermometer was an accurate 
 and uniform measurer of temperature, to the extent of show- 
 ing whether the temperature of a mixture of hot and cold 
 water is the mean of the temperatures of the hot and cold 
 water before mixing. Having found that such was the 
 case, Cavendish proceeded to determine the effect of mixing 
 dissimilar liquids at different temperatures. "One would 
 naturally imagine," he says, "that if cold mercury, or any 
 other substance, is added to hot water, the heat of the 
 mixture would be the same as if an equal quantity of water 
 of the same degree of heat had been added, or, in other 
 words, that all bodies heat and cool each other when mixed 
 together equally in proportion to their weights." 
 
 He then shows by experiment that such is not the case. 
 He mixed quicksilver and water together at different tempera- 
 tures, and found that if it required 1 Ib. of water at a known 
 temperature to cool a certain weight of hot water through 
 a certain number of degrees, it would require 30 Ibs. of quick- 
 silver to cool the same weight of hot water through the same 
 interval of temperature. He made trials with various metals, 
 with sulphur, glass, charcoal, and many other bodies, and he 
 concludes " that the true explanation of these phenomena seems 
 to be that it requires a greater quantity of heat to raise the 
 heat of some bodies a given number of degrees by the 
 thermometer than it does to raise other bodies the same 
 number of degrees." 
 
 We have here the first clear enunciation of a very im- 
 portant matter : if Cavendish had communicated his discovery 
 to the world when he made it, namely in 1764, he would 
 have had priority over those who are generally styled the 
 discoverers of the fact of specific heat. 
 
 Cavendish did much to improve the mercurial thermometer. 
 
76 Henry Cavendish iv 
 
 He pointed out several sources of error in the methods of 
 making and using it. He was the first to insist on the 
 necessity of correcting its indications when the whole of 
 the mercury is not within the space of which the temperature 
 is to be ascertained, and the first to draw up special directions 
 to ensure uniformity in the mode of graduating it. He also 
 accurately determined the temperature at which quicksilver 
 freezes, and found it to 39 degrees below the point at which 
 water is ordinarily turned into ice. But it would require an 
 entire evening to tell you all that Cavendish did on the 
 subject of heat. That it occupied much of his attention is 
 obvious from the number and character of his experiments, 
 and the excellence of his numerical results. It is evident, too, 
 that he thought deeply on the nature of heat. He rejected 
 the doctrine that it was material, rather holding, as he tells 
 us, "Sir Isaac Newton's opinion, that heat consists in the 
 internal motions of the particles of bodies " ; the theory in fact 
 which is now, I should suppose, universally current. And it is 
 worthy of remark that one of the greatest exponents of this 
 theory was the director of one of the finest physical labora- 
 tories in the world a laboratory erected at Cambridge to the 
 memory of Cavendish by .his descendant, the late Duke of 
 Devonshire. 1 
 
 Cavendish was a -natural philosopher in the widest sense of 
 the term, for he occupied himself in turn with every branch of 
 physical science known in his time. But it is to his dis- 
 coveries in chemistry that his fame is chiefly due ; and here 
 again we may trace the influence of Black in directing the 
 current of his early inquiries. Chemists, up to the middle of 
 the last century, had no clear conception of the existence of a 
 variety of gaseous substances perfectly distinct from one another. 
 They were inclined to believe that all the different forms of 
 gas they met with were merely modifications of one and the 
 same substance. Their distinctive characters were supposed 
 
 1 The late Professor Clerk Maxwell. 
 
IV 
 
 Henry Cavendish 77 
 
 to arise from their being " tainted," or " infected with fumes, 
 vapours, or sulphurous spirits." The publication of a cele- 
 brated essay by Black on " Magnesia Alba," marked an epoch 
 in the history of chemistry by demonstrating the existence of 
 at least one gaseous body totally distinct from the air we 
 breathe. Black showed that the difference between chalk and 
 quicklime was due to the presence of a gas in the chalk which 
 was not in the quicklime. Quicklime, indeed, had the pro- 
 perty of fixing this air, and of thus being converted into chalk. 
 Black named this air, which was so capable of entering into 
 the composition of bodies, " fixed air " ; nowadays we call it 
 carbon dioxide, a name which denotes its composition, of 
 which Black was ignorant. Black did very little towards 
 investigating this gas in the free state. The first full account 
 of its properties was given by Cavendish in 1766. Cavendish 
 prepared the fixed air with which he experimented by 
 dissolving marble, which is, chemically speaking, the same 
 thing as chalk, in spirits of salt, or hydrochloric acid. He 
 found that the gas dissolved in its own bulk of water at 
 common temperatures, and that cold water dissolves more 
 of it than hot water ; indeed, he says, " water heated to the 
 boiling point is so far from absorbing the air that it parts 
 with what it had already absorbed." Lime and alkalies, 
 especially if dissolved in water, rapidly absorb the gas, but it 
 may be collected and preserved over quicksilver for any 
 length of time ; indeed chemists owe the idea of using quick- 
 silver to collect and preserve certain gases which are absorbed 
 by water to Mr. Cavendish. 
 
 Although you are blessed here in Manchester with one of 
 the best water supplies in the kingdom, you doubtless have 
 heard of what are called " hard " waters ; you may even 
 know that some of these hard waters are made "soft" by 
 boiling, and that the kind of hard water which is softened by 
 boiling deposits a crust or "fur" in the tea-kettle, and a 
 "cake" in the steam-boiler. Now this "fur" is mainly 
 
7 8 Henry Cavendish iv 
 
 composed of chalk, kept in solution in the water by the fixed 
 air dissolved therein. When the water is boiled the fixed air 
 is expelled, as Cavendish tells us, and accordingly the chalk is 
 deposited. This explanation of the origin of the "fur "was 
 first given by Cavendish. Possibly some of you may know 
 that such hard waters are frequently softened on the large 
 scale by adding lime to them. The lime combines with the 
 fixed air (the agent, you bear in mind, which keeps the chalk 
 in solution), and accordingly the chalk is deposited, together 
 with that formed by the union of the fixed air with the added 
 lime. The fact that water could be thus deprived of its 
 dissolved chalk was pointed out by Cavendish. When the 
 carbon dioxide is allowed gradually to escape from the solu- 
 tion, the carbonate of lime is deposited in small crystals, the 
 shapes of which are often exceedingly curious and beautiful ; 
 indeed, there is no substance which has such a diversity of 
 crystalline form as this carbonate of lime. 
 
 In various parts of the world,, particularly in districts 
 where limestone abounds, there are large caves, or grottoes, 
 from the roofs of which depend long icicle-shaped masses of 
 carbonate of lime termed stalactites. If you notice one of 
 these masses you will observe that occasionally a drop of 
 water falls from the end of it to the floor, or rather upon a 
 similar mass of carbonate of lime on the floor, exactly under- 
 neath that which hangs from the roof. The lower mass, 
 which appears to stretch up towards the upper one, is termed 
 a stalagmite. Occasionally the two masses meet one another 
 and unite to form a continuous column. The origin of 
 these masses these stalactites and stalagmites will readily 
 occur to you : the rain-water percolating through the rock 
 above the cave contains carbonic acid in solution, by which it 
 dissolves the carbonate of lime in the rock. As it drips from 
 the roof it gives up a portion of its carbonic acid to the air in 
 the cavern, and accordingly a portion of the carbonate of lime 
 is deposited ; the next drop runs over the mass so deposited, 
 
IV 
 
 Henry Cavendish 79 
 
 and by giving out another portion of dissolved carbonic acid 
 deposits another portion of carbonate of lime on the first 
 deposition ; and so the process goes on, each portion of water 
 from the roof running down the icicle of carbonate of lime 
 which is formed, and continually adding to its length. But the 
 drops fall off to the floor long before they have given up the 
 whole of their carbonic acid, and accordingly long before they 
 have yielded up all the chalk which they held in solution. 
 Accordingly the escape of the carbonic acid goes on from the 
 water after it has fallen on the floor, and so you get this 
 second deposit of carbonate of lime this stalagmite formed 
 underneath the stalactite. 
 
 Cavendish also showed that fixed air was considerably 
 heavier than common air by weighing a bladder filled first 
 with the one gas and then with the other. The fixed 
 air he found to be one-and-a-half times heavier than the 
 common air. 
 
 The old chemists, who in days gone by greatly busied 
 themselves to discover a more direct method of turning things 
 into gold than is practised by their successors in the chemical 
 arts, have left us some marvellous stories concerning the 
 behaviour of a gas which seems to be evolved from certain 
 metals when they are brought into contact with acids, such 
 as oil of vitriol, or muriatic acid. The exact nature of this 
 gas remained unknown until Cavendish investigated its 
 properties. This gas, which we now call hydrogen, is highly 
 inflammable, and Cavendish showed that, like many other 
 inflammable bodies, it cannot burn without the assistance of 
 common air. When mixed with rather more than double its 
 volume of air, it explodes violently on the approach of a light. 
 He also weighed this gas by the same method which he 
 had employed to weigh the fixed air, and he found it to be 
 eleven times lighter than common air. Cavendish, however, 
 under-estimated the lightness of this gas ; in reality it is about 
 fourteen-and-a-half times lighter than air. 
 
8o Henry Cavendish iv 
 
 When giving you an account of Priestley's work, I 
 described to you his method of analysing the air. It was 
 based on the fact that when the gas known as nitric oxide 
 comes in contact with air, the oxygen in the air combines 
 with the nitric oxide to form a product soluble in water. If 
 the mixture of gases is made in a tube standing over water, 
 the diminution in volume, consequent on the removal of the 
 oxygen, is a measure of the amount of that gas in the air. 
 As the quality of the air was supposed to depend upon the 
 diminution of volume which it suffered by being mixed with 
 nitric oxide, the instruments designed to make the tests were 
 termed eudiometers, from two Greek words denoting a "measure 
 of goodness." Without going into details I may say that this 
 method of analysis is liable to an objection from the cause 
 first worked out by our illustrious townsman, John Dalton, 
 that the same volume of oxygen can combine with different 
 volumes of the nitric oxide. This fact was indeed known to 
 Cavendish, and he made a great number of experiments in 
 order to ascertain the best method of mixing the gases so as 
 to obtain constant results. 
 
 By means of the apparatus he devised he was enabled to 
 show that the composition of the atmosphere is sensibly 
 constant. He tells us that " during the last half of the year 
 1781 I tried the air of near sixty different days . . . but 
 found no difference that I could be sure of, though the wind 
 and weather on those days were very various, some of them 
 being very fair and clear, others very wet, and others very 
 foggy." This conclusion is in harmony with the results of 
 later experimenters. The atmosphere has practically the same 
 composition all the world over, and all the year round. 
 Although there are slight variations in the relative propor- 
 tion of the constituents, methods of the highest precision 
 are required in order to detect them. Cavendish gives us 
 the numerical results of his experiments, and from these 
 it appears that, when expressed in the manner we now 
 
iv Henry Cavendish 81 
 
 adopt, the mean composition of the air is in 100 parts by 
 
 measure : 
 
 Oxygen .... 20'8 
 Nitrogen . . . 7 9 '2 
 
 The most refined analytical methods of modern times have 
 shown that the average numbers are 
 
 Oxygen .... 20'9 
 Nitrogen . . . .79-1 
 
 A result, you see, almost identical with that deduced from 
 Cavendish's observations, and one which illustrates in a very 
 striking manner the extreme care and accuracy with which 
 he worked. 
 
 Cavendish next proceeded to determine the cause of the 
 diminution in volume which common air occasionally suffers 
 when substances are caused to burn in it. 
 
 Among the many experiments which he made in order to 
 elucidate this matter there is one which is especially re- 
 markable, as it led him to his greatest discovery, that of the 
 composition of water a discovery which will make the name 
 of Cavendish for ever memorable. Dr. Priestley relates in 
 one of his volumes of Experiments and Observations on Air, 
 that when a mixture of common air and inflammable 
 air is exploded by the electric spark in a glass vessel, " the 
 inside of the glass, though clear and dry before, immediately 
 became dewy." "As this experiment," says Cavendish, 
 " seemed likely to throw great light on the subject I had 
 in view, I thought it well worth examining more closely." 
 Cavendish repeated this experiment in his characteristically 
 careful manner. The inflammable air and common air 
 were mixed in varying but known proportions, and the 
 diminution in volume which attended the explosion was 
 accurately noted in each case, and the amount of oxygen 
 remaining in the air was determined by the eudiometer. 
 Cavendish found that the greatest diminution of volume 
 
 G 
 
82 Henry Cavendish iv 
 
 occurred when two volumes of hydrogen were mixed with 
 five volumes of air. 
 
 He tells us that when this mixture is exploded, " 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." Cavendish continues : " The better to 
 examine the nature of this dew 500,000 grain measures of 
 inflammable air were burnt with about two-and-a-half times 
 that quantity of common air, and the burnt air made to pass 
 through a glass cylinder 8 feet long and f inch in diameter, 
 in order to deposit the dew. The two airs were con- 
 veyed 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 air nor common air can 
 burn by themselves, there was no danger of the flame spread- 
 ing into the magazines from which they were conveyed. . . . 
 By this means upwards of 135 grains of water were con- 
 densed in the cylinder, which had no taste nor smell, and 
 which left no sensible sediment when evaporated to dryness ; 
 in short, it seemed pure water. ... By the experiments 
 with the globe it appeared that when inflammable air and 
 common air are exploded in a proper proportion, almost 
 all the inflammable air and near one-fifth of the common 
 air lose their elasticity, 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." 
 
 Cavendish then repeated the experiment with pure oxygen, 
 or " dephlogisticated air," as this gas was then termed. I will 
 give you the result in his own words, for the account has a 
 great historical interest : "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 exhausted by an air- 
 pump, and then filled with a mixture of inflammable and 
 
iv Henry Cavendish 83 
 
 dephlogisticated 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 in water, and containing a mixture of 
 19,500 grain measures of dephlogisticated air, and 37,000 of 
 inflammable ; so that on opening 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 in it, 
 without any fresh exhaustion of the globe." Cavendish, how- 
 ever, found that in many of his trials the condensed water 
 was sensibly acid to the taste, and by saturation with alkali, 
 and evaporation, it yielded nitre. The search for the cause 
 of the formation of this acid led Cavendish to another dis- 
 covery namely, that of the composition of nitric acid, an 
 acid which is probably familiar to you under its old name of 
 spirits of nitre or aquafortis. He showed that the formation 
 of this acid was not an essential part of the process of the 
 union of the oxygen and hydrogen, but that it was due to the 
 presence of impurities in the gases used. Whenever the 
 amount of oxygen was larger than could combine with all the 
 hydrogen in the mixture, a portion of that oxygen united 
 with the nitrogen of the common air present, and so formed 
 the nitric acid. 
 
 Such, then, were the experiments which led to the discovery, 
 firstly, of the compound nature of water; secondly, of the 
 character of its constituents ; and thirdly, of the proportions 
 in which these constituents are combined together. It would 
 be impossible to over-estimate the value of this discovery : it 
 marks one of the great epochs in the history of chemistry. 
 
84 Henry Cavendish iv 
 
 Who could have predicted that this most familiar of all 
 liquids a liquid, too, long regarded as the very type of a 
 chemical element was composed of two colourless invisible 
 gases the one the inflammable hydrogen, the lightest sub- 
 stance known the other, oxygen, the life-sustaining principle 
 in the air we breathe nay, the element which has been styled 
 " the chemical centre in the scheme of nature " 1 
 
 Nearly every important discovery has to pass through two 
 ordeals it is first impugned as not true, and then as not 
 new; and this great discovery which I have ascribed to 
 Cavendish formed no exception to this rule. Not many years 
 ago there was a great controversy concerning the question 
 Who was the discoverer of the composition of water ? I am 
 not now going to rake up the matter, for it is gradually being 
 forgotten; but I think that every chemist now allows that 
 the claims of Cavendish have been incontestably proved. The 
 fact is the time was ripe for this discovery. Everybody 
 familiar with the chemical work of the latter half of the last 
 century will admit that the labours of a dozen of Cavendish's 
 contemporaries were tending more or less directly to the same 
 goal, and had Cavendish proved unequal to his opportunities 
 his grandest discovery would not have been long delayed. It 
 has been said that the discovery of law is regulated By law, 
 and the history of the discovery of the composition of water 
 affords a striking exemplification of the truth of this remark. 
 
 The time will scarcely allow me to tell you more of what 
 Cavendish did ; but, if I am not trespassing too much on your 
 patience, I should like just to mention another great work of 
 his, since any account of Cavendish's labours would be very 
 incomplete without some reference to it. An ancestor of 
 Cavendish's was one of the first to sail round the earth. 
 Cavendish himself was one of the first to attempt to weigh it. 
 Cavendish, in fact, undertook to determine how much heavier 
 the earth is than a sphere of water of equal size. The appar- 
 atus which he employed consisted of a long light wooden rod 
 
iv Henry Cavendish 85 
 
 suspended horizontally by a thin wire. At the ends of the 
 rod were leaden balls about two inches in diameter, and near 
 these could be brought two large spherical masses of metal. 
 By the mutual attraction of the balls, big and little, the long rod 
 was caused to move slightly. The amount of the deviation, 
 and the force necessary to produce it, being known, together 
 with the weight of the balls, and the distances from their 
 centres, the attraction of a sphere of water of the same 
 diameter as the earth upon the ball on its surface can be 
 calculated, from which can also be calculated the relation of 
 the earth's density to that of water. From his experiments, 
 Cavendish concluded that the earth is about five-and-a-half 
 times heavier than water a result which the subsequent 
 labours of Mr. Baily, made with extraordinary care and 
 patience, have shown to be very near the truth. It deserves 
 to be mentioned, however, that Newton, with that marvellous 
 insight which nowadays seems to us nothing less than divina- 
 tion, had predicted that the earth would be found to be 
 between five and six times heavier than water. 
 
 One more remark and I have done. A celebrated French 
 chemist, whose patriotism we admire scarcely less than his 
 genius, has declared that " Chemistry is a French Science, its 
 founder was Lavoisier, of immortal memory." The merit of 
 Lavoisier is undoubtedly great, and the influence which he 
 exerted on the development of chemistry was profound. It is 
 accounted the chief glory of Lavoisier that he first clearly pointed 
 out that the principles of gravitation lie at the basis of chem- 
 istry; that chemistry is in fact a science of quantitative relations. 
 But let us take a retrospect of Cavendish's labours. He fixed 
 the weight of the earth ; he established the proportions of the 
 constituents of the air ; he occupied himself with the quanti- 
 tative study of the laws of heat ; and lastly, he demonstrated 
 the nature of water and determined its volumetric composition. 
 Earth, air, fire, and water each and all came within the 
 range of his observations. Now, I ask you, what" is the 
 
86 Henry Cavendish 
 
 IV 
 
 most obvious peculiarity of all this labour 1 ? Is it not its 
 thoroughly quantitative character*? Weighing, measuring, 
 calculating; such, indeed, was pre-eminently the essential 
 nature of Cavendish's work. If, then, the claim of any one 
 to be styled the founder of chemistry as a science rests upon 
 his recognition of its quantitative relations, may we not also, 
 and with equal truth, say that " Chemistry is an English 
 Science its founder was Cavendish, of immortal memory ? " 
 
V 
 
 ANTOINE-LAUEENT LAVOISIER 
 
 CONTEMPORARY REVIEW, DECEMBER 1890. 
 
 " IL a ete assez heureux ou assez sage, pour que Ton ne sache 
 presqu'autre chose de lui, et qu'il n'y ait dans son histoire 
 d'autre incidens que des decouvertes." These words were 
 spoken by Cuvier, the perpetual secretary of the French 
 Academy, on the occasion of his doge on Cavendish, the dis- 
 coverer of the compound nature of water, who, in his old age, 
 had been elected a member of the Institute. At first sight 
 they may seem a mere paraphrase of a saying which has 
 become almost trite, but to those who heard them for the first 
 time they had a significance which must have been realised 
 with something like a pang. For at such a time, not one of 
 Cuvier's hearers could have been unmindful of 1794, or have 
 been unmoved by the recollection of a tragedy in which the 
 most illustrious of Cavendish's contemporaries, a man whose 
 life had been dedicated to the cause of humanity, and whose 
 services to science have reflected an imperishable lustre upon 
 France, was sacrificed to the blind fury of his countrymen. 
 Indeed, to the lively and sympathetic intelligence of such an 
 auditory, quickened as it must have been by the singular^ 
 charm of the speaker's style, his profound sensibility, and 
 rhetorical skill, the strong dramatic element in the situation 
 
88 Antoine- Laurent Lavoisier v 
 
 could hardly have remained unperceived. Lavoisier and 
 Cavendish were, in a sense, national types ; they were, too, 
 when at the summit of their intellectual power, the ac- 
 knowledged representatives of two opposing schools of thought. 
 Both were aristocrats, and both, from being poor, became very 
 rich : Cavendish, indeed, was, as M. Biot has said, " le plus 
 riche de tous les savans et probablement aussi le plus savant de 
 tous les riches." But here the resemblance ends : in character, 
 temperament, and genius, in everything that constitutes 
 individuality, the men were as wide asunder as the poles. 
 Cavendish has been described by his biographer Wilson as the 
 most passively selfish of mortals a sort of scientific anchorite, 
 who maintained, during the fourscore years of his existence, 
 a rigid, undeviating indifference to the affairs of his fellow- 
 men. This embodiment of a clear, cold, passionless intelli- 
 gence was dead to every aesthetic sense, and had no element 
 of anything that was enthusiastic or chivalrous in its composi- 
 tion. To Cavendish science was, in truth, measurement. 
 " His Theory of the Universe," says Wilson, " seems to have 
 been that it consisted solely of a multitude of objects which 
 could be weighed, numbered, and measured ; and the vocation 
 to which he considered himself called was to weigh, number, 
 and measure as many of these objects as his allotted three- 
 score years and ten would permit. He weighed the Earth ; he 
 analysed the Air; he discovered the compound nature of 
 Water ; he noted with numerical precision the obscure actions 
 of the ancient element, Fire." But all this work was done 
 primarily for himself, and to satisfy the questionings of his 
 own intelligence. To give the results of it to the world 
 was hardly a part of his plan, for he cared nothing for the 
 world, and was absolutely indifferent to the interests or judg- 
 ment of his fellows. And yet Cavendish was revered, even 
 if he was not loved, during his long and uneventful life, 
 and at his death was laid to rest with every mark of 
 honour and respect in the splendid tomb which his ances- 
 
v A ntoine- Laurent Lavoisier 89 
 
 tress, Elizabeth Hardwicke, had built for herself and her 
 descendants. 
 
 On the other hand, Lavoisier was a man in whom the 
 elements were kindly mixed. No one could more truly say of 
 himself, " Homo sum : humani nihil a me alienum puto." 
 He was ardent, enthusiastic, fond of the society of his fellows, 
 a man of generous impulses, of catholic tastes, and of lofty 
 aims. As a philosopher his influence throughout Europe was 
 supreme, and the manner in which his renown was won was 
 of a kind to strike the national imagination and to minister 
 to the national pride. At the zenith of his fame he was as 
 much a Dictator in the world of science as Napoleon became 
 in the world of politics. But in the very plenitude of this 
 power he was struck at by Fouquier-Tinville, and he who had 
 laboured unceasingly for the glory and well-being of his 
 country was declared guilty of complicity in a conspiracy 
 " against the French people tending to favour by all possible 
 means the success of the enemies of France." Lavoisier's 
 crime was that he had been a Fermier-gMral. He was 
 accused, in the words of the indictment, " of adding to tobacco 
 water and other ingredients detrimental to the health of the 
 citizens." It was a feeble enough weapon to throw even at a 
 Fermier-gdn'eral, but it was thrown with terrible effect. Even 
 to be suspected of tampering with the tobacco of a " citizen " 
 sufficed for the tribunal before which he was brought, although 
 it taxed the ingenuity of Liendon to show how this alleged 
 sophistication brought the accused within the same section of 
 the penal code that swept the Dantonists to the scaffold. 
 Coffinhal, the Vice-President of the Tribunal, pronounced the 
 judgment: "The Eepublic has no need of men of science," 
 and within twenty-four hours the tumbrel was on its way to 
 the Place de la Kevolution, and, as the proems-aerial sets forth, 
 "sur un 6chaffaud dresse* sur la dite place, le dit Lavoisier, en 
 notre presence, subi la peine de mort." Well might Lagrange 
 say to Delambre : " It required but a moment to strike off 
 
Antoine- Laurent Lavoisier 
 
 this head, and probably a hundred years will not suffice to 
 reproduce such another." l 
 
 The main events in the scientific career of the great French 
 chemist are tolerably well known, and his position in the 
 history of the development of chemistry is now fully assured. 
 The story of his scientific life has recently been told by 
 M. Berthelot with all the charm and tact which characterise 
 the dloges which it is the duty of the secretaries of the 
 Academy from time to time to prepare. Although English 
 men of science may think that M. Berthelot occasionally fails 
 to mete out the strict justice to their countrymen that 
 historical accuracy demands, there cannot be a doubt, in spite 
 of all legitimate deductions, that Lavoisier remains the 
 dominant figure in the chemical world of the last century. 
 There is much, however, in his life and work, and especially 
 in the circumstances which led to his untimely death, on 
 which we would gladly have more information. Amongst 
 the crop of literature which the centenary of the Eevolution 
 has brought forth in France, the historian of science has 
 welcomed, therefore, with special interest, the admirable 
 monograph on Lavoisier which we owe to the patient industry 
 and patriotic zeal of Professor Grimaux. 2 
 
 It must have struck many people, as M. Grimaux tells us 
 it has struck him, that, in spite of the glory which surrounds 
 the name of Lavoisier, it is remarkable that the life of the 
 creator of modern chemistry had still to be written. Beyond 
 the short biographical notices by Lalande, Fourcroy, and 
 Cuvier, which deal mainly with Lavoisier as a man of science, 
 we know practically nothing of the story of a life which was 
 
 1 The Republic, a few months afterwards, found also that it had no need 
 of Coffinhal : he fell with Robespierre, and was guillotined on the 18th ther- 
 midor of the year II. Fouquier-Tinville and some half dozen others who 
 had been concerned in the trial of Lavoisier were also brought to the scaffold 
 at about the same time. 
 
 2 Lavoisier, 1743-1794. "D'apres sa correspondance, ses manuscrits 
 ses papiers de famille, et d'autres documents inedits." Par Edouard Grimaux. 
 Paris : Felix Alcan, 1888. 
 
v Antoine- Laurent Lavoisier 91 
 
 wholly devoted to the public good. Even the world of 
 science knows scarcely anything of his private life, of his 
 virtues, of his intelligent philanthropy, and of the services 
 which he rendered to his country as an academician, an 
 economist, an agriculturist, and a financier. Luckily for his 
 biographer, Lavoisier was a man of perfect method, and he 
 preserved all his manuscripts without exception. After his 
 death these papers were religiously guarded by Madame 
 Lavoisier, from whom they passed to Madame Leon de 
 Chazelles, her grandniece. This, together with other material 
 preserved at the Chateau de la Caniere, where also are kept 
 Lavoisier's books and instruments, has served M. Grimaux 
 as the basis of his book. In addition, he has searched through 
 the public archives, with the result that we have now presented 
 to us for the first time the details of Lavoisier's political life 
 and the true story of his trial and condemnation. 
 
 Antoine -Laurent Lavoisier was born in Paris on 26th 
 August 1743. His father, -Jean- Antoine, was an advocate ; 
 his mother, nfo Punctis, died when he was five years old, and 
 he and a young sister, who only lived a few years, were taken 
 charge of by the grandmother and her daughter, Mdlle. 
 Constance Punctis. The family was rich, and was able to 
 send the young Antoine to the College Mazarin, where he 
 seems to have acquired that passion for natural science which 
 was the motive power of his life. He studied mathematics 
 with the Abbe La Caille, well known for his measurement of 
 an arc of the meridian at the Cape of Good Hope, and for his 
 determination of the length of a seconds pendulum ; he learnt 
 botany from Bernard de Jussieu, and geology and mineralogy 
 from Guettard. But it was principally by Rouelle's teaching 
 that the particular direction of Lavoisier's scientific activity 
 was shaped. Guillaume-Fra^ois Rouelle is mainly re- 
 membered by chemists to-day as having just missed the 
 discovery of the Law of Combination by Definite Proportions. 
 By his contemporaries he was considered to have said 'more 
 
92 Antoine-Laurent Lavoisier v 
 
 "good things" than any man of his time. In spite of his 
 oddities he exercised an extraordinary influence as a teacher ; 
 his lecture-room at the Jardin du Roi was crowded by 
 auditors from all parts of Europe, and among his pupils were 
 Macquer, Bucquet, d'Arcet, and Lavoisier, the men who were 
 destined to make the end of the eighteenth century one of the 
 most stirring epochs in the history of chemistry. 
 
 Lavoisier was originally intended for the profession of the 
 law, and actually became a licentiate in 1764, but at the 
 instigation of Guettard, whom he accompanied in his journeys 
 through France, and to whom he was of assistance in the 
 preparation of his great Mineralogical Atlas, he abandoned 
 that career and gave himself up to science. In 1765 he sent 
 his first paper to the Academy a modest enough communica- 
 tion on gypsum, but noteworthy as giving for the first time 
 the true explanation of the setting of plaster of paris, and of 
 the reason that overburnt gypsum will not rehydrate. 
 
 In the following year he was awarded a medal by the 
 Academy for an essay on the lighting of large towns, and in 
 the same year he was placed upon the list of candidates for 
 election into that august body. The Academic des Sciences 
 has suffered frequent internal changes, but in the middle of 
 the eighteenth century it was subject to the constitution of 
 1699, as modified in 1716. It was composed of members of 
 very different orders, enjoying very unequal rights. There 
 were twelve honorary members chosen from among the great 
 nobles, and from whom were selected the president and vice- 
 presidents ; eighteen pensionaries, twelve associates, and twelve 
 adjoints distributed among the geometers, astronomers, mecha- 
 nicians, chemists, and botanists ; in addition there were a 
 number of free associates, superannuated associates, and 
 pensionaries. The honorary members and the pensionaries 
 had alone a deliberative voice in the elections, and in the 
 business of the Academy. The two associates in the class in 
 which there was a vacancy were, however, called upon, in 
 
v Antoine- Laurent Lavoisier 93 
 
 company with three pensionaries, to draw up the list of 
 candidates. The adjoints had practically no privileges beyond 
 that of sitting next to an associate when there was room ; at 
 other times they sat upon the benches placed behind the arm- 
 chairs of the associates. 
 
 The 18th of May 1768, when the young Lavoisier gained 
 his seat upon the back benches, was a red-letter day in the 
 history of the house of Punctis. It was no less important 
 in the history of the Academy, for the young adjoint was 
 destined to be its champion and do battle for its existence 
 during the dark and terrible time of the Kevolution. 
 Lavoisier's extraordinary power of work, his intellectual 
 keenness, and range of knowledge, were quickly recognised, 
 and in spite of his youth he was charged with the preparation 
 of numerous Reports. This part of an academician's duty 
 was as difficult and irksome as it was delicate. During the 
 twenty-five years of his connection with the Academy he 
 contributed upwards of two hundred reports on such dis- 
 connected matters as the theory of colours, the areometer of 
 Cartier, modes of determining longitudes, arm-chairs for 
 invalids, prison reform, water supply, the cold of the winter 
 of 1776, the pretensions of Mesmer, the aerostatic inventions 
 of Montgolfier, the imposture of the divining-rod, etc., etc. 
 
 Almost immediately after Lavoisier had thus planted his 
 foot on the ladder of fame, he set it unconsciously on the first 
 step of the scaffold. Adjoint of the Academic des Sciences, 
 he now became adjoint of the Ferme-gSndral. His friends, 
 the academicians, looked somewhat askance at this action. 
 Lalande tells us that in his election they had been influenced 
 by the consideration that a young man of parts and activity, 
 whose private means placed him beyond the necessity of 
 seeking another profession, would naturally be useful to 
 science, and they now feared that the new duties would clash 
 with what they imagined was to be the real work of his 
 life. But, luckily, there are always some to offer consola- 
 
94 Antoine- Laurent Lavoisier 
 
 tion. " Tant mieux ! " said the geometer Fontaine, " the 
 dinners that he will give us will be all the better.'' Although 
 Lavoisier had inherited his mother's fortune, it was hardly 
 sufficient for the career which he now planned for himself, 
 and by the advice of a friend of the family, M. de La 
 Galaiziere, he became adjoint of the Fermier-g6neral Baudon, 
 in return for a third of his interest in the lease of Alaterre. 
 
 But there were doubtless other reasons for the disapproval 
 of the Academy. The Ferme-g6n6ral was a part of the rotten 
 financial system which ultimately landed France in disaster. 
 It was a company of financiers, to whom the State conceded, 
 for a fixed annual sum, payable in advance, the right of 
 collecting the indirect taxes of the country. Created 
 originally by Colbert, its constitution and functions were 
 modified by successive finance-ministers during the reigns of 
 Louis XIV. and Louis XV., as the will of the King, or the 
 exigencies of the national Exchequer determined. At the 
 time that Lavoisier entered it, the number of the Fermiers- 
 gendmux was sixty, and the sum to be paid in advance for the 
 lease of six years was 90,000,000 livres, together with a 
 douceur of 300,000 livres for the Controller-General. The 
 Fermiers-gSndraux received sums on account during the con- 
 tinuance of the lease, but the actual result of the speculation 
 was known only at its expiration. They had to bear all the 
 expenses of management and collection, to enforce the customs 
 and excise regulations, and their profits were subject to all 
 sorts of rebates, perquisites, pensions, and pots-de-vin. It need 
 hardly be said that in the time of the Grand Monarch and his 
 worthy great-grandson, the Ferine was a very hot-bed of 
 jobbery, corruption, and malversation. There existed no 
 public audit ; none, indeed, was possible. Even the Finance 
 Minister could gain but little information of the details of its 
 monetary transactions. In 1774, Terray, towards the con- 
 clusion of the first lease in which Lavoisier was interested, 
 addressed a confidential inquiry to the Fermiers-ge'ne'raux as to 
 
Antoine- Laurent Lavoisier 95 
 
 the number of beneficiaries which the will of the Court, i.e. 
 the king or his mistresses, had imposed upon the Ferme-gdndraL 
 Through the indiscretion of a clerk the list was made public. 
 Paris was scandalised to learn that the pensions alone 
 amounted to upwards of 400,000 livres annually. In 
 addition, the king secured a sixtieth share of the property 
 of the Ferme ; his sisters and aunts disposed of 50,000 livres ; 
 the nurse of the Duke of Burgundy, 10,000 livres ; Madame 
 Du Barry's physician, 10,000 livres ; the Abbe Voisenon, 3000 
 livres ; a court singer, 2000 livres ; and so on. Altogether, 
 the Court and its creatures netted in this way fourteen- 
 sixtieths of the proceeds of the lease of Alaterre. Many of 
 the Fermiers-gdneraux themselves outraged public opinion by 
 their prodigality and the luxury of their hotels and petites- 
 maisons. The organisation was detested throughout the 
 length and breadth of France. The peasants, too far from 
 the capital to hear the curses which Mercier flung at the 
 Hotel des Fermes, were constantly witness of the hardships it 
 inflicted, and the terrible retribution which followed any 
 contravention of its decrees. The taxes were most unequally 
 levied; each province had its own frontier, and to a population 
 impoverished and on the verge of starvation there was every 
 temptation to smuggle ; conflicts with its officers were of 
 almost daily occurrence ; no house was safe against domiciliary 
 visits, and hundreds of persons were yearly sent to the galleys 
 for the most trifling acts of contraband. It is true there was 
 the Court des aides, to which the peasant might appeal against 
 the imposition of the Ferme, but too frequently he found that 
 the " gratuitous justice " thus dealt out to him meant only 
 "justice by gratuities." Nor was it only on the frontiers 
 that smuggling prevailed. It was calculated that at least 
 one-fifth of the merchandise that entered Paris was contraband. 
 To render the collection of the octroi more certain, and to 
 check irregularities, the Ferme proposed to surround the city 
 with a wall. Public feeling against the project was intense. 
 
96 Antoine- Laurent Lavoisier v 
 
 A wit of the period declared that " le mur murant Paris rend 
 Paris murmurant." Military opinion also was adverse to 
 the proposal ; the Duke de Nivernais, a Marshal of France, is 
 reported to have said that its author deserved hanging from 
 one of his own towers ; and Marat subsequently denounced 
 Lavoisier as the originator of what the citizens were taught to 
 regard as an ingenious method of robbing them of the pure 
 air of the country. 
 
 There were, of course, honest Fermiers-gSndram men like 
 Delahante, Paulze, d'Arlincourt, and others, and Lavoisier was 
 of the number, who discharged their trust honourably, and 
 who sought to introduce order and good management into 
 the affairs of the society. With the advent of the better 
 times which the beginning of the reign of Louis XVI. seemed 
 to promise, and under the administration of Turgot, the 
 character of the Ferme-g6n6ml improved. With each new 
 lease the position and influence of Lavoisier was strengthened, 
 until, in 1703, he was placed by d'Ormesson upon the Com- 
 mittee of Administration, the most important of the whole, 
 and the only one which had direct relations with the Govern- 
 ment. He was thus enabled to remedy many abuses, and to 
 mitigate in various ways the burden of imposition under 
 which France groaned. But it was too late. Nothing the 
 Ferme, could do would ever wipe out the memories of its 
 exactions. With the growth of Lavoisier's power and influ- 
 ence in the Ferme, the odium with which it was regarded 
 seemed gradually to concentrate itself upon him. His rectitude, 
 his public services, the purity of his private life, the splendour 
 of his scientific achievements, were unheeded. In the day 
 of reckoning he was remembered only as Lavoisier the 
 Fermier-gdneral. 
 
 M. Grimaux has been at considerable pains to lay the de- 
 tails of Lavoisier's connection with the Ferme-g6neml before 
 us. He estimates that, in all, he acquired, from 1768 to 178 6, 
 nearly 1,200,000 livres. He continued to be a member of the 
 
v Ant oine- Laurent Lavoisier 97 
 
 Ferme until it was suppressed by a decree of the National 
 Assembly in 1791, when its liquidation was confided to six of 
 his colleagues. 
 
 Lavoisier's success in administration induced Turgot to 
 consult him on the means of ensuring a regular supply of gun- 
 powder for the service of the State. Prior to Turgot's 
 Ministry the manufacture of the gunpowder required for the 
 national defence was entrusted to a financial company, with 
 the result that, on more than one occasion, France was 
 obliged to sue for peace from inability to provide herself with 
 the munitions of war. The Ferme des Poudres was managed 
 solely in the interest of its members : waste, peculation, and 
 jobbery were as rampant as in the old days of the Ferme- 
 gtin&ral. Turgot changed all this. In 1775 he created the 
 Regie des Poudres and nominated four commissioners, who 
 should be directly responsible to the State for the manufacture 
 of gunpowder. Lavoisier is expressly named as one of the 
 commissioners, as being known, not only for his chemical 
 knowledge, so necessary for administrative work of this kind, 
 but also for the diligence, capacity, and honesty with which 
 he discharged his duties as a Fermier-ge'ne'raL At his suggestion, 
 Turgot invited the Academy to offer a prize for the best 
 essay on the economical production of saltpetre, with a view of 
 obtaining information on the modes of manufacture practised 
 in various parts of Europe. No detail of administration was 
 too minute to escape his attention. He regulated the con- 
 ditions under which the employe's were selected ; he simplified 
 the methods of manufacture and refining of saltpetre, and by 
 successive improvements in composition and modes of mixing 
 he greatly increased the ballistic properties of gunpowder. 
 He who was condemned in 1794 as an enemy to his country 
 was in 1780 recognised as having contributed to its triumphs 
 by augmenting the force of its arms. At times the exercise of 
 his duties placed him in considerable danger, as, for example, 
 in the explosion which resulted in the experiments made to 
 
 H 
 
98 Antoine- Laurent Lavoisier v 
 
 introduce Berthollet's newly discovered chlorate of potash in 
 the place of nitre. But no gunpowder-mill under Lavoisier's 
 charge was half so explosive as Paris in 1789. The events of 
 July had demoralised the city, and it was only too ready to 
 give heed to the slanders and coarse invective of the Plre 
 Duchesne of Marat and of other self-styled "Friends of the 
 People." The air was full of plots and counter-plots. An 
 order to transport some gunpowder was maliciously miscon- 
 strued ; the report was spread that it was vto be given to the 
 enemies of the . nation, and Lavoisier and his fellow-commis- 
 sioner, Le Faucheux, nearly fell victims to an angry mob 
 which surged round the gates of the arsenal. 
 
 Lavoisier's journey ings through France in connection with 
 the work of the Mineralogical Atlas and as a Fermier-gtndral, 
 had taught him much concerning the life of the peasajit. In- 
 deed, no Frenchman of his time knew his country better, or 
 was more keenly alive to the vast economic movement which 
 was slowly gathering strength during the latter half of the 
 eighteenth century. His interest in this movement was no 
 doubt quickened by, even if it did not originate in, his con- 
 nection with the Ferme. It was obvious to him that the 
 whole fiscal system of the country fell with the most crushing 
 effect upon the class least able to bear it, and in the numerous 
 commissions in which he took part he repeatedly indicated the 
 economic disadvantages with which the cultivators of the soil 
 had to contend. In 1785 he became a member, and immedi- 
 ately afterwards secretary of the Committee of Agriculture 
 a consultative body created by Calonne for the purpose of 
 enlightening the controller-general on agronomic matters in 
 general. Lavoisier not only held the pen ; he was the direct- 
 ing spirit of the Committee. He drew up reports and in- 
 structions on the cultivation of flax, of the potato, on the 
 liming of wheat ; he prepared a scheme for the establishment 
 of experimental farms, and for the collection and distribution 
 of agricultural instruments, for the better adjustment of the 
 
v Antoine- Laurent Lavoisier 99 
 
 tithes and of the rights of pasturage, etc. He was no mere 
 theorist in these matters. In 1778, when he acquired the 
 demesne of Frechines, the condition of the peasant was 
 wretched in the extreme. Cultivated grazing land was un- 
 known ; the farmers, from the impossibility of feeding their 
 cattle during the winter, had but few beasts ; the fields were 
 unmanured ; and the yield of corn, even in the best years, was 
 only about five times the weight of the seed. With a view of 
 demonstrating how much might be done by improved methods 
 of tillage, he decided to make trials on above 80 hectares 
 of the worst land on the demesne ; and he divided about 240 
 hectares into three farms, of which he directed the cultivation 
 with all the precision of laboratory trials. He introduced the 
 cultivation of the beetroot and potato, hitherto unknown in 
 the Blesois. He improved the breed of sheep by the importa- 
 tion of rams and ewes from Spain, and that of cows by the 
 introduction of animals from the model farm of Chanteloup. 
 In 1788, when he presented to the Society of Agriculture the 
 results of his ten years' experience, he again set forth the 
 various disadvantages under which the cultivator laboured 
 short leases, insecurity of tenure, want of capital, and of 
 credit; and he made a strong appeal to the proprietors to 
 spend more on the amelioration of their land in order to im- 
 prove the condition of those who were obliged to live upon 
 it. Each succeeding year saw a change for the better in the 
 lot of the peasants at Frechines. In 1793 the crop of 
 wheat had doubled itself, and was more than ten times the 
 weight of the seed, and the number of beasts on the estate 
 had increased fivefold. In the following year came the end, 
 but the memory of the man who was a veritable father of his 
 people is still cherished in the district of Blois. 
 
 Lavoisier's position as a landed proprietor was doubtless 
 the cause of his selection as a member of the Assembly of the 
 Orleanais, a sort of County Council created in 1787, accord- 
 ing to a plan devised by Necker during his first administration. 
 
ioo Antoine-Laurent Lavoisier v 
 
 It was composed of twenty-five members selected by the king, 
 six for the clergy, six for the nobility, and twelve for the 
 third estate, together with the Duke of Luxembourg as presi- 
 dent. The twenty-five so nominated were directed to elect 
 an equal number of colleagues, the same proportion being 
 observed for the three orders. The duties of the Assembly 
 were to determine the modes of levying the taxes, to under- 
 take the construction and maintenance of the highways, and 
 to consider how the commerce and industry of the province 
 might best be developed. Lavoisier, although an esquire, was 
 chosen as a member of the third estate, and he at once became 
 the leader of that section. In the town library of Orleans are 
 preserved the minutes of the Provincial Assembly, together 
 with such of the manuscripts of Lavoisier as relate to its busi- 
 ness. During the greater part of its existence the Assembly 
 was engaged in attempts to settle the mode of incidence and 
 collection of the taxes. The third estate demanded the aboli- 
 tion of the exemptions enjoyed by the nobles ; the substitution 
 of a fixed subscription for the tithes, which fell with especial 
 severity on the smaller proprietors ; and the abolition of the 
 corvfo, which compelled the peasants to undertake the con- 
 struction and maintenance of the roads. On all these questions 
 Lavoisier was the mouthpiece of his order. He also intro- 
 duced schemes for the founding of saving and discount banks, 
 workhouses, and insurance societies, for the creation of nursing 
 establishments, for the formation of canals, and for the ex- 
 ploitation of the mineral productions of the province. " Celui 
 qui fait tout, qui anime tout, qui se multiplie en quelque sorte, 
 c'est Lavoisier; son nom reparait a chaque instant." 1 
 
 Few, if any, of these projects were realised. The Pro- 
 vincial Assemblies might initiate, but they were power- 
 less to execute, and in 1790 they became merged into 
 the States-General, to which Lavoisier was sent as D6putt 
 suppUant for the bailiwick of Blois, having for his colleague 
 1 Leouce de Lavergne, Les Assemblies Provinciales. 
 
v Antoine-La^t,rent Lavoisier 101 
 
 the unfortunate Vicomte de Beauharnais, whose widow, 
 Josephine Tascher de la Pagerie, became the wife of Bona- 
 parte. In the same year he was elected a member of the 
 Commune of Paris, and of the famous club of 89, of which he 
 was ultimately secretary. This institution, which sought to 
 develop, defend, and propagate the principles of constitutional 
 liberty, numbered amongst its adherents all who were eminent 
 in art, literature, science, and politics in France. It had, 
 however, but little influence on the main currents of political 
 thought, and absolutely none on the political -action of 
 the time; it dealt too largely with questions of political 
 metaphysics to stem the forces which ultimately gained an 
 overwhelming strength. It ended by being suspected of 
 " aristocratism," and it became a crime to have been one of its 
 members. At the beginning of 1794 the Jacobins expelled 
 from their club all who had been part of the Society of 89 as, 
 ipso facto, guilty of "incivism." 
 
 Dark clouds were now rapidly gathering ; the days of the 
 Great Terror were approaching, and Lavoisier found himself 
 menaced on every side. The first attack came from Marat. 
 Marat had sought, at the outset of his career, to make a name 
 in science by publishing a Treatise on Fire, full of the crudest 
 and most ridiculous speculations on the nature of combustion, 
 and which he caused the Journal de Paris to announce had 
 been received with approbation by the Academy. The state- 
 ment was absolutely baseless, and Lavoisier, as director of the 
 Academy, said so in a few disdainful words. Marat now 
 vented his rage on the Academy, and in a miserable pamphlet 
 traduced men like Laplace, Monge, and Cassini, accusing them 
 of malversation, and of spending in disgraceful orgies the sums 
 voted for the study of aerostation. But it was specially on 
 Lavoisier that he concentrated all his venom and rancour. 
 "Lavoisier, the putative father of all the discoveries which 
 are noised abroad, having no ideas of his own, fastens on those 
 of others ; but, incapable of appreciating them, he abandons 
 
iO2 Antoine-Laurent Lavoisier v 
 
 them as readily as he adopts them, and changes his systems as 
 he does his shoes ! " 
 
 In his paper, the Ami du Peuple, he is even more furious : 
 
 I denounce this Corypheus of the Charlatans, Sieur Lavoisier, 
 son of a land-grabber (grippe-sol), chemical apprentice, pupil of the 
 Genevese stock-jobber, fermier-general, regisseur of powder and 
 saltpetre, administrator of the Discount Bank, secretary of the 
 king, member of the Academy of Sciences. . . . Would to heaven 
 that he had been strung to the lamp-post on the 6th of August. 
 The electors of La Culture would then not have to blush for having 
 nominated him. 
 
 At the same time, Lavoisier, as Fermier-gdndral, was the 
 object of repeated and violent attacks in the journals and in 
 various political clubs. The leaders of the Revolutionary 
 party, who clamoured for the abolition of all State control 
 over the manufacture of war material, denounced his admini- 
 stration at the E6gie des Po r i(dres l and he was shortly afterward 
 removed by the National Assembly. The king, however, so 
 far intervened in his behalf as to order that he should be 
 allowed to remain in undisturbed possession of his rooms in 
 the Arsenal, where he had established a laboratory, on which 
 he had expended a large portion of his private fortune. He 
 had been appointed a member of the National Treasury in 
 1791, but in 1793, to the regret of his colleagues, he requested 
 to be relieved of his functions. In truth, the strain of a 
 constant anxiety was beginning to re-act upon him ; he was 
 becoming weary of the incessant struggle against enemies who 
 were as vindictive as they were unscrupulous, and longed for 
 the peace and quietude which he found only in his laboratory. 
 To have property was, in the eyes of the Eevolutionary 
 tribunals, to be guilty of "incivism"; and "incivism" was a 
 crime against the Republic. Lavoisier told Lalande that he 
 expected to be stripped of everything, but he added he was 
 not too old to work, and he would begin life again as an 
 apothecary. 
 
v Ant oine- Laurent Lavoisier 103 
 
 On quitting the Treasury, he was re-appointed to the 
 Bfyie des Poudres, hut a few months afterwards he resigned 
 the position, although he engaged to continue his studies on 
 the manufacture of powder, and on the methods for the 
 analysis of nitre. It is possible that he may have had some 
 warning of what followed. Three days after his resignation, 
 a commission of the Assembly suddenly entered the Arsenal, 
 placed the papers under seal, and ordered the removal of the 
 commissioners to La Force. The elder Le Faucheux, one of 
 Lavoisier's colleagues, enfeebled by age and infirmities, killed 
 himself in despair, and the son was thrown into prison. 
 
 But however desirous Lavoisier might have been to relin- 
 quish political life, it was impossible for him to escape from the 
 penalties and responsibilities of his position. In 1791 he had 
 been named secretary and treasurer of the famous Commission 
 of Weights and Measures, which had undertaken to realise the 
 long-cherished idea of supplying France and the world with 
 an international system of weights and measures based upon 
 a natural unit. He was not only the administrative officer of 
 the Commission ; he contributed to the nomenclature of the 
 system, and took a prominent part in directing the determina- 
 tion of the various physical constants on which the measure- 
 ments ultimately rested, and especially in the determination 
 of the weight of the unit volume of water, on which the value 
 of the standard of mass was based. The project had to be 
 carried out under conditions which could not possibly have been 
 more disadvantageous. Its realisation largely depended on the 
 cordial co-operation of other nations, and the work of measure- 
 ment could only properly be conducted at a time of peace. 
 France was torn and distracted by internal dissensions ; her 
 national credit was gone ; and she was threatened on all sides. 
 Delambre has left us an account of the extraordinary diffi- 
 culties and dangers under which the geodetical observations 
 were executed. Lavoisier's work in Paris as treasurer was 
 hardly less onerous or less hazardous. The project was more 
 
104 Antoine- Laurent Lavoisier v 
 
 than once imperilled by the vacillating action of the Con- 
 vention. The sums voted by the Assembly were not always 
 forthcoming from the Treasury, and Lavoisier was occasionally 
 under the necessity of depending upon his own means, or his 
 private credit, for the money which Mechain required in order 
 to extend the measurement of the arc to Barcelona. 
 
 Doubtless, much of the difficulty was due to the attitude 
 of the Convention towards the Academy. In turn with every 
 monarchical institution of the time, the Academy was suspected 
 of " incivism," and its destruction was already being compassed. 
 Lavoisier, who had been named treasurer in succession to 
 Tillet, whose long illness had thrown the financial affairs of 
 the learned body into confusion, now found himself confronted 
 with new troubles. The salaries of the Academicians, many 
 of whom were old men, and in straitened circumstances, were 
 in arrears. Lavoisier was again under the necessity of ad- 
 vancing money from his private purse in certain of the more 
 urgent cases. The Society continued to hold its meetings as 
 usual until the spring of 1792, when an unexpected motion by 
 Fourcroy revealed to the Academicians the danger in Avhich 
 they stood. Fourcroy demanded that the Academy should 
 expel such of its members as were known for their " incivism." 
 The motion was resisted on the ground that the Academy had 
 no concern with the political opinions of its members : the 
 progress of science was its sole business. Fourcroy insisted 
 on his motion, when the geometer Cousin found the way of 
 escape from a position which it was evident had been most 
 skilfully chosen, by proposing that the question should be 
 submitted to the Minister, who would make such erasures 
 from the list as he thought necessary, whilst the Academy 
 should continue to pursue its more intellectual occupations. 
 
 This suggestion was adopted, but Fourcroy was not a man 
 to submit tamely to a rebuff, and the Academy soon felt the 
 effect of his resentment. Although the responsible Ministers 
 of the Government still recognised it as the intellectual centre 
 
v Antoine-La^irent Lavoisier 105 
 
 of France, its enemies within the Convention were unceasing 
 in their efforts to overthrow it. The outlook was gloomy in 
 the extreme. The shadow of its impending doom seemed to 
 hang over its meetings. We find at this time in its minutes 
 no mention of the members present, nor of the discussions in 
 which they engaged. Even during the dark days of 1793, 
 Lavoisier, active, hopeful, and courageous as ever, strained 
 every nerve to maintain the continuity of its work ; he was 
 the life and soul of the Society, and the ever-watchful guardian 
 of its interests. Together with Haiiy and Borda he laboured 
 incessantly at the work of the Commission. He obtained for 
 Vicq d'Azir 8400 livres for the continuation of his treatise on 
 human and comparative anatomy ; Jeurat received 300 livres 
 for the calculations for his new lunar tables ; Berthollet the 
 100 louis which he required for his work on applied chemistry. 
 Even Sage, one of the most bitter opponents of the new 
 chemistry, and Fourcroy still obtained the money which they 
 needed for the prosecution of their investigations. He exerted 
 all his influence with Ministers, with the administrators of the 
 Directory, and with the commissioners of the Treasury, to 
 induce the Government to fulfil its obligations towards the 
 Academy. The eloquence of Gregoire, and the courage of 
 Lakanal for a time averted the final blow, but the enemies of 
 the Academy eventually found they had a majority in the 
 Convention, and they hastened to make use of it. The 
 painter David pronounced the doom of all the learned 
 societies of France, and on August 8, 1793, the Convention 
 decreed their suppression. 
 
 Fourcroy had triumphed ; too timorous to work in the 
 open, he had been the unseen power behind the Convention 
 which had steadily undermined the influence of the Academy, 
 and had at length effected its destruction. Still Lavoisier did 
 not despair. He appealed to the Committee of Public Instruc- 
 tion to allow the members of the Academy to continue their 
 labours, and he entreated that the work of the Commission of 
 
io6 Antoine-Laurent Lavoisier v 
 
 Weights and Measures might not be interrupted. True to his 
 trust, he pleaded for those of his colleagues who had been 
 reduced to poverty by the decree of the Convention : 
 
 It is unnecessary to add, citizens, that the continuance of their 
 salaries to those who have earned them is demanded by justice ; 
 there is not an academician who, if he had applied his intelligence 
 and means to other objects, would not have been able to secure a 
 livelihood and a position in society. It is on the public faith that 
 they have followed a career, honourable without doubt, but hardly 
 lucrative. Many of them are octogenarians and infirm ; several of 
 them have spent their powers and their health in travel and 
 investigations undertaken gratuitously for the Government ; the 
 sense of rectitude of Frenchmen will not allow the nation to 
 disappoint their hopes ; they have at least an absolute right to the 
 pensions decreed in favour of all public functionaries. . . . 
 Citizens, the time presses ; if you allow the men of science who 
 composed the defunct Academy to retire to the country, to take 
 other positions in society, and to devote themselves to lucrative 
 occupations, the organisation of the sciences will be destroyed, and 
 half a century will not suffice to regenerate the order. For the 
 sake of the national honour, in the interests of society, as you 
 regard the good opinion of foreign nations, I beseech you to make 
 some provision against the destruction of the arts which would be 
 the necessary consequence of the annihilation of the sciences. 
 
 The Convention was inexorable and Fourcroy was relent- 
 less. He now acted as if his object was to crush Lavoisier, 
 and by an adroit move he caused him to be stigmatised as a 
 counter-revolutionist. A few days afterwards the Convention 
 ordered the arrest of Lavoisier, together with the rest of the 
 Fermiers-gdndraux who had signed the leases of David, Salzard, 
 and Mager, and he was conducted to the prison of Port-Libre. 
 Every effort on the part of his friends was put forth to save 
 him. The Commission of Weights and Measures, headed by 
 Borda and Haiiy, appealed to the Committee of Public Safety. 
 It refused to discuss the petition, and two days afterwards, on 
 the advice of the Committee of Public Instruction, of which 
 Fourcroy and Guyton Morveau were members, the names of 
 Borda, Lavoisier, Laplace, Coulomb, Brisson, and Delambre 
 
v Antoine-Laiirent Lavoisier 107 
 
 were removed from the Commission. The Committee of 
 Assignats requested in vain that Lavoisier might be allowed 
 to work in his laboratory. The Bureau de Consultation des 
 Arts et Metiers, of which Lavoisier was president at the time 
 of his arrest, addressed a memorial extolling the value of his 
 public services, and drawing especial attention to the fact 
 that the scheme of national instruction then before the 
 Convention was entirely of his creation. All was in vain. 
 The Terrorists were in complete ascendency in the Convention. 
 Robespierre had swept Hebert and Danton from his path, 
 and the work of " purification " was going on merrily. On 
 May 8, 1794, the Fermiers-gdntraux were brought to trial, 
 but their condemnation had already been pronounced. 
 Liendon, in the turgid rhetoric of the period, demanded the 
 heads of the prisoners . . . "the measure of the crimes of 
 these vampires is filled to the brim . . . the immorality of 
 these creatures is stamped on public opinion ; they are the 
 authors of all the evils that have afflicted France for some 
 time past." Halle attempted to intervene on behalf of 
 Lavoisier, and presented the memorial of the Bureau de 
 Consultation : Coffinhal, who presided, pushed it aside, with 
 the memorable words : " La Republique n'a pas besoin de 
 savants ; il faut que la justice suive son cours." The twenty- 
 eight Fermiers-gdndmux were found guilty of death. They 
 were sentenced to be executed within twenty-four hours, and 
 it was ordered that their property should be confiscated to 
 the Republic. Such was the haste of the judges that the 
 decision of the jury was omitted from the minute of judgment 
 an act of informality which Dobsen used with terrible 
 effect a few months later, when Fouquier-Tinville and Coffmhal 
 found themselves in the place of the unfortunate Fermiers- 
 
 On the following morning the condemned men were taken 
 from the Conciergerie to the Place de la Revolution. They 
 bade each other farewell ; Papillon d'Auteroche, seeing the 
 
loS Antoine- Laurent Lavoisier v 
 
 crowd en carmagnole as the carts passed through the streets, 
 raised a smile as he said disdainfully, in allusion to the con- 
 fiscation of his effects : " What annoys me is to have such dis- 
 agreeable heirs." They were guillotined in the order of their 
 names on the indictment. Lavoisier saw fall the head of his 
 father-in-law, and was himself the fourth to suffer. In common 
 with all his companions, he bore himself with dignity, and 
 met his end calmly and with courage. The spectacle of such 
 fortitude awed the crowd into silence, and no reproach or 
 insult reached the ears of the dying man. 
 
 Thus perished, at the age of fifty-one, one of the most 
 remarkable men of whom history has any record. All that 
 was mortal of him was thrown into the cemetery of Madeleine, 
 and the place of his interment was forgotten. The news of 
 this great crime profoundly affected the intellectual world. 
 Eighteen months before, our own Royal Society had sent 
 Lavoisier the Copley medal, the highest gift it has to bestow. 
 It came to him as a ray of encouragement, if not of hope, 
 during the dark hours of his struggle to save the Academy. 
 There was not a scientific body in Europe that failed to 
 give utterance to its sense of shame and sorrow. With 
 the fall of Robespierre this feeling penetrated France. On 
 October 22, 1795, Lalande pronounced an eloge on Lavoisier 
 before the Lyceum of Arts, and in the midst of the extra- 
 ordinary revulsion of popular feeling which preceded the days 
 of the Directory the same body decreed a solemn funeral 
 ceremony in his honour. It was, in truth, a lugubrious farce, 
 marked by all the extravagances of taste and sentiment which 
 were then in fashion, and it was crowned by an 6loge . . . 
 from Fourcroy. Time-serving and timorous as ever, Fourcroy 
 had no other extenuation than an appeal to the memories of 
 the Great Terror. " Carry yourselves back to that frightful 
 time . . . when terror separated even friends from each other, 
 when it isolated even the members of a family at their very 
 fireside, when the least word, the slightest mark of solicitude 
 
v Ant oine- Laurent Lavoisier 109 
 
 for the unfortunate beings who were preceding you along the 
 road to death, were crimes and conspiracies." For Fourcroy 
 to plead that he was pusillanimous hardly serves to exculpate 
 him. He would have us believe that he was powerless to 
 avert the catastrophe he now affects to deplore ; but he stands 
 charged, on his own showing, with participation in acts which 
 largely contributed to it, and the charge rests heavily on his 
 memory. 
 
VI 
 
 PRIESTLEY, CAVENDISH, LAVOISIER, AND 
 LA REVOLUTION CHIMIQUE 
 
 THE PRESIDENTIAL ADDRESS TO THE CHEMICAL SECTION OF THE 
 BRITISH ASSOCIATION, LEEDS, 1890. 
 
 LEEDS has one most notable association with chemistry of 
 which she is justly proud. In the month of September 1767 
 Dr. Joseph Priestley took up his abode in this town. The 
 son of a Yorkshire cloth-dresser, he was born in 1733 at 
 Fieldhead, a village about six miles hence. His relatives, who 
 were strict Calvinists, on discovering his fondness for books, 
 sent him to the Academy at Daventry to be trained for the 
 ministry. In spite of his poverty and of certain natural 
 disadvantages of speech and manner, he gradually acquired, 
 more especially by his controversial and theological writings, 
 a considerable influence in Dissenting circles. A pressing 
 invitation and the offer of one hundred guineas a year, induced 
 him to accept an invitation to take charge of the congregation 
 of Mill Hill Chapel here. He was already known to science 
 by his History of Electricity, and the effort was made to 
 attach him still more closely to its cause by the offer of an 
 appointment as naturalist to Cook's Second Expedition to 
 the South Seas. But, thanks to the intervention of some 
 worthy ecclesiastics on the Board of Longitude who had the 
 direction of the business, and who, as Professor Huxley once 
 
VI 
 
 Priestley, Cavendish, Lavoisier \ 1 1 
 
 put it, " possibly feared that a Socinian might undermine 
 that piety which in the days of Commodore Trunnion so 
 strikingly characterised sailors," he was allowed to remain in 
 Leeds, where, as he tells us in his Memoirs, he continued six 
 years, " very happy with a liberal, friendly, and harmonious 
 congregation," to whom his services (of which he was not 
 sparing) were very acceptable. " In Leeds," he says, " I had 
 no unreasonable prejudices to contend with, and I had full 
 scope for every kind of exertion." x 
 
 We have every reason to feel grateful to the "worthy 
 ecclesiastics," since their action indirectly occasioned Priestley 
 to turn his attention to chemistry. The accident of living 
 near a brewery led him to study the properties of " fixed air," 
 or carbonic acid, which is abundantly formed in the process of 
 fermentation, and which at that time was the only gas whose 
 separate and independent existence had been definitely 
 established. From this happy accident sprang that extra- 
 ordinary succession of discoveries which earned for their 
 author the title of the Father of Pneumatic Chemistry, and 
 which were destined to completely change the aspect of 
 chemical theory and to give it a new and unexpected 
 development. 
 
 I have been led to make this allusion to Priestley, not so 
 much on account of his connection with this place as for 
 the reason that, as it seems to me, there has been a disposition 
 to obscure his true relation to the marvellous development of 
 chemical science which made the close of the last century 
 memorable in the history of learning. Our distinguished 
 fellow-worker, M. Berthelot, the Perpetual Secretary of the 
 French Academy, has recently published, under the title of 
 La Revolution Chimique, a remarkable book, written with 
 great skill, and with all the charm of style and perspicacity 
 
 1 Leeds still enjoys one of the fruits of Priestley's insatiable power of 
 work in her admirable Proprietary Library. He seems to have suggested its 
 formation, and was its first honorary secretary. 
 
1 1 2 Priestley, Cavendish, Lavoisier, vi 
 
 which invariably characterises his work, in which he claims 
 for Lavoisier a participation in discoveries which we count 
 among the chief scientific glories of this country. From the 
 eminence of M. Berth elot's position in the world of science his 
 book is certain to receive in his own country the attention 
 which it merits, and as it is issued as one of the volumes of 
 the Bibliotheque Scientifique Internationale it will probably 
 obtain through the medium of translations a still wider 
 circulation. I trust that I shall not be accused of being 
 unduly actuated by what Mr. Herbert Spencer terms "the 
 bias of patriotism," in deeming the present a fitting occasion 
 on which to bring these claims to your notice with a view of 
 determining how far they can be substantiated. 
 
 All who are in the least degree familiar with the history of 
 chemical science during the last hundred years, will recognise, 
 as I proceed, that the claims which M. Berthelot asserts on 
 behalf of his illustrious predecessor are not put forward for 
 the first time. Explicitly made, in fact, by Lavoisier himself, 
 they were uniformly and consistently disallowed by his con- 
 temporaries. M. Berthelot now seeks to support them by addi- 
 tional evidence and to strengthen them with new arguments, 
 and asks us thereby to clear the memory of Lavoisier from 
 certain grave charges which lie heavily on it. You have 
 doubtless anticipated that these claims have reference to 
 Lavoisier's position in relation to the discovery of oxygen 
 gas and the determination of the non-elementary nature of 
 water. 
 
 The substance we now call oxygen a name we owe to 
 Lavoisier was discovered by Priestley on August 1, 1774; 
 he obtained it, as every schoolboy knows, by the action of 
 heat upon the red oxide of mercury. We all remember the 
 characteristically ingenuous account which Priestley gives of 
 the origin of his discovery. M. Berthelot sees in it merely 
 the evidence of the essentially empirical character of his 
 work. "Priestley," he says, "the enemy of all theory and of 
 
vi and '" La Revolution Chimique" 113 
 
 every hypothesis, draws no general conclusion from his 
 beautiful discoveries, which he is pleased, moreover, not 
 without affectation, to attribute to chance. He describes 
 them in the current phraseology of the period with an 
 admixture of peculiar and incoherent ideas, and he remained 
 obstinately attached to the theory of phlogiston up to his 
 death, which occurred in 1804 " (p. 40). 
 
 Such statements are calculated to give an erroneous idea 
 of Priestley's merit as a philosopher. That the implication 
 contained in the passage is wholly opposed to the real spirit 
 of his work might be readily shown by numerous quota- 
 tions from his writings. Perhaps this will suffice : "It is 
 always our endeavour, after making experiments, to generalise 
 the conclusions we draw from them, and by this means 
 to form a theory or system of principles to which all 
 the facts may be reduced, and by means of which we may 
 be able to foretell the result of future experiments." 
 This quotation is taken from the concluding chapter of his 
 Experiments and Observations on Different Kinds of Air, 
 in which he actually seeks to draw "general conclusions" 
 concerning the constituent principles of the various gases 
 which he himself made known to us, and to show the bearing 
 of these conclusions on the doctrine of phlogiston. That he 
 was content to rest in the faith of Stahl's great generalisation, 
 even to the end, is true, and the fact is the more remarkable 
 when we recall the absolute sincerity of the man, his extra- 
 ordinary receptivity, and, as he says of himself, his proneness 
 " to embrace what is generally called the heterodox side of 
 almost every question." If it is argued that this merely shows 
 Priestley's inability to appreciate theory, it must be at least 
 admitted that there is no proof that he was inimical to it. 
 His position is clearly evident from the concluding words 
 of the section of his work from which I have already quoted : 
 "This doctrine of the composition and decomposition of 
 wa,ter has been made the basis of an entirely new system of 
 
 I 
 
ii4 Priestley, Cavendish, Lavoisier, vi 
 
 chemistry, and a new set of terms has been invented and 
 appropriated to it. It must be acknowledged that substances 
 possessed of very different properties may, as I have said, be 
 composed of the same elements in different proportions and 
 different modes of combination. It cannot, therefore, be said 
 to be absolutely impossible but that water may be composed of 
 these two elements or any other. But then the supposition 
 should not be admitted without proof ; and if a former theory 
 will sufficiently account for all the fads there is no occasion 
 to have recourse to a new one, attended with no peculiar 
 advantage (loc. cit. p. 543). ... I should not feel much reluc- 
 tance to adopt the new doctrine, provided any new and 
 stronger evidence be produced for it. But though I have 
 given all the attention that I can to the experiments of M. 
 Lavoisier, etc., I think that they admit of the easiest explana- 
 tion on the old system " (loc. cit. p. 563). 
 
 The fact that Priestley was the first to consciously isolate 
 oxygen is not contested by M. Berthelot, although he is 
 careful to point out, what is not denied, that the exact date 
 of the discovery depends on Priestley's own statement, and 
 that his first publication of it was made in a work published 
 in London in 1775. It was known before Priestley's famous 
 experiment that the red oxide of mercury, originally formed 
 by heating the metal in contact with air, would again yield 
 mercury by the simple action of heat and without the inter- 
 vention of any reducing agent. Bayen, six months before the 
 date of Priestley's discovery, had observed that a gas was thus 
 disengaged, but he gave no description of its nature, content- 
 ing himself merely by pointing out the analogy which his 
 experiments appeared to possess to those of Lavoisier on the 
 existence of an elastic fluid in certain substances. After- 
 wards, when the facts were established, Bayen drew atten- 
 tion to his earlier experiments and claimed, not only the 
 discovery of oxygen, but all that Lavoisier deduced from 
 it. " But," says M. Berthelot, in reference to this circum- 
 
vi and " La Revolution Chimique" 115 
 
 stance, " his contemporaries paid little heed to his pretensions, 
 nor will posterity pay more " (La Revolution Chimique, p. 60). 
 
 M. Berthelot, however, does not dismiss Lavoisier's claims 
 to a participation in the discovery in the same summary 
 fashion. On the contrary, whilst not explicitly claiming for 
 him the actual isolation, in the first instance, of oxygen, the 
 whole tenor of his argument is to palliate, and even to 
 justify, his demand to be regarded as an independent dis- 
 coverer of the gas. He begins by asserting that Lavoisier 
 had already a presentiment of its existence in 1774, and he 
 quotes, in support of this assumption, an abstract from 
 Lavoisier's memoir, published in December 1774, in the 
 Journal de Physique of the Abbe Rozier : " This air, deprived 
 of its fixable portion (by metals during calcination), is in some 
 fashion decomposed, and this experiment would seem to 
 afford a method of analysing the fluid which constitutes our 
 atmosphere and of examining the principles of which it is 
 composed. ... I believe I am in a position to affirm that the 
 air, as pure as it is possible to suppose it, free from moisture 
 and from every foreign substance, far from being a simple 
 body, or element, as is commonly thought, should be placed, 
 on the contrary, ... in the group of the mixtures, and 
 perhaps even in that of the compounds." 
 
 M. Berthelot further asserts that Lavoisier was at this time 
 the first to recognise the true character of air, and he expresses 
 his belief that it is probable that he would himself have 
 succeeded in isolating its constituents if the path of inquiry had 
 been left to him alone. It is no disparagement to Lavoisier's 
 prescience to say that there is nothing in these lines, nor in 
 the memoir which deals with the repetition of Boyle's experi- 
 ments on the calcination of tin to which they refer, to show 
 that Lavoisier had made any advance beyond the position of 
 Hooke and Mayow. It has been more than once pointed out 
 that the chemists of the seventeenth century understood the 
 true nature of combustion in air much better than their 
 
1 6 Priestley, Cavendish, Lavoisier, 
 
 VI 
 
 brethren of the last quarter of the eighteenth century. Hooke, 
 in the Micrographia, and Mayow, in his Opera Omnia 
 Medicophysica, indicated that combustion consists in the 
 union of something with the body which is being burnt ; and 
 Mayow, both by experiment and inference, demonstrated in 
 the clearest way the analogy between respiration and com- 
 bustion, and showed that in both processes one constituent 
 only of the air is concerned. He distinctly stated that not 
 only is there increase of weight attending the calcination of 
 metals, but that this increase is due to the absorption of the 
 same spiritus from the air that is necessary to respiration and 
 combustion. Mayow's experiments are so precise, and his 
 facts so incontestable, that, as Chevreul has said, it is sur- 
 prising that the truth was not fully recognised until a century 
 after his researches. (Fide Watts' Dictionary of Chemistry, 
 by Morley and Muir, art. " Combustion," p. 242.) 
 
 It is now necessary to examine Lavoisier's claims rather 
 more closely and in the light of M. Berthelot's book. A resume 
 of his work On the Calcination of Tin was given by 
 Lavoisier to the Academy in November 1774, but the complete 
 memoir was not deposited until May 1777. A careful com- 
 parison of an abstract of what was stated to the Academy in 
 November 1774, contributed by Lavoisier himself, in Decem- 
 ber 1774, to the Journal de Physique of the Abbe Eozier, 
 makes it evident that very substantial additions were made to 
 the communication before it was finally printed in the 
 Mdmoires de VAcad6mie des Sciences. The possibility of 
 this is allowed by M. Berthelot. He says (p. 58): "A 
 summary communication, often given viva wee to a learned 
 society, such as the Academy of Sciences of Paris or the 
 Eoyal Society of London, would immediately call forth 
 verifications, ideas, and new experiments, which would develop 
 the range and even the results of such communication. The 
 original author, when printing his memoir, would in return 
 and for this he is hardly blamable embody these additional 
 
vi and 4 ' La Revolution Chimique " 117 
 
 results and later interpretations. It thus becomes most 
 difficult to assign impartially to each his share in a rapid 
 succession of discoveries " (loc. cit. p. 58). 
 
 But although, as we shall see, Lavoisier was certainly 
 aware of Priestley's great discovery, no allusion is made to 
 the gas, nor to Priestley's previous work on the other 
 constituent of air which is printed in the Philosophical 
 Transactions for 1772, and for which he was awarded the 
 Copley Medal by the Royal Society. It is simply impossible 
 to believe that Lavoisier could have been uninfluenced by 
 this work. Indeed, we venture to assert that the full and 
 clear recognition of the non-elementary nature of air which 
 he eventually made was based upon it. It is noteworthy 
 that in the early part of his memoir he states his opinion that 
 the addition not only of powdered charcoal, but of any 
 phlogistic substance to a metallic calx is attended with the 
 formation of fixed air. It is certain that at this period he 
 had not only not consciously obtained any gas resembling 
 Priestley's dephlogisticated air from any calx with which 
 he had experimented, but that none of his experiments had 
 afforded him any idea that the gas absorbed during calcina- 
 tion was identical with it. 
 
 At Easter 1775 Lavoisier presented a memoir to the 
 Academy " On the Nature of the Principle which Combines 
 with Metals during Calcination." This was "relu le 8 aout, 
 1778." To the memoir there is a note stating that the first 
 experiments detailed in it were performed more than a year 
 before ; those on the red precipitate were made by means of 
 a burning glass in the month of November 1774, and were 
 repeated in the spring of 1775 at Montigny in conjunction 
 with M. Trudaine. In this paper Lavoisier first distinctly 
 announces that the principle which unites with metals during 
 their calcination, which increases their weight, and which 
 transforms them into calces, is nothing else " than the purest 
 and most salubrious part of the air ; so that if that air which 
 
u8 Priestley, Cavendish, Lavoisier, vi 
 
 has been fixed in a metallic combination again becomes free, 
 it reappears in a condition in which it is eminently respirable, 
 and better adapted than the air of the atmosphere to support 
 inflammation and the combustion of substances" (CEuvres 
 de Lavoisier, official edition, vol. ii. p. 123). He then describes 
 the method of preparing oxygen by heating the red oxide of 
 mercury, and compares the properties of the gas with those 
 of fixed air. There is, however, no mention of Priestley, nor 
 any reference to his experiments. It can hardly be doubted 
 that in this memoir Lavoisier intended his readers to believe 
 that he was " the true and first discoverer " of the gas which 
 he afterwards named oxygen. This is borne out by certain 
 passages in his subsequent memoir " On the Existence of Air 
 in Nitrous Acid " ; lu le 20 avril, 1776, remis en dfoembre 1777." 
 He had occasion incidentally to prepare the red oxide of 
 mercury by calcining the nitrate, and says that he obtained 
 from it a large quantity of an air "much purer than common 
 air, in which candles burnt with a much larger, broader, and 
 more brilliant flame, and which in no one of its properties 
 differed from that which I had obtained from the calx of 
 mercury, known as mercurius precipitatus per se, and which 
 Mr. Priestley had procured from a great number of substances 
 by treating them with nitric acid." 
 
 In another part of this memoir he says that " perhaps, 
 strictly speaking, there is nothing in it of which Mr. Priestley 
 would not be able to claim the original idea ; but as the same 
 facts have conducted us to diametrically opposite results, I 
 trust that, if I am reproached for having borrowed my proofs 
 from the works of this celebrated philosopher, my right at 
 least to the conclusions will not be contested." M. Berth elot 
 remarks on the irony of this passage : we may infer from it 
 that the friends of the English chemist had not been altogether 
 idle. In his memoir " On the Eespiration of Animals," read 
 to the Academy in 1777, he again appears to admit the claim 
 of Priestley to at least a share in the discovery : " It is known 
 
vi and "La Revolution Chimique" 119 
 
 from Mr. Priestley's and my experiments that mercurius 
 precipitatus per se is nothing but a combination," etc. In 
 several subsequent communications Priestley's name is men- 
 tioned in very much the same connection, until we come 
 to the classical memoir " On the Nature of the Acids," when 
 it is said : "I shall henceforth designate the dephlogisticated 
 air, or the eminently respirable air ... by the name of the 
 acidifying principle, or, if it is preferred to have the same 
 signification under a Greek word, by that of the l principe 
 oxygine.' " 
 
 In none of the memoirs after that of Easter 1775 is the 
 claim for participation more than implied; it is made ex- 
 plicitly for the first time in the paper "On a Method of 
 Increasing the Action of Fire," printed in the Mtmoires de 
 I'Acade'mie for 1782, and in these words : "It will be remem- 
 bered that at the meeting of Easter 1775 I announced the 
 discovery, which I had made some months before with M. 
 Trudaine, 1 in the laboratory at Montigny, of a new kind of air, 
 up to then absolutely unknown, and which we obtained by 
 the reduction of mercurius precipitatus per se. This air, which 
 Mr. Priestley discovered at very nearly the same time as I, 
 and I believe even before me, and which he had procured 
 mainly from the combination of minium and of several other 
 substances with nitric acid, has been named by him dephlogis- 
 ticated air." 
 
 In the "Traite" Elementaire de Chimie" the claim for 
 participation is again asserted in these words : " This air, 
 which Mr. Priestley, Mr. Scheele, and I discovered at about 
 the same time." . . . 
 
 Now there is no question that Lavoisier knew of the 
 existence of oxygen some months before he made the experi- 
 ments with the burning glass of M. Trudaine at Montigny, for 
 the simple reason that Priestley had already told him of it. 
 Priestley left Leeds in 1773 to become the librarian and 
 1 M. Trudaine de Montigny died in 1777. 
 
I2O Priestley, Cavendish, Lavoisier, vi 
 
 literary companion of Lord Shelburne, and in the autumn of 
 1774 he accompanied his lordship on to the Continent, and 
 spent the month of October in Paris. Lavoisier was famous 
 for his hospitality ; his dinners were celebrated ; and Priestley, 
 in common with every foreign savant of note who visited 
 Paris at that period, was a welcome guest. What followed is 
 best told in Priestley's own words : " Having made the dis- 
 covery [of oxygen] some time before I was in Paris, in the 
 year 1774, I mentioned it at the table of Mr. Lavoisier, when 
 most of the philosophical people of the city were present, 
 saying that it was a kind of air in which a candle burnt 
 much better than in common air, but I had not then given it 
 any name. At this all the company, and Mr. and Mrs. 
 Lavoisier as much as any, expressed great surprise. I told 
 them I had gotten it from precipitate per se and also from reel 
 lead. Speaking French very imperfectly, and being little 
 acquainted with the terms of chemistry, I said plombe rouge, 
 which was not understood till Mr. Macquer said I must 
 mean minium" 
 
 In his account of his own work on dephlogisticated air, 
 given in his Observations, etc., 1790 edition, he further says, 
 vol. ii. p. 108 : " Being in Paris on the October following [the 
 August of 1774], and knowing that there were several very 
 eminent chemists in that place, I did not omit the opportunity, 
 by means of my friend Mr. Magellan, 1 to get an ounce of 
 mercurius calcinatus prepared by Mr. Cadet, of the genuineness 
 of which there could not possibly be any suspicion ; and, at 
 the same time, I frequently mentioned my surprise at the 
 kind of air which I had got from this preparation to Mr. 
 Lavoisier, Mr. Le Roy, and several other philosophers, who 
 honoured me with their notice in that city, and who, I dare- 
 say, cannot fail to recollect the circumstance." 
 
 1 Prof. Grimaux (Lavoisier, p. 51), says : " Un de ses [Lavoisier's] amis 
 qui habitait Londres, Magalhaens ou Magellan, de la famille du celebre navi- 
 gateur, lui envoyait tons les memoires sur les sciences qui paraissaient en 
 Angleterre et le tenait au courant des decouvertes de Priestley." 
 
vi and "La Rdvohttion Ckimique" 121 
 
 If any further evidence is required to prove that Lavoisier 
 was not only not " the true and first discoverer " of oxygen, 
 but that he has absolutely no claim to be regarded even as a 
 later and independent discoverer, it is supplied by M. Berthelot 
 himself. Not the least valuable portion of M. Berthelot's 
 book, as an historical work, is that which he devotes to the 
 analysis of the thirteen laboratory journals of Lavoisier, 
 which have been deposited, by the pious care of M. de 
 Chazelles, his heir, in the archives of the Institute. M. 
 Berthelot has given us a synopsis of the contents of almost 
 every page of these journals, with explanatory remarks, and 
 dates when these could be ascertained. As he well says, 
 these journals "are of great interest because they inform us of 
 Lavoisier's methods of work and of the direction of his mind 
 I mean the successive steps in the evolution of his private 
 thought." On the fly-leaf of the third journal is written, "du 
 23 mars, 1774, au 13 fivrier, 1776." From p. 30 we glean 
 that Lavoisier visited his friend M. Trudaine at Montigny 
 about ten days after his conversation with Priestley, and re- 
 peated the latter's experiments on the marine acid and alkaline 
 airs (hydrochloric acid gas and ammonia). He is again at 
 Montigny some time between February 28 and March 31, 
 1775, and repeats not only Priestley's experiments on the 
 decomposition of mercuric oxide, presumably by means of M. 
 Trudaine's famous burning glass, but also his observations on 
 the character of the gas. The fly-leaf of the fourth journal in- 
 forms us that it extends from February 13, 1776, to March 3, 
 1778. On p. 1 is an account of experiments made February 
 13, on " precipite per se de chez M. Baume," in which the 
 disengaged gas is spoken of as "I'air ddphlogistique de M. 
 Frisky" (sic). Such a phrase in a private notebook is ab- 
 solutely inconsistent with the idea that at this time Lavoisier 
 considered himself as an independent discoverer of the gas. 
 Ho'w he came to regard himself as such we need not inquire. 
 Nor is it necessary to occupy your time by any examination 
 
 
122 Priestley, Cavendish, Lavoisier, \\ 
 
 of the arguments by which M. Berthelot, with the skill of a 
 practised advocate, would seem to identify himself with the 
 case of his client. We would do him the justice of recognis- 
 ing the difficulty of his position. He seeks to discharge an 
 obligation, of which the acknowledgment has been too long 
 delayed. The Academic des Sciences a year ago awoke to the 
 sense of its debt of gratitude to the memory of the man who 
 had laboured so zealously for its honour, and even for its 
 existence, during the stormy period of which France has just 
 celebrated the centenary, and out of the Sloge on Lavoisier 
 which M. Berthelot, as Perpetual Secretary, was commissioned 
 to deliver, has grown La Evolution Chimigue. To write 
 eulogy, however, is not necessarily to write history. We 
 cannot but think that M. Berthelot has been hampered by his 
 position, and that his opinion, or at least the free expression 
 of it, has been fettered by the conditions under which he has 
 written. We imagine we discern between the lines the con- 
 sciousness that, to use Brougham's phrase, the brightness of 
 the illustrious career which he eulogises is dimmed with spots 
 which a regard for historical truth will not permit him wholly 
 to ignore. 
 
 Two cardinal facts made the downfall of phlogiston com- 
 plete the discovery of oxygen and the determination of the 
 compound nature of water. M. Berthelot's contention is that 
 not only did Lavoisier effect the overthrow, but he also dis- 
 covered the facts. In other words, he has not only a claim to 
 a participation in the discovery of oxygen, but he is also " the 
 true and first discoverer" of the non-elementary nature of 
 water. This second claim is directly and explicitly stated. 
 Although it is supported by a certain ingenuity of argument, 
 we venture to think that we shall be able to show it has no 
 greater foundation in reality than the first. 
 
 Members of the British Association who are at all familiar 
 with its history, will recall the fact that this is not the first 
 occasion on which the attempt to transfer "those laurels 
 
VI 
 
 and "La Revolution Chimique" 123 
 
 which both time and truth have fixed upon the brow of 
 Cavendish " has had to be resisted. At the Birmingham 
 Meeting of 1839 the Rev. W. Vernon Harcourt, who then 
 presided, devoted a large portion of his address to an able and 
 eloquent vindication of Cavendish's rights. The attack came 
 then as now from the Perpetual Secretary of the French 
 Academy, and the charges were also formulated then, as now, 
 in^an doge read before that learned body. The assailant was 
 M. Arago, who did battle, not for his countryman Lavoisier, 
 whose claims are dismissed as " pretensions," but on behalf of 
 James Watt, the great engineer, who was one of the foreign 
 members of the Institute. 
 
 It is not my wish to trouble you at any length with the 
 details of what has come to be known in the history of scien- 
 tific discovery as the Water Controversy a controversy which 
 has exercised the minds and pens of Harcourt, Whewell, 
 Peacock, and Brougham in England; of Brewster, Jeffrey, 
 Muirhead, and Wilson in Scotland ; of Kopp in Germany ; 
 and of Arago and Dumas in France. This controversy, it has 
 been said, takes its place in the history of science side by side 
 with the discussion between Newton and Leibnitz concerning 
 the invention of the Differential Calculus, and that between 
 the friends of Adams and Leverrier in reference to the dis- 
 covery of the planet Neptune. Up to now it has practically 
 turned upon the relative merits of Cavendish and Watt. M. 
 Berthelot is the first French savant of any note who has 
 seriously put forward the claims of Lavoisier, his countryman 
 and predecessor Dumas having deliberately rejected them. 
 
 At the risk of wearying you with detail, I am under the 
 necessity of restating the facts in order to make the position 
 clear. Some time before April 18, 1781, Priestley made what 
 he called " a random experiment " for the entertainment of a 
 few philosophical friends. It consisted in exploding a mixture 
 of inflammable air (presumably hydrogen) and common air, 
 contained in a closed glass vessel, by the electric spark, in the 
 
124 Priestley, Cavendish, Lavoisier, vi 
 
 manner first practised by Volta in 1776. The experiment was 
 witnessed by Mr. John Warltire, a lecturer on natural philo- 
 sophy and a friend of Priestley, who had rendered him the 
 signal service of giving him the sample of the mercuric oxide 
 from which he had first obtained oxygen. Warltire drew 
 Priestley's attention to the fact that after the explosion the 
 sides of the glass vessel were bedewed with moisture. Neither 
 of the experimenters attached any importance to the circum- 
 stance at the time, Priestley being of opinion that the moisture 
 was pre-existent in the gases, as no special pains were taken 
 to dry them. Warltire, however, conceived the notion that 
 the experiment would afford the means of determining whether 
 heat was ponderable or not, and hence he was led to repeat 
 it, firing the mixture in a copper vessel for greater safety. 
 The results of these observations are contained in Priestley's 
 Experiments and Observations on Air, vol. v., 1781, App. p. 395. 
 At this period Cavendish was engaged on a series of experi- 
 ments " made, as he says, 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" (Cavendish, Philosophical Transactions, 1784, p. 119). 
 On the publication of Priestley's work he repeated Warltire's 
 experiment, for, he says, as it " seemed likely to throw great 
 light on the subject I had in view, I thought it well worth 
 examining more closely." The series of experiments which 
 Cavendish was thus induced to make, and which he made 
 with all his wonted skill in quantitative work, led him at some 
 time in the summer of 1781 to the discovery that a mixture 
 of two volumes of the inflammable air from metals (the gas 
 we now call hydrogen) with one volume of the dephlogisticated 
 air of Priestley combine together under the influence of the 
 electric spark, or by burning, to form the same weight of 
 water. If Cavendish had published the results of these obser- 
 vations at or near the time he obtained them, there would 
 
vi and "La Revolution Chimique" 125 
 
 have been no Water Controversy. But in the course of the 
 trials he found that the condensed water was sometimes acid, 
 and the search for the cause of the acidity (which incidentally 
 led to the discovery of the composition of nitric acid) occa- 
 sioned the delay. The main result that a mixture of two 
 volumes of inflammable air and one volume of dephlogisticated 
 air could be converted into the same weight of water was, 
 however, communicated to Priestley, as he relates in a paper 
 in the Philosophical Transactions for 1783. Priestley was at 
 this time interested in an investigation on the seeming 
 convertibility of water into air, and he was led to repeat 
 Cavendish's experiments, some time in March 1783, on what 
 was apparently the converse problem. Priestley, however, 
 made a fatal blunder in the repetition. With the praiseworthy 
 idea of obviating the possibility of any moisture in the gases, 
 he prepared the dephlogisticated air from nitre, and the 
 inflammable air by heating what he calls "perfectly made 
 charcoal " in an earthenware retort. At this period, it must be 
 remembered, there was no sharp distinction between the 
 various kinds of inflammable air : hydrogen, sulphuretted 
 hydrogen, marsh gas and olefiant gas, coal gas, the vapours of 
 ether and turpentine, and the gas from heated charcoal con- 
 sisting of a mixture of carbonic oxide, marsh gas, and carbonic 
 acid were indifferently termed "inflammable air." Priestley 
 attempted to verify Cavendish's conclusion on the identity of 
 the weight of the gases used with that of the water formed ; 
 but his method in this respect, as in his choice of the in- 
 flammable air, was wholly defective, and could not possibly 
 have given him accurate results. It consisted in wiping out 
 the water from the explosion vessel by means of a weighed 
 piece of blotting-paper, and determining the increase of weight 
 of the paper. He says, however : " I always found as near as 
 I could judge the weight of the decomposed air in the moist- 
 ure acquired by the paper. ... I wished, however, to have 
 had a nicer balance for this purpose ; the result was such as 
 
126 Priestley, Cavendish, Lavoisier, vi 
 
 to afford a strong presumption that the air was reconverted 
 into water, and therefore that the origin of it had been water." 
 These results, together with those on the conversion of water 
 into air, were communicated towards the end of March 1783 
 by Priestley to Watt, who began to theorise upon them, and 
 then to put his thoughts together in the form of a letter 
 to Priestley, dated April 26, 1783, and which he requested 
 might be read to the Royal Society on the occasion of the 
 presentation of Priestley's memoir. In this letter Watt says : 
 "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 cooling 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. Are we not then authorised 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 elementary 
 heat and light, etc. ? " 
 
 This letter, although shown to several Fellows of the 
 Socie'ty, was not publicly read at the time intended. Priestley, 
 before its receipt, had detected the fallacy of his experiments 
 on the seeming conversion of water into air, and as much of 
 the letter was concerned with this matter Watt requested 
 that it should be withdrawn. Watt, however, as he tells 
 Black 1 in a letter dated June 23, 1783, had not given up 
 his theory as to the nature of water, and on November 26, 
 1783, he restated his views more fully in a letter to De Luc. 
 In the meantime Cavendish, having completed one section of 
 his investigation, sent in a memoir to the Eoyal Society, which 
 was read on January 15, 1784, in which he gives an account 
 of his experiments, and announces his conclusion "that de- 
 1 Watt, Correspondence, p. 31. 
 
VI 
 
 and "La Revolution Chimique" 127 
 
 phlogisticated air is in reality nothing but dephlogisticated 
 water, or water deprived of its 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." Watt thereupon requested that his letter to 
 De Luc should be published, and it was accordingly read to 
 the Royal Society on April 29, 1784. Which of the two-^- 
 Cavendish or Watt is, under these circumstances, to be con- 
 sidered as " the true and first discoverer " of the compound 
 nature of water is the question which has been hitherto the 
 main subject of the Water Controversy. 
 
 Let us now consider the matter as it affects Lavoisier. In 
 1783 Lavoisier had publicly declared against the doctrine of 
 phlogiston, or rather, as M. Dumas puts it, "against the 
 crowd of entities of that name which had no quality in common 
 except that of being intangible by every known method" 
 (Lemons sur la Philosophie Chimique, p. 161). How completely 
 Lavoisier had dissociated himself from the theory may be 
 gleaned from his memoir of that year. " Chemists," he says, 
 "have made a vague principle of phlogiston which is not 
 strictly defined, and which in consequence accommodates itself 
 to every explanation into which it is pressed. Sometimes this 
 principle is heavy and sometimes it is not ; sometimes it is 
 free fire, and sometimes it is fire combined with the earthy 
 element ; sometimes it passes through the pores of vessels, and 
 sometimes they are impenetrable to it : it explains at once 
 causticity and non-causticity, transparency and opacity, colours 
 and the absence of colours. It is a veritable Proteus which 
 changes its form every moment." 
 
 But Lavoisier had merely renounced one fetich for another. 
 At the time that he penned these lines he was as much under 
 the thraldom of le principe oxygine as the most devoted follower 
 of Stahl was in the bondage of phlogiston. The idea that the 
 calcination of metals was but a slow combustion had been fully 
 
128 Priestley, Cavendish, Lavoisier, \\ 
 
 recognised. M. Berthelot tells us that as far back as the 
 March of 1774 Lavoisier had written in his laboratory journal : 
 " I am persuaded that the inflammation of inflammable air is 
 nothing but a fixation of a portion of the atmospheric air, a 
 decomposition of air. ... In that case in every inflammation 
 of air there ought to be an increase of weight," and he tried 
 to ascertain this by burning hydrogen at the mouth of a 
 vessel from which it was being disengaged. In the following 
 year he asks, What remains when inflammable air is burnt 
 completely 1 ? According to the theory by which he is now 
 swayed it should be an acid, and he made many attempts to 
 capture this acid. In 1777 he and Bucquet burnt six pints 
 of the inflammable air from metals in a bottle containing 
 lime-water, in the expectation that fixed air would be the 
 result. And in 1781 he repeated the experiment with 
 Gengembre, with the modification that the oxygen was caused 
 to burn in an atmosphere of hydrogen, but not a trace of any 
 acid product could be detected. Of course there must have 
 been considerable quantities of water formed in these experi- 
 ments, but Lavoisier was preoccupied with the conviction that 
 oxidation meant acidification, and the presence of the water was 
 unnoticed, or, if noticed, was unheeded. Macquer, in 1776, 
 had drawn attention to the formation of water during the 
 combustion of hydrogen in air, but Lavoisier has stated that 
 he was ignorant of that observation. What was it then that 
 put him on the right track 1 We venture to think that M. 
 Berthelot has himself supplied the answer. He says (p. 114) : 
 "Rumours of Cavendish's trials had spread throughout the 
 scientific world during the spring of 1783. . . . Lavoisier, 
 always on the alert as to the nature of the products of the- 
 combustion of Irydrogen, was now in such position that the 
 slightest hint would enable him to comprehend its true nature. 
 He hastened to repeat his trials, as he had the right to do, 
 never having ceased to occupy himself with a question which 
 lay at the very heart of his doctrine." 
 
and " La Revolution Chimique" 129 
 
 "On the 24th of June 1783," continues M. Berthelot, "he 
 repeated the combustion of hydrogen in oxygen, and he 
 obtained a notable quantity of water without any other 
 product, and he concluded from the conditions under which 
 he had worked that the weight of the water formed could not 
 be other than equal to that of the two gases which had formed 
 it. The experiment was made in the presence of several men 
 of science, among whom was Blagden, a member of the Royal 
 Society of London, who on this occasion recalled the observations 
 of Cavendish (qui rappela a cette occasion les observations de 
 Cavendish)." 
 
 On the following day Lavoisier published his results. The 
 following is the official minute of the communication, trans- 
 lated from the register of the sittings of the Academic des 
 Sciences : 
 
 Meeting of Wednesday, 25th June 1783. 
 
 MM. Lavoisier and De Laplace announced that they had lately 
 repeated the combustion of Combustible Air with Dephlogisticated Air ; 
 they worked with about 60 pints of the airs, and the combustion was 
 made in a closed vessel : the result was very pure water. 
 
 The cautious scribe who penned that minute did not 
 commit himself too far. M. Berthelot, however, regards it 
 as the first certain date of publication, established by authentic 
 documents, in the history of the discovery of the composition 
 of water ; "a discovery," he adds, " which, on account of its 
 importance, has excited the keenest discussion." 
 
 You will search in vain through the laboratory journals, as 
 given by M. Berthelot, for any indications either of experi- 
 ments or reflections which would enable you to trace the 
 course of thought by which Lavoisier was guided to the 
 truth. There is absolutely nothing on the subject until in 
 the eighth volume (25 mars 1783, au fitrier 1784), and on 
 p. 63 we come to the experiment of 24th June, and we read : 
 "In presence of Messieurs Blagden, of [name illegible], 
 de Laplace, Vandermonde, de Fourcroy, Meusnier, 
 
 K 
 
130 Priestley, Cavendish, Lavoisier, vi 
 
 and Legendre, we have combined in a bell-jar 
 dephlogisticated air and inflammable air drawn 
 from iron by means of sulphuric acid, etc. . . . The 
 amount of water may be estimated at 3 drachms: 
 the amount which should have been obtained was 
 1 ounce 1 drachm and 12 grains. Thus we must 
 suppose that there was a loss of two-thirds of the 
 amqunt of the air, or that there has been a loss of 
 weight." 
 
 And this is the experiment which, according to M. Berthelot, 
 enabled Lavoisier to conclude that " the weight of the water formed 
 could not be other than equal to that of the two gases which had 
 formed it " ! It is on this single experiment, hurriedly and 
 imperfectly done, that Lavoisier's claim to the discovery of 
 the compound nature of water is based. M. Berthelot 
 objects to the assumption that it was hurriedly done. He 
 says, on p. 114: "Lavoisier caused a new apparatus to be 
 made, with a couple of tubes and two reservoirs for the gases ; 
 an arrangement which would require a certain amount of time 
 to put together; this circumstance proves that it could not 
 have been an improvised trial." To what extent it was 
 improvised will be seen immediately. 
 
 Now although the laboratory journals do not in this case 
 " inform us of Lavoisier's methods, and of the direction of 
 his mind . . . the successive steps in the evolution of his 
 private thought," we have other means of ascertaining how 
 he arrived at his knowledge. The method was simplicity 
 itself : he was told of the fact, and his informant was none other 
 than Cavendish's assistant, Blagden. 
 
 Cavendish's memoir was published in 1784. Before ifwas 
 struck off its author caused the following addition to be made : 
 "During the last summer also a friend of mine gave some 
 account of them [the experiments] to M. Lavoisier, as well as 
 of the conclusion drawn from them, that dephlogisticated air 
 is only water deprived of phlogiston ; but at that time so far 
 
vi and '" La Revolution Chimique" 131 
 
 was M. Lavoisier from thinking any such opinion warranted 
 that, till he was prevailed 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." This 
 addition, as I have had the opportunity of verifying by an 
 inspection of the original MSS. in the archives of the Eoyal 
 Society, was made in the handwriting of Cavendish's assistant 
 and amanuensis, Blagden. 
 
 When Lavoisier's memoir appeared it was found to contain 
 the following reference to this circumstance : "It was on the 
 24th of June that M. de Laplace and I made this experiment 
 in presence of MM. le Roi, Vandermonde, and several other 
 Academicians, and of Mr. Blagden, the present Secretary of 
 the Eoyal Society of London. The latter informed us (ce 
 dernier nous apprti) that Mr. Cavendish had already tried, in 
 London, to burn inflammable air in closed vessels, and that 
 he had obtained a very sensible quantity of water." 
 
 This reference was so partial, and its meaning so ambiguous, 
 that Blagden addressed the following letter to Crell, to be 
 published in his Chemische Annalen (Crell's Annalen, 1786, 
 vol i., p. 58). 
 
 It is so direct and conclusive that I offer no apology for 
 giving it almost entire l : 
 
 I can certainly give you the best account of the little dispute 
 about the first discoverer of the artificial generation of water, as I 
 was the principal instrument through which the first news of the 
 discovery that had been already made was communicated to Mr. 
 Lavoisier. The following is a short statement of the history : 
 
 In the spring of 1783 Mr. Cavendish 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 con- 
 clusion that deplilogisticated air was nothing else than water 
 deprived of its phlogiston ; and, vice versd, that water was dephlo- 
 gisticated air united with phlogiston. About the same time the 
 
 1 Mr. Muirhead's translation. Vide Watt, Correspondence, Composition 
 of Water, p. 71. 
 
132 Priestley, Cavendish, Lavoisier, \\ 
 
 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 Mr. 
 Lavoisier and of some other members of the Eoyal 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 experiments, and particularly that Dr. 
 Priestley had repeated them. They did not doubt that in such 
 manner a considerable quantity of water might be obtained, 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 de- 
 posited 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 preparations, to 
 repeat the experiment, on a somewhat larger scale, as early as 
 possible. This desire he complied with on the 24th June 1783 
 (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 expected that a sort of acid would be produced by their union. 
 In general, Mr. Lavoisier cannot be convicted of having advanced 
 anything contrary to truth ; 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, apprised him of Mr. Cavendish'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 
 remarkable circumstance namely, that the experiment was made 
 in consequence of what I had informed him of. He should likewise 
 have stated in his publication 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 together. More- 
 over, 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, 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 accom- 
 
vi and " La Revolution Chimique" 133 
 
 modates it to his old theory, which banishes phlogiston. . . . 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 induced to institute again such experiments, solely by 
 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 demon- 
 strated in England. 
 
 To this letter, reflecting so gravely on his honour and 
 integrity, Lavoisier made no reply. Nor did Laplace, Le Roi 
 Vandermonde, or any one of the Academicians concerned, 
 vouchsafe any explanation. De non apparentibus et de non 
 existentibus eadem ratio. No explanation appeared, because 
 none was possible. M. Berthelot ignores this letter, which 
 is the more remarkable, since reference is made to it in more 
 than one of the publications which he tells us he has consulted 
 in the preparation of his account of the Water Controversy. 
 If he knew of it he must regard it either as unworthy of an 
 answer or as unanswerable. 
 
 It would be heaping Ossa on Pelion to adduce further 
 evidence from letters of the time of what Lavoisier's con- 
 temporaries thought of his claims. De mortuis nil nisi bonum. 
 I would much more willingly have dwelt upon the virtues of 
 Lavoisier, and have let his faults lie gently on him ; but I 
 have felt it incumbent on me on this occasion to make some 
 public answer to M. Berthelot's book, and in no place could 
 that answer be more fittingly given than in this town, which 
 saw the dawn of that work out of which these grand dis- 
 coveries arose. It may be that much of what I have had to 
 say is as a twice-told tale to many of you. I trust I need 
 make no apology on that account. The honour of our 
 ancestors is in our keeping, and we should be unworthy of 
 our heritage and false to our trust if we were slow to resent 
 or slack to repel any attempt to rob them of that glory which 
 is their just right and our proud boast. 
 
134 Priestley, Cavendish, Lavoisier, vi 
 
 ADDENDUM 
 
 Translations of the foregoing Address appeared in several 
 French periodicals devoted to popular science, accompanied by 
 criticisms, for the most part hostile. The Revue Sdentifique of 
 25th October 1890 also published the Address, to which, on 
 the invitation of the editor, M. Charles Kichet, M. Berthelot 
 prefixed a letter, which may be translated as follows : 
 
 I have no direct concern in the republication of Mr. Thorpe's 
 address which you purpose making in the Revue. Personally, I 
 have not any reason to complain of his courtesy, and I should have 
 been silent so far as he is concerned, holding that one is not 
 bound to enter into a controversy which is purely critical, where 
 no new fact is alleged, and where the judgment of public opinion 
 suffices to set things in their true place ; however, I comply with 
 your request to let your readers know what my opinion is. 
 
 To my mind, nothing is more opposed to truth and justice than 
 the introduction of national prejudices into the history of science. 
 All civilised nations are at one in proclaiming the glory of Newton, 
 the greatest of astronomers, and yet the majority of English men of 
 science, refusing to treat his rivals with equity, are not agreed to 
 recognise Leibnitz's rights to the invention of the differential cal- 
 culus : they are as prejudiced in this respect as was Newton him- 
 self. Something analogous occurs in regard to the discoveries 
 which created modern chemistry a hundred years ago. 
 
 Unquestionably, Priestley and Cavendish are recognised by all 
 as great discoverers. I have myself taken pains to describe Priest- 
 ley's discovery of the principal gases in terms of admiration (La 
 Revolution Chimique, p. 39), and especially that of oxygen, which 
 I unreservedly attribute to him (pp. 61, 62). I have also detailed, 
 with the encomiums which they merit, the investigations of 
 Cavendish, " one of the most powerful scientific minds of the last 
 century," and particularly his fruitful research on (to use Blagden's 
 phrase) the artificial generation of water. But the well-merited 
 praise accorded to these English savants does not prevent some of 
 their countrymen from persistently denying the right of Lavoisier 
 to the discovery and co-ordination of those general ideas on which 
 rest our actual conception of matter, more especially in relation to 
 the composition of air and water. This, I venture to repeat, is an 
 
vi and "La Revolution Chimiqne" 135 
 
 incident in the long-standing feud, continually being renewed in 
 the history of science, between the sagacious discoverers of particular 
 facts and the men of genius who frame general theories. The 
 opinion of most Continental men of science seems, however, to be 
 decided on this special point, as may be seen from the judgment 
 given, not only by Dumas, but by Hoefer in his History of 
 Chemistry, by H. Kopp in his careful account of the discovery 
 of the composition of water, and by many others. I have merely 
 concurred with them. 
 
 It was in this spirit that I sought to trace the history of the dis- 
 coveries which constituted the doctrine of modern chemistry, by 
 faithfully reproducing all its phases, whilst at the same time 
 indicating the continuity of sequence in the facts and the paternity 
 of the ideas. I did this with an impartiality which has brought 
 upon me the reproach that I have been indifferent to the reputa- 
 tion of my countrymen the very opposite to the accusations which 
 are now directed against me. 
 
 As regards the composition of air, it is easy to separate facts 
 from ideas. It is certain that the discovery of oxygen is due to 
 Priestley. But, said Lavoisier, " If I am reproached for having 
 borrowed my proofs from the works of this celebrated philosopher, 
 at least none will contest my right to the conclusions, which are 
 often diametrically opposed to his." 
 
 Priestley, obstinately adhering to the theory of phlogiston, 
 regarded his now gas as consisting of the very substance of air 
 deprived simply of its phlogiston ; whilst nitrogen, according to 
 him, was formed also of this same substance combined with a com- 
 plementary portion of phlogiston. He remained faithful to this 
 doctrine, which obscured the true nature of the greater number of 
 chemical phenomena, until the moment when, like Lavoisier, perse- 
 cuted by his countrymen, who now proclaim his fame, driven from 
 home, his laboratory burnt by a mob, and threatened with death, 
 he fled to America, where he died in sadness and in solitude. 
 Even more unfortunate was Lavoisier ! 
 
 But whatever may have been the personal fate of these two 
 great men, if it is true that Priestley discovered oxygen, it is not 
 the less certain that the true theory of the nature of air is due 
 to Lavoisier. 
 
 The history of the composition of water is more complicated. 
 In reality the discovery of the facts belongs neither wholly to 
 Cavendish who undoubtedly played a most important part, inas- 
 much as he gave the impetus towards the definitive solution-^nor 
 to Lavoisier, who first established a knowledge of the facts by his 
 
136 Priestley, Cavendish, Lavoisier, vi 
 
 public experiments and his published writings nor even to the 
 two combined. They had predecessors, and at the moment even 
 when the light came, Monge played an essential part in the rigor- 
 ous demonstration of which Mr. Thorpe apparently has no sus- 
 picion. Thus each man's share in this history cannot be settled 
 by a word : we require to follow exactly the gradual progress of 
 experiment and publication. But here, again, if Lavoisier is not 
 the principal discoverer of the facts, it is he who has the incontest- 
 able merit of having furnished the exact interpretation of the 
 phenomena, freed from the mists of phlogiston, to which Cavendish 
 seems to have remained faithful to the day of his death. 
 
 I have elsewhere laid bare all these facts, and I have no 
 intention of reproducing here the details of a controversy exhausted 
 even in Lavoisier's time, and in which Mr. Thorpe does no more 
 than reproduce the unjustifiable imputations of Blagden, who, 
 impelled by passion, went so far as to interpolate and falsify, with 
 his own hand, the manuscript memoirs of Cavendish, in order to 
 gain arguments in support of his accusations. 
 
 Moreover, nothing more decisively establishes the part played by 
 Lavoisier, and his right to the institution of our modern theories, 
 than the letter of a contemporary English savant, Black, as cele- 
 brated for his discoveries in physics as in chemistry, and who 
 might have put forward claims on his own account. In 1791 he 
 wrote to Lavoisier, in a letter equally honourable to both : " The 
 numerous experiments which you have made on a large scale, and 
 which you have so well devised, have been pursued with so much 
 care and with such scrupulous attention to details, that nothing can 
 be more satisfactory than the proofs you have obtained. The 
 system which you have based on the facts is so intimately con- 
 nected with them, is so simple and so intelligible, that it must 
 become more and more generally approved and adopted by a great 
 number of chemists who have long been accustomed to the old 
 system. . . . Having for thirty years believed and taught the 
 doctrine of phlogiston as it was understood before the discovery of 
 your system, I, for a long time, felt inimical to the new system, 
 which represented as absurd that which I had hitherto regarded 
 as sound doctrine ; but this enmity, which springs only from the 
 force of habit, has gradually diminished, subdued by the clearness 
 of your proofs and the soundness of your plan." 
 
 We can but hope to see the day when the scientific men of 
 England will conform to the opinion of one of the most illustrious 
 of their countrymen. 
 
 M. BERTHELOT, of the Institute. 
 
VI 
 
 and " La Revolution Chimique " 137 
 
 Certain passages in M. Berthelot's letter, more especially 
 those reflecting on the character of Blagden, seemed to me to 
 require some notice. I therefore addressed the following 
 remarks to Nature of 6th November 1890 : 
 
 I quite agree with M. Berthelot that nothing is more 
 opposed to truth and justice than the introduction of national 
 prejudices into the history of science. It was for that reason 
 that I felt compelled, in the Leeds address, to protest against 
 the spirit and bias of the accounts of the discovery of the 
 facts relating to oxygen and the composition of water given 
 in La Revolution Chimique. Although M. Berthelot's letter 
 somewhat confuses the issues, there is, in reality, but small 
 difference between us. What I ventured to criticise was the 
 general tone and tendency of M. Berthelot's argument, which 
 seems to palliate, and even to justify, Lavoisier's pretensions 
 to a discovery in which he has no right even to be considered 
 as a participator. M. Berthelot now tells us in his letter 
 that he attributes the discovery of oxygen unreservedly 
 to Priestley. So far so good. It is something gained to 
 have thus secured such an unqualified statement from one 
 who occupies the position of authority in the world of 
 chemistry in France that is enjoyed by the present Perpetual 
 Secretary of the Academy. We may well hope, therefore, 
 that this particular question has been finally set at rest. 
 
 M. Berthelot need not ask British men of science to con- 
 form to the opinion of Black. They already do so. That to 
 Lavoisier, and to Lavoisier alone, belongs the merit of having 
 effected the overthrow of the theory of phlogiston, and of 
 having to that extent laid the foundation of modern chemistry, 
 is not questioned on this side of the Channel. So far as I 
 know, it has only been among Lavoisier's own countrymen 
 that any doubt on this point has been raised. We all re- 
 member the passionate scorn with which Lavoisier repudiated 
 and protested against the attempts of his compatriots to .rob 
 him of his rights : " Cette theorie n'est done pas comme je 
 
VI 
 
 138 Priestley, Cavendish, Lavoisier, 
 
 1'entends dire la theorie des chimistes frai^ais; elle est la 
 mienne, et c'est une propriete que je reclame aupres de mes 
 contemporains et de la posterite." It is true, as M. Berthelot 
 implies, that Black has claims. Lavoisier himself admits as 
 much. It would be easy, if it were not beside the points 
 at issue, to match the letter which M. Berthelot quotes by 
 others from Lavoisier in which he ascribes to Black the germs 
 of his doctrine. M. Berthelot, I repeat, confuses the issues. 
 This particular point was never raised by me in the address. 
 What I said was : " Two cardinal facts made the downfall of 
 phlogiston complete the discovery of oxygen, and the de- 
 termination of the compound nature of water. M. Berthelot's 
 contention is, that not only did Lavoisier effect the overthrow, 
 but he also discovered the facts." I, in common, I venture to 
 assert, with every British chemist, admit unreservedly that 
 Lavoisier effected the overthrow, but we deny that he dis- 
 covered the facts. It is altogether beside the question for M. 
 Berthelot now to say in effect : " Have I not praised your men 
 of science, and thereby drawn down upon myself the wrath of 
 my countrymen 1 And yet you are not satisfied ! " We are 
 sorry for M. Berthelot ; he is in the position of the man with 
 many friends, and his friends for the moment are a little 
 angry. He has either not the courage of his convictions, or 
 he has halted between two opinions with the usual conse- 
 quences. 
 
 With respect to the discovery of the compound nature of 
 water, M. Berthelot now takes up a different position from 
 that which he occupies in La Evolution Chimigue. His con- 
 tention there was that by every legitimate canon the experi- 
 ment of 24th June 1783 gives to Lavoisier the priority of 
 discovery. He now admits that Cavendish played " tin role 
 capital car il donna le branle aux esprits vers la solution 
 definitive." But how was this possible when Cavendish's 
 memoir was not published until January 1784? There is 
 really only one answer it was given simply by the interven- 
 
vi and " La Revolution Chimique" 139 
 
 tion of Blagden. I repeat that Blagden told Lavoisier of 
 Cavendish's researches and of his conclusions, and that it was 
 in the light of that knowledge that the experiment of 24th 
 June 1783 was made. There can be no question of this. 
 Blagden's testimony, as given in the letter to Crell, is as 
 direct and decisive as it is damning. It was never contra- 
 dicted by Lavoisier, nor by Laplace, Vandermonde, Fourcroy, 
 Meusnier, or Legendre, who were present on the occasion 
 when Lavoisier himself admits that he received the informa- 
 tion. M. Berthelot does not contradict it, but, instead, he 
 asperses the moral character of Blagden. This method of 
 treating a witness whose evidence cannot be rebutted is apt, 
 when unsuccessful, to recoil on him who attempts it. It is 
 perfectly true that Blagden interpolated the famous passage 
 in Cavendish's memoir : 
 
 During the last summer, also, a friend of mine gave some 
 account of them [the experiments] to M. Lavoisier, as well as of 
 the conclusion drawn from them. . . . But at that time, so far was 
 M. Lavoisier from thinking any such opinion warranted that, till 
 he was prevailed 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. 
 
 This passage, however, was inserted with Cavendish's know- 
 ledge and consent, and by his assistant and amanuensis, who 
 happened to be the very man who had a personal knowledge 
 of the facts. Assuming the statement to be true, where is the 
 immorality of the proceeding ? 
 
 Everything that we can learn authoritatively concerning 
 Blagden goes to show that he was an upright and honourable 
 man. Sir Joseph Banks. has testified to his abilities and in- 
 tegrity. Dr. Johnson spoke of his copiousness and precision 
 of communication, with the characteristic addition : "Blagden, 
 sir, is a delightful fellow." Laplace, Cuvier, Berthollet, and 
 Benjamin Delessert were among his friends. 1 He was rich, 
 
 1 Many of the letters of Berthollet to Blagden are still in existence. 
 In one of these, elated " 19 Mars, 1785," he writes from Paris : " L'on s'est 
 
140 Priestley, Cavendish, Lavoisier, vi 
 
 and was understood to have speculated to profit in the French 
 funds. For thirteen years he was a Secretary of the Royal 
 Society, and in 1792 he was knighted for his services to 
 science. Every year he spent a considerable time on the Con- 
 tinent, and was frequently in Paris. The gossip of the period 
 states that he aspired to the hand of Madame Lavoisier, who 
 preferred Count Rumford. He died in Berthollet's house at 
 Arcueil, on 26th March 1820. In an obituary notice in the 
 Moniteur of 22nd September 1820, M. Jomard testifies to his 
 benevolence and generosity, and states that "none of his 
 countrymen have done more justice to the labours and dis- 
 coveries of the French, or have contributed more than he to 
 the happy relations which have subsisted for six years (1814- 
 20) between the savans of the two countries." By his will he 
 provided liberally for his scientific friends : Berthollet, the 
 daughter of Madame Cuvier, and the daughter of Count 
 Rumford each received 1000; and Laplace 100, "to pur- 
 chase a ring." M. Berthelot asperses the character, not only 
 of Blagden, but also of his countrymen, by his insinuations. 
 Would he have us believe that Berthollet, Cuvier, and Laplace 
 would extend their friendship to, and receive pecuniary 
 benefits from, one whom they believed had foully stabbed 
 their compatriot in the back 1 It is surely incumbent on M. 
 Berthelot, on every ground, either to substantiate his implica- 
 tions or to withdraw them. 
 
 M. Berthelot makes the gratuitous assumption that I am 
 ignorant of the work of Monge. Whether I am or not is 
 altogether beside the mark. There is, indeed, no question of 
 Monge. Monge distinctly disclaims priority to Cavendish, 
 
 beaucoup occupe ici ces derniers terns de la belle decouverte de Mr. Cavendish, 
 sur la composition de 1'eau : Mr. Lavoisier a tache de porter sur cet objet 
 toute 1'exactitude dont il est susceptible. . . . Mr. Lavoisier veut repeter 
 1' experience en faisant bruler 1'air dephlogistique dans le gas inflammable, et 
 il y a apparence qu'alors on n'aura point d'acide nitreux, selon les belles obser- 
 vations de Mr. Cavendish." Is this language consistent with the belief that 
 Berthollet, who must have known the facts, regarded Lavoisier as the real 
 discoverer of the compound nature of water ? 
 
vi and u La Revolution Chimique" . 141 
 
 nor did he attempt to establish a right to be considered an in- 
 dependent discoverer of the true nature of water. In his 
 memoir, " Sur le Kesultat de I'lnflammation du Gas inflam- 
 mable et de 1'Air dephlogistique dans les Vaisseaux Clos," he 
 tells us that the experiments recorded in it were made in June 
 and July 1783, and repeated in October of the same year. 
 " I did not then know," he adds, " that Mr. Cavendish had 
 made them several months before in England, though on a 
 smaller scale ; nor that MM. Lavoisier and Laplace had made 
 them about the same time at Paris in an apparatus which did 
 not admit of as much precision as the one which I employed." 
 I fail to see what M. Berthelot gains by his reference to 
 Monge. 
 
 M. Berthelot reproaches Priestley and Cavendish for their 
 adherence to phlogistonism. I say it with all respect but is 
 it seemly for M. Berthelot, of all men, to cast this stone *? Is 
 not he himself an exemplification of that conservatism which 
 he deplores 1 A generation ago the doctrine of Avogadro be- 
 came the corner-stone of that edifice of which M. Berthelot 
 asserts that Lavoisier laid the foundations. Indeed, the in- 
 troduction of that doctrine effected a revolution hardly less 
 momentous than that of which Lavoisier was the leader. But 
 what has been M. Berthelot's consistent attitude towards this 
 teaching 1 We can illustrate it by a single example. He is 
 the sole teacher in Europe of any position who continues to 
 symbolise the constitution of that very substance of which he 
 claims that Lavoisier discovered the composition by a formula 
 which is as obsolete as any conception of phlogistonism. 
 
VII 
 
 MICHAEL FARADAY 
 
 A REVIEW OF DR. BENCE JONES'S "LIFE AND LETTERS OF FARAD AY. "- 
 MANCHESTER GUARDIAN, 1870. 
 
 MICHAEL FARADAY, one of the greatest experimental philo- 
 sophers of this or indeed of any other century, was born at 
 Newington, in Surrey, on the 22nd September 1791. Shortly 
 after the birth of Michael, their third child, his parents settled 
 permanently in London ; but through the continued ill-health 
 of the father, who was a blacksmith by trade, the family were 
 always in straitened circumstances. During the distress of 
 1801 they received public relief, and to the little Michael one 
 loaf of bread was given each week, and it had to serve him for 
 that length of time. Of his mother Faraday always spoke in 
 the most affectionate terms, and to her care and solicitude may 
 be attributed the great influence which his home had upon his 
 character. Although unable to enter into his occupations, she 
 was exceedingly proud of her son ; so much so that Faraday 
 asked his wife not to talk to his mother so much about him 
 or his honours, saying she was quite proud enough of him, 
 and it would not be good for her. Poor as the parents were, 
 they managed to afford their children some little school 
 learning, and Michael obtained the rudiments of reading, 
 writing, and arithmetic at a common day-school. AYhen 
 twelve years old the young Faraday went on trial for a year 
 
vii Michael Faraday 143 
 
 as an errand boy to Mr. George Eiebau, a bookseller and 
 bookbinder in Blandf ord Street, near Manchester Square. He 
 tells us "that it was his duty, when he first went, to carry 
 round the papers that were lent out by his master. Often on 
 a Sunday morning he got up very early and took them round, 
 and then he had to call for them again ; and frequently, when 
 he was told the paper was not done with, 'You must call 
 again,' he would beg to be allowed to have it, for his next 
 place might be a mile off, and then he would have to return 
 over the ground again, losing much time and being very un- 
 happy if he was unable to get home to make himself neat, 
 and to go with his parents to their place of worship." The 
 Faradays were members of a Sandemanian congregation, and 
 to this sect Faraday adhered throughout his life, and for 
 many years was an elder of their chapel. 
 
 We are told that in after-life the remembrance of his 
 earliest occupation was often brought to the mind of Faraday. 
 One of his nieces said that he rarely saw a newspaper boy 
 without making some kind remark about him. "I always 
 feel a tenderness for those boys," he said on one occasion, 
 " because I once carried newspapers myself." 
 
 The year of probation having expired, Faraday was appren- 
 ticed to his master, who, as it is written in the indentures, 
 required no premium in consideration of his previous faithful 
 service. The young Faraday was by no means precocious in dis- 
 position, but his great originality of mind quickly showed itself. 
 Few books passed under his hands without his obtaining some 
 knowledge of their contents. Watts On the Mind, he said, 
 first made him think, and Mrs. Marcet's Conversations on 
 Chemistry, and the article "Electricity," in an encyclopaedia 
 he was employed to bind, first turned his attention to science. 
 His amiability, and the intelligent nature of his conversation, 
 soon attracted the attention of his master's customers ; and 
 one of them, a Mr. Dance, afforded him the opportunity of 
 hearing Sir Humphry Davy lecture at the Royal Institution. 
 
1 44 Michael Faraday vn 
 
 Davy was then near the zenith of his fame; his brilliant 
 discovery of the compound nature of the alkalies and alkaline 
 earths created an epoch in the history of chemistry, and 
 stamped the discoverer as one of the greatest workers of his 
 time. Probably no English philosopher ever enjoyed a higher 
 degree of popularity than did Davy about this time. Science 
 was just then in fashion, and chemistry all the rage. 
 Albemarle Street was often blocked with the carriages of the 
 fine ladies and gentlemen who thronged to hear the great 
 chemist expound the new theories which his own discoveries 
 had helped to inaugurate. Some may think that there was 
 much in the career of Davy to have excited the young 
 Faraday's aspirations ; in their origin at least the baronet and 
 the bookbinder had something in common, and by the same 
 steps by which the one had risen the other might mount. But 
 it is more than probable that then, and for a long time subse- 
 quently, the desire to emulate the titled lecturer never once 
 crossed the mind of his humble auditor, perched over the 
 clock in the gallery. Davy's example may have stimulated 
 his hopes, but it did not create them. The bias to his in- 
 clinations had already been given. Faraday's occupation as 
 a bookbinder was going, if not gone. His longing to escape 
 from trade continually breaks out in his correspondence. 
 " The desire," he says, " to be engaged in scientific occupation, 
 even though of the lowest kind, induced me to write, in my 
 ignorance of the world and simplicity of my mind, to Sir 
 Joseph Banks, then President of the Eoyal Society. Naturally 
 enough 'no answer' was the reply left with the porter." His 
 thoughts at this time, when he was "giving up trade and 
 taking to science," are well seen in his letters to his friend 
 Abbott. Mr. Abbott was a confidential clerk in the City, 
 whose acquaintance Faraday had made during a course of 
 lectures on natural philosophy given by Mr. Tatum. Abbott 
 was apparently well educated, and the characteristic deference 
 paid by Faraday to his friend's superior school-learning may 
 
vii Michael Faraday 145 
 
 repeatedly be seen in the course of their long correspondence. 
 "These letters to Abbott," says Dr. Bence Jones, "possess an 
 interest almost beyond any other letters which Faraday after- 
 wards wrote. It is difficult to believe that they were 
 written by one who had been a newspaper boy, and who was still 
 a bookbinder's apprentice, riot yet twenty-one years of age, 
 and whose only education had been the rudiments of reading, 
 writing, and arithmetic. Had they been written by a highly- 
 educated gentleman, they would have been remarkable for 
 the energy, correctness, and fluency of their style, and for the 
 courtesy, kindness, candour, deference, and even humility 
 of the thoughts they contain." This is high praise, but it is 
 fully merited. Some of the letters are indeed models of 
 epistolary style. 
 
 Faraday was not content with simply listening to Davy, 
 but made careful notes of the lectures, afterwards writing 
 them out in a fuller form, and interspersing them with such 
 drawings as he could make. His own words to Dr. Paris, the 
 biographer of Davy, written seventeen years after, will best 
 show what he then did with these notes : " My desire to 
 escape from trade, which I thought vicious and selfish, and to 
 enter into the service of science, which I imagined made its 
 pursuers amiable and liberal, induced me at last to take the 
 bold and simple step of writing to Sir Humphry Davy, ex- 
 pressing my wishes, and a hope that if an opportunity came 
 in his way he would favour my views ; at the same time I 
 sent the notes I had taken of his lectures." Davy, at their 
 first meeting, wished to dissuade the young aspirant from the 
 course which he contemplated taking, telling him that science 
 was a harsh mistress, and in a pecuniary point of view but 
 poorly rewarded those who devoted themselves to her service. 
 He smiled at Faraday's notion of the superior moral feelings 
 possessed by scientific men, and said that a few years' experi- 
 ence would set him right on this matter ; which it most 
 certainly did, as we shall hereafter show. Some time after 
 
 L 
 
1 46 Michael Faraday vn 
 
 this interview Faraday was startled late at night by a loud 
 knock at the street door, and was still more astonished to see 
 a footman alight from a carriage and leave a note for him. 
 The note was from Sir Humphry to inform him that the 
 position of laboratory-assistant at the Koyal Institution was 
 then vacant, and if he were still minded to leave his present 
 occupation the place was at his disposal. A few days after 
 Faraday commenced his duties at Albemarle Street at a salary 
 of 25s. a week, with two rooms at the top of the house. 
 
 Such was the origin of his connection with the Royal Institu- 
 tion a connection which lasted nearly to the end of his long 
 life, and raised the Institution to the eminence which it at 
 present occupies. The very nature of his first duties there 
 shows that he must have already acquired no inconsiderable 
 amount of manipulative skill from the experiments which he 
 made in the course of his self-tuition in Blandford Street. 
 Davy was at that time engaged on the study of the so-called 
 nitrogen trichloride, perhaps the most explosive compound 
 known to chemists. That he should allow Faraday to assist 
 him in a research where a single blunder might be attended 
 with the most serious consequences, indicates that Davy, 
 himself no mean experimenter, fully recognised the other's 
 ability. Throughout the course of the investigation Faraday 
 was exposed to constant peril, and it was only through con- 
 tinual care and precaution that no very sad results attended 
 the numerous explosions of this singularly unstable compound. 
 
 In the autumn of this year (1813), Sir Humphry Davy pro- 
 posed to go abroad, and offered to take Faraday with him as 
 amanuensis, promising that he should resume his situation at 
 the Institution upon his return. During his travels on the 
 Continent with Davy, which lasted about a year and a half, 
 Faraday kept a journal, in which he noted down his impres- 
 sions of the journey. This journal, which occupies a consider- 
 able portion of the first volume of Dr. Bence Jones's work, is 
 as remarkable for the vividness and accuracy of the descrip- 
 
vii Michael Faraday 147 
 
 tions of what he saw, as for the entire absence of any 
 particulars relating to those with whom he travelled. His 
 cautious reticence on this latter point is scarcely less apparent 
 in his letters ; but the little that does escape him shows that 
 his journey was not one of unmixed pleasure. His relation to 
 Sir Humphry Davy was not very clearly denned ; to his 
 duties as an amanuensis he was not unf requently obliged to add 
 those of a valet, and this service was especially annoying to 
 him, the more so that it was entirely unexpected. Perhaps 
 no one ever possessed more real humility than did Faraday, 
 and the very genuineness of his humility is shown by its 
 never degenerating into servility. In one of his letters to 
 Abbott he writes : "I fancy I have cause to grumble, and 
 yet I can scarcely tell why. If I approve of the system of 
 etiquette and valuation formed by the world, I can make 
 a thousand complaints ; but, perhaps, if I acted influenced by 
 the pure and unsullied dictates of common sense, I should 
 have nothing to complain of, and therefore all I can do is to 
 give you the circumstances." He then relates how it came to 
 pass that he was obliged to undertake duties so irksome to 
 him. But he concludes by saying that it was, perhaps, the 
 name more than the thing which hurts. " I should have but 
 little to complain of were I travelling with Sir Humphry alone, 
 or were Lady Davy like him ; but her temper makes it often- 
 times go wrong with me, with herself, and with Sir Hum- 
 phry." In another letter he writes : " I am quite ashamed of 
 dwelling so often on my own affairs but as I know you wish 
 it, I shall briefly inform you of my situation.". . . He then 
 goes on to say that Sir Humphry was unable to meet with a 
 valet to his satisfaction. "This, of course, throws things into 
 my duty which it was not my agreement, and is not my wish, 
 to perform, but which are, if I remain with Sir Humphry, un- 
 avoidable. These, it is true, are very few ; for, having been 
 accustomed in early years to do for himself, he continues to do 
 so at present, and he leaves very little for a valet to perform ; 
 
148 Michael Faraday vn 
 
 and as he knows that it is not pleasing to me, and that I do 
 not consider myself as obliged to do them, he is always as 
 careful as possible to keep those things from me which he 
 knows would be disagreeable. But Lady Davy is of another 
 humour. She likes to show her authority, -and at first I 
 found her extremely earnest in mortifying me. This occa- 
 sioned quarrels between us, at each of which I gained ground 
 and she lost it; for the frequency made me care nothing 
 about them, and weakened her authority, and after each she 
 behaved in a milder manner." 
 
 But his ardent desire for improvement and the oppor- 
 tunity he possessed of adding to his knowledge of chemistry 
 and of the other sciences continually induced him to pro- 
 ceed. At Geneva Faraday met Volta, but the only record 
 of his interview with the great electrician is contained in 
 the following lines : " Friday 17th. Saw M. Volta, who 
 came to Sir Humphry Davy, a hale, elderly man, bearing 
 the red ribbon, and very free in conversation." If the 
 young and diffident amanuensis could have foreseen the 
 glorious destiny that awaited him, what emotions this meeting 
 must have raised. At Geneva Faraday also made the acquaint- 
 ance of De La Rive, who, " undazzled by the brilliancy of 
 Davy's reputation, was able to see the true worth of his 
 assistant. This led him on one occasion to place Faraday 
 even then on a par with Davy. He invited them both to 
 dinner. Davy, it is said, declined to dine with one who, in 
 some things, acted as his servant. De La Rive expressed his 
 feelings only by saying he was sorry he should have to give 
 two dinners instead of one. In 1858 Faraday wrote to Mr. 
 A. De La Rive : " I have some such thoughts (of gratitude) 
 even as regards your own father, who was, I may say, the 
 first who personally at Geneva, and afterwards by corre- 
 spondence, encouraged, and by that sustained me." 
 
 Having thus travelled through France, Italy, Switzer- 
 land, and the Tyrol, Faraday returned to England in the 
 
VII 
 
 Michael Faraday 149 
 
 spring of 1815, and immediately resumed his duty at the 
 Royal Institution. Davy could no longer withhold the 
 acknowledgment of the energy and worth of his assistant. 
 On the other hand, Faraday had now full knowledge of " his 
 master's genius and power. He had compared him with the 
 French philosophers whilst helping him in his discovery of 
 iodine ; and he was just about to see him engage in those 
 researches on fire-damp and flame which ended in the glorious 
 invention of the Davy Lamp, and gave to Davy a popular 
 reputation, even beyond that which he had gained in science 
 by the greatest of all his discoveries potassium." Dr. Jones 
 is slightly in error here; iodine was discovered in 1812 by 
 Courtois, a saltpetre manufacturer in Paris ; Sir Humphry 
 Davy, however, first conclusively demonstrated its elementary 
 nature. 
 
 In the following year Faraday commenced lecturing. He 
 delivered his first lecture on January 17, 1816, at the City 
 Philosophical Society, on " the general properties of matter." 
 In the very full notes which Dr. Bence Jones has pre- 
 served to us of this and of the subsequent lectures delivered 
 during the year at the same Society, we think we can trace 
 the germs of that great success which attended Faraday's 
 career as a lecturer. These notes are remarkable for their 
 originality of thought and fulness of illustration. In his 
 accurate digests of contemporary knowledge, we have evidence 
 of the diligence with which Faraday set about educating him- 
 self for his new vocation. Lecturing became with him an art, 
 to be carefully and systematically studied. His letters to 
 Abbott, and his commonplace book, show that he had pre- 
 viously framed pretty accurate ideas respecting the province 
 and functions of the lecturer whilst attending Mr. Brande and 
 Mr. Powell in their lectures at the Eoyal Institution. He 
 now took private lessons in elocution, and prevailed on his 
 teacher to attend his lectures in order that the errors of his 
 address and delivery might be brought home to him. Eleven 
 
1 50 Michael Faraday vn 
 
 years after the date of this early attempt, Faraday delivered 
 his first lecture at the Eoyal Institution. As he steps upon the 
 place where, fifteen years before, Davy had stood, we wonder 
 if his thoughts revert to the memory of the young bookbinder's 
 apprentice, seated in the gallery over the clock ! " For thirty- 
 eight years," says his biographer, " his lectures were the life of 
 the Eoyal Institution. His singular power of making himself 
 one of his audience was felt in his juvenile lectures, in his 
 theatre courses, and in his Friday evening addresses. In his 
 juvenile lectures, his simple words and his beautiful experiments, 
 his quickness and his clearness, kept the attention and fixed 
 his instruction in the mind even of the youngest of his hearers, 
 whilst the most practised teacher would find old experiments 
 shown in a new form, which the genius of Faraday only could 
 have invented, and which his handicraft enabled him to carry 
 out. In his theatre lectures his matter was always over 
 abundant, his experiments were always successful, his know- 
 ledge was always at the furthest limits to which it had at the 
 time been extended by himself or by others, and yet his con- 
 sideration for those who knew but little never failed. But it 
 was in his Friday evening discourses that his great power as a 
 lecturer came out. His manner was so natural that the 
 thought of any art in his lecturing never occurred to any one. 
 Eapidly, and yet clearly, he made the object of his lecture 
 known. Those who had but little knowledge could see his 
 starting-point, and they thought they saw where he was 
 going. Those who knew most followed him beyond the 
 bounds of their own knowledge, forgetting almost the lecturer, 
 who seemed to forget himself, in his words and his experi- 
 ments, and who appeared to be trying only to enable them to 
 judge what his latest discoveries were worth ; and when he 
 brought the discoveries of others before his hearers, one object, 
 and one alone, seemed to determine all he said and did, and 
 that was, " without commendation and without censure, to do 
 the utmost that could be done for the discoverer." 
 
viz Michael Faraday 1 5 1 
 
 In 1821, when twenty-nine years of age, Faraday married 
 Miss Sarah Barnard, the daughter of an elder of the Sande- 
 manian Chapel. Many years after he wrote in the notes 
 of his own life: "On June 12, 1821, he married an event 
 which more than any other contributed to his earthly happiness 
 and healthful state of mind. The union has continued for 
 twenty-eight years, and has nowise changed, except in the 
 depth and strength of its character." 
 
 About this time Faraday received his first scientific honour ; 
 it came from the Cambridge Philosophical Society. Perhaps 
 no scientific man ever obtained during his lifetime such an 
 extended recognition of his services as did Faraday ; in all he 
 received no less than ninety-five honorary titles and marks of 
 merit from the various learned societies scattered throughout 
 Europe and America. In 1838 he wrote : "One title, that of 
 F.K.S., was sought and paid for; all the rest are spontaneous 
 offerings of kindness and goodwill." Writing, in 1854, to 
 Lord Wrottesley, then Chairman of a Parliamentary Committee 
 of the British Association, he says : " Through the kindness of 
 all, from my Sovereign downwards, I have that which supplies 
 all my need ; and in respect of honours I have, as a scientific 
 man, received from foreign countries and sovereigns those 
 which, belonging to very limited and select classes, surpass, 
 in my opinion, anything that it is in the power of rny own to 
 bestow. I cannot say that I have not valued such distinctions ; 
 on the contrary, I esteem them very highly, but I do not 
 think that I have ever worked for or sought after them." 
 
 In 1829 he was made a member of the Scientific Advising 
 Committee of the Admiralty, and from about this time dates 
 his connection with the Government, which lasted nearly to the 
 end of his life. To Lord Auckland he wrote : "I have always, 
 as a good subject, held myself ready to assist the Government 
 if in my power not for pay, for except in one instance (and 
 then only for the sake of the person joined with me), I 
 refused to take it." The exception to which he here refers 
 
VII 
 
 152 Michael Faraday 
 
 was in the case of the Has well Colliery explosion, when he 
 was sent down by the Government, together with Sir (then 
 Mr.) Charles Lyell, to attend the inquest. Faraday, how- 
 ever, squared the account with his conscience by subscribing 
 most liberally to the fund raised for the widows and children 
 of those who had perished in the catastrophe. 
 
 In 1836 he was appointed Scientific Adviser to the Trinity 
 House ; and his work, extending over a period of thirty years, 
 was of the most miscellaneous character, including "the venti- 
 lation of lighthouses ; the arrangements of their lightning con- 
 ductors ; the analysing and supervising of their drinking waters ; 
 the examination of their optical apparatus ; the determination 
 of the worth of the different propositions made to the Trinity 
 House regarding the lights, extending from the practical use 
 of the magneto-electric light down to the samples of cottons, 
 oils, and paints that were used." When he was appointed he 
 spoke to the deputy-master "of his indifference to his pro- 
 position as a matter of interest, though not as a matter of 
 kindness." The value of this appointment was, in the words of 
 Dr. Jones, "an unlimited amount of kindness and 200 a year." 
 
 In 1816 Faraday made his first contribution to science. 
 It consisted of an analysis of a specimen of native caustic 
 lime. Sir Humphry Davy had given him the analysis to 
 make as a first attempt in chemistry "at a time," as he tells 
 us, "when his fear was greater than his confidence, and 
 both far greater than his knowledge; at a time, also, 
 when he had no thought of ever writing an original 
 paper on science." His activity of mind at this time was 
 marvellous. From the date of his first paper until 1820 he 
 contributed no less than thirty-seven notices and papers to 
 the Quarterly Journal of Science. 
 
 But the work which made Faraday the wonder of the 
 scientific world was yet to be done, and the records of the 
 next eleven years show how carefully and how patiently he 
 educated himself for his great task. In 1823 he published 
 
vii Michael Faraday 153 
 
 his first paper on the condensation of the gases. The first gas 
 which he liquefied was chlorine. Acting upon a suggestion 
 made by Davy, Faraday, who was then working upon the 
 hydrate of chlorine, sealed up some of the crystals of this sub- 
 stance in a bent tube, and subjected them to heat. The result 
 was the formation in the bent portion of the tube of a quantity 
 of a yellow oily liquid which, as Faraday "puzzled out" for 
 himself, could only be condensed chlorine. 
 
 This discovery immediately attracted universal attention ; 
 but the merit of it was claimed by another. The claimant 
 was no other than Davy. A feeling of jealousy had gradu- 
 ally been growing up in the mind of the Honorary 
 Professor of Chemistry at the Eoyal Institution towards 
 his assistant, and this discovery exposed it to the world. 
 Charges of plagiarism were freely whispered about, but it 
 was only after the lapse of many years, when the question 
 was again revived by the late Dr. Davy in the Life of his 
 illustrious brother, that Faraday was prevailed upon to set 
 the matter in its proper light. Faraday was always very 
 much averse to scientific controversy, and it was difficult to 
 move him to take up his pen in his own defence. Many 
 years afterwards he attempted to mediate between Matteucci 
 and Du Bois Raymond, who were at variance. Writing 
 to the former, he says : " Who has not to put up in his 
 day with insinuations and misrepresentation in the accounts 
 of his proceedings given by others, bearing for the time 
 the present injustice, which is often unintentional and often 
 originates in hasty temper, and committing his fame and 
 character to the judgment of the men of his own and 
 future time. I see that that moves you which would move 
 me most namely, the imputation of a want of good faith; and 
 I cordially sympathise with any one who is so charged unjustly. 
 Such cases have seemed to me almost the only ones for which 
 it is worth while entering into controversy. I have felt myself 
 not unfrequently misunderstood, often misrepresented, some- 
 
154 Michael Faraday vn 
 
 times passed by, as in the cases of specific inductive capacity, 
 magneto - electric currents, definite electrolytic action, etc. ; 
 but it is only in the cases where moral turpitude has been 
 implied that I reply. . . . These polemics of the scientific 
 world are very unfortunate things ; they form the great stain 
 to which the beautiful edifice of scientific truth is subject. 
 Are they inevitable ? They surely cannot belong to science 
 itself, but to something in our fallen nature." Faraday's 
 defence of himself in the affair of the condensation of the 
 gases is very explicit. It was written to his friend, Eichard 
 Phillips, and was published in the Philosophical Magazine for 
 1836. He concludes it as follows : 
 
 I have never remarked upon or denied Sir H. Davy's share of 
 the condensation of chlorine or the other gases ; on the contrary, I 
 think that I long ago did him full justice in the papers themselves. 
 How could it be otherwise ? He saw and revised the manuscripts ; 
 through his hands they went to the Koyal Society, of which he was 
 president at the time ; and he saw and revised the printer's proofs. 
 Although he did not tell me of his expectations when he suggested 
 heating the crystals in a closed tube, yet I have no doubt that he 
 had them ; and, though perhaps I regretted losing my subject, I 
 was too much indebted to him for much previous kindness to think 
 of saying that that was mine which he said was his. But observe 
 (for my sake) that Sir H. Davy nowhere states that he told me what 
 he expected, or contradicts the passages in the first paper of mine, 
 which describe my course of thought, and in which I claim the de- 
 velopment of the actual results. All this activity in the condensing 
 of gases was simultaneous with the electro-magnetic affair, and I 
 had learned to be .cautious upon points of right and priority. 
 When, therefore, I discovered in the course of the same year that 
 neither I nor Sir H. Davy had the merit of first condensing the 
 gases, and especially chlorine, I hastened to perform what I thought 
 right, and had great pleasure in spontaneously doing justice and 
 honour to those who deserved it. Monge and Clouet had con- 
 densed sulphurous acid probably before the year 1800 ; Northmore 
 condensed chlorine in the years 1805 and 1806 (Nicholson's Journal). 
 I therefore published on January 1 in the following year, 1824, a 
 historical statement of the liquefaction of gases (Quarterly Journal 
 of Science). . . . The value of this statement of mine has since been 
 fully proved, for, upon Mr. Northmore's complaint, ten years after, 
 
VII 
 
 Michael Faraday 155 
 
 with some degree of reason, that great injustice had been done to 
 him in the affair of the condensation of gases, and his censure on 
 the " conduct of Sir H. Davy, Mr. Faraday, and several other 
 philosophers for withholding the name of the first discoverer," I was 
 able, by referring to the statement, to convince him and his friends 
 that if my papers had done him wrong, I at least had endeavoured 
 also to do him right (Philosophical Magazine, 1834). Believing that 
 I have now said enough to preserve my own "honest fame" from 
 any injury it might have risked from the mistakes of Dr. Davy, I 
 willingly bring this letter to a close, and trust I shall never again 
 have to address you on the subject. 
 
 Davy's jealousy culminated in active opposition to the 
 election of Faraday as a Fellow of the Koyal Society. His 
 certificate as a candidate was drawn up by his friend Phillips, 
 and the first signatures were those of Wollaston, Children, 
 Babington, and Sir W. Herschel. Many years after Faraday 
 gave the following account of what had passed between him 
 and Davy relative to the matter of his election : " Sir H. 
 Davy told me 1 must take down my certificate. I replied 
 that I had not put it up ; that I could not take it down, as it 
 was put up by my proposers. He then said I must get my 
 proposers to take it down. I answered that I knew they 
 would not do so. Then he said : I, as president, will take it 
 down. I replied that I was sure Sir H. Davy would do what 
 he thought was for the good of the Eoyal Society." One of Fara- 
 day's* proposers bears witness that " Sir H. Davy had walked 
 for an hour round the courtyard of Somerset House arguing 
 that Faraday ought not to be elected." Davy's prediction to 
 the aspiring young bookbinder that his notions of the superior 
 moral feelings of philosophic men would be set right by a 
 few years' experience was signally verified. But on the ballot 
 being taken Faraday was almost unanimously elected ; there 
 was only one black ball. 
 
 About this time Faraday discovered benzene, or, as he then 
 termed it, bicarburet of hydrogen, among the products of the 
 condensed oil-gas manufactured by the Portable Gas Company. 
 
156 Michael Faraday \\\ 
 
 Faraday may thus be said to have laid the foundation of that 
 immense industry which recent discoveries in chemistry have 
 so rapidly developed the manufacture of the so-called aniline 
 dyes. Enormous quantities of benzene are now employed in 
 the production of these beautiful colours. 
 
 In 1831 the great work of his life commenced by the 
 publication in that year of the first series of his immortal 
 Experimental Researches in Electricity. Our limited space en- 
 tirely prevents any attempt to do justice to the nature and 
 extent of his researches on magneto -electricity, voltaic induc- 
 tion, definite electro -chemical decomposition ; nor, we regret 
 to add, can we refer our readers to the book before us for 
 a more detailed account. In our opinion Dr. Bence Jones 
 fails to present any clear conception of the nature of Fara- 
 day's discoveries. Dr. Jones has in one sense performed 
 his duty as a biographer most conscientiously, perhaps 
 rather too conscientiously ; like the famous Cid Hamet, he is 
 the most punctual and diligent searcher after the minutest 
 circumstances, " even to the very atoms of his true history," 
 and the result is that too much is left to the judgment and 
 discrimination of his reader in the matter of Faraday's dis- 
 coveries. Thus we see on the same page, with no attempt at 
 distinction, an account of a paper on the general magnetic 
 relations and characters of the metals, together with one on 
 such a comparatively unimportant subject as a supposed new 
 sulphate and oxide of mercury. Happily, however, Faraday 
 does not want an interpreter. We can refer our readers to no 
 clearer exponent of his labours than Professor Tyndall, whose 
 charming book, Faraday as a Discoverer, is eminently worthy 
 the attention of those who desire to know more of the great 
 philosopher's work. 
 
 We have already spoken of Faraday as a good subject, 
 and we should like to dwell for a moment on the manner 
 in which he fulfilled his duties as a good citizen. He took 
 the warmest interest in all the great questions of the day. 
 
vii Michael Faraday 157 
 
 His desire for sanitary reform was the occasion of his letter 
 to the Times on the state of the river Thames. Who is not 
 familiar with Leech's cartoon of Faraday giving his card to 
 Father Thames, with the hope that the " Dirty fellow will 
 consult the learned professor?" Within recent years the 
 question of the position of natural science in the various 
 curricula of our schools and universities has attracted con- 
 siderable attention. Faraday's opinion on this subject is 
 especially valuable. " I do think," he says, " that the study 
 of natural science is so glorious a school for the mind that, 
 with the laws impressed on all created things by the Creator, 
 and the wonderful unity and stability of matter and the 
 forces of matter, there cannot be a better school for the 
 education of the mind." When examined before the Public 
 School Commissioners, he said : " That the natural knowledge 
 which had been given to the world in such abundance during 
 the last fifty years, I may say, should remain untouched, and 
 that no sufficient attempt should be made to convey it to the 
 young mind, growing up and obtaining its first views of these 
 things, is to me a matter so strange that I find it difficult to 
 understand; though I think I see the opposition breaking 
 away, it is yet a very hard one to be overcome. That it ought 
 to be overcome I have not the least doubt in the world." 
 
 In 1835 Faraday was told that Sir Eobert Peel, then 
 Prime Minister, contemplated offering him a pension of 300 
 a year. His first impulse was to refuse it, on the ground that 
 he could not accept a pension whilst he was able to work for 
 his living. He was induced, however, by his relatives to 
 reconsider his determination, and waited upon Lord Melbourne, 
 who was then in office, to learn his intentions in the matter. 
 During their conversation his lordship expressed himself, as 
 he himself admits, in rather " too blunt and inconsiderate a 
 manner." According to Dr. Jones it is probable that he 
 designated the system of giving pensions to literary and 
 scientific men as a piece of humbug. However, on the 
 
1 5 8 Michael Faraday . v 1 1 
 
 same evening, Faraday left his card with the following note 
 at Lord Melbourne's office : 
 
 October 26. 
 
 MY LORD The conversation with which your Lordship 
 honoured me this afternoon, including, as it did, your Lordship's 
 opinion of the general character of the pensions given of late to 
 scientific persons, induces me respectfully to decline the favour 
 which, I believe, your Lordship intends for me ; for I feel that I 
 could not with satisfaction to myself accept at your Lordship's 
 hands that which, though it has the form of approbation, is of the 
 character which your Lordship so pithily applied to it. 
 
 The matter, however, was ultimately amicably settled, and 
 Faraday enjoyed his well-merited pension to the end of his 
 Says. 
 
 In 1858, through the kind consideration of the Prince 
 Consort, the Queen offered him a house on Hampton Court 
 Green, in which he passed the rest of his life. He was now 
 nearly seventy years of age. The dreaded reaction of that 
 intense mental strain to which his mind had been subjected 
 had long since set in ; but thanks to the watchful care and 
 tender solicitude of his wife, the evil consequences were but 
 very gradual in their growth. In 1841, when he was scarcely 
 fifty years of age, he was obliged, through loss of memory 
 and giddiness, to discontinue his researches for a time. He 
 then rested almost entirely for a year, spending much of his 
 time in Switzerland ; and during the four succeeding years no 
 further experiments in electricity were made, with the ex- 
 ception of an inquiry into the mode of working of Sir W. 
 Armstrong's hydro-electric machine. 
 
 His mind was now gradually breaking up, and the know- 
 ledge of his increasing infirmities compelled him to resign, 
 one by one, his various appointments. He now seldom left 
 Hampton Court. A friend from London asked how he was : 
 "Just waiting," was the reply. At another time he wrote : 
 " I bow before Him who is Lord of all, and hope to be kept 
 waiting patiently for His time and mode of releasing me 
 
vii Michael Faraday 159 
 
 according to His divine Word, and the great and precious 
 promises whereby His people are made partakers of the 
 divine nature." 
 
 On August 25, 1867, he passed quietly and peacefully 
 away, dying, with scarcely a premonitory symptom, in his 
 chair in his study. His funeral was strictly private; and, 
 in accordance with his wishes, a gravestone " of the most 
 ordinary kind " in Highgate Cemetery marks the last resting- 
 place of one of the greatest and truest of experimental 
 philosophers, and of one of the humblest and most tender- 
 hearted of men. 
 
 In the foregoing sketch of the life and labours of Faraday 
 we have had occasion more than once to offer our opinion as 
 to the manner in which his biographer, Dr. Bence Jones, has 
 accomplished his task. The autobiographical details of the 
 work have been arranged with great tact and discrimination, 
 and the desire to set forth the singular beauty and purity of 
 his friend's character is evident on every page. It is im- 
 possible to over-estimate the amount of good which such a 
 book may do. On reading it one feels the more constrained 
 to admit that " a mind fraught with integrity is the noblest 
 possession." 
 
VIII 
 
 THOMAS GKAHAM 
 
 A LECTURE (WITH ADDITIONS), DELIVERED IN THE YORKSHIRE COLLEGE, 
 LEEDS, INTRODUCTORY TO THE EVENING CLASS SESSION, 1877-78. 
 
 THOMAS GRAHAM, one of the most original chemical thinkers 
 of this century, was born in Glasgow on 21st December 1805. 
 The house in St. Andrew's Square, in the east end of the city, 
 in which he first saw the light, is still standing. The Grahams 
 belonged to Perthshire, but the father of the chemist, James 
 Graham, had removed to Glasgow when very young, and 
 ultimately became what was then styled a manufacturer. His 
 business was sufficiently prosperous to enable him to give his 
 son the benefit of a sound education. When scarcely six 
 years old young Graham was sent to an English preparatory 
 school, whence he was removed in 1814 to the High School, 
 and at fourteen years of age he began his university career, 
 entering, amongst others, the classes of Thomas Thomson on 
 Chemistry and Meikleham on Natural Philosophy. He was 
 a quiet, studious boy, conscientious and diligent in his work, 
 but not otherwise remarkable among his fellows. 
 
 Thomas Thomson seems to have possessed, in a high 
 degree, the faculty of communicating his own spirit of inquiry 
 to his pupils. "Don't you think, Doctor," said Graham on 
 one occasion to his teacher, "that when liquids absorb gases 
 the gases themselves become liquids ? " This remark, coming 
 
vin Thomas Graham 161 
 
 from so young a pupil, and uttered at a time when the mutual 
 relations of the physical states of matter were more vaguely 
 understood than now, naturally impressed Thomson. The 
 interest thus awakened in the young enthusiast never subse- 
 quently slumbered, and it was remarked by many that, in 
 their meetings as members of the Philosophical Society of 
 Glasgow, Thomson invariably treated Graham with an amount 
 of respect and even deference which that brusque and quick- 
 tempered old philosopher too frequently failed to extend to 
 others. 
 
 Thomson's teaching gave a fixity to the purpose of 
 Graham's after-life, and a desire to unravel some of those 
 secrets of nature which Thomson's lectures had set him 
 pondering upon took complete possession of his mind. His 
 father had intended that Graham should enter the ministry, 
 but his dislike to a calling for which he felt that he was not 
 naturally fitted strengthened even to repugnance as he learned 
 by a somewhat painful experience how inflexible was the 
 determination of his parent. But Graham's mother sym- 
 pathised with, even if she could not share in, the thoughts 
 and aspirations of her son ; and mainly by her self-sacrifice he 
 was enabled to continue his studies for about two years in 
 Edinburgh. He was in the habit of writing at great length 
 to her, and his letters show the depth of his gratitude and 
 affection. Whilst in Edinburgh he earned his first fee 
 some five pounds, by literary work the whole of which he 
 expended in presents to his benefactress. 
 
 In Edinburgh he attended the lectures and enjoyed the 
 friendship of Hope and Leslie, and doubtless the teaching of 
 these distinguished men in no small degree contributed to 
 direct his attention to that particular domain in science the 
 great borderland between physics and chemistry in which 
 his greatest triumphs were won. Keturning to Glasgow, 
 and acting on the advice of Meikleham, he sought to give 
 lessons in mathematics; but he quickly threw up this precarious 
 
 M 
 
1 62 Thomas Graham 
 
 VIII 
 
 means of livelihood, and established a private laboratory of 
 the most modest description in Portland Street. In 1829 he 
 was appointed Lecturer on Chemistry at the Mechanics' 
 Institution in place of Dr. Clark, who afterwards occupied 
 the chemical chair at Aberdeen; but in the following year 
 the Lectureship in Chemistry in Anderson's College fell 
 vacant, and Graham was elected in succession to Dr. Ure, of 
 dictionary fame. This event was the turning-point in his 
 career. Although there was no endowment attached to the 
 chair, and the laboratory was but scantily furnished, he had 
 what he so long coveted the means and the opportunity to 
 carry out the promptings of his genius for investigation. 
 
 It would be impossible to over-estimate the influence on 
 science of the seven years which Graham spent at Anderson's 
 College. During that time were sown all the seeds of the 
 rich harvest of his after years. Whilst in Glasgow he was 
 elected into the Royal Society of London, in whose Transac- 
 tions he had published his memorable "Researches on the 
 Arsenates, Phosphates, and Modifications of Phosphoric Acid." 
 In 1837 he removed to London, as the successor of Edward 
 Turner in the recently founded University of London, now 
 called University College. His election was in no small 
 degree due to the good offices of Lord Brougham, whose vote 
 was largely determined by the encomiums which Humboldt 
 had passed upon the young philosopher. In Gower Street 
 Graham's ability found adequate scope, and no teacher of 
 chemistry in England at the time exercised a greater influence. 
 The success of his lectures was due more to his philosophic 
 method of exposition, to the logical arrangement of his matter, 
 to his suggestiveness, and to the accuracy and extent of his 
 learning, than to eloquence or fluency of speech. Not that 
 Graham was altogether careless of such matters ; he was too 
 conscientious and painstaking a teacher to neglect any legiti- 
 mate means of impressing the minds of his pupils with the 
 ideas which he wished to convey. But even to the last he 
 
Thomas Graham 163 
 
 never quite overcame a certain nervousness and hesitancy of 
 manner, which, to an occasional listener, seemed to obscure 
 the real enthusiasm which was moving him, and of which his 
 students were fully conscious. 
 
 In 1841 was founded the Chemical Society of London, and 
 chemical science in England will for ever remain indebted to 
 Graham for the share he took in the establishment of that 
 learned body. He was its first president, and the early pro- 
 ceedings of the Society indicate the zeal with which he dis- 
 charged the duties of his office. This interest in the diffusion 
 of chemical knowledge was seen also in the share which he 
 took, in 1846, in founding the Cavendish Society, which, by 
 means of its translations, has enriched the chemical literature 
 of this country with a series of works of great value. 
 
 By his appointment, in 1854, to the Mastership of the 
 Mint, came what the world regarded as his crowning distinc- 
 tion. This position, rendered honourable by a succession of 
 some of the most illustrious names in our scientific history, 
 was, however, no sinecure to Graham. At this time, when 
 it was generally thought that he was enjoying well-merited 
 repose, his energies were wholly devoted to the self-created 
 duties of his office, and he was experiencing some of the 
 most vexatious troubles of his life, since the greatest firm- 
 ness was necessary to carry out the rigid system of control 
 which his sense of rectitude prompted him to institute. 
 Several years elapsed before his name re-appeared in the 
 Transactions of the Eoyal Society ; these were years of 
 incalculable loss to science. It was only about the year 1860 
 that he seems to have acquired the requisite leisure to con- 
 tinue his scientific work, and now memoir after memoir 
 appeared to testify to his unwearied energy. His last paper, 
 on Hydrogenium, was published only a few months before his 
 death. This incessant mental activity rapidly told on a con- 
 stitution naturally feeble. In the summer of 1869 he showed 
 symptoms of decay, but his nearest friends were hardly pre- 
 
 
VIII 
 
 164 Thomas Graham 
 
 pared for the suddenness of his end. He died in London, at 
 his house, No. 4 Gordon Square, on the 16th September 
 1869. 
 
 Graham's first paper, published when he was twenty-one 
 years of age, in the Annals of Philosophy for 1826, relates to 
 the question on which he had already speculated when a 
 student with Thomson that is, the absorption of gases by 
 liquids. The supposition that gases are only vapours remote 
 from their points of liquefaction was not unheard of even during 
 the first years of this century, but the fact was first definitely 
 established in 1823, when Faraday succeeded in liquefying a 
 considerable number of gases. Graham, reasoning from the 
 relations of mixed liquids to heat, seeks to prove that gases 
 are absorbed by liquids by reason of their capability of being 
 liquefied ; and he contends that solutions of gases in liquids 
 are mixtures of a more volatile with a less volatile liquid, and 
 therefore obey the laws which hold for such mixtures. The 
 detention of the gas in the solvent is owing to the mutual 
 affinity between liquids. This affinity, which occasions the 
 miscibility of liquids, affects the bulk or density of the 
 mixture, and frequently diminishes the volatility of the more 
 easily vapourised liquid in the mixture. In this way the 
 phenomena of the absorption of gases are brought into the 
 same class as those of the miscibility of liquids. It is un- 
 necessary to point out in detail the objections which may be 
 urged against this theory of gaseous-absorption. The paper 
 is now only of historical interest. It augured well, however, 
 for the future of the young philosopher, as it is characterised 
 by a certain dignity of language, by precision of statement, close 
 reasoning, and ingenuity and skill in the presentation of the 
 argument. It was followed in the same year, first, by a short 
 speculative paper "On the Heat of Friction," in which the 
 attempt is made to reconcile the substantial existence of heat 
 with its appearance in friction ; and secondly, by a note on the 
 nature of panary fermentation, which was shown to be attended 
 
vin Thomas Graham 165 
 
 with the production of alcohol. In order to avoid the possible 
 introduction of the alcohol by the yeast or brewers' barm then 
 exclusively employed in bread-making, Graham used leaven, 
 and obtained from the loaf, during the process of baking, 
 alcohol of sufficient strength to burn, and to ignite gunpowder 
 by its combustion. Some years ago, a Mr. Hicks patented a 
 method for recovering the alcohol volatilised in panification, but 
 after about 20,000 had been spent in futile efforts to combat 
 the prejudice of the London public for bread " with the gin in 
 it," the process was abandoned. 
 
 In the early part of the following year, 1827, Graham pub- 
 lished in the Philosophical Magazine a short paper "On the 
 Finite Extent of the Atmosphere." According to Wollaston 
 there is necessarily a limit to the atmosphere, for the reason 
 that the mere weight of. the matter of gaseous substances must 
 afford, at a certain degree of rarefaction, a balancing resistance 
 to further expansion. Faraday attempted to gain evidence in 
 support of this hypothesis from experiments on the vapour 
 of mercury. Graham seeks to show that this limit must be 
 reached in consequence of the decrease of temperature as we 
 ascend through the atmosphere, whereby the air is eventually 
 reduced to a temperature which involves the loss of its elastic 
 state, and possibly even effects its solidification. Reasoning 
 from analogy, he infers that the condensation of the elastic air 
 into solid particles may be attended with emission of the 
 accumulated stores of light and heat. "These luminous 
 appearances will be more frequent and striking at the polar 
 regions, from the temperature there approaching more closely 
 to the condensing point of the gaseous substances constituting 
 the atmosphere. Their proper sites will be the thermal poles, 
 or points on the earth's surface of lowest temperature. . . . 
 Let us suppose a determination to condensation to take place 
 in the superior regions of the atmosphere at the thermal pole, 
 the surrounding elastic air would rush in and expand,' to fill 
 the vacuity occasioned by the condensation. But this rare- 
 
1 66 Thomas Graham vm 
 
 faction, with its attendant fall in temperature, would frequently 
 be productive of condensation and deposition in these masses 
 of air themselves. In this way the tendency to condensation, 
 originating perhaps at the thermal pole, would be widely and 
 rapidly propagated, and the attending streams of light would 
 appear to shoot from that point. Here we recognise the 
 brilliant phenomena of the aurora borealis." 
 
 A paper "On Nitrification," which appeared in the 
 Philosophical Magazine for the same year, consists mainly of a 
 critical examination of the theory of Longchamp relative to 
 the formation of nitric acid from the elements of the atmo- 
 sphere. This question, which excited the attention of chemists 
 even before the time of Lavoisier, has only recently received 
 an adequate solution. The only original feature in Graham's 
 communication is in<his view of the part played by carbonic 
 acid in the process. 
 
 A communication " On Exceptions to the Law that Salts 
 are more Soluble in Hot than in Cold Water, with a new 
 instance," also published in the Philosophical Magazine for 
 1827, deals principally with the case of magnesium phosphate, 
 a saturated solution of which, on heating, was found by 
 Graham to become turbid and to deposit the salt in the 
 anhydrous form. This phenomenon is precisely analogous to 
 that observed by Dalton in the case of lime, and by Gay 
 Lussac in that of sodium sulphate. The explanation given 
 by Graham is that in all these cases the apparent anomaly is 
 due to a change of hydration. 
 
 In the course of an inquiry made in 1827 as to the best 
 mode of dehydrating ordinary alcohol, which Graham found 
 to be by means of quicklime, he was led to the observation 
 that calcium chloride, one of the substances most commonly 
 employed by chemists as a dehydrant, forms a definite com- 
 pound with absolute alcohol. Combinations of a similar 
 nature were also observed to be produced with the nitrates of 
 calcium and magnesium, and with the chlorides of manganese 
 
VIII 
 
 Thomas Graham 167 
 
 and zinc. These alcoates, as they are termed by Graham, are 
 solid crystalline substances in which the alcohol appears to 
 play the part of water of crystallisation in the hydrated salts. 
 
 In this connection may be mentioned his paper, published 
 long subsequently in the Journal of the Chemical Society (vol. 
 iii. 1851), on " Etherification," in which he seeks to combat 
 the generally accepted opinion that the formation of sul- 
 phovinic acid is a necessary stage in the transformation of 
 common alcohol into ether. According to Graham the sul- 
 phuric acid acts on the alcohol in a manner similar to 
 that in which it acts upon certain essential oils that is, 
 by an action akin to polymerisation. Oil of turpentine, for 
 example, when mixed with one-twentieth of its volume of 
 sulphuric acid is largely converted into terebene and colo- 
 phene. This view of etherification is, in fact, an expres- 
 sion of the contact -theory of the process advocated by 
 Mitscherlich. Graham's experiments are suggestive, but they 
 are hardly conclusive. At the same time, no one can read 
 his accounts of them, or follow the argument which he bases 
 upon them, without admitting that the last word on the 
 theory of etherification has not yet been said. 
 
 It has long been known that a piece of phosphorus glowing 
 in air has its luminosity instantly destroyed when immersed 
 in oxygen. Pure oxygen at atmospheric tension has no 
 action upon phosphorus. When the tension of the oxygen 
 is reduced, the glow reappears, as observed by Bellani de 
 Monza, with the simultaneous appearance of a white fume 
 due to the formation of phosphoric oxide. If, instead of 
 reducing its tension, the oxygen is mixed with hydrogen, 
 nitrogen, nitric oxide, carbonic oxide, carbonic acid, etc., the 
 glow equally reappears. Certain gases and vapours, e.g. 
 olefiant gas, naphtha, oil of turpentine, and ether, prevent the 
 glow, whether in air or in attenuated oxygen, and no oxida- 
 tion of the phosphorus is found to occur. Phosphorus -may 
 be melted and kept for any length of time at 100 without 
 
1 68 Thomas Graham vm 
 
 alteration in air mixed with its own volume of olefiant gas. 
 Graham, in a paper contributed to the Quarterly Journal of 
 Science in 1829, gives an account of a number of observations 
 on the glow of phosphorus dealing with these and similar 
 facts. He found that the proportion of the gases necessary to 
 prevent the slow combustion depends upon the density. One 
 four-hundredth part of olefiant gas prevents the glow in air 
 at ordinary pressures, but the phosphorus becomes luminous 
 even when the air is mixed with its own volume of olefiant 
 gas if the pressure is diminished to that of half an inch of 
 mercury. Graham offers no explanation of these facts, which 
 are in all probability connected with the formation or presence 
 of ozone, the existence of which was only indicated by Schon- 
 bein some years after the date of Graham's paper. 
 
 The remarkable differences in inflammability observed in 
 phosphuretted hydrogen, depending on its origin or on the 
 admixture of various substances with it, were long misunder- 
 stood by chemists. Heinrich Eose was disposed to believe in 
 the existence of two isomeric modifications of hydrogen phos- 
 phide, only one of which was spontaneously inflammable. 
 Graham, who in 1835 held "the general doctrine of Isomerism 
 as problematical," made a -number of observations on phos- 
 phuretted hydrogen, from which he concluded that its 
 spontaneous inflammability was due to adventitious matter. 
 He found that the addition of a minute quantity of the higher 
 oxides of nitrogen is capable of rendering phosphuretted 
 hydrogen spontaneously inflammable, and he concluded that 
 the "adventitious matter" in the ordinary spontaneously 
 inflammable variety was a volatile compound of phosphorus 
 and oxygen, analogous to nitrous acid. Subsequent observa- 
 tions have shown that Graham was right in the surmise that 
 the spontaneous inflammability was due to "adventitious 
 matter," but wrong as to its nature. The effect is caused, as 
 shown by Thenard, by the presence of the dihydride of 
 phosphorus. 
 
VIII 
 
 Thomas Graham 169 
 
 Graham's first important experimental work relates to the 
 absorption of vapours by liquids. An account of the investiga- 
 tion was given to the Eoyal Society of Edinburgh on 3rd March 
 1828, and is printed in the Edinburgh Journal of Science for 
 the same year. He shows that a relation exists between the 
 boiling-point of a saline or acid solution and its power of 
 absorbing the vapour of the solvent. The higher the boil- 
 ing-point of the solution the greater the amount of the 
 vapour absorbed. The degree of absorption is apparently 
 independent of the nature of the salt. A saturated solution 
 of common salt, which contains less than a third of its weight 
 of non- deliquescent saline matter, absorbs aqueous vapour 
 much more powerfully than a solution of the deliquescent 
 carbonate of potash in thrice its weight of water. Even sea- 
 water is capable of absorbing moisture from air saturated with 
 it at the same temperature. A number of saline and acid 
 solutions made of such strength that they all boiled at the 
 same temperature, viz., 224 Fahr., were found to absorb prac- 
 tically the same amount of aqueous vapour. A solution of 
 hydrochloric acid exposed to damp air absorbs moisture until 
 its specific gravity is diminished to 1'096 ; on the other hand, 
 an acid solution of lower specific gravity evolves aqueous 
 vapour until its specific gravity becomes 1-096, when it 
 acquires a constant boiling-point, as already observed by 
 Dalton. 
 
 In a short paper " On the Influence of the Air in determin- 
 ing the Crystallisation of Saline Solutions," originally pub- 
 lished in the Philosophical Magazine for 1828, Graham deals 
 with a question which had already attracted considerable 
 attention long before his time, but which, in spite of much 
 subsequent work, is still imperfectly understood, viz., the 
 causes which induce the crystallisation of supersaturated 
 solutions.. By confining hot saturated solutions of Glauber's 
 salt in phials or other vessels over warm mercury, Graham 
 showed that solidification could be induced in the liquid when 
 
170 Thomas Graham vm 
 
 cold by the admission of certain gases, which, by their 
 solution, cause the precipitation of a certain amount of the 
 salt, and so bring about crystallisation of the excess of saline 
 matter. According to Graham the influence of the gas is 
 related to the degree in which it is absorbed by the solvent : 
 the more soluble the gas the more readily does it effect 
 crystallisation. 
 
 In the following year (1829) Graham published his first 
 paper on the subject on which his fame chiefly rests. It is 
 entitled, "A Short Account of Experimental Eesearches on 
 the Diffusion of Gases through each other, and their separation 
 by Mechanical Means," and appeared in the Quarterly Journal of 
 Science, ii. 1829, pp. 74-83. The experimental work was of 
 the simplest possible description. A cylindrical vessel, shaped 
 like a test-tube, about 9 inches in length and O9 inch 
 internal diameter, was divided into 150 equal parts, and pro- 
 vided with an accurately ground glass stopper, through which 
 was fitted, also by grinding, a short piece of stout tube 0*12 
 inch in bore and 2 inches in length, and bent in the middle 
 at right angles. The vessel was filled in succession with 
 various gases, the stopper and tube inserted, and the whole 
 supported in a horizontal position upon a frame, with the end 
 of the bent tube pointing upwards when the contained gas 
 was heavier than air, and downwards when the gas was 
 lighter, to avoid any tendency of the gas to flow out of the 
 receiver. After the gas had been allowed to diffuse into the 
 air through the tube for a certain time, the cylindrical vessel 
 was transferred to the pneumatic trough, and the quantity of 
 air which had entered, and of gas that remained, ascertained. 
 It was found that as much hydrogen gas left the vessel in two 
 hours as of carbonic acid in ten hours. Jlence hydrogen is 
 five times more diffusive than carbonic acid. Graham con- 
 cludes : "It is evident that the diffusiveness of the gases is 
 inversely as some function of their density apparently the 
 square root of their density." He next studied the diffusion 
 
VIII 
 
 Thomas Graham 
 
 of a mixture of gases into air in order to determine whether 
 each gas left the vessel independently of the other, and in the 
 ratio of its individual diffusiveness, and he found that " in the 
 case of mixed gases the law is that the more diffusive gas 
 leaves the receiver in a greater proportion than in the case of 
 the solitary diffusion of the same gas, and the less diffusive 
 gas in the mixture in a less proportion than in its solitary 
 diffusion." 
 
 In a subsequent paper, entitled " On the Law of the Diffu- 
 sion of Gases," read before the Eoyal Society of Edinburgh, 19th 
 December 1831, and published in the Philosophical Magazine, ii. 
 1833, Graham definitely establishes the relation between the 
 rate of diffusion of a gas and its density, and states this 
 relation in these words : " The diffusion or spontaneous 
 intermixture of two gases in contact is effected by an inter- 
 change in position of indefinitely minute volumes of the gases, 
 which volumes are not necessarily of equal magnitude, being, 
 in the case of each gas, inversely proportional to the square 
 root of the density of that gas." He refers in the outset to 
 the observation of Dobereiner on the escape of hydrogen 
 through a fissure or crack in a glass bell-jar filled with the 
 gas and standing over water in the pneumatic trough, when it 
 was found that the water gradually rose in the jar to a height 
 of several inches above the level of that in the trough. With 
 oxygen, nitrogen, or atmospheric air, no such phenomenon was 
 observed. Dobereiner was disposed to regard the effect as 
 due to the capillary action of the fissure ; he supposed that the 
 hydrogen only is attracted by the fissure, and escapes through 
 it by reason of the extreme smallness of its atoms. Graham 
 points out the insufficiency of this explanation. As already 
 shown by Saussure, hydrogen, of all gases, is absorbed or 
 condensed in smallest quantity by charcoal and other porous 
 substances; and, moreover, there is no a priori reason to 
 suppose that the particles of hydrogen are smaller than those 
 of other gases. On repeating the experiment he found that, 
 
VIII 
 
 172 Thomas Graham 
 
 as the hydrogen escaped, a certain amount of air invariably 
 entered the jar, through the fissure, in its place ; and if care 
 was taken to maintain the water in the jar at the level of that 
 in the pneumatic trough, so that the air should not be drawn 
 in nor the hydrogen thrust out mechanically, then the air 
 which entered by diffusion amounted to between one-fifth 
 and one-fourth of the volume of the hydrogen which passed 
 out of the bell- jar in the same time. Similar experiments 
 were made with other gases, but the method was not suffi- 
 ciently accurate to furnish precise results, although these 
 were at all times compatible with, and indeed illustrative 
 of, the law. Graham next tried tubes made of unglazed 
 stoneware, such as were used by Priestley and other 
 chemists at the latter end of the last century for furnace 
 experiments, and found that the effects were much more 
 striking. Indeed Priestley himself had discovered that the 
 gases of the fire would readily permeate such vessels. From 
 unglazed stoneware he passed to plaster of paris or stucco, 
 and this material was found so suitable that the rest of the 
 experiments detailed in the memoir were made by means of 
 it. The apparatus employed was extremely simple. It 
 consisted of a glass tube from 6 to 14 inches in length and 
 half an inch in width, fitted at one end with a thin stucco plug, 
 about a fifth of an inch in thickness. The diffusion tube, 
 as the instrument was termed, was graduated into hundredths 
 of a cubic inch. It was filled with the particular gas 
 under investigation over the mercurial or water pneumatic 
 trough, with special precautions in the latter case to avoid 
 wetting the plug. The tube over the trough was then 
 allowed to stand in free contact with the air for a certain 
 time, after which the ratio of the volume of the gas remaining 
 in the tube to that of the air which had entered through 
 the stucco was determined by analysis. Thus in the case 
 of hydrogen, if we take the specific gravity of this gas as 
 0-0694 (air = l), the square root of this number is 0'2635 ; 
 
VIII 
 
 Thomas Graham 
 
 and according to the law of diffusion 1 volume of hydrogen 
 should be replaced by 0*2635 volume of air that is, 1 of 
 air should replace 3*7947 of hydrogen. The mean of a large 
 number of experiments, made with instruments varying in 
 shape and size, showed that the amount of hydrogen replac- 
 ing 1 volume of air was 3*83 volumes, in fair accord with the 
 theoretical number. The following table contains the results 
 of experiments made with such of the gases as were available 
 at the time : 
 
 TABLE OF EQUIVALENT DIFFUSION-VOLUMES OF GASES. 
 
 AIR = 1. 
 
 
 By 
 
 Experiment. 
 
 Theory. 
 
 Specific 
 Gravity. 
 
 Hydrogen 
 
 3-83 
 
 3-7947 
 
 0-0694 
 
 Carburetted Hydrogen 
 
 1-344 
 
 1-3414 
 
 0-555 
 
 Olefiant Gas . 
 
 1-0191 
 
 1-0140 
 
 0-972 
 
 Carbonic Oxide 
 
 1-0149 
 
 1-0140 
 
 0-972 
 
 Nitrogen 
 
 1-0143 
 
 1-0140 
 
 0-972 
 
 Oxygen . 
 Sulphuretted Hydrogen 
 
 0-9487 
 0-95 
 
 0-9487 
 0-9204 
 
 1-111 
 1-1805 
 
 Protoxide of Nitrogen 
 
 0-82 
 
 0-8091 
 
 1-527 
 
 Carbonic Acid . 
 
 0-812 
 
 0-8091 
 
 1-527 
 
 Sulphurous Acid . 
 
 0-68 
 
 0-6708 
 
 2-222 
 
 The agreement between theory and experiment, although 
 not absolute, is sufficiently close to leave no doubt of the 
 validity of the law. Perfect concordance, indeed, could not 
 be expected. All the gases are condensed to a greater or 
 less extent by the porous stucco; moreover, the water of 
 hydration of the plaster affects the results in some instances. 
 Indeed in the cases of chlorine, hydrochloric acid gas, 
 ammonia, and cyanogen, the observations were vitiated by 
 these causes, and no proper values for the equivalent diffusion- 
 volumes could be obtained for these gases. 
 
 Graham then points out that, admitting the law, the specific 
 
174 Thomas Graham vm 
 
 gravity of the gases may be determined by the principle of 
 
 /A\ 2 
 
 diffusion ; it is given by the formula D = ( ) , where G is the 
 
 HJT 
 
 volume of gas submitted to diffusion, and A the volume of the 
 return air, and he proceeds to indicate a form of apparatus 
 which may be conveniently employed for the purpose. As is 
 well known, Bunsen has devised an instrument on the same 
 principle, which obviates the use of stucco, and which is 
 capable of affording results of a high degree of accuracy. 
 
 This " interchange in position of indefinitely minute volumes 
 of gases " is a property inherent in the gases ; inequality of 
 density is not an essential requisite to diffusion. Graham 
 proves this by connecting together two vessels, one containing 
 nitrogen and the other carbon monoxide, which have the same 
 density, by means of a short tube containing a stucco plug. 
 The two vessels were allowed to remain connected together for 
 about twenty-four hours, when the gases were found to be 
 uniformly diffused through both vessels. 
 
 The relations of diffusion to evaporation and respiration are 
 then indicated, and the memoir concludes with the statement 
 that the "law," being merely a description of the appearances, 
 involves no hypothesis, and " is certainly not provided for in 
 the corpuscular philosophy of the day." It is altogether so 
 extraordinary that Graham trusts he " may be excused for 
 not speculating further upon its cause, till its various bearings, 
 and certain collateral subjects, be fully investigated." 
 
 The path of inquiry thus opened up was pursued by 
 Graham, with certain deviations to be afterwards pointed out, 
 until the close of his life. Thirteen years, however, elapsed 
 before his next important contribution to the subject made its 
 appearance. In 1846 he sent to the Royal Society the 
 first part of a long memoir on "The Motion of Gases," 
 (Philosophical Transactions, iv. 1846, pp. 573-632) ; the second 
 part was not published until 1849 (Philosophical Transactions, 
 ii. 1849, pp. 349-362). In this memoir he draws attention, 
 
VIII 
 
 Thomas Graham 175 
 
 at the outset, to the necessity of distinguishing between 
 the passage of a gas through a small aperture in a thin 
 plate, and its passage through a tube of sensible length. 
 The phenomena of the first class are well-defined, simple, and 
 in accordance with the law of diffusion ; those of the second 
 class were also regular in cases where the tubes were strictly 
 " capillary," or where they were of great length, or, if short, of 
 extremely small diameter. Capillary glass tubes varying in 
 length from 20 feet to 2 inches were found equally available, 
 and gave similar results, provided that sufficient resistance was 
 offered to the passage of the gas. The result was independent 
 of the nature of the material of the tube, and had no simple 
 relation to the density of the gas. The two classes of pheno- 
 mena are subject therefore to apparently essentially different 
 laws. To mark the distinction, Graham terms the passage of 
 gases through an aperture in a thin plate effusion, whilst its 
 passage through a tube he calls transpiration. It is the object 
 of his work to determine the coefficients of effusion and trans- 
 piration of various gases. 
 
 With respect to the effusion experiments Graham found 
 that " different gases pass through minute apertures into a vacuum 
 in times which are as the square roots of their respective specific 
 gravities, or with velocities which are inversely as the square roots 
 of their specific gravities that is, according to the same law as 
 gases diffuse into each other." In the case of a mixture of 
 gases the rate was in strict accordance with the specific gravity 
 of the mixture ; thus in the case of a mixture of equal volumes 
 of carbonic oxide and oxygen the time of effusion was as the 
 square root of the density of the mixture. As regards the 
 effects of pressure on the effusion-rate of a gas no very definite 
 results were obtained; doubling the density of the air by 
 compression scarcely affected the time of effusion of equal 
 volumes. Air at different temperatures has an effusion time 
 proportional to the square root of its density at each tempera- 
 ture. " As the velocity of the effusion of air does not increase 
 
176 Thomas Graham vm 
 
 at a rate so rapid as the direct proportion of its expansion by 
 heat, it follows that the flow of air through a small aperture 
 is retarded by heating the air that is, the same absolute 
 quantity or weight of air will take a longer time to pass, when 
 rarefied by heat, than when in a dense state." 
 
 The experiments on transpiration led to the following 
 general conclusions : 
 
 1. The velocities with which different gases pass through 
 capillary tubes bear a constant relation to each other. This 
 constancy of relation was observed for tube resistances varying 
 in amount from 1 to 1000. These relations are apparently 
 more simple in their expression than the densities of the gases, 
 and seem to depend upon a peculiar and fundamental property 
 of the gaseous form of matter. 
 
 The velocity of hydrogen is exactly double that of nitrogen 
 and carbonic oxide. 
 
 The velocities of nitrogen and oxygen are inversely as the 
 specific gravities of these gases. 
 
 The velocity of nitric oxide is the same as that of nitrogen 
 and carbonic oxide. 
 
 The velocities of carbonic acid and nitrous oxide are equal, 
 and when compared with oxygen directly proportional to their 
 specific gravities. 
 
 The velocity of methane is 0'8 when that of hydrogen is 1. 
 
 The velocity of chlorine is 1 J times that of oxygen ; the 
 vapours of bromine and sulphur trioxide have the same velocity 
 as oxygen. 
 
 Ether vapour appears to have the same velocity as hydro- 
 gen gas. ^ 
 
 Olefiant gas, ammonia, and cyanogen appear to have equal 
 or nearly equal velocities, which approach closely to double 
 the velocity of oxygen. 
 
 Sulphuretted hydrogen and carbon bisulphide vapour appear 
 to have equal or nearly equal velocities. 
 
 2. The resistance of a capillary tube of uniform bore to the 
 
Thomas Graham 177 
 
 passage of any gas is directly proportional to the length of 
 the tube. 
 
 3. The velocity of passage of equal volumes of air of the 
 same temperature but of different densities is directly propor- 
 tional to the density. 
 
 4. Rarefaction by heat exerts a similar and precisely equal 
 effect in diminishing the velocity of the transpiration of equal 
 volumes of air, as the loss of density by diminution o! 
 pressure. 
 
 It would appear, then, that transpiration is promoted by 
 increase of density, and equally, no matter whether the in- 
 creased density is due to compression, to cold, or to the 
 addition of an element in combination ; thus the velocity of 
 oxygen is increased by combining it with carbon, which unites 
 with it without change of volume to form carbonic acid. 
 
 Graham lastly points out that the distribution of coal gas 
 in the mains of our cities must proceed in accordance with the 
 laws of gaseous transpiration, for the reason that although the 
 pipes may be many inches in diameter, their length is much 
 beyond 4000 times their width, the limiting ratio required in 
 order that the flow shall be "capillary." 
 
 In a memoir " On the Molecular Mobility of Gases," which 
 appeared in the Philosophical Transactions for 1863, Graham 
 returns to the question of the passage of gases under pressure 
 through a thin, porous plate or septum, and to the partial sepa- 
 ration of mixed gases, which can be effected by such means. 
 He had discovered that a much better material than stucco for 
 such a septum existed in the artificially-compressed graphite of 
 Mr. Brockedon, which could -be obtained in small cubic masses 
 about two inches square, and from which slices of a millimeter 
 or two in thickness could be readily cut by means of a saw of 
 steel spring. By rubbing the surface of the slice without 
 wetting it upon a flat sandstone, the thickness might be further 
 reduced to about one-half of a millimeter. A wafer of this 
 material could be readily affixed to the end of a tube by 
 
 N 
 
178 Thomas Graham vm 
 
 means of a resinous cement, and the whole constituted a diffusio- 
 meter which presented many points of advantage over the 
 forms hitherto employed. Native graphite is of lamellar 
 structure, and has little or no porosity : hence it cannot be 
 substituted for the artificial variety as a diffusion-septum. 
 " The pores of artificial graphite appear to be really so minute, 
 that a gas in mass cannot penetrate the plate at all. It seems 
 that molecules only can pass ; and they may be supposed to 
 pass wholly unimpeded by friction, for the smallest pores that 
 can be imagined to exist in the graphite must be tunnels in 
 magnitude to the ultimate atoms of a gaseous body. The 
 sole motive agency appears to be that intestine movement of 
 molecules which is now generally recognised as an essential 
 property of the gaseous condition of matter." 
 
 Graham then points out that the rate of passage of 
 different gases through a minute aperture in a thin plate is 
 regulated by their specific gravities, according to a law which 
 was deduced by Robison from Torricelli's well-known theorem 
 of the velocity of efflux of fluids. "A gas rushes into a 
 vacuum with the velocity which a heavy body would acquire 
 by falling from the height of an atmosphere composed of the 
 gas in question, and supposed to be of uniform density 
 throughout. The height of the uniform atmosphere would 
 be inversely as the density of the gas ; the atmosphere of 
 hydrogen, for instance, being sixteen times higher than that of 
 oxygen. But as the velocity acquired by a heavy body in 
 falling is not directly as the height, but as the square root of 
 the height, the rate of flow of different gases into a vacuum 
 will be inversely as the square root of their respective 
 densities. The velocity of oxygen being 1, that of hydrogen 
 will be 4, the square root of 16." 
 
 The memoir next deals with the consideration of the question 
 of the diffusion of mixed gases into a vacuum, and several 
 methods of effecting the atmolysis of mixed gases are described ; 
 and the paper concludes with an account of some experi- 
 
viii Thomas Graham 179 
 
 ments on the inter-diffusion of gases without an intervening 
 septum. 
 
 By a natural association of ideas, easy to trace, Graham 
 was led to pass from the study of the molecular movement of 
 gases to that of liquids. His classical memoir "On the 
 Diffusion of Liquids" formed the subject of the Bakerian 
 Lecture to the Royal Society in 1849. It contains the first 
 results of a lengthened inquiry into the rates of movement 
 which substances, principally saline, exhibit in passing out of 
 an aqueous solution into pure water. The method of experi- 
 ment, as in all Graham's investigations, was extremely 
 simple. In its final form it consisted in placing a small phial, 
 of about 4 oz. capacity, and of about \\ inches in diameter at 
 the neck, on the bottom of a cylindrical glass jar partially 
 filled with water. The phial was charged to within half 
 an inch of the top with the saline solution to be examined, 
 and the rest of the space was cautiously filled with pure 
 water in such manner as not to disturb the saline solu- 
 tion. The phial was next covered with a glass plate, and 
 water was poured into the outer vessel to the height of 
 1 inch above the plate, the amount of water thus needed 
 being about 30 oz., i.e. more than seven times the volume 
 of the saline solution. The glass plate was then carefully 
 removed, and the "diffusion cell," as the entire apparatus 
 may be fitly termed, was left to itself for a definite number 
 of days at a constant temperature. At the expiration of 
 the time the phial was again covered with the glass plate and 
 withdrawn from the jar, and the amount of the salt which had 
 passed into the outer liquid was determined either by evapora- 
 tion or by analysis. 
 
 The results obtained by Graham from a large number of 
 observations can only be briefly summarised here. In the 
 first place it was found that the mere density of the solutions 
 had no direct influence on the rate of diffusion. A number 
 of aqueous solutions of acids and salts were prepared of the 
 
180 Thomas Graham 
 
 VIII 
 
 uniform density of 1 2, and these were allowed to diffuse in 
 the manner described. It was found that the rates were very 
 unequal, ranging from 1 to 0'1333, and evidently depended on 
 the character of the substance. In the case of moderately dilute 
 solutions (4 or 5 per cent), the amount of any one salt diffused 
 in equal intervals of time is directly proportional to the 
 quantity of the salt in the diffusing solution. The quantity 
 of salt diffused increases with, and is apparently in direct 
 relation to, the temperature; but the proportionality in the 
 diffusion with strength of the saline solution is maintained 
 at different temperatures. The various classes of substances 
 show the widest possible differences in rapidity of diffusion. 
 Thus albumen is more than twenty times less diffusible than 
 common salt. Cane-sugar and starch-sugar, which are equi- 
 diffusive, have double the rate of gum-arabic, but less than 
 half the rate of common salt. These great differences 
 appeared to Graham to promise the possibility of a delicate 
 method of proximate analysis specially applicable to animal 
 and vegetable fluids. The low diffusibility of albumen is 
 significant in connection with the retention of the serous 
 fluids within the blood-vessels. A solution of albumen, in 
 spite of its viscidity, does not impair the diffusion of salts 
 which may be present with it in the solution. Sodium chloride, 
 urea, and sugar are found to diffuse out quite as freely from 
 the albuminous liquid as from an equal volume of pure 
 water. 
 
 Isomorphous salts are equi-diffusive. Thus sal-ammoniac 
 and potassium chloride diffuse at the same rate; so do nitre 
 and ammonium nitrate ; Epsom salts and white vitriol ; and 
 the nitrates of lime, strontia, and baryta. The relation ob- 
 served is the more remarkable, in that it is of equal weights, 
 and not of equi-molecular weights. Density of the aqueous 
 solutions, in the case of the several pairs, or a difference in the 
 solubility of the salts, appears to have no influence on the result. 
 It must, however, be stated that equality or similarity of 
 
Thomas Graham 181 
 
 diffusion is not necessarily confined to the isomorphous groups 
 of salts. 
 
 Hydrochloric, hydrobromic, and hydriodic acids, which 
 are among the most diffusive substances known, are also equi- 
 diffusive, despite the differences in the boiling points and 
 specific gravities of their solutions. Hence it appears that a 
 considerable diversity of physical properties may be compatible 
 with equal diffusibility. Hydrocyanic acid, on the other hand, 
 is considerably less diffusive than the halogen hydracids. The 
 alkaline iodides, bromides, and chlorides, when strictly isomor- 
 phous, are also equi-diffusive. 
 
 In the case of a solution containing a mixture of salts, 
 which, so far as is known, exert no chemical action on each 
 other, it might be anticipated that each salt would diffuse 
 separately and independently, according to its special rate. 
 Experiments with mixtures of two salts showed that the less 
 soluble of the two diffused more slowly than when in the 
 unmixed state. This is true even in the case of a mixture of 
 two isomorphous salts, which when diffused singly were equi- 
 diffusive. 
 
 Inequality of diffusion- may evidently be made the basis of 
 a method of separating, to a greater or less extent, certain 
 salts from one another, just as unequally volatile substances 
 may be separated by fractional distillation. For example, the 
 potash salts are invariably more diffusive than the correspond- 
 ing soda salts ; hence it follows that if a solution of the mixed 
 salts be placed within the phial, the potash salt will escape in 
 larger proportion into the outer liquid, whilst the soda salt will 
 be relatively concentrated within the phial. Even sea-water, 
 when subjected to this treatment, gives up its saline contents in 
 very different proportions. Graham sees in this behaviour a 
 possible explanation of the discrepancies in the analyses which 
 have been published from time to time of the water of the Dead 
 Sea, in which the relative proportions of the various constituents 
 are very discordant. " The lake in question," he says, " falls 
 
1 82 Thomas Gra/iam vm 
 
 in level 10 or 12 feet every year by evaporation. A sheet of 
 fresh water of .that depth is thrown over the lake in the 
 wet season, which water may be supposed to flow over 
 a fluid nearly 1-2 in density without greatly disturbing it. 
 The salts rise from below into the superior stratum by the 
 diffusive process, which will bring up salts of the alkalies with 
 more rapidity than salts of the [alkaline] earths, and chlorides 
 of either class more rapidly than sulphates. The composition 
 of water near the surface must therefore vary greatly as this 
 process is more or less advanced." 
 
 This process of liquid diffusion is capable of throwing much 
 light on the question of the nature and constitution of salts 
 when dissolved. Graham found, for example, that a solution 
 of acid sulphate of potassium behaved like a mixture of the 
 normal salt and free sulphuric acid. It was possible, in fact, 
 to effect an almost complete separation of the two components. 
 Common potash-alum, in like manner, on solution was appar- 
 ently resolved into potassium sulphate and aluminium sulphate. 
 Other so-called double salts were found to be decomposed in 
 like manner ; thus Rochelle salt was found to be resolved 
 into the tartrates of potash and soda. 
 
 The question whether a double salt is formed at once when 
 its constituent salts are dissolved together, or is produced only 
 in the act of crystallisation, may therefore be answered. It 
 appears that such double salts are not necessarily formed 
 immediately on solution of their constituent salts. As 
 Graham points out, many practices in the chemical arts which 
 seem empirical may have their foundation in facts of this 
 kind, as, for example, the manufacture of potassium chloride 
 from carnallite. 
 
 The investigation of the diffusion of one salt into the solu- 
 tion of another salt has a special interest, as serving to indi- 
 cate how far the phenomena of liquid and gaseous diffusion are 
 really analogous. In the case of gases it is found that oxygen, 
 for example, freely diffuses into the space already occupied 
 
VIII 
 
 Thomas Graham 183 
 
 by hydrogen, whilst hydrogen, in return, passes with equal 
 freedom into the space occupied by oxygen. Does anything 
 precisely analogous to this occur with saline solutions 1 In 
 the case of dilute solutions, at least, observation shows there 
 is the very closest resemblance. The presence of one salt 
 exercises no resistance to, or interference with, the diffusion of 
 the other. To use Graham's phrase, "salts are therefore 
 inelastic to each other, like two different gases." 
 
 It is not at all improbable that these results may be greatly 
 modified in concentrated solutions. " There is," says Graham, 
 " reason to apprehend that the phenomena of liquid diffusion 
 are exhibited in the simplest form by dilute solutions, and 
 that concentration of the dissolved salt, like compression of a 
 gas, is attended often with a departure from the normal char- 
 acter. On approaching the degree of pressure which occasions 
 the liquefaction of a gas, an attraction appears to be brought 
 into play which impairs the elasticity of the gas ; so on 
 approaching the point of saturation of a salt, an attraction of 
 the salt molecules for each other, tending to produce crystal- 
 lisation, comes into action, which will interfere with and 
 diminish that elasticity or dispersive tendency of the dissolved 
 salt which occasions its diffusion. . . . The analogy of liquid 
 diffusion to gaseous diffusion and vaporisation is borne out in 
 every character of the former which has been examined. 
 Mixed salts appear to diffuse independently of each other, like 
 mixed gases, and into a water atmosphere already charged 
 with another salt as into pure water. Salts also are unequally 
 diffusible, like the gases, and separations both mechanical and 
 chemical (decompositions) are produced by liquid as well as by 
 gaseous diffusion." 
 
 In concluding his memoir Graham points out that " the 
 fact that the relations in diffusion of different substances refer 
 to equal weights of those substances, and not to their atomic 
 [molecular] weights or equivalents, is one which reaches to the 
 very basis of molecular chemistry. The relation most fre- 
 
184 Thomas Graham vm 
 
 quently possessed is that of equality, the relation of all others 
 most easily observed. In liquid diffusion we appear to deal no 
 longer with chemical equivalents or the Daltonian atoms, but 
 with masses even more simply related to each other in weight. 
 Founding still upon the chemical atoms, we may suppose that 
 they can group together in such numbers as to form new and 
 larger molecules of equal weight for different substances, or, if 
 not of equal weight, of weights which appear to have a simple 
 relation to each other. It is this new class of molecules which 
 appears to play a part in solubility and liquid diffusion, and 
 not the atoms of chemical combination." 
 
 In a short paper, communicated to the Chemical Society 
 in 1851, Graham gives the following table, showing the 
 amount of 
 
 SALT DIFFUSED FROM A 1 PER CENT SOLUTION IN EQUAL TIMES. 
 
 Grains. 
 
 Potash . . . . 4-84 
 
 Soda . . . 4-03 
 
 Ammonium chloride . 3 -4 2 
 
 Potassium chloride . 3 -42 
 
 Sodium chloride 2 '85 
 
 Grains. 
 
 Sodium sulphate . 2-35 
 
 Calcium chloride . 2-02 
 
 Magnesium chloride . 2 '03 
 
 Calcium sulphate . 1'21 
 
 Magnesium sulphate . 1-21 
 
 These are the latest, and perhaps the best determined, diffusi- 
 bilities observed by Graham, and serve to confirm many of the 
 results already referred to. They show, in the first place, 
 that potash compounds are more diffusive than the correspond- 
 ing compounds of soda ; and, in the second, that isomorphous 
 compounds are equi-diffusive. 
 
 The rest of the paper is concerned with a description of 
 experiments on the decomposition of the sulphates of soda and 
 potash, and of the chlorides of potassium and sodium by means 
 of lime, in which it may be expected that the affinity of that 
 base for an acid is aided by the high diffusibility of the potash 
 or soda. It was found that both the sulphates were decom- 
 posed, and that the alkaline hydrates made their appearance 
 
vin Thomas Graham 185 
 
 in the liquid in the outer vessel at rates dependent on their 
 specific diffusibility, whereas the calcium sulphate formed, on 
 account of its low diffusive power, only slowly escaped from 
 the phial, where, indeed, it was deposited in crystals. The 
 decomposition of potassium sulphate by lime, with deposition 
 of calcium sulphate, was observed by Scheele, and explained by 
 Berthollet as dependent on the insolubility of the latter salt. 
 
 A solution of calcium carbonate in water charged with 
 carbonic acid is also capable of decomposing the sulphates of 
 potassium and sodium, but to a less extent than lime alone, 
 and without deposition of calcium sulphate. The alkaline 
 chlorides are not decomposed by lime-water, nor by a solution 
 of chalk. On the other hand, a mixture of lime-water and 
 calcium sulphate solution, when boiled with the chlorides, gave 
 diffusates containing free alkalies. This is explained by 
 Graham as due to the transformation of the alkaline chloride 
 into alkaline sulphate, which is then decomposed by the lime 
 in the manner already indicated. 
 
 Graham ends his paper by a reference to a possible 
 bearing of liquid diffusion on agriculture which is not with- 
 out interest. The mode in which the soil is moistened 
 by rain is, he says, "peculiarly favourable to separations 
 by diffusion. The soluble salts of the soil may be supposed to 
 be carried down together, to a certain depth, by the first 
 portion of rain which falls, while they find afterwards an 
 atmosphere of nearly pure water, in the moisture which falls 
 last and occupies the surface stratum of the soil. Diffusion of 
 the salts upwards into the water, with its separations and 
 decompositions, must necessarily ensue. The salts of potash 
 and ammonia, which are most required for vegetation, possess 
 the highest diffusibility, and will rise first. The pre-eminent 
 diffusibility of the alkaline hydrates may also be called into 
 action in the soil by hydrate of lime, particularly as quicklime 
 is applied for a top-dressing to grass lands." 
 
 The remarkable differences in the diffusive power of sub- 
 
1 86 Thomas Graham vm 
 
 stances naturally led Graham to consider the practicability of 
 employing the process as an analytical agent, and in a paper 
 published in the Philosophical Transactions for 1861 he de- 
 scribes how liquid diffusion may be so made use of. To begin 
 with, he draws attention to the fact that soluble substances 
 may be broadly divided into two main classes dependent on 
 their diffusibility. The one class, of low diffusibility, is 
 characterised by the absence of the power to crystallise. 
 Among such substances Graham mentions " hydrated silicic 
 acid, hydrated alumina, and other metallic peroxides of the 
 aluminous class, when they exist in the soluble form, with 
 starch, dextrin, and the gums, caramel, tannin, albumen, 
 gelatine, and vegetable and animal extractive matters." Low 
 diffusibility is not the only property which these bodies 
 possess in common. "They are distinguished by the 
 gelatinous character of their hydrates. Although often 
 largely soluble in water, they are held in solution by a 
 most feeble force. They appear singularly inert in the 
 capacity of acids and bases, and in all the ordinary chemical 
 relations. But, on the other hand, their peculiar physical 
 aggregation, with the chemical indifference referred to, appears 
 to be required in substances that can intervene in the organic 
 processes of life. The plastic elements of the animal body are 
 found in this class. As gelatine appears to be its type, it is 
 proposed to designate substances of this class as colloids, and 
 to speak of their peculiar form of aggregation as the colloidal 
 condition of matter." 
 
 The other class, of relatively high diffusive power, is 
 broadly characterised by the power to crystallise. " Substances 
 affecting the latter form will be classed as crystalloid. The 
 distinction is no doubt one of intimate molecular con- 
 stitution." 
 
 "Although chemically inert in the ordinary sense, colloids 
 possess a compensating activity of their own, arising out of 
 their physical properties. While the rigidity of the crystal- 
 
viii Thomas Graham 187 
 
 line structure shuts out external impressions, the softness of 
 the gelatinous colloid partakes of fluidity, and enables the 
 colloid to become a medium for liquid diffusion, like water 
 itself. The same penetrability appears to take the form of 
 cementation in such colloids as can exist at a high tempera- 
 ture. . . . Another and eminently characteristic quality of 
 colloids is their mutability. Their existence is a continued 
 metastasis. . . . The colloidal is, in fact, a dynamical state of 
 matter; the crystalloidal being the statical condition. The 
 colloid possesses ENERGIA. It may be looked upon as the 
 probable primary source of the force appearing in the pheno- 
 mena of vitality. To the gradual manner in which colloidal 
 changes take place (for they always demand time as an 
 element), may the characteristic protraction of chemico-organic 
 changes also be referred." 
 
 Liquid diffusion may be made use of for analytical 
 purposes, either with or without an intervening septum. In 
 the latter case the solution of the substance to be submitted 
 to diffusive separation is brought, by means of a fine pipette, 
 to the bottom of a column of water some 5 or 6 inches 
 high, and after some days the upper layers of the water are 
 syphoned off, and the dissolved matter recovered by 
 evaporation or other suitable process. 
 
 A more generally applicable method, however, is to use a 
 septum : to such a mode of separation Graham applies the 
 convenient term dialysis. The most suitable of all substances 
 for the dialytic septum he found to be what is known as 
 vegetable - parchment or parchment - pape'r, prepared by 
 immersing unsized paper in oil of vitriol or zinc chloride 
 solution. This is stretched between two concentric and 
 tightly - fitting hoops of gutta-percha, so as to form a 
 tambourine-shaped vessel or dialyser capable of floating on the 
 surface of water. The mixed fluid to be dialysed is poured 
 over the parchment-paper to the depth of about half an inch, 
 and the dialyser is then floated upon water contained in a basin. 
 
1 88 Thomas Graham vm 
 
 The first method has the particular advantage that it 
 affords the means of ascertaining the absolute rate or velocity 
 of diffusion. It thus becomes possible to state the distance 
 which a salt travels per second in terms of the meter. " It 
 is easy to see," says Graham, " that such a constant must enter 
 into all the chronic phenomena of physiology, and that it 
 holds a place in vital science not unlike the time of the falling 
 of heavy bodies in the physics of gravitation." 
 
 Graham's observations lead to the following relative 
 
 APPROXIMATE TIMES OF EQUAL DIFFUSION. 
 
 Hydrochloric acid . 1 
 
 Sodium chloride . . 2-33 
 Sugar .... 7 
 
 Magnesium sulphate . 7 
 Albumen . . .49 
 Caramel 98 
 
 A question of the greatest importance in regard to the 
 real nature of solution was raised by Graham in studying the 
 effect of the acid in influencing the diffusibility of basic 
 radicles. If the acids are of equal diffusibility, there seems 
 no reason why the acids should affect the amount of separation. 
 "But if," says Graham, "the acids are unlike in diffusibility, 
 the case is not so clear. If, for instance, the potassium were 
 in the form of chloride, and the sodium in that of sulphate, 
 might not the diffusion of the potassium be promoted by the 
 highly diffusive chlorine with which it is associated, and the 
 diffusion of the soda, on the other hand, be retarded by its 
 association with the slowly diffusive sulphuric acid 1 ? Will, 
 in fine, the separation of the metals be greater from a mixture 
 of chloride of potassium and sulphate of soda, or even from 
 sulphate of potash and chloride of sodium, than from the two 
 chlorides or from the two sulphates *? The inquiry, it will be 
 remarked, raises the whole question of the distribution of 
 acid and base in solutions of mixed salts." The answer given 
 by Graham to this question is very significant. It was found 
 that the diffusion of the basic radicles was not affected by the 
 
VIII 
 
 Thomas Graham 189 
 
 acid with which they were considered to be combined. This 
 result is in harmony, as Graham points out, with Berthollet's 
 view that the acids and bases are indifferently combined, or 
 that a mixture of sodium sulphate, and potassium chloride 
 is the same thing as a mixture of potassium sulphate, and 
 sodium chloride when the mixtures are in a state of 
 solution. 
 
 As regards the second or dialytic method, it was found 
 that the diffusive process was but slightly interfered with by 
 the intervention of the septum. Provided that it was a true 
 colloid, the nature of the septum whether gelatinous starch, 
 coagulated albumen, gum-tragacanth, or parchment -paper 
 had no influence on the result. The relative diffusibility of 
 salts seemed to be unchanged ; mixed salts were separated in 
 exactly the same manner as in the absence of the septum, 
 and so-called double salts were found to be decomposed 
 and their proximate constituents to part company as already 
 described. 
 
 The method of dialysis is admirably adapted to the pre- . 
 paration of colloid substances in a state of purity ; and not 
 the least interesting part of Graham's memoir is concerned with 
 the description of the properties of a number of these singular 
 bodies, which were obtained in this manner. Thus when a 
 solution of silica, obtained by pouring silicate of soda into a large 
 excess of dilute hydrochloric acid, is placed on a dialyser of 
 parchment-paper, the sodium chloride, together with the rest 
 of the hydrochloric acid, passes through the septum, whilst a 
 pure solution of silicic acid remains. This may be concentrated 
 by boiling in a flask, and forms a perfectly limpid colour- 
 less liquid, having little viscidity, even when containing 
 14 per cent of silicic acid. It gradually, however, becomes 
 opalescent, and eventually forms a transparent colourless 
 jelly, which slowly contracts and hardens. The coagulation of 
 the silicic acid is rapidly effected by a minute trace of- any 
 alkaline or earthy carbonate, but not by caustic ammonia, nor 
 
VIII 
 
 i go Thomas Graham 
 
 by neutral or acid salts. The common acids, alcohol or sugar 
 seem to have no coagulating effect. A trace of hydrochloric 
 acid, or of potash or soda, appears to render the solution more 
 stable. The pure solution has an acid reaction, greater than 
 that of carbonic acid. The jelly, when dried in vacua, forms 
 a transparent, vitreous, insoluble mass of considerable lustre. 
 Certain colloids, as gelatine, alumina, and ferric oxide, 
 precipitate the silicic acid ; gum-arabic and caramel appear to 
 have no action. The precipitates seem to be weak chemical 
 combinations ; the gelatine compound is a flaky, white, and 
 opaque substance, insoluble in water, and not decomposed by 
 washing. It may be obtained containing almost half its 
 weight of gelatine. The proportion, however, is not constant, 
 but varies with the mode of preparation. Graham, in a 
 subsequent paper, describes combinations of colloidal silicic 
 acid with ethyl alcohol, ether, benzene, carbon bisulphide, and 
 glycerin. 
 
 The existence of a soluble form of alumina was known 
 before the publication of Graham's paper. It was dis- 
 covered by Mr. Walter Crum, and is obtained by heating a 
 solution of alumina acetate, when the whole of the acetic 
 acid is expelled, whilst the alumina remains dissolved. 
 According to Graham, another modification of soluble alumina 
 may be obtained by dialysing a solution of basic aluminium 
 chloride. Normal aluminium chloride passes through the 
 septum, and eventually a solution of colloidal alumina is left 
 on the dialyser. The solution is very unstable, and is 
 coagulated by minute traces of many foreign substances. 
 This form of alumina acts as a mordant ; its solution may be 
 concentrated by boiling, but is apt to coagulate suddenly. It 
 has a feeble alkaline reaction, and is readily dissolved by 
 acids. Meta-alumina, as Graham terms Crum's modification, 
 has no mordanting action, and when once precipitated is not 
 dissolved by an excess of acid. 
 
 A similar colloidal form of ferric hydrate may also be 
 
VIII 
 
 Thomas Graham 191 
 
 obtained by dialysing basic ferric chloride solution. A liquid 
 remains on the dialyser, of the dark red colour of venous 
 blood ; an aqueous solution containing only 1 per cent of the 
 colloidal ferric oxide has the colour of blood. It may be con- 
 centrated to a certain extent, but readily coagulates to a deep 
 red jelly, somewhat resembling a clot of blood. Graham con- 
 siders that native haematite, which is found in mammillary 
 concretions, is in all probability colloidal. A soluble ferric 
 hydrate, analogous to the meta-alumina of Crum, was obtained 
 by Pean de Saint-Gilles by the action of heat upon ferric 
 acetate. Its solution has an orange-red colour, and is more or 
 less opalescent. 
 
 Chromic hydrate exists in similar colloidal modifications. 
 Copper ferrocyanide also appears to be a colloid, and may be 
 obtained in a soluble form by dialysing its solution in 
 ammonium oxalate. The greater part of the latter salt passes 
 through the parchment paper, and there is left a red solution of 
 the ferrocyanide, which may be heated without change, but 
 which is coagulated by foreign substances with great readiness. 
 
 A colloidal modification of Prussian blue and of TurribuWs 
 blue may be obtained by dialysing the oxalic acid solutions of 
 these colouring matters. 
 
 The blue liquid obtained by adding caustic potash to a 
 solution of cupric chloride and sugar also contains a colloidal 
 substance; it consists apparently of cupric oxide combined 
 with sugar, and is readily precipitated by salts and acids. 
 Similar compounds of sugar with ferric and uranic hydrates 
 appear to exist. 
 
 Stannic and titanic hydrates are soluble in aqueous solu- 
 tions of their chlorides, or in hydrochloric acid, but when 
 these are submitted to dialysis they yield the hydrates in 
 semi-transparent gelatinous cakes. Colloidal modifications of 
 tungstic and molybdic acids are also known. 
 
 Dialysis has proved of much service in toxicological 
 investigations, where the poisonous substance has to be 
 
VIII 
 
 1 92 Thomas Graham 
 
 searched for in fluid mixtures containing, it may be, a con- 
 siderable amount of colloidal matter. The fluid, diluted, if 
 necessary, with water, is placed on the dialyser, when such 
 poisons as arsenious acid, tartar-emetic, and strychnine pass 
 through the parchment-paper, and may be detected in the 
 diffusate. The process has the great advantage of introducing 
 no metallic substance or chemical reagent into the organic 
 fluid from which the poison has to be separated. 
 
 Graham concludes his memoir with a short summary of the 
 general characters of the colloidal condition of matter, and 
 with some interesting and suggestive observations on osmose. 
 He points out that a radical distinction in intimate molecular 
 constitution must exist between crystalloids and colloids. 
 "Every physical and chemical property is characteristically 
 modified in each class. They appear like different worlds of 
 matter, and give occasion to a corresponding division of chemi- 
 cal science. The distinction between these kinds of matter is 
 that subsisting between the material of a mineral and the 
 material of an organised mass. 
 
 " The colloidal character is not obliterated by liquefaction, 
 and is therefore more than a modification of the physical con- 
 dition of solid." In their relations to water e.g. solubility, 
 power of combination the colloids exhibit as great diversity 
 as the crystalloids. " The phenomena of the solution of a salt 
 or crystalloid probably all appear in the solution of a colloid, 
 but greatly reduced in degree. . . . The change of tempera- 
 ture usually occurring in the act of solution becomes [in the 
 case of the colloid] barely perceptible. The liquid is always 
 sensibly gummy or viscous when concentrated. The colloid, 
 although often dissolved in a large proportion by its solvent, 
 is held in solution by a singularly feeble force. Hence 
 colloids are generally displaced and precipitated by the 
 addition to their solution of any substance from the other 
 class. Of all the properties of liquid colloids, their slow 
 diffusion in water, and their arrest by colloidal septa, are the 
 
Thomas Graham 193 
 
 most serviceable in distinguishing them from crystalloids. 
 Colloids have feeble chemical reactions, but they exhibit at 
 the same time a very general sensibility to liquid reagents, as 
 has already been explained. 
 
 " While soluble crystalloids are always highly sapid, soluble 
 colloids are singularly insipid. It may be questioned whether 
 a colloid, when tasted, ever reaches the sentient extremities 
 of the nerves of the palate, as the latter are probably pro- 
 tected by a colloidal membrane impermeable to soluble sub- 
 stances of the same physical constitution. 
 
 " It has been observed that vegetable gum is not digested 
 in the stomach. The coats of that organ dialyse the soluble 
 food, absorbing crystalloids and rejecting all colloids. This 
 action appears to be aided by the thick coating of mucus 
 which usually lines the stomach. . . . 
 
 "Ice itself presents colloidal characters at or near its melting- 
 point, paradoxical although the statement may appear. When 
 ice is formed at temperatures a few degrees under C., it has 
 a well-marked crystalline structure, as is seen in water frozen 
 from a state of vapour, in the form of flakes of snow and 
 hoar-frost, or in water frozen from dilute sulphuric acid, as 
 observed by Mr. Faraday. But ice formed in contact with 
 water at is a plain homogeneous mass, with a vitreous 
 fracture, exhibiting no facets or angles. This must appear 
 singular when it is considered how favourable to crystallisation 
 are the circumstances in which a sheet of ice is slowly pro- 
 duced in the freezing of a lake or river. . . . Further, ice, 
 although exhibiting none of the viscous softness of pitch, has 
 the elasticity and tendency to rend, seen in colloids. In the 
 properties last mentioned, ice presents a distant analogy to 
 gum incompletely dried, to glue, or any other firm jelly. 
 Ice further appears to be of the class of adhesive colloids. 
 The redintegration (regelation of Faraday) of masses of 
 melting ice, when placed in contact, has much of a colloid 
 character. A colloidal view of the plasticity of ice de- 
 
 
 
194 Thomas Graham vm 
 
 monstrated in the glacier movement will readily develop 
 itself." 
 
 The osmotic process, which is obviously closely connected 
 with the action of colloidal septa, appears to Graham to depend, 
 so far as regards the water movement, on the hydration and 
 dehydration in the substance of the membrane or other 
 colloidal septum; the diffusion of the saline solution placed 
 within the osmometer has little or nothing to do with the 
 osmotic result otherwise than as it affects the state of hydra- 
 tion of the septum. An animal membrane is much affected 
 by the liquid medium in which it is placed, and is hydrated 
 to a higher degree by pure water than by neutral saline solu- 
 tions. " Hence the equilibrium of hydration is diiferent on the 
 two sides of the membrane of an osmometer. The outer sur- 
 face of the membrane, being in contact with pure water, tends 
 to hydrate itself in a higher degree than the inner surface 
 does, the latter surface being supposed to be in contact with 
 a saline solution. When the full hydration of the outer 
 surface extends through the thickness of the membrane and 
 reaches the inner surface, it there receives a check. The 
 degree of hydration is lowered, and water must be given 
 up by the inner layer of the membrane, and it forms the 
 osmose." 
 
 The conditions affecting the flow of liquids through narrow 
 tubes next engaged Graham's attention. He had shown that 
 a gas passes through a capillary tube in a manner altogether 
 different from that in which it passes through an orifice in an 
 extremely thin plate, or into an atmosphere of another gas 
 without the intervention of a septum. In other words, the 
 transpiration and the diffusion of gases are governed by 
 altogether different laws. In view of the analogy existing 
 between the diffusion of a gas and a liquid, it became of 
 interest to study the transpiration of liquids. This subject 
 had already been attacked by Poiseuille, who had ascertained 
 the experimental conditions under which comparative measure- 
 
viii Thomas Graham 195 
 
 ments can be accurately made, and had determined the 
 relations between the rate of flow, the dimensions of the 
 capillary tube, and the pressure under which the transpiration 
 is effected. Poiseuille's measurements were, however, con- 
 fined to a few liquids standing to one another in no definite 
 chemical relationship. Graham sought to extend the inquiry, 
 and his memoir " On the Capillary Transpiration of Liquids 
 in relation to Chemical Composition," communicated to the 
 Eoyal Society in 1861, contains the results of the determina- 
 tion of the transpiration rates of a number of substances. The 
 method adopted was essentially that of Poiseuille, in which 
 the time required for a given volume of the liquid to flow 
 through a capillary of known dimensions under a definite 
 pressure is noted. Graham made his measurements at the 
 uniform temperature of 20, under the assumption, apparently, 
 that this was a truly comparable condition. No definite 
 results could possibly follow from such a method of inquiry, 
 and indeed there is reason to believe that he merely regarded 
 his observations as preliminary to a much wider investigation. 
 The main object, in the outset, was to ascertain the exist- 
 ence of definite hydrates of the acids by noting the effect of 
 the added water on the times of flow, Poiseuille having 
 already found that the addition of water to ethyl-alcohol 
 gradually retarded the transpiration up to a certain point, 
 apparently corresponding with a combination of one molecule 
 of alcohol with three molecules of water. Although the exist- 
 ence of such hydrates seemed to be indicated in a few cases, 
 in others the observations were equivocal. A number of 
 measurements were made on the pure alcohols, acids, and on 
 mixed ethers, from which Graham inferred that the increase 
 of the transpiration time, as the series is ascended in each 
 particular case, is connected with the increasing weight of the 
 molecule. The general conclusion is that a relation between 
 the transpirability of liquids and their chemical composition 
 undoubtedly exists. " It is a relation analogous in character 
 
196 Thomas Graham vm 
 
 to that subsisting between the boiling-point and composition, 
 so well defined by M. Kopp." 
 
 Graham continued to speculate and to work on the 
 subject of the molecular movement of substances until his 
 death ; and no mode of attack that occurred to him as likely 
 to furnish fresh light on the great problem which had 
 occupied his thoughts during the whole of his scientific life 
 was neglected. The remarkable observation by Dr. Mitchell 
 of Philadelphia, made in 1830, that unvulcanised india-rubber 
 absorbs the various gases in very different degrees, was the 
 occasion of the memoir "On the Absorption and Dialytic 
 Separation of Gases by Colloid Septa," which Graham com- 
 municated to the Eoyal Society in 1866. It is interesting to 
 note in this paper the tenacity with which he clings to the 
 ideas which had actuated him in his earliest investigations. 
 Indeed this was characteristic of the man. Graham's con- 
 victions were not lightly formed; often the result of pro- 
 longed and patient thought, when once arrived at they were, 
 as in the case of most independent thinkers, adhered to 
 with a firmness which occasionally verged on obstinacy. Dr. 
 Mitchell's observations "On the Penetrativeness of Fluids," 
 as his memoir is entitled, led Graham to the generalisation 
 that those gases penetrate most readily which are easily 
 liquefied by pressure, and which are also " generally highly 
 soluble in water or other liquids." " Two considerations," he 
 says, " appear to be essential to the full comprehension of the 
 phenomena namely, that gases undergo liquefaction when 
 absorbed by liquids and such colloid substances as india- 
 rubber, and that their transmission through liquid and colloid 
 septa is then effected by the agency of liquid, and not gaseous 
 diffusion. Indeed the complete suspension of the gaseous 
 function during the transit through colloid membranes cannot 
 be kept too much in view." 
 
 It must be admitted that Graham's own experimental 
 determinations lend little support to his hypothesis of the 
 
Thomas Graham 197 
 
 nature of the process by which gases pass through rubber. 
 The order of ' penetrativeness ' exhibits no exact relation either 
 to the solubility of the gases in ordinary solvents or to their 
 coercibility. This will be evident from the following table, 
 showing the 
 
 PENETRATION OP KUBBER BY EQUAL VOLUMES OF GAS. 
 
 Time. 
 
 Carbonic acid ... . " 1 
 
 Hydrogen . . . . .* 2*4YO 
 
 Oxygen . . . . . . 5*316 
 
 Marsh gas . . . . 6*325 
 
 Atmospheric air . . . . 11*850 
 
 Carbonic oxide .. . . 12*203 
 
 Nitrogen . . . . 13*585 
 
 Carbonic acid, the most easily liquefied in the series, and 
 the most soluble of the whole, certainly comes first ; but it is 
 followed by hydrogen, which is the only one of the group 
 which has resisted all attempts to effect its liquefaction, and 
 which is the least soluble in water. Nor do the other gases 
 follow in the order demanded by Graham's supposition. If, 
 as Graham argues, the absorption of the gas by rubber de- 
 pends upon a kind of chemical affinity analogous to the 
 attraction which appears to exist between a soluble body and 
 its solvent, conducing to solution, it has still to be proved 
 that rubber is so peculiar in its action that the order of 
 solubility is altogether different from that exhibited by other 
 solvents. In the light of our present knowledge it is even 
 more difficult to assume that an actual liquefaction of hydrogen 
 takes place. 
 
 Graham found that the penetrability of rubber was much 
 affected by temperature, the film becoming more and more 
 permeable as it becomes heated. This, at first sight, seems to 
 militate against his hypothesis, since increase of temperature 
 tends to prevent liquefaction. Graham, however, seeks an 
 
198 Thomas Graham vm 
 
 explanation in the tendency of the colloid to become more 
 soft when heated, and, as he expresses it, " to acquire more of 
 liquid and less of solid properties." 
 
 Owing to the very different rates at which oxygen and 
 nitrogen pass through rubber the ' penetrativeness ' of 
 oxygen being more than two and a half times that of nitrogen 
 Graham found that it was possible to effect what he terms 
 a dialytic separation of the two gases from atmospheric air. 
 This may be accomplished by filling a balloon of thin rubber 
 one of the toy-balloons of the shops answers admirably 
 with hydrogen or carbonic acid, and after the expiration of 
 a few hours, when the balloon will be found to have become 
 less distended, analysing the gaseous residue. In one ex- 
 periment with hydrogen the ratio of the oxygen to the nitrogen 
 in the gaseous residue was as 41*6 per cent to 58 '4 per cent. 
 .With carbonic acid the dialytic separation can be very readily 
 demonstrated, since the residual carbonic acid may be quickly 
 removed from the gaseous mixture by means of a solution of 
 caustic potash or soda, when, under favourable circumstances, 
 it will be found that the remaining gas contains sufficient 
 oxygen to inflame a glowing splint. Bags or balloons of 
 india-rubber, or long lengths of vulcanised rubber - tubing, 
 attached to the Sprengel pump, may also be made use of to 
 show this dialytic separation. The bag, or length of tubing 
 (the latter closed, of course, at the unattached end), is rapidly 
 exhausted in the usual way, and the gas, which thereafter 
 slowly permeates the rubber, is collected at the bottom of the 
 fall-tube. This gas readily rekindles a glowing splint, and on 
 analysis is found to contain from 38 to 41 per cent by volume 
 of oxygen, the amount depending on the temperature and the 
 nature of the septum ; but in any case a very notable increase 
 on the 21 per cent in the undialysed air. 
 
 The analogy which these facts exhibit to the passage of 
 gases, and more particularly of hydrogen, through heated 
 plates of platinum or iron, as observed by Deville and Troost, 
 
VIII 
 
 Thomas Graham 199 
 
 led Graham to experiment on the action of metallic septa at a 
 red heat. He seems, however, to be sensible that this analogy 
 lends no very strong support to his views as to the real nature 
 of the penetrative process. " It must be admitted," he says, 
 " that such an hypothesis as that of liquefaction can only be 
 applied in a general and somewhat vague manner to bodies 
 so elastic and volatile at an elevated temperature as the gases 
 generally must be, and hydrogen in particular. Still some degree 
 of absorbing and liquefying power can scarcely be denied to 
 a soft or liquid substance, in whatever circumstances it may 
 be found, with such a patent fact before us as the retention 
 by fused silver of 18 or 20 volumes of oxygen at a red 
 heat. It may be safely assumed that the tendency of gases 
 to liquefaction, however much abated by temperature, is 
 too essential a property of matter to be ever entirely obliter- 
 ated." He seeks to strengthen his conjecture by an appeal 
 to analogy. " The absorption of gas by a liquid or by a 
 colloid substance," he says, "is not a purely physical effect. 
 The absorption appears to require some relation in com- 
 position as where both the gas and the liquid are hydro- 
 carbons, and the affinity or attraction of solution comes 
 into play. May a similar analogy be looked for, of hydrogen 
 to liquid, or colloid bodies of the metallic class 1 ?" The 
 analogy is ingenious and even daring, but is not the courage 
 that of a forlorn hope 1 Graham, it may be remarked, seldom 
 trusts himself to the guidance of analogy alone ; like Davy, he 
 was aware how fruitful a parent of error it may be. To 
 argue that the penetrability of hydrogen through platinum 
 or iron is remotely due to the so-called metallic nature of 
 hydrogen, is surely straining the analogy to the utmost limit. 
 Graham would not apply the same reasoning to explain the 
 solubility of oxygen in silver. 
 
 A large number of experiments were made to ascertain 
 whether other gases than hydrogen would pass through red- 
 hot platinum, but with negative results. Carbonic acid, which 
 
2oo Thomas Graham 
 
 VIII 
 
 shows the greatest power of passing through rubber, was found 
 to be incapable of permeating heated platinum. Ammonia gas 
 and vapour of water easily coercible substances are also 
 unable to penetrate the red-hot metal. 
 
 The greater part of the rest of the memoir is devoted to 
 a study of the behaviour of hydrogen towards platinum and 
 other metals. Graham found that hydrogen was not only 
 absorbed by the red-hot platinum, but that it could be retained 
 at a temperature under redness for an indefinite time. " It 
 may be allowable to speak of this as a power to occlude (to 
 shut up) hydrogen, and the result as the occlusion of hydrogen 
 by platinum." 
 
 The power of finely divided platinum especially the so- 
 called platinum black to absorb hydrogen was already known, 
 but no exact determinations of the amount so absorbed, or any 
 study of the conditions of retention, had been hitherto made. 
 Graham found that the volume of gas absorbed, even under 
 the most favourable conditions, was never more than about 
 five times that of the metal, and was usually much less. 
 
 Of all the metals investigated, palladium appears to possess 
 the power of absorbing hydrogen in the highest degree. 
 Indeed its capacity in this respect is altogether peculiar. 
 Graham found that welded palladium absorbs hydrogen to 
 the extent of 600 times its volume at a temperature below the 
 boiling-point of water ; at 245 upwards of 500 volumes are 
 absorbed. Even at ordinary temperatures a considerable 
 quantity of the gas is occluded. On the other hand, palladium 
 charged with hydrogen at or under 100 begins to evolve gas 
 when exposed to the air or placed in vacuo at the original 
 temperature of absorption; at 200 the gas is freely dis- 
 engaged. 
 
 When palladium charged with hydrogen is left exposed to 
 the atmosphere, the metal is apt to become suddenly hot, and 
 to lose its gas entirely by spontaneous oxidation. A wire of 
 the charged metal, if rubbed with magnesia (to make the 
 
viii Thomas Graham 201 
 
 flame luminous) burns like a waxed thread when ignited in 
 the flame of a lamp. 
 
 The condensed hydrogen, as might be anticipated, is chemi- 
 cally active. A palladium wire charged with hydrogen, and 
 immersed in a solution of a ferric salt, reduces it to the state 
 of a ferrous salt ; potassium f erricyanide becomes f errocyanide ; 
 chlorine water forms hydrochloric acid ; and iodine becomes 
 hydriodic acid. Solutions of mercuric chloride, of certain 
 oxy-salts, and of vanadic acid are also found to be reduced 
 by the occluded hydrogen. In respect to its chemical activity 
 the condensed hydrogen is related to ordinary hydrogen much 
 as ozone is related to oxygen. 
 
 Graham sees in these facts a strong confirmation of the valid- 
 ity of his hypothesis as to the real nature of the phenomenon. 
 "It is probable," he says, "that hydrogen enters palladium in 
 the physical condition of liquid, whether the phenomenon 
 proves to be analogous to the imbibition of ether, chloroform, 
 and such solvents, by the colloid india-rubber, or whether a 
 certain porosity of structure in the palladium is required. The 
 porosity of the metal is supposed to be of that high degree 
 which will admit liquid but not gaseous molecules." 
 
 Graham further found that when coal-gas was led round the 
 outside of a palladium tube attached to, and made vacuous by, 
 a Sprengel pump, it was possible, on heating the tube to 270, 
 to sift out the hydrogen, to the exclusion of the other gases. 
 Indeed the isolation is so exact that Graham considers that 
 a quantitative determination of the hydrogen in a gaseous 
 mixture might be based on this principle. It is noteworthy 
 that the only other volatile body which was observed to pass 
 through a plate of palladium is common ether : the vapour of 
 this substance permeated palladium even at ordinary tempera- 
 tures. 
 
 Osmium -iridium and antimony have no power to absorb 
 hydrogen ; copper, gold, silver, and iron absorb only a small 
 amount, seldom exceeding half the volume of the metal. Silver, 
 
 OF THE 
 TT TJ T XT ft F? c- T T "V 
 
2O2 Thomas Graham 
 
 VIII 
 
 however, is remarkable for its power of absorbing oxygen, and 
 iron for its capacity for retaining carbonic oxide. Graham 
 found that pure iron is capable of taking up at a low red heat, 
 and holding when cold, upwards of four times its volume of 
 carbonic oxide. This fact, he thinks, has an important bearing 
 upon the process of steel-making, or acieration, by the cementa- 
 tion process. "Hitherto," he says, "the decomposing action 
 of the iron upon carbonic oxide has been supposed to be 
 exercised only at the external surface of the metal. A surface- 
 particle of the iron has been supposed to assume one half of 
 the carbon belonging to an equivalent of carbonic oxide [2 CO], 
 while the remaining elements diffused away into the air as 
 carbonic acid (C0 2 ) to reacquire carbon from the charcoal 
 placed near, and to become capable of repeating the original 
 action. It is now seen that such a process need not be con- 
 fined to the surface of the iron bar, but may occur throughout 
 the substance of the metal, in consequence of the prior pene- 
 tration of the metal by carbonic oxide. ... It appears that 
 the diffused action of carbonic oxide is the proper means of 
 distributing the carbon through the mass of iron. The blis- 
 tering of the bar appears to testify to the necessary production 
 and evolution of carbonic acid, owing to the decomposition of 
 the carbonic oxide in the interior of the bar." 
 
 This memoir, although containing many important and 
 suggestive facts, and of classical interest as giving the first 
 intimation of the remarkable and peculiar capacity of palla- 
 dium for occluding hydrogen, is hardly on a par with Graham's 
 earlier papers in point of literary merit. It seems to have 
 been somewhat hurriedly put together, and has in parts 
 the appearance of being a mere transcript of a laboratory 
 journal ; the language is occasionally obscure, and there is a 
 certain awkwardness of style, in striking contrast to that of the 
 greater number of the memoirs which its author communicated 
 to the Philosophical Transactions. That Graham was conscious 
 of this may be inferred from the many corrections and deletions 
 
viii Thomas Graham 203 
 
 which were found to have been made in his own copy ; these 
 are indicated in the late Dr. Young's reprint of his memoirs. 
 There is no doubt that during its composition he was greatly 
 worried with the business of the Mint ; its affairs occupied, 
 practically, the whole of his thoughts at that time, and con- 
 sumed much of his nervous energy. 
 
 The remarkable observation, made in 1867, that the 
 Lenarto meteorite when heated in a vacuum yielded gas to 
 the extent of nearly three times its volume, 86 per cent of 
 which gas was hydrogen, whereas ordinary iron when treated 
 in the same manner evolved a relatively large proportion of 
 carbonic oxide, was held by Graham to indicate that the iron of 
 the Lenarto meteorite had been " extruded from a dense mass 
 of hydrogen gas, for which we must look beyond the light 
 cometary matter floating about within the limits of the solar 
 system. . . . This meteorite may be looked upon as holding 
 imprisoned within it, and bearing to us, hydrogen of the 
 stars." It has been assumed that Graham regarded the 
 presence of occluded hydrogen as characteristic of iron of 
 extra-terrestrial origin, but there is nothing in his memoir, in 
 the Proceedings of the Royal Society (vol. xv. p. 502, 1867), to 
 justify such a supposition. Subsequent observations have 
 shown that many irons of undoubted meteoric origin evolve 
 considerable quantities of carbonic oxide and relatively little 
 hydrogen. 
 
 In a subsequent paper, published in the Proceedings of 
 the Royal Society for 1868, Graham states that a ready method 
 of charging the palladium with hydrogen consists in mak- 
 ing it the negative electrode of a voltaic couple immersed in 
 acidulated water. Under these circumstances it is observed 
 that whilst oxygen is freely evolved at the positive electrode, 
 the effervescence at the negative electrode is entirely sus- 
 pended for some twenty or thirty seconds, in consequence 
 of the hydrogen being occluded by the palladium, to the 
 extent of several hundred times its volume. Although the 
 
204 Thomas Graham vm 
 
 hydrogen in all probability pervades the whole mass of 
 the metal, the gas exhibits no disposition to leave the pal- 
 ladium, and to escape into a vacuum at the temperature of its 
 absorption. " It appears then," says Graham, " that when 
 hydrogen is absorbed by palladium, the volatility of the gas 
 may be entirely suppressed; and hydrogen may be largely 
 present in metals without exhibiting any sensible tension at low 
 temperatures. Occluded hydrogen is certainly no longer a 
 gas, whatever may be thought of its physical condition." By 
 reversing the position of the palladium in the cell, so as, 
 when charged, to make it the positive electrode, the hydrogen 
 is rapidly withdrawn from the metal. This would seem to 
 suggest that the palladium is charged mainly at the sur- 
 face ; otherwise it is not easy to understand how the oxygen, 
 which has no power, at all events in the ordinary mole 
 cular condition, of permeating the metal, acts in withdrawing 
 the hydrogen. Graham, moreover, found that not the least 
 trace of oxygen was absorbed by palladium in the position of 
 a positive electrode. Hence electrolytic oxygen, even in the 
 moment of its liberation, shows no more tendency to pass into 
 palladium than does the gas in the ordinary condition. 
 
 It is noteworthy that recent inquiries have rendered it 
 certain that the layers of gases in immediate contact with 
 solid surfaces are in a highly condensed state, and it is pos- 
 sible that this highly condensed gas possesses a degree of 
 chemical activity which the gas in its ordinary or more 
 attenuated condition fails to exhibit. 
 
 The power of platinum-sponge to ignite a jet of hydrogen, 
 as seen in the well-known Dobereiner lamp, depends, according 
 to Graham, upon the influence of the metal on the occluded 
 hydrogen. The hydrogen, he thinks, is polarised, and has its 
 attraction for oxygen greatly heightened, and he offers the 
 following representation of this phenomenon, "with an 
 apology for the purely speculative character of the explana- 
 tion." "The gaseous molecule of hydrogen being assumed to 
 
VIII 
 
 Thomas Graham 205 
 
 be an association of two atoms, a hydride of hydrogen, it would 
 follow that it is the attraction of platinum for the negative, or 
 ( chlorylous ' atom of the hydrogen molecule, which attaches 
 the latter to the metal. The tendency, imperfectly satisfied, 
 is to the formation of a hydride of platinum. The hydrogen 
 molecule is accordingly polarised, orient^ with its positive or 
 * basylous ' side turned outwards, and having its affinity for 
 oxygen greatly enlivened. It is true that the two atoms of a 
 molecule of hydrogen are considered to be inseparable ; but 
 this may not be inconsistent with the replacement of such 
 hydrogen atoms as are withdrawn, on combining with oxygen, 
 by other hydrogen atoms from the adjoining molecules. It is 
 only necessary to suppose that a pair of contiguous hydrogen 
 molecules act together upon a single molecule of the external 
 oxygen. They would form water, and still leave a pair of 
 atoms, or a single molecule of hydrogen, attached to the 
 platinum." 
 
 The capacity of palladium to absorb and retain hydrogen 
 is greatly modified by its condition. Pulverulent spongy pal- 
 ladium takes up 655 volumes of hydrogen ; when precipitated 
 from a dilute solution of the chloride on to platinum by the 
 action of a voltaic battery, it forms brilliant laminae which, 
 when detached and gently heated in hydrogen, absorb upwards 
 of 980 volumes of the gas, approximating, although not very 
 closely, to the ratio H : Pd. " But," says Graham, " the idea of 
 definite chemical combination is opposed by various considera- 
 tions. No visible change is occasioned to the metallic pal- 
 ladium by its association with the hydrogen. Hydrides of 
 certain metals are known as the hydride of copper (Wurtz), 
 and the hydride of iron (Wanklyn) ; but they are brown 
 pulverulent substances with no metallic characters." 
 
 Graham is inclined to the belief that the passage of hydrogen 
 through a plate of metal is always preceded by the condensa- 
 tion or occlusion of the gas. " But," he adds, " it must be 
 admitted that the rapidity of penetration is not in proportion 
 
206 Thomas Graham 
 
 VIII 
 
 to the volume of gas occluded ; otherwise palladium would be 
 much more permeable at a low than at a high temperature." 
 Experiments show that the velocity of penetration increases 
 in a rapid ratio with the temperature. The rapid dissemina- 
 tion of hydrogen through a soft colloid metal like palladium, 
 or platinum at a high temperature, has a certain analogy to the 
 process of liquid diffusion, the rate of which is greatly aug- 
 mented by heat. The liquid diffusion of salt in water is six 
 times as rapid at 100 as at 0. "If," says Graham, "the 
 diffusion of liquid hydrogen increases with temperature in 
 an equal ratio, it must become a very rapid movement at a 
 red heat. Although the quantity absorbed may be reduced 
 (or the channel narrowed), the flow of liquid may thus be 
 increased in velocity. The whole phenomena appear to be 
 consistent with the solution of liquid hydrogen in the colloid 
 metal." 
 
 There is no question that the discovery of the remarkable 
 behaviour of palladium with respect to hydrogen greatly 
 strengthened Graham's conviction of the validity of the 
 hypothesis by which he sought to explain the mode of passage 
 of gases through metals and through colloid septa, properly 
 so called. Indeed it may be doubted whether, in the absence 
 of this discovery, he would have continued to regard a metal 
 like platinum as belonging to the same category, as regards 
 this property, as india-rubber. The fact that the ' penetrative- 
 ness ' is most marked at high temperatures, and that practically 
 the only gases which exhibit it are hydrogen (which has 
 never yet been liquefied) and carbonic oxide (which is amongst 
 the most difficult of liquefaction) are very formidable, if not 
 insuperable objections to the liquefaction hypothesis. 
 
 In his last paper, published a few months before his death, 
 Graham is still concerned with the relation of hydrogen to 
 palladium. The so-called "metallic" attributes of hydrogen 
 furnish him with what he considers may be a clue to the real 
 nature of the combination between the hydrogen and the 
 
VIII 
 
 Thomas Graham 207 
 
 palladium. "It has often been maintained," he says, "on 
 chemical grounds that hydrogen gas is the vapour of a highly 
 volatile metal. The idea forces itself upon the mind that 
 palladium, with its occluded hydrogen, is simply an alloy of 
 this volatile metal, in which the volatility of the one element 
 is restrained by its union with the other, and which owes its 
 metallic aspect equally to both constituents." 
 
 He then seeks to determine the characters of what, 
 on the assumption of its metallic character, he names Hydro- 
 genium. 
 
 Palladium charged with hydrogen increases in bulk to 
 the extent of more than 4 per cent for a charge of 900 
 vols., and hence its specific gravity is lowered. The exact 
 specific gravity of the " alloy " cannot be accurately determined 
 in the ordinary way, as it continues to give off gas in minute 
 bubbles when immersed in a liquid. By measuring the 
 increase in length of a piece of palladium wire charged with 
 hydrogen, of which the amount is subsequently ascertained 
 by heating the wire in vacuo, some idea of the specific gravity 
 of the hydrogenium may be obtained on the assumption 
 "that the two metals do not contract nor expand, but re- 
 main of their proper volume on uniting." From a number 
 of such measurements the mean density of hydrogenium 
 was found to be 1'95, which is considerably greater than that 
 of metallic magnesium, viz., 1*74. The expansion experienced 
 by the charged palladium is, as Graham says, enormous if 
 viewed as a change of bulk in the metal only, due to any 
 conceivable physical force, amounting as it does to sixteen 
 times the dilatation of palladium when heated from 
 to 100. 
 
 Palladium behaves in a very remarkable manner when the 
 hydrogen is discharged from it : the wire contracts to an extent 
 as much below the original length as when charged it expands 
 beyond it. There is, however, no alteration in the specific gravity 
 of the metal. " The result is the converse of extension by wire- 
 
208 Thomas Graham vm 
 
 drawing. The retraction of the wire is possibly due to an 
 effect of wire-drawing in leaving the particles of metal in a 
 state of unequal tension, a tension which is excessive in the 
 direction of the length of the wire. The metallic particles 
 would seem to become mobile, and to right themselves in 
 proportion as the hydrogen escapes ; and the wire contracts in 
 length, expanding, as appears by its final density, in other 
 directions at the same time." 
 
 This retraction could be effected either by heating the 
 charged wire or by making it the positive electrode, and on 
 charging and discharging the same wire repeatedly the 
 retraction continued and seemed to be interminable. The 
 metal, however, under these circumstances gradually lost 
 much of its power to absorb hydrogen, indicating apparently 
 some molecular or mechanical change in its nature. Indeed 
 it was found, after a number of repetitions of the experi- 
 ment, that the wire became fissured longitudinally, acquired a 
 " thready " structure, and was much disintegrated. 
 
 The tenacity of the "alloy" is considerably less than pure 
 palladium, in the ratio of 81 to 100. Its electric conductivity 
 is also about 25 per cent lower. Palladium was placed by 
 Faraday at the head of the paramagnetic elements ; on 
 charging the metal with hydrogen it becomes distinctly 
 magnetic. Hydrogenium, therefore, would appear to take its 
 place among the strictly magnetic metals, i.e. with iron, nickel, 
 cobalt, chromium, and manganese. 
 
 Graham's most important contribution to pure chemistry 
 was his classical memoir "On the Arseniates, Phosphates, and 
 Modifications of Phosphoric Acid." It was communicated to 
 the Royal Society by his predecessor in the chair of chemistry 
 at University College, Edward Turner, and is published in 
 the Philosophical Transactions for 1833. This paper, which 
 exhibits Graham at his best, exercised an immediate and 
 profound influence on chemical theory. It established, in 
 the first place, the existence of what we now know as the 
 
VIII 
 
 Thomas Graham 209 
 
 three modifications of phosphoric acid ortho-, pyro-, and 
 metaphosphoric acid. Ortho- or ordinary phosphoric acid 
 was known to Boyle, and its widespread diffusion in nature 
 was pointed out by Gahn and Scheele. Pyrophosphoric acid 
 was discovered by Clark, a fellow townsman and contemporary 
 of Graham's, whose name, perhaps, is best known in 
 connection with the lime-process of " softening " water. The 
 existence of the metaphosphoric acid is demonstrated for the 
 first time by Graham in this memoir. Graham's work is 
 memorable inasmuch as it definitely determined what is 
 termed the basicity of the various modifications of phosphoric 
 acid that is, their power of combining with bases to form 
 salts. Graham pointed out that the facts he indicated are 
 most easily explained on the hypothesis that ordinary or 
 orthophosphoric acid is characterised to use his own 
 words by " a disposition to form salts which contain three 
 atoms of base to the double atom of acid. Of these salts 
 the most remarkable is the yellow subphosphate of silver 
 [triargentic phosphate, Ag 3 POJ, which the soluble phosphates 
 precipitate when added to nitrate of silver. This acid does 
 not affect albumen ; and the other modifications pass directly 
 into the condition of this acid on keeping their aqueous 
 solutions for some days, and more rapidly on boiling these 
 solutions, or upon fusing the other modifications or their 
 salts with at least three proportions of fixed base. 
 
 " Pyrophosphoric acid, or the acid which exists in the fused 
 phosphate of soda, is remarkably disposed to form salts having 
 two atoms base, which is the constitution of the white pyro- 
 phosphate of silver, formed on testing the pyrophosphate of 
 soda with a salt of silver. Such salts of the preceding acid 
 as contain no more than two atoms of fixed base pass into 
 pyrophosphates when heated to redness. The acid under con- 
 sideration, when free, does not disturb albumen, nor produce a 
 precipitate in muriate of barytes. 
 
 " The metaphosphoric acid is disposed to form salts, which 
 
 P 
 
2io Thomas Graham 
 
 VIII 
 
 contain one atom of base to the double atom of acid. The 
 other modifications pass into metaphosphoric acid when 
 heated to redness per se, or when heated to redness in contact 
 with no more than one atomic proportion of certain fixed 
 bases, such as soda. This acid, when free, occasions precipi- 
 tates in solutions of the salts of barytes and of most of the other 
 earths and metallic oxides, and forms an insoluble compound 
 with albumen." ..." Now it is a matter of certainty that if we 
 take one combining proportion of any modification of phos- 
 phoric acid, and fuse it with soda or its carbonate, we shall 
 form a metaphosphate, a pyrophosphate, or a phosphate [ortho- 
 phosphate] according as we employ one, two, or three pro- 
 portions of base. The acid, when separated from the base, will 
 possess, and retain for some time, the characters of its peculiar 
 modification. ... I suspect that the modifications of phos- 
 phoric acid, when in what we would call a free state, are still 
 in combination with their usual proportion of base, and that 
 that base is water. Thus the three modifications of phos- 
 phoric acid may be composed as follows : 
 
 Phosphoric Acid, H 3 P 
 Pyrophosphoric Acid, H 2 P 
 Metaphosphoric Acid, HP " 
 
 Graham here uses the notation of Berzelius, in which each 
 dot denotes an atom of oxygen, and writes the, formula as 
 binary or dualistic, in accordance with the views of the 
 Swedish chemist. When translated into the language of 
 modern theory, the student will at once recognise that these 
 facts are the common property of the text-books but in spite of 
 the condensation of statement which almost invariably awaits 
 the original description of a discovery, in no text-book of 
 to-day are they more concisely or clearly given than in 
 Graham's own words. 
 
 The peculiar part apparently played by water in the con- 
 
VIII 
 
 Thomas Graham 211 
 
 stitution of many salts, to which Graham's attention was 
 forcibly drawn by his investigation of the phosphates, was 
 still further elucidated by him in a series of memoirs which 
 appeared at various times between 1834 and 1843. Nothing, 
 in fact, is more characteristic of Graham's work than the 
 mode in which it appears to group itself round certain funda- 
 mental conceptions. He seems to fasten, as it were, in the 
 outset, upon some dominant idea, which he follows to the 
 furthest limits that are possible to him. It would not be diffi- 
 cult to classify the forty and odd papers with which he has 
 enriched chemical literature, in accordance with the half- 
 dozen leading ideas which appear to have inspired them. 
 Thus the main principle which constitutes the basis of the 
 most original, and perhaps the most important section of his 
 labours, was the conception of molecular motion a conception 
 at the bottom, not only of his work on the diffusion and tran- 
 spiration of gases, but also of that on the diffusion of saline 
 solutions, and the transpiration or viscosity of liquids. So, too, 
 the whole of his work on salts, embodied in about a dozen 
 memoirs, is dominated by the central idea of the relations of 
 water to the constitution and chemical nature of this class of 
 substances. 
 
 Graham communicated a short paper to the meeting of the 
 British Association in 1834, which indicates that he was at 
 that time occupied with an investigation, of which the results 
 were first fully made known in a memoir entitled " Water as a 
 Constituent of Salts," published in the Transactions of the Eoyal 
 Society of Edinburgh for 1836. In this paper he points out 
 that the water which is associated with the salts generically 
 known as the magnesian sulphates, or the vitriols, plays two 
 distinct parts. Thus, in ordinary zinc sulphate or white 
 vitriol, of the seven molecules of water which the salt con- 
 tains, one molecule is essential to, or bound up with, the 
 constitution of the salt, whereas the remaining six molecules 
 appear to be concerned only with its crystalline form. The 
 
212 Thomas Graham vm 
 
 six molecules of water of crystallisation are expelled when 
 the salt is heated to 100, or when it is placed over oil of 
 vitriol in vacuo at the ordinary temperature, whilst the one mole- 
 cule of water the saline water, or " water of constitution," as 
 it may be termed is retained up to 240. This one molecule 
 may, however, be replaced by potassium sulphate, or with 
 more difficulty by sodium sulphate, and a double salt formed 
 of the type ZnS0 4 . M 2 S0 4 . 6H 2 0, where M is the alkali metal. 
 The six molecules of water play apparently the same part as 
 in the white vitriol, although they require a somewhat higher 
 temperature for their expulsion than in the case of that salt. 
 
 Similar results were obtained with copper sulphate or blue 
 vitriol. This salt usually crystallises with five molecules of 
 water, four of which are expelled at the temperature of boiling 
 water, whilst the fifth is retained up to about 240, when the 
 residue becomes white. This last molecule may be replaced 
 by potassium sulphate, when a double salt, CuS0 4 . K 2 S0 4 . 
 6H 2 0, is formed, which parts with the whole of its water at 
 about 130. It is worthy of note, however, that the anhy- 
 drous double salt still retains its blue colour ; it may, indeed, 
 be fused at a red-heat without becoming white like the dehy- 
 drated copper sulphate. The corresponding salt, formed with 
 sodium sulphate, behaves in a similar manner. The sulphates 
 of magnesia, iron, manganese, nickel, and cobalt were found 
 to exhibit a like behaviour ; a certain proportion of the water 
 in these salts either four or six molecules, depending on the 
 nature of the salt is expelled at 100, or at ordinary tem- 
 peratures in vacuo, whilst one molecule is in all cases retained 
 up to at least 200. This saline or constitutional water is in 
 most cases replaceable by an alkaline sulphate. 
 
 The behaviour of calcium sulphate or selenite is peculiar. 
 This salt is associated with two molecules of water, which are 
 not expelled at 100; at about 130 the substance loses three- 
 fourths of its water, and if care has been taken not to 
 exceed this temperature, it will recombine with water to form 
 
viii Thomas Graham 213 
 
 the original salt. If the sulphate is heated to above 180, 
 it refuses to slake or rehydrate, as already observed by 
 Lavoisier, and is now technically known as "burnt stucco." 
 Although double salts with alkaline sulphates are known, 
 calcium sulphate shows much less disposition to form such 
 salts than the vitriols a fact which Graham is disposed to 
 refer to the feeble affinity which calcium sulphate manifests 
 for " saline " water. Graham's mental attitude, with respect 
 to the part played by water in salts, is significantly illustrated 
 in the little note he contributed in the same year to the 
 Philosophical Magazine, " On the Water of Crystallisation of 
 Soda- Alum." This salt was supposed, prior to Graham's more 
 accurate determination, to crystallise with twenty-six molecules 
 of water, although it is isomorphous with potash-alum, which 
 contains only twenty-four molecules. If the soda salt contains 
 two molecules more of water than the potash-salt, the con- 
 clusion which follows is, he thinks, not that soda and potash 
 are isomorphous bodies, but that soda plus two molecules of 
 water is isomorphous with potash,- as ammonia^fe one molecule 
 of water is isomorphous with the same body. Graham is con- 
 strained to admit "that the last analogy is superficial, and 
 likely to prove illusory." Illusory it certainly proved to be ; 
 nevertheless it led him to correct the error into which his 
 predecessors had fallen as to the amount of water contained 
 in soda-alum ; this, as in all the true alums, was found to be 
 twenty-four molecules. 
 
 Graham was now convinced that what, in the language of 
 the dualistic theory, were termed the hydrated acids, were 
 constitutionally analogous to salts. The sulphate of water, 
 S0 3 +H0, according to him, is constituted like the sulphate 
 of magnesia, S0 3 +MgO. In a memoir entitled "Inquiries 
 respecting the Constitution of Salts, of Oxalates, Nitrates, 
 Phosphates, Sulphates, and Chlorides," published in the Philo- 
 sophical Transactions for 1837, he seeks to show how this 
 generalisation may be extended. There was nothing essentially 
 
VIII 
 
 214 Thomas Graham 
 
 novel in the fundamental conception ; Davy and Dulong had 
 independently arrived at the same conclusion, and had stated 
 it in language in closer accord with that of modern theory. 
 It is, however, interesting to trace the successive steps by 
 which Graham was led to his conviction. His reasoning was 
 based entirely on his own experimental work, and his con- 
 clusions were reached, unlike those of his predecessors, more 
 by observation than by analogy. The paper is noteworthy 
 also as containing a description of certain double salts up to 
 that time unknown, as, for example, the beautiful grass- 
 green ferric - potassium oxalate which is familiar to every 
 photographer who makes use of the ordinary platinotype 
 process. It presents us with new views as to the constitution 
 of the oxalates, many of which are here analysed for the first 
 time, and as to the nature of what in Graham's period were 
 known as sub-salts, but which, in accordance with the termin- 
 ology with which he has familiarised us, are to-day classed as 
 basic salts. The idea of basicity as a primary attribute of 
 an acid is further worked out by Graham in his suggested 
 nomenclature for the phosphates, which he constructed in order 
 to get rid of the trivial names pyrophosphates, metaphosphates, 
 and common phosphates, which he thinks have tended to keep 
 up an erroneous impression that the phosphoric acid is of a 
 different nature in these classes of salts, or is modified in some 
 unknown way. Metaphosphoric acid was henceforth to be 
 known as monobasic phosphate of water ; pyrophosphoric acid as 
 bibasic phosphate ofivater, and ordinary phosphoric acid as tribasic 
 phosphate of water. Common sodium phosphate was termed 
 tribasic phosphate of soda and water ; microcosmic salt was 
 tribasic phosphate of soda, ammonia, and water; whilst magnesium 
 ammonium phosphate was tribasic phosphate of magnesia and 
 ammonia. This nomenclature was very generally adopted in 
 England, mainly as the result of Graham's teaching at Uni- 
 versity College, and has only recently been supplanted by a 
 more systematic and more comprehensive terminology. 
 
VIII 
 
 Thomas Graham 215 
 
 Graham found experimental support for his views concern- 
 ing the essentially different parts played by the water in the 
 vitriols in the investigations of Andrews on the heat evolved 
 in combination. If, he argues, the saline water in magnesium 
 sulphate is replaceable, say, by potassium sulphate, it follows 
 that the water and the potassium sulphate may be looked 
 upon as equivalent in the construction of the two salts; 
 and hence he concludes the substitution of the salt for the 
 water should occur without evolution of heat. This, indeed, 
 Andrews found to be the case, and Graham, on repeating the 
 experiments, obtained the same result. He was thus led to 
 believe that such thermal measurements might throw con- 
 siderable light upon the general question, and accordingly, in 
 1842, he made an extensive series of measurements on the heat 
 disengaged in combinations, accounts of which are to be found 
 in the first two volumes of the Memoirs of the Chemical Society. 
 Although the papers contain the results of a large number of 
 observations, Graham was unable to deduce from them any 
 important or far-reaching theoretical conclusions. His method 
 of experiment, indeed, was hardly susceptible of the degree of 
 accuracy needed in measurements of this character, and the 
 results are, in many cases, undoubtedly affected by considerable 
 errors, as is evident on comparing them with the subsequent 
 work of Thomsen, Pfaundler, and others. At the same time 
 certain general conclusions may be drawn from the work, which 
 are not without interest. Equivalent quantities of the vitriols, 
 containing seven molecules of water, appear to absorb nearly 
 the same amount of heat on solution in water, and the same 
 is true of the double sulphates which the vitriols form with the 
 alkaline sulphates. On the other hand, the quantity of heat 
 disengaged in the complete hydration of the anhydrous sul- 
 phates differs not only with the amount of water with which 
 these substances may be assumed to combine, but also seems 
 to vary with the particular sulphate. As regards the heat 
 produced by the combination of the first molecule of water 
 
2i6 Thomas Graham 
 
 VIII 
 
 the basic or constitutional water in the magnesian sulphates, 
 it was found that the sulphates of water, of copper, and of 
 manganese evolved substantially the same amount, whereas 
 quite different quantities were disengaged in the case of the 
 sulphates of magnesia and of zinc. In all cases the amount of 
 heat disengaged by the union of the first molecule of water is 
 much larger than that evolved by the combination of any 
 subsequent molecule, which would seem to indicate an essential 
 difference in the relation of this first molecule from that- of 
 the others. 
 
 Although Graham's intellectual powers were thus largely 
 spent on questions of chemical philosophy, he was by no 
 means lacking in sympathy with other departments of 
 chemical science. From time to time he was consulted by 
 the Government and by public bodies on matters altogether 
 outside his special province, and with which, it might be 
 supposed, he could have no possible concern. However 
 uncongenial such work might seem to be, Graham's know- 
 ledge and skill were always freely given in the public interest, 
 whether it was on the question of protecting the revenue in 
 the matter of methylated alcohol, or protecting the consumer 
 in that of adulterated coffee. Questions of technology, par- 
 ticularly when they involved the application of chemical 
 principles hitherto unused in the arts, had always a special 
 attraction for him, and many chemical manufacturers of the 
 last generation were indebted to Graham for valuable sug- 
 gestions and advice. As instances of his interest in applied 
 chemistry may be quoted his papers on the " Preparation of 
 Chlorate of Potash," and " On the Useful Applications of the 
 Refuse-lime of Gasworks," to be found amongst the early 
 memoirs of the Chemical Society. 
 
 Graham served science for more than forty years. Every 
 distinction which its votaries could render was accorded to 
 him, and the most learned societies of the world counted him 
 among their members. In 1833 he received the Keith Medal 
 
VIII 
 
 Thomas Graham 217 
 
 from the Royal Society of Edinburgh for his great work on 
 the "Laws of Gaseous Diffusion." In 1837 the Royal Society 
 of London awarded him a Royal Medal for his memoir on the 
 " Constitution of Salts " ; and the same Society granted him a 
 second Royal Medal in 1850 for his work on the "Molecular 
 Movements of Gases." In 1862 he received the Copley 
 Medal, the highest distinction of the kind the Society can 
 bestow. It was at one time proposed that he should allow 
 himself to be nominated for the Presidentship, but fearing 
 that the office would interfere with his duties at the Mint, 
 he declined the proffered honour. 
 
 ON CERTAIN MODERN DEVELOPMENTS OF GRAHAM'S IDEAS 
 CONCERNING THE CONSTITUTION OF MATTER. 
 
 THE THIRD TRIENNIAL "GRAHAM" LECTURE, DELIVERED BEFORE THE 
 PHILOSOPHICAL SOCIETY OF GLASGOW IN ANDERSON'S COLLEGE, 
 16TH MARCH 1887. 
 
 THERE is a certain fitness in our selecting this place to do 
 honour to-night to the memory of Thomas Graham. For it 
 was in the chemical laboratory of this institution that Graham 
 carried out, upwards of half a century ago, the experimental 
 investigations which culminated in his memorable discovery 
 of the law connecting the rate of movement of a gas with its 
 density. This law, combined with that of Boyle, which con- 
 nects the volume of a gas with the pressure to which it is 
 subjected, and with the law of Dalton, which expresses the 
 relations of the volumes of gases to heat, has done more to 
 give precision to our knowledge of the constitution of matter 
 than all the speculations of twenty centuries of schoolmen. 
 
 Graham was made Professor of Chemistry in the Ander- 
 sonian Institution in 1830, and it was from here that he gave 
 
 CFTHF 
 
 TJNIVERSITT 
 
218 Thomas Graham 
 
 VIII 
 
 to the world his classical paper " On the Law of the Diffusion 
 of Gases," read before the Royal Society of Edinburgh 19th 
 December 1831. I am fully conscious that my only claim to 
 be regarded as worthy to pronounce this eulogium of Graham 
 arises from the circumstance that I also have had the good 
 fortune to hold the Lectureship of Chemistry in this place ; and 
 with forerunners like Birkbeck, Gregory, and Graham, I may 
 well be proud of an honourable and distinguished ancestry. 
 This association with the Andersonian Institution naturally 
 quickened my interest in Graham and his works, and my fre- 
 quent opportunities of conversation with the late Dr. James 
 Young, of Kelly, who for so many years was its President, and 
 who was, as we all know, also one of Graham's "discoveries," 
 and for a long time, both here and in London, one of his most 
 trusted assistants, enabled me to learn much of Graham's per- 
 sonal character and mode of work. On the occasion of the 
 gift of Brodie's fine statue of Graham to the city by Dr. 
 Young, it fell to my lot to prepare the short biographical 
 notice of my distinguished predecessor, which, with other 
 papers relating to the matter, is, I understand, deposited in 
 the archives of your Corporation. And I may be pardoned, 
 perhaps, for recalling with what mingled feelings of pride and 
 trepidation I set myself to the execution of that task. 
 
 In the preface to the admirable reprint of Graham's papers, 
 which we also owe to the filial piety of Dr. James Young, 
 the late Dr. Angus Smith has indicated in precise and even 
 luminous language Graham's position in that chain of thinkers 
 which includes Leucippus, Lucretius, Newton, and Dalton. 
 Indeed, of all Angus Smith's papers with which I am acquainted, 
 there is none, to my thinking, more charming than this little 
 introductory essay of a dozen octavo pages, in which, with 
 unwonted perspicacity, he has defined Graham's place in the 
 history of speculative philosophy. In this paper Angus Smith 
 has crystallised out, as it were, the thoughts of a lifetime of 
 literary research and meditation. Probably no man certainly 
 
vin Thomas Graham 219 
 
 no contemporary of Graham's was better fitted by knowledge 
 and by sympathy to form a sound critical estimate of such a 
 position than the biographer of John Dalton. Angus Smith's 
 mind was steeped in the old Hellenic philosophy. To him 
 Kapila was more than a name, and the atomic systems of 
 India matters of more than conjecture or of passing interest. 
 Indeed there was much in Smith's intellectual nature to 
 make such inquiries congenial to him. With all his leaning 
 towards objective science, he had a Highlander's love of the 
 mystical, and a Lowlander's passion for metaphysics. And 
 yet nothing is more admirable than the manner in which 
 in this essay these qualities and this wealth of learning are 
 subordinated and held in check ; and nothing is more striking 
 than the way in which, in a few graphic strokes, done with a 
 master hand, lightly yet firmly, with a consciousness of power 
 and a sense of restraint, Graham's place in the evolution of the 
 atomic philosophy is set forth. 
 
 It is here claimed for Graham that he was a true descendant 
 of the early Greeks, and that to him belonged as of right the 
 mantle of Leucippus. Atoms and Eternal Motion were as 
 much fixed articles of his creed as they were of that of Hera- 
 clitus. But with no one of the older Greeks was Graham's 
 thought more in harmony than with that of Leucippus. He, 
 with his wider knowledge of the so-called "elemental" forms 
 of matter, and of the persistency with which the specific pro- 
 perties which we associate with our "Elements" are retained, 
 could yet share with the old Greek his conceptions of the 
 essential oneness of matter. It was with Graham, as Smith says 
 of Leucippus, that " the action of the atom as one substance, 
 taking various forms by combinations unlimited, was enough 
 to account for all the phenomena of the world. By separation 
 and union, with constant motion, all things could be done." 
 
 In one respect Graham's position as an atomist is unique. 
 No man before him had dedicated his life to the study of 
 atoms and atomic motion. These fundamental ideas are inter- 
 
22O Thomas Graham vm 
 
 twined to make up, so to say, the silver thread which runs 
 through the work of forty years. They were the dominant 
 conceptions of his life. Even in his earliest paper, published 
 when he was just twenty-one, in which he treats of the absorp- 
 tion of gases by liquids, we are able to detect in the phraseo- 
 logy employed that his mind had been already permeated by 
 the notion of atomic movement. That he should be familiar, 
 even at this time, with the conception of atoms in the Dal- 
 tonian sense is hardly surprising, when we remember that he 
 had already come under the influence of Thomas Thomson, 
 whose place in the history of science is probably that of the 
 first great exponent of Dalton's theory of chemical combina- 
 tion. But the idea of motion was never with Dalton an 
 integral or essential part of his theory, nor, in so far as it was 
 necessary as serving to explain the phenomena of chemical 
 union, was it held by Thomson. And this is the more remark- 
 able when we remember that Dalton had discovered for him- 
 self the fact of the molecular mobility of a gas, and that his 
 first glimpses of the truth of his great law were obtained by 
 the study of the chemical combination of gases. Graham was 
 doubtless cognisant in a general way of the speculations of 
 the early Greeks, but there is no evidence in any of his 
 writings, nor has anything been preserved in the reminiscences 
 of his friends and contemporaries, to indicate that he was 
 knowingly influenced by them. This continuity of idea is, 
 indeed, the most striking characteristic of Graham's labours ; 
 all his work seemed to centralise round this fundamental con- 
 ception of atomic motion. " In all his work," says Smith, " we 
 find him steadily thinking on the ultimate composition of 
 bodies. He searches after it in following the molecules of 
 gases when diffusing ; these he watches as they flow into a 
 vacuum or into other gases, and observes carefully as they 
 pass through tubes, noting the effect of weight and of com- 
 position upon them in transpiration. He follows them as they 
 enter into liquids and pass out, and as they are absorbed or 
 
vni Thomas Graham 221 
 
 dissolved by colloid bodies, such as caoutchouc \ he attentively 
 inquires if they are absorbed by metals in a similar manner, 
 and finds the remotest analogies, which, by their boldness, 
 compel one to stop reading and to think if they be really 
 possible. He follows gases at last into metallic combination, 
 and the lightest of them all he makes into a compound with 
 one of the heavier metals, chasing it finally through various 
 lurking-places until he brings it into an alloy and the form of 
 a medal, and puts upon it the stamp of the Mint. Indeed, he 
 is scarcely satisfied even with this, and he finds in bodies from 
 stellar spaces in meteoric iron this same metallic hydro- 
 genium, which he draws out from its long prison in the form 
 of a gas. . . . If we examine his work on Salts and on Solu- 
 tions we have a similar train of thought. One might have 
 slighted the importance which he attached to the water of 
 salts, and the temperature at which it was reduced, but in 
 his hands it was a revelation of some of the most mysterious 
 internal phenomena of these bodies. 
 
 "A chemist must take great pleasure in following Graham 
 when he seeks the laws of the diffusion of liquids, and traces 
 their connections, especially when they lead to such results as 
 he expressed by dialysis, a process founded on a new classi- 
 fication of substances, and promising still the most valuable 
 truths. We see in the inquiry how Graham thought on the 
 internal constitution of bodies, by examining the motion of 
 the parts, and from the most unpromising and hopeless masses 
 under the chemist's hands amorphous precipitates of alumina 
 or of albumen brought out analogies which connected them 
 with the most interesting phenomena of organic life. Never 
 has a less brilliant-looking series of experiments been made 
 by a chemist, whilst few have been so brilliant in their results, 
 or promise more to the inquirer who follows into the wide 
 region opened." 
 
 In a short paper entitled " Speculative Ideas respecting the 
 Constitution of Matter " originally published in the Proceedings 
 
222 Thomas Graham 
 
 VIII 
 
 of the Royal Society for 1863, Graham has left us his Con- 
 fession of Faith upon the subject to which he had devoted the 
 whole of a thoughtful life. He conceives that the various 
 kinds of matter, now recognised as different elementary sub- 
 stances, may possess one and the same ultimate or atomic 
 molecule existing in different conditions of movement. Graham 
 traces the harmony of this hypothesis of the essential unity 
 of matter with the equal action of gravity upon all bodies. 
 He recognises that the numerous and varying properties of 
 the solid and liquid, no less than the few grand and simple 
 features of the gas, may all be dependent upon atomic and 
 molecular mobility. Let us imagine, he says, one kind of 
 substance only to exist ponderable matter ; and further that 
 matter is divisible into ultimate atoms, uniform in size arid 
 weight. We shall have one substance and a common atom. 
 With the atom at rest the uniformity of matter would be 
 perfect. But the atom possesses always more or less motion, 
 due, it must be assumed, to a primordial impulse. This motion 
 gives rise to volume. The more rapid the movement the 
 greater the space occupied by the atom, somewhat as the orbit 
 of a planet widens with the degree of projectile velocity. 
 Matter is thus made to differ only in being lighter or denser 
 matter. The specific motion of an atom being inalienable, 
 light matter is no longer convertible into heavy matter. In 
 short, matter of different density forms different substances 
 different inconvertible elements, as they have been con- 
 sidered. 
 
 It should be said that Graham uses the terms atom and 
 molecule in a wider sense than that which the limitations of 
 modern chemistry have imposed upon them, and that he is 
 referring to a lower order of molecules or atoms than those 
 which more immediately relate to gaseous volume. The com- 
 bining atoms of which he conceives the existence are not the 
 molecules whose movement is sensibly affected by heat, with 
 gaseous expansion as the result. 
 
VIII 
 
 Thomas Graham 223 
 
 According to Graham the gaseous molecule must itself be 
 viewed as composed of a group or system of the inferior atoms, 
 following as a unit laws similar to those which regulate its 
 constituent atoms. He is, in fact, applying to the lower order 
 of atoms ideas suggested by the gaseous molecule, just as 
 views derived from the solar system are extended to the sub- 
 ordinate system of a planet and its satellites. We cannot as 
 yet fix any limit to this process of molecular division. To 
 Graham the gaseous molecule is a reproduction of the inferior 
 atom on a higher scale. The diffusive molecules, the mole- 
 cules or systems which are affected by heat, are to be supposed 
 uniform in weight, but to vary in velocity of movement, in 
 correspondence with their constituent atoms. Hence, the 
 molecular volumes of different elementary substances have the 
 same relation to each other as the subordinate atomic volumes 
 of the same substances. 
 
 On this basis Graham builds up a conception of chemical 
 combination. He points out, in the first place, that these 
 more and less mobile, or light and heavy, forms of matter 
 have a singular relation connected with equality of volume. 
 Equal volumes of two of them can coalesce together, unite 
 their movement, and form a new atomic group, retaining the 
 whole, the half, or some simple proportion of the original 
 movement and consequent volume. Chemical combination 
 thus becomes directly an affair of volume, and is only in- 
 directly connected with weight. Combining weights are 
 different because the densities, atomic and molecular, are 
 different. The volume of combination is uniform, but the 
 fluids measured vary in density. This fixed combining 
 measure Graham's metron of simple substances weighs 1 
 for hydrogen, 16 for oxygen, and so on with the other 
 " Elements." 
 
 Graham, however, points out that the hypothesis admits 
 of another expression. Just as in the theory of light we have 
 had the alternative hypotheses of emission and undulation, so 
 
224 Thomas Graham vm 
 
 in molecular mobility the motion may be assumed to reside 
 either in separate atoms and molecules, or in a fluid medium 
 caused to undulate. A special rate of vibration or pulsation 
 originally imparted to a portion of the fluid medium enlivens 
 that portion of matter with an individual existence, and con- 
 stitutes it a distinct element or substance. 
 
 The idea of the essential unity of matter finds its analogy, 
 to Graham's thinking, in the continuity of the so-called 
 physical states of matter. He clearly perceived that there is 
 no real incompatibility in the different states of gas, liquid, 
 and solid. These physical conditions are, indeed, often found 
 together in the same substance. The liquid and the solid 
 conditions supervene, as Graham puts it, upon the gaseous 
 condition, rather than supersede it. They do not appear as 
 the extinction or suppression of the gaseous condition, but 
 as something super added to that condition. Graham conceives 
 that the three conditions (or constitutions) probably always 
 co -exist in every liquid or solid substance, but one pre- 
 dominates over the others, just as the colloidal condition or 
 constitution which intervenes between the liquid and crystal- 
 line states extends into both, and probably affects all kinds of 
 solid and liquid matter in a greater or less degree. Hence, 
 according to Graham, the predominance of a certain physical 
 state in a substance appears to be a distinction analogous to 
 those distinctions in natural history which are produced by 
 unequal development. Liquefaction or solidification does not 
 involve the suppression of the atomic or molecular movement, 
 but only the restriction of its range. 
 
 Such, then, are Graham's ideas, formulated in 1863, re- 
 specting the probable constitution of matter. I have pur- 
 posely stated them in great detail, and, for the most part, 
 in Graham's own words. The paper is very short, but it has 
 evidently been put together with great care, and it is im- 
 possible not to be struck with the evidence it affords of 
 Graham's insight, his grasp of principles, and power of 
 
VIII 
 
 Thomas Graham 225 
 
 co-ordination. Consider, for example, what he says respect- 
 ing the continuity of the so-called physical states of matter, 
 and bear in mind upon what an extremely small experimental 
 basis it rested at that time. The observations of Cagniard 
 de la Tour were almost forgotten, or at all events their 
 significance was not understood. The classical work of 
 Andrews was not yet published. And yet this work, com- 
 bined with that of a dozen experimentalists in France, 
 Russia, and Germany, has only served to confirm and expand 
 Graham's fundamental conception. The whole paper shows 
 Graham in a very different light from that in which the student 
 of to-day might be apt to regard him. The greater number 
 of his memoirs are mainly the records of measurements, but 
 Graham was not a great measurer in the sense in which we 
 apply that term to such men as Eegnault, Magnus, or Bunsen. 
 Very little of his work was done by his own hands, and it 
 must be confessed that the earlier experimental portion was 
 occasionally entrusted to apparently inexperienced assistants. 
 Graham had, however, the Forscherblick which characterises 
 the true investigator, and he possessed a really marvellous 
 faculty of sifting out the small grain of fact which often lay 
 hidden beneath a mass of imperfect observation. And yet he 
 was in no hurry to theorise. He patiently added fact to fact, 
 repeating and verifying his observations long after he had got 
 an inkling of the truth towards which they were tending. 
 He laboured like Faraday, ohne Hast, ohne Bast, and his 
 work is a monument of patient, concentrated thought, and of 
 a singleness of purpose that never swerved. 
 
 " Experimentarian philosophers " of Graham's type (to use 
 a phrase which Hobbes of Malmesbury once flung at the 
 progenitors of the Royal Society) have very similar intel- 
 lectual tendencies. One is insensibly led to compare Graham 
 with the greatest of our English atomists, John Dalton. If 
 you will turn to Dr. Henry's Life of Dalton, and read ' the 
 careful analysis of Dalton's mental characteristics, made by one 
 
 Q 
 
226 Thomas Grakam 
 
 VIII 
 
 who knew him well, and who had studied him thoroughly, 
 you will find that practically all that is there stated is equally 
 applicable to Graham. Both men were pre-eminently endowed 
 with the faculty of contemplating abstract relations of space 
 and number, and each began his researches with the ex- 
 pectation that all empirical phenomena were to be brought 
 under the control of mathematical laws. Thus Dalton strove 
 to prove that the changes produced in the gaseous and liquid 
 states of matter vary as the square, cube, or some other simple 
 function of the temperature. Graham, in like manner, sought 
 to show that the movement of his diffusive molecules, whether 
 in liquids or in gases, was related to some equally simple 
 function of their mass. Henry says of Dalton that "his 
 inmost mental nature and all its outward manifestations were, 
 in the language of the German metaphysicians, emphatically 
 subjective. Thus in special or objective chemistry he has 
 left absolutely no sign of his presence ; no great monograph 
 on an individual body and its compounds ; no memorable 
 analysis of a substance deemed simple, into yet simpler 
 elements ; no new element no Neptune added to the 
 domain of chemistry." Every word of these sentences could 
 be applied with equal truth to Graham. The tendencies of 
 both men were essentially introspective. Each was capable 
 of the most patient and concentrated thought, and of steady, 
 prolonged attention, wholly abstracted from external objects 
 and events. I have heard the late Dr. Young narrate the 
 most extraordinary instances of Graham's power of mental 
 abstraction. Dalton said of himself that " If I have succeeded 
 better than many who surround me, it has been chiefly, nay, 
 I may say, almost solely from unwearied assiduity. It is not 
 so much from any superior genius that one man possesses 
 over another, but more from attention to study and persever- 
 ance in the objects before them, that some men rise to greater 
 eminence than others." 
 
 It seems like a contradiction in terms, when we reflect for 
 
VIII 
 
 Thomas Graham 227 
 
 a moment upon the characteristic features and tendency of his 
 work, to say that Graham, like Dalton, was utterly devoid 
 of the quality we call imagination. Henry says of Dalton 
 that imagination had absolutely no part in his discoveries, 
 except, perhaps, as enabling him to gaze in mental vision 
 upon the ultimate atoms of matter, and as shaping forth those 
 pictorial representations of unseen things by which his earliest 
 as well as his latest philosophical speculations were illustrated. 
 Graham would not even allow his fancy that amount of play. 
 Even in the speculative essay from which I have quoted so 
 largely, it seems as if every word had been weighed, and 
 every sentence put together with slow, laborious thought. 
 This passionless aspect of his work seems to have greatly 
 impressed Angus Smith, himself a man of lively sympathy 
 and of quick susceptibility. " His works," says Smith, " are 
 full of care, but not of joy." 
 
 A quarter of a century has elapsed since Graham formu- 
 lated his conceptions concerning the constitution of matter. 
 I wish now to indicate, as briefly as may be, how these 
 conceptions have developed during these five - and - twenty 
 years. 
 
 The idea of the essential unity of matter has a singular 
 fascination for the human mind. It may be that it has its 
 germ in the persistency with which every mind, even that of 
 a child, seeks to get at first principles. The most superficial 
 reader of the history of intellectual evolution cannot fail to 
 perceive how greatly it has modified and directed the 
 development of scientific thought. The whole course of 
 chemistry, for example, has been controlled by this funda- 
 mental conception. The unreflecting student of to-day may 
 smile at the notion of the transmutation of the metals which 
 held such sway over the minds of the early alchemists, but the 
 men who followed this ignis fatuus with weary, faltering steps, 
 and who frequently sank under the burden of disappointed 
 hope, realising that to them it was not given to know the 
 
228 Thomas Graham 
 
 VIII 
 
 light, felt that this idea rested on a rational basis. They, like 
 ourselves, could give a reason for the faith that was in them ; 
 and yet no article of scientific doctrine has, in these later 
 times, suffered greater vicissitudes. Men's ideas concerning the 
 essential unity of things must have received a rude shock 
 when it was found that such a thing as water was not only 
 complex, but was made of bodies strangely contrasted in pro- 
 perties; that the air was still less simple in composition; 
 and that, as it appeared, almost every form of earth could, 
 by torture, be made to give up some dissimilar thing. The 
 brilliant discoveries of Davy, which made the early years of 
 this century memorable in the history of science, seemed to 
 open out a vista to which there was no conceivable ending. 
 The order of things was not towards simplification, but rather 
 towards complexity; and yet Davy himself seemed unable 
 or unwilling to push his way along the path of which 
 the world regarded him as the pioneer. It may be that he 
 was unable to shake himself free from the domination of the 
 schoolmen, or that he unconsciously felt the truth of the prin- 
 ciple to which his own discoveries seemed opposed. It is 
 difficult otherwise to account for the tardiness with which 
 he accepted the hypothesis of Dalton ; even to the last the 
 Daltonian atom had nothing distinctive to him beyond its 
 combining weight. Davy never wholly committed himself to 
 a belief in the indivisibility of the atom ; that indivisibility 
 was the very essence of Dalton's creed. In arguing with a 
 friend concerning the principle of multiple proportion, Dalton 
 would clinch the discussion by some such statement as " thou 
 knows IT MUST BE so, for no man can split an atom" Even 
 Thomas Thomson, whom I have already characterised as the 
 first great exponent of Dalton's generalisation, was swayed by 
 conflicting beliefs until he found peace in the hypothesis of 
 Prout and Meinecke, that the atomic weights of all the 
 so-called elements are multiples of a 'common unit, a concep- 
 tion he sought to establish by some of the worst quantita- 
 
vni Thomas Graham 229 
 
 tive determinations to be found in chemical literature. It is 
 curious to note the bondage in which the old metaphysical 
 quibble concerning the divisibility or indivisibility of the atom 
 held the immediate followers of Dalton. Graham, however, 
 never felt such trammels ; to him the atom meant something 
 which is not divided, not something which cannot be divided. 
 With Graham, as with Lucretius, the original atom may be 
 far down. Every philosophic thinker to-day has, I should 
 imagine, come to be of this opinion. Not many years ago it 
 was the fashion to maintain that Stas's great work had for- 
 ever demolished the doctrine of the primordial yU, and that 
 Koger Bacon's aphorism that " barley is a horse by possibility, 
 and wheat is a possible man, and man is possible wheat," was 
 henceforth an idle saying. Stas's work is a monument of 
 experimental skill, and it has furnished us with a set of 
 numerical ratios which are among the best determined of any 
 physical constants. It may be that it demolished Prout's 
 hypothesis in its original form, but it has not touched the 
 wider question ; indeed it is very doubtful whether the wider 
 question is capable of being reached by direct experiments of 
 the nature of those of Stas, unless the weight of the common 
 atom is some very considerable fraction, say one-half or one- 
 fourth of that of the hydrogen atom. Dumas has, as you 
 know, modified Prout's hypothesis in this sense by assuming 
 as the common divisor half the atomic weight of hydrogen, 
 but there is no a priori reason why we should stop at this 
 particular subdivision. The exact relation of Stas's work 
 to Prout's law has, I think, been fairly stated by Professor 
 Mallet at the conclusion of his admirable paper "On the Atomic 
 Weight of Aluminium," in the Philosophical Transactions for 
 1880 (vol. 171, 1033). Stas's main result, says Mallet, " is no 
 doubt properly accepted if stated thus, that the differences 
 between the individual determinations of each of sundry 
 atomic weights which have been most carefully examined are 
 distinctly less than their difference, or the difference of their 
 
230 Thomas Graham vm 
 
 mean from the integer which Prout's law would require. But 
 the inference which Stas himself seems disposed to draw, and 
 which is very commonly taken as the proper conclusion from 
 his results, namely, that Prout's law is disproved or is not 
 supported by the facts, appears much more open to dispute. It 
 must be remembered that the most careful work which has 
 been done by Stas and others, only proves by the close agree- 
 ment of the results that fortuitous errors have been reduced 
 within narrow limits. It does not prove that all sources of 
 constant error have been avoided, and indeed this never can 
 be absolutely proved, as we never can be sure that our know- 
 ledge of the substances we are dealing with is complete ; of 
 course, one distinct exception to the assumed law would 
 disprove it, if that exception were itself fully proved, but this 
 is not the case. As suggested by Marignac and Dumas, any 
 one who will impartially look at the facts can hardly escape 
 the feeling that there must be some reason for the frequent 
 recurrence of atomic weights differing by so little from 
 accordance with the numbers required by the supposed law." 
 Professor Mallet in tabulating the atomic weights which may 
 be fairly considered as determined with the greatest attainable 
 precision, or a very near approach thereto, and without dis- 
 pute as to the methods employed, points out that out of the 18 
 numbers so given, 10 approximate to integers within a range of 
 variation less than one-tenth of a unit. He then proceeds to 
 calculate the degree of probability that this is purely accidental, 
 as those hold who carry to the extreme the conclusions of Ber- 
 zelius and Stas, and he finds that the probability in question is 
 only equal to 1 : 1097*8, and he concludes that not only is 
 Prout's law not as yet absolutely overturned, but that a heavy 
 and apparently increasing weight of probability in its favour, 
 or in favour of some modification of it, exists and demands 
 consideration. 
 
 It would be impossible for me to attempt to traverse even 
 so much of the whole ground of this question as has been 
 
vin Thomas Graham 231 
 
 opened up during the past fifteen or twenty years. Even if I 
 could claim the time and your indulgence, there is hardly the 
 necessity for such a demand on your patience. Mr. Crookes, 
 only so recently as September last, gave an admirably com- 
 plete exposition of the present state of the case in his address 
 to the Chemical Section of the British Association at the 
 Birmingham Meeting, and for me to go over the field again 
 with you would be simply to plough with Mr. Crookes' heifer. 
 Some years ago Mr. Norman Lockyer, as you doubtless know, 
 approached the subject from another point of view, and in 
 his recent work, The Chemistry of the Sun, you will find a 
 summary of the evidence which the spectroscope has afforded 
 us concerning the dissociation of "elementary" matter at 
 such transcendental temperatures as we have in stars like 
 Sirius. 
 
 Now, when we pass in review all this evidence ; when we 
 reflect upon the mode of distribution of the elements, and 
 especially their tendency to associate in correlated groups; 
 when we bear in mind the absolute analogy which exists in 
 the general behaviour and mode of action of the radicles 
 which are confessedly compound with those which are 
 assumed to be simple ; when we have regard to the pheno- 
 mena of allotropy, isomerism, and homology, the mind 
 insensibly appeals to the principle of continuity and refuses 
 to believe that the seventy and odd "elemental" forms, to 
 which our processes of analysis have reduced all the kinds of 
 matter we see around us, differ in essence from bodies which 
 are known to be compound. 
 
 The connection between the properties of the " elements " 
 and the relative weights of their atoms, as developed by 
 Newlands, Mendeleeff, Lothar Meyer, Carnelley, and others, 
 has served to strengthen this conviction. The discovery that 
 the physical and chemical properties of the elements are 
 periodic functions of their atomic weights is unquestionably 
 the most important generalisation we have had in chemical 
 
232 fc Thomas Graham vm 
 
 philosophy during the last five-and-twenty years. Its bear- 
 ings upon the question of the origin of the " elements " have 
 been worked out in the Presidential Address I have already 
 referred to. Mr. Crookes, like Mr. Lockyer before him, in 
 seeking to apply to this question of the genesis of the 
 " elements " the same principles of evolution which Laplace 
 has already applied to the creation of the heavenly bodies, 
 and which Lamarck, Darwin, and Wallace have applied to 
 that of the organic world, is again appealing to the law of 
 continuity. The mind which holds that nature is one har- 
 monious whole is fain to believe that the probability that the 
 elements have originated by chance, and are eternally self- 
 existent, is just as remote as that the animals and plants of 
 to-day are primordially created things. I think, in what I am 
 now saying I may fairly claim to be reflecting the opinion on 
 this matter of every philosophic thinker of to-day. Nay, 
 more : you must allow that the germ which has been kept 
 alive for so many centuries, and which has come down to us 
 through the brains of a succession of thinkers like Leucippus, 
 Aristotle, Lucretius, Bacon, Newton, Dalton, and Graham, 
 has become quickened and endowed, by the light which modern 
 science has shed upon it from all sides, with a vitality which 
 will persist and strengthen. 
 
 Having thus traced the development of the idea held by 
 Graham of the essential oneness of matter, let us spend the 
 few remaining moments in considering, in the most general 
 way, how the science of the last twenty-five years has worked 
 out and extended his conceptions concerning the properties of 
 the atom and its mode of motion. 
 
 The treatment which " the few grand and simple features 
 of the gas," to quote Graham's phrase, has received at the 
 hands of Clausius, Clerk Maxwell, Helmholtz, Sir William 
 Thomson, and of a score of workers in this country and on the 
 Continent who have been actuated by their influence, has 
 served to dispel much of the metaphysical fog which has 
 
Thomas Graham 233 
 
 enshrouded the notion of the atom, and to-day we are able to 
 reason about atoms, as physical entities, having extension and 
 figure, and to speak of their number and dimensions and 
 peculiarities of movement, with a confidence based on well- 
 ascertained facts. We have, of course, not yet attained to a 
 complete molecular theory of gases. But we know the 
 relative masses of the molecules of various gases, and we have 
 calculated in miles per second their average velocity. The 
 phenomena of diffusion indicate that the molecules of one and 
 the same gas are all equal in mass. For, as was pointed out 
 by Clerk Maxwell, if they were not, Graham's method of 
 using a porous septum would enable us to separate the mole- 
 cules of smaller mass from those of greater, as they would 
 stream through porous substances with greater velocity. We 
 should thus be able to separate a gas, say hydrogen, into two 
 portions, having different densities and other physical pro- 
 perties, different combining weights', and probably different 
 chemical properties of other kinds. As no chemist has yet 
 obtained specimens of hydrogen differing in this way from 
 other specimens, we conclude that all the molecules of hydro- 
 gen are of sensibly the same mass, and not merely that their 
 mean mass is " a statistical constant of great stability." (See 
 Art. "Atom," Encyclopedia Britannica, 9th ed.) This line of 
 argument has, it seems to me, an important bearing upon a ques- 
 tion which has been raised by Marignac, Schiitzenberger, and 
 others, and which has again been raised by Mr. Crookes in the 
 address I have already referred to. Mr. Crookes thinks that 
 it may well be questioned whether there is an absolute 
 uniformity in the mass of every ultimate atom of the same 
 chemical element, and that it is probable that our atomic 
 weights merely represent a mean value, around which the 
 actual atomic weights of the atoms vary within certain narrow 
 limits, or, in other words, that the mean mass is "a statistical 
 constant of great stability." The facts of diffusion would 
 seem to lend no support to such a supposition^ 
 
 "*"*'E LIBft/4/jyV^ 
 OF THE ^V 
 
 UNIVIIRSITT) 
 
234 Thomas Graham vm 
 
 Graham was still living when Loschmidt published what 
 Exner calls his epoch-making paper "On the Size of the 
 Air Molecule." Although the numerical estimate which 
 Loschmidt deduced from the mean free path of* the molecules 
 and their volume has now only an historical interest, it has 
 exercised a profound influence on the development of mole- 
 cular physics in demonstrating that in dealing with molecules 
 we are dealing with masses of finite dimensions, and further, 
 that these dimensions are by no means immeasurably small. 
 The very manner in which Loschmidt stated his conclusions 
 was well calculated to rivet attention. He showed that these 
 magnitudes, small as they are, are yet comparable with those 
 which can be reached by mechanical skill. The German 
 optician Nobert has ruled lines on a glass plate so close 
 together that it requires the most powerful microscope to 
 observe the intervals between them; he has drawn, for 
 example, as many as 4000 lines in the breadth of a millimeter 
 that is, about 112,000 lines to the inch. Now, if we assume 
 with Maxwell that a cube whose side is the 4000th of a milli- 
 meter is the smallest volume observable at present, it would 
 follow from Loschmidt's calculations that such a cube would 
 contain from 60 to 100 millions of molecules of oxygen or nitro- 
 gen ; and if we further assume that the molecules of organised 
 bodies contain on an average 50 " elementary " atoms, it further 
 follows that the smallest organised particle visible under the 
 microscope contains about 2 million molecules of organic matter 
 And as at least half of every living organism is made up of 
 water, we arrive at the conclusion that the smallest living 
 being visible under the microscope does not contain more than 
 about a million organic molecules. I could have wished, had 
 time permitted, to dwell a little upon the intensely interest- 
 ing questions which such a conclusion at once raises. In the 
 article "Atom" in the Encyclopaedia Britannica, from which 
 I have quoted, you will find Clerk Maxwell points out its 
 relation to physiological theories, and especially to the 
 
Thomas Graham 235 
 
 doctrine of Pangenesis. "Molecular science," says Maxwell, 
 "forbids the physiologist from imagining that structural 
 details of infinitely small dimensions can furnish an explana- 
 tion of the infinite variety which exists in the properties and 
 functions of the most minute organisms." 
 
 In the year following Graham's death Sir William Thom- 
 son still further developed the modes of molecular measure- 
 ment, and from a variety of considerations, based upon the 
 kinetic theory of gases, upon the thickness of the films of 
 soap bubbles, and from the electrical contact between copper 
 and zinc, he arrived at estimates which, although sensibly 
 different from that of Loschmidt, are still commensurable 
 with it. In a lecture at the Royal Institution, given about 
 four years ago, he extends the lines of his argument 
 and arrives at the conclusion that in any ordinary liquid, 
 transparent solid, or seemingly opaque solid, the mean 
 distance between the centres of contiguous molecules is less 
 than the one five-millionth and greater than the one thousand- 
 millionth of a centimeter ; and in order to give us some con- 
 ception of the degree of coarse-grainedness implied by this 
 conclusion, he asks us to imagine a globe of water or glass, as 
 large as a football, to be magnified up to the size of the earth, 
 each constituent molecule being magnified in the same propor- 
 tion. The magnified structure would be more coarse-grained 
 than a heap of small shot, but probably less coarse-grained 
 than a heap of footballs (Nature, 19th July 1883). 
 
 Here, I think, we may leave the subject, at all events for 
 to-night. I am painfully conscious that I have left unsaid 
 much that ought to have been said, and possibly said some 
 things that might well have been left unsaid. But my main 
 purpose will have been served if I have succeeded in indicat- 
 ing to you Graham's position as an atomist, and in showing 
 you how his ideas respecting the constitution of matter have 
 germinated, and, like the seed which fell upon good ground, 
 have borne fruit an hundredfold. 
 
IX 
 
 FEIEDRICH WOHLER 
 
 A LECTURE DELIVERED AT THE ROYAL INSTITUTION, ALBEMARLE 
 STREET, ON FRIDAY EVENING, 15TH FEBRUARY 1884. 
 
 IT seems fitting that these walls, which have vibrated in 
 sympathy with that brilliant eulogy of Liebig, which Professor 
 Hofmann pronounced some nine years ago, should hear some- 
 thing of him whose life -long association with Liebig has 
 exercised an undying influence on the development of scientific 
 thought. The names of Friedrich Wohler and Justus Liebig 
 will be linked together throughout all time. The work which 
 they did in common marks an epoch in the history of chemistry. 
 No truer indication of the singular strength and beauty of 
 their relations could be given than is contained in a letter 
 from Liebig to Wohler, written on the last day of the year 
 1871. "I cannot let the year pass away," writes Liebig to 
 Wohler, " without giving thee one more sign of my existence, 
 and again expressing my heartfelt wishes for thy welfare and 
 the welfare 6f those that are dear to thee. We shall not for 
 long be able to send each other New- Years' greetings, yet, 
 when we are dead and mouldering, the ties which have united 
 us in life will still hold us together in the memory of men as 
 a not too frequent example of faithful workers who, without 
 envy or jealousy, have zealously laboured in the same field, 
 linked together in the closest friendship." 
 
ix Friedrich Wohler 237 
 
 And yet, bound as they were in the ties of a friendship, 
 the purity and warmth of which were but characteristic of the 
 men, and although each influenced the other's walk and work 
 in life to a degree which it is almost impossible to gauge, such 
 was the strength of their individuality, and such the force of 
 their genius that, without a doubt, either would have been a 
 great figure in the history of science if the other had not 
 existed. 
 
 The conditions under which minds of the highest type arise 
 and develop have on more than one occasion engaged the 
 attention of this audience. Although there were circumstances 
 in Wohler's surroundings which in early life may have in- 
 fluenced the bent of his mind, it is not easy to see whence 
 sprang that passionate love of nature which was so strikingly 
 exhibited in the man. His father, August Anton Wohler, was 
 formerly an equerry in the service of the Elector William II. 
 of Hesse ; he afterwards came to live at Frankfort, and became 
 a leading citizen of that town. His wise liberality and public 
 spirit are commemorated in the Wohler Foundation and 
 Wohler School, institutions known to every Frankforter. His 
 mother was connected by marriage with the minister of 
 Eschersheim, a village near Frankfort, and it was in the 
 minister's house that Friedrich Wohler first saw the light, on 
 31st July 1800. Even in early youth his passion for experi- 
 menting and collecting manifested itself, to the neglect not 
 unfrequently of the lessons of the gymnasium; indeed, it 
 would appear that during his school career Wohler was not 
 characterised by either special diligence or knowledge. The 
 bent of his mind towards natural science was directed by Dr. 
 Buch, a retired physician, who had devoted himself to the 
 study of chemistry and physics ; and it was in the kitchen of 
 his patron's house that he prepared the then newly-discovered 
 element selenium, of which an account was afterwards sent by 
 Dr. Buch to Gilbert's Annalen, with Wohler's name at the 
 head of it. The elder Wohler appears to have been a man of 
 
238 Friedrich Wohler ix 
 
 considerable artistic feeling, and under his direction the son 
 was taught sketching, and otherwise educated in that per- 
 ception of natural beauty which comes out so strikingly in his 
 after life ; and he was encouraged to make himself familiar 
 with the literature which the genius of Schiller and Goethe 
 has ennobled. He had, moreover, to thank his father for 
 that love of physical exercise and passion for out -door life 
 which reacted so beneficially upon his development, and con- 
 tributed so largely to the uniformly good health which he 
 enjoyed to within a few days of his death. Mainly, it would 
 seem, because his father had been there before him, Wohler, 
 in his twentieth year, entered the University of Marburg. It 
 was his own and the family's wish that he should study 
 medicine, and he accordingly put his name down for the 
 lectures of Biinger on Anatomy, Gerling on Physics and 
 Mathematics, and Wenderoth on Botany. He found time also 
 to attend Ullmann's classes on Mineralogy ; and although he 
 declined to hear Wurzer's lectures on Chemistry, he by no 
 means neglected that science. He transformed his living- 
 room into a laboratory, and to the great, and perhaps not 
 undeserved, disgust of his landlady, occupied himself with the 
 preparation and study of the properties of prussic acid, 
 thiocyanic acid, and other cyanogen compounds. He dis- 
 covered at that time, without knowing that Sir Humphry 
 Davy had anticipated him, the beautifully crystalline but 
 intensely poisonous iodide of cyanogen; and in the little 
 paper on cyanogen compounds, which his good friend Dr. Buch 
 communicated to Gilbert's Annalen for him, we have the first 
 description of the remarkable behaviour of mercuric thio- 
 cyanate on heating, which has astonished and amused us in 
 the so-called " Pharaoh's Serpent." 
 
 Wohler, attracted by the fame of Leopold Gmelin, left 
 Marburg for Heidelberg. His main idea was to hear the 
 lectures of that distinguished man, but Gmelin declared this 
 to be unnecessary and a waste of time. Wohler in fact never 
 
IX 
 
 Friedrich Wohler 239 
 
 attended any systematic lectures on chemistry ; he had access, 
 however, to the old cloisters which at that time constituted 
 the Heidelberg laboratory, and there began the work on cyanic 
 acid which, some four or five years later, was destined to 
 culminate in the great discovery of the synthesis of urea. 
 His association, at this time, with Tiedemann, who was en- 
 gaged in physiological chemical investigations with Gmelin, 
 had also considerable influence in determining the direction of 
 much of his future work, whilst its immediate effect was the 
 publication in Tiedemann's Zeitschrifl fur Physiologic of the 
 results of an inquiry into the transformation experienced by 
 various substances, organic and inorganic, in their passage 
 through the organism. 
 
 In 1823 Wohler obtained his degree, when, on Gmelin's 
 advice, he determined to follow his master's example, and 
 abandon medicine for chemistry. At that time the great 
 Swedish chemist Berzelius was at the summit of his fame ; 
 his masterly analytical skill, no less than his labours to- 
 wards the development of chemical theory, had made him 
 supreme among the chemists of Europe; and to Stockholm, 
 therefore, Wohler, acting on the advice of Gmelin, determined 
 to go. He was warmly welcomed by Berzelius, on whom his 
 communications to Gilbert's Annalen had made a favourable 
 impression, and with the offer of a place in the private labor- 
 atory of the illustrious Swede, Wohler set out for the 
 Scandinavian capital. Of his experiences with Berzelius his 
 pupil has left us a delightful description. It is valuable not only 
 as a charming character-sketch of the great teacher, but also 
 from the side-light it throws upon the nature and disposi- 
 tion of Wohler himself. It is interesting, too, as an account 
 of the mode in which Berzelius worked and taught, and as 
 showing how the typical laboratory of that time contrasted 
 with the temples which have since been reared by the disciples 
 of Hermes. 
 
 "With a beating heart," says Wohler, "I stood before 
 
IX 
 
 240 Friedrich Wohler 
 
 Berzelius's door and rang the bell. It was opened by a well- 
 clad, portly, vigorous-looking man. It was Berzelius himself. 
 . . . As he led me into his laboratory I was as in a dream, 
 doubting if I could really be in the classical place which was 
 the object of my aspirations. ... I was at that time the only 
 one in the laboratory; before me were Mitscherlich and 
 Heinrich and Gustav Rose; after me came Magnus. The 
 laboratory consisted of two ordinary rooms furnished in the 
 simplest possible way; there were no furnaces or draught 
 places ; neither gas nor water service. In one of the rooms 
 were two common deal tables ; on one of these worked 
 Berzelius, the other was intended for me. On the walls were 
 a few cupboards for the reagents ; in the middle was a 
 mercury trough, whilst the glass-blower's lamp stood on the 
 hearth. In addition was a sink, with an earthenware cistern 
 and tap, standing over a wooden tub, where the despotic 
 Anna, the cook, had daily to clean the apparatus. In the 
 other room were the balances, and some cupboards contain- 
 ing instruments ; close to was a small workshop fitted with a 
 lathe. In the neighbouring kitchen, in which Anna prepared 
 the meals, was a small but seldom-used furnace and the never- 
 cool sand-bath." 
 
 Wohler's first exercises were in mineral analysis, made 
 in order that he might become acquainted with Berzelius's 
 special methods and manipulative procedure. At that time 
 he prepared, among other products, some new compounds of 
 tungsten, notably the beautifully crystallised monoxychloride, 
 and the tungsten sodium - bronze (Na 2 W 3 9 ), which, some 
 twenty-five years later, was introduced into the arts as a 
 bronze powder. It was, however, with his investigation on 
 cyanic acid that both he and Berzelius were mainly inter- 
 ested. To Berzelius the existence of this body was of im- 
 portance from the light it seemed to him to throw upon the 
 validity of the new chlorine theory. "I was surprised," says 
 Wohler, " to hear him, the hitherto steadfast upholder of the 
 
ix Fnedrick Wohler 
 
 241 
 
 old notion, now always talk of chlorine instead of 'oxidised 
 hydrochloric acid.' Once, when Anna, in cleaning some 
 vessel, remarked that it smelt strongly of oxymuriatic acid, 
 Berzelius said, 'Hearest thou, Anna; thou must no longer 
 speak of oxidised muriatic acid; thou must call it chlorine: 
 that is better.'" With what feelings would Davy have 
 listened to that colloquy between the Swedish philosopher 
 and his factotum ! Chlorine was discovered by Berzelius's 
 countryman, Scheele, but its true nature was first demon- 
 strated in the laboratory of the Eoyal Institution. 
 
 A couple of months were now spent in travel with 
 Berzelius, in company with the two Brongniarts, Alexandre 
 the geologist and Adolphe the botanist, during which they 
 explored the greater portion of the geologically interesting 
 parts of Southern Sweden and Norway, and collected rich 
 stores of those wonderful minerals for which Scandinavia is 
 famous. Scandinavia is no less famous for salmon and trout ; 
 and it was on his return from a fishing expedition in Nor- 
 way that the travellers met with Davy, who, as readers of 
 Salmonia know, handled his rod with great zest and skill. 
 Wohler, who as a boy had learned the story from his friend 
 Dr. Buch of the isolation of the alkali metals by Davy, and 
 who, aided by his little sister, whose business it was to 
 blow the bellows, had toiled, not unsuccessfully, to make 
 potassium in the kitchen fire, was presented to the famous 
 chemist. 
 
 At the end of the tour Wohler took leave of Berzelius 
 and returned to Germany. Of his association with the great 
 teacher Wohler had ever the kindliest memories. Although 
 the outcome of much of his subsequent work, or at least 
 much of that which he did in concert with Liebig, might 
 be said to bring him in occasional conflict with Berzelius's 
 cherished convictions on points of chemical theory,, the 
 master and pupil remained to the end in the ties of the 
 warmest friendship. Scarcely a month passed without an 
 
 R 
 
242 Friedrich Wohler ix 
 
 exchange of letters. Those from Berzelius were carefully 
 preserved by Wohler, who, after his master's death in 1848, 
 presented them, to the extent of some hundreds, to the 
 Swedish Academy of Sciences. We are told that in the later 
 letters the "trauliche Du" appears in place of the more 
 formal " Sie," and that Totus et tantus tuus is a not unfre- 
 quent signature. 
 
 Wohler's gratitude and almost filial reverence are seen 
 in the circumstance that even in the full tide of his vigour, 
 and when time was doubly precious to him, he continued 
 to charge himself with the yearly translation of Berzelius's 
 Jahresbericht into German. It is easy to trace the influence of 
 Wohler's contact with Berzelius in his after-work. To begin 
 with, the men had much in common ; their sympathies were 
 as catholic as science itself, and they ranged at will over 
 every department of chemical knowledge. Wohler attacked 
 the composition of a mineral with as much ardour as he did 
 the preparation of an organic compound ; to him the problems 
 of physiological chemistry were not more important than the 
 isolation of a rare earth or the perfection of some analytical 
 method. The artificial barriers and arbitrary lines of demar- 
 cation in the science seemed to have no existence for him ; 
 indeed, it was the crowning triumph of his work to break 
 down such barriers almost at a stroke, and to demonstrate 
 the irrationality of attempts to draw distinctions in the absence 
 of differences. The history of chemistry is indeed like that 
 of the nation which has done so much to advance it ; its unity 
 to-day is as complete as that of Germany itself. 
 
 Wohler, now back again in Germany, prepared to embark 
 on his academic career, and on the advice of Gmelin and 
 Tiedemann he decided to settle in Heidelberg as a privat 
 docent. But to Heidelberg he was not destined to go. His 
 work had already been gauged by Leopold von Buch, Poggen- 
 dorff, and Mitscherlich, and these, without his knowledge, 
 strongly recommended that he should be elected to the vacant 
 
ix Friedrich Wohler 243 
 
 teachership of chemistry in the newly-founded Trade School 
 in Berlin. Berzelius advised him to accept the post, and 
 accordingly to Berlin Wohler went in 1825. He was now in 
 possession of a laboratory which he could call his own, and 
 he had to justify that possession by the use which he made 
 of it. One of the problems which he at this time attacked 
 was the isolation of aluminium, a metallic radicle more abundant 
 and more widely diffused than any other of the fifty substances 
 we are accustomed to designate as metals. He succeeded in 
 obtaining the metal by the method which, nearly twenty years 
 later, was worked out on a manufacturing scale by Sainte- 
 Claire Deville. Deville caused the first bar of aluminium 
 thus procured to be struck into medals, with the image of 
 Napoleon III. on the one side, and the name Wohler with 
 the date 1827 on the other, and some time afterwards the 
 Emperor simultaneously designated the two chemists officers 
 of the Legion of Honour. 
 
 But of the twenty-two memoirs and papers which Poggen- 
 dorff's Annalen exhibits as the outcome of Wohler's activity 
 and power of work during his six years' stay in Berlin, that on 
 the artificial formation of urea is by far the most important. 
 No single chemical discovery of this century has exercised so 
 great an influence on the development of scientific thought, 
 and the words with which Wohler closes his account of the 
 molecular transformation of ammonium cyanate a body of 
 purely inorganic origin into urea a substance which of all 
 that might be named is most characteristic of the action of the 
 so-called vital force are full of meaning : " This unexpected 
 result," he says, " is a remarkable fact, in so far as it presents 
 an example of the artificial formation of an organic body, and 
 indeed one of animal origin, out of inorganic materials." " The 
 synthesis of urea," says Professor Hofmann in his account of 
 Wohler's life-work, " was an epoch-making discovery in the 
 real sense of that word. With it was opened out a new 
 domain of investigation, upon which the chemist instantly 
 
244 Friedrich Wohler ix 
 
 seized. The present generation, which is constantly gathering 
 such rich harvests from the territory won for it by Wohler, can 
 only with difficulty transport itself back to that remote period 
 in which the creation of an organic compound within the body 
 of a plant or an animal appeared to be conditioned in some 
 mysterious way by the vital force, and they can hardly realise 
 the impression which the building up of urea from its elements 
 then made upon men's minds. And yet it cannot be said 
 that chemists were unprepared for this discovery. Men were 
 long ago in the habit of perceiving that bodies of mineral 
 origin were but the types of those met with in the animal and 
 vegetable organism in both classes there were the same 
 differences in states of aggregation, the same mutual trans- 
 formations, the same crystalline forms, the same constancy in 
 combining relations, the same conjunction of the elements 
 according to the weights of their atoms or in multiples of 
 these, in both classes the appearance of the same species of 
 compounds. But all attempts to build up organic compounds 
 from their elements, as this for a large number of mineral 
 substances had already been done, had hitherto been futile. 
 The chemists of that period had nevertheless the presentiment 
 that even this barrier must fall, and one can conceive the 
 feeling of joy with which the gospel of a new unified chemistry 
 was hailed by the intellect of that time. With the revolu- 
 tion thus effected in the ideas of men, science was directed 
 into new paths and unto new goals. Who does not know 
 with what zeal these paths have been trodden, and how many 
 of these goals have been reached ! " 
 
 But if at this time Wohler made a great discovery for the 
 world, he also, at about the same time, made a great discovery 
 for himself : he found Liebig. The manner in which the 
 two men were brought together is worth mentioning, for it 
 would seem almost as if the hand of destiny was in it. 
 At about the period that Wohler was in Stockholm thinking 
 and working on cyanic acid, Liebig was in Paris engaged with 
 
IX 
 
 Friedrich Wohler 245 
 
 Gay Lussac in the study of the metallic compounds of ful- 
 minic acid, which obtains its not inappropriate name on 
 account of the formidable explosive character of its salts. 
 Liebig, with rare skill and courage, had determined the 
 composition of that acid, and had been rewarded by the 
 honour of a waltz with Gay Lussac, it being the habit of that 
 distinguished philosopher, as he explained to the astonished 
 young German doctor, to express his ecstasy on the occasion 
 of a new discovery in the poetry of motion. But the most 
 extraordinary result of that investigation was to show that 
 the terribly explosive fulminic acid and the innocuous cyanic 
 acid were of identical composition. The idea that bodies 
 could exist of identical ultimate composition that is, com- 
 posed of the same elements united in the same proportion 
 and yet possess essentially different properties in other 
 words be absolutely dissimilar things was new to science. 
 Berzelius, the great chemical lawgiver of his time, scouted 
 the notion as absurd ; to him it was impossible to conceive 
 that identity in elementary composition should not result in 
 identity of properties. And yet, later on, Berzelius was forced 
 to realise the fact by Wohler's discovery of the molecular 
 transformation of ammonium cyanate into urea, and to coin 
 for us the word isomerism, by which that fact is denoted. 
 
 It was thus, from the singular circumstance that Wohler 
 and Liebig were at the outset of their careers engaged upon 
 the elucidation of the nature of two bodies of identical 
 composition, but of dissimilar origin, dissimilar relations, 
 and very different properties, that they were brought into 
 juxtaposition. They desired to know each other ; they met 
 in the house of a mutual friend at Frankfort, and henceforth 
 the names of Liebig and Wohler became linked together for 
 all time. 
 
 The origin of the partnership, so fruitful in consequences 
 for science, may be seen from the following characteristic 
 letter : 
 
246 Friedrich Wohler ix 
 
 FRIEDRICH WOHLER TO JUSTUS LIEBIG. 
 
 SACROW, NEAR POTSDAM, 8th June 1829. 
 
 DEAR PROFESSOR The contents of your last letter to Poggendorff 
 have been communicated to me by him, and I am glad that they 
 afford me an opportunity of resuming the correspondence which we 
 began last winter. It must surely be some wicked demon that 
 again and again imperceptibly brings us into collision by means of 
 our work, and tries to make the chemical public believe that we 
 purposely seek these apples of discord as opponents. But I think 
 he is not going to succeed. If you are so minded, we might, for 
 the humour of it, undertake some chemical work together, in order 
 that the result might be made known under our joint names. Of 
 course, you would work in Giessen, and I in Berlin, when we are 
 agreed upon the plan, and we could communicate with each other 
 from time to time as to its progress. I leave the choice of subject 
 entirely to you. 
 
 I am very glad that you have also determined the identity of 
 pyrouric acid, and cyanic [cyanuric] acids. L. Gmelin would say : 
 " God be thanked, there is one acid the less ! " . . . Yours, 
 
 WOHLER. 
 
 Liebig acceded to the proposition at once, and suggested 
 some problem on the chemical nature of nitrogen; this 
 Wohler found himself unable to undertake, as it involved the 
 use of chlorine, to the action of which he was at all times 
 extremely susceptible. On the other hand, he proposed to 
 Liebig that they should continue in common a research on 
 mellitic acid, which he had himself begun. Their joint 
 investigation on this body made its appearance in the course 
 of the following year. 
 
 It would be quite impossible within the limits of an hour 
 to attempt to give you anything approaching to a complete 
 analysis of Wohler's work. In all, he was the author of 275 
 memoirs and papers, and of these fifteen were published in 
 concert with Liebig. I must therefore confine my selection 
 from this vast amount of material to those papers which are 
 of paramount importance by reason of the influence which 
 
ix Friedrich Wohler 247 
 
 they have exerted on chemical theory or on the development 
 of the chemical arts. 
 
 Very shortly after the publication of the work on mellitic 
 acid, Wohler proposed to Liebig a joint investigation on 
 cyanuric acid, in the course of which he observed the extra- 
 ordinary transformation of that acid into cyanic acid, and the 
 reconversion of the cyanic acid into cyanuric acid one of the 
 most remarkable instances of molecular rearrangement known 
 to the chemist. The work progressed little for some months, 
 owing to the demands made by Berzelius's Jahresbericht on 
 Wohler's time. "Wirf die Schreiberei zum Teufel," wrote 
 Liebig, "und gehe in das Laboratorium, wohin Du gehorst." 
 In due time, doubtless, that functionary carried off the 
 writing to his master, the printer, and Wohler went back 
 to his laboratory, and in a few weeks the two investigators 
 obtained the clue to the puzzle. .Liebig wrote to Wohler : 
 "Now that I have received your experiments, the whole 
 thing is cleared up, and with what satisfaction for us ! 
 The matter is now decided ; the cyanic acid of Serullas is 
 identical with that from urea. . . . Ich bin ganz narrisch vor 
 Freude, dass unser Kindlein nun fehlerlos in die Welt gesetzt 
 wird, ohne Buckel oder Klumpfuss." 
 
 It had been suggested to attack the fulminic acid again. 
 " The fulminic acid we will allow to remain undisturbed. 
 Like you, I have vowed to have nothing more to do with this 
 stuff. Some time back I wanted, in connection with our 
 work, to decompose some fulminating silver by means of 
 ammonium sulphide ; at the moment the first drop fell into 
 the dish the mass exploded under my nose. I was thrown 
 backwards, and was deaf for a fortnight, and became almost 
 blind." 
 
 The work on cyanic acid appeared in Poggendorffs 
 Annalen during the last month of 1830, and Wohler was able 
 to send the "Kindlein" "im neuen Kleide," as he says, with 
 a New Year's greeting to his friend. Liebig had suggested 
 
248 Friedrich Wohler ix 
 
 fresh work, but at the moment Wohler was in no humour to 
 attack anything organic. The Swedish chemist Sefstrom had 
 just announced the existence of a new element in the slag of 
 certain iron ores, and this very substance had slipped through 
 Wohler's fingers unperceived. " I was an ass," he wrote to 
 his friend, " not to have detected it two years ago in the lead 
 ore from Zimapan in Mexico. I was busy with its analysis, 
 and had found something strange in it, when I was laid up 
 for some months in consequence of breathing hydrofluoric 
 acid, and so the matter was allowed to rest. Meanwhile 
 Berzelius sends me word of its discovery by Sefstrom in 
 Swedish bar iron and in slag. It is very like chromium, and 
 just as remarkable. Moreover, it is the same metal that Del 
 Eio found in the Mexican lead ore, and called erythronium : 
 Descotils, however, had declared this ore to be lead 
 chromate." 
 
 Wohler, no doubt, found a ready sympathiser in Liebig, to 
 whom, not many years before, a similar experience had 
 happened. We all know the story of the young chemist 
 whose unscientific use of the imagination cost him the 
 discovery of the element bromine. Wohler had sent some 
 of the substance from the Zimapan ore to Stockholm, and 
 Berzelius wrote as follows : 
 
 JAKOB BERZELIUS TO FRIEDRICH WOHLER. 
 
 STOCKHOLM, 22nd January 1831. 
 
 As to the small quantity of the body marked ? I will relate 
 the following story: "In the far north there lived in the olden 
 time the goddess Vanadis, as beautiful as she was gracious. One 
 day there came a knock at her door. The goddess was in no hurry, 
 and thought, ' They can knock again ' ; but no further knock 
 came, for he who knocked had passed on. The goddess, wondering 
 who it could be that cared so little to be let in, ran to the window 
 and recognised the departing one. ' Ah ! ' said she to herself, ' it 
 is that lazy fellow Wohler ! He richly deserves his name, since 
 he cares so little to come in.' Some days after, some one else 
 
ix Fried/rich Wohler 249 
 
 knocked, repeatedly and loud. The goddess opened the door 
 herself ; it was Sefstrom who entered, and, as a consequence 
 vanadium came to light." Your specimen with the ? is, in fact, 
 vanadium oxide. 
 
 But he that has found the mode of artificially forming an 
 organic body can well renounce the discovery of a new metal ; 
 indeed, one might have discovered ten unknown elements without 
 as much skill as is seen in the masterly work which you and Liebig 
 have carried out together and have just communicated to the 
 scientific world. 
 
 In 1831 Wohler was called from Berlin to Cassel, and for 
 some little time he was wholly engaged in the planning and erec- 
 tion of his new laboratory at the Gewerbe-Schule in that town. 
 In the spring of the following year he was again ready for a 
 new research ; and this time it was to be the most fruitful piece 
 of work that the two investigators jointly engaged in. It was, 
 in fact, to be the classical research on bitter almond oil. On 
 16th May 1832 Wohler wrote to Liebig : " Ich sehne mich nach 
 einer ernsten Arbeit, sollten wir nicht die Confusion mit dem 
 Bittermandelol in's Eeine bringen 1 Aber woher Material 1 " 
 It must have been something akin to inspiration which led 
 Wohler to take up this subject; but neither he nor Liebig 
 could have been wholly conscious of the consequences which 
 were to follow from their work. To-day oil of bitter almonds 
 is made artificially in Germany by the hundredweight ; at that 
 time the investigators could only obtain it in small quantities 
 from Paris. They had indeed to thank Pelouze for the 
 material with which they worked. Wohler made this, his 
 greatest research, under the cloud of a great sorrow: after 
 barely two years of married life he lost his wife. Liebig, 
 in the tenderest manner, brought him over to Giessen, and 
 sought to win him from his grief and the sense of his 
 loneliness by his company and the wholesome distraction 
 of their joint work, done side by side. 
 
 On 30th August 1832 Wohler wrote to Liebig from 
 Cassel : 
 
250 Friedrich Wohler 
 
 IX 
 
 " I am here back again in my darkened solitude. I do not 
 know how I shall thank you for the affection with which you 
 received me and kept me by you for so long. How happy 
 was I that we could work together face to face. 
 
 " I send you with this the memoir on bitter almond oil. The 
 writing has taken me longer than I anticipated. I want you 
 to read through the whole with the greatest care, and to 
 notice particularly the numbers and formulae. What does not 
 please you, alter at once. I have often felt that there was 
 something not quite right, without being able to detect what 
 was wrong." 
 
 I shall not attempt to dwell upon the outcome of this great 
 work. The investigation on the radicle of benzoic acid will 
 ever remain one of the greatest achievements in the history 
 of organic chemistry ; the work was indeed epoch-making in 
 the far-reaching nature of its consequences. It was full of 
 facts and rich in the promise of new material a veritable 
 mine from which subsequent workers like Cannizzaro, Feh- 
 ling, Piria, Stas, and Hlasiwetz have dug rich treasure. The 
 immediate effect of the paper was to establish the doctrine of 
 organic radicles by demonstrating the existence of groups of 
 bodies which had their analogues and prototypes in inorganic 
 chemistry. The concluding words of the memoir strike, in 
 fact, the keynote of the whole investigation. "In once more 
 reviewing and connecting together the relations described 
 in this memoir," so wrote Liebig and Wohler, " we find that 
 they may be grouped round a common nucleus which pre- 
 serves intact its nature and composition in its associations 
 with other bodies. This stability has induced us to regard 
 this nucleus as a kind of compound element, and to propose 
 for it the special name of 'benzoyl.' " 
 
 A significant feature in the memoir was that each of the 
 substances described and correlated was the type of a distinct 
 group of bodies, some of which were known, but of which 
 the analogies and relations were unperceived ; others of these 
 
ix Friedrich Wohler 251 
 
 bodies were yet to be discovered, a matter of little difficulty 
 when the modes of their origin had been indicated. The 
 effect of this memoir on the chemical world was instantaneous. 
 Berzelius was delighted. " The facts put forward by you," he 
 wrote to Wohler and Liebig, " give rise to such considerations 
 that they may well be regarded as the dawn of a new day in 
 vegetal chemistry. On this account I would propose that this 
 first discovered radicle composed of more than two elements 
 should be named proin (from Trpcol', the beginning of day) or 
 orthrin (op9po$, daybreak), terms from which names like proic 
 acid, orthric acid, proic chloride, orthric chloride, etc., could be 
 readily derived." 
 
 Wohler remained in Cassel for nearly five years. In the 
 autumn of 1835 died Stromeyer, Professor of Chemistry in 
 the University of Gottingen. Opinions were divided as to his 
 successor ; the choice lay between Liebig and Wohler. Event- 
 ually Wohler was selected, and entered on his work at Got- 
 tingen in the early part of 1836. He was succeeded at Cassel 
 by Bunsen, who was at that time privat docent in Gottingen. 
 In the October of that year Wohler was again ready for fresh 
 work. He writes to Liebig : " I am like a hen which has laid 
 an egg and straightway sets up a great cackling. I have this 
 morning found how oil of bitter almonds containing prussic 
 acid may be obtained from amygdalin, and would propose 
 that we jointly undertake the further investigation of the 
 matter, as it is intimately related to the benzoyl research, and 
 it would seem strange if either of us should work alone again 
 in this field, denn es lasst sich gar nicht absehen wie weit es 
 sich erstreckt, und ich glaube es ist gewiss fruchtbar, wenn es 
 mit Deinem Mist gediingt wird. ..." In a couple of days 
 afterwards Wohler was ready with the fundamental facts which 
 constituted the basis of the research, and had sketched out its 
 plan. He writes : 
 
 " I have just made a most remarkable discovery in relation 
 to the amygdalin. Since it appeared that bitter almond oil 
 
252 Friedrich Wohler ix 
 
 might be obtained from amygdalin, it occurred to me that the 
 one might be converted into the other by simply distilling 
 almonds with water by an action similar to that of a fer- 
 ment upon sugar, the change in this case being due, in all 
 probability, to the albumen in the almonds. And this 
 idea seems to be completely established. The facts are as 
 follows : 
 
 "1. Amygdalin, dissolved in water and digested with a 
 bruised sweet almond, begins almost immediately to smell of 
 bitter almond oil, which after a time may be distilled off in 
 such quantity that it would appear that the amygdalin was 
 wholly transformed into it. 
 
 " 2. A filtered emulsion of sweet almonds produces the 
 same effect. 
 
 " 3. A boiled emulsion of sweet almonds, in which, there- 
 fore, the albumen is coagulated, affords not the smallest trace 
 of oil with amygdalin. 
 
 " 4. Bruised sweet almonds, covered with alcohol, and 
 freed therefrom by pressure, transform, as before, amygdalin 
 into bitter almond oil. 
 
 "5. Bruised peas, or the albumen they contain, give no oil 
 with amygdalin. 
 
 "There are three points, therefore, to be ascertained 
 
 "a. What is the substance in bitter or sweet almonds 
 which, in contact with amygdalin and water, forms bitter 
 almond oil 1 
 
 " ft. Is the action by double decomposition or catalytic, like 
 that of a ferment 1 
 
 " c. What is the other product which, in all probability, is 
 formed in addition to the oil and prussic acid ? " 
 
 The merest tyro in organic chemistry to-day is familiar 
 with the broad features of this investigation, and knows the 
 answers which Liebig was able to give to his friend's inter- 
 rogatories. The third substance Liebig discovered to be sugar. 
 Under the influence of a nitrogenised ferment, termed by 
 
ix Friedrick Wohler '253 
 
 Liebig and Wohler emulsin, amygdalin, in presence of water, 
 is decomposed into benzaldehyde (bitter almond oil), prussic 
 acid, and sugar (glucose), thus : 
 
 C 20 H 2r NO u + 2H 2 = C r H 6 + CNH + 2C 6 H 12 6 . 
 
 Amygdalin. Water. Benzaldehyde. Prussic Glucose. 
 
 acid. 
 
 It simply remains to explain why this reaction only occurs 
 when the almonds are bruised and digested with water. Both 
 the emulsin and the amygdalin exist together in the almonds, 
 but are contained in separate cells, and are only brought 
 into contact by the rupture of the cell -walls and the solvent 
 action of the water. Amygdalin was the prototype of a 
 large and important group of substances now classed together 
 as the glucosides. 
 
 At the instigation of Wohler, the friends again returned to 
 the question of the chemical nature of uric acid, and the 
 memoir which they eventually published on the subject is of 
 the profoundest interest, not only to the chemist, but also to 
 the physiologist. Uric acid, originally discovered by Scheele, 
 was shown in 1815, by William Prout, then a boy of nineteen, 
 to be the main constituent of the solid excreta of reptiles ; 
 other chemists had succeeded in obtaining various derivatives 
 from it ; indeed, Prout himself had prepared from it the so- 
 called purpuric acid, a substance which years after, as murexide, 
 obtained a transitory importance in the arts as a colouring 
 matter. But nothing was known concerning the constitution 
 of the body or of its relations to its derivatives until Wohler 
 and Liebig attacked the problem. The extraordinary muta- 
 bility of uric acid, which had baffled and deceived previous 
 investigators, was to Wohler and Liebig the clue to a 
 labyrinth leading to a veritable treasure - house, and the 
 wonderful insight and rare analytical skill of these two great 
 men were never more clearly indicated than in the way in 
 which they trod this intricate maze. No fewer than fifteen 
 
254 Friedrich Wohler ix 
 
 new bodies were added to the list of chemical compounds, and 
 these were correlated with the same masterly lucidity that was 
 so strikingly exhibited in the memoir on the radicle of benzoic 
 acid. Some of the greatest triumphs of modern chemistry 
 are seen in the synthesis of organic bodies. That organic 
 chemistry was about to advance along this line was clearly 
 foreseen by Wohler and Liebig. In opening their account of 
 this, the last great work they did in common, they say : 
 "From this research the philosophy of chemistry will draw 
 the conclusion that the ultimate synthetical formation in our 
 laboratories of all organic bodies, in so far as they are not 
 organised (in so weit sie nicht mehr dem Organismus 
 angehoren), may be regarded as not only probable but as 
 certain. Sugar, salicin, morphin will be artificially obtained. 
 As yet we know nothing of the way by which this result is to 
 be attained, inasmuch as the proximate materials for form- 
 ing these bodies are unknown ; but we shall come to know 
 them." 
 
 Henceforth the friends worked but little together. Liebig's 
 energies were spent in other directions, and Wohler turned 
 his attention to inorganic chemistry. Time allows only the 
 very briefest mention of his more important discoveries in 
 this department of the science. We have first his isola- 
 tion of crystalline boron, and the preparation of the com- 
 pounds of boron with aluminium and nitrogen, work done 
 in concert with Sainte- Claire Deville. The readiness with 
 which boron unites with nitrogen, and the mode in which 
 the compound may be decomposed, led Wohler to a con- 
 ception of the origin of boric acid and borax in the 
 volcanic waters in which they are frequently found. In 
 collaboration with Buff he discovered the spontaneously in- 
 flammable hydride of silicon, the analogue of marsh gas, the 
 simplest of the hydrides of carbon, and thereby laid the 
 foundation-stone of a superstructure, which in time to come 
 may be only less imposing than that built up of the com- 
 
ix Friedrich Wohler 255 
 
 pounds of carbon. Many years ago Wollaston noted the 
 presence in the slags from the iron blast-furnaces of beauti- 
 ful lustrous copper -coloured cubes, which he assumed to be 
 metallic titanium ; Wohler proved this substance to be a com- 
 pound of carbon, nitrogen, and titanium, and showed how it 
 might be obtained. Of all the elements known to the 
 chemist up to the period of Wohler's cessation from work, it 
 may be safely averred that there was not one but had passed 
 through his hands in some form or other. Now he was busy 
 with chromium, then with cerium, next with uranium and 
 the platinum metals; titanium, tantalum, thorium, thallium, 
 tungsten all came in for some share of his attention. Of 
 the minerals and meteorites he analysed the number is legion ; 
 indeed, as Professor Hofmann says, whoever sent him a piece 
 of meteoric iron gained his heart. His untiring activity was a 
 continual source of wonder to his friends. " How happy art 
 thou in thy work ! " wrote Liebig on one occasion ; " thou art 
 like the man in the Indian fable who, when he laughed, 
 dropped roses from his mouth." 
 
 The names of Liebig and Wohler are now so closely inter- 
 twined in the history of chemistry that it is hardly possible 
 to avoid comparing the men. Such a comparison has already 
 been drawn by one who of all others is most fitted to draw it. 
 "Liebig," says Dr. Hofmann, "fiery and impetuous, seizing a 
 new thought with enthusiasm, and giving to it the reins of 
 his fancy, tenacious of his convictions, but open to the recog- 
 nition of error, sincerely grateful, indeed, when made con- 
 scious of it, Wohler, calm and deliberate, entering upon a 
 fresh problem after full reflection, guarding himself against 
 each rash conclusion, and only after the most rigorous testing, 
 by which every chance of error seemed to be excluded, giving 
 expression to his opinion, but both following the path of 
 inquiry in their several ways, and both animated by the same 
 intense love of truth ! Liebig, irritable and quick to' take 
 offence, hot-tempered, hardly master of his emotions, which 
 
256 Friedrich Wohler ix 
 
 not unfrequently found vent in bitter words, involving him in 
 long and painful quarrels, Wohler, unimpassioned, meeting 
 even the most malignant provocation with an immovable 
 equanimity, disarming the bitterest opponent by the sobriety 
 of his speech, a firm enemy to strife and contention, and yet 
 both men penetrated by the same unswerving sense of recti- 
 tude ! Can we marvel that between two such natures, so 
 differently ordered, and yet so complementary, there should 
 ripen a friendship which both should reckon as the greatest 
 gain of their lives 1 " 
 
 Who can fully gauge the influence of such a personality as 
 Wohler's ? How it was exerted on Liebig is indicated in the 
 following letter : 
 
 FRIEDRICH WOHLER TO JUSTUS LIEBIG. 
 
 GOTTINGEN, 9th March 1843. 
 
 To make war against Marchand, or, indeed, against anybody 
 else, brings no contentment with it, and is of little use to science. 
 . . . Imagine that it is the year 1900, when we are both dis- 
 solved into carbonic acid, water, and ammonia, and our ashes, it 
 may be, are part of the bones of some dog that has despoiled our 
 graves who cares then whether we have lived in peace or anger ; 
 who thinks then of thy polemics, of the sacrifice of thy health and 
 peace of mind for science ? Nobody. But thy good ideas, the 
 new facts which thou hast discovered, these, sifted from all that is 
 immaterial, will be known and remembered to all time. But how 
 comes it that I should advise the lion to eat sugar ? 
 
 It was thus in philosophic contentment, happy in his work, 
 in his home life, and in his friendships, that Wohler lived out 
 his fourscore years and two. He made Gottingen famous as 
 a school of chemistry ; at the time of the one-and-twentieth 
 year of his connection with the university it was found that 
 upwards of 8000 students had listened to his lectures or 
 worked in his laboratory. There was hardly an academy of 
 science or a learned society which did not in some way or 
 
ix Fried/rich Wbhler 257 
 
 other recognise his services to science. He was made a 
 Foreign Member of the Royal Society in 1854, a Correspond- 
 ing Member of the Berlin Academy in 1855, Foreign Associate 
 of the Institute of France in 1864, and in 1872 he received 
 the Copley Medal from the Eoyal Society. He died on 
 23rd September 1882. 
 
JEAN BAPTISTS ANDRE DUMAS 
 
 A LECTURE DELIVERED TO THE ROYAL DUBLIN SOCIETY, MARCH 1885. 
 
 JEAN BAPTISTE ANDRE DUMAS was born on 14th July 1800 
 at Alais, in the department of Gard, where his father held 
 the position of town -clerk. After having passed through 
 the small school of his native town, it was intended that 
 young Dumas should enter the navy, but the disasters of 
 1814-15 put an end to the project, and he was eventually 
 apprenticed to an apothecary in Alais. There was much that 
 was congenial to the boy's tastes in such a calling. The 
 bent of his mind towards natural science had already declared 
 itself, and the career of a pharmacist seemed to offer op- 
 portunities for its pursuit. Moreover, there were many 
 things in and about Alais to stimulate his interest in matters 
 relating to chemistry. In its glass works, and manufactories 
 of earthenware, in its limekilns, and its smelting -houses of 
 lead and antimony, the young apothecary had occasion to 
 observe the connection of the science with technical processes ; 
 and in his subsequent writings we find frequent mention of 
 his early impressions. 
 
 Alais, however, did not hold Dumas long. He was barely 
 sixteen years of age when he determined to leave his native 
 town ; and he set out on foot for Geneva, where he had rela- 
 tives, and entered the pharmaceutical laboratory of Le Royer. 
 
x Jean Baptist e Andrt Dumas 259 
 
 Geneva was then, as now, a centre of academic life, and 
 the boy found everything there to stimulate his intellectual 
 activity and to quicken his thirst for knowledge. Gaspard 
 de la Rive at that time lectured on chemistry, Pictet on 
 physics, and De Candolle on botany all honoured names 
 in the history of science. 
 
 It was said of Dumas in later years that he seemed 
 predestined to presidency, and we find him even in his 
 student days taking a leading place in the various scientific 
 associations and social gatherings of his fellows. They 
 suggested that he should give them a course of instruction 
 in experimental chemistry ; and it was with the aid of a 
 few glass tubes, a syringe for an air-pump, lamp chimneys 
 made into gas jars, and a balance constructed by a watch- 
 maker, that he made his delut as professor. He came under 
 the notice of Theodore de Saussure and of De Candolle ; 
 and probably at their instigation, or possibly prompted by 
 his latent naval predilections, he sought to qualify himself 
 for service in an exploring expedition. One outcome of 
 this work of preparation was a monograph on the Gentian^ 
 compiled with a view of familiarising himself with the con- 
 ceptions and terms of botanical science. 
 
 But Dumas soon turned into other paths. As his know- 
 ledge increased the range of his horizon widened. The 
 brilliant discoveries of Davy, of Berzelius, and of Gay Lussac 
 and Thenard, had fired his enthusiasm, and to an active 
 vigorous mind like his to peruse their memoirs was to con- 
 ceive of new problems and fresh fields of work. The chemical 
 student of that period was not over-burdened with text-books. 
 Dumas was nurtured on such fare as the great Treatise of 
 Lavoisier and the Statique Chimique of Berthollet, and in the 
 Annales de Chimie et de Physique he had a series of magnificent 
 models of the art of scientific investigation. He was soon led 
 to try his 'prentice hand at this art. The story of his first 
 attempts was told by him to Professor Hofmann, to whom 
 
260 Jean Baptiste Andrt Dumas x 
 
 I am indebted not only for this, but also for many other 
 accounts of incidents in Dumas's personal history. " When 
 analysing various sulphates, and other salts of commerce, 
 Dumas had observed that the water they contained was 
 present in definite equivalents. He had not found this 
 recorded anywhere, and had therefore taken great pains to 
 establish the accuracy of his observations. When the in- 
 vestigation was finished, he went one morning early to M. 
 de la Rive, and timidly submitted to him the manuscript 
 embodying the results of his inquiry. Whilst glancing 
 over it, M. de la Rive could not conceal his surprise. 
 When he had come to the end he said to the young student, 
 'Is it you, my boy, who have made these experiments?' 
 ' Certainly.' ' And they have taken you a good deal of 
 time to perform 1 ' 'Of course they have.' ' Then I must 
 tell you that you have had the good fortune to meet Berze- 
 lius .on the same field of research. He has preceded you; 
 but he is older than you, and so you ought not to bear 
 him ill-will on this account. . . . Come along and break- 
 fast with me.'" The kindly feeling thus shown to Dumas 
 by his teacher never subsequently failed, and on more than 
 one occasion De la Rive gave him substantial proof of his 
 friendship. 
 
 Nor was his next excursion along the road of discovery 
 attended with more success. "He thought that, knowing 
 the atomic weight of a solid or liquid body, and likewise 
 its density, it might be possible to arrive at the volume of 
 the solid or liquid atom. He was thus led to determine, 
 with great accuracy, the density of a number of simple and 
 compound substances, the purity of which could be depended 
 upon. Having worked for some time, he drew up a paper 
 upon the subject, which was presented to M. de la Rive. 
 But his friend, though admitting the novelty of the point of 
 view from which the question was treated, did not encourage 
 him to pursue this line of research. Young Dumas was 
 
x Jean Baptiste Andrd Dumas 261 
 
 rather disheartened when he left his patron. 'The first 
 time,' he said to himself, 'my experiments were good, but 
 they were not new; this time they are new, but they 
 do not appear to be good. I shall have to try again.'" 
 Dumas was thus the forerunner along a line of research 
 which is inseparably associated with the name of Hermann 
 Kopp, whose work on the specific volumes of solid and 
 liquid substances constitutes one of the classics of chemical 
 physics. 
 
 Dumas's name first appears in chemical literature when he 
 was eighteen years of age, and in connection with Coindet's 
 method of healing that extraordinary enlargement of the 
 thyroid gland known as goitre, which is so prevalent in certain 
 parts of Switzerland. Prior to the year 1818, the most 
 successful mode of treating this disease was by the employ- 
 ment of carbonised sponge, in which Coindet, from its habitat, 
 was led to suspect the presence of the element iodine, which 
 Courtois had discovered some six years before in the liquid 
 obtained by the lixiviation of burnt sea-weed. Dumas, at Dr. 
 Coindet's request, examined sponges for iodine ; he detected 
 the presence of the new element, and suggested its employ- 
 ment as a tincture, as potassium iodide, and as iodised 
 potassium iodide, all of which preparations are nowadays well 
 established remedies in the treatment of goitre and other 
 glandular swellings. 
 
 Dumas's association with Coindet led to his being requested 
 by the physiologist Prevost to undertake the isolation of the 
 active principle of digitalis, the foxglove of our fields, which 
 was introduced into therapeutics as far back as the sixteenth 
 century. The methods of organic chemistry in vogue at the 
 time were, however, utterly inadequate to effect the separation 
 of a substance which is of so indefinite a character that even 
 to-day, despite a dozen memoirs on the subject, we have still 
 much to learn respecting its chemical nature. But the con- 
 nection with Prevost led to labours in physiology and physio- 
 
262 Jean Baptiste Andrt Dumas x 
 
 logical chemistry which were productive of the most fruitful 
 results. 
 
 Prevost and Dumas clearly recognised that it was on the 
 lines indicated by Spallanzani, with whom the study may be 
 said to have taken its rise, that comparative physiology would 
 most rapidly progress. A host of questions, which the methods 
 of the professed physiologists of the day, as represented by 
 Magendie, left untouched, suggested themselves to the two 
 naturalists. What, for example, is the proximate nature of 
 blood, and what is the function of its various constituents 1 
 What is the structure of the red-blood cell, and how does it 
 differ in various animals? The answers which Prevost and 
 Dumas were able to give to these queries are to be found in a 
 paper in the Bibliothkque Universelle for 1821. Their experi- 
 ments on the transfusion of blood, made at the period when 
 the death of the Princess Charlotte excited a feeling of pro- 
 found sorrow throughout Europe, attracted considerable 
 attention, and gave fresh interest to the question of the 
 possibility of prolonging human life by the process. The 
 mode of secretion of the waste nitrogen of the tissue and the 
 seat of the formation of urea were next attacked. The par- 
 ticular question which they set themselves to answer was, in 
 fact, part of the general problem of the function of the organs 
 of secretion whether, in fact, these organs actually generate 
 the products which they separate from blood or lymph, or 
 whether they merely act in eliminating these products. By 
 experiments made on nephrotomised animals, Dumas and 
 Prevost were able to demonstrate that the urea continued to 
 be produced within the system, and could be detected in the 
 blood. Whether the conclusions of the Geneva naturalists will 
 continue to be held by physiologists in the future is doubtful, 
 and the question of the true function of the kidneys is still 
 far from being definitely settled. 
 
 The chemistry of embryology next attracted the attention 
 of Prevost and Dumas, who must, therefore, be regarded as 
 
x Jean Baptist e Andrd Dumas 263 
 
 the immediate precursors of Baer, whose great work on the 
 genesis of the ovum in the mammalia appeared some three 
 years after the publication of their papers. Their observations 
 on the chemical changes accompanying the development of the 
 chick in the egg deserve notice, as embodying the first exact 
 statements on a subject which has still its attractions for 
 modern physiologists. Another of their joint papers, on the 
 phenomena accompanying the contraction of muscular fibre, 
 which they suggested might be explained by the aid of 
 Ampere's discovery of the mode of action between two parallel 
 electric currents flowing in the same direction, may also be 
 mentioned in connection with the hypothesis of the identity 
 of the nervous principle with electricity. 
 
 The appearance of Biot's Treatise on Physics had a con- 
 siderable, even if an indirect, influence in determining the 
 direction of much of Dumas's earlier work. He had been 
 struck, as many subsequent chemists have been, with the some- 
 what arbitrary and even irrational mode in which physicists 
 occasionally select substances to form the groundwork of an 
 investigation intended to elucidate a general physical law. 
 For example, Dumas found that Biot had attempted to 
 develop the law of the thermal expansion of liquids by the aid 
 of Deluc's observations on the change of volume of the fixed 
 oils by heat substances confessedly impure, and mixtures of 
 very dissimilar bodies. With a view of obtaining more 
 definite information, Dumas had proposed to himself to study 
 the thermal expansion of some one group of correlated sub- 
 stances, each member of which should be a homogeneous 
 substance that is, a chemical individual capable of being 
 obtained in a state of purity. He selected as the basis of his 
 work the class of bodies known to chemists as the compound 
 ethers. The research, however, developed in a direction alto- 
 gether different from that originally intended. Unexpected 
 difficulties in the way of obtaining these compound ethers in a 
 state of sufficient purity presented themselves ; and no rigor- 
 
264 Jean Baptiste Andre" Dumas x 
 
 ous guarantee of their individuality was possible with the 
 means of analysis at that time known. The analytical results 
 obtained by Dumas were, however, sufficiently precise to make 
 him assured of one fact viz., that the mode in which these 
 substances had hitherto been viewed by chemists was at 
 variance with their true nature. At that period the ethers 
 were assumed to be compounds of alcohol with the anhydrous 
 acids. Dumas, however, pointed out that alcohol could not 
 be regarded as a proximate principle of these bodies a view 
 which, as we shall see immediately, he afterwards developed 
 in a research which exercised a very powerful influence upon 
 the progress of organic chemistry. 
 
 Dumas was now twenty-two years of age. He was apparently 
 settled at Geneva, and at the pharmacy of Le Royer, and was 
 rapidly securing for himself a recognised position in the intel- 
 lectual society of the town, when a very little incident 
 changed the whole direction of his career. There is, we 
 know, a tide in the affairs of men which, taken at the flood, 
 leads on to fortune. And the tide in Dumas's affairs bore 
 him towards Paris. How this happened Dumas has himself 
 related. "One day," he said, "when I was in my study com- 
 pleting some drawings at the microscope, and it must be 
 added, rather negligently attired, in order to enable me to 
 move more freely, some one mounted the stairs, stopped on 
 my landing, and gently knocked at the door. * Come in,' said 
 I without looking up from my work. On turning round I 
 was surprised to find myself face to face with a gentleman in 
 a bright blue coat with metal buttons, a white waistcoat, nan- 
 keen breeches, and top-boots. This costume, which might 
 have been the fashion under the Directory, was then quite out 
 of date. The wearer of it, his head somewhat bent, his eyes 
 deep-set but keen, advanced with a pleasant smile, saying, 
 ' Monsieur Dumas ^ ' ' The same, sir ; but excuse me.' 
 ' Don't disturb yourself I am M. de Humboldt, and did not 
 wish to pass through Geneva without having had the pleasure 
 
x Jean Baptiste Andrd Dumas 265 
 
 of seeing you.' Throwing on my coat, I hastily reiterated my 
 apologies. I had only one chair. My visitor was pleased to 
 accept it, whilst I resumed my elevated perch on the drawing 
 stool. Baron Humboldt had read the papers published by M. 
 Prevost and myself on Blood, which had just appeared in the 
 Bibliothkque Universelle, and was anxious to see the preparations 
 I had by me. His wish was soon gratified. ' I am going to 
 the Congress at Verona,' said he, ' and I intend to spend some 
 days at Geneva, to see old friends and to make new ones, and 
 more especially to become acquainted with young people who 
 are beginning their career. Will you act as my cicerone ? I 
 warn you, however, that my rambles begin early and end 
 late. Now, could you be at my disposal, say, from six in the 
 morning till midnight 1 ' This proposal, which was of course 
 accepted with alacrity, proved to me a source of unexpected 
 pleasure. Baron Humboldt was fond of talking ; he passed 
 from one subject to another without stopping. He obviously 
 liked being listened to, and there was no fear of his being 
 interrupted by a young man who, for the first time, heard 
 Laplace, Berthollet, Gay Lussac, Arago, Thenard, Cuvier, and 
 many others of the Parisian celebrities, spoken of with famili- 
 arity. I listened with a strange delight ; a new horizon 
 began to dawn upon me. . . . Sometimes he turned to 
 science, and then astronomy and physics, chemistry and the 
 natural history branches, would in rapid succession come in 
 for their share in the dialogue, or rather monologue, which, 
 spoken in a low, somewhat monotonous tone, would have 
 scarcely appeared impressive, had it not been for some wag- 
 gish pleasantry which now and then escaped, as it were, 
 involuntarily. But, at any rate, if his voice failed to be effect- 
 ive, the glance of his eye was sufficient to rivet his hearer's 
 attention. 
 
 " At the end of a few days Baron Humboldt left Geneva. 
 After his departure the town seemed empty to me. I felt as 
 if spell-bound. The memorable hours I had spent with that 
 
 OF THE 
 
266 Jean Baptiste Andre Dumas x 
 
 irresistible enchanter had opened a new world to my mind. I 
 had been more especially impressed with what he had told me 
 of Parisian life, of the happy collaboration of men of science, 
 and of the unlimited facilities which the French capital offered 
 to young men wishing to devote themselves to scientific pur- 
 suits. I began to think that Paris was the only place where, 
 under the auspices of the leaders of physical and chemical 
 science, with whom, I had no doubt, I should soon become 
 acquainted, I might hope to find the advice and assistance 
 which would enable me to carry out the labours over which I 
 had been pondering for some time. My mind was soon made 
 up I must go to Paris." 
 
 Before a twelvemonth had elapsed Dumas found himself in 
 Paris, and in a very short time he was an active participator 
 in the intellectual life of the capital. Almost at the very out- 
 set of his career in Paris he had the rare fortune to become 
 acquainted with two men of about his own age, with whom he 
 was subsequently on terms of the closest intimacy, and who 
 exercised a very great influence on the development of his 
 scientific activity. The one was Adolphe Brongniart, the 
 botanist the other was Milne Edwards, the physiologist. 
 
 Of the manner in which he was received by the leaders of 
 science in the French capital, we may judge from the follow- 
 ing little story : it was on the occasion of his debut in the 
 Academy of Sciences. He had finished the reading of the 
 paper by Prevost and himself on Muscular Contraction, of 
 which mention has been already made, and was about to 
 retire, when a white-haired man of a dignified countenance 
 rose on the other side of the table and approached him. 
 " Monsieur Dumas, will you do me the honour of dining with 
 me on Wednesday next ?- " The invitation was accepted, and 
 after the exchange of a few civilities the veteran savant 
 returned to his place. " With whom am I to dine 1 " asked 
 Dumas of a bystander. " Did you not know it is M. de 
 Laplace 1 " This was the beginning of a friendship which 
 
x Jean Baptist e Andrd Dumas 267 
 
 ceased only with Laplace's death. Madame la Marquise de 
 Laplace survived her husband many years ; it is an indication 
 of the warmth and cordiality of Dumas's relations with the 
 household, that he should have been requested, as the friend of 
 the family, to supervise the publication of the magnificent 
 edition of the works of the author of the Mecanique Cdeste 
 which his son and grand-daughter gave to the world as the 
 most enduring monument to the genius of their illustrious 
 progenitor. 
 
 Dumas was now admitted to that brilliant galaxy of men 
 of science the most brilliant of any age or country, which at 
 that period was the glory of France Laplace, Berthollet, 
 Vauquelin, Gay Lussac, Thenard, Alex. Brongniart, Cuvier, 
 Geoffroy St. Hilaire, Arago, Ampere, Poisson. That con- 
 stellation has set 
 
 the world in vain 
 Must hope to look upon their like again. 
 
 But how did our hero live? With what did he occupy 
 himself 1 Thanks to his friends and patrons he had not long 
 to wait for a congenial occupation. The place of Rtpttiteur de 
 Chimie at the ficole Polytechnique being vacant, Dumas was 
 appointed at Arago's suggestion. Almost immediately after- 
 wards the professorship of chemistry at the Athenaeum, an 
 association somewhat similar in design and character to that 
 which I have the honour of addressing [the Royal Irish 
 Academy], fell vacant by the resignation of Robiquet a 
 name known in the history of chemical science as the dis- 
 coverer of the dye alizarin, and Dumas, at Ampere's in- 
 stigation, was elected to the chair. He was now installed 
 in a laboratory whose traditions he had to maintain. As 
 Thenard's assistant he might be supposed to be in the enjoy- 
 ment of unlimited facilities for research, but great was his 
 disappointment to find that all that remained of the mag- 
 nificent equipment of which Gay Lussac and Thenard had 
 
268 Jean Baptiste Andre" Dumas x 
 
 made such signal use was so much of the apparatus and 
 preparations as could be employed in the demonstrations in 
 a course of lectures on general chemistry. But even if the 
 instruments of precision had been there, the time in which to 
 use them was wanting. Dumas found that his offices were no 
 sinecures. The work involved in the preparation of the 
 lectures and in their experimental illustration was consider- 
 able, and the audiences of the Athenaeum were exacting. 
 Moreover, he had embarked in a literary enterprise with 
 Audouin and Brongniart : 1824 saw the foundation of the 
 Annales des Sciences Naturelles. At the same time, too, he 
 had projected his great work, On Chemistry Applied to the 
 ArtSj of which the first volume appeared in 1828. And there 
 was still a third and perhaps the most cogent reason he was 
 engaged to be married. In 1826 he was united to Mdlle. 
 Herminie Brongniart, the sister of his coadjutor Adolphe, and 
 the daughter of Alexandre Brongniart, the geologist. 
 
 Dumas's first contribution to pure chemistry appeared in 
 the Annales de Chimie et de Physique in 1826. It had reference 
 to the nature of the spontaneously inflammable gas which is 
 evolved by the action of water and of hydrochloric acid upon 
 calcium phosphide, a substance which to-day finds application 
 as a signal fire. His next contribution was a note on the 
 remarkable flash of light which attends the solidification of 
 fused boric acid. 
 
 These matters have their interest from the fact that they 
 are among Dumas's earliest papers. Far more important, how- 
 ever, was his classical memoir on " Some Points in the Atomic 
 Theory " classical by reason of its influence on the develop- 
 ment of chemical philosophy. The enquiry opens with the 
 precise conceptions which form the groundwork of modern 
 chemical theory. Dumas for the first time recognises the 
 relations of the doctrine of Avogadro to the atomic theory of 
 Dalton. " I am engaged," he says, " in a series of experiments 
 intended to fix the atomic weights of a considerable number 
 
x Jean Baptist e Andre 1 Dumas 269 
 
 of bodies by determining their density in the state of gas or 
 vapour. There remains in this case but one hypothesis to be 
 made, which is accepted by all physicists. It consists in sup- 
 posing that in all elastic fluids observed under the same 
 conditions, the molecules are placed at equal distances, ie. 
 that they are present in them in equal numbers. An 
 immediate consequence," he goes on to say, " of this mode of 
 looking at the question has already been the subject of a 
 learned discussion on the part of Ampere, to which, however, 
 chemists, with the exception, perhaps, of M. Gay Lussac, 
 appear to have given as yet but little attention. It consists 
 in the necessity of considering the molecules of the simple 
 gases as capable of a further division a division occurring at 
 the moment of combination and varying with the nature of 
 the compound." Dumas, in a word, realises the conception 
 of the difference between the chemical atom and the molecule 
 which we all accept to-day. The good seed, however, fell on 
 unprepared ground, and more than a quarter of a century was 
 needed for it to germinate. The immediate value of Dumas's 
 memoir lay in its description of the particular method of 
 determining vapour -density with which his name is asso- 
 ciated. The simplicity of this method is one of its great 
 merits ; it instantly found its way into chemical laboratories, 
 and has proved of incalculable service to science. A number 
 of determinations of the vapour-densities of various substances 
 were made by Dumas, who thereby established the relative 
 weights of the molecules of phosphorus, arsenic, and boron. 
 Another result of Dumas's work, as given in this memoir, was 
 the discovery of the real nature of silica, and therefore, 
 indirectly, of vast numbers of substances occurring in the 
 mineral kingdom. His enunciation of the constitution of 
 silicic acid brought him, however, into collision with Berzelius. 
 At that period the influence of the great Swedish chemist 
 was supreme; his opinions had all the force of legislative 
 enactments. Immediately before the publication of Dumas's 
 
270 Jean Baptiste Andrd Dumas x 
 
 paper Berzelius had given to the world his views on the con- 
 stitution of the natural silicates, and his conception of the 
 chemical nature of silicic acid was very different from that of 
 the young French chemist. Berzelius defended his formula 
 for silicic acid with considerable warmth ; he advised Dumas 
 to be more careful in interpreting his experiments, and 
 warned him not to allow himself to be carried away by the 
 evidence of a single experiment. The view which Dumas 
 promulgated has, however, prevailed, and the opinion that 
 the molecule of silica contains two atoms of oxygen is the 
 settled conviction of modern chemistry. 
 
 We have seen that whilst in Geneva Dumas had attempted 
 to prepare the compound ethers with a view of studying some 
 of their physical properties, but that he had been deterred 
 from the prosecution of his work by the difficulty of obtaining 
 these substances in a state of purity. Moreover, the analyses 
 of the compounds which he had been able to prepare did 
 not appear to be in conformity with the current opinions 
 as to the nature of these substances. In conjunction with 
 his assistant Boullay he now resumed their study. At the 
 period of these researches common alcohol was regarded as 
 a combination of one volume of olefiant gas with one volume 
 of water ; common ether as a combination of two volumes 
 of olefiant gas with one volume of water. Hence ether might 
 be regarded as derived from alcohol by the abstraction of 
 water. 
 
 Dumas and Boullay began their investigation by supplying 
 new experimental data in confirmation of this view of repre- 
 senting the composition of these substances. In the notation 
 of to-day their formulae were 
 
 Alcohol. . . .. C 2 H 4 .H 2 0. 
 Ether . . 2C 2 H 4 .H 2 0. 
 
 In the preparation of ether from alcohol there is a product 
 formed, known even before the time of Dumas, and called 
 
x Jean Baptist e Andre Dumas 271 
 
 sulphovinic acid; the mode of origin of this compound is 
 explained by Dumas and Boullay, and represented by an 
 equation identical with that which we now employ. 
 
 These researches supplied us for the first time with a 
 number of well-ascertained facts respecting one of the most 
 important groups of organic compounds. But this was not by 
 any means their chief merit. Dumas and Boullay conclude 
 their memoir with a suggestive synoptical review of the re- 
 lation of these compounds to the salts of ammonia. The nature 
 of this relationship may be seen from the following table : 
 
 Hydrochlorate of bicarburetted hydrogen . C 2 H 4 . HC1. 
 
 Nitrite of bicarburetted hydrogen . . . C 2 H 4 . HN0 2 . 
 
 Sulphate of bicarburetted hydrogen . . C 2 H 4 . H 2 S0 4 . 
 
 Alcohol .... . . . C 2 H 4 .H 9 0. 
 
 Ether ... . (C 2 H 4 ) 2 /H 2 0. 
 
 Ammonia hydrochlorate .... NH 3 . HC1. 
 
 Ammonia nitrite . . . . . . NH 3 . HN0 2 . 
 
 Acid ammonia sulphate .... NH 3 . H 2 S0 4 . 
 
 Aqueous ammonia ..... NH 3 . H 2 0. 
 
 In a word, these derivatives of alcohol may be considered 
 to be compounds containing olefiant gas, in the same way 
 that ammonia is held to be contained in the ammoniacal 
 salts. This view of the constitution of the ethers was at 
 first opposed by Berzelius, but was subsequently adopted 
 by him, and became known as the etherin theory, from the 
 name which he gave to the radicle C 9 H 4 . The etherin 
 theory, however, never gained general acceptance. Dumas 
 and Boullay, in fact, sought to make it too comprehensive. 
 Moreover, the analogy with the ammoniacal salts broke down 
 from the circumstance that it was not possible to build up the 
 compound ethers by bringing together their proximate con- 
 stituents, as in the case of the ammoniacal salts. As regards the 
 latter point modern chemistry has shown that such synthetical 
 formations are actually possible ; and had the facts of to-day 
 been known to the contemporaries of Dumas the etherin 
 
272 Jean Baptist e Andrd Dumas x 
 
 theory might have had a longer lease of existence than it 
 actually enjoyed. The etherin theory had, however, the 
 great merit of familiarising chemists with the conception 
 of organic radicles. It further indicated that the reactions 
 of organic chemistry are truly comparable with those of 
 inorganic chemistry, and can be represented by equations 
 as precise and as simple in character as those which ex- 
 press the chemical transformations of the mineral kingdom. 
 Berzelius, by his adoption of the etherin theory, removed 
 the barrier which he himself had set up between the two 
 main divisions of the science. In a living structure, said 
 Berzelius, the elements obey laws totally different from those 
 which regulate the formation of compounds in the inanimate 
 world, and the products which result from the mutual action 
 of these elements differ from those which are presented to 
 us in inorganic nature. To-day we recognise no such dis- 
 tinction; the doctrine of the specific action of a so-called 
 vital force derives no support from chemistry. 
 
 But the analogy between the compounds of etherin and 
 ammonia was fruitful in another direction. Some years after 
 the publication of Dumas and Boullay's memoir, the late 
 Sir Robert Kane drew attention to the fact that the con- 
 stitution of the alcoholic derivatives could be better explained 
 on the assumption that they contained a radicle which differed 
 from etherin, in the same manner that the ammonium of 
 Ampere and Berzelius differed from ammonia. In the Dublin 
 Journal of Medical and Chemical Science for 1833 there is a 
 paper by Sir Eobert Kane on the Theory of the Ethers, in 
 which this view is developed, and in which he denotes by 
 the name of ethereum the hypothetical body formed by the 
 union of etherin with hydrogen (following Berzelius, who 
 termed the combination of ammonia with an atom of hydrogen, 
 ammonium), and in the paper the constitution of some of the 
 more important of the alcoholic derivatives is expressed by 
 its aid. Fifty years ago it would seem that Dublin had 
 
x Jean Baptiste Andrd Dumas 273 
 
 such little interest in questions relating to chemical theory 
 that, in a subsequent paper, Sir Robert Kane was fain to 
 confess that his speculations were regularly a subject of amuse- 
 ment and ridicule in the chemical circles of this city. But the 
 whirligig of time brings about its revenges ; and to-day my 
 friend the Professor of Chemistry in Trinity College, Dublin, 
 in common with his fellow-chemists, explains the relations of 
 alcohol to its many derivatives by the aid of the conception 
 of Kane. 
 
 An infallible test of the value of a scientific paper is 
 afforded by the number and variety of the issues it suggests ; 
 and measured by this criterion, the memoir of Dumas and 
 Boullay must rank among the classics of organic chemistry. 
 In the attempt to isolate ether from the ethereal salts Dumas 
 discovered the nature of oxamide and of ethyl oxamate, proto- 
 types of compounds of great theoretical interest to the chemist. 
 
 The paper on Wood-Spirit, which Dumas published in 
 conjunction with Peligot in 1832, may be here referred 
 to. It was known from the researches of Taylor, made 
 in 1812, that when .wood is heated in closed vessels it 
 yields, in addition to acetic acid, a very volatile and in- 
 flammable fluid, termed by Taylor pyroligneous ether, a sub- 
 stance which, in many of its characters, resembles ordinary 
 alcohol, but which differs from it by not yielding ether 
 on treatment with sulphuric acid. The nature of wood- 
 spirit had been the subject of investigation by many 
 chemists since the time of Boyle, but without any definite 
 result until Dumas and Peligot succeeded in isolating its 
 main constituent. By determinations of its vapour-density, 
 and by the study of its behaviour towards various reagents, 
 they established its composition and chemical nature. They 
 showed that the body was in fact analogous to common 
 alcohol ; that it gave rise to compound ethers, and to an 
 acid corresponding with acetic acid. These views of its rela- 
 tions they embodied in the name which they gave to it of 
 
 T 
 
274 Jean Baptiste Andrt Duinas x 
 
 methyl alcohol the word methyl being derived from the Greek, 
 and signifying the wine of wood. 
 
 Closely following on the publication of this memoir was 
 another on the nature of Spermaceti, which had already been 
 made the subject of inquiry by the veteran Chevreul. Dumas 
 and Peligot showed that spermaceti the fatty substance 
 found in cavities in the head of the sperm-whale yields 
 on saponification a substance which, from its chemical 
 transformations, they regarded as akin to common alcohol, 
 but which differs from that body and from methyl alcohol 
 by multiples of the number of carbon and hydrogen atoms 
 they contain. The full value of these discoveries was first 
 clearly indicated some years later by Gerhardt. Methyl 
 alcohol is, in fact, the first term of a series of homologous 
 substances, of which ordinary alcohol and cetyl alcohol, the 
 alcoholic substance contained in spermaceti, are widely 
 separated members. The discovery of these alcohols led 
 directly to the classification of organic compounds in 
 homologous series a mode of classification which has been 
 singularly valuable in enriching organic chemistry with 
 substances whose existence would otherwise have been 
 unsuspected. 
 
 Dumas was now in the full tide of his chemical activity, 
 and memoir followed memoir in quick succession. His work 
 was distinguished by its universality; it ranged literally 
 over every department of chemistry, whether pure or applied, 
 organic or inorganic. Now it was on the nature of solution, 
 then on the determination of specific heat; next on the 
 composition of the more important varieties of glass known 
 to commerce, the nature of minium, the preparation of the 
 metal calcium, the compounds of phosphorus, the treatment 
 of iron ores, the composition of the materials used in the 
 thirteenth-century frescoes these, and a host of other pro- 
 blems, attracted his attention. During a tour in Switzerland 
 he was shown, by the apothecary Pagenstecher, a sample 
 
x Jean Baptiste Andrd Dumas 275 
 
 of essential oil obtained by distilling the flowers of meadow 
 sweet, Spircea ulmaria ; this he promptly recognised as salicyl 
 aldehyde. A chance observation of an efflorescence on the 
 walls of a bath-house at Aix-les-Bains led to the discovery of 
 the mode of oxidation of sulphuretted hydrogen to sulphuric 
 acid by the action of porous materials containing air. 
 
 We must not, however, so summarily dismiss certain of 
 the memoirs, for it is no figure of speech to say of some 
 of them that they were momentous in their consequences. 
 The origin of one of these researches perhaps the most 
 fruitful in its results was somewhat singular. 
 
 One evening, at a soirfe at the Tuileries, given during 
 the ill-starred reign of Charles X., the guests were greatly 
 annoyed by the presence of acid vapours diffused through 
 the air of the apartments; these were observed to be due 
 to the burning of the wax candles. Dumas's father-in-law, 
 Alexandre Brongniart, was at the time director of the 
 porcelain manufactory at Sevres, and hence, by tradition, 
 was regarded as the chemical adviser of the royal house- 
 hold; he was commissioned, therefore, to inquire into the 
 cause of the peculiar behaviour of the candles. The actual 
 investigation was intrusted to Dumas, who had no difficulty 
 in determining that the acid vapours were caused by hydro- 
 chloric acid, produced by the combustion of wax which had 
 been bleached by chlorine. The amount of chlorine contained 
 in the wax was too considerable for it to be regarded as an 
 accidental contamination ; it was evident that it had entered 
 into combination with the organic matter. This circumstance 
 led Dumas to study the action of chlorine upon organic 
 bodies in greater detail than had hitherto been done, with 
 results which have exerted a profound influence upon the 
 development of organic chemistry. 
 
 At the time that Dumas began these researches, the electro- 
 chemical theory of Berzelius reigned supreme. When water 
 is subjected to electrolysis, the hydrogen makes its appearance 
 
276 Jean Baptiste Andrd Dumas x 
 
 at the negative electrode ; whilst the oxygen is evolved at the 
 positive pole. Hydrochloric acid, when electrolysed, is like- 
 wise decomposed, the hydrogen being liberated at the negative 
 pole, and the chlorine at the positive pole. Moreover, when 
 a metallic chloride is decomposed by electrolysis, the metal 
 makes its appearance at the negative pole, whilst the chlorine 
 is evolved at the positive pole. Hence hydrogen and the 
 metals were termed electro-positive elements; chlorine and 
 oxygen electro-negative elements. Facts of this order were 
 generalised by Berzelius into a theory of chemical combina- 
 tion. According to this theory chemical combination is the 
 result of the union of substances of different electric polarities. 
 These substances might be elementary atoms, or they might 
 be groups of atoms going in and out of combination like 
 simple bodies. All compound substances were regarded as 
 formed by the juxtaposition of two proximate constituents 
 which might be simple or compound : if compound, they were 
 also formed by the union of two components, and so on. This 
 dualistic theory explained a sufficient number of facts to cause 
 its acceptance by the entire chemical world prior to 1832. It 
 was held that the electro-chemical character of an element or 
 compound radicle determined its behaviour and influenced the 
 nature of the compounds into which it entered. Potassium 
 oxide, K 9 0, was a basic substance formed by the union of 
 electro-positive potassium with electro-negative oxygen ; this 
 binary compound united with S0 3 to form a binary compound 
 of the second order, K 2 + S0 3 . Water, H 2 0, was also formed 
 by the union of the electro -positive hydrogen with electro- 
 negative oxygen, and it too was regarded as a basic substance, 
 inasmuch as it could combine, say, with S0 3 to form a body 
 H 2 O -f S0 9 , analogous in constitution to potassium sulphate. 
 At that time the formulae of these substances were almost 
 universally written in this manner, so as to imply their binary 
 constitution. 
 
 Dumas observed that when chlorine acts upon a number of 
 
x Jean Baptist e A ndrd Dumas 277 
 
 organic bodies, it turns out the hydrogen, atom after atom, 
 and takes the place of each hydrogen atom so expelled that 
 is, the atom of electro -negative chlorine occupies the same 
 position as the atom of electro - positive hydrogen. As an 
 historical fact, it should be noted, this circumstance had 
 been observed by others. Gay Lu'ssac had noticed that 
 prussic acid, when treated with chlorine loses hydrogen, 
 and for each atom of hydrogen lost, an atom of chlorine 
 was gained. Faraday, too, had observed that Dutch liquid, 
 C ? H C1 2 , is by the continued action of chlorine converted 
 into C.,01,, or CgOlClg. But these facts were too few 
 and isolated for their bearing on the dualistic theory of 
 chemical combination to be perceived. Their significance, 
 however, was quickly appreciated by Dumas; he greatly 
 extended them, and throwing down the gauntlet, he boldly 
 attacked the generalisation of Berzelius. "These electro- 
 chemical conceptions, this special polarity which has been 
 assigned to the elementary atoms, do they really rest on 
 such evident facts that they are to be accepted as articles of 
 faith 1 ? Or if we regard them only as hypotheses, do they 
 possess the property of adapting themselves to facts ; are 
 they capable of explaining them ; can we assume them with 
 such a complete certainty that in chemical investigations 
 they appear as useful guides? We must admit," replies 
 Dumas, "that such is not the case." 
 
 It is impossible to set forth here the array of facts with 
 which Dumas and the French school of which he was the leader 
 confronted the arguments, and even the scorn and ridicule, of 
 Berzelius and his adherents. Every hypothesis advanced by 
 the Swedish chemist required to be sustained by fresh as- 
 sumptions, until the binary theory absolutely sank under the 
 load of contradictions and anomalies it had to carry. The 
 followers of Berzelius gradually deserted him, and the electro- 
 chemical theory, which he had elaborated with such zeal and 
 argumentative power, fell to pieces. 
 
278 Jean Baptiste Andrd Dumas x 
 
 But the conception of metalepsis, as the doctrine of sub- 
 stitution was styled, was even more constructive than de- 
 structive in its results. A revolution which brings nothing 
 but disorder is baneful. It is the chief glory of the doctrine 
 of substitution that it has been the fruitful mother of specu- 
 lations by which the superstructure of modern chemical 
 philosophy has been raised. 
 
 By a natural and logical process of transition, the doctrine 
 of substitution became gradually merged into the doctrine of 
 types. The ideas of Dumas were amplified by Laurent and 
 Gerhardt ; Laurent, indeed, pushed the theory of substitution 
 in a direction which Dumas was at first disinclined to follow, 
 by boldly stating that chemical substances owed their pro- 
 perties much less to the nature of their elementary atoms 
 than to the mode of arrangement of these atoms within the 
 compound. The creation of types by Gerhardt was the 
 necessary outcome of substitutional conceptions, and out of 
 the types which, in the hands of Williamson and Odling, 
 have rendered such signal service to chemistry, have sprung 
 our present notions of the intrinsic difference in the atom- 
 fixing power of the elementary and compound radicles that 
 is, the doctrine of valency which we owe to Frankland. 
 If we compare the chemistry of to-day with that of the stirring 
 times when Dumas, half a century ago, was matched almost 
 single handed against the German school against such 
 Titans as Berzelius, Liebig, Wohler we are amazed at the 
 wealth of material which has been opened out. The change, 
 thus directly or indirectly traceable to the labours and con- 
 ceptions of Dumas, is as great or even greater than that achieved 
 by the overthrow of the Phlogistians. If Lavoisier was the 
 author of the first French Revolution in Chemistry, Dumas was 
 the creator of the second. Liebig, fiery and impulsive as he 
 was, was a generous-hearted opponent, and it was a significant 
 compliment to his quondam antagonist when, on being taxed 
 with his desertion of organic chemistry, he replied ; " I have 
 
x Jean Baptiste Andrd Dumas 279 
 
 withdrawn from organic chemistry, for with the theory of 
 substitution as a foundation, the edifice of chemical science 
 may be built up by workmen." This remark was uttered 
 post-prandially, it is true, yet it had a meaning which was 
 fully realised and appreciated by the company to which it 
 was addressed. 
 
 But victory to Dumas meant a fresh campaign. We have 
 seen how he had been led to the conception of the homologous 
 series of the alcohols by the discovery of methyl alcohol, and 
 the alcohol which functions in spermaceti. "The recognition 
 of an alcohol," he said, " enriches organic chemistry with a 
 series of compounds comparable with those with which mineral 
 chemistry is endowed by the discovery of a new metal. As 
 yet we know only how to transform an alcohol into the 
 corresponding acid ; of equal if not greater importance would 
 be the inverse process, the conversion of acids into alcohols. 
 There can be no doubt that before long this problem will also 
 be solved." 
 
 Dumas then pointed out the existence of homology in the 
 fatty acids in the series of acids of which palmitic and 
 margaric acids, no less than acetic acid, are members. In 
 1843 he showed that as many as fifteen acids might be 
 assumed to exist between margaric acid and formic acid, the 
 acid obtained by the oxidation of methyl alcohol of which 
 nine were already known. When the missing links in the 
 chain were indicated, their discovery followed almost as a 
 matter of course. 
 
 There is no branch of technical chemistry which has 
 made more rapid progress or which exhibits more striking 
 triumphs than that concerned with the tinctorial arts. In 
 the minds of many people nowadays, the operations of 
 modern chemistry are confined to the discovery of coal-tar 
 colours. Dumas, who worked in every field of chemistry, 
 has left his mark on this department of the science. The 
 nature of indigo, and of the relation of white indigo to blue 
 
280 Jean Baptiste Andrd Dumas x 
 
 indigo, and of the chemical changes occurring in the indigo 
 vat, were first correctly traced by him. One of the im- 
 portant dyeing materials of these later days is picric acid, a 
 body of a beautiful yellow colour and of great dyeing power. 
 It is obtained by the action of nitric acid upon phenol, better 
 known perhaps as carbolic acid. The true nature of picric 
 acid was first interpreted by Dumas ; it is phenol, in which 
 three atoms of hydrogen are replaced by an equivalent amount 
 of the compound radicle N0 2 . 
 
 Phenol . ' . : C 6 H 6 0. 
 Picric acid . C 6 H S (N0 2 ) 3 0. 
 
 Hence the body is now known by the systematic name of 
 trinitrophenol. 
 
 The vegetable dyes contained in the lichens and in archil 
 were also the subject of investigation by him. He established 
 the formula of orcinol and of the beautiful red compound which 
 is obtained from it by the action of ammonia and oxygen, and 
 which is known as orcein. 
 
 Orcinol . . . C 7 H g 2 . 
 Orcein , . . C 7 H r (N0 2 )0 2 . 
 
 C 7 H 8 O 2 + NH ;3 + 3 = C 7 H 7 lSr0 3 + 2H 2 0. 
 
 He investigated also the essential oil of mustard; the 
 products obtained by the distillation of resin ; the constitution 
 of the more important vegetable acids, such as citric and 
 tartaric acid ; and, in conjunction with Pelletier, the composi- 
 tion of such of the vegeto-alkaloids as were at that time 
 known. 
 
 We may here allude to the service rendered to analytical 
 chemistry by the process which Dumas devised for the deter- 
 mination of the amount of nitrogen in organic substances. 
 This method is in frequent use to-day, and is characterised by 
 accuracy and simplicity, and by the fact that it is of general 
 
x Jean Baptist e Andrt Dumas 281 
 
 application. It consists in heating the organic substance, 
 mixed with oxide of copper, in a glass tube, passing the 
 evolved gases over metallic copper, and collecting them in a 
 measuring vessel filled with caustic potash. The carbonic acid 
 gas is absorbed by the potash, and from the volume of the 
 residual nitrogen the weight of that element in the organic 
 compound is readily calculated. 
 
 The quantity of carbon contained in an organic body is 
 almost invariably ascertained by heating the substance with 
 an appropriate oxidising agent, collecting and weighing the 
 carbonic acid formed, and calculating the amount of carbon 
 from the ratio of the oxygen to carbon. Everything depends 
 upon the accuracy with which this ratio is established, and 
 accordingly some of the greatest masters of analytical 
 chemistry, beginning with Lavoisier, have made it the sub- 
 ject of the most rigorous experiments. In conjunction with 
 his pupil Stas, Dumas carried out a series of very accurate 
 determinations of the amount of carbon which unites with 
 oxygen, with the result of showing that the numbers in 
 vogue at the time were inaccurate. By burning diamonds, 
 which constitute the purest form of carbon, in a stream of 
 oxygen, they found that 12 parts of carbon united with 32 
 parts of oxygen to form 44 parts of carbon dioxide a result 
 confirmed by similar experiments made with graphite. This 
 ratio is universally accepted by chemists to-day. 
 
 The amount of hydrogen in an organic body is also 
 invariably ascertained by burning the hydrogen to water, and 
 from the ratio of the weight of hydrogen to oxygen in the 
 water calculating the quantity of hydrogen in the organic 
 substance. The exactitude of the ratio is obviously all 
 important. The volumetric composition of water had been 
 definitely established by the experiments of Cavendish and of 
 Gay Lussac and Humboldt, and the gravimetric composition 
 could be calculated, provided that the relative weights of 
 equal volumes of hydrogen and oxygen were accurately 
 
 or THE 
 UNIVERSITT 
 
282 Jean Baptist e Andrt Dumas x 
 
 known. Dumas sought to solve the problem by directly 
 combining oxygen and hydrogen that is, by determining 
 the weight of the water formed by the union of a known 
 weight of oxygen. The weight of the water being known, 
 together with that of the oxygen which was contained in it, 
 the difference is of course due to the hydrogen; and hence 
 the ratio of weight in which the oxygen and hydrogen have 
 combined together to form water could be ascertained. 
 
 The relative atomic weights of hydrogen, oxygen, and 
 carbon are perhaps the most important of the fundamental 
 factors of analytical chemistry. They are the constants most 
 frequently needed in chemical calculations ; they are indeed 
 as necessary to the chemist in the identification of a vast 
 number of chemical substances as are certain fundamental 
 astronomical data to the mariner who seeks to ascertain his 
 position at sea ; and for these constants, determined with a 
 precision and scrupulous regard to manipulative detail which 
 have never been surpassed, chemistry will for ever remain 
 indebted to Dumas. 
 
 It was characteristic of Dumas that, having thus estab- 
 lished the composition of water, he should next turn 
 his attention to that of air. Indeed the question of the 
 gravimetric composition of atmospheric air followed as the 
 necessary consequence of his experiments upon water. The 
 volumetric composition of air was known with approximate 
 accuracy, but the proportion by weight of its components 
 could not be accurately determined by calculation so long as 
 the relative weights of oxygen and nitrogen remained 
 imperfectly, ascertained. In conjunction with his friend 
 Boussingault, Dumas now attacked the question of the pon- 
 deral composition of atmospheric air. 
 
 As the result of their experiments, it was ascertained that 
 1 00 parts by weight of atmospheric air, free from carbonic acid 
 and aqueous vapour, contained 23 of oxygen and 77 of nitrogen. 
 Now the volumetric ratio of the two gases might be determined, 
 
x Jean Baptiste Andrd Dumas 283 
 
 provided the volume-weights of the nitrogen and oxygen were 
 accurately known. On dividing each number by the specific 
 gravity of the gas, as at that time determined, it was found 
 that a notable deficiency occurred far greater than was 
 warranted by the errors incidental to the methods of ex- 
 periment. Hence Dumas and Boussingault were led to 
 doubt the correctness of the generally received values for 
 the volume-weight of oxygen and nitrogen, and on a care- 
 ful repetition of the experiments required to ascertain the 
 specific gravities of these gases, they found numbers differing 
 from those at that time accepted as accurate. This research, 
 therefore, not only served to give precision to our knowledge 
 respecting the gravimetric composition of air, but also led 
 to the correct determination of the specific gravities of its 
 components. 
 
 At the close of their memoir, Dumas and Boussingault 
 entered into some interesting calculations respecting the 
 influence of the numerous agencies which serve to affect 
 the composition of the air. Among the causes which tend to 
 abstract the oxygen from the air may be enumerated (1) 
 The respiration of animals; (2) The combustion of organic 
 matter; (3) The decay and putrefaction of organic sub- 
 stances ; (4) The disintegration of rocks ; and (5) The ulti- 
 mate oxidation of inorganic matter, as, for example, the 
 conversion of the lower oxides of iron to the state of peroxides. 
 In this last case oxygen would appear to be permanently lost 
 to the atmosphere, since it is only in rare instances, as in the 
 smelting of iron ore, that it can be again restored by processes 
 of reduction. A very little calculation will serve to show 
 that the reservoir of oxygen contained in the atmosphere is 
 amply sufficient to maintain its numerous functions. If we 
 suppose the atmosphere to be put into a huge vessel, and 
 suspended from the arm of a gigantic balance, it would require 
 581,000 cubes of copper, each having a side of 1 kilometer in 
 length, to equipoise it. If we also assume that each individual 
 
284 Jean Baptist e Andrd Dumas x 
 
 consumes 1 kilogram of oxygen per day, and that the popula- 
 tion of the earth is one thousand millions, and further, that 
 the oxygen consumed in the respiration of other animals, and 
 in the oxidation of organic matter, amounts to four times that- 
 required by man, and also that the oxygen disengaged by 
 plants compensates only for the causes of diminution of oxygen 
 not specified then, even in this exaggerated case, the amount 
 of oxygen abstracted from the air in a century would only 
 amount to 15 or 16 of the copper tubes; or, in other 
 words, the abstraction in a century would only be ^oVo^h 
 of the whole quantity of oxygen contained in the air an 
 amount barely appreciable by the most exact eudiometric 
 methods known to us. 
 
 These calculations have been recently revised, and their 
 substantial accuracy confirmed, by Professor Le Conte. Cer- 
 tain of the data employed by Dumas and Boussingault were 
 of necessity only imperfectly known at the time, but the main 
 conclusion has not been disturbed by the more accurate know- 
 ledge which we possess to-day. 
 
 Probably the most important contribution made by Dumas 
 to determinative chemistry, important as regards its influence 
 upon the development of chemical philosophy, was his revision 
 of the relative atomic masses of the elementary bodies. These 
 values are not only the fundamental constants of chemistry ; 
 their characters and relations as mere numbers are of the 
 highest significance in relation to the theory of the essen- 
 tial nature of matter. It was this philosophic aspect of 
 the question which mainly attracted Dumas, and which 
 supported him through perhaps the most tedious and 
 most exacting of all his researches. The determination of the 
 atomic mass, even of a single element, if made in such a 
 manner as to satisfy the requirements of modern science, 
 necessitates a combination of analytical skill and manipulative 
 dexterity with unlimited patience and an unbending resolu- 
 tion not to swerve from the highest ideals of quantitative 
 
x Jean Baptiste Andrd Dumas 285 
 
 accuracy. What, then, must be the strain both on the mental 
 and moral energy of him who sets himself the gigantic task of re- 
 determining the atomic weights of all the elements, with the 
 precision required by contemporary science 1 It is not sur- 
 prising that Dumas's determinations should require many years 
 for their accomplishment. Even when they were finished, 
 nearly two years were occupied in arranging the results for 
 publication. 
 
 The immediate effect of their appearance was twofold. 
 In the first place, they secured to Dumas a position on a par 
 with that of Berzelius as a master of determinative chemistry ; 
 the Swedish chemist had devoted many years of his life to 
 the same work, and all Europe regarded him as facile princeps 
 in this particular domain. In the next place, it again brought 
 the French school into direct antagonism with the followers 
 of Berzelius. To Berzelius the different elements were so 
 many different forms of matter ; their molecules had nothing 
 in common beyond their unalterability and their eternal 
 existence. It had been pointed out that the numerical re- 
 lations of the values for the atomic masses indicated the 
 existence of some intimate connection among them, and 
 Prout had timidly revived the doctrine of a materia prima 
 to account for this connection ; the elements, he said, are but 
 modifications of one primordial substance, and he sought for 
 the experimental confirmation of this hypothesis in the circum- 
 stance that all the values might be regarded as multiples by 
 integral numbers of that of hydrogen. There was nothing 
 unphilosophic in such a notion ; the physicist had established 
 the idea of the correlation of the forces electricity, magnetism, 
 heat, chemical action, are but modifications of the same agent ; 
 and just as to-day we find that the conceptions of evolution 
 have permeated every department of intellectual activity, it 
 was but natural that the doctrine of the unity of force -should 
 be enlarged so as to include the idea of the unity of matter. 
 
 Dumas seems to have been attracted by this idea with peculiar 
 
286 Jean Bap lisle Andre 1 Dumas x 
 
 force. The very nature of his previous work had in fact 
 prepared his mind for its reception and fertilisation. To the 
 man who had been one of the pioneers of organic chemistry, 
 who had led the way in the inception of the notion of com- 
 pound radicles, bodies often absolutely dissimiliar in their 
 physical and chemical attributes, although composed of the 
 same elements, and who had familiarised himself and the 
 world with the ideas of substitution and homology to him 
 there was nothing repugnant in the hypothesis of a materia 
 prima ; it indeed was the natural outcome of the whole of 
 his philosophy. Dumas's re-examination of the experimental 
 evidence on which Prout's hypothesis was based led him to 
 modify that hypothesis in certain essential particulars. As 
 the result of his determinations of the atomic weights of 
 thirty elementary bodies, Dumas found that in twenty-two cases 
 the atomic weights are multiples by whole numbers of that of 
 hydrogen, in seven they are multiples by half, and in three of 
 one-fourth of that value. 
 
 A number of questions suggested themselves to Dumas 
 at the outset of these inquiries, to which his experiments 
 seemed to afford definite answers. It had been already 
 noticed that in a so-called family of elements, i.e. in a 
 group of bodies like chlorine, bromine, and iodine, or of 
 metals like lithium, sodium, and potassium, the members 
 of which are possessed of many properties in common, 
 the individuals in the family show a remarkable gradational 
 order in their atomic weights ; the atomic weight of sodium is 
 almost exactly the arithmetic mean of the atomic weights of 
 lithium and potassium, and the atomic weight of bromine is 
 the mean of that of chlorine and iodine. Is this a natural 
 law 1 Are the chemical attributes of an elementary body a 
 function of its atomic weight 1 Affirmative answers to ques- 
 tions of this kind would obviously tend to strengthen the 
 validity of Prout's hypothesis. A certain amount of positive 
 evidence has been accumulated. Thus : 
 
Jean Baptist e Andre 1 Dumas 287 
 
 2 
 
 =23. 
 
 K + Cs nr 39+133 
 
 - = xtD, or - = ot>. 
 
 =24-5. 
 =68-5. 
 =75-5. 
 =120. 
 
 Other examples of relationships of this order might be 
 adduced, but these quoted are sufficiently numerous to indicate 
 that some intimate connection would seem to exist between 
 the individual members of well-defined groups of elementary 
 bodies; and that the absolute individuality postulated by 
 Berzelius is, in all probability, not the order of nature. 
 
 Dumas also pointed out the existence of differences in the 
 atomic weights of the elements in a family, similar to those 
 exhibited by the molecular weights of homologous organic 
 compounds. Thus : 
 
 Li . . .7. 
 
 Na . . . 7 + [lxl6] = 23. 
 
 K . . 7+[2xl6] = 39. 
 
 O . .16. 
 
 S 16 + [1 x 16] = 32. 
 
 Se . . 16 + [4 x 16] = 80 (79). 
 
 Te . . . 16 + [7 x 16]= 128 (126-3). 
 
 Mg . . . 24. 
 
 Ca . . . 24 + [1 x 16] = 40. 
 
 Sr . 24 + [4x16] = 88 (87-2). 
 
 Ba . . 24 + [7x16] =136 (136-4). 
 
288 Jean Baptiste Andrd Dumas x 
 
 The "numerics" of the chemical elements have received 
 much attention since the date of Dumas's memoir, and there is 
 a conviction in the minds of many chemists that their relation- 
 ships are determined by some natural law concerning which 
 we have as yet but the merest inkling. Prout's hypothesis 
 or rather the fundamental conception at the base of it is 
 still an open question. Since the time of the publication of 
 Dumas's papers that is, during the last quarter of a century 
 a number of atomic weights have been redetermined with the 
 very highest degree of precision attainable by modern chemical 
 science, with the result of showing that the hypothesis is in a 
 stronger position than ever. 
 
 The question has been examined from many different 
 sides ; the spectroscope, for example, has shown the possibility 
 of progressive dissociation at very high temperatures among 
 the forms of matter which we call elements, and the discovery 
 by Victor Meyer of the breaking up of the molecule of iodine 
 and of bromine has demonstrated the existence of atomic group- 
 ings about which we are as yet entirely ignorant. The chemical 
 molecule of iodine or of bromine that is, the smallest quantity 
 which can exist in the free state is at high temperatures 
 different from the chemical molecule at low temperatures. 
 
 The time will not permit me to dwell longer upon the 
 chemical labours of Dumas. I should like to have said 
 something concerning certain of his other researches in pure 
 chemistry, since some of them, as, for example, his investiga- 
 tions on the nitriles, mark important points of departure. In 
 his later years Dumas returned to many of the chemico- 
 physiological problems with which, in association with Prevost, 
 he began his career as an investigator. Some of these prob- 
 lems he carried forward into the new field of vegetal 
 physiology, and traced many of the connecting links between 
 animal and vegetable life. The question of the formation of 
 fat within the animal has long troubled physiologists. The 
 evidence afforded by chemistry was equivocal. Dumas and 
 
x Jean Baptist e Andrd Dumas 289 
 
 Boussingault maintained that the fat accumulating in the 
 body of the animal was supplied pre-formed by plants. On 
 the other hand, Liebig was of opinion that the animal had the 
 power of converting carbohydrates, e.g. sugar and starch, into 
 fat. Dumas himself supplied experimental confirmation of 
 the validity of Liebig's opinion by his remarkable observations 
 on the origin of bees'-wax. The nature of this substance was 
 first revealed by the investigations of the late Sir Benjamin 
 Brodie, who had shown that it consists mainly of compounds 
 of fatty acids belonging in fact to the same group of bodies as 
 acetic acid itself. Dumas found that bees, even when fed 
 exclusively upon sugar, still retained the power of producing 
 wax, contrary to the opinion of Swammerdam and Maraldi, 
 who were of opinion that the bee secreted the wax at the 
 same time it extracted the honey from the flower. 
 
 The subject of fermentation has had special attractions for 
 French chemists. The conditions of the transformation of 
 sugar into alcohol under the influence of a ferment were the 
 subject of one of Dumas's latest papers. Although he decides 
 in favour of the physiological theory as opposed to the 
 catalytic theory of Berzelius, or the eremacausis theory of 
 Liebig, Dumas points out that alcoholic fermentation may be 
 studied in the same way as any other chemical phenomenon ; 
 the conversion of sugar into alcohol and carbonic acid is a 
 purely chemical phenomenon, but a chemical phenomenon 
 caused by vital and not exclusively by chemical and physical 
 forces. 
 
 Few scientific men have displayed the many-sidedness of 
 Dumas, and any sketch of the man which failed to clearly 
 bring out this feature would be wanting in biographical truth. 
 I will briefly glance, therefore, at the characteristics of Dumas 
 as a man of letters, as an educationist, and as a politician ; in 
 all three capacities he has influenced the intellectual and 
 political development of his country. 
 
 Clearness of statement and elegance of diction are among 
 
 U 
 
2 go Jean Baptist e Andrt Dumas x 
 
 the chief characteristics of French style, and in the exercise 
 of these qualities no French scientific writer has surpassed 
 Dumas. Much of his influence among his countrymen is to 
 be traced to the attractive and even graceful manner in which 
 he sets before his readers what he has to say. The logical 
 precision of his ideas apparently made composition an easy 
 task to him. Your easy writing, said Byron, paraphras- 
 ing Sheridan's well-known saying, is usually damned hard 
 reading; but no one could say this of Dumas. The nine 
 volumes of his Treatise on Chemistry applied to the Arts, form 
 a monument, not only to his industry and skill in compila- 
 tion, but to his power of co-ordination, and to the ex- 
 cellence of his literary faculty. His literary power is 
 even more strikingly evident in his "Lectures on Chemical 
 Philosophy," delivered during the summer of 1836 in the 
 College de France. It is not often that our lecture rooms 
 resound with passages so pregnant with "fervency, free- 
 dom, fluency of thought," as may be gathered from the 
 pages of this book. This, for example, is how he delineates 
 the method of chemical inquiry "And what is this method, 
 which, old as our science itself, is still what it was in the days 
 of its infancy 1 It is an absolute belief in the testimony of 
 the senses, a boundless confidence in experiment, a blind 
 submission to the supreme authority of facts. Chemists, 
 ancient or modern, desire to see with the eyes of the body, 
 before using the eyes of the mind; they think it right to 
 make theories for facts established, but not to seek facts for 
 theories preconceived." 
 
 The death of Lavoisier is probably the most tragic event 
 in the history of science, and we can well imagine the thrill 
 which must have passed through every auditor, as Dumas, on 
 the forty-second anniversary of that event, recalled the cir- 
 cumstances under which that brilliant career came to its 
 untimely close. "It was at the time that Lavoisier had con- 
 ceived the idea of publishing a collection of his memoirs. , . . 
 
x Jean Baptist e Andrt Dumas 291 
 
 But whilst preparing this publication he was struck down by 
 an atrocious death, and the collection remains incomplete, the 
 most touching monument presented by the history of science. 
 Nothing is more painful than to glance at this work, of which 
 the second volume only is finished, whilst the first and third, 
 in process of printing, appear to be cut off by the same axe 
 which laid their author low. The sentence is broken off at 
 the place where the pen stopped as the executioner laid hold 
 of him. Nothing, I repeat, can possibly excite more acute 
 emotion nothing a deeper sense of the tragic element in the 
 fate of man than the sight of those doleful pages, the con- 
 tinuation of which is hidden by a veil of blood." 
 
 Years afterwards Dumas was the means of making France 
 pay the debt of gratitude which the world owes to Lavoisier 
 by completing, in truly imperial style, the edition of the 
 works of the famous chemist. He first began to move in the 
 matter in 1843, and at his instigation an influential committee 
 was nominated by the Academy to inquire into the best 
 manner of publishing the works of Lavoisier, but it was only 
 after repeated applications to successive Ministers of Instruc- 
 tion that the necessary decree was obtained. The result was 
 the publication, in a series of magnificent quarto volumes, 
 superbly illustrated, of the memoirs and treatises of the 
 great French master a fitting monument of his imperishable 
 genius. 
 
 Dumas's power as an orator was remarkably exemplified in 
 the Faraday Lecture, which, on the invitation of the Council of 
 the Chemical Society of London, he delivered in the theatre 
 of the Royal Institution in Albemarle Street, in the very 
 lecture hall which is sacred to the memory and genius of the 
 illustrious philosopher. It was the first of the series of 
 addresses which the Society has instituted to commemorate 
 the services of Faraday to science and to humanity. 'No one 
 who had the good fortune to be present on that occasion 
 can ever forget the manner in which Dumas discharged the 
 
29 2 Jean Baptist e Andrt Dumas x 
 
 duty which had been entrusted to him. The lecture hall at 
 the Royal Institution has been the scene of many a rhetorical 
 triumph, and its audiences have been held spell -bound by 
 some of the most glowing and eloquent periods which the 
 literature of science has preserved for us, but they have listened 
 to no truer or more beautiful words than those in which 
 Dumas dwells upon the sentiments of respect and admiration 
 with which civilised humanity regards the memory of Fara- 
 day. " The name of your illustrious fellow-countryman is not 
 one which any single nation can claim as its exclusive pro- 
 perty ; his labours and discoveries are as widely recognised in 
 France, in Germany, and in America, as in England. Faraday 
 belongs to the whole world. There is not a spot on this 
 earth, to which civilisation has penetrated, that does not 
 claim the right of participating in the respect and gratitude 
 you entertain for him. . . . Faraday is the type of the most 
 fortunate and most accomplished of the learned men of our age. 
 His hand, in the execution of his conceptions, kept pace with 
 his mind in designing them ; he never lacked boldness when 
 he undertook an experiment, never lacked resources to ensure 
 success, and was full of discretion in interpreting results. His 
 hardihood, which never halted when once he had undertaken a 
 task, and his wariness, which felt its way carefully in adopting 
 a received conclusion, will ever serve as models for the experi- 
 mentalist." 
 
 Dumas's memorial addresses are indeed examples of their 
 kind : it is impossible to know what to admire most in them 
 the grace of style, the lucidity of exposition, the wealth 
 of illustration, the rare sympathy, or the marvellous faculty 
 of presenting to us, by a few bold and graphic strokes, a 
 striking and lifelike conception of the person commemorated. 
 These addresses range over all subjects and over almost every 
 department of human knowledge. The series opens with that 
 on Berard, and the estimate of the famous surgeon's relations 
 to the science of his time might have been drawn up by a 
 
x Jean Baptiste Andrd Dumas 293 
 
 specialist. The same mastery of his subject is seen in the 
 commemorative addresses on Geoffrey Saint -Hilaire, the 
 anatomist, and on Auguste de la Rive, the physicist. In his 
 address on the Brongniarts, Alexandre the geologist, and 
 Adolphe the botanist, he shows with admirable grasp of 
 detail the outcome of their scientific work in fields remote 
 from his own special sphere, and his comparison between the 
 labours of Cuvier and the elder Brongniart forms a chapter in 
 the history of palaeontology. Of peculiar interest to chemists 
 are his monographs on Pelouze, who began life in the Rue 
 Copeau, where he dined on bread and water, and had to open 
 the window of his apartment in order to pull on his coat, and 
 who ended it as Master of the Mint in a palatial residence on 
 the Quai de Conti and on Balard, the discoverer of the ele- 
 ment bromine a man remarkable for the Spartan simplicity 
 of his habits and his supreme contempt for wealth and luxury. 
 As Secretary of the Institute, Dumas in 1876 became a 
 member of the French Academy, in succession to Fontenelle, 
 Condorcet, Fourier, Cuvier, and Flourens, his predecessors 
 in office, and it fell to his duty to deliver the commemora- 
 tion address on Guizot. The task was unusually difficult, but 
 Dumas accomplished it with his never-failing tact and grace, 
 and we have a vivid picture of the statesman, the man of 
 letters, and the philosopher, who for so many years guided 
 the destinies of France, and whose own career was but the 
 reflex of much of his country's history. 
 
 Dumas's position in the Institute necessarily entailed upon 
 him many onerous and conflicting duties, and endless is the 
 series of reports in the Comptes Eendus in which he was con- 
 cerned. Among the most recent, the best known are perhaps 
 those relating to the diseases of the silkworm and to the action 
 of the dreaded Phylloxera vastatrix. One of the great sources of 
 the national prosperity of France seemed to lie at the mercy of 
 this parasite. We learn from Dumas's report, presented to the 
 Academy in 1873, that Phylloxera, up to that time unknown 
 
294 Jean Baptist e Andrd Dimias x 
 
 both to the cultivators of the vineyards and to naturalists, 
 first made its appearance in the department of Gard in the 
 year 1865. Its devastating action was confined to this region 
 up to 1872, when it gradually spread over other wine-produc- 
 ing districts, and threatened the Gironde. The report traces 
 the natural history of Phylloxera, so far as this is known, 
 and shows that in the early stage of its development the pest 
 is very susceptible to the action of numerous destructive 
 agencies, such as phenol, decoctions of tobacco, quassia, etc. 
 On the whole, however, the most generally efficient substances 
 seem to be the salts known as the thiocarbonates, the employ- 
 ment of which was first suggested by Dumas. 
 
 No record of Dumas's literary services would be complete 
 without some reference to his connection with the Annoles de 
 Chimie et de Physique. This journal, at one time the leading 
 scientific periodical of the world more renowned even than 
 our own Philosophical Transactions was instituted in 1790 by 
 that band of scientific men of which Lavoisier was the 
 dominant figure. In 1840 Dumas became one of the editors, 
 and he remained an active member of the committee of pub- 
 lication down to the time of his death. He was thus for 
 upwards of forty years connected with the responsible 
 management of the journal, to which his own contributions 
 extend over a period of half a century. 
 
 Probably no teacher in France has exercised so widespread 
 an influence on the development of chemistry on French 
 soil as Dumas. Public laboratories of the type which 
 Germany first instituted were unknown in France until 
 recently. That country owes their establishment to the 
 example of Dumas. In 1832 he founded and supported 
 a laboratory of research, entirely at his own expense, at 
 the Polytechnic School, and afterwards at the Rue Cuvier. 
 It was in these buildings, surrounded by a little knot 
 of workers, comprising Piria, Stas, Melsens, Leblanc, and 
 others, that those classical researches of which mention has 
 
x Jean Baptiste Andr Dumas 295 
 
 been made were executed. The troubles of 1848 reacted 
 disastrously upon the fortunes of Dumas, and he was 
 unable to afford the' heavy annual expense of a public 
 laboratory, to which all students were admitted gratuitously ; 
 and for a time he was compelled to relinquish experimental 
 teaching. Offers of assistance, however, were not wanting; 
 and Dumas has himself related how, on a certain day during 
 the troubled times which followed the Revolution of 1848, 
 he received a visit from a man of strange appearance and 
 brusque demeanour. "They tell me," he said, "that you 
 have shut up your laboratory; but you have no right to 
 do so. If you are in want of money there " (and he threw 
 down a roll of bank notes) ; " take what you want, do not 
 stint yourself ; I am rich, a bachelor, and have but a short 
 time to live." 
 
 Dumas felt himself unable to accept the proffered aid. 
 Within a couple of years his visitor died, leaving 200,000 
 francs to the Academy of Sciences to found an annual prize 
 for the promotion of research in organic chemistry. The 
 Jecker Prize is now one of the most coveted distinctions of the 
 Academy. 
 
 Dumas's career as a politician began with the Revolution of 
 1848, and he was sent by the electors of the arrondissement 
 of Valenciennes to the newly-created Legislative Assembly. 
 Shortly afterwards he was designated by the President of 
 the Republic as Minister of Agriculture and Commerce, and 
 was entrusted with the conduct of a number of enactments 
 dealing with the social amelioration of the working classes. 
 On the creation of the Empire, Dumas was made a senator, 
 and he occupied this position down to 1870. During eighteen 
 years' tenure of the office, scarcely a session passed without 
 Dumas bringing his influence or his knowledge to bear upon 
 some matter of social or economical importance. Questions 
 of high policy he left to others ; but on the subjects of coinage, 
 or drainage, on trade marks, on the treaties of commerce 
 
296 Jean Baptiste Andrd Dumas x 
 
 between England and France, and on questions relating to 
 education when Dumas ascended the tribune it was to be 
 listened to with the respect and interest which his knowledge 
 and oratorical skill invariably commanded. 
 
 Shortly after his elevation to the Senate, Dumas was made 
 a member of the Municipal Council of Paris, of which body 
 he became Vice-President in 1855, and President in 1859, 
 and he took a leading part in that wonderful transformation 
 of the capital which is one of the chief glories of the 
 Second Empire. Under his administration and direction 
 Paris acquired her present systems of water-supply, lighting, 
 and drainage. 
 
 The catastrophes of 1870 brought Dumas's career as a 
 politician and administrator to a close, and he was henceforth 
 able, like Guizot, undiscouraged and unembittered, to forget 
 the minister in the man of science. The renunciation of 
 his work as an investigator had brought many regrets with 
 it ; and near the close of his life he was heard to declare 
 that throughout his career, full of triumphs as it was, he had 
 nowhere felt the peace and happiness which his laboratory 
 in the old days had afforded him. "My life," he wrote 
 to one of his friends, " has been divided between the service 
 of science and that of my country. I would rather have 
 remained the servant of science alone ; but, sprung from 
 the obscure ranks of democracy, I have always thought that my 
 country had done so much for me that no devotion on my 
 part could be refused to it. If I have deceived myself, 
 science itself will not hold me guilty. In limiting myself 
 to scientific pursuits, I should have been happier, my life 
 would have been a less anxious one, and perhaps I should 
 have attained a larger view of truth." 
 
 One of the last of the more important public duties of 
 Dumas was the inauguration of the French Association of 
 Science a body modelled on lines similar to those of our 
 own British Association. How loyally the heart of " the old 
 
x Jean Baptiste Andrd Dumas 297 
 
 man eloquent " remained true to science may be gathered from 
 the following noble passage in the address he then delivered : 
 " Truth is beautiful enough in itself to merit a homage abstract 
 and pure ; the role of science noble enough to satisfy the aspira- 
 tions of the most exalted intellects ; its field vast enough to offer 
 a harvest to every worker. Some cut down rich crops, others 
 are content to glean ; but that which each gathers or discovers 
 all enjoy; among men of science goods are in common; and 
 the torch, kindled by genius, is not extinguished, even when 
 it has communicated, from place to place, its quickening flame 
 to the entire world. 
 
 "Allow me to add that the recollections of an already 
 long life have permitted me to become acquainted with 
 a great variety of personages. And if I call on memory 
 to picture to me how the type of true happiness is realised 
 on earth, I do not see it under the form of the powerful 
 man clothed in high authority, nor under that of the rich 
 man to whom the splendours of luxury and the delicacies 
 of well-being are granted, but under that of the man of science, 
 who consecrates his life to penetrating the secrets of nature 
 and to the discovery of new truths. Laplace, following 
 out, for half a century, the application of the laws of the 
 cosmic system to the movements of celestial bodies ; Cuvier, 
 inventing comparative anatomy and creating anew the ancient 
 population of the globe ; De Candolle, writing the elementary 
 theory of botany and the description of all the known plants ; 
 Brongniart, showing how to classify soils by the fossils 
 characterising them, these illustrious men of science, and 
 others, who, taking them as models, have done honour to 
 your city, and whose names are on all your lips, have known 
 a happy life. Animated by the love of truth, and indifferent) 
 to the enjoyments of fortune, they have found their reward/ 
 in public esteem." 
 
 Such outward and visible signs of appreciation as poten- 
 tates and public bodies could bestow Dumas reaped to the full. 
 
 OP THE 
 
298 Jean Baptiste Andrd Dumas x 
 
 Nearly every academy in Europe delighted to honour him. 
 At the age of thirty-two he became a member of the Insti- 
 tute ; Correspondent of the Berlin Academy in 1834; and 
 a Foreign Member of the Eoyal Society of London in 1840. 
 In 1843 the Eoyal Society bestowed upon him its highest 
 distinction by the award of the Copley Medal, and he was 
 the first recipient of the Faraday Medal from the Chemical 
 Society of London. He was made a Knight of the Prussian 
 Order pour U mdrite, and he received the Grand Cross of 
 the Legion of Honour. 
 
 Blessed with a singularly equable temperament and a 
 vigorous constitution, and with a nature as warm and sunny 
 as that of his native province, Dumas maintained his habits 
 of "iron industry" to the last. At the beginning of 1884 
 he first showed indications of impaired physical powers ; 
 and, after a brief illness, he died at Cannes on the llth of 
 April, having nearly completed his eighty-fourth year. He 
 was buried at Mont Parnasse. " Such a commanding figure 
 cannot pass into forgetfulness. Your memory, Dumas, shall 
 be perpetuated ; your name transmitted from age to age. 
 You will live in your works, in the example you have given, 
 in the immortal productions and rare qualities of your mind : 
 Forma mentis ceterna" And Wurtz himself, alas ! too near 
 the bourn of that undiscovered country into which his great 
 compatriot had passed in uttering these words expressed the 
 sentiment of the civilised world. 
 
XI 
 
 HEKMANN KOPP 
 
 AN ADDRESS DELIVERED TO THE FELLOWS OF THE CHEMICAL SOCIETY, 
 20TH FEBRUARY 1893. 1 
 
 BY the death of Hermann Kopp, a year ago to-day, the army 
 of science lost one of its generals of division, and our own 
 Society one of the oldest and most distinguished of the eminent 
 company we are proud to call our Foreign Members. It is 
 significant of Kopp's power and promise, and of the position 
 that he so early won for himself in the commonwealth of 
 science, that he should have been elected a Foreign Fellow of 
 our Society so far back as 1849, when he was barely thirty-two 
 years of age. With the exception of his illustrious colleague 
 Bunsen, who is the doyen of the Forty, and whose jubilee as 
 a Foreign Member we celebrated last year, and of the veteran 
 Fresenius, who was elected in 1844, he was, at the time of 
 his decease, the Senior Member on the list. 
 
 As the end of the century draws near, one after another of 
 the men who have made this century what it is are passing 
 over to the majority. It was characteristic of Kopp, in whom 
 humour and pathos were happily blended, that he should have 
 taken leave of Hofmann, at what proved to be their last 
 meeting, with the closing words of the song : 
 
 1 Chemical Society's Memorial Lectures, No. II. 
 
oo Hermann Kopp 
 
 Der Herr im Himmel schenk ein gniidig End 
 Tins letzen Zelm vom vierten Regiment. 
 
 It would seem as if, in the sunset of life, he had seen the 
 shadow of a coming event. Both the friends have now 
 submitted themselves to the strict arrest of the fell sergeant, 
 and have gone 
 
 to join 
 
 The innumerable caravan which moves 
 To that mysterious realm where each shall take 
 His chamber in the silent halls of death. 
 
 The nineteenth century has witnessed an extraordinary ex 
 pansion of that branch of science which it is the proper 
 business and true function of this Society to foster. The 
 history of learning can show no parallel to it. Contrast the 
 condition of chemistry in the eighteenth century with its position 
 to-day. It is true there were giants in those days : Black, 
 Scheele, Cavendish, Priestley, Lavoisier, are men never to be 
 forgotten. But their merit rests not more on the number or 
 magnitude of their discoveries than on the influence they 
 exercised on an intellectual movement, which it is at once the 
 privilege and the glory of this century to have furthered and 
 accelerated. Indeed we venture to think that the dis- 
 passionate historian of this movement, who, with "the cold 
 neutrality of an impartial judge," weighs and assesses the part 
 which successive workers have had in its progress, will 
 recognise in the giants of our own time men whose names 
 are familiar in our mouths as household words the signs of 
 a mental stature not only as great as, but possibly even 
 greater than, that of the greatest of their predecessors. 
 
 The history of an epoch is the history of its leading men. 
 They are the centres and sources of intellectual energy. In 
 them the ever-widening waves of mental progress have their 
 origin, and it is under their vivifying influence that science 
 and learning grow and spread. 
 
xi Hermann Kopp 301 
 
 Hence, therefore, we do well, from time to time, to gauge 
 our gain in knowledge by contemplating the life work of the 
 men who have fashioned it, and who have stamped it with 
 the marks of their power and individuality. It is this con- 
 sideration that has induced your Council to see in the 
 occasions which the stern act of death compels us to notice, 
 opportunities, not only of recording our sense of reverence, 
 esteem, and admiration for those who have so faithfully 
 tended the lamp of learning, but also of tracing the immediate 
 outcome of their labours, and of measuring its effect on con- 
 temporary science. 
 
 By the wish of your Council I appear this evening, on this, 
 the first anniversary of the death of Kopp, to discharge what 
 is to me a pious duty. Five-and-twenty years ago it was my 
 good fortune as a student in Heidelberg to come into contact 
 with Kopp, and to be influenced by his work and teaching. 
 
 To know Kopp was to love him, and to love him was, as 
 Steele wrote of another, a liberal education. For to his 
 friends he was ever ready to display the ample treasures of a 
 mind rich not only in the lore of an ancient learning, but 
 stored with the knowledge of a time of great achievement and 
 of profound historical interest the time which stretches from 
 the closing years of Berzelius down to the final decade of the 
 century ; which covers the period of the grand movement 
 which had its inception in the little laboratory on the banks 
 of the Lahn, and which witnessed those memorable intellectual 
 combats between the champions of opposing schools of 
 chemical thought, the echoes of which are only faintly heard, 
 if heard at all, by the student of to-day. Kopp's colloquial 
 powers were admirable ; like the Great Lexicographer, he 
 loved to fold his legs and have his talk out.' His strong 
 common sense ; his vigorous, incisive thought ; the range of 
 his information of men and letters ; his quick, retentive 
 memory ; his felicity of expression ; his fund of anecdote ; 
 his ready wit and genial humour all made him delightful to 
 
;o2 Hermann Kopp 
 
 XI 
 
 listen to. To watch the play of his features as he talked was 
 in itself a recreation. Every line in the quaint, impressive 
 face was instinct with intelligence, the outward and visible 
 sign of the active, restless geist behind it. Not that there was 
 any sense of unrest about the man. When I first knew him, 
 a quarter of a century ago, he may be said to have passed the 
 noontide of his intellectual career ; he was living the quiet, 
 contemplative, post-meridian life of a philosopher whose 
 period of active service as a researcher was wellnigh spent, 
 happy in his surroundings and in his occupation ; his social 
 sympathies satisfied by his relations with colleagues like 
 Bunsen, Kirchhoff, Helmholtz, Renaud, Konigsberger, and 
 Zeller ; and his mental activity finding scope for itself in his 
 lectures, in the exercise of the various offices connected with 
 the management of the University which he was called upon 
 to fill, and in his literary labours. His life, like that of the 
 greater number of men of science, had not been what the 
 world calls eventful ; the successive steps in his preferment as 
 a teacher and the appearance of his books and memoirs were 
 the main incidents which marked the even tenor of his way. 
 Born 30th October 1817, at Hanau, he was early attracted 
 towards the study of natural science. His father, Johann 
 Heinrich Kopp, a distinguished physician, seems to have 
 occasionally occupied himself with experimental chemistry, 
 and Leonhard's Tasclienbuch and Gehlen's Journal contain 
 papers by him on mineral analysis, and on investigations 
 relating to physiological chemical products. The younger 
 Kopp received his school training at the gymnasium of his 
 native town, where he acquired that knowledge of Latin and 
 Greek, and that love for classical learning which he turned to 
 such signal account in the preparation of his great work on 
 the History of Chemistry. When eighteen he proceeded to 
 Heidelberg, to the University which eventually claimed him as 
 Professor, where he studied chemistry under Leopold Gmelin, 
 and physics under Wilhelm Muncke. Gmelin, who became 
 
XI 
 
 Hermann Kopp 303 
 
 Ordinary Professor of Medicine and Chemistry in the 
 University in the year in which Kopp was born, is mainly 
 known by his Handbuch der Chemie, of which an English 
 translation by the late Henry Watts, the first editor of our 
 Journal, was published by the Cavendish Society. Muncke 
 is chiefly remembered on account of his share in the 
 production of Gehler's Physilcalisches Worterbucli, and by his 
 work on the thermal expansion of liquids. Wohler has told 
 us something of the conditions under which practical 
 chemistry was studied in Heidelberg during the first quarter 
 of the century, from which we may gather that Kopp could 
 have had but few opportunities of gaining experience of 
 manipulative work in the old cloisters which at that time did 
 duty as the University laboratory. He left Heidelberg for 
 Marburg, where he graduated in 1838, presenting to the 
 Philosophical Faculty as his thesis an essay entitled, " De 
 oxydorum densitatis calculo reperiendse modo," from which it is 
 evident that he had already, whilst barely twenty-one years 
 of age, been attracted by those problems which were to 
 constitute the chief experimental labours of his life. From 
 Marburg he passed to Giessen, drawn thither by the influence 
 which has made the Giessen laboratory famous in the annals 
 of chemistry. At Liebig's instigation, and under his direction, 
 he studied the mode of decomposition of mercaptan by 
 nitric acid. This, which was for the most part a repetition 
 of the work of Lowig and Weidmann on ethyl-sulphonic acid 
 and its salts, is, practically, the only investigation in pure 
 chemistry that Kopp ever published. Work of this kind had 
 evidently few attractions for him, and he quickly returned to 
 those studies which, as his inaugural dissertation shows, he 
 felt that he was most fitted to pursue. 
 
 In 1841 Kopp became & privat-docent in the Giessen Univer- 
 sity, lecturing alternately on theoretical chemistry, crystallo- 
 graphy, meteorology, and physical geography. At about this 
 time that is, when twenty-four years of age he began his 
 
304 Hermann Kopp 
 
 History of Chemistry, and, as his material accumulated, he 
 added this subject to the list of his lecture courses. In 1843 
 he became Extraordinary Professor, and on the removal of 
 Liebig to Munich in 1852, he and Heinrich Will were together 
 made Ordinary Professors, and were entrusted with the 
 charge of the Giessen laboratory. But to a man like Kopp 
 such a position was certain to prove uncongenial ; he was not 
 fitted, either by temperament or by training, to carry on the 
 traditions of a place so indissolubly associated with the name 
 and fame and field of work of another, and after a year he 
 resigned the sole control to his friend and colleague. Kopp 
 remained in Giessen nearly five-and-twenty years, and all his 
 most important experimental work was done there. In 1863 
 he received a call from Heidelberg, which he accepted ; here, 
 as has been said, he remained until his death, occupying him- 
 self latterly with lectures on the history of chemistry and on 
 chemical crystallography. He was repeatedly solicited to 
 accept a position in some one of the larger universities, 
 notably in Leipsic and in Berlin ; but all attempts to draw 
 him from his dear Ruperto-Carolina were unavailing. " Even 
 Bunsen alone," he was wont to say, " keeps me fast in Heidel- 
 berg." And by no one is Kopp's departure more keenly felt 
 than by Bunsen, his friend and colleague for more than a 
 quarter of a century. The strollers on the Anlage still miss 
 the quaint figure on its way to the daily visit to the old 
 veteran, who, rich in honour and in years, is now the last of 
 that famous group which has made Heidelberg renowned as a 
 centre of intellectual life and scientific activity. 
 
 Kopp is best known to the literary world by his History of 
 Chemistry. The first volume of this work, a monument of 
 learning and of patient labour, of constructive skill and 
 sagacious criticism, appeared in 1843, and the fourth and 
 final volume in 1847. His life-long friend Hofmann, who 
 was with him at Giessen, has told us that, by the publication 
 of this classical work, Kopp, then barely thirty years old, 
 
XI 
 
 Hermann Kopp 305 
 
 suddenly found himself famous. " With one accord his con- 
 temporaries recognised that here was a production which, 
 whether they regarded the thoroughness of research that it 
 displayed, or the manner in which the material resulting from 
 that research was sifted and arranged, was without a parallel 
 in the literature of any other country. And even to-day, 
 after the lapse of nearly half a century, there is no historical 
 work on chemistry that can be even remotely compared with 
 it. Numbers of books relating to the same subject, some of 
 considerable merit, have since been published in Germany 
 and France, but it is not difficult to perceive that they are all 
 grounded on Kopp's great work." For upwards of forty 
 years Kopp had it in contemplation to bring out a new 
 edition, and much of the later historical work he published, 
 such as his Beitrage zur Geschichte der Chemie, which appeared 
 between 1869 and 1875, and the EntwicEung der Chemie in der 
 neueren Zeit, printed under the auspices of the Historical Com- 
 mission of the Bavarian Academy in 1873, together with the 
 two volumes on Die Alchemie in alter er und neuerer Zeit, grew 
 out of the materials he had gathered together. "But," again 
 to quote Hofmann, " the better is here the enemy of the good. 
 Kopp postponed the ' vermehrte und verbesserte Auflage ' year 
 after year, in the hope of being able to make a fuller study . 
 of certain special periods. Whoever is familiar with the mass 
 of profoundly interesting matter he had accumulated, or who 
 has had the opportunity of seeing the bulky note-books in 
 which it was stored, must deeply lament that the hand which 
 could alone arrange these treasures is now stiffened in death." 
 On the death of Berzelius in 1848 the leaders of the 
 Giessen school determined to carry on the work which had 
 chiefly occupied the closing years of the Swedish chemist. 
 Berzelius's Year Book had become a power in the chemical 
 world, mainly on account of the authority wielded by the 
 greatest chemical critic of his time. The Jaliresbericht of 
 Liebig and Kopp differed, however, fundamentally, both in 
 
 x 
 
306 Hermann Kopp 
 
 XI 
 
 plan and execution, from its Swedish prototype. It was to 
 be a review of the year's progress, not only in chemistry, but 
 also in all those sciences which were associated with chemistry, 
 or were, in any definite sense, ancillary to it ; it was to be 
 done impartially, and with no special reference to any set of 
 dogmas or particular school of chemical thought. Practically 
 the whole of the more active members of the scientific side of 
 the Philosophical Faculty of the University were concerned 
 in its production. To Kopp fell the greater share of the 
 arrangement and of the general editorial management; in 
 addition, he undertook the summaries relating to Theoretical, 
 Physical, and Inorganic Chemistry. To Buff and Zamminer 
 were entrusted Pure Physics; to Heinrich Will, Organic 
 Chemistry; to Knapp, Technical Chemistry; to Ettling, 
 Mineralogy ; and to Dieffenbach, Chemical Geology. The first 
 volume appeared towards the close of 1849. and consisted of 
 a review of the work of 1847 and 1848. Liebig continued 
 to be associated with Kopp as editor for some years after 
 he left Giessen, but in 1857 his place was taken by Will, 
 who acted as co-editor until 1862, when Kopp resigned his 
 share in the responsible direction of the publication prior to 
 his removal to Heidelberg. No chemist active in the pro- 
 secution of research needs to be reminded of the value of the 
 Jahresbericht. It has undoubtedly exercised a most beneficent 
 influence on the development of chemical science in Germany, 
 and it has been of the greatest service to those chemists in 
 this country to whom German is not an unknown tongue. 
 The attempt was made to introduce the Jahresbericht to Eng- 
 lish readers by means of a translation published under the 
 direction of Hofmann and Warren De la Rue, but the good 
 seed fell upon stony places, and after a year or two the enter- 
 prise was abandoned. Matters in 1849 were doubtless better 
 with us than Liebig found them to be in 1837, when he told 
 Berzelius that England was not the land of science, and that 
 our chemists were ashamed to call themselves so because the 
 
XI 
 
 Hermann Kopp 307 
 
 apothecaries had appropriated the name. 1 Possibly the reason 
 for the ill success of the venture is to be found in the fact that 
 the Journals of this Society have, from the outset, taken note, 
 in a more or less systematic way, of current chemical work in 
 other countries. Be that as it may, there is practically no 
 longer room for the German publication in this country; 
 since 1871 our Society has taken in hand an English Jahres- 
 bericht, and issues to its members monthly abstracts of all 
 papers relating to, or bordering on, chemistry, in which, as 
 regards fulness, comprehensiveness, and promptitude of pub- 
 lication, we have striven to emulate the example, and possibly 
 even bettered the instruction, of our distinguished Foreign 
 Member. 
 
 In 1851 Kopp joined Liebig and Wohler in the production 
 of the Annalen der Chemie und Pharmacie, and for many years 
 he took the responsible share in its management. His name 
 as editor appears on the title-page of no fewer than 190 
 volumes of this famous periodical, which, under its present 
 designation of Justus Liebig's Annalen der Chemie, constitutes 
 an abiding monument to the influence and power of its great 
 progenitor. 
 
 Kopp's services to the literature of our science were, how- 
 ever, by no means confined to its journalism. Engrossing and 
 arduous as his duties as an editor must have been, he yet 
 found time to write the admirable Introduction to Crystallography, 
 and to prepare the section on " Theoretical Chemistry " in that 
 well-known text-book, Graham- Otto's Lehrbuch der Chemie. 
 These works enjoyed great popularity in Germany, and have 
 
 1 " Ich bin einige Monate in England gewesen, liabe ungeheuer viel gesehen 
 und wenig gelernt. England ist nicht das Land der Wisseiischaft, es existirt 
 dor.ten nur ein weitgetriebener Dilettantismus, die Chemiker schamen sich 
 Chemiker zu heissen, weil die Apotheker, welche verachtet sind, diesen 
 Namen an sich gezogen haben. Mit dem Volke war ich ausserordentlich 
 zufrieden, Zuvorkommenheit, Gastfreiheit, kurz ich habe sonst an ihnen alle 
 Tugenden gefunden. Graham macht auch in wissenschaftlicher Hinsicht die 
 scha'tzbarste Ausnahme, er ist ein vortrefllicher Mensch, auch Gregory, der an 
 seine Stelle in Glasgow gekommen ist. "Liebig to Berzelius, 26th November 
 1837. 
 
308 Hermann Kopp xi 
 
 exercised no inconsiderable influence on the education of the 
 present generation of chemists in that country. The Intro- 
 duction to Crystallography was indeed written specially for 
 chemists with a view of interesting them in a study which is 
 still too frequently neglected by them ; and the " Theoretical 
 Chemistry" proved of signal service in disseminating the 
 doctrines which constituted the "new chemistry" of thirty 
 years ago. 
 
 No record of Kopp's literary activity would be complete 
 without a reference to his occasional writings, some of which 
 are among the most typical and most characteristic of his 
 productions; as, for example, his Aus der Molecularwelt, 
 written for Bunsen's seventieth birthday, and the Aurea catena, 
 Homeri, with which he greeted Wohler when fourscore years 
 of age. In the Molecularwelt, Kopp's delicate fancy and quaint 
 humour are seen at their best ; the book attracted consider- 
 able attention even beyond chemical circles, and rapidly ran 
 through a number of editions. His lecture Sonst und Jetzt 
 in der Chemie, which appeared in 1867, may still be read with 
 interest as an historical account of the changes which have 
 conduced to the present development of chemical theory. His 
 pen, indeed, in spite of frequent illness and waning strength, 
 was busy to the last, and he closed a long half century of 
 literary labour in preparing for Ostwald's " Chemical Classics," 
 an annotated edition of Liebig and Wb'hler's famous memoir 
 on the radicle of benzoic acid the memoir which, it will be 
 remembered, Berzelius hailed as the dawn of a new day. 
 
 Kopp's scientific papers relating to his experimental and 
 critical labours appeared mainly in Poggendorff's Annalen and 
 in the Annalen der Chemie und Pharmacie. Two or three of 
 his early communications were printed in the Philosophical 
 Magazine, and his elaborate memoir on the specific heat of 
 compound substances, in which he sought to develop Neumann's 
 law, was published by the Eoyal Society. 
 
 Compared with those of his great contemporaries, Liebig 
 
XI 
 
 Hermann Kopp 309 
 
 and Wohler, the number of his scientific papers may seem 
 small. But, in estimating Kopp's industry and power of work 
 as an investigator, the character of his experimental researches 
 must be considered. The nature of the relations which he 
 strove to elucidate often necessitated the determination of 
 the physical constants of some scores of substances, many of 
 which could only be prepared in a state of sufficient purity 
 by lengthy operations. Moreover, these innumerable measure- 
 ments were not only troublesome and tedious in themselves, 
 but they were followed, very frequently, by long and weari- 
 some calculations. The rich field of chemical physics will 
 indeed only yield its fruit by patient and incessant tillage. 
 
 Kopp occupies an almost unique position as an investigator. 
 The one consistent purpose of his work was to establish a 
 connection between the physical and chemical nature of sub- 
 stances ; to prove, in fact, that all physical constants are to be 
 regarded as functions of the chemical nature of molecules. It 
 is not implied, of course, that the conception of such an intra- 
 dependence originated with him. As a matter of fact, almost 
 immediately after the publication of Dalton's New System of 
 Chemical Philosophy, in which the doctrine of atoms was 
 revived to account for the fundamental facts of chemical 
 union, the endeavour was made to connect the chemical 
 attributes of a substance with one of its best-defined physical 
 constants, viz. its atomic mass. Prout's hypothesis is, in 
 reality, the generalised expression of such an attempt ; it is an 
 adumbration of Mendeleeff's great discovery of the Law of 
 Periodicity. But it may be justly claimed for Kopp that no 
 one before him made any systematic effort to connect such of 
 the physical qualities of substances as admit of quantitative 
 statement with the stoichiometrical values of such bodies. The 
 sporadic attempts made prior to 1840 were practically fruitless 
 on account of the imperfect nature of the physical data up to 
 that time extant. 
 
 When Kopp began his inquiries, very few boiling points 
 
310 Hermann Kopp 
 
 XI 
 
 were known, even approximately ; and he had, as a pre- 
 liminary step, to ascertain the conditions under which such 
 observations must be made in order that accurate and com- 
 parable results could be obtained. The thermal expansions 
 of barely half a dozen liquids had been measured, and the 
 very methods of making such measurements with precision 
 had to be worked out. 
 
 At the outset of his investigations, Kopp found the physical 
 constants with which he was more immediately concerned 
 very much as Berzelius found Dalton's values of the relative 
 weights of the atoms ; at the close of his work, they were 
 hardly less accurately known than were those stoichiometric 
 numbers to the ascertainment of which the great Swedish 
 chemist had dedicated his life. 
 
 It would be quite impossible within the limits of such an 
 address as this to attempt to give an analysis of each of Kopp's 
 memoirs. I must, therefore, content myself with essaying to 
 lay before you a generalised statement of the main outcome of 
 his work, and of the development which it has received at the 
 hands of his successors. Fortunately for the purpose of such 
 a summary, Kopp's more important memoirs readily and 
 naturally fall into comparatively few groups, viz. (1) those 
 concerning the relations between the specific gravities of 
 substances and their molecular weights; (2) those treating 
 of the relations between boiling point and chemical composi- 
 tion; and (3) the papers relating to the specific heats of 
 solids and liquids. As regards the other papers, only the 
 briefest notice is here possible. 
 
 In the paper on Solubility (Annalen, 34, 260 (1840)), Kopp 
 seeks to determine the behaviour of a solvent towards a mix- 
 ture, in excess, of two soluble salts, or, in other words, to 
 ascertain how far the solubility of one substance is affected 
 by the presence of another when the conditions are such that 
 chemical change is a priori impossible. Are the salts, he asks, 
 dissolved in the ratios of their specific solubilities ; or is the 
 
XI 
 
 Hermann Kopp 3 1 1 
 
 solubility of the one salt unaffected by the presence of the 
 other ; or can the aggregate amount of the dissolved saline 
 matter be deduced from the specific solubilities of the 
 constituents? He finds, as regards the solubility of two 
 salts possessing a common basic radicle, that they are never 
 present in the saturated solution in the exact amount 
 required by their specific solubilities. In the case of two salts 
 containing an acid radicle in common, it was observed that 
 the salt having the "stronger" base preserved its specific 
 solubility, and that the other salt dissolved in the solution to 
 an extent depending on its particular character, the quantity 
 being sometimes greater and sometimes less than the cal- 
 culated amount. He also shows how such determinations 
 afford a method of recognising the existence of double salts in 
 solution, but which, as in the well-known case of carnallite, 
 are more or less decomposed on crystallisation. Lastly, he 
 points out how the temperature corresponding to the change 
 of hydration, or some other condition, in a salt, either in the 
 dissolved or undissolved portion as, for example, in the case 
 of sodium sulphate may be deduced from the formula ex- 
 pressing the relation of solubility to temperature, where, as in 
 that salt, we have to do with two solubility curves. 
 
 This investigation is noteworthy as being the precursor of 
 the extensive inquiries which we owe to Karsten, Hauer, 
 Riidorff, and Engel. In the note on the Solubility of Common 
 Salt in aqueous Alcohol of different strengths (Annalen, 40, 
 266), Kopp opens up a field of labour which, twenty years 
 later, taxed the energies of Schiff and Gerardin. No general 
 law as to the partition of a soluble substance between two 
 solvents, or as to the action of a mixture of two mutually 
 miscible liquids in one of which the substance is insoluble, 
 has hitherto been traced. 
 
 In the short paper on the Cohesion of Liquids (Annalen, 
 35, 230), he describes a simple method for the quantitative 
 estimation of the resistance which liquids offer to rupture. 
 
312 Hermann Kopp 
 
 XI 
 
 The power which a liquid possesses of resisting any tendency 
 to internal separation of its parts has hitherto received but 
 scant attention from physicists, presumably on account of the 
 experimental difficulty of the problem. It is, as shown by 
 Donny, Osborne Keynolds, and Worthington, more consider- 
 able than we are apt to imagine, and is indeed comparable 
 with that of solids. It would be interesting to submit Kopp's 
 method to a careful experimental criticism, for it is so easy of 
 execution that, if found accurate, valuable data could rapidly 
 be accumulated by its aid. 
 
 In the paper "Ueber die Bildung von Krystallen mit 
 Kernen" (Annalen, 94, 118 (1855)), Kopp describes a charac- 
 teristically ingenious method of throwing light upon the mode 
 in which natural crystals are made to enclose foreign sub- 
 stances, as in the case of fluorspar, which frequently surrounds 
 cubes of iron pyrites, and where, too, as is obvious from the 
 nature of the cleavage, no very firm adhesion exists between 
 the substances. The plan consisted in coating the crystal to 
 be enclosed with a thin film of coloured collodion and then 
 placing it in a solution of the salt which was to surround it. 
 In spite of Kopp's interest in chemical crystallography, which 
 under his direction became a most fascinating study, he only 
 published a couple of notes on the subject; in the first he 
 treats of the pleomorphism of magnesium sulphate, and in 
 the second he discusses the bearing of analogous atomic com- 
 position on crystalline form (Annalen, 125, 369 (1863)). 
 
 In nothing was Kopp's originality or ingenuity more 
 strikingly manifested than in the construction of his apparatus. 
 To a great extent he was his own instrument maker, and his 
 materials were, for the most part, glass and cork. But no 
 Japanese worker, with his few and primitive tools, ever pro- 
 duced results which, in point of delicacy, finish, and accuracy, 
 surpassed those which Kopp obtained by means of his simple 
 contrivances. It is told of Wollaston that when a distinguished 
 foreigner called to see his laboratory, he had his chemical 
 
XI 
 
 Hermann Kopp 313 
 
 utensils brought in on a tray. "This," said he, "is all the 
 laboratory I possess." I venture to say that the whole of 
 the apparatus which Kopp employed in the course of his 
 researches on physical chemistry could be put on a very much 
 smaller tray than must have been needed to hold the furniture 
 of Wollaston's laboratory. 
 
 Kopp's first contribution to the literature of science con- 
 sisted of an account in Poggendorffs Annalen, done when he 
 was a student at Marburg, of a differential barometer which 
 he had constructed (Poggendorffs Annalen, 40, 62 (1837)). His 
 volumenometer (Annalen, 35, 17 (1840)), is an improvement on 
 the stereometers of Say, Leslie, and W. H. Miller, not so much 
 in simplicity of construction or of use, as in the greater con- 
 venience of its form, and in the more accurate results it is 
 capable of affording. It may be readily made with materials 
 ordinarily found in laboratories, and is especially useful for 
 the determination of the specific gravities of such substances 
 as sugar, starch, silk, cotton, wool, flax, etc. 
 
 His ingenuity is further seen in his method (Annalen, 81, 
 1 (1852)), of determining the thermal expansion of substances 
 which, like sulphur, galena, zinc, blende, fluorspar, etc., can 
 only be obtained in irregular fragments, and frequently of no 
 great size. Much of our knowledge respecting the thermal 
 expansion of minerals is in fact based on Kopp's work. 
 
 Closely related to this memoir is that on the change of 
 volume which substances experience in passing from the solid 
 to the liquid state (Annalen, 94, 129 (1855)). With the 
 exception of the work of Keaumur, in 1726, which was only 
 qualitative in character, practically nothing was known on 
 this subject prior to Kopp's investigation. By means of an 
 apparatus which is simplicity itself, and which could be put 
 together in a few moments, Kopp determined the relation of 
 the volume, when solid to that when liquid, of a large number 
 of substances, such as ice, phosphorus, sulphur, stearic acid, 
 calcium chloride, sodium thiosulphate, etc. The value of the 
 
 OF THE 
 
314 Hermann Kopp xi 
 
 apparatus lay, however, not so much in its simplicity as in 
 the skilful work put into it, and in the exactitude of the 
 results which came out of it. Although subsequent workers 
 have had occasion to repeat Kopp's observations by other 
 and far more elaborate apparatus, as, for example, that of 
 Pettersson, the substantial accuracy of his observations has not 
 been challenged. The main conclusions which may be drawn 
 from his work are now the common property of the text- 
 books. As a rule, the expansion coefficient of a solid substance 
 increases very rapidly in the neighbourhood of the melting 
 point, the most striking exceptions being phosphorus and ice. 
 The increase in volume which a substance experiences in pass- 
 ing from the solid to the liquid condition depends, for the 
 most part, on this rapid increase in the expansion coefficient 
 and on the sudden expansion at the moment of melting. In 
 some substances, like phosphorus, the change in the expansion 
 coefficient is small, but the increase due to liquefaction is 
 comparatively great ; in wax, on the other hand, the increase 
 in volume is chiefly due to the change in the coefficient of 
 expansion. Kopp was particularly attracted by the extra- 
 ordinary behaviour of Rose's fusible metal, which had already 
 been the subject of a careful examination by Erman in 1827. 
 This alloy a mixture of 2 parts of bismuth, 1 part of lead, 
 and 1 part of tin expands on warming from to 59 in the 
 ratio of 1 to 1'0027, but on further heating contracts, until at 
 82 it occupies the same volume as at ; it continues to con- 
 tract until 95, when its relative volume is 0'9947 ; it melts 
 between 95 and 98, when its volume suddenly becomes 
 1-0101. The nature of alloys had always a special interest 
 for Kopp, and two of his shorter papers, " Ungleiche Mischung 
 von Metall-Legirungen," etc. (Annalen, 40, 184 (1841)), and 
 "Dichtigkeit des Cadmium- Amal gams " (Annalen, 40, 186, 
 (1841)) had reference to this subject. 
 
 Kopp, as an investigator, will be mainly known hereafter 
 by his attempts to connect the physical constants of substances 
 
XI 
 
 Hermann Kopp 315 
 
 with their molecular weights and chemical composition. The 
 greater number of his memoirs indeed are concerned with 
 these relations. As already stated, his earliest paper on the 
 subject was the dissertation he presented for his doctorate to 
 the Philosophical Faculty of the University of Marburg. 
 
 I shall first treat of his work on the specific heats of 
 bodies ; then of his attempts to connect the boiling points of 
 liquids with their chemical nature; and lastly, of his long- 
 continued efforts to trace the relations between the volumes 
 and molecular weights of substances. 
 
 In 1818 Dulong and Petit found that when the atomic 
 weights of the elements are multiplied by their respective 
 specific heats approximately the same number is obtained. 
 This fact was subsequently embodied by them in the state- 
 ment that "the atoms of all simple bodies have exactly the 
 same capacity for heat." In 1831 this generalisation was 
 extended by Neumann (Poggendorffs Annalen, 23, 1) so as to 
 include compounds, and what is now known as Neumann's 
 law was thus expressed by its discoverer : "In bodies of 
 analogous chemical composition the specific heats are inversely 
 as the stoichiometrical quantities, or what is the same, stoichio- 
 metrical quantities of bodies of analogous chemical composition 
 have the same capacity for heat." 
 
 Subsequent observers, among whom may be named Avo- 
 gadro, Hermann, and especially Eegnault, Person, and Pape, 
 added greatly to the experimental material on which the 
 validity of Neumann's law is founded. The whole question 
 was, however, reopened by Kopp in 1864. By means of a 
 simple modification of the method of mixtures, Kopp de- 
 termined the specific heats of a large number of substances, 
 for the most part compound in their nature. He concluded 
 that each solid substance, at a sufficient distance, from 
 its melting point, has a specific heat which may vary some- 
 what with physical conditions (temperature, greater or less 
 density, amorphous or crystalline nature, etc.) ; but the differ- 
 
316 Hermann Kopp 
 
 ences are never so great as must be the case if a variation 
 in the specific heat of a substance is to be held as a reason for 
 explaining why the determinations of the specific heats of 
 solid elements do not even approximately obey Dulong and 
 Petit's law, nor those of solid compounds of analogous chemical 
 constitution Neumann's law. Neither law is universally valid, 
 although Kopp found that Neumann's law applies in the case 
 of many compounds of analogous composition to which, on 
 account of their totally different chemical deportment, different 
 formula are. assigned; and even in cases in which these laws 
 have hitherto been considered as essentially true, the diver- 
 gences from them are material. Each element has the same 
 specific heat in its solid free state as in its solid compounds. 
 From the specific heats to be assigned to the elements, either 
 directly from experimental determination, or indirectly by 
 calculation on the basis of the law just stated, the specific 
 heats of their compounds may be calculated. 
 
 Kopp concludes his memoir with certain suggestive con- 
 siderations as to the nature of the chemical elements. What 
 substances, he asks, are to be regarded as chemical elements 1 
 Does the mere fact that they are non-decomposable determine 
 this 1 Or may a body be non-decomposable in point of fact, 
 and yet from reasons of analogy be regarded not as an 
 element but as a compound 1 He reminds us that the history 
 of chemistry furnishes numerous examples of cases in which 
 sometimes one and sometimes another mode of view led 
 to results which at present are regarded as accurate. The 
 earths were non-decomposable in point of fact in 1789, when 
 Lavoisier expressed the opinion that they were compounds, 
 oxides of unknown metals. Lavoisier's argument was based 
 on the fact that the earths enter as bases into salts, and 
 that it was to be assumed in regard to all salts that they 
 contained an oxygen acid and an oxygen base. But the 
 view, founded on the same basis, that common salt contains 
 oxygen, and the subsequent view that what is now called 
 
XI 
 
 Hermann Kopp 317 
 
 chlorine contained a further quantity of oxygen besides the 
 elements of an oxygen acid, did not find an equally per- 
 manent recognition. On the basis of the actual non- 
 decomposability of chlorine, Davy, about 1810, maintained 
 its elementary character ; and this view became general when 
 Berzelius adopted it more, Kopp thinks, because he was 
 outvoted than because he was convinced. 
 
 It cannot be maintained that the bodies which chemists 
 regard as elements are absolutely simple substances. How 
 far a body is to be regarded as an element is so far relative 
 that it depends on the development of the means of de- 
 composition which practical chemistry has at its disposal, 
 and on the trustworthiness of the conclusions which theo- 
 retical chemistry can deduce. A discussion as to whether 
 chlorine or iodine is an elementary substance can be taken 
 only in the sense whether chlorine is as simple a body as 
 oxygen or manganese, or nitrogen; or whether it is a 
 compound body, as peroxide of manganese or peroxide of 
 hydrogen, for example. 
 
 If Dulong and Petit's law were universally valid, it could 
 be used as a test for the elementary nature of a substance 
 whose atomic weight was known. That iodine, from a direct 
 determination, and chlorine, by an indirect determination 
 of specific heat, had atomic heats agreeing with Dulong 
 and Petit's law would be a proof that iodine and chlorine, 
 if compounds at all, are not more so than other so-called 
 elements for which this law is regarded as valid. 
 
 According to Neumann's law, compounds of analogous 
 molecular composition have approximately equal molecular 
 heats. In general, compounds whose molecule consists of 
 a large number of undecomposable atoms, or is of more 
 complex constitution, have greater molecular heats ; especially 
 in those compounds all of whose elements follow Dulong 
 and Petit's law, is the magnitude of the molecular heat a 
 measure of the complexity. If Dulong and Petit's law were 
 
3i 8 Hermann Kopp 
 
 universally valid, it might be concluded with great certainty 
 that the so-called elements, if they are really compounds 
 of unknown simple substances, are compounds of the same 
 order. If we start from the elements at present assumed 
 in chemistry, we must rather admit that the magnitude of 
 the molecular heat of a body depends not only on the number 
 of elementary atoms contained in one molecule of it, or 
 on the complexity of its composition, but also on the atomic 
 heat of the elementary atoms entering into its composition. 
 It is possible that a decomposable body may have the same 
 atomic heat as a non-decomposable one. 
 
 In a very great number of compounds the molecular 
 heat gives more or less accurately a measure of the com- 
 plexity of their composition, and this is also the case with 
 those compounds which, from their chemical deportment, 
 are comparable with the undecomposed bodies. 
 
 If ammonium or cyanogen had not been decomposed, 
 or could not be so by the chemical means at present available, 
 the greater molecular heats of their compounds, compared 
 with those of analogous chlorine or potassium compounds, 
 and the greater molecular heats of ammonium and cyanogen 
 obtained by indirect determination, as compared with those 
 of. potassium and chlorine, would indicate the compound 
 nature of these so-called compound radicles. The conclusion 
 appears legitimate that, for the so - called elements, the 
 directly or indirectly determined atomic heats are a measure 
 of the complexity of their composition (Philosophical Trans- 
 actions, 1865, 155). 
 
 These conclusions are, it should be stated, largely based 
 upon the fact of the abnormally low atomic heats of bodies 
 of low atomic weight, such as carbon, silicon, boron, gluci- 
 num, etc., when taken at comparatively low temperatures. 
 Kopp would regard bodies of low atomic weight as of a 
 low order of complexity. But since it has been recognised 
 that the specific heat of such bodies is very largely affected 
 
Hermann Kopp 319 
 
 by temperature, and in such manner that their atomic heats 
 at high temperatures more and more closely approximate 
 to the value required by Dulong and Petit's law, the force 
 of Kopp's argument is materially weakened. 
 
 In 1841, Kopp, from observations on methyl and ethyl 
 derivatives, drew attention to the fact that in many analogous 
 chemical compounds the same difference in composition fre- 
 quently occasions the same difference in boiling point (Annalen, 
 41, 87, d seq.). He also pointed out that in many other 
 similar compounds, mostly alcohols, acids, and esters of 
 the fatty series, a difference of #CH 2 apparently corre- 
 sponds with a difference of about ic!9 in the boiling point; 
 that an acid boils 40 higher than the corresponding alcohol ; 
 and that an ester boils 82 lower than the isomeric acid. 
 On comparing analogous compounds differing only in the 
 number of C atoms, he further concluded that the boiling 
 point of the compound having xG atoms more than the 
 other was x x 29 higher, and that a compound having H 
 atoms more than the other boiled x x 5 lower. He subse- 
 quently found that this difference of 19, corresponding with 
 an increment of CH 2 , is not observed in all homologous series. 
 Thus, in the benzene hydrocarbons #CH 2 = z24 ; in the 
 fatty ketones and aldehydes it is 22 ; in the alkyl chlorides 
 it is 31; and in the fatty anhydrides it is 12 '5. Isomeric 
 compounds of the same type and of the same chemical 
 character have the same boiling point; if of the same type 
 but of different character, or if of different type, their boiling 
 points are different. Hence Kopp concluded that the boiling 
 point of a liquid was a function partly of molecular weight 
 and partly of chemical constitution. The influence of mole- 
 cular weight alone may be studied by comparing bodies 
 of strictly analogous constitution, e.g. the normal fatty acids. 
 If Kopp's main contention is valid, the relations should 
 hold good at other temperatures than that of the boiling 
 point under atmospheric pressure, and by observations on 
 
320 Hermann Kopp xi 
 
 the vapour pressures of the normal fatty acids, Landolt 
 concluded that such was the case. 
 
 Further and more accurate observations showed, how- 
 ever, that Kopp's original propositions must be materially 
 modified. Wanklyn found that the increment for CH 2 in 
 an homologous series became less and less as the series was 
 ascended. Schorlemmer (Philosophical Transactions, 172, 123 
 (1872)) observed that in the homologues of marsh gas the 
 difference corresponding to CH 2 appears to become steadily 
 less by 4 until it reaches the value 1 9. Linnemann 
 (Annalen, 162, 39), by means of his well-known fractionating 
 apparatus, determined with great accuracy a number of 
 boiling points of members of correlated groups of fatty 
 compounds, from which he concluded that equal differences 
 in chemical composition do not give rise to equal differences 
 in boiling point, but that the differences diminish, at least 
 in the lower members of the greater number of the series, 
 as the series is ascended. Series, however, are known, as 
 for example the alcohols, in which the differences for CH 9 
 are approximately constant; in some, too, the differences 
 increase as the series is ascended. Schumann, in 1881, 
 studied the vapour pressures of esters of the fatty acids, 
 from which he deduced conclusions in harmony with those 
 of Landolt on the fatty acids in so far as they showed 
 that the relations obtained were independent within certain 
 limits of the magnitude of the pressure. At the same time, 
 the relations themselves lent no support to Kopp's general 
 conclusions. 
 
 The observations on boiling points which have accumu- 
 lated since the time of Linnemann have confirmed the 
 conclusions put forward by him. In homologous series 
 the boiling point differences may either increase or decrease, 
 or may vary irregularly as the series is ascended. Although 
 in all cases it is not yet possible to assign causes for these 
 apparent irregularities, they may to some extent be ex- 
 
XI 
 
 Hermann Kopp 321 
 
 plained by considerations recently advanced by Dobriner 
 and extended by Lossen. 
 
 It is possible to regard any three consecutive homologues 
 containing carbon, hydrogen, and oxygen as methyl, ethyl, 
 and propyl compounds. For example, the first three mem- 
 bers of the series of normal fatty alcohols may be written 
 
 MeOH, 
 EtOH, 
 PrOH. 
 
 Formulating the compounds in this way, Dobriner would 
 term them a triad of oxygen compounds of the alkyls, for 
 in each case the alkyl group is linked to oxygen. If, how- 
 ever, ethyl alcohol be taken as the initial member of the 
 triad, the formulae of ethyl, propyl, and butyl alcohols 
 would be 
 
 MeCELOH, 
 
 EtCH 2 OH, 
 
 PrCH 2 OH, 
 
 and as here the methyl, ethyl, and propyl groups are linked 
 to carbon, the triad would be spoken of as one of "carbon 
 compounds " of the alkyls. Calling the difference between 
 the boiling points of the methyl and ethyl compounds of 
 any triad the " first boiling point difference," and that 
 between the boiling points of the ethyl and propyl com- 
 pounds the "second boiling point" difference, Dobriner 
 deduced the following two rules : In any triad of oxygen 
 compounds the first difference is less than the second. In 
 any triad of carbon compounds the first difference is greater 
 than the second. These conclusions are in harmony with 
 the exceptions to regularity frequently observed in the lowest 
 members of homologous series, and the general applicability 
 of the rules has been tested by Lossen. Lossen finds that, 
 so far as trustworthy data go, triads of oxygen compounds 
 almost invariably conform to the rule ; in the case of carbon 
 
 y 
 
322 Hermann Kopp 
 
 XI 
 
 compounds, however, although in most cases Dobriner's rule 
 is obeyed, there are exceptions, notably in the case of the 
 alcohols, where the boiling points have been often and 
 carefully determined. 
 
 In triads containing the alkyl groups linked to sulphur, 
 nitrogen, the halogens, and the metals, Lessen finds that in 
 some cases the first difference is less, whilst in others it is 
 greater, than the second difference. 
 
 As regards the boiling points of isomers, subsequent work 
 has proved that in no case are the boiling points identical. 
 
 In 1868 Hinrichs stated that the more symmetrical the 
 formula of an isomeric molecule is, the lower is the boiling 
 point. Neumann extended this idea, and in 1874 put forward 
 for paraffin derivatives the only rules which are capable of 
 anything like general application. His conclusions are That 
 the more nearly the grouping of the atoms in an isomeric 
 molecule deviates from the rectilinear or chain type, and 
 approaches the spherical type, the lower is the boiling point. 
 In metameric bodies of similar chemical character and other- 
 wise corresponding structure containing carbon, hydrogen, and 
 oxygen, the more nearly the oxygen atom stands to the 
 middle of the chain of atoms the lower is the boiling point. 
 These two rules applied singly or in conjunction, accord with 
 the great majority of the facts. There are exceptions, however, 
 among which some of the esters carefully examined by Gar- 
 tenmeister may be noticed. 
 
 For isomers of aromatic series practically no generalisations 
 have as yet been established. 
 
 Several attempts have been made to deduce formulae 
 whereby boiling points may be calculated. In the case of 
 homologues, expressions such as those of Goldstein, Mills, and 
 Hinrichs are no doubt successful in reproducing the observa- 
 tions for the particular series to which the formulae refer, but 
 they do not afford a basis for calculating boiling points in 
 general. 
 
xi Hermann Kopp 323 
 
 Before entering upon an examination of Kopp's memoirs on 
 specific volume, it may be interesting to give a brief history of 
 the attempts made prior to his time to trace relations between 
 chemical combination and the equivalent volumes of solid and 
 liquid substances. 1 
 
 These attempts may be said to have grown out of Gay 
 Lussac's memorable discovery in 1808, that gaseous bodies 
 combine together in simple volumetric proportions. The first 
 endeavour to apply similar considerations to solids and liquids 
 was made in 1821 by "Le Eoyer, Pharmacien, and J. A. 
 Dumas, son eleve," the latter of whom is none other than our 
 eminent Foreign Fellow, and the first of our Faraday Lecturers, 
 the late Perpetual Secretary of the French Academy. In their 
 paper in the Journal de Physique, 92, 408, Le Royer and 
 Dumas attempted to determine the equivalent volumes of the 
 elements by dividing their atomic weights by their respect- 
 ive specific gravities, the values so obtained being termed by 
 them atomic volumes. They were led to conclude that these 
 volumes formed an arithmetical series, a supposition which, it 
 must be admitted, was hardly warranted by the facts then 
 known, and which has since been completely disproved by 
 
 1 Objection lias been raised to the term " specific volume " on the ground 
 that as specific gravity is the weight of unit volume, specific volume should, 
 by analogy, be the volume of unit weight the reciprocal of specific gravity, 
 and not the product of this reciprocal and molecular weight. Hence, of late 
 years, the term " molecular" volume has been more generally preferred. It 
 is, however, questionable whether the change is worth making, in view of the 
 confusion which is almost certain to occur from the varying sense in which 
 the term will be used by physicists and chemists. The real molecular volume 
 is obviously the mass of a molecule divided by its density. Although such 
 values are not yet known with any degree of precision, it can hardly be 
 doubted that we are within measurable distance of this knowledge. The 
 term specific volume is certainly not free from objection, but inasmuch as it 
 has acquired, by definition, a distinctive meaning, no difficulty need be ap- 
 prehended from its continued use. 
 
 Specific gravity referred to water at 4 is the weight in grams of the unit 
 volume. If, then, the molecular weight be expressed in grams, we may 
 define specific volume as the number of cubic centimetres occupied by this 
 weight. The molecular weights here used refer to the gaseous state : the ob- 
 jection which has been urged against the employment of such weights has, 
 however, lost much of its force, now that the conception of the continuity of 
 the gaseous and liquid states is generally accepted. 
 
324 Hermann Kopp xi 
 
 more accurate observation. This idea of combination among 
 solids in definite volumetric proportion was further developed 
 in 1824 by W. Herapath in a paper read before the Bristol 
 Society of Inquirers (Philosophical Magazine, November 1824), 
 in which it was sought to prove that the volume of the oxygen 
 in a metallic oxide bears a simple ratio to that of the metal 
 with which it is combined. Almost simultaneously the same 
 problem was attacked by Karsten (Schweigg. Journal, 65, 394), 
 and subsequently in 1830 by Boullay, but with no definite 
 theoretical result. Ammermiiller, however, in 1840, was led 
 to conclude (Poggendorff's Annalen, 49, 341 ; id. 50, 406), that 
 the specific volumes of compounds containing the same ele- 
 ments in different proportions are either identical or stand to 
 one another in rational proportions. Persoz, in his Introduction 
 to the Study of Molecular Chemistry, recognised that equivalent 
 amounts of many bodies of analogous composition occupy the 
 same volume, and he inferred that the specific volumes of all 
 substances are multiples of one and the same number, a con- 
 clusion also drawn by Le Royer and Dumas, but which is not 
 supported by facts. 
 
 Kopp's first memoir on the subject of specific volume 
 appeared in Poggendorffs Annalen for 1839 under the title 
 "Ueber die Vorausbestimmung des specifischen Gewichts 
 einiger Klassen chemischer Verbindungen " (Poggendorff's An- 
 nalen, 47, 133). In this paper he discusses the specific grav- 
 ities of a number of compounds of metals and non-metals, 
 and by means of certain assumptions he deduces general 
 formulae from which he is able to calculate the specific 
 gravities of certain oxides and haloid salts with results which 
 show, in general, a fair agreement with the observed values. 
 In the same manner he calculates formulae for other anhydrous 
 salts, such as sulphates, carbonates, and nitrates, on the 
 supposition that such salts consist of combinations of oxides 
 and acids, or that they are made up of a radicle, acid, plus 
 oxygen. By means of these formulae he infers that it is 
 
XI 
 
 Hermann Kopp 325 
 
 possible to draw conclusions concerning the specific gravity 
 of metals for which this constant is unknown. Kopp 
 here uses the term specific volume for the first time, and he 
 defines it as the molecular weight (Mischungsgemcht) of a body 
 divided by its specific gravity. He finds that the specific 
 volumes of similarly reactive elements, as, for example, 
 chlorine, bromine, and iodine ; tungsten, molybdenum, chrom- 
 ium, iron, manganese, nickel, cobalt, etc., are respectively 
 equal or nearly equal. In other cases, as silver and gold, 
 potassium and sodium, the specific volumes stand to each 
 other in simple relations. Elements which, like barium 
 and strontium, form isomorphous compounds show identity 
 in specific volume, and Kopp sees in this fact an argument 
 for the validity of the theory of hydrogen acids j for, if we 
 conceive that baryta replaces the strontia in an isomorphous 
 strontium salt, it follows that the baryta will occupy a wholly 
 different volume from the strontia ; whereas if barium re- 
 places strontium in equivalent proportions, then since each 
 element occupies practically the same volume, there is no 
 a priori reason for any sensible change in crystalline form, 
 which is in accordance with observation. 
 
 The conception of specific volume is still further expanded 
 in a lecture given by Kopp to the Chemical Section of the 
 " Naturforscher Versammlung " the equivalent of our British 
 Association for the Advancement of Science at Erlangen, in 
 1840 (Annalen, 36, 1 (1840)). He first attempts to prove 
 that the specific weight of isomorphous substances is propor- 
 tional to their atomic weight; or that isomorphous bodies 
 possess the same atomic value. Strictly speaking, this 
 law can hold only for those substances which are perfectly 
 isomorphous. The bodies termed isomorphous are, in 
 general, only approximately so, for we find the angles .of their 
 crystals deviating several degrees from one another ; and the 
 relations between the axes of bodies thus denominated 
 isomorphous are not perfectly equal. The more nearly the 
 
326 Hermann Kopp 
 
 XI 
 
 crystalline forms of isomorphous substances are identical, the 
 more nearly will their atomic volumes be the same. This is 
 made evident by a comparison of the axial ratios of wither- 
 ite, strontianite, arragonite, and cerussite ; and of the car- 
 bonates of zinc and magnesium, mesitin-spar, the carbonates 
 of iron and manganese, and dolomite and calcspar. It is 
 seen that there is a direct comparison in the case of the 
 latter compounds between the length of the principal axis a 
 and the atomic volume V, such that a 4 ' 739 = 0*0127 67 IV, 
 from which it is possible, of course, to deduce the specific 
 gravity of the substance from its crystalline form. It also 
 follows that an increase of atomic volume is occasioned by an 
 increase in the length of the axis a. If we heat one of these 
 crystals the density decreases, the axis a must therefore 
 increase in length, whilst the angle E, becomes less obtuse. 
 This fact, indeed, was discovered by Mitscherlich, who found 
 that the specific gravity of calcspar decreased in the ratio 
 
 of 1 to - on being heated through 100. The specific 
 
 gravity of calcspar is 27220, when a = 0*8544 and K= 105 5'. 
 By heating it through 100, the sp. gr. becomes 2*7167, or its 
 atomic volume changes from 36*73 to 36*80. If we determine 
 the length of the axis a by means of the above formula, we 
 find it 0*85672, corresponding to an angle R of 104 57', or a 
 difference of 8', which closely agrees with that actually 
 observed by Mitscherlich (Philosophical Magazine [3], 18, 255). 
 Kopp's memoir, which gave to the specific gravity of a 
 solid and liquid substance a new and important significance, 
 attracted much attention and occasioned no little controversy. 
 Schroder (PoggendorfFs Anndlen, 553, (1840)), starting from 
 the observation of Ammermiiller, that equal volumes of the two 
 oxides of copper contain the same amounts of copper and 
 multiple amounts of oxygen, assumed that the volume of the 
 copper, as of the oxygen, is equal in the two substances, but 
 that the amount of the oxygen in the cuprous oxide stands to 
 
XI 
 
 Hermann Kopp 327 
 
 that in the cupric oxide as 1 to 2. Hence Schroder drew the 
 general conclusion that the same element can have different 
 specific volumes in different compounds, but that the several 
 values for the specific volumes stand in simple relations to 
 each other. He saw in this hypothesis not only an ex- 
 planation of the condensation which accompanies chemical 
 union, but also a rational basis for the belief that the volume 
 of a compound is equal to the sum of the volumes of its 
 components. 
 
 Schroder's ideas, to begin with, had something in common 
 with those of Kopp, but they underwent frequent modifi- 
 cations during the next thirty years. The characteristic 
 manner in which the two philosophers presented their views 
 was thus sketched by Berzelius : " Schroder is invariably of 
 opinion that he has discovered what is right : to his thinking, 
 the proofs he cites are evident ; he is always convinced and 
 insists that his reader is equally so. ... Kopp, on the other 
 hand, draws attention not only to that which supports a 
 statement, but also to that which is adverse to it. ... He 
 searches for truth, but he indicates, without reserve, what he 
 provisionally regards as only probable." (Quoted by Ostwald, 
 Stochiometrie, p. 620). 
 
 Kopp's conceptions on the subject at this time took more 
 formal shape in the small book he published in 1841, at 
 Frankfort, On the Specific Gravity of Chemical Compounds. A 
 summary of this work appeared in the Philosophical Magazine 
 for 1842, from which the following abstract in made : Kopp 
 points out that Schroder's contentions are weakened by the 
 great number of arbitrary assumptions on which they are 
 based. Schroder, in fact, would seem to forget that the pro- 
 bability of a theory becomes less in proportion as the number 
 of assumptions on which it is founded becomes greater. Kopp 
 believed that the state of knowledge at that time did not 
 enable a perfect and consistent theory to be framed ; all he 
 asserted was, that one may be proposed of which a measure of 
 
328 Hermann Kopp xi 
 
 its probability may be inferred from the fact that it explains 
 the greatest number of experimental facts by the fewest 
 possible assumptions. The atomic volume of a compound is 
 seldom equal to the sum of the atomic volumes of its elements 
 that is, the " primitive atomic volumes " calculated from the 
 specific gravity of the elements in the isolated state. If the 
 atomic volume of a compound is greater than the primitive 
 atomic volumes of either of its components, it is impossible, a 
 priori, to say whether one or both of the elements are con- 
 tained in it with an atomic volume different from the primitive 
 value ; but it is certain that one element in a compound does 
 not possess its primitive atomic volume if the atomic volume 
 of the compound is smaller than the primitive atomic volume 
 of that element. It is not as yet possible to state for every 
 compound which element enters into it with its primitive 
 atomic volume, or whether both acquire different ones. It is 
 only possible to infer this with any degree of probability in 
 the case of analogous compounds which have one element in 
 common. 
 
 Schroder found that if in a series of analogous bodies AO, 
 BO, CO, of which the specific volumes are known, we subtract 
 from these values the primitive atomic volumes of A, B, and 
 respectively, we obtain a constant remainder. This he 
 found to be the case with the oxides of lead, cadmium, and 
 zinc, and hence he inferred that the metal in these oxides 
 retains its primitive atomic volume. Kopp assumes that this 
 is equally true of the salts of the heavy metals, but with the 
 salts of the metals of the alkalis and alkaline earths, this is 
 impossible, as the specific volumes of the salts are, as a rule, 
 smaller than the primitive atomic volumes of the component 
 metals. He has consequently to assume for these metals a 
 specific atomic volume, which, however, remains the same in all 
 the salts. He determines these values as follows : Suppose 
 M -f E to be a compound of a heavy metal, m + R the 
 analogous compound of a light one; suppose A to be the 
 
xi Hermann Kopp 329 
 
 known specific volume of M + R, and a that of m + E, B the 
 primitive atomic volume of M, and b that of m. 
 
 Then, 
 
 M + R = A, 
 and 
 
 M = B. 
 
 Therefore the atomic volume with which R is contained in the 
 compound is A - B, say x. 
 
 It is assumed that R retains its value in m + R, 
 
 and since 
 
 ra + R = a, 
 and 
 
 therefore atomic volume of m (or b) = a - x. The specific 
 volume of CO in the carbonates is assumed to be 24 '2, whence 
 we have 
 
 PbC0 3 
 CdC0 3 
 FeC0 3 
 MnCOg . 
 
 Mol. vol. calc. 
 
 Sp. gr. calc. 
 
 Sp. gr. obs. 
 
 . 42-4 
 
 6-30 
 
 6'43 to 6-47 
 
 . 38-1 
 
 4-52 
 
 4-42 4-49 
 
 . 31-4 
 
 3-70 
 
 3-83 3-87 
 
 . 31-9 
 
 3-61 
 
 ,3-55 3-59 
 
 . 44-8 
 
 6-15 
 
 6-08 
 
 33-6 
 
 3-72 
 
 4-34 to 4-45 
 
 ZnC0 3 
 
 With the exception of ZnC0 3 , the observed and calculated 
 specific gravities are fairly concordant. 
 
 By means of the values for the alkalis and alkaline earths, 
 
 obtained as described, Kopp deduces the following specific 
 volumes and specific gravities : 
 
 Mol. vol. calc. Sp. gr. calc. Sp. gr. obs. 
 
 BaC0 3 . . 47-1 4-19 4'24 to 4'30 
 
 CaC0 3 . . 33-8 2'96 2'70 -300 
 
 K 2 C0 3 . . 61:6 2-25 2-26 
 
 MgC0 3 . . 30-6 2-75 2*61 
 
 Na 2 C0 3 . . 45-0 2'36 2'47 
 
 SrC0 3 . . 41-5 3-56 3-60 to 3'62 
 
330 Hermann Kopp 
 
 XI 
 
 The specific volume of N0 g is, in like manner, found to 
 be 28-6. 
 
 Mol. vol. calc. Sp. gr. calc. Sp. gr. obs. 
 
 Pb(N0 3 ) 2 . . 75-5 4'40 4-40 
 
 AgN0 3 . . . 78-1 4-36 4'36 
 
 NH 4 N0 3 . . 92-1 1-74 T74 
 
 Ba(N0 3 ) 2 . . 80-1 3-20 3-19 
 
 KN0 3 . . . 94-7 2-14 2'10 
 
 NaNO 3 . . 78-1 2-19 2'19 
 
 Sr(N0 3 ) 2 . . 77'6 2-84 2'89 
 
 In certain of the sulphates, the value of the group S0 4 
 appears to be 37 '8. 
 
 Sp. gr. calc. Sp. gr. obs. 
 
 CuS0 4 . . . 3-56 3-57 
 
 Ag 2 S0 4 . . .5-34 5-34 
 
 ZnS0 4 . . . 3-42 3'40 
 
 CaS0 4 . . . 2-90 2'93 
 
 MgSO 4 . . . 2-75 2-61 
 
 Na 2 S0 4 . . . 2-44 2-46 
 
 In other sulphates, however, the group S0 4 appears to have 
 the value 29-8. 
 
 Sp. gr. calc. Sp. gr. obs. 
 PbS0 4 . . . 6-32 6-30 
 
 BaS0 4 . . . 4-43 4-45 
 
 K 2 S0 4 . r ... . 2-60 2-62 
 
 SrS0 4 . . .3-90 3-95 
 
 In the chromates, O0 4 = 36 > 5; and in the tungstates, 
 39-0. 
 
 Calc. sp. gr. Sp. gr. obs. 
 
 PbCr0 4 . . .5-98 5-95 
 
 K 2 Cr0 4 . . . 2-69 2'64 
 
 PbW0 4 . . . 8-04 8-00 
 
 FeW0 4 . . . 6-67 7'10 
 
 CaW0 4 . . .6-05 6-0.4 
 
 01, like S0 4 , appears to have two distinct values, viz. 157 
 and 19-8. 
 
xi Hermann Kopp 331 
 
 
 Sp. gr. calc. 
 
 Sp. gr. obs. 
 
 PbCl 2 . 
 
 . 5-60 
 
 5-68 
 
 AgCf . 
 
 . 5-50 
 
 5-50 
 
 BaCl 2 . 
 
 . 3-83 
 
 3-86 
 
 NaCf 
 
 . 2-25 
 
 2-26 
 
 NH 4 C1 . 
 CaCl 2 . 
 
 . 1-44 
 . 2-29 
 
 1-45 
 
 2'27 
 
 KC1 
 
 . 1'94 
 
 1-94 
 
 CuCl 2 . 
 
 . 3'70 
 
 3-68 
 
 Hg 2 01 2 . 
 
 . 6-90 
 
 6-99 
 
 HgCl 2 . 
 
 . 5-05 
 
 5-14 
 
 SrCL 
 
 . 2-80 
 
 2-80 
 
 The density of many oxides may be calculated on the 
 assumption that the specific volume of O = 5'l. 
 
 Sp. gr. calc. Sp. gr. obs. 
 
 PbO . . . 9-55 9-50 
 
 CdO . . . 7'05 6-95 
 
 CuO . . . 6-53 6'43 
 
 MnO . . . 5-87 4'73 
 
 HgO . . . 10-9 11-00 
 
 ZnO . . .5-48 5'43 
 
 SnO . . . 6-28 6-67 
 
 Mo0 2 . . . 6-01 5'67 
 
 Ti0 2 . . . 4-16 4-18 
 
 Pb0 2 . . . 8'40 8'90 
 
 Sb 2 O 3 . . . 5-69 5-78 
 
 Pb 2 O 3 . . . 8-91 8-94 
 
 Fe 2 3 . . . 5-31 5-25 
 
 Co 2 3 . . .5-64 5'69 
 
 Fe 1 Oo 4-78 4-78 
 
 JL 1 J 
 
 Bi 2 O 3 . .' . 8-09 8-17 
 
 The agreement, with the exception of the cases of MnO, 
 SnO, Mo0 2 , and PbO 2 , is fairly good. 
 
 In other oxides, = 2'55, and in a third group 10'2, all the 
 values, it will be observed, being multiples of a common 
 number. 
 
 Sp. gr. calc. Sp. gr. obs. 
 
 Sb0 2 . . . 6-53 6-53 
 
 SnO 2 . . . 7-03 6-96 
 
 Cr 2 O 3 . . . 5-39 5-21 
 
33 2 Hermann Kopp 
 
 XI 
 
 
 Sp. gr. calc. 
 
 Sp. gr. obs. 
 
 Cu 2 
 
 . 5-87 
 
 5-75 
 
 Hg 2 
 
 ... . 10-5 
 
 10-69 
 
 Ag 2 
 
 . : .' . 7-48 
 
 7-25 
 
 MoO a 
 
 . . . 3-44 
 
 3-46 
 
 WO, 
 
 . 5-68 
 
 5-27 
 
 The specific gravity of a large number of the sulphides 
 may, in like manner, be calculated, with a similar degree of 
 approximation to the observed values, by assuming that 
 sulphur, like its analogue, oxygen, has three values, viz. 
 8-5, 15-0, and 17 '6. 
 
 Kopp also showed that the densities of the hydrated 
 oxides, and of a number of hydrated salts, may be calculated 
 with considerable accuracy by assuming certain definite values 
 for water in a state of combination. It ought to be stated, 
 however, in this connection, that subsequent researches have 
 indicated that Kopp's conclusions respecting the specific 
 volume of water of crystallisation must be slightly modified. 
 Schiff, many years ago, showed that the members of certain 
 classes of hydrated salts have practically the same specific 
 volume. Thus, all the alums have a specific volume of about 
 277 ; double sulphates of the form M 2 M" (S0 4 ) 2 .6H 2 0, have a 
 common volume of 207 ; and all the vitriols that is, salts of 
 the form M"S0 4 .7H 2 whether isomorphous or not, have the 
 specific volume 146. 
 
 Lord Playfair sought, many years ago, to determine the 
 precise relation of the specific volume of a salt to its degree 
 of hydration. This work, the natural sequence of the mem- 
 orable investigations which we owe to Playfair and Joule, 
 was first made known through the medium of a paper com- 
 municated to this Society by your lecturer and Mr. John I. 
 Watts ("On the Specific Volume of Water of Crystallisation," 
 Trans., 37, 102 (1880)). On learning that we were engaged 
 on this question, Lord Playfair placed the very ample notes of 
 the investigation, which he was not able to complete, at our 
 disposal, and although, at his suggestion, we went over the 
 
Hermann Kopp 333 
 
 whole of the ground again, much of the experimental matter 
 of our communication was based upon his previous observa- 
 tions. The main result of the inquiry was to show that the 
 volume occupied by the several molecules of water varies with 
 the degree of hydration of the salt. In the case of the so- 
 called magnesian sulphates, the first molecule of water, the 
 constitutional water, or " water of halhydration," of Graham, 
 occupies considerably less bulk than the remaining molecules ; 
 its mean relative value is 10*7. Each additional molecule 
 appears to occupy a gradually increasing volume. The differ- 
 ence between the monohydrate and dihydrate is 1 3 *3 ; between 
 the dihydrate and trihydrate it is 14*5; between the trihy- 
 drate and the tetrahydrate it is 15 '4 ; and between the hexhy- 
 drate and heptahydrate it is 16 '2. These observations are 
 so far in harmony with Kopp's general conclusions that in the 
 substances containing only a small number of water mole- 
 cules (1 to 3) the specific volume of the water is 12 -4; in 
 others containing a larger number (2 to 7) it is 13*4 ; whereas 
 in a third class, containing the largest number (from 3 to 10), 
 its mean value is 15*3. It need hardly be pointed out that 
 the main conclusion agrees with general experience. Chemical 
 combination results, as a rule, in contraction, and the stability 
 of the compound is connected with the degree of this contrac- 
 tion. Now, it is well known that the different molecules of 
 water in a hydrated salt are held with varying degrees of 
 tenacity, as shown by the different amounts of heat required 
 to expel them, and the different amounts, too, which are 
 evolved in the rehydration of the salt. 
 
 Kopp finally seeks to disprove the assumption of Schroder 
 that the specific volume with which an element is contained in 
 a compound bears a simple relation (^, -J J; -J, |; y, 
 |-f ) to its primitive specific volume, an assumption which 
 plays a not inconsiderable part in Schroder's subsequent 
 papers, and in those of Hermann (/. pr. Chem., 13, 28 (1876)) 
 and E. Wilson (Proc. Roy. Soc., 32, 457). 
 
334 Hermann Kopp 
 
 Kopp had hitherto mainly concerned himself with the 
 study of inorganic compounds, and for the most part with 
 solid substances. He next turned to the consideration of 
 organic bodies, and in his papers of 1842, on the " Vorausbe- 
 stimmung einiger physikalischen Eigenschaften bei mehreren 
 Reihen organischer Verbindungen " (Annalen, 41, 79 ; ibid., 
 41, 169), we have the first of a series of memoirs, on which 
 his fame as an observer will ultimately rest. For his pur- 
 pose, the study of organic compounds presented many features 
 of importance. In the first place, the variety of elements 
 which enter into the composition of organic compounds is 
 much smaller than in inorganic substances ; and in the second, 
 there are more liquid substances and a wider range in the 
 mode of combination among the compounds of carbon than of 
 any other element. These liquids, too, may for the most 
 part be easily obtained of a sufficient degree of purity ; they 
 are readily characterised, and the determination of their 
 specific gravity can be made with a higher degree of pre- 
 cision than in the case of solids. On the other hand, liquids 
 are more expansible by heat than solids, and the question of 
 the conditions under which specific volumes are comparable 
 becomes of much greater importance in the one case than in 
 the other. The main conclusion of this paper may be stated 
 as follows : If we imagine a number of analogous organic 
 compounds arranged under the following scheme : 
 
 A + a B + a C + o, D + a, .... 
 
 A + J3 B + /2 C + /3 
 
 A + 7 B + y C + 7 
 
 B + 5 C + 8 
 
 where A, B, C, D, a, /3, 7, S, are certain bodies or combina- 
 tions of elements, then it is only necessary to become acquainted 
 with one horizontal and one vertical series to know the most import- 
 
XI 
 
 Hermann Kopp 335 
 
 ant physical properties of all the combinations contained in such a 
 table. If the properties' of the compounds contained in one hori- 
 zontal or in one vertical series are known the mere knowledge of one 
 of these compounds is sufficient in order to ascertain the properties 
 of all the compounds arranged in any other horizontal or vertical 
 series. 
 
 If the specific volumes and the boiling points of the com- 
 pound A + a, A + /3, A + 7, etc., are known, and we also know 
 the specific gravity and boiling point of B -f- a, we can at once 
 ascertain the specific gravities and boiling points of the bodies 
 B -f /3, B + 7, B + 8. For between the specific volumes and 
 boiling points of 
 
 A + a and B + a 
 A + ft and B + /3 
 A + y and B + y 
 etc. 
 
 B + a and D + a 
 B + /3andD + 
 B + y and D + y 
 etc. 
 
 A + a and A + 8, 
 B + a and B + 8, 
 C + 8 and C + 3, 
 etc. 
 
 the differences are the same. 
 
 A similar regularity occurs in the physical properties in 
 cases of substitution, as, for example, that of chlorine for 
 hydrogen. Let A represent a combination of oxygen and 
 carbon which remains unaltered, a hydrogen, ft chlorine, m, ft, 
 x, y numbers ; we have then 
 
 A + ma + nf3, 
 
 A + (m-x)a+.(n + x)/3, 
 -y)a + (m + y)j3. 
 
 The sum of the atoms a and /3 remains the same in each 
 compound. If in any compound x atoms of hydrogen are 
 replaced by x atoms of chlorine, the specific volume of the 
 new compound is increased by x. 12*5 (approximately). 
 
 The numerical basis upon which these generalisations rest 
 was undoubtedly affected by the fact that Kopp at this period 
 was unable to determine the precise conditions under which 
 the comparisons of specific volume are valid; indeed, he is 
 
336 Hermann Kopp 
 
 XI 
 
 disposed to recognise in this circumstance the chief ground 
 for the differences between the observed and theoretical values. 
 But, in reality, the nature of the experimental material itself 
 was hardly sufficient to afford absolute proof that Kopp's laws 
 were capable of the mathematical precision with which he 
 stated them. This fact was, indeed, recognised by Liebig in 
 a note which he appended to Kopp's paper in the Annalen, and 
 in which he called upon his fellow-workers to give increased 
 attention to the ascertainment of those physical constants 
 which serve to distinguish a chemical compound. Kopp's 
 generalisations were undoubtedly first approximations to the 
 expression of physical truths, but the limits of their applica- 
 tion could only be determined by fuller and more accurate 
 data, and by a clearer conception of the conditions under 
 which the comparisons should be made. 
 
 In Kopp's next memoir, "Ueber den Zusammenhang 
 zwischen der chemischen Constitution und einigen physikal- 
 ischen Eigenschaften bei fliissigen Verbindungen " (Annalen, 
 50, 71, (1844)), this last problem is more particularly attacked. 
 The specific volumes of liquids are obviously dependent on 
 heat ; hence they may be said to be comparable at temperatures 
 at which heat exercises the same effect upon the liquids, say 
 at their boiling points, or, in general, at temperatures at which 
 their vapour pressures are equal. Fifty years ago, however, 
 the vapour pressures of but three liquids were known, and 
 these only with approximate accuracy, viz. water, alcohol, 
 and ether ; and hence, since Kopp assumed that the specific 
 volume of alcohol was the sum of the specific volumes of water 
 and ether, there were only two equations possible to determine 
 the three unknown values of 0, H, and at all temperatures 
 below the boiling points. On the assumption which observa- 
 tion showed to be probable that one atom of oxygen can 
 replace two atoms of hydrogen in a compound without 
 sensible alteration in specific volume, that the comparison 
 may be made at equal distances of temperature from the 
 
Hermann Kopp 337 
 
 boiling point instead of at the temperature of equal vapour 
 pressures, and that the elements in combination have the same 
 inherent expansibility, or, in other words, that the relation 
 between the specific volumes of (C), (0), and (H) in a com- 
 pound is the same at all distances from the boiling point, 
 Kopp was able to deduce values for C, H, and O which 
 enabled the specific gravity of a liquid consisting of these 
 elements to be calculated at any temperature below its boiling 
 point with a certain approximation to accuracy. He found 
 that the specific volume of a liquid compound, consisting of 
 (a) atoms of carbon; (b) atoms of hydrogen; (c) atoms of 
 oxygen ; (d) atoms of chlorine ; (e) atoms of nitrogen ; and 
 (/) atoms of sulphur, is, for a temperature distant D from its 
 boiling point, approximately expressed by 
 
 (l-28a + 0-486 + O96c + 2'34d + T44e + 2'4/) x (9'75 - O'OID). 1 
 
 Kopp warns his reader that this formula has no other value 
 than as expressing the specific volume, and, indirectly, the 
 specific gravity, of a liquid consisting of the above-named 
 elements, with, on the whole, a fair degree of accuracy. He 
 is careful to point out that it rests on assumptions for which 
 definite experimental evidence is, in great measure, wanting. 
 If both the form of the formula and the values of its con- 
 stants were accurate, it would be possible to infer the boiling 
 point of a liquid from a knowledge of its composition and its 
 specific gravity. It would also follow, from the nature of the 
 formula, that the contraction which a liquid experiences on 
 cooling through X from its boiling point was invariably pro- 
 portional to X ; whereas observation shows that the con- 
 traction for a given temperature interval becomes smaller 
 and smaller as the distance from the boiling point increases. 
 Moreover, it assumes that two liquids, having the same 
 
 1 The values were originally calculated on the basis of Berzelius's atomic 
 weights ; they have been transformed to the corresponding values when 
 H = l. 
 
338 Hermann Kopp 
 
 volume at the boiling point, must necessarily possess the 
 same volume at D from the boiling point, which is also 
 contrary to experience. 
 
 Kopp ventured to conclude, then, that in all probability 
 
 1. Equal differences in composition corresponded with 
 
 equal differences in specific volume. 
 
 2. Equivalent amounts of oxygen and hydrogen in liquid 
 
 compounds occupy nearly the same volume. 
 
 3. The specific volume of a compound is equal to the sum 
 
 of the specific volumes of its components. The same 
 element almost invariably preserves the same specific 
 volume. Isomeric compounds have the same specific 
 volume ; polymeric compounds have specific volumes 
 which stand to one another in the same relation as 
 the molecular weights of the compounds. Variations 
 in the chemical constitution of isomeric compounds 
 are without effect on their specific volume. 
 
 4. Comparisons of specific volumes of liquids are only valid 
 
 at temperatures at which the vapour pressures of the 
 liquids are equal. 
 
 These conclusions, as Kopp clearly recognised, rested on no 
 very firm experimental basis; the necessary data, indeed, 
 were not to hand to test them rigorously. Accordingly, he 
 resolved to make accurate determinations of all the physical 
 constants needed to ascertain, with the highest possible pre- 
 cision, the specific volumes of a large number of liquids. 
 
 In 1855 Kopp published the first of the series of memoirs 
 in which he gave the results of his ten years' experimental 
 labours. These memoirs are, without doubt, the most re- 
 markable and most characteristic of his scientific papers. 
 They exhibit in a striking degree all the attributes of a 
 successful investigator ingenuity, manipulative skill, a rigid 
 sense of accuracy, illimitable patience, insight, and inductive 
 power. 
 
XI 
 
 Hermann Kopp 339 
 
 His main conclusions may thus be summarised : 
 
 1. The selection of the temperature of equal vapour tension 
 
 as a basis of comparison seemed to be warranted by 
 the fact that regularities are thereby made evident 
 which otherwise are not apparent. 
 
 2. Differences of specific volume are proportional to differ- 
 
 ences in chemical composition. 
 
 3. Isomeric liquids of the same chemical type have equal 
 
 specific volumes. 
 
 4. The substitution of hydrogen for an equivalent amount 
 
 of oxygen only slightly affects the specific volume. 
 
 5. One atom of carbon can replace two atoms of hydrogen 
 
 without alteration in specific volume. 
 
 It was further shown that the specific volume of a liquid 
 was determined, not only by its composition, but also by its 
 constitution. Kopp found, for example, that the relative 
 position of the oxygen atom in a molecule affected its specific 
 volume ; carbonyl-oxygen and hydroxyl-oxygen have two very 
 different values. Sulphur, in like manner, would appear to 
 have two specific volumes, depending upon its position or 
 mode of combination in a molecule. 
 
 Definite values for the specific volumes of carbon, hydrogen, 
 and oxygen were obtained from the following considerations : 
 An increment of CH 2 corresponds to an increase of specific 
 volume of 22. Since C and H 2 occupy the same volume, we 
 have C = 11 and H = 5*5. The replacement of H 2 by carbonyl 
 O is attended by a slight increase in the specific volume. 
 Kopp found that the most probable value for this form of 
 oxygen was 12*2. For hydroxyl-oxygen it is 7 '8, obtained by 
 subtracting the value for H 2 (11) from the specific volume 
 of water, 18*8. Hence the specific volume of a compound 
 C ft H & O c O' tZ , where is carbonyl-oxygen and 0' hydroxyl- 
 oxygen, may be expressed by the formula 
 
340 Hermann Kopp 
 
 XI 
 
 which gives results in no case varying more than 4 per cent 
 from the observed value, and, in the great majority of cases, 
 much less. 
 
 Determinate values for the halogens, and, with less pre- 
 cision, for phosphorus, arsenic and antimony, silicon, titanium, 
 and tin, were also obtained. As regards nitrogen it was 
 found that in the amines N = 2'3. The group CN = 28 ; 
 that of N0 2 =33. If, then, carbon and oxygen preserved 
 their ordinary values in these radicles, X must possess at least 
 three different values depending on the mode of combination. 
 There is, however, no evidence to disprove the supposition 
 that the values for the carbon and oxygen atoms are not equally 
 affected in these groups. This, indeed, suggests the possibility 
 that compound radicles like CO, HO, N0 2 , CN, etc., may 
 possess definite specific volumes which are not necessarily the 
 sum of the specific volumes of the component atoms as 
 ordinarily ascertained. 
 
 It remains to indicate how far these conclusions have stood 
 the test of criticism and subsequent research, especially when 
 viewed from the standpoint of modern dynamics and in the 
 light of our present conceptions concerning constitution. In 
 1865 H. L. Buff (Annalen, 4, (Suppl.), 129) sought to 
 show that the specific volume of carbon, like that of oxygen 
 and sulphur, is affected by its mode of combination or, in 
 other words, that carbon in unsaturated compounds has a 
 greater specific volume than in saturated bodies ; from which 
 he surmised that the specific volume of an element is in general 
 determined by its particular atomic value. With this ex- 
 ception, the subject received practically no further experi- 
 mental treatment until about 1880, when a number of papers 
 followed each other in rapid succession. Only the briefest 
 summary is here possible. It was found that isomeric liquids 
 have not invariably the same specific volume. Between 
 ethylene and ethidene chlorides, for example, there is a greater 
 difference than 4 per cent; indeed, ethylene compounds in 
 
XI 
 
 Hermann Kopp 341 
 
 general appear to have smaller volumes than those calculated 
 by Kopp's values. Stadel further showed that in the series 
 of the chlorinated and brominated ethanes and ethylenes, the 
 isomer of higher boiling point, i.e., the ethylene derivative, 
 has invariably the lower specific volume. Since these com- 
 pounds are all saturated and the only variable constituent is a 
 monovalent element (Cl or Br), it would appear probable that 
 the specific volume of the halogen is also variable. Isomeric 
 hydrocarbons manifest similar differences, whence it is obvious 
 that either one or both of the elements must have a slightly 
 variable volume, depending on grouping or mode of com- 
 bination; it may be that the iso- group, like the groups 
 carbonyl, hydroxyl, nitryl, etc., has a special volume, which is 
 not necessarily the sum of the volumes of the component 
 atoms as deduced from Kopp's values. Kopp himself found 
 that the volumes of isomers were, in a number of cases, only 
 approximately equal, and in others quite unequal. The term 
 " chemical type," used in the sense in which Gerhard t employs 
 it, is not sufficiently distinctive to denote the differences, say, 
 between the normal and iso-compounds, or between aniline 
 and picoline, and it is questionable whether Kopp would have 
 considered such cases as coming within his rule. 
 
 The observed specific volumes of the aromatic compounds, 
 also, are frequently lower than the calculated values. Indeed, 
 our views as to the constitution of the aromatic compounds 
 would lead us to expect that the specific volume of benzene 
 (and the derivatives in which the benzene group functions) 
 would probably be different from that deduced from observa- 
 tions made, for the most part, on compounds of totally 
 different constitution. Kopp (Annalen (Suppl.), 5, 303, (1867)) 
 showed from Louguinine's observations that whilst benzene 
 has an abnormally low specific volume, its homologues show 
 the constant increase of 22 for an increment of CH 2 , which 
 is what might be anticipated, since these bodies are produced 
 by the addition (substitution) of methyl, ethyl, etc., to the 
 
34 2 Hermann Kopp 
 
 XI 
 
 benzene group. Jungflei sen's observations on the specific 
 volumes of the chlorine substitution products of benzene also 
 seem to show that the positions of the chlorine atoms affect, 
 in a very marked manner, the specific volume of the product 
 (Compt. rend., 64, 911). Further observation has shown that 
 Kopp's conclusion, that liquid elements and radicles have the 
 same volume in combination as in the free state, is well 
 founded. Thus the observed volume of N0 9 = 32'0 calculated, 
 31-5 ; observed volume of Br = 53'6 calculated, 53'4 ; observed 
 volume of CN = 28'9 calculated, 28'9. The observed specific 
 volume of Cl from Knietsch's careful determinations of the 
 specific gravity of liquid chlorine is 22*8 ; the mean calculated 
 value is 22*7. Kopp surmised that members of the same 
 chemical family would be found to have the same specific 
 volume ; observation shows, however, that the specific volumes 
 gradually increase with the increase of atomic mass. 1 
 
 Thanks to Roberto Schiff, Lothar Meyer, and his pupils, and 
 especially to Lossen and his pupils, a very large amount of 
 experimental material has been accumulated during the last 
 ten years, from which important deductions may be drawn as 
 to the general validity and limitations of Kopp's conclusions. 
 Schiff (Annalen, 220, 71, (1883)), by means of an improved 
 form of an apparatus first suggested by Ramsay (Trans., 1879, 
 35, 463), concluded that whilst it is generally true that 
 isomeric compounds have slightly different specific volumes, it 
 is almost invariably the case that the substance possessing the 
 higher boiling point has also the higher specific volume (com- 
 pare Stadel). In the case of the metameric esters of the fatty 
 acids, it is found that, as a rule, the specific volumes increase 
 with the diminution of the number of carbon atoms in the 
 acid radicle and with the increase in the alcohol radicle. At 
 the same time it would appear that the differences between 
 
 1 Thorpe : " On the Relation between the Molecular Weights of Substances 
 and their Specific Gravities when in the Liquid State," Trans., 1880, 
 37, 141 ; ibid., 327. 
 
XI 
 
 Hermann Kopp 343 
 
 the observed and calculated values are mainly due to the 
 alcohol, the acid apparently having but slight influence. This 
 is in conformity with Lossen's observations, that whilst the 
 ethers and acids give experimental values which are almost 
 in exact accordance with Kopp's values, the aldehydes and 
 alcohols show wider variations, methyl alcohol giving too 
 great an observed value, whilst the others give smaller and 
 smaller values as the amount of carbon increases. It is, how- 
 ever, noteworthy that the differences between the aldehydes 
 and derived alcohols remain almost constant, which is not the 
 case with the aldehydes and acids, where it appears to increase 
 with the molecular weight. Hence the differences between 
 the homologous aldehydes are very nearly equal to those 
 between the corresponding homologous alcohols (Lossen). 
 The mode in which carbon is combined in an organic com- 
 pound has, according to Schiff, a distinct influence on its 
 specific volume ; like Buff, he finds that double-linked carbon 
 occupies a smaller volume than when single-linked. It is, 
 however, very doubtful whether the facts at present known 
 are sufficient to establish this conclusion. 
 
 The examination of the very large quantity of experi- 
 mental material which is now before us forces us to the con- 
 clusion that molecular volume is not a purely additive property. 
 There is no longer room for doubt that the molecular volumes 
 of substances are affected by far more conditions than we 
 have hitherto taken cognisance of. The value CH 2 = 22 has 
 no other significance than as expressing the average increment 
 in volume in successive members of a homologous series. 
 Indeed, as the physical data increase, it becomes doubtful 
 whether even this mean value is correct. Later observations 
 appear to show that the value augments as the series is 
 ascended. The relation C = 2H no longer applies to carbon 
 compounds in general. What is true of carbon and hydrogen 
 is equally true of oxygen, whether as carbonyl- or as hydroxyl- 
 oxygen. No definite or uniform values can be assigned to 
 
344 Hermann Kopp xi 
 
 oxygen such that the molecular volume of a liquid can be a 
 priori determined. The values given by Kopp are simply 
 mean values, but the actual volumes are affected by conditions 
 of which, as yet, we have no very precise knowledge or any 
 certain means of measuring. The values for the other 
 elements are, of course, affected by these considerations. 
 Thus the specific volume of chlorine is obtained on the 
 assumption that the values for carbon and hydrogen are con- 
 stant. All, then, tends to show that the molecular volume 
 is not the sum of constant atomic volumes. 
 
 Lossen has attempted, and with considerable success, to 
 devise formulae which shall take note, or express the measure, 
 of the influences which affect the uniformity in the values of 
 specific volumes in organic compounds (Annalen, 254, 42). 
 These formula, as yet, can only be considered as first 
 approximations, but their value will be evident from the fact 
 that they serve to reproduce the observed values with a 
 greater approach to accuracy than has hitherto been possible. 
 Out of the 407 compounds which constituted the experi- 
 mental material on which these formulae are based, the 
 observed molecular volumes of 352 differ by less than 2 per 
 cent from the calculated volumes. Comparatively few of 
 these differences may be ascribed to experimental errors. In 
 the main, they are caused by influences of structure and com- 
 position which, as yet, we have no certain means of measuring, 
 such as the effect of substituted chlorine, or the special effect 
 of the iso-group, or of the ortho-, meta-, or para-position, etc. 
 
 No summary of the present state of our knowledge respect- 
 ing this question would be complete without some reference 
 to Schroder's later views. For nearly fifty years Schroder 
 laboured unremittingly to throw light on the connection 
 between volume and molecular weight, and the final form of 
 his theory is too suggestive to be passed over in silence. 
 Schroder regards the atomic volume of an element in com- 
 bination as variable within limits determined by the nature 
 
XI 
 
 Hermann Kopp 345 
 
 of the chemical compound. In any one compound, however, 
 all the elementary atoms occupy either equal or multiple 
 volumes. Hence every molecular volume is a multiple of a 
 certain space-unit or stere, the value of which may vary 
 between 6 -7 and 7*4, depending on the number, nature, and 
 mode of union of the atoms. Ostwald, to whom I am 
 indebted for this presentation of Schroder's argument, thus 
 explains how Schroder obtains his determinate relations. The 
 molecular volumes of formic, acetic, and propionic acids 
 increase about 22 units for each increment of CH in the 
 case of alcohols the increase is about 20 units. The volume 
 of formic acid is 41 '8 that is, 2 X 20 '9 ; that of methyl alcohol 
 is 42 -7 or 2 x 21-4. Hence it follows that in formic acid, 
 CH 2 2 , the 2 occupies the same volume as CH 2 ; and in 
 methyl alcohol, CH 9 0, the H 2 has the same volume as CH 9 . 
 In like manner, ethyl alcohol, C 9 H fi O, has the volume 62*2 
 that is, 3x20-7. Since 2 xCH 2 = 2x20-7, then H 2 = 20'7. 
 Acetic acid has the volume 63*5 that is, 3x21-2; 2CH is 
 2x21-2 and 2 = 212. The volume of acetaldehyde is 56-9 
 that is, about 6*6 smaller than that of acetic acid; this would 
 indicate that the substitution of OH by H lowers the volume 
 by 6-6. Since H 2 = 21'4, it follows that the hydrogen and 
 oxygen in hydroxyl each occupy one space-unit or stere. As 
 CH 2 = 21, we find that carbon also occupies one stere or space- 
 unit. Now from the volume of formic acid, which contains 
 6 steres, it is found on subtracting 3 steres for CH., and 1 
 stere for hydroxyl-oxygen, that the carbonyl-oxygen must 
 occupy 2 steres. 
 
 We obtain then the following rule : The number of space- 
 units or steres of the saturated compounds of carbon, hydrogen, and 
 oxygen corresponds to the number of the atoms, increased by as 
 many units as there are atoms of carbonyl-oxygen present. 
 
 If we calculate, by means of this rule, the steres' of the 
 saturated compounds, we find that they vary within narrow 
 limits, and for the most part increase with m&coaoing 
 
 ^r 
 
 UNIVERSITY 
 
346 Hermann Kopp 
 
 XI 
 
 cular weight. In the greater number of cases, the values 
 range between 6 '9 and 7 '2. Ostwald has calculated the value 
 of the stere for a large number of aliphatic compounds with 
 the following results : 
 
 Hydrocarbons, 6'89 ; 6'99 ; 6'82 ; 7'11 ; 7'23. 
 
 Alcohols, 7-12 ; 6'91 ; 6'77 ; 6'88 ; 6'78 ; 6'78 ; 6'81 ; 6'74; 
 
 7-09. 
 
 Acids, 6-97 ; 7'06 ; I'll ; 7'19 ; 7'24 ; 7'24; 6'85. 
 Esters, 7 '04 ; 7'08 ; 7'05 ; 7'14 ; 7*26 ; 7'43 ; 7'45 ; 7'47. 
 Aldehydes, 7'11 ; 7'05 ; 7-18 ; 7'01 ; 7-18 ; 6'93; 7'27. 
 
 In the series of the hydrocarbons, the acids, and the esters, 
 the steres, in the case of the normal compounds, increase 
 regularly with increasing molecular weight ; in that of the 
 alcohols they decrease up to the third member and then 
 increase. The secondary and tertiary compounds, have, as a 
 rule, smaller steres than the normal compounds. It is in- 
 structive to note the different manner in which Kopp and 
 Schroder arrived at the volume relations of these elements. 
 Kopp concluded from the approximately equal volumes of the 
 alcohols and corresponding acids, that H 2 and are volumet- 
 rically equivalent ; and from the equivalence of the volumes 
 of benzyl and amyl compounds he inferred that C 2 and H 4 are 
 mutually replaceable without alteration of volume ; hence 
 he assumed that the hydrogen atom occupies only half the 
 volume of the oxygen or carbon atom. Schroder establishes 
 the volume equivalence of CH 9 , HOH, and O'O, and he in- 
 ferred from the difference in volume between alcohol and 
 aldehyde that hydroxyl oxygen has the same volume as 
 hydrogen and carbon, whilst carbonyl-oxygen has twice the 
 volume. Whilst then Kopp assumes (approximately) H 9 = C 
 = 0, Schroder makes H = C = 0. 
 
 In the case of unsaturated and aromatic compounds, 
 Schroder assumes that each double linkage is attended with 
 an increase of volume amounting to one stere ; hence the fore- 
 going rule has to be modified in this sense when applied to 
 
XI 
 
 Hermann Kopp 347 
 
 compounds of this class. The value of the stere in a number 
 of unsaturated compounds is found to be 
 
 Hydrocarbons, 6'87 ; 7'09 ; 6-93 ; 6'99. 
 
 Alcohols, 6-72. 
 
 Esters and ethers, 7 '14 ; 7 '13. 
 
 The values vary, practically, within the same limits as in 
 the aliphatic compounds. 
 
 As regards aromatic compounds, it would seem to follow, 
 from the identity in the volumes of benzoyl and amyl com- 
 pounds, as indicated by Kopp, as well as from the corre- 
 sponding relation between the isobutyl and phenyl compounds, 
 that C 6 H 5 comprises the same number of steres as C 4 H 9 that 
 is, 13. Of these, 5 are occupied by hydrogen; so that the 
 carbon group C 6 occupies 8 steres. 
 
 The values of the stere in a number of aromatic compounds 
 are as follows : 
 
 Hydrocarbons, 6'85 ; 6'94 ; 6'98 ; 7 -00 ; 6*95 ; 7'04 ; 7'04 ; 
 
 7-04 ; 7'06 ; 6'84. 
 Other compounds, 6'91 ; 6'87 ; 7'05; 6'97 ; 7'16 ; 7'26 ; 
 
 7'50; 7-28; 7'14 ; 6'96 ; 7'07. 
 
 The value of the stere here also varies within the usual 
 limits; it is comparatively small for the hydrocarbons (6 '8 
 7'0), larger in the case of the alcohols, and still larger in that 
 of the esters (7 '2 7*5). These relations, if substantiated, 
 would seem to indicate that the law of volumetric combina- 
 tion among the masses of liquid molecules is essentially not 
 more complex than the law of combination between those of 
 gaseous molecules. 
 
 There is one consideration which is vital to the whole 
 question, and to which, therefore, a brief reference must be 
 made. It relates to the choice of conditions under which the 
 values we term molecular or specific volumes are really com- 
 parable. Although Horstmann and Lossen have advanced 
 
348 Hermann Kopp 
 
 XI 
 
 reasons against the practice, contending that at any other tem- 
 perature, say 0, relations similar to those now established are 
 made manifest, it has been the custom, in accordance with 
 Kopp's direction, to compare the specific volumes of liquids at 
 the temperatures of their respective boiling points under a 
 standard atmosphere. Whether, however, the temperature of 
 the boiling point, under these circumstances, is a truly com- 
 parable condition is open to question. It has been urged by 
 Horstmann that, since what we call atomic volume is the 
 space not merely filled by an atom, but also that in which " it 
 moves, and lives, and has its being," it is not a priori probable 
 that a temperature which differs, say, by 300, as, for example 
 in the case of C 4 H 1Q (boiling point 1) and C lg H 38 (boiling 
 point 317), these volumes will be the same. Moreover, as 
 pointed out by Bartoli, the boiling point cannot, in the nature 
 of things, be a strictly comparable condition, since it is affected 
 by pressure to a different extent in the case of different 
 liquids. Objections of even greater weight may be urged 
 against the suggestions of Tschermak and Krafft, to take the 
 melting point as a comparable state. 
 
 No doubt, theoretically speaking, a valid condition should 
 be when pressure, volume, and temperature are expressed in 
 terms of their critical values. But that certain regularities in 
 the molecular volumes at the boiling points have, in spite of 
 this, been discovered, may be explained, as Guldberg has 
 shown, when we compare the values of T I} the absolute boil- 
 ing point, with those of T, the absolute critical temperature ; 
 in those cases in which these two constants are known, the 
 ratio T/Tj approximates to f . Hence it follows that qualities 
 like molecular volumes, which alter only slowly with tempera- 
 ture, are comparable at the ordinary boiling points (Zeits. fur. 
 PhysiM Chem., 5, 374). 
 
 It ought, perhaps, to be stated that subsequent observa- 
 tions show that the so-called "corresponding temperatures" 
 deduced from Van der Waal's generalisations have not that 
 
XI 
 
 Hermann Kopp 349 
 
 degree of validity as temperatures of comparison which they 
 were originally assumed to possess. Indeed, the present con- 
 dition of knowledge warrants the statement that Kopp's 
 original method of comparison is as valuable as any yet 
 indicated. 
 
 Kopp continued to the last to interest himself in the 
 problem which had been the mainspring of his scientific 
 activity. Shortly before his death he gave to the world, 
 through the Annalen (250, 1889, 1), a critical account, written 
 with the dignity and calm that befits the well-earned leisure 
 of a veteran controversialist, of the many strivings which had 
 been made to solve it since the tentative efforts he put forth 
 in his thesis of 1838. 
 
 We rise from the perusal of this memoir with the convic- 
 tion that, after all, the work thus summarised takes us but 
 little beyond the threshold of the fundamental truth of which 
 its author was the first to perceive the indication. 
 
 As yet we see through a glass darkly, and know only in 
 part ; but with the fuller light of a rapidly advancing know- 
 ledge, we shall most certainly get an insight into the causes 
 which affect the universality of Kopp's conclusions. The dis- 
 crepancies, if we could only read them aright, contain within 
 them the clues to a broader generalisation which will more 
 clearly connect the chemical nature of molecules with their 
 physical attributes. Our experimental material will soon be 
 sufficient for the basis of this generalisation, even if it is not 
 so already. What is wanted is another Kopp to interpret it 
 correctly. 
 
XII 
 
 DMITRI IVANOWITSH MENDELEEFF 
 
 "SCIENTIFIC WORTHIES," No. XXVI. NATURE, 27ra JUNE 1889. 
 
 DMITRI IVANOWITSH MENDELEEFF was born on 7th February 
 (N.S.), 1834, at Tobolsk, in Siberia. He was the seventeenth 
 and youngest child of Ivan Paolowitsh Mendeleeff, Director of 
 the Gymnasium at that place. Soon after the birth of Dmitri 
 his father became blind, and was obliged to resign his position, 
 and the family became practically dependent upon the mother, 
 Maria Dmitrievna Mendeleeva a woman of great energy and 
 remarkable force of character. She established a glass-works 
 at Tobolsk, the management of which for many years de- 
 volved entirely upon her, and on the profits of which she 
 brought up and educated her large family. The story of 
 Mendeleeff's youth is given in the preface to his great work 
 On Solutions, which he dedicated to the memory of his 
 mother in a passage of singular beauty and power. Having 
 passed through the Gymnasium at Tobolsk, Mendeleeff, at the 
 age of sixteen, was sent to St. Petersburg, with the intention 
 that he should study chemistry at the University, under Zinin. 
 He was, however, transferred to the Pedagogical Institute, the 
 aim of which was to train teachers for the District or Govern- 
 mental Gymnasiums throughout the Empire. The Institute 
 (which was abolished in 1858) was established in the same 
 building as the University, and was divided into two Faculties 
 
xii Dmitri Ivanoivitsh Mendeleeff 3 5 1 
 
 Historico - philological and Physico - mathematical. Men- 
 deleeff attached himself to the natural sciences, and thus came 
 under the influence of Woskresenky in chemistry, of Emil 
 Lenz in physics, of Ostrogradsky in mathematics, of Ruprecht 
 in botany, of F. Brandt in zoology, of Kutorga in mineralogy, 
 and of Sawitsh in astronomy, most of whom were professors 
 of the same sciences in the University. Whilst at the Institute 
 he wrote his first paper on " Isomorphism," and on the termina- 
 tion of his course of instruction he was appointed to the 
 Gymnasium at Simferopol, in the Crimea. During the 
 Crimean war he was transferred to one of the Gymnasiums at 
 Odessa, and in 1856 he was admitted to the degree of Magister 
 ChemicB of the Physico-mathematical Faculty of the University 
 of St. Petersburg, and was made Privat-Docent in the University. 
 Even at this early period of his career we find Mendeleeff 
 speculating on the great problems with which his name is 
 inseparably connected. The relations between the specific 
 gravities of substances and their molecular weights had begun 
 to attract increased attention. Kopp had just published the 
 first instalment of that long and laborious series of experi- 
 mental observations which constitutes the real foundation of 
 all our knowledge concerning the specific volumes of liquids, 
 when the young Siberian philosopher laid a number of theses 
 on problems relating to specific volumes before the Physico- 
 mathematical Faculty of the University. He pointed out 
 that magnetic elements have smaller specific volumes than 
 diamagnetic elements. He also showed that Avogadro's 
 supposition, that electro-positive elements have larger specific 
 volumes than electro -negative elements, was in accordance 
 with the greater number of well-established facts. When we 
 remember how slowly, in spite of the powerful advocacy of 
 Williamson, the ideas of Laurent and Gerhardt, and what came 
 to be known as the modern French school, found favour in 
 this country, it is remarkable, as indicating the radical and 
 progressive character of his mind, and the keenness of his 
 
35 2 Dmitri Ivanowitsk Mendeleeff xn 
 
 mental vision, to find Mendeleeff, as far back as 1856, insisting 
 that to Gerhardt was due the best mode of determining the 
 chemical molecule ; that the molecule of oxygen was expressed 
 by the symbol O 2 ; those of arsenic and phosphorous by As 
 
 p TT -v 
 
 and P 4 respectively ; that of alcohol by -^~ j- ; and that 
 
 of ether by 
 
 TT "V 
 
 \ 0. 
 
 2 H 5 ) 
 
 MendeleefFs researches on specific volumes were begun 
 in 1855, and were continued, with intermissions, down to 
 1870; but part only of the work has been published. In 
 1859 he obtained permission from the Minister of Public 
 Instruction to travel, and repaired to Heidelberg, where he 
 established a small private laboratory, and occupied himself 
 with the determination of the physical constants of chemical 
 compounds. He returned home in 1861, and in 1863 was 
 named Professor of Chemistry at the Technological Institute 
 of St. Petersburg. In 1866 he became Professor of Chemistry 
 at the University, and was made Doctor of Chemistry after a 
 public defence of his dissertation " On the Combinations of 
 Water with Alcohol." He is now Emeritus Professor, and 
 until recently delivered lectures on general chemistry. 
 
 Mendeleeff is so prolific a writer that it is impossible within 
 the limits of an article of this kind to do justice to his work. 
 There is, in fact, no section of chemical science which he has 
 not enriched by his contributions. Some of his earliest work 
 related to questions of mineralogy and chemical geology ; and 
 at times, as in his papers on (Enanthol- Sulphurous Acid, on 
 Fermentation Propyl Alcohol, and on the Nitriles, he culti- 
 vated the rapidly extending domain of organic chemistry. 
 But his reputation mainly rests upon his contributions to 
 physical chemistry and to chemical philosophy. In his papers 
 on Specific Volumes he extends Kopp's generalisations, and 
 traces the specific volumes of substances through various 
 phases of chemical change. He shows that in the thermal 
 
xii Dmitri Ivanowitsh Mendeleeff 353 
 
 expansion of homologous liquids the expansion - coefficient 
 diminishes in a regular manner as the series is ascended, and 
 he indicates the intimate connection which exists between ex- 
 pansion and cohesion in the case of liquids, and the role played 
 by molecular cohesion in the determination of chemical 
 activity. His paper on the thermal expansion of liquids above 
 their boiling points is noteworthy as demonstrating that the 
 empirical expressions given by Kopp, Pierre, and others, for 
 the expansion of liquids up to their boiling points, are equally 
 applicable to far higher temperatures, and that the expansion- 
 coefficient gradually increases with the diminution in molecular 
 cohesion of the liquid, until, as in ether at 133, it becomes 
 even greater than that of the gas. The expansion -coefficient 
 of ether increases to 0'0054: at the temperature of its absolute 
 boiling point that is, at about 190. The absolute boiling 
 point is defined by Mendeleeff as that temperature at which 
 the cohesion and latent heat of vaporisation are nil, and 
 at which the liquid becomes gaseous independently of pres- 
 sure and volume. It is, in fact, that temperature which the 
 researches of Andrews have made us familiar with as the 
 "critical -point." In this paper Mendeleeff presents us for 
 the first time with a number of determinations of the critical- 
 temperatures of various substances, founded partly on his own 
 determinations, and partly on those of Cagniard de la Tour, 
 Wolff, and Drion. 
 
 Other papers on physical chemistry relate to Contact 
 Action, to Fractional Distillation, and to the Heat of Com- 
 bustion of Organic Substances. In 1883 Mendeleeff was made 
 an honorary member of our Chemical Society, and in the 
 following year he contributed a remarkable paper to the 
 Journal of the Society (Transactions of the Chemical Society, 
 45, 126), in which he developed an extremely simple general 
 expression for the expansion of liquids under constant pressure 
 between and their boiling points. This expression may be 
 written l/V t = 1 - U, in which V f is the volume at f (that 
 
 2 A 
 
354 Dmitri Ivanowitsh Mendeleeff xn 
 
 at being unity), and k is a quantity which varies with 
 different substances, but which may for any one substance be 
 considered invariable between C. and the neighbourhood of 
 the boiling point. This formula is analogous to that which 
 expresses Dalton's law of the uniformity of expansion of 
 gases. But just as the formula, V = 1 + kt, applies only to 
 a so-called ideal gas, Mendeleeff 's expression is in like 
 manner to be regarded only as a first approximation that 
 is, as applicable only to ideal liquids. The deviations are 
 not large in either case; they are, as might be expected, 
 largest near temperatures at which the states of the bodies 
 change. In the case of actual liquids the deviations from 
 the ideal form of expansion increase not only as the liquid 
 approaches the point at which its state of aggregation is 
 changed, but also augment with diminishing density, increas- 
 ing cohesion, and diminishing molecular weight. This last 
 cause is especially noteworthy since Mendeleeff showed, more 
 than a dozen years ago (vide supra), that the deviations from 
 Dalton's law were related to the molecular weights of the 
 gases. The well-known irregularities in the expansion of 
 water are, according to Mendeleeff, connected with its small 
 molecular weight, its high surface-energy, and the compara- 
 tively small temperature -interval within which its state of 
 aggregation is unchanged. Subsequent observers, by applying 
 Van der Waal's theory of the general relation between the 
 pressure, volume, and temperature of bodies to Mendeleeff's 
 expression for the thermal expansion of an ideal liquid, 
 have shown that the reciprocal of the constant k is the 
 number obtained by subtracting 273 from the product of 
 the critical temperature into a quantity which should be the 
 same for all substances. The value of this quantity is 
 approximately 2, and since the range of its variation is 
 apparently very small, at all events for certain classes of 
 substances, the development of Mendeleeff's formula affords 
 a simple and ready method of calculating the critical tern- 
 
xii Dmitri Ivanowitsh Mendeleeff 355 
 
 perature of bodies from observations of their expansions as 
 liquids. 
 
 Mendeleeff's skill in physical measurement is well illustrated 
 by his determinations of the Specific Gravities of Aqueous 
 Solutions of Alcohol. Such determinations have been fre- 
 quently made the subject of rigorous experiment in this 
 and other countries, inasmuch as they constitute the basis 
 of the methods of assessing the duty on spirits, which is so 
 important a factor in the national income of many States. 
 Mendeleeff's work has served to confirm and extend that of 
 Drinkwater, Fownes, and Squibb, and has been utilised by 
 certain continental Governments (e.g. that of Holland) for the 
 purposes of revenue. But it was not the utilitarian aspect of 
 this subject which alone attracted Mendeleeff. In a paper com- 
 municated a couple of years ago to our Chemical Society (Trans- 
 actions of the Chemical Society, 51, 778), these determinations 
 are applied towards the elucidation of a theory of solution in 
 which it is sought to reconcile Dalton's doctrine of the atomic 
 constitution of matter with modern views respecting dissocia- 
 tion and the dynamical equilibrium of molecules. According 
 to Mendeleeff, solutions are to be regarded as containing strictly 
 definite atomic chemical combinations at temperatures higher 
 than their dissociation temperature, and just as definite chemical 
 substances may be either formed or decomposed at temperatures 
 which are higher than those at which dissociation commences, 
 so we may have the same phenomenon in solutions; at 
 ordinary temperatures they can be either formed or de- 
 composed. In addition, the equilibrium between the quantity 
 of the definite compound and of its products of dissociation is 
 defined by the laws of chemical equilibrium, which require a 
 relation between the masses of the active components present 
 in equal volumes (loc. cit. p. 779). It follows from this hypo- 
 thesis that the specific gravities of solutions depend on the 
 extent to which active substances are produced, or that the 
 expression for the specific gravity, s, as a function of the 
 
356 Dmitri Ivanowitsh Mendeleeff xn 
 
 percentage composition, p, may be represented by the general 
 equation 
 
 s = + Ap + Bp 2 . 
 
 Between the densities of two definite compounds exist- 
 ing in solution, the differential coefficient ds/dp is a linear 
 function of p 
 
 = A + 2Bp. 
 
 By the application of this method to the case of aqueous 
 solutions of ethyl alcohol, Mendeleeff infers the existence of 
 three definite hydrates, viz. EtH0.12H 2 0; EtH0.3H 2 0; and 
 3EtHO.H 2 0, the first two of which he has isolated by sub- 
 jecting the mixture to low temperatures. The hypothesis 
 respecting the linear character of the differential coefficient 
 ds/dp has been proved to be correct for solutions of many 
 salts, of acids, and of ammonia. 
 
 We have the consummation of this work on solution in the 
 monograph published by Mendeleeff in 1889. This volume, 
 the fruit of many years of labour, is unquestionably one of 
 the most important contributions to the theory of solution yet 
 given to science. 
 
 Much of Mendeleeff 's scientific activity since 1871 has 
 been absorbed in an extended work on the elasticity of the 
 gases, which he has executed in conjunction with his pupils, 
 Kirpitshoff, Hemilian, Bogusky, and Kajander. Portions only 
 of the results have as yet appeared. The first volume, pub- 
 lished in Russian in 1875, contains details of the modes of 
 measurement ; these involved many forms of apparatus new to 
 physical science. A summary of the principal results obtained 
 was published in the form of a pamphlet in 1881. Eegnault 
 found that the product p.v = const. i.e. Boyle's law was true 
 for ideal gases only. Between one atmosphere and thirty 
 atmospheres the deviations were positive in the case of 
 hydrogen, and negative in those of all other gases. Mendeleeff 
 
xii Dmitri Ivanowitsh Mendeleeff 357 
 
 pointed out that the deviations must become positive for all 
 gases at sufficiently high pressures, and the fact has since 
 been confirmed by the observations of Amagat and Cailletet. 
 Mendeleeff, more particularly, made observations at low 
 pressures, i.e. below one atmosphere ; and here the deviations 
 were again found to be positive and relatively very large. It 
 was found, in fact, that, at the limit of condensation, the 
 gases seemed to behave like solid bodies -i.e. the molecules 
 were incapable of being separated or brought nearer together 
 to any appreciable extent by varying pressure. Mendeleeff 
 has further determined the real coefficients of thermal ex- 
 pansion of gases. This, for air between and 100 under a 
 standard atmosphere, was found to be 0-0036829. Determina- 
 tions made in the case of other gases have shown that the 
 coefficients of expansion increase with increasing molecular 
 weight, gases of the same molecular weight giving the same 
 coefficient. 
 
 Molecular weight. Coefficient of 
 expansion. 
 
 Hydrogen ... 2 0-00367 
 
 ^ en * 
 
 Carbon monox 
 
 Nitrous oxide 
 
 * ' 1 28 0-00373 
 
 Carbon monoxide . . j 
 
 . A nrQ>7Q 
 
 r , -.. ., 44 000373 
 
 Carbon dioxide 
 
 .) 
 > 
 . J 
 
 Sulphur dioxide . . 64 . 0-00385 
 Hydrogen bromide . 81 . 0-00386 
 
 The coefficient of expansion is found to decrease with 
 increasing pressure in the case of hydrogen. Thus at 
 
 200 mm 0-00369 
 
 760 . . . . . 0-00367 
 
 8 atmos. 0-00366 
 
 But with the so-called coercible gases the reverse is found 
 to take place. Thus, in the case of carbon dioxide, 
 
 120 mm. pressure .... 0-00372 
 220 , 0-00370 
 
358 Dmitri Ivanowitsh Mendeleeff xn 
 
 760 mm. pressure . . / . 0-00373 
 3 atmos. 0-00389 
 
 8 0-00413 
 
 The decrease of the coefficient of expansion with increas- 
 ing pressure is a normal phenomenon of gases, the positive 
 deviation observed in the case of hydrogen being found to 
 hold equally good for all gases at very high and very low 
 pressures. Hence the laws of Boyle and Dalton are only 
 valid at points of the curve where the deviation changes 
 from positive to negative, or vice versd. 
 
 These experiments have also borne fruit in various 
 meteorological papers on the physical nature of the highly 
 rarefied air existing in the upper strata of the atmosphere. 
 In this connection it may be stated that Mendeleeff has 
 attempted to organise meteorological observations in the 
 upper regions of the atmosphere by means of balloons, 
 and hence he has been led to study aeronautics. His prac- 
 tical acquaintance with the subject induced him to make 
 an ascent from Klin during the total solar eclipse of 19th 
 August 1887, for the purpose of observing the extension 
 and structure of the corona when seen through highly 
 rarefied air. 
 
 Eussia is indebted to Mendeleeff for the training of two 
 generations of her chemists. His writings have largely 
 modified the mode of teaching chemical science in that 
 country. His treatise on Organic Chemistry was the standard 
 work of its time, and exercised great influence in spreading 
 abroad the conceptions which are associated with the develop- 
 ment of modern chemistry. His Principles of Chemistry, 
 published in 1869, and repeatedly reprinted, is a veritable 
 treasure-house of ideas, from which investigators have 
 constantly borrowed suggestions of new lines of research. 
 This book is one of the classics of chemistry ; its place in 
 the history of science is as well assured as the ever-memorable 
 work of Dalton. Mendeleeff, indeed, might with equal 
 
xii Dmitri Ivanowitsh Mendeleeff 359 
 
 fitness have styled his book a "New System of Chemical 
 Philosophy." In it he has developed the great generalisation 
 which is known under the name of the " Periodic Law " a 
 generalisation which is exerting a profound influence on 
 the development of chemical science in all countries in which 
 its study is actively prosecuted. Mendeleeff first drew 
 attention to the principles upon which the Periodic Law 
 is based in a paper read to the Eussian Chemical Society 
 in 1869, in the following series of propositions : 
 
 (1) The elements, if arranged according to their atomic 
 weights, exhibit an evident periodicity of properties. 
 
 (2) Elements which are similar as regards their chemical 
 properties have atomic weights which are either of nearly 
 the same value (e.g. platinum, iridium, osmium), or which 
 increase regularly (e.g. potassium, rubidium, caesium). 
 
 (3) The arrangement of the elements, or of groups of 
 elements, in the order of their atomic weights, corresponds 
 with their so-called valencies, as well as, to some extent, with 
 their distinctive chemical properties; as is apparent, among 
 other series, in that of lithium, beryllium, boron, carbon, 
 nitrogen, oxygen, and fluorine. 
 
 (4) The elements which are the most widely diffused 
 have small atomic weights. 
 
 (5) The magnitude of the atomic weight determines the 
 character of the element, just as the magnitude of the 
 molecular weight determines the character of a compound 
 body. 
 
 (6) We must expect the discovery of many yet unknown 
 elements for example, elements analogous to aluminium 
 and silicon whose atomic weight would be between 65 
 and 75. 
 
 (7) The atomic weight of an element may sometimes be 
 amended by a knowledge of those of the contiguous- elements. 
 Thus the atomic weight of tellurium must lie between 123 
 and 126, and cannot be 128. 
 
360 Dmitri Ivanowitsh Mendeleeff xn 
 
 (8) Certain characteristic properties of elements can be 
 foretold from their atomic weights. 
 
 In his memorable Faraday Lecture delivered to the 
 Chemical Society, and from which these words are taken, 
 Mendeleeff has indicated the lines upon which the evolution 
 of his theory proceeded. In the first place, it is to be noted 
 that it is based wholly on experiment ; it is as much the 
 embodiment of fact as are the laws of chemical combination 
 formulated by Dalton. Without the knowledge of certain 
 data it could not possibly have been discovered; with this 
 knowledge its appearance, says Mendeleeff, is natural and 
 intelligible. Three series of data were necessary to pave 
 the way for its enunciation : 
 
 (1) The adoption of the definite numerical values of the 
 atomic weights founded on the conceptions of Avogadro and 
 Gerhard t, as insisted upon by Cannizzaro. (2) The re- 
 cognition that the relations between the atomic weights of 
 analogous elements were governed by some general law. 
 Many chemists, and more especially Dumas, Gladstone, 
 and Strecker, had drawn attention to the numerical relation- 
 ship existing between correlated groups of elements, but no 
 one before Newlands in England, and De Chancourtois in 
 France, had sought to generalise this conception, and to 
 extend it to all the elements by considering their properties 
 as functions of their atomic weights. (3) A more accurate 
 knowledge of the relations and analogies of the rarer ele- 
 ments, such, for example, as that given to us by Roscoe 
 in the case of vanadium, and by Marignac in that of niobium. 
 The law of periodicity was the systematised expression of 
 these data ; it was, to use Mendeleeff's language, " the direct 
 outcome of the stock of generalisations of established facts 
 which had accumulated by the end of the decade 1860-70." 
 
 We can only very rapidly allude to some of the more 
 striking services which Mendeleeff's generalisation has ren- 
 dered to science during the twenty years of its existence. 
 
xii Dmitri Ivanowitsh Mendeleeff 361 
 
 By a more systematic arrangement and co-ordination of the 
 known chemical elements, it has not only indicated the 
 existence of new forms of elementary matter, but it has 
 pointed out the probable sources of the undiscovered sub- 
 stances, and has enabled us to know their properties even 
 before we have knowledge of their existence. It was this 
 power of divination inherent in the law which, perhaps 
 more than any other feature, first attracted attention to it, 
 and quickened the interest with which its development was 
 regarded by men of science. There are now three instances 
 of elements of which the existence and properties were 
 foretold by the periodic law : (1) That of gallium, discovered 
 by Boisbaudran, which was found to correspond with the 
 eka- aluminium of Mendeleeff; (2) That of scandium, corre- 
 sponding to elca-loron, discovered by Nilson; and (3) That 
 of germanium, which turns out to be eka-silicium, by Winckler. 
 No one who was present on the occasion of the delivery of 
 the Faraday Lecture will forget the enthusiasm which fol- 
 lowed the reading of these words of Mendeleeff s : " When, 
 in 1871, I described to the Eussian Chemical Society the 
 properties, clearly defined by the periodic law, which such 
 elements ought to possess, I never hoped that I should live 
 to mention their discovery to the Chemical Society of Great 
 Britain as a confirmation of the exactitude and the generality 
 of the periodic law." 
 
 Up to the time of the formulation of the law, the deter- 
 mination of the atomic value or valency of an element was 
 a purely empirical matter, with no apparent necessary relation 
 to the atomic value of other elements. But to-day this 
 value is as much a matter of a priori knowledge as is the 
 very existence of the element or any one of its properties. 
 Striking examples of the aid which the law affords in deter- 
 mining the substituting value of an element are presented 
 by the cases of indium, cerium, yttrium, beryllium, scandium, 
 and tJwrium. In certain of these cases, the particular value 
 
 OF THE 
 
362 Dmitri Ivanowitsh Mendeleeff xn 
 
 demanded by the law, and the change in representation of 
 the molecular composition of the compounds of these ele- 
 ments, have been confirmed by all those experimental criteria 
 on which chemists are accustomed to depend. One of the 
 most interesting instances of the kind is afforded by uranium., 
 the atomic weight of which was formerly regarded as 120, 
 then as 180, but which, on the authority of the periodic law, 
 is now established as 240, a value confirmed by the independ- 
 ent experiments of Zimmermann and Rammelsberg. Uranium 
 has a special interest in being the last term in the series ; 
 no element of higher atomic weight is at present known. 
 
 As examples of the value of the law in enabling us to 
 correct the atomic weights of elements whose valencies and 
 true position were well known, we may cite the cases of 
 gold, tellurium, and titanium, the values of which were ap- 
 parently higher than those demanded by it. In each of 
 these cases a redetermination of the atomic weight has resulted 
 in a value which is in conformity with the previsions of 
 the periodic law. 
 
 The law has, moreover, enabled many of the physical 
 properties of the elements to be referred to the same 
 principle of periodicity. At the Moscow Congress of Russian 
 physicists in August 1869, Mendeleeff pointed out the 
 relations which existed between the density and the atomic 
 weights of the elements ; these were subsequently more fully 
 examined by Lothar Meyer, and are embodied in the well- 
 known curve in his Modern Theories of Chemistry. Simi- 
 lar relations have been discovered in certain other properties, 
 such as ductility, fusibility, hardness, volatility, crystalline 
 form and thermal expansion; in the refraction equivalents 
 of, the elements, and in their conductivities for heat and 
 electricity ; in their magnetic properties and electro-chemical 
 behaviour; in the heats of formation of their haloid com- 
 pounds; and even in such properties as their elasticity, 
 breaking stress, etc. 
 
xii Dmitri Ivanowitsh Mendeleeff 363 
 
 In the Faraday Lecture, Mendeleeff indicated the bearing 
 of the law of periodicity upon the doctrine of constant 
 valency, and especially on the conception of a primordial 
 matter. The mind almost instinctively clings to the notion 
 that the law can only find its rational interpretation in the 
 idea of unity in the formative material, and it is not sur- 
 prising that the promulgation of the law has been heralded 
 by some as the most convincing proof of the validity of 
 the Pythagorean conception that experiment has yet been 
 able to adduce. But the author of the periodic law will 
 not admit that his generalisation has either sprung from 
 this conception or has any relations towards it. "The 
 periodic law, based as it is on the solid and wholesome 
 ground of experimental research, has been evolved inde- 
 pendently of any conception as to the nature of the elements ; 
 it does not in the least originate in the idea of an unique 
 matter; and it has no historical connection with that relic 
 of the torments of classical thought ; and therefore it affords 
 no more indication of the unity of matter or of the com- 
 pound nature of the elements than do the laws of Avogadro 
 and Gerhardt, or the law of specific heats, or even the con- 
 clusions of spectrum analysis. None of the advocates of 
 an unique matter has ever tried to explain the law from 
 the standpoint of ideas taken from a remote antiquity, when 
 it was found convenient to admit the existence of many 
 gods and of an unique matter." 
 
 No record of Mendeleeff's intellectual activity would be 
 complete without some reference to his influence on the 
 development of the industrial resources of Russia. In 1863 
 he brought out the first encyclopaedia of chemical technology 
 of any magnitude which the literature of that country 
 possessed, and he has been frequently commissioned to re- 
 port on the progress of chemical industry as manifested at 
 the various International Exhibitions. But it was on the 
 petroleum industry of Baku, on the Caspian, that this 
 
364 Dmitri Ivanowitsh Mendeleeff xn 
 
 influence has been most widely felt. Fifteen years ago the 
 production of petroleum in Russia was a monopoly, and 
 was accompanied by all the evils which usually spring from 
 monopolies; the trade was exceedingly limited, and appar- 
 ently incapable of development. Thanks largely to his 
 action, both on the platform and in the press, the opening 
 up of the boundless supplies of the peninsula of Apsheron 
 was thrown open to the world, with the result that petroleum 
 threatens to effect an industrial revolution in Eastern Europe 
 and in Asia. Indeed, it is not too much to say that the 
 oil industry of Baku is rapidly becoming, directly and in- 
 directly, one of the most powerful factors in the Central 
 Asian problem. MendeleefFs interest in the development 
 of the Baku industry has led to his being sent to the 
 Caucasus and to Pennsylvania, to report upon the best modes 
 of working the wells, and of separating and utilising the 
 products. Last year, during the coal crisis in Southern 
 Russia, he was commissioned to study the economic condition 
 of the industry in the rich coal-basin of Donetz. 
 
 No man in Russia has exercised a greater or more lasting 
 influence on the development of physical science than Men- 
 deleeff. His mode of work and of thought is so absolutely 
 his own, the manner of his teaching and lecturing is so 
 entirely original, and the success of the great generalisation 
 with which his name and fame are bound up is so strikingly 
 complete, that to the outer world of Europe and America 
 he is to Russia what Berzelius was to Sweden, or Liebig 
 to Germany, or Dumas to France. Nowhere has Mendeleeff 's 
 pre-eminence been more quickly or more fully recognised 
 than in this country. In 1882 the Royal Society gave him 
 the Davy Medal; and in 1889 the Chemical Society, which 
 is proud to number him among its Honorary Fellows, con- 
 ferred upon him the highest distinction in its power by 
 the award of the Faraday Medal. To the great regret of 
 the large gathering of British chemists which had assembled 
 
xii Dmitri Ivanowitsh Mendeleeff 365 
 
 to welcome him and to listen to the remarkable address on 
 the subject which he of all others is best fitted to expound, 
 Mendeleeff was unable to receive the gift in person ; but the 
 circumstances of his absence awakened a deep feeling of 
 commiseration and sympathy, and served to intensify the 
 sentiment of respect and admiration with which he is regarded 
 by all British men of science. 1 
 
 1 I have to express my grateful acknowledgments to Professor Menshutkin 
 and M. Gorboff, of St. Petersburg, and to Dr. B. Brauner, of the University 
 of Prague, for much of the information on which this article is based. 
 
XIII 
 
 THE EISE AND DEVELOPMENT OF SYNTHETICAL 
 CHEMISTRY 
 
 THE PRESIDENTIAL ADDRESS TO THE SUTTON COLDFIELD INSTITUTE, 
 1892 ; SUBSEQUENTLY PUBLISHED IN THE FORTNIGHTLY REVIEW. 
 
 CHEMISTRY, as an art, dates back from the very dawn of 
 civilisation itself ; as a science it is barely a couple of centuries 
 old. To the alchemists its pursuit was, in the main, but the 
 pursuit of wealth. Now and again we find men among them 
 like Thomas Aquinas, Libavius, and Glauber, who were 
 impelled by a higher motive than the love of gold to seek for 
 the hidden meaning of things, but the mystical tendencies of 
 the Middle Ages were as scales to their eyes, and such devious 
 groping for the light as they were able to make too frequently 
 ended in utter darkness. Even in the therapeutic crudities of 
 Paracelsus, who was sufficiently sincere in his profession as a 
 thaumaturgist to affirm that magic was the culminating point 
 of all human knowledge, what there was of science was 
 summed up in the aphorism, which in fact passed as an axiom 
 among his disciples : Man is a chemical compound ; his 
 are due to some alteration in his composition, and can only 
 by the influence of other chemical compounds. It may be ques- 
 tioned whether modern therapeutics has advanced much 
 beyond this position. 
 
 In strict truth, it is only within the present century that 
 
xiii Development of Synthetical Chemistry 367 
 
 men have seriously set themselves to search for the causes and 
 conditions of chemical change. Phlogistonism, it is true, had 
 in it the semblance of a philosophical doctrine, but it was 
 founded on an utterly false basis, and ultimately fell and was 
 crushed by the weight of its own absurdities. The recogni- 
 tion of the real nature of combustion, itself a manifestation of 
 chemical union, paved the way towards a clearer conception of 
 the essential nature of chemical combination ; and this concep- 
 tion acquired a beauty, order, and harmony until then unknown 
 to chemical teaching by the application'of the atomic hypothesis 
 as an explanation of the fundamental facts of chemical affinity. 
 Indeed, it has become a truism to say that this conception, the 
 fruit of patient and sustained induction, is to chemistry what 
 the theory of universal gravitation is to astronomy. For the 
 first time in its history chemistry was illumined and vivified 
 by a single, consistent theory, founded on quantitative rela- 
 tions, and making use of definite mathematical expression; 
 and it was at length recognised that the science must 
 ultimately be referred to mathematical laws similar to those 
 which had been established in regard to the mechanical 
 properties of matter. 
 
 It in nowise detracts from the merit of Dalton to affirm 
 that the atomic theory was a product of the age. It is 
 certain that even if the simple, unassuming Cumberland 
 Quaker had never lived, or that if the boarding-school at 
 Kendal, "where youth was carefully instructed in English, 
 Latin, Greek, and French; also writing, arithmetic, mer- 
 chant's accounts, and the mathematics," for the modest sum 
 of ten -and -sixpence a quarter, had absorbed the whole of 
 his intellectual energies, we should still have had the atomic 
 theory. Thomas Thomson, who stood sponsor to the infant 
 doctrine, always maintained that in the absence of Dalton, 
 Wollaston would have been its discoverer. A younger, bolder, 
 and more vigorous intellect than Wollaston's was also on its 
 track, and Sweden had well-nigh secured the glory which 
 
368 Development of Synthetical Chemistry xm 
 
 indisputably belongs to Britain. Jons Jakob Berzelius had 
 clearly grasped the real significance of Eichter's labours, and, 
 before he had even heard of Dalton's theory, had dedicated 
 his life to the determination of the stoichiometric relations on 
 which the atomic doctrine ultimately depends. His keen 
 mental vision saw proofs of its validity where Dalton failed to 
 find them. He was aware also of its limitations ; like Wollas- 
 ton, he perceived that the mutual action of atoms requires a 
 geometrical conception of their relative arrangement in all 
 the three dimensions of solid extension. 
 
 Whatever may be the ultimate fate of the theory which 
 found deliberate expression in the New System of Chemical 
 Philosophy and no one can say that it is not destined to give 
 place to a higher and even nobler generalisation, which shall 
 more clearly connect matter with the forces associated with 
 it it is certain that the ages to come will reckon it as the 
 central, dominant conception which has actuated the chemistry 
 of the nineteenth century. The characteristic feature of the 
 chemistry of our time is, in a word, the development and 
 elaboration of Dalton's doctrine for every great advance in 
 chemical knowledge during the last ninety years finds its 
 interpretation in his theory. 
 
 The discovery by Gay Lussac in 1808, that the weights of 
 equal volumes of both simple and compound gases," when 
 measured under like conditions of temperature and pressure, 
 are either proportional to or are simple multiples of their 
 empirical combining weights ; and the explanation of this fact, 
 given by Avogadro in 1811, by the assumption that all gases, 
 when measured under comparable conditions, contain the 
 same number of particles, as indicated by the similarity in 
 behaviour of all truly gaseous substances under the influence 
 of temperature and pressure, were the first striking proofs of 
 the validity, if not the sufficiency, of Dalton's fundamental 
 conception. Then followed the discovery of Dulong and 
 Petit, in 1819, that the capacity for heat of the elements is 
 
xin Development of Synthetical Chemistry 369 
 
 inversely proportional to their atomic weights, which finds its 
 simplest expression in the general law that the atoms of 
 elementary substances have the same capacity for heat ; and 
 almost simultaneously, the discovery by Mitscherlich that an 
 equal number of atoms similarly combined produces similarity 
 of crystalline form; similarity of crystalline form being 
 independent of the chemical nature of the atoms, and only 
 determined by their number and arrangement. The recogni- 
 tion, about 1823, of the existence of Isomerism that is, of the 
 fact that the same elements may combine together in the 
 same proportion and yet give rise to totally distinct com- 
 pounds ; Faraday's discovery in 1833, "that the equivalent 
 weights of bodies are simply those quantities of them which 
 contain equal quantities of electricity," or, in other words, 
 that the atoms of bodies have equal quantities of electricity 
 naturally associated with them ; the detection by Kopp and 
 Schroder in Germany, and by Playfair and Joule in this 
 country, of the relations between mass and volume in solids 
 and liquids ; these constitute so many proofs of the soundness 
 and comprehensiveness of the hypothesis. It does not weaken 
 the argument that these generalisations were not invariably 
 accepted by the leaders of chemical opinion at the time they 
 were promulgated. Dalton himself, for example, was unable 
 to recognise the great support his doctrine derived from the 
 discovery of the law of volumes by Gay Lussac. Berzelius 
 long failed to appreciate the significance of the discovery of 
 Dulong and Petit, and although he was eventually driven to 
 recognise the occurrence of isomerism he, indeed, coined 
 that very word in the outset he stoutly maintained 
 that the idea involved a contradiction in terms. It is true 
 that a fuller knowledge has shown that each of these general- 
 isations has its limitations : that all are, so to say, only first 
 approximations to exact mathematical statement; but this 
 circumstance has in no wise diminished the support they afford 
 to the doctrine of Dalton, for, as Liebig has well stated, " one 
 
 2B 
 
370 Development of Synthetical Chemistry xm 
 
 of the most cogent arguments for the soundness of our views 
 respecting the existence of atoms is, that these deviations are 
 explicable upon certain considerations attaching to the atomic 
 theory." 
 
 Corpuscular theories are now altogether banished from 
 certain domains of physics. Indeed, the most weighty of the 
 attacks yet made on the atomic hypothesis have been delivered 
 by those who are mainly occupied with the problems and 
 abstract conceptions of energy. It is significant that Faraday, 
 who began his scientific career as a chemist, seems to have 
 gradually loosened his hold on the atomic theory as he became 
 more and more absorbed in the contemplation of purely 
 physical phenomena. On the other hand, the belief in the 
 existence of atoms has been enormously strengthened by a 
 profounder study of the laws which affect the thermal relations 
 of gases and their behaviour under pressure; the very fact 
 that these laws are not capable of the strict mathematical 
 expression originally given to them, finds its fullest explanation 
 in the atomic theory; the deviations follow, indeed, as a 
 necessary consequence of the theory, thereby affording an 
 additional proof of the truth of Liebig's remark. 
 
 But the chemist who concerns himself mainly with con- 
 siderations drawn from his own science sees in the past course 
 and present tendency of organic chemistry the strongest proofs 
 of the influence and value of Dalton's doctrine. All the 
 fundamental conceptions of organic chemistry are essentially 
 atomic. The significance of isomerism has already been 
 referred to; it is in the domain of organic chemistry that 
 isomerism finds its most numerous and most striking examples. 
 As far back as 1823 Gay Lussac and Liebig clearly recognised 
 the existence of isomerism, and also the fact that it must 
 ultimately depend on differences in the mode in which the 
 atoms of the constituent elements are combined. The dis- 
 covery by these chemists of the identity in qualitative and 
 quantitative composition of silver fulminate and silver cyanate, 
 
xin Development of Synthetical Chemistry 371 
 
 was in reality one of the most momentous discoveries of the 
 century. It was followed in quick succession by Faraday's 
 discovery of a liquid hydrocarbon in oil gas, having the same 
 percentage composition as the well-known olefiant gas ; by 
 Wohler's epoch-making transformation of ammonium cyanate 
 into urea bodies made up of the same elements united in 
 the same proportion, and yet possessing wholly dissimilar 
 properties ; and, lastly, by Berzelius's discovery that racemic 
 acid and tartaric acid are identical in composition. These 
 facts profoundly influenced chemical thought, by demonstrat- 
 ing that the attributes of bodies depend not merely on the 
 nature and number of their components, but also on the 
 mode in which these components are arranged and distributed. 
 Chemists, for the first time, clearly recognised that their 
 business was not only to determine the quality and quantity 
 of the various atoms in a compound, but also the manner in 
 which those atoms are grouped and held together. This, 
 indeed, is the great problem of modern chemistry, and each 
 successive theory of the last half century is to be valued in 
 proportion as it has ministered to this end. The idea of 
 atomic grouping lay at the basis of the doctrine of radicles, 
 by means of which the chemists of sixty years ago sought 
 to make evident that organic compounds are fundamentally 
 similar to inorganic substances. It lay, too, at the basis of 
 the unitary views which, with the discovery of the principle 
 of substitution by Dumas, began to gain ground in organic 
 chemistry. The fact of substitution, indeed, is as inexplicable 
 as the law of multiple proportions, except upon the atomic 
 hypothesis. The nucleus theory of Laurent, and the different 
 type theories of the French school, and of their successors in 
 England, all tacitly recognised the existence of atoms. 
 
 The limits of this address preclude the possibility of the 
 attempt to show how these various theories have given place to 
 more rational modes of viewing the structure of organic com- 
 pounds. Unquestionably the two most powerful factors in 
 
37 2 Development of Synthetical Chemistry xm 
 
 determining the present character of organic chemistry have 
 been, firstly, the recognition by Frankland in 1852 of the fact 
 that the atom of every element is inherently endowed with a 
 specific combining power varying within certain limits, whereby 
 it is able to unite with a definite number of atoms of other 
 elements ; and, secondly, the hypotheses of Kekule and 
 Couper, which graft themselves directly on Frankland's dis- 
 covery, concerning certain peculiarities in the mode of com- 
 bination of the element carbon, the organic element par 
 excellence. Although nothing is known as to the real cause of 
 valency that is to say, of the cause which enables the atom 
 of carbon to take to itself and hold in stable union four atoms 
 of hydrogen or of chlorine, and no more than four, and 
 which forbids the atom of hydrogen or of chlorine to do 
 the same thing as regards carbon it will be obvious that 
 the fundamental idea of valency is essentially atomic in 
 conception. 
 
 From this time the attempts of chemists to unravel the 
 internal structure or constitution, to use the term first intro- 
 duced by Butlerow, of organic compounds took a new 
 departure. Great numbers of compounds hitherto unknown 
 and undreamt of were prepared because theory indicated their 
 existence. The mode of genesis and the nature of the 
 transformations of these substances threw fresh light on 
 the manner of the grouping of the atoms in bodies already 
 known ; and the knowledge thus gained enabled chemists to 
 conceive of methods by which such compounds might be 
 synthetically prepared. Indeed, it may be safely asserted 
 that whenever the constitution of an organic substance is 
 clearly made out, its synthetical formation comes within the 
 sphere of practical chemistry. 
 
 It may not be uninteresting to take a survey of the pro- 
 gress which has been made in synthetical chemistry during 
 the last fifty or sixty years. 
 
 Such a survey, however rapid, will lead us into every 
 
xin Development of Synthetical Chemistry 373 
 
 department of the organic world. During the past half- 
 century the chemist has succeeded in forming the active 
 principles or characteristic products of many plants ; he has 
 built up substances which have hitherto been regarded as 
 made only by the very process of living of an animal ; and he 
 has formed substances which were thought to be produced 
 only by changes in organised matter after death. 
 
 That particular day in 1828, when Wohler first observed 
 the transformation of ammonium cyanate into urea, should be 
 accounted a red-letter day in the history of science. This 
 discovery virtually gave the death-blow to the doctrine that 
 the operations which are concerned in the formation of the 
 chemical products of the organic world are fundamentally 
 different from those which take place in the inorganic world. 
 Urea, as the final product of a series of tissue changes, is 
 pre-eminently a typical product of animal life : no more 
 characteristic example of a substance formed by the action of 
 the so-called vital force could possibly be adduced. By 
 demonstrating that urea can be made synthetically by 
 ordinary laboratory processes and from substances inorganic 
 in their origin, Wohler proved that vital force is only 
 another name for chemical action; and that an animal is 
 nothing but a laboratory in which a multitude of chemical 
 changes, similar to those which occur in our test-tubes and 
 controlled by essentially the same conditions, is continually 
 taking place. 
 
 Since the date of Wohler's discovery urea has been 
 synthetically prepared by many reactions. Thus it was 
 obtained by Natanson by the action of ammonia on carbonyl 
 chloride, and by Basarow by heating commercial carbonate of 
 ammonia ; its formation in this case is due to the circumstance 
 that ordinary carbonate of ammonia, or "smelling salts," 
 always contains a greater or less quantity of ammonium 
 carbamate, which on heating is resolved into urea and water. 
 These reactions have a special interest from the circumstance 
 
374 Development of Synthetical Chemistry xm 
 
 that all the substances taking part in them can be formed 
 directly or indirectly from their ultimate elements. 
 
 Associated with urea as a product of the oxidation of the 
 nitrogenous compounds in the organism are uric, acid, xanthine 
 and sarcine. These bodies are met with in greater or less 
 quantity in urine, and in certain forms of urinary calculi ; and 
 they are invariably present in blood and muscle juice. In 
 chemical composition they differ from each other simply in 
 the amount of oxygen they contain. Urea was first artificially 
 transformed into uric acid by Horbaczewski. Its synthesis 
 has also been effected by Behrend and Roosen by methods 
 which afford evidence of the validity of the view of its con- 
 stitution originally propounded by Medicus. 
 
 Closely related in chemical composition to these bodies are 
 theobromine and caffeine, the active principles respectively of 
 cocoa (the fruit of Theobroma cacao) and of coffee and tea. 1 
 Caffeine, indeed, is contained in a large number of vegetable 
 products, infusions of which are used as beverages in various 
 parts of the world. Thus, in addition to tea and coffee, it 
 is found in mate, or Paraguay tea (the leaves of Hex 
 paraguayensis) ; in "guarana," the dried paste prepared from 
 the seeds of Paullinia sorbilis, growing in South America ; and 
 also in the kola-nut, which is used as an article of food in 
 Central Africa. This widespread use of caffeine-containing 
 products is undoubtedly of great physiological import, and its 
 interest is enhanced by the intimate relationship which is now 
 shown to exist between caffeine and the products derived 
 from the oxidation of nitrogenous matters within the 
 organism. Xanthine, indeed, has been recently transformed 
 into theobromine by Emil Fischer by a method which 
 is identical in principle with that used in 1860 by Strecker to 
 effect the conversion of theobromine into caffeine. These 
 
 1 It has been surmised, from the results of physiological experiments, that 
 caffeine, the characteristic principle of coffee, differs from theine, the active 
 principle of tea. Recent observations by Professor Duustan have, however, 
 conclusively demonstrated the identity of the two substances. 
 
xiii Development of Synthetical Chemistry 375 
 
 bodies are closely related to guanine, a substance contained, as 
 its name implies, in guano. Guanine, in fact, was transformed 
 into xanthine by Strecker. Hence the active principle of 
 tea and coffee could be obtained from guano, or if some 
 method of transforming uric acid into xanthine could be devised 
 this transformation was at one time supposed to have been 
 effected caffeine could be synthetically made through the 
 intervention of urea and uric acid from inorganic materials. 
 The following scheme shows the successive steps of the 
 synthesis : 
 
 1. Carbon and oxygen give carbonic oxide. Priestley; 
 CruikshanL 
 
 2. Carbonic oxide and chlorine give carbonyl chloride. 
 /. Davy. 
 
 3. Carbonyl chloride and ammonia give urea. Natanson. 
 
 4. Urea gives uric acid. Horbaczewski, Behrend and Roosen. 
 
 5. Uric acid to be transformed into xanthine. 
 
 6. Xanthine yields theobromine. Strecker. 
 
 7. Tlieobroinine gives caffeine. Fischer. 
 
 Of late years much attention has been paid to the study of 
 the putrefaction of albuminous substances of animal origin, 
 with the result that a considerable number of basic nitrogenous 
 bodies, some of which are highly poisonous, have been isolated. 
 These compounds were classed by the Italian toxicologist 
 Selmi under the generic name of the ptomaines (Trrco/jLa, a 
 corpse). They are the products of the vitality of the micro- 
 organisms which are concerned in setting up the putrefactive 
 change. Their discovery has greatly modified our views as to 
 the mode of action of pathogenic organisms, and it is now 
 regarded as not improbable that the disturbances are due 
 rather to the poisonous products elaborated by the organisms 
 than to the mere presence of the organisms themselves. It 
 ought to be stated, however, that the attempts hitherto made 
 to isolate the toxic substances which may be formed by the 
 growth of pathogenic organisms have been attended with only 
 
376 Development of Synthetical Chemistry xm 
 
 partial success. Thus Nencki was unable to detect any toxic 
 substance among the products of anthrax, and Staphylococcus 
 aureus, a common organism in abscesses, yields only a non- 
 poisonous base. On the other hand, Brieger, to whom we 
 owe the detection of a large number of these so-called 
 cadaveric alkaloids, has found that the typhoid bacillus yields 
 a poisonous substance which he has named typhotoxine ; and 
 he has also discovered that the bacillus of tetanus forms a 
 base, now called tetanine, which gives rise to symptoms 
 which have a strong resemblance to those occasioned 
 by the inoculation of the bacilli. All the ptomaines 
 hitherto isolated are comparatively simple in composition 
 and not very complex in chemical constitution. Some 
 of them have been shown to be identical with bodies 
 already known. Thus choline (%o\^, bile), a non-poisonous 
 alkaloid, originally found by Strecker in bile, in the brain, 
 and in yolk of egg, and now known to be a product of the 
 putrefaction of meat or fish, has been synthesised by Wurtz ; 
 whilst neurine (vevpov, nerve), a derivative of brain substance, 
 originally confounded with choline, but differing from it in 
 composition and in possessing intense poisonous properties, 
 has been artificially produced by Baeyer and by Hofmann. 
 Choline and neurine are closely related substances, and can 
 be readily transformed into each other. Another of the 
 so-called corpse alkaloids, cadaverine, has also been synthetically 
 formed by Ladenburg. 
 
 In 1870 Schmiedeberg and Kopp isolated the poisonous 
 principle of the fungus Agaricus muscarius, which they named 
 muscarine. Subsequently, Schmiedeberg and Harnack ob- 
 tained muscarine by the oxidation of choline, which indeed 
 accompanies it in many fungi, and from which it differs only 
 in containing an additional atom of oxygen. It is noteworthy 
 that muscarine also occurs with choline among the products 
 of the putrefaction of flesh. 
 
 It is, however, among the products of plant life that some 
 
xiii Development of Synthetical Chemistry 377 
 
 of the most notable syntheses of modern times have been 
 effected. Tartaric acid, the characteristic acid of unripe 
 grapes, and citric acid, the acid which gives sourness to limes, 
 lemons, and oranges, have each been artificially prepared. 
 The synthesis of tartaric acid may now be effected from its 
 elements by a comparatively simple series of steps. The first 
 step involves the artificial formation of ordinary alcohol. 
 This was effected by Berthelot in the following way. When 
 carbon is intensely heated in a stream of hydrogen gas a 
 poisonous gaseous hydrocarbon termed acetylene is produced, 
 which is characterised by giving a red powder with certain 
 compounds of copper. Indeed, by means of this reaction the 
 presence of acetylene in ordinary coal-gas, and as a product of 
 the imperfect combustion of many illuminating flames, may 
 be recognised. This compound of copper and acetylene, 
 under the influence of reducing reagents, may be made to 
 yield ethylene, or olefiant gas ; this gas, as Faraday showed, 
 is soluble in strong oil of vitriol with the formation of 
 ethyl -sulphuric acid, a substance which only requires dis- 
 tillation with water to convert it into ethyl (i.e. ordinary) 
 alcohol. 
 
 Ordinary alcohol, under the influence of oxidising agents, 
 gives rise to glyoxylic acid, from which, as recently shown by 
 Genvresse, the optically inactive modification of tartaric acid, 
 the racemic acid discovered by Berzelius, may be formed. 
 Racemic acid, as demonstrated by Pasteur, is a mixture of 
 two modifications of tartaric acid which neutralise each 
 other's optical activity. By taking advantage of certain 
 remarkable differences in the crystalline characters of the 
 sodium-ammonium salts formed from racemic acid, which he 
 was the first to detect, Pasteur succeeded in separating the 
 two constituents of racemic acid, and in showing that one 
 of these is the particular variety which occurs in the grape 
 and other fruits, and which constitutes the tartaric acid 
 of commerce. Hence the racemic acid obtained from 
 
378 Development of Synthetical Chemistry xm 
 
 the oxidation product of alcohol only requires treatment by 
 Pasteur's method to yield the tartaric acid of the grape. 
 
 Many attempts have been made at various times to effect 
 the artificial formation of plant -alkaloids, such as quinine, 
 morphine, strychnine, etc., but as yet with only partial success. 
 There is little doubt, however, that such syntheses will be 
 accomplished when the constitution of these complex sub- 
 stances is better understood. Up to the present only two 
 alkaloids have been synthesised one completely, viz. conine, 
 the poisonous principle of hemlock (Conium maculatum), which 
 has been made artifically by Ladenburg, and the other only 
 partially, viz. atropine, one of the active substances in Atropa 
 Belladonna. 
 
 The history of the synthesis of conine has a special interest. 
 The naturally occurring conine obtained by Giesecke in 1827 
 has the power of turning the plane of polarised light to the 
 right, whilst the conine first synthesised by Ladenburg was 
 found to have no action on polarised light. Further research 
 has shown that this conine stands to the naturally occurring 
 alkaloid in the same relation that the artificially prepared 
 racemic acid of Genvresse stands to the tartaric acid of fruits. 
 By combining the artificial conine with tartaric acid, it is 
 broken up into laevo-conine and into dextro-conine, the latter 
 of which is identical with the natural variety. 
 
 Closely related to conine is nicotine, the poisonous constitu- 
 ent of tobacco. The constitution of this body is now fairly 
 well understood, and its synthetical formation may be con- 
 fidently looked for. Its parent substance is contained in coal- 
 tar, and in the foetid liquid obtained by distilling bones. 
 
 A considerable number of the odoriferous principles of 
 plants have been obtained artificially, such, for example, as 
 bitter-almond oil and oil of mustard. Indeed, the synthetically 
 prepared oil of mustard has largely replaced the natural pro- 
 duct in medicine as a vesicant and counter-irritant. The 
 sweet-smelling principle of Spircea ulmaria, or meadow-sweet, 
 
xiii Development of Synthetical Chemistry 379 
 
 is readily formed by heating a solution of carbolic acid in soda 
 with chloroform. This substance may, as shown by Dr. 
 Perkin, be readily transformed into coumarin, the crystalline 
 odoriferous principle of the tonka bean and of wood-ruff. The 
 Maiweinessenz used in Germany in place of wood-ruff in the 
 manufacture of Maiwein is an alcoholic solution of artifically 
 prepared coumarin. 
 
 Salicylic acid, which is now largely used as an antiseptic, 
 could formerly only be obtained from oil of winter-green 
 (Gaultheria procumbens). It is now prepared on a manufactur- 
 ing scale by heating a compound of soda and carbolic acid in 
 carbonic acid gas, and the synthetic product has practically 
 replaced the natural variety. 
 
 Vanillin, the aromatic principle of the dried fermented pods 
 of certain orchids belonging to the genus Vanilla (Span. 
 vaynilla, dim. of vaina, a pod), has had its constitution un- 
 ravelled, with the result that it can now be synthetically pre- 
 pared. Artificial vanillin is, in fact, made on an industrial 
 scale in Germany, and threatens to supplant the natural pro- 
 duct of Eeunion and Mauritius as a flavouring agent in 
 chocolate and confectionery. It is interesting to note that 
 vanillin is found to be chemically related to the odoriferous 
 constituents of cloves and all-spice, and can be prepared from 
 these substances. 
 
 Other plant products, of which the synthetic formation 
 may be confidently looked for, are caoutchouc and oil of turpen- 
 tine ; and, curiously enough, the one will be obtained through 
 the other, and both, indirectly, from coal-tar. 
 
 The story of the artificial formation of alizarin from coal- 
 tar derivatives by Graebe and Liebermann in 1868, and of its 
 successful commercial manufacture by Perkin in this country, 
 and by Caro in Germany, is too well known to be repeated 
 here. The synthetic formation of alizarin created nothing less 
 than a revolution in one of our leading industries, and com- 
 pletely destroyed a staple trade of France, Holland, Italy, and 
 
380 Development of Synthetical Chemistry xm 
 
 Turkey. Alizarin is one of the main products of the madder 
 plant, the roots of which have been used from time imme- 
 morial for the sake of the dyes which they contain. Pliny tells 
 us that in his time madder was well known " to the sordid and 
 avaricious ; and this because of the large profits obtained from 
 it owing to its employment in dyeing wool and leather." 
 Originally it was grown almost exclusively in India, Persia, 
 and the Levant. The Moors introduced it into Spain, whence 
 it found its way into the Netherlands. Alsace and Avignon 
 were long celebrated for their madder. Twenty years ago it 
 was the most important of the natural dye-stuffs used by the 
 calico printer and Turkey-red dyer ; and the annual import of 
 it into this country was valued at 1,250,000 sterling, the 
 South Lancashire district alone consuming upwards of 150 
 tons weekly. The chemist has changed all this, and the cul- 
 tivation of the various species of the Rubiacece for the purposes 
 of the dyer, which has continued for thousands of years 
 down to our own time, is now practically at an end. It is 
 the remnant of a primeval vegetation that has displaced the 
 vegetation of to-day. 
 
 The remarkable industrial results which followed Graebe's 
 and Liebermann's discovery naturally roused chemists to 
 attempt the artificial formation of a dye-stuff not less import- 
 ant, viz. indigo. This has been accomplished, independently, 
 by Baeyer, by Heumann, and by Heymann, but by methods 
 which as yet do not allow the artificially formed indigo to 
 compete successfully with the natural product. Now, however, 
 that an insight into the chemical constitution of indigo has 
 been gained, no one can say that its synthetic formation may 
 not at any time become commercially successful. 
 
 No synthesis of recent years has created a keener or more 
 widespread interest than that of the sugars, dextrose and levu- 
 lose, which has been recently effected by Emil Fischer. It is 
 interesting not merely as an instance of the artificial produc- 
 tion of well-known substances, but also on account of the 
 
xiii Development of Synthetical Chemistry 381 
 
 light it is calculated to throw upon the origin and mode of 
 formation of the sugars in the vegetable kingdom. It is not 
 possible, without entering into details too technical in charac- 
 ter to be in place here, to trace the successive steps of the 
 process by which this synthesis has been effected ; but it may 
 be interesting to note that it has been accomplished through 
 the medium of glycerin, a proximate constituent of the fats, 
 and itself capable of being formed from ordinary alcohol, 
 which in its turn can be produced, as already stated, from its 
 elements. Hence it is possible to indicate a method by which 
 sugar can now be formed from its ultimate elements that is, 
 from inorganic sources. 
 
 The advance in every section of chemistry during this cen- 
 tury, and especially during the latter half of it, has literally 
 been by leaps and bounds. Although practically a creation 
 of our own time, no branch has been more fruitful in result, 
 in suggestion, or in possibility, than that of organic synthesis. 
 The mere gain in the knowledge of fact is immeasurable ; it is 
 even more impossible to gauge the profound effect of that 
 knowledge on other departments of human effort and intel- 
 lectual activity. 
 
 Past history shows only too well that there is a tide in the 
 affairs of science, as in all other things that constitute affairs 
 of men. There are periods of ebb and flow, of advance and 
 retrogression. But of this we are certain in chemistry the 
 flood has only just set in, and it is still very far from high- 
 water mark. 
 
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