LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 Class 
 
ESSAYS IN HISTORICAL CHEMISTRY 
 
MACMILLAN AND CO., LIMITED 
 
 LONDON BOMBAY CALCUTTA 
 MELBOURNE 
 
 THE MACMILLAN COMPANY 
 
 NEW YORK BOSTON CHICAGO 
 ATLANTA SAN FRANCISCO 
 
 THE MACMILLAN CO. OF CANADA, LTD. 
 
 TORONTO 
 
ESSAYS 
 
 IN 
 
 HISTOBICAL CHEMISTKY 
 
 BY 
 
 SIE EDWAED THOEPE, C.B., LL.D., F.E.S. 
 
 PROFESSOR OF GENERAL CHEMISTRY, 
 IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY, LONDON 
 
 MACMILLAN AND CO., LIMITED 
 ST. MAKTIN'S STKEET, LONDON 
 
 1911 
 
^ 
 
 .Fir.tf Edition, Extra Crown 8v0, 1894 
 
 Second Edition, 8z'0, 1902 
 
 Third Edition, 1911 
 
PEEFACE 
 
 THIS book consists mainly of lectures and addresses 
 given at various times, and to audiences of very 
 different type, during the last forty 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 contri- 
 buted to its development. The book has no pretensions 
 to be considered a history of chemistry, even of the 
 time to which its narratives relate. Many honoured 
 names as Black, Dalton, 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 arrang- 
 ing 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 lectures, when delivered, were 
 illustrated by experiments of which mention was made 
 in the accounts originally published. It seemed useless 
 to retain these references, and they have consequently 
 
 V 
 
 223056 
 
vi PEEFACE 
 
 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 composed 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 
 repetitions ; 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 many 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 and Know- 
 ledge 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 Advance- 
 ment of Science for permission to reprint the Presiden- 
 tial Address delivered to the Chemical Section of the 
 Association at the meeting in Leeds in 1890. Messrs. 
 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, those on Kopp, Victor Meyer, and Julius 
 
PKEFACE vii 
 
 Thomsen, and the Presidential Address of 1900 ; the 
 Council of the Philosophical Society of Glasgow, the 
 Graham Lecture, given in 1887 ; and the Council of the 
 Greenock Philosophical Society, the Watt Anniversary 
 Address of 1898. 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. 
 
 LONDON, May 1911. 
 
CONTENTS 
 
 i 
 
 ROBERT BOYLE 
 
 PAGE 
 
 (One of the Free Evening Lectures delivered in connection with 
 the Loan Collection of Scientific Apparatus at South Ken- 
 sington in 1876) . . . . . .1 
 
 II 
 
 JOSEPH PRIESTLEY 
 
 (A Lecture delivered in the Hulme Town Hall, Manchester, on 
 
 18th November 1874. Manchester Science Lectures) . 32 
 
 III 
 
 CARL WILHELM SCHEELE 
 
 (An Address to the Owens College Chemical Society, at the Open- 
 ing Meeting, 24th October 1893 ; subsequently published in 
 
 the Fortnightly Review) . . . . .60 
 
 IV 
 HENRY CAVENDISH 
 
 (A Lecture delivered in the Hulme Town Hall, Manchester, on 
 
 24th November 1875. Manchester Science Lectures) . 79 
 
x CONTENTS 
 
 V 
 JAMES WATT 
 
 PAGE 
 
 (Being the Watt Anniversary Lecture delivered before the Greenock 
 
 Philosophical Society on llth March 1898) . . . 98 
 
 VI 
 
 ANTOINE-LAURENT LAVOISIER 
 (Contemporary Review, December 1890) . . . .123 
 
 VII 
 
 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) . 149 
 
 ADDENDUM 
 
 (M. Berthelot and the Address to the Chemical Section of the 
 
 British Association at Leeds, 1890) .... 176 
 
 VIII 
 MICHAEL FARADAY 
 
 (A Review of Dr. Bence Jones's " Life and Letters of Faraday." 
 
 Manchester Guardian, 1870) . . . .185 
 
 IX 
 
 -^ ^/ 
 
 THOMAS GRAHAM 
 
 (A Lecture (with Additions) delivered in the Yorkshire College, 
 
 Leeds, introductory to the Evening Class Session, 1877-78) . 206 
 
 The Third Triennial " Graham " Lecture, delivered before the Philo- 
 sophical Society of Glasgow in Anderson's College, 16th March 
 1887 271 
 
CONTENTS xi 
 
 FRIEDRICH WO'HLER 
 
 PAGE 
 
 (A Lecture delivered at the Royal Institution, Albemarle Street, 
 
 on Friday Evening, 15th February 1884) . . .294 
 
 (x) 
 
 JEAN BAPTISTE ANDRE DUMAS 
 (A Lecture delivered to the Royal Dublin Society, March 1885) . 318 
 
 XII 
 
 HERMANN KOPP 
 
 (Memorial Lecture delivered to the Fellows of the Chemical Society, 
 20th February 1893 ; published in the Transactions of the 
 Chemical Society, 1893) . . . . .364 
 
 XII} 
 
 W 
 
 VICTOR MEYER 
 
 (Memorial Lecture delivered to the Fellows of the Chemical Society, 
 8th February 1900 ; published in the Transactions of the 
 Chemical Society, 1900) ..... 423 
 
 T 
 
 DMITRI IVANOWITSH MENDELEEFF 
 (" Scientific Worthies," No. XXVI. Nature, 27th June 1889) . 483 
 
 STANISLAO CANNIZZARO 
 ("Scientific Worthies," No. XXX. Nature, 6th May 1897) . 500 
 
xii CONTENTS 
 
 XVI 
 JULIUS THOMSEN 
 
 PAGE 
 
 (Memorial Lecture delivered to the Fellows of the Chemical Society, 
 17th February 1910 ; published in the Transactions of the 
 Chemical Society, 1910) . . . . .515 
 
 XVII 
 
 THE RISE AND DEVELOPMENT OF SYNTHETICAL CHEMISTRY 
 
 (The Presidential Address to the Sutton Coldfield Institute, 1892 ; 
 
 subsequently published in the Fortnightly Review] . .533 
 
 XVIII 
 
 ON THE PROGRESS OF CHEMISTRY IN GREAT BRITAIN AND 
 IRELAND DURING THE NINETEENTH CENTURY 
 
 (The Presidential Address to the Chemical Society, 29th March 
 1900 ; published in the Transactions of the Chemical Society, 
 1900) ....... 551 
 
 XIX 
 
 ON THE DEVELOPMENT OF THE CHEMICAL ARTS DURING 
 THE REIGN OF QUEEN VICTORIA 
 
 (An Address delivered at the East London Technical College, 8th 
 
 February 1897 ; subsequently published in Knowledge) . 590 
 
EGBERT BOYLE 
 
 ONE OP 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 para- 
 doxes. 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 legis- 
 lative reforms enacted ; blow after blow was aimed at 
 
 i B 
 
EGBERT BOYLE 
 
 and made its mark upon spiritual 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 and ennobled 
 by the sublime genius of Milton and the brilliant fancy 
 of Dry den. 
 
 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 historians. 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 pervaded 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 any preparatory bustle, anonymously and un- 
 dedicated. 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 
 
I EGBERT BOYLE 
 
 of the small world of the virtuosi, but of that infinitely 
 larger public of thinking men who felt a growing im- 
 patience of the dogmas of the schools. The book was 
 entitled the " Sceptical Chymist : or Chernico-Physical 
 Doubts and Paradoxes touching the Experiments, where- 
 by vulgar Spagyrists 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 ; neverthe- 
 less, 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 ? 
 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 permitted to enter, had fallen upon him. The 
 writer was soon identified as a young gentleman, 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 man 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 Hertfordshire family which could 
 trace its ancestry back to the times of Edward the 
 Confessor, despairing of employment at home, had 
 
4 KOBEKT BOYLE i 
 
 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 competent linen, a couple of tokens, a 
 trusty rapier and dagger, and twenty -seven pounds 
 three shillings in ready money. From these inconsider- 
 able 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 the mother 
 of Kobert Boyle we learn little beyond that she was the 
 daughter of Sir Geoffrey Fen ton, 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 gentleman himself, and 
 well skilled in the art of making others so. Here the 
 studious sickly boy with his uncouth 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 
 
i KOBEET BOYLE 5 
 
 Clarendon, overcame his inclination to accept an office 
 to which his habits and associations disposed 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 cul- 
 minated in the death of Charles I., seeking in his books 
 and in his laboratory some diversion from the con- 
 templation 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 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, after- 
 wards Bishop of Chester ; Jonathan Goddard, Warden 
 of Merton ; Samuel Foster, Professor of Astronomy 
 at Gresham College ; and Theodore Haak, a German 
 resident in London, who appears to have first suggested 
 the meetings. These were held weekly at each other's 
 lodgings in London or at Gresham College, " to dis- 
 course and consider of philosophical inquiries and such 
 as related thereunto (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, afterwards 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 
 
6 EOBEKT BOYLE I 
 
 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 Eoyal 
 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. Eeligion, 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 affec- 
 tion 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 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 
 
I EOBEET BOYLE 7 
 
 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 Royal 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, Kector 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 bitter- 
 ness, and hard knocks were freely given and returned, 
 as was the manner of the time. Fate decreed, however, 
 that Glanvill should have the last word, for his ad- 
 versary 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 Koyal 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 1666 gave the Society an 
 opportunity, and much of what was good in the arrange- 
 ment in the new city was the result of their deliberations 
 and counsel. Science became even fashionable. The 
 King set up a laboratory, and amused himself by making 
 weather observations with the newly invented baroscope ; 
 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 
 
8 EOBEET BOYLE I 
 
 at Will's conversed of the Vacua Boyliano and the 
 spring of air. Moreover, 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 ob- 
 tained ? A few years before a very learned Frenchman, 
 Kene* Descartes, 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 explanations 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 itelf to the readers of his 
 Dialogus Physicus de Natura Aeris : " If 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 place 
 for it [the air] to go into, unless either by thrusting 
 away the next contiguous air it proceed by continual 
 endeavour to the hole at the top, where it may enter 
 and succeed in the place of the water that floweth out, 
 
i EOBEKT BOYLE 9 
 
 or else by resisting the endeavour of the water down- 
 wards 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 plenitude 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. Richard 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 ? 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. 
 
10 EGBERT BOYLE i 
 
 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 gentle- 
 man, 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 
 Von Guericke's method. He accordingly sought to 
 devise a more perfect form of instrument, and with the 
 assistance of Robert Hooke, a man of remarkable in- 
 ventive powers, he, about the year 1658, contrived his 
 " Pneumatical Engine." 
 
 It consisted of a large pear-shaped vessel holding 
 about thirty wine-quarts, fitted with a stopper at the 
 top and connected 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," and the cylinder 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 
 
I EOBEET BOYLE 11 
 
 opportunely turning the key [of the stopcock] and stop- 
 ping 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 experi- 
 ment and the intention of him that makes it." 
 
 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 permit, and thereby expanding 
 the whole parcel of air these elastical bodies compose." 
 Boyle pictured to himself this process 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- 
 
12 EGBERT BOYLE I 
 
 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 com- 
 pressed wool doth, as it were, spontaneously expand or 
 display itself towards the recovery of its 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. Hum- 
 boldt, indeed, calls him " the cautious and doubting 
 Kobert Boyle." He was well aware that other modes of 
 explaining the elasticity 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 particles swim, 
 are so whirled round that each corpuscle endeavours 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 
 
i EOBEKT BOYLE 13 
 
 and knock away each other, and consequently require 
 more room than they would need if compressed. 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 endea- 
 vour of some subtle ambient body whose passage may 
 be stopped or obstructed, or else its pressure unequally 
 resisted by reason of the new shape or magnitude, which 
 the bending of a 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 materi- 
 ality 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 containing 
 air and counterpoised with metallic weights appears to 
 weigh more in vacuo than in the air ; and the familiar 
 experiment 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 
 
14 EOBEKT BOYLE i 
 
 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 the 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 quicksilver, 
 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 atmo- 
 sphere 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 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 distension of 
 the bladder, in consequence of the expansion of the 
 included air, as the rarefaction 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 
 
I ROBEET BOYLE 15 
 
 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 specu- 
 lation." 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 
 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 complete, 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 recog- 
 
16 EGBERT BOYLE i 
 
 nised 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 pro- 
 mised 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 speculations 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 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 
 
i EOBEKT BOYLE 17 
 
 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 discovery 
 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 corpuscular 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 in the water ? On the whole, 
 he inclines to the latter supposition, but mainly for 
 the reason that all experience showed that water was 
 elementary, indestructible, and inconvertible. He argues 
 
18 KOBEKT BOYLE i 
 
 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 
 
i EGBERT BOYLE 19 
 
 the observations of his predecessors on this point are so 
 discordant that he feels himself obliged to re-determine 
 the relation, firstly by observing the heights of counter- 
 balancing 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 disparity 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 conjectures 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- vivi- 
 section days, to tell you how many cats, mice, sparrows, 
 fishes, tadpoles, and snails fell victims to his zeal. Not 
 that he inflicted needless suffering, 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 
 
20 EOBEKT BOYLE i 
 
 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. 
 
 The last experiment that Boyle describes is one of 
 the 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 school- 
 men speak) divers of the operations of that vehement 
 and tumultuous agitation of the small parts of bodies, 
 wherein the nature of 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 wonderfully 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 im- 
 possible 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 
 
I KOBEET BOYLE 21 
 
 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 
 Forscherblick 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 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 argu- 
 ments 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 
 
22 KOBEKT BOYLE i 
 
 lawful to return it, 1 ' 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 
 Torricellian experiment is upheld not by the pressure of 
 the air but by a certain nondescript internal cord ; and 
 Boyle undertakes 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/ ' 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. In the answer to Linus he gives two new 
 experiments touching 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 
 subdivided 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 
 
I KOBEKT BOYLE 23 
 
 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 continuing 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 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 mercurial 
 cylinder of about 29 inches, as we are taught by the 
 Torricellian experiment ; so here the same air being 
 
24 EGBERT BOYLE I 
 
 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 complete 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 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 restagnant mercury, and con- 
 sequently unfilled therewith, the prominent 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 
 
I EOBEKT BOYLE 25 
 
 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 afterwards 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 restag- 
 nant 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 mercurial 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 thorough- 
 ness with which 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 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 
 detailed are given in the following tables : 
 
26 
 
 EGBERT BOYLE 
 
 A TABLE OF THE CONDENSATION OF THE AIR 
 
 48 
 46 
 44 
 42 
 40 
 38 
 36 
 34 
 32 
 30 
 28 
 26 
 24 
 23 
 22 
 21 
 20 
 19 
 18 
 17 
 16 
 15 
 14 
 13 
 12 
 
 B 
 
 00 
 
 06 
 
 91 3 
 ZL 1& 
 
 37 
 
 45 
 
 TF 
 
 63- 
 
 D 
 
 3 A 
 
 37 
 
 50 
 
 - 
 
 ** 
 
 82A| 
 87JA 
 
 IOO T V 
 
 1071f 
 
 E 
 
 33^ 
 35 
 
 38 
 
 46f 
 50 
 
 58| 
 
 60i| 
 
 63^ 
 
 66^ 
 
 70 
 
 77| 
 
 82^ 
 
 t>y 
 107^ 
 
 AA 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 compressed 
 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. 
 
 What that pressure should be according to the hypothesis that supposes 
 the pressure and expansion to be in reciprocal proportion. 
 
EOBEET BOYLE 
 
 27 
 
 A TABLE OF THE RAREFACTION OF THE AIR 
 
 A 
 
 1 
 
 4 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 12 
 14 
 16 
 18 
 20 
 24 
 28 
 32 
 
 B 
 
 00 
 
 10| 
 
 151 
 
 24 
 
 26" 
 
 27* 
 27| 
 271 
 
 28| 
 284 
 
 ^ 
 
 -i 
 
 S 
 
 J 
 
 02 
 
 A The number of equal spaces at the 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 in- 
 cluded 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 super- 
 ficially, the whole ground of Boyle's work, although 
 there is much in it of special interest at 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 
 
28 EGBERT BOYLE i 
 
 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 Experiments 
 about the Superficial Figures of Fluids, especially of 
 Liquors contiguous to other Liquors, he breaks ground 
 which has taxed the energies of our greatest mathe- 
 maticians. His Treatise on Cold abounds with striking 
 and original experiments : thus he demonstrates the 
 expansive power of freezing water by bursting 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 Ex- 
 periments 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 Government 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 
 
I EGBERT BOYLE 29 
 
 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. 
 
 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 Peri- 
 patetics, 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 
 
30 KOBEKT BOYLE i 
 
 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 mysti- 
 cism 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 
 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 them- 
 selves, they could not write otherwise than confusedly 
 of what they had confusedly apprehended : they could 
 scarcely keep themselves from being confuted but by 
 keeping themselves from being clearly understood 
 home-thrusts which must have made many a Helmontian 
 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 published towards the close of the 
 seventeenth century. 
 
 The Sceptical Ghymist 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 Phlo- 
 gistian would be to-day. Boyle indeed seems to incline 
 
i EGBERT BOYLE 31 
 
 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 proportions 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 conse- 
 quently of the phenomena of nature, seem to depend 
 upon the motion and contrivance of the small parts of 
 bodies." 
 
II 
 
 JOSEPH PRIESTLEY 
 
 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 outcome 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 English- 
 men 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 
 
 32 
 
II 
 
 JOSEPH PKIESTLEY 33 
 
 cause of 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 
 embarrassment ; 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 require 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 relating 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 The Rudiments 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, 
 
34 JOSEPH PEIESTLEY n 
 
 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 
 rooms, built of stones 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 distinction, 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, 
 
II JOSEPH PEIESTLEY 35 
 
 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 thank- 
 ful for it, that my health received the check that it did 
 when I was young ; since a muscular habit from high 
 health, and strong spirits, are not, I think, in general 
 accompanied with that sensibility of mind which is both 
 favourable 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 
 controversy, 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 
 iirst 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 
 extremities, he issued proposals to teach the classics and 
 
36 JOSEPH PEIESTLEY u 
 
 mathematics 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 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 ,. 
 
ii JOSEPH PEIESTLEY 37 
 
 and be less apt to be offended when the performances 
 they hear are but indifferent. In 1761 he was invited 
 to Warrington 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 recommending 
 him to undertake his proposed History of Electricity, 
 and furnishing him with books for the purpose. In 
 connection 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 Koyal Society, and a Doctor of Laws of Edinburgh 
 University. Priestley by this time was married, but 
 seeing no prospect of providing for his family at War- 
 rington, 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 experi 
 mental philosophy, and began that brilliant series of 
 discoveries by which others were to accomplish the over- 
 throw 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 
 
38 JOSEPH PEIESTLEY n 
 
 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 friendship of such men as Boulton 
 and Watt, the engineers ; Wedgwood, the potter ; Keir, 
 Withering, Darwin, and the Galtons. He had ample 
 leisure for his work, and no lack of encouragement 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 full liberty both to investigate, and, by 
 preaching and writing, 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 Revolution. 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 
 
ii JOSEPH PRIESTLEY 39 
 
 seemed to be concentrated upon Priestley, and he and 
 his family barely escaped with their lives, leaving 
 library, papers, and instruments 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 here (whose attach- 
 ment 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 
 
40 JOSEPH PEIESTLEY n 
 
 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 
 controversies 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 reputation will ultimately 
 rest : this will continue to hand down his name when all 
 traces of his other labours are lost. He has frequently 
 
ii JOSEPH PRIESTLEY 41 
 
 been styled the Father of Pneumatic Chemistry ; and 
 although we may question the propriety of the appella- 
 tion 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 ? " 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 combus- 
 tible substances depend partly upon the proportion of 
 the phlogiston they contain, and partly upon the nature 
 of the other constituents. When a body burns it 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 
 
42 JOSEPH PEIESTLEY n 
 
 phlogiston." If zinc be strongly heated it takes fire and 
 burns with a beautiful greenish flame, and 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 necessary 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 prolonged 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 performing 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 
 
ii JOSEPH PKIESTLEY 43 
 
 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, according to Stahl's doctrine, by 
 supposing that air had an affinity for phlogiston, and 
 that in the act of combustion the phlogiston was trans- 
 ferred from the candle to the air. Gradually, however, 
 the limited amount of air becomes saturated with 
 phlogiston that is, wholly phlogisticated and com- 
 bustion 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 phlogisticated 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 knowledge 
 of chemistry ; he was possessed of no apparatus, and 
 had scarcely the means of procuring any. But these 
 
44 JOSEPH PEIESTLEY n 
 
 very circumstances were the sources of his success, since 
 he was under the necessity of devising original processes 
 and appliances suited to his narrow means and peculiar 
 views. " If," he says, " I had been previously accus- 
 tomed 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 of experi- 
 menting with before it took its present shape. In his 
 experiments with fixed air he observed that this gas 
 conferred " 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 likewise observed that 
 " the pressure of the atmosphere assists very consider- 
 ably 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 pro- 
 perties 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 
 
ii JOSEPH PKIESTLEY 45 
 
 was inclined to suppose 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 contributed 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 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 r 
 inflammable air, I imagined, consisted of it and some- 
 thing else. However, I was then satisfied that it would 
 be in my power to determine, in a very satisfactory 
 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 
 
46 JOSEPH PEIESTLEY n 
 
 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 phlogiston" 
 
 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 some- 
 times 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 inflammable 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 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 regener- 
 ate 1 oz. of lead from the yellow calx is 4 '6 grains no 
 great disparity, after all, from Priestley's result. The 
 377 oz. measures of hydrogen required to revive 1 oz. 
 of tin would weigh about 15*4 grains ; modern chemistry 
 
ii JOSEPH PKIESTLEY 47 
 
 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 
 crushing 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 
 inflammable air imbibed by it would sufficiently add to 
 its weight." Every sound phlogistian for at least a 
 quarter of a century after Stahl's death believed that 
 when a metal was calcined the calx must weigh less 
 than the metal : for had not phlogiston 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 Eey 
 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, 
 
48 JOSEPH PRIESTLEY n 
 
 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 gainsaid 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 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 
 
 1 A repetition of the experiments of Sulzbach. 
 
ii JOSEPH PKIESTLEY 49 
 
 it." And Priestley assuredly would have adopted it if 
 he could only have looked at the results of his experi- 
 ments otherwise than through the fogs of his prejudices. 
 He would have grasped the fact that with the disappear- 
 ance 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 bethought 
 to be favourable to the hypothesis of water being com- 
 posed 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 frequently water was formed in processes in which 
 the inflammable air played a part. 
 
 When steam is driven through a red-hot iron tube 
 inflammable air, the phlogiston of Priestley and Caven- 
 dish, 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 inflam- 
 mable air to be nothing else but one of the elements or 
 constituent parts of water. As to myself, I was a long 
 
 E 
 
50 JOSEPH PKIESTLEY n 
 
 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 con- 
 tinued 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 pneu- 
 matic 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 in- 
 flammable 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 7| 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 inflam- 
 mable 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 estab- 
 lished the correctness of Lavoisier's opinion, and disproved 
 
ii JOSEPH PRIESTLEY 51 
 
 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 inflam- 
 mable air, or hydrogen ; and the proportion 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 proportion to its fitness for this purpose ; 
 so that by this means the goodness of air may be dis- 
 tinguished much more accurately than it can be done by 
 
52 JOSEPH PKIESTLEY n 
 
 putting mice, or any other animal, 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 Ij 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 transferred 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 
 
ii JOSEPH PEIESTLEY 53 
 
 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 experi- 
 menters, less conscientious than Priestley, found the 
 differences they sought for ; but the researches of 
 Bunsen, of Regnault, 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 that, 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 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 marine acid air." Spirit of salt, 
 or, as chemists also term it, hydrochloric acid, is there- 
 fore nothing else than a solution of Priestley's marine 
 acid air in water. 
 
54 JOSEPH PRIESTLEY n 
 
 This discovery induced Priestley to try the same 
 experiment 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 
 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 1 8th century. Glass, as you 
 
ii JOSEPH PKIESTLEY 55 
 
 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 formation 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 harts- 
 horn as he had treated the spirit of salt, and he presently 
 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 composition 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 
 
56 JOSEPH PKIESTLEY n 
 
 volume, and that no part of it was soluble in water. 
 The gas, in fact, had been decomposed into its con- 
 stituents into hydrogen (the presence of which Priestley 
 recognised), and into nitrogen, which he calls phlogisti- 
 cated air, and which, he says, is contained 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 harrow- 
 ing your distracted nerves with the sight of his murder- 
 ous 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 
 bur forefathers drove him. 
 
 The crowning work of Priestley's life was, however, 
 the discovery of that gas which he termed dephlogisti- 
 cated air, but to which Lavoisier, who swept away all 
 
II JOSEPH PKIESTLEY 57 
 
 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 philosophical 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 experi- 
 ments, an account of which will be found in its proper 
 place, on the 1st of August 1774 I endeavoured to 
 extract air from mercurius calcinatus 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 
 calcinatus, I was utterly at a loss how to account for 
 it." His astonishment was still further increased when 
 
58 JOSEPH PKIESTLEY n 
 
 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 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 afterwards. Who can tell 
 but that in time this pure air may become a fashionable 
 article in luxury ? Hitherto only two mice and myself 
 have had the privilege of breathing it. ... But, per- 
 haps, 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 phlogisti- 
 cated air. This new air, he concluded, was devoid of 
 phlogiston hence the term " dephlogisticated 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, " con- 
 firmed 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 
 
ii JOSEPH PKIESTLEY 59 
 
 that I observe, I mentioned this experiment also, as well 
 as those with the mercurius calcinatus, to all my philo- 
 sophical 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 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 ADDRESS TO THE OWENS COLLEGE CHEMICAL SOCIETY, AT THE 
 OPENING MEETING, 24TH 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, de*- 
 daignant tout e*clat, 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 Tart, mais presque ignore* de son 
 siecle, avoit rendu son nom immortel lorsqu'il n'avoit 
 pas encore de celebrite." l 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 experi- 
 mentalist, 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 mien Auge." 
 
 1 Eloges historiques, vol. ii. p. 19. 
 60 
 
in GAEL WILHELM SCHEELE 61 
 
 The pursuit of truth for its own sake with no thought 
 of worldly gain or reward was to him the supreme 
 object of his existence 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 in- 
 formation 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 Eetzius, 
 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 chronological history of 
 his investigations, and so exhibit his true relations as 
 
62 CARL WILHELM SCHEELE in 
 
 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 Norden- 
 skiold this valuable collection of letters and laboratory 
 memoranda has now been given to the world, and the 
 historian of chemistry is at length 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 employment in them of an obsolete 
 nomenclature, but also to decipher the laboratory notes, 
 which are for the most part rough jottings of experi- 
 mental 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 anni- 
 versary 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, 
 
 1 Carl Wilhelm Scheele : Nachgelassene Brief e und Aufzeichnungen. Heraus- 
 gegeben von A. E. Nordenskiold. Stockholm : Verlag von P. A. Norstedt & Sbner. 
 
in GAEL WILHELM SCHEELE 63 
 
 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 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 
 XI. 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 ap- 
 parently not in a position to afford his sons the advan- 
 tages 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 memoranda, 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, 
 
64 GAEL WILHELM SCHEELE m 
 
 however, that the course of his inclination 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 after- 
 wards, 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 labora- 
 tory 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 Praelectiones Chemicae, Lemery's Cours de 
 Chimie, Boerhaave's Elementa Chemicae, 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 Neu- 
 mann'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 foundations of the manipulative skill and 
 analytical dexterity on which his success as an investi- 
 gator 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. 
 
m GAEL WILHELM SCHEELE 65 
 
 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 him, 
 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 Malmo he bought as many books as his 
 small pay enabled him to procure. These he would read once or 
 twice 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 prearranged plan. He was thus enabled to learn what no 
 doctrinaire could possibly acquire, since working by no formu- 
 lated 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 Malmo 
 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. 
 
 F 
 
66 GAEL WILHELM SCHEELE m 
 
 In 1768 Scheele removed to Stockholm, where he 
 superintended the shop of an apothecary named Scharen- 
 berg. Here his opportunities for experimenting were 
 considerably restricted. 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 
 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 suc- 
 ceeded 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 iron with a solution of cream of 
 tartar. The paper was, for the most part, a description 
 of experiments ; it was unmethodically put together, 
 and was without definite theoretical result. It was 
 referred by the Academy to Bergmann, 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 
 
in GAEL WILHELM SCHEELE 67 
 
 water alone on iron filings. The theoretical value of these 
 facts will be obvious from the circumstance that Caven- 
 dish, 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 
 contribution " Chemical Experiments with Sal- 
 acetosellae" [acid potassium 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 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, 
 
68 GAEL WILHELM SCHEELE m 
 
 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 potassium 
 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 Retzius, 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 anything 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 Eetzius, 
 " which of the two, Scheele or Bergmann, was the teacher 
 or the taught. Bergmann, without a doubt, received 
 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 
 
in GAEL WILHELM SCHEELE 69 
 
 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 con- 
 tained 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 
 Eetzius, and have abandoned pharmacy for an academic 
 career. M. Nordenskiold finds an explanation in the 
 assumption that the Zunftgeist of the time would not 
 permit of the introduction of the studiosus pharmaciae 
 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 constituted 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 abund- 
 ant opportunity 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 
 
70 GAEL WILHELM SCHEELE m 
 
 Priestley s discovery, Scheele had prepared oxygen 
 from the carbonates of silver and mercury, from 
 mercuric oxide, nitre and magnesium nitrate, and by 
 the distillation of a mixture of manganese 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 Pohl, 
 whose privilege, in conformity with Swedish law, had 
 passed, on his death, to his young widow, Sara Mar- 
 garetha 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 prospect of a fairly lucrative business, and he 
 would now be able to follow his cherished projects under 
 conditions of comparative 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 was to be consecrated to 
 science. " There is no delight," 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, 
 
in GAEL WILHELM SCHEELE 71 
 
 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 Bergman n of his disappointment show how 
 deeply he felt it. Offers of assistance came from 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, nomine* M. Scheele, Membre de 
 1' Academic des Sciences de cette ville, et qui, sans 
 m'etre d'ailleurs connu, me paroit fort estime 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 invitation to Berlin with a salary of 1200 reich- 
 thalers. Crell, the editor of the well-known Neue 
 Entdeckungen and Annalen 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 statement 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 improb- 
 able. " I am utterly at a loss," says Thomson, " to 
 conceive what one individual in any of the ministries 
 
72 CARL WILHELM SCHEELE m 
 
 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 Kevolution to the 
 present time." However this may be, there is one name 
 that suggests itself as the possible author of such a pro- 
 ject, and that is Lord Shelburne. Had Thomson been 
 able to question Priestley 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 elsewhere." 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 prin- 
 cipal 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 
 
in CARL WILHELM SCHEELE 73 
 
 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 prosperous, 
 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 un- 
 complainingly ; 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-abnegation, he deliberately 
 set himself to retrieve the fallen fortunes of the widow's 
 estate. 
 
 For years his life was a continual struggle with priva- 
 tion, relieved to some extent by an annual grant of 100 
 rix-thalers, which the Academy, at Bergmann's instiga- 
 tion, made him in 1777. 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. 
 
74 GAEL WILHELM SCHEELE m 
 
 Although never of robust health, he had been fairly free 
 from illness up to his thirty-fifth year, when he con- 
 tracted 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, however. 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, 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 busi- 
 ness 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 newprovisor 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, Kjellstrom, has 
 
in GAEL WILHELM SCHEELE 75 
 
 recorded that such phrases as " Das kann sein " ; " Das 
 ist nicht rich tig " ; " 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 discovered 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 ascertained the 
 chemical nature of sulphuretted hydrogen, discovered 
 arsenetted hydrogen, and the green arsenical pigment 
 which is associated with his name. He invented new 
 processes for preparing ether, powder of algaroth, phos- 
 phorus, calomel, 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 atten- 
 tion, and was translated into almost every European 
 
V6 CARL WILHELM SCHEELE m 
 
 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 
 antumn of 1770, and partly during the earlier portion 
 of his stay in Upsala 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 
 Bergmann : " 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 assurance in his own vin- 
 dication, 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 
 
in CARL WILHELM SCHEELE 77 
 
 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 conflicting obser- 
 vations. 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 quantita- 
 tive 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 specu- 
 late on the causes which prevented Scheele from recog- 
 nising 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 surmises, as Scheele himself said, cannot 
 
78 CARL WILHELM SCHEELE in 
 
 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 
 limitations, stamps him as the greatest chemical dis- 
 coverer 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 
 HENKY CAVENDISH 
 
 A LECTURE DELIVERED IN THE HULME TOWN HALL, MANCHESTER, ON 
 24TH 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 
 
 79 
 
80 HENKY CAVENDISH iv 
 
 in the course of his fourscore years than any man who 
 ever lived so 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 shy- 
 ness, 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 gentleman, with a large frill, on the step, and 
 two or three lumbering vehicles, having set d<?wn their 
 charges, are rattling away over the rough stones into 
 the obscurity of the dimly -lighted street. My know- 
 ledge 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, 
 
iv HENRY CAVENDISH 81 
 
 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 Royal 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 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 gentle- 
 man 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 Honour- 
 able 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 con- 
 cerning, 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 inven- 
 tions. 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 
 
 G 
 
82 HENEY CAVENDISH iv 
 
 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 ner- 
 vous, 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 make the acquaintance 
 of a philosopher so profound and so universally cele- 
 brated all of which is confirmed by the foreign gentle- 
 man, 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 
 
iv HENKY CAVENDISH 83 
 
 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. Caven- 
 dish 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 three-cornered 
 hat, and then the greatcoat, 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 
 servant, 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. 
 
84 HENEY CAVENDISH iv 
 
 There is nothing lovable in such a character ; on the 
 other hand, there is nothing in it that is despicable. 
 This passionless 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 eighteenth century Dr. Black for the discovery of 
 certain fundamental 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 investigations, was whether 
 our mercurial thermometer was an accurate and uniform 
 measurer of temperature, to the extent of showing 
 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 
 
iv HENRY CAVENDISH 85 
 
 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 temperatures, 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 quicksilver to cool the same 
 weight of hot water through the same interval of tem- 
 perature. He made trials with various metals, with 
 sulphur, glass, charcoal, and many other bodies, and he 
 concludes " that the true explanation of these pheno- 
 mena 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 
 important 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 ther- 
 mometer. 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 deter- 
 mined the temperature at which quicksilver freezes, and 
 found it to be 39 degrees below the point at which water 
 
86 . HENKY CAVENDISH iv 
 
 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 experi- 
 ments, 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 
 laboratories in the world a laboratory erected at Cam- 
 bridge 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 discoveries 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 eighteenth 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 to arise from their being "tainted," or " infected 
 with fumes, vapours, or sulphurous spirits." The publi- 
 cation of a celebrated essay by Black on " Magnesia 
 Alba " marked an epoch in the history of chemistry by 
 demonstrating the existence of at least one gaseous 
 
 1 The late Professor Clerk Maxwell. 
 
iv HENEY CAVENDISH . 87 
 
 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 alkalis, especially if dissolved in water, 
 rapidly absorb the gas, but it may be collected and pre- 
 served over quicksilver for any length of time ; indeed 
 chemists owe the idea of using quicksilver 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 composed of chalk, 
 
88 HENRY CAVENDISH iv 
 
 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 solution, 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 underneath 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, 
 
iv HENRY CAVENDISH 89 
 
 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, and by giving 
 out another portion of dissolved carbonic acid deposits 
 another portion of carbonate of lime on the first deposi- 
 tion ; 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 therefore 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 consider- 
 ably 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 
 
90 HENEY CAVENDISH iv 
 
 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, underestimated the lightness of 
 this gas ; in reality it is about fourteen and a half times 
 lighter than air. 
 
 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, conse- 
 quent 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 towns- 
 man, 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 
 
iv HENEY CAVENDISH 91 
 
 half of the year 1781 I tried the air of near sixty differ- 
 ent 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 proportion 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 
 adopt, the mean composition of the air is in 100 parts 
 by measure : 
 
 Oxygen $ "- V . . . 20'8 
 Nitrogen . < - . . . 79'2 
 
 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 occasion- 
 ally 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 especi- 
 ally remarkable, 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. 
 
92 HENEY CAVENDISH iv 
 
 Dr. Priestley relates in one of his volumes of Experi- 
 ments 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 characteristic- 
 ally 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 diminu- 
 tion of volume 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 con- 
 densed 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 conveyed 
 slowly into this cylinder by separate copper pipes, pass- 
 ing 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 spreading into the magazines from 
 which they were conveyed. . . . By this means upwards 
 of 135 grains of water were condensed in the cylinder, 
 
iv HENKY CAVENDISH 93 
 
 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 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 
 
94 HENKY CAVENDISH iv 
 
 in it, without any fresh exhaustion of the globe." 
 Cavendish, however, 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 discovery namely, that 
 of the composition of nitric acid, an acid which is prob- 
 ably 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. When- 
 ever the amount of oxygen was larger than could com- 
 bine 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. 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 substance 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 " ? 
 
 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 
 
iv HENEY CAVENDISH 95 
 
 ascribed to Cavendish formed no exception to this rule. 
 Not many years ago there was a great controversy con- 
 cerning 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 eighteenth 
 century will admit that the labours of a dozen of Caven- 
 dish'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 dis- 
 covery 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 Caven- 
 dish'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 spheroid of water of equal size. The 
 apparatus which he employed consisted of a long light 
 wooden rod 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 
 
96 HENEY CAVENDISH iv 
 
 necessary to produce it, being known, together with the 
 weight of the balls, and the distances from their centres, 
 the attraction of a spheroid of water of the same diameter 
 as the earth upon the ball on its surface can be calcu- 
 lated, from which can also be calculated the relation of 
 the earth's density to that of water. From his experi- 
 ments, 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 divination, 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 chemistry ; 
 that chemistry is in fact a science of quantitative rela- 
 tions. But let us take a retrospect of Cavendish's 
 labours. He fixed the weight of the earth ; he estab- 
 lished the proportions of the constituents of the air ; he 
 occupied himself with the quantitative 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 most 
 obvious characteristic of all this labour ? Is it not its 
 
iv HENRY CAVENDISH 97 
 
 thoroughly quantitative character ? Weighing, measur- 
 ing, 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 " ? 
 
JAMES WATT 
 
 AND 
 
 THE DISCOVERY OF THE COMPOSITION OF WATER 
 
 BEING THE WATT ANNIVERSARY LECTURE DELIVERED BEFORE THE 
 GREENOCK PHILOSOPHICAL SOCIETY ON HTH MARCH 1898 
 
 WHEN your Secretary did me the honour to com- 
 municate the wish of the Committee that I should 
 deliver this lecture, he was good enough to send me a 
 list of the names of my predecessors in the position I 
 was invited to occupy, together with a statement of 
 the subjects on which they had addressed you. I 
 confess I read his letter with very mingled feelings. 
 To be asked to form one of such a distinguished 
 company was in itself an honour which I deeply 
 appreciated. On the other hand, it seemed well-nigh 
 hopeless to find any theme associated with the life and 
 work of the great man whose services to humanity we 
 are this day called upon to commemorate that had not 
 been dealt with by one or other of those who had 
 preceded me. Naturally, and as befits the subject, 
 the greater number of those who have spoken on these 
 occasions have been distinguished engineers and 
 mechanicians, and they have been able to speak with 
 a fulness of knowledge and a weight of authority on 
 the outcome of the great engineer's labours to which I, 
 
 98 
 
v JAMES WATT 99 
 
 who know nothing of engineering or machinery, can 
 have no pretensions. 
 
 It has occurred to me, however, that there might 
 be one incident in Watt's career which, in all prob- 
 ability, had not been handled by any one of those 
 whom you have invited to appear here, and on which, 
 as it comes within my own province, I thought I 
 might venture, without presumption, to engage your 
 attention. I was the more impelled to select it, in 
 that it illustrates one side of Watt's intellectual activity 
 which those who regard him only as an inventor and 
 a mechanician are apt to undervalue, or even to lose 
 sight of altogether. It serves, too, to throw additional 
 light upon his mental character and his moral worth, 
 and thus enables us to form a fuller and more just 
 appreciation of the attributes of the man we wish to 
 honour. The incident, in a word, relates to Watt's 
 share in the establishment of the true view of the 
 chemical nature of water. 
 
 To the historian of science this is doubtless an old 
 story on which it would be difficult to say anything 
 new. The literature concerned with it occupies many 
 volumes, largely owing to the circumstance that it has 
 given rise to a controversy which has engaged the active 
 interest of some of the strongest and subtlest intellects 
 of the nineteenth century. Some of the disputants 
 have been men like Brougham, Jeffrey, and Muirhead, 
 skilled in the arts of advocacy and in the faculty of 
 eliciting and weighing evidence, who have stated their 
 conclusions with all the " pomp and circumstance " of a 
 judicial finding ; others are men like Arago, Dumas, 
 Harcourt, Whewell, Peacock, Kopp, George Wilson, 
 eminent in science and literature, who have defended 
 their convictions with great power, ample knowledge, 
 
100 JAMES WATT v 
 
 much argumentative force, and occasional eloquence, 
 At one time the contest was waged with no little fury 
 and bitterness; it threatened, indeed, like the famous 
 controversy as to the proper form of a lightning-con- 
 ductor, during Sir John Pringle's presidency of the 
 Koyal Society, or like the equally famous controversy 
 as to the true discoverer of the planet Neptune, to 
 attain the dignity of a national question, far more 
 acute, I should imagine, than that which has recently 
 occasioned all right-feeling Scotchmen to approach the 
 Queen in Council on the subject of Scotland's proper 
 place and designation in Imperial concerns. 
 
 But, happily, the acrimony and ill-feeling have long 
 since passed away. There is no longer any need to 
 discuss the question either as an advocate or as a 
 partisan. What I shall attempt to-night is to treat it 
 dispassionately, and, within the compass of an hour, to 
 assess, as impartially as I am able, Watt's true place in 
 regard to this discovery. 
 
 It was indeed an epoch-making event. The dis- 
 covery of the composition of water was as momentous 
 for science as the greatest of Watt's inventions was 
 for social and economic progress. The very fact itself, 
 apart from all that flowed from it, was of transcendent 
 interest. But to those who had eyes to see, its 
 supreme importance was in its fruitful and far-reach- 
 ing consequences. It signified nothing less than the 
 passing away of an old order of things : the downfall 
 of a system of philosophy which had outlived its use- 
 fulness, in that it no longer served adequately to 
 interpret natural phenomena, and had become rather 
 a hindrance and a stumbling-block to the perception 
 of truth. The discovery at once led to the inception 
 of a more rational and more truly comprehensive 
 
v JAMES WATT , V 
 
 theory, which not only explained what was already 
 known in a fuller, clearer, and more intelligible 
 manner, but pointed the way to new facts hitherto 
 undreamt of, facts which in their turn served to 
 strengthen and extend the generalisation which led to 
 their discovery. No wonder, therefore, that those who 
 loved and revered Watt, and who were rightly jealous of 
 his honour, should have sought to do all in their power 
 to vindicate what they honestly conceived to be his just 
 title to so signal and so fundamental a discovery. 
 
 No man has a juster claim to be regarded as a 
 scientific man, in the truest and noblest sense of that 
 term, than James Watt. The scientific spirit was 
 manifest in him even in boyhood. The very circum- 
 stances of his condition, his weakly frame, the soli- 
 tariness of his school -life, and the early habit of 
 introspection thus induced in a mind forced to feed 
 only on itself, served to strengthen and develop 
 the instinct. Even his early struggles, and the 
 jealousy of the Glasgow Guilds, which forbade him to 
 practise his trade in the burgh in which he had not 
 served an apprenticeship, conduced to mould his 
 character and to determine the bent of his mind. 
 Hard and illiberal as it seemed at the time, the 
 Zunftgeist which drove him to the shelter of the old 
 College in the High Street, and secured for him the 
 abiding friendship of Black and Kobison, was in 
 reality the most fortunate circumstance of his career. 
 It brought him directly under the influence of one 
 of the greatest natural philosophers of his age, and 
 stamped him permanently as a man of science. It 
 would not be difficult to trace how this influence 
 reacted upon all that Watt subsequently did from 
 the time of his earliest speculations on the loss of 
 
;1;02 - JAMES WATT v 
 
 energy in Newcomen's engine down to the very last of 
 his mechanical pursuits in the dignified retirement of 
 Heathfield Hall. He approached the question of the 
 improvement of the steam-engine as a scientific 
 problem, and under the direct inspiration of the 
 doctrine of the great discoverer of the principle of 
 latent heat. It was this same mental attitude towards 
 scientific truth, the same receptivity for scientific 
 doctrine, the same love of pondering over and speculat- 
 ing upon the true inwardness of things, that brought 
 him the friendship of Priestley, Withering, Wedgwood, 
 and Deluc, and that ultimately made him a cherished 
 member of the foremost scientific academies of the 
 world. It will occasion little surprise to one who has 
 formed a true perception of his character to learn that 
 Watt was wont, even at periods of great mental 
 depression, and of physical suffering, amidst all the 
 toil and anxious worry of a business surrounded with 
 difficulties, to find peace in the contemplation of 
 natural phenomena, and to spend time in philosophical 
 speculation. The shrinking, diffident man, in thus 
 communing with himself and with Nature, followed a 
 true and constant impulse to withdraw from the strife 
 and turmoil of the world, and to seek his pleasure and 
 his rest in the contemplation of natural truth. No one 
 can look upon that contemplative face without being 
 struck with its expression of philosophic calm. What 
 deep, genuine pleasure these communings brought to 
 the harassed man may be gleaned from his correspond- 
 ence. In truth, Nature intended Watt to be a 
 philosopher of the pattern of Boyle, or Newton, or 
 Dalton : it was destiny that drove him into the world 
 of affairs, where, as he said, he was out of his true 
 sphere. It is necessary to dwell for a moment on this 
 
v JAMES WATT 103 
 
 aspect of Watt in order to form a just appreciation 
 both of his position and of his merits in regard to the 
 great chemical truth with which his name is associated. 
 The man of action is apt to regard the contemplative 
 mind with something akin to contempt. I once heard 
 a bustling, busy man, the head of a large engineering 
 establishment, who had enjoyed the good fortune to be 
 a pupil of Thomas Graham, say of that distinguished 
 philosopher that he was the laziest man he ever met. 
 He did not say he ever knew for how little he really 
 knew Graham was evident from the fact that at the 
 period to which he referred Graham's thoughts were 
 deeply occupied with some of the most memorable of 
 his investigations. 
 
 It was in one of these contemplative moods in 
 what he himself styled his periods of excessive indolence 
 and, as it happened, at the very time that the Soho 
 firm was struggling to protect itself against the 
 unprincipled horde that was seeking to infringe Watt's 
 fundamental patent, that he occupied himself with 
 turning over in his mind the outcome of one of his 
 friend Priestley's multitudinous experiments. Watt had 
 long held the view that air was a modification of 
 water, or, as he expressed it in a letter to his friend 
 Black, under date Dec. 13, 1782, that, as steam parts 
 with its latent heat as it acquires sensible heat, or is 
 more compressed, when it arrives at a certain point 
 it will have no latent heat, and may, under proper 
 compression, be an elastic fluid nearly as specifically 
 heavy as water ; at which point, he conceived, it would 
 again change its state and become air. As he then 
 relates, he sees a confirmation of this opinion in an 
 experiment of Priestley's, made, as he says, " in his 
 usual way of groping about." " As he [Priestley] had 
 
104 JAMES WATT v 
 
 succeeded in turning the acids into air by heat only, he 
 wanted to try what water would become in like circum- 
 stances. He undersaturated some very caustic lime 
 with an ounce of water, and subjected it to a white 
 heat in an earthen retort. . . . No water or moisture 
 came over, but a quantity of air, equal in weight to the 
 water, ... a very small part of which was fixed air, 
 and the rest of the nature of atmospheric air. . . . He 
 has repeated the experiment with the same result." 
 
 About a fortnight later Priestley wrote that he was 
 able to convert water into air " without combining it 
 with lime or anything else, with less than a boiling heat, 
 in the greatest quantity and with the least possible 
 trouble or expense." He added that " the method will 
 surprise more than the effect," but that he would defer 
 " the communication of the hocus pocus of it " until 
 such time as Watt should give him the pleasure of his 
 company in return for the pleasure he was to give Watt 
 in speculating on the subject. 
 
 These experiments, as we shall see in due course, 
 were wholly fallacious : in following them up with his 
 wonted ardour Priestley quickly found himself in a 
 maze of contradictions, and ultimately discovered that 
 this seeming conversion was absolutely mythical. 
 
 It may be useful, however, to make one or two 
 comments on these passages at the present juncture. 
 In the first place, Watt's opinion as to the relations of 
 water and air, although founded as he thought upon a 
 more philosophical basis, simply embodied the teaching 
 of the schoolmen. The notion that the so-called four 
 elements were mutually convertible, or were in essence 
 identical, ran through the doctrine of twenty centuries 
 of teachers. Despite the onslaughts of the Spagyrists, 
 and of the author of the Sceptical Cliymist, it per- 
 
v JAMES WATT 105 
 
 meated the literature of natural philosophy down to the 
 very beginning of this epoch. Watt was insensibly 
 swayed by a belief which had descended to him, like 
 the undying germ, through the ages, and he could no 
 more shake himself free of it than he could get rid of 
 the influence of heredity. The very mode in which he, 
 in common with the men of his time, uses the term 
 " air," is an indication of the manner in which this 
 ancient creed limited and cramped his thought. He 
 knew that there were various " airs," but it is very 
 doubtful if he realised that they were essentially different 
 substances. There is abundant evidence in the few 
 chemical papers that he published, and especially in his 
 letters to Black, Priestley, Deluc, Kirwan, and others, 
 that he regarded them all as constituted of the same 
 matter, affected by attributes more or less fortuitous 
 and accidental. Thus, all the varieties of inflammable 
 air were at bottom identical, with properties modified 
 by their origin, or by their varying content of the 
 hypothetical principle phlogiston that is, the principle 
 that was assumed to make them burn. 
 
 From Watt's published correspondence we are able 
 to judge how he regarded Priestley's further work on 
 this so-called conversion of water into air. He admits 
 that the facts are " in some degree contradictory to each 
 other." The apparent conversion would seem to depend 
 upon the material of the vessel in which it was made. 
 In a glass vessel no air was produced, nor was any found 
 in a gun-barrel when the distillation was done slowly, 
 but when confined by a cock, " and let out by puffs it 
 produces much air ; which," says Watt, " agrees with 
 my theory and also coincides with what I have observed 
 in steam-engines. In some cases I have seen the tenth 
 of the bulk of the water, of air extricated or made from 
 
106 JAMES WATT v 
 
 it." Davy once said "the human mind is always 
 governed, not by what it knows, but by what it believes, 
 not by what it is capable of attaining, but by what it 
 desires." However willing to catch at anything in 
 support of his belief, it is possible that Watt might 
 have been led to doubt the soundness of Priestley's 
 experiment if an apparent and wholly unlooked-for 
 confirmation of it had not now arisen. 
 
 To make the account exact, and in view of what is 
 to follow, it is necessary to go back a little, in point of 
 time. In the spring of 1781 Priestley performed what 
 he styled " a mere random experiment made to entertain 
 a few philosophical friends." It was practically a 
 repetition of Volta's experiment of firing a mixture of 
 the inflammable air from metals, that is, hydrogen, with 
 common air in a closed glass vessel by means of the 
 electric spark. After the deflagration the vessel was 
 found to be hot, and on cooling its sides were observed 
 to be bedewed. Neither Priestley nor any one of his 
 philosophical friends seems to have paid any particular 
 attention to the deposit of moisture, or at all events if 
 they did they failed to perceive its significance. One of 
 them, however, Mr. John Warltire, a Lecturer in Natural 
 Philosophy in Birmingham, imagined that the experi- 
 ment might afford the means of showing whether heat 
 was ponderable or not, and accordingly he repeated it, 
 using for greater safety a copper globe, weighed before 
 and after the passage of the spark. A minute loss of 
 weight was always noticed, " but not constantly the 
 same : upon the average it was about two grains." 
 
 Priestley, who, with Withering, was present when 
 
 1 The account of these experiments is given in a letter to Priestley, and 
 constitutes No. V. of the Appendix to Priestley's Experiments and Observations 
 relating to various branches of Natural Philosophy, etc. Vol. II., Birmingham, 
 1781. 
 
v JAMES WATT 107 
 
 the experiments were made, confirmed the apparent loss 
 of weight ; but he adds, with a caution that was not 
 habitual, that he did not think " that so very bold 
 an opinion as that of the latent heat of bodies contri- 
 buting to their weight should be received without more 
 experiments, and made upon a still larger scale." 
 
 Priestley's volume the sixth in the series was 
 published in 1781, and was certainly known to Watt; 
 indeed, in the Appendix are printed a number of obser- 
 vations made by him, apparently as the work was 
 passing through the press. Although, therefore, he 
 must have had his attention drawn at about this time 
 to the formation of the dew in Priestley and Warltire's 
 experiment, there is nothing to show that he attached 
 any importance to the circumstance, or that if he did 
 he dissented from Warl tire's conclusion that common air 
 deposits its moisture when it is phlogisticated. 
 
 For some time previous to the publication of Priest- 
 ley's book, Mr. Cavendish was engaged upon an inquiry 
 " 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 condensed." In other words, it was an 
 investigation to determine the changes experienced by 
 air when bodies were made to burn in confined portions 
 of it. On the appearance of Priestley's book he repeated 
 Warltire's experiment, thinking " it worth while to 
 examine more closely " as it " seemed likely to throw 
 great light on the subject I had in view." He confirmed 
 the observation on the formation of dew, but although 
 he made the experiment on a large scale, and with 
 varying proportions of the two airs, he was unable to 
 satisfy himself as to the loss of weight after the explosion. 
 As the result of a number of trials made both with the 
 
108 JAMES WATT v 
 
 inflammable air from zinc and from iron, that is, hydro- 
 gen, and mixed with common air in the proportion of 
 423 measures of the inflammable air to 1000 of common 
 air, he says, " we may safely conclude that when they 
 are mixed in this proportion and 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." In order to examine 
 the nature of this dew, large quantities of the hydrogen 
 were burnt with two and a half times its volume of 
 common air, and the product of the combustion was 
 caused to pass through a long glass tube whereby it was 
 condensed. "By this means 135 grains of water were 
 condensed in the cylinder, which had no taste nor smell, 
 and which left no sensible sediment when evaporated to 
 dryness ; neither did it yield any pungent smell during 
 the evaporation ; in short, it seemed pure water. . . . 
 By the experiments with the globe it appeared that 
 when the inflammable and common air are exploded in 
 a proper proportion, almost all the inflammable air and 
 near one-fifth of the common air lose their elasticity, 
 and are condensed into dew. And by this experiment 
 it appears that this dew is plain water, and, conse- 
 quently, that almost all the inflammable air and about 
 one-fifth of the common air are turned into pure water." 
 The idea that common air was for the most part a 
 mixture of two gases oxygen, or the dephlogisticated 
 air of Scheele and Priestley, and nitrogen, or the 
 mephitic air of Rutherford, the azote of Lavoisier was 
 familiar to chemists at this period as the result of the 
 teaching of Scheele and Lavoisier ; and there is reason 
 to suppose that this opinion was shared by Cavendish. 
 He had been engaged for some time past in an elaborate 
 inquiry into the constitution of atmospheric air, the 
 
v JAMES WATT 109 
 
 results of which admitted of no other interpretation 
 than that common air was composed of two different 
 gases, mixed or combined in constant relative propor- 
 tions. It is true that in the memoir containing the 
 results of his inquiry he nowhere directly gives his 
 estimate of these relative quantities, but from the data 
 he affords it is easy to deduce both the amount and 
 the constancy of the proportion. Cavendish's papers are 
 characterised by a remarkable conciseness and brevity ; 
 an experiment which must have involved the putting 
 together of elaborate and complicated apparatus, and 
 which must have occupied considerable time in its per- 
 formance, is described in a few lines, and hence it is 
 not always possible to gather with certainty the precise 
 disposition of the arrangements. He never sets out his 
 reasons or his conclusions with any great amount of 
 detail, and his published works occasionally give little 
 indication of his line of thought. But that he clearly 
 recognised that only one portion of common air was 
 concerned in the formation of water, and that this 
 portion was the dephlogisticated air, or oxygen, is 
 obvious from his next series of experiments, in which 
 he fired a mixture of about two measures of hydrogen 
 and one measure of oxygen in a previously exhausted 
 glass globe, furnished with an apparatus for firing air 
 by electricity. When the included air was fired, almost 
 all of it lost its elasticity, so that fresh quantities of the 
 explosive mixture could be introduced and the process 
 repeated until a sufficient quantity of the moisture was 
 obtained for examination. In these experiments Caven- 
 dish clearly and definitely demonstrated that the weight 
 of the water was practically equal to the weight of the 
 mixed gases which had combined to form it. In some 
 cases the water was perfectly neutral in its reaction ; in 
 
110 JAMES WATT v 
 
 others it was slightly acid, and the cause of this acidity 
 cost Cavendish much experimenting to discover, but he 
 is never in any doubt as to the main result ; he says 
 distinctly, " if those airs could be obtained perfectly 
 pure, the whole would be condensed." Now, if Caven- 
 dish had published this main result at the time he 
 obtained it, namely, in the summer of 1781, or even if 
 he had formally communicated it to one of the meetings 
 of the Koyal Society during the ensuing session, there 
 would have been no Water Controversy. But even if 
 he were ready, it was characteristic of him to delay, not 
 from inertia or indolence, but from a morbid shyness, 
 an unconquerable reticence, which constantly led him to 
 postpone any public announcement of his work. He 
 had the additional, and to him all-sufficient reason, that 
 he had not yet worked out the cause of the occasional 
 acidity of the water. What he did, however, was to 
 communicate the facts of his experiments to Priestley, 
 as Priestley himself states in a subsequent paper pub- 
 lished in the Philosophical Transactions for 1783. 
 When or how he communicated them to Priestley does 
 not appear, nor have we any means of knowing precisely 
 what was said. Something, however, on this point may 
 be inferred from what Priestley proceeded to do. It 
 appears from a letter to Wedgwood that he repeated 
 Cavendish's experiments during the March of 1783. It 
 will be remembered that he was at this period engaged 
 on his experiments on the seeming conversion of water 
 into air. He had obtained a number of contradictory 
 results, which had led Wedgwood, as far back as the 
 previous January, to put certain sagacious queries which 
 doubtless in the end had their effect in opening Priest- 
 ley's eyes to the origin of his mistake. But at the 
 time both he and Watt were seeking for fresh evidence 
 
v JAMES WATT 111 
 
 to substantiate the possibility of this conversion. Now 
 just as Cavendish thought that Warltire's experiment 
 might throw light upon the particular matter on which 
 he was then engaged, so Priestley considered that 
 Cavendish's work might afford evidence indirect, it is 
 true, but still evidence of the intimate connection 
 between water and air. Cavendish had, he thought, 
 established the converse of the proposition which he and 
 Watt were seeking to prove, in showing that " air," or 
 rather certain kinds of " air," could be converted into 
 water, weight for weight. It was no longer the original 
 Warltire experiment of exploding common air and 
 hydrogen. Cavendish had indicated the particular 
 kinds which were really concerned in the phenomenon, 
 and it was the Cavendish experiment, pure and simple, 
 that Priestley proceeded to repeat. This is obvious 
 from what he says : " Still hearing of many objections 
 to the conversion of water into air, I now gave particular 
 attention to an experiment of Mr. Cavendish's concerning 
 the reconversion of air into water by decomposing it in 
 conjunction with inflammable air." Priestley here uses 
 the word " decomposing in a sense contrary to that 
 which the context implies, but that he is consistent in 
 so using it is evident from what follows, and also from 
 similar expressions to be found in his correspondence. 
 But although he professed to repeat Cavendish's experi- 
 ment, he neglected to do so in Cavendish's manner. 
 He says : " In order to be sure that the water I might 
 find in the air was really a constituent part of it, and 
 not what it might have imbibed after its formation [i.e. 
 by contact with the water of the pneumatic trough], I 
 made a quantity of both dephlogisticated and inflam- 
 mable air, in such a manner as that neither of them 
 should ever come into contact with water, receiving 
 
112 JAMES WATT v 
 
 them as they were produced in mercury ; the former 
 from nitre, and in the middle of the process (long after 
 the water of crystallisation was come over), and the 
 latter from perfectly made charcoal. The two kinds of 
 air thus produced I decomposed by firing them together 
 by the electric explosion, and found a manifest deposi- 
 tion of water, and to appearance in the same quantity 
 as if both the kinds of air had been previously confined 
 by water. In order to judge more accurately of the 
 quantity of water so deposited, and to compare it with 
 the weight of the air decomposed, I carefully weighed a 
 piece of filtering-paper, and then having wiped with it 
 all the inside of the glass vessel in which the air had 
 been decomposed, weighed it again, and I always found r 
 as nearly as I could judge, the weight of the decomposed 
 air in the moisture acquired by the paper. ... I wished, 
 however, to have had a nicer balance for the purpose : 
 the result was such as to afford a strong presumption 
 that the air was reconverted into water, and therefore 
 that the origin of it had been air." 
 
 These passages, when compared with the accounts 
 given of his own work by Cavendish, strikingly 
 exemplify the difference in the character of the two 
 experimentalists. It would be difficult to pack a 
 greater number of blunders into a couple of paragraphs 
 than are contained in these sentences. The expressions 
 in italics show that Priestley wholly failed to com- 
 prehend the true origin of the water. In his laudable 
 anxiety to free the two gases from extraneous moisture 
 he committed blunder after blunder. His method of 
 obtaining the oxygen was bad ; that of procuring the 
 inflammable air was worse. Both the gases must have 
 been highly impure, and it was a physical impossibility 
 that they should have given their aggregate weight in 
 
v JAMES WATT 113 
 
 water, even after making every allowance for Priestley's 
 crude and imperfect method of determining it. 
 
 Bad as the experimental work was, what it 
 appeared to teach was not lost on Watt : it clearly 
 proved to him that water and air were mutually 
 convertible. How the theory took shape in his mind 
 is evident from the terms in which the two series of 
 Priestley's experiments are coupled together in his 
 letters to Gilbert Hamilton, to Deluc, and to Black. 
 Each set is regarded as complementary to the other, 
 and both taken together are held to prove that air 
 and water are mutually convertible and are therefore 
 essentially the same. Under date 21st April 1783, he 
 tells Black that "Dr. Priestley has made many more 
 experiments on the conversion of water into air, and 
 I believe I have found out the cause of it ; which I 
 have put in the form of a letter to him which will be 
 read at the Koyal Society with his paper on the 
 subject." He then proceeds to give Black a summary 
 of the three sets of facts, or supposed facts, on which 
 he bases his generalisation, and he makes use of these 
 significant words : " In the deflagration of the inflam- 
 mable and dephlogisticated airs, the airs unite with 
 violence, become red hot, and, on cooling, totally 
 disappear. The only fixed matter which remains is 
 water ; and ivater, light, and heat are all the products. 
 Are we not then authorised to conclude that water is 
 composed of dephlogisticated and inflammable air, or 
 phlogiston, deprived of part of their latent heat, and 
 that dephlogisticated, or pure air, is composed of water 
 deprived of its phlogiston and united to heat and 
 light ; and if light be only a modification of heat, or a 
 component part of phlogiston, then pure air consists 
 of water deprived of its phlogiston and of latent heat." 
 
 I 
 
114 JAMES WATT v 
 
 Very similar turns of expression and trains of reasoning 
 are to be met with in other letters to his friends 
 written at about the same period. In all, it is 
 abundantly clear that, whatever may have been his 
 surmises as to the real nature of water, it was the 
 conception of the mutual convertibility of air and 
 water that was uppermost in his mind. These passages, 
 however, constitute Watt's claim to be regarded as 
 the true and first discoverer of the compound nature 
 of water. 
 
 Three days after the letter to the Koyal Society 
 was written, or rather dated, there came a bolt from 
 the blue in the form of a letter from Priestley to Watt. 
 " Behold," it said, " with surprise and with indignation 
 the figure of an apparatus that has utterly ruined 
 your beautiful hypothesis, and has rendered some weeks 
 of my labour in working, thinking, and writing almost 
 useless." The doubts of Wedgwood, certainly no mean 
 authority on the properties of baked clay, had, in 
 fact, led Priestley to devise an experiment by which it 
 was proved beyond all doubt that this seeming con- 
 version of water into air was really due to an inter- 
 change of steam and air, effected by diffusion through 
 the porous material of the retort. Well might Priestley 
 cry to Deluc, " We are undone ! " Watt's faith in 
 the "beautiful hypothesis" was no doubt rudely 
 shaken, but it was not shattered. In his answer to 
 Priestley he denied that it was ruined : "It is not 
 founded," said he, " on so brittle a basis as an earthen 
 retort." Priestley, however, would have none of it ; 
 theories with him always excepting the all-compre- 
 hensive one of phlogiston, which was the head and 
 front of his creed, as, indeed, of his subsequent offending 
 had at no time much value, for, as Marat said of 
 
v JAMES WATT 115 
 
 Lavoisier, he abandoned them as readily as he adopted 
 them, changing his systems as he did his shoes. Indeed, 
 he rather prided himself on this capacity for quick 
 change. " We are, at all ages," he once said, " but 
 too much in haste to understand, as we think, the 
 appearances that present themselves to us. If we 
 could content ourselves with the bare knowledge of 
 new facts, and suspend our judgment with respect to 
 their causes, till by their analogy we were led to the 
 discovery of more facts of a similar nature, we should 
 be in a much surer way to the attainment of real 
 knowledge." With a candour all his own, he immedi- 
 ately added : "I do not pretend to be perfectly 
 innocent in this respect myself, but I think I have as 
 little to reproach myself with on this head as most of 
 my brethren ; and whenever I have drawn general 
 conclusions too soon, I have been very ready to abandon 
 them. ... I have also repeatedly cautioned my 
 readers, and I cannot too much inculcate the caution, 
 that they are to consider new facts only as discoveries, 
 and mere deductions from these facts as of no kind of 
 authority ; but to draw all conclusions, and form all 
 hypotheses, for themselves." 
 
 Watt's mind was of a very different cast. He did 
 not lightly adopt opinions ; his convictions were slowly 
 and deliberately formed, and were retained with a 
 corresponding tenacity. But, all the same, he 
 eventually thought it prudent to withdraw his letter, 
 and three days prior to the reading of Priestley's paper 
 which accompanied it, Priestley informed Sir Joseph 
 Banks of Watt's desire that the letter should not be 
 publicly read. That it was withdrawn on account of 
 what Watt calls Priestley's " ugly experiment," is 
 stated by him in a letter to Black, on the ground that 
 
116 JAMES WATT v 
 
 this experiment rendered " the theory useless, in so 
 far as relates to the change of water into air. . . . 
 I have not given up my theory [that is as to the 
 mutual convertibility of water and air], though neither 
 it, nor any other known one will account for this 
 experiment." 
 
 In the meantime, Cavendish had been pursuing his 
 inquiries, and towards the end of this year (1783) he 
 was prepared to give the explanation of the cause of 
 the disturbing factor in his proof of the real nature 
 of water, that is, the origin of the occasional and 
 apparently haphazard presence of small quantities of 
 nitric acid. This he demonstrated to be due to the 
 difficulty of excluding a greater or less quantity of 
 atmospheric nitrogen from the gases employed, and he 
 determined the conditions under which this nitrogen 
 led to the formation of the acid, the true nature of 
 which he thus for the first time established. The 
 account of his labours was read to the Royal Society 
 on 15th January 1784. 
 
 In the previous autumn, however, disquieting 
 rumours reached this country that the French 
 philosophers, and chief among them Lavoisier, were 
 poaching upon the English preserves. This circum- 
 stance is alluded to in a letter from Watt to Deluc, 
 dated November 30, 1783. " I was at Dr. Priestley's last 
 night. He thinks, as I do, that Mr. Lavoisier, having 
 heard some imperfect account of the paper I wrote in 
 the spring, has run away with the idea and made up 
 a memoir hastily, without any satisfactory proofs. . . . 
 I, therefore, put the query to you of the propriety of 
 sending my letter to pass through their hands to be 
 printed ; for even if this theory is Mr. Lavoisier's own, 
 I am vain enough to think that he may get some hints 
 
v JAMES WATT 117 
 
 from my letter, which may enable him to make 
 experiments and to improve his theory, and produce 
 a memoir to the Academy before my letter can be 
 printed, which may be so much superior as to eclipse 
 my poor performance, and sink it into utter oblivion ; 
 nay, worse, I may be condemned as a plagiary, for 
 I certainly cannot be heard in opposition to an 
 Academician and a Financier. . . . But after all, I 
 may be doing Mr. Lavoisier injustice." 
 
 That Lavoisier did get some hints, and possibly even 
 through the medium of Watt's letter, is beyond all 
 question. The fact that he was informed of Cavendish's 
 work is specifically stated in Cavendish's memoir, in 
 a passage interpolated by Blagden, the secretary of 
 the Koyal Society, and Cavendish's assistant and 
 amanuensis, who himself had told Lavoisier. The 
 whole of the circumstances are set out in detail in a 
 subsequent letter which Blagden addressed to the 
 editor of the Chemische Annalen in 1786. That it 
 was known to be Cavendish's experiment that was 
 being thus repeated is confirmed by a letter from 
 Laplace to Deluc, dated June 28, 1783, in which we 
 read, " Nous avons repete, ces jours derniers, Mr. 
 Lavoisier et moi, devant Mr. Blagden, et plusieurs 
 autres personnes, 1'exp^rience de Mr. Cavendish sur la 
 conversion en eau des airs dephlogistique et inflam- 
 mable, par leur combustion. . . . Nous avons obtenu 
 de cette maniere plus de 2^ gros d'eau pure, ou au 
 moins qui n'avoit aucun caractere d'acidite, et qui toit 
 insipide au gout ; mais nous ne savons pas encore, si 
 cette quantite d'eau represente le poids des airs con- 
 sumes ; c'est une experience a recommencer avec toute 
 T attention possible, et qui me paroit de la plus grande 
 importance/' The phrase " qui n'avoit aucun caractere 
 
118 JAMES WATT v 
 
 d'acidite " is of special significance. The French philo- 
 sophers, and Lavoisier in particular, could with difficulty, 
 as Blagden relates, be brought to credit the statement 
 that when inflammable air was burnt water only was 
 formed : their preconceptions concerning the part played 
 by oxygen in such a case led them to suppose that an 
 acid would be produced. Cavendish was familiar with 
 Lavoisier's doctrine, which is connoted in the very 
 word oxygen, which we owe to the French chemists, 
 and it may be that this circumstance, amongst others, 
 was one cause of the pains he took to understand the 
 origin of the acid he occasionally met with. Lavoisier 
 was led to repeat Cavendish's experiment on 24th 
 June 1783, and on the following day he announced to 
 the Academy that by " the combustion of inflammable 
 air with oxygen very pure water" was formed. It 
 is this statement that has been said to constitute 
 Lavoisier's claim to be considered as the true and 
 first discoverer of the composition of water. That he 
 has no valid claim has been implicitly admitted by 
 Lavoisier himself. The eminent Perpetual Secretary 
 of the French Academy, M. Berthelot, is no doubt 
 accurate in regarding the 25th June 1783 as the first 
 certain date of publication of the discovery that can be 
 established by authentic, i.e. official, documents, but 
 as I have elsewhere attempted to show, the circum- 
 stances under which that priority of publication was 
 secured give Lavoisier no moral right to the title of 
 the discoverer. 1 
 
 Shortly after the reading of Cavendish's memoir to 
 the Eoyal Society (January 15, 1784), Deluc wrote to 
 Watt, giving an account of its contents, and insinuating 
 
 1 Priestley, Cavendish, Lavoisier, and La Revolution Chimique: the 
 Presidential Address to the Chemical Section of the British Association, 
 1890 : see also p. 151 of the present volume. 
 
v JAMES WATT 119 
 
 that its conclusions had been formed in the light of 
 knowledge obtained from Watt's letter to the Koyal 
 Society, which although, as we have seen, not publicly 
 read, had, there is no doubt, been perused by others 
 than Priestley, to whom it was originally addressed. 
 Deluc was, no doubt, a zealous friend, but in this matter 
 his zeal outran his discretion. The letter was indeed 
 unworthy of him. He hastens to exculpate Lavoisier 
 and Laplace, but he makes a charge against the honour 
 and integrity of Cavendish for which there was absolutely 
 no justification. He stirs up Watt's suspicions, and 
 then seeks to appease them ; he rouses his anger, and then 
 counsels him to silence by an argument which shows 
 how wholly he misunderstood Watt. Watt's reply was 
 characteristic : " On the slight glance I have been able 
 to give your extract of the paper, I think his theory 
 very different from mine ; which of the two is the right I 
 cannot say : his is more likely to be so, as he has made 
 many more experiments, and consequently has more 
 facts to argue upon. 
 
 " As to what you say of making myself des jaloux, 
 that idea would weigh little ; for were I convinced I 
 had had foul play, if I did not assert my right, it would 
 either be from a contempt of the modicum of reputation 
 which could result from such a theory ; from the con- 
 viction in my own mind that I was their superior ; or 
 from an indolence that makes it easier to me to bear 
 wrongs than to seek redress. In point of interest, in so 
 far as connected with money, that would be no bar ; for 
 though I am dependent on the favour of the public, I 
 am not on Mr. C. and his friends ; and could despise the 
 united power of the illustrious house of Cavendish, as 
 Mr. Fox calls them. 
 
 "You may, perhaps, be surprised to find so much 
 
120 JAMES WATT v 
 
 pride in my character. It does not seem very com- 
 patible with the diffidence that attends my conduct in 
 general. I am diffident, because I am seldom certain that 
 I am in the right and because I pay respect to the opinion 
 of others, where I think they may merit it. At present 
 je me sens un pen blesse; it seems hard that in the first 
 attempt I have made to lay anything before the public, 
 I should be thus anticipated." 
 
 There was no desire on the part of anybody con- 
 nected with the management of the Royal Society to 
 withhold from Watt his just due, and it was eventually 
 arranged that his letter to Priestley, together with one 
 he subsequently addressed to Deluc, should be publicly 
 read to the Fellows, and they were subsequently ordered 
 to be printed in the Philosophical Transactions in such 
 manner as their author might desire. By his directions, 
 the two letters were merged together, and they appear as 
 having been read on April 29, 1784. under the title, 
 " Thoughts on the Constituent Parts of Water, and of 
 Dephlogisticated Air : with an account of some experi- 
 ments on that Subject. In a letter from Mr. James 
 Watt, Engineer, to Mr. Deluc, F.R.S." The greater 
 part of the "thoughts" are concerned with the dephlogisti- 
 cated air ; what relate to water have already been given 
 in the extracts from his correspondence. The terms of 
 the letter to Deluc, as printed in the Philosophical 
 Transactions, are substantially identical with those of 
 the letters to Black, Hamilton, Smeaton, and Fry. 
 
 I have now given all the essential facts which led to 
 the recognition of the true chemical nature of water, and 
 I have stated as accurately and as impartially as I could 
 the relative shares of Watt, Cavendish, and Lavoisier in 
 their discovery and interpretation. As regards Lavoisier, 
 it cannot be claimed that he was the first to obtain the 
 
v JAMES WATT 121 
 
 facts. To Cavendish belongs the merit of having first 
 supplied the true experimental basis upon which accurate 
 knowledge could alone be founded. Watt, on the other 
 hand, although reasoning from imperfect and indeed 
 altogether erroneous data, was the first, so far as we can 
 prove from documentary evidence, to state distinctly 
 that water is not an element, but is composed, weight 
 for weight, of two other substances, one of which he 
 regarded as phlogiston and the other as dephlogisticated 
 air. It would be a mistake, however, to suppose that 
 Watt taught precisely the same doctrine of the true 
 nature of water that we hold to-day. Nor did Caven- 
 dish utter a more certain sound. What we regard 
 to-day as the expression of the truth, we owe to 
 Lavoisier, who stated it with a directness and a precision 
 that ultimately swept all doubt and hesitation aside 
 except to the mind of Priestley, whose " random experi- 
 ment " gave the first glimmer of the truth. 
 
 In this respect the conclusion of Lord Brougham is 
 most just. It was a reluctance to give up the doctrine 
 of phlogiston, a kind of timidity on the score of that 
 long-established and deeply-rooted opinion, that pre- 
 vented both Watt and Cavendish from doing full justice 
 to their own theory ; while Lavoisier, who had entirely 
 shaken off these trammels, first presented the new 
 doctrine in its entire perfection and consistency. 
 
 We thus see that each of these eminent men took 
 an independent and, we may say, an equally important 
 share in the establishment of one of the greatest scientific 
 truths that the eighteenth century brought to light. 
 
 As regards Watt, the history of this incident serves 
 to bring out only more clearly what we know to be the 
 true character of the man. It illustrates the vigour of 
 his intellectual grasp, the keenness of his mental vision. 
 
122 JAMES WATT v 
 
 At the same time, it exhibits his love of truth for truth's 
 sake ; his unaffected modesty, and the sense of humility 
 that was not the less real because accompanied by a 
 sense of what his inherent love of rectitude taught was 
 due also to himself. The voice of envy and detraction 
 has not been unheard amongst the strife of partisans in 
 the Water Controversy, but throughout it no syllable 
 has been breathed that reflected even remotely upon his 
 honour and integrity. 
 
VI 
 ANTOINE-LAUEENT LAVOISIEK 
 
 CONTEMPORARY REVIEW, DECEMBER 1890 
 
 " IL a e*te 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 eloge on 
 Cavendish, the discoverer 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 some- 
 thing 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 
 
 123 
 
124 ANTOINE-LAUEENT LAVOISIEK vi 
 
 situation 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 acknowledged 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 four- 
 score years of his existence, a rigid, un deviating indiffer- 
 ence to the affairs of his fellow-men. This embodiment 
 of a clear, cold, passionless intelligence was dead to every 
 aesthetic sense, and had no element of anything that 
 was enthusiastic or chivalrous in its composition. 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 threescore years and ten would permit. 
 He weighed the Earth; he analysed the Air; he dis- 
 covered 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 
 
vi ANTOINE-LAUBENT LAVOISIEE 125 
 
 judgment 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 ancestress, 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-gene'ral. 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-gene'ral, 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 
 
126 ANTOINE-LAURENT LAVOISIER vi 
 
 Dantonists to the scaffold. Coffinhal, the Vice-President 
 of the Tribunal, pronounced the judgment : " The 
 Republic has no need of men of science," and within 
 twenty-four hours the tumbrel was on its way to the 
 Place de la Revolution, and, as the proces-verbal sets 
 forth, " sur un e*chafaud 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 this head, and probably 
 a hundred years will not suffice to reproduce such 
 another." 1 
 
 The main events in the scientific career of the great 
 French chemist are tolerably well known, and his posi- 
 tion 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 e'loges 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 legiti- 
 mate deductions, that Lavoisier remains the dominant 
 figure in the chemical world of the eighteenth 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 Revolution has brought forth in France, the historian 
 of science has welcomed, therefore, with special interest, 
 
 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 Thermidor 
 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. 
 
vi ANTOINE-LAUKENT LAVOISIER 127 
 
 the admirable monograph on Lavoisier which we owe 
 to the patient industry and patriotic zeal of Professor 
 Grimaux. 1 
 
 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 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 econo- 
 mist, 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 
 Le"on 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, nee Punctis, died when he 
 
 1 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. 
 
128 ANTOINE-LAUKENT LAVOISIEK vi 
 
 was five years old, and he and a young sister, who 
 lived only 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 Abb 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 Kouelle's teaching that the 
 particular direction of Lavoisier's scientific activity 
 was shaped. Guillaume- Francois Kouelle is mainly 
 remembered 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 " good things " than any man of his 
 time. In spite of his oddities, he exercised an extra- 
 ordinary influence as a teacher ; his lecture-room at 
 the Jardin du Koi 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 accom- 
 panied 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 
 
vi ANTOINE-LAURENT LAVOISIER 129 
 
 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 Academie 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, mechanicians, 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 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 
 
 K 
 
i 
 
 130 ANTOINE-LAURENT LAVOISIER vi 
 
 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 Revolution. Lavoisier's extra- 
 ordinary 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 disconnected 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 
 Academie des Sciences, he now became adjoint of the 
 Ferme-general. His friends, the academicians, looked 
 somewhat askance at this action. Lalande tells us that 
 in his election they had been influenced by the con- 
 sideration 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 consolation. " 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 
 
vi ANTOINE-LAUKENT LAVOISIEE 131 
 
 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-general Baudon, in return for 
 a third of his interest in the lease of Alaterre. 
 
 But there were doubtless other reasons for the dis- 
 approval of the Academy. The Ferme-general 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-generaux 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- 
 generaux 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 col- 
 lection, 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 Ferme 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 conclusion of the first 
 
132 ANTOINE-LAURENT LAVOISIER vi 
 
 lease in which Lavoisier was interested, addressed a 
 confidential inquiry to the Fermiers - generaux as 
 to the number of beneficiaries which the will of the 
 Court, i.e. the king or his mistresses, had imposed upon 
 the Ferme-general. 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, (TOO 
 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 physi- 
 cian, 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-generaux 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 con- 
 stantly 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 imposi- 
 tion of the Ferme, but too frequently he found that the 
 " gratuitous justice " thus dealt out to him meant only 
 
vi ANTOINE-LAUKENT LAVOISIEK 133 
 
 " 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. 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-generaux 
 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-gene'ral improved. With each new lease 
 the position and influence of Lavoisier was strengthened, 
 until, in 1783, he was placed by d'Ormesson upon the 
 Committee of Administration, the most important of 
 the whole, and the only one which had direct relations 
 with the Government. 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 influence in the Ferme, 
 
134 ANTOINE-LAUKENT LAVOISIER vi 
 
 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 splen- 
 dour of his scientific achievements, were unheeded. In 
 the day of reckoning he was remembered only as 
 Lavoisier the Fermier -general. 
 
 M. Grimaux has been at considerable pains to lay 
 the details of Lavoisier's connection with the Ferme- 
 general before us. He estimates that, in all, he acquired, 
 from 1768 to 1786, nearly 1,200,000 livres. He con- 
 tinued to be a member of the 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 gunpowder 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- 
 general. Turgot changed all this. In 1775 he created 
 the Regie des Poudres and nominated four commis- 
 sioners, 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 neces- 
 sary for administrative work of this kind, but also for 
 the diligence, capacity, and honesty with which he dis- 
 charged his duties as a Fermier -general. At his sugges- 
 
vi ANTOINE-LAUKENT LAVOISIEE 135 
 
 tion, 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 conditions under which the 
 employes 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 con- 
 siderable danger, as, for example, in the explosion which 
 resulted in the experiments made to introduce Ber- 
 thollet'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 invec- 
 tive of the Pere 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 misconstrued ; the report was 
 spread that it was to be given to the enemies of the nation, 
 and Lavoisier and his fellow-commissioner, Le Faucheux, 
 nearly fell victims to an angry mob which surged round 
 the gates of the arsenal. 
 
 Lavoisier's journeyings through France in connection 
 with the work of the Miner alogical Atlas and as a 
 Fermier-ge'neral, had taught him much concerning the 
 life of the peasant. Indeed, no Frenchman of his time 
 knew his country better, or was more keenly alive to 
 
136 ANTOINE-LAUKENT LAVOISlEIi vi 
 
 the vast economic movement which was slowly gather- 
 ing 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 connec- 
 tion 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 immediately 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 directing 
 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 collec- 
 tion and distribution of agricultural instruments, for the 
 better adjustment of the tithes and of the rights of pastur- 
 age, 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 unknown ; 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 
 
vi ANTOINE-LAURENT LAVOISIER 137 
 
 precision of laboratory trials. He introduced the culti- 
 vation of the beetroot and potato, hitherto unknown in 
 the Blesois. He improved the breed of sheep by the 
 importation 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 fol- 
 lowing 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 doubt- 
 less the cause of his selection as a member of the 
 Assembly of the Orle'anais, a sort of County Council 
 created in 1787, according to a plan devised by Necker 
 during his first administration. 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 
 president. The twenty-five so nominated were directed 
 to elect an equal number of colleagues, the same pro- 
 portion being observed for the three orders. The duties 
 of the Assembly were to determine the modes of levying 
 the taxes, to undertake the construction and maintenance 
 
138 ANTOINE-LAURENT LAVOISIER vi 
 
 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 pre- 
 served the minutes of the Provincial Assembly, together 
 with such of the manuscripts of Lavoisier as relate to 
 its business. 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 abolition 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 corvee, which compelled the peasants to undertake 
 the construction and maintenance of the roads. On all 
 these questions Lavoisier was the mouthpiece of his 
 order. He also -introduced 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 exploitation 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 reparalt a chaque instant." 
 
 Few, if any, of these projects were realised. The 
 Provincial Assemblies might initiate, but they were 
 powerless to execute, and in 1790 they became merged 
 into the States-General, to which Lavoisier was sent as 
 Depute suppleant for the bailiwick of Blois, having for 
 his colleague the unfortunate Vicomte de Beauharnais, 
 whose widow, Josephine Tascher de la Pagerie, became 
 the wife of Bonaparte. In the same year he was 
 elected a member of the Commune of Paris, and of the 
 
 1 Leonce de Lavergne, Les Assemblies Provinciates. 
 
vi ANTOINE-LAUKENT LAVOISIER 139 
 
 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, 
 
140 ANTOINE-LAURENT LAVOISIER vi 
 
 fastens on those of others ; but, incapable of appreciating 
 them, he abandons 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, fe/mier-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-general, 
 was the object of repeated and violent attacks in the 
 journals and in various political clubs. The leaders of 
 the Kevolutionary party, who clamoured for the abolition 
 of all State control over the manufacture of war material, 
 denounced his administration at the Regie des Poudres, 
 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 react 
 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 
 
vi ANTOINE-LAUEENT LAVOISIEK 141 
 
 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. 
 
 On quitting the Treasury, he was reappointed to the 
 Regie des Poudres, but 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 
 relinquish 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 administra- 
 tive officer of the Commission ; he contributed to the 
 nomenclature of the system, and took a prominent 
 part in directing the determination of the various 
 physical constants on which the measurements ulti- 
 mately 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 
 
142 ANTOINE-LAUKENT LAVOISIEK vi 
 
 had to be carried out under conditions which could not 
 possibly have been more disadvantageous. Its realisa- 
 tion largely depended on the cordial co-operation of 
 other nations, and the work of measurement 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 difficulties 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 than once 
 imperilled by the vacillating action of the Convention. 
 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 Me*chain required in order to extend the measure- 
 ment 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 advancing 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 
 
vi ANTOINE-LAURENT LAVOISIER 143 
 
 motion by Fourcroy revealed to the Academicians the 
 danger in which 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 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 ; 
 
144 ANTOINE-LAURENT LAVOISIEK vi 
 
 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 
 Gr^goire, 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 Con- 
 vention 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 influ- 
 ence of the Academy, and had at length effected its 
 destruction. Still Lavoisier did not despair. He 
 appealed to the Committee of Public Instruction to 
 allow the members of the Academy to continue their 
 labours, and he entreated that the work of the Com- 
 mission of 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 
 
vi ANTOINE-LAUKENT LAVOISIER 145 
 
 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 re- 
 lentless. 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- 
 generaux 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 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 
 
 L 
 
146 ANTOINE-LAUKENT LAVOISIER vi 
 
 arrest, addressed a memorial extolling the value of 
 his public services, and drawing special 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. Kobespierre had swept 
 He'bert and Danton from his path, and the work of 
 " purification " was going on merrily. On May 8, 
 1794, the Fermiers-generaux 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-generaux 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 Coffinhal found themselves 
 in the place of the unfortunate Fermiers-generaux. 
 
 On the following morning the condemned men were 
 taken from the Conciergerie to the Place de la Re- 
 volution. They bade each other farewell ; Papillon 
 d'Auteroche, seeing the crowd en carmagnole as the 
 
vi ANTOINE-LAUKENT LAVOISIEK 147 
 
 carts passed through the streets, raised a smile as he 
 said disdainfully, in allusion to the confiscation of his 
 effects : " What annoys me is to have such disagreeable 
 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 in the history of science. 
 All that was mortal of him was thrown into the 
 cemetery of the Madeleine, and the place of his inter- 
 ment was forgotten. The news of this great crime pro- 
 foundly affected the intellectual world. 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 
 extraordinary revulsion of popular feeling which pre- 
 ceded 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 extrava- 
 gances of taste and sentiment which were then in 
 fashion, and it was crowned by an eloge . . . from 
 Fourcroy ! Time-serving and timorous as ever, Four- 
 croy 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 
 
148 ANTOINE-LAUEENT LAVOISIEE vi 
 
 least word, the slightest mark of solicitude 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 con- 
 tributed to it, and the charge rests heavily on his 
 memory. 
 
VII 
 
 PBIESTLEY, CAVENDISH, LAVOISIER, AND 
 LA REVOLUTION CHIMIQUE 
 
 THE PRESIDENTIAL ADDRESS TO THE CHEMICAL SECTION OP THE 
 BRITISH ASSOCIATION, LEEDS, 1890 
 
 LEEDS has one most notable association with chemistry 
 of which she is justly proud. In the month of Septem- 
 ber 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 dis- 
 advantages of speech and manner, he gradually 
 acquired, more especially by his controversial and 
 theological writings, a considerable influence in Dissent- 
 ing circles. A pressing invitation and the prospect 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 
 
 149 
 
150 PEIESTLEY, CAVENDISH, LAVOISIEK vn 
 
 intervention of some worthy ecclesiastics on the Board 
 of Longitude who had the direction of the business, and 
 who, as Professor Huxley once 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 con- 
 tinued 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." l 
 
 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 extraordinary 
 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 
 
 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. 
 
vii AND 'LA BIS VOLUTION CHIMIQUE' 151 
 
 marvellous development of chemical science which made 
 the close of the eighteenth 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 per- 
 spicacity which invariably characterises his work, in 
 which he claims for Lavoisier a participation in dis- 
 coveries which we count among the chief scientific 
 glories of this country. From the eminence of M. 
 Berthelot'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 transla- 
 tions 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 deter- 
 mining 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 pre- 
 decessor are not put forward for the first time. Ex- 
 plicitly made, in fact, by Lavoisier himself, they were 
 uniformly and consistently disallowed by his contempor- 
 aries. M. Berthelot now seeks to support them by 
 additional 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 
 
152 PKIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 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. Berth elot sees in it merely the evidence of the 
 essentially empirical character of his work. " Priestley," 
 he says, " the enemy of all theory and of 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 at- 
 tached 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 quotations 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 quota- 
 tion is taken from the concluding chapter of his Ex- 
 periments and Observations on Different Kinds of 
 Air, in which he actually seeks to draw " general 
 conclusions " concerning the constituent principles of 
 
vii AND 'LA KfiVOLUTION CHIMIQUE' 153 
 
 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 water 
 has been made the basis of an entirely new system of 
 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 combina- 
 tion. 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 facts, 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 reluctance 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 explanation 
 on the old system " (loc. cit. p. 563). 
 
154 PKIESTLEY, CAVENDISH, LAVOISIER vn 
 
 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 intervention of 
 any reducing agent. Bay en, six months before the 
 date of Priestley's discovery, had noted that a gas 
 was thus disengaged, but he gave no description of its 
 nature, contenting himself merely by pointing out the 
 analogy which his observations appeared to possess to 
 those of Lavoisier on the existence of an elastic fluid in 
 certain substances. Afterwards, when the facts were 
 established, Bayen drew attention to his earlier experi- 
 ments and claimed, not only the discovery of oxygen, 
 but all that Lavoisier deduced from it. "But," says 
 M. Berthelot, in reference to this circumstance, " his 
 contemporaries paid little heed to his pretensions, nor 
 will posterity pay more " (La Revolution C/iimique, 
 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 discoverer of the gas. He begins by assert- 
 ing 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, pub- 
 
vii AND 'LA EVOLUTION CHIMIQUE ' 155 
 
 lished in December 1774, in the Journal de Physique 
 of the Abbe Rozier : " This air, deprived of its fix able 
 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 experiments 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 under- 
 stood the true nature of combustion in air much better 
 than their 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 combustion, 
 and showed that in both processes one constituent 
 
156 PKIESTLEY, CAVENDISH, LAVOISIER vn 
 
 only of the air is concerned. He distinctly stated that 
 not only is there increase of weight attending the cal- 
 cination 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 surprising that the truth 
 was not fully recognised until a century after his 
 researches. ( Vide 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 comparison of an abstract of 
 what was stated to the Academy in November 1774, 
 contributed by Lavoisier himself, in December 1774, to 
 the Journal de Physique of the Abbe Kozier, makes it 
 evident that very substantial additions were made to 
 the communication before it was finally printed in the 
 Memoir es de VAcademie des Sciences. The possibility 
 of this is allowed by M. Berthelot. He says (p. 58) : 
 " A summary communication, often given viva voce to 
 a learned society, such as the Academy of Sciences of 
 Paris or the Koyal Society of London, would immedi- 
 ately 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 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). 
 
vii AND 'LA E^VOLUTION CHIMIQUE' 15 7 
 
 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 Koyal 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 forma- 
 tion 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 
 calcination was identical with it. 
 
 At Easter 1775 Lavoisier presented a memoir to the 
 Academy " On the Nature of the Principle which Com- 
 bines 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 
 
158 PRIESTLEY, CAVENDISH, LAVOISIER vn 
 
 that air which 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 " ((Euvres 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 dis- 
 coverer " 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 decembre 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 con- 
 clusions will not be contested." M. Berthelot remarks 
 on the irony of this passage : we may infer from it that 
 
vii AND 'LA K VOLUTION CHIMIQUE' 159 
 
 the friends of the English chemist had not been alto- 
 gether idle. In his memoir " On the Kespiration 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 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 mentioned 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 
 1 principe oxygine* ' 
 
 In none of the memoirs after that of Easter 1775 is 
 the claim for participation more than implied ; it is 
 made explicitly for the first time in the paper "On a 
 Method of Increasing the Action of Fire," printed in 
 the Memoir es de V Academic for 1782, and in these 
 words : "It will be remembered 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 dephlogisticated air." 
 
 In the " Traite Ele"mentaire de Chimie " the claim 
 for participation is again asserted in these words : 
 
 1 M. Trudaine de Montigny died in 1777. 
 
160 PEIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 "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 
 experiments 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 literary companion of Lord 
 Shelburne, and in the autumn of 1774 he accompanied 
 his lordship 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 discovery [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 philo- 
 sophical 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 red 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 
 
vii AND 'LA EVOLUTION CHIMIQUE' 161 
 
 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 Koy, and several 
 other philosophers, who honoured me with their notice 
 in that city, and who, I daresay, cannot fail to recollect 
 the circumstance." 
 
 If any further evidence is required to prove that 
 Lavoisier was not only not " the true and first dis- 
 coverer" 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 ISfe'vrier, 1776." From p. 30 we glean that 
 Lavoisier visited his friend M. Trudaine at Montigny 
 about ten days after his conversation with Priestley, 
 and repeated the latter 's experiments on the marine 
 
 1 Prof. Grimaux (Lavoisier, p. 51), says : "Un de ses [Lavoisier's] amis qui 
 habitait Londres, Magalhaens ou Magellan, de la famille du celebre navigateur, 
 lui envoyait tous les m6moires sur les sciences qui paraissaient en Angleterre 
 et le tenait au courant des decouvertes de Priestley." 
 
 M 
 
162 PEIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 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 
 informs 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 
 " Fair dephlogistique de M. Prisley " (sic). Such a 
 phrase in a private note-book is absolutely inconsistent 
 with the idea that at this time Lavoisier considered 
 himself as an independent discoverer of the gas. How 
 he came to regard himself as such we need not inquire. 
 Nor is it necessary to occupy your time by any examina- 
 tion 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 recognising the difficulty of his position. 
 He seeks to discharge an obligation, of which the acknow- 
 ledgment 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 eloge on 
 Lavoisier which M. Berthelot, as Perpetual Secretary, 
 was commissioned to deliver, has grown La Revolution 
 Chimique. To write eulogy, however, is not necessarily 
 to write history. We cannot but think that M. Berthe- 
 lot has been hampered by his position, and that his 
 opinion, or at least the free expression of it, has been 
 
vii AND <LA INVOLUTION CHIMIQUE* 163 
 
 fettered by the conditions under which he has written. 
 We imagine we discern between the lines the conscious- 
 ness 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 
 complete the discovery of oxygen and the determina- 
 tion 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. 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 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 vindica- 
 tion 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 eloge 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 
 
164 PRIESTLEY, CAVENDISH, LAVOISIER vn 
 
 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 scientific 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 discovery 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, 
 [t 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 
 manner first practised by Volta in 1776. The experi- 
 ment was witnessed by Mr. John Warltire, a lecturer 
 on natural philosophy 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 
 
vii AND 'LA Efi VOLUTION CHIMIQUE' 165 
 
 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 
 circumstance 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, how- 
 ever, 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 
 experiments " 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 be- 
 comes of the air thus lost or condensed " (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 observations at or near the time he 
 
166 PEIESTLEY, CAVENDISH, LAVOISIER vn 
 
 obtained them, there would 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) 
 occasioned 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 con- 
 vertibility 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 dephlogisti- 
 cated air from nitre, and the inflammable air by heating 
 what he calls " perfectly made charcoal " in an earthen- 
 ware 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 consisting 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 
 inflammable 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 
 
vii AND <LA EVOLUTION CHIMIQUE' 167 
 
 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 moisture 
 acquired by the paper. ... I wished, however, to have 
 had a nicer balance for this purpose ; the result was such 
 as to afford a strong presumption that the air was re- 
 converted 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 ^nd 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 Eoyal Society on the occasion of the presenta- 
 tion 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 
 Society, 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 
 
168 PKIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 matter, Watt requested that it should be withdrawn. 
 Watt, however, as he tells Black l 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 mean- 
 time Cavendish, having completed one section of his 
 investigation, sent in a memoir to the Royal Society, 
 which was read on January 15, 1784, in which he gives 
 an account of his experiments, and announces his con- 
 clusion " that dephlogisticated 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. Kir wan 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 Eoyal Society on April 29, 
 1784. Which of the two Cavendish or Watt is, 
 under these circumstances, to be considered 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 " (Lepons sur la Philosophic 
 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 
 
 1 Watt, Correspondence, p. 31. 
 
vii AND 'LA KE VOLUTION CHIMIQUE' 169 
 
 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 in reality 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. That the calcination of metals 
 was but a slow combustion had been fully 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 atmo- 
 spheric 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 ? 
 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 
 
170 PRIESTLEY, CAVENDISH, LAVOISIER vn 
 
 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 experiments, 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 ? We venture to think that M. Berthelot 
 has himself supplied the answer. He says (p. 114) : 
 " Kumours 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 hydrogen, 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." 
 
 " 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 Eoyal 
 Society of London, who on this occasion recalled the 
 observations of Cavendish (qui rappela ca cette occasion 
 les observations de Cavendish)." 
 
 On the following day Lavoisier published his results. 
 
vii AND 'LA Ktf VOLUTION CHIMIQUE' 171 
 
 The following is the official minute of the communica- 
 tion, translated 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 for. 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 experiments 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 fevrier 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, 
 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 amount of the air, or that 
 there has been a loss of weight." 
 
172 PRIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 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 circum- 
 stance 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 
 it was 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 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." 
 
vii AND 'LA EVOLUTION CHIMIQUE' m 
 
 This addition, as I have had the opportunity of verifying 
 by an inspection of the original MSS. in the archives of 
 the Royal 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 Royal Society 
 of London. The latter informed us (ce dernier nous 
 apprit) 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 : 1 
 
 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 Eoyal 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 dephlogisticated air was nothing else than water 
 deprived of its phlogiston ; and, vice versa, that water was dephlo- 
 gisticated air united with phlogiston. About the same time the 
 news was brought to London that Mr. Watt, of Birmingham, had 
 
 1 Mr. Muirhead's translation. Vide Watt, Correspondence, Composition of 
 Water, p. 71. 
 
174 PEIESTLEY, CAVENDISH, LAV01SIEK vn 
 
 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 Royal 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 
 
vii AND 'LA EEVOLUTION CHIMIQUE' 175 
 
 opened the way to M. Lavoisier's present theory, which perfectly 
 agrees with that of Mr. Cavendish, only that Mr. Lavoisier accom- 
 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 Eoi, 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 con- 
 sulted 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 contemporaries 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 discoveries arose. It may be that much of what 
 I have had to say is as a twice-to]d tale to many of 
 
176 PKIESTLEY, CAVENDISH, LAVOISIEK vn 
 
 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. 
 
 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 Scientifique 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 
 Priestley's discovery of the principal gases in terms of admiration 
 (La Revolution Chimique, p. 39), and especially that of oxygen, which 
 
vii AND 'LA Kfi VOLUTION CHIMIQUE' 177 
 
 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 
 rests our actual conception of matter, more especially in relation to 
 the composition of air and water. This, I venture to repeat, is an 
 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 
 discoveries 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 new 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, 
 
 N 
 
178 PRIESTLEY, CAVENDISH, LAVOISIER vn 
 
 persecuted 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 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 
 rigorous demonstration of which Mr. Thorpe apparently has no 
 suspicion. 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 
 
vii AND 'LA EVOLUTION CHIMIQUE' 179 
 
 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. 
 
 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 followiDg 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 differ- 
 ence between us. What I ventured to criticise was 
 the general tone and tendency of M. Berthelot's argu- 
 ment, 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 
 
180 PKIESTLEY, CAVENDISH, LAVOISIEK vn 
 
 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 
 conform 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 remember the 
 passionate scorn with which Lavoisier repudiated and 
 protested against the attempts of his compatriots to 
 rob him of his rights : " Cette th^orie n'est done pas 
 comme je 1'entends dire la th^orie des chimistes 
 frangais ; elle est la mienne, et c'est une proprie^ que 
 je reclame aupres de mes contemporains et de la 
 post^rite*." 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 determination of the 
 compound nature of water. M. Berthelot's contention 
 
vii AND 'LA KEVOLUTION CHIMIQUE ' 181 
 
 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 discovered 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 ? 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 consequences. 
 
 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 Revolution 
 Chimique. His contention there was that by every 
 legitimate canon the experiment of 24th June 1783 
 gives to Lavoisier the priority of discovery. He now 
 admits that Cavendish played " un r61e 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 inter- 
 vention of Blagden. I repeat that Blagden toM 
 Lavoisier of Cavendish's researches and of his con- 
 clusions, 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 contradicted by 
 Lavoisier, nor by Laplace, Vandermonde, Fourcroy, 
 Meusnier, or Legendre, who were present on the 
 
182 PKIESTLEY, CAVENDISH, LAVOISIEE vn 
 
 occasion when Lavoisier himself admits that he received 
 the information. 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 inter- 
 polated 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 
 knowledge 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 con- 
 cerning Blagden goes to show that he was an upright 
 and honourable man. Sir Joseph Banks has testified 
 to his abilities and integrity. Dr. Johnson spoke of 
 his copiousness and precision of communication, with 
 the characteristic addition : " Blagden, sir, is a delight- 
 ful fellow." Laplace, Cuvier, Berthollet, and Benjamin 
 Delessert were among his friends. 1 He was rich, and 
 
 1 Many of the letters of Berthollet to Blagden are still in existence. In one 
 of these, dated " 19 Mars, 1785," he writes from Paris : " L'on s'est beaucoup 
 occupe ici ces derniers tems 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 vent r^peter I'exp6- 
 rience en laisant brfiler 1'air dephlogistique dans le gas inflammable, et il y a 
 apparence qu'alors on n'aura point d'acide nitreux, selon les belles observations 
 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 ? 
 
vii AND 'LA EfiVOLUTION CHIMIQUE' 183 
 
 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 consider- 
 able time on the Continent, and was frequently in 
 Paris. The gossip of the period states that he aspired 
 to the hand of Madame Lavoisier, who preferred Count 
 Eumford. 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 discoveries of the French, or have con- 
 tributed 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 
 purchase 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 ? It is surely incumbent on M. Berthelot, on 
 every ground, either to substantiate his implications 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, nor did he attempt to establish 
 a right to be considered an independent discoverer of 
 
184 PKIESTLEY, CAVENDISH, LAVOISIER vn 
 
 the true nature of water. In his memoir, " Sur le 
 R^sultat de F Inflammation du Gas inflammable 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 phlogiston ism. 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 exemplifica- 
 tion of that conservatism which he deplores? A 
 generation ago the doctrine of Avogadro became the 
 corner-stone of that edifice of which M. Berthelot 
 asserts that Lavoisier laid the foundations. Indeed, 
 the introduction 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 ? 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. 
 
VIII 
 MICHAEL FAKADAY 
 
 A REVIEW OF DR. BENCE JONES'S "LIFE AND LETTERS OF FARADAY." 
 MANCHESTER GUARDIAN, 1870 
 
 MICHAEL FARADAY, one of the greatest experimental 
 philosophers 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 black- 
 smith 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 influ- 
 ence which his home had upon his character. Although 
 unable to enter into his occupations, she was exceed- 
 ingly 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- 
 
 185 
 
186 MICHAEL FAEADAY vm 
 
 school. When twelve years old the young Faraday 
 went on trial for a year as an errand-boy to Mr. George 
 Eiebau, a bookseller and bookbinder in Blandford 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 unhappy 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 
 apprenticed 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 disposition, 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 Conversa- 
 
vin MICHAEL FAEADAY 187 
 
 tions 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. 
 Davy was then near the zenith of his fame ; his 
 brilliant discovery of the compound nature of the 
 alkalis 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 
 subsequently, 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 inclinations 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, 
 
188 MICHAEL FAKADAY vm 
 
 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 
 Royal 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 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 afterwards 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, not 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 
 
viii MICHAEL FAKADAY 189 
 
 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, 
 expressing 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' 
 experience would set him right on this matter ; which 
 it most certainly did, as we shall hereafter show. Some 
 time after 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 Royal Institution was then vacant, 
 and if he were still minded to leave his present occupa- 
 tion, 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 
 Institution a connection which lasted nearly to the 
 end of his long life, and which raised the Institution 
 to the eminence 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 
 
190 MICHAEL FAKADAY vm 
 
 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 recog- 
 nised the other's ability. Throughout the course of the 
 investigation Faraday was exposed to constant peril, 
 and it was only through continual care and precaution 
 that no very sad results attended the numerous explo- 
 sions of this singularly unstable compound. 
 
 In the autumn of this year (1813) Sir Humphry 
 Davy proposed 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 impressions of the journey. 
 This journal, which occupies a considerable portion of the 
 first volume of Dr. Bence Jones's work, is as remarkable 
 for the vividness and accuracy of the descriptions 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 
 defined ; to his duties as an amanuensis he was not 
 unfrequently 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 
 
vm MICHAEL FAKADAY 191 
 
 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 ; Jbut, perhaps, if I acted 
 influenced by the pure and unsullied dictates of common 
 sense, I should have nothing to complain of, and there- 
 fore 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 oftentimes go wrong with me, with herself, and with 
 Sir Humphry." 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, unavoidable. 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 ; 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. 
 
192 MICHAEL FAKADAY vm 
 
 This occasioned 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 
 opportunity he possessed of adding to his knowledge of 
 chemistry and of the other sciences continually induced 
 him to proceed. 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 acquaintance 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 that 
 it would then be necessary for him 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 
 spring of 1815, and immediately resumed his duty at 
 the Royal Institution. Davy could no longer withhold 
 
vm MICHAEL FARADAY 193 
 
 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 Gourtois, 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 preserved 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 origin- 
 ality 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 himself for his new vocation. Lecturing 
 became with him an art, to be carefully and systematic- 
 ally studied. His letters to Abbott, and his common- 
 place book, show that he had previously framed pretty 
 accurate ideas respecting the province and functions of 
 the lecturer whilst attending Mr. Brande and Mr. 
 Powell in their lectures at the Royal Institution. 
 He now took private lessons in elocution, and prevailed 
 
 o 
 
194 MICHAEL FARADAY vm 
 
 on his teacher to attend his lectures in order that the 
 errors of his address and delivery might be brought 
 home to him. Eleven years after the date of this early 
 attempt, Faraday delivered his first lecture at the 
 Royal 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 Royal 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 knowledge 
 was always at the furthest limits to which it had at the 
 time been extended by himself or by others, and yet his 
 consideration 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. Rapidly, 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 
 
vm MICHAEL FARADAY 195 
 
 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/ ' 
 
 In 1821, when twenty-nine years of age, Faraday 
 married Miss Sarah Barnard, the daughter of an elder 
 of the Sandemanian 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.R.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 
 
196 MICHAEL FAKADAY vin 
 
 select classes, surpass, in my opinion, anything that it 
 is in the power of my 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 was in the case of the Haswell Colliery explosion, 
 when he was sent down by the Government, together 
 with Sir (then Mr.) Charles Lyell, to attend the inquest. 
 Faraday, however, 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 ventilation of lighthouses ; the arrange- 
 ments of their lightning conductors ; 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 proposition as a matter of interest, 
 
vm MICHAEL FAKADAY 197 
 
 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 know- 
 ledge ; 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 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 substance 
 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 at- 
 tention ; but the merit of it was claimed by another. 
 The claimant was no other than Davy. A feeling of 
 jealousy had gradually been growing up in the mind 
 of the Honorary Professor of Chemistry at the Royal 
 
198 MICHAEL FAKADAY vm 
 
 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 Eaymond, 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 mis- 
 understood, often misrepresented, sometimes 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 
 
vm MICHAEL FAKADAY 199 
 
 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 them- 
 selves. How could it be otherwise ? He saw and revised the 
 manuscripts ; through his hands they went to the Royal 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 expecta- 
 tions 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 con- 
 tradicts the passages in the first paper of mine, which describe 
 my course of thought, and in which I claim the development 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 condensed 
 sulphurous acid probably before the year 1800; Northmore con- 
 densed 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, 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 
 
200 MICHAEL FAKADAY vm 
 
 wrong, I at least had endeavoured also to do him right (Philo- 
 sophical 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 Eoyal 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 I 
 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 Faraday'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 
 
vm MICHAEL FAKADAY 201 
 
 the Portable Gas Company. 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 entirely prevents any attempt to do 
 justice to the nature and extent of his researches on 
 magneto -electricity, voltaic induction, 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 
 Faraday'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 discoveries. 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 
 
202 MICHAEL FAKADAY vni 
 
 of those who desire to know more of the great philo- 
 sopher'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. 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 consider- 
 able 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 Kobert Peel, then 
 Prime Minister, contemplated offering him a pension of 
 
vni MICHAEL FAKADAY 203 
 
 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 determina- 
 tion, 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 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 days. 
 
 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 solici- 
 tude of his wife, the evil consequences were but very 
 gradual in their growth. In 1841, when he was 
 
204 MICHAEL FARADAY vni 
 
 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 exception 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 
 knowledge 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 
 according to His divine Word, and the great and 
 precious promises whereby His people are made par- 
 takers of the divine nature." 
 
 On August 25, 1867, he passed quietly and peace- 
 fully 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 
 
vni MICHAEL FAKADAY 205 
 
 character is evident on every page. It is impossible 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." 
 
IX 
 THOMAS GEAHAM 
 
 A LECTURE (WITH ADDITIONS), DELIVERED IN THE YORKSHIRE COLLEGE, 
 LEEDS, INTRODUCTORY TO THE EVENING CLASS SESSION, 1877-78. 
 
 THOMAS G&AHAM, one of the most original chemical 
 thinkers of the nineteenth 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 manu- 
 facturer. 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 
 
 206 
 
ix THOMAS GKAHAM 207 
 
 Graham on one occasion to his teacher, "that when 
 liquids absorb gases the gases themselves become 
 liquids ? " This remark, coming from so young a pupil, 
 and uttered at a time when the mutual relations of 
 the physical states of matter were more vaguely under- 
 stood than now, naturally impressed Thomson. The 
 interest thus awakened in the young enthusiast never 
 subsequently 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 sympathised 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 
 
208 THOMAS GEAHAM ix 
 
 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. Eeturning to Glasgow, and acting on the advice of 
 Meikleham, he sought to give lessons in mathematics ; 
 but he quickly threw up this precarious means of liveli- 
 hood, 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 Ander- 
 son'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 Transactions 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 
 
ix THOMAS GRAHAM 209 
 
 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 suggest - 
 iveness, 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 legitimate means of impressing the minds 
 of his pupils with the ideas which he wished to convey. 
 But even to the last he 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 proceedings of the Society 
 indicate the zeal with which he discharged 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 
 distinction. 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 
 
 P 
 
210 THOMAS GRAHAM ix 
 
 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 firmness 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 reappeared in 
 the Transactions of the Royal 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 continue his scientific work, and now 
 memoir after memoir appeared to testify to his un- 
 wearied energy. His last paper, on Hydrogenium, was 
 published only a few months before his death. This 
 incessant mental activity rapidly told on a constitution 
 naturally feeble. In the summer of 1869 he showed 
 symptoms of decay, but his nearest friends were hardly 
 prepared 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 specu- 
 lated when a student with Thomson that is, the absorp- 
 tion 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 the 
 nineteenth century, but the fact was first definitely 
 established in 1823, when Faraday succeeded in liquefy- 
 ing 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 
 
ix THOMAS GKAHAM 211 
 
 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 vaporised 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 unnecessary 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 
 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 com- 
 bustion. Some years ago, a Mr. Hicks patented a 
 method for recovering the alcohol volatilised in panifi- 
 cation, 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 
 
212 THOMAS GKAHAM ix 
 
 published in the Philosophical Magazine a short paper 
 " On the Finite Extent of the Atmosphere." According 
 to Wollaston there is necessarily a limit to the atmo- 
 sphere, 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. Seasoning 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 rarefaction, with its attendant fall in tempera- 
 ture, 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 
 
ix THOMAS GRAHAM 213 
 
 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 atmosphere. 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 Philo- 
 sophical 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 compound with absolute alcohol. Com- 
 binations of a similar nature were also observed to be 
 produced with the nitrates of calcium and magnesium, 
 and with the chlorides of manganese and zinc. These 
 alcoates, as they are termed by Graham, are solid 
 
214 THOMAS GKAHAM ix 
 
 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 " Etherifi cation," 
 in which he seeks to combat the generally accepted 
 opinion that the formation of sulphovinic acid is a 
 necessary stage in the transformation of common 
 alcohol into ether. According to Graham the sulphuric 
 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 
 colophene. This view of etherification is, in fact, an 
 expression 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 argu- 
 ment which he bases upon them, without admitting 
 that the last word on the theory of etherificatioii 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. 
 
ix THOMAS GKAHAM 215 
 
 olefiant gas, naphtha, oil of turpentine, and ether, 
 prevent the glow, whether in air or in attenuated 
 oxygen, and no oxidation of the phosphorus is found to 
 occur. Phosphorus may be melted and kept for any 
 length of time at 100 without 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 forma- 
 tion or presence of ozone, the existence of which was 
 only indicated by Schonbein 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 misunderstood by chemists. Heinrich Kose was 
 disposed to believe in the existence of two isomeric 
 modifications of hydrogen phosphide, 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 
 phosphuretted 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 
 
216 THOMAS GKAHAM ix 
 
 rendering phosphuretted hydrogen spontaneously in- 
 flammable, 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 ob- 
 servations 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. 
 
 Graham's first important experimental work relates 
 to the absorption of vapours by liquids. An account 
 of the investigation was given to the Koyal 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 
 boiling-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 practically 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 
 
ix THOMAS GKAHAM 217 
 
 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 
 determining the Crystallisation of Saline Solutions," 
 originally published 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 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. Accord- 
 ing 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 Experi- 
 mental Kesearches 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 
 0*9 inch internal diameter, was divided into 150 equal 
 parts, and provided with an accurately ground glass 
 
218 THOMAS GEAHAM ix 
 
 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. Hence 
 hydrogen is five times more diffusive than carbonic 
 acid. Graham concludes : " 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 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 
 Diffusion of Gases," read before the Koyal 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 
 
ix THOMAS GKAHAM 219 
 
 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 interchange 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, 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- 
 
220 THOMAS GKAHAM ix 
 
 jar in the same time. Similar experiments were made 
 with other gases, but the method was not sufficiently 
 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 was used by Priestley and other 
 chemists at the latter end of the eighteenth 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 con- 
 sisted 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 remain- 
 ing 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= 1), the square root of this 
 number is 0*2635 ; and according to the law of dif- 
 fusion 1 volume of hydrogen should be replaced by 
 0*2635 volume of air that is, 1 of air should replace 
 37947 of hydrogen. The mean of a large number of 
 
IX 
 
 THOMAS GKAHAM 
 
 221 
 
 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 
 
 By 
 
 Specific 
 
 
 Experiment. 
 
 Theory. 
 
 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 , ~V : ; 
 
 1-0143 
 
 1-0140 
 
 0-972 
 
 Oxygen 
 
 0-9487 
 
 0-9487 
 
 0-111 
 
 Sulphuretted Hydrogen 
 
 0-95 
 
 0-9204 
 
 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 gravity of the gases may be determined by 
 
222 THOMAS GRAHAM ix 
 
 the principle of diffusion ; it is given by the formula 
 
 D = / ) } where G is the volume of gas submitted to 
 \G/ 
 
 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 respira- 
 tion 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 
 Itoyal Society the first part of a long memoir on " The 
 
ix THOMAS GKAHAM 223 
 
 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, 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 phenomena 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 
 transpiration 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 ivhich 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 
 
224 THOMAS GKAHAM ix 
 
 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 temperature. " As the velocity of the 
 effusion of air does not increase 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. 
 
ix THOMAS GEAHAM 225 
 
 The velocity of methane is 0'8 when that of hydrogen 
 is 1. 
 
 The velocity of chlorine is 1|- 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 
 hydrogen 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 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 
 proportional to the density. 
 
 4. Karefaction by heat exerts a similar and precisely 
 equal effect in diminishing the velocity of the transpira- 
 tion of equal volumes of air, as the loss of density by 
 diminution of pressure. 
 
 It would appear, then, that transpiration is promoted 
 by increase of density, and equally, no matter whether 
 the increased 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 
 
 Q 
 
226 THOMAS GEAHAM ix 
 
 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 separation 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 millimetre 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 sand- 
 stone, the thickness might be further reduced to about 
 one-half of a millimetre. A wafer of this material could 
 be readily affixed to the end of a tube by 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." 
 
ix THOMAS GRAHAM 227 
 
 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 experiments 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 experiment, 
 
228 THOMAS GBAHAM ix 
 
 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 1^ 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 solution. 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 evaporation 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 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 
 
ix THOMAS GKAHAM 229 
 
 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 tempera- 
 tures. 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 con- 
 nection 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 observed is the more remark- 
 able, 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 diffusion is not necessarily confined to 
 the isomorphous groups of salts. 
 
 Hydrochloric, hydrobromic, and hydriodic acids, 
 
230 THOMAS GEAHAM ix 
 
 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 isomorphous, 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, accord- 
 ing 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 invari- 
 ably more diffusive than the corresponding 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 
 
ix THOMAS GKAHAM 231 
 
 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 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 there- 
 fore 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 consti- 
 tution 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 
 apparently resolved into potassium sulphate and alu- 
 minium sulphate. Other so-called double salts were 
 found to be decomposed in like manner ; thus Eochelle 
 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, 
 
THOMAS GKAHAM ix 
 
 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 solution of another salt has a special interest, as 
 serving to indicate 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 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 ? 
 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 inter- 
 ference 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 character. 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 crystallisation, comes into action, which will 
 interfere with and diminish that elasticity or dispersive 
 tendency of the dissolved salt which occasions its dif- 
 
ix THOMAS GRAHAM 233 
 
 fusion. . . . 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 (decomposi- 
 tions) 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 frequently 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 
 
234 
 
 THOMAS GKAHAM 
 
 IX 
 
 SALT DIFFUSED FROM A 1 PER CENT SOLUTION IN EQUAL TIMES. 
 
 Potash . 
 Soda . 
 
 Ammonium chloride 
 Potassium chloride . 
 Sodium chloride 
 
 Grains. 
 4-84 
 4-03 
 3-42 
 3-42 
 2-85 
 
 Sodium sulphate 
 Calcium chloride . 
 Magnesium chloride 
 Calcium sulphate . 
 Magnesium sulphate 
 
 Grains. 
 2-35 
 2-02 
 2-03 
 1-21 
 1-21 
 
 These are the latest, and perhaps the best determined, 
 diffusibilities 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 corresponding 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 ex- 
 pected 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 decomposed, and 
 that the alkaline hydrates made their appearance 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 
 
ix THOMAS GKAHAM 235 
 
 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 decom- 
 posed 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 
 without 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 substances 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 describes 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, 
 
236 THOMAS GKAHAM ix 
 
 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 indif- 
 ference 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 aggrega- 
 tion 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 constitution." 
 
 " 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 crystalline structure shuts out external 
 impressions, the softness of the gelatinous colloid par- 
 takes of fluidity, and enables the colloid to become a 
 medium for liquid diffusion, like water itself. The same 
 
ix THOMAS GEAHAM 237 
 
 penetrability appears to take the form of cementation 
 in such colloids as can exist at a high temperature. 
 . . . Another and eminently characteristic quality of 
 colloids is their mutability. Their existence is a con- 
 tinued 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 phenomena 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 sub- 
 stance 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 suit- 
 able of all substances for the dialytic septum he found 
 to be what is known as vegetable - parchment or 
 parchment-paper, 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 
 
238 THOMAS GKAHAM ix 
 
 half an inch, and the dialyser is then floated upon 
 water contained in a basin. 
 
 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 
 some unit of length. " 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 ? 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 
 
ix THOMAS GEAR AM 239 
 
 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 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 indif- 
 ferently 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 inter- 
 fered with by the intervention of the septum. Pro- 
 vided 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 
 preparation 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 
 
240 THOMAS GKAHAM ix 
 
 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 colourless 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 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 vacuo, forms 
 a transparent, vitreous, insoluble mass of considerable 
 lustre. Certain colloids, as gelatin, 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 gelatin 
 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 gelatin. 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 discovered 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 
 
ix THOMAS GKAHAM 241 
 
 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 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 concentrated to a certain extent, 
 but readily coagulates to a deep red jelly, somewhat 
 resembling a clot of blood. Graham considers that 
 native haematite, which is found in mammillary con- 
 cretions, is in all probability colloidal. A soluble ferric 
 hydrate, analogous to the meta-alumina of Crum, was 
 obtained by Pe'an 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 modifi- 
 cations. 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 parch- 
 ment-paper, and there is left a red solution of the 
 
 R 
 
242 THOMAS GKAHAM ix 
 
 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 
 TurnbuUs 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 
 solutions 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 
 searched for in fluid mixtures containing, it may be, a 
 considerable 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 
 
ix THOMAS GKAHAM 243 
 
 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 chemical 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 lique- 
 faction, and is therefore more than a modification of 
 the physical condition 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 gener- 
 ally 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 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 protected by a colloidal 
 
244 THOMAS GEAHAM ix 
 
 membrane impermeable to soluble substances 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 produced 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 demonstrated in the glacier movement 
 will readily develop itself." 
 
 The osmotic process, which is obviously closely 
 connected with the action of colloidal septa, appears 
 
: 
 ix THOMAS GRAHAM 245 
 
 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 hydration 
 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 solutions. " Hence the equilibrium of 
 hydration is different on the two sides of the membrane 
 of an osmometer. The outer surface 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 con- 
 
246 THOMAS GRAHAM ix 
 
 ditions under which comparative measurements can 
 be accurately made, and had determined the rela- 
 tions 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, confined 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 com- 
 parable 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 observa- 
 tions as preliminary to a much wider investigation. 
 The main object, in the outset, was to ascertain the 
 existence 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 existence of such 
 hydrates seemed to be indicated in a few cases, in others 
 the observations were equivocal. A number of measure- 
 ments were made on the pure alcohols, acids, and on 
 mixed ethers, from which Graham inferred that the 
 
ix THOMAS GEAHAM 24*7 
 
 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 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 obser- 
 vation 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 communicated to the 
 Royal 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 investiga- 
 tions. Indeed this was characteristic of the man. 
 Graham's convictions were not lightly formed; often 
 the result of prolonged 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 
 
248 THOMAS GKAHAM ix 
 
 of the phenomena namely, that gases undergo lique- 
 faction when absorbed by liquids and such colloid sub- 
 stances 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 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 . . . , ; . /' 2-470 
 
 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 depends upon a kind 
 of chemical affinity analogous to the attraction which 
 appears to exist between a soluble body and its solvent, 
 
ix THOMAS GKAHAM 249 
 
 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 lique- 
 faction 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 lique- 
 faction. Graham, however, seeks an 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 " penetrative- 
 ness " 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 
 experiment 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 
 
250 THOMAS GRAHAM ix 
 
 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, 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 what- 
 ever 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 obliterated." 
 He seeks to strengthen his conjecture by an appeal to 
 
ix THOMAS GKAHAM 251 
 
 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 composition 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 ? " The analogy is ingenious and 
 even daring, but is not the courage that of a forlorn 
 hope ? 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 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 tempera- 
 ture 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." 
 
252 THOMAS GKAHAM ix 
 
 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 ordin- 
 ary 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 
 disengaged. 
 
 When palladium charged with hydrogen is left ex- 
 posed to the atmosphere, the metal is apt to become 
 suddenly hot, and to lose its gas entirely by spontane- 
 ous oxidation. A wire of the charged metal, if rubbed 
 with magnesia (to make the flame luminous), burns like 
 a waxed thread when ignited in the flame of a lamp. 
 
 The condensed hydrogen, as might be anticipated, 
 is chemically 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 
 ferricyanide becomes ferrocyanide ; chlorine water forms 
 hydrochloric acid; and iodine becomes hydriodic acid. 
 Solutions of mercuric chloride, of certain oxy-salts, and 
 
ix THOMAS GKAHAM 253 
 
 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 validity 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 temperatures. 
 
 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, 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 
 
254 THOMAS GEAHAM ix 
 
 carbonic oxide. This fact, he thinks, has an important 
 bearing upon the process of steel-making, or acieration, 
 by the cementation 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 confined to the surface of the iron bar, but 
 may occur throughout the substance of the metal, in 
 consequence of the prior penetration 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 blistering 
 of the bar appears to testify to the necessary production 
 and evolution of carbonic acid, owing to the decomposi- 
 tion 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 palladium 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 
 
ix THOMAS GRAHAM 255 
 
 many corrections and deletions 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 consumed 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 making it the negative electrode of a voltaic 
 couple immersed in acidulated water. Under these 
 circumstances it is observed that whilst oxygen is 
 
256 THOMAS GEAHAM ix 
 
 freely evolved at the positive electrode, the efferves- 
 cence at the negative electrode is entirely suspended 
 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 hydrogen in all probability pervades the whole 
 mass of the metal, the gas exhibits no disposition to 
 leave the palladium, 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 surface ; otherwise it is not 
 easy to understand how the oxygen, which has no 
 power, at all events in the ordinary molecular con- 
 dition, 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 possible that this highly condensed gas possesses 
 a degree of chemical activity which the gas in its 
 
ix THOMAS GKAHAM 257 
 
 ordinary or more attenuated condition fails to ex- 
 hibit. 
 
 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 explanation." 
 " The gaseous molecule of hydrogen being assumed to 
 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 accord- 
 ingly polarised, oriente, 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 insepar- 
 able ; 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. Pul- 
 verulent spongy palladium takes up 655 volumes of 
 hydrogen ; when precipitated from a dilute solution of 
 
258 THOMAS GKAHAM ix 
 
 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 considerations. No visible change is 
 occasioned to the metallic palladium 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 condensation or occlusion of the gas. " But," 
 he adds, "it must be admitted that the rapidity of 
 penetration is not in proportion to the volume of gas 
 occluded ; otherwise palladium would be much more 
 permeable at a low than at a high temperature." Ex- 
 periments show that the velocity of penetration 
 increases in a rapid ratio with the temperature. The 
 rapid dissemination of hydrogen through a soft colloid 
 metal like palladium, or platinum at a high tempera- 
 ture, has a certain analogy to the process of liquid 
 diffusion, the rate of which is greatly augmented 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 move- 
 ment 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." 
 
ix THOMAS GKAHAM 259 
 
 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 " penetrativeness " is most marked at high tempera- 
 tures, and that practically the only gases which exhibit 
 it are hydrogen and carbonic oxide (which are amongst 
 the most difficult of liquefaction), are very formi- 
 dable, 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 com- 
 bination between the hydrogen and the 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 
 Hydrogenium. 
 
 Palladium charged with hydrogen increases in bulk 
 
260 THOMAS GKAHAM ix 
 
 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 ascer- 
 tained 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 remain 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., 174. 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-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, 
 
ix THOMAS GKAHAM 261 
 
 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 experiment, 
 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 Koyal Society by his pre- 
 decessor 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 pro- 
 found influence on chemical theory. It established, in 
 the first place, the existence of what we now know as 
 the three modifications of phosphoric acid ortho-, 
 pyro-, and metaphosphoric acid. Ortho- or ordinary 
 
262 THOMAS GKAHAM ix 
 
 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 8 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 con- 
 stitution of the white pyrophosphate 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 pyro- 
 phosphates when heated to redness. The acid under 
 
ix THOMAS GEAHAM 263 
 
 consideration, when free, does not disturb albumen, nor 
 produce a precipitate in muriate of barytes. 
 
 " The metaphosphoric acid is disposed to form salts, 
 which 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 precipitates 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 phosphoric acid, and fuse it with soda or its carbon- 
 ate, we shall form a metaphosphate, a pyrophosphate, 
 or a phosphate* [orthophosphate] according as we 
 employ one, two, or three proportions 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 
 phosphoric acid, when in what we would call a free 
 state, are still in combination with their usual pro- 
 portion of base, and that that base is water. Thus the 
 three modifications of phosphoric 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 
 formulae as binary or dualist ic, in accordance with the 
 views of the Swedish chemist. When translated into 
 
264 THOMAS GKAHAM ix 
 
 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 
 constitution of many salts, to which Graham's attention 
 was forcibly drawn by his investigation of the phos- 
 phates, 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 fundamental 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 
 difficult 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 con- 
 stitutes 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 transpiration 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 
 
ix THOMAS GKAHAM 265 
 
 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 Koyal 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 contains, 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 six molecules of water of crystal- 
 lisation 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 molecule 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 sul- 
 phate, 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 tempera- 
 ture 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 
 
266 THOMAS GRAHAM ix 
 
 anhydrous double salt still retains its blue colour ; it 
 may, indeed, be fused at a red-heat without becoming 
 white like the dehydrated copper sulphate. The corre- 
 sponding 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 temperatures 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 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 
 
ix THOMAS GKAHAM 267 
 
 twenty-four molecules. If the soda salt contains two 
 molecules more of water than the potash-salt, the 
 conclusion 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 plus one molecule of water is isomorphous 
 with the same body. Graham is constrained to admit 
 " that the last analogy is superficial, and likely to prove 
 illusory." Illusory it certainly proved to be; never- 
 theless 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 Con- 
 stitution 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 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 
 conclusions 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, 
 
268 THOMAS GRAHAM ix 
 
 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 terminology 
 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 phos- 
 phates, 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 of 
 water, and ordinary phosphoric acid as tribasic phos- 
 phate 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 University College, and has only recently 
 been supplanted by a more systematic and more 
 comprehensive terminology. 
 
 Graham found experimental support for his views 
 concerning 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 
 
ix THOMAS GKAHAM 269 
 
 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 considerable light upon the general 
 question, and accordingly, in 1842, he made an ex- 
 tensive 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, contain- 
 ing 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 hydra- 
 tion of the anhydrous sulphates differs not only with 
 the amount of water with which these substances may 
 be assumed to combine, but also seems to vary with the 
 
270 THOMAS GEAHAM ix 
 
 particular sulphate. As regards the heat produced by 
 the combination of the first molecule of water 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 knowledge 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, 
 particularly 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 suggestions 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 
 
ix THOMAS GKAHAM 271 
 
 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 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, 
 
272 THOMAS GKAHAM ix 
 
 combined with that of Boyle, which connects 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 
 Andersonian Institution in 1830, and it was from here 
 that he gave to the world his classical paper " On the 
 Law of the Diffusion of Gases," read before the Koyal 
 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 In- 
 stitution naturally quickened my interest in Graham 
 and his works, and my frequent 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 personal 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. 
 
ix THOMAS GKAHAM 273 
 
 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 medi- 
 tation. Probably no man certainly 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 Low- 
 lander'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 subordin- 
 ated 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 conscious- 
 ness 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 be- 
 
 T 
 
274 THOMAS GEAHAM ix 
 
 longed 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 Heraclitus. 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 properties 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 intertwined 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 
 absorption of gases by liquids, we are able to detect 
 in the phraseology 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 Daltonian 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 
 combination. But the idea of motion was never with 
 
ix THOMAS GEAHAM 275 
 
 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 remarkable when we remember 
 that Dalton had discovered for himself 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 conception 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 the tubes, 
 noting the effect of weight and of composition upon 
 them in transpiration. He follows them as they enter 
 into liquids and pass out, and as they are absorbed or 
 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 
 
276 THOMAS GEAHAM ix 
 
 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 the same metallic hydrogenium, which 
 he draws out from its long prison in the form of a 
 gas. ... If we examine his work on Salts and on 
 Solutions 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 classification 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 precipi- 
 tates 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 respect- 
 ing the Constitution of Matter " originally published in 
 the Proceedings of the Koyal Society for 1863, 
 Graham has left us his Confession of Faith upon 
 the subject to which he had devoted the whole of a 
 
ix THOMAS GRAHAM 277 
 
 thoughtful life. He conceives that the various kinds 
 of matter, now recognised as different elementary 
 substances, 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 and 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 sub- 
 stances different inconvertible elements, as they have 
 been considered. 
 
 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 combining atoms of 
 
278 THOMAS GKAHAM ix 
 
 which he conceives the existence are not the molecules 
 whose movement is sensibly affected by heat, with 
 gaseous expansion as the result. 
 
 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 sug- 
 gested by the gaseous molecule, just as views derived 
 from the solar system are extended to the subordinate 
 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 molecules 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 con- 
 nected 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 move- 
 ment and consequent volume. Chemical combination 
 thus becomes directly an affair of volume, and is only 
 indirectly connected with weight. Combining weights 
 are different because the densities, atomic and molecular, 
 are different. The volume of combination is uniform, 
 
ix THOMAS GKAHAM 279 
 
 but the fluids measured vary in density. This fixed 
 combining measure Graham's metron of simple sub- 
 stances 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 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 constitutes 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 super- 
 vene, 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 superadded to that condition. Graham 
 conceives that the three conditions (or constitutions) 
 probably always co-exist in every liquid or solid 
 substance, but one predominates over the others, just 
 as the colloidal condition or constitution which inter- 
 venes between the liquid and crystalline 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 
 
280 THOMAS GRAHAM ix 
 
 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, 
 respecting the probable constitution of matter. I have 
 purposely 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 impossible not to be struck with the evidence 
 it affords of Graham's insight, his grasp of principles, 
 and power of co-ordination. Consider, for example, 
 what he says respecting 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, combined 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 Regnault, 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 in- 
 experienced assistants. Graham had, however, the 
 
ix THOMAS GEAHAM 281 
 
 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 Rast, 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 intellectual 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 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 expectation 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 
 
282 THOMAS GKAHAM ix 
 
 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 indi- 
 vidual 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 
 perseverance 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 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 
 
ix THOMAS GRAHAM 283 
 
 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 
 formulated 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 fundamental 
 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 light, felt that 
 this idea rested on a rational basis. They, like our- 
 selves, 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 
 
284 THOMAS GRAHAM ix 
 
 such a thing as water was not only complex, but was 
 made of bodies strangely contrasted in properties ; 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 re- 
 garded 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 principle 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 state- 
 ment 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 
 conception he sought to establish by some of the worst 
 quantitative determinations to be found in chemical 
 
ix THOMAS GEAHAM 285 
 
 literature. It is curious to note the bondage in which 
 the old metaphysical quibble concerning the divisibil- 
 ity 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 yle, 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 Trans- 
 actions for 1880 (vol. clxxi. 1033). Stas's main result, 
 
286 THOMAS GRAHAM ix 
 
 says Mallet, " is no doubt properly accepted if stated 
 thus, that the differences between the individual de- 
 terminations of each of sundry atomic weights which 
 have been most carefully examined are distinctly less 
 than their difference, or the difference of their 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 agreement 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 knowledge of the substances we are 
 dealing with is complete ; of course, one distinct ex- 
 ception 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 dispute 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 
 
ix THOMAS GKAHAM 287 
 
 this is purely accidental, as those hold who carry to the 
 extreme the conclusions of Berzelius and Stas, and he 
 finds that the probability in question is only equal to 
 1 : 109 7 '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 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 complete 
 exposition of the present state of the case in his 
 address to the Chemical Section of the British Associa- 
 tion at the Birmingham Meeting, and for me to go 
 over the field again wdth 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 ; 
 
288 THOMAS GEAHAM ix 
 
 when we have regard to the phenomena 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 
 philosophy during the last five-and-twenty years. Its 
 bearings 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 harmonious 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 primordi- 
 ally 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 
 
ix THOMAS GEAHAM 289 
 
 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 -Max well, 
 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 en- 
 shrouded 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 
 
290 THOMAS GKAHAM ix 
 
 enable us to separate the molecules 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 
 properties, 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 hydrogen 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 question 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. 
 
 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 molecular physics in 
 
ix THOMAS GKAHAM 291 
 
 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 millimetre 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 millimetre 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 nitrogen ; 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 interesting 
 questions which such a conclusion at once raises. In 
 the article "Atom" in the Encyclopedia Britannica, 
 from which I have quoted, you will find Clerk-Maxwell 
 points out its relation to physiological theories, and 
 especially to the doctrine of Pangenesis. " Molecular 
 
292 THOMAS GBAHAM ix 
 
 science," says Maxwell, " forbids the physiologist from 
 imagining that structural details of infinitely small 
 dimensions can furnish an explanation 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 
 Thomson still further developed the modes of molecular 
 measurement, and from a variety of considerations, 
 based upon the kinetic theory of gases, upon the thick- 
 ness 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 
 Eoyal 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 centimetre ; and in order to give us 
 some conception 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 proportion. 
 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 
 
ix THOMAS GKAHAM 293 
 
 succeeded in indicating 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. 
 
FRIEDKICH 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 something of him whose lifelong 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 express- 
 ing my heartfelt wishes for thy welfare and the 
 welfare of 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 
 
 294 
 
x FKIEDKICH WOHLER 295 
 
 jealousy, have zealously laboured in the same field, 
 linked together in the closest friendship." 
 
 And yet, bound as they were in the ties of a friend- 
 ship, the purity and warmth of which were but char- 
 acteristic 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 influenced 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 liber- 
 ality 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 experimenting and 
 collecting manifested itself, to the neglect not unfre- 
 quently 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 
 
296 FKIEDRICH WOHLEE x 
 
 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 
 considerable artistic feeling, and under his direction the 
 son was taught sketching, and otherwise educated in 
 that perception 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 outdoor life which reacted so 
 beneficially upon his development, and contributed 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 
 discovered at that time, without knowing that Sir 
 Humphry Davy had anticipated him, the beautifully 
 
x FEIEDKICH WOHLEPt 297 
 
 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 thiocyanate 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 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 engaged in physiological chemical investigations 
 with Gmelin, had also considerable influence in deter- 
 mining the direction of much of his future work, whilst 
 its immediate effect was the publication in Tiedemann's 
 Zeitschrift fur Physiologic of the results of an inquiry 
 into the transformation experienced by various sub- 
 stances, organic and inorganic, in their passage through 
 the organism. 
 
 In 1823 Wohler obtained his degree, when, on 1 
 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 towards the development of 
 chemical theory, had made him supreme among the 
 chemists of Europe; and to Stockholm, therefore, 
 
298 FKIEDKICH WOHLEK x 
 
 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 laboratory of the illustrious Swede, 
 t .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 
 disposition 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 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 Kose ; 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, 
 
x FEIEDEICH WOHLEK 299 
 
 had daily to clean the apparatus. In the other room 
 were the balances, and some cupboards containing 
 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 interested. To 
 Berzelius the existence of this body was of importance 
 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 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 
 demonstrated in the laboratory of the Royal 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, 
 
300 FKIEDEICH WOHLER x 
 
 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 Norway 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 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 unfrequent 
 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 
 
x FKIEDKICH WOHLER 301 
 
 continued to charge himself with the yearly translation 
 of Berzelius's Jahresbericht into German. It is easy to x 
 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 demarcation 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" 1 
 Leopold von Buch, Poggendorff, and Mitscherlich, and 
 these, without his knowledge, strongly recommended 
 that he should be elected to the vacant teachership of 
 chemistry in the newly founded Trade School in Berlin. 
 Berzelius advised him to accept the post, and accordingly 
 to Berlin Yv^ohler went in 1825. He was now in 
 possession of a laboratory which he could call his own }j 
 and he had to justify that possession by the use which 
 
302 FKIEDKICH WOHLER x 
 
 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 after- 
 wards the Emperor simultaneously designated the two 
 chemists officers of the Legion of Honour. 
 
 But of the twenty-two memoirs and papers which 
 PoggendorfFs 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 seized. The present generation, 
 
x FEIEDKICH WOHLER 303 
 
 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 transforma- 
 tions, 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 
 revolution 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 
 
304 FKIEDKICH WOHLER x 
 
 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 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 
 
 I cyanic acid were of identical composition. The idea 
 that bodies could exist of identical ultimate composition 
 that is, composed 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 
 
 r 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, 
 
x FKIEDEICH WOHLER 305 
 
 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 conse- 
 quences for science, may be seen from the following 
 characteristic letter : 
 
 FRIEDRICH WOHLER TO JUSTUS LIEBIG. 
 
 SACROW, NEAR POTSDAM, 8th June, 1829. 
 
 DEAR PROFESSOR The contents of your last letter to Poggen- 
 dorff 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 under- 
 take, 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 
 
306 FKIEDRICH WOHLEK x 
 
 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 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 extraordinary 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 Labor atorium, 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 
 
x FKIEDKICH WOHLEK 307 
 
 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 PoggendorfF s 
 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 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 remark- 
 able. Moreover, it is the same metal that Del Kio 
 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 
 
308 FKIEDKICH WOHLEB x 
 
 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. c 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 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 erection 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 
 
x FKIEDKICH WOHLEK 309 
 
 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 ? Aber woher Material ? " 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 con- 
 sequences 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 : 
 
 " 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 
 
310 PKIEDEICH WOHLER x 
 
 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 X3ne 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, Fehling, 
 Piria, Stas, and Hlasiwetz have dug rich treasure. The 
 
 1 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 
 preserves 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 
 
 V'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 unper- 
 ceived ; others of these 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 
 
x FKIEDEICH WOHLEE 311 
 
 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 Trpati, the beginning of day) or 
 orthrin (fyQpos, 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 yeara 
 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. Eventually Wohler was selected, 
 and entered on his work at Gottingen in the early part 
 of 1836. He was succeeded at Cassel by Bunsen, who' 
 was at that time privat decent 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 gedtingt 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 
 
312 FEIEDEICH WOHLEK x 
 
 bitter almond oil 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 ferment 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, 
 therefore, 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 ? 
 
 "6. Is the action by double decomposition or 
 catalytic, like that of a ferment ? 
 
 " 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 
 
x FRIEDKICH WOHLEE 313 
 
 to his friend's interrogatories. The third substance 
 Liebig discovered to be sugar. Under the influence of 
 a nitrogenised ferment, termed by 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 27 N0 11 + 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 gluco- 
 sides. 
 
 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 rela- 
 tions to its derivatives until Wohler and Liebig attacked 
 the problem. The extraordinary mutability of uric 
 
314 FRIEDKICH WOHLEK x 
 
 acid, which had baffled and deceived previous investi- 
 gators, 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 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 
 forming these bodies are unknown ; but we shall come 
 to know them." 
 
 Henceforth the friends worked but little together. 
 
 I 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 isolation of crystalline boron, and the 
 
 preparation of the compounds of boron with aluminium 
 
 and nitrogen, work done in concert with Sainte- Claire 
 
x FKIEDKICH WOHLER 315 
 
 Deville. The readiness with which boron unites with 
 nitrogen, and the mode in which the compound may be 
 decomposed, led Wohler to a conception 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 inflammable 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- 
 pounds of carbon. Many years ago Wollaston noted 
 the presence in the slags from the iron blast-furnaces 
 of beautiful lustrous copper-coloured cubes, which he 
 assumed to be metallic titanium ; Wohler proved this 
 substance to be a compound 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 
 intertwined in the history of chemistry that it is 
 hardly possible to avoid comparing the men. Such 
 
316 FEIEDEICH WOHLEK x 
 
 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 
 recognition of error, sincerely grateful, indeed, when 
 made conscious 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 not unfrequently found vent in bitter 
 words, involving him in long and painful quarrels, 
 Wohler, unimpassioned, meeting even the most malig- 
 nant 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 rectitude ! Can we marvel that between two such 
 natures, so differently ordered, and yet so comple- 
 mentary, there should ripen a friendship which both 
 should reckon as the greatest gain of their lives ? " 
 
 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. 
 
x FKIEDKICH WOHLEK 317 
 
 . . . Imagine that it is the year 1900, when we are both dissolved 
 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 other 
 recognise his services to science. He was made a 
 Foreign Member of the Royal Society in 1854, a 
 Corresponding 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 
 Royal Society. He died on 23rd September 1882. 
 
XI 
 JEAN BAPTISTS ANDKE DUMAS 
 
 A LECTURE DELIVERED TO THE EOYAL DUBLIN SOCIETY, MARCH 1885. 
 
 JEAN BAPTISTE ANDR 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 opportunities 
 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 manu- 
 factories 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 
 
 318 
 
XT JEAN BAPTISTE ANDKfi DUMAS 319 
 
 leave his native town ; and he set out on foot for 
 Geneva, where he had relatives, and entered the 
 pharmaceutical laboratory of Le Eoyer. 
 
 Geneva was then, as now, a centre of academic life, n 
 and the boy found everything there to stimulate his 
 intellectual activity and to quicken his thirst for know- 
 ledge. 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 watchmaker, that he made his debut 
 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 Gentiance, 
 compiled with a view of familiarising himself with the 
 conceptions and terms of botanical science. 
 
 But Dumas soon turned into other paths. As his 
 knowledge 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 conceive of new problems and fresh 
 fields of work. The chemical student of that period 
 was not overburdened with text-books. Dumas was 
 
320 JEAN BAPTISTE ANDKti DUMAS xi 
 
 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 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 
 investigation was finished, he went one morning early 
 to M. de la Kive, and timidly submitted to him the 
 manuscript embodying the results of his inquiry. 
 Whilst glancing over it, M. de la Eive 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 ? ' ' Of course 
 they have.' ' Then I must tell you that you have had 
 the good fortune to meet Berzelius 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 breakfast with me/ ' 
 The kindly feeling thus shown to Dumas by his teacher 
 never subsequently failed, and on more than one 
 occasion De la Eive 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 
 
xi JEAN BAPTISTE ANDE^ DUMAS 321 
 
 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 Eive. But 
 his Mend, 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 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 employment of car- 
 bonised 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 employment as a tincture, as potassium 
 iodide, and as iodised potassium iodide, all of which 
 
 Y 
 
322 JEAN BAPTISTE ANDES DUMAS xi 
 
 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 
 connection 'with Prevost led to labours in physiology 
 and physiological chemistry which were productive of 
 the most fruitful results. 
 
 Pre* vost 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 physiolo- 
 gists of the day, as represented by Magendie, left un- 
 touched, suggested themselves to the two naturalists. 
 What, for example, is the proximate nature of blood, 
 and what is the function of its various constituents ? 
 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 Bibliotheque 
 Universelle for 1821. Their experiments on the trans- 
 fusion of blood, made at the period when the death of 
 the Princess Charlotte excited a feeling of profound 
 sorrow throughout Europe, attracted considerable at- 
 tention, and gave fresh interest to the question of the 
 possibility of prolonging human life by the process. 
 
xi JEAN BAPTISTE ANDRfi DUMAS 323 
 
 The mode of secretion of the waste nitrogen of the 
 tissue and the seat of the formation of urea were next 
 attacked. The particular 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 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 
 
324 JEAN BAPTISTE ANDK^ DUMAS xi 
 
 considerable, even if an indirect, influence in deter- 
 mining the direction of much of Dumas's earlier work. 
 He had been struck, as many subsequent chemists have 
 been, with the somewhat 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 substances, 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. Unex- 
 pected difficulties in the way of obtaining these compound 
 ethers in a state of sufficient purity presented themselves ; 
 and no rigorous 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 after- 
 
xi JEAN BAPTISTE ANDKtf DUMAS 325 
 
 wards 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 Eoyer, and was rapidly securing for himself a recog- 
 nised position in the intellectual 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 completing 
 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, nankeen 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 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 Bibliotlieque Universelle, and was 
 
 fli A'U 
 
326 JEAN BAPTISTS ANDKfi DUMAS xi 
 
 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 mid- 
 night ? ' 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 familiarity. 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 mono- 
 logue, which, spoken in a low, somewhat monotonous 
 tone, would have scarcely appeared impressive, had it 
 not been for some waggish pleasantry which now and 
 then escaped, as it were, involuntarily. But, at any 
 rate, if his voice failed to be effective, 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 irresistible enchanter had opened 
 a new world to my mind. I had been more especially 
 
xi JEAN BAPTISTE ANDKfi DUMAS 327 
 
 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 pursuits. 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 outset 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 following 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 him- 
 self 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 
 
328 JEAN BAPTISTE ANDEfi DUMAS xi 
 
 savant returned to his place. " With whom am I to 
 dine ? " asked Dumas of a bystander. " Did you not 
 know it is M. de Laplace ? " This was the beginning 
 of a friendship which ceased only with Laplace's death. 
 Madame la Marquise de Laplace survived her husband 
 many years ; it is an indication of the warmth and 
 ordiality 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 
 Celeste 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 constellation 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? Thanks to his friends and patrons, he 
 had not long to wait for a congenial occupation. The 
 place of Repetiteur de Chimie at the Ecole Poly- 
 technique being vacant, Dumas was appointed at 
 Arago's suggestion. Almost immediately afterwards 
 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 Eoyal 
 Irish Academy], fell vacant by the resignation of 
 Kobiquet a name known in the history of chemical 
 science as the discoverer of the dye alizarin, and 
 
xi JEAN BAPTISTE ANDES DUMAS 329 
 
 Dumas, at Ampere's instigation, 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 enjoyment of 
 unlimited facilities for research, but great was his dis- 
 appointment to find that all that remained of the 
 magnificent equipment of which Gay Lussac and 
 Thenard had 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 want- 
 ing. 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' 7 
 time, too, he had projected his great work, On 
 Chemistry Applied to the Arts, 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 remark- 
 
330 JEAN BAPTISTE ANDKfi DUMAS xi 
 
 able 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, however, was his classical memoir on 
 "Some Points in the Atomic Theory" classical by 
 reason of its influence on the development of chemical 
 philosophy. The inquiry opens with the precise con- 
 ceptions 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 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 
 supposing that in all elastic fluids observed under the 
 same conditions, the molecules are placed at equal 
 distances, i.e. 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 
 
xi JEAN BAPTISTE ANDKfi DUMAS 331 
 
 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 associated. 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 the silicic acid brought him, how- 
 ever, 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 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 pro- 
 mulgated 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 
 
332 JEAN BAPTISTE ANDES DUMAS xi 
 
 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 
 
 r 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 representing the composition of these 
 substances. In the notation of to-day their formulae 
 were 
 
 Alcohol . . ; . ,,.' C 2 H 4 . H 2 O. 
 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 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 relation of these compounds to 
 the salts of ammonia. The nature of this relationship 
 may be seen from the following table : 
 
xi JEAN BAPTISTS ANDKtf DUMAS 333 
 
 Hydrochlorate of bicarburetted hydrogen . C 2 H 4 . HC1. 
 
 Nitrate of bicarburetted hydrogen . . . C 2 H 4 . HNO 2 . 
 
 Sulphate of bicarburetted hydrogen . . C 2 H 4 . H 2 S0 4 . 
 
 Alcohol C 2 H 4 . H 2 0. 
 
 Ether (C 2 H 4 ) 2 . H 2 0. 
 
 Ammonia hydrochlorate .... NH 3 . HCL 
 
 Ammonia nitrite ..... NH 3 . HN0 2 . 
 
 Acid ammonia sulphate .... NH 3 . H 2 S0 4 . 
 
 Aqueous ammonia . . . . . NH 3 . H O. 
 
 In a word, these derivatives of alcohol may be con-^ 
 sidered 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 subse- 
 quently adopted by him, and became known as the etherin 
 theory, from the name which he gave to the radicle C 2 H^j 
 The etherin theory, however, never gained general accept- 
 ance. 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 constituents, 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 theory might have had a longer lease of existence 
 than it actually enjoyed. The etherin theory had,^ v 
 however, the great merit of familiarising chemists with 
 the conception of organic radicles. It further indicated 
 that the reactions of organic chemistry are truly com- 
 parable with those of inorganic chemistry, and can be 
 represented by equations as precise and as simple in 
 character as those which express the chemical trans- 
 formations of the mineral kingdom. Berzelius, by his^ 
 
334 JEAN BAPTISTE ANDES DUMAS xi 
 
 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 distinction ; 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 constitution 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 Robert Kane on the Theory of 
 the Ethers, in which this view is developed, and in 
 which he denotes by the name of ether eum the hypo- 
 thetical body formed by the union of etherin with 
 hydrogen (following Berzelius, who termed the combina- 
 tion 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 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 amusement and ridicule in the chemical 
 
xi JEAN BAPTISTE AKDKfi DUMAS 335 
 
 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, prototypes 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 inflammable fluid, termed by Taylor 
 pyroligneous ether, a substance 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 relations they embodied 
 
336 JEAN BAPTISTE ANDKfi DUMAS xi 
 
 in the name which they gave to it of 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 classifica- 
 tion 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 
 
xi JEAN BAPTISTE ANDKfi DUMAS 33*7 
 
 ores, the composition of the materials used in the 
 thirteenth-century frescoes these, and a host of other 
 problems, attracted his attention. During a tour in 
 Switzerland he was shown, by the apothecary Pagen- 
 stecher, a sample 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 soiree 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 procelain manufactory at 
 Sevres, and hence, by tradition, was regarded as the 
 chemical adviser of the royal household ; he was com- 
 missioned, therefore, to inquire into the cause of the 
 peculiar behaviour of the candles. The actual investiga- 
 tion was intrusted to Dumas, who had no difficulty in 
 determining that the acid vapours were caused by 
 hydrochloric 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 ; 
 
 z 
 
338 JEAN BAPTISTE ANDES DUMAS xi 
 
 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 at the negative electrode ; whilst 
 the oxygen is evolved at the positive pole. Hydrochloric 
 acid, when electrolysed, is likewise 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 combination. According to this theory 
 chemical combination is the result of the union of 
 substances of different electric polarities. These sub- 
 stances 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 com- 
 pound radicle determined its behaviour and influenced 
 
xi JEAN BAPTISTE AKDKfi DUMAS 339 
 
 the nature of the compounds into which it entered. 
 Potassium oxide, K 2 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 -f S0 3 , 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 organic bodies, it turns out the hydrogen, 
 atom after atom, and takes the place of each hydrogen 
 atom so expelled r-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 Lussac 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 2 H 4 C1 2 , 
 is by the continued action of chlorine converted into 
 C 2 C1 6 , or C 2 C1 4 G1 2 . But these facts were too few and 
 isolated for their bearing on the dualistic theory of 
 chemical combination to be perceived. Their signifi- 
 cance, 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 ele- 
 mentary atoms, do they really rest on such evident 
 
340 JEAN BAPTISTE ANDK& DUMAS xi 
 
 facts that they are to be accepted as articles of faith ? 
 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 assumptions, until the 
 binary theory absolutely sank under the load of contra- 
 dictions 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. 
 
 But the conception of metalepsis, as the doctrine of 
 substitution was styled, was even more constructive 
 than destructive 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 speculations by which the super- 
 structure 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 properties 
 much less to the nature of their elementary atoms than 
 to the mode of arrangement of these atoms within the 
 
xi JEAN BAPTISTE ANDKfi DUMAS 341 
 
 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 differ- 
 ence 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 conceptions 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 Kevolution 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 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 
 
342 JEAN BAPTISTE ANDKE DUMAS xi 
 
 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 indigo, and of the chemical changes 
 occurring in the indigo vat, were first correctly traced 
 by him. One of the important 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 . 
 
xi JEAN BAPTISTE ANDBfi DUMAS 343 
 
 Phenol . . . C 6 H 6 0. 
 Picric acid . . C 6 H 3 (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 8 2- 
 Orcein . . . C 7 H 7 (N0 2 )0 2 . 
 C 7 H 8 2 + NH 3 + 3 = C r H 7 N0 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 composition 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 determination 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 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 
 
344 JEAN BAPTISTS ANDKfi DUMAS xi 
 
 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 subject 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 uni- 
 versally 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 experi- 
 ments 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 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 
 
xi JEAN BAPTISTE ANDK& DUMAS 345 
 
 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 astro- 
 nomical 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 
 established 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 deter- 
 mined 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 ponderal composition 
 of atmospheric air. 
 
 As the result of their experiments, it was ascertained 
 that 100 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, provided the 
 
346 JEAN BAPTISTE ANDBfi DUMAS xi 
 
 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 experiment. 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 careful 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 (l) The respiration of animals; (2) The 
 combustion of organic matter ; (3) The decay and 
 putrefaction of organic substances ; (4) The disintegra- 
 tion of rocks ; and (5) The ultimate 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 
 
xi JEAN BAPTISTE ANDES DUMAS 347 
 
 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 kilometre in length, to 
 equipoise it. If we also assume that each individual 
 consumes 1 kilogram of oxygen per day, and that the 
 population 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 cubes ; or, in other 
 words, the abstraction in a century would only be 
 sife o^ n f 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 revised, and their 
 substantial accuracy confirmed, by Professor Le Conte. 
 Certain of the data employed by Dumas and Bous- 
 singault were of necessity only imperfectly known at 
 the time, but the main conclusion has not been dis- 
 turbed by the more accurate knowledge 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 
 essential nature of matter. It was this philosophic 
 
348 JEAN BAPTISTS ANDES DUMAS xi 
 
 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 combina- 
 tion of analytical skill and manipulative dexterity with 
 unlimited patience and an unbending resolution not to 
 swerve from the highest ideals of quantitative accuracy. 
 What, then, must be the strain both on the mental and 
 moral energy of him who sets himself the gigantic task 
 of redetermining the atomic weights of all the elements, 
 with the precision required by contemporary science ? 
 It is not surprising 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 two- 
 fold. 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 unalter- 
 ability and their eternal existence. It had been pointed 
 out that the numerical relations 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 
 
xi JEAN BAPTISTE ANDKfi DUMAS 349 
 
 of one primordial substance, and he sought for the 
 experimental confirmation of this hypothesis in the 
 circumstance 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 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 compound radicles, 
 bodies often absolutely dissimilar 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 determina- 
 tions 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. 
 
350 JEAN BAPTISTS ANDKE DUMAS xi 
 
 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 ? Are the chemical attributes of an 
 elementary body a function of its atomic weight ? 
 Affirmative answers to questions of this kind would 
 obviously tend to strengthen the validity of Front's 
 hypothesis. A certain amount of positive evidence has 
 been accumulated. Thus : 
 
 Li + K 7 + 39 
 
 - = Na, or - - = 23. 
 2 2 
 
 K + Cs 39 + 133 
 
 - = Kb, or -- = 86. 
 
 Ca + Ba 40+136-4 
 
 = Sr, or - = 88-2 
 
 v<vO 2 2 
 
 Ga , or !iii? = 68-5. 
 
 P + Sb 31 + 120 
 
 g = As, or - -- = 75-5. 
 
 P + Bi 31 + 209 
 
 - = Sb,or -- = 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 
 
xi JEAN BAPTISTS ANDKfi DUMAS 351 
 
 to exist between the individual members of well-defined 
 groups of elementary bodies ; and that the absolute 
 individuality postulated by Berzelius is, in all prob- 
 ability, 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. 
 
 . . . .16. 
 
 S . . - : . . 16 + [lxl6] = 32. 
 
 Se ....- .: -..' . 16 + [4 x 16] = 80 (79). 
 
 Te *. ..,. , . . 16 + [7x16] = 128 (126-3). 
 
 Mg . _: : i -V 24. 
 
 Ca %g! . *. , . 24 + [lx 16] = 40. 
 
 Sr .,'.. ../" . 24 + [4x16] = 88 (87-2). 
 
 Ba . ; : . . 24 + [7x16] =136 (136-4). 
 
 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 relationships 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 re- 
 determined 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 
 
352 JEAN BAPTISTE ANDRE DUMAS xi 
 
 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 groupings 
 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 investigations 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 Provost, he began his career as an 
 investigator. Some of these problems 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 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 observa- 
 tions on the origin of bees' -wax. The nature of this 
 substance was first revealed by the investigations of 
 
xi JEAN BAPTISTE ANDKfi DUMAS 353 
 
 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 attrac- 
 tions for French chemists. The conditions of the trans- 
 formation 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 want- 
 ing 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 the chief characteristics of French style, and 
 in the exercise of these qualities no French scientific 
 writer has surpassed Dumas. Much of his influence 
 
 2 A 
 
354 JEAN BAPTISTE ANDKfi DUMAS xi 
 
 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, paraphrasing 
 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 compilation, but to his power of co-ordina- 
 tion, and to the excellence 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, freedom, 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 ? It is an absolute belief 
 in the testimony of the senses, a boundless confidence in 
 experiment, a blind submission to the supreme author- 
 ity 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 circumstances under which 
 that brilliant career came to its untimely close. "It 
 
xi JEAN BAPTISTE ANDKfi DUMAS 355 
 
 was at the time that Lavoisier had conceived the idea 
 of publishing a collection of his memoirs. . . . 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 continuation 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 
 Instruction 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 exempli- 
 fied in the Faraday Lecture, which, on the invitation 
 of the Council of the Chemical Society of London, he 
 delivered in the theatre of the Koyal Institution in 
 
356 JEAN BAPTISTS ANDKti DUMAS xi 
 
 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 duty which had been entrusted to him. 
 The lecture hall at the Eoyal Institution has been the 
 scene of many a rhetorical triumph, and its audiences 
 have been held spellbound 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 Faraday. " The name of your 
 illustrious fellow-countryman is not one which any 
 single nation can claim as its exclusive property ; 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 
 
xi JEAN BAPTISTS ANDRfi DUMAS 35*7 
 
 adopting a received conclusion, will ever serve as 
 models for the experimentalist." 
 
 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 con- 
 ception of the person commemorated. These addresses 
 range over all subjects and over almost every depart- 
 ment of human knowledge. The series opens with that 
 on Be'rard, and the estimate of the famous surgeon's 
 relations to the science of his time might have been 
 drawn up by a 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 element 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, Con- 
 
358 JEAN BAPTISTE ANDRfi DUMAS xi 
 
 dorcet, Fourier, Cuvier, and Flourens, his predecessors 
 in office, and it fell to his duty to deliver the com- 
 memoration address on Guizot. The task was un- 
 usually 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 Rendus 
 in which he was concerned. 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 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 - producing 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 employment of which was first 
 suggested by Dumas. 
 
xi JEAN BAPTISTE ANDKfi DUMAS 359 
 
 No record of Dumas's literary services would be 
 complete without some reference to his connection with 
 the Annales de Chimie et de Physique. This journal, 
 at one time the leading scientific periodical of the 
 world more renowned even than our own Philo- 
 sophical 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 publication 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 wide- 
 spread 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 build- 
 ings, surrounded by a little knot of workers, comprising 
 Piria, Stas, Melsens, Leblanc, and others, that those 
 classical researches of which mention has 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 j 
 teaching. Offers of assistance, however, were not 
 wanting ; and Dumas has himself related how, on a 
 certain day during the troubled times which followed 
 
360 JEAN BAPTISTE ANDKfi DUMAS xi 
 
 the Kevolution of 1848, lie 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 
 Kevolution 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 Kepublic as 
 Minister of Agriculture and Commerce, and was en- 
 trusted 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 
 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. 
 
xi JEAN BAPTISTS ANDKfi DUMAS 361 
 
 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 unem- 
 bittered, 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 Associa- 
 tion of Science a body modelled on lines similar to 
 those of our own British Association. How loyally the 
 heart of "the old man eloquent" remained true to 
 
362 JEAN BAPTISTE ANDKfi DUMAS xi 
 
 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 aspirations 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 
 
xi JEAN BAPTISTE ANDKfi DUMAS 363 
 
 enjoyments of fortune, they have found their reward 
 in public esteem." 
 
 Such outward and visible signs of appreciation as 
 potentates and public bodies could bestow Dumas 
 reaped to the full. Nearly every academy in Europe 
 delighted to honour him. At the age of thirty-two he 
 became a member of the Institute ; Correspondent of 
 the Berlin Academy in 1834; and a Foreign Member 
 of the Royal Society of London in 1840. In 1843 the 
 Royal 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 le me'rite, 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. 
 
XII 
 
 HEEMANN KOPP 
 
 AN ADDRESS DELIVERED TO THE FELLOWS OF THE CHEMICAL 
 SOCIETY, 20TH FEBRUARY 1893 J 
 
 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 
 
 1 Chemical Society's Memorial Lectures, No. II. 
 364 
 
xii HEKMANN KOPP 365 
 
 of Hofmann, at what proved to be their last meeting, 
 with the closing words of the song : 
 
 Der Herr im Himmel schenk ein gnadig End 
 Uns letzen Zehn vom vierten Eegiment. 
 
 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 extra- 
 ordinary expansion 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 dispassionate 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 
 
366 HEKMANN KOPP xii 
 
 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 vivify- 
 ing influence that science and learning grow and 
 spread. 
 
 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 in- 
 dividuality. It is this consideration 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 
 contemporary 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 ; 
 
xii HEEMANN KOPP 367 
 
 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 oppos- 
 ing 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 
 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 surround- 
 ings and in his occupation ; his social sympathies 
 satisfied by his relations with colleagues like Bunsen, 
 Kirchhoff, Helmholtz, Eenaud, 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 
 
368 HEEMANN KOPP xn 
 
 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 dis- 
 tinguished physician, seems to have occasionally 
 occupied himself with experimental chemistry, and 
 Leonhard's Taschenbuch and Gehlen's Journal contain 
 papers by him on mineral analysis, and on investiga- 
 tions 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 Ordinary Professor of 
 Medicine and Chemistry in the University in the year 
 in which Kopp was born, is mainly known by hi& 
 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 Physikalisches Worter- 
 buch, and by his work on the thermal expansion of 
 liquids. Wohler has told us something of the con- 
 ditions 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 
 
xii HEKMANN KOPP 369 
 
 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 
 reperiendae 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 a Privatdozent in the Giessen 
 University, lecturing alternately on^theoretical chemistry, 
 crystallography, meteorology, and physical geography. 
 At about this time that is, when twenty-four years of 
 age he began his History of Chemistry, and, as his 
 material accumulated, he added this subject to the list 
 of his lecture courses. In 1 843 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 
 
 2 B 
 
370 HEKMANJST KOPP xn 
 
 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 ex- 
 perimental 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 Euperto-Carolina 
 were unavailing. " Even Bunsen alone," he was wont 
 to say, " keeps me fast in Heidelberg." 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, suddenly 
 found himself famous. " With one accord his con- 
 temporaries recognised that here was a production which, 
 whether they regarded the thoroughness of research 
 
xii HEKMANN KOPP 371 
 
 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 consider- 
 able 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 Beitrdge zur Geschichte der 
 Chemie, which appeared between 1869 and 1875, and 
 the Entwicklung der Chemie in der neueren Zeit, 
 printed under the auspices of the Historical Commission 
 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 pro- 
 foundly 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 
 
372 HERMANN KOPP xn 
 
 wielded by the greatest chemical critic of his time. The 
 Jahresbericht of Liebig and Kopp differed, however, 
 fundamentally, both in 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 Diefienbach, 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 prosecution 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 English readers 
 
xii HEKMANIST KOPP 373 
 
 by means of a translation published under the direction 
 of Hofmann and Warren De la Kue, but the good seed 
 fell upon stony places, and after a year or two the 
 enterprise 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 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 Jahresbericht, 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 publication, 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 
 
 1 ' ' Ich bin einige Monate in England gewesen, habe ungeheuer viel gesehen 
 und wenig gelernt. England ist nicht das Land der Wissenschaft, es existirt 
 dorten 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 schatzbarste 
 Ausnahme, er ist ein vortrefflicher Mensch, auch Gregory, der an seine Stelle 
 in Glasgow gekommen ist." Liebig to Berzelius, 26th November 1837. 
 
3*74 HEKMANN KOPP xn 
 
 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, 
 however, 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 
 exercised no inconsiderable influence on the education 
 of the present generation of chemists in that country. 
 The Introduction 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 Molecular welt, 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 considerable 
 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 
 
xii HERMANN KOPP 375 
 
 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 anno- 
 tated edition of Liebig and Wohler'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 Royal Society. 
 
 Compared with those of his great contemporaries, 
 Liebig 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 
 measurements were not only troublesome and tedious 
 in themselves, but they were followed, very frequently, 
 by long and wearisome 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 
 
376 HEKMANN KOPP xii 
 
 and chemical nature of substances ; 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 
 intradependence 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 en- 
 deavour 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 MendeleefFs 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 were known, even approximately ; and he had, 
 as a preliminary step, to ascertain the conditions under 
 which such observations must be made in order that 
 accurate and comparable 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 
 
xii HEKMANN KOPP 377 
 
 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 composition ; 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, xxxiv. 260 
 (1840)), Kopp seeks to determine the behaviour of a 
 solvent towards a mixture, 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 
 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 
 
378 HEKMANN KOPP xn 
 
 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 calculated 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 formulae expressing 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, Klidorff, and Engel. In the note on 
 the Solubility of Common Salt in aqueous Alcohol of 
 different strengths (Annalen, xl. 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, xxxv. 230), he describes a simple method 
 for the quantitative estimation of the resistance which 
 liquids offer to rupture. The power which a liquid 
 
xii HEKMANN KOPP 379 
 
 possesses of resisting any tendency to internal separa- 
 tion of its parts has hitherto received but scant attention 
 from physicists, presumably on account of the experi- 
 mental difficulty of the problem. It is, as shown by 
 Donny, Osborne Keynolds, and Worthington, more con- 
 siderable 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 " Uber die Bildung von Krystallen mit 
 Kernen " (Annalen, xciv. 118 (1855)), Kopp describes 
 a characteristically ingenious method of throwing light 
 upon the mode in which natural crystals are made to 
 enclose foreign substances, 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 
 composition on crystalline form (Annalen, cxxv. 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 instru- 
 ment maker, and his materials were, for the most part, 
 
380 HEEMANN KOPP xn 
 
 glass and cork. But no Japanese worker, with his few 
 and primitive tools, ever produced results which, in 
 point of delicacy, finish, and accuracy, surpassed those 
 which Kopp obtained by means of his simple con- 
 trivances. It is told of Wollaston that when a 
 distinguished foreigner called to see his laboratory, he 
 had his chemical 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 
 consisted of an account in PoggendorfFs Annalen, 
 done when he was a student at Marburg, of a dif- 
 ferential barometer which he had constructed (Poggen- 
 dorfFs Annalen, xl. 62 (1837)). His volumenometer 
 (Annalen, xxxv. 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 convenience 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 deter- 
 mination of the specific gravities of such substances 
 as sugar, starch, silk, cotton, wool, flax, etc. 
 
 His ingenuity is further seen in his method 
 (Annalen, Ixxxi. 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 expan- 
 sion of minerals is in fact based on Kopp's work. 
 
xii HEKMANN KOPP 381 
 
 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, xciv. 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 thio- 
 sulphate, etc. The value of the apparatus lay, how- 
 ever, 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 passing 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 
 
382 HEKMANN KOPP xii 
 
 the change in the coefficient of expansion. Kopp was 
 particularly attracted by the extraordinary behaviour 
 of Eose'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 contract 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, 
 xl. 184 (1841)), and " Dichtigkeit des Cadmium- 
 Amalgams" (Annalen, xl. 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 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 sub- 
 stances. 
 
 In 1818 Dulong and Petit found that when the 
 atomic weights of the elements are multiplied by 
 their respective specific heats approximately the same 
 
xii HEKMANN KOPP 383 
 
 number is obtained. This fact was subsequently 
 embodied by them in the statement that " the atoms 
 of all simple bodies have exactly the same capacity for 
 heat." In 1831 this generalisation was extended by 
 Neumann (PoggendorfFs Annalen, xxiii. 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, stoichiometrical 
 quantities of bodies of analogous chemical composition 
 have the same capacity for heat." 
 
 Subsequent observers, among whom may be named 
 Avogadro, 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 determined the specific heats 
 of a large number of substances, for the most part com- 
 pound in their nature. He concluded that each solid 
 substance, at a sufficient distance from its melting 
 point, has a specific heat which may vary somewhat 
 with physical conditions (temperature, greater or less 
 density, amorphous or crystalline nature, etc.) ; but the 
 differences 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 
 
384 HEEMANN KOPP xii 
 
 to which, on account of their totally different chemical 
 deportment, different formulae are assigned; and even 
 in cases in which these laws have hitherto been con- 
 sidered as essentially true, the divergences 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 ele- 
 ments, 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 
 considerations as to the nature of the chemical elements. 
 What substances, he asks, are to be regarded as chemical 
 elements ? Does the mere fact that they are non- 
 decomposable determine this ? 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 ? 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 chlorine contained a further quantity of oxygen 
 besides the elements of an oxygen acid, did not find an 
 equally permanent recognition. On the basis of the 
 
xii HEKMANN KOPP 385 
 
 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 decomposition which 
 practical chemistry has at its disposal, and on the 
 trustworthiness of the conclusions which theoretical 
 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 undecompos- 
 able 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, 
 
 2c 
 
386 HERMANN KOPP xn 
 
 is the magnitude of the molecular heat a measure of 
 the complexity. If Dulong and Petit' s law were 
 universally valid, it might be concluded with great 
 certainty that the so-called elements, if they are really 
 compounds of unknown simple substances, are com- 
 pounds 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 
 complexity 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 com- 
 pounds, compared with those of analogous chlorine or 
 potassium compounds, and the greater molecular heats 
 of ammonium and cyanogen obtained by indirect deter- 
 mination, 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 
 Transactions, 1865, 155). 
 
xii HERMANN KOPP 387 
 
 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, glucinum, 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 by temperature, and 
 in such manner that their atomic heats at high tempera- 
 tures 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 differ- 
 ence in composition frequently occasions the same 
 difference in boiling point (Annalen, xli. 87 et seq.). 
 He also pointed out that in many other similar com- 
 pounds, mostly alcohols, acids, and esters of the fatty 
 series, a difference of #CH 2 apparently corresponds 
 with a difference of about #19 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 xH atoms more 
 than the other boiled x x 5 lower. He subsequently 
 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 xCH 2 = #24 ; 
 in the fatty ketones and aldehydes it is 22 ; in the 
 alkyl chlorides it is 31 ; and in the fatty anhydrides 
 
388 HEEMANN KOPP xn 
 
 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 
 molecular 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 tempera- 
 tures than that of the boiling point under atmospheric 
 pressure, and by observations on the vapour pressures 
 of the normal fatty acids, Landolt concluded that such 
 was the case. 
 
 Further and more accurate observations showed 
 however, that Kopp's original propositions must be 
 materially modified. Wanklyn found that the in- 
 crement for CH 2 in an homologous series became less 
 and less as the series was ascended. Schorlemmer 
 (Philosophical Transactions, clxxii. 123 (1872)) ob- 
 served 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 19. Linnemann 
 (Annalen, clxii. 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 2 are 
 
xii HEKMANN KOPP 389 
 
 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 
 accumulated since the time of Linnemann have con- 
 firmed 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 explained 
 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 members 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, however, ethyl alcohol be taken as the 
 initial member of the triad, the formulae of ethyl, 
 propyl, and butyl alcohols would be 
 
390 HEKMANN KOPP xn 
 
 MeCH 2 OH, 
 EtCHjOH, 
 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 compounds 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 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, 
 Lossen 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 
 
xii HEKMAKNT KOPP 391 
 
 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 otherwise corresponding structure con- 
 taining 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 
 Gartenmeister may be noticed. 
 
 For isomers of aromatic series practically no general- 
 isations 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 repro- 
 ducing the observations for the particular series to 
 which the formulae refer, but they do not afford a basis 
 for calculating boiling points in general. 
 
 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 sub- 
 stances. 1 
 
 1 Objection has been raised to the term "specific volume" on the ground 
 that as specific gravity is the weight of unit volume, specific volume should, 
 
392 HEKMANN KOPP xn 
 
 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 propor- 
 tions. The first endeavour to apply similar considera- 
 tions to solids and liquids was made in 1821 by "Le 
 Koyer, 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, xcii. 408, Le Royer 
 and Dumas attempted to determine the equivalent 
 volumes of the elements by dividing their atomic 
 weights by their respective 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 more accurate observation. This idea of combination 
 among solids in definite volumetric proportion was 
 further developed in 1824 by W. Herapath in a paper 
 
 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 
 apprehended 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 
 objection 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. 
 
XII 
 
 HERMANN KOPP 393 
 
 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, Ixv. 394), 
 and subsequently in 1830 by Boullay, but with no 
 definite theoretical result. Ammermuller, however, in 
 1840, was led to conclude (PoggendorfFs Annalen, xlix. 
 341 ; id. 1. 406), that the specific volumes of com- 
 pounds containing the same elements in different 
 proportions are either identical or stand to one 
 another in rational proportions. Persoz, in his Intro- 
 duction 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 conclusion 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 " 
 (PoggendorfFs Annalen, xlvii. 133). In this paper he 
 discusses the specific gravities 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 
 J nitrates, on the supposition that such salts consist of 
 
394 HERMANN KOPP xn 
 
 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 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 (Miscliungsgewiclit) 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, 
 chromium, 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 iso- 
 morphous compounds show identity in specific volume, 
 and Kopp sees in this fact an argument for the validity 
 of the theory of hydrogen acids ; 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 replaces 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 Advance- 
 ment of Science at Erlangen, in 1840 (Annalen, xxxvi. 
 1 (1840)). He first attempts to prove that the 
 specific weight of isomorphous substances is propor- 
 tional to their atomic weight ; or that ismorphous 
 
xii HERMANN KOPP 395 
 
 bodies possess the same atomic value. Strictly speak- 
 ing, 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 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 
 witherite, strontianite, arragonite, and cerussite ; and 
 of the carbonates 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 = 0'012767lV, 
 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 R becomes less obtuse. 
 This fact, indeed, was discovered by Mitscherlich, 
 who found that the specific gravity of calcspar de- 
 creased in the ratio of 1 to on being heated 
 
 through 100. The specific gravity of calcspar is 
 27220, when a = 0'8544 and R = 105 5'. By heat- 
 ing it through 100, the sp. gr. becomes 27167, 
 or its atomic volume changes from 3673 to 36*80. 
 If we determine the length of the axis a by means 
 
396 HERMANN KOPP xn 
 
 of the above formula, we find it 0*85672, correspond- 
 ing to an angle E of 104 57', or a difference of 
 8', which closely agrees with that actually observed 
 by Mitscherlich (Philosophical Magazine [3], xviii. 
 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 Annalen, 
 553 (1840)), starting from the observation of Ammer- 
 miiller, 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 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 explanation 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 modifications 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 
 
xii HEKMANN KOPP 397 
 
 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 is 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 probability 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 its probability may be inferred from the 
 fact that it explains the greatest number of experi- 
 mental 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 contained in it with an atomic 
 volume different from the primitive value; but it is 
 certain that one element in a compound does not 
 
398 HERMANN KOPP xii 
 
 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 C 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 con- 
 sequently 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 + R to be a compound of a heavy metal, ra + R the 
 analogous compound of a light one ; suppose A to be 
 the known specific volume of M + R, and a that of 
 m + R, B the primitive atomic volume of M, and b 
 that of m. 
 
 Then, 
 
 M + R = A, 
 
 and 
 
 M = B. 
 
xii HEEMANN KOPP 399 
 
 Therefore the atomic volume with which E is con- 
 tained in the compound is A B, say x. 
 
 It is assumed that E retains its value in m + E, 
 
 and since 
 
 m + R = a, 
 
 and 
 
 therefore atomic volume of m (or 6) = a x. The 
 specific volume of C0 2 in the carbonates is assumed to 
 be 24*2, whence we have 
 
 Mol. vol. calc. Sp. gr. calc. Sp. gr. obs. 
 
 PbC0 3 -, -./ . 42-4 6-30 6-43 to 6-47 
 
 CdC0 3 ,;. 
 
 FeC0 3 ;. 
 MnCO 3 
 Ag 2 C0 3 . 
 ZnCO 3 
 
 With the exception of ZnC0 3 , the observed and cal- 
 culated specific gravities are fairly concordant. 
 
 By means of the values for the alkalis and alkaline 
 earths, obtained as described, Kopp deduces the follow- 
 ing 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 
 K 2 C0 3 
 MgC0 8 
 Na 2 C0 3 
 SrC0 3 
 
 The specific volume of N0 3 is, in like manner, found 
 to be 28'6. 
 
 Mol, vol. calc. Sp. gr. calc. Sp. gr. obs. 
 Pb(NOg) 2 . . . 75-5 4-40 4-40 
 
 AgN0 3 ". . . . 78-1 4-36 4-36 
 
 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 
 
 33-8 
 
 2-96 
 
 2-70 -300 
 
 61-6 
 
 2-25 
 
 2-26 
 
 30-6 
 
 2-75 
 
 2-61 
 
 45-0 
 
 2-36 
 
 2-47 
 
 41-5 
 
 3-56 
 
 3-60 to 3-62 
 
400 HEKMANN KOPP xn 
 
 Mol. vol. calc. Sp. gr. calc. Sp. gr. obs. 
 92-1 1-74 1-74 
 
 80-1 3-20 3-19 
 
 NH 4 NO. ? . . 92-1 1-74 1-74 
 
 KN0 3 . . 94-7 2-14 2'10 
 
 NaN0 3 . - 78-1 2-19 2-19 
 
 Sr(NCg 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 
 
 MgS0 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 . . . 2-60 2-62 
 
 SrS0 4 ' . , . 3-90 3-95 
 
 In the chromates, Cr0 4 = 36 '5 ; and in the tungstates, 
 W0 4 = 39'0. 
 
 Sp. gr. calc. 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 6-04 
 
 Cl, like S0 4 , appears to have two distinct values, 
 viz. 157 and 19 '8. 
 
 Sp. gr. calc. Sp. gr. obs. 
 
 PbClg . . . 5-60 5-68 
 
 AgCl . . 5-50 5-50 
 
 BaCl 2 . . . 3-83 3-86 
 
xii HEKMANN KOPP 401 
 
 Sp. gr. calc. Sp. gr. obs. 
 
 NaCl . . .2-25 2-26 
 
 NH 4 C1 . . .1-44 1-45 
 
 CaCl 2 . . . 2-29 2-27 
 
 KC1 ... 1-94 1-94 
 
 CuCl 2 . . . 3-70 3-68 
 
 HggClg . . . 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 = 5*1. 
 
 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 8 3* . . 5-69 5-78 
 
 Pb 2 O 3 . . .8-91 8-94 
 
 Fe 2 s . . . 5-31 5-25 
 
 Co 2 O 3 . . . 5-64 5-69 
 
 Fe\ 
 Ti}3 
 
 . 4-78 4-78 
 
 Bi 2 O 3 . . . 8-09 8-17 
 
 The agreement, with the exception of the cases of 
 MnO, SnO, Mo0 2 , and Pb0 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 
 
 2 D 
 
Sp. gr. calc. 
 . 5-87 
 
 Sp. gr. obs. 
 5-75 
 
 . 10-5 
 
 10-69 
 
 . 7-48 
 
 7-25 
 
 . 3-44 
 
 3-46 
 
 5-68 
 
 5-27 
 
 402 HEEMANN KOPP xn 
 
 Cu 2 
 Hg 2 
 Ag 2 
 Mo0 3 
 W0 3 
 
 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 memorable investigations which we owe 
 to Playfair and Joule, was first made known through 
 the medium of a paper communicated to this Society 
 by your lecturer and Mr. John I. Watts ("On the 
 Specific Volume of Water of Crystallisation," Trans. 
 
XII 
 
 HEEMANN KOPP 403 
 
 xxxvii. 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 whole of the ground 
 again, much of the experimental matter of our com- 
 munication was based upon his previous observations. 
 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 107. Each additional molecule appears to 
 occupy a gradually increasing volume. The difference 
 between the monohydrate and dihydrate is 13*3 ; 
 between the dihydrate and trihydrate it is 14*5 ; 
 between the trihydrate and tetrahydrate it is 15*4 ; 
 and between the hexhydrate 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 molecules (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 com- 
 pound is connected with the degree of this contraction. 
 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 
 
404 HEEMANN KOPP xii 
 
 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 
 (if i-i; i l"t; T> f-i) to its primitive specific 
 volume, an assumption which plays a not inconsiderable 
 part in Schroder's subsequent papers, and in those of 
 Hermann (J. pr. Chem. xiii. 28 (1876)) and E. Wilson 
 (Proc. Roy. Soc. xxxii. 457). 
 
 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 " Vorausbestimmung einiger physikalischen 
 Eigenschaften bei mehreren Keihen organischer Yerbin- 
 dungen" (Annalen, xli. 79; ibid. xli. 169), we have 
 the first of a series of memoirs, on which his fame as an 
 observer will ultimately rest. For his purpose, 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 character- 
 ised, and the determination of their specific gravity can 
 be made with a higher degree of precision 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 
 
xn HEEMANN KOPP 405 
 
 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 + a D + a, .... 
 
 A + y B + y C + y D + y, 
 
 B + S C + 8 D + S, 
 
 where A, B, C, D, a, ft, 7, S, are certain bodies or 
 combinations of elements, then it is only necessary to 
 become acquainted with one horizontal and one vertical 
 series to know the most important physical properties 
 of all the combinations contained in such a table. 
 If the properties of the compounds contained in one 
 horizontal or in one vertical series are known, the mere 
 knoivledge 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 
 compound A + a, A + /3, A + 7, etc., are known, and we 
 also know the specific gravity and boiling point of 
 B + a, we can at once ascertain the specific gravities 
 and boiling points of the bodies B + /3, B + 7, B + S. 
 For between the specific volumes and boiling points of 
 
 A + a and B + a 
 
 A + y and B + y 
 
 B + a and D + a 
 
 B + y and D + y 
 etc. 
 
 A + a and A + S, 
 
 B + a and B + 8, 
 
 C + Sand C + 8, 
 
 etc. 
 
 the differences are the same. 
 
 A similar regularity occurs in the physical properties 
 in cases of substitution, as, for example, that of chlorine 
 
406 HEEMANN KOPP xn 
 
 for hydrogen. Let A represent a combination of oxygen 
 and carbon which remains unaltered, a hydrogen, /3 
 chlorine, m, n, x, y numbers ; we have then 
 
 A + ma + nj3, 
 
 The sum of the atoms a and j3 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 
 #.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 disposed to recognise in this cir- 
 cumstance 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 un- 
 doubtedly first approximations to the expression of 
 physical truths, but the limits of their application 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 
 
xii HERMANN KOPP 407 
 
 physikalischen Eigenschaften bei fliissigen Verbin- 
 dungen" (Annalen, 1. 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 C, H, and at all temperatures 
 below the boiling points. On the assumption which 
 observation showed to be probable that one atom of 
 oxygen can replace two atoms of hydrogen in a com- 
 pound without sensible alteration in specific volume, 
 that the comparison may be made at equal distances of 
 temperature from the 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 
 compound is the same at all distances from the boiling 
 point, Kopp was able to deduce values for C, H, and 
 which enabled the specific gravity of a liquid consist- 
 ing 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 ; 
 (6) atoms of hydrogen ; (c) atoms of oxygen ; (d) atoms 
 of chlorine ; (e) atoms of nitrogen ; and (f) atoms of 
 
408 HEEMANN KOPP xn 
 
 sulphur, is, for a temperature distant D from its 
 boiling point, approximately expressed by 
 
 (l-28a + 0-486 + 0'96c + 2-34<2+ l-44e + 2-4/)x (975 -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 constants 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 proportional to X ; whereas observation 
 shows that the contraction 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 volume at the boiling 
 point, must necessarily possess the same volume atD from 
 the boiling point, which is also contrary to experience. 
 
 Kopp ventured to conclude, then, that in all prob- 
 ability 
 
 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 com- 
 
 1 The values were originally calculated on the basis of Berzelius's atomic 
 \veights ; they have been transformed to the corresponding values when H = l. 
 
XH HEKMANN KOPP 409 
 
 ponents. 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 iso- 
 meric 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 determina- 
 tions of all the physical constants needed to ascertain, 
 with the highest possible precision, 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 remarkable 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. 
 
 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. 
 
410 HERMANN KOPP xn 
 
 2. Differences of specific volume are proportional to 
 
 differences 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 = 11 and H = 5'5. 
 The replacement of H 2 by carbonyl 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 H 5 O c O' d , where is carbonyl-oxygen and 
 0' hydroxyl-oxygen, may be expressed by the formula 
 
 which gives results in no case varying more than 4 per 
 
xii HERMANN KOPP 411 
 
 cent from the observed value, and, in the great majority 
 of cases, much less. 
 
 Determinate values for the halogens, and, with less 
 precision, 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 ON = 28 ; that of N0 2 = 33. If, then, carbon and 
 oxygen preserved their ordinary values in these radicles, 
 N 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 , ON, 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, 
 iv. (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 de- 
 termined by its particular atomic value. With this 
 exception, the subject received practically no further ex- 
 perimental 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 
 
412 HEEMANN KOPP xn 
 
 volume. Between ethylene and ethidene chlorides, for 
 example, there is a greater difference than 4 per cent ; 
 indeed, ethylene compounds in general appear to have 
 smaller volumes than those calculated by Kopp's values. 
 Stadel further showed that in the series of the chlorin- 
 ated and brominated ethanes and ethylenes, the isomer 
 of higher boiling point, i.e. the ethylene derivative, 
 has invariably the lower specific volume. Since these 
 compounds are all saturated and the only variable 
 constituent is a monovalent element (01 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 combination ; 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 
 Gerhardt 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 com- 
 pounds, 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 de- 
 rivatives in which the benzene group functions) 
 would probably be different from that deduced from 
 
xii HEKMANN KOPP 413 
 
 observations made, for the most part, on compounds 
 of totally different constitution. Kopp (Annalen 
 (SuppL), v. 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 benzene group. Jungfleisch'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. Ixiv. 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 2 = 32'0 
 calculated, 31*5; observed volume of Br=53*6 
 calculated, 53'4; observed volume of ON = 28*9 
 calculated, 28*9. The observed specific volume of 01 
 from Knietsch's careful determinations of the specific 
 gravity of liquid chlorine is 22*8 ; the mean calculated 
 value is 227. 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 Eoberto Schiff, Lothar Meyer, and his 
 pupils, and especially to Lossen and his pupils, a very 
 large amount of experimental material has been accumu- 
 lated during the last ten years, from which important 
 
 1 Thorpe : "On the Relation between the Molecular Weights of Substances 
 and their Specific Gravities when in the Liquid State," Trans. 1880, xxxviu 
 141 ; ibid. 327. 
 
414 HEKMANN KOPP xii 
 
 deductions may be drawn as to the general validity and 
 limitations of Kopp's conclusions. Schiff (Annalen, ccxx. 
 71 (1883)), by means of an improved form of an appar- 
 atus first suggested by Kamsay (Trans. 1879, xxxv. 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 (compare Sta'del). 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 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, however, note- 
 worthy 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 compound 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. 
 
xii HEEMANN KOPP 415 
 
 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 
 experimental material which is now before us forces 
 us to the conclusion 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 in- 
 crease, 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 com- 
 pounds 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 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 constant. 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 
 
416 HERMANN KOPP xii 
 
 in the values of specific volumes in organic compounds 
 (Annalen, ccliv. 42). These formulae, 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 experimental 
 material on which these formulae are based, the 
 observed molecular volumes of 352 differ by less 
 than 2 per cent from the calculated volumes. Com- 
 paratively few of these differences may be ascribed to 
 experimental errors. In the main, they are caused by 
 influences of structure and composition 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 
 respecting 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 combina- 
 tion as variable within limits determined by the 
 nature of the chemical compound. In any one com- 
 pound, 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 
 
xii HEKMANN KOPP 417 
 
 relations. The molecular volumes of formic, acetic, 
 and propionic acids increase about 22 units for each 
 increment of CH 2 ; in the case of alcohols the increase 
 is about 20 units. The volume of formic acid is 41*8 
 that is, 2x20*9; that of methyl alcohol is 427 or 
 2 x 21*4. Hence it follows that in formic acid, CH 2 2 , 
 the occupies the same volume as CH 2 ; and in 
 methyl alcohol, CH 2 0, the H 2 has the same volume 
 as CH 2 . In like manner, ethyl alcohol, C 2 H 6 0, has 
 the volume 62*2 that is, 3x207. Since 2xCH 2 = 
 2x207, then H 2 = 207. Acetic acid has the 
 volume 63'5 that is, 3x21'2; 2CH 2 is 2 x 2T2 
 and 2 = 21'2. 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 2 
 and 1 stere for hydroxyl-oxygen, that the carbonyl- 
 oxygen must occupy 2 steres. 
 
 We obtain then the following rule : TJie 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 increasing molecular weight. In the greater 
 number of cases, the values range between 6*9 and 
 7 '2. Ostwald has calculated the value of the stere 
 
 2 E 
 
418 HEKMANN KOPP xii 
 
 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 ; 7-11; 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 instructive to note the 
 different manner in which Kopp and Schroder arrived 
 at the volume relations of these elements. Kopp con- 
 cluded from the approximately equal volumes of the 
 alcohols and corresponding acids that H 2 and are 
 volumetrically 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 2 , HOH, and O'O, and he 
 inferred 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 2 = 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 foregoing rule has to be modified in this 
 
xii HERMANN KOPP 419 
 
 sense when applied to compounds of this class. The 
 value of the stere in a number of unsaturated com- 
 pounds 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 compounds, as indicated by Kopp, as well 
 as from the corresponding 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 hydro- 
 carbons (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 combination 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 
 
420 HERMANN KOPP xn 
 
 must be made. It relates to the choice of conditions 
 under which the values we term molecular or specific 
 volumes are really comparable. Although Horstmann 
 and Lossen have advanced reasons against the practice, 
 contending that at any other temperature, 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, how- 
 ever, the temperature of the boiling point, under these 
 circumstances, is a truly comparable 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 10 (boiling point 1) 
 and C 18 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 p the absolute boiling point, 
 with those of T, the absolute critical temperature ; in 
 
xii HEKMANN KOPP 421 
 
 those cases in which these two constants are known, 
 the ratio T/T X approximates to f . Hence it follows 
 that qualities like molecular volumes, which alter only 
 slowly with temperature, are comparable at the ordinary 
 boiling points (Zeits. fur Physikal Chem. v. 374). 
 
 It ought perhaps to be stated that subsequent 
 observations show that the so-called " corresponding 
 temperatures " deduced from Van der Waal's generalisa- 
 tions have not that degree of validity as temperatures 
 of comparison which they were originally assumed to 
 possess. Indeed, the present condition 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 (ccl., 1889, 1) a 
 critical account, written with the dignity and calm 
 that befits the well-earned leisure of a veteran con- 
 troversialist, 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 
 conviction that, after all, the work thus summarised 
 takes us but little beyond the threshold of the funda- 
 mental 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 knowledge, we shall most certainly get an 
 insight into the causes which affect the universality of 
 Kopp's conclusions. The discrepancies, if we could 
 only read them aright, contain within them the clues 
 
422 HEEMANN KOPP xn 
 
 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. 
 
XIII 
 VICTOK MEYEE 
 
 AN ADDRESS DELIVERED TO THE FELLOWS OF THE CHEMICAL 
 SOCIETY, STH FEBRUARY 1900 1 
 
 BY the untimely death of Victor Meyer, on 8th August 
 1897, under circumstances of peculiar sadness, and at 
 the comparatively early age of forty-nine, our sister 
 Society in Berlin lost her President of the year, and, 
 at the same moment, we were deprived of one of the 
 most brilliant of that band of eminent men whom we 
 distinguish as our Honorary Foreign Members. The 
 Council have deemed it fitting that the attempt should 
 be made to put on record our appreciation of the 
 remarkable services Victor Meyer rendered to the 
 science which he cultivated, during the all too short 
 period of his activity, with such striking assiduity and 
 success. As a friend of nearly thirty years' standing, 
 and as one who worked, literally, side by side with 
 him in the famous laboratory which he lived to direct, 
 and died whilst directing, I have charged myself with 
 the execution of this duty. 
 
 Of Meyer's early life that is, of the period before 
 I first knew him at Heidelberg as a girlish-looking, 
 bright-eyed youth, quick of movement and active in 
 thought, ready and fluent of speech, full of zeal, and 
 
 1 Chemical Society's Memorial Lectures, No. IX. 
 423 
 
424 VICTOR MEYER xm 
 
 intensely interested in the higher work of the place 
 I know little, beyond that he was born in Berlin and 
 was the son of a calico manufacturer. 1 Once, in the 
 course of some discussion on the characteristic differ- 
 ences in the school training of English and German 
 lads, he made reference to his own experiences in the 
 gymnasium, from which I gathered that his inclination 
 towards science was in nowise shaped by what he saw 
 or heard in early youth. Nor, so far as can be 
 determined, was there anything in his home life which 
 inclined him to take to chemistry. In the case of many 
 who have become eminent in physical science and 
 doubtless also in the case of more who have not their 
 first love has sprung from the passion of experimenting 
 But at this time Meyer, apparently, had neither the 
 opportunity nor the desire to make experiments. 
 Indeed, the home atmosphere tended to make him 
 literary or artistic. There can be no doubt that he 
 owed to this environment, and more especially to the 
 example and precept of his mother, herself a woman 
 of considerable intellectual power, certain strongly 
 marked features of character which are not usually 
 associated with men of science. According to his friends 
 Liebermann and Jacobson, his own wish was to become 
 an actor, and that he would have succeeded in such 
 a profession is highly probable. He had, indeed, all 
 the natural gifts of the born actor dramatic sense, 
 emotional power, a fine voice, an impressive manner, 
 and a handsome presence. When he became a teacher 
 of chemistry these attributes were turned to good 
 account. His early love of declamation, combined 
 with his elocutionary ability, eventually made him 
 one of the most striking and effective lecturers in 
 
 1 The date of his birth was 8th September 1848. 
 
xm VICTOK MEYER 425 
 
 Germany. The traditions of the University lecture- 
 theatre no doubt exercised their restraining influence, 
 but Meyer was too much under the sway of his artistic 
 temperament and too impatient of conventionality to 
 repress altogether his natural bent. Moreover, he was 
 not insensible to the effect he created, or unmindful 
 of the influence he gained, when, to use the common 
 phrase, he "let himself go," and by his trenchant, 
 impressive language, and the brilliancy of his illus- 
 tration, communicated something of his own enthusiasm 
 to even the most listless of back-bench men. This 
 power of exposition was quickly perceived, and no 
 doubt its early recognition served to bring him the 
 more speedily to the front. 
 
 At Heidelberg, as in many other centres of chemical 
 instruction, there was a small Chemical Society, com- 
 posed of the Extraordinary Professors, the Privat- 
 docenten, and assistants, together with the senior 
 or more active students in the various laboratories 
 who were elected into it by favour of the teachers. 
 In my time it numbered amongst its members Erlen- 
 meyer, Ladenburg, Horstmann, Ludwig, Cohen (the 
 mineralogist), Eose, and Emmerling. Its president 
 was Bunsen, and the occasions on which he took the 
 chair were the red-letter days of the session. "We 
 invariably sent him home happy, his pockets filled 
 with all the good champagne corks we could collect. 
 The formal business of the Society if formal it can 
 be called was preceded by an Abendessen, and if not 
 accompanied, at least succeeded, by a considerable 
 manifestation of das gemuthliche Element. No man 
 was more popular at these gatherings than Meyer. His 
 nimble mind and retentive memory, his gift of ready 
 speech, his sense of humour and genial manner combined 
 
426 VICTOR MEYER xm 
 
 to make it pleasant to listen to him no matter whether 
 he was, in accordance with the rules of the Society, 
 called upon to give an account of some work which 
 had just been published, or whether he was discussing 
 and criticising a communication from a fellow-member. 
 From time to time we had reports of the condition of 
 such investigations as were in progress in the Heidelberg 
 laboratories, or of which the results were to appear in 
 the forthcoming issue of the Annalen, for, at the period 
 of which I write, the Berichte was a thin and puny 
 publication, hardly out of its swaddling clothes, and 
 with little sign of the vitality which has since enabled 
 it to assimilate practically the whole outcome of German 
 chemical activity. 
 
 Of his own laboratory work we had nothing from 
 Meyer, for there was little or nothing at the time to 
 be told. He had entered the University in the autumn 
 of 1865, when barely seventeen years of age, and 
 apparently with no very definite conception of a career. 
 Suddenly he elected to study chemistry, and attached 
 himself to Bunsen with the idea of ultimately becoming 
 a teacher. It is not improbable that his choice was 
 in a measure determined by the circumstance that he 
 had attended some of Hofmann's lectures in Berlin in 
 the preceding summer, and had thus been influenced 
 by that great teacher, then in the fulness of his 
 intellectual vigour. Those were the palmy days of 
 Heidelberg the days of Bunsen, Kopp, KirchhofF, 
 Helmholtz and Meyer came under the spell of them 
 all. His progress as a student was exceptionally rapid, 
 and the brilliant manner in which he gained his 
 doctorate without the adventitious aid of a thesis 
 strongly impressed the whole philosophical faculty. 
 Bunsen especially was greatly struck with the power 
 
XIII 
 
 VICTOR MEYER 427 
 
 and promise of the youDg Jew, then one of the 
 youngest students in the University, and soon selected 
 him as one of his assistants. It was in this capacity 
 that I first made the acquaintance of Meyer. Bunsen 
 for some years previously had been engaged in the 
 examination of the mineral waters of South Germany, 
 and Meyer at the time I entered the Heidelberg 
 laboratory was acting as water analyst. However 
 great the disciplinary value of such work might be 
 (and no one who has practised Bunsen's method of 
 water analysis, with its system of check and control, 
 can doubt that it is one of the most rigorous 
 quantitative exercises possible), I fear it was not 
 altogether congenial to the active mind of the young 
 assistant, who was yearning to try his 'prentice hand 
 at original research. Accordingly, towards the end 
 of 1868 he threw up the position, and entered 
 Baeyer's little laboratory at the Gewerbeakademie in 
 Berlin. Although in a sense overshadowed by the 
 more magnificently appointed University laboratories of 
 Hofmann in the Georgenstrasse, and of Kekule" in 
 Bonn, both at that time comparatively new, the 
 modest laboratory of the Gewerbeakademie, with its 
 twenty workers, was already one of the most famous 
 schools of organic chemistry in Europe. Baeyer 
 himself had recently published his brilliant investiga- 
 tion of mellitic acid ; and Graebe, at first alone, and 
 subsequently in conjunction with Liebermann and with 
 Caro, was at work on those remarkable series of 
 inquiries which served to establish the true chemical 
 nature and relationships of alizarin, and led eventually, 
 with the independent collaboration of Perkin, to its 
 artificial production on a commercial scale. I well 
 remember the interest and excitement which these 
 
428 VICTOK MEYEK xm 
 
 discoveries created in Germany : they unquestionably 
 gave an enormous impetus to the study of organic 
 chemistry and attracted eager aspirants for chemical 
 fame from all parts of the world, quickened, no doubt, 
 by the perception of the rich promise of material benefit 
 thus suddenly opened up. Heidelberg at that period 
 was pre-eminently a school of inorganic chemistry ; 
 organic chemistry was represented by Delffs and was 
 mainly studied by prospective apothecaries. Erlen- 
 meyer had been called to the Polytechnic at Munich, 
 and the influence of Kekule"s teaching was as yet 
 hardly felt by any of the Privat-docenten. 
 
 Baeyer quickly recognised the power and ability of 
 his pupil, and to Baeyer was undoubtedly due the 
 impulse which started him on his career. As a 
 Vorgeriickter he attended no more lectures, and 
 thus it happened that he who became one of the 
 greatest organic chemists of his time never followed 
 a course on organic chemistry. Shortly after his 
 entrance into the laboratory he began the series of 
 half-dozen investigations which characterised his activity 
 during his three years' stay in Berlin. His first paper, 
 published in the Berichte, was a note on the action 
 of trimethylamine upon monochlorhydrin, which sub- 
 stances form a basic condensation product, the chloride 
 and the gold salt of which he described (Ber. 1869, ii. 
 186). This was quickly followed by a short paper on 
 diethyl thiodicarbonate, S(C0 2 Et) 2 , which he obtained 
 by the action of ethyl chloroformate upon sodium 
 sulphide (Ber. 1869, ii. 297). 
 
 A far more ambitious production appeared in the 
 following year, dealing with the constitution of the 
 disubstituted benzenes (Annalen, 1870, clvi. 265). 
 In this memoir Meyer described a new method of 
 
xm VICTOK MEYEE 429 
 
 introducing a carboxyl group into the molecule of 
 aromatic compounds, no matter whether the substance 
 already contained a carboxyl group or not. This was 
 effected by the action of sodium formate upon the 
 potassium salt of the aromatic sulpho-acid. 
 
 Of the acids prepared synthetically by this method, 
 isophthalic acid was the most important on theoretical 
 grounds, as its production under these conditions led 
 to a revision of the views then held with respect to 
 the orientation of -the radicles in the " ortho " and 
 " meta " (salicylic) series. Isophthalic acid had been 
 shown by Baeyer to be a 1 : 3 -derivative. " Ortho "- 
 sulphobenzoic acid, obtained from benzoic acid, was 
 thought to have its radicles in contiguous positions. 
 Meyer's experiments showed that isophthalic acid was 
 the only dicarboxylic acid formed from the sulpho-acid 
 by interaction with a formate, whence he argued that 
 " ortho "-sulphobenzoic acid, and the chloro-, bromo-, 
 nitro-, amido-, and hydroxy-benzoic acids correspond- 
 ing with it in constitution, must, like the isophthalic 
 acid, be 1 : 3 -derivatives. It followed that the " meta " 
 (salicylic) series of compounds are the 1 : 2 -compounds. 
 
 The main facts of this paper have long since taken 
 their place in the history of our knowledge of aromatic 
 compounds, but the memoir has an especial interest as 
 being Meyer's first excursus into the realm of chemical 
 theory. In a subsequent extension of the work, in 
 conjunction with Ador (Annalen, 1871, clix. 1), he 
 showed that in sulphanilic acid the substituent groups 
 S0 3 H and NH 2 were in the 1 : 4 positions. The phenol- 
 sulphonic acid from sulphanilic acid he proved to 
 be identical with Kekul^'s paraphenolsulphonic acid, 
 and hence to have the position 1 : 4. Potassium 
 monobromobenzoate fused with sodium formate yields 
 
430 VICTOK MEYEE xm 
 
 isophthalic acid ; hence this bromobenzoic acid belongs 
 to the 1 : 3 series. At the conclusion of their memoir, 
 the authors gave a list of the disubstituted derivatives 
 of benzene then known, arranged in columns according 
 to whether the second substituent element or radicle is 
 attached to the second, third, or fourth carbon atom, as 
 deduced from the experimental evidence put forward. 
 Their views as to the orientation of the substances there 
 named, except in the case of the dihydroxybenzenes, 
 have not been materially modified by subsequent inquiry. 
 Pending the publication of this work, Meyer essayed 
 to solve that arcanum of aromatic chemistry, the con- 
 stitution of camphor (Ber. 1870, iii. 116). He sought 
 to show in the first place that camphoric acid is a 
 dicarboxylic acid, C 8 H 14 (C0 2 H) 2 . Since camphor yields, 
 by the action of dehydrants, an homologue of benzene, 
 namely, cymene, he reasoned that it must contain the 
 benzene nucleus, and hence the remaining four carbon 
 atoms must exist in the side-chains. But by the 
 oxidation of camphor to camphoric acid, the side-chains 
 apparently are not attacked ; the action would seem to 
 be on two of the carbon atoms in the benzene ring. 
 The carboxyl groups cannot be attached to one and the 
 "same carbon atom, otherwise camphor would not yield 
 an homologue of benzene by abstraction of water. It 
 would follow therefore that, in all probability, camphor 
 ought to have the constitution expressed by one or other 
 of the following formulae : 
 
 (1) COH-C 8 H 14 iCH. 
 
 (2) C(OH):C 8 H 14 :CH. 
 
 (3) CH:C 8 H 14 :CH. 
 
 ! I 
 
 The first, or aldehydic, formula, suggested by Berthelot, 
 was practically disproved by the work of Fittig and 
 
xm VICTOR MEYER 431 
 
 Tollens. The second formula, which contains the 
 hydroxyl group, was rendered improbable by Berthelot, 
 and the improbability was further strengthened by 
 Meyer, who found that acetic chloride was without 
 action on camphor. The third formula then would 
 seem of the three to be the most probable. The con- 
 stitution of the group C 8 H 14 can only be inferred from 
 that of the camphor cymene. This, as shown by Fittig 
 and his pupils, is probably for the most part methyl- 
 propylbenzene. 1 Hence camphor would appear to have 
 the constitution 
 
 
 
 and camphoric acid 
 
 C0 2 H-C(CH 3 )-CH 2 -CH 2 -C(C 3 H 7 )-C0 2 H. 
 
 Borneol would be CH(OH) : C 8 H U : CH 2 . These views 
 have now only an historical interest. All that is certain 
 in them is that Meyer's conception of camphoric acid as 
 a dicarboxylic acid is correct. The work of Claisen and 
 Manasse has rendered it practically certain, as long 
 
 QTT 
 
 surmised, that camphor has the grouping C 8 H 14 <^ i 2 . 
 
 It has, however, required the labour of a generation of 
 workers, and the accumulation of a literature which, as 
 regards its bulk, is without a parallel in any other 
 department of chemistry, to unravel the true relations 
 of camphoric acid to camphor, and hence to get an 
 insight into the constitution of a substance which has 
 been known in Europe and prized as a medicine since 
 the twelfth century. 
 
 Meyer acquired some experience in tuition, even in 
 
 1 Widman (Ber. 1891, xxiv. 450) subsequently proved that cymene is 
 methylisopropylbenzene, but this does not affect Victor Meyer's argument. 
 
432 VICTOK MEYER xm 
 
 the early Heidelberg days, as a " coach," and in Berlin 
 he added to his means, which were slender enough, by 
 similar work. His success as a teacher induced Baeyer 
 to recommend him to Fehling, who sought assistance, 
 especially in modern organic chemistry and in laboratory 
 teaching, in connection with his duties at the Stuttgart 
 Polytechnic. His departure from Berlin was a great 
 loss to the little circle in the Gewerbeakademie, where 
 his high spirits and geniality made him universally 
 popular. He was an omnivorous reader and the power 
 of his memory was astonishing, so much so that on his 
 leaving, Baeyer exclaimed " Jetzt werden wir ja wieder 
 die Literatur nachschlagen mussen." 
 
 He remained in the Wiirtemberg capital barely a 
 year. How he came to leave it has already been told 
 by Professor Liebermann. Johannes Wislicenus had 
 just been called from the Zurich Polytechnic to 
 Wiirzburg, and the President of the school, Kappeler, 
 was engaged in searching for a successor. He came to 
 Stuttgart, and, unknown to Meyer, attended one of 
 his lectures. Although Kappeler, as he himself relates, 
 knew little of chemistry, he was so struck with Meyer's 
 power of lucid and stimulating exposition that the 
 decision to invite him to Zurich was immediately made. 
 At the close of the lecture he communicated to the 
 unsuspecting young teacher his idea, expressing, how- 
 ever, his fear that in comparison with his future students 
 he might prove to be still too ^oung. As Meyer 
 laughingly promised to do his best, day by day, to repair 
 this fault, the invitation was given, and thus, when 
 barely twenty-four years of age, he found himself 
 Ordinarius and Director of the chemical laboratory of 
 the Zurich Polytechnic. 
 
 The Zurich Polytechnic has enjoyed a succession of 
 
xiii VICTOE MEYEE 433 
 
 distinguished teachers, and Meyer worthily sustained 
 and, indeed, greatly extended the fame of its chemical 
 chair. He was now in possession of a well-equipped 
 laboratory, and surrounded by eager, active students, 
 stimulated and encouraged by the enthusiasm of a 
 teacher as active and eager, and, it may be added, as 
 high-spirited as themselves. The thirteen years of 
 Meyer's stay at Zurich constitute the most fruitful and 
 the most brilliant period of his career : before its close, 
 he had brought himself within the foremost rank of 
 contemporary investigators. Some idea of his wonderful 
 power of work, and of the stimulus he gave to others, 
 may be gleaned from the fact that during that period 
 the Zurich laboratory, under Meyer's direction, gave 
 close upon 130 papers and memoirs to chemical literature. 
 It is, of course, impossible here to do more than indicate, 
 in the briefest possible outline, the outcome and signi- 
 ficance of the more important of them. 
 
 During his short stay at Stuttgart he sent some half- 
 dozen papers to the Berichte, some of them in con- 
 tinuation of work which had occupied him in Berlin. 
 The chief of these were put together in a memoir, in 
 conjunction with Stiiber, on the aromatic amines, which 
 appeared in 1873 (Annalen, 1873, clxv. 161). The 
 main object of the work was to gain further evidence in 
 favour of Meyer's view, that in the case of the chloro-, 
 bromo-, iodo-, and nitro-derivatives of aromatic amines, 
 obtained by direct substitution, it is always the 
 hydrogen immediately contiguous to the amido-group 
 which is replaced, or, in other words, that the NH 2 
 group exercises an attractive influence on the sub- 
 stituent. It was assumed by Kekule that Kiche 
 and Berard's dibromaniline, obtained by the reduc- 
 tion of dibromonitrobenzene, was identical with the 
 
 2 F 
 
434 VICTOE MEYEE xm 
 
 dibromaniline from acetanilide. Meyer and Stiiber 
 proved that such was not the case. It was found that 
 Eiche and Berard's dibromaniline yields, or is derived 
 from, a liquid dibromobenzene, which boils at 219*4, 
 and remains liquid at 28 C . Eiese had previously 
 obtained a liquid dibromobenzene boiling at 224 and 
 crystallising below 1. All the three possible 
 dibromobenzenes were thus made known. Meyer's 
 surmise that the new dibromobenzene was the 1 : 3 
 variety has since been established. The authors also 
 made known the existence of a new tribromobenzene 
 melting at 119, the symmetric or 1 : 3 : 5-derivative. 
 The isomerism of the liquid dibromobenzenes was 
 subsequently conclusively demonstrated (Ber. 1874, vii. 
 1560) by the crystallographic examination of their 
 mononitro-derivatives by Groth and Bodewig. 
 
 In this connection may be mentioned a short paper, 
 in conjunction with Wurster, " On some derivatives of 
 solid Dibromobenzene " (Annalen, 1874, clxxii. 57). In 
 the attempt to prepare a nitrated phenylenediamine 
 by acting upon dibromonitrobenzene with alcoholic 
 ammonia, in the same manner that Walker and Zincke 
 obtained nitraniline from monobromonitrobenzene, they 
 found that only a moiety of the bromine could be 
 displaced, the resultant product being a new substance, 
 bromonitraniline, in which the N0 2 group is next to the 
 NH 2 group. By converting this substance into bromo- 
 phenylenediamine, the two NH 2 groups would be in 
 close proximity ; on denominating this compound, the 
 resulting phenylenediamine was found to be identical 
 with that discovered by Griess (m. p. 99), whose 
 surmise that the NH 2 groups were united to contiguous 
 carbon atoms was confirmed. 
 
 Meyer began also an inquiry on the chemical nature 
 
xm VICTOE MEYEE 435 
 
 of chloral hydrate, a substance which, in consequence of 
 Liebreich's discovery of its anaesthetic action, had by 
 that time become of considerable industrial importance, 
 and was readily procurable. By the action of acetic 
 chloride upon chloral hydrate, tetrachlorethyl acetate, 
 CC1 3 'CHC1-0'CO-CH 3 , is obtained, identical with the 
 product formed by the condensation of chloral and 
 acetic chloride, or by the action of acetic chloride on 
 acetaldehyde. Chloral alcoholate with acetic chloride 
 
 /OP TT 
 yields CCl 8 -CH\Q.g^ CH - , indicating that the alco- 
 
 holate, as already shown by Henry on other chemical 
 grounds, is the ethyl ether of trichlorethylidene glycol. 
 By dissolving chloral hydrate in glacial acetic acid, 
 Meyer obtained a white, crystalline substance, melting 
 at 80, which he regarded as isomeric with ordinary 
 chloral hydrate (m. p. 55). 
 
 The chloral hydrates may have respectively the con- 
 
 stitution 
 
 (i) CC1 3 -COH + H 2 0. 
 
 , (2) 
 
 It is not proved, however, that they are not 
 polymeric (Annalen, 1874, clxxi. 65). It is possible 
 that the substance thus obtained is identical with the 
 uniaxial form observed by Pope which slowly changes 
 into the biaxial modification stable at ordinary 
 temperatures (Trans. 1899, Ixxv. 458). Meyer does not 
 definitely decide which of the two formulse represents 
 the constitution of ordinary chloral hydrate, but he 
 inclines to regard it as trichlorethylidene glycol, which 
 Perkin's observations on its magnetic rotation definitely 
 indicate that it is. 
 
 Wallach's observation of the conversion of chloral 
 into dichloracetic acid was shown by Meyer to be in 
 
436 VICTOK MEYEE xin 
 
 accordance with a general property of aldehydes in 
 alkaline solutions to take up the elements of water, one 
 molecule of aldehyde being thereby reduced, whilst 
 another is oxidised. 
 
 Meyer, in conjunction with his pupil Haffter, devised 
 a very simple and rapid method of estimating the 
 actual quantity of pure chloral in the commercial 
 product, founded on the fact that chloral hydrate is 
 rapidly decomposed by an aqueous solution of an alkali 
 into chloroform and an alkaline formate (Ber. 1873, vi. 
 600). 
 
 Although Meyer's papers up to this time had amply 
 demonstrated his power of investigation, and afforded 
 to critics like Kekule' and Baeyer abundant proof of the 
 clearness and keenness of his vision, he had hitherto 
 worked upon somewhat conventional lines. His memoir 
 " On the Nitro - compounds of the Fatty Series " 
 (Annalen, 1874, clxxi. 1), which appeared shortly after 
 his removal from Stuttgart to Zurich, at once stamped 
 him as an original investigator of a very high order. In 
 anticipation that two series of alkyl nitrites would be 
 found to exist, denoted in the methyl series by CH 3 *N0 2 
 and CH 3 '0'NO, Meyer, whilst still at Stuttgart, had 
 studied the action of amyl iodide upon silver nitrite 
 and had obtained a colourless liquid, having the 
 ordinary smell of amyl compounds, boiling between 
 150 and 160, which on analysis was found to have the 
 composition C 6 H n N0 2 . Hence it was isomeric with 
 amyl nitrite, a yellow liquid of a peculiar, disagreeable 
 smell, which boils at 99. To the new compound Meyer 
 gave the name of nitropentane. The reaction was 
 found to be general. He now entered upon an elaborate 
 investigation of the nitro-compounds of the alkyl series 
 and their derivatives, and of questions incidental to the 
 
xiii VICTOK MEYEE 437 
 
 main subject, which, in conjunction with his pupils, 
 among whom may be mentioned Stiiber, Eilliet, 
 Chojnacki, Wurster, Constam, Janny, Lecco, Locher, 
 Tcherniac, Ceresole, Miiller, Demuth, Keppler, and 
 Ziiblin, continued to occupy him at intervals for 
 upwards of twenty years. 
 
 One peculiarity which distinguishes aromatic from 
 aliphatic compounds consists in the ease with which 
 " nitration," that is, the replacement of hydrogen by 
 the group N0 2 with the elimination of water may be 
 effected in the first -named substances. A reaction 
 analogous to that by which nitrobenzene is formed from 
 benzene was scarcely known among fatty compounds, 
 the most familiar instance being the production of 
 chloropicrin by the action of strong nitric acid upon 
 chloroform. The constitutional difference between the 
 nitroparanins, as the new group came to be called, and 
 the alkyl nitrites consisted in the fact that, in the first- 
 named substances, the N0 2 group is directly connected 
 with a carbon atom, as in nitrobenzene, whereas in the 
 alkyl nitrites the NO group is intermediately linked 
 with the hydrocarbon radicle by means of oxygen. The 
 alkyl nitrites are true esters capable of being resolved 
 into alcohols and nitrous acid by the hydrolytic action 
 of alkalis or acids. The nitroparanins, on the other 
 hand, are incapable of hydrolysis. By reduction, they 
 yield alkyl hydroxylamines and then the corresponding 
 amine. By reduction, however, the alkyl nitrites lose 
 their nitrogen and form the corresponding alcohol. 
 
 Meyer's view that the nitroparanins were veritable 
 nitro-compounds was not at once accepted. Geuther, 
 and subsequently Getting, assumed that nitroethane 
 was acetamidoxide, CH 3 *CO*NH 2 0, whilst Kissel 
 regarded it as acethydroxylamine, CH 3 'CO'NH(OH). 
 
438 VICTOE MEYEK xm 
 
 It is true, as found by Meyer, that nitroethane, under 
 the hydrolytic influence of strong acids, splits up into 
 hydroxylamine and acetic acid, but since phosphoric 
 chloride is without action upon nitroethane, an hydroxyl 
 group must be assumed to be absent. As for Geuther's 
 view of the constitution of these substances, Meyer had 
 little difficulty in showing that it wholly failed to 
 explain all their known reactions. 
 
 The general characteristics of the nitroparaffins, 
 namely, the power of forming salts possessed by the 
 primary and secondary compounds, the absence of this 
 power in the tertiary series, together with the remark- 
 able differences in the behaviour of bromine, and of 
 the action of acids upon the primary and secondary 
 nitroparaffins, were carefully studied by Meyer and his 
 pupils. He found that when a solution of a primary 
 nitroparaffin in potash is mixed with an alkaline nitrite 
 and treated with sulphuric acid, the liquid acquires 
 a blood-red colour which disappears on the further 
 addition of acid. On shaking the whole with ether, 
 there is obtained a solution of a new acid, known as a 
 
 nitrolic acid, of the general formula CJEE 27l+1 *C. - 
 
 In the case of nitroethane, the formation of the ethyl- 
 nitrolic acid may be represented as follows : 
 
 CH ' C + ON:OH - H 
 
 That such is the constitution of ethylnitrolic acid is 
 indicated by its formation by the action of hydroxyl- 
 amine on dibromonitroethane, 
 
 H 2 N ' OH = 2HBr + CH 3' C \NO, H - 
 
 The nitrolic acids are colourless, sweet-tasting substances 
 of a strong acid reaction, readily soluble in water, and 
 
xm VICTOK MEYER 439 
 
 for the most part easily crystallisable. In alkaline 
 solution they give an intense blood-red coloration and 
 form characteristic precipitates with salts of the heavy 
 metals. They slowly decompose on standing, and on 
 heating are quickly resolved into the corresponding 
 fatty acid, nitrogen, and nitrogen dioxide. On treating 
 the nitrolic acids with sodium amalgam, substances 
 known as azaurolic acids are formed. They are strongly 
 coloured, sparingly soluble substances, and differ from 
 the corresponding nitrolic acid by containing two atoms 
 of oxygen less. The best known member of the series 
 is ethylazaurolic acid, C 2 H 4 N 2 0, or more probably 
 C 4 H S N 4 2 . On heating, it yields, together with forma- 
 tion of nitrous oxide and water, ethylleucazone, C 4 H 7 N 3 0, 
 a substance possessing both acid and basic properties, and 
 in its general characteristics resembling an amido-acid. 
 
 The secondary nitroparaffins, when treated with 
 nascent nitrous acid, behave quite differently from 
 the primary compounds. On adding sulphuric acid 
 to the mixed solutions, a deep blue colour is produced 
 and insoluble substances are formed, isomeric with the 
 nitrolic acids, but which have no acid character. They 
 were called by Meyer pseudonitroles, and have been 
 regarded as nitrosonitro-compounds. 
 
 OH, NO 
 
 CH 3 ><N0 2 ' 
 
 Their formation may be thus represented 
 
 (CH 3 ) 2 CH-N0 2 + OH-NO = H 2 + (CH 3 ) 2 C(NO)-N02. 
 
 Scholl subsequently discovered that these substances 
 may be obtained by the action of nitrogen peroxide 
 upon the ketoximes : thus with acetoxime : 
 
 4(CH 3 ) 2 C:N-OH + 3N 2 4 = 4(CH 3 ) 2 C<^ + 2H 2 O + 2NO, 
 
 a mode of formation which, as Meyer pointed out, 
 
440 VICTOR MEYER xra 
 
 indicated that they may be regarded as the nitrates 
 of the oximes, (CH 3 ) 2 C:N'0'N0 2 . Their formation from 
 the secondary nitro-compounds may be supposed to 
 occur in the following phases : 
 
 (CH 3 ) 2 CH-N<? + HN0 2 = (CH 3 ) 2 CH-N<^-2, 
 2 - H 2 = (CH 3 ) 2 C:N-ON0 2 . 
 
 Meyer was inclined to give the preference to the latter 
 view of their constitution, as it is generally very doubt- 
 ful whether compounds containing a nitroso-group (NO) 
 directly linked to a carbon atom are capable of existence. 
 
 Tertiary nitro-compounds are unchanged by the 
 action of nascent nitrous acid. 
 
 Meyer pointed out how the characteristic colour 
 reactions afforded by the behaviour of nitrous acid 
 with the primary and secondary nitroparaffins, and 
 its inability to act upon the tertiary compounds, offered 
 a ready means of distinguishing primary, secondary, 
 and tertiary alcohol radicles. The iodide to be tested 
 is distilled with silver nitrite, the distillate shaken with 
 a solution of potassium nitrite in strong potash, diluted 
 with water, and mixed drop by drop with dilute 
 sulphuric acid. If the liquid acquires a red colour 
 (formation of nitrolic acid) which disappears with excess 
 of acid and reappears on the addition of alkali, we are 
 dealing with a primary radicle : should the liquid give 
 a blue colour (formation of pseudonitrole) soluble in 
 chloroform, the compound is derived from a secondary 
 alcohol radicle ; the non-formation of colour indicates a 
 tertiary radicle. The test ceases to be of much practical 
 value beyond the 5 carbon series (compare Meyer and 
 Jacobson, Lehrbuch der Organischen Chemie, 1893, 253, 
 et seq.) 
 
xm VICTOR MEYEK 441 
 
 The same line of inquiry was extended to the other 
 main groups of aliphatic substances, and resulted in 
 the discovery of new types of compounds. Thus, by 
 the reduction of the isonitrosoketones and the iso- 
 nitrosoacetoacetic esters, Meyer, in conjunction with 
 Treadwell, obtained a series of volatile bases having 
 apparently the generic formula OJH 2ri _ 4 N 2 , which they 
 termed ketines and subsequently aldines. This group 
 of substances is now generally known as the azines, 
 and the substance first described by Meyer and Treadwell 
 is dimethylpyrazine, 
 
 / C(CH 3 ):CH Sv 
 
 2CH 3 -COCH:N-OH + 6H = N/ ->N + 4H 2 0. 
 
 \CH:C(CH 3 )/ 
 
 Meyer had the faculty of keeping more irons hot 
 at a time than any man of his period. Although much 
 of his thought and energy was directed in the first 
 years of his sojourn in Zurich to the development of 
 the new field of inquiry which his discovery of the 
 nitroparafrins opened out, he continued his work on 
 aromatic compounds, partly in defending positions he 
 had already secured, and partly in breaking new ground. 
 In the latter connection, reference may be made to his 
 discovery, with Michler, of diazoxybenzoic acid, and 
 to the new class of azo-compounds which he described 
 in conjunction with Ambuhl. 
 
 A point of some little interest at the time (1875) 
 was his discovery that hydroxylamine and nitrous acid 
 together yield nitrous oxide and water, NH 3 + N0 2 H = 
 2H 2 + N 2 0, in the same manner that nitrous acid and 
 ammonia form nitrogen and water. The production of 
 nitrous oxide by mixing together concentrated aqueous 
 solutions of hydroxylamine sulphate and sodium nitrite 
 constitutes a neat and striking lecture experiment. He 
 
442 VICTOK MEYER xm 
 
 also showed, with Locher, that hydroxylamine may be 
 obtained by a number of new reactions, as, for example, 
 by acting on dinitropropane or ethylnitrolic acid with 
 tin and dilute hydrochloric acid, when, in the one case, 
 the amine is liberated in conjunction with acetone, and, 
 in the other, together with acetic acid. 
 
 (1) CH 3 -C(N0 2 ) 2 -CH 3 + 8H = CH 8 -CO-CH 8 + 2NH 3 + H 2 0. 
 
 (2) CH 3 -C(N-OH)-N0 2 + 4H + H 2 = CH 3 'C0 2 H + 2NH 3 6. 
 
 These reactions showed that the rule, hitherto regarded 
 as universally true, that nascent hydrogen reduces 
 nitroxyl to amidogen, has its exceptions. 
 
 But perhaps the most important of Meyer's dis- 
 coveries at this period was that of the oximes. He 
 had observed that dibromonitroethane, under the 
 action of hydroxylamine, passes into ethylnitrolic acid, 
 and he anticipated that the analogous nitrosoacetone 
 would be formed in like manner from unsymmetrical 
 dichloracetone. Experiment showed, however, that 
 the chlorine in dichloracetone was replaced by a 
 hydroxylamine rest, whilst the ketonic oxygen was 
 replaced by the oximido-group, forming a compound 
 termed by Meyer acetoximic acid, but now known as 
 methylglyoxime, CH 3 'C(:N'OH)-CH(:N-OH). The fact 
 that hydroxylamine would thus react upon carbonyl 
 oxygen induced him, in conjunction with Janny, to 
 study the action of this reagent upon ordinary ketones 
 and aldehydes, and thus led to the discovery of the 
 ketoximes and the aldoximes. This discovery has a 
 twofold significance. The reaction not only serves 
 to indicate the existence of carbonyl oxygen in 
 compounds, and hence is of value as a mode of 
 determining constitutional problems, but it brought 
 into existence a number of substances yielding deriv- 
 
xiii VICTOK MEYEE 443 
 
 atives of considerable interest. Further, it is not 
 too much to say that the stereochemistry of nitrogen 
 takes its rise from the discovery of the oximes. 
 
 With Janny, he likewise obtained a-nitrosopropionic 
 acid by the action of hydroxylamine on pyroracemic 
 acid, a reaction which is almost quantitative and cap- 
 able of being used as a test for pyroracemic acid. 
 
 Lossen discovered hydroxylamine as far back as 
 1865. Although it was quickly recognised as an 
 exceedingly reactive substance, its use was greatly 
 curtailed by the difficulty and expense of preparing it 
 in quantity. Much of it, prior to 1883, was obtained 
 by Dumreicher's process, namely, by reducing ethyl 
 nitrate by means of stannous chloride and hydrochloric 
 acid. Meyer showed how the irksomeness of the 
 method, entailed by the necessity of removing the tin 
 by sulphuretted hydrogen, and of dealing with the 
 large volume of liquid produced, might be materially 
 lightened, and considerable quantities of hydroxylamine 
 salts were made by the modified process in the Zurich 
 laboratory. 
 
 The position which hydroxylamine occupies between 
 ammonia and nitric acid, which at that time were held 
 to be the main nitrogenous foods of plants, as well 
 as its great chemical activity when compared with 
 the inertness of the other substances, seemed to Meyer 
 to point to a possible formation of hydroxylamine 
 within the plant, and to its playing an important part 
 in the assimilation of starch and in the formation 
 of albuminoids. In conjunction with Schulze, he 
 therefore made comparative experiments on the action 
 of hydroxylamine, ammoniacal salts, and nitrates upon 
 plants, when it was quickly found that hydroxylamine 
 acted as a poison to vegetable organisms. Meyer, 
 
444 VICTOR MEYEK xin 
 
 however, points out that it may still be possible that 
 hydroxylamine may be formed in transition products, 
 and yet act as a poison when taken up by the roots, 
 just as peptone behaves as a poison when injected into 
 the veins of animals. 
 
 Reference may here be made to Meyer's attempts 
 to elucidate the constitution of ammonium salts. It 
 was found that the dimethyldiethylammonium iodide, 
 obtained by the action of ethyl iodide on dimethylamine, 
 is identical with that produced by acting with methyl 
 iodide on diethylamine, and no difference can be 
 detected in the character of their salts. As the 
 substances, although identical, were obtained by dif- 
 ferent reactions, it was inferred that they could not 
 be "molecular" compounds, that is, combinations of 
 a tertiary base with an alkyl haloid, but must contain 
 pentavalent nitrogen, whence, by analogy, ammonium 
 
 chloride would be 
 
 ,H 
 
 This assumption is only sound on the supposition that, 
 in the formation of the salts, no change had taken 
 place in the position of the alcohol radicles. The main 
 conclusion would be invalidated if, for example, ethyl 
 iodide, when reacting on trimethylamine, did not com- 
 bine directly with it but was decomposed, as Lossen had 
 suggested, as follows : 
 
 N(CH 3 ) 3 + C 2 H 5 I = CH 8 I + N(CH 3 ) 2 C 2 H 5 . 
 
 To ascertain if such an interchange occurred, Meyer, 
 in conjunction with Lecco (Annalen, 1876, clxxx. 173), 
 studied the action of ethyl iodide upon tetramethyl- 
 
xin VICTOE MEYEE 445 
 
 ammonium iodide. If Lossen's contention were sound, 
 the reaction should be 
 
 N(CH 3 ) 4 I + C 2 H 5 I = CH 3 I + NCCHjgCgH,.!. 
 
 No action, however, was found to occur either with 
 ethyl or methyl iodide alone at any temperature up 
 to 180, or in presence of methyl alcohol or water. 
 Ladenburg and Struve tested Meyer's conclusion by 
 making similar experiments with benzyl iodide and 
 triethylamine, and with ethyl iodide and benzyldiethyl- 
 amine, and were disposed to regard the resultant 
 compounds as isomeric, although closely alike in most 
 of their properties. On repeating the observations, 
 Meyer found that no difference existed ; the substances 
 prepared in the two ways were absolutely identical. 
 
 Suggestive and fruitful in ideas as Meyer was, he was 
 seldom at a loss in devising means to put them to the 
 test of trial. In many of his mental characteristics not 
 unlike Davy, as an experimentalist, he had all Davy's 
 resourcefulness with far more than his patience. 
 
 As I knew him in Heidelberg, he was an excellent 
 manipulator ; still his temperament would never have 
 permitted him to better the example of the great master 
 under whom he was trained. We could all look on and 
 marvel at the patient, concentrated power with which 
 Bunsen would devise, elaborate, and perfect some new 
 form of apparatus, or some new method of analysis. 
 The first steps were very simple so simple indeed that 
 it was frequently impossible to divine their ultimate 
 purpose. It was from such small beginnings that we 
 obtained the whole process of gasometric analysis, the 
 burner, the photometer, the various voltaic batteries, 
 the spectroscope, the filter -pump, the ice -calorimeter, 
 the flame reactions, etc. Before Bunsen gave a piece of 
 
446 VICTOK MEYEK xm 
 
 apparatus to the chemical world, he left it practically 
 perfect; the striving after perfection was a veritable 
 passion with him, and numerous were the forms or 
 modifications through which the apparatus or the method 
 passed before he rested satisfied with it. Although 
 Meyer's genius was of a different order, the influence of 
 the Heidelberg training is to be recognised in the various 
 forms of laboratory apparatus with which his name is 
 connected. Chief among these are his modes of determin- 
 ing vapour densities. The elegant modification of Gay 
 Lussac's method introduced by Hofmann left nothing 
 to be desired in the case of comparatively volatile 
 substances unacted upon by mercury, but many bodies 
 were known, and their number was being rapidly 
 increased, in which this method was inapplicable. 
 Meyer accordingly, in 1876, devised his displacement 
 method (Ber. 1876, ix. 1216). This in principle was 
 similar to the method suggested by W. Marshall Watts 
 as far back as 1867, from which it differed in that 
 Wood's metal an alloy of bismuth, lead, tin, and 
 cadmium, melting below 70 replaced the mercury, 
 and that the volatilisation was effected at the tempera- 
 ture of boiling sulphur, that is, at 444. This process 
 allowed of the determination of the vapour density of 
 many substances which could be vaporised at tempera- 
 tures below the boiling point of sulphur, and compounds 
 like diphenyl, methylanthracene, triphenylamine, para- 
 dibromobenzene, and paradiphenylbenzene, had their 
 vapour densities ascertained for the first time by means 
 of it. 
 
 The method was further modified in the following 
 year (Ber. 1877, x. 2068), mercury being used instead 
 of Wood's metal and the vapours of boiling water, 
 aniline, ethyl or amyl benzoate or diphenylamine 
 
xiii VICTOK MEYEK 447 
 
 depending on the temperature required were employed 
 as a bath instead of sulphur vapour. 
 
 The Luftverdrdngung Methode the simple and 
 extremely convenient process which will for all time 
 be associated with the name of Victor Meyer, was devised 
 in 1877 (Ber. 1877, XL 1867). The apparatus is now 
 one of the commonest articles of laboratory furniture, 
 and it is not too much to say that, thanks to the ease 
 with which the whole operation may be carried out, 
 more vapour densities have been determined by its aid 
 than by any other means. 
 
 The apparatus is usually constructed of glass, but by 
 making it of glazed porcelain, determinations can be 
 effected at very high temperatures. Except for special 
 reasons, neither the temperature of the heated bulb nor 
 its volume need be known : all that is required is that 
 the temperature should be sufficiently high to gasify the 
 substance under examination. A variety of liquids 
 water, xylene, aniline, ethyl benzoate, amyl benzoate, 
 diphenylamine depending on the temperature needed 
 to effect complete vaporisation, may be used as media 
 for heating the bulb. For temperatures exceeding 300, 
 a bath of molten lead may be employed, the glass bulb 
 of the apparatus being coated, as suggested by Watson 
 Smith and Davis, with a moderately thick film of soot 
 before immersion in the bath so as to diminish the risk 
 of fracture. 
 
 Mr. Watson Smith, who was with Meyer at Zurich, 
 and who has kindly sent me some reminiscences of him 
 at this period, writes : " It was somewhat singular that 
 just as Victor Meyer, with Carl Meyer (no relation), 
 had completed their vapour density apparatus for bodies 
 of very high boiling point, I had just obtained in the 
 pure state specimens of the three isomeric dinaphthyls, 
 
448 VICTOE MEYEK xm 
 
 all of which urgently awaited the determination of their 
 vapour densities. They were the first new high boiling 
 substances with which the apparatus and method were 
 tried. Victor Meyer was immensely pleased and in- 
 terested with this circumstance, and we practically all 
 three worked the determination together, the results amply 
 proving the reliability and accuracy of the new method. 
 Of course in these cases the lead bath was used " (com- 
 pare Trans. 1879, xxxv. 226; 1880, xxxvii. 491). 
 
 The molecular weights of a number of substances 
 were quickly ascertained by this method, for example, 
 phosphorus pentasulphide, indium chloride, cuprous 
 chloride, stannous chloride, arsenious oxide, antimonous 
 oxide, cadmium bromide, etc. Volatilised in an atmo- 
 sphere of hydrogen chloride, ferrous chloride yielded 
 values between Fe01 2 and Fe 2 Cl 4 . Ferric chloride at no 
 temperature showed a vapour density corresponding 
 with Fe 2 Cl 6 , whilst at 750 and 1077 its molecule would 
 seem to be FeCl 3 . Potassium iodide at 1320 in an 
 atmosphere of nitrogen had a density corresponding 
 with KL Arsenic and phosphorus at a white heat had 
 densities approaching the values for As 2 and P 2 , whilst 
 zinc at 1400, and bismuth at 1700, were found to be 
 monatomic, and thallium at 1700 diatomic. 
 
 In 1879 the two Meyers, Victor and Carl, astonished 
 the chemical world by announcing (Ber. 1879, xii. 
 1426), as the result of determinations of their vapour 
 densities at high temperatures, that the halogens were 
 capable of undergoing dissociation or possibly decom- 
 position. As regards chlorine, this announcement at 
 once threatened to re-open a question which had been 
 regarded by most people as practically settled since 
 12th July 1810, when Davy read to the Koyal Society 
 his classical memoir on oxymuriatic acid. Davy, it is 
 
xni VICTOK MEYER 449 
 
 true, had never stated that chlorine was an element in 
 the absolute sense of that term. What he inferred was 
 that it was a substance which "has not as yet been 
 decompounded," and therefore is " elementary as far as 
 our knowledge extends." The very name chlorine, 
 which he suggested, inculcated this view. " To call a 
 body which is not known to contain oxygen and which 
 cannot contain muriatic acid, oxymuriatic acid, is 
 contrary to the principles of that nomenclature in which 
 it is adopted. . . . After consulting some of the most 
 eminent philosophers in this country, it has been 
 judged most proper to suggest a name founded upon 
 one of its obvious and characteristic properties its 
 colour, and to call it chlorine, or chloric gas. Should 
 it hereafter be discovered to be compound, and even to 
 contain oxygen, this name can imply no error, and 
 cannot necessarily require a change." 
 
 Had chlorine then been " decompounded " ? Did it 
 contain oxygen ? Were Berzelius and Murray right 
 after all ? Was there such an entity as murium ? The 
 pages of the popular scientific periodicals of the time 
 show how these questions agitated the minds of 
 chemists. The indications of the spectroscope were 
 advanced as confirmatory of Meyer's results, and there 
 was much exercise of "the intelligent anticipation of 
 events before they occur " which occasioned him some 
 annoyance at the time. However sanguine he might be 
 that he had decomposed chlorine, and however freely he 
 might talk with his colleagues, he never committed 
 himself in print to any statement of the kind. To 
 begin with, the amount of oxygen he had obtained was 
 very small, and there was uncertainty as to the action 
 of the chlorine upon the silica or alumina of the 
 porcelain at the high temperature, and whether the 
 
 2 G 
 
450 VICTOK MEYEE xm 
 
 materials employed were wholly free from moisture. I 
 have it, on the authority of Professor Lunge, whose 
 knowledge was derived from daily intercourse with him, 
 that Meyer himself refused to consider the fact as 
 established until he had worked in an apparatus made 
 of material devoid of oxygen, and to this end he 
 obtained a special grant from the Zurich authorities to 
 defray the cost of a vessel of platinum. 
 
 Meanwhile Meyer's observations on chlorine were 
 repeated, and their validity impugned by Crafts 
 (Compt. rend. 1880, xc. 183 et seq.) t who found, by a 
 modification of Meyer's method, that the gas, even at 
 the highest temperature of the Perrot furnace, showed 
 no change indicative of dissociation or decomposition. 
 Meyer, in conjunction with Ziiblin, at once repeated 
 Crafts' determinations on pre-formed chlorine and con- 
 firmed their accuracy. 
 
 As regards bromine and iodine, however, the 
 observers were in substantial agreement. 
 
 Thus with iodine : 
 
 Victor Meyer. Crafts and Meier. 
 
 Temp. Density. D'jD. Temp. Density. D'/D. 
 
 450 8-85 445 8'74 
 
 586 8-72 0-99 830 880 8'07 0-92 
 
 842 6-76 0-77 1020 1050 7'01 0'80 
 
 1030 5-75 0-66 1275 5-82 0'66 
 
 1570 5-70 0'65 1390 5-28 0'60 
 
 Naumann showed from these results, on the 
 assumption that the molecule I 2 splits up into two 
 atoms I -f I, that the course of the dissociation is in 
 accordance with the result required by the mechanical 
 theory of gases, namely, that the increments of decom- 
 position corresponding to equal differences of tempera- 
 ture increase gradually from the temperature at which 
 dissociation begins up to that at which 50 per cent of 
 
xm VICTOR MEYER 451 
 
 the vapour is decomposed, and then decrease in a 
 similar manner up to that temperature at which 
 dissociation is complete. 
 
 In conjunction with Langer, Meyer greatly extended 
 these observations, and subsequently published them as 
 a monograph, entitled Pyrochemische Untersuchungen 
 (Braunschweig: Vieweg u. Sohn, 1885). 
 
 As regards bromine, they found that the gas, when 
 sufficiently diluted with air, had a normal density, 
 namely 5*52 even at the ordinary temperature, and no 
 sensible change occurred up to 900 even when diluted 
 with eleven times its volume of nitrogen. At 1200 
 the density had diminished to 4*3 on dilution with five 
 volumes of nitrogen. At a white heat the density of 
 the diluted bromine fell to 3*9. Experiments at higher 
 temperatures were not possible, as at above 1600 the 
 platinum apparatus is rapidly attacked by both bromine 
 and chlorine. 
 
 The alteration in density of bromine vapour at high 
 temperatures has recently been studied by Dr. Perman 
 and Mr. Atkinson, who have found that no sensible 
 diminution occurs up to about 750 at atmospheric 
 pressure, at which point dissociation becomes just 
 appreciable, especially at low pressures, and gradually 
 increases with increasing temperature (Proc. Roy. Soc. 
 1900, Ixvi. 10). 
 
 In the case of chlorine, it was found by Meyer and 
 Langer that no analogous change occurred below 1200, 
 no matter whether pure or highly diluted chlorine was 
 employed. At 1400, however, the density of the 
 diluted chlorine fell from the normal value 2*45 to 2*02. 
 
 Similar observations with carbon monoxide seemed 
 to show that at 1690 this gas is partially decomposed 
 into carbon dioxide and carbon, 2 CO = C + C0 9 . Carbon 
 
452 VICTOE MEYER xm 
 
 dioxide itself experiences no change in density at this 
 temperature in a platinum apparatus, although when 
 passed through a porcelain tube filled with broken 
 pieces of porcelain it undergoes dissociation, as already 
 shown by Deville. This phenomenon may be connected 
 with the remarkable observation of Menschutkin and 
 Konowaloff that dissociable vapours are far more 
 rapidly broken up in presence of asbestos, or pieces 
 of glass, or even of the roughened sides of glass, than 
 when the interior of the glass vessel is perfectly smooth. 
 
 Nitrous oxide is entirely resolved into oxygen and 
 nitrogen at 900 when heated in a porcelain tube, and 
 at 1690 when heated in a platinum tube. Nitric oxide 
 remains unchanged up to 1200; at 1690 it is com- 
 pletely decomposed into its elements. Hydrogen 
 chloride also appears to be partially, whilst sulphuretted 
 hydrogen is entirely, decomposed at the latter tempera- 
 ture. Cyanogen has a normal density up to 800 ; at 
 1200, it suffers decomposition. 
 
 Meyer made his pyrochemical investigations under 
 very unfavourable conditions. The magnificent chemical 
 institution which Zurich now possesses was not then 
 built. The old laboratory was a low building to the 
 east of the main block of the Polytechnicum, and the 
 only room which could be spared for the purpose was 
 so small that, in spite of the best ventilation possible, 
 the temperature not unfrequently rose to 50. More- 
 over, both he and his assistants suffered greatly from 
 the strenuous ardour with which the work was carried 
 on, and he himself eventually broke down under the 
 strain of it. I saw him in Zurich in the autumn of 
 this year (1879), and was surprised and shocked to 
 notice, although it was at the end of the vacation, how 
 nervous and jaded he seemed. I believe the distressing 
 
xin VICTOK MEYEE 453 
 
 insomnia from which he suffered at times throughout 
 the rest of his life began at about this period. In 
 reference to this time, Mr. Watson Smith writes : 
 " Meyer had a most excitable mind and was a tre- 
 mendous worker. His assistant, Carl Meyer, told me 
 that on several occasions he was so overworked, not by 
 compulsion, but through the mere influence of Meyer's 
 presence, his mental power, and enthusiasm, that he 
 came very near committing suicide during the fits of 
 depression following exhaustion after long -continued 
 spells of work." 
 
 Pyrochemical problems continued to interest Meyer 
 to the end, and he was quick to take advantage of 
 any hint which seemed to promise the possibility of 
 their solution. In a lecture before the Naturforscher 
 Versammlung in Heidelberg, he regretted that the lack 
 of vessels of sufficiently refractory material prevented 
 him from working at the higher limits of temperature 
 even then attainable. " There can be no doubt/' he 
 said, "that new ,and undreamt-of discoveries will 
 manifest themselves that a new chemistry will disclose 
 itself, when we are furnished with vessels that will 
 enable us to work at temperatures at which water can 
 no longer exist, and at which oxy -hydrogen gas becomes 
 an uninflammable mixture." 
 
 Shortly before his death, he returned to the subject 
 with new apparatus made of a platinum-iridium alloy 
 capable of withstanding a far higher temperature than 
 pure platinum, and he was in hopes of being able to 
 construct vessels of magnesia which would allow of the 
 application of temperatures over 2000. 
 
 Meyer, at the time he announced his discovery of 
 the dissociation of the halogens, was thirty-one years 
 of age. He was now on the flood-tide of his prosperity. 
 
454 VICTOK MEYEK xm 
 
 His published work had shown him to be an investigator 
 of uncommon power and originality, and students 
 flocked to him from all parts, to participate in the 
 pioneering work which his astonishing energy and 
 enthusiasm opened out. In its triumphs it was indeed 
 a time of "joyous yesterdays and confident to-morrows." 
 He was happily married to the friend of his youth, 
 Fraiilein Hedwig Davidson, whose Verlobungstag 
 was the very day on which he received his call to 
 Zurich. What she was to Meyer only those who were 
 privileged to know his home circle can fully realise. 
 
 Meyer's first great grief came to him with the 
 death of his eldest daughter, and in 1882 he lost his 
 friend Wilhelm Weith, Professor of Chemistry in the 
 University. How close and intimate was their friend- 
 ship was evident to all who frequented the meetings 
 of the Zurich Ghemische Gesellschaft, where the two 
 professors were generally to be found seated side by 
 side at the head of the table ; it is reflected too in 
 the obituary notice of his colleague which Meyer wrote 
 for the Berichte. 
 
 In the autumn of 1882 Meyer was requested to 
 undertake the delivery of the series of University 
 lectures, on! benzene derivatives which had been 
 interrupted -by Weith's death. I have already 
 attempted to indicate what Meyer was as a teacher. 
 No one could possibly take greater pains in the 
 preparation of his lectures, or study more to make 
 them instructive and interesting. It is generally 
 supposed that organic chemistry does not lend itself 
 to effective lecture illustration. Such was not the 
 case when Meyer had to teach it. "I well recollect/' 
 writes Mr. Watson Smith, "that the word most 
 frequently used in Zurich in defining the opinions of 
 
xiii VICTOR MEYEK 455 
 
 Victor Meyer's students of his lectures was ' brilliant ' ! " 
 Another of our Fellows, Mr. John I. Watts, who 
 attended his course in 1879-80, writes : 
 
 What particularly struck me about his lectures was their 
 finished style. He made fairly constant use of notes, speaking 
 with great rapidity. Yet his treatment of the subject was very 
 clear, and his language perfect. The experiments were always 
 well prepared and exceptionally successful. Indeed, his lectures 
 were most popular, and both at his work and outside the 
 Polytechnic there was no professor who was more respected and 
 admired by all students than Victor Meyer. Young, handsome, 
 well-dressed for a German professor, with a quick wit and a 
 genial manner, he was a welcome addition to any gathering. 
 When, in 1881, he had a "call" to Aachen and elected to 
 remain at Zurich, the students treated him to a torchlight pro- 
 cession and a grand Kommers. Meyer watched the Fackelzug of 
 over 1000 students from a balcony, and later, sitting as the 
 honoured guest in a still greater throng, he seemed indeed a 
 happy man. 
 
 Similar testimony is given by Dr. Sudborough, who 
 was with him in Heidelberg, and who writes : 
 
 As a lecturer, Meyer was clear, concise, and extremely lucid, 
 and his delivery was easy and natural. His lectures were given 
 by the aid of carefully written notes, and were fully illustrated 
 by experiments, the table being always crowded with apparatus 
 both in the organic and inorganic lectures. It was very rare 
 indeed for an experiment to fail ; this was firstly due to Meyer's 
 own dexterity as a manipulator, and also to the care which was 
 bestowed upon the preparation of the experiments. 
 
 It was in the course of these lectures on benzene 
 derivatives that Meyer came upon what is perhaps the 
 most brilliant of all his discoveries that of thiophen. 
 How he lighted upon it is well known, but the story 
 bears repetition. He desired to show his class the 
 so-called indophenin reaction of Baeyer, at that time 
 held to be indicative of benzene, but to his astonishment 
 
456 VICTOK MEYEB xm 
 
 not a trace of the characteristic blue colour made its 
 appearance, although, as was his wont, he had rehearsed 
 the experiment just prior to the lecture. It appeared 
 that his assistant, Sandmeyer himself one of Meyer's 
 "discoveries" had handed him a sample of the 
 benzene made in the lecture course by heating benzoic 
 acid with lime, and at once drew his attention to the 
 fact that the rehearsal had been made with the ordinary 
 laboratory supply the Benzol purissim. crystallisatum 
 of the dealers, and, of course, derived from coal-tar. 
 Meyer, at the moment, was so fully occupied that he 
 might well have put aside the incident, or have given 
 no immediate heed to its significance. But that was 
 not his way. Fortune scatters her chances indifferently, 
 and every man may have his share, but it is not given 
 to each to perceive when he is favoured, or to know 
 when to grasp " the skirts of happy chance." Madame 
 de Stael once said that a most interesting book might 
 be written on the important consequences which spring 
 from little differences, and it was the little difference 
 that riveted itself on Meyer's mind. He at once began 
 the investigation of the cause. All kinds of benzene 
 to be found in Zurich were tested, and it was soon 
 definitely established that it was only coal-tar benzene 
 that gave the indophenin reaction. Meyer's first idea 
 was that it might be occasioned by an isomeric a 
 second benzene found in coal-tar. Within less than 
 a month he had ascertained that the reaction was 
 due to some sulphuretted product accompanying coal- 
 tar benzene, and that Baeyer's indophenin was probably 
 a sulphur compound. Meyer's action was characteristic 
 of him. Before communicating with Baeyer, he care- 
 fully repeated his experiments, and only when all 
 ground for doubt was removed did he inform his friend 
 
xin VICTOK MEYER 457 
 
 of his observations and of the inferences he had formed. 
 Baeyer at once sent him a specimen of his indophenin, 
 and the fact that it actually was a sulphuretted 
 compound was then established. Meyer found that 
 coal-tar benzene, after repeated shaking with oil of 
 vitriol, no longer reacted with isatin, and hence he 
 determined to search among the sulphonic acids so 
 formed for the reactive substance. By distilling the 
 product obtained by shaking 10 litres of benzene with 
 oil of vitriol, he obtained a few cubic centimetres of 
 a clear, thin, mobile liquid containing sulphur, which 
 boiled at about 83 and remained liquid in a freezing 
 mixture of ice and salt. It gave a most intense 
 reaction for indophenin. The amount of the new 
 substance present in coal-tar benzene was very small, 
 at most not more than 0*5 per cent. 
 
 Thanks to the co-operation of his friends, Messrs. 
 Bindschedler, Busch and Co., of Basle, he was enabled 
 to repeat this experiment on a large scale, as much as 
 250 litres of coal-tar benzene being operated upon at 
 a time, and the sulphonic acids converted into the 
 lead salts, which were then mixed with sal ammoniac 
 and distilled. The crude product, which contained 
 about 28 per cent of sulphur, was found to react 
 strongly with bromine, forming a heavy, colourless, 
 highly refractive liquid, boiling at 211, greatly re- 
 sembling dibromobenzene, but showing on analysis 
 the composition C 4 H 2 Br 2 S. The new compound was 
 the dibromo-substitution product of a substance which 
 Meyer was at first inclined to call thianthren, then 
 thiophan, next thiol, and lastly thiophen, to denote 
 that it was a sulphur-containing substance giving 
 derivatives analogous to those of phenyl. 
 
 In the early part of the following June, that is, 
 
458 VICTOK MEYEK xm 
 
 within about six months of his first observation, he had 
 obtained a considerable quantity of thiophen, and was 
 in a position to show to the Swiss Naturforscher 
 Versammlung, which met during that summer in Zurich, 
 that its chemistry was hardly less extensive than that 
 of benzene itself. Thus it was that a chance observation 
 the observation of a little difference added a new 
 section to organic chemistry. 
 
 It would be quite impossible within the limits at my 
 disposal to show how this section was developed by 
 Meyer and his pupils. In 1888 he published, in the 
 form of a monograph, dedicated to his friend and patron, 
 President Kappeler, dem hochherzigen Forderer wissen- 
 schaftlicher Bestrebungen, an account of its condition 
 at that time (Die Thiophengruppe. Braunschweig : 
 Vieweg u. Sohn), from which it appears that during the 
 preceding five years no fewer than 106 contributions to 
 its history had been made from his own laboratory, and 
 some 40 from those of others. How fertile the field 
 still continues may be gleaned from the circumstance 
 that upwards of 50 papers on the same subject have 
 since made their appearance in various journals. 
 
 Meyer's restless energy had now begun to react most 
 seriously upon his general health. At times he was 
 almost prostrated by nervous exhaustion ; he had 
 frequent spells of insomnia, and his friends viewed with 
 alarm the signs of physical decay which now set in, in 
 spite of the occasional holidays, mainly among the Alps, 
 which he gave himself. In 1884 he again broke down, 
 and although at the moment he was immersed, with his 
 colleague Lunge, in the plans for the new chemical 
 laboratory of the Polytechnic in which, as he states, he 
 had hoped ultimately to resume his pyrochemical labours 
 under more favourable conditions, he was obliged to 
 
xm VICTOE MEYEK 459 
 
 relinquish, for a time, all idea of work, and towards the 
 end of the year was ordered away to the Kiviera, where 
 he wintered. In the following spring he received a 
 " call " to Gottingen as the successor of Hiibner. This 
 he eventually decided to accept, and entered upon- his 
 duties there in the summer session of 1885. 
 
 He was not able, as he had hoped, to take leave of 
 his Zurich students at the time, but what they thought 
 of him with what affection and respect he was regarded 
 was seen in the terms of the Address they sent to him 
 on the occasion of his opening lecture at Gottingen. 
 It was seen, too, in the way he was received by them 
 during a visit to Zurich some months later, on the 
 occasion of the seventieth birthday of his friend 
 Kappeler. Professor Goldschmidt, who was present, 
 thus describes the scene : "I see him even now before 
 me as he spoke to the students at the Kommers in the 
 evening. The * Ziircher Polytechnikers ' have, as a rule, 
 but little opportunity of knowing the professors outside 
 their special faculty, and have, therefore, but little 
 interest in those who are not their own teachers. As 
 Victor Meyer's slender form appeared on the platform, 
 and as his bright blue eyes glanced round the assembly, 
 there broke forth a shout of welcome from all en- 
 gineers, machinists, architects, as well as from his old 
 students the chemists to be ended in a whirlwind of 
 applause at the close of a speech, sparkling and witty 
 
 as ever." 
 
 With renewed health and vigour, he now set about 
 the plans for the new laboratory which the authorities 
 had decreed should adorn the " Georgia-Augusta," for 
 Wohler's old place no longer sufficed to contain the 
 chemical workers which Gottingen had now to receive. 
 Whilst it was being erected, he continued his pyro- 
 
460 VICTOK MEYER xm 
 
 chemical work, and his investigation of the thiophen 
 derivatives, and began with Paul Jacobson the admir- 
 able Text-book of Organic Chemistry ', which, in the 
 critical selection and arrangement of its material, is still 
 unsurpassed. 
 
 With Auwers, he resumed the study of benzil and its 
 derivatives which he had begun with Wittenberg and 
 Goldschmidt. With Miinchmeyer, he began the study 
 of the behaviour of phenylhydrazine towards various 
 groups of oxygen compounds, and he sent a short paper 
 to the Berichte on thiodiglycol compounds, and on an 
 easy method of preparing /3-iodopropionic acid from 
 glycerol. With Demuth, he undertook the investigation 
 of the sulphuranes, a group of disulphides of the general 
 formula C 2 H 3 *S'C 2 H 4 *SR. Other papers were on the 
 density of nitric oxide, which showed no evidence of 
 association or molecular duplication even at 100 ; on 
 isophthalaldehyde ; on the negative nature of the phenyl 
 group ; and on isodibromosuccinic acid. 
 
 It was characteristic of his receptivity that Meyer 
 should be among the earliest workers in Germany to 
 perceive the value of Raoult's method of ascertaining 
 molecular weights ; it was first used in the Gottingen 
 laboratory to determine the molecular weight of some 
 derivatives of benzil which yielded two series of isomeric 
 compounds, both series having the same constitution, in 
 the ordinary sense, but which were yet distinct from one 
 another, and yielded different derivatives. 
 
 Other papers of this period were on the thio-deriva- 
 tives of deoxybenzoin and its analogues (desaurins), and, 
 with Kiecke, on the carbon atom and valency. The 
 latter paper is of interest as an example of Meyer's 
 " scientific use of the imagination," and may be studied 
 in connection with an earlier paper in 1876 (Annalen, 
 
xm VICTOE ME YEE 461 
 
 1876, clxxx. 192) on the same subject, as showing how 
 he grafted the theoretical conceptions of van't Hoff upon 
 the teaching of Kekule. According to Meyer, the 
 carbon atom is surrounded by an ethereal shell which, 
 in the case of an isolated atom, has a spherical form ; 
 the atom itself is the carrier of the specific affinities, the 
 surface of the shell is the seat of the valencies ; each 
 affinity is determined by the existence of two opposite 
 electrical poles, which are situated at the end-points of 
 a straight line small in comparison with the diameter 
 of the ethereal shell. Such a system of two electric 
 poles is called a double- or di-pole. The four valencies 
 of a carbon atom would be represented by four such 
 di-poles, the middle points of which are situated on the 
 surface of the ethereal shell, but freely movable within 
 it. The di-poles themselves can rotate freely round 
 their middle point. The carbon atom has a greater 
 attraction for positive than for negative electricity, and 
 the positive pole of a valency is slightly stronger than 
 the negative pole. This hypothesis explains why the 
 four valencies take up the position of a regular tetra- 
 hedron ; why they can be diverted from this position ; 
 why the valencies of one and the same carbon atom 
 cannot combine together, whilst the valencies of different 
 carbon atoms can do so ; why there are two kinds of 
 single-binding, one stable, and the other allowing free 
 rotation ; and lastly, why free rotation ceases in cases 
 of double- or treble-binding (Ber. 1888, xxi. 946 ; 
 compare Abstr. 1888, 549). 
 
 Stereochemical questions we owe the phrase to 
 Meyer were indeed at this time occupying much of 
 his thought. In a paper with Auwers (Ber. 1888, 
 xxi. 784), he pointed out that the existence of the 
 two isomeric dioximes of benzil, discovered by him 
 
462 VICTOK MEYEK xm 
 
 in conjunction with Goldschmidt, would, if the 
 formula 
 
 C 6 H 5 -C(N-OH)-C(N-OH)-C 6 H 5 
 
 were established for both, be in direct contradiction 
 to the hypothesis of van't Hoff that two carbon atoms 
 united by a single affinity are free to rotate, the axis 
 of rotation being the bond of union, and that isomerism 
 is only possible for those substances of the type 
 ^C C^, which cannot, by rotation round the common 
 axis, be converted into the same form. The two 
 dioximes were carefully compared as regards their 
 melting points, solubilities in water, alcohol, ether, or 
 acetic acid, and the conditions under which the a-form 
 is converted into the /3-modification were ascertained. 
 To further remove all doubt as to the possibility of 
 merely physical isomerism, and to prove that the 
 oximes are not only different from one another, but 
 yield different derivatives reconvertible into their 
 respective oximes, the propionic and isobutyric deriv- 
 atives were prepared and compared. The result 
 showed that the dioximes were of identical chemical 
 composition, and hence it appeared that van't HofFs 
 hypothesis must be so altered as to admit of cases in 
 which free rotation round the axis cannot take place, 
 as otherwise no explanation of the isomerism of the a- 
 and /3-dioximes is possible (compare Abstr. 1888, 597). 
 
 Meyer subsequently showed how the work of Beth- 
 mann, Graebe, and Baeyer confirmed these views. Wis- 
 licenus' theory as to the free rotation of singly-bound 
 carbon atoms would appear to be limited to certain cases ; 
 absolutely free rotation is probably possible only when 
 the substituting atoms or groups are identical ; where, 
 as is the case in the majority of compounds, the atoms 
 or groups are not identical, there will be some definite 
 
xm VICTOR MEYER 463 
 
 position of equilibrium ; only in cases where the 
 substituting atoms or groups are equally negative 
 will there be several positions of equilibrium (Ber. 
 1890, xxiii. 2079 ; Abstr., 1890, 1083). 
 
 Meyer's perspicacity and critical insight are well 
 illustrated in a lecture which he gave to the German 
 Chemical Society in 1890 " On the Results and Aims 
 of Stereochemical Research." It is of interest to the 
 student as giving a fairly complete historical account 
 of the development of space formulae, and more 
 especially for its criticism of the work of Baeyer and 
 Wislicenus on the stereochemical formulae of single-, 
 double-, and treble-linked carbon compounds, and of 
 the stereochemical conceptions of Hantzsch and Werner 
 in the case of nitrogen compounds. 
 
 With regard to the assumption that the nitrogen 
 atom may be represented as a tetrahedron, and that 
 the isomerism of the benzaldoximes may be similar to 
 that of fumaric and maleic acids, it is pointed out that 
 the structure of the oximes is in all probability not 
 identical. Two isomeric forms of each of the unsym- 
 metrical oximes* of the formula OH N:CXY are 
 indicated by the hypothesis of Hantzsch and Werner, 
 but they do not appear to exist. If the tetrahedral 
 representation of the nitrogen atom were tenable, we 
 should have to assume that substituted ammonias can 
 
 / H / H 
 
 exist in the isomeric forms N<J a and N<~6 , but 
 
 such bodies are not known. We must therefore 
 assume that in ammonia the hydrogen atoms are 
 placed symmetrically with regard to the nitrogen atom, 
 and this can only find expression in a plane formula 
 (Ber. 1890, xxiii. 567 ; compare Abstr. 1890, 719). 
 
464 VICTOE MEYER xm 
 
 Reference may be made here to the short paper on 
 isomeric oximes of unsymmetrical ketones and the 
 configuration of hydroxylamine, in conjunction with 
 Auwers (Ber. 1890, xxiii. 2403), in which the authors 
 advance further evidence that the isomerism of the 
 oximes cannot depend upon structural dissimilarity, 
 but must be sought for in the nature of the hydroxy- 
 lamine group. Assuming the correctness of the theories 
 of van't Hoff and Wislicenus regarding the arrangement 
 of atoms in space, the combined effect of the attraction 
 of the nitrogen and oxygen on the hydroxylic hydrogen 
 of hydroxylamine would cause it to be in a plane 
 different from that occupied by the remaining atoms 
 in the molecule. The hypothesis suffices to explain all 
 observed facts : unsymmetrical oximes would therefore 
 
 a ** 
 
 exist in two forms, G:N'0 and C:N*0. The difference 
 
 b 6 H 
 
 between this theory and that of Hantzsch and Werner 
 is shown by the two formulae, 
 
 OH H 
 
 C:N and C:N O 
 
 (Hantzsch and Werner). (Auwers and Meyer). 
 
 The formation of an oxime by the action of nitrous 
 acid is readily accounted for on the ground that it is a 
 substituted hydroxylamine ; moreover, the fact that no 
 case of geometrical isomerism has ever been observed in 
 the azo-, azoxy-, and imido-compounds tells in favour of 
 this theory (compare Abstr. 1890, 1263). 
 
 To this period belongs also the work on the azines ; 
 on deoxybenzoin ; on the aromatic nitriles ; on tetra- 
 methylsuccinic acid ; and on the oximes of phenanthra- 
 quinone. 
 
xm VICTOE MEYEE 465 
 
 Meyer was not destined to remain long in Gottingen. 
 The new laboratory was barely finished, when, in 1889, 
 he received a "call" to Heidelberg. Bunsen, full of 
 years as of honours the Nestor of Chemistry, as his 
 friends were wont to call him had expressed a wish to 
 retire, and of all his many students there was none, he 
 said, whom he wished more to take his place than he 
 who, twenty-one years before, had worked with him in 
 the modest little room of some four or five places, which 
 had constituted his private laboratory. To Heidelberg 
 accordingly Meyer went, with the coveted title of 
 Geheimrath, and the promise of a new and enlarged 
 laboratory. Although only forty years of age, he was 
 now, so far as worldly position was concerned, at the 
 summit of his career ; he had returned to his Alma 
 Mater, and the rest of his days were to be given to her 
 service. 
 
 During his four years' stay in Gottingen he had in 
 great measure recovered his health and with it the 
 elasticity of his active, buoyant temperament. I saw 
 him in Heidelberg in the spring of 1891, when he was 
 busy with the enlargement of the old laboratory, and it 
 was with a glance of pride a pardonable pride that 
 he pointed out the places where he and I had worked 
 with " Papa " Bunsen, 
 
 So kindly modest, all accomplished, wise, 
 
 in the corner place near the window, towering above 
 both of us. It was strange, too, to hear the sound of 
 children's voices and their laughter, and the bustle of 
 servants in what were formerly the silent, half-deserted 
 rooms, overlooking the Wredeplatz ; and stranger still 
 to me was it, as we together called upon Bunsen, sitting 
 solitarily in his rooms overlooking the Bunsenstrasse, 
 
 2 H 
 
466 VICTOR MEYER xm 
 
 to behold the meeting and to listen to the greeting of 
 these two men the memory of whose names and fame 
 Heidelberg will cherish so long as Heidelberg exists. 
 To all of us life has its dramas, and in some of these 
 the incidents are as moving as those ever conjured up 
 by playwright or poet. 
 
 This was the last occasion on which I saw Meyer. 
 How well I remember it ! He was as bright, as active, 
 as mentally vigorous as of old, although it was but too 
 obvious that his physical strength was not the equal of 
 his nervous energy. 
 
 Meyer's earliest experimental work at Heidelberg 
 was mainly concerned with the continuation of investi- 
 gations begun at Gottingen. But he was perpetually 
 breaking new ground or seeking to clear up doubtful 
 points in ground already partially explored. 
 
 The classical labours of Frankland on zinc ethyl 
 might be thought to have definitely established the 
 chemistry of that substance, but even on such a com- 
 paratively simple matter as the action of oxygen on 
 zinc ethyl there was room for still further inquiry. The 
 white compound obtained by Frankland, as the result 
 of the oxidation of zinc ethyl, was regarded by him as 
 a mixture of zinc oxide, ethoxide, and acetate. It was 
 found, however, by Meyer and Demuth to contain no 
 acetate, but to be mainly composed of a peroxide, 
 ZnEt'O'OEt, as proved by its power of liberating iodine 
 from potassium iodide. The explosive character of the 
 substance is thus explained. Zinc ethoxide, in fact, 
 does not appear to have been prepared (Ber. 1890, 
 xxiii. 394). 
 
 In conjunction with a number of his pupils Krause, 
 Freyer, Askenasy, and others Meyer in 1891 began 
 the investigation of a subject already associated with 
 
xiii VICTOK MEYEE 467 
 
 the name of his predecessor, namely, on the conditions 
 determining both the gradual and the explosive combus- 
 tion of gaseous mixtures. Although a considerable 
 amount of experimental work was done, the results 
 obtained, curious and interesting as they were in some 
 particulars, led to no very definite general conclusions. 
 
 It was found that the temperature at which combina- 
 tion occurred varied with the nature of the vessel, and 
 depended upon whether the gases were confined or 
 not. Ignition takes place at a lower temperature when 
 the mixture is in a closed vessel than when passing 
 freely through an open tube. If, however, an open 
 vessel containing the mixture is heated suddenly, ex- 
 plosion takes place at a lower temperature. In the cases 
 of gradual union, no relation between time and amount 
 of combination could be perceived. As showing the 
 influence of the nature of the surface, it was found that, 
 when the bulbs were silvered inside, the union of oxygen 
 and hydrogen was rapidly effected at a temperature of 
 about 200, whereas in an unsilvered bulb the gaseous 
 mixture had to be heated to above 530 before any 
 sensible amount of water was produced. The principal 
 quantitative results are embodied in the following table 
 in which the mixture did not explode at the lower 
 temperature in each column, but did so at the higher : 
 
 Equivalent mixtures. Free current. Closed bulbs. 
 
 Hydrogen, oxygen . . . 650 730 530 606 
 
 Methane, oxygen .... 650 730 606 650 
 
 Ethane, oxygen . . . . 606 650 530 606 
 
 Ethylene, oxygen . . . 606 650 530 606 
 
 Carbon monoxide, oxygen . . 650 730 650 730 
 
 Hydrogen sulphide, oxygen . . 315 320 250 270 
 
 Hydrogen, chlorine . . . 430 440 240 270 
 
 In a subsequent paper with Munch (Ber. 1893, xxvi. 
 2421), the temperatures of explosion of gaseous mixtures 
 
468 VICTOK MEYER xm 
 
 were determined by placing the vessel containing the 
 gases inside the bulb of an air thermometer immersed in 
 a metal bath. The mixture of a gas with the amount 
 of oxygen theoretically necessary for its complete com- 
 bustion was passed through a fine tube to the bottom 
 of the internal vessel, and lighted as it issued from the 
 mouth of the exit tube. At a certain temperature, the 
 flame ran down the tube and the contents of the vessel 
 exploded. This temperature the temperature of explo- 
 sion was determined by displacing the air contained 
 in the air thermometer by means of hydrogen chloride, 
 collecting it over water, and measuring it. In thirty- 
 eight experiments with a mixture of hydrogen and oxygen 
 (pure electrolytic gas), the temperature of explosion 
 varied from 620 to 680, being about 650 in mean. 
 The temperature is not affected by variations in the 
 rapidity with which the gaseous mixture enters the 
 glass vessel, or by the presence of fragments of glass 
 or sand. In presence of platinum, the gases combine 
 quietly, and if the glass vessel is very small no explo- 
 sion occurs. 
 
 The temperatures of explosion of a number of aliphatic 
 hydrocarbons, mixed with equivalent amounts of oxygen, 
 were then determined as follows : 
 
 Methane . 656 678 Propane . . 545 548 
 
 Ethane . 605622 Propylene . 497511 
 
 Ethylene . 577 590 isoButane .. 545 550 
 
 Acetylene . 509 515 isoButylene . 537 548 
 
 Coal-gas with 3 times its volume of oxygen . . 647 649 
 
 It would thus appear that the temperature of explo- 
 sion falls as the number of the carbon atoms in the 
 molecule increases ; that it is probably lower for prim- 
 ary than for corresponding secondary hydrocarbons ; 
 and is less for hydrocarbons containing a double bond 
 
xm VICTOK MEYER 469 
 
 than for those containing only single bonds, and still 
 less for those containing a triple bond (compare Abstr. 
 1894, ii. 11). 
 
 Mention may here be made of the work done, in 
 conjunction with Bodenstein, on the decomposition of 
 gaseous hydrogen iodide by heat. This gas was 
 selected for the reason that the action of heat upon 
 it is reversible, and hence it might be expected that 
 the establishment of a condition of equilibrium will 
 be in no way influenced by the many disturbing 
 circumstances which were found to occur in the case 
 of other gaseous mixtures. 
 
 Combination of hydrogen and iodine vapour takes 
 place even at 444 (b. p. of sulphur), and the hydrogen 
 iodide formed is far more stable, at all events in the 
 dark, than has hitherto been supposed. It is, however, 
 very sensitive to light. In bulbs which were exposed 
 for ten days to direct sunshine, 58 per cent of the gas 
 was decomposed, and when exposed throughout the 
 summer, practically the whole of the gas is resolved 
 into its constituents. Experiments on the relation 
 of the amount of decomposition to temperature gave 
 the following results : 
 
 * Relative amount of HI decomposed, as 
 
 determined 
 
 Temperature of boiling. By decomposition. By direct union. 
 
 Sulphur . . ; , 444 0-2150 0-2104 
 
 Retene ... . 394 0-1957 
 
 Mercury . . 350 0-1731 0-1738 
 
 At 310 (b. p. of diphenylamine) the relative amount 
 of HI decomposed was 0*1669, instead of 0*1550 as 
 calculated from the above numbers. The difference 
 between the observed and calculated results is due 
 to the circumstance that the heat of formation of 
 hydrogen iodide is, at ordinary temperatures, negative 
 
470 
 
 VICTOK MEYEE 
 
 XIII 
 
 ( 1600, Thomson), but from the fact that the decom- 
 position at temperatures such as 350 444 increases 
 with rising temperatures, it follows from van 't HofFs 
 principle (Principe de Vequilibre mobile) that the 
 heat of formation at these temperatures is positive. 
 There must, therefore, be a temperature at which the 
 heat of formation is zero, and at which also the decom- 
 position is at a minimum. This point, as the experi- 
 ments show, lies between 310 and 350, and calculation 
 by van 't Hoffs formula showed that it is at 324. As 
 it was found that two bulbs heated under the same 
 conditions always gave the same result, it was possible 
 to study the decomposition as a time reaction, and by 
 the formula given by Nernst. The constancy in the 
 values actually obtained for each of the foregoing 
 temperatures showed that, in the case of the decom- 
 position of hydrogen iodide by heat, the change occurs 
 in a perfectly regular manner (Ber. 1893, xxvi. 1146; 
 compare Abstr. 1893, ii. 369). 
 
 This short account of Meyer's labours in physical 
 chemistry may conclude with a brief reference to the 
 determinations of the fusing points of salts melting 
 only at relatively high temperatures, which he made 
 in concert with his pupils. These he was able to obtain 
 by the aid of the platinum air-thermometer he described 
 in conjunction with Freyer. The following is a list of 
 his final values : 
 
 Sodium chloride 
 Sodium bromide 
 Sodium iodide 
 Potassium chloride 
 Potassium bromide 
 Potassium iodide 
 Potassium carbonate 
 Sodium carbonate . 
 (Compare Heycock and 
 
 Sodium biborate . 
 Sodium sulphate. 
 Potassium sulphate 
 Caesium iodide . 
 Calcium chloride 
 Strontium chloride 
 Barium chloride . 
 Rubidium iodide 
 Neville, Trans. 1895, Ixvii. 190). 
 
 e . 
 
 
 
 815 
 
 e . 
 
 
 
 757 
 
 
 
 
 661 
 
 ide 
 
 
 
 800 
 
 tide 
 
 
 
 722 
 
 [e . 
 
 
 
 684 
 
 mate 
 
 
 
 878 
 
 ite. 
 
 
 
 849 
 
 878 
 863 
 1078 
 621 
 806 
 832 
 921 
 641 
 
xra VICTOE MEYER 471 
 
 In 1892 Meyer and Wachter made known the 
 possibility of the existence of a class of aromatic 
 derivatives, known as the iodoso-compounds, in which 
 the monovalent group 10 replaces hydrogen. The 
 first representative of the series was iodosobenzoic acid, 
 C r H 5 I0 3 , which they obtained by the action of fuming 
 nitric acid or a boiling and acidified solution of pot- 
 assium permanganate upon orthoiodobenzoic acid. It 
 is a crystalline, solid substance, melting at about 
 200, sparingly soluble in water or ether. It liberates 
 iodine from potassium iodide, and chlorine from hydro- 
 chloric acid, forming orthoiodobenzoic acid. It is an 
 extremely feeble acid, and its silver salt when dry is 
 highly explosive. 
 
 No iodoso-derivatives could be obtained from meta- 
 or para-iodobenzoic acids. Of the two iodoparatoluic 
 acids, the one in which the iodine atom occupies the 
 ortho-position to the carboxyl group yields an iodoso- 
 derivative similar to iodosobenzoic acid, but the isomeric 
 acid does not yield a corresponding compound. If, 
 however, paraiodobenzoic acid be previously nitrated, 
 it may be converted by the further action of fuming 
 nitric acid into an iodoso-derivative, IO'C 6 H 3 (N0 2 )'C0 2 H. 
 In like manner, the iodoparatoluic acid may be made 
 to yield an iodoso-compound by previous nitration 
 (Ber. 1893, xxvi. 1354). 
 
 By the further action of oxygen on an alkaline 
 solution of iodosobenzoic acid, iodoxybenzoic acid, 
 I0 2 *C 6 H 4 *C0 2 H, is formed, a white, crystalline substance, 
 turning red on exposure to light, and decomposing with 
 explosion at 233. It is a much stronger acid than the 
 iodoso-derivative, forms moderately stable salts, and gives 
 characteristic colour reactions with aniline and phenol 
 (Ber. 1893, xxvi. 1727 ; compare Abstr. 1893, i. 577). 
 
472 VICTOK MEYER xm 
 
 Hartmann and Meyer found that when iodoso 
 benzene, C 6 H 5 10, is dissolved in strong sulphuric acid, 
 the solution, on dilution with water, yields the sulphate 
 of a base, phenyliodophenyliodonium hydroxide, 
 
 A similar change occurs with paraiodosotoluene. 
 The free bases have a strong alkaline reaction, and 
 form characteristic crystalline salts. 
 
 Meyer was thus led to the discovery of a remarkable 
 group of substances known as the iodonium compounds, 
 the simplest aromatic representative of which is dipheny- 
 1 iodonium hydroxide, 
 
 These bases are compounds in which two of the 
 valencies of the iodine atom are satisfied by aromatic 
 radicles, whilst the third is satisfied in the free base 
 by hydroxyl, and in the salts by an acid radicle. The 
 iodonium bases are readily soluble in water, are strongly 
 alkaline, and in their behaviour, as in that of their 
 salts, show a remarkable similarity with the derivatives 
 of silver, lead, and, more particularly, thallium. These 
 bases are formed by the decomposition of the iodoso- 
 and iodo-hydrocarbons under various conditions ; for 
 example, by the action of moist silver oxide upon an 
 intimate mixture of equivalent proportions of iodoso- 
 benzene and iodoxybenzene, 
 
 C 6 H 6 -IO + I0 2 -C 6 H 5 + AgOH = b 
 
 By the addition of potassium iodide to the aqueous 
 solution, diphenyliodonium iodide is precipitated. This 
 compound stands in the same relation to iodobenzene 
 that trimethylsulphonium iodide does to methyl sul- 
 
xin VICTOK MEYER 473 
 
 phide, and as tetramethylammonium iodide does to 
 trimethylamine. It crystallises from alcohol in long, 
 pale yellow needles, and decomposes on heating almost 
 quantitatively into iodobenzene, 
 
 C 12 H 10 I 2 = 2C 6 H 5 I. 
 
 If the decomposition is started at one point, it proceeds 
 through the whole mass with development of heat. 
 
 The existence of these remarkable bases and salts, 
 which recall the sulphonium-, ammonium-, arsonium- 
 compounds, etc., shows that a complex which is 
 composed of one iodine atom and two molecules 
 of phenyl, that is, of constituents which are otherwise 
 negative, possesses strongly basic properties. From the 
 general behaviour of the iodonium compounds, it is 
 
 /C H 
 
 evident that the complex -I\p 6 Tj 5 or in general 
 
 XO 6 1 5 
 
 I<f p (where R and R x are aromatic radicles) possesses 
 
 the function of a metal analogous to thallium (compare 
 Lehrbuch der organischen Chemie, Meyer and Jacob- 
 son, ii. 127). 
 
 It is interesting to note that the physiological 
 action of the diphenyliodonium chloride resembles that 
 of ammonium salts on the one hand, and of heavy 
 metals, such as lead and thallium, on the other. Doses 
 of 0*02 0'03 gram produce total paralysis in frogs, 
 both the motor nerve-ending and the muscle substance 
 being affected. A dose of 0*08 per kilo proves fatal to 
 rabbits, the spinal cord and medulla oblongata being 
 also affected. 
 
 A study of the conditions determining the forma- 
 tion and hydrolysis of ethereal salts of aromatic acids 
 occupied Meyer, in conjunction with his pupils, and 
 more especially Sudborough, from 1894 up to the year 
 
474 VICTOE MEYEE xm 
 
 of his death. It was found that benzole acid and its 
 substituted products, as a rule, readily yield practically 
 the theoretical quantity of an ethereal salt when treated 
 with methyl alcohol and hydrochloric acid in the cold. 
 On the other hand, the symmetrical trisubstitution 
 products of benzoic acid yield no ethereal salts whatever 
 under these conditions. This rule holds absolutely for 
 all 1:3: 5 -trisubstitution derivatives of benzoic acid 
 (Me, No 2 , 01, Br, I, and C0 2 H), except those containing 
 one or more hydroxyl groups. The same is true of all 
 substituted benzoic acids in which the 2 : 6 -hydrogen 
 atoms (C0 2 H=1) have been replaced by other atoms 
 or groups. 
 
 The acids which do not yield ethereal salts when 
 treated with alcohol and hydrochloric acid can readily 
 be converted into these substances by the action of 
 methyl iodide on their silver salts, or of methyl alcohol 
 on the acid chlorides. 
 
 This remarkable difference in behaviour may be 
 ascribed to a stereochemical cause, the substituent 
 groups being supposed to hinder the introduction of the 
 alkyl group to such an extent that under the prescribed 
 conditions the reaction does not proceed. 1 Acids in 
 which the carboxyl group is linked with the benzene 
 nucleus by one or more carbon atoms readily undergo 
 etherification. The constitution of a substituted benzoic 
 acid may, therefore, be ascertained in this way, and the 
 method may also be used for isolating or purifying 
 those acids which will not undergo etherification. 
 
 The nitrophthalic acids behave similarly : dinitroph- 
 
 1 This supposition has been modified by Wegscheider, who introduces 
 Henry's conception of the formation of an additive compound between the 
 alcohol and the acid. According to Wegscheider, the ortho - substituents 
 prevent the formation of such additive compounds (compare, however, Davis, 
 Trans. 1900, Ixxvii. 33). 
 
xm YICTOE MEYEE 475 
 
 thalic acid [N0 2 : C0 2 H : C0 2 H : N0 2 = 1 : 2 : 3 : 4] gives 
 no ethereal salt, whilst the acid [N0 2 : C0 2 H : C0 2 H : N0 2 
 = 1:3:4:5] yields inonalkyl salts. 1:2: 6-Dinitro- 
 benzoic acid gives no ethereal salt (Abstr. 1895, i. 93). 
 Chloronitrobenzoic acid [C0 2 H : N0 2 : Cl = 1:2:6] yields 
 no ethereal salt, showing that the rule applies when the 
 substituents are dissimilar. Diortho-substituted benzoic 
 acids are not etherified at low temperatures when one of 
 the substituents is hydroxyl. 
 
 Meyer was of opinion that ether ificat ion, in the case 
 of analogous compounds, is diversely influenced by 
 substituents of different relative mass. He imagined 
 that those radicles which prevent etherification at high 
 temperatures have a much greater relative mass than 
 those which only hinder it at low temperatures, but it 
 is probable that the methyl group and its normal 
 homologues will produce almost identical effects, since 
 the action is chiefly due to that carbon atom which is 
 directly linked to the benzene nucleus. According to 
 theory, those ethereal salts which are formed with 
 greatest difficulty should be hydrolysed least readily, 
 and such Meyer found to be generally the case. 1 
 
 These conclusions have been tested by Kellas (Zeit. 
 phys. Chem. 1897, xxiv. 221), who has measured the 
 velocity of etherification for a large number of mono- 
 substitution derivatives of benzoic acid. From a study 
 of the influence of temperature, and of the nature of 
 the substituent, he has more precisely indicated the 
 limits within which they may be regarded as gener- 
 ally true. 
 
 Considerations of space preclude more than a bare 
 reference to the work on the derivatives of ethyl 
 
 1 This is approximately true for the benzoic series of acids, but does not 
 obtain for the acetic and probably other series (compare Sudborough and Lloyd, 
 Trans. 1899, Ixxv. 467). 
 
476 VICTOR MEYER xm 
 
 dinitrophenylacetate ; on the indoxazen group ; on the 
 laws of substitution in the aliphatic series ; on the 
 synthesis of triphenylacrylonitrile and on the isomerides 
 of triphenylacrylic acid ; on the modes of introduction 
 of acetyl groups into aromatic hydrocarbons ; on the 
 substitution of the hydrogen in trinitrobenzene by 
 alkaline metals ; on the fusibility of platinum ; on the 
 formation of tetriodoethylene from diiodoacetylene ; on 
 the durenecarboxylic acids ; on the action of potassium 
 permanganate on hydrogen, methane, and carbon 
 monoxide ; on the slow oxidation of hydrogen and 
 carbon ; on the evolution of oxygen during reduction ; 
 on hexahydrobenzophenone and its oximes ; and on 
 diphenylamine from orthobromobenzoic acid. 
 
 Meyer contributed to the literature of chemistry, 
 either alone or in conjunction with his pupils, upwards 
 of 300 memoirs and papers. 
 
 No account of Meyer's scientific activity would be 
 complete without some allusion to the various pieces 
 of apparatus with which he enriched operative chemistry. 
 Reference has already been made to his methods of 
 determining vapour density, and to his mode of 
 ascertaining the melting points of substances fusible 
 only at high temperatures. He also greatly improved 
 the methods of accurately determining the solubilities 
 of substances at various temperatures. His form of 
 water-bath is to be met with in many modern labora- 
 tories, surmounted, it may be, with the funnel-shaped 
 cover which he devised to prevent access of dust to the 
 evaporating liquid. Particularly neat and convenient 
 are the drying ovens he constructed in which constant 
 temperatures are obtained by means of liquids of 
 different boiling points, for example, toluene, xylene, 
 anisoil, etc. 
 
xm VICTOR MEYER 47*7 
 
 Analytical chemistry had little attraction for Meyer, 
 and, beyond his node of diagnosing primary, secondary, 
 and tertiary alcohols and alcoholic radicles by colour 
 reactions (see p. 440) ; and the method he devised, with 
 Jannasch, for the simultaneous determination of carbon, 
 hydrogen, and nitrogen in the elementary analysis of 
 organic substances, he made no contribution to this 
 department of the science. 
 
 As the director of a large chemical laboratory, and 
 as a laboratory teacher, Meyer worthily followed in 
 the footsteps of Bunsen. In proof of this, I may here 
 quote the testimony of some of our Fellows who have 
 worked under him. 
 
 Mr. John I. Watts thus refers to him in the Zurich 
 days : 
 
 Victor Meyer as a teacher had a wonderful faculty of infusing 
 enthusiasm into his students. He was constantly in the labora- 
 tory, and whether the pupil was engaged upon the analysis of some 
 simple, well-known substance, or was pursuing original investiga- 
 tion, he seemed somehow to succeed in making him feel how 
 interesting was his work. Possessed of a very quick and active 
 intelligence, he would point out the reason of the difficulties 
 almost before the student had finished recounting them. He 
 was himself a constant worker, and when engaged in his work 
 he always appeared to be in a high state of pleasurable ex- 
 citement. 
 
 Similar testimony is afforded by English chemists 
 who were with him at Heidelberg. Dr. J. T. Hewitt 
 writes : 
 
 Professor Meyer was universally liked by the men who had 
 the privilege of working under him. He had an extraordinary 
 capacity for hard work, and his example, together with the 
 interest he took in his men, induced in them a more or less 
 similar love of work. After the morning lecture, which in the 
 summer semester was at eight, he would come round the 
 laboratory and see how every one was getting on, though of 
 
478 VICTOK MEYER xm 
 
 course he spent more time with those who were doing joint work 
 with him than with those who were working with the other 
 professors. We used very often to see him again during the 
 morning, and at least once in the afternoon. In 1891, when I 
 first went to Heidelberg, the most important work being done 
 was on the slow combustion of electrolytic gas, and, not only 
 those who were actually working on this subject, but every one 
 else in the laboratory, used to take great interest in what was going 
 on. Meyer's way of taking up old pieces of his work again and 
 again meant that a very varied sort of work was done in 
 the laboratory ; for example, in consequence of Nef s criticism, 
 nitro-fatty compounds were again examined, the result on the 
 students being excellent, in that their general interest in chemistry 
 was aroused. Meyer, as you well know, was an excellent speaker, 
 not only in the lecture room, but in taking the chair at meetings 
 of the Heidelberger Chemische Gesellschaft, when he was seen to 
 great advantage. 
 
 Dr. Sudborough, who served him as an assistant 
 when in Heidelberg, writes : 
 
 As organiser and director of the laboratories, Meyer undoubtedly 
 exhibited great business qualities, and everything worked ex- 
 tremely smoothly, owing probably to the fact that his staff had 
 been with him for a number of years and were all on intimate 
 terms of friendship with him. During the time I was an 
 assistant, I had opportunities of observing with what care he 
 entered into even the minutest financial details in connection with 
 the department. 
 
 In the laboratories he was extremely genial and pleasant, 
 always having a kindly word for the students, and taking a great 
 interest in their work. Characteristic, too, was the hopeful way 
 in which he always looked forward to the successful termination 
 of each piece of work, and by this means endeavoured to keep up 
 the interest of the student. Every student who worked under 
 him respected and honoured him as a scientific leader of the first 
 rank, but in addition they felt a deep friendliness towards him on 
 account of the kindly interest he took in them and in their work. 
 A goodly percentage of those carrying out " Arbeits " under him 
 were either English or American ; in fact, Meyer appears to have 
 had a predilection for English and American students. 
 
xm VICTOE MEYEK 479 
 
 Mention must also be made of Meyer's connection with the 
 Heidelberg Chemical Society, of which he was an ardent supporter 
 in fact, may be said to have been its soul : he and Bernthsen 
 (of the Badische Anilin- u. Soda-Fabrik) were the two presidents in 
 my time and both were frequent contributors. 
 
 Dr. Jocelyn F. Thorpe writes : 
 
 Perhaps that which impressed one most about Victor Meyer, 
 besides his power and ability as an exponent and lecturer, was the 
 faculty he possessed of conferring some of his enthusiasm upon 
 the students who worked under him. Be his interest ever so 
 slight and his knowledge of the subject ever so small, 
 no student could work long with Victor Meyer without feeling 
 that he had a part in a system ; that he was, in fact, one of the 
 instruments by which the plans and ideas of a master mind were 
 being shaped. Noticeable, too, was his wonderful power of 
 grasping and remembering every little detail of the researches 
 upon which he was at the moment engaged. At times, as many 
 as thirty men would be working under him on subjects widely 
 varying in character, yet in no case would he forget what each 
 individual had been doing when he last visited him ; occasionally 
 he would astonish the student by asking, him what had become 
 of some (by the student) long-forgotten substance, the properties 
 of which he could remember most distinctly. 
 
 Every morning after his lecture he would enter the laboratories 
 and personally not only visit the students who were working 
 directly under him, but also those who were engaged in research 
 with the other Professors and Privatdozenten of the department. 
 
 Not only will Victor Meyer live in the memory of those who 
 worked under him as a leader in chemistry, but many will 
 remember him as the genial and kindly host. On many evenings 
 during the semester he would give either supper-parties or small 
 dances, and occasionally a ball, to which his students were 
 welcomed, and when his camaraderie and great tact were 
 especially noticeable to those of us who, being foreigners newly 
 arrived, were unacquainted with the language and social customs 
 of his country. 
 
 Towards the last his wonderful memory began to fail. I 
 remember meeting him in Heidelberg the year before his death 
 and asking him something, I cannot now remember what, but at 
 
480 VICTOE MEYER xm 
 
 any rate he was unable to answer me at the time, and asked me to 
 call and see him the next day. He, however, stopped and tied a 
 knot on his pocket-handkerchief, saying, with a sad smile, "my 
 memory is not what it was." 
 
 Meyer's literary ability, combined with his power of 
 lucid exposition, made him an admirable writer of what 
 are called popular science articles. He was a frequent 
 contributor to the Naturwissenschaftlichen Rundschau, 
 and a number of his essays appeared under the title of 
 Aus Natur und Wissenschaft (Heidelberg, 1892). 
 His love of natural scenery and his power of graphi- 
 cally describing it may be seen in his Mdrztage in 
 Kanarischen Archipel (Leipzig, 1893), a record of 
 travel, written during the enforced rest following upon 
 one of his too frequent periods of nervous prostration. 
 
 One who had studied him carefully and knew him 
 well thus writes of his personal qualities and of the 
 influence and attraction he exerted upon all who came 
 in contact with him : 
 
 Victor Meyer had a remarkable power over men. Where he 
 entered, there he soon became the centre ; each one listened to 
 him, all collected round him. In the fascination he exercised 
 there was nothing intentional or self-conscious ; it was far less the 
 influence of a commanding strength than the working of an 
 incomparably attractive and many-sided nature. To this, too, his 
 appearance contributed : the finely chiselled head with the splendid 
 blue eyes might, at first sight, betoken the artist, were it not that 
 there was in the expressive features a rare blending of the lively 
 temperament with the contemplative calm of the philosopher. 
 
 In the circle of his fellows he captivated all by the eagerness 
 with which he followed anything new, discussing and elucidat- 
 ing it in a manner peculiarly his own; by the joyous, often 
 enthusiastic, recognition of other men's work, and by the warm- 
 hearted interest he displayed in the scientific struggles of his 
 juniors. In society, he showed himself an accomplished 
 conversationalist and raconteur, an intelligent and warmly 
 
xiii VICTOK MEYEK 481 
 
 appreciative connoisseur of the arts of music and literature. As 
 a host, he studied the comfort of every guest in his house. At 
 the " Biertisch " his sunny humour and overflowing wit diffused a 
 general harmony ; and his enthusiastic love of natural scenery 
 made him the most delightful of travelling companions (Paul 
 Jacobson, in Naturwiss. Rundschau, xii. 43 and 44, p. 19). 
 
 Meyer's merits were recognised in every land where 
 science is cultivated. He was a corresponding member 
 of the Academies of Munich, Berlin, Upsala, and 
 Gottingen, and an honorary member of many learned 
 societies. The University of Konigsberg made him an 
 Honorary Doctor of Medicine. The Royal Society gave 
 him the Davy Medal in 1891. 
 
 He was elected an Honorary Foreign Member of 
 our Society in 1883, and attended the celebration of 
 our Jubilee in the spring of 1891. Many of our 
 Fellows will no doubt recall the stirring speech, instinct 
 with a true eloquence, which he made at the banquet in 
 responding to the toast of " Our Foreign Members," 
 with its striking peroration: "Moge die Chemical 
 Society neben alien ihren anderen schonen Aufgaben 
 auch in Zukunft ihre volkerverbindenden Ziele in so 
 erfolgreicher Weise anstreben wie bisher, moge Sie 
 bliihen und gedeihen als eine Pflegstatte der Wissen- 
 schaft, fur ihr Vaterland vorerst, aber nicht minder fur 
 alle Volker, welche sich im friedlichen Wettbewerb 
 wissenschaftlicher Arbeit verbiindet wissen." 
 
 May this aspiration be fulfilled ! May the Chemical 
 Society, in the years to come, continue, as in the past, 
 to recognise, with a full and generous appreciation, the 
 work of those across the seas who engage with us in the 
 friendly rivalry of scientific labour ! 
 
 And may our action in thus recording the services in 
 our own annals of the gifted man whose 
 
 2 I 
 
482 VICTOK MEYER xm 
 
 prosperous labour fills 
 The lips of men with honest praise, 
 
 tend in some degree, however small, to that consumma- 
 tion for which he so earnestly and so eloquently 
 pleaded ! 
 
XIV 
 DMITRI IVANOWITSH MENDELEEFF 
 
 "SCIENTIFIC WORTHIES," No. XXVI. NATURE, 27TH 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 devolved entirely upon her, and 
 on the profits of which she brought up and educated 
 her large family. The story of MendeleefFs 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 Governmental 
 Gymnasiums throughout the Empire. The Institute 
 
 483 
 
484 DMITKI IVANOWITSH MENDELEEFF xiv 
 
 (which was abolished in 1858) was established in the 
 same building as the University, and was divided into 
 two Faculties Historico-philological and Physico- 
 mathematical. Mendeleeff 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 termination 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 Chemice 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 
 experimental observations which constitutes the real 
 foundation of all our knowledge concerning the specific 
 volumes of liquids, when the young Siberian philo- 
 sopher 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 
 
xiv DMITKI IVANOWITSH MENDELEEFF 485 
 
 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 keen- 
 ness of his 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 
 2 ; those of arsenic and phosphorus by As 4 and P 4 
 
 C H 1 
 
 respectively ; that of alcohol by -^j- 5 j- ; and that of 
 
 ether by ~ 0. 
 
 ^2^5) 
 
 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 Techno- 
 logical 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 
 
486 DMITKI IVANOWITSH MENDELEEFF xiv 
 
 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 QEnanthol- Sulphurous Acid, on Fermenta- 
 tion Propyl Alcohol, and on the Nitriles, he cultivated 
 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 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 expansion 
 and cohesion in the case of liquids, and the rdle played 
 by molecular cohesion in the determination of chemi- 
 cal activity. His paper on the thermal expansion of 
 liquids above their boiling points is noteworthy as demon- 
 strating 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 gradu- 
 ally 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 pressure and volume. It is, 
 in fact, that temperature which the researches of 
 
xiv DMITKI IVANOWITSH MENDELEEFF 487 
 
 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 
 Combustion 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, xlv. 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 
 1/Vf = 1 kt, in which V t is the volume at t (that at 
 being unity), and k is a quantity which varies with 
 different substances, but which may for any one sub- 
 stance 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, Mendeleeffs 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 devia- 
 tions 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, increasing cohesion, and diminish- 
 
488 DMITRI IVANOWITSH MENDELEEFF xiv 
 
 ing 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 comparatively small tempera- 
 ture-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 MendeleefPs formula affords a simple and 
 ready method of calculating the critical temperature 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 frequently 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 Drink- 
 water, Fownes, and Squibb, and has been utilised by 
 certain continental Governments (e.g. that of Holland) 
 
xiv DMITEI IVANOWITSH MENDELEEFF 489 
 
 for the purposes of revenue. But it was not the 
 utilitarian aspect of this subject which alone attracted 
 Mendeleeff. In a paper communicated a couple of 
 years ago to our Chemical Society (Transactions of the 
 Chemical Society, li. 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 dissociation 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 decom- 
 posed at temperatures which are higher than those at 
 which dissociation commences, so we may have the 
 same phenomenon in solutions ; at ordinary temper- 
 atures they can be either formed or decomposed. 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 hypothesis 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 percentage 
 composition, p, may be represented by the general 
 
 equation 
 
 s = C + Ap + Ep 2 . 
 
 Between the densities of two definite compounds 
 existing in solution, the differential coefficient 
 is a linear function of p 
 
 ds/dp = A + 2Bp. 
 
490 DMITRI IVANOWTTSH MENDELEEFF xiv 
 
 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 ; 
 EtH0.3H 2 0; and 3EtHO.H 2 0, the first two of which 
 he has isolated by subjecting 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 Mendeleeffs 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, published in Eussian 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. Regnault 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 pointed out 
 that the deviations must become positive for all gases 
 afc sufficiently high pressures, and the fact has since 
 been confirmed by the observations of Amagat and 
 Cailletet. MendeleefF, more particularly, made observa- 
 tions at low pressures, i.e. below one atmosphere ; and 
 
xiv DMITEI IVANOWITSH MENDELEEFF 491 
 
 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. Mendeleeif 
 has further determined the real coefficients of thermal 
 expansion of gases. This, for air between and 100 
 under a standard atmosphere, was found to be 0*0036829. 
 Determinations 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. 
 
 Coefficient of 
 Molecular weight. 
 
 expansion. 
 
 Hydrogen ... 2 . 0-00367 
 
 ) 
 
 J 
 
 \ 
 
 J 
 
 ) 28 0-00373 
 
 Carbon monoxide . . J 
 
 Nitrous oxide 
 
 Carbon dioxide . 
 
 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 
 
 760 . , . . 0-00373 
 
 3 atmos. . . . -. 0'00389 
 
 8 .... 0-00413 
 
 The decrease of the coefficient of expansion with 
 
492 DMITEI IVANOWITSH MENDELEEFF xiv 
 
 increasing 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 practical 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 development 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. J^is book is one 
 of the classics of chemistry"-! its place in the history 
 
 , / * i 
 
 of science is as well assured as the ever-memorable 
 work of Dalton. Mendeleeff, indeed, might with equal 
 fitness have styled his book a " New System of 
 
 \ 
 
xiv DMITRI IVANOWITSH MENDELEEFF 493 
 
 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/y Mendeleeff first drew attention to 
 the principles upon which the Periodic Law is based in 
 a paper read to the Russian Chemical Society in 1869, 
 in the following series of propositions : 
 
 1(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, indium, 
 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, corre- 
 sponds 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 
 
494 DMITEI IVANOWITSH MENDELEEFF xiv 
 
 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. 
 
 (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 recognition 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 relationship 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 elements, 
 such, for example, as that given to us by Eoscoe in the 
 case of vanadium, and by Marignac in that of niobium. 
 The law of periodicity was the systematised expression 
 
xiv DMITRI IVANOWITSH MENDELEEFF 495 
 
 of these data ; it was, to use MendeleefFs 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 MendeleefFs generalisation has 
 rendered to science during the twenty years of its 
 existence. 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 substances, 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, 
 corresponding to eka-boron, 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 followed the reading 
 of these words of MendeleefFs : " When, in 1871, I 
 described to the Kussian Chemical Society the properties, 
 clearly defined by the periodic law, with 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." 
 
496 DMITRI IVANOWITSH MENDELEEFF xiv 
 
 Up to the time of the formulation of the law, the 
 determination 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 determin- 
 ing the substituting value of an element are presented 
 by the cases of indium, cerium, yttrium, beryllium, 
 scandium, and thorium. In certain of these cases, 
 the particular value demanded by the law, and the 
 change in representation of the molecular composition 
 of the compounds of these elements, have been con- 
 firmed 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 con- 
 firmed by the independent experiments of Zimmermann 
 and Kammelsberg. 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 apparently higher than those 
 demanded by it. In each of these cases a redetermina- 
 tion 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 
 
xiv DMITKI IVANOWITSH MENDELEEFF 497 
 
 principle of periodicity. At the Moscow Congress of 
 Kussian 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. Similar relations 
 have been discovered in certain other properties, such 
 as ductility, fusibility, hardness, volatility, crystalline 
 form and thermal expansion ; in the refraction equiva- 
 lents 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 compounds ; and even in such properties 
 as their elasticity, breaking stress, etc. 
 
 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 surprising 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 independently 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 
 
 2 K 
 
498 DMITEI IVANOWITSH MENDELEEFF xiv 
 
 of classical thought ; and therefore it affords 'no more 
 indication of the unity of matter or of the compound 
 nature of the elements than do the laws of Avogadro 
 and Gerhardt, or the law of specific heats, or even the 
 conclusions 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 report on the progress of 
 chemical industry as manifested at the various Inter- 
 national Exhibitions. But it was on the petroleum 
 industry of Baku, on the Caspian, that this 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 apparently incapable of development. 
 Thanks largely to his action, both on the platform and 
 in the press, the exploitation 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 indirectly, 
 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 
 
xiv DMITEI IVANOWITSH MENDELEEFF 499 
 
 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. 
 
 [fro man in Eussia has exercised a greater or more 
 lasting influence on the development of physical science 
 than MendeleeflTf 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, conferred 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 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. 
 
XV 
 STANISLAO CANNIZZARO 
 
 "SCIENTIFIC WORTHIES," No. XXX. NATURE, GTH MAY 1897. 
 
 IN the autumn of last year (1896) there occurred in Rome 
 an event which attracted the attention of the whole 
 scientific world, and more especially of that portion of 
 it which is concerned with chemistry. The occasion 
 was the celebration of the seventieth anniversary of the 
 birth of Prof. Stanislao Cannizzaro, Senator of the 
 Kingdom of Italy, and Professor of Chemistry in the 
 University of Rome. The pages of this journal have 
 already borne witness to the feelings of esteem and 
 gratitude which that event evoked. At the public 
 meeting called to do him honour, all the learned bodies 
 in the world which have any concern with science, or 
 have any regard for its welfare, combined to offer their 
 felicitations, and vied with each other in the warmth 
 of their expressions of appreciation and goodwill, and a 
 multitude of letters and telegrams were received from 
 chemists in all parts of Europe and America. The 
 place of honour in the list of the addresses, as enumerated 
 in the interesting account of the ceremony since published, 
 is given to that from the Royal Society, which repeated 
 the terms in which the Council had previously made 
 known to Prof. Cannizzaro its reason for awarding him 
 
 500 
 
xv STANISLAO CANNIZZAEO 501 
 
 the highest distinction in its power. Next comes that 
 from the Chemical Society, which recalls with pride 
 that the name of Cannizzaro has given lustre to the roll 
 of its foreign members for more than half the period 
 of his lifetime. 
 
 In what follows we desire to give an account of the 
 life and labours of one whom men of all nations have 
 thus shown themselves eager to honour. 
 
 Stanislao Cannizzaro, the fourth and youngest son of 
 Mariano Cannizzaro and Anna Dibenedetto, was born 
 on 13th July 1826 at Palermo, where his father was a 
 magistrate, Director-General of the Sicilian Police, and 
 subsequently President of the High Court of Chancery. 
 The future chemist was educated partly at home and 
 partly at the normal school of his native city, and on 
 the death of his father in 1836, he was placed in the 
 Caroline Calasanzio College. The cholera epidemic of 
 1837 ravaged Palermo, the young Cannizzaro lost two 
 of his brothers, he himself was attacked by the terrible 
 scourge, and it was only after a tedious convalescence 
 that he was able to resume his studies. Elementary 
 education in Sicily at that time was wholly under the 
 control and direction of the priests : grammar, rhetoric, 
 poetry, and philosophy, with a very small modicum of 
 mathematics and geography, constituted the pabulum 
 on which the youth of the period was fed. The 
 physical sciences, of course, had no place in a system 
 which was essentially mediaeval. The boy soon gave 
 evidence of his power, and after a school career of 
 distinction he entered, in 1841, the University of 
 Palermo with the intention of devoting himself to 
 medicine. 
 
 The subject, however, proved uncongenial, and the 
 youth tried in vain to pass the necessary examinations. 
 
502 STANISLAO CANNIZZAKO xv 
 
 Stimulated, however, by Fodera, who at that time 
 taught physiology in Palermo, and with whom the 
 young student became intimately acquainted, he was 
 led to take up experimental work in connection with 
 chemical physiology. It is needless to say that at 
 this period Palermo possessed no laboratory accom- 
 modation, and all the manipulative essays that the 
 young experimentalist could venture upon had to be 
 done at his home, and with such improvised appliances 
 as he could command. In the autumn of 1845 he 
 went to Naples, where he came in contact with Melloni, 
 the most eminent Italian physicist of his time, with 
 whom he contracted a warm friendship. Mainly 
 through the recommendation of Melloni, who quickly 
 learned to appreciate the character and power of his 
 young friend, Piria, who is honourably known to 
 chemists by his researches on plant products, was led 
 to offer the young Sicilian the post of preparateur in 
 the chemical laboratory of the University of Pisa. To 
 Pisa accordingly he went, and the step decided his 
 career. What Melloni was to physics in Italy at that 
 period, Piria was to chemistry. The young assistant 
 could have had no better master. Raffaele Piria, then 
 in the full tide of his vigour, was an admirable, albeit 
 a most exacting teacher. A distinguished pupil of 
 Dumas, and a remarkable expositor, his lectures were 
 distinguished by the same love of method, of orderly 
 arrangement, of precision, neatness, and even elegance, 
 that characterised his laboratory work ; and Cannizzaro 
 and his fellow-assistant Bertagnini must at times have 
 been sorely exercised to satisfy the rigorous ideal of 
 exactitude and of manipulative skill required by the 
 Professor in the experimental illustration of his lectures. 
 When not employed in the class-room, his duty was 
 
xv STANISLAO CANNIZZAKO 503 
 
 to wait on Piria in the laboratory. Piria during that 
 period was engaged upon those inquiries on salicin, 
 populin, asparagin, and their derivatives, by which he 
 is best known to the chemists of this time. The 
 greater part of the experimental labour connected with 
 these investigations was done by Piria himself during 
 the eight hours that he daily spent in his laboratory, 
 Cannizzaro being for the most part, as he says, a simple 
 looker-on, observing attentively and in silence the rare 
 skill and manipulative ability with which the work was 
 executed. Occasionally, however, the assistant would 
 be called upon to continue some experiment or analysis 
 which Piria had begun, or to prepare some material 
 he needed ; all of which he was required to perform 
 in literal compliance with the instructions he received 
 from the master. Most of the work of preparation in 
 connection with the lectures had to be done in the 
 early morning, before Piria descended from his apart- 
 ments to the laboratory. These preparations were 
 carefully scrutinised by the Professor, who would 
 tolerate no slovenliness or negligence, and whose 
 aesthetic sense demanded that the apparatus should 
 not only work well but look well. Although a silent 
 worker during the daytime, and a most severe judge 
 of his assistant's duty whether in the laboratory or 
 in the lecture-room, Piria could unbend in his hours 
 of ease, and many an evening was spent by Cannizzaro 
 with his master, who would then freely discuss chemical 
 subjects with his young assistant, and explain the 
 object and meaning of the work on which he had 
 been engaged during the day. 
 
 This severe discipline, to which Cannizzaro frankly 
 confesses he owes much of the success of his after career 
 as a chemist, was interrupted by events which, as they 
 
504 STANISLAO CANNIZZAKO xv 
 
 have turned out, had no small share in determining 
 also his success in his career as a politician. Eeturning 
 to Sicily at the end of July 1847, presumably to spend 
 his vacation at home, the ardent young Liberal of 
 twenty-one, mindful of the events of 1836, naturally 
 found himself in active sympathy with the movement 
 of the time, and when the revolution broke out in 
 January 1848, he became an officer of artillery at 
 Messina. Having been elected deputy for Francavilla 
 in the Sicilian Parliament, he went to Palermo at the 
 end of March, and, as the youngest member of the 
 Assembly, he was required to act as its Secretary. 
 After the bombardment and fall of Messina on 
 7th September 1848, he was sent to Taormina to 
 organise resistance to the advance of the royal troops. 
 The armistice of 13th September, extorted by the 
 combined fleets of England and France to put a stop 
 to the atrocities of Ferdinand's army, stayed for the 
 moment further hostilities, but Cannizzaro was ordered 
 to remain at his post as Commissioner of the provisional 
 Government. The armistice ended in the following 
 March, and after the disaster of Novara, and with it 
 the abdication of Charles Albert, the Sicilian movement 
 utterly collapsed. The royal troops were everywhere 
 victorious, the insurgents retreated first to Catania and 
 thence by Castrogiovanni to Palermo, and, in May 1849, 
 Cannizzaro, with a number of his compatriots, succeeded 
 in escaping for Marseilles on board the Sicilian frigate 
 Indipendente. He was now in exile, and led for a while 
 a somewhat wandering and aimless existence. After a 
 short stay in Marseilles, he passed on to Aries, and visited 
 in turn Avignon, Lyons, Mmes, and Montpellier. In time, 
 however, he again betook himself to his chemical studies, 
 although his means were very limited and his oppor- 
 
xv STANISLAO CANNIZZARO 505 
 
 tunities few. He had, of course, no laboratory, but he 
 read such books as he could obtain, and visited such 
 chemical factories as would admit him. When the 
 body of the unfortunate and broken-hearted Charles 
 Albert was brought back from Oporto, to be buried in 
 the land for whose liberty he had sacrificed his kingship, 
 Cannizzaro joined his fellow-refugees in Turin in order 
 that they might testify by their presence at the obsequies 
 of the dead monarch their grateful memory of his 
 services, and their resolution that his tomb on the 
 Superga should be to them the symbol of an undying 
 aspiration. 
 
 Towards the end of October, Cannizzaro found 
 himself in Paris. Thanks to a letter from Piria, he 
 became acquainted with Cahours, who introduced him 
 into the little laboratory of Chevreul attached to the 
 theatre in the Jardin des Plantes, where he found Cloez 
 installed as assistant. He had now abundant oppor- 
 tunities for work, and with the characteristic ardour 
 of his Southern blood he embraced them all. The 
 excitement of political disquietude in Paris has never 
 seemed to react disastrously on the progress of science 
 there. Curiously enough, for some inscrutable reason, 
 it would appear to stimulate it. Indeed, some of the 
 darkest and most unsettled periods of the political 
 history of France have been among the brightest and 
 most glorious epochs in the annals of science. The 
 stir of 1848, and the unrest which followed it, were 
 contemporaneous with an extraordinary activity in 
 chemical and physical inquiry in Paris, and Cannizzaro 
 participated to the full in the busy movement going 
 on around him. Dumas, it is true, had been swept by 
 his political convictions into the Legislative Assembly, 
 to become Minister of Agriculture and Commerce ; and 
 
506 STANISLAO CANNIZZARO XT 
 
 his laboratory in the Rue Cuvier, in spite of the 
 seductive offer of Jecker, was closed. 
 
 Still, if Cannizzaro never came under the spell of 
 Dumas, he could witness Fremy's experiments in the 
 laboratory of Gray Lussac, and could attend Regnault's 
 lectures in the College de France. But it was to the 
 chemical work-table he mainly turned, and on this he 
 spent the greater part of his time and energies. He 
 took up the study of the amines, the existence of which 
 had recently been made known by Wurtz, and, with 
 Cloez, prepared cyan amide by the action of ammonia 
 on cyanogen chloride. An account of the nature and 
 properties of this compound, published in 1851 in 
 conjunction with Cloez, constitutes Cannizzaro ; s first 
 contribution to the literature of chemistry. The 
 reaction by which they obtained the substance proved 
 exceedingly fruitful, and, by the substitution of amines 
 for ammonia, Cahours and Cloez subsequently prepared 
 the alkyl cyanamides. Moreover, cyanamide itself, by 
 the ease with which it suffers polymerisation, gives rise 
 to a number of isomeric series of homologous amides 
 of considerable theoretic interest. Congenial and in- 
 spiriting as the atmosphere of Paris might be, man 
 cannot live on air alone. But there were too many 
 young and eager aspirants, of French nationality, for 
 the few posts which practically only Paris was able 
 to offer, to justify the hope that the young Sicilian 
 could obtain a position, sufficiently lucrative even for 
 his modest requirements, in the land of his exile. 
 Piedmont, of all the Italian States, could alone afford 
 an asylum to him, and accordingly, towards the end 
 of 1851, he accepted the position of Professor of 
 Physical Chemistry and Mechanics in the National 
 College of Alessandria, an institution modelled some- 
 
xv STANISLAO CANNIZZAKO . 507 
 
 what on the lines of a German Realschule. Here, 
 thanks to the action of the municipality, he was 
 provided with a small laboratory, together with an 
 assistant, and, although much occupied by his public 
 lectures on chemistry and mechanics given to the 
 townspeople, in addition to his regular class instruction, 
 he began the study of the action of alkylamines on 
 cyanogen chloride, only to find himself forestalled by 
 Cloez and Cahours. At about the same time he dis- 
 covered benzyl alcohol, which he obtained by the 
 action of alcoholic potash on bitter almond oil, and 
 the properties and modes of decomposition of which 
 he described in a series of letters to Liebig and Wohler, 
 published in the Annalen. His vacations were usually 
 spent with Piria at Pisa, or at Montignoso, near Massa- 
 Carrara, with his old collaborates Bertagnini, with 
 whom he worked on anisic alcohol (Ann. de Chimie, 
 xlvii. 285). 
 
 In October 1855 he was called to the chair of 
 Chemistry at the University of Genoa, and at the same 
 time Piria was moved from Pisa to Turin. Although 
 the new position at Genoa was one of greater dignity 
 and emolument, Cannizzaro found himself, so far as 
 laboratory accommodation was concerned, less favour- 
 ably situated than at Alessandria ; the only place at his 
 disposal was a damp and dimly -lighted room, without 
 the slightest convenience for even the most elementary 
 experiments. For some months he found it impossible 
 to carry on the work he had begun at Alessandria. In 
 the following year he obtained a room on the upper 
 floor of the University building, and this, with the aid 
 of an assistant and a couple of pupils, he turned into 
 a fairly convenient laboratory, where he resumed his 
 work on the aromatic alcohols. At Genoa Cannizzaro 
 
508 . STANISLAO CANNIZZAKO xv 
 
 began the studies on chemical philosophy which were 
 to culminate in the great generalisation with which his 
 name will continue to be associated. Admirable as his 
 experimental labours are, his chief claim to the esteem 
 and gratitude of his contemporaries and of posterity 
 rests upon his critical contributions to the philosophy 
 of chemistry. In what this signal service consisted will 
 be shown subsequently. 
 
 During the whole of this time Italy was in a state 
 of political ferment. The astute Cavour had gradually 
 secured his ascendency in the parliamentary councils of 
 the little Sardinian kingdom, and with it his position in 
 the councils of Europe. Slowly, and in spite of many 
 checks, the cause of Italian unity gained ground. 
 Magenta and Solferino secured Lombardy, and although 
 Victor Emmanuel was forced to give up Savoy, the very 
 cradle of his dynasty, as the price of Louis Napoleon's 
 co-operation, Italy gained Tuscany, Modena, Parma, and 
 Eomagna ; and in 1860 the annexation of Central Italy 
 was complete. Bombino still held his grip on the two 
 Sicilies, but the islanders made one more effort to throw 
 off the hateful yoke. The time seemed propitious, and 
 Palermo, Messina, and Catania were soon ablaze ; and 
 before the middle of May Garibaldi and his famous 
 "Mille" had accomplished the liberation of the island. 
 Cannizzaro immediately returned to Palermo. He found 
 here his aged mother and sisters, whom he had not seen 
 since 1849, and at once threw himself into the labour of 
 organising and consolidating the work of the revolution, 
 taking an active part in the debates of the States Council 
 convened to define the relation of Sicily to Italian unity. 
 The affair of Spartivento to all intents and purposes 
 decided the fate of Lower Italy, and by the first week 
 of September Garibaldi was in Naples, and with the 
 
xv STANISLAO CANNIZZAKO 509 
 
 shutting up of the last and feeblest of the Neapolitan 
 Bourbons in Gaeta, the emancipation of Italy was 
 practically secured. What remained to be done time 
 would effect. 
 
 Cannizzaro now returned to Genoa, passing through 
 Naples, where Piria had been called to reorganise the 
 system of public instruction, and resumed his work at 
 the University. In the preceding March he had been 
 offered, but had declined, the Professorship of Organic 
 Chemistry in the University of Pisa. He was now 
 invited to occupy the chair on the same subject in the 
 University of Naples, and this he also refused. He was 
 then claimed by his native town, and in October 1861 
 he was named Professor of Inorganic and Organic 
 Chemistry, and Director of the Laboratory of the 
 University of Palermo. What he had to " direct " 
 was contained in a few cupboards, in the same class- 
 room that he had sat in as a student in 1842, and was 
 barely sufficient for even the most elementary illustra- 
 tions. The whole of the following year was spent in 
 organising his courses and in superintending the arrange- 
 ment and plenishing of the rooms he ultimately acquired 
 on the top floor of the University building. 
 
 Cannizzaro remained at Palermo for about ten years ; 
 he took an active share in the management of the Univer- 
 sity, and for a time was its Rector. Its influence as a 
 school of chemistry may be judged of from the fact 
 that he had as co-workers Adolph Lieben, Wilhelm 
 Koerner, and lastly Paterno, who has succeeded him in 
 the chair. For the most part he occupied himself, as 
 regards his laboratory work, with the study of aromatic 
 compounds, and in extending and completing his re- 
 searches on the amines. 
 
 If Cannizzaro was useful to the world as a chemist. 
 
510 STANISLAO CANNIZZAKO xv 
 
 he was so far mindful of Priestley's example as to strive 
 to be equally useful to Palermo as a citizen, and much 
 of his time and ability was freely given in the service 
 of her municipal government, more particularly on sub- 
 jects relating to elementary and secondary education. 
 
 In 1871 Cannizzaro was called to occupy his present 
 position of Professor of Chemistry in the University of 
 Home, and Director of the Chemical Institute in the Orto 
 di S. Lorenzo in Panisperma, and here, for the last five- 
 and-twenty years, he has annually delivered his two 
 courses, each of three lectures a week, on general and 
 organic chemistry, and has worked out, partly alone and 
 partly in conjunction with his pupils Amato, Blaserna, 
 Carnelutti, Sestini, Valente, Fabris, and Andreocci, the 
 chemistry of santonin. At the same time that he was 
 called to Eome he was made a Senator of the kingdom, 
 and as a moderate Liberal he has taken his share in the 
 consolidation of the constitution of regenerated Italy. 
 
 Cannizzaro, when compared with such men as 
 Berthelot and certain of the leaders of the German 
 schools of chemistry, or even with some of the younger 
 generation of Italian chemists, cannot be called a 
 voluminous writer. In all about eighty memoirs have 
 proceeded from his laboratory. It is on the special 
 quality and character of his published work, rather 
 than on its extent, or on the range and variety of its 
 subject-matter, that his fame depends. In this respect 
 he resembles the late August Kekule'. The names of 
 both men will for ever be associated in the history of 
 chemistry with the promulgation of generalisations 
 which mark epochs in the development of chemical 
 science. Cannizzaro's great merit consisted in being 
 the first to clearly point out the bearing on chemical 
 theory of the hypothesis which is commonly associated 
 
xv STANISLAO CANNIZZARO 511 
 
 with the name of his countryman Avogadro, but which 
 Cannizzaro himself, in his well-known lecture delivered 
 before the Fellows of the ^Chemical Society in 1872, 
 associated also with the names of Ampere, Kronig, and 
 Clausius. This, perhaps, is not the time and the place 
 to discuss the question of whatever claims John Dalton 
 may have to be the first to recognise the fundamental 
 truth embodied in the statement that gases, under com- 
 parable conditions, contain in equal volumes equal 
 numbers of molecules, whatever may be their nature 
 and their weight. For the moment we are concerned 
 only with the fact that it remained to Cannizzaro to 
 show that the hypothesis afforded the means of placing 
 the most important of all chemical constants the 
 atomic weights of the elements on a definable and 
 intelligible basis, and thereby of rendering our con- 
 ceptions of atoms and molecules, atomic weight and 
 molecular weight, of gaseous volumes and valency, and 
 of all that is associated with or follows from these 
 conceptions, more logical, consistent, and harmonious. 
 What Cannizzaro did, in a word, was to throw light 
 upon what was obscure, to introduce order where all 
 was confused and contradictory. Hence his Summary 
 of a Course of Chemical Philosophy, published in 
 1858, will occupy in the history of chemical doctrine 
 a position as a classic, not less honourable than Dalton 's 
 ever-memorable New System. There were, of course, 
 difficulties to be overcome, and inconsistencies to be 
 reconciled ; certain facts, indeed, appeared to be hope- 
 lessly opposed to the hypothesis which Cannizzaro 
 sought to make the corner-stone of the edifice of modern 
 chemistry. But these difficulties have been gradually 
 swept away, and the very facts which at first seemed 
 incapable of being brought into line are now seen to 
 
512 STANISLAO CANNIZZAKO xv 
 
 afford the strongest support to the truth and univer- 
 sality of the theory. 
 
 The theory of Avogadro, indeed, has been approached 
 from independent, although converging standpoints, and 
 its position is now secured by the concurrence of inde- 
 pendent testimony. Mathematical conceptions of the 
 nature of gases have shown its necessity. Chemical 
 facts, for a time, were seemingly opposed to it, and hence 
 it was neglected and ultimately forgotten by chemists. 
 They were, however, being driven back to it in spite of 
 themselves ; and it in no sense detracts from his merit 
 to affirm that even if Cannizzaro had not perceived the 
 truth, the rapidly accumulating mass of evidence would 
 have forced others to recognise it. Indeed the sub- 
 stantial unanimity with which Cannizzaro's doctrine 
 was received, immediately that it became generally 
 known, is a proof that the time was ready for it. It is 
 not too much to say that its effect on the minds of 
 chemical thinkers was as profound as that described by 
 Cannizzaro himself in the memorable lecture before 
 alluded to, when he reminded us of Thomas Thomson's 
 account of the impression produced upon him by 
 Dalton's own verbal explanation of the atomic theory. 
 To paraphrase his words : they were enchanted with 
 the new light which burst upon their minds, and saw at 
 a glance the immense importance of such a theory. 
 
 Hence, then, when Cannizzaro visited this country in 
 1872, to deliver the Faraday lecture to the Fellows of 
 the Chemical Society, of which he has been a Foreign 
 Member since 1862, he spoke to willing and receptive 
 ears, and to a body of men to whom his doctrine was 
 already an established article of their chemical creed. 
 
 Cannizzaro is a Foreign Member of many learned 
 Societies ; nearly every Academy in Europe, indeed, has 
 
xv STANISLAO CANNIZZARO 513 
 
 delighted to Honour him. In 1889 he was elected a 
 Foreign Member of our Royal Society, and two years 
 later he was awarded the Copley Medal for his services 
 to chemical theory. May he long be spared to wear the 
 many honours he has so worthily earned, and to enjoy, 
 in health and increasing prosperity, the respect and 
 esteem of a multitude of friends in both hemispheres ! 
 
 ADDENDUM 
 
 Cannizzaro died at Rome on May 10, 1910, at the age 
 of eighty -three. By his death another link between the 
 chemistry of to-day and that of the mid- Victorian era 
 was broken a link which perhaps more than any other 
 served to connect two well-defined and sharply differen- 
 tiated epochs in the history of nineteenth - century 
 chemistry. 
 
 It is not too much to say that the publication, in 
 1858, of his Summary of a Course of Chemical Philo- 
 sophy created a revolution in chemical thought hardly 
 less momentous than that which followed the appear- 
 ance of Dalton's New System. Nay, more : it may be 
 said to have saved the position of the atomic theory. 
 The early 'sixties of the last century were a period of 
 much perturbation ; there was then a sort of parting of 
 the ways. Williamson had laboured to stem the tide of 
 infidelity, but many were unconverted, and some even 
 hardened their hearts. We hear little or nothing 
 to-day of the scepticism which was fashionable among 
 the young bloods of fifty years ago. It is largely due 
 to Cannizzaro that our faith has been strengthened and 
 purified. 
 
 There was something dramatic in the circumstance 
 that Cannizzaro should have passed away at the time 
 
 2 L 
 
514 STANISLAO CANNIZZAKO xv 
 
 that all Italy was celebrating the achievements of 
 Garibaldi and his never-to-be-forgotten Thousand in 
 effecting the establishment of Italian unity, a cause in 
 which Cannizzaro had himself struggled and suffered, 
 and in which he was destined to take a share in shaping 
 to a successful issue. 
 
 At the time of his death he was the oldest foreign 
 member of the Chemical Society of London. " Nature" 
 May 19, 1910. 
 
XVI 
 
 JULIUS THOMSEN 
 
 AN ADDRESS DELIVERED TO THE FELLOWS OF THE CHEMICAL 
 SOCIETY, I?TH FEBRUARY 19 10. 1 
 
 AMONG the Danes whose names are inscribed as men of 
 science on the eternal bead-roll of fame, that of Julius 
 Thomsen stands pre-eminent linked indeed with that 
 of Oersted. It is significant of the position which 
 Thomsen acquired in physical science, and of the respect 
 which that position secured for him in the eyes of his 
 countrymen, that his statue should have been erected 
 during his lifetime and placed in the vicinity of that 
 of Oersted in the courtyard of the Polytechnic High 
 School of Copenhagen. Thomsen, in fact, played many 
 parts in the intellectual, industrial, and social develop- 
 ment of Denmark. To Europe in general he was mainly 
 known as a distinguished man of science. By his fellow- 
 citizens he was further recognised as an educationist of 
 high ideals, actuated by a strong common sense and a 
 stern devotion to duty ; as an able and sagacious ad- 
 ministrator ; as a successful technologist and the creator 
 of an important and lucrative industry based upon his 
 own discoveries ; and as a man of forceful character, who 
 brought his authority, skill, and knowledge of men and 
 affairs to the service of the communal life of Copenhagen. 
 
 1 Chemical Society's Memorial Lecture. 
 515 
 
516 JULIUS THOMSEN xvi 
 
 Thomsen was a municipal councillor of that city for 
 more than a third of a century. He occupied a com- 
 manding position on the Council, and was invariably 
 listened to with respect. The gas, water, and sewage 
 works of Copenhagen are among the monuments to his 
 civic activity. From 1882 up to the time of his death 
 he was a member of the Harbour Board of the port. In 
 these respects Thomsen sought to realise Priestley's ideal 
 of the perfect man that he should be a good citizen 
 first and a man of science afterwards. 
 
 Hans Peter Jiirgen Julius Thomsen was born in 
 Copenhagen on February 16, 1826. He was educated 
 at the church school of St. Peter in that city, and subse- 
 quently at von Westens Institute. In 1843 he com- 
 menced his studies at the Polytechnic, and in 1846 
 graduated there in Applied Science, and became an 
 assistant to Professor E. A. Scharling. Of his earliest 
 years comparatively little is known. Thomsen, always a 
 reserved and taciturn man, talked little about himself 
 even to his intimate friends and least of all about the 
 days of his youth. It was known to a few that these 
 days had not been smooth. Those who were best 
 informed were conscious that to these early struggles 
 much of that dour and resolute nature which formed a 
 distinguishing trait in his character was due. Thomsen, 
 indeed, began life as a fighter, and a fighter he remained 
 to the end of his fourscore years. 
 
 In 1847 he became assistant to Forchhammer, 
 passing rich, like Goldsmith's pedagogue, on 40 a year. 
 Georg Forchhammer, whose earliest work dates back to 
 the period when Berzelius was in his prime, was an 
 active and industrious investigator of the old school, 
 mainly in inorganic chemistry, and more particularly 
 on problems of chemical geology and physiography. 
 
xvi JULIUS THOMSEN 517 
 
 He was a frequent visitor to this country, and was 
 well known to early members of the British Association. 
 Although doubtless influenced, in common with all 
 teachers in Northern Europe, by the example and 
 methods of Berzelius, such influence as he himself was 
 able to exert died with him. Forchhammer attracted 
 few pupils, and created no school, and Thomsen prob- 
 ably derived no inspiration or acquired any stimulus 
 from this association. For a time Thomsen supple- 
 mented his scanty income by teaching agricultural 
 chemistry at the Polytechnic. In 1853 he obtained a 
 travelling scholarship, and spent a year in visiting 
 German and French laboratories. He probably owed 
 this scholarship in great measure to his first contribution 
 to the literature of chemistry, namely, his memoir, 
 " Bidrag til en Thermochemisk System " (contributions 
 to a thermochemical system), communicated to the 
 Eoyal Society of Sciences of Copenhagen in 1852, and 
 for which he received the silver medal of the Society 
 and a sum of ten guineas to enable him to procure a 
 more accurate apparatus. In this memoir he sought to 
 develop the chemical side of the mechanical theory of 
 heat, doubtless under the influence of Ludwig Augustus 
 Colding, an engineer in the service of the Municipality 
 of Copenhagen, and a pioneer, like Mayer, in the 
 development of that theory. Indeed, the Danes now 
 claim for Colding, who had made experiments on the 
 relation between work and heat as far back as 1842, 
 but whose labours were practically ignored by his con- 
 temporaries, the position which the Germans assign to 
 Mayer (see Mach's Development of the Theory of 
 Heat). In 1861 Thomsen further developed his 
 ideas in a memoir on the " General Nature of Chemical 
 Processes, and on a Theory of Affinity based thereon," 
 
518 JULIUS THOMSEN xvi 
 
 published in the Transactions of the Danish Academy 
 of Sciences. In this paper he laid the foundations of 
 the chief scientific work of his life. 
 
 In 1853 Thomsen patented a method of obtaining 
 soda from cryolite, so-called " Greenland," or ice-spar, 
 a naturally occurring fluoride of sodium and aluminium, 
 Al 2 F 6 ,6NaF, found largely, indeed almost exclusively, 
 in Greenland, and particularly at Ivigtut. It derives 
 its mineralogical name from its ice-like appearance and 
 ready fusibility even in the flame of a candle. It seems 
 to have been first brought to Europe in 1794, and to 
 have been described by Schumacher in the following 
 year. Klaproth first showed that it contained soda, 
 and its composition was further established by 
 Vauquelin, Berzelius, and Deville. 
 
 Thomsen's process consists in heating a finely divided 
 mixture of cryolite and chalk in a reverberatory furnace, 
 whereby carbon dioxide is expelled and calcium fluoride 
 and sodium aluminate are formed. The roasted mass is 
 lixiviated with water, so as to dissolve out the sodium 
 aluminate, which is then treated with carbon dioxide. 
 Alumina is precipitated, and sodium carbonate remains 
 in solution. The alumina is either sold as such, or con- 
 verted into sulphate (so-called " concentrated alum " or 
 "alum-cake"), and the sodium carbonate is separated 
 by crystallisation. Both products are obtained in a 
 remarkably pure condition, and the cryolite-soda yields 
 excellent " caustic." 
 
 Thomsen's process, although simple enough in 
 principle, requires considerable skill and pains in its 
 practical execution, and most of the manufacturing 
 details were worked out by him, or under his direction. 
 Success largely depends upon the maintenance of a 
 proper temperature ; the decomposition begins below a 
 
xvi JULIUS THOMSEN 519 
 
 red-heat, but requires to be finished at that temperature, 
 and care must be taken to avoid fusion or even sintering 
 of the mass. In 1854 Thomsen obtained the exclusive 
 right of mining for cryolite and of working up the 
 mineral in Denmark for soda and alumina. Actual 
 manufacturing operations were begun on a small scale 
 in 1857, and in the following year Thomsen planned the 
 present large factory at Oeresund, near Copenhagen, 
 which was opened on his thirty-fourth birthday. The 
 importance of this industry to Denmark may be seen 
 from the circumstance that during the fifty years of its 
 existence the firm have paid the Danish Government 
 nearly 300,000 for the concession. Other factories 
 were started in Germany, Bohemia, and Poland, but 
 met with little success. The Pennsylvania Salt- 
 manufacturing Company at Natrona, near Pittsburg, 
 eventually obtained the right to work up two -thirds 
 of all the cryolite mined in Greenland. From the 
 start Thomsen took a large share in the management 
 of the Oeresund works, and, by his energy, foresight, 
 and skill, placed the undertaking on a sound commercial 
 basis. 
 
 Although Thomsen died a rich man, mainly as the 
 result of the industry he created, in the outset of his 
 career as a teacher and a technologist his means were 
 very straitened. He came of poor parents, of no 
 social position or influence, and they were unable to 
 further his inclinations towards an academical career. 
 In 1854 he applied unsuccessfully for a position as 
 teacher of chemistry at the Military High School in 
 Copenhagen. During three years from 1856 to 1859 
 while still engaged in developing his cryolite process, 
 he acted as an adjuster of weights and measures to the 
 Municipality of Copenhagen. It was a poorly paid 
 
520 JULIUS THOMSEN xvi 
 
 position, but it kept the wolf from the door. At about 
 this period he betook himself to literature, and published 
 a popular book on general subjects connected with 
 physics and chemistry somewhat in the style of 
 Helmholtz's well-known work entitled Travels in 
 Scientific Regions, which had a considerable measure 
 of success. He was, however, not altogether unknown 
 even at this time as an author, since in 1853 he had 
 collaborated with his friend Colding in producing a 
 memoir on the causes of the spread of cholera and on the 
 methods of prevention, which attracted much attention 
 at the time of its appearance. 
 
 In 1859, whilst engaged in the Oeresund factory, he 
 again applied to the authorities for a position as teacher 
 at the Military High School, and succeeded in obtaining 
 an appointment to a lectureship in physics, which he 
 held until 1866. During his tenure of this office he 
 devised his polarisation battery, which received many 
 awards at International Exhibitions and was used for a 
 time in the Danish telegraph service. 
 
 In 1859-60 he was "viearius" for Scharling at the 
 University, and in 1865 became a teacher, and in the 
 following year Professor of Chemistry and Director of 
 the Chemical Laboratory, a position which he retained 
 active to the last until 1901, when he retired in his 
 seventy-fifth year of age. 
 
 Before his connexion with the University, he founded 
 and edited, from 1862 to 1878, in association with his 
 brother, August Thomsen, the Journal of Chemistry 
 and Physics, one of the principal organs of scientific 
 literature in Denmark. 
 
 In 1863 he was elected a member of the Commission 
 of Weights and Measures, and was instrumental in 
 bringing about the adoption of the metric system and 
 
xvi JULIUS THOMSEN 521 
 
 the assimilation of the Danish system to that of the 
 Scandinavian Kingdom. 
 
 In 1883 Thomsen became Chancellor of the Poly- 
 technic High School of Copenhagen a position which 
 he held for about nine years. During this period he 
 entirely changed the character and spirit of the school, 
 and stamped it with the impress of his earnestness and 
 industry. Under his direction, new buildings were 
 erected and arranged in accordance with the best 
 Continental and American models. Thomsen's adminis- 
 tration was in marked contrast to that of his somewhat 
 easy-going predecessor, but it is doubtful if it brought 
 him popularity in the school. The students respected 
 and even feared him, but his cold and unsympathetic 
 nature evoked no warmer feeling. It was said of him 
 by one who knew him intimately that he never learned 
 to draw the young to him, to create in them an interest 
 for his work, to form a school. Thomsen was a homely 
 man, but not even in his home, says the same authority, 
 was it possible for him to change his active, earnest, 
 strenuous disposition what his friends called his fighting 
 character. But if he was always the serious master of 
 the house, he was also its obedient servant. In reality 
 he was a man of deep feeling, and was not without power 
 to give that feeling expression in words, sometimes in 
 verse, and occasionally even in music. 
 
 It was while occupying the position of Director of 
 the Chemical Laboratory of the University that Thomsen 
 executed the thermochemical investigations which con- 
 stitute the experimental development of the ideas he had 
 formulated in his memoir of 1861. The results of these 
 inquiries were first made known in a series of papers 
 published from 1869 to 1873 in the Transactions of 
 the Koyal Danish Society of Sciences, and from 1873 
 
522 JULIUS THOMSEN xvi 
 
 onwards by the Journal fur PraJctische Chemie. The 
 papers were republished in collected form in four volumes 
 (1882-1886) by a Leipzig house under the title of 
 Thermochemische Untersuchungen. A summary of this 
 experimental labour, which extended over a third of a 
 century, was subsequently prepared by Thomsen, and 
 published in 1905 in Danish under the title of 
 Thermokemiske Resultater. 
 
 In this work he reviewed the whole of the numerical 
 and theoretical results, to the exclusion of the greater 
 portion of the experimental details. A translation of 
 this volume by Miss Katharine A. Burke, entitled 
 Thermochemistry, renders it readily accessible to 
 English readers. Miss Burke has supplemented the 
 original work by a short account, taken from the 
 Thermochemische Untersuchungen, of the experimental 
 methods employed, thereby rendering the whole more 
 intelligible to the student. Moreover, in the English 
 edition a partial attempt has been made to translate 
 Thomsen's deductions into the language of modern 
 theory based on the conception of ionisation, which, of 
 course, was not known to science at the time the 
 Thermochemische Untersuchungen was published. 
 
 It is impossible within the limits of such a notice as 
 this to deal in detail with the immense mass of experi- 
 mental material which this work embodies, and I shall 
 not attempt, therefore, to do more than to offer a 
 generalised statement, based mainly upon the admirable 
 account of Thomsen's work given by Professor Bronsted 
 to the Chemical Society of Copenhagen on the occasion 
 of the meeting held on March 2, 1909, to com- 
 memorate Thomsen's services to science. 
 
 The conception of affinity as a cause and determining 
 condition of chemical change is traceable in some of the 
 
xvi JULIUS THOMSEN 523 
 
 earliest efforts to co-ordinate and explain chemical 
 phenomena. It certainly existed long prior to the time 
 of Boyle, and was at the basis of every philosophical 
 system after his period. We need only mention the 
 names of Bergman, Wenzel, and Berthollet to indicate 
 this fact. But to Thomsen belongs the credit of being 
 the first to make the attempt to measure the relative 
 value or strength of affinity quantitatively, and to 
 express it numerically in definite terms which admitted 
 of exact comparison. Thomsen's theory of affinity, as 
 enunciated by him in his 1851 paper, was based upon 
 his conviction that affinity could be measured quantita- 
 tively by estimating the amount of heat evolved in the 
 chemical process. We are not immediately concerned 
 to show whether the theory is right or wrong, or in 
 what respect it fails. The point is that the enunciation 
 of this principle upwards of half a century ago con- 
 stituted an important step forward, inasmuch as it 
 sought to estimate affinity in relation to a quantity 
 which can be fixed by experiment, and is capable of 
 expression by numbers. 
 
 In this and in the subsequent paper of which 
 mention has been made already, he thus defines his 
 conception of thermochemistry, and discusses, for the 
 first time, its laws : 
 
 The force which unites the component parts of a chemical 
 compound is called affinity. If a compound is split up, whether 
 by the influence of electricity, heat, or light, or by the addition 
 of another substance, this affinity must be overcome. A certain 
 force is required the amount of which depends on the strength of 
 the affinity. 
 
 If we imagine, on the one side, a compound split up into its 
 component parts, and on the other side these parts again united 
 to form the original compound, then we have two opposite pro- 
 cesses the beginning and end of which are alike. It is therefore 
 
524 JULIUS THOMSEN xvi 
 
 evident that the amount of the force required to split up a 
 certain compound must be the same as that which is evolved 
 if the compound in question is again formed from its component 
 parts. 
 
 The amount of force evolved by the formation of a compound 
 can be measured in absolute terms ; it is equal to the amount of 
 heat evolved by the formation of the compound. 
 
 Every simple or complex action of a purely chemical nature 
 is accompanied by evolution of heat. 
 
 By considering the amount of heat evolved by the formation 
 of a chemical compound as a measure of the affinity, as a measure 
 of the work required again to resolve the compound into its 
 component parts, it must be possible to deduce general laws for 
 the chemical processes, and to exchange the old theory of affinity, 
 resting on an uncertain foundation, for a new one, resting on the 
 sure foundation of numerical values. 
 
 As has been proved by later theoretical and experi- 
 mental investigations, the theory of thermochemical 
 affinity is not absolutely correct at ordinary temperatures. 
 But, on the other hand, it has been shown that a com- 
 paratively large number of processes are approximately 
 in unison with it. Not only do they agree qualitatively, 
 that is to say, that heat is evolved during the process, 
 but also in the fact that the results which newer and 
 more exact methods for estimating affinity have pro- 
 duced agree numerically with what would be required 
 by the thermochemical theory. We meet here with a 
 fundamental phenomenon which Thomsen deserves great 
 credit for having first pointed out, but the explanation 
 of which could not be given at the time he indicated it. 
 It can be demonstrated theoretically that the lower we 
 reduce the temperature and the nearer we get to the 
 absolute zero, the more nearly is the condition for the 
 theory fulfilled, so that at the absolute zero the theory 
 would be found to be an exact law of nature. If it 
 were possible to work at such low temperatures it would 
 
xvi JULIUS THOMSEN 525 
 
 be found that the evolution of heat, or the evolution of 
 energy by the chemical process, would be an exact 
 measure of the affinity of the process, and that under 
 this condition the theory of Thomsen would be the 
 accurate expression of a natural law. 
 
 But under ordinary conditions this is not so, for in 
 reality an ever-increasing number of endothermic pro- 
 cesses are found to occur, that is, processes which 
 proceed with the absorption of heat. Thomsen tried at 
 first to explain these phenomena in such a way as to 
 keep them within his system, and he drew a distinction 
 between a purely chemical process running conformably 
 to his theory and a physico-chemical process which did 
 not fall within the law. But he was gradually con- 
 vinced that his theory could not be maintained in its 
 entirety. It is to his credit that he did not seek to 
 uphold an untenable principle, or try to defend it as did 
 Berthelot, who almost to his dying day maintained the 
 validity of the principle in spite of all facts. 
 
 These ideas have, in the words of Ostwald, been the 
 scientific confession of faith of chemists throughout half 
 a century. They have had the greatest influence on 
 scientific thought in every branch of chemistry. It is 
 on the basis of them that we have arrived at a theory of 
 affinity which at the present moment is being developed 
 into one of the most perfect chemical theories. Lastly, 
 it is due to these ideas that the experimental material 
 has been produced which during all time will place the 
 name of Julius Thomsen in the first rank of men of 
 science. 
 
 To go through this material in detail is, as I have 
 said, impossible here. It may be stated generally that 
 practically every simple inorganic process has been 
 investigated calorimetrically by Thomsen, or can be 
 
526 JULIUS THOMSEN xvi 
 
 calculated by means of the calorimetric data furnished 
 by him. In the case of organic substances, data have 
 been given for estimating the heat of combustion of a 
 large number of compounds. All these estimations 
 were made by Thomsen personally, according to a pre- 
 arranged plan, and in systematic succession during a 
 period of more than thirty years. They comprise more 
 than 3500 calorimetrical estimations. It has been truly 
 said that this work is unique in the chemical history of 
 any country. 
 
 Among the results of Thomson's thermochemical 
 inquiries which have special value for physical chemistry 
 is his investigation of the phenomena of neutralisation, 
 in which he shows that the basicity of acids can be 
 estimated thermochemically, and that it can in this way 
 be proved whether or not a point of neutrality exists. 
 His observation that the heat of neutralisation is the 
 same for a long series of inorganic acids, such as hydro- 
 chloric acid, hydrobromic acid, hydriodic acid, chloric 
 acid, nitric acid, etc., supports the theory of electrical 
 dissociation, inasmuch as this requires that the heat of 
 neutralisation of the strong acids must in all cases be 
 independent of the nature of the acid, because the 
 process of neutralisation for all of them is the com- 
 bination of the ion of hydrogen in the acid with the ion 
 of hydroxyl of the base to form water. These investiga- 
 tions also led to the important thermochemical result 
 that the heat of neutralisation of acids (or the heat of 
 their dissociation) cannot be considered as a measure of 
 the strength of the acids. 
 
 Another important result is the proof by experiment 
 of the connexion which exists between the changes of 
 the heat-effect with the temperature and the specific 
 heat of the reacting substances. The first law of 
 
xvi JULIUS THOMSEN 527 
 
 thermodynamics requires the relation indicated by 
 Kirchhoff : - = d - C 2 , where U is the heat-effect, T 
 
 the temperature, and Cj and C 2 are the heat capacities 
 of the two systems before and after the reaction, and 
 Thomsen showed by investigation of the heat of neutral- 
 isation, the heat of solution, and the heat of dilution, 
 that this relation was satisfied. For the purpose of his 
 inquiry, the specific heats of a large number of solutions 
 of salts were estimated by an ingenious method, and 
 with an exactness hitherto unattained. 
 
 Of no less importance are Thomson's thermochemical 
 investigations on the influence of mass. In the year 
 1867 Guldberg and Waage published their theory of the 
 chemical effect of mass. But they had only verified the 
 theory to a small extent and in particularly simple cases. 
 They had not investigated the complete homogeneous 
 equilibrium, because at that time no method existed for 
 experimental investigation of such homogeneous equi- 
 librium. Thomsen showed that the estimation could be 
 made thermochemically. By allowing, for instance, an 
 acid to act on a salt of another acid in an aqueous 
 solution, the latter acid will be partly replaced by the 
 first, which will form a salt. By mixing, for instance, 
 a solution of sodium sulphate and nitric acid, there is 
 formed sodium nitrate and sulphuric acid, but the process 
 will not proceed to completion. If we have estimated 
 the heat of neutralisation of the two acids with sodium 
 hydroxide, the difference between these two heat- 
 phenomena will give the amount of heat corresponding 
 to the total decomposition of the sodium sulphate, and 
 the heat found experimentally by mixing the two 
 solutions will therefore show to what degree the trans- 
 formation has taken place. It would be possible to 
 
528 JULIUS THOMSEN xvi 
 
 estimate thermochemically the amount of the four 
 substances in solution, and thereby, by varying the con- 
 centration or the proportion between the initial quantities 
 of substances, to calculate whether the Guldberg-Waage 
 theory on the effect of mass was confirmed in this case. 
 
 Thomsen applied this method to a large number of 
 different acids and bases, and was enabled thereby to 
 prove the agreement with the law of the influence of 
 mass in all the cases which he examined. He found 
 particularly that the proportion of the one acid which 
 remained combined with the base was constant with 
 mixtures of constant proportion. On this basis he pro- 
 pounded the term avidity, which he defined as the 
 tendency of the acid to unite with the base, and he 
 showed that the avidity was independent of the con- 
 centration, and only to a small extent varied with the 
 temperature. The term avidity has since acquired great 
 importance, particularly since other and more exact 
 methods for its estimation have been found. Concur- 
 rently with this, its meaning has been made clear by the 
 theory of electrolytic dissociation. 
 
 On the basis of these estimations, Thomsen drew up 
 the first table, based on experiments, of the relative 
 strength of the acids, and the numbers in this table have 
 been found to agree with the results obtained by 
 examining the electrical conductivity of the acids. 
 
 It is worth noting that Thomsen not only produced 
 the experimental proof of the correctness of the Guldberg- 
 Waage theory of the effect of mass soon after the 
 appearance of this theory, but also that he was the first 
 to acknowledge and adopt it. It is remarkable that this 
 work of Thomsen received so little attention, although 
 it appeared in a widely circulated German journal, and 
 it was not until ten years later that the law of the effect 
 
xvi JULIUS THOMSEN 529 
 
 of mass was generally recognised, as the result of the 
 work of Ostwald and van't Hoff. 
 
 Although Thomsen's title to scientific fame rests 
 
 o 
 
 mainly upon his thermochemical work, his interests 
 extended beyond this particular department of physical 
 chemistry. He worked on chloral hydrate, selenic acid, 
 on ammoniacal platinum compounds, and on glucinum 
 platinum chloride, on iodic acid and periodic acid, on 
 hydrogen peroxide, hypophosphorous acid, and hydro- 
 genium. He early recognised the importance of 
 MendeleefFs great generalisation, and contributed to the 
 abundant literature it produced. His paper of 1895, 
 " On the Probability of the Existence of a Group of 
 Inactive Elements," may be said to have foreshadowed 
 the discovery of the congeners of argon. He pointed 
 out that in periodic functions the change from negative 
 to positive value, or the reverse, can only take place by 
 a passage through zero or through infinity ; in the first 
 case, the change is gradual, and in the second case it i 
 sudden. The first case corresponds with the gradual 
 change in electrical character with rising atomic weight 
 in the separate series of the periodic system, and the 
 second case corresponds with a passage from one series to 
 the next. It therefore appears that the passage from 
 one series to the next in the periodic system should take 
 place through an element which is electrically indifferent. 
 The valency of such an element would be zero, and 
 therefore in this respect also it would represent a tran- 
 sitional stage in the passage from the univalent electro- 
 negative elements of the seventh to the univalent 
 electropositive elements of the first group. This indicates 
 the possible existence of a group of inactive elements 
 with the atomic weights 4, 20, 36, 84, 132, the first five 
 numbers corresponding fairly closely with the atomic 
 
 2 M 
 
530 JULIUS THOMSEN xvi 
 
 weights respectively of helium, neon, argon, krypton, 
 and xenon (Zeitsch. anorg. Chem., 1895, 9, 283 ; Journ. 
 Chem. Soc. 9 1896, 70, II. 16). He subsequently made 
 known the existence of helium in the red fluorite from 
 Ivigtut. 
 
 As evidence of Thomsen's manipulative ability and 
 his power of accurate work may be mentioned his 
 determination of the atomic weights of oxygen and 
 hydrogen, and incidentally of aluminium. For the 
 atomic weight of hydrogen he obtained the value 
 1*00825 when = 16, which is practically identical 
 with that of Morley and Noyes. He further made 
 most accurate estimations of the relative densities of 
 these gases, and of the volumetric ratios in which they 
 enter into the composition of water. His value for the 
 atomic weight of aluminium is nearly identical with 
 that adopted in the last Report of the International 
 Committee on Atomic Weights. 
 
 Thomsen maintained his interest in thermochemical 
 problems up to the end, and was a keen and clear- 
 sighted critic of the work which appeared from time 
 to time during the later years of his life. This interest 
 occasionally gave rise to controversy, and some of his 
 latest papers were wholly polemical. 
 
 Thomsen was a pronounced atomist, and to him a 
 chemical process was a change in the internal structure 
 of a molecule, and the chief aim of chemistry was to 
 investigate the laws which control the union of atoms 
 and molecules during the chemical process. He con- 
 sidered that chemistry should be treated mathematically 
 as a branch of rational mechanics. But no one insisted 
 more strongly than he how little we really know of 
 these questions. In summarising his theoretical ideas 
 in the ThermoJcemische Resultater, he says, " An almost 
 
xvi JULIUS THOMSEN 531 
 
 impenetrable darkness hides from us the inner structure 
 of molecules and the true nature of atoms. We know 
 only the relative number of atoms within the molecule, 
 their mass, and the existence of certain groups of atoms 
 or radicles in the molecule, but with regard to the forces 
 acting within the molecules and causing their formation 
 or destruction our knowledge is still exceedingly 
 limited." He fully realised that his own work was only 
 the foundation on which the future elucidation of these 
 questions must rest. " He worked," says Bronsted, 
 "in the conviction that what we somewhat vaguely 
 call the affinity of the atoms their interaction, their 
 attraction, and varying effect, etc. follows the general 
 laws of mechanics, and that, as he worded it, the 
 principle that * might is right ' holds good in chemistry 
 as in mechanics. On this foundation he hoped to be 
 able to evolve the laws for the statics and dynamics of 
 chemical phenomena, even although the true nature of 
 the action is unknown." 
 
 Thomsen's merits as an investigator received formal 
 recognition from nearly every country in the civilised 
 world. As far back as 1860 he was elected one of the 
 thirty-five members of the Danish Royal Society of 
 Sciences of Copenhagen, and from 1888 until his death 
 he was its President. In 1876 he became an Honorary 
 Foreign Member of the Chemical Society of London. 
 On the occasion of the fourth centenary of the founda- 
 tion of the University of Upsala (created in 1477), 
 he received the degree of Doctor of Philosophy honoris 
 causa. In 1879 he was made an honorary M.D. of the 
 University of Copenhagen. Two years later he was 
 made a Foreign Member of the Physiographical Society 
 of Lund, and in 1888 he was elected a member of the 
 Society of Science and Literature of Gothenburg. In 
 
532 JULIUS THOMSEN xvi 
 
 1885 lie became a member of the Royal Society of 
 Sciences of Upsala, and in 1886 of the Stockholm 
 Academy of Sciences. 
 
 In 1883 he and Berthelot were together awarded 
 the Davy Medal of the Royal Society a fitting and 
 impartial recognition on the part of the Society of the 
 manner in which the two investigators, whose work 
 not infrequently brought them into active opposition, 
 had jointly and severally contributed to lay the 
 foundations of thermochemistry. 
 
 In the same year Thomsen was made a member of 
 the Accademia dei Lincei of Rome, and in the following 
 year he was elected into the American Academy of 
 Arts and Sciences in Boston, and of the Royal Academy 
 of Sciences of Turin. In 1887 he was made a member 
 of the Royal Belgian Academy. 
 
 In 1886-87 and again in 1891-92 he was Rector 
 of the University of Copenhagen. In 1888 he became 
 Commander of the Dannebrog, and in 1896, and on his 
 seventieth birthday, he was made Grand Commander 
 of the same order. On the same occasion the Danish 
 chemists caused a gold medal to be struck in his 
 honour. In 1902 he became a Privy Councillor 
 (Geheime Konferenz raad). In the same year he was 
 elected a Foreign Member of the Royal Society of 
 London. 
 
 He died on February 13, 1908, full of years as of 
 honours, and was buried on the eighty-third anniversary 
 of his birth and on the jubilee of the opening of the 
 Oeresund factory. His wife, Elmine Hansen the 
 daughter of a farmer on Langeland predeceased him 
 in 1890. 
 
XVII 
 
 THE RISE 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 ail- 
 ments are due to some alteration in his composition, 
 and can only be cured ~by the influence of other 
 chemical compounds. It may be questioned whether 
 
 533 
 
534 EISE AND DEVELOPMENT OF xvn 
 
 modern therapeutics has advanced much beyond this 
 position. 
 
 In strict truth, it is only within the present century 
 that 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 recognition 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 
 conception 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 relations, and making use of definite 
 mathematical expression ; and it was at length recog- 
 nised 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, merchant's accounts, and the 
 
xvii SYNTHETICAL CHEMISTEY 535 
 
 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 indisputably belongs 
 to Britain. Jons Jakob Berzelius had clearly grasped 
 the real significance of Kichter'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 Wollaston, he perceived that the 
 mutual action of atoms requires a geometrical con- 
 ception 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 
 
536 EISE AND DEVELOPMENT OF xvn 
 
 weights of equal volumes of both simple and compound 
 gases, when measured under like conditions of tempera- 
 ture 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 funda- 
 mental conception. Then followed the discovery of 
 Dulong and Petit, in 1819, that the capacity for heat 
 of the elements is 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 simultane- 
 ously, 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 recognition, 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 compounds ; 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 Play fair and Joule 
 in this country, of the relations between mass and 
 volume in solids and liquids ; these constitute so many 
 
xvii SYNTHETICAL CHEMISTEY 537 
 
 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 isomer- 
 ism he, indeed, coined that very word in the outset 
 he stoutly maintained that the idea involved a contra- 
 diction in terms. It is true that a fuller knowledge 
 has shown that each of these generalisations has its 
 limitations : that all are, so to say, only first approxi- 
 mations to exact mathematical statement ; but this 
 circumstance has in nowise diminished the support 
 they afford to the doctrine of Dalton, for, as Liebig has 
 well stated, " one 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 
 
538 KISE AND DEVELOPMENT OF xvn 
 
 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 addi- 
 tional proof of the truth of Liebig's remark. 
 
 But the chemist who concerns himself mainly with 
 considerations 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 discovery by these chemists of the 
 identity in qualitative and quantitative composition of 
 silver fulminate and silver cyanate 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 demonstrating that the attributes of bodies 
 
xvii SYNTHETICAL CHEMISTRY 539 
 
 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 compounds. Unquestionably the 
 two most powerful factors in 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 
 
540 KISE AND DEVELOPMENT OF xvii 
 
 of Kekule* and Couper, which graft themselves directly 
 on Frankland's discovery, concerning certain peculiarities 
 in the mode of combination 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 introduced 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 con- 
 ceive 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 
 progress which has been made in synthetical chemistry 
 during the last fifty or sixty years. 
 
 Such a survey, however rapid, will lead us into every 
 department of the organic world. During the past 
 half-century the chemist has succeeded in forming the 
 active principles or characteristic products of many 
 
xvii SYNTHETICAL CHEMISTEY 541 
 
 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 con- 
 cerned 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 com- 
 mercial 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 
 
542 EISE AND DEVELOPMENT OF xvn 
 
 reactions have a special interest from the circumstance 
 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 Koosen 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 Ilex 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 
 
 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 Dunstan have, however, 
 conclusively demonstrated the identity of the two substances. 
 
xvii SYNTHETICAL CHEMISTEY 543 
 
 and the products derived from the oxidation of nitro- 
 genous 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 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 ; Gruikshank. 
 
 2. Carbonic oxide and chlorine give carbonyl chloride. J. 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. Theobromine 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 (?rTw^a, 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 
 
544 KISE AND DEVELOPMENT OF xvn 
 
 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 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 con- 
 stitution. Some of them have been shown to be 
 identical with bodies already known. Thus choline 
 (#0X77, 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 com- 
 position, and in possessing intense poisonous properties, 
 has been artificially produced by Baeyer and by 
 Hofmann. Choline and neurine are closely related sub- 
 stances, and can be readily transformed into each other. 
 Another of the so-called corpse alkaloids, cadaverine, 
 has also been synthetically formed by Ladenburg. 
 
xvii SYNTHETICAL CHEMISTKY 545 
 
 In 1870 Schmiedeberg and Kopp isolated the poison- 
 ous principle of the fungus Agaricus muscarius, which 
 they named muscarine. Subsequently, Schmiedeberg 
 and Harnack obtained 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 putrefac- 
 tion of flesh. 
 
 It is, however, among the products of plant life that 
 some 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 illumin- 
 ating 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 distillation 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 
 
 2N 
 
546 RISE AND DEVELOPMENT OF xvn 
 
 recently shown by Genvresse, the optically inactive 
 modification of tartaric acid, the racemic acid dis- 
 covered by Berzelius, may be formed. Eacemic acid, 
 as demonstrated by Pasteur, is a mixture of two modi- 
 fications of tartaric acid which neutralise each other's 
 optical activity. By taking advantage of certain re- 
 markable differences in the crystalline characters of the 
 sodium-ammonium salts formed from racemic acid, which 
 he was the first to detect, Pasteur succeeded in separat- 
 ing 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 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 con- 
 stitution of these complex substances is better under- 
 stood. 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 artificially by Ladenburg, 'and the other 
 only partially, viz. atropine, one of the active sub- 
 stances 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 
 
xvii SYNTHETICAL CHEMISTRY 547 
 
 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 Isevo-conine and into 
 dextro-conine, the latter of which is identical with the 
 natural variety. 
 
 Closely related to conine is nicotine, the poisonous 
 constituent of tobacco. The constitution of this body 
 is now fairly well understood, and its synthetical 
 formation may be confidently 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 product in medicine as 
 a vesicant and counter-irritant. The sweet-smelling 
 principle of Spircea ulmaria, or meadow-sweet, 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 woodruff. The Maiweinessenz 
 used in Germany in place of woodruff in the manu- 
 facture of Maiwein is an alcoholic solution of artificially 
 prepared coumarin. 
 
 Salicylic acid, which is now largely used as an anti- 
 septic, could formerly only be obtained from oil of winter- 
 green (Gaultheria procumbens). It is now prepared on 
 a manufacturing scale by heating a compound of soda 
 and carbolic acid in carbonic acid gas, and the synthetic 
 product has practically replaced the natural variety. 
 
548 KISE AND DEVELOPMENT OF xvn 
 
 Vanillin, the aromatic principle of the dried fer- 
 mented pods of certain orchids belonging to the genus 
 Vanilla (Span, vaynilla, dim. of vaina, a pod), has had 
 its constitution unravelled, with the result that it can 
 now be synthetically prepared. Artificial vanillin is, 
 in fact, made on an industrial scale in Germany, and 
 threatens to supplant the natural product of Reunion 
 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 con- 
 stituents of cloves and all-spice, and can be prepared 
 from these substances. 
 
 Other plant products, of which the synthetic forma- 
 tion may be confidently looked for, are caoutchouc and 
 oil of turpentine ; 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 completely destroyed 
 a staple trade of France, Holland, Italy, and Turkey. 
 Alizarin is one of the main products of the madder 
 plant, the roots of which have been used from time 
 immemorial for the sake of the dyes which they con- 
 tain. 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, 
 
xvii SYNTHETICAL CHEMISTKY 549 
 
 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 Lanarkshire district alone consuming upwards 
 of 150 tons weekly. The chemist has changed all this, 
 and the cultivation of the various species of the 
 Rubiacece for the purposes of the dyer, which has con- 
 tinued 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 important, 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 success- 
 fully 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 levulose, which has been recently effected 
 by Emil Fischer. It is interesting not merely as an 
 instance of the artificial production of well-known 
 substances, but also on account of the light it is cal- 
 culated to throw upon the origin and mode of forma- 
 tion of the sugars in the vegetable kingdom. It is not 
 possible, without entering into details too technical in 
 
550 SYNTHETICAL CHEMISTEY xvn 
 
 character 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 century, 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 possi- 
 bility, 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 know- 
 ledge 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 con- 
 stitute 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. 
 
XVIII 
 
 ON THE PROGRESS OF CHEMISTRY IN GREAT 
 BRITAIN AND IRELAND DURING THE 
 NINETEENTH CENTURY 
 
 PART I. -FROM THE BEGINNING OF THE CENTURY TO 
 THE FOUNDATION OF THE CHEMICAL SOCIETY (1841) 
 
 THE PRESIDENTIAL ADDRESS TO THE CHEMICAL SOCIETY, 
 29TH MARCH 1900 
 
 ALTHOUGH Century-summaries run a risk of being re- 
 garded as flat, stale, and unprofitable, I have ventured 
 to think that it would not be uninteresting or altogether 
 unuseful if, at this time, I sought to indicate in the 
 broadest possible outline what our countrymen have 
 done during the past hundred years in gaining and 
 extending knowledge within the special province of 
 intellectual activity with which we, as a Society, 
 primarily concern ourselves. 
 
 In examining the century's accounts, we naturally 
 inquire into the nature of the balance with which it 
 started. How much better it was felt to be than at 
 the corresponding period of the eighteenth century may 
 be gleaned from the circumstance that the Council of 
 the Royal Society actually the contemporaries of 
 Newton entered upon 1701 with the complaint, more 
 petulant than dignified, that " the discouraging neglect 
 of the great, the impetuous contradiction of the ignorant, 
 
 551 
 
552 PEOGKESS OF CHEMISTRY xvm 
 
 and the reproaches of the unreasonable, had unhappily 
 thwarted them in their design to perpetuate a succession 
 of useful inventions." During the years that followed, 
 the achievements of Newton's successors, Franklin, 
 Dollond, Maskelyne, Canton, Priestley, Hunter, made 
 the Fellows feel that they were not wholly dependent 
 upon the patronage of the great, although, as the battle 
 over the lightning conductors too plainly showed, they 
 were not altogether unmindful of the frowns and re- 
 proaches of the ignorant and unreasonable. 
 
 Let us then try to realise what was the state of 
 things, so far as it may be thought to affect Chemistry 
 and its pursuit, in the year 1800. To begin with, the 
 population of these isles was less than half of what it 
 now is. London contained only about 800,000 persons, 
 and I need hardly say that the whole social and 
 economic conditions of the people were vastly different 
 from what they are to-day. In one respect, at least, 
 the circumstances of this and that time were alike we 
 were at war. But the condition of the nation now is 
 halcyon compared with what it was in 1800. England 
 was then in such straits as she never was before. Her 
 very existence as a nation was at stake. The harvest 
 over a great part of the country had failed. Corn was 
 upwards of 9 a quarter, and famine and pestilence 
 brooded over the land. Whilst Napoleon's attempt at 
 invasion had roused the nation to a defiant and stubborn 
 resistance, the governing classes were torn asunder by 
 party faction and seemingly more eager to secure political 
 supremacy than to devise means to resist the common 
 enemy. 
 
 Under such untoward conditions, it might well be 
 supposed that science would languish and decay. Such, 
 however, was not the case. It is a singular fact, and 
 
xvm DURING THE NINETEENTH CENTURY 553 
 
 the circumstance is not peculiar to our own history, 
 that it is precisely during the lean years during periods 
 of national stress and strain that some of our greatest 
 intellectual triumphs have been won. In the history of 
 Science, and especially of Chemistry, France was never 
 more glorious than during the turmoil which preceded 
 and followed the Reign of Terror, and in our own case 
 never were such chemical triumphs achieved as during 
 the gloomy period covering the dying years of the last 
 century and the opening years of that which is now 
 drawing to its close. 
 
 What, then, was the condition of chemical science in 
 Great Britain in the year 1800? Who were its culti- 
 vators and what were they doing ? Black had died in 
 the preceding November ; Priestley, who had suffered 
 " the slings and arrows of outrageous fortune" in vainly 
 buffeting with the times, had been settled some six 
 years on the banks of the Susquehanna, occupying him- 
 self with his beloved theology and in futile efforts to 
 resuscitate the dying doctrine of phlogiston. For, in 
 1800, phlogistonism had only been scotched in this 
 country. Mr. Kichard Kirwan, President of the Royal 
 Irish Academy and Inspector-General of His Majesty's 
 Mines in the Kingdom of Ireland, had, it is true, some 
 years previously tried conclusions with the French 
 chemists in his Essay on Phlogiston, which had been 
 translated by Mme. Lavoisier, in order to be refuted, 
 point by point, by Lavoisier, Morveau, Laplace, Monge, 
 Berthollet, and Fourcroy. The new theory was, in fact, 
 indebted to this opposition for some of the strongest 
 proofs on which it is founded. The nimble- witted Irish- 
 man found he was no match for this formidable battalion. 
 He confessed himself vanquished, and, as he wrote to 
 Berthollet, laid down his arms. Rather, he might have 
 
554 PROGRESS OF CHEMISTRY xvm 
 
 said, he went over to the enemy, for during the few 
 years of activity which remained to him he preached 
 the new doctrine with all the zeal of the convert, albeit 
 a little restive at times under the tyranny of the nomen- 
 clature it imposed upon the chemical world. National 
 prejudice, and the authority of Priestley and Cavendish 
 no doubt retarded its general adoption in this country. 
 Cavendish, at the close of the last century, was in his 
 sixty-ninth year ; he had ceased to engage in chemical 
 inquiry, although still keenly interested in its progress. 
 James Watt, who played so notable a part in the events 
 which led to the discovery of the composition of water, 
 and younger by some five years than his quondam rival, 
 was no longer actively occupied with chemical specula- 
 tion. Wollaston, as dispassionate and hardly less re- 
 served than Cavendish, was in hig thirty-fourth year, 
 struggling to get together the medical practice which 
 his singularly cold and taciturn manner forbade him to 
 expect. John Dalton, also in his thirty-fourth year, 
 had just resigned his post as tutor at the Manchester 
 Academy, where, as the Trustees were pleased to report, 
 " he had uniformly acquitted himself to their entire, 
 satisfaction in the province of mathematics, natural 
 philosophy, and chemistry," on the spacious salary of 
 80 a year, and was now looking out for pupils in those 
 branches of learning at the rate of two shillings a lesson. 
 Thomas Thomson was twenty-seven ; Andrew Ure, of 
 dictionary fame, was twenty-two the same age as 
 Humphry Davy, who was still at the Bristol Pneumatic 
 Institute, where he had published his Researches, 
 Chemical and Philosophical, chiefly concerning Nitrous 
 Oxide. William Thomas Brande was a lad of twelve ; 
 and little Michael Faraday a child of eight, who lived 
 in a mews near Manchester Square, keeping body and 
 
xvm DUBING THE NINETEENTH CENTUKY 555 
 
 soul together on the weekly loaf he got from public 
 charity, and whiling away his leisure in playing marbles 
 in Spanish Place. 
 
 Of course, the results of the more important chemical 
 investigations of the period were laid before the Royal 
 Society, and were published in the Philosophical 
 Transactions, and subsequently in Nicholson's Journal 
 or Tilloch's Philosophical Magazine. The Society at 
 that time was, and had been for the previous twenty-two 
 years, under the benevolent despotism of Sir Joseph Banks. 
 The other officers were Wegg, Planta, Gray, and Layard. 
 The meetings were held in the evening at eight o'clock, 
 and, of course, for the most part by candle-light, in one 
 of the large rooms in Somerset House, or Somerset 
 Place as it was then termed. The Society had moved, 
 in 1780, from Crane Court into apartments provided 
 for them by the munificence of their patron, George III., 
 and the skill of his architect, Sir William Chambers, 
 which habitation, in the language of the Council, " it 
 was hoped would confer on them an external splendour 
 in some measure proportional to the consideration in 
 which they had been held for more than a century." 
 Hard by was the Crown and Anchor Tavern, where the 
 Royal Society Club held its pious orgies ; the expense 
 of the dinner was limited to five shillings, and black 
 puddings were a standing dish. It is evident that the 
 drowsy philosophers did no violence to their digestion 
 by a too prolonged attention to the intellectual fare of 
 the evening, for even a comparatively short communica- 
 tion not unfrequently occupied two if not three sittings. 
 The President, when in town, lived in the then fashion- 
 able neighbourhood of Soho Square. Cavendish's town 
 house was at the corner of Montague Place and Gower 
 Street, and from here he might be descried, in a faded 
 
556 PKOGRESS OF CHEMISTKY xvm 
 
 violet court-dress, frilled shirt-front and wrists, with a 
 greatcoat of grayish-green, and a three-cornered cocked 
 hat over his knocker-tailed periwig, slouching along, 
 one hand behind his back, on the way to his library in 
 Dean Street, Soho. Wollaston lived in Hunter Street, 
 Brunswick Square, and subsequently in Dorset Street, 
 Manchester Square ; Smithson Tennant oscillated be- 
 tween his farm at Cheddar and his chambers in the 
 Temple ; and Charles Hatchett resided in the rural 
 district of Hammersmith. Other notable chemical 
 workers at this period were William Henry, of 
 Manchester, William Haseldine Pepys, and Eichard 
 Chenevix. 
 
 There were, of course, other publishing agencies at 
 work, with aims similar to those of the Eoyal Society, 
 such as the Royal Society of Edinburgh, which grew 
 out of a Society founded in 1731 by the leading medical 
 men of that city ; and the Royal Irish Academy, 
 founded in 1782, and of which Kirwan was President 
 for some years. Many of the provincial towns, too, 
 had their Literary and Philosophical Societies, but with 
 the exception of that at Manchester, to which the 
 Henrys and Dalton were frequent contributors, their 
 Proceedings and Transactions contain few important 
 chemical memoirs during the first years of the century. 
 
 Theoretical chemistry was taught in the Universities, 
 and in some of them, following the example set by 
 Black, by means of experimental courses of lectures. 
 At Oxford there had been Beddoes, but his political 
 opinions were distasteful to the University, and he had 
 resigned. At Cambridge there were F. J. Wollaston 
 and Farish. Hope, who first made known the existence 
 of strontia, lectured at Edinburgh ; Robert Cleghorn at 
 Glasgow; and Dr. French, who is credited with the 
 
xvm DUKING THE NINETEENTH CENTUKY 557 
 
 saying that " Humphry Davy was a verra troublesome 
 person in chemistry," taught at Aberdeen. Moreover, 
 almost every large town had one or more teachers men 
 of the type of Varley, Garnett, and Aikin who gave 
 lessons at their private houses. Faraday relates how, 
 during his bookbinding days, his master allowed him 
 to go occasionally of an evening to hear the lectures 
 delivered by Mr. Tatum, at his house in Dorset Street, 
 of which he obtained knowledge by bills in the streets 
 and shop windows. The hour was eight o'clock in the 
 evening, and the charge was one shilling. More 
 ambitious or more self-important people than Mr. 
 Tatum announced their prospective courses among the 
 Miscellanea of Tilloch's or Nicholson's Magazines. 
 Thus, Dr. Beddoes informs the world that his " Lectures 
 are to be calculated for both sexes and different ages ; 
 and that there may be little chance of exclusion by 
 reason of narrow circumstances, the subscription is fixed 
 at one guinea ; but unless fifty persons shall have 
 entered their names by the 31st of March, the Lectures 
 will not go on, as without a tolerably numerous audience, 
 Dr. B. thinks he could bestow his time in a manner 
 more advantageous to the public." 
 
 The principal manuals of the time were Kerr's trans- 
 lation of Lavoisier's Elements ; Chaptal's Elements, the 
 standard text-book on applied chemistry ; Parkinson's 
 Chemical Pocket-book or Memoranda Chemica; Heron's 
 Elements ; Brisson's Physical Principles of Chemistry ; 
 Accum's System of Theoretical and Practical 
 Chemistry ; and Marcet's Conversations. 
 
 The first two decades of this century are unquestion- 
 ably the most momentous and the most brilliant of any 
 period in the history of chemistry in our country. They 
 witnessed the establishment of the fundamental laws of 
 
558 PROGRESS OF CHEMISTRY xvm 
 
 chemical combination and the atomic theory ; the dis- 
 covery of the so-called gaseous laws and of the real 
 nature of the atmosphere ; the application of voltaic 
 electricity as an analytic agent ; the isolation of the 
 metals of the alkalis and of the alkaline earths ; the de- 
 termination of the chemical nature of the halogens ; and 
 in the discovery of tantalum, palladium, iridium, osmium, 
 and rhodium a considerable addition to the list of the 
 metallic elements. These, in 1802, were only twenty- 
 three in number, as against about sixty at the present 
 time. 
 
 A number of new compounds were brought to light 
 or identified during the same period such as fulminat- 
 ing mercury and fulminating silver, carbonic oxide, 
 acetylene, phosgene gas for the most part substances 
 deemed at the time of their discovery to be merely 
 chemical curiosities, incapable from their very nature 
 of being turned to useful account, but all of which 
 are now of important practical application. The same 
 period witnessed the invention of the reflecting gonio- 
 meter and of the miner's safety lamp. It saw the 
 establishment of gas-lighting, and with it the creation 
 of an industry which has exercised a profound effect on 
 the development of the chemical arts. It saw, too, the 
 first attempt to control, by the aid of chemical analysis, 
 the hygienic character of the drinking water supplied 
 to a large community. The statement, in 1808, of 
 Dr. Andrew Ure, who became Professor of Chemistry in 
 Anderson's College in 1818, that the water from the 
 wells in Glasgow, which were then the chief sources of 
 supply, contained "a surprising quantity of heterogeneous 
 matters in solution," paved the way for the action of 
 Telford and Kobertson Buchanan in bringing in " the 
 inexhaustible supply from the river Clyde by means 
 
xvm DURING THE NINETEENTH CENTUEY 559 
 
 of pipes and steam-engines." In the Philosophical 
 Magazine for 1808 we read that this was the first 
 occasion on which the whole of a public supply was 
 filtered " by means of reservoirs constructed for the 
 purpose. . . . This salutary process is effected by 
 making the water filter through sand and gravel from 
 the large reservoir into which it is first elevated by the 
 steam-engine into a second reservoir posited a little 
 lower and from which the conveying-pipes receive their 
 supply. " It is not often that Glasgow is willing to take 
 a lesson from Paisley, but it is interesting to read that 
 a Paisley * buddy ? first practised the filtration of water 
 intended for public supply, and it is satisfactory to learn 
 further that " this public spirited adventurer was amply 
 remunerated for his expenditure." 
 
 The promulgation of the atomic theory and the 
 importation of the ideas of constancy of chemical com- 
 position and of definite numerical ratio gave an 
 immediate impetus to analytical chemistry, of which 
 the operations were at length seen to be subject to 
 a numerical check and control hitherto unknown and 
 barely suspected. Whilst the reflecting goniometer, on 
 the one hand, served to define the geometrical form of a 
 substance and to establish the constancy of that form 
 with a precision unattainable by the graphometer of 
 Carangeau, the balance, on the other, rendered more and 
 more perfect, in response to the demands of the chemist 
 upon the mechanician, in order to satisfy the conditions 
 imposed by the fundamental laws of Dalton's hypothesis, 
 served to determine its exact atomic composition. The 
 first use to which Wollaston, in 1810, put his reflecting 
 goniometer was to measure with exactitude the primary 
 angles of calcspar, the composition of which had been 
 accurately ascertained by Kichard Phillips in 1803. A 
 
560 PROGRESS OF CHEMISTRY xvm 
 
 number of compounds indeed had their real nature and 
 composition established during this period, and in the 
 light of the atomic theory. In fact, the memoir by 
 Thomson on the Oxalates (Phil. Trans. 1808), and that 
 by Wollaston " On super-acid and sub-acid Salts " (Phil. 
 Trans. 1808), were of the greatest service as proving 
 the validity of Dalton's theory of chemical combination. 
 Smithson Tennant analysed emery ; Hatchett ascertained 
 the composition of magnetic pyrites ; Chenevix that of 
 the arseniates of copper and iron, and of bournonite ; 
 Thomson that of sodalite, fluorspar, and allanite. 1 
 Edward Clarke, of Cambridge, analysed petalite, gehlen- 
 ite, the purple of Cassius, and examined the newly - 
 discovered metal cadmium and its salts. 
 
 It would be impossible to exaggerate the influence 
 which the discoveries of the first twenty years of the 
 century exerted on the spirit of the age. They seemed, 
 indeed, to presage a new era the coming of a glorious 
 day of which the dawn had already begun. No 
 generalisation was more opportune in its announcement 
 than that of Dalton ; it was indeed, to use the common 
 phrase, " in the air " ; the teaching of a long succession 
 of philosophers and the experimental labours of many 
 workers had paved the way for its acceptance, and it is 
 practically certain that had Dalton not formulated it, 
 Wollaston or Berzelius would have done so. As it was, 
 each of these distinguished men was almost immediately 
 able to supply the strongest experimental proof of its 
 soundness. Wollaston, from the outset, was well aware 
 of the limitations of Dalton's explanation of the facts 
 of chemical combination ; and he recognised that the 
 arithmetical relation alone of the proportions of 
 
 1 Allanite, in addition to cerium, contained, as he supposed, a new metal 
 which he proposed to distinguish by the name of "junonium." 
 
xvm DUEING THE NINETEENTH CENTUEY 561 
 
 elementary atoms is insufficient to explain their 
 mutual action. As he says, " we shall be obliged to 
 acquire a geometrical conception of their relative 
 arrangement in all the three dimensions of solid exten- 
 sion." How Berzelius received the news of Dalton's 
 discovery he has himself related in his memorable paper 
 in Gilbert's Journal. This view of the combinations of 
 bodies, he says, " appeared capable of illustrating so 
 greatly the doctrine of affinity, that the confirmation of 
 Dalton's hypothesis seemed to be the greatest step that 
 chemistry, as a science, would have made during the 
 whole time of its existence." How it was confirmed by 
 Berzelius it is not necessary here to state, nor need we 
 set out in detail how the whole course of modern 
 chemistry, however complex and many-sided it may 
 seem, is really one vast elaboration of the atomic theory : 
 in fact, as Liebig has said, all our ideas are so interwoven 
 with that theory that it is difficult to carry ourselves 
 back to the time when it did not exist. Dalton was the 
 first recipient of one of the Koyal medals which the 
 Sovereign, on the recommendation of the Eoyal Society, 
 annually bestows, and no more just award was ever 
 made. Davy, in making known, as he said, " this first 
 testimony of royal benevolence to science," stated that 
 this discovery of the simple principle, universally ap- 
 plicable to the facts of chemistry, laid the foundations 
 for future labours respecting the sublime and tran- 
 scendental parts of the science of corpuscular motion. 
 Dalton's merit, in this respect, resembles that of Kepler 
 in astronomy. " The causes of chemical change are as 
 yet unknown, and the laws by which they are governed ; 
 but in their connection with electrical and magnetic 
 phenomena there is a gleam of light pointing to a new 
 dawn in science ; and may we not hope that in another 
 
 2 o 
 
562 PKOGKESS OF CHEMISTKY xvm 
 
 century, chemistry having, as it were, passed under the 
 dominion of the mathematical sciences, may find some 
 happy genius, similar in intellectual powers to the 
 highest and immortal ornament of this Society, capable 
 of unfolding its wonderful and mysterious laws." 
 
 Volta's famous letter of 20th March 1800 to Sir 
 Joseph Banks, was as the " order of the day " of a great 
 leader. No more momentous document was ever given 
 to the scientific world. " The voltaic battery," said 
 Davy, in one of his characteristically happy phrases, 
 " was as an alarm-bell to experimenters in every part of 
 Europe ; and it served no less for demonstrating new 
 properties in electricity, and for establishing the laws 
 of this science, than as an instrument of discovery in 
 other branches of knowledge ; exhibiting relations be- 
 tween subjects before apparently without connection, 
 and serving as a bond of unity between chemical and 
 physical philosophy." 
 
 It is not necessary here to dilate upon what this 
 " instrument of discovery " in the hands of our country- 
 men has done for the development of chemistry. April 
 30, 1800, when Nicholson and Carlisle first effected 
 the decomposition of water by electrolysis, is a red- 
 letter day in the history of our science. The Trans- 
 actions of the Royal Society ', Nicholson 's Journal, and 
 the Philosophical Magazine in the first years of the 
 century show with what ardour and with what a lively 
 expectancy "the new galvanic apparatus of Mr. Volta" 
 was applied. 1 
 
 Although even as far into the century as the date 
 of Waterloo the theory of the compound nature of 
 
 1 This at the time was usually constructed of plates of silver and zinc, with 
 intervening pieces of cloth. "Most of our philosophers, " we are told, "have 
 used half-crowns for the silver plates," and zinc could be bought at 8d. per Ib. 
 at the White Lion in Foster Lane, and cast in moulds of chalk. 
 
xvm DUKING THE NINETEENTH CENTUEY 563 
 
 water was regarded by some as " nothing more than a 
 fanciful conjecture " and " a bare assertion without any 
 proof whatever," there can be no question that Nichol- 
 son and Carlisle's discovery was of the greatest service 
 in affording what was then, and long subsequently, 
 looked upon as one of the strongest analytical proofs 
 of the validity of the fact. But in their effect upon the 
 popular imagination these discoveries altogether paled 
 before that of Davy. The isolation of potassium is, 
 in reality, one of the most dramatic episodes of an 
 epoch fruitful in striking incidents. The remarkable 
 nature of the substance itself, its intense chemical 
 activity, its significant chemical relationships, and the 
 astonishing and far-reaching possibilities which its very 
 existence seemed to open out, were all calculated to 
 impress the minds of virtuosi and vulgar alike. Davy's 
 triumph, indeed, was regarded as the realisation of a 
 confident anticipation that the most important dis- 
 coveries in chemistry were about to be made by the 
 help of galvanism an anticipation which found ex- 
 pression in almost every issue of the scientific journals 
 of the time. There is little wonder, therefore, that a 
 succession of scientific events of such magnitude as 
 those which characterised the opening years of this 
 century should have powerfully excited the imagina- 
 tions of all cultured persons, and that optimists in 
 every country, under the sway of ideas which made up 
 the social and political philosophy of the time, should 
 look forward in sure and certain hope to the immediate 
 advent of a new era to the coming of a regenerated 
 humanity in a golden age. Thus Christopher Gir- 
 tanner, of Gottingen, whose name lives only in connec- 
 tion with the fact that he was the first German chemist 
 to appreciate and teach the new doctrines of the French 
 
564 PROGRESS OF CHEMISTRY xvm 
 
 School, was convinced that in the nineteenth century 
 the transmutation of the metals would be generally 
 known and practised. " Every chemist," he says, 
 " every artist, will make gold ; kitchen utensils will be 
 of silver, and even gold. . . . There will be no other 
 riches than natural riches the productions of the 
 soil ; artificial riches, such as gold, silver, and paper 
 money, will vanish in the hands of those who have 
 accumulated them. What a revolution in society ! 
 Every enlightened chemist, however, will agree with 
 me that this revolution is not only probable, but at no 
 great distance. " Unhappily for Dr. Girtanner's reputa- 
 tion as a prophet, the social revolution he foretold may 
 not be reckoned among the achievements of the nine- 
 teenth century. Enlightened chemists still appear to 
 have an eye to artificial riches, not scorning even paper 
 money ; and although, unfortunately, the precious metals 
 do occasionally vanish in our hands, it is not because 
 we convert them into kitchen utensils. 
 
 Even the sober-minded Faraday was not insensible 
 to the visions thus created. In the course of his lectures 
 on the metals, given in 1818 to the City Philosophical 
 Society, he says, " to decompose the metals, then to 
 reform them, to change them from one to another, and to 
 realise the once absurd notion of transmutation, are the 
 problems now given to the chemist for solution. Let 
 none start at the difficult task, and think the means far 
 beyond them. Let us but look to the means which 
 have given us these bodies, and to their gradual develop- 
 ment, and we shall then gain confidence to hope for 
 new and effective powers for their removal from the 
 elementary ranks. . . . Consider the improvement when, 
 by a variety of manipulations, the early chemist of the 
 last century separated a small quantity of a metallic 
 
xvm DUKING THE NINETEENTH CENTUEY 565 
 
 substance from five or six other bodies, where it existed 
 in strong combination, and then passed to the perfection 
 of these means as exhibited in the admirable researches 
 of Tennant and Wollaston ; lastly, glance but at the 
 new, the extraordinary powers which the chemist of our 
 own nation put in action so successfully for the reduction 
 of the alkalies and earths, and you will then no longer 
 doubt that powers still progressive and advanced may 
 exist and put at some favourable moment the bases of 
 the metals in our hands." 
 
 It is interesting to note that even as far back as 
 1806 an effort was made to form a Chemical Society 
 independent of the Koyal Society, to be called the 
 London Chemical Society, but it received scant en- 
 couragement from persons in high places, and few 
 chemists of note joined its ranks. Sir Joseph Banks, 
 indeed, frowned down upon all such attempts. " I see 
 plainly," he once said, " that all these new-fangled 
 associations will finally dismantle the Royal Society, 
 and not leave the old lady a rag to cover her." And 
 the frown of the masterful old President meant social 
 ostracism to all who chose to disregard it. But, unlike 
 his predecessor, Sir John Pringle, who, on a certain 
 memorable occasion, confessed to George III. that he 
 was unable to reverse the laws and operations of nature, 
 and was then told he had better resign, Banks, if he 
 could not reverse, could at least control and modify a 
 natural tendency, and with the aid of Wollaston, Davy, 
 Hatchett, and Brande he managed to keep chemistry 
 for a time almost exclusively under the cloak of " the 
 old lady." 
 
 Priestley died on 9th February 1804. Although he 
 lived long enough to have read of Dalton's explanation 
 of the laws of chemical combination, as explained in 
 
566 PKOGKESS OF CHEMISTKY xvm 
 
 Thomson's System, and although he must have heard of 
 the electrolytic decomposition of water by Nicholson 
 and Carlisle in 1800, nothing apparently could shake 
 his conviction of the essential and inherent truth of the 
 conception of phlogiston. The last of his published 
 writings was his memoir on " The Doctrine of Phlogiston 
 established, and that of the Composition of Water re- 
 futed." Tolerant and receptive as he was in all other 
 matters of opinion, and especially in matters of religious 
 belief, he seemed utterly incapable of appreciating the 
 real significance of the rapidly accumulating mass of 
 facts, or of drawing any correct inferences from them. 
 
 Cavendish, " le plus riche de tous les savants et pro- 
 bablement aussi le plus savant de tous les riches," died 
 in 1810. His work belongs to a preceding age, for on 
 the downfall of phlogistonism he had ceased to occupy 
 himself with chemical pursuits, and it must ever remain 
 doubtful how far he gave in his adhesion to the new 
 doctrine to which his own cardinal discovery so largely 
 contributed. 
 
 In the year 1815 appeared in Thomson's Annals of 
 Philosophy (vi. 321) an anonymous essay "On the 
 Kelation between the Specific Gravities of Bodies in 
 their Gaseous State and the Weights of their Atoms," 
 which the author states he submits " to the public with 
 the greatest diffidence ; for, although he has taken the 
 utmost pains to arrive at the truth, yet he has not that 
 confidence in his abilities as an experimentalist as to 
 induce him to dictate to others far superior to himself 
 in chemical acquirements and fame." With this modest 
 preamble the author proceeds to discuss certain conse- 
 quences which seem to him to follow from the doctrine 
 of volumes as first generalised by Gay Lussac. The 
 paper is remarkable, in spite of its errors and crudities, 
 
xvm DUKING THE NINETEENTH CENTUKY 567 
 
 for its originality and lucidity. Its author was eventu- 
 ally discovered to be William Prout, then a young 
 medical student, who lived to become eminent as a 
 physiological chemist. His work thus tentatively put 
 forward has become classical as containing or, rather, 
 suggesting, the hypothesis that the atomic weights of 
 the elements are multiples of that of hydrogen. For it 
 is noteworthy that the paper nowhere contains in explicit 
 terms the statement of what is now known as Prout's 
 law. Its main purpose was to set out more clearly 
 than had hitherto been perceived the relation between 
 the doctrine of gaseous volumes and of atoms, and it is 
 only incidentally remarked that he " had often observed 
 the near approach to round numbers of many of the 
 weights of the atoms," and that " Dr. Thomson appears 
 also to have made the same remark." He further points 
 out that it would appear from his tables " that all ele- 
 mentary numbers, hydrogen being considered as 1, are 
 divisible by 4, except carbon, azote, and barytium, and 
 these are divisible by 2, appearing, therefore, to indicate 
 that they are modified by a higher number than that of 
 unity or hydrogen. Is the other number 16 or oxygen ? 
 And are all substances compounded of these two 
 elements ?" Prout's "law" has been frequently so stated 
 as to imply that all substances are " compounded " of 
 hydrogen. But, as will be seen, his own words convey 
 no such idea. 
 
 It is not improbable that the idea that all atomic 
 weights were actually integers would have attracted 
 little, if any, attention, had it not been adopted by 
 Thomson and given currency by means of his System 
 of Chemistry, then, and for some years subsequently, 
 one of the leading British text-books. 
 
 Smithson Tennant, Professor of Chemistry in the 
 
568 PKOGKESS OF CHEMISTEY xvm 
 
 University of Cambridge, a man who, it was said 
 in Johnson's well-known words, is " to be mentioned 
 with reverence rather for the possession than the 
 exertion of uncommon abilities/' died in 1815 acci- 
 dentally killed whilst riding in the neighbourhood of 
 Boulogne. Born at Selby in 1761, and a pupil of 
 Black, he was early attracted to the study of chemistry, 
 which he continued to prosecute at Cambridge as a 
 Fellow Commoner of Christ's College. His private 
 fortune exempted him from the necessity of following 
 actively any profession. Although a man of wide 
 reading, and of a quick and active mind, we are told 
 that there was a singular air of carelessness and indiffer- 
 ence in his habits and mode of life, his manners, 
 appearance, and conversation being the most remote 
 from those of a professed student. " His college rooms 
 exhibited a strange, disorderly appearance of books, 
 papers, and implements of chemistry, piled up in heaps, 
 or thrown in confusion together." He was fond of 
 foreign travel, and in the course of one of his journeys 
 made the acquaintance of Scheele, for whom he had a 
 high admiration. He was also on terms of friendship 
 with many of the leading French chemists of his time. 
 Chemistry in Germany at this period was a mixture of 
 science and credulity, the philosopher's stone was 
 spoken of with respect, and Tennant relates that he 
 received from a man of science and character an 
 introduction to a person who was reputed to be in 
 possession of that treasure, with whom he conversed in 
 Latin, and who exhibited to him the mysterious powder, 
 " enlarging upon its transcendent qualities with much 
 pomp, and in flowing and sonorous periods." 
 
 Tennant is best known for his analysis of carbon 
 dioxide, his work on the nature of the diamond, and on 
 
xvm DURING THE NINETEENTH CENTURY 569 
 
 the injurious effects of magnesia in agriculture, his 
 chemical examination of emery, and his discovery of 
 iridium so-named from the various colours of its 
 solutions, and osmium which owes its name to the 
 smell of certain of its oxides. In the course of an 
 inquiry by a Committee of the Koyal Society, formed 
 at the request of the Government to investigate the 
 danger that might attend the general introduction of 
 gas-lighting in the metropolis, he made the observation 
 that flame will not pass through small tubes, a discovery 
 which in the hands of Davy led to the invention of the 
 safety lamp. 
 
 The third decade of the century saw the rise of 
 Faraday, Graham, and Edward Turner. Faraday had 
 thrown up bookbinding in 1813, and attached himself 
 to the Koyal Institution, getting his " baptism of fire " 
 in working upon Dulong's newly-discovered nitrogen 
 chloride, which was then occupying Davy's attention. 
 He assisted Davy, too, in his work on iodine, on the 
 torpedo, on the nature of the diamond, on euchlorine, 
 and on the chlorides of phosphorus ; and in his memoir 
 on " Some combinations of Phosphorus " the master 
 pays a well -merited tribute to the "accuracy and 
 steadiness of manipulation of his assistant." 
 
 Although Davy had propounded his proofs of the 
 elementary nature of chlorine as far back as 1810, and 
 although these had been strengthened by his work on 
 iodine in 1814, his doctrine was not universally accepted, 
 the Scotch teachers in particular, notably Murray and 
 Ure, even as late as 1818, making repeated and deter- 
 mined attempts to subvert it. Faraday did yeoman 
 service in repelling the attack, which eventually de- 
 generated into a wordy warfare between Murray and 
 John Davy. 
 
570 PKOGRESS OF CHEMISTRY xvm 
 
 With the beginning of 1820 Faraday may be said to 
 have served his apprenticeship to science. He had 
 already contributed some two-score notices and papers 
 to the Quarterly Journal of Science, and had published 
 his remarkable work with Stodart, a surgical instrument- 
 maker, on wootz and other alloys of steel. He had 
 discovered tetrachlorethylene, perchlorethane and ethy- 
 lene di-iodide, an account of which constitutes his first 
 paper in the Philosophical Transactions, and shortly 
 afterwards he described, with Richard Phillips, a new 
 compound of chlorine and carbon, first observed by 
 Julin, of Abo, and now known as hexachlorobenzene. 
 In 1823 appeared his memorable paper "On fluid 
 chlorine," and immediately afterwards were liquefied 
 hydrogen chloride, sulphur dioxide, carbon dioxide, 
 sulphuretted hydrogen, euchlorine, and nitrous oxide. 
 It should be stated, however, that Monge and Clouet 
 had already condensed sulphur dioxide, probably before 
 the year 1800, and that Northmore, with the assistance 
 of Accum, had obtained liquid chlorine in 1806 by 
 compression at ordinary temperatures (Nicholson's 
 Journal, 12 and 13). Northmore's description of the 
 properties of liquid chlorine is so explicit that it is 
 remarkable that the significance of his observation 
 should have escaped notice. The name and fame of the 
 Royal Institution are indissolubly connected with the 
 work so auspiciously begun by Faraday, and with the 
 liquefaction and solidification of air and hydrogen by 
 my predecessor in this chair this chapter in the history 
 of physical science closes with the closing years of the 
 century. It will ever be accounted among the triumphs 
 of the nineteenth century that it has effected the removal 
 of those artificial boundaries the hard-and-fast lines of 
 demarcation implied by terms which have now no 
 
xvm DUKING THE NINETEENTH CENTUEY 571 
 
 other rational meaning than as denoting states of 
 physical aggregation. Nor will it be forgotten that it 
 is largely to the labours of our countrymen, Dalton, 
 Faraday, Andrews, and Dewar, that this achievement is 
 to be ascribed. 
 
 In 1825 Faraday discovered benzene. He found it 
 among the products furnished by the operations of the 
 Portable Gas Company. Although he ascertained that 
 the density of its vapour was 39, hydrogen being 1, 
 the significance of that circumstance was not perceived 
 at the time. The work of Ampere and Gay Lussac, 
 in fact, was not really understood or appreciated at 
 this period, and the conception of Avogadro lay 
 dormant. " With regard to the composition of this 
 substance," wrote Faraday, " my experiments tend to 
 prove it a binary compound of carbon and hydrogen, 
 two proportionals of the former element being united to 
 one of the latter." What Faraday's bicarburet of 
 hydrogen has developed into need not now be told. 
 The work which has accumulated round this single 
 substance during the seventy-five years which have 
 elapsed since it has been known constitutes one of the 
 most astonishing records of intellectual and industrial 
 activity of which history has any record. 
 
 Faraday's next contribution to aromatic chemistry 
 consisted in a study of the action of sulphuric acid on 
 naphthalene, or " naphthaline " as it was then termed 
 a name which we owe to Dr. John Kidd, who lectured 
 on chemistry at Oxford in the early part of the century, 
 and who accurately described the main properties of the 
 hydrocarbon, which appears to have been first observed 
 in 1819 by Alexander Garden, of Old Compton Street, 
 Soho, where the London Chemical Society had its 
 habitation. The products obtained by Faraday are 
 
572 PEOGKESS OF CHEMISTRY xvra 
 
 now known as a- and /3-naphthalenesulphonic acids, the 
 salts of which he described. It is noteworthy that in 
 this year (1826) the Friday evening discourses at the 
 Royal Institution were instituted by Faraday, with a 
 view, as he says, to facilitate our object of attracting 
 the world and making ourselves, with science, " attrac- 
 tive to it," and that this work on naphthalenesulphonic 
 acid was the subject of the first chemical discourse of 
 the series. Unpromising as it might seem, we may be 
 quite sure that Faraday made it attractive. 
 
 Although Faraday continued to occupy himself at 
 times with chemical subjects, even to the end of his 
 tenure of the Fullerian professorship at the Royal Insti- 
 tution, he gradually became more and more absorbed 
 in those memorable physical researches with which his 
 name will ever be associated. The more important 
 portion of his chemical work was practically all done 
 before the end of 1826, and, curiously enough, one of 
 the last inquiries with which he concerned himself in 
 that year serves to connect him with Graham, whose 
 services to science began in that year. It happened 
 that Faraday, in 1823, had made some observations, 
 perhaps among the earliest ever made, which served to 
 establish what we now know as the transpiration of 
 gases, but their accuracy had been doubted by Davy, 
 who, three years later, repeated them. Davy's experi- 
 ments on this subject constitute, in fact, the last ever 
 performed by him in the laboratory of the Royal In- 
 stitution. Faraday independently repeated the observa- 
 tions of 1823 and established their validity. 
 
 Graham's chief work, of course, lay in the border- 
 land between physics and chemistry. The finite extent 
 of the atmosphere ; the absorption of vapours by liquids ; 
 the law of the diffusion of gases ; the motion of gases ; 
 
xvm DUKING THE NINETEENTH CENTUEY 573 
 
 the diffusion of liquids ; osmotic force ; on liquid trans- 
 piration ; on molecular mobility of gases ; the absorption 
 and dialytic separation of gases by colloid septa ; on 
 occlusion of gases ; hydrogenium however different 
 may be the titles of his papers, all his work centred 
 round conceptions of atoms and molecules and their 
 motions. Of his contributions to pure chemistry, the 
 most important was that " On the arseniates, phos- 
 phates, and modifications of phosphoric acid " the first 
 of his papers sent to the Eoyal Society, to which it was 
 communicated by Edward Turner, whom he succeeded 
 a few years later in the Chair of Chemistry at Univer- 
 sity College. This memoir established the existence 
 of three modifications of phosphoric acid ortho-, pyro-, 
 and meta-phosphoric acid. The first, or ordinary phos- 
 phoric acid, has been known for at least three centuries ; 
 pyrophosphoric acid was discovered by Clark, whom 
 Graham succeeded as Lecturer on Chemistry at the 
 Mechanics' Institute, Glasgow ; metaphosphoric acid 
 was now made known for the first time. The paper is 
 memorable from the circumstance that it first definitely 
 indicated the idea of basicity. 
 
 Graham's memoirs on the part played by water as 
 a constituent of salts, and on the constitution of salts, 
 are logically connected with and dependent on this 
 paper. Indeed, nothing is more remarkable in Graham's 
 work than the continuity of idea which pervades it. 
 Just as the long succession of memoirs on the molecular 
 movements of gases and liquids gave a definiteness and 
 precision to the conception of the intestinal motions 
 in matter, so his work on acids and salts served to 
 establish the constitutional analogy between these 
 substances. 
 
 Edward Turner was born in Jamaica in 1798, and 
 
574 PEOGKESS OF CHEMISTRY xvm 
 
 after studying medicine at Edinburgh, passed over to 
 Gottingen, where he worked under Stromeyer. In 1824 
 he became a lecturer in Edinburgh, and here published 
 an Introduction to the Study and Laws of Chemical 
 Combination, which he subsequently worked into his 
 excellent Elements of Chemistry, one of the standard 
 text-books of the time, and by which he is mainly 
 remembered. In 1828 he was made Professor of 
 Chemistry in the newly-created University of London, 
 now known as University College, and died in 1837 in 
 the fortieth year of his age. Among his pupils was the 
 late Sir Richard Quain, who described him as a lucid 
 lecturer and a good analyst. Turner was indeed an 
 excellent manipulator, and his analytical and determina- 
 tive work was of a high order. He is especially to be 
 remembered for his determinations of the atomic weights 
 of lead, chlorine, silver, barium, mercury, nitrogen, and 
 sulphur ; they were the first atomic weights to be 
 accurately ascertained by a British chemist, and are 
 worthy to be ranked with the determinations of Berzelius. 
 Turner's numbers were not only valuable as constants, 
 but they were of theoretical importance as directly 
 impugning the validity of Prout's hypothesis, which, 
 mainly on the authority of Thomas Thomson, who had 
 sought to support it by what is perhaps the weakest 
 experimental evidence ever put forward, was part of the 
 current doctrine of the time in this country. On Thom- 
 son's work Berzelius had passed what is probably the 
 most scathing criticism he ever uttered : " This work 
 belongs to those few productions from which science will 
 derive no advantage whatever. Much of the experi- 
 mental part, even of the fundamental experiments, 
 appears to have been made at the writing desk ; and the 
 greatest civility which his contemporaries can show 
 
xvm DUKING THE NINETEENTH CENTUEY 575 
 
 its author, is to forget that it was ever published" 
 (Jahresber., 1827, 77). 
 
 Turner pointed out (1) that the atomic weights 
 hitherto commonly used by British chemists had been 
 adopted without due inquiry, and that several of the 
 most important ones were erroneous, and (2) that the 
 hypothesis that all equivalents are multiples of a whole 
 number of the equivalent of hydrogen was inconsistent 
 with the state of chemical knowledge at the time, being 
 at variance with experiment. " Under such circum- 
 stances, Dr. Prout's hypothesis, as advocated by Dr. 
 Thomson that all atomic weights are simple multiples 
 of that of hydrogen can no longer be maintained. I 
 grant most willingly that a system of whole numbers, 
 considered as moderate approximations, may, with 
 advantage, be retained for the use of medical men, 
 students, and manufacturers ; but as the strict repre- 
 sentative of scientific truth, applicable to all the purposes 
 of science, this hypothesis is at present untenable. Let 
 me not, however, be misunderstood : I mean simply to 
 affirm that the experiments by which it has been 
 attempted to prove the truth of this hypothesis are 
 inaccurate ; I may go further, and declare it to be not 
 only unsupported by evidence, but to be at variance 
 with the most exact analytic researches which have been 
 conducted. I deny not that some simple relation sub- 
 sists among atomic weights, and that their ratios may 
 possibly be expressed by some series of numbers ; but at 
 present no one has assigned any physical cause for the 
 existence of such a relation ; no such relation has 
 hitherto been discovered ; nor, as it appears to me, has 
 analytical chemistry attained that degree of perfection 
 which can justify any one in finally asserting or denying 
 its existence." The position thus taken up by Turner is 
 
576 PKOGEESS OF CHEMISTEY xvin 
 
 precisely that to which Stas arrived half a century later, 
 after an inquiry which will ever remain a model of 
 analytical skill. 
 
 William Hyde Wollaston died on 22nd December 
 1828, at the age of sixty-two ; Thomas Young on 10th 
 May 1829, aged fifty-six ; and Humphry Davy on 29th 
 May 1829, aged fifty-one. The passing away of three 
 such men in the ripeness of their intellectual vigour and 
 in such quick succession profoundly affected the whole 
 scientific world. They had been colleagues during life, 
 each holding high office in the Councils of the Eoyal 
 Society, and were, with Dalton, the brightest ornaments 
 of one of the most glorious epochs in the history of 
 physical science in this country. At present we are 
 only concerned with Wollaston and Davy. On Davy's 
 triumphs, on his mental powers, and on the characteristics 
 of his genius it is unnecessary now to dwell ; with the 
 exception of that of Dalton, there is probably no 
 personality in the history of British chemistry with 
 which we are more familiar. Wollaston is less well 
 known ; his achievements, indeed, were less calculated 
 to strike the popular imagination than those of his great 
 contemporaries. But this silent, austere man, who lived 
 in and for his laboratory and his library, his only re- 
 laxation being an occasional evening among his fellows 
 at the Eoyal Society Club, or at the gatherings of the 
 Koyal Society, had a wonderfully clear intelligence and 
 an astonishingly penetrative insight. No man ever 
 more justly earned the title of philosopher. He was not 
 so prolific or so diffuse as Priestley, but his learning was 
 infinitely deeper and broader, and there is not a single 
 branch of the science of his day which he did not 
 illumine and adorn chemistry, astronomy, optics, 
 mechanics, acoustics, mineralogy, crystallography, 
 
xviii DUEING THE NINETEENTH CENTURY 577 
 
 botany, physiology, pathology each in turn waa the 
 subject of his intellectual activity. It is, however, only 
 with his chemical work that we have here to do. 
 Keference has already been made to the part which 
 Wollaston's paper, " On super-acid and sub-acid Salts," 
 played in securing attention to the atomic theory ; his 
 " Synoptical scale of chemical equivalents " was of special 
 service to the student and the manufacturer in facilitat- 
 ing the application of the laws of chemical combination 
 to operative chemistry. His " Description of a reflective 
 Goniometer " is a classic in the literature of chemical 
 crystallography and marks an epoch in the history of 
 that subject. His discovery of a process by which 
 platina may be rendered malleable proved of incalculable 
 service to practical chemistry and the arts. Some idea 
 of what that service has been may be gained by recalling 
 what we have secured, and secured only by our crucibles 
 and other vessels of platinum, and by the use of platinum 
 foil and wire, and by imagining what our position 
 would be if we were wholly deprived of these articles. 
 Platinum had been known for some sixty years before 
 Wollaston's time, but as has been stated, "the very 
 properties which made its value certain if it were 
 wrought into vessels, forbade its being easily fashioned 
 into them," and whole cargoes of the native metal are 
 said to have lain unpurchased for years in London, as 
 it could not be turned to account. Wollaston, foiled 
 in his attempts to make a living by medical practice, 
 became, as is well known, rich by his process of working 
 platinum, which he carried on in secret and with the aid 
 of a faithful old servant in his laboratory, a small 
 detached building at the bottom of his garden in Hunter 
 Street, Brunswick Square. 
 
 In the early part of the century the price of 
 
 2 p 
 
578 PKOGKESS OF CHEMISTRY xvm 
 
 manufactured platinum was less than half its present 
 value. In 1805 platinum crucibles were to be obtained 
 from Mr. Carey, 182 Strand, at 17s. 6d. the ounce, 
 whilst wire was 16s. At the time of the foundation of 
 the Chemical Society the price of manufactured platinum 
 had more than doubled. 
 
 Wollaston first made known his process in the 
 Bakerian lecture of 1828 the year of his death and 
 the Council of the Koyal Society " deemed themselves 
 bound to express their strong approbation of this 
 interesting memoir by awarding a Koyal medal to its 
 author, and they anticipate with confidence a general 
 approbation of what they have done." The further 
 development of the metallurgy of platinum in this 
 country is associated with the firm of Johnson, Matthey, 
 and Co., who worked platinum for many years before 
 any other commercial manufactory was established. 
 The process of Wollaston appears to have been first 
 worked, sometime between 1800 and 1808, by Mr. 
 Thomas Cock, a relative of Mr. Percival Johnson, who 
 began the refining and manufacture of platinum in 
 Hatton Garden. 
 
 Wollaston 's name is further connected with the 
 platinum group of metals by his discovery of rhodium, 
 which he published in 1804, immediately after the 
 existence of iridium and osmium had been announced 
 by Smithson Tennant, and also by his discovery of 
 palladium. The manner in which the last-named metal 
 was made known constitutes one of the most singular 
 episodes in the history of scientific discovery, and affords 
 a curious commentary on certain phases of Wollaston 's 
 character. In fact, one or two points in Wollaston's 
 connection with the discovery and working of the 
 platinum metals are somewhat obscure. 
 
xvm DURING THE NINETEENTH CENTURY 5*79 
 
 In 1803 appeared an anonymous circular which was 
 sent to a number of persons, amongst them the editors 
 of Nicholson's and Tilloch's Journals, stating that a new 
 metal palladium or new silver could be purchased 
 from Mrs. Forster, 26 Gerrard Street, Soho, in samples 
 of five shillings, half a guinea, and one guinea each, the 
 price being at the rate of one shilling per grain. Certain 
 of the properties of palladium were given in the ad- 
 vertisement to show that it was " a new noble metal." 
 This announcement attracted the attention of Chenevix, 
 an Irish gentleman, well known as a Fellow of the 
 Koyal Society and for his analyses of certain minerals 
 and for his work on oxygenised and hyperoxygenised 
 muriatic acid. The mode adopted to make known a 
 discovery of so much importance, without the name of 
 any creditable person except the vendor, appeared to 
 Mr. Chenevix unusual in science and not calculated to 
 inspire confidence. Accordingly, with a view to detect 
 what he conceived to be an imposition, Mr. Chenevix 
 procured a specimen and eventually the whole quantity 
 which had been left for sale with Mrs. Forster, who, she 
 stated, was totally unacquainted with the person who 
 brought the metallic substance and the printed paper 
 to her house. Chenevix found all the statements in the 
 paper to be correct with the exception of that of the 
 specific gravity, which he stated to be different by one 
 or two per cent. He made a long and elaborate 
 investigation of the matter, and concluded that the 
 pretended new metal was a combination of platinum 
 and mercury. He sent in his memoir to the Koyal 
 Society, and two evenings were spent in the reading 
 of it. " 
 
 The Journal Book of the Society, the entries of which 
 were made under the direction of the Secretaries, if not 
 
580 PROGRESS OF CHEMISTRY xvm 
 
 actually by them, gives a precis of this paper. We 
 read : " Thus, after having been baffled in his attempts 
 to discover, by analysis, the component parts of this 
 substance, which he (the author) could never bring 
 himself to consider as a new metal, a synthetic process 
 at length led him to the discovery that the whole 
 pretence was an imposition, and that the substance is, 
 in fact, a combination of platina and mercury ; in which 
 the latter, while it masks the most characteristic pro- 
 perties in the former; loses the greater number of its own 
 distinctive qualities. 
 
 " The singular fact that an alloy of two metals should 
 be produced, the specific gravity of which is little more 
 than one-half of what it ought to be by calculation, is, 
 no doubt, worthy of particular attention ; and as quick- 
 silver was in this process brought to a fixed state under 
 circumstances never before observed, a notion might be 
 entertained that the great desideratum in alchemy, the 
 fixation of mercury, was by no means a visionary object. 
 . . . Those who cultivate chemistry with any degree of 
 ardour will be gratified to see in this paper the pains 
 taken by the author, and the various modes he has 
 devised, to produce this compound metal in its most 
 perfect state of combination." 
 
 A few months later the editors of the various scientific 
 periodicals received " under cover of the twopenny 
 post," an unsigned paper offering a reward of 20 for 
 the artificial production of palladium. The editor of 
 Nicholson's Journal says the paper " is written in the 
 same hand as a note which covered a small piece of 
 palladium mentioned to have been received by me last 
 midsummer. Upon inquiry, I find that Mrs. Forster 
 has received the sum of 20 with instructions conform- 
 able to this paper." The paper ran as follows : 
 
xvm DURING THE NINETEENTH CENTURY 581 
 
 December 16, 1803. 
 
 SIR, 
 
 As I see it said in one of your journals, that the new metal 
 I have called palladium, is not a new noble metal, as I have said 
 it is, but an imposition and a compound of platina and quicksilver, 
 I hope you will do me justice in your next, and tell your readers 
 I promise a reward of 20 now in Mrs. Forster's hands, to any 
 one that will make only 20 grains of real palladium, before any 
 three gentlemen chymists you please to name, yourself one if you 
 like. 
 
 That he may have plenty of his ingredients, let him use 20 
 times as much quicksilver, 20 times as much platina, and in short 
 of anything else he pleases to use : neither he nor I can make a 
 single grain. 
 
 Pray be careful in trying what it is he makes, for the 
 mistake must happen by not trying it rightly. 
 
 My reason for not saying where it was found, was, that I 
 might make some advantage of it, as I have a right to do. 
 
 If you think fit to publish this, I beg you to give the names 
 of the umpires, as I have desired Mrs. Forster to keep the money 
 till next midsummer, and to deliver it only in case they can 
 assure her that the real metal is made by a certificate signed by 
 you, and by them, on this check. 
 
 I hope a little bit of whatever is made may be left with Mrs. 
 Forster. 
 
 Mr. Nicholson nominated Hatchett and Edward 
 Howard to join himself as judges of the product which 
 might be made in their presence; but the 20 was 
 never claimed, and in 1805 Wollaston, in a memoir 
 contributed to the Philosophical Transactions, an- 
 nounced that he was the discoverer of the new metal, to 
 which he had given the name palladium, " from the 
 planet which had been discovered, nearly at the same 
 time, by Dr. Olbers." 
 
 What was Wollaston's motive in bringing his dis- 
 covery to the notice of the scientific world in so extra- 
 ordinary a manner can only be surmised. From the 
 
582 PEOGKESS OF CHEMISTKY xvm 
 
 account of his memoir given in the Journal Book of the 
 Society, in which no mention is made of Chenevix and 
 his work, he refers to the " concise delineation of its 
 character" given in the advertisement of the metal, in 
 which he says he " avoided directing the attention of 
 chemists to the source from where it had been obtained, 
 and thereby reserved to himself a more deliberate ex- 
 amination of many phenomena that yet remained unex- 
 plained in the analysis of platina, by which he was 
 subsequently led to the discovery of rhodium." No 
 proper explanation was given of the circumstance that 
 he, as Secretary of the Society, allowed Chenevix's paper 
 to appear in the Transactions. It must have been his 
 duty actually to read this paper at the two meetings 
 when it was brought before the Fellows ; he must also 
 have been responsible for the account which appears in 
 the Journal Book, and which, as one now peruses it, in 
 the light of what subsequently happened, is almost 
 cutting in its sardonic humour and irony. It has been 
 stated that Wollaston did all in his power to persuade 
 Chenevix to withhold or withdraw his paper. Be this 
 as it may, there is no doubt that Chenevix keenly felt 
 the humiliation he suffered. He retired to the Continent, 
 and all his subsequent papers were published in France. 
 In the year of Davy's death, Edward Turner wrote, 
 " The sera of brilliant discovery in chemistry appears to 
 have terminated for the present." Although the number 
 of workers in the science was probably greater than 
 during the first few years of the century, the volume of 
 chemical literature actually produced, judged by the 
 number of contributions to the various societies and to 
 scientific periodicals, had been steadily declining during 
 the previous ten years, and was actually not much more 
 than half what it was in 1802. The work of the first 
 
xvm DUKING THE NINETEENTH CENTUKY 583 
 
 quarter of the century had, in fact, been that of the 
 pioneers, and it was now necessary to secure and con- 
 solidate what had been gained rather than to push on 
 into new territory. " The time is arrived/' continues 
 Turner, "for reviewing our stock of information, and 
 submitting the principal facts and fundamental doctrines 
 of the science to the severest scrutiny. The activity of 
 chemists should now, I conceive, be especially employed, 
 not so much in searching for new compounds or new 
 elements, as in examining those already discovered ; in 
 ascertaining with the greatest possible care the exact 
 ratio in which the elements of compounds are united ; 
 in correcting the erroneous statements to which inac- 
 curate observation has given rise; and exposing the 
 fallacy of opinions which partial experience or false facts 
 have produced." Stoichiometrical considerations were, 
 in fact, becoming of increasing importance. The atomic 
 theory was now a part of the settled doctrine of chemistry. 
 To use the words of Davy, chemistry had now passed 
 under the dominion of the mathematical sciences. The 
 exact numerical relations of the elements and their com- 
 binations, both by weight and by volume, Prout's hypo- 
 thesis and all that it implied, were types of the questions 
 which seemed most urgently to require solution. The 
 idea of stating the course of chemical change with a 
 more mathematical precision than had hitherto been 
 possible is reflected, too, in the attempts which were 
 made at about this period to express such changes by 
 means of equations. Chemical symbols have been used 
 from time immemorial, but the notion of attaching a 
 definite numerical value to them had a rational basis 
 only after the promulgation of the atomic theory. 
 
 Berzelius is usually credited with having been the 
 first to suggest, in principle, the system of notation at 
 
584 PKOGKESS OF CHEMISTRY xvm 
 
 present employed by chemists, although there is a 
 tradition in Glasgow that the merit should be ascribed 
 to Dr. Thomas Thomson. Herschel, in his paper on 
 " Hyposulphurous acid" in the Edinburgh Philosophical 
 Journal for 1819, uses algebraic expressions to describe 
 the reaction between silver nitrate and calcium thio- 
 sulphate. The idea of using a mathematical notation 
 to express the chemical composition of substances and 
 their mutual actions, although in common use in 
 Sweden, France, and Germany, for a time made little 
 progress r: in England, partly from the conservatism of 
 chemists who, like Kichard Phillips, failed to perceive 
 its necessity or convenience, and to whom the language 
 of symbols 
 
 . . . was a Babylonish dialect 
 Which learned chemists much affect ; 
 It is a party-coloured dress 
 Of patch'd and piebald languages ; 
 'Tis English cut on Greek and Latin, 
 Like fustian heretofore on satin ; 
 
 and partly from the strictures of mathematicians, chief 
 among whom was Whewell, who condemned the 
 Berzelian system for what he regarded as its "gross 
 anomalies" and "disfigurements," and its want of 
 " mathematical symmetry and consistency " " a system 
 which violates mathematical propriety so entirely that 
 it must always be disagreeable to see an example of it, 
 for any person who has acquired the first rudiments of 
 algebra." 
 
 Whewell, whose " forte was science, and whose 
 foible was omniscience," of course recognised that a 
 mathematical notation might be of the greatest service 
 in chemistry, and, indeed, could not ultimately be 
 dispensed with, and he made a vigorous attempt " to 
 
xvm DURING THE NINETEENTH CENTURY 585 
 
 purify and improve the foreign system." One of the 
 chief rocks of offence to Whewell was the method 
 adopted by Berzelius of connecting the symbols of the 
 elements to represent compound substances. Chemical 
 combination is essentially an operation of addition, 
 whereas the symbolic notation, if understood algebraic- 
 ally, would indicate that the constituents were multi- 
 plied by each other. There is not much force in this 
 objection, although, as Whewell points out, we probably 
 owe to the symbols being read algebraically the 
 ambiguity of the words factor and product, which are 
 sometimes used to express the ingredients producing 
 a chemical compound by their addition, as well as the 
 compound itself, but which in algebra properly refer 
 to parts producing a number by multiplication. Still 
 more objectionable to Whewell was the use of the sign 
 + ; this he characterised as " a wanton and superfluous 
 violation of analogy." 
 
 Whewell's objections were rather more pedantic than 
 practical. It was pointed out that the juxtaposition 
 of symbols and the employment of an index figure, as 
 practised by Berzelius, would lead the chemist into 
 no error, because their subjects are not susceptible of 
 algebraic powers, or of being multiplied into each other. 
 
 On general grounds, too, Whewell's system failed to 
 commend itself to chemists, even to those who were 
 not unmindful of the mathematical proprieties. It only 
 approximated to mathematical consistency, and failed 
 altogether as regards brevity and clearness. The mul- 
 tiplication of lines and brackets which it entailed, 
 although algebraically just, gave a perplexing appear- 
 ance to the formula, and destroyed its graphic character. 
 The unvarying sign -f alternately with every letter was 
 also objectionable. Whewell, who was not insensible 
 
586 PKOGRESS OF CHEMISTRY xvm 
 
 to these defects in his system, suggested a method of 
 contraction, but the compromise failed to realise the 
 graphic perspicuity of the Berzelian notation, whilst, 
 as an analytical expression, it was inferior to the 
 extended system from which it was evolved. Whewell, 
 moreover, avowedly put it forward as more suitable for 
 the purposes of mineralogy than of chemistry, and the 
 objection was naturally raised that a system which 
 required new contrivances and contractions to suit 
 different points of reasoning, and was so partial and 
 so incomplete an expression of chemical composition in 
 general, was certain to lead to interminable confusion 
 and difficulty. 
 
 The serial chemical literature of the early thirties 
 contains a number of interesting papers on chemical 
 notation, not only by Whewell, but by Phillips, 
 Prideaux, Warington, and Graham, and the merits of 
 the various systems proposed were fairly discussed, with 
 the result that the Berzelian method was at length 
 universally adopted. As an example of the confusion 
 which reigned at the time, we give, from one of Phillips's 
 papers, the composition of common phosphate of soda 
 as expressed in the different systems of notation then 
 in vogue. 
 
 Berzelius . . . . . NaP + 24 Aq. 
 Na 2 IM-24H. 
 
 Graham Na 2 H 24 P. 
 
 Eose NaO + P0 5 + 24HO. 
 
 Whewell . . . . N +p' + 24 q. 
 
 Brande S+#' + 24q. 
 
 Turner So + P + 2jO + 24 aq. 
 
 Johnstone P + So-f24H. 
 
 Prideaux NP + 24 Aq. 
 
 Warington Po + So + 24H. 
 
xvm DUKING THE NINETEENTH CENTUKY 587 
 
 With the exception of Graham, it cannot be said 
 that British or Irish chemists made any very! remark- 
 able contributions to science during the decade from 
 1830 to 1840. The number of workers was doubtless 
 greater than at any previous period of the century. 
 The volume of literature, as measured by the number 
 of papers published, was more than double that of the 
 first decade one of the most momentous periods of our 
 chemical history. But the efforts of workers at the 
 time were spent more on points of detail, on the filling 
 in of little gaps in the chemical structure, as it then 
 existed, than in attempts at new developments. 
 
 Thomas Clark, mainly remembered for his method 
 of determining the hardness of water, and for his 
 discovery of pyrophosphoric acid, was studying the 
 metallurgy of iron. Apjohn, whose name is best known 
 in connection with his formula for determining the 
 dew-point from the indications of the wet bulb hygro- 
 meter, contributed a few papers on mineral chemistry ; 
 Daubeny, a professor of chemistry to botanists, and 
 a professor of botany to chemists, occupied himself 
 principally with geological and botanical chemistry ; 
 Colonel Yorke studied the action of air and water on 
 lead ; Everitt investigated the behaviour of dilute 
 sulphuric acid with potassium ferrocyanide, and dis- 
 covered the salt which is associated with his name ; 
 Johnston made analyses of mineral substances of 
 organic origin, investigated paracyanogen, certain 
 cyanides, and double haloid salts ; Kane analysed a 
 few minerals and inorganic salts, the chlorides of iodine, 
 and studied the action of ammonia on the chlorides and 
 oxides of mercury, the composition of essential oils, and 
 the nature of wood spirit. Penny made a remarkably 
 accurate series of atomic weight determinations of 
 
588 PROGRESS OF CHEMISTRY xvin 
 
 chlorine, nitrogen, potassium, and sodium, which served 
 still further to strengthen the case against the hypo- 
 thesis that all equivalent numbers are simple multiples 
 of that of hydrogen ; and Gregory, the successor of 
 Graham at the Andersonian College, a follower of 
 Liebig, and one of the earliest chemists to introduce his 
 methods into Britain, occupied himself with the study 
 of pharmacological and organic products, the analysis of 
 petroleum, and the destructive distillation of caoutchouc. 
 Other chemical workers at this period were Pepys, 
 Porrett, Edmund Davy, Brooke, Cooper, Daniel, John 
 Mercer, William Herapath, Walter Crum, William West, 
 Hennell, Scanlan, Teschemacher, Hugh L. Pattinson, 
 Warington, Andrews, Richardson, Robert D. Thomson, 
 Denham Smith, Golding Bird, Solly, Fownes, Stenhouse, 
 George Wilson, and Griffin. 
 
 But the general condition of scientific chemistry 
 with us during this period was, no doubt, accurately 
 characterised by Liebig, when he wrote to Berzelius in 
 1837: "leh bin einige Monate in England gewesen, 
 habe ungeheuerviel gesehen und wenig gelernt. England 
 ist nicht das Land der Wissenschaft, es existirt dorten 
 nur ein weitgetriebener Dilettantismus, die Chemiker 
 .schamen sich Chemiker zu heissen, weil die Apotheker, 
 welche verachtet sind, diesen Namen an sich gezogen 
 haben. . . . Graham macht auch in wissenschaftlicher 
 Hinsicht die schatzbarste Ausnahme, er ist ein vor- 
 trefflicher Mensch, auch Gregory, der an seine Stelle in 
 Glasgow gekommen ist." 
 
 It was at this low ebb in our fortunes that the 
 Chemical Society was founded. It might seem, at first 
 sight, an unpropitious time at which to launch a new 
 Society for the purpose of publishing the work of 
 chemical investigators, when chemical investigation 
 
xvni DURING THE NINETEENTH CENTURY 589 
 
 itself was so languidly pursued. But the seventy-seven 
 gentlemen from all parts of the kingdom who enrolled 
 themselves as the founders of the Chemical Society 
 appeared to have had a robust faith in its ultimate 
 success, and in the influence it was bound to exercise 
 in stimulating chemical inquiry in these islands. 
 
 How far their faith was well founded how far 
 indeed this Society has succeeded in stimulating chemi- 
 cal research in this kingdom, I may possibly have an 
 opportunity of showing on some future occasion. I 
 hope also to be able to offer some account of the 
 development of our means of teaching chemistry in this 
 country during the century. 
 
XIX 
 
 ON THE DEVELOPMENT OF THE CHEMICAL 
 ARTS DURING THE REIGN OF QUEEN 
 VICTORIA 
 
 AN ADDRESS DELIVERED AT THE EAST LONDON TECHNICAL COLLEGE, 
 STH FEBRUARY 1897 
 
 ON the 20th of this coming June (1897) all here, I trust, 
 will be celebrating, in some way or other, the sixtieth 
 anniversary of our Queen's accession to the throne ; we 
 shall thus be participators in an event which is unique 
 in the history of this kingdom. Her Most Gracious 
 Majesty's reign will be memorable not only for the 
 number of its years, but for the fact that it is without a 
 parallel in the history of nations in respect to the in- 
 crease in material benefits and in general well-being 
 which it has witnessed. Under the beneficent sway of 
 our Queen this country has advanced by leaps and 
 bounds in those arts which civilisation brings in its 
 train ; knowledge has increased ; the incalculable stores 
 of energy in nature have been drawn upon and turned 
 to account ; every branch of industry has developed, and 
 new and undreamt of forms of it have been created. We 
 have pushed our commerce to the uttermost parts of the 
 earth, and our influence is felt in every region. 
 
 All this need be said in no spirit of vainglory or 
 boasting : it is the plain and simple expression of a fact 
 
 590 
 
xix DEVELOPMENT OF THE CHEMICAL ARTS 591 
 
 which cannot be questioned, which every man and 
 woman in this room knows and feels, and for which in 
 our heart of hearts we each and all are, or should be, 
 profoundly grateful. We know it and we feel it, in that 
 throughout the whole of our waking existence we are 
 constantly witness of what this sixty years of progress 
 means to us all. The general standard of well-being 
 and of comfort has been raised enormously ; and the 
 means to reach and maintain that standard have been 
 multiplied a hundred-fold. What were luxuries to our 
 grandparents are among the necessities of our daily 
 lives : things which to them were marvels and but rarely 
 seen, if seen at all, are the commonplaces of our exist- 
 ence. I do not wish to say that everything is yet of 
 the best and for the best in the best of all possible 
 worlds. There are two periods in a man's life when he 
 is disposed to take, if not an optimistic, at least a 
 cheerful view of things when he is young and ardent, 
 eager and sanguine ; and when he is old, and inclined to 
 rest and be thankful. I am in the unfortunate position 
 of being neither young enough for the one, nor old 
 enough for the other. But I may be allowed to give 
 utterance to this conviction a conviction which is 
 deepened and strengthened when I seek to gain a retro- 
 spect across the span of these sixty years that the man 
 who is insensible to the fact that there is such a thing 
 as an evolution of social order, making for good in the 
 same quiet, gradual, resistless way, as in the evolution 
 in the organic world ; or who fails to perceive that the 
 mutual play of social forces the action and reaction 
 amongst every class of a community blessed with free 
 and enlightened institutions is surely tending to the 
 amelioration of the common lot by the operation of laws 
 as certain in their effect as the law of gravitation itself : 
 
592 DEVELOPMENT OF THE CHEMICAL AKTS xix 
 
 that man is very short-sighted or very ignorant 
 ignorant of the true lessons which sociology teaches 
 or incapable of perceiving their real significance. 
 
 The old Eoman proverb which bids us to hasten 
 slowly is, in matters relating to the social organism, the 
 expression of a profound historical truth. The material 
 fabric is not the less durable because the cementing 
 union between its various sections has taken longest to 
 consolidate. The disintegrating influence of the ages is 
 most surely resisted by those structures which have taken 
 most time to put together, and in which most time and 
 most pains have been spent in adjusting the several parts. 
 
 It seems to me, then, particularly fitting that here 
 in the Queen's Hall, we should on the eve, as it were, of 
 the Queen's Diamond Jubilee, as it has come to be called, 
 seek to trace, it can only be in the broadest possible 
 outline, some of the more significant features in the 
 growth in intellectual and material welfare of Her 
 Majesty's subjects during the threescore years that she 
 has controlled the destinies of her mighty empire. 
 
 Believe me, it is a lofty and inspiriting theme, but all 
 too vast to be dealt with by one poor brain. I am 
 therefore constrained to follow the advice of the old 
 proverb which says that the shoemaker should not go 
 beyond his last, and to confine myself to those matters 
 concerning which it may be thought that by experience, 
 reflection, and reading I may have some little claim to 
 venture upon an opinion. 
 
 It has been said that you may gauge the civilisation 
 of a country by the amount that it spends on soap, and 
 it hardly requires a moment's thought to see the signifi- 
 cance and truth of that remark. Indeed, as I walk 
 along the streets, or ride in omnibuses, or look out 
 of the windows of railway carriages, I am constantly 
 
xix IN QUEEN VICTOKIA'S EEIGN 593 
 
 reminded of the saying, and as my eye lights upon a 
 succession of alluring but obtrusive posters, not always 
 in the best style of decorative art, I console myself with 
 the reflection that after all they are so many appeals to 
 the highest instincts of our nature. I do not, however, 
 now wish to speak of soap in its ethical and moral 
 aspects. For the moment, I take much lower ground. 
 Soap is a manufactured article in the production of 
 which many industries are concerned, and, therefore, if 
 soap is an index of civilisation, the prosperity of the 
 industries concerned in the production is also the out- 
 ward and visible sign of a civilising agency. Now the 
 characteristic of these industries is that they are in the 
 main chemical. I am not conscious of any fault in my 
 logic, even on the restricted basis from which I started, 
 if I claim that the position of the chemical arts in a 
 country is a measure of the material prosperity and 
 civilising power of that country. It is not necessary for 
 me to labour this point. Chemistry and its applications 
 concern us at every turn. There is hardly a single 
 industrial operation which could be named with which 
 this science has not some relations, either proximately 
 or remotely. Whether we are rich or poor, industrious 
 or idle, in health or in sickness, we are beholden to 
 chemistry and the chemical arts for a thousand benefi- 
 cent things. People nowadays have very short political 
 memories, but I daresay there are some in this room who 
 can still recall that oracular utterance in which the late 
 Lord Beaconsfield, from his place of power in Parliament, 
 congratulated the country on the prosperity of its trade 
 in chemicals. A good deal of cheap and harmless chaff 
 was levelled at that statesman in consequence, all of 
 which I have no doubt he took with the serene indiffer- 
 ence and philosophic calm that characterised him. And 
 
 2Q 
 
594 DEVELOPMENT OF THE CHEMICAL ARTS xix 
 
 I venture to think you will agree with me he had good 
 reason for so doing, as there was more wisdom in the 
 remark than the critics of the hour choose to give him 
 credit for. Lord Beaconsfield had a sounder view of 
 what constituted an index of a nation's prosperity than 
 those who sought to make merry at his expense. 
 
 Now it is of the material progress of this country, as 
 manifested by the difference in the position of chemistry 
 and of the chemical arts at the period of the Queen's 
 accession and in their position at present, that I wish to 
 dwell for a few moments. The time at my disposal is 
 far too short to enable me to do more than indicate, as it 
 were, in a few touches and in the very broadest outline, 
 the main points of contrast. Let us throw our mental 
 eye backwards and try and realise the state of things in 
 chemistry, pure and applied, at the time of the Queen's 
 coming to the throne. What was the condition of 
 chemical science in Great Britain in 1837 ? Who were 
 engaged in discovering its truths, and in promulgating 
 its doctrine ? And how were the facts of the doctrine 
 being made subservient to the welfare and material 
 interests of the nation ? To ask a man who is abreast 
 of the chemistry of to-day and if he is abreast he is 
 also in all probability ahead ; that is, he is seeking to 
 push his way beyond the frontiers of contemporary 
 knowledge, to ask such a man to look at chemistry 
 from the standpoint of sixty years ago, and to try and 
 form to himself a mental picture of its condition at that 
 period, is really like asking the historian to jump back 
 into prehistoric times. Chemistry, as an art, has been 
 practised, of course, from time immemorial, and a great 
 variety of chemical products metals, salts, acids, dyes, 
 pigments, were made long before the Christian era, 
 although I must confess that soap is a comparatively 
 
xix IN QUEEN VICTOKIA'S EEIGN 595 
 
 late invention, a fact which, it may be argued, 
 serves to explain the peculiar and restricted character 
 of the ancient forms of civilisation. Chemistry as a 
 science, however, is barely a century old. It is 
 based upon the atomic theory, and the idea of ex- 
 plaining chemical phenomena by the conception of 
 atoms was first clearly and definitely stated by 
 John Dalton during the first decade of this century. 
 The whole course of chemistry, however complex and 
 many-sided it may seem, is really one vast elaboration 
 of the atomic theory. As Liebig has said : "All our 
 ideas are so interwoven with Dalton's theory, that we 
 cannot carry ourselves back to the times in which that 
 theory did not exist. " And yet this fundamental 
 hypothesis, as understood by chemists, had barely come 
 of age when the Queen came to the throne ; it was not 
 much older at the time than she herself. The illustrious 
 philosopher who gave this conception to the world was 
 still living, but stricken down, I regret to add, with the 
 paralytic attack, the beginning of the brain disintegra- 
 tion, which seven years later ended in his death. The 
 great Sir Humphry Davy, a younger man than Dalton, 
 and the pioneer in the vast field of electro-chemistry 
 which to-day is yielding such rich treasure, had only 
 been dead about eight years, and Michael Faraday, of 
 revered memory, blacksmith's son, newspaper boy and 
 bookbinder's apprentice, reigned in his stead at the 
 Koyal Institution. The Fullerian Professor of Chemistry, 
 as he had come to be designated, was then in his forty- 
 fifth year, in the full maturity of his intellectual power, 
 and near the meridian of his scientific fame. But all his 
 work in pure chemistry was practically done, and he was 
 almost wholly engaged upon those great problems of 
 electrical science which have made the extraordinary 
 
596 DEVELOPMENT OF THE CHEMICAL AETS xix 
 
 development of applied electricity as we see it to-day in 
 electrolytic decompositions, in the electric light, and in 
 the applications of electricity as a source of power, alone 
 possible. The Queen, indeed, may be said to have 
 witnessed as Queen the birth of this marvellous applica- 
 tion of natural energy, to have lived with it through its 
 vigorous youth, and to have seen the promise of a 
 fruition so vast that no man can set bounds to it. She 
 might have seen the simple, fundamental, and yet ever- 
 striking experiments out of which has grown the multi- 
 farious machinery that modern industrial electricity has 
 called into existence. Try to realise the difference 
 between Faraday's simple home-made apparatus, his 
 copper discs, his bits of soft iron, wound with wire, 
 insulated with calico and twine, and the mighty dynamos 
 which are converting the energy of "a harnessed 
 Niagara " into heat and light, and chemical action, and 
 supplying power to a continent ! 
 
 And all this within the span of a single reign ; within 
 the compass of a couple of generations ! This astonishing 
 movement is what historians will ever recognise as the 
 characteristic feature of the Victorian Era. It has 
 wholly changed the economic and social condition not 
 only of our own people, but of every country which has 
 had the intelligence and the wisdom to participate in it, 
 or to avail itself of its fruits. It has acted and reacted 
 not only on industry, and on the material benefits that 
 attend on industry, but on every department of intel- 
 lectual power. It has changed, although hardly with 
 a commensurate rapidity, the face of our educational 
 system. To judge what the change has been, let us try 
 to realise how chemistry was taught in 1837. As a 
 part of school education it was practically unknown, 
 although children whose parents had the good fortune 
 
xix IN QUEEN VICTOKIA'S KEIGN 597 
 
 to be influenced by the teaching of such far-sighted men 
 as Mr. Edge worth, had their curiosity stimulated and 
 fed by occasional lectures on science. 
 
 As regards the Universities, at Oxford there was 
 Dr. Daubeny, a prolific writer on volcanoes, and on 
 rural economy. At Cambridge there was Professor 
 Gumming, who, so far as I know, has not enriched 
 the literature of chemistry proper with a single con- 
 tribution. At neither place was there anything in 
 the nature of a laboratory which the student could 
 attend. If the enterprising undergraduate desired 
 to familiarise himself with the facts of chemistry 
 by practical experiment, or to try and work out an 
 idea which might have occurred to him, he had to 
 pursue his inquiries in his own rooms, and with such 
 apparatus as his means or his opportunities could 
 command, to the imminent risk of his furniture, and to 
 the dismay and disgust of his bedmaker. It was under 
 such conditions that the late Sir John Herschel dis- 
 covered the solvent action of what the photographer 
 calls "hypo," and thereby made the photographic 
 calling possible. 
 
 In Scotland, Dr. Hope, whose name carries us back 
 into the preceding century, still enjoyed at Edinburgh 
 the fame as a lecturer which he shared with Davy at 
 the Koyal Institution, but no tuition in practical 
 chemistry was ever thought of. Matters at Glasgow 
 were a little better, and Thomas Thomson would 
 occasionally extend a brusque hospitality to the student 
 who aspired to learn the art and mystery of mineral 
 analysis, but no systematic instruction was ever 
 attempted. The youth with no knowledge of manipula- 
 tive work, and with scarcely an acquaintance with the 
 forms even of chemical apparatus, might be set at the 
 
598 DEVELOPMENT OF THE CHEMICAL AETS xix 
 
 very outset to struggle with a zeolite or grapple with 
 an atomic weight determination as best he might. In 
 London there was the promise of better things. Thomas 
 Graham, who had already made his memorable discovery 
 of the law of gaseous diffusion, whilst Professor of 
 Chemistry at Anderson's College in Glasgow, had 
 followed Ure and Birkbeck to London, and had been 
 elected to the Chair of Chemistry at University College, 
 Gower Street, up to then known as the University of 
 London. Here he created the School of Chemistry 
 which, aided by Fownes and Williamson, he made 
 famous throughout Europe. But it may be doubted 
 whether in 1837 there were more than a couple of dozen 
 persons in the British Isles altogether receiving systematic 
 instruction in practical chemistry, and even that supply 
 was probably fully equal to the demand. There was, in 
 fact, little to tempt men to take up chemistry as a means 
 of livelihood. Teacherships were few in number ; 
 analytical chemistry as a profession hardly existed, and 
 chemical manufacturing was done by rule of thumb, 
 and for the most part very badly done. I have heard 
 chemical manufacturers of two generations ago tell very 
 strange stories of the rough-and-ready manner in which 
 many of their operations were conducted. A vitriol 
 plant, for example, of sixty years ago was a very 
 different thing in point of efficiency from what it now 
 is, and such things as condensing towers in the Leblanc 
 process of converting salt into soda-ash were almost 
 unknown. All the muriatic acid was freely sent into 
 the air, and Government Inspectors never troubled the 
 peace of mind of the manufacturer. If you turn over 
 the pages of the first edition of Ure's Dictionary, or 
 look through the early reports of the British Association 
 all of them works within your own reach and com- 
 
xix IN QUEEN VICTOEIA'S KEIGN 599 
 
 pare the accounts with the specialised treatises some 
 of them almost monumental works, of which the last 
 decade has been prolific you will gain a vivid conception 
 of the vastness of the difference in the character, variety, 
 and volume of the work at the extremes of these sixty 
 years. 
 
 How the state of things appeared to a well-informed 
 and intelligent observer is well illustrated by one of 
 Liebig's letters to Berzelius, in which he recounts his 
 impressions of England, which he had just visited. 
 Under date 26th November 1837, he tells the Swedish 
 chemist that he had been some months in England, had 
 seen a vast amount, and learnt little. England, he 
 says, is not the land of science ; our chemists were 
 ashamed to call themselves chemists because the apothe- 
 caries had appropriated the name. He was extraordin- 
 arily pleased with us as a people, and delighted with 
 our hospitality and welcome, but as regards our chemists, 
 Graham was the most precious exception. " He is an 
 excellent fellow, as also is Gregory, who has succeeded 
 him in Glasgow." 
 
 But a little leaven was leavening the whole lump, 
 and the leaven was Liebig himself. Aided by the far- 
 sighted munificence of the Grand Duke of Hesse- 
 Darmstadt, he had established the little Giessen 
 Laboratory, and thither every aspirant for chemical 
 fame bent his steps. Among the earliest of these 
 chemical pilgrims were Lord Playfair, Sir Henry 
 Gilbert, Professor Williamson, Dr. Gladstone, and 
 others who might be named, some, happily, still 
 amongst us, but many of whom have now passed over 
 to the majority. All these men brought back with 
 them something of the spirit and of the method which 
 have made the little laboratory on the banks of the 
 
600 DEVELOPMENT OF THE CHEMICAL AKTS xix 
 
 Lahn famous in the history of chemistry. This influence 
 has been like the seed which fell on good ground ; it 
 has sprung up and multiplied an hundred-fold. It has 
 made Germany pre-eminent in the world of scientific 
 chemistry, and it has had a profound effect on chemical 
 activity and on the development of chemical teaching 
 in this country. 
 
 One of its first results was seen in the creation in 
 1841 of the Chemical Society a society whose function 
 and privilege it has been to foster by every means in its 
 power the spread of chemical knowledge and chemical 
 inquiry in this country. How it has achieved its 
 purpose may best be seen in the roll of its membership, 
 in the vitality and activity of its meetings, in the long 
 succession and value of its publications, and last, but 
 not least, by the helping hand it extends to the young 
 investigator, by the wise and prudent administration of 
 the funds which have been placed at its disposal by 
 private benefactors and public bodies, among whom I 
 gratefully recall the Drapers' Company. And here I 
 may be permitted to say that among all the benefactions 
 which the Company has scattered broadcast with so 
 generous a hand, there has been none better applied, or 
 been more fruitful in result, than that by which they 
 have thus fostered chemical research. I claim to say 
 this because it is my duty and privilege as the Treasurer 
 of the Chemical Society to aid in the administration of. 
 this fund, and to take note of, as a member of the 
 Committee of Publication, the memoirs and papers 
 which follow from its operation. 
 
 Another notable result of Liebig's influence, and of 
 the awakening which resulted from it in this country, 
 was the foundation in 1845 of the Koyal College of 
 Chemistry, to which Hofmann, one of the favourite and 
 
xix IN QUEEN VICTOKIA'S REIGN 601 
 
 most distinguished pupils of Liebig, was invited thanks 
 to the action of the late Prince Consort. What 
 Hofmann, fired by the example of Liebig and his own 
 innate enthusiasm, did for chemistry in England time 
 will not allow me to dwell as I should like to do. To 
 the chemical students of this place I would say there is 
 no more inspiriting or instructive chapter in the history 
 of chemistry in this country than that which records 
 the work of the.Eoyal College of Chemistry as set forth 
 in that tripartite panegyric of Hofmann the joint work 
 of Lord Playfair, Sir Frederick Abel, and Professor 
 Armstrong which you will find in the Journal of the 
 Chemical Society a publication which doubtless is to 
 be met with on your library shelves. What the Royal 
 College of Chemistry was to British science there are 
 happily many living witnesses to testify. We have still 
 amongst us Sir F. Abel, Dr. Perkin, Mr. Crookes, and 
 last, but not least, Mr. Heywood. Others have passed 
 away, among them Warren de la Rue, Mansfield, How, 
 Medlock, Rowney, Field, Nicholson, Bloxam, Noad, all 
 of whom have left their mark on the development of 
 pure or applied science in this country. But if Hofmann 
 has left us, his spirit and his example still remain and 
 actuate us. This spirit is being carried into a hundred 
 places of chemical instruction and research in these 
 islands to-day. Let us pray that it may continue and 
 increase, for it is on its continuance and growth that 
 the progress of chemical science and chemical industry 
 depends, and in so far as our national prosperity is 
 connected with the progress of the chemical arts, our 
 national prosperity depends on it also. 
 
 Printed by R. & R. CLARK, LIMITED, Edinburgh. 
 
MACMILLAN AND CO.'S 
 
 STANDARD WORKS ON CHEMISTRY 
 
 A COMPLETE TREATISE ON INORGANIC AND ORGANIC CHEMISTRY. 
 By Sir H. E. ROSCOE, F.R.S., and Prof. C. SCHORLEMMER, F.R.S. 8vo. 
 Vols. I. and II. Inorganic Chemistry : Vol. I. The Non-Metallic Elements. 
 New Edition, completely revised by Sir H. E. ROSCOE, assisted by Dr. H. G. 
 COLMAN and A. HARDEN, F.R.S. 21s.net. Vol. II. The Metals. New Edition, 
 completely revised by Sir H. E. ROSCOE and A. HARDEN, F.R.S. 30s. net. 
 Vol. III. Organic Chemistry : The Chemistry of the Hydro-Carbons and their 
 Derivatives. Parts II., IV., and VI. 21s. each. Part III. 18s. 
 
 PRACTICAL CHEMISTRY. By R. ABEGG and Prof. W. HERZ. Translated by 
 
 H. T. CALVERT, B.Sc. Crown 8vo. 6s. 
 MICROCHEMICAL ANALYSIS. By Prof. H. BEHRENS. With an Introductory 
 
 Chapter by Prof. J. W. JUDD, F.R.S. With Illustrations. Crown 8vo. 6s. 
 EXPERIMENTS FOR CHEMICAL LECTURES. By F. G. BENEDICT, Ph.D. 
 
 Crown 8vo. 8s. 6d. net. 
 PRACTICAL ORGANIC CHEMISTRY FOR ADVANCED STUDENTS. By 
 
 Prof. J. B. COHEN. Globe 8vo. 3s. 6d. 
 
 THEORETICAL ORGANIC CHEMISTRY. By Prof. J. B. COHEN. Globe 8vo. 6s. 
 PRACTICAL METHODS OF ORGANIC CHEMISTRY. By LUDWIG GATTER- 
 
 MANN, Ph.D. Translated by W. B. SHOBER. Crown 8vo. 7s. net. 
 BLOWPIPE ANALYSIS. By FREDERICK HUTTON GETMAN, F.C.S. Globe 8vo. 
 
 2s. 6d. net. 
 SYSTEMATIC SURVEY OF THE ORGANIC COLOURING MATTERS. By 
 
 Prof. ARTHUR G. GREEN. Founded on the German of Drs. G. SCHULTZ and 
 
 P. JULIUS. Third Impression. 8vo. 21s. net. 
 THE RISE AND DEVELOPMENT OF THE LIQUEFACTION OF GASES. 
 
 By WILLETT L. HARDIN, Ph.D. Globe 8vo. 6s. 6d. net. 
 METHODS OF GAS ANALYSIS. By Dr. WALTHER HEMPEL. Translated by 
 
 Dr. L. M. DENNIS. Crown 8vo. 10s. net. 
 
 LABORATORY MANUAL EXPERIMENTS TO ILLUSTRATE THE ELE- 
 MENTARY PRINCIPLES OF CHEMISTRY. By H. W. HILLYER, Ph.D. 
 
 8vo. 4s. net. 
 THE THEORY OF ELECTROLYTIC DISSOCIATION AND SOME OF ITS 
 
 APPLICATIONS. By Prof. HARRY 0. JONES. Extra Crown 8vo. 7s. net. 
 THE ELEMENTS OF PHYSICAL CHEMISTRY. By Prof. HARRY C. JONES. 
 
 8vo. 17s. net. 
 INTRODUCTION TO PHYSICAL CHEMISTRY. By Prof. HARRY C. JONES. 
 
 Crown 8vo. 7s. net. 
 PRINCIPLES OF INORGANIC CHEMISTRY. By Prof. HARRY C. JONES. 8vo. 
 
 12s. 6d. net, 
 ELEMENTS OF INORGANIC CHEMISTRY. By Prof. HARRY C. JONES. 
 
 Crown 8vo. 5s. 6d. net. 
 THE SPIRIT OF ORGANIC CHEMISTRY. By ARTHUR LACHMAN. Crown 8vo. 
 
 6s. 6d. net. 
 BLOWPIPE ANALYSIS. By J. LANDAUER. Third Edition. Translated by 
 
 J. TAYLOR, B.Sc. Globe 8vo. 4s. 6d. 
 ORGANIC CHEMISTRY. A Compendium of Laboratory Methods for the use of 
 
 Chemists, Physicians, and Pharmacists. By Dr. LASSAR-COHN. Translated 
 
 by A. SMITH, B.Sc., Ph.D. Crown 8vo. 8s. 6d. 
 A TEXT-BOOK OF ELECTRO-CHEMISTRY. By Prof. MAX LE BLANC. 
 
 Translated from the Fourth Enlarged German Edition by WILLIS R. WHITNEY, 
 
 Ph.D., and JOHN W. BROWN, Ph.D. 8vo. 11s. net. 
 
 MACMILLAN AND CO., LTD., LONDON. 
 
MACMILLAN AND CO.'S 
 
 STANDARD WORKS ON CHEMISTRY 
 
 CHEMICAL TECHNOLOGY AND ANALYSIS OF OILS, FATS, AND WAXES. 
 By Dr. J. LEWKOWITSCH. Fourth Edition, entirely rewritten and enlarged. 
 In three volumes. With Illustrations. Medium 8vo. 50s. net. 
 
 LABORATORY COMPANION TO FATS AND OILS INDUSTRIES. By Dr. 
 J. LEWKOWITSCH. 8vo. 6s. net. 
 
 CHEMISTRY OF THE PROTEIDS. By Dr. GUSTAV MANN. Based on Prof. 
 Cohnheim's "Chemie der Eiweiss Korper." 8vo. 15s. net. 
 
 ANALYTICAL CHEMISTRY. By Prof. A. MENSCHUTKIN. Translated by J. 
 LOCKE. 8vo. 17s. net. 
 
 HISTORY OF CHEMISTRY FROM THE EARLIEST TIMES TO THE 
 PRESENT DAY. By ERNST VON MEYER, Ph.D. Third Edition. Translated 
 by G. McGowAN, Ph.D. 8vo. 17s. net. 
 
 THEORETICAL CHEMISTRY. By Prof. WALTER NERNST, Ph.D. Translated by 
 C. S. PALMER. Re-edited and revised in accordance with the fourth German 
 edition by Dr. R. A. LEHFELDT. 8vo. 15s. net. 
 
 QUALITATIVE CHEMICAL ANALYSIS OF INORGANIC SUBSTANCES. 
 By A. A. NOTES, Ph.D. 8vo. 6s. 6d. net. 
 
 SCIENTIFIC FOUNDATIONS OF ANALYTICAL CHEMISTRY. By Prof. 
 W. OSTWALD. Translated by G. McGowAN, Ph.D. Crown 8vo. 6s. net. 
 
 PRINCIPLES OF INORGANIC CHEMISTRY. By Prof. W. OSTWALD. Trans- 
 lated by Dr. A. FINDLAY. Third Edition. 8vo. 18s. net. 
 
 EXPERIMENTAL PROOFS OF CHEMICAL THEORY FOR BEGINNERS. 
 By Sir WILLIAM RAMSAY, K.C.B. Pott 8vo. 2s. 6d. 
 
 GASES OF THE ATMOSPHERE : THE HISTORY OF THEIR DISCOVERY. 
 By Sir WILLIAM RAMSAY, K.C.B. Third Edition. Extra Crown 8vo. 6s.net. 
 
 A TEXT-BOOK OF INORGANIC CHEMISTRY. By Prof. IRA REMSEN. 8vo. 16s. 
 
 COMPOUNDS OF CARBON ; OR, AN INTRODUCTION TO THE STUDY OF 
 ORGANIC CHEMISTRY. By Prof. IRA REMSKN. Crown 8vo. 6s. 6d. 
 
 COLLEGE TEXT-BOOK OF CHEMISTRY. By Prof. IRA REMSEN. Second 
 Edition. 8vo. 10s. net. 
 
 A NEW VIEW OF THE ORIGIN OF DALTON'S ATOMIC THEORY. By 
 Sir H. E. ROSCOE, F.R.S., and A. HARDEN, F.R.S. 8vo. 6s. net. 
 
 INORGANIC CHEMISTRY FOR ADVANCED STUDENTS. By Sir H. E. 
 ROSCOE, F.R.S., and A. HARDEN, F.R.S. Second Edition. Globe 8vo. 4s. 6d. 
 
 OUTLINES OF INDUSTRIAL CHEMISTRY. A Text-Book for Students. By 
 FRANK HALL THORP, Ph.D. 8vo. 16s. net. 
 
 ESSAYS IN HISTORICAL CHEMISTRY. By Sir T. E. THORPE, C.B., LL.D., 
 F.R.S. Second Edition, enlarged. 8vo. 12s. net. 
 
 THE EXPERIMENTAL STUDY OF GASES. By Dr. MORRIS W. TRAVERS, 
 F.R.S. With Introduction by Sir W. RAMSAY, K.C.B. 8vo. 10s. net. 
 
 INTRODUCTION TO PHYSICAL CHEMISTRY. By Prof. JAMES WALKER, 
 F.R.S. Sixth Edition. 8vo. 10s. net. 
 
 FRACTIONAL DISTILLATION. By Prof. SYDNEY YOUNG, D.Sc., F.R.S. 
 Crown 8vo. 8s. 6d. 
 
 MACMILLAN AND CO., LTD., LONDON. 
 
J 1A- 
 
 RETURN CIRCULATION DEPARTMENT 
 
 202 Main Library 
 
 LOAN PERIOD 1 
 HOME USE 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 
 
 Ttttri 
 
 DUE AS STAMPED BELOW 
 
 SEP 1 
 
 CIRCULATION DEPT. 
 
 MAR 18 
 
 CIRCULATION 
 
 UNIVERSITY OF CALIFORNIA, BERKELEY 
 FORM NO. DD6, 60m, 1 /83 BERKELEY, CA 94720 
 
22305S