550 



^ATURB 



[April 7, 1898 



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 

 January 15, 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. The cir- 

 cumstance is alluded to in a letter from Watt to De Luc, dated 

 November 30, 1783. " I was at Dr. Priestley's last night. He 

 thinks, as I do, that Mr. Lavoisier, having heard some imper- 

 fect 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 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 Royal Society and Cavendish's assistant and 

 amanuensis, who himself told Lavoisier. The whole of the 

 circumstances are set out in detail in a subsequent letter which 

 Blagden addressed to the editor of the Cheviische Amialen in 

 1786. That it was known to be Cavendish's experiment that 

 was being thus repeated, is confirmed by a letter from La Place 

 to De Luc, 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, I'ex- 

 perience de Mr. Cavendish sur la conversion en eau des airs 

 dephlogistiques et inflammables, par leur combustion. . . . 

 Nous avons obtenu de cette maniere plus de 2\ gros d'eau pure, 

 ou au monis qui n'avoit aucun caractere d'acidite, et qui etoit 

 insipide au gout ; mais nous ne savons pas encore si cette 

 quantite d'eau represente le poids des airs consumes ; c'est une 

 experience a recommencer avec toutes I'attention possible et qui 

 me paroit de la plus grande importance." The phrase "qui 

 n'avoit aucun caractere d'acidite " is of special significance. The 

 French philosophers, 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 was, 

 amongst others, 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 June 24, 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 con- 

 stitute 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 June 25, 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 circumstances under which that priority 

 of publication was secured give Lavoisier no moral right to the 

 title of the discoverer.^ 



Shortly after the reading of Cavendish's memoir to the Royal 



1 Priestley, Cavendish, Lavoisier, and " La Revolution Chimique" : l;he 

 Presidential Address to the Chemical Section of the British Association, 

 1890 ; see also " Es5'ays;in Historical Chemistry " (MacmiJlan, iBgn). 



NO 1484, VOL. 57] 



Society (January 15, 1784), De Luc wrote to Watt, giving an 

 account of its contents, and insinuating that its conclusions had 

 been formed in the light of knowledge obtained from Watt's 

 letter to the Royal 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. De 

 Luc was, no doubt, a zealous friend, but in this letter his zeal 

 outran his discretion. The letter was, indeed, unworthy of him. 

 He hastens to exculpate Lavoisier and La Place, but 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 jalotix, 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 a conviction in my own mind that I was their superior : or 

 from an indolence, that makes it easier for 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. 



' ' Vou may, perhaps, be surprised to find so much pride in 

 my character. It does not seem very compatible with the diffi- 

 dence 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 seus tin peu blessd ; 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 connected 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 Da 

 Luc, should be publicly read to the Fellows, and they were 

 subsequently ordered to be printed in the Philosophical Trans- 

 actions 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 Dephl 3- 

 gisticated air : with an account of some experiments on that 

 subject. In a letter from Mr. James Watt, Engineer, to Mr. 

 De Luc, F. R.S." The greater part of the "thoughts" are 

 concerned with the dephlogislicated air. What relate to water 

 have already been given in the extracts from his correspondence. 

 The terms in the letter to De Luc, 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 recog- 

 nition of the true chemical nature of water, and I have stated, as 

 accurately and as impartially as I could, the relative share of 

 Watt, Cavendish and Lavoisier in their discovery and interpre- 

 tation. As regards Lavoisier, it cannot be claimed that he was 

 the first to obtain the facts. To Cavendish belongs the merit of 

 having supplied the true experimental basis upon which accurate 

 knowledge could alone be founded, ■\yatt, on the other hand, 

 although reasoning from imperfect and, indeed, altogether 

 erroneous data, was the first, so far as we can prove from docu- 

 mentary 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 dephlo- 

 gisticated 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 Cavendish 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 experiment" 

 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 timidjty on. the score of that, long-established apd deeply-, 



I 



