770 REPORT—1 890. 
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 février 1784), and on p. 63 we come to the experiment of June 
24, and we read: ‘In presence of Messieurs Blagden, of [name illegible], 
de Laplace, Vandermonde, de Fourcroy, Meusnier, and Legendre, 
we have combined ina bell-jar dephlogisticated air and inflammable 
air drawn fromiron by means of sulphuricacid &c.... 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 lossof two-thirds of the amount of 
the air or that there has been a loss of weight.’ 
And this is the experiment which, according to M. Berthelot, enabled Lavoisier 
to conclude that ‘ the weight of the water formed could not be other than equal to 
that of the two gases which had formed it!’ It is on this single experiment, 
hurriedly and imperfectly done, that Lavoisier’s claim to the discovery of the com- 
pound nature of water is based! M. Berthelot objects to the assumption that it 
was hurriedly done. He says, on p. 114: ‘ Lavoisier caused a new apparatus to be 
made, with a couple of tubes and two reservoirs for the gases; an arrangement 
which would require a certain amount of time to put together; this circumstance 
proves that it could not have been an improvised trial.’ To what extent it was 
improvised will be seen immediately. 
Now although the laboratory journals do not in this case ‘ inform us of Lavoisier’s 
methods, and of the direction of his mind . . . the successive steps in the evolution 
of his private thought, we have other means of ascertaining how he arrived at 
his knowledge. The method was simplicity itself: he was told of the fact, and his 
informant was none other than Cavendish’s assistant, Blagden. 
Cavendish’s memoir was published in 1784. Before 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 him- 
self, he found some difficulty in believing that nearly the whole of the two airs 
could be converted into water.’ This addition, as I have had the opportunity of 
verifying by an inspection of the original MS. 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 :—* 
I can certainly give you the best account of the little dispute about the first discoverer of 
the artificial generation of water, as I was the principal instrument through which the first 
news of the discovery that had been already made was communicated to Mr. Lavoisier. The 
following is a short statement of the history :— 
In the spring of 1783 Mr. Cavendish communicated to me, and other members of the 
Royal Society, his particular friends, the result of some experiments with which he had for a 
long time been occupied. He showed us that out of them he must draw the conclusion that 
1 Mr. Muirhead’s translation. Vide Watt, Correspondence, ‘Composition of Water,’ 
pivk 
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