22 HISTORY OF CHEMISTRY. [LECTURE II. 



It cannot be asserted, at least I have not been able to read 

 it out of Lavoisier's works, that he stated the principle of the 

 indestructibility of matter as an axiom. But he recognised the 

 truth of the law, for why, otherwise, should he have had con- 

 structed for one of his first investigations, " On the Conversion 

 of Water into Earth," a balance which surpassed in accuracy, 

 everything that was known at the time in such instruments ? 

 He recognises the truth of the principle, but he does not state 

 it. Proof lies with experiments, and not in words, and so he 

 holds back until a suitable opportunity : just as he held back 

 the attack upon the phlogiston theory until he saw that the 

 moment had arrived when, with a single blow, he could over- 

 throw the house of cards, held together as it was, by decaying 

 preconceived notions only. Accordingly we find his ideas 

 about this fundamental doctrine expressed in his works only 

 here and there, where it is necessary for him to furnish, at 

 once, grounds for an opinion, the experiments in support of 

 which are not yet completed. An instance is furnished, for 

 example, in his first treatise on the composition of water (which 

 substance he finds to consist of hydrogen and oxygen), where 

 he would like to prove that the weight of the water produced 

 by the union of hydrogen and oxygen is equal to the sum of the 

 weights of the two gases employed a point which he had not, at 

 that time, established by experiment. He there states that this 

 necessarily follows, since the whole is equal to its parts, 13 and 

 nothing but water is produced by the combustion. At that 

 time the priority of this discovery was disputed, and had, with- 

 out injustice, been ascribed to Cavendish and not to Lavoisier. 

 As it appears from a letter of Blagden's u and also from a 

 letter from Laplace to De Luc, 15 Lavoisier was acquainted 

 with Cavendish's investigation prior to his own experiments, 

 and hastened to publish his results. It is in this way that we 

 obtain knowledge of a fundamental doctrine which had long 

 been clear to him, but which was only at once adopted by a 



13 Lavoisier, Oeuvres. 2, 339. 14 Crell's Annalen. 1786, I, 58. 



13 Kopp, Beitrage. 3, 271. 



