44 Dr Davy's Remarks on the Claims to the 



This, his first letter on the subject, was written in the same 

 month as Dr Priestley's paper, that referred to above, and, as 

 will be mentioned fui'ther on, was quoted by Mr Cavendish. It 

 was dated April 26, 1783. From a passage in Dr Priestley's 

 paper, and from one in Mr Watt's first letter, that to Dr 

 Priestley, it may be inferred that this his hypothetical conclu- 

 sion was formed just before that letter was written. He 

 mentions in it the abandonment of an opinion that he had 

 entertained for many years " that air was a modification of 

 water," " that, by a great heat, water might be converted into 

 air." 



Now, what is Mr Cavendish's statement relative to the 

 discovery in question \ After describing his experiments in 

 proof of the pi'oduction of water by burning hydrogen in close 

 vessels with common air and dephlogisticated air, he remarks, 

 " All the foregoing experiments on the explosion of inflam- 

 mable air with common and dephlogisticated air except those 

 which relate to the cause of the acid found in the water, were 

 made in the summer of the year 1781, and were mentioned 

 by me to Dr Priestley, who, in consequence, made some ex- 

 periments of the same kind, as he relates in a paper printed 

 in the preceding volume of the Transactions. During the 

 last summer also, a friend of mine gave some account of them 

 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 pre- 

 vailed upon to repeat the experiment himself, he found some 

 difficulty in believing that nearly the whole of the two airs 

 should be converted into vvater.''| 



It has been objected to this passage that it was an inter- 

 polation, after Mr Watt's letter to M. de Luc had been read 



dish obtained 135 grains of water, ' pure water,'" as it seemed, in cue of the 

 experiments which he mentions. In Waltire's experiments, which led to Mr 

 Cavendish's, a dew was observed on the inside of the vessel in which the explo- 

 sion was made, mixed with soot, attended with a loss of weiglit. The experi- 

 menter referred tiie dew to moisture previously existing in and deposited from 

 the airs used. 



* Phil. Trans, for 1784, p. 134. 



