CAVENDISH. 95 



out, forming the flame which was produced ; and that 

 water was formed by the union of the two airs, having, 

 of course, less latent heat than was required to keep 

 them in a gaseous state ; but Mr. Cavendish did not 

 approve of this manner of stating the conclusion which 

 Mr. Watt had adopted, because of doubts which he 

 had respecting the nature of heat.* The residue of 

 the combustion, however, was two-fold : there was an 

 aeriform body left in the glass vessel, as well as liquid 

 in the bottom. This was much smaller in volume than 

 the air which had filled the globe before the combus- 

 tion, because the hydrogen gas and part of the com- 

 mon air had disappeared. This aeriform residue was 

 also of a different nature from common air; it was 

 found to be the phlogistic air of Priestley ; the azotic 

 air of Rutherford : and the air consumed in burning 

 the hydrogen gas must, therefore, be the vital air or 

 oxygen gas of the atmosphere. By another experi- 

 ment he more fully ascertained this : for, burning oxy- 

 gen gas with hydrogen gas, nearly the whole aeriform 

 contents of the globe disappeared, and water, equal in 

 weight to the two gases taken together, remained as 

 the produce of the combustion , but still an acid was 

 formed, unless in some cases, when very pure oxygen 

 gas was used. 



Thus was effected the important discovery of the 

 composition of water, which Watt had inferred some 

 time before from a careful examination of the similar 

 facts collected by former experimentalists; one of 

 whom, Warltire, had even burned the gases in a close 

 vessel, and by means of electricity. The conclusion 

 arrived at by Mr. Cavendish from his capital experi- 

 ment was, in his own words, that " dephlogisticated 

 air is in reality nothing but deplogisticated water, or 

 water deprived of its phlogiston, or in other words, 

 that water consists of dephlogisticated air united to 



* Page 140. 



