434 CAVENDISH. 



bustion, 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 combustion, 

 because the hydrogen gas and part of the common 

 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 



O 



the hydrogen gas must, therefore, be the vital air 

 or oxygen gas of the atmosphere. By another ex- 

 periment he more fully ascertained this : for, burning 

 oxygen 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 com- 

 position 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 experiment was, in 

 his own words, that " dephlogisticated air is in reality 

 nothing but dephlogisticated water, or water deprived of 

 its phlogiston, or in other words, that water consists of 

 dephlogisticated air united to phlogiston, and that 

 inflammable air is either pure phlogiston, or else water 

 united to phlogiston ;" and he then gives his reasons in 

 favour of the second inference, namely, that inflammable 

 air is water united to phlogiston ; but he repeatedly 



