438 CAVENDISH. 



of the process called the destructive distillation. The 

 substances found might have been the product, anfl npt 

 merely the educt of the process. It is knpwn that if coal 

 or oleaginous bodies be distilled in close vessels there are 

 obtained; gases and water and acids which never existed 

 in the matters subjected to the action, of the fire. The 

 component parts of these matters enter into new com- 

 binations with one another under the action of heat, just 

 as a.taljpw ca.ndlq or an oil lamp, gives lamp-black and 

 water in burning, though no w#ter> but only : hydrogen, 

 nor, ofcpurse any lamp-black;, exists an the tallow and the 

 pil< So, in, Lavoisier's, experiment, the water might 

 contain only oxygen and hydrogen, and the action of 

 the hot iron might have separated them from each other, 

 But it. was also quite ppssible that the iron gave out 

 hydrogen, and that the hot water was partly kept in 

 solution by this gas, partly combined with the iron, for 

 oi> that supposition the combined weight of the calcined 

 iron and the, hydrogen gas would be exactly equal, 

 to the united, weight of the water evaporated, and of 

 th$ iron before calcination. The previous discovery of 

 Watt and Caven.dish is liable to no such ambiguity ; 

 and it has the merit of also removing all ambiguity 

 from the experiment of Lavoisier, which it manifestly, 

 suggested. 



These great discoveries placed Cavendish in the 

 highest rank of philosophers. No one doubted of 

 nitrous acid ; that he was the undisputed discoverer of 

 the composition of water, before Mr. Watt's : claim, is 

 equally certain; nor, even r now, is . it necessary for 

 the defenders of Watt's priority to deny that Cavendish 

 made the great step without any previous knowledge 



