38 BIOGRAPHIES OF SCIENTIFIC MEN 



about one-fifth of the common air, are turned into pure 

 water." He further showed that when dephlogisticated 

 air (oxygen) and inflammable air (hydrogen) were exploded 

 together, pure water was the result. 



Although he proved the composition of water, it does 

 not appear that he viewed it as a chemical compound of 

 the two gases. His phlogistic ideas biased even his clear 

 mind to such an extent that, after the overthrow of the 

 phlogistic doctrine by the work of Lavoisier, he withdrew 

 from any active part in scientific research. 



In 1783, in a letter to Black, James Watt expressed 

 the opinion that * * water is composed of dephlogisticated 

 and inflammable airs." A long and bitter controversy 

 raged about the discovery, the priority of which was 

 claimed for Watt. It is now, however, universally ascribed 

 to Cavendish. 



Although nitric acid was known to Geber the eighth- 

 century alchemist Cavendish proved (1784-85) the exact 

 composition and mode of formation of this acid. He was 

 remarkable for the accuracy and precision of his experi- 

 mental discoveries ; but any attempt to draw him into 

 conversation was useless. " The way to talk to Cavendish," 

 said Wollaston, " is never to look at him, but to talk as 

 it were into vacancy, and then it is not unlikely you 

 may set him going." 



In 1766 Cavendish discovered inflammable air (the 

 hydrogen of to-day), producing it by the action of dilute 



