146 HISTORY OF CHEMISTRY. 



them to this conclusion. Convincing proofs of the 

 new opinion were, however, rapidly supplied. Thus, 

 when Priestley had discovered dephlogisticated air, 

 in 1774, Lavoisier showed, in 1775, that fixed air 

 consisted of charcoal and the dephlogisticated or 

 pure air ; for the mercurial calx which, heated by 

 itself, gives out pure air, gives out, when heated 

 with charcoal, fixed air 1 , which has, therefore, since 

 been called carbonic acid gas. 



Again, Lavoisier showed that the atmospheric 

 air consists of pure or vital air, and of an unvital 

 air, which he thence called azot. The vital air he 

 found to be the agent in combustion, acidification, 

 calcination, respiration ; all these processes were 

 analogous ; all consisted in a decomposition of the 

 atmospheric air, and a fixation of the pure or vital 

 portion of it. 



But he thus arrived at the conclusion, that 

 this pure air was added, in all the cases in which, 

 according to the received theory, phlogiston was 

 subtracted, and vice versa. He gave the name 2 of 

 oxygen (principe oxygene] to " the substance which 

 thus unites itself with metals to form their calces, 

 and with combustible substances to form acids." 



A new theory was thus produced, which would 

 account for all the facts which the old one would 

 explain, and had besides the evidence of the balance 

 in its favour. But there still remained some ap- 

 parent objections to be removed. In the action of 

 1 Mem. Ac. Par. 1775. * Ib. 1781, p. 448 



