EPOCH OF THE THEORY OF OXYGEN. 147 



dilute acids on metals, inflammable air was pro- 

 duced. Whence came this element ? The discovery 

 of the decomposition of water sufficiently answered 

 this question, and converted the objection into an 

 argument on the side of the theory : and thus the 

 decomposition of water was, in fact, one of the most 

 critical events for the fortune ' of the Lavoisierian 

 doctrine, and one which, more than any other, 

 decided chemists in its favour. In succeeding years, 

 Lavoisier showed the 'consistency of his theory with 

 all that was discovered concerning the composition 

 of alcohol, oil, animal and vegetable substances, and 

 many other bodies. 



It is not necessary for us to consider any further 

 the evidence for this theory, but we must record 

 a few circumstances respecting its earlier history. 

 Rev, a French physician, had in 1630, published a 

 book, in which he inquires into the grounds of the 

 increase of the weight of metals by calcination 3 . 

 He says, " To this question, then, supported on the 

 grounds already mentioned, I answer, and maintain 

 with confidence, that the increase of weight arises 

 from the air, which is condensed, rendered heavy 

 and adhesive, by the heat of the furnace." Hooke 

 and Mayow had entertained the opinion that the 

 air contains a "nitrous spirit," which is the sup- 

 porter of combustion. But Lavoisier disclaimed 

 the charge of having derived anything from these 

 sources; nor is it difficult to understand how the 



3 Thomson, Hist. Chem. ii. 95. 



L 2 



