270 LAVOISIER. 



of respiration ; . and the discovery of hydrogen being 

 evolved by it as well as carbon, was undeniably his. 



7. We have seen that to the two great discoveries of 

 oxygen and the composition of water, he can lay no 

 claim. Yet let it be borne in mind that his statement 

 of both doctrines was more precise and clear than 

 any which the authors of the experiments and original 

 framers of the theory had given. As regards the latter 

 doctrine, the obscurity of Mr. Cavendish's language, even 

 of Mr. Watt's though in a much less degree, has been 

 observed upon already. But we need only consider Dr. 

 Priestley's view of the air he had discovered, and the 

 name he gave it, in order to be satisfied how confused 

 were the notions derived from the phlogistic theory, and 

 how they obscured his naturally acute vision. When he 

 called it dephlogisticated air, he intended to say that air, 

 the atmosphere, parts with phlogiston, and the residue is 

 oxygen gas. But then if phlogiston be added, it should 

 again become common air. Now he held the calcination 

 of metals to be the evolution of phlogiston, therefore this 

 operation should have restored the gas to the state of 

 common air. But, instead of that, it absorbed it alto- 

 gether. Again : the residue, when common air is deprived 

 of the dephlogisticated portion, is another air which he 

 called phlogisticated, because it contained more phlogiston 

 than the common air. But how by this theory could the 

 union of such a phlogisticated air with a dephlogisticated 

 air make the common air? By the hypothesis, that air 

 with phlogiston added is azote, with phlogiston sub- 

 tracted is oxygen gas. Therefore mixing the two, you 

 should have produced, not the air that had been phlogis- 

 ticated in making the one, dephlogisticated in making 



