LAVOISIEK. 251 



longer a matter of doubt. Dr. Black had shewn, as early 

 as 1 757, that the combustion of charcoal produced it. M. 

 Lavoisier, in 1777, satisfied himself by his experiments on 

 pyrophorus formed by heating alum and carbonaceous mat- 

 ter together, that the union of carbonaceous matter with 

 oxygen gas produces fixed air. It is true he did not com- 

 plete this important inference till 1781, when he shewed 

 by decisive experiments that charcoal contains, beside in- 

 flammable air, water, and other impurities, a matter purely 

 carbonaceous, and which he afterwards termed carbon, 

 which, by its union with oxygen, forms fixed air, thence 

 called by him carbonic acid. But the knowledge that 

 the something contained in charcoal uniting itself with 

 oxygen gas forms fixed air, and that this fixed air is an 

 acid, had been obtained by Dr. Black, M. Lavoisier, and 

 M. Macquer before 1777. On these facts he now rea- 

 soned as well as on the composition of the acid of sugar, 

 which, with other vegetable acids, he considered as con- 

 taining oxygen. He then made his famous generaliza- 

 tion that oxygen is the acidifying principle, and from 

 thence he gave it the name. Dr. Priestley had shewn its 

 absorption by the lungs in respiration ; and thus we had 

 the general proposition established, as M. Lavoisier sup- 

 posed, that oxygen gas is necessary to combustion, calci- 

 nation, acidification, respiration, possibly to the animal 

 heat thence arising, and certainly to the red colour of 

 arterial blood ; consequently he held that all those pro- 

 cesses, so different in themselves, are really one and the 

 same, the union of oxygen with different bodies in dif- 

 ferent ways. I reserve for a subsequent stage of the 

 treatise the consideration of this important and beautiful 

 theory. 



