310 LAVOISIER. 



suppose that these experiments, which he laid before 

 the Academy in the spring of 1777,* led him to his 

 general theory. This theory is well known. It con- 

 sists in supposing that all combustion, like all calcin- 

 ation, is produced by the union of oxygen with the 

 body burnt or calcined ; and that the gas which, in 

 calcination, only gives out its heat and light slowly 

 and imperceptibly, unless when this operation is per- 

 formed very rapidly, in combustion gives out that heat 

 quickly and sensibly. Thus the doctrine is, that, by 

 applying heat to a combustible body, we so far over- 

 come the attraction of cohesion as to make the particles 

 enter into a union with those of the gas, which gives 

 out its latent heat and light, thus causing the flame 

 that marks and distinguishes the process. Calcination, 

 too, may be produced so quickly, that the process is 

 attended with red heat, and even with flame. Iron 

 burns with a bright whitish and sometimes a bluish 

 flame, gold with a duller and more lambent flame of a 

 greenish colour. 



The product of the combustion, slow or quick, was 

 next attentively considered by M. Lavoisier. In the 

 case of metals it was their calces, or as he denominated 

 them from the process of oxygenation, oxides. In the 

 case of sulphur he had found it to be vitriolic acid ; in 

 the case of phosphorus phosphoric ; nitrous gas, which 

 he erroneously supposed the base of nitrous acid, 

 formed that acid by its union with oxygen. The 

 nature of fixed air, too, was no longer a matter of 

 doubt. Dr. Black had shown, as early as 1757, 



* In his Memoir on Phlogiston in the volume for 1783, he speaks of 

 his theory of combustion as having been "published in 1777." If by 

 " published" he means read at the Academy, this may be correct, for it 

 appears to have been read 5 Sept., 1777, but the volume was not published 

 till 1780. In the same volume we find internal evidence that the other 

 papers referred to in the text were read in the opening of that year ; thus, 

 one of them read in May refers to experiments about to be performed in 

 company with M. Trudaine and M. Montigny, the former of whom died 

 in August, 1777. 



