1825.] of Claude-Louis Berthollet. 5 



once so simple and so conclusive, that one cannot avoid won- 

 dering, with Cuvier, at the modest style which he assumed in 

 arguing in support of the Antiphlogistic Theory, on the one 

 hand, and at the confident tone of the obstinate phlogistians on 

 the other. Lavoisier reasoned nearly as follows : 



A metal calcined invariably gains a considerable increase of 

 weight. In any given close vessel, only a determinate portion of 

 metal can be calcined. Heat may be applied to the vessel in 

 every various degree, and for any length of time : the quantity 

 of metal which may be calcined within it has nevertheless its 

 fixed hmits, and calcination in such a vessel, once brought to a 

 period, can never again be renewed. But if tlie vessel be now 

 opened for a short time, and a fresh supply of atmospheric air 

 admitted, the process of calcination may be renewed, and again 

 carried on, but within the same limits as before. In the open air, 

 metals may be calcined to any extent. After calcination in a 

 close vessel, the body of air originally included has lost consider- 

 ably in volume and weight, and has changed several of its proper- 

 ties. The increase of iv eight gained by the metal measures the 

 exact loss of weight sustained by the air, so that the weight of the 

 whole remains unaltered. From these premises, Lavoisier con- 

 cluded, that since the presence of atmospheric air is essential to 

 calcination, since a given quantity of air serves to calcine only a 

 given quantity of metal, and since this process invariably trans- 

 fers a given weight from the air to the metal, calcination must 

 consist in the absorption of a ponderable principle from the air. 



Surely no process of reasoning could be more simple — no 

 results seem more inevitable than these ; and just at this time an 

 experiment made by Ur. Priestley enabled Lavoisier to give an 

 analytical demonstration of his theory. 



When mercury is calcined in a close vessel, it is gradually 

 converted into a red coloured calx : at the same time a portion 

 of the confined air disappears, and the residue is incapable of 

 contributing to new calcination, or of maintainins; either com- 

 bustion or respiration. If the red calx be now exposed to a 

 stronger heat in contact with thisdeterioiated air, the metal and 

 the air simultaneously assume their original appearance, and 

 recover their original properties. The phenomena of this expe- 

 riment at once furnished Lavoisier with the analytical and syn- 

 thetical tests of his theory, and enabled him to prove that atmo- 

 spheric air is no element, but a compound substance, of which 

 one constituent can support combustion and respiration, while 

 the other cannot. 



He next generalized the subject by showing that in all com- 

 bustions, a portion of the atmospheric air combines with the 

 combustible. 



There still remained one serious deficit in the proofs of the 

 truth of this theory. This arose from a phenomenon attending 



