Chap. I. J Formation of Mcts. 3 



combination the character iftic properties both of the 

 acid and alkali are loft, and a new body is formed, 

 which is extremely inert, in comparifon with the two 

 jubilances of which it is compofed. Several of the 

 earths, and fome of the metals, are alfo capable of be- 

 ing united with acids, and the compound forms a fait 

 more or leCs perfe 61. 



Alkalis and acids, at the time they obtained 

 name of fimpie falts, were fuppofed to be really fuch; 

 modern difcoveries, however, have now led to a differ- 

 ent conclufion, and left no reafon to doubt that all the 

 aci.ls, and "at leaft one of the alkalis, are compound 

 bodies. Thfe doctrine of the formation of acids is 

 now fully elucidated} the procefTes of corr.buftion, 

 and-of the calcination of metals, which were formerly 

 attributed to the expulfion of an imaginary fubftance, 

 called phlogifton, are now proved to be only the for- 

 mation of acids ; or the union of the principle of aci- 

 dity or oxygen contained in the stmofphere, with fub- 

 ftances, the particles of which have, in cestain circum- 

 ftances, a ftronger attraction for that principle, than it 

 has for the matter of heat. The chief circumilance 

 which favours the union of the principle of acidity, or, 

 as it is called by the French cherftifts, oxygen, with 

 other bodies, is a proper degree of heat -, which, by 

 removing the particles of bodies further from each 

 ether, diminifhes their attraction, and allows room for 

 the entrance of air into their interftices. In the cal- 

 cination of metals, and in combuftion, the oxygen gas 

 of the atmofphere is decompofed, and while the -bafts 

 is attracted by the inflammable fubftance or metal, the 

 matter of heat is diiengaged, and becomes fenfible. 

 Bodies, however, may be acidified or oxygenated 

 without being expofed to the air j and this is performed 

 by placing them in contact with bodies which are 

 B 2 already 



