n8 A ft ion of Acids en Metals. [Book VI, 



quickfilver ; iron or lead, the copper; and zinc, vu ;h 

 precipitates thefe, may itfclf be precipkatcd by an 

 alkali. 



The folution of metals in the acids is attended 

 with the efcape of an elaftic vapour, and . an effer- 

 vefcence *. This appearance is proved to arife from 

 a decomposition either of the acid or the water, and 

 the elaftic fiuid differs in different cafes, according to 

 the fource from which it derives its origin ; when it 

 arifes from the decompofition of water, it is hydrogen 

 or inflammable gas, when from that of the nitrous 

 acid, nitrous gas, &c. Before the metal can be dif- 

 folved, it is neceffary that it fhould be oxygenated ; 

 and therefore when its attraction is fufficientiy ftrong, 

 it decompofes the acid or the water, by abftracting 

 their oxygen. It has been already remarked, that the 

 muriatic acid has the ftrongeft attraction for metals, 

 and the nitrous lefs than either that or the vitriolic. 

 From merely obferving the action of thefe acids on 

 metals, however, a different concluGon might be 

 drawn, for the nitrous acid acts with violence and 

 rapidity in comparifon with the other two ; and the 

 muriatic, when in its pureft ftate, has the leaft action 

 of the three.' This feeming inconfiftency depends on 

 the different degrees of attraction which the bafes of 

 the different acids have for oxygen. The reafon, there- 

 fore, why fome metals cannot be duTolved in particu- 

 lar acids, is, that they have not a fufficiently ftrong 

 attraction for oxygen to decompofe the acid. If we 

 feparate a metal from an acid by any fubftance which 

 is not capable of depriving it of oxygen, we always 



* This was formerly adduced among the proofs for the exift- 

 cnce of phlogifron, which, united with a fmall quantity of the water 

 or acid, was iuppofcd to conllitute this elaftic fluid, at the fame 

 ;ime that the metal, by its lofs, \vas deprived of its fplendour, c. 



obtain 



