t)r. tVall on AttraSlion and 'kepiijion, 465 



bbvious, thereforej that in the procefs, the action 

 of the fire expels the phlogifton from the me- 

 tallic earth, which then attradls the aerial acid, 

 cither floating in the air, or generated by the fire, 

 and continues united with ir, till by proper cir- 

 cumftances of application the phlogifton is again 

 brought to a(ft on the metallic calx, and to unite 

 \vith it; and the aerial acid being expelled the 

 metallic is revived. This, then, is one of thofe 

 cafes of eleftive attraftion, which is varied by 

 the degree of heat. To prove that what I have 

 faid above is juft, let us examine another mode 

 in which metals are deprived of their phlogifton, 

 that isj by folution. A metal, perfedlly diflblved 

 in its proper acid menftruum, is held in folution, 

 till fome fubftance is added, which has a greater 

 attrafiion to one of the ingredients, than they 

 have to each other. Thus, a mild alkali added, 

 attrads the acid, and the metallic earth is preci- 

 pitated. It is a calx, in all circumftances the 

 fame, as that obtained by perfedt calcination; 

 and here it alfo indifputably contains the aerial 

 acid. Indeed, we in a manner fee it take pof- 

 feffion of the fixed air in tlie procefs : for when 

 the alkali is added, and attrads the acid, no efFer- 

 vefcence enfues, though we know the alkali parts 

 with its air, whenever it unites with an acid. It 

 is therefore certainly abforbed by the precipitated 

 calx, and with that, by experiment, we find ic 

 united. Again, if we add to a. folution of any 

 Vol. II. H h metal 



