i66 ESSAYS AND OBSERVATIONS 



ftrong fire, fuch as lime-Jlone, marble, chalky 

 thofe Jpars and marks which efFervefce 

 with aqua fortis, all animal Jhelh and the 

 bodies called lithophyta. All of thefe, by 

 being joined with acids, yield a fet of 

 compounds which are very different from 

 thofe we have juft now defcribed Thus, if 

 a fmall quantity of any calcarious matter be 

 reduced to a fine powder and thrown into 

 fpirit of vitriol, it is attacked by this acid 

 with a brifk effervefcence ; but little or no 

 diffolution enfues. It abforbs the acid, and 

 remains united with it in the form of a 

 white powder, at the bottom of the vefTel, 

 while the liquor has hardly any tafte, and 

 (hews only a very light cloud upon the addi- 

 tion of an alkali *. 



The fame white powder is aifo formed 

 when fpirit of vitriol is added to a calca- 

 carious earth diflblved in any other acid ; 

 the vitriolic expelling the other acid, and 



joining 



* Mr. Margraafh.z.s lately demonflrated, bya fet of curious 

 and accurate experiments, that this powder is of the nature, 

 and poflefTes the properties, of the gypfeous or felenitic fub- 

 ftances. That fuch fubftances can be refolved into vitriolic 

 acid and calcarious earth, and can be again compofed by 

 joining thefe two ingredients together, Mem de TAcad. de 

 Berlin, an, 1750, p. 144. 



