1 84 Elements of Mineralogy. 



i oo parts of it contain about 24 of real 

 acid, 19 of earth, and 57 of water. 



SPECIES VI. 



Alum* 



Alum requires about 15 times its weight 

 of water to diflblve it in the temperature of 

 60. Its tafte is well known ; it fwells and 

 blifters when heated, and lofes nearly I its 

 weight. It is precipitable by all alkalis, and 

 even by magnefia, which diftinguifhes its 

 t>afis from that of Epfom.i but the precipi- 

 tate retains nearly I the weight of the acid 

 with which it was originally united, and is in 

 reality Embryon Alum ; but by digefting it in 

 volatile alkalis (for its bafis would unite to 

 fixed alkalis) it may be perfectly purified. 

 Its folution, like that of Epfom^ renders 

 nitrous folutions of filver or chalk turbid, 

 but mixes uniformly with thofe of nitrous or 

 marine alum, or of the vitriols of any metal : 

 thefe properties diftinguifh it fufEciently. 



100 parts of it contain about 24 of acid, 

 1 8 of earth, and 58 of water. 



This fait is found native in a few mineral 

 fprings*, though rarely, i Bcrgm. 280. and 



* Margr. 2 < thelle > 193. 



ia 



