Elements of Mineralogy. 

 alfo would be precipitated. If there be not 

 an excefs of acid, the faccharine acid is ftill 

 a nicer teft of calcareous Earth. 100 gr. of 

 gypfum contains about 32 of calcareous 

 Earth. 100 gr. of barofelenite contains 84 of 

 ponderous Earth. 100 gr. of faccharine fe- 

 oienite contains 45 of calcareous Earth : the 

 infolubility of barofelenite in 500 times its 

 weight of boiling water fufficiently diflin^- 

 guifhes it. From thefe data the quantities are 

 eafily inveftigated. 



3 dly - A minute proportion of ar gill in a large 

 quantity ofmagnejia, maybe difcovered either 

 by precipitating the whole and treating it 

 with diftilled vinegar, or by heating the folu- 

 tion nearly to ebullition, and adding more 

 aerated magnefia untill the folution is per- 

 fectly neutral, which it never is when argill 

 is contained in it, as this requires an excefs 

 of acid, to keep it in folution. ' By this 

 means the argill is precipitated in the ilate of 

 embryon alum which contains about \ its 

 weight of argill, (or for greater exaclnefs it may 

 be decompofed by boiling it in volatil alkali.) 

 After the precipitation the folution mould be 

 largely diluted, as the Epfom fait, which re- 

 mained in folution while hot, would preci- 

 pitate when cold and mix with the embryon 

 alum. 



.thlV, 



