430 COMPOUND SALTS 



1 atom sulphate of potash 1 1 

 1 atom sulphate of magnesia 7'5 

 7 atoms water . . 7*875 



26-375 



It is, therefore, a compound of 1 integrant par- 

 ticle of sulphate of potash with 1 integrant par- 

 ticle of sulphate of magnesia, retaining all its 

 water of crystallization. 



i- g. Potash-sulphate of alumina, or common 

 alumina, alum. The constituents of this well known salt 



are 



3 atoms sulphate of alumina 

 1 atom sulphate of potash 

 25 atoms water 



60-875 



ri- 3. Potasli-tnsulpliate of alumina. This salt, 

 formerly called alum saturated with its earth, 

 may be obtained by adding potash to a boiling 

 solution of alum, and washing the precipitate 

 till the liquid used ceases to act on muriate of 

 barytes. According to RirTault this salt is a 

 compound of 



3 atoms trisulphate of alumina .3 5*2. -5 

 1 atom sulphate of potash 11-00 



9 atoms water . 10-125 



56-375 * 



* Ann. de Chitn. et de Phvs. XVI. 355. 



