CONTAINING AMMONIA. 419 



much exceed half the quantity contained in the 

 salts before combination ; for sulphate of soda 

 contains ten atoms, and sulphate of ammonia 

 one atom of water. 



3. Ammonio-sulphate of magnesia. This salt, 



, . i t sulphate of 



which may be obtained by the same process as magnesia. 

 the preceding, crystallizes in beautiful rhom- 

 boids, which are not altered by exposure to the 

 air. It has a bitter taste, a specific gravity of 

 1*7^1, and its constituents are 



1 atom sulphate of magnesia 7 '5 



1 atom sulphate of ammonia 7'125 



7 atoms water 7*875 



22-5 



4% Ammonio-sulphate of alumina. This salt 



. , ., . sulphate of 



is precisely similar in its appearance and proper- alumina. 

 ties to common alum. Its crystals are regular 

 octahedrons ; its solubility in cold water is ra- 

 ther less than that of alum. I analyzed this salt 

 with much care, and found its constituents 



.'J atoms sulphate of alumina 21 -75 



1 atom sulphate of ammonia 7'12/> 



*2~) atoms water 28-125 



This approaches as near the weight of an inte- 

 grant particle of common alum as the constitu- 

 ents will admit. The only difference is the sub- 



i) d i 



