312 Mr Graham on Water as a Constituent of Salts. 



Sulphate of Magnesia with Saline Water: MgSH+H c . Sulphate 



of Magnesia. 



One atom of water is retained by sulphate of magnesia at 

 460°, but the other six are not entirely expelled under 270° in 

 open air. Indeed this sulphate is remarkable for a disposition 

 to retain two atoms of water, in which respect it resembles the 

 sulphate of lime. Dried at 212° in open air, the crystals of sul- 

 phate of magnesia were found in several experiments to retain 

 somewhat more than two atomic proportions of water. When 

 dried at the same temperature in vacuo over sulphuric acid, the 

 water was reduced to two proportions. Crystals placed over sul- 

 phuric acid in vacuo, without heat, were found to retain only 

 two and a quarter atomic proportions of water. 





Anhydrous 

 Salt. 



Water. 



Anhydrous 

 Salt. 



Water. 



Crystallized salt, dried in vacuo at 70° for six \ 

 days, or till it ceased to lose, ... J 



Do. heated between 41 0° and 460° for one \ 

 hour, being previously dried at 238°, . J 



Relative composition of the anhydrous salt \ 

 with one atom of water (by theory), . j 



12.34 



21.8 



4.9 



4.13 

 6.24 

 0.74 



100 

 100 

 100 



100 



33.46 

 28.62 

 15.1 



14.81 



The sulphate of magnesia and ammonia lost its six atoms of 

 water of crystallization and became anhydrous, when exposed to 

 a temperature not exceeding 270°, for one hour, having pre- 

 viously been dried at 212°. It retained of course the atom of 

 water which is essential to the ammoniacal salts. A somewhat 

 higher temperature was required to deprive the sulphate of mag- 

 nesia and potash of its whole water of crystallization. 



Hydrated Sulphate of Lime : CaSH-fH. 

 The only crystalline hydrate of sulphate of lime, which is 



