304 Mr Graham <m Water as a Constituent of Suits. 



pressure in blotting paper, are apt to undergo the same decom- 

 position, if the air is damp, and frequently impart a large quan- 

 tity of their sulphate of water to the paper in the course of 

 twenty-four hours. This circumstance must be kept in view in 

 preparing bisulphates for analysis. The facility with which these 

 salts are decomposed by water, accords well with their relation 

 to sulphate of water with saline water, which we have supposed 

 to exist. Sulphate of zinc, sulphate of magnesia, &c. are capable 

 of separating the sulphate of water from these salts, at a temper- 

 ature approaching to redness, and take its place. 



I have observed that the bisulphate of soda is more prone to 

 decomposition, when dissolved in water, than the bisulphate of 

 potash. The double salts of sulphate of soda with sulphate of 

 magnesia, &c, are also much less stable than the corresponding 

 double salts containing sulphate of potash. Indeed, I believe 

 that the former are uniformly decomposed when dissolved in 

 water. 



Sulphate of Potash, Sulphate of Soda. KS, NS. 



These salts differ from other sulphates in having no saline 

 water. Of the ten atoms water with which sulphate of soda 

 crystallizes, none is essential to its constitution. The whole 

 were lost, even at a temperature not exceeding 47° Fahrenheit, 

 when the crystals of the salt were exposed over sulphuric acid 

 in vacuo for five days. From the regular progress of the desic- 

 cation of the salt, which was observed by occasionally weighing 

 it, it was evident that no portion of the water was more strongly 

 retained than the rest. It is well known that sulphate of soda 

 crystallizes in an anhydrous condition from a hot solution. 



Sulphate of Zinc with Saline Water: ZnSH-fH 6 . Sulphate of 



Zinc. 



In the sulphate of zinc, we have the basic atom of water con- 

 tained in sulphate of water displaced by oxide of zinc, while the 



