Mr Graham on Water as a Constituent of Salts. 303 



again have occasion to allude under sulphate of lime, a body which 

 illustrates it more strikingly than the sulphate of water. 



Sulphate of Water with Sulphate of Patash : HS(KS) . Bisulphate 



of Potash. 



Of all the sulphates, the acid sulphates or bisulphates of pot- 

 ash and soda deviate least from the primary sulphate of water. 

 We have, in the one case, merely sulphate of potash ; and, in the 

 other, sulphate of soda, substituted for the saline atom of water 

 of the sulphate of water. In none of the specimens of these salts 

 which I had occasion to examine, was there any water of crystal- 

 lization, and the evidence which is given of its occasional pre- 

 sence is of a very doubtful description. The crystals could be 

 heated to 300°, without impairing their transparency ; and they 

 fused at a temperature not under 600°, without the loss of any 

 thing, except a trace of water, which had been mechanically re- 

 tained. Upon heating a bisulphate nearly to redness, a portion 

 of sulphate of water is expelled. I greatly doubt whether water 

 ever comes off in such a case unaccompanied by sulphuric acid, 

 although Berzelius appears to be of a different opinion. It is 

 well known that the sulphate of water is not entirely expelled 

 from these salts by heat alone, even the most intense. Sulphate 

 of water, however, leaves the sulphate of soda with greater faci- 

 lity than it leaves the sulphate of potash. 



These sulphates should be crystallized from concentrated so- 

 lutions at a high temperature ; for their solutions are very apt to 

 undergo decomposition at low temperatures, the neutral sulphate 

 crystallizing, and leaving " the sulphate of water with saline 

 water" in solution. I have often observed this decomposition to 

 occur, even in solutions containing a great excess of sulphuric 

 acid. At low temperatures, therefore, the affinity of sulphate of 

 water for " saline water," prevails over its affinity for sulphate of 

 potash. Crystals of bisulphate of soda, pounded and put under 



