Prof. Graham on Water as a Constituent of Salts. 421 



A crystalline crust of sulphate of manganese, deposited from 

 a warm solution, was found to contain three atoms of water. 

 It is likewise known to be deposited from a boiling solution 

 with only one atom of water, namely, the saline atom. We 

 have, therefore, sulphates of this class with no water of cry- 

 stallization, and with two, four, and six atoms. 



The sulphate of manganese and potash did not crystallize 

 on mixing the solutions of its constituents. The sulphate of 

 manganese and soda was obtained in analogous circumstances 

 with the sulphate of copper and soda, but was not examined. 



Sulphate of Iron with Saline Water: FeSH+H«. Sulphate 



of Iron. 

 Of the seven atomic proportions of water which the crystals 

 contain, 5* 48 proportions were lost in vacuo over sulphuric 

 acid; and six proportions at 238°, and probably at lower tem- 

 peratures. The saline atom of water is retained by this salt 

 at so high a temperature as 535°. But the salt can be made 

 perfectly anhydrous, with proper caution, without appreciable 

 loss of acid. 



Sulphate of Iron with Sulphate of Potash : FeS(KS)-f H^ 

 Sulphate of Iron and Potash. 



A specimen of this salt was made anhydrous by a sandbath 

 heat, which was found not to affect the saline atom of water 

 of the preceding compound. 



Sulphate of nickel was found to correspond closely with 

 sulphate of iron in the temperatures at which it lost its water 

 of crystallization, and also its saline water. And in the case 

 of both of the compounds of these salts with sulphate of pot- 

 ash, a considerably higher temperature was required to ren- 

 der them perfectly anhydrous, than in the case of the cor- 

 responding double salt of zinc. 



Sulphate of Magnesia with Saline Water : MgSH -h H^ Sul- 

 phate 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 disposi- 

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

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

 of sulphate of magnesia were found in several experiments to 

 retain somewhat more than two atomic proportions of water. 

 When dried at the same temperature i?i vacuo over sulphuric 

 acid, the water was reduced to two proportions. Crystals 



