Mr Graham on Water as a Constituent of Salts. 307 



zinc and sulphate of soda in atomic proportions : the salts uni- 

 formly crystallized apart, either in cold or in warm weather. 

 Each of the salts was also added in excess to the other, but with 

 no better effect. It appears, then, that sulphate of soda does not 

 displace the saline water of sulphate of zinc, so easily as sulphate 

 of potash does. But the desired salt was obtained by a process 

 of double decomposition, suggested from consideration of the re- 

 lations of the sulphates. Solutions of bisulphate of soda, and of 

 sulphate of zinc, were mixed together in atomic proportions, from 

 which the sulphate of zinc and soda separated in a gradual man- 

 ner in the course of a day or two, leaving sulphuric acid in solu- 

 tion. 



Sulphate of zinc with saline water, ~\ C Sulphate of zinc with sulphate of soda. 



Sulphate of water with sulphate of V yield ^ Sulphate of water with saline water, 

 soda, . . ) v. 



This salt is deposited in distinct tabular crystals, of a pecu- 

 liar form, which are often associated in tufts ; and is best obtain- 

 ed by evaporating the mixed solutions over sulphuric acid with- 

 out heat. It cannot be redissolved in pure water, without un- 

 dergoing decomposition, which accounts for the impossibility of 

 forming it by the direct process. The crystals contain four atoms 

 of water, and are about as deliquescent as nitrate of soda, in a 

 damp atmosphere. The anhydrous salt undergoes fusion, like all 

 the other double sulphates, at an incipient red heat, without the 

 evolution of acid fumes. The fused salt solidifies, on cooling, 

 into a white arid opaque mass. 



Sulphate of Copper with Saline Water : CuSH+H 4 . Sulphate of 



Copper. 



The common blue rhomboidal crystals of sulphate of cop- 

 per contain five atoms of water, four of which are readily ex- 

 pelled, by drying the salt in air at 212°; by which treatment 

 the salt loses its blue colour, and becomes white, with a dirty 



