308 Mr Graham on Water as a Constituent of Salts. 



shade of green. The sulphate of copper with one atom of water 

 was also obtained in a crystallized state by Dr Thomson, and 

 called by him green sulphate of copper. Dried over sulphuric 

 acid in vacuo for seven days, when it had ceased to lose, at a 

 temperature between 65° and 74°, the common hydrated salt re- 

 tained 21.67 parts water to 100 anhydrous salt, which is some- 

 what under two atomic proportions of water, namely 22.57 parts. 

 At a temperature between 430° and 470°, the sulphate of cop- 

 per loses its fifth, or saline, atom of water, and is found in the 

 state of a powder, which is white without any shade of colour. 

 When a few drops of water are thrown upon anhydrous sul- 

 phate of copper, it slakes and becomes blue, and so much heat is 

 evolved as to occasion the ebullition of the water. In one case 

 the temperature was observed to rise to 276°. This arises from 

 the resumption of saline water by the salt. 



Sulphate of Copper with Sulphate of Potash : CuS(KS)-fH 6 . 

 Sulphate of Copper and Potash. 



This salt may be formed by mixing sulphate of copper with 

 either sulphate or bisulphate of potash, in atomic proportions. 

 Dried in the open air, it loses six atoms water, and becomes quite 

 anhydrous at a temperature not exceeding 270° Fr. The fol- 

 lowing Table of the composition of this hydrated salt in diffe- 

 rent circumstances, illustrates three facts,- — that the salt has a 

 disposition to retain two atoms of water when dried at 212° in 

 open air, — that a greater portion of water of crystallization is 

 withdrawn from the salt by drying it over sulphuric acid in va- 

 cuo, without artificial heat, than by drying it at 212° under the 

 atmospheric pressure, and that the mechanical water retained by 

 the crystals of this salt may exceed 3 per cent, of their weight 



