418 Prof. Graham 07i Water as a Constituent of Salts. 



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

 tained by evaporating the mixed solutions over sulphuric acid 

 without heat. It caimot be redissolved in pure water, without 

 undergoing decomposition, which accounts for the impossibi- 

 lity 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 under- 

 goes 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 and opake mass. 



Sulphate of Copper with Saline Water: CuiSH-f-H*. 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 

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

 water was also obtained in a crystallized state by Dr. Thom- 

 son, 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 (S5° and 74°, the common hy- 

 drated salt retained 21-67 parts water to 100 anhydrous salt, 

 which is somewhat under two atomic proportions of water, 

 namely 22*57 parts. At a temperature between 430° and 

 470°, the sulphate of copper 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 sulphate of copper, it slakes and be- 

 comes blue, and so much heat is evolved as to occasion the 

 ebullition of the water. In one case the temperature was ob- 

 served to rise to 276°. This arises from the resumption of 

 saline water by the salt. 



Sulphate of Copper with Sulphate of Potash : CuS(KS) + H«. 

 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° Fahr. 

 The following Table of the composition of this hydrated salt 

 in different 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 crystal- 

 lization is withdrawn from the salt by drying it over sulphuric 



