Prof. Graham on Water as a Constiltient of Salts, 333 



crystallizes, none is essential to its constitution. The whole 

 were lost, even at a temperature not exceeding 47° Fahrenheit, 

 when the crystals of the salt were exposed over sulphuric acid 

 ill vacuo for five days. From the regular progress of the 

 desiccation of the salt, which was observed by occasionally 

 weighing it, it was evident that no portion of the water was 

 more strongly retained than the rest. It is well known that 

 sulphate of soda crystallizes in an anhydrous condition from 

 a hot solution. 



Sulphate of Zinc with Saline Water: ZnSH + H^. Sulphate 



of Zinc. 

 In the sulphate of zinc, we have the basic atom of water 

 contained in sulphate of water displaced by oxide of zinc, while 

 the saline atom remains; and to this compound six atoms 

 of water are attached in the common crystals. These crystals, 

 placed over sulphuric acid in vacuo^ thermometer 68°, were 

 found to lose six atoms water, retaining only one. Exposed to 

 the air at 212°, the crystals likewise readily effloresced down to 

 one atom ; and the sulphate of zinc is known to be deposited 

 from a boiling solution in crystalline grains, containing one 

 atom of water. On the other hand, the sulphate of zinc was 

 found to retain this single atom of water at the high tempera- 

 ture of 410° Fahrenheit, but to lose it, and become anhydrous, 

 at a temperature not exceeding 460°. In all such cases, the 

 hydrated salt was heated in a tube receiver, by means of an 

 oil- or solder-bath, of which the temperature was observed by 

 a thermometer. However strongly it has been heated, with- 

 out being decomposed, the sulphate of zinc always regains 

 this atom of water when moistened, slaking with the evolution 

 of heat. Common sulphate of zinc is therefore " sulphate of 

 zinc with saline water;" and the true or absolute sulphate of 

 zinc is unknown to us in the crystalline form, or in a soluble 

 state. But we may continue to designate the salt we possess 

 as sulphate of zinc, as the name is attended with no dubiety. 



Sulphate of Zinc mth Sulphate of Potash-, ZnS(KS) + H6. 

 Sulphate of Zinc and Potash, 

 In this well-known double salt, we have sulphate of potash 

 substituted for the saline water of sulphate of zinc, and the six 

 atoms of water of crystallization remain. It is readily formed, 

 on mixing together solutions of sulphate of zinc and sulphate 

 of potash, in atomic proportions. It is formed likewise, and 

 separates by crystallization, when the sulphate of zinc is added 

 to the bisulphate of potash ; and, in that case, an interesting 

 double decomposition occurs. 



