‘Mr Granam on Water as a Constituent of Salis. 305 
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 so- 
lution, 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 temperature of 410° Fahrenheit, 
but to lose it, and become anhydrous, at a temperature not ex- 
ceeding 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, without 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 there- 
fore “ sulphate of zinc with saline water ;” and the true or ab- 
solute 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 Zine with Sulphate of Potash: Zn8(KS)+H". Sul- 
phate of Zine 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 sepa- 
rates by crystallization, when the sulphate of zinc is added to the 
bisulphate of potash ; and, in that case, an interesting double de- 
composition occurs. 
VOL. XIII. PART T. aq 
