300 Mr Granam on Water as a Constituent of Salts: 
tion.” Now, in the double sulphate of zinc and potash, the single: 
atom of water in question pertaining to the sulphate of zinc is 
replaced by an atom of sulphate of potash, and the six atoms of 
water of crystallization remain. Sulphate of magnesia combines 
with sulphate of potash after the same manner, and so do all the 
other salts of the class. The constitution of the crystallized 
sulphate of zinc and potash, which may be taken as the type of 
this family of double salts, is therefore represented by the fol- 
lowing formula, 
ZnS(KS)+H’; 
which differs only from the previous formula in having the sign 
of sulphate of potash (KS) substituted for the sign (H) of the 
essential atom of water. 
From a contemporaneous examination of the supersulphates, 
the conclusion proved to be inevitable, that they also are double 
salts ; that the bisulphate of potash, for instance, is a sulphate of 
water and potash, and that its formula is as follows, 
HS(KS), 
with or without water of crystallization in addition. There is. 
likewise a provision in the constitution of hydrated sulphuric 
acid for the production of such a double salt, as in the case of 
the sulphate of zinc. Hydrated sulphuric acid of specific gra- 
vity 1.78 contains two atoms of water, and is capable of crystal- 
lizing at a temperature so high as 40° Fahrenheit. It is the only 
known crystallizable hydrate of sulphuric acid. It may be repre- 
sented by the formula, 
HSH, 
ZnSH, 
which may be compared with that of sulphate of zinc placed be- 
low it. This second atom of water present in hydrated suphuric 
acid, is replaceable by sulphate of potash, a salt; and the bisul- 
phate of potash results from the substitution. But the first 
atom of water in the acid hydrate can be replaced only by an 
