330 Prof. Graham on Water as a Constituent of Salts. 



is the only known crystallizable hydrate of sulphuric acid. It 

 may be represented by the formula, 



HSH, 



ZnSH, 



which may be compared with that of sulphate of zinc placed 

 below it. This second atom of water present in hydrated 

 sulphuric acid, is replaceable by sulphate of potash, a salt; 

 and the bisulphate of potash results from the substitution. 

 But the first atom of water in the acid hydrate can be re- 

 placed only by an alkali or true base. The function of the 

 first atom is basic, but a new term is required to distinguish 

 the function of the second atom of water, or of the essential 

 atom of water in the sulphate of zinc. The application of the 

 epithet saline to that atom of water, may, perhaps, be per- 

 mitted, to indicate that it stands in the place of a salt. The 

 hydrate of sulphuric acid in question contains, therefore, an 

 atom of basic, and an atom of saline water. It is " a sulphate 

 of water with saline water," as the hydrous sulphate of zinc is 

 " a sulphate of zinc with saline water." The bisulphate of 

 potash also is " a sulphate of water with sulphate of potash," 

 and corresponds with the sulphate of zinc and potash; which 

 last is " a sulphate of zinc with sulphate of potash." 



A reason could now be given why there exist no supersul- 

 phates (or indeed any supersalts) of magnesia, zinc, &c. A 

 bisulphate of magnesia would be a compound of sulphate of 

 water with sulphate of magnesia, on our view of supersul- 

 phates. Now sulphate of magnesia, and sulphate of water, 

 are bodies of analogous constitution, or of the same category, 

 and should have as little disposition to combine together, as 

 sulphate of zinc and sulphate of magnesia have. 



1. Sulphate of Water with Saline Water: HSH. Sulphuric 

 Acid qfsp. gr, 1-78. 



It appears, then, that in an exposition of the relations of 

 the sulphates, we may set out from this body as our primary 

 sulphate. Of the two atoms of water which it contains, that 

 atom which is basic cannot be separated from the acid, unless 

 by the agency of a stronger base. The second, or saline 

 atom of water, may be separated by heat, but not by any de- 

 gree of heat under 400° Fahrenheit, and is re-absorbed with 

 great avidity. 



A diluted sulphuric acid may, I find, be concentrated at a 

 temperature not exceeding 380°, without the loss of a particle 

 of acid ; and the quantity of water retained is reduced to two 



