Prof. Graham on Water as a Co7istituent of Salts. 331 



atoms most precisely. This in fact is an exact method of ob- 

 taining the definite sulphate of water with saline water ; which 

 may be kept at 380° or 390°, without sustaining any further 

 loss. I have observed a close approximation to the same pro- 

 portion of water, even in the case of a dilute acid concentrated 

 at a temperature not exceeding 300°. But at 400° or 410°, 

 this hydrate begins to be decomposed, and a portion of it is 

 apt to distill over with the water expelled. When, however, 

 this hydrate is distilled in vacuo, at the last-mentioned tempe- 

 rature, it loses nothing but water for some time. 



In one experiment, a small quantity of dilute sulphuric acid 

 was found to concentrate down to three atoms of water, at a 

 temperature not exceeding 212°, at which it was sustained in 

 vacuo for not less than forty hours. It consisted of 100 parts 

 dry acid united with 68*07 water, while three atomic propor- 

 tions of water are 67*32 parts. 



The concentrated acid of commerce, which is a definite sul- 

 phate of water, without the saline atom, does not freeze at a 

 temperature so low as —36°, according to Dr. Thomson. To 

 sulphuric acid of sp. gr. 1*78, I added water in the proportion 

 of two, four, and six atoms ; but all these hydrates remained 

 fluid, when kept for a short time at 0° Fahrenheit. Anhy- 

 drous sulphate of magnesia or zinc never dissolves, as such, in 

 water; or exhibits any determinate chemical character. It 

 must always combine with its saline atom of water in the first 

 instance, or with something equivalent, and it is the com- 

 pound which is soluble, &c. So it is with the sulphate of 



water, or concentrated sulphuric acid (HS). In chemical 

 character it is an incomplete hody^ There is a hiatus in its 

 constitution, which must be filled up. When it dissolves in 

 any menstruum, we may be sure that it has first acquired its 

 second or saline atom of water, or something in its place. 

 Hence a set of reactions of sulphuric acid, which are peculiar 

 to its concentrated condition, upon alcohol and many organic 

 bodies. But to this pecuhar state of bodies I shall again have 

 occasion to allude under sulphate of lime, a body which illus- 

 trates it more strikingly than the sulphate of water. 



Sulphate of Water with Sulphate of Potash : HS(KS). Bisul- 

 phate of Potash, 



Of all the sulphates, the acid sulphates or bisulphates of 

 potash and soda deviate least from the primary sulphate of 

 water. We have, in the one case, merely sulphate of potash ; 

 and, in the other, sulphate of soda, substituted for the saline 

 atom of water of the sulphate of water. In none of the speci- 



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