302 Mr Graham on Water as a Constituent of Salts. 



most precisely. This in fact is an exact method of obtaining 

 the definite sulphate of water with saline water ; which may be 

 kept at 380° or 390°, without sustaining any farther loss. I have 

 observed a close approximation to the same proportion 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 distil over with 

 the water expelled. When, however, this hydrate is distilled in 

 vacuo, at the last-mentioned temperature, 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 tem- 

 perature not exceeding 212°, at which it was sustained in vacuo 

 for not less than forty hours. It consisted of 1 00 parts dry acid 

 united with 68.07 water, while three atomic proportions 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. Anhydrous sul- 

 phate 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 compound which is 

 soluble, &c. So it is with the sulphate of water, or concentrated 

 sulphuric acid (HS). In chemical character it is an incomplete 

 body. 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 some- 

 thing 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 peculiar state of bodies I shall 



