302 Mr Granam 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 100 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 Tuomson. 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 
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