12 
Book II. 
Buengsh. a 
variousden 
sities. 
ACIDS. 
is also evolved when other proportions of acid and wa 
ter are mixed together, though not in so great quantity. 
Lavoisier and De la Place found, that when 2.625 lbs. 
troy of sulphuric acid, of the specific gravity 1.87058, 
were mixed with 1.969 lbs. troy of water, as much ca 
loric was evolved as melted 4.1226 lbs. troy of ice, or 
as much caloric as the acid and water would have given 
out had they been heated without mixture to 155.9°*. 
We have no reason to suppose that sulphuric acid, 
at the density of 2.00o, is free from all mixture of, wa 
ter ; so far from that, we know for certain that it con 
tains a considerable proportion ; for when it is combi 
ned with other bodies (barytes, for instance, or potass), 
there is a considerable quantity of water which remains 
behind, and does not enter into the combination. Now, 
is it possible to determine how much real acid and how 
much water are contained in a given quantity of acid of 
a given specific gravity? Attempts were made to an 
swer this important question by Homberg, by Berg 
man, by Wenzel, and by Wiegleb; but the differences 
between their determinations were too great to place 
any confidence in their accuracy. The subject has late 
ly been resumed, and prosecuted with much industry 
and skill by Mr Kirwan, whose results may be consi 
dered as approaching as nearly to perfect accuracy as 
the present state of the science admits. His method 
was as follows : He dissolved 86 grains of potass in wa 
ter, and saturated it exactly with sulphuric acid of a 
given specific gravity (we shall suppose of 2.00), and 
diluted it with water till its specific gravity was 1.013. 
Forty-five grains of sulphat of potass, dissolved in 1017 
* Mem. Par. 1780.