On the Metallic Salts. 35 
the muriat of lead, the nitric acid to the sulphat of silver, &c., 
promotes materially the solubility. 
In support of H.’s assertion, that metallic salts are super-salts 
with excess of oxide, he instances the formation of sulphat of 
iron; and says, that after the action ceases, if sufficient iron had 
been introduced, part of it remains uncombined, and the solu~ 
tion acid; but this arises, I conceive, from the want of contact 
between the free acid and iron, the crystals as they form sur- 
rounding it; and this, perhaps, is one reason why sulphat of iron 
is seldom obtained unmixed with the super-sulphat. 
He states also that acid is indicated on the application of the 
test to a large crystal of sulphat of copper on breaking it. I 
never had the satisfaction of obtaining a large crystal of the 
salt, and am inclined to suspect it more than probable he might 
try the blue vitriol of commerce, which is well known to be a 
super-salt, the neutral sulphat being seldom, if ever, obtained ; 
or, if he really tried a large crystal of the neutral sulphat, it is 
not unlikely that a minute portion of acid might have been re- 
tained in the interstices or between the laminz of the crystal. 
My opinion is, that there can be no solution of a metallic salt 
without acid either free or in excess. Fourcroy, as before ob- 
served, noticed this, as well as Bergman and most other chemical 
writers; and as this superabundance always appeared on the 
solution of the salt, or was required to be added to enable the 
salt to dissolve, it is natural to conclude that it is essential either 
to the existence or to the solution of the salt. I am inclined 
to adopt the latter opinion. 
Were the reasons before stated insufficient, I think the doc- 
trine of Dalton decisive in favour of the existing theory. From 
the mean of the most correct analysis,it appears that the binary 
and ternary salts are composed of an equal number of atoms of 
base and acid, or the one a multiple of the other, whether al- 
kaline, earthy, or metallic; and that, with very few exceptions, the 
neutral salts contain an equal number of atoms of base and acid, 
and in the super- and sub-salts the acid or base is a multiple of 
the other respectively ; a coincidence so strong, and in my judge- 
ment so conclusive, that if a minute quantity of acid can be de- 
tected in a neutral salt, it can only be considered in a free state, 
and by no meas a constituent part of the salt. 
I am, sir, 
Most obediently yours, 
Stoke Newington, Jan. 1, 1616. / G,.S. 
CZ 1X. On 
