168 On definite Proportions. 
a.) The oxygen of the acid in a subsalt may be either a sub- 
multiple, or a multiple, by a whole number, of that of the base. 
b.) The quantity of a base, which is combined with a given 
quentity of an acid in a subsalt, can be a multiple of the quantity 
in the neutral salt by such a number only, as is.capable of ex- 
pressing the proportion of the quantity of the oxygen of the acid 
to that of the base. For instance, in the subsulphates, the base can 
only be a multiple by 3, 6, 9, of the quantity in the neutral salt, 
and not by 2,4,5, 7,8. On the other hand, acids which con- 
tain, in their neutral salts, 2, 4, 6, or 8 times as much oxygen as 
the bases, may take up in their subsalts 2, 4, 6, or 8 times as 
much of the base as in the neutral salts; but not 3, 5, 7, or 9 
times. 
It still remains to be inquired, whether there exists a subsalt, 
in which the base-is less than double that of the neutral salt ; 
for instance, whether any subsulphate exists, in which the acid 
contains twice as much oxygen as the base, or a subnitrate, in 
which the acid contains exactly four times as much oxygen as the 
base. 
II. Laws ror Th& FoRMATION OF DOUBLE SALTS. 
The combinations which, in the first Antiphlogistic Nomen- 
clature, were called ¢ériple salts, have been latterly more properly 
denominated double salts ; being always composed of two neutral 
combinations ; and they may commonly be obtained by mixing 
the solutions, and crystallizing them together. 
These double salts may be of different kinds: containing either 
one acid and two bases; or two acids, or substances representing 
acids, and a single base. Of the former kind we are acquainted 
with several salts, of the latter with only a few, and with none 
very accurately. 
1, Double Salts of a single Acid. 
The principle of the formation of these double salts is not dif- 
ficult to be found, since we know that most of the supersalts, if 
they are saturated with a second base, afford such salts, and it has. 
been shown that the supersalts contain twice as much of the acid 
as the neutral salts. Consequently the new base must contain 
exactly the same quantity of oxygen as the base of the supersalt. 
For example, the soda, the protoxide of iron, or the protoxide of 
antimony, with which the supertartrate of potass is neutralised 
in pharmaceutical preparations, must contain as much oxygen as. 
the potass, because it neutralises an equal quantity of the acid. 
We shall find from the analysis of alum, that the existence of the 
double salt, in these cases, depends not so much on the acid, as 
en the affinity of the bases; for alum cannot be obtained by sa-! 
. turating 
