174 On definite Proportions. 
an equai quantity of oxygen with the sulphuric acid, that is, the 
oxide of copper one-third and the ammonia two-thirds as 
much. Consequently this salt isso constituted, considering both 
its bases, as to agree with the rule for a simple subsulphate. The 
quantities of oxygen are expressed by 1 for the oxide, | for the 
water, 2 for the ammonia, and 3 for the sulphuric acid. 
It is not so easy to determine the nature of the alteration which 
the cuprum ammoniatum undergoes by exposure to the air. But 
it appears, when long kept in vessels imperfectly closed, so as to 
fall into a sky-blue powder, to lose halt of its ammonia, so that 
the sulphuric acid then stands to each base in the same relation 
as inthe neutral salts. When it is changed to a green powder, 
a still greater quantity of ammonia is lost, and the residue is a 
mixture of more or less dry neutral sulphate of ammonia with 
subsulphate of oxide of copper, accordingly as the alteration has 
been made by the effect of heat, or hy exposure to the air, The 
green powder formed by heat is capable of supporting a tem- 
perature somewhat higher, without being decomposed, but after- 
wards emits sulphurous acid, sulphite of ammonia, water, and 
nitrogen, and leaves in the retort a fused dark-brown ‘mass, 
which, when water is poured on it, affords neutral sulphate of the 
oxide of copper and red protoxide of copper, 
It is probable that all other acids are capable of forming si- 
milar double salts with these two bases; but they cannot be so 
easily exhibited, because they are more soluble in alcohol. 
If it were permitted to ground a general rule on a single ex- 
ample, I should conclude that, when an acid is supersaturated 
with two bases, both of them, taken together, contain the same 
quantity of oxygen as a single base must do, in order to form a 
subsalt with the acid; and that the oxygen of the one base must 
be a multiple of that of the other by 1, 2,3... 
2, Double Salis with two Acids, or Substances representing 
Acids, and one Base. 
These salts have been little examined, and their number‘seems 
to be small. The only examples, in any degree well established, 
are afforded by the combinations of a base with sulphur and sul- ° 
phuretted hydrogen, and with sulphur and sulphuric aeid, It is 
probable, that in these cases the two [negative] substances di- 
vide the [positive] one between them, and take up either equal 
portions of it, or such portions as are in the proportion of | to 
2, 3, or 4. 
I have mentioned, in the First Continuation of my Essay, on 
occasion of the investigation of the relation of the oxygen of the 
acids to that of the bases of salts, a double salt consisting of the 
nitric and arsenic acids with protoxide of lead, When I oe 
voured 
