452 On definite Proportions. 
acid is saturated with the greatest possible quantity of a 
base, the acid contains an equal quantity of oxygen with 
the base, so far as we consider it as composed of oxygen 
and nitrogen, and do hot take into account the oxygen of 
the nitrogen. We shall obtain another confirmation of | 
this statement from the subsubnitrite of the protoxide of 
lead, to which we shall now proceed. 
III. Tue Nirtrites. 
Since the proofs which, as we have seen, may be derived 
from the analysis of the neutral nitrates in favour of the 
composition of ammonia and nitrogen, are so highly im- 
portant and indispensable, and since the ideas, to which 
they lead, are contrary to the older opinions, and will meet 
with much opposition among chemists, I have considered 
it as essentially necessary to examine more accurately every 
thing which might appear ambiguous or uncertain in these 
proofs. In order to place beyond all doubt the truth of the 
opinion that the nitric acid is composed of ammonium and 
oxygen, I resolved to employ an observation which I had 
had occasion to make in the course of my extensive inyes- 
tigations respecting the salts of lead. 
Subnitrite of the Protoxide of Lead. 
It is a fact first discovered hy Proust, and since universally 
understood, that if we boil metallic Jead with a solution of 
nitrate of the protoxide of lead, the lead is dissolved, and 
we obtain a yellow fiaid, which shoots into scaly yellow 
crystals. Mr. Proust considered this combination as a salt 
in which the lead was reduced to a lower degree of oxida- 
tion. Dr. Thomson on the other hand calls the same salt, 
which he obtained from the nitrate by means of heat, com- 
mon subnitrate of the protoxide of lead. Neither of these 
chemists had directed his attention to the alteration of the 
condition of the acid: hence arises the contradiction in 
their resulis, neither of which is more correct than the 
other. 
I had very often found, that when I dissolved lead in 
nitric acid, the solution was at Jast of a lemon colour, 
without obtaining from it the scaly salt described by Mr. 
Proust. Since these yellow solutions were less disposed to 
crystallize than the common ones, and afforded a yellow 
salt, I attempted to force them to crystallize by the. addi- 
tion of nitric acid: for it is known that several salts are 
precipitated from their solutions in water by the addition of 
uncombined acid; probably because the capacity of the 
water 
