On definite Proportions. 437 
scribed; the other, which was of the same nature with 
the first deposition, formed small brick-coloured spots, 
exactly like the fructifications of fern, which constituted a 
subsubnitrite of the protoxide, . 
By the formation of this subsubsalt, I found myself dis- 
appointed in my expectation of being able to determine the 
quantity of iead necessary for the formation of the subsalt. 
] was therefore obliged to endeavour to determine it by ap- 
proximation, boiling the nitrate of lead in distilling vessels 
with different quantities of lead, and remarking the greatest 
quantity that could be formed without the production of 
any subsubsalts. In the first experiment, 10 ¢ grains” of 
nitrate of the protoxide of lead dissolved 73 gr. of lead, 
without any traces of a subsubsalt. I then heated again the 
solution which had cooled, and put m 1 gr. of lead, with 
which I boiled it foran hour. Of this+¢8 gr. were dissolved, 
and while the solution was cooling, some groups of sub- 
subsalt were formed. Another portion of 10 gr. of nitrate 
of lead was boiled with 7-9 gr. of lead, until it was com- 
pletely dissolved ; while the solution was cooling, some 
slight trates of the subsubsalt appeared. A third quantity, 
in which 7°8 gr. of lead had been dissolved, showed indeed 
no very distinct traces of a subsubsalt; but the lowest part 
of the crystallized mass, at the bottom of the vessel, ap- 
peared to be somewhat redder than the upper part. And 
since the subsubsalt is not completely insoluble m cold 
water, I thought I had no reason to expect a more accurate 
determination of the question by this mode of approxima- 
tion. 
It is easy to compute how much lead must be dissolved 
by the nitrate of the protoxide of lead, in order that 1t may 
be changed into the subnitrite. For if, according to the 
Jater analysis already related, the neutral subnitrite of the 
protoxide of lead contains in 305°s7 parts 100 of the nitric 
acid, which, in order to become nitrous acid, must give out 
17°6 parts of oxygen, or, according to the determination 
from the volumes of the gaseous component parts of the 
nitric acid, 17°3953; the protoxide of lead, which is formed 
_ during the process, is not sufficient to bring ali the nitrous 
acid to the same degree of saturation, but there is an excess 
of 5°74 parts of mirous acid. It will be found by a very 
easy calculation, that when nitrous acid becomes nitrous 
gas, it loses a fourth of its whole quantity of oxygen, and 
consequently that two parts of nitrous acid must be decom- 
posed in order to form the protoxide of lead, which makes 
the subsalt with one part of the acid [considering the acid 
» in 
