the Nitrates and Nitrites of Lead. 405 
I have spoken in my memoir of the difficulty of determining 
the water of the subnitrite at the minimum, because the acid 
begins to be disengaged from it at a temperature of 100° centi- 
grade: in order to attain this, I heated on a sand-bath at a 
gentle heat some subnitrite at the minimum, until no more di- 
minution of weight took place. The salt when thus heated 
still retained some water. As it may be objected with reason 
that a portion of acid may have been volatilized, I made a test, 
by distilling the subnitrite with its water in a small glass retort 
communicating with a tube filled with muriate of lime: the re- 
sult of this experiment confirmed the former; only the propor- 
sion of base was a little stronger. It would be needless to detail 
this experiment; but, as M. Berzelius is of a different opinion, 
I shall describe it minutely. 
I put 100 parts of pure subnitrite at the minimum which con- 
tained 80 of base into a very small glass retort blown with a 
lamp. A tube 14 millimetres in diameter, curved, comniuni- 
eated with the retort by one of its extremities, and by the other 
to a bent tube filled with calcined muriate of lime. The ex- 
tremities of this tube by which the gases were extricated were 
inserted into mercury. The weight of the whole apparatus was 
determined with a very nice balance. I put the retort on a 
wire grating supported by bricks, and placed under it a spirit 
lamp: when the retort was heated, | surrounded it with burning 
coals: a little water was extricated, nitrous acid gas in great 
quantity, which soon filled the whole apparatus, and a part of 
which escaped. When the operation was terminated, and when 
all the liquid which moistened the sides of the retort had passed 
into the intermediary-tube, I stopped the operation : I closed 
this tube, and that containing the muriate of lime with stoppers 
previously’ weighed ; I introduced a tube into the retort, and 
blew into it, in order to drive away the nitrous vapour : without 
this, the latter would have been absorbed when the oxide of lead 
was cooled. 
When the retort was weighed, I passed joseph paper into the 
neck, in order to take up the water which might be there. I 
weighed it again, and found that it had not perceptibly di- 
minished in weight: there remained in the retort 825 of oxide, 
while the same salt decomposed in a crucible had given 80. I 
ascribe this difference to a portion of the acid not having been 
disengaged hy heat; or, in spite of the precaution which I had 
observed of blowing into the retort, a portion of the vapour had 
already entered into combination, ‘The intermediary tube con- 
tained 4-6 parts of water, and the tube with the muriate of lime 
0:5, which makes for 100 parts of subnitrite at the minimum 
5-1 of water, But this water was saturated with nitrous acid, 
Ces and 
