with the Nitric and Nitrous Acids. 267 
fire under the matrass, and took care during the whole opera- 
tion to keep up a boiling heat only. By these means there was 
but very little water to be vaporized. The experiment began 
at seven in the morning; at eight the water was boiling. T he 
air’in the bell-glass was dilated. At nine the liquor was of a 
fine yellow, At half past ten red nitrous vapour was formed in 
the tube, and it augmented gradually. When it reached the 
bell-glass absorption ‘took place, and a piece of turnsole paper 
which I introduced into it was strongly reddened. At eight in 
the evening the operation was stopped: it was evident that the 
air of the apparatus had been reduced inte azotic gas, and that 
there had been a little nitric acid condensed in the tube. This 
experim rent puts it beyond doubt, that it is not at the expense of 
the oxygén of the litharge that the lead is oxidated, but rather 
at the expense of that of the nitric acid; in the second place, that 
the nitric acid is reduced by the lead into nitrous acid, which 
yemains in combination with the oxides, and into nitrous gas 
which is liberated, I am ignorant if the decomposition goes so 
far as to give out azotic gas. 
13. This decomposition of the nitric acid fixed to one base is 
certainly very remarkable; and if actual experiments had not 
provedat, I could not have thought it possible. The acid nitrate 
of lead is not the only salt of its kind which is susceptible of 
being changed into nitrite; for, if we boil a solution of nitrate of 
potash over small pieces of lead, and if we concentrate the li- 
uor so as that the greatest part of the nitrate is. crystallized 
upon cooling, we find in the mother water plenty of nitrite of 
potash, which emits the red vapour when we mix sulphuric acid 
with it. This mother water contains merely an atom of lead, 
which sulphusetted hydrogen demonstrates. In this experiment, 
it is to all appearance the atlinity of lead for oxygen and for 
water, which determines the decomposition of the nitric acid, 
while in the former it is the affinity of lead for oxygen and for 
the nitrous acid. 
14, I have said above, that when we boiled over lead the solution 
of the acid nitrate of this metal, the liquor took a yellow colour, 
which ended by entirely disappeari ing. If we stop the eperation 
when the colour is pretty deep, we obtain, upon cooling, vellow 
leafy crystals: the liquor from which they are deposited yields, 
when concentrated and cooled, crystals of the same kind, if the 
solution of the nitrate has not boiled too long over the lead. 
This salt is the same with that described by Messrs. Proust-and 
Thomson, but it differs considerably from that which I obtained 
from the three experiments which I have mentioned: in fact, 
the latter does not colour the water which holds it in solution ; 
instead 
