j Formation of nitrous Add, 265 
€>f mercury in fpirit of nitre, but not fo ftrong ns when equal 
parts of this folution and folution of nitre were ufed. 
A folution of fixed vegetable alkali, dropped into fome of it 
diluted, produced a flight reddifh-brown precipitate, which 
afterwards aflumed a greenifh colour. 
A bit of bright copper being dipped into it, acquired an 
evident whitifh colour, though not fo white as when dipped 
into the folution of mercury in fpirit of nitre. 
From thefe experiments it appears, that the mixture of the tw r o 
airs was actually converted into nitrous acid, only the experi- 
ment was continued too long, fo that the quantity of air abforbed 
was greater than in my experiments, and the acid produced 
was fufficient, not only to faturate the foap-lees, but alio to 
diflolve fome of the mercury. The truth of the latter part is 
proved by the metallic tafte of therefiduum, its not dilcolour- 
ing the blue paper, the precipitate formed by the addition of fixed 
alkali, and the white colour given to the copper ; and the nitrous 
fumes produced by the addition of oil of vitriol, as well as the 
manner in which paper impregnated with the refiduum burnt, 
fhew as plainly, that the acid produced was of the nitrous 
kind. It is remarkable, however, that during this experi- 
ment there were no figns which fhewed when the foap-lees 
became faturated. The only time when the diminution proceeded 
much flower than ufual was on January 4. It then feemed 
to go on very {lowly ; but as the air abforbed at that time was 
only 4830 meafures, which is much lels than what feems re- 
quifite to faturate the alkali, and as the diminution imme- 
diately went on again upon adding more common air, it feems 
not likely, that the foap-lees were laturated at that time. 
On January 10, Mr. Gilpin obferved a fmall quantity of 
whitifh fediment on the furface of the mercury ; which feems 
to 
