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trous air, which had been itfelf diminilhed one half 
by wafhing in water. The fmell of them both was 
alfo the fame ; fo that I concluded it to be the fam e 
thing, that part of the nitrous air which is im- 
bibed by water being retained in this folution. 
In order to difcover whether this was the cafe, I 
made the folution boil in a fand heat. Some air 
came from it in this ftat'e, which feemed to be the 
fame thing, as nitrous air diminilhed about one fixth, 
or one eighth, by wafhing in water. When the 
fluid part was evaporated, there remained a brown 
fixed fubftance, which was obferved by Mr. Hel- 
lot, who defcribes it, Ac. Par. 1 735, M. p. 35. 
A part of this I threw into a fmall red hot cruci- 
ble ; and covering it immediately with a receiver, 
{landing in water, I obferved that very denfe red 
fumes rofe from it, and filled the receiver. This 
rednefs continued about as long as that which is 
occafioned by a mixture of nitrous and common 
air ; the air was alfoconfiderably diminifhed within 
the receiver. This fubftance, therefore, muft cer- 
tainly have contained withi'11 it the very fame 
thing, or principle, on which the peculiar pro- 
perties of nitrous air depend. It is remarkable, 
however, that though the air within the receiver 
was diminiftied about one fifth by this procefs, it 
was itfelf as much affefled with a mixture of ni- 
trous air, as common air is, and a candle burnt in 
it very well. This may perhaps be attributed to 
fome effect of the fpirit of nitre, in the compofition 
of that brown fubftance. 
Nitrous air, I find, will be confiderably dimi- 
niihed in its bulk by Handing a long time in wa~ 
