[ 2 + 5 ,] 
palling the air feveral times through cold water, 
the original quantity was diminished about In 
the remainder a candle would not burn, and a 
moufe would have died prefently. The fmell of 
this air was exceedingly pungent, but different from 
that of the putrid effluvium. A mouie lived per- 
fectly well in this air, thus afieCted with the ace- 
tous fermentation ; after it had flood feveral days 
mixed with four times the quantity of fixed air. 
All the kinds of factitious air on which I have 
yet made the experiment are highly noxious to 
animals, except that which is extracted from fait— 
petre, or alum ; but in this even a candle burned juft 
as in common air. In one quantity which I got from 
falt-petre a candle not only burned, but the flame 
was increafed, and Something was heard like a 
hifiing, Similar to the decrepitation of nitre in an 
open fire. This experiment was made when the 
air was frefh made, and while it probably con- 
tained fome particles of nitre, which would have 
been depofited afterwards. The air was extracted 
from thefe fubftances by putting them into a gun 
barrel, .which was much corroded and fbon Spoiled by 
the experiment. What effeCt this circumftance 
may have had upon the air I have not confidered. 
November 6, 1772, I had the curiofity to exa- 
mine the State of a quantity of this air, which had 
been extracted from falt-petre above a year, and 
which at firft was perfectly wholefome ; when, to* 
my very great furprize, I found that it was be- 
come, in the higheft degree, noxious. It made 
no effervefcence with nitrous air, and a moufe died 
the moment it was put into it. I had' not, how- 
ever, waffled it in. rain water quite ten minutes 
