[ I«S ] 
jn g that candles would burn, and animals live, in 
air extra&ed from faltpetre. I therefore fpent a 
good deal of time in attempting, by a burning-glafs, 
and other means, to impregnate this noxious air 
with fome effluvium of faltpetre, and, with the fame 
view, introduced into it the fumes of the fmoaking 
fpirit of nitre ; but both thefe methods were altoge- 
ther ineffectual. 
In order to try the effeCt of heat, I put a quantity 
of air, in which mice had died, into a bladder, tied 
to the end of the Item of a tobacco-pipe, at the other 
end of which was another bladder, out of which the 
air was carefully preffed. I then put the middle 
part of the Item into a chafing-diffl of hot coals, 
Itrongly urged with a pair of bellows ; and, preffing 
the bladders alternately, I made the air pafs feverai 
times through the heated part of the pipe. 1 have 
alfo made this kind of air very hot, {landing in water 
before the fire. But neither of thefe methods were of 
any ufe. 
RarefaClion and condenfation by inftruments were 
alfo tried, but in vain. 
Thinking it poffible that the earth might imbibe 
the noxious quality of the air, and thence fupply the 
roots of plants with fuch putrefcent matter as is 
known to be nutritive to them, I kept a quantity 
of air, in which mice had died, in a phial, one half 
of which was filled with fine garden mould ; but, 
though it Hood two months in thefe circumftances, 
it was not the better for it. 
I once imagined that, fince feverai kinds of air 
cannot be long feparated from common air, by being 
■confined in bladders, in bottles well corked, or even 
Vol, LXII. " B b ' clofed 
