[ 2 4 6 3 
(and perhaps lefs time would have been fufficient) 
when I found, upon trial, that it was reftored to 
its former perfe&ly wholefome (late. It efter- 
velced with nitrous air as much as the bed common 
air ever does, and even a candle burned in it very 
well, which I had never before obferved of anv kind 
ot noxious air meliorated by agitation in water. 
1 his ieries of fadls, relation- to air extracted from 
nitre, appear to me to be very extraordinary and 
important, and, in able hands, may lead to conli- 
derable difcoveries. 
There are many fubftances which impregnate the 
air in a very remarkable manner, but without 
making it noxious to animals. Among other things 
1 tried volatile alkaline (lilts, and camphire, the 
latter of which I melted with a burning glafs, in 
air incloled in a phial. Themoufe which was put 
into this air fneezed and coughed very much, efpe- 
cially after it was taken out; but it prefently re 
covered, and did not appear to have been fend bly 
injured. 
Having made feveral experiments with a mixture 
of iron filings and brimftone, kneaded to a pafte 
with water, I had the curiofity to try what would 
be the effect of fubftituting brafs dull in the place 
of the iron filings. The refult was, that when 
this mixture had flood about three weeks, in a 
given quantity of air, it had turned black, but was 
not increafed in bulk. The air alfo was neither 
fenfibly increafed nor decreafed, but the nature of 
it was' changed, for it extinguifhed flame, it would 
have killed a moufe prelently, and was not reftored 
by ftxed air, which had been mixed with it feveral 
da vs. 
I have 
