[ 225 ] 
VII. 
Of Air infected with the fumes of BURN- 
ING CHARCOAL. 
Air infedled with the fumes of burning charcoal 
is well known to be noxious ; and the Honourable 
Mr. Cavendifh favoured me with an account of fome 
experiments of his, in which a quantity of common 
air was reduced from 180 to 162 ounce meafures* 
by palling through a red-hot iron tube filled with 
the dull of charcoal. This diminution he afcribed 
to fuch a deftru&ion of common air as Dr. Hale# 
imagined to be the confequence of burning. Mr. 
Cavendifh alfo obferved, that there had been a gene- 
ration of fixed air in this procefs, but that it was 
abforbed by fope leys. This experiment I alfo re- 
peated, with a fmall variation of circumflances, and 
with nearly the fame refult. 
Afterwards, I endeavoured to afcertain, by what 
appears to me to be an eafier and a more certain me- 
thod, in what manner air is affedted with the fumes 
of charcoal, viz. by fufpending bits of charcoal 
within glafs veflels, filled to a certain height with 
water, and Handing inverted in another veflel of 
water, while I threw the focus of a burning mirror, 
or lens, upon them. In this manner I diminifhed a 
given quantity of air one fifth, which is nearly in 
the fame proportion with other diminutions of air. 
Some fixed air feems to be contained in charcoal, 
and to be fet loofe from it by this procefs *, for if I 
made ufe of lime-water, it never failed to become 
Vol. LXII. G g turbid j 
