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VII. 



Of Air infected with the fumes of burn- 

 ing CHARCOAL, 



Air infected 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 dufl of charcoal. This diminution he afcribed 

 to fuch a deftruclion of common air as Dr. Hales 

 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 circumftances, and 

 with nearly the fame refult. 



Afterwards, I endeavoured to afcertain, by what 

 appears to me to be an ealier and a more certain me- 

 thod, in what manner air is affected with the fumes 

 of charcoal, viz. by fufpending bits of charcoal 

 within glafs veffels, filled to a certain height with' 

 water, and {landing inverted in another vefTel 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. Gg turbid, 



