sSteeL 261 
heat employed in burning wood into charcoal is not suffi- 
cient for this purpose. 
The best burnt charcoal also, exposed to the air, gains 
13 per cent, in weight by imbibing moisture from the air, 
as well as the air itself. 
Hence in a gross way, even good charcoal as it is em- 
ployed at the furnaces in this country, may be regarded 
as containing by weight, 15 percent, water and air of va- 
rious kinds, oxygen and hydrogen ; 15 per cent, earthy 
ashes, and imperfectly -consumed impurities ; and 70 per 
cent, carbon. The water and atmospheric air would be 
in greater proportion, if the charcoal were purer ; for good 
charcoal imbibes them with avidity. 
From the very accurate experiments of Messrs. Allen 
hnd Pepys, which nearly confirm those of Lavoisier and 
Smithson Tennant, (but not those of Morveau) it; appears, 
that the following woods put into a crucible and covered 
with perfectly dry sand, exposed for 20 minutes to a red 
heat, and then for 40 minutes to a white heat, yielded of 
I charcoal as follows : 
Per cent. 
Fir-wood (white pine) yielded of charcoal 18T7 
Lignum vitas ■- - 17*25 
Box - - - 20*25 
Beach - - - 15.00 
Oak - - - 17*40 
Mahogany - - - 15*25 
It also appears, that perfectly charred willow wood, 
weighed while hot, gained 12 1-2 per cent, in weight, on 
being exposed to the air for 52 hours, and this additional 
weight proved to be chiefly water. 
Also, that in the common atmospheric temperature (60® 
of Fahrenheit) barometer at 30 inches, 100 grs. of car- 
bonic acid gas may be considered as containing 28*635 
