"1815.] ° the Gases ly different Bodves. 247 
absorbed some moisture from the air, which might prove injurious 
‘to the absorption, | repeated them with charcoal, which, after being 
dried in a red heat, was introduced into a glass receiver full of 
common air standing over mercury. In this case the absorption of 
~ the charcoal was somewhat greater than before; but it always re- 
mained smaller than when charcoal was used that had been heated 
to redness, obviously on account of the air left behind in the char- 
coal by the incomplete vacuum produced by the air-pump. 
To ascertain what influence the density of a gas has upon the 
volume which charcoal is capable of absorbing, I introduced a piece 
of charcoal, which had been saturated with gas under the common 
pressure of the atmosphere into a torricellian vacuum in the top of 
a barometer tube, the inner diameter of which was 0°78 inch. As 
soon as the charcoal came into the vacuum, it allowed a portion of 
its gas to escape, which caused the barometer to fall a great way, 
from which the density of the gas set free was easily deduced. From 
the bulk of the portion of the tube occupied by this gas, and this 
balk subtracted from the whole volume which the gas absorbed by 
the charcoal would occupy in this new situation, it was easy to de- 
termine the quantity of gas still remaining in the charcoal.» I 
wished to make these experiments also under other pressures of the 
atmosphere ; and on that account allowed determinate quantities of 
gas to enter into the barometer tube. 
Exper. 1.—A piece of box-wood charcoal, which under the 
barometrical pressure of, 28°91 inches, and in the temperature of 
65°, had absorbed 341 volumes of carbonic acid gas, was put into 
an atmosphere of carbonic acid gas, the density of which, after the 
separation of the gas from the charcoal, was equivalent to the pres- 
sure of 10°26 inches of mercury. Under this pressure the 341 
volumes of gas, supposing them completely extricated from the 
charcoal, would have occupied the bulk of 97°21 volumes. Of 
these 28°16 volumes had escaped out of the charcoal. It still re- 
tained 69-05 volumes. Hence it follows that charcoal absorbs a 
greater bulk of rarified carbonic acid than when it is of its usual 
density. 
Exper. 2.—I left the charcoal in the barometer tube, and in- 
creased the density till it equalled the pressure of 15°9 inches of 
mercury. At this density the 341 volumes of gas amounted to 62°74 
volumes. Of these 12°83 volumes had escaped; so that the char- 
coal still retained 49°91 volumes. 
I made several other experiments, which gave me similar results. 
It follows from the whole that the absorption of gases, if it be esti- 
mated by the volume, is far greater in a rare than in a dense atmos- 
phere ; but if we reckon this absorption by the weight, it is more 
considerable in the latter than in the former state of the atmos- 
phere. These observations, however, apply only to those gases 
that are absorbed in considerable quantities. ‘The difference is 
scarcely perceptible when the absorption amounts only to about one 
volume, 
When these experiments shall have been prosecuted, it is pro- 
~~ 
