246 Observations on the Absorption of (Ocr. 
bulb is in contact with about + of a cubic inch of charcoal several de- 
grees. The heat, as might have been expected, appears to increase with 
the absorbahility of the gas. Charcoal becomes hotter in ammo- 
niacal than in carbonic acid gas, and hotter in this gas than in the 
less absorbable oxygen gas. Hydrogen gas, which is the least ab- 
sorbable of all, gives out so little heat, that the methods which I 
employed were not sufficiently delicate to detect any. * This evolu- 
tion of heat depends much more upon the rapidity with which the 
absorption takes place than upon the degree of the condensation ; 
since, according to Gay-Lussac’s experiments, different gases when 
equally compressed give out different quantities of heat. 
4. Influence of the barometrical Pressure on the Condensation of 
Gases by Charcoal. ; 
Hitherto heat only has been employed to render charcoal fit for 
absorbing gas. I have tried to produce the same effect by means of 
the air-pamp, and have obtained nearly the same-results. 
A piece of box-wood charcoal, which had stood exposed to the 
air for some days, was put into a receiver fixed to a small portable 
plate by means of tallow, and screwed upon the plate of the air- 
pump, so as to be air-tight. The air being pumped out of the 
receiver and charcoal by an exhaustion amounting to 0°16 inch of 
mercury, the transferrer with its receiver is brought into the mer- 
curial trough, and the cock of the transferrer being opened under 
the mercury, that. liquid flows in and fills the receiver, and the 
transferrer may now be removed. The charcoal is now, without 
coming in contact with the external air, introduced into another 
receiver fiiled with carbonic acid. The absorption at the tempera- 
ture of 534° amounted to 311 volumes. Charcoal heated red-hot 
produces in the same circumstances an absorption amounting to’ 35 
volumes. 
I repeated the same experiment with oxygen gas. The absorption 
produced in this way amounted to 81 volumes of the charcoal, while 
charcoal heated to redness absorbed 91 volumes. Charcoal freed of 
air by the air-pump absorbed seven volumes of azotic gas in place 
of 71. volumes which charcoal heated to redness absorbed. 
As the charcoal which was employed in these experiments had 
* The bulb of my thermometer was 24 lines in diameter. The tube was bent 
in the form of a Y. * The end on which was the bulb was introduced through the 
mercury into the receiver. The outer arm held the scale; and served both to hold 
the instrument and to bring the bulb in contact with the charcoal, 
+ Instead of this transferrer, the following method may be employed. A small 
receiver containing the charcoal is tied by strings to a dish which is ‘filled with 
mercury, and laced under the common receiver of the air-pump, When the air 
has been pumped out of the large receiver, and likewise out of the small, a com- 
munication is opened between (he inside of the large receiver and the external air, 
The mercury in the dish js now forced into the small receiver, and fills it. The 
string is now untied, and the small receiver standing on the dish is conveyed to the 
mercurial trough, But the exhaustion produced in this way is not quite so great as 
in the other, on account of the resistance made by the mercury in the dish to the 
escape of the air from the small receiver. 
