1815.] the Gases ly different Bodies. 245 
charcoal gives out all the gas which wet charcoal is not able to 
retain. * : 
In the same manner one volume of dry charcoal, which had 
absorbed 33 volumes of carbonic acid gas, when it was drenched in 
water, gave out 17 volumes of this gas, and of course retained only 
16 volumes. This is nearly the same proportion as in the first 
experiment. A volume of dry box-wood charcoal, which had 
absorbed 74 volumes of azotic gas, when drenched in water gave 
out G1 volumes, and of course retained only one volume of this 
gas. A volume of dry box-wood charcoal, which had absorbed 94 
volumes of oxygen gas, gave out when put into water 34 volumes; + 
and one volume of charcoal saturated with hydrogen gas retained, 
after being put into water, only 0°65 of a volume of this gas. We 
shall endeavour hereafter to employ these results. 
If charcoal which has already given out its excess of gas by being 
placed in contact with water, be put into a retort filled with water, 
and exposed to a boiling heat, a considerable quantity of fresh gas 
separates from it; but this temperature is not sufficient to drive off 
the whole of the gas which it had absorbed. 
The gas driven out by water, though it had remained for several 
days in the charcoal, did not appear in the least altered in its pro- 
perties. In oxygen gas I observed no carbonic acid, no carbureted 
hydrogen gas in hydrogen gas, nor carbonic oxide in carbonic acid 
gas. ‘The gases were always contaminated with a small quantity of 
azotic gas, which probably had previously existed in the red-hot 
charcoal. Oxygen gas alone, as I have already observed, when 
charcoal remained in it for some months, contained a small mixture 
of carbonic acid gas: a process which was still farther promoted by 
the presence of water. 
3. Heat which is disengaged by the Condensation of the Gases ly 
Charcoal. 
When box-wood charcoal, or any other species which rapidly 
absorbs gases cooled in mercury, is introduced into any gas, there is 
evolved during the condensation of the gas a quantity of heat often 
sensible to the feeling, and sufficient to raise a thermometer whose 
* The water, by penetrating into the charcoal, drives out the gas with such 
force, that in close vessels, and when a sufficient quantity of charcoal! is employed, 
the expelled gas is in a state of compression. This circumstance may be employed 
in a great scale in the preparation of very concentrated artificial soda-water, 
especially when fermenting tuns are at hand. Wehave only to place within 
these basons filled with red-hot box-wood charcoal, and when the charcoal is satu- 
rated with the gas it is to be putinto thick and strong vessels, and brought in con- 
tact with water, We must take care that the charcoal does not come in contact 
with the atmospheric air, nor must it be mixed with the water till the vessels are 
made air-tight, I have myself, without attending to these necessary precautions, 
and atthe temperature of 66°, prepared in a yessel, a fourth part of which was 
filled with box-wood charcoal, and two-thirds of it with water, and which I ren- 
dered air-tight, a soda-water which coutained more than its own bulk of carboni¢ 
acid gas, 
+ La Metherie obtained a similar result when employed in these experiments, 
See Journal de Physique, yol. xxx, 
