336 Observations on the Absorption of (Nov. 
in the former. This free communication between the gases in the 
charcoal, and those surrounding it, is a proof that the gases mixed 
in the charcoal do not form any lasting combination, as would be 
the case if water were formed; but that, in consequence of their 
mutual contact in the charcoal, they are merely a little condensed. 
If charcoal free from air, but drenched in water, be brought in 
contact with oxygen gas, carbonic acid gas, or azotic gas, these 
gases, while they penetrate into its pores, drive out a portion of the 
water. It is to be presumed that Messrs. Rouppe and Norden took 
this disengaged water for new formed water. ‘This is the more pro- 
bable, as in their experiments the gases stood over water, of which: 
the charcoal, while it absorbed the gases, must have imbibed a. 
certain portion. 
I pass over the detail of the experiments which I made respecting 
the mutual expulsion of gases from charcoal with hydrogen and 
azotic gases, oxygen and azotic gases, and oxygen and carbonic ’ 
acid gases. ‘They were made with the same care as_ those’ with 
oxygen and hydrogen gases; and they furnished similar results, with: 
the exception that azotic and carbonic acid gases, when in contact 
in charcoal, do not appear to increase the condensation of each 
other. In all other respects, as may be easily conceived, these » 
mutual expulsions are so much the more conspicuous, the greater 
the difference of condensation is which hoth gases undergo when 
absorbed by charcoal. Hence it is very striking when the gases are 
hydrogen and carbonic acid; and most of all, when they are am- 
monia and hydrogen. 
From this action of the gases on each other, which expel each 
other from a porous body, it is evident that a porous body which has - 
saturated itself with atmospherical air, and which is put into a gas 
without being deprived of air, may either increase or diminish the 
volume of that gas, according as it is absorbed in greater or smaller 
quantity than common air. In like manner, a piece of charcoal or» 
of meerschaum saturated with common air will perceptibly diminish 
a given volume of carbonic acid, and increase that of hydrogen gas, 
in which it is put. It is highly probable that the odoriferous vapours 
of bodies rendered evident by moist air, and likewise the smells of 
flowers, depend upon such mutual expulsions of gaseous bodies. 
If a piece of charcoal free from air be put into a mixture of 
oxygen and hydrogen gases, an absorption takes place, which holds 
the same proportion with respect to the two gases as when the char- 
coal is first saturated with the one, and then placed in the other. I 
placed, for example, a piece of box-wood charcoal free from air 
into 16 volumes of a mixture containing } oxygen and 4 hydrogerr — 
gases; so that both gases were in the proportions requisite for the 
formation of water. Of this mixture, very nearly three volumes of 
oxygen and one volume of hydrogen were a! bsorbed. ‘This result 
corresponds very well with the proportion of single gases that would 
have been absorbed, and likewise the relative proportion in which » 
they were mixed before absorption. 
is 
