Life and Writings of Theodore de Saussure. 27 



these lines, (the Bihlioth^que Britannique as it was then named), 

 is the absorption of gases by different bodies. The fundamen- 

 tal experiment is striking when we see it for the first time. 

 If we introduce some pieces of charcoal, heated to redness, into 

 a tube placed on a mercurial trough, and filled with air, or 

 rather with one of the gases more absorbable than it, such as 

 ammoniacal gas, or muriatic acid gas, we see the gas become 

 rapidly absorbed, and the mercury soon ascend with the char- 

 coal up to the summit of the tube. It will be understood how 

 striking such an experiment is, when we know that a morsel 

 of box- wood charcoal absorbs, at the ordinary temperature, 

 ninety times its volume of the gases I have named. Theodore 

 de Saussure has divided his work into three sections, which 

 treat of the absorption of pure gases by solids, of the conden- 

 sation of mixed gases by the same agents, and, finally, of the 

 absorption of gases by liquids. 



In order to avoid the action of the air, the author submerged 

 the incandescent charcoal under the mercury, and then intro- 

 duced it into the different gases ; and when he had to use other 

 porous bodies, which it would have been inconvenient or im- 

 possible to heat, he placed them in the vacuum of a good air- 

 pump. The experiments were always made under the mercury, 

 and were performed with twelve pure gases of different kinds. 

 The result of these trials was to prove that, so far from the 

 carbon alone having this remarkable property, all porous bodies 

 absorbed a greater or less quantity of gas. This property de- 

 pends on various circumstances. Thus, the lower the temper- 

 ature is, the greater is the absorption. It is non-existent at a 

 red-heat, and this heat is even sufficient to disengage all the 

 gas with which porous bodies can be penetrated. The greater, 

 also, the pressure, the more do porous bodies absorb the pon- 

 derable parts of gas. When it is wanting, absorption ceases, 

 and we may deprive a porous body in a vacuum of all the gas 

 it had condensed. 



Independently of these circumstances, absorption varies ac- 

 cording to the nature of the gases brought in contact with the 

 porous bodies. Thus, in general, ammoniacal gas is the kind 

 which is absorbed in greatest proportion, and hydrogen in 

 smallest. But it would appear that there are differences be- 



