242 Mr. W. Crum on the Manner 



and Saxon hydrophane, which is nearly pure silica, absorbs 

 64 times its bulk. The gases enter into no combination with 

 the solid which absorbs them, for the air-pump alone destroys 

 their union. 



The manner in which gases are attracted to the surfaces of 

 solid bodies is very much like that which these exert on sub- 

 stances dissolved in water. The charcoal of bones has been 

 long employed to remove colouring matter from the brown 

 solution of tartaric acid, from syrup in the refining of sugar, 

 and from a variety of other liquids containing organic sub- 

 stances ; and it is found that the colouring matter so attracted 

 remains attached to the surface of the charcoal without effect- 

 ing any change upon it. In this animal charcoal the carbon 

 is mixed with ten times its weight of phosphate of lime, and 

 if that be washed away by an acid, the remaining charcoal has 

 nearly twice the decolorating power of an equal weight of ivory- 

 black. Bussy, who has made the action of these charcoals the 

 subject of particular investigation, informs us that if ivory- 

 black, after the extraction of its earth of bones by an acid, be 

 calcined along with potash, and the potash be afterwards 

 washed out ; or if blood be at once calcined with carbonate of 

 potash and washed, the remaining charcoal has the power of 

 decolorating twenty times as much syrup as could be done by 

 the original bone charcoal. Animal charcoal removes also 

 lime from lime water, iodine from a solution of iodide of po- 

 tassium, and metallic oxides from their solutions in ammonia 

 and caustic potash. 



A satisfactory explanation of these remarkable facts has yet 

 to be sought for. Mitscherlich calls the force which produces 

 them an action of contact, or attraction of surface ; and he 

 calculates, as we have seen, the extent of surface in propor- 

 tion to the mass as the measure of the force which it exerts. 

 On the other hand, Saussure, in his valuable paper on the 

 absorption of gases, informs us that charcoal from box- wood, 

 in the solid state, absorbs twice as much common air as when 

 it is reduced to powder. Now the effect of pulverization is 

 certainly not to diminish the extent of surface. Saussure ac- 

 counts for it in another way, and his explanation seems to 

 connect many of the facts. The condensation of gases in solid 

 charcoal goes on, he conceives, in the narrow cells of which it 

 is composed, and is analogous to the rise of liquids in capillary 

 tubes. In both, he says, the power appears to be in the in- 

 verse ratio of the size of the interior diameters of the pores or 

 tubes of the absorbing bodies. When we pulverize a body 

 containing such cells, we widen, open and destroy them. Fir 

 charcoal, whose cells are wide, absorbs 4^ times its bulk of 



