1863.] 425 



3. It does not absorb hydrogen, nitrogen, or carbonic acid for the 

 same period. 



4. Although the amount absorbed is somewhat in the relation of 

 the condensibility of the gases by pressure, this is not the only qua- 

 lity regulating the absorption, of oxygen at least. 



5. When it is sought to remove the oxygen from charcoal by 

 warmth, carbonic acid is formed, even at the temperature of boiling 

 water, and slowly even at lower temperatures. 



6. Charcoals differ extremely in absorbing power, and in the capa- 

 city of uniting with oxygen, animal charcoal possessing the latter 

 property in a greater degree than wood-charcoal. 



7. Nitrogen and hydrogen, when absorbed by charcoal, diffuse 

 into the atmosphere of another gas with such force as to depress the 

 mercury three-quarters of an inch. 



8. Water expels mercury from the pores of charcoal by an instan- 

 taneous action. 



9. The action of porous bodies is not indiscriminate but elective. 



Theoretical Considerations. 



1 . The elective nature of porous bodies may be closely allied to 

 three properties : 



a. The condensibility of the gases. 



b. The attraction and perhaps inclination to combine. 



c. The capacity of combination. 



2. In either case the attraction which results in condensation of 

 the gas is exercised at distances greater than the distances of atoms 

 or molecules in combination. 



3. The gases in porous bodies lie in strata, the outside and more 

 distant being less attracted than the atoms nearer the solid body. 



4. We cannot separate chemical from physical attraction; but 

 attraction may exist without its ultimate result (combination), which 

 is distinctly chemical. 



5. It is exceedingly probable that as physical attraction moves 

 onwards to chemical combination, it produces the phenomena which 

 have been attributed to so-called masses. 



Chemical affinity is supposed to involve an attraction which is 

 purely chemical ; we have no proof of any such attraction as a sepa- 

 rate power, we have only a proof of the combination. Attraction 



