by Smooth Surfaces. 337 



glass rods, namely 78525 cubic millimetres, the quantity of gas 

 absorbed by the spongy platinum was 510*4 cubic millimetres. 



The surface of the spongy platinum cannot be determined, 

 and hence we are unable to state the condensation due to the 

 unit of surface. The experiments show simply that in 7 grammes 

 of spongy platinum a greater condensation takes place than on 

 the surface of the glass rods, which surface amounted altogether 

 to 196704 square millimetres. 



According as the spongy platinum is more or less pressed or 

 shaken together, it takes up a smaller or a greater space. From 

 several weighings of the substance, it was found that 4 grammes 

 of it occupied a space of 1 cubic centimetre ; and as in the pre- 

 sent instance 7 grammes of spongy platinum absorbed 0*510 

 cubic centimetres, we find that spongy platinum condenses 0*29, 

 or nearly one-third of its volume of sulphurous acid at 0°. 



That a body so porous as spongy platinum should absorb so 

 much less than charcoal, which, according to De Saussure's 

 experiments, takes up sixty-five times its volume of sulphurous 

 acid, is very remarkable, the more so when we consider that, by 

 the so-called law of Henry, according to which the condensation 

 of a gas is proportional to the pressure under which the conden- 

 sation takes place, we are compelled to assume that the different 

 condensation of the same gas by different substances depends 

 only on the different extent of the surfaces of contact. It is, 

 however, difficult to conceive that the surfaces of equal volumes 

 of charcoal and spongy platinum are so different as to cause such 

 a divergence as the above in the condensation of sulphurous 

 acid. Platinum in the spongy form is not, however, in the state 

 of finest division, and it would therefore have been desirable to 

 determine the condensation produced by platinum black. This 

 substance, however, cannot be rendered sufficiently free from the 

 vapour of water without destroying it. That the number given by 

 De Saussure for charcoal is not too large, I have convinced myself 

 through experiments with finely powdered beechwood-charcoal. 



Supported by certain experiments which I carried out some 

 time ago, I believe that I am in a position to assert that the 

 quantity of carbonic acid gas absorbed by water is not propor- 

 tional to the pressure, and that therefore the law of Henry is not 

 strictly correct. From this it follows that the absorption, at least 

 to some extent, is due to an attraction between the particles of the 

 attracting solid or fluid body and those of the gas ; and, more- 

 over, to an attraction analogous to the chemical, being different 

 for different substances. This proposition is not reconcileable 

 with the views of Dalton regarding absorption ; I hope, however, 

 after a little time to be able to furnish the complete proof of the 

 proposition. 



