118 Mitchell on the Penetrativeness of Fluids. 



carbonic acid had been absorbed by the caoutchouc. A piece of 

 dry bladder was subjected to the same treatment, and produced a 

 similar rise of the column of mercury. Macerated in water for an 

 hour, and then wiped well with a dry towel, so as to obtain dry sur- 

 faces, the same piece of bladder was again placed in the gas over 

 mercury, and produced a diminution apparently equal in quantity to 

 that which, when dry, it occasioned. 



The bulk of the gum elastic was considerably increased by the 

 infiltration, so that, although easily placed in the glass vessel, it 

 was of difficult removal. This fact, added to that of the thorough 

 penetration by water of an animal membrane macerated in it, shows 

 how much of the phenomena described in this paper is attributable 

 to the organic molecular infiltration. The remainder of the effect 

 is dependent on the moleculo-porous relation of the gas or liquid to 

 the substance beyond, into which infiltration carries the permeating 

 substance. If the recipient beyond the membrane be as active as 

 the membrane, or more so, all that the membrane brings to its sur- 

 face will be transmitted as fast as it arrives ; but if that recipient be 

 pf inferior penetrability, less will pass on than the membrane could 

 carry through, and in that case the rate of penetrativeness of the 

 substance relative to the membrane is inappreciable. Any gas 

 penetrates another gas better than it does any solid, hence we ob- 

 tain for them the true rate. But liquids penetrate each other some- 

 times less rapidly than at the rate of the transmission through the 

 membrane. Such cases do not show the rate of transmissibility by 

 the membrane, but of reception beyond. 



[To be continued.] 



