DIALTTIC SEPARATION OF GASES BY COLLOID SEPTA. 415 



a body of gutta percha, softened probably by a drying-oil. From its softness and 

 thinness, this sheet of gutta percha appeared at first highly promising. But it appears 

 not to be free from small apertures for any considerable surface. When a small sound 

 portion was operated upon, air was found to percolate through it very slowly. In a tube 

 diffusiometer of 1"3 metre in length and 20 millims. in diameter, closed at the top with 

 this septum supported by stucco, the mercurial column fell from 28*7 to 22-025 inches 

 in 18^ hours. The gas which had entered above the mercury measured 13'54 cub. 

 centiras., and was found to contain 20-2 oxygen to 79-8 nitrogen — a proof that the air 

 had entered by gas-diffusion. The material is in fact of sufficient porosity to pennit the 

 molecular passage of gases in a slow manner. 



Varnishes of gelatine and of drying-oil have been tried as dialytic septa, but hitherto 

 without marked results. 



Paet II.— action of METALLIC SEPTA AT A RED HEAT. 



Platinum. 



The surprising passage of gases through the homogeneous substance of a plate of fused 

 platinum or of iron at a red heat, lately discovered by MM. H. Ste.-Claire Deville and 

 Troost, may possibly prove to be analogous in its mode of occurrence to the passage of 

 gases through the rubber septum. At the same time it must be admitted that such an 

 hypothesis as that of liquefaction can only be applied in a general and somewhat vague 

 manner to bodies so elastic and volatile at an elevated temperature as the gases generally 

 must be, and hydrogen in particular. Still some degree of absorbing and liquefying 

 power can scarcely be denied to a soft or liquid substance, in whatever circumstances it 

 may be found, with such a patent fact before us as the retention by fused silver of 18 or 

 20 volumes of oxygen at a red heat. It may safely be assumed that the tendency of 

 gases to liquefaction, however much abated by temperature, is too essential a property of 

 matter to be ever entirely obliterated. 



A little consideration also shows that the absorption of gas by a liquid or by a colloid 

 substance is not a purely physical effect. The absoBption appears to require some 

 relation in composition — as where both the gas and the liquid are hydrocarbons, and the 

 affinity or attraction of solution can come into play. May a similar analogy be looked 

 for, of hydrogen to liquid or colloid bodies of the metallic class 1 



With reference to the mechanical pores of a solid mass, liquids are probably more 

 penetrating than gases. The former show often a power of adhesion to solids, while 

 gases appear to be essentially repulsive. A degree of minute porosity is conceivable, 

 which will admit a liquid, but may be impassable to a gas, even under its molecular 

 movement of diffusion. 



Finally, there is presented to us a bold and original conjecture by M. Deville, in 

 explanation of his own observations. It is clearly expressed in the following quotation 

 taken from the last publication of M. Deville on this subject : — 



MDCCCLXVI. 3 M 



