ASPECTS OF ADSORPTION PHENOMENA 223 



be restricted to the external surface of the pieces of various size. 

 Porous solids like charcoal, even in lumps, adsorb gases, and that not 

 only on their surfaces but throughout their substance. Dauvve, indeed, 

 appears to have thought of this possibility, but regards adsorption as the 

 same thing as solid solution in such cases. 1 The distinction is, surely, 

 analogous to that between true solution and colloidal solution. 

 Although recent investigations teach that we must not draw a hard and 

 fast line between these two kinds of solution, there is no doubt that 

 the molecules or particles in suspension change their properties 

 as their dimensions increase beyond what are ordinarily called 

 molecular, and that they begin to have the properties, due to surface, 

 of matter in mass. In the same way, as I think, we ought to keep the 

 name ' solid solution ' for such cases as alloys of metals, and give the 

 name adsorption not only to the taking up of substances from their 

 solutions by surfaces, in the usual sense of the word, but also by such 

 surfaces as those forming the walls of pores. The criterion by which 

 any given case is to be decided, is, of course, the way in which the 

 relative amounts taken up vary as the concentration of the body taken 

 up changes. 



Dauwe rejects the hypothesis of chemical combination on the 

 ground that the enzyme taken up can be extracted again by an 

 appropriate solvent, for instance, pepsin from coagulated egg-white by 

 a solution of egg-white. He regards the process as one of solid 

 solution, or relative solubilities of the enzyme in the substrate and 

 water, and brings forward in support of this view the experiments of 

 Reichei and Spiro 1 on the apparent loss of rennet in the process of 

 clotting of milk. These observers showed that the disappearance of 

 the enzyme was to be accounted for by the taking up of it by the clot. 

 Now, as I understand their results, they are rather in favour of 

 adsorption. If it were a case of solid solution the percentage loss 

 would be the same whatever the rennet concentration, but if one looks 

 at the table on page 481 of the second paper referred to, it is seen 

 that the percentage loss steadily increases as the concentration of the 



1. Loc cit., p. 443. 



2. Hofmeister's Beitrage, VI, p. 68, 1905, and VII. p. 479, 1905. 



