ASPECTS OF ADSORPTION PHENOMENA 221 



Although these compounds are, no doubt, colloids, they do not 

 appear to carry a charge or only a very small one. Electrolytes have 

 a very slight effect in the sense of retarding adsorption. In the boundary 

 apparatus the behaviour of anilin-blue-methylene-blue under electric stress 

 is difficult to interpret, but since the phenomena are the same in neutral 

 acid, or alkaline solution, it does not seem to be a question of electric 

 charge. What happens is this : after the current has passed for some 

 time it will be seen that electrolysis has occurred, so that on the anode 

 side there is a layer of anilin-blue solution, and on the kathode side 

 one of methylene-blue. The upper boundaries of these two are at the 

 same level in both limbs, but the methylene-blue layer being deeper 

 than the anilin-blue it makes the level of the unaltered compound on 

 the kathode side lower than on the anode side, so that it appears as if 

 negatively charged and moving to the anode. The behaviour to 

 electrolytes, if any at all, is, on the contrary, in the sense of a positive 

 charge ; so that I am inclined to think that the behaviour in the 

 electric field is, in some way, due to different velocities of the two 

 ions. In the case of the eosin-methylene-blue there was no similar 

 difference in level of the unaltered dye, so that it may be that here the 

 two ions are more nearly equal in velocity. 



This absence of proof of any definite electric charge makes the 

 compounds less interesting from the theoretical point of view in some 

 respects. But it is, I suppose, what might be expected if these bodies 

 are formed by the mutual neutralization of electro-positive and electro- 

 negative colloids. 



On the whole it seems impossible to give, in the present state of 

 knowledge, a decided answer to the question as to the nature of these 

 dye-compounds. 



6. Antitoxins 



It has been shown by Craw 1 that the combination between toxin 

 and antitoxin follows more closely in its nature that of adsorption than 

 that of chemical combination. The puzzling fact known as the 

 ' Danysx-von-Dungern phenomenon' is, for example, satisfactorily 



l. Journ. of Hygiene, 5, p. 115, 1905, and Proc. Roy. Soc., 76 B, p. 179, 1905. 



