1903.] *i<, -face-let tiers of Solutions and " Suspensions." 161 



precisely similar phenomena at the interfaces of the liquids concerned, 

 and appear to be brought about in exactly the same way. 



15. The suggestion that the observed surface accumulations must be 

 attributed to the diminution of the " superficial energy " thereby pro- 

 duced is strongly supported by a series of experiments made with 

 watery solutions containing equal quantities of two substances each 

 of which by itself forms " mechanical surface aggregates." In such 

 mixtures there has invariably been preferential accumulation of one 

 substance to the more or less complete exclusion of the other from 

 the mechanical surface aggregate obtained. Thus 



Saponin > Egg-albumin. 



Bile-salts > Saponin. 



> Soap. 



> Gamboge. 



,, > Egg-albumin. 



,, > Sulphur. 

 Egg-albumin > Carmine. 



If the dissolved substances thus mixed exert no chemical action 

 upon each other, such preferential accumulation is not only explicable, 

 but, taking only surface-tension considerations into account, is 

 theoretically essential when one substance produces a greater diminu- 

 tion of the surface energy than the other. In actual practice, how- 

 ever, the phenomena are complicated by differences in diffusibility and 

 rate of re-solution and by limitation of independent mobility of the 

 11 dissolved " particles due to their mutual cohesions and adhesions. 



16. It has been found also that bubbles blown from mixed solutions 

 of two substances, each of which by itself forms bubbles presenting 

 recognisable and well-marked differences of character, behave precisely 

 as if they had been blown from a solution of one of these substances 

 only, and this is always the one which in a mechanical surface aggregate 

 made from the mixed solution is found to have more or less completely 

 excluded the other, e.g. : 



Saponin > Egg-albumin. 

 Bile-salts > Saponin. 



> Egg-albumin. 



Egg-albumin > Carmine. 



17. The fact that the introduction of alcohol (and of other liquids 

 of low surface-tension) into many solutions which show the above 

 described surface phenomena frequently deprives those solutions of 

 their superficial viscosity and of their power of forming bubbles 

 or of yielding mechanical surface aggregates, would seem to be 

 explicable by similar considerations, i.e., as due to preferential 



