SURFACE ACTION 73 



The rate at which adsorption takes place, when the components are already 

 approximated, appears to be very rapid, although not instantaneous. On the 

 other hand, when the substance to be adsorbed has to diffuse from distant parts 

 of the system, the rate will be controlled by diffusion and therefore accelerated 

 by rise of temperature. 



The total amount adsorbed in equilibrium is less the higher the temperature. 

 The process, by the "principle of mobile equilibrium," is, therefore, associated 

 with the production of heat. 



The mathematical form of the expression relating concentration with amount 

 adsorbed is a characteristic one and belongs to the parabolic family. 



Adsorption cannot be completely or satisfactorily explained by chemical com- 

 bination, nor by partition between phases, in accordance with relative solubility, 

 since impossible assumptions have to be made as regards molecular association, etc. 



A class of compounds exists in which, as shown by various facts, the con- 

 stituents are not chemically combined. This is shown especially by the depend- 

 ence of their composition on the relative concentration of the substances from 

 which they are produced. This class of compounds is satisfactorily explained by 

 adsorption. 



In some of these adsorption-compounds the constituents can be shown to be 

 present, side by side, but uncombined. 



Since the rate of chemical action depends on the concentration of the reagents 

 it is plain that when a substance is capable of reacting with a second one, which 

 is present as a separate phase, particles or drops, for example, the rate of reaction 

 will depend on the amount of the one adsorbed on the surface of the second. 

 Similarly, if two substances, capable of reacting with each other, are both adsorbed 

 on the surface of a third, with which they do not combine, their rate of reaction 

 with each other will be accelerated by the increased concentration, or molecular 

 approximation, due to adsorption. 



A number of cases are given where adsorption plays a controlling part in 

 phenomena of physiological interest. 



Salts when adsorbed are not electrolytically dissociated and do not therefore 

 give their characteristic reactions, neither can they be osmotically active. 



A substance which lowers surface energy more than a second one does will 

 drive off this latter from adsorption on a surface, at the same time taking its place 

 thereon. 



Adsorption plays a large part in the phenomena of dyeing and staining ; most, 

 if not all, the facts can be explained on this basis ; although, in all probability, 

 chemical reaction sometimes follows adsorption, the rate of this reaction being 

 controlled by the amount adsorbed. 



LITERATURE 



Surface Action in General. 



Freundlich (1909, pp. 1-184). Boys (1912). 



Hardy (1914). 



Adsorption. 



Wolfgang Ostwald (1909, pp. 390-445). Donnan and Barker (1911). 



Electrical Adsorption. 



Wolfgang Ostwald (1909, pp. 422, 433). Freundlich (1909, pp. 184-265). 



Perrin (1904, 1905). Baylies (1906, 1). 



Dyeing and Staining. 



A. Fischer (1899, pp. 73-201). 



Adsorption preliminary to Chemical Action, 

 Baylies (1911, 1). 



