56 BIOLOGICAL CHEMISTRY 



ELECTRICAL EFFECT OF SALTS OF COLLOIDS WITH CRYSTALLOIDS 



Limitation of diffusion of colloids by membranes may lead 

 to electrical changes. If the colloid is one that forms salts 

 and one of the ions is diffusible through membranes the partial 

 separation of the diffusible from the non-diffusible ion causes 

 an electrical potential in the same way that differences in the 

 solubility of ions in two immiscible liquids causes an electrical 

 potential. 



The ion that tends to pass through the membrane confers a 

 charge of the same sign as itself on the outside of the membrane, 

 whilst the inner side of the membrane possesses a charge 

 corresponding to the colloidal ion. 



The two ions are kept, however, from separating by their 

 opposite charges, and unless some .secondary process, such as 

 hydrolysis, occurs the separation of ions is infinitesimal ; the 

 electrical potential is a stress and only a minimal amount of 

 separation occurs.* 



ADSORPTION 



Owing to the large amount of surface possessed by colloidal 

 solutions condensation on surfaces by surface tension effects 

 become of considerable magnitude. This process of adsorp- 



x ] 

 tion can be expressed by a formula - ac n where x is the 



amount adsorbed by the surface m, from a solution whose 

 final concentration is c, a and - being constants for a particular 



surface and solution. 



The importance of the points mentioned in this chapter 

 consists in the fact that cells have surfaces, therefore surface 

 phenomena must be considered in biological processes. More- 

 over cells contain colloidal substances; the behaviour of colloids 

 has therefore an important bearing on the behaviour of cells. 



The phenomena that occur across surfaces of separation are 

 unequal distribution of substances, electrical potential and 

 surface tension. The last of these can be used to produce 

 mechanical effects by which chemical energy may be trans- 

 formed into movement. 



GENERAL REFERENCES 

 C. V. BOYS : Soap Bubbles, S.P.C.K., 1907. 



A. FINDLAY : The Phase Rule and its Applications. Longmans,Green & Co., 1911. 

 H. FREUNDLICH : Kapillarchemie, Leipzig, 1909. 

 E. HATSCHEK : An Introduction to the Physics and Chemistry of Colloids. 



J. & A. Churchill, 1913. 



A. B. MACALLUM : Ergebnisse d. Physiologic, 1911, vol. u, pp. 602-657. 

 Report of Committee on Colloid Chemistry. British Association Reports for 



1917, 1918 and 1920. 



* W. M. Bayliss, Proc. Roy. Soc., igii^B- vol. 84, p. 229. 



