ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 281 



liquid the more slowly it moves at the same pressure and conse- 

 quently the fewer ions it can tear along with it. The E.M.F. is also 

 inversely proportional to the electric conductance, for the better 

 conductor the liquid is the less of a potential difference is allowed by 

 it to develop between the two ends of the tube/^ Furthermore, E 

 is directly proportional to the dielectric constant, for the greater 

 the value of the latter, the easier it is to separate the ions from each 



other. The proportionality factor — is introduced in order to reduce 



47r 



the value to electrostatic units. This equation can be used to calcu- 

 late the potential f on the wall, after having measured the electro- 

 motive force E of the hydrodynamic current. The proof for the 

 correctness of the absolute value of so calculated potentials suffers 

 from the same difficulties as in the case of endosmosis. In this case, 



however, it depends only on the correctness of the factor — ' other- 



47r 



wise the relative correctness of the equation may be accepted as 

 having been demonstrated. 



Thus the hydrodynamic current method represents a means for 

 the study and calculation of adsorption potentials, and also for the 

 study of the influence of the chemical character of the wall and of the 

 hquid upon these potentials. These studies were made chiefly in 

 glass capillaries, and glass should have behaved, in respect to its 

 chemical properties, quite similarly to other siUcates such as clay and 

 kaolin. It is obviously of interest to find out whether the results 

 obtained by the use of these methods agree with the results obtained 

 by endosmosis and cataphoresis methods with clay and kaohn. 

 Of the not very numerous studies in this field^^ only two are par- 

 ticularly adequate in answering this question. These are the studies 

 by Kruyt^'' and by FreundUch and Rona." In general, it may be 



" It is to be noted that in the equation for electroendosmosis (page 249) 

 the conductivity did not enter directly. It entered only indirectly insofar 

 as the conductance of the liquid in the pores of the diaphragm affected the fall 

 of the potential per centimeter of the externally applied tension, or insofar 

 ab it affected the intensity of the electric field. 



» A. T. Cameron and E. Oettinger, Phil. Mag. [6] 18, 586 (1909). A. Grum- 

 bacher, Ann. d. chim. et de phys. [8] 24, 433 (1911) ; L. Riety, Ann. d. chim. et 

 de phys. [8] 30, 1 (1913). 



" H. R. Kruyt, Kolloid-Zeitschr. 22, 81 (1918). 



^' H. FreundUch and P. Rona, Sitzungsber. d. preuss. Akad. d. Wiss. 1920, 

 p. 397. 



