ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 259 



Nature of the diaphragm 



Carborundum. 



Gelatin. 



Cellulose. 



Volume of flow 



of water 



in cc./min. 



50 



60 



105 



22 

 35 





 20 

 70 



It is to be noted that he had observed that the reversal of the 

 electric charge did not always occur exactly at the neutral reaction. 

 This is most clearly shown in the table in the case of cellulose, on 

 which, as well as on iodoform, no positive charge could be produced 

 even in a 1/30 A^ HCl solution. An exact interpretation of these 

 phenomena is evidently afforded by the same considerations as those 

 applied to the theory of the isoelectric point for ampholytes in solu- 

 tion, which, at the time of Perrin's investigations, had not yet been 

 developed. And yet Perrin was farsighted enough to regard the 

 above given law as an approximation only, and as a strictly vaUd 

 law he proposed the following: 



The electric potential of any ivall (diaphragm) toward a solution is 

 always increased by the addition of an (univalent) acid and is always de- 

 creased by the addition of a (univalent) base. 



76. The isoelectric point of diaphragms; diaphragms with and 

 without an isoelectric point 



Further investigations by Bethe and Toropoff,^^ GHxelh^^ and 

 Gyemant,^'^ who employed somewhat different methods, permitting 

 of the maintenance of an exact pH at the electrodes, showed that it 

 was in principle quite incorrect to expect the reversal of the charge 



28 A. Bethe and Th. Toropoff, Zeitschr. f. physikal. Chem. 88, 686 (1914) 

 and 89, 597 (1915). 



" S. Glixelli, Bull, de I'Acad. des Sciences de Cracovie. S4rie A. 1917, p. 

 102. 



30 A. Gyemant, Kolloid-Zeitschr. 28, 103 (1921). 



