ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 275 



In the case where all of the anions are fixed in the layer adhering 

 to the wall, but where all of the cations are freely motile, we have 



mi + ni = 1; ai = bi = 0; mi>m; ni>n 



and equation (VI) becomes 



B = - aKA - (ni - n) H^O + (ni - n - b) KOH 



If the solution is neutral to begin with then n and b must be small 

 with respect to Ui, because of the slight concentration of H- and 

 OH-ions, and the KOH term in (VI) wiU be positive, i.e., the solution 

 win be alkaline on the anode side. 



Similarly, under the same conditions, the diaphragm boundary 

 on the cathode side must become acid. These predictions based on 

 the theory correspond, for most of the neutral salts, with the ex- 

 perimental findings of Bethe and Toropoff. 



The higher the concentration of the dissolved electrolytes, and, 

 it may be added, the larger the capillary spaces, the less hkely it is 

 that the adsorbable ionic species will be completely bound on the 

 walls of the pores; and, consequently, the smaller will be the changes 

 in concentration produced by the passage of the current, and, as 

 was pointed out above, the endosmotic transport of water resulting 

 from concentration changes will be diminished. 



If the sign of the charge on the diaphragm is irreversible, and the 

 diaphragm is of an acidoid character (collodion), the walls of the 

 pores adsorb only OH-ions and other anions, but no cations. Ac- 

 cording to the adsorbability of the anions, other than 0H~, which 

 may be present, they are more or less bound by the wall and par- 

 ticipate correspondingly more or less in the conductance of the 

 current within the pores. The greater the adsorbability of the ions, 

 other things being equal, the greater will be the change in hydrion 

 concentration brought about on both sides of the diaphragm on the 

 passage of the current. In fact, on comparing the effect of K- or 

 Na-salts of the different anions in displacing the originally neutral 

 reaction of a solution, Bethe and Toropoff found the following serial 

 sequence, which was to be expected : 



Citrate- > I" > Br" > SOf > CI" > NO3- 



When the anion was kept constant and the cations varied, no such 

 sharply defined series could be obtained which would be independent 



