ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 273 



anions, become attached to the wall. When an electric current is 

 sent through the pores, these attached ions do not participate in the 

 conductance of the current, which is done only by the ions that had 

 remained freeh^ motile. Therefore, the average mobihty of the anions 

 becomes diminished, and under certain conditions almost entirely 

 abolished, while that of the cations is undisturbed. Let us assume 

 that an anion A~ and a cation K+ are in solution, and naturall}^ also 

 the anion 0H~ and the cation H+. Both anions, A~ and 0H~, are 

 bound by the wall, especially the OH" ion. We find then that the 

 average mobihty of A", and that of 0H~ even more, diminished. 

 Let us now pass an electric current through this system until 96540 

 coulombs = 1 faraday has passed through any desired cross section. 

 The individual ionic species in the free solution will participate in the 

 transport of the current in a mutual relationship quite different 

 from that within the pores of the diaphragm. Let us designate the 

 products of the concentration by the mobility of each of the four 

 ionic species in the free solution by m, n, a, b and those for the solu- 

 tion within the diaphragm by mi, ni, ai, bi, so choosing our scale for 

 the mobihties that m + n + a + b = l and also mi + ni + ai + bi 

 = 1. Then the individual ionic species participate in the conductance 

 of the current as follows: 



In the free solution In the diaphragm 

 mK+ mi K + 



nH+ n, H + 



a A~ ai A~ 



b OH- bi OH- 



(where each small letter stands for a proper fraction and each capital 

 letter for an ionic species) . 



Let us now consider the state of ionic migration at one of the 

 boundaries of the diaphragm, at the anode side for instance, at the 

 end of the passage of the current. The boundary layer has gained 

 from the free solution mK+ ions and nH+ ions, and from the solution 

 within the diaphragm aiA~ ions and biOH~ ions, while it lost to the 

 free solution aA~ ions and b 0H~ ions, and to the diaphragm it lost 

 miK+ ions and niH+ ions, which may be stated diagrammatically 

 (see table 41). (The signs + and — show whether the boundary 

 layer had gained or lost the ion.) 



L I G R A R Y 



