704 RICE 



ART. L 



there is a flow of current for a moment. Electrons go round the 

 external part of the circuit towards the cathode to remove some 

 of the deficiency there; some mercury ions leave the layer ad- 

 jacent to the anode; some anions enter this layer and, together 

 with some of the anions already present there, are discharged 

 and supply electrons to the mercury anode to maintain the elec- 

 tron flow in the main circuit; for we have supposed that there 

 might be fewer anions as well as fewer cations in this layer and 

 yet the electrical conditions remain unchanged. Thus there 

 would be relatively quite considerable exchanges of ions between 

 this larger layer and the solution, which would occasion differ- 

 ences of concentration and electrochemical potentials in the 

 main body of the solution. This main body would, of course, 

 still be uncharged as a whole, but this again is quite consistent 

 with the existence of fewer cations and fewer anions in it. It 

 is not contended that the physical processes are just those pic- 

 tured, but the theory must somehow or other justify some 

 changes in the electrochemical potentials of the ions in the main 

 body of the solution if we assume changes in those in the layer 

 of electrolyte adjacent to the cathode, as we clearly do when 

 we assert the validity of an expression such as 



da = -qdV - i:V dM. 



One can hardly see how there are to be such changes in the Mr 

 of the ions in the solution if the concentrations are to remain 

 unchanged; and we have just seen that certain changes in con- 

 centrations are quite consistent with unchanged purely electric 

 conditions of the solution as a whole and of the anode surface. 



71 . Some Brief Remarks on the Fundamental Electrical Equations 



Used by Stern in His Treatment of the Distribution 



of Ions in a Solution Close to the Cathode 



of a Capillary Electrometer 



It is clear that the electrocapillary curves are insufficient in 

 themselves to unravel the complexities of the situation, without 

 some theory of the distribution of the ions in the layer of solution 

 adjacent to the cathode. This question is dealt with in the 

 second list of references given above. The most exhaustive 



