700 RICE ART. L 



chemical potentials should still be used) are dependent on the 

 values of these as well as on the other variables. If a change 

 takes place in the electric potentials and a new state of equilib- 

 rium results, the M quantities change so as to preserve the same 

 equalities and inequalities as before. The real physical signifi- 

 cance of the equivalence of M and ju + j87 can be expressed by- 

 saying that, if all the electric potentials of the various phases of 

 a system in equilibrium are increased by the same amounts, 

 then the system still remains in equilibrium, no transference of 

 ions (or other components) takes place, and the electrochemical 

 potentials are all effectively unchanged and at their original 

 values. But if the changes of electric potential in the various 

 phases are not equal, no general statement about the changes 

 in the various phases can be made beyond the one concerned 

 with the preservation of equalities, etc., in the case of a varied 

 state of equilibrium. 



70. Derivation by Means of the Postulate of ''Specific Adsorption" 



of Ions of an Equation Combining Oibbs* Terms for 



Ions with a Lippmann Term for Electrons 



In accordance with this we write the elementary change of 

 energy in a homogeneous mass in the form 



5e' = tdr]' - p8v' + Mi8mi + M^ bm^ + . . . , 

 and in a surface in the form 



5es = tbr)S J^ o-^g 4- M^bmi^ + M2 bm^^ + . . . 



As before, we prove that 



da = - rjsdt - Ti dMi - T2 dMi - ... 



Since in general each homogeneous mass is uncharged as a whole, 

 and also each surface of discontinuity, it is clear that 



TiiSi + r2/32 + TsPs + . . . =0, 



for this expression is the whole charge per unit area on the ions 

 in the region of discontinuity. Hence 



da = — -qadt — Vx dni — Fa d^ — . . ., 



