386 Conduction in Solutions and Gases, 



Since in a neutral solution the number of anions is equal to the 

 number of cations, this equation may be written 



nf = Fw-i x a function of T only ; 



it shows that when V is very large (so that the solution is very 

 dilute), n 2 is very large compared with n^ ; that is to say, the 

 salt tends towards a state of complete dissociation. 



The ideas of Arrhenius contributed to the success of Walther 

 Nernst* in perfecting Helmholtz' theory of concentration-cells, 

 and representing their mechanism in a much more definite 

 fashion than had been done heretofore. 



In an electrolytic solution let the drift-velocity of the 

 cations under unit electric force be u, and that of the anions 

 be v t so that the fraction uj(u + v} of the current is transported 

 by the cations, and the fraction v/(u + v) by the anions. If the 

 concentration of the solution be Cj at one electrode, and c 2 at the 

 other, it follows from the formula previously found for the 

 available energy that one gramme - ion of cations, in moving 

 from one electrode to the other, is capable of yielding up an 

 amountf RT log (c 2 /c,) of energy; while one gramme - ion 

 of anions going in the opposite direction must absorb the same 

 amount of energy. The total quantity of work furnished when 

 one gramme-molecule of salt is transferred from concentration 

 c t to concentration c { is therefore 



u + v 



The quantity of electric charge which passes in the circuit 

 when one gramme-molecule of the salt is transferred is pro- 

 portional to the valency v of the ions, and the work furnished 

 is proportional to the product of this charge and the electro- 



*Zeitschr. fur phys. Chem. ii (1888), p. 613; iv (1889), p. 129; Berlin 

 Sitzungsberichte, 1889, p. 83 ; Ann. d. Phys. xlv (1892), p. 360. Cf. also 

 Max Planck, Ann. d. Phys. xxxix (1890), p. 161 ; xl (1890), p. 561. 



t The correct law of dependence of the available energy on the temperature was 

 by this time known. 



