Chemistry. — "'(hi the Significance of the Volta- Effect in Measure- 

 ments of Electromotive Equilibria \ By Prof. A. Smits and 

 J. M. BiJVOF.T. (Conimnnicated by Prof. P. Zkeman). 



(Communicated in the meeting of Sept 28, 1918). 



Introduction. 



Many physicists are of opinion that the Volta effect amounts to 

 only a few railli volts, and that the electromotive force of an elec- 

 trical cell resides practically exclusively in the potential differences 

 metal-electrolyte, so that these alone need be taken into consideration ; 

 there are even those who think that the Volta-effect is theoretically 

 zero. It is chiefly the German school that assumes that the Volta- 

 effect may be neglected with respect to the potential difference 

 metal-electrolyte. On the other hand a great number of investigators 

 think they have found that the Volta-effect can constitute \, ^ and 

 even a still larger fraction of the electromotive force of a cell, and 

 can accordingly amount to as much as 1 Volt. 



The opinions concerning the value of the Volta-effect are therefore 

 greatly divided, which is owing to the great difficulties which attend 

 the determination of the Volta-effect. 



In the application of the recent views about the electromotive 

 equilibria ^) to the Volta-effect it appears, that even though this 

 effect should be small for metals in the state of internal equilibrium, 

 it must become great for phenomena of polarisation, so that we 

 may certainly not neglect the Volta-effect for these cases. 



2. The variation of the Volta-eff'ect on polarization and passivation. 



The following equation holds for the potential difference of a 

 metal in active state with respect to an electrolyte: 



0,058 K'ye{Ms')active 

 »' Ml' 



and thus we get for the passive state : 



0,058 K'ir{Ms')passive 

 ^Muassüe—L = ^Off ■_ 



»' {Ml ) 



from which follows. 



1) Zeitschr, f. physik. Chemie 88, 743 (1914). 

 . ., , 90. 723 (1916). 



