THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JUNE 1891. 



LVII. On the Role of the Cation in Voltaic Combinations ; 

 particularly those containing Chlorides of Iodine and Bro- 

 mine. By J. Brown*. 



1. QO long ago as 1851 Sir William Thomson, in referring 

 O to " galvanic arrangements adapted to allow the [che- 

 mical] combinations to take place without any evolution of 

 heat in their own localities," defined " the intensity of an 

 electrochemical apparatus " as " equal to the mechanical equi- 

 valent of as much of the chemical action as goes on with a 

 current of unit strength during a unit of time"!- It has, 

 however, been repeatedly shown that the practical application 

 of this guarded definition is in many cases very difficult, 

 mainly because of uncertainty as to the proportion of the 

 total chemical action contributing to the current as distinct 

 from other work ; an uncertainty arising from want of know- 

 ledge on the following and other points : — 



The exact nature of the surface of solids employed in the 

 cell — as when metals are coated with films of oxide, car- 

 bonate or with gas-films. 

 Possible action of the solvent on the metals — as distinct 



from the dissolved electrolysable substance. 

 Effect of minute quantities of impurities occurring in what 

 is considered " pure " material ; such as the effect of a 

 minute quantity of chlorine on the force of a platinum- 

 distilled- water-magnesiuiri cell observed by Gore J. 

 Degree of change of physical state and energy absorbed 

 thereby. 



* Communicated by the Secretaries of the Electrolysis Committee of 

 the British Association, 

 t Phil. Mag. ii. p. 434. J Proc. Poy. Soc. xliv. p. 301. 



Phil. Mag. S. 5. Vol. 31. No. 193. June 1891. 2 K 



