Platina Electrodes of a Voltaic Battery. 385 



condition. On this hypothesis the results of the other ex- 

 periments may be explained: thus the volumes of gas evolved 

 from the plates became more equal after the platina had been 

 exposed to the action of those agents which v^^ould tend to re- 

 move superficial impurities (Exp. 9, 10, &c.) ; and the intensity 

 of action on the galvanometer appeared to be connected with 

 a similar state (Exp. 1 1,) as the electric condition of the plates 

 became nearly equal, after washing them with nitric acid, a 

 deviation of only 4° taking place. What the substance is, 

 whose invisible deposition on the negative plate causes this 

 current, is conjectural ; that it is not an alkali, as Becquerel 

 has suggested, is I think proved by the positive electric con- 

 dition not being removed by dilute sulphuric acid, as well as 

 from the almost infinitesimally minute quantity of saline mat- 

 ter present in the electrolyte employed in my experiments. 

 That a very small quantity of foreign matter is sufficient to 

 produce a very considerable action on the galvanometer is 

 proved, by using for these experiments the dilute acid that 

 has been previously employed for the generation of gas from 

 the amalgamated rod, instead of fresh portions of that fluid ; 

 the minute and imperceptible portion of zinc reduced on the 

 negative electrode producing most intense action on a very 

 delicate galvanometer. 



The negative plate I found became capable of evolving as 

 large a volume of gas as the positive electrode, by scouring it 

 with nitric acid and fine sand, evidently proving its former 

 comparatively inactive state to depend upon some superficial 

 deposition ; the same result was obtained by employing both 

 plates simultaneously as positive electrodes. 



Exp. 14. Two copper wires were for this purpose screwed 

 upon the last copper plate of the battery, an end of each dip- 

 ping into one of the cups A and B, the wire from the last 

 zinc plate dipping into the dilute acid in the basin ; under 

 these circumstances both platina plates evolved oxygen, and 

 were of course positive electrodes. On then breaking battery 

 connexion and dipping the zinc rod into the acid, its wires 

 being immersed into the cups A and B, equal volumes of gas 

 were evolved, cateris paribus, from both plates. 



From the results of this investigation I think I am justified 

 in referring all the phasnomena observed to the peculiar con- 

 dition of surface assumed by the platina plate that has served 

 as the negative electrode, its inactive state quoad the ewolution 

 of hydrogen, and its active state quoad the galvanometric cur- 

 rent, depending upon one and the Same cause, viz. the depo- 

 sition of infinitesimally minute portions of foreign matter on 

 it, which serves to diminish the rapidity of the evolution of 

 Phil. Mag. S.3. Vol. 13. No. 83. Nov. 1838. 2 C 



