14 On Electricity at the Contact of Solids and Gases. 



metallic conductor would surely insulate it from the conducts 

 ing liquid. 



I will here add the description of an experiment which I 

 made, long ago, for the purpose of getting an explanation of 

 the activity of gases in the gas battery. Gaugain, in the 

 paper above mentioned, has advocated the view that the elec- 

 tromotive force of the gas battery is to be attributed solely to 

 the chemical affinity with which the oxygen of the water and 

 the hydrogen condensed by the platinum act on one another. 

 To this I objected that this proposition must be generalized, 

 since other gases also act as electromotors ; it must therefore 

 be expressed something like this : — A gas acts as an electro- 

 motor through combining, under a catalytic cooperation of 

 the platinum, with one of the elements of the water *. 

 Whether this proposition is correct can be ascertained by the 

 following experiment. In a dark room I filled up two tubes, 

 in each of which was a platinum plate, and containing, as 

 usual, diluted sulphuric acid, with chlorine. The two plates 

 showed no difference of tension. I now covered over one of 

 the tubes with a yellow-glass bell, and let the daylight fall 

 upon both tubes. Certainly the action of the chlorine upon 

 the hydrogen of the water was now much more vigorous in 

 the free than in the covered tube ; but no difference of ten- 

 sion was visible. For chlorine, therefore, the above proposi- 

 tion is certainly untenable. To hydrogen it is indeed still 

 less applicable, since otherwise the affinity of the hydrogen on 

 the platinum for the oxygen of the water would have to be 

 greater than that of the oxygen for the hydrogen already com- 

 bined with it. 



I remark finally, in reference to Graham's statement 

 (already called in question by G. Wiedemann*)") that palla- 

 dium charged with hydrogen is strongly magnetic, that I 

 have never succeeded in detecting any action of hydride of 

 palladium upon the magnetometer. 



After the above communication had been presented to the 

 Royal Academy, I received the April number of the i Philo- 

 sophical Magazine,' in which Mr. Morley publishes an inves- 

 tigation, carried out by him in Professor Foster's laboratory, 

 on Grove's gas battery. Mr. Morley is only acquainted with 

 the older writings of Grove and Schonbein and the newer 

 ones of Gaugain ; mine he seems never to have seen. 



* Pogg. Ann. cxxxii. p. 458. 



t Galvanismiis, 2nd. ed v vol. i. p. 528 ; cf. Blondlot, Beibl. vol. i. p. 634. 



