384' Dr. G. Bird on certain Properties acquired by the 



constant ; the plate of platina, which had during connexion 

 with the battery evolved hydrogen, always being positive, and 

 acted on the galvanometer like a piece of zinc. No appreci- 

 able difference in the surfaces of the platina plates with regard 

 to lustre, §j;c., was observed. From the results of these ex- 

 periments, we are, I think, hardly warranted in supposing with 

 Becquerel, that the polar state of the plates arose from a 

 film of acid and alkali adhering to them, although in other 

 cases that this may be the cause of the polarized condition of 

 the electrodes no one who has read the remarks of this distin- 

 guished philosopher on the battery of constant currents can 

 doubt {Traite, 5. 219.), and perhaps Exp. 13 may admit of an 

 explanation of this kind. The fact of the polar state being to 

 a great extent retained after washing the plates with water, 

 alkalies, exposure to the action of acids for 48 hours, &c., is 

 certainly opposed to the hypothesis of Becquerel, although I 

 am aware that films of sulphuric acid cannot be entirely re- 

 moved from plates of platina by washing, as Dr. Faraday has 

 satisfactorily shown. The direction of the secondary currents, 

 being opposed to that of the battery currents, appeared at first 

 to connect these phsenomena with those of electro-dynamic 

 induction. The fact of the secondary current being continuous 

 for some time and gradually disappearing, instead of being 

 only of momentary duration, might be supposed to arise from 

 the badly conducting nature of the fluid connecting the plates 

 of platina ; this hypothesis, suggested by some experiments, 

 was at once refuted by the secondary currents being detected 

 by the galvanometer, after emptying the glass basin and 

 filling it \\\\h fresh dilute acid. 



The cause of the evolution of a double volume of hydrogen 

 from the positive plate is less mysterious, this being evidently 

 analogous to the phsenomena observed by Dr. Faraday in his 

 researches on the action of platina plates in effecting the com- 

 bination of oxygen and hydrogen gases ; he found that the 

 plates which had served for positive electrodes were very 

 energetic in producing this combination, whilst the negative 

 electrode was quite inactive, and this difference he attributed 

 to the surface of the positive plate being more polished, and 

 freer from foreign matter than the negative. This view was 

 confirmed by the fact of the negative plates becoming active 

 by mechanically cleaning them. In the same manner I con- 

 sider that the positive plates when connected metallically 

 with the zinc rod, evolved a larger volume of hydrogen in a 

 given time than the negative, because their surfaces were per- 

 fectly free from accidental tarnish, which although not readily 

 appreciable by the eye, yet materially affects their electrical 



