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X . On the surprising intensity of current of the Zinc-iron- 

 circuit, its causes, and some allied subjects. By Prof. J. C. 



POGGENDORFF *. 



H E author read before the Berlin Academy f of the recent 

 discovery of Mr. Martyn J. Roberts,! that iron, combined 

 with zinc and dihite sulphuric acid, produces a considerably 

 more energetic current than, under like circumstances, the far 

 more negative copper. He in the first place communicated 

 some observations in confirmation and extension of this fact, 

 both interesting in a scientific point of view and important for 

 the praxis. He showed that the superiority of the current of 

 the zinc-iro7i circuit does not merely occur on employing di- 

 lute sulphuric acid, but also with dilute nitric acid, solutions 

 of caustic potash and common salt, and similar fluids; and 

 indeed not solely in reference to the zinc-copj)er circuit (even 

 one with double copper surface), but likewise in reference to 

 circuits of s/?/c and silver, or ;:inc and platina. It was, in fact, 

 necessary to give to the zinc-platina circuit plates three times 

 as lai'ge as those of the zinc-iron circuit, if its current was to 

 be of like intensity with that of the latter. On the other hand, 

 it was found that a Daniell circuit, in which, as is well known, 

 the copper is placed in a solution of the sulphate of copper, 

 and the zinc separated by membrane, developes, in acid, the size 

 and distance of the plates being the same, a greater intensity 

 of current than the zinc-iron circuit; while, on the other hand, 

 that a combination constructed after Daniell's circuit, namely, 

 a circuit in which the iron is placed in a solution of the sul- 

 phate of the protoxide of iron, produces a current of very in- 

 considerable energy. 



The author then passes on to the explanation of these phae- 

 nomena, respecting which Mr. Roberts has offered no opinion, 

 and which, indeed, according to the views at present enter- 

 tained in England on galvanism, could hardly be given in a 

 satisfactory manner. 



And yet the explanation has not far to be sought for. We 

 have long known, says the author, that the intensity of a cur- 

 rent of a voltaic circuit depends on two things, — the electromo- 

 tive force and the resistance. We know, moreover, that it is 

 the quotient from the division of the former by the latter. 



• Translated and communicated by Mr. William Francis, from Poggen- 

 dorff's Annalcn, vol. 1. p. 255. 



\ This notice is taken from the Reports of the Royal Berlin Academy, 

 and must be considered merely as a preliminary notice with reference to 

 the main subject; a more accurate numerical determination of the ele- 

 ments treated of will follow in a short time. 



X Announced by Mr. Roberts in L. and E. Phil. Mag., vol. xvi., p. 143. 



