46 Prof. Poggendorff o?2 the Zinc-Iron Circuit. 



cially in the contrary sense, i. e. cases where weakness of cur- 

 rent is connected with considerable magnitude of the electro- 

 moiive force ; but one which points to the cause so clearly as 

 the iron circuit, might perhaps not easily be found a second 

 time. 



Hitherto the author has only succeeded in discovering one 

 pair, and that moreover less prominent, analogous to the zinc- 

 iron circuit. This is a circuit of amalgamated zinc and common 

 zinc. This produces (the size and distance of the plates being as 

 above, charged with diluted sulphuric acid, and merely closed 

 by a multiplier-wire 1 1 feet long) a more powerful current, than 

 under similar circumstances, one of amalgamated zinc and cad- 

 mium or tin. Since cadmium and tin are more negative than 

 zinc, consequently the electromotive force of the latter circuits 

 greater than that of the former, it is evident that the greater 

 intensity of current of this can likewise solely be founded on 

 its slighter resistance to transition. It is likewise conceivable 

 that, Ti-om the small ness of the electromotive force of a cir- 

 cuit of amalgamated and common zinc, there can be but few 

 combinations with the first metal as positive member which 

 are inferior to it in intensity of current. And this is really 

 the case. Already a circuit of amalgamated zinc and brass 

 or copper produces, notwithstanding its greater resistance to 

 transition, a more powerful current. 



Another fact belonging here, is that the amalgamated zinc, 

 which, from its being considerably more positive than the non- 

 amalgamated, is usually regarded as far more effective than 

 the latter (which has even given rise to special explanations), 

 does in fact only produce a current of less great intensity 

 than the non-amalgamated, when it, as this, is connected with 

 the circuit by a negative metal, a dilute acid and a connecting 

 wire of moderate resistance. The current from amalgamated 

 zinc and copper is in so slight a degree stronger than that 

 from non-amalgamated zinc and copper (all other circum- 

 stances in both circuits being alike), that a momentary re- 

 moval of the plates from the acid, or any other mode of open- 

 ing the latter circuit, suffices to give to this in intensity of 

 current the ascendency over the former*. This equilibrium 

 even follows of itself after no very long time. The advantage 

 of employing amalgamated zinc in the construction of voltaic 

 piles, consists, therefore, almost solely in no metal being use- 

 lessly expended : little is gained in effect by it. 



since been known from its decrease in platina, by moistening tiiis metal 

 with nitric acid. 



* This, as well as the previously-mentioned comparisons, were made with 

 the so-called differential-galvanometer. 



