542 M. PoggendorfF on Galvanic Circuits composed of 



It is not to be supposed that the acid, thus diluted, is too 

 weak to act on the zinc; on the contrary, it attacks it very 

 violently, so energetically indeed that it becomes sensibly warm. 

 The plea, that with the dilute acid the affinity of the chlorine 

 for the zinc has become from the presence of the water weaker 

 than that of the iodine for the same metal, is therefore inad- 

 missible. 



Moreover, the same acid has with silver and with copp&r, no 

 matter whether combined with zinc (common or amalgamated) 

 iron or tin, in a high degree the ascendency over the solution of 

 the iodide of potassium, — a phsenomenon which, compared with 

 the opposite one on employing zinc-platina, at the same time 

 clearly proves what essential part the two metals of the circuit 

 take in the production of the current, and how contrary to nature, 

 therefore, that view is, according to which, in reference to the 

 voltaic current, the positive metal is termed the generating and 

 the negative the conducting metal*. 



Similar phaenomena, not favourable to the theory, are evinced 

 by the circuits oi sulphuric acid, iodide of potassium, platina and 

 a positive metal, by which, moreover, M'hen the latter consists 

 of zinc, especially non-amalgamated, those remarkable rever- 

 sions in the direction of the current occur which have already 

 been noticed in the table under No. 10. 



An experiment performed specially for this purpose, and con- 

 tinued longer than usual, made me better acquainted with them. 

 Bright filed plates of distilled zinc and non-heated plates of 

 platina were employed for this experiment. The former re- 

 mained during the whole time in the fluid ; the latter were 

 simultaneously immersed and taken out. During the first im- 

 mersion, the current proceeded constantly in the direction s > i. 



* It is not very intelligible how this notion can have gained ground, since 

 well-proved facts have long ago shown quite the contrary. If the negative 

 metal in the circuit had merely to act as it were a passive part, to perform 

 merely the function oi conducting, then evidently the best conductor must pro- 

 duce the strongest current, or, rather, the greatest electromotive force. Cop- 

 per conducts decidedly better than platina ; but yet the latter, in combination 

 with a positive metal, gives rise to a far greater electromotive force than the 

 former. How essential the negative metal of the circuit is in generating the 

 current, is most decidedly evident from the position first established by JFech- 

 ner (Schweigger's Journ. vol. Ix. 1830, p. 17, and PoggendorfF's Annalen, vol. 

 xliii. p. 433), that, as soon as the fluids do not act very alteringly on the metals, 

 the voltaic lata of the tensions is also valid for the electromotive forces of the 

 circuit, that therefore, for instance, the electromotive force of a zinc-platina 

 circuit is equal to the sum of the electromotive forces of a zinc-copper and of 

 a copper-platina circuit. The law naturally cannot be applied to the intensity 

 of the currents. The current from copper-platina is, as I have convinced my- 

 self, by far weaker than the difierence of the cun-ents from zinc-platina and 

 zinc-copper, — easily imaginable from the inequality of the resistance of transi- 

 tion. 



