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 copper ^ 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 phaenomenon 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 of sulphuric acid, iodide of potassium, platina and 
a positive metal, by which, moreover, when 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 > z. 
* 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 of 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 positiv^e 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 Fech- 
ner (Schweigger’s Journ. vol. lx, 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 law of the tensions is also valid for the electromotive forces of the 
circuit, that therefore, for instance, the electromotive force of a %inc-platina 
circuit is equal to the sum of the electromotive forces of a zinc-copper and of 
a copper-plutina 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 difference of the currents from zinc-platina and 
zinc-copper, — easily imaginable from the inequality of the resistance of transi- 
tion. 
