538 M. Poggendorff on Galvanic Circuits composed of 
Just as little, in my opinion, do the facts speak for Faraday^s 
theory. A stronger affinity must undoubtedly he attributed to 
the chlorine for zinc, iron, and tin than to the oxygen ; and 
nevertheless, in circuits containing one of these metals as positive 
member, hydrochloric acid does not act more strongly, but more 
weakly, than water* * * § . 
In the dilute sulphuric and nitric acids, according to Faraday, 
only the affinity of the oxygen of the water acts on the positive 
metal. Consequently these acids, when water acts opposed 
to them, must either produce no current, or, if the above- 
mentioned affinity is increased by their presence, develope, as 
is otherwise generally admitted, a more powerful electromotive 
force than pure water. Nevertheless the two acids act, in the 
greater number of cases examined, more weakly than waterf. 
The same observation may be applied to caustic potash and am- 
monia. In Faraday’s ^^Experimental Researches'^ we find it stated, 
§ 919, Thus, when zinc, platina, and dilute sulphuric acid are 
used, it is the union of the zinc with the oxygen of the 
water which determines the current;” further, § 932, The si- 
milarity in the action of either dilute sulphuric acid or potassa 
goes indeed far beyond this, even to the proof of identity,” and 
§ 933, But all the effects in these experiments prove, I think, 
that it is the oxidation of the metal necessarily dependent upon, 
and associated as it is with, the electrolyzation of the water, that 
produces the current ; and that the acid or alkali merely act as 
solvents by removing the oxidized zinc.” 
But in truth the caustic alkalies always act differently from 
water and differently from acidsj, and that immediately, in the 
first moment of immersion, when the zinc is still in possession 
of its full metallic lustre. There is, indeed, a certain relation to 
the attackability of the positive metal apparent, as is evident for 
* It also acts more weakly than sulphuric acid, at least with amalgamated 
zinc and platina or silver. (See Note, p. 423.) 
f Becquerel observed years ago {Ann. de Chim. et de Phys., vol. xli. p. 17) 
that when zinc and copper are placed in two cells separated by membrane and 
filled with a solution of the sulphate of zinc, and then some nitric acid is 
poured into one of them, this addition in the copper cell heightens the 
current, but in the zinc cell weakens it. This experiment, certainly, Avhen cor- 
rectly apprehended, as already observed by Berzelius {Jahreshericht, No. x. p. 
23), is no argument in favour of the chemical theory. Similar facts, have more- 
over been noticed by Fechner {Annalen, vol. xliii. p. 433). 
+ This indeed has not escaped Faraday. In § 941, he says, “ The alkali, 
in fact, is superior to the acid in bringing a metal into what is called the posi- 
tive state;” — but why? it may be asked; and how does this agree w'ith 
§ 921 ? in which it is stated, “ Oxidation or other direct action upon the metal 
itself is the source of the current, but it is of the utmost importance to observe 
that the oxygen or other body must he in the state of combination, and indeed 
in such a state of combination as to constitute an electrolyte.” 
