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 be 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 loeakly than waterf. 



The same observation may be applied to caustic potash and am- 

 monia. In Faraday's "Experimental Researches'' \\e 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 acids J, 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 witli amalgamated 

 zinc and platina or silver. (See Note, p. 423.) 



f Becquerel observed years ago {Ann. de Ckim. 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 

 cuiTcnt, but in the zinc cell weakens it. This experiment, certainly, when cor- 

 rectly appi-ehendcd, as alreadj^ 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 (Jnnalen, vol. xliii. p. 433). 



I 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 with 

 § 921 ? in which it is stated, " Oxidation or other direct action upon the metal 

 itself is the source of the cm-rent, but it is of the utmost importance to observe 

 that the oxygen or other body must be in the state of combination, and indeed 

 in such a state of combination as to constitute an electrolyte." 



