546 M. Poggendorff on Galvanic Circuits composed of 



phuric acid, without this addition of nitric acid, afford in most 

 cases the opposite result? Want of chemical action on the 

 zinc it certainly is not ! And then, how, even according to the 

 affinity-theory, is the action of the nitric acid to be explained ? 



A long discussion might here be opened ; I will, however, 

 merely touch upon one point. Faraday states that the addition 

 of nitric acid to the sulphuric acid increases the intensity of the 

 chemical action ; and, after communicating some facts from 

 which he draws the conclusion that this acid does not increase 

 the quantity of the electricity, he adds : " This mode of increa- 

 sing the intensity of the electric current, as it excludes the effect 

 dependent upon many pairs of plates, or even the effect of 

 making any one acid stronger or weaker, is at once referable to 

 the conditions and force of the chemical affinities which are 

 brought into action, and may, both in principle and practice, 

 be considered as perfectly distinct from any other mode*/^ 



Here we may with justice put the question. What measure 

 then do we possess for the intensity of a chemical action? 

 When the question is, as to the attack of an acid on a metal, 

 we have, I believe, no other measure than the quantity of the 

 metal which is dissolved from the unity of surface in the unity 

 of time. But with this, certainly the most natural, view, there 

 exists no reason why the nitric acid should enjoy any single 

 advantage over the sulphuric acid, when these acids are taken of 

 such a degree of concentration that they both dissolve just the 

 same quantity of a like zinc surface in the same time. An ad- 

 vantage, according to Faraday's theory, is the less to be expected, 

 as both acids are non-electrolytes, and their effect therefore 

 could only be of like nature, and merely consist in increasing 

 the affinity of the oxygen of the water for the zincf. But 



* Faraday's Experimental Researches, §908. Itmaybeobservederapassaw^that 

 what the P'aradayaii theory terms the increase of the quantity of the electricity 

 is the same as heightening the force of the current by diminishing the resist- 

 ance ; for instance, enlarging the surfaces, increasing the concentration of the 

 fluids, therefore precisely the same as diminishing the denominator of Ohm's 

 formula. By electrolytic intensity, or intensity of the electricity, this theory on 

 the other hand understands, at least with the simple circuit, the electromo- 

 tive force, or the numerator of this formula. But both expressions are some- 

 times used in a different sense, of which I have already given an example in 

 the Annalen, vol. xlvii. p. 128\, and of which the explanation of the differ- 

 ence between the current of the pile, and that of the simple circuit (Exp. 

 Res. § 994), — an explanation so perfectly simple, according to Ohm's theory, 

 — gives a further proof. 



f However, with the nitric acid, whether employed alone, or mixed with 

 sulphuric acid, the process is not so simple, even with the above-mentioned 



[* A Translation of the Memoir of Ohm has just appeared in Part VII. of 

 the Scientific Memoirs. — Edit.] 



