VOLTAIC EXCITEMENT AFFECTED BY DILUTION. 
107 
contrast with the definite expression as to the place of action which the chemical 
theory supplies. 
1983. All the variations which have been given are consistent with the extreme 
variety which chemical action under different circumstances possesses, but, as it still 
appears to me, are utterly incompatible with, what should be, the simplicity of mere 
contact action ; further they admit of even greater variation, which renders the 
reasons for the one view and against the other, still more conclusive. 
1984. Thus if a contact philosopher say that it is only the very strongest acids that 
can render the part of the metals in it negative, and therefore the effect does not 
happen with muriatic acid or potash (1980. 1981.), though it does with nitric and 
sulphuric acids (1977. 1978.); then, the following result is an answer to such an 
assumption. Iron in dilute nitric acid, consisting of one volume of strong acid and 
twenty of water, is positive to iron in strong acid, or in a mixture of one volume 
of strong acid with one of water, or with three, or even with five volumes of water. 
Silver also, in the weakest of these acids, is positive to silver in any of the other four 
states of it. 
1985. Or if, modifying the statement upon these results, it should be said that di- 
luting the acid at one contact always tends to give it a certain proportionate electro- 
motive force, and therefore diluting one side more than the other will still allow this 
force to come into play ; then, how is it that with muriatic acid and potassa the effect 
of dilution is the reverse of that which has been quoted in the cases with nitric 
acid and iron or silver? (1977. 1984.) Or if, to avoid this difficulty, it be assumed 
that each electrolyte must be considered apart, the nitric acid by itself, and the 
muriatic acid by itself, for that one may differ from another in the direction of the 
change induced by dilution, then how can the following results with a single acid be 
accounted for ? 
1986. I prepared four nitric acids : 
A was very strong pure nitric acid ; 
B was one volume of A and one volume of water ; 
C was one volume of A and three volumes of water; 
D was one volume of A and twenty volumes of water. 
Experimenting with these acids and a metal, I found that copper in C acid was posi- 
tive to copper in A or in D acid. Nor was it the first addition of water to the strong 
acid that brought about this curious relation, for copper in the B acid was positive 
to copper in the strong acid A, but negative to the copper in the weak acid D : the 
negative effect of the stronger nitric acid with this metal does not therefore depend 
upon a very high degree of concentration. 
1987. Lead presents the same beautiful phenomena. In the C acid it is positive 
to lead either in A or D acid : in B acid it is positive to lead in the strongest, and 
negative to lead in the weakest acid. 
p 2 
