288	Faraday's Researches	]
970.	I know it may be said in reference to the numerous	j
changes with strong and dilute acids, that the results are the	I
consequence of corresponding alterations in the contact force;	}
but this is to change about the theory with the phenomena and	j
with chemical force (862, 944,, 973; 994, 1002,, 1051); or it may	j
be alleged that it is the contact force of the solutions produced	j
at the metallic surfaces which, differing, causes difference of	'
effect; but this is to put the effect before the cause in the order	j
of time.    If the liberty of shifting the point of efficacy from	|
metals to fluids, or from one place to another, be claimed, it is
at all events quite time that some definite statement and data
respecting the active points (796) should be given. At present
it is difficult to lay hold of the contact theory by any argument
derived from experiment, because of these uncertainties or
variations, and it is in that respect in singular contrast with the
definite expression as to the place of action which the chemical
theory supplies.
 971.	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.
 972.	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 (968, 969), though it does with nitric and sul-
phuric acids (965, 966); 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.
 973.	Or if, modifying the statement upon these results, it
should be said that diluting the acid at one contact always tends
to give it a certain proportionate electromotive force, and there-
fore 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
(965, 972)?    Or if, to avoid difficulty, it be assumed that each