ctrolytic_ conduction of the current.

To explain the appearance of the products of decomposition at the
electrodes only, while the intervening solution is unaltered, we suppose
that, under the action of the electric forces, the opposite parts of the
electrolyte move in opposite directions through the liquid. These
opposite parts, named ions by Faraday, must therefore be associated with
electric charges, and it is the convective movement of the opposite
streams of ions carrying their charges with them that, on this view,
constitutes the electric current.

In metallic conduction it is found that the current is proportional to
the applied electromotive force--a relation known by the name of Ohm's
law. If we place in a circuit with a small electromotive force an
electrolytic cell consisting of two platinum electrodes and a solution,
the initial current soon dies away, and we shall find that a certain
minimum electromotive force must be applied to the circuit before any
considerable permanent current passes. The chemical changes which are
initiated on the surfaces of the electrodes set up a reverse
electromotive force of polarization, and, until this is overcome, only a
minute current, probably due to the slow but steady removal of the
products of decomposition from the electrodes by a process of diffusion,
will pass through the cell. Thus it is evident that, considering the
electrolytic cell as a whole, the passage of the current through it
cannot conform to Ohm's law. But the polarization is due to chemical
changes, which are confined to the surfaces of the electrodes; and it is
necessary to inquire whether, if the polarization at the electrodes be
eliminated, the passage of the current through the bulk of the solution
itself is proportional to the electromotive force actually applied to
that solution. Rough experiment shows that the current is proportional
to the excess of the electromotive force over a constant value, and thus
verifies the law approximately, the constant electromotive force to be
overcome being a measure of the polarization. A more satisfactory
examination of the question was made by F. Kohlrausch in the years 1873
to 1876. Ohm's law states that the current C is proportional to the
electromotive force E, or C = kR, where k is a constant called the
conductivity of the circuit. The equation may also be written as C =
E/R, where R is a constant, the reciprocal of k, known as the resistance
of the circuit.