rization
at the electrodes was eliminated, the resistance of a solution was
constant however determined, and thus established Ohm's Law for
electrolytes. The law was confirmed in the case of strong currents by G.
F. Fitzgerald and F. T. Trouton (_B.A. Report_, 1886, p. 312). Now,
Ohm's Law implies that no work is done by the current in overcoming
reversible electromotive forces such as those of polarization. Thus the
molecular interchange of ions, which must occur in order that the
products may be able to work their way through the liquid and appear at
the electrodes, continues throughout the solution whether a current is
flowing or not. The influence of the current on the ions is merely
directive, and, when it flows, streams of electrified ions travel in
opposite directions, and, if the applied electromotive force is enough
to overcome the local polarization, give up their charges to the
electrodes. We may therefore represent the facts by considering the
process of electrolysis to be a kind of convection. Faraday's classical
experiments proved that when a current flows through an electrolyte the
quantity of substance liberated at each electrode is proportional to its
chemical equivalent weight, and to the total amount of electricity
passed. Accurate determinations have since shown that the mass of an ion
deposited by one electromagnetic unit of electricity, i.e. its
electro-chemical equivalent, is 1.036 X 10^-4 X its chemical equivalent
weight. Thus the amount of electricity associated with one
gram-equivalent of any ion is 10^4/1.036 = 9653 units. Each monovalent
ion must therefore be associated with a certain definite charge, which
we may take to be a natural unit of electricity; a divalent ion carries
two such units, and so on. A cation, i.e. an ion giving up its charge at
the cathode, as the electrode at which the current leaves the solution
is called, carries a positive charge of electricity; an anion,
travelling in the opposite direction, carries a negative charge. It will
now be seen that the quantity of electricity flowing per second, i.e.
the current through the solution, depends on (1) the number of the ions
concerned, (2) the charge on each ion, and (3) the velocity with which
the ions travel past each other. Now, the number of ions is given by the
concentration of the solution, for even if all the ions are not actively
engaged in carrying the current at the same instant, they must, on any
dynamical idea of c