124 THE THEORY OF IONIZATIONtrons flow into the cell from the metallic conductor, reduction
occurs. At the anode, which is the electrode at which electrons
flow out through the metallic conductor, oxidation occurs.
The sum of the changes at the anode and cathode makes a
complete reaction of oxidation and reduction, but the location of
the oxidation is remote from the location of the reduction.
Michael Faraday studied quantitatively the extent of the chem-
ical change at the electrodes when electric currents pass through
solutions, and in 1834 he stated a law which has since borne his
name:
Faraday's Law: When the same amount of electric current is
passed through several electrochemical cells the quantities of the
new substances produced at the several electrodes are chemically
equivalent to each other.
The amount of electricity which must pass to effect the change
of one chemical equivalent (for example, to liberate 1.008 gram of
hydrogen) has been found to be 96,500 coulombs. This quantity
has been named the f araday, and it is designated by the symbol F.
The explanation of the mechanism of the electrolytic conduct-
ance in specific cases will make the application of Faraday's law
clearer.
A current is passed through a solution of copper sulphate in a
U-tube with copper electrodes in the opposite arms. At the
cathode copper ions are reduced
20 + Cu++ -> Cu°thus impoverishing the solution of Cu++ ions. At the anode
copper atoms at the surface have electrons withdrawn, thus pro-
ducing Cu++ ions
Cu° -> Cu++ + 20
and enriching the solution in Cu++ ions. It is fundamental that
every portion of the solution shall at all times remain electrically
neutral, and this condition is preserved through the movement
of the ions through the solution, the SO 4 ~~ ions moving towards
the anode and the Cu++ ions towards the cathode.
It is to be remarked that in the cell just described the SO 4
ions are not discharged. They simply migrate through the solution
to preserve the electric balance with the copper ions which are
entering the solution at the anode and leaving in equal numbers at