!Introduction to General Inorganic
Chemistry! (Century Company).

The !electrolytic dissociation theory!, as propounded by Arrhenius in
1887, assumes that acids, bases, and salts (that is, electrolytes)
in aqueous solution are dissociated to a greater or less extent into
!ions!. These ions are assumed to be electrically charged atoms or
groups of atoms, as, for example, H^{+} and Br^{-} from hydrobromic
acid, Na^{+} and OH^{-} from sodium hydroxide, 2NH_{4}^{+} and
SO_{4}^{--} from ammonium sulphate. The unit charge is that which is
dissociated with a hydrogen ion. Those upon other ions vary in sign
and number according to the chemical character and valence of the
atoms or radicals of which the ions are composed. In any solution the
aggregate of the positive charges upon the positive ions (!cations!)
must always balance the aggregate negative charges upon the negative
ions (!anions!).

It is assumed that the Na^{+} ion, for example, differs from the
sodium atom in behavior because of the very considerable electrical
charge which it carries and which, as just stated, must, in an
electrically neutral solution, be balanced by a corresponding negative
charge on some other ion. When an electric current is passed through a
solution of an electrolyte the ions move with and convey the current,
and when the cations come into contact with the negatively charged
cathode they lose their charges, and the resulting electrically
neutral atoms (or radicals) are liberated as such, or else enter at
once into chemical reaction with the components of the solution.

Two ions of identically the same composition but with different
electrical charges may exhibit widely different properties. For
example, the ion MnO_{4}^{-} from permanganates yields a purple-red
solution and differs in its chemical behavior from the ion
MnO_{4}^{--} from manganates, the solutions of which are green.

The chemical changes upon which the procedures of analytical chemistry
depend are almost exclusively those in which the reacting substances
are electrolytes, and analytical chemistry is, therefore, essentially
the chemistry of the ions. The percentage dissociation of the same
electrolyte tends to increase with increasing dilution of its
solution, although not in direct proportion. The percentage
dissociation of different electrolytes in solutions of equivalent
concentrations (such, for example, as normal solutions) varies widely,
as is indicated in the follow