vided by m, gave the equivalent
conductivity of the substance dissolved. This procedure appears
justifiable, for as long as conductivity is proportional to
concentration it is evident that each part of the dissolved matter
produces its own independent effect, so that the total conductivity is
the sum of the conductivities of the parts; when this ceases to hold,
the concentration of the solution has in general become so great that
the conductivity of the solvent may be neglected. The general result of
these experiments can be represented graphically by plotting k/m as
ordinates and [root 3]m as abscissae, [root 3]m being a number
proportional to the reciprocal of the average distance between the
molecules, to which it seems likely that the molecular conductivity may
be related. The general types of curve for a simple neutral salt like
potassium or sodium chloride and for a caustic alkali or acid are shown
in fig. 4. The curve for the neutral salt comes to a limiting value;
that for the acid attains a maximum at a certain very small
concentration, and falls again when the dilution is carried farther. It
has usually been considered that this destruction of conductivity is due
to chemical action between the acid and the residual impurities in the
water. At such great dilution these impurities are present in quantities
comparable with the amount of acid which they convert into a less highly
conducting neutral salt. In the case of acids, then, the maximum must be
taken as the limiting value. The decrease in equivalent conductivity at
great dilution is, however, so constant that this explanation seems
insufficient. The true cause of the phenomenon may perhaps be connected
with the fact that the bodies in which it occurs, acids and alkalis,
contain the ions, hydrogen in the one case, hydroxyl in the other, which
are present in the solvent, water, and have, perhaps because of this
relation, velocities higher than those of any other ions. The values of
the molecular conductivities of all neutral salts are, at great
dilution, of the same order of magnitude, while those of acids at their
maxima are about three times as large. The influence of increasing
concentration is greater in the case of salts containing divalent ions,
and greatest of all in such cases as solutions of ammonia and acetic
acid, which are substances of very low conductivity.

[Illustration: FIG. 4.]

_Theory of Moving Ions._--Kohlrausch found that, when the pola