th the dilution of
its solution. If we consider what happens during the (usually) brief
period of dilution of the solution from molal to 0.1 molal, for
example, it will be seen that on the addition of water the conditions
of concentration which led to equality in the rate of change, and
hence to equilibrium in the molal solution, cease to exist; and since
the dissociating tendency increases with dilution, as just stated,
it is true at the first instant after the addition of water that the
concentration of the undissociated acid is too great to be
permanent under the new conditions of dilution, and the reaction,
HC_{2}H_{3}O_{2} <--> H^{+} + C_{2}H_{3}O_{2}^{-}, will proceed from
left to right with great rapidity until the respective concentrations
adjust themselves to the new conditions.

That which is true of this reaction is also true of all reversible
reactions, namely, that any change of conditions which occasions
an increase or a decrease in concentration of one or more of the
components causes the reaction to proceed in one direction or the
other until a new state of equilibrium is established. This principle
is constantly applied throughout the discussion of the applications
of the ionic theory in analytical chemistry, and it should be clearly
understood that whenever an existing state of equilibrium is disturbed
as a result of changes of dilution or temperature, or as a consequence
of chemical changes which bring into action any of the constituents of
the solution, thus altering their concentrations, there is always a
tendency to re-establish this equilibrium in accordance with the law.
Thus, if a base is added to the solution of acetic acid the H^{+} ions
then unite with the OH^{-} ions from the base to form undissociated
water. The concentration of the H^{+} ions is thus diminished, and
more of the acid dissociates in an attempt to restore equilbrium,
until finally practically all the acid is dissociated and neutralized.

Similar conditions prevail when, for example, silver ions react with
chloride ions, or barium ions react with sulphate ions. In the former
case the dissociation reaction of the silver nitrate is AgNO_{3} <-->
Ag^{+} + NO_{3}^{-}, and as soon as the Ag^{+} ions unite with the
Cl^{-} ions the concentration of the former is diminished, more of the
AgNO_{3} dissociates, and this process goes on until the Ag^{+} ions
are practically all removed from the solution, if the Cl^{-} ions are
present i