In all the chemical changes produced by these alkalies, the same difference in intensity of action is shown, that is here exhibited towards indicators. If, for example, we measure the rate of change in an action, which is slow enough to be measured and which proceeds quantitatively in proportion to the concentration of hydroxide-ion, we find that the measured rates of change indicate the same ratio in the concentrations of hydroxide-ion in potassium and ammonium hydroxide solutions, as is indicated by quantitative conductivity measurements. An action suitable for the purpose is the saponification of an ester, such as ethyl acetate. Under the influence of an alkali, like potassium hydroxide, ethyl acetate is decomposed, more or less rapidly, into an acetate and alcohol: we have, for instance,
CH_{ 3}CO_{ 2}C_{ 2}H_{ 5} + KOH → CH_{ 3}CO_{ 2}K + C_{ 2}H_{ 5}OH.
The rate of saponification is found to be proportional to the ‹concentration of hydroxide-ion›, and not to the total concentration of the base, and the action may be formulated more accurately as follows:
CH_{ 3}CO_{ 2}C_{ 2}H_{ 5} + K^{ +} + HO^{ −} → CH_{ 3}CO_{ 2}^{ −} + K^{ +} + C_{ 2}H_{ 5}OH
or CH_{ 3}CO_{ 2}C_{ 2}H_{ 5} + HO^{ −} → CH_{ 3}CO_{ 2}^{ −} + C_{ 2}H_{ 5}OH.
For ammonium hydroxide we have similarly,
CH_{ 3}CO_{ 2}C_{ 2}H_{ 5} + NH_{ 4}^{ +} + HO^{ −} → CH_{ 3}CO_{ 2}^{ −} + NH_{ 4}^{ +} + C_{ 2}H_{ 5}OH.
Now, Arrhenius[140] proved that the rate of saponification of ethyl acetate by ammonium hydroxide, which is ‹very much slower› than the rate of saponification by potassium hydroxide of equivalent concentration, ‹does agree quantitatively, indeed, with the rate demanded by the theory of ionization›, when the hydroxide-ion is considered the active component of the bases, to which the saponification is due.
EXP. A rough idea of the difference in the chemical actions of the two bases may be obtained by observing their effects on the ester, methyl acetate, which is decomposed into an acetate and methyl alcohol rather rapidly. To 50 c.c. of (CO_{ 2} free) water containing some phenolphthaleïn, 10 c.c. of 0.1 molar potassium hydroxide is added; a similar mixture with 10 c.c. of 0.1 molar ammonium hydroxide solution is prepared. To each of the solutions, 2 c.c. (an excess) of methyl acetate is added (to the ammonium hydroxide solution first), and the mixtures are shaken for a moment. At room temperature, the mixture containing potassium hydroxide will become pale pink in a few minutes, and colorless soon thereafter, while the mixture [p081] containing ammonium hydroxide will still be deep red at the end of 45 minutes.[141]