Limiting the further discussion, at this moment, to potassium hydroxide and ammonium hydroxide, we should find that, since in equimolar solutions, a larger portion of the former is ionized than of the latter, ‹the potassium hydroxide solution must contain the larger proportion or concentration of hydroxide-ion, HO^{−}, which is the characteristic ion of bases›. It should, therefore, show the ‹chemical› characteristics of a base much more decidedly than the ammonium hydroxide solution. That such is the case can be very simply shown by adding equal quantities (0.1 c.c.) of the 0.1 molar solutions to equal volumes (50 c.c.) of water[138] containing some phenolphthaleïn. This is an indicator for bases and acids, like litmus, but it is less sensitive to hydroxide-ion than is litmus. We find that the potassium hydroxide causes a very decided change, producing a deep red color with the phenolphthaleïn, whereas the ammonium hydroxide only produces a pink hue.[139] [p079] 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.