Now, if both the free base and the free acid are very ‹difficultly soluble›, then the concentrations [MeOH] and [HX], respectively, in the solution ‹cannot go beyond a certain minute limit›. In view,[376] then, of the very small value, K_{Base}, of the ratio [Me^{+}] × [HO^{−}] / [MeOH] and the minute value that the second term [MeOH] has under these conditions, the first term [Me^{+}] × [HO^{−}] must have a correspondingly smaller value. It is clear, therefore, that in such a solution neither the nonionized base, MeOH, nor its ion, Me^{+}, can exist in more than minute quantities when the equilibrium constants are satisfied. The same conclusion is reached regarding the [p186] possibility of the existence of the difficultly soluble acid HX and its ion X^{−}, in more than minimal quantities. Since, then, neither the ion Me^{+} nor the ion X^{−} can be present in more than traces, their salt, MeX, which is considered readily ionizable, also ‹cannot exist in aqueous solutions›, except in traces. The ‹quantitative relations› are evident from the equilibrium equation (p. 185): [Me^{+}] × [X^{−}] / ([HX] × [MeOH]) = α^2 [Salt]^2 / ([Acid] × [Base]) = (K_{Acid} × K_{Base}) / K_{HOH} = K. It is evident that the concentration of the salt, [Salt], which is capable of existence in aqueous solution, is, in the first place, ‹the smaller the smaller the values› for K_{Acid} and K_{Base} are, ‹i.e. the weaker the acid and the base are›; and, in the second place, it is the smaller the smaller the values for [Acid] and [Base] are, which, in the present instance, represent the concentrations of the difficultly soluble acid and base in saturated solution, ‹i.e. their solubilities›. We reach the conclusion that ‹salts of very weak bases and very weak acids are very considerably decomposed by water›, and, if both the acid and the base are difficultly soluble in water, the decomposition is ‹practically complete›. ‹Conversely, such a very weak, difficultly soluble base will not combine with a very weak, difficultly soluble acid to form a salt in the presence of water.› An instance of the first kind is found in the case of aluminium sulphide, the salt of a very weak, difficultly soluble base, aluminium hydroxide, with a rather little soluble, weak acid, hydrogen sulphide (see table, p. 104). We find that when a piece of aluminium sulphide, prepared by dry methods, is dropped into water (‹exp.›), a precipitate of aluminium hydroxide is immediately formed and evolution of hydrogen sulphide occurs. We have Al_{2}S_{3} ⇄ 2 Al^{3+} + 3 S^{2−}, «6 HOH» ⇄ 6 HO^{−} + 6 H^{+} 2 Al^{3+} + 6 HO^{−} ⇄ «2 Al(OH)_{3} ↓» 3 S^{2−} + 6 H^{+} ⇄ «3 H_{2}S ↑».