Owing to the fact that hydrogen sulphide is a much stronger acid than water, the action of potassium hydrosulphide on an acid sulphide, like carbon disulphide (equation (2), p. 243), is reversed to a correspondingly greater degree than the action of potassium hydroxide on carbon dioxide[499] (equation (1), p. 243). The dissociation constant for the secondary ionization of hydrogen sulphide (HS^{−} ⇄ H^{+} + S^{2−}) is very much smaller than the constant for the primary ionization (HS^{−} is a much weaker acid than HSH), and so we find that a sulphide like K_{2}S exhibits very much stronger basic functions than do the hydrosulphides, as, for instance, in forming salts with acid-forming sulphides [p246] (equation (3), p. 243) and in neutralizing acids. There can be no question that, if we could have an aqueous solution of potassium oxide, K_{2}O, it would show, similarly, the characteristic actions of strong bases ‹even more powerfully› than the hydroxide, KOH; for instance, in acting on acid-forming oxides (equation (1), p. 243), in neutralizing acids, in saponifying esters (p. 81), and so forth. It is, in fact, on account of this property, that potassium oxide is decomposed by water. It is a salt involving the ‹secondary ionization› of water, (HO^{−} ⇄ H^{+} + O^{2−}), which has a much smaller dissociation constant even than the primary ionization (H_{2}O ⇄ H^{+} + HO^{−}). The oxide, K_{2}O, is decomposed by ‹neutralizing hydrogen ions formed by the primary ionization of water›. We have 2 K^{+} + O^{2−} + H^{+} + HO^{−} ⥂ 2 K^{+} + 2 HO^{−}, which is entirely analogous, in principle, to K^{+} + HO^{−} + H^{+} + Cl^{−} ⥂ K^{+} + Cl^{−} + HOH. «Sulphoxy-Salts.»—The close relations between the oxygen and the sulphur series are seen also in the fact that an oxygen base may be combined with an acid sulphide, and ‹vice versa›; arsenious sulphide, for instance, dissolves even in the solution of so weak a base as ammonium hydroxide (‹exp.›). The salts produced by this "crossing" are usually "hybrid" salts, partly sulpho-, partly oxygen-salts. There is, for instance, a series of ‹arseniates›,[500] Me_{3}AsO_{4}, Me_{3}AsSO_{3}, Me_{3}AsS_{2}O_{2}, Me_{3}AsS_{3}O and Me_{3}AsS_{4}. In analytical work the pure types are ordinarily utilized, rather than the mixed types. «Complex Sulphide Ions.»—The ions of the sulpho-acids, like the ions of oxygen-acids (p. 238), may also be treated as ‹complex ions›—of the positive metal ions and the sulphide-ion, S^{2−}. Ammonium sulphide combines with stannic sulphide, forming ammonium sulphostannate: SnS_{2} + (NH_{4})_{2}S ⇄ (NH_{4})_{2}SnS_{3}. If the action is considered to be the result of interactions of the ions of stannic and ammonium sulphides, we can resolve the equation into the following one: Sn^{4+} + 2 S^{2−} + 2 NH_{4}^{+} + S^{2−} ⇄ 2 NH_{4}^{+} + SnS_{3}^{2−}.