«Sulpho-Bases.»—Since one meets, in this group, ‹sulpho-acids› and ‹sulpho-salts›, corresponding to the oxygen acids and their salts, one is naturally led to inquire,[495] whether the third great class of oxygen compounds is not found duplicated among sulphur compounds, whether ‹sulpho-bases›, as well as sulpho-acids and salts, are known. One would look for such bases, with the most pronounced basic character, among the compounds obtained by the substitution of sulphur for oxygen in the strongest oxygen bases. To a certain extent potassium and sodium hydrosulphides and sulphides show, in fact, properties, which are akin to those fundamentally characteristic of ordinary bases. They combine with acid sulphides to form sulpho-salts, as the oxygen bases combine with acid oxides. To a very considerable extent they neutralize all but the very weakest acids; hydrogen sulphide, itself a very weak acid, is driven out of its salts by all stronger acids, and the latter are almost completely neutralized. For instance, we have: [p245] KOH + HCl ⥂ KCl + H_{2}O, and KSH + HCl ⥂ KCl + H_{2}S and K_{2}S + 2 HCl ⥂ 2 KCl + H_{2}S. The concentration of the hydrogen-ion is reduced most decidedly in each of these reactions. EXP.—A solution of potassium hydrosulphide is saturated with hydrogen sulphide, in order to prevent hydrolysis and the formation of potassium hydroxide[496] (p. 180), as far as possible, and the solution is added to an acid (hydrochloric) solution of methyl orange;[497] the acid color is changed to orange, as a result of the almost complete neutralization of the acid. The potassium hydrosulphide (the hydrosulphide-ion HS^{−}) neutralizes the hydrogen-ion (of hydrochloric acid), that converts methyl orange into its pink salt, and hydrogen sulphide is formed, which is too weak an acid to affect the color of the indicator (p. 79). The objection that potassium sulphide and hydrosulphide are salts, the salts of hydrogen sulphide, might be raised against the conception of their possessing a certain measure of basic functions; but the common oxygen base, potassium hydroxide, is also a salt, the salt of a still weaker acid, water. Indeed, the characteristic properties of ordinary bases are due essentially to the fact, that they are the more or less readily ionizable salts of an extremely weak acid, water, and these properties may well be duplicated by salts of other ‹weak› acids, duplicated in a ‹very much weaker› way, in proportion as the acids are stronger than water. The difference is, then, really one of ‹degree› and not of kind.[498]