[155] The ‹negative› results obtained with aluminium and magnesium are possibly more interesting than the positive action observed with zinc, but their inactivity ‹may› be due to thin films of protective chloride or oxide or to a passive condition (‹vide› Smith's ‹Inorganic Chemistry›, pp. 723, 753; ‹College Chemistry›, p. 475). [156] The work of Ostwald, Arrhenius, Nernst and many others shows conclusively that the liberation of hydrogen by metals and the precipitation of metals by one another is a function of ‹ion› concentrations (Chapter XIV). ‹Vide› Nernst, ‹Theoretische Chemie› (1905), p. 245. [157] See above. [158] In a 0.1 molar solution of potassium cyanide, the potassium hydroxide formed by the decomposition of the cyanide by water is approximately 0.0013 molar and the concentration of hydrogen-ion is reduced to 10^{−11} (Chapter X), a value roughly of the same order as that calculated above as a possible concentration of hydrogen-ion in a benzene solution of hydrogen chloride. In spite of this small concentration of hydrogen-ion in the cyanide solution, the reactions in which it is involved are, as far as known, completed in a few moments. Only for much smaller concentrations of ions have any doubts as to their ‹direct action› been aroused; in Chapter XII this question, as raised by Haber, is discussed for concentrations of ions of the order of 10^{−23}. Haber considers that ionic concentrations of 10^{−14} can still account for very fast actions. [159] ‹Cf.› Abegg., ‹Theorie der Elektrolytischen Dissociation› (1903), 255; Lehfeldt, ‹Electro-chemistry› (1904), 87. [160] There is probably ‹minimal› ionization in all these cases, especially in the case of ammonia (NH_{3} ⇄ NH_{2}^{−} + H^{+}), but not enough to yield a sufficient supply of hydrogen-ion to show its common properties. [161] ‹Vide› Jorgensen, ‹J. prakt. Chem.›, «16», 349 (1877). [162] See Chapter XII in regard to the stability of (PtCl_{6}^{2−}) as a complex ion. [163] Freshly prepared solutions must be used. [164] See Chapter XII as to the decomposition of the "complex ions." [165] K^{+} and CN^{−} are ‹colorless› ions. The yellow color of the ion moving to the positive electrode shows the presence of the iron in it—a fact that can be confirmed by testing the solution round the anode for ferricyanide by the method discussed further on in the text. [p090] CHAPTER VI «CHEMICAL EQUILIBRIUM. THE LAW OF MASS ACTION»