[442] Euler, Ber. d. chem. Ges., 36, 3403 (1903).

[443] See footnote, p. [212].

[444] See pp. [165], [210] and [213].

[445] The acid HAg(CN)2, corresponding to the salt, is crystallizable and is a strong acid. It is largely decomposed, by water, into silver cyanide and hydrocyanic acid.

[446] See the experiments described on pp. [45] and [89].

[447] In solutions containing an excess of potassium cyanide greater than 0.05 molar, the salt K2[Ag(CN)3] is formed. The dissociation or instability constant for the complex ion Ag(CN)32− is 1E−22.

[448] Z. anorg. Chem., 39, 222 (1904).

[449] The solubility-product constant for silver chloride at 25° is 2E−10. If the concentration of chloride-ion be made 1.0 by the addition of potassium chloride to a 0.05 molar solution of KAg(CN)2, then the concentration of silver-ion, necessary for the precipitation of the chloride, would be KS.P. / [Cl−] = 2E−10 gram-ion. Neglecting the fact that the complex salt is not completely ionized and putting [Ag(CN)2−] = 0.05, and calling x the concentration of the cyanide-ion just necessary to prevent the precipitation of the chloride, we have:

[Ag+] × [CN−]2 / [Ag(CN)2−] = 2E−10 × x2 / 0.05 = 10−21.

We find x = 5E−7 mole, or approximately 0.03 milligram potassium cyanide (cyanide-ion) per liter. This minute quantity of free cyanide, if not originally present in the solution used, would be formed by the liberation of potassium cyanide from the complex (according to KAg(CN)2 + KCl → AgCl + 2 KCN) as soon as 2.5E−7 mole, or 0.036 milligram, of silver chloride per liter have been formed, a quantity too small to be perceptible.