[473] The concentrations of silver-ion are large, in comparison with those in cyanide solution, and the action is, most likely, essentially an ionic one; but the argument applies with equal force to cyanide systems. [474] ‹Loc. cit.› [475] An equilibrium constant, as we have seen, is a ‹ratio› of velocity constants of balanced reactions (pp. 94, 233) and involves therefore at least ‹two unknown› velocity constants. By determining the actual ‹rate› of ‹change› with known concentrations of reacting components, ‹i.e.› by determining the velocity constants themselves, rather than their ratio, a definite conclusion as to the mechanism or path of a given reaction can often be reached (see p. 80). [476] ‹Proceedings Amer. Academy›, 1892. [477] In the absence of any added cyanide, it combines with itself. Silver cyanide, according to Bodländer's results, is, in saturated solutions, chiefly (AgCN)_{2} or Ag[Ag(CN)_{2}], ‹i.e.› Ag—[N=C=C=N—Ag]. [478] See p. 225, footnote 4. [479] Werner has developed quite a different theory of the structure of complex ions. (‹Cf.› Nernst, ‹Theoretical Chemistry›, p. 374 (1904).) [480] Sherrill, ‹Z. phys. Chem.›, «43», 721 (1903). [481] In Nessler's reagent, Fresenius' ‹Qualitative Analysis›, p. 141. [482] ‹Cf.› Remsen, ‹Am. Chem. J.›, «11», 291 (1899); «14», 81 (1892) («Stud.»). [483] For instance, for arsenious acid we have 3 H^{+} + AsO_{3}^{3−} ⇄ H_{3}AsO_{3} ⇄ As^{3+} + 3 HO^{−} and, therefore, [As^{3+}] × [HO^{−}]^3 / ([AsO_{3}^{3−}] × [HO^{+}]^3) = ‹k›_{1}. Since [H^{+}] = ‹k′›_{HOH} / [HO^{−}] (p. 176), we have further, [As^{3+}] × [HO^{−}]^6 / [AsO_{3}^{3−}] = ‹k›_{2}. And since we may derive the relation [HO^{−}]^2 = ‹k›_{3} × [O^{2−}], by considering the primary and the secondary ionization of water (see pp. 246, 278), we have, finally, [As^{3+}] × [O^{2−}]^3 / [AsO_{3}^{3−}] = ‹K›. The constants for the primary and the secondary ionization of water are included in the value of ‹K›. [484] Fitzgerald and Lapworth, ‹J. Chem. Soc.› (London), «93», 2163 (1908); Lapworth, ‹ibid.›, 2187. ‹Vide› also Franklin on the characteristics of the NH_{4}^{+} ion in liquid ammonia, ‹Am. Chem. J.›, «23», 305 (1900). [485] See the laboratory instructions, in regard to the precautions used, to avoid errors from this source. [486] On the other hand, ‹colloidal› organic substances, such as casein, glue or albumen, interfere with the precipitation of even the most insoluble sulphides, by producing ‹colloidal suspensions› of the latter (see Chap. VII; ‹cf.› Müller, ‹Allgemeine Chemie der Kolloide›, p. 56 (1907)). [487] In alcohols the hydroxide group is held by a carbon atom, whose remaining valences are satisfied by hydrogen or carbon atoms, as in ordinary or ethyl alcohol, H_{3}C—CH_{2}(OH). [488] Küster, ‹Z. Elektrochem.›, «4», 117 (1897).