The Elements of Qualitative Chemical Analysis, vol. 1, parts 1 and 2. / With Special Consideration of the Application of the Laws of Equilibrium and of the Modern Theories of Solution.

by Julius Stieglitz

It is noteworthy, however, that the equilibrium relations demand that at least traces of chlorine be liberated, and traces of ferrous salt be formed, since neither [Fe⁺⁺] nor [Cl₂] may have the value 0. If we add some sodium chloride to a solution of sodium sulphate, connected electrically, in the usual way, with a solution of ferric sulphate, a very slight momentary current is produced (exp.). The liberation of the first traces of chlorine and of ferro-ion on the electrodes is necessary, and also sufficient, to satisfy the conditions for equilibrium as expressed by the constant, until diffusion from the electrodes removes these traces.

Summary.

Chapter XIV Footnotes

[514] The oxidation by chlorine may also be represented on the basis of the conception that the chlorine molecule contains a positive and a negative chlorine atom, Cl⁺Cl⁻. (Vide W. A. Noyes, J. Am. Chem. Soc., 23, 460 (1901); Stieglitz, ibid., 23, 796 (1901); Walden, Z. phys. Chem., 43, 385 (1903); J. J. Thomson, Corpuscular Theory of Matter, p. 130 (1907)). We may consider the action to take place as follows: 2 Fe²⁺ + Cl⁺ → 2 Fe³⁺ + Cl⁻.

[515] ε⁻ is used to indicate an electron.

[516] The whole device is an adaptation of Ostwald's "Chemometer" [see Z. phys. Chem., 15, 399 (1894)]. It has been found best to convert a Weston voltmeter into a lecture table apparatus by lengthening its index to 10 inches, with the aid of a very light, hollow aluminium wire carrying an index and playing over a scale 10 inches wide, drawn on glass and divided into 150 divisions. The scale is illuminated by means of five small one-candle-power lamps. The whole is encased in a simple wooden frame. The voltmeter shows a range of 0.7 volt, but, on account of its low resistance (78 ohms), it is used only for qualitative purposes and does not register the true potentials, quantitatively. (Such adaptations of Weston voltmeters may be purchased from the Weston Electrical Instrument Co., or a similar instrument obtained from Hartmann and Braun, Frankfurt a/M, Germany.)

[517] Chemical Action at a Distance, Ostwald, Z. phys. Chem., 9, 540 (1892).

[518] Peters, Z. phys. Chem., 26, 229 (1898).

[519] See below, in regard to the quantitative relations for reactions of this nature.

[520] Exp. Ferric sulphate solution is tested with a ferricyanide.