[395] Auerbach, Z. phys. Chem., 49, 220 (1904).
[396] See footnote 1, p. [201].
[397] Knox (in Abegg's laboratory), Trans. Faraday Soc., 4, 44 (1908).
[398] The concentration of the hydrogen-ion is really a little greater than that of the hydrosulphide-ion, as a result of the ionization of the latter, but the amount of hydrogen-ion formed in this way (about 1E−15) is so minute, compared with that formed by the primary ionization, that it is negligible.
[399] We can obtain the relation, directly, from H2S ⇄ 2 H+ + S2− and [H+]2 × [S2−] / [H2S] = K = 1.1E−22. For a given pressure of the hydrogen sulphide, [H2S], expressing its solubility (about 0.1 molar at 25°), is constant, and therefore [H+]2 × [S2−] = a constant, as given in equation (IV). Putting [H2S] = 0.1, we have [H+]2 × [S2−] = 0.1 × 1.1E−22 = 1.1E−23.
[400] On account of the great mass of water, we compare (see equation, p. [176]) [H+] × [HO−] = 1.2E−14 (at 25°) with [H+] × [S2−] / [HS−] = 1.2E−15.
[401] The calculation was made by the method used by Knox (loc. cit.) for a molar solution. The degree of ionization of the salt was not considered and the correct ionization constant for ammonium hydroxide was used, 1.8E−5 in place of 2.3E−5. The latter, evidently, was used by Knox as the result of overlooking a correction, which Bredig made in his (Bredig's) first calculations of the constant; cf. Bredig, Z. phys. Chem., 13, 293, footnote. The same erroneous constant is found in Kohlrausch and Holborn, loc. cit., p. 194.
[402] For further values and for the method of calculation, see Knox, loc. cit.
[403] [S2−] = 1.1E−23 / [H+]2, according to equation (IV), p. [201].
[404] Knox's work leads to that conclusion.