Note 25 bis — Chapter XXII · IRON, COBALT, AND NICKEL
George Kamensky translation
The reaction FeX3 + KI = FeX2 + KX + I proceeds comparatively slowly in solutions, is not complete (depends upon the mass), and is reversible. In this connection we may cite the following data from Seubert and Rohrer's (1894) comprehensive researches. The investigations were conducted with solutions containing 1⁄10 gram—equivalent weights of Fe2(SO4)3 (i.e. containing 20 grams of salt per litre), and a corresponding solution of KI; the amount of iodine liberated being determined (after the addition of starch) by a solution (also 1⁄10 normal) of Na2S2O3 (see Chapter XX., Note 42). The progress of the reaction was expressed by the amount of liberated iodine in percentages of the theoretical amount. For instance, the following amount of iodide of potassium was decomposed when Fe2(SO4)3 + 2nKI was taken:
n = 1 2 3 6 10 20
After 15′ 11·4 26·3 40·6 73·5 91·6 96·0
„ 30′ 14·0 35·8 47·8 78·5 94·3 97·4
„ 1 hour 19·0 42·7 56·0 84·0 95·7 97·6
„ 10 „ 32·6 56·0 75·7 93·2 96·5 97·6
„ 48 „ 39·4 67·7 82·6 93·4 96·6 97·6
Similar results were obtained for FeCl3, but then the amount of iodine liberated was somewhat greater. Similar results were also obtained by increasing the mass of FeX3 per KI, and by replacing it by HI (see Chapter XXI., Note 26).