Studies on the Purities of Precipitate and Crystal. IV. The Investigation or Presumption of Solubility by Co-precipitation Phenomena

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The solubility of zinc oxalate has been reported by Kunschert (7×10－5 mol/l. at 25°) or F. Kohlrausch (4.2×10－5 at 18°), but, from the viewpoint of the relations between solubility and co-precipitation phenomena, it would be greater than their values, perhaps about 1.1∼1.6×10－4 mol/1. at room temperature. Measurements showed the solubility of zinc oxalate, of which composition was ZnC2O4·2H2O, to be 1.2×10－4 mol/l. at 20° ±0.05°. This is almost the same with the result obtained by Scholder, Gadene and Niemann (1.36×10－4 mol/l. as 18°) but further details are not clear. By the relations between solubility and co-precipitation phenomena, a presumption or investigation of solubility may be possible; namely, it may be determined by the use of the transition point of adsorption and occlusion of foreign ions (about 2×10－4 mol/l. at 20°). Needless to say, the formation or treatment of precipitate should be done under the same condition. The study on a mechanism for the adsorption or Balarew's occlusion phenomena is in progress.