The relative basicities of the members of the rare earth group are of fundamental importance, because many of the methods of fractionation are based upon this characteristic of the individual members of the group. It is frequently true that the methods employed for removing the last and most persistent impurities are methods which depend on differences in basicity. Hence it is important to define as sharply as possible the order of decreasing basicity within the group.Historical.-The order of decreasing basicity as reported by various authorities is given in Table I, which for convenience is divided into three zones.
\ NALYTICAL separations and determinations of elements in Groups III and IV of the periodic chart are often very difficult because of the formation of precipitates of poor quality. For example, the separation of zirconium from other positive ions by the precipitation of zirconium phosphate is often not nearly as effective as might be predicted on the basis of solubility differences.
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