HoppeSeyler, based primarily on solubilities and distribution, may be conveniently retained.
The various solubilities are shown in the following table: -
It is then dissolved in hydrofluoric acid and heated in order to expel silicon fluoride; finally the columbium, tantalum and titanium fluorides are separated by the different solubilities of their double fluorides (C. Marignac, Ann.
In order to separate caesium from rubidium, use is made of the different solubilities of their various salts.
The liquors are evaporated to dryness and the residue is ignited to obtain a very impure carbonate, which is purified by methods founded on the different solubilities of the several components.