A Chemical Method of Isolating Fluorine

Abstract

A NEW salt of exceptional interest, the first member of a series of flacrplumbates, is described by Dr. Brauner, of Prague, in the June issue of the Journal of the Chem cal Society. Dr. Brauner is well known in this country, having been Berkeley Fellow of the Owens College, Manchester, previous to his appointment to the chair of chemistry in the Bohemian University. Twelve years ago he described two compounds very rich in fluorine, CeF₄. H₂O and 3KF. 2CeF₄. 2H₂O, and showed that when heated they first gave up their water and subsequently evolved a gas which possessed an odour similar to that of hypochlorous acid, and which exhibited the chemical properties expected of Free fluorine. The compound now described is a fluorplumbate of the composition 3KF. 1IF. PbF₄. It may be obtained by thiee methods. The first consists in treating the freshly precipitated hydrated oxide of lead, Pb₅O₇. 3H₂O, a substance described by Dr. Brauner in the year 1885. with a mixture of hydrogen potassium fluoride and hydrofluoric acid. The fluorplumbate is separated from the lead difluoride simultaneously formed by crystallisation from hydrofluoric acid. The second method consists in substituting fluorine for oxygen in the plumbates of Fremy. Peroxide of lead and caustic potash, in the propoitions of the compound 3KOH. PbO₂, are fused in a silver crucible; the product is moistened with water, and then added gradually to excess of pure hydrofluoric acid. The filtered solution is evaporated to the crystallising point in a current of air, and as soon as crystals commence to form is placed in a vacuum desiccator. Crystals of the salt are then deposited. The third method consists in displacing the acetic acid in lead tetracetate by fluorine. One molecular equivalent of lead tetracetate is added to three equivalents of hydrogen potassium fluoride, HF. KF, dissolved in hydrofluoric acid; crystals of potassium fluorplumbate are formed upon evaporation, either in the air or in vacno. Analyses of the crystals prepared by all three methods indicate the composition 3KF. HF. PbF₄.