Beryllium Fluoride, BeF₂

Berzelius dissolved beryllium hydroxide in hydrofluoric acid, evaporated to dryness, and dried the residue at 100° C. Lebeau showed that this residue always retained water, and left an oxyfluoride, 5BeF₂.2BeO, on heating to redness. This solid oxyfluoride is colourless, almost transparent, soluble in water, and has a density of about 2.01 at 15° C.

The original moist residue is converted into anhydrous beryllium fluoride by heating in a current of hydrogen fluoride. Lebeau also obtained anhydrous beryllium fluoride by igniting the dry double fluoride of ammonium and beryllium, BeF₂.2NH₄F, in a current of carbon dioxide. It is a vitreous solid, with a density of 2.1 at 15° C. It softens on heating, becomes fluid at about 800° C., finally volatilises, and forms a crystalline sublimate. It is deliquescent, soluble in water in all proportions, slightly soluble in absolute alcohol, converted into an oxyfluoride by oxygen, and readily decomposed by sulphuric acid. Sodium, potassium, lithium, and magnesium, when heated with anhydrous beryllium fluoride, combine with the fluorine and set metallic beryllium free. Hydrofluoric acid does not dissolve it.