Double Sulphates of Beryllium

Beryllium forms no alum, and this fact intimates a difference between beryllium and aluminium which was considered by many to indicate that beryllium, like magnesium, is divalent.

The double sulphate, KSO₄.BeSO₄.2H₂O, crystallises out at 25° C. from supersaturated solutions containing potassium and beryllium sulphates, if the proportion of the latter in the solute lies between 37.2 and 84.8 per cent. Awdejew, during an attempt to prepare a beryllium alum, discovered this salt in 1842 by a simple evaporation of its constituents in appropriate proportions. The crystals are very small, white, slightly soluble in cold water and much more soluble in hot. Marignac also described them as opaque, hard, and mamillated. Their form has not been determined.

(NH₄)₂SO₄.BeSO₄.2H₂O has been obtained from mixed solutions of beryllium and ammonium sulphates. Atterberg originally concentrated a solution containing molecular proportions of the two sulphates over sulphuric acid. The salt is very deliquescent.

Atterberg reported BeSO₄.KSO₄.2KSO.4H₂O as needle-shaped prisms, and 3BeSO₄.2Na₂SO₄.12H₂O as needle-like crystals which radiated in star-shaped groups. Both salts were prepared by evaporating the constituent salts in mixed solution - the former solution being strongly acid.