Barium Selenate, BaSeO4, is obtained by precipitating a solution of a barium salt with selenic acid or an alkali selenate, or by fusion of an alkali selenate with a mixture of sodium and barium chlorides. By the latter method orthorhombic prisms, isomorphous with barium sulphate, and of density 4.75, are formed. They are usually colourless, but may have a sky-blue tint, and the coloured crystals show pleochroism.
The precipitated salt has a density of 4.67 at 22° C. It adsorbs foreign salts in its formation even more readily than barium sulphate, making it difficult to determine selenic acid by barium. It is more soluble in water than barium sulphate, a litre of the solution saturated at 25° C. containing 82.49 mgm. of barium selenate. When strongly heated it is completely converted into barium selenite. Reduction to selenite, accompanied by the evolution of chlorine, takes place when the salt is boiled with hydrochloric acid. |