Barium Pyrosulphate, BaS₂O₇

Barium Pyrosulphate, BaS₂O₇, may be formed by the action of fuming sulphuric acid on barium sulphate at 150° C., by the action of excess of chlorosulphonic acid on barium sulphate,

BaSO₄ + SO₃HCl = BaS₂O₇ + HCl,

or by heating together sulphur trioxide and barium sulphate in a closed tube.

Barium pyrosulphate absorbs moisture on exposure to air and reacts vigorously with water. It does not melt when heated, but decomposes at a low red heat.