Barium Dithionate, BaS₂O₄

Barium Dithionate, BaS₂O₄, may be obtained by neutralising barium hydroxide with dithionic acid, or by the interaction of manganese dithionate with barium hydroxide or sulphite. It crystallises with 2 molecules of water in hexagonal plates stable in air, or with 4 molecules in crystals similar to heavy spar, of density 3.06 at 24.5° C. It is very soluble, one part dissolving in four parts of water at 18° C., and in 1.1 parts at 100° C., forming a solution stable at ordinary temperatures. It is insoluble in alcohol. When heated it decomposes into water, sulphur dioxide, and barium sulphate. Sodium amalgam, and also zinc and hydrochloric acid, reduce it to the sulphite.

It forms a double salt with barium chloride, BaS₂O₆.BaCl₂.4H₂O.