Barium Tetrathionate, BaS₄O₆

Barium Tetrathionate, BaS₄O₆, is obtained in fine needle-shaped crystals, containing 2 or 3 molecules of water of crystallisation, by the action of tetrathionic acid on an equivalent quantity of barium acetate and precipitation with absolute alcohol. It is also formed by the action of sulphur dichloride on sulphurous acid, removal of the chloride and sulphate by lead, saturation with barium hydroxide, and precipitation by alcohol. The crystals lose 1 molecule of water in vacuo. When iodine acts upon barium thiosulphate in the presence of a little water, or when barium pentathionate spontaneously decomposes, the tetrathionate is formed.

It is decomposed at 100°-110° C., forming barium sulphate, sulphur dioxide, and sulphur. The aqueous solution is stable, but the alcoholic solution is rapidly decomposed if acid be present, giving barium thiosulphate.