Barium Pentathionate, BaS₅O₆

Barium Pentathionate, BaS₅O₆, is prepared by the neutralisation of pentathionic acid by barium carbonate, and precipitation by alcohol,15 or by the action of sulphur chloride on barium thiosulphate. It forms small oblong rectangular plates with a truncated corner, containing 2 or 3 molecules of water. It is less stable than the tetrathionate. On being heated below 100° C., barium sulphate, sulphur, and sulphur dioxide are formed. The water of hydration may be replaced by alcohol, the resulting compound being much more stable than the hydrated salt. Barium pentathionate is very soluble in water. When boiled, the solution gives sulphur dioxide. It is readily oxidised by chlorine.