Barium Persulphate, BaS₂O₈

Barium Persulphate, BaS₂O₈, may be obtained in solution by the action of persulphuric acid on barium hydroxide. It can be prepared by grinding solid barium hydroxide into a paste with a saturated aqueous solution of ammonium persulphate, driving off most of the ammonia by a current of air, and the rest in vacuo over sulphuric acid, and removing excess of baryta with carbon dioxide. On evaporating the filtrate in vacuo, small, transparent, non-deliquescent, monoclinic prisms of composition BaS₂O₈.4H₂O are obtained.

At 0° C. 100 parts of water dissolve 52.2 parts of crystallised salt. The solubility increases rapidly with temperature, but supersaturated solutions are easily obtained. The solution gradually decomposes and precipitates barium sulphate, especially if heated. The solid salt is best preserved in a moist atmosphere, but heat at once decomposes it.

By treatment with absolute alcohol the monohydrate, BaS₂O₈.H₂O, is formed. It cannot be further dehydrated without decomposition. The salt has the oxidising properties of the persulphates.