Calcium Dithionate, CaS₂O₆

Calcium Dithionate, CaS₂O₆, is obtained by the action of milk of lime on manganese dithionate, or by neutralising dithionic acid with calcium hydroxide. After concentration of the filtrate, colourless rhombohedric crystals containing 4 molecules of water of crystallisation are obtained. The crystals are stable in air and have a density of 2.18. They rotate the plane of polarisation of light. One part of dithionate is soluble in 2.46 parts of water at 19° C. and 0.8 part at 100° C., but it is insoluble in alcohol.