Calcium Periodate, Ca(IO₄)₂

Calcium Periodate, Ca(IO₄)₂, is obtained by the action of a strong solution of periodic acid on calcium carbonate and evaporation of the still acid solution over concentrated sulphuric acid.

By treating feebly acid solutions with calcium carbonate, or by allowing an alkaline periodate to react with calcium nitrate, a basic salt, Ca(IO₄)₂.CaO.9H₂O or 3H₂O, is formed. The first method of preparation gives reddish crystals and the second white. At 170° C. the basic salt loses all its water of crystallisation, and is decomposed at a still higher temperature to form the more basic compound Ca(IO₄)₂.4CaO.

Rammelsberg also obtained the compound 3Ca(IO₄)₂.5CaO as a gelatinous precipitate by the action of ammonia on a solution of the periodate.