Cobalt Phosphite, CoHPO₃

Cobalt Phosphite, CoHPO₃.2H₂O, is precipitated as a red amorphous compound on addition of ammonium phosphite to an aqueous solution of cobalt chloride. It is also formed on heating freshly precipitated cobalt carbonate with water and phosphorus trichloride, although in this latter case the yield is small. On heating to 250° C. the salt becomes anhydrous and assumes a blue colour. At higher temperatures it becomes incandescent, hydrogen being evolved and a mixture of phosphide and pyrophosphate remaining.