Lithium pyrophosphate, Li₄P₂O₇

The dihydrate, Li₄P₂O₇,2H₂O, is obtained as a bulky, crystalline precipitate by adding sodium pyrophosphate to lithium chloride in aqueous solution, dissolving the impure salt in acetic acid, and reprecipitating by means of alcohol. The water of crystallization is expelled by heating to 200° C.