Lanthanum hydrogen pyrophosphate, LaHP₂O₇

Lanthanum hydrogen pyrophosphate, LaHP₂O₇.3H₂O. - From a solution of a lanthanum salt sodium pyrophosphate throws down a white precipitate which then redissolves. On allowing the solution to stand, the acid pyrophosphate crystallises out in needles (Cleve).

The double salt LaNaP₂O₇ may be obtained in crystals by fusing together sodium metaphosphate and lanthana.