Silver pyrophosphate, Ag₄P₂O₇

Precipitation of sodium pyrophosphate with Silver nitrate yields the Silver pyrophosphate, Ag₄P₂O₇, in the form of a white powder, fusible at red heat. Secondary sodium orthophosphate converts it into silver orthophosphate. A double salt of the formula NaAg₃P₂O₇ is also known. On heating, its colour changes from white to yellow, a phenomenon which has been attributed to decomposition into sodium metaphosphate and silver orthophosphate, but which is considered by Balareff to have probably a physical origin.