Ferrous metaphosphate

Ferrous metaphosphate, Fe(P03)2, is prepared by the action of fused metaphosphoric acid on ferrous phosphate, oxalate, or chloride, or even metallic iron, at red heat in a current of carbon dioxide. The salt is obtained as a white insoluble powder, unaffected by hydrochloric or nitric acid, but attacked by hot concentrated sulphuric acid.6... 

Chromous Metaphosphate, CrlPOjla-—Attempts to produce this compound by the action of fused metaphosphoric acid on chromium or on chromous salts have not been successful, although the method succeeds for the ferrous analogue. ... 

Certain metaphosphates, for example, Cr and U will, on heating, decompose to phosphorus pent-oxide and pyrophosphate (5.107), while ferrous pyrophosphate can be prepared by reducing ferric orthophosphate (5.108), and mercury pyrophosphate by simply heating the orthophosphate (5.109). 

Long-chain sodium polyphosphate (sodium metaphosphate) melts above about 600X when it will dissolve many metallic oxides. It can be used as a flux with non-ferrous metals for cleaning crucibles, and for analytical purposes (Chapter 14.1). 

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