The most important is the normal salt, Na 4 P 2 0 7, which is readily obtained by heating disodium orthophosphate, Na 2 HPO 4.
They may be obtained by heating a monometallic orthophosphate of a fixed base, or a dimetallic orthophosphate of one fixed and one volatile base, e.g.
On boiling their solutions they yield orthophosphates, whilst those of the heavy metals on boiling with water give a trimetallic orthophosphate and orthophosphoric acid: 3AgP0 3 +3H 2 O=Ag 3 PO 4 +2H 3 PO 4.
On heating with an oxide or carbonate they yield a trimetallic orthophosphate, carbon dioxide being evolved in the latter case.
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