Metaphosphoric acid

Glass-like colorless solid; soft and transparent; deliquesces; sublimes at red heat; dissolves slowly in cold water, decomposing to phosphoric acid; soluble in alcohol.

Metaphosphoric acid is obtained as a polymeric glassy solid by prolonged heating of phosphoric acid. Either phosphoric acid, H3PO4, or pyrophosphoric acid, H4P2O7, when heated above 300°C, on cooling yields the transparent glassy mass of composition (HPO3)n.
Metaphosphoric acid also is obtained from partial hydration of phosphorus pentoxide by dissolving it in cold water.

In dentistry for making zinc oxyphosphate cement; as reagent in chemical analysis.

An inorganic reagent used for research purposes

Metaphosphoric acid is used as a dehydrating agent. Its derivative, sodium hexametaphosphate is used as a sequestrant and a food additive. It is also used as phosphorylating agent, analytical reagent and in dental cements.

ChEBI: Phosphonate(1-) is a monovalent inorganic anion obtained by deprotonation of one of the two OH groups in phosphonic acid. It is a phosphorus oxoanion and a monovalent inorganic anion. It is a conjugate base of a phosphonic acid. It is a conjugate acid of a phosphonate(2-).

meta-Phosphoric acid is a monobasic acid.