- any one of a series of oxyacids of phosphorus with the general formula H n +2 P n O 3 n +1 . The first member is pyrophosphoric acid (n = 2) and the series includes the highly polymeric metaphosphoric acid. The higher acids exist in an equilibrium mixture
- a glassy or liquid mixture of orthophosphoric and polyphosphoric acids: used industrially as a dehydrating agent, catalyst, and oxidizing agent
