Solubility of Condensed Phosphates

In a strict sense, condensed phosphates have no solubility in water. Solubility is an equilibrium quantity of a substance that will dissolve in a specified quantity of liquid at specified pressure and temperature. Most solubility measurements are made at atmospheric pressure if a substance being dissolved is a solid or a liquid. Gases are a special case. 

Since all condensed phosphates are unstable with respect to hydrolytic degradation to orthophosphates when exposed to water, a solid or liquid phase is never in equilibrium with a solution phase. Several aqueous phase diagrams of condensed phosphates have been published, including some by the author. It was recognized that these studies yielded results that were useful, but not scientifically rigidly correct. 

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