Phosphoric Acid, an acid consisting of hydrogen, phosphorus, and oxygen. There are three kinds of phosphoric acid—orthophosphoric, metaphosphoric, and pyrophosphoric.

Orthophosphoric acid is the most commonly used. It is a transparent, crystalline solid with a melting point of 108 F. (42 C.). Orthophosphoric acid is soluble in water and is used in dissolved form. Its salts and esters are called phosphates. Orthophosphoric acid is produced by burning phosphorus to form phosphorus pentoxide and then combining the oxide with water, or by treating crushed phosphate rock with sulfuric acid or hydrochloric acid. Phosphoric acid is used in fertilizers, detergents and soaps, animal feed, and soft drinks. It is also used in treating water and rustproofing metals.

The chemical formula for orthophosphoric acid is H3PO4, metaphosphoric acid, HPO3, pyrophosphoric acid, H4P2O7.