Phosphoric acid
Phosphoric acid (orthophosphoric acid or common phosphoric acid) (H3PO4) is produced by the action of sulfuric acid on natural calcium phosphate. The technical acid obtained in this way contains as impurities diphosphorus pentoxide, calcium dihydrogen phosphate, sulfur trioxide, sulfuric acid, hexafluorosilicic acid, etc. Pure phosphoric acid is obtained by controlled hydration of diphosphorus pentoxide.
Phosphoric acid can exist in the form of melting prismatic crystals, but since it is difficult to maintain in solid state, its aqueous solutions are usually prepared (for example, 65%, 90%). The concentrated solution that remains supersaturated at room temperature is sometimes called "phosphoric acid syrup."
Source: "Explanations to the Harmonized System of the Russian Federation for Foreign Economic Activity (HS of Russia)" (prepared by the Federal Customs Service of Russia) (volume 1, sections I - VI, groups 1 - 29)