A white rhombic solid, H₃PO₄; r.d. 1.834; m.p. 42.35°C; loses water at 213°C; very soluble in water and soluble in ethanol. Phosphoric(V) acid is very deliquescent and is generally supplied as a concentrated aqueous solution. It is the most commercially important derivative of phosphorus, accounting for over 90% of the phosphate rock mined. It is manufactured by two methods; the wet process, in which the product contains some of the impurities originally present in the rock and applications are largely in the fertilizer industry, and the thermal process, which produces a much purer product suitable for the foodstuffs and detergent industries. In the wet process the phosphate rock, Ca₃(PO₄)₂, is treated with sulphuric acid and the calcium sulphate removed either as gypsum or the hemihydrate. In the thermal process, molten phosphorus is sprayed and burned in a mixture of air and steam. Phosphoric(V) acid is a weak tribasic acid, which is best visualized as (HO)₃PO. Its full systematic name is tetraoxo-phosphoric(V) acid. It gives rise to three series of salts containing phosphate(V) ions based on the anions [(HO)₂PO₂]⁻, [(HO)PO₃]²⁻, and PO₄³⁻. These salts are acidic, neutral, and alkaline in character respectively and phosphate ions often feature in buffer systems. There is also a wide range of higher acids and acid anions in which there is some P–O–P chain formation. The simplest of these is pyrophosphoric acid (technically heptaoxodiphosphoric(V) acid), H₄P₂O₇, produced by heating phosphoric(V) acid (solid) and phosphorus(III) chloride oxide. Metaphosphoric acid is a glassy polymeric solid (HPO₂)_x.