A strong mineral acid having the formula HNO₃. Pure nitric acid is a colorless liquid with a density of 1.52 at 25°C (77°F); it freezes at −47°C (−53°F). Nitric acid is used in the manufacture of ammonium nitrate and phosphate fertilizers, nitro explosives, plastics, dyes, and lacquers. The principal commercial process for the manufacture of nitric acid is the Ostwald process, in which ammonia, NH₃, is catalytically oxidized with air to form nitrogen dioxide, NO₂. When the dioxide is dissolved in water, 60% nitric acid is formed. Production of 90–100% nitric acid is based on processes such as the reaction of sulfuric acid with sodium nitrate (an older method of nitric acid manufacture), dehydration of 60% acid, and oxidation of nitrogen dioxide in a solution of dilute nitric acid.