Nitric acid is an inorganic acid that is composed of approximately 22.2% nitrogen, 76.2% oxygen and 1.6% hydrogen. It is denoted by the chemical formula HNO3. It was one of the first acids to be prepared and studied. Jabir ibn Hayyan Geber (c. 721-815), an Arabic alchemist, prepared weak nitric during the 700s. Later, alchemists learned that nitric acid, known as aqua fortis (strong water), dissolves most metals but does not affect gold or platinum. They also discovered that with the addition of ammonium chloride, aqua fortis could be transformed into aqua regia (royal water), a combination of nitric acid and hydrochloric acid that dissolves both gold and silver.
When nitric acid and other mineral acids became widely available during the Middle Ages, an experimental revolution occurred. For the first time, alchemists were able to test the purity of precious metals, and to decompose substances without high temperatures and long waiting periods. In the mid-1600s, German chemist Johann Rudolf Glauber (1604-1668) improved the alchemists' methods of preparing nitric acid. In his experimental laboratory in Amsterdam, Glauber produced nitric acid by heating a nitrate called saltpeter with concentrated sulfuric acid. Later he set up a small factory for making nitric and other acids, as well as several salts; his method for preparing nitric acid was used for many years.
The chemical composition of nitric acid, however, remained a mystery until the late 1700s. Antoine-Laurent Lavoisier had already determined that the compound contained oxygen when Henry Cavendish, who was studying nitrogen at the time, produced nitric acid in 1785 by passing sparks through a jar of air confined over water. The nitrogen and oxygen in the air combined, forming nitrogen dioxide gas, which then joined with hydrogen in the water to create nitric acid. (Nitric acid is formed during thunderstorms in a similar way, when lightning electrifies moist air.) Cavendish's findings constituted the first indication that the acid contains hydrogen and nitrogen as well as oxygen.
Nitric acid, a colorless liquid, is so corrosive that it can cause painful burns if touched. In contact with moisture, it gives off strong noxious fumes. The acid is used primarily to manufacture fertilizers, explosives, plastics, dyes, and drugs. During World War I, Alice Hamilton (1869-1970), an American physician and pioneer in the field of occupational diseases, found deplorable conditions in factories that used nitric acid to make high explosives such as TNT (trinitrotoluene) and guncotton. The acid created nitrous fumes that blew up machinery and burned workers' throats and lungs, often resulting in a painful early death.
The most common method of producing nitric acid commercially was developed by German chemist Friedrich Wilhelm Ostwald in the early 1900s. In the Ostwald-Bauer process, a mixture of ammonia and air is passed over a platinum catalyst, oxidizing the ammonia and yielding nitrogen oxides that can be converted to nitric acid.
Nitric acid finds a variety of applications in industry. It is used to produce organic and inorganic compounds for fertilizers. It is used in making explosives. It is also used for the production of dyes, organic compounds, and consumer products.
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