Nitrogen, a chemical element that forms compounds that are essential to life. Free nitrogen (nitrogen not combined with other elements) is a gas at ordinary temperatures and pressures, with no taste, odor, or color. It is the most abundant element in the atmosphere, accounting for 78 per cent of the volume and 75 per cent of the weight of the atmosphere. Nitrogen does not combine readily with other elements. It dissolves in water.
All living things require nitrogen to live and grow. Nitrogen is an essential element in amino acids, the building blocks of proteins. Most living things, including animals and plants, cannot use free nitrogen; they can use only nitrogen that has been fixed—that is, combined with other elements. Most fixed nitrogen is produced by blue-green algae and certain bacteria. These microorganisms combine nitrogen from the air with other elements, forming nitrogen compounds that can be absorbed by food-making organisms such as plants. These organisms, in turn, produce nitrogen compounds that are a source of nitrogen for organisms, such as animals, that do not make their own food. When an organism dies and decays, some of the nitrogen it contains is returned to the atmosphere.
Nitrogen is produced in commercial quantities from liquid air. Nitrogen boils away from liquid air at a lower temperature than oxygen, the other main ingredient of air. Therefore when the liquid air is at the correct temperature, the nitrogen turns to vapor while the oxygen remains liquid. The nitrogen is then further treated to remove small amounts of the inert gases (particularly argon), which turn to vapor with the nitrogen. In laboratories, small amounts of nitrogen are produced by breaking down nitrogen compounds.
Nitrogen is used to replace ordinary air and provide an unreactive atmosphere for such industrial processes as the production of chemicals, the refining of metals, and the manufacture of electronic equipment. Nitrogen also helps provide an unreactive atmosphere in incandescent lamps. Nitrogen is pumped underground to raise the pressure in petroleum deposits and thus increase the production of petroleum from the deposits. Liquid nitrogen is used for the rapid freezing of meat and other food products; as it is sprayed over the food, the nitrogen quickly evaporates, absorbing heat from the food.
Ammonia, a compound of nitrogen and hydrogen, is used in the manufacture of fertilizers, dyes, plastics, explosives, and many other substances. Hydrazine, which also contains hydrogen and nitrogen, is used in a variety of products and processes, including the manufacture of pesticides. Nitrous oxide is an anesthetic. Nitrates, which contain the radical NO-3, include such substances as nitroglycerin and are used as explosives and medicines. Silver nitrate is used in the manufacture of photographic film.
Nitrites are compounds that contain a metal and the radical NO-2. They have a wide variety of uses. Some nitrites, such as sodium nitrite, are used in curing meat and fish to prevent spoilage. The United States government has established standards for the maximum allowable concentration of nitrites in cured food because studies have shown that in the human body nitrites can be converted into nitrosamines, a class of nitrogen compounds known to cause cancer.
Nitric acid is a powerful acid that is used in the production of other nitrogen compounds such as nitro compounds.
Nitrogen is present in many other compounds that are found in such substances as antibiotics, sulfa drugs, vitamins, and synthetic textiles. Nitrogen is also present in most human food. Some nitrogen oxides that are produced where combustion takes place at high temperatures, as in automobile engines, are a major source of air pollution.
Nitrogen was discovered in air in 1772 by Daniel Rutherford, a Scottish physician. He called the substance noxious air because unlike ordinary air, it did not sustain life. The name nitrogen was suggested in 1790 by Jean Antoine Claude Chaptal, a French chemist.
Until World War I, when the Germans began producing large quantities of fixed nitrogen synthetically, the major source of the world's supply of useful nitrogen was Chile saltpeter, or sodium nitrate.
Symbol: N. Atomic number: 7. Atomic weight: 14.0067. Specific gravity: 0.81 (liquid form). Melting point: -346 F. (-210 C.). Boiling point: -320.4 F. (-195.8 C.). Nitrogen has two stable isotopes: N-14 and N-15. Nitrogen belongs to Group V-A of the Periodic Table and its principal valences are -3, +3, and +5.