Nitrogen was isolated by the British physician Daniel Rutherford in 1772 and recognized as an elemental gas by the French chemist Antoine Laurent Lavoisier about 1776.Properties Nitrogen is a colorless, odorless, tasteless, nontoxic gas. It can be condensed into a colorless liquid, which can in turn be compressed into a colorless, crystalline solid. Nitrogen exists in two natural forms of isotopes, and four radioactive isotopes have been artificially prepared. Nitrogen melts at -210.01 C (-346.02 F), boils at -195.79 C (-320.42 F), and has a density of 1.251 g/liter at 0 C (32 F). The atomic weight of nitrogen is 14.007.Nitrogen is obtained from the atmosphere by passing air over heated copper or iron. The oxygen is removed from the air, leaving nitrogen mixed with some inert gases. Pure nitrogen is obtained by partial evaporation of liquid air because liquid nitrogen has a lower boiling point than liquid oxygen, the nitrogen evaporates off first and can be collected.Nitrogen composes about four-fifths (78.03 percent) by volume of the atmosphere. Nitrogen is inert and serves as a diluent for oxygen in burning and respiration processes. It is an important element in plant nutrition certain bacteria in the soil convert nitrogen from the atmosphere into a form, such as nitrate, that can be absorbed by plants, a process called nitrogen fixation. Nitrogen in the form of protein is an important component of animal tissue. The element occurs in the combined state in minerals, of which saltpeter (KNO3) and Chile saltpeter (NaNO3) are highly important products.Nitrogen combines with other elements only at very high temperatures or pressures. It is converted to an active form by passing through an electric discharge at low pressure. The nitrogen produced is very active, combining with alkali metals to form azides with the vapor of zinc, mercury cadmium, and arsenic to form nitrides and with many hydrocarbons to form nitriles. Activated nitrogen returns to ordinary nitrogen in about one minute.In the combined state nitrogen takes has many reactions it forms so many compounds that a systematic scheme of compounds containing nitrogen in place of oxygen was created by the American chemist Edward Franklin. In compounds nitrogen exists in all the combination capacity states between -3 and +5. Ammonia, and hydroxylamine represent compounds in which the combination capacity of nitrogen is -3, -2, and -1, individually. Oxides of nitrogen represent nitrogen in all the positive combination capacity states.Uses Most of the nitrogen used in the chemical industry is obtained by the fractional distillation of liquid air. It is then used to synthesize ammonia. From ammonia produced in this manner, a wide variety of important chemical products are prepared, including fertilizers, nitric acid, urea, hydrazine, and amines. In addition, an ammonia compound is used in the preparation of nitrous oxide (N2O) a colorless gas popularly known as laughing gas. Mixed with oxygen, nitrous oxide is used as an anesthetic for some types of surgery. Used as a coolant, liquid nitrogen has found widespread application in the field of cryogenics. With the recent advent of ceramic materials that become superconductive at the boiling point of nitrogen, the use of nitrogen as a coolant is increasing.