NITROGEN, is a colourless, odourless, tasteless gas, which is incombustible and does not support combustion, and is one of the most widespread and indispensable elements. Symbol N, atomic number 7, atomic weight 14.008. Its existence was first recognized by Scheele (1772) who showed that common air consists of at least two gases, which he called foul air and fire air. He obtained the foul air (nitrogen) on removal of the fire air (oxygen) by exposure to various combustible or oxidizable substances, and found that the residue would not support respiration or com bustion. Lavoisier confirmed Scheele's experiments and gave to foul air the name azote, because of its inability to support life. The name nitrogen was introduced later by Chaptal to indicate that the element is a constituent of nitre.
Nitrogen is present in the atmosphere to the extent of approxi mately 78% by volume and 75.5% by weight, and serves to dilute the oxygen. It is also found in the free state in many meteorites and in volcanic gases, whilst its presence in the atmosphere of the sun and in certain stars and nebulae is revealed by the spectro scope. Large quantities of nitrogen occur in combination with other elements, e.g., in potassium nitrate (nitre or saltpetre), so dium nitrate (Chili saltpetre), ammonium salts, in rain, soil and guano, and as complex organic compounds (proteins) in all living organisms.
( 1) The oxygen may be removed from air either by exposure to phosphorus in the cold (burning phosphorus is not so effective), to moist iron filings, an alkaline solution of pyrogallol, an acid solution of chromous chloride or cuprous chloride, or metallic copper in the presence of hydrochloric acid or ammonia, or by passing the air over red-hot copper.
On the large scale nitrogen is manufactured almost entirely by the fractional distillation of liquid air. Since it is more volatile
than oxygen it evaporates first, and is marketed in grey cylinders under a pressure of about 120 atm. This gas contains most of the helium and neon present in the air (see ATMOSPHERE) , but the argon is left with the oxygen. Some industrial nitrogen may be made by passing air over heated cooper, the copper oxide being afterwards reduced by heating in a current of water gas.
(2) Pure nitrogen is prepared from its compounds: (a) By heating a slightly acid solution of ammonium nitrite (or a mixture of sodium nitrite and ammonium chloride), (b) by heating ammonium dichromate, 4120+N,; or (c) by passing a mixture of nitric oxide and am monia gas over red-hot copper, Nitrogen gas is used in filling electric lamps to prevent the blackening of the bulb by volatilized metal from the filament and to enable the latter to be run at a higher temperature, but argon (q.v.) is superior for this purpose. High-temperature thermom eters are sometimes filled with compressed nitrogen. Large quan tities of nitrogen are also employed for the production of synthetic ammonia and other nitrogen compounds which are finally con verted into dyes, drugs, explosives or fertilizers.