Nitrogen (Gr. v, nitre, and yew&eiv, to generate), an elementary gaseous body, forming about four fifths of the bulk of the atmosphere. It derives its name from being also an essential constituent of nitre. It was discovered by Rutherford in 1772, but its properties were more particularly investigated by Lavoisier in 1775, and also by Scheele about the same time. Lavoisier estimated the proportion contained in the atmosphere, and gave it the name of azote (Gr. a privative and, life), because it is incapable of supporting life when breathed. The name nitrogen was afterward given by Chaptal. It is most conveniently obtained by removing the oxygen and carbonic acid gases from the atmosphere. The readiest mode is to burn phosphorus in a shallow vessel floating on water, in a bell jar of air. The phosphorus combines with the oxygen, forming phosphoric acid, which with the small amount of carbonic acid is absorbed by the water. A simple method is to place a stick under a jar of air over water, and let it remain three or four days, when nearly pure nitrogen will be found, occupying about four fifths of the previous volume. Other easily oxidizable substances, as moistened iron filings, will effect the same result.

Nitrogen may also be obtained by the action of chlorine on an excess of aqua ammonia, and also, in a state of purity, by decomposing nitrite of ammonia by heat. - The symbol of nitrogen is N, its atomic weight 14, and its specific gravity 0*9713. It is colorless, tasteless, and inodorous, and has thus far resisted all efforts to liquefy it. Water dissolves about 1/30 of its volume at ordinary temperatures. It is remarkable for its weak affinity for other bodies, presenting a great contrast to oxygen in this respect. It does not combine with any element with sufficient energy to produce much elevation of temperature, and therefore is not a supporter of combustion. A taper placed in it is immediately extinguished. An. animal placed in the undiluted gas soon dies, and an attempt to breathe it will produce a sense of suffocation, not from any poisonous property, but simply because it prevents the access of oxygen, which is necessary to fit the blood to perform its functions. It is therefore to be regarded as a diluter of the atmosphere. Nitrogen is an extensively distributed element, entering into the composition of a great number of bodies.

It is an essential constituent of many valuable and powerful medicines, such as quinine and morphine, and dangerous poisons, such as cyanogen and its compounds and strychnia. It is an important constituent of those tissues and fluids of plants and animals which contain albumen and fibrine, commonly known as azotized or nitrogenous tissues. The most important inorganic compounds are with hydrogen, forming ammonia; with chlorine, forming a chloride; with carbon, forming cyanogen; and with oxygen, forming a remarkable series of compounds possessing the greatest interest to the chemist and physiologist, which are called the oxides of nitrogen. They are nitrous oxide or laughing gas, N20; nitric oxide, NO; nitrous anhydride, N203, forming nitrous acid with water; peroxide of nitrogen, N02 or N204; and nitric anhydride or anhydrous nitric acid, N206, which in combination with water forms nitric acid. - Nitrous oxide will be treated in a separate article, and the other principal oxides in this place. 1. Nitric oxide, formerly called deutoxide of nitrogen, is a gaseous body produced by the partial deoxidation of nitric acid.

The direct union of nitrogen with oxygen is indeed difficult, and therefore it is usually effected indirectly. The common method is to dilute the acid with about twice its bulk of water and pour it upon copper turnings or metallic mercury in a retort or flask. A gentle heat assists the process. Red fumes appear in the retort in consequence of the production of peroxide of nitrogen; these may be absorbed by collecting the gas over water. The reaction consists in the displacement of hydrogen, the formation of a nitrate,.and the abstraction of oxygen from the remaining acid sufficient to reduce it to NO. Nitric oxide is a colorless gas having a specific gravity of 1.039. It is irre-spirable, possessing a strong disagreeable odor, and has thus far never been liquefied. It dissolves in about 20 times its bulk of water, and is more stable than the other oxides of nitrogen, resisting the decomposing power of a red heat; but when electric sparks are passed through a mixture of the gas with vapor of water, it is decomposed into nitrogen and nitric acid. In contact with moist iron filings or a sulphide of sodium or potassium, it is converted into nitrous oxide.

A lighted taper plunged into it is extinguished, and also phosphorus when first kindled; but if it is burning strongly, the heat will decompose the gas when the phosphorus will continue to burn, and with a brilliancy rivalling that afforded by pure oxygen. 2. Nitrous anhydride (N203) was formed by Dulong, by mixing in an exhausted flask one volume of oxygen with four volumes of nitric oxide, both in a dry state. Brownish red fumes of nitrous anhydride are condensed into a volatile blue liquid having a red vapor. Liebig obtained it by the action of eight parts of nitric acid on one of starch. A small quantity of water converts nitrous anhydride into nitrous acid, the liquid changing from a blue to a dark green (N203 + 2HO=2HN02). An excess of water converts it into nitric acid and nitric oxide. The body N02 which is united to hydrogen in nitrous acid is called nitrosion, a radicle, and it is this which unites with bases to form nitrites. (See Niteites.) 3. Nitric peroxide, or peroxide of nitrogen (N204 or N02), is seen in the red fumes which appear when air is admitted into a vessel containing nitric oxide. "When one volume of oxygen and two of nitric oxide, well dried, are passed through a dry tube immersed in a freezing mixture, it may be obtained in crystals.

They melt at 14° F., and form an orange-colored liquid till the temperature reaches 71'6°, when it boils and passes into a brownish red vapor. This body possesses the remarkable property of not freezing at - 6° after it has once been melted. Peroxide of nitrogen was long thought to be an anhydride, and was called hyponitric acid; but it does not form salts having a corresponding radicle, and is decomposed by bases with the formation of a nitrate and a nitrite. It is readily decomposed by water, a trace of moisture being sufficient to prevent the formation of the crystalline compound, but causing instead the production of a green liquid, probably composed of nitrous and nitric anhydride, which with water forms nitrous and nitric acids. The investigations of Playfairand Wanklyn indicate that the molecular constitution of peroxide of nitrogen at low temperatures is N204, while at high temperatures it is N02; an opinion founded principally upon the great change in the specific gravity. - Nitrides are combinations of nitrogen with the metals, and with phosphorus, boron, and silicon, without the intervention of another element. The binary combinations of nitrogen with the non-metallic elements or radicles might be considered as nitrides, but the term is restricted as above stated.

Tho metallic nitrides have the general formulas RN, R2X, R3N, the last being analogous to ammonia, and are all easily decomposed by heat, sometimes with explosion. They are usually formed by the action of ammonia on metallic oxides or chlorides, but may be obtained by the direct action of atmospheric nitrogen on the metals at the moment of their separation from their oxides by charcoal. Nitride of copper is formed by passing dry ammonia over cupric oxide at a temperature not higher than 482c F., and other metallic nitrides may be obtained in a similar way. Nitride of boron was discovered by Balmain, who obtained it by heating boric anhydride with cyanide of potassium or cyanide of zinc. The nitrides of phosphorus and silicon will be mentioned under those heads.