NITROGEN (from nitrunt, nitre, patron, Lat. nil runt + Gk. pro ducing. from gigne.Ntlicri, to become). A gaseous element discovered by Rutherford in 1 7 72. who found that when a small animal was to breathe air in a confined space for a time. and the carbon dioxide thereby produced removed by absorption, a gas still remained which was incapable of supporting respiration. On account of its presence in nitre, Chaptal named it nitrogen (drench a ; soul ow ing to its incapacity for supporting life, La voisier named it 1.1„...:oif• ( 1787 ). It is one of the most widely distributed of the elements, and is free in the atmosphere, of which it forms about four-tilths by volume. Considerable quantities of it occur in volcanic gases and in the air-Irladders of certain fishes, the bone cavities of birds, and in plants. It is likewise found in meteorites, and its presence has been demonstrated in the atmos phere of the sun. In combination it is found associated with oxygen as and nit runs acids, with hydrogen as ammonia. and with oxygen. hydro;.2,en, and carbon in many substances of organic origin. It is an essential constituent of animal and vegetable organisms. and is found in many minerals, IS saltpetre and soda nitre. The separation from nitrogen of the other gases contained tilting with it in atmospheric air was considered a very rasp matter before the discov ery of argon (q.v.). In fact. the water-vapor of the air cant he readily removed by the use of strong sulphuric acid or burnt lime or any other good dehydrating agent : the carbonic acid of the air can be removed by means of the caustic alka lies or alkaline earths: the oxygen can be re moved by passing air tIVVIr d copper. by horning phosphorus in the :tir, and by similar methods. But aroon is itself an inert substance that cannot be removed by any known chemical reagent. Nitrogen might possibly be isolated from it by liquefying the mixture and subjecting it to fractional distillation. But an easier and more 14'1111in way of obtaining pure nitrogen con sists in causing it to be liberated from certain of its compounds. Thu: pure ammonium nitrite breaks up, on heating. into pure nitrogen and water. Similarly, nitrogen may be obtained by heating a mixture of potassium nitrite and am monium chloride, or by beating equal parts of potassium nitrite and ammonium sulphate with a mixture of three parts of water and two parts of glyeerin.
Nit rogen (symbol. N : weight, 1 1.0 I ) is a colorless, tasteless. and ens, By the application of pressure at low temperature (see l'olN-r), nitrogen has been liquefied. and the liquid has been caused to freeze. In the gaseous state it is slightly soluble in water. It combines directly Whit but very few elements, although in directly it ean be made. to form compounds with a large number of the elementary bodies. Nitro gen combines with oxygen to form the following five oxides: ( I ) N g 010110d:id e, or 1611'0116 oxide, called also 'laughing gas,' was orig inally obtained by Priestley in 1 7 72. by the action of moist iron filings on nitric oxide (NO). It is now usually prepared by the of ammonium nitrate, and is a colorless gas of pleasant odor and sweetish taste. It is a valu able anaesthetic lq.v.), and is largely employed for producing insensibility during short opera tions. It may be considered as the anhydride of hyponitrous acid (q.v.). (2) .Vitrogcn. dioxide, or nitric oxide, NO, was first obtained by Van Ifelmont. who failed, however. to recognize it as a distinct chemical substance. Its properties have been clearly known since 1772, when Priest ley succeeded ill isolating it, and its composition was correctly determined by Cavendish in 1 7S4. It is formed when .1;64 amps (hydrogen, illuminating gas, wood, coal. etc.) are burned in the air. It may be irrepared by the action of .1,1 dilute uitrio avid on metallic copper (con centrated nitric acid yields laughing gas). In
the absence of oxygen it remains colorless: but it readily combines with oxygen to form red fumes of nitrogen tetroxide. Still, if heated alone to C., nitric oxide decomposes with formation of laughing gas. free nitrogen. nitrogen trioxide, and nitrogen tetroxide. Solutions of ferrous salts altsorb considerable quantities of nitric oxide. (3) Nifroyca NJI,, may be ob tained by heating nitric acid with starch in a large retort. drying the gaseous product over cal cium chloride. and liquefying it by Mean, of freezing mixtures. _\t it is a dark blue liquid and it boils below 0' C. \Vithin a few degrees above that point its vapors decompose nitric oxide and nitrogen tetroxide. The deeornposition, however, is partial. and even at as high as 150°C. the trioxide is not yet completely decomposed. The trioxide has been recommended as a disin fectant: for this purpose a mass containing one part of sodium nitrite. two parts of acid sodium sulphate, and two parts of gypsum. is kept dry when not used: on mixing it with water it yields the Irioxide of nitrogen. Nitrogen trioxide is the anhydride of nitrous acid (4) Yitrovrn tctro.rifle, or nitrogen peroxide. has the formula N.ji, at lower temperatures and NO, at high tem peratures. (See Ilissoci.kTION.) The tetroxide is formed when dry nitric. oxide comes in contact with oxypm. It may be prepared by passing it perfectly dry mixture of two pa rts (by volume) of nitric oxide and one part of oxygen into a U-tube immersed in a freezing mixture at ('., and if the mixture is absolutely dry the tet roxide is thins obtained in the form of colorless crystals. Above ('. it is usually a liquid of yellow color. the color becoming more and more intense as the temperature rises. The vapor is the more intensely colored. the inure it is dissociated. ( See Dissoci.vrioN.1 The Of the liquid. as given by difTerent observ ers, are between 22' and C. 15) pento.ridr. N was discovered by Sainte-Claire Devine in 1S-19. It may be prepared by the ac tion of phosphorus pentoxide on nitric :mid com pletely dehydrated by repeated distillations with sulphuric acid and freed from nitrogen trioxide by passing a current of dry air. The nitrogen pentuxide thus obtained is passed into a suitable receiver kept in a freezing mixture; NV hen a crystalline mass has formed in the receiver, the portion remaining liquid is decanted off; the crystals are allowed to melt, the liquid is again caused to solidify. and any portion remain ing liquid is again rejected. _By repeating this operation several times, it is easy to obtain per fectly pure nitrogen pentuxide. The colorless rhombic crystals of this substance may be pre served very long by keeping out of contact with the air and away from light. They melt at about 30° C. and the liquid boils at about 45° C., but slightly above this temperature the substance undergoes decomposition. if exposed for some time to the light the crystals melt and may de compose with explosive violence. Nitrogen pent oxide is the anhydride of nitric acid.
The compound, of nitrogen with hydrogen in clude ammonia. hydrazine, and hydra zoic acid, NJI. The most important of the com pounds of nitrogen with the halogens is nitrogen tri-chloride, NCI,. which may be considered as ammonia in which all the hydrogen has been re placed by chlorine. it is prepared by passing chlorine gas into a warm solution of ammonium chloride. It is a yellowish, volatile, extremely ex plosive, oily substance, which must be handled with extreme caution and the preparation of which should not be undertaken by any one not thoroughly accustomed to experimenting with dangerous substances. Its explosion may be brought about by the action of heat or light, or by contact with phosphorus, turpentine, and other substances.