Page:The New International Encyclopædia 1st ed. v. 14.djvu/682

NITRO-BENZENE. 582 NITROGEN. tiire being kept low by cooliug with water, and the mixture being constantly stirred with the aid of some special arrangement with which the ves- sel is provided. After all the benzene has been added, the temperature is raised for a short time to about 80° C. (170° F. ). Tlien the mixture is diluted with water and distilled with a ciirrent of steam. For laboratory purposes nitro-benzene may be purified by washing with dilute soda, drying, and subjecting to a process of fractional distillation. Nitrobenzene is a very poisonous substance, its vapors, if inhaled, being capable of causing coma and death in a few liours. NITRO-CELLULOSES. See Gu.xcoTTOX. NITROGEN (from Xeo-Lat. nitrum, nitre, natron. Lat. nitrum + t!k. -yfv/it, -genes, pro- ducing, from -ylypea-Oai, yignesthiii, to become). A gaseous clement tliscovered by Rutherford in 1772, who found that when a small animal was allowed to breathe air in a confined space for a time, and the carbon dioxide tliereby 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 (French nilrofiim-) ; and ow- ing to its incapacity for supporting life, Lavoisier named it o;o/e (1787). It is one of the most widely distributed of the elements, and is found free in the atniosi)here, of which it forms about four-fifths by volume. Considerable quantities of it occur in volcanic gases and in the air-bladders of certain fishes, the bone cavities of birds, and in plants. It is likewise found in meteorites, and its presence has been demonstrated in tlie atmos- phere of the sun. In combination it is found associated with oxygen as nitric and nitrous acids, with hydrogen as ammonia, and with oxygen, hydrogen, aiul carbon in many substances of organic origin. It is an essential constituent of animal and vegetable organisms, and is found in many minerals, as saltpetre and soda nitre. The separation from nitrogen of the other gases contained along with it. in atmospheric air was considered a very easy matter before the discov- ery of argon (<i.v.). In fact, the water-vapor of the air can be readily removed by the use of strong sulpliiiric 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 over red-hot copper, by burning phosphorus in the air. and by similar methods. But argon is itself an inert substance that cannot be removed by any known chemical reagent. Xitroyen miglit possil)ly he isolated from it by lii|Ui fyinj; (lie mixture and subjecting it to fractional distillation. Hut an easier and more certain way of obtaining ]>ure nitrogen con- sists in causing it to lie liberated from certain of its compounds. Thus pure ammoniim nitrite breaks up, on heating, into pure nitrogen and water. Similarly, nitrogen may be obtained by heating a mixlure of potassiim nitrite and am- monium chloride, or by heating equal parts of potassium nitrite and ammonium sulphate with n mixtire of three parts of water and two jiarts of filycerin. NitroL'en (symbol. X; atomic weight, 14.04) is a colorless, tasteless, and odorless gas. By the application of pressure at low' tempernture (sec C'BiTlcAt. Point), nitrogen has been liquefied, and the liquid has been caused to freeze. In the gaseous it ij 163 * state it is slightly soluble in water. It combines directly with but very few elements, although in- |l directly it can be made to form compounds with I a large number of the elementary bodies. Xitro- ( gen combines with o.xygeii to forin the following five o.xides: (1) Xiliuiicn monoxide, or nitrous i oxide, N;0, called also 'laughing gas,' was orig- I inally obtained by Priestley in 1772, by the action 'h of moist iron filings on nitric oxide (NO). It ,; is now usually prepared by the distillation of I ammonium nitrate, and is a colorless gas of ' pleasant odor and sweetish taste. It is a valu- ' able ana'sthetic (q.v.). and is largely ein]iloyed ,] for producing insensibility during short opera- ' tions. It may be considered as the anhydride of ! hyponitrous acid (q.v.). (2) Xitroficn dioxide, , or nitric o.xide, XO. was first obtained by Van •: Helmont, who failed, however, to recognize it as a distinct chemical substance. Its properties have been clearly known since 1772, when Priest- | ley succeeded in isolating it, and its composition ,] was correctly determined l)y Cavendish in 1784. 'j It is formed when various substances (hydrogen, 'J illuminating gas, wood, coal, etc.) are burned * in the air. It may he ])repared by the action of • cold dilute nitric acid on nietallic copper (con- centrated nitric acid yields laughing gas). In the absence of oxygen it remains lolorless; but readi!}- combines with oxygen to form red fumes of nitrogen tetroxide. Still, if heated alone to 520° C, nitric oxide decomposes with formation of laughing gas, free nitrogen, nitrogen trioxidc, and nitrogen tetroxide. Solutions of ferrous salts absorb considerable quantities of nitric oxide. (3) Xitroficn. trioxide, X^O^, may be ob- tained by heating nitric acid with starch in a large retort. <lrying the gaseous product over cal- cium chloride, and licpiefying it by means of freezing luixlures. At 10°C. it is a dark blue liquid ^ and it boils below 0° C. Within a few degrees > above that point its vajiors dceoinpose into nitric i oxiile and nitrogen tctro.xide. The decomposition, however, is partial, and even at as high as 1.50° C. the trioxide is not yet completely decomposed. The trioxide has been recommended as a disiil- , fectaiit : for this purpose a mass containing one / part of sodium nitrite, two parts of acid sodium I sulphate, and two parts of gypsum, is kept dry J when not used: on mixing it with water it yields V the trioxide of nitrogen. Xitrogen trioxide is the anhydride of nitrous acid (q,.v.). (4) yUrofien tetroxide, or nitrogen jieroxide, has the formula i X'.O, at lower temperatures and XO, at high tem- ^^ peratures. (See Dissociatiox.) The tetroxide ],• is formed when dry nitric oxide comes in contact ii with oxygen. It may be prepared by passing a '^ perfectly dry mixture of two jiarts (by volume) 'It of nitric oxide and one jiart of oxygen into ai) U-tube immersed in a freezing mixture at — 20' f J C, and if the mixture is absolutely dry the tet- ^ roxide is thus obtained in the form of ecdorless t' crystals. Above — 20° C. it is usually a liquid j of yellow color, the cohu' becoming more and } more intense as the temperature rises. The vapor «  is the more intensely colored, the more it is 1 dissociated. (See Dlssoclxtion.) The boiling- ' points of the liquid, as given by difTerent ohserv-' ■ ers, are between 22° and 28° C. (Ti) yitrnijen ^ l>eiilnxide, N.0,„ was discovered by Sainte-CIairei^ lleville in 184(1. It may be prepared by the nc- ^j tion of phosphorus pentoxide on nitric acid com- . pletely dehydrated by repeated distillations with .?-