The combination of nitrogen with oxygen was first brought about by Cavendish in 1785. The use of the electric arc was introduced by Sir William Crookes in 1892. The commerical manufacture of nitric acid was at empted at Niagara Falls in 1902 by Bradley and Lovejoy, who subjected a mixture of oxygen and nitro gen or air enriched with oxygen to a high ten sion arc drawn out as long as possible. Mechanically and chemically the operation was a success, as the efficiency of the process was greater than that obtained by Birkeland and Eydc in Norway in 1903. Nevertheless, the cost of power is high at Niagara Falls, and financial backing for the development was lack ing, so that the work was discontinued. In Norway, where power is much cheaper, arc processes are now being operated on a large scale. With oxygen, nitrogen forms five oxides as follows: (1) Nitrous oxide (N.0) is prepared by cautiously heating ammonium nitrate. Some of its properties are similar to those of oxygen, in that it supports the combus tion of certain materials, such as phosphorus, which also burn easily in oxygen. On the other hand, metals do not rust in it, and the haemoglobin of the blood cannot use it as a source of oxygen. Davy noticed that when taken into the lungs, it produced a mild form of intoxication or hysterical condition, which gave rise to the name of "laughing gas') by which it is commonly known. Prolonged use of the gas produced insensibility. As a result of these ob servations, a method of using it as an anaes thetic has been worked out, the method consist ing of the admixture of a sufficient amount of oxygen or air to sustain life. It is thus employed for minor operations, such as dental work, or preceding the use of ether, and when properly used has practically no after effects; (2) Nitrogen dioxide (N20.) or nitric oxide (NO) was discovered by Priestley, who called ifi "saltpetre-gas.o This is a colorless gas com monly prepared by acting upon metallic copper with cold dilute nitric acid. Nitric oxide com bines directly and readily with oxygen, the combination taking place promptly upon con tact with air, the brown colored higher oxides of nitrogen being formed. The dioxide may be liquefied by the application of cold and pres sure; the critical temperature is 93.5° C. and the critical pressure 71.2 atmospheres. The solidified gas melts as about 167° C.; (3) Nitro gen trioxide or nitrogen sesquioxide, N,01, may be prepared (though in rather an impure state) by the action of nitric acid upon starch, or upon arsenic trioxide. It is a reddish gas, which condenses to a volatile blue liquid upon being cooled by a freezing mixture. Nitro gen trioxide also dissolves in ice-cold water with the formation of a blue liquid containing nitrous acid, HNO.. (See Nations ACID). On account of the difficulty of preparing this gas in even a moderate degree of purity, its chemical and physicalproperties have not 'been determined with any degree of exactness; (4) Nitrogen peroxide, N.(1, formerly known as the "dioxide° (NO.) may be prepared by heating dry nitrate of lead, which breaks up into lead oxide, oxygen and nitrogen peroxide. It is a dark orange-colored gas, which has the molec ular formula N.04 at low temperatures, for which reason it is also called the utetroxide.* At 150° C. the gas has the molecular formula NO., as is proved by its density; and at ordinary temperatures it consists of a mixture of NO. and N,04. At about C. a further dissociation into nitric oxide and oxygen be gins, this increasing as the temperature rises, until, at about 565° C., the dissociation into nitric oxide and oxygen is complete. Nitrogen peroxide is easily liquefied and solidified. At temperatures lower than —8° C., it is a white, deliquescent, crystalline solid, which on heat ing slowly melts to a colorless liquid, becomes yellow when warmed to 0° C., and orange at 20° C. Under ordinary atmospheric pressure it boils at about 22° C., with the evolution of the gaseous peroxide; (5) Nitrogen pentoxide or nitric anhydride, may be prepared by dehydrating concentrated nitric acid by the cautious addition of phosphorous pentoxide, or by passing chlorine as over dry silver nitrate. The pentoxide is solid at ordinary temperatures, and may be obtained in the form of white, lustrous, translucent prisms, which have a specific gravity of about 1.64, and melt at 3° C. with partial decomposition into the peroxide and free oxygen. At about 46° C. the liquid boils. The pentoxide combines with water to form nitric acid (q.v.).
Ammonia.— Under very high pressures (175 to 200 atmospheres) and at high temperatures, (approx. 600° C.) with the assistance of a catalyst, nitrogen and hydrogen can be com bined directly, forming ammonia (NH.). The
first commercial development of this process was accomplished by Haber and his associates in Germany in 191Q. The apparatus used is difficult to construct, and the catalyst is easily rendered inactive, yet Germany made consider able quantities of ammonia by this method dur ing the war: the costs of production by this process, however, have not been disclosed.
Large quantities of ammonia have been manufactured during the last few years by the so-called Cyanamid process, in which calcium carbide is first manufactured in an electric fur nace; this carbide is ground fine and subjected to the action of nitrogen in suitable ovens. The resulting product is called Cyanamid and contains 20 to 23 per cent nitrogen. By sub; jetting this Cyanamid to steam, under pressure, almost the theoretical yield of ammonia is ob tained. The method has been in operation in Europe for some time as well as at Niagara Falls, Ontario. (See CYANAMID). Several processes for the production of NH, through the intermediate formation of cyanides are in process of development and show promise of successful operation. In these processes a mix ture of alkali metal compound and carbon, with or without a catalyst, is subjected to the action of nitrogen at a temperature of approximately 1000° C. Cyanides are produced which, by the action of steam, are converted into ammonia and a residue which can be returned to the cycle of operations. (See CYANIDES). Am monia can also be obtained by the hydrolysis of suitable nitrides. This process was first in troduced by Serpek in Italy. Interest in this process has recently been revived and one or more plants are in prospect. The process de pends upon the reduction of alumina in one form or another by means of carbon at a very high temperature in the presence of nitrogen. The aluminum nitride thus formed is after ward subjected to the action of steam, pro ducing ammonia and alumina. Notwithstand ing the methods described above, the fact re mains that the world still depends upon nature to supply the bulk of the ammonia required and until comparatively recently nearly all of our ammonia came from the destructive distillation of coal. An oily liquid known as chloride of nitrogen (NCI,) is formed by passing chlorine through a solution of ammonium chloride or, More conveniently, electrolyzing a solution of ammonium chloride. This compound is one of the most dangerous explosives known. A num ber of synthetic nitrogen compounds, not found in nature but now widely used, are of great im portance. In addition to the oxides and ammo nia mentioned above, there are such derivatives of nitric acid as nitroglycerine, gun cotton and a series of so-called which are either dyes or intermediates in the manu facture of dyes. A number of alkaloids that contain nitrogen show considerable physiolog ical activity and are of importance as medi cines.
Uses.— Free nitrogen gas is used in very large quantities in the manufacture of cyana mide, cyanides and synthetic ammonia. It is also used in the incandescent lamp industry as the filaments last much longer and give greater efficiency in an atmosphere of nitrogen than in one of air. Nitrogen is likewise finding an in creasing number of applications as an inert gas in various manufacturing operations, for in stance where oxidation is to be avoided. Cer tain compounds of nitrogen, e.g., nitrates, am monium salts and cyanamid (nitrolim), are used in enormous quantities as fertilizers. Nitric acid and an almost endless list of nitro com pounds obtained by treatment of various or ganic materials with nitric acid are used in very large quantities in the manufacture of dyes and explosives, drugs, celluloid and simi lar products. Ammonia is used in large quan tities in ice machines and in the manufacture of soda by the Solvay process. Cyanides are used for the extraction of the precious metals from their ores and also in considerable quantities in the electroplating industries, as well as in the manufacture of numerous small amounts of chemicals useful in the practical arts.
Bibliography.— Boyce, John C., raphy of the Production of Synthetic Nitric Acid and Synthetic Ammonia) (in Metallurgi cal and Chemical Engineering, Vol XVII, p. 328, 1917) ; (Reference List Electrical Fixation of Atmospheric Nitrogen, etc.,) Bulletin No. 63, United States Bureau of Soils; Literature of the Nitrogen Industries, 1912-16, originally published serially in the General Electric Re view and later assembled in the Journal of In dustrial and Engineering Chemistry, pp. 424 438 (1917) ; Thorpe, (Dictionary of Applied Chemistry) (Vol III, pp. 676-712, 1916).