NITRIFICATION 



5752 



NITROGEN 



should be directed to neutralising 

 the acid as quickly as possible. 

 Calcined magnesia is the best anti- 

 dote, but if this is not available, 

 sodium bicarbonate, chalk, whiten- 

 ing, ceiling plaster, etc., may be 

 administered. 



NITRATES FROM THE AIR. Nitro- 

 gen exists in the free state in the 

 atmosphere, of which it forms four- 

 fifths by bulk. Sir William Crookes. 

 in an address before the British 

 Association in 1898, showed that, as 

 the number of inhabitants in the 

 world increased, the area of wheat 

 grown must be extended. As, how- 

 ever, there is a limit to the amount 

 of arable land, he pointed out that 

 by the use of nitrates as manures 

 the quantity of wheat produced 

 per acre could be doubled. He 

 calculated that the nitrate beds 

 would be exhausted within a 

 measurable distance of time, and 

 he directed attention to the possi- 

 bility of obtaining nitrate by fixing 

 the nitrogen of the air. 



Before the Great War, nitrogen 

 fixation was being carried out in 

 Norway by the arc process, in 

 Germany by the synthetic ammo- 

 nia method or Haber process, and 

 in other countries by the cyana- 

 mide process. During the war, the 

 command of the seas being held by 

 the Allies, Germany was unable 

 to import nitrates, and was com- 

 pelled to establish factories for the 

 production of nitrates from the 

 air. In the United Kingdom it was 

 also realized that it was desirable 

 to have an alternative source of 

 nitrates, and so save tonnage. The 

 nitrogen products committee was 

 constituted in 1916, and researches 

 were carried on to find out which 

 method of fixing nitrogen was most 

 suitable for home manufacture. 

 Experimental plants for the cyana- 

 mide and synthetic ammonia pro- 

 cesses were erected, works were 

 organized, and the production of 

 these chemicals was carried out on 

 a very large scale. 



Nitrification. Term applied to 

 the formation of nitrates in soils 

 and manures through the agencies 

 of micro-organisms. Organic matter 

 in the soil, derived from the 

 remains of plants and animals and 

 the excreta of the latter, contains 

 abundant nitrogen, but not in a 

 form suitable for plant food. 

 The action of various microscopic 

 plants (bacteria) effects nitrifi- 

 cation, with formation of nitrates, 

 provided moisture and some basic 

 substance as carbonate of lime are 

 present, that the temperature is 

 sufficiently high, and that there is 

 free circulation of air. The action 

 takes place in three stages, effected 

 by three different groups of 

 bacteria : (1) Formation of ammo- 



nia by Bacillus mycoides and other 

 forms; (2) conversion of this 

 into nitrites by N itroeomonas and 

 Nitrococcus ; and (3) conversion 

 of these into nitrates by Nitro- 

 bacter. 



Nitrates are also formed by the 

 fixation of the nitrogen in the air 

 of the soil, as a result of the 

 activity of still other kinds of 

 bacteria. Some of these, such as 

 Azotobacter, live in the soil itself, 

 while others, Pseudomonas radici- 

 cola, inhabit small swellings or 

 nodules on the roots of leguminous 

 plants. Such plants are therefore 

 not only independent of nitro- 

 genous manures, but actually add 

 to the store of nitrogen in the soil, 

 and are consequently of great use 

 in rotation of crops. When a 

 leguminous crop of a particular kind 

 is grown on land for the first time, 

 nodules will not form on the roots 

 unless some soil from a field which 

 has borne the crop is employed as 

 a dressing, as this will contain the 

 required bacteria. See Humogen. 



Nitro-benzene (C 6 H 5 NO,). 

 Nitro compound manufactured 

 from benzene. First prepared by 

 Faraday in 1825 during the 

 course of some experiments with 

 benzene, it is a liquid with the 

 odour of bitter almonds, and was 

 manufactured in France under the 

 name of " essence of myrbane " 

 for use in scenting soap. Perkin 

 devised a commercial process of 

 making nitro-benzene by mixing in 

 large cast-iron cylinders benzene, 

 sulphuric acid, and sodium nitrate, 

 but later processes employ a 

 mixture of strong nitric acid and 

 concentrated sulphuric acid and 

 benzene. Nitro-benzene prepared 

 from pure benzene is sold as light 

 nitro-benzene, or " nitro-benzene 

 for blue or black," on account of its 

 use for preparing certain aniline 

 dyes, and as heavy nitro-benzene, 

 or " nitro-benzene for red," when 

 made from a mixture of benzene 

 and toluene. See Aniline ; Dyes. 



Nitro-cellulose. Product form- 

 ed by the action of nitric acid on 

 cotton, linen, or paper. The chief 

 form of nitro -cellulose is gun- 

 cotton (q.v.), which is formed with 

 a strong solution of nitric acid and 

 sulphuric acid, a weaker solution 

 forming collodion. See Celluloid ; 

 Collodion ; Cotton. 



Nitro-compounds. In chemis- 

 try, hydrocarbon derivatives con- 

 taining N0 2 groups. They are 

 made by the action of nitric acid 

 upon hydrocarbon, and the pro- 

 cess applied to the benzene series 

 is known as " nitration," examples 

 of the products being nitro- 

 benzene and nitro-toluene. Nitro- 

 glycerin and nitro-cellulose are 

 well-known explosives formed by 



the action of nitric acid on glycerin 

 and cellulose respectively. Trini- 

 trophenol or picric acid, and trini- 

 trotoluene are made by the action 

 of nitric acid on phenol and toluene, 

 and are also largely employed as 

 explosives. 



Nitrogen. One of the gaseous 

 elements. Its chemical symbol is 

 N; and atomic weight, 14'01. Dis- 

 covered in 1772 by Rutherford, 

 professor of botany in the univer- 

 sity of Edinburgh, Lavoisier shortly 

 afterwards proved the existence of 

 nitrogen in the air, and called it 

 "azote," a name by which it is 

 still known in France. Chaptal 

 first suggested the word nitrogen 

 because he discovered it in nitre or 

 saltpetre. 



Nitrogen occurs in the free state 

 in the atmosphere, of which it con- 

 stitutes about four-fifths. The 

 element also occurs in a combined 

 state as saltpetre and Chile nitre, 

 and as an essential constituent of 

 animal and vegetable organisms. 

 Animals have no power of directly 

 absorbing the nitrogen of the atmo- 

 sphere, but are dependent on the 

 nitrogenous foodstuffs which they 

 eat for their supply of this element. 

 The nitrogenous materials are 

 built up by plants which obtain 

 their nitrogen from the soil, and 

 the object of manuring the land 

 with ammonium sulphate and 

 Chile saltpetre is to replace the 

 nitrogen extracted from it by 

 plants. Natural sources of nitrates 

 found in the soil are the combina- 

 tion of oxygen and nitrogen which 

 takes place during thunderstorms. 

 The quantity so supplied amounts 

 each year to about 11 Ib. of com- 

 bined nitrogen per acre. 



Nitrogen is prepared artificially 

 by exhausting the oxj^gen from a 

 confined space of air and so leaving 

 impure nitrogen behind. This is 

 conveniently done by exposing 

 phosphorus in a bell-jar of air over 

 a trough of water. Chemical 

 methods are also employed, as 

 heating together potassium nitrite 

 and ammonium chloride, or passing 

 chlorine into ammonia. When re- 

 quired in large quantities it is best 

 prepared from the air, and is so 

 made at the Odde works in Norway 

 for the preparation of nitrolim. 

 The specific gravity of pure nitro- 

 gen is '96737. Nitrogen is incom- 

 bustible, and does not support 

 combustion. It is also distin- 

 guished by its inactivity, although 

 a form of " active " nitrogen, i.e. 

 nitrogen in the atomic form, was dis- 

 covered by Hon. B. J. Struttin 1911. 



The compounds of nitrogen and 

 h} 7 drogen are ammonia (NH :i ), 

 which can be prepared by the direct 

 union of the elements ; hydrazine or 

 diamide (N 2 H 4 ) ; and azoimide or 



