|
NITROGEN [symbol N., atomic weight 14.01, 0=16] . A non-metallic chemical element , first isolated in 1772 by D. Rutherford, who showed that on removing oxygen from air a gas remained, which was incapable of supporting combustion or respiration. Nitrogen forms approximately 79% by volume (or 77% by weight ) of the atmosphere; actual values are: % by volume79.07 (Regnault ), 79.20 (Dumas); %by weight76.87 (Regnault ), 77.00 (Dumas), 77.002 (Levey), 76.900 (Stas), 77.010 (Marignac). No absolutely accurate determinations appear to have been made recently. Free nitrogen is also found in some natural waters and has been recognized in certain nebulae. In the combined state nitrogen is fairly widely distributed, being found in nitre, Chile saltpetre, ammonium salts and in various animal and vegetable tissues and liquids. It is invariably present in soils, where compounds are formed by nitrifying bacteria.
Nitrogen may be obtained from the atmosphere by the removal of the oxygen with which it is there mixed. This may be effected by burning phosphorus in a confined volume of air, by the action of an alkaline solution of pyrogallol on air, by passing air over heated copper, or by the action of copper on air in the presence of ammoniacal solutions.
It is also prepared by heating ammonium nitrite (or a mixture of sodium nitrite and ammonium chloride): NH4NO2=2H20+N2; by heating a mixture of ammonium nitrate and chloride (the chlorine which is simultaneously produced being absorbed by milk of lime orby a solution of sodium hydroxide) : 4NH4NO3+2NH4CI =5N2 +C12+12H20; by heating ammonium dichromate (or a mixture of ammonium chloride and potassium dichromate) : (NH4)5Cr2O7 =Cr203+4H2O+N2; by passing chlorine into a concentrated solution of ammonia (which should be present in considerable excess) : 8NH3+3C12=6NH4Cl+N2; by the action of hypochlorites or hypobromites on ammonia: 3NaOl3r2NH3=3NaBr+3H20+N2; and by the action of manganese dioxide on ammonium nitrate at 180-200 C. It is also formed by the reduction of nitric and nitrous oxides with hydrogen in the presence of platinized asbestos at a red heat (G. v. Knorre and K. Arndt, Ber., 1899, 32, p. 2136) ; by the oxidation of hydroxylamine (ibid., 1900, 33, p. 30) ; and by the electrolysis of hydrazine and its salts (E. Ch. Szarvasy, Jour. Chem. Soc., 1900, 77, p. 603).
The chief importance of nitrogenous compounds depends upon their assimilation by living plants, which, in their development, absorb these compounds from the soil, wherein they are formed mainly by the action of nitrifying bacteria. Since these compounds are essential to plant life , it becomes necessary to replace the amount abstracted from the soil, and hence a demand for nitrogenous manures was created. This was met in a very large measure by deposits of natural nitre and the products of artificial nitrieres, whilst additional supplies are available in the ammoniacal liquors of the gas-manufacturer, &c. The possible failure of the nitre deposits led to attempts to convert atmospheric nitrogen into manures by processes permitting economic success. Combination can be made in five directions, viz. to form (1) oxides and nitric acids, (2) ammonia, (3) readily decomposable nitrides, (4) cyanides, (5) cyanamides. The first three will be treated here; for the others see PRUSSIC ACID and
End of Article: NITROGEN [symbol N., atomic weight 14.01, 0=16]
If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/NEW_NUM/NITROGEN_symbol_N_atomic_weigh.html">
NITROGEN [symbol N., atomic weight 14.01, 0=16]
</a>
|
