NITROGEN. 271 



instantly extinguished in this gas, and an animal soon dies in 

 it, not because the gas is injurious, but from the privation of 

 oxygen, which is required in the respiration of animals. Ni- 

 trogen appears to be chiefly useful in the atmosphere, as a 

 diluent of the oxygen, thereby repressing to a certain degree 

 the activity of combustion and other oxidating processes. The 

 evidence of the fixation of free nitrogen by plants is incomplete, 

 and therefore it cannot be said with certainty that the nitrogen 

 of the organic world is primarily derived from the atmo- 

 sphere.* When heated with oxygen, nitrogen does not burn 

 like hydrogen, nor undergo oxidation. But nitrogen may be 

 made to unite with oxygen by transmitting several hundred 

 electric sparks through a mixture of these gases in a tube, with 

 water or an alkali present, and nitric acid is produced. The 

 water formed by the combustion of hydrogen in air, or of a 

 mixture of hydrogen and nitrogen in oxygen, has often an acid 

 reaction, which is due to a trace of nitric acid. The same acid 

 is also a product of the oxidation of a variety of compounds con- 

 taining nitrogen. Ammonia mixed with air, on passing over 

 spongy platinum at a temperature of about 572, is decomposed, 

 and the nitrogen it contains is completely converted into nitric 

 acid, by combining with the oxygen of the air. Cyanogen and 

 air, under similar circumstances, occasion the formation of nitric 

 and carbonic acids.f Nitric acid is also largely produced by the 

 oxidation of organic matters during putrefaction in air, when an 

 alkali or lime is present, as in the natural nitre soils and artifi- 

 cial nitre beds. 



A suspicion has always existed that nitrogen may be a com- 

 pound body, but it has resisted all attempts to decompose it, 

 and the evidence of its elementary character is equally good 

 with that of most other bodies reputed simple. If the equiva- 

 lent of nitrogen be divided by 3, a curious parallellism is ob- 

 served between some of its compounds, and those of oxygen 

 with the same elements, to which attention has been directed 

 by M. Laurent and by M. A. Bineau.J Before considering the 

 compounds of nitrogen with oxygen, we may notice the pro- 

 perties of atmospheric air, which is regarded as a mechanical 

 mixture of these gases. 



* Boussaingault, Ann.de Ch. et de Ph. t. 67, p. 5, and 69, p. 353. 

 f Kuhlman, Phil. Mag. 3rd Series, vol. 14, page 157. 

 t An. de Ch. et de Ph. t. 67, p. 242. 



