NITROGEN, OR AZOTE. 359 



NITROGEN SYMBOL N ; ATOMIC WEIGHT 14. 



We have already made some reference to this gas when speaking of the 

 atmosphere and its constituents, of which nitrogen is the principal. From 

 its life-destroying properties it is called 

 " azote" by French chemists, and when 

 \ve wish to obtain a supply of nitrogen 

 all we have to do is to take away the 

 oxygen from the air by burning phos- 

 phorus on water under a glass. Nitrogen 

 is not found frequently in solid portions 

 of the globe. It is abundant in 

 animals. It is without colour or smell, 

 and can be breathed in air without 

 danger. It is heavy and sluggish ; 

 but if we put a taper into a jar of 



... . .... Fig. 350. Obtaining nitrogen. 



nitrogen it will go out, and animals die 



in the gas for want of oxygen, as nitrogen alone cannot support life. 



The affinity of nitrogen for other substances is not great, but it gives 

 rise to five compounds, which are as below, in the order they are combined 

 with oxygen : - 



Nitrous oxide ("laughing gas ") (Monoxide; . . N,O. 



Nitric oxide. .... Dioxide . . . N 2 O 2 . 



Nitrous acid .... Trioxide . . N S O 3 . 



Nitric peroxide . . . Tetroxide . . N 2 O 4 . 



Nitric acid .... Pentoxide . . N S O> 



These compounds are usually taken as representative examples of com- 

 bining weight, and as explanatory of the symbolic nomenclature of chemistry, 

 as they advance in such regular proportions of oxygen with nitrogen. The 

 combining weight of nitrogen is 14, and 'when two parts combine with five 

 of oxygen it makes nitric acid, and we put it .down as N 2 O 5 ; on adding 

 water, HNO 3 , as we can see by eliminating the constituents and putting in 

 the proportions. Actually it is H 2 N 2 O C , or, by division, HNO 3 . 



Nitrogen plays a very important part in nature, particularly in the 

 vegetable kingdom. Nitric acid has been known for centuries. Geber, the 

 alchemist, was acquainted with a substance called " nitric," which he found 

 would yield a dissolvent under certain circumstances. He called it " dis- 

 solving fluid." At the end of the twelfth century Albert Magnus investi- 

 gated the properties of this acid, and in 1235 Raymond Lully prepared nitre 

 with clay, and gave the liquid the name of " aqua-fortis." But till 1 849 

 nitric acid was only known as a hydrate, that is, in combination with water, 

 but now we have the anhydrous acid. 



