398 CHEMICAL DISCOVERY AND INVENTION 



matter as oxygen but in a condensed state. Its molecule consists 

 of three atoms, 3 , while the molecule of common oxygen 

 consists of two atoms, expressed as 2 . In most cases the activity 

 of ozone results from the instability of its molecule, and the 

 tendency to part with one of the atoms while common oxygen is 

 regenerated. 



An active modification of nitrogen has now been obtained, but 

 its activity is apparently due to an entirely different condition, 

 for it is not nitrogen in a condensed state. The new gas appar- 

 ently consists of free nitrogen atoms (see p. 121). 



Independently of natural agencies already referred to the 

 fixation of atmospheric nitrogen may be effected in a variety of 

 ways, and the products may take the following forms :^- 



1. Ammonia. The synthetical formation of ammonia by 

 Haber's process has been already described under Catalysis (p. 201). 



2. Metallic nitride. 



3. Cyanide. 



4. Cyanamide. 



5. Nitric oxide leading to nitrate. 



The formation of nitrides by heating the metals of the alkalis 

 or alkaline earths in contact with nitrogen gas has long been 

 recognised. A mixture of magnesium with quicklime was used 

 for absorbing nitrogen in the Rayleigh-Ramsay experiments on 

 the isolation of argon from air. Boron, silicon, titanium, and 

 some other elements also combine with nitrogen at a red heat. 

 The compounds which result are decomposed by water or steam 

 with evolution of ammonia, but the production of such com- 

 pounds on a large scale is for the present impracticable, and such 

 a process of getting nitrogen from the atmosphere has as yet no 

 technical value. 



The only process in which a nitride is concerned which has 

 received serious attention from the industrial world is that which 

 is known as the Serpek process. This is based on the production 

 of an aluminium nitride and its subsequent decomposition by 

 water or alkali with formation of ammonia and alumina. 



The process has been tested in France by the Societe Generate 

 des Nitruros, which has acquired the patents, and by the Badische 

 Anilin und Soda Fabrik at Ludwigshafen. 



Bauxite, which is natural alumina containing a good deal of 

 iron, is mixed with coke and is heated to the requisite tempera- 



