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and Jellinek found, however, that inasmuch as the combination (resulting in 

 the formation of nitric acid) is "endothermic," that is, accompanied by ab- 

 sorption of heat, it is favored by the high temperature of the gases, and they 

 found, further, that if the products are cooled quickly, the reversion that occurs 

 at the lower temperatures can be prevented. Nitric oxid is stable at tempera- 

 tures below 1000°, hence the conditions of efficiency in these processes are to 

 combine the substances at a very high temperature and cool the products 

 as quickly as possible to at least 1000°. To secure the high temperature neces- 

 sary for combination, no method other than the electric arc is yet available 

 practically. As arcs can easily be obtained at low cost by water-power, the 

 operation of such plants has been especially developed in mountainous coun- 

 tries, such as Switzerland and Scandinavia. Abundant opportunities for such 

 development exist in the United States. 



The action of the arc is not entirely by its heat, for, as noted above in con- 

 nection with Cavendish's experiments, a direct exaltation of the chemical 

 affinity of the oxygen takes place. If an electric discharge is passed thru 

 pure dry oxygen, a diminution of volume occurs and ozone is produced. 



FIXATION OF NITROGEN BY ABSORPTION 



Calcium carbid, produced by the action of finely divided carbon (coal or 

 coke) upon lime under the influence of the electric arc, has been manufactured 

 for many years in large amount for the production of acetylene. When it 

 is heated to about 1000° in a current of nitrogen, direct combination takes 

 place, with the formation of calcium cyanamid, CaN2C, the reaction being 

 CaCa + Ns^CaNzC + C. 



Calcium cyanamid may be used directly as a fertilizer, and as it contains 

 about four per cent, more of available nitrogen than sodium nitrate, it is being 

 prepared on a very large scale. For the production of calcium cyanamid, the 

 carbid must be in a fine state of division. To prevent accidents from evolu- 

 tion of acetylene, in consequence of the action of moisture, the final grinding 

 is carried out in an atmosphere of nitrogen. The process is carried out either 

 by heating the carbid by means of an electric arc within the mass, or in retorts 

 by direct outside firing. 



Unlike the combination of nitrogen and oxygen, which is endothermic, 

 the action of nitrogen on calcium carbid is "exothermic," that is, attended 



