INORGANIC NITROGEN FERTILIZERS 99 



burns almost as steadily as a candle flame. In this furnace 

 the air takes an appreciable time to travel from one end of 

 the furnace to the other, whereas in the Birkeland furnace 

 the heating and cooling is much more rapid. The gases 

 leaving the furnace contain about 2 % of nitric oxide. 



The Pauling arc flame furnace possesses the special 

 feature of a pair of water-cooled electrodes in the form of the 

 letter " V," into the base of which a strong current of air 

 is blown. The arc strikes at the lowest and closest portion, 

 but the heat causes it to rise. This device has the effect of 

 expanding the arc into the more spacious upper part of the 

 " V," the flame so produced burning with great steadiness. 

 The gases leave the furnace at about a temperature of 

 7oo-8oo C. (say 1300-! 500 F.). Ity working with a 

 " three-phase " alternating current, Kilburn Scott has 

 produced a furnace somewhat on the Pauling type, but 

 owing to the " three-phase " system, supplemented by his 

 device of " pilot sparks," it is possible to maintain a 

 continuous arc. A special and separate high tension-current 

 is produced for the purpose of maintaining a continuous 

 passage of pilot sparks. The rapid removal of the products 

 to regions of lower temperature is a great advantage, as it 

 prevents the reversal of the formation of nitric oxide. In 

 Fig. 3, p. 98, the furnace is at the bottom, and the flame 

 plays directly on the bottom and tubes of the boiler, which 

 serves the double purpose of cooling the gases and generating 

 steam for general purposes in the works. Cooling the gases 

 prevents the decomposition of nitric oxide to nitrogen and 

 oxygen, and assists the oxidation of nitric oxide to nitrogen 

 peroxide. The boiler is placed immediately above the 

 furnace, so that the temperature of the gases is rapidly 

 reduced. Further efficiency of the boiler is obtained by a 

 superheater placed above, and the gases then pass away at 

 temperatures not exceeding 200 C. (360 F.). 



The resulting gases from any arc furnace, produced by 

 the reaction N 2 + O 2 = 2NO, rarely contain more than 2 % 

 of nitric oxide, and therefore require very bulky apparatus 

 for subsequent treatment. The gases, leaving the furnace 



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