NITRIC ACID 



313 



brush discharge several feet in diameter. The figure shows a 

 cross section of the space filled by the discharge. In the center is 

 a section of one of the carbon rods. Air is blown through the 

 flame, giving 1 per cent of NO, and is cooled to permit of union of 

 the nitric oxide with oxygen, to give the tetrox- WATM ^ 

 ide, N0 2 . The air containing N0 2 is then CoOLINS I 

 passed through absorbing towers down which 

 water trickles. Here the action mentioned in 

 the last section takes place, and an aqueous 

 solution of nitric acid is produced. In peace 

 times, the nitric acid is mixed with calcium 

 hydroxide (slaked lime) : 



Ca(OH) 2 + 2HN0 3 -+ Ca(NO 3 ) 2 + 2H 2 O 



to give calcium nitrate, which, being very solu- 

 ble, is sold for use as a fertilizer. In war times, 

 the acid is concentrated for use in the manu- 

 facture of explosives. 



The Schonherr process, used in the same 

 factories in Norway, employs a discharge 

 through a tube 22 feet long (Fig. 84). The 

 column of air rotates as it traverses the tube 

 and so every part is exposed to the discharge. 



The Pauling process, used in Italy and 

 Austria, uses preheated air, and a different 

 arrangement of the discharge. The principles 

 employed are, however, the same. 



The productive capacity of plants employ- 

 ing these arc processes in 1920 was three 

 hundred thousand tons (calculated as nitrate of lime). 



FIG. 84 



Nitric Acid from Ammonia. The ammonia oxidation proc- 

 ess for the production of nitric acid was developed on a large 

 scale during the Great War, particularly in Germany. Gaseous 

 thft presence of air and a suitable catalyst undergoes 



