374 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1913. 



The gases then paws through the two cooling towers, which are 

 outside the furnace house. Each of these towers is 16 feet in diame- 

 ter and 40 feet high, and filled with fire brick. When the bricks of 

 one tower have become hot the gases are switched over to the other 

 tower. Fresh air is then drawn through the heated tower by means 

 of the chimney (8.5 feet high), and the brickwork in it is thus cooled. 



The gases are sucked out of the cooling tower by a 15-horsepower 

 fan and forced into the oxidation tower, which is built of reinforced 

 concrete and measures 83 feet diameter and 75 feet high. Here, the 

 temperature having fallen to 600° C, oxidation to NO, goes on 

 I'apidly. 



From the oxidation tower there are two pipe lines, and one takes 



some fixed gas and air back to 



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 I 

 I 





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furnaces /OOO /V 



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-The lay-out of the works by La NixROGfeNE 

 CiE, France. 



the furnaces, where it is passed 

 through the central passage 

 and comes in contact with the 

 freshly fixed nitrogen at the 

 top of the arcs. In this way 

 the fresh gas is cooled without 

 being diluted. 



A second pipe line, of alumi- 

 nium, takes the remainder of 

 the gases to the absorption 

 towers, each of which con- 

 tains 250 tons of stonew^are 

 packings. The gases pass from 

 1 to 5, whilst the water, grad- 

 ually accumulating more and 

 more acid, flows in the oppo- 

 site direction, namely, 5 to 1. 

 Montejus operated by compressed air raise the solution to the top of 

 the different towers. 



The concentration of acid at bottom of No. 5 tower is about 5° 

 Beaume ; at bottom of No. 4 it is 8° ; at bottom of No. 3 it is 15° ; 

 at bottom of No. 2 it is 25° ; and at bottom of No. 1 it is 35°, which 

 corresponds to about 40 per cent of HNO3. 



The gases from No. 5 absorption tower still contain a small amount 

 of NO and NO.,. The}' are passed through an acid filter, in which 

 the last traces of acid are condensed, and then pass to the nitrite 

 towers. These contain sodium-carbonate solution, and the gases 

 react with it to form sodium nitrite, having a concentration of 20 

 per cent. This is submitted to evaporation, the hot furnace gases 

 being used for the purpose, and white sodium-nitrite crystals are 

 obtained containing 95 per cent of nitrite and 3 per cent of nitrate. 

 The nitric acid goes to the acid concentrators, in which it passes 

 through a series of porcelain and fused quartz vessels arranged in 



