ABSORPTION OF NITRIC ACID 319 



of the equation is not produced. The most concentrated acid 

 which has so far been obtained by the condensation of nitrous 

 gases in water in the presence of oxygen corresponds to the for- 

 mula HNO 3 , 2H 2 O, and possesses a density of 40.6 B., repre- 

 senting 63.63 per cent, of anhydrous nitric acid. The forma- 

 tion of this acid takes place, according to the following equation, 

 in the Lunge and Rohrmann plate towers : 



2NO 2 +O+5H 2 O=2(HNO 3 , 2H,O), 



from which acid of 40 to 41 B. is obtained. By passing the 

 gases, however, through towers down which water flows, an 

 equimolecular mixture of nitric and nitrous acids results, which 

 at the most, can not attain a concentration greater than that 

 obtained in the Lunge towers. Attempts at further concentra- 

 tion by the passage of nitrogen peroxid through the solution, 

 simply result in an increase of nitric acid at the expense of the 

 nitrous. The strongest acid is thus never free from nitrous 

 acid, and each succeeding absorption tower contains less and 

 less nitric acid, while at the same time the nitrous acid in- 

 creases, for as the free oxygen in the gases becomes consumed 

 the NO and NO 2 tend to react as N 2 O 3 , yielding only nitrous 

 acid. It is not possible to prepare much stronger acid by frac- 

 tionating the 50 per cent, acid from the first absorption tower, 

 since a product of minimum vapor pressure, boiling at 120, 

 and containing 68 per cent, of anhydrous acid, is obtained as 

 residue. 



Thus in order to prepare the most concentrated acid by the 

 nitrogen combustion process it would be necessary to either 

 add the 50 per cent, acid to concentrated sulfuric acid until a 

 dilution of say 54 B., is obtained (54 B. equals 120 Tw. 

 equals 68.5 per cent, of H 2 SO 4 ), and distill the nitric acid; or to 

 prepare a salt of nitric acid, and distill in the usual way with 

 sulfuric acid or a bisulfate. 



An electrolytic method for concentrating and oxidizing the 

 weak tower acid has lately been patented. The process con- 

 sists in refrigerating the oxids of nitrogen evolved during elec- 

 trolysis at the cathode, and leading them in the liquid state slow- 

 ly to the anode compartment of the -cell, where in presence of 



