CHAPTER XXVI 

 NITRIC ACID 



NITRIC acid HNOs is used in large quantities for making explo- 

 sives like guncotton, picric acid and TNT, and plastics like cellu- 

 loid, as well as innumerable drugs and dyes. Nitrates are largely 

 used as fertilizers (p. 410). 



Manufacture. Nitric acid is obtained in two ways, namely, 

 by the action of sulphuric acid upon natural sodium nitrate and 

 by oxidation of the nitrogen of the atmosphere. The processes 

 which utilize the latter method will be referned to in a later section. 

 Sodium nitrate, Chile saltpeter, is found in an immense deposit 

 (2 by 220 miles) on the boundary of Chile and Peru. This salt is 

 mixed with concentrated sulphuric acid in iron retorts and gently 

 heated to drive off the nitric acid. The sodium-hydrogen sulphate 

 remains in the retort: 



NaN0 3 + H 2 S0 4 ^ NaHSO 4 + HNO 3 1 . 



The vapor is condensed in glass tubes (cooled with water) and the 



acid collected in vessels of earthen- 

 ware. Sulphuric acid (b.-p. 330) is 

 used because it is much less volatile 

 than nitric acid, and so only the latter 

 is vaporized. The acid boils at 86 

 (760 mm.), but, to present loss by 



decomposition, a lower boiling-point is secured by reducing the 

 pressure in the whole apparatus. 



In the laboratory the same action is employed, without, how- 

 ever, the reduction in the pressure (Fig. 81). 



Physical Properties. Pure nitric acid is a colorless liquid, 

 boiling at 86. It is miscible in all proportions with water. 



