CHAPTER XII 

 Nitric Acid and Nitrogen Compounds 



92. Occurrence. Nitric acid does not occur in nature 

 in a free state, but nitrates or salts of nitric acid are found 

 as natural products. Since all normal nitrates are soluble 

 in water, they are never found in great abundance in 

 soils. In regions of scant rainfall, where climatic con- 

 ditions have been favorable for the formation of nitrates, 

 deposits of nitrate of soda are occasionally found. The 

 nitrifying organisms of the soil, when supplied with 

 food, moisture, suitable temperature, and other requisite 

 conditions, produce nitrates which are utilized as food 

 by plants. The process of nitrification which takes place 

 in the soil, results in changing the inert and unavailable 

 nitrogen to a soluble and available condition. 



93. Preparation. The same principle is applied in the 

 preparation of nitric acid as in the preparation of hydro- 

 chloric acid. It is produced by the action of H 2 SO 4 upon 

 a salt ; when a chlorid is used, hydrochloric acid is the 

 product, and when a nitrate is used nitric acid is the 

 product. The reaction when sodium nitrate is used is : 

 2 NaNO 3 + H 2 S0 4 = Na 2 SO 4 + 2HNO 3 . 



Experiment 75. Preparation of nitric acid. Special care 

 should be exercised by the student in the preparation of nitric acid, 

 because if any is spilled on the hands it causes painful burns and 

 wounds that are difficult to heal. Provided the student is careful 

 and follows the directions given, there is no danger whatever in 

 the preparation of this material. Arrange the apparatus as shown 

 in Fig. 42. The delivery tube used in the preparation of NH S may 



