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NITROGENOUS FERTILIZERS 



I. NITROGEN AS NITRATE 



157. Sodium Nitrate, NaN0 3 . — The best known and most 

 important of all the nitrogen fertilizers is sodium nitrate, 

 or more commonly, nitrate of soda, or " Chile saltpeter." 

 Saltpeter itself is potassium nitrate which is too expensive 

 for ordinary use as a fertilizer, although on account of the 

 fact that it contains both potassium and nitrogen it is a 

 plant food of great value. Nitrate of soda is a salt similar 

 to potassium nitrate in many of its properties, and because 

 most of the world's supply comes from Chile, it has received 

 the name of Chile saltpeter. 



Fig. 45. — Gathering caliche. 



(a) How Obtained. — The principal deposit of nitrate of 

 soda lies on a plateau some 3000 feet above sea-level in a 

 region where rain falls but once in two or three years. The 

 crude salt, called "caliche" (Fig. 45), is found in masses which 

 average about 3 feet thick. On top are strata of gravel and 

 rock several feet thick. The rock is composed largely of 

 sand and gypsum, while the caliche contains from 17 to GO 

 per cent, sodium nitrate mixed with various impurities such 

 as sodium chloride, calcium, magnesium, and sodium sul- 

 phates, some iodates and perchlorates. Dynamite is used 



