Nitrogenous Fertilizers 51 



soluble, it readily distributes itself everywhere in the 

 soil to which it may be applied. 



Nitrate of soda. There are a few substances found 

 in nature containing nitrogen in the nitrate form. The 

 most important is nitrate of soda, a chemical compound 

 composed of sodium, oxygen and nitrogen. The occur- 

 rence of this material is limited to the rainless districts 

 of South America, mainly Chile, where the crude nitrate 

 of soda salts called Caliche are found in vast quantities. 

 These crude salts contain from 5 to 30 per cent of nitrate 

 of soda. In the process of refining for market they are 

 dissolved and recrystallized in order to remove as far as 

 possible the impurities associated with them. There 

 are great quantities of a lower grade containing 3 per cent 

 or less of nitrate of soda which are not at present con- 

 sidered sufficiently rich to refine. The chemically pure 

 salt, nitrate of soda, contains 16.47 per cent of nitrogen, 

 and the commercial article, called "Chili saltpeter," 

 contains from 15.5 to 16 per cent. The impurities which 

 remain in it consist mainly of sodium chlorid, or common 

 salt, which, together with moisture, causes a lower per- 

 centage in the commercial product. Because nitrogen 

 in nitrate of soda is in the nitrate form and, therefore, 

 soluble, it is often advanced that there is greater loss 

 from leaching into the drainage waters. Experiments 

 show this is untrue or at any rate the efficiency of this 

 material is greater than that of any other because more 

 is returned in the crop as shown in the discussion of relative 

 availability of the forms of nitrogen which follows. When 

 nitrate of soda is mixed with other materials it has a 

 tendency to cause a caking or hardening of the mixture, 

 but this is no more true of nitrate of soda than of the 

 potash salts. Unlike ammonium sulfate, nitrate of soda 



