130 AGRICULTURAL CHEMISTRY 



gous salts and compounds. Sodium is not as strong a 

 type of basic element as is potassium and can be sepa- 

 rated from its compounds more readily, although it is not 

 easily replaced by other elements or by simple chemical 

 forces. Sodium and its compounds are less expensive 

 than potassium and its compounds. In industrial opera- 

 tions, sodium salts are more extensively used, but to the 

 agricultural student, potassium is of greater importance 

 because sodium takes little or no part in plant nutrition. 

 In animal life, however, sodium chlorid plays an import- 

 ant role. Sodium is never found in nature in a free state, 

 sodium chlorid being one of the most abundant of its 

 salts. Sodium is also found as silicates and in small 

 amounts in other forms. 



160. Sodium Chlorid. Extensive deposits of this salt 

 are found in nature ; in some places it is mined, the prod- 

 uct being known as rock salt. It is present in sea- water 

 in large amounts from which it is occasionally obtained 

 in an impure form along with a large number of other 

 salts. When pure, sodium chlorid forms colorless, trans- 

 parent cubes. A large amount of commercial salt is ob- 

 tained by the evaporation of water from salt springs. In 

 some localities, water is forced into and through deposits 

 of salt which it dissolves and is then pumped out and 

 evaporated to dryness. Sodium chlorid is extensively 

 used for the preparation of sodium and other compounds 

 as hydrochloric acid. It is not found to any appreciable 

 extent in ordinary agricultural plants, but in some alkali 

 plants there are quite large amounts. When sodium 

 chlorid contains impurities, as calcium chlorid and lime 



