THE ELEMENTS OF PLANT FOOD 63 



mixture is used for disinfecting purposes and for bleach 

 ing colored cloth. 



SODIUM (Na) 



Description and Occurrence. Sodium is a metal 

 very much like potassium in appearance and properties. 

 It is not found free in nature and as an element it is 

 not of very great importance, but the compounds of 

 sodium are of the greatest importance to mankind. 

 The principal one of these compounds is common salt 

 (NaCl). 



Sodium Chloride (NaCl), common salt. This min- 

 eral compound is very necessary to human and other 

 animal life. It is widely distributed throughout the 

 world. Sea water contains two and seven tenths per 

 cent of salt, and many springs and wells have the salt 

 in solution. It is also found in solid form in large beds 

 in parts of Europe and the United States. 



The salt of commerce is obtained by evaporating 

 the sea water or the water of salt springs and wells or 

 by mining that found in beds. If the water containing 

 salt is evaporated rapidly, the salt forms in small 

 crystals and a very fine table salt is produced ; if the 

 evaporation is slower, the larger crystals form and coarse 

 salt, or rock salt, is produced. 



NaCl is used in preserving meats and in destroying 

 weeds. It has been used as a fertilizer, but it has no 

 value as a plant food. 



Sodium Nitrate (NaNO 3 ), Chile saltpeter. This com- 

 pound is a very important one to the agriculturist, for 

 the nitrogen which it contains is an essential plant 

 food. The price of nitrogen in all fertilizers is based 

 on the price of Chile saltpeter. This compound at- 



