50 THE ELEMENTS OF PLANT FOOD 



tilizer in the United States. It is the cheapest source 

 of potassium obtained from commercial fertilizers. 

 On account of the chlorine that it contains, it should 

 not be used to a great extent for tobacco, onions, 

 beets, or potatoes. 



Potassium Carbonate (K 2 CO 3 ). - - This salt is pre- 

 pared in this country by leaching wood ashes to form 

 potash lye, then evaporating the lye in large pots, 

 whence its name potash. When refined it is called 

 pearl ash. It is a very strong alkali and is used in 

 the manufacture of soft soap. The largest supply 

 is obtained as a by-product in the manufacture of 

 sugar from sugar beets. 



All crops are improved by a light application of wood 

 ashes to the soil. Such sources of potassium on the 

 farm should not be wasted nor lie out in piles un- 

 protected. Leached ashes have very little potassium 

 left in them. Besides potash, ashes contain carbonate 

 of lime and phosphoric acid, which give them added 

 value as a fertilizer. Coal ashes have no potassium 

 salts that are available as food for plants and there- 

 fore cannot be used as a substitute for wood ashes. 



Potassium nitrate (KNO 3 ), niter or saltpeter, is 

 a white solid usually seen in crystalline form. It is 

 present in most fertile soils and is used in the manu- 

 facture of nitric acid and gunpowder. It is an anti- 

 septic compound and is, therefore, often used with 

 common salt (NaCl) for preserving meat. 



Note. Gunpowder is a mixture of pulverized charcoal, pulverized 

 sulphur, and potassium nitrate (KNO 3 ). Its explosiveness is due to 

 the formation of CO 2 and N in large quantities as soon as ignition takes 

 place. The reaction may be expressed : 



2 KN0 3 + S + 3 C = K,S + 2 N + 3 CO 2 



