THE ELEMENTS OF PLANT FOOD 49 



POTASSIUM (K) (L. Kdlium) 



Description and Occurrence. --The element potas- 

 sium is a soft metal with a brilliant bluish white 

 luster. It is one of the lightest of metals and floats 

 on water. Its marked affinity for O leads to the ready 

 decomposition of water when potassium is thrown 

 on it. The liberated H catches fire and the whole 

 burns with a beautiful violet flame. Potassium is 

 not found free in nature, but in its compounds it is 

 very widely distributed. These compounds are found 

 in soils and rocks, forming one of the essential mineral 

 forms of plant food. 

 Plants take potassium 

 salts through their roots, 

 and when they are 

 burned it remains as 

 potassium carbonate in 

 the ashes. 



The metal K is not 



r , i FIG. 12. Potassium burning on Water. 



oi great importance, but 



the salts, potassium carbonate, potassium nitrate, potas- 

 sium chloride, and potassium sulphate, are of the utmost 

 importance to the farmer. 



Note. On account of its affinity for O, the metal potassium is 

 kept in petroleum or naphtha, which contains no O. The metal should 

 be cut into small pieces about the size of a pea for placing on water. 

 As there is a slight explosion as the last particle is consumed, one should 

 not stand too close to the dish. 



Potassium Chloride (KC1), sometimes called mu- 

 riate of potassium. This potassium salt, more than any 

 of the other potassium compounds, is used as a fer- 



M, & H. AG. 4 



