CHAPTER XVIII 

 Potassium, Sodium, and Their Compounds 



152. Occurrence of Potassium. Potassium is found in 

 nature largely in combination with silicon and other ele- 

 ments, forming silicates, which undergo slow disintegra- 

 tion with liberation of potassium salts which become food 

 for plants. Potassium is present in the ash of all plants 

 and food materials and is one of the elements required by 

 crops. In some " alkali" soils, small amounts are found 

 in the form of potassium salts. Deposits of various 

 double salts of potassium, supposed to have been formed 

 by crystallization from sea- water, are found at Stassfurt in 

 Prussia, and are commonly known as Stassfurt salts. These 

 are the chief source of the potassium compounds, some of 

 which are extensively used in the preparation of fertilizer. 



The element potassium is most typical of all the base 

 elements as a class. It is never found in nature in 

 a free state, but always in combination with other ele- 

 ments from which it is separated with difficulty. It is a 

 light substance with a metallic luster, and in the labora- 

 tory is kept out of contact with air and water, with which 

 it readily reacts. 



153. Potassium Hydroxid. This is a strong basic 

 compound extensively used in the laboratory and in 

 manufacturing operations. It is prepared by treating 

 K 2 CO 3 with Ca(OH) a , the reaction being K 2 CO 3 + 

 Ca(OH) 2 CaCO 3 +2KOH. CaCO 3 is insoluble and 

 can be separated by filtering from KOH which is soluble. 



