Introduction. 13 



plant food and in the soil is present in a variety of forms, as 

 calcium carbonate, calcium sulphate and calcium phosphate. 



Potassium (K) occurs in many minerals. It will be found in 

 many silicates, as orthoclase or mica, which are complex com- 

 pounds of potassium, silicon, aluminum, oxygen and other ele- 

 ments. It also occurs in sea water, from which sea weeds accu- 

 mulate large quantities of potassium compounds. The immense 

 salt deposits at Stassfurth, Germany, furnish a large proportion 

 of the potassium used in our potash fertilizers. 



The element is a lustrous metal, very soft, and so susceptible to 

 change in the air that it must be kept away from contact with 

 air or moisture by immersion in naphtha. By contact with water 

 it reacts violently, producing much heat and floating on the sur- 

 face of the water with a hissing sound. 



Potassium compounds are of the greatest importance in agri- 

 culture and are necessary constituents of all fertile soils. They 

 are intimately associated with the growth and increase of plants 

 and are always found in greatest abundance in the twigs, young 

 leaves and other rapidly growing portions. In some plants the 

 potassium is in combination with certain organic acids, as citric 

 and tartaric acids. In the ash of plants that which is left after 

 burning it generally occurs as a carbonate. Potassium salts are 

 very soluble in water, but are absorbed and retained by certain 

 constituents of the soil, so that their loss by drainage from soil 

 is little to be feared. 



Sodium (Na) is very widely distributed in nature and is a con- 

 stituent of many silicates. In the form of sodium chloride a 

 compound of sodium and chlorine it is very plentiful as rock 

 salt and as the largest saline constituent of sea-water. 



Its properties resemble those of potassium. Sodium compounds 

 are largely used in the arts and the preparation of sodium car- 

 bonate is one of the largest and most important of chemical in- 

 dustries. 



Sodium is found in the ash of most plants, but, except in the 



