32 CHEMICAL COMPOSITION OF SOILS 



Sodium is never found in the free state, but always combined 

 with other elements. At ordinary temperatm^e sodium is soft 

 hke wax, and it is so active that it must be kept under petroleum 

 oil to exclude all oxygen and moisture. Common table salt is 

 sodium combined with chlorine (sodium chloride). All sodixma 

 came originally from rocks. 



Potassium is very similar to sodium in its chemical properties. 

 This element is never foimd in its puie form. Like sodium, it is 

 a soft, silver-white, wax-like metal which reacts vigorously with 

 water. Pure potassium, therefore, must be kept under petroleum oil. 

 Potassium is widely distributed in nature. A considerable amount 

 is present in mineral soils. It is found in the ash of plants in the 

 form of a compoimd called potash. Large amounts of potassium 

 salts are found in Germany and France. Potassium is a common 

 constituent of potash fertilizers. 



Phosphorus does not occur alone in nature because of its great 

 attraction for oxygen. In its pure form it is a pale yellow, wax- 

 like solid and very poisonous. Phosphorus is also a very active 

 substance. Since it catches fire easily in air it has to be kept 

 under water in air-tight cans. Phosphorus is a common constitu- 

 ent of bones and of compounds called phosphates. Soils con- 

 tain a comparatively small amount of this element. Most phos- 

 phorus of commerce is used in making matches. 



Sulfur is a common substance. It is yellow in color and may 

 occur as crystals or as flour. Many rich deposits of sulfur are 

 found in Texas, Louisiana and Mexico. It is also found in com- 

 bination with some of the metals, as lead, iron, zinc, etc. Sulfur 

 is much used in the making of sulfuric acid, black gun-powder, 

 hard rubber, etc. 



Carbon occurs in the free state as charcoal, graphite, coke, 

 soot, lampblack, bone black, diamonds, etc. Large quantities of 

 carbon are found in the form of coal, which represent the remains 

 of vegetation of past geological ages. Carbon is the most im- 

 portant constituent of all plants and animals. When carbon 

 burns it imites with oxygen and forms carbon dioxide gas 

 (CO2). Carbon in the soil is found mostly in the organic matter 

 and carbonates. 



Nitrogen in its free state is a colorless, odorless, tasteless and 

 inert gas. Air is 76.8 per cent nitrogen by weight. In the gaseous 

 form nitrogen does not combine to assist in life processes, yet in 

 combined form this same element is absolutely essential to all life. 



