58 SOILS 



4. With humus materials when humic phosphates are 

 formed. 



Phosphorus is one of the elements usually lacking in 

 depleted soils, and when such is the case, it must be 

 supplied if productive crops are to be had. 



Chlorine: the salt maker. Chlorine is a gas of yel- 

 low-green color hence its name. In weight it is about 

 2 l / 2 times as heavy as air. When separated from its 

 compounds, it is exceedingly poisonous, and possesses 

 a very disagreeable odor. 



While it is abundant in nature its most common as well 

 as most important compound is common salt. 



Among its combinations may be mentioned: 



1. With sodium it forms common salt. 



2. With calcium and oxygen it forms chloride of lime. 



3. With mercury it forms corrosive sublimate. 



4. With ammonia and hydrogen it forms sal ammoniac. 

 Chlorine is found in all plants and soils, combined with 



other elements. 



The metals: potassium, sodium, calcium, magnesium, 

 aluminum, and iron. The chemist divides the elements 

 into two groups : the metals and the non-metals. We 

 have just discussed such non-metallic elements as are 

 used by plants. We are now to say a word about the 

 metals that are closely associated with plants. 



Potassium. This element is of a bluish-white color 

 and presents a strong metallic luster. It has a very great 

 affinity for oxygen. While potassium is somewhat widely 

 diffused, it does not exist in a native state only in com- 

 bination with other forms. When thrown on water, 

 potassium takes fire. 



In the early days before the soap factory came, water 

 was passed through wood ashes, thereby dissolving the 

 potash and leaching the same, to be collected and later 



