30 



CHEMICAL COMPOSITION OF SOILS 



plain the chemical composition of soils, the following table has been 

 constructed which may serve as a key to the knowledge of chemistry 

 required in further study. Only the more common and important 

 elements are named. The more common oxides are also named 

 for the purpose of avoiding any confusion when these names 

 are used. The chemical symbols^ and formulas will help to 

 fix in mind the differences between some of the elements 

 and their oxides. 



Chemical Composition of Dry Soils Expressed as Elements and Some of 



Their Oxides 



Mineral elements 



Symbols of 

 elements 



Oxides of elements 



Formulas of 

 oxides 



Silicon 



Aluminum.. 



Iron 



Calcium 



Magnesium . 



Sodium 



Potassium . . 

 Phosphorus . 



Sulfur 



[Non-mineral] 

 Carbon — 

 Nitrogen . . . 

 Hydrogen . . 

 Oxygen 



Al 

 Fe* 



Ca 

 Mg 



Na* 

 K* 

 P 

 S 



C 



N 



Jtl 







Silica 



Alumina . , 

 Iron rust . 



Lime 



Magnesia. 



"Potash" 



"Phosphoric add" 

 Sulfur fumes 



Carbon dioxide. 



Si02 

 AI2O3 



CaO 



MgO 



K^b 

 P2O& 



SO3 



CO2 



* It is to be observed that the symbols of ten of these elements are derived from their 

 common names. The symbols for iron, sodium and potassium are derived from their Latin 

 names; viz., ferrum (Fe), natrium (Na) and kalium (K). 



Elements Exist in Combined Forms. — These elements do not 

 exist in soils separate from each other, but occur in united forms. 

 Two or more are combined to form the soil particles which can be 

 seen. For example, a sand, silt or clay particle may represent a 

 combination of silicon and oxygen; or potassium, aluminum, 

 silicon and oxygen; or calcium, magnesium, carbon and oxygen, 

 etc. A particle of organic matter may represent a complex com- 

 bination of nitrogen with practically all the elements. 



The Elements and Their Characteristics. — Oxygen is the most 

 common and abundant element on the earth. In the free state it 

 is a colorless, odorless and tasteless gas slightly heavier than air, 



2 Chemical symbols are abbreviations to represent chemical elements and 

 formtdas represent compounds. For example, the sjnnbol for oxygen is "O," 

 for carbon "C' The formula for water is "H2O,'' meaning water is oxygen 

 united with two atoms of hydrogen. 



