CHAPTER I. 



CHEMICAL ELEMENTS NEEDED BY PLANTS AND THE COMPO- 

 SITION OF PLANTS. 



In order to thoroughly understand the subject "fertiUzers," 

 we must become familiar with the chemical elements needed 

 by plants. 



There are about 8i chemical elements known to us, but only 

 15 of these are required for plant life so far as we know. 



The Fifteen Elements. — Hydrogen, oxygen, nitrogen, carbon, 

 potassium, phosphorus, calcium, sulphur, silicon, iron, chlorine, 

 magnesium, sodium, aluminum and manganese are the elements 

 used by plants. Hydrogen, oxygen, nitrogen and chlorine, in 

 the pure state, generally occur as gases, w^hile the other ele- 

 ments are solids. 



The Symbols. — The chemist uses the following symbols for these 

 elements. 



Hydrogen (H) Oxygen (O) Nitrogen (N) 



Carbon (C) Potassium ( K ) Phosphorus ( P ) 



Calcium (Ca) Sulphur (S) Silicon (Si) 



Iron (Fe) Chlorine (CI) Magnesium (Mg) 



Sodium (Na) Aluminum ( Al) Manganese (Mn) 



Small amounts of oxygen are sometimes used by plants in the 

 elementary state. Certain plants also use nitrogen in the free 

 state. All other elements, and generally oxygen and nitrogen 

 must be combined with other of these elements to be favorable 

 for the support of plant life. 



Hydrogen. — This is a colorless invisible gas, having no smell 

 or taste. It is generally found in combination with other ele- 

 ments as water, hydrochloric acid, marsh gas, sulphuretted hy- 

 drogen, all acids and most organic (animal and vegetable) com- 

 pounds. It is mo.st commonly found as water (HoO), which 

 is the most necessary food of the plant. In the free state hydro- 

 gen occurs only in small quantities upon the earth in the gases 

 of petroleum w-ells, around volcanic eruptions, and it is evolved 

 by the fermentation and decomposition of some organic sub- 

 stances. 



