26 Practical Farming 



compacter of too light soil, and especially as a retainer of 

 moisture for the roots of crops. 



The agencies by which combinations are 

 The Chemical formed and broken up are not only chemical 

 of Soils ^^* biological, as we shall see later; for soil 



fertihty depends to a great extent on life in 

 the soil. A fertile soil is really a living soil, while a barren 

 soil is to a great extent dead. But our present lesson is 

 in regard to the chemistry of the soil. 



Chemists have discovered that the soil and air and 

 water are composed either of mixtures or chemical com- 

 binations of certain elements. An element is matter 

 reduced to its ultimate form, something in which we can 

 find but the one thing. The great advance in chemical 

 science, however, is still finding new elements, and find- 

 ing that some substances which have been regarded as ele- 

 ments may yet be divided into two or more elements. Some 

 of the well-defined elements are known as metals, such as 

 iron, potassium, aluminum, calcium, magnesium, sodium, 

 and manganese. Others exist in a gaseous form, such 

 as oxygen, nitrogen, hydrogen, etc.; while still others, 

 though non-metalHc, are found in a mineral state, as 

 silicon, carbon, sulphur, chlorine, and phosphorus. The 

 air we breathe is made up of a mixture of oxygen and 

 nitrogen, both free and not combined with each other, 

 the nitrogen being in the air as a diluent to enable us to 

 breathe the oxygen. For in free oxygen alone we should 

 soon burn up. Oxygen exists in the soil as a free gas 

 necessary to the roots of plants. It is also found in com- 

 bination with nearly all other elements and is the active 

 constituent of the mineral acids. 



