54 SOILS 



breath of fresh air, you take oxygen into your lungs. So 

 oxygen, therefore, must be a common element. And so it 

 is both common and abundant more so than any other 

 element in the world. Just think of this: one-fifth of the 

 atmosphere, three-sevenths of all the plants, one-half of 

 the entire solid crust of the globe, and eight-ninths of all 

 the water are formed of oxygen, and thousands and thou- 

 sands of other substances besides. 



Oxygen is a gas tasteless, colorless, and odorless. 

 You neither can see nor feel it, nor can you taste or smell 

 it. It is slightly heavier than air, and is moderately active 

 at ordinary temperature, but at higher temperatures it is 

 one of the most violent and powerful chemical agents 

 known. 



Oxygen possesses strong chemical affinity for other 

 elementary substances : with most of these it is found in 

 combination fluorine excepted. These combinations are 

 made with great intensity. This gas has power of sup- 

 porting combustion in an eminent degree. 



Here are just a few of its combinations: 



1. With hydrogen it forms water just common water. 



2. With nitrogen (mixed but not combined) it forms 

 air. 



3. With silicon it forms sand. 



4. With calcium and carbon it forms limestone and 

 marble. 



5. With aluminum, hydrogen, and silicon it forms mar- 

 ble and all the varieties of clay. 



Besides these inorganic combinations, oxygen is found 

 in all the tissues and fluids of plant and animal life fat, 

 starch, protein, fiber, etc. none of which can support 

 existence independently of this element. 



Hydrogen : the lightest of known substances. The 

 lightest of all known substances is hydrogen : a gas 



