OXYGEN FOUND EVERYWHERE. 7 



watery vapor, and commonly has floating in it smoke and 

 dust, and minute portions of various gases which serve as 

 food to plants, the most important of which are ammonia 

 and sulphuretted hydrogen. 



21. Oxygen is the vital part of the air that which 

 is essential to our life, and also to combustion. It is 

 invisible, and has no taste or smell. Oxygen is thought 

 to be a simple substance; that is, no person lias ever 

 succeeded in showing that it is a mixture or compound 

 of any two substances. It is therefore called an Element, 

 or elementary substance. 



It is one of the most abundant and widely diffused 

 substances known. It forms eight parts out of nine, by 

 weight, in the composition of water. It enters into the 

 composition of nearly all the rocks and different kinds of 

 earth, and is one of the constituents of all portions of the 

 bodies of plants and animals. 



22. A considerable portion of every known rock is 

 oxygen, combined with some other element. How it got 

 into the rocks we do not know. Oxygen has a strong 

 tendency to penetrate into every thing ; it has a great 

 attraction for iron, copper, lead, and most of the other 

 metals, and for nearly all the other substances of which 

 earths are composed, and combines with them intimately, 

 and completely changes their appearance and properties. 

 Iron left for any time in moist air rusts, or is gradually 

 covered with a dirty reddish substance, which we calf 

 rust, which is made up of oxygen and particles of the 

 iron with which it has united. This the chemists call 

 oxide of iron. The iron has been oxidized. 



This oxide of iron is often found in the earth in great 

 quantities, forming a brownish, heavy dirt or earth ; some 

 times beautiful rocks or ores. Similar earths or minerals 

 2 



