THE SUBSTANCES OF THE EARTH. 



9 



A Drop of Water. 

 (Magnified.) 



the other hand, we cannot form any idea of the minute- 

 ness of matter. 



Powerful microscopes have revealed forms of animal 

 life which had never before been conceived of. It is 

 known that multitudes of liv- 

 ing beings may occupy a single 

 drop of water. 



An atom is the smallest 

 particle into which matter can 

 be divided. We may repeat- 

 edly subdivide a piece of gold 

 until it is reduced to the 

 thousand-millionth part of an 

 ounce, and yet we shall be 

 far from reaching a single 

 atom. If it were possible to 

 continue the process long enough, a particle would finally 

 be obtained which could no longer be divided or changed 

 in any respect. 



An atom of oxygen is always exactly the same, whether 

 it forms a part of the soil, or of the air, or enters into the 

 structure of a plant or an animal. 



An atom is represented by the symbol which is used 

 to denote the kind of substance. The symbol may 

 denote a quantity of oxygen in general, or an atom of 

 oxygen. A number of atoms is indicated by a figure 

 written below, and to the right. 2 denotes two atoms 

 of oxygen, H G six atoms of hydrogen. 



Molecules. Atoms do not generally exist alone. They 

 possess a force of attraction which causes them to unite 

 with other atoms, either of the same kind or of a differ- 

 ent kind. 



This force is called chemical affinity. It causes atoms to 



