SIM PIE MOLECULES 103 



eighty different substances whose molecules are composed of 

 atoms which are alike. When the atoms comprising a mole- 

 cule are all alike, the substance is called an element, and is 

 said to be a simple substance. Throughout the length and 

 breadth of this vast world of ours there are only about eighty 

 known elements. An element is the simplest substance con- 

 ceivable, because it has not been separated into anything 

 simpler. Water is a compound substance. 'It can be sepa- 

 rated into oxygen and hydrogen. 



Gold, silver, and lead are examples of elements, and water, 

 alcohol, cider, sand, and marble are complex substances, or 

 compounds, as we are apt to call them. Everything, no 

 matter what its size or shape or character, is formed from the 

 various combinations into molecules of a few simple atoms, of 

 which there exist about eighty known different kinds. Per- 

 haps this can be made clearer by comparison with the con- 

 struction of our own language. Every word, no matter what 

 its size or meaning, is formed from varying combinations of 

 the twenty-six letters of the alphabet. " Too " might be 

 thought of as representing water, which is composed of two 

 distinct kinds of atoms, oxygen and hydrogen. 



