52 PROPERTIES AND MAKE-UP OF MATTER 



iron, copper, tin, aluminum, lead, zinc, mercury, gold, 

 silver, nickel. The gases hydrogen, oxygen, and nitrogen 

 are also elements. 



Most substances are compounds. The number of com- 

 pounds as compared with the number of elements in nature 

 may be illustrated in this rough way. There are only 26 

 letters in the English alphabet, but these may be combined 

 in so many different ways that we have thousands of English 

 words. Just so there are to our knowledge only about 

 eighty different elements in the world. But these elements 

 unite in so many different ways and in so many different 

 proportions that we have innumerable compounds. 



But the comparison of letters and words with elements 

 and compounds must go no farther than to show how many 

 more compounds there are than elements. The eye can 

 pick out all the different letters that compose every word. 

 But when the atoms of different kinds of elements combine 

 into molecules, the resulting compound substance is so 

 different from the elements composing it that there is no 

 apparent relationship. 



Water furnishes a good illustration. Oxygen is a gas 

 that must be present wherever there is burning. Hy- 

 drogen burns very readily in the presence of oxygen. But 

 water, every molecule of which is made up of atoms of these 

 two gases and is the result of the burning of hydrogen in 

 oxygen, is our main dependence for putting out fires. 



Physical and Chemical Changes. Experiment 16. Mix a 

 little powdered sulphur with about half as much powdered iron or 

 very fine iron filings. Examine the mixture with a magnifying glass. 

 You can easily distinguish between the particles of iron and sulphur. 

 Put the mixture into a test tube and heat it over a Bunsen burner. 

 (Figure 22.) The mixture will glow and become a solid mass. 



