$2 GENERAL SCIENCE 



it easier to raise the temperature of the match to the kind- 

 ling point. Safety matches can be lighted only on the pre- 

 pared surface of the containing box or on plates of glass 

 like window panes. They were first made in Swdeen. 



38. When any substance unites with oxygen the 

 process is called oxidation. This may occur very slowly 

 and at a low temperature, as the rust on iron is formed 

 by oxygen uniting with the iron, producing an iron oxide. 

 Most metals will unite with oxygen to form oxides, but 

 not so rapidly as iron. In all kinds of animal life oxida- 

 tion takes place, and the heat evolved produces the 

 energy that enables the animals to move about An 

 animal could not move if oxidation should stop in its 

 body. There are many one-celled, microscopic animals 

 and plants which live by eating larger dead animals and 

 plants, producing what is commonly called decay. The 

 one-celled animals and plants take in oxygen and give 

 off carbon dioxide, and so when they eat up other animals 

 and plants the process which we think of as decay is 

 really oxidation. When carbon or its compounds are oxi- 

 dized, a gas is formed which is known as carbon dioxide. 



QUESTIONS AND EXERCISES 



1. Make a collection of various kinds of matches. Which can 

 most easily be lighted? Why will some light if you step on them 

 and others will not? 



2. Why will damp hay in a barn sometimes ignite? 



3. What may happen if you store away a large pile of rags, some 

 of them oily ones? Why? 



4. What material would you use to start a wood or coal fire? 

 How would you arrange the material? 



5. What use is made of a large part of the food which we eat? 



