PART II. 



AIR. 



CHAPTER XVIII. 



Q. Of what is atmospheric AIR composed ? 



A. Principally of two gases, oxygen 

 and nitrogen; mixed together in the 

 following proportion : viz. 1 part of 

 oxygen, to 4 parts of nitrogen. 



Q. What are the uses of the OXYGEN of the 

 air ? 



A. It is the oxygen of the air which 

 supports combustion, and sustains life. 



Q. What is meant when it is said, that the 

 OXYGEN of the air " SUPPORTS COMBUSTION ?" 



A. It means this; that it is the 

 oxygen of the air which makes fuel burn. 



Q. How does the OXYGEN of the air make 



FUEL BURN ? 



