52 LIVING IN AN OCEAN OF AIR 



carbon acids kindled cold 



water weak chemical put 



vapor light action carbon 



melt germs hydrogen dark 



It is fortunate for us that (1) constantly surrounds us. 



If there were no (2) in water, fish would die. The part of 



the air that helps things to burn is (3) and (4) which makes 



up four fifths of the (5) will (6) a flame. Moist air causes 



iron to (7) in a process called (8) Combustion is (9) 



in which both (10) . and (11) are produced. Two impor- 

 tant compounds produced when a candle burns are (12) and 



(13) (14) Limewater is used to test for the presence 



of (15) (16) 



STORY TEST 



RUTH TELLS WHY AIR Is USEFUL TO MAN 



Read carefully and critically. List all the errors and suggest cor- 

 rections. 



Air is the medium which extends far out into space from the 

 earth, and if man ever reaches the moon, it will be by sailing 

 through the air which connects the two bodies. Two bodies of 

 matter cannot occupy the same space at the same time. It is 

 for this reason that there is no air in soil or in water. Air is a 

 mixture. Oxygen and hydrogen make up about 97 per cent of 

 the air. If there were no carbon dioxide in the air, fires once 

 started could not be extinguished. A burning candle adds oxygen 

 and water to the air. Iron can be burned in oxygen. The com- 

 bustion oi iron is called rusting, and the burning of coal is rapid 

 oxidation. Paint is used on iron bridges because air hardens the 

 paint and makes a tough coating, which increases the strength of 

 the bridge. Limestone is used as a test for carbon dioxide. Air 

 supplies man with helium for airships, and carbon dioxide for 

 charging soda water. The most important use of air is for air- 

 planes and airships. 



PROBLEM H. OF WHAT IMPORTANCE IS 

 ATMOSPHERIC PRESSURE? 



Why Air Can Exert Pressure. Have you ever noticed 

 how dust and other light objects, as loose papers, will rush 



