AIR IN SOIL AND WATER 



73 



the soil contracts again and more air enters to take the 

 place left by the contraction. Since plant roots need air, 

 can you see the advantage of cool nights during the sum- 

 mer? 



Water also contains air, as was learned from the last 

 experiment. In the next experiment we will see just 

 how much air is held in water when it is cold. 



Experiment 37. To Show the Presence of Air in 

 Soil and Water. 



Apparatus: Tin can, glass, two test tubes, one-hole 

 stopper, glass tube two feet long, burner. 



Materials: Soil, water. 



a. Fill the tin can nearly full of dry soil, loosely 

 packed, and quickly pour a glassful of water upon it. 

 What do you notice? What can you say about the 

 presence of air in soil? 



b. Throw away the wet soil and fill again with 

 loosely packed, dry soil. Fill the glass even 



full of water and pour it slowly upon the soil, 

 not allowing the top of the soil to be covered 

 with water at any time. Continue to add 

 water until the soil will take no more and the 

 water surface comes up to the surface of the 

 soil. How much water have you added? 

 How much air was there in the soil? 



c. Arrange the apparatus as shown in the 

 illustration. To bend glass tubing it should 

 be held in the flame of an ordinary gas 

 burner, or an alcohol lamp, or in the flame 

 produced by an attachment for the Bunsen 

 burner, as shown in the illustration, called a 



