CH. II j 



The Soil Air 



31 



When the soil becomes waterlogged, however, the 

 percentage of oxygen may fall very considerably so that 

 insufficient is left for the organisms to carry on their 



A 



Fig. 11. Apparatus for demonstrating the presence of CO2 in soil air. 



A. Aspirator. 



B. J" gas pipe driven into soil. 



C. Tube of baryta water open to air. 



D. connected to soil. 



usual functions. Undesirable changes may then set in. 

 The presence of more carbon dioxide in the soil air than 

 in the atmosphere is readily demonstrated by driving a 

 I inch gas pipe to a depth of 6 inches in the soil and con- 

 necting it with a test-tube containing 20 c.c. of baryta 



