SOIL AIR AND SOIL TEMPERATURE 



153 



a definite volume of sand. Now start as- 

 piration by opening the water-cock of the 

 bottle. When aspiration has become con- 

 stant, note time necessary to draw one liter 

 of air through the sand. 



Using clay loam in place of sand, run 

 the experiment again, bringing the water in 

 the aspirating bottle up to its original mark 

 before starting. The time necessary to pull 

 a liter of air through each soil serves as a 

 measure of the comparative rate of possible 

 air movement through them. 



Without removing the clay loam from the 

 funnel, add enough water to bring it to 

 optimum moisture condition. Repeat the 

 test above. Explain results. Fig. 26. — Apparatus 



Exercise II. — The presence of carbon *£/*$ y Jg ^tment 

 dioxide m soil an*. through soils. (A) soil in 



Materials. — Box of rich soil in good mois- funnel, (B) cotton sup- 

 ture condition, flask, limewater, tubes. P 1 ° rt ; 7 )f ) ater™^ ^ 



Procedure. — Equip a flask or bottle as 

 shown in Fig. 27 so that air from the soil may be sucked into the 

 limewater. The turbidity of the limewater indicates the presence 

 of carbon dioxide. 



j^="=J\ 



5ucuon 



Tube for ujtlhdrauJinq 

 / soil air 



Coarse sand 



Fig. 27. — Apparatus prepared for the demonstration of the presence of 

 carbon dioxide in soil air. 



