42 



PRACTICE 20 



Determination of the Rate of Percolation of Air Through 

 Soils 



This experiment requires the utmost care in order to obtain 

 satisfactory results. Use the same aspirator* for all of the soils. 

 Be sure that all connections are air tight. Use pressure tubing. 



Fill the tubes very carefully without compacting, holding them 

 vertically while filling. Attach the tubes successively to the aspirator 

 after the can has been lowered in the water to the zero mark. Allow 

 at least 4 litres of air to pass through each soil and express results in 

 time required for 10 litres of air to pass through. Empty tubes and 

 refill and run again as a check. 



Use sand, loam and clay, compacting by letting the weight fall 

 three times from the foot mark upon each measure of soil. Tabulate 

 your results for both loose and compact. 



What bearing has this experiment upon aeration? 



What effect does organic matter have on aeration? 



What effect will moisture in the soil have upon aeration? 



Try it by wetting the tube of sand and then drawing air through 

 it. 



One student may run sand with 10 grams of organic matter (peat) 

 and another clay with the same proportion and compare with the 

 results from the stock sand and clay. Give to the class for compari- 

 son. 



♦The aspirator B is made of galvanized iron, 8 inches in diameter and about 18 inches 

 long fitted with a stopcock to which the rubber tube is attached that runs to tube D in 

 which the soil is placed. The aspirator fits loosely in a can C filled with water. Tube D 

 is made of galvanized iron and is 2 inches in diameter and 18 inches lonif with a tube for 

 attaching to the rubber tube from the aspirator. A is the weight and should be at least 

 twice as heavy as can B. 



