86 SOILS AND FERTILIZERS 



Procedure. — Carefully obtain the weight of an evaporating dish 

 on the balance. Then weigh into the dish 50 grams of the soil to 

 be tested. Air dry sample in laboratory and then place it in air 

 oven at 100° C. for two hours. Cool in desiccator and weigh. The 

 loss in weight is water. Calculate the percentage of moisture 

 based on absolutely dry soil. 



Make this determination in duplicate and on a number of soils. 

 Calculate the amount of water in an acre foot of the various soils, 

 considering them to weigh 3,500,000 pounds per acre foot. Note 

 relation of soil moisture content to bare and cropped soil, kind of 

 crop, stage of growth and previous rainfall. 



Exercise II. — Capillary movement in different soils. 



Materials. — Dry samples of pulverized sandy loam, silt and 

 clay, three long glass tubes 2 inches in diameter, pans for water and 

 cheesecloth. See Plate IX. 



Procedure. — Neatly cover the ends of the three long glass cylin- 

 ders by tying over them two thicknesses of cheesecloth. Fill cylin- 

 ders with the respective soils to be studied. Be sure that the 

 compaction is uniform. Now set the ends of the cylinders in water 

 one inch deep and observe the height of capillary movement at the 

 following periods after starting : 1 hour, 2 hours, 12 hours, 1 day, 

 2 days, 3 days, 4 days, etc. Continue experiment as long as prac- 

 ticable. Tabulate data and draw curves. Explain the practical 

 importance of the results obtained. 



Exercise III. — Rate of percolation of water through soils. 



Materials. — Dry, well-pulverized sand and clay loam, two lamp 

 chimneys, cheesecloth, torsion balance. See Exercise V, Chapter V. 



Procedure. — Prepare two lamp chimneys by neatly tying two 

 thicknesses of cheesecloth over their bottoms. Place in one a 

 definite and known amount of sand. In the other place the same 

 weight of clay loam. Give each a uniform compaction. Now weigh 

 each chimney with its content of soil. 



Place the chimneys in such a position as to allow free drainage 

 and add the same amount of water to each, keeping the head of water 

 constant in each chimney. Observe the rate of the downward 

 movement of water through the two soils. When percolation has 

 begun, measure percolate for 15 minutes and express rate in cubic 

 centimeters per hour. 



Explain the reasons for the results obtained and the practical 

 importance thereof. 



