PRACTICE XXXVI 



DETERMINATION OF COEFFICIENT OF EVAPORATION 



Fill six evaporimeters l with the same soil to within 1 inch of 

 the top. Compact all uniformly. 



Fill all tubes to the top as desired, or as follows : 



No. 1, check (filled to top with the same kind of soil). 



No. 2, 1 inch of sand. 



No. 3, 1 inch of peat. 



No. 4, 1 inch of sawdust or cut straw. 



No. 5, 1 inch of gravel. 



No. 6, pan of same area-filled with water. 



The tubes should be 6| inches in diameter so as to have an 

 area of exactly 36 square inches, ^ of a square foot, or jy^i'o 

 of an acre. 



The base should be filled with water through the tube, and 

 the water allowed to come up by capillarity through the soil. 



Refill the base and place a cork or rubber stopper in the tube 

 to avoid loss of water by evaporation. 



Weigh the evaporimeter and record its weight. Weigh at 

 24-hour intervals for 1 week. 



It is absolutely essential that all evaporimeters have the same 

 exposure to heat and air currents. It may be well to conduct 

 this practice in a greenhouse or in the open air early in the 

 first or late in the second semester. 



Find the coefficient of evaporation, the loss in pounds per 

 acre during a period of 24 hours. 



Compute the amount of evaporation in tons of water per acre 

 and in acre inches per week. Tabulate results. 



REFERENCES. 



" Soils," Lyon and Fippin, pp. 195-215. 

 " The Soil," Hall, pp. 89-119. 



" Physical Properties of Soil," Warington, pp. 107-118. 

 " Soils," Hilgard, pp. 254-262. 



"Principles and Practice of Agricultural Analysis," Wiley, Vol. I, 

 pp. 160-162. 



1 An evaporimeter similar to that described by Wiley in his " Principles and 

 Practice of Agricultural Analysis," Vol. I, p. 160, has been in use here for more 

 than ten years. It is better to have a perforated bottom in the tube, whose sides 

 extend to and stand on the bottom of the base. It will be necessary to have holes in 

 the sides of the tube below the perforated bottom to admit water to the soil. 



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