PERCOLATION OF WATER 



77 



Calculation of Results. — The water-holding capacity 

 of the soil should be stated as percentage volume of 

 water contained in the soil. Thus, if 



z£; = Weight of moisture in soil, 



W = Weight of water absorbed, 



V = Volume of soil. 



Then, water-holding capacity 

 _ (ze/ + W) lOO 

 ~V 



The experiment should be 

 carried out with sand, with fine 

 earth from a loam and from a 

 clay soil, and also with a peaty 

 soil or sand mixed with organic 

 matter. The results should be 

 compared with the air-space, 

 determined as in 54. 



57. Percolation of Water in 

 Soils. 



A small percolator (Fig. 13) 

 is fitted at the bottom with a 

 piece of wire gauze, and is then 

 filled up to a definite mark, 

 about 2 inches from the top, 

 with the soil under examina- 

 tion, the sample being compacted 

 by gentle tapping. Water is 

 then added, and a constant level 

 is maintained by inverting a 

 flask filled with water at the 

 required height, as in diagram. 

 The time taken for the water to reach the bottom, 

 and the number of cubic centimetres percolating per 



Fig. 13. — Apparatus for 

 measuring the rate of per- 

 colation of water through 

 soil. 



