134 



Physics of the Soil. 



160. Influence of Distance Above Standing Water on the 

 Water Capacity of Soils. When the distance to the ground- 

 water is considerable the force of surface tension is not 

 great enough to maintain as much water in the soil as when 

 the distance is less, and the table which follows shows how 

 the amount of water retained varies with the distance. The 

 sands and soils were placed in an apparatus represented in 

 Fig. 41, arranged so as to permit free percolation but allow- 

 ing very -little evaporation from the surface. The sand 

 columns were 8 feet long and percolation was allowed to 

 continue nearly 2.5 years. The soil columns were 7 feet 

 long and percolation from them was continued during 60 

 days, at the end of which time the tubes were cut into short 

 sections and the amount of water still retained determined 

 by drying. 



Percentage distribution of water left in columns ofsand t sandy 

 loam and clay loam after percolation had continued two 

 and one-half years with the sand and 60 days with the soils. 



