Hate of Percolation of Soil Water. 



159 



impedes percolation except in those cases where wide 

 shrinkage checks and cracks have resulted. 



Where percolation is influenced chiefly by soil texture it 

 is most rapid through the sandy soils and the more granu- 

 lated clay types. It is least rapid through the puddled 



188. Rate of Percolation Through Sands. When the sim- 

 ple sands are once completely filled with water the perco- 

 lation from them is quite rapid but decreases with the size 

 of the sand grains. In the table below is given the 

 amount of water which percolated from the columns of 

 sand referred to in (160). 



fable giving the rate of percolation from sands under the 

 gravitational head of the inclosed wetter. 



It will be seea. from the above table that the rate at which 

 the water moved downward through the coarsest or No. 20 

 sand was such as to average during the first thirty minutes 

 492 inches per twenty-four hours, while for the finest or 

 Xo. 100 sand the mean rate was 58.16 inches, the flow 

 from the first being nearly 8.5 times as fast, with grains 

 not quite 6 times as large. 



After the end of the first nine days of percolation these 

 coarse sands lost about 1.7 per cent, of their dry weight in 

 each case, or only about .33 of an inch. 



189. Rate of Percolation from Soils. The percolation of 

 water from the sandy loam and from the clay soil, given 



