10 



BULLETIN 447, U. S. DEPARTMENT OF AGRICULTUEE. 



The smaller quantities of water penetrated practically as deep as 

 the larger amounts tha,t stood for a much longer time. In five min- 

 utes the water in hole No. 17 penetrated to a depth as great as was 

 reached by that in some of the others in several days. 



There is an apparent lack of consistency in the time required for 

 some of the larger quantities of water to disappear. This is due to 

 the fact that in some cases the amount of water added was sufficient 

 to raise the water level to a point that allowed it to escape laterally 

 through the cracked soil. This is shown also by the lack of differ- 

 ence in the depth of penetration of the different quantities. The 

 best measure of time and depth of penetration is found in hole No. 

 24, in which a supply of water was maintained by the addition of 

 2 gallons at three separate times. Ten days were required for the 



Fig. 4. — Diagram showing the time taken for various quantities of water to disappear 

 and the depth of penetration in each case from the bottoms of a series of holes 8 

 inches in diameter and 18 inches deep. The heavy lines indicate the lowest points 

 reached by the water from the different holes. 



disappearance of the entire quantity, but the total depth of pene- 

 tration during this time was only a little over an inch more than it 

 was from those holes in which water stood for a much less time. 

 These experiments indicate that while the water movement is com- 

 paratively rapid in the dry soil it is very slow in the wet soil. 



Since there is no evidence of a layer of soil actually impervious to 

 water, it appears that the exceedingly slow movement of water is due 

 to the fact that the soil in contact with the water quickly becomes so 

 swollen and compact that further movement of water within it is 

 very difficult. Penetration into the dry soil almost stops, not because 

 of the resistance offered by the dry soil itself, but on account of 

 the extremely slow movement of the water through the layer of wet 

 soil that is between the source of water supply and the dry soil. 



