PERCOLATION 



87 



eolation recommenced and was duly recorded, the whole 

 experiment lasting for 268 days. 



TABLE XIII 



WATER DRAINING FROM EIGHT FEET OF SATURATED SANDS, 

 PER 100 OF DRY SAND (KING) 



During the intermittent percolation of the last 259 days 

 the sands lost from 6-56-9-15 Ib. of water per square foot, or 

 considerably more than one inch of water l . This intermittent 

 percolation deserves attention ; it is doubtless due to the vary- 

 ing temperature and pressure of the atmosphere. A rise in 

 temperature will act in several ways to start percolation 

 in a soil in which the water had previously reached a state 

 of equilibrium. As the temperature rises water becomes less 

 viscous and its surface tension diminishes ; drainage therefore 

 recommences in the sand column, the water films coating the 

 upper fully drained portion becoming thinner and some of the 

 water passing downwards. The amount capable of being held 

 in the capillary passages at the foot of the column is also 

 diminished. A rapid expansion of the air within the column 

 will also cause the expulsion of a part of the water collected 



One inch of water on a square foot is roughly 5.2 Ib. 



