THE FORMS OF SOIL WATER 



215 



coarse soil. Due to these two conditions, a soil of fine 

 texture will contain considerably more capillary water 

 than one of which the texture is coarse. The maximum 

 capillary capacity of a soil is not directly proportional to 

 the surface, as was roughly proved to be the case with 

 the hygroscopic coefficient. This is probably because 

 the angle exposures between the grains increase in number 

 as the texture becomes finer much faster than the actual 

 surfaces developed by the particles are generated. The 

 capillary water in any soil varies with the height of the 

 column. This comes about from the gravity effects 

 on the liquid surrounding the particle. If the liquid had 

 no weight, gravity would not be a factor and the same 

 thickness of film would be found at 

 any point in a soil column. Such a 

 condition would greatly simplify the 

 study of soil moisture. If a number of 

 particles (see Fig. 33) carrying maxi- 

 mum capillary films are brought together 

 vertically, the weight of the whole con- 

 ducting film is thrown momentarily on 

 the capillary surfaces at the top. The 

 capillary spaces at this point immediately 

 lose water downward, so that they may 

 assume a greater curvature and thus 

 support this extra weight thrown on 

 them. This curvature must be sufficient 

 to balance the curvature pressure of the 

 particles below plus the weight of the 

 water in the connecting films. The par- 

 ticles beneath are at the same time un- 

 dergoing a similar adjustment with a set of particles still 

 farther below, losing water in order to allow a change of 



Fig. 33. — Diagram 

 showing the ad- 

 justment of the 

 capillary film in a 

 long column and 

 the appearance of 

 free or gravita- 

 tional water if the 

 weight is too 

 great for the sup- 

 porting films. 



