204 



SOIL PHYSICS AND MANAGEMENT 



from the covered and from the exposed soil and the moisture con- 

 tent determined. The results are given in the table. 



Water Per cent of Dry Soil, Covered and Uncovered, at Different Dates (King) t 



In the protected soil there was not only no gain by capillarity 

 from the sides or from below, but an actual loss occurred. 



2. Viscosity. Viscosity is the resistance that liquids offer to 

 the movement of molecules against each other. This property is 

 well seen in s} r rups, but we do not ordinarily think of water as pos- 

 sessing any large amount of viscosity or showing any variation 

 in this respect under different conditions. A somewhat higher 

 viscosity increases the surface tension of the film, but at the same 

 time retards the rate of movement by lessening the fluidity and 

 freedom of movement. 



(a) Temperature. - - Variations in the temperature of water 

 change its viscosity, a higher temperature diminishing and a lower 

 increasing it. Increasing viscosity increases surface tension. It 

 has been determined that if the viscosity of water at zero C. is taken 

 as 100, then the viscosity at 25 degrees is 50, at 30 degrees 45, and 

 at 50 degrees 31.* This variation influences the capillary move- 

 ment of moisture in soils to some extent. 



The next table shows that capillary movement is more rapid at 

 higher temperatures, indicating that the greater fluidity produced 



Effect of Temperature on Rise of Capillary Moisture, 9 University of Illinois. 

 Height in Inches in 24 Hours 



