214 soils: properties and management 



nature. A lowering of the temperature would eause a 

 change in the opposite direction. This theory lias been 

 verified by certain experiments by King, 1 in which he 

 found, other conditions being constant, a very decided 

 influence on capillary water through change of tempera- 

 ture. Wollny  has shown that a depression of from .65 

 per cent in sand to as high as 3.7 per cent in kaolin may 

 occur from a rise in temperature of twenty degrees. The 

 surface tension of a liquid may also he greatly changed 

 by the addition of salts, and, since the soil always carries 

 some material in solution, the surface tension, and conse- 

 quently the capillary capacity, might be expected to 

 increase. As a matter of fact, the soil solution is very 

 dilute, and even if large amounts of fertilizer salts were 

 added the adsorptive power of the soil would tend to 

 maintain a very dilute soil water at the surface of the 

 films. Again, as humus decay is continuously going on, 

 oily materials are probably produced which would tend 

 to spread over the capillary films and greatly reduce their 

 surface tension. Therefore, as far as is now known of the 

 two varying influences, temperature change is by far the 

 most potent in its influence on capillary capacity. 



144. Texture and the amount of capillary water. — 

 The finer the texture of a soil, the greater is the number 

 of angles between the particles in which a film of capillary 

 water may be held ; also, the actual amount of surface 

 exposed by the particles is immensely larger than in a 



1 King, F. H. Fluctuations in the Level and Rate of Move- 

 ment of Ground Water. U. S. D. A., Weather Bur., Bui. 5, 

 pp. 59-61. 1892. 



2 Wollny, E. Untersuchungen iiber die Wasserkopacitat der 

 Bodenarten. Forsch. a. d. Gebiete der Agri.-Physik, Band 9, 

 Seite 361-378. 1886. 



