Temperature and Capillary Moisture in Soils 



151 



can not be stated with certainty whether the thermal movement of water 

 would become zero at a still higher moisture content. From the theo- 

 retical point of view, however, it should not become zero, because the 

 pull due to the surface tension of water alone is not affected bv increase 

 of moisture content, but remains constant. The portion of pulling force 

 which is decreased constantly with a rise in moisture content is that 

 pertaining to the attractive power of soil for water and to the curvature 

 of the capillary film. At or near the point of saturation the pulling 

 power due to these two factors is probably zero; at this point the soil 

 may be considered to be passive. Any thermal movement of water that 

 takes place at or near 

 the point of satura- 

 tion is to be attrib- 

 uted to the surface 

 tension of the soil wa- 

 ter. If this assump- 

 tion is correct and if 

 the percentage of 

 moisture moved at 

 the highest moisture 

 contents employed is 

 to be considered as a 

 measure of the 

 amount of thermal 

 translocation due to 

 surface tension of wa- 

 ter alone, it will be 

 found that the quan- 

 tity due to this force 

 is very small indeed. 

 As will be seen from the experimental data, the percentage of moisture 

 moved at both amplitudes of temperature is reduced to an insignificant 

 value at the highest moisture contents. 



The foregoing exposition as to the cause and mechanism of the phe- 

 nomena of thermal water translocation will probably be made clearer 

 by figure 4. This diagrammatic representation, however, by no means 

 pictures the real cause and mechanism absolutely and accurately, but 

 it will serve, it is believed, to make clearer what has already been said. 



Let the abscissa represent the effective pull of the cold column of soil and 

 the willingness of the warm column of soil to part with water at a different 

 moisture content, and let the ordinates represent the different percentages 

 of water contained by the soil. By plotting the effective pull and will- 

 ingness against the moisture content it will be seen that the effective 

 pull decreases and the willingness increases with a rise in moisture 

 content. At the point where the two lines cross probably occurs the 



Diagram illustrating the cause and mechanism of moisture 



Fig. 4 

 movement from a 

 ture content. 



varm to a cold column of soil of uniform mois- 



