EXPERIMENT STATION BULLETINS. 



521 



FIG. 4. CURVES SHOWING MOISTURE MOVEMENT FROM MOIST AND WARM 



COLUMN OF SOIL TO DRY AND COLD COLUMN OF SOIL; AND FROM 



MOIST AND COLD TO DRY AND WARM COLUMN OF SOIL. 



Considering first the numerical values showing the amount of water 

 moved from the moist and warm column of soil to the dry and cold col- 

 umn of soil, which are graphically rejjresented by the upper curve of 

 each chart, it will be seen (1) that this amount is nearly twice as great 

 in the temperature amplitude of 40° as in 20° C, (2) that it is some- 

 what greater in soils with higher than with lower colloidal content, 

 and (3) that it increases with the rise in moisture content. 



By comparing these results with those obtained with column of soils 

 of uniform moisture content, some very striking contrasts are revealed. 

 The previous results show, for instance, that the maximum thermal mo- 

 tion of water occurs at a definite but comparatively low moisture con- 

 tent, and that the value amounts in some cases over 3.50 per cent. The 

 above data, show, however, that the maximum movement of water from 

 the moist and warm column to the dry and cold column of soil, takes 

 place at the highest water content, and that in the majority of cases the 

 percentage of this maximum water translocation is only one-half as great 

 as in the former case. 



These apparent differences seem to be easily explainable. The increase 

 of water movement from moist and warm soil to dry and cold soil with 

 rise in water content is natural, and only goes to prove that the water 

 is held by the soil with Ioav moisture content, with a great force, and 

 consequently it cannot be extracted readily and extensively by a greater 

 abstracting force. When the attractive forces of the soil for water are 

 satisfied, and the thickness of the surface and capillary films is increased, 

 then greater quantities of water will be removed by the same abstracting 

 force. The smaller thermal water movement which occurs in the moist 



