Oct. 25, 191S Temperature and Capillary Moisture in Soils 1 7 1 



of water from the former. This explanation is correct, of course, in so 

 far as it represents the result of the mulch, but how this mulch was 

 formed and how it was capable of accomplishing this result he fails to 

 explain correctly. In the opinion of the writer the above results offer 

 an excellent proof that temperature aids and hastens the formation of a 

 mulch, and tends to conserve the soil moisture in the manner previously 

 set forth. 



This is a remarkable paradox indeed that a temperature which causes 

 the loss of water should also cause its conservation. 



SUMMARY 



The main and most important facts presented in the foregoing series 

 of studies may be summarized as follows : 



(i) When one half of a column of soil of uniform moisture content is 

 maintained at 20° and 40° and the other half at 0° C. for eight hours the 

 percentage of water moved from the warm to the cold soil increased in 

 all the different types of soil with a rise in moisture content until a certain 

 v/ater content was reached, and then it began to decrease again with 

 further increase in moisture content. The results then plot into a para- 

 bola. The percentage of moisture at which the maximum thermal trans- 

 location of water occurred is different for the diverse classes of soil, but 

 the percentage of the maximum thermal translocation of water is about 

 the same for all classes of soil for any one of the temperature ampUtudes. 

 The percentage of moisture at which this maximum thermal transloca- 

 tion occurred is designated as the "thermal critical moisture content." 



These results are contrary to what might be expected from the laws 

 of surface tension and viscosity. They have led to the conclusion that 

 the capillary movement of water in moist soils is not controlled entirely 

 by the cur\'ature of the capillary films, as is generally believed, but also 

 by the unsatisfied attractive forces of the soil for water. 



(2) When a moist column of soil was kept at 20° and 40° and a dry 

 column of soil at 0° C. for eight hours and the two columns were sepa- 

 rated by an air space, the percentage of moisture distilled over from the 

 moist and warm column to the dry and cold column of soil was very 

 insignificant for both amplitudes of temperature and was about the same 

 for all moisture contents. 



These results lead to the conclusion (a) that the amount of water lost 

 from the soil by water vapor is very small ; (b) that there is no rising of 

 vapor during the night from the warmer soil below to th e cold soil above ; 

 and (c) that the water of the dew is not derived from the soil vapor, as 

 is commonly believed. 



(3) When a moist column of soil was in contact with a dry column of 

 soil and the former was kept at 20° and 40° and the latter at 0° C. for 

 eight hours the amount of moisture moved from the moist and wann soil 



