Temperature and Capillary Moisture in Soils 149 



when the moisture content was still about 30 per cent. As the water 

 content increases, these attractive and adhesive forces decrease. 



Of all the four assumptions the correctness of the third — namely, that 

 the attractive and adhesive forces decrease with temperature — may be 

 doubted by many and challenged by a few. The theoretical and exper- 

 imental evidences, however, are overwhelmingly in its favor. According 

 to the law of kinetic energy, the attractive and adhesive forces of solids 

 for liquids and gases or vapors should decrease with rise in temperature. 

 The investigations upon the absorption of gases and vapors at different 

 temperatures show this to be the case. The work of De Saussure (11) 

 and Von Dobeneck (6) upon the absorption of gas by different solid 

 materials, and the researches of Knop^ and Ammon (i) upon the absorp- 

 tion of water vapor by soil, seem to show conclusively that the absorptive 

 power of diverse solid materials for gases and water vapor decreases 

 with increase in temperature. The only evidence which is contrary to 

 the above is that obtained by Hilgard (7, p. 198) on the absorption of 

 water by dry soils from a saturated atmosphere. Hilgard 's results show 

 that the absorption of w^ater vapor by soils increases with rise in temper- 

 ature. The results obtained by the several investigators mentioned, as 

 well as new evidence which will subsequently be presented, tend to throw 

 considerable doubt on the correctness of Hilgard 's data. Hence, it can 

 safely be asserted that the third assumption is correct. 



Bearing these postulates in mind, the phenomena of thermal water 

 translocation observed may be explained as follows: The soil with the 

 lowest moisture content holds the water with a force of great magnitude. 

 When the temperature of a column of this soil is uniform throughout, 

 the adhesive and attractive forces are at an equilibrium. When one 

 half of this column of soil is heated to 40° and the other half to 0° C, 

 this equilibrium is disturbed. The attractive and adhesive forces of 

 the soil for water and the cohesive power or surface tension of the soil 

 water are decreased in that portion of the soil column which is maintained 

 at 40° and increased to a corresponding magnitude in that portion of the 

 soil column which is kept at 0° C. The cold column therefore exerts a 

 pull and draws water from the warm column in amount depending upon 

 the quantity that the latter is willing to give up. Since the soil possesses 

 a great attraction for water, which attraction varies with the' diverse 

 classes of soil, and inasmuch as this attractive force is not satisfied at 

 the low moisture content, the warm soil parts only with a small amount 

 of its water. Hence, the amount of water moved from the warm column 

 to the cold column of soil is small. 



At the next higher moisture content the attractive power of the soil 

 for w^ater is further satisfied and the total water content is held with 

 less force. When a column of this soil is kept at the same ampli- 

 tudes of temperature as above, the decrease and increase of the adhesive 



' Cited by Johnson, S. W. How Crops Feed. p. 164. New York [1870J. 



