EXPERlMElNt STATION BULLETINS; 507 



mental evidences, however, .are overwlielmiugl^' in its favor. According 

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

 for liquids, and gases or vapors, shonld decrease wath rise in tempera- 

 ture. The investigations upon the absorption of gases and vapors at 

 different temperatures show such to be the case. The work of de Sausure" 

 and Von Dobeneck* upon the absorption of gas by different solid ma- 

 terials, and the researches of Knop^ and Amnion^ upon the absorption of 

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

 of diverse solid materials for gases and Avater vapor, decreases with in- 

 crease in temperature. The only evidence which is contrary to the above 

 is that obtained by Hilgard^" on the absorption of Avater by dry soils from 

 a saturated atmosphere. Hilgard's results show that the absorption of 

 water vapor by soils increases with rise in temperature. The results ob- 

 tained 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 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 ad- 

 hesive and attractive forces are at an equilibrium. When one half of this 

 column of soil is heated to 40° C. and the other half to 0° C. this equi- 

 librium 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° 

 C. and increased to a corresponding magnitude in that portion of the soil 

 column which is kept at O'' C. The cold column, therefore, exerts a pull 

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

 quantity that the warm column of soil 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 Avarm column to the cold column of soil, is small. At the next higher 

 moisture content the attractive power of the soil for water is further 

 satisfied and the total water content is held Avith less force. When a 

 column of this soil is kept at the same amplitudes of temperature as 

 above, the decrease and increase of the adhesiA^e and cohesive forces, due 

 entirely to temperature, between the Avarm and cold columns of soil are 

 equal in amount as in the soil with the lowest moisture content. Water, 

 therefore, tends to moA'e from the warm to the cold soil. Inasmuch, as 

 the attraction of the soil has been further satisfied and the water films 

 further thickened, the pull of the cold soil, due only to the attractiA-e 

 forces of the soil for Avater, is decreased, but the ease Avith which the 

 w^arm soil giA'es up moisture is, on the other hand, increased. The result 

 is that even though the total eft'ectiA'e pull (which is composed of the in- 

 creased surface tension of water, increased attractive and adhesiA'e forces 

 of soil for water, and the force of the curvature of the capillary films) 



«Ann. Phvs. Gilbert, 47, 113 (1814). 



'Forsch. Aer. Phys.. 15, 163 (1892). 



8Cited by Johnson, How Crops Feed, pp. 161-162, (1870). 



"Forsch, Apr. Phys., 2, 163 (1892). 



"Soils, p. 198 (1912). 



