Oct. 25,1915 
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 1 and Ammon (1) 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 water 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 o° 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 o° 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 water 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 
1 Cited by Johnson, S. W. How Crops Feed. p. 164. New York [1870]. 
