JOURNAL OF ACRICOLTORAL RESEARCH' 
DEPARTMENT OF AGRICULTURE 
Vol. V Washington, D. C., October 25, 1915 No. 4 
EFFECT OF TEMPERATURE ON MOVEMENT OF WATER 
VAPOR AND CAPILLARY MOISTURE IN SOILS 
By G. J. Bouyoucos, 
Research Soil Physicist, Michigan Agricultural Experiment Station 
INTRODUCTION 
An investigation of the influence of temperature on the various physi¬ 
cal processes in the soil was undertaken by the writer at the Michigan 
Agricultural Experiment Station. One of the phases of this investi¬ 
gation, the effect of temperature on the movement of water vapor and 
capillary moisture in soils, will be considered in the present paper. 
MOVEMENT OF MOISTURE FROM WARM TO COLD COLUMN OF SOIL OF 
UNIFORM MOISTURE CONTENT 
A rise of temperature decreases both the surface tension and the vis¬ 
cosity of water to the extent shown by the data in Table I. 
Table I .—Relation of temperature to the surface tension and viscosity of water 
Temperature. 
Surface ten¬ 
sion. 
Viscosity. 
•c. 
0 
IOO. OO 
IOO. OO 
10 
97.96 
73-32 
20 
94-32 
56. 70 
30 
91. 62 
45. 12 
40 
88. 46 
36. 96 
50 
85 . 52 
30- 17 
It will be noted that the degree of diminution with rise in tempera¬ 
ture is considerably greater in the case of viscosity than in that of sur¬ 
face tension. 
During the warm part of the year the soil at the upper depths main¬ 
tains a rather marked temperature gradient which reverses itself be¬ 
tween day and night to the depth that the diurnal amplitude of tem¬ 
perature oscillation extends. This diurnal change of temperature 
gradient occasions an alteration in surface tension and viscosity of the 
soil moisture, the amount depending upon its variation at the different 
depths. Since capillary action is said to depend upon surface tension 
and facility of movement upon viscosity, there should occur an up- 
(141) 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
af 
Vol. V, No. 4 
Oct. 25, 1915 
Mich.—1 
