MEASUREMENT OF THE INACTIVE, OR UNFREE, MOIS¬ 
TURE IN THE SOIL BY MEANS OF THE DIEATOM- 
ETER METHOD 
By George J. Bouyoucos, 
Research Soil Physicist , Michigan Agricultural Experiment Station 
INTRODUCTION 
One of the problems in the domain of soil physics which still awaits a 
satisfactory and comprehensive solution is the relation that exists 
between the soil and the soil water. In this relation there are included 
two important and fundamental questions: (i) The effect of the soil upon 
the soil moisture and (2) the condition in which the moisture exists in the 
soil. 
In the present paper there are presented two methods—the freezing- 
point and the dilatometer methods—which appear to give very valuable 
information concerning these two important and fundamental questions. 
The freezing-point method yields only qualitative results, while the 
dilatometer method gives quantitative data. 
HISTORICAL REVIEW 
In determining the lowering of the freezing point of soils (2) 1 by the 
freezing-point method at very low and very high moisture content it was 
found that in all soils, with the exception of quartz sand and some 
extreme types of sand, the lowering of the freezing point increased at a 
far greater rate than the percentage of water decreased. In other 
words, the ratio of the freeezing-point depression and the percentage of 
water content were not inversely proportional (approximately) as might 
be expected, save only in the quartz sand and some of the extreme types 
of sand. Thus, a clay at 92.76 per cent of moisture gave a depression of 
the freezing point of 0.039° C. and at 39.28 per cent 1.075 0 C. The ratio 
of the percentage of water at the two moisture contents is only 2.37, 
while that of the depression is P7.56. 
This phenomenon was explained on the supposition that some of the 
water contained by the soils was either physically adsorbed or loosely 
chemically combined or both, in which event this portion of the water 
was not free or active to act as a solvent but was removed from the liquid 
phase and thus also from the field of action as far as the freezing-point 
lowering is concerned. Under this assumption the unusual results 
obtained could be easily explained. Thus, if a clay, for example, causes 
1 Reference is made by number to “literature cited,” p. 217. 
(19s) 
Journal of Agricultural Research, 
Washington, D. C. 
gy 
Vol. VIII, No. 6 
Feb. 5,1917 
Key No. Mich.—5 
