Feb. s, 1917 
Measurement of Inactive Moisture in Soil 
215 
dilatometer. As has already been stated, the osmotic pressure of the 
soil solution alone is about 15 atmospheres, slightly above the wilting 
coefficient. Now, if the greatest portion of the moisture at this point 
exists as physically adsorbed and loosely chemically combined water 
probably in the solid phase, then this water must be held in the soil with 
considerable force, and this force must be added to that of the solution 
alone. The total force with which the moisture is held back in the soil, 
or the “back pull/’ according to these estimations, is many times greater 
than that obtained by Shull. 
If, however, the wilting of plants is due to the slow movement of water, 
then why does not this water freeze if it is in the liquid phase and in an 
available form, since the rate of movement of water does not affect the 
freezing as it might the wilting of plants ? 
VALUE OF THE DILATOMETER METHOD 
The functions of the dilatometer method may be summarized as fol¬ 
lows: The greatest value of the method appears to be (1) in showing 
that soils cause water to become unfree or inactive, as indicated by its 
refusal to freeze; (2) in fixing an approximate estimation of the quantity 
of water thus becoming unfree; (3) in obtaining, under certain condi¬ 
tions, the wilting coefficient of soils very rapidly; and (4) in classifying, 
under certain arbitrary conditions, the water in the soil into free, capil¬ 
lary, physically adsorbed, and loosely chemically combined. This method 
promises to yield future results which will probably revolutionize our 
present knowledge concerning the moisture in the soil. 
In all these functions, therefore, the dilatometer method appears to 
be of considerable value and importance in yielding knowledge on the 
fundamental questions regarding the effect of the soil upon the soil 
moisture and the condition in which the moisture exists in the soil. 
SUMMARY 
In the present paper there is presented the dilatometer method as a 
means of showing the amount of water which the soils cause to become 
unfree or inactive, as indicated by the quantity that fails to freeze. 
The principle of the dilatometer method is based upon the fact that 
water expands upon freezing. If the amount of expansion that a given 
quantity of water, 1 gm., produces upon freezing is known, the total 
amount of water that freezes in a soil can be calculated. If also the 
total water content of the soil is known, the amount of water that does 
not freeze can be obtained by difference. 
The dilatometer (fig. 1) consists of three parts: (1) a bulb, (2) a 
thermometer, and (3) a measuring stem. 
The method of procedure consists of mixing soil and water in certain 
definite proportions, placing this moist soil in the bulb, and then filling 
