REVERSIBILITY OF THE COLLOIDAL CONDITION OF SOILS 493 
to justify the drawing of the conclusion that temperature variations of 
from 5 to 10 degrees, within the limits of the experiment, make an appreci- 
able difference in the amount of water vapor adsorbed. 
These data, being limited, are not to be taken as conclusive as regards 
the question. It was thought justifiable, however, to disregard slight 
variations in temperature and to run all tests at room temperature. In 
order to reduce the fluctuations in temperature, the apparatus was put 
into a thick-walled, insulated, wooden box. 
Water-vapor-adsorption method not equally applicable to all soils.— Origi- 
nally it was intended to use in the experiments a glacial clay subsoil of 
the Dunkirk series. The sample used was taken from an excavation at 
a depth of about eight feet. The soil was placed in a humidifier, along 
with surface soil of the same series but from a different locality. In this 
particular experiment, saturated strips of heavy cardboard were used 
instead of the cotton cloth mentioned later in connection with other 
experiments. The results of this experiment are given in table 2. A 
gradual increase in the amount of water vapor adsorbed by the subsoil 
TABLE 2. Apsorprion oF WATER VAPoR BY A NoRMAL (DUNKIRK SURFACE) AND AN 
ABNORMAL (GLACIAL SuBSOIL) Sor 
Per cent of water vapor adsorbed by 
Time exposed . Dunkirk surface soil Glacial subsoil 
Dry Moist Dry Moist 
7 GEIS. oc c.o'she 3 RRS eee 3.38 4.35 27.25 30.7 
1D COR Bocid 6 okucroe elo Roe ERs ee 3.00 4.27 38.90 40.6 
IY GEIB. aon 0 26 eee eR IRE RC aE eee eae 3.75 4.45 48.70 52.4 
23) COWS cc0 oo 6 ot ae aa RIE Cea eae 3.47 4.23 57.00 61.2 
may be noted, free water being present after seven days; whereas the 
surface soil showed no more variation in the amount adsorbed than could 
be ascribed to experimental error. 
These results show a weakness in the water-vapor-adsorption method, 
namely, that some soils adsorb an abnormal amount of water vapor and 
therefore cannot be used in such experimentation. 
The unusual adsorption appears to be due to the chemical rather than to 
the physical condition of the soil, and is therefore, properly speaking, 
