REVERSIBILITY OF THE CoLLOIDAL CONDITION oF Sorts 503 
while, as such action does not occur in nature. The soils were saturated 
or a slight excess of water was added. The dried soils were usually 
lumpy, and before sampling they were crushed by means of a wooden 
rolling-pin. 
Effect of various factors on hygroscopicity 
It has been shown by Ehrenberg and Pick (1911) that dried soils adsorb 
Jess moisture than do moist soils, and these authors used this fact as an 
argument against Mitschertich’s method of determination of hygroscopic 
moisture. it is not known whether the difference is due to the effect 
of drying upon the colloidal material, or to the layer of adsorbed air on 
the soil (Ehrenberg, 1915). 
Effect of time—In order to learn whether this difference in hygro- 
scopicity persists thruout a period of three months at least, an experiment 
was run to cover that point. The data are given in table 10: 
TABLE 10. Errect or TIME oN THE ADSORPTION OF WATER VAPOR BY CLYDE SURFACE 
Sorn 
Length of time in : Per cent of : : 
humidifier Soil treatment | water adsorbed Difference Ratio 
Tne Air-dried........ 12.15+0.30 \ 
Mita 15.9540.38 {| 2-80+0.48 1-31-20 .045 
BI OUUGIS y-sy-7= ests o's Air-dried........ 12.20+0.25\}| , 
Vioigha. Dohme abe 17,000.42 {| *-80+0.49 1.39-£0.04 
Bemonths. .......-..- Ar =Gnict se ae 12.70+0.10 \ e 
| MiGtga ee Wee 16.7540.30/| *-05+0-82 | 1.82+0.03 
It is seen that the differences do persist as long as three months 
and that they are significant. Also, the ratios between the hygroscopici- 
ties at different periods are about constant. If the difference in hygro- 
Scopicity between moist and dry soil as shown by a test of one month 
is due to a failure to establish equilibrium, it seems that this failure still 
persists at the end of three months. 
Effect of remoistening.— The second question to be studied was whether 
this drying produces a permanent effect on the hygroscopicity of the soil. 
Does remoistening restore the original condition? The data on this point 
are given in table 11. In order to preclude the possible effect of a failure 
to establish equilibrium, the remoistened soils were brought to a higher 
