REVERSIBILITY OF THE COLLOIDAL CONDITION OF SOILS 507 
With all the soils the differences between the percentages of water vapor 
adsorbed by moist and by air-dried soils are sufficiently great to be sig- 
nificant; but, except in one case — between eight and sixteen dryings of 
the Vergennes subsoil —the differences between successive dryings are 
not significant. 
Comparing the cumulative effect of thirty-two dryings with the effect 
of one drying, it is to be seen that the difference is significant with the 
two subsoils but not with the surface soils. Perhaps the surface soils do 
not show the cumulative effect because, owing to their natural subjection 
to the alternate wetting and drying actions, a sort of equilibrium has 
been established. 
No crushing tests were run on these soils, but it was observed while 
erushing them with the rolling-pin that in general the soils which had been 
dried the greatest number of times crushed the most easily. This obser- 
vation agrees with Fippin’s (1911) penetration tests on alternately wetted 
and dried soils. 
It was observed also that a mold made its appearance on the Dunkirk 
and Clyde soils, the two containing the most humus, after about eight 
wettings and dryings. This is probably due to an increased solubility 
of the organic matter caused by the treatments.’ 
Effect of drying at high temperatures.— Data on the effect of drying at 
high temperatures are given in table 14: 
TABLE 14. ApsorPTIon oF WaTER Vapor By Sorts Drigep at High TEMPERATURES 
Per cent of 
Soil Treatment water vapor Difference 
adsorbed 
Ar=Griedeee ese ee PB eines 3.02+0.01 
0.41+0.02 
Dunkirk surface Oven-driediigs ir tee aes ene ae 2.61+0.02 
1.50+0.02 
ica abh or0 LESS Mein eee ce tie Pt Cony Meena 1.11+0.01 
AGr=d ried eee rice kee reset ee eee 11.60+0.05 
1.10+0.05 
Clyde surface Oven=drlied ier eS 0a rset non ye e 10.50+0.02 
5.28+0.04 . 
Wonitedinee ets Noe vaee a eth Ae ae di 5.22+0.03 
2 It is shown later (page 516) that the drying of the soils increases the solubility of their organic matter. 
