REVERSIBILITY OF THE COLLOIDAL CONDITION OF SOILS 519 
by basic minerals than were basic dyes; and basic dyes were more strongly 
adsorbed by acid minerals. 
Diamine sky-blue was one of the few dyes strongly adsorbed by colloidal 
ferric oxide, and, of all those examined, was adsorbed the most strongly. 
It was adsorbed also by alumina, but not by silica. 
An alga and a fungus adsorbed considerable amounts of the dyes used 
in soil-adsorption work. The growth in soils of lower forms of plant life 
affects the adsorptive capacity of the soil. 
Air-dried and oven-dried colloidal silica, alumina, ferric oxide, and 
humus, immersed in dye solutions, showed a reversal of their capacity 
to adsorb dyes. They also adsorbed water vapor rapidly. 
The difference in hygroscopicity between a moist and an air-dried soil 
persists for three months at least. 
Remoistening air-dried soils to a content of moisture above that origi- 
nally held did not cause a reversal of hygroscopicity immediately, nor 
within three months. 
Alternate. wetting and drying of soils did not affect the hygroscopicity 
after the first drying. With the subsoils that had been wetted and dried 
thirty-two times there was a cumulative decrease in hygroscopicity which 
was significant. 
Hygroscopicity was decreased successively by air-drying, oven-drying, 
and ignition. The change from the moist to the air-dry condition pro- 
duced a greater change than that from the air-dry to the oven-dry; and 
from the oven-dry to the ignited condition the change was greater than 
from the air-dry to the oven-dry condition. Some ignited soils had com- 
paratively high hygroscopic values. 
Long immersion under water increased the hygroscopicity of a soil poor 
in organic matter, and decreased it in one rich in organic matter. 
Leaching a soil raised its capacity for adsorbing water vapor. 
Oven-drying and ignition reduced the adsorption of methylene blue. 
The Clyde soil, rich in organic matter, showed less effect due to drying 
than did the other soils. This was contrary to results with water-vapor 
adsorption. Effects of air-drying and alternate wetting and drying were 
so irregular, as measured by dye adsorption, as to be inconclusive. 
Immersion of a soil in water for two years increased its adsorptive 
capacity for methylene blue. 
Leaching a soil increased its adsorption of methylene blue. 
