BovieE: NON-AVAILABLE WATER IN SOILS OTF 
different degrees, so that a more or less complete separation of the 
solutes is effected. Further separation may be reached by using 
two or more adsorbents, each with an adsorbing power specific 
for each solute. A number of investigators have used organic 
substances, such as charcoal, paper, and cotton to effect such 
separations. The separation is seldom complete, the adsorbed 
substance being distributed between the adsorbent and the solvent. 
No general laws governing the ratios of such distribution have 
been established. 
The solvent itself is often adsorbed, so that it increases very 
much in density at the surface of the adsorbent. This changes 
many of its physical characteristics; for instance, it is often able 
to hold the solute in solution at a concentration many times greater 
than normal saturation. This change in concentration is often 
accompanied by temperature changes which indicate enormous 
forces at work. The pressure of the water surface about a smal] 
solid (soil grain) has been estimated to have a magnitude of from 
6000 to 25,000 atmospheres, or approximately 150,000 pounds 
per square inch.* 
Now the soil grains present acres of surface to the soil solution, 
which, existing as it does, for the most part, in surface films is 
continuously within the field of adsorptive forces. We must ex- 
pect, therefore, that adsorption will play important roles in the soil. 
Not only is the chemical content of the soil-solution affected, 
mineral nutrients stored up, and toxins held harmless,> but the 
physical relations of the soil grains themselves are influenced. f 
The field has been but little investigated, and most of the work 
has been done from the standpoint of physics and chemistry. 
Only a few investigators have taken up the problem from the 
standpoint of the plant, using it as an indicator. It would seem 
that this must be the ultimate point of attack, for the root hairs 
come into such a relation with the soil grains as to find a solution, 
the nature of which can be but little understood by any amount of 
study of the leachings from treated soils. 
*Whitney, Soils of the United States. U.S. Dept. Agric. Bur. Soils Bull. 55: 11 
1909. 
+Cameron, F. K. and Gallagher, F. E. Moisture content and physical condi- 
tion of soils. U.S. Dept. Agric. Bur. Soils Bull. 30: —. 1908. 
