Dec. io, 1913 
Selective Adsorption by Soils 
187 
decreases the adsorption of potassium from a potassium-chlorid solution 
by a soil and increases it above this concentration. They also show 
that the presence of monobasic calcium phosphate does not alter the 
adsorption of potassium from a potassium-chlorid solution appreciably, 
Fig. 2 .—Curves showing the effect of the presence of sodium nitrate and calcium phosphate on the selective 
adsorption of potassium from solutions of potassium chlorid. 
what change there is in the form of the curve being undoubtedly due 
to the removal of potassium by the calcium phosphate not in solution, 
either by a physical (adsorption) or a chemical reaction. 
SUMMARY 
Soils not only have the power of adsorbing dissolved salts from solu¬ 
tions but also of adsorbing one ion at a greater rate than the other, or 
selectively adsorbing, to a marked extent. 
The presence of bases of the soil (Ca, Mg, etc.) in solution after shak¬ 
ing certain salt solutions with or percolating through a soil is probably 
not due to a direct chemical reaction of the salt in solution with the 
silicates of the soil, but to a reaction of free acid, resulting from a 
selective adsorption of the cation, with the mineral components of 
the soil. 
The rate of adsorption of chlorin ions from solution by soils is much 
less than of potassium ions. 
The selective adsorption of potassium from a potassium-chlorid 
solution by a soil increases in amount with the concentration up to a 
certain point and then remains practically constant. 
