ESTIMATION OF COLLOIDAL MATERIAL OT SOILS. 25 
The difference in the adsorptive capacities of the extracted and 
unextracted colloids may of course be due to a difference in the 
chemical composition of the two kinds of colloids or due merely to 
a difference in the physical state, as fineness of subdivision or degree 
of induration of the colloidal material. Certain indications point to 
the latter possibility. Pressure alone, however, does not appear to 
alter the adsorptive capacity of the air-dried colloid. Dr. L. H. 
Adams, of the Geophysical Laboratory of the Carnegie Instituticn. 
very kindly subjected a sample of air-dried Sharkey colloid to pres- 
sures up to 15.000 atmospheres. The colloidal material, which con- 
tained 11 per cent of moisture when under pressure, was not changed 
in adsorptive capacity. This is evident from the results given in 
Table 7. 
Table 7. — Effect of pressure on adsorptive capacity of the Sharkey soil colloid. 
Treatment of sample. 
H2O ad- 
sorbed per 
gram of 
material. 
Gram. 
0. 3103 
Dye ad- 
sorbed per 
gram of 
material. 
Gram. 
0.4365 
Not compressed 
Exposed to 4,000 atmospheres pressure . 3082 I . 4395 
Exposed to 7.000 atmospheres pressure . 3078 . 4395 
Exposed to 1 5.000 atmospheres pressure . 2932 . 4220 
ALTERATION IN ADSORPTIVE CAPACITY OF THE COLLOID PRODUCED BY EXTRACTION. 
From data presented in Table 4. evidence can be obtained as to 
whether the adsorptive capacity of the colloidal material is affected 
by extraction. Table 4 gives the adsorptive capacity of the un- 
treated soil and the adsorptive capacities, as well as percentages, of 
the colloidal material and other fractions into which the soil was 
separated. If isolation of the colloidal material does not affect the 
adsorptive capacity of the colloidal material, the adsorptions of the 
separates into which the soil is divided (colloidal material, fine and 
coarse fractions) should amount to just what the untreated soil 
adsorbs. If, on the other hand, the quantity of dye, water, or 
ammonia adsorbed by the combined colloidal, fine and coarse frac- 
tions amounts to more or less than the quantity of these substances 
adsorbed by the untreated soil, it is apparent that the adsorptive 
capacities of the colloidal material must be altered by the process 
of fractionation. 
Table 8 gives the quantities of dye, water, and ammonia adsorbed 
by one gram of the untreated soil and the quantities of these sub- 
stances that would be adsorbed by 1 gram of the soil separates 
combined according to the percentages of each isolated from the soil. 
It is apparent from the data in Table 4 that the quantities of colloidal 
material, fine and coarse fractions isolated from a soil, do not exactly 
equal the amount of soil taken for fractionation, the quantities of 
separates recovered ranging from 95.5 per cent to 102.2 per cent of 
the original samples. The losses of soil material were probably 
•chiefly mechanical, although with the large volumes of water used 
there must have been some losses occasioned by solubility. A 
