ESTIMATION OF COLLOIDAL MATERIAL IX SOILS. 27 
material slightly more adsorptive of dye, slightly less adsorptiye of 
water, as a rule, and considerably less adsorptiye of ammonia than 
the colloidal material as it exists in the untreated soil. If the colloid 
after extraction adsorbs more than it does in the soil, this would, of 
course, make the ratio 
adsorption per gram soil 
adsorption per gram colloid 
too low and yice yersa. Such an alteration in the adsorptiye capacity 
of the colloidal material for the different substances would explain 
the fact brought out in Table 2 ; namely that in most cases where 
there is a marked disagreement in the quantities of colloid indicated 
by the dye. water, and ammonia adsorption ratios the dye ratio is 
the lowest and the ammonia ratio is the highest. 
Although the differences between the adsorptions of the untreated 
soil and the combined soil separates are small, and in most cases 
about what should be allowed for experimental error, the constancy 
with which the combined separates exceed the untreated soil in dye 
adsorption and fall short of the untreated soil in ammonia adsorp- 
tion u indicate that we have to do with a real effect. Also, the great- 
est yariations occur in the adsorption of ammonia and this determina- 
tion is probably slightly more accurate than the determination of 
dye or water adsorbed. 
Howeyer, eyen if the yalues given in Table S were absolutely ac- 
curate, they probably would not indicate the exact degree of altera- 
tions of the colloids in the process of extraction. The data given 
in Table 8 are calculated on the assumption that all the adsorptive, 
or colloidal, matter has been altered in the process of extraction. 
As a matter of fact, if there is an alteration in adsorptive capacity, 
it probably takes place chiefly or only in the colloid which is extracted. 
The unextracted colloid in the fine and coarse fractions is doubtless 
in essentially the same condition it was in the untreated soil. The 
extracted colloid, however, has been converted from the gel to the sol 
condition and this increased dispersion, or a change in the material 
incident to the increased dispersion, is possibly responsible for the 
change in adsorptive capacity. 
Table 9 shows the alteration in adsorptive capacity of the extracted 
colloid, calculated on the assumption that only the extracted colloid 
is changed in the process of extraction. Data used as the basis for 
this calculation are given in Table 4. The quantity of dye. water, or 
ammonia adsorbed by the amount of fine and coarse residues frac- 
tionated from 1 gram of soil is subtracted from the quantity of dye, 
water, or ammonia adsorbed by 1 gram of the untreated soil. The 
difference between the two adsorptions — that of the whole soil, and 
that of the combined fine and coarse fractions — must represent the 
amount adsorbed in the extractable colloid as it existed in the untreated 
soil. This calculated adsorption of the extracted colloid as in the 
soil, is compared with the determined adsorption of the colloid as 
extracted, both adsorptive capacities being expressed on the per gram 
basis. Just as in the previous calculation, it is assumed in these 
u If alteration in the adsorptive capacity of the colloid produced by extraction is a cause of the disagree- 
ment between dye, water, and ammonia ratios, one would not expect to find marked differences in alter- 
ation for dye and ammonia in the case of the Sharkey and Vega Baja soils, since the dye. water, and ammonia 
ratios on these soils agreed well. As a matter of fact there is noticeably less difference between the degree 
of alteration for dye and ammonia in the case of these soils than in the case of the others. 
