ESTIMATION OF COLLOIDAL MATERIAL IN SOILS. 23 
would expect this colloidal material to differ in adsorptive capacity 
from the material which was isolated, from the mere fact that it was 
not brought into suspension by the same treatment. 
As already pointed out. evidence as to whether the unextracted 
colloid differs in adsorptive capacity from the extracted colloid can be 
obtained by comparing the quantities of colloid determined micro- 
scopically with the quantities indicated by the adsorption ratios. If 
the adsorption ratios indicate the same percentages of colloidal 
material as the microscopical observations the colloid in the residues 
presumably has the same adsorptive capacity as the extracted colloid. 
If the adsorption ratios are lower than the microscopical determina- 
tions, it is to be assumed that the unextracted colloid in the fractions 
has a lower adsorptive capacity per gram than the colloid extracted, 
and if the adsorption ratio is higher than the microscopical determin- 
ation the unextracted colloid doubtless is more adsorptive than the 
extracted colloid. 
Comparisons of the microscopical and adsorption determinations 
given in Table 5 indicate that the unextracted colloidal material 
usually has a considerably lower adsorptive capacity for dye and 
water than the extracted colloid, but the adsorptive capacities of the 
two kinds of colloid for ammonia is as a rule approximately alike. 
It should be borne in mind that these estimations of the relative 
adsorptive capacities of the extractable and unextractable colloids 
apply on the one hand to material in the condition in which it is after 
extraction and on the other hand to material in the unextracted 
condition. If it is true that the process of extraction does not alter 
the adsorptive •capacity of either the extracted or unextracted col- 
loid, it would follow that the two kinds of colloidal material — if they 
are distinct kinds — have different adsorptive capacities as they 
exist in the untreated soil. However, data presented in the following 
pages indicate that the colloidal material after extraction probably 
has a somewhat different adsorptive capacity from what it had in 
the untreated soil. In Table 9 the adsorptive capacities of the 
extractable colloid before and after extraction are given, and the 
probable relation between the adsorptive capacities of the colloid in 
the two conditions is expressed in factors given in columns 8 to 10 of 
that table. 
For a comparison, then, of the adsorptive capacities of extractable 
and unextractable colloids as they exist in the untreated soil, it is 
necessary to correct the adsorption ratios given in Table 5 for pos- 
sible alteration produced in the extracted colloid, upon which the 
ratios are based. Factors given in Table 9 were used for this purpose. 
The corrected adsorption ratios and microscopical determinations 
on samples containing an appreciable amount of colloidal material 
are given in Table 6. 12 
Data in Table 6 show that even in the untreated soil the extractable 
and unextractable colloids usually differ considerably in adsorptive 
capacities. The difference in adsorptive capacities of the two kinds 
of colloid is not at all constant; it is large in the case of the Cecil soil 
and practically negligible in the case of the Vega Baja soil. In most 
12 Samples containing a small quantity of colloidal material had such low adsorptive capacities that the 
adsorption ratios could not be determined accurately. The comparisons of the adsorption ratios and 
microscopical determinations of colloid were, therefore, not significant in the case of these samples (Table 5) , 
and they were omitted from Table 6. 
