ESTIMATION OF COLLOIDAL MATERIAL IN SOILS. 29 
Although no great accuracy can be claimed for the ''alteration 
values" given in columns 8 to 10, it is believed, that they measure 
approximately a real effect. The alteration values explain to a con- 
siderable extent why the amounts of colloid in certain soils calcu- 
lated from the dye, water, and ammonia adsorption ratios 
adsorption per gram of soil 
adsorption per gram of colloid 
do not agree. It will be seen from the data to be given in Table 10 
that when the adsorption ratios are corrected for the differences in 
the adsorptive capacity of the colloid u as extracted" and "as in the 
soil," the dye, water, and ammonia determinations show a reasonable 
agreement. 
The chief source of inaccuracy in the calculated values given in 
Tables 8 and 9 is probably the uncertainty regarding the slight losses 
or gains of soil material occurring during separation of the colloid. 
If the loss of soil material were preponderantly colloid instead of the 
soil as a whole, the values calculated for the adsorptive capacity of 
the colloid when in the soil would be somewhat lower than those 
given in Table 9 and the amount adsorbed by the combined soil sepa- 
rates would be somewhat higher than the values given in Table 8. 
The relation between the dye, water, and ammonia values would, 
however, be little affected. For example, if in the case of the Hun- 
tington soil the 3.8 per cent loss of material were all colloid, it would 
appear that the colloid when extracted was 1.25 as adsorptive for 
dye, 1.08 as adsorptive for water and 0.89 as adsorptive for ammonia 
as the colloid when in the untreated soil. It will be noted that the 
relation between these values is virtually the same as between the 
respective values 0.99, 0.85, and 0.71 given in Table 9, calculated on 
the assumption that the 3.8 per cent loss was from the soil as a whole. 
Hence, so far as bringing about agreement in the adsorption ratios is 
concerned, it would make little difference which set of alteration 
values was used, although it would make a difference in the percent- 
age of colloid shown by the ratio to be present in the soil. 
The subject of alteration in the adsorptive capacity of the colloidal 
material on extraction should be investigated further. With a 
refinement of methods it should be possible to determine with greater 
accuracy the difference in adsorptive capacity of the colloidal material 
as it is in the soil and as it is extracted, if such a difference exists. 
Little evidence is at hand to show whether such an alteration would 
be produced by the mere increased dispersion of the colloidal particles, 
by the leaching of soluble salts, or by the manner of concentrating 
and drying the colloidal material. 
ACCURACY OF THE ADSORPTION METHOD. 
The data given in pages 14 to 29 indicate that the method of 
determining the percentage of colloid in the soil from the adsorption 
ratio, 
adsorption per gram of soil 
adsorption per gram of colloid 
may be somewhat inaccurate owing to two causes — inability to 
obtain a fair sample of all the colloidal material in the soil and 
