PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 
29 
tions of this quantity were made on four of the colloids and the 
values agreed with those given in the table within 1 to 2 per cent, 
showing that they are accurately reproducible provided the set pro- 
cedure is followed. Strictly speaking, the procedure of determina- 
tion would show the initial concentration of dye, rather than the 
quantity of dye, required to render a given concentration of colloid 
isoelectric. However, in the case of these eight colloids the dye 
appeared to be completely absorbed at the isoelectric point and some- 
what beyond, so the term " quantity " is used with the understanding 
that it is a fixed value only for the conditions of the procedure. 
Other experiments showed, however, that the quantity of dye render- 
FIG. 1. 
Z 3 *?■ 
Effect of methylene blue on migration of soil colloids 
ing 1 gram of the colloid isoelectric did not vary markedly with 
widely varying concentrations of dye and colloid. 
Table 16. — Migration velocity of soil colloids, methylene blue 
them isoelectric, and content of exchangeable 
required to render 
base 
Kind of colloid 
Migration 
velocity of 
colloid par- 
ticles in 
distilled 
water 
Methylene blue re- 
quired to render 1 gram 
of colloid isoelectric 
Exchange- 
able Ca, 
Mg, K,and 
Na per 
gram col- 
loid 
Fallon.. 
Microns 
-2.3 
-2.3 
-2.3 
-2.0 
-1.6 
-1.5 
-2.4 
-3.0 
Gram 
0.287 
.253 
.200 
.100 
.082 
.057 
.055 
.420 
Milliequiva- 
lent 
0.770 
.678 
.536 
.268 
.220 
.153 
.147 
1.126 
Milliequiva- 
lent 
1.080 
Sharkey . 
Marshall 
Huntington 
Sassafras 
.687 
.528 
.227 
Norfolk •_ 
Susquehanna 
Bentonite 
.091 
.087 
