PROPERTIES OE THE COLLOIDAL SOIL MATERIAL 
23 
other salt solutions, so it was selected for this work. The procedure 
followed was similar to that employed by Gedroiz (17) , Hissink 
(#4), and Kelley and Brown (29). Approximately 15 grams of the 
colloid were digested overnight with 250 cubic centimeters of a 
normal ammonium chloride solution at 35° C. After filtering, the 
colloid was washed with sufficient normal NH 4 C1 solution to give a 
total filtrate of 1,000 cubic centimeters. The filtrate was analyzed 
to determine the quantities of Ca, Mg, K, and Na that had been 
removed by the NH 4 C1 solution. Since it has been repeatedly shown 
that the NH 4 adsorbed is practically equivalent to the base removed, 
the NH 4 adsorbed was not determined, but was assumed to be the 
same as the total equivalents of monovalent and divalent bases re- 
moved. This assumption is not correct for acid colloids, which 
exchange H or Fe and Al in addition to the monovalent and divalent 
bases. However, values calculated on this assumption gave a rough 
comparison of the adsorptive capacities of the colloids for am- 
monium ions. 
Table 12 shows the total quantity of Ca, Mg, K, and Xa removed 
from the different soil colloids by treatment with normal NH 4 C1 
solution, the quantity being expressed as milliequivalents per gram 
of colloid. In the third column the quantity of NH 4 that would 
be adsorbed in replacing these bases is expressed as quantity of NH 3 
per gram of colloid. The fourth column gives the quantity of dry 
NH 3 gas adsorbed by the dry colloid, the figures being taken from 
Table 5. 
Table 12. — Quantity of NH S adsorbed from NH^Cl and from dry ammonia vapor 
by soil colloids 
Hind of colloid 
Ca-t-Mg+K+Ne 
removed bv 
NH4CI from 1 
gram of colloid 
NH3 that would 
be adsorbed from 
NH 4 Clbv replac- 
ing Ca, Mg, K, 
and Na from 1 
gram of colloid 
Nils gas ad- 
sorbed by dry 
colloid per 
gram 
Fallon . . 
Milliequivalents 
1.08 
.69 
.53 
.23 
.09 
.09 
Gram 
0. 0184 
.0117 
.0090 
.0039 
.0015 
.0015 
Gra m 
0. 0532 
Sharkey. . - . -- -. ..___ _. 
.0529 
Marshall .... _- .. . ------ .__.. 
.0415 
.0264 
Norfolk 
.0266 
.0177 
It is apparent that the different colloids vary widely in the total 
equivalents of exchangeable monovalent and divalent bases they con- 
tain. They seem to vary more in this constant than in particle size, 
heat of wetting, swelling, volume of floe, etc. The variation is about 
of the order previously found in the adsorptive capacity for 
malachite green (BO), which is also a base-exchange reaction. Pos- 
sibly the total equivalents of exchangeable monovalent and divalent 
bases might be regarded as more nearly a chemical constant than 
properties previously discussed. 
The quantity of NH 4 ions adsorbed by the colloid was not deter- 
mined directly, but this can be calculated approximately from the 
milliequivalents of Ca, Mg, K, and Na brought into solution. It is 
interesting to note that the adsorption of XH 4 ions from NH 4 C1 solu- 
