506 
Journal of Agricultural Research 
Vol .XXVIII, No. 6 
THE BINDING POWER OF SOIL COLLOIDS IN THE SOIL 
The binding power of the colloid in the soil was found to depend upon a num¬ 
ber of factors. One important factor has been discussed by Gile et al. {4) in a 
previous publication, namely, the extractable and unextractable colloid. It 
would seem that the portion of the colloid which is the more easily dispersed 
would have a greater binding power than that which is more difficultly dispersed. 
There is no direct evidence that this is true, but it has been noted in the case of 
moist and air-dry colloids, which is more or less analogous. It has been noted 
in this laboratory that when a colloid in the moist condition is allowed to become 
air dry or oven dry, it is very difficult to redisperse. This is no doubt due to the 
formation of aggregates in the process of drying similar to the colloidal aggre 
gates found in the soil. 
Another factor of some importance is the difficulty of determining exactly the 
amount of colloid in the soil. The methods of determining the amount of colloid 
show considerable variation in some soils, but these variations are usually of 
small consequence in themselves. However, if the amount of colloid assumed 
to be in the soil is in error by a small per cent, when this is translated into the 
load per gram of colloid, the error will be magnified several times. 
In determining the binding power of the soil colloids in the soil 17 soils in addi¬ 
tion to the five listed in Table III were made up into briquettes by the first method, 
as described on page 500 and tested in the same way. These samples were sub¬ 
samples of the same material used by Gile et al. (4) in determining the amount 
of colloid, and for this purpose the amount of colloid was assumed to be that 
shown by the water vapor adsorption. The results of these tests are shown in 
Table IV. If we assume that L, the load per gram of soil in kilograms, varies 
as C, the amount of colloid present, then 
L==kC n 
Table IV .—The binding power of soil colloids in the soil 
Soil 
Colloid 
by water 
vapor ad¬ 
sorption 
Weight 
of dry 
briquette 
Average 
load per 
briquette 
Load per 
gram of 
soil 
Load per 
gram of 
colloid 
Carrington loam soil . ___ 
Per cent 
32.4 
Grams 
22.1 
Kilograms 
476 
Kilograms 
21.5 
Kilograms 
66.5 
Carrington loam subsoil _- . _ - - _ 
29.4 
25.2 
497 
19.7 
67.1 
Cecil clay loam soil - - - - _ 
10.2 
242 
179 
7.4 
72.5 
Cecil clay loam subsoil _ 
31.5 
23.8 
410 
17.2 
54.7 
Chester loam soil_ _ - - _ _ 
8.5 
22.7 
231 
10.2 
119.6 
Chester loam subsoil _ 
24.8 
23.5 
485 
20.6 
83.3 
Manor loam soil __ _ _ _ _ _ _ _ 
18.4 
23.2 
404 
17.4 
94.6 
Manor loam subsoil_ - _ - _ - _ 
18.6 
23.3 
399 
17.1 
92.2 
Marshall silt loam soil__ _ _ * __ 
27.3 
21.0 
644 
30.7 
112.5 
Marshall silt loam subsoil -_ _ 
34.3 
22.9 
1,188 
51.9 
151.4 
Norfolk fine sandy loam soil _ _ 
10.7 
21.9 
129 
5.9 
55.0 
Norfolk fine sandy loam subsoil „ _ 
20.5 
24.4 
431 
17.7 
86.1 
Ontario loam soil__ _ - _ 
• 18.5 
21.2 
272 
12.8 
69.4 
Ontario loam subsoil _ 
11.4 
23.3 
378 
16.2 
142.2 
Orangeburg fine sandy loam soil _ _ 
6.2 
22.0 
45 
2.0 
33.0 
Orangeburg fine sandy loam subsoil __ __ 
21.5 
25.1 
361 
14.4 
. 66.9 
Sassafras silt loam soil.. _ _ __ 
8.0 
22.0 
127 
5.8 
72.2 
Sassafras silt loam subsoil _ ___-_ 
18.9 
23.0 
447 
19.4 
102.8 
Sharkey clay soil __ _ 
61.2 
21.1 
1,585 
75.2 
122.8 
Susquehanna clay subsoil . _ _ _ 
30.4 
23.8 
481 
20.2 
66.5 
Wabash silt loam soil _ _ __ 
29.8 
21.9 
1,006 
1,025 
46.0 
154.2 
Wabash silt loam subsoil - _ _ 
32.4 
22.2 
46.2 
142.5 
