2 BULLETIN 1452, U. S. DEPARTMENT OF AGEICULTUEE 
THE SOIL COLLOIDS STUDIED 
In the course of various investigations in this bureau, colloidal 
materials have been isolated from some 50 soils and subsoils from 
different parts of the United States, and certain characteristics of 
these materials have been determined. It was therefore possible to 
select for this study eight colloids which represent fairly well the 
major variations shown in one or two properties by a considerable 
number of different colloids. The ultimate chemical compositions 2 
of the eight colloidal materials isolated especially for this study are 
shown in Table 1. 
Table 1. — Chemical composition of colloidal soil materials studied 
Name of colloid SiOj TiOj | Fej0 3 Alj0 3 MnO CaO MgO KjO 
Per cent 
Fallon [ 50.49 
Sharkey < 50.13 
Marshall | 44.94 
Susquehanna | 43. 92 
Sassafras j 40.93 
Huntington I 36.65 
Norfolk | 38.46 
Aragon j 15.86 
Per cent 
.51 
.46 
.47 
1.08 
.70 
.45 
.93 
3.54 
Per cent 
10.77 
8.70 
8.91 
5.70 
11.98 
11.07 
11.43 
22. 67 
Per cent Per cent Per cent 
16.73 
21.70 
22.15 
33.82 
29.55 
29.98 
33.38 
34.38 
0.121 
.035 
.126 
.006 
.033 
.192 
.005 
2.36 
1.48 
1.12 
.18 
.37 
.53 
.28 
.21 
Per cent 
5.32 
2.54 
1.95 
.39 
1.37 
.72 
.46 
29 
Per cent 
2.24 
1.86 
2.07 
.92 
1.04 
1.93 
.55 
.27 
Name of colloid 
NajO 
PlOc 
S0 3 
Ignition 
loss 
Total 
Organic 
matter 
HjO at 
110° C. 
Mols. Si0 2 
Mols. Al203+FesOj 
Pfr cent 
Fallon.... 0.54 
Sharkey .24 
Marshall j .19 
Susquehanna I .29 
Sassafras j .31 
Huntington ! .33 
Norfolk ! .31 
Aragon j .33 
Per cent 
0.37 
.69 
.70 
.21 
.11 
.98 
.28 
Per cent 
0.11 
Per cent 
10.05 
12.56 
16.86 
13.50 
14.44 
16.82 
13.16 
21.59 
Per cent 
99.61 
100. 40 
99.70 
100.11 
100. 85 
99.92 
99.30 
99.47 
Per cent 
1.79 
3.83 
Per cent 
12.15 
11.46 
8.96 
2.38 
5.07 
4.61 
3.51 
4.51 
3.62 
3.11 
2.73 
1.99 
1.85 
1.68 
1.60 
.55 
The colloids are named for the soils from which they were ex- 
tracted. The locations and depths of the soil samples are as follows : 
Fallon loam. Depth to 12 inches. Six miles west of Fallon* 
Churchill County, Nev. 
Sharkey clay. Depth to 4 inches. Near Valley Park, Issaquena 
County, Miss. 
Marshall silt loam. Depth to 14 inches. Two miles west of 
Mynard, Case County, Nebr. 
Sassafras silt loam. Depth 8 to 22 inches. Near Easton, Talbot 
County, Md. 
Huntington loam. Depth to 8 inches. One mile west of Seneca, 
Montgomery County, Md. 
Norfolk fine sandy loam. Depth 12 to 36 inches. One-fourth mile 
south of Scottsville, Wayne County, N. C. 
Susquehanna clay. Depth about 4 feet. Takoma Park, Mont- 
gomery County, Md. 
Aragon soil. Depth 1314 to 17 feet. Turrialba, Costa Rica. 
2 Aralyses were made by the fusion method for soils, essentially as described in the 
"Methods of Analysis" of the Association of Official Agricultural Chemists (5). The 
orennic matter -was determined by dry combustion, multiplying the CO> evolved by the 
factor 0.471. 
