jowl of amm research 
Vol. XXVIII Washington, D. C. Mat 10, 1924 No. 6 
FACTORS INFLUENCING THE BINDING POWER OF SOIL 
COLLOIDS 1 
By Howard E. Middleton 
Scientist in Soil Physical Investigations , Bureau of Soils, United States Department 
of Agriculture 
INTRODUCTION 
In a previous publication by Moore et al. (7), 2 of this Bureau, the point was 
brought out that the colloidal material is evidently the principal binding material 
of the soil. Further study has not only confirmed this point but, as shown by 
Anderson et al. ( 1 ), approximately 95 per cent of the total absorption of the soil 
is due to the soil colloids. The influence of the soil colloids on 'the physical and 
chemical properties of soil is no doubt coming to be one of the most important 
studies in soil science. The binding power of the soil colloids is of particular im¬ 
portance as regards tillage operations, foundations, and the construction of dams 
and roads. With these points in mind this investigation was undertaken in order 
to determine if possible the factors influencing the binding power of the soil 
colloids and the relation of the compressive strength of the soil to the amount of 
colloidal material present in the soil. 
PREVIOUS WORK 
Various methods for the determination of the binding power of soils have been 
described. The methods of Atterberg (8) and Puchner ( 8 ) are probably the 
more important. These methods are based primarily on the breaking strength 
of briquettes. Marquis (6) describes various methods for determining the bind¬ 
ing power of soils, particularly those of Atterberg and Puchner. He found very 
wide discrepancies in the results by each of these methods. More recently Arnd 
(8) has described a method by which he determines the binding power by 
friction, rotating a cylinder of soil against a stationary prism of soil under a 
definite pressure. None of these methods, however, takes into, account the - 
colloidal content of the soil. 
Jackson (5) has described a method for determining the binding power of rock 
powder, which was modified somewhat and used in this investigation. 
METHOD OF INVESTIGATION AND APPARATUS 
For the purposes of this investigation the material 3 under consideration was 
made up into briquettes 25 mm. in diameter and 25 mm. high under a pressure 
of 2,000 pounds per square inch, with a certain predetermined amount of water, 
carefully dried, heated 18 hours at 110° C., cooled in a desiccator and subjected 
to the compression test in an Olsen universal testing machine. 4 The load 
1 Received for publication March 24, 1924. 
2 Reference is made by number (italic) to “Literature cited,” p. 513. 
3 “Material” as used in this paper refers to soil or to mixtures of soil colloids and sand. 
4 The use of this machine was granted for this purpose by the Division of Tests, Bureau of Public Roads, 
U. S. Dept, of Agriculture. 
Journal of Agricultural Research, Vol. XXVIII, No. 6 
Washington, D. C. May 10,1924 
Key No. H-8 
96036—24f-1 
(499) 
