This paper describes a working method for separation, fractionation and identification of colloid and colloidal clay minerals in soils. Technical information pertains to super-centrifugation, electron-microscopy and X-ray diffraction. On the basis of these techniques, twenty-two samples have been investigated in conjunction with a soil stud of pumping pavements.

Soils were first dispersed and separated by gravity sedimentation. Fractionation was accomplished by controlled super-centrifugation. The separated fractions were purified and then analyzed by X-ray diffraction. Computed size fractions were checked by shadow castings and lineal dimensions on electron micrographs.

Results include identification of the mineral or minerals present and the properties of the natural sample from which the colloidal fractions were extracted.

These methods furnish a basis for more extensive research relating the behavior of the clay minerals and their contributions to the properties of soils.

Report Date


Report Number

No. 39

Digital Object Identifier



Prepared for presentation at the 25th Annual Meeting of The Highway Research Board, Washington, D.C.: Session No. 4 (December 7, 1948).