UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1452 
Washington, D. C. 
October, 1926 
PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 
By M. S. Anderson and Sante Mattson, Associate Chemists, Soil Chemical 
Division, Bureau of Soils 
CONTENTS 
Page 
Introduction 1 
Soil colloids studied 2 
Properties of colloidal soil materials. 3 
Size of particles 3 
Specific gravity 5 
Heat of wetting 8 
Adsorption of vapors 10 
Swelling 18 
Viscosity 18 
Volume of fioc 20 
Adsorption of electrolytes 22 
Page 
Properties of colloidal soil mate- 
rials — Continued. 
Electrical charge 27 
Hydrogen-ion concentration 31 
Relations between the properties of 
soil colloids 32 
Relation between properties and 
chemical composition 36 
Character of colloids 42 
Summary 43 
Literature cited 44 
INTRODUCTION 
Although properties of the soil have been extensively investigated 
from the viewpoint of colloidal behavior, comparatively little infor- 
mation is available on the properties of the colloidal material itself. 
Early ideas concerning the properties of soil colloids have been 
based largely on interpretation of properties of the whole soil. Re- 
cently, however, with improvement in methods for isolating the 
colloidal material from the larger soil particles, quantitative deter- 
minations have been made of certain properties of the separated 
colloidal material. 
The adsorptive capacity, chemical composition and binding power 
of various soil colloidal materials have already been studied in this 
bureau (20, Jfl, '40), 1 This bulletin presents data on a number of 
other properties of the colloidal material. The object of this in- 
vestigation was to throw light on the nature of the colloidal soil 
material through a study of properties that characterize it as a 
colloid, rather than to explain any particular field property of the 
soil; therefore some properties were studied that do not have any 
obvious relation to the field behavior of soils. 
1 Numbers in parentheses in italic refer to " Literature cited," p. 44. 
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