UNITED STATES DEPARTMENT OF AGRICULTURE 
iBfllftPW, 
BULLETIN No. 1193 
Washington, D. C. T February 15, 1924 
ESTIMATION OF COLLOIDAL MATERIAL IN SOILS BY ADSORPTION. 
By P. L. Gile, in Charge, Soil Chemical Investigations, H. E. Middleton, Scientist in 
*Soil Physical Investigations, W. O. Robinson, W. H. Fry, and M. S. Anderson, 
Scientists in Soil Laboratory Investigations, Bureau of Soils. 
CONTENTS. 
Page. 
Introduction 1 
Colloidal and noncolloidal soil particles 2 
Previous methods of estimating colloidal material in soils 3 
Adsorption method of estimating colloidal material in soils 7 
Description of method 7 
Experimental procedure 8 
Experimental results 10 
Causes of discordant results 14 
Accuracy of the adsorption method 29 
Procedure suggested 32 
Quantity of colloidal material in soils 33 
Summary *. 38 
Literature cited 39 
INTRODUCTION. 
This bulletin is a report of progress made in developing an adsorp- 
tion method for determining the colloidal material in soils. It is 
anticipated that the method described can be improved as knowledge 
of the soil colloids is increased, but even in its present imperfect 
state it offers advantages over methods previously proposed and 
should, therefore, prove useful in soil investigations. 
Many of the most important properties of soils in general and 
many of the special characteristics of particular soils are doubtless 
associated with the colloidal matter present. It has been shown in a 
previous publication that practically all the adsorptive power of a 
soil, for certain substances at least, is localized in the colloidal material 
(Anderson, 1 i ). The colloidal material with its high adsorptive 
power probably, therefore, acts to a considerable extent as a regu- 
lator of the character of the soil solution, influencing the kind and 
concentration of the various bases in true solution and affecting the 
rate at which the soil minerals decompose. The plasticity (Davis, 6) 
and coherence of soils are evidently functions of the colloidal matter 
or of some particular part of it. It has been generally recognized 
that part of the effects produced by different methods of cultivation 
1 Reference is made by number (italic) to " Literature cited, " p. 39. 
57580—24 1 
