^ 
UNITED STATES DEPARTMENT OF AGRICULTURE 
S BULLETIN No. 1122 ^ 
Washington, D. C. 
PROFESSIONAL PAPER 
October 21, 1922 
ABSORPTION BY COLLOIDAL AND NOxNCOLLOIDAL 
SOIL CONSTITUENTS. 
By M. S. Anderson', Scientut in Soil Lohoratory Iniestigatioros, W. H. Fry, Scientist 
in Soil Laboratory Investigations. P. L. Gile, Assistant in Charge Soil Chemical 
Investigations. H. E. Middleton. Scientist in Soil Physical Investigations, and ^Y. O. 
Robinson, Scientist in Soil Laboratory Investigations. Bureau of Soils. 
CONTENTS. 
Page. 
Introduction 1 
I*revious work 2 
Distinction between colloid and noncoUoid. . . 3 
Outline of investigation 3 
Methods of determining absorption 4 
Estimation of noncoUoidal absorption from 
soil fractions 5 
Methods of separating soil colloids 5 
Preparation of soil fractions 6 
Absorption by the fractions 6 
Page 
Estimation of noncoUoidal absorption from 
mineral particles 7 
Preparation of min eral povrders S 
Absorption by the different soil minerals. 9 
Absorption by the mineral particles in the 
soil 10 
Evidence concerning the nature of the soil 
coUoids aflforded by absorption data 13 
Absorptive capacities of mineral particles 
below one rnicron in diameter 13 
Absorptive capacities of synthetic gels.. . 15 
General discussion 16 
Summary 17 
Literature cited 19 
INTR(JDUCTION. 
Absorption^ by soils has been investigated since the early days of 
soil science. Nevertheless, the parts played by the different soil 
constituents in absorption phenomena have not been accurately 
determined. It has been recognized in a general way that the finer 
sod particles are more absorptive than the larger particles and that 
organic constituents are among the most highly absorptive. How- 
ever, very few accurate quantitative data have been obtained on 
the absorptive capacities of soil particles of different sizes. 
A soil is of course a very intimate mixture of many components, 
and it would seem at first thought unreasonable to allocate such a 
general property as absorption to any one class of constituents. 
However, in 1909. Ashley {2)^ proposed the absorption of malachite 
green as a measure of the relative colloidal contents of ceramic clays. 
This was equivalent to assuming that practicalh' all the absorption 
of the clay was due to colloids and that the colloids in diflerent clays 
» The term "absorption" is used in this paper in the general sense, for which "sorption" has recently 
been r^rop-jsed. It is not intended to convey any idea of the mechanism of the process as is done by the 
term "adsorption" or by "absorption" used in a more specific sense. 
* Reference is made by number (italic) to ''Literature Cited," p. 19. 
8107— 22— Bull. 1122- 
