UNITED STATES DEPARTMENT OF AGRICULTURE 



,f BULLETIN No. 1122 1 



Washington, D. C. PROFESSIONAL PAPER October 21, 1922 



ABSORPTION BY COLLOIDAL AND NONCOLLOIDAL 

 SOIL CONSTITUENTS. 



Bj^ M. S. Anderson, Scientist in Soil Laboratory Investigations, 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 W. O. 

 Robinson, Scientist in Soil Laboratory Investigations, Bureau of Soils. 



CONTENTS. 



Page. I Page 



Introduction 1 ! Estimation of noneoUoidal absorption from 



Previous work 2 



Distinction between colloid and noncolloid ... 3 



Outline of investigation 3 



Methods of determining absorption 4 



Estimation of noncolloidal aljsorption from 



soil fractions 5 



Methods of separating soil colloids 5 



Preparation of soil fractions 6 



Absorption by the fractions 6 



mineral particles 7 



Preparation of mineral powders S 



Absorption by the different soil minerals. 9 

 Absorption by the mineral particles in the 



soil 10 



Evidence concerning the nature of the soil 



colloids afforded by absorption data 13 



Absorptive capacities of mineral particles 



below one micron in diameter 13 



Absorpti-\'6 capacities of s3^athetic gels. . . 15 



General discussion 16 



Summary 17 



Literature cited 19 



INTRODUCTION. 



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 

 soil 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 (^)^ proposed the absorption of malachite 

 green as a measure of the relative colloidal contents of ceramic clays. 

 This was equivalent to assuming that practically all the absorption 

 of the clay was due to colloids and that the colloids in different clays 



1 The term "absorption" is used in this paper in the general sense, for which "sorption" has recently- 

 been proposed. 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. 



2 Reference is made by number (italic) to "Literature Cited," p. 19. 



8107— 22— Bull. 1122 1 



