18 BULLETIN 1122, U. S. DEPARTMENT OF AGRICULTUEE. 



noncolloidal absorption might reach 10 to 20 per cent of the whole 

 soil absorption. 



Absorption by noncolloidal constituents should, therefore, not 

 seriously affect absorptive methods for determining the amount of 

 colloids in soils. 



Evidence concerning the nature of the soil colloids is afforded by 

 the absorptive capacities of various substances. Minerals ground 

 to a state of subdivision probably equal to that of the mixed soil 

 colloids, or "ultra clays," absorbed less than the average ultra clay. 

 The average absorption of peat and synthetic inorganic gels, on the 

 other hand, was more nearly like that of the ultra clays. 



Since soil colloids appear to be of quite a different nature from 

 the noncolloidal particles, and not merely finely comminuted min- 

 erals, it is understandable why such a large part of the absorption 

 of a soil should be localized in the colloidal matter. 



