PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 43 
the colloidal material, some properties being governed by it almost 
exclusively (i, 2), so that the results have an intimate bearing on the 
behavior of soils. 
The results of this investigation emphasize the conclusion arrived 
at in previous studies — that, in order to explain satisfactorily the 
behavior of a soil, it is important to determine the kind as well as 
the quantity of colloidal material present. The fact that a soil 
contains 30 per cent or 50 per cent of colloid does not give much 
indication of the behavior of the soil unless the kind of colloidal 
material is specified. Some soils of warm humid regions with 70 
per cent of colloidal material are more friable and permeable than 
soils containing 30 per cent of a colloidal material similar to the 
Fallon. It is true that the properties which have been studied are 
largely " laboratory " properties. But materials which differ so 
widely in their laboratory properties would obviously vary in their 
influence on such field properties of soils as permeability, response 
to applications of lime and fertilizer, tendency to erosion, cohesion, 
and the like. 
SUMMARY 
This investigation deals with the properties of colloidal materials 
isolated from widely different soils. Data are given on size of 
particles, specific gravity, adsorption of vapors, swelling, viscosity, 
volume of floe, adsorption of electrolytes, methylene blue required 
to render particles isoelectric, and hydrogen-ion concentration. 
The different colloidal soil materials vary considerably in all prop- 
erties except specific gravity. 
A relationship between properties is indicated by the fact that 
variations of the colloids in one property usually parallel variations 
in other properties. The correlation between variations in the prop- 
erties studied might be explained on the ground that these properties 
are dependent on a few more fundamental properties, such as chemi- 
cal nature, size, and structure of particles, and that these more funda- 
mental properties are related. 
Variations in properties of the different colloids correspond fairly 
closely to variations in the exchangeable bases and to variations in 
the A1 ~ — , i, ~ ratio. The correlation between the properties and 
Al 2 03 + Fe 2 03 F * 
the silica ratio probably does not mean that all properties of the 
colloid are chiefly governed by the silica ratio directly. Certain 
properties are evidently governed more directly by the kind or quan- 
tity of exchangeable bases than by the silica ratio. However, the ex- 
changeable bases and the silica ratio are usually correlated. 
Soil colloids appear to be more lyophobe than lyophile in char- 
acter, although they can not be looked upon as typical of either class. 
The importance of determining kind as well as quantity of colloid 
in a soil is pointed out. It is suggested that one or two properties, 
or the A1 ^ , ^ — pr- ratio, would characterize the kind of colloidal 
Al 2 \J3 + r e 2 U3 
material fairly well. 
