PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 35 
tude of variation between the lowest and highest determinations the 
same for all properties. 
The seven colloids tend to assume about the same order in the 
various determinations. The Fallon colloid is the highest in all 
properties, whereas the Xorfolk and Susquehanna are the lowest in 
most determinations. The Sharkey and Marshall colloids are usually 
above the mean and the Huntington and Sassafras somewhat below 
the mean. There are several exceptions to this order, the most notable 
occurring in the viscosity determinations. As pointed out on page 19. 
there was some ground for believing that these measurements were 
largely affected by temporary conditions of the samples, as well as by 
the more fundamental nature of the material. 
The parallelism between the variations of the colloids in one prop- 
erty and variations in another property is closer when certain groups 
of properties are considered. The properties from " heat of wet- 
ting " to " volume increase in water," as shown in Table 19 left to 
right might be regarded as one group of properties (Group 1). 
since they have to do with the behavior of the dry gel. The proper- 
ties. " volume of floe " to " concentration required to give a viscosity 
of 1.9 r ' may be regarded as another group (Group 2), since they are 
dependent on the behavior of the material in the sol condition. The 
last three properties constitute a third group in that these properties, 
according to current theory, are more directly dependent upon the 
chemical nature of the material than are the other groups of 
properties. 
Within these groups the variations of the colloids in one property 
parallel variations in another property in a nearly quantative man- 
ner. In the case of certain properties this parallelism in variations 
can be reasonably explained on the ground that both properties are 
largely determined by the same fundamental characteristic of the 
colloid. It has already been pointed out, for instance, that the 
adsorption of water vapor and ammonia gas are probably both gov- 
erned to a considerable extent by the structure of the material. 
All parallelisms in variations of the properties of the different 
colloids, however, can not be explained on this basis. For instance, 
one would not expect that a high capacity for the adsorption of 
electrolytes (high-exchangeable-base capacity) would necessarily 
accompany a high heat of wetting or a high capacity for imbibing 
water. These two properties are presumably largely determined by 
different fundamental properties of the colloid and, as a matter of 
fact, some artificial colloids which are very high in one of these two 
properties are very low in the other. In the case of silica gel, for 
instance, heat of wetting may be high and the exchange adsorption 
may be very low. 
In the case of the soil colloids, however, there is apparently a fair 
degree of Correspondence between variations in nearly all the prop- 
erties. This might be taken as indicating that in the case of these 
materials, the more fundamental properties, such as size, structure, 
and chemical nature of the particles, are usually associated in a cer- 
tain way. Small size of particles and a particular kind of structure, 
for instance, may usually accompany a certain chemical composition 
of the material. Further evidence of this will be discussed later. 
Although the correspondence between variations in different prop- 
erties of the series of soil colloids indicates that the fundamental 
