PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 
39 
It is apparent from Table 20 that variations in the properties of 
the colloids correspond about as well to variations in the total con- 
tent of exchangeable monovalent and divalent bases as to variations 
in the tta — rr^ — ?sr ratio. Also, variations in the exchangeable 
Al 2 U : .-f--r e 2 U 8 
bases follow the silica ratio fairly closely. 
While the total exchangeable bases and silica ratio may be causally 
related, there is no indication of a causal relation between kind of 
exchangeable bases and silica ratio. There is no indication that 
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SiO- 
-Relation between the NH 3 adsorbed by soil colloids and their ^j o q„ + Fe^O~ ratl ° 
the silica ratio governs the kind of exchangeable bases. As a matter 
of fact, the proportions of exchangeable Ca, Mg, K, and Na given in 
Table 14 show little relation to the silica ratios, except that there 
is some correspondence between the proportion of Ca and Mg and the 
silica ratios. 
The correspondence between a 1 n 4-V . (T ra ^° an( ^ total con- 
tent of exchangeable Ca, Mg, K, and Na might be explained on the 
ground that the natural conditions which have tended to bring about 
a certain silica ratio have tended to bring about also a certain content 
