PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 
37 
and structure of the particles. Furthermore, the fact that a paral- 
lelism exists between properties which are presumably governed 
chiefly by structure and properties which are more strictly chemical 
was explained on the ground that structure and chemical nature of 
the soil colloids probably tend to vary together. The explanations 
given are rendered more probably by the fact that a correspondence 
obtains between many properties of the colloids and their chemical 
compositions. Some instances of such correspondence have been 
given in previous publications bv Anderson and Mattson (3) and 
byGile {21). 
Other investigators have also noted a correspondence between 
certain properties of soil colloids or fine soil fractions and their 
chemical composition. Hardy (22) observed some relation between 
3 - ratio, shrinkage, and the water content at maximum 
the : 
SiOo 
plasticity of certain clay fractions. Joseph and Hancock (26) 
pointed out that the ., ^ ratio is connected with the extent the 
moisture-equivalent determination is modified by ignition of the ma- 
terial and by treatment with sodium carbonate. The correspondence 
however, is not marked. Later Joseph (27) called attention to a 
better correspondence between the . , ^ ratio, imbitional water and 
rate of evaporation of several Sudan clays. Robinson and Holmes 
showed that there is some relationship between the ratio ,, ^ , i, ^ 
and the color of soil colloids (47, p. 25) . 
The correspondence between variations in properties and in 
chemical composition of the colloids studied in this investigation is 
shown in Table 20. This table gives the molecular proportions of 
Si0 2 to A1 2 3 plus Fe 2 3 in the colloids, the exchangeable monovalent 
and divalent bases, and a summary of the properties expressed on the 
relative basis described on page 34. 2S The relative values for proper- 
ties in this table are averages of the relative values given for indi- 
vidual properties in Table 19. The properties are grouped as 
described on page 35. 
Table 20. — Correspon dence 
between properties m 
soil colloids 
d chemical compt 
sit ion of 
SiO? 
Average I Average 
Exchange- 1 relative ' relative 
Average 
relative 
Al 2 03+Fe 2 03 
Mg+K+Na 
properties > properties 
in Group 1 in Group 2 
all prop- 
erties 
Fallon 
100 
75 
56 
19 
100 
61 
44 
n 
! 
100 100 
79 46 
48 45 
12 52 
25 ! 57 
12 j 6 
13 i 8 
100 
Sharkey 
69 
Marshall • .. 
51 
Susquehanna .. . 
19 
Sassafras.. ; 
13 14 
29 
Huntington.. 
4 

15 
Norfolk 

9 
23 Several other chemical constituents and ratios of constituents show some correspond- 
ence with properties. This is to be expected, since, as previously pointed out (-'/7. p. 16), 
certain constituents of the colloidal material tend to varv directly or indirectlv with other 
SiO« 
constituents. Only the ■,. ~ ^ p ~ ratio and the exchangeable bases are given in 
Table 20, however, since these, on the whole, correspond better with th© properties. 
