PKOPERTIES OF THE COLLOIDAL SOIL MATERIAL 
17 
Table 7 shows the water imbibed by nine soil colloids, silica gel, 
bentonite, and gelatin in the Hofmeister determination, and the 
water held by seven soil colloids in the moisture-equivalent deter- 
mination. The water taken up in each case is expressed as per cent 
of the dry weight of the material. 
Table 
-Quantities of water held by different colloids 
Kind of colloid 
Water 
held by 
briquetted 
material 
Water 
held, 
moisture 
equivalent 
; 
Kind of colloid 
Water 
held by 
briquetted 
material 
Water 
held, 
moisture 
equivalent 
Gelatin. 
Per cent 
1,045 
Per cent 
Susquehanna .. . ... 
Per cent 
SS 
84 
76 
63 
60 
48 
Per cent 
67 
56 
687 ; 
139 1 120 
123 ; 94 
101 72 
62 
Fallon 
Norfolk . . . .. - .. 
62 
64 
Cecil 
The colloids held somewhat more water under the conditions of the 
briquette test than under those of the moisture equivalent. This was 
to be expected; since in the briquette method water is held against 
gravity, whereas in the moisture-equivalent method it is held against 
a force equivalent to 1,000 gravity. Other differences in the condi- 
tions of the methods also are doubtless responsible for part of the 
difference in results. For instance, the state of aggregation of the 
colloids on exposure to water w T as different. Both methods bring out 
significant differences in the water-holding capacities of the different 
soil colloids. The briquette method perhaps gives the more accurate 
comparison of the d'fferent colloids, since the materials used in this 
test were all prepared in as uniform a manner as possible. 
The different soil colloids, with the exception of the Susquehanna, 
vary in their capacities for holding liquid water almost exactly as 
they vary in their capacities for adsorbing water vapor over 30 per 
cent sulphuric acid. (Table 5.) Each colloid held approximately 7.5 
times as much water in the briquette test as in the adsorption test 
over 30 per cent sulphuric acid. Also, the quantities of water held 
by the different colloids are nearly proportional to the heats evolved 
on wett r ng. The correspondence between these determinations for a 
series of soil colloids is shown in Table 8 by means of three ratios. 
Table 8. — Proportionalities between water-holding capacity, water-vapor 
adsorption, and heat of wetting of soil colloids 
Kind of colloid 
Water 
imbibed by 
briquettes 
divided by 
water-vapor 
adsorbed 
Water 
imbibed by 
briquettes 
divided by 
heat of 
wetting 
Heat of 
wetting 
divided by 
water-vapor 
adsorbed 
Fallon - 
7.9 
9.5 
7.7 
7.5 
6.6 
7.7 
17.0 
7.9 
7.2 
7.0 
8.3 
7.9 
7.5 
16.6 
90 
Huntington - 
131 
112 
9ft 
Norfolk — 
86 
102 
Sharkey --- 
102 
6553 26 3 
