PROPERTIES OP THE COLLOIDAL SOIL MATERIAL 
19 
too long. In order to overcome the changes that some sols undergo 
on standing, and to have the different colloids in a comparable con- 
dition for testing, the sols were drawn through a Gooch crucible 
several times just before making the viscosity determination. 
Determinations were made of suspensions in pure water and in 
water containing a few drops of ammonia to promote dispersion. 
All suspensions contained the equivalent of 2 grams of oven-dried 
colloid per 100 grams of suspension. The results obtained are shown 
in Table 9. The viscosity is expressed as the viscosity ratio, which 
is the viscosity of the colloid compared with that of pure water at 
the same temperature. 
Table 9. — Relative viscosity of soil colloids 
Kind of colloid 
Fallon 
Sassafras 
Susquehanna 
Marshall 
Relative 
viscosity 
of un- 
treated 
colloid 
1.33 
1.33 
1.27 
1.23 
Relative 
viscosity 
of colloid 
treated 
with 
ammonia 
1.08 
1.04 
Kind of colloid 
Huntington- 
Sharkey 
Norfolk 
Aragon 
Relative 
viscosity 
of un- 
treated 
colloid 
Relative 
viscosity 
of colloid 
treated 
with 
I ammonia 
1.16 
1.14 
1.12 
1.14 
1.13 
1.00 
1.05 
The viscosities of the different soil colloids vary considerably. 
These variations could not be due to differences in solid volume, since 
the sols all contained the same quantity of solid material and the 
densities of the different colloids were essentially the same. Accord- 
ing to the theory of Einstein, the viscosities of colloids at equal 
volume concentrations should be the same, provided the particles 
behave as rigid spheres. Variations from this formula have fre- 
quently been explained by assuming the association of water with 
the particles, the quantity of associated liquid being influenced by 
particle size, by condition of aggregation, and perhaps by other 
factors. 
In the case of the soil colloids, the viscosities showed little or no 
relationship to average particle size. It seems probable, however, 
that the viscosities of the different colloids were largely dependent 
upon the state of aggregation. The data in Table 9 suggest this. 
A comparison of columns 2 and 3 show that somewhat lower viscosi- 
ties were obtained when the colloids were dispersed in water to 
which a little ammonia had been added to promote deflocculation 
than when pure water was used. Furthermore, the acid colloids, 
the Susquehanna, Sassafras, and Norfolk, which were difficult to 
disperse in pure water, were much more affected by the addition of 
ammonia than were the neutral or alkaline colloids, which were 
easily dispersed in pure water. 
One of the characteristic differences between tyophile and lyophobe 
colloids is the difference in the concentration at which they become 
exceedingly viscous. This suggests that the different colloids might 
be compared on the basis of the concentration required to give a high 
viscosity, as well as on the basis of their viscosities at a given con- 
centration. The seven soil colloids were therefore compared on this 
basis. 
