May 10,1924 Factors Influencing Binding Power of Soil Colloids 
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were all of the same size, the weight of the briquette is taken as a measure of the 
density. It may readily be seen from figure 4 that the maximum load cor¬ 
responds very closely to the maximum density of the briquette at the critical 
moisture content. Since the maximum load occurs at the critical moisture 
content, in comparing the breaking strength of two or more materials, each is 
made up at its critical moisture content. 
Fig. 3—Showing the effect of the amount of moisture on the height of the briquette 
TREATMENT OF THE MATERIAL 
The treatment of the material before being made up into briquettes was found 
to be one of the most important factors as well as the most difficult to standardize. 
In order to get the water thoroughly distributed through the material a consider¬ 
able amount of mixing was necessary, and in the matter of mixing the personal 
equation entered to a large extent. A mechanical method of mixing was tried 
out with but little success due to the fact that it was very difficult to control the 
amount of moisture in the mixture accurately, and the method could not be adapted 
to the small amounts of material available. 
The method which was most easily duplicated in comparative tests of soils 
was to weigh out sufficient air-dry soil to make 100 gm. on the oven-dry basis. 
The soil was weighed out in a 250 cc. beaker and sufficient water added to bring 
it slightly above the critical moisture content. The material was then trans¬ 
ferred to a glass mortar and rubbed gently with a glass pestle until the water was 
evenly distributed. It was then replaced in the beaker and allowed to stand in 
a desiccator containing distilled water for 42 hours. At the end of this time the 
material was weighed, the moisture content adjusted if necessary and the 
briquettes were made up as described above. This was designated as the first 
method. 
The second method was the same as the first up to the point where the water 
was added. In this case the water was added gradually, the material being 
stirred with a spatula until sufficient water had been added to bring it to the 
consistency of thick cream. The material was then allowed to dry in the air 
with occasional stirring until it reached the critical moisture content. It was 
then transferred to the glass mortar and treated in the same manner as in the 
