498 A. B. BEAUMONT 
The soils were exposed to the vapor of the acid solution for one week 
(Mitscherlich found five days sufficient), at room temperature in the 
desiccator, which had previously been evacuated with a suction pump 
until the vapor pressure was approximately 2 centimeters of mercury. 
After exposure of the soils for one week, air was allowed to enter the desic- 
cator very slowly. If air is allowed to enter rapidly, the cooling effect 
due to its rapid expansion causes, a condensation of water vapor on the 
contents of the desiccator. 
The soils were then quickly poured and brushed into previously weighed 
bottles fitted with ground glass stoppers. It was computed that the 
time during which the soil was exposed to the drying influence of the air 
was less than ten seconds. In that time the loss of water by evaporation 
is negligible. 
The soil was dried at a temperature of 105° C. and weighed, and the 
loss of water was computed as a percentage of the oven-dry weight. This 
is hygroscopic water, and the amount present has been considered by. 
Mitscherlich and others to depend upon the extent of surface of the soil. 
It has therefore been considered a measure of the colloidal content, and 
is so considered in this work. 
Owing to the high experimental error, which was experienced even with 
the exercise of the greatest care, it was decided to run several replicates 
of each test. Usually five replicates of each treatment were run. In 
order to make experimental conditions as uniform as possible for the 
different treatments, at least one test of each treatment was put in the 
same desiccator, and in the different desiccators the relative positions of 
these tests were changed. 
The dye-adsorption method.— Five-gram portions of oven-dry soil or 
its equivalent were used with the dye-adsorption method. The amount 
of dye used varied with both the kind of dye and the soil. It was neces- 
sary to run a preliminary test for each dye and soil in order to ascertain 
how much of the dye or its concentration was necessary. 
The dye solution and the soil were put into a shaker bottle such as is 
used in the mechanical analysis of soils (Lyon, Fippin, and Buckman, 
1915), and the volume was brought up to 150 mils by means of distilled 
water. This was shaken in a mechanical shaker for thirty minutes, it 
