May 10,1924 Factors Influencing Binding Power of Soil Colloids 
505 
Table III .—Effect of method of treatment on the breaking strength of the briquette 
Soil 
Colloid 
Moisture 
Load per gram of soil 
First 
method 
Second 
method 
Third 
method 
Norfolk fine sandy loam soil__ __ 
Marshall silt loam soil___ 
Sharkey clay soil_ .. _ 
Per cent 
10.7 
27.3 
61.2 
Per cent 
11.4 
16.0 
18.0 
14.0 
12.5 
Kilograms 
5.9 
30.7 
75.2 
12.8 
16.2 
Kilograms 
10.1 
37.5 
103.8 
19.6 
31.1 
Kilograms 
9.6 
39.8 
Ontario loam soil. 
18.5 
11.4 
Ontario loam subsoil_.. 
PRESSURE 
The pressure used in making the briquettes could be controlled very easily 
by keeping the hydraulic pressure constant. The length of time which the 
pressure was applied to the material had some effect on the height of the briquette. 
Tests were made which indicated that the material came to equilibrium in from 
30 to 60 seconds with a pressure of 2,000 pounds per square inch, so in making 
up the briquettes the pressure was applied to the material for 60 seconds. With 
the apparatus as described above it was difficult to get uniform briquettes at 
pressures less than 2,000 pounds per square inch. Tests were made with pres¬ 
sures up to 5,000 pounds per square inch, but as there was no apparent advantage 
in using more pressure than was necessary in securing uniform results, 2,000 
pounds per square inch was adopted as standard. Under these conditions it 
was possible to make up four briquettes of equal quantities of a given material 
which would be within 0.05 mm. of the same height. 
DRYING THE BRIQUETTES 
Considerable difficulty was encountered in drying the briquettes so as to avoid 
cracking and checking. By removing the moisture very slowly and uniformly 
at the beginning of the drying this difficulty was largely overome. It was 
found that after the moisture content had been reduced approximately 5 per cent 
the briquettes could be dried quite rapidly without danger of cracking. The 
method employed was to allow the briquettes to stand in a desiccator containing 
distilled water for 24 hours after being made up. At the end of this time they 
were transferred to an electrical drying oven, which was allowed to remain at 
room temperature and through which a very slow current of air nearly saturated 
with moisture was passed for 24 hours. Then the temperature of the oven was 
raised to 30° C. and the process continued 24 hours longer. The air was then 
shut off and the temperature of the oven raised to 110° C. for 18 hours. The 
briquettes were then transferred to a desiccator containing sulphuric acid and 
allowed to cool before being tested. Another method which gave equally as 
good results, but which took a little more time, was to have a series of four 
desiccators in which the saturation of air was, respectively, 100, 75, 50, and 25 
per cent. The briquettes were allowed to stand 24 hours in each desiccator and 
then transferred to the drying oven at 110° C. The principal consideration in 
any method of drying is to so regulate the system that the moisture is supplied 
to the surface of the material to be dried at the same rate that it is carried off 
by evaporation so that the surface does not become dry and allow it to shrink 
and crack. 
