8 BULLETIN 835, U. S. DEPAETMEXT OF AGEICULTUEE. 
PACKING THE BOXES. 
The boxes were packed with soil in much the same way as the 
flumes, except when the initial percentage of moisture in the wet-soil 
part of the box was relatively low. In this case, the soil was first 
wetted to the desired degree, and then placed in the box in layers one 
inch thick and packed by dropping a weight a given distance upon a 
board covering the layer of soil. The distance the weight was to be 
dropped, and the number of times it was to be dropped for each layer 
was determined by tests for each soil. The section of the box to be 
filled with air-dry soil was packed by using the hammer and block. 
PREVENTING EVAPORATION IN FLUMES. 
Those flumes in which evaporation from the top of the flume was 
to be prevented were covered with two-ply unsanded maltoid roof- 
ing paper. A strip of the roofing cut to the proper size was placed 
upon the top of the flume and reached from one end to the other. 
The side joints were made air tight. On the glass side of the flume 
the roofing was folded over and clown on the outside of the glass 
about one-half inch. The joint between the roofing and the glass 
was held in place and made tight by means of an angle-iron strip 
made of galvanized iron clamped along the upper edge of the glass 
and on top of the roofing. To prevent air-trapping, J-inch vent 
holes were cut in the roofing at intervals of about 4 feet, Tests 
of the effectiveness of this covering to prevent evaporation of 
moisture from the flumes indicate that at least 80 per cent of the 
evaporation from an open flume was prevented by this covering. 
A more effective method of preventing evaporation could be de- 
vised, but there would be great danger of the entrance of some un- 
known factors into the work. The entrance of these factors would 
prove fatal for comparison with much of the other work. 
COVERING THE BOXES. 
The plate-glass sides of the boxes were sealed to the boxes by means 
of cushions made of maltoid roofing. The glass was held in place and 
clamped tightly to the box by means of wooden strips fastened to 
the box proper by means of eyebolts fitted with thread and nut. 
Eubber cushions were tried, but did not give the same satisfaction 
that was obtained from the use of maltoid. 
CAPILLARY ACTION IN THE SOIL IN THE ABSENCE OF FREE WATER. 
The term " free water " as here used is water not held by capil- 
larity and obeying the laws of gravity. It is variously termed " free 
water/' " ground water," and " water of gravitation." (IT.) 1 
1 The figures in parentheses apply to tho references at the end of this bulletin. 
