6 BULLETIN" 835, IT. S. DEPARTMENT OF AGRICULTURE. 
the side of the flume indicating the outward extent of the wet soil 
area and the five lines above described give five definite points with 
which to locate each of the markings upon the glass side of the 
flume. The positions of these five points are determined by direct 
measurements from the surface of the water in the tank along the 
five lines parallel to the longitudinal axis of the soil column. 
The original horizontal surface of the water in the tanks was used 
as a base for all measurements of the position of the moisture in the 
soil column in all flumes rather than a transverse line coincident 
with the change in inclination of the soil column, if any, from the ver- 
tical. Inasmuch as the movement of moisture in the soil columns by 
capillarity from free water is about equal for all inclinations, from the 
vertical upward to the vertical downward, for the first foot or more, 
using the surface of the water as a base for measurements does not 
produce an appreciable error in making comparisons. 
In the experiments with wet and dry soils the initial point of 
measurement is the line of contact between the original areas of wet 
and dry soil. No water is added to the boxes after they are set up, 
but the water is added to the wet soil at the time of packing. The 
quantity of water to be added to the soil to be packed wet is calculated 
upon the dry weight of the soil and then this water is added by 
measurement. 
MAINTAINING THE WATER LEVEL IN TANKS. 
All water added to the tanks after the initial filling is added in 
measured quantities and recorded as water used by the flume. Water 
is. added sufficiently often to maintain the level of water in the tanks 
at a rather constant elevation. The water added during any 24 hours 
is recorded as the water used during the day ending at 9 a. m. Unless 
otherwise specified all references to water used per day will mean for 
the clay ending at 9 a. m. 
SAMPLING FOR MOISTURE. 
The soil is sampled for moisture with a 5-inch carpenter's auger in 
the usual way and the samples immediately placed in tared screw- 
topped glass bottles and weighed. A composite sample is made of 
t\Ue upper 5 inches of soil and another composite sample for the lower 
5 inches in each boring. The samples are taken in planes parallel to 
the planes indicating the advance of the moisture within the flumes 
at the points sampled. A boring is located by a measurement along 
the top of the flume from the water level. The samples, as soon as 
convenient after the first weighing, are placed in a water- jacketed 
oven and dried at the temperature of boiling water until a constant 
weight is obtained. Using the dry weight of the soil sample as a 
basis, the percentage of moisture in the sample is calculated. 
