6 BULLETIN 835, U. 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 day ending at 9 a. m. 



SAMPLING FOR MOISTURE. 



The soil is sampled for moisture with a § -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 

 the 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. 



