152 
Journal of Agricultural Research 
Vol. XI, No. 4 
to paraffin these. To prevent leakage of water a galvanized-iron tray, 
3 to 4 inches high and made to fit snugly, was placed in the bottom of the 
wooden box, the blotting paper extending from the top of the sides of the 
wooden box to the bottom of the metal tray. By means of metal sup¬ 
ports a wooden table was held in position i to 2 inches above the surface 
of the water and from 0.5 to i inch from each paper-lined side of the box. 
In the later determinations a table of galvanized-wire screen was substi¬ 
tuted, as it occupied less space. 
To provide a constant temperature room, we inclosed with alternate 
layers of building paper and boards a portion of the cellar of the Experi¬ 
ment Station building that was windowless and not in contact with any 
outside wall. An electric light on the outside of a double window fur¬ 
nished the necessary illumination without heating the room. The oper¬ 
ator opened and closed the door as quickly as possible on entering the 
room daily to change the soil in the trays. A maximum and minimum 
thermometer was hung in the room, and the daily readings were recorded. 
Later a recording hygrometer was added. No sudden changes in tem¬ 
perature or humidity were observed. 
We employed 24 absorption boxes, which were placed on low shelves 
against the heavy inside brick wall. From the first we had exposed sam¬ 
ples of two control soils in different absorption boxes. At first the ob¬ 
ject of this was to find the variation in the coefficient of the same soil from 
day to day, but later to indicate whether any abnormal conditions had 
prevailed in the room, the boxes, or the drying oven. Of the two control 
soils used on the same day the one was a subsoil with a coefficient of 
about 5 to 6, while the other was a finer-textured soil or subsoil with a 
coefficient between 10 and 22. The two control soils were exposed, each 
in duplicate, from day to day along with a large number of the samples 
under investigation, the latter also being in duplicate. The time of ex¬ 
posure varied from 15 to 16 hours, the boxes being filled at 4 or 5 o’clock 
in the afternoon and opened shortly after 8 o’clock on the following morn¬ 
ing. The results both with the duplicates exposed on the same day and 
with the controls from day to day were so concordant that the method 
was accepted as reliable, and some 2,000 determinations were thus made. 
We did not suspect the unreliability of the results until, through force 
of circumstances, one set had to be left in the boxes for 48 hours. On 
drying these samples it was found that the two control soils had ab¬ 
sorbed much more moisture than on any previous occasion. We then 
investigated the cause of this and finally discarded all the data and made 
new determinations. It was while trying to devise such modifications of 
the method described by Hilgard as would permit the large number of 
determinations in connection with our field moisture studies being made 
as rapidly as possible without lessening the accuracy that we secured the 
data reported below on the influence of the material of the trays, the 
effect of the temperature, previous drying, etc. 
