Dec. 4,1916 
Evaporation of Moisture from the Soil 
445 
was slightly warmer and changed air much more frequently than in 
summer. The hygrometer showed somewhat lower humidity, but it 
could not show the influence of thorough ventilation. 
The next study was made between June 4 and June 17, 1914. It was 
conducted in the same fashion, except that weighings were made twice 
daily, between 6 and 8 o'clock morning and evening. Four pans, instead 
of three, were used with each percentage from 1 to 50. The pans for 
1 per cent gained up to about 1.8 per cent and then neither lost nor gained 
noticeably. 
In addition to the pans containing wet soil, a pan of free water was 
exposed at each corner of the table on which the test was made. The 
two pans on the east and nearer the doors lost somewhat more than the 
two at the west end. All soils that approached saturation lost more 
than the free water. The losses from the 20 per cent pans were about 
equal to the average of 
those from the free¬ 
water pans. 
An almost identical 
test was made in July 
which practically dupli¬ 
cated the former results. 
As 12 weighings were 
made, the length of this 
study was equivalent to 
6 days. 
These various experi¬ 
ments are combined in 
figure 1, which gives 
results for a total of 51 
days with moisture up 
to 40 per cent, and 36 
days with moisture up to 50 per cent. The curve for the 36-day results 
shows a rapid increase in evaporation with a higher initial percentage 
of moisture in the soil up to 7 or 8 per cent; then a less rapid increase 
up to 18 or 20 per cent, from which point the increase is small. In the 
tests continued for 51 days, the same general changes in the curve are 
noted, although the total loss is decidedly more than for the 36-day test. 
In some of the trials the free water lost more by evaporation than any 
of the wet soils, but usually there was a greater loss from soil which was 
completely saturated than from the free-water surface. 
In each of these tests with Greenville loam, there seemed to be a 
number of more or less definite breaking points in the curves of loss. 
These indicate critical points where the moisture relations of the soil 
made rather sudden changes. A great deal of work will need to be done 
Fig. 
Initial Per Cent Moisture In Greenville L 01m 
1. —Evaporation from Greenville loam containing different 
initial percentages of moisture. 
