454 
Journal of Agricultural Research 
Vol. VII, No. io 
An examination of figure 19 shows a gradual increase in evaporation as 
the size of particles decrease. There are a number of irregularities prob¬ 
ably caused by the difficulty in getting a uniform surface on all the 
evaporimeters. It will be noted that in some cases the evaporation was 
greater from the wet 
sand than from water. 
In figure 11 results 
for three grades of 
pure quartz sand, for 
Greenville loam, and 
for water are shown. 
Here, as in figure 10, 
the finer grades lose 
more than the coarser. 
Figure 12 includes 
five sizes of quartz 
sand, three sizes of 
river sand, and water. 
The differences are not 
marked, but are suffi¬ 
cient to bear out previous results in showing the greater evaporation 
from the surface of the smaller particles. 
mulches 
Wherever water storage in field soils is important, mulches are used 
to decrease the evaporation loss. Ridgaway (15) and Fortier (5) both 
indicate the great sav- 
River Sand 
Fig. io.—E vaporation of water in 66 days from sand of different sizes 
with a water table maintained i cm. below the surface. 
ing due to mulches 
made by stirring the 
topsoil or by adding 
covers of dry soil. 
A number of labora¬ 
tory experiments to 
study the effectiveness 
of different mulches 
when the effect of ca¬ 
pillarity has been elim¬ 
inated were conducted. 
In these experiments 
the different mulches 
were suspended above 
the water. The mulch 
was placed on wire gauze covered with cheesecloth or on perforated 
sheet metal to keep it about i cm. from the surface of the water in the 
lower part of the vessels. No water could evaporate except through 
the mulches. 
Fig. ii.—E vaporation of water in 36 days from loam and sand of 
different sizes with a water table maintained 3 cm. below the sur¬ 
face. 
