Dec. 4,1916 
Evaporation of Moisture from the Soil 
459 
The results of this test are shown in figure 15, which brings out clearly 
the fact that as the concentration of the solution increases the evapo¬ 
ration decreases. 
The second test was conducted in porcelain crucibles, each containing 
10 gtn. of quartz sand which had been wet with 4 c. c. of solutions of 
sodium nitrate ranging in concentration from a check solution containing 
no salt up to 5 times a normal solution. There were two crucibles for 
each concentration. The crucibles were placed under a bell jar in order 
to avoid air currents and to keep the humidity as uniform as possible 
over all the crucibles. 
Weighings were made each day at first, and every two or three 
days later. The experiment was begun January 12 and continued till 
January 27, making a period of 15 days. 
The results are given in figure 16, which shows a decrease of evapo¬ 
ration from the sand the same as when the solution of sodium nitrate is 
added. A third test 
was conducted in gal- 
vanized-iron cans, 11 
inches in diameter and 
13 inches deep, partly 
filled with Greenville 
loam to which sodium 
chlorid was added in 
different quantities, 
rangingf rom the control 
containing nothing to 7 
per cent of the dry soil. 
The quantity of moist¬ 
ure that evaporated was 
added every three or 
four days through a 
tube near the bottom of the cans. In this way the surface of the soil 
was never disturbed, but there w T as a gradual accumulation of salts at the 
surface. The experiment ran from August 19 to September 25. 
The results of the experiment are given in figure 17. There is a 
gradual decrease in the evaporation as the salt content of the soil is in¬ 
creased. The can with 7 per cent of salt lost slightly more than that 
with 6 per cent. This irregularity was doubtless due to the fact that 
considerable salt was crystallized at the surface of the soil in this can, 
consequently the real concentration of the solution was decreased; and 
it is the salt actually in solution that affects vapor tension. 
From these experiments it seems clear that soluble salts in the soil 
decidedly decrease the evaporation of moisture if the concentrations are 
high, but the reduction is only slight for the solutions found in ordinary 
soils. 
Percent Sa.it 
Soil 
Fig. 17.—Evaporation of water from Greenville loam containing dif¬ 
ferent quantities of sodium chlorid. 
