254 



Journal of Agricultural Research 



Vol. X, No. s 



TablR XXIV. — Relation between evaporation from sand tanks I.g6 feet in diameter and 

 tanks 2.^0 feet in diameter, "with water table at j and J2 inches below the surface of the 

 material 



Period ending ' 



1916. 

 Aug. 9 



12 



IS 



17 



29 



Sept. 12 



25 



29 



Oct. 4 



10 



16 



Total & 



Actual evaporation (inches). 



Water table 3 inches 

 below surface. 



Tank 1.96 



feet 

 diameter. 



07 

 90 



35 

 34 

 54 

 71 

 16 

 42 

 69 

 64 

 62 



Tank 2.5 



feet 

 diameter. 



0.83 



•71 

 .26 



•47 



2. 22 



2. 52 



2. 02 



•55 



•79 



■59 



•63 



12. 44 



Water table 12 inches 

 below surface. 



Tank 1.96 



feet 

 diameter. 



o. 74 



.69 



.28 



. 21 



2. 22 



2.47 

 1.82 



■36 

 •63 

 •50 

 •50 



10. 42 



Tank 2.5 



feet 

 diameter. 



69 

 59 

 27 



38 

 91 

 01 



81 

 46 



■55 

 55 

 45 



9.67 



" The period began on Aug. 4, 1916. 



b The ratio of evaporation from the tank 2.5 feet in diameter to that from the tank 1.90 feet in diameter 



is — ^=1.073 for a 3-inch depth of water table andfor 12-inch depth of water table it is — ^ = 1.078. 

 II. S9 907 



The figures found for this comparison are used in the manner of cor- 

 rection factors in placing all evaporation results from sand upon the 

 basis of a tank 2 feet in diameter. In the tables where this correction 

 is made note is made of the change. 



Figure 1 1 shows graphically the data given in Tables XIX to XXIII. 

 It will be noted that the general slope of the lines is the same throughout. 

 The form for the laboratory soil is similar to that of sand 10, and it is safe 

 to assume that this form would be shown if more points were available 

 for sand i, the coarsest material used. The results seem consistent, with 

 this exception: The loss from the saturated surface of No. 10 is yj per 

 cent of that from the water surface, while an extension of the curve for 

 laboratory soil would tend to indicate that at saturation the loss from 

 this would be much greater than jj per cent. That evaporation from 

 saturated surfaces, under apparently the same external conditions, should 

 vary with the material of that surface seems questionable. The detailed 

 results from sand 10 show also the individual figures to be inconsistent 

 in connection with the saturated condition, being either greater or less 

 than from the water surface, the cause of which is not evident. This is 

 not true of the other figures of the series on this sand. 



As was noted earlier, some difficulty was experienced in maintaining a 

 uniform saturated condition. At no time was an automatic device used 



