18 



BULLETIN 835, U. S. DEPARTMENT OF AGRICULTURE. 



Except for the- lighter soils of the sandy type, the quantity of: 

 water required to move the moisture the first inch is about the same 

 or a little less than to move it the last inch on a basis of 30-day 

 tests. Table 3 brings out the fact that there is much less difference 

 in the quantity of water required per inch for the various heights 

 than is usually supposed. The difference in the percentage of mois- 

 ture found near the bottom and the percentage found near the top 

 of a vertical soil column containing capillary water raised from a 

 free water surface leads to the natural conclusion that more water 

 per inch is removed for the bottom inches than for the top inches. 

 However, it is observed that in flume 63 the reverse is true, although 

 the percentage of moisture near the bottom of this flume was greater 

 than it was within 4- inches of the top. Under another heading 

 in this report is given at least a partial explanation of this apparent 

 inconsistency. (See p. 56.) 



Table 4. — Water removed from tank, by days, in percentage of total removed 



in 30 days. 









Flume. 







Number 



of davs. 



























19 



43 



63 



SO 



100 



200 





Per cent- 



Per cent. 



Per cent. 



Per cent. 



Per cent. 



Per cent. 



1 



al 



47 



40 



34 



30 



77 



2 



67 



66 



50 



43 



42 



82 



3 



74 



69 



55 



60 



53 



81 



4 



75 



72 



60 



62 



60 



86 



10 

 15 

 20 

 30 



86 

 01 

 05 



100 



79 

 86 

 91 

 100 



74 

 87 

 93 

 100 



77 

 82 

 87 

 100 



79 

 89 

 92 

 100 









100 



Table 4 shows in general the relatively high percentages of water 

 removed from the tanks during the first day or two and the relatively 

 small percentages used after the first three or four days. It is found 

 that in all flumes at the end of the third day, or one-tenth of the 30 

 clays, more than 50 per cent of the water had been used, and by the 

 end of the tenth day three-fourths of the total water used in 30 days 

 had been removed from the tanks. During the last 10 days of the 

 experiment only about 10 per cent of the total water was removed 

 from the tanks. 



This table again indicates the longer continued use of the relatively 

 large quantities of water by the heavier soils and the very rapid action 

 of the lighter soils. This is of economic importance in that the loss 

 for an extended time would be much less in proportion for a heavy 

 soil than for a light soil where the loss of water is caused by capillary 

 action alone. 



