118 BULLETIN 1059, U. S. DEPARTMENT OE AGRICULTURE. 



bj^ M', and the excess over wilting coefficient by K, then in these 

 diagrams the condition is represented by 



M'=WC+K 

 rather than 



M'=WCxK, 

 since it is readily seen that the osmotic equivalents are not propor- 

 tionate to the coefficients. 



Table 6. — Osmotic equivalent of soils, in presence of solution at 20 atmos- 

 pheres, after four months exposure and other related properties. 



Station. 



Depth. 



Capillary 

 moisture. 



Moisture 

 equiva- 

 lent, 

 100-G. 



Wilting 

 coeffi- 

 cient. 



Osmotic 

 equiva- 

 lent. 



Excess 

 over 



wilting 

 coeffi- 

 cient. 



Change in 



moisture 



during 



transfer. 





Feet. 



a 



Per cent. 

 11.64 

 10.00 

 10.96 

 22.08 



Per cent. 

 4.29 

 3.60 

 4.34 

 8.25 



Per cent. 



2.31 

 .93 

 .76 



2.13 



Per cent. 



11.19 



8. 7 



8.92 



iio.oe 



Per cent. 

 8.88 

 7.34 

 8.16 

 7.93 

 8.13 



Grams. 

 +0.01 





2 



-2.39 



11 



.. 3.: 



-2.35 





Well sand 



i -0.72 





1 At. of 3 



-1.58 





a 











11.34 

 16.08 

 14.84 

 24.70 



5.41 

 5.91 

 5.86 

 9.29 



1.16 

 2.63 

 2.67 

 3.67 



7.84 



8.69 



9.58 



19.87 



6.68 

 6.06 

 6.91 

 6.20 



6.55 



-2.62 





2 



-2.20 



F-2 



...3.! 



-1.67 





Well sand 



i -1.24 





' |At. of 3 



-2.16 





In 











23.53 

 24.00 

 18.86 

 21.61 



13. 4.5 

 16.25 

 11.62 

 6.67 



4.72 



3.65 



2.99 



' .76 



11.06 

 10.72 

 10.24 

 9.90 



6.34 

 7.07 

 7.25 

 9.14 

 6.89 



-1.90 





j 2 



—1.80 



F-ll 



...\h 



-2.11 

 -1.29 





[At. of 3 



-1.94 







! 





i Average of 4 samples taken from each well, representing the surface and depths of 1, 2, and 3 feet, so that 

 mean value should be equivalent to that of soil as placed in the well. 



' Approximate. Test made on coarse sandy soil from depth of 4 feet, most nearly approaching the quality 

 of sand used in the well. 



Table 6 show^s that K varies as between different groups of samples 

 from different sources, but that within a group of similar origin K 

 is essentially a constant. Thus, it has an average value of 8.13 per 

 cent for one group, 6.55 per cent for another, and 6.89 per cent for the 

 third, and this value seems not to have any constant relation to the 

 change which occurred in the samples during their period of ex- 

 posure, so that it may be accepted as representing something near a 

 final condition. In one sample representing a limestone soil, K is 

 found to be 17.12—15.33 per cent, or 1.79 per cent. In another soil 

 of lava origin, containing less of silt and clay, but a considerable 

 amount of sodium bicarbonate, K is found to be 12.23—4.44 per 

 cent, or 7.79 per cent. 



These findings compel the following conclusions : 



1. The wilting coefficient of a given soil is probably dependent 

 both on the solutes present and upon the colloids capable of ad- 

 sorbing both the solutes and the water, but more particularly upon 

 the latter ; since only very rarely will the solutes be so abundant as 

 to create an excessively strong solution before the disappearance of 

 the free water. 



