Aug. 28. 1916 Indirect Determination of Hygroscopic Coefficient 837 



EXPERIMENTAL WORK 



The moisture equivalents were determined according to Briggs and 

 Shantz (7, p. 57), bringing the soils into equilibrium with a force 1,000 

 times that of gravity, using a centrifuge (6, p. 141) made according to 

 specifications kindly furnished by Dr. L. J. Briggs, of the Bureau of 

 Plant Industry. The determination of the moisture equivalent has been 

 found to be convenient of execution, and the results from day to day 

 are very concordant. 



In Table III are given the moisture equivalent, the hygroscopic 

 coefficient, the ratio of these to one another, and the content of organic 

 matter in 36 samples. The soils were collected from 30 virgin prairie 

 fields in Nebraska, 5 near each of the six towns indicated in the table. 

 All are from fields classified by the United States Bureau of Soils either 

 as Marshall silt loams or as Colby silt loam. In each field 10 borings 

 were made to a depth of 6 feet and composite samples prepared of each 

 foot section, thus securing 6 samples from each field. From these were 

 prepared the samples used in this work, equal weights of the correspond- 

 ing 5 field samples being combined. The details of the method of sam- 

 pling are reported elsewhere (2, p. 204). In the same article (2, p. 215) 

 are given the hygroscopic coefficients for the foot sections from each of 

 all the fields. Each value in B of Table III represents the average of 

 10 determinations. The data on the organic matter reported in D of 

 the table were calculated from the organic carbon reported in the same 

 article (2, p. 228; organic matter = Cx 1.724). The data on the moist- 

 ure equivalents are the means of duplicate determinations. 



The ratio (Table III-C) averages 2.38, varying from 2.14 to 2.73, a 

 quite similar, although somewhat narrower, range than that found by 

 Briggs and Shantz. In general, in each area it is highest in the surface 

 foot as though influenced by the proportion of the organic matter. 



