Relation of Nonavailable Water to Hygroscopic Coefficient 31 
dividual 3-inch sections were not used, but the determination was 
made on a sample of the bulk soil used, it being taken at the time 
of filling the cylinders. Thus in the case of the 8 cylinders of the 
experiment of 1909, in which 16 different soils were used, the 
hygroscopic coefficients of these 16 were determined and used in 
calculating the free water in the 192 individual sections. This 
may account for some irregularities in the free water content of 
sections adjacent to the dividing line between two different soils. 
Thus, for example, in the case of cylinder I in Table 8 (p. 41) in 
the lowest section of the fourth foot there is shown only 0.2 per 
cent free water compared with 1.1 per cent in the section above 
and 1.7 per cent in the section below. As the soil of the fourth 
and fifth feet had hygroscopic coefficients of 9.3 and 7.4 respect- 
ively, an error of one inch in filling the cylinders or in removing 
the sections would account for the irregularity. In such cases no 
attempt has been made to increase the regularity shown in the 
distribution of free water by making determinations of the hygro- 
scopic coefficient of any of the individual 3-inch samples. 
In the tables of moisture data the water content of the thin 
sand layer, about 1 inch in thickness, which was placed in the 
bottom of each 6-foot cylinder, is not reported for the reason that 
the sand in the process of removal became mixed with the over- 
lying soil in almost all cases, thus greatly altering the hygroscopic 
coefficients of the samples as actually dried and the amounts of 
free water, so rendering the data quite meaningless, unless a sep- 
arate determination of the hygroscopic coefficient of each sample 
had been made. The hygroscopic coefficient of this sand was 0.5. 
WILTING COEFFICIENT. 
The toil ting coefficient very frequently referred to in the 
following pages is that defined by Briggs and Shantz. 1 In no 
case 2 has it been determined directly, it having been calculated 
from the hygroscopic coefficient using the formula given by 
Briggs and Rhantz, viz: 
-t-tt ii 1 1 oa • hygroscopic coefficient 
Wilting coefficient = 
O.bo 
1 See p. 18. 
2 Dr. Briggs has kindly determined for the writer the moisture equiva- 
lent of the soil used in the largest number of experiments — the H O 
Subsoil (p. 47). Five determinations of the moisture equivalent gave an 
average of 14.2, from which the wilting coefficient of 7.7 and the hygro- 
scopic coefficient of 5.25 is found by the formulas of Briggs and Shantz 
(p. 19). As the figures had been completed before receiving the data 
from Dr. Briggs, the wilting coefficient 8.2, calculated from the hygro- 
scopic coefficient 5.6, as determined by the writer, is used in the various 
figures showing the moisture conditions in the cylinders in which H O 
Subsoil was employed. 
