Nov. so, 1916 Determination of Hygroscopic Coefficients of Soils 
35i 
one from New Mexico and the other from Arizona. Three residual soils 
from Nebraska, No. 4, 5, and 6, which showed very similar hygroscopic 
coefficients, differ distinctly in water capacity. 
Table VI .—Comparison of the determined hygroscopic coefficient with that calculated from 
the maximum water capacity 
Soil 
No. 
Description of soil. 
Maximum 
water 
capacity.® 
Hygr 
Directly 
deter¬ 
mined.^ 
oscopic coeffi 
Calculated 
from 
maximum 
water 
capacity.® 
dent. 
Departure 
of calcu¬ 
lated coeffi¬ 
cient from 
that found. 
A 
Dune sand, western Nebraska.. 
25. 8 
0. 6 
I. I 
a 5 
1 
Desert sand, Palm Springs, Cal. 
28. 9 
• 9 
1.9 
1.0 
2 
Sandy subsoil, Palm Springs, Cal. 
27. O 
1. 1 
1-4 
-3 
3 
Desert sand, Orogrande, N. Mex. 
27. I 
i- 7 
1.4 
“ -3 
4 
Sandy surface soil, .western Nebraska.. 
34-2 
3*3 
3 - 1 
— . 2 
5 
Sandy subsoil, A, western Nebraska... 
3 1 - 0 
3-4 
2-3 
— 1.1 
6 
Sandy subsoil, B, western Nebraska... 
36. 0 
3 - 4 
3 - 5 
. 1 
7 
Sandy loam subsoil, western Nebraska. 
46. 3 
5 - 6 
5 - 9 
. 3 
8 
Sandy loam surface, western Nebraska. 
53 - 4 
7 * 1 
7. 6 
. 5 
9 
Silt loam subsoil, A, western Nebraska. 
57 - 2 
7. 6 
8-5 
• 9 
10 
Silt loam subsoil, B, western Nebraska. 
55 - 4 
8. 2 
8. 1 
— . 1 
11 
Red loam surface, Cuervo, N. Mex_ 
49. 0 
10. 0 
6.6 
“ 3-4 
12 
Silt loam surface, A, western Nebraska. 
56.8 
10. 1 
8.4 
-1. 7 
*3 
Silt loam surface, eastern Nebraska.... 
60. 9 
10. 2 
9 - 7 
— . 5 
14 
Silt loam surface, B, western Nebraska. 
^ 3 - 7 
10. 5 
10. 0 
— . 5 
IS 
Adobe surface soil, McNeal, Ariz. 
60. 3 
12. 9 
9. 0 
- 3-9 
16 
Silt loam subsoil, eastern Nebraska- 
6S- 7 
13-3 
5 
—2. 8 
® Determined by Mr. J. C. Russel. 
6 Determined by Mr. G. R. McDole. 
c Using Briggs-Shantz formula: Hygroscopic coefficient™ (maximum water capacity—2i)Xo.234. 
Thus, while the Briggs-Shantz formula with many soils gives values 
fully in accord with those directly determined, with many others it 
gives results so widely divergent that it can not be regarded as suf¬ 
ficiently reliable for studies of available soil moisture, or even for soil- 
survey purposes. 
ESTIMATION OF THE HYGROSCOPIC COEFFICIENT FROM THE HYGRO¬ 
SCOPIC MOISTURE 
The hygroscopic coefficient indicates the maximum of hygroscopic 
moisture, the amount found when a more or less completely dried soil 
has been kept in contact with a saturated atmosphere at a constant 
temperature until the moisture in the soil is in approximate equilibrium 
with that in the atmosphere. Theoretically, actual equilibrium would 
not be attained until the moisture content of the soil equaled that of the 
same soil in actual contact with water (13, p. 448), but the time required 
for this is so great that this theoretical consideration does not affect the 
present discussion. 
If two soils, A and B, be allowed in one case to reach equilibrium with 
a saturated atmosphere and the hygroscopic coefficients thus found be a 
and b , respectively, and in another case the same soils be allowed to reach 
