348 
Journal of Agricultural Research 
Vol. VII, No. 8 
Caldwell (5, p. 15) in connection with a study of the permanent wilting 
in plants has determined both the hygroscopic coefficients and the 
water capacities of “a very pure sand, an ‘adobe’ clay loam containing 
less than 0.1 per cent of humus, and nineteen artificial mixtures of these 
two soils varying by increments of 5 per cent of loam from 95 per cent 
sand with 5 per cent loam to 95 per cent loam with 5 per cent sand.” 
The observed hygroscopic coefficients of the two soils were 2.41 and 7.51 
and the corresponding values calculated from the water capacities 2.30 
and 7.40, respectively. The calculated coefficients of the ,artificial 
mixtures agreed equally well with the directly determined values. 
Clearly the concordance is here well within the limits of experimental 
error; and if the same held true for a series of 21 natural soils with a range 
in hygroscopic coefficient from 2.5 to 7.5, this indirect method would 
leave little to be desired in respect to simplicity and reliability. 
, It must, however, be emphasized that such artificial mixtures can 
not take the place of natural soils in testing such a method, as, if a 
formula holds true on each of two components separately, it should 
hold equally true for all mixtures of these. Thus, to illustrate, in the 
case of the soils studied by Loughridge (12), No. 77 and 1147, with 
determined hygroscopic coefficients of 10.38 and 1.84 and calculated 
values of 11.21 and 1.80, respectively, might be employed to prepare 
artificial mixtures and all the latter should show water capacities such 
that the calculated hygroscopic coefficients should agree with those 
directly determined, while with similar mixtures of No. 643 and 51, with 
determined values of 13.51 and 3.17 and calculated values of 10.20 and 
6.70, respectively, the intermediate mixtures should be expected to 
show a concordance, although neither of the two soils by itself did. 
ESTIMATION OF THE HYGROSCOPIC COEFFICIENT FROM THE 
MAXIMUM WATER CAPACITY 
The determinations of the maximum water capacity were made in 
triplicate or quadruplicate, the concordance of the determinations 
being shown in Table III. 
Table III.— Concordance of quadruplicate determination of the maximum water capacity 
Soil No. 
Individual determinations. 
Aver¬ 
age. 
1 
2 
3 
4 
A. 
60. 5 
62. 2 
72.9 
61. s 
60.8 
62.3 
73 - 4 
62.3 
61. 8 
62. 5 
l 3 - 1 
63-4 
63.0 
63-7 
74*7 
61. 9 
61. s 
02. 7 
73*5 
02. 2 
B....... 
c. 
D. 
