Oct. 22, 1917 
Direct Determination of the Hygroscopic Coefficient 155 
Table III.— Comparison of trays of different materials in the determination of the 
hygroscopic coefficient 
Material of tray. 
Hygroscopic coefficients found after— 
24 hours’ exposure. 
48 
hours’ 
ex¬ 
posure. 
SoilC. 
Soil A. 
Soil F. 
Soil G. 
Soil G. 
Pasteboard lined with glazed paper. 
Paraffined pasteboard lined with glazed paper 
Paraffined pasteboard sides, but no bottom, lined 
with glazed paper.. 
Glass. 
Vulcanized rubber. 
Graniteware... 
Tin plate. 
Zinc. 
Copper. 
Aluminum. 
o. 6 
• 7 
6 
6 
6 
6 
5 
7 
7 
i 5 * 5 
18. 2 
20. 3 
19.4 
16. 6 
i 7-4 
17. 7 
17.9 
19. 2 
17.9 
20. 0 
19.7 
17.7 
19. 2 
x8. 9 
17.7 
19*5 
19.9 
The data reported in Table III show that any of the materials men¬ 
tioned, except the pasteboard, may safely be used. Even the trays with 
paraffined pasteboard sides, but with only a glazed paper bottom, appear 
allowable. The low amount of moisture absorbed by the soils when 
placed on glazed paper in the pasteboard trays with pasteboard bottoms 
is probably due to the competition of the pasteboard, which, itself, is 
hygroscopic and absorbs moisture from a saturated atmosphere. The 
somewhat low results obtained with the glazed paper used in paraffined 
pasteboard trays may be due to the competition of the lower unglazed 
surface of the glazed paper, which, when placed directly upon the table 
in the absorption box is able to absorb moisture from the air reaching it 
from below. 
That the saturation with hygroscopic moisture is practically com¬ 
plete at the end of 24 hours with all the trays except those of pasteboard 
is to be seen from the failure of the soil G to absorb additional moisture 
during the second 24 hours. All the samples of this soil were placed in the 
hygroscopic boxes at the same time, but part were removed at the end 
of the first 24 hours. During the first day the temperature in the hygro¬ 
scopic room fell from 17 0 to 16 0 C. and during the next day from 16 0 to 
14° C. 
The trays of tin plate readily rusted, and those of zinc soon corroded 
to such an extent that the soil adhered. On the whole, those of alu¬ 
minum or copper were found the most satisfactory, and in our later 
work we used trays made of the former metal, with the dimensions 
given above. 
7768°—17 - 5 
