Oct. 22; X917 Direct Determination of the Hygroscopic Coefficient 
153 
RAPID LOSS OP HYGROSCOPIC MOISTURE) 
When soils carrying the maximum amount of hygroscopic moisture— 
that is, an amount equal to the hygroscopic coefficient—are exposed to an 
ordinarily dry air, they lose water at first as rapidly as though placed in a 
desiccator containing sulphuric acid. This makes it important that the 
transfer of the exposed soil from the trays to the weighing bottles should 
be made as rapidly as possible. 
Fifty-gm. portions of two soils, A and B, which had previously been 
exposed in hygroscopic boxes until the moisture content was approxi¬ 
mately equal to the hygroscopic coefficient were placed in each of 10 
weighing bottles. The depth of soil was about 5 cm. Five bottles of 
each were placed in a desiccator containing concentrated sulphuric acid, 
while the other five were exposed on a shelf in the laboratory. All were 
weighed at intervals until those of the latter set ceased to lose weight, 
four weeks being necessary. Those in the desiccators were exposed 
nearly five months longer, and at the end of this time they were almost 
oven-dry. The changes in the case of the individual members of each of 
the four sets were so similar that only the averages need be reported 
(Table I). In a similar desiccator containing sulphuric acid and in 
weighing bottles of the same kind we exposed distilled water. The loss 
of water between February 12 and March 19 amounted to about 45 gm., 
or 90 per cent of the weight of soil A contained in similar weighing bottles. 
Table I .—Percentage of water in 50-gin. portions of soils exposed to the air of the labor¬ 
atory compared with that in a desiccator with sulphuric acid 
Date, 
Soil A. 
Soil B. 
Exposed 
to air. 
In desic¬ 
cator. 
Exposed 
to air. 
In desic¬ 
cator. 
Feb. 12.. 
5. 26 
2. 27 
I. 60 
I. 79 
I. 82 
5. 26 
2.45 
I.30 
.96 
. 61 
*44 
.40 
•25 
. 12 
11. OO 
6. 18 
4. 07 
4. 09 
4. 17 
IT. OO 
6. 70 
4.04 
2-95 
1.91 
1.49 
1*35 
.88 
•43 
18... 
26 . 
Mar. 5. 
10. 
Apr. 1 . 
8. 
May 21. 
Aug. 10. 
At the end of two weeks both soils appeared to have reached equi¬ 
librium with the air of the laboratory. 
In the case of the absorption boxes and trays, an operator, after a 
little practice, will be able to open a box, transfer the samples from 
the two trays to weighing bottles, and stopper these within the space of 
30 seconds. 
