156 
Journal of Agricultural Research 
Vol. XI, No. 4 
INFLUENCE OP TIME OP EXPOSURE 
In handling a large number of absorption boxes 8 hours’ actual 
exposure necessitates a working day in the laboratory of about io hours, 
on account of the additional time required in the morning to place the 
samples in the trays and in the afternoon to transfer them to weighing 
bottles. Twelve hours, the maximum exposure used by Hilgard, also 
is inconvenient, as usually it will necessitate an extra trip to the labora¬ 
tory. We tried various intervals. The soils exposed on the metal 
trays, unlike those on the glazed paper used by Hilgard, in most cases 
continued to gain in weight during the first 18 hours, thus rendering 
both the 8- and 12- hour exposures too brief. As, under our conditions, 
from 22 to 24 hours was the most convenient interval, we compared 
this with longer exposures. Except in the case of very fine textured 
soils like I, after the first 20 hours there was generally no important 
increase in weight (Table IV). As under our working conditions it 
was not possible to maintain the temperature constant during long 
periods, this increase with such very hygroscopic soils may have been 
caused by dew formation resulting from a depression of the tempera¬ 
ture after the atmosphere had become saturated. In some prolonged 
exposures there was a slight decrease in weight during the later portion 
of the period. 
Table IV. —Influence of the length of the time of exposure upon the amount of moisture 
absorbed 
Experiment No. 
Time of exposure in hygro¬ 
scopic boxes. 
Tempera¬ 
ture. 
Absorbed moisture. 
Soil H. 
Soil G. 
Soil I. 
I. 
23 hours. 
°c. 
18.5 
19. 0 
18. 0 
18. s 
19. O 
19. 0 
19. 0 
18. 0 
17.0 
17. 0 
17. 0 
Per cent. 
6-3 
6. 0 
5-8 
6.4 
6.9 
6.8 
6.6 
Per cent. 
Per cent. 
2. 
23 hours... 
3. 
41 hours. 
4. 
e days. 
5. 
6 days. 
6. 
7 days. 
7. 
11 days. 
8. 
25 hours. 
or 0 
9. 
4 days. 
23.1 
10. 
24 hours. 
x 9 * 5 
19. 4 
11. 
48 hours. 
INFLUENCE OF TEMPERATURE 
The variation in the temperature of the room in which the absorption 
boxes were kept was so little that from April 27 to October 1, 1911, the 
thermometer readings lay between 22 0 and 24 0 C. so much of the time 
that the data from days with either lower or higher temperatures are too 
few to be of service in the present connection. The same applies to the 
interval extending from January 4 to April 22, 1913, when the tempera¬ 
tures on nearly every day were between 17 0 and 20° C. 
