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E. W. Hilgard—Silt,analysis of Soils and Clays. 295 
eight liters) must therefore be again stirred up, and the pro- 
per time allowed for the sediments 0 0-25™™", and over, to sub- 
side, The dilution being very great, a pretty accurate separa- 
tion is thus accomplished; the sediments being then ready for 
the elutriator. 
Treatment of the “ Clay Water.”—I have based on the well- 
known property of clay, of remaining suspended in pure water 
for weeks and even months, an obvious method of separation 
from at least the greater portion of silts finer than 0°25"™ 
hydraulic value (< 0°25). 
_ The clay water is placed for subsidence in a cylindrical vessel 
(in which it may conveniently occupy 200 in height), and 
is there allowed to settle for at least 24 hours. This interval 
of time was at first chosen arbitrarily; but I subsequently 
found it to be about the average time required by the finest 
siliceous silt usually present in soils, to sink through 200™" o 
pure water. So long as any sensible amount of clay is present, 
the time of course is longer, say from 40 to 60 hours, or even 
column, indicating silt of successive sizes, with a break between. 
gradually, until, near the bottom of the vessel, it becomes en- 
tirely opaque. ae Meat ae 
After decantation of the clay water, the remaining liquid is 
Water is then again poured on (agitating as much as possible, 
to break up the molecular aggregates) to the proper height, 
and another 24 hours subsidence allowed. This operation 1s 
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