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August 1948 ET-261
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
AI APPARATUS TO FACILITATE DDT EXTRACTION FROM SOIL SAMPLES
By Irving Keiserl/ and C. F. Henderson
Division of Domestic Plant Quarantines
The use of DDT against white-fringed beetles (Graphognathus spp.)
is now of paramount importance, both as foliage applications to kill
adults and as a larvicide in soil. For both these uses the development
of formulas, dosages, and other pertinent relations involves numerous
and repeated series of chemical analyses of foliage and soil samples to
recover the DDT present. In either ease a solvent (benzene) is shaken,
stirred, or kept mixed with the sample for a considerable period to
extract any DDT present, and the solution thus obtained is then analyzed
for its DDT content.
The lengthy and continuous agitation of numerous samples needed to
insure complete solvent action entails excessive time and labor if done
by hand; therefore mechanical agitators were developed. In the early
period, when foliage samples were largely concerned, a shaking device
was constructed. It consisted essentially of a platform activated hori-
zontally by an eccentric on which six samples could be simultaneously
kept in constant agitation for a 1-hour period of extraction.
This device served well for stripping foliage samples, but when
investigations on the larvicidal action of DDT began to require analysis
of large numbers of soil samples, it was found to be unsuitable. The
horizontal motion allowed the heavier soil mass to pack at the bottom
of the container without securing the needed constant mixture with the
solvent; moreover, it was necessary to provide for a larger sample.
Consequently another agitating apparatus employing a "roll-mix" principle
was devised, specially adapted to soil sample needs but equally effective
for foliage samples.
The essential details of this device are indicated in figure 1. It
consists of a vertical plywood disk, 3 feet in diameter, mounted with its
axle on a suitable support. Powered by a small electric motor (1/ hp.)
through a reducing jack to an axle pulley, the disk assembly is slowly
revolved at a rate of about 10 revolutions per minute. On the face of
the disk, near the edge, 10 evenly spaced holes are cut, in which the
tops of 10 quart-size Mason jars can be inserted to their shoulders. To
hold these jars in place two bolts are firmly fixed in the disk at either
side of each jar opening, their threaded ends extending beyond the base
of the jar. A plywood saddle plate tightened across .each jar base by
wing nuts on the bolt ends holds each jar firmly in position.
1/ J. F. Latil constructed the apparatus, C. W. Pittard prepared the
working drawings, and William Breland assisted with the chemical analyses.
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When jars loaded with soil and solvent are', fastened in place hori-
zontally, the slow turning of the disk keeps the contents continually
mixed and moving, so that the coil is thoroughly penetrated by the ex-
tractant. Rings made of materials resistant to benzene should be sub-
stituted for the usual rubber rings.
The efficiency of this roll-mix motion in securing DDT extraction
has been tested by a run of 10 soil samples, eight of these containing
measured additions of DDT at the rate of 5 parts per million and the re-
maining two without DDT as checks. Recovery analysis of two jars each
was made after 20, 40, 60, and 80 minutes of operation, the last inelud-
ing the checks. DDT recovery was approximately 100 percent in all cases.
even after 20 minutes.
Working drawings and a list of materials for construction of this
apparatus may be secured on request from the Bureau of Entomology and
Plant Quarantine, Division of Dcmestic Plant Quarantines, Washington 2,
Figure l.--Apparatus to facilitate extraction of DDT from soil samples.