SOIL ARTHROPOD SAMPLING
25
may be brought to the surface by subsequent stirring and bubbling air
through the liquid.
Evidently much further progress is possible in the field of separation
of arthropods by exploitation of differential wetting properties.
4. Flotation
Flotation is a complex process which incorporates both sedimentation and differential wetting to extents which have not always been
clearly appreciated. It was first introduced by Berlese (1921) in a
simple apparatus described and tested by Balogh (1938), which consisted of a boiling tube with a constricted neck and a plunger. Material
from the “Berlese funnel” was mixed with salt solution by agitating
in the tube. When animals had floated to the surface the plunger was
raised and the surface solution poured off, leaving mineral matter
behind. This principle was developed further (independently?) by
Ladell (193G) for wireworm extraction from arable soils. After washing
through a series of sieves, in the same way as Morris had done, the
material of intermediate size was mixed with magnesium sulphate
solution and subjected to stirring and bubbling. Plant and animal matter were carried upward, floated over a sedimentation tank and retained
by a sieve. The precise role of the bubbling seems rather uncertain and
was, perhaps, more concerned with stirring the material than achieving
separation by differential wetting. The same principles were then used
by Salt and Hollick (1944) for extracting smaller arthropods and by
Raw (1955) who added in turn the important stages of separation a t an
interface (mentioned above) and of pre-treatment with sodium hexametaphosphate (“Calgon”) followed by subjection to a vacuum pump
and then freezing. This has the effect of breaking up clay soils and
liberating the animals much more readily from the mineral material
when the samples are subsequently washed.
As flotation processes these methods all seem to depend primarily
on the differential density effect of mixing with magnesium sulphate
solution and a combination of floating wit,h differential wetting such
as is used in mineral dressing doe8 not seem to have been attempted.
Simpler flotation techniques are often useful for limited applications.
Thus Edwards (1958) has described the use of plain water and of magnesium sulphate solution in a beaker or other container to obtain
Symphyla in large numbers from arable soil. Similarly Nielsen (1053)
in a special extraction method deliberately drives enchytraeids into
sand of uniform particle size and then separates them from it by simple
washing. A similar technique has been used for extracting mud-living
harpactids.
Flotation methods obviously have a number of distinct advantages
25
may be brought to the surface by subsequent stirring and bubbling air
through the liquid.
Evidently much further progress is possible in the field of separation
of arthropods by exploitation of differential wetting properties.
4. Flotation
Flotation is a complex process which incorporates both sedimentation and differential wetting to extents which have not always been
clearly appreciated. It was first introduced by Berlese (1921) in a
simple apparatus described and tested by Balogh (1938), which consisted of a boiling tube with a constricted neck and a plunger. Material
from the “Berlese funnel” was mixed with salt solution by agitating
in the tube. When animals had floated to the surface the plunger was
raised and the surface solution poured off, leaving mineral matter
behind. This principle was developed further (independently?) by
Ladell (193G) for wireworm extraction from arable soils. After washing
through a series of sieves, in the same way as Morris had done, the
material of intermediate size was mixed with magnesium sulphate
solution and subjected to stirring and bubbling. Plant and animal matter were carried upward, floated over a sedimentation tank and retained
by a sieve. The precise role of the bubbling seems rather uncertain and
was, perhaps, more concerned with stirring the material than achieving
separation by differential wetting. The same principles were then used
by Salt and Hollick (1944) for extracting smaller arthropods and by
Raw (1955) who added in turn the important stages of separation a t an
interface (mentioned above) and of pre-treatment with sodium hexametaphosphate (“Calgon”) followed by subjection to a vacuum pump
and then freezing. This has the effect of breaking up clay soils and
liberating the animals much more readily from the mineral material
when the samples are subsequently washed.
As flotation processes these methods all seem to depend primarily
on the differential density effect of mixing with magnesium sulphate
solution and a combination of floating wit,h differential wetting such
as is used in mineral dressing doe8 not seem to have been attempted.
Simpler flotation techniques are often useful for limited applications.
Thus Edwards (1958) has described the use of plain water and of magnesium sulphate solution in a beaker or other container to obtain
Symphyla in large numbers from arable soil. Similarly Nielsen (1053)
in a special extraction method deliberately drives enchytraeids into
sand of uniform particle size and then separates them from it by simple
washing. A similar technique has been used for extracting mud-living
harpactids.
Flotation methods obviously have a number of distinct advantages