38
Exercise 3
clamp and carefully remove the glass tube, keeping the terminal end uppermost so
as to avoid mixing of the salt solution with the clear water.
3. Carefully remove excess ice from the surface, avoiding turbulent motions that
might extend into the region of the chemocline. Record water temperatures and
make additional measurements with the spare thermometer or thermistor
thermometer in the region of the chemocline.
4. Turn on the lamp and record this time as the beginning of the experiment. Leave
the lamp on without any wind for 40 min.
5. Distribute catechol violet liberally over the surface so as to cause the upper quarter
of the aquarium to become well colored with descending streaks of red dye.
6. With a moderate wind, cause the dye to be distributed in a homogeneously colored
layer at the top (the epilimnion). The red layer should now occupy the upper third
of the aquarium, the blue layer the lower third, and the middle layer will be
essentially colorless. Record temperatures with extra measurements as necessary.
7. With forced oscillations from the wind source, create an internal seiche in the
thermocline region. Note that another seiche develops in the chemocline region.
Measure the period of both seiches simultaneously (different observers). Take care
not to use too strong a wind that would destroy the three-layered system. Describe
the motions.
8. When the seiches have died down, on one side of the aquarium introduce slowly
from a beaker, whose liquid is level with the "lake" surface, about 50 ml of the
thick bentonite-Congo red suspension. Try to obtain an even flow from the
beaker to the "lake" water. Observe the vertically descending density current
and watch it move along the upper part of the chemocline as a discrete layer.
Why?
9. Dilute the suspension of bentonite-Congo red with cold distilled water to a point
where you think it might flow along the thermocline. With a medicine dropper or
pipet, add a portion to the end of the aquarium opposite that at which the thick
bentonite-Congo red solution was added. When the solution sinks below the
thermocline, it should be diluted further. Now slowly add about 25 ml of the dilute
bentonite-Congo red suspension to the appropriate end of the aquarium. The
solution will flow as a discrete layer along the thermocline. Watch what happens
with time. The larger clay particles will begin to settle out in discrete, fingerlike
projections sometimes separating into separate "blobs." How do you explain this?
What does it mean with respect to studies made on sinking rates of small
particles?
10. Enclose an Alka-Seltzer tablet in wire mesh and allow it to drop to the bottom of
the aquarium. Note the great turbulence generated by the bubbles and the mixing
of the water masses.
Apparatus and Supplies
1. Aquarium filled two-thirds full with tap water and excess ice.
2. Heat lamp, thermometers, catechol violet. etc., as in Lake Modell.
3. Approximately 10 1 per aquarium of a 0.3~ 0 salt solution containing methylene blue
or other non-red dye.
4. A thick suspension of bentonite clay in distilled water with addition of Congo red
dye to give a strong red color.
5. Alka-Seltzer' tablets enclosed in wire screening.
6. Hydrometers covering the range 1.0000 to 1.0050 sp. gr.
Exercise 3
clamp and carefully remove the glass tube, keeping the terminal end uppermost so
as to avoid mixing of the salt solution with the clear water.
3. Carefully remove excess ice from the surface, avoiding turbulent motions that
might extend into the region of the chemocline. Record water temperatures and
make additional measurements with the spare thermometer or thermistor
thermometer in the region of the chemocline.
4. Turn on the lamp and record this time as the beginning of the experiment. Leave
the lamp on without any wind for 40 min.
5. Distribute catechol violet liberally over the surface so as to cause the upper quarter
of the aquarium to become well colored with descending streaks of red dye.
6. With a moderate wind, cause the dye to be distributed in a homogeneously colored
layer at the top (the epilimnion). The red layer should now occupy the upper third
of the aquarium, the blue layer the lower third, and the middle layer will be
essentially colorless. Record temperatures with extra measurements as necessary.
7. With forced oscillations from the wind source, create an internal seiche in the
thermocline region. Note that another seiche develops in the chemocline region.
Measure the period of both seiches simultaneously (different observers). Take care
not to use too strong a wind that would destroy the three-layered system. Describe
the motions.
8. When the seiches have died down, on one side of the aquarium introduce slowly
from a beaker, whose liquid is level with the "lake" surface, about 50 ml of the
thick bentonite-Congo red suspension. Try to obtain an even flow from the
beaker to the "lake" water. Observe the vertically descending density current
and watch it move along the upper part of the chemocline as a discrete layer.
Why?
9. Dilute the suspension of bentonite-Congo red with cold distilled water to a point
where you think it might flow along the thermocline. With a medicine dropper or
pipet, add a portion to the end of the aquarium opposite that at which the thick
bentonite-Congo red solution was added. When the solution sinks below the
thermocline, it should be diluted further. Now slowly add about 25 ml of the dilute
bentonite-Congo red suspension to the appropriate end of the aquarium. The
solution will flow as a discrete layer along the thermocline. Watch what happens
with time. The larger clay particles will begin to settle out in discrete, fingerlike
projections sometimes separating into separate "blobs." How do you explain this?
What does it mean with respect to studies made on sinking rates of small
particles?
10. Enclose an Alka-Seltzer tablet in wire mesh and allow it to drop to the bottom of
the aquarium. Note the great turbulence generated by the bubbles and the mixing
of the water masses.
Apparatus and Supplies
1. Aquarium filled two-thirds full with tap water and excess ice.
2. Heat lamp, thermometers, catechol violet. etc., as in Lake Modell.
3. Approximately 10 1 per aquarium of a 0.3~ 0 salt solution containing methylene blue
or other non-red dye.
4. A thick suspension of bentonite clay in distilled water with addition of Congo red
dye to give a strong red color.
5. Alka-Seltzer' tablets enclosed in wire screening.
6. Hydrometers covering the range 1.0000 to 1.0050 sp. gr.