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GES 175, Science of Soils
Fall 2002
Laboratory Exercise, Week 3
WATER DYNAMICS
Impact of Capillary Forces
To illustrate capillary forces, we will first make comparative measurements of capillary
rise in a series (four to be exact) small-diameter tubes. Next we will test the ‘wicking’ of
water into two different brands of paper towels. Finally, we will use a set of sponges to
illustrate capillary forces and, along with gravitational forces, their impact on soil water
retention and movement. Recall that a sponge is nothing more than a microporous
material and is similar to an aggregation of clay-size soil particles. (NOTE: You do not
have to do the experiments (demonstrations) in the order listed below.)
Part 1: Measure the capillary rise resulting in four different glass tubes. You will need
the (nearly) exact measurement in your write-up, so be sure to record the height.
Question 1-1: What are the radii of the four different glass tubes?
Part 2: Compare (measure) the height to which water rises (wicks) in the two different
bands of paper towels. Again, make sure your record the height.
Question 2-1: What is the ‘average’ pore-diameter within each of the paper
towels?
Part 3:
a) Take a sponge and submerse it in water until you are certain it is saturated.
b) Next, place the sponge flat and allow it to drain freely.
c) Now, turn the sponge on end. Note the bottom of the sponge and the surface
in contact with it.
d) Re-wet the sponge, allow it to drain in the flat position, then place it over a
bed of sand. Try to determine whether water drains under this condition.
e) The final act is to now place the saturated sponge on another sponge that is
just moist. Again, determine whether water drains under this placement.
Questions:
3-1 Why does water drain from the sponge when it is turned on end?
3-2 Why does water ‘drain’ from a saturated sponge into a moist sponge but not
a sand surface?
3-3 Explain the forces acting within the sponge that retain or drain the water.
2
Part 4:
a) place a sponge over a bed of sand
b) Using a graduated cylinder (and after noting the initial water level) begin
pouring ‘red’ water (dyed with food coloring) into it.
c) Note the point at which water begins moving into the sand and record the
volume of water added.
d) Now take two moist sponges that have not been dyed and place them over a
bed of sand.
e) Using a graduated cylinder, again pour ‘red’ water into the top sponge and
note the point at which the second (bottom) sponge begins to become wet.
f) Record the volume of water added.
g) One last quick test. Now place a sponge on a little sand, then put sand over
the top of the sponge (add about an inch or two on top).
h) For the final time, begin pouring in water and determine how much water is
added before it moves through the sand into the sponge. (HINT: Add the
water very slowly).
Questions:
4-1 Would a greater volume of water be held in a clay layer deposited (a) over
sand or (b) over a second clay layer? Explain the reason for your answer.
4-2 Does placing a sand layer beneath the surface of a heavy (clay-rich) soil
promote water movement?
4-3 What is an easy means of improving the infiltration rate of a soil?
Sodium Ion Effect
We will now move away from sponges and start getting dirty. The next exercise will
hopefully demonstrate the impact of sodium on infiltration along with the influence of
soil mineralogy.
Part 5
a) take four filtration funnels and place them over polycarbonate (plastic) bottles
b) place a filter in each
c) in two of the filters, add one scoop of soil A. To the other filters, add a scoop
of soil B to each.
d) Now its time for a race. Take the bottles having CaCl2 and NaCl and get
ready to add the salts to each of the soils. Let’s start with soil A. To make it a
fair race, you need to add the salts simultaneously and in about the same
quantity. To one of the A soils, add CaCl2 and to the other add NaCl. Wait a
3
e)
f)
g)
h)
i)
few moments and note whether there is a difference in water movement
through the soils. Record your qualitative results
Repeat the same test (race) with soil B
Now let’s compare soil A against soil B. Take the NaCl treated soils from ‘d’
and ‘e’ above and allow them to drain. Now added a fresh volume of NaCl to
each and note the difference in infiltration rates.
Repeat the test of soil A and B but this time use CaCl2 as the infiltrating fluid.
Feel each soil to get an idea of its physical properties. Also make sure to note
the colors (general) of each.
Help clean-up
Questions
5-1 On the basis of color and feel for the each soil, make a guess at its
mineralogy.
5-2 How do the infiltration rates compare for Na versus Ca treated soils
(compare within each soil type)?
5-3 Explain why there was or wasn’t a difference in infiltration rates between the
soils for (i) CaCl2 additions and (ii) NaCl additions
REPORT
In a short laboratory report (no more than 5 pages), answer the questions provided
for each of the three experimental sections (repeated below for your convenience). In
your report, please also provide an explanation of the physical and chemical factors that
are the basis for the phenomena observed within these demonstrations.
Questions:
1-1. What are the radii of the four different glass tubes?
2-1. What is the ‘average’ pore-diameter within each of the paper towels?
3-1 Why does water drain from the sponge when it is turned on end?
3-2 Why does water ‘drain’ from a saturated sponge into a moist sponge but not a
sand surface?
3-3 Explain the forces acting within the sponge that retain or drain the water.
4-1 Would a greater volume of water be held in a clay layer deposited (a) over
sand or (b) over a second clay layer? Explain the reason for your answer.
4-2 Does placing a sand layer beneath the surface of a heavy (clay-rich) soil
promote water movement?
4-3 What is an easy means of improving the infiltration rate of a soil?
5-1 On the basis of color and feel for the each soil, make a guess at its mineralogy.
5-2 How do the infiltration rates compare for Na versus Ca treated soils (compare
within each soil type)?
5-3 Explain why there was or wasn’t a difference in infiltration rates between the
soils for (i) CaCl2 additions and (ii) NaCl additions.