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This article incorporates, in modified form, material from the not-yet-published Illustrated Guide to Forensics Investigations: Uncover Evidence in Your Home, Lab, or Basement.

Many soils can easily be differentiated from each other by observing such physical characteristics as color, density, settling time, and particle size distribution. Physical soil tests have been widely used forensically since the late 19th century. As is true of so many other fields of forensic science, Sherlock Holmes led the way. In the first Holmes novel, Watson has just met Holmes and is trying to figure out just what Holmes’ eclectic studies are intended for. Watson lists Holmes’ areas of knowledge, including:

“Knowledge of Geology: Practical, but limited. Tells at a glance different soils from each other. After walks has shown me splashes upon his trousers, and told me by their colour and consistence in what part of London he had received them.” –Arthur Conan Doyle, A Study in Scarlet, 1888

Which makes Sherlock Holmes the world’s first forensic geologist. Although it can’t be established firmly, we think it likely that Holmes also devised many of the other standard physical soil tests that are still used in forensics laboratories.

In this lab session, we’ll examine several physical characteristics of our soil specimens to determine if we can discriminate them based on these physical characteristics.

Required Equipment and Supplies

  • goggles, gloves, and protective clothing
  • balance and weighing papers
  • beaker, 600 mL (see Substitutions and Modifications)
  • graduated cylinder, 100 mL (6; but see Substitutions and Modifications)
  • test tubes (6) and rack (but see Substitutions and Modifications)
  • stirring rod
  • disposable pipette (2)
  • wash bottle
  • powder funnel (see Substitutions and Modifications)
  • reaction plate
  • paint chips (see Substitutions and Modifications)
  • ultraviolet light source (optional)
  • sieves (see Substitutions and Modifications)
  • foam cups (30, but see Procedure Part III)
  • watch, clock or other timing device
  • acetone (300 mL; optional; see Procedure Part II)
  • dishwashing liquid (a few drops)
  • water
  • dry soil specimens, known and questioned

All of the specialty lab equipment and chemicals needed for this and other lab sessions are available individually from the Maker Shed or other laboratory supplies vendors. Maker Shed also offers customized laboratory kits at special prices, and a wide selection of microscopes and microscope accessories.

sciRoomCAUTION2.gif CAUTION

None of the activities in this lab session present any real hazard, but as a matter of good practice you should always wear splash goggles, gloves, and protective clothing when working in the lab.

Substitutions and Modifications

  • You may substitute any container of similar or larger size for the 600 mL beaker. You’ll use this container to wash your soil specimens, so it must be large enough to contain the soil specimens with some room to spare.
  • The 100 mL graduated cylinders are used in the density and settling time tests. Depending on the composition of your soil specimens, settling time may range from less than a minute to 24 hours or more. Samples that contain clay are notorious for slow settling. Our soil specimens contained clay, so for efficiency we used six 100 mL graduated cylinders and allowed the specimens to settle overnight. If your soil specimens contain clay and you have only one graduated cylinder, it’s obviously impractical to run the settling time tests with a graduated cylinder, so you can skip them if you wish. You can still do the density tests, because they do not require that the soil specimen be fully settled, but merely that the entire specimen be immersed in water. If you have only one graduated cylinder but still want to do the settling tests, you can substitute six test tubes for those tests using the alternative procedure described in Part II of the Procedure section.
  • A powder funnel has a wide stem and is used to introduce the soil specimens into the graduated cylinder(s) for the density and settling time tests. You can substitute any funnel, including one you make with a cone of paper, as long as it allows the soil specimens to flow freely into the graduated cylinder.
  • The paint chips are used as a color comparison standard. Professional forensics labs use Munsell Soil Color Charts, but a set of those costs $115. Urk. Instead, we visited our local paint store and obtained a full set of paint chips in browns, tans, and other earth tones. (We don’t feel too guilty about pillaging their paint chips; we also bought several gallons of paint to repaint our kitchen, dining room, and library.)
  • Sieves are used in the particle size distribution test. Professional forensics labs use a wide range of sieves for these tests, typically in 20, 40, 60, 80, 100, 120, 150, and 200 mesh sizes. You can obtain sieves in these standard mesh sizes in pottery supply stores, but even there the cost is not trivial. (The least expensive sieves we found were $14 for each mesh size.) Understanding the concept doesn’t require a formal set of sieves, though. What’s important is not the exact mesh size, but using the concept of separating soil specimens by particle size. We separated our specimens into only four fractions, using an old piece of window screen, a discarded kitchen strainer with a mesh about half the size of the window screen, and a discarded permanent coffee filter made from a very fine metal mesh.

Procedure

This lab has three parts. In Part I, we’ll observe and categorize soil color. In Part II, we’ll determine the density and settling time for each of our known and questioned soil specimens. In Part III, we’ll determine the particle size distribution of our specimens.

Part I – Observe and categorize soil color

The most obvious characteristic of a soil specimen is its color. If the color of the questioned soil specimen is consistent with a known specimen, it’s possible (although not certain) that the questioned specimen originated from the same source as that known. Obviously, if the color of the questioned specimen differs significantly from any of the known specimens, it’s likely (although not certain) that the questioned specimen did not originate from the same source as any of the known specimens against which it was compared.

It’s important to dry the soil specimens completely before doing color comparisons. Some soils have similar color whether they are dry or moist, while the color of other soils may vary significantly. It’s also important to use consistent lighting when comparing colors. The standard used by professional forensics labs is open shade (daylight from a clear north sky; not direct sunlight). Soil colors may appear significantly different if viewed under incandescent or fluorescent lighting. One very different form of lighting is useful, however. Two soil specimens that appear identical in daylight may appear very different under ultraviolet lighting. The overall color may be quite different, and some soil specimens contain natural or artificial materials that fluoresce under ultraviolet lighting.

It’s also important to use a standard specimen size. If you’ve ever chosen a paint color from a small sample chip and painted a room in that color, you know that the paint appears very different when it’s on the wall than it did when you looked at the small sample chip. (Although, if you hold the chip up to the painted wall, you’ll find that the colors are in fact identical.) We placed our specimens in a reaction plate, as shown in Figure 5-6, to ensure consistent sample size.

figure-05-06-hfl.jpg

Figure 5-6. Questioned and known soil specimens in a reaction plate

We had plenty of our questioned soil specimen available, so we filled all six cells in the bottom (D) row with it to make it easier to compare against the known specimens in the row above (C). To make sure the lighting or viewing angle wasn’t affecting our judgment, we also filled cell C1 (to the far left) with the questioned specimen. Visually, all six D-row cells and cell C1 appear nearly identical. Cells C2 and C5 are much darker than the questioned specimen, and cells C3 and C4 are somewhat darker. Cell C6, which contains Known #5 (K5), is extremely similar visually to the questioned specimen.

Finally, for forensic purposes, it’s important to be able to categorize the color of soil specimens unambiguously. In day-to-day life, it’s acceptable to describe a color as “a chocolate brown with a hint of purple” or “a reddish sand,”, but that obviously won’t do for forensics. It’s necessary to assign a specific color description that can be reproduced by others. Ideally, we’d use the Munsell Soil Color Charts for that purpose, but using paint chips instead is much cheaper and works surprisingly well.

With all of that in mind, let’s compare the colors of our soil specimens.

  1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
  2. Place your reaction plate on a sheet of white paper, and fill a row of five adjacent wells to near the top with portions of your questioned specimen.
  3. Compare the color of the questioned specimen with your paint chip samples, and record the name of the closest paint chip on Line A of Table 5-1.
  4. Fill an adjacent row of five wells with your known specimens, as shown in Figure 5-6, noting which well contains which known.
  5. Under even daylight lighting, compare Known #1 (K1) against the questioned specimen (Q1) to determine how closely it matches the unknown specimen. Fill in a short narrative description (for example, “match,” “close match,” or “no match” on Line B of the middle column of Table 5-1.
  6. Repeat step 5 for K2 through K5, and record your observations on the appropriate line in the middle column of Table 5-1.
  7. Darken the room as much as possible, and then turn on your ultraviolet light source. Record the appearance of the questioned specimen (Q1) and the known specimens (K1 through K5) on the appropriate lines of the right column of Table 5-1. Note any fluorescence and whether the glow appears uniform or is emitted by only some particles in the specimen.
  8. Compare your questioned specimen against your color charts and note the best match in Table 5-1.

figure-05-07-hfl.jpg

Figure 5-7. Comparing paint chip samples against a soil specimen

Figure 5-7 shows the first paint chip sample we chose, based on eyeballing the questioned specimens and the paint chip samples. As you can see, the match is not at all close. We finally settled on a paint chip that was considerably darker than those shown here. It was not an exact match, but came very close.

Table 5-1. Color comparisons of unknown and known soil specimens – observed data

Soil specimen Color chart match Daylight appearance versus questioned UV appearance versus questioned
A. Questioned (Q1)
n/a
n/a
B. mass of cup + water
n/a
C. Known #2 (K2)
n/a
D. Known #3 (K3)
n/a

Part II – Determine soil density and settling time

The density of soils varies over a wide range, depending on the composition of the soil, how tightly it is compacted, how moist it is, and other factors. Average soil has a density of about 1.5 g/mL to about 2.7 g/mL. The least-dense soils, often found in forested areas, contain a high percentage of organic matter, and may have average densities lower than 1.0 g/mL (less dense than water). The densest soils are made up primarily of very dense minerals, and may have densities of 4.0 g/mL or higher. In general, the organic (vegetable, animal, and some plastics) content of soils is of low density, often low enough to float on water. The presence of large amounts of material of low density makes it difficult or impossible to obtain good values for density. There are at least two ways to work around this problem:

  • You can wash the soil specimens to remove as much light material as possible, leaving only the heavier mineral. (Your results remain valid even though you are testing only a subset of the material in the specimen because you have eliminated only the light materials from all specimens and are testing the same subset of the material for each specimen.) The drawbacks to this method are that some soil specimens require considerable time (hours to days) to settle completely, and that you will have to thoroughly dry each specimen after washing so that you can weigh out a known mass of it.
  • You can substitute a less dense liquid for water in determining density by displacement. Acetone, 95% ethanol, or 91% isopropanol–all of which are available inexpensively at the drugstore or hardware store–all have densities around 0.79 g/mL, which means that most of the light soil components that float in water sink in one of these solvents.

If you decide to use water as a solvent, run a quick test on each specimen to determine if most or all of the soil components sink. If not, you’ll need to wash the soil. Prepare each soil specimen by stirring it into a large amount of water, allowing it to settle, and then skimming off any floating material. If necessary, repeat this procedure two or three times or until you’re satisfied that all of the light material has been removed from the specimen. Once the specimen has been washed thoroughly, dry it completely before proceeding.

Whether you use water or another solvent, add one drop of liquid dishwashing detergent per 100 mL of solvent, which helps the solvent wet the soil granules and prevent surface tension and trapped air from causing them to float.

Settling time is a commonly used metric in soil analysis. The amount of time required for a suspension of soil to settle completely out of a solvent depends on many factors, including the solvent used, the average size of the particles, and their density. Some soils, such as very sandy soils, settle very quickly, sometimes in a minute or less. Other soils, particularly those that contain significant amounts of clay, form suspensions that are almost colloidal, and may require anything from hours to literally days to settle completely.

Let’s get started on our tests of soil density and settling time. In this procedure, we assume you have six 100 mL graduated cylinders available, or are willing to wait for settling to occur using only one graduated cylinder. If your soil specimens are slow settling but you have only one graduated cylinder, you can substitute six test tubes for the settling tests, as described in the alternative procedure following this one.

  1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
  2. Weigh out about 50.0 g of the dry questioned specimen and record its mass to the resolution of your balance on Line A of Table 5-2.
  3. Fill a 100 mL graduated cylinder to the 50.0 mL line, using a disposable pipette to add solvent dropwise until the cylinder contains as close as possible to 50.00 mL. Record this initial volume as accurately as possible on Line B of Table 5-2.
  4. Withdraw a few mL of the solvent with each of the two disposable pipettes. Set them aside, inverted to make sure none of the solvent leaks from the pipettes.
  5. Using the funnel, transfer the questioned soil specimen to the graduated cylinder. Make sure as little as possible of the soil specimen adheres to the walls of the cylinder above the liquid level. Your goal is to make sure all of the soil is immersed in the liquid. If you get air bubbles under the surface of the liquid, tap the cylinder or use the stirring rod to eliminate them.
  6. Use the liquid stored in the disposable pipettes to rinse down any soil that adheres to the inside surface of the graduated cylinder above the liquid line. Make sure to expel all of the liquid from both of the disposable pipettes, restoring the exact amount of liquid to the cylinder that was present at the initial measurement.
  7. Observe the new liquid volume and record it as accurately as possible on Line C of Table 5-2.
  8. Subtract the initial volume from the final volume to determine the volume of liquid displaced by the specimen. Record this volume on Line D of Table 5-2.
  9. Divide the mass of the specimen (Line A) by the volume displaced (Line D) to determine the density of the specimen in grams per milliliter. Record this calculated value on Line E of Table 5-2.
  10. Set the 100 mL graduated cylinder aside for later settling tests.
  11. Repeat steps 1 through 8 for each of the known specimens.
  12. After you have determined the density of each of the specimens, use the stirring rod to agitate the contents of the first graduated cylinder to suspend the questioned soil specimen in the liquid. Immediately note the start time on Line F of Table 5-2. Set the cylinder aside and allow the specimen to settle undisturbed, keeping an eye on progress, as shown in Figure 5-8.
  13. When the soil appears to have settled completely, record the finish time on Line G of Table 5-2.
  14. Subtract the start time from the end time to determine the elapsed time needed for the specimen to settle completely. Record that elapsed time on Line H of Table 5-2.
  15. Repeat steps 10 through 12 for the graduated cylinders that contain specimens K1 through K5. Unless your specimens settle very quickly, you’ll have time to start some or all of the remaining cylinders before settling completes in the first cylinder.
figure-05-08-hfl.jpg

Figure 5-8. Determining soil density and settling time

For the run shown in Figure 5-8, we started with 50.0 mL of water and 50.0 g of soil. The final volume was about 82.1 mL, so our 50.0 g of soil displaced 32.1 mL. To calculate the density of the specimen, we divided 50.0 g by 32.1 mL to give about 1.56 g/mL. This is on the low side of normal soil density, but not unexpectedly low for a soil specimen from a residential yard that is frequently fertilized and mulched.

Table 5-2. Soil density and settling time – observed and calculated data

Item Q1 K1 K2 K3 K4 K5
A. Mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
B. Initial volume
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
C. Final volume
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
D. Volume displaced (C – B)
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
___.__ mL
E. Density (A/D)
__.__ g/mL
__.__ g/mL
__.__ g/mL
__.__ g/mL
__.__ g/mL
__.__ g/mL
F. Start time
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__
G. Finish time
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__
H. Settling time (G – A)
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__
__: __ :__

If you have only one 100 mL graduated cylinder available, use steps 1 through 7 of the procedure just described to determine the density of the questioned specimen and the five known specimens, emptying the graduated cylinder and rinsing it out between specimens. Then use the following alternative procedure to determine settling time.

  1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
  2. Label six test tubes Q1 and K1 through K5.
  3. Weigh about 10 grams of the questioned specimen and transfer it to tube Q1. (You needn’t record the mass of the specimen).
  4. Add water (or an alternative solvent) until the tube is about half full. (Remember to use solvent with detergent added to ensure wetting.)
  5. Agitate the contents of the tube to suspend the soil in the liquid, and immediately note the start time on Line F of Table 5-2. Replace the tube in the rack and observe it as the soil settles.
  6. When the soil appears to have settled completely, record the finish time on Line G of Table 5-2.
  7. Subtract the start time from the end time to determine the elapsed time needed for the specimen to settle completely. Record that elapsed time on Line H of Table 5-2.
  8. Repeat steps 3 through 7 for specimens K1 through K5. Unless your specimens settle very quickly, you’ll have time to start some or all of the remaining tubes before settling completes in the first tube.

With soils that contain a lot of clay, the finest particles may remain suspended for literally days or longer. In soils with clay particles fine enough to form true colloids, the fine particles remain suspended permanently. We suggest that you observe settling time for no longer than one hour, by which time most or all of the soil may have settled out. If after that time the liquid remains cloudy, simply note that fact and move along.

Part III – Determine soil particle size distribution

Particle size distribution is an important characteristic of a soil specimen. Some soils, particularly sandy soils, may have relatively uniform particle sizes, with 90% or more of the particles contained with a size range of perhaps 5:1 or less. Other soils, particularly clay soils, may span a much broader range of particle sizes, with the largest particles being pea-sized pieces of gravel and the smallest being barely large enough to discern under a microscope at high magnification.

The particle size distribution of a soil specimen is an important aspect forensically, providing just one more piece of the “fingerprint” of that specimen. In a professional forensics lab, a soil specimen may be passed through as many as 10 sieves of different sizes, and the mass percentage of each fraction calculated and recorded for that specimen.

It’s important to understand that the observed particle size distribution for a soil specimen depends on how that specimen is prepared and tested. For example, dry sieving is not normally used because particles in a dry specimen tend to adhere, creating deceptively large fractions of larger particle sizes. Those fractions can also vary noticeably, even within a single relatively small specimen. Wet sieving–basically adding water to convert the specimen to mud and using the sieve to separate the wet fractions–yields more reproducible results, but requires drying the separated fractions thoroughly before weighing. Wet sieving, shown in Figure 5-9, also reduces the overall mass of many soil specimens, because any soluble salts present in the specimen are dissolved and so pass through even the finest mesh.

figure-05-09-hfl.jpg

Figure 5-9. Wet sieving a soil specimen

The presence of some fertilizers and other chemicals, natural or artificial, may also have an effect on observed particle size distribution. For example, any lime, limestone, or carbonates present in the specimen may function as a sort of glue that causes fine particles to aggregate into larger particles. Wet sieving eliminates some but not all of this aggregation. Treating the specimen with dilute hydrochloric acid (~ 3 M) eliminates most aggregation because the acid reacts with carbonates and other “glue” chemicals to produce gases and soluble compounds. Obviously, acid treatment may also reduce the mass of the specimen significantly.

In this part of the lab session, we’ll use wet sieving to separate our soil specimens into several fractions. We’ll then dry each fraction and determine its mass. By dividing the mass of each fraction by the total mass of all fractions, we’ll determine the mass percentage for each fraction.

Making Do

This lab session can be quite time consuming and resource intensive because we’ll be operating on six soil specimens–one questioned and five known–and separating each of those specimens into multiple fractions, each of which must be dried and weighed separately. For example, we used three mesh sizes–window screen, a kitchen strainer, and a permanent mesh coffee filter–so we ended up with a total of 24 fractions.

The exact procedure you use will depend on the physical form and other characteristics of your meshes. For example, our coarsest mesh was a 15 cm square of window screen, which we placed flat on the top of a large funnel and poured our specimens through, capturing the water and finer particles in a large flask. After pouring all of the wet initial specimen through the window screen, we used a wash bottle to rinse the captured particles to make sure that all of the finer particles had passed through the window screen. We then rinsed the captured particles off the window screen onto a large Pyrex saucer, and placed it in the oven to dry. With that fraction isolated and drying, we then passed the remaining wet specimen through the kitchen strainer to capture the second fraction, which we again rinsed thoroughly to ensure that all particles that would pass that mess did so. We transferred that wet fraction to another Pyrex saucer and placed it in the oven to dry. We then passed the remaining wet specimen through our old metal mesh coffee filter, isolated that fraction, and dried it. The final fraction–the particles small enough to pass the coffee filter–were by then suspended in a large amount of water. We poured that last fraction into a large beaker for which we’d recorded its dry mass and heated the beaker to boil off the excess water and dry the remaining fraction. Subtracting the initial mass of the beaker from the mass of the beaker with the dried final fraction gave us the mass of the final fraction. Whew!

We then repeated that procedure for each of the five known specimens. All told, it took us three full days to complete the workup of all six specimens, although most of that time was spent waiting for specimens to dry. In terms of actual hands-on work, the entire lab session took less than two hours. Accordingly, we’ve modified the recommended procedure for this lab session to use natural drying by evaporation, which minimizes the amount of work required at the expense of extending the lab over a period of a week or so. Note that natural drying by evaporation does not completely dry a specimen, so using this method introduces some error. If you want your results to be as accurate as possible and are willing to put in the work to get those better results, you can reproduce the procedure described above.

  1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
  2. Assuming that you have six soil specimens, label six foam drink cups Q1, K1, K2, K3, K4, and K5.
  3. Assuming that you will separate each soil specimen into four fractions, label four foam drink cups “Q1-F1″ through “Q1-F4″, four more cups “K1-F1″ through K1-F4″, and so on until you have 24 labeled fraction cups, four for each of the six soil specimens.
  4. Weigh each fraction cup and record its mass to the maximum resolution of your balance. Write the mass of each cup on the cup itself.
  5. Weigh about 100.0 g of the questioned specimen to the maximum resolution of your balance and record that mass on Line A of Table 5-3.
  6. Transfer the specimen to cup Q1, and add sufficient water to the cup to form a soupy mix.
  7. Swirling the cup to keep the soil suspended, pour the suspension through your largest mesh, capturing the liquid and solids that pass the mess in another container. Add more water to the cup as necessary to make sure that all of the soil in the cup is rinsed into the mesh, but try to use as little water as possible while still transferring all of the soil.
  8. Transfer the soil particles captured by the first mesh into cup Q1-F1. If necessary, use the wash bottle to rinse particles off the mesh, but try to use as little water as possible.
  9. The large particles captured by the first mesh should settle very quickly. Once those particles have settled, use the eyedropper or Beral pipette to remove and discard as much water as possible from cup Q1-F1 to speed drying. Make sure not to remove any of the soil particles. Set cup Q1-F1 aside to dry.
  10. Set up your second sieve, and pour the soil/water suspension that passed the first sieve through the second sieve, again capturing the liquid and solids that pass the mesh in another container. Make sure that all of the soil is transferred from the cup into the second sieve, using as little water as possible to rinse the soil into the sieve.
  11. Transfer the soil particles captured by the second mesh into cup Q1-F2, again using as little water as possible to do a complete transfer. Once the particles have settled, again use the eyedropper or Beral pipette to remove as much water as possible from the cup without removing any soil particles. Set cup Q1-F2 aside to dry.
  12. Repeat the preceding steps with each of your sieves until you have isolated each fraction into its own fraction cup and set it aside to dry.
  13. Repeat the preceding steps with soil specimens K1 through K5.
  14. At this point, you have a large array cups, all of which contain damp (or wet) soil specimen fractions. You can allow these specimens to dry naturally, which may require several days. Alternatively, you can dry them in an oven set to its lowest temperature (typically about 120F or 50C). Before you do that, do a test with an empty cup to make sure it won’t melt.
  15. Once all of your specimens are dry, weigh each cup to the maximum resolution of your balance, as shown in Figure 5-10. Subtract the empty mass of the cup from the mass of the cup with the specimen fraction to determine the mass of the specimen fraction, and record that value in the appropriate box on Lines B through E of Table 5-3.
figure-05-10-hfl.jpg

Figure 5-10. Determining the mass of a soil specimen fraction

In our session, the mass of the foam cup was 4.03 g. With the Q1-F1 soil specimen fraction added, the mass was 131.93 g. Subtracting the mass of the empty cup gives us the mass of the Q1-F1 soil fraction, (131.93 – 4.03) = 127.90 g.

  1. For each soil specimen, add the masses of fractions 1, 2, 3, and 4 (Lines B through E), and enter that value on Line F of Table 5-3.
  2. For each soil specimen fraction, divide the mass of that fraction by the total mass of all fractions, multiply that result by 100 to determine the fraction mass percentage, and enter that value in the appropriate box on Lines G through J of Table 5-3. Note that we are calculating the fraction mass percentages based on the total mass of all fractions isolated rather than on the initial mass of the specimen. That’s because some of the material in the original specimen may have been soluble and so dissolved in the water we used to separate the fractions.
  3. We have the data necessary to calculate one more possibly useful value, the insoluble mass percentage of each of our specimens. We know the original mass of each specimen (Line A), and we know the total mass of all of the fractions we isolated for each specimen (Line F). Divide Line F by Line A and multiply by 100 to determine the percentage of the original specimen that was insoluble in water, and enter that value on Line K of Table 5-3.

Table 5-3. Soil particle size distribution – observed and calculated data

Item Q1 K1 K2 K3 K4 K5
A. Initial specimen mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
B. F1 fraction mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
C. F2 fraction mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
D. F3 fraction mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
E. F4 fraction mass
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
F. Total fraction mass (B+C+D+E)
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
____.___ g
G. F1 fraction mass percentage ([B/F]·100)
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
H. F2 fraction mass percentage ([C/F]·100)
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
I. F3 fraction mass percentage ([D/F]·100)
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
J. F4 fraction mass percentage ([E/F]·100)
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
K. Insoluble fraction mass percentage ([F/A]·100)
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %
___.___ %

Disposal

All of the material used in this lab can be disposed of with household waste.

Review Questions

Q1: Based on the physical characteristics you observed for your soil specimens, how well can you discriminate between the specimens?

Q2: Which of the physical tests were most and least useful in discriminating between specimens? Why?

Q3: Why is it useful to perform several different physical tests on each soil specimen?

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