Experiment #18
Forensic Soil Analysis
I. Objectives
1. Learn the different procedures used for the forensic identification of soil.
2. Be familiar with the methods used in the proper search and collection of soil
evidence for laboratory examination.
3. Understand the value of soil evidence in criminal investigation.
II. Apparatus/Materials
Compound microscope, glass slide, cover slip, tripod, tirril burner, thermometer,
weighing scale, graduated cylinder, test tube, test tube rack, oven, soil samples
III. Procedure
1. Microscopic Examination
1.1. Mount on a glass slide a small amount of thoroughly mixed questioned soil
sample.
1.2. Observe under the low power magnification of a compound microscope the
presence of foreign particles like glass fragment, paint chips, and others.
1.3. Record and illustrate your observations.
2. Texture of Soil Determination
2.1. Place a small amount of known soil sample into the palms of your hand and
moisten it. Press and fold it until it has the consistency of a putty.
2.2. Using your thumb and forefinger, form it into a ribbon.
If the ribbon forms easily, stays together and is also flexible, the soil is
40% or more clay. Hence, it is classified as clay soil.
If the ribbon forms but breaks easily, the soil is 27-40% clay and is
called clay loam soil.
If the ribbon is not formed, the sample contains less than 27% clay
and is called loam soil.
Since the sand gives a gritty feeling to the soil, if a clay soil could have
a lot of sand on it is called sandy clay soil.
Silt feels like talc, so a loam with smooth talc like feel is a silt loam.
2.3. Follow the same procedure for your questioned soil sample.
2.4. Record and illustrate your observations.
3. Color of Soil Determination
3.1. Obtain one gram each of standard and questioned soil samples.
3.2. Dry each of the soil samples in separate beakers at 100 degree Celsius for
one hour.
3.3. Compare the color of both samples after heating.
3.4. Record and illustrate your observations.
4. Density Measurement
4.1. Dry one gram each of the questioned and standard soil samples in separate
beakers at 100 degree Celsius for one hour.
4.2. Cool the samples and pulverize each sample by hand.
4.3. Sieve the soil samples into different sizes of particles; a fine to medium mesh
sieve sample is recommended.
4.4. Weigh about 0.5 g each of the dried questioned and standard soil samples.
4.5. Place each sample on a graduated cylinder of uniform size. This will serve
as the column.
4.6. Fill each of the two columns with the following liquids of varying densities.
Take note that the first liquid to be placed is Bromoform which is the heaviest liquid
followed by the liquids of decreasing densities.
4.6.1 One Bromoform(density=2.89)
4.6.2. One part Xylene: five parts Bromoform
4.6.3. Two parts Xylene:four parts Bromoform
4.6.4. Three parts Xylene:three parts Bromoform
4.6.5. Four parts Xylene:two parts Bromoform
4.6.6. Five parts Xylene: one part Bromoform
4.6.7. Xylene (Density=0.88)
4.7. Allow the columns to stand upright for about 24 hours until the liquids have
had the chance to be mixed by diffusion.
4.8. The known and questioned soil samples are added to their respective
columns. Within a few hours, the individual particles of the soil will settle to their
density level. Finer particles may take up to two days to settle.
4.9. Observe the density distribution of both samples, only after the soil particles
already ceased to move in both columns.
4.10. Record and illustrate your observations.
IV. Observation
1. Microscopic Examination
1.1. Identify any foreign particle in the:
1.1.1. Known Soil Sample
1.1.2. Questioned Soil Sample
1.2. List the foreign particles which you observe in both samples.
1.3. Why do you have to thoroughly mix the soil sample before getting a small
amount for microscopic examination?
2. Texture of Soil Determination
2.1. After pressing and folding, describe what happens to the:
2.1.1. Moistened Questioned Soil Sample
2.1.2. Moistened Known Soil Sample
2.2. Is ribbon formed from both samples?
2.3 From the initial examination of the texture of the soil, can you determine what
class of soil does your known and questioned soil sample belong?
3. Color of Soil Determination
3.1. What do you do to both standard and questioned soil samples before
subjecting them to color examination?
3.2. What is the temperature used in drying the soil sample?
3.3. What happens when both soil samples are heated over a flame or in an
oven for one hour?
3.4. Describe the color of the dried standard and questioned soil sample.
3.5. Do you observe any difference in color? What does this indicate?
4. Density Measurement
4.1. Why is there a need to pulverize by hand each of the dried soil samples?
4.2. What is the recommended size of the soil particles that will be subjected to
density measurement?
4.3. What is the analytical technique you employ in determining the density of the
known and questioned soil samples?
4.4. What is the purpose of adding different liquids of varying densities to the
different columns where the known and questioned soil samples are to be placed?
4.5. Compare the density distribution of the known and questioned soil samples.
Are they the same or different? Explain.
4.6. What scientific information do you obtain in relation to the examination that
is conducted?
4.7. How will this information provide a good investigative lead to the
investigator-on-case?
V. Post Laboratory Discussion
Guide Questions
1. What is a soil?
2. What are the different types of soil?
3. What are the major constituents of soil? Describe each.
4. What are the naturally occurring crystals that are commonly found in soils?
5. What are the forensic characteristics of soils?
6. What forensic examinations can be conducted to identify the questioned soil
samples?
7. Explain the density gradient tube technique?
8. What sophisticated instruments will help in the forensic identification of soil?
9. What is the value of soil evidence in criminal investigation?
10. Where do you search/look for soil samples?
11. How do you collect soil samples from:
11.1. an indoor crime scene?
11.2. an outdoor crime scene?
VI. Conclusion
VII. Illustration
VIII. Documentation
