Chapter 10 Checkpoint Questions
1. Consider what indicators might place soil near the following:
a. a highway
Residual lead from past us of leaded fuel; bits of concrete or tar; white or yellow line
paint with glass reflector beads; salt or CaCl
b. a home
Roof pebbles, paint chips, fertilizer
c. a commercial building
Gravel from a flat roof, pieces of brick or concrete
d. the ocean
Sand, broken seashells, coral
e. a garden or farm
Fertilizer, pesticide residues
f. a river
Rounded sand grains, fish bones, snail shells
g. a gas station
Hydrocarbons, lead, methyl tertiary-butyl ether (MTBE)
h. a railroad track
Cinders, hydrocarbon residues
i. a forest
Humus
j. a volcano
Ash, pumice, basalt
2. Why is sand not as useful as soil as evidence?
There isn’t much variation laterally and vertically; it doesn’t cling or stick as well to clothing,
shoes and other objects.
3. A burglar entered a house by jimmying open a back window above a flower garden. Muddy
footprints were found in the house, on the windowsill, and in the garden below the window.
Police apprehended a suspect with muddy shoes. How would you investigate the crime scene and
any evidence? Define the exemplars and the questions material.
Investigators should photograph the footprints and make a cast of the footprint in the garden
before collecting any of the soil. These are the questioned samples. A cast or print of the
suspect’s shoes and the dirt from them are the exemplars. Of course fingerprints should also be
considered.
4. Glass and sand are composed predominantly of ____________. How could one tell them
apart?
Silicon dioxide or silica. Glass is amorphous; sand may be mostly quartz, which is crystalline
and, therefore, birefringent
5. Would a body decay faster if buried in the A and upper B horizon, or in the lower B and upper
C horizon?
A and B because these layers have more organisms to eat the body
6. Taxonomy is the science of classification. A hierarchical organization system arranges item
into groups with common properties for use in making comparison, establishing relationships,
and managing and locating data. For example, the Henry-FBI system is used to classify
fingerprints; chemistry has many classification systems, the periodic table being the most
fundamental, Linnaeus worked out an extensive system of classification for plants and animals.
What other systems can you think of? The mail system first sorting by zip code, then street, then
house number; or a family genealogical tree.
Is there such a classification system for soils? If so, describe it.
For the thousands of types of soils, there is a classification system, generally described in any
Earth science text.
7. Here is a “back-of-an-envelope-calculation”: How many grains of 40 mesh sand are there in
one cubic foot of dry beach sand, assuming a 25 percent pore volume? There are 2.54 cm per
inch, so 2.54x12=1ft; so a cubic foot = (2.54x12)3cc. Multiply by 1000 to convert to cubic
millimeters. A grain of sand on the 40 mesh screen has a diameter of 0.425mm. The volume of a
sphere is 4/3π3, so 4/3 X π X (0.21)3mm X 1.25= 0.048mm3. the 1.25 accounts for the added 25
percent pore volume, or packing efficiency. Doing the arithmetic gives about 6 X 108 grains of
sand.
How much would one cubic foot weigh? Knowing the sample weight, calculate the density and
multiply by the volume of a cubic foot.
Would one cubic foot of 40 to 100 mesh beach sand weigh more, the same, or less? The 40 to
100 mesh should be heavier. Why? It packs better.
8. You are on the stand as an expert witness on the comparative analysis of glass fragment. You
must define and explain to the jury (generally consider a jury to have the equivalent of a seventhgrade level of understanding) the following terms:
a. fluorescence
Absorption of light of a shorter wavelength, then reemission at a longer wavelength
b. density and specific gravity
Density is mass per unit volume; the ratio of a substance’s density to that of water is its
specific gravity
c. reflection and refraction
Reflection occurs when light bounces off a shiny surface such as a mirror. Refraction is
the bending
d. refractive index
The ratio of the speed of light in a vacuum to its speed in a specified substance
e. glass and how it is made
Glass is a substance made from mostly silica, like very pure sea sand, that has been
melted and had some chemicals added, then was formed into different shapes by heat.
f. Becker line
The light halo around each piece of a material immersed in a substance when determining
refractive index
g. class evidence
Evidence that cannot be traced with certainty to an individual
h. the circumstances under which glass evidence can be individualized
If the pieces can be fitted together to form a match, as in a jigsaw puzzle, the evidence
can be individualized
9. How are layer of dirt related, in a general sense, to layer of paint from a vehicle?
The more layers, the more individual the story the material tells
10. What are the similarities in the physical property of amorphous and isotopic substances?
Structurally, how do they differ?
Amorphous and isotropic substances show the same properties in all directions; amorphous
substances are noncrystalline, but an isotropic substance can be crystalline
11. How would you “calibrate” a density solution or column?
By adding crystals of known density; see Table 10.3 on page 291 for examples.
12. Density and refractive index seem to be proportionally related. Why?
The more dense an object is, the more interaction with light rays
13. Does a Galileo thermometer work?
By buoyancy and the relationship between density and temperature
14. You used the flotation method to find a material’s density. Is there another method for
determining density? Archimedes’ principle and buoyancy.
Would it work here? No, the sample is too small.
15. What would weaken your argument that glass fragments from the suspect and from the crime
scene appear to have a common origin?
Lack of precision of analytical results; variability within small samples; many random samples
have the same values
16. How would you differentiate among fragments of clear polystyrene, glass, and quartz?
Glasses are isotropic, that is, their properties are the same in all directions. Most crystalline
substances are anisotropic. The refractive index of silica glass (SiO2) is the same in all
directions (n= 1.458), whereas natural quartz (siO2) has two indices of refraction (n=1.544 and
1.553). The difference between the two indices of refraction in the quartz is termed
birefringence. When glass is rotated between crossed polarizing filters, no light is transmitted.
When quartz is rotated under the same conditions, a point is reached when light will pass through
the crystal. Tempered auto glass is birefringent because by being slowly cooled during
manufacture, it crystalizes and, therefore, fractures into many small pieces. Polystyrene also
exhibits birefringence, and its density is less than 1.