Ch 4 - Physical Properties:
Glass and Soil
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Physical and chemical properties.
Metric and British systems.
Celsius (Centigrade) vs Fahrenheit.
Mass vs Weight.
Density
Refractive Index
Crystalline vs Amorphous solids.
Double refraction and birefringence.
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Dispersion of light through a prism.
Flotation and immersion methods for
comparing glass specimens.
Examining glass fractures to determine the
direction of impact from a projectile.
Proper collection of glass evidence.
Forensic properties of soil.
Density-gradient tube technique.
Proper collection of soil evidence.
http://www.fbi.gov/hq/lab/handbook/examglas.htm
http://www.fbi.gov/hq/lab/handbook/examsoil.htm
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Physical property: describes the behavior
of a substance without having to alter the
substance’s composition through a
chemical reaction
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Chemical property: describes the
behavior of a substance when it reacts or
combines with another substance
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Fahrenheit scale: the temperature scale using
the melting point of ice as 320 and the boiling
point of water as 2120, with 180 equal divisions or
degrees between them.
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Celsius scale: the temperature scale using the
melting point of ice as 00 and the boiling point of
water as 1000, with 100 equal divisions or degrees
between
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Weight: a property of matter that depends on the
mass of a substance and the effects of gravity on
that mass
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Mass: a constant property of matter that reflects
the amount of material present
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Density: a physical property of matter that is
equivalent to the mass-per-unit volume of a
substance
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Refraction: the bending of a light wave as it
passes from one medium to another
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Refractive index: the ratio of the speed of
light in a vacuum to its speed in a given
substance
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Crystalline solid: a solid in which the
constituent atoms have a regular arrangement
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Atom: the smallest unit of an element; not
divisible by ordinary chemical means. Atoms
are made up of electrons, protons, and
neutrons plus other subatomic particles
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Amorphous solid: a solid in which the constituent
atoms or molecules are arranged in random or
disordered positions. There is no regular order in
amorphous solids.
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Birefringence: a difference in the two indices of
refraction exhibited by most crystalline materials
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Dispersion: the separation of light into its
component wavelengths
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Tempered glass: glass to which strength is added
by introducing stress through the rapid heating and
cooling of the glass surfaces
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Becke line: a bright halo that is observed
near the border of a particle immersed in a
liquid of different refractive index
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Radial fracture: a crack in a glass that
extends outward like the spoke of a wheel
from the point at which the glass was struck
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Concentric fracture: a crack in a glass that
forms a rough circle around the point of
impact
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Mineral: a naturally occurring crystalline
solid
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Density-gradient tube: a glass tube filled
from bottom to top with liquids of
successively lighter densities; used to
determine the density destruction of soil
Ch. 4 – Glass and Soil
Properties of Matter
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The distinguishing characteristics of a
substance used in its identification &
description
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characteristics by which people are recognized
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hair color, tone of voice, walk, shape of nose
chemical substances are recognized by how they
look & behave
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each chemical substance has a unique set of properties
that distinguish it from all other substances
Properties of Matter
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Chemical Properties
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a characteristic of a substance that describes the way
the substance undergoes or resists change to form a
new substance
Physical Properties
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a characteristic of a substance that can be observed
without changing the substance into another
substance
Physical Properties
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Extensive Properties
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depend on the amount of sample
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volume, mass
Intensive Properties
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do not depend on the amount of sample
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melting point, density
Density
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The ratio of the mass of an object to the
volume occupied by that object
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d = m/V
Densities of solids & liquids are often compared
to the density of water
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g/cm3 (solids); g/mL (liquids)
sink or float
Varies with temperature
Refraction
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The bending that occurs when a light wave
passes at an angle from one medium to another
(air to glass)
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bending occurs because the velocity of the wave
decreases
Refractive Index (ND)
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The ratio of the velocity of light in a vacuum to
the velocity of light in a given medium
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ND (water) = 1.333
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light travels 1.333 time faster in vacuum than in water
An intensive property
Varies with temperature and the light frequency
Double Refraction
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Crystals refract a beam of light into two
different light-ray components
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extraordinary ray
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ordinary ray
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refracted (bent)
path unchanged
Causes a double image to be seen
No double refraction with isometric crystals
Birefringence
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The difference between the two indices of
refraction
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for calcite: 1.486 & 1.658
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birefringence for calcite is 0.172
Use in identifying crystals
Dispersion
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Occurs when
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an incident parallel beam of light to fans out
according to the refractive index of the glass for
each of the component wavelengths, or colors.
Glass
The Basics
What is Glass?
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One of the oldest of all manufactured materials
A simple fusion of sand, soda & lime (all
opaque)
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produces a transparent “solid” when cooled
What is Glass?
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An extended, 3D network of atoms which lacks
the repeated, orderly arrangement typical of
crystalline materials
The viscosity is such a high value that the
amorphous material acts like a solid
What is Glass?
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glass is formed upon the cooling of a molten
liquid in such a manner that the ordering of
atoms into a crystalline formation is prevented
materials which form glasses are relatively rare
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SiO2 (silica) is the most common example
Structure of Glass
Physical Properties
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At ordinary temp.
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internal structure resembles a fluid
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random molecular orientation
external structure displays the hardness & rigidity of
of a solid
Does not show a distinct melting point
on heating gradually softens
 on cooling gradually thickens
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Physical Properties
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Common Properties
hard
 perfectly elastic
 brittle
 non-conductors of electricity
 chemically stable
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Types of Glass
Oxide Glasses
Types of Glasses
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~a thousand chemical formulations
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each has its own combination of properties
more than 700 compositions in commercial use
Most common type encountered by the forensic
scientist is “flat” glass
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glass used in windows & doors
Components
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Formers
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forms the glassy, non-crystalline structure
fluxes
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improve melting properties but impart low
chemical resistance
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typically alkali or alkaline earth oxides
modifiers (stabilizers or intermediates)
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a material that improves stability
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typically oxides of Ca, Al, or Zn
Common Glass Components
FORMERS
INTERMEDIATES MODIFIERS
SiO2
B2O3
GeO2
P2O5
V2O5
As2O3
Al2O3
PbO
Sb2O3
ZnO
TiO2
BeO
Na2O
CaO
K2 O
MgO
Li2O
BaO
Soda-lime-glass
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Silica itself makes a glass (fused silica)
high mp (3133 oF or 1723 oC)
 high viscosity in liquid state
 difficult to melt & work
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Na2O (soda) lowers melting temp (A flux)
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glass lacks durability (soluble in water)
CaO (lime) increases stability
Borosilicate Glass
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Over 5% B2O3 added to the silica
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a heat resistant glass that expands only ~1/3 as much as
silicate glass
more resistant to breaking on rapid heating & cooling
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Pyrex
Uses
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laboratory ware & thermometers
household glassware
sealed-beam headlights
Lead Glasses
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Incorporates up to 80% PbO
Has high refractive index & high electrical resistivity
 Suitable for hand fabrication
 Uses
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“crystal” tableware
 costume jewelry
 fine chandeliers
 neon sign tubing
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Colored Glasses
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Metallic oxides or sulfides added to soda-lime
glass
chromium oxide (green)
 cobalt oxide (blue)
 cadmium or selenium sulfide (red)
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Colloidal particles of iron & sulfur produces the
“carbon” brown beer bottle
Decolorized Glass
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General term for the soda-lime-glass marketed as
“clear” for windows
Color caused by impurities present in the raw materials
removed or masked
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destruction of carbonaceous matter
oxidation of Fe(II) (blue) to Fe(III) (yellow)
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NaNO3, KNO3,, BaNO3
Most “clear” glass is not absolutely colorless
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observable by viewing on edge
Light Sensitive Eyeglass Lenses
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Contain colloidal particles of silver halide
Identified by exposure to uv light
Glass Production
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Flat Glass
until late 1950s produced by sheet * plate processes
 primarily produced by the float glass process today
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molten glass is “floated” over a bath of molten time
 produces a distortion-free sheet
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Glass Fracture
Examination
Types of Fractures
Impact Fractures
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Impact causes a pane of
glass to bulge
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Side opposite the impact
will stretch more &
rupture first
Radial cracks are rapidly
propagated in short
segments from the point
of impact
Impact Fractures
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Ridges will be seen as irregularities on the broken edge
of a radial crack
Impact Fractures
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If the pane is held firmly on both sides
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a circular pattern of cracks (concentric) will form around
point of impact
Forensic Examination
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Ridges on radial cracks can be used to determine
on which side of pane impact occurred
To perform examination
identify one or more pieces which have cracks
terminating at a point of impact
 fit these pieces onto one or more pieces marked
“inside” or “outside”
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Four R Rule
Ridges on Radial cracks
are at Right angles to the
Rear (side opposite the
impact)
Four R Rule
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Exceptions
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tempered glass
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very small windows held tightly in frame
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“dices” without forming ridges
can’t bend or bulge appreciably
windows broken by heat or explosion
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no “point of impact”
Heat Fractures
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typical heat crack is curved
has a smooth edge (“mirror edge”)
no indication of point of impact
Fractures Caused by Projectiles
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High-velocity projectiles
crater-like hole surrounded by a nearly symmetrical
pattern of radial and concentric cracks
 the size of the hole & diameter of crater are
relatively independent of the size of the projectile
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Fractures Caused by Projectiles
Bullet Analysis
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If a window is broken by a
bullet, it is possible to
determine the bullet's direction
by noting the side of the coneshaped hole left by the bullet.
The small opening is on the
entrance side and the large
opening is on the exit side.
A determination of the
sequence of bullet holes can
be made by noting the radial
fractures. Radial fractures
caused by the passage of a
bullet will stop at any preexisting fracture.
Glass Cutters
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score the surface of glass by forcing out tiny
chips along a line
small chips will be missing on one side of the
pane along the break
Cutter type can’t be accurately determined
Association to a particular cutter possible only
when glass chips are deposited on a cutter
Mechanical Fit
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Examiner can determine that two or more
pieces of glass were broken from the same pane
or object
Because glass is amorphous, no two glass objects
will break the same way
Figure 4-10 p. 98
Saferstein
Comparing Glass
Fragments
Using Physical Properties
Glass as Forensic Evidence
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Films of breaking glass have shown that glass
flies backward from all parts of the window
where cracks appear
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not just from point of impact
Results in a shower of minute glass particles
onto the window breaker
Glass as Forensic Evidence
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Glass fragments recovered from clothing
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number & distribution are important
a piece of glass embedded in a shoe has low probative
value
 many small fragments from a shirt or sweater can be
highly significant
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Glass must be classified
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window glass vs broken bottle glass
Individualization may be possible
Classification Tests
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Physical properties can be used to place glass
into a class
Density
 Refractive Index (RI)
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Individualization can’t be determined from these
properties alone
Can be used to evaluate the significance of a
glass comparison
Flotation Test
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Based on density
Glass is not perfectly homogeneous
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test allows for small internal density variations
The control glass chip (known density)
immersed in mixture of bromoform &
bromobenzene
 composition of mixture altered until the chip
remains suspended
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Flotation Test
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The crime object (glass of unknown density)
immersed in liquid mixture
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remains suspended
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liquid, control & unknown have same density
sinks
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unknown is more dense than control
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different origins
Accurate density measurements can be obtained
with a Density Meter
Refractive Index By Immersion
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Entails finding the temp at which a glass particle
& a liquid, into which the chip has been
immersed, have identical refractive indices
refractive index of glass is relatively unaffected by
changing temp
 refractive index of liquid varies with temp
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dN/dT=-4 x 10-4/oC
Refractive Index By Immersion
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Immerse glass in high boiling liquid
Increase temp at rate of 0.2 oC/min
At match point the refractive index of liquid &
glass are the same
Becke line disappears
 minimum contrast between glass & liquid
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If all glass fragments have similar match points,
they have comparable RI
Figure 4-12 p. 101
Saferstein
Refractive Index By Immersion
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Internal RI variations may vary by 0.0002
Differences in RI must be greater than 0.0002
between suspect & crime glass to be significant
The measurement of RI alone can be of limited
use for classification because RI distributions of
flat glasses and container glasses overlap
Histogram = flat glasses
Curve = container glasses
Other Classification Methods
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Microscopy
float glass is absolutely flat
 wine glasses are slightly curved
 bottles have microscopic defects from mould
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Fluorescence
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when excited by uv radiation, many glasses exhibit
fluorescence
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caused by heavy metals (including tin)
Fluorescence
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Can differentiate
between float and
non-float window glass
Can differentiate
between different
samples of float glass in
some cases
(a) non-float glass or non-float side
(b) float side Sample #1
(c) float side Sample #2
Scanning Electron Microcopy
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Can detect
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Si
Na
Ca
Mg
K
very small samples can
be analyzed (50
micrograms)
X-ray Fluorescence
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Can detect major
elements in glass samples
sometimes detects minor
& trace level
components
Elemental Analysis
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Many of the trace elements enter the glass via
trace impurities in the raw materials
Comparison of elemental analysis of crime glass
& reference glass
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if ranges of elements overlap for every element
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indistinguishable
if ranges of one or more elements are different
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samples are distinguishable
Red= flat
blue= container
RI=1.5177-1.5183
black= tableware
Soil Analysis
What Is Soil?
Mixture of organic and inorganic
material
 May range from 100% inorganic
(sand) to nearly 100% organic
(peat)
 Inorganic part is minerals
 Organic part is decayed plant and
animal material and is sometimes
called humas
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Soil Analysis
"For example, observation shows me that you have been to
the Wigmore Street Post-Office this morning, but deduction lets
me know that when there you dispatched a telegram."
"Right!" said I. "Right on both points! But I confess that I
don't see how you arrived at it. It was a sudden impulse upon my
part, and I have mentioned it to no one."
"It is simplicity itself," he remarked, chuckling at my
surprise--"so absurdly simple that an explanation is superfluous;
and yet it may serve to define the limits of observation and of
deduction. Observation tells me that you have a little reddish
mould adhering to your instep. Just opposite the Wigmore Street
Office they have taken up the pavement and thrown up some
earth, which lies in such a way that it is difficult to avoid treading
in it in entering. The earth is of this peculiar reddish tint which is
found, as far as I know, nowhere else in the neighbourhood. So
much is observation. The rest is deduction."
(From The Sign of Four by Arthur Conan Doyle)
Soil Analysis
Forensic Geology is the scientific application
of earth sciences to legal matters.
 Identifying, analyzing, and comparing earth
materials, such as soil, rocks, minerals, and
fossils found on or in a receptor (e.g., a
suspect, a vehicle or other medium of transfer,
such as water) to possible source areas (e.g., a
crime scene, an alibi location, and/or a point of
disposal/release).
 Goal 
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establish the degree of probability that the
material was or was not derived from a particular
location
determine the time an incident occurred, the
cause of an incident and/or responsibility for an
incident.
Soil Analysis
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Bulk analysis
Density gradient
Particle size distribution (sieving)
Inorganic components
Color (dissolve in water)
Petrography - mineral analysis
Organic components
Liquid chromatography
Oxygen availability
Bacterial DNA?
Soil Analysis
Hit and Run: - Under-fender dirt/soil deposited at
impact with the victim was used to locate the car/driver;
also, matching the grease on the victim with the grease
under the car provided supporting evidence.
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Rape: - Soil on clothing of a suspected rapist was
used to place the suspect at the crime scene and to
eliminate the suspect's alibi.
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Murder: - Soil found on murder victims used to
determine the location of homicides, especially when the
murder occurs in one location and the body is then
moved. Using water-current measurements,
bodies/objects thrown into water can be located and
where a discovered body/object originally entered the
water determined.
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Assault: - Identifying the type of rocks used as
weapons led to the source of the rocks and helped locate
suspects.
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Soil Analysis
Soil provided strong evidence against a rape suspect when
comparison of soil samples on each knee of his pants matched
the soil types from the right and left knee impressions at the rape
scene. In other cases, analyses of soil on clothing have been
used to support alibis and show no connection of the suspect to
the crime scene.
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By identifying the nature and extent of groundwater
contamination, a forensic geologist determined the time a
chemical release contaminated water supplies. In another case,
a similar analysis showed that contamination in groundwater at a
company originated at another property and a different company
was responsible for cleanup.
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By analyzing road maintenance records and techniques used
to sample an unpaved road, a forensic geologist provided
evidence that eliminated the validity of the opposition's roadway
data and skid testing in a motor vehicle accident case. Geologic
analyses of roadways in other cases have shown that unpaved
roads were improperly constructed and/or improperly maintained.
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Soil Analysis
(1908) A man with a bad reputation was under investigation for the
murder of Margaeth Filbert in Bavaria, Germany. Investigating mud on
the suspect's shoes helped solve the case.
The suspect's wife testified that she had cleaned her husband's
shoes the day before the crime. Those shoes had three layers of soil
adhering to the leather in front of the heel with the innermost layer as
the oldest. It contained goose droppings et al, matching samples from
the walk outside the suspect's home. The second layer contained red
sandstone fragments that compared with samples taken where Filbert's
body had been found. The last layer contained brick, coal dust,
cement and other materials that matched samples taken outside a
castle where the suspect's gun and clothing had been found.
The suspect claimed he'd been walking in his fields the day of the
crime. The lie didn't stick. Those fields were underlain by porphyry
with milky quartz, and the soil had been wet that day. But they found
no such material on the suspect's shoes.
Soil Analysis
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Soil is frequently found on clothing, shoes, or
tools and in the wheel wells of vehicles.
Most soil analysis consists of comparing two
or more samples by their mineral content,
color, and density. The presence of pesticides
and herbicides have also been used in soil
comparison.
Soil Analysis
THE CAMARENA CASE
In 1985, an agent with the U.S. Drug Enforcement Agency,
Enrique Camarena Salazar, was kidnapped near
Guadalajara. The U.S. government demanded that the
Mexican government and Mexican Federal Judicial Police (MFJP)
find Camarena. Eventually the MFJP announced finding
Camarena's body on the El Mareno ranch in Michoacan State,
the site of a shootout between Mexican police and alleged drug
dealers.
But an investigation by the FBI showed that Camarena's
body had been buried elsewhere before arriving at the
ranch. The clue was a specific tuffaceous rhyolite ash found in
material adhering to Camarena's exhumed body. The ash
helped investigators find Camarena's original burial site - a
grave in a state park called Bosques de la Primavera, far from
the ranch. The body had been removed from that site to the
ranch, and the investigation helped reveal a cover-up by the
MFJP.
Soil Analysis
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Microscopic fossils called diatoms were once very
prominent on Earth, and collectively deposited to form
a sedimentary rock called diatomaceous earth. Some
manufacturers use diatomaceous earth for insulating
safes, that are used to store valuables. Burglary
crimes have been solved by examining white specks
from suspects' hair and clothing to determine that the
specks were actually diatoms that came from broken
safes at crime scenes, and not dandruff as the
suspects had claimed.