jimtrue.com : school : CJT2141 : 04: Weights & Measure, Glass & Soil
Posted by Jim True on February 5, 2003 6:00 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
Physical Properties: Glass & Soil
In identification, looking at chemical and physial properties
Properties:
Physical - describe a substance without reference to any other substance
Chemical - describe the behaviour of a substance when it reacts or combines
with another substance.
Physical Properties -
1. Temperature
(melting point - solid to liquid/
boiling point - liquid to vapor)
States of Matter: solid, liquid, vapor
Same compound will always have a specific melting point or boiling point
Sublimation - directly from solid to vapor (like dry ice)
2. Weight & Mass,
on the surface of the earth, these items are the same
the Pull of gravity is what makes mass into weight
Weight = Mass * Gravity
(on the surface of the earth, weight=mass)
Measurement of weight is based on mass AND gravity.
3. Density
Density = mass/volume (mass per unit of volume)
Takes up more space, more dense (Smaller volume, same mass, more dense)
Pound of Rocks -- Pound of Feathers, same mass, different volumes
REMEMBER Density = Mass/volume (mass per unit volume, NOT WEIGHT)
4. Refractive Index
Refractive Index - Velocity of light in vacuum/ velocity of light in medium
(refraction is the same as bending, bending the light waves, which changes the
appearance)
Bending the light to make things appear larger, changing the speed of light.
Measuring the light which gives the refractive index value (the shift)
Two types of materials:
Crystalline - atoms are arranged in definite geometric forms that can be seen
microscopically, evenly arranged and organized
Amorphous - atoms are arranged in random or disordered positions, no regular
order in amorphous solids.
With Crystalline Solids, can look at another factor of Refractive indexes,
called Birefrigence (see Figure 4-1)
Difference of the two indices of refraction exhibited by most crystalline
materials, along the latitudinal and longitudinal axis.
Although the crystal is 3 dimensional, the scanning electron microscope along
looks at two dimensions.
METRIC SYSTEM
Based on 100 parts/BASE 10
Length meters (m) inches
Mass grams (g) pounds
Volume liters (l) ounces
Divided in 10's
Centi 1/100
Kilo 1000
milli 1/1000
Deci 1/10
Conversion Factors: KNOW FOR TEST
1 inch = 2.54 cm
1 m = 39.37 inches
1 l = 1.06 quarts
1 lb = 454g (453.6 g)
1 kg = 2.2 lbs
GLASS
Sand - Silica (Si)
Sodium Carbonate Na2Co3
Lime CaO
Transparent
Windows: Automotive, Structural
Containers:
Glass is considered Class Evidence because Glass is made in such large
quantities.
Individual Characteristic with a Fracture Match
Automotive glass has a clear plastic coating that prevents it from shattering
Two properties of Glass to identify:
Density
Refractive Index
Density Gradient Tube (liquids of known density)
Water 1.0
Chloroform 1.5
Floats, less dense
Sinks, more dense
Equalizes, same density
Make sure you can correlate the glass back to the crime scene or the suspect.
For control collection, must be taken from the same pane as the fracture.
Collect the control evidence sample from the area where the damage occurred (1
" square)
Same thing with Automotive paint sample.
Also going to use solutions which have known refractive indices.
Becke Line, physical property to determine if the sample has a higher or lower
refractive index from a known solution.
Becke Line is a halo that will display into the sample if it has a lower
refractive index, if the fluid
* Becke Lines will moves towards the substance that has the higher refractive
index
If glass has the higher index, becke line will be INSIDE the glass, if the
fluid has the higher index, the halo/becke line will be OUTSIDE the glass.
If liquid has the higher index,
CLASS EVIDENCE CAN EXONERATE A VICTIM VERY QUICKLY. Multiple combinations of
class evidence can assist in building a case.
Radial Fractures will terminate at existing fractures (determines which break
occurred first).
Side of the glass with the bigger hole is where the projectile exited. This is
more visible when the projectile has a higher velocity.
when collecting glass, mark the glass as to which was the interior and which
was the exterior.
Rigid container for collecting glass.
Head lamps - determine if the light on at the time of the accident.
If light was on, filament will be rusted, oxidized with glass fragments
attached (because it was hot and fragments will adhere).
If light was off, filament will be burnt, but not oxidized.
If light was already broken, the filament will be broken, but there will be no
oxidation.
SOIL
1. Color (visual comparison)
2. Texture
3. Density Gradient
Use a Density Gradient tube, 5 different solutions with different densities.
Components in soil will separate at different density gradients.
collect soil sample in a rigid container, control samples in several different
locations, collect at least several inches deep.
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