Headlight glass has an IR of 1.47 - 1.49 by 2VuOzX


									Name: ______________________
Glass Fragment Lab

"There was a hit and run car accident in the school parking lot this morning. The police have
requested that the students from this class compare the glass fragments found at the crime scene
with those taken from two suspect vehicles. You will need to report your findings to the police
department as soon as possible."

Directions: In this lab, you will be required to note physical characteristics of individual glass
fragments as well as determine their density and refractive index. For each glass fragment, try to use
a descriptive physical property that will distinguish one fragment from the next (for example, color,
thickness etc.,be detailed). Next determine the density (d = m/v) using the method below. Then do
the refractive index for each glass fragment in each type of liquid. Then try to match the suspect with
the crime scene.


                     1. Obtain a balance, a beaker and a piece of wire
                     2. Obtain the Sample glass fragment
                     3. Mass the Sample fragment and record the value.
                     4. Place the beaker filled ¾ of the way with water on the balance and zero the balance
                     5. Wrap the wire around the glass fragment and suspend the wire and glass fragment from the glass rod.
                     6. Weigh the glass fragment suspended in water (adjust holding the rod so that the glass is not touching
                        the walls of the beaker)
                     7. Record the weight of the glass fragment and convert to milliliters.
                        (1g water =1ml)
                     8. Repeat this process for the other samples
                     9. Determine the density of each fragment in your data table

                   Physical characteristics         Mass             Volume (ml) Density (g/ml)
                   (thickness in mm,                (grams)
                   texture, clarity, color
Window glass

Bottle glass


Light bulb

                   Physical characteristics     Mass          Volume (ml) Density (g/ml)
                   (thickness in mm,            (grams)
                   texture, clarity, color
Crime Scene

Suspect #1

Suspect #2

Refractive Index test


   1. With forceps, lower a sample piece of glass into a beaker with liquid of a known refractive index. Does
       it seem to disappear?
   2. Test each type of glass in each type of liquid.
   3. Record the liquid in which the sample tends to disappear. Using the following scale to rate:
              1 = No change just looks larger
              2= Blurs but can still see glass sample
              3= slightly disappears but can still make out edges
              4=disappears completely
   4. Repeat with each liquid available.
Sample             Corn oil            Castor Oil         Mineral Oil        Water         Honey
                   RI=1.473            RI = 1.482         RI = 1.476         RI = 1.330    RI = 1.484-1.494

Window Glass

Laminated Glass

Bottle Glass

Tempered Glass

Light bulbs

Crime Scene

Suspect #1

Suspect #2
Headlight glass has an IR of 1.47 - 1.49
Window glass and most bottles have an IR of 1.51 – 1.5

Write a conclusion for the Lab should be in paragraph format; be sure to include answers to the
following questions in your conclusion:

       1. List three methods used by forensic scientists to analyze glass fragments.

       2. Describe the difference between physical and chemical properties.

       3. What chemicals are used to make glass?

       4. Where would a crime scene technician look for glass fragments?

       5. Describe the glass making process. What changes in this process result in the difference
          between windows and tempered glass?

       6. Why is laminated glass used for the windshields of vehicles?

       7. Explain how refractive index is found.

       8. Who committed the crime and what type of glass was found at the crime scene and in the
       two suspects vehicles?

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