Glass and Soil

1. Glass and Soil

2. Physical vs. Chemical Properties • Physical properties: describes substances without reference to other substances. • Mass, density, color, weight, volume, boiling point, and melting point

3. Physical vs. Chemical Properties • Chemical properties: describes the behavior of substances when it reacts or combines with another substance. • Ex. Wood burning, Oxidation, reaction to indicators • Starch: iodine, brown  purplish black • Heroin: Marquis reagent, turns purple

4. Properties Assessment • The property we choose to observe and measure will depend on the type of material that is being examined. • Properties must: • be assigned a numerical value • Relate to a standard system of measurement accepted throughout the scientific community

5. Physical Properties: Temperature • Melting and boiling point. • Temperature: the measure of heat intensity • Fahrenheit • 32o F freezing point, 212o F Boiling point • Celsius (centigrade) • 0o C freezing point, 100o C Boiling point

6. Temperature

7. Density • The relationship of Mass per unit volume • D=m/v Water at 20o C 0.998g/mL = 1g/1.002 mL • NOT dependent on the size of an object. • Same regardless of the size of the substance. • Solids (more dense) liquids gases

8. Volume • The amount of occupied space • Regular Shaped Objects =LxWxH (cm3) • Irregular Shaped Objects • Volume of displaced fluid in a graduated cylinder.

9. Physical Properties: Density • Silver 10.5 (g/mL) • Lead 11.5 • Window glass 2.47-2.54 • Mercury Liquid 13.6 • Water at 4 C 1.00 • Ice 0.92

10. VII. Physical properties of glass • Refraction: the bending of a light wave as it passes from one medium to another.(a change in velocity, slows down) • Index = • water at 25C =1.333 (1.333 times faster in a vacuum then in water at that temp. velocity of light in vacuum velocity of light in medium

11. Refractive Index Ratio of speeds in a vacuum vs a medium • At a specific temperature • And Wavelength Frequency V of light in Vacuum V of light in medium RI=

12. Refractive Index • Water at 25C =1.333 (1.333 times faster in a vacuum then in water at that temp. • Dependent on temperature and the frequency of the wavelength of light • Sodium D light: STANDARD wavelength • 589.3 nanometers

13. Refractive Index • Transparent solids immersed in a liquid having a similar RI, light will not be refracted as it passes from liquidsolid. • Reason why the eye unable to distinguish between the solidliquid boundary.

14. Becke line: http://www.hfni.gsehd.gwu.edu/~forchem/BeckeLine/BeckeLinePage.htm

15. nglass >nmedium nglass < nmedium                    nmedium  = 1.525                      nglass    = 1.60                    nmedium = 1.525                    nglass    = 1.34 Becke line:

16. List the four major types of glass and describe how they are made.

17. Glass Objectives Types Matching Fractures Preservation

18. Comparing Glass Fragments Composed of silicon oxides mixed with metal oxides

19. Matching glass fragments • Suspect and crime scene fragments must fit together to be from same source • Physical properties of density and refractive index are used most successfully for characterizing glass particles. • Flotation test in density column!! 0.0001 • Immersion Method • GRIM 2: Glass RI measurement (automated)

20. Flotation test in density column!! • Control glass added to liquid • Density of liquid adjusted until control glass suspended • Unknown is then added to see if it floats or sinks

21. Matching glass fragments: • Immersion method: • Glass put into liquid • RI of liquid adjusted by temperature until a match point is reached. • Point when Becke line disappears because both liquid and glass have same RI. • Becke line: a bright halo that is observed near the border of a particle immersed in a liquid of a different RI

22. Matching glass fragments: Becke line: a bright halo that is observed near the border of a particle immersed in a liquid of a different RI

23. What If? • Density and RI values do not match: • Then not from the same source • Density and RI values Match! • Still cannot ID from same source • Must compare results to frequencies in society • Must develop meaningful assessment as to probability that fragments were at one time from one source.

24. Glass Fractures • If the force is greater then glass’s elasticity, it fractures • Fractures provide valuable information at the crime scene. • Ex: • Force • Direction • Object used

25. Information Obtained • Small hole: small stone thrown hard, small bullet • Shattered glass: close range shot, large stone(obvious gunpowder deposits) • Hole from projectile can determine direction • Hole is wider at exit side • As projectile decreases irregularity of shape and cracks increase

26. Fracture patterns • Radial fractures: cracks extend outward like spokes of a wheel from point of impact • Concentric Fractures: forms rough circle around point of impact

28. Glass Fractures Sequence:

29. Counting the bullet holes

30. Collecting and preservation of glass evidence. • All glass must be found to include odds of matching pieces from suspect to C.S. • Must Obtain Controls: suspect, C.S. • Control from area closest to point of break • Glass placed in solid containers • Individually wrap garments from suspect. • To be later check for glass fragments!!!