Unit 3 Physical Properties of Glass and Soil, Organic and Inorganic Analysis of Evidence

1. Unit 3Physical Properties of Glass and Soil, Organic and Inorganic Analysis of Evidence Chapters 4-6

2. Physical Properties of Glass and Soil Unit 3: Part 1

3. Physical Properties of Glass Unit 3: Part 1 DO NOW: What is glass ? Homework: Complete Pre-lab assignment.

4. Today students will: • Determine which chemical and physical properties provide distinguishing characteristics of matter • Determine procedure for analysis of glass fragments • Develop an investigation plan to recognize differences in glass fragments Learning Objectives

5. The forensic scientist must determine the properties which give distinguishing characteristics to matter, allowing for a unique identity. • Physical properties such as weight, volume, color, boiling point, and melting point describe a substance without reference to any other substance. • A chemical property describes the behavior of a substance when it reacts or combines with another substance. Physical vs. Chemical Properties

6. Temperature is a measure of heat intensity, or the hotness or coldness of a substance. • In science, the most commonly used temperature scale is the Celsius scale. This scale is derived by assigning the freezing point of water a value of 0°C and its boiling point a value of 100°C. • Weight is the force with which gravity attracts a body. • Mass refers to the amount of matter an object contains independent of gravity. • The mass of an object is determined by comparison to the known mass of standard objects. Important Physical Properties

7. Density: (D = M/V) • Density is an intensive property of matter, meaning it remains the same regardless of sample size. • It is considered a characteristic property of a substance and can be used as an aid in identification. Important Physical Properties

8. Put water into the beaker until it is ½ full • Place a pen or pencil into the water • Observe what happens to the pen/pencil • Make notes in your notebook • Answer the following questions: • Why do you think this happens? • What is happening to create this effect? • Would using a different liquid cause a different effect? • Could this property be used to identify or compare glass samples? • Explain Observing another physical characteristic

9. Explain your observations • Offer possible explanations Report Out

10. Silently read background info. (12 min) • In small groups discuss answers to the following question: (7 min) • Define refraction and refraction index • Explain how this property can be used to identify class evidence • Which other properties of glass will be used, distinguish chemical and physical properties Investigation Background

11. Define refraction and refraction index • Explain how this property can be used to identify class evidence • Which other properties of glass will be used, distinguish chemical and physical properties Report out Findings

12. Names of lab partners • Question you will be investigation • Background information summary, most important to investigation • Hypothesis • Explanation of the procedures to be followed in the lab (must be in your own words, what will you do?) VIP: A completed pre-lab is your entrance ticket into the experiment, without it you will not be allowed to begin working in the lab! Complete Pre-lab

13. Today students will: • Determine which chemical and physical properties provide distinguishing characteristics of matter • Define refractive index. • Distinguish crystalline from amorphous solids. • Define double refraction and birefringence. • Describe the dispersion of light through a prism • Determine how glass samples are analyzed Learning Objectives

14. Light waves travel in air at a constant velocity until they penetrate another medium, such as glass or water, then they are suddenly slowed • This causes the rays to bend. • The bending of light waves because of a change in velocity is called refraction. • Refractive index :the ratio of the velocity of light in a vacuum to the velocity of light in the medium under examination. Important Physical Properties

15. Example: at 25oC the refractive index of water is 1.333. • This means that light travels 1.333 times faster in a vacuum than it does in water at 25oC. • Like density, refractive index is an intensive property and will serve to characterize a substance. Refractive Index

16. refraction

17. Glass is a hard, brittle, amorphous substance that is composed of silicon oxides mixed with various metal oxides. • Amorphous solids have their atoms arranged randomly, unlike crystals. • Tempered glass is stronger than normal glass due to rapid heating and cooling. • Laminated glass found in car windshields has a layer of plastic between two pieces of ordinary window glass. Glass Fragments

18. CRYSTALLINE SOLIDS • Crystalline solids have the following fundamentals properties. • 1. They have characteristic geometrical shape. • 2. They have highly ordered three-dimensional arrangements of particles. • 3. They have sharp melting and boiling points. • Examples: • Copper Sulphate (CuSO4), NiSO4, Diamond, Graphite, NaCl, Sugar etc Two Types of Solids

19. AMORPHOUS SOLIDS • Solids that don’t have a definite geometrical shape are known as Amorphous Solids. • 1. In these solids particles are randomly arranged in three dimension. • 2. They don’t have sharp melting points. • 3. Amorphous solids are formed due to sudden cooling of liquid. • 4. Amorphous solids melt over a wide range of temperature • 5. Examples: Coal, Coke, Glass, Plastic, rubber etc Two Types of Solids

20. For the forensic scientist, the problem of glass comparison is one that depends on the need to find and measure those properties that will associate one glass fragment with another while minimizing or eliminating other sources. • To compare glass fragments, a forensic scientist evaluates two important physical properties: density and refractive index. Glass Fragments

21. Today students will: • Define double refraction and birefringence. • Describe the dispersion of light through a prism • Determine how glass samples are analyzed • Define the Becke line Learning Objectives

22. Domestic Glass Samples

23. The flotation method is a rather precise and rapid method for comparing glass densities. • In the flotation method, a glass particle is immersed in a liquid. • The density of the liquid is carefully adjusted by the addition of small amounts of an appropriate liquid until the glass chip remains suspended in the liquid medium. • At this point, the glass will have the same density as the liquid medium and can be compared to other relevant pieces of glass which will remain suspended, sink, or float. Flotation Method of Density Analysis

25. Crystalline solids have definite geometric forms because of the orderly arrangement of their atoms. • These solids refract a beam of light in two different light-ray components. • This results in double refraction. • Birefringence is the numerical difference between these two refractive indices. • Not all solids are crystalline in nature. For example, glass has a random arrangement of atoms to form an amorphous or non-crystalline solid. Refractive Light Method

27. http://Birefringence Birefringence

28. The flotation and the immersion methods are best used to determine a glass fragment’s density and refractive index, respectively. • The latter involves immersing a glass particle in a liquid medium whose refractive index is varied until it is equal to that of the glass particle. • At this point, known as the match point, the Becke line disappears and minimum contrast between liquid and particle is observed. • The Becke line is a bright halo near the boarder of a particle that is immersed in a liquid of a different refractive index. Immersion Method

29. The flotation and the immersion methods are best used to determine a glass fragment’s density and refractive index, respectively. • The immersion method: involves immersing a glass particle in a liquid whose refractive index is changed until it is equal to that of the glass particle. • At this point, known as the match point, the Becke line disappears and minimum contrast between liquid and particle is observed. • The Becke line is a bright halo near the boarder of a particle that is immersed in a liquid of a different refractive index. Immersion Method

30. Refractive Index of Glass Uses Becke Line - a bright halo of light that appears around the perimeter of a particle when the indices of refraction of the particle and surrounding medium are  different.  Glass has higher refractive index Becke line seen inside Rays converge RI(glass) > RI(solvent) Glass Analysis Glass has lower refractive index Becke line seen outside Rays diverge RI(glass) < RI(solvent)

31. Refractive Index of Class Hot stage microscope used Glass is immersed in RI liquid which is higher RI than glass. Temperature is raised until Becke line disappears. Rate of change of RI in liquid is known (-3x10-4/degree) so the RI of the unknown can be determined The point where the Becke line disappears: RI of the sample = the RI of the liquid Glass Analysis

32. The penetration of window glass by a projectile, whether it is a bullet or a stone, produces cracks which radiate outward (radial fractures) and encircle the hole (concentric fractures). • By analyzing the radial and concentric fracture patterns in glass, the forensic scientist can determine the direction of impact. Analyzing Cracks

33. Two kinds of fractures, radial fractures (those radiating from the center) and concentric fractures. Glass Analysis

34. The direction of force in breaking a window pane can be determined by the direction of the rib marks (stress marks left on broken edges of glass that are perpendicular to one side and that curve tangentially, run almost parallel, to the other side). Glass Analysis

35. On radial fractures (those radiating from the center) the direction of the force is on the same side as the tangential (almost parallel) parts of the rib marks. The edge of the glass where the rib lines are perpendicular is not the side of the glass that the force came from. This is the little R rule—radial cracks make right angles to the rear. Glass Analysis

36. On concentric fractures, the perpendicular part of the rib mark is the side from which the breaking force came. The rib fractures DO make a right angle to the side the force came from. If you’re standing inside and break a pane of glass, most of the glass will land outside—but some will fly backwards towards you, landing inside the house and depositing tiny shards on your clothing. Glass Analysis

37. Concentric Crack Radial Crack Radial cracks make Right angles to the Rear. Fracture Analysis

38. Area on a windshield where only one wiper blade sweeps Area on a windshield where the wiper blades cross Windshield Glass Scratches on a side window from grit caught in the rubber

39. A high-velocity projectile such as a bullet often leaves a hole that is wider at the exit side, and hence its examination is important in determining the direction of impact. • The direction of impact can also be accomplished by applying the 3R Rule: Radial cracks form a Right angle on the Reverse side of the force. • The sequence of impacts when there have been successive penetrations of glass is frequently possible to determine because a fracture always terminates at an existing line of fracture. Analyzing Cracks

40. If a window is broken by a bullet, it is possible to determine the bullet's direction by noting the side of the cone-shaped 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 pre-existing fracture. Glass Analysis

41. A bullet makes a clean-cut hole in the side of entrance and causes a saucer-shaped or coning depression on the exit side, with a greater diameter than the entrance hole. Glass fractures caused by a blunt object will show a pattern of fractures like, but not as regular as, the pattern from a bullet. Fractures due to heat are wave-shaped. They do not show a regular pattern of radial and concentric lines like fractures caused by impact. Glass Analysis

42. If even the remotest possibility exists that glass fragments may be pieced together, every effort must be made to collect all the glass found. • When an individual fit is thought improbable, the evidence collector must submit all glass evidence found in the possession of the suspect along with a representative sample of broken glass remaining at the crime scene. Collection of Glass

43. The glass fragments should be packaged in solid containers to avoid further breakage. • If the suspect’s shoes and/or clothing are to be examined for the presence of glass fragments, they should be individually wrapped in paper and transmitted to the laboratory. Collection of Glass

44. Physical Measurements and Chemical Composition of Glass: Density Refractive Index (most glass is the same - but can tell if two samples are different) Polarizing Microscopy (determine tempered glass) IC-MS (inductively coupled mass spectrometer) Glass Analysis

45. Physical Measurements and Chemical Composition of Glass: Density Floatation Method Gradient Tubes Volumetric Measurements (mass measurement and volume by displacement) Glass Analysis

46. Sequence the fractures on the given hand outs Examine Glass Fractures

47. Soils and Soil Analysis Do Now: How can soil play a role in a forensic investigation?

48. Today students will: • List the important forensic properties of soil. • Explain soils analysis techniques • Describe the proper collection of soil evidence • Analyze several important cases in which soil evidence played a major role Learning Objectives

49. 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 humus What Is Soil?

50. Soil is class evidence - cannot be individualized to a particular location There is no classification system for soils Soils can be easily transported Soils within a few meters horizontally or vertically differ Forensic Significance of Soil