Physical Properties of Glass & Soil

Glass Basics  Glass is a hard, but brittle, amorphous solid composed of _________________ mixed with various compounds  Types:  – composed of sodium carbonate (Na 2 CO 3 ) and lime (CaO) and is used in most windows and bottles  – (Safety Glass) rapidly heated and cooled to make it stronger and dice when broken  – composed of boron oxide (B 2 O 3 ) and is used in headlights and pyrex glass  – stronger because a layer of plastic is sandwiched in between 2 layers of glass

Methods for Distinguishing Glass

Densities of Some Common Materials

Methods for Distinguishing Glass

Refractive Index  Refractive Index Tutorial Refractive Index Tutorial Refractive Index Tutorial

Methods for Determining Refractive Index  The FBI has a database off over 2000 refractive indexes of different types of glass which shows that glass is very distinctive and helps assign an appropriate statistical probability that the two pieces of glass share a common source.

Methods for Determining Refractive Index  Becke Line

Methods for Determining Refractive Index

Glass Fracture Patterns

Collection of Glass Evidence  Standard reference glass should be taken from the crime scene (1 in 2 )  Package in solid containers to prevent breakage  Preserve garment (shoe, pants, shirt) with glass on it

Soil Characteristics  Mixture of:

Soil Analysis  1 st – Gross Analysis

Soil Analysis  2 nd – __________ Analysis  Rock and Mineral Analysis  Minerals have physical properties like color, crystal shape, density, and refractive index  2,200 minerals (40 common)

Soil Analysis  Microscopic Analysis con’t Humus Pollen

Collection of Soil Evidence  Collect samples at various intervals in a 100 yard radius of crime scene  Top surface of soil is usually enough  Preserve garment (shoe, pants) with soil on it  Note layering of soil (as on car tires) when collecting soil evidence

The End