Physical Properties: Physical Properties: Glass & SoilGlass & Soil

Chapter 4Chapter 4

Physical & Chemical Physical & Chemical PropertiesProperties

Physical properties describe a substance without Physical properties describe a substance without reference to any other substance.reference to any other substance. Ex. Weight, volume, color, boiling point, & melting pointEx. Weight, volume, color, boiling point, & melting point

Chemical property describes the behavior of a Chemical property describes the behavior of a substance when it reacts or combines with another substance when it reacts or combines with another substance.substance. Ex. Wood burning or to test for heroin chemical reagent Ex. Wood burning or to test for heroin chemical reagent

Marquis reagent turns purple when positive Marquis reagent turns purple when positive

Comparing Glass FragmentsComparing Glass Fragments

Glass is hard, brittle, Glass is hard, brittle, amorphous that is made sand, amorphous that is made sand, silicon oxides & metal oxidessilicon oxides & metal oxides

Borosilicates use boron oxides Borosilicates use boron oxides to increase heat resistance ex) to increase heat resistance ex) pyrex, headlightspyrex, headlights

Tempered Glass- increased Tempered Glass- increased strength by adding stress strength by adding stress through rapid heating & through rapid heating & cooling; it doesn’t shatter, it cooling; it doesn’t shatter, it dices into small squares ex) dices into small squares ex) side and rear windows of carsside and rear windows of cars

Laminated glass- 2 sheet of Laminated glass- 2 sheet of glass sandwiching plasticglass sandwiching plastic

•Glass that can not be physically pieced together glass is comparedwith refractive index and density

Methods for Distinguishing GlassMethods for Distinguishing Glass DensityDensity

Densities of Some Common Densities of Some Common MaterialsMaterials

Methods for Distinguishing GlassMethods for Distinguishing Glass

Refractive IndexRefractive Index When light travels When light travels

from one medium to from one medium to another its speed another its speed changes relative to the changes relative to the density of the medium. density of the medium. This can be observed This can be observed as the light bends as the light bends when traveling from when traveling from one medium to one medium to another.another.

Refractive IndexRefractive Index

Refractive Index Tutorial

Methods for Determining Methods for Determining Refractive IndexRefractive Index

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

Methods for Determining Methods for Determining Refractive IndexRefractive Index

Becke LineBecke Line

Methods for Determining Methods for Determining Refractive IndexRefractive Index

Refractive Index changes with temperatureRefractive Index changes with temperature

Glass Fracture PatternsGlass Fracture Patterns

Impact causes a paneImpact causes a paneof glass to bulgeof glass to bulge

––Side opposite theSide opposite theimpact will stretchimpact will stretchmore & rupture more & rupture

firstfirst

• • Radial cracks areRadial cracks are r rapidly apidly propagated inpropagated in s short hort segments from the point segments from the point of impactof impact

Impact Fractures

Glass FracturesGlass Fractures

Fracture pattern of glass is radial (extends outward like spoke o a Fracture pattern of glass is radial (extends outward like spoke o a wheel) & concentric lines (rough circle around point of impact)wheel) & concentric lines (rough circle around point of impact)

Crater-shaped hole in glass made by penetration indicates the exit Crater-shaped hole in glass made by penetration indicates the exit side of glassside of glass

Stress marks on the edge of a radial crack near the point of impact Stress marks on the edge of a radial crack near the point of impact are parallel to the side on which the force was appliedare parallel to the side on which the force was applied

Glass Fracture PatternsGlass Fracture Patterns

Glass Fracture PatternsGlass Fracture Patterns

Glass Fracture PatternsGlass Fracture Patterns

3R rule – Radial cracks form a Right angle on the Reverse side of the force

Stress MarksStress Marks

Stress marks on the edge Stress marks on the edge of a radial crack near the of a radial crack near the point of impact are point of impact are parallel to the side on parallel to the side on which the force was which the force was appliedapplied

Three ‘R’ RuleThree ‘R’ Rule

RRadial adial cracks are atcracks are at RRightight angles to angles to the the RRearear (side opposite the(side opposite theimpact)impact)

ExceptionsExceptions––tempered glasstempered glass“dices” without forming ridges“dices” without forming ridges––very small windows held tightly in framevery small windows held tightly in framecan’t bend or bulge appreciablycan’t bend or bulge appreciably –– windows broken by heat or explosionwindows broken by heat or explosionno “point of impact”no “point of impact”

Scenario: A storefront window is broken and Scenario: A storefront window is broken and a robbery committed. A suspect is later found a robbery committed. A suspect is later found running from the scene. Examination of his running from the scene. Examination of his shoes reveals glass particles embedded in a shoes reveals glass particles embedded in a heel. Describe the proper collection and heel. Describe the proper collection and preservation of glass evidence for laboratory preservation of glass evidence for laboratory examination.examination.

The entire shoe is to be The entire shoe is to be submitted for lab submitted for lab examination. The evidence examination. The evidence collector is to avoid removing collector is to avoid removing glass evidence from the shoe glass evidence from the shoe unless there is a distinct unless there is a distinct possibility that the glass will possibility that the glass will be lost in transit.be lost in transit.

Shoes are to be packaged in Shoes are to be packaged in a box or paper bag and sent a box or paper bag and sent to the lab.to the lab.

A control glass from the A control glass from the broken window is to be broken window is to be submitted for laboratory submitted for laboratory examination. Normally a examination. Normally a square-inch piece of glass square-inch piece of glass will suffice.will suffice.

A pillbox, druggist fold or vial A pillbox, druggist fold or vial are convenient containers for are convenient containers for small glass fragments.small glass fragments.

All packages are to be All packages are to be properly labeled for id. properly labeled for id. Minimal info should contain Minimal info should contain evidence collector’s name, evidence collector’s name, date and sampling location. date and sampling location. All evidence are to be All evidence are to be described in field notes.described in field notes.

Collection of Glass EvidenceCollection of Glass Evidence

Standard reference glass should be taken Standard reference glass should be taken from the crime scene (1 infrom the crime scene (1 in22))

Package in solid containers to prevent Package in solid containers to prevent breakagebreakage

Preserve garment (shoe, pants, shirt) with Preserve garment (shoe, pants, shirt) with glass on itglass on it

Comparing SoilsComparing Soils MineralMineral: 2,200 naturally occurring crystal: 2,200 naturally occurring crystal

Physical properties: color, geometric Physical properties: color, geometric shape, density, refractive index shape, density, refractive index (birefringence) (birefringence) The difference between the two indices of refractionThe difference between the two indices of refraction

for calcite: 1.486 & 1.658for calcite: 1.486 & 1.658birefringence for calcite is 0.172birefringence for calcite is 0.172

Density-gradient tube: Density-gradient tube: a glass tube a glass tube filled from bottom to top with liquids offilled from bottom to top with liquids ofsuccessively lighter densities; used to successively lighter densities; used to determine the density destruction of soildetermine the density destruction of soil

Soil CharacteristicsSoil Characteristics

Mixture of:Mixture of: Weathered rock and minerals (quartz, mica, Weathered rock and minerals (quartz, mica,

feldspar)feldspar) Humus (decomposed organic material)Humus (decomposed organic material) Other vegetable matter (leaves, pine needles, Other vegetable matter (leaves, pine needles,

pollen, etc)pollen, etc) Manufactured materials (asphalt, paint, glass)Manufactured materials (asphalt, paint, glass)

Soil AnalysisSoil Analysis

11stst – Gross Analysis – Gross Analysis Color and Texture Color and Texture

AnalysisAnalysis 1,100 distinguishable 1,100 distinguishable

colors of soil colors of soil Darker when wetDarker when wet

Soil AnalysisSoil Analysis

22ndnd – Microscopic – Microscopic AnalysisAnalysis Rock and Mineral Rock and Mineral

AnalysisAnalysis Minerals have physical Minerals have physical

properties like color, properties like color, crystal shape, density, crystal shape, density, and refractive indexand refractive index

2,200 minerals 2,200 minerals (40 common)(40 common)

Soil AnalysisSoil Analysis

Microscopic Analysis Microscopic Analysis con’tcon’t

Humus

Pollen

Collection of Soil EvidenceCollection of Soil Evidence

Collect samples at various intervals in a Collect samples at various intervals in a 100 yard radius of crime scene100 yard radius of crime scene

Top surface of soil is usually enoughTop surface of soil is usually enough Preserve garment (shoe, pants) with soil Preserve garment (shoe, pants) with soil

on iton it Note layering of soil (as on car tires) when Note layering of soil (as on car tires) when

collecting soil evidencecollecting soil evidence

Scenario: A suspect has been found Scenario: A suspect has been found miles from the scene of a murder. miles from the scene of a murder. SoilSoil is found adhering to the suspect’s is found adhering to the suspect’s shoe. Describe the proper collection shoe. Describe the proper collection and preservation of soil evidence that and preservation of soil evidence that will permit a thorough comparison of will permit a thorough comparison of the soil on the shoe to soil at the crime the soil on the shoe to soil at the crime site.site.

Do not remove soil from shoes. Each object that Do not remove soil from shoes. Each object that has soil on it is to be packaged in a leak proof has soil on it is to be packaged in a leak proof containercontainer

Collect representative control soils at the crime Collect representative control soils at the crime scene and at various locations within a 100 yard scene and at various locations within a 100 yard radius of the scene. Package in solid containers radius of the scene. Package in solid containers or druggist foldsor druggist folds

Collect soil at all possible alibi locations the Collect soil at all possible alibi locations the suspect may claim.suspect may claim.

Collect approximately 1-2 tablespoons of soil, Collect approximately 1-2 tablespoons of soil, top layer only.top layer only.

Label all specimens collected. Evidence Label all specimens collected. Evidence collector’s name or initials, the date and collector’s name or initials, the date and sampling location are to be shown. All items sampling location are to be shown. All items collected are to be described in the evidence collected are to be described in the evidence collector’s field notes.collector’s field notes.

The EndThe End