Glass and SoilGlass and Soil
A. Physical vs. Chemical PropertiesA. Physical vs. Chemical Properties
Physical properties:Physical properties: describes describes substances without reference to other substances without reference to other substances.substances.– Mass, density, color, weight, volume, Mass, density, color, weight, volume,
boiling point, and melting pointboiling point, and melting point
A. Physical vs. Chemical PropertiesA. Physical vs. Chemical Properties
Chemical propertiesChemical properties:: describes the describes the behavior of substances when it reacts or behavior of substances when it reacts or combines with another substance.combines with another substance.– Ex. Wood burning, Oxidation, reaction to Ex. Wood burning, Oxidation, reaction to
indicatorsindicators• Starch: iodine, Starch: iodine, brown brown purplish black purplish black
• Heroin: Marquis reagent, Heroin: Marquis reagent, turns purpleturns purple
B. Properties AssessmentB. Properties Assessment
The property we choose to observe and The property we choose to observe and measure will depend on the type of material measure will depend on the type of material that is being examined. that is being examined.
Properties must:Properties must:– be assigned a numerical valuebe assigned a numerical value
– Relate to a standard system of measurement Relate to a standard system of measurement accepted throughout the scientific communityaccepted throughout the scientific community
D. Physical Properties: D. Physical Properties: TemperatureTemperature
Melting and boiling point.Melting and boiling point.Temperature: the measure of heat Temperature: the measure of heat
intensityintensity–Fahrenheit Fahrenheit
–3232oo F freezing point, 212 F freezing point, 212oo F Boiling point F Boiling point
–Celsius Celsius (centigrade)(centigrade)–00oo C freezing point, 100 C freezing point, 100oo C Boiling point C Boiling point
1. Temperature1. Temperature
Celsius
(00oo C) C)
Fahrenheit
((oo F) F)
freezing pointfreezing point 0 32
Boiling pointBoiling point 100 212
Body Body temperaturetemperature
37 98.6
Room Room TemperatureTemperature
23 69
Weight:Weight: force with which gravity attracts a force with which gravity attracts a body. body.
• ((180lb) 81 kg on earth, (30lb) 13.6 kg on moon 180lb) 81 kg on earth, (30lb) 13.6 kg on moon gravity gravity
• The moon force of gravity is 1/6 of earthThe moon force of gravity is 1/6 of earth• W=mg, W=mg, (mass x acceleration by gravity)(mass x acceleration by gravity)
• SO the large mass weighs more then a small SO the large mass weighs more then a small mass.mass.
2. Weight and Mass2. Weight and Mass
Mass:Mass: amount of matter an objects amount of matter an objects contains and is independent of it’s contains and is independent of it’s location on earthlocation on earth–81 kg on earth, 81 kg on moon81 kg on earth, 81 kg on moon
2. Weight and Mass2. Weight and Mass
When we “weigh” something against a When we “weigh” something against a known sampleknown sample we are actually identifying we are actually identifying the objects MASS!!!!!the objects MASS!!!!!
We Use:We Use:– Triple beam balance Triple beam balance – Top loading Balance Top loading Balance – Analytical BalanceAnalytical Balance
Physical Properties: Weight and MassPhysical Properties: Weight and Mass
The amount of occupied spaceThe amount of occupied space Regular Shaped ObjectsRegular Shaped Objects
=LxWxH (cm3)=LxWxH (cm3) Irregular Shaped ObjectsIrregular Shaped Objects
– Volume of displaced fluid in a graduated Volume of displaced fluid in a graduated cylinder.cylinder.
3. Volume3. Volume
The relationship of Mass per unit volumeThe relationship of Mass per unit volume – D=m/vD=m/vWater at 20Water at 20oo C 0.998g/mL = 1g/1.002 mL C 0.998g/mL = 1g/1.002 mL
An intensive propertyAn intensive property: property NOT : property NOT dependent on the size of an object.dependent on the size of an object.– Same regardless of the size of the substance.Same regardless of the size of the substance.– Solids (more dense)Solids (more dense) liquids liquids gases gases
4. Density4. Density
Silver Silver 10.5 (g/mL)10.5 (g/mL) Lead Lead 11.511.5 Window glass Window glass 2.47-2.542.47-2.54 Mercury LiquidMercury Liquid 13.6 13.6 Water at 4 C Water at 4 C 1.001.00 IceIce 0.920.92
Physical Properties: DensityPhysical Properties: Density
VII. Physical properties of glassVII. Physical properties of glass Refraction:Refraction: the bending of a light the bending of a light
wave as it passes from one medium wave as it passes from one medium to another.(a change in velocity, to another.(a change in velocity, slows down) slows down)
IndexIndex = =
water at 25C =1.333 (1.333 times water at 25C =1.333 (1.333 times faster in a vacuum then in water at faster in a vacuum then in water at that temp.that temp.
velocity of light in vacuum velocity of light in vacuum velocity of light in mediumvelocity of light in medium
Refractive IndexRefractive IndexRatio of speeds in a vacuum vs a mediumRatio of speeds in a vacuum vs a medium
– At a specific temperatureAt a specific temperature
– And Wavelength FrequencyAnd Wavelength Frequency
V of light in VacuumV of light in Vacuum
V of light in mediumV of light in mediumRI=RI=
Refractive IndexRefractive Index Water at 25C =1.333 (1.333 times faster Water at 25C =1.333 (1.333 times faster
in a vacuum then in water at that temp.in a vacuum then in water at that temp.
Dependent on temperature and the Dependent on temperature and the frequency of the wavelength of lightfrequency of the wavelength of light
Sodium D light: STANDARD wavelengthSodium D light: STANDARD wavelength– 589.3 nanometers589.3 nanometers
Refractive IndexRefractive Index
Transparent solids immersed in a Transparent solids immersed in a liquid having a similar RI, light will liquid having a similar RI, light will not be refracted as it passes from not be refracted as it passes from liquidliquidsolid.solid.
Reason why the eye unable to Reason why the eye unable to distinguish between the soliddistinguish between the solidliquid liquid boundary.boundary.
Becke line:Becke line:
http://www.hfni.gsehd.gwu.edu/~forchem/BeckeLine/BeckeLinePage.htm
Becke line:Becke line:
nglass >nmedium nglass < nmedium
nmedium = 1.525 nglass = 1.60
nmedium = 1.525 nglass = 1.34
List the four major types of List the four major types of glass and describe how they glass and describe how they are made. are made.
Glass ObjectivesGlass Objectives
TypesTypesMatchingMatchingFracturesFracturesPreservationPreservation
Comparing Glass Comparing Glass FragmentsFragmentsComposed of silicon oxides mixed with metal oxidesComposed of silicon oxides mixed with metal oxides
Soda-lime glassSoda-lime glass Soda (NaCo3)Soda (NaCo3)
Lime (CaO)Lime (CaO)
windows windows bottlesbottles
Pyrex Pyrex BorosilicatesBorosilicates
use Boron oxide, use Boron oxide, Can with stand Can with stand HIGH heatsHIGH heats
Test tubesTest tubes
HeadlightsHeadlights
Tempered Glass:Tempered Glass: Rapid heating and Rapid heating and cooling does not cooling does not shattershatter
Shower doorsShower doors
Side + rear Side + rear windowswindows
Laminated GlassLaminated Glass Plastic or Glass and Plastic or Glass and glues and sandwichglues and sandwich
windshieldswindshields
Matching glass fragmentsMatching glass fragments Suspect and crime scene fragments must Suspect and crime scene fragments must
fit together to be from same sourcefit together to be from same source Physical properties of density and Physical properties of density and
refractive index are used most refractive index are used most successfully for characterizing glass successfully for characterizing glass particles.particles.
1.1. Flotation test in density column!! 0.0001Flotation test in density column!! 0.00012.2. Immersion MethodImmersion Method3.3. GRIM 2: Glass RI measurement (GRIM 2: Glass RI measurement (automated)automated)
Flotation test in density Flotation test in density column!!column!!
Control glass added to Control glass added to liquidliquid
Density of liquid Density of liquid adjusted until control adjusted until control glass suspendedglass suspended
Unknown is then added Unknown is then added to see if it floats or sinksto see if it floats or sinks
Matching glass fragments: Matching glass fragments:
Immersion method:Immersion method:– Glass put into liquidGlass put into liquid– RI of liquid adjusted by temperature until a RI of liquid adjusted by temperature until a
match point is reached.match point is reached.•Point when Becke line disappears because Point when Becke line disappears because both liquid and glass have same RI.both liquid and glass have same RI.
Becke line:Becke line: a bright halo that is observed a bright halo that is observed near the border of a particle immersed in near the border of a particle immersed in a liquid of a different RI a liquid of a different RI
Matching glass fragments: Matching glass fragments:
Becke line:Becke line: a bright halo that is a bright halo that is observed near the border of a particle observed near the border of a particle immersed in a liquid of a different RI immersed in a liquid of a different RI
What If?What If? Density and RI values do not match:Density and RI values do not match:
•Then not from the same sourceThen not from the same source
Density and RI values Match!Density and RI values Match!•Still cannot ID from same source Still cannot ID from same source •Must compare results to frequencies in Must compare results to frequencies in societysociety
•Must develop meaningful assessment as to Must develop meaningful assessment as to probability that fragments were at one time probability that fragments were at one time from one source.from one source.
Glass Fractures: Glass Fractures: force is force is greater then glass’s greater then glass’s elasticity, It fractureselasticity, It fractures Fractures provide valuable information Fractures provide valuable information at the crime scene. Ex: Force and at the crime scene. Ex: Force and direction direction
Radial fractures: Radial fractures: cracks extend outward cracks extend outward like spokes of a wheel from point of like spokes of a wheel from point of impactimpact
Concentric Fractures:Concentric Fractures: forms rough forms rough circle around point of impactcircle around point of impact
Glass Fractures Styles:Glass Fractures Styles: Small hole:Small hole: small stone thrown hard, small stone thrown hard,
small bulletsmall bullet
Shattered glass:Shattered glass: close range shot, close range shot, large stonelarge stone (obvious gunpowder deposits)(obvious gunpowder deposits)
Hole from projectile can determine directionHole from projectile can determine direction– Hole is wider at exit sideHole is wider at exit side
As projectile decreases irregularity As projectile decreases irregularity of shape and cracks increaseof shape and cracks increase
Glass Fractures Sequence:Glass Fractures Sequence:1.1. Fractures form on surface opp. the forceFractures form on surface opp. the force
2.2. Radial cracks are formed on opp. Radial cracks are formed on opp. surfacesurface
3.3. Continued force on surface causes Continued force on surface causes concentric cracks on surface side of the concentric cracks on surface side of the force.force.
Production of Production of Radial and Concentric FracturesRadial and Concentric Fractures
Glass Fractures Sequence:Glass Fractures Sequence:
Counting the bullet holesCounting the bullet holes
Collecting and preservation of Collecting and preservation of glass evidence.glass evidence. All glass must be found to include odds All glass must be found to include odds
of matching pieces from suspect to of matching pieces from suspect to C.S.C.S.
Must Obtain Controls: suspect, C.S.Must Obtain Controls: suspect, C.S.– Control from area closest to point of Control from area closest to point of
breakbreak– Glass placed in solid containersGlass placed in solid containers– Individually wrap garments from suspect.Individually wrap garments from suspect.
•To be later check for glass fragments!!!To be later check for glass fragments!!!