Glass and Soil

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

A. 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 blackStarch: iodine, brown  purplish black Heroin: Marquis reagent, turns purpleHeroin: Marquis reagent, turns purple

B. 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

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

1. Temperature Celsius 0 o C) (0 o C) Fahrenheit ( o F) freezing point 032 Boiling point Body temperature Room Temperature 2369

 Weight: force with which gravity attracts a body. (180lb) 81 kg on earth, (30lb) 13.6 kg on moon gravity(180lb) 81 kg on earth, (30lb) 13.6 kg on moon gravity The moon force of gravity is 1/6 of earthThe moon force of gravity is 1/6 of earth W=mg, (mass x acceleration by gravity)W=mg, (mass x acceleration by gravity) SO the large mass weighs more then a small mass.SO the large mass weighs more then a small mass. 2. Weight and Mass

 Mass: amount of matter an objects contains and is independent of it’s location on earth –81 kg on earth, 81 kg on moon 2. Weight and Mass

 When we “weigh” something against a known sample we are actually identifying the objects MASS!!!!!  We Use: –Triple beam balance –Top loading Balance –Analytical Balance Physical Properties: Weight and Mass

 The amount of occupied space  Regular Shaped Objects =LxWxH (cm3)  Irregular Shaped Objects –Volume of displaced fluid in a graduated cylinder. 3. Volume

 The relationship of Mass per unit volume –D=m/v Water at 20 o C 0.998g/mL = 1g/1.002 mL  An intensive property: property NOT dependent on the size of an object. –Same regardless of the size of the substance. –Solids (more dense)  liquids  gases 4. Density

 Silver 10.5 (g/mL)  Lead 11.5  Window glass  Mercury Liquid 13.6  Water at 4 C 1.00  Ice0.92 Physical Properties: Density

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

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=

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

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.

Becke line:

Becke line: n glass >n medium n glass < n medium n medium = n glass = 1.60 n medium = n glass = 1.34

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

Glass Objectives  Types  Matching  Fractures  Preservation

Comparing Glass Fragments Composed of silicon oxides mixed with metal oxides Soda-lime glass Soda (NaCo3) Lime (CaO) windows bottles Pyrex Borosilicates use Boron oxide, Can with stand HIGH heats Test tubes Headlights Tempered Glass: Rapid heating and cooling does not shatter Shower doors Side + rear windows Laminated Glass Plastic or Glass and glues and sandwich windshields

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. 1.Flotation test in density column!! Immersion Method 3.GRIM 2: Glass RI measurement ( automated)

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

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.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

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

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

Glass Fractures: force is greater then glass’s elasticity, It fractures  Fractures provide valuable information at the crime scene. Ex: Force and direction  Radial fractures: cracks extend outward like spokes of a wheel from point of impact  Concentric Fractures: forms rough circle around point of impact

Glass Fractures Styles:  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

Glass Fractures Sequence: 1. Fractures form on surface opp. the force 2. Radial cracks are formed on opp. surface 3. Continued force on surface causes concentric cracks on surface side of the force.

Production of Radial and Concentric Fractures

Glass Fractures Sequence:

Counting the bullet holes

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!!!To be later check for glass fragments!!!