Forensics Glass Test (Ch. 5)
Density
Commonly expressed as g/cm^3 or g/mL
Properties, existence
Comparing glass consists of finding and measuring the __________ that will associate one glass fragment with another while minimizing or eliminating the possible _________ of other sources.
Edges, irregularities, striations
Comparisons of glass require piecing together irregular ______ of broken glass as well as matching all ______________ and _________ on the broken surfaces.
Filaments
Examining a car's headlight's _________ at a crime scene may reveal whether an automobile's headlights were on or off before the impact, for example.
Mass
The amount of matter an object contains independent of gravity. Determined by comparison to this known value of standard objects
Atom
The basic particle of an element
Refraction
The bending of light waves because of a change in velocity
Density, refractive indexes
The two physical properties that are used most successfully for classifying glass particles (class characteristics)
Laminated
The windshields of all cars manufactured in the US are constructed from _________ glass. This glass derives its strength by sandwiching one layer of plastic between two pieces of ordinary window glass.
Concentric
Then the continued motion of the force place tension on the front surface of the glass, resulting in the formation of __________ cracks.
Radial cracks form a Right angle on the Reverse side of the force
3R Rule
Bullet
A ______ passing through a pane of glass will cause the glass to shatter.
Non-bullet
A __________ projectile passing through a pane of glass will not always cause the glass to shatter.
Becke line
A bright halo observed near the border of a particle immersed in a liquid of a different refractive index. The halo disappears when the medium and fragment have similar refractive indices
Radial fracture
A crack in a glass that extends outward like the spoke of a wheel from the point at which the glass was struck
Fracture
A fracture does not terminate at an existing line of ________.
Glass
A hard, brittle, amorphous substance composed of sand (silicon oxides) mixed with various metal oxides. Sand is mixed with other metal oxides, melted at high temperatures, and then cooled to a rigid condition without crystallization to made this
Refractive index
A highly distinctive property of glass and is thus useful for defining its frequency of occurrence and hence its evidential value
Temperature
A measure of heat intensity, or the hotness or coldness of a substance.
Greater, lower, equal
A solid particle will float in a liquid medium of _______ density, sink in a liquid of _____ density, and remain suspended in a liquid of _____ density.
Float, sink
Alcohols have a density less than 1.00 g/cm^3 and some objects that _____ in water will ____ in alcohol.
Glass
Amorphous solids, such as _____, have their atoms arranged randomly, unlike crystals
Stress markings
An examination of the edges of the radial and concentric cracks frequently reveals ______ ________ whose shape can be related to the side on which the window first cracked. They are shaped like arches that are perpendicular to one glass surface and curved nearly parallel to the opposite surface. The perpendicular end is always found opposite the side from which the force of impact was applied
Matter
Anything that has a mass and occupies space
Refractive index
As with density, glass fragments removed from a single sheet of plate glass may not have a uniform __________ _____ value; instead their values may vary by as much as 0.0002.
1.333
At 25 degrees C the refractive index of water is
Direction
By examining a bullet hole in a pane of glass it is possible to identify the _________ of the bullet.
Size
By examining a bullet hole in a pane of glass, it is NOT possible to identify the ____ of the penetrating bullet.
Substances
Can change from one phase of matter to another without forming a new chemical species
Mass/volume
Density=
Chemical property
Describes the behavior of a substance when it reacts or combines with another substance. (Ex. Toxicity, oxidation states, heat of combustion, flammability, reactivity, etc.)
Photons
Discrete particles of light
No
Do radial and concentric fracture lines appear only in tempered glass?
Birefringence
Double refraction- the numerical differences between these two refractive indices of the crystalline solids
Concentric
For a ___________ fracture, the perpendicular end always faces the surface on which the force originated.
Perpendicular
For a concentric fracture, the ____________ end always faces the surface on which the force originated.
Smaller, smooth
For small projectiles, the entry is a ______ hole and a ______ surface
Force, direction
Frequently, fracture window glass reveals information about the _____ and _________ of an impact; such knowledge may be useful for reconstructing events at a crime scene investigation.
Jigsaw puzzle
Glass analysis has its greatest impact as evidence when the glass can be identified with only one source. Such a determination can only be made if fragments can be collected and physically pieced together in a perfect fit like a ______ ______. Since this rarely happens, when it does, it becomes compelling evidence.
Elasticity
Glass bends in response to any force that is exerted on any one of its surfaces; when the limit of its __________ is reached, the glass fractures.
Tempered glass
Glass to which strength is added by introducing stress through rapid heating and cooling of the glass surfaces; stronger than ordinary window glass
Crystalline solids
Have definite geometric forms because of the orderly arrangement of their atoms
5
How many beads were added to the water in the graduated cylinder?
20
How many mL of distilled water was originally put in the 100 mL graduated cylinder?
Shoes, clothing
If the suspect's ______ and/or ________ are to be examined for the presence of glass fragments, they should be individually wrapped in paper and transmitted to the laboratory, unless absolutely necessary to do otherwise for preservation.
Standard, reference
In a method known as flotation, a _______/________ glass particle is immersed in a liquid; a mixture of bromoform and bromobezene may be used. The composition of the liquid is carefully adjusted by adding small amounts of bromoform or bromobenzene until the glass chip remains suspended in the liquid medium. At this point, the liquid and the particle have the same density. The unknown is then added, and if both the first particles and the unknown stay suspended, their densities are equal to each other and to that of the liquid.
Density
In many forensic cases, the physical glass pieces do not fit together easily. Another technique that can then be used involves determining the _______ of glass pieces and then comparing it to those of known glass sources.
Flotation, immersion
The ________ method is to determine a glass fragment's density, the _________ to determine its refractive index.
Isopropyl alcohol
In the lab, if the beads floated, we poured out the water and put in 20 mL of _________ _______ into the graduated cylinder. From there, if they sunk in this, we added distilled water to the graduated cylinder 1 mL at a time.
Sugar solution
In the lab, if the beads sank, we added _____ ________ to the distilled water 1 mL at a time, until all the beads were floating at the top.
Volume
In the lab, we needed to use five beads because of their small ______.
Bend
Light waves travel in air at a constant velocity until they penetrate another medium, such as glass or water, at which point they are suddenly slowed, causing the rays to ____.
Denisty
Mass per unit volumes an intensive property of matter, meaning it remains the same regardless of sample size. Considered a characteristic property of a substance and can be used as an aid in ID
Density gradient
Measure of flotation; solutions of decreasing densities are placed in a long column and then the object is placed into the column. By comparing the point of suspension, the density can be identified and different glasses can be compared
Sink, float
Objects with a density greater than 1.00 g/cm^3 will ____ in pure water. Objects with a density less than 1.00 g/cm^3 will _____ in pure water.
Hot stage,
One approach to changing the temperature of a liquid to change the refractive index is to heat the liquid in a special apparatus known as a ___ _____. The glass is immersed in a boiling liquid, usually a silicone oil, and heated at the rate of 0.2°C/minute until the match point is reached. If all glass fragments examined have similar match points, it can be concluded that they have comparable refractive indices.
Class characteristics
Properties of evidence that can be associated only with a group and never with a single source.
Physical properties
Qualities such as weight, volume, color, boiling point, and melting point that describe a substance without reference to any other substance.
Opposite
Radial fracture lines form on the surface ________ that of the penetrating force.
Visible light
Ranges in color from red to violet in the electromagnetic spectrum
Annealing
Slowly heating and then cooling glass to distinguish between tempered and non tempered glass particles- the change in the refractive index value for tempered glass during this process is significantly greater when compared to non tempered glass and thus serves as a point of distinction
Increase
Solutions, such as sugar water, have a density greater than 1.00 g/cm^3. The density of a sugar solution will ________ as the concentration of sugar in the solution increases.
Pyrex glass
Special type of glass that can withstand very high temperatures, manufactured by adding boron oxide to the oxide mix (known as borosilicates
Density, refractive index
The FBI Laboratory has collected _______ and _________ _____ values from glass submitted to it for examination. What has emerged is a data bank correlating these values to their frequency of occurrence in the glass population of the US. THis collection is available to all forensic labs in the US.
Homogeneous
The density of a single sheet of window glass is not completely ___________ throughout. It has a range of values that can differ by as much as 0.0003 g/mL.
1.00, 20
The density of pure water is ____ g/cm^3 at __ degrees C.
Wavelength
The distance between two successive crests (or one trough to the next)
Electromagnetic spectrum
The entire range of radiation energy from the most energetic cosmic rays to the least energetic radio waves.
Match point
The exact numerical value of the glass refractive index can be calculated at the _____ _____ temperature.
Opposite, radial
The first fractures form on the surface ________ that of the penetrating force and develop into _____ fractures.
Weight
The force with which gravity attracts a body
Float glass
The forensic scientist is often asked to analyze soda-lime glass, which is used for manufacturing most window and bottle glass. Usually the molten glass is cooled on top of a bath of molten tin. This process produces flat glass typically used for windows. This type of glass is called?
0, 100
The freezing point of water is __ degrees C, the boiling point is __ degrees C.
Chemical composition, trace elements
The general ________ ___________ of various window glasses within the capability of current analytical methods has so far been found to be relatively uniform among various manufacturers and thus offers no basis for individualization. However, as more sensitive analytical techniques are developed, _____ ________ present in glass may prove to be distinctive and measurable characteristics.
Exit
The hole made by a high-velocity projectile is inevitably wider on the ____ side. However, as the velocity of the penetrating projectile decreases, the irregularity of the shape of the hole and its surrounding cracks increases, at which point looked at the radial and concentric fracture lines may help determine the direction.
Frequency
The number of crests (or troughs) passing through any one given point per unit of time
Gunpowder
The presence of _________ deposits on the shattered glass fragments points to damage caused by a firearm. This helps since the size and shape of a hole can not always determine by itself if it was made by a bullet or some other projectile.
Refractive index
The ratio of the velocity of light in a vacuum to that in the medium under examination
Temperature
The refractive index of an immersion fluid is best adjusted by changing the ___________ of the liquid.
Flotation
The simplest comparative density technique; based on the principle that a solid particle will float in a liquid medium of greater density, sink in a liquid of lower density, and remain suspended in a liquid of equal density.
Element
The simplest substance known and provides the building block from which all matter is composed
Molecule
The smallest unit of a compound
Continuous wave, discrete energy particles
Two models describe the behavior of light: Light is described as a ____________ _____. Light is depicted as a stream of ________ _______ _________.
Compoud
Two or more elements
Laminated glass
Two sheets of ordinary glass bonded together with a plastic film
White light
When ______ ______ passes through a prism it is dispersed into a continuous spectrum of colors.
Tempered
When ________ glass breaks, it does not shatter but rather fragments or "dices" into small squares with little splintering. Used in side and rear view windows of cars
Breakage
When an individual fit is improbable, the evidence collector must submit all glass evidence found in the possession of the suspect along with a sample of broken glass remaining at the crime scene. This standard/reference glass should always be taken from any remaining glass in the window or door frames, as close as possible to the point of ________.
radial
When an object begins to penetrate a pane of glass, ______ fractures are the first to form.
Exterior
When it is not immediately apparent which is the exterior/interior surface of the glass, the presence of dirt, paint, grease or putty may indicate the ________ surface of the glass.
Round, crater
When it penetrates glass, a high-velocity projectile such as a bullet often leaves a ______, ______-shaped hole surrounded by a nearly symmetrical pattern of radial and concentric cracks.
Soda, lime
When making glass, ____ (sodium carbonate) is normally added to the sand to lower its melting point and make it easier to work with. Another necessary ingredient is ____ (Calcium oxide) to prevent the glass from dissolving in water.
Farther, interrupted
When two holes are placed in a pane of glass in close proximity to one another, it is possible to identify the order of penetration. The first fracture's cracks are spreading _______, and the cracks of the second fracture are ___________.
Plain, tempered
_____ and ________ glass have more uniform cracks/fracture patterns when a bullet passes through them
Tempered
________ glass is stronger than normal glass due to rapid heating and cooling
Concentric
__________ fracture lines do NOT form on the surface opposite that of the penetrating force.
Concentric fracture
a crack in a glass that forms a rough circle around the point of impact
Immersion method
determines refractive index; Glass particles are immersed in a liquid medium whose refractive index is adjusted until it equals that of the glass particles, at which point the Becke line disappears
Density column
layering of substances based on density; more dense substances will be at the bottom with less dense items at the top
Molotov cocktail
typically a bottle filled with flammable liquid with the purpose of lighting on fire.
