Types and Properties of Glass

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Questions and Answers

What is the correct procedure to begin observing soil samples under a stereomicroscope?

Mix the soil sample with water before observation.

Place the soil sample in a test tube.

Place the slide/plate with the soil sample on the viewing stage of the stereomicroscope. (correct)

Use a regular microscope instead of a stereomicroscope.

Which color of particles in soil indicates the presence of iron oxide?

Red particles (correct)

Green particles

Colorless particles

Black particles

What does the presence of bubbles when adding hydrochloric acid to a soil sample indicate?

Insoluble carbonates (correct)

Presence of soluble iron

Colorless quartz grains

Dried vegetation particles

What is the primary purpose of conducting an ignition test on a soil sample?

To test the water holding capacity or moisture content of the soil Signup and view all the answers

Which method is used to observe the acid-alkali behavior of soil?

Measuring the pH value after dissolving the soil in distilled water. Signup and view all the answers

What is the significance of adding potassium ferrocyanide solution to the soil sample?

To confirm the presence of soluble iron. Signup and view all the answers

Which step is included in particle size distribution analysis of soil?

Arranging sieves in numerical order and shaking the soil. Signup and view all the answers

What type of particles may be observed as traces of foreign materials in the soil?

Glass fragments Signup and view all the answers

Which method is preferred to observe soil samples under a microscope?

Making a thin layer of soil on a clean microscopic slide Signup and view all the answers

What should be done with soil samples before examination under a microscope?

Create a thin layer on a clean microscopic slide Signup and view all the answers

Which of the following is NOT a step in preparing soil samples for microscopic examination?

Apply heat to the sample before examination Signup and view all the answers

Why is it important to make a thin layer of soil on the slide for microscopy?

To improve light penetration and visibility Signup and view all the answers

What should be avoided when preparing soil for microscopic examination?

Creating a thick layer of soil on the slide Signup and view all the answers

Which of the following equipment is used to view soil samples microscopically?

Stereomicroscope Signup and view all the answers

What can affect the visibility of soil components under a microscope?

Thickness of the soil layer on the slide Signup and view all the answers

What is the first step in the microscopic examination of a soil sample?

Create a thin layer of soil on a slide Signup and view all the answers

What observation indicates that the refractive index of a glass fragment is the same as that of the surrounding liquid?

The Becke line does not appear Signup and view all the answers

What does it mean if the Becke line appears inside the glass fragment?

The refractive index of the glass is higher than that of the liquid Signup and view all the answers

What is the main purpose of using the immersion method in refractive index study?

To visualize the Becke line more clearly Signup and view all the answers

How is density calculated?

Density = mass / volume Signup and view all the answers

What apparatus is used to observe the disappearance of the Becke line when increasing temperature?

A hot stage microscope Signup and view all the answers

Which of the following liquids has the highest density?

Bromoform Signup and view all the answers

What indicates a successful physical matching of glass pieces collected from a crime scene?

The pieces join smoothly without force Signup and view all the answers

What is the significance of observing the Becke line under a microscope?

It assists in determining the refractive index Signup and view all the answers

Study Notes

Glass

Glass is a hard, amorphous material made by melting sand, lime, and sodium oxide at high temperatures.
Its atoms are randomly arranged.
Main component is silicon dioxide (silica).

Characteristics of Glass

Hard, amorphous solid
Usually transparent
Primarily composed of silica with oxides
Brittle
Exhibits conchoidal fracture

Types of Glass

Soda-lime Glass: Most common (approx. 90%). Used in windows, containers, and light bulbs. Inexpensive to produce and can be reheated and recycled easily.
Soda-lead Glass: Used in fine tableware and art objects. Higher density and refractive index than soda-lime, making it more brilliant.
Borosilicate Glass: Heat-resistant, like Pyrex. Used for cooking and laboratory equipment. High resistance to temperature changes and chemicals.
Silica/Fused Silica Glass: Used in chemical equipment and space shuttle windows. Strongest and most thermally stable.
Tempered Glass: Used in car windows and phone screens. Stronger and safer than annealed glass; shatters into small, less sharp pieces when broken.
Laminated Glass: Consists of two sheets of tempered glass bonded with PVB. Used in car windshields for safety and security.
Colored/Tinted Glass: Tinted with metallic salts during manufacturing.
Wire Mesh Glass: Glass with embedded metal wire. Helps hold broken pieces together.

Glass as Forensic Evidence

Broken glass is important evidence.
Different types have unique properties.
Fragments can travel up to 9 feet.
Can be found on clothing, shoes, or hair.
Fracture patterns provide clues about the object and the angle of impact.
Experts analyze the breakage to understand projectiles causing the break.

Handling of Crime Scene Glass

Identify and photograph any glass samples.
Collect largest fragments possible.
Look for trace evidence (hair, fibers, blood).
Package fragments carefully in boxes padded with cotton.
Submit with a control sample of the type of glass from the crime scene.

Forensic Examination of Glass

Compare glass samples' physical and chemical properties.
Analyze optical properties (color, refractive index).
Evaluate non-optical characteristics (surface wear, thickness, and density).
Examine chemical properties (additives, trace elements).
Goals are: -Identify glass types present. -Determine how the glass was fractured. -Individualize glass fragments to a source.

Physical Characteristics of Glass

Color
Thickness
Fluorescence
Patterns/Designs
Markings (striations, dimples)
Density
Refractive index

Physical Matching of Glass

Match larger fragments based on physical similarities.
Counting fragments and how they fit together to determine source.

Refractive Index Study

A measure of how glass bends light.
Immersion method: Immerse a glass fragment in liquid with similar refractive index to see if invisible or a halo ("Becke line") appears
Becke line: used to observe if the fragment's refractive index matches the liquid.
Observation:
No Becke Line: Fragment and Liquid have same refractive index.
Becke Line inside glass: Fragment's refractive index is higher than the liquid.
Becke Line outside glass: Fragment's refractive index is lower than the liquid.
Hot stage: Increasing the temperature can get to the match point when the Becke line disappears

Density Study

Measures of density (mass/volume) using displacement.
Different types of liquids with varying densities
Determine the glass type from its density.
Direct method: Measuring of mass and volume using displacement method.

Fracture Study & Sequencing

Fracture patterns are unique and help determine the origin, direction of force, and sequence of impacts.
Radial fractures: originate on the opposite side of the force.
Concentric fractures: originate on the same side as the force.
Cone fractures: Caused by high-velocity projectiles, resulting in a crater-shaped hole surrounded by fractures.

Soil

Soil is any disintegrated material on or near the earth (natural or manufactured).
Soil has unique properties useful for forensic examination.
Types of Soil
Sediment
Sandy Soil
Silt Soil
Clay Soil
Loamy Soil
Peaty Soil

Soil as Evidence

Soil from a crime scene or related items can be compared to standard/reference samples for a comparison.
Collected for comparison within a 100-yard radius of the crime scene, from similar environments.

Collection of Soil Samples

Handling/Collection:
Use appropriate tools (spatula, trowel) for sample collection and placement in containers.
Remove the lids from containers to allow for gradual drying if necessary
Containers (rigid, airtight, waterproof) for sample storage.

Preservation of Soil Samples

Store samples immediately after collection, using refrigerated or dark, cool areas.
Avoid freezing.

Microscopy Observations

Examine soil particles visually under a stereomicroscope. -Examine under several magnification levels for more detail
Examine particle color, shape, and size.

Chemical Reagent Observations

Observe the reaction of the soil under chemical reagents for possible indication of substances.
Confirm identification of observed substances using confirmatory reagents.

Particle Size Distribution of Soil

Separate soil using a set of sieves to divide the soil samples by size.
Measure the weight of each soil size for percentage analysis.

Ignition Test (Soil)

Heat the sample to determine water content and weight loss.
Compare the weight loss of a suspect soil sample with a known soil sample from a given area (comparison soil sample)

pH Measurement (Soil)

pH is useful in determining soil acidity/alkalinity.
Prepare a known soil sample in a liquid of controlled volume.
Measure and compare the pH values of the soil samples to determine compatibility.

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Description

This quiz explores the composition, characteristics, and various types of glass, including soda-lime and borosilicate glass. Learn about their uses, properties, and how they differ from one another. Test your knowledge on this important material in both everyday items and specialized applications.