Topic 8

Question 1

is important as physical evidence because it breaks and pieces are scattered at the crime scene and on the suspect. It is a common type of thing carried away evidence in and burglary and vehicle hit and run cases. The evidence maybe fragments of a headlight leads found at the scene of a hit and run accident, window glass from the scene of robbery, or glass through which a bullet was fired.

Answer 1

Glass

Question 2

– This refers to a super cooled liquid which possesses high viscosity and rigidity. It is a non – crystalline inorganic substance.

Answer 2

Glass

Question 3

base of commercial glass

Answer 3

1. Silica (SiO2)

Question 4

acts as flux for silica

Answer 4

2. Soda (Na2O)

Question 5

gives the glass chemical durability which it otherwise lack because of the water – soluble Na2O

Answer 5

3. Lime (CaO)

Question 6

present as impurity or substitute for CaO

Answer 6

4. Magnesis (MgO)

Question 7

gives the glass greater chemical durability lower coefficient of expansion, and greater freedom fromdevitrification

Answer 7

5. Alumina (Al2O2)

Question 8

for chemical durability and resistance to devitrification

Answer 8

6. Potash (KO)

Question 9

The most important problem commonly referred to a forensic chemist is the comparison of two or more samples of glass.

Answer 9

Analysis of Glass

Question 10

– an instrumental method of analysis which determines the presence of trace elements. Shows the constituent elements of glass. It will not give sufficient information to establish is the origin of the samples examined. A rapid examination and an adequate method for glass analysis since it requires only a small amount of sample. In the absence of trace elements it may be difficult to determine whether two samples of common type of glass are identical. If similar trace elements are found of both samples it is obvious they come from the source.

Answer 10

Spectrographic Test

Question 11

– not as effective as the spectrographic analysis. It determines the type of pattern of glass. The type of pattern depends upon the composition of glass.

Answer 11

X – ray Diffraction Test

Question 12

– the most sensitive method of determining differences of composition in glass samples and depends upon the study of the physical properties of glass. Properties like specific gravity and density, refractive index. Density and refractive index can be measured with great accuracy. Density or specific gravity is an especially important physical property from the viewpoint of the forensic chemist.

Answer 12

Physical Properties Examination

Question 13

– a rapid and convenient method of determining the density of small glass fragments. Procedure and principle is the same as in soil Method of Measuring the Refractive Index of Glass

Answer 13

Flotation Method

Question 14

– method used to measure the refractive index of a glass. It is difficult to distinguish between two samples of glass by density and refractive index. It may be mentioned that two glass from independent sources can vary conceivably have the same index of refraction or the same density but it is quite improbable that they would have both index of refraction and density the same.

Answer 14

Immersion Method

Question 15

– determines the differences in the appearance of the fluorescent thus indication of physical and chemical differences.

Answer 15

Ultraviolet Light Examination

Question 16

– optical glass and other fine glasswares are usually polished. In the polishing of glass fine marks are often left on the surface which can sometimes serve as a basis of comparison.

Answer 16

Polish Marks