Quiz 11: Hairs and Fibers
(should include points such as): -The entire shoe should be submitted for laboratory examination. The evidence collector should avoid removing glass evidence from the shoe unless there is a distinct possibility that the glass will be lost in transit. -Shoes are to be packaged in a box or paper bag and sent to the laboratory. -A control piece of glass from the broken window is to be submitted for laboratory examination. Normally a square-inch piece of glass will suffice. -A pillbox, druggist fold, or vials are convenient containers for small glass fragments. -All packages are to be properly labeled for identification. Minimal information should contain the evidence collector's name or initials, the date, and sampling location. All items collected are to be described in the evidence collector's field notes.
(should include points such as): Flotation is a process used to compare the densities of glass samples. In flotation, a standard/reference glass particle is immersed in a liquid. The composition of the liquid is carefully adjusted until the glass remains suspended in the liquid. Glass chips of approximately the same size and shape as the standard/reference are then added to the liquid for comparison. If both the unknown and the standard/reference particles remain suspended in the liquid, their densities are equal to each other and to that of the liquid. Particles of different densities either sink or float, depending on whether they are more or less dense than the liquid, respectively.
(should include points such as): The physical properties of density and refractive index are used most successfully for characterizing glass particles. The main drawback of using these properties to characterize glass is that they are class characteristics, and as such will not provide the sole criteria for individualizing glass to a common source.