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B.
Classification — Categorization with Like Items
Before the analyst can even decide whether classification or individualization
is the goal, he must have some idea of the type of material being examined.
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Classification, Identification, and Individualization
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The first level of examination involves nothing more than human sensory
perception. Is it a solid, liquid, or gas? How big is it? What color is it? What
shape is it? What is its texture? What are its obvious optical qualities? Does
it have an odor? What does it sound like?* Although the days when scientists
took a judicious whiff from a can to determine if it contained a flammable
liquid or used the tactile method to detect semen stains on bedsheets are
long past, a thoughtful preliminary assessment of the sample is still required.
We are reminded of a student who gave a presentation on the analysis
of paint. She was so dazzled by the sophisticated, instrumental methods for
paint analysis, such as pyrolysis GC-MS and FTIR, that she never even
thought to simply look at it with her eyes, never mind a microscope, to
determine its color. It is not necessary to do a DNA analysis to put an elephant
in a different category than a turnip. In addition to human senses, simple
chemical, physical, and optical tests can be very useful in delimiting the class
of substances to which an item belongs. What does it look like under low-
power or higher-power magnification? How much does it weigh? Is it organic
or inorganic? Is it soluble or insoluble in certain solvents? How does it react
to certain presumptive tests? These are all tools that help us classify unknown
substances or objects.
Because the process of classification relies on our ability to place materials
into categories, we must know something about the characteristics common
to any particular class of objects. To do this, we must understand the prop-
erties of these 
 
class characteristics
, their mode of creation, and the limitations
of any conclusions based solely on them.