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Preliminary Tests

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  345

2026-08-09

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Preliminary Tests

The first test done on a drug exhibit is visual. The package should be opened (protective gloves should be worn. LSD can be absorbed through the skin, causing significant hallucinations.) The appearance of the exhibit should be noted. Plant materials may be treated differently than white powders or marked tablets. The exhibit is then weighed. Over the past 50 years or so, a number of presumptive tests have been developed that react with various common controlled drugs, usually resulting in a visual color change to the reagent when the drug is added. These are valuable tests in that they can give the examiner some possible avenues for further examination. For example, the Ruybal (or Scott) test consists of three reagents that are added in turn to an exhibit suspected to be or contain cocaine. The final result of the test is a turquoise color in a chloroform layer at the bottom of the test tube where the test is run. This test is said to be presumptive for cocaine. It is not specific, there are other substances that give similar results to this test, but it does give the analyst a direction to proceed, namely to continue to test for the presence of cocaine. Some of the more common presumptive tests and the drugs they are used on are given below.

Figure 1 is a field test kit commonly used by narcotics and other law enforce ment agents.