Identifying Unknown Substances
The Federal Drug Enforcement Agency was alerted to a suspicious cargo ship from Columbia that was arriving in New York Harbor. During the raid of this ship, officers found bags of white powder. In order to arrest the importers of this cargo, the Agency had to accurately identify the substance. The first test done was the Scott test to determine if the powder was cocaine. Agents mixed a 2 percent solution of cobalt thiocyanate with one part each of water and glycerin. When the white powder was added to this solution, the solution turned blue immediately, indicating that it was cocaine. Then, hydrochloric acid was added to the solution, turning it from blue to pink, further confirming the substance as cocaine.
Any unknown substance can be found in the course of an investigation. In order to solve a mystery, we often need to identify poisons, gunshot residue and other substances. Color, odor, and reaction to other substances are unique for individual substances and can help to identify important clues. A forensic scientist will first observe the substance to gather information about its properties. Try the following activity to simulate how forensic scientists use chemistry to identify substances.
Directions:
- Set out samples of baking soda, sugar, salt and cornstarch and perform the following tests.
Use the data sheet (Adobe PDF Reader required)to record your findings.
Tests:
- Appearance - use a magnifying glass to describe the appearance of the powder
- Texture - feel the substance by pinching some between your fingers
- Smell - carefully - without inhaling any - smell the substance
- Reaction to water - add a drop of water to a sample of each powder and record what happens
- Reaction to iodine - add a drop of iodine to a sample of each powder
- Reaction to vinegar - add a drop of vinegar to a sample of each powder
- Have someone give you a sample of one powder from the list. See if you can identify the powder based on lab tests.
Adapted from Wiese, J. (1996) Detective Science. New York: John Wiley & Sons, Inc.