How do CST ( crime scene technicians) use chemistry?

Chemistry is used at crime scenes mostly in preliminary tests for chemicals that may be present. For example, the presence of drugs is usually first tested for using chemical reactions with known reagents. Blood is usually located by its reaction with a pH indicator (phenolthalein) or luminol. Other body fluids can be identified through the use of other chemical tests, although biochemical (immunological) tests are more common.