This presumptive test is designed to identify THC in Marijuana. This original chemistry was the foundation for the three ampoule Duquenois-Levine (more specific) but is recognized as an excellent test for THC. The 1st ampoule should be agitated for sixty (60) seconds. No color should develop (THC is a clear colored substance). If a color does develop, you may have a false positive. The 2nd ampoule with show a very fleeting flash Green color before developing a definitive midrange Purple. Like all our NARK narcotic field tests, the Mayers Reagent is meant for presumptive field drug testing. 10 test/box.