A presumptive test for amphetamines, methamphetamines, and heroin. Mecke's reagent consists of 1 gram of selenious acid in 100 ml of concentrated sulphuric acid. Different substances give different results. Ecstasy, for example, gives a light blue colour, turning to turquoise, and then dark blue. Heroin gives a yellow colour changing to green. LSD gives an olive-green colour, changing to black. Mescaline gives a brownish-orange colour.