A presumptive test for methamphetamines. The Simon reagent consists of 1 gram of sodium nitroprusside (Na2Fe(CN)5 NO) and 2 ml of acetaldehyde (ethanal) in 50 ml of water. A 2% solution of sodium carbonate is then added. MDA gives a turquoise colour; MDMA gives an initial turquoise, which changes to dark blue.