text: Marquis reagent was first discovered in 1896 and described by the Russian (Estonian) pharmacologist, Eduard Markus (1871&ndash;1944) () in his magister dissertation in 1896; and named after him, and was tested for the first time at the University of Dorpat. The reagent should be stored in the freezer for maximum shelf life.
  It is the primary presumptive test used in Ecstasy reagent testing kits. It can also be used to test for such substances as opiates (e.g. codeine, heroin), and phenethylamines (e.g. 2C-B, mescaline).
  The test is performed by scraping off a small amount of the substance and adding a drop of the reagent (which is initially clear and colorless).  The results are analyzed by viewing the color of the resulting mixture, and by the time taken for the change in color to become apparent: