Reagent Colour after 1 min. Marquis Pink to purple Mecke Green to blue green Froehde Strong violet Mandelin Muddy brown Add 1 drop of 2 N hydrochloric acid to the remaining filtrate from 2. and add up to 5 drops of ferric sulphate solution. Opium gives a persistent red colour in both portions. Use this acid digest for the next two tests and for thin layer chromatography. If opium is present, the acid digest gives an immediate gelatinous white precipitate.
Opium gives an immediate blackish precipitate.
A pink colour develops in the paper as the fluid spot dries, usually within 5 minutes. Heat to boiling about 1 mg. Both materials yield characteristic odours. Further confirmation may be obtained from the solution derived in the previous test using any other published test, such as the Marquis test. In routine practice, in experienced hands, the General Analytical Scheme tests constitute adequate confirmation of both raw and prepared opium.