The above photo shows the positive results of the number 2 Marquis reagent presumptive drug test when used with a sample of opium.
The Marquis test is conducted by placing a small sample of suspect material (about the size of the tip of a typical pocket knife) inside the test vial. The bottom ampoule, containing a concentrated form of sulfuric acid with formaldehyde is crushed and the tube shaken. The dark brown final color of the liquid is indicative of a presumptive positive result for opium.
This photo was created as part of a training program to assist the Afghan National Army in properly investigating, forensically testing and prosecuting drug crimes.
Ref: Color Test Reagents/Kits for Preliminary Identification of Drugs of Abuse NIJ Standard–0604.01