extract 1 g of the sample, in powder, with 10 ml of chloroform, shake occasionally for 20 minutes,and filter. Evaporate 2 ml of the filtrate to dryness, dissolve the residue in 2 ml of acetic anhydride, and add slowly 1ml of sulfuric acid to make two layers: a brown colour forms at the zone of contact and the upper layer is green.