(I) A portion is mixed with about 5 c.c. of water in a test-tube, and 2-4 drops of a solution of mercuric nitrate are added. The tube is then heated for five to ten minutes in boiling water. If dulcin is present, a faint violet coloration is obtained, which becomes deeper on adding a little lead dioxide.1 The mercuric nitrate solution is made by dissolving 1-2 grams of freshly precipitated mercuric oxide in nitric acid, diluting the solution, and adding caustic soda solution in sufficient quantity just to give a little permanent precipitate. The liquid is then diluted to about 15 c.c, allowed to settle, and the clear portion decanted off for use.
(II) Another portion of the residue is mixed with 2-3 drops of pure phenol and an equal volume of strong sulphuric acid, and the mixture heated to boiling for a short time. After cooling, a little of the product is poured into a test-tube, water added to about half fill the tube, and the mixture shaken up well. On carefully-pouring a little ammonia or sodium hydroxide solution on to the liquid, a blue ring is obtained at the surface of contact if dulcin was present.