In a 1-l. three-necked flask, fitted with a thermometer, a reflux condenser, and an inlet tube extending to the bottom of the flask and drawn out to a small opening, are placed 600 cc. of dry carbon tetrachloride, 154 g. (0.5 mole) of di-o-nitrophenyl disulfide, m.p. 193–195° (Org. Syn. Coll. Vol. I, 1941, 220), and 0.25 g. of iodine. To the upper end of the condenser is attached a glass tube which dips below the surface of a little carbon tetrachloride contained in a test tube. A current of chlorine, dried with sulfuric acid, is passed into the reaction mixture, the temperature of which is maintained at 50–60°. The rate of flow of the chlorine (about 16–17 g. per hour) is regulated so that little or no gas escapes through the carbon tetrachloride trap. The yellow di-o-nitrophenyl disulfide gradually disappears, and after two to two and one-half hours a homogeneous, dark yellow solution is obtained (Note 1). The warm solution is filtered from a small amount of dark residue through a warm Büchner funnel, the flask and filter being rinsed with 30 cc. of warm carbon tetrachloride. The yellow filtrate (Note 2) is cooled to 5° and the product allowed to crystallize. The cake of crystals is broken with a rod, collected on a Büchner funnel, and drained well. The product is dried rapidly (two hours) at 50° and bottled (Note 3). This material melts at 73–74.5° and weighs 126–135 g. (66–71 per cent of the theoretical amount). A further crop is obtained by removing the solvent from the mother liquor by distillation from a water bath (Note 4), the dark, residual oil being poured into an evaporating dish. The last traces of carbon tetrachloride are removed by drying at 50°, during which process the oil crystallizes. This material melts at 67–72° and weighs 48–58 g. It is pure enough for most purposes (Note 5). The total yield is 183–184 g. (96–97 per cent of the theoretical amount) (Note 6) and (Note 7).