A 2-l. round-bottomed flask, surrounded by an ice-water bath and provided with a stirrer, a separatory funnel, and an outlet tube, is set up in a good hood. To the flask are added 500 g. (160 cc., 3.1 moles) of bromine and 50 cc. of water (Note 1). To the stirred mixture is added gradually a solution of 170 g. of sodium cyanide (3.5 moles) in 1.2 l. of warm water. The temperature of the reaction mixture is kept below 30°. When the reaction is complete (about two hours or less) the cyanogen bromide is distilled from a steam bath, using a 500-cc. flask (Note 2) as a receiver. The distillate is warmed with about 100 g. of anhydrous calcium chloride, filtered, and again distilled, preferably with the distilling flask used as a receiving vessel connected directly to the flask from which the cyanogen bromide is being distilled. The product boils at 60–62°. It is melted in the receiver (Note 3) (Hood) and poured into a warm tared bottle. The yield of white crystalline solid (Note 4) melting at 49–51° is 239–280 g. (73–85 per cent of the theoretical amount).