The U.S . Pharmacopeia 471 oxyegn flask combustion procedure is provide as the preparatory step in the determination of bromine , chlorine, iodine selenium and sulphur in some pharmacoecial articles. It is consists of heavy walled conical deeply lippped 500ml or 1000ml flask fitted with a ground - glass stopper 34/45 joint size to which is fused a test specimen carrier conssiting of heavy -guage platinum wire and a piece of welded platinum guaze measuring about 12x12mm , consists of 22 or 18 - heavy paltinum wire gauze , U shaped .