Bromine water is used to test for unsaturated oils because it changes color in their presence. The BBC states that pure bromine water, a solution of water and bromine, has a brownish orange hue. When mixed with an unsaturated oil, the bromine water becomes colorless. Its color does not change when mixed with saturated oils.
According to the Centers for Disease Control, bromine water releases a vapor that causes serious respiratory consequences when inhaled. It also irritates skin and causes chemical burns. Swallowing bromine results in vomiting.
Iodine also turns colorless when mixed with unsaturated oils. To obtain accurate test results using either bromine water or iodine, a researcher fills a test tube halfway with either substance. The researcher then adds the oil, seals the test tube with a rubber stopper and shakes vigorously.
Iodine is also potentially dangerous. When inhaled, it causes immediate, long-lasting and severe irritation of the trachea and lungs. According to the Chemistry Department of Iowa State University, undiluted iodine is highly corrosive and burns exposed skin. Some individuals also suffer kidney and thyroid damage from prolonged exposure to concentrated iodine.
To perform the bromine water or iodine oil test safely, researches need to wear protective gloves and paper face masks.