Answer:
Iodine was discovered by the French chemist Barnard Courtois in 1811. Courtois was extracting sodium and potassium compounds from seaweed ash. Once these compounds were removed, he added sulfuric acid (H2SO4) to further process the ash. He accidentally added too much acid and a violet colored cloud erupted from the mass. The gas condensed on metal objects in the room, creating solid iodine. Today, iodine is chiefly obtained from deposits of sodium iodate (NaIO3) and sodium periodate (NaIO4) in Chile and Bolivia.
Trace amounts of iodine are required by the human body. Iodine is part of thyroxin, a hormone produced by the thyroid gland that controls the body's rate of physical and mental development. A lack of iodine can also cause a goiter, a swelling of the thyroid gland. Iodine is added to salt (iodized salt) to prevent these diseases.
Iodine is used as a test for starch and turns a deep blue when it comes in contact with it. Potassium iodide (KI) is used to make photographic film and, when mixed with iodine in alcohol, as an antiseptic for external wounds. A radioactive isotope of iodine, iodine-131, is used to treat some diseases of the thyroid gland.