Jennifer Zubach, age 13, of Rock Island, I11., for her question:
WHERE DO WE GET IODINE?
Iodine is a chemical element that occurs both on land and in the sea. The human body needs traces of iodine and it is part of a substance called thryroxine, a hormone produced by the thyroid gland.
Thyroxine controls the body's rate of physical and mental development. Therefore, a shortage of iodine in the body can hinder a person's growth. It can also cause a goiter, which is a swelling in the neck. For these reasons, manufacturers market iodized salt, which is salt with iodine added, in regions where the iodine level in food and water is low.
Iodine occurs widely in nature, but not in large amounts. It is always found with chlorine, a chemical element 2,000 times more common than iodine.
Pure iodine occurs moat frequently as a compound with sodium or potassium. Iodine compounds occur in the sea. Many kinds of animals and plants that live in the sea concentrate iodine in their bodies. A kind of seaweed called kelp is especially rich in iodine, and was one of the earliest sources of the element.
A French chemist named Bernard Courtois discovered iodine in seaweed in 1811.
The chief commercial sources of iodine are the nitrate deposits
in Chile and Bolivia. Iodine occurs in these deposits in small amounts as sodium iodate or as sodium periodate.
Iodine sublimes when heated. This means that it changes directly from a solid to a vapor, without becoming a liquid. Iodine vapor is purple. It has an irritating smell.
Iodine dissolves only slightly in pure water. But it dissolves more easily if the water contains an iodide, or salt of iodine. The iodide and iodine combine to form polyiodides, which are able to dissolve. Iodine also dissolves in various organic liquids, forming brown, red or violet solutions.
Iodine belongs to the halogen family of chemical elements along with chlorine and fluorine.
Iodine was once commonly used as an antiseptic. But it can burn the akin and damage the tissues of the eye and nose, and moat doctors
prefer not to prescribe it today. Pure iodine is poisonous if taken internally.
Iodine is used in chemical analysis. It gives .a deep blue color
when it comes in contact with starch and can be used to show traces of starch in plant tissues. A compound of iodine and potassium, called potassium iodide, is used in making photographic film.
Iodine combines with sulfur, phosphorus, iron and mercury. Most
of its reactions involve capturing an electron from a metal atom, oxidizing the metal in the process. Iodine can also give up an electron and become positively charged.
Iodine has the chemical symbol I. Its atomic number is 53 and its atomic weight is 126.9044. Iodine melts at 113.5 degrees Centigrade and boils at 184 degrees Centigrade.