For the photo, a tiny grain of iodine was applied over an object slide with a cover slip on top. After gently melting it over a spirit flame and then solidifying, a crystal structure appears, which can be seen with the help of polarization.
Iodine was discovered in 1811 by the French chemist Barnard Courtois. Courtois was extracting sodium and potassium from the ashes of seaweed. Once these substances were removed, he added sulfuric acid (H2SO4) for the further processing of the ash. Once he accidentally added too much sulfuric acid, so that a brightly colored cloud escaped from the ashes. The gas condensed on metal objects in the room and formed pure iodine. Currently, iodine is extracted from deposits of various substances (NaIO3 and NaIO4) in Chile and Bolivia.
People need certain amounts of iodine to keep their body healthy. Iodine is a part of the hormone thyroxine, a hormone that regulates the physical and mental development of the human body. Iodine deficiency can cause thyroid swelling. To prevent this, iodine is nowadays added to table salt. It is an ingredient of bread, sea fish and oceanic flora. Iodine is naturally present in the ocean and some plants and animals store it in their tissues. Many medicines and cleaning products for skin wounds contain iodine. It is also a component of water purification tablets that are used in drinking water preparation.
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