What Is It?
Iodine and its compounds are primarily used in medicine, photography and in dyes. Although
it is rare in the solar system and Earth's crust, the iodides are very soluble in water, and
the element is concentrated in seawater. This mechanism helps to explain how the element came
to be required in trace amounts by all animals and some plants, being by far the heaviest
element known to be necessary to living organisms.
Iodine was discovered by Bernard Courtois in 1811. He was born to a manufacturer of
saltpeter (a vital part of gunpowder). At the time of the Napoleonic Wars, France was at
war and saltpeter was in great demand. Saltpeter produced from French niter beds required
sodium carbonate, which could be isolated from seaweed washed up on the coasts of Normandy
and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash then washed
with water. The remaining waste was destroyed by adding sulfuric acid. One day Courtois
added too much sulfuric acid and a cloud of purple vapor rose. Courtois noted that the
vapor crystallized on cold surfaces making dark crystals. Courtois suspected that this
was a new element but lacked the money to pursue his observations.
However he gave samples to his friends, Charles Bernard Desormes (1777–1862) and Nicolas
Clément (1779–1841), to continue research. He also gave some of the substance to Joseph Louis
Gay-Lussac (1778–1850), a well-known chemist at that time, and to André-Marie Ampère
(1775–1836). On 29 November 1813, Dersormes and Clément made public Courtois’ discovery.
They described the substance to a meeting of the Imperial Institute of France. On December 6,
Gay-Lussac announced that the new substance was either an element or a compound of oxygen.
Ampère had given some of his sample to Humphry Davy (1778–1829). Davy did some experiments on
the substance and noted its similarity to chlorine. Davy sent a letter dated December 10 to
the Royal Society of London stating that he had identified a new element. A large argument
erupted between Davy and Gay-Lussac over who identified iodine first but both scientists
acknowledged Courtois as the first to isolate the chemical element.
Much more than Iodine is discussed back at the Natural Source Vitamins Homepage