Iodine's discovery... Science

An eye for iodine

We’ll stay with France this time around as well, but move from the first-manned flights to the depths of the oceans and the seaweeds that gather along the coasts. For, these seaweeds turned out to be one of those unlikely places that yielded a new element and led to the serendipitousdiscovery of iodine.

Born in 1777, Bernard Courtois was the son of Jean Baptiste Courtois. Despite being a saltpeter manufacturer, Jean Baptiste regularly assisted Guyton de Morveau, a lawyer, in his oft-praised chemistry lectures. Courtois hence divided his time between his father’s saltpeter works and the Academy’s laboratories.

Courtois took to his limited opportunities to dabble with pure chemistry with enthusiasm. It was perhaps this approach that ultimately led to his discovery, even though he had minimal resources.

Accidental discovery

On one occasion in 1811, Courtois was working with seaweed ash, which was valued for its sodium and potassium compounds. To process the ash and extract these compounds, Courtois added sulphuric acid, which was used to destroy the sulphur compounds.

On this particular day, Courtois added more acid accidentally, giving rise to lovely clouds of violet vapour, accompanied with an irritating odour, similar to that of chlorine. The gas produced condensed on cold objects in the room, with a lustre similar to that of a metal.

Courtois observed that this substance did not readily combine with oxygen or carbon to form compounds, but instead reacted with hydrogen and phosphorous. It formed an explosive compound with ammonia and decomposed at red heat.

Confirmation and announcement

Even though Courtois noticed these distinct properties and suspected the presence of a new element, he believed that he lacked the necessary equipment for a thorough investigation. He therefore asked two of his friends from Dijon, Charles Bernard esormes and Nicolas Clement, to continue his research in their laboratories.

While Desormes took to applied chemistry, Clement continued the research pertaining to Courtois’ discovery. He was able to prepare the new substance by following Courtois’ instructions and also extensively study its properties.

Clement believed this new element was similar in nature to chlorine, which was confirmed independently by Joseph-Louis Gay-Lussac and Sir Humphry Davy. It was Gay-Lussac who suggested the name iode, the Greek term for violet, after the purple hue in its vapours.

On November 29, 1813, Clement announced the discovery of iodine at the French Institute, in the name of it’s discoverer, Courtois. Courtois, however, gained little from his discovery during his lifetime, and eventually died in poverty. It might now be an essential part of nutrition and medicine, but iodine did little to alleviate the difficulties endured by its discoverer.


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Printable version | Jul 29, 2021 12:23:34 AM | https://www.thehindu.com/in-school/sh-science/An-eye-for-iodine/article16726304.ece

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