Historedia
EuropeEvent

Bernard Courtois discovers iodine

When
1811–1813
Where
Normandy and Brittany shores; Imperial Institut de France; Paris
Episodes
4

Bernard Courtois discovered iodine in 1811 while producing saltpetre from seaweed ash. Gay-Lussac identified it as a new element in 1813, naming it after the Greek word for violet. Desormes and Clément publicized the discovery, and Davy and Gay-Lussac acknowledged Courtois as the true discoverer.

Episodes

  1. 1811 · Normandy and Brittany shoresDiscovery from Seaweed Ash

    Courtois discovered iodine in late 1811 by adding sulfuric acid to seaweed ash while producing saltpetre.

  2. 1813 · ParisRecognition of Courtois

    Davy and Gay-Lussac acknowledged Courtois as the true discoverer despite arguments over identification.

  3. 29 November 1813 · Imperial Institut de FrancePublic Announcement

    Desormes and Clément made Courtois' discovery public at the Imperial Institut de France in November 1813.

  4. 6 December 1813 · ParisGay-Lussac Identification

    Gay-Lussac announced the substance was an element on 6 December 1813 and named it iode in 1813.

Background and detail

Background. By 1811, the Napoleonic Wars caused a shortage of wood ashes for saltpetre production. Courtois, from a family of saltpetre manufacturers, derived potassium nitrate from seaweed abundant on Normandy and Brittany shores. While isolating sodium and potassium compounds from seaweed ash, he added sulfuric acid and discovered iodine.

Recognition. Arguments erupted between Davy and Gay-Lussac over who identified iodine first. However, both ultimately recognized Courtois as the true discoverer of the element. Courtois was acknowledged by Humphry Davy and Joseph Louis Gay-Lussac as the true discoverer of iodine.

People involved

Sources

  1. Iodine Wikipedia, revision of 2026-10-01
  2. Bernard Courtois Wikipedia, revision of 2026-07-21
  3. Joseph Louis Gay-Lussac Wikipedia, revision of 2026-08-31

Machine-drafted from the cited Wikipedia passages and checked by a reviewing model, not by a human editor. Every passage cites the revision it was written from; dates and places follow those passages.