Deep purple, metallic looking solid which readily gives off a violet colored vapor m.p. 113.5 ºC; 236.3 ºF b.p. 184.35 ºC; 363.83 ºF density (gas) 0.01127; (solid) 4.93 g/cc; (gas) 0.70356; (solid) 307.77 pound/cubic foot	memory peg
	1811 Bernard Courtois, France
	ιοειδης [ioeidès] = violet coloured (Greek)

Iodine was discovered in May 1811 by Bernard Courtois (1777-1838) in Dijon. Courtois was manufacturer of salpeter (potassium nitrate, KNO₃), a major component of gunpowder. In the early 19th century, France was at war and needed enormous quantities of gunpowder. The manufacture of salpeter requires a plentiful supply of Sodium carbonate (Na₂CO₃), which is obtained by extraction from wood ashes. Wood ashes was made from seaweed, gathered at the coasts of Normandy and Brittany. After the process, the various Sulphur compounds produced during calcination (burning), were destroyed by adding sulphuric acid. In 1811 Courtois accidentally added excess sulphuric acid resulting in a violet vapor cloud that condensed on colder objects forming dark, lustrous crystals. He observed that the new substance combined with Hydrogen, Phosphorus and certain metals but not readily with Oxygen or Carbon. It did not decompose under red heat, but formed an explosive with ammonia. (note)

Courtois suspected it was a new element, but because of lack of money he had to turned over further investigation to his friends, the French physicist and chemist Charles-Bernard Désormes (1777-1862), who did almost all his scientific work in collaboration with his son-in-law Nicolas Clément (1779-1841). They announced the discovery on 29 November 1813 at a meeting of the Imperial Institute of France.

Other specimens were given by Courtois to Louis-Joseph Gay-Lussac (1778-1850) and André M. Ampère (1775–1836). On 6 December 1813 he suggested that the new substance was either an element or a compound of oxygen.

In the mean time, Ampère had given his sample to the English chemist Sir Humpry Davy (1778-1829), who visited Paris travelling to Italy. Davy always carried a compact chest of laboratory apparatus when he traveled and did some experiments with this samples. He sent off a paper to the Royal Society of London, dated 10 December 1813 (note), describing his experiments and recognizing the similarities between the new substance and Chlorine. He named it Iodine, after the Greek ιοειδης [ioeidès] = violet coloured (from ιον [ion] = violin), which was analogous to Chlorine and Fluorine. Although a quarrel over priority rights followed, Gay-Lussac and Davy both acknowledged Courtois as the discoverer of Iodine. Gay-Lussac’s major publication on Iodine was read on 1 August 1814. He named the new element Iode.

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 708-719.
• Louis Rosenfeld, "Discovery and Early Uses of Iodine." Chemistry for everyone. Journal of Chemical Education, Vol. 77 No. 8 August 2000 (pdf-file on-line)