It’s chemistry time again, folks… Today we celebrate the birthday of Bernard Courtois (8 Feb 1777 – 27 Sep 1838), the French chemist from Dijon who discovered iodine.

Iodine, courtesy of Bernard Courtois.(© All Rights Reserved)
Iodine, courtesy of Bernard Courtois.
(© All Rights Reserved)

Courtois’ father worked as a saltpeter manufacturer, and instilled in his son an interest in chemistry and pharmacy. He studied pharmacy and, while working with Armand Seguin at the Ecole Polytechnique, he investigated opium. During this period, Courtois and Seguin managed to isolate pure morphine, the first known alkaloid, from opium.

His greatest contribution, however, came after he returned to Dijon to assist in his father’s saltpeter business. Traditionally, wood ash was used as the source of potassium nitrate for the saltpeter, but due to a wood ash shortage they turned to using seaweed as an alternative source. In 1811, while extracting sodium and potassium extracts from seaweed ash, Courtois accidentally stumbled upon a new element – adding sulfuric acid to the ash resulted in the appearance of a beautiful violet vapor that condensed into deep violet crystals resembling graphite.

Iodine has since proved an important trace element in human and animal biology. It is a key constituent of the thyroid hormones thyroxine and triiodothyronine. The thyroid gland requires about 70 µg/day to synthesize these hormones, but additional iodine (RDA 150 µg/day for adults) is necessary to support the function of a range of biological systems in the body. Since iodine is scarce in nature (it is mainly available, as Courtois discovered 200 years ago, in ocean-based sources such as seaweed) it is often included as an additive in iodised salt, for example, to ensure that we get a sufficient daily dose.

Even though Courtois did not, at the time, realise that he had discovered a new element, he was subsequently acknowledged as the true discoverer of iodine. In 1831 he received the Montyon Prize from the L’Academie royale des sciences for his work. He never gained any financial benefit from his discovery, though, and his obituary in the Journal de chimie médicale strikes quite a sad note:

“Bernard Courtois, the discoverer of iodine, died at Paris the 27th of September, 1838, leaving his widow without fortune. If, on making this discovery, Courtois had taken out a certificate of invention, he would have realized a large estate.”

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