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Courtois was born in Dijon and grew up in the prestigious surroundings of his father's workplace at the Dijon Academy. The Academy, where the family lived, was a small hotel that had been converted for scientific studies. Courtois' father, Jean-Baptiste, worked for the chemist Louis-Bernard Guyton de Morveau as well as for the Academy as a pharmacist and was called by his family pharmacien de l'Academie. When Courtois was twelve the family moved to the Saint-Medard Nitrary, an experimental nitrate plant which Jean-Baptiste bought from Louis-Bernard Guyton de Morveau and his partner.[2]

Courtois and his brother Pierre learned the trade of making potassium nitrate for gunpowder for the French Revolution. Courtois, however, branched off from this venture to learn chemistry. Courtois lived at Saint-Medard Nitrary until he was about eighteen, when he left his family home to begin his trade apprenticeship in chemistry in Auxerre. Here for three years he was a student of M. Frémy, the future grandfather of Edmond Frémy. He then obtained a position with Antoine-François de Fourcroy at the École Polytechnique in Paris. In 1799 Courtois served as a pharmacist in military hospitals. In 1801 he returned to the École Polytechnique to work in the laboratory of Louis Jacques Thénard.[3]

In 1802, Courtois worked with Armand Séguin at the École Polytechnique on the study of opium. In conjunction with Séguin, Courtois isolated morphine, the first known alkaloid, from opium. Séguin presented his first memoir on opium to the French Institute in 1804.[4] L. G. Toraude adds a note at the end of the biography of Courtois:

“

There is one point, I am afraid, which seems to me has not been extended or explained sufficiently in the course of this study. It is about the participation of Courtois in the discovery of morphine. Although Courtois had been, on this occasion, his direct collaborator, Séguin nevertheless did not name him ... Yet, two testimonies of totally different character seem right to confirm it: one, a testimony from the scientist Frémy who relates in one of his letters that he has seen Courtois trying to produce the organic alkalis artificially; the other, a testimony of an illiterate person who is none other than the widow of Courtois and who writes 20 years after the death of her husband : he was a salpêtrier under the reign of Napoléon. For a long time, he gave himself up to serious work on morphine. These are two testimonies of great significance in our eyes and not to be disregarded.[5]

”

Séguin's and Courtois' opium research came to an end at the École Polytechnique in 1804. Courtois then went to his father's business in Paris for making potassium nitrate. By 1805 his father's business was failing and he was put in debtors' prison until the end of 1807. Courtois managed the family business meanwhile until his father was released. No details are known of the demise of Courtois' father after his release. Courtois is recorded as a Parisian businessman in 1806 as a salpêtrier. In 1808 Courtois married the daughter of a Parisian hairdresser. Records show he continued to operate the family saltpeter factory until 1821, with the possible exception of years 1815, 1816, and 1817.[6]

By 1811 the war had made the government-controlled saltpeter business taper off since there was by then a shortage of wood ashes with which potassium nitrate was made. As an alternative, the needed potassium nitrate was derived from seaweed that was abundant on the Normandy and Brittany shores. The seaweed also had another, yet undiscovered, important chemical. One day towards the end of 1811 while Courtois was isolating sodium and potassium compounds from seaweed ash, he discovered iodine after he added sulfuric acid to the seaweed ash.[7] He was investigating corrosion of his copper vessels when he noticed a vapor given off. It was in the form of an unusual purple vapor. Humphry Davy later records,

“

This substance was discovered accidentally, 2 years ago by Courtois, a Paris manufacturer. In the course of the procedure by which he obtained soda from seaweed ash, he found that the metal vessels he used were corroded and he looked for the cause, when he discovered the new substance. It appeared when a little sulfuric acid was added to the ash after extracting carbonate of soda. When the acid is concentrated enough to produce a strong heat the new substance appears as a beautiful violet vapor and condenses in crystals which are the color and lustre of graphite.

Courtois was acknowledged by Humphry Davy and Joseph Louis Gay-Lussac as the true discoverer of iodine. He went into manufacturing high-quality iodine and its salts in 1822. In 1831 he was awarded 6,000 francs as part of the Montyon Prize by L'Academie royale des sciences for the medicinal value of this element. He struggled financially for the rest of his life and died September 27, 1838. He was 62 years old and had no assets left for his widow or son.[8] In the year of his death, the Journal de chimie médicale drily noted his passing under the heading Obituary as:

"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."[9]