Iodine, a nonmetallic element, element symbol I, element 53 in the periodic table of elements, is in the fifth cycle in the periodic table of chemical elements, and is one of the VII A and halogen group elements. In 1811, the French pharmacist Kuteva first discovered simple iodine. The elemental iodine is purple-black crystal, easy to sublimate, easy to sublimate after sublimation, toxic and corrosive. Simple iodine will turn blue and purple when it meets starch. It is mainly used for making drugs, dyes, iodine wine, test paper and iodine compounds.
Iodine is one of the essential trace elements of human body. The total amount of iodine in healthy adults is 30 mg (20~50 mg). The national standard for adding iodine to salt is 20-30 mg/kg. Iodine is a component of thyroid hormone and plays different physiological functions through thyroid hormone, mainly including promoting growth and development, participating in brain development, regulating metabolism, etc.
In 2021, the iodine-powered spacecraft completed the in-orbit test for the first time.
At the end of the 18th century and the beginning of the 19th century, the French emperor Napoleon launched a war that required a large amount of potassium nitrate to produce gunpowder. At that time, most of the potassium nitrate ores in Europe were from India, but the reserves were limited. Europeans found a large number of saltpeter deposits from Chile in South America, but its composition is sodium nitrate, which is hygroscopic and not suitable for manufacturing gunpowder. In this case, in 1809, a Spanish chemist found a way to convert natural sodium nitrate or other nitrates into potassium nitrate by using the solution of seaweed or algal ash. Because seaweed or seaweed contains potassium compounds.
At that time, Kurtuva, a saltpeter merchant and pharmacist in Dijon, France, produced potassium nitrate in this way. He uses the solution of seaweed ash to react with calcium nitrate. During a period in 1811, he found that the copper container containing seaweed ash solution was soon corroded. He believed that the seaweed ash solution contained an unknown substance that interacted with copper, so he conducted a study.
He poured sulfuric acid into the seaweed ash solution and found that a beautiful purple gas was emitted. This gas does not form liquid after condensation, but turns into dark crystal with metallic luster.
On the discovery of iodine in Kurtuva, the first issue of Nature published by the former Soviet Union in 1947（ природа) In the magazine, there is a signed article "On the History of Roentgen Ray Discovery", It mentioned the discovery of iodine: "... Kurtuva at work has two glass bottles, one for his pharmaceutical use, containing seaweed ash and alcohol, and the other containing the solution of iron in sulfuric acid. Kurtuva is eating, and a male cat jumps onto his shoulder. Suddenly, the male cat jumps down and knocks down the sulfuric acid bottle and the medicine bottle juxtaposed together. The vessel is broken, the liquid is mixed, and a ray of blue and purple gas rises from the ground..."
Chemical reaction principle: when sulfuric acid meets the alkali metal iodide contained in seaweed ash - potassium iodide (KI) and sodium iodide (NaI), hydrogen iodide (HI) is generated.
It reacts with sulfuric acid to produce free iodine:
H2SO4 + 2HI → 2H2O + SO2 + I2↑
The lack of potassium nitrate to make gunpowder in France during Napoleon's war is the historical condition for the discovery of iodine. The abundance of iodine in nature is not large, but everything contains iodine. No matter the hard earth or rock, or even the purest transparent crystal, there are quite a lot of iodine atoms. The sea water contains a lot of iodine, the soil and running water also contain a lot of iodine, and the animals, plants and human body contain more iodine, which is the internal cause of iodine discovery.
Kurtuva has been engaged in the production of potassium nitrate from iodine-containing seaweed ash for a long time. He accidentally obtained iodine because he was able to grasp the accidental discovery, but also because he had certain chemical knowledge and strong thirst for knowledge, rather than an ordinary saltpeter manufacturer. In 1813, he published the paper "Discovery of New Substances in Seaweed Ash", and sent the iodine he obtained to the French chemists Clemen, Desomet, and Galisac for research and identification, which was affirmed by them.
It is Gallusac who named it iode, which comes from the Greek word purple. The Latin name of iodine and the element symbol I are obtained.
People have not forgotten Kurtuva's contribution. A street in Dijon is named after his surname. Only a few people who discovered chemical elements have won such honor.