Iodine

Iodine was first observed by Bernard Courtois, a French chemist engaged in saltpetre (KNO₃) manufacture. He used seaweed ash as his source of potassium. One day, in 1811, he added sulfuric acid to saltpetre and was surprised to see purple fumes. When he repeated the reaction in a retort, the fumes condensed to give beautiful black crystals with a metallic lustre. Courtois suspected that this was a new element, and it was soon proved to be so by Joseph Gay-Lussac, who based the element's name on the Greek word iodes, which means violet-like.