Iodine, No.53 in the Periodic Table of Elements, is one of the halogen elements in Group ⅶ A of the Periodic Table of Chemical Elements. Elemental iodine was first discovered by French pharmacist Courtois B. in 18 1 1 year. Element iodine is a purple-black crystal, which is easy to sublimate and condense after sublimation. Toxic and corrosive. Iodine turns blue-purple when it meets starch. Mainly used in the manufacture of drugs, dyes, iodine, test paper and iodine compounds. Iodine is one of the essential trace elements for human body. The total amount of iodine in healthy adults is 30mg (20 ~ 50mg), and the national salt iodization standard is 20-30mg/kg.