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A dark color crystalline element of the halogen family. Iodine was discovered in 1811 by Bernard Courtois while studying Kelp. It has an abundance of 300 ppb in the earth's crust and 0.3 ppb in seawater. Iodine is commercially extracted from Caliche (Chile, Japan, Indonesia, Michigan, Oklahoma) and Seaweed. Crystalline iodine occurs as dense, shiny, bluish-black plates or granules. It sublimes at room temperature forming a corrosive violet vapor. Iodine dissolves in aqueous solutions containing inorganic iodide salts to form a dark brown solution. These solutions are used as indicators for the presence of Starch. Iodine reacts with Amylose to form a dark blue color and with Amylopectin to produce a red to purple stain (Book and Paper catalog). It will form a brown stain on raw Cotton and a blue stain on Mercerized cotton. Alcoholic iodine solutions were used for over a century as antiseptics and germicides. It is still used as an additive to salt (iodized salt) and as tablets to sterilize drinking water. Iodine is also used in dyes, x-ray contrast media, photographic film, printing reproductive processes, and as a reagent to detect unsaturation in organic compounds.

Synonyms and Related Terms

I; Jood (Ned.); iode (Fr.); Iod (Deut.); iodio (It.); Iodo (Port.); yodo (Esp.); Jod (Sven.)


  • Toxic by ingestion and inhalation. Skin contact causes irritation and burns.
  • ThermoFisher: SDS

Physical and Chemical Properties

Soluble in ethanol, chloroform, ether, carbon disulfide, carbon tetrachloride, glycerol, acetic acid. Insoluble in water.

Composition I (atomic no. 53)
CAS 7553-56-2
Melting Point 113.5-113.6 C
Density 4.98 g/ml
Molecular Weight atomic wt = 126.9045
Boiling Point 184-185 C

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Book and Paper Group, Paper Conservation Catalog, AIC, 1984, 1989
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976 Comment: discovery = 182
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 5034: discovery = 1811
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998 Comment: discovery = 1811
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979