Tincture of iodine, iodine tincture, or weak iodine solution is an antiseptic. It is usually 2 to 3% elemental iodine, along with potassium iodide or sodium iodide, dissolved in a mixture of ethanol and water. Tincture solutions are characterized by the presence of alcohol. It was used from 1908 in pre-operative skin preparation by Italian surgeon Antonio Grossich.[1][2] In the United Kingdom, the development of an iodine solution for skin sterilisation was pioneered by Lionel Stretton. The British Medical Journal published the detail of his work at Kidderminster Infirmary in 1909.[3] Stretton used a much weaker solution than that used by Grossich. He claimed in 1915 that Grossich had been using a liquid akin to Liquor Iodi Fortis, and that it was he, Stretton, who had introduced the method using Tincture of Iodine BP which came to be used across the world. [4] USP formulas See also: United States Pharmacopeia USP Tincture of Iodine is defined in the U.S. National Formulary (NF) as containing in each 100 mL, 1.8 to 2.2 grams of elemental iodine, and 2.1 to 2.6 grams of sodium iodide. Alcohol is 50 mL, and the balance is purified water. This "2% free iodine" solution has 0.08 mol/L of I2, which provides about 1 mg of free iodine per 0.05 mL drop. The "2% free iodine" description is based on the quantity of elemental iodine, not sodium/potassium iodide.[citation needed] USP Strong Iodine Tincture is defined in the NF as containing in each 100 mL, 6.8 to 7.5 gram of iodine, and 4.7 to 5.5 gram of potassium iodide. Purified water is 50 mL and the balance is alcohol. This 7% tincture solution is about 3.5 times more concentrated than USP 2% tincture.[citation needed] As in the case of Lugol's iodine, the role of iodide in the solution is to increase the solubility of the elemental iodine, by turning it to the soluble triiodide anion I3−. However, since iodine has moderate solubility in ethanol, it is also assisted by this solvent directly. Lugol's iodine, by contrast, has no alcohol, and has twice the mass of potassium iodide as of elemental iodine. Alcohol content in the tincture of iodine can be determined by the methods of Alcock, Roscoe – Schorlemmer and Thurston – Thurston