<P> 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 provides about one mg of free iodine per drop . </P> <P> 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 . </P> <P> 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 I . 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 . </P> <P> As both USP solutions contain elemental iodine, which is moderately toxic when ingested in amounts larger than those required to disinfect water, tincture of iodine is sold labelled "for external use only," and used primarily as a disinfectant . </P>

What is the solvent in tincture of iodine