The Relative Germicidal Activity of Triiodide and Diatomic Iodine

A freshly prepared aqueous solution of iodine at a pH less than eight will contain mainly two forms of free iodine, namely diatomic iodine, I2, and triiodide, Ii,. The ratio of these two forms is determined by the concentration of iodide which is usually added to bactericidal prepaa-tions for the purpose of increasing the solubility of the iodine. The solubility of diatomic iodine at 25 C is 0.034 per cent. In the presence of an iodide salt like potasium iodide the solubility of free iodine may be increased several hundred-fold, the increase being in the form of triiodide according to the equation: (1) Ta+ 1- Ir. A quantitative investigation of the relative sporicidal activity of diatomic iodine and tri-