Iodine number of wool: A method for determining the action of various chemical reagents on wool and other proteins

Abstract

The purpose of this research was to find a method for determining the action of various chemical reagents upon wool. The iodine number provides a qualitative measure of the extent to which the amino groups are affected by various treatments of the protein. Amino acids and proteins exhibit iodine numbers as determined by the standard method. The iodine numbers of such substances do not indicate ordinary unsaturation but are shown to be related to the free amino nitrogen content. The iodine numbers of some typical proteins are reported and a general correspondence between the iodine numbers and the isoelectric points of the proteins is shown. Conversion of amino groups to hydroxyl groups, combination of amino groups with strong acids, and other chemical reactions which affect the amino groups reduce the iodine numbers of amino acids (with the exception of cysteine) to zero. Part of the iodine number of wool is shown to be due to cysteine which is very susceptible to oxidation. The iodine number of wool is therefore affected by reactions of chemical reagents with the amino or the cysteine groups. This method will distinguish, for example, between reversibly adsorbed and chemically combined acid. The latter can be removed by the action of an alkali and this restores the original iodine number of the wool.