Application of the Donnan Equilibrium to the Distribution of Dye and Inorganic Ions between Wool and Solutions

Abstract

The Donnan equilibrium equations, expressed in measurable quantities, derived for wool in salt solutions in an earlier paper [3] have been extended to include dyeing equilibria. These are supported by experimental dyeings over a wide range of pH. , The wool behaves as an amphoteric ion exchanger, the charge on the fiber depending on the amount of bound anion (or vice versa). Two ways are shown for arriving at , constants describing the binding of dye anions. It is shown that while the product K_wK_d of the constants describing dye and hydrogen ion binding is constant over a wide range of dye adsorption, the individual "constants" vary with the charge on the fiber. An empirical relation is obtained to show the variation of the apparent Kd with amount of bound dye. Further, it is shown that the apparent constants vary with dye and salt concentration, and approximate activity coefficients are derived. The total number of parameters needed to fully characterize the behavior of a dye are discussed and values of these given for two dyes, C.I. 15510 and C.I. 15620.