Some Factors in the Measurement of Affinities of Vat Dyes for Cellulose

Isotherms have been obtained for the adsorption of Caledon Red BN and Caledon Red 5G by cuprammonium rayon yarn at 40c. in the presence of varying concentrations of sodium chloride and sodium hydroxide. It is shown that consistent values for the affinity of these dyes are obtained only when account is taken of the absorption of hydroxyl ions by the fibre. The use of the “equivalent chloride” ion concentration in calculating the affinity is discussed and shown to be satisfactory.