54—characterization of the Cortical Structures of Keratin Fibres by Urea-Bisulphite Solubility

The urea-bisulphite-solubility test has been examined to determine its utility for characterizing the cortical structures of keratin fibres with respect to their ortho-para natures. Low values for urea-bisulphite solubility (ca. 15%) are exhibited by human hair, previously considered a para fibre; intermediate values (45—55%) by crimped, apparel wool fibres, previously considered ortho-para with bilateral asymmetry; and high values (ca. 75%) by kid mohair, previously considered chiefly ortho. The results of measurements of rates of fibre attack by the urea-bisulphite reagent and of microscopical observations of the treated fibres are in accord with these views. The urea-bisulphite solubilities have also been measured for B.A. fleece and Lincoln wools, cashmere, vicuna, and alpaca; the results are discussed. The effect of prior heating of a crimped, apparel wool has been found to be that of decreasing urea-bisulphite solubility; the solubility decreases smoothly with increasing times of heating, and the effect is found not to be reversible by a mild wetting-out treatment. In a series of experiments, wherein urea-bisulphite solutions were stored at 21°C for varying times up to ca. 530 hr, marked losses in the reducing power of the urea-bisulphite reagent are found and these losses are paralleled by corresponding reductions in the solubility of a crimped, apparel wool in the reagent. The kinetics of this reagent decomposition appear to be zero-order with respect to stoichiometric sulphite. Solutions containing bisulphite in the absence of urea have been found to be far more stable over the same periods of storage.