Relations between Small-Angle Interferences of Silk and the Wax Content

Abstract

IN previous papers¹ it has been established that alkali treatment of fresh preparations of silk fibroin gives rise to the appearance of new equatorial small-angle reflexions which were believed to be higher orders of a ground-period of 45 A. At first this effect was ascribed to a structural change of the silk lattice. Continued investigations, however, made it very likely that the new reflexions are due to some waxy substances. This assumption has now been confirmed by means of the following experiments: (1) The new reflexions disappear if the sample is treated with 1: 1 ether–alcohol for 8 hr. at 40° C. (2) After removing the solvent by evaporation, a waxy substance (1.6 per cent of the weight of the degummed silk) is obtained. This is in good accordance with the data of other authors, who have found 1–2 per cent wax in Bombyx mori silk². The extracted substance shows sharp reflexions corresponding with the net-plane distances given in column 2 of the accompanying table. Column 1 gives the net-plane distances of alkali-treated fresh silk samples, and shows the good accordance between the inner reflexions of the extract and the strongest ones of the alkali-treated silk. The outer reflexions of the extract identify the substance as probably a wax. It is to be noticed, however, that the reflexion corresponding to the smallest angles is not so sharp. (3) Extracting the alkali-treated silk with ether–alcohol gives also a waxy residue (1.6 per cent of the degummed silk) showing practically the same diagram as is described under (2). (4) The ether–alcohol solution shows absorption bands in the ultra-violet at 3,700 and 4,400 mm.⁻¹ which are characteristic for conjugated unsaturated fatty acids. The extracted fat (or wax) contained 0.8 per cent conjugated dienes and 0.2 per cent trienes.