pH titrations with KOH were made of fibroin, alkali treated fibroin and urea formaldehyde resin treated Fibroin. During alkali treatment, new groups are produced. The active groups in resin treated fibroin seem to be changed. From the slope of titration curve, we may judge the degree of denaturation and the degree of the effect of resin finishing. The addition of metal ions lowers the pH titration curve of fibroin in the presence of KCl. The addition of metal ions to o-aminobenzoic acid which

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... s free amino and carboxyl group lowers greatly the lower pH buffer region and appreciable chelation occures even in the strong acid region. The pH titration curves of glycine anhydride show that no chelation occures in the cases of Cu and of Al. Interaction of o-aminobenzoic acid with Cu and Al is greater than that of Fibroin with the same metals. Experiments were made in order to investigate the effect of introduction of chelate bond to silk fibroin on mechanical and dyeing properties. Following the method mentioned in the previous report, the authors made pH titration on silk fibroin with and without heavy metals in the presence of KCl. Then the strength and elongation of the fibroin treated with heavy metals in various pH solutions were compared with those of the same fibroin in the corresponding pH solutions without metals. The strength of the treated fibroin increases in acidic region in all cases in comparison with those of the fibroin untreated and treated without heavy metals. The elongation has a tendency to decrease. Chelation seems to be produced in fiber, as the strength of the fiber increases in the pH region where we may expect to occure chelation. Chelation did not show bad effects on dyeing in the cases of Sunchromine Brown R H cone. and of Alizarine Red S. Cu, Al, and Fe were used as heavy metals throughout those experiments. (Received 23. 5. 1956)