The torsional rigidity and modulus of rigidity of raw silk (20°C, 65% R. H.) were tested, and the following results were obtained.
1) The modulus of rigidity of raw silk, assuming that the cross section is circular, was 1.38_??_1.49×1010 dynes/cm2 (141_??_152kg/mm2).
2) The modulus of rigidity, correcting the sectional shape, was about 1.8×1010dynes/cm2 (180kg/mm2).
3) The variation of rigidity in tension (0.08_??_0.8g/d) was not recognized.
4) The relaxation of rigidity of raw silk is considerably large in such a small torsion as 20 turns/m in the case of 21d silk. The moment is approximately lowered linearly with logarithmic time. The modulus of relaxed rigidity at 20 sec. and 1 min. after torsioning was 1.13±0.04×1010 and 1.07±0.04×1010 dynes/cm2 respectively.
5) Experimentally the same torsional moment is obtained from different denier raw silk by torsioning to the angle proportional to inverse square of denier.
6) The raw silk taken from the outer layer of cocoons has high modulus of rigidity than that taken from the inner layer.