Investigations on the Browning of Scoured Silk. (Ⅲ) On the cause of browning occured by the action of sunlight.

We have studied on the browning of those silk. silk in vacuum， and paper which was purposely made to contain tyrosine under the exposure to the sunlight and ultra-violet rays. From the results obtained the browning that occured on the boiled-off silk by the action of sunlight can be deduced as follows. It seems that the browning occurs mainly by melanin and the like which is produced by the oxidation of tyrosine, i.e. the phenol group of tyrosine in the silk becomes active by the absorbtion of ultra-violet rays ;on the other hand oxygen and moisture which are contained in air as well as in fibres become also active. Here upon the active oxygen and moistue oxidise the activated tyrosine. In addition to this other amino acids contained in the silk fibre and such impurities as ca-soap on the fibre can also be oxidised and cause the browning of fibre feebly