BLEACHING OF SILK AND OTHER FABRICS Raw silk has a comparatively dull appearance, which is due to the coating of sericine or silk gum, which is present to the extent of about 19-25%. This is removed by treating the silk with 3o% of its weight of soap dissolved in water and heated to a tempera ture just below the boiling point for about three hours. The gum is ultimately dissolved and leaves the fibre substance (fibroin) with the characteristic lustre. The silk is then rinsed in weak soda solution and is suitable for dyeing, but if it is to be sold as white the material in the hank form is tied with tape and put into coarse linen bags and boiled in soap solution half as strong as the first. Whitening is effected by stoving, as in the case of wool, but blueing or otherwise tinting is effected after stoving. Bleaching with hydrogen peroxide is only adopted for certain kinds of spun silk and tussore.
Ornamental feathers are best bleached by steeping in hydrogen peroxide rendered alkaline with a little ammonia, and the same treatment is applied to the bleaching of ivory. Hydrogen peroxide is a very efficient bleaching agent, and can be applied with safety to both animal and vegetable substances. It is the active con stituent (or is produced in solution) of a number of preparations sold in powder form for household bleaching. The more extensive application of hydrogen peroxide is largely a matter of cost.
(E. Hr.)