BLEACHING OF WOOL In the case of woollen goods it is not possible to obtain the degree of whiteness which is characteristic of well bleached cot ton or linen, but considerable improvement in the appearance is effected either by treating the wool with sulphurous acid or by means of hydrogen peroxide. The first method, which is techni cally known as "stoving," consists in exposing the washed goods in a damp condition to the action of the fumes of burning sulphur. After being scoured yarn is hung, wetted, and slightly blued, and the cloth is passed slowly up and down over a number of rollers in a room in which the sulphur dioxide is produced. The goods are left overnight. This is the process which is generally adopted and which is also employed in bleaching many other kinds of animal hair, including bristles. In the case of wool, it is possible to obtain a bleach by steeping the goods in a fairly strong solution of bisulphite of soda. Whether sulphurous acid or bisulphite of soda is used for bleaching, the natural colour of the wool returns on washing with soap. A more per manent bleach can be obtained by the action of hydrogen peroxide (one part of a z 2-volume solution being diluted with three parts of water), rendered slightly alkaline with ammonia or silicate of soda. Black or brown wool cannot be bleached white, but assumes a golden colour which is often desired in human hair.