BLEACHING OF Woof, is never accomplished by B. powder. but recourse is bad to sulphurous acid, which disguises the color of the wool by combining with it to form a colorless compound. Originally the wool is contaminated with a greasy substance called the yolk, which naturally exudes from the skin of the sheep, and this unctuous matter mainly consists of a kind of soap soluble in water. The first stage in the B. of W. is to get rid of the yolk, which can be done by long-continued washing in water; but as this is tedious, the general plan is to steep the wool in a vat containing one part of stale urine and five parts of water, then boil for some time, and ultimately strain the wool and wash well. The agent in the stale urine which acts upon the yolk is carbonate of ammonia, and this acting upon the oily matters forms a soap which can be readily washed away. NVIten woolen cloth is to be bleached, it is customary to substitute .carbonate of soda (washing soda) for the stale urine, and this forms an alkaline lye,, which performs the same part as the carbonate of ammonia. Soap is sometimes used an auxiliary. The second stage of bleaching wool is the sulphuring, which takes place in a small wooden apartment, in which the damp cloth is suspended in regular folds from the roof to the floor, and a small pan of ignited sulphur being introduced, the doors, etc., are firmly closed. There are little openings round the sides of the chamber, for the admission of air, which can be closed at pleasure. The sulphur (S) in burning take up two atoms of oxygen from the air, forming sulphurous acid (SO,), which is the bleaching agent; and in about 24 hours the operation is finished, and the woolen material only requires to be thoroughly washed with water, which may contain a little potash or soda. Where
the wool is naturally high-colored, it is necessary to repeat the various stages of the pro cess several times before the bleaching is complete. Instead of applying sulphurous acid in the gaseous form, a solution of it in water is sometimes used. An economical method of preparing the solution of sulphurous acid is to introduce a mixture of sulphate of iron and sublimed sulphur into an earthenware retort, and apply a low red heat, when sulphurous acid is disengaged. which is passed through a vessel containing some porous matter, such as moss, to retain mechanical impurities, and then transmitted through a series of bottles containing water, where it is dissolved to the extent of forty volumes of the gas for every one volume of the water. The bleaching of wool by sulphur , acid is not so complete as the bleaching of cotton or linen by chlorine. In the er case, the color is destroyed, but in the former, the sulphurous acid merely com 1 .es with the coloring matter to produce a colorless compound, from which the color ..n again be revived, culler by soaking the wool in a dilute acid, such as sulphuric acid, (- a dilute alkali, such as soda. Hence it is that new woolen cloth or garments, such as flannel, blankets, and underclothing, though almost colorless when purchased, yet after being washed several times, return to their natural yellow; for the soda used, as well as the soap which contains potash or soda, destroys the colorless compound formed in the texture of the wool during the sulphuring, and resuscitates the original color.