Bleaching

the process of whitening, or removing the natural greyish or yellowish color from new linen, silk, cotton cloth, chip hats, nuts, etc. It is the opposite of dyeing. The Egyptians appear to have employed a method of bleaching by means of weak lye. The method of bleaching corresponding in age to the historic hand loom is the simple one of dipping a web of cloth in water, or else sprinkling it with water and spreading it out on a grass plot to dry. Dew was supposed to be particularly serviceable. This process of sprinkling and drying was kept up sometimes for weeks to obtain the desired degree of whiteness.

Linen holds its vegetable yellow more tenaciously than cotton, but it is exquisitely white at the last. Under the impression that the waters or else the climate of Haarlem were especially suited, British linen, particularly Scotch linen, was long sent to Holland for bleaching. It was retained for a year or so and was known in the trade as Hollands.

The old picturesque methods of the hand loom and grassy bleaching plot have given way in most places to bleaching in large factories by a chemical agent. Grass bleaching, or "crofting" as it is called technically, is still practiced extensively in both Scotland and Ireland. The process includes a number of boilings, rubbings, and lye baths, besides the actual exposure of the fabric to sun and air. Thirty-one days are required for crofting linen. Many housekeepers still prefer to buy unbleached sheeting and trust to repeated launderings to make the cloth white, claiming that the cloth is stronger than that bleached by modern chemical methods.

The details of the modern bleaching processes are chiefly those of steaming, steeping, boiling, and washing in chlorine water and other lye and cleansing waters. The webs of cloth are sewed together in one continuous piece measuring from 300 to 1,000 yards in length. This cloth is drawn through the various solutions by the action of rollers on which it is wound.

Chlorine is prepared for use by introducing chlorine gas into a chamber, the floor of which is covered with pure slaked lime. By dint of occasional stirring the lime absorbs over half of its own weight of chlorine. Large factories at Niagara Falls are employed in the production of this chloride of lime or bleaching powder for use in linen and cotton mills.

If either cotton or linen is to be printed, it must be bleached until chemically pure, or the action of the coloring matter may be interfered with. This is called "print-bleaching." If it is to remain plain white, it need be bleached only until it satisfies the eye. This is "white bleaching."

Wool and silk are bleached with sulphur. The goods are hung in the upper part of a close room called a "sulphur stove," and subjected to the fumes of burning sulphur. The natural coloring matter is not destroyed by this process, but the sulphur combines with the coloring matter to produce a colorless compound. If wool or silk fabric bleached by this process is subjected to several washings with soap containing potash, this colorless compound is destroyed and the natural yellowish color of the fiber reappears. This is why wool and silk are said to "grow yellow" by washing.