Bleaching
2 of the 6 encyclopedias on this shelf carry an entry for Bleaching. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
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.
Collier's New Encyclopedia (1921)
Important: Safety Warning
This page directs the use of hazardous substances — such as benzine, gasoline, lye, or strong acids — for household tasks. These materials are highly flammable, corrosive, or poisonous, and the practices described have caused fires, burns, and poisonings.
This information has been left in for historical purposes but should not be acted upon.
the art of rendering materials colorless. This is done by exposing them to the actinic rays of the sun, or by the action of bleaching agents. The chief of these is called bleaching powder. It is chloride of lime, and is prepared by exposing moistened quickpre lime to the action of chlorine, when hypochlorite and chloride of calcium are formed, the former being the bleaching agent. By the action of an acid on good bleaching powder 30 per cent. of chlorine is liberated. Substances are bleached by alternately dipping them in dilute solutions of bleaching powder and of dilute sulphuric acid. Bleaching powder is also used to purify an offensive or infectious atmosphere.
What Has Changed in the Last Century
Aiton's 1910 account still had one foot in the bleachfield, noting that crofting linen took thirty-one days and was practiced widely in Scotland and Ireland; commercial grass bleaching has since vanished entirely, and the chloride-of-lime powder both entries treat as the master agent has largely been displaced by liquid sodium hypochlorite and, in industry, by hydrogen peroxide. The biggest shift came in the late 1980s, when dioxins were found in effluent from chlorine-bleached wood pulp; mills moved to chlorine dioxide (elemental-chlorine-free) or oxygen and peroxide (totally chlorine-free) processes, exactly the trend the editor's note describes. A change neither entry could anticipate is that much modern "whiteness" is not bleaching at all: fluorescent optical brighteners, added to detergents and papers from the 1940s onward, absorb ultraviolet and re-emit blue light so fabric merely looks whiter. Collier's remark that bleaching powder can "purify an offensive or infectious atmosphere" survives in altered form as hypochlorite surface disinfection, though airborne use is now discouraged as a respiratory hazard.
Written for this edition, 2026.