Bleaching. Under this head are included general receipts for bleaching and decolorizing. The methods employed for special purposes, such as bleaching fabrics for dyeing, removing stains, etc., will be found in their proper places by reference to the index.

1715. To Bleach Cotton Pure White

1715.    To Bleach Cotton Pure White. Boil for 3 hours in water containing 1 gill to the gallon of either caustic potassa or caustic soda; wash well from the lye, then lay the yarn or fabric to steep for 4 or 5 hours in cold water containing 1 pint of bleaching liquor (see No. 104 (To Make Bleaching Liquor)) to the gallon; then lift out and steep for an hour in a sour of 1 wine-glassful of sulphuric acid to the gallon of water; lift, and wash well; then boil for 2 hours in a caustic lye, half the strength of the first; wash from this, and steep again for 4 hours in the bleaching liquor; wash from this and steep again for 1 hour in a clean sour, made in the same manner as the first; wash well from this, and dry. A little smalt blue is put into the last washing water to clear the white.

1716. To Bleach Wool

1716.    To Bleach Wool. The first kind of bleaching to which wool is subjected, is to free it from grease. This operation is called scouring. In manufactories, it is generally performed by an ammoniacal lye, formed of 5 measures of river water and 1 of stale urine; the wool is immersed for about 20 minutes in a bath of this mixture heated to about 130° Fahr; it is then taken out, suffered to drain, and rinsed in running water. This manipulation softens the wool, and gives it the first degree of whiteness. It is then repeated a second, and even a third time; after which the wool is fit to be employed. In some places, scouring is performed with water slightly impregnated with soap; and indeed, for valuable articles, this process is preferable; but it is too expensive for articles of less value. Bisulphide of carbon and benzine have been employed in cleansing wool. The fat may be saved by distilling off the solvent, which may be used over and over again. (See No. 439 (To Clean Kid Gloves).) Sulphurous acid gas unites very easily with water; and in this combination it may be employed for bleaching wool and silk.

1717. Sulphuration

1717. Sulphuration. The process by which silk, cotton, woolen, and straw goods, are bleached or decolored by exposure to the fumes of burning sulphur. This is effected in a close chamber of a size proportioned to the scale on which the operation is conducted, and supplied with only just sufficient air to keep up the slow combustion of the sulphur, the fumes of which are sulphurous acid. {See Nos. 360 (Methods of Removing Various Stains) and 364.)

1718. To Prepare Sulphurous Acid for Bleaching

1718.    To Prepare Sulphurous Acid for Bleaching. Sulphurous acid is used either as gas or in solution in water, which dissolves 50 times its volume of the gas. In the former case sulphur is burned in a close room in which the stuffs (moistened) are hung; for small articles a barrel with a lid answers well. 2 exposures, of 24 hours each, suffice for wool. {See No. 360 (Methods of Removing Various Stains).) To get a solution of sulphurous acid, the cheapest and best plan is to heat in a glass retort 12 ounces sulphuric acid and 2 ounces sulphur. The gas, which comes off quietly, is collected in a large glass bottle partially filled with water; or, better, a series of bottles so connected together that the gas must pass successively through the water contained in each.