Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/310

280] trees, shrubs, grass, corn, &c. and this devastation is at times extended over whole tracts of ground.  Blatta. See.  BLEACHING is the art of whitening linen cloth, thread, cotton, &c. In the present advanced state of the linen and cotton manufactures of Great Britain and Ireland, the art of bleaching is one of the most interesting and important. Its object is to reduce ,, , or the ' or ' manufactured from them, to a state of perfect whiteness. To attain this end, oils, metallic oxides, earthy impregrations, resins, and other animal, vegetable, or mineral particles, containing any colouring matter, must be discharged from the texture of the substances manufactured.

The process of bleaching is divided into five parts, viz. 1. Steeping and milling; 2. Bucking and boiling; 3. Alternate watering and drying; 4. Souring; and, 5. Rubbing with soap and warm water, starching and blueing. By the first of these methods, the cloth is in a great degree freed from its superficial foulness, and is rendered more pliant and soft. The second process is the most important of the whole. Its object is to loosen and carry off, by means of alkaline lies, that particular substance in cloth, which is the cause of its brown colour. The operation of alternate watering and drying is as follows: After the cloth has been bucked, it is carried out to the field, and frequently watered, during the first six hours. For, if in the course of that time it be allowed to dry, while strongly impregnated with salts, the latter, by approaching closer together, and being assisted by a degree of heat which increases in proportion to the dryness of the cloth, act with greater force, and destroy its texture. After this time, dry spots are suffered to appear before it receives any water.

By the continual evaporation which takes places on the surface of the cloth, it is evident that this operation is intended to carry off some impurities that remain after the former process of bucking. This is clearly proved from the fact, that the upper side of the cloth, where the evaporation is strongest, attains to a greater degree of whiteness than the reverse side; and the whole likewise turns much lighter on being exposed to the influence of the sun, air, and winds.

Souring. Every person, who possesses the smallest knowledge of chemistry, is aware that alkaline salts may, by various methods, be converted into absorbent earths. One of these is, frequent solution in water, and again evaporating it. A transmutation, therefore, of these salts must be continually going forwards in the cloth, during the alternate waterings and dryings of the former process. The souring process is sooner completed in cold, than in warm weather; and it is now experimentally ascertained, that vitriol is preferable to milk sours in bleaching.

The next is, hand rubbing with soap and warm water, rubbing-boards, starching, and blueing. After the cloth has been sufficiently soured, it is washed in the mill, to deprive it of the acrid particles which adhere to its surface. From the mill, it is taken to be washed by the hand, with soap and a water, to free it from the oily particles which could not be dis-