BLEACHING (AS. b/cRean, to grow pale, Ger. bleichen, to whiten; cf. E. bleak, Ger. bleich, pale, AS., blue, blire, pale, shining). The art of removing coloring matters from animal and veg etable substances. leaving the material uninjured but of a light or white color, so that, as in the case of fabrics, they may be readily dyed to some desired shade. The origin of bleaching is un known, but the art is believed to have been prac ticed before the Christian Era, and the 'fine linen' mentioned in the Bible is supposed to have been bleached. It is thought to have been practiced by the ancient Babylonians. Egyptians, and other Eastern peoples, and was for the most part ap plied to vegetable fabrics, such as flax, hemp, and cotton, or the cloths made from them, although the bleaching of silk has long been known in China. Originally, the atmosphere and the sun's rays alone were used for bleaching. and the plan followed was to spread the cloth on a grass-field called a bleaching-green. The fabric was sprin kled with water several times a day, and after several months of exposure it became white. No improvements of importance occurred until the Eighteenth Century. when Holland became the principal seat of the industry, and there the ma terial was steeped in a solution of potash lye for several days and then in buttermilk for about a week, after which it was washed and bleached on the ground. The satisfactory results thus ob
tained led to the name 'HoBands' being given to the excellent. fabrics bleached in that way, while a quality of linen, much in demand, which was spread on grass fields, was called 'lawn.' The next improvement was the use of dilute sulphuric acid in place of buttermilk, by which the duration of the process, formerly about eight mouths, was re duced to one•ialf that time. In 1785 the remark able bleaching properties of chlorine were dis covered by Berthollet, and its application to the bleaching of cloth soon followed. At first the chlorine was used in its gaseous state, and it was found that it destroyed color by uniting chem ically with the coloring principle, thus decom posing the color; but as the chlorine also united with the hydrogen of the fibre it destroyed the fabric. Subsequently javelle-water. obtained by dissolving chlorine in dilute potassium hydrox ide, was employed: but in 1;99 the dry chloride of lime, or bleaching-powder, came into use, and is still largely employed, although for some pur poses hydrogen peroxide is now preferred.