BLATTI. MALEAL. Sonneratia acida. BLEACHING.
Nikbarna, . . . HIND. I Salary pannukiradu, TAM. Khumbi karna, . „ j Nana padam, . . TEL.
In India, the substances present in goods which oppose the bleaching process are first removed by scouring in an alkaline lye ; afterwards natives usually dung the cloths which are to be bleached, and then steam them over the mouth of an earthen pot set in a clay fireplace. But little science enters into the process, and generally the goods suffer much from the water iu which they are scoured being overcharged with lime. Bleached cloth, particularly of tents, is far less durable than that which has merely had the dressing and filth thoroughly removed by washing. This is easily explained, as cotton goods have a certain resinous substance in them that obstructs the absorption of moisture. Besides the removal of this, cloth sustains much damage from the abuse of the caustic lye bath. Cloths should be scoured more than once at intervals during the process of bleaching, because many of the substances can not be removed but after exposure to the light and air.
Wool, also, is protected by a peculiar varnish, exceeding three per cent. of its weight, which must be removed by scouring. Warm water must be employed. Wool is further bleached by sulphuring, either in close • chambers in which sulphur is burnt, or by the sulphuric bath. In either case it acquires a brittleness which must be removed by washing in soap and water.
Several seats of the cotton manufacture, such as Dacca and Baroach, are famous for their bleach ing. This has been ascribed to the excellence of the water in the neighbourhood of these places. At Dacca fine muslins are merely steeped in water; other cloths are first washed. But all, of whatever texture they may be, are next immersed for some hours in an alkaline lye, composed of soap and of sajji mattee, that is, impure carbonate of soda. They are then spread over the grass, and occasion ally sprinkled with water, and when half dried are removed to the boiling-house in order to be steamed. This is effected by twisting the cloths
into the form of loose bundles, and placing them upon a broad clay platform, Which is on a level with, and surrounds, the neck of a boiler sunk into the ground. They are then arranged in circular layers, one above the other, around a bamboo tube, which is kept upright by means of transverse supporters projecting from it, the whole forming a conical pile that rises to a height of five or six feet above the boiler. The fire is kindled in the excavation below, and as the ebullition' of the water proceeds, the steam diffuses itself through the mass of the cloths above, swelling by its high temperature the threads of the latter. The opera tion of steaming is commenced in the evening, and continued all night till the following morning. The cloths are then removed from the boiler, steeped in alkaline lye, and spread on the grass as on the preceding day, and again steamed at night. These alternate processes of bucking and crofting, as they are technically called, during the day, and of steaming at night, are repeated for ten or twelve days, until the cloths are perfectly bleached. After the last steaming, they are steeped in clear filtered water acidulated with lime-juice, in the proportion generally of one large lime to each piece of cloth. Lime-juice has long been used in bleaching in all parts of. India ; and Tavernier describes Broach as famous as a bleaching station on account of its extensive meadows, and the large quantity of lemons reared there. Mixed fabrics of cotton and Muga silk are steeped in water mixed with lime-juice and coarse sugar, which latter article is said to have the effect of brightening the natural colour of the silk—Boyle, Arts, etc. of India, p. 481 ; Rohde, MSS.