(1) The washed substances are put into a weak bath containing 6 1/4 to 8 lb. bleaching powder per 22 gal.; after 6 to 12 hours they are washed and boiled for 2 to 4 hours with carbonate of soda (1 oz. per gal.). If the fibres are very hard, they are treated with sulphuric acid ( 1/3 oz. per gal.), and well drained before boiling with the soda. Finally they are placed in a bath of 6 1/4 to 8 1/4 lb. of bleaching powder and 1 3/4 lb. of soda per 22 gal. for 4 to 6 hours. (2) The fibres are passed through an alkaline chlorine bath, containing, excess of caustic alkali; 5 per cent, is used for linen, cotton, etc.; 25 per cent, for jute and other substances difficult to bleach. The temperature should not exceed 122° F. (50° C). The bath is readily made by adding excess of soda carbonate to chloride of Time.
(3) Gas-bleaching half-stuff is almost indispensable for the coarse linen rags so plentiful in Russia. The half-stuff must contain sufficient moisture, or the outside only will be bleached, and that but indifferently. An effective test of the moisture is to squeeze the stuff between the hands, when, if the pressure causes no escape of water, but leaves the mass with a damp appearance, bleaching may be proceeded with. It is conducted as follows: - Put 1600 lb. of the half-stuff loosely into a stone chamber, and lute all apertures. Into the leaden retort, connected with this chamber by leaden pipes, pour 3 pails of water and 66 lb. of common salt; stir thoroughly, add 65 lb. manganese, stir again, and close the retort. Next charge a leaden vessel with 119 lb. oil of vitriol, and let the acid drop into the retort containing the water, salt, and manganese, through a bell-mouthed bent siphon, which admits the vitriol while preventing the escape of gas. The acid should occupy 3 hours in dropping into the retort. Then heat the retort with steam for 7 hours, and allow 2 hours for the gas to escape up the factory chimney. For fine stuff, such as " wil-lowed" rope, 1 hour extra must be allowed for the escape of the gas.
No. 1. (1600 lb. half-stuff): 50 lb. manganese, 50 lb. salt, 80 lb. vitriol.
No. 3. (1600 lb. half-stuff): 60 lb. manganese, 60 lb. salt, 100 lb. vitriol.
No. 4. (1600 lb. half-stuff): 65 lb. manganese, 66 lb. salt, 119 lb. vitriol.
Ropes, for copying paper (1400 lb. half-stuff): 81 lb. manganese, 91 lb. salt, 124 lb. vitriol. (Dunbar.)
(4) For potching half-stuffs previously gas bleached, the quantities are: -
No. 1. (600 lb. stuff): 15 gal. chlorine at 4 1/2°.
No. 3. (600 lb. stuff): 20 gal. chlorine at 4 1/2°.
No. 4. (500 lb. stuff): 12 gal. chlorine at 5°.
The quantities of half-stuff filled into the potching engine should be uniform. When the engine is filled, wash for some time with a finer wire than is used on the breaker. When thoroughly washed, raise the washer, and introduce the bleaching liquor. In the case of vitriol (concentrated sulphuric acid) being used, a small leaden vessel must be placed in such a position that the vitriol will drop into the engine at the rate of 1 lb. in 20 minutes. The vitriol is previously diluted. When the bleaching is finished, the stuff is emptied into stone chests fitted with perforated zinc strainers at the bottom and back, and left for a fixed time. (Dunbar.)