Besides the bleaching agents at present employed, many others have at different times been proposed, e. g. silicate of soda, stannate of soda, petroleum oil, &c. Tessid du 1VIothay and Rousseau patented, in 1866, the use of permanganate of soda for bleaching, which, though in some styles of work it has had a shsre of success, has not by any means been able to supplant the bleaching powder. Various patents, too, have been taken out for the use of ozone, and, at the present time, (1879), a liquid preparation called " ohlorozone," discovered by M. D. Brochocki, of Paris, is being introduced to the bleachers throughout Britain by the makers, Messrs. Nathaniel Holmes and partners, Warrington and London. Chlorozone is obtained by saturating a cold, caustic alkaline ley with a mixed current of hypochlorous aoid and air. Ite action in bleaching ie similar to that of a solution of chloride of lime or soda ; but it ie said to possess a much greater decolouring power, without having any injurious action on the fibre. No doubt ozone has been the real bleaching agent, from the earliest times (when the cloth was exposed on the grass to air, light, and moisture) until now. It is known that ozone is constantly present to a greater or less degree in the atmosphere. In the rapid bleaching process of to-day, the general opinion is, that the really active agent is the ozone produced by the bleaching powder, the use of which simply replaces the old custom of exposing ou the graes. According to this view, chlorine gas is evolved by the decomposition of the bleaching powder, it combines with the hydrogen of the water, and oxygen in the nascent state (ozone and antozone) is liberated. Where, however, the goods are washed between chemicking and souring (and this is decidedly the beet plan), it is hypochlorous acid which is evolved, and, by its rapid decomposition into chlorine and oxygen (ozone), bleaches with double power, the chlorine liberating additional oxygen (ozone) from the water preeent. It must always be remembered that in these reactions there is a production of hydroehloric acid in the nascent state within the fibre, to which, probably, the tendering action of the chemicking is in a large measure due.
At one time or another, every bleacher has his attention involuntarily directed to the annoying occurrence of stains. Some of these are visible in the white cloth when dried, others only after being dyed. The former class may be simply dirt from the workmen's shoes, or other obvious causee easily remedied. Others may arise from dirty water being driven into the kiers along with the steam, from loose packing in the pipe-joints, grease, Ste. This last may come from the stuffing box of the piston-rod of the engine, from steam drying cylinder stuffing-boxes, &c. Iron stains often arise from rusty nails in the roof or on stillages, and from the inner sides of the kiers, to avoid which it is customary to whitewash the interior of the kiers with lime from time to time. Iron supports, brackets, &c., under the roof should be occasionally painted, and all wooden stillsges should be pegged with wood instead of using nails. Holes, cuts, tears, &c., form another class of
damages more or less frequent in all bleach-houses. As a rule, their occurrence to any large extent shows careless working or defective machinery. Soroe may ariee from rubbiug of the pieces against the sides of the kier through tremulous boiling, others may be caused by pebbles and cinders from the water, and even nails, becoming accidentally imbedded in the bowls of the washing machines. Cracked pot-eyes, and wooden rails worn to a cutting edge by the lengthened friction of the pieces in transit, are also occasionally a source of damage, and should bc periodically examined.
With regard to the alteration in weight, length, and breadth of calico pieces during the present processes of singeing and bleaching, the following are the results of personal observation.
One piece best cloth, 72 reeds, 36 in. broad, 25 yards long, and weighing 5 lb. 4 oz., showed : Loss of weight in singeing .. .. 3 to 4 oz. = 3.5 to 4.7 per cent.
Loss of weight in bleaching .. .. 10 to 12 oz. = 11.9 to 14.2 Loss in breadth 2i in. = 6.9 19 Gain in length I to 1 yard = 3.0 to 4.0 As already stated, the loss of weight in bleaching may vary considerably, according to the quantity and quality of the sizeing which is in the warps.
O'Neill gives the following interesting results of experiments in testing the tensile strength of the cotton threads before and after bleaching, by measuring the strain required to break the thread. The calico experimented on was of good quality, and had sixteen to eighteen threads to the inch ; the length of thread for testing varied from 0.25 in. to 2.1 in. : " It is seen," says the author, " that in two cases out of three, the warp threads are stronger after bleaching than before, and in one case a little weaker. All that can be safely concluded from numerous trials made, is that the tensile strength of the cotton yarn is not injured by a careful but complete bleaching, and probably it may bo strengthened by the wetting and pressure causing a more complete and effective binding of the separate cotton hairs or filaments, the twisting together of which makes the yarn." An idea of how little change has been made in the madder-bleaching process during the last thirty years, will be gained from the following sketch of the process as carried on at the celebrated print works of Messrs. Thomson, Clitheroe, Laucashire, in 1845 and 1850, in comparison with the process of to-day, as conducted at the equally famous print works of Messrs. W. Crum and Co., near Glasgow, and with two other processes also in actual use.
1895 Process (Thomson's). 12,000 lb. Cloth. Low-press Kiers.
1. Wa,sh after singeing.
2. Lime boil, 4301b. lime, 10 hours boil, wash.
3. Lime sour, hydrochloric acid 2° Tw., 1 hour steep.
4. First ash work, 215 lb. soda ash, 10 hours boil, wash.
5. First chemick, 137 lb. bleaching powder in solution at 1° Tw., 10 hours steep.
6. First white sour, sulphuric acid 2,1° Tw., 1 hour steep, wash.
7. Second ash work, 130 lb. soda asb, 10 hours boil, wash.