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DYEING AND CALICO PRINTING.
is that constituted by the deposit of sulphate of lime and other matters whichform in chloride of manganese settlers. These deposited matters have to beremoved in the state of thin mud, largely mixed, that is to say, with solution'of chloride of manganese. Unless this mud be well washed after its removalfrom the chloride of manganese settlers, and the washings be returned to theprocess, the manganese lost with this mud amounts to fully 5 per cent, or evenmore; but by suitable washing the manganese thrown away with the mudfrom chloride of manganese settlers can be reduced to below 2 per cent. Theonly other sources of loss are—leakage of vessels, and the running away ofmud by careless workmen with the chloride of calcium solution from the mud-settlers. The former of these sources of loss ought, practically, never toexist, and the latter is now being eliminated at several works by the chlorideof calcium solution, instead of being run away directly from the mud-settler,being run first into catch-pools, in which any mud which may be run off withit from the mud-settlers is allowed to deposit.
“ Beyond the sulphate of lime and other bodies which are deposited in thechloride of manganese settlers, the only residual product of the process, andthe only other thing which has to be thrown away, is solution of chloride ofcalcium. As this solution represents all the lime and all the limestone usedin the process, and two-thirds of the chlorine contained in the acid employed,and as an industrial process is, of course, imperfect in proportion as anythingwhatever which is manipulated in it has to be simply thrown away, and espe-cially in proportion as its yield of the commodity, the production of which isits sole object, falls below the total quantity contained in the materials used, Ihave tried to use, in the oxidiser, magnesia instead of lime, afterwards decom-posing, by heat, the resulting chloride of magnesium into magnesia, for useover again, and hydrochloric acid. In that form, the process is capable ofyielding, undiluted with other gases, all the chlorine contained in the acidemployed, and, apart from mechanical loss, employs no materials which arenot used over and over again, excepting coal and air. This form of the processhas already stood the test of a certain amount of experience on the largescale ; and I venture to believe that, when the time shall have arrived when itwill be desirable to obtain, from a given quantity of hydrochloric acid, morechlorine than can be obtained therefrom by means of peroxide of manganeserecovered by means of lime, peroxide of manganese recovered by means ofmagnesia will prove to be the reagent by which chlorine can be most econo-mically manufactured.”
The various hypochlorites are easily prepared when the chlorine is provided.The most important is that known as chloride of lime.
Chloride of lime, bleaching-powder (or more accurately, according to Fre-senius, a mixture of 1 molecule of Ca(C10) 2 and 2 molecules of basic chlorideof calcium, CaCl 2 ,2CaH 2 0 2 -|-2H 2 0), occurs in commerce as a moist whitepowder, 1 part of which is soluble in 10 parts of water. As a bleaching agent,the presence of an acid is required to develope its full properties—a matter ofadvantage in Turkey-red dyeing in the production of white patterns by printingon a thin paste of tartaric acid, the fabric being afterwards immersedmomentarily in a solution of bleaching-powder. For the acid, sulphate orchloride of zinc may be substituted, the hypochlorous acid being set free, whilesulphate of lime and oxide of zinc are thrown down.