CHLORINE .

133

These are the principal methods without manganese. The adtion of sul-phuric acid upon salt is supplemented by the addition of peroxide of manganese,the result being the formation of sulphate of soda, sulphate of manganese,and chlorine. In some cases, for the common salt is substituted hydrochloricacid, to form sulphate of manganese and water, all the chlorine beingevolved.

Undoubtedly the most important plan yet adopted is that of Mr. WalterWeldon. The process is performed in a series of vessels arranged at fivesuccessive elevations, so that> after having been pumped up to the highest ofthem, the liquor operated upon can afterwards descend to all the others byits own gravity. The lowest of these vessels is a well, which is furnishedwith a mechanical agitator. The slightly acid chloride of manganese liquor withwhich the process commences runs from the stills in which it is produced intothis well, and is there treated with finely-divided carbonate of lime, the adtionof which is facilitated by energetic agitation. When the neutralisation of thefree acid which is at first contained in this liquor, and the decomposition ofthe sesquichloride of iron and sesquichloride of aluminium which are also atfirst contained in it, are completed, the liquor is pumped up into settling tanksplaced nearly at the top of the apparatus, and known as “ the chloride ofmanganese settlers.” It now consists of a quite neutral mixed solution ofchloride of manganese and chloride of calcium, containing in suspensionconsiderable quantities of sulphate of lime and small quantities of oxide ofiron and alumina. These solid matters deposit in the chloride of manganesesettlers, leaving the bulk of the liquor perfectly bright and clear, and of a faintrose-colour. The next step is to run off the clear portion of the contents ofthe chloride of manganese settlers into a vessel placed immediately below thesettlers, and called the “ oxidiser.” This is usually a cylindrical iron vessel,about 12 feet in diameter and about 22 feet deep. Two pipes go down nearlyto the bottom of the oxidiser,—a large one for conveying a blast of air from ablowing-engine, and a smaller one for the injection of steam. The latter isfor the purpose of raising the temperature of the contents of the oxidiserwhen necessary to between 130° and 160° or 170° F. Immediately above theoxidiser is a reservoir containing milk of lime. The oxidiser having receiveda charge of clear liquor from the chloride of manganese settlers, and thisliquor having been heated up to the proper point, blowing is begun, and milkof lime is then run into the oxidiser as rapidly as possible, until the filtratefrom a sample ceases to give a manganese reaction with solution of bleaching-powder. A certain further quantity of milk of lime is then added, and theblowing is continued until peroxidation ceases to advance. That point isusually attained when from about 80 to 85 per cent of the manganese presenthas become oxidised into peroxide. The contents of the oxidiser are now athin black mud, consisting of solution of chloride of calcium containing insuspension about 2 lbs. of peroxide of manganese per cubic foot; these 2 lbs.of peroxide of manganese being combined with varying quantities of protoxideof manganese and lime. This thin mud is now run off from the oxidiser intoone or other of a range of settling-tanks (mud-settlers) placed below it,and is there left at rest until it has settled as far as it will, usually until aboutone-half of its volume has become clear. The clear part, consisting simply ofsolution of chloride of calcium, is then decanted, and the remainder, containing