CHEMISTRY. 167 



is facilitated by energetic agitation. When the neutralization of 

 the free acid which is at first contained in this liquor, and the 

 decomposition of the sesquichloride of iron and sesquichloride of 

 aluminum, which are also at first contained in it, are completed, 

 the liquor is pumped up into settling-tanks placed nearly at the 

 top of the apparatus and known as the chloride of manganese 

 settlers. It now consists of a quite neutral mixed solution of 

 chloride of manganese and chloride of calcium, containing in 

 suspension considerable quantities of sulphate of calcium and small 

 quantities of oxide of iron and alumina. These solid matters 

 rapidly deposit in the chloride of manganese settlers, leaving the 

 bulk of the liquor perfectly bright and clear and of a faint rose- 

 color. The next step is to run off the clear portion of the con- 

 tents of the chloride of manganese settlers into a vessel placed 

 immediately below those settlers, and called the oxidizer. This 

 is usuall}' a cylindrical iron vessel, about 12 feet in diameter and 

 about 22 feet deep. Two pipes go down nearly to the bottom of 

 the oxidizer, a large one for conveying a blast of air from a 

 blowing-engine, and a smaller one for the injection of steam. 

 The latter is for the purpose of raising the temperature of the 

 contents of the oxidizer, when necessary, for sometimes the 

 chloride of manganese liquor reaches the oxidizer sufficiently 

 hot, to somewhere between 130 and 160 or 170 F. Immedi- 

 ately above the oxidizer is a reservoir containing milk of lime. 

 The oxidizer having received a charge of clear liquor from the 

 chloride of manganese settlers, and this liquor having been heated 

 up to the proper point, if it was not already hot enough, blowing is 

 begun, and milk of lime is then run into the oxidizer as rapidly 

 as possible, until the filtrate from a sample taken at a tap placed 

 nearly at the bottom of the oxidizer ceases to give a manganese 

 reaction with solution of bleaching-powder. A certain further 

 quantity of milk of lime is then added, and the blowing is 

 continued until peroxidation ceases to advance. That point is 

 usually attained when from about 80 to 85 per cent, of the man- 

 ganese present has been converted into peroxide. The contents 

 of the oxidizer are now a thin black mud, consisting of solution 

 of chloride of calcium containing in suspension about 2 pounds of 

 peroxide of manganese per cubic foot, these two pounds of per- 

 oxide of manganese being combined with varying quantities of 

 protoxide of manganese and lime. This thin mud is now run 

 off from the oxidizer into one of a range of settling tanks 

 (mud-settlers} placed below it, and is there left at rest until about 

 one-half of its volume has become clear. The clear part, con- 

 sisting simply of a solution of chloride of calcium, is then decanted, 

 and the remainder, containing about 4 pounds of peroxide of 

 manganese per cubic foot, is then ready to be used in the stills. 

 There it reacts upon chlorhydric acid, liberating chlorine, with 

 reproduction of exactly such a residual solution as was com- 

 menced with. With that solution the round of operations is 

 begun again ; and so on, time after time, indefinitely. 



In regard to the amount of lime necessary : The lime 

 used is slaked with as nearly as possible an equivalent of water 



