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TEE AGRICULTURAL JOURNAL. 



digo, as the clay will not settle on the 

 plant in the steeping-vat, and a portion is 

 apt to pass through in to the beating vat, 

 and being carried down and settling with 

 the precipitating indigo passes on with it, 

 its removal not being possible in the later 

 stages of manufacture. The addition of 

 a suitable amount of alum to the water 

 causes the particles of this clay to become 

 entangled with the other precipitated im- 

 purities, which can be removed very 

 cheaply by settling or filtering, leaving a 

 clear and very bright water perfectly suit- 

 able for manufacture. This process 

 works well on a large scale. 



Beating. 



The beating process has for its object 

 the conversion of the solution of indican, 

 or indigo- white, into insoluble indigo-blue 

 or impure indigotin. This oxidation may 

 be performed by hand or mechanical 

 means. When hand beating is used each 

 steeping-vat is provided with a corres- 

 ponding beating- vat of a similar capacity, 

 and situated at a lower level. 



As soon as the steeping is finished the 

 opening in the vat is opened, and the 

 liquid flows into the beating- vat, where it 

 is agitated by a number of coolies, who, 

 standing in the liquid, beat it with plun- 

 gers formed of a disc of wood, the centre 

 of which is attached at right angles to a 

 short handle. The liquid as it enters the 

 vat is of a clear, brownish-yellow colour, 

 and the first effect of the beating is to 

 raise a thick white foam. As the agita- 

 tion proceeds the foam disappears, or if 

 persistent may be removed ; the liquid 

 turns green, then bluish, and finally looks 

 quite black, and no foam rising to the 

 surface. After beating for one or two 

 hours, more or less, the precipitation is 

 finished, which is shown by the fact that 

 on the removal of a small quantity of the 

 liquid in a white plate, the precipitate is 

 flocculent and inclined to settle ; also, on 

 filtering through a coarse cloth the fi-trate 

 is clear, with no tinge of blue. 



For beating by machinery, instead of a 

 series of independent square vats, one 

 long tank is used, which receives the 

 liquor from a number of steeping-vats. 

 The long vat is divided into two by a 

 partition wall running longitudinally up 

 the middle, and extending to within a 

 few feet of either end. On one side, 



between the middle and the outer wall, is 

 placed a paddle-wheel similar to that on 

 a small paddle-steamer, with the floats 

 removed, the agitation caused by the pas- 

 sage of the iron arms through the liquid 

 being suiScient for the purpose intended. 

 This beating wheel is driven by a steam 

 engine, and when working causes the 

 liquid to flow down on one side, round 

 the end of the partition wall, and up the 

 other channel, the liquid thus circulating 

 rapidly round the tank and passing con- 

 tinually under the revolving wheel. 



Other systems of beating are also in 

 use, but they do not seem to possess any 

 special advantages. By one process the 

 liquid is pumped continually to the top 

 of an inclined plane, and flows down to be 

 pumped up again ; while a system has 

 been tried in which the liquid is raised 

 to a height and allowed to fall as a shower 

 into the tank below ; the injection of air 

 has also been suggested. But whatever 

 system of agitation is employed the re- 

 sults are much the same, although for 

 some reason the indigo produced by hand 

 beating seems to command a higher price 

 than that in the manufacture of which 

 machinery is employed. It appears that 

 the yield obtained in the beating process 

 is almost theoretical, practically the whole 

 of the indigo originally present in the 

 vat being removed. Any improvement 

 in this connection would be purely of a 

 mechanical kind, and designed to save 

 labour or time. 



Settling. 



When the beating is finished the liquid 

 is left at rest until the indigo has com- 

 menced to settle, and the supernatant 

 water has become clear. This water is 

 drawn off either by removal of a series of 

 pegs placed in holes, which holes range 

 from the bottom to the top of the vat, the 

 uppermost peg naturally being the first 

 removed ; or another device is employed 

 in which an outlet pipe is capable of 

 being moved so that the opening is just 

 under the surface of the water, the mouth 

 of this pipe being depressed as the water 

 level sinks. The supernatant liquid being 

 thus drained off, under favourable cir- 

 cumstances, in a few hours time the 

 indigo remains as a black slush or magna 

 (mahl) at the bottom of the vat, while the 

 water (seat water) is run to waste or is 



