XIII INDIGO 



257 



to the air, and the process may be accelerated by occasional 

 agitation of the fluid. 



When manufactured on a large scale, however, large wooden Vats. 

 vats, or stone cisterns, placed like steps, one higher than the 

 other, are necessary. The upper cistern, usually called the cisterns. 

 steeper^ sixteen feet square and two and a half feet deep, has 

 a bottom sloping gradually towards the end from whence the 

 contents are discharged into the second cistern by means of 

 a cock inserted near to the bottom. The second cistern, 

 called the beater^ should be twelve feet square and four and 

 a half feet deep, and these cisterns will be sufficient to manu- 

 facture the dye from plants growing on seven acres of land. 

 Below the beater a third cistern may be placed into which 

 the contents of the beater is run and allowed to stand for 

 the dye to settle at the bottom. But, unless the operations 

 be done on a large scale, the settling of the dye can take 

 place in the second cistern, which should be furnished with 

 several cocks, at different elevations, so as to allow the clear 

 fluid above to drain off from the precipitated indigo. 



Bundles of freshly cut plants brought from the fields are Manufac- 

 put into the first cistern or vat in regulars layers until they |nd!go^ 

 reach to within ten inches of the top. Planks are then laid 

 on the plants and wedged down by some mechanical contri- 

 vance, and water is run in so as to cover the plants to a depth 

 of three or four inches. The water must be pure, clear river p^^^ ^^^j, 

 water giving the best results ; and, as a large quantity is essential, 

 necessary, indigo cannot be manufactured with success in 

 places where an abundant supply of water is unobtainable. 

 A few hours after the water has been run into the cistern, Permen- 

 fermentation will begin, and it should last from twelve to nation, 

 sixteen hours. When the leaves become of a pale colour, 

 and the tops are tender, fermentation has gone far enough ; 

 for, if it be continued after this stage, putrefaction will set in 

 and the dye will be destroyed. The water, which has dis- 

 solved out the soluble substances that become indigo after 

 they have taken up oxygen, is of a light green colour, and it 



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