254 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Nov., 1904. 



Hungary. It is not generally used for dyeing per se, 

 but is employed in the preparation of certain indigo 

 vats. 



The indigo plant is herbaceous, and grows to a 

 height of from three to four feet, having a single stem 

 about half an inch in diameter. The land on which 

 the pl.'uit is grown is ploughed in October or Novem- 

 ber and sown with the indigo seed at about the end of 

 March or the beginning of April. The plant is of 

 rapid growth, and is cut for the first crop in about 

 the middle of June to the beginning of July — if 'the 

 weather has been propitious, usually at the earlier 

 date. The indigo plant is cut when it is just mature, 

 as indicated by the opening of the flower buds. After 

 about eight weeks a second crop is obtained, but the 

 yield of indigo is not so good as from the first crop. 



Treatment of Plants. 



We will not here describe all the different methods 

 which are employed for obtaining the indigo from the 



tranquil the liquor is run off into the beating vats. At 

 this stage it varies in colour from a pale to a golden 

 yellow — the darker the colour the greater the yield of 

 indigo, but the light-coloured liquor, though yielding 

 less, gives a finer product. In the beating vat the 

 liquor is agitated by means of wooden paddles or 

 shovels, which are worked by hand. (In many fac- 

 tories the beating is now done by machinery.) As the 

 beating is continued the yellow liquor gradually 

 changes from green to blue, and finally solid indigo 

 begins to separate out. After the beating is finished 

 tlie blue fluid containing the suspended indigo is run 

 into the settling tank, where the indigo slowly falls to 

 the bottom, leaving the clear liquid above. The super- 

 natant liquor is then run off and the mud of indigo 

 [Jumped up into a caldron and boiled. This boiling 

 serves to prevent a second and destructive fermentation 

 setting in, which would both spoil the quality and the 

 qLiantity of the indigo ; it also serves to wash it and 

 remove impurities. After boiling it is run on to a 





Fig. 3- 



plant, but will merely give an idea how the process is, 

 in general, carried out. It must, in the first place, be 

 understood that the indigo does not exist in the free 

 state, /.(•., in the form of :i blue dve, but is there as 

 a ghicosidc — th.at is, combined with a kind of sugar 

 called iiidif^Incui, and this compound has first to be 

 split up before the indigo can be obtained. 



The indigo plants after cutting are tied up into 

 bundles, and the bimdlcs carefully and tightly packed 

 into vats built of brickwork and lined with stone or 

 cement. When the vat is completely filled with the 

 indigo plant, beams of wood are wedged across the 

 bundles .and water is run in so as to completely cover 

 the plant. The object of wedging the bundles down is 

 to keep them below the water and to prevent them 

 being forced out when they swell, after the water has 

 been added. In a short time an active fermentation 

 sets in, which generally lasts from 10 to 15 hours ac- 

 cording to the temperature of the .'lir and the condition 

 of the plant. As soon as the fermentation becomes 



large filter called the dripping \at, which may be from 

 JO feet long by 10 feet wide and 3 feet deep, the size, 

 h(>\\e\er, \ari.'s in clilTerent works. 



.Alter draining lor about ^4 hours the pasty indigo 

 is placed in perforated cloth-lined wooden boxes and is 

 subjected to a gradually increasing pressure until no 

 more liquid runs out. It is then cut into small blocks 

 with a knife or brass wire, in much the same way that 

 cheese is cut ; the blocks being usually about 3 inches 

 square. The cubes of indigo are then placed on a 

 trellised staging covered with matting, which is con- 

 tained in open sheds and dried by exposure to the air, 

 direct sunlight being carefully excluded. The quantity 

 of indigo obtained from each fermenting vat varies 

 from 30 to 50 lbs. 



I''ig. 3 shows in a somewhat picturesque manner 

 .111 indigo factory. A is the fermentation vat 

 with the pfxsts DD to hold the bars HH, which are 

 em|iIoycil to press down the bundles of the indigo 

 plant. \\ is the pipe through which the fermented 



