80 



INDIGO. 



our particulars mainly From the methods pursued in 

 the East Indies, where, through the well directed 

 efforts of the English, this article is prepared in its 

 greatest perfection. The plant requires a rich, light 

 soil, and a warm exposure. It succeeds best on 

 newly cleared lands, on account of their moisture; 

 it requires protection against high winds, and needs 

 irrigation in times of drought. The ground, after 

 being properly prepared for the reception of the seed 

 by ploughing, is sown pretty thickly, the time of 

 sowing being so chosen that rain may fall upon the 

 plant as soon as it shows itself above the ground, by 

 which it is not only greatly invigorated, but cleansed 

 from those innumerable insects which otherwise are 

 liable to destroy it. From this time, comparatively 

 little rain is needed; for the dews are so copious as 

 to supply nearly all the moisture required; and, be- 

 sides, its spindle-shaped root, which descends into 

 the ground perpendicularly, to the depth of nearly 

 three feet, enables it to endure temporary droughts. 

 The prevalence of cloudy weather and much mois- 

 ture, however, cause the indigo plant to thrive more 

 luxuriantly, but occasion a great deficiency in the 

 colouring matter, which, as it contains an extra- 

 ordinary quantity of carbon, requires the plant to 

 decompose carbonic acid gas very abundantly,. an 

 operation which it is unable to perform when de- 

 prived of the direct influence of the sun's rays. As 

 the young shoots furnish larger and more numerous 

 leaves, it is usual to plant every year; but the 

 Egyptians, who seem to cultivate it most successfully, 

 plant only every third or fourth year. As the plant 

 approaches to maturity, the leaves undergo a sudden 

 change in colour, from a light to a dark green. As 

 soon as this change is observed, the branches are 

 severed from the parent stem early in the morning, 

 and spread out in the sun till the afternoon, by which 

 time they become sufficiently dry to be beaten from 

 the branches by a stick. The leaves, so separated, 

 are housed in warehouses, closely packed, and well 

 trodden down by natives. The plants, from which 

 the leaves have been severed, send forth a new crop, 

 which is gathered, when mature, like the first. 

 Rain, however, is necessary after the cutting, to en- 

 able the plant to shoot again in a thrifty manner. 

 The cuttings, in a favourable season, are repeated 

 three or four times, after which the ground is 

 ploughed up for another sowing; but each successive 

 growth of the branches produces an increased deteri- 

 oration of the qualities of the leaves, so that one part 

 of the leaves of the first cutting yields as much indigo 

 as two parts of the third crop. The dried leaves are 

 not immediately used, but are kept packed for one 

 month, during which time they suffer a material 

 change, which is indicated by their having passed to 

 a light lead colour. By additional keeping, the lead 

 colour gradually darkens, until it becomes black. 

 The maximum quantity of indigo is to be obtained 

 when the lead colour is effected; and any delay in 

 extracting it, after it has reached this point, is 

 attended with a loss in the quantity of the indigo. 

 The lead colour, however, does not appear in a 

 month after the leaves are gathered, unless, from 

 fear of rain, or any other cause, they were cut before 

 being ripe; and, on the other hand, if the cutting 

 was deferred till after the plant was fully ripe, the 

 leaves will not require to be kept so long. The 

 dried leaves, after having suffered the change of 

 colour alluded to, are transferred to the steeping vat 

 (an uncovered reservoir, thirty feet square, and 

 twenty-six inches deep, constructed of brick, and 

 lined with stucco), where they are mingled with 

 water, in the proportion of alwut one volume of 

 leaves to six of water, and allowed to remain two 

 hours. The great affinity of indigo for oxygen is 



here very manifest, in the quick change of the colour 

 of the leaves which float on the surface, and are ex- 

 posed to the action of the atmosphere, to a blackish 

 blue, when contrasted with those below, which remain 

 unchanged. On this account, the vat is frequently 

 stirred, so that the floating leaves may be immersed. 

 After two hours' infusion, the water, which, from 

 the solution of imperfectly oxygenized indigo, has ac- 

 quired a fine green colour, is allowed to run off from 

 the leaves, through strainers, into the beating-vat, 

 where it is agitated by the paddles of ten or twelve 

 natives for about two hours, during which time the 

 fine green liquor gradually darkens to a blackish 

 blue. This part of the process requires a longer or a 

 shorter time, depending on the former preparation of 

 the leaf, and the immediate influence of the sun. 

 The criteria for judging when it is completed are 

 derived from the incipient separation of the particles 

 of indigo, which become visible by pouring a small 

 quantity of the fluid into a white earthen dish. At 

 this time, lime-water is thrown into the vat, and 

 thoroughly agitated with the whole mass of fluid. 

 The mass is then left to subside for the space of 

 three hours, when the supernatant liquid, which is of 

 a fine bright Madeira colour, is withdrawn, by ori- 

 fices in the vat, at different heights. The indigo is 

 then removed to the covered part of the manufactory, 

 where it is put on a straining cloth, and allowed to 

 drain throughout the night. On the following morn- 

 ing, it is transferred to a copper boiler, where it ia 

 mingled with a quantity of water, and raised to ebul- 

 lition. As the mass is gradually heating, a quantity 

 of scum rises, which is immediately removed, and, as 

 soon as the whole is brought to the boiling point, the 

 fire is withdrawn. The contents of the copper are 

 retaken to the strainers, and the drained indigo is 

 then divided into small portions, and each portion 

 well worked by the hands of the natives, in order to 

 free it from air bubbles. It is then carried to the 

 pressing-boxes, which are usually square, and of suf- 

 ficient depth to leave the cake about two inches and 

 a quarter in thickness. By means of a powerful 

 screw, the water is separated from the indigo; the 

 cakes are gradually dried in the shade, and thus ren- 

 dered fit for exportation. 



In the West Indies and America, the old process, 

 formerly employed in India, of fermenting the leaves 

 as soon as cut, instead of drying them, and obtaining 

 the indigo by simple infusion, is still in use. The 

 plant is allowed to stand until it is fully in blossom, 

 when it is cut down with rape-hooks, tied in loads, 

 and carried to the works, where it is deposited in 

 strata in the steeping vat. As soon as the vat is 

 filled with the green plant, water is admitted suf 

 ficient to cover it, and the whole is left to digest and 

 ferment, until the greatest part of the pulp is ex- 

 tracted, without letting the tender tops run to putre- 

 faction; and it is the management of this point which 

 occasions the planter the greatest difficulty; for, if he 

 draws off the water but two hours too soon, he ine- 

 vitably loses the greatest part of the pulp, and if the 

 fermentation runs but two hours too long, the whole 

 is spoiled. Nine-tenths of the indigo of the United 

 States, it is asserted, are more or less injured by an 

 excessive fermentation. To ascertain the due degree 

 of fermentation, the workman draws out, from time 

 to time, a handful ot the plant, and, when he finds 

 the tops grow very tender and pale, and observes the 

 stronger leaves change their colour to a less lively 

 pale, he draws the liquor off without delay. An 

 experienced manufacturer will also form a tolerable 

 estimate of the degree of fermentation by the grain 

 of the infusion, of which he frequently beats a little 

 in a silver cup. When the pulp is believed to be 

 extracted, the infusion is drawn off into the beating- 



