The plant is sold in Bengal by the bundle, which is measured by a chain. In the Doab it is sold for 1 rupee for 5 to G mounds. 200 to 225 mounds of plant to a maund (75 lbs.) of indigo, is a fair average produce. Therefore it would cost about 36 to 40 rupees for the plant necessary to make 75 lbs. of indigo. The expense of manu facturing would be but little.
Tho finest quality of dye is produced by factories in the Jessore and Kislinagar districts. An ordinary plantation there comprises 4000 acres of land, which may yield on an average 1000 mainids of 82 lbs. each. The annual outlay for labour, seed, etc., on this one branch of industry, is seldom less than a million and a half sterling, of which fully nineteen-twentieths are expended by Europeans. The cultivation is generally one of hazard, as the fields are always liable to be swept of their produce during any heavy or sudden fall of rain. The plant often suffers from long drought. With a few good seasons, favourable soil, a thorough knowledge of the business, and a certain degree of industry, an indigo planter may reckon on realizing an inde pendence in less than a dozen years, supposing him to have started with ample means.
In South Arcot, Kurnool, and Cuddapah, indigo is largely cultivated, and especially in the last named district, which is well suited for the culti vation of the staple. The average growth in the Madras Presidency covers 304,676 acres,, two thirds of which are in the South Arcot, Cuddapah, Nellore, Kistna, and Kurnool districts. Cuddapah indigo is grown by ryots on contract to deliver so much indigo plant at the factory at a fixed rate per bundle. The agents of the Madras firms avoid occupying the same taluks, so that there is no system of forcing the cultivation upon the ryots, who are much too independent to submit to such a process. The trade is quite free, and the system of advances to the tenantry has done a great deal to improve their condition, as well as facilitated the collection of the revenue. The cultivation of indigo is not fixed ; it extends or contracts with the demand for the article. It has, however, been steadily increasing of late years ; many of the richer ryots cultivate it, and manufacture it on their own account. Native capitalists also engage in the trade. Mr. Wedderburn estimated the cultivation and manufacture of indigo by natives, without European superintendence, in the ratio of 10 to 1 of that produced under European management. Eight lakhs of rupees were drawn by bills in 1859, on the Cuddapah Treasury, by Madras mercantile houses. And eight lakhs scarcely represent one-hall of the sum paid for indigo, the out-turn of which, on .30,000 acres, cultivated in the year 1860, at an average profit of 50 rupees per acre, will show a value of 18 lakhs of rupees.
Mr. Rohde, (MS.) mentions that two methods of preparing indigo are in use in the Madras territories. That called Karpa indigo, and which is known in the market as Madras indigo, is pre pared from the dried leaves ; the Bimlipatain indigo is from the recent leaves upon the Bengal plan. He says that in the indigo factories of Bengal, using the recent leaves, there are two large stone-built cisterns, the bottom of the first being nearly upon a level with the top of the second, in order to allow the liquid contents to be run out of the one into the other. The upper most is called the. fermenting vat or the steeper, its area is 20 feet square, and its depth 3 feet ; the lowermost, called the beater or beating vat. is as broad as the other, but one-third longer. The cuttings of the plant as they come from the field are stratified in the steeper till this be filled within 5 or G inches of its brim. In order that the plant during its fermentation may not swell and rise out of the vat, beams of wood and twigs of bamboo are braced tight over the surface of the plants, after which water is pumped upon them till it stands within three or four inches of the edge of the vessel, and an active fermentation speedily commences, which is completed within fourteen or fifteen hours, a little longer or shorter according to the temperature of the air, the pre vailing winds, the quality of the water, and the ripeness of the plants. Nine or ten hours after immersion of the plant, the condition of the vat must be examined, for then bubbles appear, which rise like little pyramids, are at first of a white colour, but soon become grey, blue, and then deep purple red. The fermentation is at this time violent, the fluid is in constant commotion, innumerable bubbles mount to the surface, and a copper - coloured dense scum covers the whole. As long as the liquor is agitated, the fermentation must not be disturbed, but when it becomes more tranquil, the liquor is to be drawn off into the lower cistern. It is of the utmost consequence not to push the fermentation too far, because the quality of the whole indigo is thereby deteriorated ; but rather to cut it short, in which case there is, indeed, a loss of weight, but the article is better. The liquor• possesses now a glistening yellow colour, which, when the indigo precipitates, changes to green. The average temperature of the liquor is commonly 85° Fahr. ; its specific gravity at the surface is 1001.5, and at the bottom
1003. So soon as the liquor has been run into the lower cistern, ten men are set to work to beat it with oars or shovels four feet long, called basquets ; paddle-wheels have also been employed for the same purpose. Meanwhile two other labourers clear away the compressing beams and bamboos from the surface of the upper vat, remove the exhausted plant, set it to dry for fuel, clean out the vessel, and stratify fresh plants in it. The fermented plant appears still green, but it has lost three-fourths of its bulk in the process, or from 12 to 14 per cent, of its weight, chiefly water and extractive matter. The liquor in the vat must be strongly beaten for an hour and a half, when the indigo begins to agglomerate in flocks, and to precipitate. This is the moment for judging 'whether there has been any error committed in tho fermentation, which, if so, must be corrected by the operation of beating. If the fermentation has been defective, much froth rises in the beating, which must be allayed with a little oil, and then a reddish tinge appears. If large round granulations are formed, the beating is continued, in order to see if they will grow smaller. If they become as small as fine sand, and if the water clear up, the indigo is allowed quietly to subside. Should the vat have been over-fermented, a thick fat-looking crust covers the liquor, which does not disappear by the introduction of the flask of oil. In such a case the beating must bo moderated. Whenever the granulations become round and begin to subside, and the liquor clears up, the beating must be discontinued. The froth or scum diffuses itself spontaneously into separate minute particles, that move about the surface of the liquor, which are marks of an excessive fel'. mentation. On the other hand, a rightly fermented vat is easy to work ; the froth, though abundant, vanishes whenever the granulations make their appearance. The colour of the liquor when drawn out of the steeper into the beater is bright green, but so soon as the agglomerations of the indigc commence, it assumes the colour of „Madeira wine, and speedily afterwards, in the course of beating, a small round grain is formed, which on separat ing makes the water transparent, and falls down, when all the turbidity and froth vanish. The object of beating is threefold : first, it tends tc disengage a great quantity of carbonic acid pre sent in the fermented liquor; secondly, to give the newly-developed indigo its requisite dose of oxygen by the most extensive exposure of its particles to the atmosphere ; thirdly, to agglo merate the indigo in distinct flocks or granula tions. In order to hasten the precipitation, lime water is occasionally added to the fermented liquor in the progress of beating, but it is not indispensable, and has been supposed capable of deteriorating the indigo. In the front of the beater a beam is fixed upright, in which three or more holes are pierced a few inches in diameter. These are closed with plugs during the beating ; but two or three hours after it, as the indigo sub sides, the upper plug is withdrawn, to run off the supernatant liquor, and then the lower plugs in succession. The state of this liquor being examined, affords an indication of the success of both the processes. When the whole liquor is run off, a labourer enters the vat, and sweeps all the pre cipitate into one corner, and empties the thinner part into a spout which leads into a cistern along side of a boiler 20 feet long, 3 feet wide, and 3 deep. When all the liquor is once collected, it is pumped through a bag for retaining the impur ities into the boiler, and heated to ebullition. The froth soon subsides, and shows an oily-looking film upon the liquor. The indigo is by this pro cess not only freed from the yellow extractive matter, but is enriched in the intensity of its colour, and increased in weight. From the boiler the mixture is run, after two or three hours, into a general receiver, called the dripping vat or table, which, for a factory of twelve pairs of preparation vats, is 20 feet long, 10 feet wide, and 3 feet deep, having a false bottom 2 feet under the top edge. This cistern stands in a basin of masonry made water-tight with chunam hydraulic cement, the bottom of which slopes to one end in order to facilitate the drainage ; a thick woollen veil is stretched along the bottom of the inner vessel to act as a filter. So long as the liquor passes through turbid, it is pumped back into the receiver. Whenever it runs clear, the receiver is covered with another piece of cloth to exclude the dust, and allowed to drain at its leisure. Next morning the drained indigo is put into a strong bag and squeezed in a press. The indigo is then\ carefully taken out of the bag, and cut with a brass wire into bits about 3 inches cube, which are dried, in an airy house upon shelves of wicker - work. During the drying, a whitish efflorescence comes upon the pieces, which must be carefully removed with a brush. In some places, particularly on the coast of Coromandel, the dried indigo lumps arc allowed to effloresce in a cask for some time, and when they become hard, they are wiped and packed for exportation.