In the western provinces from sixteen to twenty maunds of plant is considered a good produce per biggah. In the upper provinces the produce of the best crop, which is sown directly the rains commence, is not more then ten maunds per biggah. The factory maund is equal to about seventy-eight pounds. One thousand maunds of plant are considered as producing quite an average quantity of indigo if this amounts to four maunds. Adopting another mode of estimate, Mr. Ballard says, that in Bengal an average crop may he considered to be from ten to twelve bundles, over an extensive cultivation, in a good season, from each Bengal biggah; the sheaf or bundle being measured by a six-feet cord or chain. Speaking of the produce in Tirhoot, the same gentleman says the "luggie," or measuring rod, varies throughout the district. The common Tirhoot biggah, is, I believe, equal to two-and-a-half or three Bengal biggahs (about an English acre). Its produce varies according to the size of the luggie, the fertility of the soil, and accidents of season; eight to ten hackery loads, however, is generally considered a good average return. South and east of Tirhoot, one hundred maunds from six hundred biggahs, including "khoonti," or a second cutting, is reckoned a successful result. In another part of the district, including Sarun, where the "luggie" is larger, the average produce is about one-third better. As we measure our plant on the ground (he adds), the bundle system is unknown here; but, I believe, forty-five or fifty Tirhoot hackery loads of plants (estimated to yield a maund of dry indigo), will be found equal to two hundred Bengal bundles.—("Trans. Agri. Hort. Soc., vol. ii. p. 23.")
In Oude the jamowah, or crop sown in May, yields on an average twenty maunds, or say thirteen bundles, per biggah (160 feet square). The "assaroo," or rain sowings, producing a very inferior plant, the average return is not more than three maunds, or two bundles. The "khoonti," or crop of the next year from the same plants, averages fifteen maunds, or ten bundles per biggah.
In Central and Western India, the plants are allowed to produce the second and even the third year, according to some statements; but in Bengal the same stocks are rarely suffered to yield a second crop: being nearly all on lands that are under water in the height of the inundation, the stock is rotted in the ground. Mr. Ballard, speaking of the duration of the plant, says that, as for three years' plant and "khoonti," it is a mere chimera, like the many others with which the planters have hitherto deluded themselves, and which it only requires a little reflection to overthrow. A biggah may be cut here and there, on an extensive cultivation, but it can never be relied upon as forming a part of the cultivation.
The uncertainty of the indigo crop has been already noticed, and is, indeed, as proverbial as that from the hop plant in England. In Bengal the crop is particularly subject to be destroyed by the annual inundation of the river, if it occurs earlier than usual. A storm of wind, accompanied by rain and hail, as completely ruins the crop as if devoured by the locust; neither from this latter scourge is the crop exempt.
This proneness to injury extends throughout its growth. The seedlings are liable to be destroyed by an insect closely resembling the turnip-fly, as well as by the frog. Caterpillars feed upon the leaves of older plants, and the white ant destroys them by consuming their roots. To these destructive visitations are to be added the more than ordinary liability of the plant to injury, not merely from atmospheric commotions, but even from apparently less inimical visitations. Thus not only do storms of wind, heavy rains, and hail, destroy the indigo planter's prospects, but even sunshine, if it pours out fervently after showers of rain, is apt, as it is properly termed, to scorch the plants; and if it occurs during the first month of their growth, is most injurious to their future advance. The reason of this effect appears to be the violent change from a state of imbibing to a rapid transpiration of moisture. No human invention or foresight can preserve the crop from the atmospheric visitations. To destroy and drive away the little coleopterous insects which attack the seedlings, it would be a successful method to spread dry grass, &c., over the surface intended to be cultivated, and to burn the litter immediately before the sowing. The heat and smoke produced has been found perfectly efficacious against the turnip-fly in England. To destroy the caterpillar, slacked lime dusted over the leaves, while the dew is upon them, is an effectual application. The white ants may be driven away or destroyed by frequent hoeings, which is the best preventive of the scorching, for hoeing preserves the soil in an equable and fitting state of moisture.
The great supply of seed for Bengal cultivation is obtained from the western provinces, and forms an article of trade of no inconsiderable magnitude. The stubble in the low lands of Bengal is generally submerged before it has time to throw out fresh shoots, on which the blossom and subsequent seed-pod are formed. There are, however, some high tracts reserved for that purpose, and on these the plant is found well in flower in September, and the seed fit to gather in November or early in December.
Two methods are pursued to extract the indigo from the plant; the first effects it by fermentation of the fresh leaves and stems; the second, by maceration of the dried leaves; the latter process being most advantageous. They are thus described by Dr. Ure, in his "Dictionary of Arts and Manufactures:"—
1. From the recent leaves.—In the indigo factories of Bengal, 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 uppermost is called the fermenting vat, or the steeper; its area is twenty feet square, and its depth three 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 five or six 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. 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 prevailing winds, the quality of the water, and the ripeness of the plants. Nine or ten hours after the immersion of the plant, the condition of the vat must be examined; frothy 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, apparently boiling, innumerable bubbles mount to the surface, and a copper colored 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 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 color, which, when the indigo precipitates, changes to green. The average temperature of the liquor is commonly 85 deg. Fahr.; its specific gravity at the surface is 1.0015; and at the bottom 1.003.
As 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 busquets. Paddle wheels have also been employed for the same purpose. Meanwhile two other laborers 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 twelve to fourteen per cent. of its weight, chiefly water and extractive matter.
The liquor in the lower 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 the fermentation, which 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 clears 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 a flask of oil. In such a case the beating must be 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 fermentation. On the other hand, a rightly fermented vat is easy to work; the froth, though abundant, vanishes whenever the granulations make their appearance. The color of the liquor, when drawn out of the steeper into the beater, is bright green; but as soon as the agglomerations of the indigo commence, it assumes the color of Madeira wine; and speedily afterwards, in the course of beating, a small round grain is formed, which, on separating, makes the water transparent, and falls down, when all the turbidity and froth vanish.