INDIGO. 473 



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'OOIS ; 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 fermen- 

 tation, 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 al- 

 lowed 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 spontane- 

 ously 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 agglomera- 

 tions 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. 



The object of the beating is three-fold ; first, it tends to disengage a great 

 quantity of carbonic acid present in the 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 agglomerate the indigo in distinct 

 flocks or granulations. In order to hasten the precipitation, lime water is oc- 

 casionallv 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 



