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.

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 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are closed with plugs during the beating, but two or three hours after it, as the indigo subsides, the upper plug is withdrawn to run off the supernatant liquor, and then the lower plugs in succession.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 laborer enters the vat, sweeps all the precipitate into one corner, and enters the thinner part into a spout which leads into a cistern, alongside of a boiler, twenty feet long, three feet wide, and three feet deep.  When all this liquor is once collected, it is pumped through a bag, for retaining the impurities, into the boiler, and heated to ebullition.  The froth soon subsides, and shows an oily looking