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plug is withdrawn to run off the supernatant liquor, and then the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 film on the liquor. The
indigo is by this process not only freed from the yellow extractive
matter, but is enriched in the intensity of its color, and increased
in we