[Illustration: INDIGO BEATERS AT WORK IN THE VATS.]

During the beating, two processes are going on simultaneously. One is
chemical--oxygenation--turning the yellowish green dye into a deep
intense blue: the other is mechanical--a separation of the particles of
dye from the water in which it is held in solution. The beating seems
to do this, causing the dye to granulate in larger particles.

When the vat has been beaten, the coolies remove the froth and scum
from the surface of the water, and then leave the contents to settle.
The fecula or dye, or _mall_, as it is technically called, now settles
at the bottom of the vat in a soft pulpy sediment, and the waste liquor
left on the top is let off through graduated holes in the front. Pin
after pin is gradually removed, and the clear sherry-coloured waste
allowed to run out till the last hole in the series is reached, and
nothing but dye remains in the vat. By this time the coolies have had a
rest and food, and now they return to the works, and either lift up the
_mall_ in earthen jars and take it to the mall tank, or--as is now more
commonly done--they run it along a channel to the tank, and then wash
out and clean the vat to be ready for the renewed beating on the
morrow. When all the _mall_ has been collected in the mall tank, it is
next pumped up into the straining room. It is here strained through
successive layers of wire gauze and cloth, till, free from dirt, sand
and impurity, it is run into the large iron boilers, to be subjected to
the next process. This is the boiling. This operation usually takes two
or three hours, after which it is run off along narrow channels, till
it reaches the straining-table. It is a very important part of the
manufacture, and has to be carefully done. The straining-table is an
oblong shallow wooden frame, in the shape of a trough, but all composed
of open woodwork. It is covered by a large straining-sheet, on which