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 the mall settles; while the waste water trickles through and is carried away by a drain. When the mall has stood on the table all night, it is next morning lifted up by scoops and buckets and put into the presses. These are square boxes of iron or wood, with perforated sides and bottom and a removeable perforated lid. The insides of the boxes are lined with press cloths, and when filled these cloths are carefully folded over the _mall_, which is now of the consistence of starch; and a heavy beam, worked on two upright three-inch screws, is let down on the lid of the press. A long lever is now put on the screws, and the nut worked slowly round. The pressure is enormous, and all the water remaining in the _mall_ is pressed through the cloth and perforations in the press-box till nothing but the pure indigo remains behind.