(A) The pulp can be bleached in the washing engine directly the grass has been sufficiently cleaned. In this case the flow of fresh water is stopped and as much water as possible removed by means of the drum-washer. The drum-washer is then raised out of the pulp and a known volume of bleaching powder solution corresponding to a definite weight of dry powder is added to the contents of the breaking engine. The amount used depends on the quantity of dry grass in the breaking engine, the usual proportion being 8 to 10 per cent. on the calculated air-dry weight of raw grass. As the stuff circulates round the engine the colour gradually changes from dark yellow to white. The process is sometimes hastened by blowing a small quantity of steam into the mixture and thereby raising its temperature. Considerable care must be exercised in using heat, because pulp bleached quickly by this means is liable to lose colour at the later stages of manufacture. When the pulp has been bleached to the required extent, the drum-washer is again lowered into contact with the bleached pulp, and the latter is thoroughly washed so as to be quite free from traces of bleach and other soluble impurities. (B) Esparto is often bleached in a "Tower" bleaching engine which consists of a tall cylindrical vessel of 9 feet diameter, and 15 or 16 feet deep, at the bottom of which is fixed a small centrifugal pump. The boiled grass together with sufficient water and clear bleaching powder solution is placed in the engine; the centrifugal pump draws the mixture from the bottom of the vessel and discharges it, by means of a large external pipe, direct into the top of the vessel, where, as it falls, it comes into contact with a circular baffle-plate, which distributes the pulp evenly over the surface of the mixture in the vessel. A continuous and rapid circulation is thus maintained, and the process is said to be very effective. The bleached pulp is subsequently washed free from any traces of bleach. (C) Esparto is frequently bleached by the "steeping" process. In this case the pulp is washed in the breaking engine, mixed with the required quantity of bleach, and at once discharged through the outlet pipes of the engine into large brick tanks, where the bleach is allowed to act quietly upon the boiled grass. This method produces a pulp of good colour and is economical. Whichever process of bleaching is adopted, it is necessary to remove all the by-products formed during the process, as these soluble by-products if left in the mixture produce a lowering of colour.