The boiling being completed, the pressure is allowed to fall, either by cooling or by blowing off from a cock usually provided for that purpose, and the liquor allowed to collect at the bottom of the boiler. It is then run off by the cock J (Fig. 18), and the rags drained as much as possible. Water is then run in to give the rags a preliminary washing. If time permits the steam may be turned in and the operation assisted. After again draining, the rags are withdrawn from the boiler into any suitable receptacle. A convenient form is that of a rectangular iron box on wheels, which can be readily transferred from one part of the mill to another. {85} The next process is that of washing. This is usually performed in a washer or breaker, the construction of which is shown in Fig. 19. [Illustration: FIG. 19.] It consists essentially of a rectangular vessel with rounded ends, in the centre of which, but not extending the whole {86} way, is a partition B, known as the “mid-feather.” The roll A, which is furnished with a number of steel knives G, and driven from the wheel H, revolves in one of the compartments formed by the mid-feather. In this compartment the floor is inclined in such a way as to bring the pulp well under the roll, as shown by the dotted line D. Immediately under the roll is what is called the “bed-plate,” the end of which is seen at I, extending up to the mid-feather, and fitted with knives similar to those in the roll A. The arrangement of the knives, both in the bed-plate and the roll, is similar to that given in Figs. 33 and 34. The distance between the roll and the bed-plate can be varied at will by means of the handle E, which is so arranged as to raise both ends of the roll simultaneously. In those breakers of an older pattern, one end only of the roll was raised, and thus the knives became worn unequally. After passing between the roll and the bed-plate, the pulp flows down the “back-fall” D′, and finds its way round to the other side of the mid-feather. On the inclined part of the floor, and immediately in front of the bed-plate I, a small depression is made, covered with an iron grating, for the purpose of catching buttons, small pieces of stone, and other heavy substances that may have found their way into the rags. There is generally a similar grating with rather finer openings on the other side of the mid-feather. The engine is constructed of iron, generally made in one casting.