The dirty water from the rags is removed by the “drum-washer” C. It is divided into compartments by the partitions shown by the dotted line _c_. The centre of the drum is formed of a conical tube, the narrow end of which is towards the mid-feather. The ends of the drum are generally made of mahogany, as this is found to stand the action of alkali better than any other wood. The periphery is covered with fine copper or brass wire-cloth, laid on to a backing of a much coarser material. An improved form of backing has been introduced lately, which is much more durable than wire. It is formed of brass cut into the form shown in {87} Fig. 20. The drum can be raised or lowered by the small wheel F, and it is driven by a belt on the shaft that bears the roll. [Illustration: FIG. 20.] The wash-water passes through the wire cloth into the compartments formed by the partitions _c_, and finding its way down to the narrow end of the inner conical tube, flows out through the side of the drum into a trough which is placed across the washer to receive it. Or it may, as shown in the drawing, be conducted through the mid-feather itself, which is made hollow at this part for the purpose. Another form of drum-washer, called the siphon-washer, is sometimes used. Its construction will be understood by reference to Figs. 21 and 22. The drum is simply a hollow cylinder of wire cloth, the ends of which are formed of wood. Inside the cylinder is the siphon tube A, into which the water passing through the wire cloth flows. The continuation of the siphon tube B (Fig. 22) is made of flexible tubing. The action of the siphon is commenced by filling it with water through the cock C (Fig. 22). The water then flows in the direction indicated by the arrows. The tube A is fixed, and passes through a hollow journal fitted on to the end of the drum. {88} The other end is connected with the rod E, on which the driving pulley D is placed. [Illustration: FIG. 21.] [Illustration: FIG. 22.] The water passing through the wire cloth on the drum carries with it a certain amount of fibre which, unless special precautions are taken (see “Save-all,” p. 154) is lost. The amount is considerable in the case of weak rags, and care should therefore be taken that the washing is not prolonged more than is consistent with proper cleansing, and that the pulp should not be too much broken up at this stage. The washed and broken pulp goes by the name of “half-stuff.” {89} The following is the usual plan of treating rags in the washer:—It is first half-filled with water, and the rags from the boiler put in gradually until nearly filled. Water is now allowed to flow in at the opposite end to where the drum-washer is placed. This, by the action of the roll, mixes thoroughly with the pulp and extracts all the soluble matter, and also carries with it fine insoluble impurities.