The shaded portions A represent the stationary disc. It is furnished for about two-thirds of its circumference with steel bars or knives, placed tangentially. B represents the {125} revolving disc on which similar knives are placed radially round the whole circumference. The direction that the pulp takes is indicated by the arrows. After passing between the plates it is thrown violently into the trough at G, the result being that it is very thoroughly mixed. The distance between the plates can be regulated by means of the gearing H. The engine is driven by the pulley C fixed on the shaft F. It is claimed that by means of this form of beater a great saving in time and power is effected, and that moreover the pulp is obtained in a more even condition. [Illustration: FIG. 38.] [Illustration: FIG. 39.] The quality of the water used to furnish the engine is a matter of very great importance, especially in the manufacture of high-class papers. Above all it should be free from suspended matter, and from dissolved iron; the former finds its way directly into the paper, and the latter is liable to become precipitated in the pulp as oxide, thus injuriously affecting its colour. Careful settling and filtration are sufficient to eliminate insoluble matter; soluble impurities are more difficult of removal; therefore the water should, if possible, be free from them. In most mills settling ponds are provided, for the purpose of removing suspended matter, and in addition it is usual to employ woollen filter-bags {126} fastened to the nozzle of the pipe that supplies the beaters with water. For methods of purifying water see p. 211. The beaters are generally driven from a separate engine, and are connected with it by a system of spur-wheels, pinions, and belts. Messrs. G. and W. Bertram have lately introduced a system of direct driving of beaters, whereby a great saving in power is effected. It is illustrated in plan and elevation in Figs. 38 and 39. The crank-shaft of the engine is coupled direct on to the main driving-shaft. Large pulleys are keyed on to this shaft, from which the power is taken directly on to the pulleys connected with the rolls. {127} CHAPTER IX. LOADING, SIZING, COLOURING, ETC.