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.
The bleached half-stuff as it leaves the steeping chests usually contains an excess of bleaching liquor, which can be removed in two ways, viz. by washing or by decomposition with an “antichlor.” The first method has the advantage of not only removing the bleach, but of also eliminating the chloride of calcium, partly existing ready formed, and also that resulting from the decomposition of the calcium hypochlorite originally present in the bleach. On the other hand, this method takes some time, and consumes a large amount of water, which in some mills is a matter of considerable importance. For this purpose, many beaters are provided with one or more drum washers (see Fig. 36). An additional objection to this method lies in the fact that a certain quantity of fibre passes through the meshes of the wire-cloth covering the washers, and is thus lost.
The more usual plan is to remove the bleach by decomposing it with an “antichlor.” The substance generally employed for this purpose is sodium hyposulphite, or thiosulphate as it is now called, which, in presence of calcium hypochlorite, is oxidized to sodium sulphate, the latter being reduced to calcium chloride. Double decomposition then takes place between these salts, with the formation of calcium sulphate and sodium chloride. The reactions which take place may be expressed by the following equation:—
2 (Ca(ClO)2)
Calcium
hypochlorite.
+
Na2S2O3
Sodium
thiosulphate.