The logs, usually of spruce or poplar, are first split, as seen at the bottom of [Fig. 127], then placed in the chipper, where a revolving disc with knives cuts them into small chips, which are fed to an elevator and raised to a screening device, seen at the top, to remove saw-dust, dirt and knots. In the sulphite process the chips are then delivered into the digesters shown in [Fig. 128], which are supplied with sulphurous acid generated in a plant shown in [Fig. 129]. In the digesters the gummy and resinous matters are dissolved by the heat and chemicals, and the woolly fibre left behind is bleached, washed, and dried, and afterwards made into paper upon the Fourdrinier machine.
FIG. 127.—CHIPPING LOGS FOR PAPER PULP.
FIG. 128.—DIGESTER FOR WOOD PULP.
