The Para rubber is very liable to have impurities embedded in it. Stones are common and these and all other foreign matter must be extracted from the mass. Washing machines remove all dirt which has escaped examination. The rubber is masticated between rollers armed with steel teeth and washed with hot water.
After the rubber has come out of the washing machines it is put on frames and dried in ovens where it is kept for several hours as it is most important that no moisture be carried to the further processes, Pure rubyer alone is not mechanically strong enough and is liable to rapid deterioration, and to rectify this an expensive compound of minera] oxide must be added to the pure rubber, After preparation, the rubber compound is put through a calendering tha chine which rolls the rubber into thin sheets on ai cotton blanket to prevent adhesion.
The next process is the stranding of the single copper wires into cables before the insulating material is applied.
Text read from the printed page and cleaned; old type leaves the occasional error.