It has already been pointed out that in dealing with the pure samples of rubber now produced on estates, the preliminary cleansing operations, necessary in the case of all ordinary commercial samples, will probably be omitted from the series of manufacturing processes in the rubber factories of the future. The washing machines used in factories are generally similar to those employed upon estates, but are usually larger and more powerful. They are generally driven from shafting through powerful clutches, and special arrangements are often introduced for throwing the machinery automatically out of gear in case of accident, for example when large stones or other bodies liable to cause damage are encountered. Prior to the actual process of washing, large commercial blocks are softened by soaking in hot water, and are sliced into smaller pieces by special machines, either before or after the softening process. A series of washing machines is usually employed, and the rollers through which the rubber first passes have coarser grooves and are set further apart than the later members of the series. The arrangement thus resembles to some extent the series of rollers in a modern flour mill, although the processes of rubber washing and flour milling have little other resemblance. By passing repeatedly through the washing rollers under a stream of water, the impurities present in most kinds of commercial rubber are gradually washed away, and the rubber finally emerges in the form of a thin crÍpe convenient for drying. The rubber itself undergoes much tearing and stretching during the process, and it is important that this mechanical action should not be carried further than is absolutely necessary in order to ensure a sufficient degree of purity, since the "nerve" of the rubber is largely destroyed by the forcible treatment involved.