The electrolysing vat consists of a rectangular vessel of slate or other suitable material. The negative electrode may be constructed of zinc; for the positive it is necessary to employ platinum. The electrolysed solution has been found to possess very remarkable properties, which have considerable bearing upon the economy of the process. If a solution be taken of equal {116} oxidising efficiency with one of calcium hypochlorite, as indicated by the arsenious acid test (see p. 206), it is found that the former possesses greater _bleaching_ efficiency than the latter in the proportion of 5 to 3. Moreover, the bleaching is much more rapid, and the loss of weight which the substances undergo is less, for equal degrees of whiteness obtained. It has been shown that by the electrolytic method the bleaching of paper pulp can be effected at nearly one-half the cost of bleaching powder. The process is now being industrially carried out. Those interested in the subject are referred to a paper by the authors in the ‘Journal of the Society of Chemical Industry’ for April 1887. {117} CHAPTER VIII. BEATING. The bleached pulp is now ready for the final treatment. If it were attempted to make paper from the pulp in the state in which it leaves the “potchers” or “steeping” chests, it would be found to be wanting in evenness of texture and uniformity of surface. This result can only be secured by an elaborate process of comminution or disintegration. This is in effect the result produced by the action of the “beaters.”