if desired, it may be regenerated by ignition. It forms a very useful mixture with pulp fibre. All the above decolorizing materials are insoluble and hydrophobe, and act in virtue of their finely divided conditions, which causes them to have a large specific surface; but there is another type or branch of substances, whose effect is due to surface action of rather a different type. These are the hydrophile gels. In a gelatine sol the colloid particles have largely adsorbed the colouring matters which it is desired to remove. This adsorption, which is after all only an equilibrium, is reduced by introducing another very strong adsorbent. This latter, by adsorption from the continuous phase, reduces the adsorption of colouring matters by the gelatine particles. In the case under discussion another lyophile colloid is introduced, and after bringing about such an action is removed by appropriate means. The use of albumin has long been known for such a purpose, its special advantage being that after its admixture and adsorptive action, it may easily be removed by raising the temperature above 70° C., when coagulation takes place, and by subsequent mechanical filtration. The coagulated albumin takes down the adsorbed colouring matters. Albumin has been used in this way not only for gelatine and glue liquors, but also for tanning extracts (Part I., Section III.) and other commercial preparations. Into this class of decolorizing agents fall the insoluble inorganic gels which have been advocated by W. Gordon Bennett, _e.g._ alumina cream. Freshly precipitated alumina hydrate is a colloid gel with very considerable adsorptive powers. It has also the advantage that it is quite insoluble, easily removed in filtration, and has a powerful adsorptive action upon other objectionable impurities, especially the poisonous metals, arsenic, copper, zinc and lead. Its use is an undoubted advantage when in addition to the other clarifying agents and adsorbents. It is conceivable, in some cases, that when alum is employed as clarifying agent in an alkaline gelatine liquor, some alumina may be formed, and as such contribute to the total effect. SECTION V.--BLEACHING