2. Dr. Gunning’s experiment of the waters of the River Maas, by reducing the turbidity with .032 gramme of perchloride of iron into one litre of water. 3. Dr. Bischoff’s (Jr.) process of removing organic matter by spongy iron, prepared by heating hydrated oxide of iron with carbon. 4. Spencer’s process of sand filtration with crushed grains of a carbide of iron. The carbide, it is claimed, does not require frequent removal. 5. Sheet-iron strips placed in water decomposes organic matter rapidly. It is recommended by eminent authority. 6. Charcoal is, possibly, the best substance for removing organisms chemically; but its efficiency is destroyed by an insoluble precipitate of either lime or iron. Messrs. Adkins & Co., of London, have patented a method to overcome this objection, by use of charcoal plates that may be easily scraped. _Filtration through spongy iron_ (by Rivers Pollution Commission--Parts in 100,000 parts): ORGANIC ORGANIC PREVIOUS CARBON. NITROGEN. SEWAGE. Thames water, before .120 .013 1340 Thames water, after .025 .004 10 _Filtration through animal charcoal_: ORGANIC ORGANIC PREVIOUS CARBON. NITROGEN. SEWAGE. Grand Junction Co.’s water, before .164 .030 320 Grand Junction Co.’s water, after .010 .002 950 SUBSIDENCE is the most popular method of clarification of water by the deposition of heavy matter, accomplished in large storage reservoirs. “If the reservoir be very small and shallow, and containing not more than a day’s supply, for example, it is plain there can be but little opportunity for subsidence; but even in such cases, if the reservoir be kept full, or nearly full, the floating impurities might never enter the circulation. In the case of a large reservoir, holding many days’ supply, it is quite different. Time is then afforded for the heavier impurities to settle to the bottom; and, if the water is admitted at one end and taken out at the other end of the reservoir, very little, if any, of the heavier particles can pass into the circulation; and we can see no reason why any of the superficial impurities, such as remain on or near the surface, should ever be allowed to enter the circulation.”--(From Water Supply Commission of Engineers, Philadelphia, 1875.) Fanning says: “Subsidence does not completely clarify the water even in a fortnight or three weeks’ time.” London has 262 acres of subsiding reservoirs for removing the turbidity of the Thames and Lea Rivers, and used as storage at times of sudden freshets.