Results of analyses of sewage and effluent from septic tanks show an efficiency of from 85 to 90 percent in the organic matter in suspension. Very little change takes place in the matter in solution. The result of experiments with a single contact bed at Sutton, England, from November 1896 to March 1898 shows a purification of 64 percent; if, however, two beds are used in series, a further purification of 50 percent is obtained or a total purification of 82 percent of the crude sewage. The capacities of irrigation, and intermittent downward filtration plants, and contact beds are usually stated in terms of the number of gallons per acre per day. TABLE III. _RATE OF SEWAGE TREATMENT._ System. Location. Sewage treated in gallons per acre per day. ----------------------------------------------------------------------- IRRIGATION. Berlin, Germany. 18,000. Manchester, Eng.—Estimated but not constructed. 18,500. INTERMITTENT DOWNWARD FILTRATION. Framingham, Mass. 19,000. Leicester, Mass. 38,750. Brockton, Mass. 44,000. Marlborough, Mass. 54,000. Gardner, Mass. 140,000. Mendota, Ills. 184,000. Worcester,[1] Mass. 322,000. Worcester,[1] Mass. (Fletcher’s estimate). 500,000. Madison,[1] Wis. 8,000,000. CONTACT BEDS. Manchester, Eng. (crude sewage) 500,000. Manchester,[1] Eng. 700,000. Manchester, Eng. (storm water sewage) 2,500,000. Footnote 1: Secondary filtration. Table III shows the capacity of representative plants. Best authorities consider 100,000 gallons per acre per day to be the maximum rate permissible under the best conditions for the treatment of crude sewage by the intermittent downward filtration system. With unfavorable conditions the quantity of sewage should be limited to as low as 20,000 gallons. Wherever too large a dose is applied to the bed the sewage is not properly purified and the beds soon become clogged up and unfit for further use. When the beds are used for secondary purification, 750,000 gallons may be treated per acre per day.