This schedule of rates was carried out in a general way with all the filters, with the exception of Nos. 5 and 6. For these, the rates were found to be higher than could be maintained for any great length of time, owing to the deeper penetration of the mud in the filter sand, which caused high initial losses of head, short runs, and deep scrapings. A rate of about 30,000,000 gal. was maintained in the case of Filter No. 5 from the time it was started on September 9th, 1908, until November 8th, 1909, when it was reduced to about 17,000,000 gal., which rate was maintained thereafter until the filter was shut down in February, 1910. [Illustration: ~Figure 7--Plan of Filter-House and Equipment.~] In the case of Filter No. 6, it was found impossible to maintain a rate of 100,000,000 gal. for more than a very few days at a time. It was started at about this rate, however, at the beginning of each run, and kept as high as possible for the remainder of the time during the first seven runs. At the end of the seventh run, on October 17th, 1908, the filter was given a very deep scraping and re-sanded. [Illustration: ~Figure 8--Diagrammatic Sketch Showing Arrangements for Testing "Puech" System of Water Filtration at Washington D. C., U. S. A.~] The layer of clean sand restored the original capacity, and the filter was operated as before, but with gradually decreasing rates until December, 1908, when the rate was reduced to about 40,000,000 gal. Even this lower rate was too high to be maintained without removing and replacing a large part of the sand. The rates, therefore, gradually decreased to about 23,000,000 gal. on March 13th, 1909, when the filter was again re-sanded. After this re-sanding the rate was reduced to about 20,000,000 gal., and the filter was operated at approximately that rate until it was again re-sanded on November 13th, 1909, when the rate was again reduced to about 14,000,000 gal., which was maintained until the filter was put out of service on February 28th, 1910. This experimental plant was in service from September, 1908, to the latter part of February, 1910, or for about 1-1/2 years, and the leading results are summarized in Table 20. ~Table 17--Record of Experimental Filter Plant No. 1.~ Columns: A - Rate, millions of gallons per acre daily. B - Loss of head. C - Rate, millions of gallons per acre daily. D - Loss of head. E - Applied water. F - Effluent preliminary filter. G - Effluent final filter. H - Applied water. I - Effluent preliminary filter. J - Effluent final filter.