============+======+=============+=============+============== | Raw |Filter No. 1.|Filter No. 2.|Filter No. 3. Date. |water.|------+------+------+------+------+------- | | A | B | C | D | E | F ------------+------+------+------+------+------+------+------- January 12th| 40 | 10 | 1 | 12 | 1 | 2 | 0 January 13th| 110 | 45 | 2 | 51 | 2 | 2 | 0 January 14th| 210 | 95 | 3 | 113 | 4 | 2 | 0 January 15th| 325 | 190 | 12 | 222 | 15 | 3 | 0 January 16th| 360 | 210 | 37 | 247 | 42 | 5 | 0 January 17th| 242 | 122 | 24 | 147 | 26 | 6 | 0 January 18th| 137 | ... | ... | 73 | 7 | 6 | 0 January 19th| 117 | 40 | 12 |clean-| ... | 5 | 0 | | | | ing | | | January 20th| 72 | 31 | 6 | sand | ... |clean-| 0 | | | |filter| | ing | January 21st| 55 | 20 | 4 | 25 | 4 | sand | ... January 22d | 49 | 17 | 3 | 21 | 4 |filter| ... January 23d | 40 | 12 | 3 | 15 | 3 | 3 | 0 January 24th| 40 | 11 | 3 | 13 | 3 | 3 | 0 ============+======+======+======+======+======+======+======= It is unfortunate that this system was not in operation in January, 1908, when the water was cold and turbid. The results, however, indicate that it would be no more successful than either Filter Plant No. 1 or No. 2. _Experimental Rate Studies._--In September, 1908, an experimental plant consisting of six small filters was put in operation. The object of these experiments was to study the relative efficiencies and cost for the operation of slow sand filters when operated at different rates. The units of the plant consisted of cylindrical galvanized-iron tanks 4 ft. in diameter and 9 ft. high. The filter sand in these tanks was taken from the supply for the main filters. It was supported on gravel layers and supplied with under-drains of suitable sizes for the proposed rate of flow in each case. The units of the experimental plant were designated as Nos. 1, 2, 3, 4, 5, and 6, and it was the original intention to operate them at rates of 1,000,000, 3,000,000, 6,000,000, 10,000,000, 30,000,000, and 100,000,000 gal. per acre daily, respectively.