FILTER FOR MASON CITY.
Mason City, Ia., has installed a filter 170 ft. from the shore, on a sandy bottom. It consists of an inner tank 3x6x8 ft. and built of 2-in. plank, with a 1-in. space between the planks on each side and the top and bottom watertight. Outside of this is another box, of somewhat smaller dimensions, but of the same make, except that the top is open. Outside of that, again, is one just like it, except that both top and bottom are open. In each box the spaces between the planks are covered with heavy wire screening; the outer and middle boxes are filled with sand and gravel; and the inner box is also covered with gravel to the depth of about l ft. The entire filter is supposed to be about 3 ft. below the surface of the lake, and the water will filter through 4 ft. of sand and gravel—enough to keep out frogs and lizards, but surely not sufficient to purify very impure water.
Mason City, Ia., has installed a filter 170 ft. from the shore, on a sandy bottom. It consists of an inner tank 3x6x8 ft. and built of 2-in. plank, with a 1-in. space between the planks on each side and the top and bottom watertight. Outside of this is another box, of somewhat smaller dimensions, but of the same make, except that the top is open. Outside of that, again, is one just like it, except that both top and bottom are open. In each box the spaces between the planks are covered with heavy wire screening; the outer and middle boxes are filled with sand and gravel; and the inner box is also covered with gravel to the depth of about l ft. The entire filter is supposed to be about 3 ft. below the surface of the lake, and the water will filter through 4 ft. of sand and gravel—enough to keep out frogs and lizards, but surely not sufficient to purify very impure water.
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