=======================+=======================+======================= | BEFORE FILTRATION. | AFTER FILTRATION. +-----------+-----------+-----------+----------- | ORGANIC | ORGANIC | ORGANIC | ORGANIC | CARBON. | NITROGEN. | CARBON. | NITROGEN. +-----------+-----------+-----------+----------- |In parts of|In parts of|In parts of|In parts of | 100,000. | 100,000. | 100,000. | 100,000. -----------------------+-----------+-----------+-----------+----------- West Middlesex Works | .209 | .071 | .198 | .043 Grand Junction Works | .262 | .042 | .231 | .032 Southwark & Vauxhall, | | | | Hampton Works | .321 | .063 | .273 | .042 Battersea “ | .239 | .047 | .226 | .035 Lambeth Works | .273 | .067 | .258 | .038 Chelsea Works | .325 | .076 | .258 | .032 New River, Lea River | .287 | .067 | -- | -- “ New River | .375 | .059 | .227 | .043 “ “ | .350 | .084 | .246 | .042 East London Co., | | | | Lea Water | .363 | .082 | -- | -- Waltham St. Res | .481 | .092 | .305 | .041 Thames Water | -- | -- | .159 | .030 -----------------------+-----------+-----------+-----------+----------- Dimensions of filter beds for given volumes (from Fanning): For 1 million gallons per diem 3 beds 60 feet × 100 feet. For 2 “ “ “ 3 “ 80 “ × 150 “ For 3 “ “ “ 3 “ 100 “ × 180 “ For 4½ “ “ “ 4 “ 100 “ × 180 “ For 6 “ “ “ 4 “ 100 “ × 240 “ For 8 “ “ “ 4 “ 120 “ × 270 “ For 10 “ “ “ 5 “ 120 “ × 270 “ Analysis of sand from filter beds (in 100,000 parts) ORGANIC ORGANIC ORGANIC MATTER. CARBON. NITROGEN. As removed from filter bed, unwashed 1523.40 314.160 38.674 After washing 804.41 94.921 16.973 It can not be doubted that a small amount of organic matter undergoes oxidation and destruction during the passage of the water through the sand; but, independent of this, it appears, from the above analytical numbers, that one ton of dry sand, washed after previous use, is capable of removing from water and retaining 16.1 lbs. of peaty matter. _Chemical_ filtration may be arranged under the following heads: 1. By use of alum and borax to reduce turbidity.