The proper number of beds and the area of each bed corresponding to the number of persons to be served by the sewer are given in Table IV. This table also gives the required dimensions of siphon chambers (assuming that this chamber forms a separate compartment of the settling tank) for the capacities necessary in order that the effluent may be distributed in proper quantities over each bed or over each pair of beds, as in the case of plants serving two hundred or more persons. The widths of siphon chambers given correspond in general with the widths of settling tanks given in Table I. As in Table III, the dimensions of siphon chambers given are based on a drawing down of the effluent in the tank when the siphons discharge, amounting to from four to eight inches. The last column in the table gives the space which should be left between the roof of the tank and the top of the dividing wall between the settling tank and the siphon chamber to provide for this draught upon the settling-tank contents. It will be seen that no draught upon the contents of the settling tank when the siphons discharge is arranged for in the case of tanks serving from four to twenty-five persons. TABLE IV FOR USE IN CONSTRUCTING INTERMITTENT SAND FILTERS ═════════╤═════════╤═════════╤════════════╤═════════╤═════════ Persons │ No. of │ Area of │ Mean Width │Diameter │Distance Served by│ Beds. │Each Bed │ and Length │of Siphon│from Roof Sewer. │ │ (Square │ of Siphon │(Inches).│ of │ │ Feet). │ Chamber │ │Settling │ │ │ (Feet). │ │ Tank to │ │ │ │ │ Top of │ │ │ │ │ Wall │ │ │ │ │ between │ │ │ │ │Settling │ │ │ │ │Tank and │ │ │ │ │ Siphon │ │ │ │ │ Chamber │ │ │ │ │(Inches). ─────────┼─────────┼─────────┼────────────┼─────────┼───────── 4│ 3│ 60│ 3 × 3 │ 3│ 12 8│ 3│ 120│ 3 × 5 │ 3│ 12 12│ 3│ 180│ 4 × 5 │ 3│ 12 15│ 3│ 224│ 4 × 6.5│ 3│ 12 25│ 3│ 350│ 4 × 6 │ 5│ 12 35│ 3│ 480│ 4.5 × 5 │ 5│ 16 50│ 3│ 660│ 5 × 6 │ 5│ 16 75│ 3│ 1000│ 6 × 7 │ 5│ 18 100│ 3│ 1320│ 7 × 8 │ 5│ 18 125│ 3│ 1660│ 5.5 × 8 │ 6│ 20