Dosing apparatus, Ansonia automatic, 43 three kinds of, 53 Drain pipe from settling tank, 26 Emscher or Imhoff tanks, 34 Excavation for settling tanks, 25 Fertilizing elements in sewage, value of, 98 Forms for building settling tanks, 22 Grease traps in connection with sand filters, 78 Imhoff or Emscher tanks, 34 Irrigation, amount of water necessary for, 101 of orchards, 108 value of sewage for, 99 Laws against disposal of sewage into streams, 3 Manholes through settling-tank roof, 29 Overflow pipe from siphon chamber, 31 Roof of settling tank, construction of, 27 Sand filters, alternating flow of effluent to different beds composing, 83 artificially constructed, 79 details of construction of, 74 devices for dosing, 82 distribution of effluent over, 78 preparation for winter of, 84 quality of sand suitable for, 86 scraping surface of, 84 settling of sewage before application to, 77 table for use in constructing, 76 underdrainage of, 81 Sand filtration, 74 Screening of sewage, 5 Settling-tank floors, necessary slope of, 26 tanks compared with septic tanks, 11 construction of floors of, 25 description of, 16 dimensions for, 18 function of, 14 location of, 20 near sub-surface irrigation field, 31 materials for and construction of, 20 operation of, 32 partial treatment only provided by, 16 water-tight, construction of, 24 Sewage, composition and character of, 4 disposal—an engineering problem, 1 Sewage disposal: by dilution, 3 in soils, three essential conditions for, 8 need of, 2 plants, permissible rates of operation of, 8 preliminary and final methods of, 11 Sewage filters, 73 proper operation necessary to success of, 96 relative efficiency of various types of, 73 Sewer, size and gradient of effluent, 63, 77 Siphon chamber, depth of sewage in, 38 Siphon chambers, 21, 60 necessity for, 37 Siphon, Miller, 45 simplest form of, 44 Van Vranken, 44 Siphons, alternating air-lock, 52 discharging depth or draught of, 77 for automatic discharge of sewage effluent, 42 how to place, in position, 25, 64, 77 Merritt, 50 placing two in one chamber for alternating flow, 47 plural alternating, 48 sketches of and directions for setting furnished by manufacturers of, 53 Size of dose in disposal plants, 10 Sludge pipe from settling tank, 27 Soils and their suitability in purifying sewage, 7 Sprinkling filters, 93 construction and operation of, 94 Sub-surface irrigation, conditions favorable to, 71 description of, 55 fields, location of, 58 soils suitable for, 57 special advantages of, for country home, 57 system—advantages over cesspools, 56 systems, alternate use of different portions of, 68 details of construction of, 58, 63 value of underdrainage in, 69 tables for use in constructing, 59 underdrains for, 69