Danger of clogging sewers 35–36–37 Disposal of Street Refuse 38 Experience of cities 38 Length of haul 38 Used as fill 38 Relative Cost of Street Cleaning 39 Experts, opinions of 39 U. S. Census Bureau, investigation of 39 SEWAGE DISPOSAL Bureau of Surveys, Philadelphia Testing Station 72 Composition of Sewage 72 Importance of Sewage Disposal Problem 71 Massachusetts State Board of Health conclusions 72 Preliminary Study 72 The Sewerage System 73 Authorities, opinion of 73–74 Domestic Wastes 74 Degree of Purification 75 Trade and industrial wastes 77 Processes of Treatment 78 Main group 78 Chemical precipitation 91–92 Colloidal tanks 85 Dilution 80–81 Grit Chambers 82–83 Plain sedimentation 84–85 Preliminary or preparatory 78 Screening 81–82 Septic tank treatment 85 Imhoff tanks 87–88–89–90–91 Cameron tanks 85–86–87 Single contact beds 93–94 Straining or roughing 83–84 Slate beds 92–93 Final process 78 Dosing chambers 93 Double contact beds 93–94–95–96 Trickling-sprinkling filters 96–97 Intermittent sand filters 98–99 Broad irrigation 100–101