Parts per 1,000,000 +----------------------------------------------------------------------------+ ¦ ¦ April 20, 1900 ¦ May 4, 1900 ¦ +----------------------+--------------------------+--------------------------¦ ¦ ¦Sewage¦Effluent¦Efficiency¦Sewage¦Effluent¦Efficiency¦ +----------------------+------+--------+----------+------+--------+----------¦ ¦Oxygen consumed: ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 48.5 ¦ 6.50 ¦ 86% ¦ 27.7 ¦ 12.0 ¦ 55% ¦ ¦ In suspension¦ 33.4 ¦ ¦ ¦ 15.5 ¦ 4.6 ¦ 70% ¦ ¦ In solution ¦ 15.1 ¦ ¦ ¦ 12.2 ¦ 7.4 ¦ 40% ¦ ¦Nitrogen as albuminoid¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ Total ¦ 10.4 ¦ .32 ¦ 97% ¦ 3.68 ¦ .768 ¦ 79% ¦ ¦ In suspension¦ 9.28 ¦ ¦ ¦2.816 ¦ .416 ¦ 85% ¦ ¦ In solution ¦ 1.12 ¦ ¦ ¦ .864 ¦ .352 ¦ 59% ¦ ¦Total organic nitrogen¦17.960¦ .920 ¦ 95% ¦ 9.60 ¦ 1.860 ¦ 81% ¦ ¦ In suspension¦15.04 ¦ ¦ ¦7.500 ¦ 1.152 ¦ 85% ¦ ¦ In solution ¦ 2.92 ¦ ¦ ¦2.100 ¦ .708 ¦ 66% ¦ ¦Nitrogen as free ¦ ¦ ¦ ¦ ¦ ¦ ¦ ¦ ammonia ¦ 7.20 ¦ 2.40 ¦ 67% ¦ 3.84 ¦ 1.28 ¦ 67% ¦ ¦Nitrogen as nitrites ¦ .675 ¦ .375 ¦ ¦ 000 ¦ 000 ¦ ¦ ¦Nitrogen as nitrates ¦ 4.00 ¦ 18.00 ¦ ¦ .120 ¦ .120 ¦ ¦ ¦Chlorine as chlorides ¦ 53.0 ¦ 49.0 ¦ ¦ 47.0 ¦ 44.0 ¦ ¦ +----------------------------------------------------------------------------+ _Chemical Precipitation_ When certain chemicals are added to sewage a precipitate is formed which under favorable conditions may carry down with it all the suspended matter as well as a portion of the dissolved organic matter. The addition of the chemicals together with the working of the various appliances for grinding and mixing the same, the decanting of the effluent, and the caring for the sludge all constitute what is known as the chemical treatment of sewage, the complete process being in reality partly chemical and partly mechanical. The following matter concerning the theory of precipitation is taken from Baker and Rafter’s Sewage Disposal.