0.001 c.c....| 6 | 6 | 5 | 6 | 3 | 3 ------------------+--------+--------+--------+---------+---------+-------- Number samples positive, effluent: 10 c.c........| 100 | 109 | 134 | 98 | 94 | 106 1 c.c........| 51 | 61 | 55 | 56 | 46 | 50 0.1 c.c......| 9 | 13 | 16 | 16 | 4 | 13 0.01 c.c.....| 0 | 0 | 0 | 0 | 0 | 0 0.001 c.c....| 0 | 0 | 0 | 0 | 0 | 0 ------------------+--------+--------+--------+---------+---------+-------- Percentage of samples showing _bacillus coli_ in influent: 10 c.c........| 41.2 | 44.2 | 42.2 | 59.2 | 41.9 | 45.2 1 c.c........| 22.7 | 25.0 | 23.9 | 24.3 | 24.2 | 27.2 0.1 c.c......| 10.5 | 12.8 | 11.9 | 12.3 | 13.5 | 13.2 0.01 c.c.....| 5.1 | 7.7 | 7.5 | 8.2 | 8.8 | 8.2 0.001 c.c....| 1.2 | 1.4 | 1.2 | 1.5 | 1.0 | 1.0 ------------------+--------+--------+--------+---------+---------+-------- Percentage of samples showing _bacillus coli_ in effluent: 10 c.c........| 19.5 | 24.1 | 29.5 | 24.2 | 31.7 | 34.3 1 c.c........| 10.0 | 13.4 | 12.0 | 13.8 | 15.4 | 16.1 0.1 c.c......| 1.9 | 3.1 | 3.8 | 4.2 | 1.5 | 4.5 0.01 c.c.....| 0 | 0 | 0 | 0 | 0 | 0 0.001 c.c....| 0 | 0 | 0 | 0 | 0 | 0 ------------------+--------+--------+--------+---------+---------+-------- Cost per million | | | | | | gallons for | | | | | | sand handling.....| $0.43 | $0.25 | $0.29 | $0.33 | $0.54 | $0.60 ------------------+--------+--------+--------+---------+---------+-------- Interest charges | | | | | | at 3%...........| 6.85 | 2.25 | 1.12 | 0.73 | 0.32 | 0.22 ------------------+--------+--------+--------+---------+---------+-------- Total.........| 7.28 | 2.50 | 1.41 | 1.06 | 0.86 | .82 ==================+========+========+========+=========+=========+========= _Coli_ tests presumptive. DISCUSSION ~Allen Hazen, M. Am. Soc. C. E.~ (by letter).--This paper contains a most interesting and instructive record of the actual operation of a large filter plant, and also a record of a number of experiments. The author has described some useful arrangements for improving the efficiency or reducing the cost.