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.

The utility of raking, as an intermediate treatment between
scrapings, seems to ha