on, while the third
consisted of sedimentation and coagulation. The sedimentation tank
was of sufficient size, when compared with the area of the
experimental slow sand filter, to represent the Georgetown and
McMillan Park Reservoirs when used in connection with the large
filters. The first preliminary filter was very similar in construction
and operation to a mechanical filter. The sand for this filter was
taken from the main filters, and, consequently, was finer than is
generally used in mechanical filters. The second preliminary filter
was a Maignen scrubber. It consisted of a cylindrical concrete tank,
4 ft. in diameter and 8-1/2 ft. deep, which contained 12 in. of
cobble-stones on the bottom, then, successively, 12 in. of egg-size
coke, 12 in. of stove-size coke, 24 in. of nut-size coke, and 24 in.
of sponge clippings as the final or top layer.

~Table 14--Cost Per Million Gallons Filtered.~
(_A_) ~Labor~.
=============+===========+==========+==================
| Office | | ~Filter~
| and | Pumping | ~operations~:
Month. |laboratory.| station. +------------------
| | | Sand |Repairs
| | |handling.| etc.
-------------+-----------+----------+---------+--------
1909.
-------------+-----------+----------+---------+--------
July | $0.73 | $0.57 | $0.86 | ...
August | 0.75 | 0.64 | 0.59 | ...
September | 0.83 | 0.67 | 0.80 | ...
October | 0.72 | 0.66 | 0.73 | ...
November | 0.87 | 0.76 | 0.42 | ...
December | 0.90 | 0.69 | 0.27 | ...
-------------+-----------+----------+---------+--------
1910.
-------------+-----------+----------+---------+--------
January | 0.81 | 0.63 | 0.33 | ...
February | 0.94 | 0.74 | 0.35 | $0.07
March | 0.92 | 0.81 | 0.30 | 0.07
April | 0.93 | 0.83 | 0.49 | 0.03
May | 0.86 | 0.72 | 0.36 | 0.03
June | 0.88 | 0.67 | 0.38 | ...
-------------+-----------+----------+---------+--------
Average | 0.84 | 0.70 | 0.27 |[1]0.25
-------------+-----------+----------+---------+--------
Fiscal years:
-------------+-----------+----------+---------+---