ion in the sand layer,
however, seems plainly evident.

In corroboration of the third point mentioned in the theoretical
consideration of turbidity removal in the filters, the daily
turbidities of the filtered water have been classified and
summarized for different turbidities in the applied water, and also
for different temperatures. The average turbidities thus obtained
are given in Table 31.

~Table 31--Turbidity in Filtered Water at
Different Temperatures Produced by
Given Turbidity in Applied Water.~
==========+=================================================
Turbidity |
of | ~Temperature, in Degrees, Fahrenheit.~
applied |---------+---------+---------+---------+---------
water. | 40 | 40 - 50 | 50 - 60 | 60 - 70 | 70
----------+---------+---------+---------+---------+---------
20 | 1.8 | 1.3 | 1.2 | 1.5 | 1.7
20-40 | 4.8 | 5.0 | 3.5 | 3.0 | 2.6
40-60 | 7.9 | 6.9 | 5.4 | ... | 3.7
60-80 | 10.7 | 7.7 | ... | ... | 5.4
80-100 | 11.3 | ... | ... | ... | ...
100 | ... | ... | ... | ... | 12.0[1]
==========+=========+=========+=========+=========+=========

[Footnote 1: For an average turbidity = 150. approximately.]

The influence of the temperature of the water on the turbidity of
the effluent is very pronounced. For a temperature of less than 40 deg.
Fahr. (actual average temperature about 35 deg.), the turbidity of the
filtered water for a given turbidity of the applied water is
practically twice as great as for a temperature greater than 70 deg.
(actual average temperature about 75 deg.). This fact fits in very
nicely with the influence of temperature on sedimentation. Referring
again to this temperature relation, as set forth on a previous page,
the hydraulic subsiding value of a particle in water, of a size so
small that viscosity is the controlling factor in its downward
velocity, is approximately twice as great at 75 deg. as at 35 degrees.
We would then expect to find that, in order to obtain a given
turbidity in the filtered water, a raw water may be applied at 75 deg.,
having twice the turbidity of the water applied at 35 deg., to produce
the same turbidity; and further, as the turbidity of the filtered
water, for a given temperature condition, varies quite directly in
proportion t