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9
Expressed in terms of an acre these quantities would represent, on the days the beds were
actually at work during the first period of the experiment with one filling per day, the following
volumes—
Itagstone 551,060 gallons per acre per day.
Coke 688,825 „ „ „
and during the second period of the experiment, with two fillings per day—
Ragstone 782,290 gallons per acre per day.
Coke 815,407 „ „ „
The detailed results obtained by the chemical examination of the sewage and of the effluents
are tabulated on pp. 17 to 19. The average purification, as measured by the oxygen absorbed from
permanganate in four hours, during the whole continuance of the experiment was as follows—
Description of bed.
Oxygen absorbed from
permanganate.
Percentage purification.
Ragstone, coarse bed 3.015 20.6
Coke „ 2.944 22.5
Ragstone, fine bed 1.933 49.l
Coke „ 1.396 63.2
Crude sewage, for comparison 3.797

It will thus be seen that coke gives better results than ragstone in the removal of
organic matters in solution; the results are slightly better on the primary treatment, and considerably
better on the secondary treatment. It will also be observed that, with the exception
of the fine coke-bed, which showed a slight decline, two fillings a day gave a rather better
result than was obtained with one filling per day, showing that although the purifying
power of the beds, owing probably to the large size of the material, was in itself low and
unsatisfactory, still the beds were not being overworked. It points to the conclusion that from 20
to 23 per cent. purification was all that could be obtained by a one-contact treatment of the
unsedimented crude sewage dealt with in a bed composed of material of so large a size that it would
pass a 4-inch mesh and be rejected by a ½-inch mesh.
Effect of the Effluents on Fish life—The effluents from the primary beds killed gold and
silver fish in a few hours, but those from the secondary beds sustained fish life as readily as fresh
tap-water does.
It should be stated that the raw sewage which was supplied to the beds was of the heaviest
kind. It was drawn from a level about a foot from the bottom of the sewer, and passed through
a ^-inch screen to the beds without any previous sedimentation.

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