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Table A (page 9) shows the varying capacities of these beds, and proves that the cokebeds
became choked more quickly than the ragstone-beds.
During the first four months after starting the primary coke-bed it choked at the rate of 3 6
gallons per week, or 0.73 per cent. of the total capacity of the tank, and during the next two
months the rate of choking was 3.4 gallons per week, or 0.68 per cent. of the total capacity of the tank.
The ragstone-bed during the six months choked regularly at the rate of 11 gallons per week,
or 0.22 per cent. of the total capacity of the tank.
Early in April, 1899, it was considered that the beds had reached their maximum power for
purifying the sewage. They were then being filled twice a day, and were dealing with the
sewage at the following rates—Ragstone, 947,430 gallons per acre per day; coke, 914,760 gallons
per acre per day, and the average percentage purification effected during that month was—
Description of bed.
Percentage purification,
as measured by oxygen absorbed
from permanganate.
Percentage purification,
as measured by albuminoid
ammonia.
Ragstone, primary, coarse bed 17.5 32.6
Coke „ „ 16.5 21.3
Ragstone, secondary, fine bed 48.8 64.4
Coke „ „ 60.9 62.4
The amount of nitrification produced had fallen very low in the case of all the beds.
Abnormal amounts of nitrate were found in the first effluent from the ragstone fine bed
after the bed had rested at Easter, from 29th March until 5th April, and it appeared probable
that nitrates had been formed in the bed during the rest and had then been washed out by the
first filling with sewage. A similar result was not found in any of the other beds.
The series of experiments with these beds terminated on the 15th April, 1899, after a
period of 29 weeks' working. The average percentage purification effected during the last week was as
follows—
Description of bed.
Percentage purification,
as measured by oxygen absorbed
from permanganate.
Percentage purification,
as measured by
albuminoid ammonia.
Ragstone, coarso bed 21.3 43.2
Coke „ 18.8 29.7
Ragstone, fine bed 50.7 66.5
Coke „ 58.5 68.6

The two coarse beds were thus shown to be doing very unsatisfactory work. It was hoped
that an improved effect would be produced if a reduction were made in the size of the material
in the bed. That this expectation was justified will be seen by the fact that the results obtained
in the next series of experiments, when the primary beds were composed of coke fragments onehalf
to two inches in diameter, showed an average purification of 43.8 per cent.
With regard to the secondary treatment of the primary effluent with fine material, the
results furnished by the ragstone did not at all come up to expectations, and were far less
satisfactory than those obtained with the coke. The amount of nitrification produced by this
bed was, however, much greater than that produced in the corresponding coke-bed. it has
recently been shown that the presence of nitrates in an effluent may prevent the putrifaction of a
certain amount of organic substances from occurring in another effluent with which the nitrateeffluent
has been mixed; hence the nitrifying power of the ragstone beds is not without importance.
The beds were filled once a day from.22nd September, 1898, to 9th January, 1899, both inclusive.
The filling was, however, not carried out on Sundays or on Christmas holidays, and occasionally one
or two days were missed when the boiler was undergoing cleaning. In all, filling was carried
on on 83 days out of the 110. During this period the ragstone-beds dealt with a total of 16,800
gallons, which was equivalent to 415,800 gallons per acre per day, including all resting periods;
while the coke-beds dealt with one-fourth more than this quantity. From 11th January, 1899,
to 15th April, 1899, when the experiment terminated, the beds were filled twice daily on 73 days
out of the total of 95. During this period the ragstone-beds dealt with a total of 20,976 gallons,
which is equivalent to 601,128 gallons per acre per day, while the coke-beds dealt with a total of
21,864 gallons, equivalent to 626,576 gallons per acre per day, all resting periods included. The
total volume of sewage dealt with over the whole period of the experiment was therefore—
Ragstone beds 37,776 gallons.
Coke beds 42.864 „