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flows, the alternate plates being connected respectively with the
positive and negative terminals of a dynamo. The sewage is
entirely split up by the electrical action, suspended matters and
part of the organic matter, as before stated, being precipitated, the
soluble organic matters being oxidized and burnt up by the nascent
oxygen and the chlorine oxides envolved—to whatever extent may
be desired. It is stated that thirty effective horse-power is required
for treating one million gallons of London sewage in twentyfour
hours—the quantity that would be produced by a town of
30,000 people—assuming 450 tons of iron to be laid down. This
is equal to ten years' supply, the iron consumed being forty-five
tons per million gallons per annum. But as the amount of iron
laid down is in inverse proportion to the horse-power required,
these two factors can be varied. The larger the quantity of iron
laid down the longer it lasts, and the cheaper it is in the long run.
The cost of plant, not including iron, for one million gallons daily,
is said to be ±'2000. For larger quantities the proportional cost
is less, e.g., £10,000 for ten million gallons of sewage. The
annual outlay would be for coal and iron consumed, and for labour.
Labour for dealing with one million gallons is required in the proportion
of two shifts of two men each. The cost of coal and iron
would be in proportion to the amount of sewage treated. It is
stated that the resultant effluent is fit to discharge into any river.
It contains, however, three grains per gallon of suspended matter,
almost entirely iron oxides, and innocuous. This can be removed
by filtration through a few inches of sand, and then the effluent is
fit to go into any stream. Should higher purification be required,
it can be obtained by the use of an electric filter,
constructed of alternate layers of small coke, separated by
sand, or perforated tiles, the first layer of material being sand
to separate suspended matter. By suitable connections the layers
of coke form positive and negative electrodes. Disease germs
cannot be propagated, owing to the nascent oxygen and chlorine
produced when the filter is in action. In experiments at Paris,
with ordinary treatment by means of iron electrodes, it has been
found that 5,000,000 organisms in a cubic centimetre of sewage