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the second, the mehter in charge has simply to open the discharge valve of the
former and set the fluid contents free to find its way to the ground set apart for
cultivation, upon which it should be distributed as in irrigation. In some cases it may
be found preferable to resort to continuous downward filtration in the second stage;
that is to say, that the effluent from the first upward bed will be simply discharged
on to the surface of the downward filter and allowed to pass down and through it in
a gentle equable trickle to the outlet where it will at once escape to the channel
which conducts it to the irrigation ground. In this case the equable distribution
of the fluid over the whole surface of the filter is a point of importance and many
devices to secure this are described in the books devoted to the subject; the writer
has found a perforated pipe fountain sprinkler, attached to the outlet pipe of the
first upward bed, very efficacious. In this case the walls of the filter may be
perforated with air-holes to admit oxygen, and the necessity of opening the outlet
valve is obviated; the filters will also do more work, but even so, the amount
passed through them must be regulated, a simple matter if the preliminary mixing
tank, to be alluded to later, be adopted. This, briefly, shows that the rôle of the
human agent is reduced to a minimum, and an intelligent mehter after a week's
training is quite equal to the task, though, of course, it should be arranged, that
the working of the apparatus be supervised by some responsible European,
conservancy Sergeant or other.*
Plate I. gives in rough outline an idea of the structural details of the
apparatus, as arranged to accommodate the sewage of 1,000 men for whom
3 gallons per head of flushing water are provided. The first upward filter
bed will hydrolyse the sewage of 1,000 Europeans even if the dilution of the
excreta ranges from a minimum of 3 gallons to a maximum of 8 or 10 gallons or
more per head, so that no modification will be required in its size when the sewage of
one regiment only is to be dealt with. The filters, on the contrary, must be made of
sufficient capacity to hold the total quantity of the hydrolysed sewage, and obvi--
ously they will (unlike the first upward tank) vary in size according to the amount
of dilution of the sewage. In constructing these beds it may be taken that their
capacity when full of filtering material is 2-5ths or 1-3rd of that of the empty beds,
so that, if the filters are only charged once a day, their total capacity when empty
(before putting in the filtering material) must be 2½ to 3 times that of the daily
amount of sewage to be treated. The simplest arrangement is to have two large
filters, each of a capacity to hold half the total volume of the sewage; but any
number of filters may be constructed according to the exigencies of the site,
though this slightly increases the demand made on the man in charge in con--
nexion with the due devolution of the sewage on to the different filter beds. The
* This question of short "contact" or of continuous downward filtration is to be decided by the course of the
processes in the first upward tank; a simple after for the che. ists' decision. It may confidently be asserted that
if hydrolysis be well effected, the latter system of working the filters will be easier and quite effectual.
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