by Prof. Bischof. His ordinary portable domestic filter consists
of an inner, or spongy iron, vessel, resting in an outer case. The
latter holds the “prepared sand,” the regulator arrangement, and the
receptacle for filtered water. The unfiltered water is, in this form
of filter, mostly supplied from a bottle, which is inverted into the
upper part of the inner vessel. After passing through the body of
spongy iron, the water ascends through an overflow pipe. The object
of this is to keep the spongy iron, when once wet, constantly under
water, as otherwise, if alternately exposed to air and water, it is
too rapidly oxidised.
On leaving the inner vessel, the water contains a minute trace of
iron in solution, as carbonate or ferrous hydrate, which is separated
by the prepared sand underneath. This consists generally of 3 layers,
namely, commencing from the top, of pyrolusite (manganese black
oxide), sand, and gravel. The former oxidises the protocompounds of
iron, rendering them insoluble, when they are mechanically retained
by the sand underneath. Pyrolusite also has an oxidising action upon
ammonia, converting it more or less into nitric acid.
The regulator arrangement is underneath the perforated bottom, on
which the prepared sand rests. It consists of a tin tube, open at
the inner, and closed by screw caps at its outer end. The tube is
cemented water-tight into the outer case, and a solid partition under
the perforated bottom referred to. It is provided with a perforation
in its side, which forms the only communication between the upper
part of the filter and the receptacle for filtered water. The flow
of water is thus controlled by the size of such perforation. Should
the perforation become choked, a wire brush may be introduced, after
removing the screw cap, and the tube cleaned. Thus, although the user
has no access to the perforation allowing of his tampering with it,
he has free access for cleaning. Another advantage of the regulator
arrangement is that, when first starting a filter, the materials may
be rapidly washed without soiling the receptacle for filtered water.
This is done by unscrewing the screw cap, when the water passes out
through the outer opening of the tube, and not through the lateral
perforation.
Various modifications had, of course, to be introduced into
the construction of spongy iron filters, to suit a variety of
requirements. Thus, when filters are supplied by a ball-cock from
a constant supply, or from a cistern of sufficient capacity, the
inner vessel is dispensed with, as the ball-cock secures the spongy
iron remaining covered with water. This renders filters simpler and
cheaper.
As the action of spongy iron is dependent upon its remaining covered
with water, whilst the materials which are employed in perhaps all
other filters lose their purifying action very soon, unless they
are run dry from time to time, so as to expose them to the air, the
former is peculiarly suited for cistern filters.
Cistern filters are frequently constructed with a top screwed on to
the filter case, by means of a flange and bolts, a U-shaped pipe
passing down from this top to near the bottom of the cistern. This
tube sometimes supplies the unfiltered water, or in some filters
carries off the filtered water, when upward filtration is employed.
This plan is defective, because it practically gives no access to
the materials; and unless the top is jointed perfectly tight, the
unfiltered water, with upward filtration, may be sucked in through
the joint, without passing at all through the materials. This is
remedied by loosely surrounding the filter case with a cylindrical
mantle of zinc, which is closed at its top and open at the bottom.
Supposing the filter case to be covered with water, and the mantle
placed over the case, an air valve is then opened in the top of the
mantle, when the air escapes, being replaced by water. After screwing
the valve on again, the filter is supplied with water by the siphon
action taking place between the mantle and filter case and the column
of filtered water, which passes down from the bottom of the filter
to the lower parts of the building. These filters are supplied with
a regulator arrangement on the same principle as ordinary domestic
filters. The washing of materials, on starting a filter, is easily
accomplished by reversing 2 stop-cocks, one leading to the regulator,
the other to a waste pipe.
The use of spongy iron has now been applied on a large scale to the
water obtained from the river Nette, for the supply of the city
of Antwerp. Dr. Frankland has visited the Antwerp Waterworks at
Waelheim, about 15 miles above that city, and reported on the result
of his inquiry. He attaches especial value to the fact that spongy
iron filtration “is absolutely fatal to _Bacteria_ and their germs,”
and he considers it would be “an invaluable boon to the Metropolis
if all water supplied from the Thames and Lea were submitted to this
treatment in default of a new supply from unimpeachable sources.”
Many preparations of iron have long been known to possess a purifying
influence on water containing organic impurities. Thus Scherer, years
ago, recommended a solution of iron sulphate where the impurities
were present in large quantity. Later still, iron chloride was
proposed as suitable, the salt being precipitated in the presence of
organic matter as ferric oxide, the oxide thus formed acting also
mechanically on the suspended impurities in course of precipitation,
very much as white of egg acts in clarifying liquids, when it
coagulates and carries impurities with it to the bottom. Other iron
preparations have a similar action, notably dialysed iron, while
several oxidising agents, such as potash permanganate, are also well
known to possess a powerful effect on organic impurities. It will
at once be seen, however, that all such substances are inadmissible
as filtering media, or purifying agents for potable waters, for the
reason, that in the case of some at least of the agents mentioned,
decompositions take place, which in themselves might prove dangerous,
while in the case of all an excess (and it would be almost impossible
to avoid an excess) of the purifying agent would be equally bad, and
would render the water quite unfit for domestic purposes. It has
been found, however, that various kinds of native rock containing
iron protoxide effect the filtration of water very completely, and
Spencer, acting on this idea, after experimenting, found that when
the iron protoxide was isolated as magnetic oxide, it both freed the
water from turbidity and effected decoloration very quickly. Thus
bog-water, as dark as porter, when filtered through it speedily lost
its colour and became clear and sweet, the carbonic acid given off
during the process of decomposition rather tending to improve the
water. The purifying power of the magnetic oxide does not deteriorate
with use. The oxide gets coated with a slimy deposit, owing to the
deposition of decomposed organic matter, but this being removed, it
is as powerful as ever in its purifying action. Unfortunately this
iron rock is not found native to any extent, but the fact of its
action being determined, Spencer continued his experiments with the
result that it can now be produced artificially, and forms one of the
most efficient and useful filters for domestic purposes.
Metallic iron is employed by Jennings & Hinde. The filtering material
consists of fine iron or steel shavings, filings, turnings, or
borings obtained from the swarf or skin of cast iron, wrought iron,
or steel; this material may either be used by itself, or it may be
used with other materials, either mixed with them or in separate
layers. The iron or steel shavings, &c., are obtained from iron or
steel that has been brought to a state of fusion either by melting or
the processes necessary for making cast iron, wrought iron, or steel,
and being separated from many of the impurities contained in the
ore from which it was obtained, will have but a comparatively small
portion of earthy impurities mixed with it, and will be for this
reason superior to iron which is obtained from native ores or oxides
without fusion.
By filtering water through small divided swarf or skin of cast
iron, wrought iron, or steel, free oxygen will be withdrawn from
the water, and consequently any insects or animalculæ contained in
the water will be deprived of life, and any germs contained in the
water will be deprived of the oxygen necessary for their development
and life, and the water will be consequently purified and rendered
wholesome. A convenient way of forming a filter is to use a layer of
the turnings, shavings, &c., together with layers of other filtering
material resting upon a perforated partition placed across a closed
vessel. The materials are cleaned by boiling them in hot water
with a small quantity of ordinary washing soda, to remove any oil
or grease that might accidentally be associated with the materials
above mentioned. Afterwards the iron borings should be well washed
before being put into the filter. The filter vessel may be of any
ordinary construction and shape. If sand is used in conjunction with
the above-mentioned materials, it is preferable to place some of the
sand at the bottom of the filtering vessel, and the iron or steel
materials, or both, over the sand, and then more sand over them.
These materials are disposed so that they may be partially separated
from each other by perforated plates of earthenware, glass, or other
suitable material. But this partial separation, though convenient, is
not essential, as the perforated plates may be dispensed with and the
material placed over and under each other in layers without plates to
separate them.
Porous Pottery.--Chamberland has found that the liquid in which
microbes have been cultivated becomes absolutely pure if passed
through unglazed porcelain. Its purity can be demonstrated by mixing
it with liquids sensitive to the action of microbes, such as veal
broth, milk, and blood, in which it produces no alteration.
[Illustration: 16. Chamberland Filter.]
A tube _a_ (Fig. 16) of unglazed porcelain is enclosed in another
_b_ of metal, and the water to be filtered is admitted to the space
between the two by turning a stop-cock. Thence it slowly filters
through to the inside of the porcelain tube, and flows out at the
bottom. Under a pressure of 2 atmospheres, or 30 lb. to the sq. in.,
a tube 8 in. in length, with a diameter of 1 in., will yield about
5 gal. of water daily. For a larger supply, it is only necessary to
increase the size or the number of the tubes.
In cleansing the filter, the porcelain tube is removed, and the
microbes and other matter that have accumulated on the outer face of
it are brushed off. The tube may also be plunged in boiling water in
order to destroy any germs that may be supposed to have penetrated
beneath its surface; or it may be heated in a gas jet or in a
furnace. In fact, it can be more readily and more thoroughly cleaned
than most of the domestic filters in ordinary use.
It is interesting to remark that some of the earliest filtering
vessels of which we have any knowledge are simply made of porous
earthenware. After all our modern researches after antiseptic
filtering media, we are reverting to the ways of our remotest
forefathers.
Filtering Cisterns.--The following is a description of a filter which
purifies foul water from organic impurities held in solution as well
as from suspended solids. Take any suitable vessel with a perforated
false bottom, and cover it with a layer of animal charcoal, on the
top of that spread a layer of iron filings, borings, or turnings,
the finer the better, mixed with charcoal dust; on the top of the
filings place a layer of fine clean siliceous sand, and you will have
a perfect filter. Allow the foul water to filter slowly through the
above filter, and you will produce a remarkably pure drinking-water.
Before placing the iron filings in the filter, they must be well
washed in a hot solution of soda or potash, to remove oil and other
impurities, then rinse them with clean water; the filings should be
mixed with an equal measure of fine charcoal. If the water is very
foul, it must be allowed to filter very slowly. The deeper the bed of
iron filings is the quicker they will act.
In Bailey-Denton’s cistern filter, the principal novelty is that it
runs intermittently, and thus allows the aëration of the filtering
material, and the oxidation of the impurities detached from the
water. The oxidation is effected by the perfect aëration of the
filtrating material, which may be of any approved kind, through which
every drop of water used in the kitchen, bedrooms, and elsewhere
must pass as it descends from the service cistern for use. As water
is withdrawn from this filter, fresh water comes in automatically by
the action of a ball-tap; and this fresh water immediately passes
through the aërated material into a lower chamber, forming the supply
cistern of filtered water for the whole house. The advantages claimed
for the filter are that it secures pure water for the whole house. It
is attached by pipe to, but is distinct from, the service cistern;
it can be placed in any part of the house, and it cannot get out of
order. Any approved filtering material may be used, and being aërated
between each passage of water through it, oxidation is made certain.
A slate or iron cistern and filter combined may be made by dividing
the cistern with a vertical partition perforated at the bottom, and
placing in the half of the cistern which receives the water, a bed of
filtering material, say 6 in. of gravel at the bottom, 6 in. animal
charcoal in granular form in the middle, and 6 in. clean sharp sand
at the top, covering all by a perforated distributing slab.
[Illustration: 17. Filter Cistern.]
Fig. 17 illustrates a method of preparing an ordinary house cistern
for filtering. The pipe and fittings should be of galvanised iron;
black or plain iron is better as long as it lasts, as it rusts fast;
in either case it is better to waste the water first drawn, for the
water absorbs both the zinc and the iron when standing overnight. The
zinc is not healthy, and the taste of the iron is unpleasant.
The perforations should equal 3 or 4 times the area of the suction
pipe, which in ordinary cisterns may be 1¼ in. pipe, while the
branches may be ¾ in. pipe. The holes, if ⅛ in., should number at
least 200, distributed along the lower half of the pipes. Smaller
holes are preferable; of 1/16 in. holes, 800 will be required.
For the filtering material we recommend a layer of fine gravel or
pebbles for the bottom, 3 or 4 in. in depth, or heaped up over the
perforated pipes; upon this a layer of sharp, clean sand, 9 in. in
depth; upon this a stratum of pulverised charcoal, not dust, but
granulated to size of peas or beans, or any of the material above
mentioned, 4 in. deep; and upon this a stratum of fine, clean sand 6
to 12 in. in depth.
Such a filter should be cleansed at least twice in a year by pumping
out all the water, taking out the mud or settlings, and one-half the
depth of the top layer, and replacing with fresh sand.
The double filter cistern, Fig. 18, has much to recommend it, having
a large receiving basin which in itself is a filter placed in a
position for easy cleaning. The recess at the bottom may be covered
with a perforated plate of galvanised sheet iron, upon which may be
laid a filter bed of gravel, sand, charcoal, spongy iron, and sand in
the proportions as stated above. This enables the frequent cleaning
by removing the top layer of the filter bed without disturbing the
water supply. The cover should fit tight enough to keep out insects
and vermin.
A double-bottomed basin perforated and filled with clear, sharp sand
and charcoal should be attached to the bottom of the pump pipe, as
shown.
This enables the small filter to be drawn up and cleaned, without the
necessity of emptying the cistern or interrupting the water supply.
[Illustration: 18. Filter Cistern. 19. Keg Filter.]
The half barrel or keg filter, as illustrated in Fig. 19, is a
convenient form of cistern filter where filtered water is required
from cisterns already filled.
This is also a convenient form for readily cleaning or changing
the filter without the necessity of discharging the water from the
cistern.
This filter can be made from an oak keg or half barrel, such as is
used for liquors or beer. Take out one of the heads and cut away the
edge, so that it will just drive into the end of the keg, fasten 2
battens of oak across the head with oak pins left long enough to
serve for legs for the filter to rest upon.
Bore this head full of holes ¼ in. diameter. In the other head bore
a hole 1¼ in. diameter, and bolt an iron flange into which the pump
pipe is to be screwed. Let the bolts also fasten upon the inside a
raised disc of galvanised sheet iron, perforated with a sharp point
or chisel. Proceed to charge the filter by turning the top or flanged
head down, and placing next the perforated plate a layer of fine
gravel 3 in. thick, then a layer of sharp, clean sand 3 in. thick,
then a layer of pulverised charcoal free from dust, 3 in. thick,
then a layer of sharp clean sand mixed with spongy iron, pulverised
magnetic iron ore, or blacksmiths’ scales, followed by a layer of
coarse sand, gravel, and broken stone, or hard burnt bricks broken
into chips to fill up. Place the perforated bottom in as far as the
head was originally; bore and drive a half-dozen oak pegs around the
chine to fasten the head. Then turn over the filter, screw the pump
pipe into the flange, and let it down into the cistern.
Such a filter requires to be taken out and the filtering renewed in 6
to 12 months, depending upon the cleanliness of the water catch. With
the precautions mentioned above in regard to the care of the roof,
such a filter should do good work for one year.
=Sanitation.=--This heading is intended to embrace the removal and
disposal of the various kinds of refuse and waste produced in the
dwelling from day to day. Endless volumes have been written on the
subject, but in plain words the whole art resolves itself into
sound pipes for the conveyance of the fluid portion and efficient
ventilation of the receptacles and conduits.
_House Drains._--It was pointed out by Burton,[1] before the Society
of Arts, that where, as in London, the sewerage system is fairly
good, dangers to health arise not from the sewers direct, but either
from the sewers by means of the house drains, or even more often
from the house drains themselves. It is quite agreed by medical
authorities that diseases may arise from gases evolved from the
drains, or even discharge pipes in a house, entirely apart from any
specific infection such as may be conveyed by means of sewers.
This being the case, it will be seen that the thing which most
behoves us is to make sure that the house system is efficiently
doing its work. It is evident that the objects to be aimed at in
constructing a system of house drainage, are as follows:--
First. All matter placed in any of the sanitary appliances in the
house must be carried, with the greatest possible expedition, clear
of the premises, leaving behind it as little deposit as possible.
Second. All sewer air must be prevented from entering the houses by
the channels which serve to carry away the sewage.
Third. Since it is impossible to have house drains absolutely clean,
that is, devoid of all decomposing matter, all air from house drains,
and even from sink, bath, and other waste pipes must be kept out of
the dwelling-rooms.
To which might be added a fourth, that a constant current of fresh
air must be established along every pipe in which it is possible that
any decomposing matter may remain, so that such matter may be rapidly
oxidised, or rendered innocuous.
The number of houses in which sanitary inspectors find the drainage
arrangements to be thoroughly good, and to be fulfilling these
conditions, is surprisingly small. In fact, in all the houses they
are called upon to examine, except those which have been arranged,
within the last dozen years or so, by some engineer, builder, or
plumber who has made a special study of the matter, are found defects
which interfere with the due fulfilment of one or other of these
conditions.
Attention is called to Fig. 20, in which the drainage arrangements
are shown to be defective. Here Burton has taken such a state of
affairs as is by no means uncommon in a London house. Alongside it is
a drawing which illustrates a well-drained house (Fig. 21). By their
juxtaposition, the defects exhibited will be made more patent.
[Illustration: 20. Ill-arranged House.]
[Illustration: 21. Well-arranged House.]
The first point demanding attention is the condition of the main
drain. It will be seen that it is little other than an elongated
cesspool. The size is unnecessarily large. As a consequence,
even if it were perfect in all other respects, it would not be
self-cleansing, inasmuch as there can never pass down the drain which
serves for a single house enough water to scour out pipes of the size
illustrated, namely, 9 in. diameter.
It will be seen, however, that the state of affairs is far from
correct, apart from the size of the pipes. In the first place, the
joints are not tight; sewage will soak out into the ground through
them. In the second place, although there is ample allowance between
the two ends of the drain for a good fall, or incline, this fall has
all been confined to a few feet of its length, the part underneath
the house being laid almost level. This is done simply to avoid the
trouble of excavating the ground to a sufficient depth.
Let us now follow the action of a drain of this kind, and see what it
will lead to. Sewage matter finds its way into it. As we all know,
this matter depends on water to carry it forward. It is probable
that, while the drain is new and the ground comparatively solid
around it, sufficient water will remain in it to carry the greater
part of the sewage to the sewer. But this state of affairs will not
last. Before long, some unusually heavy or obstinate matter will get
into the drain. It will be carried only so far, and will then stick.
Any water now coming behind it will “back up,” to a certain extent,
and will very soon find its way into the soil, from one or more
points behind the obstruction--not yet amounting to a stoppage. As a
consequence, sewage now passing into the drain, loses its carrying
power, and gets no farther than a certain distance. Before long, a
complete stoppage takes place, and all the sewage of the house soaks
into the ground under the basement. After this, things go from bad to
worse. The saturated ground no longer properly supports the pipes,
which, as a consequence, will become more and more irregular, and all
hope of the drain clearing itself is lost. It is only a question of
time, with a drain such as that shown, and the inmates of the house
will be living over a cesspool.
As a matter of fact, total obstruction or stoppage has been
discovered in 6 per cent. of the houses which have been inspected.
The next point worthy of attention is the soil pipe; this term being
at present used to signify the vertical portion of the drain only,
although it very often is also used as meaning the almost horizontal
drain under the house.
The soil pipe is of lead. This is an excellent material if the pipe
be properly arranged, but here it is not. The great fault is that
there is no ventilation. As a consequence, the upper part of the
pipe will always be filled with sewer gas, which tends to rise in a
somewhat concentrated state. Now, sewer gas has a powerful action on
lead, and, therefore, a soil pipe arranged without ventilation never
stands many years before it becomes “holed,” that is to say, is worn
through at its upper part. When this occurs, of course, there is
ventilation enough, but it is into the house. The ventilation in this
case will, in fact, be most active, because every house, on account
of the fires in it, acts, especially in winter, as a chimney, and
draws in sewer or other gas from every possible crevice.