National Republican., 1875-07-12
POTOMAC 9 WATER. VI! Ter

three feet, it Is because the surface is being rap
Idly closed; the weight Of the water comes then
ready referred TO- and leads to the labor Of loosen.
ing up the material during the process Of cleans
ing. Sometimes, when this amount Of head is ex-
through at points where some slight difference in
the material gives 1t opportuni y. 1t will then
flow through In veins. damaging the hlter bed.
Such overstraining Of the filters is rare. The ef-
feet can readily be brought about by oYerworking
The best size of filter bed for such city as St.
sand area OF 81 40 square feet This area, at the
rate Of one half cubic foot Of water Per hour per
square foot OF bed, gives filtration Of 1920 cubic
40 $50 cubic feet or 1880 SAT United States gal
Ions, in twenty -four hours.
filters of this size would be necessary, on the sup
position that the now Of water through four Of
them is continuous through the twenty four hours
should be large enough to receive the water pass
ing through the filters during the night hours,
accumulating It there for the day service.
ability to store up one third Of the calculated
daily consumption would meet the case. have
very little Information in regard to
THE PRECISE COST
of filtration in England, no separate account be-
ing ordinarily kept Of Its particular expenses. At
charge for filtering averaged four shil,sngs and
six pence per annum per tenement. II each ten
ant consumed 500 imperial gallons per diem, this
charge would be equal to one cent Ispecie) for
each 1.314 United States gallons. The charge
probably includes some profit.
A tss SSs ng
nearly floO sterling per annum for q million Inn.
persi gallons filtered daily, for each S65 900
t6dHsand United states gallons or Al tspecie5 5
per million United States gallons. For delivery
of II 900 United States gallons daily this would
tenance equal to d, ,e97 (specie) per snnum.
At West Middlesex water works, London, the
cost of tering is about 10 shilings 40 specie)
very economically managed, and this amount in
cludes the capital invested. On the supposition,
as before, that each tenement used 800 imperial
gallons per diem or 109, 500 per annum, equal to
l3l 435 United States gallons, the cost per tene-
ment is in this case but 13 pence equal to 20 cents
(speeie1
THE FIRST COST
Of such works varies with the nature Of the
ground, the cost of material at the particular
place, and the character of the construction. We
cannot, therefore, infer from any one place, ex-
a nOP
water supply.
1 have already said that the use of settling
basins form necessary and an economical pre-
liminary to the use Of the flter-bed in all cases.
and especially during those months Of the year
when the water is verv turbid.
In temperate cmmate, such as England, II Is
of little consequence how large these settling
basins are made, provided that the depth of water
is not less than or 10 feet and that II is not held
our warm climate. il viii be adyantsgeous to have
the settling basins as small as practicable, con-
sistent with the due preparation of the water for
the filters.
This preparation, our experiments on the Mis-
sissippf water have shown, can be secured in
twenty -four hours. Within that time, in still
water, the heavier
PORTION OF THE SEDIMENT
IN suspension sinks TO the bottom, leaving the
fer m az
respects weight, very small part Of the original
matter. This part, which even in still water set
bR
alter, leaving the water invariably clear and
impid
Under this arrangement we have the water but
wenty hours STILL during the rest Of the time it is
IN motion.
To make the arrangement efficient under all
circumstances there should be four settling
gallons with not less than twelve feet in depth Of
water when full. When greater capacity is re-
luired the walls should be carried up, and
With the four basins there would be one filling,
me in which the water was still undergoing set
of, and one upon which the process of removing
The stuff deposited on the bottom could be going
on without lnterrupting the duty required Of the
others.
waste pipes from each settling basin to the
river would enable the attendants to scour or
flush of at intervals the lowest three feet of the
y ater, and Dy some MANIPULATION to pass Oh with
It more or less Of the accumulated sediment. 1t
never was supposed that this deposit would flow
,f without this kind of assistance, and it can
'nly be
DETERMINED BY EXPERIENCE
whether it viii be cheaper to run it out By wheel
0arrows or TO carry It OF by mixing IL with water.
II 1t should be desired to gse settling basins
Without filters, they ought to be much larger than
;esuIts. They would not be SO economical IN nrst
,ost IL Of SUFFICIENT size, but they might be more
1 In ~. 1ut II L. 70 be renen.
probable dimensions, they would be an expert
nent which 1t might be interesting to have made,
but which could not be advised, that l know Of,
on the faith Of its having succeeded elsewhere.
Even where very large gathering reservoirs have
been available, as at Liverpool and at Dublin,
hitter beds have been constructed on the usual
remains in large bodies Of water, and
10 meet the turbid character of such water where
he reservoir is low as well as to intercept the or
ganic impurities referred to elsewhere.
1t remains to speak Of the natural filter, of
which we have specimens at Genoa, Toulouse,
Lyons, Anglers and Perth.
The descriptions of the works at these places
will show that this mode Of obtaining supply of
clear water has been emiDently successful as re-
CARDS the quality, If not always are regards the
quantity.
THE CHARACTER OF THE WATER
1t the places referred to is indeed unobjectiona-
Bile; the slight increase Of hardness at Lyons,
with the Rhone water, being too small
10 be Of any moment. The water, indeed, In this
process; It is received from the underground flow
Is from springs and has not been exposed to light
Dr. to suriase contamination Of any kind.
tervals narrow plains Of gravel or sand brought
DOWN and deposited there by the river under the
varying positions ofits channel way. When these
he neig hboring stream they will always be found
saturated with water mainly derived from that
stream, and however turbld the water of the river,
hnf
provided that We tap 1t at reasonable distance
rom the channel way. The cities referred to de-
i've their supplies Of water from gravel accumu-
lance from the city, but the other places in the
immediate vicinity Of the several cities.
covERED GALLERIES
have been carried through these beds Of gravel at
1epths sufficiently below the channel of the neigh
he gallery during the lowest stages of its water
The water in these gravel beds rises and falls with
he height Of the water in the river, and unless
hey would obviously become dry and would cease
10 deliver at its lowest stage. These galleries are
of various sizes and of various widths, eight 70
But the experience Of one place will seldom be
applicable to another The character Of the neigh
boring stream and the hneness or coursensss Of
he gravel or sand in which the galleries are
placed influence Importantly the rate Of supply.
These galleries are all Of stone masonry, open
It the bottom; The water in all these Eases en-
mated rate Of delivery in these galleries Is gener.
lily referred to the area Of the bottom.
The food into them must be at q velocity which
hall not carry sand or any kind of material
Nth the water. There is, therefore, no danger of
undermining
THE SIDE WALLS.
The first galleries built at Toulouse and Lyons
we're too small in size to give the best results
here. The latest galleries have been made
arger-at Toulouse * feet Wild, at Lyons 50
eet wide. The galleries at Anglers and Perth
re too small for our purpose.
If we suppose the galleries to be 20 feet In
width, and that rate of 200 United States gal
ons per square foot Of bottom could be obtained
rom them at low water Of the Mississippi, the
epgth Of the gallery required to give 900 900
Il Il 900 900 gallons it would require q length Of
900 feet. In other words,
THE BOTTOM AREA,
o produce this last quantity, would be $4,000
Qusre feet. The hlterinR galleries and basins at
ytying, at low water Of the Rhone, q daily deliv-
~ Of about 5000, 900 United States gallons but
he galleries OF the other cities give much higher
esults, as you have seen, than the Lyons gal.
cries. -. .'.
The river which finds its way into the deposit of
and or gravel where the galleries are placed,
must have deposited somewhere the sediment
leld BY II In suspension while in the river chan
lel. could not learn, however, that the filter.
sufe. The deposit which takes placeupon the
tyer bottom in the ordinary and in the low stage
4 It's water is removed, II is asserted In time Of
ioods, when the bottom is secured of all its light
natter, and the coarser earths competing 1t be-
ome in this way periodically exposed. This and