The times., 1899-12-26
SYSTEMS OF FILTRATION
Studies Made for Leading Ameri-
can Cities.
Opinion Almost Equally Divided BE-
tween sand Beds and Mechanical
Devices - Immense Quantity OF
Water Used in Greater New York
The Methods of It's Publication.

In the Greater New York something like
daily In the boroughs of Manhattan and
The Bronx last spring the average amount
used was 264 eco ,000 gallons daily, and IN
the borough of Brooklyn a trihe over 95.-
900, GEO The day may possible come when
a considerable portion of this water will be
subjected to filtration. But at the present
time less than 100000 gallons of avail
able water are withheld from the city
mains because of suspected contamination
This is over on Long Island. When the
necessary money can be had--about $170, ,00G
bids will be invited for providing filters
for that amount, and it is probable that
what are called mechanical" filters will
be used.
To sanitary and waterworks engineers
two general systems of filtration are now
known These are the SLOW sand" and the
mechanical" systems The former. EN-
ployed at Hamburg and several other for
eign cities. and also tried extensively at
Lawrence, Mass, under the auspices of the
Massachusetts Board Of Health is some
times called the English plan. The work
of publication is here done by two agents
wide beds Of sand through which the water
is allowed to percoIate, and millions OF
beuefcent bacteria that are cultivated ana
reside therein At intervals of a few
months the upper stratum of sand is re-
moved and replaced with fresh material
and after a few days, when a new crop
of bacteria has developed, the filter is
again Ia good working order.
-.
effected is chiefly a straining operation,
without any aid from bacteria 1t is usual
to divide the labor among a number of
tanks. each containing sand or ground
quartz. At intervals varying from a few
hours to a few days the filter is tempo
rariiy relieved from duty the sand is
washed by a current running in the oppo-
site direction from the usual flow, and the
hltering material is vigorously agitated
in the mean time If during filtration the
water passes through the device under the
impulse Of gravitation only the filter is
known as a gravity filter and that is
the case with about 90 per cent of the
mechanical filters now in use perhaps.
But when in order to save time additional
force is employed TO urge the fluid on its
way, the distinguishing adjective pres
sure" is used TO describe il. In mechani
cal filtration some chemical, the choice of
water to be treated is added in small guam
titles before it enters the filter The me-
chanical system is sometimes called the
American method of filtration.
NJ ~ Baker. associate editor of the
Engineering News" and editor Of The
Manual Of American WaterwOrks" who
has studied this subject carefully. said last
week: The excellent results attaiEei for
over half a century with slow sand II ira
ton and the fact that until recently most
of The information 10 be had concerning
mechanical filtration came from peTs sons
who were financially interested in it. at
first created a slight prejudice against the
latter system. Independent evidence, how
ever was at length forthcoming
"One of the first cities to institute an in
ycstigation was Providence. The work was
conducted by Edmund r. Weston, engineer
in charge of the waterworks department
lie did not carry his tests with sand itTa-
ton very far, and his experiments with
mechanical filtration were conducted on a
small scale Hence the comparison was not
as thorough as il might have been. But the
conclusion which he reached was that Tor