Evening star., 1901-02-09


follow the removes ozB Bthe pollution.
2 Publication Of water by alum. The
use of alum as q: purifier Of water seems
than a century. Particular attention how
ever, was directed to its use by Jennet, in
1o65 in an article published in the Moniteur
Scientifque, Paris. stHe found that z3
grains of alum to a gallon of water rem
dered it drinkabIe, even when 1t contained
considerable quintf1y of foreign matter.
The great argument IN favor Of alum as
purifier of water!is that it is cheap. But
by many it is coaisidered injurious, IL not
highly poisonous
3. Filtration Chief among the subjects
discussed at the FArisscongress, already re-
water by artificial filtration, and some ex-
periments were related to show that nox-
lous micro-organfsmsSma may be removed, or
at least rendered harmless, by certain
methods Of filtration. Filtration Is no doubt
an excellent practice, and one which, how
ever 1t is accomplished, has at least the
merit OF rendering water more pleasing to
the eye, II not to the palate; but 1t cannot
be too widely known that some forms OF
filter do no more than this, and that water
which Is very bright and sparkling may
YET contain noxious matters in solution
4. sand filtration. The great progress
maze during the last quarter OF century
IN the science of water publication tends
strongly to the Endorsement of sand fltra-
ton as safeguard against the propaga-
uon OF diseases through the medium OF
bacteria. But it is not to the perfection
OF layer of sand IS a mechanical strainer
that the removal Of bacteria IS mainly due,
put rather to the formation of film or
deposit or organized matter on and in the
sand itself. For this reason 1t is found
that sand filter, when freshly cleaned, has
far less efficiency in retaining or removing
bacteria than when the sand has become
ripe by the coating of its surface and
grams with film derived from the sus-
pended matter contained in the water. This
Is accounted for in two ways: First that
certain inorganic matters, Of chalky or
mineral nature, held In the water are de-
posted on the filter bed and form a good
hitering medium; second, that another thin
deposit takes place on the surface OF the
hltering bed and in the sand composed OF
minute bacteria, which, through their de-
purating power. add greatly to the efficiency
of the filter bed. But the operation comes
soon to an end. and cannot be resumed
until this deposit Is removed. Owing to
for cleansing. such an immense amount of
manual labor or such a large number OF
filter beds Is required to filter the water
supply, even of a small town, as to render
the cost very burdensome. This. however,
can be avoided and the filter effectually
cleaned If reverse current OF water Is
made to pass through the upper stratum of
the filter bed with sufficient force to agi-
depth of several inches from the top sur
face. thereby freeing 1t Of those Impurities
which stop filtration, or to use common
phrase, "clog the filter.
In pamphlet, Die Principien der Rein
wasser, Gewinnung vermittelst Filtration"
published by Piefke, the well-known scien-
tific superintendent of the Berlin water
works, 1t Is stated that the microbe remov-
ing powers of the sand filters at the Stra-
lare works remained rather defective for
fourteen days. and then only began to be
regular and better, until the filter bed e
CURED cleaning In 1893 Prof Koch pub
-Krankheiten''-in which 1t is pointed out
that the coating Of slime formed on the
filter bed must be removed periodically,
when 1t has become too thick. and conse-
quently not sufficiently permeable. A fur
ther fact is brought out. that the cleansing
of the filters is followed by q period Of
several days to q asweek during which the
filter does not actfefffcfently. The renewal
of the sand caused still greater deficiency
In fltering power, which lasts for longer
period, generally abont fourteen days.
1t is well known that while ordinary sand
filtration has little or no effect in removing
color from peaty water, it also frequently
falls to remove the 0palescent appearance
to which the presence of clay gives rise;
and which. under ordinary sand filtration,
will generally be observed in filtered Po-
tomac water, during times Of flood. With
some waters. such as those Of the Missis-
sippi, Missouri or the Nile, which carry
down immense quantities of clay, the most
careful sand filtration leaves turbid,
"hlliSh iiltIdlt water OI lHlS nature,
however, is readily acted upon by agitation
with metallic iron, the whole Of the sus-
PENDED clay coaguladng with very great
rapidity as soon as the ferric oxide begins
to form, and produces coarse precipitate
which can be removed at a high rate of
filtration. In case Of the peat-stained Po-
tomac water, the removal of color Is, of
course, more difficult to accomplish; but 1t
can, nevertheless, cbe completely effected by
proper filtrants, and such may be suggested
for the publication Of the water supply of
Washington city.
So complete is the satisfaction given by
the metallic iron process Of filtration which
has been in operation at Antwerp for over
ten years, that the same system has been
quite recently applied at Gonda and Dort-
recht, Holland. at Boulogne-Sur-Seine
France, and at Aqua, a large city Of India,
which draws its water supply from the
river Qumna, In india
The Antwerp water supply is obtained
from the Nethe a tidal river fed during
the rainy season from surface water and
springs, much discOlored by contact with
peat and clay, and to a large extent drain
ing off the highly cultivated districts of
Northeast Belgium. The water of the
Nethe, even after being deprived by twenty
four hours settlement Of the matter 1t
holds in suspension, is yellow and thick,
but after publication by the iron process it
be comes limpid and brilliant In appearance.
DIR. Miguel, the well-known French micro
biologist, on the effect of metallic iron fl
tration Of water at Boulogne- ur-Seine, in
which he shows that the number Of bacter-
ia in the original water was reduced y9.57
pe- cent, after publication and filtration.
c. w. CHANCELLOR.