Sacramento daily record-union., 1890-07-19
WATER FILTRATION.
Sand Filters Not Impervious to Bacteri.

Sand Filters Not Impervious to Bacteria
Interesting Experiments.
From the Engineering and Building Record.
The evidence which has been collected
of late years with regard to the efficiency
of filters of various kinds in removing
from water the specific germs of such dis
eases as cholera and typhoid is somewhat
contradictory. As regards filtration of
municipal water supplies on the large
scale by means of sand, it has been shown
by the experiments of Frankland, of the
Massachusetts State Board of Health and
elsewhere, that a very large proportion of
the ordinary bacteria are removed by such
filtration if it is not made to 90 on too
rapidly.
A recent outbreak of typhoid fever in
Berlin has led to a fresh and more care
full investigation of the effects of the sand
filters used in that city, and the results are
OF much practical interest. For the eight
years, 1SSO-SS, there was comparatively
little typhoid fever in Berlin, the annual
number of deaths from this cause being
only little over two in 10000 living pop
ulation. In the early part of 1879 an epi-
demic of about 700 cases of typhoid
occurred in the eastern part of the city,
which is supplied with water from the
River Spree, taken through the sand filters
at Stralan. In the western part of the
city, supplied from Lake Tegel, there was
little or no typhoid.
This led to series of experiments by
Frankel and Piefke, which demonstrated
that certain proportion of many forms of
bacteria, and especially those of cholera
and typhoid, do pass through the sand
filters. Their trials were first made with
the Bacillus uiolacens, because its presence
is easily recognized in gelatin cultures by
the blue-colored spots which it produces.
The Spree water, containing a small
amount Of this peculiar organism was
passed through sand filter and the efflu-
ent test, this being continued for thirty
days. Through one of these filters the
water was passed at the rate of 100 milli-
meters per hour, and through another with
three times this velocity. 1t was found
that in each filter, and from the very be-
ginning of the filtration, some of the blue
bacteria passed through; that when the
filtration went on slowly the proportion
found in the effluent was about l per cent.
of that in the supply, and when the ve-
| locity of the filtration was three times in
creased the proportion of bacteria in the
efiiuent also increased to per cent.
Having settled this, experiments were
next made with the bacillus ef typhoid
| and that Of cholera in the same manner,
and with precisely the same results
1t appears, then, that certain proper
ton of dangerous bacteria will go through
sand filters, and that the absolute number
which pass depends on the number in the
| unhltered water, the rapidity of the filtra-
| ton, and the length of time during which
| the filter has been used. No experiments
| seem to have been made upon the effects
Of successive filtration, with intermediate
aeration-that is, the sending through a
| fresh sand filter the water which has al
| ready passed through one filter. The
effect of this would not be the same as
that produced by passing the water once
| through double thickness Of sand.
The French Minister of War states, in a
recent report, that steps have been taken
to provide filters for all military posts
where thoroughly satisfactory drinking
water for the troops is not furnished. These
are to be porcelain filters of the Cumber-
land pattern, and it is estimated that for
! the garrisons in France and Algeria about
| $4,000 of thes filter tubes will berequired
That something should be done to secure
purer drinking water for the French SOL
diers is evident from the great prevalence
of typhoid among them, and from the fact
that out of lS7 specimen Of water from
different sources examined in the labora.
tory of the Military School of Val dc
Grace. 81 contained bacteria of putrefac
tion. contained the typhoid bacillus, and
q were contaminated by human excreta
1t is more than doubtful whether the
Chamberlain filters will remove all germ.
after continuous use under pressure fol-
several months, but they are undoubtedly
safer than sand filters as a sole reliance fol
securing drinking water. 1t would seen
wise in all cases to use the sand filter fol
the general supply, for it greatly improve
the water, though it does not absolutely
purify it. 1t should be remembered tina
when in any house, barrack or tow
two kinds OF water are furnished, one es
pecially for drinking and the other fo
cleansing purposes, the more impur
water will occasionally be used for drink
ing through the ignorance, Incidence o
carelessness of servants, and that therefor
the presence of an accessible supply Q
impure water is always source of danger
and should be avoided as far as possible.
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