CHEMISTRY AND PHYSICS. 49 
tained from our western rivers, an example of which is St. Louis, Mo., which in 
this manner treats thirty-two million gallons per diem. In Europe, where water 
purification by the use of sand filters is general, the rate of descent of the water 
through the sand of the filter varies with the degree of turbidity, ordinarily, but 
about sixty galions per square foot per twenty-four hours, or 2,500,000 gallons 
per acre per diem. 
The action of these filters is not alone that of strainers. The fermentation of 
the organic substances in the bed of the filter changes the organic constituents 
to inorganic nitrites and nitrates by the agency of bacteria. The mechanical fil- 
ters act only as strainers, as the rate of passage of the water through the filter, 
130 million gallons per acre per diem, is too rapid to allow of the reduction of the 
organic compounds by fermentation. 
In the process of purifying water containing organic matter by filtration, that 
portion in a state of suspension will be retained on the filter as a strainer, while 
that carried down by subsidence will be mingled with the other precipitated im- 
purities. In either case they will by decomposition be rendered insoluble, and in 
the case of the filter will pass off with the filtered water; or in the case of by sub- 
sidence will be mingled with the purified water in the settling basin; in each case 
containing the spores of any bacterial life there may be in the water, together 
with the soluble matters as a nidus for their development; for which reasons the 
requirement is to use sand-filtered water soon after it has been purified. The 
value of filtration as a means for purifying water by the removal of bacteria can 
be judged from the following: 
Doctor Currier, biologist for the Syracuse Water Commission, experimented 
with a variety of filters, and found, even with the justly celebrated Chamberlain- 
Pasteur filter, under the hydrant pressure of New York city, when the flow was 
but drop by drop, that, when the filter had been sterilized by steaming for five 
hours, no bacteria passed through with the water; but that after three days’ con- 
tinued use the number of bacteria increased to 2500 per cc., and after five days 
of such use the number had increased to 400,000 per cc. These processes, which 
may be regarded as standard, take no account of the removal of inorganic sub- 
stances in solution in water. These substances are earth salts, rendered soluble 
by the solvent action of gases contained in the water, mainly carbonic and sul- 
phuric acid gases, so objectionable in water used for washing or for use in steam 
boilers. Doctor Frankland, chemist to the Parliamentary Rivers Pollution Com- 
mission in England, regards the softening of water by the removal of lime, mag- 
nesia, etc., as so important that he recommended, in a report to the above-named 
commission, that all companies should ‘be compelled to provide for softening 
water-supplies before being allowed to raise additional capital for the extension 
of water-works. It was estimated that the chalk contained in the water-supply 
of London was 160 tons per diem, and that the saving in soap, if that were re- 
moved, would be, approximately, £250,000, equal to $1,250,000; and a cost of one 
penny applied for purifying water would effect a saving of soap of three shillings 
and eight pence, or forty-four times as much. 
While the character of these impurities has been understood in a general way, 
it is only of late that any account has been taken of the effects, on nutrition and 
health, of hard water used dietetically. Based on mortuary statistics of a number 
of cities, it has been held that the hardness of water had no material effect on 
the death-rate; and, while it may be true that there is no direct evidence of this, 
there is much evidence that they exert a marked influence in inducing diseases, 
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