View report page

97
either the presence or absence of sunshine, or high
or low temperature.” Bearing in mind the numbers
of microbes found in the unfiltered water, the efficiency
of the filtration carried out by the water
companies is clearly demonstrated when it is found
that the filters of the West Middlesex Water Company
remove on an average 99.65 per cent. (99.98
as a maximum and 99.04 as a minimum) and those
of the Grand Junction Company, 98.06 as an
average, 99.85 as a maximum and 84.89 as a minimum.
It has already been stated that the Grand
Junction Company filters at the rate of 1.9 gallons
per hour per square foot of bed, against 1.3 in the case
of the West Middlesex, but on this point the experiments
made by Professor Frankland, confirmed by a
very elaborate and lengthy series of observations in
Massachusetts, show that the rate of flow through
the filters, if uniform, has scarcely any effect on the
purification. In the series of experiments in Massachusetts,
the subjects of inquiry were:—
1. The effect, upon bacterial purification, of rate of filtration;
2. The effect of size of sand grains upon bacterial
fication;
3. The effect of depth of material upon bacterial purification;
4. The effect of scraping the filters upon bacterial
fication.
The results of the experiments, so far, is to show
that the first three have but little influence on the
process, but that the fourth does cause a reduction
in the number of bacteria arrested. This is in