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entirely due to the presence of bi-carbonate of lime in solution.
This bi-carbonate of lime can be readily removed by treating the
water with lime before delivery, as is so successfully done by the
Colne Valley Company; whereby the hardness of that Company's
water is reduced to about one fourth of its original amount—in
1891 from 29°.4 to 88.9: the hardness of the Thames water was
20º.3. This mode of softening is by far the most economical, for
it entails only about one eightieth of the expense which devolves
upon the private consumer in the shape of additional soap required
for washing purposes. The hardness of the river water is similarly
reducible. The small proportion of organic matter which the solid
matters contain, "is of the greatest importance in connection with the
use of the water for drinking purposes:" some of it may be of the
"most objectionable character, on account of its (animal) origin, such
as the drainage from manured land, the effluents from sewage works,
or even raw sewage itself." This animal matter, it is stated, may at
any time be accompanied by zymotic poisons dangerous to health:
the chances, however, of such substances reaching the consumer are
reduced by filtration, and by the exclusion of flood-waters from the
reservoirs. The Companies are endeavouring to substitute, as far as
possible, water from subterranean sources for raw river water, whilst
the Conservators have almost completely stopped the discharge of
untreated town sewage into the Thames. As a rule, the best Thames
water was delivered by the Chelsea Company which also possesses
by far the largest storage reservoirs. The waters derived from the
Lea were generally superior to the Thames-derived waters, the New
River Company's water often rivalling the deep well waters in respect
of organic purity.
Bacteriological Examination.—In a Table, the results
are given of the bacteriological investigation of the waters by the
method of the gelatine plate culture devised by Dr. Koch.
"The vast majority of microbes found in potable waters are,
as far as is known, entirely harmless;" on some rare occasions
however pathogenic bacteria have been found among them; but
never in any water supplied to London: nevertheless, "it must not on
this account be concluded that they are never present." The use of
these examinations, "in the present state of our knowledge, is simply