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total impurity, and nearly 2 degrees or grains to the gallon
of organic matter. "
Organic impurity consists of vegetable and animal matter,
either living and proper to the water, or dead and almost
entirely introduced in its course, such as sewage matter,
refuse, &c. The amount varies, of course, being much
increased by heavy rains, &c. The amount of organic impurity
contained in the Thames water is so great, that in the
tanks or butts of the vessels which contain it for the supply
of the crews during their voyage, it undergoes a fermenting
process—during which the organic matter is got rid of,
* The figures here represent something like a maximum. In the analysis by
Dr. D. Thomson, of the water supplied by the London Companies, published
in the Registrar-General's weekly returns for the last week, the amount is
shown to be less;—as it may be useful, I append the extract from the report.
Composition of the Water supplied by Eight ok the
Metropolitan Water Companies, in May, 1858.
The amount of impurity is expressed in degrees, each degree being equivalent
to 1 grain of foreign matter present per gallon. The analyses were made
by Dr. Thomson. F.R.S., of St. Thomas's Hospital.
Companies.
Total
Impurity.
grs. or º
Organic
Impurity,
grs. or º
Distilled water 0.0 —
Kent25.36 2.40
New River 17.16 1.80
Grand Junction 17.08 1.80
Southwark 16.84 1.76
Chelsea 18.20 1.68
Lambeth 18.48 1.60
East London 15.92 1.48
West Middlesex 16.36 1.12
All the samples were taken from the mains, with the exception of the
Lambeth specimen, which was procured from a service-pipe at Champion-hill.
The present table, when compared with that for the preceding month, exhibits
a greater equality in the composition of the waters generally, in
consequence of the absence of rain, which has a tendency to augment the