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52
WATER-SUPPLY.
of the City of London is substantially of one kind.
The River Lea, on which the East London Company
entirely depends, furnishes likewise much of the supply
conveyed by the New River*. The springs in
which the latter originate are of the same chemical
kind as those which contribute to the Lea; and the
artificial aqueduct runs its forty miles of course
through much the same country as the natural river.
Chemically, therefore, one description may
apply to both; and I the rather speak of them conjointly,
as any extension of its resources for our
supply which the New River might obtain, would
apparently be provided by increasing considerably
its present draught from the Lea.
The pipe-water consumed in the City has for its
general chemical character, that it contains a considerable
quantity of carbonate of lime, held in solution
by an excess of carbonic acid. To this and
another salt of lime (the sulphate) the water chiefly
owes the property which is complained of under the
name of hardness: it is by reason of these salts,
namely, that (if used as drawn) it decomposes a
certain large proportion of whatever soap is used
* It appears that the New River Company at present derives
about two thirds of its supply from the River Lea, and proposes
to draw from this source a still larger proportion. Any chemical
difference of quality in the City pipe-water (as between that supplied
by the New River and that by the East London Company)
would probably not exceed those limits of difference which prevail
in respect of waters gathered under varying circumstances from one
and the same source.