d, whether the supply of excellent water which
the chalk holds in store could not be rendered available for London.
Many of the most eminent engineers and chemists have ardently
recommended this source, and have sought to show, not only that its
purity is unrivalled, but that its quantity is practically
inexhaustible. Data sufficient to test this are now, I believe, in
existence; the number of wells sunk in the chalk being so
considerable, and the quantity of water which they yield so well
known.

But this water, so admirable as regards freedom from mechanical
impurity, labours under the disadvantage of being rendered very hard
by the carbonate of lime which it holds in solution. The chalk-water
in the neighbourhood of Watford contains about seventeen grains of
carbonate of lime per gallon. This, in the old terminology, used to
be called seventeen degrees of hardness. This hard water is bad for
tea, bad for washing, and it furs our boilers, because the lime held
in solution is precipitated by boiling. If the water be used cold,
its hardness must be neutralised at the expense of soap, before it
will give a lather. These are serious objections to the use of
chalk-water in London. But they are successfully met by the fact that
such water can be softened inexpensively, and on a grand scale. I had
long known the method of softening water called Clark's process, but
not until recently, under the guidance of Mr. Homersham, did I see
proof of its larger applications. The chalk-water is softened for the
supply of the city of Canterbury; and at the Chiltern Hills it is
softened for the supply of Tring and Aylesbury. Caterham also enjoys
the luxury.

I have visited all these places, and made myself acquainted with the
works. At Canterbury there are three reservoirs covered in and
protected, by a concrete roof and layers of pebbles, both from the
summer's heat and the winter's cold. Each reservoir holds 120,000
gallons of water. Adjacent to these reservoirs are others containing
pure slaked lime--the so-called 'cream of lime.' These being filled
with water, the lime and water are thoroughly mixed by air forced by
an engine through apertures in the bottom of the reservoir. The water
soon dissolves all the lime it is capable of dissolving. The
mechanically suspended lime is then allowed to subside to the bottom,
leaving a perfectly transparent lime-water behind.

The softening process is this: Into one of the empty