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DUST AND DISEASE. 321

zonspicuous ; you see the track of the beam, but it is not
the thick and muddy track revealed in London waters. It
has been a subject much debated 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 that not only is its
purity unrivalled, but that its quantity is practically inex-
haustible. Data suflicient to test this are now, I believe,
in existence; the number of wells sunk in the chalk is so
considerable and the quantity of Water which they yield is
so well known.

But this water, so admirable as regards freedom from
mechanical impurity, labors under the disadvantage of
being very hard. It is rendered hard by the large quantity
of carbonate of lime which it holds in solution. The chalk-
Water in the neighborhood of Watford holds in solution
about seventeen grains of carbonate of lime per gallon.
This, in the old terminology, used to be called seventeen
degrees of hardness. Now this hard water is bad for tea,
bad for washing; it furs your boilers, because the lime
held in solution is precipitated by boiling. If the water be
used cold, its hardness must be neutralized at the expense
of soap before it will give a lather. These are serious ob-
jections to the use of chalk-water in London. But they
are now successfully met by the experimental demonstration
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; at the Chiltern Hills it
is softened for the supply of Tring and Aylesbury. Carter-
ham also enjoys the luxury.

I have visited all these places, and made myself ac‘

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