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3 2 0 FRAGMEN TS OF SCIENCE.

pended in it. But when we remember that this perfection
of blue is approached gradually through stages of less per-
fect blue; and when we consider that a blue in all re-
spects similar is demonstrably obtainable from particles
mechanically suspended, we should hesitate, I think, to
conclude that we have arrived here at the last stage of pu-
rification. The evidence, I think, points distinctly to the
conclusion that, could we push the process of purification
still further, even this last delicate trace of blue would dis-
appear.

Chal/c - Water. Clark’s Softening Process.

But is it not possible to match the water of the Lake
of Geneva here in England ? Undoubtedly it is. We have
in England a kind of rock which constitutes at once an ex-
ceedingly clean recipient and a natural filter, and from which
we can obtain water extremely free from mechanical im-
purities. I refer to the chalk-formation, in which large
quantities of water are held in store. Our chalk-hills are
in most cases covered with thin layers of soil, and with
very scanty vegetation. Neither opposes much obstacle
the entry of the rain into the chalk, where any organic
impurity which the water may carry in is soon oxidized
and rendered harmless. Those who have scampered like
myself over the downs of Hants and Wilts will remember
the scarcity of water in these regions. In fact, the rain-
fall, instead of washing the surface and collecting in streams,
sinks into the fissured chalk and percolates through it, and
when this formation is suitably tapped We obtain water of
exceeding briskness and purity. Here is a large globe filled
with the water of a well near Tring. It is wonderfully free
from mechanical impurity; indeed, it stands to reason that
water Wholly withdrawn from surface contamination and
percolating through so clean a substance should be pure.
Sending a beam through this glass of water its purity is

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