may be sure that all
impurity has been thus removed from the surface of the ice. The water
obtained in this way is the purest hitherto obtained. Still I should
hesitate to call it absolutely pure. When condensed light is sent
through it, the track of the beam is not invisible, but of the most
exquisitely delicate blue. This blue is purer than that of the sky,
so that the matter which produces it must be finer than that of the
sky. It may be and indeed has been, contended that this blue is
scattered by the very molecules of the water, and not by matter
suspended in the water. But when we remember that this perfection of
blue is approached gradually through stages of less perfect blue; and
when we consider that a blue in all respects 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
purification. The evidence, I think, points distinctly to the
conclusion that, could we push the process of purification still
farther, even this last delicate trace of blue would disappear.

Chalk-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 exceedingly clean recipient and a natural
filter, and from which we can obtain water extremely free from
mechanical impurities. 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 to the entry of the rain
into the chalk, where any organic impurity which the water may carry
in is soon oxidised 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 rainfall, instead of
washing the surface and collecting in streams, sinks into the fissured
chalk and percolates through it. When this formation is suitably
tapped, we obtain water of exceeding briskness and purity. A large
glass globe, filled with the water of a well near Tring, shows itself
to be 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reason that water wholly withdrawn from surface contamination, and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. It has been
a subject much debate