rrangement for giving the necessary pressure. An increase in the
porosity of the filtering tube is not to be thought of, as this would allow
very small germs to pass. This filter being a perfect one, we must expect
to see it soil quickly. Filters that do not get foul are just the ones that
do not filter. But with the arrangement that I have adopted the solid
matters deposit upon the external surface of the filter, while the inner
surface always remains perfectly clean. In order to clean the tube, it is
only necessary to take it out and wash it vigorously. As the tube is
entirely of porcelain, it may likewise be plunged into boiling water so as
to destroy the germs that may have entered the sides or, better yet, it may
be heated over a gas burner or in an ordinary oven. In this way all the
organic matter will be burned, and the tube will resume its former
porosity.--_M. Chamberland, La Nature._

* * * * *

SIMPLE DEVICES FOR DISTILLING WATER.

The alchemists dreamed and talked of that universal solvent which they so
long and vainly endeavored to discover; still, for all this, not only the
alchemist of old, but his more immediate successor, the chemist of to-day,
has found no solvent so universal as water. No liquid has nearly so wide a
range of dissolving powers, and, taking things all round, no liquid
exercises so slight an action upon the bodies dissolved--evaporate the
water away, and the dissolved substance is obtained in an unchanged
condition; at any rate, this is the general rule.

The function of water in nature is essentially that of a solvent or a
medium of circulation; it is not, in any sense, a food, yet without it no
food can be assimilated by an animal. Without water the solid materials of
the globe would be unable to come together so closely as to interchange
their elements; and unless the temperatures were sufficiently high to
establish an igneous fluidity, such as undoubtedly exists in the sun, there
would be no circulation of matter to speak of, and the earth would be, as
it were, locked up or dead.

When we look upon water as the nearest approach to a universal solvent that
even the astute scientist of to-day has been able to discover, who can
wonder that it is never found absolutely pure in nature? For wherever it
accumulates it dissolves something from its surroundings. Still, in a
rain-drop just formed we have very nearly pure water; but even this
contains