In
many countries, fresh
water is scarce, and
that?s a serious problem.
Drinking water can
often be obtained by
distilling sea water,
though this is a very
expensive process.
Would you like to
see how it's done?
What
you need:
A
sheet of
transparent
plastic,
like the
plastic
used to
wrap up
food.
A
weight (e.g.
some stones)
A
salad bowl
Water,
salt and some
instant coffee
powder
Down
to business
The
first thing
is to pour
water with
lots of salt
in it, and
stained with
the coffee,
into the bowl
until the water
level is 2
cm high (just
under an inch)
BUT DON?T EVEN
THINK ABOUT
DRINKING THIS
CONCOCTION!
Now
place an empty
cup in the
bowl, and cover
the bowl with
the plastic
sheet, though
without stretching
it very taut.
Then put the
stones in the
middle of the
plastic, to
make it sag
a little in
the middle.
Take
the covered
bowl out onto
the balcony,
or anywhere
where it will
be exposed
to the sunlight
for two or
three hours.
After
that, you can
uncover the bowel.
Try the water
in the cup and
SURPRISE, SURPRISE!
It's turned into
fresh, completely
pure water.
So
what's going
on?
The
vapour that
formed owing
to the effect
of the sun's
heat picks
up the water
but leaves
the other substances
we put in it
behind the
salt and the
coffee. So
the water that
condensed on
the underside
of the plastic
cover is pure
water: DISTILLED
WATER.
