45 / 230
CONTINUOUS
DISTILLATION.
45
large
size,
and
used
for
distilling
simple
fluids,
is
called
a
still.
Those
for
experiments
in
a small
way,
and
also
for
distilling
acids,
ammonia,
ether,
&c.,
are
called
retorts;
the
vessel
that
receives
the
distilled
matter
being
called
a
receiver.
When
the
worm-tub
is
employed,
the
still
requires
such
a
shape
that
the
greatest
possible
surface
may
be
exposed
to
the
fire.
Its
shape
is
then
that
of
a
frustum
of
a
cone.
The
neck
should
be
of
such
width
as
to
con-
vey
the
vapour
away
as
fast
as
formed.
The
height
of
the
neck
is
regulated
by
the
nature
of
the
substance
operated
upon
:
if
it
is
mucilaginous,
the
neck
should
be
longer,
to
prevent
its
boiling
over
;
and
the
exterior
of
the
lower
part
should
be
polished
to
prevent
the
escape
of
heat
;
the
descending
part
painted
black,
and
its
end
inserted
into
the
end
of
the
worm.
The
worm-tub
is
a
wooden
vessel,
about
six
or
eight
times
the
capacity
of
the
still
;
the
length
to
the
diameter
should
be
about
ten
to
seven.
The
worm
consists
of a
spiral
tube,
which
enters
on
one
side
of
the
tub
at
the
top
;
it
then
passes
spirally,
in
six
or
eight
convolutions,
to
the
bottom,
where
it
comes
out
of
the
side in
order
to
discharge
the
liquid
arising
from
the
vapour
condensed
within
it
by
the
agency
of
the
cold
water
with
which
the
tub
is
filled.
The
water
is
constantly
changing,
by
the
warm
water
running
away
from
the
top,
while
a
supply
of
fresh
water
comes
in
at
the
bottom.
The
section
of
the
tube
being
a
circle,
its
capacity
should
not
be
less
than
one-fifth
of
that
of the
still
;
the
diameter
of
the
ends
of
the
tube
being
about
three
to
one.
The
object
is
not
merely
to
effect
a condensation,
but
to
cool
the
liquid
:
the
means