DOC.
9
CRITICAL OPALESCENCE
249
dt
dt
_
dk
dv 3v
dk,
we
can
rewrite
the
formula
(17a)
in
the
form
v
CM
n tA\
Jo
M'
VaJtl
$
2
(17d)
_
=
iL

coszp.
/ N
d(\ogp")
[A.
J
(4*D)2
dk
This
formula,
which
now
contains
only
quantities
accessible to
experiment,
completely
determines the
opalescent properties
of
binary
liquid
mixturesto
the
extent
that their
saturated
vapors
can
be treated
as
ideal
gasesup
to
a
small
region
in
the immediate
vicinity
of the
critical
point.
But because of the
strong absorption
of
light
and
its
great
dependence on
the
temperature,
a
quantitative
investigation might
well
be ruled
out
here
anyhow.
Let
us
repeat
here the
meanings
of the
symbols
that
appear
in this
formula
insofar
as they
have not
been
explained
along
with
formula
(17b):
M" is
the molecular
weight
of the second
component
in
the
vapor
phase,
v
is
the
volume
of the
liquid
mixture in which
the unit
mass
of the
first
component is
contained,
k
is
the
mass
of
the second
component
which falls to
the share of
the
unit
mass
of
the first
component,
p"
is
the
vapor pressure
of the
second
component.
Lest
it
not look
peculiar
that the
two
components
play
different roles
in
(17d),
let
me
mention the
wellknown
thermodynamic
relation
J_

J_ ldp'
M"
p
~ M' k
p'
From
this
relation
one can
conclude that
it
does
not matter which
component is
treated
as
the
first,
and
which
as
the
second.
A
quantitative experimental
investigation
of the
phenomena
here considered
would
be
of
great
interest:
on
the
one
hand,
it would be valuable to know
whether Boltzmann's
principle
gives
indeed
a
correct account
of the
phenomena
here
considered,
and
on
the
other
hand, such
investigations
could
lead
to accurate values
for the number
N.
Zurich,
October
1910. (Received
on
8
October
1910)