DOC.
16
123
Doc.
16
ON
THE MOVEMENT OF SMALL
PARTICLES
SUSPENDED
IN
STATIONARY
LIQUIDS
REQUIRED
BY THE MOLECULAR-KINETIC
THEORY OF HEAT
by
A.
Einstein
[Annalen
der
Physik 17
(1905):
549-560]
It will
be
shown
in this
paper
that,
according
to
the
molecular-kinetic
theory
of heat, bodies of
microscopically
visible size
suspended
in
liquids
must,
as a
result of thermal
molecular motions,
perform motions
of
such
magnitude
that
these
motions
can
easily be
detected
by
a
microscope.
It is
possible
that the
motions to be
discussed here
are
identical with the
so-called
"Brownian
molecular
motion";
however,
the data available
to
me
on
the latter
are so
imprecise
that
I
could
not form
a
definite
opinion
on
this
[1]
matter.
If it is really
possible to
observe the
motion to
be
discussed here,
along
with the
laws
it is
expected to
obey,
then classical
thermodynamics
can
no longer
be
viewed
as
strictly
valid
even
for
microscopically distinguishable
spaces,
and
an
exact
determination of the real size
of atoms becomes possible.
Conversely,
if the
prediction of
this
motion
were
to be
proved wrong,
this
fact
would
provide
a
weighty
argument
against
the
molecular-kinetic
conception
of heat.
[2]
§1.
On
the osmotic
pressure
attributable
to
suspended
particles
Let
z
gram-molecules
of
a
nonelectrolyte
be
dissolved in the partial
volume
V*
of
a
liquid of total
volume
V.
If
the
volume
V*
is
separated
from
the
pure
solvent
by a
wall that is
permeable
to
the solvent but
not to
the dissolved
substance,
then this wall
is
subjected to
the so-called
osmotic
pressure,
which at
sufficiently
large
values
of
V*/z
satisfies the
equation
pV*
=
RTz.
[3]