12 DIFFERENCE IN POTENTIALS
Doc.
2
ON
THE THERMODYNAMIC THEORY
OF
THE
DIFFERENCE IN POTENTIALS
BETWEEN METALS
AND FULLY
DISSOCIATED SOLUTIONS OF
THEIR
SALTS
AND
ON
AN
ELECTRICAL
METHOD FOR
INVESTIGATING
MOLECULAR FORCES
By
A.
Einstein
[Annalen
der
Physik 8 (1902):
798-814]
§1.
A
hypothetical
extension
of
the second
law of
the
mechanical theory of
heat
The
second
law
of the
mechanical theory of
heat
can
be
applied
to
such
physical
systems
which
are
capable of
passing,
with
any
desired
approximation,
through
reversible
cyclic
processes.
In
accordance with the derivation
of
this
law
from
the
impossibility of
converting
latent heat into mechanical
energy,
it is here
necessary
to
assume
that those
processes
are
realizable.
However,
in
an
important
application of
the mechanical
theory
of
heat,
namely
the
mixing
of
two
or more
gases
by
means
of
semipermeable
membranes,
it is
doubtful whether this postulate is satisfied.
The thermodynamic
theory of
dissociation
of
gases
and
the
theory
of dilute solutions
are
based
on
the
[1]
assumption
that
this
process
is realizable.
As
is well
known,
the
assumption to
be
introduced is
as
follows:
For
any
two
gases
A
and
B
it should
be
possible
to
produce
two
partitions
such
that
one
is
permeable
for
A
but
not
for
B,
while
the other
is
permeable
for
B
but
not
for
A.
If the mixture consists
of
more
than
two
components,
then
this
assumption becomes
even
more
complicated and improbable.
Since the
results of the
theory have been completely confirmed
by
experiment
despite the
fact that
we
worked
with
processes whose
realizability could
indeed
be
doubted,
the
question
arises
whether
the
second
law
could
not be
applied
to
ideal
processes
of
a
certain kind without
contradicting
experience.
In this
sense, on
the basis
of
the
experience
obtained,
we
certainly
can
advance
the proposition:
One
remains
in
agreement
with
experience
if
one
extends the
second
law to physical
mixtures
whose
individual
components
are
restricted
to
certain
subspaces
by
conservative forces
acting
in certain
planes.
We
shall
hypothetically generalize
this
proposition
to
the
following: