202 DOC.
201
MARCH
1916
Answer.
I
measure
what
is
referred to
as
the
solution’s
spec.
heat
in all
thermodynamic
calculations.
I
thus
contend:
Strictly
speaking, only
the
spec.
heat
of the solution
is
measurable in
a manner
of
use
to
thermodynamics.
The fact that
I
can
also
measure
that
of
a
particular
chemical
compound
is
because
I
can
choose
the
reaction
rate at
will
within broad
limits. In
the
present case,
for
ex.,
I
can
reduce
it
optionally by
making
the bond
openings
between
two
chambers smaller and in
this
way keep
the
molecule in
a
particular
chamber
throughout
the
entire
duration
of
cooling.
If
I
do
not
succeed
in
this,
then
my
measurement
is
useless;
s[ee]
Nernst,
iodine’s
spec.
heat distorted
by
latent
heat.[2]
The
situation
is
exactly
the
opposite
when
I
want to
measure
the
solution’s
spec.
heat.
Then
I must
make
the
bond
openings very large (add
a
diffusion
catalyst)
and cool
very
slowly.
It
is
clear
that
as
the
temperature
drops,
it
soon
comes
to
a
limit at which
measurement
becomes unfeasible
practically,
but this
does
not disturb
the
thermodynamics
theorist in the
least,
since he has
an
infinite amount
of
time.
That these
questions
of
rate
play
no
role
can
be
seen
very nicely
in
the
model
when the
energy
differences
between
the
chambers
are
made
very large.
The
solution’s
entropy
is
then
very
close
to
equaling zero already
at
temperatures
high enough
for the diffusion
rate
still
to
be
very great.[3]
Unfortunately
the letter
has
again
become
very
long;
orally
I
would
certainly
have
come
to
concurring
with
you
within
a
couple
of
minutes.[4]
With
cordial
greetings, yours,
Otto
Stern.
[3]Draft
version:
“That
these
questions
of rate
are
inconsequential
for
statistical
thermodynamic
considerations
can
be
seen
very nicely
in
the
model,
in
the
following
way.
We make
the
energy
differences between
the chambers
very large
and
these
chambers
themselves
very small,
then
the
molecule
generates
there
are
quite
high
temperatures
at
which,
on
the
one
hand,
the
molecule’s
velocity
determined
by
T
is
so
large
that
during
any
time
period needed
for
practical measurement,
however
short
it
may
be,
the
molecule
frequently
is
present
in
the chamber with the
highest
energy,
and the
probabilities (determined by
e-E/T)
of
the individual chambers
varies
so
much
that the
molecule
spends
the
largest
part
of
the time
in
the chambers with the
lowest
energy.
As
the
temperature rises,
the
probabilities
of
the individual
chambers
will
then
gradually
and
steadily
become
increasingly
similar to
one
another. Then
clearly