DOC.

12

COMMENTS ON

EÖTVÖS'S

LAW

407

[2]See Eötvös 1886.

The

difference

between

t

and the critical

temperature is

about

6°

for

most

substances.

See,

e.g.,

Freundlich

1922, pp.

43-45,

for

more

details. Eötvös's

law

and the

experi-

mental work

bearing

on

it

are

also reviewed in Nernst

1893,

which is

mentioned in Einstein's

Scratch Notebook

(Appendix

A),

[p.

20].

[3]This

assumption,

which

is

sometimes called

Guldberg's

rule,

is

only

valid

if

the critical

pressures

of the

compared

substances

are

not too

different; see,

e.g.,

Kamerlingh

Onnes and

Keesom

1912, p.

932.

[4]See

Nernst

1909,

pp. 277-279,

for

a

discussion of Trouton's

rule

(also

in

connection with

Guldberg's

rule).

[5]Ds

is

the molar heat of

evaporation.

[6]See

also Einstein

1901

(Vol.

2,

Doc.

1),

p. 514,

for Einstein's earlier

use

of the linear

dependence

of

y

on

the

temperature.

See

Freundlich

1922,

pp.

38-40,

for

a

discussion of the

temperature dependence

of the surface tension.

[7]Uf should

be

Uf.

[8]See,

e.g.,

Van

der

Waals

1894,

which contains calculations similar

to

the

ones

that lead

to

the

expression

for

Uf

below. A reference to

this

paper,

which also discusses Eötvös's

law,

appears

in

Einstein's Scratch Notebook

(Appendix

A),

[p.

20].

[9]N

is

Avogadro's

number.

[10]A

factor

of

1\2

is missing

in

the

right-hand

side.

[11]The

expression

for

K2

corrects

a

mistake

in

Einstein

1901

(Vol. 2,

Doc.

1).

See note

1.

[12]In

a

letter

to

Einstein of

1

February 1912,

Richard Swinne

pointed

out

that, in

fact,

there

might

be

no

contradiction between

eqs. (1b)

[or

(1c)]

and

(2)

since

experimental investigations

seemed

to

indicate that

in

(1b)

the factor

y2/3

should

be

replaced

by

vs

(see, e.g.,

Walden

1909).

Swinne also noted

that

experiments

had shown that

yu2/3

was

not

a

linear function of

tempera-

ture

under

all

circumstances

(see, e.g.,

Walden

1911).

[13]Validity of

eq. (2)

implies

that

eqs.

(1),

(1a),

and

(1b) are

linear

in

vs,

and thus

in

M,

the

molecular

weight.

Since

the denominator of

(1b)

is

linear

in

M

as well,

M would

drop

out

of

the

quotient.

[14]In

a

review

of Einstein's

paper,

Sackur remarked

that

this

assumption

is

clearly not

valid for

all fluids

(Sackur 1910,

p.

16).

[15]The

molecular model introduced

here-the

lattice

picture together

with the

assumption

that

only neighboring

molecules

interact-is

applied

to

solids

in

Einstein

1911b

(Doc.

13),

which

immediately

followed the

present paper

in

the

same

issue of

the Annalen

der

Physik.

[16]Georg

Bredig (1868-1944)

was

Professor of Physical Chemistry and Electrochemistry at

the ETH.

[17]n

should

be

1/n

in

the

sentence

beginning,

"Es

ergibt

sich."