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Title: James Joule's Work in Electrochemistry and the Emergence of the First Law of Thermodynamics

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James Joule's Work in Electrochemistry and the Emergence of the First Law of
Thermodynamics
Author(s): William H. Cropper
Source: Historical Studies in the Physical and Biological Sciences, Vol. 19, No. 1 (1988), pp. 1-15
Published by: University of California Press
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WILLIAM H. CROPPER*
James Joule's work in electrochemistry
law of thermodynamics

and the emergence of the first

a long memoir
1852, james Joule published
summarizing his last
The work reported had been done in
experiments in electrochemistry.
a series of experiments started in
1844 and 1845, and it culminated
and interpreting quantitative
1840 and concerned with demonstrating
among electrical, chemical, and heating effects. Joule's
equivalences
of the mechanical
many refinements of his determination
equivalent
of heating effects are well known. That work was preceded by, and in
fact suggested by, the earlier electrochemistry experiments: Joule was
In

an electrochemist before he was a physicist.
in 1846,
The
1852 paper was submitted to the Paris Academy
a
to
in
too
the best
late
be
for
considered
competition
unfortunately
on
heat
Joule
"the
of
combinations."
chemical
essay
evidently misun
and the paper "was deemed
derstood the rules of the competition,
to examine
appointed
ineligible, but was referred to the Commission
memoirs presented on the subject."1 Nothing more was done with the
six years later in
paper until Joule finally had it published unchanged
on
the
the Philosophical magazine.2
paper has been very
Commentary
limited. It has been dismissed as a rehash, or mistaken
interpretation,
the paper, however,
of earlier work. Wilhelm Ostwald understood
assessment
and
it
its
author:3
this
of
gave
appreciative

and

Here we find that Joule obtained his results by a method not widely
understood in those days. So far this man has been assessed almost
exclusively

as

the first to carry

of the mechanical

out

accurate

equivalent of heat_In

experimental

measurements

discussing this research we

13617.
St. Lawrence
Canton, ny.,
*Chemistry Department,
University,
are used:
The
abbreviations
PM,
Philosophical
magazine;
following
Prescott Joule, The scientific papers (2 vols., London,
1884), vol. 1.
1. SP, 205.
2.

Joule,

"On

the heat disengaged

481; reprinted in SP, 205-235.
3. Wilhelm
Ostwald,
Electrochemistry:
New Delhi,
1980), 2, 769.

in chemical
History

combinations"
and

theory [1896]

[1846],

SP,

PM,

(English

HSPS,

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James

3 (1852),
tr., 2 vols.,

19:1 (1988)

2

CROPPER

come to know Joule from another side. We
dent thinker of outstanding originality.

find that he is an indepen

and more.
By 1846 he had all
in
the ingredients?an
law accurately demonstrated
earlier electrochemistry research, unique mastery of the techniques of
arrive at
calorimetry, and several sources of theoretical inspiration?to
an entirely correct application
Law
of the First
of Thermodynamics.
Joule's experimental
circuits containing
systems were complicated
both voltaic and electrolysis cells, not familiar even to modern
ther
Joule deserves

these compliments
electrical heating

and certainly "not widely understood
in those days."
modynamicists,
the
the
of
electrochemical
effect, he was able to
Through
intermediary
determine
that are still
combustion-reaction
equivalents
heating
their
The
for
of
Joule's
calculations
accuracy.
impressive today
style
the
of
features
anticipated
important
input-output analysis developed
in the early 1850s by Rudolf Clausius
to
and William
Thomson
the
Law.
First
express
In this study, I shall focus on this neglected paper, written in 1846
but not published
until 1852, the fifth of Joule's electrochemistry
I
shall
the conceptual
examine
and experimental background
papers.
he brought to this work; touch on an earlier approach, as seen in the
fourth of the electrochemistry papers; and show how Joule came to
famous work, the determination
of the mechanical
begin his most
of
heat.
equivalent
1. ELECTROCHEMISTRY
Measurements

One of the major themes in Joule's research from beginning to end
the calculation
and measurement
of equivalences
relating chemi
effects. The first electrochem
cal, electrical, thermal, and mechanical
among the first
istry paper presented an extensive list of equivalences
three of these effects, and seemed to be probing for a general princi
ple;4 but even though the work was outstanding by the standards of
the time, it lacked the theoretical and experimental basis to meet the
In the remaining papers
in this
challenge, as Joule soon realized.
the narrower problem of determining heats of
series, he emphasized
and
combustion
from
thermal
data.
electrical
Equivalence
still had his attention, but he apparently felt that more
phenomena
cases
determined
studies of carefully chosen
quantitative
special

was

4.

Joule,

"On

battery during

the heat

electricity,"

evolved
PM,

conductors
by metallic
19 (1841), 260; reprinted

of electricity,
in SP, 60-81.

and

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in cells of a

ELECTROCHEMISTRY

3

would be more revealing. He was beginning to understand, well ahead
of his contemporaries,
that unambiguous
equivalence
principles could
be obtained only by the strictest attention to experimental accuracy.
Joule measured
heating effects in simple calorimeter devices that
gave surprisingly few problems related to heat losses. He measured
temperature changes in the calorimeters with sensitive mercury ther
mometers, which he could read to 0.005 ?F in the later experiments.5
To determine the heat produced
internally in a calorimeter, he both
measured
and
calorimeter heat capacities using an electrical method
calculated them from tables of specific heats.6 The thermal quantity
=
in which Cp is a constant-pressure
calorimeter heat capa
Q
CPAT,
a
AI
in
and
measured
temperature change, was fundamental
city
Joule's calculations.
in Joule's work was of current
The primary electrical measurement
made with a galvanometer
of the tangent kind.7 To obtain resistance
and batteries whose
law, current measurements,
values, he used Ohm's
to be constant. He made his
force values he assumed
electromotive
batteries of cells of the Daniell
design, with an electromotive force of
about 1.0 volt.8
In
Joule was always careful and ingenious in his choice of units.
to the modern calorie
the 1852 paper, his heating unit was equivalent
and his resistance unit was the resistance of a standard coil of silver
He
read current units directly from the galvanometer.
wire. He
=
I
IR.
shall
defined his potential ("intensity") unit via Ohm's
law, E
It will help to know that
usually quote Joule's data in his own units.
to 3.93
his current, resistance, and potential
units are equivalent
ohm
and
1.87
volt.
ampere, 0.476
At the center of all Joule's work in electrochemistry was his empir
in a calorimeter by a
the heating Q produced
ical law determining
resistance R
carrying a current / for a time t. Joule's discovery,
introduced in his first electrochemistry paper,9 was that Q is propor
In each of three electrolysis studies (of copper sulfate,
tional to I2Rt.
zinc sulfate, and sulfuric acid solutions) that he reported in the 1852

in the possession
5. J.R. Ashworth,
"Joule's
thermometers
and Philosophical
Society," Journal of scientific instruments,
6. SP, 226-227.

of the Manchester
7(1930),

Literary

361-363.

see J.C. Maxwell,
A treatise on electricity and magne
7. For the tangent galvanomer,
tism, 3rd ed. (2 vols., London,
1852), 2, 354-355.
8. See J.R. Partington, A history of chemistry (4 vols., London,
for
1964), 4, 685-688,
the Daniell
cell.
9. SP,

65.

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4

CROPPER

paper, he redetermined his heating law. His
translate to the three equations:10
minations
?

Q
Q

=

data

for the three deter

\.16\2I2Rt

= L160\I2Rt
(1)
= \J592I2RL

of these statements gives a good
Comparison
in his calorimetric
precision Joule achieved

indication of the superb
and electrical measure

ments.

E.

to Ohm's
law, IR in the heating law can be replaced
According
Written this way, the first statement of the heating law becomes

Q

by

= \J6\2EIt.
(2)

Concepts
firm belief
in the fundamental
of
importance
and
Joule's
chemical
theoretical
among
equivalences
physical effects,
electrochemical
equipment included a working knowledge of Faraday's
to the Davy-Berzelius
laws and a commitment
electrical theory of
chemical action.11 In the 1852 paper, he summarized what were for
him the important features of the latter:12
Aside

from his

1st, that when two atoms combine by combustion a current of electri
city passes from the oxygen to the combustible; 2nd, that the quantity
of this curent is fixed and definite; and, 3rd, that it is themeans of the
evolution of light and heat, precisely as is any other current of electri
city whatever.

The Davy-Berzelius
theory was primarily concerned with simple
chemical reactions not involving electrochemical
effects. Joule applied
the theory to circuits containing voltaic cells as sources of current and
to electrolysis cells in which he supposed
the combustion
reactions
took place in reverse (usually accompanied
To
by other reactions).
an important
he had to make
this complicated
develop
application,
10.

Joule did

more

complicated
from Joule's data,

not write
than

these

equations;

simple proportions.
translate his quantitative

in a mathematical
rarely wrote
language
I shall derive
and other equations
These,
statements but do not change his reasoning

he

and conclusions.
on the Davy-Berzelius
11. For more
of
theory and Joule's
interpretation
of energy: The work
and the conservation
of James
Forrester,
"Chemistry
in the history and philosophy
Joule," Studies
of science, 6 (1975), 285-289.
12. SP, 208.

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it, see J.
Prescott

ELECTROCHEMISTRY

5

extension of the theory. He eventually (in the fourth electrochemistry
paper) arrived at the idea that the current generated by the electro
chemical reaction in a voltaic cell could carry the reaction's "calorific

effect" or "chemical heat" away from the primary reaction site either
to an external resistance where it could be converted to "free heat," or
to an electrolysis cell where it could be invested as "latent heat" in the
electrolysis reaction or reactions.

Joule expressed these concepts at the close of the fourth electro
chemistry paper: "Electricity may be regarded as a grand agent for
cited an
carrying, arranging, and converting chemical heat."13 He
an elec
current
to
in
heat
chemical
which
electrical
"carries"
example
a
to
cell
where
converted
the
latent
heat
decom
it
is
of
trolysis
mostly
so
In
little
free
evolved."
another
heat
is
position reaction,
"very
example, he pointed out that heating that might otherwise appear
within a voltaic battery is prevented by placing the battery in a circuit
with a resistance which is much larger than the battery's internal resis
tance: "nearly the whole of the heat due to chemical change taking
place in the battery will be evolved by [the external resistance]; while
the battery itself will remain cool."
Calculations
One

of Joule's aims was

to use his theory and his uniquely precise
calculate the quantity of chemical
electrolysis cell, a result he could
For this he
electrolysis reaction.
heat was delivered to the cell in a

electrolysis and calorimetric data to
heat converted to latent heat in the
interpret as the heat of the overall
needed to know how much chemical

to this problem in the 1852
time / by a current /. Joule's approach
paper displayed mastery of both the conceptual and the experimental
law to deter
He used current measurements
and Ohm's
problems.
mine the value of a resistance Re of a wire which could replace the
cell without causing any other electrical changes. He knew that if the
voltaic cell's current were supplied to such a resistance the chemical
heat carried by the current would all be converted to an amount of
free heat Qe which

he could

tion (2),

Qe

calculate

=

from his heating

law, say equa

\.16\2I2Ret (3)

the equivalent
of the chemical heat
This was what Joule needed,
received by the electrolysis cell. It was also a measure
of the heating
that would have been observed if no electrolysis reaction had occurred
13. SP,

120.

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6

CROPPER

in the cell.
Joule found that the actual heating Qt in the electrolysis cell, meas
was always substantially less than Qe.
as
ured calorimetrically
CpAT,
He understood
the difference to represent what he wanted to calculate,
chemical heat converted to the latent heat of the electrolysis reaction.
heat transformed to latent heat was "lost to the circuit:"14 it
Chemical
caused no heating. Representing
the electrolysis reaction's latent heat
Joule wrote

by Qn

Qr

=

Qe-Qt

(4)

to a modern

statement of the First Law of Thermo
=
to
it also calculates the net heat
dynamics.15 Rearranged
Qt
Qe-Qn
ing effect Qt in the cell resulting from the input Qe supplied by the

This

is equivalent

electrical

current and

the output Qr

absorbed

by the electrochemical

reaction.

To recapitulate
the general features of the method
reported by
Joule in his 1852 paper, we can do no better than quote his concise
of the experiment,
the calculation,
and the interpreta
description
tion.16

I take a glass vessel filledwith the solution of an electrolyte, and prop
erly furnished with electrodes. I place this electrolytic cell in the voltaic
circuit for a given length of time, and carefully observe the quantity of
decomposition and the heat evolved [Qt]. By the law of Ohm I then
ascertain the resistance [Re] of a wire capable of obstructing the current
equally with the electrolytic cell. Then, by the [heating] law we have
proved, I determine the quantity of heat [Qe] which would have been
14. SP,
15. The

119.

to ArH,
the enthalpy change for the electrolysis
quantity Qr is equivalent
as a calorime
evaluated
cell doubling
for the electrolysis
reaction; Qt is equal to CpAT
the heating equivalent
to the
of the electrical work We
ter; and Qe measures
supplied
cell. That Qe has a simple work interpretation
follows from equation
(2) and others like
for IR, Qe =
\.16\2EIt.
is the electrica! work
substituted
The potential E
it; with E
to
the cell per unit of electrical charge, El
is the rate of work input per second,
supplied
Elt

is the total work

work Wr
pressed
That

1.7612 Elt
expresses
input in time t, and Joule's quantity
in terms of its heating effect. This further translation of Joule's calculation
=
.
in our equation
(4) transforms it to ArH
We-CpAT
this is a legitimate statement of the First Law
for Joule's electrochemical

the
ex

sys
tems follows from a general statement of the First Law for constant pressure conditions,
AH = Q + We, with Q > 0 and We>0
heat and electrical work
input,
representing
are caused
and AH =
which
asserts that enthalpy
tempera
by
changes
+ArH,
CpAT
=
=
ture and chemical
For the calorimeter
Com
situation, O
0, so AH
changes.
We.
=
we
this
result
with
the
second
for
have
, or
AH,
bining
equation
+ArH
We
CpAT
?
=
as
expected.
ArH
We
CpAT,
16. SP, 221-222.

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ELECTROCHEMISTRY

7

evolved had a wire of such resistance been placed in the circuit instead
of the electrolytic cell. This theoretical quantity, being compared with
the heat [Qt] actually evolved in the electrolytic cell, is always found to
exceed the latter considerably. The difference between the two [Qe-Qt]
evidently gives the quantity of heat [Qr] which is due to the reverse
chemical combination by combustion or other means.
the details of experi
Joule's incomparable
genius for organizing
He found ways to deter
mental design is nowhere better displayed.
mine the two quantities he needed for his calculation, Qt and Qe, by
taking full advantage of the extraordinarily refined techniques he had
earlier for measuring
temperatures and electrical currents.
developed
in
He determined Re by applying Ohm's
law to current data obtained
cells and various combi
three circuits containing a battery of Daniell
the unit
resistance Ru
the cell's
nations
of three resistances,
equivalent resistance Re, and the resistance Ru derived from the leads
to be constant).17
and the battery's
internal resistance
(assumed
Joule's three currents, which he labelled A, B, and C, were measured
+ Ru

with the resistances Ru, Ru
calculated Re from

Re

=

and Ru

then

C(A-B)'
cell was

current through the electrolysis
equation (3), would be
=

in the circuit. He

B(A-C)

The

Qe

+ Re

C,

so Qe,

according

to

\.16\2{A-C)BCt
A-B

the actual heating Qt in an electrolysis cell, Joule
determine
for
his
employed
heating law to develop an accurate electrical method
the
heat
He
measured
first
cell's
the
determining
capacity CP.IS
current through a mercury resistance and the heating it caused
in a
To

standard calorimeter whose
heat capacity he had calculated
from
the current through the
tables of specific heats. He also measured
for the same length of
mercury resistance and the heating produced
time in the cell. The cell's heat capacity Cp>cen could then be calcu
lated from the heat capacity CpMd of the standard calorimeter.
(/2)cell(Ar)std
(/2)std(Ar)cell
17. SP,
18. SP,

220.
227.

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8

CROPPER

The I2 and AT ratios were calculated with currents and temperatures
and thermometer scales.
read directly from uncalibrated
galvanometer
in each of the three series of electrolysis
He repeated this procedure
A temperature
rise Ar
experiments
reported in the 1852 paper.
a
in
cell could be multiplied
measured
by a heat capacity Cp to calcu
late Qt .
Data
Joule's ultimate purpose was to use his electrolysis data to make
accurate determinations
In one of his studies,
of heats of combustion.
concerned with electrolysis of sulfuric acid solutions, he could assume
reaction whose

that the decomposition

heat his quantity Qr measured

was

H20(1) -> H2(g) + l/202(g),
reaction.
simply the inverse of the hydrogen combustion
these experiments Joule's current measurements
indicated

(A^C
A -B

In one of

= 3 26()7

in his current units. Our equation for the heating law in this case
= \
so Qe for 10minutes of heating was
J952I2Rr,
Qe
Qe~

_

=

is

\.1592{A-C)BCt
A-B

(1.7592)(3.2607)(600)

= 3441.7cal.
= 1155.0cals
Joule measured
deg"1 for the cell's heat capacity and
Cp
=
in his thermometer units for heating in the cell
found Ar
40.381
to 23.38 of
during electrolysis. One degree centigrade was equivalent
his thermometer units. Therefore,
AT

Qt

=

=
=

40.381/23.38

CPAT

=

1155.0(40.381/23.38)

1949.8 cal.

Joule concluded
Qr

=

?C,

that

Qe-Qt

= 3441.7-1994.8
=

1446.9 cal.

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