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RESEARCHES
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LONDON ^ TORONTO J-M- DENTS' SONS
LTD. ^2 NEW YORK
E-P-DUTTON
ÆTHERFORCE

.... FIRST ISSUE OF THIS EDITION . 1914

REPRINTED

1922

ÆTHERFORCE

INTRODUCTION 1

BY JOHN TYNDALL

WHEN from an Alpine height the eye of the climber ranges
over the mountains, he finds that for the most part they

resolve themselves into distinct groups, each consisting of

a dominant mass surrounded by peaks of lesser elevation.

The power which lifted the mightier eminences, in nearly all cases lifted others to an almost equal height. And so it is
with the discoveries of Faraday. As a general rule, the

dominant result does not stand alone, but forms the culmi-

nating point of a vast and varied mass of inquiry. In this

way, round about his great discovery of magneto-electric

induction, other weighty labours group themselves. His investigations on the extra current; on the polar and other

condition of diamagnetic bodies; on lines of magnetic force,

their definite character and distribution; on the employment

of the induced magneto-electric current as a measure and test

of magnetic action; on the revulsive phenomena of the

magnetic field, are all, notwithstanding the diversity of title,

researches in the domain of magneto-electric induction.

Faraday's second group of researches and discoveries embrace the chemical phenomena of the current. The

dominant result here is the great law of definite electro-

chemical decomposition, around which are massed various

researches on electro-chemical conduction and on electrolysis both with the machine and with the pile. To this group also

belong his analysis of the contact theory, his inquiries as to the source of voltaic electricity, and his final development

of the chemical theory of the pile.

His third great discovery is the magnetisation of light,
which I should liken to the Weisshorn among mountains

high, beautiful, and alone.

The dominant result of his fourth group of researches is the

discovery of diamagnetism, announced hi his memoir as the

1 These

pages

form

the

"

"

Summary

and

the

concluding

passages

of

Faraday the Discoverer : 1869.

vii

2O54789

ÆTHERFORCE

viii

Faraday's Researches

magnetic condition of all matter, round which are grouped

his inquiries on the magnetism of flame and gases; on magne-

crystallic action, and on atmospheric magnetism, in its

relations to the annual and diurnal variation of the needle, the

full significance of which is still to be shown,

These are Faraday's most massive discoveries, and upon them his fame must mainly rest. But even without them,

sufficient would remain to secure for him a high and lasting

We scientific reputation.

should still have his researches on

the liquefaction of gases; on frictional electricity; on the

electricity of the gymnotus; on the source of power in the

hydro-electric machine, the two last investigations being

untouched in the foregoing memoir; on electro-magnetic

rotations; on regelation; all his more purely chemical re-

searches, including his discovery of benzol. Besides these

he published a multitude of minor papers, most of which, in some way or other, illustrate his genius. I have made no

allusion to his power and sweetness as a lecturer. Taking

him for all and all, I think it will be conceded that Michael

Faraday was the greatest experimental philosopher the world

has ever seen; and I will add the opinion, that the progress

of future research will tend, not to dim or to diminish, but to

enhance and glorify the labours of this mighty investigator.
Thus far I have confined myself to topics mainly interesting
to the man of science, endeavouring, however, to treat them in a manner unrepellent to the general reader who might wish to obtain a notion of Faraday as a worker. On others will

fall the duty of presenting to the world a picture of the man.
But I know you will permit me to add to the foregoing analysis

a few personal reminiscences and remarks, tending to connect

Faraday with a wider world than that of science namely,
with the general human heart.
One word in reference to his married life may find a place here. As in the former case, Faraday shall be his own spokes-
man. The following paragraph, though written in the third
person, is from his hand: "On June 12, 1821, he married,
an event which more than any other contributed to his earthly happiness and healthful state of mind. The union

has continued for twenty-eight years and has in no wise

changed, except in the depth and strength of its character."

Faraday's immediate forefathers lived in a little place
called Clapham Wood Hall, in Yorkshire. Here dwelt Robert Faraday and Elizabeth his wife, who had ten children, one

ÆTHERFORCE

Introduction

ix

of them, James Faraday, born in 1761, being father to the
philosopher. A family tradition exists that the Faradays
came originally from Ireland. Faraday himself has more
than once expressed to me his belief that his blood was in part Celtic, but how much of it was so, or when the infusion took

place, he was unable to say. He could imitate the Irish

brogue, and his wonderful vivacity may have been in part

due to his extraction. But there were other qualities which

we should hardly think of deriving from Ireland. The most

prominent of these was his sense of order, which ran like a luminous beam through all the transactions of his life. The

most entangled and complicated matters fell into harmony

in his hands. His mode of keeping accounts excited the admiration of the managing board of this institution. And

his science was similarly ordered. In his experimental

researches, he numbered every paragraph, and welded their

various parts together by incessant reference. His private

notes of the experimental researches, which are happily

preserved, are similarly numbered: their last paragraph bears

the figure 16,041. His working qualities, moreover, showed

the tenacity of the Teuton. His nature was impulsive, but

there was a force behind the impulse which did not permit it
to retreat. If in his warm moments he formed a resolution,

in his cool ones he made that resolution good. Thus his fire

was that of a solid combustible, not that of a gas, which

blazes suddenly, and dies as suddenly away.

And here I must claim your tolerance for the limits by which I am confined. No materials for a life of Faraday are

in my hands, and what I have now to say has arisen* almost

wholly out of our close personal relationship.

Letters of his, covering a period of sixteen years, are before

me,

each

one

of

which

contains

some

characteristic

utterance ;

strong, yet delicate in counsel, joyful in encouragement,
and warm in affection. References which would be pleasant to such of them as still live are made to Humboldt, Biot,

Dumas, Chevreul, Magnus, and Arago. Accident brought

these

names

prominently

forward ;

but many others would

be required . to complete his list of continental friends. He prized the love and sympathy of men prized it almost more

than the renown which his science brought him. Nearly

my a dozen years ago it fell to

lot to write a review of his

Experimental Researches for the Philosophical Magazine.
After he had read it, he took me by the hand, and said,

* 576

ÆTHERFORCE

x

Faraday's Researches

" Tyndall,

the

sweetest

reward

of

my

work

is

the

sympathy

and good will which it has caused to flow in upon me from all

quarters of the world." Among his letters I find little sparks

of kindness, precious to no one but myself, but more precious
to me than all. He would peep into the laboratory when he thought me weary, and take me upstairs with him to rest.
And if I happened to be absent he would leave a little note for me, couched in this or some other similar form: " Dear

Tyndall, I. was looking for you, because we were at tea

we have not yet done

will

you

come

"
up ?

I frequently

my shared his early dinner; almost always, in fact, while

lectures were going on. There was no trace of asceticism in
his nature. He preferred the meat and wine of life to its

locusts and wild honey. Never once during an intimacy of

fifteen years did he mention religion to me, save when I drew
him on to the subject. He then spoke to me without hesita-
tion or reluctance; not with any apparent desire to " improve
the occasion," but to give me such information as I sought. He believed the human heart to be swayed by a power to

which science or logic opened no approach, and right or wrong,

this faith, held in perfect tolerance of the faiths of others,

strengthened and beautified his life.

From the letters just referred to, I will select three for

publication here. I choose the first, because it contains a

passage revealing the feelings with which Faraday regarded

his vocation, and also because it contains an allusion which

will give pleasure to a friend.

"

(Royal Ventnor, Isle of

Institution.)
Wight, June

28,

1854.

" MY DEAR TYNDALL, You see by the top of this letter

how much habit prevails over me; I have just read yours

from thence, and yet I think myself there. However, I have
left its science in very good keeping, and I am glad to learn

that you are at experiment once more. But how is the

health? Not well, I fear. I wish you would get yourself

strong first and work afterwards. As for the fruits, I am sure

they will be good, for though I sometimes despond as regards
myself, I do not as regards you. You are young, I am old.

.

.

.

But then our subjects are so glorious, that to work at

them rejoices and encourages the feeblest ; delights and enchants

the strongest.

" I

have

not

yet

seen

anything

from

Magnus.

Thoughts

ÆTHERFORCE

Introduction

xi

We of him always delight me.

shall look at his black sulphur

together. I heard from Schonbein the other day. He tells

me that Liebig is full of ozone, i.e. of allotropic oxygen.

"
Good-bye

for

the

present.

Ever, my dear

Tyndall,

yours truly,

M. FARADAY."

The contemplation of nature, and his own relation to her, produced in Faraday a kind of spiritual exaltation which makes itself manifest here. His religious feeling and his
philosophy could not be kept apart; there was an habitual

overflow of the one into the other.

Whether he or another was its exponent, he appeared to
take equal delight in science. A good experiment would
make him almost dance with delight. In November 1850, he wrote to me thus: " I hope some day to take up the point

respecting the magnetism of associated particles. In the

meantime I rejoice at every addition to the facts and reasoning

connected with the subject. When science is a republic,

then it gains: and though I am no republican in other matters,

am I

in that." All his letters illustrate this catholicity of

feeling. Ten years ago, when going down to Brighton, he

carried with him a little paper I had just completed, and

afterwards wrote to me. His letter is a mere sample of the
sympathy which he always showed to me and my work.

" Brighton, December 9, 1857.
" MY DEAR TYNDALL, I cannot resist the pleasure of saying
how very much I have enjoyed your paper. Every part has given me delight. It goes on from point to point beautifully. You will find many pencil marks, for I made them as I read.

I let them stand, for though many of them receive their answer

as the story proceeds, yet they show how the wording im-

presses a mind fresh to the subject, and perhaps here and there

may you

like to alter it slightly, if you wish the full idea, i.e.

not an inaccurate one, to be suggested at first; and yet after

all I believe it is not your exposition, but the natural jumping

We my to

a
"

conclusion that affects or has affected
return on Friday, when I will return

pencil.
you the paper.

Ever truly yours,

M. FARADAY."

The third letter will come in its proper place towards the
end.
While once conversing with Faraday on science, in its
ÆTHERFORCE

xii

Faraday's Researches

relations to commerce and litigation, he said to me that at

a certain period of his career he was forced definitely to ask

himself, and finally to decide, whether he should make wealth or science the pursuit of his life. He could not serve both

masters, and he was therefore compelled to choose between

them. After the discovery of magneto-electricity his fame

was so noised abroad that the commercial world would hardly

have considered any remuneration too high for the aid of

abilities like his. Even before he became so famous, he had

done

a

little

" professional

business."

This was the phrase

he applied to his purely commercial work. His friend,

Richard Phillips, for example, had induced him to undertake a number of analyses, which produced, in the year 1830, an

addition to his income of more than a thousand pounds ; and
in 1831, a still greater addition. He had only to will it to

raise in 1832 his professional business income to 5000 a year.

Indeed, this is a wholly insufficient estimate of what he

might, with ease, have realised annually during the last thirty

years of his life.

While restudying the experimental researches with reference

to the present memoir, the conversation with Faraday here

my alluded to came to

recollection, and I sought to ascertain

the period when the question, " wealth or science," had

presented itself with such emphasis to his mind. I fixed upon the year 1831 or 1832, for it seemed beyond the range of human

power to pursue science as he had done during the subsequent years, and to pursue commercial work at the same time. To

test this conclusion I asked permission to see his accounts,

my and on

own responsibility, I will state the result. In

1832, his professional business-income, instead of rising to
5000, or more, fell from ^1090 45. to ^155 95. From this

it fell with slight oscillations to ^92 in 1837, and to zero in

1838. Between 1839 and 1845, it never, except in one
instance, exceeded ^22; being for the most part much under

this. The exceptional year referred to was that in which he

and Sir Charles Lyell were engaged by Government to write

a report on the Haswell Colliery explosion, and then his
business income rose to 112. From the end of 1845 to the

day of his death, Faraday's annual professional business

income was exactly zero. Taking the duration of his life

into account, this son of a blacksmith, and apprentice to a

bookbinder, had to decide between a fortune of \ 50,000

on the one side, and his undowered science on the other.

ÆTHERFORCE

Introduction

xiii

He chose the latter, and died a poor man. But his was the glory of holding aloft among the nations the scientific name
of England for a period of forty years. The outward and visible signs of fame were also of less
account to him than to most men. He had been loaded with

scientific honours from all parts of the world. Without,

I imagine, a dissentient voice, he was regarded as the prince of the physical investigators of the present age. The highest

scientific position in this country he had, however, never filled.
When the late excellent and lamented Lord Wrottesley

resigned the presidency of the Royal Society, a deputation from the council, consisting of his lordship, Mr. Grove, and

Mr. Gassiot, waited upon Faraday, to urge him to accept the

president's chair. All that argument or friendly persuasion

could do was done to induce him to yield to the wishes of the

council, which was also the unanimous wish of scientific men.
A knowledge of the quickness of his own nature had induced

in Faraday the habit of requiring an interval of reflection,

before he decided upon any question of importance. In the

present instance he followed his usual habit, and begged for

a little time.

On the following morning, I went up to his room, and said

on entering that I had come to him with some anxiety of mind.

He

demanded

its

cause,

and

I

responded

" lest

you

should

have decided against the wishes of the deputation that waited
on you yesterday." " You would not urge me to undertake my this responsibility," he said. " I not only urge you," was
reply, " but I consider it your bounden duty to accept it."
He spoke of the labour that it would involve; urged that it

was not in his nature to take things easy; and that if he

became president, he would surely have to stir many new

questions, and agitate for some changes. I said that in such

cases he would find himself supported by the youth and

strength of the royal society. This, however, did not seem

to satisfy him. Mrs. Faraday came into the room, and he

appealed to her. Her decision was adverse, and I deprecated

her decision.

" Tyndall,"

he said

at length,

" I

must

remain

plain Michael Faraday to the last; and let me now tell you,

that if I accepted the honour which the royal society desires

to confer upon me, I would not answer for the integrity of my
intellect for a single year." I urged him no more, and Lord

Wrottesley had a most worthy successor in Sir Benjamin

Brodie.

ÆTHERFORCE

xiv

Faraday's Researches

After the death of the Duke of Northumberland, our board
of managers wished to see Mr. Faraday finish his career as President of the institution which he had entered on weekly wages more than half a century before. But he would have
nothing to do with the presidency. He wished for rest, and
the reverent affection of his friends was to him infinitely more precious than all the honours of official life.

In the year 1835, Sir Robert Peel wished to offer Faraday
a pension, but that great statesman quitted office before he
was able to realise his wish. The minister who founded these

pensions intended them, I believe, to be marks of honour
which even proud men might accept without compromise of
independence. When, however, the intimation first reached
Faraday, in an unofficial way, he wrote a letter announcing
his determination to decline the pension; and stating that
he was quite competent to earn his livelihood himself. That letter still exists, but it was never sent, Faraday's repugnance
having been overruled by his friends. When Lord Melbourne
came into office, he desired to see Faraday; and probably in utter ignorance of the man for, unhappily for them and

us, ministers of state in England are only too often ignorant

of great Englishmen his Lordship said something that must

have deeply displeased his visitor. The whole circumstances

were once communicated to me, but I have forgotten the

details.

The

term

"
humbug,"

I

think,

was

incautiously

employed by his lordship, and other expressions were used

of a similar kind. Faraday quitted the minister with his

own resolves, and that evening he left his card and a short

and decisive note at the residence of Lord Melbourne, stating

that he had manifestly mistaken his lordship's intention of

honouring science in his person, and declining to have any-

thing whatever to do with the proposed pension. The good-

humoured nobleman at first considered the matter a capital

joke; but he was afterwards led to look at it more seriously.
An excellent lady, who was a friend both to Faraday and the

minister, tried to arrange matters between them; but she

found Faraday very difficult to move from the position he had

assumed. After many fruitless efforts, she at length begged

of him to state what he would require of Lord Melbourne to

induce him to change his mind.

He replied,

"
I

should

require from his lordship what I have no right or reason to

expect that he would grant a written apology for the words

ÆTHERFORCE

Introduction

xv

he permitted himself to use to me." The required apology came, frank and full, creditable, I thought, alike to the
prime minister and the philosopher. Considering the enormous strain imposed on Faraday's
intellect, the boy-like buoyancy even of his later years was
astonishing. He was often prostrate, but he had immense
resiliency, which he brought into action by getting away from London whenever his health failed. I have already indicated the thoughts which filled his mind during the evening of his life. He brooded on magnetic media and lines of force; and

the great object of the last investigation he ever undertook
was the decision of the question whether magnetic force
requires time for its propagation. How he proposed to attack this subject we may never know. But he has left some
beautiful apparatus behind; delicate wheels and pinions, and associated mirrors, which were to have been employed in the investigation. The mere conception of such an inquiry is an
illustration of his strength and hopefulness, and it is impossible to say to what results it might have led him. But the work was too heavy for his tired brain. It was long before he could bring himself to relinquish it, and during this struggle he often suffered from fatigue of mind. It was at this period, and
before he resigned himself to the repose which marked the
last two years of his life, that he wrote to me the following letter one of many priceless letters now before me which
reveals, more than anything another pen could express, the state of his mind at the time. I was sometimes censured in

my his presence for

doings in the Alps, but his constant reply

was, " Let him alone, he knows how to take care of himself."

In this letter, anxiety on this score reveals itself, for the first

time.
" MY DEAR TYNDALL,

"
Hampton Court, August i, 1864.
I do not know whether my letter

will catch you, but I will risk it, though feeling very unfit
to communicate with a man whose life is as vivid and active

as yours; but the receipt of your kind letter makes me to
know that though I forget, I am not forgotten, and though I am not able to remember at the end of a line what was said

at the beginning of it, the imperfect marks will convey to you
some sense of what I long to say. We had heard of your
illness through Miss Moore, and I was therefore very glad
to learn that you are now quite well; do not run too many risks or make your happiness depend too much upon dangers,

ÆTHERFORCE

xvi

Faraday's Researches

or the hunting of them. Sometimes the very thinking of you,
and what you may be about, wearies me with fears, and then the cogitations pause and change, but without giving me rest. I know that much of this depends upon my own wornout nature, and I do not know why I write it, save that when
I write to you I cannot help thinking it, and the thoughts
stand in the way of other matter.

" See what a strange desultory epistle I am writing to you,
and yet I feel so weary that I long to leave my desk and go
to the couch.
" My dear wife and Jane desire their kindest remembrances: I hear them in the next room: ... I forget but not you, my dear Tyndall, for I am ever yours,
" M. FARADAY."

This weariness subsided when he relinquished his work, and I have a cheerful letter from him, written in the autumn of
1865. But towards the close of that year he had an attack
of illness, from which he never completely rallied. He con-
tinued to attend the Friday evening meetings, but the advance of infirmity was apparent to us all. Complete rest became
finally essential to him, and he ceased to appear among us. There was no pain in his decline to trouble the memory of those who loved him. Slowly and peacefully he sank towards his final rest, and when it came, his death was a falling asleep.
In the fulness of his honours and of his age he quitted us; the good fight fought, the work of duty shall I not say of glory done. The " Jane " referred to in the foregoing letter is Faraday's niece, Miss Jane Barnard, who, with an affection raised almost to religious devotion, watched him and tended him to the end.
I saw Mr. Faraday for the first time on my return from
Marburg in 1850. I came to the Royal Institution, and sent
up my card, with a copy of the paper which Knoblauch and myself had just completed. He came down and conversed with me for half-an-hour. I could not fail to remark the
wonderful play of intellect and kindly feeling exhibited by
his countenance. When he was in good health the question
of his age would never occur to you. In the light and laughter
of his eyes you never thought of his grey hairs. He was then
on the point of publishing one of his papers on magne-crystallic action, and he had time to refer in a flattering note to the

ÆTHERFORCE

Introduction

xvii

memoir I placed in his hands. I returned to Germany, worked there for nearly another year, and in June 1851 came

back finally from Berlin to England. Then, for the first time,

and on my way to the meeting of the British Association, at Ipswich, I met a man who has since made his mark upon
the intellect of his time; who has long been, and who by the

strong law of natural affinity must continue to be, a brother

We to me.

were both without definite outlook at the time,

needing proper work, and only anxious to have it to perform.

The chairs of natural history and of physics being advertised as vacant in the university of Toronto, we applied for them,

he for the one, I for the other; but, possibly guided by a

prophetic instinct, the university authorities declined having
anything to do with either of us. If I remember aright, we

were equally unlucky elsewhere.
One of Faraday's earliest letters to me had reference to this Toronto business, which he thought it unwise in me to
neglect. But Toronto had its own notions, and in 1853, at

the instance of Dr. Bence Jones, and on the recommendation

of Faraday himself, a chair of physics at the royal institution

was offered to me. I was tempted at the same time to go
elsewhere, but a strong attraction drew me to his side. Let
me say that it was mainly his and other friendships, precious to me beyond all expression, that caused me to value my

position here more highly than any other that could be offered
to me in this land. Nor is it for its honour, though surely that is great, but for the strong personal ties that bind me
to it, that I now chiefly prize this place. You might not credit me were I to tell you how lightly I value the honour of being

Faraday's successor compared with the honour of being

Faraday's friend. his " mantle " is a

His friendship burden almost

was energy and too heavy to be

inspiration borne.

;

Sometimes during the last year of his life, by the permission

or invitation of Mrs. Faraday, I went up to his rooms to see him. The deep radiance, which in his time of strength flashed

with such extraordinary power from his countenance, had

subsided to a calm and kindly light, by which my latest
memory of him is warmed and illuminated. I knelt one day
beside him on the carpet and placed my hand upon his knee;

he stroked it affectionately, smiled, and murmured, in a low

soft voice, the last words that I remember as having been
spoken to me by Michael Faraday.

It was my wish and aspiration to play the part of Schiller

ÆTHERFORCE

xviii

Faraday's Researches

to this Goethe: and he was at times so strong and joyful
his body so active, and his intellect so clear as to suggest
to me the thought that he, like Goethe, would see the younger man laid low. Destiny ruled otherwise, and now he is but

a memory to us all. Surely no memory could be more beautiful. He was equally rich in mind and heart. The fairest

traits of a character sketched by Paul, found in him perfect

illustration.

For

he

was

" blameless,

vigilant,

sober,

of

good

behaviour, apt to teach, not given to filthy lucre." He had

not

a

trace

of

worldly

ambition ;

he declared his duty to his

sovereign by going to the levee once a year, but beyond this he never sought contact with the great. The life of his spirit and of his intellect was so full that the things which men most strive after were absolutely indifferent to him. " Give
me health and a day," says the brave Emerson, " and I will make the pomp of emperors ridiculous." In an eminent degree Faraday could say the same. What to him was the

splendour of a palace compared with a thunderstorm upon Brighton downs ? what among all the appliances of royalty

to compare with the setting sun ? I refer to a thunderstorm

and a sunset, because these things excited a kind of ecstasy in his mind, and to a mind open to such ecstasy the pomps

and pleasures of the world are usually of small account.

Nature, not education, rendered Faraday strong and refined.
A favourite experiment of his own was representative of himself. He loved to show that water in crystallising excluded
all foreign ingredients, however intimately they might be
mixed with it. Out of acids, alkalis, or saline solutions, the

crystal came sweet and pure. By some such natural process

in the formation of this man, beauty and nobleness coalesced,
to the exclusion of everything vulgar and low. He did not

learn his gentleness in the world, for he withdrew himself

from its culture; and still this land of England contained no truer gentleman than he. Not half his greatness was incor-

porate in his science, for science could not reveal the bravery

and delicacy of his heart. But it is time that I should end these weak words, and

lay my poor garland on the grave of this

JUST AND FAITHFUL KNIGHT OF GOD.

ÆTHERFORCE

The following is a list of the works of Michael Faraday:

Some Observations on the Means of Obtaining Knowledge, 1817;

History of the Progress of Electro-Magnetism, 1821; Chemical Manipula-

tion, 1827; edition On the Alleged Decline of Science in England, 1831; On the Practical Prevention of Dry Rot in Timber, 1833; Experimental

Researches in Electricity, 3 vols., 1839-55; Observations on Mental

Education, 1855; Experimental Researches in Chemistry and Physics

(reprinted from Philosophical Transactions, The Journal of the Royal

Institution, etc.), 1859; The Various Forces of Matter (six lectures edited

by Sir Wm. Crookes), 1860; The Chemical History of a Candle (six lectures

edited

by

Sir

Wm.

Crookes),

1861 ;

Some Thoughts on the Conservation of

Force, 1865; The Liquefaction of Gases (papers given, 1823-45), 1896.

LIFE. Prof. J. Tyndall, Faraday as a Discoverer, 1868; J. B. A. Dumas, Eloge historique de M. Faraday, 1868; Dr. Bence Jones, The Life and Letters of Faraday, 2 vols., 1870; Dr. J. H. Gladstone, 1872;
W. Jerrold, Michael Faraday, Man of Science, 1893; Silvanus P. Thompson, Michael Faraday: His Life and Work, 1898; The Letters of Faraday and Schoenbein, 1836-62, edited by G. W. A. Kahlbaum and
F. V. Darbishire, 1899.

NOTE. The present select edition of the Experimental Researches in Electricity consists of Series III. -VIII. and XVI., XVII. of the original issue in three volumes (1839-55), with the plates and figures distributed for the reader's convenience in the text, and the sections and paragraphs
consecutively renumbered.

XIX
ÆTHERFORCE

CONTENTS

PAGE

I.

i. IDENTITY OF ELECTRICITIES FROM DIFFERENT SOURCES .
...... i. Voltaic Electricity ..... ii. Ordinary Electricity ...... iii. Magneto-Electricity ...... iv. Thermo-Electricity ...... v. Animal Electricity

I
3 7 22 24 24

2. RELATION BY MEASURE OF COMMON AND VOLTAIC

II. III.

ELECTRICITY .

.

.

.

.

.

.

.27

.... 3. NEW LAW OF ELECTRIC CONDUCTION

32

.... 4. ON CONDUCTING POWER GENERALLY

41

.... 5. ELECTRO-CHEMICAL DECOMPOSITION

47

....... If i- New Conditions of Electro-chemical Decom-

position

48

If ii. Influence of Water in such Decomposition . 54

1f iii. Theory of Electro-chemical Decomposition . 55

IV. 6. POWER OF PLATINA, ETC., TO INDUCE COMBINATION . 84

.in V. 5. ELECTRO-CHEMICAL DECOMPOSITION Continued (NOMEN-

CLATURE)

.

.

.

.

.

.

.

If iv. Some General Conditions of Electro-chemical

Decomposition
H v. Volta-electrometer

..... .

.

.

.

.115

122

If vi. Primary and Secondary Results .

.

. 133

Tj vii. Definite Nature and Extent of Electro-

chemical Forces .

.

.

.

145

7. ABSOLUTE QUANTITY OF ELECTRICITY IN THE MOLECULES

........ OF MATTER

163

.... VI. 8. ELECTRICITY OF THE VOLTAIC PILE

172

..... U i. Simple Voltaic Circles .

.

.

.

.172

If ii. Electrolytic Intensity

203

f iii. Associated Voltaic Circles; or Battery .

. 211

If iv. Resistance of an Electrolyte to Decomposition 218

U v. General Remarks on the Active Battery xxi

. 226

ÆTHERFORCE

xxii

Faraday's Researches

PAGE

VII. 9. ON THE SOURCE OF POWER IN THE VOLTAIC PILE . 232

....... If i. Exciting Electrolytes being Good Conductors .
If ii. Inactive Conducting Circles containing an Elec-

238

....... trolyte

241

If iii. Active Circles containing Sulphuret of Potas-

sium

259

VIII. q. ON THE SOURCE OF POWER IN THE VOLTAIC PILE Continued 271

If iv. The Exciting Chemical Force affected by

Temperature .

.

.

.

.

.271

...... U v. The Exciting Chemical Force affected by

Dilution.

284

t vi. Differences in the Order of the Metallic

Elements of Voltaic Circles

.

.

. 295

..... ^f vii. Active Voltaic Circles and Batteries without

Metallic Contact

298

1f viii. Considerations of the Sufficiency of Chemical

....... Action

302

.... H ix. Thermo-electric Evidence

308

....... If x. Improbable Nature of the Assumed Contact

Force

312

ON A PECULIAR VOLTAIC CONDITION OF IRON (SCHOENBEIN) .

. 317

Ox A PECULIAR VOLTAIC CONDITION OF IRON (FARADAY)

. 321, 330

INDEX

333

ÆTHERFORCE

EXPERIMENTAL RESEARCHES
IN ELECTRICITY

I. IDENTITY OF ELECTRICITIES DERIVED FROM DIFFERENT SOURCES. 2. RELATION BY MEASURE OF COMMON AND VOLTAIC ELECTRICITY

i. Identity of Electricities derived from different sources

i. THE progress of the electrical researches which I have had the honour to present to the Royal Society, brought me to a

point at which it was essential for the further prosecution of

my inquiries that no doubt should remain of the identity or

distinction of electricities excited by different means. It is per-

fectly

true

that

2
Cavendish,

3
Wollaston,

Colladon 4

and

others,

have in succession removed some of the greatest objections to

the acknowledgment of the identity of common, animal and

voltaic electricity, and I believe that most philosophers con-

sider these electricities as really the same. But on the other

hand it is also true, that the accuracy of Wollaston's experi-

ments

has

been

denied 5 ;

and

also

that

one

of

them,

which

really is no proper proof of chemical decomposition by common

electricity (45, 63), has been that selected by several experi-

menters as the test of chemical action (72, 82). It is a fact,

too, that many philosophers are still drawing distinctions

between the electricities from different sources; or at least

doubting whether their identity is proved. Sir Humphry

Davy,

for

instance,

in

his

paper

on

the

6
Torpedo,

thought

it

1 Third Series, original edition, vol. i. p. 76.

2 Phil. Trans. 1776, p. 196.

* Ibid. 1801, p. 434.

4 6

Annales de Chimie, 1826, 1 hil. Trans. 1829, p. 17.

p."

62, etc.
Common

*

Phil. Trans. electricity is

1832, p. 282, note.
excited upon non-

conductors, and is readily carried off by conductors and imperfect con-

ductors. Voltaic electricity is excited upon combinations of perfect and

imperfect conductors, and is only transmitted by perfect conductors or

imperfect conductors of the best kind. Magnetism, if it be a form of

electricity, belongs only to perfect conductors; and, in its modifications,

to a peculiar class Phil. Trans. 1832,

of them."
p. 294.)

"

(Dr. Ritchie has shown this is not Animal electricity resides only in

the case, the im-

perfect conductors forming the organs of living animals, etc."

ÆTHERFORCE

2

Faraday's Researches

probable that animal electricity would be found of a peculiar

kind; tricity

and referring to it, to and magnetism, has

common
"
said,

electricity, voltaic elec-
Distinctions might be

established in pursuing the various modifications or properties
of electricity in these different forms, etc." Indeed I need only
refer to the last volume of the Philosophical Transactions to show that the question is by no means considered as settled. 1

2. Notwithstanding, therefore, the general impression of the identity of electricities, it is evident that the proofs have not been sufficiently clear and distinct to obtain the assent of all
those who were competent to consider the subject; and the question seemed to me very much in the condition of that which
Sir H. Davy solved so beautifully, namely, whether voltaic electricity in all cases merely eliminated, or did not in some
actually produce, the acid and alkali found after its action upon water. The same necessity that urged him to decide the
doubtful point, which interfered with the extension of his views,
and destroyed the strictness of his reasoning, has obliged me to ascertain the identity or difference of common and voltaic
electricity. I have satisfied myself that they are identical, and I hope the experiments which I have to offer, and the proofs
flowing from them, will be found worthy the attention of the

Royal Society.

3. The various phenomena exhibited by electricity may, for

the purposes of comparison, be arranged under two heads;

namely, those connected with electricity of tension, and those

belonging to electricity in motion. This distinction is taken at

1 Phil. Trans. 1832, p. 259. Dr. Davy, in making experiments on the torpedo, obtains effects the same as those produced by common and voltaic

electricity, and says that in its magnetic and chemical power it does not

How seem to be essentially peculiar, p.
are other points of difference: and

274; after

but he then says, referring to them,

p. 275," there adds,

are these differences to be explained? Do they admit of explanation

similar to that advanced by Mr. Cavendish in his theory of the torpedo;

or may we suppose, according to the analogy of the solar ray, that the

electrical power, whether excited by the common machine, or by the

voltaic battery, or by the torpedo, is not a simple power, but a combination

of powers, varieties of

which may occur variously electricity with which we are

associated,

and "

acquainted?

produce

all

the

At p. 279 of the same which the following are

volume of
extracts:

"TrCaonsmamcotinonesleicstrDirc.itRyitics hdiief'fsuspeadpeorv,erfrtohme

surface of the metal; voltaic electricity exists within the metal. Free

electricity is conducted over the surface of the thinnest gold leaf as

effectually as over a mass of metal having the same surface; voltaic

ealgeacitnr,ic"itTy hreequsiurpepsostehdickanneaslsogoyf

metal for its conduction," p.
between common and voltaic

280: and
electricity,

which was so eagerly traced after the invention of the pile, completely

fails in this case, which was thought toafford the most striking resemblance,"

p. 291.

ÆTHERFORCE

Voltaic Electricity

3

present not as philosophical, but merely as convenient. The
effect of electricity of tension, at rest, is either attraction or
repulsion at sensible distances. The effects of electricity in
motion or electrical currents may be considered as ist, Evolu-
tion of heat; 2nd, Magnetism; 3rd, Chemical decomposition;
4th, Physiological phenomena; 5th, Spark. It will be my
object to compare electricities from different sources, and
especially common and voltaic electricities, by their power of
producing these effects.

I. Voltaic Electricity

4. Tension. When a voltaic battery of 100 pairs of plates
has its extremities examined by the ordinary electrometer, it is well known that they are found positive and negative, the gold leaves at the same extremity repelling each other, the gold leaves at different extremities attracting each other, even when half an inch or more of air intervenes.

5. That ordinary electricity is discharged by points with

facility through air; that it is readily transmitted through highly rarefied air; and also through heated air, as for instance a flame; is due to its high tension. I sought, therefore, for

similar effects in the discharge of voltaic electricity, using as a test of the passage of the electricity either the galvanometer

or chemical action produced by the arrangement hereafter to

be described (48, 52).

my 6. The voltaic battery I had at

disposal consisted of 140

pairs of plates four inches square, with double coppers. It was

insulated throughout, and diverged a gold leaf electrometer

about one-third of an inch. On endeavouring to discharge this

battery by delicate points very nicely arranged and approxi-

mated, either in the air or in an exhausted receiver, I could

obtain no indications of a current, either by magnetic or chemical action. In this, however, was found no point of discordance
between voltaic and common electricity; for when a Leyden
battery (27) was charged so as to deflect the gold leaf electrometer to the same degree, the points were found equally unable
to discharge it with such effect as to produce either magnetic
or chemical action. This was not because common electricity could not produce both these effects (43, 46), but because when of such low intensity the quantity required to make the effects
visible (being enormously great (107, in) ) could not be transmitted in any reasonable time. In conjunction with the other

ÆTHERFORCE

4

Faraday's Researches

proofs of identity hereafter to be given, these effects of points also prove identity instead of difference between voltaic and
common electricity 7. As heated air discharges common electricity with far
greater facility than points, I hoped that voltaic electricity
might in this way also be discharged. An apparatus was there-
fore constructed (fig. i), in which
A B is an insulated glass rod
upon which two copper wires,
C, D, are fixed firmly; to these wires are soldered two pieces of
fine platina wire, the ends of which are brought very close to each other at e, but without
touching ; the copper wire C was connected with the positive pole of a voltaic battery, and
the wire D with a decomposing
apparatus (48, 52), from which the communication was com-
pleted to the negative pole of the battery. In these experiments only two troughs, or twenty pairs of plates, were used.
8. Whilst in the state described, no decomposition took place at the point a, but when the side of a spirit-lamp flame was
applied to the two platina extremities at e, so as to make them
bright red-hot, decomposition occurred; iodine soon appeared at the point a, and the transference of electricity through the
heated air was established. On raising the temperature of the
points e by a. blowpipe, the discharge was rendered still more free, and decomposition took place instantly. On removing
the source of heat, the current immediately ceased. On
putting the ends of the wires very close by the side of and parallel to each other, but not touching, the effects were perhaps
more readily obtained than before. On using a larger voltaic
battery (6), they were also more freely obtained.
9. On removing the decomposing apparatus and interposing
a galvanometer instead, heating the points e as the needle would swing one way, and removing the heat during the time of its return (38), feeble deflections were soon obtained: thus
also proving the current through heated air; but the instrument used was not so sensible under the circumstances as
chemical action.
10. These effects, not hitherto known or expected under this form, are only cases of the discharge which takes place through

ÆTHERFORCE

Voltaic Electricity

5

air between the charcoal terminations of the poles of a powerful
battery, when they are gradually separated after contact. Then the passage is through heated air exactly as with common electricity, and Sir H. Davy has recorded that with the original
battery of the Royal Institution this discharge passed through a space of at least four inches. 1 In the exhausted receiver the electricity would strike through nearly half an inch of space, and the combined effects of rarefaction and heat was such

upon the inclosed air as to enable it to conduct the electricity

through a space of six or seven inches.

11. The instantaneous charge of a Leyden battery by the

poles of a voltaic apparatus is another proof of the tension, and

also the quantity, of electricity evolved by the latter. Sir H.

Davy

2
says.

"

When

the

two

conductors

from

the

ends

of

the

combination were connected with a Leyden battery, one with

the internal, the other with the external coating, the battery

instantly became charged; and on removing the wires and

making the proper connections, either a shock or a spark could

be perceived : and the least possible time of contact was sufficient

to renew the charge to its full intensity."

12. In motion : i. Evolution of heat. The evolution of heat

in wires and fluids by the voltaic current is matter of general

notoriety.
13. ii. Magnetism. No fact is better known to philosophers
than the power of the voltaic current to deflect the magnetic needle, and to make magnets according to certain laws ; and no effect can be more distinctive of an electrical current.

14. iii. Chemical decomposition. The chemical powers of the voltaic current, and their subjection to certain laws, are also
perfectly well known. 15. iv. Physiological effects. The power of the voltaic
current, when strong, to shock and convulse the whole animal system, and when weak to affect the tongue and the eyes, is
very characteristic.
16. v. Spark. The brilliant star of light produced by the discharge of a voltaic battery is known to all as the most
beautiful light that man can produce by art.

17. That these effects may be almost infinitely varied, some
being exalted whilst others are diminished, is universally ac-
knowledged; and yet without any doubt of the identity of character of the voltaic currents thus made to differ in their

1 Elements of Chemical Philosophy.

* Ibid. p. 154.
ÆTHERFORCE

6

Faraday's Researches

effect. The beautiful explication of these variations afforded by Cavendish's theory of quantity and intensity requires no
support at present, as it is not supposed to be doubted. 18. In consequence of the comparisons that will hereafter
arise between wires carrying voltaic and ordinary electricities, and also because of certain views of the condition of a wire or
any other conducting substance connecting the poles of a voltaic apparatus, it will be necessary to give some definite expression of what is called the voltaic current, in contradistinction to any supposed peculiar state of arrangement, not progressive,
which the wire or the electricity within it may be supposed to assume. If two voltaic troughs P N, P' N', fig. 2, be sym-
N metrically arranged and insulated, and the ends P' connected
by a wire, over which a magnetic needle is suspended, the wire will exert no effect over the needle; but immediately that the

ÆTHERFORCE

Ordinary Electricity

7

rather than an arrangement, but I am anxious to avoid stating
unnecessarily what will occur to others at the moment.

II. Ordinary Electricity

20. By ordinary electricity I understand that which can be obtained from the common machine, or from the atmosphere,
or by pressure, or cleavage of crystals, or by a multitude of
other operations; its distinctive character being that of great intensity, and the exertion of attractive and repulsive powers,
not merely at sensible but at considerable distances. 21. Tension, The attractions and repulsions at sensible
distances, caused by ordinary electricity, are well known to be
so powerful in certain cases, as to surpass, almost infinitely,
the similar phenomena produced by electricity, otherwise excited. But still those attractions and repulsions are exactly of the same nature as those already referred to under the head Tension, Voltaic electricity (4); and the difference in degree between them is not greater than often occurs between cases
of ordinary electricity only. I think it will be unnecessary to
enter minutely into the proofs of the identity of this character
in the two instances. They are abundant; are generally admitted as good; and lie upon the surface of the subject:
and whenever in other parts of the comparison I am about to
draw, a similar case occurs, I shall content myself with a mere announcement of the similarity, enlarging only upon those parts where the great question of distinction or identity still
exists.
22. The discharge of common electricity through heated air is a well-known fact. The parallel case of voltaic electricity
has already been described (8, etc.). 23. In motion : i. Evolution of heat. The heating power of
common electricity, when passed through wires or other substances, is perfectly well known. The accordance between it
and voltaic electricity is in this respect complete. Mr. Harris has constructed and described l a very beautiful and sensible instrument on this principle, in which the heat produced in a
wire by the discharge of a small portion of common electricity
is readily shown, and to which I shall have occasion to refer
for experimental proof in a future part of this paper (80). 24. ii. Magnetism. Voltaic electricity has most extraordinary

1 Philosophical Transactions, 1827, p. 18.
Harris on a New Electrometer, etc., etc.

Edinburgh Transactions, 1831.
ÆTHERFORCE

Faraday's Researches

and exalted magnetic powers. If common electricity be

identical with it, it oifght to have the same powers. In render-

ing needles or bars magnetic, it is found to agree with voltaic

electricity, and the direction of the magnetism, in both cases,
is the same; but in deflecting the magnetic needle, common

electricity has been found deficient, so that sometimes its

power has been denied altogether, and at other times distinc-

tions have been hypothetically assumed for the purpose of

avoiding

the

1 difficulty.

25. M. Colladon, of Geneva, considered that the difference
might be due to the use of insufficient quantities of common electricity in all the experiments before made on this head;

and in a memoir read to the Academic des Sciences in 1826,r

describes experiments, in which, by the use of a battery, points,

and a delicate galvanometer, he succeeded in obtaining de-
flections, and thus establishing identity in that respect. MM.

Arago, Ampere, and Savary, are mentioned in the paper as

having witnessed a successful repetition of the experiments.
But as no other one has come forward in confirmation, MM.

Arago, Ampere, and Savary, not having themselves published
(that I am aware of) their admission of the results, and as some

have not been able to obtain them, M. Colladon's conclusions

have been occasionally doubted OF denied; and an important
point with me was to establish their accuracy, or remove them

entirely from the body of received experimental research. I
am happy to say that my results fully confirm those by M.

Colladon, and I should have had no occasion to describe them,

but that they are essential as proofs of the accuracy of the
final and general conclusions I am enabled to draw respecting

the magnetic and chemical action of electricity (96, 102, 103,

113, etc.).
26. The plate electrical machine I have used is fifty inches in diameter; it has two sets of rubbers; its prime conductor
consists of two brass cylinders connected by a third, the whole length being twelve feet, and the surface in contact with air
about 1422 square inches. When in good excitation, one re-
volution of the plate will give ten or twelve sparks from the conductors, each an inch in length. Sparks or flashes from
ten to fourteen inches in length may easily be drawn from the conductors. Each turn of the machine, when worked moderately,
occupies about four-fifths of a second.

1 Demonferrand's Manuel d'Electricite dynatnique, p. 121. * Annales de Chimie, xxxiii. p. 62.

ÆTHERFORCE

Magnetic Effects

9

27. The electric battery consisted of fifteen equal jars. They

are coated eight inches upwards from the bottom, and are

twenty-three inches in circumference, so that each contains

184 square inches of glass, coated on both sides; this is in-

dependent of the bottoms, which are of thicker glass, and

contain each about fifty square inches.

A 28.

good discharging train was arranged by connecting

metallically a sufficiently thick wire with the metallic gas pipes

of the house, with the metallic gas pipes belonging to the public

gas works of London, and also with the metallic water pipes

of London. It was so effectual in its office as to carry off

instantaneously electricity of the feeblest tension, even that

of a single voltaic trough, and was essential to many of the

experiments.

29. The galvanometer was one or the other of those formerly

1
described,

but

the

glass

jar

covering

it

and

supporting

the

needle was coated inside and outside with tinfoil, and the upper

part (left uncoated, that the motions of the needle might be

examined) was covered with a frame of wirework, having
numerous sharp points projecting from it. When this frame

and the two coatings were connected with the discharging

train (28), an insulated point or ball, connected with the machine when most active, might be brought within an inch of any

part of the galvanometer, yet without affecting the needle

within by ordinary electrical attraction or repulsion.

30. In connection with these precautions, it may be neces-

sary to state that the needle of the galvanometer is very liable

to have its magnetic power deranged, diminished, or even

inverted by the passage of a shock through the instrument. If

1 The galvanometer was roughly made, yet sufficiently delicate in its indications. The wire was of copper covered with silk, and made sixteen
or eighteen convolutions. Two sewing-needles were magnetised and fixed
on to a stem of dried grass parallel to each other, but in opposite directions, and about half an inch apart; this system was suspended by a fibre of unspun silk, so that the lower needle should be between the convolutions
of the multiplier, and the upper above them. The latter was by much the most powerful magnet, and gave terrestrial direction to the whole; fig. 3 represents the direction of the wire and of the needles when the instrument was placed in the magnetic meridian: the ends of the wires
are marked A and B. The letters S and N designate the south and north Nends of the needle when affected merely by terrestrial magnetism ; the end
is therefore the marked pole. The whole instrument was protected by a glass jar, and stood about eight feet from, and about sixteen or seventeen degrees on one side of, the large magnet (which was composed of about 450 bar magnets, fifteen inches long, one inch wide, and half an inch thick, arranged in a box so as to present at one of its extremities two
external poles).
ÆTHERFORCE

io

Faraday's Researches

the needle be at all oblique, in the wrong direction, to the coils of the galvanometer when the shock passes, effects of this kind

are sure to happen.

31. It was to the retarding power of bad conductors, with

the intention of diminishing its intensity without altering its

quantity, that I first looked with the hope of being able to

make common electricity assume more of the characters and

power of voltaic electricity, than it is usally supposed to have.

32. The coating and armour of the galvanometer were first

connected with the discharging train (28);

B the end

(fig. 3)

of the galvanometer wire was connected with

the outside coating of the battery, and then

both these with the discharging train; the
end A of the galvanometer wire was con-

Fig. 3.

nected with a discharging rod by a wet

thread four feet long; and finally, when the

battery (27) had been positively charged by about forty turns

of the machine, it was discharged by the rod and the thread

through the galvanometer. The needle immediately moved.

33. During the time that the needle completed its vibration in the first direction and returned, the machine was worked, and the battery recharged; and when the needle in vibrating resumed its first direction, the discharge was again made through
the galvanometer. By repeating this action a few times, the
vibrations soon extended to above 40 on each side of the line

of rest.

34. This effect could be obtained at pleasure. Nor was it varied, apparently, either in direction or degree, by using a short thick string, or even four short thick strings in place of the long fine thread. With a more delicate galvanometer, an excellent swing of the needle could be obtained by one dis-

charge of the battery.
35. On reversing the galvanometer communications so as to pass the discharge through from B to A, the needle was equally
well deflected, but in the opposite direction. 36. The deflections were in the same direction as if a voltaic
current had been passed through the galvanometer, i.e. the positively charged surface of the electric battery coincided with the positive end of the voltaic apparatus (4), and the negative surface of the former with the negative end of the latter.
37. The battery was then thrown out of use. and the com-
munications so arranged that the current could be passed from the prime conductor, by the discharging rod held against it,

ÆTHERFORCE

Deflection of Magnet

ii

through the wet string, through the galvanometer coil, and into the discharging train, by which it was finally dispersed.

This current could be stopped at any moment, by removing

the discharging rod, and either stopping the machine or con-

necting the prime conductor by another rod with the discharging train; and could be as instantly renewed. The needle was so adjusted, that whilst vibrating in moderate and small arcs, it required time equal to twenty-five beats of a watch to

pass in one direction through the arc, and of course an equal

time to pass in the other direction. 38. Thus arranged, and the needle being stationary, the

current, direct from the machine, was sent through the galvano-

meter for twenty-five beats, then interrupted for other twenty-

five beats, renewed for twenty-five beats more, again interrupted for an equal time, and so on continually. The needle soon

began to vibrate visibly, and after several alternations of this

kind, the vibration increased to 40 or more.
39. On changing the direction of the current through the
galvanometer, the direction of the deflection of the needle was

also changed. In all cases the motion of the needle was in direction the same as that caused either by the use of the

electric battery or a voltaic trough (36).
40. I now rejected the wet string, and substituted a copper

wire, so that the electricity of the machine passed at once into

wires communicating directly with the discharging train, the

galvanometer coil being one of the wires used for the discharge. The effects were exactly those obtained above (38).

41. Instead of passing the electricity through the system, by

bringing the discharging rod at the end of it into contact with the conductor, four points were fixed on to the rod; when the

current was to pass, they were held about twelve inches from the conductor, and when it was not to pass, they were turned away. Then operating as before (38), except with this variation, the needle was soon powerfully deflected, and in perfect con-

sistency with the former results. Points afforded the means by which Colladon, in all cases, made his discharges.

42. Finally, I passed the electricity first through an exhausted receiver, so as to make it there resemble the aurora

borealis,

and

then

through

the

galvanometer

to

the

earth ;

and

it was found still effective in deflecting the needle, and apparently

with the same force as before.

43. From all these experiments, it appears that a current of common electricity, whether transmitted through water or

B 576

ÆTHERFORCE

12

Faraday's Researches

metal, or rarefied air, or by means of points in common air,
is still able to deflect the needle: the only requisite being, apparently, to allow time for its action: that it is, in fact, just as magnetic in every respect as a voltaic current, and that in this character therefore no distinction exists.

44. Imperfect conductors, as water, brine, acids, etc., etc., will be found far more convenient for exhibiting these effects than other modes of discharge, as by points or balls; for the former convert at once the charge of a powerful battery into a feeble spark discharge, or rather continuous current, and involve little or no risk of deranging the magnetism of the
needles (30).
45. iii. Chemical decomposition. The chemical action of voltaic electricity is characteristic of that agent, but not more characteristic than are the laws under which the bodies evolved

by decomposition arrange themselves at the poles. Dr.

Wollaston showed l these effects, and "

that

common

electricity

resembled

it

in "

that they are both essentially the same;

but he mingled with his proofs an experiment having a re-

semblance, and nothing more, to a case of voltaic decomposi-

tion, which however he himself partly distinguished; and this

has been more frequently referred to by some, on the one hand,

to piove the occurrence of electro-chemical decomposition, like that of the pile, and by others to throw doubt upon the whole paper, than the more numerous and decisive experiments which

he has detailed.

my 46. I take the liberty of describing briefly

results, and

of thus adding my testimony to that of Dr. Wollaston on the

identity of voltaic and common electricity as to chemical action,

not only that I may facilitate the repetition of the experiments, but also lead to some new consequences respecting electro-

chemical decomposition (112, 113).

47. I

first

repeated

Wollaston's

fourth

2
experiment,

in

which the ends of coated silver wires are immersed in a drop

of sulphate of copper. By passing the electricity of the machine
through such an arrangement, that end in the drop which received the electricity became coated with metallic copper.
One hundred turns of the machine produced an evident effect; two hundred turns a very sensible one. The decomposing action was however very feeble. Very little copper was pre-

cipitated, and no sensible trace of silver from the other pole

appeared in the solution.

1
Philosophical

Transactions,

1801,

pp.

427,

434.

* Ibid. 1801, p. 429.

ÆTHERFORCE

Identity of Electricities

13

48. A much more convenient and effectual arrangement for
chemical decompositions by common electricity is the following. Upon a glass plate, fig. 4, placed over, but raised above a
piece of white paper, so that shadows may not interfere, put
two pieces of tinfoil a, b ; connect one of these by an insulated

Fig. 4-

wire c, or wire and string (37), with the machine, and the other

g, with the discharging train (28) or the negative conductor;

provide two pieces of fine platina wire, bent as in fig. 5, so

f that the part d, shall be nearly upright, whilst the whole is

resting on the three bearing points p, c,f; place these as in

fig. 4; the points p, n then become the decomposing poles. In

this way surfaces of contact, as minute as possible, can be

obtained at pleasure, and the connection can be broken or

renewed in a moment, and the sub-

stances acted upon examined with the

utmost facility.

A 49.

coarse line was made on the

glass with solution of sulphate of copper,

and the terminations p and n put into

i

it; the foil a was connected with the

positive conductor of the machine by

wire and wet string, so that no sparks

Fig- 5

passed : twenty turns of the machine caused the precipitation
of so much copper on the end n, that it looked like copper

wire ;

no apparent change

took

place at p.

A 50.

mixture of equal parts of muriatic acid and water

was rendered deep blue by sulphate of indigo, and a large drop

put on the glass, fig. 4, so that p and n were immersed at

opposite sides: a single turn of the machine showed bleaching

effects round p, from evolved chlorine. After twenty revolu-
tions no effect of the kind was visible at n, but so much chlorine

ÆTHERFORCE

14

Faraday's Researches

had been set free at p, that when the drop was stirred the

whole became colourless.

A 51. drop of solution of iodide of potassium mingled with

starch was put into the same position at p and n ; on turning

the machine, iodine was evolved at p, but not at n.
A 52. still further improvement in this form of apparatus

consists in wetting a piece of filtering paper in the solution to

be experimented on, and placing that under the points p and n,

on the glass: the paper retains the substance evolved at the

point of evolution, by its whiteness renders any change of

colour visible, and allows of the point of contact between it and

the decomposing wires being contracted to the utmost degree.
A piece of paper moistened in the solution of iodide of potas-

sium and starch, or of the iodide alone, with certain precautions

(58), is a most admirable test of electro-chemical action; and when thus placed and acted upon by the electric current, will

show iodine evolved at p by only half a turn of the machine.

With these adjustments and the use of iodide of potassium

on paper, chemical action is sometimes a more delicate test

of electrical currents than the galvanometer (9). Such cases

occur when the bodies traversed by the current are bad con-

ductors, or when the quantity of electricity evolved or trans-

mitted in a given time is very small.

A 53. piece of litmus paper moistened in solution of common

A salt or sulphate of soda was quickly reddened at p.

similar

piece moistened in muriatic acid was very soon bleached at p.
No effects of a similar kind took place at n.
A 54. piece of turmeric paper moistened in solution of sul-

phate of soda was reddened at n by two or three turns of the

machine, and in twenty or thirty turns plenty of alkali was
there evolved. On turning the paper round, so that the spot

came under p, and then working the machine, the alkali soon

disappeared, the place became yellow, and a brown alkaline

spot appeared in the new part under . 55. On combining a piece of litmus with a piece of turmeric

paper, wetting both with solution of sulphate of soda, and

putting the paper on the glass, so that p was on the litmus and n on the turmeric, a very few turns of the machine sufficed to

show the evolution of acid at the former and alkali at the latter,

exactly in the manner effected by a volta-electric current.

56. All these decompositions took place equally well, whether

the electricity passed from the machine to the foil a, through

water, or through wire only; by contact with the conductor,

ÆTHERFORCE

Chemical Action

15

or by sparks there; provided the sparks were not so large as to cause the electricity to pass in sparks from p to n, or towards n ; and I have seen no reason to believe that in cases of true
electro-chemical decomposition by the machine, the electricity passed in sparks from the conductor, or at any part of the current, is able to do more, because of its tension, than that which is made to pass merely as a regular current.
57. Finally, the experiment was extended into the following
form, supplying in this case the fullest analogy between common and voltaic electricity. Three compound pieces of litmus and
turmeric paper (55) were moistened in solution of sulphate of soda, and arranged on a plate of glass with platina wires, as
m in fig. 6. The wire was connected with the prime conductor

Fig. 6.
of the machine, the wire t with the discharging train, and the wires r and s entered into the course of the electrical current
by means of the pieces of moistened paper; they were so bent as to rest each on three points, n, r, p ; n, s, p, the points r and s being supported by the glass, and the others by the papers: the three terminations -p, p, p rested on the litmus, and the
other three n, n, n on the turmeric paper. On working the
machine for a short time only, acid was evolved at all the poles or terminations p, p, p, by which the electricity entered the solution, and alkali at the other poles n, n, n, by which the
electricity left the solution.
58. In all experiments of electro-chemical decomposition by
the common machine and moistened papers (52), it is neces-
sary to be aware of and to avoid the following important source of error. If a spark passes over moistened litmus and turmeric paper, the litmus paper (provided it be delicate and not too alkaline) is reddened by it; and if several sparks are passed, it becomes powerfully reddened. If the electricity pass a little
ÆTHERFORCE

i6

Faraday's Researches

way from the wire over the surface of the moistened paper,
before it finds mass and moisture enough to conduct it, then the reddening extends as far as the ramifications. If similar ramifications occur at the termination n, on the turmeric paper, they prevent the occurrence of the red spot due to the alkali, which would otherwise collect there: sparks or ramifications from the points n will also redden litmus paper. If paper moistened by a solution of iodide of potassium (which is an admirably delicate test of electro-chemical action) be exposed to the sparks or ramifications, or even a feeble stream of elec-
tricity through the air from either the point p or n, iodine will be immediately evolved.
59. These effects must not be confounded with those due to the true electro-chemical powers of common electricity, and must be carefully avoided when the latter are to be observed.
No sparks should be passed, therefore, in any part of the
current, nor any increase of intensity allowed, by which the
electricity may be induced to pass between the platina wires and
the moistened papers, otherwise than by conductidn; for if it burst through the air, the effect referred to above (58)
ensues.
60. The effect itself is due to the formation of nitric acid
by the combination of the oxygen and nitrogen of the air, and is, in fact, only a delicate repetition of Cavendish's beautiful experiment. The acid so formed, though small in quantity, is in a high state of concentration as to water, and produces the
consequent effects of reddening the litmus paper; or preventing the exhibition of alkali on the turmeric paper; or, by acting on
the iodide of potassium, evolving iodine.
61. By moistening a very small slip of litmus paper in solu-
tion of caustic potassa, and then passing the electric spark over its length in the air, I gradually neutralised the alkali, and ultimately rendered the paper red; on drying it, I found that nitrate of potassa had resulted from the operation, and that the paper had become touch paper.
62. Either litmus paper or white paper, moistened in a strong solution of iodide of potassium, offers therefore a very simple, beautiful, and ready means of illustrating Cavendish's experiment of the formation of nitric acid from the atmosphere.
63. I have already had occasion to refer to an experiment (i, 45) made by Dr. Wollaston, which is insisted upon too much, both by those who oppose and those who agree with the accuracy of his views respecting the identity of voltaic and

ÆTHERFORCE

Wollaston's Experiment

17

ordinary electricity. By covering fine wires with glass or other insulating substances, and then removing only so much matter

as to expose the point, or a section of the wires, and by passing

electricity through two such wires, the guarded points of which

were immersed in water, Wollaston found that the water could

be decomposed even by the current from the machine, without

sparks, and that two streams of gas arose from the points,

exactly resembling, in appearance, those produced by voltaic

electricity, and, like the latter, giving a mixture of oxygen and

hydrogen gases. But Dr. Wollaston himself points out that

the effect is different from that of the voltaic pile, inasmuch as

bitthoat"tha"ovxeiynrgyefcanlcotasnetdhiemhiyrtdeasrtieoomgnbelnoafnatrcheeeeigvsaollnvvoaetndiccformpophmleenetoaemc,he"npaaon,led";

he calls but adds does not

trust to it to establish the principles correctly laid down in his

paper.

64. This experiment is neither more nor less than a repetition,

in

a refined manner, of

that

made

by

Dr.

Pearson

in

1
I797,

and previously by MM. Pacts Van Troostwyk and Deiman in

1789 or earlier. That the experiment should never be quoted

as proving true electro-chemical decomposition, is sufficiently

evident from the circumstance, that the law which regulates

the transference and final place of the evolved bodies (14, 45) has no influence here. The water is decomposed at both poles

independently of each other, and the oxygen and hydrogen

evolved at the wires are the elements of the water existing

the instant before in those places. That the poles, or rather

points, have no mutual decomposing dependence, may be
shown by substituting a wire, or the finger, for one of them, a

change which does not at all interfere with the other, though it

stops all action at the changed pole. This fact may be observed

by turning the machine for some time; for though bubbles

will rise from the point left unaltered, in quantity sufficient

to cover entirely the wire used for the other communication, if

they could be applied to it, yet not a single bubble will appear

on that wire.

65. When electro-chemical decomposition takes place, there

is great reason to believe that the quantity of matter decom-

posed is not proportionate to the intensity, but to the quantity

of electricity passed (56). Of this I shall be able to offer some

proofs in a future part of this paper (in, 113). But in the

experiment under consideration, this is not the case. If, with

1 Nicholson's Journal, 4to, vol. i. pp. 241, 299, 349.
ÆTHERFORCE

18

Faraday's Researches

a constant pair of points, the electricity be passed from the

machine in sparks, a certain proportion of gas is evolved; but

if

the

sparks

be

rendered

shorter,

less

gas

is

evolved ;

and if f

no sparks be passed, there is scarcely a sensible portion of

gases set free. On substituting solution of sulphate of soda for

water, scarcely a sensible quantity of gas could be procured even

with powerful sparks, and nearly none with the mere current;

yet the quantity of electricity in a given time was the same in

all these cases.

66. I do not intend to deny that with such an apparatus
common electricity can decompose water in a manner analogous to that of the voltaic pile ; I believe at present that it can. But when what I consider the true effect only was obtained, the
quantity of gas given off was so small that I could not ascertain whether it was, as it ought to be, oxygen at one wire and hydrogen at the other. Of the two streams one seemed more copious than the other, and on turning the apparatus round, still the same side in relation to the machine gave the largest
stream. On substituting solution of sulphate of soda for pure
water (65), these minute streams were still observed. But
the quantities were so small, that on working the machine for half an hour I could not obtain at either pole a bubble of gas larger than a small grain of sand. If the conclusion which I have drawn (113) relating to the amount of chemical action be
correct, this ought to be the case.
67. I have been the more anxious to assign the true value of
this experiment as a test of electro-chemical action, because I
shall have occasion to refer to it in cases of supposed chemical
action by magneto-electric and other electric currents (72, 82) and elsewhere. But, independent of it, there cannot be now a doubt that Dr. Wollaston was right in his general conclusion; and that voltaic and common electricity have powers of chemical decomposition, alike in their nature, and governed by the same law of arrangement.
68. iv. Physiological effects. The power of the common
electric current to shock and convulse the animal system, and
when weak to affect the tongue and the eyes, may be considered
as the same with the similar power of voltaic electricity, account being taken of the intensity of the one electricity and duration
of the other. When a wet thread was interposed in the course of the current of common electricity fr.om the battery (27)
charged by eight or ten l revolutions of the machine in good

1 Or even from thirty to forty.

ÆTHERFORCE

Atmospheric Electricity

19

action (26), and the discharge made by platina spatulas through the tongue or the gums, the effect upon the tongue and eyes was

exactly that of a momentary feeble voltaic circuit. 69. v. Spark. The beautiful flash of light attending the
discharge of common electricity is well known. It rivals in brilliancy, if it does not even very much surpass, the light from
the discharge of voltaic electricity; but it endures for an instant only, and is attended by a sharp noise like that of a small explosion. Still no difficulty can arise in recognising it to be the
same spark as that from the voltaic battery, especially under certain circumstances. The eye cannot distinguish the differ-
ence between a voltaic and a common electricity spark, if they

be taken between amalgamated surfaces of metal, at intervals

only, and through the same distance of air.
70. When the Leyden battery (27) was discharged through
a wet string placed in some part of the circuit away from the place where the spark was to pass, the spark was yellowish, flamy, having a duration sensibly longer than if the water had not been interposed, was about three-fourths of an inch in length, was accompanied by little or no noise, and whilst losing part of its usual character had approximated in some degree
to the voltaic spark. When the electricity retarded by water
was discharged between pieces of charcoal, it was exceedingly luminous and bright upon both surfaces of the charcoal, re-

sembling the brightness of the voltaic discharge on such surfaces.
When the discharge of the unretarded electricity was taken
upon charcoal, it was bright upon both the surfaces (in that respect resembling the voltaic spark), but the noise was loud, sharp, and ringing.
71. I have assumed, in accordance, I believe, with the opinion

of every other philosopher, that atmospheric electricity is of the same nature with ordinary electricity (20), and I might

therefore refer to certain published statements of chemical

effects produced by the former as proofs that the latter enjoys

the power of decomposition in common with voltaic electricity.

But the comparison I am drawing is far too rigorous to allow

me to use these statements without being fully assured of their

accuracy; yet I have no right to suppress them, because, if

accurate, they establish what I am labouring to put on an

my undoubted foundation, and have priority to

results.

72. M. Bonijol of Geneva l is said to have constructed very

delicate apparatus for the decomposition of water by common

ÆTHERFORCE 1 Bibliotheque

Universelle,

1830,

tome

xlv.

p.

213.

2o

Faraday's Researches

electricity. By connecting an insulated lightning rod with his

apparatus, the decomposition of the water proceeded in a con-

tinuous and rapid manner even when the electricity of the

atmosphere was not very powerful. The apparatus is not

described ;

but as the diameter of the wire is mentioned as very

small, it appears to have been similar in construction to that of

Wollaston (63); and as that does not furnish a case of true

polar electro-chemical decomposition (64), this result of M.
Bonijol does not prove the identity in chemical action of common

and voltaic electricity.

73. At the same page of the Bibliotheque Universelle, M.

Bonijol is said to have decomposed potash, and also chloride of

silver, by putting them into very narrow tubes and passing

electric sparks from an ordinary machine over them. It is

evident that these offer no analogy to cases of true voltaic de-

composition, where the electricity only decomposes when it is

conducted by the body acted upon, and ceases to decompose,

according to its ordinary laws, when it passes in sparks. These

effects are probably partly analogous to that which takes place

with water in Pearson's or Wollaston's apparatus, and may be

due to very high temperature acting on minute portions of

matter; or they may be connected with the results in air (58).

As nitrogen can combine directly with oxygen under the in-

fluence of the electric spark (60), it is not impossible that it

should even take it from the potassium of the potash, especially

as there would be plenty of potassa in contact with the acting

particles to combine with the nitric acid formed. However

distinct all these actions may be from true polar electro-chemical

decompositions, they are still highly important, and well worthy

of investigation.

74. The late Mr. Barry communicated a paper to the Royal

l
Society

last

year,

so

distinct

in

the

details,

that it would

seem

at once to prove the identity in chemical action of common and

voltaic electricity; but, when examined, considerable difficulty

arises in reconciling certain of the effects with the remainder.
He used two tubes, each having a wire within it passing through

the closed end, as is usual for voltaic decompositions. The tubes

were filled with solution of sulphate of soda, coloured with

syrup of violets, and connected by a portion of the same solution,

in the ordinary manner; the wire in one tube was connected

by a gilt thread with the string of an insulated electrical kite,

and the wire in the other tube by a similar gill thread with the

1
Philosophical

Transactions,

1831,

p.

165.

ÆTHERFORCE

Identity of Electricities

21

ground. Hydrogen soon appeared in the tube connected with the kite, and oxygen in the other, and in ten minutes the liquid in the first tube was green from the alkali evolved, and that in the other red from free acid produced. The only indication

of the strength the expression,

or "

intensity

the usual

of the atmospheric electricity is in shocks were felt on touching the

string."
75. That the electricity in this case does not resemble that
from any ordinary source of common electricity, is shown by
several circumstances. Wollaston could not effect the decom-

position of water by such an arrangement, and obtain the gases
in separate vessels, using common electricity; nor have any of the numerous philosophers, who have employed such an appa-
ratus, obtained any such decomposition, either of water or of a neutral salt, by the use of the machine. I have lately tried the large machine (26) in full action for a quarter of an hour, during which time seven hundred revolutions were made, without

producing any sensible effects, although the shocks that it would

then give must have been far more powerful and numerous

than could have been taken, with any chance of safety, from

an electrical kite-string; and by reference to the comparison

hereafter to be made (107), it will be seen that for common

electricity to have produced the effect, the quantity must have

been awfully great, and apparently far more than could have

been

conducted

to

the

earth

by
"

a

gilt

thread,

and

at

the

same

time only have produced the usual shocks."

76. That the electricity
voltaic electricity is evident,

was
for

thaepp"aruesnutallyshnooctksan"aloongloyuwserteo

produced, and nothing like the terrible sensation due to a voltaic

battery, even when it has a tension so feeble as not to strike

through the eighth of an inch of air.

77. It seems just possible that the air which was passing by

the kite produce

and " string,
the usual

being shocks

in an electrical state sufficient to " only, could still, when the elec-

tricity was drawn off below, renew the charge, and so continue

the current. The string was 1500 feet long, and contained two

double threads. But when the enormous quantity which must

have been thus collected is considered (107, 112), the explanation

seems very doubtful. I charged a voltaic battery of twenty

pairs of plates four inches square with double coppers very

strongly, insulated it, connected its positive extremity with the discharging train (28), and its negative pole with an appa-

ratus like that of Mr. Barry, communicating by a wire inserted
ÆTHERFORCE

22

Faraday's Researches

i .

three inches into the wet soil of the ground. This battery

thus arranged produced feeble decomposing effects, as nearly

as I could judge answering the description Mr. Barry has given.

Its intensity was, of course, far lower than the electricity of the

kite-string, but the supply of quantity from the discharging

train was unlimited. " usual shocks " of a

It gave no
kite-string.

shocks

to

compare

with

the

78. Mr. Barry's experiment is a very important one to repeat
and verify. If confirmed, it will be, as far as I am aware, the

first recorded case of true electro-chemical decomposition of
water by common electricity, and it will supply a form of elec-

trical current, which, both in quantity and intensity, is exactly

intermediate with those of the common electrical machine and

the voltaic pile.

III. Magneto-Electricity

79. Tension. The attractions and repulsions due to the

tension of ordinary electricity have been well observed with

that evolved by magneto-electric induction. M. Pixii, by using

an apparatus, clever in its construction and powerful in its

1
action,

was

able

to

obtain

great

divergence

of

the

gold

leaves

of an electrometer. 2

80. In motion : i. Evolution of heat. The current produced by magneto-electric induction can heat a wire in the manner of ordinary electricity. At the British Association of Science at Oxford, in June of the present year, I had the pleasure, in

conjunction with Mr. Harris, Professor Daniell, Mr. Duncan,

and others, of making an experiment, for which the great magnet

in the museum, Mr. Harris's new electrometer and the magneto-

electric coil 3 were put in requisition. The latter had been

modified

in

the

manner

I

have

elsewhere

4
described,

so

as

to

produce an electric spark when its contact with the magnet was

made or broken. The terminations of the spiral, adjusted so as

to have their contact with each other broken when the spark was

to pass, were connected with the wire in the electrometer, and

it was found that each time the magnetic contact was made

1 Annales de Chimie, 1. p. 322.

2 Ibid. li. p. 77.

3 A combination of helices was constructed upon a hollow cylinder of

pasteboard: there were eight lengths of copper wire, containing altogether

220 feet; four of these helices were connected end to end, and then with

the galvanometer; the other intervening four were also connected end to

end, and the battery of one hundred pairs discharged through them.

* Phil. Mag. and Annals, 1832, vol. xi. p. 405.

ÆTHERFORCE

Identity of Electricities

23

and broken, expansion of the air within the instrument occurred, indicating an increase, at the moment, of the temperature of
the wire.

81. ii. Magnetism. These currents were discovered by their

magnetic power.
82. iii. Chemical decomposition. I have made many en-

deavours to effect chemical decomposition by magneto-elec-

tricity, but unavailingly. In July last I received an anonymous

letter

(which

has

since

been

x
published)

describing

a

magneto-

electric apparatus, by effected. As the term

which the
" guarded

decompo"sition of points is used,

water was I suppose

the apparatus to have been Wollaston's (63, etc.), in which case

the results did not indicate polar electro-chemical decom-

position. Signer Botto has recently published certain results

which

he

has

obtained ;

2

but

they

are,

as

at

present

described,

inconclusive. The apparatus he used was apparently that of

Dr. Wollaston, which gives only fallacious indications (63, etc.).

As magneto-electricity can produce sparks, it would be able to show the effects proper to this apparatus. The apparatus

of M. Pixii already referred to (79), has however, in the hands

of

himself 3

and

M.

4
Hachette,

given

decisive

chemical

results,

so as to complete this link in the chain of evidence. Water was

decomposed by it, and the oxygen and hydrogen obtained in

separate tubes according to the law governing volta-electric

and machine-electric decomposition.

A 83. iv. Physiological effects.

frog was convulsed in the

earliest experiments on these currents. The sensation upon

the tongue, and the flash before the eyes, which I at first

obtained only in a feeble degree, have been since exalted by

more powerful apparatus, so as to become even disagreeable.

84. v. Spark. The feeble spark which I first obtained with

these currents has been varied and strengthened by Signori

Nobili and Antinori, and others, so as to leave no doubt as to

its identity with the common electric spark.

1 Land, and Edinb. Phil. Mag. and Journ. 1832, vol. i. p. 161.

2 Ibid. 1832, vol. i. p. 441.

* Annales de Chimie, li. p. 77.

4 Ibid. li. p. 72.

ÆTHERFORCE

24

Faraday's Researches

IV. Thermo-Electricity
85. With regard to thermo-electricity (that beautiful form of electricity discovered by Seebeck), the very conditions under which it is excited are such as to give no ground for expecting that it can be raised like common electricity to any high degree of tension; the effects, therefore, due to that state are not to be expected. The sum of evidence respecting its analogy to
the electricities already described, is, I believe, as follows:
Tension. The attractions and repulsions due to a certain degree of tension have not been observed. In currents : i. Evolution
of heat. I am not aware that its power of raising temperature
has been observed, ii. Magnetism. It was discovered, and is best recognised, by its magnetic powers, iii. Chemical decomposition has not been effected by it. iv. Physiological effects. Nobili has shown l that these currents are able to cause con-
tractions in the limbs of a frog. v. Spark. The spark has not yet been seen.
86. Only those effects are weak or deficient which depend upon a certain high degree of intensity; and if common electricity be reduced in that quality to a similar degree with the thermo-electricity, it can produce no effects beyond the latter.

V. Animal Electricity

87. After

an

examination

of

the

experiments

of

2
Walsh,

3
Ingenhousz,

4
Cavendish,

Sir

H.

5
Davy,

and

Dr.

6
Davy,

no

doubt remains on my mind as to the identity of the electricity of
the torpedo with common and voltaic electricity ; and I presume

my that so little will remain on the minds of others as to justify

refraining from entering at length into the philosophical proofs

of that identity. The doubts raised by Sir H. Davy have

been removed by his brother Dr. Davy; the results of the latter

being the reverse of those of the former. At present the sum

of evidence is as follows :

88. Tension. No sensible attractions or repulsions due to

tension have been observed.

89. In motion: i. Evolution of heat; not yet observed; I

1
Bibliotheque

Universelle,

xxxvii.

15.

2 Philosophical Transactions, 1773, p. 461.

4 Ibid. 1776, p. 196.

* Ibid. 1829, p. 15.

3 Ibid. 1775, p. i. Ibid. 1832, p. 259.

ÆTHERFORCE

Animal Electricity

25

have little or no doubt that Harris's electrometer would show

it (23, 95).

90. ii. Magnetism. Perfectly distinct. According to Dr.

1
Davy,

the

current

deflected

the

needle

and

made

magnets

under the same law, as to direction, which governs currents of

ordinary and voltaic electricity.

91. iii. Chemical decomposition. Also distinct; and though

Dr. Davy used an apparatus of similar construction with that

of Dr. Wollaston (63), still no error in the present case is

involved, for the decompositions were polar, and in their nature

truly electro-chemical. By the direction of the magnet, it was

found that the under surface of the fish was negative, and the

upper positive; and in the chemical decompositions, silver and

lead were precipitated on the wire connected with the under

surface, and not on the other; and when these wires were either

steel or silver, in solution of common salt, gas (hydrogen?)

rose from the negative wire, but none from the positive.

92. Another reason for the decomposition being electro-

chemical is, that a Wollaston's apparatus constructed with wires,

coated by sealing-wax, would most probably not have decom-

posed water, even in its own peculiar way, unless the elec-

tricity had risen high enough in intensity to produce sparks in

some part of the circuit; whereas the torpedo was not able to

A produce sensible sparks.

third reason is, that the purer the

water in Wollaston's apparatus, the more abundant is the

decomposition: and I have found that a machine and wire

points which succeeded perfectly well with distilled water, failed

altogether when the water was rendered a good conductor by

sulphate of soda, common salt, or other saline bodies. But in

Dr. Davy's experiments with the torpedo, strong solutions of salt,

nitrate of silver, and superacetate of lead were used success-

fully, and there is no doubt with more success than weaker ones.

93. iv. Physiological effects. These are so characteristic, that

by them the peculiar powers of the torpedo and gymnotus are

principally recognised.
94. v. Spark. The electric spark has not yet been obtained, or at least I think not; but perhaps I had better refer to the

evidence on this point. Humboldt, speaking of results obtained

by

M.

Fahlberg,

of

Sweden,

says,

" This

philosopher

has

seen

an electric spark, as Walsh and Ingenhousz had done before

him at London, by placing the gymnotus in the air, and inter-

rupting the conducting chain by two gold leaves pasted upon

1 Philosophical Transactions, 1832, p. 260.
ÆTHERFORCE

26

Faraday's Researches

glass, and a line distant from each other." l I cannot, how-
ever, find any record of such an observation by either Walsh or Ingenhousz, and do not know where to refer to that by M. Fahlberg. M. Humboldt could not himself perceive any
luminous effect.

Again, Sir John Leslie, in his dissertation on the progress of

mathematical and physical science, prefixed to the seventh

edition of the
says, " From

EanchyecallotpheydisapBerciitmaennni"ca,ofEdtihnebuSriglhu,ru1s830el,ecpt.ri6c2u2s,,

"

meaning rather the sparks were drawn in

gymnotus, a darkened

exhibited
room; " but

in
he

London, vivid does not say he

saw them himself, nor state who did see them; nor can I find

any account of such a phenomenon; so that the statement is

doubtful. 2

95. In concluding this summary of the powers of torpedinal electricity, I cannot refrain from pointing out the enormous absolute quantity of electricity which the animal must put in circulation at each effort. It is doubtful whether any common electrical machine has as yet been able to supply electricity
sufficient in a reasonable time to cause true electro-chemical

decomposition of water (66, 75), yet the current from the torpedo has done it. The same high proportion is shown by the magnetic effects (32, 107). These circumstances indicate
that the torpedo has power (in the way probably that Caven-
dish describes) to continue the evolution for a sensible time, so that its successive discharges rather resemble those of a voltaic arrangement, intermitting in its action, than those of a
Leyden apparatus, charged and discharged many times in suc-
cession. In reality, however, there is no philosophical difference between these two cases.

96. The general conclusion which must, I think, be drawn

from this collection of facts is, that electricity, whatever may

be its source, is identical in its nature. The phenomena in the

five kinds of species quoted, differ, not in their character but

only in degree; and in that respect vary in proportion to the

variable

circumstances

of

quantity

and

3
intensity

which

can

at

pleasure be made to change in almost any one of the kinds of

electricity, as much as it does between one kind and another.

1 Edinburgh Phil. Journal, ii. p. 249.
2 Mr. Brayley, who referred me to these statements, and has extensive

knowledge of recorded facts, is unacquainted with any further account

relating to them.

3 The term quantity in electricity is perhaps sufficiently definite as to

am sense; the term intensity is more difficult to define strictly. I

using

the terms in their ordinary and accepted meaning.

ÆTHERFORCE

Measure of Electricities

27

Table of the experimental Effects common to the Electricities
derived from different Sources. 1

ÆTHERFORCE

28

Faraday's Researches

meter, under different circumstances, would cause the same
deflection of the needle. An arbitrary scale was therefore
attached to the galvanometer, each division of which was equal to about 4, and the instrument arranged as in former experiments (32). The machine (26), battery (27), and other parts of the apparatus were brought into good order, and retained for the time as nearly as possible in the same condition. The
experiments were alternated so as to indicate any change in the condition of the apparatus and supply the necessary
corrections.
99. Seven of the battery jars were removed, and eight retained for present use. It was found that about forty turns would fully charge the eight jars. They were then charged by thirty turns of the machine, and discharged through the galvanometer, a thick wet string, about ten inches long, being included in the circuit. The needle was immediately deflected five divisions and a half, on the one side of the zero, and in
vibrating passed as nearly as possible through five divisions and a half on the other side.
100. The other seven jars were then added to the eight, and the whole fifteen charged by thirty turns of the machine. The
Henley's electrometer stood not quite half as high as before;
but when the discharge was made through the galvanometer,
previously at rest, the needle immediately vibrated, passing exactly to the same division as in the former instance. These experiments with eight and with fifteen jars were repeated several times alternately with the same results.
101. Other experiments were then made, in which all the battery was used, and its charge (being fifty turns of the machine) sent through the galvanometer: but it was modified by being passed sometimes through a mere wet thread, sometimes through thirty-eight inches of thin string wetted by distilled water, and sometimes through a string of twelve times the thickness, only twelve inches in length, and soaked in dilute acid (34). With the thick string the charge passed at once; with the thin string it occupied a sensible time, and with the thread it required two or three seconds before the electrometer fell entirely down. The current therefore must have varied extremely in intensity in these different cases, and yet the deflection of the needle was sensibly the same in all of them. If any difference occurred, it was that the thin string and thread caused greatest deflection; and if there is any lateral transmission, as M. Colladon says, through the silk in the galvano-

ÆTHERFORCE

Definite Magnetic Action

29

meter coil, it ought to have been so, because then the intensity is lower and the lateral transmission less.

1 02. Hence it would appear that if the same absolute quantity

of electricity pass through the galvanometer, whatever may be its

intensity, the deflecting force upon the magnetic needle is the same.

103. The battery of fifteen jars was then charged by sixty

revolutions of the machine, and discharged, as before, through

the galvanometer. The deflection of the needle was now as

nearly as possible to the eleventh division, but the graduation
was not accurate enough for me to assert that the arc was

exactly

double

the

former

arc ;

to the eye it appeared to be so.

The probability is, that the deflecting force of an electric current

is directly proportional to the absolute quantity of electricity passed,
at whatever intensity that electricity may be. 1
104. Dr. Ritchie has shown that in a case where the intensity

of the electricity remained the same, the deflection of the

magnetic needle was directly as the quantity of electricity passed

through

the

2
galvanometer.

Mr. Harris has shown that the

heating power of common electricity on metallic wires is the

same for the same quantity of electricity whatever its intensity might have previously been. 3

105. The next point was to obtain a voltaic arrangement

A producing an effect equal to that just described (103).

platina

and a zinc wire were passed through the same hole of a draw-

plate, being then one-eighteenth of an inch in diameter; these

were fastened to a -support, so that their lower ends projected,

were parallel, and five-sixteenths of an inch apart. The upper

ends were well connected with the galvanometer wires. Some

acid was diluted, and, after various preliminary experiments,

that adopted as a standard which consisted of one drop strong

sulphuric acid in four ounces distilled water. Finally, the time was noted which the needle required in swinging either from right to left or left to right : it was equal to seventeen beats of
my watch, the latter giving one hundred and fifty in a minute.
The object of these preparations was to arrange a voltaic apparatus, which, by immersion in a given acid for a given time, much less than that required by the needle to swing in one

1 The great and general value of the galvanometer, as an actual measure

of the electricity passing through it, either continuously or interruptedly, must be evident from a consideration of these two conclusions. As con-

structed by Professor Ritchie with glass threads (see Philosophical Transac-

tions, 1830, p. 218, and Quarterly Journal of Science, New Series, vol. i. p. 29),

it apparently seems to leave nothing unsupplied in its own department.

New 1 Quarterlv Journal of Science,

Series, vol. i. p. 33.

3 Plymouth Transactions, p. 22.

ÆTHERFORCE

30

Faraday's Researches

direction, should give equal deflection to the instrument with the
discharge of ordinary electricity from the battery (99, 100);
and a new part of the zinc wire having been brought into position
with the platina, the comparative experiments were made.
1 06. On plunging the zinc and platina wires five-eighths of
an inch deep into the acid, and retaining them there for eight beats of the watch (after which they were quickly withdrawn), the needle was deflected, and continued to advance in the same
direction some time after the voltaic apparatus had been removed from the acid. It attained the five-and-a-half division, and
then returned swinging an equal distance on the other side.
This experiment was repeated many times, and always with the
same result.

107. Hence, as an approximation, and judging. from magnetic

force only at present (112), it would appear that two wires,

one of platina and one of zinc, each one-eighteenth of an inch

in diameter, placed five-sixteenths of an inch apart and im-

mersed to the depth of five-eighths of an inch in acid, consisting

of one drop oil of vitriol and four ounces distilled water, at a

temperature about 60, and connected at the other extremities

by a copper wire eighteen feet long and one-eighteenth of an

inch thick (being the wire of the galvanometer coils), yield as

my much electricity in eight beats of

watch, or in T f^ths of a

minute, as the electrical battery charged by thirty turns of the

large machine, in excellent order (99, 100). Notwithstanding

this apparently enormous disproportion, the results are perfectly

in harmony with those effects which are known to be produced

by variations in the intensity and quantity of the electric fluid.

108. In order to procure a reference to chemical action, the

wires were now retained immersed in the acid to the depth of

five-eighths of an inch, and the needle, when stationary, observed :

it stood, as nearly as the unassisted eye could decide, at 5^

division. Hence a permanent deflection to that extent might

be considered as indicating a constant voltaic current, which
in eight beats of my watch (105) could supply as much electricity

as the electrical battery charged by thirty turns of the machine.

109. The following arrangements and results are selected

from many that were made and obtained relative to chemical

A action.

platina wire one-twelfth of an inch in diameter,

weighing two hundred and sixty grains, had the extremity

rendered plain, so as to offer a definite surface equal to a circle

of the same diameter as the wire; it was then connected in turn

with the conductor of the machine, or with the voltaic apparatus

ÆTHERFORCE

Definite Chemical Force

31

(105), so as always to form the positive pole, and at the same time retain a perpendicular position, that it might rest, with its whole weight, upon the test paper to be employed. The test paper itself was supported upon a platina spatula, connected either with the discharging train (28), or with the negative wire of the voltaic apparatus, and it consisted of four thicknesses, moistened at all times to an equal degree in a standard
solution of hydriodate of potassa (52).
no. When the platina wire was connected with the prime
conductor of the machine, and the spatula with the discharging train, ten turns of the machine had such decomposing power as to produce a pale round spot of iodine of the diameter of the wire; twenty turns made a much darker mark, and thirty turns made a dark brown spot penetrating to the second thickness of the paper. The difference in effect produced by two or three turns, more or less, could be distinguished with facility.
in. The wire and spatula were then connected with the
voltaic apparatus (105), the galvanometer being also included in the arrangement; and, a stronger acid having been prepared, consisting of nitric acid and water, the voltaic apparatus was immersed so far as to give a permanent deflection of the needle to the 5^ division (108), the fourfold moistened paper intervening as before. 1 Then by shifting the end of the wire from place to place upon the test paper, the effect of the current for five, six, seven, or any number of the beats of the watch (105) was observed, and compared with that of the machine. After
alternating and repeating the experiments of comparison many
times, it was constantly found that this standard current of voltaic electricity, continued for eight beats of the watch, was equal, in chemical effect, to thirty turns of the machine ; twentyeight revolutions of the machine were sensibly too few.
112. Hence it results that both in magnetic deflection (107) and in chemical force, the current of electricity of the standard voltaic battery for eight beats of the watch was equal to that of the machine evolved by thirty revolutions.
113. It also follows that for this case of electro-chemical de-
composition, and it is probable for all cases, that the chemical
power, like the magnetic force (102), is in direct proportion to the absolute quantity of electricity which passes.
114. Hence arises still further confirmation, if any were
required, of the identity of common and voltaic electricity,
1 Of course the heightened power of the voltaic battery was necessary to compensate for the bad conductor now interposed.
ÆTHERFORCE

32

Faraday's Researches

and that the differences of intensity and quantity are quite sufficient to account for what were supposed to be their dis-
tinctive qualities.
115. The extension which the present investigations have
enabled me to make of the facts and views constituting the
theory of electro-chemical decomposition, will, with some other points of electrical doctrine, be almost immediately submitted to the Royal Society in another series of these Researches.

December 15, 1832.

II 1

3. ON A NEW LAW OF ELECTRIC CONDUCTION.
CONDUCTING POWER GENERALLY

4. ON

3. On a new Law of Electric Conduction
116. IT was during the progress of investigations relating to electro-chemical decomposition, which I still have to submit to the Royal Society, that I encountered effects due to a very general law of electric conduction not hitherto recognised; and
though they prevented me from obtaining the condition I sought for, they afforded abundant compensation for the momentary disappointment, by the new and important interest which they
gave to an extensive part of electrical science. 117. I was working with ice, and the solids resulting from
the freezing of solutions, arranged either as barriers across a substance to be decomposed, or as the actual poles of a voltaic battery, that I might trace and catch certain elements in their
transit, when I was suddenly stopped in my progress by finding
that ice was in such circumstances a non-conductor of elec-
tricity; and that as soon as a thin film of it was interposed, in the circuit of a very powerful voltaic battery, the transmission of electricity was prevented, and all decomposition ceased.
118. At first the experiments were made with common ice,
during the cold freezing weather of the latter end of January 1833; but the results were fallacious, from the imperfection
1 Fourth Series, original edition, vol. i. p. no.

ÆTHERFORCE

New Law of Electric Conduction 33
of the arrangements, and the following more unexceptionable form of experiment was adopted.
119. Tin vessels were formed, five inches deep, one inch and a quarter wide in one direction, of different widths from threeeighths to five-eighths of an inch in the other, and open at one extremity. Into these were fixed by corks, plates of platina, so that the latter should not touch the tin cases; and copper wires having previously been soldered to the plates, these were easily connected, when required, with a voltaic pile. Then distilled water, previously boiled for three hours, was poured into the vessels, and frozen by a mixture of salt and snow, so that pure transparent solid ice intervened between the platina and tin : and finally these metals were connected with the opposite extremities of the voltaic apparatus, a galvanometer being at the same time included in the circuit.
120. In the first experiment, the platina pole was three inches and a half long, and seven-eighths of an inch wide ; it was wholly immersed in the water or ice, and as the vessel was four-eighths of an inch in width, the average thickness of the intervening ice was only a quarter of an inch, whilst the surface of contact with it at both poles was nearly fourteen square inches. After the water was frozen, the vessel was still retained in the frigorific mixture, whilst contact between the tin and platina respectively was made with the extremities of a well-charged
voltaic battery, consisting of twenty pairs of four-inch plates, each with double coppers. Not the slightest deflection of the
galvanometer needle occurred.
121. On taking the frozen arrangement out of the cold mixture, and applying warmth to the bottom of the tin case, so
as to melt part of the ice, the connection with the battery being in the meantime retained, the needle did not at first move; and
it was only when the thawing process had extended so far as to
liquefy part of the ice touching the platina pole, that conduction took place; but then it occurred effectually, and the galvanometer needle was permanently deflected nearly 70.
122. In another experiment, a platina spatula, five inches in length and seven-eighths of an inch in width, had four inches fixed in the ice, and the latter was only three-sixteenths of an inch thick between one metallic surface and the other; yet this
arrangement insulated as perfectly as the former.
123. Upon pouring a little water in at the top of this vessel on the ice, still the arrangement did not conduct; yet fluid water was evidently there. This result was the consequence
ÆTHERFORCE

34

Faraday's Researches

of the cold metals having frozen the water where they touched it, and thus insulating the fluid part; and it well illustrates
the non-conducting power of ice, by showing how thin a film could prevent the transmission of the battery current. Upon
thawing parts of this thin film, at both metals, conduction
occurred.

124. Upon warming the tin case and removing the piece of ice, it was found that a cork having slipped, one of the edges

of the platina had been all but in contact with the inner surface

of the tin vessel; yet, notwithstanding the extreme thinness of

the interfering ice in this place, no sensible portion of electricity

had passed.

125. These experiments were repeated many times with the

same results. At last a battery of fifteen troughs, or one hundred and fifty pairs of four-inch plates, powerfully charged,

was used; yet even here no sensible quantity of electricity

passed the thin barrier of ice.

126. It seemed at first as if occasional departures from these

effects occurred ;

but they could always be traced to some inter-

fering circumstances. The water should in every instance be

well frozen; for though it is not necessary that the ice should

reach from pole to pole, since a barrier of it about one pole

would be quite sufficient to prevent conduction, yet, if part

remain fluid, the mere necessary exposure of the apparatus to the

air, or the approximation of the hands, is sufficient to produce,

at the upper surface of the water and ice, a film of fluid, ex-

tending from the platina to the tin; and then conduction occurs.

Again, if the corks used to block the platina in its place are

damp or wet within, it is necessary that the cold be sufficiently

well applied to freeze the water in them, or else when the surfaces of their contact with the tin become slightly warm

by handling, that part will conduct, and the interior being ready

to conduct also, the current will pass. The water should be

pure, not only that unembarrassed results may be obtained, but

also that, as the freezing proceeds, a minute portion of concen-

trated saline solution may not be formed, which remaining fluid,

and being interposed in the ice, or passing into cracks resulting

from contraction, may exhibit conducting powers independent

of the ice itself.

127. On one occasion I was surprised to find that after thawing much of the ice the conducting power had not been restored ;

but I found that a cork which held the wire just where it joined

the platina, dipped so far into the ice, that with the ice itself

ÆTHERFORCE

Fused Chloride of Lead Conducts 35

it protected the platina from contact with the melted part long after that contact was expected.
128. This insulating power of ice is not effective with elec-
tricity of exalted intensity. On touching a diverged gold-leaf
electrometer with a wire connected with the platina, whilst the tin case was touched by the hand or another wire, the electrometer was instantly discharged (155).
129. But though electricity of an intensity so low that it cannot diverge the electrometer, can still pass (though in very
limited quantities (155) ) through ice; the comparative relation of water and ice to the electricity of the voltaic apparatus is not less extraordinary on that account, or less important in its

consequences.

130. As it did not seem likely that this law of the assumption

of conducting power during liquefaction, and loss of it during

congelation, would be peculiar to water, I immediately pro-

ceeded to ascertain its influence in other cases, and found it to

be very general. For this purpose bodies were chosen which
were solid at common temperatures, but readily fusible; and of

such composition as, for other reasons connected with electro-

chemical action, led to the conclusion that they would be able

A when fused to replace water as conductors.

voltaic battery

of two troughs, or twenty pairs of four-inch plates (120), was

used as the source of electricity, and a galvanometer introduced

into the circuit to indicate the presence or absence of a current.
131. On fusing a little chloride of lead by a spirit-lamp on a

fragment of a Florence flask, and introducing two platina wires

connected with the poles of the battery, there was instantly

powerful action, the galvanometer was most violently affected,
and the chloride rapidly decomposed. On removing the lamp,

the instant the chloride solidified all current and consequent

effects ceased, though the platina wires remained inclosed in

the chloride not more than the one-sixteenth of an inch from

each other. On renewing the heat, as soon as the fusion had

proceeded far enough to allow liquid matter to connect the

poles, the electrical current instantly passed.
132. On fusing the chloride, with one wire introduced, and

then touching the liquid with the other, the latter being cold,

caused a little knob to concrete on its extremity, and no current

passed ; it was only when the wire became so hot as to be able

to admit or allow of contact with the liquid matter, that con-

duction took place, and then it was very powerful.
133. When chloride of silver and chlorate of potassa were

ÆTHERFORCE

36

Faraday's Researches

experimented with, in a similar manner, exactly the same

results occurred.

134. Whenever the current passed in these cases, there was

decomposition of the substances; but the electro-chemical part

of this subject I purpose connecting with more general views

in

a

future

1
paper.

135. Other substances, which could not be melted on glass,

were fused by the lamp and blowpipe on platina connected

with one pole of the battery, and then a wire, connected with

the other, dipped into them. In this way chloride of sodium,

sulphate of soda, protoxide of lead, mixed carbonates of potash

and soda, etc., etc., exhibited exactly the same phenomena as

those already described: whilst liquid, they conducted and

were decomposed; whilst solid, though very hot, they insulated

the battery current even when four troughs were used.

136. Occasionally the substances were contained in small

bent tubes of green glass, and when fused, the platina poles

intr6duced, one on each side.

In such cases the same gen-

eral results as those already described were procured ; but
a further advantage was ob-

tained, namely, that whilst the substance was conduct-

Fig- 7-

ing and suffering decom-

position, the final arrangement of the elements could be

observed. Thus, iodides of potassium and lead gave iodine at

the positive pole, and potassium or lead at the negative pole.

Chlorides of lead and silver gave chlorine at the positive, and

metals at the negative pole. Nitre and chlorate of potassa

gave oxygen, etc., at the positive, and alkali, or even potassium,

at the negative pole.

A 137. fourth arrangement was used for substances requiring

A very high temperatures for their fusion.

platina wire was

connected with one pole of the battery; its extremity bent into

a small ring, in the manner described by Berzelius, for blow-

pipe experiments; a little of the salt, glass, or other substance,

1
are

In 1801, Sir H. Davy knew that " dry conductors of galvanism when rendered

nitre, caustic potash,
fluid by a high degree

and soda of heat "

(Journals of the Royal Institution, 1802, p. 53), but was not aware of the

general law that eleven

which I have been engaged years after that, he should

siany,de"veTlhoepirneg.are

It is remarkable,
no fluids known

except such as contain water, which are capable of being made the medium

of connection between the metal or metals of the voltaic apparatus."

Elements of Chemical Philosophy, p. 169.

ÆTHERFORCE

Bodies Subject to the New Law

37

was melted on this ring by the ordinary blowpipe, or even in some cases by the oxy-hydrogen blowpipe, and when the drop, retained in its place by the ring, was thoroughly hot and fluid, a platina wire from the opposite pole of the battery was made to touch it, and the effects observed.
138. The following are various substances, taken from very different classes chemically considered, which are subject to this law. The list might, no doubt, be enormously extended; but I have not had time to do more than confirm the law by a sufficient number of instances.
First, Water.
Amongst oxides ; -potassa, protoxide of lead, glass of antimony, protoxide of antimony, oxide of bismuth.
Chlorides of potassium, sodium, barium, strontium, calcium,
magnesium, manganese, zinc, copper (proto-), lead, tin (proto-),
antimony, silver. Iodides of potassium, zinc and lead, protiodide of tin, perio-
dide of mercury; fluoride of potassium; cyanide of potassium;
sulpha- cyanide of potassium.
Salts. Chlorate of potassa; nitrates of potassa, soda, baryta,
strontia, lead, copper, and silver; sulphates of soda and lead,
proto-sulphate of mercury; phosphates of potassa, soda, lead, copper, phosphoric glass or acid phosphate of lime; carbonates of potassa and soda, mingled and separate; borax, borate of lead, per-borate of tin; chromate of potassa, bi-chromate of potassa, chromate of lead; acetate of potassa.
Sulphurets. Sulphuret of antimony, sulphuret of potassium
made by reducing sulphate of potassa by hydrogen; ordinary
sulphuret of potassa. Silicated potassa; chameleon mineral. 139. It is highly interesting in the instances of those sub-
stances which soften before they liquefy, to observe at what period the conducting power is acquired, and to what degree it is exalted by perfect fluidity. Thus, with the borate of lead, when heated by the lamp upon glass, it becomes as soft as treacle, but it did not conduct, and it was only when urged by the blowpipe and brought to a fair red heat, that it conducted.
When rendered quite liquid, it conducted with extreme
facility.
140. I do not mean to deny that part of the increased conducting power in these cases of softening was probably due to
the elevation of temperature (168, 181); but I have no doubt that by far the greater part was due to the influence of the
ÆTHERFORCE

38

Faraday's Researches

general law already demonstrated, and which in these instances came gradually, instead of suddenly, into operation.
141. The following are bodies which acquired no conducting power upon assuming the liquid state:
Sulphur, phosphorus; iodide of sulphur, per-iodide of tin; orpiment, realgar; glacial acetic acid, mixed margaric and oleic
acids, artificial camphor; caffeine, sugar, adipocire, stearine of
cocoa-nut oil, spermaceti, camphor, naphthaline, resin, gum
sandarach, shell lac. 142. Perchloride of tin, chloride of arsenic, and the hydrated
chloride of arsenic, being liquids, had no sensible conducting power indicated by the galvanometer, nor were they decom-

posed.
143. Some of the above substances are sufficiently remarkable

as exceptions to the general law governing the former cases.

These are orpiment, realgar, acetic acid, artificial camphor, periodide of tin, and the chlorides of tin and arsenic. I shall

have occasion to refer to these cases in the paper on Electro-

chemical Decomposition. 144. Boracic acid was raised to the highest possible tempera-
ture by an oxy-hydrogen flame (137), yet rUgained no conducting powers sufficient to affect the galvanometer, and underwent no apparent voltaic decomposition. It seemed to be quite as bad a conductor as air. Green bottle-glass, heated in the same

manner, did not gain conducting power sensible to the galvanometer. Flint glass, when highly heated, did conduct a little and decompose; and as the proportion of potash or oxide of lead was increased in the glass, the effects were more powerful. Those glasses, consisting of boracic acid on the one hand, and oxide of lead or potassa on the other, show the assumption of conducting power upon fusion and the accompanying decom-

position very well. 145. I was very anxious to try the general experiment with

sulphuric acid, of about specific gravity 1.783, containing that

proportion of water which gives it the power of crystallising at

40

Fahr. ;

but I found it impossible to obtain it so that I could

be sure the whole would congeal even at o Fahr. A ten-

thousandth part of water, more or less than necessary, would,

upon cooling the whole, cause a portion of uncongealable liquid to separate, and that remaining in the interstices of the solid

mass, and moistening the planes of division, would prevent the

correct observation of the phenomena due to entire solidifica-

tion and subsequent liquefaction.

ÆTHERFORCE

Degree of Conducting Power Conferred 39
146. With regard to the substances on which conducting power is thus conferred by liquidity, the degree of power so given is generally very great. Water is that body in which this acquired power is feeblest. In the various oxides, chlorides, salts, etc., etc., it is given in a much higher degree. I have not had time to measure the conducting power in these cases, but it is apparently some hundred times that of pure water. The increased conducting power known to be given to water by the addition of salts would seem to be in a great degree dependent upon the high conducting power of these bodies when in the liquid state, that state being given them for the time, not by heat but solution in the water.
147. Whether the conducting power of these liquefied bodies is a consequence of their decomposition or not (149), or whether the two actions of conduction and decomposition are essentially connected or not, would introduce no difference affecting the
probable accuracy of the preceding statement.
148. This general assumption of conducting power by bodies as soon as they pass from the solid to the liquid state, offers a new and extraordinary character, the existence of which, as far as I know, has not before been suspected; and it seems importantly connected with some properties and relations of the
particles of matter which I may now briefly point out.
149. In almost all the instances, as yet observed, which are
governed by this law, the substances experimented with have been those which were not only compound bodies, but such as contain elements known to arrange themselves at the opposite poles; and were also such as could be decomposed by the elec-
trical current. When conduction took place, decomposition
occurred; when decomposition ceased, conduction ceased also; and it becomes a fair and an important question, Whether the
conduction itself may not, wherever the law holds good, be a
consequence not merely of the capability, but of the act of de-
composition? And that question may be accompanied by
another, namely, Whether solidification does not prevent conduction, merely by chaining the particles to their places, under the influence of aggregation, and preventing their final separation in the manner necessary for decomposition ?
150. But, on the other hand, there is one substance (and
others may occur), the per-iodide of mercury, which, being ex-
perimented with like the others (136), was found to insulate when solid, and to acquire conducting power when fluid; yet it did not seem to undergo decomposition in the latter case.
ÆTHERFORCE

4-Q

Faraday's Researches

151. Again, there are many substances which contain elements
such as would be expected to arrange themselves at the opposite poles of the pile, and therefore in that respect fitted for decomposition, which yet do not conduct. Amongst these are

the iodide of sulphur, per-iodide of zinc, per-chloride of tin,

chloride of arsenic, hydrated chloride of arsenic, acetic acid, orpiment, realgar, artificial camphor, etc.; and from these it might perhaps be assumed that decomposition is dependent upon conducting power, and not the latter upon the former. The true relation, however, of conduction and decomposition in
those bodies governed by the general law which it is the object of this paper to establish, can only be satisfactorily made out from a far more extensive series of observations than those I

have

yet

been

able

to

1
supply.

152. The relation, under this law, of the conducting power

of electricity to that for heat, is very remarkable, and seems

to imply a natural dependence of the two. As the solid becomes

a fluid, it loses almost entirely the power of conduction for

heat, but gains in a high degree that for electricity; but as

it reverts back to the solid state, it gains the power of conduct-

ing heat, and loses that of conducting electricity. If, therefore,

the properties are not incompatible, still they are most strongly

We contrasted, one being lost as the other is gained.

may

hope, perhaps, hereafter to understand the physical reason of this very extraordinary relation of the two conducting powers, both of which appear to be directly connected with the corpus-

cular condition of the substances concerned.

153. The assumption of conducting power and a decomposable condition by liquefaction, promises new opportunities of,
and great facilities in, voltaic decomposition. Thus, such bodies

as the oxides, chlorides, cyanides, sulpho-cyanides, fluorides,
certain vitreous mixtures, etc., etc., may be submitted to the action of the voltaic battery under new circumstances; and
indeed I have already been able, with ten pairs of plates, to
decompose common salt, chloride of magnesium, borax, etc., etc.,
and to obtain sodium, magnesium, boron, etc., in their separate

states.

1 See 414, etc., etc. December 1838.

ÆTHERFORCE

Conduction by Ice and Solid Salts 41

4. On Conducting Power generally l

my 154. It is not

intention here to enter into an examination

of all the circumstances connected with conducting power, but

to record certain facts and observations which have arisen

during recent inquiries, as additions to the general stock of

knowledge relating to this point of electrical science.

155. I was anxious, in the first place, to obtain some idea of

the conducting power of ice and solid salts for electricity of high tension (128), that a comparison might be made between

it and the large accession of the same power gained upon lique-

faction. For this purpose the large electrical machine (26) was brought into excellent action, its conductor connected with

a delicate gold-leaf electrometer, and also with the platina in-

closed in the ice (119), whilst the tin case was connected with
the discharging train (28). On working the machine moderately,

the gold leaves barely separated; on working it rapidly, they

could be opened nearly two inches. In this instance the tin

case was five-eighths of an inch in width; and as, after the

experiment, the platina plate was found very nearly in the

middle of the ice, the average thickness of the latter had been

five-sixteenths of an inch, and the extent of surface of contact

with tin and platina fourteen square inches (120). Yet, under these circumstances, it was but just able to conduct the small

quantity of electricity which this machine could evolve (107).

even

when

of

a

tension

competent

to

open

the

leaves

two

inches ;

no wonder, therefore, that it could not conduct any sensible

portion of the electricity of the troughs (120), which, though

almost infinitely surpassing that of the machine in quantity, had a tension so low as not to be sensible to an electrometer.

156. In another experiment, the tin case was only four-eighths of an inch in width, and it was found afterwards that the
platina had been not quite one-eighth of an inch distant in the
ice from one side of the tin vessel. When this was introduced

into the course of the electricity from the machine (155), the gold leaves could be opened, but not more than half an inch;
the thinness of the ice favouring the conduction of the electricity, and permitting the same quantity to pass in the same time,
though of a much lower tension.
157. Iodide of potassium which had been fused and cooled

1 In reference to this refer to paragraph 718, and the results connected with it. December 1838.

ÆTHERFORCE

42

Faraday's Researches

was introduced into the course of the electricity from the machine. There were two pieces, each about a quarter of an inch in thickness, and exposing a surface on each side equal to about half a square inch; these were placed upon platina plates, one connected with the machine and electrometer (155), and
the other with the discharging train, whilst a fine platina wire connected the two pieces, resting upon them by its two points.
On working the electrical machine, it was possible to open the
electrometer leaves about two-thirds of an inch.

158. As the platina wire touched only by points, the facts show that this salt is a far better conductor than ice; but as
the leaves of the electrometer opened, it is also evident with what difficulty conduction, even of the small portion of electricity produced by the machine, is effected by this body in the
solid state, when compared to the facility with which enormous quantities at very low tensions are transmitted by it when in the

fluid state.

159. In order to confirm these results by others, obtained

from the voltaic apparatus, a battery of one hundred and fifty

plates, four inches square, was well charged: its action was

good; the shock from it strong; the discharge would continue

from copper to copper through four-tenths of an inch of air,

and the gold-leaf electrometer before used could be opened

nearly a quarter of an inch.

1 60. The ice vessel employed (156) was half an inch in width:

as the extent of contact of the ice with the tin and platina was

nearly fourteen square inches, the whole was equivalent to a

plate of ice having a surface of seven square inches of perfect

contact at each side, and only one-fourth of an inch thick.

It was retained in a freezing mixture during the experiment.

161. The order of arrangement in the course of the electric

current was as follows. The positive pole of the battery was

connected

by

a

wire

with

the

platina

plate

in

the

ice ;

the plate

was in contact with the ice, the ice with the tin jacket, the

jacket with a wire, which communicated with a piece of tin foil,

on which rested one end of a bent platina wire (48), the other

or decomposing end being supported on paper moistened with

solution of iodide of potassium (52): the paper was laid flat

on a platina spatula connected with the negative end of the

battery. All that part of the arrangement between the ice

vessel and the decomposing wire point, including both these,

was insulated, so that no electricity might pass through the

latter which had not traversed the former also.

ÆTHERFORCE

Conduction by Ice

43

162. Under these circumstances, it was found that a pale

brown spot of iodine was slowly formed under the decomposing

platina point, thus indicating that ice could conduct a little of

the electricity evolved by a voltaic battery charged up to the

degree of intensity indicated by the electrometer. But it is

quite evident that notwithstanding the enormous quantity of

electricity which the battery could furnish, it was, under present

circumstances, a very inferior instrument to the ordinary

machine ;

for the latter could send as much through the ice as it

could carry, being of a far higher intensity, i.e. able to open

the electrometer leaves half an inch or more (155, 156).

163. The decomposing wire and solution of iodide of potas-

sium were then removed, and replaced by a very delicate galvano-

meter; it was so nearly astatic, that it vibrated to and fro in

about sixty-three beats of a watch giving one hundred and fifty

beats in a minute. The same feebleness of current as before

was still indicated; the galvanometer needle was deflected, but it required to break and make contact three or four times (33) before the effect was decided.

164. The galvanometer being removed, two platina plates

were connected with the extremities of the wires, and the

tongue placed between them, so that the whole charge of the

battery, so far as the ice would let it pass, was free to go through

the tongue. Whilst standing on the stone floor, there was

shock, etc., but when insulated, I could feel no sensation. I

think a frog would have been scarcely, if at all, affected.

165. The ice was now removed, and experiments made with

other solid bodies, for which purpose they were placed under the

end of the decomposing wire instead of the solution of iodide of

potassium (161). For instance, a piece of dry iodide of potassium

was placed on the spatula connected with the negative pole of

the battery, and the point of the decomposing wire placed upon

it, whilst the positive end of the battery communicated with the

A latter.

brown spot of iodine very slowly appeared, indi-

cating the passage of a little electricity, and agreeing in that

respect with the results obtained by the use of the electrical

machine (157). When the galvanometer was introduced into

the circuit at the same time with the iodide, it was with

difficulty that the action of the current on it could be rendered

sensible.
A 166. piece of common salt previously fused and solidified
being introduced into the circuit was sufficient almost entirely to destroy the action on the galvanometer. Fused and cooled

C 576

ÆTHERFORCE

44

Faraday's Researches

chloride of lead produced the same effect. The conducting power of these bodies, when fluid, is very great (131, 138).
167. These effects, produced by using the common machine
and the voltaic battery, agree therefore with each other, and with the law laid down in this paper (130); and also with the opinion I have supported, in the First Part of these Researches,
of the identity of electricity derived from different sources (96). 1 68. The effect of heat in increasing the conducting power
of many substances, especially for electricity of high tension, is well known. I have lately met with an extraordinary case of
this kind, for electricity of low tension, or that of the voltaic
pile, and which is in direct contrast with the influence of heat
upon metallic bodies, as observed and described by Sir Humphry
1
Davy. 169. The substance presenting this effect is sulphuret of
silver. It was made by fusing a mixture of precipitated silver and sublimed sulphur, removing the film of silver by a file
from the exterior of the fused mass, pulverising the sulphuret, mingling it with more sulphur, and fusing it again in a green glass tube, so that no air should obtain access during the process. The surface of the sulphuret being again removed by a file or knife, it was considered quite free from uncombined silver.
170. When a piece of this sulphuret, half an inch in thick-
ness, was put between surfaces of platina, terminating the poles
of a voltaic battery of twenty pairs of four-inch plates, a galvanometer being also included in the circuit, the needle was
slightly deflected, indicating a feeble conducting power. On
pressing the platina poles and sulphuret together with the fingers, the conducting power increased as the whole became
warm. On applying a lamp under the sulphuret between the
poles, the conducting power rose rapidly with the heat, and at last the gahanometer needle jumped into a fixed position, and the sulphuret was found conducting in the manner of a metal.
On removing the lamp and allowing the heat to fall, the effects
were reversed, the needle at first began to vibrate a little, then gradually left its transverse direction, and at last returned to a position very nearly that which it would take when no current
was passing through the galvanometer. 171. Occasionally, when the contact of the sulphuret with the
platina poles was good, the battery freshly charged, and the commencing temperature not too low, the mere current of electricity from the battery was sufficient to raise the temperature
1 Philosophical Transactions, 1821, p. 431.

ÆTHERFORCE

Increase of Conducting Power by Heat 45

of the sulphuret; and then, without any application of extraneous heat, it went on increasing conjointly in temperature
and conducting power, until the cooling influence of the air limited the effects. In such cases it was generally necessary to cool the whole purposely, to show the returning series of

phenomena. 172. Occasionally, also, the effects would sink of themselves,
and could not be renewed until a fresh surface of the sulphuret had been applied to the positive pole. This was in consequence of peculiar results of decomposition, to which I shall have occasion to revert in the section on Electro-chemical Decom-

position, and was conveniently avoided by inserting the ends of two pieces of platina wire into the opposite extremities of a portion of sulphuret fused in a glass tube, and placing this arrangement between the poles of the battery.
173. The hot sulphuret of silver conducts sufficiently well to give a bright spark with charcoal, etc., etc., in the manner of a
metal.

174. The native grey sulphuret of silver, and the ruby silver

ore, both presented the same phenomena. The native malleable

sulphuret of silver presented precisely the same appearances

as the artificial sulphuret.
175. There is no other body with which I am acquainted,

that, like sulphuret of silver, can compare with metals in con-

ducting power for electricity of low tension when hot, but which,

unlike them, during cooling, loses in power, whilst they, on the

contrary, gain. Probably, however, many others may, when

sought for, be found.

176. The proto-sulphuret of iron, the native per-sulphuret

of iron, arsenical sulphuret of iron, native yellow sulphuret of

copper and iron, grey artificial sulphuret of copper, artificial

sulphuret of bismuth, and artificial grey sulphuret of tin, all

conduct the voltaic battery current when cold, more or less,

some giving sparks like the metals, others not being sufficient

for that high effect. They did not seem to conduct better

when heated

than before ;

but I had not time to enter accurately

into the investigation of this point. Almost all of them became

much heated by the transmission of the current, and present

some very interesting phenomena in that respect. The sulphuret

of antimony does not conduct the same current sensibly either

hot or cold, but is amongst those bodies acquiring conducting

power when fused (138). The sulphuret of silver and perhaps

some others decompose whilst in the solid state; but the

ÆTHERFORCE

46

Faraday's Researches

phenomena of this decomposition will be reserved for its proper

place in the next series of these Researches.

177. Notwithstanding the extreme dissimilarity between

sulphuret of silver and gases or vapours, I cannot help suspect-

ing the action of heat upon them to be the same, bringing them

all into the same class as conductors of electricity, although with

those great differences in degree which are found to exist
under common circumstances. When gases are heated, they increase in conducting power, both for common and voltaic electricity (7); and it is probable that if we could compress and
condense them at the same time, we should still further increase

their conducting power. Cagniard de la Tour has shown that

a substance, for instance water, may be so expanded by heat

whilst in the liquid state, or condensed whilst in the vaporous

state, that the two states shall coincide at one point, and the

transition from one to the other be so gradual that no line of

demarcation

can

be

pointed

out x ;

that,

in

fact,

the

two

states

shall become one; which one state presents us at different times with differences in degree as to certain properties and

relations; and which differences are, under ordinary circum-

stances, so great as to be equivalent to two different states. 178. I cannot but suppose at present that at that point where

the liquid and the gaseous state coincide, the conducting pro-

perties are the same for both; but that they diminish as the

expansion of the matter into a rarer form takes place by the

removal of the necessary pressure; still, however, retaining, as might be expected, the capability of having what feeble con-

ducting power remains increased by the action of heat.

179. I venture to give the following summary of the conditions

of electric conduction in bodies, not however without fearing

that I may have omitted some important points.
1 80. All bodies conduct electricity in the same manner from

metals to lac and gases, but in very different degrees.

181. Conducting power is in some bodies powerfully in-

creased by heat, and in others diminished, yet without our per-

ceiving any accompanying essential electrical difference, eithei

in the bodies or in the changes occasioned by the electricity

conducted.

A 182. numerous class of bodies, insulating electricity of low
intensity, when solid, conduct it very freely when fluid, and are

then decomposed by it.

183. But there are many fluid bodies which do not sensibly

1 Annales de Chimie, xxi. pp. 127, 178.

ÆTHERFORCE

Electro-Chemical Decomposition 47
conduct electricity of this low intensity; there are some which conduct it and are not decomposed; nor is fluidity essential to
1
decomposition.
184. There is but one body yet discovered 2 which, insulating a voltaic current when solid, and conducting it when fluid, is not decomposed in the latter case (150).
185. There is no strict electrical distinction of conduction which can, as yet, be drawn between bodies supposed to be elementary, and those known to be compounds.
April 15, 1833.

Ill 3

5. ON ELECTRO-CHEMICAL DECOMPOSITION. NEW ^[ i. CON-
DITIONS OF ELECTRO-CHEMICAL DECOMPOSITION. ^j ii. INFLUENCE OF WATER IN ELECTRO-CHEMICAL DECOMPO-
SITION. ^[ iii. THEORY OF ELECTRO-CHEMICAL DECOM-
POSITION

5. On Electro-chemical Decomposition 4

186. I HAVE in a recent series of these Researches (i) proved

my (to

own satisfaction, at least) the identity of electricities

derived from different sources, and have especially dwelt upon

the proofs of the sameness of those obtained by the use of the

common electrical machine and the voltaic battery.

187. The great distinction of the electricities obtained from

these two sources is the very high tension to which the small

quantity obtained by aid of the machine may be raised, and

the enormous quantity (107, 112) in which that of compara-

tively low tension, supplied by the voltaic battery, may be pro-

cured; but as their actions, whether magnetical, chemical, or

of any other nature, are essentially the same (96), it appeared

evident that we might reason from the former as to the manner

of action of the latter; and it was, to me, a probable conse-

quence, that the use of electricity of such intensity as that

afforded by the machine, would, when applied to effect and

1 See the next part of these Experimental Researches. * It is just possible that this case may, by more delicate experiment,
hereafter disappear. 3 Fifth Series, original edition, vol. i. p. 127. 4 Refer to the note after paragraph 783. December 1838.

ÆTHERFORCE

48

Faraday's Researches

elucidate electro-chemical decomposition, show some new conditions of that action, evolve new views of the internal arrangements and changes of the substances under decomposition, and
perhaps give efficient powers over matter as yet undecomposed. 1 88. For the purpose of rendering the bearings of the different
parts of this series of researches more distinct, I shall divide
it into several heads.

Tf i. New conditions of Electro-chemical Decomposition
189. The tension of machine electricity causes it, however
small in quantity, to pass through any length of water, solutions, or other substances classing with these as conductors, as fast as it can be produced, and therefore, in relation to quantity, as fast as it could have passed through much shorter portions of the same conducting substance. With the voltaic battery the case is very different, and the passing current of electricity supplied by it suffers serious diminution in any substance, by considerable extension of its length, but especially in such bodies as those mentioned above.
190. I endeavoured to apply this facility of transmitting the current of electricity through any length of a conductor, to an investigation of the transfer of the elements in a decomposing body, in contrary directions, towards the poles. The general form of apparatus used in these experiments has been already described (48, 52); and also a particular experiment (55), in
which, when a piece of litmus paper and a piece of turmeric paper were combined and moistened in solution of sulphate of soda, the point of the wire from the machine (representing the positive pole) put upon the litmus paper, and the receiving point
from the discharging train (28, 52), representing the negative pole, upon the turmeric paper, a very few turns of the machine sufficed to show the evolution of acid at the former, and alkali at the latter, exactly in the manner effected by a volta-electric current.
191. The pieces of litmus and turmeric paper were now placed each upon a separate plate of glass, and connected by an insulated string four feet long, moistened in the same solution of sulphate of soda: the terminal decomposing wire points were
placed upon the papers as before. On working the machine,
the same evolution of acid and alkali appeared as in the former instance, and with equal readiness, notwithstanding that the places of their appearance were four feet apart from each other. Finally, a piece of string, seventy feet long, was used. It was

ÆTHERFORCE

Decomposition by a Single Pole 49
insulated in the air by suspenders of silk, so that the electricity passed through its entire length: decomposition took place exactly as in former cases, alkali and acid appearing at the two
extremities in their proper places.
192. Experiments were then made both with sulphate of soda and iodide of potassium, to ascertain if any diminution of decomposing effect was produced by such great extension as those just described of the moist conductor or body under
decomposition; but whether the contact of the decomposing
point connected with the discharging train was made with
turmeric paper touching the prime conductor, or with other turmeric paper connected with it through the seventy feet of
string, the spot of alkali for an equal number of turns of the machine had equal intensity of colour. The same results occurred at the other decomposing wire, whether the salt or the iodide were used; and it was fully proved that this great extension of the distance between the poles produced no effect whatever on the amount of decomposition, provided the same quantity of electricity were passed in both cases (113).
193. The negative point of the discharging train, the turmeric paper, and the string were then removed; the positive point was left resting upon the litmus paper, and the latter
A touched by a piece of moistened string held in the hand.
few turns of the machine evolved acid at the positive point as
freely as before.
194. The end of the moistened string, instead of being held
in the hand, was suspended by glass in the air. On working
the machine the electricity proceeded from the conductor through the wire point to the litmus paper, and thence away by the intervention of the string to the air, so that there was (as in the last experiment) but one metallic pole; still acid was evolved there as freely as in any former case.
195. When any of these experiments were repeated with
electricity from the negative conductor, corresponding effects were produced whether one or two decomposing wires were used. The results were always constant, considered in relation to the direction of the electric current.
196. These experiments were varied so as to include the action of only one metallic pole, but that not the pole connected with the machine. Turmeric paper was moistened in solution of sulphate of soda, placed upon glass, and connected with the discharging train (28) by a decomposing wire (48); a piece of wet string was hung from it, the lower extremity of which
ÆTHERFORCE

50

Faraday's Researches

was brought opposite a point connected with the positive prime conductor of the machine. The machine was then worked for
a few turns, and alkali immediately appeared at the point of the discharging train which rested on the turmeric paper. Corresponding effects took place at the negative conductor, of a machine.
197. These cases are abundantly sufficient to show that electrochemical decomposition does not depend upon the simultaneous action of two metallic poles, since a single pole might be used, decomposition ensue, and one or other of the elements liberated, pass to the pole, according as it was positive or negative. In considering the course taken by, and the final arrangement of, the other element, I had little doubt that I should find it had receded towards the other extremity, and that the air itself had acted as a pole, an expectation which was fully confirmed in the following manner.
A 198. piece of turmeric paper, not more than 0.4 of an inch

Fig. 8.

in length and 0.5 of an inch in width, was moistened with

sulphate of soda and placed upon the edge of a glass plate

opposite to, and about two inches from, a point connected

with the discharging train (fig. 8); a piece of tinfoil, resting

upon the same glass plate, was connected with the machine,

and also. with the turmeric paper, by a decomposing wire a

)^ The machine was then worked, the positive electricity

passing into the turmeric paper at the

point p, and out at the extremity n.

After forty or fifty turns of the machine,

Fig. 8a.

the extremity n was examined, and the two points or angles found deeply

coloured by the presence of free alkali (fig. 8a).

A 199.

similar piece of litmus paper, dipped in solution of

ÆTHERFORCE

No Metallic Poles Used

51

sulphate of soda w, fig. 9, was now supported upon the end of the discharging train a, and its extremity brought opposite
to a point p, connected with the conductor of the machine. After working the machine for a short time, acid was developed at both the corners towards the point, i.e. at both the corners receiving the electricities from the air. Every precaution was
taken to prevent this acid from being formed by sparks or

brushes passing through the air (58); and these, with the accompanying general facts, are sufficient to show that the acid was really the result of electro-chemical decomposition

(202).

200. Then a long piece of turmeric paper, large at one end

and pointed at the other, was moistened in the saline solution,

and immediately connected with the conductor of the machine,

so that its pointed extremity was opposite a point upon the
discharging train. When the machine was worked, alkali was

evolved at that point; and even when the discharging train

was removed, and the electricity left to be diffused and carried

off altogether by the air, still alkali was evolved where the

electricity left the turmeric paper.

201. Arrangements were then made in which no metallic

communication with the decomposing matter was allowed, but

both poles (if they might now be called by that name) formed

A of air only.

piece of turmeric paper a, fig. 10, and a piece

of litmus paper b, were dipped in solution of sulphate of soda,

put together so as to form one moist pointed conductor, and

supported on wax between two needle points, one p connected

by a wire with the conductor of the machine, and the other, ,

with the discharging train. The interval in each case between

the points was about half an inch: the positive point p was

ÆTHERFORCE

52

Faraday's Researches

opposite the litmus paper; the negative point n opposite the turmeric. The machine was then worked for a time, upon which evidence of decomposition quickly appeared, for the point of the litmus b became reddened from acid evolved there,

Fig. 10.
and the point of the turmeric a red from a similar and simultaneous evolution of alkali.
2os. Upon turning the paper conductor round, so that the litmus point should now give off the positive electricity, and the turmeric point receive it, and working the machine for a short time, both the red spots disappeared, and as on continuing the action of the machine no red spot was re-formed at the
litmus extremity, it proved that in the first instance (199) the effect was not due to the action of brushes or mere electric dis-
charges causing the formation of nitric acid from the air (58). 203. If the combined litmus and turmeric paper in this ex-
periment be considered as constituting a conductor independent of the machine or the discharging train, and the final places of the elements evolved be considered in relation to this con-
ductor, then it will be found that the acid collects at the negative or receiving end or pole of the arrangement, and the alkali at the positive or delivering extremity.
204. Similar litmus and turmeric paper points were now placed upon glass plates, and connected by a string six feet long, both string and paper being moistened in solution of
sulphate of soda; a needle point connected with the machine was brought opposite the litmus paper point, and another needle point connected with the discharging train brought
opposite the turmeric paper. On working the machine, acid
appeared on the litmus, and alkali on the turmeric paper; but
the latter was not so abundant as in former cases, for much of the electricity passed off from the string into the air, and
diminished the quantity discharged at the turmeric point.
ÆTHERFORCE

Polar Decompositions in Air

53

205. Finally, a series of four small compound conductors, consisting of litmus and turmeric paper (fig. n) moistened in solution of sulphate of soda, were supported on glass rods, in a line at a little distance from each other, between the points p and n of the machine and discharging train, so that the elec-
tricity might pass in succession through them, entering in at the litmus points b, b, and passing out at the turmeric points a,
a. On working the machine carefully, so as to avoid sparks and

Fig. ii.

brushes (58), I soon obtained evidence of decomposition in each of the moist conductors, for all the litmus points exhibited free acid, and the turmeric points equally showed free alkali.
206. On using solutions of iodide of potassium, acetate of
lead, etc., similar effects were obtained; but as they were all consistent with the results above described, I refrain from

describing the appearances minutely. 207. These cases of electro-chemical decomposition are in
their nature exactly of the same kind as those affected under

ordinary circumstances by the voltaic battery, notwithstanding
the great differences as to the presence or absence, or at least as to the nature of the parts usually called poles; and also of the final situation of the elements eliminated at the electrified

boundary surfaces (203). They indicate at once an internal

action of the parts suffering decomposition, and appear to show

that the power which is effectual in separating the elements is

exerted there, and not at the poles. But I shall defer the

consideration of this point for a short time (229, 254), that I

may previously consider another supposed condition of electro-

chemical

1
decomposition.

1 I find (since making and describing these results) from a note to Sir
Humphry Davy's paper in the Philosophical Transactions, 1807, p. 31, that
that philosopher, in repeating Wollaston's experiment of the decomposition
of water by common electricity (63, 66) used an arrangement somewhat like some of those I have described. He immersed a guarded platina point
connected with the machine in distilled water, and dissipated the electricity
from the water into the air by moistened filaments of cotton. In this way he states that he obtained oxygen and hydrogen separately from each other. This experiment, had I known of it, ought to have been quoted in an earlier part of these Researches (78) ; but it does not remove any of the objections I have made to the use of Wollaston's apparatus as a test of
true chemical action (67).

ÆTHERFORCE

54

Faraday's Researches

^f ii. Influence of Water in Electro-chemical Decomposition

208. It is the opinion of several philosophers, that the presence of water is essential in electro-chemical decomposition, and

also for the evolution of electricity in the voltaic battery itself.

As the decomposing cell is merely one of the cells of the battery,

into which particular substances are introduced for the purpose

of experiment, it is probable that what is an essential condition

in the one case is more or less so in the other. The opinion,

therefore, that water is necessary to decomposition, may have

been founded on the statement made by Sir Humphry Davy,
that " there are no fluids known, except such as contain water,

which are capable of being made the medium of connection between the metals or metal of the voltaic apparatus: " l and again, " when any substance rendered fluid by heat, consisting

of water, oxygen, and inflammable or metallic matter, is exposed

to those wires, similar phenomena (of decomposition) occur." 2

209. This opinion has, I think, been shown by other philo-

sophers not to be accurate, though I do not know where to

refer for a contradiction of it. Sir Humphry Davy himself

said

in

3
i8oi,

that

dry

nitre,

caustic

potash

and

soda

are

con-

ductors of galvanism when rendered fluid by a high degree of

heat; but he must have considered them, or the nitre at least,

as not suffering decomposition, for the statements above were
made by him eleven years subsequently. In 1826 he also
pointed out, that bodies not containing water, as fused litharge and chlorate of polassa, were sufficient to form, with platina and zinc, powerful electromotive circles; 4 but he is here speaking of the production of electricity in the pile, and not of its
effects when evolved; nor do his words at all imply that any
correction of his former distinct statements relative to decom-

position was required.
210. I may refer to the last part of these Experimental
Researches (116, 138) as setting the matter at rest, by proving that there are hundreds of bodies equally influential with water

in this respect; that amongst binary compounds, oxides, chlorides, iodides, and even sulphurets (138) were effective; and that amongst more complicated compounds, cyanides and salts, of equal efficacy, occurred in great numbers (138).

1 Elements of Chemical Philosophy, p. 169, etc. 3 Journal of the Royal Institution, 1802, p. 53.
* Philosophical Transactions, 1826, p. 406.

2 Ibid. pp. 144, 145.

ÆTHERFORCE

Electro-Chemical Decomposition 55

211. Water, therefore, is in this respect merely one of a very numerous class of substances, instead of being the only one and essential ; and it is of that class one of the worst as to its

capability of facilitating conduction and suffering decomposition.
The reasons why it obtained for a time an exclusive character

which it so little deserved are evident, and consist, in the

general necessity of a fluid condition (130); in its being the

only one of this class of bodies existing in the fluid state at
common temperatures ; its abundant supply as the great natural

solvent; and its constant use in that character in philosophical

investigations, because of its having a smaller interfering,

injurious or complicating action upon the bodies, either dis-

solved or evolved, than any other substance.

212. The analogy of the decomposing or experimental cell

to the other cells of the voltaic battery, renders it nearly certain

that any of those substances which are decomposable when

my fluid, as described in

last paper (138), would, if they could

be introduced between the metallic plates of the pile, be equally

effectual with water, if not more so. Sir Humphry Davy found

that litharge and chlorate of potassa were thus effectual. 1 I

have constructed various voltaic arrangements, and found the
above conclusion to hold good. When any of the following

substances in a fused state were interposed between copper

and platina, voltaic action more or less powerful was produced.

Nitre; chlorate of potassa; carbonate of potassa; sulphate of

soda; chloride of lead, of sodium, of bismuth, of calcium;

iodide of lead; oxide of bismuth; oxide of lead: the electric
current was in the same direction as if acids had acted upon
the metals. When any of the same substances, or phosphate of soda, were made to act on platina and iron, still more power-
ful voltaic combinations of the same kind were produced.
When either nitrate of silver or chloride of silver was the fluid

substance interposed, there was voltaic action, but the electric current was in the reverse direction.

^| iii. Theory of Electro-chemical Decomposition
213. The extreme beauty and value of electro-chemical decompositions have given to that power which the voltaic pile possesses of causing their occurrence an interest surpassing that of any other of its properties; for the power is not only
intimately connected with the continuance, if not with the
1
Philosophical Transactions, 1826, p. 406.
ÆTHERFORCE

56

production, of the electrical phenomena, but it has furnished us with the most beautiful demonstrations of the nature of

many compound bodies; has in the hands of Becquerel been
employed in compounding substances; has given us several new combinations, and sustains us with the hope that when
thoroughly understood it will produce many more. 214. What may be considered as the general facts of electro-
chemical decomposition are agreed to by nearly all who have written on the subject. They consist in the separation of the
decomposable substance acted upon into its proximate or sometimes ultimate principles, whenever both poles of the pile are
in contact with that substance in a proper condition; in the

evolution of these principles at distant points, i.e. at the poles

of the pile, where they are either finally set free or enter into

union with the substance of the poles; and in the constant

determination of the evolved elements or principles to particular

poles according to certain well ascertained laws.
215. But the views of men of science vary much as to the

nature of the action by which these effects are produced; and as it is certain that we shall be better able to apply the power

when we really understand the manner in which it operates,

this difference of opinion is a strong inducement to further

inquiry. I have been led to hope that the following investiga-

tions might be considered, not as an increase of that which is

doubtful, but a real addition to this branch of knowledge.

216. It will be needful that I briefly state the views of electro-

chemical decomposition already put forth, that their present

contradictory and unsatisfactory state may be seen before I give that which seems to me more accurately to agree with
facts; and I have ventured to discuss them freely, trusting that

I should give no offence to their high-minded authors; for I

felt convinced that if I were right, they would be pleased that

their views should serve as stepping-stones for the advance of

science; and that if I were wrong, they would excuse the zeal

which misled me, since it was exerted for the service of that

great cause whose prosperity and progress they have desired.

217. Grotthuss, in the year 1805, wrote expressly on the

decomposition

of

liquids

by

voltaic

1
electricity.

He considers

the pile as an electric magnet, i.e. as an attractive and repulsive

agent; the poles having attractive and repelling powers. The

pole from whence resinous electricity issues attracts hydrogen

and repels oxygen, whilst that from which vitreous electricity

1 Annales de Chimie, 1806, torn. Iviii. p. 64.

ÆTHERFORCE

Electro-Chemical Decomposition 57

proceeds attracts oxygen and repels hydrogen; so that each of the elements of a particle of water, for instance, is subject to an attractive and a repulsive force, acting in contrary directions, the centres of action of which are reciprocally opposed. The action of each force in relation to a molecule of water situated in the course of the electric current is in the

inverse ratio of the square of the distance at which it is exerted,

thus giving (it is stated) for such a molecule a constant force*
He explains the appearance of the elements at a distance from

each other by referring to a succession of decompositions and

recompositions

occurring

amongst

the

intervening

2 particles,

and he thinks it probable that those which are about to separate

at the poles unite to the two electricities there, and in consequence

become

3 gases.

218. Sir Humphry Davy's celebrated Bakerian Lecture on

some chemical agencies of electricity was read in November

1806, and is almost entirely occupied in the consideration of

electro-chemical decompositions. The facts are of the utmost

value, and, with the general points established, are universally

known. The mode of action by which the effects take place

is stated very generally, so generally, indeed, that probably a

dozen precise schemes of electro-chemical action might be drawn

up, differing essentially from each other, yet all agreeing with

the statement there given.
219. When Sir Humphry Davy uses more particular ex-

pressions, he seems to refer the decomposing effects to the

attractions pression of

of

the
"

poles.

facts given

This is the case at pp. 28 and 29

in of

the the

" general exPhilosophical

Transactions for 1807, also at p. 30. Again at p. 160 of the

Elements of Chemical Philosophy, he speaks of the great attract-
ing powers of the surfaces of the poles. He mentions the pro-

bability of a succession of decompositions and recompositions throughout the fluid, agreeing in that respect with Grotthuss; 4

and supposes that the attractive and repellent agencies may be

communicated from the metallic surfaces throughout the whole

of the menstruum,5 being communicated from one particle to

another

particle

of

the

same

6
kind,

and

diminishing

in

strength

from the place of the poles to the middle point, which is neces-

sarily neutral. 7 In reference to this diminution of power at

1 Annales de Chimie, pp. 66, 67, also torn. Ixiii. p. 20.

* Ibid, torn Iviii. p. 68, torn. Ixiii. p. 20. s Ibid, torn Ixiii. p. 34.

4
Philosophical Transactions, 1807, pp. 29, 30.

* Ibid. p. 39.

* Ibid. p. 29.

7 Ibid. p. 42.

ÆTHERFORCE

58

Faraday's Researches

increased distances from the poles, he states that in a circuit
of ten inches of water, solution of sulphate of potassa placed four inches from the positive pole did not decompose; whereas
when only two inches from that pole, it did render up its
elements. 1

220. When in 1826 Sir Humphry Davy wrote again on this

subject, he stated that he found nothing to alter in the funda-

mental

theory

laid

down

in

the

original

2
communication,

and

uses the terms attraction and repulsion apparently in the same

sense as before.3

221. Messrs. Riffault and Chompre experimented on this

subject in 1807. They came to the conclusion that the voltaic

current caused decompositions throughout its whole course in

the humid conductor, not merely as preliminary to the recom-

positions spoken of by Grotthuss and Davy, but producing final

separation of the elements in the course of the current, and

elsewhere than at the poles. They considered the negative

current as collecting and carrying the acids, etc., to the positive

pole, and the positive current as doing the same duty with the

bases, and collecting them at the negative pole. They likewise

consider the currents as more powerful the nearer they are to

their respective poles, and state that the positive current is superior in power to the negative current.4

222. M. Biot is very cautious in expressing an opinion as to

the cause of the separation of the elements of a compound

5
body.

But as far as the effects can be understood, he refers

them to the opposite electrical states of the portions of the

decomposing substance in the neighbourhood of the two poles.

The fluid is most positive at the positive pole: that state

gradually diminishes to the middle distance, where the fluid is

neutral or not electrical; but from thence to the negative pole

it

becomes

more

and

more

6
negative.

When a particle of

salt is decomposed at the negative pole, the acid particle is

considered as acquiring a negative electrical state from the pole,

stronger than that of the surrounding undecomposed particles,

and is therefore repelled from amongst them, and from out of

that portion of the liquid towards the positive pole, towards

which also it is drawn by the attraction of the pole itself and

the

particles

of

positive

undecomposed

fluid

around

7 it.

1 Philosophical Transactions, 1807, p. 42.

* Ibid. 1826, p. 383.

* Ibid. pp. 389, 407, 415.

* Annales de Chitnie, 1807, torn. Ixiii. p. 83, etc.

* Precis Elcmentaire de Physique, 3me edition, 1824, torn. i. p. 641.

* Ibid. p. 637.

' Ibid. pp. 641, 642.

ÆTHERFORCE

Electro-Chemical Decomposition 59

223. M. Biot does not appear to admit the successive de-

compositions and recompositions spoken of by Grotthuss, Davy,

etc.,

etc. ;

but seems to consider the substance whilst in transit

as combined with, or rather attached to, the electricity for the

1
time,

and

though

it

communicates

this

electricity

to

the

sur-

rounding undecomposed matter with which it is in contact, yet

it retains during the transit a little superiority with respect to

that kind which it first received from the pole, and is, by virtue

of that difference, carried forward through the fluid to the

2
opposite pole.

224. This theory implies that decomposition takes place at

both poles upon distinct portions of fluid, and not at all in the

intervening parts. The latter serve merely as imperfect con-

ductors, which, assuming an electric state, urge particles elec-

trified more highly at the poles through them in opposite

directions, by virtue of a series of ordinary electrical attractions

and

3
repulsions.

225. M. A. de la Rive investigated this subject particularly,

and

published

a

paper

on

it

in

4
1825.

He thinks those who

have referred the phenomena to the attractive powers of the

poles, rather express the general fact than give any explication
of it. He considers the results as due to an actual combination

of the elements, or rather of half of them, with the electricities

passing from the poles in consequence of a kind of play of

affinities

between

the

matter

and

5 electricity.

The current

from the positive pole combining with the hydrogen, or the

bases it finds there, leaves the oxygen and acids at liberty, but

carries the substances it is united with across to the negative

pole, where, because of the peculiar character of the metal

as

a

6
conductor,

it

is

separated

from

them,

entering

the

metal

and leaving the hydrogen or bases upon its surface. In the

same manner the electricity from the negative pole sets the

hydrogen and bases which it finds there, free, but combines

with the oxygen and acids, carries them across to the positive

pole, and there deposits them. 7 In this respect M. de la Rive's
hypothesis accords in part with that of MM. Riffault and

Chompre (221).

226. M. de la Rive considers the portions of matter which

are

decomposed

to

be

those

contiguous

to

both

8
poles.

He

1 Freds Elementaire de Physique, 3me 6dition, 1824, torn. i. p. 636.

2 Ibid. p. 642.

* Ibid. pp. 638, 642.

4 Annales de Chimie, torn, xxviii. p. 190.

. * Ibid. pp. 200, 202.

* Ibid. p. 202.

' Ibid. p. 201.

* Ibid. pp. 197, 198.

ÆTHERFORCE

60

Faraday's Researches

does not admit with others the successive decompositions and

recompositions in the whole course of the electricity through the humid conductor/ but thinks the middle parts are in them-

selves unaltered, or at least serve only to conduct the two

contrary currents of electricity and matter which set off from

the

opposite

2
poles.

The decomposition, therefore, of a particle

of water, or a particle of salt, may take place at either pole, and when once effected, it is final for the time, no recombina-

tion taking place, except the momentary union of the transferred

particle with the electricity be so considered.
227. The latest communication that I am aware of on the

subject is by M. Hachette:

its

date

is

October

3
1832 .

It is

incidental to the description of the decomposition of water by

the magneto-electric currents (82). One of the results of the

experiment is, that "it is not necessary, as has been supposed,

that for the chemical decomposition of water, the action of the

two electricities, positive and negative, should be simultaneous."

228. It is more than probable that many other views of

electro-chemical decomposition may have been published, and

perhaps amongst them some which, differing from those above,
might, even in my own opinion, were I acquainted with them,

my obviate the necessity for the publication of

views. If such

my be the case, I have to regret

ignorance of them, and apologise

to the authors.

229. That electro-chemical decomposition does not depend upon any direct attraction and repulsion of the poles (meaning thereby the metallic terminations either of the voltaic batter)', or ordinary electrical machine arrangements (48), upon the elements in contact with or near to them, appeared very evident from the experiments made in air (198, 201, etc.), when the substances evolved did not collect about any poles, but, in obedience to the direction of the current, were evolved, and I
would say ejected, at the extremities of the decomposing substance. But notwithstanding the extreme dissimilarity in the character of air and metals, and the almost total difference existing between them as to their mode of conducting electricity, and becoming charged with it, it might perhaps still be contended, although quite hypothetically, that the bounding portions of air were now the surfaces or places of attraction, as the metals had been supposed to be before. In illustration of this and

1 Annales de Chimie, torn, xxviii. pp. 192, 199.

* Ibid. p. 200.

3 Ibid. torn. li. p. 73.

ÆTHERFORCE

Electro-Chemical Decomposition 6r

other points, I endeavoured to devise an arrangement by which I could decompose a body against a surface of water, as well as against air or metal, and succeeded in doing so unexceptionably in the following manner. As the experiment for very
natural reasons requires many precautions to be successful,
and will be referred to hereafter in illustration of the views I

shall venture to give, I must describe it minutely.

A 230.

glass basin (fig. 12), four inches in diameter and

four inches deep, had a division of mica a, fixed across the upper

part so as to descend one inch and a half below the edge, and

be perfectly water-tight at the sides: a

plate of platina b, three inches wide,
was put into the basin on one side of the division a, and retained there by a

glass block below, so that any gas

produced by it in a future stage of the

experiment should not ascend beyond

the mica, and cause currents in the

A liquid on that side.

strong solution

of sulphate of magnesia was carefully

poured without splashing into the basin,

until it rose a little above the lower

edge of the mica division a, great care being taken that the glass or mica on

the unoccupied or c side of the division

in the figure should not be moistened by

A agitation of the solution above the level to which it rose.

thin

piece of clean cork, well wetted in distilled water, was then care-

fully and lightly placed on the solution at the c side, and distilled

water poured gently on to it until a stratum the eighth of an

inch in thickness appeared over the sulphate of magnesia;

all was then left for a few minutes, that any solution adhering

to the cork might sink away from it, or be removed by the water on which it now floated; and then more distilled water

was added in a similar manner, until it reached nearly to the

top of the glass. In this way solution of the sulphate occupied
the lower part of the glass, and also the upper on the right-hand side of the mica; but on the left-hand side of the division a stratum of water from c to d, one inch and a half in depth, reposed upon it, the two presenting, when looked through
A horizontally, a comparatively definite plane of contact.
second platina pole e was arranged so as to be just under the surface of the water, in a position nearly horizontal, a little
ÆTHERFORCE

62

Faraday's Researches

inclination being given to it, that gas evolved during decomposition might escape: the part immersed was three inches and a half long by one inch wide, and about seven-eighths of an inch of water intervened between it and the solution of sulphate of
magnesia.
231. The latter pole e was now connected with the negative end of a voltaic battery, of forty pairs of plates four inches square, whilst the former pole b was connected with the positive end. There was action and gas evolved at both poles; but
from the intervention of the pure water, the decomposition was very feeble compared to what the battery would have effected in a uniform solution. After a little while (less than a
minute), magnesia also appeared at the negative side: it did not make its appearance at the negative metallic pole, but in the water, at the plane where the solution and the water met; and on looking at it horizontally, it could be there perceived lying in the water upon the solution, not rising more than the fourth of an inch above the latter, whilst the water between it and
the negative pole was perfectly clear. On continuing the action,
the bubbles of hydrogen rising upwards from the negative pole impressed a circulatory movement on the stratum of water, upwards in the middle, and downwards at the side, which
gradually gave an ascending form to the cloud of magnesia in the part just under the pole, having an appearance as if it were there attracted to it; but this was altogether an effect
of the currents, and did not occur until long after the phenomena looked for were satisfactorily ascertained.
232. After a little while the voltaic communication was
broken, and the platina poles removed with as little agitation as possible from the water and solution, for the purpose of examining the liquid adhering to them. The pole e, when touched by turmeric paper, gave no traces of alkali, nor could anything but pure water be found upon it. The pole b, though drawn through a much greater depth and quantity of fluid, was found so acid as to give abundant evidence to litmus paper, the tongue, and other tests. Hence there had been no interference
of alkaline salts in any way, undergoing first decomposition, and then causing the separation of the magnesia at a distance from the pole by mere chemical agencies. This experiment was repeated again and again, and always successfully.
233. As, therefore, the substances evolved in cases of electro-
chemical decomposition may be made to appear against air (201, 205), which, according to common language, is not a

ÆTHERFORCE

Electro-Chemical Decomposition 63

conductor, nor is decomposed, or against water (231), which is a conductor, and can be decomposed, as well as against the metal poles, which are excellent conductors, but undecom-

posable, there appears but little reason to consider the pheno-
mena generally, as due to the attraction or attractive powers of the latter, when used in the ordinary way, since similar

attractions can hardly be imagined in the former instances.

234. It may be said that the surfaces of air or of water in

these cases become the poles, and exert attractive powers; but what proof is there of that, except the fact that the matters evolved collect there, which is the point to be explained, and
cannot be justly quoted as its own explanation? Or it may be
said, that any section of the humid conductor, as that in the

present case, where the solution and the water meet, may be
considered as representing the pole. But such does not appear
to me to be the view of those who have written on the subject,

certainly not of some of them, and is inconsistent with the

supposed laws which they have assumed, as governing the

diminution of power at increased distances from the poles.

235. Grotthuss, for instance, describes the poles as centres
of attractive and repulsive forces (217), these forces varying inversely as the squares of the distances, and says, therefore, that a particle placed anywhere between the poles will be acted upon by a constant force. But the compound force, resulting from such a combination as he supposes, would be anything but a constant force; it would evidently be a force greatest at the poles, and diminishing to the middle distance. Grotthuss

my is right, however, in the fact, according to

experiments

(238, 241), that the particles are acted upon by equal force

everywhere in the circuit, when the conditions of the experi-

ment are the simplest possible; but the fact is against his

theory, and is also, I think, against all theories that place the

decomposing effect in the attractive power of the poles.
236. Sir Humphry Davy, who also speaks of the diminution
of power with increase of distance from the poles 1 (219), supposes that when both poles are acting on substances to decompose
them, still the power of decomposition diminishes to the middle
distance. In this statement of fact he is opposed to Grotthuss, and quotes an experiment in which sulphate of potassa, placed at different distances from the poles in a humid conductor of
constant length, decomposed when near the pole, but not when at a distance. Such a consequence would necessarily result

1
Philosophical Transactions, 1807, p. 42.

ÆTHERFORCE

64

Faraday's Researches

theoretically from considering the poles as centres of attraction and repulsion; but I have not found the statement borne out by other experiments (241); and in the one quoted by him
the effect was doubtless due to some of the many interfering
causes of variation which attend such investigations.
A 237. glass vessel had a platina plate fixed perpendicularly
across it, so as to divide it into two cells: a head of mica was

fixed over it, so as to collect the gas it might evolve during

experiments; then each cell, and the space beneath the mica,

was filled with dilute sulphuric acid. Two poles were provided,

consisting each of a platina wire terminated by a plate of the

same metal; each was fixed into a tube passing through its

upper end by an air-tight joint, that it might be moveable, and

yet that the gas evolved at it might be collected. The tubes

were filled with the acid, and one immersed in each cell. Each

platina pole was equal in surface to one side of the dividing

plate in the middle glass vessel, and the whole might be con-

sidered as an arrangement between the poles of the battery of

a humid decomposable conductor divided in the middle by the

interposed platina diaphragm. It was easy, when required, to

draw one of the poles further up the tube, and then the platina

diaphragm was no longer in the middle of the humid conductor.

But whether it were thus arranged at the middle, or towards

one side, it always evolved a quantity of oxygen and hydrogen

equal

to

that

evolved

by

both

the

extreme

1
plates.

238. If the wires of a galvanometer be terminated by plates, and these be immersed in dilute acid, contained in a regularly formed rectangular glass trough, connected at each end with a voltaic battery by poles equal to the section of the fluid, a part of the electricity will pass through the instrument and cause a certain deflection. And if the plates are always retained at the same distance from each other and from the sides of the trough, are always parallel to each other, and uniformly placed relative to the fluid, then, whether they are immersed near the middle

of the decomposing solution, or at one end, still the instrument will indicate the same deflection, and consequently the same

electric influence.

239. It is very evident, that when the width of the decomposing conductor varies, as is always the case when mere wires

or plates, as poles, are dipped into or are surrounded by solution,

1 There are certain precautions, in this and such experiments, which can only be understood and guarded against by a knowledge of the phenomena to be described in the first part of the Fourth Part of these Researches.

ÆTHERFORCE

Constant Chemical Action of Electricity 65
no constant expression can be given as to the action upon a single particle placed in the course of the current,, nor any conclusion of use, relative to the supposed attractive or repulsive force of the poles, be drawn. The force will vary as the distance from the pole varies; as the particle is directly between the poles, or more or less on one side; and even as it is nearer to or further from the sides of the containing vessels, or as the shape of the vessel itself varies; and, in fact, by making variations in the form of the arrangement, the force upon any single
particle may be made to increase, or diminish, or remain constant,
whilst the distance between the particle and the pole shall remain
the same; or the force may be made to increase, or diminish,
or remain constant, either as the distance increases or as it
diminishes.
240. From numerous experiments, I am led to believe the
following general expression to be correct; but I purpose
examining it much further, and would therefore wish not to be considered at present as pledged to its accuracy. The sum of chemical decomposition is constant for any section taken across
a decomposing conductor, uniform in its nature, at whatever
distance the poles may be from each other or from the section; or however that section may intersect the currents, whether
directly across them, or so oblique as to reach almost from pole to pole, or whether it be plane, or curved, or irregular in the utmost degree; provided the current of electricity be retained constant in quantity (113), and that the section passes through every part of the current through the decomposing conductor.
241. I have reason to believe that the statement might be made still more general, and expressed thus : That for a constant
quantity of electricity, whatever the decomposing conductor may be, whether water, saline solutions, acids, fused bodies, etc., the amount
of electro-chemical action is also a constant quantity, i.e. would always be equivalent to a standard chemical effect founded upon ordinary chemical affinity. I have this investigation in hand, with several others, and shall be prepared to give it in the next part but one of these Researches.
242. Many other arguments might be adduced against the
hypotheses of the attraction of the poles being the cause of electro-chemical decomposition; but I would rather pass on to the view I have thought more consistent with facts, with this single remark; that if decomposition by the voltaic battery depended upon the attraction of the poles, or the parts about them, being stronger than the mutual attraction of the particles
ÆTHERFORCE

66

Faraday's Researches

separated, it would follow that the weakest electrical attraction was stronger than, if not the strongest, yet very strong chemical attraction, namely, such as exists between oxygen and hydrogen, potassium and oxygen, chlorine and sodium, acid and alkali, etc., a consequence which, although perhaps not impossible, seems in the present state of the subject very unlikely.
243. The view which M. de la Rive has taken (225), and also
MM. Riffault and Chompre (221), of the manner in which

electro-chemical decomposition is effected, is very different to that already considered, and is not affected by either the argu-
ments or facts urged against the latter. Considering it as stated
by the former philosopher, it appears to me to be incompetent

to account for the experiments of decomposition against surfaces of air (198, 205) and water (231), which I have described; for if the physical differences between metals and humid conductors, which M. de la Rive supposes to account for the trans-
mission of the compound of matter and electricity in the latter, and the transmission of the electricity only with the rejection of the matter in the former, be allowed for a moment, still the

analogy of air to metal is, electrically considered, so small, that instead of the former replacing the latter (198), an effect the very reverse might have been expected. Or if even that were

allowed, the experiment with water (231) at once sets the
matter at rest, the decomposing pole being now of a substance
which is admitted as competent to transmit the assumed com-
pound of electricity and matter.
244. With regard to the views of MM. Riffault and Chompre

(221), the occurrence of decomposition alone in the course of the current is so contrary to the well-known effects obtained in
the forms of experiment adopted up to this time, that it must be proved before the hypothesis depending on it need be con-

sidered.

245. The consideration of the various theories of electrochemical decomposition, whilst it has made me diffident, has
also given me confidence to add another to the number; for it
is because the one I have to propose appears, after the most attentive consideration, to explain and agree with the immense
collection of facts belonging to this branch of science, and to

remain uncontradicted by, or unopposed to, any of them, that

I have been encouraged to give it. 246. Electro-chemical decomposition is well known to depend
essentially upon the current of electricity. I have shown that

(m) in certain cases

the decomposition is proportionate to the

ÆTHERFORCE

Various Views of the Electric Current 67

quantity of electricity passing, whatever may be its intensity or
its source, and that the same is probably true for all cases (113), even when the utmost generality is taken on the one hand, and
great precision of expression on the other (241).

247. In speaking of the current, I find myself obliged to be still more particular than on a former occasion (19), in conse-

quence of the variety of views taken by philosophers, all agreeing in the effect of the current itself. Some philosophers, with Franklin, assume but one electric fluid; and such must agree together in the general uniformity and character of the electric current. Others assume two electric fluids; and here singular differences have arisen.

248. MM. Riffault and Chompre, for instance, consider the

positive and negative currents each as causing decomposition,

and state that the positive current is more -powerful than the

negative

1
current,

the

nitrate

of

soda

being,

under

similar

circumstances, decomposed by the former, but not by the

latter.

249.

M.

Hachette

states 2

that

"
it

is

not

necessary,

as

has

been believed, that the action of the two electricities, positive

and negative, should be simultaneous for the decomposition of

water." The passage implying, if I have caught the meaning

aright, that one electricity can be obtained, and can be applied

in effecting decompositions, independent of the other.

250. The view of M. de la Rive to a certain extent agrees with

that of M. Hachette, for he considers that the two electricities

decompose

separate

portions

of

water

3 (226).

In one passage

he speaks of the two electricities as two influences, wishing

perhaps to avoid offering a decided opinion upon the independent

existence of electric fluids but as these influences are considered ;

as combining with the elements set free as by a species of chemical affinity, and for the time entirely masking their character,

great vagueness of idea is thus introduced, inasmuch as such

a species of combination can only be conceived to take place between things having independent existences. The two elemen-

tary electric currents, moving in opposite directions, from pole
to pole, constitute the ordinary voltaic current. 251. M. Grotthuss is inclined to believe that the elements of
water, when about to separate at the poles, combine with the electricities, and so become gases. M. de la Rive's view is the
exact reverse of this: whilst passing through the fluid, they are,

1 Annales de Chimie, 1807, torn, Ixiii. p. 84. 3 Ibid. 1825, torn, xxviii. pp. 197, 201.

* Ibid. 1832, toin. li. p. 73.
ÆTHERFORCE

68

Faraday's Researches

according to him, compounds with the electricities; when
evolved at the poles, they are de-electrified.

252. I have sought amongst the various experiments quoted in support of these views, or connected with electro-chemical decompositions or electric currents, for any which might be considered as sustaining the theory of two electricities rather than that of one, but have not been able to perceive a single fact which could be brought forward for such a purpose: or, admitting the hypothesis of two electricities, much less have I been able to perceive the slightest grounds for believing that one electricity in a current can be more powerful than the other, or that it can be present without the other, or that one can be varied or in the slightest degree affected, without a corresponding variation in the other. If, upon the supposition of two electricities, a current of one can be obtained without the other,
or the current of one be exalted or diminished more than the

other, we might surely expect some variation either of the
chemical or magnetical effects, or of both; but no such variations have been observed. If a current be so directed that it

may act chemically in one part of its course, and magnetically

in another, the two actions are always found to take place

A together.

current has not, to my knowledge, been produced

which could act chemically and not magnetically, nor any which

can

act

on

the

magnet,

and

not

at

the

same

time

1
chemically.

2 53- Judging from facts only, there is not as yet the slightest

reason for considering the influence which is present in what

we call the electric current, whether in metals or fused bodies

or humid conductors, or even in air, flame, and rarefied elastic

media, as a compound or complicated influence. It has never

been resolved into simpler or elementary influences, and may

perhaps best be conceived of as an axis of power having contrary

forces, exactly equal in amount, in contrary directions.

254. Passing to the consideration of electro-chemical decom-
position, it appears to me that the effect is produced by an
internal corpuscular action, exerted according to the direction of the electric current, and that it is due to a force either super-
added to, or giving direction to the ordinary chemical affinity of
the bodies present. The body under decomposition may be
considered as a mass of acting particles, all those which are
1 Thermo-electric currents are of course no exception, because when they
fail to act chemically they also fail to be currents.

ÆTHERFORCE

Electro-Chemical Decomposition 69
included in the course of the electric current contributing to the
final effect; and it is because the ordinary chemical affinity is relieved, weakened, or partly neutralised by the influence of the electric current in one direction parallel to the course of the latter, and strengthened or added to in the opposite direction, that the combining particles have a tendency to pass in opposite
courses.
255. In this view the effect is considered as essentially dependent upon the mutual chemical affinity of the particles of opposite kinds. Particles a a, fig. 13, could not be transferred
N or travel from one pole towards the other P, unless they
found particles of the opposite kind b b, ready to pass in the contrary direction: for it is by virtue of their increased affinity for those particles, combined with their diminished affinity for such as are behind them in their course, that they are urged
forward: and when any one particle a, fig. 14, arrives at the
pole, it is excluded or set free, because the particle b of the
opposite kind, with which it was the moment before in combi-
nation, has, under the superinducing influence of the current, a greater attraction for the particle a, which is before it in its course, than for the particle a, towards which its affinity has been weakened.
256. As far as regards any single compound particle, the case may be considered as analogous to one of ordinary decomposi-
tion, for in fig. 14, a may be conceived to be expelled from
the compound a b by the superior attraction of a for b, that
superior attraction belonging to it in consequence of the relative position of a b and a to the direction of the axis of electric power (253) superinduced by the current. But as all the compound particles in the course of the current, except those actually in contact with the poles, act conjointly, and consist of elementary particles, which, whilst they are in one direction expelling, are in the other being expelled, the case becomes more complicated, but not more difficult of comprehension.
257. It is not here assumed that the acting particles must be
in a right line between the poles. The lines of action which may
be supposed to represent the electric currents passing through
a decomposing liquid, have in many experiments very irregular
ÆTHERFORCE

70

Faraday's Researches

forms; and even in the simplest case of two wires or points immersed as poles in a drop or larger single portion of fluid, these lines must diverge rapidly from the poles; and the direction in which the chemical affinity between particles is most
powerfully modified (255, 256) will vary with the direction, of these lines, according constantly with them. But even in refer-
ence to these lines or currents, it is not supposed that the particles which mutually affect each other must of necessity be parallel to them, but only that they shall accord generally with
their direction. Two particles, placed in a line perpendicular
to the electric current passing in any particular place, are not supposed to have their ordinary chemical relations towards each other affected; but as the line joining them is inclined one way to the current their mutual affinity is increased ; as it is inclined
in the other direction it is diminished; and the effect is a
maximum, when that line is parallel to the current. 258. That the actions, of whatever kind they may be, take
place frequently in oblique directions, is evident from the circumstance of those particles being included which in numerous cases are not in a line between the poles. Thus, when wires are used as poles in a glass of solution, the decompositions and
recompositions occur to the right or left of the direct line between the poles, and indeed in every part to which the currents
extend, as is proved by many experiments, and must therefore
often occur between particles obliquely placed as respects the current itself; and when a metallic vessel containing the solution
is made one pole, whilst a mere point or wire is used for the other, the decompositions and recompositions must frequently be still more oblique to the course of the currents.
259. The theory which I have ventured to put forth (almost) requires an admission, that in a compound body capable of electro-chemical decomposition the elementary particles have a mutual relation to, and influence upon each other, extending beyond those with which they are immediately combined. Thus in water, a particle of hydrogen in combination with oxygen is
considered as not altogether indifferent to other particles of oxygen, although they are combined with other particles of hydrogen; but to have an affinity or attraction towards them, which, though it does not at all approach in force, under ordinary circumstances, to that by which it is combined with its
own particle, can, under the electric influence, exerted in a definite direction, be made even to surpass it. This general rela-
tion of particles already in combination to other particles with

ÆTHERFORCE

Electro-Chemical Decomposition 7 1
which they are not combined, is sufficiently distinct in numerous results of a purely chemical character; especially in those where partial decompositions only take place, and in Berthollet's experiments on the effects of quantity upon affinity: and it probably has a direct relation to, and connection with, attraction of aggregation, both in solids and fluids. It is a remarkable circumstance, that in gases and vapours, where the attraction
of aggregation ceases, there likewise the decomposing powers of electricity apparently cease, and there also the chemical action of quantity is no longer evident. It seems not unlikely,
that the inability to suffer decomposition in these cases may be
dependent upon the absence of that mutual attractive relation of the particles which is the cause of aggregation.
260. I hope I have now distinctly stated, although in general
terms, the view I entertain of the cause of electro-chemical decomposition, as far as that cause can at present be traced and understood. I conceive the effects to arise from forces which
are internal, relative to the matter under decomposition and
not external, as they might be considered, if directly dependent upon the poles. I suppose that the effects are due to a modification, by the electric current, of the chemical affinity of the particles through or by which that current is passing, giving them the power of acting more forcibly in one direction than in another, and consequently making them travel by a series of successive decompositions and recompositions in opposite directions, and finally causing their expulsion or exclusion at the boundaries of the body under decomposition, in the direction of the current, and that in larger or smaller quantities, according as the current is more or less powerful (113). I think, therefore, it would be more philosophical, and more directly expressive of the facts, to speak of such a body, in relation to the current passing through it, rather than to the poles, as they are usually called, in contact with it; and say that whilst under decomposition, oxygen, chlorine, iodine, acids, etc., are rendered at its negative extremity, and combustibles, metals, alkalies, bases, etc., at its positive extremity (203). I do not believe
that a substance can be transferred in the electric current ,
beyond the point where it ceases to find particles with which
it can combine; and I may refer to the experiments made in
air (201), and in water (231), already quoted, for facts illustrating these views in the first instance; to which I will now add others.
261. In order to show the dependence of the decomposition
ÆTHERFORCE

72

Faraday's Researches

and transfer of elements upon the chemical affinity of the sub-

stances present, experiments were made upon sulphuric acid

in the following manner. Dilute sulphuric acid was prepared:

A its specific gravity was 1021.2.

solution of sulphate of soda

was also prepared, of such strength that a measure of it con-

tained exactly as much sulphuric acid as an equal measure of

A the diluted acid just referred to.

solution of pure soda, and

another of pure ammonia, were likewise prepared, of such

strengths that a measure of either should be exactly neutralised

by a measure of the prepared sulphuric acid.

262. Four glass cups were then arranged, as in fig. 15; seven-

teen measures of the free sulphuric acid (261) were put into

each of the vessels a and b, and seventeen measures of the
A solution of sulphate of soda into each of the vessels and B.

Asbestus, which had been well washed in acid, acted upon by

the voltaic pile, well washed in water, and dried by pressure,
A was used to connect a with b and with B, the portions being
as equal as they could be made in quantity, and cut as short as was consistent with their performing the part of effectual com-
A munications, b and were connected by two platina plates
or poles soldered to the extremities of one wire, and the cups a
and B were by similar platina plates connected with a voltaic
battery of forty pairs of plates four inches square, that in a
being connected with the negative, and that in B with the posi-
tive pole. The battery, which was not powerfully charged, was retained in communication above half an hour. In this manner
it was certain that the same electric current had passed through
a b and A B, and that in each instance the same quantity and
strength of acid had been submitted to its action, but in one case merely dissolved in water, and in the other dissolved and also combined with an alkali.
263. On breaking the connection with the battery, the por-
ÆTHERFORCE

Transference of Acid and Alkali 73

tions of asbestus were lifted out, and the drops hanging at the

ends allowed to fall each into its respective vessel. The acids

in a and b were then first compared, for which purpose two

evaporating dishes were balanced, and the acid from a put into

one, and that from b into the other; but as one was a little

heavier than the other, a small drop was transferred from the

heavier to the lighter, and the two rendered equal in weight.

Being neutralised by the addition of the soda solution (261),,

that from a, or the negative vessel, required 15 parts of the

soda solution, and that from b, or the positive vessel, required

16.3 parts. That the sum of these is not 34 parts is principally

due to the acid removed with the asbestus; but taking the

mean of 15.65 parts, it would appear that a twenty-fourth part

of the acid originally in the vessel a had passed, through the

influence of the electric current, from a into b.

A 264. In comparing the difference of acid in

and B, the

necessary equality of weight was considered as of no conse-

quence, because the solution was at first neutral, and would not,.

the;efore, affect the test liquids, and all the evolved acid would
A be in B, and the free alkali in A. The solution in required

3.2 measures of the prepared acid (261) to neutralise it, and the
solution in B required also 3.2 measures of the soda solution

(261) to neutralise it. As the asbestus must have removed a.

little acid and alkali from the glasses, these quantities are by so

much too small; and therefore it would appear that about a.
A tenth of the acid originally in the vessel had been transferred

into B during the continuance of the electric action.

265. In another similar experiment, whilst a thirty-fifth part

of the acid passed from a to b in the free acid vessels, between
a tenth and an eleventh passed from A to B in the combined

acid vessels. Other experiments of the same kind gave similar

results.

266. The variation of electro-chemical decomposition, the transfer of elements and their accumulation at the poles, accord-
ing as the substance submitted to action consists of particles, opposed more or less in their chemical affinity, together with

the consequent influence of the latter circumstances, are sufficiently obvious in these cases, where sulphuric acid is acted upon in the same quantity by the same electric current, but in one case opposed to the comparatively weak affinity of water for it, and in the other to the stronger one of soda. In the
latter case the quantity transferred is from two and a half to three times what it is in the former; and it appears therefore
ÆTHERFORCE

74

Faraday's Researches

very evident that the transfer is greatly dependent upon the

mutual action of the particles of the decomposing bodies. 1

267. In some of the experiments the acid from the vessels a

and b was neutralised by ammonia, then evaporated to dryness,

heated to redness, and the residue examined for sulphates.

In
.

these cases more sulphate was always obtained from a than

from b; showing that it had been impossible to exclude

saline bases (derived from the asbestus, the glass, or perhaps

impurities originally in the acid), and that they had helped in

transferring the acid into b. But the quantity was small, and

the acid was principally transferred by relation to the water

present.
268. I endeavoured to arrange certain experiments by which saline solutions should be decomposed against surfaces of water; and at first worked with the electric machine upon a piece of bibulous paper, or asbestus moistened in the solution, and in contact at its two extremities with pointed pieces of paper moistened in pure water, which served to carry the electric current to and from the solution in the middle piece. But I found numerous interfering difficulties. Thus, the water and solutions in the pieces of paper could not be prevented from mingling at the point where they touched. Again, sufficient acid could be derived from the paper connected with the dis-
charging train, or it may be even from the air itself, under the
influence of electric action, to neutralise the alkali developed at the positive extremity of the decomposing solution, and so not merely prevent its appearance, but actually transfer it on to the
metal termination : and, in fact, when the paper points were not allowed to touch there, and the machine was worked until
alkali was evolved at the delivering or positive end of the turmeric paper, containing the sulphate of soda solution, it was merely necessary to place the opposite re'ceiving point of the paper connected with the discharging train, which had been moistened by distilled water, upon the brown turmeric point and press them together, when the alkaline effect immediately

disappeared.
269. The experiment with sulphate of magnesia already described (231) is a case in point, however, and shows most clearly that the sulphuric acid and magnesia contributed to each other's transfer and final evolution, exactly as the same acid and
soda affected each other in the results just given (263, etc.); .and that so soon as the magnesia advanced beyond the reach of
1 See the note to 410. December 1838.

ÆTHERFORCE

Evolution of Bodies at the Poles

75

the acid, and found no other substance with which it could combine, it appeared in its proper character, and was no longer able to continue its progress towards the negative pole.

270. The theory I have ventured to put forth appears to me
to explain all the prominent features of electro-chemical decomposition in a satisfactory manner.
271. In the first place, it explains why, in all ordinary cases,
the evolved substances appear only at the poles ; for the poles are the limiting surfaces of the decomposing substance, and except at them, every particle finds other particles having a contrary tendency with which it can combine.
272. Then it explains why, in numerous cases, the elements or evolved substances are not retained by the poles; and this is no small difficulty in those theories which refer the decompos-
ing effect directly to the attractive power of the poles. If, in accordance with the usual theory, a piece of platina be supposed to have sufficient power to attract a particle of hydrogen from the particle of oxygen with which it was the instant before combined, there seems no sufficient reason, nor any fact, except
those to be explained, which show why it should not, according
to analogy with all ordinary attractive forces, as those of gravitation, magnetism, cohesion, chemical affinity, etc., retain that particle which it had just before taken from a distance and from previous combination. Yet it does not do so, but allows it to
escape freely. Nor does this depend upon its assuming the gaseous state, for acids and alkalies, etc., are left equally at
liberty to diffuse themselves through the fluid surrounding the pole, and show no particular tendency to combine with or
adhere to the latter. And though there are plenty of cases
where combination with the pole does take place, they do not at all explain the instances of non-combination, and do not there-
fore in their particular action reveal the general principle of

decomposition.

273. But in the theory that I have just given, the effect

appears to be a natural consequence of the action : the evolved

substances are expelled from the decomposing mass (254, 255),

not drawn out by an attraction which ceases to act on one

particle without any assignable reason, while it continues to act

on another of the same kind: and whether the poles be metal,

water, or air, still the substances are evolved, and are sometimes

set free, whilst at others they unite to the matter of the poles,

according to the chemical nature of the latter, i.e. their chemical

D 576

ÆTHERFORCE

j6

Faraday's Researches

relation to those particles which are leaving the substance under
operation.
274. The theory accounts for the transfer of elements in a
manner which seems to me at present to leave nothing unex-
plained; and it was, indeed, the phenomena of transfer in the numerous cases of decomposition of bodies rendered fluid by heat (116, 138), which, in conjunction with the experiments in air, led to its construction. Such cases as the former where
binary compounds of easy decomposability are acted upon, are perhaps the best to illustrate the theory.
275. Chloride of lead, for instance, fused in a bent tube (136), and decomposed by platina wires, evolves lead, passing to what is usually called the negative pole, and chlorine, which being evolved at the positive pole, is in part set free, and in part
combines with the platina. The chloride of platina formed,
being soluble in the chloride of lead, is subject to decomposition, and the platina itself is gradually transferred across the decomposing matter, and found with the lead at the negative pole.
276. Iodide of lead evolves abundance of lead at the negative pole, and abundance of iodine at the positive pole.
277. Chloride of silver furnishes a beautiful instance, especially
when decomposed by silver wire poles. Upon fusing a portion of it on a piece of glass, and bringing the poles into contact with it, there is abundance of silver evolved at the negative pole, and an equal abundance absorbed at the positive pole, for no chlorine is set free: and by careful management, the negative wire may be withdrawn from the fused globule as the
silver is reduced there, the latter serving as the continuation of
the pole, until a wire or thread of revived silver, five or six inches in length, is produced; at the same time the silver at the positive pole is as rapidly dissolved by the chlorine, which seizes upon it, so that the wire has to be continually advanced as it is melted away. The whole experiment includes the action of only two elements, silver and chlorine, and illustrates in a beautiful manner their progress in opposite directions, parallel to the electric current, which is for the time giving a uniform general direction to their mutual affinities (260).
278. According to my theory, an element or a substance not
decomposable under the circumstances of the experiment (as, for instance, a dilute acid or alkali) should not be transferred, or pass from pole to pole, unless it be in chemical relation to som other element or substance tending to pass in the opposite direction, for the effect is considered as essentially due to the

ÆTHERFORCE

Uncombined Bodies not Transferable 77

mutual relation of such particles. But the theories attributing the determination of the elements to the attractions and re-

pulsions of the poles require no such condition, i.e. there is no

reason apparent why the attraction of the positive pole, and the

repulsion of the negative pole, upon a particle of free acid,

placed in water between them, should not (with equal currents

of electricity) be as strong as if that particle were previously

combined with alkali ;

but, on the contrary, as they have not a

powerful chemical affinity to overcome, there is every reason to

suppose they would be stronger, and would sooner bring the

acid

to

rest

at

the

positive

1
pole.

Yet such is not the case, as

has been shown by the experiments on free and combined acid

(262, 264).
279. Neither does M. de la Rive's theory, as I understand it, require that the particles should be in combination: it does not even admit, where there are two sets of particles capable of combining with and passing by each other, that they do combine, but supposes that they travel as separate compounds of matter and electricity. Yet in fact the free substance cannot travel, the combined one can.

280. It is very difficult to find cases amongst solutions or fluids which shall illustrate this point, because of the difficulty of finding two fluids which shall conduct, shall not mingle and in which an element evolved from one shall not find a com-

binable element in the other. Solutions of acids or alkalies will

not answer, because they exist by virtue of an attraction; and increasing the solubility of a body in one direction, and diminishing it in the opposite, is just as good a reason for transfer as modifying the affinity between the acids and alkalies themselves. 2 Nevertheless the case of sulphate of magnesia is in point (230, 231), and shows that one element or principle only has no power of transference or of passing towards either pole.
281. Many of the metals, however, in their solid state, offer
very fair instances of the kind required. Thus, if a plate of platina be used as the positive pole in a solution of sulphuric acid, oxygen will pass towards it, and so will acid; but these
are not substances having such chemical relation to the platina as, even under the favourable condition superinduced by the current (254, 260), to combine with it; the platina therefore remains where it was first placed, and has no tendency to pass

1 Even Sir Humphry Davy considered the attraction of the pole as being
communicated from one particle to another of th6 same kind (219).
1 See the note to 410. December 1838.

ÆTHERFORCE

78

Faraday's Researches

towards the negative pole. But if a plate of iron, zinc, or copper,

be substituted for the platina, then the oxygen and acid can

combine with these, and the metal immediately begins to travel

(as an oxide) to the opposite pole, and is finally deposited

there. Or if, retaining the platina pole, a fused chloride,, as

of lead, zinc, silver, etc., be substituted for the sulphuric acid,

then, as the platina finds an element it can combine with, it

enters into union, acts as other elements do in cases of voltaic

decomposition, is rapidly transferred across the melted matter,

and expelled at the negative pole.

282. I can see but little reason in the theories referring the

electro-chemical decomposition to the attractions and repulsions

of the poles, and I can perceive none in M. de la Rive's theory,

why the metal of the positive pole should not be transferred

across the intervening conductor, and deposited at the negative

pole, even when it cannot act chemically upon the element

of the fluid surrounding it. It cannot be referred to the attrac-

tion of cohesion preventing such an effect; for if the pole be made of the lightest spongy platina, the effect is the same.

Or if gold precipitated by sulphate of iron be diffused through

the solution, still accumulation of it at the negative pole will

not take place; and yet in it the attraction of cohesion is

almost perfectly overcome, the particles are so small as to remain
for hours in suspension, and are perfectly free to move by the

slightest impulse towards cither pole; and if in relation by

chemical affinity to any substance present, are powerfully

determined

to

the

negative

1
pole.

283. In support of these arguments, it may be observed that

as yet no determination of a substance to a pole, or tendency
to obey the electric current, has been observed (that I am aware

of)

in

cases

of

mere

mixture ;

i.e. a substance diffused through

a fluid, but having no sensible chemical affinity with it, or with

substances that may be evolved from it during the action, does

not in any case seem to be affected by the electric current.

1 In making this experiment, care must be taken that no substance be present that can act chemically on the gold. Although I used the metal very carefully washed, and diffused through dilute sulphuric acid, yet in the first instance I obtained gold at the negative pole, and the effect was repeated when the platiaa poles were changed. But on examining the clear liquor in the cell, after subsidence of the metallic gold, I found a little of that metal in solution, and a little chlorine was also present. I therefore
well washed the gold which had thus been subjected to voltaic action, diffused it through other pure dilute sulphuric acid, and then found, that on subjecting it to the action of the pile, not the slightest tendency to the
negative pole could be perceived.

ÆTHERFORCE

Uncombined Bodies not Transferable 79
Pulverised charcoal was diffused through dilute sulphuric acid, and subjected with the solution to the action of a voltaic battery, terminated by platina poles; but not the slightest tendency of the charcoal to the negative pole could be observed. Sublimed sulphur was diffused through similar acid,, and submitted to the same action, a silver plate being used as the negative pole; but the sulphur had no tendency to pass to that pole, the silver was not tarnished, nor did any sulphuretted hydrogen appear. The case of magnesia and water (231, 269), with those of comminuted metals in certain solutions (282), are also of this kind; and, in fact, substances which have the instant before been powerfully determined towards the pole, as magnesia from sulphate of magnesia, become entirely indifferent to it the
moment they assume their independent state, and pass away,
diffusing themselves through the surrounding fluid.
284. There are, it is true, many instances of insoluble bodies
being acted upon, as glass, sulphate of baryta, marble, slate, basalt, etc., they form no exception; for the substances they give up are in direct and strong relation as to chemical affinity with those which they find in the surrounding solution, so that these decompositions enter into the class of ordinary
effects.
285. It may be expressed as a general consequence, that the
more directly bodies are opposed to each other in chemical affinity, the more ready is their separation from each other in cases of electro-chemical decomposition, i.e. provided other circumstances, as insolubility, deficient conducting power, proportions, etc., do not interfere. This is well known to be the case with water and saline solutions and I have found it to be
;
equally true with dry chlorides, iodides, salts, etc., rendered subject to electro-chemical decomposition by fusion (138). So that in applying the voltaic battery for the purpose of decomposing bodies not yet resolved into forms of matter simpler than
their own, it must be remembered, that success may depend
not upon the weakness, or failure upon the strength, of the affinity by which the elements sought for are held together,
but contrariwise; and then modes of application may be devised
by which, in association with ordinary chemical powers, and
the assistance of fusion (130, 153), we may be able to penetrate much further than at present into the constitution of our
chemical elements.
286. Some of the most beautiful and surprising cases of
ÆTHERFORCE

80

Faraday's Researches

electro-chemical decomposition and transfer which Sir Humphry

Davy

described

in

his

celebrated

1
paper,

were

those

in

which

acids were passed through alkalies, and alkalies or earths through

acids 2 ;

and

the

way

in

which

substances

having

the

most

powerful attractions for each other were thus prevented from

combining, or, as it is said, had their natural affinity destroyed

or suspended throughout the whole of the circuit, excited the

utmost astonishment. But if I be right in the view I have

taken of the effects, it will appear that that which made the

wonder is in fact the essential condition of transfer and decom-

position, and that the more alkali there is in the course of an acid, the more will the transfer of that acid be facilitated from pole to pole; and perhaps a better illustration of the difference between the theory I have ventured, and those previously existing, cannot be offered than the views they respectively give of such facts as these.

287. The instances in which sulphuric acid could not be

passed

through

baryta,

or

baryta

through

sulphuric

3
acid,

because of the precipitation of sulphate of baryta, enter within

the pale of the law already described (116, 148), by which

liquidity is so generally required for conduction and decom-

position. In assuming the soHd state of sulphate of baryta,

these bodies became virtually non-conductors to electricity of

so low a tension as that of the voltaic battery, and the power

of the latter over them was almost infinitely diminished.

288. The theory I have advanced accords in a most satis-

factory manner with the fact of an element or substance find-

ing its place of rest, or rather of evolution, sometimes at one

pole and sometimes at the other. Sulphur illustrates this

effect very well. 4 When sulphuric acid is decomposed by the

pile, sulphur is evolved at the negative pole; but when sul-

phuret of silver is decomposed in a similar way (172), then the

sulphur appears at the positive pole; and if a hot platina pole

be used so as to vaporise the sulphur evolved in the latter case,

then the relation of that pole to the sulphur is exactly the same

as the relation of the same pole to oxygen upon its immersion

in water. In both cases the element evolved is liberated at

the pole, but not retained by it; but by virtue of its elastic,

1 Philosophical Transactions, 1807, p. i.

2 Ibid. p. 24, etc.

3 Ibid. p. 25, etc.

4 At 416 and 492 of Part V. will be found corrections of the statement

here made respecting sulphur and sulphuric acid. At present there is no

well-ascertained fact which proves that the same body can go directly to

either of the two poles at pleasure. December 1838.

ÆTHERFORCE

Bodies which Pass to Either Pole 81

uncombinable, and immiscible condition passes away into the surrounding medium. The sulphur is evidently determined in
these opposite directions by its opposite chemical relations to oxygen and silver; and it is to such relations generally that I have referred all electro-chemical phenomena. Where they do not exist, no electro-chemical action can take place. Where
they are strongest, it is most powerful; where they are reversed, the direction of transfer of the substance is reversed with

them.

289. Water may be considered as one of those substances which can be made to pass to either pole. When the poles
are immersed in dilute sulphuric acid (263), acid passes towards the positive pole, and water towards the negative pole; but when they are immersed in dilute alkali, the alkali passes towards the negative pole, and water towards the positive

pole.

290. Nitrogen is another substance which is considered as

determinable to either pole ; but in consequence of the numerous

compounds which it forms, some of which pass to one pole,

and some to the other, I have not always found it easy to

A determine the true circumstances of its appearance.

pure

strong solution of ammonia is so bad a conductor of electricity

that it is scarcely more decomposable than pure water; but if

sulphate of ammonia be dissolved in it, then decomposition

takes place very well; nitrogen almost pure, and in some cases

quite, is evolved at the positive pole, and hydrogen at the

negative pole.
291. On the other hand, if a strong solution of nitrate of ammonia be decomposed, oxygen appears at the positive pole,
and hydrogen, with sometimes nitrogen, at the negative pole. If fused nitrate of ammonia be employed, hydrogen appears at
the negative pole, mingled with a little nitrogen. Strong nitric acid yields plenty of oxygen at the positive pole, but no gas
(only nitrous acid), at the negative pole. Weak nitric acid
yields the oxygen and hydrogen of the water present, the acid apparently remaining unchanged. Strong nitric acid with nitrate of ammonia dissolved in it, yields a gas at the negative pole, of which the greater part is hydrogen, but apparently a little nitrogen is present. I believe that in some of these cases
a little nitrogen appeared at the negative pole. I suspect, however, that in all these, and in all former cases, the appear-
ance of the nitrogen at the positive or negative pole is entirely

ÆTHERFORCE

82

Faraday's Researches

a secondary effect, and not an immediate consequence of the decomposing power of the electric current. 1

A 292. few observations on what are called the poles of the
voltaic battery now seem necessary. The poles are merely the surfaces or doors by which the electricity enters into or passes out of the substance suffering decomposition. They limit the
extent of that substance in the course of the electric current,
being its terminations in that direction: hence the elements evolved pass so far and no further.
293. Metals make admirable poles, in consequence of their
high conducting power, their immiscibility with the substances generally acted upon, their solid form, and the opportunity afforded of selecting such as are not chemically acted upon by
ordinary substances.
294. Water makes a pole of difficult application, except in a few cases (230), because of its small conducting power, its miscibility with most of the substances acted upon, and its general relation to them in respect to chemical affinity. It consists of elements, which in their electrical and chemical relations are directly and powerfully opposed, yet combining to produce a body more neutral in its character than any other. So that there are but few substances which do not come into
relation, by chemical affinity, with water or one of its elements; and therefore either the water or its elements are transferred
and assist in transferring the infinite variety of bodies which, in association with it, can be placed in the course of the electric
current. Hence the reason why it so rarely happens that the
evolved substances rest at the first surface of the water, and
why it therefore does not exhibit the ordinary action of a pole.
295. Air, however, and some gases are free from the latter
objection, and may be used as poles in many cases (197, etc.);
but, in consequence of the extremely low degree of conducting power belonging to them, they cannot be employed with the voltaic apparatus. This limits their use; for the voltaic apparatus is the only one as yet discovered which supplies
sufficient quantity of electricity (107, 112) to effect electrochemical decomposition with facility.
296. When the poles are liable to the chemical action of
the substances evolved, either simply in consequence of their natural relation to them, or of that relation aided by the influence
1 Refer for proof of the truth of this supposition to 483, 487, etc. December 1838.

ÆTHERFORCE

Character and Nature of the Poles 83
of the current (254), then they suffer corrosion, and the parts dissolved are subject to transference, in the same manner as the particles of the body originally under decomposition.
An immense series of phenomena of this kind might be quoted
in support of the view I have taken of the cause of electrochemical decomposition, and the transfer and evolution of the elements. Thus platina being made the positive and negative poles in a solution of sulphate of soda, has no affinity or attraction for oxygen, hydrogen, acid, or alkali evolved, and refuses to combine with or retain them. Zinc can combine with the
oxygen and acid; at the positive pole it does combine, and immediately begins to travel as oxide towards the negative pole. Charcoal, which cannot combine with the metals, if made the negative pole in a metallic solution, refuses to unite to the bodies which are ejected from the solution upon its surface; but if made the positive pole in a dilute solution of sulphuric acid, it is capable of combining with the oxygen evolved there, and consequently unites with it, producing both carbonic acid and carbonic oxide in abundance.
A 297. great advantage is frequently supplied, by the oppor-
tunity afforded amongst the metals of selecting a substance for the pole, which shall or shall not be acted upon by the elements to be evolved. The consequent use of platina is notorious. In the decomposition of sulphuret of silver and other sulphurets, a positive silver pole is superior to a platina one, because in the former case the sulphur evolved there combines with the silver, and the decomposition of the original sulphuret is rendered evident; whereas in the latter case it is dissipated, and
the assurance of its separation at the pole not easily obtained.
298. The effects which take place when a succession of conducting decomposable and undecomposable substances are placed in the electric circuit, as, for instance, of wires and solutions, or of air and solutions (201, 205), are explained in the simplest possible manner by the theoretical view I have given.
In consequence of the reaction of the constituents of each
portion of decomposable matter, affected as they are by the
supervention of the electric current (260), portions of the proximate or ultimate elements proceed in the direction of the current as far as they find matter of a contrary kind capable of
effecting their transfer, and being equally affected by them; and where they cease to find such matter, they are evolved in their free state, i.e. upon the surfaces of metal or air bounding the extent of decomposable matter in the direction of the current.
ÆTHERFORCE