Experimental Researches In Electricity

EVERYMAN’S LIBRARY
EDITED BY ERNEST RHYS

SCIENCE

FARADAY’S SELECT RESEARCHES
IN ELECTRICITY • with an appre¬
ciation BY PROFESSOR TYNDALL

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EXPERI-
ME.NTAL
RESEARCHES
IN C-

TRICITV
MICHAEL
FARADAV
D.C.L.iiKR.S.

LONDOHPUBLISHED
tyJMDENTSSONSlS
ANP IN NEW YORK

INTRODUCTION^

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—
,dwgh, beautiful, and alone.

. The dominant result of his fourth group of researches is the
discovery of diamagnetism, announced in his memoir as the

g ^ These pages form the “Summary” and the concluding passages of
^araday t-he^ Discoverer: 1869.

tOMEM iiUTiTUTE OF TECMIULfl

THE iltlllT LiaiUHT

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
scientific reputation. We 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

Introduction

IX

of them, James Faraday, bom 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 par^
Celtic, but how much of it was so, or when the infusion tool^'
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 quahties, 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
a dozen years ago it fell to my 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,

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
qf kindness, precious to no one but myself, but more precious
lo 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
shared his early dinner; almost always, in fact, while my
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 Institution.)

Ventnor, Isle of 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

of him aiws
together,
me that Lie

“ Good-b
yours truly

The coni
produced i
makes itse
philosophy
overflow ol

Whether
take equa^
make him
he wrote tc
respecting
meantime
connected
then it gah
I am in t
feeling. 1
carried wi
afterwards
sympathy

“ My di
how very
given me <
You will f
I let them
as the stc
presses a x
you may '
not an inc
' all I belie^
to a concl
i “ We re

I Ever trul]

I The thi

i end.

While

Introduction

XI

of him always delight me. We 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 rej oice at every addition to the facts and reasoning
connected with the subject. When science is a repubhc,
then it gains: and though I am no republican in other matters,
I am 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
you may lilce 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
to a conclusion that afiects or has affected my pencil.

“ We return on Friday, when I will return you the paper.—
Ever truly yours, M. Faraday.”

The third letter will come m its proper place towards the
end.

While once conversing with Faradcty on science, in its

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 j

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 1

done a little '' professional business.” This was the phrase 1

he applied to his purely commercial work. His friend, >

Richard Phillips, for example, had induced him to undertake j

a number of analyses, which produced, in the year 1830, an i

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. j

Indeed, this is a wholly insuificient estimate of what he j

might, with ease, have I'ealised annually during the last thirty i

years of his life. j

While restudying the experimental researches with reference j

to the present memoir, the conversation with Faraday here j

alluded to came to my recollection, and I sought to ascertain |

the period when the question, '' wealth or science,” had 1

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, |

and on my own responsibility, I will state the result. In |

1832, his professional business-income, instead of rising to
£5000, or more, fell from ;^I090 4s. to £iS 5 9 ^* From this |

it fell with slight oscillations to £g2 in 1837, and to zero in I

1838. Between 1839 and 1845, it never, except in one '}

instance, exceeded £22 being for the most part much under j

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 ;^ii2. From the end of 1845 to the J

day of his death, Faraday’s annual professional business {

income was exactly zero. Taking the duration of his life j

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

bookbinder, had to decide between a fortune of 150,000 i

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

_ — -J

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
England for a period of forty years.
ofThe outward and visible signs of fame were also of less
account to him than to most men. He haa 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 requking an interval of reflection,
before he decided upon any question of importance. In the
present iustance he followed his usual habit, and begged for
a little time.

On the followiag 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
this responsibility," he said. “ I not only urge you," was my
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 I

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.

THE fiUiilT LIBBA8Y

uanmi mmiirt nc rcnuHninffv u

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 o£&cial life.

In the year 1835, Sir Robert Peel wished to offer Faraday
a pension, but that great statesman quitted ofi&ce 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 declmmg 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

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
his presence for my 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 $rst
time.

“ Hampton Court, August i, 1864.

‘‘ My dear Tyndall, —I do not know whether my letter
will catch you, but I wHl 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,

h

xvi Faraday’s Researches

or the hunting of them. Sometimes the very thinking of you,
and what you may be about, wearies m& with fears, and then
the cogitations pause and change, but without giving me
rest. I know that much of this depends upon my own worn-
out 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
1 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 afiection
raised almost to religious devotion, watched him and tended
him to the end.

‘ '11 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

Introduction xvii

memoir I placed in his hands. I returned to Germany,
worked there for nearly another year, and in June 1S51 came
back finally from Berlin to England. Then, for the first iinu\
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
to me. We 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 w^as 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 b<^ offered
to me in this land. Nor is it for its honour, though surely
that is great, but for the strong personal tics tha,t 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. IJis friendship was energy and inspiration;
his " mantle " is a burden almost too heavy to be borne.

Sometimes during the last year of his life, by the permission
or invitation of Mrs. Faraday, I went up to his rooms to set^
him. The deep radiance, which in his time of strcuigth Hashed
with such cxtra.(>rdinary ])ower from his counlcuiaru'c, had
subsided to a calm and kindly light, by which my laiest
memory of him is wanmul and illuminated, i km'lt one day
beside him on the carpet and ])]accd my hand upon his knee;
he stroked it affectionately, smiled, and murmured, in a low
soft voice, llic last words tha,t 1 nunember as ha,ving been
spoken to m(i by Michael b'araday.

It was my wish and aspiration to ])lay tlu; part of Schiller

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 beauti¬
ful. 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.

BIBLIOGRAPHY

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.), X859; The Various Forces of Matter (six lectures edited
by Sir Wm. Crookes), i860; 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.

CONTENTS

PAGE

IT. § I. Identity of Electricities from Different Sources . r

i. Voltaic Electricity ...... 3

ii. Ordinary Electricity ..... 7

iii. Magneto-Electricity .... . .22

iv. Thermo-Electricity ...... 2.j

V. Animal Electricity . . . . . .24

§ 2. Relation by Measure of Common and Voltak'.

Electricity . . . . . . . .27

II* § 3* New Law of Electric Conduction .... 3.^

§ 4. On Conducting Power generally . . . . .| r

III. § 5. Electro-chemical Decomposition . . . • 17

i. New Conditions of Electro-chemical Decom¬
position ....... 4'*^

^ ii. Influence of Water in such Dccompo.sition . 54

If iii. Theory of Electro-chemical Decomposition .

IV. § 6. Power of Platina, etc., to induce Combination . S4

V. § 5. Electro-chemical Decomposition —Coniinnnl (Nomkn-

CLATURE) . . . . . . . .Ill

If iv. Some General Conditions of lilcctro-chemical

Decomposition . . . . .115

Tf V. Volta-elcctromcter . . . . .122

If vi. Primary and Secondary Results . . . 133

Ifvii. Definite Nature and Extent of lilectro-

chcmical Porccs , . . . p 143

§ 7. Absolute Quantity of Electricity in the Molecules

OF Matter . . . . , , _ ^

VI. §8. Electricity of the Voltaic Pile ... 17^

If i. Simple Voltaic Circles . . . . .174

If ii. Electrolytic Intensity . . . . I

If iii. Associated Voltaic Circle.s; or Patt(‘ry . . ju

Ifiv. Resistance of an Electrolyte to Di'Oo.ni.ositioti f iK
H V. General Remarks on the Active Battery . a;(>

xxi

xxii Faraday’s Researches

PAGE

VII. § 9. On the Source of Power in the Voltaic Pile . 232-

^ i. Exciting Electrolytes being Good Conductors . 23&

^ ii. Inactive Conducting Circles containing an Elec¬
trolyte ....... 241

^ iii. Active Circles containing Sulphuret of Potas¬
sium ....... 259

VIII. § 9. On the Source of Power in the Voltaic Pile— Continued 271
*11 iv. The Exciting Chemical Force affected by

Temperature ...... 271

^ V. The Exciting Chemical Force affected by

Dilution. ...... 284

*[[ vi. Differences in the Order of the Metallic

Elements of Voltaic Circles . . . 295

*[[ vii. Active Voltaic Circles and Batteries without

Metallic Contact . . . . . 29S

^ viii. Considerations of the Sufficiency of Chemical

Action ....... 302

^ ix. Thermo-electric Evidence .... 308

^ X. Improbable Nature of the Assumed Contact

Force ....... 312

On a Peculiar Voltaic Condition of Iron (Schoenbein) . . 317

On a Peculiar Voltaic Condition of Iron (Faraday) . 321, 330

Index .. 333

EXPERIMENTAL RESEARCHES
IN ELECTRICITY

II

§ 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 Cavendish, ^ Wollaston,^ Colladon ^ 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; ^ 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 Torpedo,® thought it

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

^ Phil. Trans. 1776, p. 196. ^ Ihid. 1801, p. 434.

^ Annales de Chimie, 1826, p. 62, etc. ^ Phil. Trans. 1832, p. 282, note.

® Phil. Trans. 1829, p. I 7 - “ Common electricity is 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 of them.” (Dr. Ritchie has shown this is not the case,
Phil. Trans. 1832, p. 294.) “Animal electricity resides only in the im¬
perfect conductors forming the organs of living animals, etc.”

A

..'i-.-id

2 Faraday’s Researches

probable that animal electricity would be found of a peculiar
kind; and referring to it, to common electricity, voltaic elec¬
tricity and magnetism, has said, ‘‘ 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.^

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
Iloyal 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

^ 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
seem to be essentially peculiar,—p. 274; but he then says, p. 275, there
are other points of difference: and after referring to them, adds, “ How
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, which may occur variously associated, and produce all the
varieties of electricity with which we are acquainted? ”

At p. 279 of the same volume of Transactions is Dr. Ritchie’s paper, from
which the following are extracts: “ Common electricity is diffused over the
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
electricity requires thickness of metal for its conduction,” p. 280: and
again, “ The supposed analogy between common and voltaic electricity,
which was so eagerly traced after the invention of the pile, completely
fails ill this case, which was thought to afford the most striking resemblance,”
p. 291.

Voltaic Electricity

present not as philosophical; but merely as convenient.^ Ihc
effect of electricity of tension; at rest; is either attiaction oi
repulsion at sensible distances. The effects of elcctiicity 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 ni}'
object to compare electricities from different sources; and
especially common and voltaic electricities; by their power ol
producing these effects.

I. Voltaic Electricity

4. Tension .—When a voltaic battery of 100 pairs of f>lal('s
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 gol<l
leaves at different extremities attracting each other; even wlien
half an inch or more of air intervenes.

5. That ordinary electricity is discharged by points witli
facility through air; that it is readily transmitted through
highly rarefied air; and also through heated air; as for instanc(‘
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 tlic gaivanoinet<s'
or chemical action produced by the arrangement hereafter to
be described (48; 52).

6. The voltaic battery I had at my disposal consisted of i.|n
pairs of plates four inches square; with double coj)pcrs. 11 was
insulated throughout; and diverged a gold leaf ehictroinetei'
about one-third of an inch. On endeavouring to dis(^liarg(i t.his
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 clujiuical
action. In thiS; however, was found no point of discordaiUK-
between voltaic and common electricity; for when a Leyden
battery (27) was charged so as to deflect the gold kjaf electro¬
meter to the same degree; the points were found equally unable
to discharge it with such effect as to produce eitlier imignetic
or chemical action. This was not because common (‘kiclricit.v
could not produce both these effects (43^ 46); but beca.us(5 wIhm)
of such low intensity the quantity required to make the. (‘ffiMhs
visible (being enormously great (107; xii)) could not he trans
mitted in any reasonable time. In conjunction with the other

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. ij, in which
A B is an insulated glass rod

A 3 upon which two copper wires,

|p C, D, are fixed firmly; to these
V wires are soldered two pieces of

\ \ fine platina wire, the ends of

\ \ which are brought very close to

r ^ I • \ pTvj each other at but without

touching ; the copper wire C

V““ ' AtyHl was connected with the positive

j 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
onl}^ 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 ^ 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 instru¬
ment 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

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 witli common
electricity, and Sir H. Davy has recorded that witli the original
battery of the Royal Institution this discharge passed through
a space of at least four inches.^ In the exhausted receiver tlie
electricity would strike through nearly half an inch of space,
and the combined effects of rarefaction and heat was sucli
upon the inclosed air as to enable it to conduct the electricit.\'
through a space of six or seven inches.

11. The instantaneous charge of a Leyden l)attery by tlu'
poles of a voltaic apparatus is another proof of the tension, and
also the quantity, of electricity evolved by the latter. Sir il.
Davy says,^ When the two conductors from the ends of tint
combination were connected with a Leyden battery, one with
the internal, the other with the external coating, the batter\-
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 possi])lc time of contact was sufficient
to renew the charge to its full intensity.”

12. In motion : i. Evolution of heat. —The e\’'olution of

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

13. ii. Magnetism. —No fact is l)ctter knf)wn to j)hil()soplu‘rs
than the power of the voltaic current to flcflect the magneUV
needle, and to make magnets according to certain laws; and no
effect can be more distinctive of an ele('trical currcait.

14. ^ iii. Chemical decomposition. —The chemical powers of tlui
voltaic current, and their subjection to certain laws^ im) also
perfectly well known.

15. iv. Physiological effects.— power of the voltai(‘
current, when strong, to shock and convulse the whole animal
system, and when weak to affect the; tongue and the c^y(^s, is
very characteristic,

_i6. v. N/w/vc---ILe brilliant star of light produced by the
discharge of a voltaic battery is known to all a,s the most
beautiful light tha,t man can i)roducc l)y art.

17. That these effects may b(^ almost infinitely varied, .some
being exalted whilst others are diminished, is iiniverstilly ae-
knowlcdged; and yet without any doubt of tlu; ichsitity of
character of the voltaic; currents thus made to diffes* in tlua’r
^ Elements of Chemical Philosophy. Jhid. p. \ p

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.

i8. 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 vol¬
taic apparatus, it will be necessary to give some definite ex¬
pression 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¬
metrically arranged and insulated, and the ends N 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

Fig. 2.

ends P N' are connected by another wire, the needle will be
deflected, and will remain so as long as the circuit is complete.
Now if the troughs merely act by causing a peculiar arrange¬
ment in the wire either of its particles or its electricity, that
arrangement constituting its electrical and magnetic state,
then the wire N P' should be in a similar state of arrangement
before P and N' were connected, to what it is afterwards, and
should have deflected the needle, although less powerfully,
perhaps to one-half the extent which would result when the
communication is complete throughout. But if the magnetic
effects depend upon a current, then it is evident why they could
not be produced in any degree before the circuit was complete;
because prior to that no current could exist.

19. By current, I mean anything progressive, whether it be
a fluid of electricity, or two fluids moving in opposite directions,
or merely vibrations, or, speaking still more generally, pro¬
gressive forces. By arrangement, I understand a local adjust¬
ment of particles, or fluids, or forces, not progressive. Many
other reasons might be urged in support of the view of a current

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 motio 7 i: i. Evolution of heat. —The heating power of
common electricity, when passed through wires or other sub¬
stances, is perfectly well known. The accordance between it
and voltaic electricity is in this respect complete. Mr. Harris
has constructed and described^ 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. —Voltaicelectricity has most extraordinary

^ Philosophical Transactions, 1827, p. 18. Edinburgh Transactions,

Harris on a New Electrometer, etc., etc

8 Faraday’s Researches

and exalted magnetic powers. If common electricity be
identical with it; it ought 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 difficulty.^

25. M. ColladoU; 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 Academie des Sciences in 1826;^
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; Amp^rC; 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 or 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 themachine, when worked moderately;
occupies about four-fifths of a second.

^ Demonferrand’s Manuel d'Electricite dynamigue, p. 121.

^ Annales de Chimie, xxxiii. p. 62.

:ity be
render-
voltaic
li cases,
:ommon
mes its
dis tine-
pose of

fference'
common
s head;
1 1826,^

, points,
ling de-
MM.
aper as
riments.
>n, MM.
jblished
as some
elusions
iportant
ve them
irch. I
i by M.
le them,
^ of the
specting
D2, 103,

j inches
nductor
le whole
ivith air
one re-
rom the
es from
rom the
lerately,

Magnetic Effects 9

I 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.

28. A 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

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
I examined) was covered with a frame of wirework, having

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

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

f to have its magnetic power deranged, diminished, or even

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

!

j ^ 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 direc¬
tions, and about half an inch apart; this system was suspended by a fibre
I 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
I are marked A and B. The letters S and N designate the south and north
ends of the needle when affected merely by terrestrial magnetism; the end
N 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).

lo 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); the end B (fig. 3)

of the galvanometer wire was connected with
I tbe 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 oufof use, and the com¬
munications so arranged that the current could be passed from
the prime conductor, by the discharging rod held against it,

Deflection of Magnet 11

through the wet strings 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 dis¬
charging train; and could be as instantl}^ renewed. The needle
was so adjusted, that wh 1st 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 plassing 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 ex¬
hausted 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

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. hi. 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^ that common electricity resembled it in
these effects, and '' 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 prove 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.

46. I take the liberty of describing briefly my 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 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.

^Philosophical Transactions, iSoi, pp. 427, 434. ^ I hid. 1801, p. 429.

Identity of Electricities i 3

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, h ; connect one of these by an insulated

wire c, or wire and string (37), with the machine, and the other
with the discharging train (28) or the negative conductor;
provide two pieces of fine platina wire, bent as in fig. 5, so
that the part d, f 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.

49. A coarse line was made on the
glass with solution of sulphate of copper,
and the terminations p and n put into
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.

50. A 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

ITfE ffUir irBRJUIT
mm ttiiiTiin Of jEfiUMLflffr

14 Faraday’s Researches

had been set free at that when the drop was stirred the
whole became colourless.

51. A 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.

52. A 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 ii,
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.

53. A piece of litmus paper moistened in solution of common
salt or sulphate of soda was quickly reddened at p. A similar
piece moistened in muriatic acid was very soon bleached at p.

No effects of a similar kind took place at n.

54. A 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 n.

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.

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 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
in fig- 6. The wire m was connected with the prime conductor

of the machine, the wire t with the discharging train, and the
wires r and 5 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, r, p ; n, s, py the points r and
5- 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, 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

I 6 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 frevent 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 conduction; 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.

6r. 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

Wollaston s Isxperiment 17

ordinary electricity. By covering fine wires with glass or other
insulating substances^ and then removing only so much matter
as to expose the pointy 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
both oxygen and hydrogen are evolved from each pole; he calls
it “ a very close wiitaiion of the galvanic phenomena,’’ but adds
that “ in fact the resemblance is not complete,” and 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 1797/
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

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

B

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
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 bC; 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. 1 have been the more anxious to assign the true value of
this experiment as a test of electro-chemical action; because I
shall Iiave 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 affe(;t 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
(d the other. When a wet thread was interposed in the course
of the current of common electricity from the battery (27)
charged by eight or ten^ revolutions of the machine in good

1 Or even from thirty to forty.

Atmospheric Electricity

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 ex¬
plosion. 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 electricit}*.
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
■undoubted foundation, and have priority to my results.

72. M. Bonijol of Geneva ^ is said to have constructed very
delicate apparatus for the decomposition of water by common

^ Bihliotheque Universelle, 1830, tome xlv. p. 213.

20

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.
IBonijol does not prove the identity in chemical action of common
and voltaic electricity.

73. At the same page of the Bihliotheque 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
})articles to combine with the nitric acid formed. However
distinct all these actions may be from true polar electro-chemical
decompositions, the}" are still highly important, and well worthy
of investigation.

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

^Philosophical Transactions, 1831, p. 165.

21

Identity of Electricities

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 or intensity of the atmospheric electricity is in
the expression, ‘‘ the usual 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 was apparently not analogous to
voltaic electricity is evident, for the ‘‘ usual shocks ” only were
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 and string, being in an electrical state sufficient to
produce the “ usual shocks ” only, could still, when the elec¬
tricity was drawn off below, renew the charge, and so continue
the current. The string was 1500 feet Jong, 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

22

Faraday’s Researches

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. It gave no shocks to compare with the
“ usual shocks ’’ of a kite-string.

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-Electriciiy

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
action,^ was able to obtain great divergence of the gold leaves
of an electrometer.-

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 coiP were put in requisition. The latter had been
modified in the manner I have elsewhere 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 Cliimie, 1 . p. 322. ^ 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.

n

Identity of Electricities 23

and broken^ expansion of the air within the instrument occurred^
indicating an increase^ at the moment^ of the temperature of
tlie 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 published) ^ describing a magneto¬
electric apparatus^ by which the decomposition of water was
effected. As the term '' guarded points is used^ I suppose
the apparatus to have been Wollaston’s (63, etc.); in which case
the results did not indicate polar electro-chemical decom¬
position. Signor Botto has recently published certain results
which he has obtained; ^ but they arC; 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 ^ and M. 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.

83. iv. Physiological effects ,—A frog was convulsed in the
earliest experiments on these currents. The sensation upon
the tonguC; 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 disagree .ble.

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.

^ Land, and Edinh. Phil. Mag. and Journ. 1832, vol. i. p. 161.

2 Ibid. 1832, vol, i. p. 441. ^ Annales de Chimie, li. p. 77.

^ Ibid. li. p. 72.

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
l^e 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 decom¬
position has not been effected by it. iv. Physiological effects.
Nobili has shown ^ 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 elec¬
tricity 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 Walsh,“
Ingenhousz,^ Cavendish,^ Sir H. Davy,® and Dr. 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
that so little will remain on the minds of others as to justify m\’
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

^ BibliotMque Universelle, xxxvii. 15.

- Philosophical Transactions, 1773, P* 461. ® Ibid. 177$, p. i.

^ Ibid. 1776, p. 196- ® Ibid. 1829, P- I 5 * * 1832, p. 259.

Animal Electricity 25

have little or no doubt that Harris’s electrometer would show
't( 23 , 9 S)-

90. ii. Magnetism, —Perfectly distinct. According to Dr.
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
produce sensible sparks. A 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 arc
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

^ Philosophical Transactions, 1832, p. 260.

1

I

i

26

Faraday’s Researches

glass, and a line distant from each other.” ^ I cannot, how¬
ever, find any record of such an observation by either Walsh
or Ingenhousz, and do not know wdiere 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 Encyclopcedia Briiannica^ Edinburgh, 1830, p. 622,
says, “ From a healthy specimen ” of the Silurus electricus,
meaning rather the gymnotus^ exhibited in London, vivid
sparks were drawn in a darkened room; ” but he 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.^

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 electricityj whatever may
he 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 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.

^ 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.

® The term quantity in electricity is perhaps sufficiently definite as to
sense; the term intensity is more difficult to define strictly. I am using
the terms in their ordinary and accepted meaning.

Measure of Electricities

27

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

II

o;+-

^Magnetic

Deflection.

;

li i -i

bfl rt 1 5

i

Heating
Powei.

True

Chemical

Action.

Attraction

and

Repulsion.

Discharge

by

Hot Air.

I. Voltaic electricity .

X

X

X

X

X

X

X

X

2. Common electricity

X

X

X

X

X

X

X

X

3. Llagneto-electricity

X

X

X

X

X

X

X

4. Thermo-electricity .

X

X

-h ! +

4 -

+

5. Animal electricity .

X

X

1

X

+ i

X

§ 2. Relation by Measure of Common and Voltaic Electricity ^

97. Believing the point of identity to be satisfactorily estab¬
lished,, I next endeavoured to obtain a common measure^ or
a known relation as to quantity^ of the electricity excited by a
machine^ and that from a voltaic pile; for the purpose not only
of confirming their identity (114); but also of demonstrating
certain general principles (102^ 113, etc.); and creating an
extension of the means of investigating and applying the
chemical powers of this wonderful and subtile agent.

98. The first point to be determined waS; whether the same
absolute quantity of ordinary electricity; sent through a galvano-

^ Many of the spaces in this table originally left blank may now be filled.
Thus with thermo-electricity^ Botto made magnets and obtained polar
chemical decomposition: Antinori produced the spark; and if it has not
been done before, Mr. Watkins has recently heated a wire in Harris’s
thermo-electrometer. In respect to animal electricity, Matteucci and
Linari have obtained the spark from the torpedo, and I have recently
procured it from the gymnotus: Dr. Davy has observed the heating power
of the current from the torpedo. I have therefore filled up these spaces
with crosses, in a different position to the others originally in the table.
There remain but five spaces unmarked, two under attraction and repulsion,
and three under discharge by hot air; and though these effects have not
yet been obtained, it is a necessary conclusion that they must be possible,
since the spark corresponding to them has been procured. For when a
discharge across cold air can occur, that intensity which is the only
essential additional requisite for the other effects must be present.—
December 13, 1838.

^ In further illustration of this subject, see 590-608 in Part V.— December
1838.

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 experi¬
ments (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 necessarx'
corrections.

99. Seven of the battery jars were removed, and eight re¬
tained 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, some¬
times through thirty-eight inches of thin string wetted by dis¬
tilled 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 de¬
flection 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 trans¬
mission, as M. Colladon says, through the silk in the galvano-

Definite Magnetic Action 29

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

102. Hence it would appear that if the same absolute quantity
of electricity pass through the galvanometer, whatever may he its
inie 7 isity, the deflecting force iipon the magnetic needle is the same.

103. The batter}" 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 gi'aduation
was not accurate enough for me to assert that the arc w^as
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.^

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 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.^

105. The next point was to obtain a voltaic arrangement
producing an effect equal to that just described (103). A 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 appa¬
ratus, which, by immersion in a given acid for a given time,
much less than that required by the needle to swing in one

^ 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.

" Quarterly Journal of Science, New Series, vol. i. p. 33.

3 Plymouth Transactions, p. 22.

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.

106. 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
much electricity in eight beats of my watch, or in i-f o’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 5J
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
action. A 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

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 weighty upon the test paper to be employed. The
test paper itself was supported upon a platina spatula^ con¬
nected either with the discharging train (28), or with the negative
wire of the voltaic apparatus, and it consisted of four thick¬
nesses, moistened at all times to an equal degree in a standard
solution of hydriodate of potassa (52).

no. When the platina wire w’-as 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.

111. 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 5J division (108), the fourfold moistened paper inter¬
vening as before.^ 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 man}^
limes, it was constantly found that this standard current of
voltaic electricity, continued for eight beats of the watch, w^as
equal, in chemical effect, to thirty turns of the machine; twenty-
eight 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 electricit}^ 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
powtr, 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,

^ Of course the heightened power of the voltaic battery was necessary
to compensate for the bad conductor now interposed.

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
(‘iiabled me to make of the facts and views constituting the
theory of electro-chemical decomposition^ will^ with some other
[joints of electrical doctrine, be almost immediately submitted
to the Royal Society in another series of these Researches.

December 15 , 1832 .

§ 3. ON A NEW LAW OF ELECTRIC CONDUCTION, § 4. ON
CONDUCTING POWER GENERALLY

§ 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
t hough 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 ])e decomposed, or as the actual poles of a voltaic
1 Kittery, 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 (dectricity was prevented, and ail decomposition ceased.

j 18. 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 1 'ourth Series, original edition, vol. i. p. no.

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 three-
eighths 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 dis¬
tilled 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 frigo-
rific mixture, whilst contact between the tin and platina re¬
spectively 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 galvano¬
meter 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 \vas the consequence

c

34 Faraday’s Researches j

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 him, 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
effttets occurred; but they could always be traced to some inter¬
fering circumstances. The water should in every instance be
w{‘ll 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
(lamp or wet within, it is necessary that the cold be sufficiently
wtdl 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
t(‘) conduct also, the current will pass. The water should be
pure, not only that unembarrassed results may be obtained, but
!iIso lhat, as the freezing proceeds, a minute portion of concen¬
trated saline solution may not be formed, which remaining fluid,
and being intcjrposcd in the ice, or passing into cracks resulting
from contraction, may exhibit conducting powers independent

of the ice itself. ^ 1 . r.

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

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 elec¬
trometer 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
when fused to replace water as conductors. A 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

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 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

introduced, 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.

137. A fourth arrangement was used for substances requiring
very high temperatures for their fusion. A 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 In 1801, Sir H. Davy knew that “ dry nitre, caustic potash, and soda
are conductors of galvanism when rendered fluid by a high degree of heat ”
{Journals of the Royal Institution, 1802, p. 53), but was not aware of the
general law which I have been engaged in developing. It is remarkable,
that eleven years after that, he should say, “ There are 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,'

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 anti¬
mony, 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;
sidpho-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 con¬
ducting power in these cases of softening was probably due to
the elevation of temperature (i68, i8i); but I have no doubt
that by far the greater part was due to -the influence of the

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 h3drated
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, per-
iodide 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 it gained 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 galvano¬
meter. 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 0° 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.

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 ^ 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 im¬
portantly 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 con¬
duction, 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 oj 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.

40 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 de¬
composition^ 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
UDon 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 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
contrasted, one being lost as the other is gained. We 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 decom¬
posable 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.

^ See 414, etc., etc .—December 1838.

Conduction by Ice and Solid Salts 41

§ 4. On Conducting Power generally ^

154. It is not my 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

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

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 elec¬
tricity 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.

160. 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.

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, tliere 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
latter. A brown spot of iodine very slowly appeared, indi¬
cating the passage of a little electricit}^ 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.

166. A 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

44 Faraday’s Researches

chloride of lead produced the same effect. The conducting
power of these bodies^ when fluid, is very great (13I; 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).

168. 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
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 gal¬
vanometer 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 galvanometer 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 elec¬
tricity from the battery was sufficient to raise the temperature

^ Philosophical Transactions, 1S21, p. 431.

Increase of Conducting Power by Heat 45

of the sulphuret; and then^ without any application of extra¬
neous 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

46 Faraday’s Researches |

phenomena of this decomposition will be reserved for its proper j
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 i
under common circumstances. When gases are heated, they j
increase in conducting power, both for common and voltaic ;
electricity (7); and it is probable that if we could compress and i
condense them at the same time, we should still further increase j
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 i

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

demarcation can be pointed out; ^ that, in fact, the two states 1

shall become one;—which one state presents us at different
times with differences in degree as to certain properties and I
relations; and which differences are, under ordinary circum- |

stances, so great as to be equivalent to two different states. I

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 j

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. , t

180. All bodies conduct electricity in the same manner fromi 1

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

181. Conducting power is in some bodies powerfully in- 1

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

ceiving any accompanying essential electrical difference, either j

in the bodies or in the changes occasioned by the electricity 1

conducted' '

182. A numerous class of bodies, insulating electricity of low I

intensity, when solid, conduct it very freely when fluid, and are j
then decomposed by it. j

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

^ Annates de Chimie^ xxi. pp. 127, 178. !

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
decomposition.^

184. There is but one body yet discovered - 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 caU; as yet; be drawn between bodies supposed to be
elementary; and those known to be compounds.

April 15, 1833.

IIP

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

^ On Electro-chemical Decomposition ^

186. I HAVE in a recent series of these Researches (i) proved
(to my 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 mC; a probable conse¬
quence; that the use of electricity of such intensity as that
afforded by the machine; would; when applied to effect and

^ See the next part of these Experimental Researches.

“It is just possible that this case may, by more delicate experiment^
hereafter disappear.

“ Fifth Series, original edition, vol. i. p. 127.

^ Refer to the note after paragraph 783 .—December 1838,

48 Faraday’s Researches

elucidate electro-chemical decomposition^ show some new con¬
ditions of that action, evolve new views of the internal arrange¬
ments and changes of the substances under decomposition, and
perhaps give efficient powers over matter as yet undecomposed.

188. 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.

^ 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 teet 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 w ire four feet apart from each other.
Finally, a piece of string, seventy feet long, was used. It was

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
stringy 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 ex¬
tension’ 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 tur¬
meric paper, and the string were then removed; the positive
point was left resting upon the litmus paper, and the latter
touched by a piece of moistened string held in the hand. A
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

D

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 electro¬
chemical decomposition does not depend upon the simulta¬
neous 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.

198. A 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
(48). 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,
the extremity n was examined, and the
two points or angles found deeply
coloured by the presence of free alkali (fig. 8a).

199. A similar piece of litmus paper, dipped in solution of

No Metallic Poles Used

5 ^

sulphate of soda n, 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
of air only. A 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
])y a wire with the conductor of the machine, and the other, n,
with the discharging train. The interval in each case between
the points was about half an inch: the positive point p was

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 h became reddened from acid evolved there,

Fig. 10.

and the point of the turmeric a red from a similar and simul¬
taneous evolution of alkali.

202. 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 continu¬
ing 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.

m

.._j

Polar Decompositions in Air 53

205. Finally, a series of four small compound conductors,
consisting of litmus and turmeric paper (fig. ii) 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 ?z 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 decomposition.^

^ 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).

54

Faraday’s Researches

^ 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: ” ^ and
again, “ when any substance rendered fluid by heat, consisting
of mater, 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 1801,^ 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 potassa, were sufficient to form, with platina
and zinc, powerful electromotive circles; ^ but he is here speak¬
ing 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 ccpially 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).

^ Elements of Chemical Philosophy, p. 169, etc. * Ibid. pp. 144, 145. ;

* Journal of the Royal Institution, 1802, p. 53. *

^ Philosophical Transactions, 1826, p. 406.

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 suffeing 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 (i3o)r; 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 evolvedj 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
fluids as described in my 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
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 de¬
compositions 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

^Philosophical Transactions, 1826, p. 406.

56 Faraday’s Researches

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 some¬
times 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 pilcj 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 wrongs 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 electricity.^ He considers
the pile as an electric magnet, i,e, as an attractive and repulsive
agent; the poles having aiiraciive and repellwg powers. The
pole from whence resinous electricity issues attracts hydrogen
and repels oxygen, whilst that from which vitreous electricity

^ Annales de Chimie, 1806, tom. Iviii. p. 64.

•*., • ...i

Electro-Chemical Decomposition 57

pi'oceeds attracts oxygen and repels hydrogen; so that each
of the elerrents 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 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 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 of the poles. This is the case in the general ex¬
pression of facts ” given at pp. 28 and 29 of the Philosophical
Traiisactions 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; ^
and supposes that the attractive and repellent agencies may be
communicated from the metallic surfaces throughout the whole
of the menstruum,^ being communicated from one particle to
another particle of the same hind^ and diminishing in strength
from the place of the poles to the middle point, which is neces¬
sarily neutral.'^ In reference to this diminution of power at

^ Annates de Chimie, pp. 66, 67, also tom. Ixiii. p. 20.

^ Ibid, tom Iviii. p. 68, tom. Ixiii. p. 20.

^ Ibid, tom Ixiii. p. 34.

^Philosophical Transactions, 1807, pp. 29, 30.

^ Ibid. p. 39. ® Ibid, p, 29. Ibid. p. 42.

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.^

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 communication/^ and
uses the terms attraction and repulsion apparently in the same
sense as before.^

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 7 iegative 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.^

222. M. Biot is very cautious in expressing an opinion as to
the cause of the separation of the elements of a compound
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 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 undccomposed 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 it.”^

^ Philosophical Transactions^ 1807, p. 42.

2 Ibid. 1826, p. 383. ® Ibid. pp. 389, 407, 415.

^ Annales de CMmi«,-i8o7, tom. Ixiii. p. 83, etc.

® Precis Elcmeniaire de Physique, sme Edition, 1824, tom. i. p. 64 t.

® Ibid. p. 637. ’ Ihid. pp. 6.11, 642.

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
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
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 repulsions.^

225. M. A. de la Rive investigated this subject particularly,
and published a paper on it in 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 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 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.'^ 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 poles.® He

^ Precis EUmenlaire de Physique^ 3me Edition, 1824, tom. i. p. 636.

^ Ibid. p. 642. ^ Ibid. pp. 638, 642.

* Annates de Chimie, tom. xxviii. p. 190. ® Ibid, pp. 200, 202.

® Ibid, p, 202. Ibid. p. 201. ® Ibid. pp. 197, 198.

6o

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 sei*ve only to conduct the two
contrary currents of electricity and matter which set off from
the opposite 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 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,
obviate the necessity for the publication of my views. If such
be the case, I have to regret my 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 battery,
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 sub¬
stance. 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

^ Annales de Chimie, tom. xxviii. pp. 192, 199.

2 Ibid, p. 200. ^ Ibid, tom. li. p. 73.

Electro-Chemical Decomposition 6i

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 unexcep-
tionably in the following manner. As the experiment for ver}^
natural reasons requires many precautions to be successful,
and will be referred to hereafter in illustration of the views t
shall venture to give, I must describe it minutely.

230. A 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
liquid on that side. A 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
agitation of the solution above the level to which it rose. A 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
horizontally, a comparatively definite plane of contact. A
second platina pole e was arranged so as to be just under the
surface of the water, in a position nearly horizontal, a little

62 Faraday’s Researches

inclination being given to it, that gas evolved during decom¬
position 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, pf 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
ivaier, 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 w^ater 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

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 ht
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
is right; however; in the fact^ according to my 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 dimijiution
of power with increase of distance from the poles ^ (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

^ Philosophical Transactions, 1807, p. 42.

64 Faraday’s Researches

theoretically from considering the poles as centres of attraction [

.and repulsion; but I have not found the statement borne out i

by other experiments (241); and in the one quoted by him 1

the effect was doubtless due to some of the many interfering |

causes of variation which attend such investigations. |

237. A glass vessel had a platina plate fixed perpendicularly I

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 j

yet that the gas evolved at it might be collected. The tubes |

were filled with the acid, and one immersed in each cell. Each i

platina pole was equal in surface to one side of the dividing '

plate in the middle glass vessel, and the whole might be con- j

sidered as an arrangement between the poles of the battery of |

a humid decomposable conductor divided in the middle by tlie !

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. j

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 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 i

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 decom¬
posing conductor varies, as is always the case when mere wires
or plates, as poles, are dipped into or are surrounded by solution,

^ There are certain precautions, in this and such experiments, which can
•only be understood and guarded against by a knowledge of the phenomena
ito be described in the first part of the Fourth Part of these Researches.

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 varia¬
tions 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/or a constant
quantity of electricity^ whatever the decomposing conductor may he,
whether water, saline solutions, acids, fitsed bodies, etc., the amount
of electro-clmnical action is also a constant quantity, i.e. would
always he 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

E

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 hydro¬
gen, potassium and oxygen, chlorine and sodium, acid and
alkali, etc., a consequence which, although perhaps not impos¬
sible, 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 con¬
ductors, 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 Chompr6
(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 electro¬
chemical 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
in certain cases (in) the decomposition is proportionate to the

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 agree¬
ing in the effect of the current itself. Some philosophers, with
Franklin, assume but one electric fluid; and such must agree
together in the genera] 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 potverful than the
negative current,^ the nitrate of soda being, under similar
circumstances, decomposed. by the former, but not by the
latter.

249. M. Hachette states ^ 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 {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 chemi¬
cal 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, tom. Ixiii. p. 84. ^ Ihid, 1832, tom. li. p. 73.

■ Ibid. 1825, tom. xxviii. pp. 197, 201.

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 correspond¬
ing 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 varia¬
tions 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
together. A 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 chemically.^

253- 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

^ Thermo-electric currents are of course no exception, because when they
fail to act chemically they also fail to be currents.

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 de¬
pendent upon the muUial chemical affinity of the particles of
opposite kinds. Particles a a, fig. 13, could not be transferred
or travel from one pole N towards the other P, unless they
found particles of the opposite kind h 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 h of the
opposite kind, with which it was the moment before in combi-

Fig. 13. Fig. 14.

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 <2, 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 hy the superior attraction of a for b, that
superior attraction belonging to it in consequence of the relative
position Q>i a b and a to the direction of the axis of electric
power (253) superinduced by the current. But as all the com¬
pound 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

JO 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 fluids
these lines must diverge rapidly from the poles; and the direc¬
tion 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 par¬
ticles 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 cir¬
cumstance 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 ordi¬
nary circumstances, to that by which it is combined with its
own particle, can, under the electric influence, exerted in a defi¬
nite direction, be made even to surpass it. This general rela¬
tion of particles already in combination to other particles with

Electro-Chemical Decomposition 7 r

which they are not combined^ is sufficiently distinct in nume¬
rous 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 ceasC; 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 modi¬
fication; 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, there¬
fore, it would be more philosophical, and more directly expres¬
sive 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 illus¬
trating these views in the first instance; to which I will now
add others.

261. In order to show the dependence of the decomposition

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,;
its specific gravity was 1021.2. A 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
the diluted acid just referred to. A 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 and seventeen measures of the
solution of sulphate of soda into each of the vessels A and B.
Asbestus; which had been well washed in acid; acted upon by

the voltaic pile; well washed in water; and dried by pressure;
was used to connect a with b and A 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¬
munications. h and A 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-

Transference of Acid and Alkali 73

tions of asbestos were lifted out^ and the drops hanging at the
ends allowed to fall each into its respective vessel. The acids
in a and h 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 h, 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.

264. In comparing the difference of acid in A and B, the
necessary equality of weight was considered as of no conse¬
quence, because the solution was at first neutral, and would not,
therefore, affect the test liquids, and all the evolved acid would
be in B, and the free alkali in A. The solution in A 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 sp
much too small; and therefore it would appear that about a
tenth of the acid originally in the vessel A 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 suffi¬
ciently 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

74 Faraday’s Researches

very evident that the transfer is greatly dependent upon the
mutual action of the particles of the decomposing bodies.^

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 receiving 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

See the note to 410 .—December 1838.

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 decom¬
position 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 gravita¬
tion, 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

76 Faraday’s Researches i

relation to those particles which are leaving the substance under I
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 j
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 decom- !

posing matter, and found with the lead at the negative pole. 1

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 I

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 1

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, i

or pass from pole to pole, unless it be in chemical relation to i

som other element or substance tending to pass in the opposite |

direction, for the effect is considered as essentially due to the

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 pole.^ Yet such is not the case, as
has been shown by the experiments on free and combined acid
i (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.

I 280. It is very difficult to find cases amongst solutions or
fluids which shall illustrate this point, because of the difficulty
I of finding two fluids which shall conduct, shall not mingle and
1 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 diminish¬
ing it in the opposite, is just as good a reason for transfer as
modifying the affinity between the acids and alkalies them¬
selves.^ 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
1 current (254, 260), to combine with it; the platina therefore
remains where it was first placed, and has no tendency to pass

i ^ Even Sir Humphry Davy considered the attraction of the pole as being
; communicated from one particle to another of the same kind (219).

^ See the note to 410 .—December 1838.

7 ^ 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 either pole; and if in relation by
chemical affinity to any substance present, are powerfully
determined to the negative 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.

* III making this experiment, care must be taken that no substance be
r^resent 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
r<!p{*at(‘d when the platina poles were changed. But on examining the
clear liquor in the cell, after subsidence of the metallic gold, I found a little
of that iiKital in solution, and a little chlorine was also present. I therefore
well washed the gold which had thus been subjected to voltaic action,
<JiffiiS(‘cl 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.

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 couId 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. 'fhere 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, pro¬
portions, 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 decom¬
posing 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

8o

Faraday’s Researches

€lectro--cherrLical decomposition and transfer which Sir Humphry
Davy described in his celebrated paper^^ were those in which
acids were passed through alkalies^ and alkalies or earths through
acids; ^ and the way in which substances having the most
powerful attractions for each other were thus prevented from
combinings or^ as it is said^ had their natural affinity destroyed
or suspended throughout the whole of the circuits excited the
utmost astonishment. But if I be right in the view I have
taken of the effectSs it will appear that that which made the
wonder is in fact the essential condition of transfer and decom¬
positions and that the more alkali there is in the course of an
acids 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 ventureds and those previously exist-
ings 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 barytas or baryta through sulphuric acids^
because of the precipitation of sulphate of barytas enter within
the pale of the law already described (ii6s i48)s by which
liquidity is so generally required for conduction and decom¬
position. In assuming the solid state of sulphate of barytas
these bodies became virtually non-conductors to electricity of
so low a tension as that of the voltaic batterys 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 rests or rather of evolutions sometimes at one
pole and sometimes at the other. Sulphur illustrates this
effect very well.^ When sulphuric acid is decomposed by the
piles sulphur is evolved at the negative pole; but when sul-
phuret of silver is decomposed in a similar way (i72)s 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 poles but not retained by it; but by virtue of its elastic;

^ Philosophical Transactions, iSoy, p. i. ^ Ibid, p, 24, etc.

® Ibid. p. 25, etc.

* 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. .

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
determine the true circumstances of its appearance. A 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

F

82

Faraday’s Researches

a secondary effect^ and not an immediate consequer
decomposing power of the electric current.^

292. A few observations on what are called the pc
voltaic battery now seem necessary. The poles are r
surfaces or doors by which the electricity enters intc
out of the substance suffering decomposition. They
extent of that substance in the course of the electri
being its terminations in that direction: hence the
evolved pass so far and no further.

293. Metals make admirable poles^ in consequenc
high conducting power^ their immiscibility with the 5
generally acted upon^ their solid form^ and the oj
afforded of selecting such as are not chemically acte(
ordinary substances.

294. Water makes a pole of difficult application^ e
few cases (230)^ because of its small conducting ;
miscibility with most of the substances acted upoi
general relation to them in respect to chemical af
consists of elements; which in their electrical and
relations are directly and powerfully opposed^ yet
to produce a body more neutral in its character than
So that there are but few substances which do not
relation^ by chemical affinity^ with water or one of its
and therefore either the water or its elements are 1
and assist in transferring the infinite variety of bod
in association with it^, can be placed in the course of 1
current. Hence the reason why it so rarely happen
evolved substances rest at the first surface of the ^
why it therefore does not exhibit the ordinary action

295. Air^ however, and some gases are free from
objection^ and may be used as poles in many cases <
but^ in consequence of the extremely low degree of <
power belonging to them,, they cannot be employee
voltaic apparatus. This limits their use; for t
apparatus is the only one as yet discovered whic
sufficient quantity of electricity (107^ 112) to effe
chemical decomposition with facility.

296. When the poles are liable to the chemical
the substances evolved^, either simply in consequen
natural relation to them^ or of that relation aided by tt

^ Refer for proof of the truth of this supposition to 483,
P^eember 1838.

Character and Nature of the Poles 85

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 electro¬
chemical 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 attrac¬
tion 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.

297. A 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 solu¬
tions, 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.

84 Faraday’s Researches

299. Having thus given my theory of the mode in which
electro-chemical decomposition is effected, I will refrain for the
present from entering upon the numerous general considera¬
tions which it suggests, wishing first to submit it to the test of
publication and discussion.

June 1833.

IV"

§ 6. ON THE POWER OF METALS AND OTHER SOLIDS TO INDUCE
THE COMBINATION OF GASEOUS BODIES

300. The conclusion at which I have arrived in the present
communication may seem to render the whole of it unfit to form
part of a series of researches in electricity; since, remarkable as
the phenomena are, the power which produces them is not to
be considered as of an electric origin, otherwise than as all
attraction of particles may have this subtile agent for their
•common cause. But as the effects investigated arose out of
electrical researches, as they are directly connected with other
effects which are of an electric nature, and must of necessity
be understood and guarded against in a very extensive series
of electro-chemical decompositions (442), I have felt myself
fully justified in describing them in this place.

301. Believing that I had proved (by experiments hereafter
to be described (440)) the constant and definite chemical action
of a certain quantity of electricity, whatever its intensity might
be, or however the circumstances of its transmission through
•either the body under decomposition or the more perfect con¬
ductors were varied, I endeavoured upon that result to construct
a new measuring instrument, which from its use might be called,
at least provisionally, a Volta-electrometer (475).^

302. During the course of the experiments made to render
the instrument efficient, I was occasionally surprised at observ¬
ing a deficiency of the gases resulting from the decompositions
■of water, and at last an actual disappearance of portions which
had been evolved, collected, and measured. The circumstances
of the disappearance were these, A glass tube, about twelve

^ Sixth Series, original edition, voL i. p. 165.

^ Or Voltameter .—December 1838.

Dis^^ppearance of Gases Around the Poles 85

inches in length and three-fourths of an inch in diameter, had
two platina poles fixed into its upper, hermetically sealed,
extremity: the poles, where they passed through the glass, were
of wire; but terminated below in plates, which were soldered to
the wires with gold (fig. 16). The tube was filled
with dilute sulphuric acid, and inverted in a cup
of the same fluid; a voltaic battery was con¬
nected with the two wires, and sufficient oxygen
and hydrogen evolved to occupy four-fifths of
the tube, or by the graduation, 116 parts. On
separating the tube from the voltaic battery the
volume of gas immediately began to diminish,
and in about five hours only 13 ’ parts remained,
and these ultimately disappeared.

303. It was found by various experiments
that this effect was not due to the escape or
solution of the gas, nor to recombination of the
oxygen or hydrogen in consequence of any
peculiar condition they might be supposed to
possess under the circumstances; but to be
occasioned by the action of one or both of the
poles within the tube upon the gas around them.

On disuniting the poles from the pile after they
had acted upon dilute sulphuric acid, and introducing them
into separate tubes containing mixed oxygen and hydrogen,
it was found that the positive pole effected the union of the
gases, but the negative pole apparently not (324). It was
ascertained also that no action of a sensible kind took place
between the positive pole with oxygen or hydrogen alone.

304. These experiments reduced the phenomena to the con¬
sequence of a power possessed by the platina, after it had been
the positive pole of a voltaic pile, of causing the combination of
oxygen and hydrogen at common, or even at low, temperatures.
This effect is, as far as I am aware, altogether new, and was
immediately followed out to ascertain whether it was really of
an electric nature, and how far it would interfere with the
determination of the quantities evolved in the cases of electro¬
chemical decomposition.

305. Several platina plates were prepared (fig. 17). They

were nearly half an inch wide, and two inches and a half long:
some were of an inch, others not more than -(r-J-^^dth,

whilst some were as much as yoth of an inch in thickness. Each
had a piece of platina wire, about seven inches long, soldered to

86

Faraday’s Researches

it by pure gold. Then a number of glass tubes were prepared:
they were about nine or ten inches in lengthy, five-eighths of an
inch in internal diameter^ were sealed hermetically at one

37

I ^ ...

Fig. 17.

•extremity; and were graduated. Into these tubes was put a
mixture of two volumes of hydrogen and one of oxygeU; at the
water pneumatic trough, and when one of the plates described
had been connected with the positive or negative pole of the
voltaic battery for a given time, or had been otherwise prepared,
it was introduced through the water into the
gas within the tube; the whole set aside in a
test-glass (fig. 18), and left for a longer or
shorter period, that the action might be
observed.

306. The following result may be given as an
illustration of the phenomenon to be investi¬
gated. Diluted sulphuric acid, of the specific
gravity 1.336, was put into a glass jar, in which
was placed also a large platina plate, con¬
nected with the negative end of a voltaic
battery of forty pairs of four-inch plates, with
double coppers, and moderately charged. One
of the plates above described (305) was then
connected with the positive extremity, and im¬
mersed in the same jar of acid for five minutes,
after which it was separated from the battery,
washed in distilled water and introduced
through the water of the pneumatic trough into
a tube containing the mixture of oxygen and
hydrogen (305). The volume of gases immediately began to
lessen, the diminution proceeding more and more rapidly until
about three-fourths of the mixture had disappeared. The
upper end of the tube became quite warm, the plate itself so
hot that the water boiled as it rose over it; and in less than a
minute a cubical inch and a half of the gases were gone, having
been combined by the power of the platina, and converted into
water.

307. This extraordinary influence acquired by the platina at
the positive pole of the pile, is exerted far more readily and

Preparation of the Platina Plates 87

efEectively on oxygen and hydrogen than on any other mixture
of gases that I have tried. One volume of nitrous gas was
mixed with a volume of hydrogen^ and introduced into a tube
with a plate which had been made positive in the dilute sulphuric
acid for four minutes (306). There was no sensible action in an
hour; being left for thirty-six hourS; there was a diminution of
about one-eighth of the whole volume. Action had taken place,
but it had been veiy^ feeble.

308. A mixture of two volumes of nitrous oxide with one
volume of hydrogen was put with a plate similarly prepared
into a tube (305, 306). This also showed no action immedi¬
ately; but in thirty-six hours nearly a fourth of the whole had
disappeared, i.e, about half of a cubic inch. By comparison
with another tube containing the same mixture without a plate,
it appeared that a part of the diminution was due to solution,
and the other part to the power of the platina; but the action
had been very slow and feeble.

309. A mixture of one volume olefiant gas and three volumes
oxygen was not affected by such a platina plate, even though
left together for several days (376, 377).

310. A mixture of two volumes carbonic oxide and one
volume oxygen was also unaffected by the prepared platina
plate in several days (381, etc.).

311. A mixture of equal volumes of chlorine and hydrogen was
used in several experiments, with plates prepared in a similar
manner (306). Diminution of^bulk soon took place; but when
after thirty-six hours the experiments were examined, it was
found that nearly all the chlorine had disappeared, having been
absorbed, principally by the water, and that the original volume
of hydrogen remained unchanged. No combination of the
gases, therefore, had here taken place.

312. Reverting to the action of the prepared plates on
mixtures of oxygen and hydrogen (306), I found that the power,
though gradually diminishing in all cases, could still be retained
for a period, varying in its length with circumstances. When
tubes containing plates (305) were supplied with fresh portions
of mixed oxygen and hydrogen as the previous portions were
condensed, the action was found to continue for above thirty
hours, and in some cases slow combination could be observed
even after eighty hours; but the continuance of the action
greatly depended upon the purity of the gases used (374).

313. Some plates (305) were made positive for four minutes
in dilute sulphuric acid of specific gravity 1.336: they were

88

Faraday’s Researches

rinsed in distilled water, after which two were put into a smaB
bottle and closed up, whilst others were left exposed to the air.
The plates preserved in the limited portion of air were found
to retain their power after eight days, but those exposed to the
atmosphere had lost their force almost entirely in twelve hours,
and in some situations, where currents existed, in a much
shorter time.

314. Plates were made positive for five minutes in sulphuric
acid, specific gravity 1.336. One of these was retained in similar
acid for eight minutes after separation from the battery: it then
acted on mixed oxygen and hydrogen with apparently undimi¬
nished vigour. Others were left in similar acid for forty hours,
and some even for eight days, after the electrisation, and then
acted as well in combining oxygen and hydrogen gas as those
which were used immediately after electrisation.

315. The effect of a solution of caustic potassa in preserving
the platina plates was tried in a similar manner. After being
retained in such a solution for forty hours, they acted exceed¬
ingly well on oxygen and hydrogen, and one caused such rapid •
condensation of the gases, that the plate became much heated,
and I expected the temperature would have risen to ignition.

316. When similarly prepared plates (305) had been put into
distilled water for forty hours, and then introduced into mixed
oxygen and hydrogen, they were found to act but very slowly
and feebly as compared with those which had been preserved
in acid or alkali. When, howeyer, the quantity of water was
bu small, the power was very little unpaired after three or four
days. As the water had been retained in a wooden vessel,
portions of it were redistilled in glass, and this was found to
preserve prepared plates for a great length of time. Prepared
plates were put into tubes with this water and closed up; some
of them, taken out at the end of twenty-four days, were found
very active on mixed ox3^gen and hydrogen; others, which were
left in the water for fifty-three days, were still found to cause
the combination of the gases. The tubes had been closed only
by corks.

317. The act of combination always seemed to diminish, or
apparently exhaust, the power of the platina plate. It is true,
that in most, if not all instances, the combination of the gases,
at first insensible, gradually increased in rapidity, and some¬
times reached to explosion; but when the latter did not happen,
the rapidity of combination diminished; and although fresh
portions of gas were introduced into the tubes, the combination

Power of the Plates Affected 89

went on more and more slowly^ and at last ceased altogether.
The first effect of an increase in the rapidity of combination
depended in part upon the water flowing off from the platina
plate, and allowing a better contact with the gas, and in part
upon the heat evolved during the progress of the combination
(366). But notwithstanding the effect of these causes, diminu¬
tion, and at last cessation of the power, always occurred. It
must not, however, be unnoticed, that the purer the gases
subjected to the action of the plate, the longer was its combining
power retained. With the mixture evolved at the poles of the
voltaic pile, in pure dilute sulphuric acid, it continued longest;
and with oxygen and hydrogen, of perfect purity, it probably
would not be diminished at all.

318. Different modes of treatment applied to the platina plate,
after it had ceased to be the positive pole of the pile, affected
its power ver}.^ curiously. A plate which had been a positive
pole in diluted sulphuric acid of specific gravity 1.336 for four
or five minutes, if rinsed in water and put into mixed oxygen
and hydrogen, would act very well, and condense perhaps one
cubic inch and a half of gas in six or seven minutes; but if that
same plate, instead of being merely rinsed, had been left in
distilled water for twelve or fifteen minutes, or more, it would
rarely fail, when put into the oxygen and hydrogen, of becoming,
in the course of a minute or two, ignited, and would generally
explode the gases. Occasionally the time occupied in bringing
on the action extended to eight or nine minutes, and sometimes
even to forty minutes, and yet ignition and explosion would
result. This effect is due to the removal of a portion of acid
which otherwise adheres firmly to the plate.’-

319. Occasionally the platina plates (305), after being made
the positive pole of the battery, were washed, wiped with filter¬
ing-paper or a cloth, and washed and wiped again. Being then
introduced into mixed oxygen and hydrogen, they acted ap¬
parently as if they had been unaffected by the treatment.
Sometimes the tubes containing the gas were opened in the air
for an instant, and the plates put in dry; but no sensible
difference in action was perceived, except that it commenced
sooner.

320. The power of heat in altering the action of the prepared
platina plates was also tried (331). Plates which had been
rendered positive in dilute sulphuric acid for four minutes were
well washed in water, and heated to redness in the flame of a

^ In proof that this is the case, refer to 774 .—December 1838.

90 Faraday’s Researches

spirit-lamp: after this they acted very well on mixed oxygen
and hydrogen. Others, which had been heated more powerfully
by the blowpipe, acted afterwards on the gases, though not so
powerfully as the former. Hence it appears that heat does not
take away the power acquired by the platina at the positive
pole of the pile: the occasional diminution of force seemed
always referable to other causes than the mere heat. If, for
instance, the plate had not been well washed from the acid, or
if the flame used was carbonaceous, or was that of an alcohol
lamp trimmed with spirit containing a little acid, or having a
wick on which salt, or other extraneous matter, had been placed,
then the power of the plate was quickly and greatly diminished
< 37 °, 372)-

321. This remarkable property was conferred upon platina
when it was made the positive pole in sulphuric acid of specific
gravity 1.336, or when it was considerably weaker, or when
stronger, even up to the strength of oil of vitriol. Strong and
dilute nitric acid, dilute acetic acid, solutions of tartaric, citric,
and oxalic acids, were used with equal success. When muriatic
acid was used, the plates acquired the power of condensing the
oxygen and hydrogen, but in a much inferior degree.

322. Plates which were made positive in solution of caustic
potassa did not show any sensible action upon the mixed oxygen
and hydrogen. Other plates made positive in solutions of
carbonates of potassa and soda exhibited the action, but only
in a feeble degree.

323. When a neutral solution of sulphate of soda, or of nitre,
•or of chlorate of potassa, or of phosphate of potassa, or acetate
•of potassa, or sulphate of copper, was used, the plates, rendered
positive in them for four minutes, and then washed in water,
acted very readily and powerfully on the mixed oxygen and
hydrogen.

324. It became a very important point, in reference to the
cause of this action of the platina, to determine whether the
positive pole only could confer it (303), or whether, notwith¬
standing the numerous contrary cases, the negative pole might
not have the power when such circumstances as could interfere
with or prevent the action were avoided. Three plates were
therefore rendered negative, for four minutes in iluted sul¬
phuric acid of specific gravity 1.336, washed in distilled water,
•and put into mixed oxygen and hydrogen. All of them acted,
though not so strongly as they would have done if they had
been rendered positive. Each combined about a cubical inch

Clean Platina Induces Combination 91

and a quarter of the gases in twenty-five minutes. On every
repetition of the experiment the same result was obtained; and
when the plates were retained in distilled water for ten or twelve
minutes^ before being introduced into the gas (318); the action
was very much quickened.

325. But when there was any metallic or other substance
present in the acid^ which could be precipitated on the negative
plate^ then that plate ceased to act upon the mixed oxygen and
hydrogen.

326. These experiments led to the expectation that the power
of causing oxygen and hydrogen to combine, which could be
conferred upon any piece of platina by making it the positive
pole of a voltaic pile, was not essentially dependent upon the
action of the pile, or upon any structure or arrangement of parts
it might receive whilst in association with it, but belonged to
the platina at all times, and was always effective when the surface
was perfectly clean. And though, when made the positive pole
of the pile in acids, the circumstances might well be considered
as those which would cleanse the surface of the platina in the
most effectual manner, it did not seem impossible that ordinary
operations should produce the same result, although in a less
eminent degree.

327. Accordingly, a platina plate (305) was cleaned by being
rubbed with a cork, a little water, and some coal-fire ashes upon
a glass plate: being washed, it was put into mixed oxygen and
hydrogen, and was found to act at first slowly, and then more
rapidly. In an hour, a cubical inch and a half had disappeared.

328. Other plates were cleaned with ordinary sand-paper and
water; others with chalk and water; others with emery and
water; others, again, with black oxide of manganese and water;
and others with a piece of charcoal and water. All of these
acted in tubes of oxygen and hydrogen, causing combination of
the gases. The action was by no means so powerful as that
produced by plates having been in communication with the
battery; but from one to two cubical inches of the gases dis¬
appeared, in periods extending from twenty-five to eighty or
ninety minutes.

329. Upon cleaning the plates with a cork, ground emery,
and dilute sulphuric acid, they were found to act still better.
In order to simplify the conditions, the cork was dismissed, and
a piece of platina foil used instead; still the effect took place.
Then the acid was dismissed; and a solution of potassa used,
but the effect occurred as before.

92 Faraday’s Researches

330. These results are abundantly sufficient to show that the
mere mechanical cleansing of the surface of the platina is suf¬
ficient to enable it to exert its combining power over oxygen
and hydrogen at common temperatures.

331. I now tried the effect of heat in conferring this property
upon platina (320). Plates which had no action on the mixture
of oxygen and hydrogen were heated by the flame of a freshly
trimmed spirit-lamp^ urged by a mouth blowpipe^ and when
cold were put into tubes of the mixed gases: they acted slowly
at first, but after two or three hours condensed nearly all the
gases.

332. A plate of platina, which was about one inch wide and
two and three-quarters in length, and which had not been used
in any of the preceding experiments, was curved a little so as
to enter a tube, and left in a mixture of oxygen and hydrogen
for thirteen hours: not the slightest action or combination of
the gases occurred. It was withdrawn at the pneumatic trough
from the gas through the water, heated red hot by the spirit-
lamp and blowpipe, and then returned when cold into the same
portion of gas. In the course of a few minutes diminution of
the gases could be observed, and in forty-five minutes about one
cubical inch and a quarter had disappeared. In many other
experiments platina plates when heated were found to acquire
the power of combining oxygen and hydrogen.

333. But it happened not unfrequently that plates, after being
heated, showed no power of combining oxygen and hydrogen
gases, though left undisturbed in them for two hours. Some¬
times also it would happen that a plate which, having been
heated to dull redness, acted feebly, upon being heated to white¬
ness ceased to act; and at other times a plate which, having
been slightly heated, did not act, was rendered active by a more
pov/erful ignition.

334. Though thus uncertain in its action, and though often
diminishing the power given to the plates at the positive pole
of the pile (320), still it is evident that heat can render platina
active which before was inert (331). The cause of its occa¬
sional failure appears to be due to the surface of the metal
becoming soiled, either from something previously adhering to
it, which is made to adhere more closely by the action of the heat,
or from matter communicated from the flame of the lamp, or
from the air itself. It often happens that a polished plate of
platina, when heated by the spirit-lamp and a blow-pipe,
becomes dulled and clouded on its surface by something either

Platina Cleansed by Acids and Alkalies 93

formed or deposited there; and this, and much less than this,
is sufficient to prevent it from exhibiting the curious power
now under consideration (370, 372). Platina also has been
said to combine with carbon; and it is not at all unlikely that
in processes of heating, where carbon or its compounds are
present, a film of such a compound may be thus formed, and
thus prevent the exhibition of the properties belonging to pure
platina.^

335. The action of alkalies and acids in giving platina this
property was now experimentally examined. Platina plates
(305) having no action on mixed oxygen and hydrogen, being
boiled in a solution of caustic potassa, washed, and then put
into the gases, were found occasionally to act pretty well, but
at other times to fail. In the latter case I concluded that the
impurity upon the surface of the platina was of a nature not to
be removed by the mere solvent action of the alkali, for when
the plates were rubbed with a little emery, and the same solution
of alkali (328), they betame active.

336. The action of acids was far more constant and satis¬
factory. A platina plate was boiled in dilute nitric acid: being
washed and put into mixed oxygen and hydrogen gases, it
acted well. Other plates were boiled in strong nitric acid for
periods extending from half a minute to four minutes, and then
being washed in distilled water, were found to act very well,
condensing one cubic inch and a half of gas in the space of
eight or nine minutes, and rendering the tube warm (306).

337. Strong sulphuric acid was very effectual in rendering
the platina active. A plate (305) was heated in it for a minute,
then washed and put into the mixed oxygen and hydrogen,
upon which it acted as well as if it had been made the positive
pole of a voltaic pile (306).

338. Plates which, after being heated or electrised in alkali,
or after other treatment, were found inert, immediately received
power by being dipped for a minute or two, or even only for
an instant, into hot oil of vitriol, and then into water.

339. When the plate was dipped into the oil of vitriol, taken
out, and then heated so as to drive off the acid, it did not act,
in consequence of the impurity left by the acid upon its surface.

340. Vegetable acids, as acetic and tartaric, sometimes
rendered inert platina active, at other times not. This, I believe,

^ When heat does confer the property it is only by the destruction or
dissipation of organic or other matter which had previously soiled the
plate (368, 369, 370 ).—December 1838.

Faraday’s Researches

depended upon the character of the matter previously soili
the plates, and which may easily be supposed to be sometiir
of such a nature as to be removed by these acids, and at otf
times not. Weak sulphuric acid showed the same differcni
but strong sulphuric acid (337) never failed in its action.

341. The most favourable treatment, except that of maki
the plate a positive pole in strong acid, was as follows. T
plate was held over a spirit-lamp flame, and when hot, rubh
with a piece of potassa fusa (caustic potash), which melth
covered the metal with a coat of very strong alkali, and t
was retained fused upon the surface for a second or two: ^
was then put into water for four or five minutes to wash off 1
alkali, shaken, and immersed for about a minute in hot strc
oil of vitriol; from this it was removed into distilled wat
where it was allowed to remain ten or fifteen minutes to remc
the last traces of acid (318). Being then put into a mixti
of oxygen and hydrogen, combination immediately began, a
proceeded rapidly; the tube became watm, the platina beca
red hot, and the residue of the gases was inflamed. This eff
could be repeated at pleasure, and thus the maximum phe
menon could be produced without the aid of the voltaic batte

342. When a solution of tartaric or acetic acid was substitut
in this mode of preparation, for the sulphuric acid, still
plate was found to acquire the same power, and would of
produce explosion in the mixed gases; but the strong sulphi
acid was most certain and powerful.

343. If borax, or a mixture of the carbonates of potash j
soda, be fused on the surface of a platina plate, and that p]
be well washed in water, it will be found to have acquired
power of combining oxygen and hydrogen, but only ii
moderate degi*ee; but if, after the fusion and washing, it
dipped in the hot sulphuric acid (337), it will become \
active.

344. Other metals than platina were then experimented w
(xold and palladium exhibited the power either when made
positive pole of the voltaic battery (306), or when acted or
hot oil of vitriol (337). When palladium is used, the ac
of the battery or acid should be moderated, as that meh
soon acted upon under such circumstances. Silver and co]
could not be made to show any eflect at common temperati

^ The heat need not be raised so much as to make the alkali tamisl
platina, although if that effect does take place it does not prevem
ultimate action.

Dulong and Thenard on Platina 95

345. There can remain no doubt that the property of in¬
ducing combination, which can thus be conferred upon masses
of platina and other metals by connecting them with the poles
of the battery, or by cleansing processes either of a mechanical
or chemical nature, is the same as that which was discovered
by Dobereiner,^ in 1823, to belong in so eminent a degree to
spongy platina, and which was afterwards so well experimented
upon and illustrated by MM. Dulong and Thenard,^ in 1823.
The latter philosophers even quote experiments in which a
very fine platina wire, which had been coiled up and digested
in nitric, sulphuric, or muriatic acid, became ignited when put
into a jet of hydrogen gas.^ This effect I can now produce at
pleasure with either wires or plates by the processes described
(306, 337, 341); and by using a smaller plate cut so that it
shall rest against the glass by a few points, and yet allow the
water to flow off (fig. 19), the loss of heat is less, the metal is
assimilated somewhat to the spongy state, and the probability
of failure almost entirely removed.

Fig. 19.

C —^

346. M. Dobereiner refers the effect entirely to an electric
action. He considers the platina and hydrogen as forming a
voltaic element of the ordinary kind, in which the hydrogen,
being very highly positive, represents the zinc of the usual
arrangement, and like it, therefore, attracts oxygen and combines
with it.^

347. In the two excellent experimental papers by MM. Dulong
and Thenard,® those philosophers show that elevation of tempera¬
ture favours the action, but does not alter its character; Sir
Humphry Davy’s incandescent platina wire being the same
phenomenon with Dobereiner’s spongy platina. They show
that all metals have this power in a greater or smaller degree,
and that it is even possessed by such bodies as charcoal,
pumice, porcelain, glass, rock-crystal, etc., when their tempera¬
tures are raised; and that another of Davy’s effects, in which
oxygen and hydrogen had combined slowly together at a heat
below ignition, was really dependent upon the property of the

1 Annales de Chimie, tom. xxiv. p. 93.

2 Ibid. tom. xxiii. p. 440; tom. xxiv. p. 380. ^ Ibid. tom. xxiv. p. 383.

* Ibid. tom. xxiv. pp. 94, 95. Also BibliotMqiie Universelle, tom. xxiv,.

p. 54

Ibid. tom. xxiii. p. 440; tom. xxiv. p. 380.

g 6 Faraday’s Researches

heated glass^ which it has in common with the bodies named
above. They state that liquids do not show this effect, at
least that mercury, at or below the boiling point, has not the
power; that it is not due to porosity; that the same bod}^
varies very much in its action, according to its state; and that
many other gaseous mixtures besides oxygen and hydrogen
are affected, and made to act chemically, when the temperature
is raised. They think it probable that spongy platina acquires
its power from contact with the acid evolved during its re¬
duction, or from the heat itself to which it is then submitted.

348. MM. Dulong and Thenard express themselves with
great caution on the theory of this action; but, referring to
the decomposing power of metals on ammonia when heated to
temperatures not sufficient alone to affect the alkali, they re¬
mark that those metals which in this case are most efficacious,
are the least so in causing the combination of oxygen and
hydrogen; whilst platina, gold, etc., which have least power of
decomposing ammonia, have most power of combining the
elements of water:—from which they are led to believe that
amongst gases, some tend to unite under the influence of metals,
whilst others tend to separate, and that this property varies
in opposite directions with the different metals. At the close
of their second paper they observe, that the action is of a
kind that cannot be connected with any known theory; and
though it is very remarkable that the effects are transient, like
those of most electrical actions, yet they state that the greater
number of the results observed by them are inexplicable, by
supposing them to be of a purely electric origin.

349. Dr. Fusinieri has also written on this subject, and
given a theory which he considers as sufficient to account for
the phenomena.^ He expresses the immediate cause thus:

The platina determines upon its surface a continual renova¬
tion of concrete lamince of the combustible substance of the gases
or vapours, which flowing over it are burnt, pass away, and are
renewed: this combustion at the surface raises and sustains the
temperature of the metal.” The combustible substance, thus
reduced into imperceptible laminse, of which the concrete parts
are in contact with the oxygen, is presumed to be in a state
combinable with the oxygen at a much lower temperature than
when it is in the gaseous state, and more in analogy with what
iis called the nascent condition. That combustible gases should
lose their elastic state, and become concrete, assuming the form
1 Giornale di Fisica, etc., 1825, tom. viii. p. 259.

Cleanness the Essential Condition 97

of exceedingly attenuated but solid strata, is considered as
proved by facts, some of which are quoted in the Giornale di
Fisica for 1824; ^ and though the theory requires that they
should assume this state at high temperatures, and though the
similar films of aqueous and other matter are dissipated by the
action of heat, still the facts are considered as justifying the
conclusion against all opposition of reasoning.

350. The power or force which makes combustible gas or
vapour abandon its elastic state in contact with a solid, that it
may cover the latter with a thin stratum of its own proper sub¬
stance, is considered as being neither attraction nor affinity.
It is able also to extend liquids and solids in concrete laminse
over the surface of the acting solid body, and consists in a
repulsion, which is developed from the parts of the solid body
by the simple fact of attenuation, and is highest when the
attenuation is most complete. The force has a progressive
development, and acts most powerfully, or at first, in the direc¬
tion in which the dimensions of the attenuated mass decrease,
and then in the direction of the angles or comers which from
any cause may exist on the surface. This force not only causes
spontaneous diffusion of gases and other substances over the
surface, but is considered as very elementary in its nature, and
competent to account for all the phenomena of capillarity,
chemical affinity, attraction of aggregation, rarefaction, ebulli¬
tion, volatilisation, explosion, and other thermometric effects,
as well as inflammation, detonation, etc., etc. It is considered
as a form of heat to which the term native caloric is given, and is
still further viewed as the principle of the two electricities and
the two magnetisms.

351. I have been the more anxious to give a correct abstract
of Dr. Fusinieri’s view, both because I cannot form a distinct
idea of the power to which he refers the phenomena, and because
of my imperfect knowledge of the language in which the memoir
is written. I would therefore beg to refer those who pursue the
subject to the memoir itself.

352. Not feeling, however, that the problem has yet been
solved, I venture to give the view which seems to me sufficient,
upon known principles, to account for the effect.

353. It may be observed of this action, that, with regard to
platina, it cannot be due to any peculiar, temporary condition,
either of an electric or of any other nature: the activity of plates
rendered either positive or negative by the pole, or cleaned with

1PP. 138, 371.

G

98 Faraday’s Researches

such different substances as acidS; alkalies^ or water; charcoal^
emery, ashes, or glass; or merely heated, is sufficient to negative
such an opinion. Neither does it depend upon the spongy and
porous, or upon the compact and burnished, or upon the massive
or the attenuated state of the metal, for in any of these states it
may be rendered effective, or its action may be taken away.
The only essential condition appears to be a perfectly clemi and
metallic surface, for whenever that is present the platina acts,
whatever its form and condition in other respects may be; and
though variations in the latter points will very much affect the
rapidity, and therefore the visible appearances and secondary
effects, of the action, i.e, the ignition of the metal and the
inffammation of the gases, they, even in their most favourable
state, cannot produce any effect unless the condition of a clean,
pure, metallic surface be also fulfilled.

354. The effect is evidently produced by most, if not all, solid
bodies, weakly perhaps by many of them, but rising to a high
degree in platina. Dulong and Thenard have very philosophic¬
ally extended our knowledge of the property to its possession
by all the metals, and by earths, glass, stones, etc. (347); and
every idea of its being a known and recognised electric action
is in this way removed.

355. All the phenomena connected with this subject press
upon my mind the conviction that the effects in question are
entirely incidental and of a secondary nature; that they are
dependent upon the natural conditions of gaseous elasticity,
combined with the exertion of that attractive force possessed
by many bodies, especially those which are solid, in an eminent
degree, and probably belonging to all; by which they are drawn
into association more or less close, without at the same time
undergoing chemical combination, though often assuming the
condition of adhesion; and which occasionally leads, under
very favourable circumstances, as in the present instance, to
the combination of bodies simultaneously subjected to this
attraction. I am prepared myself to admit (and probably
many others are of the same opinion), both with respect to the
attraction of aggregation and of chemical affinity, that the
sphere of action of particles extends beyond those other particles
with which they are immediately and evidently in union (259),
and in many cases produces effects rising into considerable
importance: and I think that this kind of attraction is a deter¬
mining cause of Dobereiner^s effect, and of the many others of
a similar nature.

Combining Power of Pktina 99

356. Bodies which become wetted by fluids with which they
do not combine chemically^ or in which they do not dissolve^
are simple and well known instances of this kind of attraction.

357. All those cases of bodies which being insoluble in water
and not combining with it are hygrometric, and condense its
vapour around or upon their surface, are stronger instances of
the same power, and approach a little nearer to the cases under
investigation. If pulverised clay, protoxide or peroxide of iron,
oxide of manganese, charcoal, or even metals, as spongy platina
or precipitated silver, be put into an atmosphere containing
vapour of water, they soon become moist by virtue of an attrac¬
tion which is able to condense the vapour upon, although not
to combine it with, the substances; and if, as is well known,
these bodies so damped be put into a dry atmosphere, as, for
instance, one confined over sulphuric acid, or if they be heated,
then they yield up this water again almost entirely, it not being
in direct or permanent combination.^

358. Still better instances of the power I refer to, because
they are more analogous to the cases to be explained, are
furnished by the attraction existing between glass and aii", so
well known to barometer and thermometer makers, for here the
adhesion or attraction is exerted between a solid and gases,
bodies having very different physical conditions, having no
power of combination with each other, and each retaining,
during the time of action, its physical state unchanged.^ When
mercury is poured into a barometer tube, a film of air will
remain between the metal and glass for months, or, as far as is
known, for years, for it has never been displaced except by the
action of means especially fitted for the purpose. These consist
in boiling the mercury, or in other words, of forming an abund¬
ance of vapour, which coming in contact with every part of
the glass and every portion of surface of the mercury, gradually
mingles with, dilutes, and carries off the air attracted by, and
adhering to, those surfaces, replacing it by other vapour, subject
to an equal or perhaps greater attraction, but which when
cooled condenses into the same liquid as that with which the
tube is filled.

^ I met at Edinburgh with a case, remarkable as to its extent, of hygro-
metric action, assisted a little perhaps by very slight solvent power. Some
turf had been well dried by long exposure in a covered place to the atmo
sphere, but being then submitted to the action of a hydrostatic press, i
yielded, by the mere influence of the pressure^ 54 per cent, of water. •

=* Fusinieri and Bellani consider the air as forming solid concrete films •
these cases .—Giornale di Fisica, 1825, tom. viii. p. 262.

lOO

Faraday’s Researches

359. Extraneous bodies^ which, acting as nuclei in crystallising
or depositing solutions, cause deposition of substances on them,
when it does not occur elsewhere in the liquid, seem to produce
their effects by a power of the same kind, ix. a power of attrac¬
tion extending to neighbouring particles, and causing them to
become attached to the nuclei, although it is not strong enough
to make them combine chemically with their substance.

360. It would appear from many cases of nuclei in solutions,
and from the effects of bodies put into atmospheres containing
the vapours of water, or camphor, or iodine, etc., as if this
attraction were in part elective, partaking in its characters both
of the attraction of aggregation and chemical affinity: nor is
this inconsistent with, but agreeable to, the idea entertained,
that it is the power of particles acting, not upon others with
which they can immediately and intimately combine, but upon
such as are either more distantly situated with respect to them,
or which, from previous condition, physical constitution, or
feeble relation, are unable to enter into decided union with them.

361. Then, of all bodies, the gases are those which might be
expected to show some mutual action whilst jointly under the
attractive influence of the platina or other solid acting substance.
Liquids, such as water, alcohol, etc., are in so dense and com¬
paratively incompressible a state, as to favour no expectation
that their particles should approach much closer to each other
by the attraction of the body to which they adhere, and yet that
attraction must (according to its effects) place their particles as
near to those of the solid wetted body as they are to each other,
and in many cases it is evident that the former attraction is the
stronger. But gases and vapours are bodies competent to suffer
very great changes in the relative distances of their particles by
external agencies; and where they are in immediate contact
with the platina, the approximation of the particles to those of
the metal may be very great. In the case of the hygrometric
bodies referred to (357), it is sufficient to reduce the vapour to
the fluid state, frequently from atmospheres so rare that without
this influence it would be needful to compress them by mechanical
force into a bulk not more than one-tenth or even one-twentieth
of their original volume before the vapours would become liquids.

362. Another most important consideration in relation to
this action of bodies, and which, as far as I am aware, has not
hitherto been noticed, is the condition of elasticity under which
the gases are placed against the acting surface. We have but
very imperfect notions of the real and intimate conditions of

Favourable Condition of the Gases loi

the particles of a body existing in the solid^ the liquid, and the
gaseous state; but when we speak of the gaseous state as being
due to the mutual repulsions of the particles or of their atmo¬
spheres, although we may err in imagining each particle to be a
little nucleus to an atmosphere of heat, or electricity, or aii}^
other agent, we are still not likely to be in error in considering
the elasticity as dependent on mutuality of action. Now this
mutual relation fails altogether on the side of the gaseous
particles next to the platina, and we might be led to expect
d priori a deficiency of elastic force there to at least one-half;
for if, as Dalton has shown, the elastic force of the particles of
one gas cannot act against the elastic force of the particles of
another, the two being as vacua to each other, so is it far less
likely that the particles of the platina can exert any influence
on those of the gas against it, such as would be exerted by
gaseous particles of its own kind.

363. But the diminution of power to one-half on the side of
the gaseous body towards the metal is only a slight result of
what seems to me to flow as a necessary consequence of the
known constitution of gases. An atmosphere of one gas or
vapour, however dense or compressed, is in effect as a vacuum
to another; thus, if a little water were put into a vessel contain¬
ing a dry gas, as air, of the pressure of one hundred atmospheres,
as much vapour of the water would rise as if it were in a perfect
vacuum. Here the particles of watery vapour appear to have
no difficulty in approaching within any distance of the particles
of air, being influenced solely by relation to particles of their
own kind; and if it be so with respect to a body having the
same elastic powers as itself, how much more surely must it be
so with particles, like those of the platina, or other limiting body,
which at the same time that they have not these elastic powers,
are also unlike it in nature. Hence it would seem to result that
the particles of hydrogen or any other gas or vapour which are
next to the platina, etc., must be in such contact with it as if
they were in the liquid state, and therefore almost infinitely
closer to it than they are to each other, even though the metal
be supposed to exert no attractive influence over them.

364. A third and very important consideration in favour of
the mutual action of gases under these circumstances is their
perfect miscibility. If fluid bodies capable of combining
together are also capable of mixture, they do co^nhine when they
are mingled, not waiting for any other determining circumstance;
but if two such gases as oxygen and hydrogen are put together,

I 02

Faraday’s Researches

though they are elements having such powerful affinity as to
unite naturally under a thousand different circumstances^ they
do not combine by mere mixture. Still it is evident that^ from
their perfect association^ the particles are in the most favourable
state possible for combination^ upon the supervention of any
determining cause^, such either as the negative action of the
platina in suppressing or annihilating^ as it were; their elasticity
on its side; or the positive action of the metal in condensing
them against its surface by an attractive force; or the influence
of both together.

365. Although there are not many distinct cases of combina¬
tion under the influence of forces external to the combining
particleS; yet there are sufficient to remove any difficulty which
might arise on that ground. Sir James Hall found carbonic
acid and lime to remain combined under pressure at tempera¬
tures at which they would not have remained combined if the
pressure had been removed; and I have had occasion to observe
a case of direct combination in chlorine;^ which being com¬
pressed at common temperatures will combine with water, and
form a definite crystalline hydrate, incapable either of being
formed or of existing if that pressure be removed.

366. The course of events when platina acts upon, and com¬
bines oxygen and hydrogen, may be stated, according to these
principles, as follows. From the influence of the circumstances
mentioned (355, etc.), i.e. the deficiency of elastic power and
the attraction of the metal for the gases, the latter, when they
are in association with the former, are so far condensed as to be
brought within the action of their mutual affinities at the exist¬
ing temperature; the deficiency of elastic power, not merely
subjecting them more closely to the attractive influence of the
metal, but also bringing them into a more favourable state
for union, by abstracting a part of that power (upon which
depends their elasticity), which elsewhere in the mass of gases
is opposing their combination. The consequence of their com¬
bination is the production of the vapour of water and an eleva¬
tion of temperature. But as the attraction of the platina for
the water formed is not greater than for the gases, if so great,
(for the metal is scarcely hygrometric), the vapour is quickly
diffused through the remaining gases; fresh portions of the
latter, therefore, come into juxtaposition with the metal, com¬
bine, and the fresh vapour formed is also diffused, allowing
new portions of gas to be acted upon. In this way the process

^ Philosophical Transactions, 1823, p. 161.

m

Combining Power of Platina 103

advances, but is accelerated by the evolution of heat, which is
known by experiment to facilitate the combination in propor¬
tion to its intensity, and the temperature is thus graduall}’
exalted until ignition results.

367. The dissipation of the vapour produced at the surface of
the platina, and the contact of fresh oxygen and hydrogen with
the metal, form no difficulty in this explication. The platina is
not considered as causing the combination of any particles with
itself, but only associating them closely around it; and the
compressed particles are as free to move from the platina, being
replaced by other particles, as a portion of dense air upon the
surface of the globe, or at the bottom of a deep mine, is free to
move by the slightest impulse, into the upper and rarer parts of
the atmosphere.

368. It can hardly be necessary to give any reasons why
platina does not show this effect under ordinary circumstances.
It is then not sufficiently clean (353), and the gases are pre¬
vented from touching it, and suffering that degree of effect
which is needful to commence their combination at common
temperatures, and which they can only experience at its sur¬
face. In fact, the very power which causes the combination
of oxygen and hydrogen, is competent, under the usual casual
exposure of platina, to condense extraneous matters upon its
surface, which soiling it, take away for the time its power of
combining oxygen and hydrogen, by preventing their contact
with it (334).

369. Clean platina, by which I mean such as has been made
the positive pole of a pile (306), or has been treated with acid
(341), and has then been put into distilled water for twelve or
fifteen minutes, has a peculiar friction when one piece is rubbed
against another. It wets freely with pure water, even after it
has been shaken and dried by the heat of a spirit-lamp; and if
made the pole of a voltaic pile in a dilute acid, it evolves minute
bubbles from every part of its surface. But platina in its
common state wants that peculiar friction: it will not wet freely
with water as the clean platina does; and when made the posi¬
tive pole of a pile, it for a time gives off large bubbles which
seem to cling or adhere to the metal, and are evolved at distinct
and separate points of the surface. These appearances and
effects, as well as its want of power on oxygen and hydrogen,
are the consequences, and the indications, of a soiled surface.

370. I found also that platina plates which had been cleaned
perfectly soon became soiled by mere exposure to the air; for

104 Faraday’s Researches

after twenty-four hours they no longer moistened freely with
water, but the fluid ran up into portions, leaving part of the
surface bare, whilst other plates which had been retained in
water for the same time, when they were dried (316) did moisten,
and gave the other indications of a clean surface.

371. Nor was this the case with platina or metals only, but
also with earthy bodies. Rock crystal and obsidian would not
wet freely upon the surface, but being moistened with strong
oil of vitriol, then washed, and left in distilled water to remove
all the acid, they did freely become moistened, whether they
were previously dry or whether they were left wet; but being
dried and left exposed to the air for twenty-four hours, their
surface became so soiled that water would not then adhere
freely to it, but ran up into partial portions. Wiping with a
cloth (even the cleanest) was still worse than exposure to air;
the surface either of the minerals or metals immediately became
as if it were slightly greasy. The floating upon water of small
particles of metals under ordinary circumstances is a consequence
of this kind of soiled surface. The extreme difficulty of cleaning
the surface of mercury when it has once been soiled or greased
is due to the same cause.

372. The same reasons explain why the power of the platina
plates in some circumstances soon disappear, and especially
upon use: MM. Dulong and Thenard have observed the same
effect with the spongy metal,^ as indeed have all those who
have used Dobereiner’s instantaneous light machines. If left
in the air, if put into ordinary distilled water, if made to act
upon ordinary oxygen and hydrogen, they can still find in all
these cases that minute portion of impurity which, when once
in contact with the surface of the platina, is retained there, and
is sufficient to prevent its full action upon oxygen and hydrogen
at common temperatures: a slight elevation of temperature is
again sufficient to compensate this effect, and cause combination.

373. No state of a solid body can be conceived more favour¬
able for the production of the effect than that which is possessed
by platina obtained from the ammonia-muriate by heat. Its
surface is most extensive and pure, yet very accessible to the
gases brought in contact with it: if placed in impurity, the
interior, as Thenard and Dulong have observed, is preserved
clean by the exterior; and as regards temperature, it is so bad
a conductor of heat, because of its divided condition, that
almost all which is evolved by the combination of the first por-

Annales de Chimie, tom. xxiv. p. 386.

Olefiant Gas 105

tions of gas is retained within the mass^ exalting the tendency
of the succeeding portions to combine.

374. I have now to notice some very extraordinary inter¬
ferences with this phenomenon^ dependent, not upon the nature
or condition of the metal or other acting solid, but upon the
presence of certain substances mingled with the gases acted
upon; and as I shall have occasion to speak frequently of a
mixture of oxygen and hydrogen, I wish it always to be under¬
stood that I mean a mixture composed of one volume oxygen
to two volumes of hydrogen, being the proportions that form
water. Unless otherwise expressed, the hydrogen was alwa3^s
that obtained by the action of dilute sulphuric acid on pure
zinc, and the oxygen that obtained by the action of heat from
the chlorate of potassa.

375. Mixtures of oxygen and hydrogen with azV, containing
one-fourth, one-half, and even two-thirds of the latter, being
introduced with prepared platina plates (306, 341) into tubes,
were acted upon ahnost as well as if no air were present: the
retardation was far less than might have been expected from
the mere dilution and consequent obstruction to the contact of
the gases with the plates. In two hours and a half nearly all
the oxygen and hydrogen introduced as mixture was gone.

376. But when similar experiments were made with olefiant
gas (the platina plates having been made the positive poles of
a voltaic pile (306) in acid), very different results^ occurred.
A mixture was made of 29.2 volumes hydrogen and 14.6 volumes
oxygen, being the proportions for water; and to this was added
another mixture of three volumes oxygen and one volume
olefiant gas, so that the olefiant gas formed but ^tvth part of the
whole; yet in this mixture the platina plate would not act in
forty-five hours. The failure was not for want of any power in
the plate, for when after that time it was taken out of this
mixture and put into one of oxygen and hydrogen, it immediately
acted, and in seven minutes caused explosion of the gas. This
result was obtained several times, and when larger proportions
of olefiant gas were used, the action seemed still more hopeless.

377. A mixture of forty-nine volumes oxygen and hydrogen
(374) with one volume of olefiant gas had a well-prepared
platina plate introduced. The diminution of gas was scarcely
sensible at the end of two hours, during which it was watched;
but on examination twenty-four hours afterwards, the tube was
found blown to pieces. The action, therefore, though it had

io6 Faraday’s Researches

been very much retarded^ had occurred at last, and risen to a
maximum.

378. With a mixture of ninety-nine volumes of oxygen and
hydrogen (374) with one of olefiant gas, a feeble action was
evident at the end of fifty minutes; it went on accelerating (366)
until the eighty-fifth minute, and then became so intense that
the gas exploded. Here also the retarding effect of the olefiant
gas was very beautifully illustrated.

379. Plates prepared by alkali and acid (341) produced
effects corresponding to those just described.

380. It is perfectly clear from these experiments that olefiant
gas, even in small quantities, has a very remarkable influence
in preventing the combination of oxygen and hydrogen under
these circumstances, and yet without at all injuring or affecting
the power of the platina.

381. Another striking illustration of similar interference may
be shown in carbonic oxide ; especially if contrasted with carbonic
acid. A mixture of one volume oxygen and hydrogen (374)
with four volumes of carbonic acid was affected at once by a
platina plate prepared with acid, etc. (341); and in one hour
and a quarter nearly all the oxygen and hydrogen was gone.
Mixtures containing less carbonic acid were still more readily
affected.

382. But when carbonic oxide was substituted for the carbonic
acid, not the slightest effect of combination was produced;
and when the carbonic oxide was only one-eighth of the whole
volume, no action occurred in forty and fifty hours. Yet the
plates had not lost their power; for being taken out and put
into pure oxygen and hydrogen, they acted well and at once.

383. Two volumes of carbonic oxide and one of oxygen were
mingled with nine volumes of oxygen and hydrogen (374).
d'his mixture was not affected by a plate which had been made
])ositive in arid, though it remained in it fifteen hours. But
when to the same volumes of carbonic oxide and oxygen were
added thirty-three volumes of oxygen and hydrogen, the carbonic
oxide being then only ]\tl\ part of the whole, the plate acted,
slowly at first, and at the end of forty-two minutes the gases
exploded.

384. These experiments were extended to various gases and
vapours, the general results of which may be given as follow.
Oxygen, hydrogen, nitrogen, and nitrous oxide, when used to
dilute the mixture of oxygen and hydrogen, did not prevent
the action of the plates even when they made four-fifths of

Interferences of Various Substances 107

the whole volume of gas acted upon. Nor was the retardation
so great in any case as might have been expected from the
mere dilution of the oxygen and hydrogen, and the consequent
mechanical obstruction to its contact with the platina. The
order in which carbonic acid and these substances seemed to
stand was as follows, the first interfering least with the action:
nitrous oxide, hydrogen, carbonic acid, nitrogen, oxygen: but it
is possible the plates were not equally well prepared in all
the cases, and that other circumstances also were unequal;
consequently more numerous experiments would be required
to establish the order accurately.

385. As to cases of retardation, the powers of olefiant gas
and carbonic oxide have been already described. Mixtures of
oxygen and hydrogen, containing from ^^th to o\,th of sul¬
phuretted hydrogen or phosphuretted hydrogen, seemed to show
a little action at first, but were not further affected by the
prepared plates, though in contact with them for seventy hours.
When the plates were removed they had lost all power over
pure oxygen and hydrogen, and the interference of these gases
was therefore of a different nature from that of the two former,
having permanently affected the plate.

386. A small piece of cork was dipped in sulphuret of carbon
and passed up through water into a tube containing oxygen
and hydrogen (374), so as to diffuse a portion of its vapour
through the gases. A plate being introduced appeared at first
to act a little, but after sixty-one hours the diminution was
very small. Upon putting the same plate into a pure mixture
of oxygen and hydrogen, it acted at once and powerfully, having
apparently suffered no diminution of its force.

387. A little vapour of ether being mixed with the oxygen
and hydrogen retarded the action of the plate, but did not pre¬
vent it altogether. A little of the vapour of the condensed oil¬
gas liquor^ retarded the action still more, but not nearly so
much as an equal volume of olefiant gas would have done. In
both these cases it was the original oxygen and hydrogen
which combined together, the ether and the oil-gas vapour
remaining unaffected, and in both cases the plates retained the
power of acting on fresh oxygen and hydrogen.

388. Spongy platina was then used in place of the plates,
and jets of hydrogen mingled with the different gases thrown
against it in air. The results were exactly of the same kind,
although presented occasionally in a more imposing form,

'^Philosophical Transactions, 1825, p. 440.

io8 Faraday’s Researches

Thus, mixtures of one volume of olefiant gas or carbonic oxide
with three of hydrogen could not heat the spongy platina when
the experiments were commenced at common temperatures;
but a mixture of equal volumes of nitrogen and hydrogen acted
very well, causing ignition. With carbonic acid the results
were still more striking. A mixture of three volumes of that
gas with one of hydrogen caused ignition of the platina, yet
that mixture would not continue to burn from the jet when
attempts were made to light it by a taper. A mixture even of
seven volumes of carbonic acid and one of hydrogen will thus
cause the ignition of cold spongy platina, and yet, as if to supply
a contrast, than which none can be greater, it cannot burn
at a taper^ but causes the extinction of the latter. On the
other hand, the mixtures of carbonic oxide or olefiant gas,
which can do nothing with the platina, are inflamed by the
taper, burning well.

389. Hydrogen mingled with the vapour of ether or oihgas
liquor causes the ignition of the spongy platina. The mixture
with oil-gas bums with a flame far brighter than that of the
mixture of hydrogen and olefiant gas already referred to, so
that it would appear that the retarding action of the hydro¬
carbons is not at all in proportion merely to the quantity of
carbon present.

390. In connection with these interferences, I must state
that hydrogen itself, prepared from steam passed over ignited
iron, was found when mingled with oxygen to resist the action
of platina. It had stood over water seven days, and had lost
all fetid smell; but a jet of it would not cause the ignition
of spongy platina, commencing at common temperatures; nor
would it combine with oxygen in a tube either under the influence
of a prepared plate or of spongy platina. A mixture of one
volume of this gas with three of pure hydrogen, and the due
proportion of oxygen, was not affected by plates after fifty
hours. I am inclined to refer the effect to carbonic oxide present
in the gas, but have not had time to verify the suspicion. The
power of the plates was not destroyed (376, 382).

391. Such are the general facts of these remarkable inter¬
ferences. Whether the effect produced by such small quantities
of certain gases depends upon any direct action which they
may exert upon the particles of oxygen and hydrogen, by
which the latter are rendered less inclined to combine, or
whether it depends upon their modifying the action of the plate
temporarily (for they produce no real change on it), by invest-

Relation of Liquid and Vaporous Particles 109

ing it through the agency of a stronger attraction than that of
the hydrogen^ or otherwise, remains to be decided by more
extended experiments.

392. The theory of action which I have given for the original
phenomena appears to me quite sufficient to account for all the
effects by reference to known properties, and dispenses with the
assumption of any new power of matter. I have pursued this
subject at some length, as one of great consequence, because I
am convinced that the superficial actions of matter, whether
between two bodies, or of one piece of the same body, and the
actions of particles not directly or strongly in combination, are
becoming daily more and more important to our theories of
chemical as well as mechanical philosophy.^ In all ordinary
cases of combustion it is evident that an action of the kind con¬
sidered, occurring upon the surface of the carbon in the fire,
and also in the bright part of a flame, must have great influence
over the combinations there taking place.

393. The condition of elasticity upon the exterior of the
gaseous or vaporous mass already referred to (362, 363) must
be connected directly with the action of solid bodies, as nuclei,
on vapours, causing condensation upon them in preference to
any condensation in the vapours themselves; and in the well-
known effect of nuclei on solutions a similar condition may have
existence (359), for an analogy in condition exists between the
parts of a body in solution, and those of a body in the vaporous
or gaseous state. This thought leads us to the consideration
of what are the respective conditions at the surfaces of contact
of two portions of the same substance at the same temperature,
one in the solid or liquid, and the other in the vaporous state;
as, for instance, steam and water. It would seem that the
particles of vapour next to the particles of liquid are in a different
relation to the latter to what they would be with respect to any
other liquid or solid substance; as, for instance, mercury or

^ As a curious illustration of the influence of mechanical forces over
chemical affinity, I will quote the refusal of certain substances to effloresce
when their surfaces are perfect, which yield immediately upon the surface
being broken. If crystals of carbonate of soda, or phosphate of soda, or
sulphate of soda, having no part of their surfaces broken, be preserved from
external violence, they will not effloresce. I have thus retained crystals
of carbonate of soda perfectly transparent and unchanged from September
1827 to January 1833; and crystals of sulphate of soda from May 1832
to the present time, November 1833. If any part of the surface were
scratched or broken, then efflorescence began at that part, and covered the
whole. The crystals were merely placed in evaporating basins and
covered with paper.

I lO

Faraday’s Researches

platina^ if they were made to replace the water, i,e, if the view
of independent action which I have taken (362^ 363), as a con¬
sequence of Dalton’s principles, be correct. It would also seem
that the mutual relation of similar particles, and the indifference
of dissimilar particles which Dalton has established as a matter
of fact amongst gases and vapours, extends to a certain degree
amongst solids and fluids, that is, when they are in relation by
contact with vapours, either of their own substance or of other
bodies. But though I view these points as of great importance
with respect to the relations existing between different sub¬
stances and their physical constitution in the solid, liquid, or
gaseous state, I have not sufficiently considered them to venture
any strong opinions or statements here.^

394. There are numerous well-known cases, in which sub¬
stances, such as oxygen and hydrogen, act readily in their
nascent state, and produce chemical changes which they are not
able to effect if once they have assumed the gaseous condition.
Such instances are very common at the poles of the voltaic pile,
and are, I think, easily accounted for, if it be considered that at
the moment of separation of any such particle it is entirely
surrounded by other particles of a different kind with which it is
in close contact, and has not yet assumed those relations and
conditions which it has in its fully developed state, and which it
can only assume by association with other particles of its own
kind. For, at the moment, its elasticity is absent, and it is in
the same relation to particles with which it is in contact, and
for which it has an affinity, as the particles of oxygen and
hydrogen are to each other on the surface of clean platina
(362,363).

395. The singular effects of retardation produced by very
small quantities of some gases, and not by large quantities of
others (376, 381, 388), if dependent upon any relation of the
added gas to the surface of the solid, will then probably be found
immediately connected with the curious phenomena which are
presented by different gases when passing through narrow tubes
at low pressures, which I observed many years ago; ^ and this
action of surfaces must, I think, influence the highly interesting
phenomena of the diffusion of gases, at least in the form in which
it has been experimented upon by Mr. Graham in 1829 and

^ In reference to this paragraph and also 362, see a correction by Dr. C.
Henry, in his valuable paper on this curious subject —Philosophical
Magazine, 1835, vol. vi. p. 365 .—December 1838.

^Quarterly Journal of Science, 1819, vol. vii. p. 106.

Peculiar Conditions of Metals 111

1831/ and also by Dr. Mitchell of Philadelphia ^ in 1830. It
seems very probable that if such a substance as spongy platina
were used^ another law for the diffusion of gases under the
circumstances would come out than that obtained by the use
of plaster of Paris.

396. I intended to have followed this section by one on the
secondary piles of Ritter^ and the peculiar properties of the
poles of the pile^ or of metals through which electricity has
passed^ which have been observed by Ritter, Van Marum,
Yelin, De la Rive, Marianini, Berzelius, and others. It appears
to me that ail these phenomena bear a satisfactory explanation
on known principles, connected with the investigation just
terminated, and do not require the assumption of any new state
or new property. But as the experiments advanced, especialh^
those of Marianini, require very careful repetition and examina¬
tion, the necessity of pursuing the subject of electro-chemical
decomposition obliges me for a time to defer the researches to
which I have just referred.

November 30, 1833.

V3

§ 5. ON ELECTRO-CHEMICAL DECOMPOSITION, CONTINUED.^ % iv.
ON SOME GENERAL CONDITIONS OF ELECTRO-DECOMPOSITION.
*|j V. ON A NEW MEASURER OF VOLTA-ELECTRICITY. ^ vi.
ON THE PRIMARY OR SECONDARY CHARACTER OF BODIES
EVOLVED IN ELECTRO-DECOMPOSITION. vii. ON THE
DEFINITE NATURE AND EXTENT OF ELECTRO-CHEMICAL
DECOMPOSITIONS. § 7. ON THE ABSOLUTE QUANTITY OF
ELECTRICITY ASSOCIATED WITH THE PARTICLES OR ATOMS
OF MATTER

Preliminary

397. The theory which I believe to be a true expression of the
facts of electro-chemical decomposition, and which I have there¬
fore detailed in a former part of these Researches, is so much
at variance with those previously advanced, that I find the

^ Quarterly Journal of Science, vol. xxviii. p. 74, and Edinburgh Transac¬
tions, 1831.

^Journal of the Royal Institution for 1831, p. loi.

® Seventh Series, original edition, vol. i. p. 195.

^ Refer to the note after 783, Part VI.— December 1838.

112 Faraday’s Researches

greatest difficulty in stating results^ as I think, correctly, whilst
limited to the use of terms which are current with a certain
accepted meaning. Of this kind is the term pole, with its
prefixes of positive and negative, and the attached ideas of
attraction and repulsion. The general phraseology is that the
positive pole attracts oxygen, acids, etc., or more cautiously,
that it determines their evolution upon its surface; and that
the negative pole acts in an equal manner upon hydrogen,
combustibles, metals, and bases. According to my view, the
determining force is not at the poles, but within the bod}" under
decomposition; and the oxygen and acids are rendered at the
negative extremity of that body, whilst hydrogen, metals, etc.,
are evolved at the positive extremity (254, 260).

398. To avoid, therefore, confusion and circumlocution, and
for the sake of greater precision of expression than I can other¬
wise obtain, I have deliberately considered the subject with two
friends, and with their assistance and concurrence in framing
them, I purpose henceforward using certain other terms, which
I will now define. The poles, as they are usually called, are
only the doors or ways by which the electric current passes into
and out of the decomposing body (292); and they of course,
when in contact with that body, are the limits of its extent
in the direction of the current. The term has been generally
applied to the metal surfaces in contact with the decomposing
substance; but whether philosophers generally would also apply
it to the surfaces of air (201, 207) and water (229), against which
I have effected electro-chemical decomposition, is subject to
doubt. In place of the term pole, I propose using that of
Electrode^ and I mean thereby that substance, or rather sur¬
face, whether of air, water, metal, or any other body, which
bounds the extent of the decomposing matter in the direction
of the electric current.

399. The surfaces at which, according to common phraseo¬
logy, the electric current enters and leaves a decomposing body,
are most important places of action, and require to be distin¬
guished apart from the poles, with which they are mostly, and
the electrodes, with which they are always, in contact. Wishing
for a natural standard of electric direction to which I might
refer these, expressive of their difference and at the same time
free from all theory, I have thought it might be found in the
earth. If the magnetism of the earth be due to electric currents
passing round it, the latter must be in a constant direction,

^ ip^GKTpov, and 6 d 6 s a way.

Definitions of New Terms 11 3

which; according to present usage of speech; would be from
east to west; or; which will strengthen this help to the memory,
that in which the sun appears to move. If in any case of
electro-decomposition we consider the decomposing body as
placed so that the current passing through it shall be in the
same direction, and parallel to that supposed to exist in the
earth; then the surfaces at which the electricity is passing into
and out of the substance would have an invariable reference,
and exhibit constantly the same relations of powers. Upon
this notion we purpose calling that towards the east the anode^
and that towards the west the cathode ; ^ and whatever changes
may take place in our views of the nature of electricity and
electrical action, as they must affect the natural standard
referred to, in the same direction, and to an equal amount with
any decomposing substances to which these terms may at any
time be applied, there seems no reason to expect that they will
lead to confusion, or tend in any way to support false views.
The anode is therefore that surface at which the electric current,
according to our present expression, enters: it is the negative
extremity of the decomposing body; is where oxygen, chlorine,
acids, etc., are evolved; and is against or opposite the positive
electrode. The cathode is that surface at which the current
leaves the decomposing body, and is its positive extremity; the
combustible bodies, metals, alkalies, and bases, are evolved
there, and it is in contact with the negative electrode.

400. I shall have occasion in these Researches, also, to class
bodies together according to certain relations derived from their
electrical actions (557); and wishing to express those relations
without at the same time involving the expression of any h3q)0-
thetical views, I intend using the following names and terms.
Many bodies are decomposed directly by the electric current,
their elements being set free; these I propose to call electro¬
lytes? Water, therefore, is an electrolyte. The bodies which,
like nitric or sulphuric acids, are decomposed in a secondary
manner (487, 492), are not included under this term. Then
for electro-chemically decomposed, I shall often use the term
electrolysed, derived in the same way, and implying that the
body spoken of is separated into its components under the
influence of electricity: it is analogous in its sense and sound
to analyse, which is derived in a similar manner. The term

^ 6 .VW upwards, and 656 ? a way ; the way which the sun rises.

^ Kara downwards, and 656 s a way ; the way which the sun sets.

^ ijXeKrpoVj and solvo. N.

fiMWE USniyiE Of IE&&0108T

114 Faraday’s Researches

elecirolyttcal will be understood at once: muriatic acid is electro-
lytical, boracic acid is not.

401. Finally^ I require a term to express those bodies which
can pass to the electrodes, or^ as they are usually called, the
poles. Substances are frequently spoken of as being electro¬
negative, or electro-positive, according as they go under the
supposed influence of a direct attraction to the positive or nega¬
tive pole. But these terms are much too significant for the
use to which I should have to put them; for though the mean¬
ings are perhaps right, they are only hypothetical, and may be
wrong; and then, through a very imperceptible, but still very
dangerous, because continual, influence, they do great injury to
science, by contracting and limiting the habitual views of those
engaged in pursuing it. I propose to distinguish such bodies
by calling those anions ^ which go to the anode of the decom¬
posing body; and those passing to the cathode, cations ; ^ and
when I have occasion to speak of these together, I shall call
them ions. Thus, the chloride of lead is an electrolyte, and when
electrolysed evolves the two ions, chlorine and lead, the former
being an anion, and the latter a cation.

402. These terms being once well defined, will, I hope, in
their use enable me to avoid much periphrasis and ambiguity of
expression. I do not mean to press them into service more
frequently than will be required, for I am fully aware that names
are one thing and science another.^

403. It will be well understood that I am giving no opinion
respecting the nature of the electric current now, beyond what
I have done on former occasions (19, 253); and that though
I speak of the current as proceeding from the parts which are
positive to those which are negative (399), it is merely in accord¬
ance with the conventional, though in some degree tacit, agree¬
ment entered into by scientific men, that they may have a
constant, certain, and definite means of referring to the direction
of the forces of that current.

^ avLOiv that which goes up. (Neuter participle.)

“ KCLTiibv that which goes down.

^ Since this paper was read, I have changed some of the terms which
were first proposed, that I might employ only such as were at the same
time simple in their nature, clear in their reference, and free from
hypothesis.

Electro-Chemical Decomposition 115

^ iv. On some general conditions of Electro-chemicdL
Decomposition

404. From the period when electro-chemical decomposition
was first effected to the present time^ it has been a remark, that
those elements which, in the ordinary phenomena of chemical
affinity, were the most directly opposed to each other, and com¬
bined with the greatest attractive force, were those which were
the most readily evolved at the opposite extremities of the
decomposing bodies (285).

405. If this result was evident when water was supposed to
be essential to, and was present, in almost every case of such
decomposition (208), it is far more evident now that it has
been shown and proved that water is not necessarily concerned
in the phenomena (210), and that other bodies much surpass
it in some of the effects supposed to be peculiar to that substance.

406. Water, from its constitution and the nature of its ele¬
ments, and from its frequent presence in cases of electrolytic
action, has hitherto stood foremost in this respect. Though a
compound formed by very powerful affinity, it yields up its
elements under the influence of a very feeble electric current;
and it is doubtful whether a case of electrolysation can occur,
where, being present, it is not resolved into its first principles.

407. The various oxides, chlorides, iodides, and salts, which
I have shown are decomposable by the electric current when in
the liquid state, under the same general law with water (138),
illustrate in an equally striking manner the activity, in such
decompositions, of elements directly and powerfully opposed to
each other by their chemical relations.

408. On the other hand, bodies dependent on weak affinities
very rarely give way. Take, for instance, glasses: many of
those formed of silica, lime, alkali, and oxide of lead, may be
considered as little more than solutions of substances one in
another.^ If bottle-glass be fused, and subjected to the voltaic
pile, it does not appear to be at all decomposed (144). If flint
glass, which contains substances more directly opposed, be
operated upon, it sufers some decomposition; and if borate of
lead glass, which is a definite chemical compound, be experi¬
mented with, it readily yields up its elements (144).

409. But the result which is found to be so striking in the
instances quoted is not at all borne out by reference to other

^ Philosophical Transactions^ 1S30, p. 49.

ii6 Faraday’s Researches

cases where a similar consequence might have been expected.
It may be said^ that my own theory of electro-chemical decom¬
position would lead to the expectation that all compound bodies
should give way under the influence of the electric current with
a facility proportionate to the strength of the affinity by which
their elements^ either proximate or ultimate^ are combined. I
am not sure that that follows as a consequence of the theory;
but if the objection is supposed to be one presented by the
facts^ I have no doubt it will be removed when we obtain a
more intimate acquaintance with, and precise idea of, the
nature of chemical affinity and the mode of action of an electric
current over it (254, 260): besides which, it is just as directly
opposed to any other theory of electro-chemical decomposition
as the one I have propounded; for if it be admitted, as is gene¬
rally the case, that the more directly bodies are opposed to each
other in their attractive forces, the more powerfully do they
combine, then the objection applies with equal force to any of
the theories of electrolysation which have been considered, and
is an addition to those which I have taken against them.

410. Amongst powerful compounds which are not decom¬
posed, boracic acids stands prominent (144). Then again, the
iodide of sulphur, and the chlorides of sulphur, phosphorus, and
carbon, are not decomposable under common circumstances,
though their elements are of a nature which would lead to a
contrary expectation. Chloride of antimony (138, 426), the
hydro-carbons, acetic acid, ammonia, and many other bodies
undecomposable by the voltaic pile, would seem to be formed
by an affinity sufficiently strong to indicate that the elements
were so far contrasted in their nature as to sanction the expec¬
tation that the pile would separate them, especially as in some
cases of mere solution (266, 280), where the affinity must by
comparison be very weak, separation takes place.^

411. It must not be forgotten, however, that much of this
difficulty, and perhaps the whole, may depend upon the absence
of conducting power, which, preventing the transmission of the
current, prevents of course the effects due to it. All known
compounds being non-conductors when solid, but conductors
when liquid, are decomposed, with perhaps the single exception
at present known of periodide of mercury (414, 426); and even
water itself, which so easily yields up its elements when the

^ With regard to solution, I have met with some reasons for supposing
that it will probably disappear as a cause of transference, and intend
resuming the consideration at a convenient opportunity.

Proportions of Elements in Electrolytes 117

current passes^ if rendered quite pure^ scarcely suffers change,
because it then becomes a very bad conductor.

412. If it should hereafter be proved that the want of decom¬
position in those cases where, from chemical considerations, it
might be so strongly expected (404, 407, 409), is due to the
absence or deficiency of conducting power, it would also at the
same time be proved that decomposition depends upon con¬
duction, and not the latter upon the former (149); and in water
this seems to be very nearly decided. On the other hand, the
conclusion is almost irresistible, that in electrolytes the power
of transmitting the electricity across the substance is dependeyit
upon their capability of suffering decomposition; taking place
only whilst they are decomposing, and being proportionate to
the quantity of elements separated (556). I may not, however,
stop to discuss this point experimentally at present.

413. When a compound contains such elements as are known
to pass towards the opposite extremities of the voltaic pile, still
the proportions in which they are present appear to be inti¬
mately connected with capability in the compound of suffering
or resisting decomposition. Thus, the protochloride of tin
readily conducts, and is decomposed (138), but the perchloride
neither conducts nor is decomposed (142). The protiodide of
tin is decomposed when fluid (138); the periodide is not (143).
The periodide of mercury when fused is not decomposed (426),
even though it does conduct. I was unable to contrast it with
the protiodide, the latter being converted into mercury and
periodide by heat.

414. These important differences induced me to look more
closely to certain binary compounds, with a view of ascertaining
whether a law regulating the decomposability according to some
relation of the proportionals or equivalents of the elements, could
be discovered. The proto compounds only, amongst those just
referred to, were decomposable; and on referring to the sub¬
stances quoted to illustrate the force and generality of the law
of conduction and decomposition which I discovered (138), it
will be found that all the oxides, chlorides, and iodides subject
to it, except the chloride of antimony and the periodide of
mercury (to which may now perhaps be added corrosive subli¬
mate), are also decomposable, whilst many per compounds of
the same elements, not subject to the law, were not so (141, 142).

415. The substances which appeared to form the strongest
exceptions to this general result were such bodies as the sul¬
phuric, phosphoric, nitric, arsenic, and other acids.

ii8 Faraday’s Researches

416. On experimenting with sulphuric acid; I found no reason
to believe that it was by itself a conductor of; or decomposable
by; electricity; although I had previously been of that opinion
(288). When very strong it is a much worse conductor than if
diluted.^ If then subjected to the action of a powerful battery;
oxygen appears at the anode, or positive electrode; although
much is absorbed (463); and hydrogen and sulphur appear at
the cathode, or negative electrode. Now the hydrogen has with
me always been pure; not sulphuretted; and has been deficient
in proportion to the sulphur present; so that it is evident that
when decomposition occurred water must have been decom¬
posed. I endeavoured to make the experiment with anhydrous
sulphuric acid; and it appeared to me that; when fused; such
acid was not a conductor; nor decomposed; but I had not
enough of the dry acid in my possession to allow me to decide
the point satisfactorily. My belief iS; that when sulphur appears
during the action of the pile on sulphuric acid; it is the result of
a secondary action; and that the acid itself is not electrolysable

(492)-

417. Phosphoric acid iS; I believe; also in the same condition;
but I have found it impossible to decide the point; because of
the difficulty of operating on fused anhydrous phosphoric acid.
Phosphoric acid which has once obtained water cannot be
deprived of it by heat alone. When heated; the hydrated acid
volatilises. Upon subjecting phosphoric acid; fused upon the
ring end of a wire (137); to the action of the voltaic apparatus,
it conducted; and was decomposed; but gas, which I believe to
be hydrogen, was always evolved at the negative electrode, and
the wire was not affected as would have happened had phos¬
phorus been separated. Gas was also evolved at the positive
electrode. From all the facts, I conclude it was the water and
not the acid which was decomposed.

418. Arsenic acid. This substance conducted, and was de¬
composed ; but it contained water, and I was unable at the time
to press the investigation so as to ascertain whether a fusible
anhydrous arsenic acid could be obtained. It forms, therefore,
at present no exception to the general result.

419. Nitrous acid; obtained by distilling nitrate of lead, and
keeping it in contact with strong sulphuric acid, was found to
conduct and decompose slowly. But on examination there were
strong reasons for believing that water was present, and that
the decomposition and conduction depended upon it. I en*

Bodies not Electrolysable Alone 119

deavoured to prepare a perfectly anhydrous portion^ but could
not spare the time required to procure an unexceptionable
result.

420. Nitric acid is a substance which I believe is not decom¬
posed directly by the electric current. As I want the facts in
illustration of the distinction existing between primary and
secondary decomposition^ I will merely refer to them in this
place (487).

421. That these mineral acids should confer facility of con¬
duction and decomposition on water^ is no proof that they are
competent to favour and suffer these actions in themselves.
Boracic acid does the same things though not decomposable.
M. de la Rive has pointed out that chlorine has this power also;
but being to us an elementary substance^ it cannot be due to
its capability of suffering decomposition.

422. Chloride of stdphur does not conduct^ nor is it decom¬
posed. It consists of single proportionals of its elements, but
is not on that account an exception to the rule (414), which
does not affirm that all compounds of single proportionals of
elements are decomposable, but that such as are decomposable
are so constituted.

423. Protochloride of phosphorus does not conduct nor become
decomposed.

424. Protochloride of carbon does not conduct nor suffer
decomposition. In association with this substance, I submitted
the hydro-chloride of carbon from olefiant gas and chlorine to
the action of the electric current; but it also refused to conduct
or yield up its elements.

425. With regard to the exceptions (414), upon closer ex¬
amination, some of them disappear. Chloride of antimony (a
compound of one proportional of antimony and one and a half
of chlorine) of recent preparation was put into a tube (fig. 28)
(524), and submitted when fused to the action of the current,
the positive electrode being of plumbago. No electricity passed,
and no appearance of decomposition was visible at first; but
when the positive and negative electrodes were brought very
near each other in the chloride, then a feeble action occurred
and a feeble current passed. The effect altogether was so
small (although quite amenable to the law before given (130)),
and so unlike the decomposition and conduction occurring in
all the other cases, that I attribute it to the presence of a minute
quantity of water (for which this and many other chlorides have
strong attractions, producing hydrated chlorides), or perhaps

120 Faraday’s Researches

of a true protochloride consisting of single proportionals (430,

531)* ^1

426. Periodide of mercury being examined in the same manner^
was found most distinctly to insulate whilst solid, but conduct
when fluid, according to the law of liquido-conduction (138);
but there was no appearance of decomposition. No iodine
appeared at the anode, nor mercury or other substance at the
cathode. The case is, therefore, no exception to the rule, that
only compounds of single proportionals are decomposable; but
it is an exception, and I think the only one, to the statement,
that all bodies subject to the law of liquido-conduction are
decomposable. I incline, however, to believe, that a portion of
protiodide of mercury is retained dissolved in the periodide, and
that to its slow decomposition the feeble conducting power is
due. Periodide would be formed, as a secondary result, at the
anode ; and the mercury at the cathode would also form, as a
secondary result, protiodide. Both these bodies would mingle
with the fluid mass, and thus no final separation appear, not¬
withstanding the continued decomposition.

427. When per chloride of mercury was subjected to the voltaic
current, it did not conduct in the solid state, but it did conduct
when fluid. I think, also, that in the latter case it was decom¬
posed; but there are many interfering circumstances which
require examination before a positive conclusion can be drawn.

428. When the ordinary protoxide of antimony is subjected to
the voltaic current in a fused state, it also is decomposed, although
the effect from other causes soon ceases (138, 536). This oxide
consists of one proportional of antimony and one and a half of
oxygen, and is therefore an exception to the general law assumed.
But in working with this oxide and the chloride, I observed
facts which lead me to doubt whether the compounds usually
called the protoxide and the protochloride do not often contain
other compounds, consisting of single proportions, which are
the true proto compounds, and which, in the case of the oxide,
might give rise to the decomposition above described.

429. The ordinary sulphuret of antimony is considered as
being the compound with the smallest quantity of sulphur, and
analogous in its proportions to the ordinary protoxide. But I
find that if it be fused with metallic antimony, a new sulphuret
is formed, containing much more of the metal than the former,
and separating distinctly, when fused, both from the pure
metal on the one hand, and the ordinar}^ grey sulphuret on the
other. In some rough experiments, the metal thus taken up

Compound Combinations 121

by the ordinary sulphuret of antimony was equal to half the
proportion of that previously in the sulphuret^ in which case
the new sulphuret would consist of single proportionals.

430. When this new sulphuret was dissolved in muriatic acid^
although a little antimony separated^ yet it appeared to me that
a true protochloride, consisting of single proportionals, was
formed, and from that, by alkalies, etc., a true protoxide, con¬
sisting also of single proportionals, was obtainable. But I
could not stop to ascertain this matter strictly by analysis.

431. I believe, however, that there is such an oxide; that it
is often present in variable proportions in what is commonly
called protoxide, throwing uncertainty upon the results of its
analysis, and causing the electrolytic decomposition above
described.^

432. Upon the whole, it appears probable that all those
binary compounds of elementary bodies which are capable of
being electrolysed when fluid, but not whilst solid, according
to the law of liquido-conduction (130), consist of single pro¬
portionals of their elementary principles; and it may be because
of their departure from this simplicity of composition, that
boracic acid, ammonia, perchlorides, periodides, and many
other direct compounds of elements, are indecomposable.

433- With regard to salts and combinations of compound
bodies, the same simple relation does not appear to hold good.
I could not decide this by bisulphates oj the alkalies, for as long
as the second proportion of acid remained, water was retained
with it. The fused salts conducted, and were decomposed;
but hydrogen always appeared at the negative electrode.

434. A biphosphate of soda was prepared by heating, and
ultimately fusing, the ammonia-phosphate of soda. In this
case the fused bisalt conducted, and was decomposed; but a
little gas appeared at the negative electrode; and though I
believe the salt itself was electrolysed, I am not quite satisfied
that water was entirely absent.

435. Then a biborate of soda was prepared; and this, I think,
is an unobjectionable case. The salt, when fused, conducted,
and was decomposed, and gas appeared at both electrodes:
even when the boracic acid was increased to three proportionals,
the same effect took place.

436. Hence this class of compound combinations does not

^ In relation to this and the three preceding paragraphs, and also 536,
see Berzelius’s correction of the nature of the supposed new sulphuret and
oxide, Phil. Mag. 1836, vol. viii. 476 .—December 1838.

122 Fai'aday’s Researches

seem to be subject to the same simple law as the former class
of binaiy combinations. Whether we may find reason to con¬
sider them as mere solutions of the compound of single pro¬
portionals in the excess of acid^ is a matter which, with some
apparent exceptions occurring amongst the sulphurets^ must
be left for decision by future examination.

437. In any investigation of these points^ great care must be
taken to exclude water; for if present, secondary effects are
so frequently produced as often seemingly to indicate an electro¬
decomposition of substances, when no true result of the kind
has occurred (477; etc.).

438. It is evident that all the cases in which decomposition
does not occur, may depend upon the want of conduction (412,
149); but that does not at all lessen the interest excited by
seeing the great difference of effect due to a change, not
in the nature of the elements, but merely in their proportions;
especially in any attempt which may be made to elucidate and
expound the beautiful theory put forth by Sir Humphry Davy,^
and illustrated by Berzelius and other eminent philosophers,
that ordinary chemical affinity is a mere result of the electrical
attractions of the particles of matter.

^ V. On a new Measurer of Volta-electricity

439. I have already ^id, when engaged in reducing common
and voltaic electricity to one standard of measurement (113),
and again when introducing my theory of electro-chemical
decomposition (240, 241, 246), that the chemical decomposing
action of a current is constant for a constant quantity of electricity,
notwithstanding the greatest variations in its sources, in its
intensity, in the size of the electrodes used, in the nature of the
conductors (or non-conductors) through which it is passed, or
in other circumstances. The conclusive proofs of the truth of
these statements shall be given almost immediately (518, etc.).

440. I endeavoured upon this law to constmct an instrument
which should measure out the electricity passing through it,
and which, being interposed in the course of the current used
in any particular experiment, should serve at pleasure, either as
a comparative standard of effect, or as a positive measurer of
this subtile agent.

441. There is no substance better fitted, under ordinary
circumstances, to be the indicating body in such an instrument

^ Philosophical Transactions, 1807, pp. 32, 39; also 1826, pp. 387, 389.

New Measurer of Voltaic-Electricity 123

than water; for it is decomposed with facility when rendered
a better conductor by the addition of acids or salts; its elements
may in numerous cases be obtained and collected with¬
out any embarrassment from secondary action^ and^
being gaseous^ they are in the best physical condition
for separation and measurement. Water^ therefore^
acidulated by sulphuric acid, is the substance I shall
generally refer to, although it may become expedient
in peculiar cases or forms of experiment to use other
bodies (578).

442. The first precaution needful in the construction
of the instrument was to avoid the recombination of
the evolved gases, an effect which the positive electrode
has been found so capable of producing (307). For this
purpose various forms of decomposing apparatus were
used. The first consisted of straight tubes, each con¬
taining a plate and v/ire of platina soldered together by
gold, and fixed hermetically in the glass at the closed extremity

of the tube (fig. 20). The tubes were about eight
inches long, 0.7 of an inch in diameter, and gradu¬
ated. The platina plates were about an inch long;
as wide as the tubes would permit, and adjusted as
near to the mouths of the tubes as was consistent
with the safe collection of the gases evolved. In
certain cases, where it was required to evolve the
elements upon as small a surface as possible, the
metallic extremity, instead of being a plate, con¬
sisted of the wire bent into the form of a ring
(fig. 21). When these tubes were used as measurers,
they were filled with the dilute sulphuric acid,
inverted in a basin of the same liquid (fig. 22),
and placed in an inclined position, with their
mouths near to each other, that as little decom¬
posing matter should intervene as possible; and also, in such a
direction that the platina plates
should be in vertical planes

(455)-

443. Another form of appar¬
atus is that delineated (fig. 23).

The tube is bent in the middle;
one end is closed; in that end
is fixed a wire and plate, a, proceeding so far downwards, that,
when in the position figured, it shall be as near to the angle as

Fig. 22.

Fig. 21.

124 Faraday’s Researches

possible, consistently with the collection, at the closed extremity
of the tube, of all the gas evolved against it. The plane of this
plate is also perpendicular (455)* The other metallic termina¬
tion, by is introduced at the
\ time decomposition is to be

effected, being brought as near
angle as possible, without
causing any gas to pass from
it towards the closed end of
instrument. The gas
. evolved against it is allowed

444. The third form of ap¬
paratus contains both electrodes in the same tube; the trans¬
mission, therefore, of the electricity and the consequent
decomposition, is far more rapid than in the separate tubes.
The resulting gas is the sum of the portions evolved at the
two electrodes, and the instrument is better adapted than either
of the former as a measurer of the quantity of voltaic electricity
transmitted in ordinary cases. It consists of a straight tube
(fig. 24) closed at the upper extremity, and graduated, through
the sides of which pass platina wires (being fused into the
glass), which are connected with two plates within. The tube
is fitted by grinding into one mouth of a
double-necked bottle. If the latter be one-
half or two-thirds full of the dilute sulphuric [
acid (441), it will, upon inclination of the whole, f

flow into the tube and fill it. When an electric f

current is passed through the instrument, the [
gases evolved against the plates collect in the f
upper portion of the tube, and are not subject |
to the recombining power of the platina. \ [

445. Another form of the instrument is ^

given at fig. 25.

446. A fifth form is delineated (fig. 26).

This I have found exceedingly useful in ex- ^

periments continued in succession for days .

together, and where large quantities of indi-

eating gas were to be collected. It is fixed on Fig. 24.

a weighted foot, and has the form of a small

retort containing the two electrodes: the neck is narrow, and

sufficiently long to deliver gas issuing from it into a jar placed

in a small pneumatic trough. The electrode chamber, sealed

Definite Action with Varying Electrodes 125

hermetically at the part held in the stands is five inches in
lengthy and 0.6 of an inch in diameter; the neck about nine
inches in lengthy and 0.4 of an inch in diameter internally.
The figure will fully indicate the construction.

447. It can hardly be requisite to remark^ that in the arrange¬
ment of any of these forms of apparatus, they, and the wires
connecting them with the substance, which is collaterally sub¬
jected to the action of the same electric current, should be so far
insulated as to ensure a certainty that all the electricity which
passes through the one shall also be transmitted through the
other.

448. Next to the precaution of collecting the gases, if mingled,
out of contact with the platinum, was the necessity of testing
the law of a definite electrolytic action, upon water at least, under
all varieties of condition; that, with a conviction of its certainty,
might also be obtained a knowledge of those interfering circum¬
stances which would require to be practically guarded against.

449. The first point investigated was the influenc ■ or indif¬
ference of extensive variations in the size of the electrodes, for
which purpose instruments like those last described (444, 445,
446) were used. One of these had plates 0.7 of an inch wide,
and nearly four inches long; another had plates only 0.5 of an
inch wide, and 0.8 of an inch long; a third had wires 0.02 of an
inch in diameter, and three inches long; and a fourth, similar
wires only half an inch in length. Yet when these were filled
with dilute sulphuric acid, and, being placed in succession, had
one common current of electricity passed through them, very
nearly the same quantity of gas was evolved in all. The
difference was sometimes in favour of one, and sometimes on

126 Faraday’s Researches

the side of another; but the general result was that the largest
quantity of gases was evolved at the smallest electrodes^, namely^
those consisting merely of platina wires.

450. Experiments of a similar kind were made with the single-
plate^ straight tubes (442)^ and also with the curved tubes
(443)^ with similar consequences; and when these, with the
former tubes, were arranged together in various ways, the
result, as to the equality of action of large and small metallic
surfaces when delivering and receiving the same current of elec¬
tricity, was constantly the same. As an illustration, the follow¬
ing numbers are given. An instrument with two wires evolved
74.3 volumes of mixed gases; another with plates 73.25 volumes;
whilst the sum of the oxygen and hydrogen in two separate
tubes amounted to 73.65 volumes. In another experiment the
volumes were 55.3, 55.3, and 54.4.

451. But it was observed in these experiments, that in single¬
plate tubes (442) more hydrogen was evolved at the negative
electrode than was proportionate to the oxygen at the positive
electrode; and generally, also, more than was proportionate to
the oxygen and hydrogen in a double-plate tube. Upon more
minutely examining these effects, I was led to refer them, and
also the differences between wires and plates (449), to the solu¬
bility of the gases evolved, especially at the positive electrode.

452. When the positive and negative electrodes are equal in
surface, the bubbles which rise from them in dilute sulphuric
acid are always different in character. Those from the positive
plate are exceedingly small, and separate instantly from every
part of the surface of the metal, in consequence of its perfect
cleanliness (369); whilst in the liquid they give it a hazy ap¬
pearance, from their number and minuteness; are easily carried
down by currents; and therefore not only present far greater
surface of contact with the liquid than larger bubbles would do,
but are retained a much longer time in mixture with it. But
the bubbles at the negative surface, though they constitute twice
the volume of the gas at the positive electrode, are nevertheless
very inferior in number. They do not rise so universally from
every part of the surface, but seem to be evolved at different
points; and though so much larger, they appear to cling to the
metal, separating with difficulty from it, and when separated
instantly rising to the top of the liquid. If, therefore, oxygen
and hydrogen had equal solubility in, or powers of combining
with, water under similar circumstances, still under the present
conditions the oxygen would be far the most liable to solution;

Variation of the Electrodes

I 27

but when to these is added its well-known power of forming a
compound with, water^ it is no longer surprising that such a
compound should be produced in small quantities at the positive
electrode; and indeed the bleaching power which some philo¬
sophers have observed in a solution at this electrode^ when
chlorine and similar bodies have been carefully excluded; is
probably due to the formation there; in this manner; of oxy-
water.

453. That more gas was collected from the wires than from
the plateS; I attribute to the circumstance; that as equal quan¬
tities were evolved in equal times; the bubbles at the wires
having been more rapidly produced; in relation to any part of
the surface; must have been much larger; have been therefore
in contact with the fluid by a much smaller surface; and for a
much shorter time than those at the plates; hence less solution
and a greater amount collected.

454. There was also another effect produced; especially by
the use of large electrodes; which was both a consequence and
a proof of the solution of part of the gas evolved there. The
collected gaS; w^hen examined; was found to contain small
portions of nitrogen. This I attribute to the presence of air dis¬
solved in the acid used for decomposition. It is a well-known
fact; that when bubbles of a gas but slightly soluble in water or
solutions pass through them; the portion of this gas which is
dissolved displaces a portion of that previously in union with
the liquid: and sO; in the decompositions under consideration;
as the oxygen dissolves; it displaces a part of the air; or at
least of the nitrogen; previously united to the acid; and this
effect takes place most extensively with large plateS; because
the gas evolved at them is in the most favourable condition for
solution.

455. With the intention of avoiding this solubility of the gases
as much as possible; I arranged the decomposing plates in a
vertical position (442; 443); that the bubbles might quickly
escape upwards; and that the downward currents in the fluid
should not meet ascending currents of gas. This precaution I
found to assist greatly in producing constant resultS; and
especially in experiments to be hereafter referred tO; in which
other liquids than dilute sulphuric acid; as for instance solution
of potash; were used.

456. The irregularities in the indications of the measurer
proposed; arising from the solubility just referred tO; are but
small; and may be very nearly corrected by comparing the results

128

Faraday’s Researches

of two or three experiments. They may also be almost entirely
avoided by selecting that solution which is found to favour them
in the least degree (463); and still further by collecting the
hydrogen only^ and using that as the indicating gas; for being
much less soluble than oxygen^ being evolved with twice the
rapidity and in larger bubbles (552)^ it can be collected more
perfectly and in greater purity.

457. From the foregoing and many other experiments^ it
results that variation in the size of the electrodes causes no varia-
iion in the chemical action of a given quantity of electricity upon
water,

458. The next point in regard to which the principle of con¬
stant electro-chemical action was tested^ was variation of in¬
tensity, In the first place^ the preceding experiments were
repeated^ using batteries of an equal number of plates, strongly
and wecikly charged; but the results were alike. They were
then repeated, using batteries sometimes containing forty, and
at other times only five pairs of plates; but the results were
still the same. Variations therefore in the inte^isity^ caused by
difference in the strength of charge, or in the number of alterna¬
tions used, produced no difference as to the eqttal action of large
and small electrodes.

459. Still these results did not prove that variation in the
intensity of the current was not accompanied by a correspond¬
ing variation in the electro-chemical effects, since the actions at
all the surfaces might have increased or diminished together.
The deficiency in the evidence is, however, completely supplied
by the former experiments on different-sized electrodes; for
with variation in the size of these, a variation in the intensity
must have occurred. The intensity of an electric current
traversing conductors alike in their nature, quality, and length,
is probably as the quantity of electricity passing through a given
sectional area perpendicular to the current, divided by the time
(96, note); and therefore when large plates were contrasted with
wires separated by an equal length of the same decomposing
conductor (449), whilst one current of electricity passed through
both arrangements, that electricity must have been in a very
different state, as to tension^ between the plates and between
the wires; yet the chemical results were the same.

460. The difference in intensity, under the circumstances
described, may be easily shown practically, by arranging two
decomposing apparatus as in fig. 27, where the same fluid is

Variations of the Current

subjected to the decomposing power of the same current of
electricity, passing in the vessel A between large platina plates,
and in the vessel B between small wires. If a third decom¬
posing apparatus, such as , ,

that delineated, fig. 26 (446), ^ J L a' b' "O"

be connected with the wires ——^ (-

at a b, fig. 27, it will serve r'lO

sufficiently well, by the de-
gree of decomposition occur-
ring in it, to indicate the

relative state of the two a 15

plates as to intensity ; and .

if it then be applied in the ^

same way, as a test of the -^

state of the wires at a' b', it

will, by the increase of decomposition within, show how much
greater the intensity is there than at the former points. The
connections of P and N with the voltaic battery are of course
to be continued during the whole time.

461. A third form of experiment in which difference of in¬
tensity was obtained, for the purpose of testing the principle of
equal chemical action, was to arrange three volta-electrometers,
so that after the electric current had passed through one, it
should divide into two parts, each of which should traverse one
of the remaining instruments, and should then reunite. The
sum of the decomposition in the two latter vessels was always
equal to the decomposition in the former vessel. But the in¬
tensity of the divided current could not be the same as that it
had in its original state; and therefore variation of intensity
has no influence on the results if the quantity of electricity remain
the same. The experiment, in fact, resolves itself simply into
an increase in the size of the electrodes (460).

462. The third point, in respect to which the principle of
equal electro-chemical action on water was tested, was variation
of the strength of the solution used. In order to render the
water a conductor, sulphuric acid had been added to it (442);
and it did not seem unlikely that this substance, with many
others, might render the water more subject to decomposition,
the electricity remaining the same in quantity. But such did
not prove to be the case. Diluted sulphuric acid, of different
strengths, was introduced into different decomposing apparatus,
and submitted simultaneously to the action of the same electric

I

130 Faraday’s Researches

current (449). Slight differences occurred^ as before^ some¬
times in one direction^ sometimes in another; but the final
result waSj that exactly ike same quantity of water was deco 7 n-
posed in all the solutions by the same quantity of electricity, though
the sulphuric acid in some was seventy-fold what it was in
others. The strengths used were of specific gravity 1.495;
downwards.

463. When an acid having a specific gravity of about 1.336
was employed^ the results were most uniform^ and the oxygen
and hydrogen (451) most constantly in the right proportion to
each other. Such an acid gave more gas than one much weaker
acted upon by the same current^ apparently because it had less
solvent power. If the acid were very strong, then a remark¬
able disappearance of oxygen took place; thus, one made by
mixing two measures of strong oil of vitriol with one of water,
gave forty-two volumes of hydrogen, but only twelve of oxygen.
The hydrogen was very nearly the same with that evolved from
acid of the specific gravity of 1.232. I have not yet had time to
examine minutely the circumstances attending the disappear¬
ance of the oxygen in this case, but imagine it is due to the
formation of oxywater, which Thenard has shown is favoured
by the presence of acid.

464. Although not necessary for the practical use of the
instrument I am describing, yet as connected with the important
point of constant electro-chemical action upon water, I now
investigated the effects produced by an electric current passing
through aqueous solutions of acids, salts, and compounds, ex¬
ceedingly different from each other in their nature, and found
them to yield astonishingly uniform results. But many of them
which are connected with a secondary action will be more usefully
described hereafter (513).

465. When solutions of caustic potassa or soda, or sulphate of
magnesia, or sulphate of soda, were acted upon by the electric
current, just as much oxygen and hydrogen was evolved from
them as from the diluted sulphuric acid, with which they were
compared. When a solution of ammonia, rendered a better
conductor by sulphate of ammonia (290), or a solution of sub¬
carbonate of potassa was experimented with, the hydrogen
evolved was in the same quantity as that set free from the
diluted sulphuric acid with which they were compared. Hence
changes in the nature of the solution do not alter the constancy of
electrolytic action upon water.

Definite Electrolysation of Water 131

466. I have already said^ respecting large and small electrodes,
that change of order caused no change in the general effect (450).
The same was the case with different solutions, or with different
intensities; and however the circumstances of an experiment
might be varied, the results came forth exceedingly consistent,
and proved that the electro-chemical action was still the same.

467. I consider the foregoing investigation as sufficient to
prove the very extraordinary and important principle with
respect to water, that when subjected to the influence of the
electric current, a quantity of it is decomfosed exactly profortionate
to the quantity of electricity which has passed, notwithstanding
the thousand variations in the conditions and circumstances
under which it may at the time be placed; and further, that
when the interference of certain secondary effects (477, etc.),
together with the solution or recombination of the gas and the
evolution of air, are guarded against, the products of the decom¬
position may be collected with such accuracy, as to afford a very
excellent and valuable measurer of the electricity concerned in their
evolution,

468. The forms of instrument which I have given, figs. 24,
25, 26 (444, 445, 446), are probably those which will be found
most useful, as they indicate the quantity of electricity by the
largest volume of gases, and cause the least obstruction to the
passage of the current. The fluid which my present experience
leads me to prefer, is a solution of sulphuric acid of specific
gravity about 1.336, or from that to 1.25; but it is very essential
that there should be no organic substance, nor any vegetable
acid, nor other body, which, by being liable to the action of
the oxygen or hydrogen evolved at the electrodes (508, etc.),
shall diminish their quantity, or add other gases to them.

469. In many cases when the instrument is used as a com¬
parative standard, or even as a measurer, it may be desirable to
collect the hydrogen only, as being less liable to absorption or
disappearance in other ways than the oxygen; whilst at the
same time its volume is so large as to render it a good and
sensible indicator. In such cases the first and second form of
apparatus have been used, figs. 22, 23 (442, 443). The indica¬
tions obtained were very constant, the variations being much
smaller than in those forms of apparatus collecting both gases;
and they can also be procured when solutions are used in
comparative experiments, which, yielding no oxygen or only
secondary results of its action, can give no indications if the

132 Faraday’s Researches

educts at both electrodes be collected. Such is the case when
solutions of ammonia, muriatic acid, chlorides, iodides, acetates ;
or other vegetable salts, etc., are employed.

470. In a few cases, as where solutions of metallic salts liable !

to reduction at the negative electrode are acted upon, the j

oxygen may be advantageously used as the measuring substance. ’

This is the case, for instance, with sulphate of copper. ‘

471. There are therefore two general forms of the instrument

which I submit as a measurer of electricity; one in which both !

the gases of the water decomposed are collected (444, 445, 446), i

and the other in which a single gas, as the hydrogen only, is * i
used (442, 443). When referred to as a comparative instrument j

(a use I shall now make of it very,extensively), it will not often ;

require particular precaution in the observation; but when I

used as an absolute measurer, it will be needful that the baro- !

metric pressure and the temperature be taken into account, and \

that the graduation of the instruments should be to one scale; j

the hundredths and smaller divisions of a cubical inch are quite 1

fit for this purpose, and the hundredth may be very conveniently f

taken as indicating a degree of electricity. |

472. It can scarcely be needful to point out further than has !

been done how this instrument is to be used. It is to be intro- |

duced into the course of the electric current, the action of which i

is to be exerted anywhere else, and if 60° or 70° of electricity !

are to be measured out, either in one or several portions, the
current, whether strong or weak, is to be continued until the gas j

! in the tube occupies that number of divisions or hundredths of i

a cubical inch. Or if a quantity competent to produce a certain ;

effect is to be measured, the effect is to be obtained, and then '

the indication read off. In exact experiments it is necessary to >

correct the volume of gas for changes in temperature and 1

3 pressure, and especially for moisture.^ For the latter object the '

I volta-electrometer (fig. 26) is most accurate, as its gas can be ;

I measured over water, whilst the others retain it over acid or |

j saline solutions. j

i 473. I have not hesitated to apply the term^degree (471), in

I analogy with the use made of it with respect to another most

I important imponderable agent, namely, heat; and as the definite

] expansion of air, water, mercury, etc., is there made use of to

j measure heat, so the equally definite evolution of gases is here

1 turned to a similar use for electricity.

^ For a simple table of correction for moisture, I may take the liberty j
of referring to my Chemical Manipulation^ edition of 1830, p. 376. ’

Use of the Voltameter

133

474. The instrument offers the only actiLal measurer of voltaic
electricity which we at present possess. For without being at
all affected by variations in time or intensity, or alterations in
the current itself, of any kind, or from any cause, or even of
intermissions of action, it takes note with accuracy of the
quantity of electricity which has passed through it, and reveals
that quantity by inspection; I have therefore named it a volta-

ELECTROMETER.

475. Another mode of measuring volta-electricity may be
adopted with advantage in many cases, dependent on the
quantities of metals or other substances evolved either as
primary or as secondary results; but I refrain from enlarging
on this use of the products, until the principles on which their
constancy depends have been fully established (526, 578).

476. By the aid of this instrument I have been able to
establish the definite character of electro-chemical action in its
most general sense; and I am persuaded it will become of the
utmost use in the extensions of the science which these views
afford. I do not pretend to have made its detail perfect, but to
have demonstrated the truth of the principle, and the utility
of the application.^

^ vi. On the f rimary or secondary character of the bodies evolved
at the Electrodes

477. Before the volta-electrometer could be employed in deter¬
mining, as a general law, the constancy of electro-decomposition,
it became necessary to examine a distinction, already recognised
among scientific men, relative to the products of that action,
namely, their primary or secondary character; and, if possible,
by some general rule or principle, to decide when they were of
the one or the other kind. It will appear hereafter that great
mistakes respecting electro-chemical action and its consequences
have arisen from confounding these two classes of results
together.

478. When a substance under decomposition yields at the
electrodes those bodies uncombined and unaltered which the
electric current has separated, then they may be considered
as primary results, even though themselves compounds. Thus

1 As early as the year 1811, Messrs. Gay Lussac, and Thenard, employed
chemical decomposition as a measure of the electricity of the voltaic pile.
See Recherches Physico-chymiques, p. 12. The principles and precautions
by which it becomes an exact measure were of course not then known.—
December 1838.

134 Faraday’s Researches

the oxygen and hydrogen from water are primary results; and
so also are the acid and alkali (themselves compound bodies)
evolved from sulphate of soda. But when the substances
separated by the current are changed at the electrodes before
their appearance, then they give rise to secondary results,
although in many cases the bodies evolved are elementary.

479. These secondary results occur in two ways, being some¬
times due to the mutual action of the evolved substance and
the matter of the electrode, and sometimes to its action upon
the substances contained in the body itself under decomposition.
Thus, when carbon is made the positive electrode in dilute
sulphuric acid, carbonic oxide and carbonic acid occasionally
appear there instead of oxygen; for the latter, acting upon the
matter of the electrode, produces these secondary results. Or
if the positive electrode, in a solution of nitrate or acetate of
lead, be platina, then peroxide of lead appears there, equally
a secondary result with the former, but now depending upon an
action of the oxygen on a substance in the solution. Agam,
when ammonia is decomposed by platina electrodes, nitrogen
appears at the anode ; ^ but though an elementary body, it is a
secondary result in this case, being derived from the chemical
action of the oxygen electrically evolved there, upon the
ammonia in the surrounding solution (290). In the same
manner when aqueous solutions of metallic salts are decomposed
by the current, the metals evolved at the cathode, though
elements, are always secondary results, and not immediate
consequences of the decomposing power of the electric current.

480. Many of these secondary results are extremely valuable;
for instance, all the interesting compounds which M. Becquerel
has obtained by feeble electric currents are of this nature; but
they are essentially chemical, and must, in the theory of elec¬
trolytic action, be carefully distinguished from those which are
directly due to the action of the electric current.

481. The nature of the substances evolved will often lead to
a correct judgment of their primary or secondary character, but
is not sufficient alone to establish that point. Thus, nitrogen
is said to be attracted sometimes by the positive and sometimes
by the negative electrode, according to the bodies with which
it may be combined (290, 291), and it is on such occasions
evidently viewed as a primary result; ^ but I think I shall show
that, when it appears at the positive electrode, or rather at the
anode, it is a secondary result (483). Thus, also. Sir Humphry

^ Annales de Chimie, 1804, tom. U. p. 167. ^ Ibid, p. 172.

Primary or Secondary Results 135

Davy/ and with him the great body of chemical philosophers
(including myself)^ have given the appearance of copper^ lead,
tin, silver, gold, etc., at the negative electrode, when their
aqueous solutions were acted upon by the voltaic current, as
proofs that the metals, as a class, were attracted to that surface;
thus assuming the metal, in each case, to be a primary result.
These, however, I expect to prove, are all secondary results;
the mere consequence of chemical action, and no proofs either
of the attraction or of the law announced respecting their
places.^

482. But when we take to our assistance the law of constant
electro-chemical action already proved with regard to water (467),
and which I hope to extend satisfactorily to all bodies (556), and
consider the quantities as well as the nature of the substances
set free, a generally accurate judgment of the primary or
secondary character of the results may be formed: and this
important point, so essential to the theory of electrolysation,
since it decides what are the particles directly under the influ¬
ence of the current (distinguishing them from such as are not
affected), and what are the results to be expected, may be
established with such degree of certainty as to remove innumer¬
able ambiguities and doubtful considerations from this branch
of the science.

483. Let us apply these principles to the case of ammonia,
and the supposed determination of nitrogen to one or the other
electrode (290, 291). A pure strong solution of ammonia is as
bad a conductor, and therefore as little liable to electrolysation,
as pure water; but when sulphate of ammonia is dissolved in it,
the whole becomes a conductor; nitrogen almost and occasion¬
ally quite pure is evolved at the anode^ and hydrogen at the
cathode; the ratio of the volume of the former to that of the
latter varying, but being as i to about 3 or 4. This result
would seem at first to imply that the electric current had de¬
composed ammonia, and that the nitrogen had been determined
towards the positive electrode. But when the electricity used
was measured out by the volta-electrometer (442, 471), it was
found that the hydrogen obtained was exactly in the proportion

^ Elements of Chemical Philosophy, pp. 144, 161.

^ It is remarkable that up to 1804 it was the received opinion that the
metals were reduced by the nascent hydrogen. At that date the general
opinion was reversed by Hisinger and Berzelius {Annales de Chimie, 1804,
tom. li. p. 174), who stated that the metals were evolved directly by the
electricity: in which opinion it appears, from that time, Davy coincided
[Philosophical Transactions, 1826, p. 388).

136 Faraday’s Researches

which would have been supplied by decomposed water^ whilst
the nitrogen had no certain or constant relation whatever.
WheU; upon multiplying experiments^ it was found that^ by
using a stronger or weaker solution^ or a more or less powerful
battery, the gas evolved at the anode was a mixture of oxygen
and nitrogen, varying both in proportion and absolute quantity,
whilst the hydrogen at the cathode remained constant, no doubt
could be entertained that the nitrogen at the anode was a
secondary result, depending upon the chemical action of the
nascent oxygen, determined to that surface by the electric
current, upon the ammonia in solution. It was the water,
therefore, which was electrolysed, not the ammonia. Further,
the experiment gives no real indication of the tendency of the
element nitrogen to either one electrode or the other; nor do I
know of any experiment with nitric acid, or other compounds
of nitrogen, which shows the tendency of this element, under
the influence of the electric current, to pass in either direction
along its course.

484. As another illustration of secondary results, the effects
on a solution of acetate of potassa may*be quoted. When a
very strong solution was used, more gas was evolved at the
anode than at the cathode^ in the proportion of 4 to 3 nearly:
that from the anode was a mixture of carbonic oxide and car¬
bonic acid; that from the cathode pure hydrogen. When a
much weaker solution was used, less gas was evolved at the
anode than at the cathode ; and it now contained carburetted
hydrogen, as well as carbonic oxide and carbonic acid. This
result of carburetted hydrogen at the positive electrode has a
very anomalous appearance, if considered as an immediate con¬
sequence of the decomposing power of the current. It, how¬
ever, as well as the carbonic oxide and acid, is only a secondary
result; for it is the water alone which suffers electro-decom¬
position, and it is the oxygen eliminated at the anode which,
reacting on the acetic acid, in the midst of which it is evolved,
produces those substances that finally appear there. This is
fully proved by experiments with the volta-electrometer (442);
for then the hydrogen evolved from the acetate at the cathode
is always found to be definite, being exactly proportionate to
the electricity which has passed through the solution, and, in
quantity, the same as the hydrogen evolved in the volta-elec¬
trometer itself. The appearance of the carbon in combination
with the hydrogen at the positive electrode, and its non-appear¬
ance at the negative electrode, are in curious contrast with the

Secondary Results with Nitric Acid 137

results which might have been expected from the law usually
accepted respecting the final places of the elements.

485. If the salt in solution be an acetate of lead^ then the
results at both electrodes are secondary, and cannot be used to
estimate or express the amount of electro-chemical action,
except by a circuitous process (578). In place of oxygen or
even the gases already described (484), peroxide of lead now
appears at the positive, and lead itself at the negative electrode,
^^en other metallic solutions are used, containing, for instance,
peroxides, as that of copper, combined with this or any other
decomposable acid, still more complicated results will be ob¬
tained; which, viewed as direct results of the electro-chemical
action, will, in their proportions, present nothing but con¬
fusion, but will appear perfectly harmonious and simple if they
be considered as secondary results, and will accord in their
proportions with the oxygen and hydrogen evolved from water
by the action of a definite quantity of electricity.

486. I have experimented upon many bodies, with a view to
determine whether the results were primary or secondary. I
have been surprised to find how many of them, in ordinary
cases, are of the latter class, and how frequently water is the
only body electrolysed in instances where other substances have
been supposed to give way. Some of these results I will give
in as few words as possible.

487. Nitric acid ,—^When very strong, it conducted well, and
yielded oxygen at the positive electrode. No gas appeared at
the negative electrode; but nitrous acid, and apparently nitric
oxide, were formed there, which, dissolving, rendered the acid
yellow or red, and at last even effervescent, from the spon¬
taneous separation of nitric oxide. Upon diluting the acid with
its bulk or more of water, gas appeared at the negative electrode.
Its quantity could be varied by variations, either in the strength
of the acid or of the voltaic current: for that acid from which
no gas separated at the cathode, with a weak voltaic battery,
did evolve gas there with a stronger; and that battery which
evolved no gas there with a strong acid, did cause its evolution
with an acid more dilute. The gas at the anode was always
oxygen; that at the cathode hydrogen. When the quantity of
products was examined by the volta-electrometer (442), the
oxygen, whether from strong or weak acid, proved to be in the
same proportion as from water. When the acid was diluted
to specific gravity 1.24, or less, the hydrogen also proved to be
the same in quantity as from water. Hence I conclude that

138 Faraday’s Researches

the nitric acid does not undergo electrolysation^ but the water
only; that the oxygen at the anode is always a primary result,
but that the products at the cathode are often secondary^ and
due to the reaction of the hydrogen upon the nitric acid.

488. Nitre. — K solution of this salt yields very variable
results^ according as one or other form of tube is used^ or as
the electrodes are large or small. Sometimes the whole of the
hydrogen of the water decomposed may be obtained at the
negative electrode; at other times^ only a part of it, because of
the ready formation of secondary results. The solution is a
very excellent conductor of electricity.

489. Nitrate of ammonia^ in aqueous solution, gives rise to
secondary results very varied and uncertain in their proportions.

490. Sulphurous acid. —Pure liquid sulphurous acid does not
conduct nor suffer decomposition by the voltaic current,^ but,
when dissolved in water, the solution acquires conducting power
and is decomposed, yielding oxygen at the anode, and hydrogen
and sulphur at the cathode.

491. A solution containing sulphuric acid in addition to the
sulphurous acid was a better conductor. It gave very little
gas at either electrode; that at the anode was oxygen, that at
the cathode pure hydrogen. From the cathode also rose a white
turbid stream, consisting of diffused sulphur, which soon
rendered the whole solution milky. The volumes of gases were
in no regular proportion to the quantities evolved from water
in the voltameter. I conclude that the sulphurous acid was not
at all affected by the electric current in any of these cases, and
that the water present was the only body electro-chemically
decomposed; that, at the anode, the oxygen from the water
converted the sulphurous acid into sulphuric acid, and, at the
cathode, the hydrogen electrically evolved decomposed the sul¬
phurous acid, combining with its oxygen, and setting its sulphur
free. I conclude that the sulphur at the negative electrode
was only a secondary result; and, in fact, no part of it was
found combined with the small portion of hydrogen which
escaped when weak solutions of sulphurous acid were used.

492. Sulphuric acid. —I have already given my reasons for
concluding that sulphuric acid is not electrolysable, i.e. not
decomposable directly by the electric current, but occasionally
suffering by a secondary action at the cathode from the hydrogen
evolved there (416). In the year 1800, Davy considered the

^ See also De la Rive, Bihliothique Universelle, tom. xl. p, 205; or
Quarterly Journal of Science^ vol. xxvii. p. 407.

Electrolysation of Muriatic Acid 139

sulphur from sulphuric acid as the result of the action of the-
nascent hydrogen.^ In 1804^ Hisinger and Berzelius stated
that it was the direct result of the action of the voltaic pile/'
an opinion which from that time Davy seems to have adopted^
and which has since been commonly received by all. The-
change of my own opinion requires that I should correct what
I have already said of the decomposition of sulphuric acid in a
former part of these Researches (288): I do not now think
that the appearance of the sulphur at the negative electrode is.
an immediate consequence of electrolytic action.

493. Muriatic acid .—strong solution gave hydrogen at
the negative electrode^ and chlorine only at the positive elec¬
trode; of the latter^ a part acted on the platina and a part was.
dissolved. A minute bubble of gas remained; it was not
oxygen^ but probably air previously held in solution.

494. It was an important matter to determine whether the
chlorine was a primary result^ or only a secondary product^ due-
to the action of the oxygen evolved from water at the anode
upon the muriatic acid; i.e. whether the muriatic acid was
electrolysable, and if so, whether the decomposition was
definite.

495. The muriatic acid was gradually diluted. One part
with six of water gave only chlorine at the anode. One part
with eight of water gave only chlorine; with nine of water, a
little oxygen appeared with the chlorine: but the occurrence or-
non-occurrence of oxygen at these strengths depended, in part,
on the strength of the voltaic battery used. With fifteen parts
of water, a little oxygen, with much chlorine, was evolved at the-
anode. As the solution was now becoming a bad conductor of
electricity, sulphuric acid was added to it: this caused more-
ready decomposition, but did not sensibly alter the proportion
of chlorine and oxygen.

496. The muriatic acid was now diluted with 100 times its
volume of dilute sulphuric acid. It still gave a large pro¬
portion of chlorine at the anode^ mingled with oxygen; and the
result was the same, whether a voltaic battery of forty pairs of
plates or one containing only five pairs were used. With acid
of this strength, the oxygen evolved at the anode was to the-
hydrogen at the cathode, in volume, as seventeen is to sixty-four;,
and therefore the chlorine would have been thirty volumes, had
it not been dissolved by the fluid.

^Nicholson’s Quarterly Journal, vol. iv. pp. 280, 281.

* Annales de CJiimie, 1804, tom. li. p. 173.

140 Faraday’s Researches

497. Next with respect to the quantity of elements evolved.
On using the volta-electrometer^ it was found that^ whether the
strongest or the weakest muriatic acid were used^ whether
chlorine alone or chlorine mingled with oxygen appeared at the
anode, still the hydrogen evolved at the cathode was a constant
quantity^ i.e. exactly the same as the hydrogen which the same
quantity of electricity could evolve from water.

498. This constancy does not decide whether the muriatic
acid is electrolysed or not^ although it proves that if sO; it must
be in definite proportions to the quantity of electricity used.
Other considerations may^ however^ be allowed to decide the
point. The analogy between chlorine and oxygen^ in their
relations to hydrogen^ is so strong, as to lead almost to the
certainty, that, when combined with that element, they would
perform similar parts in the process of electro-decomposition.
They both unite with it in single proportional or equivalent
quantities; and the number of proportionals appearing to have
an intimate and important relation to the decomposability of a
body (432), those in muriatic acid, as well as in water, are the
most favourable, or those perhaps even necessary, to decom¬
position. In other binary compounds of chlorine also, where
nothing equivocal depending on the simultaneous presence of it
and oxygen is involved, the chlorine is directly eliminated at the
anode by the electric current. Such is the case with the chloride
of lead (131), which may be justly compared with protoxide of
lead (138), and stands in the same relation to it as muriatic acid
to water. The chlorides of potassium, sodium, barium, etc., are
in the same relation to the protoxides of the same metals and
present the same results under the influence of the electric
current (138).

499. From all the experiments, combined with these con¬
siderations, I conclude that muriatic acid is decomposed by the
direct influence of the electric current, and that the quantities
evolved are, and therefore the chemical action is, definite for a
definite quantity of electricity. For though I have not collected
and measured the chlorine, in its separate state, at the anode,
there can exist no doubt as to its being proportional to the
hydrogen at the cathode ; and the results are therefore sufficient
to establish the general law of constant electro-chemical action
in the case of muriatic acid.

500. In the dilute acid (496), I conclude that a part of the
water is electro-chemically decomposed, giving origin to the
oxygen, which appears mingled with the chlorine at the anode.

imary or Secondary Decomposition 141

/"gen may be viewed as a secondary result; but I incline
ve that it is not so: for_, if i-i^ were, it might be expected
st proportion from the stronger acid, whereas the reverse
act. This consideration, with others, also leads me to
e that muriatic acid is more easily decomposed by the
current than water ; since, even when diluted with eight
times its quantity of the latter fluid, it alone gives way,
er remaining unaffected.

Chlorides. On using solutions of chlorides in water—
ance, the chlorides of sodium or calcium—there was
►n of chlorine only at tlie positive electrode, and of
;n, with the oxide of the base, as soda or lime, at the
2 electrode. The process of decompositionmay be viewed
ceding in two or three ways, all terminating in the same
Perhaps the siinplest is to consider the chloride as the
ce electrolysed, its chlorine being determined to and
at the ajwde, and its metal passing to the cathode,
[inding no more chlorine, it acts upon the water, pro¬
hydrogen and an oxide as secondary results. As the
on would detain me from more important matter, and
f immediate consequence, I shall defer it for the present.
>wever, of <^real coiisequejice to state, that, on using the
ectrometer, the hydrogen in both cases was definite;
die results do not prove the definite decomposition of
s (which shall be proved elsewhere—524, 529, 549),
j not in the slightest degree opposed to such a conclusion,
support the general hm,

flydriodic arid.- A solution of hydriodic acid was
exactly in tiic same manner as muriatic acid. When
Jiydrogen wiis cvoh'cd at the negative electrode, in
proportion to the (piantity of electricity which had
z.e. in the same proportion as was evolved by the same
from water; and itxltne without any oxygen was evolved
>ositive electrode. Put when diluted, small quantities
Ml a])pcared with the iodine at the anode, the proportion
)gen at the cathode remaining undisturbed.

I believe the decomposition of the hydriodic acid in this
be dinsit, for the reasons already given respecting
c acid (498, .1

Iodides.--A solution of iodide of potassium being
id to the voltaic ('urnmt, iodine appeared at the positive
e (without any oxygen), and hydrogen with free alkali
negative electrode. 'The same observations as to^the

142 Faraday’s Researches

mode of decomposition are applicable here as were made in i
relation to the chlorides when in solution (501).

505. Hydro-fluoric acid and fluorides, —Solution of hydro¬
fluoric acid did not appear to be decomposed under the influence

‘Of the electric current: it was the water which gave way ap- I

parently. The fused fluorides were electrolysed (153); but |

having during these actions obtained fluorine in the separate i

rstate^ I think it better to refer to a future series of these Re- j

•searches^ in which I purpose giving a fuller account of the
results than would be consistent with propriety here.^ '

506. Hydro-cyanic acid in solution conducts very badly. I

The definite proportion of hydrogen (equal to that from water) |

was set free at the cathode^ whilst at the anode a small quantity !

^of oxygen was evolved and apparently a solution of cyanogen !

formed. The action altogether corresponded with that on a |

dilute muriatic or hydriodic acid. When the hydro-cyanic 1

•acid was made a better conductor by sulphuric acid^ the same ,

results occurred. !

Cyanides. —^With a solution of the cyanide of potassium^ the |
result was precisely the same as with a chloride or iodide. No
oxygen was evolved at the positive electrode^ but a brown
solution formed there. For the reasons given when speaking
'of the chlorides (501)^ and because a fused cyanide of potas¬
sium evolves cyanogen at the positive electrode^^ I incline to
helieve that the cyanide in solution is directly decomposed.

507. Ferro-cyanic acid and the ferro-cyanides^ as also sulpho-

^cyanic acid and the sulpho-cyanides, presented results correspond- ,
ing with those just described (506). I

508. Acetic acid. —Glacial acetic acid^ when fused (141);, is 1

not decomposed by, nor does it conduct, electricity. On add- I

ing a little water to it, still there were no signs of action; on
.adding more water, it acted slowly and about as pure water I

would do. Dilute sulphuric acid was added to it in order to i

make it a better conductor; then the definite proportion of j

hydrogen was evolved at the cathode^ and a mixture of oxygen '

in very deficient quantity, with carbonic acid, and a little
carbonic oxide, at the anode. Hence it appears that acetic acid

i

I have not obtained fluorine: my expectations, amounting to con- !
viction, passed away one by one when subjected to rigorous examination;
some very singular results were obtained.— December 1838.

2 It is a very remarkable thing to see carbon and nitrogen in this case
determined powerfully towards the positive surface of the voltaic battery;
but it is perfectly in harmony with the theory of electro-chemical decom- '
position which I have advanced.

lary or Secondary Decomposition 143

trolysable, but that a portion of it is decomposed b3’'

} evolved at the anode^ producing secondary results,
itb. the strength of the acid, the intensity of the
i-ci other circumstances.

^'tcztes ,—One of these has been referred to already,
only secondary results relative to the acetic acid
thi many of the metallic acetates the results at both
are secondary (481, 485).

of soda fused and anhydrous is directly decomposed,
f believe, a true electrolyte, and evolving soda and
the cathode and anode. These, however, hav^e no
ura.tion, but are immediately resolved into other
; charcoal, sodiuretted hydrogen, etc., being set free
ner^ and, as far as I could judge under the circum-
:et:ic acid mingled with carbonic oxide, carbonic acid,
i latter.

'^tcivic acid .—Pure solution of tartaric acid is almost
;oncluctor as pure water. On adding sulphuric acid,
edL well, the results at the positive electrode being
r secondary in different proportions, according to
irx the strength of the acid and the power of the
Teixt (487). Alkaline tartrates gave a large proportion
ry results at the positive electrode. The hydrogen
itive electrode remained constant unless certain triple
Its were used.

iitions, of salts containing other vegetable acids, as the
of sugar, gum, etc., dissolved in dilute sulphuric
isixXy albumen, etc., dissolved in alkalies, were in turn
to the electrolytic power of the voltaic current. In
rses, secondary results to a greater or smaller extent
iced at the positive electrode.

concluding this division of these Researches, it cannot
to the mind that the final result of the action of the
Trent upon substances placed between the electrodes,
being simple may be very complicated. There are
s by which these substances may be decomposed,
he direct force of the electric current, or by the action
vbich that current may evolve. There are also two
wbich new compounds may be formed, t.e. by com-
f the evolving substances whilst in their nascent
directly with the matter of the electrode; or else
)ina.tion with those bodies, which being contained
)cia.ted with, the body suffering decomposition^ are

144 Faraday’s Researches

necessarily present at the anode and cathode. The complexity is
rendered still greater by the circumstance that two or more of
these actions may occur simultaneously^ and also in variable
proportions to each other. But it may in a great measure be
resolved by attention to the principles already laid down (482).

513. When aqueous solutions of bodies are used; secondary
results are exceedingly frequent. Even when the water is not
present in large quantity^ but is merely that of combination^
still secondary results often ensue: for instance; it is very pos¬
sible that in Sir Humphry Davy’s decomposition of the hydrates
of potassa and soda; a part of the potassium produced was the
result of a secondary action. HencC; also, a frequent cause for
the disappearance of the oxygen and hydrogen which would
otherwise be evolved: and when hydrogen does not appear at
the cathode in an aqueous solution^ it perhaps always indicates
that a secondary action has taken place there. No exception
to this rule has as yet occurred to my observation.

514. Secondary actions are not confined to aqueous solutions,
or cases where water is present. For instance; various chlorides
acted upon; when fused (138); by platina electrodeS; have the
chlorine determined electrically to the anode. In many cases,
as with the chlorides of lead; potassium, barium, etc., the
chlorine acts on the platina and forms a compound with it,
which dissolves; but when protochloride of tin is used, the
chlorine at the anode does not act upon the platina, but upon
the chloride already there, forming a perchloride which rises in
vapour (525, 539). These are, therefore, instances of secondary
actions of both kinds, produced in bodies containing no water.

515. The production of boron from fused borax (138, 153) is
also a case of secondary action; for boracic acid is not decom¬
posable by electricity (144), and it was the sodium evolved at
the cathode which, re-acting on the boracic acid around it, took
oxygen from it and set boron free in the experiments formerly
described.

516. Secondary actions have already, in the hands of M.
Becquerel; produced many interesting results in the formation
of compounds; some of them new, others imitations of those
occurring naturally.^ It is probable they may prove equally
interesting in an opposite direction, i.e. as affording cases of
analytic decomposition. Much information regarding the com¬
position, and perhaps even the arrangement, of the particles of
such bodies as the vegetable acids and alkalies, and organic

^ Annales de Chimie, tom. xxxv. p. 113.

Definite Electro-Chemical Decomposition 145

compounds generally^ will probably be obtained by submitting
them to the action of nascent oxygen^ hydrogen^ chlorine^ etc.^
at the electrodes; and the action seems the more promising,
because of the thorough command which we possess over
attendant circumstances, such as the strength of the current,
the size of the electrodes, the nature of the decomposing con¬
ductor, its strength, etc., all of which may be expected to have
their corresponding influence upon the final result.

517. It is to me a great satisfaction that the extreme variety
of secondary results has presented nothing opposed to the
doctrine of a constant and definite electro-chemical action, to
the particular consideration of which I shall now proceed.

^ vii. On the definite nature and extent of Electro-chemical
Decomposition

518. In the first part of these Researches, after proving the
identity of electricities derived from different sources, and
showing, by actual measurement, the extraordinary quantity of
electricity evolved by a very feeble voltaic arrangement (107,
112), I announced a law, derived from experiment, which
seemed to me of the utmost importance to the science of elec¬
tricity in general, and that branch of it denominated electro¬
chemistry in particular. The law was expressed thus: The
chemical power of a current of electricity is in direct proportion to
the absolute quantity of electricity which passes (113).

519. In the further progress of the successive investigations,
I have had frequent occasion to refer to the same law, some¬
times in circumstances offering powerful corroboration of its
truth (192, 240, 241); and the present series already supplies
numerous new cases in which it holds good (439, 457, 461, 467).
It is now my object to consider this great principle more closely,
and to develop some of the consequences to which it leads.
That the evidence for it may be the more distinct and applicable,
I shall quote cases of decomposition subject to as few inter¬
ferences from secondary results as possible, effected upon bodies
very simple, yet very definite in their nature.

520. In the first place, I consider the law as so fully established
with respect to the decomposition of water, and under so many
circumstances which might be supposed, if anything could, to
exert an influence over it, that I may be excused entering into
further detail respecting that substance, or even summing up
the results here (467). I refer, therefore, to the whole of the

K

146 Faraday’s Researches

subdivision of this series of Researches which contains the
account of the volta-electrometer (439^ etc.).

521. In the next place^ I also consider the law as established
with respect to muriatic acid by the experiments and reasoning
already advanced^ when speaking of that substance^ in the
subdivision respecting primary and secondary results (493, etc.).

522. I consider the law as established also with regard to
hydriodic acid by the experiments and considerations already
advanced in the preceding division of this series of Researches
(502, 5 ° 3 )-

523. Without speaking with the same confidence^ yet from
the experiments described, and many others not described,
relating to hydro-fluoric, hydro-cyanic, ferro-cyanic, and sulpho-
cyanic acids (505, 506, 507), and from the close analogy which
holds between these bodies and the hydracids of chlorine,
iodine, bromine, etc., I consider these also as coming under
subjection to the law, and assisting to prove its truth.

524. In the preceding cases, except the first, the water is
believed to be. inactive; but to avoid any ambiguity arising

from its presence, I sought for substances from which
it should be absent altogether; and, taking advantage
of the law of conduction already developed (116, etc.),
I soon found abundance, amongst which protochloride
T of tin was first subjected to decomposition in the
following manner. A piece of platina wire had one
extremity coiled up into a small knob, and, having
been carefully weighed, was sealed hermetically into a
piece of bottle-glass tube, so that the knob should be
at the bottom of the tube within (fig. 28). The tube
was suspended by a piece of platina wire, so that the
heat of a spirit-lamp could be applied to it. Recently
fused protochloride of tin was introduced in sufficient
quantity to occupy, when melted, about one half of the
^ ■ tube; the wire of the tube was connected with a
volta-electrometer (446), which was itself connected with the
negative end of a voltaic battery; and a platina wire con¬
nected with the positive end of the same battery was dipped
into the fused chloride in the tube; being however so bent,
that it could not by any shake of the hand or apparatus touch
the negative electrode at the bottom of the vessel. The whole
arrangement is delineated in fig. 29.

525. Under these circumstances the chloride of tin was
decomposed: the chlorine evolved at the positive electrode

Definite Electro-Chemical Decomposition 147

formed bichloride of tin (514), which passed away in fumes,
and the tin evolved at the negative electrode combined with the
platina, forming an alloy, fusible at the temperature to which
the tube was subjected, and therefore never occasioning metallic
communication through the decomposing chloride. When the
experiment had been continued so long as to yield a reasonable
quantity of gas in the volta-electrometer, the battery connection
was broken, the positive electrode removed, and the tube and
remaining chloride allowed to cool. When cold, the tube was
broken open, the rest of the chloride and the glass being easily
separable from the platina wire and its button of alloy. The

latter when washed was then reweighed, and the increase gave
the weight of the tin reduced.

526. I will give the particular results of one experiment, in
illustration of the mode adopted in this and others, the results
of which I shall have occasion to quote. The negative elec¬
trode weighed at first 20 grains; after the experiment, it, with
its button of alloy, weighed 23.2 grains. The tin evolved by
the electric current at the cathode weighed therefore 3.2 grains.
The quantity of oxygen and hydrogen collected in the volta-
electrometer = 3.85 cubic inches. As 100 cubic inches of
oxygen and hydrogen, in the proportions to form water, may
be considered as weighing 12.92 grains, the 3.85 cubic inches
would weigh 0.49742 of a grain; that being, therefore, the
weight of water decomposed by the same electric current as
was able to decompose such weight of protochloride of tin as
could yield 3.2 grains of metal. Now 0.49742 : 3.2 : : 9 the
equivalent of water is to 57.9^ which should therefore be the
equivalent of tin, if the experiment had been made without

148 Faraday’s Researches

error, and if the electro-chemical decomposition is in this case
also definite. In some chemical works 58 is given as the che¬
mical equvialent of tin, in others 57.9. Both are so near to the
result of the experiment, and the experiment itself is so subject
to slight causes of variation (as from the absorption of gas in
the volta-electrometer (451), etc.), that the numbers leave little
doubt of the applicability of the law of definite action in this
and all similar cases of electro-decomposition.

527. It is not often I have obtained an accordance in num¬
bers so near as that I have just quoted. Four experiments
were made on the protochloride of tin, the quantities of gas
evolved in the volta-electrometer being from 2.05 to 10.29 cubic
inches. The average of the four experiments gave 58.53 as
the electro-chemical equivalent for tin.

528. The chloride remaining after the experiment was pure
protochloride of tin; and no one can doubt for a moment that
the equivalent of chlorine had been evolved at the anode, and,
having formed bichloride of tin as a secondary result, had
passed away.

529. Chloride of lead was experimented upon in a manner
exactly similar, except that a change was made in the nature of
the positive electrode; for as the chlorine evolved at the anode
forms no perchloride of lead, but acts directly upon the platina,
it produces, if that metal be used, a solution of chloride of
platina in the chloride of lead; in consequence of which a por¬
tion of platina can pass to the cathode, and would then pro¬
duce a vitiated result. I therefore sought for, and found in
plumbago, another substance, which could be used safely as
the positive electrode in such bodies as chlorides, iodides, etc.
The chlorine or iodine does not act upon it, but is evolved in
the free state; and the plumbago has no re-action, under the
circumstances, upon the fused chloride or iodide in which it is
plunged. Even if a few particles of plumbago should separate
by the heat or the mechanical action of the evolved gas, they
can do no harm in the chloride.

530. The mean of three experiments gave the number of
100.85 the equivalent for lead. The chemical equivalent is
103.5. The deficiency in my experiments I attribute to the
solution of part of the gas (451) in the volta-electrometer; but
the results leave no doubt on my mind that both the lead and
the chlorine are, in this case, evolved in definite quantities by
the action of a given quantity of electricity (549, etc.).

531. Chloride of antimony, —It was in endeavouring to obtain

Definite Electro-Chemical Decomposition 149

the electro-chemical equivalent of antimony from the chloride^
that I found reasons for the statement I have made respecting
the presence of water in it in an earlier part of these Researches
(425, 428, etc.).

532. I endeavoured to experiment upon the oxide of lead
obtained by fusion and ignition of the nitrate in a platina
crucible^ but found great difficulty, from the high temperature
required for perfect fusion, and the powerful fluxing qualities of
the substance. Green-glass tubes repeatedly failed. I at last
fused the oxide in a small porcelain crucible, heated fully in a
charcoal fire; and, as it was essential that the evolution of the

Fig. 30. Fig. 31.

lead at the cathode should take place beneath the surface, the
negative electrode was guarded by a green-glass tube, fused
around it in such a manner as to expose only the knob of platina
at the lower end (fig. 30), so that it could be plunged beneath
the surface, and thus exclude contact of air or oxygen with
the lead reduced there. A platina wire was employed for the
positive electrode, that metal not being subject to any action
from the oxygen evolved against it. The arrangement is given
in fig. 31.

533. In an experiment of this kind the equivalent for the
lead came out 93.17, which is very much too small. This, I
believe, was because of the small interval between the positive
and negative electrodes in the oxide of lead; so that it was not
unlikely that some of the froth and bubbles formed by the
oxygen at the anode should occasionally even touch the lead
reduced at the cathode, and re-oxidise it. When I endeavoured
to correct this by having more litharge, the greater heat required

150 Faraday’s Researches

to keep it all fluid caused a quicker action on the crucible wb.icl
was soon eaten through^ and the experiment stopped. ^

534. In one experiment of this kind I used borate of lea^c
(144, 408). It evolves lead; under the influence of the electiri*
current; at the anode, and oxygen at the cathode ; and as tin
boracic acid is not either directly (144) or incidentally decom
posed during the operation; I expected a result dependent 01
the oxide of lead. The borate is not so violent a flux as tJon
oxide; but it requires a higher temperature to make it quit
liquid; and if not very hot; the bubbles of oxygen cling to tli'
positive electrode; and retard the transfer of electricity. Tli<
number for lead came out 101.29; which is so near to 103.5 ^
to show that the action of the current had been definite.

535. Oxide oj bismuth ,—I found this substance required t:o<
high a temperature; and acted too powerfully as a fluX; to allo'v
of any experiment being made on it; without the application o
more time and. care than I could give at present.

536. The ordinary protoxide of antimony, which consists o
one proportional of metal and one and a half of oxygen; wa
subjected to the action of the electric current in a green-gins
tube (524); surrounded by a jacket of platina foil; and hea,t:e<
in a charcoal fire. The decomposition began and proceeded
very well at first; apparently indicating; according to t:li
general law (414; 432); that this substance was one contaimiri
such elements and in such proportions as made it amenable t
the power of the electric current. This effect I have alrend'
given reasons for supposing may be due to the presence of
true protoxide; consisting of single proportionals (43I; 428'
The action soon diminished; and finally ceased; because of t:b
formation of a higher oxide of the metal at the positive elec
trode. This compound; which was probably the peroxide; bein
infusible and insoluble in the protoxide; formed a crystallin
crust around the positive electrode; and thus insulating i‘
prevented the transmission of the electricity. Whether; if '
had been fusible and still immiscible; it would have decomposec
is doubtful; because of its departure from the required compos
tion (432). It was a very natural secondary product at 1:1
positive electrode (514). On opening the tube it was found tli2
a little antimony had been separated at the negative electro cl<
but the quantity was too small to allow of any quantita.1:i*s
result being obtained.^

^This paragraph is subject to the corrective note now appended
paragraph 431 .—December 1838.

Iodides

537. Iodide of lead. —This substance can be experimented
with in tubes heated by a spirit-lamp (524); but I obtained
no good results from it; whether I used positive electrodes of
platina or plumbago. In two experiments the numbers for the
lead came out only 75.46 and 73.45, instead of 103.5. This I
attribute to the formation of a periodide at the positive elec¬
trode, which, dissolving in the mass of liquid iodide, came in
contact with the lead evolved at the negative electrode, and
dissolved part of it, becoming itself again protiodide. Such a
periodide does exist; and it is very rarely that the iodide of
lead formed by precipitation, and well washed, can be fused
without evolving much iodine, from the presence of this per-
compound; nor does crystallisation from its hot aqueous solution
free it from this substance. Even when a little of the protiodide
and iodine are merely rubbed together in a mortar, a portion of
the periodide is formed. And though it is decomposed by being
fused and heated to dull redness for a few minutes, and the
whole reduced to protiodide, yet that is not at all opposed to
the possibility, that a little of that which is formed in great
excess of iodine at the anode^ should be carried by the rapid
currents in the liquid into contact with the cathode.

538. This view of the result was strengthened by a third
experiment, where the space between the electrodes was in¬
creased to one-third of an inch; for now the interfering effects
were much diminished, and the number of the lead came out
89.04; and it was fully confirmed by the results obtained in
the cases of transfer to be immediately described (553).

The experiments on iodide of lead therefore offer no exception
to the general law under consideration, but on the contrary may,
from general considerations, be admitted as included in it.

539. Protiodide of tin. —This substance, when fused (138),
conducts and is decomposed by the electric current, tin is
evolved at the anode^ and periodide of tin as a secondary result
(514, 525) at the cathode. The temperature required for its
fusion is too high to allow of the production of any results fit
for weighing.

540. Iodide of potassmm was subjected to electrolytic action
in a tube, like that in fig. 28 (524). The negative electrode was
a globule of lead, and I hoped in this way to retain the potas¬
sium, and obtain results that could be weighed and compared
with the volta-electrometer indication; but the difficulties
dependent upon the high temperature required, the action
upon the glass, the fusibility of the platina induced by the

152 Faraday’s Researches

presence of the lead^ and other circumstances, prevented me
from procuring such results. The iodide was decomposed with
the evolution of iodine at the anode, and of potassium at the
cathode, as in former cases.

541. In some of these experiments several substances were
placed in succession, and decomposed simultaneously by the
same electric current: thus, protochloride of tin, chloride of
lead, and water, were thus acted on at once. It is needless to
say that the results were comparable, the tin, lead, chlorine,
oxygen, and hydrogen evolved being definite in quantity and
electro-chemical equivalents to each other.

542. Let us turn to another kind of proof of the definite
chemical action of electricity. If any circumstances could be
supposed to exert an influence over the quantity of the matters
evolved during electrolytic action, one would expect them to
be present when electrodes of different substances, and possess¬
ing very different chemical affinities for such matters, were
used. Platina has no power in dilute sulphuric acid of com¬
bining with the oxygen at the anode, though the latter be evolved
in the nascent state against it. Copper, on the other hand,
immediately unites with the oxygen, as the electric current sets
it free from the hydrogen; and zinc is not only able to combine
with it, but can, without any help from the electricity, abstract
it directly from the water, at the same time setting torrents of
hydrogen free. Yet in cases where these three substances
were used as the positive electrodes in three similar portions
of the same dilute sulphuric acid, specific gravity 1.336, precisely
the same quantity of water was decomposed by the electric
current, and precisely the same quantity of hydrogen set free
at the cathodes of the three solutions.

543. The experiment was made thus. Portions of the dilute
sulphuric acid were put into three basins. Three volta-electro-
meter tubes, of the form figs. 20, 22, were filled with the same
acid, and one inverted in each basin (442). A zinc plate,
connected with the positive end of a voltaic battery, was
dipped into the first basin, forming the positive electrode there,
the hydrogen, which was abundantly evolved from it by the
direct action of the acid, being allowed to escape. A copper
plate, which dipped into the acid of the second basin, was con¬
nected with the negative electrode of the first basin; and a
platina plate, which dipped into the acid of the third basin,
was connected with the negative electrode of the second basin.
The negative electrode of the third basin was connected with a

Definite Electro-Chemical Action 153

volta-electrometer (446); and that with the negative end of the
voltaic battery.

544. Immediately that the circuit was complete, the electro¬
chemical action commenced in all the vessels. The hydrogen
still rose in, apparently, undiminished quantities from the
positive zinc electrode in the first basin. No oxygen was evolved
at the positive copper electrode in the second basin, but a sul¬
phate of copper was formed there; whilst in the third basin
the positive platina electrode evolved pure oxygen gas, and was
itself unaffected. But in all the basins the hydrogen liberated
at the negative platina electrodes was the same in quantity, and
the same with the volume of hydrogen evolved in the volta-
electrometer, showing that in all the vessels the current had
decomposed an equal quantity of water. In this trying case,
therefore, the chemical action of electricity proved to be perfectly
definite.

545. A similar experiment was made with muriatic acid
diluted with its bulk of water. The three positive electrodes
were zinc, silver, and platina; the first being able to separate and
combine with the chlorine without the aid of the current; the
second combining with the chlorine only after the current had
set it free; and the third rejecting almost the whole of it. The
three negative electrodes were, as before, platina plates fixed
within glass tubes. In this experiment, as in the former, the
quantity of hydrogen evolved at the cathodes was the same for
all, and the same as the hydrogen evolved in the volta-electro¬
meter. I have already given my reasons for believing that in
these experiments it is the muriatic acid which is directly de¬
composed by the electricity (499); and the results prove that
the quantities so decomposed are perfectly definite and pro¬
portionate to the quantity of electricity which has passed.

546. In this experiment the chloride of silver formed in the
second basin retarded the passage of the current of electricity,
by virtue of the law of conduction before described (130), so
that it had to be cleaned off four or five times during the course
of the experiment; but this caused no difference between the
results of that vessel and the others.

547. Charcoal was used as the positive electrode in both
sulphuric and muriactic acids (543, 545); but this change pro¬
duced no variation of the results. A zinc positive electrode,
in sulphate of soda or solution of common salt, gave the same
constancy of operation.

548. Experiments of a similar kind were then made with

154 Faraday’s Researches

bodies altogether in a different state^ i.e, fused chlorides^
iodideS; etc. I have already described an experiment with
fused chloride of silver^ in which the electrodes were of metallic
silver^ the one rendered negative becoming increased and
lengthened by the addition of metal, whilst the other was dis¬
solved and eaten away by its abstraction. This experiment
was repeated, two weighed pieces of silver wire being used as
the electrodes, and a volta-electrometer included in the circuit.
Great care was taken to withdraw the negative electrode so
regularly and steadily that the crystals of reduced silver should
not form a metallic communication beneath the surface of the
fused chloride. On concluding the experiment the positive elec¬
trode was re-weighed, and its loss ascertained. The mixture
of chloride of silver, and metal, withdrawn in successive portions
at the negative electrode, was digested in solution of ammonia,
to remove the chloride, and the metallic silver remaining
also weighed: it was the reduction at the cathode, and exactly
equalled the solution at the anode; and each portion was as
nearly as possible the equivalent to the water decomposed in
the volta-electrometer.

549. The infusible condition of the silver at the temperature
used, and the length and ramifying character of its crystals,

render the above experiment

difficult to perform, and un¬

certain in its results. I

therefore wrought with chlo-
ride of lead, using a green-
glass tube, formed as in
hg. 32. A weighed platina
Pig ^2 wire was fused into the bot¬

tom of a small tube, as before
described (524). The tube was then bent to an angle, at about
half an inch distance from the closed end; and the part between
the angle and the extremity being softened, was forced upward,
as in the figure, so as to form a bridge, or rather separation,
producing two little depressions or basins a, h, within the tube.
This arrangement was suspended by a platina wire, as before,
so that the heat of a spirit-lamp could be applied to it, such
inclination .being given to it as would allow all air to escape
during the fusion of the chloride of lead. A positive electrode
was then provided, by bending up the end of a platina wire

into a knot, and fusing about twenty grains of metallic lead
on to it, in a small closed tube of glass, which was afterwards

Electrolysation of Chloride of Lead 155

broken away. Being so furnished; the wire with its lead was
weighed; and the weight recorded.

^550. Chloride of lead was now introduced into the tube; and
carefully fused. The leaded electrode was also introduced;
after which the metal; at its extremity; soon melted. In this
state of things the tube was filled up to c with melted chloride
of lead; the end of the electrode to be rendered negative was
in the basin b, and the electrode of melted lead was retained
in the basin a, and; by connection with the proper conducting
wire of a voltaic battery; was rendered positive. A volta-
electrometer was included in the circuit.

551. Immediately upon the completion of the communication
with the voltaic battery; the current passed; and decomposition
proceeded. No chlorine was evolved at the positive electrode;
but as the fused chloride was transparent; a button of alloy
could be observed gradually forming and increasing in size at
h, whilst the lead at a could also be seen gradually to diminish.
After a time; the experiment was stopped; the tube allowed to-
cool; and broken open; the wireS; with their buttons; cleaned
and weighed; and their change"in weight compared with the
indication of the volta-electrometer.

552. In this experiment the positive electrode had lost just
as much lead as the negative one had gained (530); and the
loss and gain were very nearly the equivalents of the water de¬
composed in the volta-electrometer; giving for lead the number
101.5. It is therefore evident; in this instance; that causing
strong affinityj or no affinity, for the substance evolved at the
anode, to be active during the experiment (542); produces no
variation in the definite action of the electric current.

553. A similar experiment was then made with iodide of lead^
and in this manner all confusion from the formation of a perio-
dide avoided (538). No iodine was evolved during the whole
action; and finally the loss of lead at the anode was the same as
the gain at the cathode, the equivalent number; by comparison
with the result in the volta-electrometer; being 103.5.

554. Then protochloride of tin was subjected to the electric
current in the same manner; using; of course; a tin positive elec¬
trode. No bichloride of tin was now formed (514; 525). On
examining the two electrodes; the positive had lost precisely as
much as the negative had gained; and by comparison with the
volta-electrometer; the number for tin came out 59.

555. It is quite necessary in these and similar experiments
to examine the interior of the bulbs of alloy at the ends of the

156 Faraday’s Researches

conducting wires; for occasionally, and especially with those :
which have been positive, they are cavernous, and contain
portions of the cloride or iodide used, which must be removed
before the final weight is ascertained. This is more usually
the case with lead than tin.

556. All these facts combine into, I think, an irresistible i

mass of evidence, proving the truth of the important proposition j

which I at first laid down, namely, that the chemical power of a [

c^irre 7 'it of electricity is in direct proportion to the absolute quantity j

of electricity which passes (113, 518). They prove, too, that this ;

is not merely true with one substance, as water, but generally |

with all electrolytic bodies; and, further, that the results i

obtained with any one substance do not merely agree amongst |

themselves, but also with those obtained from other substances, 1

the whole combining together into one seines of definite electro- i

chemical actions (241). I do not mean to say that no exceptions !

will appear: perhaps some may arise, especially amongst sub- j

stances existing only by weak affinity; but I do not expect that |

any will seriously disturb the result announced. If, in the well
considered, well examined, and, I may surely say, well ascer- !
tained doctrines of the definite nature of ordinary chemical '

affinity, such exceptions occur, as they do in abundance, yet, ,

without being allowed to disturb our minds as to the general
conclusion, they ought also to be allowed if they should present j

themselves at this, the opening of a new view of electro-chemical ;

action; not being held up as obstructions to those who may be ,

engaged in rendering that view more and more perfect, but laid i

aside for a while, in hopes that their perfect and consistent
explanation will ultimately appear. !

557. The doctrine of definite electro-chemical action just laid |

down, and, I believe, established, leads to some new views of j

the relations and classifications of bodies associated with or ■

subject to this action. Some of these I shall proceed to consider. •

558. In the first place, compound bodies may be separated
into two great classes, namely, those which are decomposable

by the electric current, and those which are not: of the latter, .
some are conductors, others non-conductors, of voltaic elec- j
tricity.^ The former do not depend for their decomposability ;
upon the nature of their elements only; for, of the same two
elements, bodies may be formed of which one shall belong to 1

^ I mean here by voltaic electricity, merely electricity from a most
abundant source, but having very small intensity. |

General Propositions 157

one class and another to the other class; but probably on the
proportions also (432). It is further remarkable^ that with
very few, if any, exceptions (150, 426), these decomposable
bodies are exactly those governed by the remarkable law of
conduction I have before described (130); for that law does
; not extend to the many compound fusible substances that are

i excluded from this class. I propose to call bodies of this, the

; decomposable class. Electrolytes (400).

, 559. Then, again, the substances into which these divide,.

S under the influence of the electric current, form an exceedingly

I important general class. They are combining bodies; are

i directly associated with the fundamental parts of the doctrine of

i chemical affinity; and have each a definite proportion, in which

1 they are always evolved during electrolytic action. I have pro-

i posed to call these bodies generally ions^ or particularly anions

I and cations^ according as they appear at the anode or cathode

(401); and the numbers representing the proportions in which
i they are evolved electro-chemical equivalents. Thus hydrogen^

' oxygen, chlorine, iodine, lead, tin are ions; the three former
are anions^ the two metals are cations, and i, 8, 36, 125, 104, 58,,

I are their electro-chemical equivalents nearly.

' 560. A summary of certain points already ascertained respect¬

ing electrolytes, ions, and electro-chemical equivalents, may be
given in the following general form of propositions, without, I
hope, including any serious error.

' 561. i. A single ion, i.e. one not in combination with another,

will have no tendency to pass to either of the electrodes, and
will be perfectly indifferent to the passing current, unless it be
itself a compound of more elementary ions, and so subject to
actual decomposition. Upon this fact is founded much of the
proof adduced in favour of the new theory of electro-chemical
decomposition, which I put forth in a former part of these
Researches (254, etc.).

562. ii. If one ion be combined in right proportions (432)
with another strongly opposed to it in its ordinary chemical
relations, i.e. if an anion be combined with a cation, then both
will travel, thd one to the anode, the other to the cathode, of the
decomposing body (266, 278, 283).

563. iii. If, therefore, an ion pass towards one of the elec¬
trodes, another ion must also be passing simultaneously to the
other electrode, although, from secondary action, it may not
make its appearance (478).

564. iv. A body decomposable directly by the electric current.

158 Faraday’s Researches

i,e. an electrolyte^ must consist of two ions, and must also render I
them up during the act of decomposition.

565. V. There is but one electrolyte composed of the same two !

elementary ions ; at least such appears to be the fact (432)^
dependent upon a law^ that 07 ily single electro-chemical equivalents ;
of elementary ions can go to the electrodes, and not multiples. |

566. vi. A body not decomposable when aione^ as boracic ,

acid^ is not directly decomposable by the electric current when j
in combination (515). It may act as an ion going wholly to the
anode or cathode, but does not yield up its elements, except I
occasionally by a secondary action. Perhaps it is superfluous
for me to point out that this proposition has no relation to such i
cases as that of water, which, by the presence of other bodies, is
rendered a better conductor of electricity, and therefore is more
freely decomposed.

567. vii. The nature of the substance of which the electrode

is formed, provided it be a conductor, causes no difference in
the electro-decomposition, either in kind or degree (542, 548):
but it seriously influences, by secondary action (479), the state
in which the ions finally appear. Advantage may be taken of
this principle in combining and colFecting such ions as, if evolved I
in their free state, would be unmanageable.^ |

568. viii. A substance which, being used as the electrode, |
can combine with the ion evolved against it, is also, I believe,
an ion, and combines, in such cases, in the quantity represented {
by its electro-chemical equivalent. All the experiments I have !
made agree with this view; and it seems to me, at present, to |
result as a necessary consequence. Whether, in the secondary '
actions that take place, where the ion acts, not upon the matter

of the electrode, but on that which is around it in the liquid i
(479), the same consequence follows, will require more extended !
investigation to determine.

569. ix. Compound ions are not necessarily composed of
electro-chemical equivalents of simple ions. For instance, sul¬
phuric acid, boracic acid, phosphoric acid, are ions, but not I
electrolytes, i.e. not composed of electro-chemical equivalents of I
simple ions.

^ It will often happen that the electrodes used may be of such a nature as, '
with the fluid in which they are immersed, to produce an electric current, !
either according with or opposing that of the voltaic arrangement used, |
and in this way, or by direct chemical action, may sadly disturb the results. 1
Still, in the midst of all these confusing effects, the electric current, which '
actually passes in any direction through the body suffering decomposition, '
will produce its own definite electrolytic action.

' Electro-Chemical Equivalents 159

1 570. X. Electro-chemical equivalents are always consistent;

I i.e. the same number which represents the equivalent of a sub-

I stance A when it is separating from a substance will also

; represent A when separating from a third substance C. Thus^

j 8 is the electro-chemical equivalent of oxygen, whether separat-

1 ing from hydrogen, or tin, or lead; and 103.5 is the electro-

i chemical equivalent of lead, whether separating from oxygen,

I or chlorine, or iodine.

j 571. xi. Electro-chemical equivalents coincide, and are the
I same, with ordinary chemical equivalents.

572. By means of experiment and the preceding propositions,
a knowledge of io 7 ^s and their electro-chemical equivalents may
be obtained in various w^ays. .

573. In the first place, they may be determined directly, as
has been done with hydrogen, oxygen, lead, and tin, in the
numerous experiments already quoted.

574. In the next place, from propositions ii. and hi. may be
deduced the knowledge of many other ions^ and also their

I equivalents. When chloride of lead was decomposed, platina
being used for both electrodes (131), there could remain no
more doubt that chlorine was passing to the anode, although it
combined with the platina there, than when the positive elec¬
trode, being of plumbago (529), allowed its evolution in the free
state; neither could there, in either case, remain any doubt that
for every 103.5 parts of lead evolved at the cathode, 36 parts
of chlorine were evolved at the anode, for the remaining chloride
of lead was unchanged. So also, when in a metallic solution
one volume of oxygen, or a secondary compound containing that
proportion, appeared at the anode, no doubt could arise that
hydrogen, equivalent to two volumes, had been determined to
the cathode, although, by a secondary action, it had been em¬
ployed in reducing oxides of lead, copper, or other metals, to
the metallic state. In this manner, then, we learn from the
experiments already described in these Researches, that chlorine,
iodine, bromine, fluorine, calcium, potassium, strontium, mag¬
nesium, manganese, etc., are ions, and that their electro-chemical
equivalents are the same as their ordinary chemical equivalents.

575. Propositions iv. and v. extend our means of gaining
information. For if a body of known chemical composition is
found to be decomposable, and the nature of the substance
evolved as a primary or even a secondary result (478, 512) at
one of the electrodes, be ascertained, the electro-chemical
equivalent of that body may be deduced from the known con-

i6o Faraday’s Researches

stant composition of the substance evolved. Thus^ when fused
protiodide of tin is decomposed by the voltaic current (539)^
the conclusion may be drawn that both the iodine and tin are
ions^ and that the proportions in which they combine in the fused
compound express their electro-chemical equivalents. Again^,
with respect to the fused iodide of potassium (540), it is an
electrolyte; and the chemical equivalents will also be the
electro-chemical equivalents.

576. If proposition viii. sustain extensive experimental in¬
vestigation, then it will not only help to confirm the results
obtained by the use of the other propositions, but will give
abundant original information of its own.

577. In many instances, the secondary results obtained by
the action of the evolved ion on the substances present in the
surrounding liquid or solution will give the electro-chemical
equivalent. Thus, in the solution of acetate of lead, and, as
far as I have gone, in other proto-salts subjected to the reducing
action of the nascent hydrogen at the cathode, the metal precipi¬
tated has been in the same quantity as if it had been a primary
product (provided no free hydrogen escaped there), and there¬
fore gave accurately the number representing its electro¬
chemical equivalent.

578. Upon this principle it is that secondary results may
occasionally be used as measurers of the volta-electric current
(441, 475); but there are not many metallic solutions that
answer this purpose well: for unless the metal is easily precipi¬
tated, hydrogen will be evolved at the cathode and vitiate the
result. If a soluble peroxide is formed at the anode, or if the
precipitated metal crystallise across the solution and touch
the positive electrode, similar vitiated results are obtained. I
expect to find in some salts, as the acetates of mercury and zinc,
solutions favourable for this use.

579. After the first experimental investigations to establish
the definite chemical action of electricity, I have not hesitated
to apply the more strict results of chemical analysis to correct
the numbers obtained as electrolytic results. This, it is evident,
may be done in a great number of cases without using too much
liberty towards the due severity of scientific research. The
series of numbers representing electro-chemical equivalents
must, like those expressing the ordinary equivalents of chemi¬
cally acting bodies, remain subject to the continual correction
of experiment and sound reasoning.

580. I give the following brief table of ions and their electro-

Electro-Chemical Equivalents i6i

chemical equivalents rather as a specimen of a first attempt
than as anything that can supply the want which must very
quickly be felt_, of a full and complete tabular account of this
class of bodies. Looking forward to such a table as of extreme
utility (if well constructed) in developing the intimate relation
of ordinary chemical affinity to electrical actions^ and identify¬
ing the twO; not to the imagination merely^ but to the conviction
of the senses and a sound judgment, I may be allowed to express
a hope that the endeavour will always be to make it a table of
real, and not hypothetical, electro-chemical equivalents; for
we shall else overrun the facts, and lose ail sight and conscious¬
ness of the knowledge lying directly in our path.

581. The equivalent numbers do not profess to be exact,
and are taken almost entirely from the chemical results of other
philosophers in whom I could repose more confidence, as to
these points, than in myself.

Oxygen.

.. 8

Chlorine.

• -35.5

Iodine.

.126

Bromine.

• -78.3

Fluorine.

,..18.7

Cyanogen .

. .26

Sulphuric acid .

..40

Hydrogen .. .

. .. I

Potassium

.. 39.2

Sodium.

•• 23.3

Lithium ....

.. 10

Barium.

.. 68.7

Strontium .. .

.. 43.8

Calcium.

.. 20.5

Magnesium ..

.. 12.7

Manganese ..

.. 27.7

Zinc.

•• 32.5

Tin .

•• 57.9

Lead.

••103.5

Iron.

.. 28

Copper .

.. 31-6

582. Table of Ions.

Anions,

Selenic acid .. .

,. .64

Nitric acid .. ..

• .54

Chloric acid .. .

' • -75.5

Phosphoric acid

.•35.7

Carbonic acid ..

. .22

Boracic acid . -.

. .24

Acetic acid .. ..

..51

Cations,

Cadmium.

55.8

Cerium .

46

Cobalt.

29-5

Nickel .

29-5

Antimony.

64.6?

Bismuth .

71

Mercury .

200

Silver .

108

Platina.

98.6?

Gold.

(?)

Ammonia .

17

Potassa.

47-2

Tartaric acid.66

Citric acid.58

Oxalic acid.36

Sulphur (?) .16

Selenium (?).

Sulpho-cyanogen..

Soda .

•• •• 31.3

Lithia .

. ... 18

Baryta.

. ... 76.7

Strontia ....

.. .. 51.8

Lime .

.. .. 28.5

Magnesia .. .

. ... 20.7

Alumina ...

.... (?)

Protoxides generally.

Quima.

. ... 171.6

Cinchona .. .

. ... 160

Morphia ....

.. . .290

Vegeto-alkalies gener-

ally.

583. This table might be further arranged into groups of
such substances as either act with, or replace, each other.
Thus, for instance, acids and bases act ’ in relation to each
other; but they do not act in association with oxygen, hydrogen,

L

162 Faraday’s Researches

or elementary substances. There is indeed little or no doubt,
that; when the electrical relations of the particles of matter
come to be closely examined; this division must be made. The
simple substances; with cyanogen; sulpho-cyanogeU; and one
or two other compound bodieS; will probably form the first
group; and the acids and baseS; with such analogous com¬
pounds as may prove to be ions, the second group. Whether
these will include all ions, or whether a third class of more
complicated results will be required; must be decided by future
experiments.

584. It is fr oh able that all our present elementary bodies
are ions, but that is not as yet certain. There are some; such
as carbon; phosphorus; nitrogen; silicon; boron; aluminium; the
right of which to the title of ion it is desirable to decide as
soon as possible. There are also many compound bodieS;
and amongst them alumina and silica; which it is desirable to
class immediately by unexceptionable experiments. It is also
possible that all combinable bodieS; compound as well as simple;
may enter into the class of ions; but at present it does not
seem to me probable. Still the experimental evidence I have
is so small in proportion to what must gradually accumulate
around; and bear upon; this point; that I am afraid to give a
strong opinion upon it.

585. I think I cannot deceive myself in considering the
doctrine of definite electro-chemical action as of the utmost
importance. It touches by its facts more directly and closely
than any former fact; or set of factS; have done; upon the
beautiful idea that ordinary chemical affinity is a mere conse¬
quence of the electrical attractions of the particles of different
kinds of matter; and it will probably lead us to the means by
which we may enlighten that which is at present so obscure; and
either fully demonstrate the truth of the idea; or develop that
which ought to replace it.

586. A very valuable use of electro-chemical equivalents will
be to decide; in cases of doubt; what is the true chemical equiva¬
lent; or definite proportional; or atomic number of a body;
for I have such conviction that the power which governs electro¬
decomposition and ordinary chemical attractions is the same;
and such confidence in the overruling influence of those natural
laws which render the former definite; as to feel no hesitation
in believing that the latter must submit to them also. Such
being the case; I can have no doubt that; assuming hydrogen
as I; and dismissing small fractions for the simplicity of expres-^

Electricity Associated with Matter 163

sion^ the equivalent number or atomic weight of oxygen is 8,
of chlorine 36^ of bromine 78.4, of lead 103.5, of tin 59, etc.,
notwithstanding that a very high authority doubles several of
these numbers.

On the absolute quantity of Electricity associated with
the particles or atoms of Matter

587. The theory of definite electrolytical or electro-chemical
action appears to me to touch immediately upon the absolute
quantity of electricity or electric power belonging to different
bodies. It is impossible, perhaps, to speak on this point with¬
out committing oneself beyond what present facts will sustain;
and yet it is equally impossible, and perhaps would be impolitic,
not to reason upon the subject. Although we know nothing
of what an atom is, yet we cannot resist forming some idea of
a small particle, which represents it to the mind; and though
we are in equal, if not greater, ignorance of electricity, so as
to be unable to say whether it is a particular matter or matters,
or mere motion of ordinary matter, or some third kind of power
or agent, yet there is an immensity of facts which justify us
in believing that the atoms of matter are in some way endowed
or associated with electrical powers, to which they owe their
most striking qualities, and amongst them their mutual chemical
affinity. As soon as we perceive, through the teaching of
Dalton, that chemical powers are, however varied the circum¬
stances in which they are exerted, definite for each body, we
learn to estimate the relative degree of force which resides in
such bodies; and when upon that knowledge comes the fact,
that the electricity, which we appear to be capable of loosening
from its habitation for a while, and conveying from place to
place, ivhilst it retains its chemical force, can be measured out,
and being so measured is found to be as definite in its action
as any of those portions which, remaining associated with the
particles of matter, give them their chemical relation; we seem
to have found the link which connects the proportion of that
we have evolved to the proportion of that belonging to the
particles in their natural state.

588. Now it is wonderful to observe how small a quantity of a
compound body is decomposed by a certain portion of electricity.
Let us, for instance, consider this and a few other points in
relation to water. One grain of water, acidulated to facilitate
conduction, will require an electric current to be continued for

164 Faraday’s Researches

three minutes and three-quarters of time to effect its decom¬
position^ which current must be powerful enough to retain
a platina wire rvr^rth of an inch in thickness/ red hot; in the air
during the whole time; and if interrupted anywhere by charcoal
pointS; will produce a very brilliant and constant star of light.
If attention be paid to the instantaneous discharge of electricity
of tension; as illustrated in the beautiful experiments of Mr.
Wheatstone;^ and to what I have said elsewhere on the relation
of common and voltaic electricity (107; in); it will not be too
much to say that this necessary quantity of electricity is equal
to a very powerful flash of lightning. Yet we have it under
perfect command; can evolve; direct; and employ it at pleasure;
and when it has performed its full work of electrolysation; it
has only separated the elements of a single grain of water,

589. On the other hand; the relation between the conduction
of the electricity and the decomposition of the water is so close
that one cannot take place without the other. If the water is
altered only in that small degree which consists in its having
the solid instead of the fluid state; the conduction is stopped;
and the decomposition is stopped with it. Whether the con¬
duction be considered as depending upon the decomposition;
or not (i49; 438); still the relation of the two functions is equally
intimate and inseparable.

590. Considering this close and twofold relation, namely,
that without decomposition transmission of electricity does not
occur; and, that for a given definite quantity of electricity
passed; an equally definite and constant quantity of water or
other matter is decomposed; considering also that the agent,
which is electricit}?*; is simply employed in overcoming electrical
powers in the body subjected to its action; it seems a probable,

^ I have not stated the length of wire used, because I find by experiment,
as would be expected in theory, that it is indifferent. The same quantity
of electricity which, passed in a given time, can heat an inch of platina
wire of a certain diameter red hot, can also heat a hundred, a thousand, or
any length of the same wire to the same degree, provided the cooling
circumstances are the same for every part in all cases. This I have proved
by the volta-electrometer. I found that whether half an inch or eight
inches were retained at one constant temperature of dull redness, equal
quantities of water were decomposed in equal times. When the half inch
was used, only the centre portion of wire was ignited. A fine wire may even
be used as a rough but ready regulator of a voltaic current; for if it be
made part of the circuit, and the larger wires communicating with it be
shifted nearer to or further apart, so as to keep the portion of wire in the
circuit sensibly at the same temperature, the current passing through it
will be nearly uniform.

^Literary Gazette^ 1833, March i and 8. Philosophical Magazine, 1833,
p. 204. Ulnstitut, 1833, P- 261.

The Voltaic Pile 165

and almost a natural consequence^ that the quantity which
passes is the equivalent of, and therefore equal to, that of the
particles separated; i.e. that if the electrical power which holds
the elements of a grain of water in combination, or which makes
a grain of oxygen-and hydrogen in the'right proportions unite
into water when they are made to combine, could be thrown
into the condition of a current, it would exactly equal the current
required for the separation of that grain of water into its ele¬
ments again.

591. This view of the subject gives an almost overwhelming
idea of the extraordinary quantity or degree of electric power
which naturally belongs to the particles of matter; but it is not
inconsistent in the slightest degree with the facts which can be
brought to bear on this point. To illustrate this I must say a
few words on the voltaic pileT

592. Intending hereafter to apply the results given in this
and the preceding series of Researches to a close investigation
of the source of electricity in the voltaic instrument, I have
refrained from forming any decided opinion on the subject;
and without at all meaning to dismiss metallic contact, or the
contact of dissimilar substances, being conductors, but not
metallic, as if they had nothing to do with the origin of the
current, I still am fully of opinion with Davy, that it is at least
continued by chemical action, and that the supply constituting
the current is almost entirely from that source.

593. Those bodies w^hich, being interposed between the
metals of the voltaic pile, render it active, are all of them elec¬
trolytes (212); and it cannot but press upon the attention of
eveiy one engaged in considering this subject, that in those
bodies (so essential to the pile) decomposition and the trans¬
mission of a current are so intimately connected, that one can¬
not happen without the other. This I have shown abundantly
in water, and numerous other cases (138, 212). If, then, a
voltaic trough have its extremities connected by a body capalole
of being decomposed, as water, we shall have a continuous-
current through the apparatus; and whilst it remains in this
state we may look at the part where the acid is acting upon the
plates, and that where the current is acting upon the water, as

^ By the term voltaic pile, I mean such apparatus or arrangement of
metals as up to this time have been cailled so, and which contain water,,
brine, acids, or other aqueous solutions or decomposable substances (212),.
between their plates. Other kinds of electric apparatus may be hereafter
invented, and I hope to construct some not belonging to the class of
instruments discovered by Volta.

166 Faraday’s Researches

the reciprocals of each other. In both parts we have the two
conditions inseparable in such bodies as these, namely^ the passing
of a currentj and decomposition; and this is as true of the cells
in the battery as of the water cell; for no voltaic battery has
as yet been constructed in which the chemical action is only that
of combination: decomposition is always included, and is^ I
believe, an essential chemical part.

594. But the difference in the two parts of the connected
battery, that is, the decomposition or experimental cell, and
the acting cells, is simply this. In the former we urge the
current through, but it, apparently of necessity, is accompanied
by decomposition: in the latter we cause decompositions by
ordinary chemical actions (which are, however, themselves
electrical), and, as a consequence, have the electrical current;
and as the decomposition dependent upon the current is definite
in the former case, so is the current associated with the decom¬
position also definite in the latter (597, etc.).

595. Let us apply this in support of what I have surmised
respecting the enormous electric power of each particle or
atom of matter (591). I showed in a former part of these
Researches on the relation by measure of common and voltaic
electricity, 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 immersed to the depth of five-eighths of
an inch in acid, consisting of one drop of oil of vitriol and four
ounces of distilled water at a temperature of about 60° Fahr.,
and connected at the other extremities by a copper wire eighteen
feet long, and one-eighteenth of an inch in thickness, yielded
as much electricity in little more than three seconds of time as
a Leyden battery charged by thirty turns of a very large and
powerful plate electric machine in full action (107). This
quantity, though sufficient if passed at once through the head
of a rat or cat to have killed it, as by a flash of lightning, was
evolved by the mutual action of so small a portion of the zinc
wire and water in contact with it, that the loss of weight sus¬
tained by either would be inappreciable by our most delicate
instruments; and as to the water which could be decomposed
by that current, it must have been insensible in quantity, for
no trace of hydrogen appeared upon the surface of the platina
during those three seconds.

596. What an enormous quantity of electricity, therefore, is
required for the decomposition of a single grain of water! We
have already seen that it must be in quantity sufficient to sus-

Quantity of Electric Force in Matter 167

tain a platina wire ^-J 4 th of an inch in thickness^ red hot; in con¬
tact with the ah; for three minutes and three-quarters (588); a
quantity which is almost infinitely greater than that which
could be evolved by the little standard voltaic arrangement to
which I have just referred (595; 107). I have endeavoured to
make a comparison by the loss of weight of such a wire in a
given time in such an acid; according to a principle and experi¬
ment to be almost immediately described (597); but the pro¬
portion is so high that I am almost afraid to mention it. It
would appear that 8oO;Ooo such charges of the Leyden battery
as I have referred to above; would be necessary to supply
electricity sufficient to decompose a single grain of water; or;
if I am right; to equal the quantity of electricity which is
naturally associated with the elements of that grain of water;
endowing them with their mutual chemical affinity.

597. In further proof of this high electric condition of the
particles of matter; and the identity as to quantity of that be¬
longing to them with that necessary for their separation^ I will
describe an experiment of great simplicity but extreme beauty;
when viewed in relation to the evolution of an electric current
and its decomposing powers.

598. A dilute sulphuric acid; made by adding about one part
by measure of oil of vitriol to thirty parts of water; will act
energetically upon a piece of zinc plate in its ordinary and
simple state: but; as Mr. Sturgeon has showU;^ not at all; or
scarcely sO; if the surface of the metal has in the first instance
been amalgamated; yet the amalgamated zinc will act power¬
fully with platina as an electromotor, hydrogen being evolved
on the surface of the latter metal, as the zinc is oxidised and
dissolved. The amalgamation is best effected by sprinkling a
few drops of mercury upon the surface of the zinc, the latter
being moistened with the dilute acid, and rubbing with the
fingers or tow so as to extend the liquid metal over the whole
of the surface. Any mercury in excess, forming liquid drops
upon the zinc, should be wiped oft'.^

599. Two plates of zinc thus amalgamated were dried and
accurately weighed; one, which we will call A, weighed 163.1
grains; the other, to be called B, weighed 148.3 grains. They

^ Recent Experimental Researches^ etc., 1830, p. 74, etc.

2 The experiment may be made with pure zinc, which, as chemists well
know, is but slightly acted upon by dilute sulphuric acid in comparison
with ordinary zinc, which during the action is subject to an infinity of
voltaic actions. See De la Rive on this subject, Bibliotheque Universelle^
1830, p. 391 .

I 68 Faraday’s Researches

were about five inches long, and' 0.4 of an inch wide. An
earthenware pneumatic trough was filled with dilute sulphuric
acid, of the strength just described (598), and a gas jar, also
filled with the acid, inverted in it.^ A plate of platina of nearly
the same length, but about three times as wide as the zinc plates,
was put up into this jar. The zinc plate A was also introduced
into the jar, and brought in contact with the platina, and at the
same moment the plate B was put into the acid of the trough,
but out of contact with other metallic matter.

600. Strong action immediately occurred in the jar upon the
contact of the zinc and platina plates. Hydrogen gas rose from
the platina, and was collected in the jar, but no hydrogen or
other gas rose from either zinc plate. In about ten or twelve
minutes, sufficient hydrogen having been collected, the experi¬
ment was stopped; during its progress a few small bubbles had
appeared upon plate B, but none upon plate A. The plates
were washed in distilled water, dried, and reweighed. Plate B
weighed 148.3 grains, as before, having lost nothing by the
direct chemical action of the acid. Plate A weighed 154.65
grains, 8.45 grains of it having been oxidised and dissolved
during the experiment.

601. The hydrogen gas was next transferred to a water-
trough and measured; it amounted to 12,5 cubic inches, the
temperature being 52°, and the barometer 29.2 inches. This
quantity, corrected for temperature, pressure, and moisture,
l)ecomes 12.15453 cubic inches of dry hydrogen at mean tem¬
perature and pressure; which, increased by one-half for the
oxygen that must have gone to the anode, i,e. to the zinc, gives
18.232 cubic inches as the quantity of oxygen and hydrogen
evolved from the water decomposed by the electric current.
According to the estimate of the weight of the mixed gas before
adopted (526), this volume is equal to 2.3535544 grains, which
therefore is the weight of water decomposed; and this quantity
is to 8.45, the quantity of zinc oxidised, as 9 is to 32.31. Now
taking 9 as the equivalent number of water, the number 32.5 is
given as the equivalent number of zinc; a coincidence suffi¬
ciently near to show, what indeed could not but happen, that
for an equivalent of zinc oxidised an equivalent of water must
be decomposed.^

1 The acid was left during a night with a small piece of unamalgamated
zinc in it, for the purpose of evolving such air as might be inclined to
se^parate, and bringing the whole into a constant state.

2 The experiment was repeated several times with the same results.

Voltaic Decomposition of Water 169

602. But let us observe how the water is decomposed. It is
electrolysed, i.e. is decomposed voltaically, and not in the ordi¬
nary manner (as to appearance) of chemical decompositions;
for the oxygen appears at the anode and the hydrogen at the
cathode of the body under decomposition, and these were in
many parts of the experiment above an inch asunder. Again^
the ordinary chemical affinity was not enough under the circum¬
stances to effect the decomposition of the water, as was abund¬
antly proved by the inaction on plate B; the voltaic current
was essential. And to prevent any idea that the chemical
affinity was almost sufficient to decompose the water, and that a
smaller current of electricity might, under the circumstances^
cause the hydrogen to pass to the cathode^ I need only refer to the
results which I have given (542, 548) to show that the chemical
action at the electrodes has not the slightest influence over the
quantities of water or other substances decomposed between
them, but that they are entirely dependent upon the quantity
of electricity which passes.

603. What, then, follows as a necessary consequence of the
whole experiment ? Why, this: that the chemical action upon
32.31 parts, or one equivalent of zinc, in this simple voltaic
circle, was able to evolve such quantity of electricity in the
form of a current, as, passing through water, should decompose
9 parts, or one equivalent of that substance: and considering
the definite relations of electricity as developed in the preceding
parts of the present paper, the results prove that the quantity
of electricity which, being naturally associated with the particles
of matter, gives them their combining power, is able, when
thrown into a current, to separate those\ particles from their
state of combination; or, in other words, that the electricity
which decomposesj and that which is evolved by the decomposition
of, a certain quantity of matter, are alike.

604. The harmony which this theory of the definite evolution
and the equivalent definite action of electricity introduces into-
the associated theories of definite proportions and electro¬
chemical affinity, is very great. According to it, the equivalent
weights of bodies are simply those quantities of them which
contain equal quantities of electricity, or have naturally equal
electric powers; it being the electricity which determines
the equivalent number, because it determines the combining
force. Or, if we adopt the atomic theory or phraseology, then
the atoms of bodies which are equivalents to each other in their
ordinary chemical action, have equal quantities of electricity

170 Faraday’s Researches

naturally associated with them. But I must confess I am
jealous of the term atom ; for though it is very easy to talk of
atoms, it is very difficult to form a clear idea of their nature,
especially when compound bodies are under consideration.

605. I cannot refrain from recalling here the beautiful idea
put forth, I believe, by Berzelius (438) in his development of
his views of the electro-chemical theory of affinity, that the heat
and light evolved during cases of powerful combination are the
consequence of the electric discharge which is at the moment
taking place. The idea is in perfect accordance with the view
I have taken of the quantity of electricity associated with the
•particles of matter.

606. In this exposition of the law of the definite action of
electricity, and its corresponding definite proportion in the par¬
ticles of iDodies, I do not pretend to have brought, as yet, every
case of chemical or electro-chemical action under its dominion.
There are numerous considerations of a theoretical nature,
especially respecting the compound particles of matter and the
resulting electrical forces which they ought to possess, which I
hope will gradually receive their development; and there are
numerous experimental cases, as, for instance, those of com¬
pounds formed by weak affinities, the simultaneous decompo¬
sition of water and salts, etc., which still require investigation.
But whatever the results on these and numerous other points
may be, I do not believe that the facts which I have advanced,
or even the general laws deduced from them, will suffer any
serious change; and they are of sufficient importance to justify
their publication, though much may yet remain imperfect or
undone. Indeed, it is the great beauty of our science, chemis ¬
try , that advancement in it, whether in a degree great or small,
instead of exhausting the subjects of research, opens the doors
to further and more abundant knowledge, overflowing with
beauty and utility, to those who will be at the easy personal’pains
of undertaking its experimental investigation.

607. The definite production of electricity (603) in associa¬
tion with its definite action proves, I think, that the current of
electricity in the voltaic pile is sustained by chemical decompo¬
sition, or rather by chemical action, and not by contact only.
But here, as elsewhere (592), I beg to reserve my opinion as to
the real action of contact, not having yet been able to make up
my mind as to whether it is an exciting cause of the current,
or merely necessary to allow of the conduction of electricity,
otherwise generated, from one metal to the other.

Definite Electro-Chemical Action 171

608. But admitting that chemical action is the source of
electricity^ what an infinitely small fraction of that which is
active do we obtain and employ in our voltaic batteries! Zinc
and platina wires^ one-eighteenth of an inch in diameter and
about half an inch long^ dipped into dilute sulphuric acid^ so
weak that it is not sensibly sour to the tongue^ or scarcely to our
most delicate test papers^ will evolve more electricity in one-
twentieth of a minute (595) than any man would willingly allow
to pass through his body at once. The chemical action of a
grain of water upon four grains of zinc can evolve electricity
equal in quantity to that of a powerful thunder-storm (603,
596). Nor is it merely true that the quantity is active; it can
be directed and made to perform its full equivalent duty (602 ^
etc.). Is there not, then, great reason to hope and believe that,
by a closer experimental investigation of the principles which
govern the development and action of this subtile agent, we
shall be able to increase the power of our batteries, or invent
new instruments which shall a thousandfold surpass in energy
those which we at present possess ?

609. Here for a while I must leave the consideration of the
definite chemical action of electricity. But before I dismiss this
series of Experimental Researches, I would call to mind that, in
a former series, I showed the current of electricity was also
definite in its magnetic action (102, 103, 112, 113); and, though
this result was not pursued to any extent, I have no doubt that
the success which has attended the development of the chemical
effects is not more than would accompany an investigation of
the magnetic phenomena.

December 31, 1833.

172

Faraday’s Researches

VP

§ 8. ON THE ELECTRICITY OF THE VOLTAIC PILE; ITS SOURCE,
QUANTITY, INTENSITY, AND GENERAL CHARACTERS. ^ i.
ON SIMPLE VOLTAIC CIRCLES. % iL ON THE INTENSITY
NECESSARY FOR ELECTROLYSATION. ^ iii. ON ASSOCIATED
VOLTAIC CIRCLES, OR THE VOLTAIC BATTERY. ^ iv. ON
THE RESISTANCE OF AN ELECTROLYTE TO ELECTROLYTIC
ACTION. ^ V. GENERAL REMARKS ON THE ACTIVE VOLTAIC
BATTERY

^ i. On simple Voltaic Circles

610. The great question of the source of electricity in the
voltaic pile has engaged the attention of so many eminent
philosophers, that a man of liberal mind and able to appreciate
their powers would probably conclude, although he might not
have studied the question, that the truth was somewhere
revealed. But if in pursuance of this impression he were induced
to enter upon the work of collating results and conclusions, he
would find such contradictory evidence, such equilibrium of
opinion, such variation and combination of theory, as would
leave him in complete doubt respecting what he should accept
as the true interpretation of nature: he would be forced to take
upon himself the labour of repeating and examining the facts,
and then use his own judgment on them in preference to that
of others.

611. This state of the subject must, to those who have made
up their minds on the matter, be my apology for entering upon
its investigation. The views I have taken of the definite action
of electricity in decomposing bodies (518), and the identity of
the power so used with the power to be overcome (590), founded
not on a mere opinion or general notion, but on facts which,
being altogether new, were to my mind precise and conclusive,
gave me, as I conceived, the power of examining the question
with advantages not before possessed by any, and which might
compensate, on my part, for the superior clearness and extent
of intellect on theirs. Such are the considerations which have
induced me to suppose I might help in deciding the question,
^ Eighth Series, original edition, vol. i. p. 259.

Electricity of the Voltaic Pile 173

and be able to render assistance in that great service of removing
doubtjul knowledge. Such knowledge is the early morning light
of every advancing science, and is essential to its development;
but the man who is engaged in dispelling that which is deceptive
in it, and revealing more clearly that which is true, is as useful
in his place, and as necessary to the general progress of the
science, as he who first broke through the intellectual darkness,
and opened a path into knowledge before unknown to man.

612. The identity of the force constituting the voltaic current
or electrolytic agent, with that which holds the elements of elec¬
trolytes together (590), or in other words with chemical affinity,
seemed to indicate that the electricity of the pile itself was
merely a mode of exertion, or exhibition, or existence of true
chemical action^ or rather of its cause; and I have consequently
already said that I agree with those who believe that the supply
of electricity is due to chemical powers (592).

613. But the great question of whether it is originally due
to metallic contact or to chemical action, i.e. whether it is the
first or the second which originates and determines the current,
was to me still doubtful; and the beautiful and simple experi¬
ment with amalgamated zinc and platina, which I have described
minutely as to its results (598, etc.), did not decide the point;
for in that experiment the chemical action does not take place
without the contact of the metals, and the metallic contact is
inefficient without the chemical action. Hence either might
be looked upon as the determining cause of the current.

614. I thought it essential to decide this question by the
simplest possible forms of apparatus and experiment, that no
fallacy might be inadvertently admitted. The well-known
difficulty of effecting decomposition by a single pair of plates,
except in the fluid exciting. them into action (598), seemed to
throw insurmountable obstruction in the way of such experi¬
ments; but I remembered the easy decomposability of the
solution of iodide of potassium (52), and seeing no theoretical
reason, if metallic contact was not essential^ why true electro¬
decomposition should not be obtained without it, even in a
single circuit, I persevered and succeeded.

615. A plate of zinc, about eight inches long and half an
inch wide, was cleaned and bent in the middle to a right angle,
fig- 33? A plate of platina, about three inches long and half
an inch wide, was fastened to a platina wire, and the latter bent
as in the figure, b. These two pieces of metal were arranged
together as delineated, but as yet without the vessel and

174 Faraday’s Researches

its contents, which consisted of dilute sulphuric acid mingled
with a little nitric acid. At x a piece of folded bibulous paper^
moistened in a solution of iodide of potassium^, was placed on the
zinc^ and was pressed upon by the end of the
platina wire. When under these circumstances the
plates were dipped into the acid of the vessel c,
there was an immediate effect at x, the iodide
being decomposed, and iodine appearing at the
anode (399); i.e. against the end of the platina wire.

616. As long as the lower ends of the plates
remained in the acid the electric current continued,
and the decomposition proceeded at x. On re¬
moving the end of the wire from place to place
on the paper, the effect was evidently very power-
Fig. 33. ful; and on placing a piece of turmeric paper
between the white paper and zinc, both papers
being moistened with the solution of iodide of potassium,
alkali was evolved at the cathode (399) against the zinc, in
proportion to the evolution of iodine at the anode. Hence the
decomposition was perfectly polar, and decidedly dependent
upon a current of electricity passing from the zinc through the
acid to the platina in the vessel c, and back from the platina
through the solution to the zinc at the paper x.

617. That the decomposition at x was a true electrolytic
action, due to a current determined by the state of things in the
vessel and not dependent upon any mere direct chemical
action of the zinc and platina on the iodide, or even upon any
current which the solution of iodide might by its action on
those metals tend to form at x, was shown, in the first place,
by removing the vessel c and its acid from the plates, when all
decomposition at x ceased, and in the next by connecting the
metals, either in or out of the acid, together, when decom¬
position of the iodide at x occurred, but in a reverse order ; for
now alkali appeared against the end of the platina wire, and
the iodine passed to the zinc, the current being the contrary
of what it was in the former instance, and produced directly by
the difference of action of the solution in the paper on the two
metals. The iodine of course combined with the zinc.

618. When this experiment was made with pieces of zinc
amalgamated over the whole surface (598), the results were
obtained with equal facility and in the same direction, even
when only dilute surphuric acid was contained in the vessel c
(fig. 33). Whichsoever end of the zinc was immersed in the

Decomposition by a Pair of Plates 175

acid^ still the effects were the same: so that for a moment^
the mercury might be supposed to supply the metallic contact,
the inversion of the amalgamated piece destroys that objection.
The use of unamalgamated zinc (615) removes all possibility
of doubt.^

619. When in pursuance of other views (665)^ the vessel c
was made to contain a solution of caustic potash in place of
acid, still the same results occurred. Decomposition of the
iodide was effected freely, though there was no metallic contact
of dissimilar metals, and the current of electricity was in the
same direction as when acid was used at the place of excitement.

620. Even a solution of common salt in the glass c could
produce all these effects.

621. Having made a galvanometer with platina wires, and
introduced it into the course of the current between the platina
plate and the place of decomposition x, it was affected, giving
indications of currents in the same direction as those shown
to exist by the chemical action.

622. If we consider these results generally, they lead to very
important conclusions. In the first place, they prove, in the
most decisive manner, that metallic contact is not necessary for
the production of the voltaic current. In the next place, they
show a most extraordinary mutual relation of the chemical
affinities of the fluid which excites the current, and the fluid
which is decomposed by it.

623. For the purpose of simplifying the consideration, let us
take the experiment with amalgamated zinc. The metal so
prepared exhibits no effect until the current can pass: it at
the same time introduces no new action, but merely removes an
influence which is extraneous to those belonging either to the
production or the effect of the electric current under investiga¬
tion (736); an influence also which, when present, tends only
to confuse the results.

1 The following is a more striking mode of making the above elementary
experiment. Prepare a plate of zinc, ten or twelve inches long and two
inches wide, and clean it thoroughly: provide also two discs of clean platina,
about one inch and a half in diameter:—dip three or four folds of bibulous
paper into a strong solution of iodide of potassium, place them on the
clean zinc at one end of the plate, and put on them one of the platina discs:
finally dip similar folds of paper or a piece of linen cloth into a mixture of
equal parts nitric acid and water, and place it at the other end of the zinc
plate with the second platina disc upon it. In this state of things no
change at the solution of the iodide will be perceptible; but if the two discs
be connected by a platina (or any other) wire for a second or two, and then
that over the iodide be raised, it will be found that the whole of the surface
beneath is deeply stained with evolved iodine.—December 1838.

176 Faraday’s Researches

624. Let two plates, one of amalgamated zinc and the other
of platina, be placed parallel to each other (fig, 34), and intro¬
duce a drop of dilute sulphuric acid, y,
between them at one end: there will be
no sensible chemical action at that spot
unless the two plates are connected
somewhere else, as at P Z, by a body

capable of conducting electricity. If that body be a metal or
certain forms of carbon, then the current passes, and, as it
circulates through the fluid at y, decomposition ensues.

625. Then remove the acid from y, and introduce a drop of
the solution of iodide of potassium at x (fig, 35). Exactly the
same set of effects occur, except that when the metallic com-
munica' ion is made at P Z, the electric current is in the opposite
direction to what it was before, as is indicated by the arrows,
which show the courses of the currents (403).

•b

Fig. 34 -

-

-^

_^_LJ:\

Fig. 35-

?

y Z a;-

Fig. 36.

626. Now both the solutions used are conductors, but the
conduction in them is essentially connected with decomposition
(593) ^ certain constant order, and therefore the appearance

of the elements in certain places shows in what direction a
current has passed when the solutions are thus employed. More¬
over, we find that when they are used at opposite ends of the
plates, as in the last two experiments (624,625), metallic contact
being allowed at the other extremities, the currents are in
opposite directions. We have evidently, therefore, the power
of opposing the actions of the two fluids simultaneously to each
other at the opposite ends of the plates, using each one as a
conductor for the discharge of the current of electricity, which
the other tends to generate; in fact, substituting them for
metallic contact, and combining both experiments into one
(fig. 36). Under these circumstances, there is an opposition of
forces: the fluid, which brings into play the stronger set of
chemical affinities for the zinc (being the dilute acid), over¬
comes the force of the other, and determines the formation and
direction of the electric current; not merely making that current
pass through the weaker liquid, but actually reversing the
tendency which the elements of the latter have in relation to
the zinc and platina if not thus counteracted, and forcing them

Use of Metallic Contact 177

in the contrary direction to that they are inclined to follow^
that its own current may have free course. If the dominant
action at y be removed by making metallic contact there, then
the liquid at x resumes its power; or if the metals be not
brought into contact at y, but the affinities of the solution there
weakened, whilst those active at x are strengthened, then the
latter gains the ascendency, and the decompositions are produced
in a contrary order.

627. Before drawing a final conclusion from this mutual
dependence and state of the chemical affinities of two distant
portions of acting fluids (651), I will proceed to examine more
minutely the various circumstances under which the reaction of
the body suffering decomposition is rendered evident upon the
action of the body, also undergoing decomposition, which pro¬
duces the voltaic current.

628. The use of metallic contact in a single pair of plates, and
the cause of its great superiority above contact made by other
kinds of matter, become now very evident. When an amalga¬
mated zinc plate is dipped into dilute sulphuric acid, the force
of chemical affinity exerted between the metal and the fluid is
not sufficiently powerful to cause sensible action at the surfaces
of contact, and occasion the decomposition of water by the
oxidation of the metal, although it is sufficient to produce such
a condition of the electricity (or the power upon which chemical
affinity depends) as would produce a current if there were a
path open for it (651, 691); and that current would complete
the conditions necessary, under the circumstances, for the
decomposition of the water.

629. Now the presence of a piece of platina touching both
the zinc and the fluid to be decomposed, opens the path required
for the electricity. Its direct communication with the zinc is
effectual, far beyond any communication made between it
and that metal {i.e. between the platina and zinc), by means
of decomposable conducting bodies, or, in other words, elec¬
trolytes, as in the experiment already described (626); because,
when they are used, the chemical affinities between them and
the zinc produce a contrary and opposing action to that which
is influential in the dilute sulphuric acid; or if that action be
but small, still the affinity of their component parts for each
other has to be overcome, for they cannot conduct without
suffering decomposition; and this decomposition is found experi¬
mentally to react back upon the forces which in the acid tend
to produce the current (639, 645, etc.), and in numerous cases

178 Faraday’s Researches

entirely to neutralise them. Where direct contact of the zinc
and platina occurs^ these obstructing forces are not brought
into action, and therefore the production and the circulation of
the electric current and the concomitant action of decomposition
are then highly favoured.

630. It is evident, however, that one of these opposing actions
may be dismissed, and yet an electrolyte be used for the purpose
of completing the circuit between the zinc and platina immersed
separately into the dilute acid; for if, in fig. 33, the platina wire
be retained in metallic contact with the zinc plate a, at x, and
a division of the platina be made elsewhere, as at then the
solution of iodide placed there, being in contact with the platina
at both surfaces, exerts no chemical affinities for that metal; or
if it does, they are equal on both sides. Its power, therefore, of
forming a current in opposition to that dependent upon the
action of the acid in the vessel c, is removed, and only its
resistance to decomposition remains as the obstacle to be over¬
come by the affinities exerted in the dilute sulphuric acid.

631. This becomes the condition of a single pair of active
plates where metallic contact is allowed. In such cases, only one
set of opposing affinities are to be overcome by those which are
dominant in the vessel c ; whereas, when metallic contact is not
allowed, two sets of opposing affinities must be conquered
(629).

632. It has been considered a difficult, and by some an
impossible thing, to decompose bodies by the current from a
single pair of plates, even when it was so powerful as to heat
bars of metal red hot, as in the case of Hare’s calorimeter,
arranged as a single voltaic circuit, or of Wollaston’s powerful
single pair of metals. This difficulty has arisen altogether from
the antagonism of the chemical affinity engaged in producing
the current with the chemical affinity to be overcome, and
depends entirely upon their relative intensity; for when the sum
of forces in one has a certain degree of superiority over the
sum of forces in the other, the former gain the ascendency,
detenmine the current, and overcome the latter so as to make
the substance exerting them yield up its elements in perfect
accordance, both as to direction and quantity, with the course of
those which are exerting the most intense and dominant action.

633. Water has generally been the substance, the decomposi¬
tion of which has been sought for as a chemical test of the
passage of an electric current. But I now began to perceive a
reason for its failure, and for a fact which I had observed long

Electrolysation by a Pair of Plates 179

before (51, 52) with regard to the iodide of potassium, narnely,
that bodies would differ in facility of decomposition by a given
electric current^ according to the condition and intensity of their
ordinary chemical affinities. This reason appeared in their
reaction upon the affinities tending to cause the current; and it
appeared probable that many substances might be found which
could be decomposed b}^ the current of a single pair of zinc and
platina plates immersed in dilute sulphuric acid, although water
resisted its action. I soon found this to be the case, and as the
experiments offer new and beautiful proofs of the direct relation
and opposition of the chemical affinities concerned in producing
and in resisting the stream of electricity, I shall briefly describe
them.

634. The arrangement of the apparatus was as in hg. 37. The

vessel V contained dilute sulphuric acid; Z and P are the zinc
and platina plates; a, b, and c are platina wires; ^

the decompositions were effected at and ^ k

occasionally, indeed generally, a galvanometer ^ .

was introduced into the circuit at g: its place

only is here given, the circle at g having no refer-
ence to the size of the instrument. Various
arrangements were made at according to the v

kind of decomposition to be effected. If a drop ^
of liquid was to be acted upon, the two ends
were merely dipped into it; if a solution con- pig. 37.
tained in the pores of paper was to be decom¬
posed, one of the extremities was connected with a platina plate
supporting the paper, whilst the other extremity rested on the
paper, <?, fig. 44: or sometimes, as with sulphate of soda, a
plate of platina sustained two portions of paper, one of the ends
of the wires resting upon each piece, c, fig. 46. The darts
represent the direction of the electric current (403).

635. Solution of iodide of potassium, in moistened paper,
being placed at the interruption of the circuit at was readily
decomposed. Iodine was evolved at the anode^ and alkali at
the cathode, of the decomposing body.

636. Froiochloride of tin, when fused and placed at a;, was
also readily decomposed, yielding perchloride of tin at the anode
(514), and tin at the cathode.

637. Fused chloride of silver, placed at x, was also easily
decomposed; chlorine was evolved at the anode, and brilliant
metallic silver, either in films upon the surface of the liquid, or
in crystals beneath, evolved at the cathode.

i8o Faraday’s Researches

638. Water acidulated with sulphuric acid^ solution of muriatic
acidj solution of sulphate of soda^ fused nitre^ and the fused
chloride and iodide of lead were not decomposed by this single
pair of plates^ excited only by dilute sulphuric acid.

639. These experiments give abundant proofs that a single
pair of plates can electrolyse bodies and separate their elements.
They also show in a beautiful manner the direct relation and
opposition of the chemical affinities concerned at the two points
of action. In those cases where the sum of the opposing
affinities at x was sufficiently beneath the sum of the acting
affinities in decomposition took place; but in those cases
where they rose higher^ decomposition was effectually resisted
and the current ceased to pass (626).

640' It is^ however^ evident that the sum of acting affinities
in V may be increased by using other fluids than dilute sulphuric
acid^ in which latter case^ as I believe^, it is merely the affinity
of the zinc for the oxygen already combined with hydrogen in
the water that is exerted in producing the electric current (654):
and when the affinities are so increased^ the view I am supporting
leads to the conclusion that bodies which resisted in the pre¬
ceding experiments would then be decomposed^ because of the
increased difference between their affinities and the acting
affinities thus exalted. This expectation was fully confirmed
in the following manner.

641. A little nitric acid was added to the liquid in the vessel

so as to make a mixture which I shall call diluted nitro-

sulphuric acid. On repeating the experiments with this mixture,
all the substances before decomposed again gave way, and much
more readily. But, besides that, many which before resisted
electrolysation now yielded up their elements. Thus, solution
of sulphate of soda, acted upon in the interstices of litmus and
turmeric paper, yielded acid at the anode and alkali at the
cathode; solution of muriatic acid tinged indigo yielded
chlorine at the a^iode and hydrogen at the cathode ; solution of
nitrate of silver yielded silver at the cathode. Again, fused nitre
and the fused iodide and chloride of lead were decomposable by
the current of this single pair of plates, though they were not
by the former (638).

642. A solution of acetate of lead was apparently not decom¬
posed by this pair, nor did water acidulated by sulphuric acid
seem at first to give way (708).

643. The increase of intensity or power of the current produced
by a simple voltaic circle, with the increase of the force of the

Electrolysation by a Pair of Plates iSi

chemical action at the exciting place^ is here sufficiently evident.
But in order to place it in a clearer point of view^ and to show
that the decomposing effect was not at all dependent^ in the
latter cases^ upon the mere capability of evolving more elec¬
tricity^ experiments were made in which the quantity evolved
could be increased without variation in the intensity of the
exciting cause. Thus the experiments in which dilute sulphuric
acid was used (634) were repeated^ using large plates of zinc and
platina in the acid; but still those bodies which resisted decom¬
position before^ resisted it also under these new circumstances.
Then again^ where nitro-sulphuric acid was used (641 mere
wires of platina and zinc were immersed in the exciting acid;
yet^ notwithstanding this change^ those bodies were now decom¬
posed which resisted any current tending to be formed by the
dilute sulphuric acid. For instance^ muriatic acid could not be
decomposed by a single pair of plates when immersed in dilute
sulphuric acid; nor did making the solution of sulphuric acid
strong^ nor enlarging the size of the zinc and platina plates
immersed in it^ increase the power; but if to a weak sulphuric
acid a very little nitric acid was added^ then the electricity
evolved had power to decompose the muriatic acid^ evolving
chlorine at the anode and hydrogen at the cathode, even when
mere wires of metals were used. This mode of increasing the
intensity of the electric current^ as it excludes the effect depen¬
dent upon many pairs of plates^ or even the effect of making
any one acid stronger or weaker^ is at once referable to the
condition and force of the chemical affinities which are brought
into action^, and may^ both in principle and practice^ be con¬
sidered as perfectly distinct from any other mode.

644. The direct reference which is thus experimentally made
in the simple voltaic circle of the intensity of the electric current
to the uitensity of the chemical action going on at the place
where the existence and direction of the current is determined,
leads to the conclusion that by using selected bodies^ as fused
chlorides, salts, solutions of acids, etc., which may act upon the
metals employed with different degrees of chemical force; and
using also metals in association with platina, or with each other,
which shall differ in the degree of chemical action exerted
between them and the exciting fluid of electrolyte, we shall be
able to obtain a series of comparatively constant effects due ta
electric currents of different intensities, which will serve to-
assist in the construction of a scale competent to supply the

182 Faraday’s Researches

means of determining relative degrees of intensity with accuracy
in future researches.

645. I have already expressed the view which I take of the
decomposition in the experimental place^ as being the direct
consequence of the superior exertion at some other spot of the
same kind of power as that to be overcome^ and therefore as
the result of an antagonism of forces of the same nature (626,
639). Those at the place of decomposition have a re-action
upon^ and a power ovei% the exerting or determining set pro¬
portionate to what is needful to overcome their own power;
and hence a curious result of resistance offered by decompo¬
sitions to the original determining force, and consequently to
the current. This is well shown in the cases where such bodies
as chloride of lead, iodide of lead, and water would not decom¬
pose with the current produced by a single pair of zinc and
platina plates in sulphuric acid (638), although they would with
a current of higher intensity produced by stronger chemical
powers. In such cases no sensible portion of the current
passes (702); the action is stopped; and I am now of opinion
that in the case of the law of conduction which I described in
the second part of these Researches (149), the bodies which
are electrolytes in the fluid state cease to be such in the solid
form, because the attractions of the particles by which they are
retained in combination and in their relative position, are then
too powerful for the electric current. The particles retain
their places; and as decomposition is prevented, the transmis¬
sion of the electricity is prevented also; and although a battery
of many plates may be used, yet if it be of that perfect kind
which allows of no extraneous or indirect action (736), the
whole of the affinities concerned in the activity of that battery
are at the same time also suspended and counteracted.

646. But referring to the resistance of each single case of
decomposition, it would appear that as these difer in force
according to the affinities by which the elements in the substance
tend to retain their places, they also would supply cases con¬
stituting a series of degrees by which to measure the initial
intensities of simple voltaic or other currents of electricity, and
which, combined with the scale of intensities determined by
different degrees of acting force (644), would probably include
a sufficient set of differences to meet almost every important
case where a reference to intensity would be required.

647. According to the experiments I have already had occa¬
sion to make, I find that the following bodies are electrolytic

Electrolytic Intensity 183

in the order in which I have placed them^ those which are first
being decomposed by the current of lowest intensity. These
currents were always from a single pair of plates^ and may be
considered as elementary voltaic forces.

Iodide of potassium (solution).

Chloride of silver (fused).

Protochioride of tin (fused).

Chloride of lead (fused).

Iodide of lead (fused).

Muriatic acid (solution).

Water; acidulated with sulphuric acid.

648. It is essential that; in all endeavours to obtain the
relative electrolytic intensity necessar}^ for the decomposition of
different bodies^ attention should be paid to the nature of the
electrodes and the other bodies present which may favour
secondary actions (721). If in electro-decomposition one of the
elements separated has an affinity for the electrode; or for
bodies present in the surrounding fluid; then the affinity resist¬
ing decomposition is in part balanced by such power; and the
true place of the electrolyte in a table of the above kind is
not obtained: thuS; chlorine combines with a positive platina
electrode freely, but iodine scarcely at all, and therefore I
believe it is that the fused chlorides stand first in the preceding
table. Again, if in the decomposition of water not merely
sulphuric but also a little nitric acid be present, then the water
is more freely decomposed, for the hydrogen at the cathode is
not ultimately expelled, but finds oxygen in the nitric acid, wdth
which it can combine to produce a secondary result; the affini¬
ties opposing decomposition are in this way diminished, and
the elements of the water can then be separated by a current
of lower intensity.

649. Advantage may be taken of this principle to interpolate
more minute degrees into the scale of initial intensities already
referred to (644, 646) than is there spoken of; for by combining
the force of a current constant in its intensity, with the use of
electrodes consisting of matter, having more or less affinity for
the elements evolved from the decomposing electrolyte, various
intermediate degrees may be obtained.

650. Returning to the consideration of the source of electricity
(613, etc.), there is another proof of the most perfect'kind that
metallic contact has nothing to do with the 'production of
electricity in the voltaic circuit, and further, that electricity

184 Faraday’s Researches

is only another mode of the exertion of chemical forces. It is,
the production of the electric spark before any contact of metals
is made^ and by the exertion of pure and unmixed chemical
forces. The experimentwhich will be described further on
(691);, consists in obtaining the spark upon making contact
between a plate of zinc and a plate of copper plunged into
dilute sulphuric acid. In order to make the arrangement as
elementary as possible^ mercurial surfaces were dismissed^, and
the contact made by a copper wire connected with the copper
plate^ and then brought to touch a clean part of the zinc plate.
The electric spark appeared, and it must of necessity have
existed and passed before the zinc and the copper 20ere in contact.

651. In order to render more distinct the principles which I
have been endeavouring to establish, I will restate them in their
simplest form, according to my present belief. The electricity
of the voltaic pile (591, note) is not dependent either in its
origin or its continuance upon the contact of the metals with
each other (615,650). It is entirely due to chemical action (617),
and is proportionate in its intensity to the intensity of the
affinities concerned in its production (643); and in its quantity
to the quantity of matter which has been chemically active
during its evolution (604). This definite production is again
one of the strongest proofs that the electricity is of chemical
origin.

652. As volta-electro-generation is a case of mere chemical
action, so volta-electro-decomposition is simply a case of the
preponderance of one set of chemical affinities more powerful
in their nature, over another set which are less powerful: and
if the instance of two opposing sets of such forces (626) be
considered, and their mutual relation and dependence borne in
mind, there appears no necessity for using, in respect to such
cases, any other term than chemical affinity (though that of
electricity may be very convenient) or supposing any new agent
to be concerned in producing the results; for we may consider
that the powers at the two places of action are in direct com¬
munion and balanced against each other through the medium
of the metals (626), fig. 36, in a manner analogous to that in
w-hich mechanical forces are balanced against each other by the
intervention of the lever (767).

653. All the facts show us that that power commonly called
chemical affinity, can be communicated to a distance through
the metals and certain forms of_^carbon; that the electric cur-

Origin of the Power of the Pile 185

rent is only another forna of the forces of chemical affinity; that
its power is in proportion to the chemical affinities producing it,
that when it is deficient in force it may be helped by calling in
chemical aid, the want in the former being made up by an
equivalent of the latter; that, in other words, the forces termed
chemical affinity and electricity are one and the same.

654. When the circumstances connected with the production
of electricity in the ordinary voltaic circuit are examined and
compared, it appears that the source of that agent, always
meaning the electricity which circulates and completes the cur¬
rent in the voltaic apparatus, and gives that apparatus power
and character (682, 732), exists in the chemical action which
takes place directly between the metal and the body with which
it combines, and not at all in the subsequent action of the sub¬
stance so produced with the acid present.^ Thus, when zinc,,
platina, and dilute sulphuric acid are used, it is the union of
the zinc with the oxygen of the water which determines the
current; and though the acid is essential to the removal of the
oxide so formed, in order that another portion of zinc may act
on another portion of water, it does not, by combination with
that oxide, produce any sensible portion of the current of
electricity which circulates; for the quantity of electricity is
dependent upon the quantity of zinc oxidised, and in definite
proportion to it: its intensity is in proportion to the intensit}^
of the chemical affinity of the zinc for the oxygen under the
circumstances, and is scarcely, if at all, affected by the use of
either strong or weak acid (643).

655. Again, if zinc, platina, and muriatic acid are used, the
electricity appears to be dependent upon the affinit}^ of the zinc
for the chlorine, and to be circulated in exact proportion to the
number of particles of zinc and chlorine which unite, being in
fact an equivalent to them.

656. But in considering this oxidation, or other direct action
upon the metal itself, as the cause and source of the electric
current, it is of the utmost importance to observe that the
oxygen or other body must be in a peculiar condition, namely,
in the state of combination ; and not only so, but limited still
further to such a state of combination and in such proportions
as will constitute an electrolyte (558). A pair of zinc and platina
plates cannot be so arranged in oxygen gas as to produce a
current of electricity, or act as a voltaic circle, even though the

^ Wollaston, Philosophical Transactions, 1801, p. 427.

I 86 Faraday’s Researches

temperature may be raised so high as to cause oxidation of the
zinc far more rapidly than if the pair of plates were plunged into
dilute sulphuric acid; for the oxygen is not part of an electrolyte,
and cannot therefore conduct the forces onwards by decom¬
position, or even as metals do by itself. Or if its gaseous state
embarrass the minds of some, then liquid chlorine may be taken.
It does not excite a current of electricity through the two plates
by combining with the zinc, for its particles cannot transfer
the electricity active at the point of combination across to the
platina. It is not a conductor of itself, like the metals; nor
is it an electrolyte, so as to be capable of conduction during
decomposition, and hence there is simple chemical action at
the spot, and no electric current.^

657. It might at first be supposed that a conducting body,
not electrolytic, might answer as the third substance fctween
the zinc and the platina; and it is true that
we have some such capable of exerting
chemical action upon the metals. They
must, however, be chosen from the metals
themselves, for there are no bodies of this
kind except those substances and charcoal.
To decide the matter by experiment, I made
the following arrangement. Melted tin was
put into a glass tube bent into the form of
the letter V, fig. ,38 so as to fill the half of
each limb, and two pieces of thick platina
wire, p, w, inserted, so as to have their
ends immersed some depth in the tin: the whole was then
allowed to cool, and the ends p and w connected with a delicate
galvanometer. The part of the tube at x was now reheated,
whilst the portion y was retained cool. The galvanometer was
immediately influenced by the thermo-electric current produced.
The heat was steadily increased at x, until at last the tin and
platina combined there; an effect which is known to take place
with strong chemical action and high ignition; but not the
slightest additional effect occurred at the galvanometer. No
other deflection than that due to the thermo-electric current

^ I do not mean to affirm that no traces of electricity ever appear in such
cases. What I mean is, that no electricity is evolved in any way, due or
related to the causes which excite voltaic electricity, or proportionate to
them. That which does appear occasionally is the smallest possible
fraction of that which the acting matter could produce if arranged so as
to act voltaically, probably not the one-hundred-thousandth, or even the
millionth part, and is very probably altogether different in its source.

Water as an Electrolyte 187

was observable the whole time. Hence^ though a conductor^
and one capable of exerting chemical action on the tin^ was
used; yet; not being an electrolyte, not the slightest effect of an
electrical current could be observed (682).

658. From this it seems apparent that the peculiar character
and condition of an electrolyte is essential in one part of the
voltaic circuit; and its nature being considered; good reasons
appear why it and it alone should be effectual. An electrolyte
is always a compound body: it can conduct; but only vdiilst
decomposing. Its conduction depends upon its decomposition
and the transmission of its particles in directions parallel to the
current; and so intimate is this connection; that if their transi¬
tion be stopped; the current is stopped also; if their course be
changed; its course and direction changes with them; if they
proceed in one direction; it has no power to proceed in any other
than a direction invariably dependent on them. The particles
of an electrolytic body are all so mutually connected; are in
such relation with each other through their whole extent in the
direction of the current; that if the last is not disposed of; the
first is not at liberty to take up its place in the new combination
which the powerful affinity of the most active metal tends to
produce; and then the current itself is stopped; for the depen¬
dencies of the current and the decomposition are so mutual;
that whichsoever be originally determined; i.e. the motion of
the particles or the motion of the current; the other is invariable
in its concomitant production and its relation to it.

659. Consider; then; water as an electrolyte and also as an
oxidising body. The attraction of the zinc for the oxygen is
greater; under the circumstances; than that of the oxygen for
the hydrogen; but in combining with it; it tends to throw into
circulation a current of electricity in a certain direction. This
direction is consistent (as is found by innumerable experiments)
with the transfer of the hydrogen from the zinc towards the
platina; and the transfer in the opposite .direction of fresh
oxygen from the platina towards the zinc; so that the current
can pass in that one line; and; whilst it passeS; can consist with
and favour the renewal of the conditions upon the surface of
the zinC; which at first determined both the combination and
circulation. Hence the continuance of the action there; and
the continuation of the current. It therefore appears quite as
essential that there should be an electrolyte in the circuit; in
order that the action may be transferred forward; in a certain

' constant direction, as that there should be an oxidising or other

188 Faraday’s Researches

body capable of acting directly on the metal; and it also appears
to be essential that these two should merge into one^ or that the
principle directly active on the metal by chemical action should
be one of the ions of the electrolyte used. Whether the voltaic
arrangement be excited by solution of acidS;, or alkalies^ or
sulphurets/ or by fused substances {212), this principle has
always hitherto^ as far as I am aware^ been an anion (678); and
I anticipate^ from a consideration of the principles of electric
action^, that it must of necessity be one of that class of bodies.

660. If the action of the sulphuric acid used in the voltaic
circuit be considered^ it will be found incompetent to produce
any sensible portion of the electricity of the current by its com¬
bination with the oxide formed^, for this simple reason^ it is
deficient in a most essential condition: it forms no part of an
electrolyte^ nor is it in relation with any other body present in
the solution which will permit of the mutual transfer of the
particles and the consequent transfer of the electricity. It is
true, that as the plane at which the acid is dissolving the oxide
of zinc formed by the action of the water is in contact with the
metal zinc^ there seems no difficulty in considering how the
oxide there could communicate an electrical state^ proportionate
to its own chemical action on the acid^ to the metal^ which is a
conductor without decomposition. But on the side of the acid
there is no substance to complete the circuit: the water^ as
water;, cannot conduct it;, or at least only so small a proportion
that it is merely an incidental and almost inappreciable effect
(705); and it cannot conduct it as an electrolyte^ because an
electrolyte conducts in consequence of the mutual relation and
action of its particles; and neither of the elements of the water^
nor even the water itself^ as far as we can perceive^ are ions with
respect to the sulphuric acid (583).^

661. This view of the secondar}^ character of the sulphuric
acid as an agent in the production of the voltaic current^ is
further confirmed by the fact^ that the current generated and
transmitted is directly and exactly proportional to the quantity
of water decomposed and the quantity of zinc oxidised (603,
727)^ and is the same as that required to decompose the same
quantity of water. AS;, therefore^ the decomposition of the
water shows that the electricity has passed by its means^ there

^ It will be seen that I here agree with Sir Humphry Davy, who has
experimentally supported the opinion that acids and alkalies in combining
do not produce any current of electricity .—Philosophical Tmmactions,
1826, p. 398.

Use of the Exciting Acid 189

remains no other electricity to be accounted for or to be referred
to any action other than that of the zinc and the water on
each other.

662. The general case (for it includes the former one (659) )
of acids and bases may theoretically be stated in the following
manner. Let fig. 39^, be supposed to be a dry oxacid; and
h a dry base^ in contact at c, and in electric
communication at their extremities by plates
of platina f p, and a platina wire w. If this
acid and base were fluid; and combination
took place at with an affinity ever so
vigorous; and capable of originating an electric
current; the current could not circulate in any
important degree; because; according to the experimental results,
neither a nor b could conduct without being decomposed; for they
are either electrolytes or else insulators, under all circumstances;
except to very feeble and unimportant currents (705, 721).
Now the affinities at c are not such as tend to cause the elements
either of a or b to separate, but only such as would make the
two bodies combine together as a whole; the point of action is,
therefore, insulated, the action itself local (656, 682), and no
current can be formed.

6630 If the acid and base be dissolved in water, then it is
possible that a small portion of the electricity due to chemical
action may be conducted by the water without decomposition
(701; 719); but the quantity will be so small as to be utterly
disproportionate to that due to the equivalents of chemical
force; will be merely incidental; and, as it does not involve
the essential principles of the voltaic pile, it forms no part of the
phenomena at present under investigation.^

664. If for the oxacid a hydracid be substituted (662)—as
one analogous to the muriatic, for instance—then the state of
things changes altogether, and a current due to the chemical
action of the acid on the base is possible. But now both the
bodies act as electrolytes, for it is only one principle of each
which combine mutually—as, for instance, the chlorine with the
metal—and the h3^drogen of the acid and the oxygen of the base
are ready to traverse with the chlorine of the acid and the metal

^ It will I trust be fully understood that in these investigations I am
31 ot professing to take an account of every small, incidental, or barely
possible effect, dependent upon slight disturbances of the electric fluid
during chemical action, but am seeking to distinguish and identify those
actions on which the power of the voltaic battery essentially depends.

190 Faraday’s Researches

of the base in conformity with the current and according to
the general principles already so fully laid down.

665. This view of the oxidation of the metal;, or other direct
chemical action upon it^ being the sole cause of the production
of the electric current in the ordinary voltaic pile^ is supported
by the effects which take place when alkaline or sulphuretted
solutions (666^ 678) are used for the electrolytic conductor
instead of dilute sulphuric acid. It was in elucidation of this
point that the experiments without metallic contact, and with
solution of alkali as the exciting fluid, already referred to (619),
were made.

666. Advantage was then taken of the more favourable con¬
dition offered, when metallic contact is allowed (630), and the
experiments upon the decomposition of bodies by a single pair
of plates (634) were repeated, solution of caustic potassa being
employed in the vessel v, fig. 37, in place of dilute sulphuric
acid. All the effects occurred as before: the galvanometer
was deflected; the decompositions of the solutions of iodide of
potassium, nitrate of silver, muriatic acid, and sulphate of soda
ensued at x; and the places where the evolved principles ap¬
peared, as well as the deflection of the galvanometer, indicated
a cuiTent in the same direction as when acid was in the vessel v ;
i.e. from the zinc through the solution to the platina, and back
by the galvanometer and substance suffering decomposition to
the zinc.

667. The similarity in the action of either dilute sulphuric
acid or potassa goes indeed far beyond this, even to the proof
of identity in quantity as well as in direction of the electricity
produced. If a plate of amalgamated zinc be put into a solu¬
tion of potassa, it is not sensibly acted upon; but if touched
in the solution by a plate of platina, hydrogen is evolved on the
surface of the latter metal, and the zinc is oxidised exactly as
when immersed in dilute sulphuric acid (598). I accordingly
repeated the experiment before described with weighed plates
of zinc (599, etc.), using however solution of potassa instead of
dilute sulphuric acid. Although the time required was much
longer than when acid was used, amounting to three hours for
the oxidisement of 7.55 grains of zinc, still I found that the
hydrogen evolved at the platina plate was the equivalent of the
metal oxidised at the surface of the zinc. Hence the whole of
the reasoning which was applicable in the former instance
applies also here, the current being in the same direction, and

Use of the Exciting Acid 191

its decomposing effect in the same degree; as if acid instead of
alkali had been used (603).

668. The proof; therefore; appears to me complete; that the
combination of the acid with the oxide; in the former experi¬
ment; had nothing to do with the production of the electric
current; for the same current is here produced when the action
of the acid is absent; and the reverse action of an alkali is
present. I think it cannot be supposed for a moment that the
alkali acted chemically as an acid to the oxide formed; on the^
contrary; our general chemical knowledge leads to the conclu¬
sion that the ordinary metallic oxides act rather as acids to
the alkalies; yet that kind of action would tend to give a reverse
current in the present case; if any were due to the union of
the oxide of the exciting metal with the body which combines
with it. But instead of any variation of this sort; the direction
of the electricity was constant; and its quantity also directly
proportional to the water decomposed; or the zinc oxidised.
There are reasons for believing that acids and alkalieS; when
in contact with metals upon which they cannot act directly; still
have a power of influencing their attractions for oxygen (676);
but all the effects in these experiments prove; I think; that it
is the oxidation of the metal necessarily dependent upon; and
associated as it is with; the electrolysation of the water (656;
658) that produces the current; and that the acid or alkali
merely act as solvents; and by removing the oxidised zinC;
allow other portions to decompose fresh water; and so continue
the evolution or determination of the current.

669. The experiments were then varied by using solutibn of
ammonia instead of solution of potassa; and as it; when pure;
is like water; a bad conductor (290); it was occasionally improved
in that power by adding sulphate of ammonia to it. But in
all the cases the results were the same as before; decomposi¬
tions of the same kind were effected; and the electric current
producing these was in the same direction as in the experiments
just described.

670. In order to put the equal and similar action of acid and
alkali to stronger proof, arrangements were made as in fig. 40;
the glass vessel A contained dilute sulphuric acid; the corre¬
sponding glass vessel B solution of potassa; P P was a plate of
platina dipping into both solutions; and Z Z two plates of
amalgamated zinc connected with a delicate galvanometer.
When these were plunged at the same time into the two vessels;,
there was generally a first feeble effect; and that in favour of

192 Faraday’s Researches

the alkalij i.e. the electric current tended to pass through the
vessels in the direction of the arrow^ being the reverse direction
of that which the acid in A would have produced alone: but
the effect instantly ceased, and the action of the plates in the
vessels was so equal, that, being contrary because of the con¬
trary position of the plates, no permanent current resulted.

671. Occasionally a zinc plate was substituted for the plate
P P, and platina plates for the plates Z Z; but this caused no
difference in the results: nor did a further change of the middle
plate to copper produce any alteration.

672. As the opposition of electro-motive pairs of plates pro¬
duces results other than those due to the mere difference of
their independent actions (747, 781), I devised another form
of apparatus, in which the action of acid and alkali might be

Fig. 40. Fig. 41. Fig. 42.

more directly compared. A cylindrical glass cup, about two
inches deep within, an inch in internal diameter^ and at least a
quarter of an inch in thickness, was cut down the middle into
halves, fig. 41. A broad brass ring, larger in diameter than
the cup, was supplied with a screw at one side; so that when
the two halves of the cup were within the ring, and the screw
was made to press tightly against the glass, the cup held any
fluid put into it. Bibulous paper of different degrees of per¬
meability was then cut into pieces of such a size as to be easily
introduced between the loosened halves of the cup, and served
when the latter were tightened again to form a porous division
•down the middle of the cup, sufficient to keep any two fluids
on opposite sides of the paper from mingling, except very
slowly, and yet allowing them to act freely as one electrolyte.
The two spaces thus produced I will call the cells A and B,
fig. 42. This instrument I have found of most^ general appli¬
cation in the investigation of the relation of fluids and metals
amongst themselves and to each other. By combining its use

Exciting Action of Acid and Alkali 193

with that of the galvanometer^ it is easy to ascertain the relation
of one metal with two fluids^ or of two metals with one fluids
or of two metals and two fluids upon each other.

673. Dilute sulphuric acid^ sp. gr. 1.25^ was put into the cell
A, and a strong solution of caustic potassa into the cell B;
they mingled slowly through the paper, and at last a thick crust
of sulphate of potassa formed on the side of the paper next to
the alkali. A plate of clean platina was put into each cell and
connected with a delicate galvanometer, but no electric current
could be observed. Hence the contact of acid with one platina
plate, and alkali with the other, was unable to produce a current;
nor was the combination of the acid with the alkali more
effectual (660).

674. When one of the platina plates was removed and a zinc
plate substituted, either amalgamated or not, a strong electric
current was produced. But, whether the zinc were in the acid
whilst the platina was in the alkali, or whether the reverse
order were chosen, the electric current was always from the
zinc through the electrolyte to the platina, and back through
the galvanometer to the zinc, the current seeming to be strongest
when the zinc was in the alkali and the platina in the acid.

675. In these experiments, therefore, the acid seems to have
no power over the alkali, but to be rather inferior to it in force.
Hence there is no reason to suppose that the combination of the
oxide formed with the acid around it has any direct influence
in producing the electricity evolved, the whole of which appears
to be due to the oxidation of the metal (654).

676. The alkali, in fact, is superior to the acid in bringing a
metal into what is called the positive state; for if plates of the
same metal, as zinc, tin, lead, or copper, be used both in the
acid or alkali, the electric current is from the alkali across the
cejji to the acid, and back through the galvanometer to the
alkali, as Sir Humphry Davy formerly stated.^ This current is
so powerful, that if amalgamated zinc, or tin, or lead be used,
the metal in the acid evolves hydrogen the moment it is placed
in communication with that in the alkali, not from any direct
action of the acid upor h, for if the contact be broken the action
ceases, but because it is powerfully negative with regard to the
metal in the alkali.

677. The superiority of alkali is further proved by this, that
if zinc and tin be used, or tin and lead, whichsoever metal is

^ Elements of Chemical Philosophy, p. 149: or Philosophical Transactions,
1826, p. 403.

N

194 Faraday’s Researches

put into the alkali becomes positive, that in the acid being
negative. Whichsoever is in the alkali is oxidised, whilst that
in the acid remains in the metallic state, as far as the electric
current is concerned.

678. When sulphuretted solutions are used (665) in illus¬
tration of the assertion that it is the chemical action of the
metal and one of the ions of the associated electrolyte that pro¬
duces all the electricity of the voltaic circuit, the proofs are
still the same. Thus, as Sir Humphry Davy^ has shown, if
iron and copper be plunged into dilute acid, the current is from
the iron through the liquid to the copper; in solution of potassa
it is in the same direction, but in solution of sulphuret of potassa
it is reversed. In the two first cases it is oxygen which com¬
bines with the iron, in the latter sulphur which combines with
the copper, that produces the electric current; but both of these
are ions^ existing as such in the electrolyte, which is at the
same moment suffering decomposition; and, what is more, both
of these are anions, for they leave the electrolytes at their
anodes, and act just as chlorine, iodine, or any other anion
would act which might have been previously chosen as that
which should be used to throw the voltaic circle into activity.

679. The following experiments complete the series of proofs
of the origin of the electricity in the voltaic pile. A fluid
amalgam of potassium, containing not more than a hundredth
of that metal, was put into pure water, and connected through
the galvanometer with a plate of platina in the same water.
There was immediately an electric current from the amalgam
through the electrolyte to the platina. This must have been
due to the oxidation only of the metal, for there was neither
acid nor alkali to combine with, or in any way act on, the body
produced.

680. Again, a plate of clean lead and a plate of platina were
put into pure water. There was immediately a powerful current
produced from the lead through the fluid to the platina: it
was even intense enough to decompose solution of the iodide
of potassium when introduced into the circuit in the form of
apparatus already described (615), fig. 33. Here no action of
acid or alkali on the oxide formed from the lead could supply
the electricity: it was due solely to the oxidation of tile metal.

681. There is no point in electrical science which seems to

^ Elements of Chemical Philosophy, p. 148.

Local and Current Chemical Force 195

me of more importance than the state of the metals and the
electrolytic conductor in a simple voltaic circuit before and at
the moment when metallic contact is first completed. If clearly
understood; T feel no doubt it would supply us with a direct
key to the laws under which the great variety of voltaic excite¬
ments, direct and incidental, occur, and open out new fields of
research for our investigation.

682. We seem to have the power of deciding to a certain
extent in numerous cases of chemical affinity (as of zinc with the
oxygen of water, etc., etc.) which of two modes of action of the
attractive power shall be exerted (732). In the one mode we can
transfer the power onwards, and make it produce elsewhere its
equivalent of action (602, 652); in the other, it is not trans-
fen*ed, but exerted wholly at the spot. The first is the case
of volta-electric excitation, the other ordinary chemical affinity:
but both are chemical actions and due to one force or principle.

683. The general circumstances of the former mode occur
in all instances of voltaic currents, but may be considered as in
their perfect condition, and then free from those of the second
mode, in some only of the cases; as in those of plates of zinc
and platina in solution of potassa, or of amalgamated zinc and
platina in dilute sulphuric acid.

684. Assuming it sufficiently proved, by the preceding ex¬
periments and considerations, that the electro-motive action
depends, when zinc, platina, and dilute sulphuric acid are used,
upon the mutual affinity of the metal zinc and the oxygen of
the water (656, 659), it would appear that the metal, when
alone, has not power enough, under the circumstances, to take
the oxygen and expel the hydrogen from the water; for, in
fact, no such action takes place. But it would also appear that
it has power so far to act, by its attraction for the oxygen of the
particles in contact with it, as to place the similar forces already
active between these and the other particles of oxyge.i and the
particles of hydrogen in the water, in a peculiar state of tension
or polarity, and probably also at the same time to throw those
of its own particles which are in contact with the water into a
similar but opposed state. Whilst this state is retained, no
further change occurs; but when it is relieved, by completion
of the circuit, in which case the forces determined in opposite
directions, with respect to the zinc and the electrolyte, are
found exactly competent to neutralise each other, then a series
of decompositions and recompositions takes place amongst the
particles of oxygen and hydrogen constituting the water_,.

196 Faraday’s Researches

between the place of contact with the platina and the place
where the zinc is active; these intervening particles being
evidently in close dependence upon and relation to each other.
The zinc forms a direct compound with those particles of oxygen
which were^ previously, in divided relation to both it and the
hydrogen: the oxide is removed by the acid, and a fresh surface
of zinc is presented to the water, to renew and repeat the «>
action.

685. Practically, the state of tension is. best relieved by
dipping a metal which has less attraction for oxygen than the
zinc, into the dilute acid, and making it also touch the zinc.
The force of chemical affinity, which has been influenced or
polarised in the particles of the water by the dominant attraction
of the zinc for the oxygen, is then transferred, in a most extra¬
ordinary manner, through the two metals, so as to re-enter upon
the circuit in the electrolytic conductor, which, unlike the metals
in that respect, cannot convey or transfer it without suffering
decomposition; or rather, probably, it is exactly balanced and
neutralised by the force which at the same moment completes
the combination of the zinc with the oxygen of the water. The
forces, in fact, of the two particles which are acting towards
each other, and which are therefore in opposite directions, are
the origin of the two opposite forces, or directions of force, in
the current. They are of necessity equivalent to each other.
Being transferred forward in contrary directions, they produce
what is called the voltaic current: and it seems to me im¬
possible to resist the idea that it must be preceded by a state of
tension in the fluid, and between the fluid and the zinc; first
consequence of the affinity of the zinc for the oxygen of the
water.

686. I have sought carefully for indications of a state of
tension in the electrolytic conductor; and conceiving that it
might produce something like structure, either before or during
its discharge, I endeavoured to make this evident by polarised
light. A glass cell, seven inches long, one inch and a half
wide, and six inches deep, had two sets of platina electrodes
adapted to it, one set for the ends, and the other for the sides.
Those for the sides were seven inches long by three inches
high, and when in the cell were separated by a little frame of
wood covered with calico; so that when made active by con¬
nection with a battery upon any solution in the cell, the bubbles
of gas rising from them did not obscure the central parts of
the liquid.

Polarised Light Across the Electrolyte 197

687. A saturated solution of sulphate of soda was put into the
cell, and the electrodes connected with a battery of 150 pairs
of 4-inch plates: the current of electricity was conducted across
the cell so freely, that the discharge was as good as if a wire
had been used. A ray of polarised light was then transmitted
through this solution, directly across the course of the electric
current, and e:Kamined by an analysing plate; but though it
penetrated seven inches of solution thus subject to the action
of the electricity, and though contact was sometimes made,
sometimes broken, and occasionally reversed during the observa¬
tions, not the slightest trace of action on the ray could be
perceived.

688. The large electrodes were then removed, and others
introduced which fitted the ends of the cell. In each a slit was
cut, so as to allow the light to pass. The course of the polarised
ray was now parallel to the current, or in the direction of its
axis (253); but still no effect, under any circumstances of
contact or disunion, could be perceived upon it.

689. A strong solution of nitrate of lead was employed
instead of the sulphate of soda, but no effects could be detected.

690. Thinking it possible that the discharge of the electric
forces by the successive decompositions and recompositions of
the particles of the electrolyte might neutralise and therefore
destroy any effect which the first state of tension could by
possibility produce, I took a substance which, being an excellent
electrolyte when fluid, was a perfect insulator when solid, namely,
borate of lead, in the form of a glass plate, and connecting the
sides and the edges of this mass with the metallic plates, some¬
times in contact with the poles of a voltaic battery, and some¬
times even with the electric machine, for the advantage of the
much higher intensity then obtained, I passed a polarised ray
across it in various directions, as before, but could not obtain
the slightest appearance of action upon the light. Hence I
conclude, that notwithstanding the new and extraordinary state
which must be assumed by an electrolyte, either during decom¬
position (when a most enormous quantity of electricity must be
traversing it), or in the state of tension which is assumed as
preceding decomposition, and which might be supposed to be
retained in the solid form of the electrolyte, still it has no power
of affecting a polarised ray of light; for no kind of structure or
tension can in this way be rendered evident.

691. There is, however, one beautiful experimental proof of
a state of tension acquired by the metals and the electrolyte

198 Faraday’s Researches

before the electric current is produced^ and before contact of
the different metals is made (650); in fact^ at that moment
when chemical forces only are efficient as a cause of action. I
took a voltaic apparatus^ consisting of a single pair of large
plates^ namely^ a cylinder of amalgamated zinc^ and a double
cylinder of copper. These were put into a jar containing dilute
sulphuric acid/ and could at pleasure be placed in metallic
communication by a copper wire adjusted so as to dip at the
extremities into two cups of mercury connected with the two
plates.

692. Being thus arranged^ there was no chemical action
whilst the plates were not connected. On making the con¬
nection^ a spark was obtained/ and the solution was immediately
decomposed. On breaking it^ the usual spark was obtained^
and the decomposition ceased. In this case it is evident that
the first spark must have occurred before metallic contact was
made^ for it passed through an interval of air; and also that it
must have tended to pass before the electrolytic action began;
for the latter could not take place until the current passed; and
the current could not pass before the spark appeared. Hence
I think there is sufficient proof; that as it is the zinc and water
which by their mutual action produce the electricity of this
apparatus; so these; by their first contact with each other; were
placed in a state of powerful tension (687); which; though it
could not produce the actual decomposition of the water; was
able to make a spark of electricity pass between the zinc and a
fit discharger as soon as the interval was rendered sufficiently
small. The experiment demonstrates the direct production of
the electric spark from pure chemical forces.

693. There are a few circumstances connected with the pro¬
duction of this spark by a single pair of plateS; which should
be known; to ensure success to the experiment. When the
amalgamated surfaces of contact are quite clean and dry; the
spark; on making contact; is quite as brilliant as on breaking it;
if not even more so. When a film of oxide or dirt was present
at either mercurial surface; then the first spark was often feebk;

1 When nitro-sulphuric acid is used, the spark is more powerful, but local
chemical action can then commence, and proceed without requiring
metallic contact.

2 It has been universally supposed that no spark is produced on making
the contact between a single pair of plates. I was led to expect one from
the considerations already advanced in this paper. The wire of com¬
munication should be short; for with a long wire, circumstances strongly
affecting the spark are introduced.

Local Chemical Action

199

and often failed^ the breaking spark, however, continuing very
constant and bright. When a little water was put over the
mercury, the spark was greatly diminished in brilliancy, but
very regular both on making and breaking contact. When the
contact was made between clean platina, the spark was also
very small, but regular both ways. The true electric spark is,
in fact, very small, and when surfaces of mercury are used, it
is the combustion of the metal which produces the greater part
of the light. The circumstances connected with the burning
of the mercury are most favourable on breaking contact; for
the act of separation exposes clean surfaces of metal, whereas,
on making contact, a thin film of oxide, or soiling matter, often
interferes. Hence the origin of the general opinion that it is
only when the contact is broken that the spark passes.

694. With reference to the other set of cases, namely, those
of local action (682) in which chemical affinity being exerted
causes no transference of the power to a distance where no
electric current is produced, it is evident that forces of the
most intense kind must be active, and in some way balanced in
tlieir activity, during such combinations; these forces being
directed so immediately and exclusively towards each other,
that no signs of the powerful electric current they can produce
become apparent, although the same final state of things is
obtained as if that current had passed. It was Berzelius, I
believe, who considered the heat and light evolved in cases of
combustion as the consequences of this mode of exertion of the
electric powers of the combining particles. But it will require
a much more exact and extensive knowledge of the nature of
electricity, and the manner in which it is associated with the
atoms of matter, before we can understand accurately the action
of this power in thus causing their union, or comprehend the
nature of the great difference which it presents in the two
modes of action just distinguished. We may imagine, but such
imaginations must for the time be classed with the great mass
of doubtful knowledge (611) which we ought rather to strive to
diminish than to increase; for the very extensive contradictions
of this knowledge by itself shows that but a small portion of it
can ultimately prove true.

695. Of the two modes of action in which chemical affinity is
exerted, it is important to remark, that that which produces
the electric current is as definite as that which causes ordinary
chemical combination; so that in examining the 'production or

200

Faraday’s Researches

evolution of electricity in cases of combination or decomposition,
it will be necessary, not merely to observe certain effects depen¬
dent upon a current of electricity, but also their quantity: and
though it may often happen that the forces concerned in any
particular case of chemical action may be partly exerted in
one mode and partly in the other, it is only those which are
efficient in producing the current that have any relation to
voltaic action. Thus, in the combination of oxygen and hydrogen
to produce water, electric powers to a most enormous amount
are for the time active (596, 608); but any mode of examining
the flame which they form during energetic combination, which
has as yet been devised, has given but the feeblest traces.
These therefore may not, cannot, be taken as evidences of the
nature of the action; but are merely incidental results, incom¬
parably small in relation to the forces concerned, and supplying
no information of the way in which the particles are active on
each other, or in which their forces are finally arranged.

696. That such cases of chemical action produce no current
of electricity, is perfectly consistent with what we know of the
voltaic apparatus, in which it is essential that one of the com¬
bining elements shall form part of, or be in direct relation with,
an electrolytic conductor (656, 658). That such cases produce
no free electricity of tension, and that when they are converted
into cases of voltaic action they produce a current in which the
opposite forces are so equal as to neutralise each other, prove the
equality of the forces in the opposed acting particles of matter,
and therefore the equality of electric power in those quantities
of matter which are called electro-chemical equivalents ( 559 ).
Hence another proof of the definite nature of electro-chemical
action (518, etc.), and that chemical affinity and electricity are
forms of the same power (652, etc).

697. The direct reference of the effects produced by the
voltaic pile at the place of experimental decomposition to the
chemical affinities active at the place of excitation (626, 652),
gives a very simple and natural view of the cause why the bodies
(or ions) evolved pass in certain directions; for it is only when
they pass in those directions that their forces can consist with
and compensate (in direction at least) the superior forces which
are dominant at the place where the action of the whole is
determined. If, for instance, in a voltaic circuit, the activity of
which is determined by the attraction of zinc for the oxygen of
water, the zinc move from right to left, then any other cation
included in the circuit, being part of an electrolyte, or forming

Mutual Relations of Ions

201

part of it at the moment^ will also move from right to left: and
as the oxygen of the water^ by its natural affinity for the zinc,
moves from left to right, so any other body of the same class
with it {i.e. any other anion), under its government for the time,
will move from left to right.

698. This I may illustrate by reference to fig. 43, the double
circle of which may represent a complete voltaic circuit, the
direction of its forces being determined by supposing for a

moment the zinc b and the platina c as representing plates of
those metals acting upon water, d, e, and other substances, but
having their energy exalted so as to effect several decomposi¬
tions by the use of a battery at a (725). This supposition may
be allowed, because the action in the battery will only consist
of repetitions of what would take place between b and c, if
they really constituted but a single pair. The zinc b, and the
oxygen d by their mutual affinity, tend to unite; but as the
oxygen is already in association with the hydrogen e, and has
its inherent chemical or electric powers neutralised for the time
by those of the latter, the hydrogen e must leave the oxygen d,

202

Faraday’s Researches

and advance in the direction of the arrow head^ or else the
zinc b cannot move in the same direction to unite to the oxygen
dj nor the oxygen d move in the contrary direction to unite to
the zinc the relation of the similar forces of h and e, in con¬
trary directions^ to the opposite forces of d being the preventive.
As the hydrogen e advances^ it^ on coming against the platina

c, f, which forms a part of the circuity communicates its electric
or chemical forces through it to the next electrolyte in the circuity
fused chloride of lead; g, where the chlorine must move in
conformity with the direction of the oxygen at d, for it has to
compensate the forces disturbed in its part of the circuit by
the superior influence of those between the oxygen and zinc at

d, h, aided as they are by those of the battery a; and for a
similar reason the lead must move in the direction pointed out
by the arrow head, that it may be in right relation to the first
moving body of its own class, namely, the zinc h. If copper
intervene in the circuit from i to k, it acts as the platina did
before; and if another electrolyte, as the iodide of tin, occur
at Z, m, then the iodine Z, being an anion, must move in con¬
formity with the exciting anion, namely, the oxygen d, and the
cation tin m move in correspondence with the other cations h, e,
and h, that the chemical forces may be in equilibrium as to
their direction and quantity throughout the circuit. Should it
so happen that the anions in their circulation can combine with
the metals at the anodes of the respective electrolytes, as would
be the case at the platina / and the copper h, then those bodies
becoming parts of electrolytes, under the influence of the
current, immediately travel; but considering their relation to
the zinc b, it is evidently impossible that they can travel in
any other direction than what will accord with its course, and
therefore can never tend to pass otherwise than from the anode
and to the cathode.

699. In such a circle as that delineated, therefore, all the
known anions may be grouped within, and all the cations with¬
out. If any number of them enter as ions into the constitution
of electrolytes, and, forming one circuit, are simultaneously sub¬
ject to one common current, the anions must move in accord¬
ance with each other in one direction, and the cations in the
other. Nay, more than that, equivalent portions of these
bodies must so advance in opposite directions: for the advance
of every 32.5 parts of the zinc b must be accompanied by a
motion in the opposite direction of 8 parts of oxygen at d, of
36 parts of chlorine at g, of 126 parts of iodine at Z; and in the

Electrolytic Intensity 203

same direction by electro-chemical equivalents of hydrogen,
lead, copper, and tin, at k, and m.

700. If the present paper be accepted as a correct expression
of facts, it will still only prove a confirmation of certain general
views put forth by Sir Humphry Davy in his Bakerian Lecture
for 1806,^ and revised and re-stated by him in another Bakerian
Lecture, on electrical and chemical changes, for the year 1826.^
His general statement is, that chemical and electrical attractions
were produced by the same cause^ acting in one case on particles,
in the other on masses, of matter ; and that the same property,
under different modifications, was the cause of all the phenomena
exhibited by different voltaic combinationsT ^ This statement I
believe to be true; but in admitting and supporting it, I must
guard myself from being supposed to assent to all that is asso¬
ciated with it in the two papers referred to, or as admitting the
experiments which are there quoted as decided proofs of the
truth of the principle. Had I thought them so, there would
have been no occasion for this investigation. It may be sup¬
posed by some that I ought to go through these papers, distin¬
guishing what I admit from what I reject, and giving good
experimental or philosophical reasons for the judgment in both
cases. But then I should be equally bound to review, for the
same purpose, all that has been written both for and against
the necessity of metallic contact,—for and against the origin
of voltaic electricity in chemical action,—a duty which I may
not undertake in the present paper.^

^ ii. On the Intensity necessary for Electrolysation

701. It became requisite, for the comprehension of many of
the conditions attending voltaic action, to determine positively,
if possible, whether ^ectrolytes could resist the action of an
electric current when beneath a certain intensity? whether

1 Philosophical Transactions, 1807. ^ Ibid. 1S26, p. 383.

Ibid. 1826, p. 389.

I at one time intended to introduce here, in the form of a note, a table
of reference to the papers of the different philosophers who have referred
the origin of the electricity in the voltaic pile to contact, or to chemical
action, or to both; but on the publication of the first volume of M.
Becquerel’s highly important and valuable Traite de VElectriciU et du
Magnetism, I thought it far better to refer to that work for these references,
and the views held by the authors quoted. See pages 86, 91, 104, no, 112,
ri7, 118, 120, 151, 152, 224, 227, 228, 232,'233, 252, 255, 257, 258, 290,
etc .—July 3, 1834.

2 04 Faraday’s Researches

the intensity at which the current ceased to act would be the
same for all bodies? and also whether the electrolytes thus
resisting decomposition would conduct the electric current as
a metal does, after they ceased to conduct as electrolytes, or
would act as perfect insulators ?

702. It was evident from the experiments described (639,
641) that different bodies were decomposed with very different
facilities, and apparently that they required for their decom¬
position currents of different intensities, resisting some, but
giving way to others. But it was needful, by very careful and
express experiments, to determine whether a current could
really pass through, and yet not decompose an electrolyte (645).

703. An arrangement (fig. 44) was made, in which two glass
vessels contained the same dilute sulphuric acid, sp. gr, 1.25.

The plate z was amalgamated zinc, in con-
. K\ nection, by a platina wire with the platina
A plate e\ b was a platina wire connecting the

'''\ two platina plates P P'; c was a platina

^ wire connected with the platina plate P".

i .j On the plate e was placed a piece of paper

, r ~ ^ moistened in solution of iodide of potas-

sium: the wire c was so curved that its
"" I '' ' end could be made to rest at pleasure on

this paper, and show, by the evolution of
A y y iodine there, whether a current was passing;

or, being placed in the dotted position, it
p. formed a direct communication with the

platina plate e, and the electricity could
pass without causing decomposition. The object was to produce
a current by the action of the acid on the amalgamated zinc
in the first vessel A; to pass it through the acid in the second
vessel B by platina electrodes, that its power of decomposing
water might, if existing, be observed; and^to verify the existence
of the current at pleasure, by decomposition at e, without involv¬
ing the continual obstruction to the current which would arise
from making the decomposition there constant. The experiment,
being arranged, was examined and the existence of a current
ascertained by the decomposition at e ; the whole was then left
with an end of the wire c resting on the plate e, so as to form a
constant metallic communication there.

704. After several hours, the end of the wire c was replaced
on the test paper at e: decomposition occurred, and the proof
of a passing current was therefore complete. The current was

Electrolytic Intensity 205

very feeble compared to what it had been at the beginning of
the experiment; because of a peculiar state acquired by the
metal surfaces in the second vessel, which caused them to oppose
the passing current by a force which they possess under these
circumstances (776). Still it*was proved, by the decomposition,
that this state of the plates in the second vessel was not able
entirely to stop the current determined in the first, and that
was all that was needful to be ascertained in the present
inquiry.

705. This apparatus was examined from time to time, and
an electric current always found circulating through it, until
twelve days had elapsed, during which the water in the second
vessel had been constantly subject to its action. Notwith¬
standing this lengthened period, not the slightest appearance
of a bubble upon either of the plates in that vessel occurred.
From the results of the experiment, I conclude that a current
had. passed, but of so low an intensity as to fall beneath that
degree at which the elements of water, unaided by any second¬
ary force resulting from the capability of combination with the
matter of the electrodes, or of the liquid surrounding them,
separated from each other.

706. It may be supposed, that the oxygen and hydrogen had
been evolved in such small quantities as to have entirely dis¬
solved in the water, and finally to have escaped at the surface,
or to have reunited into water. That the hydrogen can be so
dissolved was shown in the first vessel; for after several days
minute bubbles of gas gradually appeared upon a glass rod,
inserted to retain the zinc and platina apart, and also upon the
platina plate itself, and these were hydrogen. They resulted
principally in this way:—notwithstanding the amalgamation of
the zinc, the acid exerted a little direct action upon it, so that
a small stream of hydrogen bubbles was continually rising from
its surface; a little of this hydrogen gradually dissolved in the
dilute acid, and was in part set free against the surfaces of the
rod and the plate, according to the well-known action of such
solid bodies in solutions of gases (359, etc.).

707. But if the gases had been evolved in the second vessel
by the decomposition of water, and had tended to dissolve, still
there would have been every reason to expect that a few bubbles
should have appeared on the electrodes, especially on the
negative one, if it were only because of its action as a nucleus
on the solution supposed to be formed; but none appeared even
after twelve days.

2o6

Faraday’s Researches

708. When a few drops only of nitric acid were added to the
vessel A, fig. 44, then the results were altogether different. In
less than five minutes bubbles of gas appeared on the plates P'
and P" in the second vessel. To prove that this was the effect
of the electric current (which by trial at e was found at the same
time to be passing), the connection at e was broken, and plates
P' P'' cleared from bubbles and left in the acid of the vessel B,
for fifteen minutes: during that time no bubbles appeared upon
them; but on restoring the communication at a minute did
not elapse before gas appeared in bubbles upon the plates. The
proof, therefore, is most full and complete, that the current
excited by dilute sulphuric acid with a little nitric acid in
vessel A, has intensity enough to overcome the chemical affinity
exerted between the oxygen and hydrogen of the water in the
vessel B, whilst that excited by dilute sulphuric acid alone has
not sufficient intensity.

709. On using a strong solution of caustic potassa in the
vessel A, to excite the current, it was found by the decom¬
posing effects at e, that the current passed. But it had not
intensity enough to decompose the water in the vessel B; for
though left for fourteen days, during the whole of which time
the current was found to be passing, still not the slightest
appearance of gas appeared on the plates P' P"', nor any other
signs of the water having suffered decomposition.

710. Sulphate of soda in solution was then experimented
with, for the purpose of ascertaining with respect to it, whether

a certain electrolytic intensity was also

/-^ required for its decomposition in this

^—I ^1^ state, in analogy with the result estab-

^ lished with regard to water (709). The
apparatus was arranged as in fig. 45;
P and Z are the platina and zinc plates
dipping into a solution of common salt;
a and b are platina plates connected by
wires of platina (except in the galvano¬
meter g) with P and Z; ^ is a connecting
wire of platina, the ends of which can be
made to rest either on the plates a, b, or on the papers moistened
in solutions which are placed upon them; so that the passage
of the current without decomposition, or with one or two decom¬
positions, was under ready command, as far as arrangement
was concerned. In order to change the anodes and cathodes at
the places of decomposition, the form of apparatus, fig. 46, was

Fig. 45.

Electrolytic Intensity 207

occasionally adopted. Here only one platina plate;, c, was
used; both pieces of paper on which decomposition was to be
effected were placed upon it^ the wires from P and Z resting
upon these pieces of paper^ or upon the plate according as
the current with or without decomposition of the solutions was
required,

711. On placing solution of iodide of potassium in paper at
one of the decomposing localities, and solution of sulphate of
soda at the other, so that the electric current should pass
through both at once, the solution of iodide was slowly decom¬
posed, yielding iodine at the anode and alkali at the cathode;
but the solution of sulphate of soda exhibited no signs of de¬
composition, neither acid nor alkali being evolved from it. On
placing the wires so that the iodide alone was subject to the

Fig. 46.

action of the current (635), it was quickly and powerfully de¬
composed; but on arranging them so that the sulphate of soda
alone was subject to action, it still refused to yield up its
elements. Finally, the apparatus was so arranged under a wet
bell-glass, that it could be left for twelve hours, the current
passing during the whole time through a solution of sulphate of
soda, retained in its place by only two thicknesses of bibulous
litmus and turmeric paper. At the end of that time it was
ascertained by the decomposition of iodide of potassium at the
second place of action, that the current was passing and had
passed for the twelve hours, and yet no trace of acid or alkali
from the sulphate of soda appeared.

712. From these experiments it may, I think, be concluded
that a solution of sulphate of soda can conduct a current of
electricity, which is unable to decompose the neutral salt
present; that this salt in the state of solution, like water,
requires a certain electrolytic intensity for its decomposition;
and that the necessary intensity is much higher for this sub-

2o8 Faraday’s Researches

Stance than for the iodide of potassium in a similar state of
solution.

713. I then experimented on bodies rendered decomposable
by fusion^ and first on chloride of lead. The current was excited
by dilute sulphuric acid without any nitric acid between zinc
and platina plates^ fig. 47, and was then made to traverse a
little chloride of lead fused upon glass at a, a paper moistened
in solution of iodide of potassium at b, and a galvanometer at g.
The metallic terminations at a and b were of platina. Being
thus arranged^ the decomposition at h and the deflection at g
showed that an electric current was passing, but there was no
appearance of decomposition at a, not even after a metallic
communication at b was established. The experiment was re¬
peated several times, and I am led to conclude that in this case
the current has not intensity sufficient to cause the decom¬
position of the chloride of lead; and further, that, like water
(709), fused chloride of lead can conduct an electric current
having an intensity below that required to effect decom¬
position.

714. Chloride of silver was then placed at a, fig. 47, instead
of chloride of lead. There was a very ready decomposition of
the solution of iodide of potassium at b, and when metallic
contact was made there, very considerable deflection of the
galvanometer needle at g. Platina also appeared to be dissolved
at the anode of the fused chloride at a, and there was every
appearance of a decomposition having been effected there.

715. A further proof of decomposition was obtained in the
following manner. The platina wires in the fused chloride at
a were brought very near together (metallic contact having been
established at b), and left so; the deflection at the galvanometer
indicated the passage of a current, feeble in its force, but
constant. After a minute or two, however, the needle would
suddenly be violently affected, and indicate a current as strong
as if metallic contact had taken place at a. This I actually
found to be the case, for the silver reduced by the action of the
current crystallised in long delicate spiculse, and these at last
completed the metallic communication; and at the same time
that they transmitted a more powerful current than the fused
chloride, they proved that electro-chemical decomposition of
that chloride had been going on. Hence it appears that the
current excited by dilute sulphuric acid between zinc and platina
has an intensity above that required to electrolyse the fused
chloride of silver when placed between platina electrodes.

)f

ie

d

lC

a

d

7

3

g

g

o

;e

it

d

'.c

.e

d

7

.e

it

n.

;r

it

d

g

7

.e

5 t

e

d

.e

a

d

^7

Electrolytic Intensity 209

although it has not intensity enough to decompose chloride of
lead under the same circumstances.

716. A drop of water placed at a instead of the fused chlorides^
showed as in the former case (705)^ that it could conduct a
current unable to decompose it, for decomposition of the
solution of iodide at h occurred after some time. But its con¬
ducting power was much below that of the fused chloride of
lead (713).

717. Fused nitre at a conducted much better than water: I
was unable to decide with certainty whether it was electrolysed,
but I incline to think not, for there was no discoloration against
the platina at the cathode. If sulpho-nitric acid had been used
in the exciting vessel, both the nitre and the chloride of lead
would have suffered decomposition like the water (641).

718. The results thus obtained of conduction without decom¬
position, and the necessity of a certain electrolytic intensity for
the separation of the ions of different electrolytes, are immedi¬
ately connected with the experiments and results given in § 4
of the second part of these Researches (154,159,180,185). But
it will require a more exact knowledge of the nature of intensity,
both as regards the first origin of the electric current, and also
the manner in which it may be reduced, or lowered by the
intervention of longer or shorter portions of bad conductors,
whether decomposable or not, before their relation can be
minutely and fully understood.

719. In the case of water, the experiments I have as yet

I made appear to show that, when the electric current is reduced

') in intensity below the point required for decomposition, then

i the degree of conduction is the same whether sulphuric acid,

I or any other of the many bodies which can affect its trans-

I ferring power as an electrolyte, are present or not. Or, in other

j words, that the necessary electrolytic intensity for water is the

I same whether it be pure, or rendered a better conductor by the

i addition of these substances; and that for currents of less in-

j tensity than this, the water, whether pure or acidulated, has

1 equal conducting power. An apparatus, fig. 44, was arranged

j with dilute sulphuric acid in the vessel A, and pure distilled

S water in the vessel B. By the decomposition at e, it appeared

• as if water was a hetter conductor than dilute sulphuric acid

j for a current of such low intensity as to cause no decomposition.

! I am inclined, however, to attribute this apparent superiority of

j water to variations in that peculiar condition of the platina elec-

I trodes which is referred to further on in this part (776), and

210

Faraday’s Researches

which is assumed^ as far as I can judge^ to a greater degree
in dilute sulphuric acid than in pure water. The power^ there¬
fore^ of acidSj alkalies^ salts^ and other bodies in solution^ to
increase conducting power^ appears to hold good only in those
cases where the electrolyte subject to the current suffers de-
composition^ and loses all influence when the current transmitted
has too low an intensity to affect chemical change. It is
probable that the ordinary conducting power of an electrolyte in
the solid state (155) is the same as that which it possesses in the
fluid state for currents the tension of which is beneath the due
electrolytic intensity.

720. Currents of electricity^ produced by less than eight or
ten series of voltaic elements^ can be reduced to that intensity
at which water can conduct them without suffering decom¬
position^ by causing them to pass through three or four vessels
in which water shall be successively interposed between platina
surfaces. The principles of interference upon which this effect
depends will be described hereafter (745^ 754); but the effect
may be useful in obtaining currents of standard intensity^
and is probably applicable to batteries of any number of pairs
of plates.

721. As there appears every reason to expect that all elec¬

trolytes will be found subject to the law which requires an
electric current of a certain intensity for their decomposition,
but that they will differ from each other in the degree of intensity
required; it will be desirable hereafter to arrange them in a
table, in the order of their electrolytic intensities. Investiga¬
tions on this point must, however, be very much extended,
and include many more bodies than have been here mentioned
before such a table can be constructed. It will be especially
needful in such experiments to describe the nature of the elec- ;
trodes used, or, if possible, to select such as, like platina or
plumbago in certain cases, shall have no power of assisting the
separation of the ions to be evolved (648). ■

722. Of the two modes in which bodies can transmit the 1
electric forces, namely, that which is so characteristically ex¬
hibited by the metals, and usually called conduction, and that in i
which it is accompanied by decomposition, the first appears i
common to all bodies, although it occurs with almost infinite '
degrees of difference; the second is at present distinctive of
the electrolytes. It is, however, just possible that it may here- ■
after be extended to the metals; for their power of conducting
without decomposition may, perhaps justly, be ascribed to their '

Necessary Electrolytic Intensity 211

requiring a very high electrolytic intensity for their decom¬
position.

723. The establishment of the principle that a certain elec¬
trolytic intensity is necessary before decomposition can be
effected; is of great importance to all those considerations which
arise regarding the probable effects of weak currents^ such for
instance as those produced by natural thermo-electricity; or
natural voltaic arrangements in the earth. For to produce an
effect of decomposition or of combination; a current must not
only exist; but have a certain intensity before it can overcome
the quiescent affinities opposed to it; otherwise it will be con¬
ducted; producing no permanent chemical effects. On the other
hand; the principles are also now evident by which an opposing
action can be so weakened by the juxtaposition of bodies not
having quite affinity enough to cause direct action between
them (648); that a very weak current shall be able to raise the
sum of actions sufficiently high; and cause chemical changes
to occur.

724. In concluding this division on the intensity necessary for
electrolysation j I cannot resist pointing out the following remark¬
able conclusion in relation to intensity generally. It would
appear that when a voltaic current is produced; having a certain
intensity; dependent upon the strength of the chemical affinities
by which that current is excited (651); it can decompose a
particular electrolyte without relation to the quantity of elec¬
tricity passed; the intensity deciding whether the electrolyte
shall give way or not. If that conclusion be confirmed; then
we may arrange circumstances so that the same quantity of
electricity may pass in the same time, in at the same surface^
into the sarne decomposing body in the same state, and yet;
differing in intensity; will decompose in one case and in the other
not :—for taking a source of too low an intensity to decompose;
and ascertaining the quantity passed in a given time; it is easy
to take another source having a sufficient intensity; and reducing
the quantity of electricity from it by the intervention of bad
conductors to the same proportion as the former current; and
then all the conditions will be fulfilled which are required tr
produce the result described.

^ iii. On associated Voltaic Circles, or the Voltaic Battery

725. Passing from the consideration of single circles (6
etc.) to their association in the voltaic battery; it is a ver

212 Faraday’s Researches

evident consequence^ that if matters are so arranged that two
sets of affinities^ in place of being opposed to each other as in
figs. 33, 36 (615, 626), are made to act in conformity, then,
instead of either interfering with the other, it will rather assist
it. This is simply the case of two voltaic pairs of metals arranged
so as to form one circuit. In such arrangements the activity of
the whole is known to be increased, and when ten, or a hundred,
or any larger number of such alternations are placed in con¬
formable association with each other, the power of the whole
becomes proportionably exalted, and we obtain that magnificent
instrument of philosophic research, the voltaic battery,

726. But it is evident from the principles of definite action
already laid down, that the quantity of electricity in the current
cannot be increased with the increase of the quantity of metal
oxidised and dissolved at each new place of chemical action.
A single pair of zinc and platina plates throws as much electricity
into the form of a current, by the oxidation of 32.5 grains of the
zinc (603), as would be circulated by the same alteration of a
thousand times that quantity, or nearly five pounds of metal
oxidised at the surface of the zinc plates of a thousand pairs
placed in regular battery order. For it is evident that the
electricity which -passes across the acid from the zinc to the
platina in the first cell, and which has been associated with, or
even evolved by, the decomposition of a definite portion of water
in that cell, cannot pass from the zinc to the platina across the
acid in the second cell, without the decomposition of the same
quantity of water there, and the oxidation of the same quantity
of zinc by it (659, 684). The same result recurs in every other
cell; the electro-chemical equivalent of water must be decom¬
posed in each, before the current can pass through it; for the
quantity of electricity passed and the quantity of electrolyte
decomposed must be the equivalents of each other. The action
in each cell, therefore, is not to increase the quantity set in
motion in any one cell, but to aid in urging forward that quantity,
the passing of which is consistent with the oxidation of its own
zinc; and in this way it exalts that peculiar property of the
cun'ent which we endeavour to express by the term intensity,
without increasing the quantity beyond that which is propor¬
tionate to the quantity of zinc oxidised in any single cell of the
series.

727. To prove this, I arranged ten pairs of amalgamated zinc
and platina plates with dilute sulphuric acid in the form of a
battery. On completing the circuit, all the pairs acted and

Current of a Voltaic Battery 213

evolved gas at the surfaces of the platina. This was collected
and found to be alike in quantity for each plate; and the
quantity of hydrogen evolved at any one platina plate was in
the same proportion to the quantity of metal dissolved from
any one zinc plate^ as was given in the experiment with a single
pair (599, etc.). It was therefore certain that just as much
electricity and no more had passed through the series of ten pair
of plates as had passed through^ or would have been put into
motion by^ any single pair^ notwithstanding that ten times the
quantity of zinc had been consumed.

728. This truth has been proved also long ago in another
way^ by the action of the evolved current on a magnetic needle;
the deflecting power of one pair of plates in a battery being equal
to the deflecting power of the whole^ provided the wires used be
sufficiently large to carry the current of the single pair freely;
but the cause of this equality of action could not be understood
whilst the definite action and evolution of electricity (518^ 604)
remained unknown.

729. The superior decomposing power of a battery over a
single pair of plates is rendered evident in two ways. Electro-
l3rtes held together by an affinity so strong as to resist the
action of the current from a single pair^ yield up their elements
to the current excited by many pairs; and that body which is
decomposed by the action of one or of few pairs of metals^ etc.,
is resolved into its ions the more readily as it is acted upon by
electricity urged forward by many alternations.

730 Both these effects are, I think, easily understood.
Whatever intensity may be (and that must of course depend
upon the nature of electricity, whether it consist of a fluid or
fluids, or of vibrations of an ether, .or any other kind or com
dition of matter), there seems to be no difficulty in compre¬
hending that the degree of intensity at which a current of
electricity is evolved by a first voltaic element, shall be increased
when that current is subjected to the action of a second voltaic
element, acting in conformity and possessing equal powers with
the first: and as the decompositions are merely opposed actions,
but exactly of the same kind as those which generate the current
(652), it seems to be a natural consequence that the affinity
which can resist the force of a single decomposing action may
be unable to oppose the energies of many decomposing actions,
operating conjointly, as in the voltaic battery.

731. That a body which can give way to a current of feeble
intensity should give way more freely to one of stronger force.

214 Faraday’s Researches

and yet involve no contradiction to the law of definite electro¬
lytic action^ is perfectly consistent. All the facts and also the
theory I have ventured to put forth^ tend to show that the act
of decomposition opposes a certain force to the passage of the
electric current; and, that this obstruction should be overcome
more or less readily, in proportion to the greater or less intensity
of the decomposing current, is in perfect consistency with all
our notions of the electric agent.

732. I have elsewhere (682) distinguished the chemical action
of zinc and dilute sulphuric acid into two portions; that which,
acting effectually on the zinc, evolves hydrogen at once upon
its surface, and that which, producing an arrangement of the
chemical forces throughout the electrolyte present (in this case
water), tends to take oxygen from it, but cannot do so unless
the electric current consequent thereon can have free passage,
and the hydrogen be delivered elsewhere than against the zinc.
The electric current depends altogether upon the second of
these; but when the current can pass, by favouring the electro¬
lytic action it tends to diminish the former and increase the
latter portion.

733. It is evident, therefore, that when ordinary zinc is used
in a voltaic arrangement, there is an enormous waste of that
power which it is the object to throw into the form of an electric
current; a consequence which is put in its strongest point of
view when it is considered that three ounces and a half of zinc,
properly oxydised, can circulate enough electricity to decompose
nearly one ounce of water, and cause the evolution of about
2400 cubic inches of hydrogen gas. This loss of power not
only takes place during the time the electrodes of the battery
are in communication, being then proportionate to the quantity
of hydrogen evolved against the surface of any one of the zinc
plates, but includes also all the chemical action which goes on
when the extremities of the pile are not in communication.

734. This loss is far greater with ordinary zinc than with the
pure metal, as M. de la Rive has shown.^ The cause is, that
when ordinary zinc is acted upon by dilute sulphuric acid,
portions of copper, lead, cadmium, or other metals which it
may contain, are set free upon its surface; and these, being in
contact with the zinc, form small but very active voltaic circles,
which cause great destruction of the zinc and evolution of
hydrogen, apparently upon the zinc surface, but really upon the

1 Quarterly Journal of Science, 1831, p. 388; or Bibliotheque Universelle,
JS30, p. 391.

Amalgamated Zinc in the Battery 2 r 5

surface of these incidental metals. In the same proportion as
they serve to discharge or convey the electricity back to the zinc^
do they diminish its power of producing an electric current
which shall extend to a greater distance across the acid^ and be
discharged only through the copper or platina plate which is
associated with it for the purpose of forming a voltaic apparatus.

735. All these evils are removed by the emplo3mient of an
amalgam of zinc in the manner recommended by Mr. Kemp/
or the use of the amalgamated zinc plates of Mr. Sturgeon (598)^
who has himself suggested and objected to their application in
galvanic batteries; for he says^ “Were it not on account of
the brittleness and other inconveniences occasioned by the
incorporation of the mercury with the zinc^ amalgamation of
the zinc surfaces in galvanic batteries would become an import¬
ant improvement; for the metal would last much longer^ and
remain bright for a considerable time^ even for several successive
hours; essential considerations in the employment of this
apparatus.” ^

736. Zinc so prepared, even though impure, does not sensibly
decompose the water of dilute sulphuric acid, but still has such
affinity for the oxygen, that the moment a metal which, like
copper or platina, has little or no affinity, touches it in the acid,
action ensues, and a powerful and abundant electric current is
produced. It is probable that the mercury acts by bringing
the surface, in consequence of its fluidity, into one uniform
condition, and preventing those differences in character between
one spot and another which are necessary for the formation of
the minute voltaic circuits referred to (734). If any difference
does exist at the first moment, with regard to the proportion of
zinc and mercury, at one spot on the surface, as compared with
another, that spot having the least mercury is first acted on,
and, by solution of the zinc, is soon placed in the same condition
as the other parts, and the whole plate rendered superficially
uniform. One part cannot, therefore, act as a discharger to
another; and hence all the chemical power upon the water at
its surface is in that equable condition (684), which, though
it tends to produce an electric current through the liquid to
another plate of metal which can act as a discharger (685),
presents no irregularities by which any one part, having weaker

^Jameson’s Edinburgh Journal, October 1828.

® Recent Experimental Researches, p. 4.2, etc. Mr. Sturgeon is of course
unaware of the definite production of electricity by chemical action, and
is in fact quoting the experiment as the strongest argument against th^
chemical theory of galvanism.

216 Faraday’s Researches

affinities for oxygen, can act as a discharger to another. Two
excellent and important consequences follow upon this state of
the metal. The first is, that the full equivalent of electricity is
obtained for the oxidation of a certain quantity of zinc; the
second, that a battery constructed with the zinc so prepared,
and charged with dilute sulphuric acid, is active only whilst
the electrodes are connected, and ceases to act or be acted upon
by the acid the instant the communication is broken.

737. I have had a small battery of ten pairs of plates thus
constructed, and am convinced that arrangements of this kind
will be very important, especially in the development and illus¬
tration of the philosophical principles of the instrument. The
metals I have used are amalgamated zinc and platina, con¬
nected together by being soldered to platina wires, the whole
apparatus having the form of the couronne des lasses. The
liquid used was dilute sulphuric acid of sp. gr. 1.25. No action
took place upon the metals except when the electrodes were in
communication, and then the action upon the zinc was only in
proportion to the decomposition in the experimental cell; for
when the current was retarded there, it was retarded also in
the batter}^ and no waste of the powers of the metal was incurred.

738. In consequence of this circumstance, the acid in the
cells remained active for a very much longer time than usual.
In fact, time did not tend to lower it in any sensible degree: for
whilst the metal was preserved to be acted upon at the proper
moment, the acid also was preserved almost at its first strength.
Hence a constancy of action far beyond what can be obtained
by the use of common zinc.

739. Another excellent consequence was the renewal, during
the interval of rest, between two experiments of the first and
most efficient state. When an amalgamated zinc and a platina
plate, immersed in dilute sulphuric acid, are first connected,
the current is very powerful, but instantly sinks very much in
force, and in some cases actually falls to only an eighth or a
tenth of that first produced (772). This is due to the acid
which is in contact with the zinc becoming neutralised by the
oxide formed; the continued quick oxidation of the metal being
thus prevented. With ordinary zinc, the evolution of gas at
its surface tends to mingle all the liquid together, and thus
bring fresh acid against the metal, by which the oxide formed
there can be removed. With the amalgamated zinc battery,
at every cessation of the current, the saline solution against the
zinc is gradually diffused amongst the rest of the liquid; and

Amalgamated Zinc Battery 217

Upon the renewal of contact at the electrodes^ the zinc plates are
found most favourably circumstanced for the production of a
ready and powerful current.

740. It mi ht at first be imagined that amalgamated zinc
would be much inferior in force to common zinc, fccaus of the
lowering of its energy, which the mercury might be supposed
to occasion over the whole of its surface* but this is not the
case. When the electric currents of two pairs of platina and
zinc plates were opposed, the difference being that one of the
zincs was amalgamated and the other not, the current from
the amalgamated zinc was most powerful, although no gas was
evolved against it, and much was evolved at the surface of the
unamalgamated metal. Again, as Davy has shownif amal¬
gamated and unamalgamated zinc be put in contact, and dipped
into dilute sulphuric acid, or other exciting fluids, the former
is positive to the latter, i.e. the current passes from the amalga¬
mated zinc, through the fluid, to the unprepared zinc. This he
accounts for by supposing that there is not any inhe ent and
specific property in each metal which gives it the electrical
character, but that it depends upon its peculiar state—on that
form of aggregation which fits it for chemical change.”

741. The superiority of the amalgamated zinc is not, how¬
ever, due to any such cause, but is a very simple consequence
of the state of the fluid in contact with it; for as the unprepared
zinc acts directly and alone upon the fluid, whilst that which is
amalgamated does not, the former (by the oxide it produces)
quickly neutralises the acid in contact with its surface, so that
the progress of oxidation is retarded, whilst at the surface of
the amalgamated zinc, any oxide formed is instantly removed
by the free acid present, and the clean metallic surface is always
ready to act with full energy upon the water. Hence its
superiority (773).

742. The progress of improvement in the voltaic battery and
its applications, is evidently in the contrary direction at present
to what it was a few years ago; for in place of increasing the
number of plates, the strength of acid, and the extent alto¬
gether of the instrument, the change is rather towards its first
state of simplicity, but with a far more intimate knowledge and
application of the principles which govern its force and action.
Effects of decomposition can now be obtained with ten pairs of
plates (153), which required five l undred or a thousand pairs
for their production in the first instance. The capability of

^ Philosophical Transactions, 1826, p. 405.

21 8 Faraday’s Researches

decomposing fused chlorides^ iodides, and other compounds,
according to the law before established (ii6, etc.), and the
opportunity of collecting certain of the products, without any
loss, by the use of apparatus of the nature of those already
described (524, 549, etc.), render it probable that the voltaic
battery may become a useful and even economical manufactur¬
ing instrument; for theory evidently indicates that an equiva¬
lent of a rare substance may be obtained at the expense of three
or four equivalents of a very common body, namely, zinc: and
practice seems thus far to justify the expectation. In this
point of view I think it very likely that plates of platina or
silver may be used instead of plates of copper with advantage,
and that then the evil arising occasionally from solution of the
copper, and its precipitation on the zinc (by which the electro¬
motive power of the zinc is so much injured), will be avoided

(783)-

^ iv. On the Resistance of an Electrolyte to Electrolytic
Actionj and on Interpositions

743. I have already illustrated, in the simplest possible form
of experiment (626, 645), the resistance established at the place
of decomposition to the force active at the exciting place. I
purpose examining the effects of this resistance more generally;
but it is rather with reference to their practical interference
with the action and phenomena of the voltaic battery, than
with any intention at this time to offer a strict and philosophical
account of their nature. Their general and principal cause is
the resistance of the chemical affinities to be overcome; but
there are numerous other circumstances which have a joint
^ influence with these forces (770, 776, etc.), each of

I which would require a minute examination before a

correct account of the whole could be given.

J rJ 744. As it will be convenient to describe the experi-
I ments in a form different to that in which they were
made, both forms shall first be explained. Plates of
platina, copper, zinc, and other metals, about three-
4 V quarters of an inch wide and three inches long, were

Fig. 48 associated together in pairs by means of platina

wires to which they were soldered, fig. 48, the plates
of one pair being either alike or different, as might be required.
These were arranged in glasses, fig. 49, so as to form Volta’s
crown of cups. The acid or fluid in the cups never covered

Resistance to Electrolysis 219

the whole of any plate; and occasionally small glass rods were
put into the cups^ between the plates^ to prevent their contact.
Single plates were used to terminate the series and
complete the connection with a galvanometer, or with
a decomposing apparatus (634, 703, etc.), or both.

Now if fig. 50 be examined and compared with fig. 51, !
the latter may be admitted as representing the former j
in its simplest condition; for the cups, i, ii, and iii of | 1

the former, with their contents, are represented by
the cells i, ir, and iii of the latter, and the metal pig, 4^,
plates Z and P of the foimer by the similar plates
represented Z and P in the latter. The only difference, in fact,
between the apparatus, fig. 50, and the trough represented
fig. 51, is that twice the quantity of surface of contact between
the metal and acid is allowed in the first to what would occur
in the second.

745. When the extreme plates of the arrangement just de¬
scribed, fig. 50, are connected metalli¬
cally through the galvanometer g, then
the whole represents a battery con¬
sisting of two pairs of zinc and platina
plates urging a current forward, which
has, however, to decompose water
unassisted by any direct chemical
affinity before it can be transmitted
across the cell in, and therefore before
itTcan circulate. This decomposition
of water, which is opposed to the
passage of the current, may, as a
matter of convenience, be considered
as taking place either against the
surfaces of the two platina plates which constitute the electrodes
in the cell ni, or against the two surfaces of that platina plate
which separates the cells ii and iir, fig. 51, from each other.
It is evident that if that plate were away,
the battery would consist of two pairs of plates
and two cells, arranged in the most favourable
position for the production of a current. The
platina plate therefore, which being introduced
as at ^c, has oxygen evolved at one surface
and hydrogen at the other (that is, if the
decomposing current passes), may be considered as the cause
of any obstruction arising from the decomposition of water by

2 20 Faraday’s Researches

the electrolytic action of the current; and I have usually called
it the interposed plate.

746. In order to simplify the conditions^ dilute sulphuric
acid was first used in all the cells^ and platina for the interposed
plates; for then the initial intensity of the current which tends
to be formed is constant^ being due to the power which zinc
has of decomposing water; and the opposing force of decompo¬
sition is also constant^ the elements of the water being unassisted
in their separation at the interposed plates by any affinity or
secondary action at the electrodes (479), arising either from
the nature of the plate itself or the surrounding fluid.

747. When only one voltaic pair of zinc and platina plates
was used; the current of electricity was entirely stopped to all
practical purposes by interposing one platina plate^ fig. 52^ i.e,
by requiring of the current that it should decompose water, and

Fig. 52. Fig. 53. Fig. 54.

evolve both its elements, before it should pass. This conse¬
quence is in perfect accordance with the views before given
(645, 652, 708). For as the whole result depends upon the
opposition of forces at the places of electric excitement and
electro-decomposition, and as water is the substance to be
decomposed at both before the current can move, it is not to be
expected that the zinc should have such powerful attraction for
the oxygen, as not only to be able to take it from its associated
hydrogen, but leave such a surplus of force as, passing to the
second place of decomposition, should be there able to effect a
second separation of the elements of water. Such an effect
would require that the force of attraction between zinc and
oxygen should under the circumstances be at least twice as
great as the force of attraction between the oxygen and
hydrogen.

748. When two pairs of zinc and platina exciting plates were
used, the current was also practically stopped by one interposed
platina plate, fig. 53. There was a very feeble effect of a current
at first, but it ceased almost immediately. It will be referred
to, with many other similar effects, hereafter (753).

Resistance to Electrolysis 221

749. Three pairs of zinc and platina plates, fig. 54, were able
to produce a current which could pass an interposed platina
plate, and effect the electrolysation of water in cell iv. The
current was evident, both by the continued deflection of the
galvanometer, and the production of bubbles of oxygen and
hydrogen at the electrodes in cell iv. Hence the accumulated
surplus force of three plates of zinc, which are active in decom¬
posing water, is more than equal, when added together, to the
force with which oxygen and hydrogen are combined in water,
and is sufficient to cause the separation of these elements from
each other.

750. The three pairs of zinc and platina plates were now
opposed by two intervening platina plates, fig. 55. In this case
the current was stopped.

751. Four pairs of zinc and platina plates were also neutral¬
ised by two interposed platina plates, fig. 56.

752. Five pairs of zinc and platina, with two interposed
platina plates, fig. 57, gave a feeble current; there was per¬
manent deflection at the galvanometer, and decomposition in
the cells vi and vii. But the current was very feeble; veiy^

Fig. 57 * 58.

much less than when all the inteimediate plates were remr
and the two extreme ones only retained: for when they
placed six inches asunder in one cell, they gave a po"^
current. Hence five exciting pairs, with two interposed ob
ting plates, do not give a current at all comparable to th
a single unobstructed pair.

753. I have already said that a very Jeehle current pas
when the series included one interposed platina and two pa

222

Faraday’s Researches

of zinc and platina plates (748). A similarly feeble current
passed in every case^ and even when only one exciting pair and
four intervening platina plates were used^ fig. 58^ a current
passed which could be detected at both by chemical action
on the solution of iodide of potassium^ and by the galvanometer.
This current I believe to be due to electricity reduced in intensity
below the point requisite for the decomposition of water (705^
719); for water can conduct electricity of such low intensity
by the same kind of power which it possesses in common with
metals and charcoal^ though it cannot conduct electricity of
higher intensity without suffering decomposition^ and then
opposing a new force consequent thereon. With an electric
current of;, or under this intensity^ it is probable that increasing
the number of interposed platina plates would not involve an
increased difficulty of conduction.

754. In order to obtain an idea of the additional interfering
power of each added platina plate^ six voltaic pairs and four
intervening platinas were arranged as in fig. 59; a very feeble
current then passed {720, 753). When one of the platinas
was removed so that three intervened^ a current somewhat
stronger passed. With two intervening platinas a still stronger
current passed; and with only one intervening platina a very
fair current was obtained. But the effect of the successive
plates^ taken in the order of their interposition^ was very dif¬
ferent^ as might be expected; for the first retarded the current
more powerfully than the second^ and the second more than
the third.

755. In these experiments both amalgamated and unamal¬
gamated zinc were used^ but the results generally were the
same.

756. The effects of retardation just described were altered
altogether when changes were made in the nature of the liquid
used between the plates^ either in what may be called the
exciting or the retarding cells. Thus^ retaining the exciting-
force the same^ by still using pure dilute sulphuric acid for that

Resistance to Electrolysis 223

purpose^ if a little nitric acid were added to the liquid in the
retarding cells^ then the transmission of the current was very
much facilitated. For instance^ in the experiment with one
pair of exciting plates and one intervening plate (747)^ fig. ^2^
when a few drops of nitric acid were added to the contents of
cell ii) then the current of electricity passed with considerable
strength (though it soon fell from other causes (772^ 776));
and the same increased effect was produced by the nitric acid
when many interposed plates were used.

757. This seems to be a consequence of the diminution of
the difficulty of decomposing water when its hydrogen^ instead
of being absolutely expelled^ as in the former cases^ is transferred
to the oxygen of the nitric acid^ producing a secondary result
at the cathode (487); for in accordance with the chemical views
of the electric current and its action already advanced (648)_,
the water^ instead of opposing a resistance to decomposition
equal to the full amount of the force of mutual attraction
between its oxygen and hydrogen^ has that force counteracted
in part, and therefore diminished by the attraction of the
hydrogen at the cathode for the oxygen of the nitric acid which
surrounds it, and with which it ultimately combines instead
of being evolved in its free state.

758. When a little nitric acid was put into the exciting cells,
then again the circumstances favouring the transmission of the
current were strengthened, for the intensity of the current itself
was increased by the addition (641). When therefore a little
nitric acid was added to both the exciting and the retarding cells,
the current of electricity passed with very considerable freedom.

759. When dilute muriatic acid was used, it produced and
transmitted a current more easily than pure dilute sulphuric
acid, but not so readily as dilute nitric acid. As muriatic acid
appears to be decomposed more freely than water (500), and as
the affinity of zinc for chlorine is very powerful, it might be
expected to produce a current more intense than that from the
use of dilute sulphuric acid; and also to transmit it more freely
by undergoing decomposition at a lower intensity (647).

760. In relation to the effect of these interpositions, it is
necessary to state that they do not appear to be at all dependent
upon the size of the electrodes, or their distance from each
other in the acid, except that when a current can pass, changes
in these facilitate or retard its passage. For on repeating the
experiment with one intervening and one pair of exciting plates
(747), fig. 52, and in place of the interposed plate P using some-

224 Faraday’s Researches

times a mere wire, and sometimes very large plates (744), and
also changing the terminal exciting plates Z and P, so that they
were sometimes wires only and at others of great size^ still the
results were the same as those already obtained.

761. In illustration of the effect of distance^ an experiment
like that described with two exciting pairs and one intervening
plate (748)^ fig. 53^ was arranged so that 'the distance between
the plates in tl-ie third cell could be increased to six or eight
inches^ or diminished to the thickness of a piece of intervening
bibulous paper. Still the result was the same in both cases^ the
effect not being sensibly greater^ when the plates were merely
separated by the paper, than when a great way apart; so that
the principal opposition to the current in this case does not
depend upon the quantity of intervening electrolytic conductor,
but on the relation of its elements to the intensity of the current,
or to the chemical nature of the electrodes and the surrounding
fluids.

Fig. 60. Fig. 61. Fig. 62.

762. When the acid was sulphuric acid, increasing its strength !

in any of the cells caused no change in the effects; it did not j

produce a more intense current in the exciting cells (643), or ;

cause the current produced to traverse the decomposing cells i

more freely. But if to very weak sulphuric acid a few drops of |

nitric acid were added, then either one or other of those efects j

could be produced; and, as might be expected in a case like i

this, where the exciting or conducting action bore a direct j

reference to the acid itself, increasing the strength of this (the j
nitric acid) also increased its powers. j

763. The nature of the interposed plate was now varied to show j

its relation to the phenomena either of excitation or retardation, ;

and amalgamated zinc was first substituted for platina. On j

employing one voltaic pair and one interposed zinc plate, fig. 60, j

there was as powerful a current, apparently, as if the interposed 1

zinc plate was away. Hydrogen was evolved against P in I

cell II, and against the side of the second zinc in cell i; but no |

gas appeared against the side of the zinc in cell ir, nor against I
the zinc in cell 1. I

Resistance to Electrolytes 225

764. On interposing two amalgamated zinc plates^ fig, 6i^
instead of one^ there was still a powerful current^ but interference
had taken place. On using three intermediate zinc plates^
fig. 62^ there was still further retardation^ though a good current
of electricity passed,

765. Considering the retardation as due to the inaction of the
amalgamated zinc upon the dilute acid^ in consequence of the
slight though general effect of diminished chemical power pro¬
duced by the mercury on the surface^ and viewing this inaction
as the circumstance which rendered it necessary that each plate
should have its tendency to decompose water assisted slightly
by the electric current^, it was expected that plates of the metal
in the unamalgamated state would probably not require such
assistance^ and would offer no sensible impediment to the
passing of the current. This expectation was fully realised in
the use of two and three interposed unamalgamated plates. The
electric current passed through them as freely as if there had
been no such plates in the way. They offered no obstacle^
because they could decompose water without the current; and
the latter had only to give direction to a part of the forces^
which would have been active whether it had passed or not.

766. Interposed plates of copper were then employed. These
seemed at first to occasion no obstruction, but after a few
minutes the current almost entirely ceased. This effect appears
due to the surfaces taking up that peculiar condition (776) by
which they tend to produce a reverse current; for when one or
more of the plates were turned round, which could easily be
effected with the couronne des lasses form of experiment, fig. 50,
then the current was powerfully renewed for a few moments,
and then again ceased. Plates of platina and copper, arranged
as a voltaic pile with dilute sulphuric acid, could not form a
voltaic trough competent to act for more than a few minutes,
because of this peculiar counteracting effect.

767. All these effects of retardation, exhibited by decom¬
position against surfaces for which the evolved elements have
more or less affinity, or are altogether deficient in attraction,
show generally, though beautifully, the chemical relations and
source of the current, and also the balanced state of the affinities
at the places of excitation and decomposition. In this way they
add to the mass of evidence in favour of the identity of the two;
for they* demonstrate, as it were, the antagonism of the chemical
powers at the electromotive part with the chemical powers at
the interposed parts; they show that the first are producing

p

226 Faraday’s Researches

electric effects^, and the second opposing them; they bring the
two into direct relation; they prove that either can determine
the other, thus making what appears to be cause and effect
convertible, and thereby demonstrating that both chemical and
electrical action are merely two exhibitions of one single agent
or power (651, etc.). |

768. It is quite evident, that as water and other electrolytes

can conduct electricity without suffering decomposition (721),
when the electricity is of sufficiently low intensity, it may not j
be asserted as absolutely true in all cases, that whenever elec¬
tricity passes through an electrolyte, it produces a definite effect ,
of decomposition. But the quantity of electricity which can ;
pass in a given time through an electrolyte without causing 1
decomposition is so small as to bear no comparison to that !
required in a case of very moderate decomposition, and with !
electricity above the intensity required for electrolysation, I {
have found no sensible departure as yet from the law of definite
electrolytic action developed in the preceding parts of these j
Researches (518, etc.). ;

769. I cannot dismiss this division of the present paper [

without making a reference to the important experiments of '
M. Aug. de la Rive on the effects of interposed plates.^ As I i
have had occasion to consider such plates merely as giving rise !
to new decompositions, and in that way only causing obstruction ;
to the passage of the electric current, I was freed from the j
necessity of considering the peculiar effects described by that '
philosopher. I was the more willing to avoid for the present
touching upon these, as I must at the same time have ;
entered into the views of Sir Humphry Davy upon the same
subject,^ and also those of Marianini ^ and Ritter,^ which are i
connected with it. ,

1

^ V. General Remarks on the active Voltaic Battery

770. When the ordinary voltaic battery is brought into >
action, its very activity produces certain effects, which react !
upon it, and cause serious deterioration of its power. These
render it an exceedingly inconstant instrument as to the quantity '
of effect which it is capable of producing. They are already,

^ Annates de Chimie, tom. xxviii. p. 190; and Memoires de Geneve.

2 Philosophical Transactions, 1826, p. 413.

Annales de Chimie, tom. xxxiii. pp. 117, 119, etc. 1

^ Journal de Physique, tom. Ivii. pp. 349, 350.

On the Active Battery 227

in part^ known and understood; but as their importance^ and
that of certain other coincident results^ will be more evident
by reference to the principles and experiments already stated
and described^ I have thought it would be useful^ in this investi¬
gation of the voltaic pile^ to notice them briefly here.

771. When the battery is in action^ it causes such substances
to be formed and arranged in contact with the plates as very
much weaken its power, or even tend to produce a counter
current. They are considered by Sir Humphry Davy as suffi¬
cient to account for the phenomena of Ritter’s secondary piles,
and also for the effects observed by M. A. de la Rive with
interposed platina plates.^

772. I have already referred to this consequence (739) as
capable, in some cases, of lowering the force of the current to
one-eighth or one-tenth of what it was at the first moment,
and have met with instances in which
its interference was very great. In
an experiment in which one voltaic
pair and one interposed platina plate
were used with dilute sulphuric acid
in the cells, fig. 63, the wires of
communication were so arranged
that the end of that marked 3 could
be placed at pleasure upon paper
moistened in the solution of iodide
of potassium at x, or directly upon the platina plate there. If,
after an interval during which the circuit had not been com¬
plete, the wire 3 were placed upon the paper, there was evidence
of a current, decomposition ensued, and the galvanometer was
affected. If the wire 3 were made to touch the metal of a com¬
paratively strong sudden current was produced, affecting the
galvanometer, but lasting only for a moment; the effect at the
galvanometer ceased, and if the wire 3 were placed on the paper
at X, no signs of decomposition occurred. On raising the wire 3,
and breaking the circuit altogether for a while, the apparatus
resumed its first power, requiring, however, from five to ten
minutes for this purpose; and then, as before, on making contact
between 3 and p, there was again a momentary current, and
immediately all the effects apparently ceased.

773. This effect I was ultimately able to refer to the state
of the film of fluid in contact with the zinc plate in cell i. The
acid of that film is instantly neutralised by the oxide formed;

1 Philosophical Transactions, 1826, p. 413.

220 raradays Researches

the oxidation of the zinc cannot; of course; go on with the
same facility as before; and the chemical action being thus
interrupted; the voltaic action diminishes with it. The time of
the rest was required for the diffusion of the liquid; and its re¬
placement by other acid. From the serious influence of this
cause in experiments with single pairs of plates of different
metalS; in which I was at one time engaged; and the extreme
care required to avoid it; I cannot help feeling a strong suspicion
that it interferes more frequently and extensively than ex¬
perimenters are aware of; and therefore direct their attention
to it.

774. In considering the effect in delicate experiments of
this source of irregularity of action in the voltaic apparatus; it
must be remembered that it is only that very small portion of
matter which is directly in contact with the oxidisable metal
which has to be considered with reference to the change of its
nature; and this portion is not very readily displaced from its
position upon the surface of the metal (328; 341); especially if
that metal be rough and irregular. In illustration of this effect,
I will quote a remarkable experiment. A burnished platina plate
(305) was put into hot strong sulphuric acid for an instant only:
It was then put into distilled water; moved about in it; taken
out; and wiped dry: it was put into a second portion of distilled
water; moved about in it; and again wiped: it was put into a
third portion of distilled water; in which it was moved about
for nearly eight seconds; it was then; without wiping; put into
a fourth portion of distilled water; where it was allowed to
remain five minutes. The two latter portions of water were
then tested for sulphuric acid; the third gave no sensible appear¬
ance of that substance; but the fourth gave indications which
were not merely evident; but abundant for the circumstances
under which it had been introduced. The result sufidciently
shows with what difficulty that portion of the substance which
is in contact with the metal leaves it; and as the contact of the
fluid formed against the plate in the voltaic circuit must be as
intimate and as perfect as possible; it is easy to see how quickly
and greatly it must vary from the general fluid in the cellS; and
how influential in diminishing the force of the battery this
effect must be.

775. In the ordinary voltaic pilC; the influence of this effect
will occur in all variety of degrees. The extremities of a trough
of twenty pairs of plates of Wollaston’s construction were con¬
nected with the volta-electrometer; fig. 26 (446); of the fifth

On the Active Battery 229

part of these Researches^ and after five minutes the number
of bubbles of gas issuing from the extremity of the tube^ in
consequence of the decomposition of the water^ noted. With¬
out moving the plates, the acid between the copper and zinc
was agitated by the introduction of a feather. The bubbles
were immediately evolved more rapidly, about twice the
number being produced in the same portion of time as before.
In this instance it is very evident that agitation by a feather
must have been a very imperfect mode of restoring the acid in
the cells against the plates towards its first equal condition;
and yet imperfect as the means were, they more than doubled
the power of the battery. The first effect of a battery which is
known to be so superior to the degree of action which the
battery can sustain, is almost entirely due to the favourable
condition of the acid in contact with the plates.

776. A second cause of diminution in the force of the voltaic
battery, consequent upon its own action, is that extraordinary
state of the surfaces of the metals (704) which was first
described, I believe, by Ritter,^ to which he refers the powers
of his secondary piles, and which has been so well experimented
upon by Marianini, and also by A. de la Rive. If the appa¬
ratus, fig. 63 (772), be left in action for an hour or two, with
the wire 3 in contact with the plate so as to allow a free
passage for the current, then, though the contact be broken for
ten or twelve minutes, still, upon its renewal, only a feeble
current will pass, not at all equal in force to what might be
expected. Further, if and be connected by a metal wire,
a powerful momentary current will pass from P^ to P^ through
the acid, and therefore in the reverse direction to that produced
by the action of the zinc in the arrangement; and after this has
happened, the general current can pass through the whole of
the system as at first, but by its passage again restores the
plates P^ and P^ into the former opposing condition. This,
generally, is the fact described by Ritter, Marianini, and De la
Rive. It has great opposing influence on the action of a pile,
especially if the latter consist of but a small number of alterna¬
tions, and has to pass its current through many interpositions.
It varies with the solution in which the interposed plates are
immersed, with the intensity of the current, the strength of the
pile, the time of action, and especially with accidental dis¬
charges of the plates by inadvertent contacts or reversions of
the plates during experiments, and must be carefully watched

^ Journal de Physique, Ivii. p. 349.

230 Faraday’s Researches

in every endeavour to trace the source^ strength^ and variations
of the voltaic current. Its effect was avoided in the experi¬
ments already described (772, etc.)^ by making contact between
the plates and before the effect dependent upon the state
of the solution in contact with the zinc plate was observed,
and by other precautions.

777. When an apparatus like %. 58 (753) with several
•platina plates was used, being connected with a battery able to
force a current through them, the power which they acquired,
of producing a reverse current, was very considerable.

778. Weak and exhausted charges should never be used at
the same time with strong and fresh ones in the different cells
of a trough, or the different troughs of a battery: the fluid
in all the cells should be alike, else the plates in the weaker
cells, in place of assisting, retard the passage of the electricity
generated in, and transmitted across, the stronger cells. Each
zinc plate so circumstanced has to be assisted in decomposing
power before the whole current can pass between it and the
liquid. So that, if in a battery of fifty pairs of plates, ten of the
cells contain a weaker charge than the others, it is as if ten
decomposing plates were opposed to the transit of the current of
forty pairs of generating plates (767). Hence a serious loss of
force, and hence the reason why, if the ten pairs of plates were
removed, the remaining forty pairs would be much more power¬
ful than the whole fifty.

779. Five similar troughs, of ten pairs of plates each, were
prepared, four of them with a good uniform charge of acid, and
the fifth with the partially neutralised acid of a used battery.
Being arranged in right order, and connected with a volta-elec-
trometer (446), the whole fifty pairs of plates yielded i.i cubic
inch of oxygen and hydrogen in one minute: but on moving one
of the connecting wires so that only the four well-charged
troughs should be included in the circuit, they produced with the
same volta-electrometer 8.4 cubical inches of gas in the same
time. Nearly seven-eighths of the power of the four troughs
had been lost, therefore, by their association with the fifth trough.

780. The same battery of fifty pairs of plates, after being
thus used, was connected with a volta-electrometer (446), so
that by quickly shifting the wires of communication, the
current of the whole of the battery, or of any portion of it, could
be made to pass through the instrument for given portions of
time in succession. The whole of the battery evolved 0.9 of a
cubic inch of oxygen and hydrogen in half a minute; the forty

On the Active Battery 231

plates evolved 4.6 cubic inches in the same time; the whole
then evolved i cubic inch in the half minute; the ten weakly-
charged evolved 0.4 of a cubic inch in the time given: and
finally the whole evolved 1.15 cubic inch in the standard time.
The order of the observations was that given: the results suffi¬
ciently show the extremely injurious effect produced by the
mixture of strong and weak charges in the same battery.^

781. In the same manner associations of strong and weak
pairs of plates should be carefully avoided. A pair of copper
and platina plates arranged in accordance with a pair of zinc
and platina plates in dilute sulphuric acid^ were found to stop
the action of the latter^ or even of two pairs of the latteras
effectually almost as an interposed plate of platina (747); or
as if the copper itself had been platina. It^ in fact^ became an
interposed decomposing plate^ and therefore a retarding instead
of an assisting pair.

782. The reversal, by accident or otherwise^ of the plates in
a battery has an exceedingly injurious effect. It is not merely
the counteraction of the current which the reversed plates can
produce^ but their effect also in retarding even as indifferent
plateS; and requiring decomposition to be effected upon their
surface^ in accordance with the course of the current, before the
latter can pass. They oppose the current, therefore, in the
first place, as interposed platina plates would do (747-754);
and to this they add a force of opposition as counter-voltaic
plates. I find that, in a series of four pairs of zinc and platina
plates in dilute sulphuric acid, if one pair be reversed, it very
nearly neutralises the power of the whole.

783. There are many other causes of reaction, retardation,,
and irregularity in the voltaic battery. Amongst them is the^
not unusual one of precipitation of copper upon the zinc in the
cells, the injurious effect of which has before been adverted to
(742). But their interest is not perhaps sufficient to justify
any increase of the length of this paper, which is rather intended
to be an investigation of the theory of the voltaic pile than a
particular account of its practical application.

'Note. —Many of the views and experiments in this part of
my Experimental Researches will be seen at once to be correc¬
tions and extensions of the theory of electro-chemical decom-

^ The gradual increase in the action of the whole fifty pairs of plates was
due to the elevation of temperature in the weakly charged trough by the
passage of the current, in consequence of which the exciting energies of the
fluid within were increased.

position^, given in the third and fifth parts of these Researctic
The expressions I would now alter are those which conce;
the independence of the evolved elements in relation to tl
poles or electrodes, and the reference of their evolution •
powers entirely internal^ (260, 273, 397). The present pa,p
fully shows my present views; and I would refer to paragrap]
626, 639, 645, 652, 653, 682, 698, 743, 767, etc., as stating whj
they are. I hope this note will be considered as sufficient :
the way of correction at present; for I would rather def<
revising the whole theory of electro-chemical decompositic
until I can obtain clearer views of the way in which the pow<
under consideration can appear at one time as associated wit
particles giving them their chemical attraction, and at anotlic
as free electricity (229, 692).—M. F.

March 31,1834.

VIP

§ 9. ON THE SOURCE OF POWER IN THE VOLTAIC PILE.

EXCITING ELECTROLYTES, ETC., BEING CONDUCTORS O
THERMO AND FEEBLE CURRENTS. ^ ii. INACTIVE COIS
DUCTING CIRCLES CONTAINING AN ELECTROLYTIC FLXJir
^ iii. ACTIVE CIRCLES EXCITED BY SOLUTION OF SULPHUTRE'
OF POTASSIUM, ETC.

§ 9. On the Source of Power in the Voltaic Pile

78-11. What is the source of power in a voltaic pile? Tlii
question is at present of the utmost importance in the theory
and to the development of electrical science. The opinion
held respecting it are various; but by far the most importan-
are the two which respectively find the source of power ii
contact, and in chemical force. The question between then
touches the first principles of electrical action; for the opinion;
are in such contrast, that two men respectively adopting then
are thenceforward constrained to differ, in every point, respect¬
ing the probable and intimate nature of the agent or force or
which all the phenomena of the voltaic pile depend.

785. The theory of contact is the theory of Volta, the greai
discoverer of the voltaic pile itself, and it has been sustained
smce his day by a host of philosophers, amongst whom, in
^Sixteenth Series, original edition, vol. ii. p. 18.

Source of Power in the Voltaic Pile 233

recent timeS; rank such men as Pfaff^ Marianini^ Fechner,
Zamboni^ Matteucci^ Karsten^ Bouchardat; and as to the
excitement of the power, even Davy; all bright stars in the
exalted regions of science. The theory of chemical action was
first advanced by Fabroni/ Wollaston/ and Parrot/ and has
been more or less developed since by CErsted, Becquerel, De la
Rive, Ritchie, Pouillet, Schoenbein, and many others, amongst
whom Becquerel ought to be distinguished as having contri¬
buted, from the first, a continually increasing mass of the
strongest experimental evidence in proof that chemical action
always evolves electricity;^ and De la Rive should be named
as most clear and constant in his views, and most zealous in his
production of facts and arguments, from the year 1827 to the
present time.®

786. Examining this question by the results of definite
electro-chemical action, I felt constrained to take part with
those who believed the origin of voltaic power to consist in
chemical action alone (610, 700), and ventured a paper on it
in April, 1834 ® (610, etc.), which obtained the especial notice
of Marianini.'^ The rank of this philosopher, the observation
of Fechner,® and the consciousness that over the greater part
of Italy and Germany the contact theory still prevailed, have
induced me to re-examine the question most carefully. I
wished not merely to escape from error, but was anxious to
convince myself of the truth of the contact theory; for it was
evident that if contact electromotive force had any existence,
it must be a power not merely unlike every other natural power
as to the phenomena it could produce, but also in the far higher
points of limitation, definite force, and finite production (1053).

787. I venture to hope that the experimental results and
arguments which have been thus gathered may be useful to
science. I fear the detail will be tedious, but that is a neces¬
sary consequence of the state of the subject. The contact

1 A.D. 1792, 1799. Becquerel’s Traiie de VEleciricite, i. pp. 81-91, and
Nicholson’s Quarto Journal, iii. 308, iv. 120, or Journal de Physique, vi. 348.

^ A.D. 1801. Philosophical Transactions, 1801, p. 427.

® A.D. 1801. Annales de Chimie, 1S29, 45 5 1831, xlvi. 361.

^ A.D. 1824, etc. Annales de Chimie, 1824, xxv. 405; 1827, xxxv. 113;
1831, xlvi. 265, 276, 337; xlvii. 113; xlix. 131.

^ Ibid. 1828, xxxvii. 225; xxxix. 297; 1836, Ixii. 147: or Memoires de
Geneve, 1829, iv. 285; 1832, vi. 149; 1835, vii.

^Philosophical Transactions, 1834, p. 425.

’ Memorie della Societd Italiana in Modena, 1837, xxi. p. 205.

® Philosophical Magazine, 1838, xiii. 205; or Poggendorfs Annalen, xlii.
p. 481. Fechner refers also to Pfaff’s reply to my paper. I never cease to
regret that the German is a sealed language to me.

2 34 Faraday’s Researches

theory has long had possession of men’s minds^ is sustained by
a great weight of authority, and for years had almost undisputed
sway in some parts of Europe. If it be an error, it can only
be rooted out by a great amount of forcible experimental evi¬
dence ; a fact sufficiently clear to my mind by the circumstance,
that De la Rive’s papers have not already convinced the workers
upon this subject. Hence the reason why I have thought it
needful to add my further testimony to his and that of others,
entering into detail and multiplying facts in a proportion far
beyond any which would have been required for the proof and
promulgation of a new scientific truth (1005). In so doing I
may occasionally be only enlarging, yet then I hope strengthen¬
ing, what others, and especially De la Rive, have done.

788. It will tend to clear the question, if the various views

of contact are first stated. Volta’s theory is, that the simple
contact of conducting bodies causes electricity to be developed
at the point of contact without any change in nature of the
bodies themselves; and that though such conductors as water
and aqueous fluids have this property, yet the degree in which
they possess it is unworthy of consideration in comparison with
the degree to which it rises amongst the metals.^ The present
views of the Italian and German contact philosophers are, I
believe, generally the same, except that occasionally more im¬
portance is attached to the contact of the imperfect conductors
with the metals. Thus Zamboni (in 1837) considers the metallic
contact as the most powerful source of electricity, and not that '
of the metals with the fluids; ^ but Karsten, holding the con- '
tact theory, transfers the electromotive force to the contact of i
the fluids with the solid conductors.^ Marianini holds the same
view of the principle of contact, with this addition, that actual
contact is not required to the exertion of the exciting force,
but that the two approximated dissimiliar conductors may
affect each other’s state, when separated by sensible intervals |
of the ^<y^oo^^th of a line and more, air intervening.^ |

789. De la Rive, on the contrary", contends for simple tmd
strict chemical action, and, as far as I am aware, admits of no '
current in the voltaic pile that is not conjoined with and depen¬
dent upon a complete chemical effect. That admirable elec¬
trician Becquerel, though expressing himself with great caution,

^ Annales de Chimie, 1802, xl. p. 225.

^ Bibliotheque Universelle, 1836, v. 387; 1837, viii. 189.

3 1 'Institute No. 150. ;

^ Mem, della Soc. Ital. in Modena, 1837, xxi. 232-237,

The Contact Theory 235

seems to admit the possibility of chemical attractions being
able to produce electrical currents when they are not strong
enough to overcome the force of cohesion, and so terminate in
combination.^ Schoenbein states that a current may be pro¬
duced by a tendency to chemical action, i.e. that substances
which have a tendency to unite chemically may produce a
current, though that tendency is not followed up by the actual
combination of the substances.^ In these cases the assigned
force becomes the same as the contact of Volta, inasmuch as the
acting matters are not altered whilst producing the current.
Davy’s opinion was, that contact like that of Volta excited the
current or was the cause of it, but that chemical changes sup¬
plied the current. For myself I am at present of the opinion
which De la Rive holds, and do not think that, in the voltaic
pile, mere contact does anything in the excitation of the current,,
except as it is preparatory to, and ends in, complete chemical
action.

790. Thus the views of contact vary, and it may be said that
they pass gradually from one to another, even to the extent of
including chemical action: but the two extremes appear to me
irreconcilable in principle under any shape; they areas follows.

• The contact theory assumes that when two different bodies
being conductors of electricity are in contact, there is a force
at the point of contact by which one of the bodies gives a part
of its natural portion of electricity to the other body, which the
latter takes in addition to its own natural portion; that, though
the touching points have thus respectively given and taken
electricity, they cannot retain the charge which their contact
has caused, but discharge their electricities to the masses
respectively behind them (1055): that the force which, at the
point of contact, induces the particles to assume a new state,
cannot enable them to keep that state (1057): that all this
happens without any permanent alteration of the parts that
are in contact, and has no reference to their chemical forces
(1053,1057).

791. The chemical theory assumes that at the place of action
the particles which are in contact act chemically upon each
other and are able, under the circumstances, to throw more
or less of the acting force into a dynamic form (682, 732):
that in the most favourable circumstances, the whole is con-

1 Annales de Chimie, 1835, lx. 171; and Traiie de VElectricite, i. pp. 253,
258.

^Philosophical Magazine^ 1838, xii. 227, 311^ 314; also Bibliotheque
Univcrselle, 1838, xiv. 155, 395.

236 ^ Faraday’s Researches

verted into dynamic force (736): that then the amount of
current force produced is an exact equivalent of the original
chemical force employed; and that in no case (in the voltaic
pile) can any electric current be produced^ without the active
exertion and consumption of an equal amount of chemical force^
ending in a given amount of chemical change.

792. Marianini’s paper ^ was to me a great motive for
re-examining the subject; but the course I have taken was not so
much for the purpose of answering particular objections, as for
the procuring evidence, whether relating to controverted points
or not, which should be satisfactory to my own mind, open to
receive either one theory or the other. This paper, therefore, is
not controversial, but contains further facts and proofs of the
truth of De la Rive’s views. The cases Marianini puts are of
extreme interest, and all his objections must, one day, be
answered, when numerical results, both as to intensity and
quantity of force, are obtained; but they are all debatable,
and, to my mind, depend upon variations of quantity which
do not affect seriously the general question. Thus, when that
philosopher quotes the numerical results obtained by considering
two metals with fluids at their opposite extremities which tend
to form counter currents, the difference which he puts down to
the effect of metallic contact, either made or interrupted, I
think accountable for, on the facts partly known respecting
opposed currents; and with me differences quite as great, and
greater, have arisen, and are given in former papers (782), when
metallic contacts were in the circuit. So at page 213 of his
memoir, I cannot admit that e should give an effect equal to the
difference of b and d ; for in b and d the opposition presented to
the excited currents is merely that of a bad conductor, but in
the case of e the opposition arises from the power of an opposed
acting source of a current.

793. As to the part of his memoir respecting the action of
sulphuretted solutions,^ I hope to be allowed to refer to the
investigations made further on. I do not find, as the Italian
philosopher, that iron with gold or platina, in solution of the
sulphuret of potassa, is positive to them,® but, on the contrary,
powerfully negative, and for reasons given in the sequel (1037).

794. With respect to the discussion of the cause of the spark
before contact,^ Marianini admits the spark, but I give it up

^ Memorie della. Society Italiana in Modena^ 1827, xxi, p. 205.

^ Ibid, p, 217. 2 Ibid. p. 217. ^ Ibid. p. 225.

Investigation by the Galvanometer 237

altogether. Jacobi’s paper ^ convinces me I was in error as to
that proof of the existence of a state of tension m the metals
before contact (650^ 691). I need not therefore do more at
present than withdraw my own observations.

795. I now proceed to address myself to the general argument^
rather than to particular controversy^ or to the discussion of
cases feeble in power and doubtful in nature; for I have been
impressed from the first with the feeling that it is no weak
influence or feeble phenomenon that we have to account for,
but such as indicates a force of extreme power, requiring, there¬
fore, that the cause assigned should bear some proportion, both
in intensity and quantity, to the effects produced.

796. The investigations have all been made by aid of currents
and the galvanometer, for it seemed that such an instrument
and such a course were best suited to an examination of the
electricity of the voltaic pile. The electrometer is no doubt a
most important instrument, but the philosophers who do use it

a. zinc b in, c

copper

Fig. 64.

are not of accord in respect to the safety and delicacy of its
results. And even if the few indications as yet given by the
electrometer be accepted as correct, they are far too general to
settle the question of, whether contact or chemical action is the
exciting force in the voltaic battery. To apply that instrument
closely and render it of any force in supplying affirmative argu¬
ments to either theory, it would be necessary to construct a
table of contacts, or the effects of contacts, of the different
metals and fluids concerned in the construction of the voltaic
pile, taken in pairs (856), expressing in such table both the
direction and the amount of the contact force.

797. It is assumed by the supporters of the contact theory,
that though the metals exert strong electromotive forces at their
points of contact with each other, yet these are so balanced in a
metallic circuit that no current is ever produced whatever their
arrangement may be. So in fig. 64, if the contact force of copper
and zinc is 10 —and a third metal be introduced at m, the
effect of its contacts, whatever that metal may be, with the zinc
^ Philosophical Magazine^ 183S, xiii. 401*

- ' . ..—

238 Faraday’s Researches

and copper at b and c, will be an amount of force in the opposite
direction=io. Thus^ if it were potassium^ its contact force
at h might be 5 —but then its contact force at c would be

—15: or if it were gold^ its contact force at b might be ^—19,
but then its contact force at c would be 9 —This is a very ;

large assumption, and that the theory may agree with the facts ^

is necessary: still it is, I believe, only an assumption, for I am |

not aware of any data, independent of the theory in question, !

which prove its truth.

798. On the other hand, it is assumed that fluid conductors,

and such bodies as contain water, or, in a word, those which I
have called electrolytes (400, 558, 656), either exert no contact !

force at their place of contact with the metals, or if they do :

exert such a power, then it is with this most important difference, i

that the forces are not subject to the same law of compensation

or neutralisation in the complete circuit, as holds with the ;
metals (797). But this, I think I am justified in saying, is an
assumption also, for it is supported not by any independent
measurement or facts (796), but only by the theory which it is '
itself intended to support. 1

799. Guided by this opinion, and with a view to ascertain |

what is, in an active circle, effected by contact and what by ,

chemical action, I endeavoured to find some bodies in this latter ,

class (798), which should be without chemical action on the
metals employed, so as to exclude that cause of a current, and

yet such good conductors of electricity as to show any currents
due to the contact of these metals with each other or with the
fluid: concluding that any electrolyte which would conduct ;
the thermo current of a single pair of bismuth and antimony I
plates would serve the required purpose, I sought for such, and
fortunately soon found them.

^ i. Exciting Electrolytes^ etc.^ being Conductors of Thermo

and Feeble Currents ;

800. Sulphuret of potassium. —This substance and its solution |

were prepared as follows. Equal weights of caustic potash j

(potassa fusa) and sulphur were mixed with and heated gradually 1

in a Florence flask, till the whole had fused and united, and the ;

sulphur in excess began to sublime. It was then cooled and dis- i

solved in water, so as to form a strong solution, which by j

standing became quite clear. ^ i

801. A portion of this solution was included in a circuit '

containing a galvanometer and a pair of antimony and bismuth |

Electrolytes Good Conductors 239

plates; the connection with the electrolyte was made by two
platinum plates^ each about two inches long and half an inch
wide: nearly the whole of each was immersed, and they were
about half an inch apart. When the circuit was completed^
and all at the same temperature, there was no current; but the
moment the junction of the antimony and bismuth was either
heated or cooled, the corresponding thermo current was pro
duced, causing the galvanometer-needle to be permanently
deflected, occasionally as much as 8o°. Even the small dif¬
ference of temperature occasioned by touching the Seebeck
element with die finger, produced a very sensible current
through the electrolyte. When in place of the antimony-
bismuth combination mere wires of copper and platmum, or iron
and platinum were used, the application of the spirit-lamp to
the junction of these metals produced a thermo current which
instantly travelled round the circuit.

802. Thus this electrolyte will, as to high conducting power,
fully answer the condition required (799). It is so excellent in
this respect, that I was able to send the thermo current of a
single Seebeck’s element across five successive portions con¬
nected with each other by platinum plates.

803. Nitrous acid .—^Yellow anhydrous nitrous acid, made
by distilling dry nitrate of lead, being put into a glass tube and
included in a circuit with the antimony-bismuth arrangement
and the galvanometer, gave no indication of the passage of the
thermo current, though the immersed electrodes consisted each
of about four inches in length of moderately thick platinum
wire, and were not above a quarter of an inch apart.

804. A portion of this acid was mixed with nearly its volume
of pure water; the resulting action caused depression of tem¬
perature, the evolution of some nitrous gas, the formation of
some nitric acid, and a dark green fluid was produced. This
was now such an excellent conductor of electricity that almost
the feeblest current could pass it. That produced by Seebeck’s
circle was sensible when only one-eighth of an inch in length
of the platinum wires dipped in the acid. When a couple of
inches of each electrode was in the fluid, the conduction was
so good that it made very little difference at the galvanometer
whether the platinum wires touched each other in the fluid or
were a quarter of an inch apart.^

^ De la Rive has pointed out the facility with which an electric current
passes between platinum and nitrous acid .—Annales de Chimie, 1828,
xxxvii. 278.

240 Faraday’s Researches

805. Nitric acid. —Some pure nitric acid was boiled to drive
off all the nitrous acid, and then cooled. Being included in
the circuit by platinum plates (801), it was found to conduct
so badly that the effect of the antimony-bismuth pair, when
the difference of temperature was at the greatest, was scarcely
perceptible at the galvanometer.

806. On using a pale yellow acid, otherwise pure, it was
found to possess rather more conducting power than the former.
On employing a red nitric acid, it was found to conduct the
thermo current very well. On adding some of the green nitrous
acid (804) to the colourless nitric acid, the mixture acquired
high conducting powers. Hence it is evident that nitric acid
is not a good conductor when pure, but that the presence of
nitrous acid in it (conjointly probably with water) gives it this
power in a very high degree amongst electrolytes.^ A very
red strong nitric acid, and a weak green acid (consisting of one
volume strong nitric acid and two volumes of water, which had
been rendered green by the action of the negative platinum
electrode of a voltaic battery), were both such excellent con¬
ductors that the thermo current could pass across five separate
portions of them connected by platinum plates, with so little
retardation, that I believe twenty interruptions would not have
stopped this feeble current.

807. Sulphuric acid .—Strong oil of vitriol, when between
platinum electrodes (801), conducted the antimony-bismuth
thermo current sensibly, but feebly. A mixture of two volumes
acid and one volume water conducted much better, but not
nearly so well as the two former electrolytes (802, 804). A
mixture of one volume of oil of vitriol and two volumes saturated
solution of sulphate of copper conducted this feeble current very
fairly.

Potassa.—A strong solution of caustic potassa, between
platinum plates, conducted the thermo current sensibly, but
very feebly.

808. I will take the liberty of describing here, as the most
convenient i)lacc, other results relating to the conducting power
of bodies, wiiich will be required hereafter in these investiga-
ihm. (ialena, yellow sulphuret of iron, arsenical pyrites, native
sulphuret of copper and iron, native grey artificial sulphuret of

1 Sch(rub<‘in’s experiments on a compound of nitric and nitrous acids
will prubahly b(‘ar upon and illustrate this subject.— Btbliotheqtie Umver-
1H17, -"i"' 406.

Inactive Conducting Circles 241

copper, sulphurets of bismuth, iron, and copper, globules of
oxide of burnt iron, oxide of iron by heat or scale oxide, con¬
ducted the thermo current very well. Native peroxide of
manganese and peroxide of lead conducted it moderately well.

809. The following are bodies, in some respect analogous in
nature and composition, which did not sensibly conduct this
weak current when the contact surfaces were small:—artificial
grey sulphuret of tin, blende, cinnabar, haematite, Elba iron-
ore, native magnetic oxide of iron, native peroxide of tin or
tinstone, wolfram, fused and cooled protoxide of copper, per¬
oxide of mercury.

810. Some of the foregoing substances are very remarkable
in their conducting power. This is the case with the solution
of sulphuret of potassium (8oi) and the nitrous acid (804), for
the great amount of this power. The peroxide of manganese
and lead are still more remarkable for possessing this power,
because the protoxides of these metals do not conduct either the
feeble thermo current or a far more powerful one from a voltaic
battery. This circumstance made me especially anxious to
verify the point with the peroxide of lead. I therefore prepared
some from red-lead by the action of successive portions of nitric
acid, then boiled the brown oxide, so obtained, in several por¬
tions of distilled water, for days together, until every trace of
nitric acid and nitrate of lead had been removed; after which
it was well and perfectly dried. Still, when a heap of it in
powder, and consequently in very imperfect contact throughout
its own mass, was pressed between two plates of platinum and
so brought into the thenno-electric circuit (801), the current
was found to pass readily.

II ii. Inactive Condiicling Circles containing a Fluid or Electrolyte

811. De la Rive has already quoted the case of potash, iron
and platina,^ to show that where there was no chemical action
there was no current. My object is to increase the number of
such cases; to use other fluids than potash, and such as have
good conducting power for weak currents; to use also strong
and weak solutions; and thus to accumulate the conjoint
experimental and argumentative evidence by which the great
question must finally be decided.

812. I first used the sulphuret of potassium as an electrolyte
of good conducting power, but chemically inactive (799) when

^Philosophical Magazine, 1837, xi. 275.

Q

Faraday’s Researches

ylodtimjaru

j>2cdinza?v

242

associated with iron and platinum in a circuit. The arrange¬
ment is given in fig. 65, where D, E represent two test-glasses
containing the strong solution of sulphuret of potassium (800);
and also four metallic plates^ about 0.5 of an inch wide and
two inches long in the immersed part^ of which the three marked
cc P; Pj P were platinum,

and that marked I, of
clean iron: these were
connected by iron and
platinum wires, as in
fig. 65, a galvanometer
being introduced at G.
In this arrangement there
were three metallic con¬
tacts of platinum and
iron, b, and x; the first
two, being opposed to
each other, may be con¬
sidered as neutralising
each other’s forces; but
the third, being unop¬
posed by any other
metallic contact, can be compared with either the difference
of a and b when one is warmer than the other, or with itself
when in a heated or cooled state (818), or with the force of
chemical action when any body capable of such action is
introduced there (819).

^813. When this arrangement is completed and in order, there
is”|absolutely no current circulating through it, and the galvano¬
meter-needle rests at 0°; yet is the whole circuit open to a very
feeble current, for a difference of temperature at any one of
the junctions a, b, or causes a corresponding thermo current,
which is instantly detected by the galvanometer, the needle
standing permanently at 30° or 40°, or even 50°.

814. But to obtain this proper and normal state, it is neces¬
sary that certain precautions be attended to. In the first
place, if the circuit be complete in every part except for the
immcnsion of the iron and platinum plates into the cup D, then,
upon their introduction, a current will be produced directed
from the platinum (which appears to be positive) through the
solution to the iron; this will continue perhaps five or ten
minutes, or if the iron has been carelessly cleaned, for several
hours; it is due to an action of the sulphuretted solution on

Inactive Conducting Circles 243

oxide of iron, and not to any effect on the metallic iron; and
when it has ceased^ the disturbing cause may be considered as
exhausted. The experimental proofs of the truth of this
explanation I will quote hereafter (1037).

815. Another precaution relates to the effect of accidental
movements of the plates in the solution. If two platinum
plates be put into a solution of this sulphuret of potassium, and
the circuit be then completed, including a galvanometer, the
arrangement, if perfect, will show no current; but if one of the
plates be lifted up into the air for a few seconds and then re¬
placed, it will be negative to the other, and produce a current
lasting for a short time.^ If the two plates be iron and plati¬
num, or of any other metal or substance not acted on by the
sulphuret, the same effect will be produced. In these cases,
the current is due to the change wrought by the air on the film
of sulphuretted solution adhering to the removed plate; ^ but
a far less cause than this will produce a current, for if one of
the platinum plates be removed, washed well, dried, and even
heated, it will, on its re-introduction, almost certainly exhibit
the negative state for a second or two.

816. These or other disturbing causes appear the greater in
these experiments in consequence of the excellent conducting
power of the solution used; but they do not occur if care be
taken to avoid any disturbance of the plates or the solution, and
then, as before said, the whole acquires a normal and perfectly
inactive state.

817. Here then is an arrangement in which the contact of
platinum and iron at is at liberty to produce any effect which
such a contact may have the power of producing; and yet what
is the consequence.? absolutely nothing. This is not because
the electrolyte is so bad a conductor that a current of contact
cannot pass, for currents far feebler than this is assumed to
be pass readily (801); and the electrolyte employed is vastly
superior in conducting power to those which are commonly
used in voltaic batteries or circles, in which the current is still
assumed to be dependent upon contact. The simple conclusion
to which the experiment should lead is, in my opinion, that
the contact of iron and platinum is absolutely without any
electromotive force (823, 847, 877).

^ Marianini observed effects of this kind produced by exposure to the air, of
one of two plates dipped in nitric acid .—Annales de Chimie, 1830, xlv. p. 42.

^ Becquerel long since referred to the effect of such exposure of a plate,
dipped in certain solutions, to the air. Generally the plate so exposed
became positive on reimmersion .—Annales de Chimie, 1824, xxv. 405*

244 Faraday’s Researches

8 18. If the contact be made really active and effective^
according to the beautiful discovery of Seebeck, by making its
temperature different to that of the other parts of the circuity
then its power of generating a current is shown (812). This
enables us to compare the supposed power of the mere contact
with that of a thermo contact; and we find that the latter
comes out as infinitely greater than the former^ for the former
is nothing. The same comparison of mere contact and thermo
contact may be made by contrasting the effect of the contact c
at common temperatures, with either the contact at a or at h,
either heated or cooled. Very moderate changes of tempera¬
ture at these places produce instantly the corresponding current,
but the mere contact at does nothing.

819. So also I believe that a true and philosophic and even
rigid comparison may be made at x, between the assumed effect
of mere contact and that of chemical action. For if the metals
at be separated, and a piece of paper moistened in dilute acid,
or a solution of salt, or if only the tongue or a wet finger be
applied there, then a current is caused, stronger by far than
the thermo currents before produced (818), passing from the
iron through the introduced acid or other active fluid to the
platinum. This is a case of current from chemical action with¬
out any metallic contact in the circuit on which the effect can
for a moment be supposed to depend (614); it is even a case
where metallic contact is changed for chemical action, with
the result that where contact is found to be quite ineffectual,
chemical action is very energetic in producing a current.

820. It is of course quite unnecessary to say that the same
experimental comparisons may be made at either of the other
contacts, aor b.

821. Admitting for the moment that the arrangement proves
that the contact of platinum and iron at has no electromotive
force (823, 847), then it follows also that the contact of either
platinum or iron with any other metal has no such force. For
if another metal, as zinc, be interposed between the iron and
platinum at x, fig, 65, no current is produced; and yet the test
application of a little heat at <2 or ^ will show by the corre¬
sponding current that the circuit being complete will conduct
any current that may tend to pass. Now that the contacts
of zinc with iron and with platinum are of equal electromotive
force is not for a moment admitted by those who support the
theory of contact activity; we ought therefore to have a result¬
ing action equal to the differences of the two forces, producing

Contact of Metals Perfectly Passive 245

a certain current. No such current is produced; and I conceive;
with the admission above; that such a result proves that the
contacts iron-zinc and platinum-zinc are entirely without
electromotive force.

822. Gold; silver; potassium; and copper were introduced
at X with the like negative effect; and so no doubt might every
other metal; even according to the relation admitted amongst
the metals by the supporters of the contact theory (797). The
same negative result followed upon the introduction of many
other conducting bodies at the same place; aS; for instance;
those already mentioned as easily conducting the thermo
current (808); and the effect proveS; I think; that the contact
of any of these with either iron or platinum is utterly ineffective
as a source of electromotive force.

823. The only answer which; as it appears to me, the contact
theory can set up in opposition to the foregoing facts and
conclusions is to say that the solution of sulphuret of potassium
in the cup D, fig. 65; acts as a metal would do (797); and so the
effects of all the contacts in the circuit are exactly balanced.
I will not stop at this moment to show that the departure with
respect to electrolytes; or the fluid bodies in the voltaic pile;
from the law which is supposed to hold good with the metals
and solid conductors; though only an assumption; is still essential
to the contact theory of the voltaic pile (798; 849); ^ nor to
prove that the electrolyte is no otherwise like the metals than
in having no contact electromotive force whatever. But be¬
lieving that this will be very evident shortly; I will go on with
the experimental results; and resume these points hereafter
(847,877).

824. The experiment was now repeated with the substitution
of a bar of nickel for that of iron; fig. 65 (812); all other things
remaining the same.^ The circuit was again found to be a good
conductor of a feeble thermo current; but utterly inefficient as
a voltaic circuit when all was at the same temperature; and due
precautions taken (1039). The introduction of metals at the

^ See Fechner’s words .—Philosophical Magazine, 1838, xiii. 377.

® There is another form of this experiment which I sometimes adopted,
in which the cup E, fig. 65, with its contents, was dismissed, and the
platinum plates in it connected together. The arrangement may then be
considered as presenting three contacts of iron and platinum, two acting
in one direction, and one in the other. The arrangement and the results
are virtually the same as those already given. A still simpler but equally
conclusive arrangement for many of the arguments, is to dismiss the iron
between a and h altogether, and so have but one contact, that at jv, to
consider.

. . . . I

246 Faraday’s Researches

contact was as ineffective as before (822); the introduction '
of chemical action at .v was as striking in its influence as in the
former case (8ig); all the results were, in fact, parallel to those
already obtained; and if the reasoning then urged was good, it
will now follow that the contact of platinum and nickel with |
each other, or of either with any of the different metals or solid i
conductors introduced at x, is entirely without electromotive |
force.^ I

825. Many other pairs of metals were compared together in '

the same manner; the solution of sulphuret of potassium con- ,

necting them together at one place, and their mutual contact |

doing that office at another. The following are cases of this |

kind: iron and gold; iron and palladium; nickel and gold; ;

nickel and palladium; platina and gold; platina and palladium. j

In all these cases the results were the same as those already |

given with the combinations of platinum and iron. |

826. It is necessary that due precaution be taken to have |

the arrangements in an unexceptionable state. It often hap- !

pened that the first immersion of the plates gave deflections; |

it is, in fact, almost impossible to put two plates of the same |

metal into the solution without causing a deflection; but this !

generally goes off very quickly, and then the arrangement may |

be used for the investigation (814). Sometimes there is a |

feeble but rather permanent deflection of the needle; thus when 1

platinum and palladium were the metals, the first effect fell and
left a current able to deflect the galvanometer-needle 3®, indi¬
cating the platinum to be positive to the palladium. This effect '
of 3®, however, is almost nothing compared to what a mere
thermo current can cause, the latter producing a deflection of
60° or more; besides which, even supposing it an essential effect j

of the arrangement, it is in the wrong direction for the contact |

theory. I rather incline to refer it to that power which platinum j

and other substances have of effecting combination and decom- i

position without themselves entering into union; and I have '

occasionally found that when a platinum plate has been left for
some hours in a strong solution of sulphuret of potassium (800) '

a small quantity of sulphur has been deposited upon it. What- ,
ever the cause of the final feeble current may be, the effect is

^ One specimen of nickel was, on its immersion, positive to platinum for '
seven or eight minutes, and then became neutral. On taking it out it
seemed to have a yellowish tint on it, as if invested by a coat of sulphuret;
and I suspected this piece had acted like lead (873) and bismuth (883). '

It is diffi-cult to get pure and also perfectly compact nickel; and if porous,
then the matter retained in the pores produces currents.

Inactive Voltaic Circles

247

too small to be of any service in support of the contact theory;
while, on the other hand, it affords delicate, and, therefore,
strong indications in favour of the chemical theory.

827. A change was made in the form and arrangement of
the cup D, fig- 65, so as to allow of experiments with other bodies
than the metals. The solution of
sulphuret of potassium was placed
in a shallow vessel, the platinum
plate was bent so that the immersed
extremity corresponded to the bot¬
tom of the vessel; on this a piece
of loosely folded cloth was laid in
the solution, and on that again the
mineral or other substance to be
compared with the platinum; the
fluid being of such depth that only part of that substance was
in it, the rest being clean and dry; on this portion the platinum
wire, which completed the circuit, rested. The arrangement
of this part of the circuit is given in section at fig. 66, where H
represents a piece of galena to be compared with the platinum P.

828. In this way galena, compact yellow copper pyrites,
yellow iron pyrites, and globules of oxide of burnt iron, were
compared with platinum (the solution of sulphuret of potassium
being the electrolyte used in the circuit), and with the same
results as were before obtained with metals (817, 821).

829. Experiments hereafter to be described gave arrange¬
ments in which, with the same electrolyte, sulphuret of lead was
compared with gold, palladium, iron, nickel, and bismuth (873,
874); also sulphuret of bismuth with platinum, gold, palladium,
iron, nickel, lead, and sulphuret of lead (882), and always with
the same result. Where no chemical action occurred there
no current was formed; although the circuit remained an
excellent conductor, and the contact existed by which, it is
assumed in the contact theory, such a current should be
produced.

830. Instead of the strong solution, a dilute solution of the
yellow sulphuret of potassium, consisting of one volume of strong
solution (800) and ten volumes of water, was used. Plates
of platinum and iron were arranged in this fluid as before
(812): at first the iron was negative (1037), but in ten minutes
it was neutral, and the needle at o. Then a weak chemical
current excited at (819) easily passed: and even a thermo
current (818) was able to show its effects at the needle. Thus

248 Faraday’s Researches

a strong or weak solution of this electrolyte showed the same
phenomena.^ By diluting the solution still further, a fluid
could be obtained in which the iron was, after the first effect,
permanently but fe bly positive. On allowing time, however,
it was found that in all such cases black sulphuret formed here
and there on the iron. Rusted iron was negative to platinum
(1037) in this very weak solution, which by direct chemical
action could render metallic iron positive.

831, In all the preceding experiments the electrolyte used
has been the sulphuret of potassium solution; but I now
changed this for another, very different in its nature, namely,
the green nitrous acid (804), which has already been shown to
be an excellent conductor of electricity. Iron and platinum
were the metals employed, both being in the form of wires.
The vessel in which they were immersed was a tube like that
formerly described (803); in other respects the arrangement
was the same in principle as those already used (812, 824).
The first effect was the production of a current, the iron being
positive in the acid to the platina; but this quickly ceased, and
the galvanometer-needle came to 0°. In this state, however,
the circuit could not in all things be compared with the one
having the solution of sulphuret of potassium for its electrolyte
(812); for although it could conduct the thermo current of
antimony and bismuth in a certain degree, yet that degree was
very small compared to the power possessed by the former
arrangement, or to that of a circle in which the nitrous acid was
between two platinum plates (804). This remarkable retarda¬
tion is consequent upon the assumption by the iron of that
peculiar state which Schoenbein has so well described and illus¬
trated by his numerous experiments and investigations. But
though it must be admitted that the iron in contact with the
acid is in a peculiar state (939, 989, 1021), yet it is also evident
that a circuit consisting of platinum, iron, peculiar iron, and
nitrous acid, does not cause a current though it have sufficient
conducting power to carry a thermo current.

832. But if the contact of platinum and iron has an electro¬
motive force, why does it not produce a current ? The applica¬
tion of heat (818), or of a little chemical action (819) at the
place of contact, does produce a current, and in the latter case

^ Care was taken in these and the former similar cases to discharge the
platinum surface of any reacting force it might acquire from the action of
the previous current, by separating it from the other metals, and touching
it in the liquid for an instant with another platinum plate.

Inefficiency of Contact 249

a strong one. Of if any other of the contacts in the arrange-
naent can produce a current^ why is not that shown by some
corresponding effect? The only answers are^ to say^ that the
peculiar iron has the same electromotive properties and relations
as platinum, or that the nitrous acid is included under the
same law with the metals (797, 823); and so the sum of the
effects of all the contacts in the circuit is nought, or an exact
balance of forces. That the iron is like the platinum in having
no electromotive force at its contacts without chemical action,
I believe; but that it is unlike it in its electrical relations, is
evident from the difference between the two in strong nitric
acid, as well as in weak acid; from their difference in the
power of transmitting electric currents to either nitric acid or
sulphuret of potassium, which is very great; and also by other
differences. That the nitrous acid is, as to the power of its
contacts, to be separated from other electrolytes and classed
with the metals in what is, with them, only an assumption, is a
gratuitous mode of explaining the difficult}^, which will come
into consideration, with the case of sulphuret of potassium,
hereafter (823, 847, 877, 1048).

833. To the electro-chemical philosopher, the case is only
another of the many strong instances, showing that where
chemical action is absent in the voltaic circuit, there no current
can be formed; and that whether solution of sulphuret of potas¬
sium or nitrous acid be the electrolyte or connecting fluid
used, still the results are the same, and contact is shown to be
inefficacious as an active electromotive condition.

834. I need not say that the introduction of different metals
between the iron and platinum at their point of contact, pro¬
duced no difference in the results (821, 822) and caused no
current; and I have said that heat and chemical action applied
there produced their corresponding effects. But these parallels
in action and non-action show the identity in nature of this
circuit (notwithstanding the production on the surface of peculiar
iron on that metal), and that with solution of sulphuret of
potassium: so that all the conclusions drawn from it apply
here; and if that case ultimately stand firm as a proof against
the theory of contact force, this will stand also.

835. I now used oxide of iron and platinum as the extremes
of the solid part of the circuit, and the nitrous acid as the fluid;
i.e. I heated the iron wire in the flame of a spirit-lamp, cover¬
ing it with a coat of oxide in the manner recommended by
Schoenbein in his investigations, and then used it instead of

250 Faraday’s Researches i

the clean iron (831). The oxide of iron was at first in the
least degree positive, and then immediately neutral. This >

circuit, then, like the former, gave no current at common '
temperatures; but it differed much from it in conducting power,
being a very excellent conductor of a thermo current, the oxide j

of iron not offering that obstruction to the passage of the j

current which the peculiar iron did (831, 832). Hence scale j
'oxide of iron and platinum produce no current by contact, the j
third substance in the proof circuit being nitrous acid; and so
the result agrees with that obtained in the former case, where
that third substance was solution of sulphuret of potassium. |

836. In using nitrous acid it is necessary that certain pre- >

cautions be taken, founded on the following effect. If a circuit ;
be made with the green nitrous acid, platinum wires, and a |
galvanometer, in a few seconds all traces of a current due to
first disturbances will disappear; but if one wire be raised into !

the air and instantly returned to its first position, a current is i

formed, and that wire is negative, across the electrolyte, to the |

other. If one wire be dipped only a small distance into the |

acid, as for instance one-fourth of an inch, then the raising that |

wire not more than one-eighth of an inch and instantly restoring j

it, will produce the same effect as before. The effect is due ;

to the evaporation of the nitrous acid from the exposed wire |

(925). I may perhaps return to it hereafter, but wish at present I

only to give notice of the precaution that is required in con¬
sequence, namely, to retain the immersed wires undisturbed
during the experiment.

837. Proceeding on the facts made known by Schoenbein
respecting the relation of iron and nitric acid, I used that acid
as the fluid in a voltaic current formed with iron and platinum.
Pure nitric acid is so deficient in conducting power (805) that ;
it may be supposed capable of stopping any current due to
the effect of contact between the platinum and iron; and it

is further objectionable in these experiments, because, acting
feebly on the iron, it produces a chemically excited current, ;
which may be considered as mingling its effect with that of
contact: whereas the object at present is, by excluding such
chemical action, to lay bare the influence of contact alone.

Still the results with it are consistent with the more perfect i
ones already described; for in a circuit of iron, platinum, and
nitric acid, the joint effects of the chemical action on the iron
and the contact of iron and platinum, being to produce a current

Nitrous Acids

251

of a certain constant force indicated by the galvanometer^ a
little chemical action^ brought into play where the iron and
platinum were in contact as before (819X produced a current
far stronger than that previously existing. If then^ from the
weaker current^ the part of the effect due to chemical action
be abstracted; how little room is there to suppose that any
effect is due to the contact of the metals!

838. But a red nitric acid with platinum plates conducts a
thermo current well; and will do so even when considerably
diluted (806). When such red acid is used between iron and
platinum; the conducting power is such; that one half of the
permanent current can be overcome by a counter thermo
current of bismuth and antimony. Thus a sort of comparison is
established between a thermo current on the one hand; and a
current due to the joint effects of chemical action on iron and
contact of iron and platinum on the other. Now considering
the admitted weakness of a thermo current; it may be judged
what the strength of that part of the second current due to
contact can at the utmost be; and how little it is able to
account for the strong currents produced by ordinary voltaic
combinations.

839. If for a clean iron wire one oxidised in the flame of a
spirit-lamp be used; being associated with platinum in pure
strong nitric acid; there is a feeble current; the oxide of iron
being positive to the platinum; and the facts mainly as with
iron. But the further advantage is obtained of comparing the
contact of strong and weak acid with this oxidised wire. If
one volume of the strong acid and four volumes of water be
mixed; this solution may be used; and there is even less deflec¬
tion than with the strong acid: the iron side is now not sensibly
active; except the most delicate means be used to observe
the current. Yet in both cases if a chemical action be intro¬
duced in place of the contact; the resulting current passes well;
and even a thermo current can be made to show itself as more
powerful than any due to contact.

840. In these cases it is safest to put the whole of the oxidised
iron under the surface and connect it in the circle by touching
it with a platinum wire; for if the oxidised iron be continued
through from the acid to the air; it is almost certain to suffer
from the joint action of the acid and air at their surface of
contact.

841. I proceeded to use a fluid differing from any of the

2§2 Faraday’s Researches

former: this was solution of potassa, which has already been
employed by De la Rive (8ii) with iron and platina^ and which ,
when strong has been found to be a substance conducting so
well;, that even a thermo current could pass it (807), and there¬
fore fully sufficient to show a contact current, if any such |
exists.

842. Yet when a strong solution of this substance was ar- |

ranged with silver and platinum (bodies differing sufficiently ;
from each other when connected by nitric or muriatic acid), as |
in the former cases, a very feeble current was produced, and
the galvanometer-needle stood nearly at zero. The contact of
these metals therefore did not appear to produce a sensible
current; and, as I fully believe, because no electromotive power
exists in such contact. When that contact was exchanged for |

a very feeble chemical action, namely, that produced by inter- I

posing a little piece of paper moistened in dilute nitric acid i

(819), a current was the result. So here, as in the many former !

cases, the arrangement with a little chemical action and no !

metallic contact produces a current, but that without the
chemical action and with the metallic contact produces none. !

843. Iron or nickel associated with platinum in this strong 1

solution of potassa was positive. The force of the produced I

current soon fell, and after an hour or so was very small. Then I

annulling the metallic contact at x, fig. 65, and substituting ■

a feeble chemical action there, as of dilute nitric acid, the :

current established by the latter would pass and show itself. |

Thus the cases are parallel to those before mentioned (837, etc.),
and show how little contact alone could do, since the effect of ;
the conjoint contact of iron and platinum and chemical action

of potash and iron were very small as compared with the con¬
trasted chemical action of the dilute nitric acid.

844. Instead of a strong solution of potassa, a much weaker |

one consisting of one volume of strong solution and six volumes '
of water was used, but the results with the silver and platinum
were the same: no current was produced by the metallic con¬
tact as long as that only was left for exciting cause, but on
substituting a little chemical action in its place (819), the
current was immediately produced. !

845. Iron and nickel with platinum in the weak solution also ;
produced similar results, except that the positive state of these '
metals was rather more permanent than with the strong solu- '
tion. Still it was so small as to be out of all proportion to <
what was to be expected according to the contact theory.

Inefficiency of Contact of Electrolytes 253

846. Thus these different contacts of metals and other well¬
conducting solid bodies prove utterly inefficient in producing a
current^ as well when solution of potassa is the third or fluid
body in the circuit; as when that third body is either solution
of sulphuret of potassium; or hydrated nitrous acid; or nitric
acid; or mixed nitric and nitrous acids. Further; all the argu¬
ments respecting the inefficacy of the contacts of bodies inter¬
posed at the junction of the two principal solid substances^
which were advanced in the case of the sulphuret of potassium
solution (821); apply here with potassa; as they do indeed in
every case of a conducting circuit where the interposed fluid is
without chemical action and no current is produced. If a case
could be brought forward in which the interposed fluid is with¬
out action; is yet a sufficiently good conductor; and a current is
produced; then; indeed; the theory of contact would find evi¬
dence in its favour; which; as far as I can perceive; could not
be overcome. I have most anxiously sought for such a case^
but cannot find one (786).

847. The argument is now in a fit state for the resumption
of that important point before adverted to (823; 832); which;
if truly advanced by an advocate for the contact theory; would
utterly annihilate the force of the previous experimental results,
though it would not enable that theory to give a reason for the
activity of, and the existence of a current in, the pile; but
which; if in error, would leave the contact theory utterly
defenceless and without foundation.

848. A supporter of the contact theory may say that the
various conducting electrolytes used in the previous experi¬
ments are like the metals; i.e. that they have an electromotive
force at their points of contact with the metals and other solid
conductors employed to complete the circuit; but that this is
of such consistent strength at each place of contact, that, in a
complete circle, the sum of the forces is o (797). The actions
at the contacts are tense electromotive actions, but balanced,
and so no current is produced. But what experiment is there
to support this statement? where are the measured electro¬
motive results proving it (796)? I believe there are none.

849. The contact theory, after assuming that mere contacts
of dissimilar substances have electromotive powers, further
assumes a difference between metals and liquid conductors (798)
without which it is impossible that the theory can explain the
current in the voltaic pile: for whilst the contact effects in a

254 Faraday’s Researches

metallic circuit are assumed to be always perfectly balanced; it
is also assumed that the contact effects of the electrolytes or
interposed fluid with the metals are not balanced; but are so
far removed from anything like an equilibrium; as to produce
most powerful currents; even the strongest that a voltaic pile
can produce. If sO; then why should the solution of sulphuret
of potassium be an exception? it is quite unlike the metals:
it does not appear to conduct without decomposition; it is an
excellent electrolyte; and an excellent exciting electrolyte in
proper cases (868); producing most powerful currents when it
acts chemically; it is in all these points quite unlike the metalS;
and; in its action; like any of the acid or saline exciting electro¬
lytes commonly used. How then can it be allowed that; with¬
out a single direct experiment; and solely for the purpose of
avoiding the force of those which are placed in opposition; we
should suppose it to leave its own station amongst the elec-
trol3d:eS; and class with the metals; and that toO; in a point of
character; which; even with them; is as yet a mere assumption

(797)?

850. But it is not with the sulphuret of potassium alone that
this freedom must be allowed; it must be extended to the
nitrous acid (831; 835); to the nitric acid (837; etc.); and even
to the solution of potash (842); all these being of the class of
electrolytes; and yet exhibiting no current in circuits where
they do not occasion chemical action. Further; this exception
must be made for weak solutions of sulphuret of potassium (830)
and of potassa (844); for they exhibit the same phenomena as
the stronger solutions. And if the contact theorists claim it
for these weak solutions; then how will they meet the case of
weak nitric acid which is not similar in its action on iron to
strong nitric acid (965); but can produce a powerful current?

851. The chemical philosopher is embarrassed by none of
these difficulties; for he first; by a simple direct experiment;
ascertains whether any of the two given substances in the
circuit are active chemically on each other. If they are; he
expects and finds the corresponding current; if they are not;
he expects and he finds no current, though the circuit be a
good conductor and he look carefully for it (817).

852. Again; taking the case of iron, platina, and solution
of sulphuret of potassium, there is no current; but for iron
substitute zinc, and there is a powerful current. I might for
zinc substitute copper, silver, tin, cadmium, bismuth, lead, and
other metals; but I take zinc, because its sulphuret dissolves

Contact Contradictions 255

and is carried off by the solution, and so leaves the case in a
very simple state; the fact, however, is as strong with any of
the*" other metals. Now if the contact theory be true, and if
the iron, platina, and solution of sulphuret of potassium give
contacts which are in perfect equilibrium as to their electro^
motive force, then why does changing the iron for zinc destroy
the equilibrium ? Changing one metal for another in a metallic
circuit causes no alteration of this kind: nor does changing one
substance for another among the great number of bodies which,
as solid conductors, may be used to form conducting (but
chemically inactive) circuits (855, etc.). If the solution of
sulphuret of potassium is to be classed with the metals as to its
action in the experiments I have quoted (813, etc.), then, how
comes it to act quite unlike them, and with a po^^ftr equal to
the best of the other class, in the new case; of zinc, copper,
silver, etc. (870, 873, etc.)?

853. This difficulty, as I conceive, must be met, on the part
of the contact theorists, by a new assumption, namely, that this
fluid sometimes acts as the best of the metals, or first class of
conductors, and sometimes as the best of the electrolytes or
second class. But surely this would be far too loose a method
of philosophising in an experimental science (857); and further,
it is most unfortunate for such an assumption, that this second
condition or relation of it never comes on by itself, so as to give
us a pure case of a current from contact alone; it never comes
on without that chemical action to which the chemist so simply
refers all the current which is then produced.

854. It is unnecessary for me to say that the same argument
applies with equal force to the cases where nitrous acid, nitric
acid, and solution of potash are used; and it is supported with
equal strength by the results which they have given (831,
837, 841).

855. It may be thought that it was quite unnecessary, but
in my desire to establish contact electromotive force, to do
which I was at one time very anxious, I made many circuits of
three substances, including a galvanometer, all being conductors,
with the hope of finding an arrangement, which, without chemi¬
cal action, should produce a current. The number and variety
of these experiments may be understood from the following
summary; in which metals, plumbago, sulphurets and oxides,
all being conductors even of a thermo current, were thus com¬
bined in various ways:

256

Faraday’s Researches

1. Platinum.

2. Iron.

3. Zinc.

4. Copper.

5. Plumbago.

6 . Scale oxide of iron.

7. Native peroxide of manganese.

S. Native grey sulphuret of copper.

9. Native iron pyrites.

10. Native copper pyrites.

11. Galena.

12. Artificial sulphuret of copper.

13. Artificial sulphuret of iron.

14. iVrtificial sulphuret of bismuth.

I and 2 with 6, 7, 8, 9, 10, ii, 12, 13. 14, in turn.

I and 3 with 5, 6, 7, 8, 9, 10, ii, 12, 13, 14.

I and 5 with 6, •], 8^ 9^ 10^ ii^ 12^ 13, 14.

3 and 6 with 7^ 8^ 9^ 10^ ii^ 12^ 13, 14.

4 and 5 with 6, 7^ 8, g, lo^ ii, 12^ 13, 14.

4 and 6 with 7^ 8^ 9^ 10^ ii^ 12^, 13, 14.

4 and 7 with 8^ 9^ 10^ ii^ 12^ 13^ 14.

4 and 8 with 9^ 10^ ii^ 12^ 13^ 14.

4 and 9 with 10^ ii^ 12^ 13, 14.

4 and 10 with ii^ 12^ 13^ 14.

4 and II with 12^ 13, 14.

4 and 12 with 13^ 14.

4 and 13 with 14.

I and 4 with 1 2 .

856. Marianini states from experiment that copper is positive
to sulphuret of copper; ^ with the Voltaists^ according to the
same philosopher^ sulphuret of copper is positive to iron (866),
and with them also iron is positive to copper. These three
bodies therefore ought to give a most powerful circle: but on
the contrary, whatever sulphuret of copper I have used, I have
found not the slightest effect from such an arrangement.

857. As peroxide of lead is a body causing a powerful current
in solution of sulphuret of potassium, and indeed in every case
of a circuit where it can give up part of its oxygen, I thought
it reasonable to expect that its contact with metals would
produce a current, if contact ever could. A part of that which
had been prepared (810), was therefore well dried, which is

^ Mcmorie della Socieid Italiana in Modena, 1827, xxi. 224.

Insufficiency of Contact Theory 257

quite essential in these cases, and formed into the following
combinations:

Platinum. Zinc. Peroxide of lead.

Platinum. Lead. Peroxide of lead,-

Platinum. Cadmium. Peroxide of lead.

Platinum. Iron. Peroxide of lead.

Of these varied combinations, not one gave the least signs of
a current, provided differences of temperature were excluded;
though in every case the circle formed was, as to conducting
power, perfect for the purpose, i.e. able to conduct even a very
weak thermo current.

858. In the contact theory it is not therefore the metals alone
that must be assumed to have their contact forces so balanced
as to produce, in any circle of them, an effect amounting to
nothing (797); but all solid bodies that are able to conduct,
whether they be forms of carbon, or oxides, or sulphurets, muse
be included in the same category. So also must the electrolytes
already referred to, namely, the solutions of sulphuret of potas¬
sium and potash, and nitrous and nitric acids, in every case
where they do not act chemically. In fact all conductors that
do' not act chemically in the circuit must be assumed, by the
contact theory, to be in this condition, until a case of voltaic
current without chemical action is produced (846).

859. Then, even admitting that the results obtained by Volta
and his followers with the electrometer prove that mere contact
has an electromotive force and can produce an effect, surely all
experience with contact alone goes to show that the electro¬
motive forces in a circuit are always balanced. How else is it
likely that the above-named most varied substances should be
found to agree in this respect? unless indeed it be, as I believe,
that all substances agree in this, of having no such power at
all. If so, then where is the source of power which can account
by the theory of contact for the current in the voltaic pile?
If they are not balanced, then where is the sufficient case of
contact alone producing a current? or where are the numerical
data which indicate that such a case can be (796, 856)? The
contact philosophers are bound to produce, not a case where
the current is infinitesimally small, for such cannot account for
the current of the voltaic pile, and will always come within the
debatable ground which De la Rive has so well defended, but
a case and data of such distinctness and importance as may be

258 Faraday’s Researches

worthy of opposition to the numerous cases produced by the
chemical philosopher (880); for without them the contact
theory as applied to the pile appears to me to have no support,
and, as it asserts contact electromotive force even with the
balanced condition, to be almost without foundation.

860. To avoid these and similar conclusions, the contact
theory must bend about in the most particular and irregular
way. Thus the contact of solution of sulphuret of potassium
with iron must be considered as balanced by the joint force of
its contact with platinum, and the contact of iron and platinum
with each other; but changing the iron for lead, then the con¬
tact of the sulphuret with the latter metal is no longer balanced
by the other two contacts, it has all of a sudden changed its
relation: after a few seconds, when a film of sulphuret has been
formed by the chemical action, then the current ceases, though
the circuit be a good conductor (873); and now it must be
assumed that the solution has acquired its first relation to the
metals and to the sulphuret of lead, and gives an equilibrium
condition of the contacts in the circle.

861. So also with this sulphuretted solution and with potassa,
dilution must, by the theory, be admitted as producing no
change in the character of the contact force; but with nitric
acid, it, on the contrary, must be allowed to change the character
of the force greatly (965). So again acids and alkalies (as
potassa) in the cases where the currents are produced by them,
as with zinc and platinum for instance, must be assumed as
giving the preponderance of electromotive force on the same
side, though these are bodies which might have been expected
to give opposite currents, since they differ so much in their
nature.

862. Every case of a current is obliged to be met, on the part
of the contact advocates, by assuming powers at the points of
contact, in the particular case, of such proportionate strengths
as will consist with the results obtained, and the theory is made
to bend about, having no general relation for the acids or
alkalies, or other electrolytic solution used. The result there¬
fore comes to this: The theory can predict nothing regarding
the results; it is accompanied by no case of a voltaic current
produced without chemical action, and in those associated with
chemical action it bends about to suit the real results, these
•contortions being exactly parallel to the variations which the
pure chemical force, by experiment, indicates.

863. In the midst of all this, how simply does the chemical

Circles with Sulphuret of Potassium 259

theory meet^ include^ combine, and even predict, the numerous
experimental results! When there is a current there is also
chemical action; when the action ceases, the current stops (870,
873, 882); the action is determined either at the anode or the
cathode, according to circumstances (1027, 1029), and the
direction of the current is invariably associated with the direc¬
tion in which the active chemical forces oblige the anions and
cations to move in the circle (697, 1040).

864. Now when in conjunction with these circumstances it
is considered, that the many arrangements without chemical
action (813, etc.) produce no current; that those with chemical
action almost always produce a current; that hundreds occur in
which chemical action without contact produces a current
(1005, etc.); and that as many with contact but without
chemical action (855) are known and are inactive; how can
we resist the conclusion, that the powers of the voltaic battery
originate in the exertion of chemical force?

Hiii- Active Circles excited by Solution of Sulphuret of
Potassium

865. In 1812 Davy gave an experiment to show, that of two
different metals, copper and iron, that having the strongest
attraction for oxygen was positive in oxidising solutions, and
that having the strongest attraction for sulphur was positive in
sulphuretting solutions.^ In 1827 De la Rive quoted several
such inversions of the states of two metals, produced by using
different solutions, and reasoned from them, that the mere
contact of the metals could not be the cause of their respective
states, but that the chemical action of the liquid produced
these states.^

866. In a former paper I quoted Sir Humphry Davy’s ex¬
periment (678), and gave its result as a proof that the contact
of the iron and copper could not originate the current pro¬
duced; since when a dilute acid was used in place of the sul¬
phuret, the current was reverse in direction, and yet the contact
of the metals remained the same. M. Marianini^ adds, that
copper will produce the same effect with tin, lead, and even
zinc; and also that silver will produce the same results as
copper. In the case of copper he accounts for the effect by

^ Elements of Chemical Philosophy, p. 148.

^ Annales de Chimie, 1828, xxxvii. 231-237; xxxix. 299.

® Memorie della Societd Italiana in Modena, 1837, xxi. p. 224.

260 Faraday’s Researches

referring it to the relation of the iron and the new body formed
on the copper^ the latter beings according to Volta^ positive to
the former.^ By his own experiment the same substance was
negative to the iron across the same solution.^

867. I desire at present to resume the class of cases where
a solution of sulphuret of potassium is the liquid in a voltaic
circuit; for I think they give most powerful proof that the
current in the voltaic battery cannot be produced by contact^
but is due altogether to chemical action.

868. The solution of sulphuret of potassium (800) is a most
excellent conductor of electricity (802). When subjected
between platinum electrodes to the decomposing power of a
small voltaic battery^ it readily gave pure sulphur at the
anode^ and a little gas^ which was probably hydrogen, at the
cathode. When arranged with platinum surfaces so as to form
a Ritter’s secondary pile, the passage of a feeble primary current,
for a few seconds only, makes this secondary battery effective
in causing a counter current; so that, in accordance with
electrolytic conduction (658), it probably does not conduct
without decomposition, or if at all, its point of electrolytic
intensity (701, 718) must be very low. Its exciting action
(speaking on the chemical theory) is either the giving an anion
(sulphur) to such metallic and other bodies as it can act upon,
or, in some cases, as with the peroxides of lead and manganese,
and the protoxide of iron (1034), the abstraction of an anion
from the body in contact with it, the current produced being
in the one or the other direction accordingly. Its chemical
affinities are such, that in many cases its anion goes to that
metal, of a pair of metals, which is left untouched when the
usual exciting electrolytes are employed; and so a beautiful
inversion of the current in relation to the metals is obtained;
thus, when copper and nickel are used with it, the anion goes
to the copper; but when the same metals are used with the
ordinary electrolytic fluids, the anion goes to the nickel. Its
excellent conducting power renders the currents it can excite
very evident and strong; and it should be remembered that the
strength of the resulting currents, as indicated by the galvano¬
meter, depends jointly upon the energy (not the mere quantity)
of the exciting action called into play, and the conductive ability
of the circuit through which the current has to run. The
value of this exciting electrolyte is increased for the present

^ Memorie della Societd Italiana in Modena, 1837, xxi. p. 219.

* Ibid. p. 224.

Circles with Sulphuret of Potassium 26 i

investigation, by the circumstance of its giving, by its action on
the metals, resulting compounds, some of which are insoluble,
whilst others are soluble; and, of the insoluble results, some
are excellent conductors, whilst others have no conducting
power at all.

869. The experiments to be described were made generally
in the following manner. Wires of platinum, gold, palladium,
iron, lead, tin, and the other malleable metals, about one-
twentieth of an inch in diameter and six inches long, were
prepared. Two of these being connected with the ends of the
galvanometer-wires, were plunged at the same instant into the
solution of sulphuret of potassium in a test-glass, and kept there
without agitation (907), the effects at the same time being
observed. The wires were in every case carefully cleansed with
fresh fine sand-paper and a clean cloth; and were sometimes
even burnished by a glass rod, to give them a smooth surface.
Precautions were taken to avoid any difference of temperature
at the junctions of the different metals with the galvanometer
wires.

870. Tin and flaiinum ,—When tin was associated with
platinum, gold, or, I may say, any other metal which is
chemically inactive in the solution of the sulphuret, a strong
electric current was produced, the tin being positive to the
platinum through the solution, or, in other words, the current
being from the tin through the solution to the platinum. In a
very short time this current fell greatly in power, and in ten
minutes the galvanometer-needle was nearly at 0°. On then
endeavouring to transmit the antimony-bismuth thermo current
(813) through the circuit, it was found that it could not pass,
the circle having lost its conducting power. This was the
consequence of the formation on the tin of an insoluble, invest¬
ing, non-conducting sulphuret of that metal; the non-con¬
ducting power of the body formed is not only evident from- the
present result, but also from a former experiment (809).

871. Marianini thinks it is possible that (in the case of copper,
at least (866), and, so I presume, for all similar cases, for surely
one law or principle should govern them), the current is due
to the contact force of the sulphuret formed. But that applica¬
tion is here entirely excluded; for how can a non-conducting
body form a current, either by contact or in any other way^?
No such case has ever been shown, nor is it in the nature of
things; so that it cannot be the contact of the sulphuret that
here causes the current; and if not in the present, why in any

... . .

262 Faraday’s Researches

case? for nothing happens here that does not happen in any
other instance of a current produced by the same exciting i
electrolyte,

8;;?2.^ On the other hand^ how beautiful a proof the result
gives in confirmation of the chemical theory! Tin can take 1
sulphur from the electrolyte to form a sulphuret; and whilst i
it is doing so^ and in proportion to the degree in which it is
doing sOj it produces a current; but when the sulphuret which i
is formed, by investing the metal, shuts off the fluid and pre- |
vents further chemical action, then the current ceases also.

Nor is it necessary that it should be a non-conductor for this j
purpose, for conducting sulphurets will perform the same office
(873, 882), and bring about the same result. What, then, can !
be more clear, than that whilst the sulphuret is being Jormed ,
a current is produced, but that when formed its mere contact |
can do nothing towards such an effect? ;

873. Lead .—This metal presents a fine result in the solution |

of sulphuret of potassium. Lead and platinum being the j

metals used, the lead was at first highly positive, but in a few , |
seconds the current fell, and in two minutes the galvanometer- |

needle was at 0°. Still the arrangement conducted a feeble
thermo current extremely well, the conducting power not
having disappeared, as in the case of tin; for the investing I

sulphuret of lead is a conductor (808). Nevertheless, though a 1

conductor, it could stop the further chemical action; and that I

ceasing, the current ceased also. J

874. Lead and gold produced the same effect. Lead and ^

palladium the same. Lead and iron the same, except that the ;
circumstances respecting the tendency of the latter metal under 1
common circumstances to produce a current from the elec-
trolyte to itself, have to be considered and guarded against ■
(814, 1037). Lead and nickel also the same. In all these |

cases, when the lead was taken out and washed, it was found 1

beautifully invested with a thin polished pellicle of sulphuret of i
lead. j

875. With lead, then, we have a conducting sulphuret formed, j

but still there is no sign that its contact can produce a current, j

any more than in the case of the non-conducting sulphuret of j
tin (870). There is no new or additional action produced by j
this conducting body; there was no deficiency of action with
the former non-conducting product; both are alike in their
results, being, in fact, essentially alike in their relation to that
on which the current really depends, namely, an active chemical

Inconsistency of the Contact Hypothesis 263

force. A piece of lead put alone into the solution of sulphuret
of potassium^ has its surface converted into sulphuret of lead^
the proof thus being obtained^ even when the current cannot
be formed^ that there is a force (chemical) present and active
under such circumstances; and such force can produce a
current of chemical force when the circuit form is given to
the arrangement. The force at the place of excitement shows
itself; both by the formation of sulphuret of lead and the pro¬
duction of a current. In proportion as the formation of the
one decreases the production of the other diminishes; though
all the bodies produced are conductors; and contact still remains
to perform any work or cause any effect to which it is competent.

876. It may perhaps be said that the current is due to the
contact between the solution of sulphuret and the lead (or tin;
as the case may be); which occurs at the beginning of the ex-

Fig. 67.

periment; and that when the action ceaseS; it is because a new
body, the sulphuret of lead; is introduced into the circuit; the
various contacts being then balanced in their force. This
would be to fall back upon the assumption before resisted;
namely; that the solution may class with metals and such like
bodieS; giving balanced effects of contact in relation to some
of these bodieS; as in this case; to the sulphuret of lead pro¬
duced; but not with others, as the lead itself; both the lead and
its sulphuret being in the same category as the metals generally

(797, 858)-

877. The utter improbability of this as a natural effect; and
the absence of all experimental proof in support of it; have
been already stated (849; 859); but one or two additional reasons
against it now arise. The state of thing may perhaps be made
clearer by a diagram or twO; in which assumed contact forces
may be assigned; in the absence of all experimental expression;
without injury to the reasoning. Let fig. 67 represent the
electromotive forces of a circle of platinum; iron; and solution
of sulphuret of potassium; or platinum; nickel, and solution
of sulphuret; cases in which the forces are, according to the

264 Faraday’s Researches

contact theory, balanced (848). Then fig. 68 may represent
the circle of platinum, lead, and solution of sulphuret, which
does produce a current, and, as I have assumed, with a resulting
force of II ■—This in a few minutes becomes quiescent,
ix. the current ceases, and fig. 69 may represent this new case
according to the contact theory. Now is it at all likely[that

platinzcm

Fig. 68.

by the intervention of sulphuret of lead at the contact c, fig. 68,
and the production of two contacts d and e, fig. 69, such an
enormous change of the contact force suffering alteration
should be made as from 10 to 21? the intervention of the
same sulphuret either at a or 3 (822, 828) being able to do
nothing of the kind, for the sum of the force of the two new
contacts is in that case exactly equal to the force of the contact
which they replace, as is proved by such interposition making
no change in the effects of the circle (855, 828). If therefore the
intervention of this body between lead and platinum at a, or

Fig. 69.

between solution of sulphuret of potassium and platinum at b
(fig. 68) causes no change, these cases including its contact with
both lead and the solution of sulphuret, is it at all probable
that its intervention between these two bodies at c should
make’a difference equal to double the amount of force previously
existing, or indeed any difference at all?

878. Such an alteration as this in the sum assigned as the
amount of the forces belonging to the sulphuret of lead by
virtue of its two places of contact, is equivalent I think to say¬
ing that it partakes of the anomalous character already supposed

Circles with Sulphuret of Potassium 265

to belong to certain fluids^ namely^ of sometimes giving balanced
forces in circles of good conductors^ and at other times not (853).

879. Even the metals themselves must in fact be forced into
this constrained condition; for the effect at a point of contact^
if there be any at all, must be the result of the joint and mutual
actions of the bodies in contact. If therefore in the circuit, fig.
68, the contact forces are not balanced, it must be because of
the deficient joint action of the lead and solution at c} If the
metal and fluid were to act in their proper character, and as
iron or nickel would do in the place of the lead, then the force
there would be <— 21, whereas it is less, or according to the
assumed numbers only -<— 10. Now as there is no reason
why the lead should have any superiority assigned to it over
the solution, since the latter can give a balanced condition
amongst good conductors in its proper situation as well as the
former; how can this be, unless lead possess that strange
character of sometimes giving equipoised contacts, and at other
times not (853)?

880. If that be true of lead, it must be true of all the metals
which, with this sulphuretted electrolyte, give circles producing
currents; and this would include bismuth, copper, antimony,
silver, cadmium, zinc, tin, etc., etc. With other electrolytic
fluids iron and nickel would be included, and even gold,
platinum, palladium; in fact all the bodies that can be made to
yield in any way active voltaic circuits. Then is it possible
that this can be true, and yet not a single combination of this
extensive class of bodies be producible that can give the current
without chemical action (855), considered not as a result, but
as a known and pre-existing force 7

881. I will endeavour to avoid further statement of the argu¬
ments, but think myself bound to produce (787) a small pro¬
portion of the enormous body of facts which appear to me to
bear evidence all in one direction.

882. Bismuth .—^This metal, when associated with platinum,
gold, or palladium in solution of the sulphuret of potassium,
gives active circles, the bismuth being positive. In the course
of less than half an hour the current ceases; but the circuit is
still an excellent conductor of thermo currents. Bismuth with
iron or nickel produces the same final result with the reserva¬
tion before made (814). Bismuth and lead give an active

^ My numbers are assumed, and if other numbers were taken, the
reasoning might be removed to contact b, or even to contact a, but the end
of the argument would in every case be the same.

266

Faraday’s Researches

circle; at first the bismuth is positive; in a minute or two the
current ceases, but the circuit still conducts the thermo current |
well.

883. Thus whilst sulphuret of bismuth is in the act of forma¬

tion the current is produced; when the chemical action ceases
the current ceases also; though contact continues and the
sulphuret be a good conductor. In the case of ‘bismuth and
lead the chemical action occurs at both sides, but is most ;

energetic at the bismuth, and the current is determined accord- i

ingly. Even in that instance the cessation of chemical action i
causes the cessation of the current.

884. In these experiments with lead and bismuth I have

given their associations with platinum, gold, palladium, iron,
and nickel; because, believing in the first place that the results
prove all current to depend on chemical action, then, the '
quiescent state of the resulting or final circles shows that the
contacts of these metals in their respective pairs are without force i

(817): and upon that again follows the passive condition of '

all those contacts which can be produced by interposing other j

conducting bodies between them (821); an argument that I
need not again be urged. |

885. Copper. —This substance being associated with platinum, i

gold, iron, or any metal chemically inactive in the solution of I
sulphuret, gives an active circle, in which the copper is positive j
through the electrolyte to the other metal. The action, though *
it falls, does not come to a close as in the former cases, and 1

for these simple reasons; that the sulphuret formed is not i

compact but porous, and does not adhere to the copper, but
separates from it in scales. Hence results a continued renewal ;
of the chemical action between the metal and electrolyte, and ;
a continuance of the current. If after a while the copper plate ^ i
be taken out and washed and dried, even the wiping will remove |

part of the sulphuret in scales, and the nail separates the rest i

with facility. Or if a copper plate be left in abundance of the |

solution of sulphuret, the chemical action continues, and the '
coat of sulphuret of copper becomes thicker and thicker. i

886. If, as Marianini has shown,^ a copper plate which has

been dipped in the solution of sulphuret, be removed before j

the coat formed is so thick as to break up from the metal |

beneath, and be washed and dried, and then replaced, in associa- ;
tion with platinum or iron, in the solution, it will at first be 1

neutral, or, as is often the case, negative (815, 826) to the j

^ Memorie della Societd Italiana in Modena, 1837, xxi. 224. j

Circles with Sulphuret of Potassium 267

Other metal^ a result quite in opposition to the idea^ that the
mere presence of the sulphuret on it could have caused the
former powerful current and positive state of the copper (885,
866). A further proof that it is not the mere presence, but
the formation, of the sulphuret which causes the current, is,
that if the plate be left long enough for the solution to pene¬
trate the investing crust of sulphuret of copper and come into
activity on the metal beneath, then the plate becomes active,
and a current is produced.

887. I made some sulphuret of copper, by igniting thick
copper wire in a Florence flask or crucible in abundance of
vapour of sulphur. The body produced is in an excellent
form for these experiments, and a good conductor; but it is
not without action on the sulphuretted solution, from which
it can take more sulphur, and the consequence is, that it is
positive to platinum or iron in such a solution. If such sul¬
phuret of copper be left long in the solution and then be washed
and dried, it will generally acquire the final state of sulphura-
tion, either in parts or altogether, and also be inactive, as
the sulphuret formed on the copper was before (886); i.e.
when its chemical action is exhausted, it ceases to produce a
current.

888. Native grey sulphuret of copper has the same relation
to the electrolyte: it takes sulphur from it and is raised to a
higher state of combination; and, as it is also a conductor
(808), it produces a current, being itself positive so long as
the action continues.

889. But when the copper is fully sulphuretted, then all
these actions cease; though the sulphuret be a conductor, the
contacts still remain, and the circle can carry with facility a
feeble thermo current. This is not only shown by the quiescent
cases just mentioned (886), but also by the utter inactivity of
platinum and compact yellow copper pyrites, when conjoined
by this electrolyte, as shown in a former part of this paper (828).

• 890. Antimony .—This metal, being put alone into a solution
of sulphuret of potassium, is acted on, and a sulphuret of
antimony formed which does not adhere strongly to the metal,
but wipes off. Accordingly, if a circle be formed of antimony,
platinum, and the solution, the antimony is positive in the
electrolyte, and a powerful current is formed, which continues.
Here then is another beautiful variation of the conditions under
which the chemical theory can so easily account for the effects,
whilst the theory of contacts cannot. The sulphuret produced

268 Faraday’s Researches

in this case is a non-conductor whilst in the solid state (138);
it cannot therefore be that any contact of this sulphuret can 1
produce the current; in that respect it is like the sulphuret of j
tin (870). But that circumstance does not stop the occurrence
of the chemical current; for^ as the sulphuret forms a porous j

instead of a continuous crusty the electrolyte has access to the |

metal and the action goes on.

891. Silver. —This metal, associated with platinum, iron, or |

other metals inactive in this electrolyte, is strongly positive, j

and gives a powerful continuous current. Accordingly, if a j

plate of silver, coated with sulphuret by the simple action of .

the solution, be examined, it will be found that the crust is
brittle and broken, and separates almost spontaneously from !

the metal. In this respect, therefore, silver and copper are I

alike, and the action consequently continues in both cases; j

but they differ in the sulphuret of silver being a non-conductor s

(170) for these feeble currents, and, in that respect, this metal j

is analogous to antimony (890). I

892. Cadmium. —Cadmium with platinum, gold, iron, etc., '
gives a powerful current in the solution of sulphuret, and the I
cadmium is positive. On several occasions this current con- i
tinned for two or three hours or more; and at such times, the j
cadmium being taken out, washed^ and wiped, the sulphuret
was found to separate easily in scales on the cloth used.

893. Sometimes the current would soon cease; and then 1

the circle was found not to conduct the thermo current (801). i

In .these cases, also, on examining the cadmium, the coat of s

sulphuret was strongly adherent, and this was more especially i

the case when prior to the experiment the cadmium, after
having been cleaned, was burnished by a glass rod (869). Hence

it appears that the sulphuret of this metal is a non-conductor,
and that its contact could not have caused the current (871)
in the manner Marianini supposes. All the results it supplies
are in perfect harmony with the chemical theory and adverse
to contact theory.

894. Zuic. —This metal, with platinum, gold, iron, etc., and !
the solution of sulphuret, produces a very powerful current,
and is positive through the solution to the other metal. The :
current was permanent. Here another beautiful change in i
the circumstances of the general experiment occurs. Sul¬
phuret of zinc is a non-conductor of electricity (809), like the ?
sulphurets of tin, cadmium, and antimony; but then it is
soluble in the solution of sulphuret of potassium; a property

Circles with Protosulphuret of Potassium 269

easily ascertainable by putting a drop of solution of zinc into
a portion of the electrolytic solution^ and first stirring them a
little^ by which abundance of sulphuret of zinc will be formed;
and then stirring the whole well together^ when it will be redis¬
solved. The consequence of this solubility is^ that the zinc
when taken out of the solution is perfectly free from investing
sulphuret of zinc. HencCj therefore^ a veiy^ sufficient reason^
on the chemical theory^ why the action should go on. But
how can the theory of contact refer the current to any contact
of the metallic sulphuret^ when that sulphuret is^ in the first
place;, a non-conductor^ and^ in the next^ is dissolved and
carried off into the solution at the moment of its formation?

895. Thus all the phenomena with this admirable electrolyte
(S68)j whether they be those which are related to it as an active
(867) or as a passive (813, etc.) body^ confirm the chemical
theory^ and oppose that of contact. With tin and cadmium
it gives an impermeable non-conducting body; with lead and
bismuth it gives an impermeable conducting body; with
antimony and silver it produces a permeable non-conducting
body; with copper a permeable conducting body; and with
zinc a soluble non-conducting body. The chemical action
and its resulting current are perfectly consistent with all these
variations. But try to explain them by the theory of contact^
and^ as far as I can perceive, that can only be done by twisting
the theory about and making it still more tortuous than before;
special assumptions being necessary to account for the effects
which, under it, become so many special cases.

896. Solution of protosulphuret of potassium, or hihydro-
sulphuret of potassa .—I used a solution of this kind as the
electrolyte in a few cases. The results generally were in ac¬
cordance with those already given, but I did not think it neces¬
sary to pursue them at length. The solution was made by
passing sulphuretted hydrogen gas for twenty-four hours
through a strong solution of pure caustic potassa.

897. Iron and platinum with this solution formed a circle
in which the iron was first negative, then gradually became
neutral, and finally acquired a positive state. The solution
first acted as the yellow sulphuret in reducing the investing
oxide (1037), and then, apparently, directly on the iron, dis¬
solving the sulphuret formed. Nickel was positive to platinum
from the first, and continued so though producing only a weak
current. When weak chemical action was substituted for
metallic contact at x, fig. 65 (819), a powerful current passed.

270 Faraday’s Researches

Copper was highly positive to iron and nickel; as also to plath
num^ gold^ and the other metals which were unacted upon by
the solution. Silver was positive to iron^ nickel^ and even lead;
as well as to platinum^ etc. Lead is positive to platinum^
then the current falls^ but does not cease. Bismuth is also
positive at firsts but after a while the current almost entirely
ceases^ as with the yellow sulphuret of potassium (882).

898. Native grey sulphuret of copper and artificial sulphuret
of copper (887) were positive to platinum and the inactive
metals: but yellow copper pyrites, yellow iron pyrites, and
galena, were inactive with these metals in this solution; as
before they had been with the solution of yellow or bisulphuret
of potassium. This solution, as might be expected from its
composition, has more of alkaline characters in it than the
yellow sulphuret of potassium.

899. Before concluding this account of results with the
sulphuretted solutions, as exciting electrolytes, I will mention
the varying and beautiful phenomena which occur when copper
and silver, or two pieces of copper, or two pieces of silver, form
a circle with the yellow solution. If the metals be copper and
silver, the copper is at first positive and the silver remains
untarnished; in a short time this action ceases, and the silver
becomes positive; at the same instant it begins to combine with
sulphur and becomes covered with sulphuret of silver; in the
course of a few moments the copper again becomes positive;
and thus the action will change from side to side several times,
and the current with it, according as the circumstances become
in turn more favourable at one side or the other.

900. But how can it be thought that the current first produced
is due in any way to the contact of the sulphuret of copper
formed, since its presence there becomes at last the reason why
that first current diminishes, and enables the silver, which is
originally the weaker in exciting force, and has no sulphuret as
yet formed on it, to assume for a time the predominance, and
produce a current which can overcome that excited at the
copper (899)? What can account for these changes, but
chemical action? which, as it appears to me, accounts, as far
as we have yet gone, with the utmost simplicity, for all the
effects produced, however varied the mode of action and their
circumstances may be.

December 12, 1839.

Exciting Force Affected by Heat 271

VIII1

§ 9. OK SOURCE OF POWER IN THE VOLTAIC PILE— Con-

iinued. Tl iv. the exciting chemical force affected
BV' temperature. ^ V. THE EXCITING CHEMICAL FORCE
AFFE^CTED by dilution. ^ vi. DIFFERENCES IN THE ORDER
OF the METALLIC ELEMENTS OF VOLTAIC CIRCLES. ^ vii.
active VOLTAIC circles AND BATTERIES WITHOUT METALLIC

cokttact. viii. considerations of the sufficiency
OF chemical action. ^ ix. thermo-electric evidence.

^ X- IMPROBABLE NATURE OF THE ASSUMED CONTACT FORCE

^ iv. The Exciting Chemical Force affected by Temperature

901. Ojk the view that chemical force is the origin of the electric
current in the voltaic circuit, it is important that we have the
power o£ causing by ordinary chemical means, a variation of
that force within certain limits, without involving any alteration
of the metallic or even the other contacts in the circuit. Such
variations should produce corresponding voltaic effects, and
it appeared not improbable that these differences alone might
be made effective enough to produce currents without any
metallic contact at all.

902. IDe la Rive has shown that the increased action of a
pair of metals, when put into hot fluid instead of cold, is in a
great measure due to the exaltation of the chemical affinity on
that metal which was acted upon.^ My object was to add to
the argnment by using but one metal and one fluid, so that the
fluid might be alike at both contacts, but to exalt the chemical
force at one only of the contacts by the action of heat. If such
difference produced a current with circles which either did not
generate a thermo current themselves, or could not onduct
that of an antimony and bismuth element, it seemed probable
that the effect would prove to be a result of pure chemical
force, contact doing nothing.

903. The apparatus used was a glass tube (fig. 70), about five
inches long and 0.4 of an inch internal diameter, open at both

^ Seventeenth Series, original edition, vol. ii. p. 5,9-.

® Annales de Chimu, 1828, xxxvii. p. 242.

272 Faraday’s Researches

ends^ bent and supported on a retort-stand. In this the liquid
was placed^ and the portion in the upper part of one limb could
then easily be heated and retained so^ whilst that in the other
limb was cold. In the experiments I will call the left-hand
side and the right-hand side B; taking care to make no

change of these designations.
C and D are the wires of metal
(869) to be compared; they were
formed into a circuit by means
of the galvanometer^ and^ often
alsO; a Seebeck’s thermo-ele¬
ment of antimony and bismuth;

Fig. 70. both these^ of course^ caused no

disturbing ef ect so long as the
temperature of their various junctions was alike. The wires
were carefully prepared, and when two of the same metal were
used, they consisted of the successive portions of the same
piece of wire.

904. The precautions which are necessary for the elimination
of a correct result are rather numerous, but simple in their
nature.

905. Effect of first immersion .—It is hardly possible to have
the two wires of the same metal, even platinum, so exactly
alike that they shall not produce a current in consequence of
their difference; hence it is necessary to alternate the wires and
repeat the experiment several times, until an undoubted result
independent of such disturbing influences is obtained.

906. Effect of the investing fluid or substance .—^The fluid
produced by the action of the liquid upon the metal exerts, as
is well known, a most important influence on the production of
a current. Thus when two wires of cadmium were used with
the apparatus, fig. 70 (903), containing dilute sulphuric acid,
hot on one side and cold on the other, the hot cadmium was It
first positive, producing a deflection of about 10°; but in a
short time this effect disappeared, and a current in the reverse
direction equal to 10° or more would appear, the hot cadmium
being now negative. This I refer to the quicker exhaustion of
the chemical forces of the film of acid on the heated metallic
surface, and the consequent final superiority of the colder
side at which the action was thus necessarily more powerful.
Marianini has described many cases of the effects of investing
solutions, showing that if two pieces of the same metal (iron,
tin, lead, zinc, etc.) be used, the one first immersed is negative

Effect of Motion in the Fluids 273

to the other^ and has given his views of the cause.^ The pre¬
caution against this efect was not to put the metals into the
acid until the proper temperature had been given to both parts
of itj and then to observe the first effect produced, accounting
that as the true indication, but repeating the experiment until
the result was certain.

907. Effect of motion .—This investing fluid (906) made it
necessary to guard against the effect of successive rest and
motion of the metal in the fluid. As an illustration, if two tin
wires (869) be put into dilute nitric acid, there will probably
be a little motion at the galvanometer, and then the needle will
settle at 0°. If either wire be then moved, the other remaining
quiet, that in motion will become positive. Again, tin and
cadmium in dilute sulphuric acid gave a strong current, the
cadmium being positive, and the needle was deflected 80°.
When left, the force of the current fell to 35°. If the cadmium
were then moved it produced very little alteration; but if the
tin were moved it produced a great change, not showing, as
before, an increase of its force, but the reverse, for it became
more negative, and the current force rose up again to 80°.^
The precaution adopted to avoid the interference of these actions,
was not only to observe the first effect of the introduced wires,
but to keep them moving from the moment of the introduction.

908. The above effect was another reason for heating the
acids, etc. (906) before the wires were immersed; for in the
experiment just described, if the cadmium side were heated to
boiling, the moment the fluid was agitated on the tin side by
the boiling on the cadmium side, there was mor effect by far
produced by the motion than the heat: for the heat at the cad¬
mium alone did little or nothing, but the jumping of the acid
over the tin made a difference in the current of 20° or 30°.

909. Effect of air .—Two platinum wires were put into cold

1 Annales de Chimie, 1830, xlv. p. 40.

^Tin has some remarkable actions in this respect. If two tins be
immersed in succession into dilute nitric acid, the one last in is positive
to the other at the moment: if, both being in, one be moved, that is for
the time positive to the other. But if dilute sulphuric acid be employed,
the last tin is always negative: if one be taken out, cleaned, and re-
immersed, it is negative: if, both being in and neutral, one be moved, it
becomes negative to the other. The effects with muriatic acid are the
same in kind as those with sulphuric acid, but not so strong. This effect
perhaps depends upon the compound of tin first produced in the sulphuric
and muriatic acids tending to acquire some other and more advanced
state, either in relation to the oxygen, chlorine or acid concerned, and so
adding a force to that which at the first moment, when only metallic tin
and acid are present, tends to determine a current.

S

274 Faraday’s Researches

strong solution of sulphuret of potassium (800), fig. 70; and
the galvanometer was soon at 0°. On heating and boiling the
fluid on the side A (903) the platinum in it became negative;
cooling that side^ by pouring a little water over it from a jug^
and heating the side B; the platinum there in turn became
negative; and, though the action was irregular, the same
general result occurred however the temperatures of the parts
were altered. This was not due to the chemical effect of the
electrolyte on the heated platinum. Nor do I believe it was a
true thermo current (921); but if it were the latter, then the
heated platinum was negative through the electrolyte to the
cold platinum. I believe it was altogether the increased effect
of the air upon the electrolyte at the heated side; and it is
evident that the application of the heat, by causing currents in
the fluid and also in the air^ facilitates their mutual action at
that place. It has been already shown, that lifting up a plati¬
num wire in this solution, so as to expose it for a moment to
the air (815), renders it negative when reimmersed, an effect
which is in perfect accordance with the assumed action of the
heated air and fluid in the present case. The interference of
this effect is obviated by raising the temperature of the elec¬
trolyte quietly before the wires are immersed (906), and observ¬
ing only the first effect.

910. Effect of heat .—In certain cases where two different
metals are used, there is a very remarkable effect produced on
heating the negative metal. This will require too much detail
to be described fully here; but I will briefly point it out and
illustrate it by an example or two.

911. When two platinum wires were compared in hot and
cold dilute sulphuric acid (923), they gave scarcely a sensible
trace of any electric current. If any real effect of heat occurred,
it was that the hot metal was the least degree positive. When
silver and silver were compared, hot and cold, there was also
no sensible effect. But when platinum and silver were com¬
pared in the same acid, different effects occurred. Both being
cold, the silver in the A side, fig. 70 (903), was positive about 4°,
by the galvanometer; moving the platina on the other side B
did not alter this effect, but on heating the acid and platinum
there, the current became very powerful, deflecting the needle
30°, and the silver was positive. Whilst the heat continued,
the effect continued; but on cooling the acid and platinum it
went down to the first degree. No such effect took place at
the silver; for on heating that side, instead of becoming

Remarkable Effect of Heat 275

negative^ it became more positive, but only to the degree of
deflecting the needle i6°. Then, motion of the platinum (907)
facilitated the passing of the current and the deflection in¬
creased, but heating the platinum side did far more.

912. Silver and copper in dilute sulphuric acid produced very
little effect; the copper was positive about by the galvano¬
meter; moving the copper or the silver did nothing; heating
the copper side caused no change; but on heating the silver
side it became negative 20°. On cooling the silver side this
effect went down, and then, either moving the silver or copper,
or heating the copper side, caused very little change: but
heating the silver side made it negative as before.

913. All this revolves itself into an effect of the following
kind; that where two metals are in the relation of positive and
negative to each other in such an electrolyte as dilute acids
(and perhaps others), heating the negative metal at its contact
with the electrolyte enables.the current, which tends to form,
to pass with such facility, as to give a result sometimes tenfold
more powerful than would occur without it. It is not displace¬
ment of the investing fluid, for motion will in these cases do
nothing: it is not chemical action, for the effect occurs at that
electrode where the chemical action is not active; it is not a
thermo-electric phenomenon of the ordinary kind, because it
depends upon a voltaic relation; i.e, the metal showing the
effect must be negative to the other metal in the electrolyte;
so silver heated does nothing with silver cold, though it shows
a great effect with copper either hot or cold (912); and platinum
hot is as nothing to platina cold, but much to silver either hot
or cold.

914. Whatever may be the intimate action of heat in these
cases, there is no doubt that it is dependent on the current
which tends to pass round the circuit. It is essential to re¬
member that the increased effect on the galvanometer is not
due to any increase in the electromotive force, but solely to the
removal of obstruction to the current by an increase probably
of discharge. M. de la Rive has described an effect of heat, on
the passage of the electric current, through dilute acid placed
in the circuit, by platinum electrodes. Heat applied to the
negative electrode increased the deflection of a galvanometer
needle in the circuit, from 12° to 30° or 45°; whilst heat applied
to the positive electrode caused no change.^ I have not been
able to obtain this nullity of effect at the positive electrode

^ Bibliotheque Universelle, 1837, vii. 388.

276 Faraday’s Researches

when a voltaic battery was used; but I have no doubt the
present phenomena will prove to be virtually the same as those
which that philosopher has described.

915. The effect interferes frequently in the ensuing experi¬
ments when two metals^ hot and cold^ are compared with each
other; and the more so as the negative metal approximates in
inactivity of character to platinum or rhodium. Thus in the
comparison of cold copper^ with hot silver^ gold;, or platinum^
in dilute nitric acid; this effect tends to make the copper appear
more positive than it otherwise would do.

916. Place of the wire terminations .—It is requisite that the
end. of the wire on the hot side should be in the heated fluid.

Two copper wires were put into diluted solu¬
tion of sulphuret of potassium^ fig. 7I; that
portion of the liquid extending from C to D
was heated; but the part between D and E
remained cold. Whilst both ends of the wires
were in the cold fluid, as in the figure; there
were irregular movements of the galvano¬
meter; small in degree; leaving the B wire positive. Moving
the wires about; but retaining them as in the figure; made no
difference; but on raising the wire in A; so that its termination
should be in the hot fluid between C and D; then it became
positive and continued so. On lowering the end into the cold
part; the former state recurred; on raising it into the hot part;
the wire again became positive. The same is the case with
two silver wires in dilute nitric acid; and though it appears
very curious that the current should increase in strength as the
extent of bad conductor increases; yet such is often the case
under these circumstances. There can be no reason to doubt
that the part of the wire which is in the hot fluid at the A side;
is at all times equally positive or nearly so; but at one time the
whole of the current it produces is passing through the entire
circuit by the wire in B; and at another; a part; or the whole; of
it is circulating to the cold end of its own wire; only by the fluid
in tube A.

917. Cleaning the wires .—That this should be carefully done
has been already mentioned (869); but it is especially necessary
to attend to the very extremities of the wireS; for if these circular
spaceS; which occur in the most effective part of the circle; be
left covered with the body produced on them in a preceding
trial; an experimental result will often be very much deranged;
or even entirely falsified.

I

/

Fig. yi.

Voltaic Excitement

277

918. Thus the best mode of experimenting (903) is to heat
the liquid in the limb A or fig. 71^ first; and^ having the
wires well cleaned and connected^ to plunge both in at once^
and^ retaining the end of the heated wire in the hot part of the
fluid; to keep both wires in motion^ and observe; especially; the
first effects: then to take out the wireS; reclean them; change
them side for side and repeat the experiment; doing this so
often as to obtain from the several results a decided and satis¬
factory conclusion.

919. It next becomes necessary to ascertain whether any
true thermo current can be produced by electrolytes and metals,
which can interfere with any electro-chemical effects dependent
upon the action of heat. For this purpose diflerent combina¬
tions of electrolytes and metals not acted on chemically by
them; were tried; with the following results.

920. Platinum and a very strong solution of potass a gave; as
the result of many experiments, the hot platinum positive
across the electrolyte to the cold platinum; producing a current
that could deflect the galvanometer needle about 5°, when the
temperatures at the two junctures were 60° and 240°. Gold
and the same solution gave a similar result. Silver and a
moderately strong solution, of specific gravity 1070, like that
used in the ensuing experiments (936) gave the hot silver posi¬
tive, but now the deflection was scarcely sensible, and not more
than 1°. Iron was tried in the same solution, and there was a
constant current and deflection of 50° or more, but there was
also chemical action (936).

921. I then used solution of the sulphuret of potassium (800).
As already said, hot platinum is negative in it to the cold metal
(909); but I do not think the action was thermo-electric.
Palladium with a weaker solution gave no indication of a
current.

922. Employing dilute nitric acid, consisting of one volume
strong acid and fifty volumes water, platinum gave no certain
indication: the hot metal was sometimes in the least degree
positive, and at others an equally small degree negative. Gold
in the same acid gave a scarcely sensible result; the hot metal
was negative. Palladium was as gold.

923. With dilute sulphuric acid, consisting of one by weight
of oil of vitriol and eighty of water, neither platinum nor gold
produced any sensible current to my galvanometer by the mere
action of heat.

924. Muriatic acid and platinum being conjoined, and heated

278 Faraday’s Researches

as before^ the hot platinum was very slightly negative in strong
acid: in dilute acid there was no sensible current.

925. Strong nitric acid at first seemed to give decided results.

Platinum and pure strong nitric acid being heated at one of
the junctions^, the hot platinum became constantly negative
across the electrolyte to the cold metal^ the deflection being
about 2°. When a yellow acid was used;, the deflection was
greater; and when a very orange-coloured acid was employed^
the galvanometer needle stood at 70°;, the hot platinum being
still negative. This effect^ however^ is not a pure thermo cur¬
rent;, but a peculiar result due to the presence of nitrous acid
(836). It disappears almost entirely when a dilute acid is used *

(922); and what effect does remain indicates that the hot ^

metal is negative to the cold. !

926. Thus the potash solution seems to be the fluid giving ;

the most probable indications of a thermo current. Yet there !

the deflection is only 5°_, though the fluid; being very strong; I

is a good conductor (807). When the fluid was diluted; and ,

of specific gravity 107O; like that before used (920); the effect I

was only 1°; and cannot therefore be confounded with the j

results I have to quote. '

927. The dilute sulphuric (923) and nitric acids used (922)
gave only doubtful indications in some cases of a thermo current. I
On trial it was found that the 'thermo current of an antimony- I
bismuth pair could not pass these solutions; as arranged in these

and other experiments (937, 938); that; therefore; if the little |
current obtained in the experiments be of a thermo-electric !
nature; this combination of platinum and acid is far more
powerful than the antimony-bismuth pair of Seebeck; and yet !
that (with the interposed acid) it is scarcely sensible by this
delicate galvanometer. Further; when there is a current; the
hot metal is generally negative to the cold; and it is therefore ;
impossible to confound these results with those to be described ■
where the current has a contrary direction. '

928. In strong nitric acid; again; the hot metal is negative. !

929. If; after I show that heat applied to metals in acids or j

electrolytes which can act on them produces considerable cur- 1
rentS; it be then said that though the metals which are inactive 1

in the acids produce no thermo currents; those which; like !

copper; silver; etc.; act chemically; may; then; I say; that such
would be a mere supposition; and a supposition at variance with '
what we know of thermo-electricity; for amongst the solid I
conductors; metallic or non-metallic (855); there are none; I !

Voltaic Currents Determined by Heat 279

believe^ which are able to produce thermo currents with some
of the metals^ and not with others. Further^ these metals^
copper^ silver^ etc.; do not always show effects which can be
mistaken or pass for thermo-electriC; for silver in hot dilute
nitric acid is scarcely different from silver in the same acid cold
(938); and in other caseS; again^ the hot metals become negative
instead of positive (941).

Cases oj one Metal and one Electrolyte ; one Junction
being heated

930. The cases I have to adduce are far too numerous to
be given in detail; I will therefore describe one or twO; and
sum up the rest as briefly as possible.

931. Iron in diluted sulphuret of potassium, —^The hot iron
is well positive to the cold metal. The negative and cold wire
continues quite clean; but from the hot iron a dark sulphuret
separates; which becoming diffused through the solution dis¬
colours it. When the cold iron is taken out; washed and wiped;
it leaves the cloth clean; but that which has been heated leaves
a black sulphuret upon the cloth when similarly treated.

932. Copper and the sulphuretted solution. —^The hot copper
is well positive to the cold on the first immersion; but the effect
quickly falls; from the general causes already referred to (906).

933. Tin and solution of potass a. —The hot tin is strongly and
constantly positive to the cold.

934. Iron and dilute sulphuric acid (923).—^The hot iron was
constantly positive to the cold; 60° or more. Iron and diluted
nitric acid gave even a still more striking result.

I must now enumerate merely; not that the cases to be
mentioned are less decided than those already given; but to
economise time.

935. Dilute solution of yellow sulphuret of potassium, consist¬
ing of one volume of the strong solution (800); and eighteen
volumes of water.—Iron; silver; and copper; with this solution;
gave good results. The hot metal was positive to the cold.

936. Dilute solution of caustic potassa (920).—Iron, copper;
tin; zinC; and cadmium gave striking results in this electrolyte.
The hot metal was always positive to the cold. Lead produced
the same effect; but there was a momentary jerk at the galvano¬
meter at the instant of immersion; as if the hot lead was negative
at that moment. In the case of iron it was necessary to continue
the application of heat; and then the formation of oxide at it

200 Faraday’s Researches

could easily be observed; the alkali gradually became turbid,
for the protoxide first formed was dissolved, and becoming
peroxide by degrees, was deposited, and rendered the liquid
dull and yellow.

937. Dilute sulphuric acid (923).—Iron, tin, lead, and zinc,
in this electrolyte, showed the power of heat to produce a
current by exalting the chemical affinity, for the hot side was
in each case positive.

938. Dilute nitric acid is remarkable for presenting only
one case of a metal hot and cold exhibiting a striking dif erence,
and that metal is iron. With silver, copper, and zinc, the hot
side is at the first moment positive to the cold, but only in the
smallest degree.

939. Strong nitric acid. —Hot iron is positive to cold. Both
in the hot and cold acid the iron is in its peculiar state (832,

9S9)- . .

940. Dilute muriatic acid: i volume strong muriatic acid,
and 29 volumes water. —^This acid was as remarkable for the
number of cases it supplied as the dilute nitric acid was for the
contrary (938). Iron, copper, tin, lead, zinc, and cadmium
gave active circles with it, the hot metal being positive to the
cold; all the results were very striking in the strength and
permanency of the electric current produced.

941. Several cases occur in which the hot metal becomes
negative instead of positive, as above; and the principal cause
of such an effect I have already adverted to (906). Thus with
the solution of the sulphuret of potassium and zinc, on the first
immersion of the wires into the hot and cold solution there was
a pause, i.e. the galvanometer needle did not move at once, as
in the former cases; afterwards a current gradually came into
existence, rising in strength until the needle was deflected 70®
or 80®, the hot metal being negative through the electrolyte to
the cold metal. Cadmium in the same solution gave also the
first pause and then a current, the hot metal being negative;
but the effect was very small. Lead, hot, was negative, pro¬
ducing also only a feeble current. Tin^gave the same result,
but the current was scarcely sensible.

942. In dilute sulphuric acid. —Copper and zinc, after having
produced a first positive effect at the hot metal, had that
reversed, and a feeble current was produced, the hot metal
being negative. Cadmium gave the same phenomena, but
stronger (906).

Inefficacy of Contact 281

943. In dilute nitric acid .—Lead produced no effect at the
first moment; but afterwards an electric current, gradually
increasing in strength, appeared, which was able to deflect the
needle 20° or more, the hot metal being negative. Cadmium
gave the same results as lead. Tin gave an uncertain result:
at first the hot metal appeared to be a very little negative, it
then became positive, and then again the current diminished,
and went down almost entirely.

944. I cannot but view in these results of the action of heat,
the strongest proofs of the dependence of the electric current
in voltaic circuits on the chemical action of the substances con¬
stituting these circuits: the results perfectly accord with the
known influence of heat on chemical action. On the other
hand, I cannot see how the theory of contact can take cogni¬
sance of them, except by adding new assumptions to those
already composing it (862). How, for instance, can it explain
the powerful effects of iron in sulphuret of potassium, or in
potassa, or in dilute nitric acid; or of tin in potassa or sulphuric
acid; or of iron, copper, tin, etc., in muriatic acid; or indeed
of any of the effects quoted? That they cannot be due to
thermo contact has been already shown by the results with
inactive metals (919, 929); and to these may now be added
those of the active metals, silver and copper in dilute nitric
acid, for heat produces scarcely a sensible effect in these cases.
It seems to me that no other cause than chemical force (a very
sufficient one), remains, or is needed to account for them.

945. If it be said that, on the theory of chemical excitement,
the experiments prove either too much or not enough, that, in
fact, heat ought to produce the same effect with all the metals
that are acted on by the electrolytes used, then, I say, that
that does not follow. The force and other circumstances of
chemical affinity vary almost infinitely with the bodies exhibit¬
ing its action, and the added effect of heat upon the chemical
affinity would, necessarily, partake of these variations. Chemi¬
cal action often goes on without any current being produced;
and it is well known that, in almost every voltaic circuit, the
chemical force has to be considered as divided into that which
is local and that which is current. Now heat frequently assists
the local action much, and, sometimes, without appearing to be
accompanied by any great increase in the intensity of chemical
affinity; whilst at other times we are sure, from the chemical
phenomena, that it does affect the intensity of the force. The

282 Faraday’s Researches

electric current, however, is not determined by the amount of
action which takes place, but by the intensity of the affinities I
concerned; and so cases may easily be produced, in which that 1
metal exerting the least amount of action is nevertheless the
positive metal in a voltaic circuit; as with copper in weak
nitric acid associated with other copper in strong acid (963),
or iron or silver in the same weak acid against copper in the ,
strong acid (984). Many of those instances where the hot side '
ultimately becomes negative, as of zinc in dilute solution of
sulphuret of potassium (941), or cadmium and lead in dilute j
nitric acid (943), are of this nature; and yet the conditions and
result are in perfect agreement with the chemical theory of !
voltaic excitement (906). I

946. The distinction between currents founded upon that I
difference of intensity which is due to the difference in force of
the chemical action which is their exciting cause, is, I think, a
necessary consequence of the chemical theory, and in 1834 I
adopted that opinion.^ De la Rive in 1836 gave a still more
precise enunciation of such a principle,^ by saying, that the
intensity of currents is exactly proportional to the degree of
affinity which reigns between the particles, the combination

or separation of which produces the currents.

947. I look upon the question of the origin of the power in
the voltaic battery as abundantly decided by the experimental
results not connected with the action of heat. I further view
the results with heat as adding very strong confirmatory evidence
to the chemical theory; and the numerous questions which
arise as to the varied results produced, only tend to show how
important the voltaic circuit is as a means of investigation into
the nature and principles of chemical affinity (955). This
truth has already been most strikingly illustrated by the re- |
searches of De la Rive made by means of the galvanometer, and
the investigations of my friend Professor Daniell into the real 1
nature of acid and other compound electrolytes.^

Cases of two Metals and one Electrolyte ; one Junction being j
heated \

948. Since heat produced such striking results with single !

metals, I thought it probable that it might be able to affect the ;

1 Philosophical Transactions, 1834, p. 428. i

^ Annales de Cliimie, 1836, Ixi. p. 44, etc. |

® Philosophical Transactions, 1839, p. 97. !

Relation of Metals Inverted by Heat 283

mutual relation of the metals in some cases, and even invert
their order: on making circuits with two metals and electro¬
lytes, I found the following cases.

949. In the solution of sulphuret of potassium , hot tin is well
positive to cold silver: cold tin is very slightly positive to hot
silver, and the silver then rapidly tarnishes.

950. In the solution of potassa, cold tin is fairly positive to
hot lead, but hot tin is much more positive to cold lead. Also
cold cadmium is positive to hot lead, but hot cadmium is far
more positive to cold lead. In these cases, therefore, there
are great differences produced by heat, but the metals still
keep their order.

951. In dilute sulphuric acid, hot iron is well positive to cold
tin, but hot tin is still more positive to cold iron. Hot iron is
a little positive to cold lead, and hot lead is very positive to cold
iron. These are cases of the actual inversion of order; and
tin and lead may have their states reversed exactly in the same
manner.

952. In dilute nitric acid, tin and iron, and iron and lead
may have their states reversed, whichever is the hot metal being
rendered positive to the other. If, when the iron is to be
plunged into the heated side (918) the acid is only moderately
warm, it seems at first as if the tin would almost overpower the
iron, so beautifully can the forces be either balanced or rendered
predominant on either side at pleasure. Lead is positive to tin
in both cases; but far more so when hot than when cold.

953. These effects show beautifully that in many cases,
when two different metals are taken, either can be made positive
to the other at pleasure, by acting on their chemical affinities;
though the contacts of the metals with each other (supposed
to be an electromotive cause) remain entirely unchanged. They
show the effect of heat in reversing or strengthening the natural
differences of the metals, according as its action is made to
oppose or combine with their natural chemical forces, and thus
add further confirmation to the mass of evidence already
adduced.

954. There are here, as in the cases of one metal, some
instances where the heat renders the metal more negative than
it would be if cold. They occur, principally, in the solution of
sulphuret of potassium. Thus, with zinc and cadmium, or zinc
and tin, the coldest metal is positive. With lead and tin, the
hot tin is a little positive, cold tin very positive. With lead and

284 Faraday’s Researches

zinC; hot zinc is a little positive, cold zinc much more so. With
silver and lead, the hot silver is a little positive to the lead, the
cold silver is more, and well positive. In these cases the current
is preceded by a moment of quiescence (941), during which the
chemical action at the hot metal reduces the efficacy of the
electrolyte against it more than at the cold metal, and the
latter afterwards shows its advantage.

955. Before concluding these observations on the effects of
heat, and in reference to the probable utility of the voltaic
circuit in investigations of the intimate nature of chemical
affinity (947), I will describe a result which, if confirmed, may
lead to very important investigations. Tin and lead were con¬
joined and plunged into cold dilute sulphuric acid; the tin was
positive a little. The same acid was heated, and the tin and
lead, having been perfectly cleaned, were reintroduced, then the
lead was a little positive to the tin. So that a difference of
temperature not limited to one contact, for the two electrolytic
contacts were always at the same temperature, caused a difier-
ence in the relation of these metals the one to the other. Tin
and iron in dilute sulphuric acid appeared to give a similar result;
ix. in the cold acid the tin was always positive, but with hot
acid the iron was sometimes positive. The effects were but
small, and I had not time to enter further into the investigation.

956. I trust it is understood that, in every case, the pre¬
cautions as to very careful cleansing of the wires, the places
of the ends, simultaneous immersion, observation of the first
effects, etc., were attended to.

^ V. The Exciting Chemical Force affected by Dilution

957. Another mode of affecting the chemical affinity of these
elements of voltaic circuits, the metals and acids, and also
applicable to the cases of such circuits, is to vary the proportion
of water present. Such variation is known, by the simplest
chemical experiments, to affect very importantly the resulting
action, and, upon the chemical theory, it was natural to expect
that it would also produce some corresponding change in the
voltaic pile. The effects observed by Avogadro and QErsted
in 1823 are in accordance with such an expectation, for they
found that when the same pair of metals was plunged in suc¬
cession into a strong and a dilute acid, in certain cases an in-

Chemical Force Affected by Dilution 285

version of the current took place.^ In 1828 De la Rive carried
these and similar cases much further^ especially in voltaic com¬
binations of copper and iron with lead.^ In 1827 BecquereP
experimented with one metal^ copper^ plunged at its two ex¬
tremities into a solution of the same substance (salt) of different
strengths; and in 1828 De la Rive^ made many such experi¬
ments with one metal and a fluid in different states of dilution^
which I think of very great importance.

958. The argument derivable from effects of this kind ap¬
peared to me so strong that I worked out the facts to some
extent, and think the general results well worthy of statement.
Dilution is the circumstance which most generally exalts the
existing action, but how such a circumstance should increase
the electromotive force of mere contact did not seem evident to
me, without assuming^ as before (862), exactly those influences
at the points of contact in the various cases which the prior
results, ascertained by experiments, would require.

959. The form of apparatus used was the bent tube already
described (903), fig. 70. The precautions before directed with
the wires, tube, etc., were here likewise needful. But there
were others also requisite, consequent upon the current produced
by combination of water with acid, an effect which has been
described long since by Becquerel,^ but whose influence in the
present researches requires explanation.

960. Figs. 72 and 73 represent the two arrangements of
fluids used, the part below m in the tubes being strong acid,
and that above diluted. If the fluid was nitric acid and the
platinum wires as in the figures, drawing the end of the wire
D upwards above or depressing it from above m downwards,
caused great changes at the galvanometer; but if they were
preserved quiet at any place, then the electro-current ceased,
or very nearly so. Whenever the current existed it was from
the weak to the strong acid through the liquid.

^ Annales de Chimie, 1823, xxii. p. 361. ^ Ihid. 1828, xxxvii. p. 234.

^ Ibid, 1827, XXXV. p. 120. ^ Ihid. 1828, xxxvii. pp. 240, 241.

s Traite de !Electricite, ii. p. 81.

286 Faraday’s Researches

961. When the tube was arranged, as in fig. 72, with water
or dilute acid on one side only^ and the wires were immersed
not more than one-third of an inch, the effects were greatly
diminished; and more especially if, by a little motion with a
platinum wire, the acids had been mixed at m, so that the transi¬
tion from weak to strong was gradual instead of sudden. In
such cases, even when the wires were moved, horizontally, in
the acid, the effect was so small as to be scarcely sensible, and
not likely to be confounded with the chemical effects to be
described hereafter. Still more surely to avoid such inter¬
ference, an acid moderately diluted was used instead of water.
The precaution was taken of emptying, washing, and rearrang¬
ing the tubes with fresh acid after each experiment, lest any of
the metal dissolved in one experiment should interfere with the
results of the next.

962. I occasionally used the tube with dilute acid on one
side only, fig. 72, and sometimes that with dilute acid on both
sides, fig. 73. I will call the first No. i, and the second No. 2.

963. In illustration of the general results I will describe a
particular case. Employing tube No. i with strong and dilute
nitric acid,^ and two copper wires, the wire in the dilute acid
was powerfully positive to the one in the strong acid at the
first moment, and continued so. By using tube No. 2, the
galvanometer-needle could be held stiffly in either direction,
simply by simultaneously raising one wire and depressing the
other, so that the first should be in weak and the second in
strong acid; the former was always the positive piece of metal.

964. On repeating the experiments with the substitution of
platinum, gold, or even palladium for the copper, scarcely a
sensible effect was produced (961).

965. Strong and dilute nitric acid }—The following single
metals being compared with themselves in these acids, gave
most powerful results of the kind just described with copper
(963); silver, iron, lead, tin, cadmium, zinc. The metal in
the weaker acid was positive to that in the stronger. Silver
is very changeable, and after some time the current is often
suddenly reversed, the metal in the strong acid becoming
positive: this again will change back, the metal in the weaker
acid returning to its positive state. With tin, cadmium, and
zinc, violent action in the acid quickly supervenes and mixes all

^ The dilute acid consisted of three volumes of strong nitric acid and two
volumes of water.

Chemical Force Affected by Dilution 287

up together. Iron and lead show the alternations of state in the
tube No. 2 as beautifully as copper (963).

966. Strong and dilute sulfhuric acid. —I prepared an acid
of 49 by weighty strong oil of vitriol^ and 9 of water^ giving a
sulphuric acid with two proportions of water^ and arranged the
tube No. I (962) with this and the strongest acid. But as
this degree of dilution produced very little effect with the iron^
as compared with what a much greater dilution effected^ I
adopted the plan of putting strong acid into the tube^ and then
adding a little water at the top at one of the sides^ with the
precaution of stirring and cooling it previous to the experiment
(961).

967. With iron, the part of the metal in the weaker acid
was powei*fully positive to that in the stronger acid. With
copper, the same result, as to direction of the current, was
produced; but the amount of the effect was small. With silver,
cadmium, and zinc, the difference was either very small or un¬
steady, or nothing; so that, in comparison with the former
cases, the electromotive action of the strong and weak acid
appeared balanced. With lead and tin, the part of the metal in
the strong acid was positive to that in the weak acid; so that they
present an effect the reverse of that produced by iron or copper,

968. Strong and dilute muriatic acid. —I used the strongest
pure muriatic acid in tube No. i, and added water on the top
of one side for the dilute extremity (961), stirring it a little as
before. With silver, copper, lead, tin, cadmium, and zinc, the
metal in the strongest acid was positive, and the current in most
cases powerful. With iron, the end in the strongest acid was
first positive: but shortly after the weak acid side became
positive and continued so. With palladium, gold, and platinum,
nearly insensible effects were the results.

969. Strong and dilute solution of caustic potassa. —With iron,
copper, lead, tin, cadmium, and zinc, the metal in the strong
solution was positive: in the case of iron slightly, in the case of
copper more powerfully, deflecting the needle 30° or 38°, and
in the cases of the other metals very strongly. Silver, palladium,
gold, and platinum gave the merest indications (961).

Thus potash and muriatic acid are, in several respects, con¬
trasted with nitric and sulphuric acids. As respects muriatic
acid, however, and perhaps even the potash, it may be admitted
that, even in their strongest states, they are not fairly comparable
to the very strong nitric and sulphuric acids, but rather to those
acids when somewhat diluted (973).

288

.. —gg——

Faraday’s Researches 1

970. I know it may be said in reference to the numerous j

changes with strong and dilute acids^ that the results are the !

consequence of corresponding alterations in the contact force; |

but this is to change about the theory with the phenomena and j

with chemical force (862^ 944^ 973^ 994^ 1002^ 1051); or it may i

be alleged that it is the contact force of the solutions produced j

at the metallic surfaces which^ differing, causes difference of I

effect; but this is to put the e:ffect before the cause in the order j

of time. If the liberty of shifting the point of efficacy from |

metals to fluids, or from one place to another, be claimed, it is |

at all events quite time that some definite statement and data [

respecting the active points (796) should be given. At present

it is difficult to lay hold of the contact theory by any argument
derived from experiment, because of these uncertainties or |

variations, and it is in that respect in singular contrast with the |

definite expression as to the place of action which the chemical i

theory supplies. !

971. All the variations which have been given are consistent
with the extreme variety which chemical action under different
circumstances possesses, but, as it still appears to me, are utterly ,
incompatible with, what should be, the simplicity of mere
contact action; further they admit of even greater variation, !
which renders the reasons for the one view and against the other
still more conclusive.

972. Thus if a contact philosopher say that it is only the very

strongest acids that can render the part of the metals in it i

negative, and therefore the effect does not happen with muriatic ;

acid or potash (968, 969), though it does with nitric and sul- '

phuric acids (965, 966); then the following result is an answer

to such an assumption. Iron in dilute nitric acid, consisting of •
one volume of strong acid and twenty of water, is positive to |
iron in strong acid, or in a mixture of one volume of strong acid |
with one of water, or with three, or even with five volumes of ,
water. Silver also, in the weakest of these acids, is positive to |

silver in any of the other four states of it. |

973. Or if, modifying the statement upon these results, it
should be said that diluting the acid at one contact always tends
to give it a certain proportionate electromotive force, and there¬
fore diluting one side more than the other will still allow this
force to come into play; then, how is it that with muriatic acid i
and potassa the effect of dilution is the reverse of that which
has been quoted in the cases with nitric acid and iron or silver
(965, 972)? Or if, to avoid difficulty, it be assumed that each i

Insufficiency of the Contact Theory 289

electrolyte must be considered apart, the nitric acid by itself,
and the muriatic acid by itself, for that one may differ from
another in the direction of the change induced by dilution, then
how can the following results with a single acid be accounted for?

974. I prepared four nitric acids:

A was very strong pure nitric acid;

B was one volume of A and one volume of water;

C was one volume of A and three volumes of water;

D was one volume of A and twenty volumes of water.

Experimenting with these acids and a metal, I found that
copper in C acid was positive to copper in A or D acid. Nor
was it first addition of water to the strong acid that brought
about this curious relation, for copper in the B acid was positive
to copper in the strong acid A, but negative to the copper in the
weak acid D: the negative e:ffect of the stronger nitric acid with
this metal does not therefore depend upon a very high degree
of concentration.

975. Lead presents the same beautiful phenomena. In the
C acid it is positive to lead either in A or D acid: in B acid it
is positive to lead in the strongest, and negative to lead in the
weakest acid.

976. I prepared also three sulphuric acids:

E was strong oil of vitriol;

F one volume of E and two volumes of water;

G one volume of E and twenty volumes of water.

Lead in F was well negative to lead either in E or G. Copper
in F was also negative to copper in E or G, but in a smaller
degree. So here are two cases in which metals in an acid of
a certain strength are negative to the same metals in the same
acid, either stronger or weaker. I used platinum wires ulti¬
mately in all these cases with the same acids to check the inter¬
ference of the combination of acid and water (961); but
the results were then almost nothing, and showed that the
phenomena could not be so accounted for.

977. To render this complexity for the contact theory still
more complicated, we have further variations, in which, with
the same acid strong and, diluted, some metals are positive in
the strong acid and others in the weak. Thus, tin in the
strongest sulphuric acid E (976) was positive to tin in the
moderate or weak acids F and G; and tin in the moderate acid
F was positive to the same metal in G. Iron, on the contrar\'',

T

290 Faraday’s Researches

being in the strong acid E was negative to the weaker acids F
and G; and iron in the medium acid F was negative to the same
metal in G.

978. For the purpose of understanding more distinctly what
the contact theory has to do here, I will illustrate the case by
a diagram. Let fig. 74 represent a circle of metal and sulphuric
acid. If A be an arc of iron or copper, and B C strong oil of

^ vitriol, there will be no determinate

/---\ current: or if B C be weak acid, there

will be no such current: but let it be
stroug acid at B, aud diluted at C,
B c and an electric current will run

Fig. 74. round A C B. If the metal A be

silver, it is equally indifferent with
the strong and also with the weak acid, as iron has been found
to be as to the production of a current; but, besides that, it is
indifferent with the strong acid at B and the weak acid at C.
Now if the dilution of the electrolyte at one part, as C, had so
far increased the contact electromotive force there, when iron
or copper was present, as to produce the current found by
experiment; surely it ought (consistently with any reasonable
limitations of the assumptions in the contact theory) to have
produced the same effect with silver: but there was none.
Making the metal A lead or tin, the difficulty becomes far
greater; for though with the strong or the weak acid alone any
effect of a determinate current is nothing, yet one occurs upon
dilution at C, but now dilution must be supposed to weaken
mstead of strengthen the contact force, for the current is in the
reverse direction.

979. Neither can these successive changes be referred to a
gradual progression in the effect of dilution, dependent upon
the order of the metals. For supposing dilution more favourable
to the electromotive force of the contact of an acid and a metal,
in ^proportion as the metals were in a certain order, as for
instance that of their efficacy in the voltaic battery; though
such an assumption might seem to account for the gradual
diminution of effect from iron to copper, and from copper to
silver, one would not expect the reverse effects, or those on the
other side of zero, to appear by a return back to such metals
as lead and tin (967, 977), but rather look for them in platinum
or gold, which, however, produce no results of the kind (964,
976). To increase still further this complexity, it appears, from
what has been before stated, that on changing the acids the

m

Order of Metals Changed by Dilution 291

order must again be changed (969); nay^ more, that with the
same acid, and merely by changing the proportion of dilution,
such alteration of the order must take place (974, 976).

980. Thus it appears, as before remarked (970), that to apply
the theory of contact electromotive force to the facts, that
theory must twist and bend about with every variation of
chemical action; and after all, with every variety of contact,
active and inactive, in no case presents phenomena independent
of the active exertion of chemical force.

981. As the influence of dilution and concentration was so
strong in affecting the relation of different parts of the same
metal to an acid, making one part either positive or negative to
another, I thought it probable that, by mere variation in the
strength of the interposed electrolyte, the order of metals when
in acids or other solutions of uniform strength might be changed.
I therefore proceeded to experiment on that point, by com¬
bining together two metals, tin and lead, through the galva¬
nometer (903); arranging the electrolytic solution in tube No. i,
strong on one side and weak on the other: immersing the wires
simultaneously, tin into the strong, and lead into the weak
solution, and after observing the effect, re-cleaning the wires,
rearranging the fluid, and reimmersing the wires, the tin into
the weak, and the lead into the strong portion. De la Rive has
already stated ^ that inversions take place when dilute and
strong sulphuric acid is used; these I could not obtain when
care was taken to avoid the effect of the investing fluid (906):
the general statement is correct, however, when applied to
another acid, and I think the evidence very important to the
consideration of the great question of contact or chemical action.

982. Two metals in strong and weak solution of potash. —Zinc
was positive to tin, cadmium, or lead, whether in the weak or
strong solution. Tin was positive to cadmium, either in weak
or strong alkali. Cadmium was positive to lead both ways, but
most when in the strong alkali. Thus, though there were
differences in degree dependent on the strength of the solution,
there was no inversion of the order of the metals.

983. Two 7 netals in strong and weak sulphuric acid. —Cadmium
was positive to iron and tin both ways: tin was also positive to
iron, copper, and silver; and iron was positive to copper and
silver, whichever side the respective metals were in. Thus none
of the metals tried could be made to pass the others, and so
take a different order from that which they have in acid uniform

^Annates de Chimie, 1828, xxxvii. p. 240.

I

^92 Faraday’s Reseaixhes

Strength, Still there were great variations in degree; thus
^p- in strong acid was only a little positive to silver in weak
t»ut iron in weak acid was very positive to silver in strong
^*-cid.^ Generally the metal, usually called positive, was most |

positive in the weak acid; but that was not the case with lead, !

9-nd zinc. !

9^4- Two metals in strong and weak nitric acid. —^Here the I
^^Gigree of change produced difference in the strength of the |
j^cid was so great as to cause not merely difference in degree, !

but inversions of the order of the metals, of the most striking i

nature. Thus iron and silver being in tube No. 2 (962), which- |

^ver metal was in the weak acid was positive to the other in the ^

•""trong acid. It was merely requisite to raise the one and lower
other metal to make either positive at pleasure (963).
kopper in weak acid was positive to silver, lead, or tin in strong
acid. Iron in weak acid was positive to silver, copper, lead,

^unc, or tin in strong acid. Lead in weak acid was positive to |

copper, silver, tin, cadmium, zinc, and iron in strong acid. j

‘"Silver in weak acid was positive to iron, lead, copper, and, j

fhough slightly, even to tin in strong acid. Tin in weak acid ;

was positive to copper, lead, iron, zinc, and silver, and either |
neutral or a little positive to cadmium in strong acid. Cadmium
in weak acid is very positive, as might be expected, to silver,
f'opper, lead, iron, and tin, and, moderately so, to^ zinc in the ;
strong acid. When cadmium is in the strong acid it is slightly
positive to silver, copper, and iron in weak acid. Zinc in weak
acid is very positive to silver, copper, lead, iron, tin, and ;

cadmium in strong acid: when in the strong acid it is a little |

positive to silver and copper in weak acid.

985. Thus wonderful changes occur amongst the metals in ,

f'ircuits containing this acid, merely by the effect of dilution; ;
“^0 that of the five metals, silver, copper, iron, lead, and tin, any |
one of them can be made either positive or negative to any other, 1
with the exception of silver positive to copper. ^ The order of j
these five metals only may therefore be varied about one j
hundred different ways in the same acid, merely by the effect ;
rd dilution. ^ ^ . . . '

986. So also zinc, tin, cadmium, and lead; and likewise zinc, j

tin, iron, and lead, being groups each of four metals; any one j
of these metals may be made either positive or negative to any |
other metal of the same group, by dilution of this acid. I

i

987. But the case of variation by dilution may, as regards the j

Voltaic Excitement Affected by Dilution 293

opposed theories, be made even still stronger than any yet
stated; for the same metals in the same acid of the same strength
at the two sides may be made to change their order, as the
chemical action of the acid on each particular metal is affected,
by dilution, in a smaller or greater degree.

988. A voltaic association of iron and silver was dipped, both
metals at once, into the same strong nitric acid; for the first
instant, the iron was positive; the moment after, the silver
became positive, and continued so. A similar association of
iron and silver was put into weak nitric acid, and the iron was
immediately positive, and continued so. With iron and copper
the same results were obtained.

989. These, therefore, zxt finally cases of such an inversion
(987), but as the iron in the strong nitric acid acquires a state
the moment after its immersion which is probably not assumed
by it in the weak acid (831, 939, 1021), and as the action on the
iron in its ordinary state may be said to be to render it positive
to the silver or copper, both in the strong or weak acid, we will
not endeavour to force the fact, but look to other metals.

990. Silver and nickel being associated in weak nitric acid,
the nickel was positive; being associated in strong nitric acid,
the nickel was still positive at the first moment, but the silver
was finally positive. The nickel lost its superiority through the
influence of an investing film (906); and though the effect might
easily pass unobserved, the case cannot be allowed to stand,
as fulfilling the statement made (987).

991. Copper and nickel were put into strong nitric acid; the
copper was positive from the first moment. Copper and nickel
being in dilute nitric acid, the nickel was slightly but clearly
positive to the copper. Again, zinc and cadmium in strong
nitric acid; the cadmium was positive strongly to the zinc; the
same metals being in dilute nitric acid, the zinc was very
positive to the cadmium. These I consider beautiful and
unexceptionable cases (987).

992. Thus the nitric acid furnishes a most wonderful variety
of effects when used as the electrolytic conductor in voltaic
circles; and its difference from sulphuric acid (983) or from
potassa (982) in the phenomena consequent upon dilution, tend,
in conjunction with many preceding facts and arguments, to
show that the electromotive force in a circle is not the con¬
sequence of any power in bodies generally, belonging to them
in classes rather than as individuals, and having that simplicity

294 Faraday’s Researches

of character which contact force has been assumed to have; but
one that has all the variations which chemical force is known to
exhibit.

993. The changes occurring where any one of four or five
metals, differing from each other as far as silver and tin, can be
made positive or negative to the others (985, 986), appears to me
to shut out the probability that the contact of these metals with
each other can produce the smallest portion of the effect in these
voltaic arrangements; and then, if not there, neither can they
be effective in any other arrangements; so that what has been
deduced in that respect from former experiments (817, 821) is
confirmed by the present.

994. Or if the scene be shifted, and it be said that it is the
contact of the acids or solutions which, by dilution at one side,
produce these varied changes (862, 970, 979, 1002, 1048), then
how utterly unlike such contact must be to that of the numerous
class of conducting solid bodies (797, 855)! and where, to give
the assumption any show of support, is the case of such contact
(apart from chemical action) producing such currents?

995. That it cannot be an alteration of contact force by mere
dilution at one side (994) is also shown by making such a change,
but using metals that are chemically inactive in the electrol;^e
employed. Thus when nitric or sulphuric acids were diluted at
one side, and then the strong and the weak parts connected by
platinum or gold (964), there was no sensible current, or only
one so small as to be unimportant.

996. A still stronger proof is afforded by the following
result. I arranged the tube, hg. 72 (960), with strong solution
of yellow sulphuret of potassium (800) from A to m, and a
solution consisting of one volume of the strong solution, with
six of water from w to B. The extremities were then con¬
nected by platinum and iron in various ways; and when the
first effect of immersion was guarded against, including the first
brief negative state of the iron (1037), the effects were as follows.
Platinum being in A and in B, that in A, or the strong solution,
was very slightly positive, causing a permanent deflection of 2°.
Iron being in A and in B, the same result was obtained. Iron
being in A and platinum in B, the iron was positive about 2°
to the platinum. Platinum being in A and iron in B, the
platinum was now positive to the iron by about 2°. So that
not only the contact of the iron and platinum passes for nothing,
but the contact of strong and weak solution of this electrolyte
with either iron or platinum is ineffectual in producing a

Order of Metals in Voltaic Circles 295

currentc The current which is constant is very feeble, and'
evidently related to the mutual position of the strong and weak
solutions, and is probably due to their gradual mixture.

997. The results obtained by dilution of an electrolyte capable
of acting on the metals employed to form with it a voltaic circuit
may in some cases depend on making the acid a better electro¬
lyte. It would appear, and would be expected from the chemi¬
cal theory, that whatever circumstance tends to make the fluid
a more powerful chemical agent and a better electrolyte (the
latter being a relation purely chemical and not one of contact),
favours the production of a determinate current. Whatever
the cause of the effect of dilution may be, the results still tend to-
show how valuable the voltaic circle will become as an investi¬
gator of the nature of chemical affinity (947).

^ vi. Differences in the Order of the Metallic Elements of
Voltaic Circles

998. Another class of experimental arguments, bearing upon
the great question of the origin of force in the voltaic battery, is
supplied by a consideration of the different order in which the
metals appear as electromotors when associated with different
exciting electrolytes. The metals are usually arranged in a
certain order; and it has been the habit to say that a metal
in the list so arranged is negative to any one above it, and
positive to any one beneath it, as if (and indeed upon the con¬
viction that) they possessed a certain direct power one with
another. But in 1812 Davy showed inversions of this order in
the case of iron and copper^ (678); and in 1828 De la Rive
showed many inversions in different cases ^ (865); gave a strong
contrast in the order of certain metals in strong and dilute nitric
acid;^ and in objecting to Marianini’s result most clearly says
that any order must be considered in relation only to that
liquid employed in the experiments from which the order is
derived.^

999. I have pursued this subject in relation to several solu¬
tions, taking the precautions before referred to (905, etc.), and
find that no such single order as that just referred to can be-
maintained. Thus nickel is negative to antimony and bismuth,
in strong nitric acid; it is positive to antimony and bismuth ia.

^ Elements of Chemical Philosophy^ p. 149.

® Annales de Chimie, 1828. xxxvii. p. 232.

^ Ibid, p. 235. ^ Ibid. p. 243.

296 Faraday’s Researches

^ dilute nitric acid; it is positive to antimony and negative to
bismuth in strong muriatic acid; it is positive to antimony and
bismuth in dilute sulphuric acid; it is negative to bismuth and
antimony in potash; and it is very negative to bismuth and
antimony, either in the colourless or the yellow solution of
sulphuret of potassium.

1000. In further illustration of this subject I will take ten
metals, and give their order in seven different solutions, as on
opposite page.

1001. The dilute nitric acid consisted of one volume strong
acid and seven volumes of water; the dilute sulphuric acid, of
one volume strong acid and thirteen of water; the muriatic acid,
of one volume strong solution and one volume water. The
strong nitric acid was pure, and of specific gravity 1.48. Both
strong and weak solution of potassa gave the same order. The
yellow sulphuret of potassium consisted of one volume of strong
solution (800) and five volumes of water, The metals are
numbered in the order which they presented in the dilute acids
(the negative above), for the purpose of showing, by the com¬
parison of these numbers in the other columns, the striking
departures there from this, the most generally assumed order.
Iron is included, but only in its ordinary state; its place in
nitric acid being given as that which it possesses on its first
immersion, not that which it afterwards acquires.

1002. The displacements appear to be most extraordinary,
as extraordinary as those consequent on dilution (993); and
thus show that there is no general ruling influence of fluid con¬
ductors, or even of acids, alkalies, etc., as distinct classes of such
conductors, apart from their pure chemical relations. But how
can the contact theory account for these results? To meet
such facts it must be bent about in the most extraordinary
manner, following all the contortions of the string of facts (862,
944, 980, 994, 1051), and yet never showing a case of the pro¬
duction of a current by contact alone, i.e. unaccompanied by
chemical action.

1003. On the other hand, how simply does the chemical
theory of excitement of the current represent the facts 1 as far
as we can yet follow them they go hand in hand. Without
chemical action, no current; with the changes of chemical
action, changes of current; whilst the influence of the strongest
cases of contact^ as of silver and tin (985) with each other, pass
for nothing in the result. In further confirmation, the exciting
power does not rise, but fall, by the contact of the bodies pro-

Order of Metals

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298 Faraday’s Researches

ducedj as the chemical actions producing these decay or are
exhausted; the consequent result being well seen in the effect
of the investing fluids produced (906^ 941^ 954).

1004. Thus, as De la Rive has said, any list of metals in their
order should be constructed in reference to the exciting fluid
selected. Further, a zero point should be expressed in the
series; for as the electromotive power may be either at the
anode or cathode (1028, 1040), or jointly at both, that sub¬
stance (if there be one) which is absolutely without any exciting
action should form the zero point. The following may be given,
by way of illustration, as the order of a few metals, and other
substances in relation to muriatic acid:

Peroxide of leadj
Peroxide of manganese,

Oxide of iron,

Plumbago,

Rhodium,

Platinum,

Gold,

Antimony,

Silver,

Copper,

Zinc:

in which plumbago is the neutral substance; those in italics
are active at the cathode, and those in Roman characters at the
anode. The upper are of course negative to the lower. To
make such lists as complete as they will shortly require to be,
numbers expressive of the relative exciting force, counting
from the zero point, should be attached to each substance.

^ vii. Active Voltaic Circles and Batteries without Metallic Contact

1005. There are cases in abundance of electric currents pro¬
duced by pure chemical action, but not one undoubted instance
of the production of a current by pure contact. As I conceive
the great question must now be settled by the weight of evidence,
rather than by simple philosophic conclusions (787), I propose
adding a few observations and facts to show the number of
these cases, and their force. In the sixth part of these
Researches ^ (April 1834) I gave the first experiment, that I
am aware of, in which chemical action was made to produce an
electric current and chemical decomposition at a distance, in a

^ Philosophical Transactions^ 1834, p. 426.

Yoltaic Circles Without Metallic Contact 399

simple circuit, without any contact of metals (615^ ^tc.).
was f'ci^ther shown that when a pair of zinc and platinum plates
were excited at one end of the dilute nitro-sulphuric acid (615)^
Qj. solution of potash (619), or even in some cases a solution of
corninon salt (620), decompositions might be produced at the
other end, of solutions of iodide of potassium (635), protochloride
of tin (636), sulphate of soda, muriatic acid, and nitrate of
silver (641); or of the following bodies in a state of fusion:
nitre, chlorides of silver and lead, and iodide of lead (637, 641);
no metallic contact being allowed in any of the experiments.

X006. I will proceed to mention new cases; and first, those
already referred to, where the actionof a little dilute acid produced
a current passing through the solution of the sulphuret of potas¬
sium (S19); green nitrous acid (832), or the solution of potassa
(842); for here no metallic contact was allowed, and chemical
action was the evident and only cause of the currents produced.

1007. On the following page is a table of cases of similar excite¬
ment and voltaic action, produced by chemical action without
metallic contact. Each horizontal line contains the four sub¬
stances forming a circuit, and they are so arranged as to give
the direction of the current, which was in all cases from left to
right through the bodies as they now stand. All the combi¬
nations set down were able to effect decomposition, and they
are but a few of those which occurred in the course of the
investigation.

xooS,~- See next page.

1009. It appears to me probable that any one of the very
numerous combinations which can be made out of the follow¬
ing table, by taking one substance from each column and
arranging them in the order in which the columns stand, would
produce a current without metallic contact, and that some of
these currents would be very powerful.

Rhodium

Gold

Platinum

Palladium

Silver

Nickel

Copper

Lead

Tin

Zinc

Cadmium ^

c

p

s 'B

4-> 9

b/) S

C 2 3

2 -So.

Iron

' Dilute nitric acid
Dilute sulphuric acid
Muriatic acid

Solution of vegetable acids
Iodide of potassium
Iodide of zinc
Solution of salt
^ Many metallic solutions

300

Faraday’s Researches
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Batteries Without Metallic Contact 301

loio. To these cases must be added the many in which one
metal in a uniform acid gave currents when one side was heated
(93O; etc.). Also those in which one metal with an acid strong
and diluted gave a current (965^ etc.).

roll. In the cases where by dilution of the acid one metal
can be made either positive or negative to another (984^ etc.)^
one half of the results should be added to the above^ except
that they are too strong; for instead of proving that chemical
action can produce a current without contact^ they go to the
extent of showing a total disregard of it^ and production of the
current against the force of contact^ as easily as with it.

1012. That it is easy to construct batteries without metallic
contact was shown by Sir Humphry Davy in 1801/ when he
described various effective arrangements including only one
metal. At a later period Zamboni constructed a pile in which
but one metal and one fluid was used^^ the only difference being
extent of contact at the two surfaces. The following forms,
which are dependent upon the mere effect of dilution, may be
added to these.

c c CO

1013. Let ah^ah^ah^ fig. 75, represent tubes or other vessels,
the parts at a containing strong nitric or sulphuric acid, and
the parts at b dilute acid of the same kind; then connect these
by wires, rods, or plates of one metal only, being copper, iron,
silver, tin, lead, or any of those metals which become positive
and negative by difference of dilution in the acid (967, etc.).
Such an arrangement will give an effective battery.

1014. If the acid used be the sulphuric, and the metal
employed be iron, the current produced will be in one direc¬
tion, thus —, through the part figured; but if the metal
be tin, the resulting current will be in the contrary direction,
thus—>

^ Philosophical Transactions, 1801, p. 397. Also Journals of the Royal
Institution, 1802, p. 51; and iNicholson^s Journal, 8vo, 1802, vol. i. p. 144.

^ Quarterly Journal of Science, viii. 177; or Annales de Chimie, 1819,
xi. 190.

302 Faraday’s Researches

1015. Strong and weak solutions of potassa being employed
in the tubes^ then the single metals zinc^ lead;, copper^ tin^ and
cadmium (969) will produce a similar battery.

1016. If the arrangements be as in fig. 76^ in which the vessels
I;. 3;. 5> etc. contain strong sulphuric acid^ and the vessels
2^ 4., etc. dilute.sulphuric acid; and if the metals a, a
are tin^ and b, b, b are iron (967); a battery electric current
will be produced in the direction of the arrow. If the metals
be changed for each other^ the acids remainmg; or the acids
be changed; the metals remaining; the direction of the current
will be reversed.

^ viii. Considerations of the Sufficiency of Chemical Action

1017. Thus there is no want of cases in which chemical
action alone produces voltaic currents (1005); and if we pro¬
ceed to look more closely to the correspondence which ought
to exist between the chemical action and the current produced,
we find that the further we trace it the more exact it becomes;
in illustration of which the following cases will suffice.

1018. Chemical action does evolve electricity .—^This has been
abundantly proved by Becquerel and De la Rive, BecquereFs
beautiful voltaic arrangement of acid and alkali^ is a most
satisfactory proof that chemical action is abundantly sufficient
to produce electric phenomena. A great number of the results
described in the present papers prove the same statement.

1019. Where chemical action has been, but diminishes or
ceases, the electric current diminishes or ceases also .—^The cases
of tin (870; 872), lead (873); bismuth (883); and cadmium (893);
in the solution of sulphuret of potassium; are excellent instances
of the truth of this proposition.

1020. If a piece of grain tin be put into strong nitric acid; it
will generally exert no action; in consequence of the film of

^ Annales de Chimie, 1827, xxxv. p. 122. Bibliothique Universelle, 1838,
xiv. 129, 171*

Excitement and Chemical Action 303

oxide which is formed upon it by the heat employed in the
process of breaking it up. Then two platinum wireS; connected
by a galvanometer, may be put into the acid, and one of them
pressed against the piece of tin, yet without producing an
electric current. If, whilst matters are in this position, the tin
be scraped under the acid by a glass rod, or other non-conduct¬
ing substance capable of breaking the surface, the acid acts on
the metal newly exposed, and produces a current; but the
action ceases in a moment or two from the formation of oxide of
tin and an exhausted investing solution (906), and the current
ceases with it. Each scratch upon the surface of the tin re¬
produces the series of phenomena.

1021. The case of iron in strong nitric acid, w^hich acts and
produces a current at the first moment (831, 939, 989), but is
by that action deprived of so much of its activity, both chemical
and electrical, is also a case in point.

1022. If lead and tin be associated in muriatic acid, the
lead is positive at the first moment to the tin. The tin then
becomes positive, and continues so. This change I attribute
to the circumstance that the chloride of lead formed partly
invests that metal, and prevents the continuance of the action
there; but the chloride of tin, being far more soluble than that
of lead, passes more readily into the solution; so that action
goes on there, and the metal exhibits a permanent positive
state.

1023. The effect of the investing fluid already referred to in
the cases of tin (907) and cadmium (906), some of the results
with two metals in hot and cold acid (954); and those cases
where metal in a heated acid became negative to the same
metal in cold acid (941, etc.), are of the same kind. The latter
can be beautifully illustrated by two pieces of lead in dilute
nitric acid: if left a short time, the needle stands nearly at 0°,
but on heating either side, the metal there becomes negative
20° or more, and continues so as long as the heat is continued.
On cooling that side and heating the other, that piece of lead
which before was positive now becomes negative in turn, and
so on for any number of times.

1024. When the chemical action changes the current changes
also ,—This is shown by the cases of two pieces of the same
active metal in the same fluid. Thus if two pieces of silver be
associated in strong muriatic acid, first the one will be positive
and then the other; and the changes in the direction of the
current will not be slow as if by a gradual action, but exceedingly

304 Faraday’s Researches

sharp and sudden. So if silver and copper be associated in a
dilute solution of sulphuret of potassium^ the copper will be
chemically active and positive^ and the silver will remain clean;
until of a sudden the copper will cease to acty the silver will
become instantly covered with sulphuret; showing by that the
commencement of chemical action there; and the needle of
the galvanometer will jump through 180°. Two pieces of silver
or of copper in solution of sulphuret of potassium produce the
same effect.

1025. If metals be used which are inactive in the fluids
employed; and the latter undergo no change during the time;
from other circumstances; as heat; etc. (826; 925); then no
currents; and of course no such alterations in direction; are
produced.

1026. Where no chemical action occurs no current is produced.
—This in regard to ordinary solid conductors is well known
to be the case; as with metals and other bodies (855). It has
also been shown to be true when fluid conductors (electrolytes)
are used; in every case where they exert no chemical action;
though such different substances as acid; alkalies and sulphurets

^ have been employed (831; 841;

^ "x 813; 817). These are very

striking facts.

K 1027. But a current will occur

^ /V ^ chemical action com-

/iy niences. —This proposition may
xix vix illustrated by the fol

p. lowing experiment. Make an

arrangement like that in fig.
77: the two tubes being charged with the same pure; pak;
strong nitric acid; the two platinum wires p p being connected
by a galvanometer; and the wire i^ of iron. The apparatus is
only another form of the simple arrangement; fig. 78; where; in
imitation of a former experiment (624); two plates of iron and
platinum are placed parallel; but

separated by a drop of strong nitric ? . . . —

acid at each extremity. Whilst in —d

this state no current is produced in Fig. ys.

either apparatus; but if a drop of

water be added at b, fig. 78; chemical action commences; and a
powerful current is produced, though without metallic or any
additional contact. To observe this with the apparatus, fig. 77,
a drop of water was put in at b. At first there was no chemical

Excitement and Chemical Action 305

action and no electric current; though the water was there; so
that contact with the water did nothing: the water and acid
were moved and mixed together by means of the end of the
wire i; in a few moments proper chemical action came on; the
iron evolving nitrous gas at the place of its action; and at
the same time acquiring a positive condition at that part;
and producing a powerful electric current.

1028. When the chemical action which either has or could
have produced a current in one direction is reversed or undone^
the current is reversed (or undone) also,

1029. This is a principle or result which most strikingly
confirms the chemical theory of voltaic excitement; and is
illustrated by many important facts. Volta in the year 1802 ^
showed that crystallised oxide of manganese was highly negative
to zinc and similar metalS; giving; according to his theory;
electricity to the zinc at the point of contact. Becquerel
worked carefully at this subject in 1835;^ and came to the com
elusion; but reservedly expressed; that the facts were favourable
to the theory of contact. In the following year De la Rive
examined the subject;^ and showS; to my satisfaction at least;
that the peroxide is at the time undergoing chemical change
and losing oxygeU; a change perfectly in accordance with the
direction of the current it produces.

1030. The peroxide associated with platinum in the green*
nitrous acid originates a current; and is negative to the platinum;,
at the same time giving up oxygen and converting the nitrous-
acid into nitric acid; a change easily shown by a common
chemical experiment. In nitric acid the oxide is negative*-to-
platinum; but its negative state is much increased if a little-
alcohol be added to the acid; that body assisting in the reduc¬
tion of the oxide. When associated with platinum in solution of
potash; the addition of a little alcohol singularly favours the*
increase of the current for the same reason. When the per¬
oxide and platinum are associated with solution of sulphuret
of potassium, the peroxide, as might have been expected, is
strongly negative.

1031. In 1835 M. Muncke^ observed the striking power of
peroxide of lead to produce phenomena like those of the per¬
oxide of manganese, and these M. de la Rive in 1836 immedi¬
ately referred to corresponding chemical changesM. Schoenbein

^ Annales de CMmie, 1802, xl. 224. ^ Ibid, 1835, lx. 164, 171.

® Ibid. 1836, Ixi. 40; and Bibliotheque Universelle, 1836, i. 152, 158.

^ BibliotMque Universelle, 1836, i. 160. ® Ibid. 1836, i., 154 162.

U

306 Faraday’s Researches

does not admit this inference^, and bases his view of ‘‘ currents sulphui

of tendency on the phenomena presented by this body and manner

its non-action with nitric acid.^ My own results confirm these b

those of M. de la Rive^ for by direct experiment I find that was on

the peroxide is acted upon by such bodies as nitric acid. Potash 1035.

and pure strong nitric acid boiled on peroxide of lead readily iron. ]

dissolved it; forming protonitrate of lead. A dilute nitric of such

acid was made and divided into two portions; one was tested not at i

by a solution of sulphuretted hydrogen; and showed no signs current

of lead: the other was mingled with a little peroxide of lead But if

(810) at common temperatures; and after an hour filtered and and dri

tested in the same manner; and found to contain plenty of lead. sulphur

1032. The peroxide of lead is negative to platinum in solutions or pota:

of common salt and potash; bodies which might be supposed be mois

to exert no chemical action on it. But direct experiments washed

•show that they do exert sufficient action to produce all the , with pi
‘effects. A circumstance in further proof that the current in produce

the voltaic circuit formed by these bodies is chemical in its iron dui

origin is the rapid depression in the force of the current pro- 1036.

duced; after the first moment of immersion. fully

1033. The most powerful arrangement with peroxide of lead; toxide

platinum; and one fluid; was obtained by using a solution of 1037.

the yellow sulphuret of potassium as the connecting fluid. A guarded

convenient mode of making such experiments was to form the 874). 1

peroxide into a fine soft paste with a little distilled water; to a dilute

cover the lower extremity of a platinum plate uniformly with to platii

this paste; using a glass rod for the purpose; and making the if it be

coat only thick enough to hide the platinum well; then to dry becomes

it weU; and finally; to compare that plate with a clean platinum perfecth

plate in the electrolyte employed. Unless the platinum plate be nega'
were perfectly covered; local electrical currents took place ; cleansed
which interfered with the result. In this way; the peroxide is , is (f^e t(
easily shown to be negative to platinum either in the solution during ;

of the sulphuret of potassium or in nitric acid. Red lead gave after re

the same results in both these fluids. be consi

1034. But using this sulphuretted solution; the same kind characte

of proof in support of the chemical theory could be obtained fire spor

from protoxides as before from the peroxides. ThuS; some ' dipped i
pure protoxide of lead; obtained from the nitrate by heat and atmosph

fusion; was applied on the platinum plate (1033); and found to film of

be strongly negative to metallic platinum in the solution of is^ there

^Philosophical Magazine^ 1838, xii. 226, 311; and BibliothSque Univer- produce(

selle, 1838, xiv. 155. 1038.

Excitement at the Cathode

307

sulphuret of potassium. White lead applied in the same
manner was also found to acquire the same state. Either of
these bodies when compared with platinum in dilute nitric acid
waS; on the contrary^ very positive.

1035. The same effect is well shown by the action of oxidised
iron. If a plate of iron be oxidised by heat so as to give an oxide
of such aggregation and condition as to be acted on scarcely or
not at all by the solution of sulphuret^ then there is little or no
current; such an oxide being as platinum in the solution (828).
But if it be oxidised by exposure to air^ or by being wetted
and dried; or by being moistened by a little dilute nitric or
sulphuric acid and then washed; first in solution of ammonia
or potassa; and afterwards in distilled water and dried; or if it
be moistened in solution of potassa; heated in the air; and then
washed well in distilled water and dried; such iron associated
with platinum and put into a solution of the sulphuret will
produce a powerful current until all the oxide is reduced; the
iron during the whole time being negative.

1036. A piece of rusty iron in the same solution is power¬
fully negative. So also is a platinum plate with a coat of pro¬
toxide; or peroxide; or native carbonate of iron on it (1033).

1037. This result is one of those effects which has to be
guarded against in the experiments formerly described (814;
874). If what appears to be a clean plate of iron is put into
a dilute solution of the sulphuret of potassium, it is first negative
to platinum; then neutral, and at last generally feebly positive;
if it be put into a strong solution, it is first negative, and then
becomes neutral, continuing so. It cannot be cleansed so
perfectly with sand-paper but that when immersed it will
be negative, but the more recently and well the plate has been
cleansed; the shorter time does this state continue. This effect
is due to the instantaneous oxidation of the surface of the iron
during its momentary exposure to the atmosphere, and the
after reduction of this oxide by the solution. Nor can this
be considered an unnatural result to those who consider the
characters of iron. Pure iron in the form of a sponge takes
fire spontaneously in the air; and a plate recently cleansed, if
dipped into water, or breathed upon, or only exposed to the
atmosphere, produces an instant smell of hydrogen. The thin
fibrn of oxide which can form during a momentary exposure
is, therefore, quite enough to account for the electric current
produced.

1038. As a further proof of the truth of these explanations.

308 Faraday’s Researches

I placed a plate of iron under the surface of a solution of the
sulphuret of potassium^ and rubbed it there with a piece of
wood which had been soaking for some time in the same sul¬
phuret. The iron was then neutral or very slightly positive
to platinum connected with it. Whilst in connection with the
platinum it was again rubbed with the wood so as to acquire a
fresh surface of contact; it did not become negative^ but con¬
tinued in the least degree positive^ showing that the former
negative current was only a temporary result of the coat of
oxide which the iron had acquired in the air.

1039. Nickel appears to be subject to the same action as
iron^ though in a much slighter degree. All the circumstances
were parallel, and the proof applied to iron (1038) was applied
to it also, with the same result.

1040. So all these phenomena with protoxides and peroxides
agree in referring the current produced to chemical action;
not merely by showing that the current depends upon the
action, but also that the direction of the current depends upon
the direction which the chemical affinity determines the exciting
or electromotive anion to take. And it is, I think, a most
striking circumstance, that these bodies, which when they can
and do act chemically produce currents, have not the least
power of the kind when mere contact only is allowed (857),
though they are excellent conductors of electricity, and can
readily carry the currents formed by other and more effectual
means.

1041. With such a mass of evidence for the efficacy and
sufficiency of chemical action as that which has been given
(866, 1040); with so many current circuits without metallic
contact (1005) and so many non-current circuits with (855);
what reason can there be for referring the effect in the joint
cases where both chemical action and contact occur, to contact,
or to anything but the chemical force alone Such a reference
appears to me most unphilosophical: it is dismissing a proved
and active cause to receive in its place one which is merely
h3q)othetical.

^ ix. Thermo-electric Evidence

1042. The phenomena presented by that most beautiful dis¬
covery of Seebeck, thermo-electricity, has occasionally and,
also, recently been adduced in proof of the electromotive

Voltaic Excitement not Due to Contact 309

influence of contact amongst the metals^ and such-like solid
conductors ^ (797^ 855). A very brief consideration is^ I think^
sufficient to show how little support these phenomena give to
the theory in question.

1043. If the contact of metals exert any exciting influence
in the voltaic circuity, then we can hardly doubt that thermo¬
electric currents are due to the same force; i.e. to disturbance,
by local temperature, of the balanced forces of the different
contacts in a metallic or similar circuit. Those who quote
thermo effects as proofs of the effect of contact must, of course,
admit this opinion.

1044. Admitting contact force, we may then assume that
heat either increases or diminishes the electromotive force of
contact. For if in fig. 79, A be antimony and B bismuth, heat

R^A VA

Fig. 79.

Fig. 80.

applied at x causes a current to pass in the direction of the
arrow; if it be assumed that bismuth in contact with antimony
tends to become positive and the antimony negative, then heat
diminishes the effect; but if it be supposed that the tendency
of bismuth is to become negative, and of antimony positive,
then heat increases the effect. How we are to decide which
of these two views is the one to be adopted, does not seem to
me clear; for nothing in the thermo-electric phenomena alone
can settle the point by the galvanometer,

1045. If for that purpose we go to the voltaic circuit, there
the situation of antimony and bismuth varies according as one
or another fluid conductor is used (1000). Antimony, being
negative to bismuth with the acids, is positive to it with an
alkali or sulphuret of potassium; still we find they come nearly
together in the midst of the metallic series. In the thermo
series, on the contrary, their position is at the extremes, being
as different or as much opposed to each other as they can be.
This difference was long ago pointed out by Professor Gumming
how is it consistent with the contact theory of the voltaic pile ?

1046. Again, if silver and antimony form a thermo circle

See Fechner’s words .—Philosophical Magazine, 1838, xiii. p. 206.

^ Annals of Philosophy, 1823, vi. 177.

. . . .

310 Faraday's Researches

(fig. 80)^ and the junction x be heated, the current there is
from the silver to the antimony. If silver and bismuth form a
thermo series (fig. 81), and the junction x be heated, the cur- |
rent is from the bismuth to the silver; and assuming that heat
increases the force of contact (1044), these results will give the |

acid, or strong nitric acid, or solution of potassa (1000) are used; |
so that metallic contact, like that in the thermo circle, can at
all events have very little to do here. In the yellow sulphuret
of potassium the current is from both antimony and bismuth
to the silver at their contacts, a result equally inconsistent with ;
the thermo effect as the former. When the colourless hydro-
sulphuret of potassium is used to complete the voltaic circle,
the current is from bismuth to silver, and from silver to anti- !
mony at their points of contact; whilst, with strong muriatic j
acid, precisely the reverse direction occurs, for it is from silver !
to bismuth, and from antimony to silver at the junctions. !

1047. Again;—by the heat series copper gives a current to ;

gold; tin and lead give currents to copper, rhodium, or gold; i

zinc gives one to antimony, or iron, or even plumbago; and !
bismuth gives one to nickel, cobalt, mercury, silver, palladium,
gold, platinum, rhodium, and plumbago; at the point of contact !
between the metals:—currents which are just the reverse of :
those produced by the same metals, when formed into voltaic
circuits and excited by the ordinary acid solutions (1000). '

1048. These, and a great number of other discrepancies,

appear by a comparison, according to theory, of thermo con¬
tact and voltaic contact action, which can only be accounted
for by assuming a specific effect of the contact of water, acids, 1
alkalies, sulphurets, and other exciting electrolytes, for each
metal; this assumed contact force being not only unlike thermo- ,
metallic contact, in not possessing a balanced state in the
complete circuit at uniform temperatures, but also having no
relation to it as to the order of the metals employed. So bis- 1

muth and antimony, which are far apart in thermo-electric |

order, must have this extra character of acid contact very ■

greatly developed in an opposite direction as to its result, to ;

Fig. 81.

direction of contact force between
these metals, antimony <— silver^
and bismuth ■—> silver. But in the
voltaic series the current is from the
silver to both the antimony and bis¬
muth at their points of contact,
whenever dilute sulphuric or nitric

Thermo-Electric and Voltaic Effects 311

render them only a feeble voltaic combination with each other:
and with respect to silver^ which stands between tin and zinc
thermo-electrically^ not only must the same departure be re-
quiredj but how great must the effect of this, its incongruous
contact^ be, to overcome so completely as it does, and even
powerfully reverse the differences which the metals (according-
to the contact theory) tend to produce!

1049. In further contrast with such an assumption, it must
be remembered that, though the series of thermo-electric bodies
is different from the usual voltaic order (looo), it is perfectly
consistent with itself, i.e. that if iron and antimony be weak
with each other, and bismuth be strong with iron, it will also
be strong with antimony. Also that if the electric current pass
from bismuth to rhodium at the hot junction, and also from
rhodium to antimony at the hot junction, it will pass far more
powerfully from bismuth to antimony at the heated junction.
To be at all consistent with this simple and true relation, sul¬
phuric acid should not be strongly energetic with iron or tin
and weakly so with silver, as it is in the voltaic circuit, since
these metals are not far apart in the thermo series: nor should
it be nearly alike to platinum and gold voltaically, since they
are far apart in the thermo series.

1050. Finally, in the thermo circuit there is that relation to
heat which shows that for every portion of electric force evolved
there is a corresponding change in another force, or form of
force, namely heat, able to account for it; this, the united
experiments of Seebeck and Peltier have shown. But contact
force is a force which has to produce something from nothing,
a result of the contact theory which can be better stated a little
further on (1057, 1059, 1061).

1051. What evidence then for mere contact excitement,
derivable from the facts of thermo-electricity, remains, since
the power must thus be referred to the acid or other electrolyte
used (1048) and made, not only to vary uncertainly for each
metal, but to vary also in direct conformity with the variation
of chemical action (862, 944, 980, 994, 1002)?

1052. The contact theorist seems to consider that the advo¬
cate of the chemical theory is called upon to account for the
phenomena of thermo-electricity. I cannot perceive that See-
beck’s circle has any relation to the voltaic pile, and think that
the researches of Becquerel ^ are quite sufficient to authorise;
that conclusion.

^ Annales de Chimie, 1829, xli. 355; xlvi. 275.

312

Faraday’s Researches

^ X. Improbable Nature of the Assumed Contact Force

1053. I have thus given a certain body of experimental
-evidence and consequent conclusions^ which seem to me fitted
to assist in the elucidation of the disputed pointy in addition
to the statements and arguments of the great men who have
already advanced their results and opinions in favour of the
chemical theory of excitement in the voltaic pile^ and against
that of contact. I will conclude by adducing a further argu¬
ment founded upon the^ to me^ unphilosophical nature of the
force to which the phenomena are, by the contact theory,
referred.

1054. It is assumed by the theory (790) that where two dis¬
similar metals (or rather bodies) touch, the dissimilar particles
act on each other, and induce opposite states. I do not deny
this, but on the contrary think that in many cases such an
effect takes place between contiguous particles; as for instance,
preparatory to action in common chemical phenomena, and also
preparatory to that act of chemical combination which, in the
voltaic circuit, causes the current (726, 731).

1055. But the contact theory assumes that these particles,
which have thus by their mutual action acquired opposite elec¬
trical states, can discharge these states one to the other, and yet
remain in the state they were first in, being in every point entirely
unchanged by what has previously taken place. It assumes
also that the particles, being by their mutual action rendered
plus and minus, can, whilst under this inductive action, dis-
-charge to particles of like matter with themselves and so produce
a current.

1056. This is in no respect consistent with known actions.
If in relation to chemical phenomena we take two substances,
as oxygen and hydrogen, we may conceive that two particles,
one of each, being placed together and heat applied, they induce
contrary states in their opposed surfaces, according, perhaps,
to the view of Berzelius (727), and that these states becoming
more and more exalted end at last in a mutual discharge of
the forces, the particles being ultimately found combined, and
unable to repeat the effect. Whilst they are under induction
and before the final action comes on, they cannot spontaneously
lose that state; but by removing the cause of the increased
inductive effect, namely the heat, the effect itself can be lowered
to its first condition. If the acting particles, are involved in

Inconsistency of Contact Exciting Force 313

the constitution of an electrolyte^ then they can produce current
force (656^ 659) proportionate to the amount of chemical force
consumed (603).

1057. But the contact theory^ which is obliged^ according to
the facts^ to admit that the acting particles are not changed
(790^ 1055) (for otherwise it would be the chemical theory)^ is
constrained to admit also that the force which is able to make
two particles assume a certain state in respect to each other, is
unable to make them retain that state; and so it virtually
denies the great principle in natural philosophy, that cause and
effect are equal (1059). If a particle of platinum by contact
with a particle of zinc willingly gives of its own electricity to
the zinc, because this by its presence tends to make the platinum
assume a negative state, why should the particle of platinum
take electricity from any other particle of platinum behind it,
since that would only tend to destroy the very state which the
zinc has just forced it into? Such is not the case in common
induction (and Marianini admits that the effect of contact may
take place through air and measurable distances ^); for there a
ball rendered negative by induction will not take electricity
from surrounding bodies, however thoroughly we may uninsu¬
late it; and if we force electricity into it, it will, as it were, be
spurned back again with a power equivalent to that of the
inducing body.

1058. Or if it be supposed rather, that the zinc particle, by its
inductive action, tends to make the platinum particle positive,
and the latter, being in connection with the earth by other
platinum particles, calls upon them for electricity, and so
acquires a positive state; why should it discharge that state to
the zinc, the very substance which, making the platinum assume
that condition, ought of course to be able to sustain it? Or
again, if the zinc tends to make the platinum particle positive,
why should not electricity go to the platinum from the zinc,
which is as much in contact with it as its neighbouring platinum
particles are? Or if the zinc particle in contact with the plati¬
num tends to become positive, why does not electricity flow to
it from the zinc particles behind, as well as from the platinum?^

1 Memorie della Societd Italiana in Modena, 1837, xxi. 232, 233, etc.

21 have spoken, for simplicity of expression, as if one metal were active
and the other passive in bringing about these induced states, and not, as
the theory implies, as if each were mutually subject to the other. But this
makes no difference in the force of the argument; whilst an endeavour
to state fully the joint changes on both sides would rather have obscured
the objections which arise, and whic^^gt either view.

314 ■ Faraday’s Researches

There is no sufficient probable or philosophic cause assigned
for the assumed action; or reason given why one or other of
the consequent effects above mentioned should not take place:
and^ as I have again and again said^ I do not know of a single
fact^ or case of contact current^ on which^ in the absence of
such probable cause^ the theory can rest.

1059. The contact theory assumes, in fact, that a force which
is able to overcome powerful resistance, as for instance that of
the conductors, good or bad, through which the current passes,
and that again of the electrolytic action where bodies are decom¬
posed by it, can arise out of nothing; that, without any change
in the acting matter or the consumption of any generating
force, a current can be produced which shall go on for ever
against a constant resistance, or only be stopped, as in the
voltaic trough, by the ruins which its exertion has heaped up
in its own course. This would indeed be a creation of fower,
and is like no other force in nature. We have many processes
by which the form of the power may be so changed that an
apparent conversion of one into another takes place. So we
can change chemical force into the electric current, or the current
into chemical force. The beautiful experiments of Seebeck
and Peltier show the convertibility of heat and electricity; and
others by (Ersted and myself show the convertibility of elec¬
tricity and magnetism. But in no cases, not even those of the
Gymnotus and Torpedo (778), is there a pure creation of force;
a production of power without a corresponding exhaustion of
something to supply it.^

1 [Note, March 29, 1840).—I regret that I was not before aware of most
important evidence for this philosophical argument, consisting of the
opinion of Dr. Roget, given in his treatise on Galvanism in the Library
of Useful Knowledge, the date of which is January 1829. Dr. Roget is,
upon the facts of the science, a supporter of the chemical theory of excita¬
tion ; but the striking passage I desire now to refer to is the following, at
§ 113 of the article Galvanism. Speaking of the voltaic theory of contact,
he says, “ Were any further reasoning necessary to overthrow it, a forcible
argument might be drawn from the following consideration. If there could
exist a power having the property ascribed to it by the hypothesis, namely,
that of giving continual impulse to a fluid in one constant direction,
without being exhausted by its own action, it would differ essentially from
all the other known powers in nature. All the powers and sources of
motion, with the operation of which we are acquainted, when producing
their peculiar effects, are expended in the same proportion as those effects
are produced; and hence arises the impossibility of obtaining by their
agency a perpetual effect; or, in other words, a perpetual motion. But
the electromotive force ascribed by Volta to the metals when in contact is
a force which, as long as a free course is allowed to the electricity it sets
in motion, is never expended, and continues to be excited with undiminished
power, in the production of a never-ceasing effect. Against the truth of
such a supposition, the probabilities are all but infinite.”— Roget.

Combination of Acids and Bases 315

1060. It should ever be remembered that the chemical theory
sets out with a power the existence of which is pre-proved, and
then follows its variations^ rarely assuming anything which is
not supported by some corresponding simple chemical fact.
The contact theory sets out with an assumption^ to which it
adds others as the cases require^ until at last the contact force,
instead of being the firm unchangeable thing at first supposed
by Volta, is as variable as chemical force itself.

1061. Were it otherwise than it is, and were the contact
theory true, then, as it appears to me, the equality of cause
and effect must be denied (1057). Then would the perpetual
motion also be true; and it would not be at all difficult, upon the
first given case of an electric current by contact alone, to pro¬
duce an electro-magnetic arrangement, which, as to its principle,
would go on producing mechanical effects for ever.

December 26, 1839.

Note

1062. In a former part (660, etc.) I have said that I do not
think any part of the electricity of the voltaic pile is due to the
combination of the oxide of zinc with the sulphuric acid used,
and that I agreed so far with Sir Humphry Davy in thinking
that acids and alkalies did not in combining evolve electricity
in large quantity when they were not parts of electrolytes.

This I would correct; for I think that BecquereFs pile is a
perfect proof that when acid and alkali combine an electric
current is produced.^

I perceive that Dr. Mohr of Coblentz appears to have shown
that it is only nitric acid which amongst acids can in combining
with alkalies produce an electric current.^

For myself, I had made exception of the hydracids (664) on
theoretical grounds. I had also admitted that oxyacids when
in solution might in such cases produce small currents of elec¬
tricity (663 and note)] and Jacobi says that in BecquereFs
improved acid and alkaline pile, it is not above a thirtieth part
of the whole power which appears as current. But I now wish
to say, that though in the voltaic battery, dependent for its
power on the oxidisement of zinc, I do not think that the

^ Bibliotheque Universelle, 1838, xiv. 129, 171. Comptes Rendus, i. p. 455.
Annales de Chimie, 1827, xxxv. 122.

^Philosophical Magazine, 1838, xiii. p. 382; or Poggendorfs Annalen,
xlii. p. 76.

316 Faraday’s Researches

quantity of electricity is at all increased or affected by the com¬
bination of the oxide with the acid (668^ 680), still the latter
circumstance cannot go altogether for nothing. The researches
of Mr. Daniell on the nature of compound electrolytes^ ties
together the electrolysation of a salt and the water in which it
is dissolved, in such a manner as to make it almost certain that,
in the corresponding cases of th.t formation of a salt at the place
of excitement in the voltaic circuit, a similar connection between
the water and the salt formed must exist: and I have little
doubt that the joint action of water, acids, and bases, in Bec-
querel’s battery, in DanielFs electrolysations, and at the zinc
in the ordinary active pile, are, in principle, closely connected
together.

Philosophical Transactions, 1839, P- 27 -

CORRESPONDENCE ON ELECTRICITY

FROM THE ‘'philosophical MAGAZINE/^ ETC.

On a peculiar Voltaic Condition of Iron, hy Professor Schoen>
BEIN^ of Bale ; in a Letter to Mr. Faraday: with further
Experiments on the same subject^ hy Mr. Faraday, com¬
municated in a Letter to Mr. Phillips.^

To Michael Faraday, D.C.L., F.R.S., etc.

Sir, —^As our continental and particularly German periodicals
are rather slow in publishing scientific papers, and as I am
anxious to make you as soon as possible acquainted with some
new electro-chemical phenomena lately observed by me, I take
the liberty to state them to you by writing. Being tempted
to do so only by scientific motives, I entertain the flattering
hope that the contents of my letter will be received by you with
kindness. The facts I am about laying before you seem to me
not only to be new, but at the same time deserving the attention
of chemical philosophers. Les void.

If one of the ends of an iron wire be made red hot, and after
cooling be immersed in nitric acid, sp. gr. 1.35, neither the end
in question nor any other part of the wire will be affected,
whilst the acid of the said strength is well known to act rather
violently upon common iron. To see how far the influence of
the oxidised end of the wire goes, I took an iron wire of 50'
in length and o" '.5 in thickness, heated one of its ends about
3" in length, immersed it in the acid of the strength above men¬
tioned, and afterwards put the other end into the same fluid.
No action of the acid upon the iron took place. From a similar
experiment made upon a cylindrical iron bar of 16' in length
and 4" ' diameter the same result was obtained. The limits of
this protecting influence of oxide of iron with regard to quan¬
tities I have not yet ascertained; but as to the influence of heat,
I found that above the temperature of about 75° the acid acts
in the common way upon iron, and in the same manner also,
at common temperatures, when the said acid contains water
1 Lond. and Edinb. Phil. Mag., 1836, vol. ix. p. 53.

317

..... . mmmMmmmmmmrn I I . ...I... .

318 Faraday’s Researches !

beyond a certain quantity, for instance, i, lo, loo, and even .
1000 times its volume. By immersing an iron wire in nitric i

acid of sp. gr. 1.5 it becomes likewise indifferent to the same j

acid of 1.35.

But by far the most curious fact observed by me is, that any
number of iron wires may be made indifferent to nitric acid
by the following means. An iron wire with one of its ends
oxidised is made to touch another common iron wire; both j

are then introduced into nitric acid of sp. gr. 1.35, so as to 1

immerse the oxidised end of the one wire first into the fluid, i

and have part of both wires above the level of the acid. Under !

these circumstances no chemical action upon the wires will !

take place, for the second wire is, of course, but a continuation |

of that provided with an oxidised end. But no action occurs, |
even after the wires have been separated from each other. If j

the second wire having become indifferent be now taken out of i

the acid and made to touch at any of its parts not having been j
immersed a third wire, and both again introduced into the '

acid so as to make that part of the second wire which had pre- 1

viously been in the fluid enter first, neither of the wires will be |

acted upon either during their contact or after their separation. j

In this manner the third wire can make indifferent or passive |
a fourth one, and so on. |

Another fact, which has as yet, as far as I know, not been I

observed, is the following one. A wire made indifferent by 1

any of the means before mentioned is immersed in nitric acid of |

sp. gr. 1.35, so as to have a considerable part of it remaining i

out of the fluid; another common wire is put into the same 1

acid, likewise having one of its ends rising above the level of j
the fluid. The part immersed of this wire will, of course, be '

acted upon in a lively manner. If the ends of the wires which i

are out of the acid be now made to touch one another, the
indifferent wire will instantly be turned into an active one,
whatever may be the lengths of the parts of the wires not
immersed. [If there is any instance of chemical affinity being
transmitted in the form of a current by means of conducting
bodies, I think the fact just stated may be considered as such.] ;

It is a matter of course that direct contact between the two !

wires in question is not an indispensably necessary condition j

for communicating chemical activity from the active wire to
the passive one; for any metal connecting the two ends of the j
wires renders the same service. j

Before passing to another subject, I must mention a fact j

A Peculiar Condition of Iron 319

which seems to be one of some importance. An iron wire
curved into a fork is made to touch at its bend a wire provided
with an oxidised end; in this state of contact both are intro¬
duced into nitric acid of sp. gr. 1.35 and 30°^ so as first to
immerse in the acid the oxidised end; the fork will^ of course^
not be affected. If now a common iron wire be put into the
acid^ and one of the ends of the fork touched by it^ this end will
immediately be acted upon, whilst the other end remains passive;
but as soon as the iron wire with the oxidised end is put out of
contact with the bend of the fork, its second end is also turned
active. If the parts of the fork rising above the level of the
acid be touched by an iron wire, part of which is immersed and
active in the acid, no communication of chemical activity will
take place, and both ends of the fork remain passive; but by the
removal of the iron wire (with the oxidised end) from the bend
of the fork this will be thrown into chemical action.

As all the phenomena spoken of in the preceding lines are,
no doubt, in some way or other dependent upon a peculiar
electrical state of the wires, I was very curious to see in what
manner iron would be acted upon by nitric acid when used as
an electrode. For this purpose I made use of that fomi of the
pile called the couromte des lasses^ consisting of fifteen pairs of
zinc and copper. A platina wire was connected with (what we
call) the negative pole of the pile, an iron wire with the positive
one. The free end of the platina wire was first plunged into
nitric acid sp. gr. 1.35, and by the free end of the iron wire the
circuit closed. Under these circumstances the iron was not in
the least affected by the acid; and it remained indifferent to the
fluid not only as long as the current was passing through it, but
even after it had ceased to perform the function of the positive
electrode. The iron wire proved, in fact, to be possessed of all
the properties of what we have called a passive one. If such a
wire is made to touch the negative electrode, it instantaneously
becomes an active one, and a nitrate of iron is formed; whether
it be separate from the positive pole or still connected with it,
and the acid be strong or weak.

But another phenomenon is dependent upon the passive state
of the iron, which phenomenon is in direct contradiction with
all the assertions hitherto made by philosophical experimenters.
The oxygen at the anode arising from the decomposition of water
contained in the acid does not combine with the iron serving as
the electrode, but is evolved at it, just in the same manner as
if it were platina, and to such a volume as to bear the ratio of

320 Faraday’s Researches

I : 2 to the quantity of hydrogen evolved at the cathode. To
obtain this result I made use of an acid containing 20 times its
volume of water; I founds however, that an acid containing
400 times its volume of water still shows the phenomenon in a
very obvious manner. But I must repeat it, the indispensable
condition for causing the evolution of the oxygen at the iron
wire is to close the circuit exactly in the same manner as above
mentioned. For if, exempli gratia, the circuit be closed with the
negative platina wire, not one single bubble of oxygen gas makes
its appearance at the positive iron; neither is oxygen given out
at it, when the circuit is closed, by plunging first one end of the
iron wire into the nitric acid, and by afterwards putting its other
end in connection with the positive pole of the pile. In both
cases a nitrate of iron is formed, even in an acid containing
400 times its volume of water; which salt may be easily observed
descending from the iron wire in the shape of brownish-yellow-
coloured streaks.

I have still to state the remarkable fact, that if the evolution
of oxygen at the anode be ever so rapidly going on, and the iron
wire made to touch the negative electrode within the acid, the
disengagement of oxygen is discontinued, not only during the
time of contact of the wires, but after the electrodes have been
separated from each other. A few moments holding the iron
wire out of the acid is, however, sufficient to recommunicate to
it the property of letting oxygen gas evolve at its surface. By
the same method the wire acquires its evolving power again,
whatever may have been the cause of its loss. The evolution
of oxygen also takes place in dilute sulphuric and phosphoric
acids, provided, however, the circuit be closed in the manner
above described. It is worthy of remark, that the disengage¬
ment of oxygen at the iron in the last-named acids is much easier
stopped, and much more difficult to be caused again^ than is
the case in nitric acid. In an aqueous solution of caustic potash
oxygen is evolved at the positive iron, in whatever manner the
circuit may be closed; but no such disengagement takes place
in aqueous solutions of hydracids, chlorides, bromides, iodides,
fluorides. The oxygen, resulting in these cases from the decom¬
position of water, and the anion (chlorine, bromine, etc.) of the
other electrolyte decomposed combine at the same time with
the iron.

To generalise these facts, it may be said that independently
of the manner of closing the circuit, oxygen is always disengaged
at the positive iron, provided the aqueous fluid in which it is

A Peculiai' Condition of Iron 321

imiiiersed do not (in a sensible manner) chemically act upon it;
and that no evolution of oxygen at the anode in contact with
iron under any circumstances takes place^ if besides oxygen
another anion is set free possessed of a strong affinity for iron.
This metal having once had oxygen evolved at its elf ^ proves
always to be indifferent to nitric acid of a certain strength^
whatever may be the chemical nature of the fluid in which the
phenomenon has taken place.

I have made a series of experiments upon silver^ copper, tin,
lead, cadmium, bismuth, zinc, mercury, but none showed any
resemblance to iron, for all of them were oxidised when serving
as positive electrodes. Having at this present moment neither
cobalt nor nickel at my command, I could not try these mag¬
netic metals, which I strongly suspect to act in the same manner
as iron does.

It appears from what I have just stated that the anomalous
bearing of the iron has nothing to do with its degree of affinity
for oxygen, but must be founded upon something else. Your
sagacity, which has already penetrated into so many mysteries
of nature, will easily put away the veil which as yet covers the
phenomenon stated in my letter, in case you should think it
worth while to make it the object of your researches.

Before I finish I must beg of you the favour of overlooking
with indulgence the many faults I have, no doubt, committed
in my letter. Formerly I was tolerably well acquainted with
your native tongue; but now, having been out of practice in
writing or speaking it, it is rather hard work to me to express
myself in English.

It is hardly necessary to say that you may privately or
publicly make any use of the contents of this letter.—I am, Sir,
your most obedient Servant,

C. T. SCHOENBEIN,

Bale, May 17, 1836. Prof, of Chem. in the University of Bale.

Dear Phillips, —The preceding letter from Professor Sciioeii-
bein, which I received a week or two ago, contains facts of such
interest in relation to the first principles of chemical electricity,
that I think you will be glad to publish it in your Philosofhical
Magazine. I send it to you unaltered, except in a word or two
here and there; but am encouraged by what I consider the
Professor’s permission (or,irather the request with which he has
honoured me), to add a few results in confirmation of the eEects

322 Faraday’s Researches

described, and illustrative of some conclusions that may be
drawn from the facts.

The influence of the oxidised iron wire, the transference of
the inactive state from wire to wire, and the destruction of that
state, are the facts I have principally verified; but they are so
well described by Professor Schoenbein that I will not add a
word to what he has said on these points, but go at once to other
results.

Iron wire, as M. Schoenbein has stated, when put alone into
strong nitric acid, either wholly or partly immersed, acquires
the peculiar inactive state. This I find takes place best in a
long narrow close vessel, such as a tube, rather than in a fiat
broad open one like a dish. When thus rendered quiescent by
itself, it has the same properties and relations as that to which
the power has been communicated from other wires.

If a piece of ordinary iron wire be plunged wholly or in part
into nitric acid of about specific gravity 1.3 or 1.35, and after
action has commenced it be touched by a piece of platina wire,
also dipping into the acid, the action between the acid and the
iron wire is instantly stopped. The immersed portion of the
iron becomes quite bright, and remains so, and is in fact in the
same state, and can be used in the same manner as the iron
rendered inactive by the means already described. This pro¬
tecting power of platina with respect to iron is very constant
and distinct, and is the more striking as being an effect the very
reverse of that which might have been anticipated prior to the
knowledge of M. Schoenbein’s results. It is equally exerted if
the communication between it and the iron is not immediate,
but made by other metals; as, for instance, the wire of a
galvanometer; and if circumstances be favourable, a small
surface of platina will reduce and nullify the action of the acid
upon a large surface of iron.

This efiect is the more striking if it be contrasted with that
produced by zinc; for the latter metal, instead of protecting the
iron, throws it into violent action with the nitric acid, and
determines its quick and complete solution. The phenomena
are weU observed by putting the iron wire into nitric acid of
the given strength, and touching it in the acid alternately by
pieces of platina and zinc: it becomes active or inactive accord¬
ingly; being preserved by association with the platina, and
corroded by association with the zinc. So also, as M. Schoen¬
bein has stated, if iron be made the negative electrode of a
battery containing from two to ten or more pairs of plates in

A Peculiar Condition of Iron 323

such acid^ it is violently acted upon; but when rendered the
positive electrode^ although oxidised and dissolved^ the process,
comparatively, is extremely slow.

Gold has the same power over iron immersed in the nitric
acid that platina has. Even silver has a similar action; but
from its relation to the acid, the effect is attended with peculiar
and changeable results, which I will refer to hereafter.

A piece of box-wood charcoal, and also charcoal from other
sources, has this power of preserving iron, and bringing it into
the inactive state. Plumbago, as might be expected, has the
same power.

When a piece of bright steel was first connected with a piece
of platina, then the platina dipped into the acid, and lastly the
steel immersed, according to the order directed in the former
cases by Professor Schoenbein, the steel was preserved by the
platina, and remained clear and bright in the acid, even after
the platina was separated from it, having, in fact, the properties
of the inactive iron. When immersed of itself, there was at
first action of the usual kind, which, being followed by the
appearance of the black carbonaceous crust, known so well in
the common process of examining steel, the action immediately
ceased, and the steel was preserved, not only at the part im¬
mersed, but upon introducing a further portion, it also remained
clean and bright, being actually protected by association with
the carbon evolved on the part first immersed.

When the iron is in this peculiar inactive state, as M. Schoen¬
bein has stated, there is not the least action between it and
the nitric acid. I have retained such iron in nitric acid, both
alone and in association with platina wire for thirty days, with¬
out change; the metal has remained perfectly bright, and not a
particle has been dissolved.

A piece of iron wire in connection with platina wire was
entirely immersed in nitric acid of the given strength, and the
latter gradually heated. No change took place until the acid
was nearly at the boiling-point, when it and the iron suddenly
entered into action, and the latter was instantly dissolved.

As an illustration of the extent and influence of this state, I
may mention that with a little management it can be shown
that the iron has lost, when in the peculiar state, even its power
of precipitating copper and other metals. A mixture of about
equal parts of a solution of nitrate of copper and nitric acid
was made. Iron in the ordinary, or even in the peculiar state,
when put into this solution, acted, and copper was precipitated;

324 Faraday’s Researches

but if the inactive iron was first connected with a piece of
platina dipping into the solution^ and then its own prepared
surface immersed, after a few seconds the platina might be
removed, and the iron would remain pure and bright for some
time. At last it usually started into activity, and began to
precipitate copper, being itself rapidly corroded. When silver is
the metal in solution, the effect is still more striking, and will
be referred to immediately.

I then used a galvanometer as the means of connection
between the iron and other metals thus associated together in
nitric acid, for the purpose of ascertaining, by the electric
currents produced, in what relative condition the metals stood
to each other; and I will, in the few results I may have to
describe, use the relations of platina and zinc to each other as
the terms of comparison by which to indicate the states of these
metals under various circumstances.

The oxidised iron wire of Professor Schoenbein is, when in
association with platina, exactly as another piece of platina
would be. There is no chemical action, nor any electric current.
The iron wire, rendered inactive either by association with the
oxidised wire or in any other way, is also as platina to the
platina, and produces no current.

When ordinary iron and platina in connection by means of
the galvanometer are dipped into the acid (it matters not which
first), there is action at the first moment on the iron, and a
very strong electric current, the iron being as zinc to the platina.
The action on the iron is, however, soon stopped by the
influence of the platina, and then the current instantly ceases,
the iron now acting as platina to the platina. If the iron be
lifted into the air for a moment until action recommences on it,
and be then reimmersed, it again produces a current, acting
as zinc to the platina; but as before, the moment the action
stops, the current is stopped also.

If an active or ordinary, and an inactive or peculiar iron wire
be both immersed in the nitric acid separately, and then con¬
nected either directly or through the galvanometer, the second
does not render the first inactive, but is itself thrown into
action by it. At the first moment of contact, however, a strong
electric current is formed, the first iron acting as zinc, and the
second as platina. Immediately that the chemical action is
re-established at the second as well as the first, all current
ceases, and both pieces act like zinc. On touching either of
them in the acid with a piece of platina, both are protected.

A Peculiar Condition of Iron 325

and cease to act; but there is no current through the galvano¬
meter^ for both change together.

When iron was associated with gold or charcoal^ the pheno¬
mena were the same. Using steel instead of iron, like effects
ensued.

One of the most valuable results in the present state of this
branch of science which these experiments afford^ is the addi¬
tional proof that voltaic electricity is due to chemical action^ and
not to contact. The proof is equalty striking and decisive with
that which I was able to give in the sixth part of my Ex¬
perimental Researches (par. 615). What indeed can show more
evidently that the current of electricity is due to chemical
action rather than to contact^ than the fact that though the
contact is continued, yet when the chemical action ceases, the
current ceases also?

It might at first be supposed that in consequence of the
peculiar state of the iron, there was some obstacle, not merely
to the formation of a current, but to the passage of one; and
that, therefore, the current which metallic contact tended to
produce could not circulate in the system. This supposition
was, however, negatived by removing the platina wire into a
second cup of nitric acid, and then connecting the two cups by
a compound platina and iron wire, putting the platina into the
first vessel, and the iron attached to it into the second. The
second wire acted at the first moment, producing its correspond¬
ing current, which passed through the first cup, and conse¬
quently through the first and inactive wire, and affected the
galvanometer in the usual way. As soon as the second iron
was brought into the peculiar condition, the current of course
ceased; but that very cessation showed that the electric current
was not stopped by a want of conducting power, or a want of
metallic contact, for both remained unchanged, but by the
absence of chemical action. These experiments, in which the
current ceases whilst contact is continued, combined with those
T formerly gave, in which the current is produced though
contact does not exist, form together a perfect body of evidence
in respect to this elementary principle of voltaic action.

With respect to the state of the iron when inactive in the
nitric acid, it must not be confounded with the inactive state
of amalgamated or pure zinc in dilute sulphuric acid: The
distinction is easily made by the contact of platina with either
in the respective acids, for with the iron such association do"''
nothing, whereas with the zinc it develops the full force of f

326 Faraday’s Researches

metal and generates a powerful electric current. The iron is
in fact as if it had no attraction for oxygen^ and therefore could
not act on the electrol5rte present^ and consequently could pro¬
duce no current. My strong impression is that the surface
of the iron is oxidised^ or that the superficial particles of the
metal are in such relation to the oxygen of the electrolyte as
to be equivalent to an oxidation; and that having thus their
affinity for oxygen satisfied^ and not being dissolved by the acid
under the circumstances, there is no renewal of the metallic
surface, no reiteration of the attraction of successive particles
of the iron on the elements of successive portions of the elec¬
trolyte, and therefore not those successive chemical actions by
which the electric current (which is definite in its production
as well as in its action) can be continued.

In support of this view, I may observe, that in the first
experiment described by Professor Schoenbein, it cannot be
doubted that the formation of a coat of oxide over the iron
when heated is the cause of its peculiar and inactive state: the
coat of oxide is visible by its colour. In the next place, all the
forms of experiment by which this iron, or platina, or charcoal,
or other voltaic arrangements are used to bring ordinary iron
into the peculiar state, are accompanied by a determination of
oxygen to the surface of the iron; this is shown by the electric
current produced at the first moment, and which in such cases
always precedes the change of the iron from the common to
the peculiar state. That the coat of oxide produced by common
means might be so thin as not to be sensible and yet be
effectual, was shown by heating a piece of iron an inch or two
from the end, so that though blue at the heated part, the end
did not seem in the slightest degree affected, and yet that end
was in the peculiar state. Again, whether the iron be oxidised in
the flame much or only to the very slight degree just described,
or be brought into the peculiar state by voltaic association
with other pieces or with platina, etc., still if a part of its surface
were removed even in the smallest degree and then the new
surface put into contact with the nitric acid, that part was
at the first moment as common iron; the state being abundantly
evident by the electrical current produced at the instant of
immersion.

Why the superficial film of oxide, which I suppose to be
formed when the iron is brought into the peculiar state by
voltaic association, or occasionally by immersion alone into
nitric acid, is not dissolved by the acid, is I presume dependent

A Peculiar Condition of Iron 327

upon the peculiarities of this oxide and of nitric acid of the
strength required for these experiments; but as a matter of
fact it is well known that the oxide produced upon the surface of
iron by heat^ and showing itself by thin films of various colours^
is scarcely touched by nitric acid of the given strength though
left in contact with it for days together. That this does not
depend upon the film having any great thickness^ but upon its
peculiar condition^ is rendered probable from the fact that
iron oxidised by heat^ only in that slight degree as to offer no
difference to the eye^ has been left in nitric acid of the given
strength for weeks together without any change. And that
this mode of superficial oxidation, or this kind of oxide, may
occur in the voltaic cases, is rendered probable by the results
of the oxidation of iron in nitrate of silver. When nitrate of
silver is fused and common iron dipped into it, so as to be
thoroughly wetted, being either alone or in association with
platina, the iron does not commence a violent action on the
nitrate and throw down silver, but it is gradually oxidised on
the surface with exactly the same appearances of colour, uni¬
formity of surface, etc., as if it were slowly oxidised by heat
in the air.

Professor Schoenbein has stated the case of iron when acting
as the positive electrode of a couronne des tosses. If that
instrument be in strong action, or if an ordinary battery be
used containing from two to ten or more plates, the positive
iron instantly becomes covered in the nitric acid with a coat
of oxide, which though it does not adhere closely still is not
readily dissolved by the acid when the connection with the
battery is broken, but remains for many hours on the iron,
which itself is in the peculiar inactive state. If the power of
the voltaic apparatus be very weak, the coat of oxide on the
iron in the nitric acid often assumes a blue tint like that of the
oxide formed by heat. A part of the iron is however always
dissolved in these cases.

If it be allowed that the surface particles of the iron are
associated with oxygen, are in fact oxidised, then all the other
actions of it in combination with common iron and other metals
will be consistent; and the cause of its platina-like action, of
its forming a strong voltaic current with common iron in the
first instance, and then being thrown into action by it, will be
explained by considering it as having the power of determining
and disposing of a certain portion of hydrogen from the elec¬
trolyte at the first moment and being at the same time brought

328 Faraday’s Researches

into a free metallic condition on the surface so as to act after¬
wards as ordinary iron.

I need scarcely refer here to the probable existence of a
very close connection between the phenomena which Professor
Schoenbein has thus pointed out with regard to iron^ and those
which have been observed by others, as Ritter and Marianini,
with regard to secondary piles, and A. de la Rive with respect
to peculiar affections of platina surfaces.

In my Experimental Researches (par. 212) I have recorded a
case of voltaic excitement, which very much surprised me at the
time, but which I can now explain. I refer to the fact stated,
that when platina and iron wire were connected voltaically in
association with fused nitrate or chloride of silver, there was an
electric current produced, but in the reverse direction to that
expected. On repeating the experiment, I found that when
iron was associated with platina or silver in fused nitrate or
chloride of silver, there was occasionally no current, and when
a current did occur it was almost constantly as if the iron was
as platina, the silver or platina used being as zinc. In all such
cases, however, it was a thermo-electric current which existed.
The volta-electric current could not be obtained, or lasted only
for a moment.

When iron in the peculiar inactive state was associated with
silver in nitric acid sp. gr. 1.35, there was an electric current,
the iron acting as platina; the silver gradually became tarnished
and the current continued for some time. When ordinary iron
and silver were used in the nitric acid there was immediate
action and a current, the iron being as zinc, to the silver as
platina. In a few moments the current was reversed, and the
relation of the metals was also reversed, the iron being as
platina, to the silver as zinc; then another inversion took
place, and then another, and thus the changes went on some¬
times eight or nine times together, ending at last generally in
a current constant in its direction, the iron being as zinc, to
the silver as platina: occasionally the reverse was the case, the
predominant current being as if the silver acted as zinc.

This relation of iron to silver, which was before referred to,
page 324, produces some curious results as to the precipitation
of one metal by another. If a piece of clean iron is put into
an aqueous solution of nitrate of silver, there is no immediate
apparent change of any kind. After several days the iron will
become slightly discoloured, and small irregular crystals of silver
will appear; but the action is so slow as to require time and

A Peculiar Condition of Iron

329

care for its observation. When a solution of nitrate of silver
to which a little nitric acid had been added was used^ there
was still no sensible immediate action on the iron. When the
solution was rendered very acid, then there was direct imme¬
diate action on the iron; it became covered with a coat of
precipitated silver: the action then suddenly ceased, the silver
was immediately redissolved, and the iron left perfectly clear,
in the peculiar condition, and unable to cause any further
precipitation of the silver from the solution. It is a remarkable
thing in this experiment to see the silver rapidl}^ dissolve away
in a solution which cannot touch the iron, and to see the iron
in a clean metallic state unable to precipitate the silver.

Iron and platina in an aqueous solution of nitrate of silver
produce no electric current; both act as platina. When the
solution is rendered a little acid by nitric acid, there is a very
feeble current for a moment, the iron being as zinc. When
still more acid is added so as to cause the iron to precipitate
silver, there is a strong current whilst that action lasts, but
when it ceases the current ceases, and then it is that the silver
is redissolved. The association of the platina with the iron
evidently helps much to stop the action.

When iron is associated with mercury, copper, lead, tin, zinc,
and some other metals, in an aqueous solution of nitrate of
silver, it produces a constant electric current, but always acts
the part of 'platinum. This is perhaps most striking with mer¬
cury and copper, because of the marked contrast it affords to
the effects produced in dilute sulphuric acid and most ordinary
solutions. The constancy of the current even causes crystals
of silver to form on the iron as the negative electrode. It
might at first seem surprising that the power which tends to
reduce silver on the iron negative electrode did not also bring
back the iron from its peculiar state, whether that be a state
of oxidation or not. But it must be remembered that the
moment a particle of silver is reduced on the iron, it not only
tends to keep the iron in the peculiar state according to the
facts before described, but also acts as the negative electrode;
and there is no doubt that the current of electricity which con¬
tinues to circulate through the solution passes essentially between
it and the silver, and not between it and the iron, the latteT
metal being merely the conductor interposed between the silvei
and the copper extremities of the metallic arrangement.

1 am afraid 57'ou will think I have pursued this matter to a
greater length than it deserves; but I have been exceedingly

. ...

330 Faraday’s Researches

interested by M. Schoenbein’s researches^^ and cannot help
thinking that the peculiar condition of iron which he has
pointed out will (whatever it may depend upon) enable us
hereafter more closely to examine the surface-action of the
metals and electrolytes when they are associated in voltaic
combinations, and so give us a just knowledge of the nature
of the two modes of action by which particles under the influence
of the same power can produce either local effects of combination
or current affinity.^— I am, my dear Phillips, very truly yours,

M. Fap^day.

Royal Institution, June 16, 1836.

Letter from Mr. Faraday to Mr. Brayley on some former Re- '
searches relative to the peculiar Voltaic Condition of Iron
reohserved hy Professor Schoenbein, supplementary to cr i
Letter to Mr. Phillips, in ike last Number? i

Royal Institution, July 8, 1836.

My dear Sir, —I am greatly your debtor for having pointed
out to me Sir John F. W. HerschePs paper on the action of
nitric acid on iron in the Annales de Chimie et de Physique: I

I read it at the time of its publication, but it had totally escaped
my memory, which is indeed a very bad one now. It renders
one-half of my letter (supplementary to Professor Schoenbein’s)
in the last number of the Philosophical Magazine, page 57 (or
page 321 of this volume), superfluous; and I re.gret only that
it did not happen to be recalled to my attention in time for me
to rearrange my remarks, or at all events to add to them an
account of Sir John HerschePs results. However, I hope the
editors of the Phil, Ma^. will allow my present letter a place
in the next number; and entertaining that hope I shall include
in it a few references to former results bearing upon the extra¬
ordinary character of iron to which M. Schoenbein has revived
the attention of men of science. j

“ Bergman relates that upon adding iron to a solution of j
silver in the nitrous acid no precipitation ensued.” ® *

Keir, who examined this action in the year 1790,^ made many '
excellent experiments upon it. He observed that the iron '

acquired a peculiar or altered state in the solution of silver; j

i

* Exp. Researches;, Pars. 682, 732. s

^ T and. and Edinh. Phil. Ma^. 1836, vol. ix. p. 122.
a Phil. Trans. 1700, p. 374. thid. pp. 374 '

A Peculiar Condition of Iron 331

that this state was only superficial; that when so altered it
was inactive in nitric acid; and that when ordinary iron was
put into strong nitric acid there was no action, but the metal
assumed the altered state.

Westlar, whose results I know only from the Annales des
Mines for 1832/ observed that iron or steel which had been
plunged into a solution of nitrate of silver lost the power of
precipitating copper from its solutions; and he attributes the
effect to the assumption of a negative electric state by the part
immersed, the other part of the iron having assumed the positive
state.

Braconnot in 1833 ^ observed that filings or even plates of
iron in strong nitric acid are not at all affected at common
temperatures, and scarcely even at the boiling-point.

Sir John Herschel’s observations are in reality the first which
refer these phenomena to electric forces; but Westlar’s, which
do the same, were published before them. The results obtained
by the former, extracted from a private journal dated August
1825, were first published in 1833.^ He describes the action of
nitric acid on iron; the altered state which the metal assumes;
the superficial character of the change; the effect of the contact
of other metals in bringing the iron back to its first state; the
power of platina in assisting to bring on the altered or prepared
state; and the habits of steel in nitric acid: he attributes the
phenomena to a certain permanent electric state of the surface of
the metal. I should recommend the republication of this paper
in the Philosophical Magazine.

Professor Daniell, in his paper on Voltaic Combinations ^
(Feb. 1836), found that on associating iron with platina in a
battery charged with nitro-sulphuric acid, the iron would not
act as the generating metal, and that when it was afterwards
associated with zinc it acted more powerfully than platina
itself. He considers the effect as explicable upon the idea of
a force of heterogeneous attraction existing between bodies, and
is inclined to believe that association with the platina cleanses
the surface of the iron, or possibly causes a difference in the
mechanical structure developed in this particular position.

In my letter, therefore, as published in the Philosophical
Magazine for the present month (July), what relates to the
preserving power of platina on iron ought to be struck out, as

^ Annales des Mines, 1832, vol. ii. p. 322; or Mag. de Pharm. 1830.

® Annales de Chimie et de Physique, vol. lii. p. 288.

^ Ihid. 1833, vol. liv. p. 87. * Phil. Trans. 1836, p. 114.

332 Faraday’s Researches

having been anticipated by Sir John Herschel^ and also much
of what relates to the action of silver and iron, as having been
formerly recorded by Keir. The facts relating to gold and
carbon in association with iron; the experimental results as to
the electric currents produced; the argument respecting the
chemical source of electricity in the voltaic pile; and my opinion
of the cause of the phenomena as due to a relation of the super¬
ficial particles of the iron to oxygenare what remain in the
character of contributions to our knowledge of this very beautiful
and important case of voltaic condition presented to us by the
metal iron.—I am^ my dear Sir^ yours very truly,

M. Faraday.

E. W, Brayley^ Esq.

Lo 7 idon FmHtntion,

INDEX

electrolysis of, 136, 143 Chloride of sulphur, electrolysis of,

, electrolysis of, 142 ' 119

dkah, transference of, 72,! Chloride of tin, electrolysis of, 146

Chlorides, fused, electrolysis of, 146,
>a.ses, combination of, 315; j 154; in solution, electrolysis of, 141
iTL voltaic pile, 189 CoUadon cited, i, 8

on voltaic excitement. Combined bodies, transference of, 76
electric pole, 48, 50, 82 , Common electricity, 7; chemical de-

a. non-conductor, 81, 135 ! composition by, 12; evolution of
scribed, 114, 157; action] heat by, 7; identity with voltaic
c circle, 200 electricity, 31; physiological effects

bribed, 113, 157 ' of, 28; spark produced by, 19

compounds, electrolytic | Conducting circles. See Voltaic
is of, 120; voltaic effects] • circles.

oret of potassium, 267 i Conduction, 41, 46; bodies not sub-
■d., 118 ' ject to law of, 38; bodies subject

ic electricity, 19 to law of, 37; consequent on

chemical, modes of: fusion, 35; new law of, 32
95; hygrometric, 99, 100; ] Conductors, particular, liquid and
Les, 98, 100 j sohd, 238, 240

i Contact theory of voltaic electricity,
diecomposition by atmo-| 232, 233, 243, 244, 253, 257, 263,

■lectricity, 20 I 281, 288, 294, 308

See Voltaic battery | Copper, voltaic effects in sulphuret

:y of electro-chemical de- i of potassium, 266

.ion, 58 Correspondence on electricity by

''oltaic effects in sulphuret author, 317

sium, 265 Current, voltaic, defined, 6, 172;

decomposition by atmo- various views of, 66
dectricity, 19 Cyanides in solution, decomposition

of, 142

voltaic effects in sulphuret

dum, 268 Davy, Sir Humphrey, i, 2, 57

xide, combining power of Decomposition, electro-chemical, by
prevented by, 106 animal electricity, 25; by com-

iescribed, 113, 157; ex- mon electricity, 12; b5?'single pair

. at, 298, 306 of plates, 167, 178, 180; by single

sscribed, 114, 157; table pole, 49; chemical affinity of par¬

ticles in, 69, 72, 79; conditions of,
cited, I, 16 47, 115; constant electrolytic

b-enucal, for battery, 227; action in, 122,125; definite nature

on of, 230 and extent of, 145 ; dependent on

action, affected . by tern- electric current, 60, 66, 71; elec-

, 271, 274; essential for trolytic intensity necessary for,

5ixt in voltaic pile, 304; 206; experiments with various

f electricity, 179, 180, 181, substances [g.v.), 118-154; general

190, 233, 302 propositions relating to, 157; in air,

t lead, electrolysis of, 208; 50; by magneto-electricity, 23; op-

3 conductor, 35 posed distant chemical actions in,

333

334 Faraday’s Researches

177; polar, 12, 15, 53; resistance
of electrolyte to, 218; retarding
e:ffect of interposed plates, 218-
225; secondary results of, 144;
theories of, 55, 60, 68; trans¬
ference of elements in, 69, 72, 76;
water, influence of, 54; without
metallic contact, 173, 175, 177
De ia Rive, theory of electro-chemi¬
cal decomposition, 59, 67
Dilution, effect on voltaic excite¬
ment, 284, 290

Dobereiner on combination effected
by platina, 95

Dulong and Thenard on combination
eflected by platina and solids, 95

Electricities, identity of, i, 7, 26
Electricity, absolute quantity in
different bodies, 163; animal, 24;
common, 7; conduction of, 46;
definite chemical action of, 30, 65,
152, 381, 382; magnetic action of,
29; magneto-, 22; phenomena
exhibited by, 2, 3; thermo-, 24;
of voltaic pile, 3, 170, 183, 194.
See also Voltaic pile
Electro-chemical equivalents, 157-
162, 200; forces of matter, 200
Electrodes, character of bodies
evolved at, 133; definition of, 112
Electrolysis, 113, 133. See Decom¬
position, electro-chemical
Electrolytes, 113, 157; action of,
187, 238; chemically inactive,
241; nature of, 185; polarised
light in relation to, 197; propor¬
tion of, in relation to decom¬
position, 117, 121; resistance to
decomposition, 218; thermo-cur-
rents in, 274

Ether, combining power of platina
prevented by, 107

Faraday’s correspondence on pecu¬
liar voltaic condition of iron, 321,

330

Fluorides fused, electrolysis of, 142
Fusinieri on combination effected
by platina, 96

Galvanometer, the, 8, 29
Gaseous bodies, combination of, 84
Gases, elasticity of, 98, 109
Glass, attraction for air, 99; de¬
composition of, 115
Grotthuss, theory of electro-chemical
decomposition, 56

Hachette, theory of electro-chemical
decomposition, 60, 67
Fleat, conducting power increased
by, 44, 46; effect on voltaic ex¬
citement, 270, 271, 274, 281;
evolved by animal electricity, 24;
by common electricity, 7; by mag¬
neto-electricity, 22; by thermo¬
electricity, 24; by voltaic elec¬
tricity, 3, 5

Hydriodic add, electrolysis of, 141
Hydrogen and oxygen, action of .
platina on, 86, 94, 102; and
spongy platina, 108

Ice a non-conductor of electricity,

32, 41 ‘

Identity of electricities, i, 7, 26 1

Iodide of potassium, conduction by, !
41; electrolysis of, 207; test of
chemical action, 14

Iodides, fused, electrolysis of, 151; j
in solution, electrolysis of, 141 i
Ions, 157, 161, 162; mutual rela- '
tions in circuit, 200; table of, 161
Iron, Faraday on voltaic condition
of, 321, 330; Schdnbein on voltaic
condition of, 317 '

j

Lead, voltaic effects in sulphuret of j
potassium, 262 I

Liquefaction, conduction consequent ■
upon, 32, 35, 39, 46 ^

Magnetic effects of animal electridty, ’
25; of common electricity, 7;
of magneto-electricity, 23; of
thermo-electricity, 24; of voltaic j
electricity, 5, 7 I

Magneto-electridty, 22 j

Marianini on source of power in
voltaic pile, 233, 234, 261 t

Matter, quantity of electricity in, 163
Measure for volta-electricity, 122 I

Metal, poles of, 82 '

Metallic contact. See Contact theory
Metals, order as electromotors, 295; i
power of indudng combination, ^

300

Muriatic acid, electrolysis of, 139; j
order of metals as electromotors i'
in, 298

Nitric acid, 118, 240; electrolysis 1

of, 137 !

Nitrogen determined to either pole, I

81, 135, 137 I

Nitrous acid in voltaic circles, 239, i
248 ,

o;

R

S(

Si

S]

Si

s-

Si

I

00 didid’d’ did ds(dd(d dd

Index 335

gas, combining power of Sulphuret of potassium, active
I?prevented by, 105^ Io8 circles excited by, 259, 265;

j-JXKie of lead, electrolysis of, 149 alternating currents in, 270; and

and hydrogen, action of heated metals, 279; as conductor,
platina on, S 6 , 94* 102 238, 241

p . Sulphuret of silver, conducting

p^^.^icles, nascent state of, no power of, 44

p^^^ociide of mercury, 120 Sulphuretted solutions, exciting

■L wosphoric acid not an electrolyte, action of, 194
p,^^^ . ' Sulphuric acid, conduction by, 3^,

-tiysiological effects of common 72, 138, 188, 240
electricity, 18; of magneto - elec- Sulphurous acid, electrolysis of,
bricity, 23; of thermo-electricity, 138
^ 24; of voltaic electricity, 5

1 fates, interposed, causing retarda- Tartaric acid, electrolysis of, 143
P bion of electrolysis, 218-225 Thermo - currents in electrolytes,

1 iatina, cleanliness essential, 98, 277

103; combining power of, 85-91, Thermo-electricity, 24
94 , gS, 102 — interferences with. Thermo-electric phenomena, 308
^05; spongy, in relation to Tin, voltaic effects in sulphuret of
dydrogen, 104, 107, loS potassium, 261

Polar decomposition, 12, 15, 53 Torpedo fish, electric discharge of.
Polarised light in relation to elec- 26

trolyte, 197 Transference of bodies. See Decom-

Pole defined, 112 position, electro-chemical

Poles, electric, nature of, 50, 63, 82;

evolved bodies at, 75—character Volta-electrometer, 84, 122

133; of 48, 50, 82; of Voltaic battery, 211; current in,
ixietal, 82; of platina, 83, 85, 90; 212, 213; in action, general

of water, 61, 74, 81 remarks on, 226-232; without

I’^otassium nitrate, electrolysis of, metallic contact, 298; zinc in,

209 214, 215

f^otassium, sulphuret of. See Sul- Voltaic circles. Fig. 43, p. 201;

l>liuret of potassium active, 259; associated, 211;

Protochloride of carbon, 119 combinations of substances em-

i^rotosulphuret of potassium as ployed in, 256; effect of air, 274;

electrolyte, 269 effect of dilution, 284, 290; effect

of interposed plates, 218-225;
Kiffault and Chompre on electro- effect of motion of fluids, 273;

chemical decomposition, 58, 66 effect of temperature, 271, 274,

279, 281; inactive, 241 et seq.;
Sclioiibein on voltaic condition of order of metals in, 295; proto-

iron, 316 sulphuret of potassium in, 269;

Silver chloride, electrolysis of, 76, relation of ions in, 200; simple,

X54, 208; voltaic effects in sul- 172; sulphuret of potassium in,

lohuret of potassium, 268 238, 241, 259, 265; without

Spark, produced by animal elec- metallic contact, 175, 298
triciby, 25; by common electri- ’/oltaic current, 6, 175
city, 19; by magneto-electricity, Voltaic electricity, 3; chemical
^3 f b)y thermo-electricity, 24; action as source of, 179, 180, 181,

by voltaic electricity, 5; without 185,190,282; chemical effects of,

iiietallic contact, 198 5; discharged by hot air, 4;

Suix>hate of soda, electrolysis of, evolution of heat by, 5; identity

j2o 6 with common electricity, 8, 12,

Sulx^huxet of antimony not an elec- 16, 31; magnetic force of, 5, 7;

trolyte, 120 physiological effects of, 5; rela-

Sulphuret of carbon, combining tion by measure to common

power of platina prevented by, electricity, 27; spark produced

107 by, 5

lsf«

336 Faraday’s

Voltaic forces, eleineiitaiy, 183
\'oltaic pile, 165; action of elements
of, 195, 196; chemical theory of
origin, 179, 180, 181,184,185, 190,
~33, 302; contact theory of origin,
232, 234, 243, 244, 253, 257, 263,
281, 288, 294, 308, 312; elec¬
tricity of, 170, 172, 1S3; excite¬
ment dependent on chemical
action, 304; exciting acids and
alkalies employed in, 188, 191;
oxidation as source of electric
current, 185, 190; place and care

Researches

j of wires in, 276; relation of
metals inverted by heat in, 282;
source of power in, 232, 271

Water, as electric pole, 61, 74, 81;
as electrolyte, 113; determined
to either pole, Si; direct conduc¬
tion by, 209; electrolysis of, 122,
131, 166 et seq .—intensity neces¬
sary for, 204; electro-chemical
decomposition against, 61, 74

Zinc in voltaic battery, 214, 215

I

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THE TEMPLE PRESS, PRINTERS, LETCHWORTH