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Full text of "Experimental researches in electricity"

EVERY/AAN. 
I WILL GO WITH 

THEE. 
& BE-THY GVIDE 
1NTHYMO5TNEED' 
1OGOBYTHY5JDE 




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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LONDON: J. M. DENT & SONS LTD. 
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EXPERI ~ 
MENTAL 

RESEARCHES 

IN 



^MICHAEL 

FARADAY 
D.CJL.JiRR.S 



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



FIRST ISSUE OF THIS EDITION . 1914 
REPRINTED .... 1922 



INTRODUCTION 1 

BY JOHN TYNDALL 

WHEN from an Alpine height the eye of the climber ranges 
over the mountains, he finds that for the most part they 
resolve themselves into distinct groups, each consisting of 
a dominant mass surrounded by peaks of lesser elevation. 
The power which lifted the mightier eminences, in nearly all 
cases lifted others to an almost equal height. And so it is 
with the discoveries of Faraday. As a general rule, the 
dominant result does not stand alone, but forms the culmi- 
nating point of a vast and varied mass of inquiry. In this 
way, round about his great discovery of magneto-electric 
induction, other weighty labours group themselves. His 
investigations on the extra current; on the polar and other 
condition of diamagnetic bodies; on lines of magnetic force, 
their definite character and distribution; on the employment 
of the induced magneto-electric current as a measure and test 
of magnetic action; on the revulsive phenomena of the 
magnetic field, are all, notwithstanding the diversity of title, 
researches in the domain of magneto-electric induction. 

Faraday's second group of researches and discoveries 
embrace the chemical phenomena of the current. The 
dominant result here is the great law of definite electro- 
chemical decomposition, around which are massed various 
researches on electro-chemical conduction and on electrolysis 
both with the machine and with the pile. To this group also 
belong his analysis of the contact theory, his inquiries as to 
the source of voltaic electricity, and his final development 
of the chemical theory of the pile. 

His third great discovery is the magnetisation of light, 
which I should liken to the Weisshorn among mountains 
high, beautiful, and alone. 

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

1 These pages form the " Summary " and the concluding passages of 
Faraday the Discoverer : 1869. 

vii 



2O54789 



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, born in 1761, being father to the 
philosopher. A family tradition exists that the Faradays 
came originally from Ireland. Faraday himself has more 
than once expressed to me his belief that his blood was in part 
Celtic, but how much of it was so, or when the infusion took 
place, he was unable to say. He could imitate the Irish 
brogue, and his wonderful vivacity may have been in part 
due to his extraction. But there were other qualities which 
we should hardly think of deriving from Ireland. The most 
prominent of these was his sense of order, which ran like 
a luminous beam through all the transactions of his life. The 
most entangled and complicated matters fell into harmony 
in his hands. His mode of keeping accounts excited the 
admiration of the managing board of this institution. And 
his science was similarly ordered. In his experimental 
researches, he numbered every paragraph, and welded their 
various parts together by incessant reference. His private 
notes of the experimental researches, which are happily 
preserved, are similarly numbered: their last paragraph bears 
the figure 16,041. His working qualities, moreover, showed 
the tenacity of the Teuton. His nature was impulsive, but 
there was a force behind the impulse which did not permit it 
to retreat. If in his warm moments he formed a resolution, 
in his cool ones he made that resolution good. Thus his fire 
was that of a solid combustible, not that of a gas, which 
blazes suddenly, and dies as suddenly away. 

And here I must claim your tolerance for the limits by 
which I am confined. No materials for a life of Faraday are 
in my hands, and what I have now to say has arisen* almost 
wholly out of our close personal relationship. 

Letters of his, covering a period of sixteen years, are before 
me, each one of which contains some characteristic utterance ; 
strong, yet delicate in counsel, joyful in encouragement, 
and warm in affection. References which would be pleasant 
to such of them as still live are made to Humboldt, Biot, 
Dumas, Chevreul, Magnus, and Arago. Accident brought 
these names prominently forward ; but many others would 
be required . to complete his list of continental friends. He 
prized the love and sympathy of men prized it almost more 
than the renown which his science brought him. Nearly 
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, 
* 576 



x Faraday's Researches 

" Tyndall, the sweetest reward of my work is the sympathy 
and good will which it has caused to flow in upon me from all 
quarters of the world." Among his letters I find little sparks 
of kindness, precious to no one but myself, but more precious 
to me than all. He would peep into the laboratory when he 
thought me weary, and take me upstairs with him to rest. 
And if I happened to be absent he would leave a little note 
for me, couched in this or some other similar form: " Dear 
Tyndall, I. was looking for you, because we were at tea 
we have not yet done will you come up ? " I frequently 
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 



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 rejoice at every addition to the facts and reasoning 
connected with the subject. When science is a republic, 
then it gains: and though I am no republican in other matters, 
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 like to alter it slightly, if you wish the full idea, i.e. 
not an inaccurate one, to be suggested at first; and yet after 
all I believe it is not your exposition, but the natural jumping 
to a conclusion that affects 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 in its proper place towards the 
end. 

While once conversing with Faraday 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 
or science the pursuit of his life. He could not serve both 
masters, and he was therefore compelled to choose between 
them. After the discovery of magneto-electricity his fame 
was so noised abroad that the commercial world would hardly 
have considered any remuneration too high for the aid of 
abilities like his. Even before he became so famous, he had 
done a little " professional business." This was the phrase 
he applied to his purely commercial work. His friend, 
Richard Phillips, for example, had induced him to undertake 
a number of analyses, which produced, in the year 1830, an 
addition to his income of more than a thousand pounds ; and 
in 1831, a still greater addition. He had only to will it to 
raise in 1832 his professional business income to 5000 a year. 
Indeed, this is a wholly insufficient estimate of what he 
might, with ease, have realised annually during the last thirty 
years of his life. 

While restudying the experimental researches with reference 
to the present memoir, the conversation with Faraday here 
alluded to came to my recollection, and I sought to ascertain 
the period when the question, " wealth or science," had 
presented itself with such emphasis to his mind. I fixed upon 
the year 1831 or 1832, for it seemed beyond the range of human 
power to pursue science as he had done during the subsequent 
years, and to pursue commercial work at the same time. To 
test this conclusion I asked permission to see his accounts, 
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 ^1090 45. to ^155 95. From this 
it fell with slight oscillations to ^92 in 1837, and to zero in 
1838. Between 1839 and 1845, it never, except in one 
instance, exceeded ^22; being for the most part much under 
this. The exceptional year referred to was that in which he 
and Sir Charles Lyell were engaged by Government to write 
a report on the Haswell Colliery explosion, and then his 
business income rose to 112. From the end of 1845 to the 
day of his death, Faraday's annual professional business 
income was exactly zero. Taking the duration of his life 
into account, this son of a blacksmith, and apprentice to a 
bookbinder, had to decide between a fortune of \ 50,000 
on the one side, and his undowered science on the other. 



Introduction xiii 

He chose the latter, and died a poor man. But his was the 
glory of holding aloft among the nations the scientific name 
of England for a period of forty years. 

The outward and visible signs of fame were also of less 
account to him than to most men. He had been loaded with 
scientific honours from all parts of the world. Without, 
I imagine, a dissentient voice, he was regarded as the prince 
of the physical investigators of the present age. The highest 
scientific position in this country he had, however, never filled. 
When the late excellent and lamented Lord Wrottesley 
resigned the presidency of the Royal Society, a deputation 
from the council, consisting of his lordship, Mr. Grove, and 
Mr. Gassiot, waited upon Faraday, to urge him to accept the 
president's chair. All that argument or friendly persuasion 
could do was done to induce him to yield to the wishes of the 
council, which was also the unanimous wish of scientific men. 
A knowledge of the quickness of his own nature had induced 
in Faraday the habit of requiring an interval of reflection, 
before he decided upon any question of importance. In the 
present instance he followed his usual habit, and begged for 
a little time. 

On the following morning, I went up to his room, and said 
on entering that I had come to him with some anxiety of mind. 
He demanded its cause, and I responded " lest you should 
have decided against the wishes of the deputation that waited 
on you yesterday." " You would not urge me to undertake 
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 
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. 



xiv Faraday's Researches 

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

In the year 1835, Sir Robert Peel wished to offer Faraday 
a pension, but that great statesman quitted office before he 
was able to realise his wish. The minister who founded these 
pensions intended them, I believe, to be marks of honour 
which even proud men might accept without compromise of 
independence. When, however, the intimation first reached 
Faraday, in an unofficial way, he wrote a letter announcing 
his determination to decline the pension; and stating that 
he was quite competent to earn his livelihood himself. That 
letter still exists, but it was never sent, Faraday's repugnance 
having been overruled by his friends. When Lord Melbourne 
came into office, he desired to see Faraday; and probably 
in utter ignorance of the man for, unhappily for them and 
us, ministers of state in England are only too often ignorant 
of great Englishmen his Lordship said something that must 
have deeply displeased his visitor. The whole circumstances 
were once communicated to me, but I have forgotten the 
details. The term " humbug," I think, was incautiously 
employed by his lordship, and other expressions were used 
of a similar kind. Faraday quitted the minister with his 
own resolves, and that evening he left his card and a short 
and decisive note at the residence of Lord Melbourne, stating 
that he had manifestly mistaken his lordship's intention of 
honouring science in his person, and declining to have any- 
thing whatever to do with the proposed pension. The good- 
humoured nobleman at first considered the matter a capital 
joke; but he was afterwards led to look at it more seriously. 
An excellent lady, who was a friend both to Faraday and the 
minister, tried to arrange matters between them; but she 
found Faraday very difficult to move from the position he had 
assumed. After many fruitless efforts, she at length begged 
of him to state what he would require of Lord Melbourne to 
induce him to change his mind. He replied, " I should 
require from his lordship what I have no right or reason to 
expect that he would grant a written apology for the words 



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 first 
time. 

" Hampton Court, August i, 1864. 

" MY DEAR TYNDALL, I do not know whether my letter 
will catch you, but I will risk it, though feeling very unfit 
to communicate with a man whose life is as vivid and active 
as yours; but the receipt of your kind letter makes me to 
know that though I forget, I am not forgotten, and though 
I am not able to remember at the end of a line what was said 
at the beginning of it, the imperfect marks will convey to you 
some sense of what I long to say. We had heard of your 
illness through Miss Moore, and I was therefore very glad 
to learn that you are now quite well; do not run too many 
risks or make your happiness depend too much upon dangers, 



xvi Faraday's Researches 

or the hunting of them. Sometimes the very thinking of you, 
and what you may be about, wearies me with fears, and then 
the cogitations pause and change, but without giving me 
rest. I know that much of this depends upon my own 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 
I have a cheerful letter from him, written in the autumn of 
1865. But towards the close of that year he had an attack 
of illness, from which he never completely rallied. He con- 
tinued to attend the Friday evening meetings, but the advance 
of infirmity was apparent to us all. Complete rest became 
finally essential to him, and he ceased to appear among us. 
There was no pain in his decline to trouble the memory of 
those who loved him. Slowly and peacefully he sank towards 
his final rest, and when it came, his death was a falling asleep. 
In the fulness of his honours and of his age he quitted us; 
the good fight fought, the work of duty shall I not say of 
glory done. The " Jane " referred to in the foregoing letter 
is Faraday's niece, Miss Jane Barnard, who, with an affection 
raised almost to religious devotion, watched him and tended 
him to the end. 

I saw Mr. Faraday for the first time on my return from 
Marburg in 1850. I came to the Royal Institution, and sent 
up my card, with a copy of the paper which Knoblauch and 
myself had just completed. He came down and conversed 
with me for half-an-hour. I could not fail to remark the 
wonderful play of intellect and kindly feeling exhibited by 
his countenance. When he was in good health the question 
of his age would never occur to you. In the light and laughter 
of his eyes you never thought of his grey hairs. He was then 
on the point of publishing one of his papers on magne-crystallic 
action, and he had time to refer in a flattering note to the 



Introduction xvii 

memoir I placed in his hands. I returned to Germany, 
worked there for nearly another year, and in June 1851 came 
back finally from Berlin to England. Then, for the first time, 
and on my way to the meeting of the British Association, 
at Ipswich, I met a man who has since made his mark upon 
the intellect of his time; who has long been, and who by the 
strong law of natural affinity must continue to be, a brother 
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 was mainly his and other friendships, precious 
to me beyond all expression, that caused me to value my 
position here more highly than any other that could be offered 
to me in this land. Nor is it for its honour, though surely 
that is great, but for the strong personal ties that bind me 
to it, that I now chiefly prize this place. You might not credit 
me were I to tell you how lightly I value the honour of being 
Faraday's successor compared with the honour of being 
Faraday's friend. His 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 see 
him. The deep radiance, which in his time of strength flashed 
with such extraordinary power from his countenance, had 
subsided to a calm and kindly light, by which my latest 
memory of him is warmed and illuminated. I knelt one day 
beside him on the carpet and placed my hand upon his knee; 
he stroked it affectionately, smiled, and murmured, in a low 
soft voice, the last words that I remember as having been 
spoken to me by Michael Faraday. 

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



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. 



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

Some Observations on the Means of Obtaining Knowledge, 1817; 
History of the Progress of Electro-Magnetism, 1821; Chemical Manipula- 
tion, 1827; edition On the Alleged Decline of Science in England, 1831; 
On the Practical Prevention of Dry Rot in Timber, 1833; Experimental 
Researches in Electricity, 3 vols., 1839-55; Observations on Mental 
Education, 1855; Experimental Researches in Chemistry and Physics 
(reprinted from Philosophical Transactions, The Journal of the Royal 
Institution, etc.), 1859; The Various Forces of Matter (six lectures edited 
by Sir Wm. Crookes), 1860; The Chemical History of a Candle (six lectures 
edited by Sir Wm. Crookes), 1861 ; Some Thoughts on the Conservation of 
Force, 1865; The Liquefaction of Gases (papers given, 1823-45), 1896. 

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

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



XIX 



CONTENTS 

PAGE 

I. i. IDENTITY OF ELECTRICITIES FROM DIFFERENT SOURCES . I 

i. Voltaic Electricity ...... 3 

ii. Ordinary Electricity ..... 7 

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

iv. Thermo-Electricity ...... 24 

v. Animal Electricity ...... 24 

2. RELATION BY MEASURE OF COMMON AND VOLTAIC 

ELECTRICITY . . . . . . . .27 

II. 3. NEW LAW OF ELECTRIC CONDUCTION .... 32 

4. ON CONDUCTING POWER GENERALLY .... 41 

III. 5. ELECTRO-CHEMICAL DECOMPOSITION .... 47 

If i- New Conditions of Electro-chemical Decom- 
position ....... 48 

If ii. Influence of Water in such Decomposition . 54 

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

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

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

If iv. Some General Conditions of Electro-chemical 

Decomposition . . . . .115 
H v. Volta-electrometer ..... 122 
If vi. Primary and Secondary Results . . . 133 
Tj vii. Definite Nature and Extent of Electro- 
chemical Forces . . . . 145 

7. ABSOLUTE QUANTITY OF ELECTRICITY IN THE MOLECULES 

OF MATTER ........ 163 

VI. 8. ELECTRICITY OF THE VOLTAIC PILE .... 172 
U i. Simple Voltaic Circles . . . . .172 

If ii. Electrolytic Intensity ..... 203 

f iii. Associated Voltaic Circles; or Battery . . 211 

If iv. Resistance of an Electrolyte to Decomposition 218 

U v. General Remarks on the Active Battery . 226 
xxi 



xxii Faraday's Researches 



PAGE 

VII. 9. ON THE SOURCE OF POWER IN THE VOLTAIC PILE . 232 
If i. Exciting Electrolytes being Good Conductors . 238 
If ii. Inactive Conducting Circles containing an Elec- 
trolyte ....... 241 

If iii. Active Circles containing Sulphuret of Potas- 
sium ....... 259 

VIII. q. ON THE SOURCE OF POWER IN THE VOLTAIC PILE Continued 271 
If iv. The Exciting Chemical Force affected by 

Temperature . . . . . .271 

U v. The Exciting Chemical Force affected by 

Dilution. ...... 284 

t vi. Differences in the Order of the Metallic 

Elements of Voltaic Circles . . . 295 
^f vii. Active Voltaic Circles and Batteries without 

Metallic Contact ..... 298 

1f viii. Considerations of the Sufficiency of Chemical 

Action ....... 302 

H ix. Thermo-electric Evidence .... 308 

If x. Improbable Nature of the Assumed Contact 

Force ....... 312 

ON A PECULIAR VOLTAIC CONDITION OF IRON (SCHOENBEIN) . . 317 
Ox A PECULIAR VOLTAIC CONDITION OF IRON (FARADAY) . 321, 330 
INDEX 333 



EXPERIMENTAL RESEARCHES 
IN ELECTRICITY 



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

i. Identity of Electricities derived from different sources 

i. THE progress of the electrical researches which I have had 
the honour to present to the Royal Society, brought me to a 
point at which it was essential for the further prosecution of 
my inquiries that no doubt should remain of the identity or 
distinction of electricities excited by different means. It is per- 
fectly true that Cavendish, 2 Wollaston, 3 Colladon 4 and others, 
have in succession removed some of the greatest objections to 
the acknowledgment of the identity of common, animal and 
voltaic electricity, and I believe that most philosophers con- 
sider these electricities as really the same. But on the other 
hand it is also true, that the accuracy of Wollaston's experi- 
ments has been denied ; 5 and also that one of them, which 
really is no proper proof of chemical decomposition by common 
electricity (45, 63), has been that selected by several experi- 
menters as the test of chemical action (72, 82). It is a fact, 
too, that many philosophers are still drawing distinctions 
between the electricities from different sources; or at least 
doubting whether their identity is proved. Sir Humphry 
Davy, for instance, in his paper on the Torpedo, 6 thought it 

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

2 Phil. Trans. 1776, p. 196. * Ibid. 1801, p. 434. 

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

6 1 hil. Trans. 1829, p. 17. " 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." 



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. 1 

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

3. The various phenomena exhibited by electricity may, for 
the purposes of comparison, be arranged under two heads; 
namely, those connected with electricity of tension, and those 
belonging to electricity in motion. This distinction is taken at 

1 Phil. Trans. 1832, p. 259. Dr. Davy, in making experiments on the 
torpedo, obtains effects the same as those produced by common and voltaic 
electricity, and says that in its magnetic and chemical power it does not 
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 in this case, which was thought toafford the most striking resemblance," 
p. 291. 



Voltaic Electricity 3 

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

I. Voltaic Electricity 

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

5. That ordinary electricity is discharged by points with 
facility through air; that it is readily transmitted through 
highly rarefied air; and also through heated air, as for instance 
a flame; is due to its high tension. I sought, therefore, for 
similar effects in the discharge of voltaic electricity, using as 
a test of the passage of the electricity either the galvanometer 
or chemical action produced by the arrangement hereafter to 
be described (48, 52). 

6. The voltaic battery I had at my disposal consisted of 140 
pairs of plates four inches square, with double coppers. It was 
insulated throughout, and diverged a gold leaf electrometer 
about one-third of an inch. On endeavouring to discharge this 
battery by delicate points very nicely arranged and approxi- 
mated, either in the air or in an exhausted receiver, I could 
obtain no indications of a current, either by magnetic or chemical 
action. In this, however, was found no point of discordance 
between voltaic and common electricity; for when a Leyden 
battery (27) was charged so as to deflect the gold leaf electro- 
meter to the same degree, the points were found equally unable 
to discharge it with such effect as to produce either magnetic 
or chemical action. This was not because common electricity 
could not produce both these effects (43, 46), but because when 
of such low intensity the quantity required to make the effects 
visible (being enormously great (107, in) ) could not be 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. i), in which 
A B is an insulated glass rod 
upon which two copper wires, 
C, D, are fixed firmly; to these 
wires are soldered two pieces of 
fine platina wire, the ends of 
which are brought very close to 
each other at e, but without 
touching ; the copper wire C 
was connected with the positive 
pole of a voltaic battery, and 
the wire D with a decomposing 

apparatus (48, 52), from which the communication was com- 
pleted to the negative pole of the battery. In these experiments 
only two troughs, or twenty pairs of plates, were used. 

8. Whilst in the state described, no decomposition took place 
at the point a, but when the side of a spirit-lamp flame was 
applied to the two platina extremities at e, so as to make them 
bright red-hot, decomposition occurred; iodine soon appeared 
at the point a, and the transference of electricity through the 
heated air was established. On raising the temperature of the 
points e by a. blowpipe, the discharge was rendered still more 
free, and decomposition took place instantly. On removing 
the source of heat, the current immediately ceased. On 
putting the ends of the wires very close by the side of and 
parallel to each other, but not touching, the effects were perhaps 
more readily obtained than before. On using a larger voltaic 
battery (6), they were also more freely obtained. 

9. On removing the decomposing apparatus and interposing 
a galvanometer instead, heating the points e as the needle 
would swing one way, and removing the heat during the time 
of its return (38), feeble deflections were soon obtained: thus 
also proving the current through heated air; but the 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 with common 
electricity, and Sir H. Davy has recorded that with the original 
battery of the Royal Institution this discharge passed through 
a space of at least four inches. 1 In the exhausted receiver the 
electricity would strike through nearly half an inch of space, 
and the combined effects of rarefaction and heat was such 
upon the inclosed air as to enable it to conduct the electricity 
through a space of six or seven inches. 

11. The instantaneous charge of a Leyden battery by the 
poles of a voltaic apparatus is another proof of the tension, and 
also the quantity, of electricity evolved by the latter. Sir H. 
Davy says. 2 " When the two conductors from the ends of the 
combination were connected with a Leyden battery, one with 
the internal, the other with the external coating, the battery 
instantly became charged; and on removing the wires and 
making the proper connections, either a shock or a spark could 
be perceived : and the least possible time of contact was sufficient 
to renew the charge to its full intensity." 

12. In motion : i. Evolution of heat. The evolution of heat 
in wires and fluids by the voltaic current is matter of general 
notoriety. 

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

14. iii. Chemical decomposition. The chemical powers of the 
voltaic current, and their subjection to certain laws, are also 
perfectly well known. 

15. iv. Physiological effects. The power of the voltaic 
current, when strong, to shock and convulse the whole animal 
system, and when weak to affect the tongue and the eyes, is 
very characteristic. 

16. v. Spark. The brilliant star of light produced by the 
discharge of a voltaic battery is known to all as the most 
beautiful light that man can produce by art. 

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

1 Elements of Chemical Philosophy. * Ibid. p. 154. 



6 Faraday's Researches 

effect. The beautiful explication of these variations afforded 
by Cavendish's theory of quantity and intensity requires no 
support at present, as it is not supposed to be doubted. 

18. In consequence of the comparisons that will hereafter 
arise between wires carrying voltaic and ordinary electricities, 
and also because of certain views of the condition of a wire or 
any other conducting substance connecting the poles of a 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 





r 


t 
N P 




IfK RL n n n r 


\ IV ft IV R- \ 


f tl rj.(^l'Yivivio,i | rv /vX 









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 motion : 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 l a very beautiful and sensible 
instrument on this principle, in which the heat produced in a 
wire by the discharge of a small portion of common electricity 
is readily shown, and to which I shall have occasion to refer 
for experimental proof in a future part of this paper (80). 

24. ii. Magnetism. Voltaic electricity has most extraordinary 

1 Philosophical Transactions, 1827, p. 18. Edinburgh Transactions, 1831. 
Harris on a New Electrometer, etc., etc. 



Faraday's Researches 

and exalted magnetic powers. If common electricity be 
identical with it, it oifght to have the same powers. In render- 
ing needles or bars magnetic, it is found to agree with voltaic 
electricity, and the direction of the magnetism, in both cases, 
is the same; but in deflecting the magnetic needle, common 
electricity has been found deficient, so that sometimes its 
power has been denied altogether, and at other times distinc- 
tions have been hypothetically assumed for the purpose of 
avoiding the difficulty. 1 

25. M. Colladon, of Geneva, considered that the difference 
might be due to the use of insufficient quantities of common 
electricity in all the experiments before made on this head; 
and in a memoir read to the Academic des Sciences in 1826, r 
describes experiments, in which, by the use of a battery, points, 
and a delicate galvanometer, he succeeded in obtaining de- 
flections, and thus establishing identity in that respect. MM. 
Arago, Ampere, and Savary, are mentioned in the paper as 
having witnessed a successful repetition of the experiments. 
But as no other one has come forward in confirmation, MM. 
Arago, Ampere, and Savary, not having themselves published 
(that I am aware of) their admission of the results, and as some 
have not been able to obtain them, M. Colladon's conclusions 
have been occasionally doubted OF denied; and an important 
point with me was to establish their accuracy, or remove them 
entirely from the body of received experimental research. I 
am happy to say that my results fully confirm those by M. 
Colladon, and I should have had no occasion to describe them, 
but that they are essential as proofs of the accuracy of the 
final and general conclusions I am enabled to draw respecting 
the magnetic and chemical action of electricity (96, 102, 103, 
113, etc.). 

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

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



Magnetic Effects 9 

27. The electric battery consisted of fifteen equal jars. They 
are coated eight inches upwards from the bottom, and are 
twenty-three inches in circumference, so that each contains 
184 square inches of glass, coated on both sides; this is in- 
dependent of the bottoms, which are of thicker glass, and 
contain each about fifty square inches. 

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, 1 but the glass jar covering it and supporting the 
needle was coated inside and outside with tinfoil, and the upper 
part (left uncoated, that the motions of the needle might be 
examined) was covered with a frame of wirework, having 
numerous sharp points projecting from it. When this frame 
and the two coatings were connected with the discharging 
train (28), an insulated point or ball, connected with the machine 
when most active, might be brought within an inch of any 
part of the galvanometer, yet without affecting the needle 
within by ordinary electrical attraction or repulsion. 

30. In connection with these precautions, it may be neces- 
sary to state that the needle of the galvanometer is very liable 
to have its magnetic power deranged, diminished, or even 
inverted by the passage of a shock through the instrument. If 

1 The galvanometer was roughly made, yet sufficiently delicate in its 
indications. The wire was of copper covered with silk, and made sixteen 
or eighteen convolutions. Two sewing-needles were magnetised and fixed 
on to a stem of dried grass parallel to each other, but in opposite direc- 
tions, and about half an inch apart; this system was suspended by a fibre 
of unspun silk, so that the lower needle should be between the convolutions 
of the multiplier, and the upper above them. The latter was by much 
the most powerful magnet, and gave terrestrial direction to the whole; 
fig. 3 represents the direction of the wire and of the needles when the 
instrument was placed in the magnetic meridian: the ends of the wires 
are marked A and B. The letters S and N designate the south and north 
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). 



io Faraday's Researches 

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

31. It was to the retarding power of bad conductors, with 
the intention of diminishing its intensity without altering its 
quantity, that I first looked with the hope of being able to 
make common electricity assume more of the characters and 
power of voltaic electricity, than it is usally supposed to have. 

32. The coating and armour of the galvanometer were first 
connected with the discharging train (28); the end B (fig. 3) 

of the galvanometer wire was connected with 

the outside coating of the battery, and then 
both these with the discharging train; the 
end A of the galvanometer wire was con- 
Fig. 3. nected with a discharging rod by a wet 
thread four feet long; and finally, when the 
battery (27) had been positively charged by about forty turns 
of the machine, it was discharged by the rod and the thread 
through the galvanometer. The needle immediately moved. 

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

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

35. On reversing the galvanometer communications so as to 
pass the discharge through from B to A, the needle was equally 
well deflected, but in the opposite direction. 

36. The deflections were in the same direction as if a voltaic 
current had been passed through the galvanometer, i.e. the 
positively charged surface of the electric battery coincided with 
the positive end of the voltaic apparatus (4), and the negative 
surface of the former with the negative end of the latter. 

37. The battery was then thrown out of use. and the com- 
munications so arranged that the current could be passed from 
the prime conductor, by the discharging rod held against it, 



Deflection of Magnet i i 

through the wet string, through the galvanometer coil, and 
into the discharging train, by which it was finally dispersed. 
This current could be stopped at any moment, by removing 
the discharging rod, and either stopping the machine or con- 
necting the prime conductor by another rod with the dis- 
charging train; and could be as instantly renewed. The needle 
was so adjusted, that whilst vibrating in moderate and small 
arcs, it required time equal to twenty-five beats of a watch to 
pass in one direction through the arc, and of course an equal 
time to pass in the other direction. 

38. Thus arranged, and the needle being stationary, the 
current, direct from the machine, was sent through the galvano- 
meter for twenty-five beats, then interrupted for other twenty- 
five beats, renewed for twenty-five beats more, again interrupted 
for an equal time, and so on continually. The needle soon 
began to vibrate visibly, and after several alternations of this 
kind, the vibration increased to 40 or more. 

39. On changing the direction of the current through the 
galvanometer, the direction of the deflection of the needle was 
also changed. In all cases the motion of the needle was in 
direction the same as that caused either by the use of the 
electric battery or a voltaic trough (36). 

40. I now rejected the wet string, and substituted a copper 
wire, so that the electricity of the machine passed at once into 
wires communicating directly with the discharging train, the 
galvanometer coil being one of the wires used for the discharge. 
The effects were exactly those obtained above (38). 

41. Instead of passing the electricity through the system, by 
bringing the discharging rod at the end of it into contact with 
the conductor, four points were fixed on to the rod; when the 
current was to pass, they were held about twelve inches from 
the conductor, and when it was not to pass, they were turned 
away. Then operating as before (38), except with this variation, 
the needle was soon powerfully deflected, and in perfect con- 
sistency with the former results. Points afforded the means 
by which Colladon, in all cases, made his discharges. 

42. Finally, I passed the electricity first through an 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 

B 576 



12 Faraday's Researches 

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

44. Imperfect conductors, as water, brine, acids, etc., etc., 
will be found far more convenient for exhibiting these effects 
than other modes of discharge, as by points or balls; for the 
former convert at once the charge of a powerful battery into 
a feeble spark discharge, or rather continuous current, and 
involve little or no risk of deranging the magnetism of the 
needles (30). 

45. iii. Chemical decomposition. The chemical action of 
voltaic electricity is characteristic of that agent, but not more 
characteristic than are the laws under which the bodies evolved 
by decomposition arrange themselves at the poles. Dr. 
Wollaston showed l 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 piove the occurrence of electro-chemical decomposition, like 
that of the pile, and by others to throw doubt upon the whole 
paper, than the more numerous and decisive experiments which 
he has detailed. 

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, 2 in 
which the ends of coated silver wires are immersed in a drop 
of sulphate of copper. By passing the electricity of the machine 
through such an arrangement, that end in the drop which 
received the electricity became coated with metallic copper. 
One hundred turns of the machine produced an evident effect; 
two hundred turns a very sensible one. The decomposing 
action was however very feeble. Very little copper was pre- 
cipitated, and no sensible trace of silver from the other pole 
appeared in the solution. 

1 Philosophical Transactions, 1801, pp. 427, 434. * Ibid. 1801, p. 429. 



Identity of Electricities 1 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, b ; connect one of these by an insulated 




Fig. 4- 

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



i 



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 



14 Faraday's Researches 

had been set free at p, 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 n, 
on the glass: the paper retains the substance evolved at the 
point of evolution, by its whiteness renders any change of 
colour visible, and allows of the point of contact between it and 
the decomposing wires being contracted to the utmost degree. 
A piece of paper moistened in the solution of iodide of potas- 
sium and starch, or of the iodide alone, with certain precautions 
(58), is a most admirable test of electro-chemical action; and 
when thus placed and acted upon by the electric current, will 
show iodine evolved at p by only half a turn of the machine. 
With these adjustments and the use of iodide of potassium 
on paper, chemical action is sometimes a more delicate test 
of electrical currents than the galvanometer (9). Such cases 
occur when the bodies traversed by the current are bad con- 
ductors, or when the quantity of electricity evolved or trans- 
mitted in a given time is very small. 

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 . 

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 n, or towards 
n ; and I have seen no reason to believe that in cases of true 
electro-chemical decomposition by the machine, the electricity 
passed in sparks from the conductor, or at any part of the 
current, is able to do more, because of its tension, than that 
which is made to pass merely as a regular current. 

57. Finally, the experiment was extended into the following 
form, supplying in this case the fullest analogy between common 
and voltaic electricity. Three compound pieces of litmus and 
turmeric paper (55) were moistened in solution of sulphate of 
soda, and arranged on a plate of glass with platina wires, as 
in fig. 6. The wire m was connected with the prime conductor 




Fig. 6. 

of the machine, the wire t with the discharging train, and the 
wires r and s entered into the course of the electrical current 
by means of the pieces of moistened paper; they were so bent 
as to rest each on three points, n, r, p ; n, s, p, the points r and 
s being supported by the glass, and the others by the papers: 
the three terminations -p, p, p rested on the litmus, and the 
other three n, n, n on the turmeric paper. On working the 
machine for a short time only, acid was evolved at all the 
poles or terminations p, p, p, by which the electricity entered 
the solution, and alkali at the other poles n, n, n, by which the 
electricity left the solution. 

58. In all experiments of electro-chemical decomposition by 
the common machine and moistened papers (52), it is neces- 
sary to be aware of and to avoid the following important source 
of error. If a spark passes over moistened litmus and turmeric 
paper, the litmus paper (provided it be delicate and not too 
alkaline) is reddened by it; and if several sparks are passed, it 
becomes powerfully reddened. If the electricity pass a little 



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 prevent the occurrence of the red spot due to the alkali, 
which would otherwise collect there: sparks or ramifications 
from the points n will also redden litmus paper. If paper 
moistened by a solution of iodide of potassium (which is an 
admirably delicate test of electro-chemical action) be exposed 
to the sparks or ramifications, or even a feeble stream of elec- 
tricity through the air from either the point p or n, iodine will 
be immediately evolved. 

59. These effects must not be confounded with those due 
to the true electro-chemical powers of common electricity, and 
must be carefully avoided when the latter are to be observed. 
No sparks should be passed, therefore, in any part of the 
current, nor any increase of intensity allowed, by which the 
electricity may be induced to pass between the platina wires and 
the moistened papers, otherwise than by conductidn; for if it 
burst through the air, the effect referred to above (58) 
ensues. 

60. The effect itself is due to the formation of nitric acid 
by the combination of the oxygen and nitrogen of the air, and 
is, in fact, only a delicate repetition of Cavendish's beautiful 
experiment. The acid so formed, though small in quantity, is 
in a high state of concentration as to water, and produces the 
consequent effects of reddening the litmus paper; or preventing 
the exhibition of alkali on the turmeric paper; or, by acting on 
the iodide of potassium, evolving iodine. 

61. By moistening a very small slip of litmus paper in solu- 
tion of caustic potassa, and then passing the electric spark over 
its length in the air, I gradually neutralised the alkali, and 
ultimately rendered the paper red; on drying it, I found that 
nitrate of potassa had resulted from the operation, and that the 
paper had become touch paper. 

62. Either litmus paper or white paper, moistened in a 
strong solution of iodide of potassium, offers therefore a very 
simple, beautiful, and ready means of illustrating Cavendish's 
experiment of the formation of nitric acid from the atmosphere. 

63. I have already had occasion to refer to an experiment 
(i, 45) made by Dr. Wollaston, which is insisted upon too 
much, both by those who oppose and those who agree with the 
accuracy of his views respecting the identity of voltaic and 



Wollaston's Experiment 17 

ordinary electricity. By covering fine wires with glass or other 
insulating substances, and then removing only so much matter 
as to expose the point, or a section of the wires, and by passing 
electricity through two such wires, the guarded points of which 
were immersed in water, Wollaston found that the water could 
be decomposed even by the current from the machine, without 
sparks, and that two streams of gas arose from the points, 
exactly resembling, in appearance, those produced by voltaic 
electricity, and, like the latter, giving a mixture of oxygen and 
hydrogen gases. But Dr. Wollaston himself points out that 
the effect is different from that of the voltaic pile, inasmuch as 
both oxygen and hydrogen are evolved from each pole; he calls 
it " a very close imitation 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 I797, 1 
and previously by MM. Pacts Van Troostwyk and Deiman in 
1789 or earlier. That the experiment should never be quoted 
as proving true electro-chemical decomposition, is sufficiently 
evident from the circumstance, that the law which regulates 
the transference and final place of the evolved bodies (14, 45) 
has no influence here. The water is decomposed at both poles 
independently of each other, and the oxygen and hydrogen 
evolved at the wires are the elements of the water existing 
the instant before in those places. That the poles, or rather 
points, have no mutual decomposing dependence, may be 
shown by substituting a wire, or the finger, for one of them, a 
change which does not at all interfere with the other, though it 
stops all action at the changed pole. This fact may be observed 
by turning the machine for some time; for though bubbles 
will rise from the point left unaltered, in quantity sufficient 
to cover entirely the wire used for the other communication, if 
they could be applied to it, yet not a single bubble will appear 
on that wire. 

65. When electro-chemical decomposition takes place, there 
is great reason to believe that the quantity of matter decom- 
posed is not proportionate to the intensity, but to the quantity 
of electricity passed (56). Of this I shall be able to offer some 
proofs in a future part of this paper (in, 113). But in the 
experiment under consideration, this is not the case. If, with 

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



1 8 Faraday's Researches 

a constant pair of points, the electricity be passed from the 
machine in sparks, a certain proportion of gas is evolved; but 
if the sparks be rendered shorter, less gas is evolved ; and if f 
no sparks be passed, there is scarcely a sensible portion of 
gases set free. On substituting solution of sulphate of soda for 
water, scarcely a sensible quantity of gas could be procured even 
with powerful sparks, and nearly none with the mere current; 
yet the quantity of electricity in a given time was the same in 
all these cases. 

66. I do not intend to deny that with such an apparatus 
common electricity can decompose water in a manner analogous 
to that of the voltaic pile ; I believe at present that it can. But 
when what I consider the true effect only was obtained, the 
quantity of gas given off was so small that I could not ascertain 
whether it was, as it ought to be, oxygen at one wire and 
hydrogen at the other. Of the two streams one seemed more 
copious than the other, and on turning the apparatus round, 
still the same side in relation to the machine gave the largest 
stream. On substituting solution of sulphate of soda for pure 
water (65), these minute streams were still observed. But 
the quantities were so small, that on working the machine for 
half an hour I could not obtain at either pole a bubble of gas 
larger than a small grain of sand. If the conclusion which I 
have drawn (113) relating to the amount of chemical action be 
correct, this ought to be the case. 

67. I have been the more anxious to assign the true value of 
this experiment as a test of electro-chemical action, because I 
shall have occasion to refer to it in cases of supposed chemical 
action by magneto-electric and other electric currents (72, 82) 
and elsewhere. But, independent of it, there cannot be now 
a doubt that Dr. Wollaston was right in his general conclusion; 
and that voltaic and common electricity have powers of chemical 
decomposition, alike in their nature, and governed by the same 
law of arrangement. 

68. iv. Physiological effects. The power of the common 
electric current to shock and convulse the animal system, and 
when weak to affect the tongue and the eyes, may be considered 
as the same with the similar power of voltaic electricity, account 
being taken of the intensity of the one electricity and duration 
of the other. When a wet thread was interposed in the course 
of the current of common electricity fr.om the battery (27) 
charged by eight or ten l revolutions of the machine in good 

1 Or even from thirty to forty. 



Atmospheric Electricity 19 

action (26), and the discharge made by platina spatulas through 
the tongue or the gums, the effect upon the tongue and eyes was 
exactly that of a momentary feeble voltaic circuit. 

69. v. Spark. The beautiful flash of light attending the 
discharge of common electricity is well known. It rivals in 
brilliancy, if it does not even very much surpass, the light from 
the discharge of voltaic electricity; but it endures for an instant 
only, and is attended by a sharp noise like that of a small 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 electricity. 
But the comparison I am drawing is far too rigorous to allow 
me to use these statements without being fully assured of their 
accuracy; yet I have no right to suppress them, because, if 
accurate, they establish what I am labouring to put on an 
undoubted foundation, and have priority to my results. 

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

1 Bibliotheque Universelle, 1830, tome xlv. p. 213. 



2o Faraday's Researches 

electricity. By connecting an insulated lightning rod with his 
apparatus, the decomposition of the water proceeded in a con- 
tinuous and rapid manner even when the electricity of the 
atmosphere was not very powerful. The apparatus is not 
described ; but as the diameter of the wire is mentioned as very 
small, it appears to have been similar in construction to that of 
Wollaston (63); and as that does not furnish a case of true 
polar electro-chemical decomposition (64), this result of M. 
Bonijol does not prove the identity in chemical action of common 
and voltaic electricity. 

73. At the same page of the Bibliotheque Universelle, M. 
Bonijol is said to have decomposed potash, and also chloride of 
silver, by putting them into very narrow tubes and passing 
electric sparks from an ordinary machine over them. It is 
evident that these offer no analogy to cases of true voltaic de- 
composition, where the electricity only decomposes when it is 
conducted by the body acted upon, and ceases to decompose, 
according to its ordinary laws, when it passes in sparks. These 
effects are probably partly analogous to that which takes place 
with water in Pearson's or Wollaston's apparatus, and may be 
due to very high temperature acting on minute portions of 
matter; or they may be connected with the results in air (58). 
As nitrogen can combine directly with oxygen under the in- 
fluence of the electric spark (60), it is not impossible that it 
should even take it from the potassium of the potash, especially 
as there would be plenty of potassa in contact with the acting 
particles to combine with the nitric acid formed. However 
distinct all these actions may be from true polar electro-chemical 
decompositions, they are still highly important, and well worthy 
of investigation. 

74. The late Mr. Barry communicated a paper to the Royal 
Society l last year, so distinct in the details, that it would seem 
at once to prove the identity in chemical action of common and 
voltaic electricity; but, when examined, considerable difficulty 
arises in reconciling certain of the effects with the remainder. 
He used two tubes, each having a wire within it passing through 
the closed end, as is usual for voltaic decompositions. The tubes 
were filled with solution of sulphate of soda, coloured with 
syrup of violets, and connected by a portion of the same solution, 
in the ordinary manner; the wire in one tube was connected 
by a gilt thread with the string of an insulated electrical kite, 
and the wire in the other tube by a similar gill thread with the 

1 Philosophical Transactions, 1831, p. 165. 



Identity of Electricities 21 

ground. Hydrogen soon appeared in the tube connected with 
the kite, and oxygen in the other, and in ten minutes the liquid 
in the first tube was green from the alkali evolved, and that in 
the other red from free acid produced. The only indication 
of the strength 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 long, and contained two 
double threads. But when the enormous quantity which must 
have been thus collected is considered (107, 112), the explanation 
seems very doubtful. I charged a voltaic battery of twenty 
pairs of plates four inches square with double coppers very 
strongly, insulated it, connected its positive extremity with 
the discharging train (28), and its negative pole with an appa- 
ratus like that of Mr. Barry, communicating by a wire inserted 



22 Faraday's Researches i . 

three inches into the wet soil of the ground. This battery 
thus arranged produced feeble decomposing effects, as nearly 
as I could judge answering the description Mr. Barry has given. 
Its intensity was, of course, far lower than the electricity of the 
kite-string, but the supply of quantity from the discharging 
train was unlimited. 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-Electricity 

79. Tension. The attractions and repulsions due to the 
tension of ordinary electricity have been well observed with 
that evolved by magneto-electric induction. M. Pixii, by using 
an apparatus, clever in its construction and powerful in its 
action, 1 was able to obtain great divergence of the gold leaves 
of an electrometer. 2 

80. In motion : i. Evolution of heat. The current produced 
by magneto-electric induction can heat a wire in the manner 
of ordinary electricity. At the British Association of Science 
at Oxford, in June of the present year, I had the pleasure, in 
conjunction with Mr. Harris, Professor Daniell, Mr. Duncan, 
and others, of making an experiment, for which the great magnet 
in the museum, Mr. Harris's new electrometer and the magneto- 
electric coil 3 were put in requisition. The latter had been 
modified in the manner I have elsewhere described, 4 so as to 
produce an electric spark when its contact with the magnet was 
made or broken. The terminations of the spiral, adjusted so as 
to have their contact with each other broken when the spark was 
to pass, were connected with the wire in the electrometer, and 
it was found that each time the magnetic contact was made 

1 Annales de Chimie, 1. p. 322. 2 Ibid. li. p. 77. 

3 A combination of helices was constructed upon a hollow cylinder of 
pasteboard: there were eight lengths of copper wire, containing altogether 
220 feet; four of these helices were connected end to end, and then with 
the galvanometer; the other intervening four were also connected end to 
end, and the battery of one hundred pairs discharged through them. 

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



Identity of Electricities 23 

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

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

82. iii. Chemical decomposition. I have made many en- 
deavours to effect chemical decomposition by magneto-elec- 
tricity, but unavailingly. In July last I received an anonymous 
letter (which has since been published) x 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. Signer Botto has recently published certain results 
which he has obtained ; 2 but they are, as at present described, 
inconclusive. The apparatus he used was apparently that of 
Dr. Wollaston, which gives only fallacious indications (63, etc.). 
As magneto-electricity can produce sparks, it would be able 
to show the effects proper to this apparatus. The apparatus 
of M. Pixii already referred to (79), has however, in the hands 
of himself 3 and M. Hachette, 4 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 tongue, and the flash before the eyes, which I at first 
obtained only in a feeble degree, have been since exalted by 
more powerful apparatus, so as to become even disagreeable. 

84. v. Spark. The feeble spark which I first obtained with 
these currents has been varied and strengthened by Signori 
Nobili and Antinori, and others, so as to leave no doubt as to 
its identity with the common electric spark. 

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

2 Ibid. 1832, vol. i. p. 441. * Annales de Chimie, li. p. 77. 
4 Ibid. li. p. 72. 



24 Faraday's Researches 



IV. Thermo-Electricity 

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

86. Only those effects are weak or deficient which depend 
upon a certain high degree of intensity; and if common 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, 2 
Ingenhousz, 3 Cavendish, 4 Sir H. Davy, 5 and Dr. Davy, 6 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 my 
refraining from entering at length into the philosophical proofs 
of that identity. The doubts raised by Sir H. Davy have 
been removed by his brother Dr. Davy; the results of the latter 
being the reverse of those of the former. At present the sum 
of evidence is as follows : 

88. Tension. No sensible attractions or repulsions due to 
tension have been observed. 

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

1 Bibliotheque Universelle, xxxvii. 15. 

2 Philosophical Transactions, 1773, p. 461. 3 Ibid. 1775, p. i. 

4 Ibid. 1776, p. 196. * Ibid. 1829, p. 15. Ibid. 1832, p. 259. 



Animal Electricity 25 

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

it (23, 95). 

90. ii. Magnetism. Perfectly distinct. According to Dr. 
Davy, 1 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 are 
principally recognised. 

94. v. Spark. The electric spark has not yet been obtained, 
or at least I think not; but perhaps I had better refer to the 
evidence on this point. Humboldt, speaking of results obtained 
by M. Fahlberg, of Sweden, says, " This philosopher has seen 
an electric spark, as Walsh and Ingenhousz had done before 
him at London, by placing the gymnotus in the air, and inter- 
rupting the conducting chain by two gold leaves pasted upon 

1 Philosophical Transactions, 1832, p. 260. 



26 Faraday's Researches 

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

Again, Sir John Leslie, in his dissertation on the progress of 
mathematical and physical science, prefixed to the seventh 
edition of the Encyclopedia Britannica, 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. 2 

95. In concluding this summary of the powers of torpedinal 
electricity, I cannot refrain from pointing out the enormous 
absolute quantity of electricity which the animal must put in 
circulation at each effort. It is doubtful whether any common 
electrical machine has as yet been able to supply electricity 
sufficient in a reasonable time to cause true electro-chemical 
decomposition of water (66, 75), yet the current from the 
torpedo has done it. The same high proportion is shown by 
the magnetic effects (32, 107). These circumstances indicate 
that the torpedo has power (in the way probably that Caven- 
dish describes) to continue the evolution for a sensible time, 
so that its successive discharges rather resemble those of a 
voltaic arrangement, intermitting in its action, than those of a 
Leyden apparatus, charged and discharged many times in suc- 
cession. In reality, however, there is no philosophical difference 
between these two cases. 

96. The general conclusion which must, I think, be drawn 
from this collection of facts is, that electricity, whatever may 
be its source, is identical in its nature. The phenomena in the 
five kinds of species quoted, differ, not in their character but 
only in degree; and in that respect vary in proportion to the 
variable circumstances of quantity and intensity 3 which can at 
pleasure be made to change in almost any one of the kinds of 
electricity, as much as it does between one kind and another. 

1 Edinburgh Phil. Journal, ii. p. 249. 

2 Mr. Brayley, who referred me to these statements, and has extensive 
knowledge of recorded facts, is unacquainted with any further account 
relating to them. 

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



Measure of Electricities 



2 7 



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





Physiologi 
cal Eftects. 


Magnetic 
Deflection. 


Magnets 
made. 


1 


Heating 
Power. 


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. Magneto-electricity 


X 


X 


X 


x 


X 


X 


X 




4. Thermo-electricity . 


X 


X 


-r 


+ 


+ 


+ 






5. Animal electricity . 


X 


x 


X 


+ 


+ 


X 







2. Relation by Measure of Common and Voltaic Electricity 2 

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- 

1 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. 



2 8 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 necessary 
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. 

1 02. Hence it would appear that if the same absolute quantity 
of electricity pass through the galvanometer, whatever may be its 
intensity, the deflecting force upon the magnetic needle is the same. 

103. The battery of fifteen jars was then charged by sixty 
revolutions of the machine, and discharged, as before, through 
the galvanometer. The deflection of the needle was now as 
nearly as possible to the eleventh division, but the graduation 
was not accurate enough for me to assert that the arc was 
exactly double the former arc ; to the eye it appeared to be so. 
The probability is, that the deflecting force of an electric current 
is directly proportional to the absolute quantity of electricity passed, 
at whatever intensity that electricity may be. 1 

104. Dr. Ritchie has shown that in a case where the intensity 
of the electricity remained the same, the deflection of the 
magnetic needle was directly as the quantity of electricity passed 
through the galvanometer. 2 Mr. Harris has shown that the 
heating power of common electricity on metallic wires is the 
same for the same quantity of electricity whatever its intensity 
might have previously been. 3 

105. The next point was to obtain a voltaic arrangement 
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 

1 The great and general value of the galvanometer, as an actual measure 
of the electricity passing through it, either continuously or interruptedly, 
must be evident from a consideration of these two conclusions. As con- 
structed by Professor Ritchie with glass threads (see Philosophical Transac- 
tions, 1830, p. 218, and Quarterly Journal of Science, New Series, vol. i. p. 29), 
it apparently seems to leave nothing unsupplied in its own department. 

1 Quarterlv 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. 

1 06. On plunging the zinc and platina wires five-eighths of 
an inch deep into the acid, and retaining them there for eight 
beats of the watch (after which they were quickly withdrawn), 
the needle was deflected, and continued to advance in the same 
direction some time after the voltaic apparatus had been removed 
from the acid. It attained the five-and-a-half division, and 
then returned swinging an equal distance on the other side. 
This experiment was repeated many times, and always with the 
same result. 

107. Hence, as an approximation, and judging. from magnetic 
force only at present (112), it would appear that two wires, 
one of platina and one of zinc, each one-eighteenth of an inch 
in diameter, placed five-sixteenths of an inch apart and im- 
mersed to the depth of five-eighths of an inch in acid, consisting 
of one drop oil of vitriol and four ounces distilled water, at a 
temperature about 60, and connected at the other extremities 
by a copper wire eighteen feet long and one-eighteenth of an 
inch thick (being the wire of the galvanometer coils), yield as 
much electricity in eight beats of my watch, or in T f ^ths of a 
minute, as the electrical battery charged by thirty turns of the 
large machine, in excellent order (99, 100). Notwithstanding 
this apparently enormous disproportion, the results are perfectly 
in harmony with those effects which are known to be produced 
by variations in the intensity and quantity of the electric fluid. 

108. In order to procure a reference to chemical action, the 
wires were now retained immersed in the acid to the depth of 
five-eighths of an inch, and the needle, when stationary, observed : 
it stood, as nearly as the unassisted eye could decide, at 5^ 
division. Hence a permanent deflection to that extent might 
be considered as indicating a constant voltaic current, which 
in eight beats of my watch (105) could supply as much electricity 
as the electrical battery charged by thirty turns of the machine. 

109. The following arrangements and results are selected 
from many that were made and obtained relative to chemical 
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 3 1 

(105), so as always to form the positive pole, and at the same 
time retain a perpendicular position, that it might rest, with 
its whole weight, upon the test paper to be employed. The 
test paper itself was supported upon a platina spatula, 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 was connected with the prime 
conductor of the machine, and the spatula with the discharging 
train, ten turns of the machine had such decomposing power as 
to produce a pale round spot of iodine of the diameter of the 
wire; twenty turns made a much darker mark, and thirty turns 
made a dark brown spot penetrating to the second thickness 
of the paper. The difference in effect produced by two or 
three turns, more or less, could be distinguished with facility. 

in. The wire and spatula were then connected with the 
voltaic apparatus (105), the galvanometer being also included 
in the arrangement; and, a stronger acid having been prepared, 
consisting of nitric acid and water, the voltaic apparatus was 
immersed so far as to give a permanent deflection of the needle 
to the 5^ division (108), the fourfold moistened paper inter- 
vening as before. 1 Then by shifting the end of the wire from 
place to place upon the test paper, the effect of the current for 
five, six, seven, or any number of the beats of the watch (105) 
was observed, and compared with that of the machine. After 
alternating and repeating the experiments of comparison many 
times, it was constantly found that this standard current of 
voltaic electricity, continued for eight beats of the watch, was 
equal, in chemical effect, to thirty turns of the machine ; 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 electricity of the standard 
voltaic battery for eight beats of the watch was equal to that of 
the machine evolved by thirty revolutions. 

113. It also follows that for this case of electro-chemical de- 
composition, and it is probable for all cases, that the chemical 
power, like the magnetic force (102), is in direct proportion to 
the absolute quantity of electricity which passes. 

114. Hence arises still further confirmation, if any were 
required, of the identity of common and voltaic electricity, 

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



32 Faraday's Researches 

and that the differences of intensity and quantity are quite 
sufficient to account for what were supposed to be their dis- 
tinctive qualities. 

115. The extension which the present investigations have 
enabled me to make of the facts and views constituting the 
theory of electro-chemical decomposition, will, with some other 
points of electrical doctrine, be almost immediately submitted 
to the Royal Society in another series of these Researches. 

December 15, 1832. 



II 1 

3. ON A NEW LAW OF ELECTRIC CONDUCTION. 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 
though they prevented me from obtaining the condition I sought 
for, they afforded abundant compensation for the momentary 
disappointment, by the new and important interest which they 
gave to an extensive part of electrical science. 

117. I was working with ice, and the solids resulting from 
the freezing of solutions, arranged either as barriers across a 
substance to be decomposed, or as the actual poles of a voltaic 
battery, that I might trace and catch certain elements in their 
transit, when I was suddenly stopped in my progress by finding 
that ice was in such circumstances a non-conductor of elec- 
tricity; and that as soon as a thin film of it was interposed, in 
the circuit of a very powerful voltaic battery, the transmission 
of electricity was prevented, and all decomposition ceased. 

118. At first the experiments were made with common ice, 
during the cold freezing weather of the latter end of January 
1833; but the results were fallacious, from the imperfection 

1 Fourth Series, original edition, vol. i. p. no. 



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 was the consequence 



34 Faraday's Researches 

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

124. Upon warming the tin case and removing the piece of 
ice, it was found that a cork having slipped, one of the edges 
of the platina had been all but in contact with the inner surface 
of the tin vessel; yet, notwithstanding the extreme thinness of 
the interfering ice in this place, no sensible portion of electricity 
had passed. 

125. These experiments were repeated many times with the 
same results. At last a battery of fifteen troughs, or one 
hundred and fifty pairs of four-inch plates, powerfully charged, 
was used; yet even here no sensible quantity of electricity 
passed the thin barrier of ice. 

126. It seemed at first as if occasional departures from these 
effects occurred ; but they could always be traced to some inter- 
fering circumstances. The water should in every instance be 
well frozen; for though it is not necessary that the ice should 
reach from pole to pole, since a barrier of it about one pole 
would be quite sufficient to prevent conduction, yet, if part 
remain fluid, the mere necessary exposure of the apparatus to the 
air, or the approximation of the hands, is sufficient to produce, 
at the upper surface of the water and ice, a film of fluid, ex- 
tending from the platina to the tin; and then conduction occurs. 
Again, if the corks used to block the platina in its place are 
damp or wet within, it is necessary that the cold be sufficiently 
well applied to freeze the water in them, or else when the 
surfaces of their contact with the tin become slightly warm 
by handling, that part will conduct, and the interior being ready 
to conduct also, the current will pass. The water should be 
pure, not only that unembarrassed results may be obtained, but 
also that, as the freezing proceeds, a minute portion of concen- 
trated saline solution may not be formed, which remaining fluid, 
and being interposed in the ice, or passing into cracks resulting 
from contraction, may exhibit conducting powers independent 
of the ice itself. 

127. On one occasion I was surprised to find that after thaw- 
ing much of the ice the conducting power had not been restored ; 
but I found that a cork which held the wire just where it joined 
the platina, dipped so far into the ice, that with the ice itself 



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. 1 

135. Other substances, which could not be melted on glass, 
were fused by the lamp and blowpipe on platina connected 
with one pole of the battery, and then a wire, connected with 
the other, dipped into them. In this way chloride of sodium, 
sulphate of soda, protoxide of lead, mixed carbonates of potash 
and soda, etc., etc., exhibited exactly the same phenomena as 
those already described: whilst liquid, they conducted and 
were decomposed; whilst solid, though very hot, they insulated 
the battery current even when four troughs were used. 

136. Occasionally the substances were contained in small 
bent tubes of green glass, and when fused, the platina poles 

intr6duced, one on each side. 
In such cases the same gen- 
eral results as those already 
described were procured ; but 
a further advantage was ob- 
tained, namely, that whilst 
the substance was conduct- 
Fig- 7- ing and suffering decom- 
position, the final arrangement of the elements could be 
observed. Thus, iodides of potassium and lead gave iodine at 
the positive pole, and potassium or lead at the negative pole. 
Chlorides of lead and silver gave chlorine at the positive, and 
metals at the negative pole. Nitre and chlorate of potassa 
gave oxygen, etc., at the positive, and alkali, or even potassium, 
at the negative pole. 

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; 
sulpha- cyanide of potassium. 

Salts. Chlorate of potassa; nitrates of potassa, soda, baryta, 
strontia, lead, copper, and silver; sulphates of soda and lead, 
proto-sulphate of mercury; phosphates of potassa, soda, lead, 
copper, phosphoric glass or acid phosphate of lime; carbonates 
of potassa and soda, mingled and separate; borax, borate 
of lead, per-borate of tin; chromate of potassa, bi-chromate 
of potassa, chromate of lead; acetate of potassa. 

Sulphurets. Sulphuret of antimony, sulphuret of potassium 
made by reducing sulphate of potassa by hydrogen; ordinary 
sulphuret of potassa. 

Silicated potassa; chameleon mineral. 

139. It is highly interesting in the instances of those sub- 
stances which soften before they liquefy, to observe at what 
period the conducting power is acquired, and to what degree 
it is exalted by perfect fluidity. Thus, with the borate of lead, 
when heated by the lamp upon glass, it becomes as soft as 
treacle, but it did not conduct, and it was only when urged by 
the blowpipe and brought to a fair red heat, that it conducted. 
When rendered quite liquid, it conducted with extreme 
facility. 

140. I do not mean to deny that part of the increased con- 
ducting power in these cases of softening was probably due to 
the elevation of temperature (168, 181); but I have no doubt 
that by far the greater part was due to the influence of the 



38 Faraday's Researches 

general law already demonstrated, and which in these instances 
came gradually, instead of suddenly, into operation. 

141. The following are bodies which acquired no conducting 
power upon assuming the liquid state: 

Sulphur, phosphorus; iodide of sulphur, per-iodide of tin; 
orpiment, realgar; glacial acetic acid, mixed margaric and oleic 
acids, artificial camphor; caffeine, sugar, adipocire, stearine of 
cocoa-nut oil, spermaceti, camphor, naphthaline, resin, gum 
sandarach, shell lac. 

142. Perchloride of tin, chloride of arsenic, and the hydrated 
chloride of arsenic, being liquids, had no sensible conducting 
power indicated by the galvanometer, nor were they decom- 
posed. 

143. Some of the above substances are sufficiently remarkable 
as exceptions to the general law governing the former cases. 
These are orpiment, realgar, acetic acid, artificial camphor, 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 rUgained no conducting 
powers sufficient to affect the galvanometer, and underwent 
no apparent voltaic decomposition. It seemed to be quite as 
bad a conductor as air. Green bottle-glass, heated in the same 
manner, did not gain conducting power sensible to the 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 o Fahr. A ten- 
thousandth part of water, more or less than necessary, would, 
upon cooling the whole, cause a portion of uncongealable liquid 
to separate, and that remaining in the interstices of the solid 
mass, and moistening the planes of division, would prevent the 
correct observation of the phenomena due to entire solidifica- 
tion and subsequent liquefaction. 



Degree of Conducting Power Conferred 39 

146. With regard to the substances on which conducting power 
is thus conferred by liquidity, the degree of power so given is 
generally very great. Water is that body in which this acquired 
power is feeblest. In the various oxides, chlorides, salts, etc., 
etc., it is given in a much higher degree. I have not had time 
to measure the conducting power in these cases, but it is 
apparently some hundred times that of pure water. The 
increased conducting power known to be given to water by the 
addition of salts would seem to be in a great degree dependent 
upon the high conducting power of these bodies when in the 
liquid state, that state being given them for the time, not by 
heat but solution in the water. 

147. Whether the conducting power of these liquefied bodies 
is a consequence of their decomposition or not (149), or whether 
the two actions of conduction and decomposition are essentially 
connected or not, would introduce no difference affecting the 
probable accuracy of the preceding statement. 

148. This general assumption of conducting power by bodies 
as soon as they pass from the solid to the liquid state, offers a 
new and extraordinary character, the existence of which, as far 
as I know, has not before been suspected; and it seems 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 of mercury, which, being ex- 
perimented with like the others (136), was found to insulate 
when solid, and to acquire conducting power when fluid; yet it 
did not seem to undergo decomposition in the latter case. 



4-Q Faraday's Researches 

151. Again, there are many substances which contain elements 
such as would be expected to arrange themselves at the opposite 
poles of the pile, and therefore in that respect fitted for 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 
upon conducting power, and not the latter upon the former. 
The true relation, however, of conduction and decomposition in 
those bodies governed by the general law which it is the object 
of this paper to establish, can only be satisfactorily made out 
from a far more extensive series of observations than those I 
have yet been able to supply. 1 

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. 

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



Conduction by Ice and Solid Salts 41 



4. On Conducting Power generally l 

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 

1 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. 

1 60. The ice vessel employed (156) was half an inch in width: 
as the extent of contact of the ice with the tin and platina was 
nearly fourteen square inches, the whole was equivalent to a 
plate of ice having a surface of seven square inches of perfect 
contact at each side, and only one-fourth of an inch thick. 
It was retained in a freezing mixture during the experiment. 

161. The order of arrangement in the course of the electric 
current was as follows. The positive pole of the battery was 
connected by a wire with the platina plate in the ice ; the plate 
was in contact with the ice, the ice with the tin jacket, the 
jacket with a wire, which communicated with a piece of tin foil, 
on which rested one end of a bent platina wire (48), the other 
or decomposing end being supported on paper moistened with 
solution of iodide of potassium (52): the paper was laid flat 
on a platina spatula connected with the negative end of the 
battery. All that part of the arrangement between the ice 
vessel and the decomposing wire point, including both these, 
was insulated, so that no electricity might pass through the 
latter which had not traversed the former also. 



Conduction by Ice 43 

162. Under these circumstances, it was found that a pale 
brown spot of iodine was slowly formed under the decomposing 
platina point, thus indicating that ice could conduct a little of 
the electricity evolved by a voltaic battery charged up to the 
degree of intensity indicated by the electrometer. But it is 
quite evident that notwithstanding the enormous quantity of 
electricity which the battery could furnish, it was, under present 
circumstances, a very inferior instrument to the ordinary 
machine ; for the latter could send as much through the ice as it 
could carry, being of a far higher intensity, i.e. able to open 
the electrometer leaves half an inch or more (155, 156). 

163. The decomposing wire and solution of iodide of potas- 
sium were then removed, and replaced by a very delicate galvano- 
meter; it was so nearly astatic, that it vibrated to and fro in 
about sixty-three beats of a watch giving one hundred and fifty 
beats in a minute. The same feebleness of current as before 
was still indicated; the galvanometer needle was deflected, but 
it required to break and make contact three or four times (33) 
before the effect was decided. 

164. The galvanometer being removed, two platina plates 
were connected with the extremities of the wires, and the 
tongue placed between them, so that the whole charge of the 
battery, so far as the ice would let it pass, was free to go through 
the tongue. Whilst standing on the stone floor, there was 
shock, etc., but when insulated, I could feel no sensation. I 
think a frog would have been scarcely, if at all, affected. 

165. The ice was now removed, and experiments made with 
other solid bodies, for which purpose they were placed under the 
end of the decomposing wire instead of the solution of iodide of 
potassium (161). For instance, a piece of dry iodide of potassium 
was placed on the spatula connected with the negative pole of 
the battery, and the point of the decomposing wire placed upon 
it, whilst the positive end of the battery communicated with the 
latter. A brown spot of iodine very slowly appeared, indi- 
cating the passage of a little electricity, and agreeing in that 
respect with the results obtained by the use of the electrical 
machine (157). When the galvanometer was introduced into 
the circuit at the same time with the iodide, it was with 
difficulty that the action of the current on it could be rendered 
sensible. 

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 

C 576 



44 Faraday's Researches 

chloride of lead produced the same effect. The conducting 
power of these bodies, when fluid, is very great (131, 138). 

167. These effects, produced by using the common machine 
and the voltaic battery, agree therefore with each other, and 
with the law laid down in this paper (130); and also with the 
opinion I have supported, in the First Part of these Researches, 
of the identity of electricity derived from different sources (96). 

1 68. The effect of heat in increasing the conducting power 
of many substances, especially for electricity of high tension, is 
well known. I have lately met with an extraordinary case of 
this kind, for electricity of low tension, or that of the voltaic 
pile, and which is in direct contrast with the influence of heat 
upon metallic bodies, as observed and described by Sir Humphry 
Davy. 1 

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 gahanometer needle jumped into a fixed position, and 
the sulphuret was found conducting in the manner of a metal. 
On removing the lamp and allowing the heat to fall, the effects 
were reversed, the needle at first began to vibrate a little, then 
gradually left its transverse direction, and at last returned to a 
position very nearly that which it would take when no current 
was passing through the galvanometer. 

171. Occasionally, when the contact of the sulphuret with the 
platina poles was good, the battery freshly charged, and the 
commencing temperature not too low, the mere current of elec- 
tricity from the battery was sufficient to raise the temperature 

1 Philosophical Transactions, 1821, 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 
place in the next series of these Researches. 

177. Notwithstanding the extreme dissimilarity between 
sulphuret of silver and gases or vapours, I cannot help suspect- 
ing the action of heat upon them to be the same, bringing them 
all into the same class as conductors of electricity, although with 
those great differences in degree which are found to exist 
under common circumstances. When gases are heated, they 
increase in conducting power, both for common and voltaic 
electricity (7); and it is probable that if we could compress and 
condense them at the same time, we should still further increase 
their conducting power. Cagniard de la Tour has shown that 
a substance, for instance water, may be so expanded by heat 
whilst in the liquid state, or condensed whilst in the vaporous 
state, that the two states shall coincide at one point, and the 
transition from one to the other be so gradual that no line of 
demarcation can be pointed out ; x that, in fact, the two states 
shall become one; which one state presents us at different 
times with differences in degree as to certain properties and 
relations; and which differences are, under ordinary circum- 
stances, so great as to be equivalent to two different states. 

178. I cannot but suppose at present that at that point where 
the liquid and the gaseous state coincide, the conducting pro- 
perties are the same for both; but that they diminish as the 
expansion of the matter into a rarer form takes place by the 
removal of the necessary pressure; still, however, retaining, as 
might be expected, the capability of having what feeble con- 
ducting power remains increased by the action of heat. 

179. I venture to give the following summary of the conditions 
of electric conduction in bodies, not however without fearing 
that I may have omitted some important points. 

1 80. All bodies conduct electricity in the same manner from 
metals to lac and gases, but in very different degrees. 

181. Conducting power is in some bodies powerfully in- 
creased by heat, and in others diminished, yet without our per- 
ceiving any accompanying essential electrical difference, eithei 
in the bodies or in the changes occasioned by the electricity 
conducted. 

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

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

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



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. 1 

184. There is but one body yet discovered 2 which, insulating 
a voltaic current when solid, and conducting it when fluid, is 
not decomposed in the latter case (150). 

185. There is no strict electrical distinction of conduction 
which can, as yet, be drawn between bodies supposed to be 
elementary, and those known to be compounds. 

April 15, 1833. 



Ill 3 

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

5. On Electro-chemical Decomposition 4 

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

1 See the next part of these Experimental Researches. 
* It is just possible that this case may, by more delicate experiment, 
hereafter disappear. 

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

4 Refer to the note after paragraph 783. December 1838. 



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. 

1 88. For the purpose of rendering the bearings of the different 
parts of this series of researches more distinct, I shall divide 
it into several heads. 

Tf i. New conditions of Electro-chemical Decomposition 

189. The tension of machine electricity causes it, however 
small in quantity, to pass through any length of water, solutions, 
or other substances classing with these as conductors, as fast 
as it can be produced, and therefore, in relation to quantity, 
as fast as it could have passed through much shorter portions 
of the same conducting substance. With the voltaic battery 
the case is very different, and the passing current of electricity 
supplied by it suffers serious diminution in any substance, by 
considerable extension of its length, but especially in such 
bodies as those mentioned above. 

190. I endeavoured to apply this facility of transmitting the 
current of electricity through any length of a conductor, to an 
investigation of the transfer of the elements in a decomposing 
body, in contrary directions, towards the poles. The general 
form of apparatus used in these experiments has been already 
described (48, 52); and also a particular experiment (55), in 
which, when a piece of litmus paper and a piece of turmeric 
paper were combined and moistened in solution of sulphate of 
soda, the point of the wire from the machine (representing the 
positive pole) put upon the litmus paper, and the receiving point 
from the discharging train (28, 52), representing the negative pole, 
upon the turmeric paper, a very few turns of the machine sufficed 
to show the evolution of acid at the former, and alkali at the 
latter, exactly in the manner effected by a volta-electric current. 

191. The pieces of litmus and turmeric paper were now 
placed each upon a separate plate of glass, and connected by an 
insulated string four feet long, moistened in the same solution of 
sulphate of soda: the terminal decomposing wire points were 
placed upon the papers as before. On working the machine, 
the same evolution of acid and alkali appeared as in the former 
instance, and with equal readiness, notwithstanding that the 
places of their appearance were four feet apart from each other. 
Finally, a piece of string, seventy feet long, was used. It was 



Decomposition by a Single Pole 49 

insulated in the air by suspenders of silk, so that the electricity 
passed through its entire length: decomposition took place 
exactly as in former cases, alkali and acid appearing at the two 
extremities in their proper places. 

192. Experiments were then made both with sulphate of 
soda and iodide of potassium, to ascertain if any diminution of 
decomposing effect was produced by such great extension as 
those just described of the moist conductor or body under 
decomposition; but whether the contact of the decomposing 
point connected with the discharging train was made with 
turmeric paper touching the prime conductor, or with other 
turmeric paper connected with it through the seventy feet of 
string, the spot of alkali for an equal number of turns of the 
machine had equal intensity of colour. The same results 
occurred at the other decomposing wire, whether the salt or the 
iodide were used; and it was fully proved that this great 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 



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 
)^ 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 




Fig. 8a. 



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

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



No Metallic Poles Used 51 

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




brushes passing through the air (58); and these, with the 
accompanying general facts, are sufficient to show that the 
acid was really the result of electro-chemical decomposition 
(202). 

200. Then a long piece of turmeric paper, large at one end 
and pointed at the other, was moistened in the saline solution, 
and immediately connected with the conductor of the machine, 
so that its pointed extremity was opposite a point upon the 
discharging train. When the machine was worked, alkali was 
evolved at that point; and even when the discharging train 
was removed, and the electricity left to be diffused and carried 
off altogether by the air, still alkali was evolved where the 
electricity left the turmeric paper. 

201. Arrangements were then made in which no metallic 
communication with the decomposing matter was allowed, but 
both poles (if they might now be called by that name) formed 
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 
by a wire with the conductor of the machine, and the other, , 
with the discharging train. The interval in each case between 
the points was about half an inch: the positive point p was 



52 Faraday's Researches 

opposite the litmus paper; the negative point n opposite the 
turmeric. The machine was then worked for a time, upon 
which evidence of decomposition quickly appeared, for the 
point of the litmus b became reddened from acid evolved there, 




Fig. 10. 

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

2os. Upon turning the paper conductor round, so that the 
litmus point should now give off the positive electricity, and 
the turmeric point receive it, and working the machine for a 
short time, both the red spots disappeared, and as on 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. 



Polar Decompositions in Air 53 

205. Finally, a series of four small compound conductors, 
consisting of litmus and turmeric paper (fig. n) moistened in 
solution of sulphate of soda, were supported on glass rods, in 
a line at a little distance from each other, between the points 
p and n of the machine and discharging train, so that the elec- 
tricity might pass in succession through them, entering in at 
the litmus points b, b, and passing out at the turmeric points a, 
a. On working the machine carefully, so as to avoid sparks and 




Fig. ii. 

brushes (58), I soon obtained evidence of decomposition in each 
of the moist conductors, for all the litmus points exhibited free 
acid, and the turmeric points equally showed free alkali. 

206. On using solutions of iodide of potassium, acetate of 
lead, etc., similar effects were obtained; but as they were all 
consistent with the results above described, I refrain from 
describing the appearances minutely. 

207. These cases of electro-chemical decomposition are in 
their nature exactly of the same kind as those affected under 
ordinary circumstances by the voltaic battery, notwithstanding 
the great differences as to the presence or absence, or at least 
as to the nature of the parts usually called poles; and also of 
the final situation of the elements eliminated at the electrified 
boundary surfaces (203). They indicate at once an internal 
action of the parts suffering decomposition, and appear to show 
that the power which is effectual in separating the elements is 
exerted there, and not at the poles. But I shall defer the 
consideration of this point for a short time (229, 254), that I 
may previously consider another supposed condition of electro- 
chemical decomposition. 1 

1 I find (since making and describing these results) from a note to Sir 
Humphry Davy's paper in the Philosophical Transactions, 1807, p. 31, that 
that philosopher, in repeating Wollaston's experiment of the decomposition 
of water by common electricity (63, 66) used an arrangement somewhat 
like some of those I have described. He immersed a guarded platina point 
connected with the machine in distilled water, and dissipated the electricity 
from the water into the air by moistened filaments of cotton. In this way 
he states that he obtained oxygen and hydrogen separately from each other. 
This experiment, had I known of it, ought to have been quoted in an 
earlier part of these Researches (78) ; but it does not remove any of the 
objections I have made to the use of Wollaston's apparatus as a test of 
true chemical action (67). 



54 Faraday's Researches 



^f ii. Influence of Water in Electro-chemical Decomposition 

208. It is the opinion of several philosophers, that the presence 
of water is essential in electro-chemical decomposition, and 
also for the evolution of electricity in the voltaic battery itself. 
As the decomposing cell is merely one of the cells of the battery, 
into which particular substances are introduced for the purpose 
of experiment, it is probable that what is an essential condition 
in the one case is more or less so in the other. The opinion, 
therefore, that water is necessary to decomposition, may have 
been founded on the statement made by Sir Humphry Davy, 
that " there are no fluids known, except such as contain water, 
which are capable of being made the medium of connection 
between the metals or metal of the voltaic apparatus: " l and 
again, " when any substance rendered fluid by heat, consisting 
of water, oxygen, and inflammable or metallic matter, is exposed 
to those wires, similar phenomena (of decomposition) occur." 2 

209. This opinion has, I think, been shown by other philo- 
sophers not to be accurate, though I do not know where to 
refer for a contradiction of it. Sir Humphry Davy himself 
said in i8oi, 3 that dry nitre, caustic potash and soda are con- 
ductors of galvanism when rendered fluid by a high degree of 
heat; but he must have considered them, or the nitre at least, 
as not suffering decomposition, for the statements above were 
made by him eleven years subsequently. In 1826 he also 
pointed out, that bodies not containing water, as fused litharge 
and chlorate of polassa, were sufficient to form, with platina 
and zinc, powerful electromotive circles; 4 but he is here 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 equally influential with water 
in this respect; that amongst binary compounds, oxides, 
chlorides, iodides, and even sulphurets (138) were effective; 
and that amongst more complicated compounds, cyanides and 
salts, of equal efficacy, occurred in great numbers (138). 

1 Elements of Chemical Philosophy, p. 169, etc. 2 Ibid. pp. 144, 145. 

3 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 suffering decomposition. 
The reasons why it obtained for a time an exclusive character 
which it so little deserved are evident, and consist, in the 
general necessity of a fluid condition (130); in its being the 
only one of this class of bodies existing in the fluid state at 
common temperatures ; its abundant supply as the great natural 
solvent; and its constant use in that character in philosophical 
investigations, because of its having a smaller interfering, 
injurious or complicating action upon the bodies, either dis- 
solved or evolved, than any other substance. 

212. The analogy of the decomposing or experimental cell 
to the other cells of the voltaic battery, renders it nearly certain 
that any of those substances which are decomposable when 
fluid, 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 I 
have constructed various voltaic arrangements, and found the 
above conclusion to hold good. When any of the following 
substances in a fused state were interposed between copper 
and platina, voltaic action more or less powerful was produced. 
Nitre; chlorate of potassa; carbonate of potassa; sulphate of 
soda; chloride of lead, of sodium, of bismuth, of calcium; 
iodide of lead; oxide of bismuth; oxide of lead: the electric 
current was in the same direction as if acids had acted upon 
the metals. When any of the same substances, or phosphate 
of soda, were made to act on platina and iron, still more power- 
ful voltaic combinations of the same kind were produced. 
When either nitrate of silver or chloride of silver was the fluid 
substance interposed, there was voltaic action, but the electric 
current was in the reverse direction. 

^| iii. Theory of Electro-chemical Decomposition 

213. The extreme beauty and value of electro-chemical 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 

1 Philosophical Transactions, 1826, p. 406. 



56 

production, of the electrical phenomena, but it has furnished 
us with the most beautiful demonstrations of the nature of 
many compound bodies; has in the hands of Becquerel been 
employed in compounding substances; has given us several 
new combinations, and sustains us with the hope that when 
thoroughly understood it will produce many more. 

214. What may be considered as the general facts of electro- 
chemical decomposition are agreed to by nearly all who have 
written on the subject. They consist in the separation of the 
decomposable substance acted upon into its proximate or 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 pile, where they are either finally set free or enter into 
union with the substance of the poles; and in the constant 
determination of the evolved elements or principles to particular 
poles according to certain well ascertained laws. 

215. But the views of men of science vary much as to the 
nature of the action by which these effects are produced; and 
as it is certain that we shall be better able to apply the power 
when we really understand the manner in which it operates, 
this difference of opinion is a strong inducement to further 
inquiry. I have been led to hope that the following investiga- 
tions might be considered, not as an increase of that which is 
doubtful, but a real addition to this branch of knowledge. 

216. It will be needful that I briefly state the views of electro- 
chemical decomposition already put forth, that their present 
contradictory and unsatisfactory state may be seen before I 
give that which seems to me more accurately to agree with 
facts; and I have ventured to discuss them freely, trusting that 
I should give no offence to their high-minded authors; for I 
felt convinced that if I were right, they would be pleased that 
their views should serve as stepping-stones for the advance of 
science; and that if I were wrong, they would excuse the zeal 
which misled me, since it was exerted for the service of that 
great cause whose prosperity and progress they have desired. 

217. Grotthuss, in the year 1805, wrote expressly on the 
decomposition of liquids by voltaic electricity. 1 He considers 
the pile as an electric magnet, i.e. as an attractive and repulsive 
agent; the poles having attractive and repelling powers. The 
pole from whence resinous electricity issues attracts hydrogen 
and repels oxygen, whilst that from which vitreous electricity 

1 Annales de Chimie, 1806, torn. Iviii. p. 64. 



Electro-Chemical Decomposition 57 

proceeds attracts oxygen and repels hydrogen; so that each 
of the elements of a particle of water, for instance, is subject 
to an attractive and a repulsive force, acting in contrary 
directions, the centres of action of which are reciprocally 
opposed. The action of each force in relation to a molecule of 
water situated in the course of the electric current is in the 
inverse ratio of the square of the distance at which it is exerted, 
thus giving (it is stated) for such a molecule a constant force* 
He explains the appearance of the elements at a distance from 
each other by referring to a succession of decompositions and 
recompositions occurring amongst the intervening particles, 2 
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. 3 

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 
Transactions for 1807, also at p. 30. Again at p. 160 of the 
Elements of Chemical Philosophy, he speaks of the great attract- 
ing powers of the surfaces of the poles. He mentions the pro- 
bability of a succession of decompositions and recompositions 
throughout the fluid, agreeing in that respect with Grotthuss; 4 
and supposes that the attractive and repellent agencies may be 
communicated from the metallic surfaces throughout the whole 
of the menstruum, 5 being communicated from one particle to 
another particle of the same kind, 6 and diminishing in strength 
from the place of the poles to the middle point, which is neces- 
sarily neutral. 7 In reference to this diminution of power at 

1 Annales de Chimie, pp. 66, 67, also torn. Ixiii. p. 20. 

* Ibid, torn Iviii. p. 68, torn. Ixiii. p. 20. 
s Ibid, torn Ixiii. p. 34. 

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

* Ibid. p. 39. * Ibid. p. 29. 7 Ibid. p. 42. 



58 Faraday's Researches 

increased distances from the poles, he states that in a circuit 
of ten inches of water, solution of sulphate of potassa placed 
four inches from the positive pole did not decompose; whereas 
when only two inches from that pole, it did render up its 
elements. 1 

220. When in 1826 Sir Humphry Davy wrote again on this 
subject, he stated that he found nothing to alter in the funda- 
mental theory laid down in the original communication, 2 and 
uses the terms attraction and repulsion apparently in the same 
sense as before. 3 

221. Messrs. Riffault and Chompre experimented on this 
subject in 1807. They came to the conclusion that the voltaic 
current caused decompositions throughout its whole course in 
the humid conductor, not merely as preliminary to the recom- 
positions spoken of by Grotthuss and Davy, but producing final 
separation of the elements in the course of the current, and 
elsewhere than at the poles. They considered the negative 
current as collecting and carrying the acids, etc., to the positive 
pole, and the positive current as doing the same duty with the 
bases, and collecting them at the negative pole. They likewise 
consider the currents as more powerful the nearer they are to 
their respective poles, and state that the positive current is 
superior in power to the negative current. 4 

222. M. Biot is very cautious in expressing an opinion as to 
the cause of the separation of the elements of a compound 
body. 5 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. 6 When a particle of 
salt is decomposed at the negative pole, the acid particle is 
considered as acquiring a negative electrical state from the pole, 
stronger than that of the surrounding undecomposed particles, 
and is therefore repelled from amongst them, and from out of 
that portion of the liquid towards the positive pole, towards 
which also it is drawn by the attraction of the pole itself and 
the particles of positive undecomposed fluid around it. 7 

1 Philosophical Transactions, 1807, p. 42. 

* Ibid. 1826, p. 383. * Ibid. pp. 389, 407, 415. 

* Annales de Chitnie, 1807, torn. Ixiii. p. 83, etc. 

* Precis Elcmentaire de Physique, 3me edition, 1824, torn. i. p. 641. 

* Ibid. p. 637. ' Ibid. pp. 641, 642. 



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, 1 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. 2 

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. 3 

225. M. A. de la Rive investigated this subject particularly, 
and published a paper on it in 1825. 4 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. 5 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, 6 it is separated from them, entering the metal 
and leaving the hydrogen or bases upon its surface. In the 
same manner the electricity from the negative pole sets the 
hydrogen and bases which it finds there, free, but combines 
with the oxygen and acids, carries them across to the positive 
pole, and there deposits them. 7 In this respect M. de la Rive's 
hypothesis accords in part with that of MM. Riffault and 
Chompre (221). 

226. M. de la Rive considers the portions of matter which 
are decomposed to be those contiguous to both poles. 8 He 

1 Freds Elementaire de Physique, 3me 6dition, 1824, torn. i. p. 636. 

2 Ibid. p. 642. * Ibid. pp. 638, 642. 

4 Annales de Chimie, torn, xxviii. p. 190. . * Ibid. pp. 200, 202. 

* Ibid. p. 202. ' Ibid. p. 201. * Ibid. pp. 197, 198. 



60 Faraday's Researches 

does not admit with others the successive decompositions and 
recompositions in the whole course of the electricity through 
the humid conductor/ but thinks the middle parts are in them- 
selves unaltered, or at least serve only to conduct the two 
contrary currents of electricity and matter which set off from 
the opposite poles. 2 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 . 3 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 batter)', 
or ordinary electrical machine arrangements (48), upon the 
elements in contact with or near to them, appeared very evident 
from the experiments made in air (198, 201, etc.), when the 
substances evolved did not collect about any poles, but, in 
obedience to the direction of the current, were evolved, and I 
would say ejected, at the extremities of the decomposing 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 

1 Annales de Chimie, torn, xxviii. pp. 192, 199. 
* Ibid. p. 200. 3 Ibid. torn. li. p. 73. 



Electro-Chemical Decomposition 6r 

other points, I endeavoured to devise an arrangement by which 
I could decompose a body against a surface of water, as well 
as against air or metal, and succeeded in doing so unexcep- 
tionably in the following manner. As the experiment for very 
natural reasons requires many precautions to be successful, 
and will be referred to hereafter in illustration of the views I 
shall venture to give, I must describe it minutely. 

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, of forty pairs of plates four inches 
square, whilst the former pole b was connected with the positive 
end. There was action and gas evolved at both poles; but 
from the intervention of the pure water, the decomposition 
was very feeble compared to what the battery would have 
effected in a uniform solution. After a little while (less than a 
minute), magnesia also appeared at the negative side: it did 
not make its appearance at the negative metallic pole, but in the 
water, at the plane where the solution and the water met; and 
on looking at it horizontally, it could be there perceived lying 
in the water upon the solution, not rising more than the fourth 
of an inch above the latter, whilst the water between it and 
the negative pole was perfectly clear. On continuing the action, 
the bubbles of hydrogen rising upwards from the negative pole 
impressed a circulatory movement on the stratum of water, 
upwards in the middle, and downwards at the side, which 
gradually gave an ascending form to the cloud of magnesia 
in the part just under the pole, having an appearance as if it 
were there attracted to it; but this was altogether an effect 
of the currents, and did not occur until long after the phenomena 
looked for were satisfactorily ascertained. 

232. After a little while the voltaic communication was 
broken, and the platina poles removed with as little agitation 
as possible from the water and solution, for the purpose of 
examining the liquid adhering to them. The pole e, when touched 
by turmeric paper, gave no traces of alkali, nor could anything 
but pure water be found upon it. The pole b, though drawn 
through a much greater depth and quantity of fluid, was found 
so acid as to give abundant evidence to litmus paper, the 
tongue, and other tests. Hence there had been no interference 
of alkaline salts in any way, undergoing first decomposition, 
and then causing the separation of the magnesia at a distance 
from the pole by mere chemical agencies. This experiment 
was repeated again and again, and always successfully. 

233. As, therefore, the substances evolved in cases of electro- 
chemical decomposition may be made to appear against air 
(201, 205), which, according to common language, is not a 



Electro-Chemical Decomposition 63 

conductor, nor is decomposed, or against water (231), which 
is a conductor, and can be decomposed, as well as against 
the metal poles, which are excellent conductors, but undecom- 
posable, there appears but little reason to consider the pheno- 
mena generally, as due to the attraction or attractive powers 
of the latter, when used in the ordinary way, since similar 
attractions can hardly be imagined in the former instances. 

234. It may be said that the surfaces of air or of water in 
these cases become the poles, and exert attractive powers; 
but what proof is there of that, except the fact that the matters 
evolved collect there, which is the point to be explained, and 
cannot be justly quoted as its own explanation? Or it may be 
said, that any section of the humid conductor, as that in the 
present case, where the solution and the water meet, may be 
considered as representing the pole. But such does not appear 
to me to be the view of those who have written on the subject, 
certainly not of some of them, and is inconsistent with the 
supposed laws which they have assumed, as governing the 
diminution of power at increased distances from the poles. 

235. Grotthuss, for instance, describes the poles as centres 
of attractive and repulsive forces (217), these forces varying 
inversely as the squares of the distances, and says, therefore, 
that a particle placed anywhere between the poles will be acted 
upon by a constant force. But the compound force, resulting 
from such a combination as he supposes, would be anything 
but a constant force; it would evidently be a force greatest at 
the poles, and diminishing to the middle distance. Grotthuss 
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 diminution 
of power with increase of distance from the poles 1 (219), supposes 
that when both poles are acting on substances to decompose 
them, still the power of decomposition diminishes to the middle 
distance. In this statement of fact he is opposed to Grotthuss, 
and quotes an experiment in which sulphate of potassa, placed 
at different distances from the poles in a humid conductor of 
constant length, decomposed when near the pole, but not when 
at a distance. Such a consequence would necessarily result 

1 Philosophical Transactions, 1807, p. 42. 



64 Faraday's Researches 

theoretically from considering the poles as centres of attraction 
and repulsion; but I have not found the statement borne out 
by other experiments (241); and in the one quoted by him 
the effect was doubtless due to some of the many interfering 
causes of variation which attend such investigations. 

237. A glass vessel had a platina plate fixed perpendicularly 
across it, so as to divide it into two cells: a head of mica was 
fixed over it, so as to collect the gas it might evolve during 
experiments; then each cell, and the space beneath the mica, 
was filled with dilute sulphuric acid. Two poles were provided, 
consisting each of a platina wire terminated by a plate of the 
same metal; each was fixed into a tube passing through its 
upper end by an air-tight joint, that it might be moveable, and 
yet that the gas evolved at it might be collected. The tubes 
were filled with the acid, and one immersed in each cell. Each 
platina pole was equal in surface to one side of the dividing 
plate in the middle glass vessel, and the whole might be con- 
sidered as an arrangement between the poles of the battery of 
a humid decomposable conductor divided in the middle by the 
interposed platina diaphragm. It was easy, when required, to 
draw one of the poles further up the tube, and then the platina 
diaphragm was no longer in the middle of the humid conductor. 
But whether it were thus arranged at the middle, or towards 
one side, it always evolved a quantity of oxygen and hydrogen 
equal to that evolved by both the extreme plates. 1 

238. If the wires of a galvanometer be terminated by plates, 
and these be immersed in dilute acid, contained in a regularly 
formed rectangular glass trough, connected at each end with a 
voltaic battery by poles equal to the section of the fluid, a part 
of the electricity will pass through the instrument and cause a 
certain deflection. And if the plates are always retained at the 
same distance from each other and from the sides of the trough, 
are always parallel to each other, and uniformly placed relative 
to the fluid, then, whether they are immersed near the middle 
of the decomposing solution, or at one end, still the instrument 
will indicate the same deflection, and consequently the same 
electric influence. 

239. It is very evident, that when the width of the decom- 
posing conductor varies, as is always the case when mere wires 
or plates, as poles, are dipped into or are surrounded by solution, 

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



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 for a constant 
quantity of electricity, whatever the decomposing conductor may be, 
whether water, saline solutions, acids, fused bodies, etc., the amount 
of electro-chemical action is also a constant quantity, i.e. would 
always be equivalent to a standard chemical effect founded upon 
ordinary chemical affinity. I have this investigation in hand, 
with several others, and shall be prepared to give it in the next 
part but one of these Researches. 

242. Many other arguments might be adduced against the 
hypotheses of the attraction of the poles being the cause of 
electro-chemical decomposition; but I would rather pass on to 
the view I have thought more consistent with facts, with this 
single remark; that if decomposition by the voltaic battery 
depended upon the attraction of the poles, or the parts about 
them, being stronger than the mutual attraction of the particles 



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 Chompre 
(221), the occurrence of decomposition alone in the course of 
the current is so contrary to the well-known effects obtained in 
the forms of experiment adopted up to this time, that it must 
be proved before the hypothesis depending on it need be con- 
sidered. 

245. The consideration of the various theories of 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 (m) 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 general uniformity and character of the electric 
current. Others assume two electric fluids; and here singular 
differences have arisen. 

248. MM. Riffault and Chompre, for instance, consider the 
positive and negative currents each as causing decomposition, 
and state that the positive current is more -powerful than the 
negative current, 1 the nitrate of soda being, under similar 
circumstances, decomposed by the former, but not by the 
latter. 

249. M. Hachette states 2 that " it is not necessary, as has 
been believed, that the action of the two electricities, positive 
and negative, should be simultaneous for the decomposition of 
water." The passage implying, if I have caught the meaning 
aright, that one electricity can be obtained, and can be applied 
in effecting decompositions, independent of the other. 

250. The view of M. de la Rive to a certain extent agrees with 
that of M. Hachette, for he considers that the two electricities 
decompose separate portions of water (226). 3 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, torn, Ixiii. p. 84. * Ibid. 1832, toin. li. p. 73. 
3 Ibid. 1825, torn, 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. 1 

2 53- Judging from facts only, there is not as yet the slightest 
reason for considering the influence which is present in what 
we call the electric current, whether in metals or fused bodies 
or humid conductors, or even in air, flame, and rarefied elastic 
media, as a compound or complicated influence. It has never 
been resolved into simpler or elementary influences, and may 
perhaps best be conceived of as an axis of power having contrary 
forces, exactly equal in amount, in contrary directions. 

254. Passing to the consideration of electro-chemical decom- 
position, it appears to me that the effect is produced by an 
internal corpuscular action, exerted according to the direction of 
the electric current, and that it is due to a force either super- 
added to, or giving direction to the ordinary chemical affinity of 
the bodies present. The body under decomposition may be 
considered as a mass of acting particles, all those which are 

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



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 mutual 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 b b, ready to pass in the 
contrary direction: for it is by virtue of their increased affinity 
for those particles, combined with their diminished affinity for 
such as are behind them in their course, that they are urged 
forward: and when any one particle a, fig. 14, arrives at the 
pole, it is excluded or set free, because the particle b of the 
opposite kind, with which it was the moment before in combi- 




nation, has, under the superinducing influence of the current, 
a greater attraction for the particle a, which is before it in its 
course, than for the particle a, towards which its affinity has 
been weakened. 

256. As far as regards any single compound particle, the case 
may be considered as analogous to one of ordinary decomposi- 
tion, for in fig. 14, a may be conceived to be expelled from 
the compound a b by the superior attraction of a for b, that 
superior attraction belonging to it in consequence of the relative 
position of a b and a to the direction of the axis of electric 
power (253) superinduced by the current. But as all the 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 



70 Faraday's Researches 

forms; and even in the simplest case of two wires or points 
immersed as poles in a drop or larger single portion of fluid, 
these lines must diverge rapidly from the poles; and the 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 1 

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 cease, and there also the chemical 
action of quantity is no longer evident. It seems not unlikely, 
that the inability to suffer decomposition in these cases may be 
dependent upon the absence of that mutual attractive relation 
of the particles which is the cause of aggregation. 

260. I hope I have now distinctly stated, although in general 
terms, the view I entertain of the cause of electro-chemical 
decomposition, as far as that cause can at present be traced and 
understood. I conceive the effects to arise from forces which 
are internal, relative to the matter under decomposition and 
not external, as they might be considered, if directly dependent 
upon the poles. I suppose that the effects are due to a 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 b, 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, b 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 asbestus were lifted out, and the drops hanging at the 
ends allowed to fall each into its respective vessel. The acids 
in a and b were then first compared, for which purpose two 
evaporating dishes were balanced, and the acid from a put into 
one, and that from b into the other; but as one was a little 
heavier than the other, a small drop was transferred from the 
heavier to the lighter, and the two rendered equal in weight. 
Being neutralised by the addition of the soda solution (261),, 
that from a, or the negative vessel, required 15 parts of the 
soda solution, and that from b, or the positive vessel, required 
16.3 parts. That the sum of these is not 34 parts is principally 
due to the acid removed with the asbestus; but taking the 
mean of 15.65 parts, it would appear that a twenty-fourth part 
of the acid originally in the vessel a had passed, through the 
influence of the electric current, from a into b. 

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,. 
the;efore, 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 so 
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. 1 

267. In some of the experiments the acid from the vessels a 
and b was neutralised by ammonia, then evaporated to dryness, 
heated to redness, and the residue examined for sulphates. . In 
these cases more sulphate was always obtained from a than 
from b; showing that it had been impossible to exclude 
saline bases (derived from the asbestus, the glass, or perhaps 
impurities originally in the acid), and that they had helped in 
transferring the acid into b. But the quantity was small, and 
the acid was principally transferred by relation to the water 
present. 

268. I endeavoured to arrange certain experiments by which 
saline solutions should be decomposed against surfaces of water; 
and at first worked with the electric machine upon a piece of 
bibulous paper, or asbestus moistened in the solution, and in 
contact at its two extremities with pointed pieces of paper 
moistened in pure water, which served to carry the electric 
current to and from the solution in the middle piece. But I 
found numerous interfering difficulties. Thus, the water and 
solutions in the pieces of paper could not be prevented from 
mingling at the point where they touched. Again, sufficient 
acid could be derived from the paper connected with the dis- 
charging train, or it may be even from the air itself, under the 
influence of electric action, to neutralise the alkali developed at 
the positive extremity of the decomposing solution, and so not 
merely prevent its appearance, but actually transfer it on to the 
metal termination : and, in fact, when the paper points were not 
allowed to touch there, and the machine was worked until 
alkali was evolved at the delivering or positive end of the 
turmeric paper, containing the sulphate of soda solution, it 
was merely necessary to place the opposite re'ceiving point of 
the paper connected with the discharging train, which had been 
moistened by distilled water, upon the brown turmeric point 
and press them together, when the alkaline effect immediately 
disappeared. 

269. The experiment with sulphate of magnesia already 
described (231) is a case in point, however, and shows most 
clearly that the sulphuric acid and magnesia contributed to each 
other's transfer and final evolution, exactly as the same acid and 
soda affected each other in the results just given (263, etc.); 

.and that so soon as the magnesia advanced beyond the reach of 
1 See the note to 410. December 1838. 



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 

D 576 



j6 Faraday's Researches 

relation to those particles which are leaving the substance under 
operation. 

274. The theory accounts for the transfer of elements in a 
manner which seems to me at present to leave nothing unex- 
plained; and it was, indeed, the phenomena of transfer in the 
numerous cases of decomposition of bodies rendered fluid by 
heat (116, 138), which, in conjunction with the experiments in 
air, led to its construction. Such cases as the former where 
binary compounds of easy decomposability are acted upon, are 
perhaps the best to illustrate the theory. 

275. Chloride of lead, for instance, fused in a bent tube (136), 
and decomposed by platina wires, evolves lead, passing to what 
is usually called the negative pole, and chlorine, which being 
evolved at the positive pole, is in part set free, and in part 
combines with the platina. The chloride of platina formed, 
being soluble in the chloride of lead, is subject to decomposition, 
and the platina itself is gradually transferred across the decom- 
posing matter, and found with the lead at the negative pole. 

276. Iodide of lead evolves abundance of lead at the negative 
pole, and abundance of iodine at the positive pole. 

277. Chloride of silver furnishes a beautiful instance, especially 
when decomposed by silver wire poles. Upon fusing a portion 
of it on a piece of glass, and bringing the poles into contact 
with it, there is abundance of silver evolved at the negative 
pole, and an equal abundance absorbed at the positive pole, 
for no chlorine is set free: and by careful management, the 
negative wire may be withdrawn from the fused globule as the 
silver is reduced there, the latter serving as the continuation of 
the pole, until a wire or thread of revived silver, five or six 
inches in length, is produced; at the same time the silver at 
the positive pole is as rapidly dissolved by the chlorine, which 
seizes upon it, so that the wire has to be continually advanced 
as it is melted away. The whole experiment includes the action 
of only two elements, silver and chlorine, and illustrates in a 
beautiful manner their progress in opposite directions, parallel 
to the electric current, which is for the time giving a uniform 
general direction to their mutual affinities (260). 

278. According to my theory, an element or a substance not 
decomposable under the circumstances of the experiment (as, 
for instance, a dilute acid or alkali) should not be transferred, 
or pass from pole to pole, unless it be in chemical relation to 
som other element or substance tending to pass in the opposite 
direction, for the effect is considered as essentially due to the 



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. 1 Yet such is not the case, as 
has been shown by the experiments on free and combined acid 
(262, 264). 

279. Neither does M. de la Rive's theory, as I understand it, 
require that the particles should be in combination: it does not 
even admit, where there are two sets of particles capable of 
combining with and passing by each other, that they do combine, 
but supposes that they travel as separate compounds of matter 
and electricity. Yet in fact the free substance cannot travel, 
the combined one can. 

280. It is very difficult to find cases amongst solutions or 
fluids which shall illustrate this point, because of the difficulty 
of finding two fluids which shall conduct, shall not mingle and 
in which an element evolved from one shall not find a com- 
binable element in the other. Solutions of acids or alkalies will 
not answer, because they exist by virtue of an attraction; and 
increasing the solubility of a body in one direction, and 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. 2 Nevertheless the case of sulphate of magnesia is in 
point (230, 231), and shows that one element or principle only 
has no power of transference or of passing towards either pole. 

281. Many of the metals, however, in their solid state, offer 
very fair instances of the kind required. Thus, if a plate of 
platina be used as the positive pole in a solution of sulphuric 
acid, oxygen will pass towards it, and so will acid; but these 
are not substances having such chemical relation to the platina 
as, even under the favourable condition superinduced by the 
current (254, 260), to combine with it; the platina therefore 
remains where it was first placed, and has no tendency to pass 

1 Even Sir Humphry Davy considered the attraction of the pole as being 
communicated from one particle to another of th6 same kind (219). 
1 See the note to 410. December 1838. 



78 Faraday's Researches 

towards the negative pole. But if a plate of iron, zinc, or copper, 
be substituted for the platina, then the oxygen and acid can 
combine with these, and the metal immediately begins to travel 
(as an oxide) to the opposite pole, and is finally deposited 
there. Or if, retaining the platina pole, a fused chloride,, as 
of lead, zinc, silver, etc., be substituted for the sulphuric acid, 
then, as the platina finds an element it can combine with, it 
enters into union, acts as other elements do in cases of voltaic 
decomposition, is rapidly transferred across the melted matter, 
and expelled at the negative pole. 

282. I can see but little reason in the theories referring the 
electro-chemical decomposition to the attractions and repulsions 
of the poles, and I can perceive none in M. de la Rive's theory, 
why the metal of the positive pole should not be transferred 
across the intervening conductor, and deposited at the negative 
pole, even when it cannot act chemically upon the element 
of the fluid surrounding it. It cannot be referred to the attrac- 
tion of cohesion preventing such an effect; for if the pole be 
made of the lightest spongy platina, the effect is the same. 
Or if gold precipitated by sulphate of iron be diffused through 
the solution, still accumulation of it at the negative pole will 
not take place; and yet in it the attraction of cohesion is 
almost perfectly overcome, the particles are so small as to remain 
for hours in suspension, and are perfectly free to move by the 
slightest impulse towards cither pole; and if in relation by 
chemical affinity to any substance present, are powerfully 
determined to the negative pole. 1 

283. In support of these arguments, it may be observed that 
as yet no determination of a substance to a pole, or tendency 
to obey the electric current, has been observed (that I am aware 
of) in cases of mere mixture ; i.e. a substance diffused through 
a fluid, but having no sensible chemical affinity with it, or with 
substances that may be evolved from it during the action, does 
not in any case seem to be affected by the electric current. 

1 In making this experiment, care must be taken that no substance be 
present that can act chemically on the gold. Although I used the metal 
very carefully washed, and diffused through dilute sulphuric acid, yet in the 
first instance I obtained gold at the negative pole, and the effect was 
repeated when the platiaa poles were changed. But on examining the 
clear liquor in the cell, after subsidence of the metallic gold, I found a little 
of that metal in solution, and a little chlorine was also present. I therefore 
well washed the gold which had thus been subjected to voltaic action, 
diffused it through other pure dilute sulphuric acid, and then found, that 
on subjecting it to the action of the pile, not the slightest tendency to the 
negative pole could be perceived. 



Uncombined Bodies not Transferable 79 

Pulverised charcoal was diffused through dilute sulphuric acid, 
and subjected with the solution to the action of a voltaic battery, 
terminated by platina poles; but not the slightest tendency 
of the charcoal to the negative pole could be observed. Sublimed 
sulphur was diffused through similar acid,, and submitted to 
the same action, a silver plate being used as the negative pole; 
but the sulphur had no tendency to pass to that pole, the 
silver was not tarnished, nor did any sulphuretted hydrogen 
appear. The case of magnesia and water (231, 269), with those 
of comminuted metals in certain solutions (282), are also of this 
kind; and, in fact, substances which have the instant before 
been powerfully determined towards the pole, as magnesia 
from sulphate of magnesia, become entirely indifferent to it the 
moment they assume their independent state, and pass away, 
diffusing themselves through the surrounding fluid. 

284. There are, it is true, many instances of insoluble bodies 
being acted upon, as glass, sulphate of baryta, marble, slate, 
basalt, etc., they form no exception; for the substances 
they give up are in direct and strong relation as to chemical 
affinity with those which they find in the surrounding solution, 
so that these decompositions enter into the class of ordinary 
effects. 

285. It may be expressed as a general consequence, that the 
more directly bodies are opposed to each other in chemical 
affinity, the more ready is their separation from each other in 
cases of electro-chemical decomposition, i.e. provided other 
circumstances, as insolubility, deficient conducting power, 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 



80 Faraday's Researches 

electro-chemical decomposition and transfer which Sir Humphry 
Davy described in his celebrated paper, 1 were those in which 
acids were passed through alkalies, and alkalies or earths through 
acids ; 2 and the way in which substances having the most 
powerful attractions for each other were thus prevented from 
combining, or, as it is said, had their natural affinity destroyed 
or suspended throughout the whole of the circuit, excited the 
utmost astonishment. But if I be right in the view I have 
taken of the effects, it will appear that that which made the 
wonder is in fact the essential condition of transfer and decom- 
position, and that the more alkali there is in the course of an 
acid, the more will the transfer of that acid be facilitated from 
pole to pole; and perhaps a better illustration of the difference 
between the theory I have ventured, and those previously exist- 
ing, cannot be offered than the views they respectively give 
of such facts as these. 

287. The instances in which sulphuric acid could not be 
passed through baryta, or baryta through sulphuric acid, 3 
because of the precipitation of sulphate of baryta, enter within 
the pale of the law already described (116, 148), by which 
liquidity is so generally required for conduction and decom- 
position. In assuming the soHd state of sulphate of baryta, 
these bodies became virtually non-conductors to electricity of 
so low a tension as that of the voltaic battery, and the power 
of the latter over them was almost infinitely diminished. 

288. The theory I have advanced accords in a most satis- 
factory manner with the fact of an element or substance find- 
ing its place of rest, or rather of evolution, sometimes at one 
pole and sometimes at the other. Sulphur illustrates this 
effect very well. 4 When sulphuric acid is decomposed by the 
pile, sulphur is evolved at the negative pole; but when sul- 
phuret of silver is decomposed in a similar way (172), then the 
sulphur appears at the positive pole; and if a hot platina pole 
be used so as to vaporise the sulphur evolved in the latter case, 
then the relation of that pole to the sulphur is exactly the same 
as the relation of the same pole to oxygen upon its immersion 
in water. In both cases the element evolved is liberated at 
the pole, but not retained by it; but by virtue of its elastic, 

1 Philosophical Transactions, 1807, p. i. 2 Ibid. p. 24, etc. 

3 Ibid. p. 25, etc. 

4 At 416 and 492 of Part V. will be found corrections of the statement 
here made respecting sulphur and sulphuric acid. At present there is no 
well-ascertained fact which proves that the same body can go directly to 
either of the two poles at pleasure. December 1838. 



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 



8 2 Faraday's Researches 

a secondary effect, and not an immediate consequence of the 
decomposing power of the electric current. 1 

292. A few observations on what are called the poles of the 
voltaic battery now seem necessary. The poles are merely the 
surfaces or doors by which the electricity enters into or passes 
out of the substance suffering decomposition. They limit the 
extent of that substance in the course of the electric current, 
being its terminations in that direction: hence the elements 
evolved pass so far and no further. 

293. Metals make admirable poles, in consequence of their 
high conducting power, their immiscibility with the substances 
generally acted upon, their solid form, and the opportunity 
afforded of selecting such as are not chemically acted upon by 
ordinary substances. 

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

295. Air, however, and some gases are free from the latter 
objection, and may be used as poles in many cases (197, etc.); 
but, in consequence of the extremely low degree of conducting 
power belonging to them, they cannot be employed with the 
voltaic apparatus. This limits their use; for the voltaic 
apparatus is the only one as yet discovered which supplies 
sufficient quantity of electricity (107, 112) to effect electro- 
chemical decomposition with facility. 

296. When the poles are liable to the chemical action of 
the substances evolved, either simply in consequence of their 
natural relation to them, or of that relation aided by the influence 

1 Refer for proof of the truth of this supposition to 483, 487, etc. 
December 1838. 



Character and Nature of the Poles 83 

of the current (254), then they suffer corrosion, and the parts 
dissolved are subject to transference, in the same manner 
as the particles of the body originally under decomposition. 
An immense series of phenomena of this kind might be quoted 
in support of the view I have taken of the cause of 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 1 

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). 2 

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 

1 Sixth Series, original edition, vol. i. p. 165. 
* Or Voltameter. December 1838. 



Disappearance 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. Fi I(5 
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 ^jjdth of an inch, others not more than ^ n dth, 
whilst some were as much as V^th 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 length, five-eighths of an 
inch in internal diameter, were sealed hermetically at one 



Fig. 17. 

extremity, and were graduated. Into these tubes was put a 
mixture of two volumes of hydrogen and one of oxygen, 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. 1 8), 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 




Fig. 18. 



Preparation of the Platina Plates 87 

effectively 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 very 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.). 

31 1 . 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 small 
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, however, the quantity of water was 
bu small, the power was very little impaired 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 oxygen 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 very 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. 1 

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 

1 In proof that this is the case, refer to ^74. 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 

(370, 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 diluted 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 
powerful 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. 1 

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 became 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, 

1 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. 



94 Faraday's Researches 

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

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

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

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

344. Other metals than platina were then experimented with. 
Gold and palladium exhibited the power either when made the 
positive pole of the voltaic battery (306), or when acted on by 
hot oil of vitriol (337). When palladium is used, the action 
of the battery or acid should be moderated, as that metal is 
soon acted upon under such circumstances. Silver and copper 
could not be made to show any effect at common temperatures. 

1 The heat need not be raised so much as to make the alkali tarnish the 
platina, although if that effect does take place it does not prevent the 
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, 1 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, 2 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. 3 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. 

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. 4 

347. In the two excellent experimental papers by MM. Dulong 
and Thenard, 5 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, torn. xxiv. p. 93. 

2 Ibid. torn, xxiii. p. 440; torn. xxiv. p. 380. 3 Ibid. torn. xxiv. p. 383. 
4 Ibid. torn. xxiv. pp. 94, 95. Also Bibliothtque Universelle, torn. xxiv. 

P- 54- 

& Ibid. torn, xxiii. p. 440; torn. xxiv. p. 380. 



96 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 body 
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. 1 He expresses the immediate cause thus: 
" The platina determines upon its surface a continual renova- 
tion of concrete laminae, 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 laminae, 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 
is called the nascent condition. That combustible gases should 
jose their elastic state, and become concrete, assuming the form 

1 Giornale di Fisicz, etc., 1825, torn. 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; x 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 laminae 
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 corners 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, 

'pp. 138, 37r. 



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 dean 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 
inflammation 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 Platina 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. 1 

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 air, 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. 2 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. 

1 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, it 
yielded, by the mere influence of the pressure, 54 per cent, of water. 

8 Fusinieri and Bellani consider the air as forming solid concrete films in 
these cases. Giornale di Fisica, 1825, torn. viii. p. 262. 



ioo Faraday's Researches 

359. Extraneous bodies, which, acting as nuclei in crystallising 
cr 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, i.e. 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 101 

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 any 
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 
a 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 combine when they 
are mingled, not waiting for any other determining circumstance ; 
but if two such gases as oxygen and hydrogen are put together, 



IO2 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, 1 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 

1 Philosophical Transaction*, 1823, p. 161. 



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 gradually 
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, 1 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- 

1 Annalcs de Chimte, torn. 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 always 
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 atr, 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 almost 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 ga<es 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 defiant 
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 defiant gas formed but f ^th 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). 
This mixture was not affected by a plate which had been made 
positive in acid, 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 T Vth 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 ^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 6xygen 
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 1 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. 

1 Philosophical Transactions, 1825, p. 440. 
E 576 



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 oil-gas 
liquor causes the ignition of the spongy platina. The mixture 
with oil-gas burns 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 1 09 

ing it through the agency of a stronger attraction than that o^ 
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. 1 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 

1 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. 



iio 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. 1 

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 

(3 62 , 3 6 3)- 

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 ; 2 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 

1 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. 

1 Quarterly journal of Science, 1819, vol. vii. p. 106. 



Peculiar Conditions of Metals 1 1 i 

, 1 and also by Dr. Mitchell of Philadelphia 2 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 all 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, especially 
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. 



V 3 

5. ON ELECTRO-CHEMICAL DECOMPOSITION, CONTINUED. 4 ^[ jV. 
ON SOME GENERAL CONDITIONS OF ELECTRO-DECOMPOSITION. 
^f V. ON A NEW MEASURER OF VOLTA-ELECTRICITY. ^| VI. 
ON THE PRIMARY OR SECONDARY CHARACTER OF BODIES 
EVOLVED IN ELECTRO-DECOMPOSITION. ^[ Vli. 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 

1 Quarterly Journal of Science, vol. xxviii. p. 74, and Edinburgh Transac- 
tions, 1831. 

2 Journal of the Royal Institution for 1831, p. 101. 

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

4 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 body 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, 

1 fjXfKTpov, and 65os a way. 



Definitions of New Terms 1 1 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, 1 
and that towards the west the cathode ; 2 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 hypo- 
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 

1 di/w upwards, and 656s a way ; the way which the sun rises. 

2 /card downwards, and 656s a way ; the way which the sun sets. 

3 i'/XeKrpov, and Xtfw, solvo. N. Electrolyte, V. Electrolyse. 



114 Faraday's Researches 

eledrolytical 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 1 which go to the anode of the decom- 
posing body; and those passing to the cathode, cations; 2 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. 3 

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. 

1 aviuv that which goes up. (Neuter participle.) 

2 Kanwv that which goes down. 

3 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 1 1 5 



^f iv. On some general conditions of Electro-chemical 
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. 1 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 suffers 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 

1 Philosophical Transactions, 1830 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. 1 

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 

1 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 1 17 

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 dependent 
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. 



1 1 8 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. 1 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- 

1 De la Rive. 



Bodies not Electrolysable Alone i I 9 

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 thing, 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 sulphur 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 



i 20 Faraday's Researches 

of a true protochloride consisting of single proportionals (430, 

530- 

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 perchloride 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 ordinary 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. 1 

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 of 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 

1 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 Faraday's Researches 

seem to be subject to the same simple law as the former class 
of binary 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, 1 
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. 

If v. On a new Measurer of Volta-electricity 

439. I have already said, 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 construct 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 

1 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- 



taming a plate and wire 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. 2 1). 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 ; 

<PifF. 22 

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- 23- 



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

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, 
flow into the tube and fill it. When an electric 
current is passed through the instrument, the 
gases evolved against the plates collect in the 
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- 
cating gas were to be collected. It is fixed on 
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 i 25 

hermetically at the part held in the stand, is five inches in 
length, and 0.6 of an inch in diameter; the neck about nine 
inches in length, 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 influence 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 127 

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, when 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 



ia8 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- 
tion 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 weakly 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 intensity, caused by 
difference in the strength of charge, or in the number of alterna- 
tions used, produced no difference as to the equal 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 



129 



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), a \ ^ ^ b - 

be connected with the wires 
at a b, fig. 27, it will serve 
sufficiently well, by the de- 
gree of decomposition occur- 
ring in it, to indicate the 
relative state of the two 
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 




Fig. 27. 



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 testad, 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 



130 Faraday's Researches 

current (449). Slight differences occurred, as before, some- 
times in one direction, sometimes in another; but the final 
result was, that exactly the same quantity of water was decom- 
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, ai ?d 
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 asmuch 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 decomposed exactly proportionate 
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, 44^)j 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 
oxygen may be advantageously used as the measuring substance. 
This is the case, for instance, with sulphate cyf 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), 
and the other in which a single gas, as the hydrogen only, is 
used (442, 443). When referred to as a comparative instrument 
(a use I shall now make of it very extensively), it will not often 
require particular precaution in the observation; but when 
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; 
the hundredths and smaller divisions of a cubical inch are quite 
fit for this purpose, and the hundredth may be very conveniently 
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 
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 
in the tube occupies that number of divisions or hundredths of 
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 
pressure, and especially for moisture. 1 For the latter object the 
volta-electrometer (fig. 26) is most accurate, as its gas can be 
measured over water, whilst the others retain it over acid or 
saline solutions. 

473. I have not hesitated to apply the term degree (471), in 
analogy with the use made of it with respect to another most 
important imponderable agent, namely, heat; and as the definite 
expansion of air, water, mercury, etc., is there made use of to 
measure heat, so the equally definite evolution of gases is here 
turned to a similar use for electricity. 

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



Use of the Voltameter 133 

474. The instrument offers the only actual 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. 1 

^f vi. On the primary 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 Recherchcs 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. Again, 
when ammonia is decomposed by platina electrodes, nitrogen 
appears at the anode ; l 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; 2 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 

1 Annales de Chimie, 1804, torn. li. p. 167. * Ibid. p. 172. 



Primary or Secondary Results 135 

Davy, 1 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. 2 

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 ae 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 

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

8 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, 
torn. 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. 
When, 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 I 37 

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. 
When 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 moreof 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. 



38 



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. A 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 oi 
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, 1 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 
Tendered the whole solution milky. The volumes of gases were 
in no regular proportion to the quantities evolved from water 
an 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 

1 See also De ; la Rive, Bibliotheque Universelle, torn. 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. 1 In 1804, Hisinger and Berzelius stated 
that it was the direct result of the action of the voltaic pile, 2 
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. A 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. 

1 Nicholson's Quarterly Journal, vol. iv. pp. 280, 281. 
* Annales de Chimie, 1804, torn. li. p. 173. 
F 576 



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. 



Primary or Secondary Decomposition 141 

The oxygen may be viewed as a secondary result; but I incline 
to believe that it is not so : for, if it were, it might be expected 
in largest proportion from the stronger acid, whereas the reverse 
is the fact. This consideration, with others, also leads me to 
conclude that muriatic acid is more easily decomposed by the 
electric current than water; since, even when diluted with eight 
or nine times its quantity of the latter fluid, it alone gives way, 
the water remaining unaffected. 

501. Chlorides. On using solutions of chlorides in water 
for instance, the chlorides of sodium or calcium there was 
evolution of chlorine only at the positive electrode, and of 
hydrogen, with the oxide of the base, as soda or lime, at the 
negative electrode. The process of decomposition may be viewed 
as proceeding in two or three ways, all terminating in the same 
results. Perhaps the simplest is to consider the chloride as the 
substance electrolysed, its chlorine being determined to and 
evolved at the anode, and its metal passing to the cathode, 
where, finding no more chlorine, it acts upon the water, pro- 
ducing hydrogen and an oxide as secondary results. As the 
discussion would detain me from more important matter, and 
is not of immediate consequence, I shall defer it for the present. 
It is, however, of great consequence to state, that, on using the 
volta-electrometer, the hydrogen in both cases was definite; 
and if the results do not prove the definite decomposition of 
chlorides (which shall be proved elsewhere 524, 529, 549), 
they are not in the slightest degree opposed to such a conclusion, 
and do support the general law. 

502. Hydriodic acid. A solution of hydrjodic acid was 
affected exactly in the same manner as muriatic acid. When 
strong, hydrogen was evolved at the negative electrode, in 
definite proportion to the quantity of electricity which had 
passed, i.e. in the same proportion as was evolved by the same 
current from water; and iodine without any oxygen was evolved 
at the positive electrode. But when diluted, small quantities 
of oxygen appeared with the iodine at the anode, the proportion 
of hydrogen at the cathode remaining undisturbed. 

503. I believe the decomposition of the hydriodic acid in this 
case to be direct, for the reasons already given respecting 
muriatic acid (498, 499). 

504. Iodides. A solution of iodide of potassium being 
subjected to the voltaic current, iodine appeared at the positive 
electrode (without any oxygen), and hydrogen with free alkali 
at the negative electrode. The same observations as to the 



142 Faraday's Researches 

mode of decomposition are applicable here as were made in 
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- 
parently. The fused fluorides were electrolysed (153); but 
having during these actions obtained fluorine in the separate 
state, I think it better to refer to a future series of these Re- 
searches, in which I purpose giving a fuller account of the 
results than would be consistent with propriety here. 1 

506. Hydro-cyanic acid in solution conducts very badly. 
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 
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, 2 I incline to 
believe that the cyanide in solution is directly decomposed. 

507. Ferro-cyanic acid and theferra-cyanides, as also sulpha- 
cyanic acid and the sulpha-cyanides, presented results correspond- 
ing with those just described (506). 

508. Acetic acid. Glacial acetic acid, when fused (141), is 
not decomposed by, nor does it conduct, electricity. On add- 
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 
would do. Dilute sulphuric acid was added to it in order to 
make it a better conductor; then the definite proportion of 
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 

1 1 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. 

* 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. 



Primary or Secondary Decomposition 143 

is not electrolysable, but that a portion of it is decomposed by 
the oxygen evolved at the anode, producing secondary results, 
varying with the strength of the acid, the intensity of the 
current, and other circumstances. 

509. Acetates. One of these has been referred to already, 
as affording only secondary results relative to the acetic acid 
(484). With many of the metallic acetates the results at both 
electrodes are secondary (481, 485). 

Acetate of soda fused and anhydrous is directly decomposed, 
being, as I believe, a true electrolyte, and evolving soda and 
acetic acid at the cathode and anode. These, however, have no 
sensible ' duration, but are immediately resolved into other 
substances; charcoal, sodiuretted hydrogen, etc., being set free 
at the former, and, as far as I could judge under the circum- 
stances, acetic acid mingled with carbonic oxide, carbonic acid, 
etc., at the latter. 

510. Tartaric acid. Pure solution of tartaric acid is almost 
as bad a conductor as pure water. On adding sulphuric acid, 
it conducted well, the results at the positive electrode being 
primary or secondary in different proportions, according to 
variations in the strength of the acid and the power of the 
electric current (487). Alkaline tartrates gave a large proportion 
of secondary results at the positive electrode. The hydrogen 
at the negative electrode remained constant unless certain triple 
metallic salts were used. 

511. Solutions, of salts containing other vegetable acids, as the 
benzoates; of sugar, gum, etc., dissolved in dilute sulphuric 
acid; of resin, albumen, etc., dissolved in alkalies, were in turn 
submitted to the electrolytic power of the voltaic current. In 
all these cases, secondary results to a greater or smaller extent 
were produced at the positive electrode. 

512. In concluding this division of these Researches, it cannot 
but occur to the mind that the final result of the action of the 
electric current upon substances placed between the electrodes, 
instead of being simple may be very complicated. There are 
two modes by which these substances may be decomposed, 
either by the direct force of the electric current, or by the action 
of bodies which that current may evolve. There are also two 
modes by which new compounds may be formed, i.e. by com- 
bination of the evolving substances whilst in their nascent 
state (394), directly with the matter of the electrode; or else 
their combination with those bodies, which being contained 
in, or associated 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. Hence, 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. 1 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 

1 Annales de Chimie, torn. 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 



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, 503). 

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 
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 




Fig. 29. 

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 as 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 tiie 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 





I 

Tig. 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, which 
was soon eaten through, and the experiment stopped. 

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

535. Oxide of bismuth. I found this substance required too 
high a temperature, and acted too powerfully as a flux, to allow 
of any experiment being made on it, without the application of 
more time and care than I could give at present. 

536. The ordinary protoxide of antimony, which consists of 
one proportional of metal and one and a half of oxygen, was 
subjected to the action of the electric current in a green-glass 
tube (524), surrounded by a jacket of platina foil, and heated 
in a charcoal fire. The decomposition began and proceeded 
very well at first, apparently indicating, according to the 
general law (414, 432), that this substance was one containing 
such elements and in such proportions as made it amenable to 
the power of the electric current. This effect I have already 
given reasons for supposing may be due to the presence of a 
true protoxide, consisting of single proportionals (431, 428). 
The action soon diminished, and finally ceased, because of the 
formation of a higher oxide of the metal at the positive elec- 
trode. This compound, which was probably the peroxide, being 
infusible and insoluble in the protoxide, formed a crystalline 
crust around the positive electrode; and thus insulating it, 
prevented the transmission of the. electricity. Whether, if it 
had been fusible and still immiscible, it would have decomposed, 
is doubtful, because of its departure from the required composi- 
tion (432). It was a very natural secondary product at the 
positive electrode (514). On opening the tube it was found that 
a little antimony had been separated at the negative electrode ; 
but the quantity was too small to allow of any quantitative 
result being obtained. 1 

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



Iodides I 5 i 

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 potassium 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 
presence of the lead, and other circumstances, prevented me 



152 Faraday's Researches 

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. with 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 
fig. 32. A weighed platina 
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, b, 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 
b, 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 affinity, 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 
mass of evidence, proving the truth of the important proposition 
which I at first laid down, namely, that the chemical power of a 
current of electricity is in direct proportion to the absolute quantity 
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 
obtained with any one substance do not merely agree amongst 
themselves, but also with those obtained from other substances, 
the whole combining together into one series of definite electro- 
chemical actions (241). I do not mean to say that no exceptions 
will appear: perhaps some may arise, especially amongst sub- 
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 
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 
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 
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- 
tricity. 1 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 1 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 
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, 
under the influence of the electric current, form an exceedingly 
important general class. They are combining bodies; are 
directly associated with the fundamental parts of the doctrine of 
chemical affinity; and have each a definite proportion, in which 
they are always evolved during electrolytic action. I have pro- 
posed to call these bodies generally ions, or particularly anions 
and cations, according as they appear at the anode or cathode 
(401); and the numbers representing the proportions in which 
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, 
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 union be combined with a cation, then both 
will travel, the 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 tons, and must also render 
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 only single electro-chemical equivalents 
of elementary ions can go to the electrodes, and not multiples. 

566. vi. A body not decomposable when alone, as boracic 
acid, is not directly decomposable by the electric current when 
in combination (515). It may act as an ion going wholly to the 
anode or cathode, but does not yield up its elements, except 
occasionally by a secondary action. Perhaps it is superfluous 
for me to point out that this proposition has no relation to such 
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 collecting such ions as, if evolved 
in their free state, would be unmanageable. 1 

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 
(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 
electrolytes, i.e. not composed of electro-chemical equivalents of 
simple ions. 

1 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. 
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 

570. x. Electro-chemical equivalents are always consistent; 
i.e. the same number which represents the equivalent of a sub- 
stance A when it is separating from a substance B, will also 
represent A when separating from a third substance C. Thus, 
8 is the electro-chemical equivalent of oxygen, whether separat- 
ing from hydrogen, or tin, or lead; and 103.5 i g tne electro- 
chemical equivalent of lead, whether separating from oxygen, 
or chlorine, or iodine. 

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

572. By means of experiment and the preceding propositions, 
a knowledge of ions and their electro-chemical equivalents may 
be obtained in various ways. 

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 iii. may be 
deduced the knowledge of many other ions, and also their 
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- 



160 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 161 

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 all 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 
Potassa . , 



17 
47-2 



Tartaric acid 66 

Citric acid 58 

Oxalic acid 36 

Sulphur (?) 16 

Selenium (?) 

Sulpho-cyanogcu . . 



Soda 31.3 

Lithia 18 

Baryta 76.7 

Strontia 51.8 

Lime 28.5 

Magnesia 20.7 

Alumina (?) 

Protoxides generally. 

Quinia 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, 



1 62 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-cyanogen, 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 probable 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, f tin 59? etc -> 
notwithstanding that a very high authority doubles several of 
these numbers. 



7. 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, whilst 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 fcr 



1 64 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 r ^ ? th of an inch in thickness, 1 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, 2 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 (149, 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 electricity, is simply employed in overcoming electrical 
powers in the body subjected to its action; it seems a probable, 

1 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. 

2 Literary Gazette, 1833, March i and 8. Philosophical Magazine, 1833, 
p 204. L'Institut, 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 pile. 1 

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 which, 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 
every 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 capable 
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 

1 By the term voltaic pile, I mean such apparatus or arrangement of 
metals as up to this time have been called 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. 



1 66 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 current, 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 
batter}', 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 r J^th of an inch in thickness, red hot, in con- 
tact with the air, 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 endeavcured 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 800,000 such charges of the Leyclen 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 shown, 1 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 off. 2 

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 

1 Recent Experimental Researches, etc., 1830, p. 74, etc. 

2 The experiment may be made with pure zinc, which, as chemi-sts 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 Univcrselle, 
1830, p. 391. 



1 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. 1 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. 

60 1. 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, 
becomes 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. 2 

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 
separate, and bringing the whole into a constant state. 

1 The experiment was repeated several times with the same results. 



Voltaic Decomposition of Water 1 69 

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 decomposes, 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 bodies, 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. 



576 



172 Faraday's Researches 



VI 1 

8. ON THE ELECTRICITY OF THE VOLTAIC PILE; ITS SOURCE, 
QUANTITY, INTENSITY, AND GENERAL CHARACTERS. ^ i. 
ON SIMPLE VOLTAIC CIRCLES, ^f ii. ON THE INTENSITY 
NECESSARY FOR ELECTROLYSATION. ^f iii. ON ASSOCIATED 
VOLTAIC CIRCLES, OR THE VOLTAIC BATTERY. If iv. ON 
THE RESISTANCE OF AN ELECTROLYTE TO ELECTROLYTIC 
ACTION. *[fv. GENERAL REMARKS ON THE ACTIVE VOLTAIC 
BATTERY 

^f i. On simple Voltaic Circles 

6 10. 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, 
1 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 
doubtful 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, 
% 33- a - 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 c, 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 *. On re- 
moving the end of the wire from place to place 
on the paper, the effect was evidently very power- 
Fig- 33- fulj an d n 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 c, 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 if, 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. 1 

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 

y *^~ z no sensible chemical action at that spot 

Fi 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 * (fig. 35). Exactly the 
same set of effects occur, except that when the metallic com- 
munication 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). 



v\ 



Fig. 35. Fig. 36. 

626. Now both the solutions used are conductors, but the 
conduction in them is essentially connected with decomposition 
(593) in a 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 Reaearches 

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 s, 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, 
determine 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, namely, 
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 by 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 fig. 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 x, and 
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- C JJ4. 



ence to the size of the instrument. Various 
arrangements were made at x, according to the 
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- Fi g . 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, e, 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 x, was readily 
decomposed. Iodine was evolved at the anode, and alkali at 
the cathode, of the decomposing body. 

636. Protochloride of tin, when fused and placed at x, 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 
acid, 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 v, 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 
v, 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 by indigo yielded 
chlorine at the anode ajid 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 1 8 r 

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 intensity 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 to 
electric currents of different intensities, which will serve to 
assist in the construction of a scale competeut to supply the 



182 Faraday's Researches 

j 

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 over, 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 differ 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). 

Protochloride 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 necessary 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, with 
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 experiment, which 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 be/ore the zinc and the copper were 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 
which 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 form 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. 1 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 intensity 
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 affinity 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 

1 Wollaston, Philosophical Transactions, 1801, p. 427. 



1 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. 1 

657. It might at first be supposed that a conducting body, 
not electrolytic, might answer as the third substance between 
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 

1 1 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 whilst 
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 



I 88 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); arid 
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). 1 

661. This view of the secondary 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 

1 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 Transactions, 
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 a, fig. 39, be supposed to be a dry oxacid, and 
b a dry base, in contact at c, and in electric 
communication at their extremities by plates 

of platina p p, and a platina wire w. If this 
acid and base were fluid, and combination 
took place at c, with an affinity ever so 
vigorous, and capable of originating an electric a ' . 

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. 

663. 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. 1 

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 hydrogen of the acid and the oxygen of the base 
are ready to traverse with the chlorine of the acid and the metal 

1 It will I trust be fully understood that in these investigations I am 
not 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. 



1 90 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 current 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 solution 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 r s Researches 

the alkali, 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. 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 fluid, 
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 
cell to the acid, and back through the galvanometer to the 
alkali, as Sir Humphry Davy formerly stated. 1 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 upon it, 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 

1 Elements of Chemical Philosophy, p. 149: or Philosophical Transactions , 
1826, p. 403. 



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 1 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 unions, 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 the metal. 

681. There is no point in electrical science which seems to 

1 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- 
ferred, 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 oxygen 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; the 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. 



Polarized 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 examined 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, 1 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, 2 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 feeble, 

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. 

* 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 
their 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 



2oo 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 enormoas 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? 



2O2 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 
d, nor the oxygen d move in the contrary direction to unite to 
the zinc b, the relation of the similar forces of b 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 circuit, communicates its electric 
or chemical forces through it to the next electrolyte in the circuit, 
fused chloride of lead, g, h, 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, b, 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 b. 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 /, m, then the iodine /, being an anion, must move in con- 
formity with the exciting anion, namely, the oxygen d, and the 
nation tin m move in correspondence with the other cations b, 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 k, 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 / ; and in the 



Electrolytic Intensity 203 

same direction by electro-chemical equivalents of hydrogen, 
lead, copper, and tin, at e, h, 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 I806, 1 and revised and re-stated by him in another Bakerian 
Lecture, on electrical and chemical changes, for the year 1826. 2 
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 combinations." 3 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. 4 

^[ 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 electrolytes could resist the action of an 
electric current when beneath a certain intensity? whether 

1 Philosophical Transactions, 1807. 1 Ibid. 1826, p. 383. 

3 Ibid. 1826, p. 389. 

4 1 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. 
Becqucrel's highly important and valuable Traite de VElectricitt 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, 
117, 118, 120, 151, 152, 224, 227, 228, 232, 233, 252, 255, 257, 258, 290^ 
etc. July 3, 1834. 

H 576 



204 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- 
nection, by a platina wire a, with the platina 
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". 
On the plate e was placed a piece of paper 
moistened in solution of iodide of potas- 
sium: the wire c was so curved that its 
end could be made to rest at pleasure on 
this paper, and show, by the evolution of 
iodine there, whether a current was passing; 
or, being placed in the dotted position, it 
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 




Fig. 44- 



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 
ort the solution supposed to be formed; but none appeared even 
after twelve days. 



206 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 e, 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 
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- 



p. meter g) with P and Z; c 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 



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 c, 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. 47- 

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- 



208 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 b 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 spiculae, 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 oi silver when placed between platina electrodes, 



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 b 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 
made appear to show that, when the electric current is reduced 
in intensity below the point required for decomposition, then 
the degree of conduction is the same whether sulphuric acid, 
or any other of the many bodies which can affect its trans- 
ferring power as an electrolyte, are present or not. Or, in other 
words, that the necessary electrolytic intensity for water is the 
same whether it be pure, or rendered a better conductor by the 
addition of these substances; and that for currents of less in- 
tensity than this, the water, whether pure or acidulated, has 
equal conducting power. An apparatus, fig. 44, was arranged 
with dilute sulphuric acid in the vessel A, and pure distilled 
water in the vessel B. By the decomposition at e, it appeared 
as if water was a better conductor than dilute sulphuric acid 
for a current of such low intensity as to cause no decomposition. 
I am inclined, however, to attribute this apparent superiority of 
water to variations in that peculiar condition of the platina elec- 
trodes which is referred to further on in this part (776), and 



2io 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 acids, 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 
electric forces, namely, that which is so characteristically ex- 
hibited by the metals, and usually called conduction, and that in 
which it is accompanied by decomposition, the first appears 
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 2 1 1 

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, 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 same 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 to 
produce the result described. 

|j iii. On associated Voltaic Circles, or the Voltaic Battery 

725. Passing from the consideration of single circles (610, 
etc.) to their association in the voltaic battery, it is a very 



2 1 2 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 
% s - 33) S^ (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 
current 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 2 I 3 

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- 
lytes 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 con- 
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. 1 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, 
1830, p. 391. 



Amalgamated Zinc in the Battery . 215 

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 employment of an 
amalgam of zinc in the manner recommended by Mr. Kemp, 1 
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." 2 

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 

1 Jameson's Edinburgh Journal, October 1828. 

z Recent Experimental Researches, p. 42, 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 the 
chemical theory of galvanism. 



2i 6 . 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 battery, 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 might at first be imagined that amalgamated zinc 
would be much inferior in force to common zinc, becaus 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 shown, 1 if 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 Kindred or a thousand i airs 
for their production in the first instance. The capability of 

1 Philosophical Transactions, 1826, p. 405. 



2 1 8 Faraday's Researches 

decomposing fused chlorides, iodides, and other compounds, 
according to the law before established (116, 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 
1783). 

^f iv. On the Resistance of an Electrolyte to Electrolytic 
Action, 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 
which would require a minute examination before a 
correct account of the whole could be given. 

744. As it will be convenient to describe the experi- 
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- 
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 
in its simplest condition; for the cups, I, n, and in of 
the former, with their contents, are represented by 
the cells i, n, and in of the latter, and the metal Fig. 49. 
plates Z and P of the former 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 
it can 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 




Fig. 50. 



surfaces of the two platina plates which constitute the electrodes 

in the cell in, or against the two surfaces of that platina plate 

which separates the cells n and in, 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 x, has oxygen evolved at one surface 

and hydrogen at the other (that is, if the 




Fig. 51- 



decomposing current passes), may be considered as the cause 
of any obstruction arising from the decomposition of water by 



220 



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. 





Fig- 55- 



Fig. 56. 



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 vn. But the current was very feeble; very 





much less than when all the intermediate plates were removed 
and the two extreme ones only retained: for when they were 
placed six inches asunder in one cell, they gave a powerful 
current. Hence five exciting pairs, with two interposed obstruc- 
ting plates, do not give a current at all comparable to that of 
a single unobstructed pair. 

753. I have already said that a very feeble current passed 
when the series included one interposed platina and two pairs 



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 x, 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. 




Fig. 59- 

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. 52, 
when a few drops of nitric acid were added to the contents of 
cell n, 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 the 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 
produce a more intense current in the exciting cells (643), or 
cause the current produced to traverse the decomposing cells 
more freely. But if to very weak sulphuric acid a few drops of 
nitric acid were added, then either one or other of those effects 
could be produced; and, as might be expected in a case like 
this, where the exciting or conducting action bore a direct 
reference to the acid itself, increasing the strength of this (the 
nitric acid) also increased its powers. 

763. The nature of the interposed plate was now varied to show 
its relation to the phenomena either of excitation or retardation, 
and amalgamated zinc was first substituted for platina. On 
employing one voltaic pair and one interposed zinc plate, fig. 60, 
there was as powerful a current, apparently, as if the interposed 
zinc plate was away. Hydrogen was evolved against P in 
cell u, and against the side of the second zinc in cell I ; but no 
gas appeared against the side of the zinc in cell u, nor against 
the zinc in cell i. 



Resistance to Electrolytes 225 

764. On interposing two amalgamated zinc plates, fig. 61, 
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 



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 
cDnvertible, 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 
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 
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 
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. 1 As 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 
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, 2 and also those of Marianini 3 and Ritter, 4 which are 
connected with it. 

Tf 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, 

1 Annales de Chimie, torn, xxviii. p. 190; and Memoires de Geneve. 

2 Philosophical Transactions, 1826, p. 413. 

3 Annales de Chimie, torn, xxxiii. pp. 117, 119, etc. 
* Journal de Physique, torn. 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. 1 

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 




I E"'^"*^- ~-~i y ^-v 

communication were so arranged [^ ^r 

that the end of that marked 3 could ^ ' 

be placed at pleasure upon paper Fig 6s 

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 p, 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; 
J Philosophical Transactions, 1826, p. 413. 



228 Faraday's Researches 



the oxidation of the zinc cannot, of course, go on with the 
sime 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 sufficiently 
shows with what difficulty that portion of the substance which 
is in contact wit'i 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 pile, 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, 1 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 p, 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 P 1 and P 2 be connected by a metal wire, 
a powerful momentary current will pass from P 2 to P 1 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 2 and P 1 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 
1 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 P 1 and P 2 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 fig. 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. 1 

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 latter, as 
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. .1 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- 

1 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. 



232 Faraday's Researches 

position, given in the third and fifth parts of these Researches. 
The expressions I would now alter are those which concern 
the independence of the evolved elements in relation to the 
poles or electrodes, and the reference of their evolution to 
powers entirely internal (260, 273, 397). The present paper 
fully shows my present views; and I would refer to paragraphs 
626, 639, 645, 652, 653, 682, 698, 743, 767, etc., as stating what 
they are. I hope this note will be considered as sufficient in 
the way of correction at present; for I would rather defer 
revising the whole theory of electro-chemical decomposition 
until I can obtain clearer views of the way in which the power 
under consideration can appear at one time as associated with 
particles giving them their chemical attraction, and at another 
as free electricity (229, 692). M. F. 

March 31, 1834. 



VII 1 

9. ON THE SOURCE OF POWER IN THE VOLTAIC PILE. ^f i. 
EXCITING ELECTROLYTES, ETC., BEING CONDUCTORS OF 
THERMO AND FEEBLE CURRENTS. If ii. INACTIVE CON- 
DUCTING CIRCLES CONTAINING AN ELECTROLYTIC FLUID. 
^f iii. ACTIVE CIRCLES EXCITED BY SOLUTION OF SULPHURET 
OF POTASSIUM, ETC. 

9. On the Source of Power in the Voltaic Pile 

784. WHAT is the source of power in a voltaic pile? This 
question is at present of the utmost importance in the theory 
and to the development of electrical science. The opinions 
held respecting it are various; but by far the most important 
are the two which respectively find the source of power in 
contact, and in chemical force. The question between them 
touches the first principles of electrical action; for the opinions 
are in such contrast, that two men respectively adopting them 
are thenceforward constrained to differ, in every point, respect- 
ing the probable and intimate nature of the agent or force on 
which all the phenomena of the voltaic pile depend. 

785. The theory of contact is the theory of Volta, the great 
discoverer of the voltaic pile itself, and it has been sustained 
since his day by a host of philosophers, amongst whom, in 
1 Sixteenth Scries, 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, 1 Wollaston, 2 and Parrot, 3 and has 
been more or less developed since by CErsted, Becquerel, De la 
Rive, Ritchie, Pouillet, Schcenbein, 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; 4 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. 5 

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 6 (610, etc.), which obtained the especial notice 
of Marianini. 7 The rank of this philosopher, the observation 
of Fechner, 8 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 Traite de I'Electricite, i. pp. 81-91, and 
Nicholson's Quarto Journal, iii. 308, iv. 120, or Journal de Physique, vi. 348. 

2 A.D. 1801. Philosophical Transactions, 1801, p. 427. 

3 A.D. 1801. Annales de Chimie, 1829, xlii. 45; 1831, xlvi. 361. 

4 A.D. 1824, etc. Annales dc Chimie, 1824, xxv. 405; 1827, xxxv. 113; 
1831, xlvi. 265, 276, 337; xlvii. 113; xlix. 131. 

6 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. 

7 Memorie delta Societd Italiana in Modena, 1837, xxi. p. 205. 

8 Philosophical Magazine, 1838, xiii. 205; or Poggendorf's 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. 



234 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. 1 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 ; 2 but Karsten, holding the con- 
tact theory, transfers the electromotive force to the contact of 
the fluids with the solid conductors. 3 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 TT7 ^ ffTS dth of a line and more, air intervening. 4 

789. De la Rive, on the contrary', contends for simple and 
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, 

1 Annales de Chimie, 1802, xl. p. 225. 

2 Bibliotheque Universelle, 1836, v. 387; 1837, viii. 189. 

3 L'Institut, No. 150. 

4 Mem. delta Soc. Hal. 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. 1 Schcenbein 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. 2 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 

, I0 57)- 

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, Ix. 171; and Traite de I'Electricite, i. pp. 253, 
258. 

8 Philosophical Magazine, 1838, xii. 227, 311, 314; also Bibliotheque 
Universelle, 1838, xiv. 155, 395. 
I 576 



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 l 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, 2 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, 3 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, 4 Marianini admits the spark, but I give it up 



1 Memorie della Societd Italiana in Modena, 1827, xxi. p. 205. 
* Ibid. p. 217. * Ibid. p. 217. 'Ibid. 



p. 225. 



Investigation by the Galvanometer 237 

altogether. Jacobi's paper l convinces me I was in error as to 
that proof of the existence of a state of tension in 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 



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 
1 Philosophical Magazine, 1838, 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 b 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, 
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. 

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 
plates would serve the required purpose, I sought for such, and 
fortunately soon found them. 

^f 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 
(potassa fusa) and sulphur were mixed with and heated gradually 
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- 
solved in water, so as to form a strong solution, which by 
standing became quite clear. 

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 80. Even the small dif- 
ference of temperature occasioned by touching the Seebeck 
element with the finger, produced a very sensible current 
through the electrolyte. When in place of the antimony- 
bismuth combination mere wires of copper and platinum, 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. 1 

1 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 (80 i), 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. 1 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 (80 1), 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 place, other results relating to the conducting power 
of bodies, which will be required hereafter in these investiga- 
tions. Galena, yellow sulphuret of iron, arsenical pyrites, native 
sulphuret of copper and iron, native grey artificial sulphuret of 

1 Schoenbein's experiments on a compound of nitric and nitrous acids 
will probably bear upon and illustrate this subject. BibliothSque Univer- 
!>e!le, 1817, x. 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 (80 1) 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 thermo-electric circuit (801), the current 
was found to pass readily. 

^f ii. Inactive Conducting Circles containing a Fluid or Electrolyte 

811. De la Rive has already quoted the case of potash, iron 
and platina, 1 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 

1 Philosophical Magazine, 1837, xi. 275. 



Faraday's Researches 







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 

P, P, 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, a, b, and x : the first 
two, being opposed to 
each other, may be con- 
sidered as neutralising 
each other's forces; but 

Fig 65 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 o ; 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 x, 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 
immersion 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. 1 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; 2 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 x 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). 

1 Marianini observed effectsof this kind produced by exposure to the air, of 
one of two plates dipped in nitric acid. Annales de Chimie, 1830, xlv. p. 42. 

1 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 1 8. 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 circuit, 
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 b, 
either heated or cooled. Very moderate changes of tempera- 
ture at these places produce instantly the corresponding current, 
but the mere contact at x 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 x 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, a or b. 

821. Admitting for the moment that the arrangement proves 
that the contact of platinum and iron at x 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 a or b 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); l 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. 2 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 

1 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 b altogether, and so have but one contact, that at x, to 
consider. 



246 Faraday's Researches 

contact x was as ineffective as before (822); the introduction 
ofjChemical action at x was as striking in its influence as in the 
former case (819); 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 
conductors introduced at x, is entirely without electromotive 
force. 1 

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. 
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 
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 
of the arrangement, it is in the wrong direction for the contact 
theory. I rather incline to refer it to that power which platinum 
and other substances have of effecting combination and decom- 
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 

1 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 difficult to get pure and also perfectly compact nickel; and if porous, 
then the matter retained in the pores produces currents. 



Inactive Voltaic Circles 



247 




Fig. 66. 



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 x (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. 1 By diluting the solution still further, a fluid 
could be obtained in which the iron was, after the first effect, 
permanently but feebly 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 o. 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 

1 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- 
ment 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 difficulty, 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 
Schcenbein in his investigations, and then used it instead of 



250 Faraday's Researches 

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 
of iron not offering that obstruction to the passage of the 
current which the peculiar iron did (831, 832). Hence scale 
oxide of iron and platinum produce no current by contact, the 
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 
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 
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 
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 Schcenbein 
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 
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 (819), 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 proceded to use a fluid differing from any of the 



252 Faraday's Researches 

former: this was solution of potassa, which has already been 
employed by De la Rive (811) 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- 
posing a little piece of paper moistened in dilute nitric acid 
(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 
solution of potassa was positive. The force of the produced 
current soon fell, and after an hour or so was very small. Then 
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- 
trolytes, 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 power 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. 

8. 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. Artificial sulphuret of bismuth. 

i and 2 with 5, 6, 7, 8, 9, 10, n, 12, 13, 14, in turn, 
i and 3 with 5, 6, 7, 8, 9, 10, n, 12, 13, 14. 
i and 5 with 6, 7, 8, 9, 10, n, 12, 13, 14. 

3 and 6 with 7, 8, 9, 10, n, 12, 13, 14. 

4 and 5 with 6, 7, 8, 9, 10, n, 12, 13, 14. 
4 and 6 with 7, 8, 9, 10, n, 12. 13, 14. 

4 and 7 with 8, 9, 10, u, 12, 13, 14. 
4 and 8 with 9, 10, n, 12, 13, 14. 
4 and 9 with 10, n, 12, 13, 14. 
4 and 10 with n, 12, 13, 14. 
4 and n with 12, 13, 14. 
4 and 12 with 13, 14. 
4 and 13 with 14. 
i and 4 with 12. 

856. Marianini states from experiment that copper is positive 
to sulphuret of copper; l 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 

1 Memorie della Societd 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, must 
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 (&8o); 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 ? 

^f iii. 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. 1 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. 2 

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 3 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 

1 Elements of Chemical Philosophy, p. 148. 

* Annales de Chimie, 1828, xxxvii. 231-237; xxxix. 299. 

3 Memorie delta 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 being, according to Volta, positive to 
the former. 1 By his own experiment the same substance was 
negative to the iron across the same solution. 2 

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 i> 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 

1 Memorie della Societd, Italiana in Modena, 1837, xxi. p. 219. 
* Ibid. p. 224. 



Circles with Sulphuret of Potassium 261 

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 -platinum. 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 o. 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 
electrolyte. 

872. On the other hand, how beautiful a proof the result 
gives in confirmation of the chemical theory! Tin can take 
sulphur from the electrolyte to form a sulphuret; and whilst 
it is doing so, and in proportion to the degree in which it is 
doing so, it produces a current; but when the sulphuret which 
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 
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 formed 
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 
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 o. 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 
sulphuret of lead is a conductor (808). Nevertheless, though a 
conductor, it could stop the further chemical action; and that 
ceasing, the current ceased also. 

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 
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 
beautifully invested with a thin polished pellicle of sulphuret of 
lead. 

875. With lead, then, we have a conducting sulphuret formed, 
but still there is no sign that its contact can produce a current, 
any more than in the case of the non-conducting sulphuret of 
tin (870). There is no new or additional action produced by 
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- 



sulphu,. pot. 



p'atmum 
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, 
i.e. the current ceases, and fig. 69 may represent this new case 
according to the contact theory. Now is it at all likely that 



J-O I . 

lead c suJpJcu^pat. 6 



platinum 
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 b (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 



sulpku,. & sulphu,. & 
leaei pot. 



platinum. 
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. 1 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 ? 

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 

1 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- 
ingly. Even in that instance the cessation of chemical action 
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 
(817): and upon that again follows the passive condition of 
all those contacts which can be produced by interposing other 
conducting bodies between them (821); an argument that 
need not again be urged. 

885. Copper. This substance being associated with platinum, 
gold, iron, or any metal chemically inactive in the solution of 
sulphuret, gives an active circle, in which the copper is positive 
through the electrolyte to the other metal. The action, though 
it falls, does not come to a close as in the former cases, and 
for these simple reasons; that the sulphuret formed is not 
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 
be taken out and washed and dried, even the wiping will remove 
part of the sulphuret in scales, and the nail separates the rest 
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. 

886. If, as Marianini has shown, 1 a copper plate which has 
.been dipped in the solution of sulphuret, be removed before 
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 
.neutral, or, as is often the case, negative (815, 826) to the 

1 Memorie della Societd Italiana in Modena, 1837, xxi. 224. 



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 

K 576 



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 
produce the current; in that respect it is like the sulphuret of 
tin (870). But that circumstance does not stop the occurrence 
of the chemical current; for, as the sulphuret forms a porous 
instead of a continuous crust, 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, 
and gives a powerful continuous current. Accordingly, if a 
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 
alike, and the action consequently continues in both cases, 
but they differ in the sulphuret of silver being a non-conductor 
(170) for these feeble currents, and, in that respect, this metal 
is analogous to antimony (890). 

892. Cadmium. Cadmium with platinum, gold, iron, etc., 
gives a powerful current in the solution of sulphuret, and the 
cadmium is positive. On several occasions this current con- 
tinued for two or three hours or more; and at such times, the 
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 
the circle was found not to conduct the thermo current (801). 
In these cases, also, on examining the cadmium, the coat of 
sulphuret was strongly adherent, and this was more especially 
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. Zinc. 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 
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. Hence, therefore, a very 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 
(868), 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 proto sulphuret of potassium, or bihydro- 
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 plati- 
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, gold, etc. Lead is positive to platinum, 
then the current falls, but does not cease. Bismuth is also 
positive at first, 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 



VIII 1 

9. ON THE SOURCE OF POWER IN THE VOLTAIC PILE Con- 
tinued, ^f iv. THE EXCITING CHEMICAL FORCE AFFECTED 
BY TEMPERATURE. ^[ V. THE EXCITING CHEMICAL FORCE 
AFFECTED BY DILUTION. ^[ vi. DIFFERENCES IN THE ORDER 
OF THE METALLIC ELEMENTS OF VOLTAIC CIRCLES. ^f vii. 
ACTIVE VOLTAIC CIRCLES AND BATTERIES WITHOUT METALLIC 
CONTACT. ^| vili. CONSIDERATIONS OF THE SUFFICIENCY 
OF CHEMICAL ACTION, ^f ix. THERMO-ELECTRIC EVIDENCE. 
^[ X. IMPROBABLE NATURE OF THE ASSUMED CONTACT FORCE 

^f iv. The Exciting Chemical Force affected by Temperature 

901. ON the view that chemical force is the origin of the electric 
current in the voltaic circuit, it is important that we have the 
power of 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. De 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. 2 My object was to add to 
the argument by using but oae 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 

1 Seventeenth Series, original edition, vol. ii. p. 59. 
1 Annales de Chimie, 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 A, 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 effect 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 at 
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. 1 The pre- 
caution against this effect was hot to put the metals into the 
acid until the proper temperature had been given to both parts 
of it, 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 o. 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 8o. 2 
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. 

2 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. 



274 Faraday's Researches 

strong solution of sulphuret of potassium (800), fig. 70; and 
the galvanometer was soon at o. 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 coo! ing 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 16. 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 i 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. 1 I have not been 
able to obtain this nullity of effect at the positive electrode 

1 Bibliothtque 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. 71, 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 wiH often be very much deranged, 
or even entirely falsified. 



Voltaic Excitement 277 

918. Thus the best mode of experimenting (903) is to heat 
the liquid in the limb A or B, 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 different 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 potassa 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 i. 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 sulphur et 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 add 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, 
is a good conductor (807). When the fluid was diluted, and 
of specific gravity 1070, like that before used (920), the effect 
was only i, and cannot therefore be confounded with the 
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. 
On trial it was found that the thermo current of an antimony- 
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 
electrolytes which can act on them produces considerable cur- 
rents, it be then said that though the metals which are inactive 
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 
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 of 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 sulphur et 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 potassa. 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 



280 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 add (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 difference, 
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, 
989). 

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 sulphur et 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 
concerned ; and so cases may easily be produced, in which that 
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 
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). 

946. The distinction between currents founded upon that 
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. 1 De la Rive in 1836 gave a still more 
precise enunciation of such a principle, 2 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 
nature of acid and other compound electrolytes. 3 

Cases of two Metals and one Electrolyte ; one Junction being 
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. 
* Annales de Chimie, 1836, Ixi. p. 44, etc. 
8 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 sulphur et 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 differ- 
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; 
i.e. 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. 1 In 1828 De la Rive carried 
these and similar cases much further, especially in voltaic com- 
binations of copper and iron with lead. 2 In 1827 Becquerel 3 
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 4 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. 





Fig. 72. Fig 73. 

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, 5 but whose influence in the 
present researches requires explanation. 

960. Figs. 72 and 73 represent the two arrangements pf 
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 m, 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. 

1 Annales de Chimie, 1823, xxii. p. 361. * Ibid. 1828, xxxvii. p. 234. 
3 Ibid. 1827, xxxv. p. 120. * Ibid. 1828, xxxvii. pp. 240, 241. 

6 Traite de I'Electriciti, 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, 1 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. 1 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 

1 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 sulphuric acid. I prepared an acid 
of 49 by weight, 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 powerfully 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. W T ith 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. W T ith 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 Faraday's Researches 

970. I know it may be said in reference to the numerous 
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 
with chemical force (862, 944, 973, 994, 1002, 1051); or it may 
be alleged that it is the contact force of the solutions produced 
at the metallic surfaces which, differing, causes difference of 
effect; but this is to put the effect before the cause in the order 
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 
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 
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 
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 



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 the 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 effect 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 contrary, 



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 
strong acid at B, and diluted at 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 
instead 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 



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 x 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 metals 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 

1 Annales de Chimie, 1828, xxxvii. p. 240. 



292 Faraday's Researches 

in strength. Still there were great variations in degree; thus 
iron in strong acid was only a little positive to silver in weak 
acid, but iron in weak acid was very positive to silver in strong 
acid. Generally the metal, usually called positive, was most 
positive in the weak acid ; but that was not the case with lead, 
tin, and zinc. 

984. Two metals in strong and weak nitric acid. Here the 
degree of change produced by difference in the strength of the 
acid was so great as to cause not merely difference in degree, 
but inversions of the order of the metals, of the most striking 
nature. Thus iron and silver being in tube No. 2 (962), which- 
ever metal was in the weak acid was positive to the other in the 
strong acid. It was merely requisite to raise the one and lower 
the other metal to make either positive at pleasure (963). 
Copper in weak acid was positive to silver, lead, or tin in strong 
acid. Iron in weak acid was positive to silver, copper, lead, 
zinc, or tin in strong acid. Lead in weak acid was positive to 
copper, silver, tin, cadmium, zinc, and iron in strong acid. 
Silver in weak acid was positive to iron, lead, copper, and, 
though 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, 
copper, 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 
circuits containing this acid, merely by the effect of dilution; 
so 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, 
with the exception of silver positive to copper. The order of 
these five metals only may therefore be varied about one 
hundred different ways in the same acid, merely by the effect 
of dilution. 

986. So also zinc, tin, cadmium, and lead; and likewise zinc, 
tin, iron, and lead, being groups each of four metals; any one 
of these metals may be made either positive or negative to any 
other metal of the same group, by dilution of this acid. 

987. But the case of variation by dilution may, as regards the 



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, are 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 electrolyte 
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, fig. 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 m 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 

current. 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). 

^f 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 1 (678); and in 1828 De la Rive 
showed many inversions in different cases 2 (865); gave a strong 
contrast in the order of certain metals in strong and dilute nitric 
acid; 3 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. 4 

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 in 

1 Elements of Chemical Philosophy, p. 149. 

2 Annales de Chimie, 1828, xxxvii. p. 232. 

3 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 ! 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 

duced, 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 lead, 

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. 

^f 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 l (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 

1 Philosophical Transactions, 1834, p. 426. 



Voltaic Circles without Metallic Contact 299 

simple circuit, without any contact of metals (615, etc.). It 
was further shown that when a pair of zinc and platinum plates 
were excited at one end of the dilute nitro-sulphuric acid (615), 
or solution of potash (619), or even in some cases a solution of 
common 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. 

1006. 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 (819), or 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. 

1008. 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. 

Dilute nitric acid 

Dilute sulphuric acid 

Muriatic acid 

Solution of vegetable acids 

Iodide of potassium 

Iodide of zinc 

Solution of salt 

Many metallic solutions 

a 



Rhodium . 
Gold 


S-g 


Platinum 
Palladium 
Silver 


'3 

88 G 
n -~ 


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Copper 
Lead 


v B~o 

. in 
b 


Tin 


bpg 


Zinc 


o is 

t* to 


Cadmium ' 


OQ 


L 576 



Iron 



300 Faraday's Researches 

1008 



g q a. g a. a. to bcT3 ex sc so 

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s o CT 30=500=50000000 PP^ Pop 

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i--aisfiiiasll s s e -1 

* S2 3 3 3 3 9 3 9 3 * *,- B 1_ 3,- 3 
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3333333333333333 



ss s 

."2 12.2.2 .H!2 

O O 'S> t/1 c/i *o 

r3 ft; t/i tf) "'pj 

o -o 00-2.22:22. "2 .So 

o 'o -ri-r: o o q q q q o-r! 

Cg Cy CO CD 




S S 

U U U IH IH U, 



Batteries Without Metallic Contact 301 

ioio. To these cases must be added the many in which one 
metal in a uniform acid gave currents when one side was heated 
(93; etc.). Also those in which one metal with an acid strong 
and diluted gave a current (965, etc.). 

ion. 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 iSoi, 1 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, 2 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. 




Fig. 75- 

1013. Let ab,ab,ab, 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 > 

1 Philosophical Transactions, 1801, p. 397. Also Journals of the Royal 
Institution, 1802, p. 51; and Nicholson's Journal, 8vo, 1802, vol. i. p. 144. 

2 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 
J j 3; 5) etc - contain strong sulphuric acid, and the vessels 
2, 4, 6, etc. dilute sulphuric acid; and if the metals a, 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 remaining; or the acids 
be changed, the metals remaining; the direction of the current 
will be reversed. 




Fig. 76. 

^f 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. Becquerel's 
beautiful voltaic arrangement of acid and alkali x 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 

1 Annales de Chimie, 1827, xxxv. p. 122. Bibliotheque 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, which 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 o, 
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 act, 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, 
813, 817). These are very 
striking facts. 

1027. But a current will occur 
the moment chemical action com- 
mences. This proposition may 
be well illustrated by the fol- 
Fi lowing experiment. Make an 

arrangement like that in fig. 
77: the two tubes being charged with the same pure, pale, 
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 varv 

separated by a drop of strong nitric r. , ^ ^\ 

acid at each extremity. Whilst in platinum, 

this state no current is produced in Fig. 78. 

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 x 
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 i835, 2 and came to the con- 
clusion, but reservedly expressed, that the facts were favourable 
to the theory of contact. In the following year De la Rive 
examined the subject, 3 and shows, to my satisfaction at least, 
that the peroxide is at the time undergoing chemical change 
and losing oxygen, 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 4 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 changes. 5 M. Schoenbein 

1 Annales de Chimie, 1802, xl. 224. * Ibid. 1835, Ix. 164, 171. 

3 Ibid. 1836, Ixi. 40; and Bibliotheque Universelle, 1836, i. 152, 158. 

4 Bibliotheque Universelle, 1836, i. 160. 8 Ibid. 1836, i., 154 162. 



306 Faraday's Researches 

does not admit this inference, and bases his view of " currents 
of tendency " on the phenomena presented by this body and 
its non-action with nitric acid. 1 My own results confirm 
those of M. de la Rive, for by direct experiment I find that 
the peroxide is acted upon by such bodies as nitric acid. Potash 
and pure strong nitric acid boiled on peroxide of lead readily 
dissolved it, forming protonitrate of lead. A dilute nitric 
acid was made and divided into two portions; one was tested 
by a solution of sulphuretted hydrogen, and showed no signs 
of lead: the other was mingled with a little peroxide of lead 
(810) at common temperatures, and after an hour filtered and 
tested in the same manner, and found to contain plenty of lead. 

1032. The peroxide of lead is negative to platinum in solutions 
of common salt and potash, bodies which might be supposed 
to exert no chemical action on it. But direct experiments 
show that they do exert sufficient action to produce all the 
effects. A circumstance in further proof that the current in 
the voltaic circuit formed by these bodies is chemical in its 
origin is the rapid depression in the force of the current pro- 
duced, after the first moment of immersion. 

1033. The most powerful arrangement with peroxide of lead, 
platinum, and one fluid, was obtained by using a solution of 
the yellow sulphuret of potassium as the connecting fluid. A 
convenient mode of making such experiments was to form the 
peroxide into a fine soft paste with a little distilled water, to 
cover the lower extremity of a platinum plate uniformly with 
this paste, using a glass rod for the purpose, and making the 
coat only thick enough to hide the platinum well, then to dry 
it well, and finally, to compare that plate with a clean platinum 
plate in the electrolyte employed. Unless the platinum plate 
were perfectly covered, local electrical currents took place 
which interfered with the result. In this way, the peroxide is 
easily shown to be negative to platinum either in the solution 
of the sulphuret of potassium or in nitric acid. Red lead gave 
the same results in both these fluids. 

1034. But using this sulphuretted solution, the same kind 
of proof in support of the chemical theory could be obtained 
from protoxides as before from the peroxides. Thus, some 
pure protoxide of lead, obtained from the nitrate by heat and 
fusion, was applied on the platinum plate (1033), and found to 
be strongly negative to metallic platinum in the solution of 

1 Philosophical Magazine, 1838, xii. 226, 311; and Biblioth&que Univer- 
selle, 1838, xiv. 155. 



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 
film 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 
hypothetical. 

^[ 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 l (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 circuit, 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 




\\\\\\\\\\\\\\\\Y/y///7///v>: 



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. ^ f r tnat 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: 2 
how is it consistent with the contact theory of the voltaic pile? 

1046. Again, if silver and antimony form a thermo circle 

1 See Fechner's words. Philosophical Magazine, 1838, xiii. p. 206. 
J 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 
^ 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- 
Fig. 81. muth at their points of contact, 

whenever dilute sulphuric or nitric 

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 
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; 
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, 
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- 
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 



Thermo-Electric and Voltaic Effects 3 1 r 

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- 
quired, 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 (1000), 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 1 are quite sufficient to authorise 
that conclusion. 

1 Annales de Chimie, 1829, xli. 355; xlvi. 275. 



312 Faraday's Researches 



^f x. Improbable Nature cf 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 point, 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 3 1 3 

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 x ); 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 ? 2 

1 Memorie delta Societa Italiana in Modena, 1837, xxi. 232, 233, etc. 

2 1 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 which yet are equally strong in 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 oi 
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 power, 
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 CErsted 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 

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 3 i 5 

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 Yolta, 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 Becquerel's pile is a 
perfect proof that when acid and alkali combine an electric 
current is produced. 1 

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. 2 

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 Becquerel's 
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 

1 Bibliotheque Universelle, 1838, xiv. 129, 171. Comptes Rendus, i. p. 455. 
Annales de Chimie, 1827, xxxv. 122. 

1 Philosophical Magazine, 1838, xiii. p. 382; or Poggendorf's Annalcn, 
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, 6So), still the latter 
circumstance cannot go altogether for nothing. The researches 
of Mr. Daniell on the nature of compound electrolytes l 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 the 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 Daniell's electrolysations, and at the zinc 
in the ordinary active pile, are, in principle, closely connected 
together. 

1 Philosophical Transactions, 1839, p. 27. 



CORRESPONDENCE ON ELECTRICITY 
FROM THE "PHILOSOPHICAL MAGAZINE," ETC. 

On a peculiar Voltaic Condition of Iron, by Professor SCHOEN- 
BEIN, of Bale; in a Letter to Mr. Faraday: with further 
Experiments on the same subject, by Mr. FARADAY, com- 
municated in a Letter to Mr. Phillips. 1 

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 Land, and Edinb. Phil. Mag., 1836, vol. ix. p. 53. 

3 1 ? 



3 1 8 Faraday's Researches 

beyond a certain quantity, for instance, i, 10, 100, and even 
1000 times its volume. By immersing an iron wire in nitric 
acid of sp. gr. 1.5 it becomes likewise indifferent to the same 
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 
are then introduced into nitric acid of sp. gr. 1.35, so as to 
immerse the oxidised end of the one wire first into the fluid, 
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 
the second wire having become indifferent be now taken out of 
the acid and made to touch at any of its parts not having been 
immersed a third wire, and both again introduced into the 
acid so as to make that part of the second wire which had pre- 
viously been in the fluid enter first, neither of the wires will be 
acted upon either during their contact or after their separation. 
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 
observed, is the following one. A wire made indifferent by 
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 
out of the fluid; another common wire is put into the same 
acid, likewise having one of its ends rising above the level of 
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 
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 
for communicating chemical activity from the active wire to 
the passive one; for any metal connecting the two ends of the 
.wires renders the same service. 

Before passing to another subject, I must mention a fact 



A Peculiar Condition of Iron 3 1 9 

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 form of the 
pile called the couronne des tasses, 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 found, 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 Peculiar Condition of Iron 321 

immersed 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 itself, 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 Schoen- 
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 Philosophical 
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 rather the request with which he has 
honoured me), to add a few results in confirmation of the effects 



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 flat 
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 effect 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 well 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 equally 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 
I 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 does 
nothing, whereas with the zinc it develops the full force of that 



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 electrolyte 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 we'll 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 lasses. 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 vohaic 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 rapidly 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 latter 
metal being merely the conductor interposed between the silver 
and the copper extremities of the metallic arrangement. 

I am afraid you will think I have pursued this matter to a 
greater length than it deserves; but I have been exceedingly 



33 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. 1 I am, my dear Phillips, very truly yours, 

M. FARADAY. 

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 
reobserved by Professor SCHOENBEIN, supplementary to a 
Letter to Mr. Phillips, in the last Number? 

ROYAL INSTITUTION, July 8, 1836. 

MY DEAR SIR, I am greatly your debtor for having pointed 
out to me Sir John F. W. Herschel's paper on the action of 
nitric acid on iron in the Annales de Chimie et de Physique ; 
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 regret 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 Herschel's results. However, I hope the 
editors of the Phil. Mag. 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. 

" Bergman relates that upon adding iron to a solution of 
silver in the nitrous acid no precipitation ensued." 3 

Keir, who examined this action in the year ijgo, 4 made many 
excellent experiments upon it. He observed that the iron 
acquired a peculiar or altered state in the solution of silver; 

1 Exp. Researches, Pars. 682, 732. 

! Lond. and Edinb. Phil. Mag. 1836, vol. ix. p. 122. 

Phil. Trans. 1790, p. 374. * Ibid. pp. 374, 379. 



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 2 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 i833. 3 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 4 
(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 

1 Annales des Mines, 1832, vol. ii. p. 322; or Mag. de Pharm. 1830. 
1 Annales de Chimie et de Physique, vol. Hi. p. 288. 
* Ibid. 1833, vol. liv. p. 87. Phil. Trans. 1836, p. 114. 

M 576 



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 oxygen, are 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. 
London Institution. 



INDEX 



ACETATES, electrolysis of, 136, 143 
Acetic acid, electrolysis of, 142 
Acid and alkali, transference of, 72, 

80, 193 
Acids and bases, combination of, 315 ; 

relation in voltaic pile, 189 
Air, effect on voltaic excitement, 

274; as electric pole, 48, 50, 82 
Ammonia a non-conductor, 81, 135 
Anions, described, 114, 157; action 

in voltaic circle, 200 
Anode described, 113, 157 
Antimony compounds, electrolytic 

properties of, 120; voltaic effects 

in sulphuret of potassium, 267 
Arsenic acid, 118 
Atmospheric electricity, 19 
Attraction, chemical, modes of 

action, 195; hygrometric, 99, 100; 

of particles, 98, 100 

Barry on decomposition by atmo- 
spheric electricity, 20 

Battery. See Voltaic battery 

Biot, theory of electro-chemical de- 
composition, 58 

Bismuth, voltaic effects in sulphuret 
of potassium, 265 

Bonijol on decomposition by atmo- 
spheric electricity, 19 

Cadmium, voltaic effects in sulphuret 
of potassium, 268 

Carbonic oxide, combining power of 
platina prevented by. 106 

Cathode, described, 113, 157; ex- 
citement at, 298, 306 

Cations, described, 114, 157; table 
of, 161 

Cavendish cited, I, 16 

Charges, chemical, for battery, 227; 
exhaustion of, 230 

Chemical action, affected by_ tem- 
perature, 271, 274; essential for 
excitement in voltaic pile, 304; 
source of electricity, 179, 180, 181, 
184, 185, 190, 233, 302 

Chloride of lead, electrolysis of, 208; 
fused, as conductor, 35 



Chloride of sulphur, electrolysis of, 
119 

Chloride of tin, electrolysis of, 146 

Chlorides, fused, electrolysis of, 146, 
154; in solution, electrolysis of, 141 

Colladon cited, i, 8 

Combined bodies, transference of, 76 

Common electricity, 7; chemical de- 
composition by, 12; evolution of 
heat by, 7; identity with voltaic 
electricity, 31 ; physiological effects 
of, 28 ; spark produced by, 19 

Conducting circles. See Voltaic 
circles. 

Conduction, 41, 46; bodies not sub- 
ject to law of, 38; bodies subject 
to law of, 37; consequent on 
fusion, 35 ; new law of, 32 

Conductors, particular, liquid and 
solid, 238, 240 

Contact theory of voltaic electricity, 
232, 233, 243, 244, 253, 257, 263, 
281, 288, 294, 308 

Copper, voltaic effects in sulphuret 
of potassium, 266 

Correspondence on electricity by 
author, 317 

Current, voltaic, denned, 6, 172; 
various views of, 66 

Cyanides in solution, decomposition 
of, 142 

Davy, Sir Humphrey, i, 2, 57 
Decomposition, electro-chemical, by 
animal electricity, 25 ; by com- 
mon electricity, 12 ; by single pair 
of plates, 167, 178, 180; by single 
pole, 49 ; chemical affinity of par- 
ticles in, 69, 72, 79 ; conditions of, 
47, 115; constant electrolytic 
action in, 122, 125 ; definite nature 
and extent of, 145 ; dependent on 
electric current, 60, 66,71; elec- 
trolytic intensity necessary for, 
206; experiments with various 
substances (q.v.), 118-154; general 
propositions relating to, 157; in air, 
50; by magneto-electricity, 23 ; op- 
posed distant chemical actions in, 



333 



334 



Faraday's Researches 



177; polar, 12, 15, 53; resistance 
of electrolyte to, 218; retarding 
effect of interposed plates, 218- 
225; secondary results of, 144; 
theories of, 55, 60, 68; trans- 
ference of elements in, 69, 72, 76; 
w?ter, influence of, 54; without 
metallic contact, 173, 175, 177 

De la 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 
effected 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; therrno- 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 

Heat, 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 acid, electrolysis of, 141 

Hydrogen and oxygen, action of 
platina on, 86, 94, 102; and 
spongy platina, 108 

Ice a non-conductor of electricity, 

32, 4i 

Identity of electricities, i, 7, 26 
Iodide of potassium, .conduction by, 

41; electrolysis of, 207; test of 

chemical action, 14 
Iodides, fused, electrolysis of, 151; 

in solution, electrolysis of, 141 
Ions, 157, rox, 162; mutual rela- 
tions in circuit, 200; table of, 161 
Iron, Faraday on voltaic condition 

of, 321, 330; Schonbein on voltaic 

condition of, 317 

Lead, voltaic effects in sulphuret of 

potassium, 262 
Liquefaction, conduction consequent 

upon, 32, 35, 39, 46 

Magnetic effects of animal electricity, 

25 ; of common electricity, 7 ; 

of magneto-electricity, 23; of 

thermo-electricity, 24; of voltaic 

electricity, 5, 7 
Magneto-electricity, 22 
Marianini on source of power in 

voltaic pile, 233, 234, 261 
Matter, quantity of electricity in, 1 63 
Measure for volta-electricity, 122 
Metal, poles of, 82 

Metallic contact. See Contact theory 
Metals, order as electromotors, 295 ; 

power of inducing combination, 

300 
Muriatic acid, electrolysis of, 139; 

order of metals as electromotors 

in, 298 

Nitric acid, 118, 240; electrolysis 

of, 137 
Nitrogen determined to either pole, 

81, 135, 137 
Nitrous acid in voltaic circles, 239, 

248 



Index 



335 



Olefiant gas, combining power of 

platina prevented by, 105, 108 
Oxide of lead, electrolysis of, 149 
Oxygen and hydrogen, action of 
platina on, 86, 94, 102 

Particles, nascent state of, no 

Periodide of mercury, 120 

Phosphoric acid not an electrolyte, 
118 

Physiological effects of common 
electricity, 18; of magneto - elec- 
tricity, 23; of thermo-electricity, 
24; of voltaic electricity, 5 

Plates, interposed, causing retarda- 
tion of electrolysis, 218-225 

Platina, cleanliness essential, 98, 
103; combining power of, 85-91, 
4, 98, 102 interferences with, 
105; spongy, in relation to 
hydrogen, 104, 107, 108 

Polar decomposition, 12, 15, 53 

Polarised light in relation to elec- 
trolyte, 197 

Pole denned, 112 

Poles, electric, nature of, 50, 63, 82 ; 
evolved bodies at, 75 character 
"f, 133; of air, 48, 50, 82; of 
metal, 82; of platina, 83, 85, 90; 
of water, 61, 74, 81 

Potassium nitrate, electrolysis of, 
209 

Potassium, sulphuret of. See Sul- 
phuret of potassium 

Protochloride of carbon, 119 

Protosulphuret of potassium as 
electrolyte, 269 

Riffault and Chompre on electro- 
chemical decomposition, 58, 66 

Schonbein on voltaic condition of 
iron, 316 

Silver chloride, electrolysis of, 76, 
154, 208; voltaic effects in sul- 
phuret of potassium, 268 

Spark, produced by animal elec- 
tricity, 25; by common electri- 
city, 19; by magneto-electricity, 
23; by thermo-electricity, 24; 
by voltaic electricity, 5 ; without 
metallic contact, 198 

Sulphate of soda, electrolysis of, 
206 

Sulphuret of antimony not an elec- 
trolyte, 1 20 

Sulphuret of carbon, combining 
power of platina prevented by, 
107 



Sulphuret of potassium, active 

circles excited by, 259, 265; 

alternating currents in, 270; and 

heated metals, 279, as conductor, 

238, 241 
Sulphuret of silver, conducting 

power of, 44 
Sulphuretted solutions, exciting 

action of, 194 
Sulphuric acid, conduction by, 38, < 

72, 138, 188, 240 
Sulphurous acid, electrolysis of, 

138 

Tartaric acid, electrolysis of, 143 

Thermo - currents in electrolytes, 
277 

Thermo-electricity, 24 

Thermo-electric phenomena, 308 

Tin, voltaic effects in sulphuret of 
potassium, 261 

Torpedo fish, electric discharge of, 
26 

Transference of bodies. See Decom- 
position, electro-chemical 

Volta-electrometer, 84, 122 

Voltaic battery, 211; current in, 
212, 213; in action, general 
remarks on, 226-232; without 
metallic contact, 298; zinc in, 
214, 215 

Voltaic circles, Fig. 43, p. 201; 
active, 259; associated, 211; 
combinations of substances em- 
ployed in, 256; effect of air, 274; 
effect of dilution, 284, 290; effect 
of interposed plates, 218-225; 
effect of motion of fluids, 273; 
effect of temperature, 271, 274, 
279, 281; inactive, 241 et seq.; 
order of metals in, 295; proto- 
sulphuret of potassium in, 269; 
relation of ions in, 200; simple, 
172; sulphuret of potassium in, 
238, 241, 259, 265; without 
metallic contact, 175, 298 

Voltaic current, 6, 175 

Voltaic electricity, 3; chemical 
action as source of, 179, 180, 181, 
185, 190, 282; chemical effects of, 
5; discharged by hot air, 4; 
evolution of heat by, 5; identity 
with common electricity, 8, 12, 
16, 31; magnetic force of, 5, 7; 
physiological effects of, 5; rela- 
tion by measure to common 
electricity, 27; spark produced 
by, 5 



33 6 



Faraday's Researches 



Voltaic forces, elementary, 183 
Voltaic pile, 165 ; action of elements 
of, 195, 196; chemical theory of 
origin, 179, 180, 181, 184, 185, 190, 
233, 302 ; contact theory of origin, 
232, 234, 243, 244, 253, 257, 263, 
281, 288, 294, 308, 312; elec- 
tricity of, 170, 172, 183; 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 



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, 81 ; 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 



PRINTED BY THE TEMPLE PRESS AT LETCHWORTH IN GREAT BRITAIN 



EVERYMAN'S LIBRARY 

SELECTED SECTIONS 

(Full Catalogue on Application) 

POETRY AND DRAMA 

41 Browning's Poems, 1833-1844. Intro, by Arthur Waugh 

42 1844-1864 

43 Golden Book of Coleridge. Edited by Stopford A. Brooke 

44 Tennyson's Poems. Vol. I., 1830-1856. Intro, by Ernest Rhys 

94 Burns' Poems and Songs. Intro, by J. Douglas 

95 Sheridan's Plays 

96 Palgrave's Golden Treasury. Intro, by Edward Hutton 
101 Keats' Poems 

148-149 Percy's Reliques of Ancient English Poetry. 2 vols. 
150 Proctor's Legends and Lyrics 

153 Shakespeare's Comedies 

154 Historical Plays, Poems and Sonnets 

155 Tragedies 

203 Wordsworth's Shorter Poems. Intro, by Ernest Rhys 

257-258 Shelley's Poetical Works. 2 vols. Intro, by A. H. Koszul 

307 Chaucer's Canterbury Tales. Edited by Principal Burrell, M.A. 

308 Dante's Divine Comedy (Gary's Translation). Specially edited 

by Edmund Gardner 

309 Herbert's Temple. Intro, by Edward Thomas 

310 Herrick's Hesperides and Noble Numbers. Intro, by Ernest Rhys 

311 Wordsworth's Longer Poems. Note by Editor 

334 Matthew Arnold's Poems, 1840-1866, including Thyrsis 

335 Goethe's Faust. Parts I. & II. Trans, and Intro. A. G. Latham 

381 Everyman and other Interludes, including eight Miracle plays. 

Edited by E. R. 

382 Longfellow's Poems. Intro. Katherine Tynan 

383 Marlowe's Plays and Poems. Intro, by Edward Thomas 

384 Milton's Poems. Intro, by W. H. D. Rouse 

415 Goldsmith's Poems and Plays. Intro, by Austin Dobson 
443-444 Spenser's Faerie Queene. Intro, by Prof. J. W. Hales. 2 vols. 
486-488 Byron's Poetical and Dramatic Works. 3 vols. 
489-490 Ben Jonson's Plays. Intro, by Prof. Schelling. 2 vols. 
491-492 Minor Elizabethan Drama. Vol. I. Tragedy. Selected, with 
Intro, by Prof. Thorndike. Vol. II. Comedy 

494 Ibsen. The Doll's House, etc. Trans. R. Farquharson Sharp 

502 Browning's The Ring and the Book. Intro, by Chas. W. Hodell 

503 The Old Yellow Book. Intro, by Charles W. Hodell 

506 The Select Plays of Beaumont and Fletcher. Intro, by Prof. 

Baker, of Harvard University 
550-551 Scott's Poems and Plays. 2 vols. Intro, by Andrew Lang 

552 Ibsen's Ghosts and other plays. Trans, by R. Farquharson Sharp 

571 Piers Plowman. By William Langland 

572 A Book of British Ballads. Selected by R. B. Johnson 

573 Leaves of Grass (I.), Democratic Vistas, etc. By Walt Whitman 

574 A Volume of Heroic Verse. Arranged by Arthur Burrell, M.A. 
604 A Volume of Restoration Plays. Intro, by Edmund Gosse 

625 BjSrnson, Three Comedies. Trans, by R. Farquharson Sharp 

626 Tennyson's Poems. Vol. II., 1863 1870 

627 Rossetti's Poems and Translations. Intro, by Edmund G. 

Gardner 

628 Gray's Poems and Letters. Intro, by John Drinkwater 

629 Shakuntala. An Indian Drama. By Kalidasa. Trans, by 

Prof. W. H. Ryder 
659 Ibsen's Plays. I. Trans, by R. Farquharson Sharp 

694 Hebbel's Plays. Trans., with an Intro., by Dr. C. K. Allen 

695 The New Golden Treasury. An Anthology of Songs and Lyrics. 

Edited by Ernest Rhys 

696 Bjornson's Plays. Vol. II. Trans, by R. Farquharson Sharp. 

" The Editor," " The Bankrupt," and " The King " 

715 Emerson's Poems. Intro, by Professor Bakewell (Yale, U.S.A.) 

716 Ibsen's Brand. Translated by F. E. Garrett 

729 Henrik Ibsen's Lady Inger of Ostraat, Love's Comedy, and The 
League of Youth. Translated by R. Farquharson Sharp 

746 The Golden Treasury of Longer Poems. Edited by Ernest Rhya 

747 Ibsen'a Peer Gynt. Trans, by R. Farquharson Sharp 



REFERENCE 

449 A Biographical Dictionary of English Literature 
451 Atlas of Ancient and Classical Geography 

495 Smith's Smaller Classical Dictionary. Revised and Edited by 

E. H. Blakeney, M.A. 

496 Literary and Historical Atlas. I. Europe. Containing 96 

coloured and many line Maps; also full Index and Gazetteer 

553 Do. Do. Do. II. America 

554 A Dictionary of Dates 

555 Wright's An Encyclopaedia of Gardening 

630-631 Roget's Thesaurus of English Words and Phrases. 2 vols. 

632 Dictionary of Non-Classical Mythology 

633 A Literary and Historical Atlas of Asia 
641-652 The Everyman Encyclopaedia. 12 vols. 

662 A Literary and Historical Atlas of Africa and Australia 

SCIENCE 

47 Huxley's Essays. Intro, by Sir Oliver Lodge 

48 White's Selborne. Intro, by Principal Windle 

98 Tyndall's Glaciers of the Alps and Mountaineering in 1861 

103 Miller's Old Bed Sandstone 

104 Darwin's Voyage of the Beagle 

262 Harvey's Circulation of the Blood. Intro, by Ernest Parkyn 

263 Galton's Inquiries into Human Faculty. Revised bv Author 
412-413 Adam Smith's The Wealth of Nations. 2 vols. 

498 Huxley's Select Lectures and Lay Sermons. Intro, by Sir 

559 Boyle's The Sceptical Chymist [Oliver Lodge 

560 George's (Henry) Progress and Poverty 

576 Experimental Researches in Electricity. By M. Faraday 
590 Ricardo's Principles of Political Economy and Taxation 

663 The Organon of the Rational Art of Healing. By Samuel 

Hahnemann. Intro, by C. E. Wheeler 
660 The Social Contract, etc. By Jean Jacques Rousseau 
700 Lyell's Antiquity of Man. With an Intro, by R. H. Rastail 

TRAVEL AND TOPOGRAPHY 

49 Sorrow's Wild Wales. Intro, by Theodore Watts- Dunton 

50 Speke's Discovery of the Source of the Nile 

99 Cook's Voyages of Discovery 

151 Sorrow's The Bible in Spain. Intro, by Edward Thomas 

152 Ford's Gatherings from Spain. Intro, by Thomas Okey 
183-184 Dennis' Cities and Cemeteries of Etruria. 2 vols. 

205 Travels of Mungo Park. Intro, by Ernest Rhys 
264, 265, 313, 314, 338, 339, 388, 389. Hakluyt's Voyages. 8 vols. 
272 Giraldus Cambrensis. Itinerary and Description of Wales 
306 Marco Polo's Travels. Intro, by John Maseneld 
315 Lane's Modern Egyptians. With many Illustrations 
337 Kinglake's Eothen. Intro, by Harold Spender, M.A. 
387 Boswell's Tour in the Hebrides with Dr. Johnson 
390 Lytton's Pilgrims of the Rhine 

446 Bates' Naturalist on the Amazon. With Illustrations 

447 Franklin's Journey to the Polar Sea. Intro, by Capt. R. F. Scott 

499 Lord Dufferin's Letters from High Latitudes 

500 Sir Richard Burton's First Footsteps in East Africa 
510 Anson's Voyages. Intro, by John Maseneld 

561 Belt's The Naturalist in Nicaragua. Intro. Anthony Belt, F.L.S. 
589 Stow'e Survey of London. Introduction by H. B. Wheatley 

638-639 Cobbett's Rural Rides. 2 vols. Intro, by Edward Thomas 

640 Letters from an American Farmer. By H. St. John Crevecceur 

664 Life in Mexico. By Mme. Calderon de la Barca 

697 George Sorrow's Gypsies in Spain. Intro, by Edward Thomas 
720 Young's Travels in France and Italy. Intro, by Thomas Okey 



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