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Title: Experimental Researches in Electricity, Volume 1

Author: Michael Faraday

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*** START OF THE PROJECT GUTENBERG EBOOK
EXPERIMENTAL RESEARCHES IN ELECTRICITY, VOLUME 1 ***

E-text prepared by Paul Murray, Richard Prairie,
and the Project Gutenberg Online Distributed Proofreading Team
from images generously made available by
the Bibliothèque nationale de France (BnF/Gallica)
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Experimental Researches In Electricity.
By Michael Faraday, D.C.L. F.R.S.

Fullerian Profesor Of Chemistry In The Royal Institution. Corresponding
Member, Etc. Of The Royal And Imperial Academies Of Science Of Paris,
Petersburgh, Florence, Copenhagen, Berlin, Gottingen, Modena,
Stockholm, Palermo, Etc. Etc.

In Two Volumes.

Vol. I.

Second Edition.

Reprinted from the Philosophical Transactions of 1831-1838.

London: Richard And John Edward Taylor, printers And Publishers To The
University Of London, Red Lion Court, Fleet Street. 1849.

Preface.
I have been induced by various circumstances to collect in One Volume the
Fourteen Series of Experimental Researches in Electricity, which have
appeared in the Philosophical Transactions during the last seven years: the
chief reason has been the desire to supply at a moderate price the whole of
these papers, with an Index, to those who may desire to have them.

The readers of the volume will, I hope, do me the justice to remember that it
was not written as a whole, but in parts; the earlier portions rarely having
any known relation at the time to those which might follow. If I had
rewritten the work, I perhaps might have considerably varied the form, but
should not have altered much of the real matter: it would not, however, then
have been considered a faithful reprint or statement of the course and
results of the whole investigation, which only I desired to supply.

I may be allowed to express my great satisfaction at finding, that the
different parts, written at intervals during seven years, harmonize so well as
they do. There would have been nothing particular in this, if the parts had
related only to matters well-ascertained before any of them were written:—
but as each professes to contain something of original discovery, or of
correction of received views, it does surprise even my partiality, that they
should have the degree of consistency and apparent general accuracy which
they seem to me to present.

I have made some alterations in the text, but they have been altogether of a
typographical or grammatical character; and even where greatest, have been
intended to explain the sense, not to alter it. I have often added Notes at the
bottom of the page, as to paragraphs 59, 360, 439, 521, 552, 555, 598, 657,
883, for the correction of errors, and also the purpose of illustration: but
these are all distinguished from the Original Notes of the Researches by the
date of Dec. 1838.

The date of a scientific paper containing any pretensions to discovery is
frequently a matter of serious importance, and it is a great misfortune that
there are many most valuable communications, essential to the history and
progress of science, with respect to which this point cannot now be
ascertained. This arises from the circumstance of the papers having no dates
attached to them individually, and of the journals in which they appear
having such as are inaccurate, i.e. dates of a period earlier than that of
publication. I may refer to the note at the end of the First Series, as an
illustration of the kind of confusion thus produced. These circumstances
have induced me to affix a date at the top of every other page, and I have
thought myself justified in using that placed by the Secretary of the Royal
Society on each paper as it was received. An author has no right, perhaps, to
claim an earlier one, unless it has received confirmation by some public act
or officer.

Before concluding these lines I would beg leave to make a reference or two;
first, to my own Papers on Electro-magnetic Rotations in the Quarterly
Journal of Science, 1822. xii. 74. 186. 283. 416, and also to my Letter on
Magneto-electric Induction in the Annales de Chimie, li. p. 404. These
might, as to the matter, very properly have appeared in this volume, but
they would have interfered with it as a simple reprint of the "Experimental
Researches" of the Philosophical Transactions.

Then I wish to refer, in relation to the Fourth Series on a new law of
Electric Conduction, to Franklin's experiments on the non-conduction of
ice, which have been very properly separated and set forth by Professor
Bache (Journal of the Franklin Institute, 1836. xvii. 183.). These, which I
did not at all remember as to the extent of the effect, though they in no way
anticipate the expression of the law I state as to the general effect of
liquefaction on electrolytes, still should never be forgotten when speaking
of that law as applicable to the case of water.

There are two papers which I am anxious to refer to, as corrections or
criticisms of parts of the Experimental Researches. The first of these is one
by Jacobi (Philosophical Magazine, 1838. xiii. 401.), relative to the possible
production of a spark on completing the junction of the two metals of a
single pair of plates (915.). It is an excellent paper, and though I have not

repeated the experiments, the description of them convinces me that I must
have been in error. The second is by that excellent philosopher, Marianini
(Memoria della Societa Italiana di Modena, xxi. 205), and is a critical and
experimental examination of Series viii, and of the question whether
metallic contact is or is not productive of a part of the electricity of the
voltaic pile. I see no reason as yet to alter the opinion I have given; but the
paper is so very valuable, comes to the question so directly, and the point
itself is of such great importance, that I intend at the first opportunity
renewing the inquiry, and, if I can, rendering the proofs either on the one
side or the other undeniable to all.

Other parts of these researches have received the honour of critical attention
from various philosophers, to all of whom I am obliged, and some of whose
corrections I have acknowledged in the foot notes. There are, no doubt,
occasions on which I have not felt the force of the remarks, but time and the
progress of science will best settle such cases; and, although I cannot
honestly say that I wish to be found in error, yet I do fervently hope that the
progress of science in the hands of its many zealous present cultivators will
be such, as by giving us new and other developments, and laws more and
more general in their applications, will even make me think that what is
written and illustrated in these experimental researches, belongs to the by-
gone parts of science.

MICHAEL FARADAY.

Royal Institution,

March, 1839.

Contents

Contents
First Series.
§ 1. Induction of Electric Currents.
§ 2. Evolution of Electricity from Magnetism.
§ 3. New Electrical State or Condition of Matter.
§ 4. Explication of Arago's Magnetic Phenomena.
Second Series.
§ 5. Terrestrial Magneto-electric Induction.
§ 6. General remarks and illustrations of the Force and
Direction of Magneto-electric Induction.
Third Series.
§ 7. Identity of Electricities derived from different sources.
I. Voltaic Electricity.
II. Ordinary Electricity.
III. Magneto-Electricity.
IV. Thermo-Electricity.
V. Animal Electricity.
§ 8. Relation by Measure of common and voltaic Electricity.
Note respecting Ampère's inductive results
Fourth Series.
§ 9. On a new Law of Electric Conduction.
§ 10. On Conducting Power generally.
Fifth Series.
§ 11. On Electro-chemical Decomposition.
¶ i. New conditions of Electro-chemical
Decomposition.
¶ ii. Influence of Water in Electro-chemical
Decomposition.
¶ iii. Theory of Electro-chemical Decomposition.
Sixth Series.
§ 12. Power of platina, &c. to induce combination.
Seventh Series.

§ 11.* Electro-chemical Decomposition continued
(nomenclature).
¶ iv. On some general conditions of Electro-
chemical Decomposition.
¶ v. On a new measure of Volta-electricity.
¶ vi. On the primary or secondary character of the
bodies evolved at the Electrodes.
¶ vii. On the definite nature and extent of Electro-
chemical Decomposition.
§ 13. On the absolute quantity of Electricity associated with
the particles or atoms of Matter.
Eighth Series.
§14. On the Electricity of the Voltaic Pile; its source,
quantity, intensity, and general characters.
¶ i. On simple Voltaic Circles.
¶ ii. On the Intensity necessary for Electrolyzation.
¶ iii. On associated Voltaic Circles, or the Voltaic
Battery.
¶ iv. On the Resistance of an Electrolyte to
Electrolytic Action, and on Interpositions.
¶ v. General Remarks on the active Voltaic Battery.
Ninth Series.
§ 15. On the influence by induction of an Electric Current on
itself:—and on the inductive action of Electric Currents
generally.
Tenth Series.
§ 16. On an improved form of the Voltaic Battery.
§ 17. Some practical results respecting the construction and
use of the Voltaic Battery (1034. &c.).
Eleventh Series.
§ 18. On Static Induction.
¶ i. Induction an action of contiguous particles.
¶ ii. On the absolute charge of matter.
¶ iii. Electrometer and inductive apparatus
employed.
¶ iv. Induction in curved lines.

¶ v. On specific induction, or specific inductive
capacity.
¶ vi. General results as to induction.
Supplementary Note to Experimental Researches in
Electricity.—Eleventh Series.
Twelfth Series.
¶ vii. Conduction, or conductive discharge.
¶ viii. Electrolytic discharge.
¶ ix. Disruptive discharge and insulation.
The electric spark or flash.
The electrical brush.
Difference of discharge at the positive
and negative conducting surfaces.
Thirteenth Series.
¶ ix. Disruptive discharge (continued).
Glow discharge.
Dark discharge.
¶ x. Convection, or carrying discharge.
¶ xi. Relation of a vacuum to electrical
phenomena.
§ 19. Nature of the electric current.
Fourteenth Series.
§ 20. Nature of the electric force or forces.
§ 21. Relation of the electric and magnetic forces.
§ 22. Note on electrical excitation.
Index.
Notes

Experimental Researches In Electricity.

First Series.
§ 1. On the Induction of Electric Currents. § 2. On the Evolution of
Electricity from Magnetism. § 3. On a new Electrical Condition of Matter. §
4. On Arago's Magnetic Phenomena.

[Read November 24, 1831.]

1. The power which electricity of tension possesses of causing an opposite
electrical state in its vicinity has been expressed by the general term
Induction; which, as it has been received into scientific language, may also,
with propriety, be used in the same general sense to express the power
which electrical currents may possess of inducing any particular state upon
matter in their immediate neighbourhood, otherwise indifferent. It is with
this meaning that I purpose using it in the present paper.

2. Certain effects of the induction of electrical currents have already been
recognised and described: as those of magnetization; Ampère's experiments
of bringing a copper disc near to a flat spiral; his repetition with electro-
magnets of Arago's extraordinary experiments, and perhaps a few others.
Still it appeared unlikely that these could be all the effects which induction
by currents could produce; especially as, upon dispensing with iron, almost
the whole of them disappear, whilst yet an infinity of bodies, exhibiting
definite phenomena of induction with electricity of tension, still remain to
be acted upon by the induction of electricity in motion.

3. Further: Whether Ampère's beautiful theory were adopted, or any other,
or whatever reservation were mentally made, still it appeared very
extraordinary, that as every electric current was accompanied by a
corresponding intensity of magnetic action at right angles to the current,
good conductors of electricity, when placed within the sphere of this action,
should not have any current induced through them, or some sensible effect
produced equivalent in force to such a current.

4. These considerations, with their consequence, the hope of obtaining
electricity from ordinary magnetism, have stimulated me at various times to
investigate experimentally the inductive effect of electric currents. I lately
arrived at positive results; and not only had my hopes fulfilled, but obtained
a key which appeared to me to open out a full explanation of Arago's
magnetic phenomena, and also to discover a new state, which may probably
have great influence in some of the most important effects of electric
currents.

5. These results I purpose describing, not as they were obtained, but in such
a manner as to give the most concise view of the whole.

§ 1. Induction of Electric Currents.

6. About twenty-six feet of copper wire one twentieth of an inch in diameter
were wound round a cylinder of wood as a helix, the different spires of
which were prevented from touching by a thin interposed twine. This helix
was covered with calico, and then a second wire applied in the same
manner. In this way twelve helices were superposed, each containing an
average length of wire of twenty-seven feet, and all in the same direction.
The first, third, fifth, seventh, ninth, and eleventh of these helices were
connected at their extremities end to end, so as to form one helix; the others
were connected in a similar manner; and thus two principal helices were
produced, closely interposed, having the same direction, not touching
anywhere, and each containing one hundred and fifty-five feet in length of
wire.

7. One of these helices was connected with a galvanometer, the other with a
voltaic battery of ten pairs of plates four inches square, with double coppers
and well charged; yet not the slightest sensible reflection of the
galvanometer-needle could be observed.

8. A similar compound helix, consisting of six lengths of copper and six of
soft iron wire, was constructed. The resulting iron helix contained two
hundred and fourteen feet of wire, the resulting copper helix two hundred
and eight feet; but whether the current from the trough was passed through

the copper or the iron helix, no effect upon the other could be perceived at
the galvanometer.

9. In these and many similar experiments no difference in action of any kind
appeared between iron and other metals.

10. Two hundred and three feet of copper wire in one length were coiled
round a large block of wood; other two hundred and three feet of similar
wire were interposed as a spiral between the turns of the first coil, and
metallic contact everywhere prevented by twine. One of these helices was
connected with a galvanometer, and the other with a battery of one hundred
pairs of plates four inches square, with double coppers, and well charged.
When the contact was made, there was a sudden and very slight effect at the
galvanometer, and there was also a similar slight effect when the contact
with the battery was broken. But whilst the voltaic current was continuing
to pass through the one helix, no galvanometrical appearances nor any
effect like induction upon the other helix could be perceived, although the
active power of the battery was proved to be great, by its heating the whole
of its own helix, and by the brilliancy of the discharge when made through
charcoal.

11. Repetition of the experiments with a battery of one hundred and twenty
pairs of plates produced no other effects; but it was ascertained, both at this
and the former time, that the slight deflection of the needle occurring at the
moment of completing the connexion, was always in one direction, and that
the equally slight deflection produced when the contact was broken, was in
the other direction; and also, that these effects occurred when the first
helices were used (6. 8.).

12. The results which I had by this time obtained with magnets led me to
believe that the battery current through one wire, did, in reality, induce a
similar current through the other wire, but that it continued for an instant
only, and partook more of the nature of the electrical wave passed through
from the shock of a common Leyden jar than of the current from a voltaic
battery, and therefore might magnetise a steel needle, although it scarcely
affected the galvanometer.

13. This expectation was confirmed; for on substituting a small hollow
helix, formed round a glass tube, for the galvanometer, introducing a steel
needle, making contact as before between the battery and the inducing wire
(7. 10.), and then removing the needle before the battery contact was
broken, it was found magnetised.

14. When the battery contact was first made, then an unmagnetised needle
introduced into the small indicating helix (13.), and lastly the battery
contact broken, the needle was found magnetised to an equal degree
apparently as before; but the poles were of the contrary kind.

15. The same effects took place on using the large compound helices first
described (6. 8.).

16. When the unmagnetised needle was put into the indicating helix, before
contact of the inducing wire with the battery, and remained there until the
contact was broken, it exhibited little or no magnetism; the first effect
having been nearly neutralised by the second (13. 14.). The force of the
induced current upon making contact was found always to exceed that of
the induced current at breaking of contact; and if therefore the contact was
made and broken many times in succession, whilst the needle remained in
the indicating helix, it at last came out not unmagnetised, but a needle
magnetised as if the induced current upon making contact had acted alone
on it. This effect may be due to the accumulation (as it is called) at the poles
of the unconnected pile, rendering the current upon first making contact
more powerful than what it is afterwards, at the moment of breaking
contact.

17. If the circuit between the helix or wire under induction and the
galvanometer or indicating spiral was not rendered complete before the
connexion between the battery and the inducing wire was completed or
broken, then no effects were perceived at the galvanometer. Thus, if the
battery communications were first made, and then the wire under induction
connected with the indicating helix, no magnetising power was there
exhibited. But still retaining the latter communications, when those with the
battery were broken, a magnet was formed in the helix, but of the second
kind (14.), i.e. with poles indicating a current in the same direction to that

belonging to the battery current, or to that always induced by that current at
its cessation.

18. In the preceding experiments the wires were placed near to each other,
and the contact of the inducing one with the buttery made when the
inductive effect was required; but as the particular action might be supposed
to be exerted only at the moments of making and breaking contact, the
induction was produced in another way. Several feet of copper wire were
stretched in wide zigzag forms, representing the letter W, on one surface of
a broad board; a second wire was stretched in precisely similar forms on a
second board, so that when brought near the first, the wires should
everywhere touch, except that a sheet of thick paper was interposed. One of
these wires was connected with the galvanometer, and the other with a
voltaic battery. The first wire was then moved towards the second, and as it
approached, the needle was deflected. Being then removed, the needle was
deflected in the opposite direction. By first making the wires approach and
then recede, simultaneously with the vibrations of the needle, the latter soon
became very extensive; but when the wires ceased to move from or towards
each other, the galvanometer-needle soon came to its usual position.

19. As the wires approximated, the induced current was in the contrary
direction to the inducing current. As the wires receded, the induced current
was in the same direction as the inducing current. When the wires remained
stationary, there was no induced current (54.).

20. When a small voltaic arrangement was introduced into the circuit
between the galvanometer (10.) and its helix or wire, so as to cause a
permanent deflection of 30° or 40°, and then the battery of one hundred
pairs of plates connected with the inducing wire, there was an instantaneous
action as before (11.); but the galvanometer-needle immediately resumed
and retained its place unaltered, notwithstanding the continued contact of
the inducing wire with the trough: such was the case in whichever way the
contacts were made (33.).

21. Hence it would appear that collateral currents, either in the same or in
opposite directions, exert no permanent inducing power on each other,
affecting their quantity or tension.

22. I could obtain no evidence by the tongue, by spark, or by heating fine
wire or charcoal, of the electricity passing through the wire under induction;
neither could I obtain any chemical effects, though the contacts with
metallic and other solutions were made and broken alternately with those of
the battery, so that the second effect of induction should not oppose or
neutralise the first (13. 16.).

23. This deficiency of effect is not because the induced current of electricity
cannot pass fluids, but probably because of its brief duration and feeble
intensity; for on introducing two large copper plates into the circuit on the
induced side (20.), the plates being immersed in brine, but prevented from
touching each other by an interposed cloth, the effect at the indicating
galvanometer, or helix, occurred as before. The induced electricity could
also pass through a voltaic trough (20.). When, however, the quantity of
interposed fluid was reduced to a drop, the galvanometer gave no
indication.

24. Attempts to obtain similar effects by the use of wires conveying
ordinary electricity were doubtful in the results. A compound helix similar
to that already described, containing eight elementary helices (6.), was
used. Four of the helices had their similar ends bound together by wire, and
the two general terminations thus produced connected with the small
magnetising helix containing an unmagnetised needle (13.). The other four
helices were similarly arranged, but their ends connected with a Leyden jar.
On passing the discharge, the needle was found to be a magnet; but it
appeared probable that a part of the electricity of the jar had passed off to
the small helix, and so magnetised the needle. There was indeed no reason
to expect that the electricity of a jar possessing as it does great tension,
would not diffuse itself through all the metallic matter interposed between
the coatings.

25. Still it does not follow that the discharge of ordinary electricity through
a wire does not produce analogous phenomena to those arising from voltaic
electricity; but as it appears impossible to separate the effects produced at
the moment when the discharge begins to pass, from the equal and contrary
effects produced when it ceases to pass (16.), inasmuch as with ordinary

electricity these periods are simultaneous, so there can be scarcely any hope
that in this form of the experiment they can be perceived.

26. Hence it is evident that currents of voltaic electricity present phenomena
of induction somewhat analogous to those produced by electricity of
tension, although, as will be seen hereafter, many differences exist between
them. The result is the production of other currents, (but which are only
momentary,) parallel, or tending to parallelism, with the inducing current.
By reference to the poles of the needle formed in the indicating helix (13.
14.) and to the deflections of the galvanometer-needle (11.), it was found in
all cases that the induced current, produced by the first action of the
inducing current, was in the contrary direction to the latter, but that the
current produced by the cessation of the inducing current was in the same
direction (19.). For the purpose of avoiding periphrasis, I propose to call
this action of the current from the voltaic battery, volta-electric induction.
The properties of the second wire, after induction has developed the first
current, and whilst the electricity from the battery continues to flow through
its inducing neighbour (10. 18.), constitute a peculiar electric condition, the
consideration of which will be resumed hereafter (60.). All these results
have been obtained with a voltaic apparatus consisting of a single pair of
plates.

§ 2. Evolution of Electricity from Magnetism.

27. A welded ring was made of soft round bar-iron, the metal being seven-
eighths of an inch in thickness, and the ring six inches in external diameter.
Three helices were put round one part of this ring, each containing about
twenty-four feet of copper wire one twentieth of an inch thick; they were
insulated from the iron and each other, and superposed in the manner before
described (6.), occupying about nine inches in length upon the ring. They
could be used separately or conjointly; the group may be distinguished by
the letter A (Pl. I. fig. 1.). On the other part of the ring about sixty feet of
similar copper wire in two pieces were applied in the same manner, forming
a helix B, which had the same common direction with the helices of A, but
being separated from it at each extremity by about half an inch of the
uncovered iron.

28. The helix B was connected by copper wires with a galvanometer three
feet from the ring. The helices of A were connected end to end so as to form
one common helix, the extremities of which were connected with a battery
of ten pairs of plates four inches square. The galvanometer was immediately
affected, and to a degree far beyond what has been described when with a
battery of tenfold power helices without iron were used (10.); but though
the contact was continued, the effect was not permanent, for the needle soon
came to rest in its natural position, as if quite indifferent to the attached
electro-magnetic arrangement. Upon breaking the contact with the batterry,
the needle was again powerfully deflected, but in the contrary direction to
that induced in the first instance.

29. Upon arranging the apparatus so that B should be out of use, the
galvanometer be connected with one of the three wires of A (27.), and the
other two made into a helix through which the current from the trough (28.)
was passed, similar but rather more powerful effects were produced.

30. When the battery contact was made in one direction, the galvanometer-
needle was deflected on the one side; if made in the other direction, the
deflection was on the other side. The deflection on breaking the battery
contact was always the reverse of that produced by completing it. The
deflection on making a battery contact always indicated an induced current
in the opposite direction to that from the battery; but on breaking the
contact the deflection indicated an induced current in the same direction as
that of the battery. No making or breaking of the contact at B side, or in any
part of the galvanometer circuit, produced any effect at the galvanometer.
No continuance of the battery current caused any deflection of the
galvanometer-needle. As the above results are common to all these
experiments, and to similar ones with ordinary magnets to be hereafter
detailed, they need not be again particularly described.

31. Upon using the power of one hundred pairs of plates (10.) with this ring,
the impulse at the galvanometer, when contact was completed or broken,
was so great as to make the needle spin round rapidly four or five times,
before the air and terrestrial magnetism could reduce its motion to mere
oscillation.

32. By using charcoal at the ends of the B helix, a minute spark could be
perceived when the contact of the battery with A was completed. This spark
could not be due to any diversion of a part of the current of the battery
through the iron to the helix B; for when the battery contact was continued,
the galvanometer still resumed its perfectly indifferent state (28.). The spark
was rarely seen on breaking contact. A small platina wire could not be
ignited by this induced current; but there seems every reason to believe that
the effect would be obtained by using a stronger original current or a more
powerful arrangement of helices.

33. A feeble voltaic current was sent through the helix B and the
galvanometer, so as to deflect the needle of the latter 30° or 40°, and then
the battery of one hundred pairs of plates connected with A; but after the
first effect was over, the galvanometer-needle resumed exactly the position
due to the feeble current transmitted by its own wire. This took place in
whichever way the battery contacts were made, and shows that here again
(20.) no permanent influence of the currents upon each other, as to their
quantity and tension, exists.

34. Another arrangement was then employed connecting the former
experiments on volta-electric induction (6-26.) with the present. A
combination of helices like that already described (6.) 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 (7.); the other intervening four were
also connected end to end, and the battery of one hundred pairs discharged
through them. In this form the effect on the galvanometer was hardly
sensible (11.), though magnets could be made by the induced current (13.).
But when a soft iron cylinder seven eighths of an inch thick, and twelve
inches long, was introduced into the pasteboard tube, surrounded by the
helices, then the induced current affected the galvanometer powerfully and
with all the phenomena just described (30.). It possessed also the power of
making magnets with more energy, apparently, than when no iron cylinder
was present.

35. When the iron cylinder was replaced by an equal cylinder of copper, no
effect beyond that of the helices alone was produced. The iron cylinder

arrangement was not so powerful as the ring arrangement already described
(27.).

36. Similar effects were then produced by ordinary magnets: thus the
hollow helix just described (34.) had all its elementary helices connected
with the galvanometer by two copper wires, each five feet in length; the soft
iron cylinder was introduced into its axis; a couple of bar magnets, each
twenty-four inches long, were arranged with their opposite poles at one end
in contact, so as to resemble a horse-shoe magnet, and then contact made
between the other poles and the ends of the iron cylinder, so as to convert it
for the time into a magnet (fig. 2.): by breaking the magnetic contacts, or
reversing them, the magnetism of the iron cylinder could be destroyed or
reversed at pleasure.

37. Upon making magnetic contact, the needle was deflected; continuing
the contact, the needle became indifferent, and resumed its first position; on
breaking the contact, it was again deflected, but in the opposite direction to
the first effect, and then it again became indifferent. When the magnetic
contacts were reversed the deflections were reversed.

38. When the magnetic contact was made, the deflection was such as to
indicate an induced current of electricity in the opposite direction to that
fitted to form a magnet, having the same polarity as that really produced by
contact with the bar magnets. Thus when the marked and unmarked poles
were placed as in fig. 3, the current in the helix was in the direction
represented, P being supposed to be the end of the wire going to the positive
pole of the battery, or that end towards which the zinc plates face, and N the
negative wire. Such a current would have converted the cylinder into a
magnet of the opposite kind to that formed by contact with the poles A and
B; and such a current moves in the opposite direction to the currents which
in M. Ampère's beautiful theory are considered as constituting a magnet in
the position figured1.

39. But as it might be supposed that in all the preceding experiments of this
section, it was by some peculiar effect taking place during the formation of
the magnet, and not by its mere virtual approximation, that the momentary
induced current was excited, the following experiment was made. All the
similar ends of the compound hollow helix (34.) were bound together by

copper wire, forming two general terminations, and these were connected
with the galvanometer. The soft iron cylinder (34.) was removed, and a
cylindrical magnet, three quarters of an inch in diameter and eight inches
and a half in length, used instead. One end of this magnet was introduced
into the axis of the helix (fig. 4.), and then, the galvanometer-needle being
stationary, the magnet was suddenly thrust in; immediately the needle was
deflected in the same direction as if the magnet had been formed by either
of the two preceding processes (34. 36.). Being left in, the needle resumed
its first position, and then the magnet being withdrawn the needle was
deflected in the opposite direction. These effects were not great; but by
introducing and withdrawing the magnet, so that the impulse each time
should be added to those previously communicated to the needle, the latter
could be made to vibrate through an arc of 180° or more.

40. In this experiment the magnet must not be passed entirely through the
helix, for then a second action occurs. When the magnet is introduced, the
needle at the galvanometer is deflected in a certain direction; but being in,
whether it be pushed quite through or withdrawn, the needle is deflected in
a direction the reverse of that previously produced. When the magnet is
passed in and through at one continuous motion, the needle moves one way,
is then suddenly stopped, and finally moves the other way.

41. If such a hollow helix as that described (34.) be laid east and west (or in
any other constant position), and a magnet be retained east and west, its
marked pole always being one way; then whichever end of the helix the
magnet goes in at, and consequently whichever pole of the magnet enters
first, still the needle is deflected the same way: on the other hand,
whichever direction is followed in withdrawing the magnet, the deflection
is constant, but contrary to that due to its entrance.

42. These effects are simple consequences of the law hereafter to be
described (114).

43. When the eight elementary helices were made one long helix, the effect
was not so great as in the arrangement described. When only one of the
eight helices was used, the effect was also much diminished. All care was
taken to guard against tiny direct action of the inducing magnet upon the
galvanometer, and it was found that by moving the magnet in the same

direction, and to the same degree on the outside of the helix, no effect on
the needle was produced.

44. The Royal Society are in possession of a large compound magnet
formerly belonging to Dr. Gowin Knight, which, by permission of the
President and Council, I was allowed to use in the prosecution of these
experiments: it is at present in the charge of Mr. Christie, at his house at
Woolwich, where, by Mr. Christie's kindness, I was at liberty to work; and I
have to acknowledge my obligations to him for his assistance in all the
experiments and observations made with it. This magnet is composed of
about 450 bar magnets, each 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 (fig. 5.). These poles projected horizontally six inches from
the box, were each twelve inches high and three inches wide. They were
nine inches apart; and when a soft iron cylinder, three quarters of an inch in
diameter and twelve inches long, was put across from one to the other, it
required a force of nearly one hundred pounds to break the contact. The
pole to the left in the figure is the marked pole2.

45. The indicating galvanometer, in all experiments made with this magnet,
was about eight feet from it, not directly in front of the poles, but about 16°
or 17° on one side. It was found that on making or breaking the connexion
of the poles by soft iron, the instrument was slightly affected; but all error
of observation arising from this cause was easily and carefully avoided.

46. The electrical effects exhibited by this magnet were very striking. When
a soft iron cylinder thirteen inches long was put through the compound
hollow helix, with its ends arranged as two general terminations (39.), these
connected with the galvanometer, and the iron cylinder brought in contact
with the two poles of the magnet (fig. 5.), so powerful a rush of electricity
took place that the needle whirled round many times in succession3.

47. Notwithstanding this great power, if the contact was continued, the
needle resumed its natural position, being entirely uninfluenced by the
position of the helix (30.). But on breaking the magnetic contact, the needle
was whirled round in the opposite direction with a force equal to the former.

48. A piece of copper plate wrapped once round the iron cylinder like a
socket, but with interposed paper to prevent contact, had its edges
connected with the wires of the galvanometer. When the iron was brought
in contact with the poles the galvanometer was strongly affected.

49. Dismissing the helices and sockets, the galvanometer wire was passed
over, and consequently only half round the iron cylinder (fig. 6.); but even
then a strong effect upon the needle was exhibited, when the magnetic
contact was made or broken.

50. As the helix with its iron cylinder was brought towards the magnetic
poles, but without making contact, still powerful effects were produced.
When the helix, without the iron cylinder, and consequently containing no
metal but copper, was approached to, or placed between the poles (44.), the
needle was thrown 80°, 90°, or more, from its natural position. The
inductive force was of course greater, the nearer the helix, either with or
without its iron cylinder, was brought to the poles; but otherwise the same
effects were produced, whether the helix, &c. was or was not brought into
contact with the magnet; i.e. no permanent effect on the galvanometer was
produced; and the effects of approximation and removal were the reverse of
each other (30.).

51. When a bolt of copper corresponding to the iron cylinder was
introduced, no greater effect was produced by the helix than without it. But
when a thick iron wire was substituted, the magneto-electric induction was
rendered sensibly greater.

52. The direction of the electric current produced in all these experiments
with the helix, was the same as that already described (38.) as obtained with
the weaker bar magnets.

53. A spiral containing fourteen feet of copper wire, being connected with
the galvanometer, and approximated directly towards the marked pole in the
line of its axis, affected the instrument strongly; the current induced in it
was in the reverse direction to the current theoretically considered by M.
Ampère as existing in the magnet (38.), or as the current in an electro-
magnet of similar polarity. As the spiral was withdrawn, the induced current
was reversed.

54. A similar spiral had the current of eighty pairs of 4-inch plates sent
through it so as to form an electro-magnet, and then the other spiral
connected with the galvanometer (58.) approximated to it; the needle
vibrated, indicating a current in the galvanometer spiral the reverse of that
in the battery spiral (18. 26.). On withdrawing the latter spiral, the needle
passed in the opposite direction.

55. Single wires, approximated in certain directions towards the magnetic
pole, had currents induced in them. On their removal, the currents were
inverted. In such experiments the wires should not be removed in directions
different to those in which they were approximated; for then occasionally
complicated and irregular effects are produced, the causes of which will be
very evident in the fourth part of this paper.

56. All attempts to obtain chemical effects by the induced current of
electricity failed, though the precautions before described (22.), and all
others that could be thought of, were employed. Neither was any sensation
on the tongue, or any convulsive effect upon the limbs of a frog, produced.
Nor could charcoal or fine wire be ignited (133.). But upon repeating the
experiments more at leisure at the Royal Institution, with an armed
loadstone belonging to Professor Daniell and capable of lifting about thirty
pounds, a frog was very powerfully convulsed each time magnetic contact
was made. At first the convulsions could not be obtained on breaking
magnetic contact; but conceiving the deficiency of effect was because of the
comparative slowness of separation, the latter act was effected by a blow,
and then the frog was convulsed strongly. The more instantaneous the union
or disunion is effected, the more powerful the convulsion. I thought also I
could perceive the sensation upon the tongue and the flash before the eyes;
but I could obtain no evidence of chemical decomposition.

57. The various experiments of this section prove, I think, most completely
the production of electricity from ordinary magnetism. That its intensity
should be very feeble and quantity small, cannot be considered wonderful,
when it is remembered that like thermo-electricity it is evolved entirely
within the substance of metals retaining all their conducting power. But an
agent which is conducted along metallic wires in the manner described;
which whilst so passing possesses the peculiar magnetic actions and force

of a current of electricity; which can agitate and convulse the limbs of a
frog; and which, finally, can produce a spark4 by its discharge through
charcoal (32.), can only be electricity. As all the effects can be produced by
ferruginous electro-magnets (34.), there is no doubt that arrangements like
the magnets of Professors Moll, Henry, Ten Eyke, and others, in which as
many as two thousand pounds have been lifted, may be used for these
experiments; in which case not only a brighter spark may be obtained, but
wires also ignited, and, as the current can pass liquids (23.), chemical action
be produced. These effects are still more likely to be obtained when the
magneto-electric arrangements to be explained in the fourth section are
excited by the powers of such apparatus.

58. The similarity of action, almost amounting to identity, between common
magnets and either electro-magnets or volta-electric currents, is strikingly
in accordance with and confirmatory of M. Ampère's theory, and furnishes
powerful reasons for believing that the action is the same in both cases; but,
as a distinction in language is still necessary, I propose to call the agency
thus exerted by ordinary magnets, magneto-electric or magnelectric
induction (26).

59. The only difference which powerfully strikes the attention as existing
between volta-electric and magneto-electric induction, is the suddenness of
the former, and the sensible time required by the latter; but even in this
early state of investigation there are circumstances which seem to indicate,
that upon further inquiry this difference will, as a philosophical distinction,
disappear (68).5

§ 3. New Electrical State or Condition of Matter.6

60. Whilst the wire is subject to either volta-electric or magneto-electric
induction, it appears to be in a peculiar state; for it resists the formation of
an electrical current in it, whereas, if in its common condition, such a
current would be produced; and when left uninfluenced it has the power of
originating a current, a power which the wire does not possess under
common circumstances. This electrical condition of matter has not hitherto
been recognised, but it probably exerts a very important influence in many

if not most of the phenomena produced by currents of electricity. For
reasons which will immediately appear (71.), I have, after advising with
several learned friends, ventured to designate it as the electro-ionic state.

61. This peculiar condition shows no known electrical effects whilst it
continues; nor have I yet been able to discover any peculiar powers exerted,
or properties possessed, by matter whilst retained in this state.

62. It shows no reaction by attractive or repulsive powers. The various
experiments which have been made with powerful magnets upon such
metals, as copper, silver, and generally those substances not magnetic,
prove this point; for the substances experimented upon, if electrical
conductors, must have acquired this state; and yet no evidence of attractive
or repulsive powers has been observed. I have placed copper and silver
discs, very delicately suspended on torsion balances in vacuo near to the
poles of very powerful magnets, yet have not been able to observe the least
attractive or repulsive force.

63. I have also arranged a fine slip of gold-leaf very near to a bar of copper,
the two being in metallic contact by mercury at their extremities. These
have been placed in vacuo, so that metal rods connected with the
extremities of the arrangement should pass through the sides of the vessel
into the air. I have then moved powerful magnetic poles, about this
arrangement, in various directions, the metallic circuit on the outside being
sometimes completed by wires, and sometimes broken. But I never could
obtain any sensible motion of the gold-leaf, either directed to the magnet or
towards the collateral bar of copper, which must have been, as far as
induction was concerned, in a similar state to itself.

64. In some cases it has been supposed that, under such circumstances,
attractive and repulsive forces have been exhibited, i.e. that such bodies
have become slightly magnetic. But the phenomena now described, in
conjunction with the confidence we may reasonably repose in M. Ampère's
theory of magnetism, tend to throw doubt on such cases; for if magnetism
depend upon the attraction of electrical currents, and if the powerful
currents at first excited, both by volta-electric and magneto-electric
induction, instantly and naturally cease (12. 28. 47.), causing at the same
time an entire cessation of magnetic effects at the galvanometer needle, then

there can be little or no expectation that any substances not partaking of the
peculiar relation in which iron, nickel, and one or two other bodies, stand,
should exhibit magneto-attractive powers. It seems far more probable, that
the extremely feeble permanent effects observed have been due to traces of
iron, or perhaps some other unrecognised cause not magnetic.

65. This peculiar condition exerts no retarding or accelerating power upon
electrical currents passing through metal thus circumstanced (20. 33.).
Neither could any such power upon the inducing current itself be detected;
for when masses of metal, wires, helices, &c. were arranged in all possible
ways by the side of a wire or helix, carrying a current measured by the
galvanometer (20.), not the slightest permanent change in the indication of
the instrument could be perceived. Metal in the supposed peculiar state,
therefore, conducts electricity in all directions with its ordinary facility, or,
in other words, its conducting power is not sensibly altered by it.

66. All metals take on the peculiar state. This is proved in the preceding
experiments with copper and iron (9.), and with gold, silver, tin, lead, zinc,
antimony, bismuth, mercury, &c. by experiments to be described in the
fourth part (132.), admitting of easy application. With regard to iron, the
experiments prove the thorough and remarkable independence of these
phenomena of induction, and the ordinary magnetical appearances of that
metal.

67. This state is altogether the effect of the induction exerted, and ceases as
soon as the inductive force is removed. It is the same state, whether
produced by the collateral passage of voltaic currents (26.), or the formation
of a magnet (34. 36.), or the mere approximation of a magnet (39. 50.); and
is a strong proof in addition to those advanced by M. Ampère, of the
identity of the agents concerned in these several operations. It probably
occurs, momentarily, during the passage of the common electric spark (24.),
and may perhaps be obtained hereafter in bad conductors by weak electrical
currents or other means (74. 76).

68. The state appears to be instantly assumed (12.), requiring hardly a
sensible portion of time for that purpose. The difference of time between
volta-electric and magneto-electric induction, rendered evident by the
galvanometer (59.), may probably be thus explained. When a voltaic current

is sent through one of two parallel wires, as those of the hollow helix (34.),
a current is produced in the other wire, as brief in its continuance as the
time required for a single action of this kind, and which, by experiment, is
found to be inappreciably small. The action will seem still more
instantaneous, because, as there is an accumulation of power in the poles of
the battery before contact, the first rush of electricity in the wire of
communication is greater than that sustained after the contact is completed;
the wire of induction becomes at the moment electro-tonic to an equivalent
degree, which the moment after sinks to the state in which the continuous
current can sustain it, but in sinking, causes an opposite induced current to
that at first produced. The consequence is, that the first induced wave of
electricity more resembles that from the discharge of an electric jar, than it
otherwise would do.

69. But when the iron cylinder is put into the same helix (31.), previous to
the connexion being made with the battery, then the current from the latter
may be considered as active in inducing innumerable currents of a similar
kind to itself in the iron, rendering it a magnet. This is known by
experiment to occupy time; for a magnet so formed, even of soft iron, does
not rise to its fullest intensity in an instant, and it may be because the
currents within the iron are successive in their formation or arrangement.
But as the magnet can induce, as well as the battery current, the combined
action of the two continues to evolve induced electricity, until their joint
effect is at a maximum, and thus the existence of the deflecting force is
prolonged sufficiently to overcome the inertia of the galvanometer needle.

70. In all those cases where the helices or wires are advanced towards or
taken from the magnet (50. 55.), the direct or inverted current of induced
electricity continues for the time occupied in the advance or recession; for
the electro-tonic state is rising to a higher or falling to a lower degree
during that time, and the change is accompanied by its corresponding
evolution of electricity; but these form no objections to the opinion that the
electro-tonic state is instantly assumed.

71. This peculiar state appears to be a state of tension, and may be
considered as equivalent to a current of electricity, at least equal to that
produced either when the condition is induced or destroyed. The current

evolved, however, first or last, is not to be considered a measure of the
degree of tension to which the electro-tonic state has risen; for as the metal
retains its conducting powers unimpaired (65.), and as the electricity
evolved is but for a moment, (the peculiar state being instantly assumed and
lost (68.),) the electricity which may be led away by long wire conductors,
offering obstruction in their substance proportionate to their small lateral
and extensive linear dimensions, can be but a very small portion of that
really evolved within the mass at the moment it assumes this condition.
Insulated helices and portions of metal instantly assumed the state; and no
traces of electricity could be discovered in them, however quickly the
contact with the electrometer was made, after they were put under
induction, either by the current from the battery or the magnet. A single
drop of water or a small piece of moistened paper (23. 56.) was obstacle
sufficient to stop the current through the conductors, the electricity evolved
returning to a state of equilibrium through the metal itself, and consequently
in an unobserved manner.

72. The tension of this state may therefore be comparatively very great. But
whether great or small, it is hardly conceivable that it should exist without
exerting a reaction upon the original inducing current, and producing
equilibrium of some kind. It might be anticipated that this would give rise
to a retardation of the original current; but I have not been able to ascertain
that this is the case. Neither have I in any other way as yet been able to
distinguish effects attributable to such a reaction.

73. All the results favour the notion that the electro-tonic state relates to the
particles, and not to the mass, of the wire or substance under induction,
being in that respect different to the induction exerted by electricity of
tension. If so, the state may be assumed in liquids when no electrical current
is sensible, and even in non-conductors; the current itself, when it occurs,
being as it were a contingency due to the existence of conducting power,
and the momentary propulsive force exerted by the particles during their
arrangement. Even when conducting power is equal, the currents of
electricity, which as yet are the only indicators of this state, may be
unequal, because of differences as to numbers, size, electrical condition,
&c. &c. in the particles themselves. It will only be after the laws which
govern this new state are ascertained, that we shall be able to predict what is

the true condition of, and what are the electrical results obtainable from,
any particular substance.

74. The current of electricity which induces the electro-tonic state in a
neighbouring wire, probably induces that state also in its own wire; for
when by a current in one wire a collateral wire is made electro-tonic, the
latter state is not rendered any way incompatible or interfering with a
current of electricity passing through it (62.). If, therefore, the current were
sent through the second wire instead of the first, it does not seem probable
that its inducing action upon the second would be less, but on the contrary
more, because the distance between the agent and the matter acted upon
would be very greatly diminished. A copper bolt had its extremities
connected with a galvanometer, and then the poles of a battery of one
hundred pairs of plates connected with the bolt, so as to send the current
through it; the voltaic circuit was then suddenly broken, and the
galvanometer observed for any indications of a return current through the
copper bolt due to the discharge of its supposed electro-tonic state. No
effect of the kind was obtained, nor indeed, for two reasons, ought it to be
expected; for first, as the cessation of induction and the discharge of the
electro-tonic condition are simultaneous, and not successive, the return
current would only be equivalent to the neutralization of the last portion of
the inducing current, and would not therefore show any alteration of
direction; or assuming that time did intervene, and that the latter current
was really distinct from the former, its short, sudden character (12. 26.)
would prevent it from being thus recognised.

75. No difficulty arises, I think, in considering the wire thus rendered
electro-tonic by its own current more than by any external current,
especially when the apparent non-interference of that state with currents is
considered (62. 71.). The simultaneous existence of the conducting and
electro-tonic states finds an analogy in the manner in which electrical
currents can be passed through magnets, where it is found that both the
currents passed, and those of the magnets, preserve all their properties
distinct from each other, and exert their mutual actions.

76. The reason given with regard to metals extends also to fluids and all
other conductors, and leads to the conclusion that when electric currents are

passed through them they also assume the electro-tonic state. Should that
prove to be the case, its influence in voltaic decomposition, and the
transference of the elements to the poles, can hardly be doubted. In the
electro-tonic state the homogeneous particles of matter appear to have
assumed a regular but forced electrical arrangement in the direction of the
current, which if the matter be undecomposable, produces, when relieved, a
return current; but in decomposable matter this forced state may be
sufficient to make an elementary particle leave its companion, with which it
is in a constrained condition, and associate with the neighbouring similar
particle, in relation to which it is in a more natural condition, the forced
electrical arrangement being itself discharged or relieved, at the same time,
as effectually as if it had been freed from induction. But as the original
voltaic current is continued, the electro-tonic state may be instantly
renewed, producing the forced arrangement of the compound particles, to
be as instantly discharged by a transference of the elementary particles of
the opposite kind in opposite directions, but parallel to the current. Even the
differences between common and voltaic electricity, when applied to effect
chemical decomposition, which Dr. Wollaston has pointed out7, seem
explicable by the circumstances connected with the induction of electricity
from these two sources (25.). But as I have reserved this branch of the
inquiry, that I might follow out the investigations contained in the present
paper, I refrain (though much tempted) from offering further speculations.

77. Marianini has discovered and described a peculiar affection of the
surfaces of metallic discs, when, being in contact with humid conductors, a
current of electricity is passed through them; they are then capable of
producing a reverse current of electricity, and Marianini has well applied
the effect in explanation of the phenomena of Ritter's piles8. M.A. de la
Rive has described a peculiar property acquired by metallic conductors,
when being immersed in a liquid as poles, they have completed, for some
time, the voltaic circuit, in consequence of which, when separated from the
battery and plunged into the same fluid, they by themselves produce an
electric current9. M.A. Van Beek has detailed cases in which the electrical
relation of one metal in contact with another has been preserved after
separation, and accompanied by its corresponding chemical effects10. These
states and results appear to differ from the electro-tonic state and its

phenomena; but the true relation of the former to the latter can only be
decided when our knowledge of all these phenomena has been enlarged.

78. I had occasion in the commencement of this paper (2.) to refer to an
experiment by Ampère, as one of those dependent upon the electrical
induction of currents made prior to the present investigation, and have
arrived at conclusions which seem to imply doubts of the accuracy of the
experiment (62. &c.); it is therefore due to M. Ampère that I should attend
to it more distinctly. When a disc of copper (says M. Ampère) was
suspended by a silk thread and surrounded by a helix or spiral, and when
the charge of a powerful voltaic battery was sent through the spiral, a strong
magnet at the same time being presented to the copper disc, the latter turned
at the moment to take a position of equilibrium, exactly as the spiral itself
would have turned had it been free to move. I have not been able to obtain
this effect, nor indeed any motion; but the cause of my failure in the latter
point may be due to the momentary existence of the current not allowing
time for the inertia of the plate to be overcome (11. 12.). M. Ampère has
perhaps succeeded in obtaining motion from the superior delicacy and
power of his electro-magnetical apparatus, or he may have obtained only
the motion due to cessation of action. But all my results tend to invert the
sense of the proposition stated by M. Ampère, "that a current of electricity
tends to put the electricity of conductors near which it passes in motion in
the same direction," for they indicate an opposite direction for the produced
current (26. 53.); and they show that the effect is momentary, and that it is
also produced by magnetic induction, and that certain other extraordinary
effects follow thereupon.

79. The momentary existence of the phenomena of induction now described
is sufficient to furnish abundant reasons for the uncertainty or failure of the
experiments, hitherto made to obtain electricity from magnets, or to effect
chemical decomposition or arrangement by their means11.

80. It also appears capable of explaining fully the remarkable phenomena
observed by M. Arago between metals and magnets when neither are
moving (120.), as well as most of the results obtained by Sir John Herschel,
Messrs. Babbage, Harris, and others, in repeating his experiments;
accounting at the same time perfectly for what at first appeared

inexplicable; namely, the non-action of the same metals and magnets when
at rest. These results, which also afford the readiest means of obtaining
electricity from magnetism, I shall now proceed to describe.

§ 4. Explication of Arago's Magnetic Phenomena.

81. If a plate of copper be revolved close to a magnetic needle, or magnet,
suspended in such a way that the latter may rotate in a plane parallel to that
of the former, the magnet tends to follow the motion of the plate; or if the
magnet be revolved, the plate tends to follow its motion; and the effect is so
powerful, that magnets or plates of many pounds weight may be thus
carried round. If the magnet and plate be at rest relative to each other, not
the slightest effect, attractive or repulsive, or of any kind, can be observed
between them (62.). This is the phenomenon discovered by M. Arago; and
he states that the effect takes place not only with all metals, but with solids,
liquids, and even gases, i.e. with all substances (130.).

82. Mr. Babbage and Sir John Herschel, on conjointly repeating the
experiments in this country12, could obtain the effects only with the metals,
and with carbon in a peculiar state (from gas retorts), i.e. only with
excellent conductors of electricity. They refer the effect to magnetism
induced in the plate by the magnet; the pole of the latter causing an opposite
pole in the nearest part of the plate, and round this a more diffuse polarity of
its own kind (120.). The essential circumstance in producing the rotation of
the suspended magnet is, that the substance revolving below it shall acquire
and lose its magnetism in sensible time, and not instantly (124.). This
theory refers the effect to an attractive force, and is not agreed to by the
discoverer, M. Arago, nor by M. Ampère, who quote against it the absence
of all attraction when the magnet and metal are at rest (62. 126.), although
the induced magnetism should still remain; and who, from experiments
made with a long dipping needle, conceive the action to be always repulsive
(125.).

83. Upon obtaining electricity from magnets by the means already
described (36 46.), I hoped to make the experiment of M. Arago a new
source of electricity; and did not despair, by reference to terrestrial

magneto-electric induction, of being able to construct a new electrical
machine. Thus stimulated, numerous experiments were made with the
magnet of the Royal Society at Mr. Christie's house, in all of which I had
the advantage of his assistance. As many of these were in the course of the
superseded by more perfect arrangements, I shall consider myself at liberty
investigation to rearrange them in a manner calculated to convey most
readily what appears to me to be a correct view of the nature of the
phenomena.

84. The magnet has been already described (44.). To concentrate the poles,
and bring them nearer to each other, two iron or steel bars, each about six or
seven inches long, one inch wide, and half an inch thick, were put across
the poles as in fig. 7, and being supported by twine from slipping, could be
placed as near to or far from each other as was required. Occasionally two
bars of soft iron were employed, so bent that when applied, one to each
pole, the two smaller resulting poles were vertically over each other, either
being uppermost at pleasure.

85. A disc of copper, twelve inches in diameter, and about one fifth of an
inch in thickness, fixed upon a brass axis, was mounted in frames so as to
allow of revolution either vertically or horizontally, its edge being at the
same time introduced more or less between the magnetic poles (fig. 7.). The
edge of the plate was well amalgamated for the purpose of obtaining a good
but moveable contact, and a part round the axis was also prepared in a
similar manner.

86. Conductors or electric collectors of copper and lead were constructed so
as to come in contact with the edge of the copper disc (85.), or with other
forms of plates hereafter to be described (101.). These conductors were
about four inches long, one third of an inch wide, and one fifth of an inch
thick; one end of each was slightly grooved, to allow of more exact
adaptation to the somewhat convex edge of the plates, and then
amalgamated. Copper wires, one sixteenth of an inch in thickness, attached,
in the ordinary manner, by convolutions to the other ends of these
conductors, passed away to the galvanometer.

87. 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 magnetized and fixed on
to a stem of dried grass parallel to each other, but in opposite directions, and
about half an inch apart; this system was suspended by a fibre of unspun
silk, so that the lower needle should be between the convolutions of the
multiplier, and the upper above them. The latter was by much the most
powerful magnet, and gave terrestrial direction to the whole; fig. 8.
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 for convenient reference hereafter. 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 (44.). The whole
instrument was protected by a glass jar, and stood, as to position and
distance relative to the large magnet, under the same circumstances as
before (45.).

88. All these arrangements being made, the copper disc was adjusted as in
fig. 7, the small magnetic poles being about half an inch apart, and the edge
of the plate inserted about half their width between them. One of the
galvanometer wires was passed twice or thrice loosely round the brass axis
of the plate, and the other attached to a conductor (86.), which itself was
retained by the hand in contact with the amalgamated edge of the disc at the
part immediately between the magnetic poles. Under these circumstances
all was quiescent, and the galvanometer exhibited no effect. But the instant
the plate moved, the galvanometer was influenced, and by revolving the
plate quickly the needle could be deflected 90° or more.

89. It was difficult under the circumstances to make the contact between the
conductor and the edge of the revolving disc uniformly good and extensive;
it was also difficult in the first experiments to obtain a regular velocity of
rotation: both these causes tended to retain the needle in a continual state of
vibration; but no difficulty existed in ascertaining to which side it was
deflected, or generally, about what line it vibrated. Afterwards, when the
experiments were made more carefully, a permanent deflection of the
needle of nearly 45° could be sustained.

90. Here therefore was demonstrated the production of a permanent current
of electricity by ordinary magnets (57.).

91. When the motion of the disc was reversed, every other circumstance
remaining the same, the galvanometer needle was deflected with equal
power as before; but the deflection was on the opposite side, and the current
of electricity evolved, therefore, the reverse of the former.

92. When the conductor was placed on the edge of the disc a little to the
right or left, as in the dotted positions fig. 9, the current of electricity was
still evolved, and in the same direction as at first (88. 91.). This occurred to
a considerable distance, i.e. 50° or 60° on each side of the place of the
magnetic poles. The current gathered by the conductor and conveyed to the
galvanometer was of the same kind on both sides of the place of greatest
intensity, but gradually diminished in force from that place. It appeared to
be equally powerful at equal distances from the place of the magnetic poles,
not being affected in that respect by the direction of the rotation. When the
rotation of the disc was reversed, the direction of the current of electricity
was reversed also; but the other circumstances were not affected.

93. On raising the plate, so that the magnetic poles were entirely hidden
from each other by its intervention, (a. fig. 10,) the same effects were
produced in the same order, and with equal intensity as before. On raising it
still higher, so as to bring the place of the poles to c, still the effects were
produced, and apparently with as much power as at first.

94. When the conductor was held against the edge as if fixed to it, and with
it moved between the poles, even though but for a few degrees, the
galvanometer needle moved and indicated a current of electricity, the same
as that which would have been produced if the wheel had revolved in the
same direction, the conductor remaining stationary.

95. When the galvanometer connexion with the axis was broken, and its
wires made fast to two conductors, both applied to the edge of the copper
disc, then currents of electricity were produced, presenting more
complicated appearances, but in perfect harmony with the above results.
Thus, if applied as in fig. 11, a current of electricity through the
galvanometer was produced; but if their place was a little shifted, as in fig.
12, a current in the contrary direction resulted; the fact being, that in the
first instance the galvanometer indicated the difference between a strong
current through A and a weak one through B, and in the second, of a weak

current through A and a strong one through B (92.), and therefore produced
opposite deflections.

96. So also when the two conductors were equidistant from the magnetic
poles, as in fig. 13, no current at the galvanometer was perceived,
whichever way the disc was rotated, beyond what was momentarily
produced by irregularity of contact; because equal currents in the same
direction tended to pass into both. But when the two conductors were
connected with one wire, and the axis with the other wire, (fig. 14,) then the
galvanometer showed a current according with the direction of rotation
(91.); both conductors now acting consentaneously, and as a single
conductor did before (88.).

97. All these effects could be obtained when only one of the poles of the
magnet was brought near to the plate; they were of the same kind as to
direction, &c., but by no means so powerful.

98. All care was taken to render these results independent of the earth's
magnetism, or of the mutual magnetism of the magnet and galvanometer
needles. The contacts were made in the magnetic equator of the plate, and at
other parts; the plate was placed horizontally, and the poles vertically; and
other precautions were taken. But the absence of any interference of the
kind referred to, was readily shown by the want of all effect when the disc
was removed from the poles, or the poles from the disc; every other
circumstance remaining the same.

99. The relation of the current of electricity produced, to the magnetic pole,
to the direction of rotation of the plate, &c. &c., may be expressed by
saying, that when the unmarked pole (44. 84.) is beneath the edge of the
plate, and the latter revolves horizontally, screw-fashion, the electricity
which can be collected at the edge of the plate nearest to the pole is
positive. As the pole of the earth may mentally be considered the unmarked
pole, this relation of the rotation, the pole, and the electricity evolved, is not
difficult to remember. Or if, in fig. 15, the circle represent the copper disc
revolving in the direction of the arrows, and a the outline of the unmarked
pole placed beneath the plate, then the electricity collected at b and the
neighbouring parts is positive, whilst that collected at the centre c and other

parts is negative (88.). The currents in the plate are therefore from the
centre by the magnetic poles towards the circumference.

100. If the marked pole be placed above, all other things remaining the
same, the electricity at b, fig. 15, is still positive. If the marked pole be
placed below, or the unmarked pole above, the electricity is reversed. If the
direction of revolution in any case is reversed, the electricity is also
reversed.

101. It is now evident that the rotating plate is merely another form of the
simpler experiment of passing a piece of metal between the magnetic poles
in a rectilinear direction, and that in such cases currents of electricity are
produced at right angles to the direction of the motion, and crossing it at the
place of the magnetic pole or poles. This was sufficiently shown by the
following simple experiment: A piece of copper plate one fifth of an inch
thick, one inch and a half wide, and twelve inches long, being amalgamated
at the edges, was placed between the magnetic poles, whilst the two
conductors from the galvanometer were held in contact with its edges; it
was then drawn through between the poles of the conductors in the
direction of the arrow, fig. 16; immediately the galvanometer needle was
deflected, its north or marked end passed eastward, indicating that the wire
A received negative and the wire B positive electricity; and as the marked
pole was above, the result is in perfect accordance with the effect obtained
by the rotatory plate (99.).

102. On reversing the motion of the plate, the needle at the galvanometer
was deflected in the opposite direction, showing an opposite current.

103. To render evident the character of the electrical current existing in
various parts of the moving copper plate, differing in their relation to the
inducing poles, one collector (86.) only was applied at the part to be
examined near to the pole, the other being connected with the end of the
plate as the most neutral place: the results are given at fig. 17-20, the
marked pole being above the plate. In fig. 17, B received positive
electricity; but the plate moving in the same direction, it received on the
opposite side, fig. 18, negative electricity: reversing the motion of the latter,
as in fig. 20, B received positive electricity; or reversing the motion of the
first arrangement, that of fig. 17 to fig. 19, B received negative electricity.

104. When the plates were previously removed sideways from between the
magnets, as in fig. 21, so as to be quite out of the polar axis, still the same
effects were produced, though not so strongly.

105. When the magnetic poles were in contact, and the copper plate was
drawn between the conductors near to the place, there was but very little
effect produced. When the poles were opened by the width of a card, the
effect was somewhat more, but still very small.

106. When an amalgamated copper wire, one eighth of an inch thick, was
drawn through between the conductors and poles (101.), it produced a very
considerable effect, though not so much as the plates.

107. If the conductors were held permanently against any particular parts of
the copper plates, and carried between the magnetic poles with them, effects
the same as those described were produced, in accordance with the results
obtained with the revolving disc (94.).

108. On the conductors being held against the ends of the plates, and the
latter then passed between the magnetic poles, in a direction transverse to
their length, the same effects were produced (fig. 22.). The parts of the
plates towards the end may be considered either as mere conductors, or as
portions of metal in which the electrical current is excited, according to
their distance and the strength of the magnet; but the results were in perfect
harmony with those before obtained. The effect was as strong as when the
conductors were held against the sides of the plate (101.).

109. When a mere wire, connected with the galvanometer so as to form a
complete circuit, was passed through between the poles, the galvanometer
was affected; and upon moving the wire to and fro, so as to make the
alternate impulses produced correspond with the vibrations of the needle,
the latter could be increased to 20° or 30° on each side the magnetic
meridian.

110. Upon connecting the ends of a plate of metal with the galvanometer
wires, and then carrying it between the poles from end to end (as in fig.
23.), in either direction, no effect whatever was produced upon the

galvanometer. But the moment the motion became transverse, the needle
was deflected.

111. These effects were also obtained from electro-magnetic poles, resulting
from the use of copper helices or spirals, either alone or with iron cores (34.
54.). The directions of the motions were precisely the same; but the action
was much greater when the iron cores were used, than without.

112. When a flat spiral was passed through edgewise between the poles, a
curious action at the galvanometer resulted; the needle first went strongly
one way, but then suddenly stopped, as if it struck against some solid
obstacle, and immediately returned. If the spiral were passed through from
above downwards, or from below upwards, still the motion of the needle
was in the same direction, then suddenly stopped, and then was reversed.
But on turning the spiral half-way round, i.e. edge for edge, then the
directions of the motions were reversed, but still were suddenly interrupted
and inverted as before. This double action depends upon the halves of the
spiral (divided by a line passing through its centre perpendicular to the
direction of its motion) acting in opposite directions; and the reason why
the needle went to the same side, whether the spiral passed by the poles in
the one or the other direction, was the circumstance, that upon changing the
motion, the direction of the wires in the approaching half of the spiral was
changed also. The effects, curious as they appear when witnessed, are
immediately referable to the action of single wires (40. 109.).

113. Although the experiments with the revolving plate, wires, and plates of
metal, were first successfully made with the large magnet belonging to the
Royal Society, yet they were all ultimately repeated with a couple of bar
magnets two feet long, one inch and a half wide, and half an inch thick;
and, by rendering the galvanometer (87.) a little more delicate, with the
most striking results. Ferro-electro-magnets, as those of Moll, Henry, &c.
(57.), are very powerful. It is very essential, when making experiments on
different substances, that thermo-electric effects (produced by contact of the
fingers, &c.) be avoided, or at least appreciated and accounted for; they are
easily distinguished by their permanency, and their independence of the
magnets, or of the direction of the motion.

114. The relation which holds between the magnetic pole, the moving wire
or metal, and the direction of the current evolved, i.e. the law which
governs the evolution of electricity by magneto-electric induction, is very
simple, although rather difficult to express. If in fig. 24, PN represent a
horizontal wire passing by a marked magnetic pole, so that the direction of
its motion shall coincide with the curved line proceeding from below
upwards; or if its motion parallel to itself be in a line tangential to the
curved line, but in the general direction of the arrows; or if it pass the pole
in other directions, but so as to cut the magnetic curves13 in the same
general direction, or on the same side as they would be cut by the wire if
moving along the dotted curved line;—then the current of electricity in the
wire is from P to N. If it be carried in the reverse directions, the electric
current will be from N to P. Or if the wire be in the vertical position, figured
P' N', and it be carried in similar directions, coinciding with the dotted
horizontal curve so far, as to cut the magnetic curves on the same side with
it, the current will be from P' to N'. If the wire be considered a tangent to
the curved surface of the cylindrical magnet, and it be carried round that
surface into any other position, or if the magnet itself be revolved on its
axis, so as to bring any part opposite to the tangential wire,—still, if
afterwards the wire be moved in the directions indicated, the current of
electricity will be from P to N; or if it be moved in the opposite direction,
from N to P; so that as regards the motions of the wire past the pole, they
may be reduced to two, directly opposite to each other, one of which
produces a current from P to N, and the other from N to P.

115. The same holds true of the unmarked pole of the magnet, except that if
it be substituted for the one in the figure, then, as the wires are moved in the
direction of the arrows, the current of electricity would be from N to P, and
when they move in the reverse direction, from P to N.

116. Hence the current of electricity which is excited in metal when moving
in the neighbourhood of a magnet, depends for its direction altogether upon
the relation of the metal to the resultant of magnetic action, or to the
magnetic curves, and may be expressed in a popular way thus; Let AB (fig.
25.) represent a cylinder magnet, A being the marked pole, and B the
unmarked pole; let PN be a silver knife-blade, resting across the magnet
with its edge upward, and with its marked or notched side towards the pole

A; then in whatever direction or position this knife be moved edge
foremost, either about the marked or the unmarked pole, the current of
electricity produced will be from P to N, provided the intersected curves
proceeding from A abut upon the notched surface of the knife, and those
from B upon the unnotched side. Or if the knife be moved with its back
foremost, the current will be from N to P in every possible position and
direction, provided the intersected curves abut on the same surfaces as
before. A little model is easily constructed, by using a cylinder of wood for
a magnet, a flat piece for the blade, and a piece of thread connecting one
end of the cylinder with the other, and passing through a hole in the blade,
for the magnetic curves: this readily gives the result of any possible
direction.

117. When the wire under induction is passing by an electromagnetic pole,
as for instance one end of a copper helix traversed by the electric current
(34.), the direction of the current in the approaching wire is the same with
that of the current in the parts or sides of the spirals nearest to it, and in the
receding wire the reverse of that in the parts nearest to it.

118. All these results show that the power of inducing electric currents is
circumferentially exerted by a magnetic resultant or axis of power, just as
circumferential magnetism is dependent upon and is exhibited by an electric
current.

119. The experiments described combine to prove that when a piece of
metal (and the same may be true of all conducting matter (213.) ) is passed
either before a single pole, or between the opposite poles of a magnet, or
near electro-magnetic poles, whether ferruginous or not, electrical currents
are produced across the metal transverse to the direction of motion; and
which therefore, in Arago's experiments, will approximate towards the
direction of radii. If a single wire be moved like the spoke of a wheel near a
magnetic pole, a current of electricity is determined through it from one end
towards the other. If a wheel be imagined, constructed of a great number of
these radii, and this revolved near the pole, in the manner of the copper disc
(85.), each radius will have a current produced in it as it passes by the pole.
If the radii be supposed to be in contact laterally, a copper disc results, in
which the directions of the currents will be generally the same, being

modified only by the coaction which can take place between the particles,
now that they are in metallic contact.

120. Now that the existence of these currents is known, Arago's phenomena
may be accounted for without considering them as due to the formation in
the copper, of a pole of the opposite kind to that approximated, surrounded
by a diffuse polarity of the same kind (82.); neither is it essential that the
plate should acquire and lose its state in a finite time; nor on the other hand
does it seem necessary that any repulsive force should be admitted as the
cause of the rotation (82.).

121. The effect is precisely of the same kind as the electromagnetic
rotations which I had the good fortune to discover some years ago14.
According to the experiments then made which have since been abundantly
confirmed, if a wire (PN fig. 26.) be connected with the positive and
negative ends of a voltaic buttery, so that the positive electricity shall pass
from P to N, and a marked magnetic pole N be placed near the wire
between it and the spectator, the pole will move in a direction tangential to
the wire, i.e. towards the right, and the wire will move tangentially towards
the left, according to the directions of the arrows. This is exactly what takes
place in the rotation of a plate beneath a magnetic pole; for let N (fig. 27.)
be a marked pole above the circular plate, the latter being rotated in the
direction of the arrow: immediately currents of positive electricity set from
the central parts in the general direction of the radii by the pole to the parts
of the circumference a on the other side of that pole (99. 119.), and are
therefore exactly in the same relation to it as the current in the wire (PN,
fig. 26.), and therefore the pole in the same manner moves to the right hand.

122. If the rotation of the disc be reversed, the electric currents are reversed
(91.), and the pole therefore moves to the left hand. If the contrary pole be
employed, the effects are the same, i.e. in the same direction, because
currents of electricity, the reverse of those described, are produced, and by
reversing both poles and currents, the visible effects remain unchanged. In
whatever position the axis of the magnet be placed, provided the same pole
be applied to the same side of the plate, the electric current produced is in
the same direction, in consistency with the law already stated (114, &c.);

and thus every circumstance regarding the direction of the motion may be
explained.

123. These currents are discharged or return in the parts of the plate on
each side of and more distant from the place of the pole, where, of course,
the magnetic induction is weaker; and when the collectors are applied, and a
current of electricity is carried away to the galvanometer (88.), the
deflection there is merely a repetition, by the same current or part of it, of
the effect of rotation in the magnet over the plate itself.

124. It is under the point of view just put forth that I have ventured to say it
is not necessary that the plate should acquire and lose its state in a finite
time (120.); for if it were possible for the current to be fully developed the
instant before it arrived at its state of nearest approximation to the vertical
pole of the magnet, instead of opposite to or a little beyond it, still the
relative motion of the pole and plate would be the same, the resulting force
being in fact tangential instead of direct.

125. But it is possible (though not necessary for the rotation) that time may
be required for the development of the maximum current in the plate, in
which case the resultant of all the forces would be in advance of the magnet
when the plate is rotated, or in the rear of the magnet when the latter is
rotated, and many of the effects with pure electro-magnetic poles tend to
prove this is the case. Then, the tangential force may be resolved into two
others, one parallel to the plane of rotation, and the other perpendicular to
it; the former would be the force exerted in making the plate revolve with
the magnet, or the magnet with the plate; the latter would be a repulsive
force, and is probably that, the effects of which M. Arago has also
discovered (82.).

126. The extraordinary circumstance accompanying this action, which has
seemed so inexplicable, namely, the cessation of all phenomena when the
magnet and metal are brought to rest, now receives a full explanation (82.);
for then the electrical currents which cause the motion cease altogether.

127. All the effects of solution of metallic continuity, and the consequent
diminution of power described by Messrs. Babbage and Herschel15, now
receive their natural explanation, as well also as the resumption of power

when the cuts were filled up by metallic substances, which, though
conductors of electricity, were themselves very deficient in the power of
influencing magnets. And new modes of cutting the plate may be devised,
which shall almost entirely destroy its power. Thus, if a copper plate (81.)
be cut through at about a fifth or sixth of its diameter from the edge, so as to
separate a ring from it, and this ring be again fastened on, but with a
thickness of paper intervening (fig. 29.), and if Arago's experiment be made
with this compound plate so adjusted that the section shall continually
travel opposite the pole, it is evident that the magnetic currents will be
greatly interfered with, and the plate probably lose much of its effect16.

An elementary result of this kind was obtained by using two pieces of thick
copper, shaped as in fig. 28. When the two neighbouring edges were
amalgamated and put together, and the arrangement passed between the
poles of the magnet, in the direction parallel to these edges, a current was
urged through the wires attached to the outer angles, and the galvanometer
became strongly affected; but when a single film of paper was interposed,
and the experiment repeated, no sensible effect could be produced.

128. A section of this kind could not interfere much with the induction of
magnetism, supposed to be of the nature ordinarily received by iron.

129. The effect of rotation on deflection of the needle, which M. Arago
obtained by ordinary magnets, M. Ampère succeeded in procuring by
electro-magnets. This is perfectly in harmony with the results relative to
volta-electric and magneto-electric induction described in this paper. And
by using flat spirals of copper wire, through which electric currents were
sent, in place of ordinary magnetic poles (Ill.), sometimes applying a single
one to one side of the rotating plate, and sometimes two to opposite sides, I
obtained the induced currents of electricity from the plate itself, and could
lead them away to, and ascertain their existence by, the galvanometer.

130. The cause which has now been assigned for the rotation in Arago's
experiment, namely, the production of electrical currents, seems abundantly
sufficient in all cases where the metals, or perhaps even other conductors,
are concerned; but with regard to such bodies as glass, resins, and, above
all, gases, it seems impossible that currents of electricity, capable of
producing these effects, should be generated in them. Yet Arago found that

the effects in question were produced by these and by all bodies tried (81.).
Messrs. Babbage and Herschel, it is true, did not observe them with any
substance not metallic, except carbon, in a highly conducting state (82.).
Mr. Harris has ascertained their occurrence with wood, marble, freestone
and annealed glass, but obtained no effect with sulphuric acid and saturated
solution of sulphate of iron, although these are better conductors of
electricity than the former substances.

131. Future investigations will no doubt explain these difficulties, and
decide the point whether the retarding or dragging action spoken of is
always simultaneous with electric currents.17 The existence of the action in
metals, only whilst the currents exist, i.e. whilst motion is given (82. 88.),
and the explication of the repulsive action observed by M. Arago (82. 125.),
are powerful reasons for referring it to this cause; but it may be combined
with others which occasionally act alone.

132. Copper, iron, tin, zinc, lead, mercury, and all the metals tried, produced
electrical currents when passed between the magnetic poles: the mercury
was put into a glass tube for the purpose. The dense carbon deposited in
coal gas retorts, also produced the current, but ordinary charcoal did not.
Neither could I obtain any sensible effects with brine, sulphuric acid, saline
solutions, &c., whether rotated in basins, or inclosed in tubes and passed
between the poles.

133. I have never been able to produce any sensation upon the tongue by
the wires connected with the conductors applied to the edges of the
revolving plate (88.) or slips of metal (101.). Nor have I been able to heat a
fine platina wire, or produce a spark, or convulse the limbs of a frog. I have
failed also to produce any chemical effects by electricity thus evolved (22.
56).

134. As the electric current in the revolving copper plate occupies but a
small space, proceeding by the poles and being discharged right and left at
very small distances comparatively (123.); and as it exists in a thick mass of
metal possessing almost the highest conducting power of any, and
consequently offering extraordinary facility for its production and
discharge; and as, notwithstanding this, considerable currents may be drawn
off which can pass through narrow wires, forty, fifty, sixty, or even one

hundred feet long; it is evident that the current existing in the plate itself
must be a very powerful one, when the rotation is rapid and the magnet
strong. This is also abundantly proved by the obedience and readiness with
which a magnet ten or twelve pounds in weight follows the motion of the
plate and will strongly twist up the cord by which it is suspended.

135. Two rough trials were made with the intention of constructing
magneto-electric machines. In one, a ring one inch and a half broad and
twelve inches external diameter, cut from a thick copper plate, was mounted
so as to revolve between the poles of the magnet and represent a plate
similar to those formerly used (101.), but of interminable length; the inner
and outer edges were amalgamated, and the conductors applied one to each
edge, at the place of the magnetic poles. The current of electricity evolved
did not appear by the galvanometer to be stronger, if so strong, as that from
the circular plate (88.).

136. In the other, small thick discs of copper or other metal, half an inch in
diameter, were revolved rapidly near to the poles, but with the axis of
rotation out of the polar axis; the electricity evolved was collected by
conductors applied as before to the edges (86.). Currents were procured, but
of strength much inferior to that produced by the circular plate.

137. The latter experiment is analogous to those made by Mr. Barlow with a
rotating iron shell, subject to the influence of the earth18. The effects
obtained by him have been referred by Messrs. Babbage and Herschel to the
same cause as that considered as influential in Arago's experiment19; but it
would be interesting to know how far the electric current which might be
produced in the experiment would account for the deflexion of the needle.
The mere inversion of a copper wire six or seven times near the poles of the
magnet, and isochronously with the vibrations of the galvanometer needle
connected with it, was sufficient to make the needle vibrate through an arc
of 60° or 70°. The rotation of a copper shell would perhaps decide the point,
and might even throw light upon the more permanent, though somewhat
analogous effects obtained by Mr. Christie.

138. The remark which has already been made respecting iron (66.), and the
independence of the ordinary magnetical phenomena of that substance and
the phenomena now described of magneto-electric induction in that and

other metals, was fully confirmed by many results of the kind detailed in
this section. When an iron plate similar to the copper one formerly
described (101.) was passed between the magnetic poles, it gave a current
of electricity like the copper plate, but decidedly of less power; and in the
experiments upon the induction of electric currents (9.), no difference in the
kind of action between iron and other metals could be perceived. The power
therefore of an iron plate to drag a magnet after it, or to intercept magnetic
action, should be carefully distinguished from the similar power of such
metals as silver, copper, &c. &c., inasmuch as in the iron by far the greater
part of the effect is due to what may be called ordinary magnetic action.
There can be no doubt that the cause assigned by Messrs. Babbage and
Herschel in explication of Arago's phenomena is the true one, when iron is
the metal used.

139. The very feeble powers which were found by those philosophers to
belong to bismuth and antimony, when moving, of affecting the suspended
magnet, and which has been confirmed by Mr. Harris, seem at first
disproportionate to their conducting powers; whether it be so or not must be
decided by future experiment (73.)20. These metals are highly crystalline,
and probably conduct electricity with different degrees of facility in
different directions; and it is not unlikely that where a mass is made up of a
number of crystals heterogeneously associated, an effect approaching to that
of actual division may occur (127.); or the currents of electricity may
become more suddenly deflected at the confines of similar crystalline
arrangements, and so be more readily and completely discharged within the
mass.

Royal Institution, November 1831.

Note.—In consequence of the long period which has
intervened between the reading and printing of the
foregoing paper, accounts of the experiments have been
dispersed, and, through a letter of my own to M.
Hachette, have reached France and Italy. That letter was
translated (with some errors), and read to the Academy
of Sciences at Paris, 26th December, 1831. A copy of it
in Le Temps of the 28th December quickly reached

Signor Nobili, who, with Signor Antinori, immediately
experimented upon the subject, and obtained many of
the results mentioned in my letter; others they could not
obtain or understand, because of the brevity of my
account. These results by Signori Nobili and Antinori
have been embodied in a paper dated 31st January
1832, and printed and published in the number of the
Antologia dated November 1831 (according at least to
the copy of the paper kindly sent me by Signor Nobili).
It is evident the work could not have been then printed;
and though Signor Nobili, in his paper, has inserted my
letter as the text of his experiments, yet the
circumstance of back date has caused many here, who
have heard of Nobili's experiments by report only, to
imagine his results were anterior to, instead of being
dependent upon, mine.

I may be allowed under these circumstances to remark,
that I experimented on this subject several years ago,
and have published results. (See Quarterly Journal of
Science for July 1825, p. 338.) The following also is an
extract from my note-book, dated November 28, 1825:
"Experiments on induction by connecting wire of
voltaic battery:—a battery of four troughs, ten pairs of
plates, each arranged side by side—the poles connected
by a wire about four feet long, parallel to which was
another similar wire separated from it only by two
thicknesses of paper, the ends of the latter were attached
to a galvanometer:—exhibited no action, &c. &c. &c.—
Could not in any way render any induction evident from
the connecting wire." The cause of failure at that time is
now evident (79.).—M.F. April, 1832.

Second Series.

The Bakerian Lecture.

§ 5. Terrestrial Magneto-electric Induction. § 6. Force and Direction of
Magneto-electric Induction generally.

Read January 12, 1832.

§ 5. Terrestrial Magneto-electric Induction.

140. When the general facts described in the former paper were discovered,
and the law of magneto-electric induction relative to direction was
ascertained (114.), it was not difficult to perceive that the earth would
produce the same effect as a magnet, and to an extent that would, perhaps,
render it available in the construction of new electrical machines. The
following are some of the results obtained in pursuance of this view.

141. The hollow helix already described (6.) was connected with a
galvanometer by wires eight feet long; and the soft iron cylinder (34.) after
being heated red-hot and slowly cooled, to remove all traces of magnetism,
was put into the helix so as to project equally at both ends, and fixed there.
The combined helix and bar were held in the magnetic direction or line of
dip, and (the galvanometer needle being motionless) were then inverted, so
that the lower end should become the upper, but the whole still correspond
to the magnetic direction; the needle was immediately deflected. As the
latter returned to its first position, the helix and bar were again inverted; and
by doing this two or three times, making the inversions and vibrations to
coincide, the needle swung through an arc of 150° or 160°.

142. When one end of the helix, which may be called A, was uppermost at
first (B end consequently being below), then it mattered not in which
direction it proceeded during the inversion, whether to the right hand or left
hand, or through any other course; still the galvanometer needle passed in
the same direction. Again, when B end was uppermost, the inversion of the
helix and bar in any direction always caused the needle to be deflected one

way; that way being the opposite to the course of the deflection in the
former case.

143. When the helix with its iron core in any given position was inverted,
the effect was as if a magnet with its marked pole downwards had been
introduced from above into the inverted helix. Thus, if the end B were
upwards, such a magnet introduced from above would make the marked
end of the galvanometer needle pass west. Or the end B being downwards,
and the soft iron in its place, inversion of the whole produced the same
effect.

144. When the soft iron bar was taken out of the helix and inverted in
various directions within four feet of the galvanometer, not the slightest
effect upon it was produced.

145. These phenomena are the necessary consequence of the inductive
magnetic power of the earth, rendering the soft iron cylinder a magnet with
its marked pole downwards. The experiment is analogous to that in which
two bar magnets were used to magnetize the same cylinder in the same
helix (36.), and the inversion of position in the present experiment is
equivalent to a change of the poles in that arrangement. But the result is not
less an instance of the evolution of electricity by means of the magnetism of
the globe.

146. The helix alone was then held permanently in the magnetic direction,
and the soft iron cylinder afterwards introduced; the galvanometer needle
was instantly deflected; by withdrawing the cylinder as the needle returned,
and continuing the two actions simultaneously, the vibrations soon extended
through an arc of 180°. The effect was precisely the same as that obtained
by using a cylinder magnet with its marked pole downwards; and the
direction of motion, &c. was perfectly in accordance with the results of
former experiments obtained with such a magnet (39.). A magnet in that
position being used, gave the same deflections, but stronger. When the helix
was put at right angles to the magnetic direction or dip, then the
introduction or removal of the soft iron cylinder produced no effect at the
needle. Any inclination to the dip gave results of the same kind as those
already described, but increasing in strength as the helix approximated to
the direction of the dip.

147. A cylinder magnet, although it has great power of affecting the
galvanometer when moving into or out of the helix, has no power of
continuing the deflection (39.); and therefore, though left in, still the
magnetic needle comes to its usual place of rest. But upon repeating (with
the magnet) the experiment of inversion in the direction of the dip (141),
the needle was affected as powerfully as before; the disturbance of the
magnetism in the steel magnet, by the earth's inductive force upon it, being
thus shown to be nearly, if not quite, equal in amount and rapidity to that
occurring in soft iron. It is probable that in this way magneto-electrical
arrangements may become very useful in indicating the disturbance of
magnetic forces, where other means will not apply; for it is not the whole
magnetic power which produces the visible effect, but only the difference
due to the disturbing causes.

148. These favourable results led me to hope that the direct magneto-
electric induction of the earth might be rendered sensible; and I ultimately
succeeded in obtaining the effect in several ways. When the helix just
referred to (141. 6.) was placed in the magnetic dip, but without any
cylinder of iron or steel, and was then inverted, a feeble action at the needle
was observed. Inverting the helix ten or twelve times, and at such periods
that the deflecting forces exerted by the currents of electricity produced in it
should be added to the momentum of the needle (39.), the latter was soon
made to vibrate through an arc of 80° or 90°. Here, therefore, currents of
electricity were produced by the direct inductive power of the earth's
magnetism, without the use of any ferruginous matter, and upon a metal not
capable of exhibiting any of the ordinary magnetic phenomena. The
experiment in everything represents the effects produced by bringing the
same helix to one or both poles of any powerful magnet (50.).

149. Guided by the law already expressed (114.), I expected that all the
electric phenomena of the revolving metal plate could now be produced
without any other magnet than the earth. The plate so often referred to (85.)
was therefore fixed so as to rotate in a horizontal plane. The magnetic
curves of the earth (114. note), i.e. the dip, passes through this plane at
angles of about 70°, which it was expected would be an approximation to
perpendicularity, quite enough to allow of magneto-electric induction
sufficiently powerful to produce a current of electricity.

150. Upon rotation of the plate, the currents ought, according to the law
(114. 121.), to tend to pass in the direction of the radii, through all parts of
the plate, either from the centre to the circumference, or from the
circumference to the centre, as the direction of the rotation of the plate was
one way or the other. One of the wires of the galvanometer was therefore
brought in contact with the axis of the plate, and the other attached to a
leaden collector or conductor (86.), which itself was placed against the
amalgamated edge of the disc. On rotating the plate there was a distinct
effect at the galvanometer needle; on reversing the rotation, the needle went
in the opposite direction; and by making the action of the plate coincide
with the vibrations of the needle, the arc through which the latter passed
soon extended to half a circle.

151. Whatever part of the edge of the plate was touched by the conductor,
the electricity was the same, provided the direction of rotation continued
unaltered.

152. When the plate revolved screw-fashion, or as the hands of a watch, the
current of electricity (150.) was from the centre to the circumference; when
the direction of rotation was unscrew, the current was from the
circumference to the centre. These directions are the same with those
obtained when the unmarked pole of a magnet was placed beneath the
revolving plate (99.).

153. When the plate was in the magnetic meridian, or in any other plane
coinciding with the magnetic dip, then its rotation produced no effect upon
the galvanometer. When inclined to the dip but a few degrees, electricity
began to appear upon rotation. Thus when standing upright in a plane
perpendicular to the magnetic meridian, and when consequently its own
plane was inclined only about 20° to the dip, revolution of the plate evolved
electricity. As the inclination was increased, the electricity became more
powerful until the angle formed by the plane of the plate with the dip was
90°, when the electricity for a given velocity of the plate was a maximum.

154. It is a striking thing to observe the revolving copper plate become thus
a new electrical machine; and curious results arise on comparing it with the
common machine. In the one, the plate is of the best non-conducting
substance that can be applied; in the other, it is the most perfect conductor:

in the one, insulation is essential; in the other, it is fatal. In comparison of
the quantities of electricity produced, the metal machine does not at all fall
below the glass one; for it can produce a constant current capable of
deflecting the galvanometer needle, whereas the latter cannot. It is quite
true that the force of the current thus evolved has not as yet been increased
so as to render it available in any of our ordinary applications of this power;
but there appears every reasonable expectation that this may hereafter be
effected; and probably by several arrangements. Weak as the current may
seem to be, it is as strong as, if not stronger than, any thermo-electric
current; for it can pass fluids (23.), agitate the animal system, and in the
case of an electro-magnet has produced sparks (32.).

155. A disc of copper, one fifth of an inch thick and only one inch and a half
in diameter, was amalgamated at the edge; a square piece of sheet lead
(copper would have been better) of equal thickness had a circular hole cut
in it, into which the disc loosely fitted; a little mercury completed the
metallic communication of the disc and its surrounding ring; the latter was
attached to one of the galvanometer wires, and the other wire dipped into a
little metallic cup containing mercury, fixed upon the top of the copper axis
of the small disc. Upon rotating the disc in a horizontal plane, the
galvanometer needle could be affected, although the earth was the only
magnet employed, and the radius of the disc but three quarters of an inch; in
which space only the current was excited.

156. On putting the pole of a magnet under the revolving disc, the
galvanometer needle could be permanently deflected.

157. On using copper wires one sixth of an inch in thickness instead of the
smaller wires (86.) hitherto constantly employed, far more powerful effects
were obtained. Perhaps if the galvanometer had consisted of fewer turns of
thick wire instead of many convolutions of thinner, more striking effects
would have been produced.

158. One form of apparatus which I purpose having arranged, is to have
several discs superposed; the discs are to be metallically connected,
alternately at the edges and at the centres, by means of mercury; and are
then to be revolved alternately in opposite directions, i.e. the first, third,
fifth, &c. to the right hand, and the second, fourth, sixth, &c. to the left

hand; the whole being placed so that the discs are perpendicular to the dip,
or intersect most directly the magnetic curves of powerful magnets. The
electricity will be from the centre to the circumference in one set of discs,
and from the circumference to the centre in those on each side of them; thus
the action of the whole will conjoin to produce one combined and more
powerful current.

159. I have rather, however, been desirous of discovering new facts and
new relations dependent on magneto-electric induction, than of exalting the
force of those already obtained; being assured that the latter would find
their full development hereafter.

*****

160. I referred in my former paper to the probable influence of terrestrial
magneto-electric induction (137.) in producing, either altogether or in part,
the phenomena observed by Messrs. Christie and Barlow21, whilst revolving
ferruginous bodies; and especially those observed by the latter when rapidly
rotating an iron shell, which were by that philosopher referred to a change
in the ordinary disposition of the magnetism of the ball. I suggested also
that the rotation of a copper globe would probably insulate the effects due
to electric currents from those due to mere derangement of magnetism, and
throw light upon the true nature of the phenomena.

161. Upon considering the law already referred to (114.), it appeared
impossible that a metallic globe could revolve under natural circumstances,
without having electric currents produced within it, circulating round the
revolving globe in a plane at right angles to the plane of revolution,
provided its axis of rotation did not coincide with the dip; and it appeared
that the current would be most powerful when the axis of revolution was
perpendicular to the dip of the needle: for then all those parts of the ball
below a plane passing through its centre and perpendicular to the dip, would
in moving cut the magnetic curves in one direction, whilst all those parts
above that plane would intersect them in the other direction: currents
therefore would exist in these moving parts, proceeding from one pole of
rotation to the other; but the currents above would be in the reverse
direction to those below, and in conjunction with them would produce a
continued circulation of electricity.

162. As the electric currents are nowhere interrupted in the ball, powerful
effects were expected, and I endeavoured to obtain them with simple
apparatus. The ball I used was of brass; it had belonged to an old electrical
machine, was hollow, thin (too thin), and four inches in diameter; a brass
wire was screwed into it, and the ball either turned in the hand by the wire,
or sometimes, to render it more steady, supported by its wire in a notched
piece of wood, and motion again given by the hand. The ball gave no signs
of magnetism when at rest.

163. A compound magnetic needle was used to detect the currents. It was
arranged thus: a sewing-needle had the head and point broken off, and was
then magnetised; being broken in halves, the two magnets thus produced
were fixed on a stem of dried grass, so as to be perpendicular to it, and
about four inches asunder; they were both in one plane, but their similar
poles in contrary directions. The grass was attached to a piece of unspun
silk about six inches long, the latter to a stick passing through a cork in the
mouth of a cylindrical jar; and thus a compound arrangement was obtained,
perfectly sheltered from the motion of the air, but little influenced by the
magnetism of the earth, and yet highly sensible to magnetic and electric
forces, when the latter were brought into the vicinity of the one or the other
needle.

164. Upon adjusting the needles to the plane of the magnetic meridian;
arranging the ball on the outside of the glass jar to the west of the needles,
and at such a height that its centre should correspond horizontally with the
upper needle, whilst its axis was in the plane of the magnetic meridian, but
perpendicular to the dip; and then rotating the ball, the needle was
immediately affected. Upon inverting the direction of rotation, the needle
was again affected, but in the opposite direction. When the ball revolved
from east over to west, the marked pole went eastward; when the ball
revolved in the opposite direction, the marked pole went westward or
towards the ball. Upon placing the ball to the east of the needles, still the
needle was deflected in the same way; i.e. when the ball revolved from east
over to west, the marked pole wont eastward (or towards the ball); when the
rotation was in the opposite direction, the marked pole went westward.

165. By twisting the silk of the needles, the latter were brought into a
position perpendicular to the plane of the magnetic meridian; the ball was
again revolved, with its axis parallel to the needles; the upper was affected
as before, and the deflection was such as to show that both here and in the
former case the needle was influenced solely by currents of electricity
existing in the brass globe.

166. If the upper part of the revolving ball be considered as a wire moving
from east to west, over the unmarked pole of the earth, the current of
electricity in it should be from north to south (99. 114. 150.); if the under
part be considered as a similar wire, moving from west to east over the
same pole, the electric current should be from south to north; and the
circulation of electricity should therefore be from north above to south, and
below back to north, in a metal ball revolving from east above to west in
these latitudes. Now these currents are exactly those required to give the
directions of the needle in the experiments just described; so that the
coincidence of the theory from which the experiments were deduced with
the experiments themselves, is perfect.

167. Upon inclining the axis of rotation considerably, the revolving ball was
still found to affect the magnetic needle; and it was not until the angle
which it formed with the magnetic dip was rendered small, that its effects,
even upon this apparatus, were lost (153.). When revolving with its axis
parallel to the dip, it is evident that the globe becomes analogous to the
copper plate; electricity of one kind might be collected at its equator, and of
the other kind at its poles.

168. A current in the ball, such as that described above (161.), although it
ought to deflect a needle the same way whether it be to the right or the left
of the ball and of the axis of rotation, ought to deflect it the contrary way
when above or below the ball; for then the needle is, or ought to be, acted
upon in a contrary direction by the current. This expectation was fulfilled
by revolving the ball beneath the magnetic needle, the latter being still
inclosed in its jar. When the ball was revolved from east over to west, the
marked pole of the needle, instead of passing eastward, went westward; and
when revolved from west over to east, the marked pole went eastward.

169. The deflections of the magnetic needle thus obtained with a brass ball
are exactly in the same direction as those observed by Mr. Barlow in the
revolution of the iron shell; and from the manner in which iron exhibits the
phenomena of magneto-electric induction like any other metal, and distinct
from its peculiar magnetic phenomena (132.), it is impossible but that
electric currents must have been excited, and become active in those
experiments. What proportion of the whole effect obtained is due to this
cause, must be decided by a more elaborate investigation of all the
phenomena.

170. These results, in conjunction with the general law before stated (114.),
suggested an experiment of extreme simplicity, which yet, on trial, was
found to answer perfectly. The exclusion of all extraneous circumstances
and complexity of arrangement, and the distinct character of the indications
afforded, render this single experiment an epitome of nearly all the facts of
magneto-electric induction.

171. A piece of common copper wire, about eight feet long and one
twentieth of an inch in thickness, had one of its ends fastened to one of the
terminations of the galvanometer wire, and the other end to the other
termination; thus it formed an endless continuation of the galvanometer
wire: it was then roughly adjusted into the shape of a rectangle, or rather of
a loop, the upper part of which could be carried to and fro over the
galvanometer, whilst the lower part, and the galvanometer attached to it,
remained steady (Plate II. fig. 30.). Upon moving this loop over the
galvanometer from right to left, the magnetic needle was immediately
deflected; upon passing the loop back again, the needle passed in the
contrary direction to what it did before; upon repeating these motions of the
loop in accordance with the vibrations of the needle (39.), the latter soon
swung through 90° or more.

172. The relation of the current of electricity produced in the wire, to its
motion, may be understood by supposing the convolutions at the
galvanometer away, and the wire arranged as a rectangle, with its lower
edge horizontal and in the plane of the magnetic meridian, and a magnetic
needle suspended above and over the middle part of this edge, and directed
by the earth (fig. 30.). On passing the upper part of the rectangle from west

to east into the position represented by the dotted line, the marked pole of
the magnetic needle went west; the electric current was therefore from north
to south in the part of the wire passing under the needle, and from south to
north in the moving or upper part of the parallelogram. On passing the
upper part of the rectangle from east to west over the galvanometer, the
marked pole of the needle went east, and the current of electricity was
therefore the reverse of the former.

173. When the rectangle was arranged in a plane east and west, and the
magnetic needle made parallel to it, either by the torsion of its suspension
thread or the action of a magnet, still the general effects were the same. On
moving the upper part of the rectangle from north to south, the marked pole
of the needle went north; when the wire was moved in the opposite
direction, the marked pole went south. The same effect took place when the
motion of the wire was in any other azimuth of the line of dip; the direction
of the current always being conformable to the law formerly expressed
(114.), and also to the directions obtained with the rotating ball (101.).

174. In these experiments it is not necessary to move the galvanometer or
needle from its first position. It is quite sufficient if the wire of the rectangle
is distorted where it leaves the instrument, and bent so as to allow the
moving upper part to travel in the desired direction.

175. The moveable part of the wire was then arranged below the
galvanometer, but so as to be carried across the dip. It affected the
instrument as before, and in the same direction; i.e. when carried from west
to east under the instrument, the marked end of the needle went west, as
before. This should, of course, be the case; for when the wire is cutting the
magnetic dip in a certain direction, an electric current also in a certain
direction should be induced in it.

176. If in fig. 31 dp be parallel to the dip, and BA be considered as the
upper part of the rectangle (171.), with an arrow c attached to it, both these
being retained in a plane perpendicular to the dip,—then, however BA with
its attached arrow is moved upon dp as an axis, if it afterwards proceed in
the direction of the arrow, a current of electricity will move along it from B
towards A.

177. When the moving part of the wire was carried up or down parallel to
the dip, no effect was produced on the galvanometer. When the direction of
motion was a little inclined to the dip, electricity manifested itself; and was
at a maximum when the motion was perpendicular to the magnetic
direction.

178. When the wire was bent into other forms and moved, equally strong
effects were obtained, especially when instead of a rectangle a double
catenarian curve was formed of it on one side of the galvanometer, and the
two single curves or halves were swung in opposite directions at the same
time; their action then combined to affect the galvanometer: but all the
results were reducible to those above described.

179. The longer the extent of the moving wire, and the greater the space
through which it moves, the greater is the effect upon the galvanometer.

180. The facility with which electric currents are produced in metals when
moving under the influence of magnets, suggests that henceforth
precautions should always be taken, in experiments upon metals and
magnets, to guard against such effects. Considering the universality of the
magnetic influence of the earth, it is a consequence which appears very
extraordinary to the mind, that scarcely any piece of metal can be moved in
contact with others, either at rest, or in motion with different velocities or in
varying directions, without an electric current existing within them. It is
probable that amongst arrangements of steam-engines and metal machinery,
some curious accidental magneto-electric combinations may be found,
producing effects which have never been observed, or, if noticed, have
never as yet been understood.

*****

181. Upon considering the effects of terrestrial magneto-electric induction
which have now been described, it is almost impossible to resist the
impression that similar effects, but infinitely greater in force, may be
produced by the action of the globe, as a magnet, upon its own mass, in
consequence of its diurnal rotation. It would seem that if a bar of metal be
laid in these latitudes on the surface of the earth parallel to the magnetic
meridian, a current of electricity tends to pass through it from south to

north, in consequence of the travelling of the bar from west to east (172.),
by the rotation of the earth; that if another bar in the same direction be
connected with the first by wires, it cannot discharge the current of the first,
because it has an equal tendency to have a current in the same direction
induced within itself: but that if the latter be carried from east to west,
which is equivalent to a diminution of the motion communicated to it from
the earth (172.), then the electric current from south to north is rendered
evident in the first bar, in consequence of its discharge, at the same time, by
means of the second.

182. Upon the supposition that the rotation of the earth tended, by magneto-
electric induction, to cause currents in its own mass, these would, according
to the law (114.) and the experiments, be, upon the surface at least, from the
parts in the neighbourhood of or towards the plane of the equator, in
opposite directions to the poles; and if collectors could be applied at the
equator and at the poles of the globe, as has been done with the revolving
copper plate (150.), and also with magnets (220.), then negative electricity
would be collected at the equator, and positive electricity at both poles
(222.). But without the conductors, or something equivalent to them, it is
evident these currents could not exist, as they could not be discharged.

183. I did not think it impossible that some natural difference might occur
between bodies, relative to the intensity of the current produced or tending
to be produced in them by magneto-electric induction, which might be
shown by opposing them to each other; especially as Messrs. Arago,
Babbage, Herschel, and Harris, have all found great differences, not only
between the metals and other substances, but between the metals
themselves, in their power of receiving motion from or giving it to a magnet
in trials by revolution (130.). I therefore took two wires, each one hundred
and twenty feet long, one of iron and the other of copper. These were
connected with each other at their ends, and then extended in the direction
of the magnetic meridian, so as to form two nearly parallel lines, nowhere
in contact except at the extremities. The copper wire was then divided in the
middle, and examined by a delicate galvanometer, but no evidence of an
electrical current was obtained.

184. By favour of His Royal Highness the President of the Society, I
obtained the permission of His Majesty to make experiments at the lake in
the gardens of Kensington-palace, for the purpose of comparing, in a
similar manner, water and metal. The basin of this lake is artificial; the
water is supplied by the Chelsea Company; no springs run into it, and it
presented what I required, namely, a uniform mass of still pure water, with
banks ranging nearly from east to west, and from north to south.

185. Two perfectly clean bright copper plates, each exposing four square
feet of surface, were soldered to the extremities of a copper wire; the plates
were immersed in the water, north and south of each other, the wire which
connected them being arranged upon the grass of the bank. The plates were
about four hundred and eighty feet from each other, in a right line; the wire
was probably six hundred feet long. This wire was then divided in the
middle, and connected by two cups of mercury with a delicate
galvanometer.

186. At first, indications of electric currents were obtained; but when these
were tested by inverting the direction of contact, and in other ways, they
were found to be due to other causes than the one sought for. A little
difference in temperature; a minute portion of the nitrate of mercury used to
amalgamate the wires, entering into the water employed to reduce the two
cups of mercury to the same temperature; was sufficient to produce currents
of electricity, which affected the galvanometer, notwithstanding they had to
pass through nearly five hundred feet of water. When these and other
interfering causes were guarded against, no effect was obtained; and it
appeared that even such dissimilar substances as water and copper, when
cutting the magnetic curves of the earth with equal velocity, perfectly
neutralized each other's action.

187. Mr. Fox of Falmouth has obtained some highly important results
respecting the electricity of metalliferous veins in the mines of Cornwall,
which have been published in the Philosophical Transactions22. I have
examined the paper with a view to ascertain whether any of the effects were
probably referable to magneto-electric induction; but, though unable to
form a very strong opinion, believe they are not. When parallel veins
running east and west were compared, the general tendency of the

electricity in the wires was from north to south; when the comparison was
made between parts towards the surface and at some depth, the current of
electricity in the wires was from above downwards. If there should be any
natural difference in the force of the electric currents produced by magneto-
electric induction in different substances, or substances in different
positions moving with the earth, and which might be rendered evident by
increasing the masses acted upon, then the wires and veins experimented
with by Mr. Fox might perhaps have acted as dischargers to the electricity
of the mass of strata included between them, and the directions of the
currents would agree with those observed as above.

188. Although the electricity obtained by magneto-electric induction in a
few feet of wire is of but small intensity, and has not yet been observed
except in metals, and carbon in a particular state, still it has power to pass
through brine (23.); and, as increased length in the substance acted upon
produces increase of intensity, I hoped to obtain effects from extensive
moving masses of water, though quiescent water gave none. I made
experiments therefore (by favour) at Waterloo Bridge, extending a copper
wire nine hundred and sixty feet in length upon the parapet of the bridge,
and dropping from its extremities other wires with extensive plates of metal
attached to them to complete contact with the water. Thus the wire and the
water made one conducting circuit; and as the water ebbed or flowed with
the tide, I hoped to obtain currents analogous to those of the brass ball
(161.).

189. I constantly obtained deflections at the galvanometer, but they were
very irregular, and were, in succession, referred to other causes than that
sought for. The different condition of the water as to purity on the two sides
of the river; the difference in temperature; slight differences in the plates, in
the solder used, in the more or less perfect contact made by twisting or
otherwise; all produced effects in turn: and though I experimented on the
water passing through the middle arches only; used platina plates instead of
copper; and took every other precaution, I could not after three days obtain
any satisfactory results.

190. Theoretically, it seems a necessary consequence, that where water is
flowing, there electric currents should be formed; thus, if a line be imagined

passing from Dover to Calais through the sea, and returning through the
land beneath the water to Dover, it traces out a circuit of conducting matter,
one part of which, when the water moves up or down the channel, is cutting
the magnetic curves of the earth, whilst the other is relatively at rest. This is
a repetition of the wire experiment (171.), but with worse conductors. Still
there is every reason to believe that electric currents do run in the general
direction of the circuit described, either one way or the other, according as
the passage of the waters is up or down the channel. Where the lateral
extent of the moving water is enormously increased, it does not seem
improbable that the effect should become sensible; and the gulf stream may
thus, perhaps, from electric currents moving across it, by magneto-electric
induction from the earth, exert a sensible influence upon the forms of the
lines of magnetic variation23.

191. Though positive results have not yet been obtained by the action of the
earth upon water and aqueous fluids, yet, as the experiments are very
limited in their extent, and as such fluids do yield the current by artificial
magnets (23.), (for transference of the current is proof that it may be
produced (213.),) the supposition made, that the earth produces these
induced currents within itself (181.) in consequence of its diurnal rotation,
is still highly probable (222, 223.); and when it is considered that the
moving masses extend for thousands of miles across the magnetic curves,
cutting them in various directions within its mass, as well as at the surface,
it is possible the electricity may rise to considerable intensity.

192. I hardly dare venture, even in the most hypothetical form, to ask
whether the Aurora Borealis and Australia may not be the discharge of
electricity, thus urged towards the poles of the earth, from whence it is
endeavouring to return by natural and appointed means above the earth to
the equatorial regions. The non-occurrence of it in very high latitudes is not
at all against the supposition; and it is remarkable that Mr. Fox, who
observed the deflections of the magnetic needle at Falmouth, by the Aurora
Borealis, gives that direction of it which perfectly agrees with the present
view. He states that all the variations at night were towards the east24, and
this is what would happen if electric currents were setting from south to
north in the earth under the needle, or from north to south in space above it.

§ 6. General remarks and illustrations of the Force and Direction
of Magneto-electric Induction.

193. In the repetition and variation of Arago's experiment by Messrs.
Babbage, Herschel, and Harris, these philosophers directed their attention to
the differences of force observed amongst the metals and other substances
in their action on the magnet. These differences were very great25, and led
me to hope that by mechanical combinations of various metals important
results might be obtained (183.). The following experiments were therefore
made, with a view to obtain, if possible, any such difference of the action of
two metals,

194. A piece of soft iron bonnet-wire covered with cotton was laid bare and
cleaned at one extremity, and there fastened by metallic contact with the
clean end of a copper wire. Both wires were then twisted together like the
strands of a rope, for eighteen or twenty inches; and the remaining parts
being made to diverge, their extremities were connected with the wires of
the galvanometer. The iron wire was about two feet long, the continuation
to the galvanometer being copper.

195. The twisted copper and iron (touching each other nowhere but at the
extremity) were then passed between the poles of a powerful magnet
arranged horse-shoe fashion (fig. 32.); but not the slightest effect was
observed at the galvanometer, although the arrangement seemed fitted to
show any electrical difference between the two metals relative to the action
of the magnet,

196. A soft iron cylinder was then covered with paper at the middle part,
and the twisted portion of the above compound wire coiled as a spiral
around it, the connexion with the galvanometer still being made at the ends
A and B. The iron cylinder was then brought in contact with the poles of a
powerful magnet capable of raising thirty pounds; yet no signs of electricity
appeared at the galvanometer. Every precaution was applied in making and
breaking contact to accumulate effect, but no indications of a current could
be obtained.

197. Copper and tin, copper and zinc, tin and zinc, tin and iron, and zinc
and iron, were tried against each other in a similar manner (194), but not the
slightest sign of electric currents could be procured.

198. Two flat spirals, one of copper and the other of iron, containing each
eighteen inches of wire, were connected with each other and with the
galvanometer, and then put face to face so as to be in contrary directions.
When brought up to the magnetic pole (53.). No electrical indications at the
galvanometer were observed. When one was turned round so that both were
in the same direction, the effect at the galvanometer was very powerful.

199. The compound helix of copper and iron wire formerly described (8.)
was arranged as a double helix, one of the helices being all iron and
containing two hundred and fourteen feet, the other all copper and
continuing two hundred and eight feet. The two similar ends AA of the
copper and iron helix were connected together, and the other ends BB of
each helix connected with the galvanometer; so that when a magnet was
introduced into the centre of the arrangement, the induced currents in the
iron and copper would tend to proceed in contrary directions. Yet when a
magnet was inserted, or a soft iron bar within made a magnet by contact
with poles, no effect at the needle was produced.

200. A glass tube about fourteen inches long was filled with strong
sulphuric acid. Twelve inches of the end of a clean copper wire were bent
up into a bundle and inserted into the tube, so as to make good superficial
contact with the acid, and the rest of the wire passed along the outside of
the tube and away to the galvanometer. A wire similarly bent up at the
extremity was immersed in the other end of the sulphuric acid, and also
connected with the galvanometer, so that the acid and copper wire were in
the same parallel relation to each other in this experiment as iron and
copper were in the first (194). When this arrangement was passed in a
similar manner between the poles of the magnet, not the slightest effect at
the galvanometer could be perceived.

201. From these experiments it would appear, that when metals of different
kinds connected in one circuit are equally subject in every circumstance to
magneto-electric induction, they exhibit exactly equal powers with respect
to the currents which either are formed, or tend to form, in them. The same

even appears to be the case with regard to fluids, and probably all other
substances.

202. Still it seemed impossible that these results could indicate the relative
inductive power of the magnet upon the different metals; for that the effect
should be in some relation to the conducting power seemed a necessary
consequence (139.), and the influence of rotating plates upon magnets had
been found to bear a general relation to the conducting power of the
substance used.

203. In the experiments of rotation (81.), the electric current is excited and
discharged in the same substance, be it a good or bad conductor; but in the
experiments just described the current excited in iron could not be
transmitted but through the copper, and that excited in copper had to pass
through iron: i.e. supposing currents of dissimilar strength to be formed in
the metals proportionate to their conducting power, the stronger current had
to pass through the worst conductor, and the weaker current through the
best.

204. Experiments were therefore made in which different metals insulated
from each other were passed between the poles of the magnet, their
opposite ends being connected with the same end of the galvanometer wire,
so that the currents formed and led away to the galvanometer should oppose
each other; and when considerable lengths of different wires were used,
feeble deflections were obtained.

205. To obtain perfectly satisfactory results a new galvanometer was
constructed, consisting of two independent coils, each containing eighteen
feet of silked copper wire. These coils were exactly alike in shape and
number of turns, and were fixed side by side with a small interval between
them, in which a double needle could be hung by a fibre of silk exactly as in
the former instrument (87.). The coils may be distinguished by the letters
KL, and when electrical currents were sent through them in the same
direction, acted upon the needle with the sum of their powers; when in
opposite directions, with the difference of their powers.

206. The compound helix (199. 8.) was now connected, the ends A and B of
the iron with A and B ends of galvanometer coil K, and the ends A and B of

the copper with B and A ends of galvanometer coil L, so that the currents
excited in the two helices should pass in opposite directions through the
coils K and L. On introducing a small cylinder magnet within the helices,
the galvanometer needle was powerfully deflected. On disuniting the iron
helix, the magnet caused with the copper helix alone still stronger
deflection in the same direction. On reuniting the iron helix, and
unconnecting the copper helix, the magnet caused a moderate deflection in
the contrary direction. Thus it was evident that the electric current induced
by a magnet in a copper wire was far more powerful than the current
induced by the same magnet in an equal iron wire.

207. To prevent any error that might arise from the greater influence, from
vicinity or other circumstances, of one coil on the needle beyond that of the
other, the iron and copper terminations were changed relative to the
galvanometer coils KL, so that the one which before carried the current
from the copper now conveyed that from the iron, and vice versa. But the
same striking superiority of the copper was manifested as before. This
precaution was taken in the rest of the experiments with other metals to be
described.

208. I then had wires of iron, zinc, copper, tin, and lead, drawn to the same
diameter (very nearly one twentieth of an inch), and I compared exactly
equal lengths, namely sixteen feet, of each in pairs in the following manner:
The ends of the copper wire were connected with the ends A and B of
galvanometer coil K, and the ends of the zinc wire with the terminations A
and B of the galvanometer coil L. The middle part of each wire was then
coiled six times round a cylinder of soft iron covered with paper, long
enough to connect the poles of Daniell's horse-shoe magnet (56.) (fig. 33.),
so that similar helices of copper and zinc, each of six turns, surrounded the
bar at two places equidistant from each other and from the poles of the
magnet; but these helices were purposely arranged so as to be in contrary
directions, and therefore send contrary currents through the galvanometer
coils K and L,

209. On making and breaking contact between the soft iron bar and the
poles of the magnet, the galvanometer was strongly affected; on detaching
the zinc it was still more strongly affected in the same direction. On taking

all the precautions before alluded to (207.), with others, it was abundantly
proved that the current induced by the magnet in copper was far more
powerful than in zinc.

210. The copper was then compared in a similar manner with tin, lead, and
iron, and surpassed them all, even more than it did zinc. The zinc was then
compared experimentally with the tin, lead, and iron, and found to produce
a more powerful current than any of them. Iron in the same manner proved
superior to tin and lead. Tin came next, and lead the last.

211. Thus the order of these metals is copper, zinc, iron, tin, and lead. It is
exactly their order with respect to conducting power for electricity, and,
with the exception of iron, is the order presented by the magneto-rotation
experiments of Messrs. Babbage, Herschel, Harris, &c. The iron has
additional power in the latter kind of experiments, because of its ordinary
magnetic relations, and its place relative to magneto-electric action of the
kind now under investigation cannot be ascertained by such trials. In the
manner above described it may be correctly ascertained26.

212. It must still be observed that in these experiments the whole effect
between different metals is not obtained; for of the thirty-four feet of wire
included in each circuit, eighteen feet are copper in both, being the wire of
the galvanometer coils; and as the whole circuit is concerned in the
resulting force of the current, tin's circumstance must tend to diminish the
difference which would appear between the metals if the circuits were of
the same substances throughout. In the present case the difference obtained
is probably not more than a half of that which would be given if the whole
of each circuit were of one metal.

213. These results tend to prove that the currents produced by magneto-
electric induction in bodies is proportional to their conducting power. That
they are exactly proportional to and altogether dependent upon the
conducting power, is, I think, proved by the perfect neutrality displayed
when two metals or other substances, as acid, water, &c. &c. (201. 186.),
are opposed to each other in their action. The feeble current which tends to
be produced in the worse conductor, has its transmission favoured in the
better conductor, and the stronger current which tends to form in the latter
has its intensity diminished by the obstruction of the former; and the forces

of generation and obstruction are so perfectly neutralize each other exactly.
Now as the obstruction is inversely as the balanced as to conducting power,
the tendency to generate a current must be directly as that power to produce
this perfect equilibrium.

214. The cause of the equality of action under the various circumstances
described, where great extent of wire (183.) or wire and water (181.) were
connected together, which yet produced such different effects upon the
magnet, is now evident and simple.

215. The effects of a rotating substance upon a needle or magnet ought,
where ordinary magnetism has no influence, to be directly as the
conducting power of the substance; and I venture now to predict that such
will be found to be the case; and that in all those instances where non-
conductors have been supposed to exhibit this peculiar influence, the
motion has been due to some interfering cause of an ordinary kind; as
mechanical communication of motion through the parts of the apparatus, or
otherwise (as in the case Mr. Harris has pointed out27); or else to ordinary
magnetic attractions. To distinguish the effects of the latter from those of
the induced electric currents, I have been able to devise a most perfect test,
which shall be almost immediately described (243.).

216. There is every reason to believe that the magnet or magnetic needle
will become an excellent measurer of the conducting power of substances
rotated near it; for I have found by careful experiment, that when a constant
current of electricity was sent successively through a series of wires of
copper, platina, zinc, silver, lead, and tin, drawn to the same diameter; the
deflection of the needle was exactly equal by them all. It must be
remembered that when bodies are rotated in a horizontal plane, the
magnetism of the earth is active upon them. As the effect is general to the
whole of the plate, it may not interfere in these cases; but in some
experiments and calculations may be of important consequence.

217. Another point which I endeavoured to ascertain, was, whether it was
essential or not that the moving part of the wire should, in cutting the
magnetic curves, pass into positions of greater or lesser magnetic force; or
whether, always intersecting curves of equal magnetic intensity, the mere
motion was sufficient for the production of the current. That the latter is

true, has been proved already in several of the experiments on terrestrial
magneto-electric induction. Thus the electricity evolved from the copper
plate (149.), the currents produced in the rotating globe (161, &c.), and
those passing through the moving wire (171.), are all produced under
circumstances in which the magnetic force could not but be the same during
the whole experiments.

218. To prove the point with an ordinary magnet, a copper disc was
cemented upon the end of a cylinder magnet, with paper intervening; the
magnet and disc were rotated together, and collectors (attached to the
galvanometer) brought in contact with the circumference and the central
part of the copper plate. The galvanometer needle moved as in former cases,
and the direction of motion was the same as that which would have
resulted, if the copper only had revolved, and the magnet been fixed.
Neither was there any apparent difference in the quantity of deflection.
Hence, rotating the magnet causes no difference in the results; for a rotatory
and a stationary magnet produce the same effect upon the moving copper.

219. A copper cylinder, closed at one extremity, was then put over the
magnet, one half of which it inclosed like a cap; it was firmly fixed, and
prevented from touching the magnet anywhere by interposed paper. The
arrangement was then floated in a narrow jar of mercury, so that the lower
edge of the copper cylinder touched the fluid metal; one wire of the
galvanometer dipped into this mercury, and the other into a little cavity in
the centre of the end of the copper cap. Upon rotating the magnet and its
attached cylinder, abundance of electricity passed through the
galvanometer, and in the same direction as if the cylinder had rotated only,
the magnet being still. The results therefore were the same as those with the
disc (218.).

220. That the metal of the magnet itself might be substituted for the moving
cylinder, disc, or wire, seemed an inevitable consequence, and yet one
which would exhibit the effects of magneto-electric induction in a striking
form. A cylinder magnet had therefore a little hole made in the centre of
each end to receive a drop of mercury, and was then floated pole upwards in
the same metal contained in a narrow jar. One wire from the galvanometer
dipped into the mercury of the jar, and the other into the drop contained in

the hole at the upper extremity of the axis. The magnet was then revolved
by a piece of string passed round it, and the galvanometer-needle
immediately indicated a powerful current of electricity. On reversing the
order of rotation, the electrical current was reversed. The direction of the
electricity was the same as if the copper cylinder (219.) or a copper wire
had revolved round the fixed magnet in the same direction as that which the
magnet itself had followed. Thus a singular independence of the magnetism
and the bar in which it resides is rendered evident.

221. In the above experiment the mercury reached about halfway up the
magnet; but when its quantity was increased until within one eighth of an
inch of the top, or diminished until equally near the bottom, still the same
effects and the same direction of electrical current was obtained. But in
those extreme proportions the effects did not appear so strong as when the
surface of the mercury was about the middle, or between that and an inch
from each end. The magnet was eight inches and a half long, and three
quarters of an inch in diameter.

222. Upon inversion of the magnet, and causing rotation in the same
direction, i.e. always screw or always unscrew, then a contrary current of
electricity was produced. But when the motion of the magnet was continued
in a direction constant in relation to its own axis, then electricity of the same
kind was collected at both poles, and the opposite electricity at the equator,
or in its neighbourhood, or in the parts corresponding to it. If the magnet be
held parallel to the axis of the earth, with its unmarked pole directed to the
pole star, and then rotated so that the parts at its southern side pass from
west to east in conformity to the motion of the earth; then positive
electricity may be collected at the extremities of the magnet, and negative
electricity at or about the middle of its mass.

223. When the galvanometer was very sensible, the mere spinning of the
magnet in the air, whilst one of the galvanometer wires touched the
extremity, and the other the equatorial parts, was sufficient to evolve a
current of electricity and deflect the needle.

224. Experiments were then made with a similar magnet, for the purpose of
ascertaining whether any return of the electric current could occur at the

central or axial parts, they having the same angular velocity of rotation as
the other parts (259.) the belief being that it could not.

225. A cylinder magnet, seven inches in length, and three quarters of an
inch in diameter, had a hole pierced in the direction of its axis from one
extremity, a quarter of an inch in diameter, and three inches deep. A copper
cylinder, surrounded by paper and amalgamated at both extremities, was
introduced so as to be in metallic contact at the bottom of the hole, by a
little mercury, with the middle of the magnet; insulated at the sides by the
paper; and projecting about a quarter of an inch above the end of the steel.
A quill was put over the copper rod, which reached to the paper, and formed
a cup to receive mercury for the completion of the circuit. A high paper
edge was also raised round that end of the magnet and mercury put within
it, which however had no metallic connexion with that in the quill, except
through the magnet itself and the copper rod (fig. 34.). The wires A and B
from the galvanometer were dipped into these two portions of mercury; any
current through them could, therefore, only pass down the magnet towards
its equatorial parts, and then up the copper rod; or vice versa.

226. When thus arranged and rotated screw fashion, the marked end of the
galvanometer needle went west, indicating that there was a current through
the instrument from A to B and consequently from B through the magnet
and copper rod to A (fig. 34.).

227. The magnet was then put into a jar of mercury (fig. 35.) as before
(219.); the wire A left in contact with the copper axis, but the wire B dipped
in the mercury of the jar, and therefore in metallic communication with the
equatorial parts of the magnet instead of its polar extremity. On revolving
the magnet screw fashion, the galvanometer needle was deflected in the
same direction as before, but far more powerfully. Yet it is evident that the
parts of the magnet from the equator to the pole were out of the electric
circuit.

228. Then the wire A was connected with the mercury on the extremity of
the magnet, the wire B still remaining in contact with that in the jar (fig.
36.), so that the copper axis was altogether out of the circuit. The magnet
was again revolved screw fashion, and again caused the same deflection of

the needle, the current being as strong as it was in the last trial (227.), and
much stronger than at first (226.).

229. Hence it is evident that there is no discharge of the current at the centre
of the magnet, for the current, now freely evolved, is up through the
magnet; but in the first experiment (226.) it was down. In fact, at that time,
it was only the part of the moving metal equal to a little disc extending from
the end of the wire B in the mercury to the wire A that was efficient, i.e.
moving with a different angular velocity to the rest of the circuit (258.); and
for that portion the direction of the current is consistent with the other
results.

230. In the two after experiments, the lateral parts of the magnet or of the
copper rod are those which move relative to the other parts of the circuit,
i.e. the galvanometer wires; and being more extensive, intersecting more
curves, or moving with more velocity, produce the greater effect. For the
discal part, the direction of the induced electric current is the same in all,
namely, from the circumference towards the centre.

*****

231. The law under which the induced electric current excited in bodies
moving relatively to magnets, is made dependent on the intersection of the
magnetic curves by the metal (114.) being thus rendered more precise and
definite (217. 220. 224.), seem now even to apply to the cause in the first
section of the former paper (26.); and by rendering a perfect reason for the
effects produced, take away any for supposing that peculiar condition,
which I ventured to call the electro-tonic state (60.).

232. When an electrical current is passed through a wire, that wire is
surrounded at every part by magnetic curves, diminishing in intensity
according to their distance from the wire, and which in idea may be likened
to rings situated in planes perpendicular to the wire or rather to the electric
current within it. These curves, although different in form, are perfectly
analogous to those existing between two contrary magnetic poles opposed
to each other; and when a second wire, parallel to that which carries the
current, is made to approach the latter (18.), it passes through magnetic
curves exactly of the same kind as those it would intersect when carried

between opposite magnetic poles (109.) in one direction; and as it recedes
from the inducing wire, it cuts the curves around it in the same manner that
it would do those between the same poles if moved in the other direction.

233. If the wire NP (fig. 40.) have an electric current passed through it in
the direction from P to N, then the dotted ring may represent a magnetic
curve round it, and it is in such a direction that if small magnetic needles lie
placed as tangents to it, they will become arranged as in the figure, n and s
indicating north and south ends (14. note.).

234. But if the current of electricity were made to cease for a while, and
magnetic poles were used instead to give direction to the needles, and make
them take the same position as when under the influence of the current, then
they must be arranged as at fig. 41; the marked and unmarked poles ab
above the wire, being in opposite directions to those a'b' below. In such a
position therefore the magnetic curves between the poles ab and a'b' have
the same general direction with the corresponding parts of the ring magnetic
curve surrounding the wire NP carrying an electric current.

235. If the second wire pn (fig. 40.) be now brought towards the principal
wire, carrying a current, it will cut an infinity of magnetic curves, similar in
direction to that figured, and consequently similar in direction to those
between the poles ab of the magnets (fig. 41.), and it will intersect these
current curves in the same manner as it would the magnet curves, if it
passed from above between the poles downwards. Now, such an
intersection would, with the magnets, induce an electric current in the wire
from p to n (114.); and therefore as the curves are alike in arrangement, the
same effect ought to result from the intersection of the magnetic curves
dependent on the current in the wire NP; and such is the case, for on
approximation the induced current is in the opposite direction to the
principal current (19.).

236. If the wire p'n' be carried up from below, it will pass in the opposite
direction between the magnetic poles; but then also the magnetic poles
themselves are reversed (fig. 41.), and the induced current is therefore
(114.) still in the same direction as before. It is also, for equally sufficient
and evident reasons, in the same direction, if produced by the influence of
the curves dependent upon the wire.

237. When the second wire is retained at rest in the vicinity the principal
wire, no current is induced through it, for it is intersecting no magnetic
curves. When it is removed from the principal wire, it intersects the curves
in the opposite direction to what it did before (235.); and a current in the
opposite direction is induced, which therefore corresponds with the
direction of the principal current (19.). The same effect would take place if
by inverting the direction of motion of the wire in passing between either
set of poles (fig. 41.), it were made to intersect the curves there existing in
the opposite direction to what it did before.

238. In the first experiments (10. 13.), the inducing wire and that under
induction were arranged at a fixed distance from each other, and then an
electric current sent through the former. In such cases the magnetic curves
themselves must be considered as moving (if I may use the expression)
across the wire under induction, from the moment at which they begin to be
developed until the magnetic force of the current is at its utmost; expanding
as it were from the wire outwards, and consequently being in the same
relation to the fixed wire under induction as if it had moved in the opposite
direction across them, or towards the wire carrying the current. Hence the
first current induced in such cases was in the contrary direction to the
principal current (17. 235.). On breaking the battery contact, the magnetic
curves (which are mere expressions for arranged magnetic forces) may be
conceived as contracting upon and returning towards the failing electrical
current, and therefore move in the opposite direction across the wire, and
cause an opposite induced current to the first.

239. When, in experiments with ordinary magnets, the latter, in place of
being moved past the wires, were actually made near them (27. 36.), then a
similar progressive development of the magnetic curves may be considered
as having taken place, producing the effects which would have occurred by
motion of the wires in one direction; the destruction of the magnetic power
corresponds to the motion of the wire in the opposite direction.

240. If, instead of intersecting the magnetic curves of a straight wire
carrying a current, by approximating or removing a second wire (235.), a
revolving plate be used, being placed for that purpose near the wire, and, as
it were, amongst the magnetic curves, then it ought to have continuous

electric currents induced within it; and if a line joining the wire with the
centre of the plate were perpendicular to both, then the induced current
ought to be, according to the law (114.), directly across the plate, from one
side to the other, and at right angles to the direction of the inducing current.

241. A single metallic wire one twentieth of an inch in diameter had an
electric current passed through it, and a small copper disc one inch and a
half in diameter revolved near to and under, but not in actual contact with it
(fig. 39). Collectors were then applied at the opposite edges of the disc, and
wires from them connected with the galvanometer. As the disc revolved in
one direction, the needle was deflected on one side: and when the direction
of revolution was reversed, the needle was inclined on the other side, in
accordance with the results anticipated.

242. Thus the reasons which induce me to suppose a particular state in the
wire (60.) have disappeared; and though it still seems to me unlikely that a
wire at rest in the neighbourhood of another carrying a powerful electric
current is entirely indifferent to it, yet I am not aware of any distinct facts
which authorize the conclusion that it is in a particular state.

*****

243. In considering the nature of the cause assigned in these papers to
account for the mutual influence of magnets and moving metals (120.), and
comparing it with that heretofore admitted, namely, the induction of a
feeble magnetism like that produced in iron, it occurred to me that a most
decisive experimental test of the two views could be applied (215.).

244. No other known power has like direction with that exerted between an
electric current and a magnetic pole; it is tangential, while all other forces,
acting at a distance, are direct. Hence, if a magnetic pole on one side of a
revolving plate follow its course by reason of its obedience to the tangential
force exerted upon it by the very current of electricity which it has itself
caused, a similar pole on the opposite side of the plate should immediately
set it free from this force; for the currents which tend to be formed by the
action of the two poles are in opposite directions; or rather no current tends
to be formed, or no magnetic curves are intersected (114.); and therefore the
magnet should remain at rest. On the contrary, if the action of a north

magnetic pole were to produce a southness in the nearest part of the copper
plate, and a diffuse northness elsewhere (82.), as is really the case with iron;
then the use of another north pole on the opposite side of the same part of
the plate should double the effect instead of destroying it, and double the
tendency of the first magnet to move with the plate.

245. A thick copper plate (85.) was therefore fixed on a vertical axis, a bar
magnet was suspended by a plaited silk cord, so that its marked pole hung
over the edge of the plate, and a sheet of paper being interposed, the plate
was revolved; immediately the magnetic pole obeyed its motion and passed
off in the same direction. A second magnet of equal size and strength was
then attached to the first, so that its marked pole should hang beneath the
edge of the copper plate in a corresponding position to that above, and at an
equal distance (fig. 37.). Then a paper sheath or screen being interposed as
before, and the plate revolved, the poles were found entirely indifferent to
its motion, although either of them alone would have followed the course of
rotation.

246. On turning one magnet round, so that opposite poles were on each side
of the plate, then the mutual action of the poles and the moving metal was a
maximum.

247. On suspending one magnet so that its axis was level with the plate, and
either pole opposite its edge, the revolution of the plate caused no motion of
the magnet. The electrical currents dependent upon induction would now
tend to be produced in a vertical direction across the thickness of the plate,
but could not be so discharged, or at least only to so slight a degree as to
leave all effects insensible; but ordinary magnetic induction, or that on an
iron plate, would be equally if not more powerfully developed in such a
position (251.).

248. Then, with regard to the production of electricity in these cases:—
whenever motion was communicated by the plate to the magnets, currents
existed; when it was not communicated, they ceased. A marked pole of a
large bar magnet was put under the edge of the plate; collectors (86.)
applied at the axis and edge of the plate as on former occasions (fig. 38.),
and these connected with the galvanometer; when the plate was revolved,
abundance of electricity passed to the instrument. The unmarked pole of a

similar magnet was then put over the place of the former pole, so that
contrary poles were above and below; on revolving the plate, the electricity
was more powerful than before. The latter magnet was then turned end for
end, so that marked poles were both above and below the plate, and then,
upon revolving it, scarcely any electricity was procured. By adjusting the
distance of the poles so as to correspond with their relative force, they at
last were brought so perfectly to neutralize each other's inductive action
upon the plate, that no electricity could be obtained with the most rapid
motion.

249. I now proceeded to compare the effect of similar and dissimilar poles
upon iron and copper, adopting for the purpose Mr. Sturgeon's very useful
form of Arago's experiment. This consists in a circular plate of metal
supported in a vertical plane by a horizontal axis, and weighted a little at
one edge or rendered excentric so as to vibrate like a pendulum. The poles
of the magnets are applied near the side and edges of these plates, and then
the number of vibrations, required to reduce the vibrating arc a certain
constant quantity, noted. In the first description of this instrument28 it is said
that opposite poles produced the greatest retarding effect, and similar poles
none; and yet within a page of the place the effect is considered as of the
same kind with that produced in iron.

250. I had two such plates mounted, one of copper, one of iron. The copper
plate alone gave sixty vibrations, in the average of several experiments,
before the arc of vibration was reduced from one constant mark to another.
On placing opposite magnetic poles near to, and on each side of, the same
place, the vibrations were reduced to fifteen. On putting similar poles on
each side of it, they rose to fifty; and on placing two pieces of wood of
equal size with the poles equally near, they became fifty-two. So that, when
similar poles were used, the magnetic effect was little or none, (the
obstruction being due to the confinement of the air, rather,) whilst with
opposite poles it was the greatest possible. When a pole was presented to
the edge of the plate, no retardation occurred.

251. The iron plate alone made thirty-two vibrations, whilst the arc of
vibration diminished a certain quantity. On presenting a magnetic pole to

the edge of the plate (247.), the vibrations were diminished to eleven; and
when the pole was about half an inch from the edge, to five.

252. When the marked pole was put at the side of the iron plate at a certain
distance, the number of vibrations was only five. When the marked pole of
the second bar was put on the opposite side of the plate at the same distance
(250.), the vibrations were reduced to two. But when the second pole was
an unmarked one, yet occupying exactly the same position, the vibrations
rose to twenty-two. By removing the stronger of these two opposite poles a
little way from the plate, the vibrations increased to thirty-one, or nearly the
original number. But on removing it altogether, they fell to between five
and six.

253. Nothing can be more clear, therefore, than that with iron, and bodies
admitting of ordinary magnetic induction, opposite poles on opposite sides
of the edge of the plate neutralize each other's effect, whilst similar poles
exalt the action; a single pole end on is also sufficient. But with copper, and
substances not sensible to ordinary magnetic impressions, similar poles on
opposite sides of the plate neutralize each other; opposite poles exalt the
action; and a single pole at the edge or end on does nothing.

254. Nothing can more completely show the thorough independence of the
effects obtained with the metals by Arago, and those due to ordinary
magnetic forces; and henceforth, therefore, the application of two poles to
various moving substances will, if they appear at all magnetically affected,
afford a proof of the nature of that affection. If opposite poles produce a
greater effect than one pole, the result will be due to electric currents. If
similar poles produce more effect than one, then the power is not electrical;
it is not like that active in the metals and carbon when they are moving, and
in most cases will probably be found to be not even magnetical, but the
result of irregular causes not anticipated and consequently not guarded
against.

255. The result of these investigations tends to show that there are really but
very few bodies that are magnetic in the manner of iron. I have often sought
for indications of this power in the common metals and other substances;
and once in illustration of Arago's objection (82.), and in hopes of
ascertaining the existence of currents in metals by the momentary approach

of a magnet, suspended a disc of copper by a single fibre of silk in an
excellent vacuum, and approximated powerful magnets on the outside of
the jar, making them approach and recede in unison with a pendulum that
vibrated as the disc would do: but no motion could be obtained; not merely,
no indication of ordinary magnetic powers, but none or any electric current
occasioned in the metal by the approximation and recession of the magnet. I
therefore venture to arrange substances in three classes as regards their
relation to magnets; first, those which are affected when at rest, like iron,
nickel, &c., being such as possess ordinary magnetic properties; then, those
which are affected when in motion, being conductors of electricity in which
are produced electric currents by the inductive force of the magnet; and,
lastly, those which are perfectly indifferent to the magnet, whether at rest or
in motion.

256. Although it will require further research, and probably close
investigation, both experimental and mathematical, before the exact mode
of action between a magnet and metal moving relatively to each other is
ascertained; yet many of the results appear sufficiently clear and simple to
allow of expression in a somewhat general manner.—If a terminated wire
move so as to cut a magnetic curve, a power is called into action which
tends to urge an electric current through it; but this current cannot be
brought into existence unless provision be made at the ends of the wire for
its discharge and renewal.

257. If a second wire move in the same direction as the first, the same
power is exerted upon it, and it is therefore unable to alter the condition of
the first: for there appear to be no natural differences among substances
when connected in a series, by which, when moving under the same
circumstances relative to the magnet, one tends to produce a more powerful
electric current in the whole circuit than another (201. 214.).

258. But if the second wire move with a different velocity, or in some other
direction, then variations in the force exerted take place; and if connected at
their extremities, an electric current passes through them.

259. Taking, then, a mass of metal or an endless wire, and referring to the
pole of the magnet as a centre of action, (which though perhaps not strictly
correct may be allowed for facility of expression, at present,) if all parts

move in the same direction, and with the same angular velocity, and
through magnetic curves of constant intensity, then no electric currents are
produced. This point is easily observed with masses subject to the earth's
magnetism, and may be proved with regard to small magnets; by rotating
them, and leaving the metallic arrangements stationary, no current is
produced.

260. If one part of the wire or metal cut the magnetic curves, whilst the
other is stationary, then currents are produced. All the results obtained with
the galvanometer are more or less of this nature, the galvanometer
extremity being the fixed part. Even those with the wire, galvanometer, and
earth (170.), may be considered so without any error in the result.

261. If the motion of the metal be in the same direction, but the angular
velocity of its parts relative to the pole of the magnet different, then currents
are produced. This is the case in Arago's experiment, and also in the wire
subject to the earth's induction (172.), when it was moved from west to east.

262. If the magnet moves not directly to or from the arrangement, but
laterally, then the case is similar to the last.

263. If different parts move in opposite directions across the magnetic
curves, then the effect is a maximum for equal velocities.

264. All these in fact are variations of one simple condition, namely, that all
parts of the mass shall not move in the same direction across the curves, and
with the same angular velocity. But they are forms of expression which,
being retained in the mind, I have found useful when comparing the
consistency of particular phenomena with general results.

Royal Institution,

December 21, 1831.

Third Series.
§ 7. Identity of Electricities derived from different sources. § 8. Relation by measure of common and voltaic
Electricity.

[Read January 10th and 17th, 1833.]

§ 7. Identity of Electricities derived from different sources.

265. 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 perfectly true that Cavendish29,
Wollaston30, Colladon31, and others, have in succession removed some of the greatest objections to the
acknowledgement of the identity of common, animal and voltaic electricity, and I believe that most philosophers
consider these electricities as really the same. But on the other hand it is also true, that the accuracy of Wollaston's
experiments has been denied32; and also that one of them, which really is no proper proof of chemical
decomposition by common electricity (309. 327.), has been that selected by several experimenters as the test of
chemical action (336. 346.). 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 Torpedo33, thought it probable that animal electricity would be found of a peculiar
kind; and referring to it, to common electricity, voltaic electricity and magnetism, has said, "Distinctions might be
established in pursuing the various modifications or properties of electricity in those different forms, &c." Indeed I
need only refer to the last volume of the Philosophical Transactions to show that the question is by no means
considered as settled35.

266. 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.

267. 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 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 1st, Evolution 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.

268. 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.

269. 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 (312. 316.).

270. 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 approximated, 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
(291.) was charged so as to deflect the gold leaf electrometer to the same degree, the points were found equally
unable to discharge it with such effect as to produce either magnetic or chemical action. This was not because
common electricity could not produce both these effects (307. 310.); but because when of such low intensity the
quantity required to make the effects visible (being enormously great (371. 375.),) could not be transmitted in any
reasonable time. In conjunction with the other proofs of identity hereafter to be given, these effects of points also
prove identity instead of difference between voltaic and common electricity.

271. 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 therefore constructed (Plate III. fig. 46.), in
which AB 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 (312. 316.), from which the communication was completed to the negative pole of the
battery. In these experiments only two troughs, or twenty pairs of plates, were used.

272. 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 (270.), they were also more freely obtained.

273. 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 (302.), feeble deflections were
soon obtained: thus also proving the current through heated air; but the instrument used was not so sensible under
the circumstances as chemical action.

274. These effects, not hitherto known or expected under this form, are only cases of the discharge which takes
place through 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 inches36. In the exhausted receiver the electricity would strike through nearly half an inch of space, and the
combined effects of rarefaction and heat were such upon the inclosed air us to enable it to conduct the electricity
through a space of six or seven inches.

275. 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 says37, "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
connexions, 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."

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

277. 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.

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

279. 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.

280. 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.

*****

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

282. In consequence of the comparisons that will hereafter arise between wires carrying voltaic and ordinary
electricities, and also because of certain views of the condition of a wire or any other conducting substance
connecting the poles of a voltaic apparatus, it will be necessary to give some definite expression of what is called
the voltaic current, in contradistinction to any supposed peculiar state of arrangement, not progressive, which the
wire or the electricity within it may be supposed to assume. If two voltaic troughs PN, P'N', fig. 42, be
symmetrically arranged and insulated, and the ends NP' connected by a wire, over which a magnetic needle is
suspended, the wire will exert no effect over the needle; but immediately that the ends PN' 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 arrangement in the wire either of its particles or its electricity, that arrangement
constituting its electrical and magnetic state, then the wire NP' 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.

283. 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, progressive forces. By arrangement, I
understand a local adjustment of particles, or fluids, or forces, not progressive. Many other reasons might be urged
in support of the view of a current rather than an arrangement, but I am anxious to avoid stating unnecessarily
what will occur to others at the moment.

II. Ordinary Electricity.

284. 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.

285. 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 (268.); 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.

286. The discharge of common electricity through heated air is a well-known fact. The parallel case of voltaic
electricity has already been described (272, &c.).

287. In motion. i. Evolution of heat.—The heating power of common electricity, when passed through wires or
other substances, is perfectly well known. The accordance between it and voltaic electricity is in this respect
complete. Mr. Harris has constructed and described38 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 (344.).

288. ii. Magnetism.—Voltaic electricity has most extraordinary and exalted magnetic powers. If common
electricity be identical with it, it ought to have the same powers. In rendering 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 distinctions have been hypothetically assumed for the purpose of avoiding the
difficulty39.

289. 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 Academie des
Sciences in 182640, describes experiments, in which, by the use of a battery, points, and a delicate galvanometer, he
succeeded in obtaining deflections, and thus establishing identity in that respect. MM. Arago, Ampère, 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, Ampère, and Savary, not having themselves published (that I am
aware of) their admission of the results, and as some have not been able to obtain them, M. Colladon's conclusions
have been occasionally doubted or denied; and an important point with me was to establish their accuracy, or
remove them entirely from the body of received experimental research. I am happy to say that my results fully
confirm those by M. Colladon, and I should have had no occasion to describe them, but that they are essential as
proofs of the accuracy of the final and general conclusions I am enabled to draw respecting the magnetic and
chemical action of electricity (360. 366. 367. 377. &c.).

290. 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 revolution 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
4/5ths of a second.

291. 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 one hundred and eighty-four square inches of glass,
coated on both sides; this is independent of the bottoms, which are of thicker glass, and contain each about fifty
square inches.

292. 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.

293. The galvanometer was one or the other of those formerly described (87. 205.), 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 wire-work, having numerous sharp points
projecting from it. When this frame and the two coatings were connected with the discharging train (292.), 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.

294. In connexion with these precautions, it may be necessary 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 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.

295. 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 usually supposed to have.

296, The coating and armour of the galvanometer were first connected with the discharging train (292.); the end B
(87.) 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 connected with a discharging rod by a wet thread four
feet long; and finally, when the battery (291.) 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.

297. 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.

298. 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 discharge of the battery.

299. 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.

300. 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
(268.) and the negative surface of the former with the negative end of the latter.

301. The battery was then thrown out of use, and the communications so arranged that the current could be passed
from the prime conductor, by the discharging rod held against it, through the wet string, through the galvanometer
coil, and into the discharging train (292), 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 connecting the prime conductor by
another rod with the discharging train; and could be as instantly renewed. The needle was so adjusted, that whilst
vibrating in moderate and small arcs, it required time equal to twenty-five beats of a watch to pass in one direction
through the arc, and of course an equal time to pass in the other direction.

302. Thus arranged, and the needle being stationary, the current, direct from the machine, was sent through the
galvanometer 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.

303. 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 (300).

304. 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 (302).

305. 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 (302.), except with this variation, the needle was soon powerfully deflected, and in perfect consistency with
the former results. Points afforded the means by which Colladon, in all cases, made his discharges.

306. Finally, I passed the electricity first through an exhausted receiver, so as to make it there resemble the aurora
borealis, and then through the galvanometer to the earth; and it was found still effective in deflecting the needle,
and apparently with the same force as before.

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

308. Imperfect conductors, as water, brine, acids, &c. &c. 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 (294.).

309. 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 showed41 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 resemblance, and nothing more, to a
case of voltaic decomposition, which however he himself partly distinguished; and this has been more frequently
referred to by some, on the one hand, to prove the occurrence of electro-chemical decomposition, like that of the
pile, and by others to throw doubt upon the whole paper, than the more numerous and decisive experiments which
he has detailed.

310. 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 electrochemical decomposition (376. 377.).

311. I first repeated Wollaston's fourth experiment42, 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 precipitated, and no sensible trace of silver from the other pole appeared in the
solution.

312. A much more convenient and effectual arrangement for chemical decompositions by common electricity, is
the following. Upon a glass plate, fig. 43, 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 wire c, or wire and string
(301.) with the machine, and the other g, with the discharging train (292.) or the negative conductor; provide two
pieces of fine platina wire, bent as in fig. 44, so that the part d, f shall be nearly upright, whilst the whole is resting
on the three bearing points p, e, f place these as in fig. 43; 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 connexion can be broken
or renewed in a moment, and the substances acted upon examined with the utmost facility.

313. 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
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.

314. 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. 43, 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 revolutions no effect of the kind was visible at n,
but so much chlorine had been set free at p, that when the drop was stirred the whole became colourless.

315. 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.

316. 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 potassium and starch, or of the iodide alone, with certain precautions (322.),
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
(273.). Such cases occur when the bodies traversed by the current are bad conductors, or when the quantity of
electricity evolved or transmitted in a given time is very small.

317. 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.

318. A piece of turmeric paper moistened in solution of sulphate of soda was reddened at n by two or three turns of
the machine, and in twenty or thirty turns plenty of alkali was there evolved. On turning the paper round, so that
the spot came under p, and then working the machine, the alkali soon disappeared, the place became yellow, and a
brown alkaline spot appeared in the new part under n.

319. 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.

320. 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, 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.

321. Finally, the experiment was extended into the following form, supplying in this case the tidiest analogy
between common and voltaic electricity. Three compound pieces of litmus and turmeric paper (319.) were
moistened in solution of sulphate of soda, and arranged on a plate of glass with platina wires, as in fig. 45. The
wire m was connected with the prime conductor 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.

322. In all experiments of electro-chemical decomposition by the common machine and moistened papers (316.), it
is necessary 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 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 electricity through the air from either the point p or n, iodine will be immediately evolved.

323. These effects must not be confounded with those due to the true electro-chemical powers of common
electricity, and must be carefully avoided when the latter are to be observed. No sparks should be passed,
therefore, in any part of the current, nor any increase of intensity allowed, by which the electricity may be induced
to pass between the platina wires and the moistened papers, otherwise than by conduction; for if it burst through
the air, the effect referred to above (322.) ensues.

324. 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.

325. By moistening a very small slip of litmus paper in solution of caustic potassa, and then passing the electric
spark over its length in the air, I gradually neutralized 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.

326. 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.

327. I have already had occasion to refer to an experiment (265. 309.) 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 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.

328. This experiment is neither more nor less than a repetition, in a refined manner, of that made by Dr. Pearson in
179743, and previously by MM. Paets 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 (278. 309.) 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.

329. When electro-chemical decomposition takes place, there is great reason to believe that the quantity of matter
decomposed is not proportionate to the intensity, but to the quantity of electricity passed (320.). Of this I shall be
able to offer some proofs in a future part of this paper (375. 377.). But in the experiment under consideration, this
is not the case. If, with a constant pair of points, the electricity be passed from the machine in sparks, a certain
proportion of gas is evolved; but if the sparks be rendered shorter, less gas is evolved; and if no sparks be passed,
there is scarcely a sensible portion of gases set free. On substituting solution of sulphate of soda for water, scarcely
a sensible quantity of gas could be procured even with powerful sparks, and nearly none with the mere current; yet
the quantity of electricity in a given time was the same in all these cases.

330. 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 (329.), 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 (377.) relating to the amount of chemical action be
correct, this ought to be the case.

331. 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 (336. 346.) 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.

332. 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 from the battery (291.) charged by eight or
ten44 revolutions of the machine in good action (290.), 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.

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

334. When the Leyden battery (291.) 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, resembling 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.

335. 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 (284.), 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.

336. M. Bonijol of Geneva45 is said to have constructed very delicate apparatus for the decomposition of water by
common electricity. By connecting an insulated lightning rod with his apparatus, the decomposition of the water
proceeded in a continuous 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 (327.); and as that does not furnish a case of true polar electro-chemical
decomposition (328.), this result of M. Bonijol does not prove the identity in chemical action of common and
voltaic electricity.

337. At the same page of the Bibliothèque 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 decomposition, 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 (322.). As nitrogen can combine directly with oxygen under the
influence of the electric spark (324.), 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.

338. The late Mr. Barry communicated a paper to the Royal Society46 last year, so distinct in the details, that it
would seem at once to prove the identity in chemical action of common and voltaic electricity; but, when
examined, considerable difficulty arises in reconciling certain of the effects with the remainder. He used two tubes,
each having a wire within it passing through the closed end, as is usual for voltaic decompositions. The tubes were
filled with solution of sulphate of soda, coloured with syrup of violets, and connected by a portion of the same
solution, in the ordinary manner; the wire in one tube was connected by a gilt thread with the string of an insulated
electrical kite, and the wire in the other tube by a similar gilt thread with the 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."

339. 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 decomposition 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 apparatus, 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 (290.) 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 (371.), 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."

340. 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.

341. 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 electricity 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 (371. 376.), 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 (292.), and its negative pole with an
apparatus like that of Mr. Barry, communicating by a wire inserted 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.

342. 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 electrical current, which, both in quantity and intensity, is exactly intermediate with those of the
common electrical machine and the voltaic pile.

III. Magneto-Electricity.

343. 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 action47, was able to obtain great divergence of the gold leaves of an electrometer48.

344. 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 (287.), and the magneto-electric coil
described in my first paper (34.), were put in requisition. The latter had been modified in the manner I have
elsewhere described49 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
and broken, expansion of the air within the instrument occurred, indicating an increase, at the moment, of the
temperature of the wire.

345. ii. Magnetism.—These currents were discovered by their magnetic power.

346. iii. Chemical decomposition.—I have made many endeavours to effect chemical decomposition by magneto-
electricity, but unavailingly. In July last I received an anonymous letter (which has since been published50,)
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 (327. &c.), in which case the results did not
indicate polar electro-chemical decomposition. Signor Botto has recently published certain results which he has
obtained51; but they are, as at present described, inconclusive. The apparatus he used was apparently that of Dr.
Wollaston, which gives only fallacious indications (327. &c.). 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 (343.) has
however, in the hands of himself52 and M. Hachctte53, 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.

347. iv. Physiological effects.—A frog was convulsed in the earliest experiments on these currents (56.). The
sensation upon the tongue, and the flash before the eyes, which I at first obtained only in a feeble degree (56.),
have been since exalted by more powerful apparatus, so as to become even disagreeable.

348. v. Spark.—The feeble spark which I first obtained with these currents (32.), 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.

IV. Thermo-Electricity.

349. With regard to thermo-electricity, (that beautiful form of electricity discovered by Seebeck,) the very
conditions under which it is excited are such as to give no ground for expecting that it can be raised like common
electricity to any high degree of tension; the effects, therefore, due to that state are not to be expected. The sum of
evidence respecting its analogy to the electricities already described, is, I believe, as follows:—Tension. The
attractions and repulsions due to a certain degree of tension have not been observed. In currents: i. Evolution of
Heat. I am not aware that its power of raising temperature has been observed. ii. Magnetism. It was discovered,
and is best recognised, by its magnetic powers. iii. Chemical decomposition has not been effected by it. iv.
Physiological effects. Nobili has shown54 that these currents are able to cause contractions in the limbs of a frog. v.
Spark. The spark has not yet been seen.

350. Only those effects are weak or deficient which depend upon a certain high degree of intensity; and if common
electricity be reduced in that quality to a similar degree with the thermo-electricity, it can produce no effects
beyond the latter.

V. Animal Electricity.

351. After an examination of the experiments of Walsh55 Ingenhousz56, Cavendish57, Sir H. Davy58, and Dr. Davy59,
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:—

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

353. In motion: i. Evolution of Heat; not yet observed; I have little or no doubt that Harris's electrometer would
show it (287. 359.).

354. ii. Magnetism.—Perfectly distinct. According to Dr. Davy60, the current deflected the needle and made
magnets under the same law, as to direction, which governs currents of ordinary and voltaic electricity.

355. iii. Chemical decomposition.—Also distinct; and though Dr. Davy used an apparatus of similar construction
with that of Dr. Wollaston (327.), 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.

356. Another reason for the decomposition being electrochemical is, that a Wollaston's apparatus constructed with
wires, coated by sealing-wax, would most probably not have decomposed water, even in its own peculiar way,
unless the electricity 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 successfully, and there is no doubt with more success than
weaker ones.

357. iv. Physiological effects.—These are so characteristic, that by them the peculiar powers of the torpedo and
gymnotus are principally recognised.

358. 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 in London, by placing the
gymnotus in the air, and interrupting the conducting chain by two gold leaves pasted upon glass, and a line distant
from each other61." I cannot, however, 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 Encyclopædia Britannica, Edinb. 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 doubtful62.

359. 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 (330. 339.), yet the current from the torpedo has done it. The
same high proportion is shown by the magnetic effects (296. 371.). These circumstances indicate that the torpedo
has power (in the way probably that Cavendish 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 succession. In reality, however, there is no philosophical
difference between these two cases.

360. 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 or 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 intensity63 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.

Table of the experimental Effects common to the Electricities derived from different Sources64.

True Attraction
Physiological Magnetic Magnets Heating
Spark. chemical and
Effects Deflection. made. Power.
Action. Repulsion
1. Voltaic
X X X X X X X
electricity
2.
Common X X X X X X X
electricity

3.
Magneto- X X X X X X X
Electricity
4.
Thermo- X X + + + +
Electricity
5. Animal
X X X + + X
Electricity

§ 8. Relation by Measure of common and voltaic Electricity.65

361. Believing the point of identity to be satisfactorily established, 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 (378.), but also of demonstrating certain general principles (366,
377, &c.), and creating an extension of the means of investigating and applying the chemical powers of this
wonderful and subtile agent.

362. The first point to be determined was, whether the same absolute quantity of ordinary electricity, sent through
a galvanometer, under different circumstances, would cause the same deflection of the needle. An arbitrary scale
was therefore attached to the galvanometer, each division of which was equal to about 4°, and the instrument
arranged as in former experiments (296.). The machine (290.), battery (291.), 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.

363. Seven of the battery jars were removed, and eight retained for present use. It was found that about forty turns
would fully charge the eight jars. They were then charged by thirty turns of the machine, and discharged through
the galvanometer, a thick wet string, about ten inches long, being included in the circuit. The needle was
immediately deflected five divisions and a half, on the one side of the zero, and in vibrating passed as nearly as
possible through five divisions and a half on the other side.

364. 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.

365. Other experiments were then made, in which all the battery was used, and its charge (being fifty turns of the
machine,) sent through the galvanometer: but it was modified by being passed sometimes through a mere wet
thread, sometimes through thirty-eight inches of thin string wetted by distilled water, and sometimes through a
string of twelve times the thickness, only twelve inches in length, and soaked in dilute acid (298.). With the thick
string the charge passed at once; with the thin string it occupied a sensible time, and with the thread it required two
or three seconds before the electrometer fell entirely down. The current therefore must have varied extremely in
intensity in these different cases, and yet the deflection of the needle was sensibly the same in all of them. If any
difference occurred, it was that the thin string and thread caused greatest deflection; and if there is any lateral
transmission, as M. Colladon says, through the silk in the galvanometer coil, it ought to have been so, because then
the intensity is lower and the lateral transmission less.

366. 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.

367. 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 be66.

368. 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 galvanometer67. 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 been68.

369. The next point was to obtain a voltaic arrangement producing an effect equal to that just described (367.). 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 apparatus, which, by immersion in a given acid for a
given time, much less than that required by the needle to swing in one direction, should give equal deflection to the
instrument with the discharge of ordinary electricity from the battery (363. 364.); and a new part of the zinc wire
having been brought into position with the platina, the comparative experiments were made.

370. 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.

371. Hence, as an approximation, and judging from magnetic force only at present (376.), 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 immersed 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 8/150ths of a minute, as the electrical battery charged by thirty turns of the large
machine, in excellent order (363. 364.). 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.

372. 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 5-1/3 division. Hence a permanent deflection to that extent might be considered as indicating a
constant voltaic current, which in eight beats of my watch (369.) could supply as much electricity as the electrical
battery charged by thirty turns of the machine.

373. 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 (369.), so as always to form
the positive pole, and at the same time retain a perpendicular position, that it might rest, with its whole weight,
upon the test paper to be employed. The test paper itself was supported upon a platina spatula, connected either
with the discharging train (292.), or with the negative wire of the voltaic apparatus, and it consisted of four
thicknesses, moistened at all times to an equal degree in a standard solution of hydriodate of potassa (316.).

374. 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.

375. The wire and spatula were then connected with the voltaic apparatus (369.), 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 5-1/3 division (372.),

the fourfold moistened paper intervening as before69. 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 (369.) 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.

376. Hence it results that both in magnetic deflection (371.) 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.

377. It also follows that for this case of electro-chemical decomposition, and it is probable for all cases, that the
chemical power, like the magnetic force (36.), is in direct proportion to the absolute quantity of electricity which
passes.

378. Hence arises still further confirmation, if any were required, of the identity of common and voltaic electricity,
and that the differences of intensity and quantity are quite sufficient to account for what were supposed to be their
distinctive qualities.

379. 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.

Royal Institution, 15th Dec. 1832.

Note.—I am anxious, and am permitted, to add to this paper a correction of an error which I
have attributed to M. Ampère in the first series of these Experimental Researches. In referring
to his experiment on the induction of electrical currents (78.), I have called that a disc which I
should have called a circle or a ring. M. Ampère used a ring, or a very short cylinder made of a
narrow plate of copper bent into a circle, and he tells me that by such an arrangement the
motion is very readily obtained. I have not doubted that M. Ampère obtained the motion he
described; but merely mistook the kind of mobile conductor used, and so far I described his
experiment erroneously.

In the same paragraph I have stated that M. Ampère says the disc turned "to take a position of
equilibrium exactly as the spiral itself would have turned had it been free to move"; and further
on I have said that my results tended to invert the sense of the proposition "stated by M.
Ampère, that a current of electricity tends to put the electricity of conductors near which it
passes in motion in the same direction." M. Ampère tells me in a letter which I have just
received from him, that he carefully avoided, when describing the experiment, any reference to
the direction of the induced current; and on looking at the passages he quotes to me, I find that
to be the case. I have therefore done him injustice in the above statements, and am anxious to
correct my error.

But that it may not be supposed I lightly wrote those passages, I will briefly refer to my
reasons for understanding them in the sense I did. At first the experiment failed. When re-made
successfully about a year afterwards, it was at Geneva in company with M.A. De la Rive: the
latter philosopher described the results70, and says that the plate of copper bent into a circle
which was used as the mobile conductor "sometimes advanced between the two branches of
the (horse-shoe) magnet, and sometimes was repelled, according to the direction of the current
in the surrounding conductors."

I have been in the habit of referring to Demonferrand's Manuel d'Electricité Dynamique, as a
book of authority in France; containing the general results and laws of this branch of science,
up to the time of its publication, in a well arranged form. At p. 173, the author, when
describing this experiment, says, "The mobile circle turns to take a position of equilibrium as a
conductor would do in which the current moved in the same direction as in the spiral;" and in

the same paragraph he adds, "It is therefore proved that a current of electricity tends to put the
electricity of conductors, near which it passes, in motion in the same direction." These are the
words I quoted in my paper (78.).

Le Lycée of 1st of January, 1832, No. 36, in an article written after the receipt of my first
unfortunate letter to M. Hachette, and before my papers were printed, reasons upon the
direction of the induced currents, and says, that there ought to be "an elementary current
produced in the same direction as the corresponding portion of the producing current." A little
further on it says, "therefore we ought to obtain currents, moving in the same direction,
produced upon a metallic wire, either by a magnet or a current. M. Ampère was so thouroughly
persuaded that such ought to be the direction of the currents by influence, that he neglected to
assure himself of it in his experiment at Geneva."

It was the precise statements in Demonferrand's Manuel, agreeing as they did with the
expression in M. De la Rive's paper, (which, however, I now understand as only meaning that
when the inducing current was changed, the motion of the mobile circle changed also,) and not
in discordance with anything expressed by M. Ampère himself where he speaks of the
experiment, which made me conclude, when I wrote the paper, that what I wrote was really his
avowed opinion; and when the Number of the Lycée referred to appeared, which was before
my paper was printed, it could excite no suspicion that I was in error.

Hence the mistake into which I unwittingly fell. I am proud to correct it and do full justice to
the acuteness and accuracy which, as far as I can understand the subjects, M. Ampère carries
into all the branches of philosophy which he investigates.

Finally, my note to (79.) says that the Lycée, No. 36. "mistakes the erroneous results of MM.
Fresnel and Ampère for true ones," &c. &c. In calling M. Ampère's results erroneous, I spoke
of the results described in, and referred to by the Lycée itself; but now that the expression of
the direction of the induced current is to be separated, the term erroneous ought no longer to be
attached to them.

April 29, 1833.

M.F.

Fourth Series.
§ 9. On a new Law of Electric Conduction. § 10. On Conducting Power generally.

Received April 24,—Read May 23, 1833.

§ 9. On a new Law of Electric Conduction.71

380. 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.

381. 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 electricity; 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.

382. 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 of the arrangements, and the following more
unexceptionable form of experiment was adopted.

383. 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 plate, these were easily connected, when required, with a voltaic pile. Then distilled water, previously boiled
for three hours, was poured into the vessels, and frozen by a mixture of salt and snow, so that pure transparent
solid ice intervened between the platina and tin; and finally these metals were connected with the opposite
extremities of the voltaic apparatus, a galvanometer being at the same time included in the circuit.

384. In the first experiment, the platina pole was three inches and a half long, and seven eighths of an inch wide; it
was wholly immersed in the water or ice, and as the vessel was four eighths of an inch in width, the average
thickness of the intervening ice was only a quarter of an inch, whilst the surface of contact with it at both poles was
nearly fourteen square inches. After the water was frozen, the vessel was still retained in the frigorific mixture,
whilst contact between the tin and platina respectively was made with the extremities of a well-charged voltaic
battery, consisting of twenty pairs of four-inch plates, each with double coppers. Not the slightest deflection of the
galvanometer needle occurred.

385. 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 connexion with the battery being in the mean time retained, the needle did not at
first move; and it was only when the thawing process had extended so far as to liquefy part of the ice touching the
platina pole, that conduction took place; but then it occurred effectually, and the galvanometer needle was
permanently deflected nearly 70°.

386. 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.

387. 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 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.

388. 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.

389. 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.

390. It seemed at first as if occasional departures from these effects occurred; but they could always be traced to
some interfering 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, extending 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 concentrated 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.

391. On one occasion I was surprised to find that after thawing much of the ice the conducting power had not been
restored; but I found that a cork which held the wire just where it joined the platina, dipped so far into the ice, that
with the ice itself it protected the platina from contact with the melted part long after that contact was expected.

392. This insulating power of ice is not effective with electricity of exalted intensity. On touching a diverged gold-
leaf electrometer with a wire connected with the platina, whilst the tin case was touched by the hand or another
wire, the electrometer was instantly discharged (419.).

393. But though electricity of an intensity so low that it cannot diverge the electrometer, can still pass (though in
very limited quantities (419.),) 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.

394. 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 proceeded 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 electrochemical 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 (384.), was used as the source of electricity, and a galvanometer introduced into
the circuit to indicate the presence or absence of a current.

395. 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.

396. 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 conduction took place, and then it was
very powerful.

397. When chloride of silver and chlorate of potassa were experimented with, in a similar manner, exactly the
same results occurred.

398. 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 paper72.

399. 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, &c. &c., 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.

400. Occasionally the substances were contained in small bent tubes of green glass, and when fused, the platina
poles introduced, one on each side. In such cases the same general results as those already described were
procured; but a further advantage was obtained, namely, that whilst the substance was conducting and suffering
decomposition, 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, &c., at the positive, and
alkali, or even potassium, at the negative pole.

401. 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 blowpipe experiments; a little of the salt, glass, or other substance, 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.

402. The following are various substances, taken from very different classes chemically considered, which are
subject to this law. The list might, no doubt, be enormously extended; but I have not had time to do more than
confirm the law by a sufficient number of instances.

First, water.

Amongst oxides;—potassa, protoxide of lead, glass of antimony, protoxide of antimony, oxide of bismuth.

Chlorides of potassium, sodium, barium, strontium, calcium, magnesium, manganese, zinc, copper (proto-), lead,
tin (proto-), antimony, silver.

Iodides of potassium, zinc and lead, protiodide of tin, periodide of mercury; fluoride of potassium; cyanide of
potassium; sulpho-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.

403. It is highly interesting in the instances of those substances 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.

404. I do not mean to deny that part of the increased conducting power in these cases of softening was probably
due to the elevation of temperature (432. 445.); but I have no doubt that by far the greater part was due to the
influence of the general law already demonstrated, and which in these instances came gradually, instead of
suddenly, into operation.

405. 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.

406. 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 decomposed.

407. 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.

408. Boracic acid was raised to the highest possible temperature by an oxy-hydrogen flame (401.), yet it gained no
conducting powers sufficient to affect the galvanometer, and underwent no apparent voltaic decomposition. It
seemed to be quite as bad a conductor as air. Green bottle-glass, heated in the same manner, did not gain
conducting power sensible to the galvanometer. Flint glass, when highly heated, did conduct a little and
decompose; and as the proportion of potash or oxide of lead was increased in the glass, the effects were more
powerful. Those glasses, consisting of boracic acid on the one hand, and oxide of lead or potassa on the other,
show the assumption of conducting power upon fusion and the accompanying decomposition very well.

409. 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 crystallizing at 40° Fahr.; but I found it impossible
to obtain it so that I could be sure the whole would congeal even at 0° Fahr. A ten-thousandth part of water, more
or less than necessary, would, upon cooling the whole, cause a portion of uncongealable liquid to separate, and that
remaining in the interstices of the solid mass, and moistening the planes of division, would prevent the correct
observation of the phenomena due to entire solidification and subsequent liquefaction.

410. 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, &c. &c., 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 water73.

411. Whether the conducting power of these liquefied bodies is a consequence of their decomposition or not
(413.), 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.

412. This general assumption of conducting power by bodies as soon as they pass from the solid to the liquid state,
offers a new and extraordinary character, the existence of which, as far as I know, has not before been suspected;
and it seems importantly connected with some properties and relations of the particles of matter which I may now
briefly point out.

413. 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 electrical 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 decomposition? And that question may be accompanied by another,
namely, Whether solidification does not prevent conduction, merely by chaining the particles to their places, under
the influence of aggregation, and preventing their final separation in the manner necessary for decomposition?

414. But, on the other hand, there is one substance (and others may occur), the per-iodide of mercury, which, being
experimented with like the others (400.), 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.

415. Again, there are many substances which contain elements such as would be expected to arrange themselves at
the opposite poles of the pile, and therefore in that respect fitted for decomposition, which yet do not conduct.
Amongst these are the iodide of sulphur, per-iodide of zinc, per-chloride of tin, chloride of arsenic, hydrated
chloride of arsenic, acetic acid, orpiment, realgar, artificial camphor, &c.; 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 supply74.

416. The relation, under this law, of the conducting power for 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 hack to the solid state, it gains
the power of conducting 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 corpuscular condition of the substances concerned.

417. The assumption of conducting power and a decomposable condition by liquefaction, promises new
opportunities of, and great facilities in, voltaic decomposition. Thus, such bodies as the oxides, chlorides,
cyanides, sulpho-cyanides, fluorides, certain vitreous mixtures, &c. &c., 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, &c. &c., and to obtain sodium, magnesium, boron, &c.,
in their separate states.

§ 10. On Conducting Power generally.75

418. 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.

419. 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 (392.), that a comparison might be made between it and the large accession of the same
power gained upon liquefaction. For this purpose the large electrical machine (290.) was brought into excellent
action, its conductor connected with a delicate gold-leaf electrometer, and also with the platina inclosed in the ice
(383.), whilst the tin case was connected with the discharging train (292.). 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 (384.). Yet, under these circumstances, it was but just
able to conduct the small quantity of electricity which this machine could evolve (371.), 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 (384.), which, though almost infinitely surpassing that of the machine in quantity, had a
tension so low us not to be sensible to an electrometer.

420. 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 (419.), 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.

421. Iodide of potassium which had been fused and cooled 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 (419.), 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.

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

423. 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.

424. The ice vessel employed (420.) 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.

425. 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 (312.), the other or decomposing end being supported on paper moistened with solution of iodide of
potassium (316.): 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.

426. 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 (419.
420.).

427. The decomposing wire and solution of iodide of potassium were then removed, and replaced by a very
delicate galvanometer (205.); 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 (297.), before
the effect was decided.

428. 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, &c., but when insulated, I could feel no
sensation. I think a frog would have been scarcely, if at all, affected.

429. 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 (125.). 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, indicating the passage of a little electricity, and agreeing in that
respect with the results obtained by the use of the electrical machine (421.). 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.

430. 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 chloride of lead produced the same effect. The
conducting power of these bodies, when fluid, is very great (395. 402.).

431. 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 (394.); and also with the opinion I have supported, in the Third
Series of these Researches, of the identity of electricity derived from different sources (360.).

432. 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 Davy76.

433. 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, pulverizing
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.

434. When a piece of this sulphuret, half an inch in thickness, was put between surfaces of platina, terminating the
poles of a voltaic battery of twenty pairs of four-inch plates, a galvanometer being also included in the circuit, the
needle was slightly deflected, indicating a feeble conducting power. On pressing the platina poles and sulphuret
together with the fingers, the conducting power increased as the whole became warm. On applying a lamp under
the sulphuret between the poles, the conducting power rose rapidly with the heat, and at last-the galvanometer
needle jumped into a fixed position, and the sulphuret was found conducting in the manner of a metal. On
removing the lamp and allowing the heat to fall, the effects were reversed, the needle at first began to vibrate a
little, then gradually left its transverse direction, and at last returned to a position very nearly that which it would
take when no current was passing through the galvanometer.

435. Occasionally, when the contact of the sulphuret with the platina poles was good, the battery freshly charged,
and the commencing temperature not too low, the mere current of electricity from the battery was sufficient to
raise the temperature of the sulphuret; and then, without any application of extraneous heat, it went on increasing
conjointly in temperature and conducting power, until the cooling influence of the air limited the effects. In such
cases it was generally necessary to cool the whole purposely, to show the returning series of phenomena.

436. 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 Decomposition, 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.

437. The hot sulphuret of silver conducts sufficiently well to give a bright spark with charcoal, &c. &c., in the
manner of a metal.

438. 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.

439. There is no other body with which I am acquainted, that, like sulphuret of silver, can compare with metals in
conducting 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 found77.

440. 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 (402.). The sulphuret of silver and perhaps some others decompose whilst in the
solid state; but the phenomena of this decomposition will be reserved for its proper place in the next series of these
Researches.

441. Notwithstanding the extreme dissimilarity between sulphuret of silver and gases or vapours, I cannot help
suspecting 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 (271.); 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 out78; 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 circumstances, so great as to be
equivalent to two different states.

442. I cannot but suppose at present that at that point where the liquid and the gaseous state coincide, the
conducting properties 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 conducting power remains, increased by the action of heat.

443. 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 points79.

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

445. Conducting power is in some bodies powerfully increased by heat, and in others diminished, yet without our
perceiving any accompanying essential electrical difference, either in the bodies or in the changes occasioned by
the electricity conducted.

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

447. But there are many fluid bodies which do not sensibly conduct electricity of this low intensity; there are some
which conduct it and are not decomposed; nor is fluidity essential to decomposition80.

448. There is but one body yet discovered81 which, insulating a voltaic current when solid, and conducting it when
fluid, is not decomposed in the latter case (414.).

449. 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.

Royal Institution,

April 15, 1833.

Fifth Series.
§ 11. On Electro-chemical Decomposition. ¶ i. New conditions of Electro-chemical Decomposition. ¶ ii. Influence
of Water in Electro-chemical Decomposition. ¶ iii. Theory of Electro-chemical Decomposition.

Received June 18,—Read June 20, 1833.

§ 11. On Electro-chemical Decomposition.82

450. I have in a recent series of these Researches (265.) 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.

451. 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 (371. 376.) in which that
of comparatively low tension, supplied by the voltaic battery, may be procured; but as their actions, whether
magnetical, chemical, or of any other nature, are essentially the same (360.), 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 consequence, that the
use of electricity of such intensity as that afforded by the machine, would, when applied to effect and elucidate
electro-chemical decomposition, show some new conditions of that action, evolve new views of the internal
arrangements and changes of the substances under decomposition, and perhaps give efficient powers over matter
as yet undecomposed.

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

¶ i. New conditions of Electro-chemical Decomposition.

453. 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.

454. 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 (312. 316); and also a
particular experiment (319.), 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 (292. 316.), 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.

455. 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 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.

456. Experiments were then made both with sulphate of soda and iodide of potassium, to ascertain if any
diminution of decomposing effect was produced by such great extension as those just described of the moist
conductor or body under decomposition; but whether the contact of the decomposing point connected with the
discharging train was made with turmeric paper touching the prime conductor, or with other turmeric paper
connected with it through the seventy feet of string, the spot of alkali for an equal number of turns of the machine
had equal intensity of colour. The same results occurred at the other decomposing wire, whether the salt or the
iodide were used; and it was fully proved that this great extension of the distance between the poles produced no
effect whatever on the amount of decomposition, provided the same quantity of electricity were passed in both
cases (377.).

457. The negative point of the discharging train, the turmeric paper, and the string were then removed; the positive
point was left resting upon the litmus paper, and the latter 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.

458. 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.

459. 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.

460. 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 (292.) by a decomposing wire (312.); a piece of wet string was hung from it,
the lower extremity of which 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.

461. These cases are abundantly sufficient to show that electrochemical decomposition does not depend upon the
simultaneous action of two metallic poles, since a single pole might be used, decomposition ensue, and one or
other of the elements liberated, pass to the pole, according as it was positive or negative. In considering the course
taken by, and the final arrangement of, the other element, I had little doubt that I should find it had receded
towards the other extremity, and that the air itself had acted as a pole, an expectation which was fully confirmed in
the following manner.

462. A piece of turmeric paper, not more than 0.4 of an inch 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 (Plate IV. fig. 47.); 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 (312.). The machine was
then worked, the positive electricity passing into the turmeric paper at the point p, and out at the extremity n. After
forty or fifty turns of the machine, the extremity n was examined, and the two points or angles found deeply
coloured by the presence of free alkali (fig. 48.).

463. A similar piece of litmus paper, dipped in solution of sulphate of soda n, fig. 49, 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 (322.); and these, with the accompanying general facts,
are sufficient to show that the acid was really the result of electro-chemical decomposition (466.).

464. 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.

465. 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. 50, 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, n, with the discharging train. The interval in each case between the points
was about half an inch; the positive point p was 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, and the point of the turmeric a red from a
similar and simultaneous evolution of alkali.

466. Upon turning the paper conductor round, so that the litmus point should now give off the positive electricity,
and the turmeric point receive it, and working the machine for a short time, both the red spots disappeared, and as
on continuing the action of the machine no red spot was re-formed at the litmus extremity, it proved that in the first
instance (463.) the effect was not due to the action of brushes or mere electric discharges causing the formation of
nitric acid from the air (322.).

467. If the combined litmus and turmeric paper in this experiment 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 conductor, 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.

468. 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.

469. Finally, a series of four small compound conductors, consisting of litmus and turmeric paper (fig. 51.)
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 electricity 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 brushes (322.), 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.

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

471. 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 (467.). 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 (493. 518.), that I may
previously consider another supposed condition of electro-chemical decomposition83.

¶ ii. Influence of Water in Electro-chemical Decomposition.

472. 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 connexion between the metals or metal of the voltaic apparatus84:" 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) occur85."

473. This opinion has, I think, been shown by other philosophers not to be accurate, though I do not know where to
refer for a contradiction of it. Sir Humphry Davy himself said in 180186, that dry nitre, caustic potash and soda are
conductors of galvanism when rendered fluid by a high degree of heat, but he must have considered them, or the
nitre at least, as not suffering decomposition, for the statements above were made by him eleven years
subsequently. In 1826 he also pointed out, that bodies not containing water, as fused litharge and chlorate of
potassa, were sufficient to form, with platina and zinc, powerful electromotive circles87; but he is here speaking of
the production of electricity in the pile, and not of its effects when evolved; nor do his words at all imply that any
correction of his former distinct statements relative to decomposition was required.

474. I may refer to the last series of these Experimental Researches (380. 402.) 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 (402.) were effective; and that amongst more
complicated compounds, cyanides and salts, of equal efficacy, occurred in great numbers (402.).

475. 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 (394.); 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 dissolved or evolved, than any other substance.

476. 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 (402.),
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 effectual88. 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 powerful 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.

477. The extreme beauty and value of electro-chemical decompositions have given to that power which the voltaic
pile possesses of causing their occurrence an interest surpassing that of any other of its properties; for the power is
not only intimately connected with the continuance, if not with the 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.

478. What may be considered as the general facts of electrochemical decomposition are agreed to by nearly all
who have written on the subject. They consist in the separation of the decomposable substance acted upon into its
proximate or sometimes ultimate principles, whenever both poles of the pile are in contact with that substance in a
proper condition; in the evolution of these principles at distant points, i.e. at the poles of the pile, where they are
either finally set free or enter into union with the substance of the poles; and in the constant determination of the
evolved elements or principles to particular poles according to certain well-ascertained laws.

479. 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 investigations might be considered, not as an increase of that which is doubtful, but a real addition to
this branch of knowledge.

480. 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.

481. Grotthuss, in the year 1805, wrote expressly on the decomposition of liquids by voltaic electricity89. 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 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 force90. 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 particles91, 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 gases92.

482. 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.

483. When Sir Humphry Davy uses more particular expressions, he seems to refer the decomposing effects to the
attractions of the poles. This is the case in the "general expression 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 attracting powers of the surfaces of the poles. He mentions the probability of a succession of
decompositions and recompositions throughout the fluid,—agreeing in that respect with Grotthuss93; and supposes
that the attractive and repellent agencies may be communicated from the metallic surfaces throughout the whole of
the menstruum94, being communicated from one particle to another particle of the same kind95, and diminishing in
strength from the place of the poles to the middle point, which is necessarily neutral96. In reference to this
diminution of power at 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 elements97.

484. When in 1826 Sir Humphry Davy wrote again on this subject, he stated that he found nothing to alter in the
fundamental theory laid down in the original communication98, and uses the terms attraction and repulsion
apparently in the same sense as before99.

485. Messrs. Riffault and Chompré 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 recompositions 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, &c. 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 current100.

486. M. Biot is very cautious in expressing an opinion as to the cause of the separation of the elements of a
compound body101. 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 negative102. 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 it103.

487. M. Biot does not appear to admit the successive decompositions and recompositions spoken of by Grotthuss,
Davy, &c. &c.; but seems to consider the substance whilst in transit as combined with, or rather attached to, the
electricity for the time104, and though it communicates this electricity to the surrounding 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 pole105.

488. 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 conductors, which, assuming an electric state, urge
particles electrified more highly at the poles through them in opposite directions, by virtue of a series of ordinary
electrical attractions and repulsions106.

489. M.A. de la Rive investigated this subject particularly, and published a paper on it in 1825107. 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 electricity108. 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 conductor109, 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 them110. In this respect M. de la Rive's hypothesis accords in part with that of
MM. Riffault and Chompré (485.).

490. M. de la Rive considers the portions of matter which are decomposed to be those contiguous to both poles111.
He does not admit with others the successive decompositions and recompositions in the whole course of the
electricity through the humid conductor112, but thinks the middle parts are in themselves unaltered, or at least serve
only to conduct the two contrary currents of electricity and matter which set off from the opposite poles113. 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 recombination taking place, except the momentary union of the transferred
particle with the electricity be so considered.

491. The latest communication that I am aware of on the subject is by M. Hachette: its date is October 1832114. It is
incidental to the description of the decomposition of water by the magneto-electric currents (346.). 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."

492. 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 apologize to the authors.

*****

493. That electro-chemical decomposition does not depend upon any direct attraction and repulsion of the poles
(meaning thereby the metallic terminations either of the voltaic battery, or ordinary electrical machine
arrangements (312.),) upon the elements in contact with or near to them, appeared very evident from the
experiments made in air (462, 465, &c.), when the substances evolved did not collect about any poles, but, in

obedience to the direction of the current, were evolved, and I would say ejected, at the extremities of the
decomposing substance. But notwithstanding the extreme dissimilarity in the character of air and metals, and the
almost total difference existing between them as to their mode of conducting electricity, and becoming charged
with it, it might perhaps still be contended, although quite hypothetically, that the bounding portions of air were
now the surfaces or places of attraction, as the metals had been supposed to be before. In illustration of this and
other points, I endeavoured to devise an arrangement by which I could decompose a body against a surface of
water, as well as against air or metal, and succeeded in doing so unexceptionably in the following manner. As the
experiment for very natural reasons requires many precautions, to be successful, and will be referred to hereafter in
illustration of the views I shall venture to give, I must describe it minutely.

494. A glass basin (fig. 52.), 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 carefully 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 inclination being given to it, that gas evolved during decomposition might escape: the part
immersed was three inches and a half long by one inch wide, and about seven-eighths of an inch of water
intervened between it and the solution of sulphate of magnesia.

495. 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.

496. 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 c, 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.

497. As, therefore, the substances evolved in cases of electrochemical decomposition may be made to appear
against air (465. 469.),—which, according to common language, is not a conductor, nor is decomposed, or against
water (495.), which is a conductor, and can be decomposed,—as well as against the metal poles, which are
excellent conductors, but undecomposable, there appears but little reason to consider the phenomena 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.

498. 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.

499. Grotthuss, for instance, describes the poles as centres of attractive and repulsive forces (481.), 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 (502.
505.), that the particles are acted upon by equal force everywhere in the circuit, when the conditions of the
experiment 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.

500. Sir Humphry Davy, who also speaks of the diminution of power with increase of distance from the poles115
(483.), 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 theoretically from considering the poles as centres of attraction and repulsion; but I have not
found the statement borne out by other experiments (505.); 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.

501. 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 considered 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 plates116.

502. 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.

503. It is very evident, that when the width of the decomposing conductor varies, as is always the case when mere
wires or plates, as poles, are dipped into or are surrounded by solution, no constant expression can be given as to
the action upon a single particle placed in the course of the current, nor any conclusion of use, relative to the
supposed attractive or repulsive force of the poles, be drawn. The force will vary as the distance from the pole
varies; as the particle is directly between the poles, or more or less on one side; and even as it is nearer to or further
from the sides of the containing vessels, or as the shape of the vessel itself varies; and, in fact, by making
variations in the form of the arrangement, the force upon any single particle may be made to increase, or diminish,

or remain constant, whilst the distance between the particle and the pole shall remain the same; or the force may be
made to increase, or diminish, or remain constant, either as the distance increases or as it diminishes.

504. 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 (377.), and that the section passes through every part of the current through the decomposing conductor.

505. 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, &c., 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 series but one of these Researches.

506. 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 separated, it would follow
that the weakest electrical attraction was stronger than, if not the strongest, yet very strong chemical attraction,
namely, such as exists between oxygen and hydrogen, potassium and oxygen, chlorine and sodium, acid and alkali,
&c., a consequence which, although perhaps not impossible, seems in the present state of the subject very unlikely.

507. The view which M. de la Rive has taken (489.), and also MM. Riffault and Chompré (485.), of the manner in
which electro-chemical decomposition is effected, is very different to that already considered, and is not affected
by either the arguments 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 (462.
469.) and water (495.), which I have described; for if the physical differences between metals and humid
conductors, which M. de la Rive supposes to account for the transmission 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 (462.), an effect the very reverse might have been expected. Or if even that were
allowed, the experiment with water (495.), at once sets the matter at rest, the decomposing pole being now of a
substance which is admitted as competent to transmit the assumed compound of electricity and matter.

508. With regard to the views of MM. Riffault and Chompré (485.), 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 considered.

509. 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.

510. Electro-chemical decomposition is well known to depend essentially upon the current of electricity. I have
shown that in certain cases (375.) the decomposition is proportionate to the quantity of electricity passing,
whatever may be its intensity or its source, and that the same is probably true for all cases (377.), even when the
utmost generality is taken on the one hand, and great precision of expression on the other (505.).

511. In speaking of the current, I find myself obliged to be still more particular than on a former occasion (283.), in
consequence of the variety of views taken by philosophers, all agreeing in the effect of the current itself. Some
philosophers, with Franklin, assume but one electric fluid; and such must agree together in the general uniformity
and character of the electric current. Others assume two electric fluids; and here singular differences have arisen.

512. MM. Riffault and Chompré, for instance, consider the positive and negative currents each as causing
decomposition, and state that the positive current is more powerful than the negative current117, the nitrate of soda
being, under similar circumstances, decomposed by the former, but not by the latter.

513. M. Hachette states118 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.

514. 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 (490.)119. In one passage he speaks of the two electricities as two
influences, wishing perhaps to avoid offering a decided opinion upon the independent existence of electric fluids;
but as these influences are considered as combining with the elements set free as by a species of chemical affinity,
and for the time entirely masking their character, great vagueness of idea is thus introduced, inasmuch as such a
species of combination can only be conceived to take place between things having independent existences. The
two elementary electric currents, moving in opposite directions, from pole to pole, constitute the ordinary voltaic
current.

515. 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, according to him, compounds with the electricities; when evolved at the poles, they are de-
electrified.

516. I have sought amongst the various experiments quoted in support of these views, or connected with electro-
chemical decompositions or electric currents, for any which might be considered as sustaining the theory of two
electricities rather than that of one, but have not been able to perceive a single fact which could be brought forward
for such a purpose: or, admitting the hypothesis of two electricities, much less have I been able to perceive the
slightest grounds for believing that one electricity in a current can be more powerful than the other, or that it can be
present without the other, or that one can be varied or in the slightest degree affected, without a corresponding
variation in the other120. If, upon the supposition of two electricities, a current of one can be obtained without the
other, or the current of one be exalted or diminished more than the other, we might surely expect some variation
either of the chemical or magnetical effects, or of both; but no such variations have been observed. If a current be
so directed that it may act chemically in one part of its course, and magnetically in another, the two actions are
always found to take place 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 chemically121.

517. 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.

*****

518. Passing to the consideration of electro-chemical decomposition, 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 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 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 neutralized 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.

519. In this view the effect is considered as essentially dependent upon the mutual chemical affinity of the particles
of opposite kinds. Particles aa, fig. 53, could not be transferred or travel from one pole N towards the other P,
unless they found particles of the opposite kind bb, 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. 54, 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 combination, 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.

520. As far as regards any single compound particle, the case may be considered as analogous to one of ordinary
decomposition, for in fig. 54, a may be conceived to be expelled from the compound ab 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 (517.) superinduced by the current. But as all the compound particles in the
course of the current, except those actually in contact with the poles, act conjointly, and consist of elementary
particles, which, whilst they are in one direction expelling, are in the other being expelled, the case becomes more
complicated, but not more difficult of comprehension.

521. 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 forms; and even in the simplest case of two wires or points immersed as poles in a drop
or larger single portion of fluid, these lines must diverge rapidly from the poles; and the direction in which the
chemical affinity between particles is most powerfully modified (519. 520.) will vary with the direction of these
lines, according constantly with them. But even in reference to these lines or currents, it is not supposed that the
particles which mutually affect each other must of necessity be parallel to them, but only that they shall accord
generally with their direction. Two particles, placed in a line perpendicular to the electric current passing in any
particular place, are not supposed to have their ordinary chemical relations towards each other affected; but as the
line joining them is inclined one way to the current their mutual affinity is increased; as it is inclined in the other
direction it is diminished; and the effect is a maximum, when that line is parallel to the current122.

522. That the actions, of whatever kind they may be, take place frequently in oblique directions is evident from the
circumstance of those particles being included which in numerous cases are not in a line between the poles. Thus,
when wires are used as poles in a glass of solution, the decompositions and recompositions occur to the right or
left of the direct line between the poles, and indeed in every part to which the currents extend, as is proved by
many experiments, and must therefore often occur between particles obliquely placed as respects the current itself;
and when a metallic vessel containing the solution is made one pole, whilst a mere point or wire is used for the
other, the decompositions and recompositions must frequently be still more oblique to the course of the currents.

523. The theory which I have ventured to put forth (almost) requires an admission, that in a compound body
capable of electro-chemical decomposition the elementary particles have a mutual relation to, and influence upon
each other, extending beyond those with which they are immediately combined. Thus in water, a particle of
hydrogen in combination with oxygen is considered as not altogether indifferent to other particles of oxygen,
although they are combined with other particles of hydrogen; but to have an affinity or attraction towards them,
which, though it does not at all approach in force, under ordinary circumstances, to that by which it is combined
with its own particle, can, under the electric influence, exerted in a definite direction, be made even to surpass it.
This general relation of particles already in combination to other particles with which they are not combined, is
sufficiently distinct in numerous results of a purely chemical character; especially in those where partial
decompositions only take place, and in Berthollet's experiments on the effects of quantity upon affinity: and it
probably has a direct relation to, and connexion 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.

524. I hope I have now distinctly stated, although in general terms, the view I entertain of the cause of electro-
chemical decomposition, as far as that cause can at present be traced and understood. I conceive the effects to
arise from forces which are internal, relative to the matter under decomposition—and not external, as they might
be considered, if directly dependent upon the poles. I suppose that the effects are due to a modification, by the
electric current, of the chemical affinity of the particles through or by which that current is passing, giving them
the power of acting more forcibly in one direction than in another, and consequently making them travel by a
series of successive decompositions and recompositions in opposite directions, and finally causing their expulsion
or exclusion at the boundaries of the body under decomposition, in the direction of the current, and that in larger

or smaller quantities, according as the current is more or less powerful (377.). I think, therefore, it would be more
philosophical, and more directly expressive of the facts, to speak of such a body, in relation to the current passing
through it, rather than to the poles, as they are usually called, in contact with it; and say that whilst under
decomposition, oxygen, chlorine, iodine, acids, &c., are rendered at its negative extremity, and combustibles,
metals, alkalies, bases, &c., at its positive extremity (467.), 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 (465.) and in water (495.), already quoted, for facts illustrating these views in the first
instance; to which I will now add others.

525. In order to show the dependence of the decomposition and transfer of elements upon the chemical affinity of
the substances present, experiments were made upon sulphuric acid in the following manner. Dilute sulphuric acid
was prepared: its specific gravity was 1.0212. A solution of sulphate of soda was also prepared, of such strength
that a measure of it contained 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 neutralized by a measure of the prepared sulphuric acid.

526. Four glass cups were then arranged, as in fig. 55; seventeen measures of the free sulphuric acid (525.) 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 communications,
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 positive 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.

527. On breaking the connexion with the battery, the portions 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 neutralized by the addition of the soda solution (525.), 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.

528. In comparing the difference of acid in A and B, the necessary equality of weight was considered as of no
consequence, because the solution was at first neutral, and would not, therefore, affect the test liquids, and all the
evolved acid would be in B, and the free alkali in A. The solution in A required 3.2 measures of the prepared acid
(525.) to neutralize it, and the solution in B required also 3.2 measures of the soda solution (525.) to neutralize 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.

529. 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.

530. The variation of electro-chemical decomposition, the transfer of elements and their accumulation at the poles,
according as the substance submitted to action consists of particles opposed more or less in their chemical affinity,
together with the consequent influence of the latter circumstances, are sufficiently obvious in these cases, where
sulphuric acid is acted upon in the same quantity by the same electric current, but in one case opposed to the
comparatively weak affinity of water for it, and in the other to the stronger one of soda. In the latter case the

quantity transferred is from two and a half to three times what it is in the former; and it appears therefore very
evident that the transfer is greatly dependent upon the mutual action of the particles of the decomposing bodies123.

531. In some of the experiments the acid from the vessels a and b was neutralized 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.

532. 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
discharging train, or it may be even from the air itself, under the influence of electric action, to neutralize the alkali
developed at the positive extremity of the decomposing solution, and so not merely prevent its appearance, but
actually transfer it on to the metal termination: and, in fact, when the paper points were not allowed to touch there,
and the machine was worked until alkali was evolved at the delivering or positive end of the turmeric paper,
containing the sulphate of soda solution, it was merely necessary to place the opposite receiving point of the paper
connected with the discharging train, which had been moistened by distilled water, upon the brown turmeric point
and press them together, when the alkaline effect immediately disappeared.

533. The experiment with sulphate of magnesia already described (495.) 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 (527, &c.); and that so soon as the magnesia
advanced beyond the reach of 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.

*****

534. The theory I have ventured to put forth appears to me to explain all the prominent features of electro-chemical
decomposition in a satisfactory manner.

535. 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.

536. 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 decomposing effect directly to the attractive power
of the poles. If, in accordance with the usual theory, a piece of platina be supposed to have sufficient power to
attract a particle of hydrogen from the particle of oxygen with which it was the instant before combined, there
seems no sufficient reason, nor any fact, except those to be explained, which show why it should not, according to
analogy with all ordinary attractive forces, as those of gravitation, magnetism, cohesion, chemical affinity, &c.
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, &c. 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
therefore in their particular action reveal the general principle of decomposition.

537. 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 (518. 519.), 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
relation to those particles which are leaving the substance under operation.

538. The theory accounts for the transfer of elements in a manner which seems to me at present to leave nothing
unexplained; and it was, indeed, the phenomena of transfer in the numerous cases of decomposition of bodies
rendered fluid by heat (380. 402.), 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.

539. Chloride of lead, for instance, fused in a bent tube (400.), and decomposed by platina wires, evolves lead,
passing to what is usually called the negative pole, and chlorine, which being evolved at the positive pole, is in part
set free, and in part combines with the platina. The chloride of platina formed, being soluble in the chloride of lead,
is subject to decomposition, and the platina itself is gradually transferred across the decomposing matter, and
found with the lead at the negative pole.

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

541. 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 (524.).

542. 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 some other element or substance tending to pass in the opposite direction, for the effect
is considered as essentially due to the mutual relation of such particles. But the theories attributing the
determination of the elements to the attractions and repulsions 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 pole124. Yet such is not the case, as has been shown by the experiments on free and combined acid
(526. 528.).

543. 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.

544. 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 combinable element in the other. Solutions of acids or alkalies will not answer, because they exist
by virtue of an attraction; and increasing the solubility of a body in one direction, and diminishing it in the
opposite, is just as good a reason for transfer, as modifying the affinity between the acids and alkalies
themselves125. Nevertheless the case of sulphate of magnesia is in point (494. 495.), and shows that one element or
principle only has no power of transference or of passing towards either pole.

545. 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 (518. 524.), to combine with it; the platina therefore remains where it was first placed,
and has no tendency to pass 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, &c., 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.

546. 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 attraction 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 the attraction of cohesion is almost perfectly overcome, the particles are in it so small as to
remain for hours in suspension, and are perfectly free to move by the slightest impulse towards either pole; and if
in relation by chemical affinity to any substance present, are powerfully determined to the negative pole126.

547. 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. 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 (495. 533.), with those of comminuted
metals in certain solutions (546.), 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.

548. There are, it is true, many instances of insoluble bodies being acted upon, as glass, sulphate of baryta, marble,
slate, basalt, &c., but 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.

549. It may be expressed as a general consequence, that the more directly bodies are opposed to each other in
chemical affinity, the more ready is their separation from each other in cases of electro-chemical decomposition,
i.e. provided other circumstances, as insolubility, deficient conducting power, proportions, &c., 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, &c., rendered subject to electro-chemical decomposition by fusion (402.). So that in
applying the voltaic battery for the purpose of decomposing bodies not yet resolved into forms of matter simpler
than their own, it must be remembered, that success may depend not upon the weakness, or failure upon the
strength, of the affinity by which the elements sought for are held together, but contrariwise; and then modes of
application may be devised, by which, in association with ordinary chemical powers, and the assistance of fusion
(394. 417.), we may be able to penetrate much further than at present into the constitution of our chemical
elements.

550. Some of the most beautiful and surprising cases of electro-chemical decomposition and transfer which Sir
Humphry Davy described in his celebrated paper127, were those in which acids were passed through alkalies, and
alkalies or earths through acids128; 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
decomposition, and that the more alkali there is in the course of an acid, the more will the transfer of that acid be
facilitated from pole to pole; and perhaps a better illustration of the difference between the theory I have ventured,
and those previously existing, cannot be offered than the views they respectively give of such facts as these.

551. The instances in which sulphuric acid could not be passed though baryta, or baryta through sulphuric acid129,
because of the precipitation of sulphate of baryta, enter within the pale of the law already described (380. 412.), by

which liquidity is so generally required for conduction and decomposition. In assuming the solid 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.

552. The theory I have advanced accords in a most satisfactory manner with the fact of an element or substance
finding its place of rest, or rather of evolution, sometimes at one pole and sometimes at the other. Sulphur
illustrates this effect very well130. When sulphuric acid is decomposed by the pile, sulphur is evolved at the
negative pole; but when sulphuret of silver is decomposed in a similar way (436.), then the sulphur appears at the
positive pole; and if a hot platina pole be used so as to vaporize 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, 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.

553. 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 (527.), 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.

554. 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.

555. 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 appearance of the nitrogen at the positive or
negative pole is entirely a secondary effect, and not an immediate consequence of the decomposing power of the
electric current131.

556. 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.

557. 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.

558. Water makes a pole of difficult application, except in a few cases (494.), 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.

559. Air, however, and some gases are free from the latter objection, and may be used as poles in many cases (461,
&c.); 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 (371. 376.) to effect electro-chemical decomposition
with facility.

560. 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 of the current (518.), 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
attraction for the 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.

561. A great advantage is frequently supplied, by the opportunity 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.

562. The effects which take place when a succession of conducting decomposable and undecomposable substances
are placed in the electric circuit, as, for instance, of wires and solutions, or of air and solutions (465, 469.), 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 (524.), 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.

563. 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 considerations which it suggests, wishing first to submit it
to the test of publication and discussion.

Royal Institution,

June 1833.

Sixth Series.
§ 12. On the power of Metals and other Solids to induce the Combination of
Gaseous Bodies.

Received November 30, 1833,—Read January 11, 1834.

564. 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 (707.), I have
felt myself fully justified in describing them in this place.

565. Believing that I had proved (by experiments hereafter to be described
(705.),) 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 conductors 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 (739.)132.

566. During the course of the experiments made to render the instrument
efficient, I was occasionally surprised at observing 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 inches in length and 3/4ths 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 (Plate V. fig. 56.). The

tube was filled with dilute sulphuric acid, and inverted in a cup of the same
fluid; a voltaic battery was connected with the two wires, and sufficient
oxygen and hydrogen evolved to occupy 4/5ths 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
13-1/2 parts remained, and these ultimately disappeared.

567. It was found by various experiments, that this effect was not due to the
escape or solution of the gas, nor to recombination of the oxygen or
hydrogen in consequence of any peculiar condition they might be supposed
to possess under the circumstances; but to be occasioned by the action of
one or both of the poles within the tube upon the gas around them. On
disuniting the poles from the pile after they had acted upon dilute sulphuric
acid, and introducing them into separate tubes containing mixed oxygen and
hydrogen, it was found that the positive pole effected the union of the gases,
but the negative pole apparently not (588.). It was ascertained also that no
action of a sensible kind took place between the positive pole with oxygen
or hydrogen alone.

568. These experiments reduced the phenomena to the consequence 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 required in the fourteenth section of these Researches.

569. Several platina plates were prepared (fig. 57.). They were nearly half
an inch wide, and two inches and a half long: some were 1/200dth of an
inch, others not more than 1/600dth, whilst some were as much as 1/70th of
an inch in thickness. Each had a piece of platina wire, about seven inches
long, soldered to it by pure gold. Then a number of glass tubes were
prepared: they were about nine or ten inches in length, 5/8ths of an inch in
internal diameter, were sealed hermetically at one 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. 58.), and left for a longer or shorter period, that the
action might be observed.

570. The following result may be given as an illustration of the
phenomenon to be investigated. Diluted sulphuric acid, of the specific
gravity 1.336, was put into a glass jar, in which was placed also a large
platina plate, connected 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 (569.) was then connected with the positive
extremity, and immersed 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 (569.). The volume of gases
immediately began to lessen, the diminution proceeding more and more
rapidly until about 3/4ths 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.

571. This extraordinary influence acquired by the platina at the positive
pole of the pile, is exerted far more readily and 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 (570.). 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.

572. A mixture of two volumes of nitrous oxide with one volume of
hydrogen was put with a plate similarly prepared into a tube (569. 570.).
This also showed no action immediately; 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.

573. 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 (640. 641.).

574. A mixture of two volumes carbonic oxide and one volume oxygen was
also unaffected by the prepared platina plate in several days (645, &c.).

575. A mixture of equal volumes of chlorine and hydrogen was used in
several experiments, with plates prepared in a similar manner (570.).
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.

576. Reverting to the action of the prepared plates on mixtures of oxygen
and hydrogen (570.), 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 (569.) 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 (638.).

577. Some plates (569.) were made positive for four minutes in dilute
sulphuric acid of specific gravity 1.336: they were 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.

578. 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 undiminished vigour. Others were left in similar
acid for forty hours, and some even for eight days, after the electrization,
and then acted as well in combining oxygen and hydrogen gas as those
which were used immediately after electrization.

579. 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 exceedingly 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.

580. When similarly prepared plates (569.) 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 but 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.

581. 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 sometimes 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 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 (630.). But notwithstanding the effect of these causes,
diminution, 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.

582. 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
133
.

583. Occasionally the platina plates (569.), after being made the positive
pole of the battery, were washed, wiped with filtering-paper or a cloth, and
washed and wiped again. Being then introduced into mixed oxygen and
hydrogen, they acted apparently 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.

584. The power of heat in altering the action of the prepared platina plates
was also tried (595.). 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 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 (634. 636.).

585. 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.

586. 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.

587. 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.

588. 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 (567.), or whether, notwithstanding 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 sulphuric 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 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 (582.), the action was very much quickened.

589. 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.

590. 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.

591. Accordingly, a platina plate (569.) 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.

592. 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 disappeared, in periods
extending from twenty-five to eighty or ninety minutes.

593. 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.

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

595. I now tried the effect of heat in conferring this property upon platina
(584.). 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.

596. 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.

597. But it happened not infrequently that plates, after being heated,
showed no power of combining oxygen and hydrogen gases, though left
undisturbed in them for two hours. Sometimes also it would happen that a
plate which, having been heated to dull redness, acted feebly, upon being
heated to whiteness 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.

598. Though thus uncertain in its action, and though often diminishing the
power given to the plates at the positive pole of the pile (584.), still it is
evident that heat can render platina active, which before was inert (595.).

The cause of its occasional 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 blowpipe, becomes dulled and clouded on its surface by
something either formed or deposited there; and this, and much less than
this, is sufficient to prevent it from exhibiting the curious power now under
consideration (634. 636.). 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 platina134.

599. The action of alkalies and acids in giving platina this property was now
experimentally examined. Platina plates (569.) 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 (592.), they became active.

600. The action of acids was far more constant and satisfactory. 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 (570.).

601. Strong sulphuric acid was very effectual in rendering the platina
active. A plate (569.) 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 (570.).

602. Plates which, after being heated or electrized 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.

603. 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.

604. Vegetable acids, as acetic and tartaric, sometimes rendered inert platina
active, at other times not. This, I believe, 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 (601.) never failed in its action.

605. 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
two135: 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 (582.). 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 phenomenon could be
produced without the aid of the voltaic battery.

606. 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.

607. 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 (601.), it will become very active.

608. Other metals than platina were then experimented with. Gold and
palladium exhibited the power either when made the positive pole of the
voltaic battery (570.), or when acted on by hot oil of vitriol (601.). 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.

*****

609. There can remain no doubt that the property of inducing 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 Döbereiner136, 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 Thenard137, 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 gas138. This effect I can now produce at
pleasure with either wires or plates by the processes described (570. 601.
605.); 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. 59.), the loss of
heat is less, the metal is assimilated somewhat to the spongy state, and the
probability of failure almost entirely removed.

610. M. Döbereiner 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 it139.

611. In the two excellent experimental papers by MM. Dulong and
Thenard140, those philosophers show that elevation of temperature favours
the action, but does not alter its character; Sir Humphry Davy's
incandescent platina wire being the same phenomenon with Döbereiner'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, &c., when their temperatures 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 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 reduction,
or from the heat itself to which it is then submitted.

612. 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 remark 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, &c., 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.

613. Dr. Fusinieri has also written on this subject, and given a theory which
he considers as sufficient to account for the phenomena141. He expresses the
immediate cause thus: "The platina determines upon its surface a continual
renovation of concrete laminæ 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 laminæ, 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 lose their elastic state,
and become concrete, assuming the form of exceedingly attenuated but
solid strata, is considered as proved by facts, some of which are quoted in
the Giornale di Fisica for 1824142; 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.

614. 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 substance, is considered as being neither
attraction nor affinity. It is able also to extend liquids and solids in concrete
laminæ 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
direction 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, ebullition,
volatilization, explosion, and other thermometric effects, as well as
inflammation, detonation, &c. &c. It is considered as a form of heat to
which the term native calorie is given, and is still further viewed as the
principle of the two electricities and the two magnetisms.

615. 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.

616. 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.

617. 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 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 clean 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.

618. 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 philosophically extended our knowledge of
the property to its possession by all the metals, and by earths, glass, stones,
&c. (611.); and every idea of its being a known and recognised electric
action is in this way removed.

619. 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 (523.), and in many cases produces effects rising into considerable
importance: and I think that this kind of attraction is a determining cause of
Döbereiner's effect, and of the many others of a similar nature.

620. 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.

621. 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 pulverized 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 attraction 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 combination143.

622. 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 unchanged144. 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 abundance

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.

623. Extraneous bodies, which, acting as nuclei in crystallizing or
depositing solutions, cause deposition of substances on them, when it does
not occur elsewhere in the liquid, seem to produce their effects by a power
of the same kind, i.e. a power of attraction 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.

624. 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, &c., 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.

625. 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, &c.,
are in so dense and comparatively 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 (621.),
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 1/10th or
even 1/20th of their original volume before the vapours would become
liquids.

626. 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 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 atmospheres, 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 à 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.

627. 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
containing 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, &c., 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.

628. 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, 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.

629. Although there are not many distinct cases of combination 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 Hull found carbonic acid and lime to remain combined under
pressure at temperatures 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 chlorine145, which being compressed 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.

630. The course of events when platina acts upon, and combines oxygen
and hydrogen, may be stated, according to these principles, as follows.
From the influence of the circumstances mentioned (619. &c.), 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 existing
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 combination is the
production of the vapour of water and an elevation 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 this latter,
therefore, come into juxtaposition with the metal, combine, and the fresh
vapour formed is also diffused, allowing new portions of gas to be acted
upon. In this way the process advances, but is accelerated by the evolution
of heat, which is known by experiment to facilitate the combination in
proportion to its intensity, and the temperature is thus gradually exalted
until ignition results.

631. 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.

632. 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 (617.), and the gases are prevented 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 surface. 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 (598.).

633. Clean platina, by which I mean such as has been made the positive
pole of a pile (570.), or has been treated with acid (605.), 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 positive 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.

634. I found also that platina plates which had been cleaned perfectly soon
became soiled by mere exposure to the air; for 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 (580.) did moisten, and
gave the other indications of a clean surface.

635. 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.

636. 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 metal146, as indeed
have all those who have used Döbereiner'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.

637. No state of a solid body can be conceived more favourable for the
production of the effect than that which is possessed by platina obtained
from the ammonio-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 portions of gas is retained within the mass,
exalting the tendency of the succeeding portions to combine.

*****

638. I have now to notice some very extraordinary interferences 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 understood that I
mean a mixture composed of one volume of 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.

639. Mixtures of oxygen and hydrogen with air, containing one-fourth, one-
half, and even two-thirds of the latter, being introduced with prepared
platina plates (570. 605.) 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

gases with the plates. In two hours and a half nearly all the oxygen and
hydrogen introduced as mixture was gone.

640. But when similar experiments were made with olefiant gas (the platina
plates having been made the positive poles of a voltaic pile (570.) 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 3 volumes oxygen and one volume
olefiant gas, so that the olefiant gas formed but 1/40th 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.

641. A mixture of forty-nine volumes oxygen and hydrogen (638.) 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 been
very much retarded, had occurred at last, and risen to a maximum.

642. With a mixture of ninety-nine volumes of oxygen and hydrogen (638.)
with one of olefiant gas, a feeble action was evident at the end of fifty
minutes; it went on accelerating (630.) 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.

643. Plates prepared by alkali and acid (605.) produced effects
corresponding to those just described.

644. 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.

645. 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 (638.) with four volumes of carbonic
acid was affected at once by a platina plate prepared with acid, &c. (605.);
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.

646. 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.

647. Two volumes of carbonic oxide and one of oxygen were mingled with
nine volumes of oxygen and hydrogen (638.). 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 1/18th part of the whole, the plate acted, slowly at
first, and at the end of forty-two minutes the gases exploded.

648. 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 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.

649. As to cases of retardation, the powers of olefiant gas and carbonic
oxide have been already described. Mixtures of oxygen and hydrogen,
containing from 1/16th to 1/20th of sulphuretted 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.

650. A small piece of cork was dipped in sulphuret of carbon and passed up
through water into a tube containing oxygen and hydrogen (638.), 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.

651. A little vapour of ether being mixed with the oxygen and hydrogen
retarded the action of the plate, but did not prevent it altogether. A little of
the vapour of the condensed oil-gas liquor147 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.

652. 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. 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.

653. 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
hydrocarbons is not at all in proportion merely to the quantity of carbon
present.

654. In connexion 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 (640. 646.).

655. Such are the general facts of these remarkable interferences. 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 investing it through the agency
of a stronger attraction than that of the hydrogen, or otherwise, remains to
be decided by more extended experiments.

*****

656. 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 philosophy148. In all ordinary cases of combustion it is evident
that an action of the kind considered, 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.

657. The condition of elasticity upon the exterior of the gaseous or
vaporous mass already referred to (626. 627.), 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 (623.), 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 platina, if they were made to replace
the water, i.e. if the view of independent action which I have taken (626.
627.) as a consequence 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
substances and their physical constitution in the solid, liquid, or gaseous
state, I have not sufficiently considered them to venture any strong opinions
or statements here149.

658. There are numerous well-known cases, in which substances, 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 (626. 627.).

659. The singular effects of retardation produced by very small quantities of
some gases, and not by large quantities of others (640. 645. 652.), 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 ago150; 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 1831151, and also by Dr.
Mitchell of Philadelphia152 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.

660. 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 examination, 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.

Royal Institution,

November 30, 1833.

Seventh Series.
§ 11. On Electro-chemical Decomposition, continued.153 ¶ iv. On some
general conditions of Electro-decomposition. ¶ v. On a new Measurer of
Volta-electricity. ¶ vi. On the primary or secondary character of bodies
evolved in Electro-decomposition. ¶ vii. On the definite nature and extent of
Electro-chemical Decompositions. § 13. On the absolute quantity of
Electricity associated with the particles or atoms of Matter.

Received January 9,—Read January 23, February 6 and 13, 1834.

Preliminary.

661. The theory which I believe to be a true expression of the facts of
electro-chemical decomposition, and which I have therefore detailed in a
former series of these Researches, is so much at variance with those
previously advanced, that I find the 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,
&c., 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, &c., are evolved at the positive extremity (518. 524.).

662. To avoid, therefore, confusion and circumlocution, and for the sake of
greater precision of expression than I can otherwise 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 (556.); 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 (465. 471.) and water (493.), against
which I have effected electro-chemical decomposition, is subject to doubt.
In place of the term pole, I propose using that of Electrode154, and I mean
thereby that substance, or rather surface, whether of air, water, metal, or any
other body, which bounds the extent of the decomposing matter in the
direction of the electric current.

663. The surfaces at which, according to common phraseology, the electric
current enters and leaves a decomposing body, are most important places of
action, and require to be distinguished 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, 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 anode155, and that towards the west the
cathode156; 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, &c., 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.

664. I shall have occasion in these Researches, also, to class bodies together
according to certain relations derived from their electrical actions (822.);
and wishing to express those relations without at the same time involving
the expression of any hypothetical 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 electrolytes.157
Water, therefore, is an electrolyte. The bodies which, like nitric or sulphuric
acids, are decomposed in a secondary manner (752. 757.), are not included
under this term. Then for electro-chemically decomposed, I shall often use
the term electrolyzed, 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 electrolytical will be understood at once: muriatic
acid is electrolytical, boracic acid is not.

665. 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 negative pole. But these terms are much too significant for
the use to which I should have to put them; for though the meanings 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 anions158 which go to the anode of the decomposing
body; and those passing to the cathode, cations159; 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 electrolyzed evolves the two ions,
chlorine and lead, the former being an anion, and the latter a cation.

666. 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.

667. 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 (283. 517.); and that though I speak of the current as proceeding
from the parts which are positive to those which are negative (663.), it is
merely in accordance with the conventional, though in some degree tacit,
agreement 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.160

¶ iv. On some general conditions of Electro-chemical Decomposition.

669. 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 combined with the greatest attractive force, were
those which were the most readily evolved at the opposite extremities of the
decomposing bodies (549.).

670. If this result was evident when water was supposed to be essential to,
and was present in, almost every case of such decomposition (472.), it is far
more evident now that it has been shown and proved that water is not
necessarily concerned in the phenomena (474.), and that other bodies much
surpass it in some of the effects supposed to be peculiar to that substance.

671. Water, from its constitution and the nature of its elements, 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 electrolyzation can occur, where, being
present, it is not resolved into its first principles.

672. 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 (402.), illustrate in an equally striking manner

the activity, in such decompositions, of elements directly and powerfully
opposed to each other by their chemical relations.

673. 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 another161. If bottle-glass be fused, and subjected to the
voltaic pile, it does not appear to be at all decomposed (408.). 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 experimented with, it readily yields up its elements
(408.).

674. But the result which is found to be so striking in the instances quoted
is not at all borne out by reference to other cases where a similar
consequence might have been expected. It may be said, that my own theory
of electro-chemical decomposition 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 (518. 524.): 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 generally 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 electrolyzation which have been considered, and is an
addition to those which I have taken against them.

675. Amongst powerful compounds which are not decomposed, boracic
acids stand prominent (408.). 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 (402. 690.), 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 expectation that, the pile would separate them, especially as in
some cases of mere solution (530. 544.), where the affinity must by
comparison be very weak, separation takes place162.

676. 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 (679. 691.)163; and even
water itself, which so easily yields up its elements when the current passes,
if rendered quite pure, scarcely suffers change, because it then becomes a
very bad conductor.

677. If it should hereafter be proved that the want of decomposition in those
cases where, from chemical considerations, it might be so strongly expected
(669, 672. 674.), is due to the absence or deficiency of conducting power, it
would also at the same time be proved that decomposition depends upon
conduction, and not the latter upon the former (413.); 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 (821.). I may
not, however, stop to discuss this point experimentally at present.

678. 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 intimately connected with capability in
the compound of suffering or resisting decomposition. Thus, the
protochloride of tin readily conducts, and is decomposed (402.), but the
perchloride neither conducts nor is decomposed (406.). The protiodide of
tin is decomposed when fluid (402.); the periodide is not (405.). The
periodide of mercury when fused is not decomposed (691.), even though it

does conduct. I was unable to contrast it with the protiodide, the latter being
converted into mercury and periodide by heat.

679. 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 substances quoted to illustrate the force and generality of the law of
conduction and decomposition which I discovered (402.), 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 sublimate,) are also decomposable, whilst many per
compounds of the same elements, not subject to the law, were not so (405.
406.).

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

681. 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 (552.). When very strong it
is a much worse conductor than if diluted164. If then subjected to the action
of a powerful battery, oxygen appears at the anode, or positive electrode,
although much is absorbed (728.), 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 decomposed. 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
electrolyzable (757.).

682. 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 volatilizes. Upon subjecting phosphoric acid, fused upon
the ring end of a wire (401.), 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 phosphorus 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.

683. Arsenic acid. This substance conducted, and was decomposed; 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.

684. 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 endeavoured to prepare a perfectly anhydrous portion, but could
not spare the time required to procure an unexceptionable result.

685. Nitric acid is a substance which I believe is not decomposed 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 (752.).

686. That these mineral acids should confer facility of conduction 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.

687. Chloride of sulphur does not conduct, nor is it decomposed. It consists
of single proportionals of its elements, but is not on that account an

exception to the rule (679.), which does not affirm that all compounds of
single proportionals of elements are decomposable, but that such as are
decomposable are so constituted.

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

689. 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.

600. With regard to the exceptions (679.), upon closer examination 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. 68.) (789.), 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
(394.)), 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 of a true protochloride consisting of single
proportionals (695, 796.).

691. 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 (402.); 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, notwithstanding the continued decomposition.

692. 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 decomposed; but there are many
interfering circumstances which require examination before a positive
conclusion can be drawn165.

693. 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 (402, 801.). 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.

694. The ordinary sulphuret of antimony its 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 gray sulphuret on the other. In
some rough experiments, the metal thus taken up 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.

695. 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,
&c., a true protoxide, consisting also of single proportionals, was
obtainable. But I could not stop to ascertain this matter strictly by analysis.

696. 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 described166.

697. Upon the whole, it appears probable that all those binary compounds
of elementary bodies which are capable of being electrolyzed when fluid,
but not whilst solid, according to the law of liquido-conduction (394.),
consist of single proportionals 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.

698. 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.

699. 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 electrolyzed, I am not quite satisfied that
water was entirely absent.

700. 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.

701. Hence this class of compound combinations does not seem to be
subject to the same simple law as the former class of binary combinations.
Whether we may find reason to consider them as mere solutions of the
compound of single proportionals 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.

702. 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 (742, &c.).

703. It is evident that all the cases in which decomposition does not occur,
may depend upon the want of conduction (677. 413.); 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 Davy167, and illustrated by
Berzelius and other eminent philosophers, that ordinary chemical affinity is
a mere result of the electrical attractions of the particles of matter.

¶ v. On a new measure of Volta-electricity.

704. I have already said, when engaged in reducing common and voltaic
electricity to one standard of measurement (377.), and again when
introducing my theory of electro-chemical decomposition (504. 505. 510.),
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 (307.)) through which it is passed, or in
other circumstances. The conclusive proofs of the truth of these statements
shall be given almost immediately (783, &c.).

705. 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.

706. There is no substance better fitted, under ordinary circumstances, to be
the indicating body in such an instrument 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 without
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 (843.).

707. 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 (571.). For this
purpose various forms of decomposing apparatus were used. The first
consisted of straight tubes, each containing a plate and wire of platina
soldered together by gold, and fixed hermetically in the glass at the closed
extremity of the tube (Plate V. fig. 60.). The tubes were about eight inches
long, 0.7 of an inch in diameter, and graduated. 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, consisted of the wire bent into the form of a ring (fig. 61.).
When these tubes were used as measurers, they were filled with the dilute
sulphuric acid, inverted in a basin of the same liquid (fig. 62.), and placed
in an inclined position, with their mouths near to each other, that as little
decomposing matter should intervene as possible; and also, in such a
direction that the platina plates should be in vertical planes (720).

708. Another form of apparatus is that delineated (fig. 63.). The tube is bent
in the middle; one end is closed; in that end is fixed a wire and plate, a,
proceeding so far downwards, that, when in the position figured, it shall be
as near to the angle as 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 (720.). The other metallic termination, 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.

709. The third form of apparatus contains both electrodes in the same tube;
the transmission, 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. 64.) 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 (706.), 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.

710. Another form of the instrument is given at fig. 65.

711. A fifth form is delineated (fig. 66.). This I have found exceedingly
useful in experiments continued in succession for days together, and where
large quantities of indicating 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 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.

712. It can hardly be requisite to remark, that in the arrangement of any of
these forms of apparatus, they, and the wires connecting them with the
substance, which is collaterally subjected 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.

*****

713. 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 circumstances which would require to be practically
guarded against.

714. The first point investigated was the influence or indifference of
extensive variations in the size of the electrodes, for which purpose
instruments like those last described (709. 710. 711.) 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 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.

715. Experiments of a similar kind were made with the single-plate, straight
tubes (707.), and also with the curved tubes (708.), 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
electricity, was constantly the same. As an illustration, the following
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.

716. But it was observed in these experiments, that in single-plate tubes
(707.) 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 (714.), to the solubility of
the gases evolved, especially at the positive electrode.

717. 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 (633.); whilst in the liquid they give it
a hazy appearance, 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 parts; 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; 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 blenching power
which some philosophers 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 oxywater.

718. That more gas was collected from the wires than from the plates, I
attribute to the circumstance, that as equal quantities 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.

719. 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
dissolved 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,

720. With the intention of avoiding this solubility of the gases as much as
possible, I arranged the decomposing plates in a vertical position (707.
708.), 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.

721. 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 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 (728.); 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 (717.), it can be collected more perfectly and in greater purity.

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

723. The next point in regard to which the principle of constant electro-
chemical action was tested, was variation of intensity. 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 alternations used, produced no difference as to the equal
action of large and small electrodes.

724. Still these results did not prove that variation in the intensity of the
current was not accompanied by a corresponding 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 (360. note); and therefore when large
plates were contrasted with wires separated by an equal length of the same
decomposing conductor (714.), 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.

725. The difference in intensity, under the circumstances described, may be
easily shown practically, by arranging two decomposing apparatus as in fig.
67, where the same fluid is 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 decomposing apparatus,
such as that delineated fig. 66. (711.), be connected with the wires at ab, fig.
67, it will serve sufficiently well, by the degree of decomposition occurring
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
will, by the increase of decomposition within, show how much greater the
intensity is there than at the former points. The connexions of P and N with
the voltaic battery are of course to be continued during the whole time.

726. A third form of experiment, in which difference of intensity 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 intensity 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 (725.).

727. The third point, in respect to which the principle of equal electro-
chemical action on water was tested, was variation of the strength of the
solution used. In order to render the water a conductor, sulphuric acid had
been added to it (707.); 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 current (714.). Slight differences occurred, as
before, sometimes in one direction, sometimes in another; but the final
result was, that exactly the same quantity of water was decomposed 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, and downwards.

728. When an acid having a specific gravity of about 1.336 was employed,
the results were most uniform, and the oxygen and hydrogen (716.) 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 remarkable
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 1.232. I have not
yet had time to examine minutely the circumstances attending the
disappearance 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.

729. Although not necessary for the practical use of the instrument I am
describing, yet as connected with the important point of constant chemical
action upon water, I now investigated the effects produced by an electro-
electric current passing through aqueous solutions of acids, salts, and

compounds, exceedingly 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 (778.).

730. When solutions of caustic potassa or soda, or sulphate of magnesia, or
sulphate of soda, were acted upon by the electric current, just as much
oxygen and hydrogen was evolved from them as from the diluted sulphuric
acid, with which they were compared. When a solution of ammonia,
rendered a better conductor by sulphate of ammonia (554.), or a solution of
subcarbonate 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.

731. I have already said, respecting large and small electrodes, that change
of order caused no change in the general effect (715.). 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.

732. 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 (742. &c.), together with
the solution or recombination of the gas and the evolution of air, are
guarded against, the products of the decomposition may be collected with
such accuracy, as to afford a very excellent and valuable measurer of the
electricity concerned in their evolution.

733. The forms of instrument which I have given, figg. 64, 65, 66. (709.
710. 711.), 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 (773. &c.), shall diminish their quantity, or add
other gases to them.

734. In many cases when the instrument is used as a comparative 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, figg. 62, 63. (707. 708.). The indications 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 educts
at both electrodes be collected. Such is the case when solutions of
ammonia, muriatic acid, chlorides, iodides, acetates or other vegetable salts,
&c., are employed.

735. 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 of copper.

736. 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 (709. 710. 711.); and the other, in which a single
gas, as the hydrogen only, is used (707. 708.). 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 barometric 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.

737. It can scarcely be needful to point out further than has been done how
this instrument is to be used. It is to be introduced 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 moisture168. For the latter
object the volta-electrometer (fig. 66.) is most accurate, as its gas can be
measured over water, whilst the others retain it over acid or saline solutions.

738. I have not hesitated to apply the term degree (736.), 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,
&c., is there made use of to measure heat, so the equally definite evolution
of gases is here turned to a similar use for electricity.

739. 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.

740. 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 (791. 848.);

741. 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
application169.

¶ vi. On the primary or secondary character of the bodies evolved at the
Electrodes.

742. Before the volta-electrometer could be employed in determining, 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
inspecting electro-chemical action and its consequences have arisen from
confounding these two classes of results together.

743. 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 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.

744. These secondary results occur in two ways, being sometimes 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 anode170; 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
(554.). 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.

745. 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 electrolytic action, be carefully distinguished from
those which are directly due to the action of the electric current.

746. The nature of the substances evolved will often lead to a correct
judgement 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 (554. 555.), and it is on such
occasions evidently viewed as a primary result171; but I think I shall show,
that, when it appears at the positive electrode, or rather at the anode, it is a
secondary result (748.). Thus, also, Sir Humphry Davy172, and with him the
great body of chemical philosophers, (including myself,) have given the
appearance of copper, lead, tin, silver, gold, &c., 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 places173.

747. But when we take to our assistance the law of constant electro-
chemical action already proved with regard to water (732.), and which I
hope to extend satisfactorily to all bodies (821.), and consider the quantities
as well as the nature of the substances set free, a generally accurate
judgement of the primary or secondary character of the results may be
formed: and this important point, so essential to the theory of

electrolyzation, since it decides what are the particles directly under the
influence of the current, (distinguishing them from such as are not affected,)
and what are the results to be expected, may be established with such
degree of certainty as to remove innumerable ambiguities and doubtful
considerations from this branch of the science.

748. Let us apply these principles to the case of ammonia, and the supposed
determination of nitrogen to one or the other electrode (554. 555,). A pure
strong solution of ammonia is as bad a conductor, and therefore as little
liable to electrolyzation, as pure water; but when sulphate of ammonia is
dissolved in it, the whole becomes a conductor; nitrogen almost and
occasionally 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 1 to about 3 or 4. This result would seem at first to imply that
the electric current had decomposed ammonia, and that the nitrogen had
been determined towards the positive electrode. But when the electricity
used was measured out by the volta-electrometer (707. 736.), it was found
that the hydrogen obtained was exactly in the proportion 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 electrolyzed, 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.

749. 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
carbonic 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
consequence of the decomposing power of the current. It, however, as well
as the carbonic oxide and acid, is only a secondary result; for it is the water
alone which suffers electro-decomposition, 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 (707.); 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-electrometer itself. The appearance of the carbon in combination
with the hydrogen at the positive electrode, and its non-appearance at the
negative electrode, are in curious contrast with the results which might have
been expected from the law usually accepted respecting the final places of
the elements.

750. 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 (843.). In
place of oxygen or even the gases already described (749.), 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 obtained; which, viewed as direct results of the
electro-chemical action, will, in their proportions, present nothing but
confusion, 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.

751. 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 electrolyzed in instances where other
substances have been supposed to give way. Some of these results I will
give in as few words as possible.

752. 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 spontaneous separation of nitric oxide. Upon diluting the acid with
its bulk or more of water, gas appeared at the negative electrode. Its
quantity could be varied by variations, either in the strength of the acid or of
the voltaic current: for that acid from which no gas separated at the cathode,
with a weak voltaic battery, did evolve gas there with a stronger; and that
battery which evolved no gas there with a strong acid, did cause its
evolution with an acid more dilute. The gas at the anode was always
oxygen; that at the cathode hydrogen. When the quantity of products was
examined by the volta-electrometer (707.), 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 the nitric
acid does not undergo electrolyzation, 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.

753. 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
of the ready formation of secondary results. The solution is a very excellent
conductor of electricity.

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

755. Sulphurous acid.—Pure liquid sulphurous acid does not conduct nor
suffer decomposition by the voltaic current174, 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.

756. A solution containing sulphuric acid in addition to the sulphurous acid,
was a better conductor. It gave very little gas at either electrode: that at the
anode was oxygen, that at the cathode pure hydrogen. From the cathode
also rose a white turbid stream, consisting of diffused sulphur, which soon
rendered the whole solution milky. The volumes of gases were in no regular
proportion to the quantities evolved from water in the voltameter. I
conclude that the sulphurous acid was not at all affected by the electric
current in any of these cases, and that the water present was the only body
electro-chemically decomposed; that, at the anode, the oxygen from the
water converted the sulphurous acid into sulphuric acid, and, at the cathode,
the hydrogen electrically evolved decomposed the sulphurous 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.

757. Sulphuric acid.—I have already given my reasons for concluding that
sulphuric acid is not electrolyzable, i.e. not decomposable directly by the
electric current, but occasionally suffering by a secondary action at the
cathode from the hydrogen evolved there (681.). In the year 1800, Davy
considered the sulphur from sulphuric acid as the result of the action of the
nascent hydrogen175. In 1804, Hisinger and Berzelius stated that it was the
direct result of the action of the voltaic pile176, 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 series of these Researches (552.): I do not now think that the
appearance of the sulphur at the negative electrode is an immediate
consequence of electrolytic action.

758. Muriatic acid.—A strong solution gave hydrogen at the negative
electrode, and chlorine only at the positive electrode; 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.

759. 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 electrolyzable, and if so, whether the decomposition was
definite.

760. 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.

761. The muriatic acid was now diluted with 100 times its volume of dilute
sulphuric acid. It still gave a large proportion of chlorine at the anode,
mingled with oxygen; and the result was the same, whether a voltaic battery
of 40 pairs of plates or one containing only 5 pairs were used. With acid of
this strength, the oxygen evolved at the anode was to the hydrogen at the
cathode, in volume, as 17 is to 64; and therefore the chlorine would have
been 30 volumes, had it not been dissolved by the fluid.

762. 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.

763. This constancy does not decide whether the muriatic acid is
electrolyzed 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 (697.), those in muriatic acid, as well as in water,
are the most favourable, or those perhaps even necessary, to decomposition.
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 (395.), which may be justly compared
with protoxide of lead (402.), and stands in the same relation to it as
muriatic acid to water. The chlorides of potassium, sodium, barium, &c., are
in the same relation to the protoxides of the same metals and present the
same results under the influence of the electric current (402.).

764. From all the experiments, combined with these considerations, 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.

765. In the dilute acid (761.), 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. 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.

766. 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
electrolyzed, 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, producing 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,—
789. 794. 814.,) they are not in the slightest degree opposed to such a
conclusion, and do support the general law.

767. Hydriodic acid.—A solution of hydriodic 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.

768. I believe the decomposition of the hydriodic acid in this case to be
direct, for the reasons already given respecting muriatic acid (763. 764.).

769. 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 mode of decomposition are applicable here as were
made in relation to the chlorides when in solution (766.).

770. Hydro-fluoric acid and fluorides.—Solution of hydrofluoric acid did
not appear to be decomposed under the influence of the electric current: it
was the water which gave way apparently. The fused fluorides were
electrolysed (417.); but having during these actions obtained fluorine in the
separate state, I think it better to refer to a future series of these Researches,
in which I purpose giving a fuller account of the results than would be
consistent with propriety here177.

771. 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
hydrocyanic 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 (766.), and because a fused cyanide of
potassium evolves cyanogen at the positive electrode178, I incline to believe
that the cyanide in solution is directly decomposed.

772. Ferro-cyanic acid and the ferro-cyanides, as also sulpho-cyanic acid
and the sulpho-cyanides, presented results corresponding with those just
described (771.).

773. Acetic acid.—Glacial acetic acid, when fused (405.), is not
decomposed by, nor does it conduct, electricity. On adding 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 is not electrolyzable, 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.

774. Acetates.—One of these has been referred to already, as affording only
secondary results relative to the acetic acid (749.). With many of the
metallic acetates the results at both electrodes are secondary (746. 750.).

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, &c., being
set free at the former, and, as far as I could judge under the circumstances,
acetic acid mingled with carbonic oxide, carbonic acid, &c. at the latter.

775. 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 (752.). 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.

776. Solutions, of salts containing other vegetable acids, as the benzoates;
of sugar, gum, &c., dissolved in dilute sulphuric acid; of resin, albumen,
&c., 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.

777. 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 combination of the
evolving substances whilst in their nascent state (658.), 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 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 (747.).

778. 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 possible 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.

779. Secondary actions are not confined to aqueous solutions, or cases
where water is present. For instance, various chlorides acted upon, when
fused (402.), by platina electrodes, have the chlorine determined electrically
to the anode. In many cases, as with the chlorides of lead, potassium,
barium, &c., 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 (790. 804.). These are,
therefore, instances of secondary actions of both kinds, produced in bodies
containing no water.

780. The production of boron from fused borax (402. 417.) is also a case of
secondary action; for boracic acid is not decomposable by electricity (408.),
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.

781. 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 naturally179. It is probable
they may prove equally interesting in an opposite direction, i.e. as affording
cases of analytic decomposition. Much information regarding the
composition, and perhaps even the arrangement, of the particles of such
bodies as the vegetable acids and alkalies, and organic compounds
generally, will probably be obtained by submitting them to the action of
nascent oxygen, hydrogen, chlorine, &c. 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 conductor, its

strength, &c., all of which may be expected to have their corresponding
influence upon the final result.

782. 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.

783. In the third series 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 (371. 376.), I announced a law, derived from
experiment, which seemed to me of the utmost importance to the science of
electricity 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 (377.).

784. In the further progress of the successive investigations, I have had
frequent occasion to refer to the same law, sometimes in circumstances
offering powerful corroboration of its truth (456. 504. 505.); and the present
series already supplies numerous new cases in which it holds good (704.
722. 726. 732.). It is now my object to consider this great principle more
closely, and to develope 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 interferences from secondary
results as possible, effected upon bodies very simple, yet very definite in
their nature.

785. 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 (732.). I refer, therefore, to the whole of

the subdivision of this series of Researches which contains the account of
the volta-electrometer (704. &c.).

786. 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 (758. &c.).

787. 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 (767. 768.).

788. 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 (770. 771. 772.), and from the
close analogy which holds between these bodies and the hydracids of
chlorine, iodine, bromine, &c., I consider these also as coming under
subjection to the law, and assisting to prove its truth.

789. 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 (380. &c.), 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. 68.). 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 (711.), which was
itself connected with the negative end of a voltaic battery; and a platina
wire connected 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. 69.

790. Under these circumstances the chloride of tin was decomposed: the
chlorine evolved at the positive electrode formed bichloride of tin (779.),
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 connexion was broken, the positive electrode
removed, and the tube and remaining chloride allowed to cool. When cold,
the tube was broken open, the rest of the chloride and the glass being easily
separable from the platina wire and its button of alloy. The latter when
washed was then reweighed, and the increase gave the weight of the tin
reduced.

791. 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 electrode 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 error, and if the electro-chemical decomposition is in this case also
definite. In some chemical works 58 is given as the chemical equivalent 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 (716.), &c.), that the numbers
leave little doubt of the applicability of the law of definite action in this and
all similar cases of electro-decomposition.

792. It is not often I have obtained an accordance in numbers 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.

793. 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.

794. 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
portion of platina can pass to the cathode, and would then produce 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, &c. 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.

795. 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 (716.) 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 (814. &c.).

796. Chloride of antimony.—It was in endeavouring to obtain 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 (690. 693. &c.).

797. I endeavoured to experiment upon the oxide of lead obtained by fusion
and ignition of the nitrate in a platina crucible, but found great difficulty,
from the high temperature required for perfect fusion, and the powerful