Full text of "The Fundamental Laws of Electrolytic Conduction: Memoirs by Faraday, Hittorf ..."

Google

This is a digital copy of a book that was preserved for generations on Hbrary shelves before it was carefully scanned by Google as part of a project

to make the world's books discoverable online.

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject

to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books

are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other maiginalia present in the original volume will appear in this file - a reminder of this book's long journey from the

publisher to a library and finally to you.

Usage guidelines

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we liave taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.
We also ask that you:

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.

+ Refrain fivm automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.

+ Maintain attributionTht GoogXt "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liabili^ can be quite severe.

About Google Book Search

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web

at |http : //books . google . com/|

■

' -'*', . ""- ^ ~-4-»r . -js -T t -iTw^ a^^.- ^r-3»m^w^

HARPER'S SCIENTIFIC MEMOIRS

EDITED BY

J. S. AMES, Ph.D.

PB0FK8S0R OF PHYSICS IN JOHNS HOPKINS UNIYERSITT

VII.
THE FUNDAMENTAL LAWS

ELECTROLYTIC CONDUCTION

THE FUNDAMENTAL LAWS

ELECTROLYTIC CONDUCTION

MEMOIBS BY FAKADAY, HITTOEF
AND F. KOHLEAUSOH

TRAKSLATKD AND EDITED

Bt H?M.' GOODWIN, Ph.D.

tniW TORE AND LONDON
BABPER & BROTHERS PUBLIS
18S0

HARPER'S SCIENTIFIC MEMOIRS.

EDITED BT

J. S. AMKS, Ph.D.,

PKOFKB80B OF FIlYtilOS IN JOUMB UOPK1N8 UNITBB81TT.

SOW READY:

THE FREE EXPANSION OF GASES. Memoira
by Gay-LuBsac, Joule, and Joule and ThomBoii.
Editor, Prof. J. S. Amks, Ph.D., Johns HopkiiiB
University. 75 cents.

PRISMATIC AND DIFFRACTION SPECTRA.
Memoirs by Ji>Beph von Frnnnhofer. Editor, Prof.
J. S. Amkb, Pb.D., Johns Hopkins University.
60 cents.

RONTGEN RAYS. Memoirs by R5utgen, Stokes,
and J. J. Thomson. Editor, Prof. Grokgk F.
Babkrb, University of Pennsylvania. 60 rents.

THE MODKRN 'I'HEORY OF SOLUTION. Me-
moirs by Pfeffer, Van*c Hi)ff, Arrhenius, and Raoult.
Editor, Dr. H. C. Jomks, Johns Hopkins University.
$100.

THE LAWS OF GASES. Memoirs by Bovle and
Ainagat. Editor, Prof.CAUL Babus, Brown University.
75 cents.

THE SECOND LAW OF THERMODYNAMK^S.
Memoirs by Carnot, Clansiiis, and Thomson. Editor,
Prof. W. F. Maoir, Princet<ni University.

THE FUNDAMENTAL LAWS OF ELECTRO-
LYTIC CONDUCTION. Memoir- by Faraday,
Hittorf, and Eohlransch. Editor, Dr. H. M. Good-
win, Mussachnsetts Institute of Technology.

fiV PREPARATION:

THE EFFECTS OF A MAGNETIC FIELD ON
RADIATION. Memoirs by Farndav, Kerr, and
Zeeraan. Editor, Dr. E. P. Lkwis, University of
California.

THE WAVE-THEORY OF LIGHT. Memoirs by
Hiiygens,Yonnir, and Frexnel. Editor, Prof. Hbnby
Crrw, Northwestern University.

THE LAWS OF GRAVITATION. Editor, Prof.
A. S. Maokrmzik, Bryn Mawr College

NRW YORK AND LONDON:
HARPER & BROTHERS, PUBLISHERS.

AU rifhta rutrHd.

T^fi' — '^^Km

GENERAL CONTENTS

tj Preface v

f^ Relation by Measure of Common and Voltaic Electricity. By Michael

-^ Faraday 3

' On Electrochemical Decomposition. By Michael Faraday 11

"^ Biographical Sketch of Faraday 44

o On the Migration of Ions during Electrolysis. By W. Hittorf 49

^ Biographical Sketch of Hittorf 80

On the Conductivity of Electrolytes Dissolved in Water in Relation to

1? the Migration of their Components. By F. Eohlrausch 85

i Biographical Sketch of Kohlrausch 92

Bibliography 94

Index. 97

OOOO^ ^

PREFACE

Ik the present volume are collected those papers on electro-
chemistry which contain the original statement of the funda-
mental laws and experiments on which the modern theory of
electrolytic conduction is based. Of these, Faraday^s law of
definite electrochemical action and electrochemical equiva-
lents, first stated in 1834, naturally takes precedence. This
law is universally recognized as one of the few rigidly exact
laws of nature, and lies at the basis of all electrochemical
theory and practice. Of the extended series of experiments in
electrochemistry, contained in the fifth and seventh series of
Faraday^s Experimental Researches, all of which touch more. or
less on the law in question, only those sections which have a
direct bearing on the establishment of the law are here pre-
sented. Faraday^s brief paper on the " Relation by Measure
of Common and Voltaic Electricity '* has been added as an in-
troduction, as it was in this article that he was first led to a
statement of the probable existence of the law to which he
afterwards devoted so much attention.

Second only to Faraday's law, the classical researches of
Hittorf on the concentration changes produced at the elec-
trodes during electrolysis, have proved of fundamental signifi-
cance in the explanation of electrolytic phenomena. The
explanation given by Hittorf in 1853 of this phenomenon is
still that generally accepted by physicists at the present time.
Of Hittorf's five papers bearing on this subject, all of which
are easily accessible in German in Ostwald's KJassiker der Ex-
akten Wissenschaften, the first only has been here translated.
This, however, is complete in itself, and contains not only a
statement of Hittorfs theory, but also a comprehensive and
remarkably careful experimental investigation of the phenom-
enon of transference. The later papers are mainly an exten-

PREFACE

Bion of the first, with applications to certain important prob-
lems of chemical constitution.

The great importance of the results obtained by Hittorf was
not generally recognized at the time of their publication, but
only after F. Kolrausch had pointed out their bearing on his
investigations on the electrical conductivity of solutions. The
elegance of method and accuracy with which these investiga-
tions have been, and are still being carried out, place them
pre-eminent among investigations of this class. Immediately
after sufficient conductivity data had been obtained, Kohl-
rausch recognized the bearing of Hittorf s investigations upon
his results, and was led to the formulation of the law of the in-
dependent migration of ions. The paper in which this law was
first presented to the Gottingen Academy in 1876 is translated
in full. It was not until 1879 that the researches, of which
this was the most important conclusion, appeared in complete
form in Wiedemann's Annalen,

With the establishment of the laws of Faraday, Hittorf, and
Kohlrausch the way was prepared for the dissociation theory
of Arrhenius, which was announced in 1886, as soon as the
theory of solutions had been formulated by Van't Hoff.

H. M. GooDWiiir.
Massachusetts Ikstitute of Technoloqt.

■ *— .

RELATION BY MEASURE

COMMON AND VOLTAIC ELECTRICITY

MICHAEL FARADAY

Head January 17, 1888, before the Boyal Society

{Philosophical Transactiom, 123. 48, 1838 ; Poggendorff's AnncUen, 29,

878, 1888 ; Experimental Researches in Electricity,

Vol. I., Series III., § 8, p. 102)

CONTENTS

Relation between Deflection of Magnetic Needle and Quantity of Elec-
tricity passing through Oa^winor/ieter 3

Equivalent Voltaic Effect 5

Relation to Chemical Action 6

First Statement of Faraday's Law 7

RELATION BY MEASURE

COMMON AND VOLTAIC ELECTRICITY

MICHAEL FARADAY

Believing the point of identity to be satisfactorily estab-
lished,* I next endeavored 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, but also of demonstrating certain
general principles and creating an extension of the means of
investigating and applying the chemical powers of this wonder-
ful and subtile agent.

The first point to be determined was, whether the same abso-
lute quantity of ordinary electricity, sent through a galva-
nometer, under different circumstances, would cause the same
deflection of the needle. An arbitrary scale was therefore
attached to the galvanometer, each division of which was equal
to about 4°, and the instrument arranged as in former experi-
ments. The machine, battery, 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.

Seven of the battery jars were removed and eight retained
for present use. It was found that about forty turns would

* [/w the paper immediately preceding this, the ** Identity of Eleetricitie>%
from Different Sources'* was experimentally demonstrated for voltaic, fric-
tional, magneto, thermo, and animal electricity.']

MEMOIRS ON THE FUNDAMENTAL

fully charge the eight jars. They were then charged by thirty
tarns 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.

The other seven jars were then added to the eight, and the
whole fifteen charged by thirty turns of the machine. The
Henley 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 fifteen jars were repeated several
times alternately with the same results.

Other experiments were then made, in which all the bat-
tery was nsed, 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. 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 defiection of the needle
was sensibly the same in all of them. If any difference oc-
curred, it was that the thin string and thread caused greatest
deflection ; and if there is any lateral transmission, as M. Col-
ladon 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.

Hence it would appear that if the same absolute quantity of
electricity passes through the galvanometer, whatever may he its
intensity y the deflecting force upon the magnetic needle is the
same.

The battery of fifteen jars was then charged by sixty revolu-
tions 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

"^rr^'j

LAWS OF ELECTROLYTIC CONDUCTION

accurate enough for me to assert that the arc was exactly double
the former arc ; to the eye it appeared to be so. The proba-
bility is that the deflecting force of an electric current is directly
proportional to the absolute quantity of electricity passed, at
whatever intensity that electricity may be.*

Dr. Ritchie has shown that in a case where the intensity of
the electricity remained the same, the deflection of the mag-
netic needle was directly as the quantity of electricity passed
through the gal vanometer. f Mr. Harris has shown that the
heating power of common electricity on metallic wires is the
same for the same quantity of electricity, whatever its intensity
might have previously been. J

The next point was to obtain a voltaic arrangement produc-
ing an effect equal to that just described. 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 fast-
ened 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
was adopted as a standard which consisted of one drop strong
sulphuric acid in four ounces of 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 ; and
a new part of the zinc wire having been brought into position
with the platina, the comparative experiments were made.

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

t Quart&f'ly JourruU of Science, New Series, vol. !., p. 83.

t Plymouth Ti-ansactions, p. 22.

MEMOIRS ON THE FUNDAMENTAL

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 re-
moved 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.

Hence, as an approximation, and judging from magnetic force
only at present, 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 vitrol and four ounces distilled water, at a temper-
ature of 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 y^ir ^^ ^ minute,
as the electrical battery charged by thirty turns of the large
machine in excellent order. Notwithstanding this apparently
enormous disproportion, the results are perfectly in harmony
with those effects which are known to be produced by varia-
tions in the intensity and quantity of the electric fluid.

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^ di-
vision. Hence a permanent deflection to that extent might be
considered as indicating a constant voltaic current, which in
eight beats of my watch could supply as much electricity as the
electrical battery charged by thirty turns of the machine.

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 di-
ameter as the wire ; it was then connected in turn with the con-
ductor of the machine or with the voltaic apparatus, so as always
to form the positive pole, and at the same time retain a perpen-
dicular position, that it might rest with its whole weight upon

LAWS OF ELECTROLYTIC CONDUCTION

the test paper to be employed. The test paper itself was sup-
ported upon a platina spatula, connected either with a dis-
charging train or with the negative wire of the voltaic appara-
tus, and it consisted of four thicknesses, moistened at all
times to an equal degree in a standard solution of hydriodate
of potassa.

When the platina wire was connected with the prime con*
ductor 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 dilBference in effect produced by two or three
turns, more or less, could be distinguished with facility.

The wire and the spatula were then connected with the vol-
taic apparatus, the galvanometer being also included in the
arrangement; and, a stronger acid having been prepared, con-
sisting of nitric acid and water, the voltaic apparatus was im-
mersed so far as to give a permanent deflection of the needle to
the 5^ division, the fourfold moistened paper intervening as
before.* Then by shifting the end of the wire from place to
place upon the test paper, the effect of the current for five, six,
seven, or any number of beats of the watch 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 elec-
tricity, 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.

Hence it results that both in magnetic deflection and in
chemical forcey the current of electricity of the standard vol-
taic battery for eight beats of the watch was equal to, that of
the machine evolved by thirty revolutions.

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

Hence arises still further confirmation, if any were required,

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

LAWS OF ELECTROLYTIC CONDUCTION

of the identity of com moil and voltaic electricity, and that the
differences of intensity and quantity are quite sufficient to ac-
count for what were supposed to be their distinctive qualities.
The extension which the present investigations have enabled
me to make of the facts and views constituting the theory of
electrochemical decomposition will, with some other points of
electrical doctrine, be almost immediately submitted to the
Royal Society in another series of the Researches.

Royal Institution, December 15, 1882

ON ELECTROCHEMICAL DECOMPOSITION

MICHAEL FARADAY

Read January 28, February 6 and 13, 1834, before the Royal Society

(Philosophical T^'ansactions, 1 24, 77, 1884 ; PoggendorfF's Annalen, 3%
801, 1884 ; Experimental Eesearehes in Electrieity,
Vol. I., Series VIL, § 11, p. Id5)

CONTENTS

Preliminary: pag«

Definition of Electrodes 11

Anode and Cathode 12

Electrolytes 13

Ions, Anions, Cations 13

On Some General Conditions of ElectrocJiemical Decomposition (Omitted).
On a New Measurer of Volta-electricity :

Bestatemsnt of Faraday^s Law 14

Forms of Oas Voltameter 15

Effect of Size of Electrodes 17

Solubility of Oases Evolved 18

Efect of Variation of Intensity of Current 20

Eiffect of Concentration 21

Experim^ents with otJier Electrolytes 22

General Conclusions 23

Absolute and Comparative Measurements 24

" The Volta Electrometer" 25

On the Primal^ or Secondary Cliaracter of the Bodies Evolved at the

Electrodes (Omitted).
On the Definite Nature and Extent of ElectrocJiemical Decomposition :

Recapitulation and Restatement of Faraday* s Law 26

Experimental Verification:

With Various Salts 27

With Various Electrodes in Solutions 32

With Various Electrodes in Fused Salts 34

Conclusion, Law of Definite ElectrocTiemicai Action 37

Electrochemical Equivalents 38

Summary of Results 38

Applications of Law 40

Preliminary Table of Ions and their Electrochemical Equivalents. . . 42

Conclusion 43

ON ELECTROCHEMICAL DECOMPOSITION

MICHAEL PAEADAY

PRELIMINAEY

The theory which I believe to be a true expression of the facts
of electrochemical decomposition, and which I have therefore
detailed in a former series of these Besearches, is so much at
variance with those previously advanced that I find the great-
est difiiculty in stating results, as I think, correctly, whilst
limited to the use of terms which are current with a certain
accepted meaning. Of this kind is the term pole, with its
prefixes of positive and negative, and the attached ideas of
attraction and repulsion. The general phraseology is that the
positive pole attracts oxygen, acids, etc., or more cautiously,
that it determines their evolution upon its surface ; and that
the negative pole acts in an equal manner upon hydrogen, com-
bustibles, metals, and bases. According to my view, the de-
termining force \'& not at the poles, but tvitkin the body under
decomposition ; and the oxygen and acids are rendered at the
negative extremity of that body, whilst hydrogen, metals, etc.,
are evolved at the positive extremity.

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 ; and they of course,* when

in contact with that bo(Jy, are the limits of its extent in the

direction of the current. The term has been generally applied

MEMOIRS ON THE FUNDAMENTAL

to the metal surfaces in contact with the decomposing sub-
stance ; but whether philosophers generally would also apply it
to the surfaces of air and water, against which I have effected
electrochemical decomposition, is subject to doubt. In place
of the term pole, I propose using that of electrode,* and I mean
thereby that substance, or rather surface, whether of air, water,
metal, or any other body, which bounds the extent of the de-
composing matter in the direction of the electric current.

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 distin-
guished apart from the poles, with which they are mostly, and
the electrodes, with which they are always, in contact. Wish-
ing 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 m^rgnetism of the earth be due to electric
currents passing round it, the latter must be in constant direc-
tion, which, according to the present usage of speech, would
be from east to west, or, which will strengthen this to help 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 refer-
ence, and exhibit constantly the same relations of powers.
Upon this notion we purpose calling that towards the east the
anode,\ and that towards the west the cathode ;% and whatever
changes may take place in our views of the nature of electricity
and electrical action, as they must affect the natural standard
referred to, in the same direction, and to an equal amount with
any decomposing substances to which these terms may at any
time be applied, there seems no reason to expect that they will
lead to confusion or tend in any way to support false views.
The anode is therefore that surface at which the electric cur-
rent, according to our present expression, enters : it is the
negative extremity of the decomposing body; is where oxygen,

* riKiKTpov, and o^oQy a way.

f ai/w, upwards, and o^if , a way : the way which the sun rises.
X Kardy downwards, and odbs, a way : the way which the sun sets.

LAWS OF ELECTROLYTIC CONDUCTION

chlorine, acids, etc., are evolved ; and is against or opposite the
positive electrode. The cathode is that surface at which the
current leaves the decomposing body. And is its positive ex-
tremity; the combustible bodies, metals, alkalies, and bases,
are evolved there, and it is contact with the negative electrode.

I shall have occasion in these Researches, also, to class bodies
together according to certain relations derived from their elec-
trical actions ; 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.*
Water, therefore, is an electrolyte. The bodies which, like ni-
tric or sulphuric acids, are decomposed in a secondary man-
ner are not included under this term. Then for electrochemi-
cally decomposedy I shall often use the term electrolyzed, derived
in the same way, and implying that the body spoken of is sep-
arated into its components under the influence of electricity :
it is analogous in its sense and sound to analyze, which is
derived in a similar manner. The term electrolytical will be
understood at once : muriatic acid is electrolytical, boracic
acid is not.

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 per-
haps right, they are only hypothetical, and maybe wrong; and
then, through a very imperceptible, but still very dangerous,
because continual, influence, they do great injury to science by
contracting and limiting the habitual views of those engaged in
pursuing it. I propose to distinguish such bodies by calling
those anions\ which go to the anode of the decomposing body ;
and those passing to the cathode, cations I; 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

• ijiXiKTpop, and \{fta,solvo. Noun, electrolyte ; verb, electrolyze.
f Avuovy that which goes up. (Neuter participle.)
X Karmv, that which goes down,

MEMOIRS ON THE FUNDAMENTAL

evolves the two ions, chlorine and lead, the former being an
anion, and the latter a cation.

These terms, being otice well defined, will, I hope, in their use
enable me to avoid much periphrasis and ambiguity of expres-
sion. 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.*

It will be well understood that I am giving no opinion re-
specting the nature of the electric current now, beyond what I
have done on former occasions ; and that though I speak of the
current as proceeding from the parts which are positive to those
which are negative, it is merely in accordance with the conven-
tional, though in some degree tacit, agreement entered into by
scientific men, that they may have a constant, certain, and defi-
nite means of referring to the direction of the forces of that
current.

[Section IV., including eight pages " On Some General Condi-
tions of Electrochemical Decomposition,^' is here omitted.^

ON" A N^EW MEASURER OF VOLTA-ELECTRICITY

I have already said, when engaged in reducing common and
voltaic electricity to one standard of measurement, f and again
when introducing my theory of electrochemical decomposition,
that the chemical decomposing action of a current is constant
for a constant quantity of electricity, notwithstanding the great-
est variations in its sources, in its intensity, in the size of the
electrodes used, in the nature of the conductors (or non-con-
ductors) through which it is passed, or in other circumstances.
The conclusive proofs of the truth of these statements shall be
given almost immediately.

I endeavored 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 s6rve at pleasure, either as
a comparative standard of effect or as a positive measurer of
this subtile agent.

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

f [See page 7.]

■ -J

, .^•--WW ■■■■*

LAWS OF ELECTROLYTIC CONDUCTION

There is no substance better fitted, under ordinary circum-
stances, 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 em-
barrassment from secondary action, and, being gaseous, they
are in the best physical condition for separation and measure-
ment. 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.

The first precaution needful in the construction of the instru-
ment was to avoid the recombination of the evolved gases, an
effect which the positive electrode has been found so capable
of producing. 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 (Fig. 1). The tubes were about 8
inches long, 0.7 of an inch in diameter, and grad-
uated. The platina plates were about an inch
long, as wide as the tubes would permit, and ad-
justed 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. 2). When these tubes were used
as measurers, they were filled with dilute sul-
phuric acid, inverted in a basin of the same liquid
(Fig. 3), 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.

Another form of apparatus is
that delineated (Fig. 4). 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

I
i

Fig.l

Fig. 2

Fig.B

MEMOIRS ON THE FUNDAMENTAL

Fig.^

in the position figured, it shall be as near to the angle as pos-
sible, 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 perpendic-
ular. The other metallic ter-
mination, h, is introduced at the
time decomposition is to be ef-
fected, 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.
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. 6) closed at the upper extremity and

graduated, through the sides of which pass platina
wires (being fused into the glass), which are con-
nected 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, 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.
Another form of the in-
strument is given in Fig. 6. A fifth form
is delineated (Fig. 7). This I have found
exceedingly useful in experiments con-
tinued in succession for days together,
and where large quantities of indicating gas were to be col-
lected. It is fixed on a weighted foot, and has the form of a

Fig.^

Fig.%

LAWS OF ELECTROLYTIC CONDUCTION

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 cham-
ber, sealed hermetically at the
part held in the stand, is 5
inches in length and 0.6 of
an inch in diameter ; the neck
is about 9 inches in length and
0.4 of an inch in diameter in-
ternally. The figure will fully
indicate the construction.

It can hardly be requisite to remark, that in the arrangement
of any of these forms of apparatus, they, and the wires con-
necting them with the substance, which is collaterally subjected
to the action of the same electric current, should be so far
insulated as to insure a certainty that all the electricity which
passes through the one shall be transmitted through the other.

Fig.l

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 inter-
fering circumstances which would require to be practically
guarded against.

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 were used (Figs.
5, 6, and 7). One of these had plates 0.7 of an inch wide and
nearly 4 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 3 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 com-
mon current of electricity passed through them, very nearly the
same quantity of gas was evolved in all. The difference was
sometimes in favor of one, and sometimes on the side of another;
but the general result was that the largest quantity of gases was
B 17

MEMOIRS ON THE FUNDAMENTAL

evolved at the smallest electrodes — namely, those consisting
merely of platina wires.

Experiments of a similar kind were made with the single-
plate straight tubes (Figs. 1, 2, 3), and also with the curved
tubes (Fig. 4), 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 metal-
lic 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 experi-
ment the volumes were 55.3, 55.3, and 54.4.

But it was observed in these experiments, that in single-plate
tubes 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 dojible-plate tube. Upon more minutely
examining these effects, I was led to refer them, and also the
differences between wires and plates, to the solubility of the
gases evolved, especially at the positive electrode.

When the positive and negative electrodes are equal in sur-
face, 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; 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 neverthe-
less very inferior in number. They do not rise so universally
from every part of the surface, but seemed to be evolved at
different points ; and though so much larger, they appear to
cling to the metal, separating with difficulty from it, and when
separated, instantly rising to the top of the liquid. If, there-
fore, oxygen and hydrogen had equal solubility in, or powers of
combining with, water under similar circumstances, still, under

n^;:^:.- ^TB^yirnirnTintH

LAWS OF ELECTROLYTIC CONDUCTION

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 bleaching 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 man-
ner, of oxy-water.

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

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 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 oxy-
gen 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 favorable condition for solution.

With the intention of avoiding this solubility of gases as
much as possible, I arranged the decomposing plates in a verti-
cal position, 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 experi-
ments to be hereafter referred to, in which other liquids than
dilute sulphuric acid — as, for instance, solution of potash — were
used.

The irregularities of the indications of the measurer pro-

MEMOIRS ON THE FUNDAMENTAL

posed, 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 favor
them in the least degree ; 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, it can be collected more per-
fectly and in greater purity.

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 »

The next point in regard to which the principle of constant
electrochemical 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 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.

Still these results did not prove that variation in the inten-
sity of the current was not accompanied by a corresponding
variation in the electrochemical effects, since the action 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 prob-
ably as the quantity of electricity passing through a given
sectional area perpendicular to the current, divided by the
time ; and therefore when large plates were contrasted with
wires separated by an equal length of the same decomposing
conductor, whilst one current of electricity passed through
both arrangements, that electricity must have been in a very
different state, as to tensio7i, between the plates and between

the wires ; yet the chemical results were the same.

Fig. 8

LAWS OF ELECTROLYTIC CONDUCTION

The difference in intensity, under the circumstances de-
scribed, may be easily shown practically, by arranging two de-
composing apparatus as in Fig. 8, 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 decom-
posing apparatus, such as that
delineated in Fig. 7, be con-
nected with the wires at ab, Fig.
8, 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 de-
composition within, show how much greater the intensity is
there than at the former points. The connections of P and N
with the voltaic battery are of course to be continued during
the whole time.

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 in-
tensity has no influence on the results if the quantity of electric-
ity remain the same. The experiment, in fact, resolves itself
simply into an increase in the size of the electrodes.

The third point, in respect to which the principle of equal
electrochemical action on water was tested, was variation of
the streyigth of the solution used. In order to render the water
a conductor, sulphuric acid had been added to it ; and it did
not seem unlikely that this substance, with many others, might
render the water more subject to decomposition, the electricity

MEMOIRS ON THE FUNDAMENTAL

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 submit-
ted simultaneously to the action of the same electric current.
Slight differences occurred, as before, sometimes in one direc-
tion, 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.

When an acid having a specific gravity of about 1.336 was
employed, the results were most uniform, and the oxygen and
hydrogen 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 disap-
pearance 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 disappear-
ance of the oxygen in this case, but imagine it is due to the
formation of oxy-water, which Thenard has shown is favored by
the presence of acid.

Although not necessary for the practical use of the instru-
ment I am describing, yet as connected with the important point
of constant electrochemical action upon water, I now investi-
gated the effects produced by an 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.

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 con-
ductor by sulphate of ammonia, or a solution of subcarbonate

LAWS OF ELECTROLYTIC CONDUCTION

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.

I have already said, respecting large and small electrodes,
that change of order caused no change in the general effect.
The same was the case with different solutions, or with differ-
ent intensities ; and however the circumstances of an experi-
ment might be varied, the results came forth exceedingly con-
sistent, and proved that the electrochemical action was still
l^e same.

I consider the foregoing investigation as sulBScient to prove
the very extraordinary and important principle with respect to
WATER, that when subjected to the- influence of the electric cur-
rent, a quantity of it is decomposed exactly proportionate to the
quantity of electricity tohich 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, 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 vol-
♦ uable measurer of the electricity concerned in their evolution.

The forms of instrument which I have given (Figs. 6, 6, 7) are
probably those which will be found most useful, as they indi-
cate 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, shall diminish their quantity, or add
other gases to them.

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 disap-
pearance in othor ways than the oxygen; whilst at the same time

its volume is so large as to render it a good and sensible indi-

MEMOIRS ON THE FUNDAMENTAL

cator. In such cases the first and second form of apparatus
have been used (Figs. 3, 4). 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 pro-
cured when solutions are used in comparative experiments,
which, yielding no oxygen or only secondary results of its ac-
tion, can give no indications if the educts at both electrodes be
collected. Such is the case when solutions of ammonia, muri-
atic acid, chlorides, iodides, acetates, or other vegetable salts,
etc., are employed.

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.

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 ; and the other,
in which a single gas, as the hydrogen only, is used. When
referred to as a comparative instrument (a use I shall now make
of it very extensively), it will not often require particular pre-
caution in the observation ; but when used as an absolute meas-
urer, 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 indi-
cating a DEGBEE of electricity.

It can scarcely be needful to point out further than has
been done how this instrument is to be used. It is to be in-
troduced into the course of the electric current, the action of
which is to be exerted anywhere else, and if 60° or 70° of elec-
tricity 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 experi-
ment it is necessary to correct the volume of gas for changes in
temperature and pressure, and especially for moisture** For

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

LAWS OF ELECTROLYTIC CONDUCTION

the latter object the volta-electrometer (Fig. 7) is most accu*
rate, as its gas can be measured over water, whilst the others
retain it over acid or saline solutions.

I have not hesitated to apply the [term degree in analogy
with the use made of it with respect to another most important
imponderable agent — namely, heat ; and as the definite expan-
sion of air, water, mercury, etc., is there made use of to meas-
ure heat, so the equally definite evolution of gases is here
turned to a similar use for electricity.

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 re-
veals that quantity by inspection ; I have therefore named it a

VOLTA-ELECTROMETER.

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.

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

[Section VL, including thirteen pages, '* On the Primary and
Secondary Character of the Bodies Evolved at tJie Electrodes," is
here omitted »^

ON THE DEFINITE NATURE AND EXTENT OF ELECTROCHEMICAL

DECOMPOSITION

In the third series of the Eesearches, after proving the

* As early as the year 1811, Messrs. Gay-Lussac and Thenard employed
chemical decomposition as a measurer of the electricity of the voltaic pile.
See Becherches Phymo-cfiymiques, p. 12. The principles and precautions
by which it becomes an exact measure were of course not then known.
December y 1838.

^^3

MEMOIRS ON THE FUNDAMENTAL

identity of electricities derived from different sources, and
showing, by actual measurement, the extraordinary quantity of
electricity evolved by a very feeble voltaic arrangement, 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 electrochemistry 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.

In the further progress of the successive investigations, I have
.^ J had frequent occasion to refer to the same law, sometimes in cir-
. "t cumstances offering powerful corroboration of its truth; and
the present series already supplies numerous new cases in which
it holds good. It is now my object to consider this great prin-
ciple more closely, and to develop some of the consequences to
which it leads. That the evidence for it may be 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.

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 infiuence over it, that I may be excused entering into
further detail respecting that substance, or even summing up
the results here. I refer, therefore, to the whole of the sub-
division of this series of Researches which contains the account
of the volta-electrometer.

In the next place, I also consider the law as established with
respect to muriatic acid by the experiments and reasoning al-
ready advanced, when speaking of that substance, in the sub-
division respecting primary and secondary results.

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.

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, and from the close analogy which holds between these
bodies and the hydracids of chlorine, iodine, bromine, etc., I

^ [See page 7.]
26

LAWS OF ELECTROLYTIC CONDUCTION

consider these also as coming under subjection to the law, and
assisting to prove ita truth.

In the preceding cases, except the first, the water ia be-
lieved to be inactive ; but to avoid any ambiguity arising from
its presence, I sought for substancGS from which it shonld bo
absent altogether ; and, taking advantage of the law of
conduction* already developed, I soon found abundance,
among which protockloride 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 beat the bottom of the tube within (Fig. 9).
The tube was suspended by a piece of platina wire, so
that the heat of a spirit-lamp could be applied to it.
Recently fnsed protochloride of tin was introduced in
enfiicient quantity to occupy, when melted, abont one-
half of the tube ; the wire of the tube was connected
with a volta-electrometer, which was itself connected ^(^.9
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,
BO 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. 10.

Under these eircnmatancea the chloride of tin was decom-
posed : the chlorine evolved at the positive electrode formed

*[TIte law referred to anerU "the general ateumption of eondueting
power bi/bodie* at too rtntllies pnMfron thetolidto tAt liquid ttate."]

MEMOIRS ON THE FUNDAMENTAL

bichloride of tin, 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 com-
munication through the decomposing chloride. When the ex-
periment had been continued so long as to yield a reasonable
quantity of gas in the volta-electrometer, the battery connection
was broken, the positive electrode removed, and the tube and
remaining chloride allowed to cool. When cold, the tube was
broken open, the rest of the chloride and the glass being easily
separable from the platina wire and its button of alloy. The
latter when washed was then reweighed, and the increase gave
the weight of the tin reduced.

I will give the particular results of one experiment, in illus-
tration 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 oxy-
gen 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
electrochemical 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 ex-
periment, and the experiment itself is so subject to slight causes
of variation (as from the absorption of gas in the volta-electrom-
eter), that the numbers leave little doubt of the applicability
of the law of definite action in this and all similar cases of elec-
tro-decomposition.

It is not often I have obtained an accordance in numbers so
near as 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

ni^'^

LAWS OF ELECTROLYTIC CONDUCTION

average of the four experiments gave 58.53 as the electrochemi-
cal equivalent for tin.

The chloride remaining after the experiment was pure pro-
tochloride of tin ; and no one can doubt for a moment that the
equivalent of chlorine had been evolved at the anode, and, hav-
ing formed bichloride of tin as a secondary result, had passed
awav.

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 plat-
ina, 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 pro-
duce a vitiated result. I therefore sought for, and found in
plumbago, another substance which could be used safely as the
positive electrode in such bodies as chlorides, iodides, etc. The
chlorine or iodine does not act upon it, but is evolved in the
free state ; and the plumbago has no reaction, under the cir-
cumstances, 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.

The mean of the 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 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.

Chloride of antimony. — It was in endeavoring to obtain the
electrochemical equivalent of antimony from the chloride,
that I found reasons for the statement I have made respect-
ing the presence of water in it in an earlier part of these
Besearches.

I endeavored to experiment upon the oxide of lead obtained
by fusion and ignition of the nitrate in a platina crucible, but
found great difficulty from the high temperature required for
perfect fusion, and the powerful fluxing qualities of the sub-
stance. Green-glass tubes repeatedly failed. I at last fused

the oxide in a small porcelain crucible, heated fully in a char-

MEMOIRS ON THE FUNDAMENTAL

■

coal fire ; and^ as it was essential that th^ eyolntion of the lead
at the cathode should take place beneath the surface, the neg-
ative electrode was guarded by a green -glass tube, fused
around it in such a manner as to expose only the
knob of piatina at the lower end (Pig. 11), so that it
could be plunged beneath the surface, and thus ex-
clude contact of air or oxygen with the lead reduced
there. A piatina wire was employed for the positive
electrode, that metal not being subject to any action
from the oxygen evolved against it. The arrangement
is given in Fig. 12.

In an experiment of this kind the equivalent for the
lead came out 93.17, which is very much too small.
This, I believe, was because of the small interval be-
tween the positive and negative electrodes in the oxide
^^ of lead ; so that it was not unlikely that some of the
froth and bubbles formed by the oxygen at the anode
should occasionally even touch the lead reduced at the cathode,
and re-oxidize it. When I endeavored to correct this by hav-
ing more litharge, the
greater heat required
to keep it all fluid
caused a quicker ac-
tion on the crucible,
which was soon eaten
through and the ex-
periment stopped.

In one experiment
of this kind I used ^ i2

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

Oxide of bismuth. — I found this substance required too high

LAWS OF ELECTROLYTIC CONDUCTION

a temperature, and acted too powerfully as a flux, to allow of
any experiment being made on it, without the application of
more time and care than I could give at present.

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

Iodide of lead. — This substance can be experimented with
in tubes heated by a spirit-lamp ; but I obtained no good results
from it, whether I used positive electrodes of platina or plum-
bago. In two experiments the numbers for the lead came out
only 75.46 and 73.45, instead of 103.5. This I attribute to
the formation of a periodide at the positive electrode, which,
dissolving in the mass of liquid iodide, came in contact with
the lead evolved at the negative electrode, and dissolved part
of it, becoming itself again protiodide. Such a periodide does
exist ; and it is very rarely that the idiode of lead formed by pre-
cipitation, and well washed, can be fused with out. evolving much
iodine from the presence of this percompound ; nor does crys-
tallization from its hot aqueous solution free it from this sub-
stance. Even when a little of the protiodide and iodine are
merely rubbed together in a mortar a portion of the periodide

MEMOIRS ON THE FUNDAMENTAL

is formed. And though it is decomposed by being fused and
heated to dull redness for a few minutes, and the whole reduced
to protiodide, yet that is not at all opposed to the possibility,
that a little of that which is formed in great excess of iodine
at the anode, should be carried by the rapid currents in the
liquid into contact with the cathode.

This view of the result was strengthened by a third experi-
ment, where the space between the electrodes was increased to
one-third of an inch ; for now the interfering effects were much
diminished, and the number of the lead came out 89.04 ; and it
was fully confirmed by the results obtained in the cases of trans-,
fer to be immediately described.

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

Protiodide of tin. — This substance, when fused, conducts
and is decomposed by the electric current, tin is evolved at the
anode, and periodide of tin as a secondary result at the cathode.
The temperature required for its fusion is too high to allow of
the production of any results for weighing.
C7()5 Iodide of potassium was subjected to electrolytic action in a
^ tube, like that in Fig. 9. The negative electrode was a globule
of lead, and I hoped in this way to retain the potassium, and
' obtain results that could be weighed and compared with the
volta-electrometer indication; but the difficulties dependent
upon the high temperature required, the action upon the glass,
the fusibility of the platina induced by the presence of the lead,
and other circumstances, prevented me from procuring such
results. The iodide was decomposed with the evolution of io-
dine at the anode, and of potassium at the cathode, as in former
cases.

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

^^ ^ Let us turn to another kind of proof of the definite chemical

action of electricity. If any circumstances could be supposed

LAWS OF ELECTROLYTIC CONDUCTION

to exert an influence over the quantity of the matters evolved
during electrolytic action, one would expect them to be present
when electrodes of different substances, and possessing very
different chemical affinities for such matters, were used. Plat-
ina has no power in dilute sulphuric acid of combining with
the oxygen at the anode, though the latter be evolved in the
nascent state against it. Copper, on the other hand, immedi-
ately unites with the oxygen, as the electric current sets it free
from the hydrogen ; and zinc is not only able to combine with
it, but can, without any help from the electricity, abstract it
directly from the water, at the same time setting torrents of
hydrogen free. Yet in cases where these three substances were
used as the positive electrodes, in three similar portions of the
same dilute sulphuric acid, specific gravity 1.336, precisely the
same quantity of water was decomposed by the electric current,
and precisely the same quantity of hydrogen set free at the
cathodes of the three solutions.

The experiment was made thus : Portions of the dilute sul-
phuric acid were put into three basins. Three volta-electrom-
eter tubes, of the form Figs. 1, 3, were filled with the same
acid, and one inverted in each basin. A zinc plate, connected
with the positive end of a voltaic battery, was dipped into the
first basin, forming the positive electrode there, the hydrogen,
which was abundantly evolved from it by the direct action of
the acid, being allowed to escape. A copper plate, which dipped
into the acid of the second basin, was connected with the nega-
tive electrode of the first basin ; and a platina plate, which
dipped into the acid of the third basin, was connected with the
negative electrode of the second basin. The negative electrode
of the third basin was connected with a volta-electrometer,
and that with the negative end of the voltaic battery.

Immediately that the circuit was complete, the electrochemi-
cal action commenced in all the vessels. The hydrogen still
rose in apparently undiminished quantities from the positive
zinc electrode in the first basin. No oxygen was evolved at the
positive copper electrode in the second basin, but a sulphate of
copper was formed there ; whilst in the third basin the positive
platina electrode evolved pure oxygen gas, and was itself un-
affected. But in all the basins the hydrogen liberated at the
negative platina electrodes was the same in quantity, and the
same with the volume of hydrogen evolved in the volta-elec-

c 33

MEMOIRS ON THE FUNDAMENTAL

trometer^ sliowing that in all the vessels the cnrrent had de-
composed an equal quantity of water. In this trying case,
therefore, the chemical action of electricity proved to be per-
fectly definite.

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

In this experiment the chloride of silver formed in the sec-
ond basin retarded the passage of the current of electricity, by
virtue of the law of conduction before described,* so that it had
to be cleaned off f 6ur or five times during the course of the ex-
periment ; but this caused no difference between the results of
that vessel and the others.

Charcoal was used as the positive electrode in both sulphuric
and muriatic acids ; but this change produced no variation of
the results. A zinc positive electrode, in sulphate of soda or
solution of common salt, gave the same constancy of operation.

Experiments of a similar kind were then made with bodies
altogether in a different state — i.e., with fused chlorides, io-
dides, etc. I have already described an experiment with fused
chloride of silver, in which the electrodes were of metallic sil-
ver, the one rendered negative becoming increased and length-
ened by the addition of metal, whilst the other was dissolved
and eaten away by its abstraction. This experiment was re-
peated, two weighed pieces of silver wire being used as the elec-
trodes, and a volta-electrometer included in the circuit. Great
care was taken to withdraw the negative electrode so regularly

* [See foot note, p, 27.]
. 34

LAWS OF ELECTROLYTIC CONDUCTION

and steadily that the crystals of reduced silver should not form
a metallic communication beneath the surface of the fused
chloride. On concluding the experiment the positive electrode
was reweighed, and its loss ascertained. The mixture of
chloride of silver and metal^ withdrawn in successive portions
at the negative electrode, was digested in solution of ammonia,
to remove the chloride, and the metallic silver remaining also
weighed : it was the reduction at the cathode, and exactly
equalled the solution at the anode; and each portion was as
nearly as possible the equivalent to the water decomposed in
the volta-electrometer.

The infusible condition of the silver at the temperature used,
and the length and ramifying character of its crystals, render
the above experiment difficult to perform, and uncertain in its
results. I therefore wrought with chloride of lead, using a
green-glass tube, formed
as in Fig. 13. A weighed
platina wire was fused
into the bottom of a
small tube, as before de-
scribed. The tube was
then bent to an angle,
at about half an inch ^^- ^

distance from the closed end ; and the part between the angle
and the extremity being softened, was forced upward, as in the
figure, so as to form a bridge, or rather separation, producing two
little depressions or basins, a, S, within the tube. This arrange-
m.ent was suspended by a platina wire, as before, so that the beat
of a spirit-lamp Could be applied to it, such inclination being
given to it as would allow all air to escape during the fusion of the
chloride of lead. A positive electrode was then provided, by
bending up the end of a platina wire into a knot, and fusing
about twenty grains of metallic lead on to it, in a small closed
tube of glass, which was afterwards broken away. Being so
furnished, the wire with its lead was weighed, and the weight
recorded.

Chloride of lead was now introduced into the tube, and care-
fully fused. The leaded electrode was also introduced, after
which the metal at its extremity soon melted. In this state of
things the tube was filled up to c with melted chloride of lead ;
the end of the electrode to be rendered negative was in the

MEMOIRS ON THE FUNDAMENTAL

basin h, and, the electrode of melted lead was retained in the
basin a, and, by connection with the proper conducting wire of
a voltaic battery, was rendered positive. A volta-electrometer
was included in the circuit.

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

In this experiment the positive electrode had lost just as
much lead as the negative one had gained, and the loss and
gain were very nearly the equivalents of the water decomposed
in the volta-electrometer, giving for lead the number 101.5. It
is therefore evident, in this instance, that causing a strong affin-
ity or no affinity, for the substance evolved at the anode, to be
active during the experiment, produces no variation in the defi-
nite action of the electric current.

A similar experiment was then made with iodide of lead, and
in this manner all confusion from the formation of a periodide
avoided. No iodine was evolved during the whole action, and
finally the loss of lead at the anode was the same as the gain at
the cathode, the equivalent number ,by comparison with the re-
sult in the volta-electrometer being ,103.5.

Then protochloride of tin was subjected to the electric cur-
rent in the same manner, using, of course, a tin positive elec-
trode. No bichloride of tin was now formed. On examining the
two electrodes, the positive had lost precisely as much as the
negative had gained ; and by comparison with the volta-elec-
trometer, the number for tin came out 59.

It is quite necessary in these and similar experiments to ex-
amine the interior of the bulbs of alloy at the ends of the con-
ducting wires ; for occasionally, and especially with those which
have been positive, they are cavernous, and contain portions of
the chloride or iodide used, which must be removed before the
final weight is ascertained. This is more usually the case with
lead than tin.

LAWS OF ELECTROLYTIC CONDUCTION

^A-l All these facts combine into, I thinks an irresistible mass of
Qvidence, proving the trath of the important proposition which
I at first laid down — namely^ that the chemical power of a current
of electricity is in direct proportion to the absolute quantity of
electricity which passes. They prove, too, that this is not merely
true of one substance, as water, bat generally with all electro-
lytic bodies ; and, farther, that the results obtained with any
one substance do not merely agree amongst themselves, but also
wrth those obtained from other substances, the whole combining
together into one series of definite electrochemical actions. I do
not mean to say that no exceptions will appear ; perhaps some
may arise, especially amongst substances existing only by weak
affinity ; but I do not expect that any will seriously disturb the
result announced. If, in the well considered, well examined,
and, I may surely say, well-ascertained doctrines of the definite
nature of ordinary chemical affinity, such exceptions occur, as
they do in abundance, yet, without being allow'ed to disturb our
minds as to the general conclusion, they ought also to be allowed
if they should present themselves at this, the opening of a new
view of electrochemical action ; not being held up as obstruc-
tions to those who may be engaged in rendering that view more
and more perfect, but laid aside for a while, in hopes that their
perfect and consistent explanation will ultimately appear.

The doctrine of definite electrochemical action just laid down,
and, I believe, established, leads to some new views of the rela-
tions and classifications of bodies associated with or subject to
this action. Some of these I shall proceed to consider.

In the first place, compound bodies may be separated into
two great classes — namely, those which are decomposable by
the electric current, and those which are not : of the latter,
some are conductors, others non-conductors, of voltaic electric-
ity.* The former do not depend for their decomposability upon
the nature of their elements only ; for, of the same two ele-
ments, bodies may be formed, of which one shall belong to one
class and another to the other class; but probably on the
proportions also. It is further remarkable, that with very
few, if any, exceptions, these decomposable bodies are exactly

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

MEMOIRS ON THE FUNDAMENTAL

those governed by the remarkable law of conduction I have
before described ; for that law does not extend to the many
compound fusible substances that are excluded from this class.
I propose to call bodies of this^ the decomposable class^ EUc-
trolytes.

Then, again^ the substances into which these divide, under
the influence of the electric current, form an exceedingly
important general class. They are combining bodies; are
directly associated with the fundamental parts of the doctrine
of chemical affinity ; and have each a definite proportion, in
which they are always evolved during electrolytic action. I
have proposed to call these bodies generally io7i8, or particular-
ly amons and cations, according as they appear at the anode
or cathode; and the numbers representing the proportions in
which they are evolved electrochemical equivalents. Thus hy-
drogen, oxygen, chlorine, iodine, lead, tin, are ions ; the three
former* are anions, the two metals are cations, and 1, 8, 36, 125,
104, 58, are their electrochemical equivalents nearly.

A summary of certain points already ascertained respecting
electrolytes, ions, and electrochemical equivalents may be given
in the following general form of propositions, without, I hope,
including any serious error.

I. A single ion, i. e., one not in combination with another,
will have no tendency to pass to either of the electrodes, and
will be perfectly indifferent to the passing current, unless it be
itself a compound of more elementary ions, and so subject to
actual decomposition. Upon this fact is founded much of the
proof adduced in favor of the new theory of electrochemical
decomposition, which I put forth in a former series of these
Researches.

II. If one ion be combined in right proportions with another
strongly opposed to it in its ordinary chemical relations, i. e., if
an anion be combined with a cation, then both will travel, the one
to the anode, the other to the cathode, of the decomposing body.

III. If, therefore, an ion pass towards one of the electrodes,
another ion must also be passing simultaneously to the other
electrode, although, from secondary action, it may not make its
appearance.

IV. A body decomposable directly by the electric current,

* [Ostygenf chlorine, and iodine are undoubtedly here referred to.]

mmegmnmaBwmtmmr^^"'^

LAWS OF ELECTROLYTIC CONDUCTION

i. e.y an electrolyte^ must consist of two ionSy and must also render
them up during the act of decomposition.

V. There is but one electrolyte composed of the same two
elementary ions ; at least such appears to be the fact, depend-
ent upon a law, that only single electrochemical equivalents of
elementary ions can go to the electrodes, and not multiples.

VI. A body not decomposable when alone, as boracic acid,
is not directly decomposable by the electric current when in
combination. It may act as an ion going wholly to the anode
or cathode, but does not yield up its elements, except occasion-
ally by a secondary action. Perhaps it is superfluous for me to
point out that this proposition has no relation to such cases as
that of water, which, by the presence of other bodies, is ren-
dered a better conductor of electricity, and therefore is more
freely decomposed.

VII. The nature of the substance of which the electrode is
formed, provided it be a conductor, causes no difference in the
electro-decomposition, either in kind or degree ; but it serious-
ly influences, by secondary action, the state in which the ions
finally appear. Advantage may be taken of this principle in
combining and collecting such io7is as, if evolved in their free
state, would be unmanageable.*

VIII. A substance which, being used as the electrode, can
combine with the ion evolved against it, is also, I believe, an ion,
and combines, in such cases, in the quantity represented by its
electrochemical equivalent. All the experiments I have made
agree with this view ; and it seems to me, at present, to result
as a necessary consequence. Whether, in the secondary actions
that take place, where the ion acts not upon the matter of the
electrode, but on that which is around it in the liquid, the
same consequence follows, will require more extended investi-
gation to determine.

IX. Compound ions are not necessarily composed of electro-
chemical equivalents of simple ions. For instance, sulphuric

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

MEMOIRS ON THE FUNDAMENTAL

acid^ boracic acid, phosphoric acid, are ions, bnt not electrolytes,
i. ^., not composed of electrochemical equivalents of simple ions.

X. Electrochemical equivalents are always consistent, i. e.,
the same number which represents the equivalent of a sub-
stance, A, when it is separating from a substance, B, will also
represent A when separating from a third substance, O.
Thus, 8 is the electrochemical equivalent of oxygen, whether
separating from hydrogen, or tin, or lead; and 103.5 is the
electrochemical equivalent of lead, whether separating from
oxygen, or chlorine, or iodine.

XL Electrochemical equivalents coincide, and are the same,
with ordinary chemical equivalents.

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

In the first place, they may be determined directly, as has
been done with hydrogen, oxygen, lead, and tin, in the numer-
^(\ ous experiments already quoted.
jMj X In the next place, from propositions 11. and III., may be de-
^/^^duced the knowledge of many other ions and also their equiva-
lents. When chloride of lead was decomposed, platina being
used for both electrodes, there could remain no more doubt
that chlorine was passing to the anode, although it combined
with the platina there, than when the positive electrode, being
of plumbago, allowed its evolution in the free state ; neither
could there, in either case, remain any doubt that for every
103.5 parts of lead evolved at the cathode, 36 parts of chlorine
were evolved at the anode, for the remaining chloride of lead
was unchanged. So also, when in a metallic solution, one
volume of oxygen, or a secondary compound containing that
proportion, appeared at the anode, no doubt could arise that
hydrogen, equivalent to two volumes, had been determined to
the cathode, although, by a secondary action, it had been em-
ployed in reducing oxides of lead, copper, or other metals, to the
metallic state. In this manner, then, we learn from the experi-
ments already described in these Researches that chlorine,
iodine, bromine, fluorine, calcium, potassium, strontium, mag-
nesium, manganese, etc., are ions, and that their electrochemical
equivalents are the same as their ordinary chemical equivalents.

Propositions IV. and V. extend our means of gaining infor-
mation. For if a body of known chemical composition is found

.»

• • ♦ •

LAWS OF ELECTROLYTIC CONDUCTION

to be decomposable^ and the nature of the snbstance evolved as
a primary or even a secondary result at one of the electrodes^
be ascertained, the electrochemical equivalent of that body
may be deduced from the known constant composition of the
substance evolved. Thus, when fused protiodide of tin is de-
composed by the voltaic current, the conclusion may be drawn
that both the iodine and tin are ions, and that the proportions
in which they combine in the fused compound express their
electrochemical equivalents. Again, with respect to the fused
iodide of potassium, it is an electrolyte ; and the chemical
equivalents will also be the electrochemical equivalents.

If proposition VIII. sustain extensive experimental investi-
gation, then it will not only help to confirm the results obtained
by the use of the other propositions, but will give abundant
original information of its own.

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

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

After the first experimental investigations to establish the
definite chemical action of electricity, I have not hesitated to
apply the more strict results of chemical analysis to correct the
numbers obtained as electrolytic results. This, it is evident,
may be done in a great number of cases, without using too
much liberty towards the due severity of scientific research.

MEMOIRS ON THE FUNDAMENTAL

The series of numbers representing electrochemical equivalents
must, like those expressing the ordinary equivalents of chemi-
cally acting bodies, remain subject to the continual correction
of experiment and sound reasoning.

I give the following brief table of ions and their electro-
chemical equivalents, rather as a specimen of a first attempt
than as anything that can supply the want, which must very
quickly be felt, of a full and complete tabular account of this
class of bodies. Looking forward to such a table as of extreme
utility (if well constructed) in developing the intimate relation
of ordinary chemical affinity to electrical actions, and identify-
ing the two, not to the imagination merely, but to the convic-
tion of the senses and a sound judgment, I may be allowed to
express a hope, that the endeavor will always be to make it a
table of real, and not hypothetical, electrochemical equivalents ;
for we shall else overrun the facts, and lose all sight and con-
sciousness of the knowledge lying directly in our path.

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

TABLE OF IONS
A17I0NS

Oxygen 8

Chlorine 35.5

Iodine 126

Bromine 78.3

Fluorine 18.7

Cyanogen 26

Sulphuric acid .... 40

Selenic acid 64

Nitric acid 54

Chloric acid .... 75.5

Phosphoric acid
Carbonic acid
Boracic acid .
Acetic acid .
Tartaric acid
Citric acid .
Oxalic acid .
Sulphur (?) .
Selenium (?) .
Sulpho-cyanogen

35.7

CATIONS

Hydrogen 1

Potassium 39.2

Sodium 23.3

Lithium 10

Barium 68.7

Strontium 43.8

Calcium .
Magnesium
Manganese
Zinc . .
Tin . . .
Lead . .

20.5
12.7
27.7
32.5
57.9
108.5

LAWS OF ELECTROLYTIC CONDUCTION

CATIONS— Continiied

Iron 28

Copper 81.6

Cadmium 65.8

Cerium 46

Cobalt 29.5

Nickel 29.5

Antimony 64.6 (?)

Bismuth 71

Mercury 200

Silver 108

Platina 98.6 (?)

Gold (?)

Ammonia 17

Potassa 47.2

Soda 81.8

Lithia 18

Baryta - 76.7

Strontia 51.8

Lime 28

Magnesia 20.7

Alumina (?)

Protoxides generally

Quinia 171.6

Ciuchona 160

Morphia 290

Vegeto-alkalies generally

This table might be farther arranged into groaps ot such
substances as either act with^ or replace^ each other. Thns^
for instance, acids and bases act in relation to each other ; bat
they do not act in association with oxygen, hydrogen, or eler
mentary sabstances. There is indeed little or no doabt that,
when the electrical relations of the particles of matter come to
be closely examined, this division mast be made. The simple
sabstances, with cyanogen, salpho-cyanogen, and one or two
other compoand bodies, will probably form the first group ;
and the acids and bases, with such analogous compounds as
may be proved to be ions, the second group. Whether these
will include all ions, or whether a third class of more com-
plicated results will be required, must be decided by future
experiments.

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

MEMOIRS ON THE FUNDAMENTAL

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

A very valuable use of electrochemical equivalents will be to
decide, in cases of doubt, what is the true chemical equivalent,
or definite proportional, or atomic number of a body ; for I
have such conviction that the power which governs electro-
decomposition and ordinary chemical attractions is the same ;
and such confidence in the overruling inflaence of those natu-
ral laws which render the former definite, as to feel no hesita-
tion in believing that the latter must submit to them also.
Such being the case, I can have no doubt that, assuming hy-
drogen as 1, and dismissing small fractions for the simplicity
of expression, the equivalent number or atomic weight of
oxygen is 8, of chlorine 36, of bromine 78.4, of lead 103.5, of
tin 59, etc., notwithstanding that a very high authority doubles
several of these numbers.

RoTAL Institution, December 31, 1:883.

Michael Faraday was born at Newington, a suburb of
London, September 22, 1791. His parents were of humble
origin, and their straitened circumstances prevented his obtain-
ing more than the rudiments of an early education. When
fourteen years old he was apprenticed to a bookbinder, and
in this capacity was able to pick up considerable scientific
knowledge himself from the books which came in for binding;
He was, moreover, able to further his education by attending
lectures on natural philosophy at the house of a Mr. Tatum, and
also occasional lectures at the Boyal Institution by Sir Humphry
Davy. It was largely on account of the remarkable excellence
of the notes which he worked up on these latter lectures, that
in March, 1813, six months after he had completed his appren-
ticeship, Davy secured for him the appointment of assistant in
chemistry at the Boyal Institution. In October of the same

LAWS OF ELECTROLYTIC CONDUCTION

year^ he left the institution to accompany Davy, as secretary
and chemical assistant, on an extended continental tour, which
proved to be of the greatest value to him, not only for the broad-
ening influence of travel it afforded, but also for the acquaint-
ances he made with all the leading scientists in Europe, many
of whom became later his friends and correspondents. On his
return to England in the spring of 1815 he obtained a reap-
pointment, and took up his residence at the Koyal Institution.
From this time he entered upon that wonderful career of
investigation which soon placed him without a peer among his
contemporaries.

In 1825 Faraday was appointed Director of the Laboratory
at the Royal Institution. The following year he instituted
the Friday Evening Lectures, and there demonstrated his
wonderful ability to interest and hold the attention of popular
audiences, by his personal magnetism and his clear and enter-
taining exposition of scientific questions. He was made a
member of many learned societies, including the Royal Socie-
ty, and received the degree of D.C.L. from the University of
Oxford. He declined positions more remunerative than that
at the Royal Institution, out of loyalty to the institution which
had done so much for his advancement, and refused to devote
his time to the commercial development of his many discov-
eries, although the pecuniary inducements were great. In 1840
he became an elder in the Sandemarian Church, of which he was
an active member.

In 1821 Faraday married Miss Sarah Barnard, the marriage
being an ideally happy one. He and his wife lived at the Royal
Institution until 1858, when the Queen placed a house at
Hampton Court at their disposal. Here he spent the remain-
ing years of his life, continuing active work, however, at the
Royal Institution until 1865.

He passed peacefully away at Hampton Court, August 25,
1867. His headstone, in Highgate Cemetery, bears the simple
inscription :

Michael Faradat
Born 22Dd September

1791
Died 25th August

1867

LAWS OF ELECTROLYTIC CONDUCTION

Faraday^s scientific publications include no less than 163
papers (see Royal Society Catalogue) on the most diverse
chemical and physical subjects. Among the most important of
these, in addition to those on electrochemistry leading to the
discovery of the law which bears his name, may be mentioned
those on the liquefaction and solidification of gases, 1823 and
1845; on the discovery of benzine, 1825; on the seat of the
electromotive force in the voltaic cell, 1834 ; on the laws of
static and electromagnetic induction and the development of
the concept of lines of force, 1831-1838 ; on the para and dia-
magnetic properties of bodies, 1846 ; and,*perhaps the greatest
of all, on the discovery of the electromagnetic rotation of polar-
ized light, 1845.

ON THE MIGRATION OF IONS DURING

ELECTROLYSIS

W. HITTORP

(Poggendorff's Annalen, 80, 177, 1863 ; OatwaXd'a Klatsiker der EttaJOen

Wi*»en»chatten, No. 21)

CONTENTS

PAGE

Orotthu88*8 Explanation of Electrolysis 49

Faradajfs Explanation of Electrolysis 50

HiUorfs Explanation of Electrolysis 53

Trantference of Ions 53

Early Experiments bearing on Transference 54

Description of Apparatus and Method 57

Experimental Results :

Copper Sulphate — Effect of Current 61

Effect of Concentration 68

Bjffect of Temperature 68

Silwr Nitrate^Effect of Concentration 68

Silver Sulphate — Effect of Different Anions 73

Silver Acetate — Effect of Different Anions , 75

Discussion of Eesults 76

Primary w. Secondary Decomposition of Water 78

Effect of Solvent^AlcoTiolic Solution of Silver Nitrate 79

ON THE MIGRATION OF IONS DURING

ELECTROLYSIS

W. HITTORF

The explanation which we now give of the process of electrol-
ysis was first proposed, in its general outlines, by Grotthuss in
1 805. According to it, the two ions which are simultaneously set
free do not come from the same molecule* of the electrolyte, but
belong to different ones— namely, those which are in immediate
contact with the electrodes. The other components of the com-
pound from which they separate unite at once with the opposite
components of the next adjacent molecules ; this process takes
place between the opposite components of all adjacent molecules
in the interior of the electrolyte, and holds them together.

'*I conclude from this,^^ remarks Grotthuss, f "that were it
possible to produce in water a galvanic current flowing in a cir-
cle, without the introduction of metallic conductors, all water
particles lying in this circle would be decomposed and immedi-
ately after recombined ; whence it follows that this water, al-
though it actually undergoes galvanic decomposition in all of
its particles, would nevertheless always remain water."

This conception of electrolysis was so natural that it could
not fail to supersede the other more or less far-fetched hy-
potheses which assumed both liberated ions to arise from the
same molecule of the electrolyte. It explained without further
assumption, the numerous experiments which H. DavyJ pub-
lished soon afterwards on the transference of components to
the electrodes.

* [Fbr greater clearness the term " atom" used throughout hy Hittorf^
has been translated ** molecule " whenever the concept of molecule is intended.]
t Phf/s, Ghem. FcTsch., p. 123.
X Gilb. Ann., 28, 26.
D 49

MEMOIRS ON THE FUNDAMENTAL

The tardy appearance of the ions of an electrolyte which is
not in direct contact with the poles^ and their failare to appear
at all when separated from the electrodes by a liqaid with which
they form an insolable compound, were excellent proofs of the
theory furnished by Davy.

Notwithstanding the clear conception of electrolysis which
Orotthuss had up to this point, as indicated in the remark which
I have given above in his own words (we easily realize to-day,
as is well known, the premise of the conclusion by an induc-
tion current), he fell into serious error in attempting to further
fathom the phenomenon. He conceived it to be produced as
follows: the metals between which the electrolyte is placed
are the seat of two forces, which vary inversely as the square of
the distance, and which, acting oppositely on the two compo-
nents, repel the one and attract the other. All physicists who
turned their attention to this subject favored this view more or
less for a long time ; the name of the poles which was given to
the immersed metals corresponded to it. Grotthuss was, how-
ever, herein so far in advance of others that he considered
(contrary to his hypothesis, to be sure) the forces acting on each
particle of the electrolyte everywhere equal in the circle, an
assumption which, as is known, is correct for the simplest con-
ditions of the experiment.

Faraday was the first to penetrate deeper into the phenome-
non. He conceived the cause of it in exactly the reverse man-
ner, and was thereby led to the great discovery of the funda-
mental electrolytic action of the current, which now forms the
basis of all investigations in electrolysis. By means of this
change he brought the theory into harmony with Ohm's law,
without knowing the latter.

'^ I conceive,'* he says, in ^ 624: othia Experimental Researches,*
"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 on the poles. I sup-
pose 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 conse-
quently making them travel by a series of successive decom-

♦Pogg. ilnn.,32, 435.
50

nm^wia

LAWS OF ELECTROLYTIC CONDUCTION

positions 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. I think, therefore, it would be more
philosophical, and more directly expressiye of the facts, to speak
of such a body, in relation to the current passing through it,
rather than to the poles, as they are usually called, in contact
with it; and say that whilst under decomposition, oxygen,
chlorine, iodine, acids, etc., are rendered at its negative extrem-
ity, and combustibles, metals, alkalies, bases, etc., at its pos-
itive extremity.

*^ The poles, § 556,* are merely the surfaces or doors by which
the electricity enters into or passes out of the substance suffer-
ing 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.^'

In this way Faraday, for the first time, explains chemical
decomposition with definiteness, as the conduction of the elec-
tric current through the electrolyte. He proves the impor-
tant relation thatf '* the sum of chemical decomposition is constant
for every section taken across a decomposing conductor, uni-
form in its nature, at whatever distance the poles may be from
each other or from the section ; . . . provided the current of
electricity be retained in constant quantity. . ."

Our conception even to-day of the process of electrolytic de-
composition is embraced in these laws. In a later paper | Fara-
day expressed the belief that they would need modification.
The chemical theory of the galvanic cell, which he so energeti-
cally sought to defend, inclined him, primarily, to make this
statement, as well as the fact that electrolytes often conduct
weak currents without any decomposition being perceptible.
Both points, however, have since been satisfactorily explained
by science, without in any way affecting the postulated laws.
On the contrary, every more exact investigation has only fur-
nished a new confirmation of them.

We usually picture the process to ourselves by means of a row

* Fogg, Ann., 32, 450.
t Ibid., 32, 426.
t Ibid., 35, 259.
51

MEMOIRS ON THE FUNDAMENTAL

of adjacent molecales^ as shown in Fig. 1. It is assumed in the
figure that the distance between the neighboring molecules of
the electrolyte is greater than that between the chemically
bound ions of each individual molecule. This assumption is
certainly permissible in those cases which we shall alone have
to consider later — namely, those in which the electrolyte is
brought into the liquid state by means of a solvent.

The first action of the current consists* in bringing the par-
ticles of the body to be decomposed into such a position that
the cation of each molecule is turned towards the cathode^ and

«3 33333333
»o €€€€€€€€•
"O 33333333 •

Pig, I

the anion towards the anode. The two ions then separate from
each other, move in opposite directions, and thereby meet with
the neighboring ions likewise migrating (Fig. 1, b). By this
process, however, they have arrived in a position where each
anion is turned towards the cathode, and each cation towards
the anode. There must therefore result a rotation of each
molecule, and the reverse position be established, if the same
constituent is to be continuously liberated at the same elec-
trode (Fig. 1, c).

It would certainly be of great importance if we could repre-
sent these motions, to which the smallest particles of an electro-
lyte are subjected during the passage of the current, more defi-
nitely than in these most general outlines. They would not only
throw light on the nature of electricity, but also on the chemi-
cal constitution of bodies.

In many cases it seems possible to determine by experiment
the relative distances through which the two ions move during
electrolysis. As we shall be concerned only with this point in
what follows, we will give prominence to it alone in the figure.

*See Faraday, § 1705 ; Pogg. Ann.; Ergdmungsband, I., 363.

LAWS OF ELECTROLYTIC CONDUCTION

For this purpose let us adopt the method of representation
given by Berzelius in his works, in which the two ions are rep-
resented one below the other, and supposed to move by each
other in a horizontal direction (Fig. 2). It is assumed that the
electrolyte is brought into the liquid state by means of an indif-
ferent non-conducting solvent.

If we can divide the liquid at any definite place, we shall
find that the ions in each portion are in a different proportion
after electrolysis has taken place than before. This propor-
tion is determined by the distance through which each ion
moves during the passage of the current.

If, for example, we make the assumption, tacitly made in
former presentations, that these distances are equal, in which
case both migrating ions meet half way between their original
positions, a glance at Fig. 2 shows, that after electrolysis, that
portion of liquid which borders on the anode will contain half
an equivalent less cations than before. The converse is of
course true for the other portion which is in contact with the
cathode. By equivalent is understood the quantity of the com-
ponent liberated.
' If the two ions do not move through equal distances — that

S888

88888888

"^88888888888

"^8888888888

'^88ii888888

oooogogg go og

is, if they do not meet each other half way — then the side of
the b'quid in which the more rapidly moving ion makes its ap-
pearance will be increased by more than half an equivalent of
it, and diminished by less than half an equivalent of the other
ion. Fig. 3 shows this for the case when the anion moves \, the
cation \ of the distance. The anode side of the liquid contains
^ of an equivalent more anions and f of an equivalent less

MEMOIRS ON THE FUNDAMENTAL

cations after the decomposition than before. The other side
shows the converse relation.

This result evidently holds generally. If one ion moves
through Vn t^G distance, and the other ^y then the side of the
liquid in which the former appears will contain Vn equivalent
more of it and ^ equivalent less of the other ion. The con-
verse relation will hold for the other side of the electrolyte.

The first experiments to determine the transference of ioQS
quantitively, were made by Faraday.* He took up the subject,
however, only as a side issue, and confined himself to two elec-

888S888S

8888888888

88888888

''8888888i!888888888
"^8888888888888888

GOOOg Jg OO O

"^88888888888888
"^^^^ 8888 888888888i
®^^^^^ 888888888888 •«

Fig.»

trolytes, dilate sulphuric acid, and a solution of sodium sul-
phate. Two pairs of cups were filled respectively with definite
amounts of these two liquids, and each pair connected to-
gether by means of asbestos. Both were then introduced into
the same circuit, and after electrolysis had continued for some
time, the asbestos was withdrawn, and the contents of the cups
subjected to analysis. It is clear that this method is very de-
fective, and that no accurate results are to be expected with it.
The results which Faraday obtained in two series of experi-
ments show this sufficiently. In the case of the sodium salt,
he determined only the sulphuric acid set free, and tacitly
assumed that half of it had been transferred.

*Exp. Beteareh., % 635-680 ; Pogg. Ann., 32, 486.

LAWS OF ELECTROLYTIC CONDUCTION

Messrs. Daniell and A. Miller,* in their beautiful inrestiga-
tions on the electrolysis of salts, were led to devote greater
attention to the subject of transference. They effected the
separation of the liquid by the introduction of a membrane.
They filled the two cells into which the vessel was divided with
accurately determined quantities of the aqueous solution of the
electrolyte, and investigated each after the galvanic decompo-
sition had taken place.

The results which they obtained are very striking. When,
namely, copper or zinc sulphate was chosen as electrolyte,
they found after electrolysis, exactly the same amount of metal
in the cell containing the cathode as they had originally intro-
duced. The quantity of reduced metal, increas^id by the quantity
still dissolved in the liquid, amounted to exactly as much as was
present before the electrolysis. According to this, copper and
zinc do not migrate at all during electrolysis. Their anion S
traverses the whole distance. An ammonium salt (salammoniac)
gave the same result ; the complex cation iVZT^ is to be classed
with the two preceding. They found a transference of the
cation with the salts potassium sulphate, barium nitrate, and
magnesium sulphate. For potassium it amounted to ^, for
barium ^, and for magnesium ^ equivalent. The authors con-
clude from their experiments that those metals which decom-
pose water a^t ordinary temperature, or whose oxides are easily
soluble in water, are subject to a progressive transference in
the voltaic cell from anode to cathode during electrolysis, while
those which do not possess so strong an affinity for oxygen re-
tain their place. They found a transference of all anions, even
the weakest ones, such as TTO^ and CO3.

In the translation of their article in Poggendorff's Annalen,
the direct numerical results of the individual experiments are
not given completely. The accuracy of the method cannot
therefore be judged. It would appear, however, that it was
not satisfactory, as the results are given only in round num-
bers. Furthermore, it is expressly stated that the experiments
are not strictly comparable, and that the figures given cannot
be regarded as absolute determinations of the transferred quan-
tity of each metal in the cell.

The introduction of the membrane entails of necessity two

* Pogg. Ann. , 64, 18.
55

MEMOIRS ON THE FUNDAMENTAL

eyils. The lesser lies in the fact that the contents of each cell
cannot be completely removed after the electrolysis, as some of
the solntion remains either in the diaphragm or comes throngh
from the other cell. The more serious is a result of the inex-
plicable phenomenon, that the quantity of liquid in the negative
cell increases, and in the positive cell diminishes, in these ex-
periments. This was frequently noticed by Daniell, and has
been very recently more carefully investigated by Wiedemann.*
The latter regards it as a motion of the liquid mass as a whole
from anode to cathode, and finds it very marked in copper and
zinc vitriol solutions. It seems doubly striking, therefore,
that Daniell and Miller found the quantity of copper unchanged
in the negative cell, since an increase should have occurred as
a result of this motion.

As proof that the diaphragm offers no obstruction to the
progress of the ions, the authors cite the phenomenon familiar
to electrotypers, that, in a copper vitriol solution, the liquid
about the negative pole becomes weaker in copper and finally
exhausted, when the negative pole is placed in the upper and
the positive pole in the lower layers of the solution. They
tried a similar experiment by filling a long tube, provided with
two upright arms, with a strong solution of copper sulphate,
and connected it by means of copper strips to a battery. The
liquid in the negative arm became noticeably lighter colored,
while, on the other hand, that in the positive arm became
darker. From this they concluded that the oxysulphur ion
(S), which separated out at the latter place, dissolved copper
from the anode, but that this copper could not migrate to the
cathode so as to replace the metal precipitated there.

This same phenomenon was reported at nearly the same time
by numerous physicists, and introduced into discussions on the
process of electrolysis. Pouilletf describes it in a gold solu-
tion which was contained in a U-shaped tube. After a current
had passed a sufficiently long time, he found the solution in the
negative arm almost completely deprived of its gold, while that
in the positive arm still contained its original gold contents.
He concludes from this "that in the decomposition of gold
chloride, and therefore all metal salts, the positive pole has no

* Fogg, Ann., 87,321.
t Tbid., 65, 474.
56

LAWS OF ELECTROLYTIC CONDUCTION

decomposing action, that all chemical force resides in the nega-
tive pole, that this takes up the gold and sends the chlorine by
a series of successive decompositions and recombinations to the
positive pole, to be there set free." **If both poles acted," he
adds, "the metal separated at the negative pole would be of
double origin ; one-half would be directly precipitated, the
other would come from the positive pole ; both arms of the
tube would then become weaker in gold to the same extent
during the whole duration of the process."

Besides the physicists mentioned, Smee * also discusses the
phenomenon.

It is astonishing how this simple experiment has been so
generally misunderstood. The dilution which the solution
undergoes at the negative pole proves in no way that the metal
does not migrate during electrolysis. We can convince ourselves
of this at once by glancing back at Fig. 2 or 3. The cation,
in the above case, is a solid body in the free state, and, as such,
leaves the solvent by the separation produced by the current.
Fig. 2 is drawn on the assumption that the ions move through
equal distances, and shows that the cathode side is increased
after electrolysis by i^ equivalent of cations. Now as one equiv-
alent becomes solid, the solution is thereby diminished by ^
equivalent — that is, diluted by ^ equivalent of the salt. Dilu-
tion must therefore occur at the negative pole, even if the
cation migrates ; and it must evidently do so in all cases, as
long as the cation does not migrate alone and the anion re-
main at rest. Only in this one case will the original concen-
tration remain the same at the cathode.

This very dilution which the cation suffers at the negative
pole where the cation leaves the solution, can be very advanta-
geously used to determine the transference quantitatively. An
exact separation of the electrolyte is easily effected without
the introduction of asbestos or of a diaphragm.

Fig. 4 represents a simple apparatus which I have constructed
for this purpose, and which was used in the experiments de-
scribed below.

A glass cylinder, which contains the solution of the electro-
lyte, is composed of two parts — a larger, a, and a smaller, b.
The former is cemented to a vessel, c, preferably of porcelain,

♦Pogg. ^wn.,65, 473.
57

MEMOIRS ON THE FUNDAMENTAL

and contains the anode d. This has the form of a circnlar
perforated plate^ and is made of metal^ the salt of which is Xa

be electrolyzed. The support fastened
to its centre passes through a small
cork in a glass plate and permits con-
nection with the galvanic cell. This
plate forms the base of the cylinder,
and is held in place by a cover which
screws on. The anode is not per-
mitted to lie on the bottom, but is
placed a little higher up, so that the
concentrated solution, which forms at
its surface during electrolysis, can
In — d flow down through the holes. The

I c P smaller part of the cylinder h is closed

above by a similar perforated glass
plate, provided with a cork, and con-
tains the cathode e, likewise fastened
to a support which projects outward.
The cathode must be given a different
form from the anode. If it consists
of a horizontal plate, the metal depos-
ited by the current on the under sur-
face cannot hold. It falls down and
sets the liquid in motion. In order
to prevent this, a metal cone is used
as cathode, which is fixed with its
apex at the centre of a horizontal
circular glass plate. The glass plate is much smaller than the
cross-section of the cylinder, and so chosen that points in its
circumference are approximately equally distant from the base
and from the apex of the cone. By this device all parts of
the surface of the cone are nearly the same distance from the
anode, and the deposited metal distributes itself nearly uni-
formly over the whole. The base of the cone presses closely
against the plate forming the cover. Its height is so chosen
that the glass plate / comes about in the middle of the cylin-
der. The cone and support are made preferably of platinum
or gold. Failing these, silver may be used, which is what I
was obliged to use.

When an experiment is to be made, the lower cemented part

Fig. 4

LAWS OF ELECTROLYTIC CONDUCTION

of the cylinder, together with the vessel c, is first filled with the
solution. The same is done with the upper part in which the
cathode is placed, care being taken that no air-bubbles remain
in the inside. By means of a glass plate, g, which is ground on
the open end of this cylinder, a definite quantity of liquid can
be measured off. When this has been done the cylinder is in-
verted and, together with the glass plate, placed in the vessel
c beside the cylinder a. For convenience of manipulation, a
silver wire, A, passes through four holes in the corners of the
plate, thereby forming two handles. The vessel c is just large
enough to permit the cylinder a and the glass plate g to rest
side by side on the bottom. The cylinder a, moreover, is so
cemented in, that its upper edge projects above the bottom by
just the thickness of the glass plate, so that it lie3 in the same
plane with the upper surface of the latter. The smaller cylin-
der filled with solution can, therefore, be easily slid along from
the plate on to the lower cylinder, thus forming a single
cylinder. In this position its contents are supported by the
atmospheric pressure.

The solution contained in the cylinder undergoes a change
only at the electrodes during electrolysis. The liquid around
the anode becomes more concentrated and, therefore, remains
in the lower part ; the solution around the cathode becomes
diluter and collects on the cover. When the current has de-
composed a sufficient quantity, the upper cylinder is slid back
again onto the glass plate, and taken out. The outside is
cleaned from adhering liquid, and the contents carefully poured
into another vessel for analysis. If the upper cylinder be now
filled with the original solution and this quantity likewise
analyzed, one has, with the quantity of metal deposited, all data
necessary for computing the transference.

The cathode projects, intentionally, only to the centre of the
upper cylinder in order that the liquid at the opening shall re-
main unchanged, and the mixing with the liquid in the vessel
Cy which occurs at^this place on sliding the cylinder back on to
the glass plate, shall occasion no error. To prevent the liquid
in c from becoming concentrated by evaporation during elec-
trolysis, the apparatus is set into a ground-glass plate, i, and
covered with a bell-glass during the experiment. Fig. 5 rep-
resents in cross-section the apparatus completely set up. The

dimensions of my apparatus are as follows: The inside diam-

MEMOIRS ON THE FUNDAMENTAL

Ftfir. 5

eter of the cylinder measures 54 mm.; the height of the lower
part^ 70 mm.; that of the upper part^ 25 mm.^ both inside meas-
urements. The glass
is 4^ mm. in thick-
nessy as it must be taken
rather thick. As the
cathode extends only
to the middle of the
upper cylinder, the ef-
fect of diffusion is de-
stroyed in our experi-
ments. During the
comparatively short
duration of the elec-
trolysis, this will be
active only between
the layers in the upper
cylinder, and will have
no effect on the mass
in the lower one; it
can, therefore, be the
cause of no error. Moreover, the motion, which, according to
Wiedemann, the electrolyte as a whole experiences from the
anode to the cathode, cannot vitiate our results, as it cannot
take place under the above conditions. The only error, so far
as I can see, which enters into my method and cannot be
avoided, arises from the fact that the metal which is separated
out by the current has a different volume from that of the salt
which is carried away from the upper part. This change in
volume is replaced by liquid flowing in or out. The values
which we obtain for the transference will be incorrect by the
contents of this quantity of liquid. Our error is, however, very
insignificant, and may be at least approximately computed.
We shall see that even in the case of very concentrated solu-
tions it does not amount to as much as the. unavoidable error
of analysis. This will be all the more true in the case of the
dilute solutions, for, as is readily seen, the error must, in gen-
eral, diminish proportional to the dilution.

Besides the apparatus, a voltameter was introduced into the
circuit. I chose for this purpose the convenient and accurate
arrangement described by Poggendorff, called a &ilver voltam-

LAWS OF ELECTROLYTIC CONDUCTION

eter. A silver dish^ which served as cathode^ contained a solution
of silver nitrate, into which dipped a silver plate as anode. The
latter was wrapped around with a linen cover to prevent little
particles, which easily come oS during solution of the anode
by the liberated anion Ji^, from falling into the dish, and thus
increasing the weight of the reduced silver. The first salt
which I decomposed was copper sulphate, with which Daniell
and Miller also worked, and which possesses special interest on
account of its application in galvanoplasty. It is the most con-
venient electrolyte for our experiments, for, as is well known,
copper deposits coherently, and consequently adheres firmly to
the surface of the silver cone.

I. COPPER SULPHATE

The solution which was subjected to electrolysis was pre-
pared by diluting a more concentrated one to about twice its
volume. Its specific gravity at 4.9° C. was 1.1036, and it con-
tained 1 part S Cu to 9.56 parts water, or 1 part (S Cu4-5 H)*
to 5.75 parts water.

Experiment A

The electrolysis was carried out at the temperature 4.7° C,
and was effected by means of a small Grove cell. The current
continued four hours and reduced 1.008 gr. Ag in the vol-
tameter, or 0.0042 gr. Agper minute.

This quantity of silver is equivalent to 0.2955 gr. Cu.

There was deposited on the silver cone, however, 0.2975 gr. Cu.

The difference, 0.002 gr., arises without doubt from an oxy-
dation of the copper ; we base all calculations on values de-
duced from results obtained by the silver voltameter.

The solution about the cathode contained :

Before electrolysis 2.8543 gr. Cu

After " 2.5897 " "

It was therefore diluted by an amount 0.2646 gr. Cu=0.2112 Cu.

The Cu was precipitated in the usual way by caustic potash,
from a boiling solution.

The amount of transferred copper is therefore

* INomenclature introduced by Berzeliua. The dote owr an element represent

the number of attaclied oxygen equivalents. Qmelin's equivalents ; i, e. , ff= 1 ,
0=8, 8=zlQ, etc. J are used throughout.^

MEMOIRS ON THE FUNDAMENTAL

0.2955
-0.2112

0.0843 gr., i.e., ^^^=^^'^ per cent, equivalent.

Oar experiment giyes a totally different resalt from that ob-
tained by Messrs. Daniell and Miller. According to their re-
suits, the solution in the upper cylinder should have lost 0.2955
gr. Cu during the electrolysis.

We will next consider whether the transference remains con-^
stant for all current strengths. To obtain an answer to this
question, the above solution was subjected to the action of a
weak and of a strong current.

Experiment B

The current from a Grove cell was so cut down by the intro-
duction of a long thin German-silver wire, that at a tempera-
ture of 5.3^ C. it reduced 1.2273 gr. Ag in 18 hours and 4 min-
utes, or 0.00113 gr. Agper minute.

The quantity of silver corresponds to 0.3597 gr. Cu.

There was deposited on the silver cone 0.3587 gr. On.

The solution about the cathode contained :

Before electrolysis 2.8543 gr. Cu

After " 2.535 " "

It was therefore diluted 0.3193 gr. Cu, or 0.2549 gr. Cu.

The quantity of transferred copper is therefore

0.3597
-0.2549

0.1048 gr., or ^^0^=29.1 per cent, equivalent.

Experiment C

The current from three Grove cells reduced at 6.5° C. 1.1503
gr. Ag in 2 hours, or 0.00958 gr. Ag a minute.
This quantity of silver corresponds to 0.3372 gr. Cu.
There was deposited on the silver cone 0.3374 gr. Cu.
, . 62

•• • •
. fc • •

» - "> •

LAWS OF ELECTROLYTIC CONDUCTION
The solution around the cathode contained :

Before electrolysis 2.8543 gr. Cu

After " 2.5541 " "

It lost therefore 0.3002 gr. Cu, or 0.2396 gr. Ou.

The quantity of transferred copper is therefore

0.3372
-0.2396

976
0.0976 gn, or ^^^=28.9 per cent, equivalent.

If we tabulate the results of these experiments :

CURRBNT TrANBFBRENCB

113 29.1

420 28.5

958 28.9 per cent.

Mean. . 28.8 per cent.

there can be no doubt that the transference is independent of
the intensity of the current. I have always avoided using very
large currents, as the rise in temperature which they produce
in the solution is disturbing. The immediate effect of this on
our data is easily obviated by not removing the electrolyzed
solution for analysis immediately after breaking the current,
but allowing it to first return to the temperature of the sur-
roundings. On the other hand, an indirect disturbance of the
rise of temperature cannot be so easily overcome. This con-
sists in the evolution of a quantity of little air-bubbles which
usually cover the surface of the glass plate under the cathode,
and which cannot be removed. That these little bubbles are
not hydrogen gas is clear from the place where they appear.
If large currents are to be used, it is judicious to free the so-
lution as far as possible from absorbed air, before filling the
apparatus ; this is most easily done under an air-pump.

The second question which we must consider has reference
to the influence of the concentration on the transference. Six
solutions of copper sulphate of very different concentration
were subjected to electrolysis.

MEMOIRS ON THE FUNDAMENTAL

Solution I

A concentrated solntion was dilated jnst snfficientlj bo that
a separation of salt on the anode was not to be feared. It had
at 4.5° C. a specific gravity of 1.1521, and contained 1 part SOn
to 6.35 parts water, or 1 part (SGn+5 H) to 3.69 parts water.

The current from a Grove cell deposited, at 5.5° C, 1.0783
gr. Ag in 4 hours. This corresponds to 0.3161 gr. Cu.

On the silver cone there was 0.3168 gr. Cu.

The solntion around the cathode contained :

Before electrolysis 4.2591 gr. Cu

After " 3.9725 " "

It lost 0.2866 gr. Cu, or 0.2288 gr. Cu.

The amount of transferred coppef is therefore

0.3161

-0.2288

873
0.0873 gr., or^j^=27.6 per cent.

The solution first electrolyzed, which gave 28.8 per cent,
transference, served as Solution II.

Solution III

Specific gravity at 3.6° C.: 1.0553.

It contained 1 part SCu to 18.08 parts water, or 1 part
(SCu-f-5 H) to 11.19 parts water.

The current from one Grove cell deposited 0.8601 gr. Ag in
5 hours, 45 minutes, at 5.5° C. This corresponds to 0.2521 gr.

Cu.
There was 0.2520 gr. Cu on the silver cone.
The solution around the cathode contained :

Before electrolysis 1.5026 gr. Cu

After *' 1.2895 " "

It lost 0.2131 gr. Cu., or 0.1701 gr. Cu.

The amount of transferred copper is therefore

0.2521
-0.1701

0.0820 gr. , or -^^ =32.5 per cent.

LAWS OF ELECTROLYTIC CONDUCTION

Solution IV

Specific gravity at 3° C. : 1.0254.

It contained 1 part SCu to 39.67 parts water, or 1 part
(SCa + 5 H) to 24.99 parts water.

The current from two Grove cells deposited at 4.5° C, 0.6969
gr. Ag in 5 hours : this is equivalent to 0.2034 gr. Cu.

The copper which covered the silver cone could no longer
be weighed, as in this dilute solution the larger part of it was
spongy.

The solution around the cathode contained :

Before electrolysis 0.6765 gr. Cu

After '' 0.5118 " ''

It lost 0.1647 gr. Cu, or 0.1315 gr. Cu.

Hence the transferepce of the copper is

0.2043
-0.1315

0.0728 gr., or ^=35.6 percent.
^ 2043 ^

Solution V

Specific gravity at 4.8° C: 1.0135.

It contained 1 part SCu to 76.88 parts water, or 1 part
(SCu 4- 5 H) to 48.75 parts water.

The current of one Grove cell reduced 0.3592 gr. Ag at 4.3°
C. This corresponds to 0.1053 gr. Cu.

The copper on the silver cone was spongy. The solution
about the cathode contained :

Before electrolysis 0.3617 gr. Cu.

After '' 0.2758 '' "

It lost 0.0859 gr. Cu, or 0.0686 gr. Cu.

Hence the transference of copper is
0.1053
-0.0686

O.0367"gr., or 4^=34.9 per cent.
® 1053 ^

K 65

MEMOIRS ON THE FUNDAMENTAL

Solution VI

Specific gravity at 4.4° C. : 1.0071.

It contained 1 part SCa to 148.3 parts water, or 1 part
(SCu+5 H) to 94.5 parts water.

The current from one Grove cell reduced 0.3850 gr. Ag in
16 hours, 25 minutes, at 4.4° C. This corresponds to 0. 1131 gr.
Ou.

The copper on the silver cone was spongy.

The solution around the cathode contained :

Before electrolysis 0.1867 gr. Cu

After " 0.0964 '' "

It lost 0.0903 gr. Cu, or 0.0721 gr. Cu.

The transference of copper is

0.1131
-0.0721

0.0410gr.,ori^=36.2 per cent,
e 1131 ^

Let us tabulate the separate results together for inspection.

NO.

III

8P. GR.

1.1521

1.1036
1.0553
1.0254
1.0135
1.0071

CONTENTS OP SOLUTION

1 pt. SCuto

((

6.35 pts. H
9.56 '' ''
18.08 '' "
39.67 '' "
76.88 '' "
148.3 *' "

TRANSFERENCE OF
COPIER

per cent.

mean, 35.6
per cent.

The transference numbers still require the small correction
which I pointed out above. We can only estimate this approx-
imately, as we cannot determine with our method, throughout
how large a portion of the solution the dilution extends. The
dilute solution, which can be easily followed with the eye during
the electrolysis, forms directly on the surface of the silver cone,
glides upward along it, and collects under the cover. To ob-
tain at least an idea of the amount of this correction, I will cal-
culate it for Solution I, under a definite assumption which will

not be far from the truth.

LAWS OF ELECTROLYTIC CONDUCTION

The liquid at the cathode lost 0.2866 gr. Cu, or 0.5762 gr.
SCu. Suppose this loss extends over such amass, x, of the
liquid that a solution of concentration II thereby results.
Before electrolysis the quantity x contains

^-? X water, and ^-- x SCu.
7.35 7.35

After electrolysis it will contain

(— a; - 0. 5762^^ gr. S Cu,
\7.35 /^

and be of concentration II ; it will therefore contain

^•^^ a: SCu to ^ a: wafer.

7.35x9.56 7.35

The mass sought is therefore obtained from the equation

^-i^- -a:=JL a; -0.5762,

7.35x9.56 7.35

and equals x =12.616 gr. Before electrolysis this mass has the

volume

^?^^ = 10.9504 c. cm.
l.lo21

It loses 0.5762 gr. S Cu by electrolysis, and the volume becomes
' =10.9095 c. cm. Hence the withdrawal of 0.5762 gr.

J.. lUoo

S Cu causes a diminution of volume of 0.0409 c. cm. According
to Marchand and Scherer,* galvanically deposited copper has a
density of 8.914. Hence the reduced 0.3161 gr. Cu occupies a
volume of 0.0355 c. cm. The diminution exceeds the increase
in volume by 0.0409-0.0355=0.0054 c. cm. This volume
is replaced by the solution flowing in. The latter weighs
0.0054x1.1521 gr. =0.0062 gr., and contains 0.00042 gr. Cu.

Hence, even in case of this most concentrated solution, the
error is of no account. This will be even more true in the other
cases.

The effect of the water on the amount of transference is evi-
dent from the experimental results. In proportion as the di-
lution increases, the transference of the cation Cu increases and
of the anion (S) decreases. In Solution IV the limit of this
influence seems to be reached. From there on the numbers
become nearly constant.

There still remains a third condition which can affect the

* Omelin, iii., 874.
67

MEMOIRS ON THE FUNDAMENTAL

transference ; I mean temperature. Our apparatus allows us
to work only at temperatures which we can give to the sur-
rounding air.

A solution was prepared which had about the same concen-
tration as Solution II.

Experiment D

During the electrolysis of this solution the temperature of the
air varied from 21° to 18° C. The current from one Grove cell
reduced 1.4247 gr. Ag in 4 hours 3 minutes. This corresponds
to 0.4176 gr. Cu.

0.419 gr. Cu was found on the silver cone.

The solution about the cathode contained :

Before electrolysis 2.8921 gr. Cu

After " 2.5191 " *'

It lost 0.3730 gr. Cu, or 0.2977 gr. Cu.

Hence the transference of the copper is

0.4176
-02977

0.1199 gr., or 11^=28.7 per cent.

The temperature has no effect between 4° and 21° C*
Copper vitriol is a salt which crystallizes from aqueous solu-
tions with five molecules of water. The remarkable influence
which the amount of water exerts on the transference made the
investigation of an anhydrous salt especially desirable. I chose

II. SILVER NITRATE

The salt was melted before dissolving in order to obtain it
absolutely neutral. The solution did not react with litmus. It
is not as convenient for electrolysis as copper sulphate, as the
silver adheres firmly to the cone only when deposited from quite
concentrated solutions, and with weak currents. Usually the
dendritic crystals grow rapidly over the glass plate underneath
the cathode and fall off.

* [This conclusion has not been verified by more recent eicperiments. See
Loeb and Nernst, Zeit, fUr Phys. Chem., 2, 948, 1888; Bein, Wied. Ann.,
46, 29, 1892.]

LAWS OF ELECTROLYTIC CONDUCTION

I chose such currents that a sufiScient amount of silver was
reduced before it began to drop ofiE. When this threatened to
occur the electrolysis was stopped.

Solution I

Specific gravity at 11.1" C: 1.3079.

It contained 1 part NAg to 2.48 parts water.

The current reduced 1.2591 gr. Ag in 1^ hours at a temper-
ature of 11.2° C.

The solution about the cathode gave :

Before electrolysis. . . 17.4624 gr. ClAg
After •* ... 16.6796 '' ''

It lost 0.7828 gr. ClAg, or 0.5893 gr. Ag.

Hence the amount of the transferred silver is

1.2591
-0.5893

6698

0.6698gr., or— =53.2 per cent.

^ 12591 ^

SolvMon II

Specific gravity at 19.2;' C: 1.2788.
It contains 1 part S^Ag to 2.735 parts water.
The current from one cell reduced 1.909 gr. Ag at 19° C.
The solution at the cathode gave :

Before electrolysis. . . 15.9364 gr. ClAg
After '' ... 14.7233 " ''

The loss is 1.2131 gr. ClAg, or 0.9132 gr. Ag.

The transference of silver is therefore

1.909
-0.9132

9958

0.9958 gr., or 4^=52.2 per cent.
® 19090 ^

Solution III

Specific gravity at 18.4° C: 1.1534.

It contains 1 part NAg to 5.18 parts water.

MEMOIRS ON THE FUNDAMENTAL

The current from one cell redaced 1.1124 gr. Ag in 1 hoar
21^ minutes at a temperature of 18.4° C.
The solution about the cathode gave :

Before electrolysis .. . 8.6883 gr. 01 Ag
After " ... 7.9569 '' ''

The loss is 0.7314 gr. 01 Ag, or 0.5506 gr. Ag.

Hence the amount of transferred silver is

1.1124
-0.5506

5618

0.5618 gr., or ———==50.5 per cent.
^ 11124 ^

Solution IV

Specific gravity at 18.8° 0.: 1.0774.

It contained 1 part S^Ag to 10.38 parts water.

The current from two cells reduced 0.4541 gr. Ag in half an
hour at 18.8° 0.

The solution about the cathode gave :

Before electrolysis.. . 4.4156 gr. OlAg
After '' ... 4.1080 " ''

The loss is 0.3076 gr. OlAg, or 0.2316 gr. Ag.

Hence the amount of transferred silver is

0.4541
-0.2316

2225

0.2225 gr., or -=49 per cent.

^ ' 4541 ^

Solution V

Specific gravity at 19.2° 0. : 1.0558.

It contained 1 part Jf Ag to 14.5 parts water.

The current from two cells reduced 0.3937 gr. Ag in 25 min-
utes at 19.2° 0.

The solution about the cathode gave :

Before efectrolysis. . . 3.1731 gr. OlAg
After " ... 2.8985 '' ''

The loss is 0.2746 gr. OlAg, or 0.2067 gr. Ag.

LAWS OF ELECTROLYTIC CONDUCTION

The amount of transferred silver is therefore

0.3937
-0.2067

1870

0.1870 gr., or _-_c=47.5 per cent.

OuOt

Solution VI

Specific gravity at 18.4° C: 1.0343.

It contains 1 part JSTAg to 23.63 parts water.

The current from two elements reduced 0.3208 gr. Ag in
half an hour at 18.4° C.

The solution at the cathode gave :

■

Before electrolysis. . . 1.9605 gr. ClAg
After *' ... 1.7358 '' ''

The loss is 0.2247 gr. ClAg, or 0.1691 gr. Ag.

Hence the amount of transferred silver is

0.3028
-0.1691

0.1517 gr., orl51!L=47.3 per cent.
^ 3208 ^

Solution VII

Specific gravity at 18.5° C: 1.0166.

It contains 1 part NAg to 49.44 parts water.

The current from two cells reduced 0.2470 gr. Ag in 45^ min-
utes at 18.5° C.

The solution around the cathode gave :

Before electrolysis. . . 0.9485 gr. ClAg
After " ... 0.7758 '' ''

The loss is 0.1727 gr. ClAg, or 0.1300 gr. Ag.

The amount of transferred silver is therefore

0.2470
-0.1300

0.1170 gr., or 11^=47.4 per cent.

2470

MEMOIRS ON THE FUNDAMENTAL

Solution VIII

Specific gravity at 18.6° C: 1.0076.

It contains 1 part NAg to 104.6 parts water.

The cnrrent from three elements reduced 0.1888 gr. Ag in 41
minutes at 18.6° C.

In this very dilute solution the silver separated out on the
silver cone at first black and spongy, as described by Poggen-
dorff,* and became afterwards yellowish-white and crystalline.

The solution about the cathode gave :

Before electrolysis. . . 0.4515 gr. ClAg
After " ... 0.3197 ''

The loss is.. . , 0.1318 gr. ClAg, or 0.0992 gr. Ag.

The amount of transferred silver is

0.1888
-0.0992

896

0.0896 gr., or -—^=47.4 per cent.
^ 1888 ^

Solution IX

Specific gravity at 9.6° C: 1.0044.

It contains 1 part J^Ag to 247.3 parts water.

The current from four elements reduced 0.0863 gr. Ag in 1
hour 3 minutes at 9.6° C.

The solution about the cathode gave :

Before electrolysis. . . 0.1916 gr. ClAg
After " ... 0.1316 ''

The loss is 0.0600 gr. ClAg, or 0.0452 gr. Ag.

Hence the transference of the silver is

0.0863
-0.0452

4.11

0.0411 gr., or iii=:47.6 per cent.

863

We will again tabulate the results obtained with the nine

different solutions.

♦ Pogg. Ann., 75, 838.

LAWS OF ELECTROLYTIC CONDUCTION

NO.

RP. OR.

CONTENTS

TRANSFERENCE OF
SILVER

1.3079

Ipt.

NAg. to 2.48

pts.H

53.2

per cent.

1.2788

" ** 2.73

52.2

(< i(

III

1.1534

" '' 5.18

50.5

i( iC

1.0774

" '' 10.38

49.

is iC

1.0558

" " 14.5

47.51

VI
VII

1.0343
1.0166

*' '' 23.63
u u 49.44

47.3

47.4

47.44 mean
per cent.

VIII

1.0076

'' " 104.6

47.4

1.0044

" '' 247.3

47. 6 J

The correction which ought to be applied to these figures is
here again, even for Solution I, so small that it falls within
the experimental error. If we make the same assumption as
in the case of copper vitriol, it amounts to 0.0005 gr. for the
0.6698 gr. of transferred silver. The effect of water in the
case of silver nitrate is opposite to that in the case of copper
vitriol. The transference of the cation Ag diminishes, that of
the anion N increases, with increasing amount of the solvent.
The effect of the water reaches a limit in Solution V. Greater
dilution does not further change the value.

In the two above salts, the ions are all different substances.
I now investigated compounds of the same cation with differ-
ent anions, and chose for this purpose silver sulphate and silver
acetate. Both of these salts are difficultly soluble in water,
but still sufficiently so to give accurate results for our purpose.

III. SILVER SULPHATE

EJDperiment A

Specific gravity of the solution at 15° C: 1.0078.

The solution contained 1 part SAg to 123 parts water.

The current from four elements reduced 0.1099 gr. Ag in
24 minutes at 15° C.

The solution about the cathode gave :

Before electrolysis. . . 0.4166 gr. ClAg
After " ... 0.3358 '' ''

The loss is 0.0808 gr. ClAg, 6r 0.0608 gr. Ag.

MEMOIRS ON THE FUNDAMENTAL

The quantity of transferred silver is therefore

0.1099
-0.0608

0.0491 gr., or -i±L =44.67 percent.
^ 1099 ^

Experiment B

The current from four elements reduced 0.1127 gr. Ag in
25 minutes.

The solution around the cathode gave :

Before electrolysis. . . 0.4090 gr. ClAg
After ** ... 0.3261 "

The loss is 0.0829 gr. ClAg, or 0.624 gr. Ag.

Hence the amount of transferred silver is

0.1127
-0.0624

503

0.0503 gr., or ^^=44.63 per cent.

Experiment C

The current from four elements reduced 0.1108 gr. Ag in
23^ minutes at 19.4° C.
The solution around the cathode gave :

Before electrolysis. . . 0.3539 gr. ClAg
After '* ... 0.2720 '' ''

The loss is 0.0819 gr. ClAg, or 0.0616 gr. Ag.

The transference of silver is therefore

0.1108
-0.0616

492

0.0492 gr., or =44.4 per cent.

lluo

The results of the three experiments :

44.67 percent.

44.63 '' "

44.4 " "

give the mean 44.57 per cent.

LAWS OF ELECTROLYTIC CONDUCTION

IV. SILVER ACETATE

Experiment A
Specific gravity of the solutioD at 14° C: 1.0060.

It contained 1 part ic Ag* to 126.7 parts water.

The current from four elements reduced 0.2197 gr. Ag in 1
hour 21 minutes at 14° C.

The solution at the cathode gave :

Before electrolysis.. . 0.3736 gr. ClAg
After '' ... 0.2631 '' ''

The loss is 0.1105 gr. ClAg, or 0.0832 gr. Ag.

Hence the transference of silver is

0.2197
-0.0832

0.1365 gr., or 1?^ = 62.13 per cent.
^ ' 2197 ^

Experiment B

The current from four elements reduced 0.1892 gr. Ag in 1
hour 7 minutes at 15° C.

The solution at the cathode gave :

Before electrolysis. . . 0.3656 gr. ClAg
After " ... 0.2728 '' ''

The loss is 0.0928 gr. ClAg, or 0.0699 gr. Ag.

The amount of transferred silver is

0.1892
-0.0699

0.1193 gr., or i±i?=63 per cent.
^ ' 1893 ^

Experiment G
Specific gravity at 15^ C. : 1.0045.

The current from four elements reduced 0.1718 gr. Ag in 1
hour 13 minutes at 15° C.

The solution at the cathode gave :

Before electrolysis 0.2825 gr. ClAg

After '' 0.1977 '' "

The loss is 0.0848 gr. ClAg, or 0.0638 gr. Ag.

* [Ac is equivalent to (7, H^ 0^ minus ^H^O in modem notation.]

MEMOIRS ON THE FUNDAMENTAL

The amount of transferred silver is

0.1718
-0.0638

0.1080 gr. , or ^^ =62.86 per cent.

From the results of these three experiments,

62.13 percent.
63 '' *'
62.86 " "

we obtain the mean. . . 62.66 percent.

If we glance at the values obtained with the three silver salts,
it is at once evident that the same cation migrates by different
amounts when in combination with different anions, the con-
dition of the solutions remaining otherwise the same.

^. 1 A / i X .1 . i. * Ag is 62.6 per cent.

With Ag(Ac) the transference of v ,, ow a \c a
°^ liC * o7.4

a te

<C Arr/\r\ (< if <(

Ag(N)
Ag(S)

Ag " 47.4

i( a

(< Arr/Q^ << *( <i

Ag " 44.6

If the explanation of the transference numbers which we
gave at the beginning of this paper is correct, then the dis-
tances traversed during electrolysis by Ag and ic, Ag and N,
and Ag and S, are in the ratio respectively of,

100 : 59.7
100 : 110.9
100 : 124.2

In these numbers a relation to chemical affinity is unmistak-
able. Of the three anions with which we are concerned, every
chemist regards the Ac as the weakest, the S as the strongest.

The same relation is evident if we compare the transference
numbers of (S) Cu and (S) Ag.. In the first of these two elec-
trolytes which contain the same anion, the migration of the S
is 64.4 per cent, and of the Cu 35.6 per cent., while at the same
concentration, the migration of S in the second electrolyte is
55.4 per cent, and of Ag 44.6 per cent. The relative distances
traversed are therefore :

For S and Cu : 100 and 55.3

For S and Ag : 100 and 80.5

I inn.

LAWS OF ELECTROLYTIC CONDUCTION

In order to explain the relation indicated, the following con-
sideration naturally offers itself. Of several anions in combina-
tion with the same cation, we will consider that one the most
electro-negative which moves the greatest distance towards the
anode. The analogous relation holds for several cations present
with the same anion. The farther apart two substances stand
from each other in the voltaic series, the stronger appears their
chemical affinity. We might therefore look for a measure of
chemical affinity in the distances through which the anions mi-
grate during electrolysis. At present, however, I am far from
ready to assign this significance to the above figures. When
we consider that copper appears more positive than silver in
its electrical aspect, and that the quantity of water exerts such
a decided influence on the transference, a theory is by no means
yet to be thought of.

I do not yet attempt to give an explanation of the influence
of the water. Whatever hypothesis we propose for this, we
must r^emember that the neutrality of the solution is not dis-
turbed by the electrolysis — that free acid never makes its ap-
pearance at the cathode. We can determine the transference
equally well in our experiments if we determine quantitively
the acid in the solution about the cathode, or if we determine
the base. I always prefer the former way in these investiga-
tions, when analytical methods permit the acid being more
sharply determined.

In my experiments with the four salts, hydrogen was never
separated out at the cathode along with the metal, although
very dilute solutions have been electrolyzed. I took, of course,
great care to make up neutral solutions and to exclude all free
acid. Although Smee* obtained a different result in the elec-
trolysis of copper sulphate, yet this is only apparently the case.
Smee cites in support of the older view of galvanic decomposi-
tion, according to which water only is decomposed, and the
metal is a result of the reduction caused by the liberated hy-
drogen, an experiment in which he decomposed a copper vitriol
solution in a tall glass vessel with copper electrodes, the upper
of which was negative and the lower positive. He observed
copper to separate out on the former, at first in a compact,
later in a spongy form, and then hydrogen evolved, while the

»Pogg.^?i7i.,66,478.

MEMOIRS ON THE FUNDAMENTAL

tipper portion of the solution gradually became completely col-
orless, and the lower positive electrode became covered with a
thick layer of copper oxide. With the exception of the re-
mark concerning the anode, I have always observed the same
results when the cathode in my apparatus had the form of a
horizontal plate. If we place it just at the surface, so that
only its underside is in contact with the liquid, the copper ap-
pears immediately in the spongy form if the current is not
too weak ; it soon falls off and leaves a surface of pure water
in contact with the cathode, whence, of course, hydrogen must
appear. This follows so clearly from Figs. 2 and 3 that a
further discussion is superfluous. To avoid this result, my
cathode was given the form of a cone.

Daniell* has already unquestionably proved the hydrogen
which is evolved during the galvanic decomposition of aqueous
solutions of the alkali or alkali earth salts, to be secondary.
It is known that when salts of iron, manganese, cobalt, and
nickel, even in perfectly neutral aqueous solution, conduct the
current, hydrogen is set free simultaneously with the metals.
Is this hydrogen likewise secondary ? Nothing is easier than
to answer this question. A solution of S Fe, which was puri-
fied from free acid by repeated crystallization, was introduced
into a circuit with a silver voltameter. An iron plate dipped
in the solution as anode, and a platinum plate as cathode.
The liquid about the latter is as neutral after the electrolysis
as before. If the hydrogen be of secondary origin, it is evolved
by a portion of the liberated iron decomposing the water by
uniting with its oxygen. Hence ferrous oxide must be mixed
with the reduced iron, and the total amount of Fe correspond-
ing will contain as much iron as is equivalent to the silver.

The two following experiments show this clearly :

Experiment A

The current from three elements reduced 3.672 gr. Ag in the
silver voltameter, which is equivalent to 0.9537 gr. Fe. The
deposited iron was dissolved in aqua regia and precipitated as
Fe by ammonia.

The Fe weighed 1.3625 gr.; it contained, therefore, 0.9542
gr. Fe.

* Pogg. Ann.^ Erffdnsbdy i., 5^.

LAWS OF ELECTROLYTIC CONDUCTION

Experiment B

The reduced silver weighed 3.0649 gr., and is equivalent to
0.7960 gr. Fe.

The Fe weighed 1.1375 gr., and contained 0.7966 gr. Fe.

We shall obtain further information of the efPect of water on
the migration if we substitute another solvent. Unfortunately,
our choice in this direction is very limited. Absolute alcohol
is the only liquid which can replace water, and this only in a
few cases, as it dissolves only a few electrolytes.

Of our four salts, silver nitrate alone is soluble in absolute
alcohol. At higher temperatures it is easily soluble ; at lower
temperatures, at which alone electrolysis can be carried out on
account of the volatility of the alcohol, it is difficultly soluble.
A solution saturated at a higher temperature contained at 5° C.
only 1 part SrAg in 30.86 parts of alcohol.

The solution which was electrolyzed was somewhat diluter.
The glass plate fastened under the cathode by sealing-wax was
replaced by an ivory plate which was screwed on, and the cyl-
inder a was sealed into the vessel c with plaster of Paris. The
solution conducted poorly.

Experiment A

The current from six elements reduced 0.2521 gr. Ag in 3
hours 32 minutes at 3.8° C.
The solution about the cathode gave :

Before electrolysis. . . 0.9181 gr. ClAg
After '' ... 0.7264 '' ''

The loss is 0.1917 gr. ClAg, or 0.1443 gr. Ag.

Hence the transference of silver is

0.2521
-0.1443

1078

0.1078 ffr., or _—--=: 42. 8 per cent.
^ 2521 ^

Experiment B

The current from six elements reduced 0.1367 gr. Ag in 2

hours 22 minutes at 5° C.

MEMOIRS ON THE FUNDAMENTAL
The solution about the cathode gave :

Before electrolysis. . . 0.8743 gr. ClAg
After '^ ... 0.7700 '' "

The loss is 0.1043 gr. ClAg, or 0.0785 gr. Ag.

The transference of silver is therefore

0.1367
-0.0785

0.0582 gr., or -^??-=42.6 per cent.

1367

Hence in alcoholic solution the transference of Ajs: is 42.7
per cent. ; of N, 57.3 per cent. ; and the relative distances trav-
ersed are 100 and 134.2 respectively.

This result, which was not anticipated, indicates the great
caution to be observed in the interpretation of our results. I
intend next to study such salts as are easily soluble in absolute
alcohol at low temperatures, and hope in the next communica-
tion to be able to present results on the salts of zinc, cadmium,
iron, manganese, etc. Wikh several of these hydrogen separates
out at the cathode during the electrolysis. As the solution
becomes diluted there, my apparatus can easily be adapted to
this investigation by a slight modification. I then also intend
to return to Daniell and Miller's method and to their discord-
ant results.

Biographical Sketch

JoHANN WiLHELM HiTTORF was bom in Bonn, May 27,
1824. He was made a member of the Philosophical Faculty of
the Eoyal Academy of Miinster in 1852, with the title of Pro-
fessor of Chemistry and Physics, having previously occupied
the position of Decent in the same institution. By the reor-
ganization of the faculty in 1876, he was relieved of the in-
struction in chemistry. As professor of physics he continued
work of instruction until 1890, when sickness compelled him
to give up active work. He was then made Professor Emeri-
tus, which position he still holds.

The valuable contributions which Hittorf has made to science,
have made him an honored member of many societies. He is

LAWS OF ELECTROLYTIC CONDUCTION

corresponding member of the Konigliehe Gesellschaf t of Gottin-
gen, Berlin, and Munich ; foreign member of tlie Danish Acad-
emy of Copenhagen, and honorary member of the Manchester
Literary and Philosophical Society, and of the London Physical
Society. The degree of M.D. was conferred on him by the
medical faculty of the University of Leipzig, and in 1897 he
was honored with the Prussian order pour le merite for science
and arts. In 1898 lie was elected Honorary President of the
German Electrochemical Society.

Of Hittorf^s published papers, most of which have appeared
in Poggendorff's and Wiedemann's Annalen since 1847, the
extended series of investigations on electrolysis, of which the
above is the first, should first be mentioned. In 1864 the
** Multiple Spectra" of the elements was established in an in-
vestigation with Pliicker. In the years 1869-1874 a series of
important papers appeared on the phenomena accompanying
the passage of electricity through rarefied gases, and on the
remarkable behavior of cathode rays.

In Chemistry may be mentioned an investigation on the al-
lotropic forms of selenium and phosphorus, in which a new
black metallic crystalline modification of the latter was dis-
covered. Quite recently Hittorf has contributed several arti-
cles to the Zeitschrift fur Physikalische Chmnie^

ON THE CONDUCTIVITY OF ELECTRO
LYTES DISSOLVED IN WATER IN
RELATION TO THE MI-
GRATION OF THEIR
COMPONENTS

F. KOHLBAUSCH
Director of tbe Beichsanstalt, Charlottenburg

Presented May 6, 1876, before the GOttingen Academy of Sciences
{Oottingen Naehriehten, 1876, 318 ; Carl, Reperiorivm, 13, 10, 1877)

CONTENTS

PACK

On t/ie Conduettmty of Aqueous Solutions 85

Law of Independent Migration of Ions 86

First Test of Law 86

Second Test of Law •. 88

Preliminary Table of Velocities of Migration 80

Calculation of Absolute Velocity in Mechanical Units 90

ON THE CONDUCTIVITY OF ELECTRO
LYTES DISSOLVED IN WATER IN
RELATION TO THE MI-
GRATION OF THEIR
COMPONENTS

F. KOHLRAUSCH

I TAKE the liberty of presenting, as an appendix to a previous
communication (these Proceedings, 1874, 405), a few remarks
on the Mechanics of Electrolysis. I have shown with Mr. Grot-
rian, in the paper mentioned, that dilute aqueous solutions of
the chlorides of all the alkalies and alkali earths possess nearly
the same conductivity when an equal number of equivalents
are dissolved.

If the differences still remaining be compared with the trans-
ference numbers of the migrating components, as determined by
Wiedemann, Weiske, and especially by Hittorf * in his classical
work on The Migration of Ions During Electrolysis^ an evident
connection between the two quantities is at once noticed. By
following this matter further, one is led to an assumption, re-
markable for its simplicity, regarding the nature of the elec-
trical resistance of dilute solutions, which I will now develop
with the aid of the previous examples, as well as by some which
I have more recently observed.

* Hittorf, Pogg. Ann., 89, 177; 98. 1; 103, 1; 106, 518. Wiede-
maoD, ibid., 99, 182. Weiske, ibid., 103, 466.

MEMOIRS ON THE FUNDAMENTAL

Pure water does not possess an appreciable conductivity, and
hence it is most natural to regard current conduction in an
aqueous solution of a body as due, not to conduction by tb«
water, but by the dissolved particles. This view is probably
held by most physicists at the present time.* According to it
the water acts only as a medium in which the electrolytic dis-
placements take place, and the electrical resistance of the solu-
tion would be the frictional resistance which the migrating
elements of the salt, etc., experience against the water particles
and against each other.

If, now, the solution be very dilute, this friction will occur for
the most part on the water particles. Hence one will be fur-
ther tempted to conclude — and this is a conclusion which to
my knowledge has never previously been drawn — that in a
dilute solution every electrochemical element {e.g., hydrogen,
chlorine, or also a radical, as NO3) has a perfectly definite resist-
ance pertaining to it, independent of the compound from which
it is electrolyzed. As we know little concerning the nature of
a solution, however, it is clear that such an assumption is justi-
fied only by experimental verification.

I think I can now prove that the facts correspond very nearly
to the above law for a large group of substances — namely, for
all the univalent acids and their salts whose conductivity has
been investigated.

For this purpose let us consider dilute solutions whicb con-
tain an equal number of electrolytic molecules in equal volumes.
I shall call such solutions electrochemically equivalent. Of course
the electrolytic molecule is not always to be regarded as the
molecule now assumed in chemistry, but only that fraction of
the latter which is decomposed by the same quantity of elec-
tricity as a molecule composed of two chemically univalent
components.

Let each solution form a column of unit cross-section, and
let it be acted on by an electric force (potential gradient),
unity. If the ions have the opposite velocities, Uq and u,
then by Faraday's law, according to which each migrating
partial molecule carries with it a quantity of electricity in-
dependent of its nature, the current is proportional to Uq+u

♦Compare, e.g., Hittorf; Quincke, Pogg. An7i., 144, 3; Wiedemann,
Gftlvairi.«mu8 (2), I., p. 471.

LAWS OF ELECTROLYTIC CONDUCTION

(and to the number of molecules contained in unit length

of the column, which, however, shall be the same in all solu-.

tions).

On the other hand, the strength of the current through unit

cross -section due to an electromotive force unity is, as well

known, nothing else than what is called the conductivity, I, of

the solution, which must therefore be proportional to Uq-^-u,

The ratio of the velocities Uq and u has been determined by

Hittorf for ja large number of solutions. We will call witli

iff
Hittorf n = — ^ the transference number of the component

which has the velocity Uq.

Now let two electrochemically equivalent solutions of two
compounds, I and II, be given, which have one component in
common — e.g., that one having the velocity Uq, while the other
components have the velocities u^ and Uz respectively. Let the
corresponding conductivities of the solutions be l^ and Zg* Then
from the above

(-^~ )

Hence our hypothesis requires that the conductivity of electro-
chemically equivalent solutions of ttvo electrolytes, having a com-
ponent in common, shall vary inversely as the transference
numbers of the common component ; or, that the product of the
conductivity of each solution and the corresp07iding transference
number of the comynon component shall he equal.

This conclusion is verified in the following compilation of
all material on electrolytes of univalent acids at my disposal.

MEMOIRS ON THE FUNDAMENTAL

TABLE

^'1

KCl

977

0.510

NaCl

807

0.63

1.21

1.23

NH4CI

949

0.51

1.03

1.00

((

CaiCl

742

0.68

1.32

1.33

((

MgiCl

712

0.69

1.37

1.35

BaiCl

800

0.62

1.22

Sr^Cl

777

0.65

1.26

1.27

HCl

3230

0.161

0.302

0.316

KNO3

927

0.495

AgNOg

810

0.53

1.14

1.07

HNO3

3360

0.142

0.275

0.287

KBr

1044

0.514

HBr

3100

0.178

0.329

0.346

1048

0.50

3190

0.258

0.328

0.516

KCl

97r

0.490

KBr

1044

0.486

0.94

0.99

1048

0.50

0.93

1.02

((

KNO3

927

0.505

1.05

1.03

«<

• (<

KCIO3

843

0.55

1.16

1.12

((

KAc

699

0.676

1.40

1.38

In the whole table there is but one considerable difference be-
tween the ratios of 7i and of I — namely, in the case of HI. But
in this very case it is probable, from the values of the transfer-
ence numbers which Hittorf gives, that u has been found too
large for iodine. Such an error is easily possible, as only one ob-
servation was made, and as control experiments cannot be made
at both electrodes in the case of acids as in the case of salts.

The assumption of the independent migration of ions may also
he tested by the transference numbers alone, and hence confirmed
or confuted in the case of substances whose conductivity is not
yet known. It is easily seen that the following relation must
hold between the transference numbers of the four compounds
which can be formed from two pairs of electrochemical atoms
A A' and BB':

Let mi Uin ?W2 ^2? ^3 ^^3* ^4 ^4 be the transference numbers
of the electrolytes A B, A B', A' B, A' B' respectively, where ?«
refers always to A, n to B, and of course m 4-^=1.

Then our assumption evidently requires that

my W4 __ W2 m^

Wj n^ 712

LAWS OF ELECTROLYTIC CONDUCTION

In the following six examples, taken from Hittorf 's determina-
tions, together with Wiedemann's values for HNO3, the devia-
tions from the required relation amount to scarcely more than
is to be expected from the uncertainty of the observations
themselves.

NO3

0.51

0.495

0.63

0.614

0.60

NO3

0.63

0.614

0.616

0.61

0.38

0.39

NO3

0.161

0.142

0.68

0.62

3.18

2.84

0.51

0.50

0.63

0.62

0.59

0.51

0.324

0.63

0.443

1.21

i;23

NO3

0.324

0.495

*0.627

0.626

1.88

1.72

From the experimental confirmation of these two conse-
quences, I am of the opinion that the law here suggested has
great probability — that is to say, that we may speak of the
mobility* of an electrolytic component in water.

I give below, as provisional, the following numbers for the
mobility u, referred to that of hydrogen as unity :

CI I K NH^

NO,

1.00

0.19

0.19 0.18 0.18 0.18

0.17

CIO3

Ba Na Ca Sr Mg

0.15

0.12 0.11 0.10 0.10 0.09

0.09

The mobility of hydrogen exceeds, therefore, that of the other
elements five to eleven times, and it may indeed be asserted
with certainty that the high conductivity of acids is due to the
fact that hydrogen is one of their migrating compoiients. Pos-
sibly the same remark also applies to the good conduction of
the alkalies in solution.

The above numbers also give the possibility of calculating
the conductivity of a dilute solution of an electrolyte the com-
ponents of which have the mobilities u and u'. If one part by
weight of the solution contains p parts by weight of the elec-

* [•* Beweglichkeit." In modem phraseology it is more customaif/ to speak
of the ** velocity of migration " ** Wanderungsgesehwindigkeit " of an ion.]

MEMOIRS ON THE FUNDAMENTAL

trolyte, and if A denotes its electrochemical molecular weight,
then the conductivity of the solution at 18° referred to mercury
is given approximately by

A ^
The factor by which p is multiplied represents, therefore, the
specific conductivity.

Finally the force which produces a definite velocity of one of
the above components may be expressed in mechanical units,
as first shown bv W. Weber and R. Kohlrausch* in the case of
water, although at that time under assumptions regarding elec-
trolysis which do not correspond to ours. By introduction of
the absolute resistance of mercury and of the electrochemical
equivalent, one obtains for hydrogen, for example, the velocity

-^-T^ -y corresponding to an electrical force of separation

10''' sec. Jr o r

unity expressed in absolute magnetic measure (millimeter,
milligram, and second as fundamental units). Prom this it
follows, that if the electromotive force of a Daniell cells acts
on a column of dilute HCl (or HBr, HNO3, etc.) a milli-
meters in length, the hydrogen will be moved along with a

velocity of 0.33 -. The velocity of any other ion under

sec.

the same conditions is obtained by multiplying this number
by w.

If the electromotive force be calculated in mechanical units
on the assumption that the hydrogen is moved by the force ex-
erted by the electromotive force on the quantity of electricity
migrating with it, it is found that in order to force the hydro-

mm.

gen electrolytically through the water with a velocity of 1 -,

sec.

a force equal to the weight of 33,000 kg. must act on each
milligram of hydrogen, f If 33,000 be divided by the product
of the electrochemical molecular weight and the value of u
for another component, the corresponding value for that com-
ponent is obtained.

* AhJiandlungen der K. Sdch^. Ges. d. Wiss., v., 270.

f These figures are based solely on resistances to conduction, and have,
therefore, nothing to do wilh the overcoming of the forces of chemical
affinity which manifest themselves in the polarization of the electrodes.

LAWS OF ELECTROLYTIC CONDUCTION

Further experiments alone can decide how far the laws here
developed may be generalized on the one hand, or must re-
main limited to certain groups of substances on the other,
and to what extent they apply rigidly or only approximately.
I must mention here, however, that of the substances whose
conductivities were investigated, one — namely, acetic acid —
stands quite isolated from the above relations, if it be assumed,
from analogy with the acetic acid salts, that hydrogen forms
one of its ions. If this be so, acetic acid should be a very
good conductor, while in reality, even in aqueous solution, it
does not even approach the worst conducting of the solutions
here considered. From this quite abnormal behavior it wouhl
follow that in acetic acid other conditions are present, either in
regard to its chemical constitution, or in the nature of its so-
lution in water,* than in the case of the other acids, or even
the acetic acid salts. An exactly similar case occurs in aqueous
ammonia, although this does not belong to the examples men-
tioned in this paper. I expected that aqueous ammonia would
conduct particularly well, since ammonia salts conduct exceed-
ingly well, and potassium and sodium hydrate, moreover, con-
duct much better than their salts. But, on the contrary, this
substance, like acetic acid, is such a poor conductor that it
evidently belongs to an entirely different class of bodies. This
fact lends support to the view of some chemists, that aqueous
ammonia does not contain the compound NH^OH correspond-
ing to the alkali hydrates, but is only a solution of NH3.

i defer the further discussion of such cases, as well as my
observations on the polybasic acids and their salts, to the
future, remarking only in the mean time that their conductiv-
ity comes out too large when calculated from the above trans-
ference numbers of their components.

In conclusion I wish to call attention to another noteworthy
point of comparison between the conductivity and the trans-
ference numbers of dissolved electrolytes, to which Mr. Hittorf
himself has very kindly called my attention. Most electrolytes
investigated show a decreasing value of the transference num-
ber of the cation with increasing concentration. A few, how-

* Hydrocyanic acid appears to act similar! v.

MEMOIRS ON THE FUNDAMENTAL

ever, retain nearly the same transference relations in strong
as in dilute solutions. This is more or less the case with the
potassium sal ts, and next to them ammoninm chloride, the only
ammoniam salt investigated.

Now the condnctiyities of the last-mentioned snhstances show
a similar agreement, in contrast to the others. In the case of
most electrolytes the ratio of the condnctivity to the percent-
age composition of the solations diminishes continnonsly and
very considerably ; so mnch so, in fact, that not infrequently
the known phenomenon of a maximum occurs. In the case of
potassium and ammonium salts, however, this ratio is much
more constant. From this relation, noticed as stated by Hit-
torf, it would follow that the resistances to motion which arise
in denser solutions affect, in general, the cation more than the
anion. But I would add at once, howeyer, that a diminished
mobility must also be ascribed to the latter, in order to explain
the observed conductivity of stronger solutions.

WuRZBVBO, May 1, 1876.

Biographical Sketch

Fbiedrich Kohlrausch, son of Rudolph Kohlrausch the
physicist, was born at Rinteln, Germany, in 1840. He was
educated at the Polytechnicum at Cassel, and at the Universi-
ties of Marburg, Erlangen, and Gottingen, making his doctor's
degree at the last-named university, under Wilhelm Weber in
1863. He then acted as assistant in the astronomical observa-
tory at Gottingen, in the laboratory of the Physical Society at
Frankfort, and in the University of Gottingen. He held the
professorship of physics in the Polytechnicum at Zurich, 1870-
71 ; at Darmstadt, 1871-75; and at the University of Wiirzburg
until 1888, when he succeeded Kundt as director of the phys-
ical laboratory at Strassburg. On the death of v. Helmholtz,
in 1894, he left Strassburg to accept the appointment of direc-
tor of the Physikalisch Technische Reichsanstalt at Charlotten-
burg, which position he now holds.

The numerous contributions of Professor Kohlrausch to
physical science have been mostly in the domain of elec-
tricity and magnetism, and are characterized by the high

LAWS OF ELECTROLYTJC CONDUCTION

degree of precision with which they have been carried out.
A number of the best methods and instruments now used in
electrical and magnetic measurements are due to him. In ad-
dition to the extensive series of researches on the electrical
conductivity of electrolytes, begun in 1868 and continued to
the present time, may be mentioned his investigations on elas-
ticity in 1866 ; his series of researches on magnetic measure-
ments, 1881-84 ; and his determination with W. Kohlrausch,
of the electrochemical equivalent of silver in 1886. He is
also the author of one of the best-known works on physical
laboratory methods, entitled Leitfaden der praktischen Physik,
which has been translated into four different languages.

BIBLIOGRAPHY*

Rbfebbncb Books

Kohlrausch and Holborn. Ldtvermogen der Electrolyte. 1898.

This contains, besides theory and details of methods of conductivity
measurement, compiled data on the conductivity of aqueous solutions
recomputed in reciprocal ohms, tables of transference numbers and
velocities of migrations of ions, and a very complete author index of
work on electrical conductivity and related subjects.
Ostwald. Lehrbuc^i der Allgemeinen C/iemie, vol. ii., part 1. 189^.

Faraday's Law, pp. 579-592; Transference Numbers, pp. 593-

620; Kohirausch's Law, p. 639.
ElectrocJiemie. Ihre Oeschichte und Lehre. 1896.
Wiedemann. Lehre von der Ekctricitdt, vol. ii. 1894.

Faraday's Law, pp. 467-475; Transference Numbers, pp.
572-586; Kohirausch's Law and Absolute Velocity of
Migration, pp. 926-933 ; Electrochemical Equivalent, vol.
iv. 1898. pp. 726-736.

Faraday's Law

Becquerel. Ann. de Chim. et de Phys., 66, 91, 1837.

Buff. Ann. d. Ghem. u. Pharm., 86, 1, 1853 ; 94, 15, 1855.

Despretz. C. E., 42, 707, 1856.

Faraday. Ea^. Researches, Ser. V., VIL, VIII.

Foucault. a R., 37, 580, 1853.

Gray. Phil Mag. (5), 22, 389, 1886 ; (5). 26, 179, 1888.

Jamin. G. R , 38, 390. 1854.

de la Rive. Pogg. Ann., 99, 626, 1856 ; Ann. de Ghim. et de Phys,

(3), 46, 41, 1856.
Logemaii and van Breda. PhU. Mag. (4), 8, 465, 1854.
Matteucce. Ann. de Ghim. et de Phys., 68, 78, 1835 ; 74, 109, 1840.

Ostwald and Nernst. Zeit.f. Phys. Ghem., 3, 120, 1889.
Shaw. Rep. Brit. Assoc, 1886, p. 318.

Phil. Mag. (6), 23, 138, 1887.
Soret. Ann. de Ghim. et de Phys. (3), 42, 257, 1854.

* No attempt has been made to make the bibliography fi^iven lielow complete. It is hoped,
however, tliut noue of the more impurtunt recent papers have been omitted.

LAWS OF ELECTROLYTIC CONDUCTION

Electrochemical Equivalent

Heydweiller. Inaug. Dissertation, Wttrzliuig, 1886.

F. Kohlrausch. Oott. Nach., 1873.

Pogg. Ann., 169, 170. 1873.
F. and W. Kohlrausch. Sitz. her. d. Phys, Med. Oes. «., Wftrzhurg, 1884.

Wied. Ann., 27 y 1. 1886.
Kahle. Zeit. f. Instrumentenkunde, 17, 144, 1897; 18, 141,

1898.
KOpsel. Wie(i. Ann., 31. 268, 1887.

Mascart. C. B., 93, 50, 1881.

Jmrn. de Phys. (2), 1, 109, 1883.

IMd . 3, 283. 1884.
Patterson and Guthe. Phys. Rev., 7, 257. 1898.
Potier and Pellat. Journ. de Phys. (2), 9, 381, 1890.

Lum. Elcc, 32, 84, 1889.
Rayleigh and Sidgwick. Phil. Trans. (A), 2, 411, 1884.

Prcc. Roy. /&?<?., 37. 144, 1884.

Bein.

Campetti.

Cattaneo.

Cliassy.
des Coudres.
Gordon.
Hittorf.

Hofgartner.

Kirrnis.

Kistiakowsky.

Kttmmell.

Kuschel.

Lassana.

Lenz.

L51) and Nernst.

Mather.

Mcintosh.

Rosenlieim.

Schrader.

Weiske.

G. Wiedemann.

Transference Numbers

Wied. Ann , 46, 29, 1892.

Zeit.f. Ph. Oh., 27, 1, 1898.

At. Tor., 29. 228, 1894; 32. 1897.

Nuov. Cim. (3). 35, 225. 1894; (4), 1. 73. 1895.

Rend. Line. (5). 6, II., 207. 1896; (5). 6. I., 279,

1897.
Ann. de Chim. et de Phys^ (6), 21 , 241. 1890.
Wied. Ann.. 67. 232. 1896.
Zeit.f. Ph. Gh.. 23.469. 1897.
Pogcr. Ann,, 89, 177. 1853; 98. 1, 1856; 103, 1,

1858 ; 106. 338, 513. 1859.
Ost W.I Id's Klassiker der Exak. Wissens., Nos. 21, 23.
Zeit.f. Ph. Gh., 26. 115, 1898.
Wied. Ann., 4:, 503, 1878.
Zeit.f Ph. Gh... «, 105. 1890.
Wied. Ann., 64, 655, 1898. •
Wied, Ann., 13, 289, 1881.
Att.Ist. Yen. (7), 3. 1111, 1892 ; 4, 1568. 1893.
Riv. Scien. Indust. Fivenze, 29. 10. 1897.
Mem. St. Pet. Ak. (7), 30, 64, 1882.
Znt.f Ph. Gh., 2. 948. 1888.
Johns Hopkins Univ., 16.45, 1897.
J. Phys. Ghem., 2, 273, 1898.
Zeit.f Anorg. Ch .11, 220. 1893.
Zeit.f Elek. Gh... 3, 498, 1896.
Poeg, Ann., 103. 466, 1858.
Pogg. Ann., 99, 177, 1856 ; 104, 162. 1858.

LAWS OF ELECTROLYTIC CONDUCTION

Velocity of Migration

For tabulated values (referred to ohms as unit of resistance and 18^ C),
see Kohlrausch & Holborn's Leitvennogen der Electrolyte, p. 201. Also
Wiedemann's ElectricitM, vol. ii., pp. 927, 929.

For values at 25° C, see Ostwald's Lehrhuch, vol. ii., part 1, p. 675.

See also F. Kohlrausch, Oott. Nachr., 1876, p. 213 ; Wied. Ann,, 6, 170,
1879 ; 26, 213, 1885 ; 60, 385, 1893 ; 66, 785, 1898.

For values of the velocity of migrution of organic anions and cations,
see literature compiled by Kohlrausch & Holborn on the electrical conduc-
tivity of organic acids and bases by Ostwald, Bredig, and others.

Absolute Velocities

Budde. Pogg, Ann., 156. 618. 1875.

F. Kohlrausch. Oott. Nachr., 1876, 213.

Wied. Ann., 6, 201, 1879 ; 50, 402. 1893.
Lodge. Brit. Assoc. Bep., 1886, 389.

Nernst. Zeit.f. Elec. Chem., 3, 308.

Sheldon and Downing. Phys. Rev., 1, 51, 1893.
Weber. Zeitf. Ph. Gh. , 4, 182, 1889.

Whetham. Phil. Trans., 184 A, 337, 1893 ; 186 A, 507, 1895.

Zeit.f. Ph. Ch., 11, 220, 1893.

INDEX

Anion, Definition of, 13.
Anode, Definition of, 12.

Berzeliti8*s Representation of Mo-
elcules, 53.

Cathode, Definition of, 12.
Cation. Definition of, 13.
Conductivity: of Solutions. 85 ; of

Acids, 88 ; Calculation of — from

Velocities of Migration, 89.
Current : Magnetic Effect of, 4, 7 ;

Heating Effect of, 5 ; Chemical

Effect of, 6.

Daniell and Miller, Experiments on

Transference, 55.
Daniell, on Secondary Electrolysis of

Hydrogen, 78.
Deflecting Force of Electric Current,

Electrochemical Equivalents, 38; Ta-
ble of, 42, 43; Application to Deter-
mination of Atomic Weights, 50.

Electrochemically Equivalent Solu-
tions, 86.

Electrode, Definition of, 12.

Electrolysis : Effect of Size of Elec-
trodes. 17; Effect of Intensity
(voltage), 20 ; Effect of Strength
of Solution, 21 ; Effect of Nature
of Solution. 22 ; Fused Salts, 27 ;
Effect of Different Electrodes, 83 ;
G 97

Theory of Grotthuss, 49 ; Theory

of Faraday, 60 ; Theory of Hit-

torf , 52.
Electrolyte, Definition of, 13.
Electrochemical Action, Law of, 7,

14, 26, 37, 51 ; Consequences of,

38.

Faraday, Biographical Sketch of, 44;
Theory of filectrolysis, 50 ; Exper-
iments on Transference, 54.

Faraday's Law, 7, 37, 38.

Galvanometer, Law of, 4.
Grotthuss, Theory of, 61.

Harris, on Heating Power of Cur-
rent, 5.
Hittorf, Biographical Sketch of, 80.

Ions, Definition of, 13 ; Laws Re-
lating to, 38-40 ; Preliminary Table
of, 4^, 43 ; Transference of (see
Transference) ; Velocity of Migra-
tion of (see Migration).

Kohlrausch, Biographical Sketch of,
92.

Migration of Ions : Law of Inde-
pendent, 86 ; Tlieoretical Conse-

INDEX

guences, 87, 89 ; Experimental
Fr<H)f, 89. 91.
Miller, A., 55.

Poles, Deflnition of, 11, 51.
Pouillet. Expenineuts on Transfer-
ence, 56.

Ritchie, on Deflective Force of Cur-
rent. 5.

Smee on Transference Phenomena,
57, 77.

Statical Electricitj', Effect of Dis-
charge through Galvanometer, 4.

Transference : Early Experiments.

57 ; Explanation of Hittorf. 53 ;
Experimental DetermitiHiioii, Ap-
paratus. 57 : Results, 61 ; Effect
of Current, 63 ; of Concentnition,
66, 73; of Temperature, 68 ; of dif-
ferent Anions, 76 ; of solvent, 79.

Velocity of Migration: Table of Rel-
ative ValufS, 90 ; Absolute Value
in Mechanical Units, 90.

Voltameters, Forms of, 15-17.

Volta-elecirometer, 25.

Voltaic ami Statical Electricity, Com-
parison of, 6.

Voltaic Electricity, Magnetic Effect
of, 5.

W .

Wiedemann, Effect of Electrical Os-
mose, 56.

THE EliTD

TEXT-BOOKS IN PHYSICS

THEORY OF PHYSICS

By Joseph S. Ames, Ph.D., Associate Professor of Physics in
Johns Hopkins University. Crown 8vo, Cloth, II 60 ;
by mail, $1 75.

In writing this book it baa been the author's aim to give a concise
statement of the experimental facts on which the science of physics is
based, and to present with these statements the accepted theories which
correlate or *' explain " them. The book is designed for those students who
have had no previous training in physics, or at least only an elementary
course, and is adapted to junior classes in colleges or technical schools.
The entire subject, as presented in the work, may be easily studied in a
course lasting for the academic year of nine months.

Perhaps the best general introduction to physics ever printed in the
English language. ... A model of comprehensiveness, directuess, arrange-
ment, and clearness of expression. . . . The treatment of each subject is
wonderfully up to date for a text-book, and does credit to the system
which keeps Johns Hopkins abreast of the times. Merely as an example
of lucid expression and of systematizution the book is worthy of careful
reading. — Jv. Y. Pres/t.

Seems to me to be thoroughly scientific in its treatment and to give
the student what is conspicuously absent in certain well-known text-l)ooks
on the subject — an excellent perspective of the verv extensive phenomena
of physics. — Professor F. E. Bbach, Sheffield bdentifie Sctwol of Yale
University,

A MANUAL OF EXPERIMENTS IN PHYSICS

Laboratory Instruction for College Classes. By Joseph S.
Ames, Ph.D., Associate Professor of Physics in Johns
Hopkins University, author of " Theory of Physics,^' and
William J. A. Bliss, Associate in Physics in Johns Hop-
kins University. 8vo, Cloth, $1 80 ; by mail, %1 95.

I have examined the book, and am greatly plensed with it. It is clear
and well arranged, and has the best and newest methods. I can cheerfully
recommend it as a most excellent work of its kind. — H. W. Harding,
Professor Emeritus of Physics^ Lehigh University.

I think the work will materially aid laboratory instructors, lead to
more scientific training of the students, and assist markedly in incentives
to more advanced and original research. — Lucien I. Blake, Professor of
Physics, University of Kansas.

It is written with that clearness and precision which are characteristic
of its authors. I am confident that the book will be of great service to
teachers and students in the physical laboratory. — Harry G. Jones, Ph»D.,
Instructor in Physical Chemistry^ Johns Hopkins University.

NEW YORK AND LONDON
HARPER & BROTHERS, PUBLISHERS