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"^
OUTLINES OF
ELECTROCHEMISTRY
BY ■
C^
HARRY' CL J^NES, i';
Asstxnatc Professor of Physical \^li<:niis1i'^' "iii dji6, J.t^hr.s Hopkins
NKW YORK:
ThK El-RUTklCAL RkVIKW PuillJSHlNli C<".
D. Van Nostrasij Companv.
190'' 4 <V
...«->
• '_*••
TABLt OF CONTENTS.
iHTaoDircTlo^. PlOM.
The meaning of tbe term electrocbem-
Istry 1
The development of electrochemletrr- ■ S
The new electrochemlstrr. -,...- - 2
CU APTEB 1— OSUOTIC PBESSUBI,
[Dtroduction , G
What Lb meant by osmotic pressure 6
The measurement of o«mot1c preeflure. ■ ■ f
Results of the measurement of osmotic
pressure ._...---.... 7
Relations between osmotic pressure and
gaa-presaure 8
Significance of the above relations. .. . , , 11
CHAPTEB II — THCORT OF ELECTHOLTTIC DISaO-
ClATlOW.
Origin of the theory of electrolytic disso-
ciation 13
Testing the theory of electrolytic disso-
ciation IS
Further lines of evidence bearing upon
the theory of electrolytic dissocia-
tion 18
An experimental demonstration of disso-
ciation 22
CBAITEH Til — SOUt APPLICATION B OF TBI
THEOnr OF ELEtTTaOLYTlC DISSOCIATION.
The neutral Iz&tl on of adds and bases-. 23
Strength of aclda and bases. . _ - - S6
Catalytic reactions 2S
Comparlaon of reactions between Inor-
ganic substances and organic eub-
stances 29
Chemical activity due to Ions- -...---.. 29
The two great generalisations. 30
CUAFTEB IV — ELECTROLYSIS AND THEORIES OF
ILECTBOLTSlfl — PART I-
The work of Faraday 3S
Testing the law of Faraday, ........... 33
Paos,
Electrochemical theories.. - 84
The electrochemical theory of Benellus 84
Thomson overthrows the objections to
the electrochemical theory of Ber-
EelluB 85
Older theories to account for elec-
trolysis 36
CHAPTCtt IV — ELC^TTttOLYSlS AflD THEOftlCS OF
ELECTBOLTSIB — PABT IL
The newer theories of electrolysis 38
This theory not sufflcleut to-day 39
The present theory of electrolysis. . , . . . 40
Testing the present theory of electro-
lysis 41
The electrolytic separation of the metals 41
CHAPTER V— OJf THE VSLOCTTt OF I0K8.
Bxperlmental determination of the rela-
tive velocities of tons- -....--...-.. 47
Influences which may affect the relative
velocities of Ions. ..--.--...-...... 4ft
The relative velocities of elementary ions
a periodic function of the atomic
weight Bl
The absolute velocities of Ions. - E2
The nature of the Ions 64
CH APTEB VI — COSDnCTlVITT OF SOLUTlOflS —
PABT I.
Specific and molecular conductivities.. Efl
The Kohtrausch method of measuring
the conductivity of solutions ET
Results of the measurement* of the con-
ductivities of solution E9
An experimental demonstration of the
different conducting powers of dif-
ferent substances '. . W
Koblrausch's law of conductivity- 61
The velocity of Ions determined by
means of the lav of Kohtrausch-.. 62
The conductivity of electrolytes as a
measure of their dissociation.--,-. 63
ti
TAnLS OF CONTENTS.
CHAFTEB VI— C0KDUCTIV1TT OF SOLTJTlOnS—
PABTH.
The dlsTOClatlng iKJwer of different flol-
vents ,..., ,,..,.--...-_-- 66
HolatloDB between the lonlilns power
of BolveotB and other properUea. , . . 69
Relation between the dilution of solu-
tloDS ODd their dlsBociatlon ,- TO
The lenlElng power of heat 72
Ways In which lone are formed- ....... 73
CHAPTtB VIT — CALCULATION Ot THE CLECTBO-
MOTIVE FOaCB OF ELEUENT8 — PAST I.
Calculation of the electromotive Torce of
eiemeaU from the oamotlc preseures
of the solutions around the elec-
trodes Tfl
The Bolutlon-tension of metals. ........ SO
A demonBtratiOD of the Bolutlon-tenBlon
of metals 82
chaptxb ¥11 — calculation of the eletttbo-
motitb foacb of bleukntb— fart ie.
Paol
Tbe calculation of the difference In po-
tential between a metal and a solu-
tion of one of Its saita SEi
Types of elementB. SS
A simple concentration element, ....... 86
The liquid element SK)
A typical two-metal cell. , 92
CHAFXEU ni^<:ALCULATION OF THB KLECTBO-
MOTIVB FOBCe OF ELEMENTS — PAET 111.
Determination of the solutlon-tenslon of
metals 9G
Are the solutlon'tenslona of the metaU
constant? 97
Some well'known elements,....,,.,... 99
Sources of the electrical energy In pri-
mary cells 101
CoQclualon 103
INTRODUCTION.
THE HEAN'ISO OF THK TEKM ELKCTRO-
0KKMI3TRY.
The term ekctrochemistrv is used to-
day ao frcquontly, not only in pure
acieuce^ but in the technical world, that
wo should inquire just what it means.
This is the more desirable since we fre-
quently find it employed rather loosely to
embrnoc n multitude of phenomrnaT some
of which have very little to do with the
subject. We can see the significance of
this term more clearly by studying the
eflrly development of the subject, than
by iiny definition, which would prob-
ably include terms less familiar than
the word which we are trying to de-
fine. In the latter part of the eighteenth
century Volta discoTered the pile which
bears his name. This consists of two
metals and an aeid, and from auch a com-
bination electricity can be obtained. When
this pile acts — i. e., produces electricity —
the metal is used up and the acid also is
iiued up. The aubatancea preaent in the
pile undergo serious chemical change, and
the result is the production of electricity,
Tliese facts show that there is some close
connection between the chemical action
going on in the cell and the production
of the eleetricity.
If. now, the electricity thus produced
is conducted through aolutionp of certain
siibatnneea, serious changes tnkc place. If
it is passed through a solution of copper
sulphate, metallic copper is deposited upon
one of the poles, and if those are of plati-
nunri. free sulphuric acid is formed around
the other pole. This fact alone would in-
dicate that the current has the power to
deeompoae ehcmieal substances, or, as we
pay, to overcome the chemical attraction
which holds them together. It was easily
recognized that there is some close connec-
tion between electricity and chemical at-
traction, but no clear conception of this
ndation could be formed until the discov-
ery of the laws of the correlation and con-
servation of energy by Mayer and Joule,
and the aubaequent development of thia
whole subject by Helmholtz. Our present
conceptions of energy relations, which are
the direct outgrowth of thia work, furnish
u9 with a clear picture of what takes place
in the experiments described above.
In the voltaic pile we have chemical en-
ergy converted into electrical. The metal
passes from a condition of greater chemi-
cal energy to one of less, and the diiference
between the chemical energy in the system
before and after the cell has acted, ift con-
verted, for the moat part, into electrical
energy. The chemical energy which has
disappeared during the ^action of the cell
ia converted chiefly into electrical energy.
This is clearly an example of the trans-
formation of chemical energy into elec-
trical.
When, on the other hand, a current is
pjissed through a solution of a salt like
cnppor sulphate, the metal is deposited in
a form containing a larger amount of
chemical energy than when preaent in the
>i\U. AYe also have electrical energy used
up in effecting the electrolysis of the salt.
INTRODUCTIOIf.
In this case we have^ then, a transfornia'-
tion of electrical energy into chemical en-
ergy.
The above experiments illustrate the
mntual transform ability of chemical and
electrical energies, and this furnishes the
subject matter of electrochemistry.
THE DEVELOPMENT OP ELECTRO-
CHEMISTRY.
Phenomena which belong to eleetro-
cheniistry were studied during the entire
nineteenth century. The work of Hum-
phrey Davy on the clectrolyaia of the
alkalies, which he effected by means of his
large voltaic pile at the very beginning
of the century, attracted attention to this
field of investig*ition, and much of the
beat work of Faraday was done along
strictly electrochemical lines. He was
particularly interestetl in the decomposi'
tions effected by tbe current, and it is dif-
ficult to overestimate the importance of
his investigations in this field on the sub-
sequent development of electrochemistry.
In connection with the development of
the theoretical side of electrochemistry
Berzelius will always be prominent. His
electrochemical theory, which is recog-
nized to-day to contain the germ of a
great truth, exercised a powerful influence
on men of science during the first half
of the nineteenth century, and attracted
attention to electrochemistry as throwing
light on the all-important problem of
chemical combination.
Many other illustrious names might be
mentioned in connection with the earlier
development of electrochemistry. That
of Hittorf must not be omitted. It was
he. as we shall learn, who first pointed out
a nu^thod of mcnsuring the relative veloc-
ities with wh\(h lilt' ions travel; nnd F.
KohlrauBch furnished us with the first
reliable method of measuring the con-
ductivity of solutions, but space will not
permit us to go farther in this connec-
tion.
THE NEW ELECTROCHEMISTRY.
The electrochemistry of to-day, as we
shall learn, differs in many respects from
that of the earlier period. Like the older
work it deals with the reciprocal trans-
formations of chemical and electrical
energy, but deals with them by entirely
new methods. These are the outcome of
certain generalizations which were reached
in 188G and 1887, and which have thrown
entirely new light over the whole field of
chemistry. These generalizations are,
that the laws of gas-pressure apply to the
osmotic pressure of solutiotts; and that
electrolytes in the presence of water are
largely dissociated into ions.
It would be impossible to follow the
more recent developments in electrochem-
istrj', without a -comprehensive grasp of the
meaning and significance of these gen-
eralizations. They are, therefore, con-
sidered at some length in the following
chapters. The recent applications of theee
generalizations to electrochemical prob-
lems, eonstitate the subject matter of the
later chapters of this book.
A word in reference to the relations of
electrochemistry to the broader subjeet of
which it is a part — physical chemistry.
Since the generalizations referred to above
were dUcovcrrd. a new branch of science
occupying a position between physics and
chemistry, has come into prominence,
This is known as physical chemistry.
Physical chemistry to-day does not
mean simply the study of the physical
properties of chemical compounds, as it
did formerly, hut hafi tn dn chieflv with the
INTRODUCTION.
energy transformations which take place
in chemical reactions. The heat changca
which always occur when substances react
ehemicfllly are studied under thermo-
chemistry — an important chapter of physi-
cal chemistry.
Physical chemistry is especially COE-
cemed with the properties of substances
m solution — the condition under which
most chemical reactions take place. It in-
cludes also the study of the velocity of
chemical reactions, and the conditions un-
der which chemical reactions come to rest,
or are in equilibrium. Finally, it in-
cludes the study of the tranaformatione of
chemical and electrical energy — in a word,
electrochemistry.
We thus see the relation of eloetrochem-
istry to the several chapters of which
physical chemistry js composed.
OUTLINES OF ELECTROCHEMISTRY,
CHAPTER I-OSMOTIC PRI^SSURE,
IT IS WELL KNOWN that In tUe \m
tvvr >ears u Dew bruDch of acienee hiu
come into existence, Since the plie-
nozniyna wilh which It deFtIf lie midwny be-
tween -physics anci chtmiatr?* it u coJIed
pbyaical chemistry, and to dig ti aguish
It from the older phjgiaal cheruLstry, from
vrhich it diff«ra fuD^Amentflllj ard in
kinil, it bus been tfinia^d the new physical
chemistry.
This subject t^Enhrncc* n numbor of
chapters, ajch aa tbc study of atoms uud
roctecoJeer of &oMds, liquidfi, ani gns^, of
thprnirtchemiBlry, eletlrfwhemislTy, chemi-
oal dycijimici And slriti<^, elc. That por-
tion of phyitical ditniJatry which concerns
U# bore hart to Ho with the trumformatioiis
of ehomicjJ c-ncr^y :iito electrii^aJ, and oi
oJcctric <^D(f^gy into chemical, and thi« oon-
etitittin ihp )iuhjrc^t mutter of 4tlof7t rr>chRm-
It it not the intention of these p&pers
to Ireat the subject of rlcctrt^chemintrv in
A eydU'Uiatio or exbauiUvc inannwrj ad
would be diono in un Hdvanoed leit-book on
thiK ftuhjtn'I, hill lo tiiki? \tp cedjiin spc-
Uona ^vhich n^f.m pnf:icu.larly intereating
and importnnt.
It wonlH he imposaible to plunge ia-
tolli^bly into the eubjoct maTt^r of de(>
trocheiTniiitry^ wllhoul first Btiidyin^ aome
pheiTomttiut whhrli lir nt ihv frnindutlcm
of l}] dcrtrwhpmislry, imd upon whi^h it
re^t*. Wrr t\\a\\ tiibc up firtt the phcnom-
eSM conndc^tod nith oatiloIio prrRAuro,,nnd
point out c^rtiiin rdations b<>tw&&n th»
o«m4>tfc pr»)Ffltire exerted by soliilione and
i>ther physical phenomena which urc woU
known.
WHAT 1« MU^T UT OSUOTIC FKU^Cfct-
It wai known (rc-m the earliest time thflt
when ciirrain ai:>lid suWlancea are hroiighl
in eonlact with certain llqutdB, the for-
mer dts40h«, ftnU vrhen qiumtitatlve tneth*
'hU k'i;[iir to be di-eyvered» it vaa ftoo©
found Ihnt tutjh aubslflnas* ijlalributed
themselves uniformly Ih/oitj^hou^ Hie ji.ol'
pent. Thia pbi^nngicnoii wm caiW'dif-
fnjicn. but the ceflre oT'diffiuion ww tv
lircly nnkn^wnn Why docs the disftolrcd
£ubst«Dee pA86 into «tery portion of the
Rfilvent imti] ihe whole ftohitioii become*
honiogeneoui, i^ach equal volume eonuin-
tng the »anie zunonijt of t}ie diHfohcd nub-
slan<:e? The quL^jfioTi could not be jfr-
Btt'LTt'd. TlUB vrnn n'.i i]\r- Uit^m norplcVinj^,
^hen it wac coniidoi'cd th'bit nibftuineci
muf-h finivir^r than lb«- HtiTn*nt vonid rifl^
from the bollom of ihe conlaiDiog-VBMel
into tlie eolvent, right against the poll of
^'ravitv. Another iaet whidi had been
kTioi^Q for a long ticao ii thfit an animal
bladder, when filled with a niivtun) of
alonh*tl am! vraU^r and phut;t*'tl iiilo jiuw
water, will inrll up and hxiTfi. It waji
obvious that there i« some prfts«nre roaai-
fceting it«(?lf in thi» com, and auch ha«
been termed cumctif^ prtit^rtt,
A pre^ire simflar to the above vru
found lo Miat at tbtr *urfatM of tionlact of
ereiy *oTuiion with the pure aolvent, and
uliK nt the purfdce of contai?t of (rvcry »i:>ln-
tion of n (rubtUnee with ev^ry othor lolO'
ikir of different concent rat ion. These oh-
wrvfltions are, of eonrw, purely quslita^
OUTLiyES OF ELECTROCHEMISTRY.
tive, boitj like the study of erery phenom-
enon Id science, we have first the qualita-
tive observations and then the quantitative
meaHurements. The earlier observers had
DO conception as to the magaittide of the
osmotic nressure which a solution will ex-
ert, and no idea how it could be measured^
THE MEASUREMENT OF OSMOTIC PBESSURE.
If we were dependent upon animal
membranes or upon any other natural
membrane to measure the magnitude of
osmotic pressure, our knowledge of this
subject would be most unsatisfactory. But
artificial membranes, which can stand
raa^jji tiijited the, pressure of any natural
,itLeniHi;&fe, havf b^^ prepared and used
^j^iiaeefe^aliy* to^^»fei>ie^the magnitude of
the "osmotic presaui^-^erted by not too
tioncentrated eolutitne.'* •
I In order that any meigbrane may he
-used to measure oenfotie pfessure it must
'^ allow the pure soliefiK'to pass through^
',-b*nt prevent the diSsglf^d-'substance from
•'^Mein^ ThiiSf W'ih^ eaRe of a solution
»Vf/anfe BUgaci^jVa^fj'the membrane must
tflldjr the water ,'to'pass readily through,
but must &e' rmpeirious to the cane sugar
molecules- The reason for this is obvious.
If the membrane which separated the solu-
tions of different concentrations allowed
the dissolved substance to pass through,
the solutions on the two sidea would bj
diffusion become of the same concentra-
tion, and no osmotic pressure would exist
between them. Such membranes, whioh
are permeable to the solvent but are im^
permeable to the dissolved substance, are
known as $emi- permeable memhraneM.
It has been found that certain precipi-
tat*B have this property of allowing water
to pass through them, but of preventing
certain substances, like cane sugar. Among
ihme should be mentioned copper ferro^
cyanide, the precipitate formed when a
solution of potassium ferrocyanide u
brought in contact with a solution of a
soluble copper salt, say copper sulphate.
The reaction is expressed by the following
equation :
K,Fe(CN),+^CuSO,= Cu,Fe(CN),+
2K.S0».
A number of other substances, such aa
calcium phosphate, Berlin bine, etc., have
been found to have the same property to
some extent.
In order that such a precipitate should
be used to measure osmotic pressure it
must be given a resistant support, and the
following device has been adopted- The
precipitate was deposited right in the walla
of a fine-grained, porcelain cup, by filling
the cup with a solution of potassium feiro-
cyanide and immersing it in a solution of
copper sulphate. Where the two aolutiona
came together in the walls of the cup the
precipitate was formed, and had the
property of semi -permeability, which is ea-
sential to the measurement of osmotic
pressure.
In preparing these membranes great
care and patience are necessary to work
out the details, but this is not the place to
discuss these details.*
Having prepared the cell containing the
semi -permeable membrane, it was filled
with the solution whose osmotic pressure
was to be mea&ured, and tightly closed by
means of a cork, through which a manom-
eter passed. The cell containing the solu-
tion was then immersed in a vessel con-
taining pure water. The water passed
through the semi-permeable membrane
into the cup, and produced a pressure
which could be read on the manometer.
uiiK^. L-lpxtf t ISTT-
OUTLINES OF ELECTROCHEMISTRY.
Water would continue to flow m until the
hydrostatic pressure on the inside was
jiast equal to the osmotic pressure which
the solution was capable of exerting
agftinat the pure soWent. By readin,'; the
maKimum pressure produced, by means of
the manometer, we have the osmotic press-
ure of the solution which is equal to it.
HESULTS OF THE MEASUREMENT OF OS-
MOTIC PRESS ORE.
The first fact which was noticed as the
result of the quantitative study of osmotic
- — b -f.-^-^'.-.-j.
PiO, 1.— DtTEHMrNAIlOW OK OSUOI K HaEf^BLHE.
pressure, was the enormous magnitude of
the pressure which even dilute solutions
can exert. From the earlier observations
on osmotic pressure, by means of which an
animal bladder was burst when it was
filled with a fairly concentrated solution
of alcohol, the conclusion was drawn that
io osmotic pressure we hare to deal with
an appreciable force; but no one imagined
for a moment that the magnitude of the^
force was as great as it is. Ffeffer, who^
is now Professor of Botany in the Univer-
sity of Tx^ipzig, found that a teuth-nor-
raal* sohition of cane sugar in water haa
an osmotic pressure of about two atmos-
pheres. Tf an oprn water manometer was
used, the coluiTin of water would rise to a
height of about 6(> feet.
Pfetfer studied the osmotic preesurea of
solutions of a nuniber of substances at
dilTcrent concentrations, und a few of his
results are given bcloV to ^lluSt^ate cer-
tain relations viiidiVill be-yoibtsHout
a little later i"':. '■• • ' ' ^ - i .'. -
' ' V-'fSZ SUGAR,
OoDoeut ailnn jTi IN=r , ' '
Osnl liy W«^hi, ^ 0<an^ io Pri-HmrBr ,,
I , 5-iS mm. Ifg '■
•i ^ l.Oift
4 '/ '> - 3.083 ■■".//.;
« » - .--^ . 3o:a -'">-' ., .
PfefTer a!^->r-.;i>ied'the effc-eV ^f-. tem-
perature on the".oa>n6£io prtssurv? -p^ a
solution of cane ^igrjrr lie used a one
per cent solution, anil me.isurcd its osmotic
pressurt^atililTiTcnl temperatures. He ob-
tained the following results:
14 .3 C
AlO nun. ITg.
044
r 0- 8C
( 22^0 C
-■MS
a6',oc
r»?0
567
rfeffer was studying osmotic pressure
from the slj-iulpoinl of a bofauir^t, and Ihe
remainder of hi^ work has to do chiefly
wilh the botanical si^nifiojinee of hia
mea?urement?. He did not puiiit out any
relalion* between the osmotic pressure of
• A normal a^Juilon of cane tiiKir U on* wlbich con-
s
OUTLINES OF ELECTROCHEMISTRY.
flolutione and the gas-pressure of gases.
This remained for aDother.
8BLATI0N9 BKTW£BN OSMOTIC PBBSaORS
AND GAG-PRBB3UBB.
That there was any relation between the
osmotic pressure of a solution and the gas-
pressure of a gas, was not suspected until
the epoiih-makiiig paper* of the great
Dutch physical chemist, Van^t Hoif, ap-
peared in 1887. This paper bears the title
**The Role of Osmotic Pressure in the
Analogy between Solutions and Gases/'
and the title ia eeif -explanatory.
Vanlt^Hi^'st at\<?^ticn was called to the
Mgoryfippfl^: woik pI;"Pfbffer by his col-
lpftgi!lj^Effi"h^irfiitorf*Tj»ijf 'Amsterdam —
,the bo^ist Be VrieB,^a3li:he took up a
I stud;^' of Pfeffer's resuTta' in connection
• -^jrtt- certain other problems in^which he
,^ji& interested at that time,^^^ He was at
'_onc^f(npressed by the rel&tCgn liietween the
TwlTMJjie .pressures of^sOiOlv*^ and their
cone6filHHoa& , Th^ dH^ogti^' pressure in-
creffa^.wil^ the c^ntSuh^tfon of the solu-
tion, atfi'the impQflanl point is that the
osmotic pressure increases proportional to
the ooncentration. This can be seen at
oneej if we divide the osmotic pressures of
the different solutions by the percentage
concentrations of the solutions, as Van*t
Hoff did. The following results will illus-
trate the point. If we repreeent the con-
oontrations by C, and the osmotic press-
ures by P; P divided by C is a constant:
H
P
If
J13^ mm, Ug,
J^A
9C
1,016
508
4f
3.083
A31
««
fl.OTr>
518
*ZtKhy.jihMt Ch™ l.<SI. EnjElith by IT C Jonr-,
S<t--rtcf Memn'r ^crifs, voJ, iv, (i. IS i Ami-r lii—\i Co >
i Vau'i HoJT wAHut that liine Hrc-ftihrtororChPinlnrr In
Amnr^rirAjji Hi* En now Prikfosujr ■)( I'hyttlcaL Gh«ni-
iitrr Jti The UDlvnliy ot Bvrllii.
iFor ruflhpr detail swTiieiTy of FJfclroljttc Dirtocl*-
lion hy H. O. Jones (Mucin llfan'O
p
The value of ,. is ae nearly constant as
could be espected, when we consider the
difficulties and large experimental erron
which ^ are necessarily involved in all
measurements of osmotic pressure.
Of what scientific value was the dis-
covery of this relation? Would it not,
after all, be just what we should expect?
If one molecule exerts a given oamolic
pressure, would not two molecules exert
twice this pressure, three molecules three
timea the pressure, and n molecules n
times the pressure? This is just what ia
expressed by the above relation; but to a
mind of the type of that of Van't Hoff it
meant a great deal more. He saw in this
relation an analogy to the Law of Boyle
for Oases, This law says that the preaaure
exerted by a gaa is proportional to the
ooncentration of the gas.
It seemed, then, from these few results
that the Law of Boyle for Gas-pressure
Applies to the Osmotic Pressure of Solu-
'tion, and that the two kinda of pressure
were analogous, at least in this one re-
spect, that they were proportional, on the
one hand to the concentration of the solu-
tion, on the other to the concentration of
the gas.
Having found that the law of Boyle for
gas-pressure applies to the osmotic pressure
of solutions, Van't Hoff naturally began
to look around for other analogies be-
tween the two kinds of pressure. We have
seen that the osmotic pressure of a solu-
tion inereaaea with increase in tempera-
ture, and it is well known that the gas-
pressure of a gas increases with increase
in temperature. Docs any relation exist
between the amount by which the osmotic
pre&sure is incrojist-d, and tho amount hy
which gas-prwpurc is incre^ased? This
OUTLIXXa OF ELECTROCHEMISTRY.
would be tested by studying the prcesurc
of ft S&8 at a giv^n t«mporfttQr9, and then
at & aocnewhat higher temperature, und
oWrvinf^ Elie IncreaHe iii preAiiure for a
givT-fi iucruue in tejuperalure. Thio, ae
is ik'tll known, hn* been very c/ircfdJy
done, nnd thi; rcnultt huvo k^d to tlu- ji^n-
IernliiAtiijn kii^wn a^ the hiw of Qay
Loftisc, whic^h snyti thnt Our prutfiuiv of »
g&fi incrt^a^is a coii&hirtt nriiaunt for (.'very
tDcreaee in lemperatuic of one degree ; and
the mcrcAAO j& pre»uro anionnla to
ooc-txru hundred oitd ecvent^y-third of the
orifi^nnl pressure of the gn* at acto Centi-
I gnvile, Ta tv^t this luw Tur osmolk prew-
■ uro Wf ahi^u^d nuiurHllj proceed na fol-
■ Jowa; The oamolic presavirc of a solution
I vould bo moaflored at a given tcmptrm-
turc, and then measured again at a eome-
vbiit higher temperature, and the dilTer-
r-ncc bcflwiwn theLwii pre»ureji noted. The
dtffvreuce hrtwt^en the two teuiperalurea
vrould nlvo bci nntciJ, and from these duta
we ct>uld cumulate ut on^ the inciettjic in
oetnottc pruMuru for a rise in tcnipeiuture
of *ine di'gri'flr
This h oxRrtly wh^it hm brtii ilorm hjr
PleDVr, as will be seen by c-xnniiiiiiig the
second at>t of hi6 reAulta, given in an car-
Ucr port of thij paper* If vo divide the
diffeKDoc buiween the oaniotic pre^uroe
st Jtnv two tctnpuriitarL'A liy the dilTi-rence
in iimipiTatunw, «4^ iihril! find thnt thr
value h not cxuelly Ibe ^anio for ijif-
ferent experiments, and ia not one-two
baodnd and eevonty-tbird of the origin^
oMQOlio pree^uxe. Thi£ might ai firat be
■ intcrpreied to mean thai the law of Gay
l«nvsncd4H!> imJ npply L<> l.hr iwniotie (irm*-
uru of noluUnns ^'^it we must nguln oon>
id<i«r the CBormoHs difficulties involved in
making good eetni-pormcablo inoml>raiK^
And In otnTing out osmotio prMSure d»-
t&rminauona with even a fair degree of
accuracy- Taking all of the«& matters into
aooouni, and, further, chat the Mjoiperalure
eijeflieiFDL of oBmoliL* pre>iauru found frnm
Uiti reaultft of PfciTur, alvayi approjicbed
tlie Vttlut oJ3o-two liundrt^d and seventy*
third, Vrta't Hoff eonclndcd thni it was
probablo thai the law of Qay Lu^ac for
Hw Iwnp^rnture copJBcwct of gae-prauure
npplicd to (he osmotic pr^aure of w>lu-
tiona,
Van't Hoff, Uowtver, made use i\l nii-
other prijuiple in twting the kw of Gay
LuftMio, A£ applinl to the oaniotic prca^uio
Qf EOlutlona. If n g&t w«re placed in a
Q]ii«ed glUiSfi Tub? and the two ^nde of the
tubci kept at ililTerBnt temperatures, ths
gfia would distribute itself throughout the
tube, eo tJiat the prcssurt would b« the aame
at every point- In the wurmcr portion of
the tube a gas moleuule would oixort a
gM'Kier pressure than in the cooler por-
tion, Jind, cuiisi'^uently, the giia would
tend to become more dilute in the wonncr
portion and more coDocntratcd in the
coolor portion of the tube. Tba diSer-
enee it eonecntrfttion cronld be ealenlatad
fliroretical ] J from the law of Gay Liisaac,
knowing the difference beuweeu the twn-
pcraturea of the two L^nde of the tube.
If a tube id filled with a bomogeDeone
lolutioD and one «nd kept at a Mgbtr t«ni*
pemluiv ihan i\\a iitlinr, thi? ■uluiiiin
will become moa* dihit4^ in the n;^iou
where the t^mpcrattiro if higher. Thia ia
known o^ th^ PrincifU of Seri\i. If the
taw of Q^y Lu^ao appliea to iha tempera-
tun codCdent of tba osmotic prwsure of
nolulitm*, we eticjhl craleufaid riie difTereicee
in concentration In.-twL'vn thi' wunn^ and
colder portiona of the tubc^ knowing the
diff^r^co in the temperature*; ju*t lu
we ^-ftn ealcnlale tho differeno^ in th«
10
OUTLINES OF ELECTROOHEMlSTRY.
concentrfltiona of a gaa, as deacribed
above.
The eiperimenta were carried out by
filling glass tubes with a homogeneous so-
lution, and keeping the tops of the tubes
at a higher eonstant temperature than the
bottoms. After the tubes had stood for
wliat was supposed to be a sufficient length
of time, a measured volume of the solu-
tion was removed from the top and ana-
lyzed, and a measured volume removed
from the bot:tom and also analyzed. Know-
ing the concentration of the original homo-
geneous solution, and the difference be-
tween the concentrations at the top and
bottom of the tube, we have all the data
necessary for testing the Principle of Soret,
as applied to solutions.
The results at first showed smaller dif-
ferences in concentration for a given dif-
ference in temperature, than would be ex-
pected if the law of Gay Lussae applied to
the temperature coefficient of the osmotic
pressure of solutions. It Ihen occurred to
Sorct and others that perhaps the solution
had not been allowed to stand long enough
at the different, constant, temperatures, in
order that equilibrium should be reached.
It is well known that the time required for
equilibrium to be established by diffusion
alone is very great, and, of course, all me-
chanical disturbance of the liquid must be
avoided in these experiments. The ei-
periments were then repeated, allowing the
tubes to remain undisturbed for a much
longer time. The result was that a larger
difference was found between the concen-
trations of the warmer and colder solu-
tions, for a given difference in tempera-
ture, than in the first series of e:tperiments.
Results were finally obtained which are
very sat ijf factory, as the following exam-
plea will show;
The two portions of a solution of cop-
per sulphate were kept at 20 degree
and 80 degrees, respectively. The change
in concentration calculated from the law
of Qioy LuEsac ia 14.3 per cent; the dif-
ference in concentration found is 14.03
per cent. In another case, where the dif-
ference calculated was 34.8 per cent, the
difference found was 23.87 per cent.
If the tubes had been allowed to remain
still longer, it seems probable that the
values found would have agreed even more
closely with those calculated. The dif-
ference is, however, so small that the con-
clusion is justified (hat the Law of Oay
Lussae fuf Gas-prfssurc Applies to the
Osmotic Pressure of ^ohitivftJi.
The applicability of the two laws of
gas-pressure thus far considered to the os-
motic pressure of solutions, simply shows
that the two Kcts of phenomena are analo-
gous, but tells us nothing as to the actual
magnitude of the two pressures, or aa to
the relations between these magnitudes.
We must now take another step and ascer-
tain, if possible, what relation exists be-
tween Ihe actual pressure e.xerted by a gaa
of given concentration and at a given tem-
perature, and the osmotic pressure of a
solution containing the same number of
dissolved parts in a given volume as there
are gaa particles in the same volume; the
osmotic pressure being, of course, meas-
ured at the same temperature as the gaa-
pressure.
Van't HoJT compared the gas-pressure
of hydrogen gas, with the osmotic pressure
of a solution of cane sugar of the same
concentration as the gas; i. e., having the
same number of sugar molecules in a given
volume of the solution as there are hydro-
gen moieeule^ in the same volume of the
gas. The result, whichis very surprising, ie
OUTLiySff OF BLSCTROVHKMi^TRY.
U
thnt, iht gnhitloH fXerUd an ostnutlc yrtsA'
eirtf Vfhich was cxacily eqaal to tki ga^-
prt^surr i^^crted btf the goo, tind aiucti ike
Loit i>f Ai'O'jO'iro Apf^Ii/^n to Cjfwtw, /(
Mratf, Ifii'yrforr. Appltj to Solritiiirw:
Thi" liw c»f AvngHilro, a* applied log;ises^
«UtG« thnt Ck]iinl vgliLiDes f>i nil gn&es at
(hetametcnipcrahirG iind pressure contain
tho MTDC UTiDibor of ultimiito parU Ae
applied lo Bi^Lutiona ii wculd t>? formu-
latH thus; ^i\na\ voIliiul^ of hH eolutioiia,
which, it the ftaiue lt'm|>tralur(^ kdvc the
aacnc o&tnotic pre^un-, conuin the aome
Duoibcr of ultimutc parU.
We have thus far seen that ihe thre^
funibrnenUI hi"'s of gji5-[)ri-ssiire HppI)' lo
thir ii*mo[ic pressure of soluliona ;* but w
know thnt there are conditiona uuder
irhicli Ihcsc Jaiva do not bold for the press-
uica ex«rt«d by gH«c& If Iho gas^^i uro
fery ronrPTtJmt<i<J, neitht-r the law of fU}y]v
^jnc,4bal of Gay hn^nc will apply to it«
^T^fiHlfG- The rojjit^ons between gns-prcH-
ure and oamolio pros^Liro aro all tlio more
ftrtkinff. in thai for the iame c^n^itioiw
urd*r which tlie laws d>> not npplj tn
ipuy**, (hey *lo nut applj lo iUl^ osiimtie
piCivun; of *nlutiGii». Although it i» iin-
pot»ib]c to mca^urt; dir^^cUy the osmotic
Ifnwuro of concijritinted ^olutionfi^ tliuro
tres nnmbor of indirGOl. methods of doing
*o; and from the Tpsiilt? obtnitiLMl by Wv^m*
mUteel iiiL'Eliod^ iL ib quiU' ccrUiii that
iieiElier the la^ of Uuylc nor that of
Gay Lu=3Uc upplles In the o&molic preeaare
of coiic<.'niratcd solutLona.
Tho relation* bttvcwu ^^ai-pressnnj and
ORiRorLC prtsmre nn tprtwinly made wry
tirWi'iDiL hv th<- ffld, tbnt tl:<* thrn' fimda-
mental lava of gas-pre^ur? nppiy to the
■ For ft fiillsr dl'diailAu {*r ifi^a *i»l'i>ci. vl'h ihvrEii«-
lADiotJcT pressure nf soluLian^, but Ihm9
relations are ccrlninly mnde much cloier,
ami ticcomc more intCT*-iting, whtn vre learn
that utkdcr exactly tho eiinic conditioD^
which present exceptions to the laws of
gas- pressure, we have eu'epdona manifest-
iDg themaelveft io Ihe same sensH, wheu
nc attempt to apply these law* to osmotic
proegiiro.
aiti.^iirJOANC'i; oir riic Aimvn oblations.
Tho full cjffnificancc of ttic above rfllft-
tlons botwova gA«-prM(ur« and oemotje
jji'esBinv, iimid br iippnvinti^d only by ont*
who ha* a comprchcnsivf knowledge of ibe
wlioli: eubjri^t of toiwlcm physical chrniis-
try- Tho importance of thceo relations
iu certuJD dirGCiicna U, Irowuvvr^ ^ obvious
Mint it :^iTinof. fnil In Yif rerflgnistd.
The fact thai lUu onxnoik preaBuro of
eolutionf] obt>'fe the gm lavs, make* it poaei-
ble to deal with iuJuiioiu in mjmy r«pecla
at we deal with j,'aie«. B<iioTt Uicno relb-
tioiia "pP^-i-e Itriown^ lli<f whole subject of w^
luliuns M^iimvl til Im^ nf ju't'iJiiihirv inter nL
and iiaportADCC It waa recoKniicd, to bo
«urc thfit most chcraicnt rcoctioca toko
place in aolutioD, but there wae no officient
Tneana of denliiig with ^oliitiona aa eueh-
Any one vl» la at all familiar with Iha
]*njK-i|di'B uf |llL^^icx kiumh full VivU Itial
matter id the gaseous alate leodt* ilsi^lf to
our mvlhodfl of inveati^LioiiT f^^^ VAptxiiiV
ly to nifltbRmaticul methods, lictEor Ihnn in
any rtther form of aj^gregalion. We cnn
rcadilv apply tht^rtnod^nainies to guve^,
and it njay be ^aid in general that ire
know far niore about matter in the cen-
diiion of A t^u than m the condition of a
liquid; and, in tarn, far moro abotil the
tirjuid eonJitx<>n tHuii ahout ihn srilld. In-
dwd. nur knowledge of matter in the «olid
fitatCr other than its cjitcmal for:n, 1% after
It
OUTLINES OF ELECTROCHEMISTRY.
all, very superficial and most uHBatisfac-
tocy.
Since we caa deal with gasea mathe-
raatically^ and since the laws of gas-press-
ure apply to the osmotic pressure of solu-
tions, we can apply mathematics to solu-
tions in a manner analogous to that which
has been used with gases. The result
is that the very greatest advances have
been made in the study of solutions,
since the relations described in this
paper were pointed out by Van't Hoff
in 1887. Since we can deal with solutions
by entirely new methods, and since solu-
tions lie at the l>a8iB of most chemi-
cal phenomena, we have new methods
opened up for dL'aling with these phenom-
ena^
The imporlance of these relations for
the subject in hand cannot easily be over-
estimated, as we shall probably see before
this series of papers is concluded. Their
influence is fe!t throughout a large porr
tion of the field of electrochemistry, and
some of the most important developmente
in electrochemistry in the last fifteen years
have been based directly upon them. To
take one es ample, the action of the
primary cell. This was not understood
and not satisfactorily explained until these
relations were discovered. It was not even
known where the chief source of the elec-
tromotive force was. We can now es-
pTain the action of the primary cell in a
satisfactory manner, and can go even far-
ther and calcuhitc the electromotive force;
into this calculation, as we shall see, the os-
motic pressures of the solutions around the
electrodes entering and playing a promi-
nent role. In the modern developments
in electrochemistry, this wide-reaching
generalization connecting osmotic press-
ure and gfls-presfiure is not the only factor.
Another generalization of even greater
importance is involved, and to this we
shall turn in the next chapter
ovTuxm or ELRcrnoonBJUisfi
CHAPTER II
THE, THEORY OF ELECTROLYTIC
DISSOCIATION.
|N TliK PEKCEDING chapter we eav
I how osmotic pmsure wna ahawn to
nhtfy the same Ihw«l wa gns-prpasure,
and bo* Viui't ITotT arrived at this goii-
eralixation, which la one of ths oiosl un-
portatit ic modtTU chomiotU aercntie.
Tlw coaolntion vrould le drawn frtim
what l>afi bec-D ^i(l thus ftir, timt the oe-
mntic pren^ure of jlH ^ub^Uoces (mq-
fomiH to the gis 1qw». SucIi i» rtot the
OtM \/J any meaoe. Icdeed. there are a
gmt many oxooptiona lo this Igw, nnd,
00 eo iK<)uentiy happens^ the exoeptions
are a£ mteresLiugH or even of greater in-
tarufit, Ihan the cattee which cniifonu to
rale.
If wie wrre to study the osmotic press-
urce oxorted by ail kntiwn ^ubBtances, wo
vouLd find ihat certain classes of com-
pound eierl jiti tmnotic pressure vrkich
B^u much grsatur thaii that exerted \>j
ottflT claMGB of flubatanoea. Indeed,
cicmical compounds vfould divido them-
«lvM into Iwo great daases, aceorJiog to
ths ma^itudo of th« osimotic pn^aure
which they would excrX. The one daia
noulj bIiow a oreseure which conform* to
t^e gia Iaw3. and which we call noma);
tfa« other a prc&?i:r»> whi^h, m some- ca*<^
'^Ha twice, in olhorn three tim<^s as gr^t.
In the fc^rmer elass wb should iltid all tiio!«
iol«b(oiws like eane sugar, the ali^oliola,
aldehydes^ elhera, ketones, dc. ; in gen-
*^i, the chcmiffllly inactive Bubutnooos,
'n th« other clnae we would have the
wiJfl, bai*>t, flTid *!ilt& ; or, in ^i-noral. those
«ulj8l&nfi» whioh atie chemically moat
Kti\t
A oloaet daniioation of the two claan^
would ihffvr thoii in the former ooQur a!'
rhoii(> suhr^^anc@s whlrh, wh^n Hla^rtlTed ii
wattT^ do nol conJucl the olecLric (current,
and only thote; oj, ia a vord^ the noft-
»fcffroii/<aff. In the latter ve hara &11
thQ6« ccmpoundfl which, wlien dtMolr^d in
water, couduol the current, and only thoiw,
liuH henc'e are kuawn rix tb? ri«(;(roi|f*wr,
Vnn't Hnff recognized clcnrly these two
great ola^^es of eubstaooca, which differed
widely from one another wilh roapeot to
the Diagnitudo of the oemotio preunfo
which [hoy could exert In the paper to
whjch I'cferente has already been frequeiit*
1y mnde, he pointed out that many aoom-
alic* ejti&t when we try to apply i^*' ?«
laws to the oemotio praeeuree of eolutiona
of enbstaucea to general ; and stated clearly
that ^'^laruples in aqueous solutions are
iimsL of Lhi' &iilt^ Uje ^t^ro^ig aciUfi, auJ tJie
strong bflaea."
Vnn't HolT was not able to offer a aatia-
fflctory c;rplnnniioD of why the nondcc-
trolyie^ g'lvg oamotJc pn^fanrea which con-
form to the gSiA 1aw«, whilf eledtTolytfla
all ftiert ^trealci t)BmotJc pro«flr«, Thia
wa* reserved for another.
nmoiN OK TiiK TiieoHT or bi kot^olttic
DiaSOCUTION.
The Swedish physicist, Arrhcnm*^ wht
lit that time wai working with Chtwald
i:x Ix'ipaig, hecame interested in the ^wt
dilTcrcnoen whieh Mianifeated fhemuelvee
between tion-elcL-lrolyLea aad electrolyte*,
and cApecially in thc> work nf, nnd oon*
clufiions reached br^ Yan't Hofl. Arrhe*
iA
OarUNES OF m-KCTHnrHBUtSTHY,
niu» pointvd out that iiou*iHoatroIvt4^
(Hffi-r frnrn i'Tc('i.ml)l<'>i nnl. nnly in ihc
QtATiKilir pn>Miri'> whioh ilu*y fxiTt, tmt iii
cortnin other properticft.
It ie well hnowa thAt when a aisbatancG
ifl dit6olv(?i ji> a snlvcTt, Ihp friH*ziiig- point
of the latter i« lowered ; the solution free^-
ili^' lowiT thnu ihtf (urt bolveut. Thin IB
wdl v3:;?mplific?d in nature in th« case
oi ts^'Vaicr. which fruvixs Icwcr thuu pm-e
VAter. I'hr work of the t'rcTich t*ht*raist,
RaoqU,* had ehovn thnt tho lowb^ring of
\f\p fh^'/inp-rifhiiiT of urIit jii'odiH'iiJ by
coii-LlL-drul^^'Its dt'jK'Lded oiil^ upon the
ratio between lie namber of molecuka of
the solvent and llio*; of tho dieaolffed siib-
stanoe; L t., upon the concent rati om of iha
solution- Anj non-uleclrolyle JtiwereJ the
frivEin^Mhiinl nf wau-r ti> jgst iho wiiiitt
extent aa any other non-electrolyte of com-
paiablo cuDccnEratioE, and by compnrablc
oonocntTation ie meant the fiAnic number
of mol«oule« of the diseoWed «ubitaiice in
ji given vohime of the solutton,
A fmU'Puli' of nuy non^i^leftnilylL* pro
diici.fi jij«t the wmc lovcring of ihc fni-x-
ing-pnint of a j«^ren number of moit^'uliTn
of ffater^ a« a inoleculc of niiy othpr non-
electrolyte.
The eleelfolyles, however, Ijehave very
tliffiTtTitly With rt^peel in their powiT to
Inrti^r iky ! tvi-rAV jZ-inuui ni a jjuhont, Thi;
loweHfiQ produetd bij thorn iffos always
grBator tbnn that prodtieLv] by the non-
electrolyt9<< Tlcre we hnvn rcEults ^imiinr
to thow obtained from a study of ihe
oftmolic presauies of eleelrolytea and non-
r|irctnjktt-s, T\i*f fornur v^^ri n i^ryntvi*
osmotic pnstnn*, iinJ producH^ a ^n^uU'r
lowering of the freezing point of the bdI-
vent Ihnn the Inltor. The ^5^6:119111 he-
tweeu the two ssU of phenomena is more
thnn *nirilil]ilive. We huve awn that thp
oh'clrolylfs escfl twlee, and in wmie ca«c«
throe timet the oamotic pre^fliirc of noD-
olecti'Olyted of comparable cooocntrHtK;nfl,
So, hero, we find that ttie eleolrolytee
lower the fri-vzin^-pfiint of watw iwicf,
dnd In surne va?e^ lliree liToea ua niudi
aa thi; nwin-lTTtrctlvtea uf :;oTnpflriible cun-
centratLonA,
Tho imnlogica between the propertioe of
the two great daises of chemicnl com-
pmintb are not yet eihaiialed. It h well
known thai the prraencd of ti diasuWed
aubstiiiif^e lovriTf th^ vApoMensiou of the
soU'cuL Ifjianlt aUo showed Ihut nun-
t»leetrolytes produce the same lowering of
th^ v^apor- tension of a solvent^ if tbt^y are
prL^aerK. ul the unriit mofLTulnr (^oncen-
iraiicn, regardle&g of tho nature of the
Qon-cloclrolytc- Electrolytes, on the other
hjind, nlweye produce greater lowering; of
tht- vapor-tonsioo than non-elect rolytee*
anO, again, in winu.' vtm-s iwiee the lower-
ing, and in other ea»ies three Uiniw th«
lowering.
Those wore some of the facta which had
to be dcnlt with by any theory which would
account for ihe diiTerence Ijetween non*
eleelrolyles and eleetrolylea in aolation in
wnter It jb cljTiouti from what Ima bwn
^nid that all three of the pr^perticf con-
sidered — osmotic pressure, lowering of
inv/mf: pomi, iitnl bwonn^ of vapor-ton-
&ifiti— -nnr properties which depend upun
iimiilnTiTi (ntfy; the mngnituile of each and
all of them dependinji;, as we have aecn,
only upon the ratio between the number
of molceuiee of the dia&olved Bubstanov
and the number of moleotilea of tbo sol-
V4-nt- If these phynnmt'nn depend only
upun niimbf!is, Jiiid if they have a ma^-
ndude grc/iter thfin wctJd be expected.
OUTLISEH OF BLUVTHOVitUMlSTHr
IS
tli« only ooncluftton is that i}itr^ am a
larger numhcr of parts pr«flrU than we
would expect.
This is esstctinllv the way Iho problem
prewnttH ilself m A rrlieniufl. We aeem,
IbeD. fon^d to [he raciduyion IhaL In kuIu*
tioQB of eIi!clralyt«B (ocida, bitH&i« and
•Hl^}. ve hnvc more pnrls present thnn
eorrespond to the molecules of the
mtpiiclivG Bubatjincefl. Th& questioa iiftt-
.mtlly aroBo, how is this pni^^tlblo f A
nolccule tft tbe eimplofit anU of b i!Om-
piMind of which we can conceive, and yet
ve miut Imvi' imrtideF in soIntloD ^vhich
are more numiT^iui Ihaii the motoc^tilo*.
TbQ mnvitublo conHu^ion i« that th«
MoJrci>h.*fl thnmpplve* m»Ht I)e bnikfln [!own
into pane. But (bu dilTicuUv was b;- no
xncaDfl as yet overcome. Hov coiild vc
coDodivc of the mij]4^culftrt of «ich nxxh-
iiMoceit hk hy^roMarlc ncul^ potftnniiin
livdro.Tiili'. <ir |viInti*iiiTn pblorule^ brfftlcing
Aowii iii tbc jmsi'Mce of water into *im-
l>]cr parts? ff a Auhstanoe liKe jKrfjAEmium
chloride should break down into putnwijim
ini chlonny, Iht poiasjium wouhJ net on
■aler wUh it* wuU-known vigor, giving
fpUiaiam hydmuli^^ ind hy<3rc^^^ii gst9.
m know, h£>wpvrr» Ibal ibih is not the
Qtt. r<»t&f«uiii chlrjriile diA^olved in
^Iw ^OM not act chamjwilly at .ill upon
tbtwator; the only chanff^ producvd Ir-
llig a flight obflngp in tompLTatyro, due
lo the •olid pns^in^ into unlntion. Wg
«M srem to bp in « hopi^li^wi rin^mma:
ptwuonwufi such a* wc have been conoid-
'^"ff dcrnandin^' thnl Lbe rnolet^ulta of
*J»npjlytes break down tn soluUonj and
the nature of electrolyte* boing sii(?h thnt
» •Wnw IrnpOHiible (h«l any audi d^com-
pf*tionn oouM tnkc place.
Anhcniua, however, did not give the
p^hlftm up, ii« men I«» oameat might
hfivc donc» bnt went to the literature to
@co whAt 30ep:Ptions had nlroady been
mode to acoounl for the condition of
acids, baecB, and ftaltg in solution. H«
found that WtlliiiEMiion had prop<^»pd a
qhisiry iii IS.*^! toairiromit Cor ihe 3ijfnthe«i*
of oHinaiy other from nulpburlo acid and
alcohol, which stated thai in nolution Ibo
moloculM were broken dowu nioru or I*:**
Qoraplelely into Jheir oonfltilucnt*, whiuh
l.li*?n fecombined fi^nning new nii:»l<!iTiileii.
Tn Kulntion iht^rf wn3, then, a continual
interchange of parts going on— n enoccs-
eion of d ceo m positions and teoombina-
tiona, This did not asaitl ArrhL-niUB very
much, aincQ It kit nnanaworcd (he qne^
tion, w]iy do not the psria (eny pntn^iura)
mil themically upon the i^uWtul water ? He
wa*, however, niort? successful whco ho
tiimod to a th(!Ory which had been propoaed
in 1S5C bv Chiu«iu«, to iiccoiint for the fBct
that St very weak cnrrc^nt vjux ilepampow
water. U had been ^bi>w» that a current
vhk-b wa4 far too weak to decompoic a
molecuk of wat^^r.can oiToct Ui6t]octm1y«4«
of vttkr lo wJuoh a ftmoll amo\mt of tn
electrolyte had boon added, If the eurront
could not dc£»0Tnpo*e one niolft-ule of
water it h obvious that it mvi!d not dc>
oompose more rhan one, and yet it cauwd
an appreciable uuiount of hydrog«ji to bo
ad free at one polo, and of oxyj^'o at tho
i>lh(T pole. To liocouut for this and aimi*
lar faetKj nLniitiiut adtiimt'd that i/truo fow
of llii? ri]ide4;'Lj)r^ of water 4r« aTresdy dw-
ooinpowd befon; the current is paawd— de-
compoood not into atoma, but into atoraa
which wurc chared with eleolrioity —
Iho OAA positive and Lh« othur nef^ativc,
:iiid -^all^i itiite. An ton w, ihcrtftrra^ a
vhafijfd aivm nt ffroup itf ahm^.
Thift ^ave Arrheni^ the duo lo the tx-
planation of vuch {^enomcoa aa we havtf
wTLtsEti or sLKcrifoctiic\fisTrrY,
b««ii consMfrmg. The elcctrolyVn gave
mall/ givai Jrpn^won ot tin: frv^ezmg-
point, and ulnormnHy irtvat dcpreaiion
of thi! vuportcTiiioa of the eolvonU be-
cause thwr molociilof were broken down
into inuB, The Ions being atoma or
groupe of Matm diaigoJ Wiih lilei^Lridly,
differed fund amen I ally in propcrtii?9 from
the fiaiue atoms or f^roupn when nnchargcd ;
tnd, eou*equciitIy, ilio difficulty that «iib-
slancoi like poliuiuLun uhlonde could not
hniak i1ii<wn int.i) thrir cr>n$tihipnU in the
pretence of water, bei^aose potuiiuiQ In
the atomic or molecular coadition acU »o
yigoroiuly upoo water, wat overcome, The
ion of polntaium hfla, scceiKahly, no prop-
erty in common with the atom of pottw-
aiiun, ijxcEpt UuiL Eif miiu, which n^niJiinH
iinohnnip:!^ vhi^ the atom bccoraca an ion.
Th\u arofi tk& ikatry cf chciroiytic «fi#-
MMation, in the hands of Arrhcnms.
It might, howeTi^rj be concluded from
what hn* bc^'H snid, iliLit ArHiL-miia did
OothJD^' rnori^ Ihan Inki- itliu ni^gcMlion
which liad been made by C]au«iu« and
apply il to lhe*c newly diioovercd phenom-
ouu, bat fiiph i« not tho cftte. The anggoe-
Ljon which had b*'en made by Clauftins
»H« piiTvIy [jiinlUad've, It aJTiipIy stated
that in water tlierv an- a /cu* iiiolpc«lt«
broken down into ioiu. Il did x\<ii aay
vhat ponxntuj^c of the molc^^ulce ts broken
down into iona, and Claueiuis did ni>t
point out any method by which this could
bo determined-
An^henius t*x»k tJiia puitdy <iualilalivp
suggeetion of UIausIuh and vonvcrled it
into a <)Uiintttattvo Lbcory, by pointmj; out
mothodA by which ihi? amount of disso-
ciation coutd b(! mffucuriid- If thu theory
vras tru«. the anionnt of didaociacicn &b
mM«nr&d by the diTcronr mpthode, must
agree. If different meihods ga?e different
rr*nlU, it wmjM he a very strong argiinu'iit
Hgninst tho correi:[.ae3B of the Llicnry of
electrolytic diwociation. We flh,ill turn
now to till a phaee of tho problom.
TCAtlNtJ TtrS TfllCOnV OF ELKCTbOLTTJC
nit^SOCJATlON.
[u hi* origi:>al |uip(.'r,* which hii* now
be<^omc a ciaaeic, ATrhcniua not only pro-|
posed tho theory of olectrolytic dissoeia-f
tion, but poinlL<d out methods by which ica
truth eould be tc-ali>d. If this is to beeome
n geiH^ral thinv of atduUon, it miiBt not
only account fnr lihe ntmormoUy large oa-
motic prc4«uiv cxcrtod by clt^ctrolyti^^, but
niao for the abnormdiy large frvc;:irLg-
point lowering, and lowing of vnpor-
lentinn proilmvd by thest! fiuhstnni:^?*- If
we [t^^erBt the Hue of reasoning and inea^
UPB the anujunt of dissociation by the ab-
normally large osmotic pressure cxcrfcd
by tlio elecbrolvt^i we thould oblaij] «X'
uetly the sume result ns wht^n we m^nanrod
Iphe disfificratiDn by l:hf? ^bnormnllT i«rg«
lowering of fretKini'-f^Miit. ur ahnt>nnaliy
large lowering of vnpor-tenaion prodnccd
by thEt^esubetaneea. Arrhoniua applied just
this leat t>> hie theary- He meaaLircd
ili^iuxjalion, on the oiie hnnd, by the low-
triiiK "f /r<^«ini^'-pciiht pi'ijducMi], wnd. on
the other, by the osmotic preaBiirt which
wrte c:icrtcd by the clcctrolytoa. ond oom-
pnrod tho Iwo «ctG of values obtained.
This matter is of auch gf^at hittorJoal
tniporl^nee iu eonneclion with the devel-
i>pin*?nl Iff i\w wlialfl 'iLeory of cWtro*
lylir dipworiation. that it musl he con-
Pidcrrd in senic detatt. The fnndam*'ntal
yirmnpiii und^rlyinR the dedurrtion of
ArrhoniHi ]« ihal an ion eyerie exactly tho
•On \\\tj T>ti*-04»| -'■1 of eii>pM4Bf«B lilBH:ir%r'1 -n Wb|*-.
i^Ftihf It^Ei* ifti'tl F, Oil. TrA|iiiUi«il liitif r.j) ll-h \ff
fl I.' JkvtiVl, hSin*"** \ttri\i-ir <^-r\t0 |v, p it. <ATQ*r.
Ot'TUS'fTS or &LBCTROrHKMttiTItY^
IT
>
prodded the fXitK- ft^vcriof of the frccx-
mif-fvoint oDtl of Uie T»pOT-te;iHioii of a
•olvcBt ii« A motiJculOi. This fnllom from
t)i« fact, whidi hn« Rlriiidy Ixmn pointed
mil, thai tlx«r phpnon^'nA d^pen^ onl/
pmd»l iti<Iitidtal», fheir inilu€iK» on Ike
]in>|)ertic» II cxuclly tlx* aamif as mcle-
Sincp wi* T'JiTt *li>iil willi ioH* ami iuo!e-
p«l(oi iurliwrimTintrlj in [Mintu'dicm wilJi
tliese pr<^rl«9, (be i:«l<mtation of th?
I>f*rccntncc <V- " i ■ ■ ■ bj moanf of oe-
Biolii: j,irt>»iiti iiix'-pfidl lo^f*rm((
bMonift tM7 tiinpT^. Suppooe we ard
dealing: wltlt a V.nnry cloofrolTte; {. «.,
whh uJir «'hi(j] tJiK^ix-iar.™ mio Iwo loD*-
I( it U not dinociatcd at all it vill «ert
the mno onnotk prcaAurc, am! produce
tlur Mint lowniciE of tbc fiwxJua- (joint as
Ba non-«loct?i7lyt« of the «flin« ^oncontno-
Hlton. If k H ccuiplctely liissociatod it
BvEll produce :«ice tliia oarootic presanro
MRil lowuriii^r of frc<zin^-poirjt- Jf it is
portlr dlMocialed ii will produce an oa-
uiolic preworo anil IuivL*rJiij; of (m^lng-
poinL which BiM comvwlioro bolwt^f-n llie^o
tainn. Ut ftir.pli? proi^irtirjii, Uie]^« ve
ohtain at odog tW amoiint of dUaocia-
lion, knovinjr the iwmoiic pnv^un; or
the lomvhDg of thf friHff;tiig.paiD£ uXi^rtod
by the vnb^tAnoc
Arr^wfliiofl prit^edtd as foUowii; TW
lowpriiix of ibi^ frt«iii^-poiot of water
produced hy a K^io-nioleoular woight of
a Don-ck-ctHvfr in a liir<r of wtution ia
l^SC, iSnvh a aoluttOD id, of ootu^, a
nofmol aoltilion, ^ ihia esLprotaion it uiod
in «hatiiUtr}-: and the quantUy. \^M, fa
known aa t^« molecalar lo^rering of tha
ira^siDir-pAiTit of v«t»»r, or tho fnH-rio^-
t oMistanI of wai4T If tho fn^^jni^*
fioiiit loi^'rHng aoiT)«ll<r ol»erred for iha
fleclrolyLe of nonnal coaceairatlan &• I**,
I ho ratio belwoen Chew two doea i»t
I^LTir Iho di^AOciaHon, Enit (tiTOs a coeffi*
cKni i; whidi. from ili diicoivrvr, hjU
come 10 be knovn aa Uiv Vnn'I llolT i.
Vram Hw fm^ifig-puint lowtring tliKu,
t'
^ " P (w ' "^'**' Ji*M»dfctiwi « ia oU»
tallied At ODOo from tilt cuefflctenii. For a
binary doctrolyt** q = i — i j for a tor-
a^try «](vtrolyto, a^ — = — •
Arrh<-'Diu^ Ihcti cakukted tbe raltta of
i from otiinouc preeaur^ u fbUova: If
wo rcpreaenl by n tlto nombor of uiidia*
»oc:ato<l roolccuk« pn^^nl, by n tba
nuiril^r of di»odatod nwlocvti?*, und 1^
i; tho numlvr nf iona into whit^i naoh
molecule diaAociatefl. vo have
Thp rallies of i v(*rv tbtw calt^laUd by
t*o ^tir*Iy differmi melho<l*i it now
roinaliitfd to «% whether llie tvo aeAa of
TaluM affTCod wiUi c«ch other, or vhf^thcr
thoy did not. If thero waa an a^fremient
it waa A fitroQg argumi^nt m favor of the
corrwtnwft of thi* new Ihenrj; if tJiew
wax not an aj^rr^mc^t it would b* uo-
Tortunate for the theory. A t«ij tew* of
eke r^ulta which vera obtaintd by Arr-
ht^mua for aeids^ boacaf aad eaU«. xtc jci*'^
b&low:
AciDa.
Nulphiitle
HBUv
1*1 ^n(
I «
I U
aff
IM
i<a
Ifc" MtP
PrWMtrv
f l«
i.ea
•Fttra rtilliT 4l««MMfli nf llili nftiBM vttb th- r«*t|la
w
OUTLINES OF ELECTROCHEMISTRY.
BASES.
L from FrenJug I from
Point OHmolLc
LowertEUf. Pressure .
Potaaluiu hjdroild«. i.fti 1.04
Sodium " x.« i,ea
Barium - i.99 if, 07
GotchiiiL <■ s.aa a.AB
AmmoDiuni I.OS 1.01
SALTS,
PotaBSium chlorldB.... I in l.H
aodtum " ... l.Sii l.ftt
immgnluin " -,,. J,8& 1,84
BfKlluin nllrutfl i aS 1>Z
Pata^Blu oacifinlfl..,. l.tK 1 83
Sodtuiti »rbATive . !.1H Hit
fltronilum nlnare. ,. <,» ».*1
Lend nkritle V 0^ S.OR
Cuprlc a«lale 1 .BS I .QG
These comparisons were made for about
15 baseBj S3 acids, and 40 sftlts, and while
Bome apparent discrepancies, appeared,
still, an unmistakeable agreement existed
between the two sole of values.
Almost as quiekly as these agreements
were points;*! out for so many electrolytes,
the theory began ito attract attention.
Here were facte which, from their nature,
eonld not be disregarded, and from their
number could not be referred to accident
There must be a large element of truth
in any generalization which accords so
well with so much experimental data.
This seems to he about the way in which
the whole subject presented itself to the
more j)rogressive men. some 14 years ago
when the paper by Arrheniua appeared.
They saw in this theory a genftalization
which was capable of accouutmg for a
large number of facts which, before it was
proposed, were entirely inexplicable in
terms of any conception known at that
time.
The theory of electrolytic dissociation,
like all wide-reaching generalizations, was
forlunate in that it did not escape criti-
cism from eonscrvalive hands. I do not
refer to that kind of criticism which is
based upon a Inck of familiarity with the
facts involved, and which was poured out
in abundance against thia theory for a
time from certain quarters; but to legiti-
mate criticism, based upon real difficul-
ties encountered when an honest attempt
was made to apply it to certain classes erf
facits — a criticism based upon an earnest
desire to arrive at the truth. I have re-
ferred to this kind of criticism aa for-
tunate, since :t puts a theory upon its
mettle, as it were, and sifts the wheat
from the chflfF. If the theory hae any
value it will be brought out, or, if it is
inherently incapable and worthless, it will
be overthrown before it has done any harm
to the advance of science. Ji was such
criticism as this that made the supporters
of the new view look around for evidence
bearing upon it. A few of the many lines
of evidence hearing upon the theory of
electrolytic dissociation will now he taken
up,
FURTHER LINES OF EVIDENCE* BEARING
UPON THE THEORY OF ELEC-
LYTIC DISSOCIATION.
The theory of electrolytic dissocia-
tion says that acids, bases, and salts in
the presence of water are broken down
into their ions, the amount of the dissocia-
tion of any compound depending chiefly
upon the oonccntration of the solution.
As the dilution increases the percentage
dissociation increases, until at a dilution
of about 1,000 litres,* the strong acids and
bases, and the snlts in general, are com-
pletely dissociated. These substances, at
this dilution, exist, then, only in the ionic
condition, there being no molecules pres-
ent.
•Th«/tw]inp*nf nvJdeDcnfi)rililHll]eory,wbkh wU>^t
coosidered it\ [h.- rrmalndi-r of l>Ms chftii'"' ■•* 'i^S-
cuiMed iiLore t-Uy ami nin^^y ollitr Jiii?? art- l&ben up iu
mr boob, to wlih'h rervrrnct? Irna alrPAiLy 1>«#Q madA.
Tlieory of EkrimlviLc IMA^ArliiUua, OlacinilJta^O
■TM* m.'jLnri n ■> Ami -n nUitr^ contairK » g:taiu-mo\tc-
DiAr wi-tght at thif til?c[n>l J le la l,i>Xtlilrei ot ihe »1d-
ticm.
OrrUA'ESS OF ELECrnOCHEMISTItr.
t»
It ia 4^vious UiftL the proporlie^ of audi
aolutioni qI these substances must be tlif
properties of the ions present, and ii«t
tho«c of the moleculu^T einct^ there are no
iiiol(K!iilo« in thi! Dolucioit- Tlitg appliee
U^ All thf^ pmpfiiir-fi rif &[]r'h ^rtiuhons, l^iot.li
phjrficBl and chonucal' We bave in this
ihc% a means of If^fLmg the corroolncse
of our theory, aa wc shall now see.
Let 118 take tip oertaln properlie^ of
tt)ni[*lfMy iliR^r'iflk'fl soliit.ioHs, «n^ iit
rtivdlier Ihej sre aiUlltivi!; i. u,^ Ihe iiiiiii
cf the corrcspf>ndmg prt>pcrti« of the ioD*
LldwA ftro pra^fil. Wc «hAll consider firel
rtttl|p^/^<? gtuvity of soMiflng of ctri&in
"If a salt Is flddLM] to water, th« volume
irf llie Holuiiun ia dilTcreiiL from that of
Ihe pijre solvent, aud olno from the eum
of the v'olumt-fl of Iho liquid and of the
•did. If the rtialting solulioTj U verj'
I ^]lt>U% tho snlt is 0Qin|>lL?t*').y iiiiodntcd
L.inlO iU ioiu. NLTuat hu,-« chf^Hn from tlie
f Mnitt» of J, TrALiW, tbflt the chnngc in
T»kBic. under i^uch condiUnne, h an addi-
'JTD piopony of ihf ions. Oivon a solu-
tfao eontaining a gram -molecular w«tght
of a nail whow ninWular weight \n M, In
m Rrame uf valer. Let the specific i^rAt*
iljr of the m>Intti>n he B. the apoci£e
grav^ity of wotur s. 77if change in veinmc
£tt, on ditsolrin^ tho ^It, will bo :
V 4- '" "I
i^v =
*he follovring refialia arc f^ven:
KC -«.T
>na - 1: T
KBr-t^ r
KAhr = 9B T
Kl = O 1
Ml =30 1
,ini* ^KH -*-*)
^ Sfftttf - <*< I ^ »i f
lEI *IIf! ^nz,
1 KOI - S«C9 ' t^O
'•*!W-mtV\ = iiA<
KBr - K«llr = ?t.l
1 Kr -\ai =v,i
*llilB narMni^t* <* nrinivd fram lite Thi^ry nf KJ««'
"ThcM toEulta flhow ihe atldilivc nature
of the dpocjtlc gravity of ^It ffoluticn^.
Tlie di^ereace botwecn the chloriDO and
the bromine iona U abon: 8,7; tetwoen
I'hioriiiti and iudijii^r IS. 5; between hro*
mine aiid iodJTiVj 9.8; while belwetiD
pntn^tum and todium it is about 8.0.
"The oddilivc nature of i\\t specific
gravity of salt eokitiong had, mdced» b90D
^oiniecL out mueh earlier hy ValBon. Be
hnd ihovn t^xncEly whaL is hraiig^hE out
ahiivt*: Otvcri wilt imluliuns of romparahle
concentration; i. t., contntnlng, say, a
^fTfim-molffiilo i>r thr pjilt per litro; the
differeneo boiwren the apocilc grovitice of
flolutiom c-ontaining tvo metals corabincid
with Ihe isnie aeld is eoiHtnnl, whatever
the juturi' of Lhe aetd, diuillaily, tJie
ditTt-rencc bctveen the fpeciOc gravitiea
<^i two Golta of the aame icid With any
nietn! ie coTiEtatrt, regardleec of the nature
of the metal Thp spi'dfie gravity of n salt
solution is then ntilniucd by bidding to a
constant number two value* — the one for
the acid, the other for the metal- These
values Val^on termed 'moduli'; and he
vorkcd out their valuee for a lirge Dum-
ber of element!.
'*Va!son eoneludod froni his work that
Uie inolnc!uh!s of *alti» mual he completely
broken down in Bohitioa But the evi-
dence in favor of such a view waa aol
etrong enough at that lime te bring it into
favor.'*
Ono other projierty of lolulion* of ialt«
vlll be conaidipri'd in thi4 conm-cLloit, that
h may be spen that the wh^ivn rt^kliafis
;tre not merely aeddentah When acids
and bdACd nentralixe one aoochcr, a chance
in volume in produced- If a litre of a nor-
mal anitition of n itnLtalenl aeid ii
brought together with a litre of n normal
solution of a tinirslcnt haae, th« nmiM-
»
OUTLISEB OF BLSCTROCniSMti^TltY.
ilLg voluiutT LH 1101 Lttu !Urt<», but some-
what Ic^t thcTv being, in ^ncral, a con-
trcctioD in vol u roc.*
"aVw? change of volume produced by
D9Utral::img actd^ with bsBO^ hag been ex-
I«DBivc]y studied ty OalwaH. The flolo-
tionj coiitaiiii-iI a grnrit-wjuUhltut of
the ncid or bnsc, in a Icilogrnni, ami wore,
therefore, not completely dissociated; so
tlkAt if Iho oliangi? in toIuuk' wjis addi-
Tivo, it woTil*! be Bbown only uppr^Jxi-
ntfltfly by »ucb salulions
"Oatwald worked with 19 acide, inchid-
ing the Btron^eet icincral acida. and eomo
of the more etrODgly dlseociated orj^aniG
aeida. He Dsalralued these with iho three
bjLArs^ ]iri1ii&sium« snilium nnd niarnoniLirii.
A few tif bis reMills ore given^ the (change
in rolumc bein^ expressed in cubic centi-
metKe The diiFcrencca in the honsontal
lineB aro Ihc i^itforonoea botwoon pota^-
eliUD, sodium^ and ammonmni, in (?oinhiiift-
tion wiih the aarr.e aeid. The clitf^renw§
in the verlkal euUtiiiiu nrf. the difference*
Wtwix^n the difTcrcnt acids in combiiiution
with the mmc ba^^f obtained by 5ub-
tmcling the value for the acid from the
valua for nitric acid.
ruiiiLtihaif
JtiiiH^lDlo Hid.
ia,9a(0«o}
lljdr»i.ia?
torn-
ItltiOIStl]
(Il,fl4>
' IT M t«.Wl
" If WO take the per|K»ndicu!or rows in
imn-ntlif*.*, w.^ fi \n\ vi-ry m*JiHy n ociiiMunt
diifcreilcv for >he iitr^n^ nrids hdiI basea.
Similaily, if ve take the homozital row«
ICtiviinil>Ut I>tiwKiuE]»Ei llMJitiinllliiirx.)
in pwrenlhese*. wc find very nearly a enn-
etant difference. This mcatts that the
differeacc in change of fijlume. produced
bj neutralizing two diffcront bafloe by a
given acidj ia n condlanT, indep^ndett of
the nntine of the acid; and^ similarly, the
difference of the chuiige jn volumi? uii neu-
traliaing two diffvrenl aciil^ by a ^rcn
ba^e is iodependcnl of the nature of the
base,
*'The change in voluni'-, wbrn afifla and
biisi^& rifjiilrnlizL* ra<'h ^Uvr, Uko fhp aprn-
fic gravity of ealt soluUonfl. is. then, an
additive property, depending lK>th upon
the natui'o of the ae:d and of the bQ£e;
and wo could work out here, aa Valaoc hai
done in llu? cas* of sjjecifie gravitiiSr Ihc
nuineriefll values of llai eonslwnU for cucb
const itucct."
A number of othor physical proper-
tics of eoluiions of com|ilatHy diMoeiiWod
enbst&ncGS have been studied in n manner
vinalogoiis to dii? ahcve, with the result
that they have been Bhown, in general^ to b€
the sum of two conslacte, the one depend-
ing upon one ion, and the other npon Ihe
other iL>ii. We ehould mmlion, especially,
the r.tiIor of soMiont of <?ompWe[y dis*o»
rialed substnucifi, OsLwntd has carried
out an elaborate study of this property of
sohitinns of nbo^il 500 colored subataticca.
Only a few of hie resuHs will be con-
sidered here^ and we wiU tak^ up one of
Ihe \iesl knu^ii And sini{>k>4t vuw^ — the
prruiftngjtnnlts. The iJciumn^aoatcs all
diagociate in a manner analogona to
pniflfisiuni permnngnnatc:
KMnO, = K -i" MnO,.
The poUfiium Ion U not colored^ aince it
rxists in aolntimii of pntjiMium rhiuride,
nitrate, Bulphaio, etc., and thi^s^ flolutiona
are colorloes. The color of such flolutiona
OVruySS op ^LBf^JROCUBUJ&TKf.
tt
mu«t be due, then, entirely to the presence
ot the MnO, ion,
Tlib fi»me line cf n.4aoTiiiig boldd for
nil |M>rmiingiinrt[eB iu w}iich the raeUl la
c61drl««£. The color of tbu soluliooa of
tiieae stilts must l»e due entirely to the
pTceence of tbo ion of permangunie acJd,
MnO^. Therondnnion U tJml I ho color
of aolutli^na nf all the pL^rniaiignnfltee, in
which the m^trtl is onlorletfi, mant be thfi
«ime. Thi* was studied hy Oatwald. vha
dclcrniinod (bo iibsorpliou speclrji oF m\yy-
ItJon« of Um\ or u dozi?ii such pcrmjmgfl'
nAti^, nnd found thnt tbe absorption bande
of sll of them f*.»II JLt eKflctl/ the snme
places in the gpectroacope- The ponitboa
I of the*c bands were measured, and Ihey
w*rc alflo phiMograpUed aod compared bv
*tiperpoiitiou. The gtnt^rai reault wjie jn^t
I whflt would be exjwt-ted if our theory were
I trnc — the colof* nf tht different pemnii-
£ftn«t<^ arc csaotiv ih*^ ^atne; nnd fur-
ther, tht mtmc na that of permanganic
tcid whieli fliwiw^iniiTf into Mn(^ *nd
Ihydrogpr, nnd Ihi- ktter intj is knnwn
*o he colorlwe ^inco soliiliona of acids like
bj'dpochloric, nitdc, ealphnric etc-, la
tvhich an ahunJanoe of hydro^^en ione are
The eonduslon from ihe study of the
colur of fioluiions, like 'bhEil from t.hn
iClidy of other jihyaicJil prtjjiertics, ]» in
perfect accord with the thwry of dectro-
Tytic diBBodntion, and it i& vet>' diJ^cuU to
•W how theec foct^ could be interpreted if
thi« f^crnliEation hail not boen rcachcd-
Evideno*' has been obtained for the Cor-
wi-'iTieM of th^! thtKiry of cleetroMif? diwo-
diticm from a study of the prop&rtUs cf
kPitt/uTWff of (tiihfltnijces. We shall tako
fii>t n mix^uiv of aubaianeei whic^li are
^iX\\y dij*r>nntrd, nrid thnn a miictnre
"f "ubstancex whiidi nri* not dirtstM-iwIrd nt
all^ Ijfil ue Uke a miztorc t>f pol«f«iuia
nitrate and sodium iodid^'. and make a
very dilute solution ot lh« mixtnn.
Sin«t both salts are readilv di^bociated nt
/[|[>fVn^le dilutions, ^e wuulJ hHve iWn
bnth completely broken doim intv their
lona, thus:
K-hXO,4-Ka+ r.
The properties of ihe mixture, both eh«^m-
ieal aad phj/Bicnlr would 1m! ihc *um of
t!ie propcrtie« of these four lona.
If Dovr vrc mix potna^mm iodide and
sodium nitrate nnd makf^ a dilute aolution
of the miiturej w^ would have both «a]tit
coinpldEely diF8oc1ated into their iona>
vhich would be:
K ^ I + Xrt H KO,,
In toriOB of OUT theory, wo would haw
GOuicUy th<* same ions in the two caws, and
t-he propertifa of the Iwo miitnrai ahoold
be identical. Such ia the fact Tlie Wo
mixture* referred to above, usin^ e^^uiva-
Icnt quantities of the dilfcnjct aubfiitaneoa,
are, in every respedi id«ntical.
If, on the other hand, we- mir twr> mil>
slanu^ which are not djbaociat^d to any
n|iprecin]>1c Client by water, and diioolve
the misturc, wc would have difTertnl boIu-
tiona, eccordin^ to th(? theory, dt-ponding
upon which AubRtance* were eomblned al
the out>«t. Thus, a miilure ^t in^thjl
aleohol and "ihyl chloride would have
properliPft whiph were the aura of the
prijjTprtiw Iff Ihe niolwule* OHiOlI anil
CsHjCL The prtjpcrtitH at a ti»iiturc of
ethyl alcohol and mrtbyl chtoridc would
be the fiiTu of tJic propcrlie* of the mole-
onlfw C",n/ill and Tllid. Sinw, hi the
two mixture* the molecule are different,
the propertjea of the Iwo mirtur« ihnuM
be differtnt- Htri-, atfiin, facU and theory
are in perfect agreement. The two mil-
tun^is bavft vi^ry diffnrtml pnipnrHaa,
tt
OVTU^HS or tiLUVTJWCUEMlBTm:
it ie not easy to Jay t<K> much »tr«6ft
apon t)ie«« fAds ae beorinf; upon tb*^ gon-
eral oorr^otii««fl of *tlw tbcorj of electro-
lytic diasooialion- Wilhout this theory
such fsiCta would be entlrdy ioexplicable ;
with it they nre juot wh&i we would ex-
pect. One could aC^rcely wish For stronger
grg^im^le in favor of the (fenerai truLh
of the t.hrc-n,- *>f elt»c(roIyti^ dissocittlbn,
Ait KSrBKlMBRTAl. DBMOSSTUATIliS OF
mSfiQCUTIOX,
This ohapltr should not be conduHed
wiUiuut re/t'renc4? to n reiy t^iniple experi-
mrnf, wliirb dniioH^trut^ to tW c/o die
disaoi^mting jjctmn of n *oivcnt like wnivr.
If n few dropn of nn alcoholic solution of
pJirnolphUmloTn nre nddo^J ffi n fvlindfT
i^rihtiuing, say, 100 c.c, of ab?fihii1, Jiiid
a drop cf aqueoiie a^uiuouia added and
thL' cylindtr fihakcu, there wiJl be ao trace
of ibu piirple color which ia chanict'?riatic
of this icdiontor in the prownce of aJka-
Wt'i. If, no^v, wflJer is nihW to the fllco-
hol, the purple color will begin to appenr,
and will bcoomt deeper and deeper w more
and more water h fiddcd.
The oxplnnation of what takce place
ll oorapftmtiTely simple- AniTnonla is a
bfiae wliich is disKoeiul^dd unly slightly,
even by so ntrong a difHi04!iaUng agent as
Vtttci. By ulcohrtl it is ecflrcL-ly disao-
dated at all. Ju orJcr that & base may
pMCt with ph«iiolphthnMii it must b<?
di«*oc>atcd to sotne extent- Ainmonia in
aleohol does not react alltttlint^ with
jJicuolphtlmHuL because it \b not siilH-
eimtly distiocialcd. If, now, water ia
added, this diniociutc^ the amnion ja, and
w« hiTo our indierator «hOH'in^ iits ebjimc-
torirtic olknlino rcafrtion. If mon: »!«>-
hoi it addcil liiB dissocUiion of th^ am-
moaia is driren back, a« we ^y, and the
color di«appfa«-
W<^ have Ehu^ a demons trail ou to the
t've of th(i diMociating action of wnlcr,
i.<i;pivs»]ng il^^lf in Che co)or of tho phonol-
phtlialem,
This demi>nhlrflli*>n beririTnefl still more
instructive if wt- eajry out in addition th*
following experiment, Let us proceed eX'
actly OS deecrfbed abo^-e, usin^ a drop of on
aqiieoug ^oluliou of potat^sLum iLydroxrdt
indtend of ammonium hydroxide. As ¥4xai
afi the potassium hydroxide U udded to the
jiU'cihtil 4'cintniniDg phpnolphJliuJi'n, the
purple color appear* without the addition
of water- This fact v»e also predicled by
us' from the theory before the experiment
was tried. Potaasiuin hydroxide \a a
strongly disEOciated ba^, and jb sufB*
ciently d'iasotueted e\cn by flloohol to show
the alkaline- r«ictLon with pheool-
[ihLhnh-in, ^
Wp lidvi; thuB presented a. very tittle
(if the tnojTiuiiift mass of evidence bearing
iipon the tJieory of electrjlytic diaeoda-
tion. While certain fauta are known
which havo givan some dilticulty whec an
attempt waa mado to fit them in wiib the
iheory, the* great prt*pondh?rauc«? of r^-
denccB pomis to ita ^tieral oorrcctceaL
It should be said that as ex|>tTimcntBl
work is more and more corefuliy done, the
number iif apparent excopliona to the
theory bt-coniBs rail her less than more; so
ihai whil<* we should always welcome real
exception? to the theory, wc should not
be iTi (<jo prcdt a hurry iv wccepl apparent
disorepanc^e* until Ihev have been thor-
miphly te^cd by exper:inrnt.T
Aecepnug the theory of electwlytic die-
^ootation ce a most fruitful working
hypothesis, wc shnll csinsider in the neirt
rhaplpTsnme flpplinfltinns which hnve heer.
madu of it.
* Juift Add All m JneT'cmi Chatuciti Jininnil. avlM,
y For iL fnH-r rt|plAnitiLt»ii ^t i|ii-t 4«xrvrimr4l, iwt
Tlii'urv<ir ElKlmKiL' [>J:**p>r-inti'iri |f<i 111 US.
liT'ii itujivu (i, Iji* iluni rbii'-'lj IV <Ti|Pi«j-iiTi?ii|<iJ rrmr. h|||
QVTUh'Ks OF t:Lr:<^KocHEyixTur.
£1
CHAPTER III SOME APPLICATIONS OF THE THEORY
OF E.LE.CTROLYT1C DISSOCIATION.
■ I AVING TIfACEP in die pmcedioK tance. The fumiwlion of thi* salt wm tljR
AVING TIfACEP in die pr;-cedmg
chapicr Uow llw tLoory of eleclro-
Ij'lio disa.oialiorL arogt-, and a fcv
Uae» of eviJeufo pomting to the cfjiiulti-
aioD tlutl il eipres^es a gjQ&t truth, we
muMi now nek nf whut service the theorjr
hu bct^u, Hjis it (TJiiUfd ■■■nt uicdwdB
of dralb^ with new problems, or hae it
furnjch«d as with new metbod« of deflling
wiih oJd pmblems? Hub It suggofltod new
Unea of inveatigalbn, or hwa U been able
to coirclatc faub wIiu^Il \^tiv appua-uLl;
<ii0CDnDecU!ii? If it Jui;^ ju^oomplUlicd any
QHC of th<W thLll"^ it IJ vdluublt'; if U bUFi
ucoinplifiliud more Ihun one, so much tho
grmtcr its vcilne.
In iliii^ cliDplrr we fihull aim l« vhow
hov ilie Ihcorv of electrolytic dbaocU-
;iOEi haa bt^cn applied to a few problQioa,
QiAiuty of a oh«miea] aritiirei and what iB
itii' cliar^cter (>f the rc^ittta cbtained.
TJiE >fi;cTiuiJ Nation
^P J-ClUti A>TU
A (iWtniciil rcjirliun whicFi is about aa
fniniliar os nny othiT, it the nriJtmlirft-
Uon of an ocid by a hn*c. It hn» long
^CftD tcnoun hiLi whenever an acid aod e
bdso jri? Li^cughE togeihor. eai^h noulralizea
'lii'rtdirr *itnl n -^dt is foiiiiiHl TIih |»f'iir.
^ lit autitralix'itbn wn» looked upoD as
t Bpeci«l act f^r ctich aclf\ and t'acU Im^e,
^hfi nature of the proceed dcpcDdmg upon
ffce naluro of tho ncid med and npon Ihc
iiaCun-of tht" hfiiac* aHEfd. U wa^ rvvfi^nhM,
E^ bi> sure, thai hi iVf nriitniIi:i^M.tiin of
•cids by b«ea water is always formed, but
ihii was regard<>d oa of ac^condary impor-
important feature, and this was diffcr^ot
for i:ach acid or cnch base employed. The
result of the «tudv of ncuiriLhmt;oa wat,
thon, th« collection of a grvni maflf of
morv or less dij^ijonntcled deliiiln, betwwn
which 00 very dose relatione vtvrv iwxig-
nizcd.
Sinoe the Iheory of obotrolvtic iijifocia-
tion was pioposed, we rt-gurd the whole
process uf D^utrjiH^jition id a& entirelj^
different light. An ncid U reprL'Scnttl \ty
the ^(^ncral cxpresAion*
iu! = ii + i1,
whuro ti js the negative ion (anion) ami
(lifTerc for cTory acid, the poiitirc ioD
<<uifion] hydrogen is the s^m* for wary
[K'id, Mild ii^ Ifie ci^n^tiLueiit which iie«^n«
Hid to acidity, Whenever we have an add
in the pro^atv of a dii^ociatin^ ^oUent
like water, we have hydroson lon^ formed,
flnd. oonueraely, whinever we have hydro-
gen ions preH'iil we hava nt^idity. A buD,
in terms of nnr theory, iit in he* rrprc-
fdjtcd thus:
Boii - B + on,
K' tjcing tho cation of thi^ bflE«, which
differs for every base employed, and the
Pinion, on, is common to all baiet.
Wherever wc hnvc a base in the presence
<'f watar we havo hydroEvJ ions, and th€
tonrere^ ia aleo rrue.that whi?revr*r wo hm
hvj^ni'Lvl iariH wv biiVf ^Hiwir pnjfwT'tieit.
WhuL tak{^ pbre, tn terms of nur
theory, when an ncid ia brought in con-
tact with n broc? The anion of tho andi
0VTUSS8 OF ULSCTMCnSMISTItV,
wliidi, att vv bave seeOt rarios from acid
to nM, and Iht c&lion of the base, which
lA the; varial>I« quality far the ba^L\ remain
in {Txuctly the lume c-omlitioa utiei Ihv
ftcid and bnsc arc brought info oonUct as
bpfan>. Thr only net which iukc* plnce h
the union of the hydrogen ion of the acid
irith the hydroxy! ion of the base, forming
ft molecule of \raicr, Theae facte would
ba fonnulatod tbuB:
K + fi + OH H- ^' = ^+ ^' -^ '' A
This 15 very &ini|iTe, but the fiiiuljimcntjil
que&tion vfill r^unin^, is It true? At firat
light it appears that it cannot be tnie,
beoaiiae wo know that whco an acid is
n^traliaed by a t>aae, a snit is formed-
Thi.* aliove «taK-nieTild and the formula do
mil Uke iulo aixiiuut »it all the fonna-
tion of any »alt. How h thia apparent
diGcrcpanoy to b^ aocoiml^d for? It to
Acoountnd for \ery readily on the ^fround
that our curlier coneeptiont tif Ihe fiir-
mation of 6a1t« from the aeiion of neidft on
boacs are in error. When a dilute solution
of on acid acta en a dilute solution of
ft baaa, tht^ro ie net tho aUi;;hti^Bt reaet^n for
•appOilng that any aalt what-?v@r ii
formed; and wv art- dealing with dihiLe
lolution* of both cniiipound^ in order (hat
both may bcr compldcly dissnciatcd. It is
true that wc obtain a «alt from the mix-
ture of an acid with a base, by ovapora^
Eion; but this doGs not prove, and, indeed*
in nut (he «1fglilt<st reason for auppcuin^.
that \i uiU cj^iatH as £uch in lh« diluti!
folution of the nii^itiuc. Indited, if wc
tike the very snlt which is obtained by
evaporating; the mixture of the aeid and
base, and prepare a dilute solution of it,
th^ iioliitioii will (^iirlaiit no trko1eeiilp«
vluite\er of tlu: ^nlt, hut only the iona
into vbich the moTcculoa harr dissociated.
Thh alone would Hhow that Lbe olO con-
ception of neutralization mudt be in error
and ia a otion^ ar^umunt in favor of the
general correctneafi of the view expre«Ged
hj the above e(|watioii.
We mufct, however, analyze the ftlovv
couLtption more closely. Aucotdtng lo
the new view, all that takca place in th«
neutral ization of an ncjd by a hn^H^, in thr
union of the hydrogen ion of the acid with
the hydioiyl ion ot the base. Thia ae-
Bunies, of courw, that hydrogen aad by-
droAjl iiJiitt in Llie presence t>C out- jiLiotht;r
do coinbin*;. If we look around for experi-
m<iUtal cojil^nnation of tbiB ouumptioQ,
we find an ubundnnct? of it. Space will not
permltof a discussion of these expert men cs,
but there are no le» than &\x or seven
separate and independent linea of invetfti-
gaiion, every one of which ha^ j^bonvn that
hydrogen and hydroxy! iona oannot OKtel
in Uie profenee of each other to any uppr«<
riahle extent uncroinbim^d. Kxperimcnt
and theury are thu£ in perfect ftccord ou
this point.
Siace the process of neutraliiation con-
e^iata in nothing but the union of the hy-
drogen 10113 of the acid with tho hydtoxyt
ions of ih;? bufiy, (lien, one procew of ncii-
trahzatjr^n i^ exactly the sjime as any otiier
— the neulraliEation of any acid hy lajr
base in oiaet.lj thu aamo aa the EiL-utruliKH—
tion of any other acid by any other baae^
This point can also be tested ex peri mental- —
!y. If all prot^psses of neutral i^talion n
the aiuuet eouHistiiLg in the forinaliou of
molecule of wotcr, then the heal which i^^
lihfTatcd when on equivalent of an ftClc ^
iwtf on an eouivolent of n has**, musl tw^^
the eame na the heat ^et free wbea ai^^
H]uivalent of any other aeid avta on Hjr:^
wjuivHitnE of ih;- ^anii or any other U^sc -
This o^nelufeiou in beautifully coafirm**^'
OUTUNES OF t^tJSOTHQVHKUlSTHr.
S
by oipcriiiiciit- It has l^ng been knoWD
IhHt thp lir'nt whiHi is lihi>rut«fl when n
ililiil^ piiluliijn fif Jt 8lrnrij{ ncid ncU on
a dilute solution of & itrong bnse, is o
k;0DlUt&iLt, jndcpoii(Ii?nt i^f the nature of the
tiidd, and icdcpondL^nl ot the njkturQ of
[ th* basv- Thli will be *pen froTii the fol-
Hri + Nnnri - i;i,:»)Orul.
VAfying th« naiure of Ihe ba^e and
k44?]]ing ihe ncUT crm^lnnt, we hjtvd:
HCI + Lion = 13,:otienl.
Ht'l + KUII = l:). 700 till.
HUl 4 W 11^ fOHji = la.SOO eal.
IICI -t- }S Utt (Oil), = V^MU eal.
Tbe thermal mea^iirementB fnrMiah a
bi<4utifii] ooitfiriiiAtiaii i.»f the theory, W
in^ cucataut, in il<^ pendent of the nature
^ the acid, unci miqpcndi;z)t o( the nature
of Iho blue, to wiUilh tho Urnitu of ex-
ponmcnti] ^rror.
The atory is, however, not yat eomplcU*-
Sup^jLife Ihnt either llie Add or ihe bue
AOt eoirjpletely di^doebted, and strll
llut bolh arp incompletely dieso-
<!Uted, what would lAke place in torrn^ of
nar tlKHjry in lheai> cases?
It I'ilhcT Ihr ii.cicl or bfL^e ia ntjt t;oin-
?lrtdy dissociated, then, as the tons al-
^ftldy prcfiont arc u^ed itp, more and more
^ the iindissocifltod molceules will break
3flwn into lona, until the diswyiniion hai
fffwwvded In thv limit ami ihr luiifrnli^a-
tjoa iu cojoplele. The disaocLation of the
*>^ij^naUy undjsfiocjatcd molecules, hov-
"*f, b accompanied by tbermAl change,
We being usu;illy liW^rali?'! as dieaocia-
toD proceeds, but in t*tn\e few case^ tieat
4 abtorlv'd, Thi' hral. *tf UfuimVtTMiojt
would, therefora, b« accompanied by the
hL'*it of ionujihifni of (he eoniponnda in
question, on^ tlje heat of ionization varl«s
with erery c^^nipound uaed.
In such ca^esn then, where either the
acjd or buao it meompietely difiociated
(and »till moru when^ both are incom-
plL'te!y disiociali'd), thp hnil whieh in wt
fret! whi.'j\ ihe two are brought togetlier
is net simply the heal of neutraliEaiion.
but this p]m the beat of ioDtzution, which
ts ufTially a poaitive quantity.
Tf wr> neutraliize a weak* acid with u
weak hnae, our LUef>ry would lead lis ti)
(ODcIude th^iL the heat let free wr>u]d not
be a eoiiAtaut for ditlcrcnt eub^tancc-a, but
would vary both with Ehe nalnro of the
>Loid and the naturn of the base.
And Kinri> tUe ht^nt of IrtoizHlSon ia
iiftually positive, it Aould lead to the coa-
cluaioD that the heat of neutnUi^tioB of
weak acida and baecs would ^'enoraMy be
greater than that wl fre« when Arongt
iieida are aeulraliat^d by strong baeea. The
foUijwiiig tnats L-onfirm very beautifully
the ronelusiou from the theory.
HBAT OF W!«TT«*IJJUTIO>f.
HF H- Xaon = lC,97'Ual-
ll,r(J. 4- NftOn = U,«3i'eiil.
Clli'LCOOHt i Ntt()ir= U.K3()c«L
The theory of tdeotralyiic divvoaiation,
Iben, not only applies to the qqaq^ when
the heats of neuIraliE/ition am con^itant,
but la equally applicable to thoH oth«r
caoce where the heaLa of oeutrahfation are
not ooaetflTit. /ind whicli would appear at
lirsl eighf to present exeepiiona to the thi0-
ory. Indeed, all of these facta are neow-
sury eonpeqoences of our llieory, arid it
would be unfortunate for the theory if they
■" Vff4t"wl'lf nrt *iiti btHHtiliiijtlrDuuiiiulii^uinH
t ^'Sctqus " ^'if ""•■"*! 4U«BvelMt»ii.
• Ukbbrvatk- mUMH
£«
ouTLisEfi or ELnrrnocffKMtHrRY.
were nof, jiml whwt [)i"y hnve been found
to bc> VVc (hii» sec how the theorj of dec-
tioiytic liiBsociaHon nccfinrl^ for all the
facts which arc kno^-n conctruing the imu-
trnlkfttion rtf adda nnd hastes ; but it hns
Brr^mpliiihi'<! U'hnl is of fur ^pntcr impor-
tcncc,
Ae h/)s aJrcady been stated, befcvrc the
theory WW proposed tmeh protireg oi nwu-
trail Ration pre«Em1ed a now problem,
(3e]jer)diTTf; iipun (he Uhlur^ of the
acid nnd the rirtturc of the base used.
It WM recognised \\vtvt ttrtter is alwaja
formed when aoida and ba&i?^ rcaot, and it
was fiuppo&od that there U some vital cua-
nef'linii bolwetTi all prnc«yiL'6 of noutrnJi-
latidi] 1 bul ffhftt this wns, was not ppi-
ctived- The problem was rendered atill
more difficult bv the? Euppo^cd fad that in
Iho process of nnutralhution a lalt i£
formed, and thia rnnut he ditfert-nt for
evpfj «fid itTid bftHc whieb is use^l- Since
a different product is obtflineJ with each
pr<>oi.'S* of ccutraliaationy it ai>ei>jed \\m-
poeeiblo to refer all proecgaos of fi^itrnli-
2a1ion lo anything like a rfinimnn enase.
Wfl nuw know that nil proL'&a**^ of ncu-
tralkation of aeida aud b^eea fire easen-
tiallv i\\*i flaiiJL', canpiBliri;! otjlv in thi.' f'>r-
mation of a molot^ule of wator, A more
or leiia Ueterop;eueouA mass of facta U re-
ferred to a t!onimrni cauRP, nud thus cor-
related in n miinner which wonid have been
irapos3il>[c without l.h<: theory of cleclro-
lytie diesocintion. We ^hail leurn that
other great naasaes nf fnoU have hi*en dpnJi
with in s Aimifur inuiLiii^r, iind gent^nili/ji-
tiouB reached through this ^reat gencrjili'
2Ation, whicJi are, in fact, but corollariee
€f tt.
»TiiKNOTit f>r Anns a?*p uases.
From r-1>p foet-noti* (n un rjirliir purt of
thia papei, it would W^'athered that then?
is a close ri?lation between the "atren^th'' of
coujpouuds and the nmounU of their dis-
sociation- Thia subject is of such intpor-
tiince Ibat it mufll be lakon up more fully.
Before The theory with which we jire deal-
in^ came into vogue, the It-rm "strength"
was applied to chemroil compounds in a
more or leas indefinite vay. Variou*
methods wore adapted and used for deter-
raining ilie etrengtbs of substaaeea, and
i\\\d reaull& oblrtinL-rl ilcpL^nilpd Inr^gely upon
the melhod which was employed. It wiia
thought for a long time that of all the
ai^ids 6ul|dmrit> is ihij dtrongcal, Thj^
idea arotie apparGutly from tlie fact that
yiilplinrie aeld ig such s vigorous reagent
on all fonus of organic matter, und. fur-
ther, becau£o sulphuric acid readily re-
places many other acida from their salt*.
This erroneous conclusion was, ihen, ar-
rived Fit ehieHy through a meJ:?iod which U
not a suITic-ii-nt imi of (he sJrtngths of
ciicmical componnds. This mclhod i» in-
aulSciontp chiefly bccmioo in the displace-
ment of one Hcjd froni its enlta by another
H<id» n mjmbiT of factors coTffce into play
Litsidt!* the relative sireuglliB of the two
acids, Thiis. one of ttie compuimda may
be volatile and escape from the field of ac-
tioa a% 60on hii it ia formed, and Lhis ulom-*
ii sufficient to determine tlie direeiion and
nm^itude of ihw reaetion; or unt* (if Ow
9ubslaiice« may be inaoluLle, and, as i»^
vii^W known, this i* quite capable of con— ^
dilioning the entire course of ihc rcacHon..
As nn example of the first case, lake thi^^
action of ^ulphiirio acid on chlorides of?
tn^'lflU wbo&e Bu]phatc« are aohiblOH W^^
know that sulphuric acid can drive outiJ^
practicjiUy all the hydmohloHe acid from^
such compoundfl, the laller escaping frori]^
the field of flclion ^^ a gnu bs rapidly^
frs it \b formed. RxnmpleH of msnlii--^
ble corapouuda being formed and oon- aft measured by Ihc velocity with whirh
dilioning Ehe entire course of the reaction, they nrv capable of «lT«cttiig a oertflin
Are BO numerous Limt it inny seem super reHotioc.
fluoiu to aelccl auy coe esfliople. A whoU' i ii
oliUG of illttBtratiooa le furaielicd hy ihc [Jj-J-^-^^^m i« o nc^o
actjon of the very weak acid, hydrogen Mird? " .,. .„ »a wo
sulphide, on the sHlf^i of Mrone acids ^th fe'-^H-"-!' " «■> ri ft
(n<- heory metals. Thus, hydrogta muU aioK-cmr-ra-fr iciuia 49 js
phide will pT«ipil«te copper. M. mer- ^^^^.^^ : ;..;■;;;. Sii « S
enry, eti^., os Bulphidc-s, from their «alU OxiHd ^ .0-* iB.f irs
with the very alroogeflt floids. such ai hy- ""*'^"!" " i-*^ *"-**
ilrnrhloric iintl citrip. The mimber nf II-
Iu*trnliotia of this principle is ftbauat Urn- Tho n^roticcnt bciwccn the diaeocia-
itlc«; indeed, qtialititite annlyaia in or- ^^^^ *>' ^^^" *^^t^> «nd Ibm ohenijo«l
game chemistry ia made poesiblo by, and H'"tivity i* unniiKlakable.
bftwd direelly upon, thU prlndpla Tlw following are « lew of the rwuJti
Bntiii^h has, however, been said to tihow which were obtained from aoiiie of tha
thAl the method involiring the diapUcis- best linofl-n baao. Column I givct the dis-
luent of one aubbtariec from thi compounds eociation, II tlic r^hcnticnl actmty:
by another, i« atone not a fulficitnt cnto 1 H
rioD of the relative airenff^hs of the two Pirti»tunift|^ninWfl .. kh.u »i,u
wbmaneeH. Anm.«i«„, - <,,« ».o
A number of oilH^r method* hdve Lcitn lirruyjowiue won ivo
aeriflcJ and uicd for determining the reta- m^fXtarijn;. \. ■"."V."""V"" S,^ m
titr atr^^ngthe of sub^tuni^i's, Ijl;I thi-si', hko Trio flthjuuiio* b.4;; t.«
\m flbove, are either iniumcient in prin-
uipir* or lire diiTlr.'tjH to currj oui; in prac"> Here, a^aiu, an unuiiatakuble ugre«metit
tict; ejtiat^
The theory of clct^trolytic dtwocintion To determine the relative strengths of
hu thrown ontircly new hght on thin compound*, at preccnt* it h acly ncoesaary
wboW problem, Tho diuodation of tlie dif- to m^flj^uru tbt'ir rulaiix*.- ditsoeintirjma;
ItrruX eeidd hm kvn worked uui* nn the but tbis in only a f^mall piirt nf the bciie-
oot hanid.and then their chemical activity, fit to be derived from The theory in 6fa\-
^d the two sets of results have been com- ing witb reactions in which theae sub-
pared, Tho following are a few of tliu stancos take part. Let vs take aome r«-
iKa]1» which hflvo been obtained for somt^ uotioD which U effeoled by &\\ acida, say,
•( the more commoTi acids, la toUimn 1 the inversion of taiiL- *ugar in the presence
iKfiv^u tJit* diasi/eia Lions of the acida re- of wnitr. Thi* n.^atiEion UW pfanc in thr(
fwr^d to hydrochloric acid as lOO; in ooU pieHnce of hydrogen ions — the common
itwi U the chomieal activity of the acids, conatitucnta of all ac\<^s — as foUowa:
WVMto !• Chip " *-"!' "" 1*1*' i<>'prLj.tf of The UnllnUrL -^ i^U -f- M ^ l flilM^ T
■■■UDCfnlliT or nliuuLii b\ il^HirUnl okibitiuii iu- TIhb 4.
*B) U powkltMd dwr* fullT, and kuet^ivr ntvthrxt n*. P IT H ^. H
■nM m Chip •!, ^•"rt"* -r u
»
OUTUyBH or m.KVTHOCUE^ISTRY.
giving lint molecule (^f dextrose ooil cne
of ievulo&e.
The velocity with which this reaction
will tahc plao«r other (hinge boin^ cquitl^
daponda upon the nuiultei nf hyi^rogcn
kin* prtut'iil; i. t., upna [ih^ fliiii^niHiinn
nf Ihp iiriiL If wi- km^w Uit diasaciatioiu
of different Jicid* wc cnn tcU at once juat
how faat they would invert cant sugar,
or accomplish any aim-lnr reaction; and,
«onvijf*el^, we oar mi'iiiurc the iJia^oiiia-
tion* of dllTerenI a^irl- by mensuring the
vvldL'itiog witli wIuL^h tlicy trffcct nnj given
rcaclion like the above.
Thf rc'inrirkE whit-h liav«>]Uflt hwn uiadt'
fionnrruiufi iiCide, np^'l.V with L'qtiiil inru-
racj to b»i6», Tuke an^' miction which
la effectpd hy Ihc Uydroxjl ion — the coni-
iiiDU iun of all bases — such Jif (he snponiti-
cation of an cetcr, which takoe flaw in
Ihe soudo of the following equation:
cn,cooc,iu + Krton = c,iuoii +
The velocity witli which rhis reaction
will take place d'penifl upon lh& nnmber
of hyilroAjl i'-re preMot ; i. e., upon the
disfiotnjvtion jf ihe hiise. If we know the
diMoriJil i<)M of difTeront bases we know the
ii'lalivc Ti-If'citicp with wliich Ihcy will ef-
fect the ah.>ve roiiotiauj and, cnnvcraoly,
if wc know thp rrklive Telctiliefi with
wML>h any given hnees wilT efTect Ihe above
Ttvketion, we know ihrir R-laltvr Ui^ocifl-
liinia or stn-upthB, Mncc the two ^xn pro-
per tional-
Wc eiin ihn* Me dipsnciation to nieas-
urft Th(! ehemicAl aclivitioe of subslanceft,
OT wff cBTi WW chi*mienl artivltie* to meas-
nre difwociatiiiu, *in(-t, n* w*? hav".- seen, a
proportional itv exists bfttwren the two.
Wi- eaiiuiil imsft over thu aLovt* rt^mrtiori
bftwwn cane sugar and water in tht' pn;a-
L'uce of acida, without making n ahght di-
^-resflion from our general thome, to call at-
luniion to one rct^nliarity which Gxisu, It
will be cihfiervcd that in rhe equation for
ihiH n'JiL'tJuM. till' hydrogen iou \h writttu
in Uie fiiUiie cinidition on iht two sides of
the ttumtion. Thjs mt'iin.' that il dott not
enter ab saoh into the reaclton. If it does
not enter into the reaction, why la it#
pri'j^frncf neL-essnry in ordi?r thut tlii.' re-
flCtion should take placo with any appre-
ciabh.' veloeily? Wc- cannot at pr^^wnt
answer tlnh quoetion, but it aocruP probibl**
that the action of the hydrogen idd la a
sjtr/nce avtion. In Ihe light of Ihia mn-
cfplion il Jtcis by eontUL-t, Liml hulU aetious
of subataiLces, of which many are known,
are termed catabjiic. Whik we at pres-
ent do not unfler^itand ihe megbaniam of
catalytic rcnetionfi, tJie problem ie cnnsid-
orably siriiptiflwl ihmugli th^ eiistence of
the thcoiy of electfitytie diaswintion.
Before ihia gco era 11 nation had been pro-
poeed it was known that acida ootild e&«ot
certain catalytic reactions, bul it waa aup-
posfd that iht^iit' rejictinna wen^ prodnoed
bj' tlic wholu niuli^cuW of the adds. We
know now that the moleaules of acids,
aa sLich, arc n^it c^iipahle of producing <uita-
lytjo rc*aotinnK> but that il is the hydrc^
gen ion into which the molecule ditso*
Hales, whieh Hctt^ cDtalytlcally — the anioa
of Ihc acid taktng no part whatever in
the reaction.
The observations which have Jiut been
made in rcfiTonot^ to the ontalylic reaction*
nf hydro^nn ions, iipplv wiib iquiil fonv
tin the cBtaljIic mactiou. nf hyiiroxyl lona.
Tlie hydnsiyl ions of basee can effect cer-
tain reactiore catalytically, }\iM, ik« the
OUTtlXBa OF ELEOTItQCHKMISmr.
hj'drogen ioDs uf acids, aod the flame rulw
which hold in the one case apply alto in
I he oihor.'
OOUPABISOK 0? EEAC'I'IONS UBTWEfiltf IN'
IJUI*AMC KCniSTAVtTBS AVD OH-
OANtC SUBSTANCea,
IE bos long Ueen kDowu thai inor-
gnnic «(ibr^tanres >□ general hav@ a much
grmtvr chimioa.l activity than organic.
Tb« 13 shown TOry well (d the relative
Tt^lociiicfi of the two set* of rL-flclionaH In-
orgaDio roactiona prooeod ^o rapidly that
in mo^l cases ir is impossiblo to lutB^ure
(lit«ir velocities. Tndted, their Telodtie*
tre fiH|ut'nl i_v so gr^n^ tbiit l.htj iisujillj
liftYc Wen rogtirded aa taking place inrifln-
It U, however, qiiit^ different with or-
gKnic r»'^actifjii?. Thpy pmci^^d, i"**lativt'Iv.
fVrj much more slowly than inorgauio,
ttod ui mriTt}' cueta the-Lr vi'ltn'ili^'s nrr
vafficienlly amdl to €^nabte them to be
reidily tDt^asured.
UTiy do<-"6 thU difT«renee eii*t? A few
jeare a^ it \vould have h^-Pti impnswiWe
to farnish a s&tiafactory answer to this
qnt«t]oii. It might have Seen said that
iMTjiinic reactions proceed more ropidly
Wanes the gubslnnc^e ore chemically
itronjer, fcut this wonlil brtvp br^en simply
tvnaaiijig the pheuumenat and not an ei-
pfisaticn fit dl
To-day we not only have fl rational ox-
[4iutioii of thc^ facU in lenns of our
tleoiy, bnt tliey are also a ae/^eHsary con-
ftdqw-Tuvp nf it. TiicipgnnM" compounds are
touch jaore strongly disaocialed than or
pQic. Indctdt the inorgauio acid* and
^MSflfO th(> most ftlrongly disBoctated 8uh.
*Mi¥a of which wn have nay knowledge,
*»lMl>'><t<*^ ivWl"' "W rouerii Hulk vl Q'fClf iDd hli
iijid the Hiltj an?T an a dusi, among tb«
uio£t str^n^ly diteocialed subslAii^es^ Thii
(Lpp]ic3 to even the salta of the metala with
weak acids, and the Eulta at strong acids
with weak bases, Since chemical activity
lA proportional io <lh&oc\ni\o% the moet
strongly di^&ociated Aubatancee muat be
the most aelivo ohemieally,
Tai(c the organic oompr^unde, a greft
majority of thenn are dissociated very
slightly, if ni all; kiii3 evi^ the nrganic
ucide and ba»c6 are among the weakly dii-
^ocialod aubstoocce. The atrongost of tb9
organic soide ia not m strong ae aulphnric
arid^ whti^h is only iibout thtv?-6fth» ai
strong *» nitric or hJH^ol^l^lo^^c iicid;
wtiile most of the organic acid« arc of the
urder of strcoglh rcprMcntcd by acetic,
inalicj or tartaric acid; t. *„ ncarooly mora
[brtn a few hundr^tb* of the ntrpngth of
ibe Htrojpgt'^t iiiinernl aeitd. The tnme gen-
t^ral remarka Apply to the organic baacs.
though, pcthapa^ to not qiuto the same
cxtent-
The organic coTnpoimdB being, thpo,
*mly elighlly d[8«odat^d, vend imich more
slowly than Uie inorganic; more ion£ bciog
formed aa the fow already prcaent are
4i£cd Up in th(^ reaulLon^ and lh]§ coniin-
tjlng uutn the end la reached, or inor«
rrKiiii^rir.Iy itiitil ei^uiUbniim i« i*alab-
lir-hL'J botwn-n the vt'locilit-a of the two
oppo^tt rt^i<.-tionB^
Our theory furiiiiihe^ na with a perfectly
tiiliKfacftiiry cxplanaliou of all of theae
facta.
citkmica:. imiviTY i>rB to xosh.
We hav* «i"ea in llie preceding pari
graphii that Hic*jnlind activity and dia*
hfictfttinn nrt- proporlioiial to ontr an*
oilier. If chcrnJcal activity i» propor-
tional to th« Tiuznbor of ioiu proiant,
then what part do 1h« nolacnI«a play
OUTLIXES OF BLECTEOCflEMtBTRr.
uriiUj forcea itself upiru m. To ajiswer
il wi* lau^ti oil Uic oiic iuQil, ixdvuli- ninlr-
culini, and ««c ^'hc'lhi^r tons react; fin^l, (m
thi> other, we muil exclu*itr ions, anil a^
vhi*thcr moltculca con reaol or nnt Tn
(jxfsliiJo molsicules i( ia onlj uei^esear}' to
prcpnrc very *^ilul^ £i>luttomt of strong
adds and ba3o?, ^ince in audi soZu-
tione all the molecules urv di^oeialed
into iona. It has be*n seon Ihnt in »tf^i-
h'oftj* tsjfiith lira compltiehj \iUxf}cuUed,
taking into account the amount of sub-
Blancc present^ the ahcmictii aciiviiif is a
maximum.
Thifl would indientt either lliat ioiH
alone CJin rnltT into chemical nctivity, ot,
at lca«t> arc much more active than mole-
cuIm. I'o decide betwueu these alterna-
tives wv mud ciLludt iune attogt-rhn-r. and
see whether molLciilr.-B Imvc an,v chenitcal
activity. This cjia be acctxnplished by ex-
cluding All traces of moi.^tur*, and aihir
solvi^ntsffhich have ^inydiesnoialing pinv*.r.
The great eicporimen!a] ditltcuUi^ involved
havt' been cvercome in a uumtitr of eisea*
with the Mltjvin^ icfulU, Unlj a few
otLitfn can be tak*a up here: Dry hydro-
chjorio acid ga/A does not doL'onipoGO cnr-
boualfB to any appreciable ecteQl, and it
dotia nut precipitate silver niiraii' clis-
Molvi^d in aiiydroLiH bmijicue «r anliydn>u&
cthcT* It dwa iiftt ohniitt<* Um^ Ittmua
rctJ, nor docs pcrftittiy anhydrous sul-
phuric add.
Dry hydrochloric acid gw does not rwiot
to any cxtejtt upon dry ammonia gaa- Jn
auch an experiment it is, of course, nccc^.
aary to take Ihe gr^^atuet precautions m
drying the gaaee, by alWiuiJ fhoni to
come in cnntact wifh the moat powerful
diyjt]^ agt.'nts, Jni!cr ihe moat fjivorable
*rin>rar>ill awiiumni] ur ihi^ iarD(jlaip» *H T]jt>irj til
condiHons, for a Iohl^' period of time.
Thie iu a very Burprjsing f.ict, liut h
even surpassed by Ihe to lowing expcrt-
nn'ML i^iy stjdiuMi nii: \\i- dijipid \\iUi ^ <i-
phuric acid, from which every trace of
mojature hat, bei^n reniovcd, without any
appreciable notion tnkmg plaee. In thii
e^pe'rimcDi, also, the grcaEV£i precautions
must, of conreo. be tnken to remove evorj
Traee of inolstiirc trom tbe subatancwa, and
from the vc^ech in which the experlmentfl
arc to be carried out.
Thcii^ oxpLTjnionis vould show that
molecules auch fl& we haw been eoosider-
ing do not have ttie power to r>.'ael chora*
icallyi bill Ib'ae expi.'nintiitft olone do not
justify Lhc- conclusion that ifher molecule*
may not react chemically, or that mole-
oulcE undvT other oonditionn may nol re-
act. Any eoueluiion on this point could
be drawn only afUr an elaborate Mludy uf
(ilii-'miciil renctioEis in ^iMcrftlj undtr vrrj
widely different condition?.
Tho roiiult of Auoh a .-tody has, howovgr,
mad*? it very probable tlial nioiv-uli^A fflJi-
not rffict cht'iHimtlif with nifilfrtilev It
IS po^aibh; tlmt molecules laay react villi
iujifi, but this is not proved.
It IB very easy for any one whoit
icaovledge of Ihe facta ca not very oompnj-
Jii-naive, lo tlitnlc tlufy have fouud «xajn<
pic* of cliymicHi aclivily svhi-re thcrt^ art
no iono pi'i'ty.'nt; hat it should he rrnnm-
berod that not only water but moit other
flolvcnu hflvc somo ionising powor, al-
though this difTera grniitlv from solTfoi to
^IvenL Fui'iher/iiore, heal has a Tery
great power of Lreaking Jowu mulecuU"*
into ions; fiiaed salts being veiy consid-
erably diosociatcd.
TILE TWO ORKAr GENBRALlZATlOKS.
In the first cliapter we tmeed the dia-
cox-ery >tf the fp?neraliiatioD that the gas-
OUTLIKEtf OF ELErTftnCBKMll^rHr
•t
lAirft applj tft the fismotic pr^^ures of
ioluiiunfi; in LKt^ second and tklri], the
oripD of tli< theory of elecbolytic disao-
oiatLoiB and a Tew <*f its applicfllioiia lo
chcHtica] problerutf-
II ii difficult to overeBtimale the impor-
Uhl-c of tht-se gtnrmli/alitniB for tiioJerTi
pfc,vsical^ and especially chemical ftcjcncc.
Upon them has Ejecn built most of the
uience of modcrD physical cbcmi«lry, of
which electrochemistry h only one chap-
XvT. It U not an evaggerafion to say that
avery iinpottan! developmciit in elwtro-
cliemUtry, in the last dozen or Afteeo
\-<iiir&, httfl ciuinJ iirfjuiid one or tho other
of Uieee generaliialions, or arocnd both.
The r^uuininj; chapters of ihU lenea of
fmpcra, will In? drvuti^il in fl disi^uaaitm of
fomc of the more intcrc-stitig and impor-
Innt ndTftnc'ji, Vfh'ith huv^ bn^n nindr in
elcdrochomifitry sinoo thoec gcncrnliza-
II nun Tw»ro df»<>ovorwi
r2
OVTU>>Mli OF KLECTROCHE^iSTRr.
CHAPTER IV-ELECTROLYSIS AND THEORIES OF
ELE-CTROLYSIS,
FART 1,
TUKRE are few Bubjwcte m eivctro-
chtinifltry whioh have attractDd
mort ktl^^iiti'm thun the power of
IKe current to dcooiQpcrae clieuiicu] ct>m-
pouncla. This action hm b^en known al-
most as long Ae thn current itself. It naa
imjxr^siljlu to study Ihese pli^fnomeTia vhon
Uie only source of elei^tfidtj wiu Hiflt
proifuccj by friction, siucv *i. cootlnuoue
■upply could not be obtained for any ap-
prccinblo Icnpth of tim<j. Almost as soon
as VoUa discovered the pile which bears
hifi namp, thfis^ phcnoiripna b^gan lo at-
bact atLcntiun; but the fli'At who made an
6itenMve aludy of the power of the current
to d^ompoBc chciaioal compounds was 2Sir
Humphrey Davy. As is well known, be
coufttru(?ted the mosl powerful eltctrical
battary whJc^h hail been dt^viaed up to that
time, nnd with this he was able to eifect de-
compoaiiiorjfl which htid never bccE B«a-
|foat«d odpoeaibh. His cUegicEil cxpcrimcntB,
^ vhich be dGcompcsed potaaflium and
•odtiiiu hydrojiidea, and diar^ovi^red the al-
kali iueU!4, an? ao well known tliat ihej
iwed only a l>ri*/ rtfor^-nce in thia conQ^JC-
tion, PcirlioDB of hU batn-ry. and hie aol<3-
boolca in which the«c and othi^r iniporfant
difccovi'riwi arc r**cord<?d, are sTJIl preserved
At the It»3'fLl Institution. I^ndon, in coa-
tusction with which much of hta work was
done.
Thnro is, however^ still one greater
□aitie in connection with &he subject
of electrolyei«, and that ib Faraday.
For a oonai'ierable lirae Davy'e aaaist-
ru^t, and latvr hia ttucc^fic^ at the
Rr.yil Inntitution, Faraday continued the
work which lldvy had begun, and made
diaeoverivs nf inccinpiirablj grenler talue.
WliUe Davy'fi work was mainly quflJitatire,
letting what decompositions the current
ooidd oflect, the work of Faraday was
quantitative. He wiahed lo fcimw how
iriuch of given ^ubslaucea are decompoat'd
by given amounts of the current, and
whollior Ihc? amount of decompoaihon wa*
alwayj} proportional to the amount of cur-
rent used, regai'dleea of the source of the
currenL He IcsLftl iht- Uder puint In this
manner: Currents of ckctneity produced
in different ways were passed through so-
lutions of the eatue Aubstanc^, and the
amount of dG composite on del^rmiued^ He
found that a given aramint of turrent al-
ways produces the ^^ame amount of decom-
position, no maltpr what tho eouree
of the current may be. He then uaed
different amounts <jf current, and studied
till? flimniDlii of decorn posit ioiv effected.
The Qmo\ii\i of ihcoinposition ti^as almajja
proporiionil to tho amoutii af ctimni
ustd. This may be termed the first law
of Faraday.
Faifiday wont much further and studied
the decompogiticr of different subHtancee
by the eamc currcol. to ace if any simple
relations existed i>etwren the amounts of
the different fiuhHtnncps decomposed He
areoiiipliilii'i^ t.hi>hv passing the ^lui*.' cur-
rent Ihrougli aolutions of salts of a number
of the metalt), and determined the amounla
of metals which wore deposited. The r©-
OUTLSy^e OF ULEcntOrBEMr^TRT,
Hull was the tlistrovi-ry of Iiis well-ltnijwn
BCCotd ]av. lliui ike amouuh of ikt differ-
ent mtUih dcjioniUd by the sumc current
<trtf propctrtiftnal to the ckem\ml Cfjuiva-
hntf of thesa metaU. It wa flre deiiling
Willi tilt *fl]U of nnivulent meful?^.. the
tunutiifU ile]i(»(iU'il nvv pro]i<Jrti(niai \o Ihe
aloQii? weight" of thf^sc eTi^mrnts: if we
arc dealing wilh bivalent c^biiicntat (he
tmonnU clcpcisiipii ure propurtionaT lo th('
itvrnic weights nf thi^ Mtinput* dividotl hy
Iwo; if with trivnli^nt, I'lrnnrnt*, fo thr
itocnic weights <lividcd I>y three; if with
nnilcnt irlcmiuiLi, to the atomic wcifshU
diiidod by n.
Thcte 1^0 InWfc iirc the moit iraportnct
liflCov^c« which havo c7or been mado in
coiui«otKii with electrolysis, and both of
Ihpm ire dvnj lo Fcirmhiy, who also gnvo Xif-
I ihe EUctrochctnical Nome/iciaiure^ which
, WD u« up to the preflout tinie. He termed
the parts in solution which move* as the
corrvnt i» pasaed, ioiis; those which move
itt It* ftoluttfin with ihe ourrent, catumit,
Vtd [ht»e wliidi move oppo^^itp tn the tur-
mat, afliVru, Tht' juhetancu which, ia solti-
tiom, imdcrgooA deoompoaJtioo by the cur-
nothc cjillod an tlcptrolyte, atid Iht- proc-
(ttty whk'h thow? i4nhs»*iri(?is nvc decom-
poaed eUciftiliimx. The pluct^s ut wltioh
Ihc ilccompoaition mamfc^led itself he
WPBMJJ the poU^ or oJcTdiro^ea; thul pole
Inward which tho cations move he callc*d
tJjp (aikodt, thiit tiswiirds whi<}h Ihc nniann
FciHiiay distingiiithed hliHiply WlweL'n
'*o dutee of conductorb , Those whioh
«*rr^T Ihe eyrrcnl without undergoing d«-
coTiipoMtion. ?iich as th& m^uls^ carbon,
ate, which he termed cr»Tiductor« of the
frrf f/as»; and tho^e wlddi iinder^ de-
f&Ta;xi-i!ioii at the i-U-c'trmli^. mtch us
which he (;r-rniw! ftondindors rjf the npflonrl
That there ia a eharp distinction betwof o
the two cluaaoa of oonductora, Meme to bo
douhlful at present Recent work has
mudr it pmhahle Ihal the mHnIs conduct
by nii'aiD of ions O-i sotutioiiA ut t-lec^lro-
lytca conduct by means of ion." ; the differ-
once m the pefiulls oblaiD^d being, in part,
due to the differen! eondilicnd which ^ur^
round the jona in tlw tin^lal uud in ihe
ftolution,
TK5T1XG TUE LAW OF rAEUDAT.
There arc few laws in nature which have
been subjected to more rigid espenmontAl
twt than the law of Faraday, Conditions
have hetn varied wheroifer it was posiaible.
It* nee whKhiT thr! hiw would hold. It ap-
peared a fi.'W vi^vir* 0^0 jip if cj^cx-plioriB
had been di»M*oTeri*d to the law. If a rur-
ronf ifl pn^Eed thirmjjh ^nliitiftij^ of wr-
lain eleotrolyt^a^ which are subjected Co
a high preiwnrd, there in alightfv \et^ de*
coiripoflitiun L-ITetted by a givtu quaulILy
of ['urn-tkl Lhcui if \\i^ nolutioix i^f thi- eltC-
trolvte i* undpr normal ]>reMur<'. This
wa£ not rxphiinc^l f«r a timo, other chan
ne nn oxcrption l*> (Iv law of Faraday.
A pcrfi'dply wtivfiK'tory nplnEXfltinn hjw.
however, been furnished. When th« lit^uid
is subjected to high prfMUrc, more of the
air above it ijs forced mto solution, and ft
small part of the oxygen, or nitrogun» or
hoLli, U luni^r^d by thtr fiulveut. The^e icint
help to carry tlic i:iirn-nl fnim on« cleo*
Irodc to the other, wilh the rpsiilt that
more current pa^fici than w<*uld corre-
spond to the amount of metal »epnraied
upon 1 1143 cathodc-
The law fif Faraday \\aa, then, withstood
all IcjLtii^ and in one of the few kwH of
uiitun; to which no cxcepUon« arc known.
OVTUKES OF BLBCTRO^HSmStar.
SLnornocncuicii. tueohigs.
Tho diecov^TT thai chemical good*
pounds c*n tie de^onipwcil by Ihp curronl,
uttil lo maker il pro!Kibli< UtAl tVn* w^ii<
\ verv cloae oaucectiOD Wlwceo chtmical
aUtActiou And electrical attrfiction. This
iiiua wa^ further mrvti^^lhcucd by the faot
Uiitt in tho Totuic Mil wo tuvc cbenalcfll
aetioa going on, ant^ an eloctric cnrreiil
prwJuwJ, Chirmioal actioti ind clcc-
irical action lhu« Kemcd. in a «cd0C^ to
be eomplcmcntarj. Wlwn an olwlric car-
r«nt vra« paasod through a eoluiion OOQ-
tatning cartain ch«uica1 ^>inpoiind«j iheae
cnrnptmndf^ «'(»n; bmkt^r Ouwii; tht* dteirii-
btfin^ ovcrcj^mc, ConvcrKlj, in iJic ci'll we
IwTC chemical compouDdd boin^ formcdt
and at the aame time a current vna gen-
era l€^.
Thwd rpUticm w«r^ thonghl I»j Havy
ti> bo ver/ cl*>*e, hs we sball see from the
theory whiali be pruposeti to accouxtL for
dii^^caJ union. Acconling to the^Jecfro-
chcmiodi 2'koory of Davy the atonu of dif-
fvront i;ub];taii(^<t6 oxist in an nnchargftd
o^imljtion; bii( whim they comp in t*nnfnct
thay Wome ohargecl — Ihe on*? pusitively
aad the other negatifdy. The6i^ po^itit-ely
and ne^lirelj oharjfcd atoma attract one
another, juat as any olhi^ poaitivi-iy und
negatively charged bodies would do; the
torn* of thp iillrAHion fciru giirtTr HinlitTicf^
depending upon (he magTiiti](.^e of the
difltrenca between the chargci. The
ekairolyirif of a compound, in terms of the
eleetrodiemicat theory of Daiy, coiui^ta
in tho lOparatioD at the pole« of the dif-
frrrTnt flpmrntu in an um'.K?irgi"d (iii]*li-
tioD. The negatively chargt-tl ntoin Is at-
tracted to the poiilivc pole, and, hating
il4 poUntiaJ raised ta ?cro by addition of
poutiTe electricity, acparaCcs on thii pole
in a niGtitnl cooditiOB. SLmiUrlj,
pLMtUt'dy charged pftrti«le U attra
thr nt'gHtiu- |jol<-, ttud tltrxiu^h udclill
of ni^giitivr pUdri^lti Lhccoimv cAectricaUy
ncutnJ nn^t scpaiatoe from the Mtati
In zhxA condition.
The eloctroehomicnt theory of Di
n^irer came inio prominenee^ snrl n»i
umDs bo h>T« cierl«id any marked i
flucnce on ehemii-^1 thcu^liD. Sbort
afrcr it va« proposed it wxt entirely ova
shadowed by onothor olectroeheinieal theo^
17; Wi., that of BcTvcliafi.
THE HLKOTnOCHEMt^AL TltBORY OT
KfiLICB,
4
iCa«9^
The eleclroeheniical theory of Befi
lioA diffeia fundanien tally frosa thai
Dar>-, in that it aafumet that the utoi
at9 charged ^of&ro thaj/ c©me in ftwii
The natural eondition of tho atom U to
ba charged, and^ indeed, \xtl\i puiitindy
and ne^alivf}ly» Thow oppn^te diargoi
exi&t upon the atom in polar arraogonent^ ,
but diher the poaitirc or negative ebarge {
prcidominatea m magnitude, eo that tba
algebraic *uni of the charget npon any
atom U atwayM villier a positire or
n negntivf quantity, and neter Mra. |
tivery atom acta, tbcn, oa if it vttt j
chorjcrd eilht^r pi^itin^iy or nc^ativdy. '
Chemical attraction i^ nothing but t he ^
eleefrlcal atfrAction of thaar (ippatitp^H|
diai'ged a[i>m«; ih^- magnitude of the a^^^
LrACtion ilcppndtng upon tlie difference be-
tween the chjirgoi upi>n the atonic whU
enter into the compound. When the dii
fi>rontly charged atonu come In coniarc<
The plprtricrtl (lifff rriif** vi>iiM <]i<fipppi
and then the alurna would fall aniDi
sLnco the attraction trhich held them 1^
^ther no lonf^er exi^^. This «eema to be
a weak point in the deeiroehem^rrrt
OVTU^t>8 or SLECrKOVHiS^lFTRr.
would AKain itUnd one anathur, end ve
iroiild tuvu a cotitTiiiLil dtcompcMitiGii and
fCQombiiuEinn taking place*
Aneibvr ^Vdion wfts urged ftgainet
thp di^tm^h^minl Iheoti^ of Berwliiu,
wbich led to iU fthaD^anai^nl f^^r ludrv
tbon hiXi t, ctnXixry. If chemical aUnic*
lion {9 Ddthinf: bal tlie clc^ctricnl Attrac-
tion of nppctfirciv chared pnrto, then tbc
propcrtitf of tbn compound foraod mast
b» ft fuficiion of ihp plrctricjil rtinrgm upwi
Ibo «tom«< If anj fvo compnurilfi nnem-
bU^d one anotbcr clcif'^W in pri>perUv«. tbe
«toctri{?al cbnrj^oft upon i]» atome muifl bo
cloiely analogous II was found thai ibe
two fiompoTiDdf. acetic acid and trichlor-
■nrfic ai'id, are dtuflrlr ulUeit iu Uiirir
chemiftf] ADi! phvficnl prapf:rti««. Id the
IfltlO' wc huTtihrcc Qtom« of dilonnt cor-
MfpondiD^ to titrcc atome of hrdrogon in
t1i« foriDPT, aK MB W M«n at one* b)' com-
parfrig thnir fcrmtilafl:
Aeeilc Add- Ttichlorapotic Acid,
cn,roon. oci,ooon.
Tt wad re-jioiied Ihat rb^ hvdro^n at-
oma hi nocLic acid, Ukc Uic hydrogvn
tttoma UDikr nil other conditions, ar«
chiirf-od podili^'dy; and tbc chlorine at-
oict which bavc n^placcd thoro, ti3co all
cHhiT Htlprinit ntrms, nn* char^i^El ntrgiu
(irplr. Wp hiivp Hioji, rrplafrd ihtcc |K«n-
tin- charj^'T in aoctic ncid bj (broe n-rjcn-
tito charc^, and baro not matcnnlly
ehan^d the nalur« of lh# cnmpound-
'Hii* arirnnti'iil vrk tnn raurh fnr IVra^-
litu, and in Fpitc of maoj altcmpta V'as
acvcr aiwirew^l ^lijifaclDrily by hira. Tbe
ifsnh vu; ihit hn tb(K>ry fHI into dure-
piit«^ aiKl VQB ftiniplT regarded as a con-
Tmi«nt mpnns of dasalfymg ■ribatoncvi.
without in any wiao being a cotkc* w-
pranon of Ibe facte-
THOMBOU l>VltUTHROWS Tlllt ODJXCTlOJra
TO TIIK KL-KCmomiZiAlCAU TirKOftT
OF B£BZSLIt8.
Thii objection to the Fkriellim thooij,
which passed musLpr for c<iQ*idecabljr
man Ihau ball a ccDturj, haa ittflfJlj
been entirdy overthrown by ihc work ol
J. J. Ttiomi-m.* Ho look a glau t\ib«,
closed al Ixitb atidt, nnd foalcd platinam
r!tctni(1rii into 11« two i-nd». A Hliu*t of
nluminiim wa# placed acroaa the middle
of the tube, but did not fit tightly affoiaat
jh*t gloF^ wolU; the tube wiu lillud with
vapor* of cMoroform, vhith ti molhanc
in wliich Ibrra of thf- bjri^n?geD ntoma
ha^ been replaced bjr chlorine. Thia will
ha ectm from the fonnalaa of the two
^ntHtanooa:
^IfitliJinr, Cbldrofomi.
If miinili gnw h cltctrolysed by paiatDg
iho current bcti^ccn the ('Icelrodci. the
hycircjfra, hk*^ other poiJtircly churned
luljMtano^ji, would iddvo toward tbu n€ff-
nUi't pole. Wi» wiiuld *iippoiw thai the
cli]onnr in rhlniof^jrtn. Icing ncgntively
charp:^. would pui to the po«itirc pob;
bat ThnniH^kn found that it alw Ljant to
thf ncgaiivs poU. This showed that tkt
rhtofinn in chUittifnrm t^ax nnt nrgativfly
fharye-d^ tu htid htm 9upp9i«iK hut wtu
^''^iitivdy chargid,
Tht^ impoHaaev- ol tliie die«>vi.-iy cau-
not ^eijy be o\^r«etiBiaied. It abowa,
r»iic]nsit«ly, thai lh« 9exi>e atom mayr
lautvi difcT«Dt conditioni, hare etitirely
difen>nt chargta upon it, uucc wt kuow
that chlorine la oeuolly tM^tivu. It
*Tot • 4V44IM4 ■rcc^ql i>r TbiXiunb'i «iHrji«al,
S6
OrVLmE., OF ELEprnoCHBMIfiTRr.
fihowft, furthnr, (Hat fdafat of positive liy-
dfOffcn lire replacsil hy atoms of positive
chlorine. Thi* throw* eatirolj n^w light
or tho whole nattiro of sub^lttuticn in
chemistry, making it prclable that alorae
cnrrying on? kincl of pli'ctricfly are only
replftcrrl ly alnms imn'ying n clmrge of
the same nature; i,*., positive atoms by
poaiUTOi, and nogulive oloms by nogntivc.
Tlie beariiig upon the nrgumynt against
tho dtrlrtichemicnl Ihoory of Bt-rwlius
i« at onRi^ uhvic;js. The tkrra pftsitive
hydro^fri atoms w acetic acid are jvpUced
by three pasttha chlorine atoms, ond the
nature of the two compounds ehould from
the theory, m thoy are in fact, be very
dostly alJwd.
We recoguuie todfl> that tlie ulectro-
chemical theory of Btrwlba contams a
large elemi'nt of truth, Jind la one of the
forerunners of the theory of electrolytic
dLSflodatSon.
OLDEK TirEDtnUS TO ACOOrNT TOft ELSO-
TR0L¥Bt3.
Ali:iont fw iiufpkly fm tht> facts eon-
nf*frlinl with elnctrolysifl W-am*- known, at-
ternpt* wcTc made to account for thaao
facts in terms of conccptiona which thou
pr^ail^d. This is the usual course of
procf>(lnre. Thf> thinking mind ia never
content witli tin? Jiht;uvi-ry of isolnted
fa^e. Dor er^n of facte which bear aouic
74guo rchtiona lo one another. It want*
10 Icuow what deep-*iatt>d relation anally
Ktista between the faet*; it de<iires to
correlati- the fueb and see if posailile
what they really mean. '^Thr aim of re-
toarob/' eaya u difitinguielicd man. of
icience, *'i* not tho discovery <if factsn hut
the diwtovery of g*?a<*niliznlionfi/' and the
more vnf. thinks orer this propo^iiion tho
more one »ccs Iho deep meaning which it
canlnins. Fat-:*, niid thi»ory or gen^raliTg-
tion^ bear about Iht same relatiiui Ut each
other as the brlekd and a magnifleent
piece of architecture. The brieJre are al>-
*olnt*iiy esaential to the strueture, but
they, in themselves, are not the aim of
the arehileot. Th*! aiEii of strieuw \s to di*-
cover theit- great trutha of nature which
we cflU genera haaLiouft, and tlic facls art
th<* esaontiala out of which lli« ediliws of
truth U huitt.
The (Iwt Ui projKiiKf n Thcarp of EIff>
trtitjfii^ WW OratiKiif^if.* in ]805» This
Uieory is now only of interest hiatorically,
yst, for tho sako of thi» dovolopmont of
OUT snhjccif tt miut he ron^idered. Thf
ftt(?1i which iuul lo be accounted for ai
that time were comparativcty fwr. U
wafi known that when n little acid la added
lo water lo make tt conducting, ag they
eaid, and a current is passed, hydrogen
was liberated nt the ealbode and oxjgeif
at the anode. This was explained by
Grctthuee aa follows: Let ua think of a
layer of water molecules between the
fl-onde and the cathode. Starting at the
cathode we would Imve a hydrogen alom
with a positive charge- This would give
up its poBttivo charge to the polo and t^-
cape aa hydrogen ga&- The oxygen atoia^
which wng originally combined with thi»
hydrogen, ia now free and conihines will*
the hydrogen atom of the next malcculw
of walor, Thte ficts free anolher oxygei»-
atom, which comblnea with the next
hydrogen, and so on natil the ojiode i^*
reached, when th^ la^st Trcc^ oxygen ilIod^
givee up ita charge to this pole and cscape^^
as oxygen ^s.
The fenluri? of Ihie theory which dis — '
tinguifihea it from suheI.'qln^nt theories _^i
is that in water every hydrogen atom ij
< 9*ii Theory of Klvlrolj'tlc ni«io«lAliBft.
OUTLINED OF ELEVTRQCHEMI8TRY.
37
firmly and fixedly combined with a defi-
nite oxygen atom, and never partB com-
pany with it onto the current ia passed-
The above theory accounted for all the
facto which were known at the time it
waa proposed, but it was soon discovered
that a current which is far too weak lo
decompose a molecule of water would
stil] effect the electrotyais of acidified
w&ter. This could not be accounted for
At all by the theoiy of Grotthuse, and led
to a new tUcirochGmicol theory, thai of
Clausius. The theory of Clausius, which
waa proposed in 1856, has already been
referred to in connection with the de-
veloproent of the theory of electrolytic
dissociation. The distinctive feature of
the theory of ClausiuSj as we have seen,
ia that it assumes that before the current
is passed a small number of water
molecules are already broken down into
parts or ions. This would account for
the fact just referred to, that an infinitesi-
mal current, which is far too weak to de-
compose a molecule of water, can effect the
electrolysis of water. The action of such
a current is simply a directing one, driv-
ing the anions toward the anode and the
cations toward the cathode, where tbey
lose their charges and separate in the
uncharged condition- We have already
seen that the theory of Clausius ia the im-
mediate forerunner of the theory of elec-
trolytic dissociation, and we shall see a
little later in this paper, is connected
quite closely with the theory of electrolysia
which we hold to-day. We shall now take
up the newer theories of electrolysis.
n
0V7UXR3 OF EhBCTHOCffRmSTRT.
CHAPTEFw IV E.LECTROLYSIS AND THEORIES Ol
£,LECTROLYSlS.
PAI<,T II.
Till! ^fKwcR ru&ontBS OP fit-iEontoLVMa.
Tho tbwry of electrolyaii* wUidi was
held until a fvn- yoar« tg^, hfA to Ukc into
ftccouDt Ibo fctllofring fflcU: Wh^n & car<
Kill \% piiMcd through n ^lution of an
Aci<1, 1iyi]rogi>n ai^qrutpii at th^ cathode
ftDd ox^'gm at the auode- T!Ua wa** tnie,
in ^crcra], lui tJicre were Kime «cep-
tioQfi tt 111 thv rflse of Iht; electrohmt* of
ft bol, ooncecitratcd, »ohitton of hjdro-
diTork iiL*i<!, wJu-Ti^ cMorinr wpnTntrd nt
till* uUiiJi;, If ihv fiiihiUat) nf Ihr nriil vak
dilaU the above ttatciaent may be taken
If n dihilo solution of a bfl«c la doo-
tTolyz^d, hydrogen fleparate» upon tb«
c&ttiGile and iiJijgen upon th«t anude, in the
wme way ax if nn Aciil wn* u»ed-
If a dilute Bt>lntion of a »It is doctrcM
!yMdj wc Will hnrc diffcn^ft rcmltn, dc-
ppnditij; upon the oflturc of the £Alt which
U "9cd If wp eelijol a fiflU of n metnl which
decomportai waU^r, Bay of the alkali«ti or
ftlkftlme earths, we will have, on elcclrol-
yais, oi}'gca tlbr^rated at iho oaode and
hydtogOD liberated at Ibe oatliode. If, on
the other hand. v@ eleclrolyxe a Batl of a
mvlAl wliioT^ Jui^ not iltoompoKe nati^r,
SA for cxttinpl« coppvrt wc wouM have
oiytfcn Mt free at the anode, and in-itead
of hviJr^iffcn bcin^ liberated at the cathode,
w« would havQ m^lallJe copper dvpwtvd
npon thU pol«.
Take flr^l the cafle of an aeiti; aay Hy-
drui;hlL>ric acid, Tbe hjdrosen i>ne oio^
vith the current over to the cathode, givo
ap their charRC to it And ueape oi bydro-
ee» g»s. Tlic chloriiHT iom more
the current over to the tnodc, give
their neKsliTC charge, but do not wotpi
lit chlorine nil lew iha «)lt;tion ia bot and
eoncj*nlrati*d, Thf eblorini" flil* upon tb*
WBti?r ir» Ihp Rrnnr of thr fiiHiiwing p<[
Hon,
forming; hydrochloric Acid and Getting o
gon free. Two arom^ of oxygen comb
forming a molpcule, which tbt^n oscapcn ti
iirdiimry f^aae^iui i>;t>^en; the bydrodilorir
acid remaining; in the solution again nt^
dcfKcn"*el<^rolyn6 aa dt-icrjWd ebore. and
the proooM IS ooniinuotu. Take :he oom
of t bate; My pf^tn»imn bydroxEde. TW
hyilioiyl ions iTtovc n^oimt IIm? cnmnt
over 1o the anode, give np their ncgntive
charges to it, and cannot rutnpe at 0x3x00
and hydrog*?n, but two hydroxyl gtoiijH
react forming a molecule ot wntw
uty^fen, thoa:
TJiP |iolfl»iiitn cation rnorc^ with
rvnt over to the oathcdv, givm
ehiTg» and h«come« a potaMinm atom. A
pot^iisitiiii ittfini eani^ot, of ooiine, exist in
the prrhFutH^of water without acting cheoi-
inilly ufton it^ in the acnw of the foltow-
ihj? equation ;
K -f- 11,0 = KOU + U
formitig pot a^ urn bydruxidc an^l tet-
ttng bydro^i*!! free. Two atoou of h . ilr
ll^en then combine, forrtiTCX a raol<^ui,
which Mcapoi as ortlinnir hydrogen gu.
The potfl8»iaai hydroxide formed under*
OTjruKES OF ELECTBOCHEMI^TRY.
39
foa ekcUolyflia u above described, and
thia proceaa^ lihc thfit vhere an acid wqh
d^tJoycd, i« a coDcmuous one.
Tik«p finally^ llie deetrotyeia of a sfllt^
Her« v^ h^ve Iwo c^^^ to i\^R\ vilh, b£
iiid alrcudy Wii KinLt^d, Tnki? I^rat the
limplor ca*c, when; the meUl in the salt
dcauot decompose tva-kr — sny copper *ul-
phato. The copper cation moves to Ihc
uthade, giT^ up ite char^ and Aeparatefi
MnHitflllir-coppf^t'- Tht SO, jiiiiiin mi^rvivt to
the *nink\ givce up its charge;, l>ut ca;moi
cKApc. It acta npi>D a molecule of vatcr.
LhUA,
Eomiiig oxygen which escapes, and gon-
adng AulpliiiriL' Hf'td^ wliirli reitjuina in
IbiolutiDn as aui^Ii if pliilinum eWlrode^
■llittgilojcd, cr acts upon the electrodes
if copper t>r a nimikr mctd la Hsfd :
fonniEig tho ^ulphntf> a^jiin irhieh then
iuid«rgo(g elect ro]_y°ii4. ne nbnvo deaerib^d.
li ooftper I'lectroi:]!^^ nre t;^^], Ihi^ proceat
^ ia eontinuous.
Ut ua nuw take tlio ^alt of a melat
•inch ducompowu wat&r-eay potassium
lilphate. The anion f^O^ passes tr> the
mode, and the pieces at fhis electrode if
iBflllj a« Jusl described, but a very diffef-
«n1oondit:oii obCuiui al I.he oAlborle The
KfD piiloisiuni nifi\i'» III i\\i'. (-Jitliaiic, )^\\vh
19 lU charjce and becomes an atom, T}iia
fwta with water, a» in th<> ease where a
U« vrac cloctrolyacd, formiiig pt>tfl3sium
hjJroiide and setting hydrogen free.
Tfce polawium fi}'dro.iidi> fonnt^J al tha
^ode reacts eheniJi-ally with the sul-
phuric acid formed at the anode, and givj**
P^sasium Bulphnte, which then under-
^ dectrolysU again ait Just desCTlb?^.
Tits would eontinu^ until nil the vater
Pieieot had been decemposud.
The «BAeutial feature of this theory it
tfiai water u dccQntiiOietl by the pruducCs
of tUciroiyeis. either at the anode d» in
t!ie case of an acid; or at the cathode in
the cat^e of a ba^e; or at the anode in the
ease of a salt wh^jge meral doe6 cot decom-
pOKe water- or nt hoTh tht imodt? nnd (!uth-
o^e ID the cape of a salt whose metal does
dccompoM wattTn The leading feature to
beer in mtnd is that the water ts not de-
conipttsed by ths cutrini directly, but that
the dttovipoicitwn, of woter is ii secondary
prvctjijt, btiiig Lffei^Led by [\tc prhnary
producta of electrolytta, which separate at
tht pole^ and then aat chi^micnlly upon thi^
water pr^pent, Uberatiug ollher oxygen or
hydrogen giu.
THIS TUfiQBlf NOT BUFFICIKJ'T ro-'DAlT,
Tho theory wiiich has jnst beer discuaflBi.!
swnis to account so saU&faetorilj for a!!
Ihc facts, that we would naturally a^k*
why look farther (or B new or different
tlieory? The above theory tra* aufficieni
fur nearly u lidlf-t-t-ulury, but fuels hnw
beru di^L-iivered in Iha hti few ypjir«
which jihow tha^ It U no lon^^er tennble-
In thL:^ tintt place it baa been »honn that
[ilthongh hydrogen and hydroxy! ions earv'
noc exist in ihe pr»4enc9 of each other
uneombined to any large exleut^ yet waUr
is dwui/n iiliiikilt/ disJft'^t'itited^ Thv th-al
r^ftilts ecetn to indicate that about onr
molecule of vattr in every millioa ejmta
in the form of xom. The ii*covc-ry of
this faot vi*ry iippreeialjly toiuplii^utea the
whole problrni ef elcetrolyiix^ tincv wc
have to take into account not nnly the
calior» and aui^in^ which come from the
elootrolyt^i but alao thoM which come
from the dissociatcf^ water which iS always
pre«ent. Tal^e the eabe of a very simple
Milt like aodlum obloride. Around the
cathode we not only have ftodtum cations.
40
OVTUKSS OP BLSCTBOC/iSAiJHTRT.
but alsc hjdro^a] calio!u; ftitd aroimd the
anode not niJf chlc^rinc aniocir but hy>
dn>xy] aniDOft, Tile qui^ticc U, Iben^ when
Ui9 current in paAUfil which ^tioru and
which nniotth uill jj^ivc up their chftrgeaf
It i» obnoii« that thou kind of calionfl and
ftniona wluch hoJd their chArjc«« ievs
firmly will giv& them tip. Accordiog to
Lh^ tho<>ry which wo have just einmiilorfldj
ihu^e ar« tlw oodium cntioiu and the
eMoncv anioiia. But this theory wotild
aUo huvc thoK lona, kvhicJi hold thoir
charges Icfd ILrmly Umn tli« bydrogeCL and
hydroxyl ions, and th^Tcforc ^ve them
up, tstfl thr chiLtgcw fnuii ihi' h/iJtu'
^en and hydronyl ions, rwjiccHTtly, be-
oOQUOi; aodium and chEoruit ioiu oguin.
Thit theory. thcTcforc, conlnint, in the
iight of T^cent «rp9iiaa«ntAl diiooveriM,
A feir-evid^nE contnidlrtinn, nml ^-^n iio
Zoii^<r be r^^i-di^d ha fiati«factory-
ritS PBSSSKT XIIBOBT OV UI.HC'TltOIAilllL
It la & very much »impl*'r mnttor to riiow
ihjit a prvvailin^ ojiivrpiii^Jii xa not ti'imliSf-,
Uuui la propose a theory which will accorj
with all the f&ct« kiLOvni, and predict raX^
tinnv OS yert undiicovoTel It \t ohvioue
from tho abovo, tiint wc mtint abandon the
theory of eltictrolynii whioh involve thu
AecooH^ry ilpcontpoEilinn of wulrr, and
l(Mjk aljQul for a roore saiiafactory cxplina-
tion, Wtf fehdll take up firct Ihi.' tlntin of
d«ctrcly«i« whiuh w held to-day, end tlwn
look to iha €11 pefi menial «Tifietiw upon
which it i« baiOil,
When « curtifJtt lii putted through a
cotillion of hydrochloric acid, we have Ibc
hjrdrogcD ions moving: toward the cathode,
and ohlorino ion^ ii>wurd the anode. ThfM
are experim^oral fnctt, whiL*h ire iade'
pendent of nay fheorj- Wo bate, then,
anjiind Iht.- E^tliode.Xvdrogen ions from the
dH#oci4tcii acid, and abo hvdrog«a iootf
fromthodiKocia1«d waler. Sisecho^
any hydr^)gcii ion ia just Ltl:e ajny otber*
hydro^n iom, it does sot maiter xrhiah
^v- regard u giving up W* charge to th*
cathodi* And ivcapiti^ a* givcouff hydrogvi.
Around th« anode, however, wc hnve tvo
di^crcnt kinds of anion»--chlorin& froei
tho diMociAted acid and hydrotyl from the
dJtaoeiated vater. Which wiU give up
charge to tJue pole? Obviotisly, the
whidi holds it lUM tirmly. According
the? old theory it itf the chlnrirvc,
aooordinc tc the nenr it ip the hy<lro3
Two hydroxyl iinioiia loio their negal
chnr^« acd 1hi>n form a moli^a of
water, &^tiii^ oxygen free whJrJi escapes
from the eolulioo* The chlorine aniotut*
suffer no chnit^c ©t the pole; tlkj nmpty
lerve to oarry the negative current to
tbii electrode, a&d reform bydroohlorir
aeid uvith t)i«^ hjdn>j;uii Ions of the water.
If we arc e]iM:troiyxing pot^*aium hy-
droxide t2ie facta txt that poteseinm loof
naovu towHrd the ctthodc, irhiic hvt^roiyl
ioQA move towort^ tlic anode. Around th(
oathode we hnvn, th^n, twf> kinds nf 4jitu
— potaMium, coming from the hydroxi
jiod hjrdrogen, coming from ibe dxMOi
portion of the water. Aroand the
bowJ^ve^r we have odv one kind of aokoa
— hydnml eoininjj f.-um the diuociaied
bitM% mid hydroiyl tinning' fmin ih« dit^cf
ciaW water. The coac ia the rcvcno of
thnt which cxiil» vrhi^n an acid waa cb-
ployed. In the latter c«JKr ihoro wa« a
oonimoa cation, hydroigan; is the cose ol
a baj&e a eomTnon ini^n, hydroiyl.
WhiMi a (TiirnaLi i» pqtoed tliroii^fh a
aolulion of a hue the hydroijl aoioDB
give up their chnrf^c* to the anode,
liif an a^e ot 4i«e^ii ii)*.
OVTUSSe OF ELBVTHQCnBMiaTnY.
41
form wiatcr oqiJ iitxygcn, At the ccthode
tJic old theory snid it viu the potABBiQin
lOUff which (^ovo u|j thoJr charges, wliilo
;he new says it i% the h}'ctri>geti idiib from
the ^Idfioeinli^d water. The polasaiam
rent to the cnthodc, and form again at
this electrode potassium hydroxide with
thfl hjdroxyl ions of the water.
The el^ctralydfi of n aalt ia a little more
ctmiplieotwl, iiui presents no M^fioue difii-
mllj. Takti sodium chJoride. who»e ionfi
ire s^ium which move to the cathode.
and elilorme which iiiuve to liie anode.
Wi> have two kinde of cations nrouiid the
oathode> soiluim aed hjdrngtTii; and two
ktmU of animm nroutifl the auode, chlnrtue
Uiij hvilrMtjl. At the cathode the hjdro-
fOt iona f^VT? up their c^hur^v;; utifl cccnpc
II ga«efMtfl hydrogen ; the potaasium
Cflliom forming ptiU^aium hydroxide with
tbc hydroxy] i<>Tis from rhe wat*?r, At ihe
mode the hydruivl anions give up their
ohargtt, formiog wattT, and ojEy^'L'Q which
9Map»; Iho chlonDO auiotie furmtng hy-
drochbrie add with tho ln"drog;en ion*
ffoni lh(» diwiociiitMl water. The hain
hnavA nt ihc rntlrndt' i.-^iu Thru ri^act with
thi acid f^^rmed at the anode nnd rc^fcn-
»nie the entt
It viil bo o'b?crved that thia theory
clJTcrs fnnda men E ally frr>iii ibe oqo which
»a* hfld f*ir Rich a long time, in Ihat it
''ITMMita the dt?ooripnsit ion of water as
b^ dTeclcTil directly hv the current
** hftvc here iA* primary t/aof>mpo*i^iofi
"Y tffljfr in ciectrolyei^, iv^hile tho older
tJifOty roproicrtf'd the dceompositiiHi of
*lter ft« A mroHchiry ptotf^sH, prndueed liy
^ product*! of rVt'lrolyi^ifl actirig chi^m-
iPtlly upon the water.
It should ho olHdrved thnt thiB theory
iffttctroljAis reaemblea In a striking man
ler the very early thcerics, in that it rep-
resente the ^vator as being dceompodcd
directly by the ciirront— the cJectroIyt«
(imply serving lo carry Ihe current
through the aolutlon, ur, aa il was aatd, Lo
aiakii tilt watf-T u cmiduettir, Tlic new
theory^ of ceurw, incorpor^lea much that
was not contumed in the old, having the
advantage of a huU^eniury of invefit:ga
non on theiin and MmiTar prohlt-ma.
It is, Ji8 we hnv.? sjiid, not mph a diffi'
cult matter lo propose a theory aa it la to
tort ite truth* How can the theory which
wo have just oonaidered be teatcd esporl-
riLt<n tally?
iBanNO TUB PltEgfiKl TIIEOaV OP BLE(>-
TKOLValK.
The theory with which we are now
dealing could be readily teatcd experl-
mentally, if we had aoine means of deter-
mining in any given case which of two
ions would givt up thtir ohorg© musl read-
ily. Such n nitnns \\n.i been furniifiL^d by
Le Blanc^ lo whom we owe the whole
theory whieh we have jugt described-
If wi? attempt to pa»; a current through
a 9oIu[icn of Hny elnctroiyte, Ihe reauli
will l>i? dependciil upon the eloctromoiive
force uf the current If this U below a
L'crtiiin laluc the aurr.nt will flow for an
inetonr tind then ceuM' to flew, ^ can bo
ihown by inierpciiing a galemiomtler in
ihe cireuU of the ci:rnmt. When lh<r cur-
rent \\nf> michcd a ci.Ttaiu ^lectroiimlive
force, wliich varies foi diflcTrent clectro-
lyfcfl employed, it will flow ooatiiiuously,
;ind ^leotrolyeis will t^Foe plaoe, aa already
described. Thia minimum elecrlromoUve
fdref^ whli'li will ju»t drive the current
cnnLinu'^rnHly through tho solLi!ion of th«
electrolyte, is known a» tlie "P*:>lnriintion
Minimum," or "Doeompoailion Vftlno" of
ilio snbstftncG m quaation. It meuu that
41
OVTUireS OF ELECTfiOCUBUlSTRT.
ihu riMtromotive force, or potential, is
required to cauw tho pnrticaUr toni vitb
vhieh 1V4 itro dcnjing to give up tlinr
chntgTc. Ily slwiyiog the iJeoompoft'iaQ
rahjcs of diffonmt olcctrol>tc«, uulu ling
aci^s, bu««, aiki! a^lts. we obtain cxit^ily
Lho data irhich wo nc<<d to lent thu Lht^uc^r
— w^loarn tJic relft(iv«**ij« with wliictj lh«
dilTiTi'iit i<^iu gitu up ihi'iT chnrgiit. A
fow of the decompnutioQ values of (ha
mon common &<:i^, bctiea, utd salts, in
Qcrmal aoluUon, ar« ^ives b«kw:
U 0n<U^«lt CO
auii'kiDto «dd 1 07 '«i *.
Min« - , i.«o *•
F^H|i1iurte " 4,4», .. ■ ,, l.tO *'
Mmirvhl'^ruvtlfl A Id ^ l,Ta "
L»(fHa™«U ■• . .... I « ■■
VHloBie -., inu -'
Uodliiin l9dn*U» |U '^
PoomTuhi *- ■i»*H«>i>. hV -
Aniuuolii'a " I.T4
Bviuu a1<ni>a .■■..»■............ L9 "
Anm lufn " .1 ....»'■•■ ^V "*
OkhiD - tit -
ftMwriun " ftlt *-
HMJniD ■» »1J "
Th<m> aro the facts. Let 111 now iwa
urtint bi!uring thnj hiivr ujioii t)ic UiLH^rj
ID hAQd< AccoixHdj; to tills ll^corj t^
cIectrol)'»iB of eik^ one satt Ib the same
firoceti^ 08 iho dc^ocro)j«Te of an; olhor
iflll, 0^noe the ions from Lh« talt sjinply
carry ILl' L-urrx-nt ; while tt is the hjilrogen
mill hjflrotyl iaun (T*ja\ Oii? diwocialeil
walfr which j^rc up their cHiirges to, nnJ
tcpomtc at thij jto\pt. The tlocompoiLitton
rmloGfi of aalU aro thi; dc^mpoiition
ralnea of hydrogi'n ;in<l hydroxyl iont,
a£ tlw cornvfitraUonii which olitnin, and
slioulO be i>rai:tical]> the tame fi>r all
Mlltf- The aboifft n>*nlts for the rlccoznpo-
ftition v&luM of mIIb show that fact and
theory are m ■atlafactorv accord.
Take tli« CEue of ^cidi. TtLvue dJaso-
ciatd into hjdrogen catioru, and into
anionf whoie nature depesdf upon the
acid uMd, Toko nilnc acid; llio hy
g^ cations move to th« <«thodo, fr^^c
Th«ir chargea aiid woape, at tq
4WTL The ajilona mova to tbo
but do nrjt g\\ti lip Uir-ir c^hnrgt*!: tl)7
hy^droxjl anions frcm the rater giia
thi.Mr charf;c4 iafkad ; an <i^uaI number
h_\fJroffrn ionii from tliv- dii^toirinl*^ «
n^maiiiing in solution and r^onn
nitric scid with Ihe aiiiona.
mtiat, thtrefort, be a cooataiit deoom
tJon value for acid», vhicb correipondi
tho poL«ntial required to dbdiarj^ hj-
drnx\1 iona on <he one band, and h>drogdt
iuQft on the utlu=r, undiT the eondittODS of
conccuiliutiojui Vkhirh ohiJiin' Such ia arm,
from the dccompoftuon ralun of acide
jliv-cn ahove, to be iho caac. Thja oorre-
(ponda to nhoui hT voJta for normal
tiniu nf add*
Tho facte and theory agr^v so well vrij
ocida, wo ^otdd natnrnilj turn next
bas9t^ Th^e yiold hydroxy] loiu ndil
gjr» lip their charge* 10 the anode,
K-atcr. and oiy^a vhidi t«ica|Mw.
eationa iaoT« to tJw csihcd«, but do
j^ffl up Ihtir charico*; the hydrofta ioaa^
trom e)ic <rat«r giviiiff up thoir ohni
tn«toad. Wo ImTc h<*zv oxacid/ the a
pTTKi^ntej taking plarr lut in ihr civrtf
yi^ifl of actdf^, ard ihc dccompoaition vnltf
■>f Ljui-« should W thr aami^ aa thai i<f
adds of ih« eantf ooncenti-ation, ainoo Itwy
«n^ rhe drooni position v»Itii>b of liydrogtfi
and hydroxy] ione, the product of vboaa
coDccntTation it a constat:!. Faft» and
iheory, Ih^refore, agree aa well in the
of hoi^ej HA of aeida and salta^
There la, hov-evor, *tUl one more
whioh mu^l Iv* coiiiidt^n^d in col
with Iho dfffi*mfn»iiion tbIuw ^renai
in order that tho line of rtaaoning from
thcAe ralurv uiar bo complctOt
OVTLlXEit OF Sr^i:CTJiUCilE\(ietTliY^
4»
''Acid** AQd \i&mi cf tbe ume concea-
tration mu^t have tbc mme: dccompoaitioD
values, oa we have neen, because the prod-
uct of 1h« number of hydrogen aad
hrilrt^x^J ioD3 in ^ufh ^oltitionfi muat,
froiK tiiP law vi iiiflhH airlion. rtlwiija re-
main con^taiLt. It ifl, however, quit« dif-
ferent ^th a Nilt, Af the ortihotle hydro-
g«ii ie libcrntpd niid a buee is formed,
vhic'h mfiflns an increase in Ehe oumber
of hydroAjf] ion& aroimd Ihh pole; and,
limiloilyr tlic fcruiatti>D of na acid
iround the anode incrcAsce tbc number of
tty^rogOD ions around tbo ADodo. Sinee
the product of rhe number of bydrogeo
tn^ bjtlroiyl ions wliich ean rfimain in a
>olutiou U a. [X^nslani^ oil iiicreAfie in the
nuni1>er of hydroxjl ions mefina a decrettee
in the number f>£ the hydrogen ions pres-
ent nronnd t.ho onthf>d<" ; anH, simiUrly, on
iDcr«flfle in the number of liydrogon ions
arouiul tbe anode would dimlnit^b the
comber of hydrusyl i«na around this pole,
Both of tbcKo itilluancee ^voold mcreafle
fkn decomposition valuo.
B(mr, 1^9 iu, theory aitd fuel are in
ptrfpcl iiccofd- A poiii|](iri«cin of the de-
COiDjftoeiUi>n vhIdes of uciils and ha^i^. vritl^
thofeof aoltfi, will shew thiit the latter arc
OQvideTAbly larj^r than the maximuio
TiluM for the former.
'Hie evidence fir the jiresent tlietiry of
dcclrolj^iis IB, llien. bo eatitfrictorj thnt wo
**iiPoi beftitate in accqitiniJ it a* n highly
Feobable oxplanation of wti&t taktie place
*^ a eurronl i& passed through a *oln-
tuMi of an t<*id- bflST:', or nalt-
Tht grfflii OilTjujIiy wliii."]i hna been en-
<»initercd in draling with a process, ap*
(•foilly no mr>re <ornp]ic!atod Ihan the
^tetpoiysiE of an aeid, should be noted.
d***i.*Iiich wilita iPuM4ilK'il milioiiBw future I*? iho
It U a ^neral fact that Nature deals oat
her truth with a sparing haofl, and onlf
as the roward of an enormous amonnt of
labor.
TUB ICLBOTUOLVTtO Slil'AR^TION OF TIT«
ujeiALa.
There are one or two other matten
which muiit bo eonsJdered before thia
chapter \& eloeedj since tb>-y are of th«
very deepest signEfieanre for the pi'a*rucal
eleeLrocheniiet. It is not only poiwible to
deposit many of the nietala from their
orofl by means of tbe current, but to aop-
aralo the metaU from on& anolher eleelro-
lyliealty. Tn obUining llie inetala from
their orcti, or in purifying them after they
havu been oblained in i crude form, Iho
eondUiona undwr whioh the oleolroly&ii is
efTeefcd are somewhat modified from caw
to ense. The great prTiblem here tti to QBe
eltfclrodes whkh are not attacked by the
products of electrolyse, &nd to so modify
thi^ oonditidiii thai "the yield" may he
made u^ hirge us |josBihle For detaiU in
this cnnm-ctiou referenep oulj can he mada
to flonn- toniprthensiiJi! work-* Suftic*? it
to Huy that podium, pocasiiumf Itthium,
htivium, caloLumr atroritiDmr aluminium,
nippiTT, fiilviT, gold, platinum, and many
nthcr meinU are rmw readily obtatupd by
eJcctrolyftiftn
The problem of dL^c'lrolyttc aoparatioa
of the mctolti is of epoolai interest Id
eonn<?eiion with thi" matten whieh we
have jn£t consideri^d. If a current ia
pas^d through n solution containinfp ncv^
<ral kindn of lone, all of theee will take
part in carrying llie current; the luuouiit
enrried by Any onp kind of iung dtpvndiug
upon the rehilive numljer of theat which
are present, and upon their felodty.
When ihose reach Ihe olcctrod^, those with
•|iArH>iJu>ni' '-RlAttTdnBUllU'tlR '
Ol^TUSEy OF m^CTnOVHE^JSTHY.
the lowvNt duf^om position valuve vill sep-
nrjili^ ftFKL If i.lir (lirffTt'tji^e iu poieiitinl
fcftwern tin- olcclrolyir* niiil electroJe Is
loM thsQ the dccompn^itioQ value of any
ion. thifc wiJl not psa up iU chnr^c.
The dcconipofiiltoD values of the dilTe^r-
cct ioti» are nr? dilForrnl. and Ihie makes
it ponibb to effect <*]ectrolytic iffparationa
of the raefalflu A curreni of electromotive
fofL^e judl. atiiall enou^Ji to oauAe the ion
witL die Iowt«L ilpi-ompoBititiii valae to nep-
ariite, iv used uV HrAl. Tlie aloclromottvo
force of the uurrent u then meroaeod un-
III the decompofiiUon value of tbe next
jun iH reuL-lKil, whviL il will ntiEidrate. and
m on. After all the ii>n» uf any given
dCfnaut haw ^eparak^d, tho current will
ceuK t? flow until Ltcs di'c'tromotivc force
bw 1m«il raivt^d to tliv di>ooriiporiilion val-
ue nf tJip iun rfjl in Um .wnc™, no Uiat it
j« nnt very difficult in pructicu to bo regu-
late thr^ oonditionA that pxiii quanlilativc
•Ufjaratioofi cofl be ofTeclctL
It haa, howevur. boin clearly r«4>ogmied
thnt cumtrt etroriLfth or enrrt-iif dt'UMity is
an impnrlnnt iat.-tor in tlfclr^tytiy w^imra-
tiODS, aince it oonr^itinna thc^ nu]iil>cr of
ion? which yr\\\ scparjitc m unj givou
timci- li the dcnsii}- la grcjitt, ihc ions arc
ruahed ovor 1o tlu> electrorle m riipidly tlmt
time is not g;ivrn for nl! tli(< morif raHJly
dietdmrged Jodh tu reach the ck-ctrode by
difEudioD. tit:., and some of tho lom vith
hi>;h'T ifi'- :iiTi|i Hifi in v^ihioe may B^parato.
Till" ri-uli I-. ili.i; miii-.r these ccntliiionit
onlv partial sfparaliona are securei].
From thd etndy of thif deconi position
vttlues of llie loris liv T-*i Ulain.^ Freuiltn-
Ihtk. hnd others in Oatwalii's laboratory,
(he whcilr Hubject uf the electrolytic sep-
arutiun^ of t[ie mi^tale wa^ oponcd up,
Tha i>leolTOlytie action of the enrrenl
hai alao heen applied To or^^io eom-
;)OundaT vlth «oiriQ remarkable reaiilt«.
Organic aindB, aa has heen stated, diaac*
i^intp intci a hydrogen cation and an anion
which contpriflca the remainder of the
mnlot^ulo. As tt ^ell known, organic an-
ions nrp always complex, and in many
r'liHP* are very oomplioated group*. These
}froup«j when tlit^y aeparute at thf^ aimdi^
arc generally incapable of eiisktLci: ai
«uch, and either combine with one another
and form new products^ or hreak down in-
fo hiin|ilci' siibstanee* Thus, tliL* anion of
ac{»tie ftcid> C1I,C00 holda ita chaise
lets firmiT than hvdroxyl, and whea it
arrivp^ nt the nnodc it gi^G^ up Jta charge,
and then, being incapable of existence aa
jiich, breakri down in Llie sense of the fol*
lowing equation;
T\vct anion of propionie add brimki
down oa followg:
TliP ek'otrolysia of organic Iibbib ha*
yiL'ldf^d Bimilar results in the few cii9C«
which havt bt-cn jtudjcd. The Cfttion oC
the organic ho^o is too ccmploi to oxirt-
uiichiu'gcrl, ami wlu^n it gives vip \x% c^hnrgc^
rcartions (iikc plncc giving rise to itev^'
rroductft. The elticlrolyns of organic^
lU'idn hna alrfidy hfcrimc an importan"*^
inpana of offooling the eynthesis of or —
jninie ciinipnuiuL^^ and. nn examination o ~tf
ihi- litrmturc will show lliat (he rr«iiilt ^
already obtained nre not only of scicntJS -^
value, but have found their way iDto th-^
factorii-s as mi«iit of syntheBizing orgonw^^
dycstnffs mitl Ilie liki\
Thc clcctrolysia of organic conipoun^M
is not limited to the acids and boaes* \>^^
hn$ been extended to oihftr claBSOe cf 9iitt^
atanees, *neh ns the eetere. Thus, wb^^ff
the inonopthvl ester of malonle acid, ^^
OCTLiyUSS OF KLKVTHOCHBMISTitY.
4B
nther^ IHr potassium salt of thi* cetcr. is
subjected to electrolysis, the following re-
telion take^ place :
3CJI,
COOK _CU.C0OC,H»
0OOC,H5"CH,COOC,H»
Kroin th« moTioesler of n dibatic acid, the
dicttfer of H <]ibasic ndd richer in cftrbon
WM thiiH obtained- WalktT fonnd Ibat
this was a morf or less getieral motho(3 for
pu«in^ from our- dibaiiio acIO to fttioth6ir
richer tn oarbon atornB.
The appheation of elecLroJysm lo or-
^ie coropounrlft h^^ Ijwb Just tii\\\y be-
piQf artd from what ha* already been ao-
coo^itished, it f^ei^ms pruLaUe that much
of istercfit to the miw of £i;iorice and also
tn th^ praoticol L'lwlridao. will be diseov-
CT*d in this field-
VTe hiive hen^ then, both in inorganic
cfiPmiAtr^ and in ursniiic, important
hnnchct of iiiduatry dt!vvk]|ied diriLMrtlv
fol of inve4tij^aiion» midortaken and ear-
tiwl nnl in the inlerest of piire srif-ncp.
Iiidfcd, thi« !£ almost mvariiibly tlie ordor
of |>TOgrfdS^ The inve^ti^^alor works A&d
'^•WVOTB th€ truth purely for ite own
"^«, jvM becauB^ he de^iri^e lo know wluit
it in The prnrtiral man applies th«
knowledge tliua bbUuii«d to Wm.-. wrlfun- of
the human mcc, often, hoTfftrer^ adding
gi-ftitlj to it. T!ic- importAQoo nr»t only of
accurate scLcnti^c knowledge, but of ect-
onlific Investigation in the factory and in
tho shop, h heiu^ felt to such, un eitent
ihat it has become an absolute ncce*i^itj,
and wc ?co today in the lar£:c Qermfla,
and oth»r fnclorioB. invoetipation being
(parried on lo an enormoua extent. Th^re
is one chemioal factory En Germany where
more than 100 trained chtiuit(L« arn em-
ployed to carry out inv^tigatioiu alonfl^
and maiiv othero with a smalbr number;
and this eng^restfa another thought. The
men selected to carry out Inveallgationfi
in the ^reat factoriea and ehopn in the
world are not mon who have had a nar-
row, oiie-aided, train m>f, i« n iavr thrngs,
bv»t thoa* who have had broad traimn^r
along pnrvh' ftt^iL-niific line's. It is now
folly recognised tliat ni«n who have been
traioe^i fir*t in pure ecit*nce (ire be*t
L'quippod for any lino of teohnicfll vork.
In a word, the proper placo to lay the
fotjndutirin for the rareer of the pmctii^Jtl
man i» in the rrnir*r«ity.
The next chapter will doal with the ve-
locities with which (he ions mOT^e thn>ugh
*ohitiui]K. end *ionie of the methods for
dr'l*»rminiiig theup velocitie*.
4<
OUTUyBS OF BLECriiOCttSUl&THr.
CHAPTER V-ON THE VELOCITY OF IONS,
WI-" HAVK fi'fvncd rcjmi^'tiJy in
mir latil ehaptei to (Uc more*
tnciit« of tlie iood during eloctxol-
jbjd; tho catiijne movui^E with iLe cur*
real towwd ihcr oaLtiodo, ihc unioiift
AgftUul th« ciirrcDt Uivard t!ie snode*
Since, from th^ law af Fflradnj, clectiicitj
aiu [lum Uiruuifh ±'>lQtioii« of electrolyte*
in cnlj one vay. bj tho aimultaiitoiu
KLOTcmcnt toward^ and eopamtion of th(^
ions At ^ olGctrodo!, it U obvious that
th« «tudy of tlitf velocitlBi wilh ivhlcli :he
jcnu travd under givni oondilioot, it^ a
matttjr of i^oDMdcTaLlc impi>riance.
There are rtally two proiblcms involvc<i
in deUinuinin^' Iho voIooLti«6 of tb<^ ion»:
Fint, th« dtft>ArmijiAticii of tho relnim
TclGcitit^ wilh whii^h the iriim tiioi^e ; snil.
iecond^ \\\as ilvt^rmluntioii i^f the absoiulc
velocities with which the ions luov*;. If
the rclatJTc yclocitic* of all Iho tons buve
cnoo boon ddormin^l, wnd tht? iibHotut<>
tolceity of any ono ion im known, thu
aWlutc veloclrif'A of a1] the ion« cnii hv.
oalcxilatc!d aL onas Wc fiUall take up flnt
the determination of tho relative T«lcoitiQd
of ioca-
Tt is not a ftiitip]« matter fo §^ at otce
hov Lim iiiun cku riiuvd with lery iljITeRait
vdocixir? luwan.1 ihr jmtn, jtnd yu^t the
Bomc numbnr or aamc ctiuivalcrjcc of iooi
Bcpatato at th« two po^M. No cation
ciui separate at the cathode until an anion
afiparstca nt the anode, and for every ion
vhich »eparateft at out? pult au lun carry'
ing the opposite chatj^ muet separate At
the othor poll*, It may^ of cour*o, happen
that oii« of thc> iomt Ia bivalcQC and th&
ether uDivaleDt In ihh cam^ for ev«rv
piion or
i
bivjiJcnt i»n ^hich «vparHtes at onie po'
two uoival&at lou^ will v^parale at
other. This b obvioua from Kartdaj'i
law, whicii refers thif whole coficeplion of
ch^iiiJcaJ vaieoca to the numher of
carrk-d hj tlw m\^.
Ici atmpidc-miii^in of tIh' confueion
aaually arific^ from the couLtfaij^a
\he above problem for the firat tim^ and
with a dceire to simplify it, UitwaFd pro-
poai^ the follovin^ illiutiatioD of wkgX
takM place erhim a cumtiit ia pa^wd
tliroa^h a sulution of «a electrolyte, vb«e
catifjni Olid nnioQa move with diJTcnaU
leiocihes. Givt'D a homogeooaua aolati
whioh ilways ooctaina Iho Bameuiusbcr
c'jiriorrv and anions, and lei uiatj that
ti^lgrity of fhe anion in twiet aj great at
thai of the L-uttoiL l^'t us rc^rewot tht
um^nj: thuf, u, and k't ix« rejircaant tii«
cati'jns thvu, -i. In auoh a tiolution
^^[iu1d h«vn the fo71f>vtng arrangommt
tilt parU:
A
O O OOjO o oo|
e e eejeee e!
Fro. :f.--ION« TH A H0U*V>CNKAr* ti«litJTU^fl^^
For cvtry anion lliere would be con^^
■ponding cAtir>n, and before the cunrnl
WJI3 pfWfod ihoi'e woiild. of ootmct b« oo
dooonipoeitJi>D of the elwtrolyte. Tho
pprpendieiilar dotted line doe* not mmn
a p<ir(itii>n runninii down through the
^luliun. but is niiinply Iq indlrife I
middic of the tolutioii.
1^1 a cvncat be now paaMtl tiiro
OUT LIS SS OP ELBCTROCHEXlfiTlfY
4t
lh« foluUon, the anwle and cathode being
plii(*'d in ihp poaitiotu imlicsit^d fn iHe
ibove sketch- We cati allow the eiirrenf
to pass until any number of Biolecnlcs are
dewrnpost'd : but fir t he &akc of simplicity
ki the imrrtnt i\ow until iAr^fl molecule*
hftro been elef^trolyzcdj nnd their i4»mi
oiuseil to 3epura(e iit tby two polte. The
foUowIng KontlitiDri wnulil Llwn obtain in
Iho »oltitioD;
A
ooioooboo
A
Geejeejeee
We would hftvc three Arions icparAted
8l the ancdCf lib shown by the ihri-Q circles
irni*air«l with cations; ami we fihould, of
cuurv, hftVTr IhriHr ciiilinna i<;[Mratsr1 at the
cfltho<Ic« as is ehown by three lined circles
unpaired with noions. The important
p4rt of iho problcrn, howover, from Ihe
>taiidf>oint of relative velocities of lone,
■till ri'irtninH fo bi- ronniriprpd lief iis dis-
^H tbc snioiit and cations which liare
A
I
o o o o o
A
e e;e e e
'^tt t— Condi TiojM v>r RjuaAiMMi SyLunow.
ffivTi up tWir chargt'H, respectively^ to
^r anodo and cathode, and consider (lie
^^sdition of Iho eolution wJiioh remains.
*t would bo as abown in Fi;^. -i.
The iainy nuinhtT of auious and cation*
**«, uf couriitr pr<?si?nt in the SHkitian,
"W their ptwitiotin telativ'* to tlu; mntral
J*lime running; throui^h tho aohtion. ore
^^Ty liiTenTnt froiTi the pdsitiona occupied
■**fnre ibo curn-nt was pnssed. Tn th*
original feclution wo had four aniona and
four ralinna nn parh sitle nf tbp ceatraJ
plnue. We have now only thni* nnioui
aad three cationa on the right «Ldc of thU
plane, and only two nnicna and two cat-
lone on tlio left mis of the plane, The
conditions are thus insrlcedly dUTwcnt;
Ibe original aulutJou having lost one
anion ami out? caCion on the right iide
next to Iho anodr<, and two anions and
two cationa on the left aide next to the
cathode.
TUis r]lu--1mlio[| [lot oiHy aeries lu show
how the AAinc nambt^r of anionii and cat-
ioua £t*parato at tho two polea, and yet
the velocttieb of the two krndb of ions ba
very ililTi-rcnI. but ako gives ua Ihe clue
to the prinf:ipl« involved id determmiDg
the telatire relocili« of ioTia. It liaa been
observed that on tlic anodo aide of the so-
lutioin there is a losa of one molecule, and
on ih^ ciithndi' M^ of the aolution there
is a losf of two tHoWcul**^ tJie total num-
ber of molecules dccompo?icd bein^ thr$6.
The above numbtTB, oco and two, bear
osactly the samo reliition tc om* another
n* Ihi' vMoeiliea witli whicli, by UypotbeKlaj
the cnlioiis and anions travel. We thus
arrive at iht general rule: 1*0 deti>rnimo
the ri'lritivo vrlocitytif ib>.^ anion. divide the
change in conevntrattcn around the cath-
ode Hy the t^ilal niimbrr of mnhviih'* de-
composed To determine the rclalirc tc*
locity of the cation divide the chanf^c in
concentration around th& nnodo by tha
total numbrr of moloculfts dvconipri«ed.
So moeh hy vay of illiiitrntirtn of (b«
principlee involved. Th? more iinporlAni
qucalion i* how cAD Ihcac rclotivc vclocitiet
he determined oxpOTinu^laHy ?
KXPBBIHKKTAL infTERhTlNATIOK OP THB
RBI^TITE TJLOCrriBS OT 10»B-
It 18 obviouB from what bae h^on
IS
OUTUSES OF ELECTROCFSMlSTltT.
said, that in order to dot^drmino the
»l&tivG velocitieB of any givvn ofttion
infl union, lE is neeeasjiry to oleclra-
iyjA'. K iBolutioa (<utTtfiitniig this ration
and Orion, and then to dclemiine the
chuBjfpe ID concentration nround the eJot
Crodof. The carrotit should l>e paewd
until nn nppn'cirtbl*? flmng*> in ctmoenlra-
tion hrts U*ii prodjiwri, hut mu&t It dis-
continued while Ihrre is Btil! a middle
layer of Lhi? en!ution nnactrd upon. W*
mu&t know, in addition to the chitngee in
contvntmtinn nrnund lite polc«, (he tutnl
arooinil of the drctrolyie dut.'umpusL\l,
Thi« con be mcaaiircd cither directly^ cr^
movo txmvitmcxitiy, by gimpiy meaeuring
thg flmounE of criiirtrnt which has p^^cd
through thp i^liTtmlytr If we know
the amoust of current which has paeaed^
fr>m raraday* law W€ can calculate at
once the amount <»f cho clocirolyto docom-
pond. In praelicf the mode of prooediire
\s OS followfi: Thi> finliitifin. U plarpd in
some convenient foiui of Apparatus
(vhich will be dcecribcd a little later)
and the cuiTL'nt paaaed until a oonaidcrabb
ohfl&ge in concentration has be^ pro-
dneeii around tlie uleetrode* ; Uii^ elec-
trirtlrti ust'd U^irij^ »f the sann- iiiftal «s
the cation of th^ solntion.
Thc volution, whojl4^ cont:QalTation vaa
originally known, i? now anivlvxc^d utound
both doctrodo*^ and th<? ohnngc in Linnocn-
tration predMced by iht* enrrent thus de-
tprrnined The amount of current which
haft pmMifd IhrougU the x^lutjim U than
dettrmiiieti by tome convenient method,
utaall)' by mcrans of n vilrcr voltameter in-
serted into the circuit; and wo have all
tha ilfllii titcesanry for efllciiTating the
relative veloeilift* of the two ioiis.
A \nTtiv Duuitwr of Utrmn of apparatus
have been enLplojed, the (object being to
secure a simple ani3 vatiefnctory aeptrn'
tion of the aolutiona around the two dec-
trodee, after the <leotrol>Kifi has bo^n
ended. It it not unfair to eay that many
of th^ forms whi^h hav^ h^n dcviaod and
ns*Ml. wmnot Ije regwrded as having ai*-
eomplished this end in a uitiafactory mAU-
oer.
One of llie moat Batisfactory forma, u
it ftppeikra to ra^, taking all aid(« of tV
problem into ai^oount, was deriaed and
used by W, T. Matl^er in the Johna Hop-
Icina UniveTfity * This apparatus ccuaietj
owontirtlly of two upright tubee. which
9hi>uld be closed at the bv)ltom by stop-
cocks. These are eonnecled nojir the tops
by a U tube, in the centre and at the
lowest part of which a afop-cock of Tcrj
large bore is inserted. The whole appara-
tna is thxu perfectly Bymmotrical on the
twtj fidea. The electroiles were inserfed
into (he boiloni of the upright lubea^ pass-
ing through giound-glaa* etoppera. It
would be niurh bi>ttcr to have the bottoms
of those tukv closed by *lop-oocks, na
sLaiod above, jtnd the electrodee pass inM
the lops of the tuhea well down info the
solutions on the two eidea. The work in
wZucU thicj apparatus was used bad to do
with ailviT eolta, confitiquently, silver dcc-
trodos were need.
The curri-nt, measured by means of a
siJvtrr vollanieter, was pafiflcd until the
i^olutiivns in Ihr two upright tuljca around
tbe elcctrodcfi had aufTered conaiderable
change in concentration. The carrent
wa^ jnTerrupted while rhoro waa Btill an
unallired Uyt-r filling the U tube, the filop-
I'rx^k in this Ltilie tta» rlwfMl, and then nil
ihe alierod solution ground each dectrode
\Mif druwn oTT mid JinwIyKi^d The change
otrruyKH or SLXcrtfocHKMtsritT.
io concentralion aroond racb electrode
p» thill il*-lerniined.
The advantage of ih'm Apparatus OTei
(AhflT forois. is th*t *fccf the clcctroLyiiU
Pio. 5. — ArPAD^TiTft rem VcuritTvu riiv
Vcu>ciTv OF' lasf,
'm cod«<] the Iwo solutions cnn be readily
Mfttnted and ea^Ilv washed uat of i\it
VMsel
It Uf la Uwory, not neowiftry to deler-
oIm the change! tn coi^cf^DtrftUon aroimcT
tok ei«clrodea, llnitt thi- mm of the»r
Aamgm u aItaj* cqnAl Xq tbu toUl
svusot of (he cJcctroljrte ileooinpo«td. Tt
VDoU b« only ncccMery to dcimninc the
BBOUt of ^mrrvDt pAAsed throagb lh#
•ofattioo, which givM the toUJ amoont of
ite^MraljriedicnnpoMd, And theehsDg^
ia csdcuvttUAlktD Around one electrode;
tii^ cfaaag^ ill conceal ration Bnnuici the
otitar electiodo bcicj^ tbc diScrcucc be-
twMn theie two (]DADtiti««.
Id pnctiee it u better to MeriBine
dinrtlj aD the i|(tAntiiiis,nikd nee the Mm
of t^ two M e check on the rtlne of the
thad.
tKrtnatOB waicn uxt Mvact rvti
tcLATmi Txtocnwoe iwil
It do«e Dot follow ihAt th« rriaute
wlocit^ of tom obUined nikdet one eH
of coadittoTu will h(4d ender ^tifterait
conditkeia. Tha rWatiir nilacitjp miflil
chiuifi^ with the ttrcftfth of cttrTMil
utcd, with the atrv^xth of ih« fotutioQi
or poefibl^ t«inpeniaro wmM Uavt ah
inl^noncp wtuch vouki he di9««e&t wiih
liifferuii iona. Them |niDla oeu be
decided onl; b; dinct OJqpnrinnBt
Lei iia tako ufi dnt the lAcI ef rAen^-
tN^ JA« ^trtngl^ ^f cmrrmt need in elw-
lrol>-sinj( tlio eoluUon. It U aetf-eviiWt
thAl the aetutt reloeitiei with which the
iona tmiel cvonld be gceetljr eHMsted
hj tlie vtrvngth of ourrent omployod; tha
^^i^fiter llie current. lhf> jfrvetor the TtToo-
ity of Ihc ioHK ro<|iiiiw) to oArry tha ouN
ront. Since tbt^ Ac>tual votoottioe woiild
Ut vo Jp^Uy chAHKiM^, It U nol imiirobnble
that the influfinfi* fm thn ililTi<riiEil Imn
voiiW bf different; in a wor4, tliet the
n^lativo iri>looitic'« would b» r.^hnnired
CurrenU of very HJIfvriTril iitraii|[1lM
wcro utfod bj Hiltorf, who itiirlioi) thla
prohloro exporiim^nult)'. lit* fonnfl tliot
for \\h» uln^n^thji of cLirrr^ikl Hhrch ite Pin*
ployed, til? rrletlTn lelodlioa ero Mtf<
piHiletii of the «trcnf th of 1li« current.
It »hoakl he odiUil tlial in alj work on
the rrielire nJooiUna cf iona rery Ainell
cnnenU muat be employed, lit evnid afrpre-
ehMe thenmil ^lianffn, and in any wUe
miiinfE the aolutlooa raeebojiically.
The neit proUfln la ik§ 4^^ of fjo^
t^ntr^iicm o/ lAe ^^Mhn on the refjtJve
▼eJodtJea. The »oft eoDOMilfnled the
eolntion tiii» ffreeler the riarwiUy, end, eott'
eeqnenilT, the ffr^al^r Ihn mUlenee offervd
4o the inerenml of the ioDe throogli It
Jl aeeiM pffoheMe Uiet the n eofentt iHe of
to
OVTLiyiEfi OF ELEfOTROCNJSMJSTny,
dopoiidiug upon thnir si^a, mjitHj otc.
Hittorf hftft fl]*n rxjifhrndiit^t! cm thU
|>nrl iif till- [trohlrJiJ, inning Kiluiiitnit of cnp'
per sulpUaU' f'angin^ in conccntrnEion from
one to twcDiv-four. and very diffcrert
relatival Telociliefl ware fourd for llie cop-
per ion. A few of his to^uIU witli oopper
I^rtu WfLlur luOfl4r P&rl
lUlkl Ivv rdlaaU J
CUL'P?! ^ulpbV<<
of Cifpprr
C«
01»
IfttI
DJM
Ttm
1U«
lUM
OJfll
Tlio v(^lont/ of coppt-r ab coinpareJ witb
tho SOj ion is Dot ctmsl^iUj hui iticrpuits
with th« dilution up to ft c«tt«m pmntj
bL'yaorl wliir-li 51 HH4 fininiJ Ui rpjiiaiii con-
vlHiil iii> iiuiU'r lnjw jxiiah fartUer Uie
dilutioD wai incrcfu^d.
Tho follcwin>: nre n few of the ri^sulle
which were obtnitW wilh tilver niirate:
riWT"Wrtl*<r *o Oi>p r»r|
Vtflnrlrj^ of itie
rttiVKr ^Krftt*
SlUvr iun.
1^
flue
14 M
0115
HTa>
o.in
A* tlic dilution of tho Eolution in^rvaacfi
tli« volocity of the s^ilver ion dccr^ae^ up
to 41 cvrtnin point, and Iticn remjiin* con-
ttflUT, iirr inml'.T flow DiiuJi Turther the
dilution is carried-
in determining the relative velocities
of xoTtA It IB. Uit^rt-foru, Tjoc'O&'^fln' to uee
vfTv dilute* (olutiQD>i^ and, ludoedn BotuLtoTLu
wliici^i an* ic^i distill- that vth'^n IIk- 'liltilioii
ill inrmrnfipil kIiII fnrUirr tho rrlativc vHoc-
i(ic« do Dot chan^. Thi« point must be
oarcfuliy oWrvod in aU work in which
the rc'lativo velooitie* of ions ari* con-
cern »3.
The t^fTtfct of tetriprrfilurv uu Llie
rchitin; vtrlt^nitrtv of ionai hud nUo Wn
mado n fnatter of rxprrimctit. It ii» diffi-
cult to 5fty jn*t what rceult wc should
expect in Ihi^ cidc- Perhaps, if tumpcra-
turn hns any influence we would GXped
It U> im-rnwe the tliJTeronce btftw^^n thv
vrlix-itips iif th>» twd iori^p BJ?(.'p!era(i]ig the
fafllirr ion at the expense of the «1ow«l
UiHorf, who worked on ihis problem over
a considorable rar^'o of Iciopomture, oon-
eluded ihflt lenipepurure has no effect on
Uie relative Tplodtie* of ihn tons In ccip-
ppr ftulphxlc,
Sulvfictjucnt workj and espcciaUy that of
Nomet on eolations of mlvcr salts, hn?
shown that hie conHiieion ia errortwa*
Hi* n?*ulis are extreme]}' int^reetiDg, in
llial with incTttuie if* tempcmtuTe the f*-
hcities of all luna Uiut to hecvme the Atinu.
HUM more vnifcmi work by Bein, in Ber-
lin, hua shown that thi» condusion i«
proba^lv porrcd. A f<'V nf Bdo'e results
nm ^iven iielow:
TEUPKR\TL-ueS.
Budlam fllilnrrdv--.,--.--, ,. O.«09 D Ul
i^LlBiuiu " ...... tt.ora o,S4<
aUsirr iilLtnle , a^TB 0,4W
'\he v'(?foi*ilii>i j^ivpn arc those i^t the
nuions^ nnd show thnt incuji^c in tempera-
ttipc *lowB up the faster ion and ftccclcratrt
Iho ebwer.
The menning of thia fact wo do not
know at present, hut it is cerLalnly very
THE uraui-ra FOB THE Moau oombios
IttSH.
TNi' n"Uii\(' v^Wiiie* t»f *imui' of Iht
more common ions, exprcwod in the tame
amt#. ofi taken from tho beet mca«nre-
monie Ihuj far made, are the Igllowing:
H ^ :^2Ji >4 M T= 65
on ^ ltd wPu = 62
K = 70,<i >4Sr = h3
ouTuym OF SLBOTMOcirriajBTitr.
51
Ag = 6»,i Br =73.0
Hydrogen is much the swifEert of
tlJ the ionSf having a velocity which ie
iHMvly twire tliuT. uf the nest awifE^t iful
— hydrpxjl, Hythoxjl. in turn, has a
rclocity which U more th^n twice ae gKni
At. iho next fnetk^r ion; and, ihon, the
T«lodtieA of the mor» common ioiu are of
Lh« ms^nitude^ ^iv^n m {hi^ Itihle
Our nlleniiun i» urtUirullj ntlrhrl«l "m
this connection oapttoinlly to the two ioDfi
hydrogen aiuJ hvdroxjl; these moving bo
much faster than imy either known eub-
(Ubc^- a moments thonght aJid we see
tTiflt llinbe nrp th« iocs whteh, when com-
bini'd, fornj water: and they are the ions
E*rmfd when water disaociatw*. This re-
olU the remarkatfU prupertifj in ijenoral
ft/ (Afl suhjitafHc, utiicr. If we cuinpsrp
ilmoet *iny properh' of waier with the
ODnvspouiliDg property of other sub-
9butcc», we hholl find that ii rcprceenla an
mrcDLc vaiiic It cittier gtnnda at the
btttd or at TJae bottom of the lUt with re-
,,"^V:'Y''""^V,''.
Qirai]L.4Mj
or Ion»,
<|wci to n s^^K'ji |>r\>ptrty, unci utniiilly at
^ hmd- TiLk4! tho BjHiciHi: h(*»t of h<iLiidji,
"^ler fcTnndiiit iho top, Titkr rh^'du'lt^c^tnc
^nsUolsor sp&^illc imhictivi; rnpacilipe of
'^nid^^ watL*r n^aiii biamh at llit- top ; with
th« piw»(hli» purvptimi of liydrn^rn tV\nx-
idc, which, howe^tr, ha« uuL buen pmved.
T&kc the power of litjuid^ to dib^ulve clher
subdtoTLceja, water is by far the be*t solvent
known. Take the powor of solvents to
ionize eketrolytet, wuliT is the elrongeit
(lis-sncinnl krown; And ■!" it g'^*w through
the loL^r li*t cf propertica which can be
compdTcd, Taking all in alU tho result of
^ich a oorapanaon would incrvilably Iwd
to the ooncluBion that woJer is by faf th9
moat r^rruitfeaitle chemical conpouttd
known ta man.
The above is a tVifcH di^Tession from
the mnin theme, hiii wa* auggcatcd by the
incomparably gr^at voloeilies *^f tho inns
w^ich iimt« and form water, and into
whii.'h water diisoeialee. If only slightly,
iintW nrdiimry ciiudilions.
TIIL RELATLVE TKLOClTlES 07 Hi-EMEVTiRY
los'fl A rvnioDic nmcnoN of thk
ATOMIC WBionr,
We know to-day that a great nmn-
ber of tho properties of the elcincnta
arc periodic functioHB of the atomic
u'eight* of liiemu element*, TY^nt rclntioni
hnve lxM?n gpm?ni] iyw! in th*i wrll-known
"Periwlic isysdi'in" of the cl^^mellt**, which
applies not only to dkc chcmicaL but alao
to the physical propertiee of theee ele-
mrtniary tvubstances. OatwaJd and BrcdJg
>iave pointed out that thii »ame periodicity
nmnifr^^U ilt«df in the rt;luliv[; veTcudUtR
*'t the ioG», If th{;«i; are plotted u onJi-
DAtcti agninvt thtr atomic wci>Ehl« aa abfcta-
ens, the holojjp^ne fall eery near the aiiixiiM
of lli« curve. Th^ alkali nnftal^ oooapy
nearly theaanie potitjoti, wbi!e at the mini-
niu wi- find throxniiuix aiid nlumiaum. Cal-
cium and ibi-otlii-rnlknlinci^rth^.bArinzrL,
i<tn>ri1i[iTri.and TLui;,m'-'*innuoct.-nrai bri^ftk<
on the dewmding arms of ihe <Tirve< while
eadiiiiiim and aini: ocrur nmr the mininia.
OUThJSES OF PiLEVTROCBEArii*TlCY.
Whil'' w* tiATa no idi^ft aa to ll>o mean-
iii^ ^f tliie recijmiic« of prupertiea an Ihe
atomic ireighU increoee, it ta certainly of
mora than ordinary interest,
TILK AUSOLUTB VBLOfJlTIEa OP 10N9-
Wc have had to do thus far entirely
with, tho m^Ative velooitic^ with which the
iosA more. This ghee jis, of coiirw, no
c1U9 whaLdOBV^^r He lo Uie ^h^luLe dis-
tances which the ionft trarol to a glvtu
tiinu under a ^iwa driving forc*e.
Two general melhoda of determming
the absolute vdcwJtieg of Ions have been
wopki'd out. Only one af iJiese will be
considerfJ here. This involves a direct
measurement of Lhe dietnnce ti'a^elcd by
a given ion in a givai time, uiid^jr a givt^n
potential gradient. Tht inetliod m quee-
tJon wfte dvvtsed by the English physicist,
Lodgo, w}k>S(? name it bearb,
A gradiiate;^ gla«s tube wae bent at
right aiigli:^ near both endg, and Alkd ^ith
an a<^coud solution of golatjnc, to which
ftOme Bodium eMoride had been add^i
Th^ contents erf Ihf lube were colored
red by phenol iilithah-iii, to whii^h j list
enough BOilium hydiOJ^itSc liad been arlded
to bring out the rod color Both end? of
thi£ glaee tube dip into vceeolB containing
a dilute BC'lnlion of ^itlphcrlc acid. Elec-
trode are inierted Into theiie ueftfiele, and
A nirrvnt passed from one to the olh'jr
tJirough the gradunlcd glass tube. The
hydrogen ions pose vrith the current into
tho graduated tubo, displace th« £i>diuro
iona frotJi the iodmm chloride, forming
hydrochloric ac-id which decoloriies th*>
j)hrno]phi}»iU'Tn, The tim« Ib lioti--d dor-
IBg which the current flown, the distance
which the hydrogen icns travel is mcus-
urod, and ttio drop in potential betiveen
the poles, vrUQ\i gives the potential gradi-
ant vlwn the dUtarice i* koown Ja deler-
nniird, and wp havp the drita necetaary
for calculutiiig the abHulutc veWitia
with which the ions travel under the po-
kiiiiol gradient in qneslion.
Th^ unit potenLul grndient is tokea kt
a drop of a volt a centimetre, and for thl«
gniilieut LodgiT found the vulodty of
hydrogen, the Awiflebt of all ions, to h^ in
round numbera three thouaandths of a
contimelro per second. In three det<»-
mlnationa ha obtained thieo valuta;
D^OOJfl cm. per Hecaml
OWW
fl moM
Enowing the ab&olute velocity of one
ion, and the relative Tdocitiea of all the
more common ions, we can calculat*^ a(
oneo ihp absi^Ute vdocitiea of all of tho»c
ions for unit potential gradient.
The above resultfi fur Uj? voJoctty of
hydrogrn. the KWLft4?6t nt all ionn, canuat
but iiupreis^ \i& by their euiall ina^uitude.
Perhaps, however, ffe should not be *ur-
pnst'd aflcr all at these 1i^]r*:e, whi*a wo
eons-ider the ejtormoufi resutanec ofTered
to the inovtmemts of the iona by Iho prw-
i-niHt of Ih4> Kdlvt^nt, whir^h hIwbvs hnn con-
ftideiablc viaooaity. The comparatively
free n^ovement« of the gaseous moleculet
through spnce cannot be compared with
the movements of the iona through the
rpslstenl solveni;*, and yet wi? are templed
to try Bnch compiiriBimis, siniw the Inw* uf
gas-prpsiure npply to the oamoUc prcMure
of solutions. It seems pretty clear that
the enueo of gaa-prc^snro ie to bo fotmd
in the impacts of the fnpidly moTing gaa-
<^ou* pHr[kli>« iigrtirt«l Ilie walls of the
(■oafining vessel. It is difliL-ult lo fumiib
any Eimilor explanation of i>$niot)c presB-
nro, especially when wc consider iiow
slowly tho iona move through tlje eolvc^t*
evoa imder a eonaidernble driving force.
Thwl the mnhn-ults move witli eiln-nw
OUTLlSm OF ELBCTnOOnBVlBTItt.
61
Bl^VDOBa through the solvent U eho^ti by
th^ enormotjs amount of time reqtiired for
diffmioD to Gstfiblish equilibrium in ao-
lutiGiu, afi becBme obvious wlien we w^re
conflidering tike pmciple of Sorct In
the light of ail tht^sc fact£> and of the
mjiny iiri9U€C4>Bdful attempts vhich h&vo
been iraiJe to eiplain oainotic preasure,
it IB odI/ fair to -sAy thai we do not knovr
what is i\i& c&uBe of os^iiotic prfaaorOi but
WG do know ^Giy much about ite reaultd
and th&ir auaJo^^ to gas-preflffuw, the
impcriance of which will appear before
tiiia eeries of papere is L-onduileU.
A m«thod for determining Lhc absolute
rebeitl^ of c(?rtaii] ione, huaed upon the
Mine gentral principle m that of Lodge,
uaji devised by WliethaTn in England^ The
m«tlioil i& so iiroplo 3d<1 jields such ^Qod
raultfi that it sliould ht considered in thia
ooonectioE. Thti apparatus ubuU consiBle
of a iongi?r pt^rpLndiouUr glatB arm. with
a shorter ann uttacbed cblijjndy to one
ijdn. Ooe electrode is introduced into
ttch arm. In ordtr that this metiLod
ahouid be upphod, it ia uot-uBttury to hare
I common ion in mtrbinRtinn with two
other ions, the one i;olorK-8ft *md Iho other
cdor«d, Thu«, vo mufit hare chlorine in
Mmbination witii coppor; i, p., a flolution
of copper ohiorido, nind aleo ehlorine in
cbmhirtation with ^ome cotorlt^^ ion Uka
immooium ; 1. 1^^^ a Aohttion of ammonium
chloride. The denser solution (copper
olilori<lo) is poured into the longr^r arm
of the apparatus iinU! it th\^t a <!i.'rtatn
dtrionce into the shorter firm, and the
l^hler solution (ammonium chloride) ie
carefully pouroJ ou to tlie top of the
^ttaer lolution in the shorter arm^ The
6>>n«Ql B non- parsed thron^b the boIu-
wn from thp iimmonhiTii to the L'OpiJt-r
*Worid«, The copper ion*, like the am-
moQium^ move with the current, and tinoc
the; arc colored and j^ivq tha odoi tft tt*
AolutioQ of cupric chloride, the boUQJiog
Iwycr bc*tween the two solutions, as it aiove»
with the ciinvnt. <^nn be eetTii.
The time during wbich the euircnt
poeaed waa noted, also tht* potential grad
lent of the current, and the distanoo trav-
eled by the hounding layer betweE*n tha
Iwo tfohitiona. From iheae data th<^ ahAo-
CvC<.
Flo, 7,— ArrAn*TP» v^n Wukthau"* >1i:tni>D
cr IhiTRRvrirENo V'Kiorrrv of lomL
Inte Tdlority of r.\\a onppr ion In ccnli-
ractres per wcond could bo at once calcu-
lated,
Thia m'^thod is, of coune, Umtled in
its app^ir^nhilily to oaact «iinilar to thf
ahovo, where the movement of Lin* ion in
qiiestioa can be traced by menus of
chnngea in color.
In tho laet few rears there have been
a number of invratE^tions*- along the
«Tlif<»*m w\J h* rlihl in Lh- idQifirwhlth *fll «««
»
OVTUySB OF ELECTfiOCtlEMlBTRr.
UnAa kkdicuted in thU paper, but the prln-
dplea involved arc esaentmlly the samo
ae ihostf already considtired. Thtae invee-
tigatioMs have Imd In da nhiet^y wJtIi ira-
provenn-'cte iti Ihc Torm <jf a|iparatii9
used, and in elTectin^j belter Mparaliooa
of Iho et>lutiom Jiftur tho uicctrolysis vaa
completed- Tbey wjU, Uierefore, not be
fartiwr ccmsidered In this paper.
TBS NATURB OF THS IONS.
TliG Til e ill Oil of electrnlyidcg fiolu-
tions, vbiirh wt liave just bi?ra pon-
atderi'ng in connection with the do-
termination of ;ho relative velocity of
ions, U alflo of vnlufr aa enabling ua to
determine which eongtitiienta form oal-
ioni* unri wliipli anions. Tii Ihe gri^iit ma-
jority of cafiptt there la no JitKculty en-
countered in auBwcriDg thia qu<^stioD.
We know that all ncicle diesootatu into a
hjdrogea cnlir>n. which gives theia their
diaractmstic properly, ard into iin anion
which compriice oil tlie remainder of the
mobcitl*, and which, of course, varies
with every acid. The general aeheme of
rliMonrnfiriii which h fnllawed by acids ia
the following:
BU = R + 3,
Where R compri&ce all the inolecide ex-
cept thi? (Ui^^allod repIocL'ablo liydrogen.
In the cflee of polybaeif? acids, thi* proo-
esa is more coinplioated, f^ulphurit? add
breaks down tlmi into HSO, uud TI mid
tlicn, a» tl:e dilution je incmcnAed^ the eom-
p1«i union fl^O^ lii-oukf] dowQ Liito SU,
and it
Tho djHatHTiiiLion of buses is just as sirn-
plf; M IIiAt of acida, uiii^aJi-nt 1ia«es diaao
clAtiDjC according to the following scheme:
R'00 = R' + OH.
The hydroxyi anion id the chapacteristic
ion of all bases, and the rem&inder of the
molecule fornifi the oation R'» Polyiicid
bftBL^fij liki? polybasic acids, may break
ilowit in ^tu^^H, and in the cuses of
nonu' of the* weak Lii.'ies almost Li*rlamljr
do 30.
In connection with acids and bo^cs it
shonld l>u stated thuL some compouuds
dififlociate nnder one set of eonJitiona as
nu tiv\{\, tin*] nnd^r oLiicr condiUoiie ns a
baae. Thus, alumiriuin hydroside in Uw
presence of a strong acid dissociates cu
a base, forming a aalt with the acid; while
ill ihs presence of a strong buse jl disBo-
eistvs Bs hh scid^ forming a salt with the
bciac,
The gcncrcl scheme according to wh;ch
salts of B^TTpIo aeidB with aimple ha»ie«
(lisMOcinte ia;
H-
RR' = E + R',
in which R is ihe aaiou of the acid and R'
thi? cation of Uxe base. But either R nr
n\ or both, may hu vtvy onmplpx, and in
these cnseB it is often diflic^ilt to nay jo»t
how the anlt will dissociate, In such
doubtful cneos the method of olectrolysi*
comes to our aid. Take the compound
polfi8«i<jni pbt.itiic rhloridn. K^rtClj:
liow will it dissociate in the presence of
wntrr? it is quite probnblc, indeed, «l-
motl certain, that th-j more slrcoicly poe-
itive potassium will rtiat in the cationio
condition; hul hnw about the platioiini?
will it also form cations or will it form
a part of thrj nnion? This ran be an-
twt^r'd by plertrolyzing a solulion of the
L-oTiipound, and then delerminijig by an-
nlysin whether the pEatiiium goes In the
cathf>de or to the anode. It goes to the
anode, forming a part of the anion, and
OUTUSSa or BLEVTROVHi^mSTRV.
a
the compo^ind, thurefore^ dififlocl&les m
K,?ta = K + K + pta.
Take Another easG, polasflium ferrocy'
fttiid? KtFetrN)j: tlie imijissinm wcjuIU
Qbrioii^ly fiirm cntionfi^ but what nbout
tbc iron, would it olflo form cationsr or
would it, iikc the platinum in the aliove
example, form part of the union? Thu
electitilysi» of ft solution of this salt in
vessels like thofie nlrc/iclj descritied in thia
chflpEer, in which thu eolutione cun be
retdily Boparatt-d after the eler^troly^iB lb
ended, wmld aiisntr the question Tlii?
iron hofi been found to gn to the anode,
and, therefore, forma part of the anion-
Other cases, conaiderably more complL-
ciited thiin the at>OTCf hjivc bt;cn Jijnlt with,
in which ih<f \k'M positive metal went
partly with thf onrniil to the catliode, and
partly agwinht the current lo the unodc,
fhowiog that it poHly disaociated as cat-
ion anil pnrtiy aa anion. The above ciam-
pies, hovr'evcr, auJTii^ to i Must rate the
manner in whieh eleotrnlygit ie made uie
of to determine hrjv miy given coiDpnand
dieaocifltes, and whnt ia the nature of the
cation snd what that of the anion.
In the next ehjipter we ghnll study the
pajwagc of the current through snltirionii
of electrolytes, or the conductivity of M-
lutione.
OVTUSEB Ot' ELBOTROCffBUtSTRY.
CHAPTELR VI-CONDUCTIVITY OF SOLUTIONS.
RliFKUKNUK h&4 bi«o fr^iuctitly
mat!* in the preceding chApti?rflT to
ao1utioit» of certain £u1)A[auceji. lodeod,
the vhdie pTOoeaa of electrolysis depencle
upon ttiD pascfl^ ef the currcmt thiotigb
eodl Bolutiona, Wo haro alec !^arat>d thai
cbemical suhatancefl differ greatly in their
povtrr to carry the current p Uie fteiiKtiaHt-tt,
and eaJtrt, forming the claae knovn aa ckc-
tmljCcj, being coitductora, vhilc all other
chumicnl oompoTinds fall into iho cIam of
non-rnnifuctors, flacT tlo not cnrrj the ciir-
rwnt thniugb their ^jlution** Wr ihiw h»ve
all cbenucal coEapounde dividing tbcm-
selTO« into two great claaaea witii rcapcct
t^ the pfoporty of conducting the current.
Again, wo shsU 09$ (hat among the el«c-
troJjtee Jhere are m;irked dilTerencca,
some oouducting to a much grfifltcr extent
und^r the i-^mt conditions Ihart others.
Wo mtiat now atudj in aomo detail the
ODDdncting powvr of aoluliona of elee-
trolytci.
SPBOinC AKt> MOLECrU^B OOyDUCTIVlTlSS.
The conducting; power of any conduct-
ing Buhstnnee dt^penils not only upon tht
nature of the auhatancc, but upon itfi
form and dimtnaionE, In order thai wc
mfty eompeTG Ihc conductinlies of differ-
ent ftubslances we mn^t, th^^rrfiirej ust
pi^es of the sfinu? form and the lUimc
dimcnsionn. The fonn chown and the
unit of dimcnftiona aclcctcd arc purely ar-
bitrary, fn stadying (ho condootivitw
of snh^tnrre*, nr their reciprocal the J9-
aLManr^s, oj* is well ktioun two untie
have be«n elected, the one a cube vho«c
edge ia a ttntimetre in length, ond the
other a cylinder one metre long ar,d odc
«(]U0Te millimetre in crota-vecUou. Tbe
r^l^tanee of the laUer unit of form and
JimwiHiuaH for any givtu nulKtanu* ih
obvioualy ten tliouaand ttma the former,
or the couduotiTi^ it one tcn-tbotmndth
of iho former. The raixtanea of thecc
uiiitii of any EubttnncA ic known as the
tpeci/ic r/^Uianrs of tkit mih^tanc*; the
reciprocal of the epeddc reueUace being
tbe sptcific conductivity,
The» term» a« applied above hold fov
»otid condnolor«. a^ich ae piceoa of metal,
oarbon, etc. The 4^uo«ticai aiiecti how oan
we apply them to conductoru of the see-
oud dado, ur di««jKrt! clwlrolytift?
Since the conduct ivi tic* of Kolntiona are
due entirely to the diuelved dcctrolytei,
we miut deal vith coraparablc qnanUtica
of tfaen Kub^Uincvx in ordor that tha rt-
iitiltK may he e<in][)ara!iTA. We might
chooic any (quantity of an electrolyte m
onr unit, but it ii mo»t convemcct beiei
led in Tnoft othr^r cnt^ca, to work with
i]tinntttiL.-j> which hrmr (he tame rclntioitf
to ore another a* tbo moT^^'uUr weights
of the anbfitancea In queation; r e., to 00
iitrnm- molecular vreighta of the different
^Uctrolyte«,
Let ua take a litre of a normal ioluti
of an electrolyte; t. a., n solution coBla
ing a gTain-mulecular weight of the elc^
trolyte in n litre, and pl&oe it Iwtveen two
oleetrodee one oGntltnetre apart. The ooc-
duetivlty of thii solution would be, ob-
vloualy. one Hiouiund timei that of ■ cube
of thii solution vhnKir v^gc wan a
metre in length.
If wc make thia general, and
'ail
OUTUySS OF ELECTROCnEHtSTny.
BT
by ft the number of cubic centimctiee of a
weight of the electrolyte, and by t the
sjwolflc condaptivity of n eiibe of this eo
Hiion whote edge is ± centimi'tn? in
Idigfh, the molecular cooductivit/ m
vould be cxprcaeed thtie:
If, OT) the ol*ier baud, we reprt*aenl by
the specific conducUrity 6, that of n cjlin-
dn ^f the aolution one mclrt iii length
ind ono aquaro millimetre in crc^£s-3cc-
tion, the mdeciilar eondtjcti^ity would ba
Qilculated from the apectific us follnw^:.
ronintiniin] tiolntion n = 1,000, honco,
tn^ff X 10,000 X i,ouc
Thct mo/actj/ar tri^nf^ut^^iuifv ia equal to
ibo sp«dfic oonduotivtty reforred to the
cubital unit mnltipb by IC, or to the
ipwiflc coiKJui-'liiity rcfi-rrLnJ ta tho tylin-
ler unit multiplied bj 10^ Givr-n cithi^r
Ibe epcoiRc or mtjIecuUr conductivity it
« 4 Tcr^- vimplc matter to tnmaform it
tQto thft other.
rnS KOlILRAl'HCEt M£TROO OF MKATtm-
IHO THE OONOI'CTIVITT OF 30-
LUTI0»6.
A Urirc number of methods have been
d«ti«cd iu the kst qnnrkr of a century for
VDOuiiring tb^ eooduciivity ot fiolutiooflr
bit all of these bove been praciieally Bup-
plicted by the mvihtyA i>f P. [vi>fi1m]ia(?h.
Wben A coutjnuiniji current i^ pjuaed
throuf^h A volution of Any electrolyte, gas
K erolrcd on onn nr both pole*, and bhe
latter become, im wr phv, poUriied. This
■odd evidcritly iniT^ai*? fho r^isEance to
thv passage of The ourn.'nU and must be
iToided. To avoid this Kohlrauecb used
tnaherniitiiiic current, irhlch wa» obtained
from a snutW ini!i]eUon ceil, and paued
tbia between platinum cJectrodea immerwict
in the solution. The methotl of Kt>hl.
lausch eouEJstG in babnciug the rcniatnncc
of the Bolniton, which ia the quantity to
be measured, tgainit a (tandard rh4K>dtat.
and determining when Ihp hnlntice la
effected by meana of a Wheatatooe bntJge.
Tbia racthod will bo caaly uoderatood by
means of tho follovinf^ diafrrom:
Fki 9.— Dt4sMAK or CoxocmriTT
I is a Huall induction eoil, wliicb witudn
an altcntatin^ current through the bridge^
AB, and aleo through tlic r<:siatance box
W, and ihe ve$»el cootaining the solution,
R. The seeond dr^uit of the eurrent ts
conth>i?tiM] wilh Ihft fimt ihrntigh ihe
bridge by mcim* of tho telephone, T,
CVhcn the resistance in tho rhecfltat, W»
i€ e^cactly eqiial to tho r<tii3*.ance in the
»o!utior in R, and ia Just half-way be-
tween A ami B, uo eurwmt will flow
through the leIe[ihonp, and, con«t?quently,
the Bound of the induction coil will not
be heard in the telephone. The wiro from
the telephono connects with the bnd^ at
C by meflnA of a tltder, k> that thiA coD'
nection cFin Iw moved along the wire.
It IS Dot neceesaxj that tlia rasutanec
of the solution ohould be exactly equal-
u
OrrUN^S OF ELECTROCIftSAtl^Tltr.
isod by tha r««iataucc thrown into the box.
Id tbis oaee tJit poml of siU'riou would not
fall ia tlie cmtre of [he hri(!ge, but thie
u of no can^cmicjiQ^, since it h only nccea-
•ary to move C along tlic vr'iit until
oquilibrium is reached, which is ahown hj
tho di^appearttnce of the sound of Uie coU
in ihs Telephone.
Ill ifiip jLJi<] nil ulhvr cti^i'^ the calculu-
Lion of t!icT ri^isbancr in uhnis oJTereO by
the solution is a Ttrry Dimple matter, using
tbc principle of the Whentalonc bridgCn
The conductivity ie but the reciproc-al of
the TrsUJflnco. If we rcpresoni AC by
a, ami BC by b, the reeisCAnoe in W by w,
and the reiistaitcc i>f thi? solution in the
cup by r, a|*|>ljijig the pruiciplc of ihi:
Wbt'fllBtont! britlgt', vtv would havu:
or
r =
Since thi^ conductivity, c, of n dolution is
the roeiprociil of ite rcsisUnei*. wt hin'i^:
a
c — —i*
teo
The GonJiK-livilien of solutions calfrii^
latcd from this uipiv&eiuu would not br
comparable with coth other, aucc it con-
UiQ» no terni which has to do ^^lUi tht*
concert ration of thu iwhiiii^ii. It is Mvry
convtJitcnt In refor nil roiiLrMtnLtiojis to
molvcular nornml, vrJiii-h coutiiiitfi n
l^m-inoWiilGr wi-ii^hl of the Hcctrolytc
ia ft Htro of *oliilioit. If wc vq^rc^cnt
th<^ EiuintMfr of litn^K of the solution which
wriUinK >L ^rHrii-molpj-tiljir ireight of the
cloctralytr by r, t^lc ftbuve equatjuii be-
Wc rickw writi' for ttic molecular coridiic-
tiTity the letter ^: and Indicating the
conccntTfltioD at wltitiJi ^ ia dotermintd
by i\ we wfite ^^
Thifi rxpri^flflion, however. dooB not ukc
into noc7oiiiit the dimeusiona of the oeEL
A cell coiiaTaot, jt, riunt be inlnwiucwl
for ("Jk-li crll flinl »li'tj"nnin*'rl brfore th'
cell con be naed for contJudivily mc«*-
iirements- Thn cqimpictc t^quiition for the
molecuhir conducUvitj n U then :
= h
vn
Id ficti^ally carrying out a condnctivity
iiie&surenieut. h large numbt-r of fiid:or«
oome into play, and many conditioju
mujjt bo obecTved. Tlio cdl cortstani, fe,
mnet ilrst bo determined by using gome
anbsfcftnee whoue moleeuUr conductivity
for a given dilation and EemperaEurs it
known. The mrc Piusi be calibrated, and
corrt'Apondinif corrections applied- WrtUr
mu^i tfc eepfciallif punficd for all con-
diictivily work, and the eonductirily of the
wafer used in preparing the solutions
mUBl alwayfi be detLTmined. The*ie and
inanj other conditions mutt be observed.
but Bpfice Will not permit of a further
discuaaion of these details in this oonneo-
LiDii. Tf i1 h dL-sJr4.'d to apply the abo7e
method, refei-ence umst bii" iiad to some of
the worlifl" which deal with this question
in deTail.
Tlip effect of temperature on the conduc-
tivity of soliilione h so pronounced and of
»M\^h A Urtturt that it cannot be p«twJ
ovar with a mere reference. The con-
ductivity of a inelaUic wire decreases
mth increase in temperature. M iht
wf-ut. Hf4 ffOEhb by OiiLOklil ADil ^olilruijuii. turf 41V
^Brt llj Joqfkft, [Ct'PdullJ*^ E'jIpIWiIu^ OXI>|Mb5.
CVTUUE& OF SLEornocuBUisrnv.
lamperalurt of a piew of im.'tiil U lowered
£]« wiidudivitj iiic!n'»i.-«'i<, umil wt nb^io-
h\t cero thir comiuctivily would become
ittfinitc. ar tiie rcsislantc aero.
k\'i!li coiiduciors of the g(x;cind cIubs, ua
»o(utifin», thi' tempernhirt coefficient has
fjfld,!^' Uio u{ii>o»ite sign. Aa thf» tem-
ptraturc is raised the conductivity in-
cTow*, and vcn' rftpidly, That i», the
lcmp«TGtiirc coet£cicEt is poeitivo for »o-
lotionc of ol^ctrolyt^s, and very Urge,
Thu magnitude* l.^iui he seen Itkww (he fol-
loiring ezpcriiUL-iiUl fnele : The luul.-o-
i^nr conductivity of a normal solution of
Mrochloric aeid at IJ* doi^nt^ ;b SSO; at
iO degrees, il is 404; at 80 dogivis, it U
M9, while at 100 degrees, il is 51^0-
la Cftrryinff out iiieasureioeutt of con-
ducliirily it is, therefore, neccsaary to
h>cp Ihe teinperatuiMi eonslani to within
rrry narrow limits, and for this purpose*
A ituiiiWr of IhernLo-rcgulLL^ors mid Iber-
JuoaULt:! baie been devised and used, lien^,
dguia, for dvtnils nrfi^rcncc must ^ hud
ta u>me of the warlcB x^hich dsal exhaust-
ively vitli thU subjwt.
KBl^VLTe OK THK MK^SClLEMEKTe OF TtlS
coxDucTivrTifis or solutions.
As quickly aA the eonduetiviti^ of
vubtilaiicw in solulioiL began to be atui]-
ird, tho Ivo jrrcnt divi»ion$ into which
aU chemical compoundc fall were dig-
Wo havo thoao sub^tnnces lik'c
augar^ drtHroup, the nk-ohols, others^
loetocftfr and, in general, the great body
of Dcuiral organic coinpoundA* whoee eo-
lutions arc no better conductors of ihc
current than pure wAk^r. Theaa non-elec-
trolytn ioelnde, rougl^ly speaking, per-
hajia half of jhe eliemii-al tompomulfl
knon-fi. ^
Wo have, on tht; otlii^r hand, thoic sub-
Mow
ciirrtnt, icr]o\*'n as electrolyit^i. These
include nJl ihu aeidi, all llie basi'«, and
oil the ^U of strong acida vith strong
Ljaaea, or of weak acids with weak ba^cs.
We tiud in this cUs* eomcthin^^ like hull
*){ the L'fieniiL'fll wiinpoiiicde known. \f we
toiue In PxsiniiKt iimce closdy Uie elinitro-
lytM thcniBelves, we find marked differcncoi
bet^^'L'trn the conducting powers of ditfcr-
oni mt^mbete of this classB. The beat con-
duc'tom artt \\i^ slrong mineral aoidfl Hke
hydrcxildoric, niiric, hydrobroiiiie, etc.
Nt^jtt in order come the ftrctng t^na^, in-
eluding tlioeo of the alkah and alkaline
earth melaK (Ueh as potassium and God-
ixixu liydroiiiJi-?, ciilcium, barium, and
^Irontium hydroxides, Lut not iimuioniuiD
hydroxide^ which 13 a poor conductor.
Finally, among the good conductors of
(he turrvnt vvhi^n in solution «Te tiie salu
in gi^nirral; but within \K\h eliisti mtirked
differ ri::nces ejcist. All the ordinary salt*
ure i^ood t'ouductor** though not aa gixfd
a& tho bit5(]£, and otiU Ics^ than the ncid^t
but iHp vMa of a few metals like oadmium
and tnt^reurj wre in general rinly fiiir con-
ductors of eU'clncity, and some of the
salts of thew two mctale, «uch oa the
baUdes, cyamdc*i, otc, aro really to bo
ranked among the poor conductors.
The above are Uie go<fd L-onduirtor^ of
fleclrieily in ^i.'lutioiw. We find, hovvevif,
among the eloctrolyt^, nearly all grades
of oonductiv'ity rvpreocntcil. Amonj? ihe
orgamo aeidi and baoek eome are quite
gurri ronduelom, Jik^ foriitu' Hhd oxalic
acid*, and tlio Mib»tilutcd aimiiouiai,
wliile acetic and hydrocyanic acids, and
ammonia are anion*; the very poor con-
duoters-
It might be thuugtit from thit that tlu^ro
arc all prudes <pf eondnctivjty rvpn.'«cnteil,
und Chut the diBtiacEioa between ekctro-
(vho6c eolutionci condiiet the lytea and non-oUctrolytse is £igt a ftharp
10
0UTUNS8 OF ELBVTHOCIIEMIQTRY,
otu'. It is true Ih^t Among the dectro-
lytofl Dcjirly all grndee of conditctivit^
are repre^^nl^, hwX them is a fihnrp dis-
tinctioiL hclwficii Ihost? Eubsl^iioofi whrdt
huve nny I'mitJiicitivity and thosi* which
have none, end thj« ia ihe line pf division,
between the dectrolytce and the non-
eltttrolylsB,
\N EKPEniMKXTAL UEMOWaTBATION OF
TilB DIlTKKaNT CONDUCTIKO l»OWKllfi
UP IJIFFKKKNT WifllHTANL'KS
hj» been furniidu'd bv Novoe and BJonch-
arJ," luid whit'h thry way wiiS devised
by Whitney. Hjilf.normwl stjtnl ions or
Kyrlrnrhloric, »uli"liurii\ i-blorflcotici urid
at^ctic ncirl» wcro prepared, and on equal
ToLtiino of ^ch iotroduccd inta a elas^
mbe a'i)f>ut 20 om, long and 3 cm. Int^nul
diariieLt^r^ kvhioh alrt^^dy oonlained a nit<Hd-
un-d volunn' uf wiitt-r filnsa ini'bes i^any-
ing copper wireA pnti^ into those tubc«
through rubber stopptTB. the wires ter-
mm.iiin^' in plnlinurn rdnt™ whif^h are
pinwd horitontTilIy nnd dip inio the solii-
ti-ons. ThRse g]ii*e lube* can b*? rondily
«hored up and down through the rubber
steppers which doae the Uipa of the lor^
gla«e tiib«e, »o that the platmum pUi4> onii
be piflo&d fit any desired position in the
gUiLS lube. Till? wire fnsiii :he luiUoni of
e*ck luhe, counecliug with a eectjod
ekctrodc, pasaea through a llO-voIt. 33-
^aodl^' power lamp^ Uw oLh**r iidi* of
i»ai?h lump hying connected with one wire
from H HO-volt alter n at Jn^-ourrent dy-
nomo. Thp olhrr win- frotH the flynniiio
count'oti with the wirca leading into the
lops u( the four ^\a.^ tiiboe.
Thf* autUcre rL't/oniuiend that li)0 oiibie
centinK'tr'w i-if waiirr, and 5 enhio centi*
mi'trf* nf one of the soUittoim he
add^ to eftcl| tuhL. AftiT the ftok-
*Jaw. jl«Hr. CMn. ««., KU. TW
tiona in the tubes have become homogen-
eiius^ the eurrt^nl is closed and the poei-
lions of the elGctrodee so adjiuled in the
four tubta that the lamps are aJl ej{uu.iy
bright, M the electrode in the hydro-
ehWic add U placed at the top ^t the
Cube, that in the sulphuric acid will be
about one- fourth from the top, that in the
ehioruceiJc acid wiJl be about thrae-fourUid
from thi> tijji, while in th<? solution of
Jirdii* Jir'id tin- riif»v:tMi' f/lirlriMle will nrar-
ly touch the electrode placed at the bottom
of tho tube. ThoBe distances bet^v^cn the
eJectrodo^s in the four tubes ahow the rela-
T- Di-tviiJ
fill. D, — Arp4itATiTA pon -Sii(m')\o Liurkv-
KNCfai IS CoamiLTiN« J^jjwhh
tive c^ndnetiyitieK of Ihti four subaiane^
iljdroebforic aujd i» tbn ln-at e^^nduetor,
ginec an equal amount of current panes
through it when (he electrodes axe iKe
farthest apnrt : sulphuric acid eomos neilt
n^qiiiring Iho olectrodL^s to be flomcwhnt
do&L*r in orrl^p thai the same ainoijnt of
current may pass; thkracetio acid nest,
anti then acetic acid, which is aucb a poor
conductor that the cloctrodoa muat be
viTV nosp Ingrllicr in oi'iler tlial tho given
amount af curri^nt may pMSfl.
The Authors alnu pnint aut That this ex-
perinienl can l^e ustxl to illufitmte another
fioint. If wc ju^l noutralJEe the acid in each
OUTU\ES OP EL^CTROCM hlMfSTRY.
cylinJer with a bts^- and f[>rm tlie corr^
ipintdirrg aaH, diid iht^n I'epeut the flbove
«Tpcrimcnt. we shall find that when the
li^U are ail e<)URlIy brilliaiLt the deo-
tm^p* in the four cvllniiers Eire equally
Ji*Unt Hpsrt This -liows llial wfdlp tlie
Fcmr acids have very diiTerent conducting
pDir«n, their salte with a given baae are
sqoallj good conductors.
SPHUtACflCll'a LAW OF CONDCCTTVITT.
M we atudy tin? toiiduotiTttv of uny^ivcn
*i«t^olyt^ -say a etrong acid— wo would
find Ihit the nwjlO(?ular conductirilj in-
iTPflnf* n* thf ililuMnn of tlie sol'itlim in-
CTnurn. This tiirjinc tlint ibp actual n--
iLiliDce cf the solution iioe« not iucrGnse
M rabidly aA the dilution of the aoliitioiiH
ThiB incroase in thi? condtictivHy with tho
dilitiiOD go«B on unill a oertain dilution le
McIimI, and beyoml ihip poiiil Ihc rrnjlt^r-
ttar conducLivily i3i)efi net further in-
erciM-, but rcmaine constant- The dilu-
^iin nt vrbieh tho molec-ular oondnetiviftw
«f ibe rtT^oDgly disfoeiated ekctKrtytee be-
mme conalant is about l ,000 litres; i. i.,
1^0 ItLrv^ of fiUL'h a ^^ululiun would cua>
Ujd a gram-molecular weight of the eltsc-
If the electroljle is a poor conductor,
Ibe nund general remarks applj- The
moTreuUr roTidnrtiTily incresups with the
t^ilutiiiri. and coitthiueH lu im.-EVii-te wen at
tTTT (jTtat dilnlionti- Indeed, if the com-
poncd in que^tifm is ench a poor oon-
dactor a» ammania or aoctic ACid, the
moUfiilar (ondnrMvitv will incmiw' witli
tWrlUntion^ rvm at th»' ;rrrul«^t (lihifiofis
to which the conductivity mrthod i:nn be
ipi^i^. In 8uch ca«ca Ihe maximom
ciiMutant value <A the molecular oonduetiv-
itr «iui«<>l Lh* f>bl«ini.'(l bv ilin-ct [ii>|ilirii-
ti:»D nf thi* eaiuluetivily method, bat some
ifidirpH rapth™! rmjut be mnployed.
This maximum {:on0tunt vnlue of the
molecular cnnd activity for any subatano
baa btien given a specific name^ It 14
tnown aa thfe /*_ for the sub^miice,
ll i» K'lwteri the valiLes of ^^ for
diiTL-i-ent ^ubfltnnces thiit Kohlmuspb dis-
covered a generalisation of wide-reaching
impurtunco. Comparing the vftluea of
f^^ for ditfvrtivt e|i*eirolytti8 eoutaiii-
iii^r 11 c?t>nunon ion, Iw obtttiniHl auch re*nlt*
as theae:
Polaaaium ehloridc, /*^ at l^'' = ISLT
Differencj? — 19-IJ
Pi.*ta8^ium bromidi\ /l at 18" = U1,0
Sodinm " " ■< =]ai.ii
l>IITtfruiiLv= 20,0
Sneh rtlatioua are genpral The differ-
tuco between the valuer of /*^ for anv
fwo componrrls rontaininfif a common ion
fombincii with two different Jonfl, is the
anme QB Ihe difference between the valufie
*>1 ^^ r<ir any other tv'i> (^onipoundF
contniiiin^ ihciM aRir« different 1009 aom-
biiu'd with any olh^r cninnH>n ion.
Irt Mrd<T that rhin may he tine the valv%
^f f-^ m'i'i bf mtjflf tip 0/ tn^a tori'
slants, th« ono dtrpcuding upon tho anion
and rhe other upon the cation. If we rep-
renenl Ihea^ eon^tants by a and c, re*peel-
ively^ the above rdhtion would be formu*
laterl that:
Since the eouduclivity of a solution d^
pendft upon the mimber of iona present
and the veloLriliei «iili whteb thej njove,
and since the valno of ^. boie to do wltii
complete di«socinhon of comparable quan-
Mlips of Rubetancea end. therefore, wilh
ihe same nnmber of ions, ils value dependa
upon the velocitim witli which tjie ions
ruvAs or BLBCTRoonBmsTrtY,
more. Tbt; two €^n4lanU, a and «, in the
^ova e^tiaUon ar^, then, ^rop&rtt^n'3^ U
tha V3l6citu€ of (A« anion and cation, r»-
spaciiDily.
Th^ above lav is gim^rally known aa th«
biw of itie ^fidepndoDl migration t*!oo-
ilie* of till! iouH. each ion ruoviug with a
Tclc*city vrhkh U iu^iepeiidcot of ihe
nature of Ehe olhi^r ion or ton^ nitli vrtuoh
it U aflnodatad in iho tohiion.
THE VULOCITY OP UlS'S UlCTKUMINtP CT
MCAMi uK THK LAVT OK KnJIt.KAlJ^OIi.
In the prvocding chapter vq dU-
oudwd m"Tb<itls for ilptnmiimng rpla-
tiTv vv1n(^il.ic« of ion£ in ^neralj and
methods for detcnDining the abaolate
Tt>locitiefl of a fcv iona. The law of
Kohlransoh opeiie up now pMiibiJitica
In ite field of lonio v*Iocllie», m we
tun reaJily ww. The sum nf « ami c, as
wo lia^u fccii, it p^, and t; tied rare citlior
the Tutoottiea of tbo aniono and oatione,
rwpectively, or are a multiple of thw*
veloriliefi, and it )iai beea ahonni that thej
aw ihf velocitit* of theae ioiittv We Um»
have dM f = z*^* From thp atncly of tho
rvlotive Tolocitioa of ions we obtained tha
Alio of f lo a. We then know r^ a
and " and earn calc-i^kto at oaco thca^wo-
lulc relodticK of the lonc.
Tho vclociliua of the ion^^ as thu» do-
k'nnloed, u*tEg Kohlrausch'a law, a^ree
v<*rv well with l!u? r«ulU ubliiiriLHl bj the
methods ilE-K<?ribeiT in thr pi^L'tMling chaj>'
UiTj at fur ai the reiulU for the same ioiu
hftfifi boon determinfrd by the different
methodc. The law of Kohlrauieh i«, thea,
um^nuhtnll}- (^rrHrl, and ^nmt!v kiinpUfiua
the whole problem of the conductivity of
«o)titioi3>.
Suppom It ie doftircd to dolcrminc cho
vvlocitiH of thd complvi anions into which
1
the organic aoida ditaociatiiL It wi>ii1
impOf«ih!e to d«t«mme dtrcolljr the vol
of f*^ for lUifi^ octdg. ainc? thtv aro u
dightly (b'sHocnaifid thai fi^ wovld
renehf^i) onlv at lufh grcnt dilntioiu
Uii? cDoilm^fi vHy mr-thod voiiM not he
applicablf to thmn. Soatc salta of thoc
acidfl would be propnrcd, any iht vodinai
>a)tr which ie complclMy diuociatcd oven
at inodi>nLC(i dilntioim, Thn valtut of ^,
for Ihe lodium tialt would be dttermlnei
from thia tho DOu»liLnt for aodium wo^Ud
be subtracted, and the rccmbidcr wooJo
be the oonilant or velocity of the anion ti
quealioD. The firtt qucntton whieh woo^
naturally ariw vould bt; what *€«!
would Iher cciiiipo»itioii of thu ion Imtr PS
itfl vdodty? At wc would cxptdt it vm
found that the more ff^mple^ the iott tbc
Jf£f it* velocity.
Tho clTcd ef the chemical cofutiltUxtt
of tho ion on ita velocity wa« atoo et^dladL
anil it wna shown by studying isomtfric
iouft, which hale the same oonipoaicioa
bLit dilT^rent ronctitution, that conriita
tion haa rcry Ijttic influence on ^
ity of oomptox organic anions.
The veIoclti«e of the complex cittt
or^'anif! LaHea were atudied by rocitm of
Kohkaundi'a law. In a ujanm*r atrktlj
anatajfotis lo that }\nt dracribcd for Ihe
complex luiionA of or^anio acida. Tfaf
value of |L^ for the poorty eondui^tin;
baae could not bo douniuned diroctly bf
1h« conductivity method, iwd t tth ti iltf
base which would be slraiigly d<(sociAt<^
wn* prtpAfc*! and the ™lae of ^^ (or
the Aoh asccrUixird. If the chloride d
the bo^ wu u^d the eoiwtAnc fc-r cbJe-
fine wojt «ubtnac-IiTd fri>m the laluv fur m,
for the lalt, 4ad the remainder, fre»
Koh]rauicb*» law, ia tho valocily of th*
eatfon of the base. Similar re«ulti
fid by Bredig for the vdocitiee of
fUplex ontioDA of organic ba^i^s. ns
itmt obtained by Ostwalil for tlie
ti 4iiiioii3 of organic flci^.
OJTDCCTITITT OF ELKCTROLTTEB AS A
BABUBH OP THEIB DISSOCIATION.
have constantly reEerred to the
.ation of electrolytes m aoludonj
lave pointed out on^ coDvenient
At based upon the lovertng of
rWTiing poini of solvents by dia-
fubsUnceft, it>T mcoauring the
it *>f iiiS8f>oiflti<>n. The oonduc-
oJ oleotrclyt^ fomishea us with
iTf and perhaps «(lI1 more onnvenient
d for meaanring diasociation. The
pie upon which the method ie baaed
y Binipte» If the snbetanc& is not
iMt^. the solution wonld have nn
tittvJty at all, as h shown by solu-
of non-eltctroljteB, which do not
Qt the current to oven a elight oi-
Thii fihowe that inoteonles ha?e no
to carry the oniTCTif, since in eohi-
if non-electro )j tea ttiere la an abun-
of molecules and yet no con-
ity.
bmve e^en that tho molecular con-
ity increases with the dilution up to
■in pointj whi-rf> it attjiiii^ u niHJCi-
coDclfint valTie. Thi« means that
) iDC^leculea have broken down ioto
When there ia no disaoeiatioti there
9, no oonducttvity; where disioeia-
c compli-^tt.' the mnduetivitj is a
lum- If tile molei-ular condHcEiTity
levrhero between zero nnil ft moii-
raluo. the diseodation ia partial;
oetvcen zero per cent and 100 per
tn the confluotivity resQlts it ts, tlien,
' A mntter of proptirtion to caTnilale
the amount of dieaooiatioa of thd elootro-
lyte. It is only recessary to divide the
nuileeular conductivity at the dilution in
question, by the ntaximuui molecular con-
is coraplrte, in order to obtain the percent-
age of the dissociation of the electrolyte at
the dilation with which we are dealing. If
we i«pr(«ent the molecular oonduelivity at
n givnn dilutioit by ^, and the ihlxu
mum moleeular conductivity for complete
diasoeiation by ^^ , the pcrcentiigo of
diflAociation u, ig obtained thua :
/»-
To measure dissociation by the conductiv-
liy mothod, it ie only n<^w0ary, tben, to
dotormJQO the molecular conductivity of
the aub^tanco at the given dilution whose
vohiJiie it II, Hud ill'? muiiiriutiL mulecular
oonductivity of the ftubsLance,
The f rat part of thia problem is always
very eimple, involving only the determina-
tioa of conductivity in the usual way.
The second part, involviug Ihp det<?rmiatt-
tion of fi^, is TK>t always »o siniple a
matter. If the elecUolyte is strongly dia-
i40ciftti>d the dotprminalifrn uf ^, pre-
sonta no a&rioud difficultiea. It ia only
neeeflsnry to increase the 6iluli<^ Kt^p by
!^tep» laeatmving tlie conductivity at eadi
dilution, until the molecular ooQductivitj
hiiB acquired a maaimujUT oouat^ut, value.
Thi« is the value of fi^. For the more
5troDgly diBsueiated electrolytes, this ?altie
ia reached at a dilution nf about 1,000
litres in water «$ a solvent, and at thia
dilution there ia no oerioua ditliculty ia
m:ilcing a c^ttductivity mooeuroment by
the Kohlrfliiseh method, if the dectrodea
in the reaiatance v^^rte) are placed close to-
^Ua^i. For Iheae high dilutiom. vhere
L
Ql
OVTUSnS OF BLSCTROCffrXfffTMY.
together in ordtr that IU»; imfriance which
Diwt bo thrown into tbc box to effect a
baUnct? nt^ir th« ct^^Atm of CUe bridge, nitty
Dot bo boo Ur^. If tho rctitttncc U Tory
(fn^t tTh? toriivtnininifl ifi ihn MqilifniiT Mre
bo^ fJtAr|>. If, on the other hand, wo «rc
v^rkio^ niUi fairly coDCcrLtratccI M>luttoiis»
vhoeo rwiitQ&co ia amntl, rho platot miut
bo cloae tof^th^r iu ord^^ that an eppre^a-
bte iviLhUince umy li« llirown Into the box
Uj bring the bnljuitv uettr thi? cmilrn of ilw.
briclf^; Anci: a aharp torte-ntiniinum i« not
obtamcd when I ho rc«ietnnec in the cir-
cuit U too Email,
DidlonllioB in ilolerminiiL)^ ^_ ansu
onljr in the cases of weakly diuodfttod
^Jeotroljlea. In such caee^ the dije*oci&tioit
iH ncfL cumpU'Ur, ifvrn ill a dxlMtinti of
10,000 Htrrx, And nt greater dilntmnH
the coniJartiyity method ia not applicable
with even a fair degree of accuracy. With
w^kly dinoeiated eleclrolytea it i*, ther^
fm*, nist jifiKnil^lp if* lipjiirnjini- jt^ hy
Uiu iru-tlitxl tjiipluyiHl wiUi Kt,rang}y rliMO-
cinted ftuhatiuiM*; t. 0,, by incirjimn^ the
dilution step by tLcp and meajurtiig the
molociilar oonduetivitj ni each dJution
until it TMchM a mazimum coD«tajit
vftlue. Some orhor method of deternUix*
ing /i, for votikly diMociated coui-
poundjt nanat be employed, or the con-
dnctivity method oould not be tued to
iiK?n«uro the dinoointiL^n of these «ub-
stances
An indiroet mothod of arrinng at the
Vfilii4-f- <if n^ Utr wrnlily di>iM'i'i»l(tl rom-
pounds hu, however, been worked out on
thf: baaia of the law of Koh)raii«ch.
While the or^nio Acida and bmoi^ ore
weakly diAAooiatc^ oompotrnda. the aalta of
theB^ «[ibstaDOC£, like salti in general, ar^
Htrmigly diRtocintud. If wr wish to dft*
tt-nuini^ the rtiinc of ^, for a weak haae
like ammonium hydroxide, the eolt of
ammonia with acme aeid like hydrocsblone
h prepan<d. and the lalue of ft^ t*?r aia*
moutum dilorido it- uno^nrnti^ is tbt
iiahu! mnnnrT, \vy incrviMng the dilntkn
fitep by aiep until the mfriecular t.^ojiduaUi^
ity ha« attAined a maxtnioiti, coDOtODt
viJue. Krom KohlraiiEich'tf biw, ^, for
ammonium nhlonde ig roAde tip of tit
couilautv, one depending upon the ao-
(ihntiuut km iind Iht* niher npnn ^he ebl^
fine ioa- If v/c subtracl from Ute valne^f
p, for ummvninm trhlorid?. the conatut
for chtonne. iho reniatodcr will be Ihe
c^^natant for the cation ammooiuni. The
VKh^iT of u^ foi ^mmoriiijin hydrc3ii<Ie i*.
fitini tlir Inw cif Kiihlniuvrh, thi' iinm <tf
the coiL*tAnt» for the eatios ammoiutint.
and the onion hydroxyl. If, ttu^rafonr
v/e ndd to the coiwtAnt foi amtnonionL,
found aa ahr>v<r dntcrib^d, the eonRlnnt for
hydruxyl, we bint the voloea oi ^^ Jm
the weakly di*«oci»tod baoe amsMmian
bydronde.
The procedure with weakly diMociahd
ncidn U vtrictly Analojfinu to that joil
d^fcribcd for weakly dig«ooiated bua^
SuppoKe VL' wiali 10 kitov tbc- \^alu«f of 1^
for seeli*^ add; this cotild not be det«N
mined directly for teaaona already fftdl*
cated. A salt of Hit acid with »ome bast
liko potaesium hydroxide ie prepared,
and the ralim of n^ for pouLtEiuA aeetalir
dftennlnofl in the uaua) manner, Tbt
L-cnuljint fur iKiliuHiuin in t^ieti aubtfMHed
from thi" value of ^_ for |>otaaaiiiiD ace-
tate, and tha remainder ia the ooDatlftA
for the anion of acetic acid Cfl^COO.
If to this conMant w« add tha ooitBiani
for the caiJon hydrop*n, the iiiro U the
\ji\%U* <lf u ffiT arolir w id
0UTL12{E3 OF ELBCTROCHBMISTRT.
66
The conductivity method can thoa be
applied to measure the disBociation of
weak acida and basea, 08 well as to meas-
ure ihe disBOciaition tif etroogly diwociat-
ed compounds.
We have, then, tw<» general methods
which oan be conveniently applied to
measure the dissociation of electrolytes
— the conductivity method, and the
freezing-point method. The question
of importance which naturally arises is,
how do the results obtained by th^e two
methods agree when they are applied to
the same solutions of the same substances?
The following comparison for a few
compounds, taken from the conductivity
measurements of Kohlrausch on the one
hand, and from the freezing-point meas-
urements of JoneSj on the other, will an-
swer this question,
SSI^V^: ^:^^^i ^^-^^
" ,0.01 a&S OH,*
" ,..,0.1 96.* " est *'
Polauium hjdroAldfl D.OOfi B§.4 " IDO.O
01 M.r ».a
D.I es.i " pes
Sodium chlDrld«. O.OOl 98 4 ' 96.0
001 DD.B '■ B8S "
.,,...0,1 84.1 S4,l "
The agreement in a long aeries of com-
parisona is about as close as we could ez-
pectj under the different conditions under
which the two sets of measurements were
made.
»
OVTUyiSS OF BLECTROVHt^MtliTnT.
CHAFTEBw VI" CONDUCTIVITY OF SOLUTIONS,
PART II.
TOB DfSdOCUTIKC POWGB OP DlPFSOSNT
BOLVEKTS.*
W« liAvc dealt thiu far in ituvc pApcTii
GxclufliT«]j ivith Dqueoua flolutian?), and
tbo cooaclut^ioji might be drawn that
tho thoor^ of •Iw*tro]yt:c diMOcifltion
ftppliM onl/ to eolnttone in n^i^ as
thd solvents We tlmll rki<^v learu liml
sucli b by no mcan^ the cue, abce there
are memjr »olTciit« which luve & marked
diiiociaticff povi^.
H'aier, ti> b« nurt, ift the etrongfflt dE««>-
mnt known^ bi^^nking dmvn pWtro1jt«i
into ioii# to a grcau-r evtenl rliau ftii\ oUiei
known tubstancG. but there are other wl-
wnla wUieh do cot stand vorv far behind
wa1«r in tM* r^Apect. We ibalt taVo up
or^unir stilvi^zilK, nnd, iliiMlly, hojiip rntK-
tarcf !>f dtStrcTit »olT(?nt«H
i.tjfjii CTfimonia hae bwn shown, eapo-
cially by tho vork of FronlEliD and iuaiu,
to have a very conaiderahle power u ad
Ionizing aoKent. Indeed, tho molecular
ocinducttviliM of c!tTrtiiiii eWLrdytM In
liquid 4nimonia are irreatcr than in water
at the wunft concentration- Tbi* alocc
WJiild not *tn7W thill thi^rc iv gnntiT di&jio
cifttion in the liqntd antmcnia th^n in
wiitor, since tho maji^iin^'iiicintfl were nia<l«
ill Uitr aiuinouitt a1 itif tjulliiig-poiulp — 3S
dfgreea. while the mt!asur^iju!nl0 wvre
mode In wAl4>r at 18 dcgvwa, or 8V dojifrev*
below fta boiling-point. In ord^-r thai tht'
two Mftx of mnilt* aJiouM h^ aom|>ttnili1i>.
■soWBRrewr oF Kolv'ftr« rr-oiiTisr tii^iai**^ hv H O
J<iOt«paQ4pii1ftln]jei] lu (tw /Imfrkun OA(fl»ro4' /uufnoJ;
nv.an
il hr ■
i
tho molecular oonductivitios tn wat^ at
boalin^'liuint tJiouId b^ conipart^l with
ThtBn* in luiTiiii umrnonin at its lioTling-
point- Further, if th? niolcciilar rondac-
livitiof iQ liquid ammonia should Cfei
prove to be gresCor, ander cocaparabk oon-
ditiODs, than in watur, tbia alono would
not allow that ammoQla haa ih« grealor
iliisvnrmlin^ ]ioir*'r, nincv Ihi' diw^Trirttimi
a is the ratio bet^iveeu ^,, Aiid ^^, anJ
^^ mi^lit bo tartar in a^inionia \\m\
\i\ wHtiT, ftiid |i^ siill larger lu tiio
ammofiia f n ihiii rafl" a wmiM be smal
Lti the aiiimujiiiL Suuh ia, indeed,
fact; the fr^^crr molecular condnfitl
in ihc Hquid Ammonia l^cini; du€ rather
tho guitki velocity with which tho iom
nov^ through thi« solvent, thnji to tbit
Ur^ luimljer of Inng present.
nitric add, in tlie liquid alate, l^aa faem
shown to hare very grcot ionlxtu|f power.
Indeed, from the few rc«ull» thua far ob-
tained it (CfTHfl to hn»c nwirjy nf grpul Ms-
mdating power as wnt^r itaelf, but the
(Iftta thi]4 far availnblo with thie aolvnit
aic far loo meagre to juatify ajay final OOD-
cluaion-
Sufphur dictide, in tJio liquid eonditias,
haa been found by Walden to li^re a eon-
nidi^nibb dtuopiattn^ power. Cocnparing
th4> molrmihir CDnduotivilifiA of a mimber
of wlti! in iulphur dioxide, with the rwolb
for th^' ftan>c enlta in water at dfirr^v*,
Walden concluded that liquid aulphar dl-
oxido di»odai«Q to from on^fonrtH In
one-Ualf the extent of water.
Of the organic solrenta idioaa dlnodat-
ln£ power \% known, formic add fiandi at
OUTLtSBS OF BLSCTR0CHSSII8TRT.
n
th^ bead of the list. Quite an elaborate
mTeatigalion en the dUaacijit.Qg power of
fftrmjc nciU wqb carrieil out by Zaimmo-
nch-Tessarin, He uaed chiefly the freez-
ing point mefhnd, but determined also the
oondtictivity of a few wilta In this aolvcnl
Ee concluded Ebat formic field ie oce of
the tftrongeat diaaociflting soJventa nest to
vatcr. The behavior of hydrochloric acid
En tbU solvent \a most reniarkabU. A1-
thniigh it is one of the moat strongly dia-
nciiito<1 liulielHiti-i'^i in watrr, it shtiw& tw
dietfociatjon wh&lcrer in formic acid, an
meaeui^^ by the frrrainR-point method.
Indeed, in the latter solvent it 10 aotaatly
polymerizt'd. Bccording to tho rosnlta ob-
tatn«il by thh method On the other
hiind, hyc!rof:blorip acid shows very
marked conductivity m tbb aolTent, indi-
Mtin^ diaaociation, This apparent die-
tJrtpftiicv Tiiflv h\} dno lo tht* frtiH, t>Lit whilo
mo«t of the molecnlea are polymerised into
large wimpTeie, some are dtstwinaf^d into
ions, wbtch conduct the current.
liidhyl nlrithol. mnong the orgnnlfi sol-
vents stflndfi npjct to formic ncid in ;te
povrer to break down mrilrciilcs into ions,
A larce number of inTestiffatorft ha^e
worked on the oondiictivity of eolutione of
el*clrolytetf In this *olvpnf, but. on the
vhoitu peThapn the vork of ZelEnaky and
Krapiwin deBenres special mention. Their
vrork included a number of aaltfi in p^re
methyl alcohol, a^ ^ell afi in a mixture of
raelHyl alrnliol and water. TF the mnlecii-
Ur conductiviliea in the methyl alcohol
are compurtcl v\\K thope in vater at the
aimc dtlutioiu wo would soe that they are
not wry different. The conductivity In
TTj»thyl alcohol h from two-thirds to thnv-
fourthi ihat in water, under the same
oondltione.
An exaniinafinn nf the ramductivity re-
sults in metliyl alcohol will show that it
ia elmo^t trnposaiblc to reach the raluce
'jf ft_ for Uio moat atroiixl^ di^flooiated
substflncfia in this solvent. The dilution
Ht which the electrolyte would be com-
pletely diwiiciflW bv r.his solvnit, is ho
great tbat it ia n^rly ini possible to
iipph" tin.: o:pndurtivity im^lhod to it.
with even a fair decree of accuracy
It is, therefore, noi poceible to m««a-
lire dissociation aecurately in ibis stri-
ven t, by Tiwiins of ihi." condiidjvjly
metliod. The flame remarks apply with
even ^eatcr force to those solvents whoM
dissociating power ia less than that of
methyl alcohol, In euch casea it is impoa-
»iMe lo (ihtjiin (li*> vhIhoh of ;t^ by tb*
tondudivity melbod, and, hence, the dJU'
aociation values obtained by thle method
can only be regarded as rough approiima-
tiona. They arc obtained by assuming
that the values of ^ in the Dolvtmt iu
quMtion are (tie «ame aa in water. An
Hfisumplmn which we know Is not correot,
aincc the friction offered by the difTcrcnt
Bohenta to the movemcnta of the iona ia
different, the volocitica of the ions through
these solvents woiild, therefore, be differ-
t<nt, and llie valni>a \.it ^. tuuAi hn ilif-
fereniL The above aasuinptlon ia, how-
ever, the beet that can he done under tlie
conditiaufl.
Another method of measuring dissocia-
tion haa been applied by Jcncs to aolvcntn
like methyl alcohcl. Attention haa al-
ready been called to the lowering of th«
YHjinr-rrn^ifin of solveiftfl hy dissolvr*! iiub-
itances. Bat lowering of vapor-tcnaion ia
proportional to rise in boiling-point, and
jf wo measure the rise in the boiling- points
of eolventa produced by diwolvod aub-
stances, we can ralcnlato the di»ociation
of the diaaolved aubstances in exactly the
Oi/TLiyiBS OF SLSCTRCCHE^tSTRY,
sajTie way, ae wo ealculaW the dUfiooicttoii
of diesoived substances From the lowering
of tha freeslDg'poinr, of the aoTvent pro-
duced by them. Very satisfactory reauire
wero obtained by tho boUing-point mt'lb-
od for Iho JisBQUiatiou <ti a number oi
aalu in methyl alcohol, and the final con-
dusii3U was reached^ a* the reaiilt of Ihis
work, that the diaaodalion in methyl al-
cohol ia, in round numbcre, nbout two-
Ihirds of Ihnt m wal«r lindur the lamo ocn-
ditiona,
Ethifl alcohol has a much Buiollcr dit-
Bociatin^ power than methyl alcohol, as
indicated by the condactivity mothodj but
Ihe dissociating power of this soh-ont can
be measured only with very rough approi-
imatioii by the conductirity method, on
account of the impos»ibility of determin-
The diBsodatioQ of a number of aaltg
in oLhyl ulwhol has beirn nieaaured by
Jonesj iisitie Ihe boilmg-pniat mi:ttiod aa
with methyl alcohol. The resvill,6 showed
(hat Ihe dif^ocinting power of ethyl alco-
hol IB from oiiL'-lhird to one-foiiHh thai
of water it ihe same dilution of the aolu-
tionfi.
The more complex alcohoU disao^iau
luurh hf<8 Ibnci I hi* :^im[TlLT MKiiLbcrs j»f the
aeries, ae is iudicaied from the conductiv-
ity raoltf, but for all slightly diaaociating
folveitte this conduflivity meosurements
must be takeo oe oiily very rough approxi-
mationa, aa a measure of diaaociation. It
has b'Tii found to hi.' a i;>'iii nil rnh' thnt.
in a homologous sorlct of compounds iht
lov-'ar jnenihcT& havij mnch htqher i<inizing
powfT than Uir more eomplf-x members
of the ecr£o*.
Tin? eoniiviclivitiee of a nunibtr of olec-
troJytf^s in ai-ett>ne and other ketones have
been meJiaored, eapedally by Oattaneo*
Carrflfn and 8l i,aEzczvmhi. Such so-
iutioQB have considGrahle conductivity,
shoving a iiiarki^d ionhaiion in these
solvenla. Th(* inniatug power of the ke*
touee in general dccreaaea with increatt-
in the complexity of the molecule.
Thy ionizing powi'r of the nitrilcs hns
also been found to deereaae with the com-
plexity nf (he nioleojle.
The diasodaling power of a number cf
other organic soWcEits has been studied^
Solutions iu i.'tiuT, gly^Jtirol, ehlorof-jrm,
the tiydrocarbons, and similar compounda,
cunduct vtry poorly. Some very siur-
pribiiig results hare been obtained in
mii^ed aolverUs, one csample of which wiii
be rcfornjd IOt While electrolytes in
methyl alcohol conduct the current very
well, the con<1 activity is considerably le»a
thim ill water. Zelinaky and Krapiwin
found that certam salt* have a greater
tjonduclivity in pure melhly aloohol, than
in a mixture of fiO per cent methyl alco-
hol and 50 percent wnter. This laahowD
!jj the following reaulte:
V is the volume of the soluticn. or the
number of htres which contain a firam-
molecular weight of ttie diaftolved anb-
atnnre. utid fi, tht- riiolei-ular conductivity
at voKiine v.
roTAsairu bhqmide.
Mr'lJ-yl
Watsr Mvlhvl AlOoM Alivirmi,
ODD hitir
b
ft
fv
Mv
10
ml
an. HI
IU
inn Fk
TflTO
«M
Vfi4
]^ 4
(H,M
00. H
nu
140-1
gn.n
Tosa
AMUOXiru
IODIDE,
l.>lltt hKir
M»<lhvt
Wrtier.
Nell^yl AlfoliDl-
AlmhnI
Onn-hiilf
Wat*r.
V
fv
/tv
t'n
M
ia&.4
TSM
rv.u
e*
131,1
BS.ttl
07. 4a
XvO
13h.7
mac
TV* a*
\D9i
US.7
iM.ru
•n R7
It is impoaBible at pre^t^nt to aay what
thc^ Burpmin^ and remarkable resultc
OVTUNffS or RLKVTHOCfiKMlsritr.
stf
niMii^ Th&j have been confiinied by the
«ork of rtthj^ra.
Similai' resulU have been obtaiiietJ by
Cohen with matures of ethyl alcohol and
«alcr> but ouJy when tlic mixture coa-
Uin^d Tory httio waUir, uod ^vhen the dilu-
lion of tho iolutioa waa quite great
ftGLATlONB BETWIlBfi TUE lONlKISO TOWEK
OF 80LVES-TS AND OTHEB TltOrBETlKa,
A number of attumpte bave been mado
to discover relations between th9 ionlzir^
potter and othtt j>rc»pi>rt]es of eolvom^
J. if, Thomaod flrat proposed the theory,
and a little later Ncniat snggeated the
fttine idea, chat ihcre should be a close re-
lation between the dissociai;iig powers of
tolr^nU and th«[r djeleetrio cooetants or
■peeiAe iaduetlve eapa^^ttiea. Those sol-
veaU vhinh have the ^p-eutest dielijctric
consEaut^ uadoubti^dlT have the greataat
diB^ciatiDg poweri- With the po.^oibleest-
eepticn of hydrogen dioxide, ubout which
there isf^till^mt (loiib»^ffiit->rhnB ihthijjh-
vf^ dii*)n'ini7 i^riTii^tniil. inid iili^o h;is ibc
grt'jitfst disftwiating powi^r. Nr-xt to Tater
Monea fonnic acid, both with roapect to
dielectric eon^lant and fji^sftcintir^' |ivhwer.
Of the more ooirnrmn nrgAiiij^ solvfcls,
methyl alrohol ha^ Ihe highest dielectric
cottfiUnt nnd alscF the greatest ionUing
power. Ethyl alcohol has a tooaJderably
amaller ditkctrie constant and. as wo hflTe
»Mi, much le5£ power to break down mole-
calcs intf] iona.
Another aug^efitioii, which we owe to
Dutott and Aston, la that the ionising
power of a solvent is cfowly connected
iviUi the ftate of s^giN^gation of ite o^m
niofectdee; the greater the complexity of
ibe molecules of any solvent the greater
it» powTr to lii'LMk diivm nioWidts uf
dis3cr!vcd wibshixneea icio iona. We have
a method of ddcrmlning the coraplwitj
of moUcul(4 of llquida. badt^d upon the
in(vi*iirii»n'ni nt i\\\*\r surfurr-triii^ion.
Thie method wji« dcvigcd and applied to a
number of liquida by It am say and Shields
«onie 10 yeera ago, with the result that
many of ihu cofiiitLon soUoniE were found
CO oonain of complex molecule*. Thru,
Ihf niolwid™ of the ah^ohnls wert, in grii-
cral. iimdi- up of moru tliaii one of the
aitnpk-ai molecule.^, and water waa found
to bo the moEt complex of all the tiquida
kuijwn. Its nioh'cult tonEit^U of four of
the aimphtit wjttiir nvih^nules — (IIiO)^,
This most assoeiated of nil tnown liquhla
ha* the strongest ianizirg power.
While there is undoubtedly an element
of truth in both of theao ^uggetitiona. they
are far from un oipression of the whole
truth. These reliiEion* fail U) hold, e*pe-
ri»lly Hinang ihL- nvukly ihsr«m'iri.i[ij;
«o1v^nt«, where it la oflen imposAible to
*fly, oiihcr from the riiclcarlc constant or
from the degree of associatioiir which of
two solvents has the greater di&flociatlrig
power. It will probflbly be ahrjwn that Ihfl
dissof.'ialing p^»wer of a solvent ia ool \
funotion of any one- phvsical or chemical
property of the ^ubfltanoe, but of them all,
Or, perhaps, more acciualely eipreMfd^
all the properties of a substanoe are a
funetion of tli<' energy- rtlations uTii,h ob-
tain Id that substance, and diHM»cjftt!ng
poA-t-r is simply one of these proportio*.
Thc! conclusion from the itudy of the loU'
i/iug power of folveni*, whfrh is of grwil-
Mt importance, is that ton* an; probably
always present when chemieal reaction
(ultpfi plncP, Wbi'M thn nirndxT (»f *idvi-nFW
whic!h can irlTvct totiination in takon into
aocount, and. further, iliac hoat and poui-
bly prsaeare oan break moleoulM down
into (heir i^uj-. il w \W \\i* i^t- '<■ \\\ \ \ \\yv >
not a chemical reacUon \vhere the ccndi-
lione for ion fomLntion do tol exiH.
OUTLINES OF ELECT RJOVHEyflETRY.
r
UJCLATION }lin WKSN TU« DILUTION OP SO-
LDTIONH ANt> THEIR DIflflOClATION.
It W alreaJj bftm pointed out that the
popoenUge diBflOciation of solutions in-
creaeee with the dilulion, but while our
knowledge wtw m this purely quaiiUitive
flbigc, w<.Mmu]*l »mrotlj hopr Itj ilc'duce uny
cc^iucqucncofi of iiuporUncc from it, A
qaantitAtiTc mlation bcrtwc^ri dilation and
dJ6Soaiation haa, howcvcri bocn worbed out
hr Odtwald; flJid hns l-?3 to such important
con^nencM iliat it mu»t be capefully
Ostwnld* was impreased by tbe relation
bdwcd-n dD clcctTolytp undergoing diaso-
cintion into Ions in tho pr<?aonc!Ci of a sol-
tent like water, bh^ a Eubstance like
Rintnfiniuni cliloFJclp undergoing di^ocla-
tic»u ioL^ the mokculeaj ammonia and hjr-
droclilorit acid, bj beat. Siace tho lawa
of j^a4-pr«afure apply to t(i<; oaiuotic
|)f«6ure of aolutions, it eeeras prob-
able that any di*3iictioGs for tlie dissoem-
lion iif a YiijUM" Uv h-at. would H]'[dy tn tlii'
di^sodatioD of an electrolyte by a fiolvent
like wfttcrn Wlnrting Willi th;^ idoa in
mind OsEwald d«Tolopod Iho following re-
lations.
Givi?n II vapor whieh w uodergijing
diBsociat ion by beat, ■ ay Ihat of am-
monium chloride. If neither of the prod-
iK'lt; <if dif^^cMintion is |ir(Mit( iti i-teL-is,
and if the temperature k maintained eon*
*tant, the following relalion obtains:
\-
-t = conai^nl,
^1
(1)
In vhl^ p la the prwBure of Ihe original
Ifaa, aud ^;, Lhatof thi^ decofii|jofiili^>n prod-
ucts. Turning now to soluticna. w< muet
'dMl wHb wmotie pressure imtcad of gae-
'l'lHii?rT rkf ia*rlpiilyTt4i I HvxH-InEtnii , p.lU
pressure. The osmotie prea^re J9 propor-
tional to Ihe amouut of uubstaniw preeeot,
and inveraely proportional to Ihe vi^Iuiue.
Let u be the ma% of the undecomposed
eleoiroljl*, ami u, the nniseof the doeom-
position produele; v Le the volume:
o = - and p, =— ,
'^ I' ^ t
Subetituling tiicse values in (1), \re have:
til'
*= constant,
(=i)
The amount of tha diffiot^intion products
E^t, ia rqiial to the relation [letween the
oonductivtl^r ut Tolnmi* i% {fiji, and the
ecndnotiHty at infinite dilation (;i^J,
". = ^-
The amount of the undi«*«ocjaled aulj-
stance u^ ie the complement of a, ;
T/^ 1 —
I"-
Subatitutlng Iheso valueH of u and n^ in
(3) we have:
— t' = conBtftnt, (8)
and this is Ihe dilution law of Oatwald.
This can, however, bo aimpliScd, H we
represent the activitj' coeffieient, or the
amount of difesociatlonj by o;
Subfliituling this vaJue in (S) wo hftre:
So much for the mathemntEoal deduc-
tion of the relation between these two
kind» of ditiETK^iiLtiun. Il now reinaina to
see whether the deduction is correct.
whether the cocclnaion ie m accord with
the fact^. Tho way to lest *hie ia to take
a solution of an electrolyte, and detttiuine
tU disaodaticn by the condueti^lty or
OUTLtKEa or ELEVTROCHKMtS7itY,
11
frwwing-pomt method; knowing the vol-
uuio Vf or tijo oonc*>iitratioii of the solu-
tion, find having ileteriTTMietl tlii* di^^oci-
atioD a* we eubbliiute thcao vmlacs in
the Above eqiiution and calculate tho value
of the ooQBtant We nrjw dilute the solu-
llon still faiiht-r, and determine tht* vului?
ofo for the newdikliot). Knowings ft>r
!he iitw Jilutiou. and hatiTig detormmcd
a, wo enbatituUi tlies*? valuta in the abov<?
oquotion snd calculate beicw the value of
Lbe oonelant for {Iti^ dilution. We pro-
cH*<i in Hxaoitly the sojce manner for a
wide ranKe of dilutions, and tiiGn see
vhcth*>r the valiups obtained for the eon-
irtant are reall)' conatont or not, ovor a
TAD^ of dilutions. Some of the results
obbiined for a few ^ubatancoe are given
Wbw :
ACETIC ACID*
V
d
CODfUDi
■
1-in
o,fom>
j
t.as
O.OOIS
m
i.«
r> IUIt<l
194
11, M
aoctiw
IIUTYHIO AOID
t
4
(telHAK.
,S
I.IJW
OOCMM
f lU
OOPUD
BM
IV .WH
0,0OL4»
rnri
IL.4I
a,VOM«
*
IJ
C4>U»tUlL
u
1 vn
ntiott
&j
»u
ont
124
rkU
O.ODB
«w
7,M
0.«0H
TKII'IIKXYLMETUAKB.
t
1
[ktOllUDt
A
«,00flU
L-
oirm
K
M
ft cwiO
^
m
oinr*
The Ostwald dilulion law dirduced
flbove, secme to holil fairly wdl for the
above eubatanccs. Oatwald applied the
liv to more than two hundred organic
adde, and BrejJig Applied it to a large
onmljer of organic baws; fintl wt held
»tisfiidotf-ily for nearly t\l of these
6iib»tance£, The conduaion mi^zht be
drawn from th^»e facU th»t the \av w»m
of Tioiversal application, but it should be
observed tliat the abt've i^ompounds. or*
gmic acids and or^nic bafiea, are aU
wcfikly diseociaU'd aubitancee. ua com-
jjEir-t^d with inorganic tubs tan KB, It
mighi be that the law would hold for the
weflkJy dUsocialed comptmniK and not
hold for Lha stronfrlv dis^'x^iattd acids,
hiisQs, and solta. This bitf^ indct^d, bocn
found to be the case. The law of Oetwald
does nat hold for a finglo strongly difi«o>
*!iaicid iiuhslBnor.
The quefilicn i£ what is to be don«?
We have a dilution Intv for the weakly
Ji£fK)ciated compounde, but wt cannot
d]«eard the strongly diasociat^d com-
poiimlft-^tlie most important iubslnncrii,
by far, from a cbcmieal standpoint. For
tunately, this is not nepeseorj since the
folJoving discovery vfo^ made.
"Rudolphi,* from a study of the oon-
ducUvity of solutions of silver nilrate of
varying concentrations, diecovered a dcv
relation which obtains for the strongly
disBociated compounds. If wo reproeent
the voluirip by v nnd ihe ronsinnt by c,
OS above, he found that when he applied
the Oatwald equation to eoluUon^ of sil-
ver nitrate, ho obtained the following
vrIu^ :
For r= UJ, tf = 0/J6.
For v= G#, p — tLi3.
Forr«2^tt, r=-0.n«A.
A glance ait thuee figurce will eh^v that
II rr-nl porstnnt would be oblvined, if tha
values iif c wptv. multiplied by the n^uare
root of I in each cni*!*; thiii*.
We mu^ then substitule for v. in (he
If 01101*4 ftoA TOMorr at Kloffircljbic JjtiBAcuuoa. r-r
ir-iM.
Ti
orTLiyBS 6F Bt,SCTirOCHirMlHTftT.
OftwiUd cxprewJOTU tho iquiin:' root of v,
when U iHworneA:
A \— ?- ■■ oonrtimt.
[1 — a}Vf
Rud^Ipha applit>d hlB oqaation to be-
tween Hfly and airt^ strongly dissociated
(ioirqjiJuuils, aiul till* vnliitm fouui] for c
approj9ch<^d n constant. While m&rk«d
deviation) arc not vaali:^^ jet Rudolphi'a
»pr»aii>& appKci lu wdi to llw itroagly
(IbtooUfed elef^Erolyit-s^ n*. (hht of OslwaM
to lh(»tT wliicb arc liw< jfri>Uglj dtHHifci-
flt«d. aa the or^imic acida And base*. This
will he tfocD from the followjoic <sxnmplM:
lljilmohlorlv
p r
«
•
p •
t *M
» 1 in
t
■
Ul
« I.ti
1110 i,ia
Th<T l^udolphi oxprrt^ion i*, of ccmne.
purely «inpiri£?al. The phv^ical aignifi-
*!ttm*** of tltc v'~y '■ '■^'^'*' f^*'" "^'ilir^'lj iin-
CJipljuTu^d, Oitit or two moilifiratioite of
tbc Kudolphj formula bavr been proposed*
but Iheflr- ore dUo ^Tiiririoal. and crLEinot
b« T^g^rdefi u oiMDti&Uy in mdv&nc^ ot
1^* onglnal "
We liftvf Uien, o^nt Oiljtion Uw lioMini^
foi lilt- w'f'jikly diseiX'UU'd *?li"tlr[>Mf'4, nnd
ano[fi<.T iip]>lyin;; to tin- Atntn^'lr thsda-
datcd eompoundt. the dilution law of
OitwaM, which apijlle* tc the vciikly dU-
i<orUtifl ciiHipoiinc)*, hit' n mlinnnT liJL*iK.
n* wc bntv *rcii; being deduced from an
etfiiation for A diuociAting Tapor, which
va& cetflbliihtjd not only empirically by
diroot exporiment. but vbioh h»ta albo
bcon deduced Ltierinody nam i fully. The
pHyniiyil siij^iiilirauiv of tJiin \wv/ is |H5r-
icctly apparent, but not wo with the dilu'
tion lu^' ijf Hudolphi, vhuh njiplii'5 tn Iho
itronjfly d:MDO-i[itod compoundo. It ha«
b^m ^litnMinhiad only hy osip^nnieiitr and
iB. fIn*rrforp, pnrvlj *^mpirifal fu rela-
tions 10 other thin^ tr^ bot knora, and
wif liJir^ Til} idtin what :k llie plijvJett ug-
nificanuo of thr; Eic|tiarv rool of v in tkk
oxprcwion. It, bowirteT, tccmf to fit
faoti in tho oosos of etroogly
giibeiancee. snd w^ may s^m^ d^y U«ni i
ti^ id chance.
^ntttft? ditution lawK are not fll
wid«-i«achtng gununiliiationf, vhk&
brace- a Urge minibcr of facta; nv impor-
tant as eut^h grnomli^tionn always arv;
but thny hiiv« A EpeHal fllgnilleflnco^ Tbs
immcricnl vnlnes of |he eonstnnts for dlf
ferent auLulanctA ^ive tt» a world 'ji
forniaEion abtmi tiieae componnda Th*
chemical aciwilic* of compc\ind6 <ra pro-
poriionat iv thM4 con$iant4^ The (nil
■jgnifl^ncc of Ihji; rvUtion muy Dot ap-
|>nar ill flrst Hi^hr. ht iinporrmi^-v vitl
become appaicni from the foUowicg coQ-
bidcrationf. By the cli*mical activity of
a eubetanee wc tucan ite power lo enter
into chemical eorabmationi vith other
• ubitumrc-*, how it will W*lw*e lo tlus pr«-
i'lii'A' of ijffiL-r t!C]nipoumh<, what r«td:H
it «ill r£Frs-ti rtnd ih*' ir\w\uv» iritli wh:ch
diioh reActiona will take plnc^-; in a word,'
Iho (^ntirri c^hcmicAl naTun> and conduiTt
A suhilancv. All tJii^ is givi^ at onoa by
th(> value of \ht} "Diwociatinu (Vinxtnnt
»f the subatanec, obtained from the dU«-
(ioii kvs which ve have just bc«D coik
biderinjf. From *iich faou we ean doc the
rt^al iiguificanoe and importane* of the
diliiliun biw», a* «-xprL-*i.iii^ tlie relation
brtn'ivn tlic diludmj of tlw BoIatioB am!
the diwocrintiou of the di»o1tcd tuhi^aiuv.
THK II>Si>;lNU ponisft Of liiu-r.
Wo hiitvc dealt thos fur with ehxirolytk
diMnciotion aa iftkitig plnci; onJj in aolu-
tione of cortoin sabaUoc^v in corUin 93I-
v^nta. A question whii^h haa ihua far been
unanawOTed ia. what effeot doe« riae In tooi*
1
OUTLIWfSS OF SLSoTitovnsmsTRy.
71
paruturc liave oti Ihe amouot of the eUc-
(ion IS made all the more prominent bj
lit rtell-Ioiiiwn Tftnt IhJii hcHt ilissooijjites
iIht vnpav^ of irmii-y ryTTiipouiidfi \\\e am-
noQiam chloriiJe^ plioephome peutii-
chloHdc, etc. ; and wt Imvc jLJst poinU'd out
AhitaUon (OelwaJd dilutioo law) Lxitwcen
iU» ditt^ciiition into mdt^ouli.^ \iy hc-at.
tad fWl rrj f T f ii' dis^x^iatioTi into ioxtt by
bruits like* wjiter.
An iiivi^tigjit.ion r»n the effecrt of tcm-
(ktmliire on deotrolytic disrocirtrNon in
jijumue wjIuHoijs hn« bitii cisrrifd out in
tbw lfihm"nti»rv* during; l>u* pH*i yrjir,
and the result hns been Uj shnw thai bc-
twrT'n dt^rce mid 35 dogrtx-a — tliL* Hmilfi
*f iht' iiivwiigfltion— tcmpcmturi' baa Ut-
tlimr no ffTc-ol on dii^eoomtion in c^ululiou,
Wu ml^^hi condude from the aUovu fuel
llint hi-itt bfiK nn powt^r tn bmak mok-cules
Oovra irrto mni^j biii sudi a concluhinD
Would not be jn&lifipd. Wc must fir*t
ttidy Iho dTcxrt (>f hcrtt alone, when there
IB no solvent preKont- To da thie vo muftt
laiiL th(» drv ^omponnd, p*Thn|w to itB
JuHiCrii puiiit, to b<^ whr^tbf-'i' in FuHeO
cJcctroIylOj there ie anj evidoace of the
pws(jnM of ion*. The reault can Ic
>UXi^i III \x w'oi'd. Mimv I'Wtroivk'e wh(»li
hiwd, ccmduot the current to a very con-
ild«rnb1(- pJitrnt- Sntny of the tntnpoiinili"
t^in far *(ii'lird an: s^vlinin otid calcium
fhlwidcff, potnsjium bromide and iodide.
lH)U»fiiim, ammoniuiii, and silvi-r iiitmtL^ft,
*tr. XU*> evidente is perfoerly eJear that
bpatf aa wPcU oa *olvvnts^ mo ionize m<jl*-
*ii1h»; V fl., can I'fTurt i*b'rtmljtic disfio-
Vr.l\'& IS' WHICH loss ABE FCiRMED.
TtiiB nvtbtT l-ong clmpt^T witl be cob-
,*B>ttHft vai soap umpBiir in ilmfr'fvii ChvuieaX
duded with some account of the diderenl
vays in whjob iona are formed from
moloeulw, TJio oonciusJon to which one
wo»ld be led at 6r3l^ from a general itudy
of the whole subjiKt, is itiat iooH aft
formed from molccNlce ii> only one way —
a rntilccuic. under ot^rlntn conditio w,
hreakinff dou^n into an oquivcdent tmmbar
Kif cathnt and anions- While this is the
riii'tbi^l uv^ht fivijuciilly rm^l with in i»k<-
trolytic dis9w:iadoii, it is by no means the
only method. That this method may \x
Tuore eluariy unJerstQod, and for the iJiko
ot oompariefin with other m^h-ocls, n few
ciKinpIfS nf di&wtfiation by Ihu TUE^thnd
are given:
a:
HLl
BiKOU).=:lJa +OII^Oa
KV\
+ ci
Raul, sK+ci-f CI
Theft* t'xampii^fi nf ncitlft, bn&e«. and
suits, fiuffior lo inustTRte the principlo,
whirb If- fisprnpliflcd whenever the*e eom-
pounda dUeolve in a *troaglj dbtiuciating
solvent liko water.
Another entirely different method of
ion formation ia ei«mplified when an oton
tnkr^ a rh(ir*jp. from an ion. hetoniirtg iUelf
<jn it>n, ihe ori^itial ion htcummg <in atom.
Thia lakca place when a metal like einc
U brought in c^nlect wMh a MlutiOQ of
a salt of another melat lik^ cDpper. The
crnpp-r Mhidi is in t^U' ioiiir AiiU- gitk-*
up ite change to Iht zmc, heooming ttntlt
an atom, while thu rmc atom, having
taken thi: charge from the coppar, booomca
ui ]i:iit. This ii:0(lc of icm fonucioii
would hi- isprt4fi<i thua:
Cii -t- 80, -f Zu — Zn ■+- SO, + Cu,
TliATc ut no rhingc urhnUrrcir iit th«
&ninn. It rcTT»iun& in the (olutioa afler
thi? rc-acUoa, in cxnctJy the wnifi condi-
tion AM bcfor«H The copper ion gives up
tU charge to tho sine And ia prodpilftUd
us miftnllic cxi[j|wr. This incd« of ion for-
ntnlion eiplniitB nU thofto chetnicsl r?9o-
Hoss ID vhich one meUI procipitdtee
anothor &i«lftl from its cftlla. All that
tnlcfv pl«c« in fiich r««c(iou ia the trans-
fi-r rf thp elpdrinU i^argfl from the
Dielal vhkh ia prwipitatotl, to t!ie metal
which pasMB into aoluticn jn the ionic
A third mo^d of ion formation difT^rt
fnndAmentJilly fmm the iwo mode* jti*t
conaidored: One tui>$Unc^ paut^ from
Mtf atom intc a cation, ancthit tuhihnc^
at ih< ^dmd iinra p<vsin^ ft^m tha atom
into (h4 r<frr4£fQnding anion. The ex-
■mplo of thJA mode of lou forniation
which 18 ufually cited, ia tlu* aoluticn of
gold in chlorine water. M«laJ]ic gold In
tha pr^onf^ of vater du^s not form tooi
to any appreoiable cxl«ni^ and chlorine
in the presenoe of water doeii Dot form
IoiL« to any i^preciabLe ojdenl. If metal-
lic gold and ordinary chlorine an? brought
into the pr«a«nca of vat^r flimultftaeouslyt
tW g*"»ld |>afl*ii'P GVi>r to thi* f;>>ionic <*on-
■litiiiij. uiid thi< rhlunni.' ruiTiit uii t'cju^^a-
knl number of aniona, in tlic aenAC of the
ff^lloirin^ equation:
All + CI + CI + c'l — ^+ n 4- ci + ci.
We hnv* th«« an insight into the morh-
auiftm of what takea place in a rwction
which waa hitherto eimply dtacribcd as
tha 'Solution of gold in chlorino waiair"
which wfl*, of (yjuwr, fsimply ronumtng
i\u* jih4*nomnnji- Thi8 U nni^thrr of llic
otmjSB9 or BLSCTnocaBMiSTitY.
many cjtauipltv nf i)t« wh> in wliii'fi
tlMOrv of dccttolytic dii4oci»tion hu
thrown light on ohcmicai problcma. We
may look upon th^ reaction thua: Thr
noulral |j;old lalcis po»ilive eUclridij
fiom th« neutral dilorine, becoming poai-
tivcly cbar^. while the chlorine having
lofft F'Oiitire «IecthfYity ia no longor eko-
tricaUy n^iral, bat becomea nogatirHy
charged.
The fourth and lut mode of ion forv
mallon ia in a oortain icnBo the mo»t iin-
porta-W, in that it doaU with many of iba
phenomena in chemistry which arv r^
fcxrfd tc as oitdalijtt and redudiua Ah
ion takes en an OiidiUiJtuil charge of tUc
tridiy^ i»nv€rii7ig an ctcm tnU> an ion
with the opposito t^rgi, Thia it vtTf
limply illnatinted hj the case of f^rroua
chlondo and chlorine. Pern^ua cblorida
in the prcaonce of dilorine beoomca fer-
ric chlorido, in the eenac of the follow
t>quntion:
p*. + CI + CI + CI — Fo + CI 4- CI
The ferrouf ion with ite two char^
lakitt up a tlxifd dwrgv mid
a trrtic ion, at tin* wnic time convL-rtiiig
a chlorine atom into a cUohne ion. 'Hiif
will be moo^iicd at onco na an etampk '
of ivhat Jrt ch4?[nUtry ii known at oidda-
tinn. The trrma niidatkn and roduo- ,
tiou in chemistry are ued in two aecvei.
They m<'4Ln Ehc addition of oxygen or tha i
addition of hydroiren. They oro alao uidd I
in an c^ti^y dilforont wnae, w moasivg
the incrvflftA or deereaw of tha raloneo <dkM
a h;i^iMtflriiv; iiiid Kiniii- wv iiav deal willflH
Talence in t«nna of Farada/a law, and
mean by it the number of charges upon
the lOHB, oxidation meana simply the in-
cT^te In the number of char^ upon the
LUD, and rfdtietjon a dvervaae in tliU num-
OVTUKES OF ELUrTJeOCUBMieTIiY,
n
Uuog oiidAtiofi in thi« latter sense we
iM that the above mode of ioo formotion
10 A£ PH!imple of it; ferroi]^ trm with
two poBilive charges pawing into feme
iron wilh three pcT^ilive G^mr^g. BeJue-
bon is, of t'fjursi', hu^w^tljr llip reveine
prnccflft; », t^. the fviHovnl of sonit of
tfic chars^ee ttlnrfldy prcwn^ npon the
ion.
W« hare, then, in this mode *>f ior for-
ni4tion. a phyaicAi ('XjilHrialion of what
Ukn place in oxidation and reduction
ructions, when these terma are utwd in
th« Hcond t>f tliu two aeosci^ n^t-rrtMi to
bIovo.
The nbovG four include aXl IW modes
by which ion* arc formed from moleculea.
If we atudy them car*ful!y in their hear-
ing on eh^micA) reactions in peni^rjil^ v"-
shrtll »^ that ihoy fumitih i\ ]rh/sianl \yn»Hi
for a Urge nmnher of HMcilotiR^ whofi-
meanirig was hitherto entirdj eoDce^lfH
In till- Ught of vhat has thuj fnr been
bi'f>ught out in tho^ pnport, wc should
Hr.'giTi to «fp thi* impnrtnupi^ of ihe lh**ofy
of eleclrol^'tie diasociation as applied l<^
chemical plieiioni«jia. In the fcjll^^wioj
chapter ihr.* htaring of this and other
genotalisouona on a etrjetly cloctrochom
iool problojn will ha pointM out.
oiTTUSEi* or KLecTnneifjSNfiiTKy,
CHAPTER VII-CALCULATION OF THE ELECTR
MOTIVE, FORCE OF E,LE,MENT5.
?AliT I.
IX tilt; tfix prccc^m^ chnplcre to havu
lnL*f*tS the tlcTcbpmcnt of tlie fundft'
mcntnl conceptions cvbich underlie
tnodcTn dootroohemi«try. In thti firtt chBp-
how ih*i ivbtioiiH Lictwixji gnv^prctiMirv
tuA oanotic pKWUTc verc di>coT«rcd,
Tht' ori^'iit of U)c Ihcorr of electrolytic
(liKtfOciation was trncvd in the noooncl ohap-
tw, Icignlbtfr with wtttp line* of eriTlerifv
hjMriif^ iip«in U. In Ibe Uijin]. certain ap-
plicJitioDd of tlii^ thc<ii^ wui^ taken iip>
Tho toarih wofi devoted to cloctrolyaie
Ukd tb(j decomposition of electrolytes iu
general, b_v the cum-nt; tlio Iheorloa to
ucctiunl for i^lt'L'troljsJw nM^^ivi^if »]HHTiHl
flCliTiilinTL CHiijJtvr f[\c vtut dcvotird to the
rictinuijintion of thu rcliitirc nnd nbso-
luto v^'lociticf of Jon*^ nnd cbnpt<ir eiJc difi-
<nu8cd the conductivity of oli^trolyt««> and
egpecifiUj' theBpplicJilion of the txindncHv-
ity mt'tliud lo die meaauri'iueiit of eZectio-
Jytic diwociation.
rJ:c0(^ cJiAptcra l^vc, in a aciQ^g, been
pnlimtnnry to thv ono which U to follow.
\Vv nhnW aim to nhovr i& tliis cbflpt^ how
th*»*' fund/imt'Titril ronia'ptioiiH hiive bottn
applied to o problem of both scjai-
tiAc and toctinicnl imporUacc — thi; colcu-
Jation of tb« olcctromotivo forco of die-
menta This problt-m i> inler^Gling tewn-
tille.illj', liecauei", for the fir*Jt Liir)e^ we wre
ttbli* Ui obtain any adtquaie conceptiou of
irbat tnlccft place in a primary battery^ and
although sncb batterica have been known
for moru than a <ttntury, tbi/ir action hoa
bMT o:cplainiy1 for only, about a Aottn
»i» I
4
The problfrm is of lochnicaJ intervsL be-
mUK it cnablef) the eupiivcr to dt^l wrih
primary o^Us in a theonjticil maunvr,
wbich la oa aiitiplc mAtbcninticolly lU wo
i.iin <-trr h^ijfi' ijiicli u prub^tM lo Wniui*-
Wo ciin, of countc^ aasniui; Uint tift
rut-tliod* of mcnaurin^ the dcctromotm
forocT of cltiincnt* arc fiiniiljar to ail, aad
flball proi^Ded at onco to the appticntton tt
the coripeptionn developed in tbne papna
to tin- jiiYililrni hi liflTid.
It sbuiild bt Aimed at the oatat.'t Uiat
imturc of the prcbUm la not e eimplo onei
The primary cill jn ila eimplc^t form ii
II oomplicatod Jevici^, inrolving a numt«r
iif pr(HH<s(r?ft iind i)[KTrationH; and tho iimHj
at ihv. nction of tbtac cvlU invoWci, B<&
tMJirily. n number of oonccptton* vhick
rouat bi" cJcArly grnirpiid before tha folbc-
ingdoduclionnpanboapprociatfld. M^tof
thr«£» ronrpptionn have altvfldy be^ cJevi»I'
oped At 6u(1jcitut length, but one or tvo
additioiial ftjat^ires mtwt be inlroduct-d in
tJie proper placea. Bc-caiiec a problem is
LI Httio complex^ houf^vrr, ahoilld be q»
hnrrier to it* *olution, but, on Ih* con-
tnir)-, «b(MiU lin an incr.nUir to fnrtlieF
■ftort. It ia bclievod that tbe followiDf
solution will oITer no mtioua dilQculty to
any ono wbo haa follow^ the prccediajE
obaptcre, and who has even an clomentarf
knowledge of tlie ca Ion Ins.
CALOULATlOy OF THE KLECiaoMOtm
uoTic rtta^UH>» or -rat stoLtTiow*.
The firnt tiim» that nnr i^rtnu't upon
bi'jti{iri£ it in smta lo prrdirf Umt i1« m
Vic^ will Bdt be folly UDclcr«to«d, Hftw h
P H poMJble to caUndatc tbe «1c€tTOCiotiTa
> force of prinAiy oelU, from the o«iuotic
prv43iifv of IhL' dtctrolyti*fl mrcund the
jk4«* ilow cculd Uirit be unj clciw <:on-
JltfctioQ bctncrn onmotic prcmirt au^ the
potriiliaJ tti a cfllf- Arc qutitftions whitli
arc aiiDo«l earo to be 4ifikt<l At thv ouuei.
Iivdcctl, it U rlitHcuIt to aM oS-hautl that
tlwre it kd; cODDCOtion 1iotwG«n tv» acU
of pk«nomctia appnrantlj m viddj iv-
movod from oac another.
A careful itsdjr of thcM pbccomcna
will brin^ out t]t« fnct that ther^ is ft r«ry
cicuv n^Atinn, ind^, betwwn them ; ae bo
frix|u«-iitljf iDiiiufrf^U iiwlf, wht-n wr cnmy
to ci>n*ifltr opparcntty disconnvcti^tl phe-
DonuDU in the lifbt of »om« rvoenilj dia-
eoTored generalizatioa
, Tt diould be stated at the outtct that
the very unpurtniEt di^iluL'tian* which nro
to be foIlawf<^ in ihU clmftcr vri^ owe fl]-
raort tnlirtJ/ to Nfm^l, who worked tJaem
out th«o^E<«lly and verified nUDj of
tbinn vxppnmcntally, while a priT^t-doceot
in ih(* liitiornron' of Ostwald, in Ldpalg.*
The fanilflua«ntal |JriudphT wtiii^h rimkw
the folWiiLg di'duflirm p[>i*ibk\ is tlut
a wc al!oiv a evh^Uncc^ imdtr one coiidi-
Tion V> pa»« Into anothcT eondition, uo-
th«nniiJly, it makes no difforccco bow
tha tniniirnmiEilion talcr« place; i. e.,
irhctber wc allow it ti bu accompUehed ob-
moti^slly bj thu fiuw of, the colv«nt fivm
one aoltibon to Aiiother^ or dcctrioally, bj
the flow of a ctuTvnl and tbt eonaoquont
iftOi'eniL'Dt of tbo Iode,
W« iBiul fitvL find out Iha mannutm
(SmounI of cjierti^l icofh which am be
obtained from a proccat, in vhich a aab-
*r«r ■ lUU*r dWwMH of Ute vho'« nlrJ#K. •>•
0<I*«U> LcarlAN^ (kf AUcravnnj Clifmlf^ Lt BMv'l
OtlmAmTU fbmnrjsi KUftrttlftlp ]]Wfr
OrT£./.Vfff OF BLeCTn0CHEJtI87XT.
TT
dtjinco paasf^ iaothervaUj from one con-
dition OTcr to anothar. Thia can ba Eooat
miility nci^omplifihed by aiartlng with a
g&a nndi^ oLe prvs^nre, and allovfiig it
to expand, taolhcTmallj, until it ia under
A comudurably dmoJIcr pn^auxc; ainoc, aa
already atat^d in theao papcra, ivc know
more about matter in the gaaooua than
Jn any other emndilion, and cnn doal with
il fur nioTv fr^it'ly.
Lcrt \n »inrt with the gaa under any
pnwmro p^ and volnmo Vi, and allow
it to cKpntid iwth^nnnny nntil it ia
under a considerably eiiiAUer pieflsure^
which wo will callj^btc iltAtinguiih It
from the firat prManre which the gae
cx^itoJ, When a gaa eiqsands thvta,
iftotherroally, it does work aa wo aoy,
in overeoming the pr<!juure of tho at-
mo«pheiv ; or, Ut \im' tintKnitnl t^rma,
it takea up htat from the mrronndin^ ob-
jecta and conrerta it into cncr^ of Tolume.
which it can o^in ipvo up- Tbc amount
of ITiiii i», from the well-known th«nno-
dynnniii- prliLi^Jplc:
-A"
(1)
A
If wc rcprcwnt the pneeuit; uf a got b^r
jr^ and H?! Tolume by Vj. the coDibin<*d oi*
prtvfiton of tha lawa of Boyle and Qay
Lurtutc in: ^j'^ltT. wbrn* R m the w^ilU
known fc^a ci3n«tniit nud T the alriohite
lempfrralurc of the im*»
Snbititutinj^ f>r— KT iti equation (1)
we have ;
an cJtpn-aikin for rtip ^xilunie ^nargy oti-
tairidhlit ffi^in an fipaudiuf i.'aa, which
con br rvadilv int<frat«^.
n
ODTLiySS OF SLECTitOVHSktiSTRY.
'Hi* integral U :
(3)
vhich Is an cipresaion of the amouDt of
CDerfiy eonvcrtGd into work, which cati be
oblamed from a gas obeying tbo gns
lavt, expflcdlng isotberrially from any
pressure /fi ta Mny otlicrr pvcwurcj^.
The qut->Uou which ariie* here i£ what
connection exiaU between tht- iiboTc dt-
diwtion for a gas and the osmotic
prcfoure of ii Bolulioii ? What hse the on*?
to dt> with Uie othor? W& will recall in
*.hm rtmnei^iidn t!ie iipiilenb of Lht- firet
chapter, where it was shown Uiat the
OBinotk pressure o^ solutions oWya the
^■lavre, arid wc mn sec ncnv oue of tlie
manj applioation*' of this highly impor-
tant general izntifjii.
Sini^ Uie UwB of gaa-preaaura apply to
the osmotic presaure of oolutiona, we can
apply any deduction from the ono sot of
phwiomona directly to the other aet. The
work obUinnMt from an id*?Jil ga.H, in paa*"-
in^ TriJin ii gan-prtsj^uie p^ to a tras-press-
ure }i% is> thoroforo, exactly equal to
that which can bo'obtainod from an ideal
HoluLion in pueaing from an oeinotic press-
ure />^l<i an tjf^nmUi' prri^Kn ri' ^v in tlie
above deduction the fc'a» had a volume if,
and passed isothermal ly from tJie one
pr(«Bure over to Uie other. In order thai
the conditions should be compfli-ablo for
the solutJmi, it must alto have n volume"
V, nud pflsi iriuUnM'uiaUy from the out?
pressuie over to the other.
The all inipoHant point lE the eakula-
tion of the clcctrornotive force of elements
from oamolie pressure, ie the followinn;;
Thi' iojii caifiot luQve in a iohitioji H-ith-
out tvjrrytTif; ivith tkem ths eht^triral
*Ui volLiTTii of IV Htlurtoia In qi'Vkni. rhv uumher at tltT«B
charges which are upon them, t
amount of work obtainobte from .
in jfOjfifing from one osmotic pra
another, can hn transfornisd in
tricul f^nt^rgy. This is the Icej to tl
deduction which follows. We \
ready seen, how to calculate tJie it
Jjiiuahlp from an igothermsl tran
tion of iona frurn one osmotic ]
to another. Since this woric con b
formed inlo electrical cncrfcy,
wjuate Ihe maximum external wor
is obtafnabk and the elc^jtricnl
which is equal to it,
We have thua far shoTffn ho*
culflte the electrical enorgy ohi
from a solution whose ions aro u:
fjsmotie pressure p^, in pjitcing
OHiuotli" pniAsurpj/^. But plwTtrit-al
i£ one tiling, and potential or dcctr
forec i£ another. This hnngs
thcf second important step, vjhai
oxUU bf^twt&n tUctricdl energy i
tmtialf
Elirctrioil energy, like every othc
festation of energy, can be rcga:
mailc up o! two factors ; the one cac^
the quftntit>' of rmerflr and the ot
intensity nf fho energy. In bri^f, '
a capacity ^nd an inUfutitp factor,
produi^t of tlieiw two ihh of cutira
to tte energy in quvetion.
In the i^ane of i^loctrioal cnoi
intejiifittf factor tj the poUntial, j
rtiptu^Hi/ /firffir w thf qitafttily t
fririh/. The prodmn of thwe two ;
to ilie eleiliiia! energy. If we re
the elcctriool encTsTf bi' H^, as U
done* f hfl (luaiuitr of dpctrioity by
the potential hy t. we have:
■ "T'v^K,
Wekn*iwK^, flineeit isefjual to tl
imnm eTieriial ^vork obtninnUlfl fr
I
otrrusBs of eiectiwcmsmistby.
n
uKbcrmnI tinnfifonrLntioT diatMaffed abovc^
wokno* E^or tim qtmutity of elooiridty
MfTiod by ft giv*in quantity of iona in
p^uiLDg froDi one ONmofic pr^^s^iire over to
auuilicr: BiiiLu frum Foinda/s liw thie Is
(Jctcrmincd om^o for ail for any given
jon, and k»<*wing tho q\iantity for imj
givon univnltul iorij wu obUic it for at\
ion &f «n}' vnlcmte Uy .imply multipljing
Uii« ^nnntit.y by thn rjdi^ncc of the ion in
qutBtioD, I'"roni equation K w* have,
w =
*Let' ua deal with a gram-molocjular
weight of anivnlerit ion*. Th?«e will t^^rrj
^^M^ coulombs of qlectriclty, and this
(|iiftiuily we will now defiignatc by E^^,
If ibo ion* nrc bivftlent th^^y will cAriy
twice aa much; if triviileat threo limos iw
mudit and ao on. Let tu r^proacnt the
valpnw of the ions by t'; then, a gram-
ujitliTHlHr w»-i^bl will CHI 17 V E^^ of
d<ctiicity. Support a grttm-mokcular
iwijEhlnf tliOAD ioDH lira chBTgwl irpoton-
tM, Tho amount of eUclrioal energy re-
quired to etTocrt tbiK charge is:
irvL^.
But llu6 electrical energy b equal lo th«
ocflOtK, calculated fllov*, where a grain-
ur>]?ciilAr wnght v/ntt Uiken inLo aLvotint.
^e late :
rpF.^ - UTIn ft or.
HTlB^
7f K.
(5)
^'bu u tho fundcmGntal iqitation for
^Icufdfing the ehctro motive force of
h*Tbbnnci«pb lBi]Ui>Wi1 ff nrri Tbrort c^ KIrglrgilfMo
flemortts. from the osmotic prcdsurcs of
the clfctrotifUfi nroh/id tkn ^icctrod^"
N'umertcal valu«« for n niuabor of th«
qnaDtltli?6 lu the above «<qiifition aiv
tuownn awA a^n be rt-jiJily iuaerUd liitii U.
Thus T, the Ab^lutc tcmpcntturc of on
ordinary room, onn bo taken as about 390
itisgr^ft i'iT-i -r it). If vo uiv iluitling
with gram-mol<^culAr wdgbls of £ub*
ntancpft, R the gfl»-corriant is two cal-
orii'*t or neux cnou^i to it for all practical
pLirpowB: and one calorie b <.<i]unl to
-1.18+ LU' erge> K^ tho quantity oi 6l«c-
Iridly carried by a gram-tnoleciUai weight
of nnivaltnt lon», ia 96,3-10 Mulombft.
Wh liAve^ then*
ST
^ = 0.0261 volt.
ftinoG a volt miUttpUcd by a ooulomb is
equal to 10' epga.
Substituting thia value \n equation S,
Wff wnuM hjivt-:
«- ^
0.02*'&1
Ifi)
If wi> wish to pttSB from tho natural to
th^ Briggsinn lognrithm, w« mu*t divide
by 0.4343, when thi? above ^ipnvcion bit-
c!irn«ii :
OUB
^%
tT)
If vo ore doling with iinivalcut iona,
t- = 1, when wc bava:
ff = 0.<>i« log '''
^'1
(«)
This ia the form in which wc nhiOl iiae
tbe <*quation in all calcuI&tionK of the r1ix>
ti'nmotivt force of elePQenlfl,
Tliia c(]iintion tjikca into aocount ndtd-
ing but the oamotic prcaaurM of the iona
in the solutions aroufid the okctTode«^ It
»
OVTUyS^ OF BbBCTROCHe^fiTnT.
cootain» uo factor vhich «o/» BUjthing
about thf natniT of the clcctrodta uBf^, or
of any relation bctvooD the «loctroiioe and
tiie eleolrolytea in vhlch Ibcy ar* Im*
merswl. Tlie nlory of th*' Dcltfwi of tb«
oall, iih lllu^ far l.cilil, i% wry mnnirlHiil, Imt
it u not the whole story. Jt 1% Mlf-^^tUmt
from our knowlodgc of primary cells that
tho cJoctrod^a Ad woU as the electrolytes
must bo taken into account, 4iid we ^sU
now st<& Llie WAV in vlii<.'li Ihia iiiilcii^. Th^
MH^und JaiiHirUnt dwlurUoji^ Ukr thn oiie
trbich vrc hnvc juvt contiidcTCt!, vc owt
to Nrrnnt, n-ho vu the first to eicpltkin tho
Af^tion of the primary oeH,
TJIK SULCTIOK-ITKVBION 0? UKTALft.
The torm sohition-W^nftion of metals is
now 90 e^tenBiVf?ly ua^^d. tbtit ^vavy one
QiuflL liavt «ciinc- ooticeplioii n» to wimt ia
mani by it. Vn>ni llii^ the term eclutioD^
tension hoc extended to every Bubfttancc
irhtdi <iiwoLvoi Id Any colvcnt, fo that
floliition-tfaidon han Vt'omo £T0(*3itfn*ivp
fcriUi Ibi^ fjTrm Rilntion ilsi^If- Whili> n
general conception ia hc^ld as to wli&t i#
meant by aolution-tenaicc. the exuct uee
of the t4?rm muat bu undoratood before it
eon bu uaed in ooiuuetion wi& tho cleo-
tmmotivi^ f<irCG of rtleinenlK- By nolutior*
tctnuion of mrtAlu wn iibould undifnUnd
that U^n^ion or ^trnin anAlofroun to a
force, which tends (o drirt' the atoms of
motiiU off into tho surrcunding aolvent
When th* atoma are driven into sohiiion,
thvy t\Tv 110 luTig^r pruturnt aa atoniK but
Ijcciimp ioii*. To ilJuitrate: wUeoi-'kLT a
bar of metal in unmerwd in water, a fev
of the mdulHc utoma pn» into the solu-
Itoii iw iona; or, ju wft u/^ the mtM dia-
Mf>1vi'ft to n ulight ritf-rit- The number of
mctnllic ions wnt ipto tht solution is very
SEoal] in liny case, and in moat C6«c« so
smaJL that Ibcy cannot be detected by or-
dinanr cfaeniical methoda, jrec we have
good theoretic ^nnd for believing
(!7*ry metal dbaolvcfi in tvery »olrait ttf
alight silent — av^n platinum dii»lvos in
TferutitT i»)to inD^iw^l tliin nlioi of Uie
Aolution-tcnaion of mctAlf, driTin^ tht
mctnilic tons into the lolvent, sn^igcstcd
that it was snalogous to the ^por-tonaioD
of liqvidB, which drivea the liquid mol<^
coles into the ftjm(?i- above ihtb Vu\uv}. uiiiil,
for a gireu teunjcraliju', a deijiiiti? i^ptir
prcMurc ia reached.' V^ai tlib preainrv is
utUinod, the vapor- to nnicn rttill c^in- i
injt to manifv«t ilwjlf — drive* ukh' > j.
into space, but ths numbCT of niolwnfM
whieh condense in & given tini? is jnat
ec|iiAL to Hie number which tva^oraUfS.
ThiB ]$ the condition known as f^uilib-
rium.
Tlu! Bulutioii*tt*iiHiun hcii in an Atu^
gouit mnnian^, driving ioiia into nolution
vinlil a ccrtoin conccutnUion is n^ehed.
vrhcn juvit nia many ions separate from th€
Ablution on to the bar of m^ah in a given
time, as pitss inu> aohition. Tn the wordA
of KerJiat:* "If, ui aet-onlauLMi with Vaul
HoiTa theory, ire aasome that tin; mole*
oulca of a substance in solution exist also
under a ddlnite prostsiiri;, wo most nsenbc
to a diiGfolring ffub^tiuico in contact with
n Hilvpnt, fiimilnrly, n pnwrr of pxpansinn,
for here alto the molecules are driven into
a space in which thoy ^xiet under a certaia
prewure. It is evident that ovctj sob-
atano4f will pa«a into aoTution^ until Gi«
osmotie partial prwivrc of th« molondM
in thr ftnltiticin \t i^qujil tn the aoliiUoo;
tension of the si^bitance."
Nemst stst^ tbo whole subject of
tfon-ton^ion of mcUJt ao cloarly in his
insl. epoch- milking paper,tn which ths
OUTUSEJi or iiLE07UOVlit:^tliTHY.
SI
tflit* of thie chnpter weri* dijurusied. that ivc
iJriiot clo bctU^r i.hnti ^ivc hiA own words
u Jitemlly a« powiblc ; Ririfw, from the im-
portanoe of tlio subject dealt with, thvjr
have become of hi^Lorkal value:
'Tjet* uft now tt>ija«lt'r wbat vill lake
phct if vr« dip u metjil whoHc dectrolytic
iioiatiDTi-tenfiioti ie P into a ^r-rliitioii at
on? of ita enlte; the oflmolio prcseurt? of
thn TEi^^l lonG in thia soli:tion bning
^, Let rti fir-t V > / ; at th" nicHTn-HT. of
ConUet a uunibtr of jKJhiLnt'lj diJirg^^d
DUlallii: ioDa, drivc^jL b^ tlii» lar^r preaa-
iJtv. w)H paiyi into (ulution. Since bj tho
Ullvr a ccrtnJn itmount of poKiti^c* dco-
Cridty is farrlod from tho m«tAl irto the
■fllutimt, tV liqiufl n'wivc* a ponitjvc
chor^'e, wliidi aiiuji^ufi itstrlf iu the furrn'
<rflht positive ionft coDUimid in the *ok-
40| oa the durfoocr of tho mcUL At the
Abb tinoo there im, of (»uree, a corrvspood-
in^nmouHt of iic|(utivu dectridty si^t fnw
10 dw motiil, whirJi nlsii jirtHs*^ to tTiP »UT-
ft« of the melftl Vir rui-c*giiiM at ouce,
t^l at the mrfflce of oontAct of metal
^d electrolyte the two kinds of electricity
niiiBt aoouinukte in the fomi of a cfouMe
QjeTr vthoBi^ ('Xttili'[if.v, a^ is wi^H knciwn,
*4» mnOiT prulmMi- lujuiir tiiii*.- «)^ij l>v Von
HclmWts. in an ontirply riiffi^rrrit wflv.
"This df^uble layor furniehee one com-
POAent of foroe, which dcte at right an^lec
to the ^urfflL^ of c<intflpt of the metal And
the tlt"Ctro]}'tr, an^ whiuh lynds to drive
— Mm? mvtulhc ionfl from the electrolyte on
BtQ the metal, nnd thus nets in oppo<vitioii
to tho folation-tcnpii^n, Eqiiilibrinm will
Jbfi, of oourw, pjjtrtblishi?*! wh(?ii these t^fo
^orc« pqnaliRe one another. The final re-
ftlrit will he the apfieainiiiee of an 4>leetrO'
vnotir« fbret- htlwwn tht inetnl and the
«kctro]jt«, vrhich vrili ^re rise to a gal-
I
vnnjc cuirent from tho metal to ihti liquid,
if bv Any device ita cxidtenet^ 1b madu poMt-
bio."
" If P < ;» the revcrae of courae lakes
place. MrtntHe jori» H^piinifLi from the
Hf'plrolylt- and Jin? priiJpiLftled \m Ui Um
mrtal, until the cloctrovtatiG component of
forpf of the poaitiTc chnrifc oi the m^-tn!
nnd the ue^atiYc charge of tho liquitl, thua
produced, are in eqiiillbrinin vtrith th« oji-
f4*fl of tiRmuiie pressure. An electromo-
tive toxw H^'itiii appanra tietwt<e[i the metal
nnd the idectrolyte, which, under fruitahle
t'^mdition*, givi* riso to a ^alvatna our-
nait, but in this ciuif oppoaite in direction
to thp rj*j fiist ooniidprv*d.
" If, fJimHy. '?:^p. tin- meuiT and elec-
imlyli- \\r\' ill eqiiitihriiim ut tJie first mo-
mi?nt of contact; Ibereforc. no dUTerenco
in t>otentifll cxiat« bf^twi^cn thci two."
Tills dear and coneipc ntnt-im^nt mjudi
no comment and bul little elnboration. Tf
th(' 4oEutioii-U'r]«iim of tlie metal it greater
\hm\ the osmotic prt'BHure of the metallic
ions in the volution, tlie action of the
do^ible Ia><T la to oppose tbo greater
prr?Mvri.', which} in this ca^*, ifi the
solution-tension of tho metal. If, on
tin? othtT hand, the osmotic prefisurr of
thr mrtal ians in scilution is ^catcr than
the wlution-timsion of tho mctaU a double
layer i* formed in such a aenee as to op-
pose again the ^fri'ator procure, but in this
CBS9 thi? greater pn-saure ii tlie oamotio
preeaure.
In the ^r«t case tb< action of the double
layer is, therefore, to diiro metallic iona
out ol tho wktion on to the motal, in op-
poaition to tho «olutton-tension ; in tho
Hecond ciiw* tin* dovihlt? layer ttiids to drive
ions nIT from Uir iimtil into the aolution,
in opposition to the OEtmoLic pre«aurc of
the ions alreadv in aolution.
41
CtfTLTKBa or liLSCTJi0vng:ilf8TK7.
Tbo ftctioTi of the double layer ia boUi
cfl«< is to <titablifch aquilibnum between
the &olutioii t^nBiou oi Um mutal and tb«
oamotic proAfcuro of the iiu-tol iona In ftolu-
tion, mid fn ifo thi« Lt mujil, of etmrfi:^
ttlwAyx nrt jtgiiin«t, Uk grciktrr font*.
"If.* now, wc inquire whicti m&tflls
havo hi^h and which low aolution-ton-
eione. w* vill find that iiiagno«ium, einc,
flliiminiiin, cn<ijniiLui, truii. r^obalt, nickd^
and (ho Hkt% arv alwiip ni'gntivu vthiui
immitntr^l in nul dl.Linm of Ihrfir own twItjL
Thi* mmn» thnt the eohtir>r-t>;ii5ion of
the metal ia niwav* greater than tht os-
motio prcesuro of th$ metfti ion, in any
sohitinn of thoir ^ta orhlch oan be pre-
jiarei}. If, on the other banO, we Inky
£o]d, aih^er. mercur/p copper, etl^, vri*
UBuallj' fiini the mpul po«ittvc wb^n im-
mcrix-ti in ii solution of it* enli This
nKiivDB Ihnt tho tolntion -tuition of (ho
nu'lnl U «fi fnnill, llml If U hv4 th^tr the
rj«nin(ic prf**-uri.* jf tht mvtnllie ion in
the solutioa. When a very dilute lolution
of fefllte of thcg^ inetala ia prepared, the
ofitnotm prL-fbiiro of the nic^lbc iooi may
iMreumv icH thun the very illght «olutiou-
t<^t!*ior of those mL'faU, m)d (hen the
nK'hkt wi>Li]d bi< mtgniivc with n^pect to
it» solution/'
A DIUfONfiTltATl»:f OP TriB S^rUTlOyTBJT-
SlriN or METALS.
Ona might ORsily Ihink that ih\t oon-
v^ptk'n f>f the solution- tension of metal*
ifi all very »i^ll. aa a iviatLt^r *yt ptire theory,
an^ may. perhupa. belp us in our ei-
pfan/itioii of the fteiion of primary eella.
but the iii'>flt important qQt>jition ia, what
eTldenco haro rro thnt it ia IrueP In*
docd, there hn« htrn nhfloliifcly no (wi-
drntr piTs^nted lhu£ fflr, and does it not.
after all, «ccin a IlttJe contradictory lo tmi
cxpemn»? If meula all diaaoire its
wiktc^r and aimilar aolTcnta, as Ihia con^
ception Oemandfl, why do they not dia-
&o]ve in qunnlUiefl ^iflHi^nt to hv d«led«il
bj our moat rtflm-il chi-miuil nirthoda.
Thia is a rcr^' natural »lntc of mind £
ono ta l« m with respect to the trluri
problem, until the evidonoe for thia vitw
i« prcsml^Kl ahlI rnrrfnlly confadf?r9d.
With n^KpiTct lo ih» point n,ited nbovo,^^
thnt if nii>tji7K like gv^ld, pUUnnm, 8nvor^|^|
ctc.> disaolTc in water, ihey dissolve in
fucb smoU quautitr ttml it cannot ^
detected, it need ocdy he n>ealled that Uic
ionft carry enonnoud iqusntitiea of dacy
(ric-ity. A giam-inoieeular might of
nmivalemt lana cnrn«» dO^iltO crjutomlw,
SB we hare alrcndy netn. Tfao aum-
tcr of ]on» which vould poaa into
volution in ordnr to otlabiiah a cooatdeis
uhlf- difference in potential betv?^ the
ni4-tnl nnd the solution* would h& veiy
fltnall indeed- It haa be«n calcnlaW Uiat
the number rct^uired to produce the dif*
fert^noe^ m potottiul winch aetnaUj oujft,
would be far too imall in the tttitit of
surh tuelaU ah thosi^ named nbow, to Ho (Ui*
teclvxl by IIk moitt reflnrd fiii'f.3it:>d« known
to man. This nppnr*;nt di»crtpaacy ifl,
then, not at all at roHance with the coo^
eoption of the aolutioii'lenfiion of metala,
hwt 18 pvartly in necord with it, and could
have heen predicted liefon^hond with th*
«:reateet certainty.
It is. hovever one thing to remore ob*
jectionfl to a theory or conccpt»>n. end it
ia quite a diiTcroi^t mailer to bring for
a'nrd poaitivu ^idrnce of Jta truth. We
nhall now ootiKtdtT n dnuondmtion of tha-
K>liittEm-tcnHon of mela^tv which eeeitia li
lea\e little to be doaired. The foUo
d«inonAtralion nae furm»hed by
OUTLlSBa OF ELEGTROCHHJJIBTHY.
83
mxtcT '- Mcrc:ury* lb a mcUL whose aolutioii'
tonuoD U very sirflll, Even when in con-
Uct with A very dilute solution of a
mercuiy aaJt, the solution- tension of the
oerciiTj fe lesE tlj£Ji lUb t^inolic pr^esure
of the mercury ioua in the eoiution, aud
wme of the mercrary ions wiU aepamt€
from tuch n solution. Giycn o, ve^Gel
wliMti Iwttom is covi^red wiKh metuUic
murcuiy, nnd over this is pliifed a eoh;-
tioa of mf'rciir(ru& uitniiv^ having a
Tdumc of fi.OOO; a few mercury ions will
wpftrate from the solution and ^vc up
(boir po^itivo charges to tho mercury.
Tbe poeitii'ely charged morcury will at-
tmctj elyotroKl^HtirHlly, m fi*w negatiT*- NO*
inoft to form the ilouhk layer. This will
be coatinnec] until a certain difTerence !□
potentiul hne botn renshecl, when equilib-
riioi will he cstabHfihi.'d, If, now, a
hop of mercury h let fall into the solu-
tion, n few mercury ions will SL-porale upon
Jl, charge it poaitiyely, and it will tlien
^tlraotan oqnal number of rnyalivf XOj,
ifiru, and drag Ihom d^wn with it
thrnigh the aohitiiiic. The neil drop of
tti^ury will behiivp in exactly the siune
inaoDer, anti thus Ihe top of the solu-
tion will become continuaUy poorer nnci
po<^r in a<.
Wheo the drop of mercury com&e in
ttMitacl with the mercnpy at the bottom
of the ftaai"l, wheru «]uiHhniun is alr^Hdy
'•tnUiBHed, what will Iiappen? When tiie
^rop has nuit^^tl with the mercury, this
*iU contain an exeeea of positive elec-
Weity and, IhorofoTfl, a gmnll quantity of
nieroury innn will pass into aolution ;
^d, indeed* exactly the sa^e number aa
^Hctb aro ^'U, ioiiB earned down from
Xttrki. i^Kt/t l*^#nl. jnf. MO. ■1*111, IftiT Atao^«Ar.
•tf* rjlhtiL,*!] V? ThpiiIv>tf.ii4i»i<^rl|ilLGhtiiiii|rpT>i1 fioq
BeisiABlaijr r>kt>iL-a] LJlipni^irj tir El C Jou^i^ whliA
the top to the bottom o>f the solulioD.
Tiie fiotation will thnfi bceomo more coo-
ccnlrated jupt fthovc the layer of mercury
on the bottom of the veBsel.
A fine gliwa t.utie from which rnervury
Hows is knomi aa a drop-trlecti-ude. To
produce chongea in concentration auB-
ciont for the purposes of ii ilemo nitration,
a very powerful drop-dec-trode ranat bs
used. This ia nmdo by in*erting a conical
glass-atopper Intn a i:N)Mii.^al gh\f,h tube> s^
that llie junction is mercury- tight, A
large number of fine groove* are then
etohed on th« onteide of tho stopper, 90
bkjrf
thnt the mercurj' will etream through as
a tine mist. To asaifit this process tho
mi.'rcury tnniiot he Allowed to tlow di-
pherea of preBaure,
Under theee conditions, however, the
mercury can not be allowed (0 flow di-
rectly into u vesflol filled with a dilute so-
lution of a mcrcui^' sfllt* aod contftmmg
meroury at the bottom, since there would
he too much commotion In the Kclution,
Tlir armngeoi^^nt which wa^i u»c<I i' fthowu
in the aceompatiyirg sketch, Pig, 10.
84
OUTLJySS OF ELf:CTROC„nMIBTItY.
Hen the tnorcury is jiLloved to Sow
direotlj icto the solclioo, but the princi-
ple iavotvei3 is cxoctiv t-he ^mc^
Thp drop-olwtrorle dips into a fun-
nd-fthapet^ v^sat?], which ib ooQut^cted by
a narrow tubt^ ami a rubb^T tuU- with a
]a,rgCir v^&ei^i Thia i& [q turn connc}cbod
with D vi'Siul whi-TP thL" f^hungL' in
conccntratwc cnn Ijo observpd. When Lhe
mercury hns been nlloivcd to flow for five
minutes und^r a prcsfiTire of five atnioe-
phoT«e, dtatjnct changee in concentration
oan bo detected.
Palmaer givos data which ah'vw that
the conctniraliari above had bif^ft <fimm-
uhcd as much as fifty per c^ni, and in-
creased hclow o.i mv-h as fort'j prr Cf.ni.
This will be recognized at once to be a
vary remarkable experiment, and before
the eonception of eolution-tennxon of
me!«)a was proposed, would have been en-
tirely mexplicablft It should be arlded
that the rcsulis of this cxp^rinient wert all
predicted before the e?fpenmeat wa*
tried.
We hare developed in the firgt sscHon
of this chapter rbe method of p*!^ul«1ing
pok-ntihl, or ekttromotive force, from the
(Osmotic prrsauie of the flotation! around
the electrodes- Also the conception of the
Holiitioa^ereion of metals, nnd the way
fn which Ihie acfa when a metal ia im-
rnerti**'! in n fvjhitioii of one of its salts.
In Lhe folkrwjng secfjoa we ehall apply
these two fundamenUI conrcptiona to the
electromotive force of primary cells.
WTLiXBe OP ELSVTltOCBBMl8Tlt\\
S&
CHAPTE-R VIl CALCULATION OF THE ELECTRO^
MOTIVE FORCE OF E^LEMENTS.
PART II.
TIIB CALCULATION OF THE PIFFERBNOB
IJ« POTEVTIAL BETWHBN A MCTAL
AND A aOLCTlOy OF OKE QF ITS
SALTS.
Wc have aln^fldy aec-n havr it i6 po^ible
Eo cdculalo poti>nti&l from the oamotic
pressure of the sohittona around the
rlivtmdfft, flnit have aUn studivnl the soUi-
I tic^Q-tmiaiuu of umtal^p anJ what takes
pJace when a. metal it^ immerseJ in a solu-
tiaa of one of ila aalte. We elial! now ap-
I }\y the^ tvvo fuudQinenlal {.-ouccptione to
the calculation of the dilference in poten-
\mI belwei^Ei a metnl nnd n solutioii of one
of iE^ snita in which it is immeraod,
I^t "s take & metal with ft aolution -ten-
lion V, and dip it into a solution of one
of itt (slte, in wbicb tli« metal iong have
ui osmotir pripesiire p; a difforenoo in
potoititil between Ibe nif^lfll and the solu-
tion nill result* and tins can be calculated
u follows from the foregoing conceptions,
TIk" raetal has a eoluti on -tension P;
ILtij! fan be converted into ions under an
ownotic pressure P, witliout any w^ork
beinj done. If the oetuotic pr«^ure of
the metal iona in the aolution b p, to con-
r«rt n metiit of solution- tension P into
iorn ct an oamotiQ preeaure p requires
Qlf HHJne ]inii:iunl rvf work, or th? Gom*?
imount iif work is obtniimblc, iin if we
itarted with the mctnl in the form of ions
tmdcr on osmotic preeeure P» and tranfl-
formed them to it condition where tbc
otmoti^ presaitre was p. Since the laws
of gas-preseure apply in (*motic presaure,
we am calcolati? the amouni of work ob-
tainable from the process where lona un-
der an osmotic pressure P are trana-
Eormi^d into ion* und«r an oamotic prcee-
ure p. from a gae under a gas-pres^urc P
when triuinforJTjL-tl to a gBA-prefi»Tire p. Tn
the Urst part of this chapter this waa
shown to bu, for a grnjn -molecular weight
of a £ae,
RT In ?
P
We have nUo i^eeu that thi^i is i^quai ^o the
electrical energy' which can be obtained
from &uch a process, since the wijrlt done
IS trail if ormabb. quftntiUUvely, into elec-
i.]"ical cniTg^', when we are f1 en ling with
solutions under suitable (^oudiliouH. TIm
oleotrieal energy H^is e<(Ua! to the poten-
liul ir, tinu^ ihu oupucit/ K^_
If then we equntu theHe two equal vaJuM
wc hntc :
r F. =Erin -
^ P
If now we intr^uce the numerical valuer
RT
already ^Wen for *g-. aiM holve for »,
at the eame time changing to Brfggfliai^
logarilhiii. wf would have:
f = O.MS lou -
P
The dilTerence between Hie potential of
a metal and a eolution of one of iU 0a]ta
in which it is tmmcnicd U, thou, equal to
a coiiiitnnl, whidi, for ^0 dc^gr^oa abeo-
lule temp<*nitun*, or the tempnnture of
tfu^ onliniirjr room, i« 0,Clft8 ifull, into the
logarithm of the soluiion-tcnffLon of the
metalt minua the loj^arithm of the osmotic
«e
nVT LINKS OF ELKCTROCHEMIBTItY,
pro88ura of the melnl ione in the solution.
We shall now apply the ronceptionis with
whidi we httve Iwcoiiie fHUiiliar to n ftfw
iy\i\ett\ ekuienta.
We know a large number of primary
w-lh, ttiul Lln*uf nre Linifltrui^U-O of wry ilif-
fcrent exibstuncefl for the electrode*, nnd
of Eolutiona of vory dtfFcront clccirolytce.
In nil Buch calU it fihouLd bo obsc^rvod
tliBt we hnr* lK>th olnwos of condtictora;
Ihosf f>f thi? fJtHt clnm f*r:>n<lMcT,irg like the
mctalA and stirvlD^ ag (he electrode, and
suirounkling tlieae are conduc^tors of the
second claaa or fioluiions of 0Omt oloc-
trolyle or elwtrolytofi- To constrmit a
primnry battery it la l.hen necessary to
Lav(? oonchic'U*rt nf the first ilass in cuii'
tact vith fondiidore of the second cltm,
A svslem of clawifi edition has heen
Bdoplud for primnry cells, which simpli-
ftefi the vhole f^jMs very ^atly. If dur-
ing' tlu' mtion of tbp oell it^ I'let-tronuitiv^^
fore* does not i-lmnge, it is called a i;on-
starU element. If it does, the dement is
ineon»iQftt. In order that the eloctro-
motIvi> force of an clesnent should remain
<"Diititrtrit, [(. U iicv'j*s¥arv thai fhi^ prooe^^
wliii^h t{wx on in the eell should ramain
uni?hunff<"d as lon^ as the cell ie in nation.
Through some conntant clcmcTit* o cnr-
rcnt can he pngei9d in a direction the op-
ptHiiti* to that ill whfrh the current would
norn^ally Tow, withf*ut changing the elet-
troraotiTe force of the element. Such
constant olemonta aru knovrn as revfrnliU.
In order that an element ahould be re-
versible it 1h neeesdary thai the reverse
current should not ehangE' the nature of
tht eleaneut. This oan ocly liappeu when
the cloctrvJcfl are immeraed in Bolutiona
of their own salts. In such eaeee the re-
ren^ current aimply causes a dep04)tion of
afjunUumonntof onemetal, aoii the solu-
tion of a coiTPsponding amoiint of the
utlier. Wht^n Ihi* revi-i-se enrrtnt ia paa^
for a rery fthort time the nature of thfl
el«iiont romaiu* csacntmlty unaltered,
TJn^rc arc oilier (Toustant t'iemtmt* tJiroujfh
which u carn?rit cannot be »ent in the
rt!Ver>^e tlirecHon »ilh(}ut ehnnging Lhe
rmturr of the r]<'meiLt Jind, coTia^uentlj,
it4 electromotive force. Such oonfltaot
elements are termed irrovgrsihU.
We shall take np drst a very simple, tfr
verei'hie, oorntflnt element, and "pply the
(xmrpplioiis already developed tu the i^alcu-
Ution of its electromotivi- forc<^.
X &:UI'I.K OONCICNTHjllieV BLKUfiNT.
Tlie aiinpletil primary cell of which
wv oiu Ltiiu'five. cuuiiiBts of one elec-
trolyte of two diScrent cionctntrationa,
and one electrode. Into a beaker pour
a coneeTitrated tcdulion of stannoua
chloride until it is about half full, Tno-
niiTSfi a liar of Tin inio thp soluHon, of
such a length that it is about half covered
with the concentrated solution of the a^t-
Theai pour carefully on to this con-
eentratet] solution a dilute eolution of the
iarne salt, H»til tli** heaker h nearlv filled.
l^et us now we what takes place iu the
above Brinngrmcnt, Where the tin ia sur-
rounded by the more concentrated aolution
fjf stannous ohloridCj it inereaBea in sue,
due lo the aeparation of the metal from
the solution fui to the \tar. The ions of
tin, when Uicy separatG in the metallic
condition, give up their charges to tLia
portion of the bur, which beeomcE chargftd
stronfily positive. This charge flows along
the whole bur, sinep the mdal ia a good
iTondiiciLor, und the rnilre bfir of tin be-
comes chftrged positively by juat so much
06 there are ione eoparalod as metal on to
the bar. If this charge could not e^oiLpo
OVTUyRB or ELKCTHOVttKMifiTllY.
in aoone way, the di^^rence bcttvecn the
poitpctial r>f the bar ntid thai, of Oie eolu-
(jt»n (which ha* l>>v(jiiie negative due lo
ti» love of positive ione) would very
quickly boconie m ^ri>at, thfit no fnrthar
HjparutkCtD of LOiiB in the form of nietfil on
lo Uw t*r would be possible. The oTig-
iiud lu^Litm wouM vtrj quicklj cease, were
it not for tht fact tlmt the ban when
cbnTgcd positively, ie just in tlic i^ouditioa
tnoet favorable to giving oil ions to the
more dilute solution of etantLous chloride,
ind it doe« bo. When a metal parses into
bolutiou a^ iotiB it muttt obtain positive
clectriftity From some aonrcep In this aise
Uif positive? eloctrkity Ib already prceoiH
on the bur, the alom£ take- it up, become
joiu, snd pass into the solution. Tliis
Irwrr* the pnlir-rilinl of Uic bar ag^iiii. auil
Tooro ions ran separate from the solution :
tnd ihc proccM ia» thua, a contiaucus one.
The oction of thia, the eimploat of all
primary clomcntfi, i& ob follows: Tin ione
lepitrfife from the more concentrated solu-
tion of staonntia nhloride, nti to that p^ir-
tiofi of the Lai' immcritd iii this ftoTntion-
They give up their chargca to thifi portion
of iJie bar. whieh are then conducted to the
portion imineraed in the niore dilute flolu-
liou- Hrn? ntoma of tin tflte up the
poftftii'L' i-li-rkif^JLyT hecoine i(*ns, ancl paflb
into solution. The chlorine ions Uave,
mfioikwhilc, trart^lod from the more con-
oditrated toA'ard the moro dilutod eolu-
lion, against the direction of flow of the
enrrent.
Th« aftion cf this eftl, liitfi th^ artion of
all concentration eUmenis, u such (xs to
dia'§a4S the concentnUion of the mort
dtttcSfitrattid .^alulifn, and to incu-ase tht
conooniraUon of th^ more dilute soluticn.
This would rfirtinue until l.h<? cnncentra-
tiouB of ihe twd Jtnhitinnp wonM btvome
the same^ when the element would eeaw
lo be nxi «l«uient.
It would be eitreiEidy difllcult to meaa*
ure the electromotive force of auch as de-
ment &£ that juEt descrihe^j, end it would,
IhtrreforOj b^ of littlo value to calculate it,
ftince it i^iuld not he verilled by experi-
ment. We will, then, age ihift eleouent AB
an iiluatration of the very Hunplt'st con-
eentration element, and proceed lo apply
our dedaotioiifl to a eouoeutratiou cU*-
meut whoue eltjclroinotivo forct eao ]k
mensLin^il-
Tlit ['h-jiifiit whi*:h w<j ehnll study, both
tltcorcttcally and practically, congiats of
Lvvc* bara of :sine, imtncr&cd, the one in a
mora concentrated solution of zinc chlo-
ride, and the othor In a nioi*e diltite^l aolu-
tifon nf Ihft wimn f^lectrolyt*?. The aira.ng^V
meul wouJd hv Lllufitiatcd by the following
sketch.
Two h&n ot zinc wi^c as the electrodee,
and are couoootod witli a etrip of £ldc.
These dip into Bolatioaa of lino chloride
of different t'Oiieont ration*, The eoncen-
tratiiiniiar«t [■upri'sunlci^ for irouv*-ji ii-nre hm
or«^-trnth and onc-hnndrodth nominl. The
two •olutieofi are eonnoctod br mcana of
A iiphon> filled either witb the tenth or
wiTh the hundredth-Fftrmal solution- The
frda of the sipban «r** filled with lno«p
rulln of filter paper, lo prevent a uie-
diAnical mixing of thd aolutiona, and to-
leascn the rate at which one solution will
diffuse over into the other. Tho tiller
paper olfcrt A comparatively slight T^
flistnnpff \it the paiMiiip' of ih^ rum^t.
It will tic obeervi^d that both electrodes
orcof the some metnl,nnd thrtt iheraro im-
moreci in solutions of the enme electrolyte;
the only difference on ihe two uidea of the
cell lieing fhal thr» solutions of the zinc
c;hloritli- are of diiTT^ri-nt coneejitratiiins.
88
QVTSJXK/i or SLMCTHOCUtSMl^THY^
HpDvtr ihr. iinmn, c/inrfatration ^Umr-tit.
Till: action of t^ia element viU be very
rcmlil/ imdcntooij from the eiplanatioa
of tho flction of tho EJinpler eoTic^i-nlmtLOQ
eli'Dicni, oonhiamg ot one bar of tia im-
mt-i-jed in iwo aaluliotui of *tiiuncui chlo*
ri<3*". TikiT flnil Um wdi! of l,hr rlmniint
on which the electrolyte is mor* concen-
trated. Zinc i« an Qlont^t, m vm ehaU e«e.
which hue a very high aoIqIjod tcneico.
This is always much gruaU^r than the os*
luotLC preMurv of ev«ii tht mo*t conosn-
trjilwl Kilutititis nf aiiic ithlciriilfl which
am Ic prc|Mirci> When a bar of xmc b
Imnif^nicH in any aolution of zittG chloride.
ft ife
Pi«. II, OosicisyiTnA'nuB Ei.tt«t»T,
it atwtfyv Kr^adp oft som« ion* into tho
Holnticin, Hiirl rRUiii!iith« ilu: ^Iwibl** layrr
in the a^nse to oppose the further ioziza-
tion fkud solution gf ihv zinc. The linc bar
tlicn becomes ni^gativc &iid the eolntion
poailive. Suppose At firat that th>? oirouit
La not dosc-dj thU will lake plac*; on both
%i6n (if UiL< cvXl, uiiltl [^luilibriuiii m kb-
Ublji^hcd bctw«<^n tho tfohition-ttneLion of
the ainc an:! the vkctricnJ doubli; layer
foEHQod. It will, however, bo re«c«iD-
berod, that when th^ w>lutinn.t^niiion of
Che metal P is greaier than the ofirotic
pivAaun? of the motal ions p^ (P > p)
tht' doublt IftytT will be formed so oa to
aMit»t Ibt oaintil4o prewnre or the ^m&llcr
imlue, in ovi>rcotning the larger valne or
thi' »rilnt^'»n-t**ti»ioiv In *uch wiflt«
nqiiilibraim will \h* rnaoSptl vrhi^i ihr- mini
nf ihr. fiftmoiic prewur* of thi? meul
iiml the aciiou of iJit donhle Uytt, mre
jtiflt oquiil to the »olation-t«nfrion of tite
motol. Therefore^ tho kr^or tho oamotk
pf^ouror the amaller tho actioa of tbr
double la^i^r which will be nocmuj to
t^jujiluv the? volution'timEion .
The osmotic prcMuii' of Ui« aiuu bos
tBj of ooi3r«c JargOT on tlie uda of the coU
ooDtJiinin^ the more coQeei3tr»t«d tch-
Hon* And, cOD»equenttyp the action of tbn
double 1a>er will be lc%v on thin aiile of;
the cell. But t!if hctiDiL of tliv ilouU*
Iaye;r dcpcndu oa the diffcrcnDo in poteo^
tial bctwcEm the mctfij &nd the •olutioo,
and thifL depends upon the nunihur of sine
iona vhich pa^e into &olutiOD^ On the
side of the c^U cotitalnitig tht ini>n! aon<
centraUid doluLioii* thr zinc will nrnA
fever ionb into the Aolution than on the
oppoaitc side, nnd, conecqticntly, ite potcc-
ttal will not bo ft« mu^ reduo^ Ae on
tho othi-r aide. The b&r of me in the
more cDnJientrAted solution. Ukc tlie bur
in tJie mui'L- dihiti^v *'^l btromt iit^lirt^
but net Jis much iic^gativc an tbc bnr in the
mori5 Jiiut* Aoiution,
Suppose, now, the twci »idrrs of tlie cell
ore connoetod, whjil will huppcn? Tho
bitr in th** mom r-onfrntnitnd solution !•
U'm ni'giitivp thnn ihp kir in fh^ more
dilate; conetquently, when tJw two an
L^onntc^cd a current will fiow from tbe
farmer to tlie hittor, or ttie former will
be the positive pole. Upon thU pole,
whi-n thi* drcruit i* e!o»i*d, wnc will be
[lypofcitcd, Thf xhtc ions givp Bji lh#ir
charges to it and aepainte in UiQ motaOi'
condition, and, conwquently, thifi lecenMS
tho cfithodt^ On the other aide of tbii
flutui- J<kir m* Tfor IB f^ftjuTiEii if>Aiii (if r*r«rABr ftl
Uv iMiiMus- LEW |iBCio«il«N« Ol H^uuciUJuQ n m<r »
I
r
OUTLTS'HS OF BLBCTltVCHUXlBTRY.
99
\
c«U liitc atouiH Are taking up positive
<hjir^a, bL-ct^nilnfi zinc ione, which «cp'
flrnt^.' from the bur and po^ into sola-
tiun. This bar, havrng lost noguiivu dt^e-
tridty, bwomes the nt^ntive polt or the
iiiroi^e. The iitiLiou of Llie ct-'ll is, then, to
decrease the number of rinc ions on the
mop*! ci^iictnt rated side, nnd to increase
Uiv DUiribvr on the more cliluto Eide; the
oiirr^^nt Howjug on the outside frem the
pule imirn-^rsi'd in the more ooiieeiilr*itt!<!
itolutlon tn tl^io ^mlc immcTsed in thi5 norE
dilute. On thf ia.'iiilc the current flovra
jtk tbc opposite liircctioij, frcm the pole
immereed m the mora dilute Aolntion;
And, fiineo the anions move againet the
<»urrc?nt,llu"ehloriinrirjna move over towfird
tike pole inimcrrned in the? more dilute
a<ilaticn of ;^inr rhWide. The more Ji-
lute eoJntioii thu& btvomes continuully
xiEiore ooncentrnted, nnd thi> more concen-
trated more dJlnte. So much by way of
^ipl&nhlinii oT u'hat takt^ pkcf. T^-t un
cuir tipply the concept jonti and dcdiic-
^ioDft vith which we hare bt^en deling in
^16 t3^pc of conei^ntrntion elements. The
poti^tial on the mori> {^oncenlrutcd sldo^
between the motal and the electrolyte
vould be eipretf)?«d thus:
a 058, P
Ti = — log "
V i» tho viili-Tice of ihti zinc ion
P the poluti«tt-t(?nfixon of Jiint,
and //, tht' osmotie iirceHury of ihe sine
ions in the Bolution. The potential on
Uic othor side U:
T. = log -
'■ ^ Pi
ThiTi* tht.' i-'oituTiun syrnhoU ha're the BBme
fi^iRcuni.'eH and p^ is the oiiinotic prces-
UK of the zinc ions in the more dilute
The dcctromotito foicc of this, oi wcJl
OS any other primary cell, is the difference
between the potentiale on the two atdeSi
therefore :
i)MH
, P
o.r»58
1*
V
'""'p.
a
log
Pi
0.058
"^7:
and eince
1 r-
= 2
V
^ l^OS.'
'■* %
<
The metal being the eainc on both eidee
of the cell baa the same flolution-temton*
on the two gidos, and being of equal value
nnd o]>pogite sign diaapp^ors from the
final t^fjuRtioTi,
Fmm FUiytlting u'^iieh hna heen esid
thus far, nc might conclude that thia was
the entire etory of the concentration ele-
ment. There is, however, still one factor
which has not bu^n taken into aeeoimt —
the elinngtf in the concentration of the
EkfluljonB which is taking place while the
current ia passing, due to the motemeDt
of the iona^t
*' If Ejj olectrit-ity paat^es from thi* e\ec-
trode into th^ plectmlj'te, n grnm-mnlw-
ular weight of univaloDt cations separates
from the electrode, diaeolrea, and In-
creasQJs by uniiy Ihe oonceatration around
this eleetrode. But, at th^ Game time,
catJonn nre moving from this electrode,
wilh the currant, »ver toward the athrr
clrrtrode. The amount depends upon the
relative vel^ities of anion and cation. I(
wv represent the relative Telocity of cation
ijy c, and of nnion by a, Ihe aumber of tie
entiona which will move over with the cur-
c
rent Is
The mcreaae in the con-
Klkiiton ft lit tti\Lc In whLcb k It (ucupi-Kd.
VTl^v fotli.-\flrijE Hn^rftiih b ^4i>'«] frcm Tbagr/ ct
la
oaruNKH Of BLatvTRocasyusrny^
ceatntioit, duo to a grtis-iniolffcalar
weight or mtitniR pAKting into col^ttoo,
tt tbea:
t -4- tf + o
Tbis fnctor ii to be oitiltiplied into Uie
forma- oqbitJcn to obtAJa Uic oaxootic
n^rkj wbicb can then be equated to Itt
ei|tiii] — the vfrclriml nni^rgy. t^t fii^
rvprc**-!*! the number of iona in a gram-
mol«cuJar w^i^bl uf Uicr eladrcljte:
or.
We baT« now tAkoi into nocouBt all the
factoTc iiiTolvod in this nmplo concontra-
tion foment. Tho ounotic proMtir«4 of
the rJttinns of the i^lM7fTi>1yt'*, the siklulion-
tenaion of the uicl&J usex! aa elcctrodce,
4Qd the v«]oc)ti« of the ioiw, haTt all teen
considered. Tlie elpclromotivc force of
fuch an element d«pond&, aeeording to the
final ^uaticn, ohicfly upon the relatlre
oiuiiotic jiri'-j«<urt'a of L(je cjiUnnH of the
electrolyte uicd \ bnc, in addition, upon the
factot
, vrhich maet bv takoii into
account for the rcaaone girtn above.
Thu ci^uaUon ban becD applied to con^
centratlon tloKimt* analojjcoua to the one
jit»t (In4crib(i[l, uml ibHr iliTiTtrmnotiTa
forcv calcuhitci] froir ihr ^jmnotic proM'
urt« of the electrolytes used, nnd the rela-
tive voiociiiw of thoir iona. The electriy-
motiro forces of the same clt^rasnta have
thni been measured, and the calculated
values comjiarwl willi thoHu fouml cA^t-ri-
mentftlly. The Ivo acta of rduea have
been foiuod to op'cc tct? utistfactorily ld
fivery ca» ivhcru a comparinon hfls been
mado.
In an dement auch ofl boa 5^ ^'^^^ ^
acribed, the ooly aoitrraa of potential 4n
at \hv surfaoca of coDtact of the eloctrodCi
with thv cWtroT/tn, and ihe siirfaicet of
oonUct of Uie tvo dectfolylea villi tmk
olhur- Thcrri? is no scarce ol potential at
tho eontaet of the tvo cAectrodea, aiiM
th^ an of Ibe eame metal. We sbo^d
like ta know hov timcti of Ihe clw^tm*
motive foice waa geucntted at tltc- 4^r>ntact
of the metda ihth the clTCtrolyiw, n&d
kov mueh at the eontactc of tho two oloc-
trolytea.
TiiE mognittida nf the pfitfmtJal at thv
contact of the clectrolytea e^n be calcitr
Inloil, and a\s> mcnaured, ae Nemat haa
ihown. To do thia we must exulud« the
oth^ totir^ of potential, isit., that at tbc
contact of the H^trodea iriih the etoctrv
Ijli^a, anrl tliii ha^ bwn doim in a fiirtii of
eknacDt vhidi vre shall dot atudj.
TUB LtqUID BLBUKNT.
To determine the pot^tJal at t&
fflj-c of c-onta^^t of tvo eleL'tr^lylei,
£&me lueial mu«l be UMd for i^uc
on both ftidea of the cell, and both e
trode« muat dip into aolutiona of the aa
electrolyte, and of thv ficuni; coneiTntrntioa
Sui^h plnnfiuta Iimvc biv^n studied bj
NiTfMt,* who ntp1ninr-il for fJie first timv
tbc action of the liquid elemc&l. Aa aft
example of the liquid dement be cd'
th« following;:
.; '^*" - m^""' - m ""- ro "^' -i^'*
Tb9 ptfltJniiin otectrod^e dip into iht
lenth-nomLfl] soluiiona of poCaaalim eh)o-
ridc at tho tw(i L<uil>, u> that nny pot<
generated hen? on oner Hide, TOtild be
eotly batnnced by Iho equal poiential
oppo«il« sign on tl:« other aide of tte
■ tXmhr. fAi*, Caf Pt, . I*. HO
n
OUTLINES OF ELSVTHOCHEMtSTRY.
M
The oolr Bources of potcnlinl in sut^h an
ti^iTK^nt TTould be at the contacts of tho
ftolutioas of the dpotrol^ifis.
ITif qui.sti*>n whioh would natuml-
ly ariac in corjotction with such an
olomcnt is. why ehould there be any po'
tmtiat at all at tho fiurfaoc of contact oi
ft'OdeotroU'teB? Norii&t thinka that this
bdoi' lo the uneqiinl velwities with which
tht >oiu move iu a soliitiorL The faster
ion IB held back ia its movementa hy the
ilowcp, and the resist ia a tension which
BianifeetB itsflf aa a potetitiai The
*ori1» of NpT-nst in this connection will
iwT giTen, intmdueirg the Bjri[:holH c und □
f« the relatiTe veli>cities of cation and
union, rtspwtiveiy, luatcud of u nnd v
which were ompIo\cd bj Ncrnel, and haTe
rti>» been ^nemUy ua^ by thos(^ who
h^^i' 'lT*ciisse^l Ujeat* prohlems.
'Sii[i I** in dectrolytes tileclricltj can
njovL' oiil\ with the ponderable maaacs,
tbeions, we wtlJ find the difference in po-
lentiaj vhieh exists between two enlutione
fit fbe siime elwiroJjte of difTt-rent con-
centralioni, which are :n contact, by caku-
iatin^ the work required to traneport the
inu»ee carryin*j the two kinds of elw-
(ricity from the one fioliilion to the othor,
Aecording to the views of Hittorf, and
thoae developed Uipr by Kolil-
the conduct-irity of a current of
intensity i, in an electrolyte in which the
eation has tho vflocity f. and the anion
tho rdocity a. is alwayg found ils follower
In unit time i — — — of poeitire clertricitj
ifiOTM in the diroetion of the current^
the apposite directinn. We haVR, There-
fore;
Tu enleuJate the work required to traofl-
port ihii' positive iuufi i*umhinn.l with E'
from the more diluted to the more con-
centraJod Bolution, and the negative ion*
eoTuhitiod with E' from tht- inori? (?oii.
ccntriiti^d to the more dilute eoIijHod;
let /J, be th? (owjiutJc) preasufp yyf Lhr
aniona and, of course, elao of the cation*,
in the one solution, and pt in the, other
sohitioa. In order lo tronapon th* poei-
tive electricity E' from thoont- to the other
eolation, together with Lbi? ponderable
masBCB combined with it from the preaaure
p^ Id tho presfiitre />,, und nt the Hunio
time the ponderable niaa^cs oombined with
nogatirc electricity K' from tht? pn^junrr
pi to tho prnnMirc j?,, tho following
amounts of work would be required;
fU pi
— ^ ( t'fip %tA - ^ i vfip
+ a J ' c + aj '^
Pi P$
whpTp t i* the volume oeeupicd by the
maw of the cation (or pfitionn) combinod
wilh a plus unit or a miiiui!i unit of elec-
tricity. If for the purpose of iutegration
we whto thi; Monottc-Boyic law iu thia
form:
P^ = Pa
whore p^ ie the pfossuri* in ■ jwlntiftn
wliii'h eontnins in unit volume unit plua
electricity ou IheaitionBjand unitQegaliire
electricity on the aniona. The sum of the
two amounts of work ie:
P,_P. = ^„ ln^'
"'^'f-+-^*''''^^g'»^'^^^'*'*^^^'«»'y™'*^^*^'^ P.U the potentit^l of the posiUve elec-
• tttehr. phym. ';hrm.. ir. JM.
n
OUTLINES OF SLSCTieOCHEMISTI^Y.
ttUrity E , buc) P, tli« potvntiftl ol th«
negntivc fltrlririlj K'-"
f\iv above woT'ds arc ^vcn becnuM of
their imporliinoe in coimocltoE with tbc
liifltcry oi tliia »ul>joct. They ciplain the
Action of th« element in hand for the
firat time, in a ciann&r wliich has stooi^
Tho nbove cqu&tlon for the eloctro-
mofivo force of €i coaccntnition elcmcnt>
iiilfrprctal in the ayml>olB and noicpn-
ckturo osed in the earlier pflrt of ihia
chApk*r, WmtneAi
r — a
T =
0.U6H log^' TOlU,
wlierc pi and jvi oro th^> usuiotit- prees-
urOf oi both caliooE ii^d aniens in tlie two
caec. Tho roe;iit£ ehow that tho olwtro-
motlve force of a liquid element is al-
V3.y^ amall, lieiog dependent, &a ^ill be
seen from tLe formula^ uidJiilj upon the
rdfttivo vdocitiL-a of thr cation and the
anioD. If ihGGc are ^ua], tho electromo-
tive force of such an elevnent U'oiild b^
Sinco the electromotive force generated
at the surface of contact of cloctrolytes ifl
ver^' Bmg.li, wc ace that the ekicf eouroe of
the electromotiTe fore? of prinmiy celld
ig at the stirfacea of cont^cl of the elec-
trodf* with the elei:trulj'te&.
It was thought for a lon^ time that the
chiof source of pottnlial was at the eur-
face of contact of the two dectrodee, and
HRTLKf
<^
PM_j-fq
K^
Viit. i:. Liqvm ElMtURST.
^-LjiiThilU--
^^ vy
<^
^
aoluiiona of electrolytes whith come in
conteci. The arrangement of the vesaela
which contfttn the eolulions oi eJectrolyte*
is ^ven by Nei nat^ aa ehown in tho accom-
panying £ki-tch.
The sketch explains iUelt The eX^-
trodt-s afu inserted into tl^e two ends
which contain tJi^ fiJLEne tolulion, and the
three intermediate AolutionB arc inacrlt-d
betve^ the end tJolutioDSt ne ihovm in the
aketch.
Ncmst colculotcd the electromotive
force of a number of inch elcmcnU, and
compared the reBulta of cttlculution wiih
Lhoau of meufiurerTienl. He fuinid a Butis-
foL^ton Hgi-(^fMH!iit li^ween tlit^ two in every
Una vrror pcrsifitt^J unUl the epoch-mak-
ing work of Nernat, which wc arc now
sti]dyin^> appeared in 18SD- Tho voJtftie
cell wiifi, therefore, discovered about &
century before it was iiiKlorKdvid^ and a
aimple mathematical Ihtory of tie action
\vorked out. We have thus far applied
tht tUcoT)^ to simple primar>' butterioa
svitU ont: mct^l as the elvctrodee- We shall
now turn to nuirn ounipbx etlls^ which
arc far bcllrr known Umn the simp1«
cases which we hovo been considering.
A TTPICAL TWO'METAL CELL.
The cells which wo hnro thus far etnd-
i*(] arn of 8ucli wiuiplc conatniction, that
thty will acarcely Iw reco^'ruBcd aa typical
OUTLINES or iSSjSCTROCriSXiXTRY.
tt
jfuaapj battcriee, by fttij one who i* not
tifuillu' wilU thi- Inter develcpmentB in
* ■ dwdodicniistry. It should be added that
mdi c&lle have little or no lochiuce] mluo,
JLEicethej oic incapable of furQishing any
coiundeTat)le iimount of elyctrii?itj for any
ipprwifible tinit
The prinmo' tclU with whicL we are
OJiiinorily fumilinr, consist generally of
■1 tBO diffopcnt eloctrodce nnd two different
" (tecticlytee. W»ere the electrodes are
IQETOimded by tlieir owd *alU, the (lietiry
vtikli we hat« jutil considered cau bo &p<
plied to ihtiti, Lvt lie Uk^ a typi^I
czAmpte of & tVD-mctal battory, caoh
metal being eurronoded by on^i of its own
tRltiL 7n prnttiee, the two motwis used
diffi>T greatly tn their sol kit ion'tcu« ions;
one hfiviiig a very grmt. 4nd the othtr a
T€r7 email solntii n-tension^ l-i?t mctid A
hard ft veiy givat eolntion-londnn, and b^
niTOiinded by ond of it« own daUa; und
Irt metii] B hftve a very ^niall Holulion-
tfrnaiou* and be 6urroumkd by a solution
of one of £U Milte.
Sinc« tbo »o]ution-leii€aoii of A is very
greAtr il will •lwa>'^ h** Urgiy than the
ocnotic prratfitira of thp rationfi in any
■olnlion of nny of Us saH^ which <:dn be
prep&red- Thia mdal vr\W, tlicrefore,
throv ecmc ione oS into the eolutton, un-
til Ibo doctrical double InytT formed
iMUbli^ho« equilibrium hotwi^rn the uum-
biT sent into th".- *diition. »nd the number
vhirh wparnles from (he ioktion. This
loeUl vill, therefore, beoomo nt^tive
wilt reapoct to the eolulioo, which will be
poaitiT^' The potential between thk
meUl and the aolittion will bn:
f being the TnUnef of the metal, V it*
solutioTi'tension, and p the osmotic preso-
ore of the nietiLi iuns in the ^lution.
The melfll on the other eide of Ihe cell
haa a small solution't£iuion> and ihe beat
r08Ulte aje obtained when the aolntion-
tension of thia metftl ie praot^oalJy in£-
nifeEiroAJ. The oamotic preasure of the
metal ions in tlie fmlution ia, thereforB,
greater than the solution-teiieioti of thia
metal, and, t'onieqticntly, metal will
aoparnte from the fiolution upon the bar.
The bar will, therefore, become positive
with resprct in the solution, which will
be ne^'ative. The difTereLLt-e in potential
betiweeo the ivo vrill be:
Wt= - log —
where i\\A tho \^leiice of lhi> mirtal, P^
itrt 8oliititiivtt^iiMiori, uml /Jj ihv om
molitr pve«Hur« of Uie metal ions in the
lolution. The electrotnotire force oi on
plcmont constructed of the abovo two
metnU, A and B, la the difforeopo between
th? potontiftla on the two ■!<!&■:
U,I>W , P 0,Ofl§, P,
Sinoe LJie metals uaod in conri meting'
primary oeUa aro in gcrncrnl biraleut;
IF :j; r, = 2 ; whon thii nhovo expa^Niiuu
bL-eumefi,
w=O.Oifl(log *"— log ^^J
This is thi? formula for calculating the
electromotive force of auch elomenlfl oa
1^ (ire eouBideriiig, It iB only neosMary
to know tho aolutioii-t^^nsiona fA the two
metale in qu^tJon, and th« oainotic pma-
nre of the nij-tal ions in the two solutiona,
in order to calculate the cloctromotiTe
fotco of such ft cell. The other faoton
M OUTLINEB OF ELBOTROCHBMIBTRY.
which come mto play, euch aa the po- surrouitded by Bonie electrolyte
tential at the contact of the two eleo- than one of ita ealta, or carbon earn
trolytefi, etc., are jo small that they can by a solution of some electrolyte; t
practically be neglected. There are a cases the theory in hand doee not
number of very much more complex el^ and we are not able to calculate th
ments known, in which we have a metal trcarotire force of Buch combinatic
OL'TLfNES OF BLEVTROVBEMlSfRY.
»
CHAPTE^R VII-CALCULATION OF THE, ELECTRO-
MOTIVE: FORCE OF ELEMENTS,
PART 111.
I
h \s> not necessflry to knew Uie vaJuee
flf the sol titioTi-lena ions of the meUle
taed as eJcclro^^fiS) m order to calculate
tlic electromotive force of ett^montfl in
*birh the Biun^ rnetal b used on both tides
*f llw cdL This will be seen bj eajiiiim-
ififf the equation for the electromotive
ffirro of euch cells. The solndoc-tenafon
of tli0 metal used ib of the same value on
tic two sideH (ff the ce]l, unci when the
wtentiaU on the two siJes ure aubtracted,
^6 tiro eqiLal vnliiev have opposite aigna
oid^ th*!rftforc, disappear from the equa-
Linn»
If, however, we are calculating the elec-
tTOinotivr forco of an element in which
^0 difTsrent metals are used as the elec-
*hd*a, it is noceasary to know the voljes
«! the aolution-ttnEiouB of both metale,
ainpeboth valutas aj>pear in the final cqun-
tini}, That such must be ttic cnw?^ com he
*Ml at once from 'lip lurt ihat the
•Dlution-tenamns of the two metaia have
diffcrott vfliuea, and when the two potcn-
tiab aro Giibtmctct] these two different
nlnw do not difinppear. We must now
itodj carefully/ the method eiiiplnjed in
Jcterminuig the solution-tenBions of the
dJITcrvELt iiictala,
Wt tare aeen that when a. metal ia im-
mersey] in a (olutiat] of one of iU aiilU^
a diffonmef in potrnMu! between thr metal
aD:d the aohition rc^HiiIis, the mugniludt,'
dcpcttding upon the aolution-ti^ngion
of the metal and the osmotic prcaeure
thu motftl ions in the solution. A
number of mcthoda have boflD deTued for
meoaurifi^ such differ^neti in poitntuU
tctwten metais and eiictf^ltftu. The ona
iu which the drop-eleotrodc waa employed
can only be referred lo,* The one whioh
we shflll etadj in stime detail iDvolvca iha
U5C of the "nonanl eJectrodc/t
*'This method is baecd upon the u>c of in
electrode wlio&e potential it known. This
is connected with the metal ImmerE^
in the solution whofte diff<^rvnce in pot^n-
tinl it i& dv!<irod to mcaaure, and the elec-
tromotive force cf the whole combination
dctormincd. 8:ncc the pottaitifil of the
nc^rinAl electrode is known, that b&tween
the metn] and the solution in which it is
immereei] is determined «t once; the elec-
tromotive force of the Iwo aide* when com-
bined, being the diffcrcnco between the
potentials on the two aidei- The form of
normal electrode used by Ostwald is shown
in the awompatiying ^kt^lcli. TTie bottom
of a eljiaa tuhr^ about tdj^ht centimctrefl
hig^ and two to two and one-hiLlf oenti-
motrcs in diameter, ia covered with mer-
cury. The morcary ia covered with a
layer of mercnroiifl chloride, and tlie vess*!
is then ftllcil with a itormni aolution of
pota^Atum chloride. A platinum wire
protniiing bcvond the end of a gUss tube
inlo which it ia fused, dips info the mer-
cury and serves bs one elertrfwl*', Th«
otlier glnfts tubu pHssiug through the corlCj
is alao filled with normal polaasinm chlo-
trv^r In mwiHimnr 4l1fTur<<ikMid tlpof*fin4l lifft^"*!!
OUTLINES OF ELECTROCHEMIBTRY.
ride. The gUse tube at the end of the
rubber tube dips into the liquid, whose po-
tential against a given metal immersed in
it^ IB to be measured.
"The metal immersed in the liquid serves
as the second electrode.
'The electromotive force of the whole
system is now measured. Knowing the
tCCP
Fio. 18. OdTWAi.D NouiAL Elfctbodr.
potential on the one side, that on the other
is obtained at once. The potential of the
normal electrode just described is 0.56
volt. The metai is poaitivcj the deetro-
lyte negative, which means that there ie
a tendency for the mercury ions present
to separate from the solution as metalUc
mercury, and this is expreaaed in poten-
tial by 0.56 volt. In such measurements
the potential of the metal is taken as zero,
and that of the electrolyte expressed as
either positive or negative. The potential
of our normal electrode is» then, ^0.56
volt,
"Differences of potential between metals
and electrolytes can be readily measured
by means of this normal electrode. Let
us take as an example, the difference in
potential between magnesium and a nor-
mal solution of magnesium chloride. The
normal electrode ie connected with the
normal solution of maf^csium chloride.
into which a bar of magnesium dips.
The electromotive force of this ajstem
was found to be 1.791 volta. The electro-
motive force of this element, as we know,
is eipressed thus:
.= 0,058 P_P,
where P is the solution-tension of mag-
nesium, p the osmotic pressure of the
magnesium ions in the solution, 2 the
valence of magnesium, P, the solution-
teneion of mercury, and p^ the oamotic
pressure of the mercury iona in the solu-
tion.
p
" We have seen that 0.058 log — ' = —
0,56 volt, and subatituting this value in
the above equation we have:
^^ log - = 1.791 -0,fia volt = 1.281 volts.
Therefore ;
p
0,029 log - = 1.331 volts;
P
which is the di^erence in potential be-
tween magnesium and a normal solution
of magnesium chloride."
Differences of potential between a
number of metals and normal or satu-
rated Bolutions of their salts, have been
measured by Neumann.* A few of his
results are given below:
BulphHtfl. ChlorJdA.
AlumlDiim ^-lOUl + 1 OIA
zidc +0.024 +i>cas
Iron + aosfl + O.DST
Nickel — onaa ' o.csD
Copper — O.MB
HerciLO' — 0.9W
SlUflt -09Ii
Qoia ... . — l.BM
P:HtlDiim ..... "1006
The above data show that eaaentiftllj
Ot/TUSi!0 or BLBCTItOCHitmSTKY.
vt
\
Uie «6]M n»ult» Are <»t>UiEL«<l wh«th«r Um
noJpbat^ or olitoniu ift uecd» aiixl ihit
rftiMv tho ^ciDition om to what oCtci \h/t
mature of the action has ou thti difftrtnc^
in poUntial btiw4€n tJu m<UU end thg
i^Mi(m^ Thtfl problem woa studied ti-
tcasivcly bv N«UTniiun, who worked vitli
n jftrge ni^Lbor of ialt« of tti&Uium, in-
do^l :^3 ^n all, and m«omrod tho ditT^r-
eDL<« in polenliol betivecn Ibo inelnl aad
its Aolutionj^ Hu concluded that for
equallX diwocbtod aiabatiimT> Uie nature
of Uio fliiion hu so inflvonco on the po-
\Vf ricnv rwtiir tn (>ic (Iiijl] mid mocl im*
pottnut [iftrt of IIh- proUpn), the oi/ctt-
laUQii of the soiviicii'tension of mciala
from the diffcrccico m potential bciwccn
tii« mcts) ADd th<> K<lulir>n of ono of iU
s«]U> This dilTerenc« in pol^niinl is d^i«,
0« Uie oiie liftjid^ to the A»1tiLiou>lviJAion
of tJio tnetAl* and on ibu other, to the
omotic pr«dsurv of ihti mctftl ioa« in tlw
lOlution. Tbow foriNM act In oppottition
lo ono iDotlu'r, nml tbo r^ult U the for-
umticin i>f ft doiihit- Injvr, ivhii^h iu«EHtJt
wtnkcT forcr. *nd, th**rcforp, Ihc
in potential with which we hart
doaJing. If we measure iku diffor-
10109 bi potcslialr and know the oemotic
ppwwnpf of the PBtioiu in The tolniinn, w*
can nrjdilj r^IculHlVp ff«m coiiiidrratiuna
abeadjr df?veJoi>cd, tlie solution- tension of
the in«ial in question.
The diff«rei>e« id poientlfll bohvooo t
&i«tol. ;iw] a tohitioti of on« of ita aalts
h) vMoh it i« immprvd in,
Lvhetv * b tluf TBtrDrw of tlie cfltioii, P
ibr «nlu1ioD-teiiJ(ifjn of llic inet&L tod p
tint orniolkc prtMura of the mdaJ ions Ln
th« Kolution. If wc know r, i\ and /f,
vu ciui, 0/ conr»^, colculato P.
T2iit seolulion-tcniiimu of jt fcir* of th*
more common tnctnls, jm calculated hj the
method jnfit dracTilfc*!, are ^ivm bdoir:
llju[ri**iuiii
jO<»
»i>c
10 •
0«iln>ikiat
J*"
In 111
W
LmiI
10-1
Ofptr
10-*
Vfivurj
>(f-«*
8i|v^
«-»•
Wo Jir^ imprnMiI hr tho mflgnitiidin of
thr Kflnti(ir]-l<]^ii4-icins of the im'tnla For
metaU like magnniiitn, alaiainunir eino>
lad the like, ttiev are almost incon-
ctifutity grcnt; ^chile for nietah like cop-
per, nwrcurif, aiUer, ^-old, platinum^ and
tJic Vi\v, ihv MtliJtJon-tL<iiHtoiv aiv of in-
finitj'fiimiil v.-l|uc^
Tho cnonnouf maja^itucic of tho ono,
and the inooncf ivnbly EmaH Taint* of tha
other metak, would lead oao to ooncluda
at flnt that there miut he toire ermr in
tliff melhod eniploir^d in iralculating tho
)iolut>OD*teniiiou» ifi the dillerent metals.
When* however, the«c raiuea are intro-
ducod into 1h4> ifquationi for tho etee^
trotnotivo force of olomuDt*, tho renjUc a*
eJilnilfllei] agree T<try Futicfiirtnrily witli
tfiUTH fuuQd hy experimfiita. The above
'%s a atTOn^ argunient m fivoir of their
t-<rr]cra] comctneaa.
iBB THR 8OL0TlOK*TEVaiOyB OF TttC
Thit qumtion nnlnraHy anfe*e a« to
irhethci the ioI«tion-tf-n:*i[«i.i ^f the metaU
tie conatanta for tho difFrrcnt mctab, or
art thoy fifTod^d hj tho eondition* to
which Ihc metiilfc are Biihjcctod? Ofttvnld,
OVTLlJfES OF ELECTROVrlEMlSTJfY^
vho has dovcloppd thie conooption miicli
fwrHiflr thnii any one else, roTicludod in
thi" jir.'(iiiiiJ duijiterof tbi&"Iiehrbridi,"that
the Aolutiou-teneion of a metal is bb con-
stant for th« mcUtl as iia atomic wi^ight.
He n>^'arui3 it oa mdoputjUent oven of
the natt;rfi of ttie folvenl in which the
mi-bil wiis imtnereeil,
r.ight wsi thrown on thia problem in an
UTii'xpected manner by work whidi was
doDtf lij Jones ill Ofitwald's kboratorj.
Ati eioinent vns coratructed coutaimns
on the one side a tonth-normnl eolulion
of ailvor nitrate in wnterT niiii on the othpr
n U-nth-ncirmal aolutinn of Bilvi?r nitrnte
in t'tlijl aK;ohol. The flret object in mind
in conitnictiBif auch an element need not
be considered hi*re. U was known that
Bilvor nitrate ie dieeooiatod by water to a
mneh greater extont ehnn bv alcohol, and
that* coni^i^qiietLlly^ fur fiolulion^ of the
Banie ooiic^iitrntion tht aqueous solution
contnjnfl ninny morp Bilrer ions than the
alcoholic. The oeniotic preesiirc oE the
silver ions in tho nquorme ^^Intion would,
thpTpforp, iie much greater than in the
alcoholic ^oluiioa The sol ut ion- tension
of the melal in (he two solrenu wm a*-
eumod to be the c-aEueu
Frnm tbcfie data it would be a p«rf*?eUY
■inipld matter to determine which side of
ihe element would be positive and which
&flg&tlTe: that pok would, of tiourse, lie
po»Uin-, m\ yrhitrh silver ions were sepnnit*
in;: ''I ihc form of metnK Since the aolu-
tion-tiMifiion of the metal is bho sfltng od
both tides of the oell, metal ions will
»Hp»rntP from the sclntion on thjil side
on which the OAinutic pre&aiire of tbe luelal
ions i« the greater. Wc have just seen
that the o*motie prtflsure of lliy silver
Ion* in the aqnooira solution is the ^reat-
<*r; eiMa<*qu*ntly, the fiole immL-rsi'd in
the aqueous solution of eikcr nitrate
would be the poailive pole.
The eo|] WHS constnictL-d as described,
and an attempt wai* mjtde to measure ita
f^lcctroni olive force. The first fuct which
1^113 discovered, waa tliat thf pole immersed
in the alcoholic solution of aiU-er nitrate
wfl^ posiiive. Thia was very emlamsa-
in^', and, at firsts seemed <?nlirely inex-
plicable, A number of eipmrnents were
rrppatod and nil gave the same result
'I'he fflcts were undoubtedly riot in ac-
cord with the ageiimptiouB which had
been made, Wliflt wag to be done? It
vas obTJou^ that there was tiomr-thio^
wrong witli tht asaumptions. We then
convinced ouradves beyond all question,
thdt silver nitmte in water is much more
strongly dissociated than iu alcohol at
thf? same concentration. This left but one
araumption ii ji (.pstwlj and that *]i£, tljat
the solutiiin-lcusion nf the metnl is n coD*
slant in the differeat solvpnts. This a*-
siiniption muat then be wronff. ond the
csLpcrimcnl wjia eo earned out as to
di?t£rmin(^ the relative solutlon-tenaionfi
nf silver In an aqueouB* and in ttn alcO'
holic solution of silver nitrate.
The t'lfjiKiit was constructed using A
Ipnth-normal solution of silver nitroto in
wrtt'^r on tlio one aidOi and a tonth-nox-
mill solution of silver nitrate in alcohol ou
the other side. The electromotiye form? of
the combination was measured, and from
this tl)e relative solution-tarisions cnlcu-
lati*d. as follows: Th^? potential in the
iiloolt^hlit? solution i^ oxproeFaod thu8»
#, s iiM» lo^ ^-'
1 1
The valence of tho silver being one,
dote pot entt'r into the formula, and since
silvt-r is an tdemont whose solution-ten*
?ion is verv smull. it is less than the oa-
orrL/.v/ffs OP ELEcrnocHBusHTnY.
I>
motic presmrc of the nivor lOtfl in tho
<«]ution. Somo ions mllj therefore, eup-
arate from the cohitjon upon th_ bar, and
tJie eolation will be negative with respect
to the bar This dtenges the aigu of the
potvTrtiiil, ixwA throws the osniQtic pressure
la thc^ nuniorator and the solution -tension
in the 4*'nomJDfltor, which 19 esoctly tho
ror<Mse of what wo hnd when the aolution-
t«D8ion of the metal wa^ ver^ ^eat with
respect to the o»mo(tc pressure of the
meUl ior^a in the solution,
The potential between the har of silver
and the aqueous solutiort of sllvet nitrate
IT, = 0,068 log ^
The electromotive foree of the element
JU a whole is the difference between tbe
potcntialc on the two aides:
Mflking P,, th^ aolution-teneion in the
aqueous iK>lutioD> ^ 1, we have,
Iiu<rtiDg into thia equation the ralues
of p, and /J,; i. * , the osmotic preei=-
tire of the silver ions in i\w alcohol and
nqucoua eolutiona, respectivffly ; we enn
Menlate P,, the fiolution-tonHon of tht*
niia>tftl in the aleohoUc eolution, in termd
of the Aolntion-tenaEoi] in the aqueous
BOlntion a» m\\iy. The nsrnoite presa-
oie Df the Bilver tons in the aqutTiua solu-
tion can be readily determined from the
Gonduotivity rcBulle, hcing proportional
to the diseociiition in this solvent The
ownotic prossure nf the silver ions in the
alcobolie ioliiU^i] cjin he determined only
Approzimat^ly. since by the conductivity
methodi as we have accn. we can meaaure
tho diasooiation of an electrolyte in aloo-
liol only approximately^ Obtaining thLi
i'aIuc aa tiecurately a^ pofsibie, and insert-
ing it In the above equation, we obtain for
Pi thft value 0.0ft, This ia in f^rma
^t wntur as unity, and means that the solu*
tion-tconon of silver in the alcoliol solu-
tion of itfi ealt, ia about one-twentieth of
the flolntion-teriaion of thia metjil in tha
aqueoua eolntion. More reeent work by
Jonea and Smith has shown that the
aolnUon-teneion of tine in an aqu^roua
solution of one of its Aftlta, ia rcrv diffi^rimt
from that in an aleoholic solution of th€
same *=alt of tht' ^anii.- eonf^ivitr^tion. The
solution 'tens ion of the mi?tal», then, vnrhn^
frem solvent to solvent.
This conception of soiution-icn«ion
Ima b(-im extended from the mctale to
otlier eubetflnet'fi, until we have come to
regard flolution in general aa due to The
3olution-t^»aion of the go5ub!e aiibstanoe.
In the^ight of thia extension of the term.
It is not at all curprising that the soln-
tion-tcTiflion of a metal vnriee from sol-
vent to solvent, sinee we know that the
M]uticD>1('Uiion or floluhLlity of chcmicflJ
oornpfinnds varii^ grt^lly frDin solrent t6
solvent. We can, then, regard solution-
tenfrjon a^ that force which drives the
subatanco into solution in tho solvent;
if it ia ft metal or an electrolyte, th« atom*
pawing over into inns, if n non-el ectrolyta
Lhe molecules dtasolve aa such in tlie sol-
vent,
8CME WBU.'KKCWK ELpEMBNTS.
The elementa which we have tbue far
studied give an clifctrouKitivo force which
L£ unchanged, and are^ tbcrc-fore* known
aa ttinjdaiit. Many of thn nlprnr'nlx which
are need In practif^p as a meitns of ob-
taining electrical energy, have an electro-
motive force wiiieh changes after a time,
and are, therefortv known u inoonttiM.
fi5«?,7^
in
OVTIJNK^ Oy ELECTIfOCHEMISTRV.
Onr- or two of the more oouimon elemeuta
will b« conaJdttrvd,
'Rie Bichromaii\ ceil i* n form of battery
Tbioli ficdft fruqacnt npplioition is coa-
nectiou with ciJPtnin Itinde of work, and
wpeeially in thw Ifttorslcrj'. The ele-
ment nnnsist* of a (carbon and a zinc &leC'
trodc^ both being imrucrwd in a solution
of poUuium biohromate nml sulphtiric
acid (chromic ncid], Tho Jiinc diasolvea
beoauac' cl ita high eolution-tt'iiaion, aad,
ther^fort-'^ Ihis bccom-'s th* negative pole
or 1.h<^ jiuoeIc, till* cnrbni* biding th<* poaitire
pole, Tliuion[il'r,Or prohjililv yicM Jifuw
flhrwnium ionn of hiifhcT vnlcncy» vrhich
pft&a ovor iL)ti) chroniii^m lona of lower
vnJc^cy, and thiw increase the elcctro-
ciotivp foree of th^ elennei^t Siuce the
ions fr^Or iiK consldntty dcCTc»«]ug iu
Bumhcr, ard tho chromium iona of lower
volotioy and alao the sine ions afo in-
oreaaing in niiTnber. tho eleetTomottTa
force of this (-lirrieiil taiinot remain eon-
fitaj^t.
Thia agreea wjlh the facte. After tho
bEchromato cell ha* b<-^en naod for a time
itfi vlectrumfitivr foivtr ru|»it]fy dr(-reH8es-
The action i>f thr Lr.danr.kp nlfmrrii* is
a little more complex.
"The polos of thie uaefiil element are
carbon, and mangniKfie dioxide &nd sino;
the electrolyte. aTrmonliim chloride. The
carbcjii aijd [naiignoc^Hfi dioiiJp are gr^n-
orally iiiixt^d with uiir atiothvr. Zinc joiia
p&ea into solution, and, oonat^ucntly^ tho
tino pole i* tho anodo. The ammonium
ioiift >J H, paafl nvpr in the cathoilo,
but thi? hydrogen ions, atreaily prpscnt an
thu result of thi^ dltutouaUoTi of WMtt.T, lose
their L-hargee moni itiaJMy tJmn ammo-
mum, and, con[K'qm>ntly, scparatf at tho
Ttw lvllf^v/^tlt |iiir«fr«p1i "v <hi l^i'l*ni.'TiA rl'-niml
HiUJr'ti from KkiripniKnr fhTHliwl Hhctnlarry, liy .Iniirii,
wl|[<A irlll iouu Sb jtabllilird by I lie Hucni^lIofK
oarbon oathodo- Thi? carboL pole would
flhsrirl* 4 liirgn amount of hydrogen. The
MnOf acta as wt would I'lpi-ct, an »e)
o«idi:£mj;f agent- This yields a few Hn lone
which t^uil to ^mesoviTintii Mn, by giring
up part of thuir oharge to the cathode- Wc
have thu6 two aetious taking plaee in the
Leolanch^ element, but the electromotive
forcfl decreases because the zinc ions be-
come iriorc and more concentrated."
A form of Laftery which haa recently
Bupplanfed many of the primary cells in
U'chnteal worlf, in known as the Accumu-
liiUiT or Srainiiarjj lattery. Thewr have
romc iutc such general uau iii thi.' last few
years, that a word h nccpsaary in refer-
ence to the action which tokce pkcc in
them, Theoretically, we could make an
accnranlator out of any reveraible cell, bj
biniply pa^tHing & ci.irn?nt throng}] it in
the direttjuii oppoiitv; to the one in which
Iho current tlowe when the element ia
olowd. Pmctienl difficulties, however,
eomc into |)lay in a majority of cns^e, so
as to render most siu-h elements um;]»a
afl accumuiatorg. In practice, the aceumu-
[ator which is nscd consists of platca of
lead, covered with lend oTJde or enlphatc,
and immersed in a solution of stilphurio
aeid of a certain specific gravity. When
a current is passed through this eli^iiunit,
the pole wher<? the current cntcra become*
covcrc<l with lend dioiidc. while mctAllie
lead is deposited on tbe oppo«it« polo.
The action of thr» charging cnim^nt ia,
therefore, to convert \ent\ anlphntji or oxid^
into metallic k-nd at one pole, and into
lead dioxide at the other.
If the cell 131 allowed to (lischargc. both
the ni<'tflllic Irail nt the one pole, and the
lead diovido at the other, pass over into
lea*l siilphnte in the preaence of the aul-
OVTLINEH OF ^LEVTRUVlHSUISTHy.
101
L
fhanc Bcid. The ohi«f source of the eloc-
tmrnotire force of an occniniLlfitor ia the
prusing^ifqnniJriv&leritleiul ioufi^ Pb, into
bivalent ioiie, Pb. The qujidrivnlent
lODQ, furnished hj the lead diosidci poee
over into blvuknt, and form vii}\ the £ieI>
plitirk acn), \f>ad milphnt^?. Met^Tlic lead
dissolvh-s at ihv uncMle, forming It^ml Iodb
which carrj the pcaitiTe electricity off
from ttiie pole into tho solution. WiUi
the SO, ious of th^ eiilplitirio ucid tbeao
ions form lead sulphate.
Till' ft4:tioii ii[ the flccuinuUtor, on i}i&-
charg'iii^. ie ci:ietl^ the opposite of that
;1flticli taki.'s plucc vrhcn it is b^ing
fihnrg4>d, aa wt would exjjL^t Charging
ooiTuifitfi in tranefonning bivalent lead ione
into qiiailrivH]ent; whili? discharging can-
UltA in the revtrse tran^fontiation of
qudrivaJoiLt lead tona into biralcmt.
SOiril{^&£ OP TirE IfLEOTmCiL ENERGY IN
PRIMAKT CRLLS.
W« ftboiild not conclude our study of
primary cells, without inquiring into the
ifourci.- of Ibf eiurrgy which ts convcrlerl by
Uivm into electrical energy- We know
from the lav of ihv coTisorvution of en-
ergy that no energy is i*reat(^d or de-
•tn^ed. 'rh&rufore, tlio large amount of
mrrgy whtrh nppj'nrH a* id<rtn<5il rnergy
in each cells, ravist come from some other
COtiTCc of energy ; the trars formation
being effooted in tho cell it«df-
lik^ ihc element which wo first studied
io detail — the f-orcenlriitioTi alcanent-
Wbat is the Huurcc of the electriuil eutTffy
in auoh a cell ? We huve & cert/iiu aruouot
ol tine in ent'b iluetrodo. and a outain
■mount of ziOL' ^hlon^k on eaeh aidtf of
ikit <'tfll- As tho cdl gtv'cs out electrical
I energy, or> tus we usually my, us th^
c#ll act** xinc di^olve^ on OttO aide, and
just a£ n^u<h siue fioparatcfi from the aota-
tiou on to the hur, on the othor aide^ Thd
on& solntion of zinc C'bloride beoomea more
eoucentratHl, arid th*^ other^ by jint the
same amount, more dilute. After thn crll
has been clo^d for any lenj^th of time
that wu cboosi?, the amounl of zinc chloride
in solution on Ulo tivo eidirs of thft
f?en is ejBotly the snnte as wh^^n tha
cell was flr*l closed, aud the ajiiount
of ainc in the two electrodes h exact-
ly the same ae at the outwt. The con-
dition of the ainc diloride and of the jsinc
ifl Giaetly th<^ same, from a chemical
standpoint^ after llie cpII has l>een in oiper-
ation 0^ bofore it w&s rbsed. Tho rliomi-
col energy in the metal and in the 80ln-
tiona IE, thareforCj the same after the cell
has been in of:]eration as before. The
eleetrifal energy whiirh has appriin^tl in
tlii: cell, thfn, rniinnt noine frorrt rhemi^wl
energy which has dia appeared as the rfr-
suit of action which haa taken place bo-
tween tho cotiatitiionta. Sine© tho eloo-
tplcfil energy whieh has appeared cannot
trom^ from chtinifal energy whkli haA ill»*
appeared (none having dihiippt-ared), it
muBt come from some external source.
Sueh olaments have th« power of tAkin^
i?p energy in the form of h.^Jil from ex-
leriial ohji?rls, and c(]Tiv«riiii>r it into
t!leciric/il energy; and this is probably the
chief source of the electrical encriff which
appt^ars in &uf?h cells,
Tn otlier forms of primary eplU, how-
ever, chHmiral energy does disappear.
This applies to all Ihe more coniintin fonuH
of »uoh ecllF^, and eapociaJlr to thotre which
are cnpablft of yielding any appreciable
qunntity of elfictnVal energy. It wdl bo
rgmcunberod that the coni*nlration tle-
ments <AR only furniiLh a very Bmall
amount of electrical energy. AH primary
OVl'UWES OF SiLE07RnCHEMl8TRY.
«loment3 vbicli have on^ conejder&ble
U<ohTii<?al valu«. mi^st bo capable of fur-
uishiiLg a L-on^idi'rable quantity of elec-
IriciU at a fnirLy liigb pctcntial, say &boul
41 volt* The clcctricftl energy, as we tjave
0(vji, is oqurtl to the quantity multiplied
by tli« potcntjnJ, When the dectricsl
pn*>rgy is Urge Sftmo rhprnirnl nr intrEnaie
vniTgy n»iist Hiftnpjw-ar
If vo Mttitty 1ho flctioD which tak»
plaet in any denipnt like Lhe Grove,
ButUH^ik, Dajiiell, Loclantht, ctc»j we shall
Jtnd that the aubatancoa which are present
in the <?dl aro ia a vory differvol oon-
4itioUj t'ht-itii<!iilly, afiur tin? cell has b&en
Aoling for a consitlernMe time, than he-
fore such fii'lion took place, TJie atiiounl
of melaJ in one or both electrodes has
changed: or iriotol hoe ln;en di?p<Mitcd on
ono ohjolrode and dissolved from the
olltt'r; and lin^re the elei!trod(js are of dif-
fiT^Tit ini^taU, i\\\A would fepn'&eot a dif-
ferent amonnt of ohemical energy in the
syrtom a* n wholo. And, furihor, the ^on-
dilion of things in &ohition has very
grwLtly i:haTigpd_ There is frequently
more of one inetat In soluUen after the
cell ha* been acting than bofore, and leae
of the other metal i and this would ropnh
sent a vei^ danertnt conditiovi with re-
spect to the luioiml of ehemical en^rpjy
|iri-hi'tit ill till.' iyjitfiii,
SiiT'h I'Temcnts n« theao transform ^^hern-
ienl energy into eleetrical; but there is
still one quefttion unanswered. Does iHe
transformation tako place quontitotivaly?
Th_t 16. does fill tho chemical onerffv
whieh diflappear» Id such elements ap-
pear as eli-ctrieal cyu'r^y? And this sug-
ge&ta A3 a corollary thi? further question^
docs all the rl«?triail tin-^r^y wliich
npprnrfi come frofr the chemical eoor-
gy? A momGnt's thought will show that
tlieso two quealione tixt cot thti fiiiina.
The firit question haa been answorad
by Loi'J Kelvin ard Helmholtitj bnlh tbro-
retieally by tlieriuodynftmics aud practi-
cnlly by eKperiraeut, All of the chemical
energy which diaoppcara in the cell ii
not necoiseanly oonvertcd into oloGtno&l
efiergy. Some of it may be t-onveried
into Ileal ami uscapi^ in this form. We
kuow of many elemeota wliich give out
heflt energy ae well as electrical energy,
und. iadeod, moat of the primary ele-
mi^^nts of livxy techni<?a] value belong to
lilts olasH.
Th« same inveatigatore have anffWersd
the second question. They have ahown
that all the electrical energy which ap-
pears in a primary cell, doee not necc&-
sariiy comt from the chomical or intrin-
Kic energy which digftp^ears. A primary
eeli may have the power of convertings
also, some ht?at energy into alectrical
coer^', and the ajnoimt of electrical
energy furaiehed by tiie cell may be
^ Router than the amount of cheinLcal
i?i^ergy whioh has dinappea-riid in the cell.
Su<^h elfinenta take up tlw heat energy
from aurroonding objectB, and^ conae-
qucntly, become colder aa the action of
the cell proceedft, Theae tflmperature
coeflicienis of primai^ cell* are, however,
mit usually very great; the amount of
litut energy g^ncratrcd in \ht onCi or ths
oiuoimt u&cd up in the other, being corn-
pom tivt?ly email
We may any, then, in general, that the
chief BOurce of the electrical engrgy wliioh
appears in the welt-known forma of pri-
mary cells, is the chemicul energy of the
suhstances present in the cell as elwtrwlea
antl electrolytes. Such celle may^ however,
convert eomo of tho chemio&l energy into
hmt ener^ which escapee, or may take up
OUTUXJ^iK or KhSCTROC-UKMlSTHY^
103
Wl mergjr from aurrotinding ctlijod^ aud
convert it into electrical energy.
CON CUT Si ON,
In Iho precwJing chapters we saw how
dut lnuvn of gftK-prtsaare apply to the 0*"
molic preH&uri? of sululicins; we Lmced
the ri»e of th« thi^ory of clectroljtic dia-
flOCiatioD luid luaUc a few applications of
it to oiiemical problemu. In Uic fiubec-
queni phaptc^rs T have emkavored to shov
hovr Lhsie two epcch-niaking gCTieraliza-
tion* hflVL- been applied, efepecially to tltc-
trochcmical probU-mHi. Lif^ht haa been
thrown, Ij moane of th^^ theory of electro-
lytic di^aocifllion, on the whole subject of
*U*lrolysis am! the electrolytie decoraposi-
tioit of subaLuiict^a in aolutioTi, Before
thiE theory was propoaetl our knowledge
UnLJtocI ntninly to the facte, and euch
lUzatione b£ had bdon reached, whilo
may in Eom« caeea have contained an
jWrocut of trutb^ were entirely iaauflieient
ftDd ijn*atisfuctory.
Tlw relation between cur theory and the
v«)cG!tie€ with which the ions move, ia too
» obvious to call for any coiameotn
Sinee the conducting power cf an
eleclTDlyte is due entirely to the looe which
fere present, new light liuii Lf^ea thrown on
thi£ dttirc field by thi^ thuoiy of lona. In-
deed, Bomo of the moet iDttiroeting appli-
eaifons of the conJuctiritj of electrolyte*
Uftvp ImJ to clu, directly or indirectly, with
B t^ determination of the amount uf dis«o-
Hflkfiion of the i^ubstnnce which conducted
^HM oarmnt. Tho relation between diseo-
mtioA and dilution of the solution haa
always been, and is atill, of more than the
arfngc* mtf^reat ; and the diuiociating pow-
er of dilTi't*^(it Holvents ie a protplcm of
grent importance, about which our kuowl'
ed^e ifi, in many cases, still acarccJj more
Umn qualitative, tt is obtjoua that all such
(jUL'Btionfi hav^ been opened up by the
tbeory of electrolytic dissociation.
When we eome to ttu; calculalioL of tlie
th'ctromotivc force of elements, w« eee
what the two gront gi^nemlizations which
form the foundation of these puper^, have
done. This most important chapt*?r of
t^lt^trochcmistry hivs boon created since
tLeiso generalizations were reociicd, and as
the direct result of their application. We
«un now interpret, in terms of them, the
action of the primary coll, and have an
intighl^ fur ihii first Lime, into wliat takes
place in the battery, which wub discovered
by Voltn more than a century ago.
These arc but relativolv f^-w cf the ap-
plications of theaif gGticrali^e lions to ol«c-
trochemical problems. If we were to in-
<^uire into their npplicationt^ in other di*
rtctione, wc abould find that they arc jiut
aa numerous and important^ The whole
science of the ii<iw phyaical chemistry,
which has grown up In the last fifteen
ycarSjCentresnroond tluii*<?geiit!ralizationB;
M\^ more \\aA been done in thia period tO'
place chemistry upon an exact mcithumati-
cal baais> and to ccirebtc it with Uie only
exact seience, phvsic«j than wak accom-
plished before this time in thp whole hi*-
tory of the Bcieiict. To ftilluw any farther
this line of thought would li^ad us be-
yond the scope of tlK'fle chapters, and
mufit be kit to the «tudent of tho whole
fleld of physical chemi*try, of which doc-
trochemiBtry i« only a part, hut nn im-
portant part.
INDE,X.
AbBoluie velccitlee of loiu ts
AccuzQul&tore - , lOD
A(^ici8, arrwiiBlii oi afl
Activity chemli-a1, due to terns. ........ 29
Avosnilro'a Ian ai>pljed to oamoLlc
preseure .,---.,,..,,,..,,,, 11
BaAf.^a, HtroiLe^lk ot.*.y 2A
BertGliuB, electrochemical thoor7 of , , . * SI
ait'IirorniUe oeTl. ....,,., 100
Boylae la^' tor oamottc prOAsure, ..-,.. t
Cak'ulaUiju uf tbe oLo<;tromotlTe forc«
of etemenlB ...
Colflulblbu of tbe potcatla] botwcon a
melnl aoil & eoluUoa of Ita catta, , , ,
Cfttatyiic r^ncLlons
Cli«QiEciil ftutirky clii« to loni, ,----, , , ,
ClftiiHlufc" thvory of elfiClrolysls. - 'I ■ 1 1
Concentration olem^ut ^ ,
Cooductlvltf » a tnoiL«urd of dLfi»octa
liou
LTonjliictlvlty, Kfttilrttt»a<>Ti'fi law of
Oondu<:t1vlty moacurcmuniB, vchuUb or,
ComlurtlvUy of JcluUoas. ,........,,, hG
COnCuttivitj ol BolutloDs aerooTiBtra-
tlOQ of.< 60
CoaDt&ncy or MlutloH'tQcelDii of meUJA, 97
DfiJtKitiflLmtkiL Of dtMoi^ui^on 21
DcmoTiAlrAtloQ of Aolutl on -tonal oa of
oiolals n2
DtmoTitilritlon of (hi- dlTf*r^nt pon-
ductlvlUcs of eclutlone <>0
DetermlnatloD of rolatlvo veloclUci ot
lona 47
Detc^roilDatloii of BoluUon-tonitfon of
jnelali ...----,-- .......,,, 8C
Deve]oi>ini>tit of «l0C(roc!iomULr7 ,--.,,, 2
DlLuiloDondatBHOclatioQ TO
Dllmlon lav of Oitwald 70
Dilution law of Kudolpbl TS
DUBO(;lAtloti &uj dlluUun* wt.. . TO
DlsAoolatloti. ttppM^^ailnn of tbeorr of
oloctrolfltc 22
7t
37
on
fii
59
UUaofl^itluii, (lemnnal ration of 2S
Die^oclatlcD moEiQured by co^ductiTity, . $t
DlH§oi!latioDH orialn of tbnoiT of elec-
trolytic - 13
DUeociatlng power ot dltfereot 9olv«nt£> til
niBsofiatiiiK power <jf aillerent Bolv«nls
bud otbor properties, ,-,--_.,.-. ' ^9
DUBOcl&tioDH testing \l\e theory of cloc
trolj-iic IB
Dlfldociatlon theory of clectrolrieB 13
DlBBOclfUlon thoory of ol«Gtrolyt«E, cvt-
denci? benrjuE itLion. _---->. '>.->> 1A
iSloctroohemlca] tboorUs Si
El Dctioc hemic al theory of Derceliufl 34
Electrocn'?nitca1 theory af Beritallut, ob-
JeotlouA to overtbro^vQ by Thomson &S
S^ei'trodiemiMry. Jt^volopuicat or..-^,- %
Eloriroi'iiemifitry. nn-aaUig of the term I
Bleotrocbemlslry. the now 1
iDlviitroUe. Gat^KiikVa aormiLl' ......... . BO
KU'cti'OlysiB. t-'lurMius' lliF*ory of. --,-,. . >T
HJIeptrolysls. Crottbus^' theory of 36
P-Iflclrolyajf', n^w^r (.boorlos of,,..,..H 3A
Kk'crrolyBlH, older theoHoe of^ SC
QlcGlrolyalB. tcptlne tb«ory of 40
ElectrolyalB. tLoorles of- 3S
ICleoLrolytic dlBBodfiilon. nppllrattoftii of
the theory of..... It
Kletirolytlc dlaHodalloD. evidence bonr-
lug upon [be tb^ry of^.--- It
Rloctrolytl*: dbso^lnilon, orlsln Of
theory or. . . . - - li
Electrolytic diBSoglailon. loBtiug the
theory of.. IE
BlecTrolytko i^lH!iOi.-1at1tia, theory of..... IS
QleHrolytlc at^pkratlon of the motals,, i%
ElectromotiTo force of elemenie. .... - TO
ElecTromotLvo force ol elements, calcu-
lation ot TO
Element. HauLd flO
KlemetiT, simple oon cant rftt Ion , 8fl
BlameiLt. two mcUtl ,.,.,,.,,..,....,.. 93
INDEX.
105
Elemeots, iy^^ of 86
Energy electric, Bource of Eq prlmarj
ceUs 101
Paraday, law of 33
Faraday, testing law of 33
Faraday, work of 32
Gu-presaure ftna oamotlc preeaure. re-
lations between ft
Gay LuBsac'H law applied tt> osmotic
presHure . , 9
GrotthuHS' theory of electrolyalfl 36
Hpat, ionizing power of .......,,,_. . 72
Heat of neutrallzatioD of acMa and
baaea 26
Inarganlc and organic anbatancoa, com-
parlBon of reactlona between...... 29
loalEing power of lieat. .... - 72
Ions, cauae of chemical activity 29
loAB, determlnatioD of relative velocl-
tfea of , , ---... 47
Ions, LnQucncea which may affect rela-
live velocities of 49
Ions, modes of formation 73
Ions, nalura of 54
^oub, velocity of 46
lone, velocity of from Kohlrauach'a
law 62
KohlrauBch's law of conductivity 61
KohJrausch'a law used to determine
the relative velocttiea of ions- ..... 62
Kohlrausch'fl method of measuring the
conductivity of BOlutions 57
L«w of Faraday. - - 33
Law of KohlrauHch 61
Law, the Ofllwald dUutlon 70
Law, the Rudolphl dilution 72
Leclanche element. ..,--....,-....,- 100
Lodge's n^ftbod of determining (lie
abaolute valocitlea of ion8.,.._-. G3
Membranes, aemlpermeable. 6
UetAlfl, demonatratlon of solut Ion-ten-
slon of 82
UetAls, determination of solution -ten-
aiOQ of 9E
HetaJa, electrolytic separation of.,-... 43
UetaU, solution-tension of 89
Holecnlar and speclflc conductivltiea. . &t
Neutralization of acids and bases 23
Neutrallzfttlofi of acids and bases, beat
of 26
New electrochemistry. 2
Newer theorle* of electrolysla 38
Normal electrode, Ostwald - 96
Organic and inorganic substancea,
comparison of reactlODB between-- 39
OrgAnIc compounds, electrolytic syntha-
sia of 44
Oamotic preeure and gas-preeeure, re
lationa between t
Osmotic pressure, Avogadro's law ap-
plied to 11
Oamotlc pressure, Boyle's law applied
to t
Osmotic presaure. Qay Luaaac'a law ap-
plied to I
Osmotic pressure, meaning of......,-. ft
Osmotfc pressure, measurement Of C
Oamotic pressure, results of measure-
ments 7
Oatwald's dilution law 70
Ofltwald'fl norma} electrode. 96
Reaction a between Inorganic and or-
ganic Bubstancee, comparison of... 29
Reactions, catalytic. .-....- ---... 28
Re lationa between oamotic pressure
and gaa-pre^ure. - 8
Relative velocitlea of tons, detorminA-
tton of 47
Relative velocities of Ions. iDfluenceB
which may affect 43
Results of conductivity measurements- G9
Eesulta of measurements of osmotic
pressure - 7
Rudolphi dilution law 72
Secondary batteries - - IDO
Semipermeable membranes. - - 6
Separation of the metsla, electrolytic. 43
SolntlDH'tenalOQ of metala. ...-..--.-.- SO
Sotutlon-tenBlon of metal a, constancy
of 07
Solutlon-tenaioQ of metals, demonstra-
tion of 82
Solution-tension of metals, determina-
tion of SB
Solvents, different dlssociatlns power
of 66
Specific and molecular conductlvitiea- - 56
Strength of acids and bases 16
Synthesis ot organic compounds 44
TeBtJng the law of Faraday- .......... 33
Thcorieg, electrochemical , 34
Theories of electrolysis - S2
lOS
INDEX,
Theorieo of electroljala, newer 38
Theories of electrolyata, older ., 36
Theory of electrolyftlH, ClauBloa' 37
Theory of electrolysis, OroUhuaa' . . . . . . 3G
Theory of electrolysis now In vogue. . . 40
Tbeory of electrolyala now In Togue,
tostlog 41
Theory of electrolytic disaociatlon. . . . . 13
Theory of electrolytic diaeocl&tlon, ap-
plications of ....,...._......,... . 23
Theory of electrolytic dissociation,
evidence bearing upon 18
Theory of electrolytic dissociation,
origin of IB
Theory of electrolytic dissociation,
testloK -.-........-.--...'--- 16
Pa<«.
Thomson overthrows obiecHon to the
electrochemical theory of BerEelius. 35
Two-metal elements 92
Types of elements, -,..._ _ . _ . 86
Velocities of ions 46
Velocities of ions, a periodic function
of atomic weights 51
Velocities of ions, absolute.....,,.^.'. G2
Velocities of lona, determination of
rtlative 47
Velocities of lone relative* determined
from Kohlrausch's law. . . .-^. • . . , 62
Velocities of ions relative, iDfluences
which may affect ... ^ ..... _ 49
Whetham's method of determining the
Telocltiee of ions. 53