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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&lt. 

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