N O T E S
E L E C T R OC H E M I S T R Y
. l E HMANN PH . D . F . G v C , y
N EW YORK
’ MCGRAW PUBLI SHIN G COMPAN Y 1 906
CHA LE R S H. SEN FF
A TO KEN OF
EST EEM AN D REGARD
P R E F A C E .
T HE principal aim kept in view in the preparation o f these notes has been the giving o f a clear and con cise presentation o f the general prin ciples which un derlie electro chemical
science . Endeavor has been made to meet the needs of students entering upon the study o f electro chemistry an d o f chemists interested in the application of electrical energy to chemical
problems . The literature o f electro chemistry counts as its o wn a ' number of standard works which treat in detail the theories
of the scien ce , the methods of electro chemical analysis , and D f e . the applications of el ctro chemistry i fering from these , the present notes aim merely to offer a general survey of the subject , to serve as an introduction to its study and to aid in the securing of a proper understanding and appreciation u of the work along individ al lines .
ha s In the chapter on ele ctrote chnolo gy , spe cial endeavor bee n made to secure the most recent and reliable data and full advantage has been taken o f the information given in leading techni cal journals and in the excellent monographs o f s : E m Wasseri er Lo u Foer ter lektro che ie g s ngen , and of : E Wright lectri c Furnaces and their Industrial Applications . It must howe ver not be forgotten that ex act data o f u technical operatio ns are o ften very difficult to proc re , and e therefore the figur s given , while well indicating the general s to conditions obtaining, cannot in all case clai m be actual
working formul ae. Prefacing each chapter there will be fo und a bibliography V i P PACE RE . o f important treatises bearing upon the subj ect- matter dis in cussed the chapter . The works so indicated have all been consulted in the preparation of these pages , and the writer would here take Opport unity to express his obligations to their authors .
. G F . W . AB L F T T E O C O N E N T S .
PRE F ACE
C I G I I S . HAPTER . ENERAL PR NC PLE
Gen e ra l Prin cipl es o f S cie n ce Ma tte r a n d Energ y
o m o f En e ea u e m ent o f a en o men F r s rg y M s r Physic l Ph a .
C II E I E G Y HAPTER . LECTR CAL NER Theo ri es o f Ele ctri c i tv R a di o - a ctivity F a cto rs o f Ele c
’ tri ca l Ene o e t e o f E e t t O m s La w rgy Pr p r i s l c rici y h .
C III E O M I S Y HAPTER . LECTR CHE TR
Ev o l uti o n o f El e ctro che mistry El e ctro lysis El e ctro
o e m o tive Fo rce Disso ci a ti o n V lta g .
C IV E O Y I D I S S O I I O HAPTE R . LECTR L T C C AT N
T he Io n T eo o n du t t a t o n o f o n h ry C c ivi y Mig r i I s .
C E O -A YS I S HAPTER V . LECTR NAL El ectro - a na l v sis Re ve rsibl e R e a cti o n s a n d Cells S o u rce s o f Cu rrent Current Mea s u rement Cu rrent Regul a ti o n El e ctro de s Cu rr rent Den sity Re co rds
Re umé s . C I HAPTER V . ELECTROTECHNOLOG Y — In tro d u ctio n Dire ct Actio n Pro ce sse s Electro depo siti o n
fro m So lutio n Electro pl a ting Chl o rin e a nd Alka li — Hydra tes In direct Actio n Pro cesses Electro depo siti o n
fro m Fu sed Ele ctro lv t e s Electro thermic Pro cesses
Electro -fu rna ces El ectro - fu rn a ce Pro du cts Electro
Orga n ic Pro cesses Dire ct Actio n Pro cesses Silent Dis
h a e E e t o -O mo c rg l c r s sis . N A M E IND EX S U B J ECT IN D E X
L TR H MI NOTES ON E EC OC E STRY.
HAPTER C I .
I GENERAL PR N CIPLES .
“ " a u e Rea d Refe n T a e V Liter t r : I G C . : e e o l I Ne w HER N , y r c bl s , . . 4 O M S W “ E Yo 19 0 . a tte ne o e a nd rk , . H L AN , M r, rg y , F rc , ” 1 9 N O Y S A A : Yo 8 . . e ne a N e w 8 . G n f Wo . e o rk rk , E , r l Pri cipl s ” ‘ N w Y 19 0 2 W M S en e e o . W D h a . C . P ysic l ci c rk , HETHA , . ” men f n e T he Re ent e e o t o a S e c . h a de a c D v l p Physic l ci P il lphi ,
190 4 .
ner l Princi les f en e Ge a p o Sci c . Before taking up for con
are sideration the subj ect to which these notes to be devoted , it will not prove amiss to refer briefly to some o f the general a ll principles whi ch underlie electro chemistry , as they do
e bran ches of physical scien c .
Scien ce is defined as systematized knowledge . Physi cal s its cience , in broader aspect , may be said to deal with all o f G h s i s phenomena nature , the reek word , p y , signify ing all
. P nature hysical scien ce , then , seeks to give a thorough o f presentation all natural phenomena , and to formulate principles whi ch will permi t o f the predi ction of such phe n mena o . There are two methods which may be legitimately followed n in scientific investigatio , experien ce , and speculation based o n experience . These two methods are mutually supple a ll mentary and interdependent , for , red uced to final terms ,
o n human science is knowledge based experien ce . The first step to be taken in experimental investigation is o f f the collection and accumulation acts . When a sufficient o f the number data have been secured , the more better , the 2 N ES E EC C EM IS O T ON L TRO H TRY .
o f proper grouping and correlation these data are required .
o f This is achieved by the process inductive reasoning . Induction consists in the drawing of con clusions from o f m observed facts , in the inference general principles fro
n o f the co sideration individual cases . e a But it is not always possibl pply the inductive method , owing to the great number and the complexity of natural
to phenomena , and , therefore , recourse is often had another
o f method reasoning , deduction . Deduction consists In the advan cing o f some general s u p position provisionally adopted to account fo r certain ph e h omena , and then submitting such supposition to the test of experiment . d All suppositions of this kind are terme hypotheses . An
hypothesis is , therefore , merely a tentative conj ecture as to
the nature and cause o f phenomena . All logi cal deductions
drawn from an hypothesis , unless supported by experimental
demonstration , are called theories . The crucial test as to the value and validity o f all hypoth
re~ eses and theories is , of course , their con cordan ce with
s ul s D f t obtained by experiment . iscovery of any act or facts no t in agreement with the tenets o f a given hypothesis
or theory , at on ce forces the modification or even abandon
ment of the theory . o f Deduction , then , consists in the derivation specific con el usions from a more general proposition ; it is obviously the
inverse of induction .
When a general theory , evolved by either the inductive or
the deductive method , has been submitted to and verified by
experi mental proof , it is termed a law . A law must not only embrace all known facts and phe . no men a to to which it refers , but must also be able account for all phenomena of like character whi ch may ever be dis l x . a w covered In fact , a must , to a certain e tent , be capable
of predi cting such phenomena . P ES 3 GENERAL PRIN CI L .
A law is simply a concise expression o f the results of ex es p eri en ce . As Whetham has so ably expr sed We must look upon natural laws merely as convenient shorthand statements of the organized information that is at present at
' o r s u dispo al . n r M co n Ma tter a nd E e gy . atter and energy are primary
‘ cepts employed to simplify and to systematize o ur impres sions o f n atural phenomena . Thetwo fun damental laws of physical scien ce are concerned with these concepts . These laws are the law of the conser
o o f m L 1789 vati n atter , due to avoisier , , and the law of the M T he s o of R 1842 . con ervati n energy , due to obert ayer ,
o f first these laws holds that matter , the second , that energy , can be neither created nor destroyed . If we are willing to accept an inseparable blending o f mat t s ub ter and energy , giving to this con cep the designation , o f a stance , then both the laws given may be in corpor ted as o ne : S , the law of substance ubstan ce can be neither created n o r destroyed . This law of substan ce is as far as human o f reason can con ceive a law of universal validity , a law h t e cosmos . o f Viewed as a component substan ce , matter must be regarded as its inert constituent ; it may be defined as that h a s x which e tension , whi ch o ccupies Space , which constitutes the tangible portion of the universe .
E o f co n nergy , the other component substance , may be s idered o f o f as the cause all changes , all physical phenomena . As Maxwell has expressed it : Energy that which in all natural phenomena is continually passing fro m o ne por E tion of matter to another . nergy cannot exist except in ” connection with matter . Y 1832 The term energy was first introduced by oung , in , 2 a s a designation o f the product mv ( v i s v i v a ) ; in the sense in is which it now commonly accepted , it has been used sin ce 1 about 860 . 4 N O ES ON E EC TROCHEJIIS Y T L TR .
o f The principle of the conservation energy , or , the first
o f fo r mu law energetics as it is sometimes called , was first lated by Robert Mayer a s a broad generalization fro m ex erimen a l 1842 p t e viden ce . About Joule furnished much direct and valuable experimental testimony of its truth , and every test ever made of this most im portant law has affirmed its correctness . Fo rms o f E er E f m n gy . nergy appears in vari ous or s , for
electri instance as mechanical , as thermal , as chemical , and as f cal energ y . These orms are mutually convertible , and when
o f o f ever a given quantity some one kind energy disappears , an exactly equi v a lent amount of some o n e other or o f several
o f other kinds energy appear .
There is , however , one li mitation that must be noted in
f o f this connection . Whereas all orms energy can be trans
o f formed into thermal energy , the complete changing ther
o r o f mal energy into mechanical , into other forms energy , c ff the annot be e ected . This prin ciple is known as second law of energeti cs . All forms of energy may be regarded as the product o f f s two factors , intensity and capacity . The ormer determine whether the energy in a given system must be active or at rest ; the capacity - factor determines the quantity o f energy f present in a given system . In all energy trans ormations a i p a rt of the orig nal energy is changed into heat , and thus , eventually , all energy is doomed to pass into this form ; at least at presen t no pro cess working to reverse this outco me is known . f n o f - Furthermore , in all trans ormatio s heat energy a part o o t f this energy passes t a lower emperature ; rad iation , con
t . d uction , and con vection aiding to bring about his result h - o f a Temperature , owever , is the intensity factor therm l f energy , and , as no wo rk can be obtained ro m heat unless ff t a s there are di eren ces in temperature , ul im tely , it seem , o f ff all energy must pass into the form di used heat . When
6 O HEM I T Y N O TES ON ELEC TR C S R .
° o f 4 cubic centimeter water at a temperature of Centigrade . It is represented by the one - thousandth part o f the Inter
“ a d o national kilogram , cylinder , ma e of the same alloy f which the standard meter is made ; it also is preserved by the M International Bureau of Weights and easures in France . Copies of these International standards are in the possession o f U G C . the nited States o vern ment at Washington , D .
C . G . S . The unit of time of the system is the solar second .
sI he - Thi s t g g l m; part of a mean solar day . The duration o f the latter IS o f co urse determined by the motion o f the earth
th s un e with respect to e , the interval between successiv
o f transits the s un over the meridian .
o f f nd a men a u a nti ies u G . . All the t l q t used in the C . S system are fixed and un variable ; and as definite amounts o f these quantities , the centimeter , the gram , and the second , have
s . S . C . G a b o been accepted , thi system is designated as an s f lu te system o units . The unit o f velo city adopted in this system is o n e centi
o f f meter per second . The unit force , that orce whi ch , acting o n o n e — o n e gram mass at rest , produces in second a velo city o f — one centimeter per second this is called a dyne . The unit o f energy is the erg : an erg is one dyne acting through o n e centi meter . Theun its o f all forms o f energy can be referred to the centi meter , the gram , and the second . In the measurement of he electrical energy there are two C . G . S . systems : t electro static and the electromagnetic system . In the electro ' static system all units a re based upon the force exerted between two quantities o f ele ctri c itv that amount o f elec tricity which attracts o r repels an equa l amount o f electri city ' h fo r o f o n e o ne centimeter distant with t e ce dyne .
We h o we e the m o t o n e n e nt mea u e o f m o d . t a b y i g , h v r , is s c v i s r ss , a n d o n e uent t e e two ter m a re f e u e nt th o u erro ne c s q ly h s s r q ly , g h sl n de e d no n mo u o u o . y , c si r sy y s E GENERAL PRIN CIPL S . 7
The electromagneti c system is based upon the force ex erted between an electric current and a magnetic pole . In this system the unit current of electri city is defin ed as that
a r c o f o ne current which , flowing through an centimeter ,
o f o ne curved to a radius centimeter , generates a unit mag
neti c pole at the center . . The electrical units in common use o n are b a sed this system . CHAPTER II .
ELECTRICAL ENERGY.
“ ite a tu e H A P a n d EV D N Phi : D S . . . . : a tu a L r r E C ANEL , , ERETT , J r l ” “ h y N e w Y 1 9 B F G u n r lo so . o 88 . . : d de Te p rk , HA ER , r riss ch ” n en E e t o e m e a u f T eo et he G u M n hen n d a e . i c isch l k r ch i h r isc r r l g i , “ ” C Re d Refe en e T V N 9 I G . : a a e l I w 18 8 . o e HER N , y r c bl s , . . B En Yo 1 9 0 4 . t a n a t o n W I Y . M rk , LE LANC , ( glish r sl i by H TNE , “ ” W E ement o f E e t o hem t o nd o n 1 9 R o . 8 6 . . l s l c r c is ry L , ” nn nnnc E En lis h t a n a t o n b SE E w w H s s . a nd , . ( g r sl i y , . . , “ E En n n N w Y B U e t a ee . e o 19 03 R NNER , l c ric l g i ri g rk , . “ ” O D E Ra d o -A t t a m d e 19 0 4 O R U F : . S Y THER R , i c ivi y C bri g , . DD , “ F : R a d o - A ti t a n E e men ta T ea t se f o m the Sta n d . i c vi y , l ry r i , r ” h T e N w Y o nt o f t e nte a t o n o . e o 19 0 4 p i Disi gr i h ry rk , .
ri es f E e tri i w Th eo o l c c ty . The ord electricity is derived
G electro n the from the reek , , amber , because manifestation
— a n —4 of certain electrical properties attr ctio , repulsion
fo r was originally noted in amber . Credit having been the n first to observe these pheno me a is generally given to Thales ,
who lived some two thousan d years ago . Introduction o f the word electricity is due to William
G o r Gilb erd 1540 ilbert , ( who has been named the
o f o f . creator the scien ce electri city His prin cipal work ,
M Ma neti cis ue Co r o rib us et M Ma De agnete , g q p , de agno g ” Ph s io lo ia N 1600 re nete Tellure , y g ova , published in , is p lete with interesting facts and observations o f magnetic
h a p eno men . Sin ce the days o f Gilbert inn umerable observations of electrical phenomena have been made , and a great number o n II f . S data beari g O them have been recorded till , although so o f o f a l much is known the properties electricity , and though electricity h a S unquestion ably become o ne o f the 8 I ELEC TR CA L ENERGY . 9
m o o f ost p tent agencies in the advan cement human welfare . the true nature o f electricity remains as yet an unsolved
problem .
u in At various times , vario s theories have been advan ced n expla ation of electrical phenomena . Thus , Benj amin Frank
170 —1 0 o n - fl i lin ( 6 79 ) suggested the e u d theory of electricity . All unelectrified bodies were supposed to possess a norm a l a mount of electri city ; a positively electrified body contained a o f s an ex cess , negatively electrified body , a deficien cy thi e lectri c fluid . Franklin was the o ne to introduce the terms positive and
to negati ve electricity . They are retained this day as con v entio n a l o ne e terms , indicating for thing forces in opposit d c irections , for instance , the direction of flow of electri currents . Du fa e 1733 two - fl uid t y , in , originally advan ced the heory
f m mm r o f electricity ; it was more precisely or ulated by Sy e . This theory holds that there are two kinds o f electricity positive and negati ve ; Imio n of equal amo unts o f the two
h n unelectrified forms the neutral fluid , w i ch is prese t in all d o f bo ies . The total amoun t electric fluid in a body is a constant quantity ; additional gain o f the o n e kind neces s i
o f tates an equivalent loss the other . Whenever an electri c current o f o ne kind flows through a cond uctor in o ne dirce
o f o f s tion , an equivalent amount current the other kind flow
in the Opposite direction . “ Both o f these fluid theories hold in co mmon that the electricity passing along a conductor — the electric current
is continuous in character . R o f ecent studies , however , made in the discharge elec
tri cit e y through gases , have brought about a decided chang o f view con cerning the nature of electricity . Such discharges o f electricity through gases are unquestion P ably convective . articles charged with positive , and par ti cles charged with negati ve electricity , are present in gases ‘ 1 0 N ES ON E E TROOHE M I TR Y O T L O S .
W n these parti cles , ions , whi ch term signifies a derers , can be
I b R6 nt en - induced n gases y g rays , by ultra violet light , and by other means . They mo ve under the influence of elec tri ca l r energy , and it is thei motion which constitutes the e lectri c current .
o f h Fro m the researches J . J . T o mson it appears that the n egatively charged p arti cleS thus present in a gas have a mass of approximately one one thousandth that of a hydrogen a to m ; positively charged parti cles of similar dimensions are not known . h The electron theory , the theory whi c pro mises to become
he r e f t leading theory of elect i city in the imm diate uture , is A based o n these studies . ccording to the electron theory o n e d I there exists but kin of electricity , that whi ch s gen e ra ll y designated as negative electricity . This negative electri city is assumed to o ccur in defin ite o f the unit charges , and these smallest parti cles electrici ty , a toms of electricity , are termed electrons . “ The term electron was originally given by G . Johnstone Stoney to the definite charges o f electricity asso ci a ted with i o f ons ; the con cept electrons as separate , distin ct individual H e p articles was only arrived at later . ow ver , in this con ' n io n i K f e ect t . . C is interesting to recall that W li ford , as arly a s 1875 : , made the following statement There is great reason to believe that every material atom ca rrIes upon it a small
e o f . lectric current , if it does not wholly consist this current
In a substance whi ch is electri cally neutral , the electrons a re so disposed with respect to the balan ce o f the matter that there is no eviden ce o f an outside electric field . o f t c In a substance which bears a positive charge elec ri ity , o f A b i there is a lack , a deficiency electrons . su stan ce wh ch
o ir is negatively charged has an excess f electrons . As S “ William Crookes has expressed it : A so called negatively m o n e o f n charged chemi cal ato is having a surplus electro s ,
' the o n tlIe v a lenc s io n number depending y , whilst a po iti ve E T I A ENERG 1 EL C R C L Y . 1
’ f i s o ne having a defici en cy of electrons . Di ferences of elec tri ca l charge may thus be likened to debits and credits in
’ o ne n s banking account , the electrons acti g as current coin of h t t e realm . On his view only the electron exists , it is the , o f w e ato m electri city , and the ords positive and negativ , s o f electro ns ignifying defect and excess , are only used for l n c onvenien ceo f o d fashioned no me clature . : i - t u Ra d o Activ i y . In this connection reference m st be had to the subject of radio activity , a theme so intimately c theo rv o f o f oncerned with the electrons , and vital interest and importance o n account o f the far reaching influen ce it is exerting o n the present trend of phy sical science in par
ticula r o f i n e . , and scientific thought gen ral i Discovery o ft he X ra y s by ROntgen ( 1895 ) led to numer o us researches to determine whether analogous radiations
o u t r . might not be given by othe substan ces Thus , Bec in 189 6 r - querel , , disco vered the adio activity of urani um , 1 9 o f r Mm . M. e . G C. S 8 8 chmidt , in , that tho ium "and and
’ M Be s i n C . urie , together mont , al o the year last ‘ with r m named , isolated the new element adiu from the mineral pitch blende . R o ut a 8 adium gives three kinds of rays , named the , and
- y rays . The a -rays are material particles bearing ch arges o f posi t ive electricity . They have a mass equal to abo ut twice the mass o f a hydrogen ato m ; they move with a v elo citv abo ut o n - i e e. tenth that of light , . , abo ut miles per second , and - are readily arrested by an air gap of a few centimeters , o f a ml by paper , and by thin layers luminium foil . The lu i nous phenomena Shown by the S p lnth a l‘ lS COp e o f Sir William ‘ Crookes are caused by the i mpact of a particles on a screen o f l o f e o f mo v m su phide zin c , th se imp acts the swiftly g par
In e o a Be t In n m 190 V o l I n t . e . 3 . th rigi l , rich V A g Ch , , “ ” “ ” . 9 6 the wo d defe t a n d ex e a re nted in e p , r s c c ss pri r verse 7 o de “ . G . r r F . . 1 2 N OTES ON ELEOTROCHEJI IS TRY
a ti cles evoking the flashes which make the screen . appear seething s ea of light . The B-rays are in all probability identical with the cathode rays which appear at the negative electrode o f a vacuum
- tube o n the passing o f an electric discharge . These Brays c onsist o f negatively charged particles having a mass o f approximately o n e one -thousandth the mass o f a hydrogen atom ; they tra vel with a velo city approximatin g to that o f o f t tt a re light . The minuteness hese li le particles will be p p
Sir C who c ia ted fro m a comparison made by William rookes , ’ if n o ne stated , that the su s diameter were taken to be about
o n - f o f and e hal million kilo meters , and that the smallest planet
- f t t o f o id about twenty our kilometers , hat hen , if an ato m
to o f hydrogen were magnified the size the sun , an electron
- o would have a diameter about two thirds that f the planetoi d . The fl- rays are the chief agents in the photo - activity o f
L a - - the radium rays . ike the rays , the Brays are also de ‘ fle ed to ct by a magneti c field , but in a direction O pposite
a - that in which the rays are turned . The y - rays are more penetrating tha n either the a o r
- Brays . They are not deflected by an electric field , and thus far no proof has been furnished that they are material par
o ti cles ; possibly they may be ethereal vibrations analogous t ,
o r ROn t en . even identical with , the g rays re Considered as a whole , radium rays exercise certain s u b markable influen ces . They evoke luminosity in so me
o f stan ces , in sulphide zin c , for instance , and in diamonds ; they destroy the po wer o f germination in seeds ; they can
e o f s xtend the larvae stage some insects , and can cause burn
and even brin g death to living organisms . The property which radium rays p ossess of ionizing dry a ir t o f and other gases , hat is , making these substances con
d u cto rs o f o f detec electricity , is taken advantage for their tion and fo r the mea surement o f the strength o f radium
a t prep rations . This de ermination is accomplished by bring
4 EM I 1 N O TES ON ELEC TROCH S TRY .
An interesting hypothesis to account fo r the usual positive
“ ' ’ electrification of the atmosphere a rfd fo r the negative electri
fi ca tio n b s P E of the earth , has been a ed by rofessor bert on
h - t e activity of radio emanations . He holds that these ema nations in passing fro m the earth into the atmosphere impart their negative charge to the capillaries of the soil thro ugh t e which hey pass , and thus enter the air with high positi v
to s . charges , whi ch they transmit the atmo phere F f a ctors o Electri ca l Energy . If one chooses to look upon
r electricity as a form of energy , then electricity , like all othe
o f forms energy , may be viewed as the product of two fac
- - tors , an intensity factor and a capacity factor . The intensity - factor o f electrical energy is termed its p o ten ti a l o r tension ; the capaci ty- factor represents quantity o f
. fo r electricity To compare electrical with thermal energy ,
instan ce , electri c potential corresponds to the temperature
of thermal energy , electric capacity corresponds to heat
capacity . Heat always passes from objects of a higher to obj ects o f a lower temperature ; the exten t o f heat - exchange between two poin ts o f unequa l temperatures is determined solely by ff the di eren ce between those temperatures , but is wholly o f independent the absolute temperatures . In a similar manner the passing o f an electric current between two points is determined by the differen ce in
- tension potential between those points . When positive elec tri cit o f y passes from a point higher to a lower potential , a corresponding amount o f negative electricity must be co n
cei v ed o f n as passi g in the opposite direction . This may , in
a way , be regarded as analogous to the conception that a given amount o f cold is raised to a higher temperature when ever an equal amount o f heat passes from a higher to a lower temperature . Pr e t s o f E c i c — E op r ie le tr ity . lectricity may be con veyed from o ne location to another either by means o f conductors E E G 15 ELEC TRICAL N R Y .
s no n o f the in which there i evide t , Simultaneous mo vement o uc o f matter of which the c nd tor con sists , or by means sub stan ces in which a transportation o f ma terial particles a o
e o n companies the transferen c of the electri c charge . C du cto rs o f the former kind are known as Conductors o f the the m a d b first class ; metals , etalli c sulphides , n carbon elon g Co n d u cto rs o f to this gro up . the other kind are called con g
“ d u cto rs the of second class ; to these belong the salts , the w u acids and bases hen in sol tion , and salts and bases also
when m a state of fusion . While the do main o f electro chemistry lies essentially with
l a ttentio n conductors of the second class , for the moment sh all be given to the pheno mena to be noted when a current
o f e n o f the fo r lectricity flows along a co ductor first class , W instance , along a metal ire . If a plate of copper an d a plate of zin c are placed in a “ two vessel containing dilute sulphuric acid , and the metal
plates are connected by a metal wire , outside of the fluid ,
observation will Show that this wire soon becomes heated , and if a break is made anywhere in this wire s o that an air
I two o f gap ntervenes between the ends of the wire , a spark light will appear the instant the break is made . r If the wi e remain unbroken , a magnetic needle brought
e near to it will b deflected fro m its normal position . If the
o f wire be wo und around a bar soft iron , the iron beco mes
magnetic , and remains so at least as long as the wire en circles
it . If the wire be cut or broken and the ends inserted in u acidulated water , b bbles will arise fro m the water , and the water will be found to suffer deco mposition into its compo nent elements , oxygen and hydrogen gases . These phenomena make evident that some pro cess is taking — a n place electric current is passing along the wire , and the phenomena referred to establish the fact that an t n electric curren can induce heating , lighting , mag etic and h f c emical e fects . 1 6 N O TES ON ELEC TROCHEM IS TR
There is e vidently a force at work which drives the electric f current along the wire . I we use two galvani c elements ii i e o f - o f 1 st ad one , connecting the zin c plate element No . with
- o f 2 the copper plate element No . , and then lead a connecting
- - w . 1 N 2 ire from the copper plate of No to the zin c plate of o . , a much stronger current will be secured than if only o ne h element had been used . It appears that t e pressure driving w the electric current along the ire has been in creased . The p ressure thus forcing the current along the wire is termed f o f electromotive orce , and the unit in terms which this is measured is the volt . The International volt is that electromotive force which will maintain o n e International ampere through a resistan ce o f o n Fo r e International ohm . practi cal purposes it is re d 1 ° presente by 1 of that of a Clark cell at 5 C.
o f o f is The cause the flow the electric current , as has been s f ff aid , a di feren ce in the electrical pressure , a di erence in e ff o f lectrical potential between di erent parts the circuit . Water standing in two connecting vessels will remain at rest w henever it stands at the same level in both vessels . If , h w f o f o ever , there is a di feren ce level in the two vessels , then the force determined by the differen ce in height o f these levels will cause a current of water to flow from the higher to the lower level . By analogy we can conceive a similar dif feren ce in electric pressure to be the cause of flow o f a n electric current . The rate o f flow of an electric current per second is termed
. C its current strength urrent strength , or current intensity , i a s s . it also called , is measured in amperes The International t ampere is the current which , under specified condi ions , will d eposit gram o f Silver per second . Amperes are comparable to the flow o f water measured
o f v in some unit olume , for instance , in liters or in cubi c f o f 20 eet per second . Thus , a flow of water liters per second u o f 50 o f 40 nder a pressure kilograms , in creases to a flow I A E E G 7 ELEC TR C L N R Y .
o f 1 liters per second under a pressure 00 kilograms . In an a nalogous manner an electric current of 20 amperes under a n electri c pressure o f 50 volts is changed to a current o f 40 amperes under a press ure of 10 0 volts . Amperes do not
r decrease by doing work , neithe does a volume of water
o f grow less in consequen ce doing work , driving a turbine , for instance ; the work done is in dire ct ratio to the drop in p otential o r pressure . II the I passing through a conductor , electric current has to
o n o vercome the resistan ce in its path . The longer the c d - uctor , a wire , for instan ce , and the smaller its cross section , the greater is the resistance to be overco me . In other r words , it may be said that the resistance varies di ectly as the length and inversely as the cross—section of the conductor a long which a current flows .
Resistance is measured in units called ohms . The Inter n ational o hm is represented by the resistan ce o f a column 0 n o f C . mercury at 0 centimeters lo g , weighing
- g rams , and having a uniform cross section . The resistan ce met by an electric current in its flo w is directly comparable to the friction en countered by a current o f water flowing t t hrough a pipe ; there , too , the fri c ion varies directly with
he o f t length the pipe and inversely with its diameter . The names o f the electrical units thus far considered are derived from the names o f men eminent in the development
o f . electrical scien ce Thus , the volt is taken fro m the name o f Alexander Volta ( 1745 the ampere fro m that o f André Marie Ampere ( 1775 the ohm fro m that of Georg Simon Ohm ( 1789 hm ’ s L O a w. There is an intimate relation between the
electromotive force , the current strength , and the resistance o f an electri c current .
If these terms be represented by their initial letters , thus ES ON ELEC‘ TROCHEM S T Y NO T I R .
‘ f
E o m fo rce . E lectr otive , Resistance
the - expression C i ca tes that the current . strength i s
u to . eq al the electro motive force divided by the resistance .
This is the famous law of Ohm , the discoverer o f the relation here expressed ; it i s a law of fundamental impor tance in electrical science . By transposition we have
E C
E CR,
stren th ' is o f and as the unit of current g the ampere , that
o hm o f c v resistan ce the , and that electromotive for e the olt , these formul a express that :
Amperes volts ohms ,
Ohms volts amperes , x Volts amperes ohms .
o In addition t the units discussed , there are several others l e which are frequent y used in consid ring electrical data . ‘ The coulomb ‘ is the u nit o f electri cal q uantity ; the word
“ ' r is derived fro m th e name o f Charles Augu stin . Co ulomb ( 1736 The International coulomb is defined as the quan tity Of electricity transferred by a Current o f
o nati onal a mpere in ne Second . Sometimes the quantity o f electricity transferred wb y a
' ‘ ‘ c u rrent o f o nei a mip ere in o ne hour is employed as a u nit ; - is —in this is called an ampere hour , and a unit much used l o h mi r e ectr c e s t v . E E I A E E C C N G . 19 L TR L R Y .
a M The f rad , derived fro m the name of ichael Faraday
1 9 1 u o f ( 7 is the nit electrical capacity , for instance ,
o a l c of a c ndenser . to hold electri c ch rges under e e tric pres
o r sure stress . The capacity in farads equals the charge in
co ulo mbs di vided by the electromotive force in volts . The
a fo r unit ctually used , however , measurements of electrical
- o ne o ne o f . capacity , is the microfarad , millionth a farad The watt is the unit o f electrical power ; the name com memo ra tes James Watt ( 1736 the pioneer o f modern
- the o h steam engineering . The power in watts is p roduct n R ta ined by multiplying volts a d amperes . epresenting
e P w pow r by , the various relations bet een power , electro
a nd motive force , current strength , resistan ce are indicated F 2 P '= by the formul a : P EC ; P ’ G R . The de R
p endence of electri c power o n both curren t strength and voltage is evident fro m a consideration of the analogy pre l v io us . y introd uced In that case , it will be recalled , the work effected by the flowing water was determined by both
- the difference in height between the two w a ter levels an d b v .
o f m o f the amo unt water passed . One kilogra water flowing
” n o f o ne u fi v e dow a height h ndred meters , will do times the work that is done by o ne kilogram of water flowing down
' f a . o height of twenty meters . The power falling water is thus meas ured in kilo gra mmeters per unit o f time (second o r minute) kilo gra mmeters per second are one metri c horse
' The flow o f water p er . seco nd corresponds to the electric current strength ; the wa terép ress u re due to the dif
o f the r - its : 73 5 544 8 ference wate levels , to voltage Thus ,
o ne - e watts are equal to metric horse pow r . One tho usand
- w t o n e a ts are called kilowatt , and are equivalent to metri c hors e
1 H - mete P . rs '
- l w a tts . H P 10 0 0 w a tt . . . s 20 N O TES ON
o f o r Th e The unit electrical energy work is the joule . term is derived fro m the naine of James Prescott Joul e ( 18 18 who practically prepared the way for the s cien tifi c study o f thermodynamics . A current o f o ne International ampere flowing through a resistan ce o f o n e International ohm for one second does one
o f joule of work . Joules are the product coulombs and w t . volts ; in o her ords , joules represent watts per second If the ampere - hour is taken as the unit o f electrical quan
o f o r tity , the corresponding unit electrical energy work is the volt - ampere - hour ; this is generally designated as the
- 1000 - m o n - watt hour ; watt hours are ter ed e kilowatt hour . The relation between electrical energy and heat energy w 1 1 a s 84 . clearly established by Joule , in This relation is “ expressed in the following law which bears his n ame : The heat generated in the whole or in a part o f an electri c circuit
o f t to in the unit ime , is proportional the resistance and to
o f he the square t current s trength . Experimen tal study has shown that ( a p p ro x i w t 1 — mately , a ts per second correspond to calorie the calorie being defined as the amount of heat necessary to raise ° ° the temperature o f o n e gram o f water from 15 to 16 hy
r to o n e o ne d ogen scale . This is regarded as equivalent hundredth o f th e amount o f heat. that will ra ise the tempera ° ° o n o f f o 1 1 ture of e gram water ro m 0 t 00 C . th erefore calorie is the heat equivalent o f o n e o ne the joule , and this means that joule will raise ° o f o temperature gram f water 1 C .
o f fo r The unit inductance is the henry , named Joseph Henry ( 179 7 This unit is used in measuring the intensity o f that property in virtue o f which changes of
o r o f current in the circuit itself , changes current in an a dj acent circuit , produce electromotive force . The henry is the quotient obtained by dividing induced volts by rate o f
change of amperes per second .
” A CH PTER III .
ELE TRO HEMI C C STRY.
Lit “ ‘ e a ture : F R D P . : G u nd der e nen u n r E CHLAN , r riss r i d a nge wa ndten ” E e t o em A “ e . . S . 19 0 B F 3 . : l k r ch i HALLE , HA ER , . Gru ndriss ” der Te n en E e t o e m e a u f T eo et e G u n d a e ch isch l k r ch i h r isch r r l g , 1 “ e 9 . O E m n 8 8 . C . : e e t o f a em L ipzig, J NES , H l s Physic l Ch istry . N w Y “ e o 190 2 . O C : O u t n f E . . e o e t o em rk , J NES , H li s l c r ch istry . N ew Yo 19 0 1 B E . . n t a n a t o n I rk , LE LANC , M ( glish r sl i by WH T ” N E W . Y . T he E e men o f E m t e t o e t . o n do n , l s l c r ch is ry L , “ 189 6 . B C M : e u de r E e m e . t o e . e LE LAN , L hrb ch l k r ch i L ipzig, 1 ” 9 0 3 . LE H F E LDT R . A E e t o em t a t I Gene a , l c r ch is ry , P r , r l “ T eo . N e w Yo 19 0 4 O T W L W : E e m . . t o e e e h ry rk , S A D , l k r ch i , ihr “ Ge te u n d 1 9 6 W I M e e . e 8 . G : Le . . e schich L hr L ipzig , ECH ANN , F tu e-no te o n T eo et a e m t N e w Yo 1 9 . 8 5 . r s h r ic l Ch is ry rk ,
u i n f E ec r ch emi s r E c Ev o l t o o l t o t y . le trochemistry Is the study of the mutual relation and transmutation o f electric a l a nd chemical energy . It deals with electri cal phenomena which are caused by chemical reactions , and with chemical e changes which result fro m the appli cation of electri cal nergy . Perhaps the earliest instance o n record of the bringing about of chemical change by electricity is the reduction of metallic zinc a nd mercury from their respective oxides by B u eccaria , abo t the seventh decade of the eighteenth century , who achieved his results by sparking the oxides of the metals named by discharges from Leyden j ars . In 1775 John Priestley discovered that electric sparks
0 passing through air a cidifv the air . Priestley believed that C the acid produced was carbonic acid , but avendish , re peat x P ing the e periments of r iestley , showed that nitrous and nitric acids were formed . M R Ten years later Van arum in otterdam , subjected many 22 E E O EM I L C TR CH S TRY . 23 ga ses fl a n d meta llic substances to the discharges o f a p OWer - f ful electrical riction machine , and among other chemical changes which h e thus effecte d was the d ec o mposition o f ” ' “ - - . co m o nen s ni en . t alkaline air (ammonia) into its p , trog and
Electrolyti c decomposition of w ater into air (hydrogen) and life ' air a cco mplished , 17 9 Pa ets Tro o stwi k Deima nn C e in 8 , by van j , , and uthbert n i ‘ a e s o . Their exper ments were most carefully m d with ’ distilled water and with wa ter fro m which the absorbed air had been remo ved under vacuum ; they thus pro v ed the
' o f o es h a wa er , belief . t t t consists hydrogen and xygen gas to be well founded . The ' speculations which were indulged in at that time h r regarding t e natu e of electricity are interesting . By
wa s . l s ome , electricity held to be a substance dua in its char a cter which entered into un ion with the elemental co nstit neu ts o f the compounds decomposed by its influence ; others believed it to be a highly con centrated form of fire and a c counted fo r its great powers o n that supposition so to The experiments far referred to , all relate the produ ction o f chemical effects by the agen cy o f electrical energy . The first attempt recorded to produce electrical phenomena by chemical agencies is the ex p eriment ' ma de by Al L L w essandro Volta , avoisier , and De aplace , hich con S isted in electrifying an isolated metallic plate by placing o n h r it , respecti vely , basins with burning c a coal and dishes in which s ulphuri c acid was po ured over iron filings . 1782 a t About the same time , in , these investigators t b ut ff tempted , al hough with indi erent success , to generate electricity by the evaporation o f water and the subsequent
' b een led t o condensation of the vapor , Volta having the conception o f this idea through his st udies o f atmo spher ic c electricity , in which he had noticed indications of the p resen e
" o f electric charges in rain a nd in fog. 24 N OTES ON E E T O HE MIS T Y L C R C R .
An incidental observation made during some physiological x G U t e periments led Aloysius al vani , professor at the niversi y
179 1 v e o f f of Bologna , in , to the disco ry a orm of electricity
' " iit anima l co n cl ud until then unknown ; he styled electricity , ing that the electricity thus made manifest in his ex p eri ments was produced by the brain o f the animals o n which w he orked , and that the electricity thus segregated fro m
- the blood passed through the nerve channels into the muscles , L these being practically a kind of eyden j ar .
the o f G Volta , although he originally shared views alvani , was gradually led to abandon the supposed biological origin o f f these electrical mani estations , and ultimately Showed
wo their origin to lie in the contact of t dissimilar metals . This discovery led him to establish the contact theory of
1792— 1793 v ea rs electri city , , which held sway for many . 1800 a n o f In Volta published account the voltaic pile , which made it possible to produce galvanic electricity “ ” t a s metalli c electri ci y , Volta termed it in sufficient quantity and of sufficiently high potential to permit o f a study of chemical actions induced by the electric current .
o f f The beginning electro chemistry proper may , there ore , be
f o f said to date rom the in vention the voltaic pile , although
no t P Fa b ro n i o f it sho uld be forgotten that rofessor , Florence , “ 1792 o f in , had suggested chemical action to be the nature ” o f the new stimulus , in speaking electricity evoked by the immersion of metals in water . 1800 S w In , the ame year in hich Volta announ ced the
o f the C construction voltaic pile , arlisle and Nicholson effected the electrolyti c decomposition o f water by means o f
a such a pile , an experiment which , it will be rec lled , had 1 already been made by the aid o f fri ctional electri city in 789 . Carlisle and Nicholson also noticed the chemical reaction s
t . taking place within the voltaic pile itself . A lit le later Dr o f M E f deco m Henry , anchester , ngland , e fected the electrolyti c
o f o f u . position ammonia , nitric acid , and of s lphuric acid HEIWI T Y . ELEC TROC S R . 25
r 180 1 D . Wollaston , in , ascertained that silver can be electrolytically plated with copper , if the silver , in connection with some metal more positive than itself , is immersed in a
1 03 His s in solution of a copper salt . In 8 Berzelius and ger effected the electrolytic deco mpo sition o f water and of some
C s u neutral salts , while abo ut the same time ruickshank g gested the use o f the electri c current for the analysis o f
the - minerals , he having Observed electro deposition of silver ,
t . copper , and lead fro m so me of heir respective salts In
- II 180 5 the electro deposi tion of gold O Silver , and the electro
b Bru n a elli deposition of zin c were disco vered y g t . In this same year Von Gro th uss o ffered an explanation to h account fo r the electrolytic deco mposition of water . At t e
o f o f o f instan t such decomposition a molecule water , the hydrogen is charged electrO p o siti v ely and the oxygen electro negatively . The former is repelled fro m the positive pole and is attracted to the negati ve pole ; the oxygen is repelled fro m the negative , and is attracted to the positive pole . The initial work the electri citv was supposed to perfo rm wa s o f b e decomposition the water molecules . This had to d u f one ere electrolysis co ld be ef ected . When the electri c current had entered the water , the hydrogen atom adjacent
a nd to the negative pole gave up its charge to that pole , .
o f having become electrically neutral , separated in the form hydrogen gas . The oxygen ato m which had been in union
t the he with this a om , combined with hydrogen atom of t next water molecule , and thus the impulse passed alon g
e until the last oxygen atom , in contact with the positiv n pole , had its charge eutralized by the charge of this pole , and then escaped as oxygen gas . The first decade o f the nineteenth century also witnessed the separation of several o f the alk a li metals from thei r Sir hydrates , by Humphrey Davy ; thus , potassium and sodium were first obtained by him in this manner in October , 1 0 7 8 . ‘
2 6 E . O ELE HEM I T Y N 0 T S N C TROC S R .
— . s Led her e o b he su r e I) a v . ad t t y t re lts of his expe iment , y
f ’ v a nce d l t ro b ab l he ffi rs t " his electro chemica heory , p y t theory
- — o f its kind e v er. formula ted ; it rests upon the a to mic hypoth
f : a s o f e o D t . r sis al on Acco ding to its te ching , the atom " s es a s no electri c the a c u ire ubstan c such bear charges , but y q
positive o r negati ve charges by contact with each other . Chemi cal affinity is caused by a nd depends o n the attraction
o f o E s such opp site electrical charges . lectrolytic deco mpo i
f o f tion is e fected by the neutralization these charges . ’ ~ e o f i This th ory Davy s met w th considerable opposition ,
a nd u was soon displaced by the views advanced by Berzeli s ,
o i n 1 812 . utlined . and published in detail two years later Berzelius held that every atom was charged with both
positive and negative electricity , and that the electrical behavior o f the atom depended upon whichever o f these
a wa s charges w s present in excess . Chemical attraction also ascribed to electrical attraction between opposite charges ; o ne o r o f the the other these predominated , and in accord a n ce therewith the resultant compound exhibited either an
e lectropositive or an electronegative character .
Objections to this theory of Berzelius were , however , ‘ not
lacking . It was held that if the electri cal charges of the t atoms determined chemical union , hat then the properties
o f a compound must be a fun ction of those charges . The fact that three atoms of chlorine (electronegati ve) co uld be p ut in the place of three atoms of hydrogen (electropositive) o f the methyl group in aceti c acid without causing a funda
m o f ental disturban ce of the nature the compo und , was an o n bstinate fact which Berzelius could not acco u t for .
fo r . . 1 895 to It remained J J Thomson , in , Show that an
e e s l ment may , according to circum tances , bear either an “ o r electropositive an electronegative charge , and that it s the would appear that the chlorine atom , in chlorine deriv o f atives methane , are charged with electricity of the same ” a s kind the hydrogen ato ms they d isplace . EM I T Y 27 ELEC TROCH S R .
’ M a The b rillia n t work and disco veries of ichael Farad y ,
“ e 11 832 the t he b ginning in , mark next important epoch in
history of ele ctro chemistry .
“ Faraday first determined the identity o f electri city p ro
’ ‘ d u ced by friction and by the voltaic pile . When he had
s . to b e e stablished this , he turned his attention the relation tween the amo unt o f electri city passing through a circuit ff and its magnetic and chemical e ects , and fo und that the a mo unt of chemical decomposition produced in an electrolyte i s proportionate to the amount o f electricity which passes
’ ’ thrOugh the electrolyte . Faraday further studied the relation between the amounts o f different elements set free from their compounds o n pass
‘ ing a given electric current through solutions o f these com n poun ds . Among the substances which he investigated i t n o f o f v his manner were solutio s some salts copper, of Sil er ,
the a mo un s l o f f and o f zinc . He thus determined that t di fer ent elements separated by the same qu a ntity o f electric ity, stand in the same relation to each other a s the chemical e quivalents of those elements . This means that all mono o f valent atoms bear the same amount electricity , and that all m o f ulti valent atoms bear some Simple multiple this amount . It must be especially noted that these laws o f Faraday e mphasize the fact that equal qu a nti ti es o f electricity sepa rate chemically equivalent amounts o f the elements ; the e e the n to ff l ctromotive force , pote tial necessary e ect this , i s no t referred to at all ; this factor has di fferent values ff with di erent electrolytes , as will be discussed later . In 1857 Clausius pointed out the shortcomings of the
" t b y Gro th uss heory ad vanced , and suggested that solutions
- o f an electrolyte must contain some part molecules in . addi
‘ - entire mo lecul es . tion to non decomposed , This hypothesis o ffered an explanation of the fact that even very a l wea k
The chemica l equ iva lent o f a n el ement is the a to mi c ma ss o f tha t e ement d ded b its a en l ivi y v l ce. \ ' O ES ON E E TROCHEM IS TR I' 28 T L C .
ff currents , in so me instances , can e ect electrolysis , the cur rent exercising a directing influence o n the part- molecules o f originally present . This work Clausius practically pre
fo r o f pared the way the theory electrolytic dissociation , l which was brought out thirty years ater . ’ f It was in 1887 that J . H . Van t Ho f published his valuable o article on the r le which osmotic pressure plays in solutions .
’ o f This paper , in the same year , inspired the hypothesis P lan ck , based on thermodynamical considerations , and the theory of electrolytic dissociation ad va nced by Svante
' o f Arrhenius , who was able to furnish experimental proof P ’ the truth of lan ck s assumptions , and who thus established the famous theory which to - day holds the leading place in electro chemical scien ce . This theory will later be con in s idered detail .
Electro lysis . Conductors of electricity in which substance mo vement of the cond ucting material accompanies the pass
' o f o f ing the electric current , have been termed conductors l the second class . In this category are in c uded all solutions
which can cond uct an electric current , and also all fused salts which can act as conductors . They are all designated b v the term electrolytes , and the parti cles into whi ch mole cules of electrolytes dissociate are termed ions . These ions are particles o f matter associated with definite
. AS his charges of electricity Von Helmholtz , in Faraday L 1881 i “ lecture delivered in ondon in , expressed t: If we a ccept the hypothesis that the elementary substan ces are o f t composed a oms , we cannot avoid con cluding that elec tricit t y also , positi ve as well as nega ive , is divided into f n n o f de i ite eleme tary portions , which behave like atoms electricity . As long as it moves about in the electrolyti c io n fluid , each remains united with its electric equivalent , . o r equivalen ts .
The terminals of the wires b v which the electric current. e nters and leaves the electroly te a re called electrodes : the
N TES E HEM IS TRY 3 0 O ON EEGT ROC .
R 1902 - ichards , in , to avoid confusing voltameters with volt V o f a re meters . arious forms co ulometers used ; the most
s . m n a ura e .ins ru e t cc t t of the kind, is probably the Silver coulo
e th a ho de~ meter in which metalli c Silver is pr cipitated on e . c t
r neutra l n so lutio n o f r f o m a nitrate of silve , the anode con
: o f sisting o f a bar pure Silver . Copper and mercury c oulo meters of an alogous construction are also frequently employed . In the former , both electrodes are o f metalli c Copper and the electrolyte is some salt o f
o f . In copper , generally sulphate copper . the me rcury coulo
a s mer meter some mercurous salt is used the electroly te ,
c u ro us fo r . n a ho nitrate , instance Both a ode and c t de co nsist
‘ o f m a lli c mer c ur a et y in glass recept cles . Another favorite form of coulometer is that in w hi ch the electrolytic decomposition o f water is effected v o f a in which the olume the resulting gases is me sured .
a nd n These gases , hydrogen oxyge , may be caught either m n separately or together , and their volume easured . O e
o ne . o f h ampere in min ute sets free C C . t ese mixed ° - mm . 7 0 . 0 C 6 . e gases , measured at and pressure In thes gas coulometers a solution o f sodi um hydrate or dilute sulphuric acid is generally used ; if the former , the electrodes are preferably made o f nickel ; if sulphuric a cid be employed as the electrolyte , the electrodes are both made of platin um . AS the q uantity of electri city passing thro ugh any given
n c ed co du tor is determin by the current strength , measured
‘ a ndnthe 'z time a n in amperes , during which the current flows , identical quantity o f current will flo w and an identi cal
o f l o r l — amount work , electro ytic other , will resu t, whether , fo r n c 100 Aa m eres fl o w 5 o r - r 250 insta e , p for seconds , whethe
a m ufl o w fo r 2 ‘ t ha th e peres seconds . It will be recalled tm " amount o fr electricity con veyed by o ne ampere in o ne;se c o n d
is the r u a ntit o f e eC termed a coulomb , and that this is q y l tri city which will deposit
ldm er co u et . a E EC C EM I $ L TRO H S TRY , 1. _ 3
t b e' equivalen t of silver . This erm must well distinguished w e fro m the expression chemical equivalent or equivalent ight , l h . t t e as it is also called The latter , i wi l be remembered, is o n a n quotient obtained di viding the , ato mic weight of ele E a i h . e c s t e ment b y its valency lements whose v l n y one , so - r called monads , have thei chemi cal equivalent identi cal E with their ato mic weight . lements whose valen cy is two ,
u o ne- r dyads , have their chemical equi valent eq al to half thei
‘ o ne- ato mic weight ; in triads, it is third the atomi c weight , ‘ e om x is etc . In the cas of c ple ions the equivalent weight
the — S um o f the equal to molecular weight that is , the
io n di v ided atomic weights of the co mplex , by its valen cy . _ ’ " o f i t Application of Faraday s second law , course , makes p a Simple matter to calculate the electro chemi cal equivalent o f - every element when - the electro chemical equivalen t o f any one element has been accurately determined exp eri mentally . let c To illustrate , a determination of the electro hemical f equivalent o z inc be required .
2 co n The ato mic weight of zin c is its valen cy is , and sequently its equivalent weight is 2 Accept
‘ ing the ato mi c weight o f Silver as and its valen cy a s t o f t one , hat quantity electrici y which will deposit grain of silver must deposit o f zinc :
: x
e h This value is therefore the el ctro c emical ; eq uivalent o f * Zin c . The chemi cal equiva lent weight-o f a subs tan ce in - grams is termed a gr am eq ui valent o f tha t s ubstance To deposit
if ’ An excellen t ta ble o f ElectrOChémi cal Eqmv a le nts ahd the ir Deri v a tiv eS B a He n , y C rl ri g , M
ew Yo a nu a 1903 . N rk , J ry , 3 2 N ES ON ELEC TROCHEM IS T Y OT R . o ne gram equivalent o f any element requires an amount of e lectricity , in coulombs , equal to the chemical equivalent of t its tha element divided by electrochemical equivalent . to Thus , deposit one gram equivalent o f Silver requires
. 00 1 118 coulombs . This value varies
f t e slightly with di feren experiment rs . The electro chemical
‘ equivalent of sil v er wa s found to be :
L R Mr s . S by ord ayleigh and edgewick ,
. K by W and F . ohlrausch ,
R C Heimwo o d by i chards , ollins , and , P Guthe by atterson and ,
by Kahle .
A o f ccepting the ato mic weight , and hen ce , course , the c o f hemical equivalent silver , as and employing the s everal electrochemical equivalents above given , the deter mination by :
L R Mrs S ord ayleigh and . edgewick coulombs , K W . and F . ohlrausch coulombs , R C Heimwo o d ichards , ollins , and coulo mbs , P Guthe atterson and coulombs , K ahle coulombs .
We will accept the value coulombs a s the ioni c charge for a mono valent gram ion , this being the value usually e mployed . It can be readily shown that coulombs are required to to o ne o f deposit or liberate gram equivalent any element , a nd o f : a this quantity electricity , viz coulombs is c lled
n o f i n a faraday . This co stant is the greatest importan ce o ne electro chemical work , for on passing faraday through an electrolyte there is always s et free one gram equivalent o f io n he o ne a an at t cathode , and gram equi v lent of an ff ion at the anode , provided that the electrolysis e ected is s imple and not complex . 33 ELEC TROCHEM IS TR Y.
o ne set If co mplex , that is , if more than kind of ion is f o n o f s um o f ree at e the electrodes , the total the ions thus s et free at that electrode amounts to one gram equivalent .
o f o ne Thus , in the electrolysis water faraday causes the liberation o f grams o f hydrogen at the cathode and o f
grams of oxygen at the anode . If , however , in the electro -analysis of an alloy two metals were to be simul ta neo usl s um y deposited on the cathode , then the of the gram equi valents o f these two metals so deposited would corre
n r s p o d to the work done by one fa aday . o ne Taking the chemical equivalent of hydrogen as unity , coulomb will liberate
00 1 1 1 x . 8 z
o f gram hydrogen .
t L R a s This value , which was de ermined by ord ayleigh K gram , and by ohlraus ch as gram ,
o f is the electro chemi cal equivalent hydrogen . The chemi cal equivalent o f any element multiplied by the electro chemi cal equivalent of hydrogen is , of co urse , the electro chemi cal e o f quivalent that element . Designating the chemi cal equivalent of any element by Z o f , the actual weight in grams such element deposited . by electrolysis is calculated by the formula : w t ,
weight in grams ,
o f chemical equi valent the element deposited , 0 current strength employed (in amperes) , t o f o f time passing current (in seconds) .
Or , designating the electro chemical equivalent of the ele z ment deposited by , this formula becomes :
w z et .
F T HE 34 N ES ON E EC C EM IS OT L TRO H TRY .
T If the time be measured not in seconds but in hours , ’ 0 7 - s a then represents ampere ho urs , that is to y , the quan
o ne tity of electri city con veyed by the current in hour , and the formula first gi ven would read :
w 0000 10 36 x 3600 ZeT ,
w Ze T ,
fo r u or , all practi cal p rposes ,
' ' w Zc l .
o f C Fro m this formula the amo unt current , , is readily de d u ced which is required to set free or to deposit a given
w : weight of an element , , in a given time
3 73 w . 0 ] Z T
t to d o The electrical power , in wat s , needed this work is calculated by the formula :
E o in which represents the electro m ti ve force , the voltage , employed . At times the actual amount o f chemical action obtained
fo r take , instan ce , the weight of a metal which should be deposited in an electro chemical pro cess — does not corre ’ s p o nd with the amount called for by Faraday s laws . There is so me diversity o f O pinion con cerning the causes P f C * dif o f such discrepancies . ro essor rocker attributes the
fi cult o f a s y , in some instances , to the liberation hydrogen g in place o f the metal which should be deposited ; this setting free o f the hydrogen may be due to an excessive current
” f ne u te V o l 22 1 9 1 . S o o o a . . ch l Mi s Q r rly , , p E E HEM I TR Y 35 L C TROC S .
i to o o f dens ty , to great a dilution the electrolyte , or to the great affi nity which some metals have for oxygen , the con sequent decomposition o f the water resulting in a liberation o o f f hydrogen . An insufficient yield metal may also be
o f due to a resolution So me of the metal by free acid , such acid being so metimes added in order to impro ve the con
f B u i i o . t d u ct v ty an electrolyte whatever the cause , if a discrepancy exist between the output actually obtained and the theoretical yield correctly figured according to Faraday ’ s laws , the fault of such discrepancy will be fo und not to rest with the latter . E r m i F E lect o o t v e orce . lectrical energy has been defined a s o f the product two factors , quantity and intensity of electricity . Attention has been given to the former phase o f o w the subj ect , n electromotive force must be considered . Electromotive force is the pressure which drives an electri c current through a conducting medium ; other terms employed to designate this concept are voltage and differen ce o f p o ia l tent . The source o f the electro motive force in an electrical cell is to be sought prin cipally at the points of contact o f the electrodes with the electrolytes in which they are res p e c ti v ely immersed ; this electromotive force is practically due to chemical action between the metallic electrodes and the chemical solutions in whi ch these are placed . In order that a chemical reaction may give rise to electro
u its motive force , the s bstances con cerned in generation must
o n e be located apart fro m another , but must be in electrical connection with each other through the agen cy of a metallic conductor and an electrolyte . Whenever the substan ces
o f which are on one and the same side the equation Sign in a .
s true chemical reaction are placed under the above condition , an electro chemical pro cess o ccurs . Consider the reaction
Cu S0 4 S C Zn Zn O. u . 36 ES ON ELEC TROCHEM I T Y NO T S R .
It will be recalled that these substances form an electro lytic cell when they are arranged so that they meet the
prescribed conditions ; that is to say , when the zin c is away from the copper sulphate and the co pper is removed from
b o th . a re the zin c sulphate , but when in electrical connection by the intervention o f an electrolytic medium and a metallic
- . f wire The system here re erred to is , in fact , the well known Da niell cell . C onversely , if under the conditions stated , electrical energy is introduced into an electrolyte , chemical changes are caused a nd electro chemical reactions are bro ught about . f . m To e fect measurement of electromotive force , it is eces sary to establish standards for comparison a n d to have instruments by means o f which these standards may be
e f compar d with the electromotive orce to be measured . An accumulator battery supplies a reliable and uniform source o f current ; a direct lighting current can also be used for this purpose \ by causing it to pass through proper resist a n ce an d by using a part o f the current for the work in hand . It is custo mary to employ either Clark cells o r Weston C t f admium cells as standards ; of these the lat er are pre erable , because they are scarcely affected at all by changes o f tem
era u re p t . Instruments u sed to record voltage are either direct
. to reading voltmeters , or potentiometers As it is desirable have these instruments use as little current as possible , they
' are generally constructed with high resistan ces , this being insured by employing n umerous windings of exceedingly fine
- wire . If a hot wire instrument is to be used as a voltmeter , w it must , of course , be put in series ith high resistan ce . Vol t meters are not as desirable as p o tentio nz eters because they consume some current and require o ccasional reca lib ra ' a o tentio meter tion . To measure electro motive force with p , the unknown force is balan ced against the electromotive
3 8 E ON E E OC E MIS NOT S L C TR H TRY .
P o f ossessed such thermal data , the heats of formation , there only remains to be learned the relation between the un it o f heat energy and the unit o f electric a l energy in order to make possible a cal culation o f the electric potential re q uired to effect electrolytic disso ciation .
o f n h The unit heat e ergy is the calorie , the amount of eat required to raise the temperature o f 1 grain o f water from ° ° 1 o f 5 16 C . . a to , hydrogen scale The unit electric l energy is the joule — the product obtained by multiplying the
o f n e coulombs and the volts an electric current . O joule ° t a t o f n o f 1 C . will raise the emper ure grai water , 1 hen ce , in round numbers , j oule calorie .
K o f o f e nowing the heat formation an el ctrolyte , it is only necessary to divide this n umber by to ascertain the j oules req uired to effect the electrolytic decomposition of
a n d the f the compound , joules thus o und , divided by — o r a multiple thereof — equal the n umber of volts re to f quired e fect the desired electrolysis .
K wa s Lord elvin the first to make calculations of this kind .
is It , however , important to remember that such calcula tions involve acceptan ce o f the assumption that a ll of the
m o f a chemical energy lost , reappears in the for electric l lw e n o a . nergy . This , however , is by means ays the case ’ fo r C e SO In some reactions , instan ce , in lark s c ll (Zn Zn 4 H SO 25 g2 , Hg) , about per cent of the chemical energy
a . lost ppears as heat In other instan ces , however , the a greement between the calculated values and the values
m r iS ' v er experi entally dete mined , y close . Thus, for the a e ] SO Cu SO Cu n D ni l cell ( Zn Zn 4 4 ) , the disso ciatio
a a voltage is , c l cul ted , volts ; experimentally deter m 0 ° e C . s . in d , by Jahn at , volt To illustrate the cal cul a tion o f dissociation voltage let us consider the electrolytic dissociation o f potassium chlo ride .
o f f o f K Cl is The heat o rmation calories . The E E T E M TR Y 3 9 L C ROCH IS . amount o f electrical energy equivalent to this amo un t o f f heat energy is , there ore ,
“ 3 joules ,
-3
hen ce , volts is the minimum voltage required to de compose potassium chloride into its constituents , potassium and chlorine .
o n e One faraday , coulombs , will decompose gram molecular weight of an electrolyte of which both components are monovalen t . Potassium chloride is such a compound ;
the ato mic weight of potassium the atomi c weight of chlorine = hen ce , the molecular weight of potassium chloride
o r u Therefore , it will require j o ules , co lombs at a potential of volts to decompose gra ms o f
n : a m o f potassium chloride into its constitue ts , viz gr s
o f potassium and grams chlorine . If the electrolyte to be decomposed h a s a divalen t co n s tituent 2 a X 2 l , far days cou ombs will
f a nd be required to e fect the desired electrolysis , it is this number which must be di vided into the joules required , to ascertain the mini mum disso ciation voltage . This minimum disso ciation voltage may also be readily calculated by divid ing the heat of formation of the compound , expressed in n f a l n i . e. o calories . by times the v e ce , the umber f n bonds . This actor , is obtained by dividi g
o for ne calorie is equal to joules .
Thus , in the case of potassium chloride , where the valence is o ne o f : , and the heat formation is calories
volts .
M l In the case of magnesium chloride . g C where there 40 N O TES ON EL EC TROCHE MIS TRY
the are two bonds to be considered , we would have taking M Cl heat o f formation of g 2 as calories :
x 2] volts . The disso ciation voltages thus found are valid for elec
l e tro y tes in aqueous solution . Fused electrolytes requir to a so mewhat lower voltages , because the heat of fusion , certain degree , assists the reaction . CHAPTER IV
ELECTROLYTIC DISSOCIATION .
W En t a n a t o n R a n d Z . V ite a ture : AB G G . L r E , , HER , ( glish r sl i by CAL E RT , “ ” 1 1 A K m t o n d o n 9 0 . T : H a t a e . . . Pr c ic l Ch is ry L , RND , “ ’ m ” B r im b e riffe der a e m e n en a he n e e . e n G d g llg i physik lisc Ch i rli , “ F n d a to en der A d m et e u n d Al a 0 0 G S . : 19 . LA E R , I ik r ci i ri k li ” “ N E x ment l W e a den 19 0 . O PK I . O O : e a m etrie . i sb , 1 H NS , M NR E p ri ” K O H L U S C H F a n d HO L N ew Yo 190 5 . . Ele ctro che mistry . rk, RA , , “ ” 1 O L Da s Leitv e r mO e n der E e t o te . e 89 8 . B RN , g l k r ly L ipzig , “ m L M e u d e r E e t o e e . e 19 0 3 . B C . : LE AN , L hrb ch l k r ch i L ipzig , “ ” m a t I Gene a T he o A E e t o e t . R . : E L D T . LE H F , l c r ch is ry , P r , r l ry “ e r E m e B W Gru n dz ii de e t o e . N w Yo 19 0 4 . O . : e rk , L E , g l k r ch i “ W : Die W en a ft en G un d a en O W . Le 1 89 7 . ipzig , ST ALD , iss sch lich r l g ” der An a t en e m e . e i 19 0 1 . K I . ly isch Ch i L ipz g , PER N , F M ” et o d o f E e t o em t . o n do n 19 0 5 . Pra ctica l M h s l c r ch is ry L ,
o n Th eo r . E D Th e I y The Theory of lectrolytic isso ciation , o r a s the Ion Theory , it is frequently termed , was formulated S by the Swedish scientist , vante Arrhenius , now professor in S the University of to ckholm , after he had become acquainted ’ o f ff e with the brilliant researches J . H . Van t Ho ; these wer “ 1887 Réle o f published in , in an article entitled , The Osmotic P ” ressure in the Analogy between Solutions and Gases . By the term osmotic pressure there is understood th e pressure exerted by the molecules o f a substan ce in solution when such solution is brought into contact with the pure w solvent , or hen such a solution is brought into contact with f ‘ another solution of a di ferent degree of concentration . All substan ces when dissol ved in water exhibit osmotic pres sure .
. c s .o f a s et b u The true au e osmotic pressure is y unknown , t the pheno mena o f os motic pressure have been carefully 41 4 2 N O TES ON ELEC TROCHEMIS TRY studied and some very important relations have been deter
mined . ’ ’ Van t Hoff s theory of osmotic pressure holds that th e osmotic pressure o f a substance in solution is the same as the pressure which that s ubstance would exert if it were in the gaseous form and o ccupied the same volume at the same
a o f temper ture . In other words , the laws gases apply also to dilute solutions ; the laws o f g a s - pressure are valid also fo r the osmotic pressure of sol utions . The ga s - equation p v R T states that the product of the volume a nd the pressure o f a gas is directly proportional
o t the absolute temperature and to the value R . p v R IS a constant In the equation o f state fo r gases
f - o f 1) . o a s volume in cc a gram molecule the g ,
p pressure in grams per square centimeter ,
T absolute temperature .
The molecular weight in grams ( 1 mol ) of a g a s at ° f h C. 76 . o a s 0 and cm Hg pressure , a volume of
o f 1 it liters ; in the space liter must , therefore , exercise a
o w o f . N pressure atmospheres it follows , according to ’ f ’ Van t Ho f s theory , that the osmotic pressure , exercised
o f 1 o f 1 m by a solution mol a substance in liter , ust like wise be equal to atmospheres . A solution o f this kind ( 1 gram - molecular weight o f a s olute in 1 liter ) is called a normal solution . A normal solution hen ce exercises a n osmotic pressure " o f atmospheres ; a tenth - normal solution exercises an o o f a o n smoti c pressure tmospheres , and so . e if It is vident , then , that the osmotic pressure of a solu ' is m o le cula r wei ht tion known , that the g of the solute can
be readily determined .
' ~ A 1 per cent solution o f sucrose gives a n o smo ti c pres
o f o f sure cm . Hg . L TROL YTI SS A T N E EC C DI OCI IO . 43
A normal solution o f sucrose would give a pressure equal
x 76 cm . H
The 1 per cent solution contains 10 grams o f sucrose per liter , hence
10 : x 2: 3 45 .
This is in close agreement with the molecular weight of s ucrose as calculated
0 12 x 12 = 144
H 22 >< 1 = 22
0 1 1 x 16 = 176 342
Many solutions which w ere examined in this way yielded returns which were found to agree with this theory and
a er which bore out its assumptions . But it was soon s c
ta ined that all the salts , acids , and bases did not behave in
accord a nce with its teachings . Solutions o f these substan ces gave osmoti c pressures gr ea ter than they would have given had they acted in co n f formity with the laws o gases . It wa s furthermore determined that those substances which in aqueous sol utions exert an osmotic pressure greater
o f a s - than is called for by the law g pressure , likewise cause
in f - o f greater lowerings the reezing point water , produce
o f - ff w g reater elevations the boiling point , and e ect a lo er
- o f : ing in the vapor tension volatile solvents last , but not
wa s o f least , it found that aqueous solutions these substances ,
a nd u these only , could cond ct the electric current .
o f To meet the exigen cies . the case it was proposed to
73 - s introduce an additional factor into the gas equation , thu making the latter read :
") p i RT . ’
15wa s f i f . This factor termed the Van t Ho f , ro m its originator H MI Y 44 N O TES ON ELEC TROC E S TR .
In all of the substan ces named , the salts , the acids , and h w t e i . the bases , value of is al ays greater than unity
o n o n e Arrhenius , reflecting this problem , the probabl ’ ’ cause of these n umerous discrep a ncies between Van t Ho ff s
o f f theory osmotic pressure and the results ound , recalled the analogous c a se o f ab normal v a por- pressures exhibited by iodine a n d by so me other substan ces when their vapor pressures were determined a t high temperatures In these inst a n ces the explanation had at last been relu e
t t o f autly accep ed , that a disso ciation the molecules prob ably o ccurred at high temperatures ” t e Therefore , wrote Arrhenius , it is na ural to assum that substan ces which in aqueous solution give pressures
to o diss o cia tet that are great , are likewise Arrhenius outlined his theo ry in a letter which he addressed i n a o f 1 7 to L se creta rv the the early p rt 88 Oliver odge , of
British Associ a tion Committee fo r Electrolysis . So mewhat later in the same year a full discussion of his views appeared
Tra ns a cti o n s o t e S wedi s h Aca dem o S ci ences in the f h y f , in w a 1883 r hich journ l there had been published , in , anothe C o f e article by Arrhenius , Galvanic onductivity Very Dilut ” S a Aqueous olutions, in which he may be s id to have , in
o f c a measure , foreshadowed the theory electrolytic disso ia f 1 7 tion whi ch he ormulated in 88 .
o f o f the The essen ce of this theory Arrhenius is , course , deduction th a t the osmoti c pressure exercised by the par ti cles into which molecules ma y beco me dissociated is the s a me as the osmo tic pressure exercised by the molecules themselves .
w io n t a e s In other ords , the theory holds , h t in dilute aqu ou " m ll a r i cles o f d solutions there are more s a es t. p t the dissolve ‘ substance (the solute ) th a n correspond to the molecula r weight o f the substan ce ; th e theory ac counts for this b v
a o f assuming th t a number molecules are disso ciated , elec tro l i ll t ca . y y disso ciated , in such solution
4 6 E E T E T N O T S ON EL C ROCH MIS R Y.
ca thio ns in derer ; cathion means descending , because the the electrolyte mo ve with the positive current towards th e
s cathode ; anion means ascending , to indicate that the anion
h e ca hi move in a direction opposite to that taken by t t o ns .
This terminology is due to Faraday .
Willia ms o n in 185 1 C 1857 , , and again lausius , in , assumed that a s mall portion o f ions preexisted in solutions and that these were capable of conducting the electric current ; these
- particles were designated a s part molecules . 1887 v In , however , it was generally belie ed that the elec tric current itself induced the breaking up o f chemical co m pounds into the particles which con veyed the electric charge thro ugh solutions capable o f conducting electricity . It was Arrhenius who determined that the number o f e pre xistent ions might be considerable , and that , up to a o f certain limit , dilution the solution increased their number . An equivalent amount o f positive and o f negative elec tri cit v n e y must always be con eyed by the io s , for no fre
t e electricity can be de ected in solutions of electrolytes , hen c fo r w every cathion hich separates at the cathode , an anion
u must give p a corresponding electric charge at the anode .
fo r Ions possess definite electric valen cies , and every dyad
o ne d o r ion which separates at electrode , another dya ion
two monovalent ions must separate at the other electrode . Among the more i mportant mono valent ca thio ns are K H (in the acids) , , Na , Ag .
Among the divalent ca thio ns
Ca M - , Ba , g , Fe (in ferro compounds) ,
Among the trivalent ca thio ns
A1 Sb f - , Bi , , Fe (in erri co mpounds)
Among the mono valent an ions
Cl NO 0 10 OH (in the bases) , , Br , I , 3 ELEC TROL YTIG DIS S OCIA TION .
Among the divalent anions
S SO Mn O , 4
The following table of the chemi cal elements in their
N M . electro chemical sequence , is given by . onroe Hopkins Each element is electropositive to every element whose
is its is name placed before own , and electronegative to all elements whose names follow its o wn
to N ega ti v e A ms .
Fl u o ri n e Chl o ri n e
ms P o s i ti v e Ato .
Pl a ti n u m Rho di u m Ru then i u m Pa ll a di u m Me rcu ry Silve r Co ppe r Ura n i u m Bism u th Ga lli u m I ndi u m Ge rm a n i u m Le a d Ca dm i u m Tha lli u m Co ba lt N icke l Iro n Zin c Ma n ga nese
no t f e It must , however , be orgotten that the t rms posi tive and negative in electricity are merely relative it all depends on the conditions in which the substan ces are placed . N OTES ON ELEC TROCHElli IS TR Y.
If two metals are placed in a solution which attacks the o ne no t metal and does attack the other , the metal which goes into solution is electropositive to the other metal ; the metal which goes into solution forms the negative pole in the outside circuit . Zin c is attacked by dilute nitric acid and by dilute s ul
h u ric o f p acid , and even in solutions ammonium chloride and pmotassium hydrate it will go into solution replacing other etals ; zin c , therefore , is electropositive to them all . It h a s been previously explained that all ions o f the same valency bear identical electric charges , although the masses o f the atoms with which these charges are asso ciated are not equal . Ions , in short , may be regarded as combinations of ma
ria l o - te s . ato ms with electric atoms , with the called electrons Ions o f different substances vary considerably in their
- a ffin it i electro y , that s , in the degree of power with which they hold their electric charges . Those ions which hold their electric charges firmly are termed strong , those which r As eadily part with their charges are called weak ions . a o f rule , strong ions are given to the forming soluble com
di sso ma te pounds , co mpounds which readily when brought
W o n a into solution . eak ions , the other h nd , are generally o f w given to the forming co mpounds hich are less soluble , t o f u hat is , to the forming co mpo nds which ionize only to a slight degree when placed into contact with a solvent . If an ion o f a low degree of electro - a ffinity en counters a n o n - ionized substan ce which p o ss es sess a greater degree of
- a ffin it electro y when in the ionic state than it itself possesses , then the electric charge will be transferred from the former o t the latter .
Fo r instan ce , if metallic zinc is. brought into contact with lead in the ionic condition the lead suffers precipitation as
metallic lead , while the zinc goes into solution , zinc ions being
. L reci i formed ead precipitates copper ; copper , in turn , p p
so . tates mercury , and on ELE TR YT S S A T N 4 9 C OL IC DI OCI IO .
When an electric current i s passed through an electrolyte the ions move through the solution to the electrodes and
o f he there give up their charges electricity , pro vided that t tension o f the electrodes is sufficient to overco me the electro f a finity o f the ions for their electric charges . When this
un happens the ato ms separate in their elemental condition , less they take part in so me secondary reactions in which
n e w they enter in to chemical relations . The capacity o f forming ions does not depend alone o n
v the substan ce which goes into solution , the sol ent plays n an important role in this tra saction . This property is
’ f o f re erred to as the dissociati ve power the solvent . Water , a s w previously mentioned , has a high disso ciant po er ; formic disso i n acid , methyl and ethyl alcohol are fairly strong c a ts . Ch loroform , ben zol , and many other organic substan ces lack t this dissociant power entirely ; these subs an ces are , there f is n o t ore , not electrolytes , that , they do conduct an electric current between electrodes immersed in them . Gram- molecul ar equivalent solutions o f most neutral salts
1000 o f are practically co mpletely ionized in liters water . As a rule , salts containing monovalent ions are ionized to a greater extent than salts o f multivalent ions .
hv d ro chlo ri c The strong acids , among which must be co unted , d hydroiodic , hydrobro mic , nitric , and sulphuric aci s , are under like conditions all ionized to about the same degree as the s alts . Phosphoric and sulphurous acids are usually ionized to the extent of only 10 per cent ; silicic acid and boracic acid are hardly ionized at all . Walker and Cormack have determined the degree o f ioniza tion o f the following substan ces in o ne-tenth normal solutions
Hydro chloric acid . Acetic acid Carbonic acid Sulphuretted hyd rogen Boracic acid N O TES ON EL EC TROCHEM IS TR Y
’ ‘ Among the strong bases are the hydroxides o f the alkalies and the hydroxides of the alkaline earthy metals . Ammonia. and magnesia are bases of a lower degree of ionization , and the hydroxides of the di and tri - valent metals and most o f a the alkaloids must be counted mong the weak bases . The ion theory has proven o f special value in the sec u r ing o f a clearer understan ding o f the problems of an alytical
is chemistry , and it is to Wilhel m Ostwald that scien ce
fo r n chiefly indebted signal achieveme ts in this direction .
o f o f ma y The study many , if not most chemical reactions , be regarded as a study o f the behavior o f ions , for ions have and preserve certain individual characteristic properties , which they exhibit without regard to the presen ce or absen ce o f other ions and molecules . The properties of aqueous solutions of most salts are but the sum o f the properties o f their constituent ions . That this point o f view materially simplifies analytical chemistry is evident when o ne considers that inste a d o f hav to o f ing study and to remember the reactions , say , one
f neces hundred di ferent co mpound substances , all that it is sary to know are the reactions o f ten ca thio ns and ten anions whi c h enter into the composition o f the abo ve - named one hundred co mpounds .
a n d The terms salt , acid , base , have here been repeatedly n used , and it will be necessary to give their definitio s as
o f o n h o rv understood in the light the i t e . Salts are com n po u ds which , when they are dissolved , break up , wholly
ca thio ns 1 . or in part , into and an ons Acids are salts in which the ca thio ns are always hydrogen ions ; bases are salts in which the anions are a oxyl ions . Strong acids are those tain numerous hydrogen ca thio ns in unit volume — for the characteristi c properties o f h ro en acids depend o n their v d g ions . Strong bases are those which contain ma n v hydroxyl
“ fo r an ions in unit volume , it is upon the presen ce of the p L YTIC S S A T N O] ELECTRO DI OCI IO . hydroxyl ions that the characteristic properties o f bases depend . u Acidity and basicity of solutions hence rest solely pon , " o f and vary with , respectively , the amount hy drogen and o f hydroxyl ions present . The hydrogen ions o f acids behave differently from hydro gen o ccurring in other co mbin ations ; the hydro xyl ions o f bases likewise react differently fro m the hy droxyl gro u ps o ccurring in other co mpo unds . Thus , the hydrogen ions o f acids will redden litmus ; the hydroxyl ions of bases will
a n turn red litmus blue . Water d hydrogen peroxide both n contain hydrogen and hydroxyl , yet either shows the above
a n mentioned reactions with litmus . Water d hydrogen n a s no t n peroxide are , therefore , at on ce recog ized belo ging
o r to either the acids bases . P ure water is ionized only to a very slight degree , less
o ne me ] s a less 18 r ra ms in than , that is to y , than g liters — 14 grams is the figure that approximates more ff . o ne closely to the real value To express it di erently , in million liters of water there are grams of hydrogen ions and grams of hydroxyl ions . These values are ° o f 1 o f the values for the temperature 8 C . The number ions in a given solution 1n crea ses very rapidly with the o f 8 n temperature , approximately at the rate per ce t per
1s so e is degree . As water slightly disso ciat d , it but n atural that hydrogen ions and hydroxyl ions when they meet in a solution should 1mmedia tely combine to form
- non disso c1a ted water . Fro m the viewpoint o f the io n theory the neutralization o f no t an acid in an aqueous solution is looked upon , as the
o f a s union an acid with a base radical , but the union of the hydrogen ions of the acid with the hydroxyl ions o f the base ; the pro cess o f neutralizatio n in an aqueous solution
hence consists essentially in the formation of water .
o f o f r : The heat neutralization , for instan ce , the eaction
HCl N a OH N a C1 H O , , 5 2 N O TES ON ELEC TROCHEMIS TR Y is due to the heat o f chemical combination o f the hydrogen
ca thio n s ions with the hydroxyl ions , the sodium and the i chlorine anions rema ning un changed in the solution . Bearing in mind that an ion consists o f the ato m of an
o r a c element plus one , two , three , more electri c charges cordin g to its valen ce a fraction o f the unit charge is never
ca n ff carried ions , in writing , be readily di erentiated from the a toms of elements by addin g to the chemical symbols fo r the latter so me con ventional sign to indicate the char
o f f acter the electric charge the ions bear , and to speci y the n umber of these charges . A s mall circle o r period has been selected to represent a
o r charge of positive electricity , a dash a comma , to typify a negative charge ; the number of these symbols indicate the number of electric charges borne by an ion . Thus , an
’ ion of hydrogen is represented by the symbol H , an ion of ' Ca Cl calcium by the symbol The anion chlorine , is ; ” H' O . oxygen O ; the complex anion hy droxyl ,
wa s The term ion , introduced by Faraday , by him em ployed in connection with the stems of the chemical names of substan ces to indicate the substan ces fro m which the ions f h . t o a s originated A systema ic nomenclature the ions , w ho ever , as yet , not been adopted , although James Walker “ h a s proposed a system of naming , as he expressed it , the material o f the ions as distinguished fro m the particles them ” a hio ns selves . C t he would indicate by adding the termi n i o n to o f ation the stem the word , and; when necessary , wo uld disclose the electrical valen cy o f the io n by p refi xin g a Greek numera l . Thus he suggested
h mi ca l s 1 1 4 1 2 e w 0 V l . . N e 9 o 8 6 . C , , , p
54 N TES ON L TROCHEM IS TR Y O E EC . the product o f the ions present in a solution bears a fixed relation to the amo unt of non - disso ciated molecules in that solution . ' l This formu a is an interestin g one . Nernst determined that the concentration of the non -disso ciated molecules does not change in a saturated solution ; in a case where both m and K are un changing the product ca must also have a constant value . This product is termed the solubility pro I duct . t represents the n umber o f grams per liter to which the con centration - product of the ions can attain and yet have the ions exist as ions in the solution . Should one add to a saturated solution wherein such an
ha s a n equilibrium obtains , any other solution which ion in common with an ion of the solution first named , then the equilibrium would be disturbed and the solubility - prod uct f having been exceeded , the respective values would su fer readj ustment . This indicates the condition which must be es tablished in order to secure a practically complete precipitation of any given substance , an excess of the pre i i in c p ta t g reagent must be employed . The same prin ciple applies to the washing o f precipitates ; in order to avoid the solvent action o f the washing-fl u id care mu st be taken to have the washing - fl u id contain ions identical with some of those instrumental in forming the precipitate .
- The ions of most of the lighter weight metals , and those o f the halogens , are colorless ; those of the heavier metals are colored ; for instance , cobalt ions are red , nickel ions
- o f and di ferri c ions are green . The use indicators in aci dimetry and alkali metry is based o n th e fact that in the in di c a to rs used the color o f the no n - disso ciated molecule is
o different fro m the color o f the ion o r ions formed therefrom . The ion theory affords a plausible explanation o f the phe no mena involved and it will be of interest to consider a case w a s in illustration ; phenolphthalein , hich is much used an
i . ndicator , will answer the purpose E E TR YT S S A T N L C OL IC DI OCI IO . 55
The formula o f phenolphthalein is Its co n figu ration is proba b ly WC H OH C C H OH “O H
o - co
P is is to s a henolphthalein a weak acid , that y , it ionizes in
- water only to a slight degree . Its non disso ciated molecule ' is H is x colorless , its cathion colorless , its co mple anion is '
. P red This anion shall here be denoted by the symbol . P . If KOH is added to a colorless (alcoholic ) solution o f phenolphthalein there will be present in the solution ’ ' a h P : H c io ns P . Ions fro m phenolphthalein t and . anions ; ' KOH : K‘ ca thio ns Fro m the solution and (OH ) anions . The H' ca thio ns of the phenolphthalein will combine with ’ the (OH ) anions o f the potass ium hydrate and form non
- n o f H' ca hio n disso ciated water molecules . Abstractio the t s w o f ill , however , induce other molecules phenolphthalein to dissociate in order to restore the equilibrium indicated by the formula Km ca
These reactions continuing , there will ultimately be present in the solution an accumul ation of K ‘ ca thio ns and o f co m x ple phenolphthalein anions . The latter , as previously s - so io n - tated , are red and hen ce says the theory the
o f red color the solution .
m - By eans of the reactions indicated , the potassium salt o f As o ta s phenolphthalein has been formed . a rule the p s ium salts of weak acids are ionized to a greater degree than the acids fro m which they are formed . In consequence , the solution contains toward the end o f the reaction a
o f e greater number phenolphthal in anions , and these impart th e red color to the solution . a n If a strong acid , hydrochloric acid , for inst ce , be added to s o f l a olution this description , then there wou d be present in the solution : 56 N O TES ON ELEC TROCHEJIIS TRY
Ions fro m the potassium-salt o f phenolphthalein : K‘ ’ c hio n a t s P P . . and . anions ' Io ns m : ‘ c a thio n s Cl fro the hydro chlo ric acid H and anions .
‘ The H ca th io n s wo uld come into cont a ct with the phe no l htha lein a a nd a s o a o f p nions , the i nization const nt phe n o l h th a lein a w o f its m p , eak acid , is smaller than that potassiu
‘ c a th io n s the salt , the H and phenolphthalein anions would
- recombine to form non disso ciated phenolphthalein . These molecules are colorless and in consequence the solution would lose its red color whi ch , it will be remembered , was caused by the phenolphthalein anions . The solution wo uld again turn colorless . Litmus is an acid indicator ; a z o lithmin is its active color m - d g principle . The non isso ciated molecules are red , the
o f anions are blue . Addition a base to litmus results in
f o f the ormation water and of a more highly ionized salt , and the blue colo r of the anions imparts a blue color to the
o f a solution . Addition a strong acid to such solution will cause so me o f the original n o n - d issoci a ted red molecul es o f f litmus to re orm , and , in consequen ce , a red color will again appear . If titrations are attempted in very dilute aqueo us solu ' ‘ ‘ c a thio ns o f ) r tions , then the H and the (O H ) anions the wate will take an active part in the reaction . This pheno menon
to a s o r . is referred hydrolytic dissociation , hydrolysis Hydrolysis is apt to prove a serious cause o f disturbance when weak acids o r weak bases are titrated . In the case
is s a thes e of strong acids and strong bases , that to y , with h is a that are ionized to a considerable extent , ydrolysis matter of but little mo ment .
‘ o f i is f b y An example hydrolytic disso c ation a forded , the ' o f n sodium salt phenol . On ionizatio this yields Na cath '
C H O . ions and phenol G 5 anions The latter enter into chem ' ical union with the H c a thio n s o f the water used as solvent
a nd a s C H OH . , a result , phenol , s 5 , is formed This can be L T YTIC O A T O E EC ROL DIS S CI I N .
“ n H ’ n disti ctly recognized by its odor . The (O ) a ions formed by the ionization of the Water i mpart an alkaline reaction to the solution . ~' An aqueous solution o f cyanide of pot a s si um affords an
' h r other illustration o f y d olytic action . In consequence o f s uch action the solution always contains an appreciable
o f H quantity Cy . The reaction of the solution is alkaline ; t his is o wing to the presen ce of hydroxyl anions . Application of the prin ciples of the ion theory to problems o f physiological chemistry ha s also led to some very inter
e o f sting . results , but a consideration these here wo uld take o o us t far afield . The prin cipal lines o f evidence to be adduced in support o f o f res u m the theory electrolyti c disso ciation , are in brief e, the following
a . s o f . The paralleli m of behavior electrolytes and gases os motic pressure pheno mena .
b - . The abnormal lowering of the freezing point of solu tions by electrolytes . Where all normal solutions of non
- e i . e. o ne lectrolytes , , solutions containing gram molecule o f l w - i o f solute in one liter of solvent , o er the freezing po nt 1 ° — 8 6 C . pure water , all electrolytes depress the freezing point o f t a s pure water to a much grea er degree , possibly again much . o f - i o f 0 . The abnormal elevation the boiling po nt water
o f no n - by electrolytes . Normal solutions electrolytes raise
- o f fo r the boiling point water by a given amount , identical all n o n - electrolytes ; electrolytes in normal solutions eff ect this to a much higher degree . t - s a nd d . The hermal neutralization pheno mena of acid
o f a n a bases . The neutralization of a normal solution cid
a o r v i ce v e s a o f h by a b se , . r , liberates an amount heat t at is constant , calories . This value represents the heat
o f o o o f w e . f rmati n at r , and only this In all neutralization
o f f is e experiments the kind re erred to , water an in variabl 5 8 N TES ON E E T O L C ROCHEMIS TR Y.
. p roduct If molecules were formed of the other constituents , b esides the molecules o f water produced by the chemical c x ombination of the hydrogen and hydro yl , their respective heats of formation would be manifest in the reaction . This , however , does not o ccur , and hen ce the inference is drawn t a s n that these constituen s exist in the solution ions , and o t a s molecules . To cite an illustration
N a OH H0 ] N a Cl H O ,
s he The heat of this reaction is calorie , t molec ular heat o f formation of water . N a Cl is 9 76 0 a The heat of formation of c lories , and yet
. " is this heat value does not appear Why not The reason , N a Cl because the compound is not formed in the reaction , the co mponents of this co mpound remain ing in the solu o f a s . tion ions , as ions of sodium and chlorine
e. The fact that chemical reactions will not take place between perfectly dry electrolytes ; a disso ciant is required to loosen the affinity between the atoms of the molecules and thus set free the ions which are assumed to be the re acting units o f all chemical changes . A great many data may be o ffered in support of the theory
o f . electrolytic disso ciation However , it must not be over
a o f looked that number facts , experimentally obtained , have a s yet not been brought into harmony with its teach ings . * Louis Kahlenberg cites amon g other objections to this o f theory , that the color of solutions is independent their ability to conduct electri c currents , whereas the ion theory h s t olds that the color of aqueous solution , at leas , is due to their ions ; he denies that free ions are the immediate
m 1 1 V l 339 Tra ns . a rad a S . J o u Ph s . he 90 o . 5 . oc rna l y C , , , p ; F y , 42 1905 V o l . 1 . . , , p E E TR YT A T L C OL IC DISS OCI ION . 9
a gents concerned in chemical reactions , for the reason that s uch reactions o ccur also in solutions that are insulators ,
for instan ce , in benzene . f Again , the theory does not , as yet , accord suf icient weight
to l the part which sol vents p ay in the formation of solutions . The interesting relations which rest o n the interdependence o f solute and solvent still c a ll for much further research and
explanation . Furthermore , numerous thermo chemical data appear to be at varian ce with the values the theory would seem to call for ; its teachings are not always valid even for
f Re chler airly dilute solutions . y actually asserts the theory o f electrolyti c disso ciation to be in opposition to many
thermochemical data secured by experiment .
N a otwithst nding these shortcomings , there can at least be no do ubt or question a s to the great value of the ion theory in the harmonization and correlation o f n umerous
d o f ata , and the stimulus which it has given to scientific n i thought and i quiry . Consider ng its bearing on the elec it is tron theory , an interesting fact that the electric charges transported by ions in electrolytes are identical with the charges conveyed by the particles in gases when electric
discharges are passed through gases . — Co ndu c iv i . B t ty y conductivity in general , there is o f meant the property of conducting a current electricity .
is f In an electrolyte , it the joint e fect of convection of the ca thio ns and anion s ; it is an additive property ; and the conductivity of an electrolyte represents the amount o f e lectricity which is con veyed in unit time by unit electro f motive orce . Conductivity is the recipro cal of resistance ; the greater
. C the latter , the smaller the conductivity onductivity is usually expressed in terms of a unit styled the mho cubic centimeter unit ; the term mho is simply the word ohm re vers ed in order to indicate that th e unit o f conductivity is
o f the reciprocal the unit of resistan ce . This unit ohm 6 0 N O TES ON
expresses the conductivity of a substan ce o ne centimeter cube o f which ha s a conductance o f o n e mho between two
parallel sides . In other words , if a current density is stated in amperes per square centimeter and the potential gradient
co nd u cti v itv b e in volts per centimeter , the will expressed in
mhos per centi met er cube . It has been experimentally demonstrated that the trans mission of electric impulses through electrolytes is p ra cti
'
cally instantaneous . This can only be accounted for b y thc assumption o f the presen ce o f free ions about the electrodes which give up their charges the instant an electric current
is sent through the electrolyte . M * From the interesting researches of N . onroe Hopkins it appears that electrolytes o f equal resistan ce conduct
o f the electric current with a definite velo city , regardless the composition o f the electrolytes o r the length of the con ” taining vessel . This investigator also determined , that an electrolyte co nd ucts the electric current j ust a s fast a s a m etallic conductor , pro vided , that an equal ohmic resist
f - o . an ce , a non inductive type , is furnished Molecular conductivity is the a ppellation given to the conductivity of solutions which cont a in o ne gram - molecule o f th e electrolyte ; it in creases with the temperature a nd
with the degree o f dilution . As first pointed o ut by Kohl rausch the molecular conductivity o f an electrolyte is equ a l
m o f o f to the s u the velocities of migration the ions .
Let m , molecular conductivity ,
a o f velocity of migration the anion ,
c n o f velocity of migratio the cathion , x o f fraction electrolyte dissociated into ions ,
t m x a c . hen , . ( )
On attaining to in finite dilution the disso ciation o f a n
s a electrolyte into its ions beco me complete , ai in that c se,
= l m a x c a c . . and +
t A S m . l S ci en . u 19 0 5 2430 p p , p . 5 .
6 2 N O TES ON ELEC TROCHEM IS TR Y. an alternating current which precludes the polarization o f n the electrodes , each of the electrodes servi g alternately as anode and as cathode .
o f K The method ohlrausch , a modi fied Wheatstone bridge n the arrangement , is frequently used in determini g resist A n an ce of an electrolyte . alternating current from the secondary o f a small induction coil is employed for th e
1v en u o f reason g , and a telephone receiver is sed in place a no t g a lvanometer . When the Wheatstone bridge is in balan ce a humming noise is heard in the telephone ; in m a king the measurement the bridge resist a nce must b e
o r adj usted in such a way as to secure silen ce , , at least , a
i o f E d ma y b e m nimum sound . lectro ynamo meters also
used in place o f the telephone arrangement . As the con d u ctiv ity of an electrolyte is great ly affected by changes
t a re in em perature , the vessel in which the measurements
made should be placed m a thermostat . Pure solids at ordi n ary temperatures have but a lo w n d co uctivity . It is therefore of interest to know that some v substan ces , notabl y the salts , exhibit a high conducti ity when fused ; this conductivity in creases with a rising tem
r r p e a tu e . The specific conductivity o f fused nitrate o f silver at 0 ° s 3 1 C. s is , for in tan ce , expressed in recipro cal ohm , equal ° o f to at 3 75 C . it is The specific conductivity s nitrate of silver in olution , disso ciated into ions to the 7 5 extent of about per cent , is only recipro cal ohms at a ° o f 25 h e o f temperature C . ; t conductivity the fused salt
o f therefore far exceeds that the salt in solution . Thus far it h a s been found impossible to determine the
o f f i degree of dissociation a used salt into ons , and their conductivity values can therefore only be determined at e * d R . L gi ven temp ratures . oren z has , however , demonstrate that the laws o f Faraday are valid also fo r fused s a lts
i tschr . Ze ur E lektr ch mi 1 0 27 190 1 . 7 5 . o e e 9 0 . 7 3 f , , p , p O YT S S C' A T N ELEC TR L IC DI O I IO . 6 3
The fact that certain metallic oxides when at very high in o f te mperatures , though not a state fusion , will con duct electricity has been taken advantage of by Nernst in the making of his in candescent lamps , the filaments o f which consist o f oxide o f magnesium ; the same property has also been made use o f in the construction o f the tantalum lamps f S Ha ls ke manu actured by iemens . f s Migra tion o Ion . An electri c field is a Space wherein
n o electrical i fluences are exerted . An i n mo ving in a field
is n a n the which uniform is acted on by a co st t force , but Speed with which it mo ves is not a uniformly accelerated
the a n o f speed , as might be supposed , because resist ce the liquid through which the ion mo ves ca u ses its v elo city to
o f be materially retarded . The intensity the electric field in which an ion mo ves determines its velo city ; this is c a ll ed nt the potential gradient , and is expressed in volts per ce i
u r eter . The velo city o f an ion under a gradient o f o n e volt per is a s centimeter is termed its mobility , and this , shown by
Bredi o f m g and Ostwald , a periodic fun ction the ato ic weight o f m s o f f n s the elements . Hence the obilitie the di fere t ion
ff o f o f di er , and the determination these values is a matter importan ce . The relative mobility o f anions and c a thio ns was deter mined by Hittorf in the follo wing manner : Two porous plates were inserted in a trough dividing the tro u gh into l three compartments . These co mpartments were all fi led
fo r o f e with an electrolyte , instan ce , with a solution sulphat o f copper ; a copper anode and a copper cathode , respectively , e s wer inserted in the end co mpartment , and an electric cur rent was passed through the solution . After the c urrent had been passed through the electrolyte
o f for a short time , samples were taken fro m each the three a comp rtments and analyzed . The sample remo ved fro m
d the the cathode chamber was foun to be less con centrated , 6 4 TE E ' N O S ON EL C TROCHE MIS TR 1 . sample fro m the anode ch a mber was found to be more con cen tra ted a than before the current was p ssed , while the sa mple from the middle chamber wa s foun d to have retained its original concentration .
u n x Taking the whole c rrent co veyed as unity , and as that
1 x part of the current conveyed by the anion , then of course represents the fraction o f the current ‘ transported
On e o n e - by the cathion . faraday requires gram equivalent o f ions for its transport , in consequen ce there must pass a cross any section in the interior o f the liq uid 2: e q u iv a lents o f anions in the direction Opposite to the direction h h t e 1 .v c a t io n s taken by current , and equivalents of in
’ a: f the direction o f the current . This is known as Hittor s f t o . number , the migration ra io the anion Electric currents produced by the movement o f the ions a re proportional to their mobilities :
ca thio ni c anionic l — x a: current current
The loss in con centration o f the solution in the cathode c o mpart ment is equal to the gain in con centration o f the
If fo r n in s olution in the anode compartment . , i stan ce ,
u h a d the c a s e j st dis cussed , faraday passed and the f to e u i v a change , in each chamber , had been ound be q n : lents , the migratio ratio of the anion would be
Values differing slightly from this have been found by dif feren t experimenters , but the true value undoubtedly closely a pproximates to the figure given . o f o u t Hittorf , the pioneer in this line work , carried a g reat n umber o f determinations o n migration ratios ; the u o f n form of apparatus for the st d y indi vidual cases bei g , o f co urse , suitably modified to meet the requirements of n fo r the occasion . A co venient model the demonstration OL YT S S A T N ELE C TR IC DI OCI IO . 6 5
’ o f o f o f ha s Hittorf s theory the migration velocities ions , * been described by Getman . Several methods have been devised fo r measuring the
a v i o f bsolute elo c ties ions , among others by Whetham and
Lodge . The latter measured the absolute velocity of hydro o gen ions in the following manner . Int a hot aqueous solu
o f tion gelatine , which he prepared , he in corporated so me sodium chloride as an electrolyte and colored the whole mass red by the addition of a little alkaline solution of phe
h h a l in no l t e . p This gelatine preparation , while hot , he poured
into a straight glass tube , both ends of which were bent at
a E o f right ngles . ach end the glass tube dipped into a be a ker containing dilute sulphuri c acid ; in o n e of these
a be kers a platinum anode was placed , in the other , a plati n u m cathode , and a voltmeter was j oined across these elec
o f trodes to indicate the potential gradient the current .
As u soon as an electric current was sent thro gh the system , hydrogen ions pro ceeded to pass fro m the anode through the gelatine preparation in the glass tube to the cathode
in the other beaker . The hydrogen ions displaced the
sodium fro m the sodium chloride , and , co mbining with the
o f chlorine , formed hydro chloric acid . This acid , course , at o f once decolori zed the phenolphthalein , and thus the progress
the reaction co uld be closely traced and accurately measured . Through careful experiments o f this kin d Lodge a s cer ta ined the velo city o f a hydrogen io n to be centi o r - t meters per minute , less than three quar ers of a meter
lo w per hour , a speed at best , and yet the hydrogen ions o f exceed all others in speed migration . The absolute velocity o f some o n e ion having been accu ra tel y determined , the absolute velo cities of other ions can f be easily ded uced ro m their relati ve velo cities , values which , ’ ca n it will be remembered , be readily determined by Hittorf s
method . S i V c ence 1 0 l 2 . 1 . 9 5 o . 1 3 , , , p 5 CHAPTER V
LECTRO-ANALYS S E I .
i e a ur L A En t a n a n b H I t t e S . t o C K W L r : C AS EN , ( glish r sl i y ER R , . H . ) “ ” m a An a E e o N u a nt ta t e e t . e w Yo Q i iv Ch ic l lysis by l c r lysis rk , “ E B K : Die A u m u a to e n Le 1 1887 . L s . . 89 6 . O PK I S , kk l r ipzig , H N “ ” Ex m n a E e t o e m t N N e e t . e w Yo . 19 0 5 M p ri l l c r ch is ry rk , . “ ” h n ri O Ele ktro c e n e wa s s e e r e u n e n . e F ERSTE R , F g L s g L ipzig , “ 1 0 O B W : Die E e t o e m e de r o a n hen 9 5 . e n . L E , l k r ch i rg isc V rbi “ A 1 0 Z R E S . 9 5 . O . : e d u n e n . . t o e m e g HALLE , L REN , l k r ch isch s ” “ n n 19 0 1 N IS S E N S O N H E a t u m Go tt e . . : n tu n en Pr k ik . i g , , i rich g
v E n o a to e n LL A S 1 o n e o t e La . . . 9 0 t 3 . l k r ly isch b r ri HA E , PETERS “ ” E e m e V l I W n 1 T F An wa n dte e t o o . . e 9 S M 1 H . : e 8 7 . g l k r ch i , i , , “ F m An a a de h a 19 0 2 E : E e t o e i a . . . l c r ch c l lysis Phil lp i , .
E ec r - h a l t o Analysis . Various con ceptions ve been and are o f i b ut entertained the nature of the electrolyt c pro cess , in w o f vie the most recent developments it may , perhaps , be best to look upon the pheno mena o ccurrin g in the electro lysi s of solutions as actions and reactions in which ions
r le play the leading O . It will be recalled that ions are defined as co mpounds
s U the n o f atoms and electron . nder influe ce of the electric , r mo v e o f current the ions towards the electrodes , course the anion s seeking the anode and ' the ca thiOns seeking the cath o o f d e . When the ions have co me within acting distan ce d w d the electrode towar s hi ch they are traveling , a ischarge , t to n i w tha is say , a neutralizatio of the electr c charges hich s they bear , takes place . This division of ion into electrons a n d h w ii i into ato ms , w ich ere held combination with these s t C n h r electron , libera es the ato ms in a o dition in w ich thei
f s chemical a finity can co me most strongly into play . Thi
a d as condition is frequently desi gn te the nascent state , the E E TR — AN A Y L C O L S IS . 6 7
status na s cendi if the ions which have thus suffered i discharge are co mpound ions , the materialistic nucle which remain are unsaturated co mpounds , and as such also display f trong che mi cal a finity . If there is no other substance present in an electrolytic solution with which the ato ms or unsaturated nuclei can
m n t m o r enter into chemical co bi a ion , these ato s nuclei fo h . r t e assume the molecular state Thus , instan ce , in
o f if electrolyti c deco mposition water , the hydrogen and o xygen set free find n o other substan ce present with which n they can enter into chemical co mbi ation , then these ele ments are liberated as hydrogen and as oxygen gas res p ec
iv el t y . The electric discharge o f ions takes place in accordan ce ’ a re ev with Faraday s laws . If the conditions such that s n eral reactions may o ccur , the speed with whi ch io s are
fo r if the re discharged is a very important factor , , speed of action o i the discharged ions with the depolarizer is greater than the speed o f disc harge of the ions then there will be n o
' liberation of th e discharged ions in the mo lecula r sta te ; this can frequently be observed in pro cesses o f oxidation a n d reduction . As electrochemical reactions are co n fined to the imme
o f w diate neighborhood the electrodes , the rate at hich such reactions pro ceed is dependent upon the con centration o f the
o f ions . But the concentration the ions is determined by
o f the current strength , the size the electrode surface , an d o f the concentration the depolarizer , and these items must therefore be very carefully considered and adj usted in every
o electrolyti c operation t ensure the desired res ult .
The chief characteristic of an electrolytic pro cess , as co m
a s pared with purely chemical process , is the con umption of energy in the former in lieu o f the consumption of material ff in the latter ;in other words , an electric current e ects changes , fo r w instan ce , oxidations and reductions , hich in chemical 6 8 N TES ON ELEC TROCHEJII T Y O S R .
o m pro cesses are induced only by the intervention f che i cals .
If a chemical change is brought a bout directly b y ' the action of electrical energy , if the electric current is allowed to
o f act upon an electrolyte , the action is spoken as a direct action ; if the electric energy must first suffer transformation
n fo r o r into some other form of e ergy , instance , into heat light , the pro cess is spoken of as an indirect action . The manner in which the electric action known as the silent dis T ff charge is e ected is as yet but little understood , although un questionably many electrochemi cal effects in nature a re brought about by this agen cy In effecting the electrolysis of organic substan ces two cases must be distinguished : the body acted upon may be a n
- electrolyte , or it may be a non electrolyte . In the latter case the ions whi ch are to tra nsport the
f e f electric charges must be urnish d ro m some other source , n through addition of some electrolyte . The io s thus intro d u ced f o f t will , under the in luence the electric current , ravel towards the electrodes , and the organi c substan ce is acted
o f upon by these ions only at the moment their discharge . A substance thus entering into chemi cal co mbination with the atomic constituent o f an ion at the moment o f its dis charge is termed a depolarizer .
o f Two classes depolarizers may be distinguished , anodi c a nd cathodic depolarizers .
Ca d c a s — tho i Depol rizer . The process taking place at the
is ca thio n s cathode termed reduction ; the prin cipal , that is ,
a n d the ions liberated at the cathode , are ions of the metals
n u b of hydrogen ; a few o rganic ca th io ns are also k own . S o r u t stances which can either take up hyd rogen give o oxygen , n w i a or do both , are k o n as reduc ble subst n ces ; in other f words , they are oxidizing agents , and their special un ction f is the neutralization o positive charges . An d c De o la ri z ers o i p . Anodic depolarizers are agents o r which destroy negative charges . If oxygen be added ,
70 N O TES ON ELECTROCHEM IS TR Y.
a instance , the origin l voltaic pile , made of zinc , sulphuric
o f t . acid , and silver , is his type The water voltameter is
a f o f a n . C o nother illustration irreversible cell ells this kind ,
a s a a f rule , furnish rather high electromotive orce at the
start ; this , however , depreciates as the action pro ceeds , for
f . R o n the electrodes su fer polarization eversible cells , the n other hand , yield a current almost co stant in electromotive f orce as long as they continue in action , for in these the ff electrodes do not su er polarization .
If the f o f is electro motive orce a cell determined , the voltage represents the difference o f potential between the
v u electrodes . Whene er there is a contact of d issimilar s b
r f stances elect o moti ve orce appears , but it is only the
' electromotive force caused by . the contact between the metal electrodes and the electrolyte in which they re
fo r . spectively are immersed , that here calls co mment To this value the term elect rode - potential is given ; it represents the work expended in con veying th e unit quantity of elec
r n t icity betwee electrode and electrolyte . * An a o f t expl n ation his action was first suggested by Nernst , who s howed th a t the pro cess might be con ceived of as an os motic pro cess by a scribing to each metal the property of
electri ca llv a forcing ch rged particles , ions , into a liquid with
1s in o f n Which the metal contact . This forcing the io s into the liq uid takes place with a pressure peculiar to each metal
r a and is in va i ble at constant temperature . The metal may thus be regarded a s a sort of reservoir of ions wherein these ions a re o r stored under a greater less pressure , and this pressure t o f is designated as the electrol y i c solution pressure the metal .
is Whenever electrical energy developed , both positi ve
n l a and egati ve electricity co me simu t neously into existen ce . w In the metallic electrodes as such , the particles are ithout
a t n electric charges ; the insta t , however , that a particle
* i c t Z e ts h i Ph s . h mz V o 1 e e 9 l . 9 C 1 88 4 2 . r f y , . , p —A AL Y I ELEC TRO N S S . 71 passes fro m a n electrode into an electrolytic solution the particle assumes a positive charge and thus becomes an ion ; a t the same instan ce the metallic electrode acquires a nega E tive charge of equal intensity . ach additional ion which enters into the solution in creases the positive charge o f the solution while the electrode beco mes correspondingl y more and more charged with negative electricity . Electric charges of O ppo site sign attract o n e another and one can thus conceive o f a layer o f positively charged ions
f ~ held in attraction by a negatively charged electrode , a di fer en ce in potential being thus established . The electrostati c attraction o f this layer opposes the tenden cy o f the electro lytic solution pressure of the electrode to force more ions into the solution , and when these counterforces are in equi librium the action comes to a halt . As the electric charges carried by the ions are very great , such equilibrium is estab lis hed even when but a few ions have passed fro m the elec trode into the solution . If a metallic electrode be immers e d in a solution o f o ne o f its o wn salts , the metalli c ions therein will by osmotic pressure O ppose the admission o f more ions o f their o wn
i o f kind . If this osmot c pressure the ions in the solution is ex a ctl v in equilibrium with the solution pressure o f the i electrode , no ons will be projected from the latter into the n o t solution , and the electrode will therefore be charged i w th negative electricity . On the other hand , if the o smotic pressure is greater than the electrolytic solution pressure , the metallic ions are driven fro m the solution o n to the electrode and the electrode is n thereby charged with positive electri city . The solutio losing so me of its positively charged ions while its content o f n o t negatively charged anions is decreased , becomes nega ti vely charged ; the electrostati c differen ce is thus contin u o usl n y in creased until it cou terbalances the osmotic pressure , and then equilibrium is restored . ’ 752 N O TES ON ELEC TROCHE MIS TR Y
The electromotive force o f a cell can be calculated fro m
s n the osmoti c pressure of the olutio s about the electrodes . f for , if a substan ce is allowed to pass isothermally rom one Condition into another it ” is immaterial how such a trans
formation o ccurs , whether osmoti cally or ele ctri cally . Knowing the maximum amoun t o f external work which a
c a n o a n pro cess acc mplish in isothermal transformation , the
r m o n e fo r w p oblem is a si ple , the o rk whi ch can be done by ions in p a ssin g fro m a given os moti c pressure to a nother f can be trans ormed without loss into electri cal energy .
' The fundamental formula by whi ch the electromotive force o f an element is calculated fro m the osmoti c pressure
1s of the solutions about the electrodes ,
R Tln
In this formula
potential ,
valen ce of the ions ,
o f quantity electricity ,
l
l l amount o f energy tra nsformed into work in a gas f whi ch expands isothermally ro m a pressure p , to a pressure p z .
This last formula also holds fo r a solution which passes
t o isothermally fro m one osmo i c pressure t another . In a Daniell cell the difference in potential between the Of two electrodes is practi cally volts . this , volt is the potential differen ce between the zin c electrode a nd the zin c sulphate solution — the electrolyte in which it is im mersed a n d ff , the balan ce , volt , is the potential di eren ce between the copper electrode and the solution o f copper
is sulphate in which this electrode i mmersed . E — L Y I EL C TRO AN A S S . 73
T he term electro - affinity is used to designate the electrod e potential in solutions which contain 1 gram - equivalent p er liter o f the ion given o ff by the electrode ; solution s o f this A n con centration are called normal solutions . electrode is
h o r its eit er positive negati ve to a normal solution of ions ,
r - a ffin it e and its elect o y is , by the maj ority of writers , d noted accordingly as positive or negative . The electro motive force of a cell whose electrodes are reversible with respect ff to any ion , is the algebrai c di eren ce between the electro
wo a ffin ities of the t ions . In normal solutions the electrode - potential increases fo r ca thio ns a nd decreases for anions with the con centration f o . a the electrolyte In other words , the electrode potenti l is determined by the con centration o f th a t part of the elec
r l w i f t o y te in actual contact ith the electrode . It s there o re important that the electrolyte be kept in motion by a stirrer , o r rev o l v m fo r , that the electrode be kept g in the solution , b v these means the con centration o f a solution is kept fairly unifor m and a n even deposition o f the metal precipitated by the electric current is secured . If so me precaution be m not taken to secure a unifor con centration of the solution , the con centration of the electrolyte about the cathode will
- n o f decrease and , in consequence , the electrode pote tial w the cathode will be lowered , hile the con centration of the
he electroly te at t anode will be in creased . and the electrode
a o f potenti l the anode will be raised in consequen ce . When
f o f w this o ccurs , a all of potential results , indicative the ork d f one in bringin g about these di feren ces in con centration . This pheno menon is known as con centration polarization ; it o ccurs whenever any perceptible amount o f chemical action is taking place .
The disso ciation voltages previously discussed are , of course , to be considered only a s minimum voltages based upon the assumption that the electrolyti c pro cess takes place slowly H and with weak currents . eavier currents in variably cause 7 4 T O E T N O ES N EL C ROCHEM IS TR Y.
con centration polarization , and to overco me this higher volt a ges are required . The electrode-potential o f an ion depends upon its chemi cal n ature and upon the amount in which this ion is present in
a n . f o f electrolyte If , there ore , more than on e kind cathion dis present in an electrolyte , that cathion will be first
- charged whi ch has the greater electrode potential . Through s uch discharge , however , its con centration will be decreased and thereby its electrode - potential will be lowered ; when
- ca thio ns the electrode potential of both is identi cal , both w a ill be discharged simult neously .
If there are two anions present in an electrolyte , that a nion having the lower potential will be the first to be dis charged ; through this its con centration will be reduced and
- n its electrode pote tial will be raised . When both anions have attained to the same electrode- potential they will suffer s i multaneous dis charge . These facts explain why the current density - the quo tient obtained by dividing the current strength by the elec t a o f rode surf ce , and generally expressed in terms amperes per 100 square centimeters of electrode surface — plays s o i mportant a part in electrolysis . Entirely distinct fro m con centration polarization is the to pheno menon termed chemical polarization . This is due s ome new chemical substan ce or substan ces formed by the electri c current and the consequent substitution o f new electrode surfaces for those electrode surfaces with which
he wa s . t electrolytic O peration begun Thus , in the elec tro ly s is o f water the gases liberated by the action of the n a n d electri c curre t , hydrogen oxygen , have a great tenden cy
to polarize the electrode su rfaces chemically .
- Such a polarization produces a back pressure , a reverse l ff e ectromotive force , which , at times , diminishes the e ecti ve
electromotive force very materially . The amount of such back - pressure can be practi cally - L Y IS ELEC TRO AN A S . 75 measured by fi rst reading the voltage across the two elec
a s t o ff trodes usual , then urning the current and noting the position at which the indicator in the voltmeter halts fo r 0 11 a brief space o f time ere it travels to zero . That point where it halts marks the polari zation voltage .
f ex eri If , for instan ce , the ull working voltage in an p 5 - 3 ment be volts , the halting point be at volts , and the a o f l i . e. mperage then the resistan ce the ce l , , the reverse electro motive force of the cell is :
m oh s .
A means o f o verco ming chemical polari zation is the plac in g of the anode in a solution o f a salt o f the metal of whi ch
o r n a so the anode is made , the use of an oxidizing age t ,
o o f called depolarizer , which oxidizes the pr duct electrolysis that would otherwise polarize the electrode . ur e f urre — In So c s o C nt . choosing a source for current
a supply for analyti c l purposes , the great consideration is the securing of a current which shall have sufficient strength ( amperage ) a nd which shall possess a potential (voltage ) a s constant as possible .
o Us e can be made f primary batteries ( cells ) , of thermo
u o f piles , dynamos , accum lators , and a direct lighting cur
rent . G enerally speaking , electri cal elements , or cells , are devices C ld fo r carrying on electro chemical reactions . ells whi ch yie
a n electrical current are called voltai c cells . These can be
o f made to serve as sources supply , but are open to several a n obj ections . Some yield too weak a current , having intern al resist a n ce which is to o high ; others polarize too
o f a o ff rapidly , and this , course , causes rapid falling in cur
rent ; others ag ain emit noxious fumes and vapors . If cells are to be us ed possibly the best is the Edison 6 T 7 N O TES ELEC TROCHEM 1S R Y.
‘
P a . o f rimary battery , or the D niell cell The latter consists
: Zn SO : Cu : Cu SO Zn , 1,
The B unsen cell is made of
n H : Z SO : C : NO . Zn , s
- o r o In this cell , the carbon , gas carbon , graphite , dips int nitric acid which is contained in a cup or cylinder of poro us
w w l m ed earthen are or clay . The z in c is generally ell ama ga at to avo id lo cal currents whi ch are very destructi ve to th e
d a o f the electro e . The chro mic cid cell is a modification Bunsen cell ; it contains potassium dichrom a te as a d ep o la is rizer the posit ive pole is carbon , the negati ve pole
e . zin c , well amalgamat d . Cells can be grouped fo r a high electro motive for ce o r
o f for an in creased quantity current .
' To obtain a high electro motive force the cells sho uld b e
o f o n e linked in series . that is , the positi ve pole cell sho uld b e o f e z in es in linked to the negative pole another c ll ; , for stance , to carbons . The total electro motive force of a set o f cells thus linked in series is equal to the voltage of an
n u t o f i dividual cell m l iplied by the n umber cells so linked .
s o f m By thu linking in series , the internal resistan ce the syste is , of co urse , also increased . To increase the quantit y of electri c current cells must b e
d 1s n d linke in parallel , that , all the positi ve poles are joi e
r n a re togethe , and all the egative poles joined together . This arrangement decreases the internal res i s tance ; the total internal resistance o f a system linked in p a rallel is equal to the resistance o f an individual cell divided b y the total n um
o L a f llel a c a ber f cells so linked . inking in p a pr cti ally mounts
o a o o f f t a summ tion f all the electrode sur aces .
co urse if f a a c a n Of , su ficient cells are vail ble , they be divided
a nd s into groups linked partly in serie , and partly in parallel . The best current - yield is obtained by linking the cells in
78 N TE O T MI T Y O S N ELEC ROCHE S R .
M Le 1 o . 89 5 t Blan c , in , was the first gi ve an explanation ,
o f the by means of the theory electrolytic disso ciation , of reactions taking place in an accumulator . According to w o f his vie s , the chief source the electro motive force of a lead acc u mulator is the transfo rmation o f tetravalent lead
f Pb O . ions ( ro m the 2 in water) into di valent lead ions The solid lead s uperoxide replenishes the tetravalent lead ions
the which are consumed , and divalent lead ions which thus appear enter into chemical co mbination with the sulphuric a f o f cid present , orming sulphate lead . At the cathode the d f metalli c lea is trans ormed into divalent lead ions , and these also co mbine with sulphuric acid to form solid sulphate o f lead . The new Edison storage - battery consists of a nickel per
NiO s oxide ( , ) anode an d an iron cathode ; causti c pota h K H ( O ) is the electrolyte used .
f o f The electro motive o rce this ac cumulator is low , about
discharge voltage , but it has certain advantages , for
o f ro instan ce , a good storage capacity per unit mass , a p no un ced stability , and moreo ver , it can be quickly charged * a n d discharged without inj ury to the plates .
- f - P a rs . t o ole p pe Wha ever the source current , pole papers s o - fo r called , are a con venient means ascertaining at once which is the positive a n d which is the negati ve pole in a given circuit . These pole - papers are small strips o f filter paper charged with a solution of so me salt and with a solution o f some indicator whi ch instantly indicates an ionic change in the
s o f o f salt u ed , solutions sodium sulphate , and phenol phthalein , for instan ce . When a piece o f filter- paper mpis ten ed with the above solutions is touched by the terminal wires conducting an
e E l c . Wo r ld a nd E n i e Co nfe : Ro e E . F . e n er 190 1 . S cho o r b r , g , p ,
- A m. S u l m. Incl 1 0 nd S c . 190 M Elect a che 9 4 a 5 . 25064 . M . . , r , , pp , , p E T O -1 1VA LYS IS EL C R . 79
e electric current , the wires being held but a s mall distan c apart , a pin k mark soon appears at the point where the
o f C p p negative pole the ircuit touches the a er , the colo r being due to the reaction o f the phenolph thalein with the alkali which is set free at the cathode .
r men E m o f Cu rrent Mea su e t . xact easurements the
o f o f working current conditions , amperage and voltage , are , course , most essential in electro chemical work . Besides a to voltameter , whi ch can be used measure current strength but which is prin cipally servi ceable in checking other meas n et uri g instruments , an ammeter and a voltm er are required . o f the There are various kinds ammeters . In electro
o f magneti c type , an electric current is sent thro ugh a coil
n o v a b le o f wire which surrounds an easily core iron . This iron Core is in connection with a poin ter which mo ves across
' a dial , and the deflection of this pointer indicates the strength o f the current which passes through the coil . The ho t- wire ammeter depends fo r its action upon t he heating by the electri c current of a very fine wire . This wire is fasten ed at two points and at its middle is connected to another fine wire whi ch passes aroun d a small drum bear
n . s ing a poi ter A spring , while at normal temperature , keep the latter wire in a state of constant tension ; when , however , a current is sent through the first wire this beco mes heated a nd 0 11 slackens , the spring draws the second wire and thus
o h drum and pointer are s et in motion . On acco unt f its a v ing a low internal resistance an ammeter can be placed any w n here directly i the circuit . Voltmeters are analogo us in construction to ammeters ; they
n o f ho - may be of the electro mag etic or the t wire type .
If of the former description , the high resistance needed is secured by the u se of a great number of windings o f very
w o f fine wire , hich reduces the consumption current to a
ho - minimum . In the t wire type the required resistance is obtained by introducing in series with the instrument the 80 N OTES ON ELE C TROCHEM IS TR Y . requisite number o f resistan c e coils ; the greater the voltage to r d the o f o f be measu e , mo re these coils generally made — w . very fine ire are required Voltmeters , having a very
a u - he high resistance , are alw ys placed in a sh nt circuit , t latter receiving only a sma ll fraction of the current whi ch
flows along the main line . The resistan ce o f a wire i s dire ctlv p o rp o rtio n a l to its
t v - leng h and in ersely proportional to its cross section . If two paths are offered an electri c current and both o f
50 o f these paths have the same resistan ce , per cent the current
. s a t ravels by each wire If , however , a given wire , let us y , A o f 10 B t wire , has a resistan ce ohms , and wire has a resis
o f 100 10 n tan ce ohms , then per cent of the curre t will pass i B 90 n W A through w re , and per ce t through ire A voltmeter can also be conveniently used as an a mpere meter pro vid ed that a known resistan ce is introduced into the electric circuit and that the terminals o f the voltmeter are attached to this resistance .
n a n d E t hen ce , if R is know is ascer ained by a voltmeter ,
C can be determined at a glan ce . n o f 1 o h m the If a resista ce is used in circuit , the values indicated by the voltmeter read directly in amperes , for
1 ampere
l o hm O. If the resistan ce introd uced is . , then each unit s 10 m indication o f the voltmeter repre ents a peres , for
10 a mperes E L E T — A AL Y C RO N S IS . 81
10 If the resistan ce employed is ohms , each unit indication
in the scale represents ampere , for
ampere
the o f It is therefo re possible , by proper selection resistan ce , e u to obtain a very wide rang of c rrent strength .
o f a n Cu rrent Regul a tion . The regulation electri cal cur rent used for electrolyti cal purposes can be achieved by the introd uction o f the proper amount of resistance into the
o f w circuit , and by a regulation the distan ce bet een the elec
trodes in the electrolyte . The s o - called resistan ce boxes usually consist o f coils or
e o f G n - o r o f h s pirals mad erma silver wire , so me ot er alloy . Among alloys speci fically m a de for this purpose are ni ck n M eline , constantan , platinoid , and ma ganin . anganin is
' o i n s an alloy manga e e , nickel and copper ; it has a very high f i resistan ce and a very small , negati ve coe fic ent of tempera
a nd is l ma n u fa c t ure , it therefore especia ly valuable for the
o f o f ture electrical apparatus , where constan cy resistance
r fo r a t vario us tempe atures is called . n A curre t passin g thro ugh a wire heats the wire , and in
n u n Fo r c o seq e ce the resistan ce rises . so me purposes it is i n very desirable to avoid such a variation the resistan ce , a n d in such instan ces use can be made to advantage of an
a lo w f lloy that has a temperature coe ficient . Platinoid is an alloy of this description ; its in creased resist 0 ° ° a n f 10 1 . nce through a ra ge of 0 C . ( ro m 0 to 00 C )
o r h - is only per cent , whereas silver , annealed ard drawn ,
o f 40 a n d o f sho ws a rise per cent , annealed copper a rise 4 3 al most per cent . Another simple and ser viceable devi ce for introducing * r - A resistance into an elect i c circuit is the lamp bank . la mp
o n n s libe . cit 1 u t o . 3 . C s l H pki , r , p 82 N OTES ON L TROCHE MIS TR Y E EC .
bank is made by arranging a n umber o f lamp -sockets partly
o f in parallel , partly in series , upon a slab slate or marble , and then inserting the necessary n umber o f lamps properly
grouped to give the desired resistan ce . The current may
co n v en ientlv t f be aken ro m a direct lighting circuit .
t re When lamps are arranged in parallel , heir combined s is ta n ce is equal to the resistance o f o n e lamp divided by the n umber o f lamps in parallel ; when arranged in series their co mbined resistan ce is equal to the resistance o f o n e l o f amp multi plied by the number lamps in series .
fo r 16 — Assume , instan ce , that eight candle power lamps are available a nd that the lamp - board is arranged in such a manner that these lamps can be used either in parallel or in
series . Let E 1 10 volts , 220 R ohms ,
and have the 8 lamps arran ged in parallel .
a therefore, in this inst n ce ,
1 m _ = x 8 4 . 0 2 20 ,
e 4 a . t. . , amperes would p ss through the lamps grouped
If the 8 lamps were arranged in series ,
1 m n o _ ' 220 x 8 176 0
only ampere would flow through the co mbination . It in is thus evident , that by grouping so me of the lamps b ff parallel and so me in series , and y using lamps of di erent
resistances , almost any desired amperage may be secured .
Of th e course , introduction of resistan ce into the circuit in such a manner is the re v erse o f econo mical ; a 1 10 - volt E -AN AL Y IS EL C TRO S . 83
4 f current cut down to , say , volts , renders no more e fecti ve 4— service than the current of a volt generator directly applied . The actual current strength in any electrolytic circuit is determined by the formula :
E o f voltage the current ,
6 - counter voltage ,
o f R resistance cell ,
R o f b e 1 resistan ce the conductor (the leads ) ,
tween generator and cell .
t In electro chemical analysis , however , the vol age is gen era lly measured directly between the termin als o f the cell o f R no t that is , the value R only is sought and the value l taken into account . The resistance o f an electrolytic cell may also be ca lcu lated by the formula : in which D distance , in centimeters , between the electrodes
these being assumed to be perfectly parallel ,
o f p the specific resistance the electrolyte ,
E . S . electrode area in square centimeters o f
each electrode . If there are three plates and the current flows fro m the
to o f v o f central plate each the other two , then the alue R
fo r n is found as above either side , and the combi ed resistan ce
o n e- o f equals half the value thus found . The resistan ce o f electrolytes v aries with their chemical
n . nature , with their con ce tration and with the temperature An in crease in temperature markedly decreases the resist 84 N OT S ON ELEC TROCHE I T r E M S R . ance of electrolytes ; in this respect electrolytes resemble the behavior of carbon .
- o f in The cross section a wire , in square milli meters , for o f stance . a copper wire used for conducting an electric cur rent , is calculated by the formula :
L . o . D J ” . in which
- G S . t cross sec ion in s quare millimeters ,
L o f w is total length conducting ire that , the sum o f the lengths o f wire leading fro m the source o f current supply and back , C the maximum current strength to be conducted
a expressed in mperes , P D . the maxi mum permissible drop in potential ex in pressed volts ,
o f i . e . specific resistan ce of copper , , the resistan ce a copper wire 1 meter long and 1 square milli
in - meter cross section .
The cross—sections o f round wires are very often given in
- o f circular mils . A mil is the one thousandth part an in ch
~- milli meter ) . A circular mil is the area o f a circle the diameter o f whi ch is o n e mil ; a circle having a diameter 2 n d has an area of d circular u nits . O e circular mil is equal to a nd o n e square milli meter , square millimeter
s i eq ual to circular mils . In calculating the cross - sections o f the conducting wires bet ween the sources o f supply and the working - st a tion a safety- margin o f fro m 20 to 25 per cent over and above the a e . amount cal cul ted , should be allow d
l - E ectrodes . The electrodes used in electro analytical
w us u a llv . ork are made of platinum The cathode may , f according to conditions , be either a crucible , a dish , a lag
o r n . or foil , a cone , a cyli der
86 N O TES ON ELEC TROCHEMIS TR Y.
‘ o form , a stronger current can be employed , and , in cons
uen ce . q , considerable time be saved o f It is also possible to make use a rotating cathode , a * platinum crucible , for instan ce , answers this purpose well . Giving such a cathode a speed o f rotation o f fro m 600 to 700 a n d n revolutions per minute , working with a ormal u 15 0 m c rrent density of fro m to amperes , to 3 inutes will suffice for an electrodeposition which ordinarily would require hours for its completion . In calculating electrode areas it is custo mary to measure the surfaces o f the electrodes only to the extent that the same are in contact with the electrolyte .
r c a ti o n o Electro de Ar F o rmu lae fo C a l ul f ea s .
d 1r diameter ,
r radius .
d “if Circumference of a circle : x ,
2 7854 : d . Area of a circle x ,
r S urfa ce a ea s .
Foil o r flag : Height x length . Cone or pyramid : Product o f perimeter of base by half
the slant height , plus the area of the base . Open - end cylinder o r prism : Perimeter o f o ne end x
height . Closed - end cylinder o r prism : Perimeter o f one end x
w o f . height , plus t i ce the area one end t Interior surface of a dish ( cu r v e s urfa ce of a segment o r
a zo ne o f a sphere) : Diameter of sphere x height o f
o r x qr segment zone .
V l 1 S ci ence o . 5 . 320 . A m. o u na l o J r f , , p E T —A AL Y EL C RO N S IS . 87
: 7T' d fik 6 . Cylindrical gauze / nlb
o f d diameter wire ,
n number of meshes per square centimeter , l t len g h f o gauze used . b width
Cu rren e s . a s desi t D n ity This term , previo usly stated , g the o f nates the ratio of the electrode area to flow current . 2 r o 1 It is custo ma y t term the current strength per 00 cm . z 1 dm o f (one square decimeter , ) electrode surface , the no rma l dens i t o f y current , and this val ue is symbolized by
N . D . 100 .
D . Fo r N . instance , 100 signifies that the current flow for every 100 s quare centi meters of electrode surface is
ampere .
Let D n , current de sity , C current strength
- E . S . electrode surface on which electro deposi
tion takes place .
_ N . D . 100
B N . . If the wo and the electrode surface are known , the cur b v rent strength is readily calculated the formula ,
E S .
D . C N . 100 x 100
Fo r : instance , let C 5 amperes E 1 0 . S . 8
“ W B eri c t n e : h e V o l . 3 2 219 2 i kl r , , p . . E T E T 88 N O TES ON LEC ROCH MIS R Y.
Then
' 100
C = 2 8 x
The current density may either b e the same or unlike at the two electrodes . If both electrode areas are alike , a
o f s n given current strength will , co ur e , ensure ide tical cur
ns i rent d e tv at both electrodes . A given current strength passing fro m a small electrode area naturally means a high current density at that electrode . Thus let :
The same current strength passing form a large electrode surface determines a lo w current density at that electrod e .
All electro chemical operations are greatly influe n ced by the current density .
R c d o f r i e or s . The records all elect o chem cal work should be kept in such a manner as to permit o f the exact repeti
o f s u ch o f tion work at any time . What the specific data
o f s such record should be , is , course , in a large mea ure deter
o f mined by the nature the work under conside ration .
9 0 N OTES ON ELEC TROCHEM IS TR Y.
6 3 . 6 x
x m gra s .
One ampere hour will thus deposit o f : S ilver , grams , C opper (fro m a cupri c salt ) grams , a nd these values are in the same ratio as the respec ti ve ( c hemi cal equi valents o f s 1lv er and o f copper
Le a s . and
Great stress must also be laid o n havi ng the current used s ufficient in amount , in other words , the current density must be sufficiently large so that the rate at whi ch a metal i s precipitated is greater than the rate at which it tends to r i n edissolve the solution fro m whi ch it is being deposited . This is proportionate to the area o f the surface of the elec
trode at whi ch the deposition o ccurs , hence the amount of
o f current per unit surface area , the current density , is a factor of pri me i mportance . W hile the various chemical elements are set free in equi v a lent to amounts at the electrodes , it is necessary remember that the amount o f electri cal energy requisite to effect an electrolyti c decomposition varies with the nature o f the c o hemi cal co mbination t be decomposed .
' .The mi nimum disso ciation voltage , the criti cal voltage ,
f Ad v a di fers for each element and is characteristi c of it . n tage is taken o f this fact to separate di fferent metals ana lyti cally . For instance , i n passing a current through a solu o f tion several metals , the metal having the lowest criti cal voltage will be deposited first ; if the voltage be then i n f creased , metal a ter metal will be precipitated , and the metal having the highest critical voltage will be the last o ne to be d eposited . ELE TR - AN AL YS IS 1 C O . 9
As a rule , thermal units are employed to measure the e nergy evolved o r absorbed in the formation o f chemi cal
co mpo unds . As pre viously stated , the thermal units em
o r C f re re ployed are either calo ries , , alories , the ormer p senting the amount o f heat needed to raise the temperature ° ° f C . 15 o f o C . o 1 one gram water one degree , fro m t 6 C . ; t o f the latter , the amo un heat needed to raise the tempera
o f C * ture one kilogram of water one degree entigrade . To e ffect an electrolytic deposition o f a chemi cal s u b
o f stance i n aqueo us solutions , an amo unt electrical energy must be used equi valent to the number of c a lories involved f in the ormation of the co mpo und to be electrolysed . The unit of electri cal energy is the joule ; o ne joule i s
C . equivalent to , practi cally , calorie , or to alorie
o f o f a n is When the heat formation electrolyte known , this value di vided by equals the j oules required to effect its
electrolysis .
1 1 x 1 the u o f joule coulo mb volt , therefore , n mber j oules di vided by o r a multiple thereof — rep re
m ne e s 116 . c s ents the criti cal voltage , the ini mum voltag e
sary to effe ct the desired ele ctrolysis . to The fundamental facts then be remembered are , that it always requires a definite quantity o f energy to effect the
o f electrolysis a gi ven substan ce at a given temperature , and that such electrolysis can only be effected by the use of a d efinite mini mum voltage .
f o f a n s In passing upon the e ficiency y electrolytic pro ces , it is necessary to pay due regard to both current e fficiency a nd to c w energy efficien y . In other ords , it is necessary to
d o f etermine how closely the weight the product obtained , compares with the weight o f the product theoreti cally p ro
d u cib le o f f by the number coulo mbs used ; urthermore , the w eight of the product obtained sho uld be compared with
’ ” o nfe : o e W R a d E e t o em a a u a t o n J o u r C r J s ph . ich r s l c r ch ic l C lc l i s ,
na l a nkli n ns ti tu te 190 6 . 13 1 . Fr I , , p 9 2 N OTES ON EL EC TROCHEM IS TRY . the amount theoreti cally obtainable by a perfect u tiliza tion o f o the total number f j o ules employed . 9 f is 90 7 Thus , if the current e ficiency in a gi ven pro cess 0 a nd the voltag e e fficiency is then the energy e fficiency is
90 x 6 0 100 x 10 0
In obtaining the electrodeposition o f an element fro m a to ff co mpo und , it is a great advantage e ect such electro depo sition fro m an o u s - salt rather than fro m an te- salt fo r the reason that the o u s co mpo und compared with the te com
w o f co ns titu po und , contains t i ce the amo unt the metalli c ent per unit weight o f the non - meta li c radi cle with whi ch
o f i t is co mbined . I n consequence an electri c current a g i ven amperage will deposit twi ce a s much metal fro m an o u s f to salt as i t will ro m an salt , and although a so mewhat a e higher voltage is required in the former c se , this is mor than co mpensated for by the i ncreased output obtained .
94 N O TES ON ELEC TROCHEM IS TR Y
a ll include electrodeposition fro m fused electrolytes , and electrothermic processes . sub - s For the sake of convenience , the following division can be made :
- E P . A . lectro inorgani c rocesses
P . I . Direct Action ro cesses f Electrodeposi tion ro m solution .
Electroplating .
- Chlorine and Alkali hydrates .
P . II . Indirect Action ro cesses
Electrodeposition fro m fused electrolytes .
Ele ctro th er ni ic pro cesses .
- E . B . lectro organic pro cesses
n I . Direct actio processes .
I I . Silent discharge processes .
- E . III . lectro osmosis
E O PRO ES E R C C C S S . A . I . DI T A TI N
r i ti o n o m lu i o n Elect o dep o s fr S o t .
C — o pper . Although several pro cesses have been devised for obtaini ng copper fro m its o res by the aid o f the electri c
o f current , not one these pro cesses has attained to any great importance in co mmercial practice .
o ne o f In of the earliest these pro cesses , that devised by M 1884 archese in , the ore was prepared and brought into the f o f o f a nd orm an impure sulphide , consisting copper , lead , wa iron . This co mpound s cast into anodes and subjected
o t electrolysis in a sulphuri c acid solution . In later pro cesses solvents are used to extract the copper
to from its ore , and the solutions thus obtained are subjected electrolysis , insoluble anodes being employed .
S - Ha ls ke Thus , in the iemens pro cess the solvent employed a s is for extracting the copper present sulphide , an aqueous T OTE HN O O Y ELEC R C L G . 95
f o f solution o f ferri c s ulphate . In e fecting the extraction the copper this ferric sulphate beco mes reduced to the fer d rous condition , but is , in turn , restored to its original con i tion by undergoing oxidation in the anode section o f the trough after the metalli c Copper has been precipitated from
s its sulphuri c acid solution at the cathode . Carbon anode are generally used . o re a n In the Hoepfner pro cess , the is not subjected to y
o f us preliminary roasting ; the copper , in the form cupro s o u t o f ulphide , is leached by means a sodium chloride solu
s tion containing cupri c chloride , cuprous chloride is thu formed and is kept in solution by means o f the sodium chlor
ele ro l i c ide which is present . The ct v t troughs are separated i nto anode and cathode chambers by means of diaphragms and the electrolyte is first passed through the cathode chambers
o f where most the copper is precipitated . In the anode chamber the remaining cuprous chloride is changed to the
is cupric form , and the process thus made a continuous one . While the extra ction o f copper fro m its ores by electro
is no t lytic action as yet well developed , the electrolyti c
o f o ne the refining copper is of the most important , if not
o f . most important , appli cation electro chemistry The first suggestion o f electrolyti c Copper winning is credited to Becquerel the first obtaining of electro
o n E n lytic copper the co mmercial scale to James B . lkingto o f England
s Two systems are employed i n copper refining , the serie i system and the multiple system ; the latter s the older . In the multiple system each anode i s connected with the conductor fro m the positive pole o f the electri c current ; each cathode with the conductor fro m the negative pole .
E o f . S . C In the series system , due to Hayden onnecticut , only o ne end - anode in each ta nk i s connected with the posi tive pole and at the opposite end onl y o ne cathode is co n nected with the negative pole . Between these electrodes , 9 6 N TES ON E E TR HEM T Y O L C OC IS R . copper plates are s et in an upright position ; the circulation o f the electrolyte may be maintained by compressed air o r by so me other devi ce .
a s The plates of crude copper whi ch serve anodes , usually f 55 75 have a sur ace of fro m to square decimeters , and are from 2 centimeters to 4 centimeters thi ck ; the cathodes con s o f o r C b e ist thin plates foils of pure opper . The distance tween the electrodes is generally maintained at from to
t o f centime ers , the electrolyte used is a solution s ulphate o f C opper acidified with sulphuri c acid . The voltage em
no t - f ployed is low , probably exceeding one hal volt . the In preparing electrolyte , copper sulphate solution and sulphuric acid , care must be taken to insure a solution rich
in copper , and to have it contain sufficient sulphuric acid to prevent the formation o f hydrated cupri c oxide ; o n the other
u o f sul hand , care must be taken to g ard against an excess
hu ri c o f p acid , as this would cause the liberation hydrogen at
o f o the cathode in the place copper . The temperature f the ° ° e a o 37 i t 3 . t electrolyte s ad vantageously h ld about 3 C C . The question o f current density is o f course a very i mpor
o ne o f N D a to tant , the value “,O r nges from possibly as to o dens itv high as However , high a current must be
i n avoided , as this causes the copper to be deposited uneven * masses , possessing but poor coherence . The tanks in whi ch the electrolytic deposition takes place are generally lined with lead ; there are often several hundred o f these in a plant . When in the course of operation the
to anodes have been reduced thi n sheets , the pro cess is inter ru ted re- p , the anodes are removed and smelted , the cathodes
a nd a - o r are likewise remo ved and recast , the node sli me ,
a s to a fo r mud , it is termed , is subjected separate tre tment . the obtainment o f the precious meta ls which occur therein
whenever such are present in the copper ores worked .
n t w e - o e T a ns a a da o c iet 19 0 o u : S . o r S 2 1 . 5 . 5 C s l C p r C l s , r F y y , , p ,
o u k n 1 4 2 1 n L A d rna l F ra n li nst 9 0 5 . a d . d . icks , J I , , p
98 ' N TES ON ELEC TROCHEM IS TR Y O .
In the same period 372 amperes will deposi t x 3 72 ' r 1 f o 0 . 606 o grams , , kilograms copper . This amo unt o f wi multiplied by the number vats in use , ll of course give 24 the total o utput i n hours .
o f As to the question energy consumption , assume a maxi the mum current efficiency , and assume that drop in poten
E v a tial is volt . ach t will thus require x 372 93 9 3
H . P watts , and this corresponds to . 74 6
H - P . f One will there ore deposit in twenty four hours ,
o f x kilograms copper , and a o f H plant 5000 P . would therefore yield x 5000
o f - kg . copper in twenty four hours . r Silv e . The principles underlying the process of re
l to fining silver electrolytically , and especial y adapted w o u t its separation fro m gold and copper , were orked by M oebius . The electrolyte used is a solution o f nitrate of silver con taining about 1 % of sil ver and from to 1 % o f free nitri c
o acid . The cathodes consist f pure silver foil and these receive a very light coating o f oil in order to permit of a
o f o f more ready removal the crystals silver , the form in which the silver separates from the electrolyte under proper current conditions . The anodes are made of crude silver , contain
9 5 7 o f ing about 90 this metal , the balance generally consisting of gold , platinum , and copper . l As stated , the silver separates in a crysta line condition and the remo val o f these crystals is effected by wooden arms w the hi ch are kept in slow movement , constantly freeing cathodes from these crystals ;if this were not done the crystals would re a dily grow to the anodes and in this manner of course n establi sh a short circuit . The anodes are i closed in a .
- sheathing of canvas and in this the anode slime accumulates . This anode residue i s o f course separately treated for the recovery of the precio us metals it contai ns . E T TE HN Y EL C RO C OLOC . 9 9
The current conditions generally employed for the electro
o f D lyti c refining silver are , voltage and N 100 i s i Go ld . The extraction of crude gold fro m t ores s gen o f o ne rally e fected either by the use of mercury , by of the so called chlorination pro cesses wherein chlorine is the active
use o f - agent , or else by potassi um cyanide acting in the presence of atmospheri c oxygen . Potassi um - cyanide is the reagent employed i n the Siemens Ha lske pro cess and the gold is reco vered electrolyti cally fro m the cyanide solution . The cyanide liquor contains not more
o f a than potassium cyanide . The nodes are generally
o f e - made iro n , altho ugh carbon , Ach so n graphite , and lead per-o xide anodes are also used ; they are inclosed in bags o f
o r canvas linen .
a nd The cathodes are made of lead , when sufficient gold has been deposited o n them they are cupeled and the gold r obtained . The crude gold thus secu ed contains about 0 85 % to 90 70 of pure gold this is subjected to electrolyti c n refining while the lead reco vered is reduced , recast , and agai
- m dc i sit is . u sed for cathodes . The current y e ployed very low
N DIOO ranges from about to the voltage from about to volts . ’ In Wo hwill s pro cess for the electrolytic refining o f gold the anodes o f crude gold are placed into a ho t solution o f hydrogen auri c chloride ( H An C14 ) containing hydro chlori c
o f o f . acid . The cathodes consist very thin sheets pure gold
- To insure a well adherent cathode deposit , the temperature ° 3 o f is kept at about 70 C . ; the electrolyte contains % gold
o and fro m 3 % to 4 % o f hydro chl ri c acid . The voltage em 1 N D 10 ployed is about volt , the IOO amperes . The pro
100 o f duct secured contains fro m to % gold . Lea d — . While there seems to be little opportunity fo r a co mmercially profitable pro cess o f winning crude lead elec tro l ti ca ll o f y y fro m its ores , the pro cess refining crude lead o ne electrolyti cally is well established , of the chief a dv a n 1 00 N OTES ON EL ECTROCHEM IS T Y R . tages of such a pro cess being that it permits the obtainmen t o f a pure lead and of a pure bismuth , the latter a common wo n i mpurity in lead by metallurgi cal processes . f ‘ o . G . ele ro l In the process A Betts , lead is obtained ct y
h dro fluo sili ci c ti cally by dissolving the metal in y acid , whi ch gives an electrolyte o f lead - sili co fi uo ride fro m whi ch metalli c lead is deposited at the cathode in the form of a dense and
o f o f smooth deposit . Addition a trace gelatine , an organi c
o f colloid , to the electrolyte insures the co ming down the electrolyti c deposit in a finely crystalline condition . The solution is kept continuously circulating through the vats .
a s The anodes are crude lead , and are apt to contain impur ities some copper , anti mony , bismuth , and silver ; these tend
- to remain in the anode slime pro vided the N D100 does not exceed ampere . If iron , nickel , and zinc are also present
is these pass into the solution . The voltage employed about o S the electrolyte is n t heated . tarting fro m a crude
' 9 5 lead containing about % of the metal , the refined product
is ra p ctically chemi cally pure . i ke — w N c l . The application of electri cal energy to the i nning o f nickel is practically confined to the refining of this metal . The conditions to be observed i n order to deposit nickel
\ successfully from an aqueous solution o f its sulphate o r its ° ° C 60 70 . chloride are a temperature of between and , an elec tro ly te containing about 3 % of ni ckel together with a trace o f free sulphuri c acid or hydro chloric acid , a normal current
density o f fro m to and a voltage o f fro m 1 to 2 volts . i Generally speaking , the h gher the current density the smoother
and the brighter the deposit secured . Electrodeposition o f ni ckel fro m ni ckel solutions by means
0 o f o f insoluble anodes is thoroughly practi cable . Anodes lead - peroxide have been used for the purpose ; when a s ul c phate salt of nickel is used as the electrolyte , the sulphuri acid set free in the operation must be neutralized with ni ckel
- hydrate Or nickel carbonate .
1 0 2 N O TES ON ELECTROCHEMIS TRY baskets ; a s cathodes they employ copper whi ch has been tinned . In the pro cess chiefly developed by the Gold s E G - chmidts in ssen , ermany , the tin plate scrap , containing a 30 is bout % of tin , placed in iron wire baskets which are s uspended , as anodes , in iron vats . The latter are made to 10 serve as cathodes , the electrolyte is a % solution o f caustic i soda . The operation s conducted at a temperature o f about 70 ° C . , the voltage employed is volts . In the tin thus d electrolyti cally eposited , lead and iron are apt to o ccur as i mpurities . The iron fro m whi ch the tin coating is originally
' is e removed fairly pure and can b reworked .
to s a Tin might also be reco vered from lead scrap , that is y , from sheet lead or fro m pipes upon whi ch a layer o f tin h a s m been rolled ; this lead s crap could be ade the anode , and s a ulphuric acid might be employed s the electrolyte . In such a pro cess of course the metallic lead would remain , barring a small percentage o f the metal whi ch wo uld be transformed
ul . into s phate , while the tin was recovered
in - E o f Z c . lectrolytic pro cesses are great value in the obtainment of zinc fro m its ores . S G In ilesia , ermany , during the last decade of the past
wa s u se century , a pro cess in wherein zinc sulphate was used a s m Of the electrolyte , the anodes employed being ade lead peroxide ; it was , however , ultimately abandoned because it could not co mpete co mmercially with other metallurgical o f pro cesses . Among more recent methods winning zinc its S electrolytically fro m ores , must be named the iemens
Ha lske pro cess , the Ashcroft pro cess , and the Hoepfner pro c esses .
S - Ha lske a s a s o f As h In the iemens pro cess , well in that e i o f croft , the or s worked are essent ally co mpo unds lead
l o f su phide and zinc sulphide , containing approximately
2 o f o 0 % zinc and 30 % f lead ; the ores are also argentiferous . In o ne of the processes by Hoepfner the crude material worked wa s essentially an iron o re containing about 10 % o f Y ELEC TROTECHN OLOG . 1 03
“ zinc ; the electrolyte used was a solution of zinc chloride ,
o f o f the anodes were made carbon , the cathodes co nsisted revolving zinc plates and the anode and cathode - chambers N D wa s 4 were separated by diaphragms . The IOO amperes , the voltage ranged between 3 and 7 volts .
E wa s In another Hoepfner pro cess , used in ngland , the zinc roasted , secured as an oxide , and then treated with a hot c oncentrated solution o f magnesium chloride in whi ch the o xide of zinc dissol ves as a basi c sal t. This solution received subsequent treatment with carbonic acid gas and with cal c i u m z 1n c u chloride solution , the appearing ltima tely as zinc
t . Ca r chloride , which solution was sub mi ted to electrolysis D 1 bon anodes were used , the N 100 ampere and the voltage about 3 Volts ;the purity of the resul ting product was A process for refining zinc electrolytically has been devised R E m by oessler and delmann . In this ethod the crude zinc , 20 Of used for anodes , contains about % impurities , among which should be noted copper , sil ver , lead , nickel , and cobalt . D t The N 100 to ampere , the vol age ranges from
l - to the electro yte is not heated . Fro m the anode slime , s ilver , copper , and lead are reco vered by separate processes . In this pro cess also the purity o f the refined product is a p proximately
Electro la ti n p g.
Elec a in — tropl t g . The first electrotechnical pro cess de vised seems to have been the electrodeposition of metals , o f o the art electrotyping . The making f exact metallic
inde en reproductions , replicas , of objects was disco vered p dentl S fi rs - y by Jacobi , by pencer , and by Jordan ; the t named o f these exhibited electrotype copies o f medals before the f o St. P 1 T wo 838 . M Academy etersburg in years later , urray discovered that non - conducting bodies when coated with graphi te would serve equally well as a base for electro dep o s i ‘ 1 O HEM I O4 N O TES ON ELEC TR C S TR Y.
o f r tion . From this pro cess elect otyping , a few years later , wa the process o f electroplating s evolved . The fundamental difference between the two pro cesses is that in electrotyping the electrolyti c deposit is meant to be
removed from the surface on which it has been formed , and therefore too firm an adh erence o f the deposit on the object o n which it is made must be avoided ; this is effected by giving " to the object a preliminary thin coating of o il or o f a solution o f a d some salt . In electroplating the deposit is meant to here as firmly to the object as if it had been welded on the same ; fo r a successf ul electroplating absol utely clean s ur
faces are therefore an essential condition . While for a long time it has been known that the chemi cal
composition , the concentration , and the temperature of the
electrolyte , as well as the current density employed , are all factors o f importance if a well - adherent electrodeposit is to
be secured , a recent study of the subject by Wilder D . Ban * E croft , On the Chemistry of lectroplating , has thrown light o n many aspects of the problem which were but little under s tood before . Among other interesting facts Bancroft found that a poor metalli c deposit is nearly always caused by the precipitation
o f o f o f f o r in some salt the metal in place the pure metal ,
s o f - tance , by the formation an oxide , a hydro oxide , or a cyan
o f ide . Therefore , the addition any chemical which will dissolve a salt o r which will prevent its formation must im
prove the quality of the desired electrodeposit . Maintenance o f pre per temperature conditions is likewise
essential , as is also the rate at which the electrolyte is stirred , fo r a sufficiently concentrated solution must always be main ta ined at the cathode ; to o dilute a solution at the cathode o f results in the formation sandy or pulverulent deposits . Determining the best conditions in individual cases re
quires considerable care and experimenting , yet the general
o u l o th nk i nst t V 4 i ut 19 0 5 o l . 1 rna e ra l n e 0 . 1 9 3 . J f F I , , , p
1 0 6 N TE O E E O S N L C TROCHEMIS TRY.
ferin o f g with the precipitation a firm , coherent deposit of the o f metal . The presence mere traces o f some other metals f more electronegative than zinc , also tends to the ormation o f spongy zinc , and such metals should therefore be removed
before electrolysis . Alloys also can be deposited by electroplating ; thus it is possible to make an electroplate o f brass by using a solution o f o f o f o f cyanide zinc and cyanide copper , both dissolved i n potassium cyanide . Bronzes , that is to say , alloys of c op per and tin , can also be electroplated , the deposition taking place fro m mixed solutions of their salts . Thus far ,
however , alloys have not been extensively used in electro
plating .
o n n a li - H dra es Chl r i e a d Alk y t .
Chlo rin a nd k a - H d a s e Al li y r te . In the electrolytic win n ing of chlorine and o f alkali - hydrates fro m solutions of a lkaline chlorides , the fundamental principle to be observed is the keeping separate o f the prod u cts produced at the the cathode fro m those produced at the anode . At cathode , a lkali and hydrogen are generated , at the anode , of course , c hlorine .
To achieve this holding apart of the products of the reaction , three different kinds o f pro cesses have been devised ; these ma y be designated respecti vely as :
I . The diaphragm pro cess .
II . The bell pro cess .
III . The mercury pro cess .
The chlorine gas whi ch is obtained by these pro cesses is
e a fo r o r ither liquefied and thus made av ilable shipment , it is transformed into bleaching powder ; the alkali obtained
c a n o f , course , be readily turned into the causti c condition . Probably the chief reason why the entire output o f caustic a lkali needed in the chemical industry is not produced exclu ELEC TRO TE CHN OLOG Y 1 0 7
siv el y by electrolytic methods , for these methods are eco
n o mica l , is the fact that there is not a sufficiently large h hi l demand for the c lorine w ch , of course , is si mu taneously
produced in quantity equi valent to the alkali obtained . The hydrogen gas whi ch is incidentally produced with the a lkali is in many factories allo wed to escape unused ; in so me
f o f f - places it is employed in the manu acture uel gas , and in o thers it is condensed under pressure and is thus made avail a ble for transportation . - The crude chemicals employed in the electrolysis o f alkali c hlorides are essentially chloride of potassium , obtained from c is arnallite and common salt . It very important that o nly pure solutions o f the alkali - chlorides be used for elec tro l sis fo r o f y , appreciable amounts impurities interfere s eriously with the working o f the pro cesses and with the q uality of the products obtained . In cases where the products liberated at the two electrodes o f are not kept separate , and where a free intermixing the
- i s cathode and anode solutions allowed , hypo chlorites and chlorates will be formed , according to the temperature and the current density employed .
The former salts , that is to say , the hypo chlorites , are pro d u ced at the anode when a low temperature and a low current a density are used ; such hypo chlorite solutions , practic lly not
2 o r 3 exceeding % in strength , are best used on the spot for
o f o n electrolytic bleaching . The formation chlorates is , the
o f other hand , favored by the use a high current density and h the presence of some alkali . Thus , potassium c lorate is now 5 made almost exclusi vely by electrolysis , about kilowatt hours being used per kilogram o f potassium chlorate pro d u ced . If this product is subjected to further electrolytic
lo w treatment with a high current density , at a temperature ,
- potassium per chlorate results . ia h r . a m Pr s I D p g o ce s . The principal problem to be s o f olved in processes this description , is to find a suitable 1 08 N TE ON E T O S EL C ROCHEM IS TR Y.
material whi ch shall pro ve resistant alike to chlorine and to
. G f o f alkali In ermany , a ter a great deal experimenting , plates of Portland cement were selected fo r the purpose
U S the in the nited tates , asbestos is material generally
used .
Fro m the very fact that any material serviceable fo r diaphragms must be sufficiently porous to p ermit o f the
o f is a passing the electri c current , it unavoid ble that a part o f set w l the hydroxyl ions free ill a so pass through , and these ,
l ea ctin m o f w naturally g with so e the chlorine hi ch is liberated ,
o f h a will cut down the output t at g s . C f l arbon anodes are pre erab y employed , the working b ° N D 85 C . temperature is held at a out , the IOO ranges from
1 2 the a a about to amperes at di phr gm . In some pro cesses the alkali —chloride solution is conducted only to th e c a thode
G m - E compartment ( rieshei lectron system ) , in others the solution o f the electrolyte flows fro m the anode compartment
m S m o f Mc Do na ld a nd o f to the cathode compart ent ( yste s ,
Hargreaves and Bird ) .
B P c f m o f I I . ell ro ess . The unda ental principle processes o f o f - - this description is the use some non porous , non con w to ducting medium , hi ch serves keep separate the solutions
i o f at the anode and at the cathode , wh le it permits those parts the solution not in contact with the gases set free at the f electrodes to intermingle reely .
o f The bell device consists essentially a vessel , techni cally w b o x o f the bell , hich is generally an open made sheet iron
- and coated with some non conducting material . This bell
o r is suspended with the Open side downward in a vat chamber , likewise constructed o f some non - conducting materi al ; into ' f a this chamber the electrolyte is placed . A per or ted carbon anode is hung inside o f the bell and the chlorine generated at this anode is carried a way by an exit- tube whi ch passes
o f through the upper part the bell . The cathode is placed in the outer vessel and the alkaline lye which is generated at the
1 1 0 N TES ON E E TR E S T Y O L C OCH MI R .
D ing i n the water and the hydrogen gas escaping . The N 100
7 c at the cathodi c mercury is about amperes , at the anodi 12 4 mercury , about amperes ; the voltage is about volts . C The product obtained by the astner pro cess is very pure .
i s n l o f The chlorine ge erally turned into ch oride li me . A pro cess differing fro m but planned o n lines similar to K ’ E those j ust referred to , is ellner s pro cess , and in ngland the Castner- Kellner Company makes use of a metho d embody
o f ' ing the fundamental principles both of these systems .
l l . E E E . R PR A I N DI CT ACTION OC SS S .
El c ro de o o n ro m F u s ed Electro l tes e t p si ti f y .
Intr du i n l o ct o . In e ectrolytic pro cesses where the prod net is obtained fro m a fused electrolyte , the electri cal energy is in part used fo r the actual electrolyti c work and in part fo r
o f the fusing the electrolyte . The relation between electri cal energy and heat energy is expressed by Joule ’ s law “ the heat developed in a conductor is proportional to the resistance enco untered and ” to the square of the strength of the current . If : resistance R current strength C heat H H C2 then , R is The heat thus generated electrically , not chemi cally , ’ termed Joule s heat . To illustrate , assume R 2 esistance equal to ohms .
Current strength equal to 50 amperes .
50 50 2 1 5000 . Then , x x x joules per second
o ne C As joule equals large alorie , or small
5000 5000 x C o r calorie, joules alories , 12 5000 x 00 calories . ' 1 1 1 ELEC TROTE CHAOLOG Y .
tr In passing thro ugh a circuit embracing an elec olyte , Joule ’ s heat is generated in all parts o f the circuit in amounts proportionate to the resistance o f the respective parts o f the circuit and to the square o f the current . Th e actual temperature to whi ch an electro lyte thus attains in a given time under given conditions o f current strength its its and resistance depends upon mass , specific heat , and o f upon the success with which loss heat by radiation , and
- b e . by other causes , can avoided An i mportant point to be borne in mind in attempting to secure a metal fro m a fused ele ctrolyte is that the boiling ‘ ‘ point of the metal must not lie too close to the p o i nt o f fusion o f the o f electrolyte , otherwise volatilization the metal would almost keep pace with its ele ctrolytic production . The metals whose productio n Zfro m a state o f fusion shall no w be briefly considered are aluminium , magnesium , and sodium . uminium Al . Various pro cesses have been devised fo r
. d the electrolyti c winning of alumini um The metho s , how e ever , principally employed are the H roult pro cess and the
two . C Hall process hemically , these pro cesses are very much A1 0 a d alike , in both , pure alumina ( 2 3 ) is dde to the fused
o f A1 F 6 double fluoride aluminium and sodium , 2 6 , Na F , a mineral called cryolite . In putting the process into O peration the cryolite is first brought into a state o f fusion in iron furnaces and then the m A anodes are lowered into it and ele ctrolysis com ences . s
is the aluminium separates at the cathode , alumina fed into the bath so as to keep the amount o f a luminium present in the electrolyte about constant . The metal being specifically
o f heavier than the fused electrolyte , sinks to the botto m the
ener a ll ' o nce fusion chamber , whence it is tapped , g y a day . o f The anodes are made carbon , the cathodes are generally
o f o f made iron , but these also can be made carbon .
: In the Hall pro cess , the amperage used per fusion chamb er 1 1 2 N O TES ON ELEC TROCHEMIS TR Y.
is 5 about amperes , the voltage employed , about volts . The temperature o f the bath is held in the neighborhood o f 1000 ° C . t , being kep as low as possible . The fusion chambers
are discharged at stated intervals . e 8000 In the H roult pro cess , about amperes per furnace are r r 3 5 D 190 equi ed , the voltage ranges from to volts , the N 100 ° ° amperes and the tempera ture is held be tween 750 and 850 C . The chemical reactions taking place during electrolysis consist in the liberation o f aluminium at the cathode and of oxygen a t the anode ; this oxygen o f course combines with the
carbon anodes to form carbon monoxide . The pure alumina which is used in the process is generally obtained fro m the
mineral bauxite , which is passed thro ugh a preliminary puri fy ing operation by roasting and by subsequent treatment
o r with caustic soda , , according to a recent pro cess devised m M . e C . by Hall , bauxite as well as oth r impure aluminiu
oxides are purified by fusion with the electri c current , the
i mpurities present being reduced in the fused bath . Esti mates vary as to the amount o f electri cal energy nec
e o f o ne ssary in the Hall process , for the production kilogram h i . Bu c erer t 30 of aluminium places at Becker at , and 22 - R . J . W . ichards at kilowatt hours Of the total electri cal energy consumed in the production
o f - fifths aluminium , it is calculated that about four are used for the heating and the balance fo r the actual electrolytic h f work . The electri cal energy , w ich is expended in e fecting the separation of metalli c aluminium fro m its chemical co m
b ina tio ns , can of co urse be recovered as heat energy when the
~ is metal is caused to re co mbine with oxygen ; this the case ,
for instance , in the Thermite pro cess . According to the report o f the United States Geologi cal ’ S o f 190 3 urvey , the world s production aluminium in was o o f ver eighteen million pounds , which seven and a half U S millions were produced in the nited tates , the balance being
S G . made in witzerland , France , and reat Britain
1 14 TE E T E T Y N O S ON EL C ROCH MIS R .
o f the cathode chamber prevents the oxidation the sodium . 3 10 ° ° The temperature is carefully held between and 330 C . 5 t The voltage used is about volts , and each furnace uses abou 1200 amperes . E A recent pro cess , devised by . A. Ashcroft , consists of a
o n cell wherein fused sodium chloride , the electrolyte , rests fused lead , which acts as cathode ; the anode is made of
carbon and the chlorine is there liberated . The sodium i alloys w th the fused lead , and this alloy is conveyed to an
outside co mpartment where it acts as the anode , the cathodes
o r o f being either iron ni ckel , and the electrolyte consisting
fused sodium hydrate . I n this outer chamber metalli c set sodium is free at the cathode .
s m A pro cess devised by Acker Bro , akes use of fused
sodium chloride as the ele ctrolyte , the same being well dried
o f before fusion . The anodes consist graphite , and fused lead
serves as cathode , as in the Ashcroft pro cess . The lead —sodium alloy is decomposed at red heat by steam
blown in under pressure , the resultant products are molten
lead , sodium hydrate , and hydrogen gas . The voltage 7 D 290 employed is about volts , the N 100 about amperes , each furnace taking 8000 amperes ; a part o f this energy is used
' to keep the sodium chlo ride in a state o f fu sio n x witho u t
application of heat fro m any outside source . The chlorine
o f evolved was formerly turned exclusively into chloride lime , but recently the Acker Pro cess Company have devised new
fo r uses the chlorine , and among other products now manu
o f facture tetrachloride o f carbon and tetrachloride tin .
Electro ther mi c Pro ces s es .
- E c a ces . o f le tro furn In conductors the first class , that is
o s a a ll ca n t y , in all metals and in carbon , electrical energy
be converted into heat energy . o f The formula by means whi ch the heat equivalent , in
calories , of a gi ven amount of electri cal energy can be figured 1 15 ELE C TRO TE CHN OLOGY.
is . , it will be recalled , very simple Designating the heat H R equivalent by , the resistance by , the current strength x is by C, the result desired , e pressed in gram calories ,
H CZR
Probably the first o ne to suggest the appli cation o f electri
fo r o n cal energy electrothermi c work a co mmercial scale ,
ir W 1 S S 0 . was illiam iemens , in 88
The transformation of electri cal energy into heat energy is , in practi ce , acco mplished in several ways , and at least fo ur types of ele ctri cal furnaces may be distinguished
1 a r . The e furnace .
2 . o r . The resistance , incandescent furnace
3 . . The transformer , or induction furnace 4 . The tube furnace .
Arc furnaces may be divided into two groups , direct and indirect arc furnaces . In the former , the material to be sub j ected to the influence of the heat generated by the trans formation of electri cal energy , is exposed directly to the electri c arc ; in the indirect type the material to be treated is not exposed to the direct action o f the a r e but receives its heat indirectly , the heat being reflected fro m the interior of the chamber in which the reaction takes place and into whi ch the electrodes project . Of course the forms which may be given to a r e furnaces are o f varied , but the principal feature embodied in all furnaces this description is a hearth constructed of so me fire- resisting
fi re- o r material , bri ck the like , an d carbon electro des , which f project into this usion chamber . The current is supplied by means o f heavy cables clamped to these carbon electrodes .
o n As before stated , the material to be acted may be either
to o f a r e so exposed the direct heat the , or else it may be placed that it receives only radiated and reflected heat fro m 1 16 TE ON E E TR E S TR Y N O S L C OCH MI .
the walls and the roof of the furnace chamber . An illustra tion of the former type is o ffered by the aluminium furnace during the ti me when the cryolite and the alumina are being f used , that is to say , before electrolysis proper has begun .
As an illustration of the indirect action type of arc furnace , there may be mentioned the furnace used by Moissan in o f Cha lmo nt f so me his famous researches , and the De urnace
fo r o f i e mployed the reduction metallic silic des , for in these the charge is also exposed only to the radiated heat of the arc . R f esistance , or incandescent urnaces , were probably first E f C . . C o C devised by . H . owles and A H owles , leveland , O 1 f 885 . hio , i n The principle upon which these urnaces are constructed is to have so me material in the circu it of the electri c current which will o ffer a high resistance to the t passage of the current , in consequence of whi ch high emper atures are generated .
Where highest temperatures are sought , the arc furnace is the indicated , but where closer regulation and control of working temperatures are demanded , resistance furnaces
f i e a o fer dec d d advant ges . The degree o f temperature attained in the resistance fur is o f nace determined by the magnitude the current , the
o f e time during which this flows , and the amount r sistance w o ffered by the circuit through hich the current passes . The ultimate temperature attained is the o utco me o f the rate at which heat is generated in the resistant body the f core , and the rate at whi ch this heat su fers dissipation . The point at which these two conditions counterbalance each f other determines the highest temperature o the furnace . f In the resistance urnace , the material to be heated can
d o r itself be made the resistant bo y , the latter can be em bod ied as a core in the materi al to be treated . In such cases , the material generally employed is carbon , coarsely grai ned . The Acheson furnaces well illustrate that type o f the
11 8 N TES ON ELECTRO HEM I T Y O C S R .
s o f o ne o f econd tube made these oxides . On this outer tube , over a layer of mica , a coil is wound in which electri cal f action is started ; the actual heating e fect , however , is pro d u ced in the interior tube . This furnace is chiefly used for o f the baking Nernst lamp glowers .
o f Among other tube furnaces , mention should be made E the one designed by A . H . ddy , used for the application of o f G enamels , and that Nernst and laser , which has a resistance tube made of electrolytic oxides , the outer tube consisting of loosely packed oxides and all inclosed in a j acket designed o t prevent loss o f heat by radiation . A very convenient electro - furnace for certain laboratory purposes is used by the Technische Rei chsanstalt at Char
lo ttenb u r . g , for high temperature work It is made of several f concentri c porcelain tubes , and the heating is e fected by passing an electric current through wires which are wound upon some of these tubes . Recently an electric furnace which can be used in connec h tion wit a vacuum , and for general analytical purposes , has
o f Hera eu s been devised by the firm , These furnaces can be used with direct current at a potential o f
2 . fro m 6 5 to 2 0 volts , and require only fro m to amperes
The uniformity of temperature , whi ch can be maintained in o f these furnaces , and the avoidance reducing gases , which the use of fuel gas often entails , are valuable features . In s o me electrothermi c furnaces the pro cess is a continu o u s one , that is to say , the pro cess is not interrupted for the introduction o f charges , nor for the withdrawal of the prod
u ct. It is , however , not always possible to arrange a working system in this way , and therefore many furnaces are inter mittent in their action . The electri c furnace undoubtedly permits the securing of a higher temperature than can be secured through any other
devi ce . Whereas the maximum temperature obtainable by
eitun 19 0 5 V o l . 29 . 1 20 9 . Chemi ker Z g, , , p E E T TE Y 1 1 9 L C RO CHN OLOG .
the co mbustion o f fuel under the most favorable conditions 2 0 000 C . is probably not abo ve , the temperature of the elec tri c arc has been estimated by Violle in 1893 a t about 3 ° 600 C . , and it will probably be reasonable to regard this as the highest temperature maintainable in arc furnaces under ordinary conditions . In furnaces provided with additional
o f prote ctio n against loss heat by radiation , for instance , in furnaces having an additional lining o f some good non - con 4 ° 000 C . ductor , like magnesia or chalk , temperatures up to
o f can be secured ; speaking , however , practical electri cal
furnaces working on a commercial scale . the working tem ° era u r p t es o f these will range fro m about 2000 to 3 500 C .
Where no electro chemi cal , but only electrothermi c work to the has to be done , preference is gi ven alternating rather
than to the direct current .
o f o f In considering the cost electri c furnaces , the cost the electri cal energy to be used is naturally 'a factor o f the great est i mportance . Where such energy has to be generated by
o f the combustion fuel , the cost will necessarily be high , 5 8 because only a small percentage , possibly from to % of the heating power o f the coal whi ch is burned under the
boiler , is actually gained in the form of electri cal energy .
- Where water power is available , the conditions are far more
favorable , and it does not appear i mprobable that in the near future wind - power may be made to serve for the cheap gen c o f fo r fo r ration electricity electrothermi c , as it now does * other purposes .
- Electro Fu rn a ce Produ cts . A number o f substances have been prepared by the aid o f the high temperatures made
- S available through electro furnaces . o me of these are metals won in the free state through the disso ci ation o f their co m pounds — for carbon at th e heat of the electro - furnace can
A D n he b e r e z v n K a u f n n P a u l la Co u r ( u s d em a is c n u s t o J . m a ) Die Wi n dkra ft u nd i hre Anwen d u n g z u m Antri e b v o n Elektri z itats VVerk n e e 1 9 0 5 . , L ipzig , 1 20 N OTES ON E E T E T Y L C ROCH MIS R . remove oxygen fro m any metallic oxide known ; other s u b stances produced are co mpounds , the chemical union o f their constituents being effected by the aid o f electri cal energy . The metallic products of electro - furnaces shall be first
considered . Ch r m um o i . This metal has been obtai ned in the electric
f If o f furnace ro m various raw materials . a mixture chromi c Or 0 f oxide ( z 3 ) and carbon are used , carbides of chromium a nd result , from these , by fusio n with lime , the greater portion
o f carbon can be removed . The metal thus p roduced con 9 7 98 tains between and % of chromium , and carbon , iron , If h and sili co n as impurities . perfectly pure c romium is
required , this can be secured by fusing together chromic
oxide , chro mic carbide , and lime .
As cherma nn 1 In the pro cess , a mixture of chrom e oxide and antimony sulphide are fused together in a graphite
o f crucible , and fro m the resultant alloy chro mium and anti
mony the latter element is remo ved by heating . r a nd — i I on Steel . Under existing econom c conditions it is evident that electro - smelting o f iron ores and the electro production o f steel is practi cally feasible only where pure ores may be worked and where electric power can be cheaply
produced . There is no question but that an o re so treated and a steel
so o f produced may be superior quality , at least when pro du ced in certain types o f electro - furnaces for in some types o f furnace the influence o f impurities can be avoided to a
great extent . A number o f electri c furnaces have been designed fo r the
purpose o f working iron ores and o f produci ng steel . P e o f 1900 aul H roult , France , was , in , the first to make steel k electri cally on a commercial scale . He devised several inds
o f - f fo r o re electro urnaces smelting and for steel refining . One of these somewhat resembles a Bessemer converter in its
1 22 TE ON E E T O HE I T Y N O S L C R C M S R .
is a s bon to be used placed between the electrodes resistance , a nd i the ore to be treated s packed around this core .
F . C . Weber has devised an arc smelting furnace in which o f the descending charge passes through a series arcs , each o ne of whi ch can be independently controlled ; this permits o f an accurate regulation o f temperature in the various z ones of the furnace . Among other pro cesses devised for iron and steel work m o f M. R ention should be made of the pro cess uthenberg , e specially adapted to the working of metalliferous sands and of
o f finely divided ores at a relatively small expenditure energy , a nd K ellin in S of the pro cess of j , weden , which , as previously m S o f entioned , is aid to pro duce a steel excellent quality . ’ Kj ellin s furnace is of the induction type ; a current of 3000 volts is supplied and the current passing through the charge i s about amperes . By avoiding the use of electrodes the steel is not open to the absorption o f i mpurities and hence the high grade product . The cost is reported to be co mpara ti v el lo w y . Ma nga nese A crude metal containing about 90 % of manganese is obtained by fusing the oxide o f manganese in an arc furnace . As manganese is rather a volatile metal the temperature conditions require to be carefully regulated , for the heat must not be allowed to become too great . An iron manganese alloy (ferro - manganese ) is prepared S by the i mon p ro cess in France , by fusing together an oxide o f fl u o rs a r P o f manganese and p . art the electri c energy 25 used is expended in electrolytic action , possibly about % o f the total being used for this purpose , while the balance f - produces the necessary heating e fect . The ferro manganese alloy resulting fro m this pro cess contains about 85 % o f o f manganese and from 7 to 8% each iron and of carbon . Mo bd num - ly e . Heating molybdenum sulphide with car bon produces a crude molybdenum which contains a p p ro x i 10 o f mately % of impurities , which carbon and iron are the Y 1 23 ELE C TRO TE CHN OLOG .
mo l b m ost important . This crude metal when mixed with y d enu m o xide and subj ected to fusion in an arc furnace wo n parts with its carbon and is in a pure condition . — o f Tita nium . The fusing point titanium is higher than that o f any metal thus far obtained by thermo - electri c M f work . oissan did not succeed in completely using a s 3 50 o f o f mall amount , possibly grams , a mixture titanic acid and carbon even by the expenditure of 2200 amperes n a d 60 volts . The metal titanium co mbines readily with nitrogen , but this co mpo und , the nitride , can be broken up by raising the temperature of the a r e sufficiently high ; in s o o f o f i doi ng , however , so me the carbon the arc s apt to i enter into chemical co mbination with the titanium , th s resulting in the formation of a carbide o f titanium fro m is no t which it most di fficult , if impossible , to obtain a pure
metal . Ura ni u m — i . This metal can be obta ned i n a pure state
i s x from t o ide by heating the latter with carbon . Uranium ° o f 1 is volatile in the electri c arc , and at a temperature 000
C . readily enters into chemi cal co mbination with nitrogen . a n a dium i V . Vanadium can be obtained by the G n pro ’l< o cess fro m the fluoride f vanadium . The anodes used are r ods especially prepared from vanadium trioxide , retort
carbon , and rosin , shaped under hydrauli c pressure and
baked at very high temperatures . The cathode is made o f N D 200 iron . The anode wO is approximately amperes , the N D 600 12 cathode mO about amperes , the voltage about
volts .
so - - Alloys with iron , the called ferro vanadium alloys , are a lso prepared by this pro cess . Tun s en M g t . oissan succeeded in preparing this metal by fusing together tungsti c acid and pure carbon . It is impor tant that an excess of carbon be avoided and that the temper
Beri cht d s V B n 19 0 3 V o l . e . Int Ko n resses itr An ew hemie e . g j g C , rli , , 4 74 4 , p . . 1 24 N T E E T E O ES ON L C ROCH M IS TR Y. ature be kept sufficiently lo w so that the metal may no t fuse
o co mpletely , for if it does , so me of the carbon will enter int chemical co mbination with it , forming carbide of tungsten .
Electro - fu rnaces are also used for the man ufa cture o f other
no m f o f substances t etals which , be ore the coming the
- n o r electro fur a ce were either unknown , were made by other processes . Of these prod ucts the following shoul d be men i d t o ne .
u dum e Al n , or artificial corundum , is an abrasive , crystallin in form , and extremely hard and sharp in grain , prepared in the electric arc furnace fro m calcined bauxite or fro m gibb site , by the Jacobs pro cess .
- - B u d C . r . a i m Hy rate . In a pro cess also devised by B
Jacobs , barium sulphate (Barytes ) is treated in an electric
o f o re furnace in the presence carbon . The is first reduced to barium sulphide and this , reacting with additional barium a sulph te , forms barium oxide and sulphur dioxide gas . The
s barium oxide is dissol ved in water , and the hydrate thu formed is obtained a s crystallized barium hydrate of high grade purity . Ca b d s r i e . A class of bodies termed the carbides is formed in the electri c furnace by reducing the oxides o f so me metals
no n- o o f E and metals in the presence f an excess carbon . ither a re o r resistance furnaces may be used fo r the purpose ; often
' both systems co me into play in one o p era t o n through the unavoidable arcing whi ch o ccurs in the working o f some resistance furnaces . While the list o f carbides embraces possibly so me twenty o dd co mpounds only a very few o f these have any appreciable
- co mmercial i mportance , calcium carbide is probably the
o f most important them all . a ium- a rb — n 2 M he C l c c ide . I 189 oissan announced tha t
' - a co m o u nd o f had made calcium carbide , p calcium and car
EM I TR Y 1 26 N O TES ON ELEC TROCH S .
carbonate to the original charge of li me and carbon ha s bee n
ad vo cated ; this pro cess is known as the Hewes pro cess . I n R , o f another pro cess , devised by athenau iron , or oxide iron , is added to the charge before fusion so that the iron may co mbine with and remo ve all of the silicon present as ferro
sili con .
f o f - In the manu acture calcium carbide , ei ther the direct o r the alternating current may be used ; for some reasons th e f latter is pre erable .
o f - The co mmercial value a gi ven calcium carbide depends , o f of course , upon the amount acetylene gas which it
will yield on reacting with water . The equation reads :
Ca C 2 Ca OH , ( ) ,
The theoretical yield of o ne kilogram o f pure calcium
3 50 o f carbide is about liters acetylene gas , at normal tem
era tu re f m p and pressure ; ro m the co mercial product , however , 85 o f generally not more than % this yield are obtained . b b - E R P Ca i h . Y d . w . a n Ne r on sulp i e Taylor , at enn ,
- f Y d b i . ork , p ro uces carbon sulphide in electri c urnaces These 4 1 16 measure about feet in height and feet in diameter , the f n diameter decreasing towards the top . These ur aces are con structed o f a steel shell and a re lined with refractory fire bri ck
o r some similar substance . ° 90 a The electrodes , four in number , are placed part and are r e- enforced in the interior o f the furn a ce by a continuous
o f o r w supply coke broken carbons , hi ch are fed into the
furnace by cond uits . The sulphur is placed at the bottom o f the working chamber
o f o the furnace and extends up t and around the electrodes . Annul ar ch a mbers situated in the l o wer part o f the furnace
w a t are kept suppl ied ith sulphur . whi ch is fed in the top and
whic h runs down into the furnace in a molten condition . o f The vapors sulphur passing through the charcoal ,
' o f f which fills the body the urnace , combine with it and form ELECTROTE H L Y 2 C N O OG . 1 7 vapor of carbon b i- sulphide ; this passes o ff through a tube n o f v ear the top the furnace into a condenser, wherein the apor becomes liquefied . A subsequent distillation insures a product almost entirely pure . The furnaces are arranged wi th a vie w to economize most o f th e heat generated in the process and are continuous in their
4 500 o f action . The output is about kilograms carbon bi 2 sulphide in 4 hours . The working power is furnished by tur
- bine water wheels , although a steam engine is held in reserve
the . in case , for any reason , water power should fail
a ss Gl . Glass when in a fused condition is an electrolyte , and a number of electrothermi c pro cesses have been devised
the for its manufacture . In some of these pro cesses as in S hade pro cess , an arc furnace is employed , in which between four and six kilowatt - hours are required to produce o ne
o kilogram f molten glass .
fo r R res is In other pro cesses , instance , in that of ei ch , a tance furnace is used . In a recently designed furnace o f the — n resistance type , kryptol whi ch is essentially pure carbo o f * The uniform grain , is utilized as the heating material . kryptol is packed aro und the vessel holding the charge o f . glass and by this arrangement the loss o f heat by radiation is
. C t e materially reduced arbon electrodes are employed , h 100 current used is about volts , and the o peratio n is carried o n at a temperature materially belo w that of an arc furnace .
fo r o f co m In still other furnaces the manufacture glass , a bination o f the arc and the resistance principle is employed ; an illustration of this type is the August Voelker furnace , which is used in Germany and which is reported to be very ff e ective in its working . ‘ G a hi e r p te . Artificial graphite r is another product mad in by the Acheson Company at Niagara Falls . It is prepared
V 4 4 4 l . 7 5 . Electri ca ev i ew 19 0 5 o . l R , , , p
o n u t T o wn en d Ele tric Wo rld 1 90 1 fo r a n to a l i . . c C s l C P s , , , his ric resu me o f tu d e o n a t a a te s i s r ifici l gr phi . 1 28 N O TES ON E E TR E S TR Y L C OCH MI .
o r Th a resistance furnace fro m anthracite coal from coke . e
f o f charge is separate ro m the core , whi ch consists carbon rods extending through the charge . At the beginning of the operation these carbon rods transmit the whole of the current
a and , in consequence , become highly he ted . The high tem
' era ture t n p thus generated , converts hat portio of the charge i mmediately adj acent to the core into graphite ; this graphite then conducts a part o f the current and thus gradu a lly the zone of reaction extends farther and farther thro ugh the
mass . C The Acheson ompany also graphitize electrodes , these in the pro cess being exposed to a temperature abo ve the temper
o f ature of volatilization sili con , iron , and aluminium . N F xa C itrogen i tion . hemical combination of atmospheric
o f s l nitrogen and oxygen , and the union the re u tant nitrogen
to f oxides with water orm nitri c acid , has been achie ved by
C . a R L . C . . . . C S . F ro cker , Br dley , and D o vejoy
The works are situated at Niagara Falls . Dry air is passed through a chamber provided with stationary negative elec trodes whi ch are placed in verti cal rows and before which there revolves a central sha ft carrying the positive electrodes
ending in fine platinum wires . The negative terminals are in
- connection with choke coils whi ch are kept submerged i n oil .
o f A current volts is employed , and about arcs per minute are flashed through the air which passes between
the electrodes . The treated air contains between two and
o HP . three per cent f nitrogen oxides . Seven hours are said to produce abo ut one- half kilogram o f nitri c acid ; this acid
a nd a calci um nitrate v lued as a fertilizer , are among the * products manufactured a t the Niagara Fa lls plant .
— o n f d o f f Ox ne . Ox e o , a used peroxi e sodium , is manu actured
Fo r a re ce nt co m p re he n sive re v i e w o f the w o rk d o n e o n a tm o s phe ric n itro gen s e e A Ne u u e Di e V er wer thu n des Lu sticksto s Zeitsch i t ur . b rg r , g fl fi , r f f 6 4 n ewa ndte hemi e 19 0 5 . 1 7 1 18 10 , 18 3 . A g C , , p p ,
13 0 N T E O E O S N LEC TROCHEMIS TR Y. o f the me tals mentioned and the -mixture fused in the elect ri c f urnace . Thes e sili cides are crystalline in structure ; when brought c into contact with water they deco mpose it , and yield a sili o s hydrate of the metal and free hydrogen gas . Of the silicide mentioned a given weight o f calcium sili cide furnishes the
u o f greatest vol me hydrogen gas , a corresponding amount of o ne- barium silicide will yield only about half as much .
C need o mmercially , these compounds are in the preparation o f hydrogen gas , and they are also employed as powerful reducing agents . Copper silicide (Cu Si ) is another member o f this group ; it is principally used as a reducing agent in the preparation
- o f t so . a cer ain class of copper alloys , the called silicon bronzes 0 o f Copper silicide contains about 30 70 sili con .
- f Ferro silicon can be made from the slags o steel furnaces .
- 30 Two ferro silicon alloys , the one containing about % and the other about 50 % of sili con and approximately 5 % of
o f carbon , are used in the manufacture steel , especially of
- ff armor plate . Ferro silicon is far more e ective than carbon 7800 as it evol ves calories , where a corresponding amount o f carbon yields approximately but 2500 calories . f n u m i n Ca rb id . ca rb o u d S li co e Technically known as , sili con carbide (SiC ) is prod u ced by the fusing of sand and a s : carbon , expressed by the equation
- . Sic + 2 co
1 o Acheson firs t made carborundum in 89 3 . The operati n is conducted in a furnace built up of loose bri ck , and each furnace serves fo r one run only . An alternating current is conveyed by leads to bronze end -plates to which the carbon
o f electrodes , bundles carbon rods , are attached ; between these electrodes the core o f coarsely powdered coke is laid .
o f The charge , consisting sand , coke , sawdust , and a little
e . E s t salt , is placed abo ut this cor ach furnace take abou ELEC TRO TECHN OLOGY 131
HP is 200 1000 . The initial voltage about volts , but this 6 o f e drops by fully 0 % as the heating the core progress s .
- - si x The total process takes fro m twenty four to twenty hours ,
fo r that is to say , the electri c current is passed that length o f dis ti me , then the furnace is allowed to cool and is
mantled .
Various products are formed , segregated i n layers . The o f central core is graphite , next to this a layer crystallized C o f arborundum , and then a layer greenish sili con carbide ,
amorpho us in structure , generally intermingled with so me of f the original charge which has not been trans o rmed . This
a nd is substan ce , essentially a co mpound of carbon silicon , termed white stuff ; all of the material beyond the white stuff i d s reincorporate with the next charge . The manufacture o f white stuff has been made the subject o f a separate patent
by Acheson . Carborund u m consists practi cally o f 70 % o f sili con a nd
30 o f is a s % carbon ; it apt to hold impurities some iron ,
aluminium , and calcium . About kilowatt- hours are required to produce one kilo gram o f carborundum and the temperature must be carefully regulated to guard against volatilization o f the silicon ; ° 3800 C . is approximately the temperature o f formation of * carborundum . This substance is used largely as an abrasive ,
fo r o f furnace linings , and for purposes deoxidation in the
f o f manu acture steel . — Silo xi co n . a s b This substance , originally obtained a y product in the production o f carborundum is now a separate
o f is o f arti cle manufacture . It a chemi cal compound the its elements carbon , silicon , and oxygen , and constitution is i S C O . expressed by the formula , , , f 2 ° o 700 C . It is made at a temperature about , in furnaces similar in construction to those used in the manufacture o f
W h c mii . t ib er it 4 i ld Electro he c f A . F tz ra . 2 . Ge . o n e . . J ri g , L p C r ; F J , ca l a nd eta llur ica l ndu str 190 M g I y , 6 , p . 53 . N TES ON ELECTROCHEM- THY O IS .
ilo xi o carbor undum . S c n is very refractory at high tempera tures and is soluble only in hydrofluori c acid ; a s it is self binding it needs only to be moistened with water and can then
be molded into any shape desired , preli minary to firing . It is fire- used for the manufacture of bri cks , crucibles , etc .
ELEC R — RG N C PR CE E T O O A I O SS S.
B 1 Dir - . . ec c i Pr cesses E t A t on o . lectro reactions in the _ o f do main organic chemistry , may also be divided into direct action and into indirect actio n pro cesses . The former group would include all actions in which electri cal energy is directly — applied , for instance , all electrolyti c p ro cesses whether
t o f o r hese be pro cesses substitution , oxidation , reduction ; f it would also embrace reactions e fected by silent discharge . The other group would include all indirect effects such as
- i - thermo electr c and photo electri c processes .
S o f o f these u peaking the first gro ps , attention has been given chiefly to pro cesses o f reduction for the reason that
e these can be . most conveniently studied with reference to
certain groups in the molecule , whereas pro cesses of oxida
a s tion are , a rule , apt to involve the molecule as a whole in
chemi cal change . Reference cannot here be made in detail to the many mteres ting and valuable results obtained in organi c chemis tr o f - - y by pro cesses electro analysis and electro synthesis , which afford the great ad vantage o f permitting the bringing about o f chemical reactions without necessitating the intro
o duction f any chemi cal reagents . It must suffice to remark that within the past decade great ad vances have been made iii the o f t e to o f application elec ri cal en rgy, the solving numer o us p ro b lems in organic chemistry a nd that the field is still y * a: v ery promising One fo r the investigator .
o f i en ult CxW xLo eb Di Elektro chemi e der r a nis chen Verbi ndun en d " t C , e g , s O g ,
19 5 .
1 34 N TES ON E E TR E S TR Y O L C OCH MI .
tri ca l energy being obliged to pass through the containing glass walls and through the gas confined between them . In
- u other forms of apparatus a metalli c foil tin foil , al minium
o f foil or silver , is used instead the acid conductors . The s i mplest form o f apparatus used for the purpose consists o f two metal plates between which the gas to be acted upon is
a t placed ; as these metal plates are , however , p to beco me w is orn and ro ughened by the discharges , there always
a some danger of spark disch rges . Aluminium is possibly the
o f metal best suited for constructions this description .
' In every case the thinner the layer of g a s through wh ch the f is electri c discharge must pass , the more e fective the f reaction . In rarefied gases the discharge is o ten a ecom
a nied s o - p by luminous pheno mena , the called Geissler tube ff e ects . As there is no appreciable elevation of temperature in these a f re ctions , endothermi c compounds may be o rmed under the
o f fo r influence the silent discharge , and this reason these phenomena and reactions are o f the greatest value in bring ing about si mple organi c syntheses , si milar to those whi ch plants effect under the influence o f sunlight . w Berthelot , experimenting ith the silent discharge , showed that atmospheric nitrogen could be bound in the form o f w complex organic co mpounds , whi ch , hen treated with
- soda lime at high temperatures yielded ammonia . The
‘ a o f to results he obt ined are special interest , as they point the possibility o f the assimilation o f atmospheri c nitrogen by
plants under the influence o f atmospheri c electri city .
T o u t w hus Berthelot pointed , that in clear eather there is a di fferen ce o f poten tial o f fro m 20 to 30 volts between
wo o f ne t layers air whi ch are but o meter apart , and in rain storms this di fference o f potential may rise to about 500 v olts . As Berthelot achieved a fixation of nitrogen by carbo
o f a ff o f 8 hydra tes by means di erence potential of volts only ,
o 0 V 2 0 l 1 1 7 . m t nd 19 o . 3 . 7 re . C p . , , p ELEC TROTECHN OLOGY 1 35
his suggestion , that in nature the silent discharge is an acti ve
- l agent in plant life and growth is certain y most plausible . A number of syntheti c re a ctions have been achieved in the
laboratory by means of the silent discharge . Thus , under its x influence , carbon mono ide and nitrogen have been made to
- a s yield formaldehyde and marsh g ( Brodie , and , it is interesting to recall that formaldehyde was used by Bu tlero w more than forty years a go in the synthesis o f
sugars . Collie * found that carbon dioxide is readily conver ted into oxygen and carbon monoxide under low p ress ure ele c tri c
: discharge , and he too calls attention to the analogy between the action of the silent discharge and the actio n of light in pl a nt life ; the polymeri zing effects o f the silent discharge are
especially notable . The action o f this agent is certai nly in part electro thermi c
and , possibly , in part electrolyti c , although it is well known that the output o f any prod uct secured by mea ns o f the silent discharge does not conform to the theo reti cal yield which would be expected were the reaction governed by Faraday ’ s l o u r aws . In the light of present knowledge i t seems most probable th a t in the silent discharge vas t amounts of kineti c energy transformable into chemi cal energy are introduced L into the system by speeding ele c tro ns q The principal technologi cal application o f the silent dis o f o f S charge is the generation o zone , by the pro cess iemens Ha l k i s e . s and A metal tube , cooled by water , inserted i n
o f a tube made mica whi ch is wound with Copper ribbon . The
s a Ce two annular p between the tubes is but narrow , and serves o f o f b e for the passage the air , the oxygen which is to trans e formed into ozone . The silent discharge pass s between the metal cylinder and the copper ribbo n o n the mica cylinder ;
“ N S n e e b ea n o f the S en t E e t Dis . o e t J . C lli , y h s s y M s il l c ric e o m n o n 19 0 4 c a T u rn h o c o d 5 . 15 0 ra ns . . e . S . h rg . J C , L , , p . W Lo e b i ber ci t 27 9 T . , L . p . . 1 3 6 N TES ON E E TROCHEM IS TR Y O L C . a series of such double tub es a re co mbined to fo rm a sort o f
An a lterna tin u 6 5 lattice work . g current is employed ; abo t a re f 6 500 18 m volts trans ormed into volts , and abo ut gra s of
r HP ozone a e produced per electri c . hour ; this amounts to practically nine times the amoun t whi ch could be secured if this reaction were electrolyti c in character .
t 1s o f - I estimated that i n the best o zone generating plants , no 15 the t more than . % of total energy supplied is con sumed in bringing about the transformation of oxygen i nto o zone . Elec o - sm sis -1 B . III . tr O o . If a porous diaphragm be intro du ced into an electrolyte and a sufficiently high voltage be
o ne e employed , the contents of electrode chamber will be forc d bodily through the diaphragm into the other electrode chamber until a certai n difference o f pressure will have been t established be ween the solutions in the two compartments .
E - o r ha s lectro osmosis , kataphoresis , as it is also termed , been known for a long time and was submitted to careful
- h no m f study by G . Wiedemann as early as This p e e f o f non is entirely di ferent fro m that osmosis , for in kata phoresis the -who le solution passes through the diaphragm
no unchanged , whereas in osmosis only the solvent passes , t
o f the solute . The pheno mena kataphoresis , as recognized b a nd y Hittorf , are also independent of electrolytic action
o f are not subject to the laws Faraday , although electrolytic pheno mena probably ac co mpany the pro cess to a certain)
extent .
l . In aqueous solutions , as a ru e , the solution travels through
the diaphragm from the anode to the cathode compartment, a lthough in certain instances the direction of this flow i s re versed ; the nature o f the solution and the nature o f the diaphragm seem to be the determini ng factors in this matter -u The cause of kataphoresis is probably the taking o n of oppo
B re i * des V 1 nt Ko n resses r An ewa ndte hemi e G d Ber . : u . g , . g i g C , V o l 4 6 4 3 . , p . .
N A M E I N D E X.
Da to n 26 96 l , Addicks , 25 26 Da vy , , e e 1 7 Amp r , 16 De Ch a lmo nt, 1 u 28 41 44 A rrh en i s , , , 23 Dei ma nn ,
B a n o ft 104 a e 23 37 cr , De La pl c , ,
B e a a 22 a e 9 cc ri , B a f y , e 112 B eck r , Eb e t 14 e 1 1 9 5 r . Becq u er l , , n to n 9 5 11 Elki g , B emo nt, th elo t 134 B er , i 24 F a b ro n , u 25 26 Berzeli s . , 19 27 52 6 2 Fa ra d a y , , , , B a d e 128 r l y , d 129 131 F itz Gera l , , Bredi 63 136 g , , te 109 Fo ers r , B o die 135 r , n n 9 Fra kli , Br u na telli 25 g , mm 105 Fro , r 112 Buch er e ,
uff 29 a a n 24 B , G lv i , n 6 5 Getma , e t 45 Ca lv r , b e t 8 Gil r , e 24 C a rlisl , G o th 137 nd h 22 r , C a ve is , u s s 25 27 Gro th , , a u u 27 28 46 Cl si s , , , 32 Guth e , ffo d 10 Cli r , e 13 5 Co lli , Ha 112 ll , in 32 C o ll s , ma 49 Co r ck ,
o u o mb 18 n 20 24 C l , He ry , ,
o w e 116 u t 120 C l s , Hero l ,
- e 96 o w e o , He 3 7 C p r C l s ss , 4 128 o e 3 , si n er 25 Cr ck r , His g , o o e 10 1 1 6 Cr k s , , H tto f 6 3 64 , 13 i r , , o 137 n 4 7 60 Cr ss , Ho pki s , . h a n 2 5 Cru icks k , C u e 1 1 ri , hb e t o n 23 Cut r s , 14 0 N AME IN DEX
Ra m a 13 s y , Ra e h 32 33 yl ig , , R h a d 30 32 9 1 112 ic r s , , , , Rent en 11 g , Ka h e 32 l , Rutherfo rd 13 Ka h enb e 58 l rg , Schmidt l l Ke e 9 7 f ll r , ed ewi 32 Ke n 38 S g , lvi , ck S emen 115 Ko h a u h 32 33 60 6 2 i s , lr sc , , , , Sm th 53 i , L a o u 1 19 So dd 13 C r , y , L a o e 3 23 S echnew 133 v isi r , , p , L e Bla ne 8 S en e 1 03 , 7 p c r , L o d e 44 5 Sto ne 10 g , , 6 y ,
L o 1 2 S trein tz 77 eb , 3 , 135 , L o en 6 2 S mmer 9 r z , y , L o e o 128 v j y , T a o 126 yl r , T ho m o n 10 26 M a ch e e 94 s , , , r s , T o wn end 127 M a xwe 3 s , ll , Ma e 3 4 y r, , V a n M a u m 22 r , Mo a n 1 16 123 124 iss . , , V a n T ro o stwi k j , 23 Mu a 103 ’ rr y , a n t Ho ff 28 4 1 42 V , , , , M liu s 105 y , o ta 17 23 24 V l , , , Vo n Helmh 0 ItZ 28 N e n t 29 4 5 54 63 70 r s , , , , ,
N eu b u e 128 W a e 49 52 rg r , lk r , , N 1cl1o lso n 24 W a tt 19 , ,
W h eth a m , 3 , 6 5 Ohm 17 , W edema nn 136 i , O twa d 29 45 50 s l , , , , W il a m o n 46 li s , W o n 125 ills , W n e 87 i kl r , W o a to n 25 ll s , W ht 13 1 rig ,
Yo ung , 3
1 4 2 S UB JE CT IN DEX .
u ent den i t 74 87 E e t o d e 84 C rr s y , , l c r s , C u ent mea u ement 79 E e t o de o tent a 74 rr s r , l c r p i l , u ent e ul a t o n 81 E e t o d e o tio n f o m fu ed e e t o C rr r g i , l c r p si r s l c r u ent o u e 75 te 1 10 C rr s rc s , ly s , E e t o de o t o n f o m o ut o n 94 l c r p si i r s l i , E e t o -fu na c e 1 14 Da n e e 38 76 l c r r s , i ll c ll , , - ’ E e t o fu na e o d u t 119 Da e e t o h e mi a th eo l c r r c pr c s , vy s l c r c c l ry , E e t o -o a n o e e 132 Ded u t o n 2 l c r rg ic pr c ss s , c i , E e t o -o mo 156 D e o a r e 68 l c r s sis , p l iz rs , E e t o te 28 D a h a m o e 106 107 l c r ly , i p r g pr c ss , , E e t o te fu ed 1 10 D e e t c co n ta nt 45 l c r ly s , s , i l c ri s , E e t o t e e ta n e 83 Diss o ci n 4 l c r ly ic c ll , r sis c , a ts , 9 E e t o t d o a t o n 28 41 D o a t o n o ta e 3 7 73 l c r ly ic iss ci i , , iss ci i v l g , , E e t o t di o a t o n theo o h l c r ly ic ss ci i ry , ectio n 5 j s , 8 Edd fu na e 118 y r c , E e t o 28 l c r lysis , Ed o n a umu a to 78 is cc l r, E e t o t o ut o n e u e 70 l c r ly ic s l i pr ss r , Ed o n ma e 76 is pri ry c ll , E e t o mo t e fo e 35 72 l c r iv rc , , E e t a rc tem e a tur e 119 l c ric , p r , E ect o n 8 10 l r , , E e t i o nd u to 15 l c r c c c rs , E e t o n th eo 10 l c r ry , E e t u ent na tu e 10 l c ric c rr , r , E e t o — a t n 103 l c r pl i g , E e t ene 8 14 l c ric rgy , , E e t o te hno o 93 l c r c l gy , E e t ht u ent 75 77 l c ric lig c rr , , E e t o th e m c o e e 114 l c r r i pr c ss s , E e t o we a u a t o n 34 l c ric p r , c lc l i , E e t o t n 103 l c r ypi g , E e t c e u e 16 l c ri pr ss r , El tro z in in 105 ec c g , ’ E e t th eo B e e u 26 l c ric ry , rz li s , E ement e e t o hem a l s , l c r c ic l E e t uni t a b o ute 21 l c ric s , s l , e uen e 47 s q c , E e t u n t a t a 21 l c ric i s , pr c ic l , Ene et a w 4 rg ics , l s , E e t i a en e 46 l c r c v l ci s , Ene o n e a tio n 3 rgy , c s rv , E e t i t a n ma 24 l c r ci y , i l , Ene d a tio n 5 rgy , issip , E e t t o nta t th eo 24 l c rici y , c c ry , Ene ef en 92 rgy fici cy , E e t it a a n 24 l c ric y , g lv ic , , Ene fa to 4 rgy c rs , E e t t na tu e 23 l c rici y , r , Ene fo m 4 rgy , r s , E e t t o e t e 14 l c rici y , pr p r i s , E u a ent o nd u t t 6 1 q iv l c c ivi y , E e t t th eo e 8 l c rici y , ri s , E o ut o n o f e e t o hem t 22 v l i l c r c is ry , E e t o -a ffi nit 48 73 l c r y , , E e t o -a na 66 a r d defi n t o n 19 l c r lysis , F a , i i , E e t o h emi a e u a ent 31 32 33 a a d a d e n t o n 3 2 l c r c c l q iv l , , , F r y , fi i i , ’ E e t o h em a e uen e 47 a a d a a w 29 6 7 l c r c ic l s q c , F r y s l s , , ’ ‘ E e t o chem a theo D a 26 a a d a e ea h e 27 l c r ic l ry , vy s , F r y s r s rc s , E e t o c h emi t e o ut o n 22 o m o f ene 4 l c r s ry , v l i , F r s rgy ,
E e t o de-a ea s a u a t o n 86 u ed e ect o te 1 10 l c r r , c lc l i , F s l r ly s , 143 . S UB J EC T IN DEX .
n d e ee 49 m - a 12 o n a t o , , G a m a r ys , I iz i gr f w a te 5 1 - ua t o n 42 I o n a t o n o , Ga s eq i , iz i r e o f e n e 1 o no en 53 G enera l principl s sci c , I g , n 120 in f u na ce 12 1 o n a d tee , G r , Ir s l 6 in o e 123 Ir e e b e e , 9 (l pr c ss , r v rsi l c lls G a 127 l ss , J a o b o e 124 Go d 99 c s pr c ss , l , J o u e d e n t o n 20 hmidt ’ o e 102 l , fi i i , Go ldsc s pr c ss , J o u e h ea t e u a ent 20 m e ui a e nt 31 l , q iv l , Gra q v l , ’ J o u e hea t 110 a h te 127 l s , Gr p i , ’ J o u e l a w 20 1 10 h m— E e t o n o e 108 l s , , Gries ei l c r pr c ss ,
Ha a u m ni u m o e 111 Ka ta h o e 136 ll l i pr c ss , p r sis ,
Ha ea e a nd B i d ro e 10 8 Ke e fu na e 121 rgr v s r p c ss , ll r r c , Hea t e u i a ent 20 Ke ne o e 1 10 q v l , ll r pr c ss , Hea t o f fo ma t o n 3 7 Kilo vv a tt d e n t o n 19 r i , , fi i i ,
’ Hea t umma t o n 37 K elli n s fu na e 1 17 s i , j r c , He u m 13 K ellin o e 122 li , j pr c ss , Hen d e n t o n 20 ry , fi i i , L a m -b a n e ta n e 81 r fu na e 1 18 p k r sis c , He a eu s , r c , La w de n tio n 2 He o u t a u m n um o e 1 11 , fi i , r l l i i pr c ss , La w o f hea t umma tio n 37 He o u t tee o e 120 s , r l s l pr c ss , Lea d 99 Hewe o e 126 , s pr c ss , ’ Lea d a umu a to 77 H tto f numb e 64 cc l r, i r s r , Len th u n t 5 Ho e fne o e e 9 5 102 103 g , i , p r pr c ss s , , , L tmu i o n a t o n 56 Ho e- o we de n t o n 19 i s , iz i , rs p r, fi i i , H d o 56 y r lysis , h a ls ke o e 129 Ma c pr c ss , H o ch o te o d u t o n 10 7 yp l ri s , pr c i , Ma ne u m 113 g si , H o th e d e n t o n 2 yp sis , fi i i , n a ne e 122 Ma g s ,
nd a to th eo 54 Ma n a n n 81 I ic rs , ry , g i , ndu t o n 2 Ma de n t o n 5 I c i , ss , fi i i , nd u ti o n fu na c e 117 Ma un t 5 I c r , ss , i , nten t fa to 14 35 Ma tte o n e a t o n 3 I si y c r , , r , c s rv i , Io n defi n t n 45 McDo na ld o e 108 , i io , pr c ss , o n ex ten e i n e e t o tes 45 Mea u ement o f h a he~ I s , is c l c r ly , s r p ysic l p o n m a t o n 6 3 no mena 5 I s , igr i , , o n mo b t 6 3 Me u o e 106 109 I s , ili y , rc ry pr c ss , , o n no men a tu e 52 M o fa a d de n tio n 19 I s , cl r , icr r , fi i , Io n ea ct o n 50 M a t o n o f io n 6 3 r i s , igr i s , Io n mb o 52 Mo b t o f io n 63 sy ls , ili y s , Io n theo 41 Mo e u a o nd u ti it 60 ry , l c l r c c v y , Io n- e o cit mea u ement 6 5 Mo b denu m 122 v l y s r , ly , 4 B 14 S U J EC T IN DEX .
N e n t a m 6 3 Re e ib e ea ct o n 69 r s l ps , v rs l r i s, N n t a nd G a e fu na c e 1 18 Ro nt en a 10 12 er s l s r r , g r ys , , N eut a iz a t o n de n itio n 5 1 Ro e er a nd Ede ma nn o ce 103 r l i , fi , ssl l pr ss, N e 100 Ru thenb e o ce 122 ick l , rg pr ss , lin 81 N ick e e, d n n N t o en xa t o n 128 Sa t, e t o 50 i r g fi i , l fi i i , n n men a tu e o f o n 52 S e e, e e a in i e 1 N o cl r i s , ci c g r l pr c pl s , ma u ent den t 87 Sha d e o e 127 N o r l c rr si y , pr c ss , S emen - Ha lsk e o e e 94 i s pr c ss s , Oh m d e n t o n 17 , fi i i , Ohm’ la w 17 s , S ent d h a e o e e 133 il isc rg pr c ss s , One fl u d th eo 9 i ry , S de 129 ilici s , O mo t e u e 4 1 42 s ic pr ss r , , S o n a b de 130 ilic c r i , Oxo ne 128 , Silo x i o n c , 13 1 O o ne ene a t o n 135 z , g r i , S e 9 8 ilv r , Simo n o e 122 - p , Pa rt mo l ecules 46 r c ss So d u m 1 13 h eno - h th a ei n i o n a t o n 55 i , P l p l , iz i , So ut o n e u e 53 ho h o u 129 l i pr ss r , P sp r s , So u e o f c u r ent 75 h a heno mena mea u e rc s r , P ysic l p , s r S a e 5 m n 5 p c , e t, ’ S e o nd u t t 6 2 a t no d 81 p cific c c ivi y , Pl i i , S nth a o e 11 o a a t o n h emi a 74 pi risc p , P l riz i , c c l , Sub ta n e o ne a tio n 3 o a a t o n o n ent a tio n 73 s c , c s rv , P l riz i , c c r ,
S mb o o f io n . 52 Po la riz a tio n vo l ta ge mea s ure y ls s men 75 t, T a nni n b a ta h o e 137 o e- a e 78 g y k p r sis , P l p p rs , Ta nta um a m 6 3 o tent o mete 36 l l ps , P i rs , Ta o o e 126 a t a e e t i c un t 21 yl r pr c ss , Pr c ic l l c r i s , o f e e t t 8 Theo ri es l c rici y , Ra d o -a t t 1 1 The ma ene 14 i c ivi y , r l rgy , Rad um 11 12 13 The mo i e 75 77 i , , , r p l s , , ’ Ra dium ema na ti o n 13 Th o m o n theo 45 s , s s ry , Ra thena u o e 126 T me de n tio n 5 pr c ss , i , fi i , n a 129 Rea d ma n a d e o e , T me unit 6 P rk r pr c ss i , , Re o d 8 8 c r s , T in 10 1 , 2 Re h o e , 1 7 T ta n u m 1 23 ic pr c ss i i ,
Re ta n e b o xe 81 r fu na e 117 sis c s , T a rnsfo r me r c ,
Re ta n e de n t o n 17 ub e fu na e 1 17 sis c , fi i i , T r c , Re ta n e fu na e 116 T un ten 123 sis c r c s , gs , 83 Re i ta n e o f e e t o t e , wo -fl uid theo 9 s s c l c r ly ic c ll T ry ,
Resu me, 89
e i b e e 6 9 U a n u m 123 R ev rs l c lls , r i ,
LBIT Y OF AL RN A L B RARY C IFO I I , BERK ELEY
IO K IS DU E ON TH E LA S T DATE THIS B C S TAM PED BEL OW no t r etu r n ed o n time a r e s u b j ect to a fi n e o f lu me a fter th e th r d a o v er u e cr ea s i i d y d , in n g l m f r th e x h B o o k s n o t ar v o u e a te si t d a y . in 137 b e r en ewed if a p p lic a tio n i s ma de b efo r e er o f lo a n p io d .
2 0 m